Rape is more easily managed for multiple  grazings than are the other brassica species.
Rape can generally be grazed at 4-week intervals.
Leave approximately 6 to 10 inches of stubble after the first grazing to promote rapid regrowth; on the final grazing, plants should be grazed close to ground level.
Rape can cause sunburn  on lightskinned animals, especially if it is grazed while the plants are immature.
Kale has more variation among varieties than most other brassica species.
Some varieties may provide grazing after about 90 days, followed by a regrowth opportunity; others may require as much as 180 days to mature.
Dry matter yield of kale can be impressive.
Swedes , like turnips, produce large edible roots.
Swedes yield more than turnips, but require 150 to 180 days to reach maximum production.
Swedes is one of the best crops for fattening lambs and flushing ewes.
Yield is maximized with a 180-day growth period for many varieties, but most hybrids produce the greatest yields when allowed to grow 60 days before first grazing and 30 days before the second grazing.
Turnips grow fast and can be grazed as early as 70 days after planting.
They reach nearmaximum production level in 80 to 90 days.
The proportion of top growth to roots for turnips can vary from 90% tops and 10% roots to 15% tops and 85% roots.
Turnips can be seeded any time from when soil temperature reaches 50F until 70 days before a killing frost.
Brassicas require good soil drainage, and soil pH should be in the range of 5.5 to 6.8.
Brassicas can be seeded into wheat stubble or no-tilled into a sod, provided it has been killed with glyphosate.
Clean-till seeding works well, but may have increased insect pressure.
If seeding after crop farming, herbicide carryover residues can be an enormous problem.
As a rule, carryover label recommendations for sugar beets are usually applicable to most brassica species.
Some producers in the Upper Midwest have had success in aerially seeding turnips into standing corn in mid-August.
The corn must be physiologically mature for this to be successful.
Fertilizer should be applied at the time of seeding to give brassicas a competitive edge on weeds.
Normally 75 to 80 pounds of nitrogen per acre and any phosphorus and potassium needed should be applied similar to what would be applied for a small grain.
Good soil moisture following seeding is key to successful establishment.
Brassicas should not comprise more than about two-thirds of cattle diets because of their low dry matter content.
Therefore, it is important to provide adjacent pasture, corn stalks, or a palatable, dry hay fed free choice to cattle when grazing these crops.
It is also desirable to introduce them to brassicas slowly by limit grazing for a couple of hours per day until their digestive systems are accustomed to them.
As with stockpiled forage, brassicas should be strip grazed.
If regrowth is desired, at least 2 inches of leaf should be left intact.
Generally animals will consume the leafy portion of the plant before progressing to the root portion.
To encourage consumption of roots, it may be necessary to disk after the tops have been grazed.
Cereal crops such as wheat, rye, oats, barley, or triticale can provide autumn or early winter grazing opportunities.
However, certain management practices need to be modified from what is normally done for grain production.
When small grains are used for grazing, they should be planted 3 to 4 weeks earlier than for grain production.
Also, between 60 and 100 pounds of nitrogen per acre is normally applied at planting time.
Recommended seeding rates vary depending on establishment method and seeding combinations.
Rye is more productive than wheat or triticale for both fall and spring production.
However, forage quality is better with triticale than with rye.
Oats seeded in the fall can be excellent quality and very productive, but will be killed by cold weather during winter.
Depending on geographical location, with adequate fall moisture, rye, triticale, and wheat should be available for grazing from October through much of December and then again in early spring.
The intended use of small grain determines what the stocking rate and grazing dates should be.
If a silage or grain harvest is planned, grazing should only be moderate, as heavy grazing can reduce grain yields.
Moderate grazing in the autumn will not result in significant silage or grain losses provided moisture and soil fertility are adequate.
In fact, fall pasturing can be beneficial where the small grain was seeded early and has made excessive growth and soil conditions are dry.
Spring grazing may be started when growth resumes.
If a grain or silage crop is to be harvested, grazing should be discontinued when the plants start to grow erect, just before jointing ; otherwise grain yield will be reduced.
Seeding date has a major impact on how early small grains can be grazed.
If the goal is to graze in late fall, seeding should be completed by late August in the Midwest and by late September in the Deep South.
With adequate moisture, growth will continue until air temperatures drop to around 40F.
Remove livestock when 3 inches of growth remain to maintain sufficient leaf area for continued growth and recovery.
Annual  ryegrass can be used as a companion species with, or as an alternative to, the small grain cereal crops to provide grazing in late autumn, early winter, and spring.
Compared to small grains, ryegrass is easier to manage, has a higher feed quality, and fewer management problems in spring, and can make rapid regrowth after initial grazing.
Annual ryegrass can be easily established into standing corn or soybeans or in these or other summer row crop fields after harvest.
It can also be notilled into old alfalfa fields.
There are differences in winterhardiness among annual ryegrass varieties, so if spring grazing is desired, it is important to plant varieties that are known to be adapted.
Seeding rates vary according to planting method and combination of species.
Wait to graze winter annual grasses until at least 8 inches of growth have accumulated.
In climates and management situations in which plants are likely to persist, it is generally advantageous to grow perennial rather than annual legumes.
However, in the Deep South, where perennial legumes such as white clover usually act like annuals, any of several winter annual legumes are a usually a better choice, depending on soils, rainfall, and producer objectives.
Various species may be grown alone, with another annual legume, or in combination with winter annual grasses.
Winter annual legumes make almost all of their growth in late winter and spring, but the distribution of growth of various species within this time period varies greatly.
Some row crop producers plant winter annuals as cover crops to provide nitrogen for a summer row crop, improve soil tilth, and protect the soil during winter.
Of course this forage can also be grazed in late winter or spring.
Hairy vetch is hardy enough to be grown as far north as the Lower Midwest, but it produces most of its growth during a few weeks in mid-spring.
Overseed winter annuals on summer grass sods
 Winter annuals, including annual ryegrass, small grains, and various annual legumes such as clovers and vetches can be seeded as a single species or in various mixtures into warm-season perennial grass sods such as bermudagrass, bahiagrass, or dallisgrass to extend the grazing season by 30 to 60 or more days.
Winter annuals should normally be overseeded about 2 or 3 weeks before
 Extend the grazing season by 30 to 60 days or more by overseeding winter annuals on summer grass sods.
the expected date of a killing frost.
Unless some tillage is provided to ensure good seed-soil contact, the existing grass should be clipped or grazed to 1 to 2 inches tall.
Producers who have pastures of both tall fescue and summer perennial grasses may be able to graze their summer grass closely to facilitate overseeding of winter annuals at the same time they are stockpiling tall fescue.
Overseeded pastures should be kept grazed closely in spring to prevent shading of summer species.
Provide supplemental feed during warm weather
 Despite the best management plans, shortages of forage commonly occur during July and August in the coolseason grass region due to drought or overstocking.
When this happens, supplemental feeding of hay or grain byproducts in July and August might be used to avoid overgrazing.
Also, a pasture or paddock of summer annual grass might be planted in anticipation of reduced pasture availability.
In areas where cool-season perennial forages dominate pastures, if pastures are short or pasture forage is of poor quality in July and August, feeding animals in a dry lot might be an option.
This may be more cost effective than overgrazing or trying to supplement animals on overgrazed pastures.
There is less hay loss when feeding hay in summer months as compared to winter.
Also, this approach allows pastures to begin recovering from overgrazing or drought and provides an opportunity to stockpile for late fall and winter grazing.
Using the same logic, some producers might also consider feeding hay in late summer or autumn to allow stockpiling of tall fescue forage.
Once livestock are removed from pastures, it may be worthwhile to apply 30 to 60 pounds per acre of nitrogen to stimulate plant recovery.
During hot weather, use of ammonium nitrate may be advisable as surface-applied urea can lose significant amounts of nitrogen through volatilization.
If using urea, the application should be made just before a rain to minimize the exposure time of the fertilizer material on a dry soil surface.
This publication emphasizes the value of grazing, but most livestock producers will need to provide hay or some other stored feed at certain times during the year.
Losses during the harvesting, storing, and feeding of hay vary considerably.
Ranges in losses are included in table 4.
Given the worstcase scenario, animals may consume only about 29% of the forage present in a hay field at harvest.
Further, the more hay wasted, the more that must be produced or purchased to feed animals at times when adequate pasture forage is not available.
The value of hay storage and feeding losses alone in the United States are estimated to exceed 3 billion dollars annually.
On some farms, hay storage and feeding losses account for over 10% of the cost of livestock production.
This is particularly objectionable because these losses occur after all the time, energy, and effort required to produce and harvest the hay have been incurred.
Also, these losses can be greatly reduced or eliminated without a great deal of expense or effort.
Table 4.
Percent loss of hay from curing through feeding.
Lax management-	Good management-
 Incremental	Additiveb	Incremental	Additiveb
 Field curing	25	25	12	12
 Harvesting	15	36	8	19
 Storage	35	58	5	23
 Feeding	30	71	8	29
 Total loss	-	71	29
 a Losses of dry matter present at the beginning of a step.
b Losses accumulate with each step.
Source: Dr.
Mike Collins, University of Kentucky.
Possible pasture combinations by region
 N umerous strategies discussed within this publication can be used to help extend grazing and reduce the number of days stored feed must be provided to livestock.
Obviously, some are appropriate only in certain geographical areas or on certain farms within an area, and some are likely to be of much more value in a specific situation than others.
No particular set of strategies is appropriate for every producer, even within a given geographical area.
In most areas, exploiting forage growth distribution differences offers much opportunity for extending grazing.
Figure 5 illustrates some forage species or categories of species that often work well for producers in selected areas of the nation.
The graphs show a few general combinations likely to be used in the Upper Midwest and Northeast, in the Tall Fescue Belt, in the Deep South, and in the Humid Southwest.
Once pasture forage growth distribution has been maximized, other strategies to lower stored feed requirements can be employed.
These may include changing the breeding season, selling animals at certain times of the year, use of creative grazing management, or implementing practices to minimize hay waste.
Almost anything a livestock producer can do to shave days off the length of time stored feed would otherwise need to be fed will favor increased profitability.
Figure 5.
Growth patterns of forage species by region.
Corn Belt, Upper Midwest, and Northeast
 Autumn and winter growth  varies due to several factors including date of planting, species planted, and geographical location.
Ten keys to a profitable forage program
 1 Remember that you are a forage farmer.
Forage typically accounts for over half the cost of production of forage-consuming animals and provides most of their nutrition.
Thus, it has a major influence on both expenses and income.
Efficient forage production and utilization are essential to a profitable operation.
2.
Know forage options, animal nutritional needs, and establishment requirements.
Forages vary as to adaptation, growth distribution, forage quality, yield, and potential uses.
Various types and classes of animals have different nutritional needs.
Good planting decisions depend on knowing forage options for your land resources and the nutritional needs of your animals.
3.
Soil test, then lime and fertilize as needed.
This practice, more than any other, affects the level and economic efficiency of forage production.
Fertilizing and liming as needed help ensure good yields, improve forage quality, lengthen stand life, and reduce weed problems.
4 Use legumes whenever feasible.
Legumes offer important advantages including improved forage quality and biological nitrogen fixation, whether grown alone or with grasses.
Once legumes have been established, proper management optimizes benefits.
5 Emphasize forage quality.
High animal gains, milk production, and reproductive efficiency require adequate nutrition.
Producing high-quality forage necessitates knowing the factors that affect forage quality and using appropriate management.
Matching forage quality to animal nutritional needs greatly increases efficiency.
6.
Prevent or minimize pests and plant-related disorders.
Variety selection, cultural practices, scouting, pesticides, and other management techniques can minimize pest problems.
Knowledge of potential animal disorders caused by plants can help avoid them.
Strive to improve pasture utilization.
The quantity and quality of pasture growth vary over time.
Periodic adjustments in stocking rate or use of cross fencing to vary the type or amount of available forage can greatly affect animal performance and pasture species composition.
Matching stocking rates with forage production is also extremely important.
8.
Minimize stored feed requirements.
Stored feed is one of the most expensive aspects of animal production, SO lowering requirements reduces costs.
Extending the grazing season with use of both coolseason and warm-season forages, stockpiling forage, and grazing crop residues are examples of ways stored feed needs can be reduced.
9.
Reduce storage and feeding losses.
Wasting hay, silage, or other stored feed is costly.
Minimizing waste with good management, forage testing, and ration formulation enhances feeding efficiency, animal performance, and profits.
10 It's up to you.
Rarely if ever, do we get something for nothing.
In human endeavors, results are usually highly correlated with investments in terms of thought, time, effort, and a certain amount of money.
In particular, the best and most profitable forage programs have had the most thought put into them.
Dr.
Don Ball Extension Agronomist/Professor Auburn University
 Ed Ballard Animal Systems Educator  University of Illinois Extension
 Mark Kennedy State Grazing Lands Specialist USDA/NRCS, Houston, MO
 Dr.
Garry Lacefield Extension Agronomist/Professor University of Kentucky
 Dr.
Dan Undersander Extension Agronomist/Professor University of Wisconsin-Madison
 James B.
Cropper USDA/NRCS Forage Management Specialist Greensboro, NC
 Leah Miller Director, Small Farm Institute Coshocton, OH
 R.L.
Dalrymple Agronomist , The Noble Foundation Ardmore, OK
 Dave Forgey Forgey's River-View Farm, Inc.
Logansport, IN
 Jim Gerrish Grazing Lands Consultant, American Grazing Lands Services, LLC May, ID
 John L.
Merrill XXX Ranch, Inc.
Crowley, TX
 Dr.
Jim Russell Professor of Animal Sciences lowa State University Ames, IA
 Kimberli R.
Stine USDA/NRCS National GLCI Coordinator Fort Worth, TX
 Dr.
Matt R.
Sanderson USDA/ARS Pasture Systems/Watershed Management Research Unit University Park, PA
Irrigation Practices efficiency of different systems determined by various factors
 An efficient irrigation system depends upon adapting equipment and practices to the soil type and contour of the land being worked.
An irrigation system which has proved satisfactory in one area will not necessarily work well in another.
The tools of irrigation are limited to a few standard ones-ditches and pipe lines for distribution of the flow to the sides of the field, delivery gates on the ditches, or siphons and outlet valves on the pipe lines.
Other devices used to bring water to the soil are the sprinkling system and the spud ditch which is used in some areas to bring the water table up into the root zone of the crop by seepage from the ditch.
Soil types range between the extremes of peat-which is wholly organic-and sand-which may be almost pure quartz.
The soil may vary in texture from the sands which are loose and porous to the clays which are sticky and relatively impervious to water.
Another basic factor for consideration in planning an irrigation system is the contour or general slope of the land, which is likely to vary greatly even in short distances.
The great variability in soil type and contour compels modification of irrigation practices from one locality to another.
In adapting the tools of irrigation to the soil type, a number of factors determine the best method of irrigation.
These determining factors include seepage, operation simplicity, maintenance, rodent destruction, life of the system, first cost, weed contamination, degree of interference with cultivation and contour of the land.
As far as seepage is concerned, use of the ditch will result in high and wasteful percolation losses when passing through sand; moderate but occasionally high losses when passing through loams, and low to negligible losses through clay.
Little or no seepage will result when a concrete pipe is used through these soils.
Four factors influencing an irrigation system are independent of soil type.
These are costs, contour of the land, weed contamination and the effect on cultivation practice.
The cost of outlets such as ditch structures and pipe line valves is extra over and above the cost of the ditches and pipe lines themselves.
It is difficult to compare them since they serve a specialized type of conduit.
Some of the effects resulting from soil type-such as washing-come after delivery of the water by these outlets.
Basins, checks, and borders are basically alike, being for the most part flat areas surrounded by earthen levees which hold the water flooded over them until it infiltrates the soil.
Basins are generally smaller, such as the square-leveed areas about individual trees.
Borders or checks are usually long and narrow with the slope down the length in the direction of irrigation.
There are several methods for applying water to the soil-basins, furrows, checks, borders and sprinklers.
The cross slope-the narrow way of borders and checks-is restricted to twotenths of one foot or less between the borders.
Sometimes the cross slope, and at other times the available water supply control the spacing of the levees.
Other irrigation devices may be used to advantage under certain conditions.
One such device is the syphon which conducts the water over the ditch bank to the field, eliminating the cutting of ditchbanks and effecting a saving in irrigation labor.
Continued on page 10
 COMPARISON OF DITCH AND PIPE LINE IRRIGATION IN RELATION TO VARIOUS FACTORS
 Factor	Soil Type	Ditch	Pipe Line
 Sand	High-wasteful	Slight to none
 Seepage	Loam	Moderate-occasionally wasteful	Slight to none
 Clay	Low-negligible waste	Slight to none
 Sand	Washing a problem	Less washing than ditch
 Operation	Loam	Some washing-may be high	Limited washing to none
 simplicity	Clay	Little or no washing	None
 Sand	Difficult to keep in shape
 Maintenance	Loam	More stable than sand	None
 Clay	Relatively stable-keeps shape
 Sand	Often not suitable for burrowing
 Rodent		None
 destruction	Loam	Burrowed readily and frequently
 Clay	Burrowed readily and frequently
 Must be remade frequently to plug ro-	Long-15 to 20 years or
 Life	All types	dent holes and control weed growth	more
 for all soil types
 Higher-from 55c for 8
 First cost	All types	Low-few cents per ft.
to $1.50 for 18" (ap-
 prox.
price laid in field)
 Weed con-	All types	Always a hazard, sometimes serious	None
 Interference	Below ground-little or
 with cultiva-	All types	Often definite obstruction to cultivation	no interference
 Can disregard grade of
 Contour of	land if all points are
 the land	All types	Must have fall toward point of delivery	below elevation of
 supply, which may be
 Black-end of Pear problem is subject of extensive field and laboratory studies
 Intensive investigations have been conducted in the field and in the laboratory since about 1930 regarding blackend or hard-end condition of pears and the relation of the rootstock to the incidence of the disease.
Investigations were extended to include many thousands of trees whose rootstocks were known.
The greatest incidence of the disorder occurred on the Japanese stock-P.
pyrifolia-although black-end was found on pear trees propagated on P.
ussuriensis, P.
betulafolia and Kieffer seedling roots.
Although the trouble has been found on trees that were said to be propagated on P.
calleryana stock, it always has been small in amount.
There have been a few cases where black-end has occurred on what has seemed to be French-P.
communis-rootstock.
The occurrence on
 French root however, has been so rare that the question might well be raised whether these particular trees might not be propagated on hybrid stock.
Records have been kept of the performance of individual trees over a period of years.
The trouble does not spread throughout the orchard.
All degrees of severity have been found; trees tend to hold their relative positions from year to year with respect to the amount of black-end produced.
The curve of incidence of the disease has been obtained by counting the number of black-end fruits on selected trees at weekly intervals.
A number of materials have been applied to the soil and injected into black-
 Continued from page 6
 The spud ditch finds favor in peat areas where the water table is already reasonably high.
It simply saturates the surrounding peat mass with water by rapid percolation through the porous peat.
Cost of irrigation naturally varies with
 end trees.
Among those applied to the soil have been: A complete fertilizer, beet lime, sulfur, iron sulfate, a combination of manure and lime.
Oxalic acid, tartaric acid, citric acid, iron sulfate, copper sulfate, boric acid, and a mixture of 12 different salts containing copper, boron, manganese, molybdenum, zinc, thorium, barium, strontium, tungsten, chromium, cadmium, and cobalt have been injected into the trees.
None of the soil applications or tree injections has changed the black-end condition of the trees.
Reciprocal and intermediate grafts have been made in an effort to transmit the disease.
In the intermediate grafts root pieces were used as the intermediates, some having soil filled boxes built around them.
None of the grafting experiments has been successful in transmitting the disease.
Several thousand inarched trees have been observed.
None of them has cured the disorder except when the original stock has been separated and the top caused to stand upon the inarches.
Young trees have been produced by propagating Bartlett on piece roots obtained from trees that produced black-end Continued on page 15
 If this total lift is in a well and a sprinkler system is operating requiring a pipe line pressure of about 40 pounds per square inch at the pump discharge, the pumping cost is increased by approximately $3 per acre-foot.
the type of system used.
It costs about $3 to pump one acre-foot of water where the total lift is 100 feet.
In contrast, some supplies for gravity systems cost as little as 50 cents or less per acre-foot.
The cost of gravity or ditch water depends upon the gross cost of the project and how rapidly it is being amortized.
N.
Johnston is Associate Professor of Irrigation, and Associate Irrigation Engineer in the Experiment Station, Davis.
Rate of Water Supply and Length of Run for Various Types of Irrigation and Slopes of Land
 Slope of	Coarse sandy soils	Medium silt loam	Very heavy clay soils
 Type of irrigation	land
 in ft./100'	Supply needed	Length of run	Supply needed	Length of run	Supply needed	Length of run
 02'	20 cubic feet per second/acre	5 cfs	2 cfs
 Basin	25'	20 cfs/acre	5 cfs	2 cfs
 58'	20 cfs/acre	5 cfs	2 cfs
 8-12	20 cfs/acre	5 cfs	2 cfs
 0-2'	1.5 cfs/10'	220'	.5 cfs/10'	550-880'	.3 cfs/10'	to 1,000
 Border or Check	25'	width	220'	width	550-880'	width	to 1,000
 58'	220'	550-880	to 1,000
 8-12'	220'	550-880'	to 1,000
 0-2'	.02 cfs each	220'	.01 cfs ea.
440-660'	.005 cfs ea.
880'
 Furrow	25'	.02 cfs each	contour	.005 cfs ea.
220-440'	.003 cfs ea.
550'
 58'	.02 cfs each	furrows 2%	.002 cfs ea.
110-220'	.002 cfs ea.
330'
 8-12'	.02 cfs each	slope
 0-2'	2" per hour	.5" per hour
 Sprinkler	25'	2" per hour	.5" per hour
 58'	1.5" per hour	.4" per hour
 8-12'	1.0" per hour	.3" per hour
Based on interaction of Extension professionals with Nebraska landowners and tenants, a common way to divide ownership is for the landowner to pay for and own all the permanent underground fixtures of a center pivot system.
This includes the pump, underground utilities, pipe, and dirt work required for installation.
If the lease with the tenant is terminated, the tenant will not remove any of the permanent underground infrastructure.
Keep in mind that real estate property taxes may rise, due to an increased value of the land if it is transitioned from dryland or gravity irrigation to center pivot irrigation.
Thus, the pivot should operate at a 90% timer setting when the end gun is off and slow to 77.4% when it is on to apply the 30 lbs/acre nitrogen both when the end gun is off, as well as when it is on.
The water application will be different  0.29 inches when the end gun is off and about 0.33 inches when it is on  but the nitrogen rate will remain the same with the constant injection rate pump.
The concept behind this method is that the pivot will irrigate the same number of acres per hour, thus the lower cost fixed-rate injection pump will work correctly.
Causes and Prevention of Emitter Plugging In Microirrigation Systems
 Microirrigation systems can deliver water and nutrients at controlled frequencies directly to the plant's root zone.
With microirrigation systems an extensive network of pipes is used to distribute water to emitters which discharge it in droplets, small streams or through mini-sprayers.
Over the last two decades, microirrigation systems continue to be used in trees and other horticultural crops because of their adaptability for both irrigation and freeze protection.
Microirrigation, properly managed, offers several potential advantages over other methods of irrigation:
 Comparable water application uniformity.
Improved water use efficiency.
If scheduled properly, minimized deep percolation and runoff.
Efficient delivery of fertilizer  and other chemicals  trough the irrigation system.
Ability to irrigate land too steep for irrigation by other means.
The plugging of emitters is one of the most serious problems associated with microirrigation use.
Emitter plugging can severely hamper water application uniformity.
Causes of Emitter Plugging
 Emitter plugging can result from physical , biological , or chemical  causes.
Frequently,
 plugging is caused by a combination of more than one of these factors.
Influence of the Water Source
 The type of emitter plugging problems will vary with the source of the irrigation water.
Water sources can be grouped into two categories: surface or ground water.
Each of these water sources produce specific plugging characteristics.
Algal and bacterial growth are major problems associated with the use of surface water.
Whole algae cells and organic residues of algae are often small enough to pass through the filters of an irrigation system.
These algal cells can then form aggregates that plug emitters.
Residues of decomposing algae can accumulate in pipes and emitters to support the growth of slime-forming bacteria.
Surface water can also contain larger organisms such as moss, fish, snail, seeds, and other organic debris that must be adequately filtered to avoid plugging problems.
Groundwater, on the other hand, often contains high levels of minerals in solution that can precipitate and form scale.
Water from shallow wells  often will produce plugging problems associated with bacteria; chemical precipitation is more common with deep wells.
Physical plugging problems are generally less severe with groundwater.
T RIALS WITH TENSIOMETERS to determine their usefulness in timing applications, as well as regulating amounts of irrigation water needed for turfgrass, were initiated by the University of California Agricultural Extension Service in Los Angeles County in 1960.
The need for modifications was soon apparent.
Subsurface installations were found necessary to avoid interference with recreational activities and cultural practices.
Such installations required protective boxes to house the instruments and moisture-proof covers for the tensiometer gauges.
These items are now available from commercial suppliers.
A thatch layer resulting in shallow rooting also interfered with the successful use of the tensiometer for determining irrigation needs.
With so many of the roots located in the thatch, grass showed severe water stress by the time tensiometers located in soil just below the thatch indicated any moisture depletion.
Data collected from several installations on golf greens indicated that mechanical aerification of the turf generally improves the
 Graph 1.
Tensiometer readings for first six months after installation of the completely automatic system at UCLA.
Numbers above the readings indicate length of time sprinklers operated.
The spaces between curves are the number of days between irrigations.
ability of tensiometer readings to indicate a need for irrigation.
Trials were established on three golf greens at the Fox Hills Country Club in Culver City-all similar in age, turf condition, and management requirements.
Previous to 1962, when these trials were initiated, all greens were on a spring and fall aerification schedule with 1/2-inch diameter spoons used, followed by top dressing with a soil mix.
The greens were treated as follows: one
 Tensiometers can be used successfully to determine frequency and duration of turfgrass irrigations, according to the trials reported here on three established golf greens.
Whether irrigation systems are manually controlled and merely guided by tensiometer readings, or completely automatic with tensiometers connected to a time-control system, this device-properly used-saves both time and water.
Data are also included on tensiometers buried at two depths rather than one, and special emphasis is placed on the importance of even distribution of water from the sprinklers, a thatch control program, and regular soil cultivation with a mechanical aerifier to reduce the effects of soil compaction.
green received the usual two aerifications; the second received the same plus one additional aerification in midsummer, using 1/4-inch diameter spoons, with the holes left open; and the third had the same spring and fall treatments, with two additional summer aerifications.
Tensiometers were installed at 2-inch and 5inch depths in each of the greens.
The green receiving two additional summer aerifications showed no turf stress at tensiometer readings of 50 cb , the green with one summer aerification showed a need for irrigation at about 30 cb; but the green receiving only spring and fall aerifications became hard and showed wilt symptoms before a tensiometer reading of 10 cb was reached.
The golf course superintendent was so impressed with the beneficial effects of the summer aerification, that he asked to aerify all the greens before the trials could be completed.
Therefore, the information received can be used only as an indication.
Graph 2.
Tensiometers continue to respond to varying climatic conditions as shown by frequency of applications during second six months after installation at UCLA.
The excessive lengths of irrigation during March and April were due to mechanical failure.
Uneven water distribution from inadequate sprinklers limits the use of tensiometers.
Tensiometers installed in areas receiving appreciably more or less water than other areas will not adequately reflect irrigation needs of the entire area.
Turf areas receiving low applications will show moisture stress before a tensiometer installed in a wetter area signals a need for water.
A completely automatic tensiometercontrolled irrigation system has been installed adjacent to Sproul Hall at the U.C campus, Los Angeles, on a turf area containing a mixture of bluegrass and fescue.
The soil is a clay loam, and the turf has been under a regular aerification program using 1/4-inch spoons with the holes left open.
Two tensiometers were installed in a location typical of the turf in the test area -one at a depth of 3 inches and the other at 8 inches.
A clock was attached to the control system to record the length of time the sprinklers operated.
The tensiometers were originally set to signal the controller for an irrigation when the shallow instrument reached a reading of 28 cb, or the deep instrument exceeded a reading of 12 cb.
After receiving the signals, the controller would operate the sprinklers only at a preset time during the night when the turf was not in use and the water pressure was good.
Irrigation would continue up to 15 minutes twice a night until the shallow instrument returned to a reading of cb, or until the deep instrument returned to a reading of 12 cb.
After two months, it became evident that too much water was being applied.
To corret this, the signal point of the shallow tensiometer was raised to 33 cb and the deep instrument to 24 cb.
Following a 15.minute sprinkler application test, using catchment cans in June, 1964, surface water was observed to flow into a runoff drain for over one hour after the sprinklers had stopped operating.
To
 correct this, the controller was adjusted to allow the sprinklers to operate for only seven minutes, twice a night, if the tensiometers signaled that water was needed.
Graphs I and 2 show tensiometer readings from the UCLA installation and the effect of climatic conditions on the irrigation intervals.
The weather in September and October of 1963 was extremely variable, with a 2-inch rain over the three-day period of September 16 to 18, and five consecutive days of over 100 F temperatures starting September 25.
This was followed by some cool overcast periods.
The lawn had been irrigated just prior to the rain and was not irrigated again for nine days.
During the extremely hot weather that followed, there were three more irrigations in seven days.
The weather cooled during October, and only 17 irrigations were applied between that time and early April, according to the needs of the turfgrass in relation to varying climatic conditions.
The recording of more than 15 minutes of irrigation in one night is evidence that the deep tensiometers had a reading high enough to signal for more water after the first 15-minute application.
The first 15 minutes will return the shallow tensiometer to a low reading.
Drying of the soil at the lower depths indicates root activity in this lower root region.
During March of 1964, a malfunction of the controller caused excessively long irrigations to be applied.
According to the manufacturer's specifications, output for the 20 full-circle and 15 half-circle sprinklers covering the UCLA test area is 145 gallons per minute at the pressure used.
Prior to these trials, irrigations were scheduled twice a week, 15 minutes at each setting, from about November to June and three times a week from June through October.
At this frequency and duration, 10.5 hours or 91,350 gallons of water would have been
 Graph 3.
Readings from the tensiometers at Whittier Narrows Golf Course show how tensiometers can be used as a guide for regulating the frequency and time length of irrigation when tensiometers are not attached to automatic timing devices.
applied from September through December of 1964.
Under the completely automatic tensiometer-controlled system, only 4.5 hours or 39,150 gallons of water were applied.
This represents about a 57% reduction in water use and cost.
A similar installation was established on a Seaside bentgrass golf green at the Deauville Country Club in Tarzana, Cali.
fornia.
A sprinkler application test showed one green to have a uniformity coefficient of 88.9% and a ratio of maximum-to-minimum application of 2 to 1.
While these trials were being conducted, the green was aerified monthly from May through September, using.inch spoons, with the holes left open.
This installation was similar to that at UCLA, except that the tensiometers were installed at 2-inch and 5-inch depths at the edge of the green.
Irrigation was initiated when the shallow instrument rose to 23 eb and terminated when it dropped to 5 cb.
Corresponding readings for the deep instrument were 28 cb and 10 cb.
The termination reading for the deep instrument has since been raised to 20 cb, for it was decided that more water was being applied than necessary.
When irrigation is needed, water is applied for 10 minutes each hour and up to eight times during the night.
Information available for the first three months' operations at the Deauville Country Club  shows that irrigation for 35 minutes every other night  would have applied 95,400 gallons in 26.5 hours.
Under the tensiometer-controlled system, only 16 hours or 57,600 gallons of water were used.
This represents about a 40% reduction in water use, The superintendent at Deauville reported that after the first five to six weeks of automatic tensiometer-controlled irrigation, about 75 to 80% less hand watering was re-
 quired on this green as compared with other nearby greens.
Tensiometers can also be beneficial without completely automatic controls, as demonstrated at the Whittier Narrows Golf Course in El Monte.
Prior to installation of the instruments at 2and 5-inch depths, irrigations were set for 15 minutes every night.
During the summer, even longer irrigations were applied.
Tensiometers were installed on June 1, 1964.
With tensiometers to schedule frequency and duration of irrigations, only 14,560 gallons of water were applied in 22.3 hours during June and July, 1964 (graph The previous schedule would have required 83,265 gallons in 151/4 hours.
This is a reduction of 83% in water use.
Often the beauty of turfgrasses used for recreational purposes is more important than savings in water and money.
However, in the trials reported here, the turf remained healthy and beautiful, and the golf greens continued in good playing condition.
Also, in many instances, deeper, more vigorous rooting resulted where tensiometers were used to determine turfgrass irrigation.
Tensiometers, therefore, can be used successfully as a guide to determine frequency and duration of irrigation for turfgrass areas-either from installations associated with manual control or from completely automatic systems.
Also, savings in both money and water are possible in varying degrees, since most turf authorities agree that overirrigation is the rule rather than the exception.
For such systems to operate successfully, however, complete irrigation management must include good distribution of water from the sprinklers with application rates not in great excess of the water infiltration capacity of the soil, a regular program of thatch control and soil aeration where needed.
Turfgrass superintendents are usually encouraged by the use of tensiometers to improve their irrigation practices.
Wayne C.
Morgan is Tur/grass Farm Advisor, Los Angeles County, and Albert W.
Marsh is Agricultural Extension Ser.
vice Irrigation and Soils Specialist, University of California, Riverside.
Information included in this report is from a paper first presented before the American Society of Agronomy, Kansas City, Missouri, November, 1964.
R ECENT FIELD EXPERIMENTS have demonstrated that certain soils in the San Joaquin Valley need to be fertilized with heavy applications of potassium  to obtain maximum production.
The question of what effect these high K additions have on the nutritional status of other plant-essential elements for cotton has never been answered.
but K-induced magnesium  deficiencies had been demonstrated for a number of crops by previous investigators.
A greenhouse experiment to evaluate the effect of K on the Mg status of the cotton plant, under California conditions, was conducted at Riverside.
Distinct K.
and Mg.deficiency symptoms, along with the associated plant tissue analyses, were developed.
Cotton  was grown for three months in sand cultures.
Each unit consisted of a 100-liter reservoir for the nutrient solution and four 3-gallon crocks filled with sand to support the plants.
The assembly was equipped so that each sandfilled pot could be periodically irrigated with the nutrient solution.
The nutrient solutions percolated through the sand and drained back into the reservoirs.
Potassium and magnesium were added in a factorial design in amounts necessary to produce solution concentrations of 1, 10, and 50 ppm.
All other nutrients were added in amounts sufficient for plant growth.
The solution concentrations in the reservoirs were maintained by periodic additions.
After a three-month growth period, the plants were weighed, the bolls were counted, and the petioles were separated for chemical analyses.
A summary of the main effects of K and Mg nutrition on the plant weight, number of bolls, and levels of K and Mg in the petioles is shown in the table.
An increase in yield, as indicated by plant weight and boll count, occurs as the level of K in the nutrient solution is increased from 1 to 50 ppm.
For Mg, an increase in yield is observed as the concentration of the nutrient solution is increased from 1
 to 10 ppm, but further increase in Mg levels did not result in increased yield.
Symptomatology and chemical analyses demonstrated that those plants grown on substrate levels of 1 and 10 ppm K were deficient in K, and those plants grown on the 1-ppm Mg substrate level were deficient in Mg.
A mutually antagonistic effect of K and Mg on the uptake of each element is indicated by the plant analysis data presented in the table.
At 50 ppm Mg in the substrate, the petiole contents of Mg drop from 1.9 to 0.3% as the K level in the substrate is increased from 1 to 50 ppm.
Similar antagonistic effects of Mg on K are indicated.
For example, at the 10-ppm level , the K content of the petioles is decreased from 2.2 to 0.9%.
Visual symptoms of plants known to be deficient in K and Mg are illustrated in the photos.
Leaf symptoms indicative of K and Mg deficiencies are sufficiently different to be distinguished from one another.
Leaves from the K-deficient plants exhibit leaf marginal chlorosis and
 Progress Reports of Agricultural Research published monthly by the University of Callfornia Division of Agricultural Sciences.
William W.
Paul Manager Agricultural Publications Jerry Lester Editor Peggy Anne Visher Assistant Editor California Agriculture
 Articles published herein may be republished or reprinted provided no advertisement for a commercial product is Implied or imprinted.
Please credit: University of California Division of Agricultural Sciences.
California Agriculture will be sent free upon request addressed to: Editor, California Agriculture, 207 University Hall.
2200 University Avenue, Berkeley.
California 94720.
To simplify the information in California Agriculture it is sometimes necessary to use trade names of products or equipment.
No endorsement of named products is intended nor is criticism implied of similar products which are not mentioned.
Automatic turf irrigation showing instrument area and cans set out to measure water distribution.
Evapotranspiration for Turf Measured with Automatic Irrigation Equipment
 S.
J.
RICHARDS L.
V.
WEEKS
 Automatic irrigation, controlled by instruments capable of detecting moisture needs of plants, has been successfully used to study evapotranspiration rates for turfgrass at Riverside.
Tests indicated that frequent, automatic sprinkling with relatively low-volume applications per irrigation might allow easy measurement of evapotranspiration.
Tensiometers, acting as hydrostats, can turn "on" irrigation water when needed, but unpredictable flow rates in soils make it necessary to use a separate timing mechanism to set the duration or amount to be applied and turn the water off.
Automatic irrigation management programs are now feasible, under many conditions, using tensiometers or other instruments responding to an energy variable of water in the soil.
However, to be accurate for evapotranspiration measurements, such procedures should account for water losses below the rooting depths in the soil.
T ENSIOMETERS measuring soil water conditions have been in use since about 1935 and the principles of automatic irrigation using a tensiometer were established as early as 1943.
Commercial development of fully automatic irrigation has progressed first in connection with systems for irrigating turf and ornamental plantings.
One such system, available for about 10 years, uses a tensiometer-type hydrostat to indicate a need for irrigation and a small electric clock motor to control the time of day or night when water is to be applied.
The duration of irrigation on each of several pipeline sections is independently controllable.
This study was conducted on a 120 220-foot turf plot located south of a large intramural field at the University's Riverside campus.
Asphalt parking and play areas occupy portions of the east and west sides.
To the south is a relatively wide expanse of trees and turf plantings.
The immediate turf area is enclosed by shrubbery borders which are watered from separate irrigation lines.
The regular sprinklers on the north half of the area were capped in July, 1961, and a separate irrigation system was installed using gear-driven rotary pop-up sprinkler heads.
The porous cup of the hydrostat was located at an average depth of 31/2 inches.
When soil suction exceeded 20 centibars at this depth, a one-hour sprinkling was started at 2 a.m.
At each irrigation, an average of 1/2 inch of water was applied automatically by meter readings.
The south half was irrigated from a semiautomatic system operating the sprinklers for a specified period each night when turned on manually.
A separate meter was installed to measure the water used under this system.
To evaluate the automated control, tensiometers were installed at five depths in two locations selected for average turf vigor.
Cans were used to measure the depth of water applied at the two instrument areas and near the hydrostat.
One instrument area and the hydrostat area received similar amounts of water, although less than the average for the area as a whole.
Water application at the hydrostat and instrument areas was thus measured eleven times directly, and the ratio of application depth to meter reading was obtained.
The average ratio was then used to convert the monthly water use, as read on the meter, to the depth of
 water applied at the hydrostat and instrument areas.
Early morning timing reduced the effects of wind on the sprinkler distribution pattern to a minimum.
The table shows monthly irrigation applications for a full year.
It also includes rainfall and air temperature records from the Citrus Research Center Weather Station located about one mile away.
Correcting the total metered values to the amounts of water applied at the instrument area, and adding the rainfall, gives a reasonable approximation of the monthly evapotranspiration for turf.
Tensiometers with cups located at 11/2-, 3-, 6-, 12-, and 20-inch depths were read daily between 4 and 5 p.m.
The readings indicated that the major amount of root activity was in the upper 4 inches of soil.
Readings from the two shallower depths showed wide variations.
Usually these instruments would read 10 to 15 centibars on the day following an irrigation and would read values above 50 on the evening before an irrigation.
During August, there were occasional days when suction values at these depths exceeded the range measurable with tensiometers.
Since only 0.35 inch of water was applied at the instrument area per irrigation, very little day-to-day change in the readings occurred at the 12and 20-inch depths.
However, starting in July and continuing through August, values at the 12-inch depth slowly increased from 7 to about 40 centibars.
With more moderate weather conditions in September, readings at the 12-inch depth gradually decreased.
By the end of November, values at this depth were similar to those during the first six months of the year.
Some adjustment in monthly evapotranspiration values might be justified because of water storage changes in the soil profile, but the amounts added to the
 MONTHLY IRRIGATION APPLICATIONS AND VALUES CORRECTED FOR NONUNIFORM DISTRIBUTION OF WATER BY SPRINKLERS, INCLUDING RAINFALL AND AIR TEMPERATURE DATA FROM THE CITRUS RESEARCH CENTER WEATHER STATION
 Depth ot water from
 1962	hydrostat	Without	meter readings, inches	hydrostat	With	Depth of water	on instrument	areo, inches	Rainfall,	inches	Evapotrans-	piration,	inches	temperature	monthly air	Mean	F	Evaporation,	inches
 January	2.14	2.17	1.4	1.9	3.3	53
 February	0.57	0.4	3.7	4.1*	51
 March	0.78	2.71	1.8	0.8	2.6	51
 April	8.64	7.76	5.2	5.2	64
 May	9.34	7.45	5.0	0.3	5.3	62
 June	9.16	7.35	4.9	4.9	68
 July	11.35	8.61	5.7	5.7	74
 August	11.96	8.36	5.5	5.5	77	8.51
 September	11.63	5.90	3.9	3.9	73	6.5
 October	4.52	4.03	2.7	2.7	64	4.3
 November	4.78	3.01	2.0	2.0	60	2.7
 December	3.71	2.63	1.7	1.7	54	2.4
 Total	78.01	60.55	40.2	6.7	46.9
 Rainfall probably exceeded evapotranspiration for February.
Estimated from measurements for only half of August.
July and August periods would in turn need to be subtracted from the September and October values.
The total change of water stored in the 4to 16-inch layer of soil, based on laboratory data, was estimated to be about 1/2 inch.
While flow velocity of water through the profile cannot be measured explicitly, some indication of its direction was obtained by evaluating the hydraulic gradient tending to cause flow.
Values of the hydraulic gradient between the 12and 20-inch depths were such that downward flow occurred from January through June.
Monthly means of daily values varied from 0.5 to 0.05.
Values for July indicated flow was upward and the monthly mean hydraulic gradient was 21 for the month of August.
Values indicating upward flow were 8 for September, 2 for October, and 1 for November.
During December, the hydraulic gradient showed downward flow.
Conductivity values for the decomposed granitic subsoil, estimated from laboratory measurements, indicated that total flow, between the 12and 20-inch depths for any one month, probably did not exceed 0.1 inch.
Again no attempt was made to correct the amounts of applied water for this transfer in the soil profile.
A 14-inch diameter insulated evaporation pan was installed in August with the water elevation about level with the turf.
Evaporation values for the last four months of the year are included in the table.
All of the measurements indicated were made while the irrigation program was completely under automatic control.
The automatic controller called for irrigation over 100 times during the year.
This frequent irrigation with relatively low volume applications per irrigation appears to be well adapted for making evapotranspiration measurements.
With relatively few additional modifications, this approach could be used to measure evapotranspiration for the wide range of conditions under which turf is being grown.
S.
J.
Richards is Soil Physicist and L.
V.
Weeks, Laboratory Technician, Department of Soils and Plant Nutrition, University of California, Riverside.
Funds for purchasing irrigation equipment were provided by the Water Resources Center, University of California, Los Angeles.
Moist O'Matic, Incorporated, Riverside, California, contributed to the installation of the automatic sprinkler system.
The kickoff event is always one of mixed emotions for attendees, as you have the new participants that are entering with eager anticipation to get started, but also the past competitors that are attending to learn what has changed, as well as continue to network and build the peer-to-peer relationships that TAPS prides itself on, said TAPS Program Manager Krystle Rhoades.
Selection and Management of Efficient Hand-move Solid Set and Permanent Irrigation System
 Prepared by: Robert Evans, Extension Agricultural Engineering Specialist R.E.
Sneed, Extension Agricultural Engineering Specialist
 Published by: North Carolina Cooperative Extension Service Publication Number: EBAE-91-152 Last Electronic Revision: June 1996 
 Rainfall is the principle source of water for North Carolina crops.
However, many farmers are turning to irrigation to supplement precipitation.
There are many types of irrigation systems.
But, most farmers have limited choices for their particular farm or field.
Some systems are inherently more water and energy efficient while others are designed to overcome limitations such as irregular field shapes, sloping land, or limited water supplies.
All of these factors should be considered before selecting a particular type of system.
Hand-move systems are normally used to irrigate small fields.
Solid-set and permanent sprinkler irrigation systems are used for irrigation, frost/freeze protection, evaporative cooling, and land application of nutrient-rich effluent.
Selection and management considerations for hand-move solidset and permanent sprinkler irrigation systems are discussed in this article.
Selection and management criteria for other types of irrigation systems are presented in articles EBAE 91-150: Self-Propelled Gun Traveler Irrigation Systems, EBAE 91-151: Center Pivot and Linear Move Irrigation Systems, and EBAE 91153: Low Volume Irrigation Systems.
Sprinkler irrigation systems have been available for more than 70 years.
The early systems used lightweight steel pipe and nonrotating sprinklers.
Rotary impact sprinklers were introduced in the late thirties.
However, it was not until after World War II, when aluminum pipe became available, that portable hand-move system became practical.
Most of the early rotary impact sprinklers were low capacity, medium pressure, and constructed of brass.
Some companies supplied gun sprinklers, but early models were not very satisfactory, because of the high application rate and potential for runoff.
Over the years, the trend has been toward larger sprinklers.
Several companies now supply a low capacity  gun sprinkler which has reduced some of the runoff problems typically associated with gun type sprinklers.
Sprinklers are now available with plastic, brass, aluminum, and some stainless steel components.
Improvements in bearings contribute to longer life and less maintenance.
Quality control has also improved.
The major change in aluminum pipe has been a trend toward thinner wall aluminum pipe and stronger alloys.
Couplers and gaskets have been improved to reduce leaks at joints.
The number of coupler manufacturers has been reduced.
Most of these changes have occurred because of the introduction of other types of irrigation systems such as self-propelled gun travelers, center pivots, linear move, low volume, and sub-irrigation.
Sprinkler spacing's for portable irrigation systems range from 40 feet by 40 feet for small sprinklers to greater than 200 feet by 200 feet for gun sprinklers.
Spacing's may be square, rectangular, or triangular.
Spacing's are usually about 60 percent of sprinkler wetted diameter, but may need to be adjusted for wind conditions.
Singleor double-nozzle sprinklers may be used.
The doublenozzle sprinkler generally provides better uniformity, because the second nozzle provides water close to the sprinkler.
Smaller sprinklers, because they are less affected by wind, provide better uniformity than gun sprinklers.
However, the labor required for moving pipe when smaller sprinklers are used is increased considerably.
Figure 1 shows a typical layout of a portable hand-move aluminum pipe system.
Two laterals are operated at one time.
Spacing between sprinklers is 60 feet and spacing between laterals is 60 feet.
The first and last sprinklers on each lateral are 30 feet from the edge of the field.
This is done to provide more uniform water distribution around the edges of the field.
Figure 1.
Schematic of a portable hand-move aluminum pipe irrigation system.
Laterals and sprinklers are typically moved twice per day which requires 4.5 days to irrigate the 30-acre field shown in Figure 1.
Each setup and movement of the pipe is referred to as a "set".
Approximately 22.5 man-hours are required to move pipe each time the field is irrigated.
For the field length and shape shown, the lateral pipe size required is 4-inch, and the main line size required is 6-inch.
A pump capacity of 425 gallons per minute  would supply an application rate of 0.28 inches per hour when two laterals are irrigated per set.
When operated for four hours , the total application to each set is just over one inch of water.
In the above example, only one inch of water could be applied per week, unless the pipe was moved and the system operated over the weekend.
Thus, the system shown only has the capacity to supply about one-half the crop water requirements during peak water use periods.
In terms of size , the 30 acre example is a relatively small system indicating that hand-move portable systems are not practical for irrigating large acreage.
There are, however, practical applications for portable, hand-move systems.
Some practical applications include the irrigation of:
 plant beds such as tobacco or sweet potato beds, which are typically moved from one year to the next;
 small acreage of high cash-value crops which also need to be rotated from year to year making solid set or permanent systems unsuitable;
 small scattered fields separated by non-cropped areas; and
 establishment and maintenance of lawns, turf areas, fruit and/or nursery trees and/or shrubs that require only an occasional irrigation, most often immediately after seeding or transplanting.
The labor required for moving pipe, and the introduction of other types of irrigation systems have diminished the popularity of hand-move potable systems.
Instead, growers have shifted to solid-set and permanent systems.
SOLID-SET AND PERMANENT IRRIGATION SYSTEMS
 The solid-set system uses aluminum pipe, but instead of moving lateral lines once or twice a day as is done with portable systems, enough lateral pipe is purchased so that pipe may be left in place during the irrigation season.
Main line for the solid-set system can be aluminum pipe or buried polyvinyl chloride  plastic pipe.
The permanent system normally uses buried main and lateral lines.
However, some growers use above ground PVC plastic lateral lines.
These systems are used more in orchards where the system is installed after the orchard is planted and in some container nursery operations.
Permanent systems have been used for many years to irrigate turf areas such as golf courses, recreational playing fields, and commercial and residential turf.
In more recent years, these systems have been used for agricultural irrigation to include nursery crop production.
Most of the solid-set and permanent systems for agricultural irrigation  are used on high value crops such as nursery crops, tree fruits, small fruits, vegetables, and, to a small extent, tobacco.
Many of the systems for fruits and vegetables are also used for environmental modification such as frost/freeze protection and crop cooling.
These uses require a dependable water supply during the critical environmental period.
For crop cooling, it may be possible to cycle the system on and off to reduce the total volume of water pumped.
Solid-set and permanent systems designed for frost/freeze protection and crop cooling normally use small sprinklers and application rates in the range of 0.12to 0.25inch per hour.
Normally, single nozzle sprinklers are used on spacing's of 40 feet by 40 feet to 66 feet by 72 feet.
Spacing's are normally 50 to 65 percent of sprinkler wetted diameter.
Lateral spacing's and sprinkler spacing's on the lateral are adjusted to meet row and tree spacing's.
Sprinkler pressures are normally 10 to 15 psi higher than those used for irrigation to give small droplets and therefore, better coverage and higher sprinkler rotation speeds.
Frost/freeze protection using sprinkler irrigation operates on the principle of latent heat of fusion.
Water, as it changes state from liquid to solid, generates heat.
The heat being given off maintains the temperature of the plant near 32 F if adequate water is being applied.
Higher sprinkler pressure provides smaller droplets and faster sprinkler rotation and, therefore, better
 protection.
But, windy conditions reduce the added protection of smaller droplets because wind causes evaporation.
The heat required to evaporate water is 7.5 times the heat given off when water freezes.
Just as smaller droplets freeze faster which improves frost/freeze protection, smaller droplets also evaporate faster.
Thus high pressure resulting in small droplets should not be used where windy conditions occur frequently.
Also, lateral line spacing's and sprinkler spacing's along the lateral should be reduced where windy conditions are prevalent.
Good frost/freeze protection requires that liquid water be available on the plant at all times.
Figure 2 shows a typical layout for a solid-set system for frost/freeze protection of strawberries.
A triangular sprinkler spacing is used.
Sprinklers are spaced 60 feet on the lateral and laterals are 60 feet apart.
The first and last laterals are 30 feet from the edge of the field.
Using the triangular spacing requires that the first and last sprinkler on every other lateral be on the edge of the field.
Lateral pipe size is 2-inch aluminum.
Main line size is 8inch aluminum.
Pump capacity required to provide frost/freeze protection for the acreage and setup shown in Figure 2 is about 900 gpm.
Figure 2.
Schematic of a layout of a solid-set irrigation system for frost/freeze protection of strawberries.
In the last several years, a number of solid-act and permanent systems have been installed for land application of nutrient-rich effluent.
Several agencies are promoting this practice as an environmentally safe method to utilize this resource.
Some land application systems are being installed on golf courses and public turf areas.
This is an approved practice in many states.
North Carolina Cost Share funds are being used to fund one intensively grazed, land application of nutrient-rich effluent demonstration in each county.
These areas are normally grazed, but producers may elect to produce hay crops rather than use the fields for grazing.
Sprinkler spacing's on land application systems are typically in the range of 80 feet by 80 feet, using single-nozzle sprinklers.
Other spacing's can be used and some of the sites use gun sprinklers on wider spacing's.
Normal spacing is 60 to 70 percent of sprinkler wetted diameter.
Figure 3 shows a typical layout for a permanent irrigation system for land application of nutrient-rich effluent.
Sprinkler spacing is 80 feet on the lateral.
Spacing of laterals is also 80 feet.
Lateral pipe size is 2.5 inch.
Main pipe size is 3 inch.
One lateral is usually operated at one time.
Sprinklers may be located on each lateral; or, sprinklers may be moved from one lateral to another lateral.
By moving sprinklers, initial system cost is reduced.
To operate one
 lateral as shown, pump capacity required is about 120 gpm.
Note that there is a 70-foot border around the edge of the field to insure that no effluent is applied outside the field.
Figure 3.
Schematic layout of a permanent irrigation system used to land apply nutrientrich effluent.
General guidelines  have been established and should be followed when designing hand-move, solid-set, and permanent systems.
For portable hand-move aluminum pipe systems, friction loss in the main and/or supply pipe should not exceed 2.0 psi for 100 feet of  pipe.
For lines that are greater than 1500 feet in length, friction loss should not exceed 1.0 to 1.5 psi per 100 feet.
For PVC plastic pipe main and/or supply lines, flow velocity is the limiting factor rather than friction loss.
Velocity should not exceed 5 feet per second to prevent pipe failure due to water hammer.
Water hammer describes the buildup and sudden release of pressure that occurs when air is trapped in the pipe.
The buildup and release of the pressure increases as the velocity of the flowing water increases.
Friction loss in aluminum and plastic lateral lines should not exceed 20 percent of recommended sprinkler operating pressure.
Following this rule will assure reasonably uniform water distribution.
As sprinkler pressure is reduced, due to friction loss down the lateral line, the volume of water applied by the sprinkler and the diameter of coverage is reduced.
Most portable, solid-set and permanent sprinkler systems are medium to moderately-high in energy consumption, depending on whether small sprinklers or gun sprinklers are used.
Certainly, gun sprinklers will require higher pressures, increasing the power required.
Many of the portable systems use gun sprinklers.
Some growers are willing to trade off the higher energy costs for the savings in labor costs.
There are some gun sprinklers that will operate satisfactorily at lower pressures and some growers are using these, but they have reduced radius of coverage and, therefore, higher application rates, assuming equal flow rates.
There are some low pressure impact sprinklers that have been marketed for the last several years.
They also have reduced radius of coverage and this may increase the application rate.
Fuel costs  are computed based on the energy required to deliver the required flow rate at the desired operating pressure.
To compute horsepower  requirements, use the formula shown in the box at the top of the next column.
[TDH  X Flow ]/ [3960 X Pump Efficiency]
 Total dynamic head  or operating pressure at the pump includes the sum of the following:
 friction loss in the main line
 friction loss in the lateral line
 elevation difference between the water supply and the highest point in the field, and
 height of sprinkler above the ground 
 Flow is the rate water is being delivered to the sprinklers.
After computing TDH, a pump efficiency should be assumed SO that horsepower can be computed using the above formula.
Refer to Extension Publication AG-452-6: Pumping Plant Performance Evaluation, for a discussion of recommended pump efficiencies to select.
Once the power requirements have been determined, the fuel cost can be computed.
By comparing costs of several operational and system alternatives  the most energy efficient system can be identified for the given situation.
If proper design guidelines are used and sprinklers are operated at the manufacturers' recommended mid-range of operating pressures, these systems should be reasonably energy efficient.
Pump selection should include the use of high efficiency pumps and matched power units.
Hand-move, solid-set, and permanent irrigation system can be energy efficient.
Solid-set and permanent systems are normally more energy efficient than portable handmove systems.
Unfortunately, some of the older systems have sprinklers, pumps, and power units that are 20 or more years old and need replacing.
Many growers have replaced sprinklers and often have several sizes of orifices on the same system.
Growers often purchase used equipment and combine components from several systems to make one system.
When this is done, little opportunity exists to incorporate recommended design guidelines to properly size and match system components.
If your system is more than three years old, you should have it evaluated.
Contact your county Extension office or local irrigation dealer for more information and assistance.
Making a profitable decision about repairs like when to replace worn system components requires a complete economic analysis of existing system performance and the projected cost of alternatives.
erraticity  n.
The quality or state of being erratic, characterized by the lack of consistency, regularity or uniformity.
That's correct, there is no such word, but you sure know it when you see it.
Unfortunately, we saw a lot of it this past season in sprinkler irrigated corn.
Figure 1.
Nonuniformity of sprinkler irrigated corn under extreme drought conditions in southwest Kansas in 2011.
These instances of erraticity resulted in low quality, lowor non-yielding corn production.
Crop water stress caused by the extreme drought in portions of the central and southern Great Plains is ultimately responsible for the erraticity.
However, there may be ways to reduce erraticity and its harmful effects by improvements in design and management of center pivot sprinklers for corn production that can minimize water losses.
SPRINKLER PACKAGE EFFECTS ON WATER LOSSES
 Center pivot sprinkler management techniques to avoid water losses begin at the design and installation stages with selection of an appropriate sprinkler package.
Typical sprinkler packages in use to today are medium and high pressure impacts which are located on top of the sprinkler span , low pressure rotating spray nozzles which are typically located on the span or at least above the crop canopy, low pressure fixed spray applicators that are located above and within the crop canopy and LEPA  that are located near the ground surface.
Commercial LEPA applicators often can apply water in multiple modes.
The popular low pressure fixed spray applicators have also been categorized by their location with respect to the canopy with the terms LESA  and MESA .
Application with MESA is typically above the crop canopy for all or most of the crop season depending on the crop.
There are numerous water loss pathways using center pivot sprinklers and each type of sprinkler package has advantages and disadvantages as outlined by Howell  that must be balanced against the water loss hazards.
Table 1.
Water loss components associated with various sprinkler packages.
Adapted from Howell.
Water Loss Component	(Impact sprinklers,	rotating or fixed	MESA	LESA	LEPA
 Canopy evaporation	Yes		
 Impounded water evaporation	No	Yes	
 Wetted soil evaporation	Yes	Yes	
 Surface water redistribution	No,		Yes,	Yes	(not major unless	Yes
 Runoff		Yes	Yes	surface storage is	not used)
 Percolation	No	No	No	No
 Windy and hot conditions during the growing season affect center pivot sprinkler irrigation uniformity and evaporative losses.
As a result many producers in the southern and central Great Plains have adopted sprinkler packages and methods that apply the water at a lower height within or near the crop canopy height, thus avoiding some application nonuniformity caused by wind and also droplet evaporative losses.
In-canopy and near-canopy sprinkler application can reduce evaporative losses by nearly 15% , but introduce a much greater potential for irrigation nonuniformity.
These sprinkler package systems are often adopted without appropriate understanding of the requirements for proper water management, and thus, other problems such as runoff and poor soil water redistribution occur.
Table 2.
Partitioning of sprinkler irrigation evaporation losses with a typical 1 inch application for various sprinkler packages..
Sprinkler package	Air	Canopy	Ground	Total	Application
 loss, %	loss, %	loss, %	loss, %	efficiency, %*
 = 14 ft height	3	12	--	15	85
 = 5 ft height	1	7	--	8	92
 = 1 ft height	--	--	2	2	98
 * Ground runoff and deep percolation are considered negligible in these data.
Traditionally, center pivot sprinkler irrigation systems have been designed to uniformly apply water to the soil at a rate less than the soil intake rate to prevent runoff from occurring.
These design guidelines need to be either followed or intentionally circumvented with appropriate design criteria when designing and managing an irrigation system that applies water within the canopy or near the canopy height where the full sprinkler wetted radius is not developed.
Peak application rates for in-canopy sprinklers such as LESA  and LEPA  might easily be 5 to 30 times greater than above-canopy sprinklers.
Runoff from LEPA sprinklers was negligible on 1% sloping silt loam soils in eastern Colorado but exceeded 30% when slopes increased to 3%.
Runoff from LEPA with basin tillage was approximately 22% of the total applied water and twice as great as MESA  for grain sorghum production on a clay loam in Texas.
Basin tillage created by periodic diking of crop furrow , rather than reservoir tillage created by pitting or digging small depressions , is often more effective at time averaging of LEPA application rates, and thus, preventing runoff.
Distance from nozzle centerline 
 Figure 2.
Application intensities for LEPA, LESA, MESA, rotating sprays on span and impact sprinklers on the span as related to the typical size of their wetting pattern.
Decreasing the application intensity is the most effective way to prevent irrigation field runoff losses and surface redistribution within the field  When runoff and surface redistribution occurs using in-canopy sprinklers because of a reduced wetting pattern, one solution would be to raise the sprinkler height.
Figure.
3.
Illustration of runoff or surface water redistribution potential for impact and LESA sprinkler application packages for an example soil.
After Howell.
One might assume that the erraticity observed in sprinkler irrigated fields in 2011 was primarily associated with the evaporative water loss components shown in Table 1, but that is probably not the case.
When using fixed plate applicators near or within the canopy , the magnitude of field runoff and particularly surface redistribution within the field may overwhelm the evaporative loss reductions possible with these packages.
Surveys conducted by Kansas State University have indicated that approximately 90% of the center pivot sprinkler systems in western Kansas use fixed plate applicators and nearly 60% have sprinkler nozzle height less than 4 ft above the soil surface.
The erraticity can be caused by failure to follow appropriate guidelines for irrigation with nearand in-canopy sprinklers.
SOME GUIDING PRINCIPLES FOR IN-CANOPY APPLICATION
 A prototype of the LEPA system was developed as early as 1976 by Bill Lyle with Texas A&M University.
Jim Bordovsky joined the development effort in 1978  and the first scientific publication of their work was in 1981.
Although, originally LEPA was used in every furrow, subsequent research  demonstrated the superiority for alternate furrow LEPA.
The reasons are not always evident, but they may result from the deeper irrigation penetration , possible improved crop rooting and deeper nutrient uptake, and less surface water evaporation.
The seven guiding principles of LEPA were given by Lyle  as:
 1) Use of a moving overhead tower supported pipe system 
 2) Capable of conveying and discharging water into a single crop furrow
 3) Water discharge very near the soil surface to negate evaporation in the air
 4) Operation with lateral end pressure no greater than 10 psi when the end tower is at the highest field elevation
 5) Applicator devices are located so that each plant has equal opportunity to the water with the only acceptable deviation being where nonuniformity is caused by nozzle sizing and topographic changes
 6) Zero runoff from the water application point
 7) Rainfall retention which is demonstrably greater than conventionally tilled and managed systems.
The other types of in-canopy and near-canopy sprinkler irrigation do not necessarily require adherence to all of these seven guidelines.
However, it is unfortunate that there has been a lack of knowledge or lack of understanding of the importance of these principles because many of the problems associated with in-canopy and near-canopy sprinkler irrigation can be traced back to a failure to follow or effectively "work around" one of these principles.
In-canopy and near-canopy application systems can definitely reduce evaporative losses
 , but these water savings must be balanced against runoff and within field water redistribution, deep percolation and other soil water nonuniformity problems that can occur when the systems are improperly designed and managed.
PROVIDING PLANTS EQUAL OPPORTUNITY TO ROOT-ZONE SOIL WATER
 The No.
5 LEPA guiding principle listed earlier emphasizes the importance of plants having equal opportunity to root-zone soil water.
Ensuring this equal opportunity requires sufficient uniformity of water application and/or soil water infiltration.
Key issues that must be addressed are irrigation application symmetry, Crop row orientation with respect to center pivot sprinkler direction of travel, and the seasonal longevity of the sprinkler pattern distortion caused by crop canopy interference.
SYMMETRY OF SPRINKLER APPLICATION
 Increased sprinkler application uniformity will often result in increased yields, decreased runoff, and decreased percolation.
Improved sprinkler uniformity can be desirable from both economic and environmental standpoints.
Their study indicated irrigation nonuniformity can result in nutrient leaching from over-irrigation and water stress from under-irrigation.
Both problems can cause significant economic reductions.
Sprinkler irrigation does not necessarily have to be a uniform broadcast application to result in each plant having equal opportunity to the irrigation water.
Equal opportunity can still be ensured using a LEPA nozzle in the furrow between adjacent pairs of crop rows provided runoff is controlled.
Figure 4.
LEPA concept of equal opportunity of plants to applied water.
LEPA heads are centered between adjacent pairs of corn rows.
Using a 5-ft nozzle spacing with 30-inch spaced crop rows planted circularly results in plants being approximately 15 inches from the nearest sprinkler.
After Lamm.
Some sprinkler application nonuniformity can also be tolerated when the crop has an intensive root system.
When the crop has an extensive root system, the effective uniformity experienced by the crop can be high even though the actual resulting irrigation system uniformity within the soil may be quite low.
Additionally, when irrigation is deficit or limited, a lower value of application uniformity can be acceptable in some cases  as long as the crop economic yield threshold is met.
Many irrigators in the U.S.
Great Plains are using wider in-canopy sprinkler spacings  in an attempt to reduce investment costs.
Surveys from western Kansas in 2005 and 2006 indicated only 34% of all sprinkler systems with nozzle height of less than 4 ft had consistent nozzle spacing less than 8 ft.
Sprinkler nozzles operating within a fully developed corn canopy experience considerable pattern distortion and the uniformity is severely reduced as nozzle spacing increases.
Figure 5.
Differences in application amounts and application patterns as affected by sprinkler nozzle height and spacing.
Center pivot sprinkler lateral is traversing parallel to the circular corn rows.
Data are from a fully developed corn canopy, July 1996, KSU Northwest Research-Extension Center, Colby, Kansas.
Data are mirrored about the nozzle centerline for display purposes.
Arrows on X-axis represent location of corn rows and thus the location for higher stemflow amounts.
Although Figure 5 indicates large application nonuniformity, these differences may or may not always result in crop yield differences.
Hart  concluded from computer simulations that differences in irrigation water distribution occurring over a distance of approximately 3 ft were probably of little overall consequence and would be evened out through soil water redistribution.
Some irrigators in the Central Great Plains contend that their low capacity systems on nearly level fields restrict runoff to the general area of application.
However, nearly every field has small changes in land slope and field depressions which do cause field runoff, in-field redistribution or deep percolation in ponded areas when the irrigation application rate exceeds the soil infiltration rate.
In the extreme drought years of 2000 to 2003 that occurred in the U.S Central Great Plains, even small amounts of surface water movement affected sprinkler-irrigated corn production.
Similarly some of the worst erraticity in sprinkler-irrigated corn observed in the summer of 2011 was for sprinklers with 10 ft spaced in-canopy sprinkler packages.
Figure 6.
Large differences in corn plant height and ear size for in-canopy sprinkler application over a short 10-ft.
distance  as caused by small field microrelief differences and the resulting surface water movement during an extreme drought year, Colby, Kansas, 2002.
The upper stalk and leaves have been removed to emphasize the ear height and size differences.
Figure 7.
Erraticity of sprinkler irrigated corn in southwest Kansas in 2011 under extreme drought conditions thought to be related to a nozzle spacing too wide  for incanopy application.
CROP ROW ORIENTATION WITH RESPECT TO DIRECTION OF SPRINKLER TRAVEL
 When using in-canopy sprinkler application, it has been recommended that crop rows be planted circularly so that the crop rows are always perpendicular to the center pivot sprinkler lateral.
Matching the direction of sprinkler travel to the row orientation satisfies the important LEPA Principles 2 and 5 noted by Lyle  concerning water delivery to one individual crop furrow and equal opportunity to water by for all plants.
Producers are often reluctant to plant row crops in circular rows because of the cultivation and harvesting difficulties of narrow or wide "guess" rows.
However, using in-canopy application for center pivot sprinkler systems in non-circular crop rows can pose two additional problems.
In cases where the CP lateral is perpendicular to the crop rows and the sprinkler spacing exceeds twice the crop row spacing, there will be nonuniform water distribution because of pattern distortion.
When the CP lateral is parallel to the crop rows there may be excessive runoff due to the great amount of water being applied in just one or a few crop furrows.
There can be great differences in incanopy application amounts and patterns between the two crop row orientations.
Figure 8.
Two problematic orientations for in-canopy sprinklers when crops are not planted in circular rows.
Figure 9.
Differences in application amounts and application patterns as affected by corn row orientation with respect to the center pivot sprinkler lateral travel direction.
Dotted lines indicate location of corn rows and stemflow measurements.
Data are from a fully developed corn canopy, July 23-24, 1998, KSU Northwest Research-Extension Center, Colby, KS.
Data are mirrored about the centerline of the nozzle.
PATTERN DISTORTION AND TIME OF SEASON
 Drop spray nozzles just below the center pivot sprinkler lateral truss rods  have been used for over 30 years in northwest Kansas.
This configuration rarely has had negative effects on corn yields although the irrigation pattern is distorted after corn tasseling.
The reasons are that there is only a small amount of pattern distortion by the smaller upper leaves and tassels and this distortion only occurs during the last 30 to 40 days of the irrigation season.
In essence, the irrigation season ends before a severe soil water deficit occurs.
Compare this situation with spray heads at a height of 1 to 2 ft that may experience pattern distortion for more than 60 days of the irrigation season.
Under dry and elevated evapotranspiration conditions in 1996, row-to-row corn height differences developed rapidly for 10-ft spaced sprinkler nozzles at a 4 ft nozzle height following a single one-inch irrigation event at the KSU Northwest Research-Extension Center, Colby Kansas.
A long term study  at the same location on a deep silt loam soil found that lowering an acceptably spaced  spinner head from 7 ft further into the crop canopy  caused significant row-to-row differences in corn yields.
Figure 10.
Crop height difference that developed rapidly under a widely spaced  in-canopy sprinkler  following a single 1 inch irrigation event at the KSU Northwest Research-Extension Center, Colby, Kansas.
Photo taken on July 6, 1996.
Figure 11.
Row-to-row variations in corn yields as affected by sprinkler height for 10 ft.
spaced in-canopy sprinklers.
Sprinkler lateral travel direction was parallel to crop rows.
Data was averaged from four irrigation levels for 1996 to 2001, KSU Northwest ResearchExtension Center, Colby, Kansas.
COMBINATION OF EFFECTS CAN CAUSE ERRATICITY
 Sometimes poor design, installation or maintenance problems can exist for years before they are visually observed as sprinkler irrigation erraticity.
It may take severe drought conditions for some of these subtle effects to combine to such an extent to be noticeable erraticity.
In addition, smaller row-to-row differences in crop yield cannot be measured with yield monitors on commercial-sized harvesters.
An example of a combination several of these subtle effects was observed during the severe drought of 2002 in northwest Kansas.
The small nozzle height difference on this sprinkler allowed at least three small effects to combine negatively to cause the sprinkler erraticity:
 1.
Since there are no pressure regulators, the small height difference results in unequal flow rates for these low pressure spray nozzles.
2.
There is a incorrect overlap of the sprinkler pattern due to the height difference with one sprinkler within the canopy while the other two nozzles are above the canopy.
3.
Evaporative losses would be greater for the nozzles above the crop canopy.
Figure 12.
Erraticity of sprinkler-irrigated corn near Colby, Kansas during the extreme drought year of 2002.
The drought that southwest Kansas experienced in 2011 was devastating to production on many sprinkler irrigated corn fields, but the erraticity did highlight some design and management issues that producer might address before the next irrigation season:
 1.
Does the selected sprinkler package strike the correct balance in reducing evaporative losses without increasing irrigation runoff or in-field water redistribution?
2.
Does the sprinkler package and its installation characteristics provide the crop with equal opportunity to applied or infiltrated water?
3.
Are the sprinkler nozzle heights and spacings appropriate for the intended cropping?
4.
Should planting of taller row crops such as corn be in circular patterns if incanopy sprinklers are used?
5.
Are there subtle irrigation system characteristics  that might combine negatively to reduce crop yields?
These design and management improvements won't change the weather conditions, but they might change how the crop weathers future droughts.
This paper is the result of cooperative efforts of the authors through the Ogallala Aquifer Program, a consortium between USDA Agricultural Research Service, Kansas State University, Texas AgriLife Research, Texas AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
This is a joint contribution from Kansas State University, USDA Agricultural Research Service and Texas A&M University.
Contribution no.
12-309-A from the Kansas Agricultural Experiment Station.
This paper was first presented at the Central Plains Irrigation Conference, February 21-22, 2012, Colby, Kansas.
It can be cited as
DOES DEFICIT IRRIGATION GIVE MORE CROP PER DROP?
Tom Trout, Walter Bausch and Gerald Buchleiter Water Management Research, USDA-Agricultural Research Service Fort Collins, CO 970-492-7419 Email: Thomas.trout@ars.usda.gov.
Past studies have shown that the reduction in yield with deficit irrigation is usually less than the reduction in irrigation water applied for example, a 30% reduction in irrigation results in only a 10% reduction in yield.
This means the marginal productivity of irrigation water applied tends to be low when water application is near full irrigation.
This results either from increased efficiency of water applications  with deficit irrigation, or from a physiological response in plants that increases productivity per unit water consumed when water is limited.
Economically managing limited water supplies will often involve deficit irrigation rather than reducing acreage.
Likewise, if water supplies can be transferred or sold for other uses and the value is higher than the value of using the water to produce maximum yields, selling the water can increase the farm income.
In Colorado, there is continuing need for additional water supplies for growing cities, groundwater augmentation, and environmental restoration.
This water is usually purchased from agriculture through "buy and dry" purchasing the water rights and fallowing the land.
Limited irrigation may be an alternative way to provide for other water needs while sustaining productive agriculture.
However, in fully allocated basins where one farmer's return flows becomes water supplies for downstream users, only the consumed portion of irrigation supplies that lost to evapotranspiration can be sold and the return flows must be maintained.
Thus, it becomes critical to evaluate limited irrigation based on reductions in water consumptive use  or equivalently, evapotranspiration  rather than irrigation applications.
Improved irrigation efficiency is not likely to produce much transferable water because it results primarily in a reduction of return flows rather than a reduction in ET.
If significant transferable water is to be produced by deficit irrigation, it must result from reduced ET.
For deficit irrigation to provide economic benefits to growers, it must result in improved efficiency of the crop to convert ET to yield.
Thus, the "maximize crop per drop" slogan must in reality be to maximize crop per consumptively used drop.
Although many limited irrigation studies have been carried out in the high plains and around the world, we feel there continues to be a need for more information on crop responses to deficit irrigation.
So, in 2008, USDA-ARS began a field study of the water productivity of 4 high plains crops corn, dry beans, wheat, and sunflower under a wide range of irrigation levels from fully irrigated to rainfed.
We are measuring ET of the crops under each of these conditions.
We also strive to better understand and predict the responses of the crops to deficit irrigation so that limited irrigation water can be scheduled and managed to maximize yields.
The Limited Irrigation Research Farm LIRF
 A 50 acre research farm northeast of Greeley, CO was developed to enable the precision water control and field measurements required to accurately measure ET of field crops.
The farm, originally known as the Potato Research Farm and later as the Northern Colorado Research and Demonstration Center had been operated collaboratively by CSU and ARS for many years , but had not been in active research for over 20 years.
The predominately sandy-loam soils and good groundwater well are ideal for irrigation research.
Four crops winter wheat, field corn, sunflower , and dry beans  are rotated through research fields on the farm.
Crops are planted, fertilized, and managed for maximum production under fully irrigated conditions, but are irrigated at 6 levels that range from fully irrigated to only 40% of the fully irrigated amount.
Deficit irrigations are timed to maximize production usually by allowing relatively higher stress during early vegetative and late maturity stages and applying extra water to reduce stress during reproductive stages.
We apply irrigation water with drip irrigation tubes placed on the soil surface in each row.
In this way we can accurately measure applications and know that the water is applied uniformly.
This is essential to be able to complete the water balance.
Water applied to each irrigation plot is measured with flow meters.
Four crops, six irrigation levels, and 4 replications results in 96 individual plots.
A CoAgMet  automated weather station is located on the farm near the center of a one acre grass plot.
Hourly weather data from the station are used to calculate ASCE Standardized PenmanMonteith alfalfa reference evapotranspiration.
Soil water content between 6 inches and 6 ft depth is measured by a neutron probe from an access tube in the center of each plot.
Soil water content in the surface 6 inches is measured with a portable TDR system.
Irrigations are scheduled using both predicted soil water depletions based on ETr measurements, and measured soil water depletion.
Plant measurements are taken periodically to determine crop responses to the water levels.
We record plant growth stage and measure canopy cover with digital cameras.
The digital cameras along with spectral radiometers and an infrared thermometer are mounted on a "high boy" mobile platform and driven through the plots weekly.
Indicators of crop water stress such as stomatal conductance, canopy temperature, and leaf water potential are measured periodically.
At the end of the season, seed yield and quality as well as total biomass are measured from each plot.
On one field on the farm, crop ET is measured with energy balance instruments  for well watered crops.
These measurements allow crop coefficients to be estimated for the crops.
On other fields on the farm, we are cooperating with CSU faculty to test wheat and dry bean varieties under varying irrigation levels.
An important part of the research is to extend the results beyond the climate and soils at LIRF.
We are working with the ARS Agricultural Systems Research group to use this field data to improve and validate crop models.
Once we have confidence in the models, we can estimate crop water use and yields over a wide range of conditions.
This project began in 2008.
We will summarize the first two years of corn results in this article.
Figure 1 shows the yield:water relationship for corn for each year.
Irrigation applications  varied from about 430 mm  for the fully irrigated crop down to 120 mm.
When precipitation is added in  each growing season), deep percolation below the root zone is subtracted out, and depletion of stored soil water is included, the evapotranspiration for the crops varied from about 590 mm  down to 380 mm.
Of that ET, about 60 90 mm was evaporation from the soil surface and the remainder was transpiration through the plants.
Soil evaporation would be higher with sprinkler or furrow irrigation.
Irrigations were timed such that plant water stress for the deficit irrigation levels was least between tasseling and soft dough.
The top  data in the figure are total above ground biomass  and the bottom lines  are grain yields.
Grain yields varied from 13 Mg/ha  at full irrigation down to 6 Mg/ha  and biomass was about double grain yields.
Hail damage in 2009 resulted in about 15% lower grain yields but little difference in total biomass.
Harvest index  ranged from 50 60% and did not vary with irrigation level.
The water production function for grain  based on applied irrigation water curves downward as the water application decreases, showing that the decrease in yield for each unit decrease in water applied is relatively small when the deficit is small, but the rate of yield decrease gets larger as the deficit
 Figure 1.
Water production functions for 2008 and 2009 corn.
Red lines  are total biomass.
Blue lines  are grain yield.
Yields are plotted relative to irrigation amount  and crop ET.
Triangles and dashed lines are 2008 data.
Squares and solid lines are 2009 data.
Figure 2.
Comparison of corn growth condition on July 31, 2008 just before tasseling.
Rows at the left and background are fully irrigated; rows at right are the lowest irrigation level.
increases.
This means that the marginal value of irrigation water is relatively low near full irrigation, showing the potential benefit to the farmer of transferring water to higher-valued uses.
The marginal value of water increases from about 1.3 kg/m  of water applied near full irrigation to 3 kg/m 3  at the lowest irrigation level.
However, the water production function for grain yield based on ET is relatively straight.
This implies that the corn is equally efficient in it's use of every additional unit of water consumed and the marginal value of the consumptively used water is fairly constant over the wide range of applications about 3 kg/mi 3.
These results imply that nearly all of the increase in the marginal value of applied water with deficit irrigation results from more effective use of precipitation and increased use of stored soil water, or conversely, the lower marginal value of water near full irrigation is due to inefficient use of rainfall and irrigation water.
The marginal value of applied water near full irrigation would be even smaller with less efficient irrigation systems since more of the applied water would be lost to runoff and deep percolation.
These results also imply that, based on consumptive use, there would be little or no yield benefit to deficit irrigation compared to fully irrigating only a portion of the land.
In fact, fully irrigating less land would likely provide the highest economic returns due to lower production costs.
These preliminary results show the importance of developing water production functions based on the correct unit of water.
If water value is based on cost of the water supply , then productivity based on applied water is important.
However, for the purpose of transferring consumptive use savings, the productivity must be based on water consumed.
The value of limited irrigation based on CU savings will likely be less, and if the crop is efficient at converting increased CU to yield, there may be no economic benefit to limited irrigation.
This limited irrigation study will be continued to confirm these initial results for each of the four crops.
Chapter: 44 Weed Management in Organic Corn Production
 In numerous surveys of organic growers, weed management and control issues rise to the top of their list of major problems in grain and vegetable cropping systems.
Undesirable plants interfere with production, may reduce yields, may cause problems with harvest, and reduce product quality.
Early emerging weeds and high weed densities usually cause the greatest yield reductions, whereas late-emerging weeds may interfere with harvest operations and taint harvested products.
Typically, a successful organic weed-management system relies on rotational cropping as a base with further control provided through integrated methods.
Most chemical control for weeds is not allowed in organic production.
Therefore, the "many little hammers" approach for weed control and management is often discussed, as a single operation will not provide acceptable control.
Weeds should be disrupted at key points during their life cycle to prevent growth and seed production.
Weed management should be a planned system over several years and include mechanical or physical methods, cultural control, and biological control techniques, where possible.
Starting with a clean seedbed helps the crop establish without weed interference.
Then, good management practices should be used that encourage faster corn growth to overtop and outcompete shorter weeds and to provide thicker and
 Role of Competitive Crops and Crop Rotations
 Conventional systems that have used synthetic fertilizers and pesticides cannot become certified as "organic systems" in a single year.
Several years are needed to transition away from these chemicals.
During the transition period, competitive crops should be grown and managed to reduce the weed seed bank in the soil.
Once organic certification is achieved, these crops can be used in rotation to aid in weed management.
Successful organic systems generally rely on multiyear, soil fertility and pest  management plans.
Crop rotations that minimize bridging of diseases and insects from one year to the next also help the main crop remain healthy and better able to withstand other abiotic and biotic stresses.
The management plan may include cover crops  and the use of crop seed free of disease and weed seed.
Critical criteria for getting a "good" start include seedbed preparation, optimal planting dates and seeding rates, and the use of approved materials.
Alfalfa can be grown for 2 to 3 years to help minimize weeds.
When planting alfalfa, choose a variety that regrows quickly and use a companion crop such as oats to help control weeds during alfalfa establishment.
In trials at South Dakota State University, it has been found that no herbicides are needed during establishment, and even though the field may be quite weedy, alfalfa can establish well.
Cut alfalfa at optimum times and heights, leaving enough plant to provide vigorous regrowth, and do not cut too late in the fall , SO that root carbohydrates have sufficient time to replenish for overwintering conditions.
In the first year, if planted with oats, cut oats at heading , and then allow the alfalfa to grow until midto late-bloom.
This typically is the only cut during the first year.
In the second and third years, alfalfa should be cut two or three times at recommended timings.
A benefit to alfalfa in the rotation is that weeds are also cut and not allowed to go to seed.
Typically, this will help deplete the weed seed bank and the fast regrowth of alfalfa will not allow new weeds to establish.
Do not allow the stand to stay in SO long that it becomes weak and noncompetitive.
Another concern if the stand stays in too long is that alfalfa will dry the soil.
These concerns must be balanced against the value of a good alfalfa crop and the weed control that it brings to the system.
When coming out of alfalfa, tillage should be done in the fall or spring, preceding corn planting.
The mechanical disruption of the terminated alfalfa will slow its regrowth, and volunteer alfalfa plants, even if present, typically do not result in reduction of corn yields.
Smother crops can provide an environment where weeds do not thrive and weed seed banks can be depleted.
Buckwheat, cereal rye, sorghum, corn for silage, and other crops may be used for this purpose.
Typically, seeding rates are high and rows are narrow to get early canopy cover.
If planted in narrow rows, cultivation is not used for in-season control, whereas wide-row plantings may require between-row weed control  to minimize weed populations.
Short-season spring crops may be followed with overwintering crops.
Residues may be left on the field to further hamper weed establishment.
Cover crops planted after a short-season spring crop or interseeded into crops after the critical weed-free period can also provide some weed suppression.
Vigorous cover crops not killed by overwinter conditions must be controlled through physical means prior to seeding cash crops because these vigorous plants will act as weeds.
Flail mowing before seed set in cereal rye has provided successful control in the spring, as has roller-crimping immediately after rye flowering.
The mowed or crimped rye can form mulch and, if thick enough , prevents emergence of weed seedlings.
Additionally, some cover-crop species, including rye and radish , have allelochemicals in the residue that are leached into the soil, further hampering weed-seed germination and reducing weed pressure.
Physical Weed Control for Weed Management
 Physical weed control is the most widely used method for immediate weed control in organic systems.
Plastic barriers and hand-hoeing may be used throughout the field to minimize weeds in high-value crops, such as sweet corn, and transplanted crops, such as tomatoes and peppers.
In grain and commodity crops, these operations may be too expensive, except in small areas where extra weed management may be needed, such as isolated patches of perennial weeds.
Other physical means of weed control include cultivation , flaming, hoeing, and abrasive-grit applications.
Many types of cultivation implements are available and may be used once or many times during the season.
Cultivation provides a clean seedbed and can be used to provide immediate control of weeds between the rows.
In the Midwest, two or three cultivations are typical for organic corn grain systems.
Timing for all cultivation operations is critical, and it may take several years to establish optimal timing for weed control in your fields.
However, complacency and performing the same operation at the same time every year will result in a spread of species other than those that were originally problematic.
Rotary hoeing and harrowing can be used if the corn and weeds are not too large.
Rotary hoeing on a diagonal, rather than up and down the rows, at 10 to 12 mph is purported to provide the greatest weed control.
Figure 44.2 Rotary hoe operation to remove small weeds.
There are challenges with cultivation that should be considered prior to adoption.
In rolling landscapes, erosion possibilities may outweigh the benefits of tillage and should be assessed because permanent damage can occur to soils with one untimely operation.
Soil health may also be reduced by untimely operations causing crusting, reduced water infiltration, and reduced organic matter and residues in surface soils.
Mulching with residues, plastic, or approved organic plant meals  hampers weed germination, establishment, and development.
Meal application rates are often very high, at hundreds of pounds per acre.
Placement should be between rows SO that crop growth and development are unimpeded.
However, within-row weed management should not be forgotten, as weeds
 closest to the crop tend to cause the greatest yield loss.
If within-row weeds become a problem, abrasive grits sprayed toward the base of the crop plants, hand-hoeing, or shielded cultivators to get as close to the crop as possible may need to be used.
Hand-hoeing is a time-tested approach to control weeds.
However, the practice is often overlooked in organic production fields because of cost and labor requirements.
Notwithstanding, new infestations of a weed, control of within-row weeds, or control of scattered plants may warrant individual attention.
Weed seeds can last in the seed bank for 3 to 50 years, and one weed can produce several hundred to several hundred thousand seeds.
"An ounce of prevention, can be worth pounds of cure" through careful management, weeds can be controlled.
Flaming, Steaming, and Microwave Systems
 Flaming, steaming, and microwave systems have been used to kill weeds through desiccation and hightemperature exposure.
Young weeds  can be killed quite readily with these practices.
Larger weeds need to be treated for a longer period of time and the growing point must be affected.
The problem with these methods is that the contact time needs to be optimized, often leading to slow operating speeds for equipment, low labor efficiency, and high fuel bills.
Caution must be Figure 44.4 An image of a propane flamer.
Typically, corn can withstand the heat if the growing point is below the soil surface, but care must be taken not to directly heat the crop, once the growing point is above ground.
Figure 44.3 Carefully tended cropping areas in Vietnam display minimal weed problems.
Abrasive-grit systems are being tested by SDSU, the University of Illinois, and USDA-ARS for their ability to control weeds.
The machine uses organically certified grits  applied at 100 psi to in-row weeds with nozzles pointed toward the base of the plant.
The grit blasts the weeds causing enough damage to kill young broadleaf weeds and injure the growing points of older weeds.
We found that two operations, one at V1 or V2 and another at V3 or V4, controlled broadleaf Figure 44.5 Four-row grit applicator for weed control weeds and maintained cash-crop yield.
If the operation in row crops designed by SDSU Ag & Biosystems occurred at V5, weeds were well-developed and, while Engineering Dept.
Ground corncob grit was used as the spray.
earlier interference, corn yield was reduced  unpublished data).
Timing on grass weeds needs more research because of the ability of a defoliated plant to regrow if the growing point is below ground at the time of treatment.
Optimization of grit types, rates, timing, and spectrum of weeds controlled are still in the early stage of research.
Robotic Hoeing and Flaming
 Recent developments in nonchemical weed control include the "Robovator," a robotic implement that hoes weeds within crop rows.
In this case, the crops have to be precision-planted and the Robovator uses a knife to remove any and all plants between the spaced crop plants.
An equally innovative implement is a robotic flame weeder that senses the presence of a crop plant and withholds a flame jet, but singes all other plants.
There are some chemical herbicides approved for use in organic production, however, the efficacy of these applications are inconsistent in South Dakota.
In 2015, sprays approved for application for weed control in organic systems with or without approved organic surfactants included: clove, cinnamon, and garlic oils; citric acid; and ammonium nonanoate.
Reports from credible research trials should be consulted prior to purchase, as rates, surfactant types, and timing of applications have had mixed results.
As with any pesticide application, always read and follow label directions.
Premium prices for organically grown crops can be financially beneficial.
However, based on numerous Camera detects crop plants surveys of organic producers, weed management is one of the most challenging aspects of growing organic crops.
As in conventional systems, there is no one "silver bullet" technique for weed control.
Understanding the biology of the weedy species infesting the area will help in planning timely operations to disrupt weed establishment and growth.
The use of many diverse techniques  and crop rotations are key aspects to minimize weed problems in organic farming.
Figure 44.6 Robovator that was developed to combine "smart sensors" with knives to mechanically hoe organic fields.
Figure 44.7 A "smart" flame weeder that uses sensors to detect weeds in the interrow of transplanted crops.
Note that some areas are being flamed and other areas are not.
MAINTAINING DRIP IRRIGATION SYSTEMS
 BY GARY A.
CLARK WILLIAM J.
LAMONT JR.
CHARLES W.
MARR DANNY ROGERS
 Drip irrigation systems are becoming more widely used for horticultural crop production, especially vegetable crops.
The system must function efficiently during the entire growing season.
Failure at a critical point in the crop production cycle can cause loss of the entire crop.
System failures often are due to inadequate maintenance of the system, especially if fertigation is being utilized to supply nutrients to the plant's root zone.
Maintenance of the drip irrigation system does take time and understanding; however, maintenance is critical for its successful use.
This guide should help you understand how to maintain drip irrigation systems.
Water for drip irrigation can come from wells, ponds, rivers, lakes, municipal water systems, or plastic-lined pits.
Water from these various sources will have large differences in quality.
Well water and municipal water is generally clean and may require only a screen or disk filter to remove particles.
However, no matter how clean the water looks, a water analysis/quality test prior to considering installation of a drip irrigation system should be completed to determine if precipitates or other contaminants are in the water.
This water quality analysis should identify inorganic solids such as sand and silt; organic solids such as algae, bacteria, and slime; dissolved solids such as iron, sulphur, sodium chlorides, and calcium; and pH of the water.
Water testing can be done by a number of laboratories in the state.
Your local Cooperative
 Extension Service  county agent can supply a list of laboratories or suggest a local lab that can do water quality analysis.
Check with the lab first to obtain a sample kit containing a sampling bottle that is clean and uncontaminated.
In addition to quality factors, ask for any additional tests that might be necessary.
If the water also is to be used as a household supply or as a drinking water source, a basic drinking water analysis, which includes bacterial counts, nitrates, or other suggested tests, should be done.
Most well water in Kansas has relatively high pH and hardness.
Shallow wells in river valleys often contain high concentrations of iron and manganese.
Hydrogen sulfide often can be detected by a bad "rotten egg" smell and is fairly rare in Kansas.
If a review of your water test indicates factors that may cause plugging , then special care in drip system maintenance needs to be practiced.
High levels of a factor might not render a well unsuitable for drip irrigation but will make appropriate water treatment a requirement before successful use in a drip irrigation system.
Any surface water such as streams, ponds, lakes, rivers, or pits will contain bacteria, algae, or other aquatic life.
Sand media filters are absolute necessities.
Even though sand media filters will be more expensive than screen or grooved-disk filters, they are highly recommended for water sources that have high levels of suspended organic and inorganic materials.
KEYS TO SUCCESSFUL ADOPTION OF SDI: MINIMIZING PROBLEMS AND ENSURING LONGEVITY
 Since 1989, research studies and demonstration studies at the Northwest and Southwest Research-Extension Centers of Kansas State University have indicated that subsurface drip irrigation  systems can be efficient, long-lived, and adaptable for irrigating corn and other deep-rooted crops.
A survey of all Kansas SDI users in 2003 revealed an estimated 14,000 acres were irrigated with SDI systems.
Though system usage has grown steadily over the years, SDI systems are currently used on less than 1% of total irrigated acres.
The 2006 Kansas Irrigation Water Use Report indicated that 10,250 acres were exclusively irrigated by SDI systems and an additional 8,440 acres were irrigated partially by SDI in combination with another system type, such as an irrigated SDI corner of a center pivot sprinkler or a surface gravityirrigated field partially converted to SDI.
Many producers have had successful experiences with SDI systems despite minor technical difficulties during the adoption process.
In a 2005 survey of SDI users, nearly 80% of Kansas producers indicated they were at least satisfied with the performance of their SDI system, and less than 4% indicated they were not satisfied.
However, even satisfied users indicated a need for additional SDI management information.
The most noted concern was the damage and repairs caused by rodents.
A few systems had failed or had been abandoned after a short-use period due to inadequate design, inadequate management or a combination of both.
Design and management are closely linked in a successful SDI system.
Research studies and on-farm producers both indicate that SDI systems result in high-yielding crops and water-conserving production practices only when the systems are properly designed, installed, operated and maintained.
A system that is improperly designed and installed will be difficult to operate and maintain and most likely will not achieve high irrigation water application uniformity and efficiency goals.
However, proper design and installation does not ensure high SDI efficiency and long system life.
An SDI system must also be operated
 according to design specifications and utilize good irrigation water management procedures to achieve high uniformity and efficiency.
An SDI system is also destined for early failure without proper maintenance.
This paper will review key factors for successful adoption of SDI for Kansas irrigated agriculture.
MINIMUM SDI COMPONENTS FOR EFFICIENT WATER DISTRIBUTION AND SYSTEM LONGEVITY
 SDI system design must consider individual management restraints and goals, as well as account for specific field and soil characteristics, water quality, well capabilities, desired crops, production systems, and producer goals.
However, certain basic features are a part of all SDI systems, as shown in Figure 1.
The long-term ability of the producer to operate and maintain the system in an efficient manner is seriously undermined if any of the minimum components are omitted during the design process.
Minimum SDI system components should not be sacrificed as design and installation cost-cutting measures.
If minimum SDI components cannot be included as part of the system, an alternative type of irrigation system or a dryland production system should be considered.
Figure 1.
Minimum components of an SDI system.
K-State Research and Extension Bulletin MF-2576, Subsurface Drip Irrigation  Component: Minimum Requirements
 Water distribution components of an SDI system include the pumping station, the main, submains and dripline laterals.
Sizing requirements for the mains and submains are somewhat similar to underground service pipe to center pivot sprinklers or main pipelines for surface-irrigated gravity systems and are determined by the flow rate and acceptable friction loss within the pipe.
In general, the flow rate and friction loss determines the dripline size  for a given dripline lateral length and land slope.
An SDI system consisting of only the distribution components would have no method to monitor system performance and the system would not have any protection from clogging or any methods to conduct system maintenance.
Clogging of dripline emitters is the primary reason for SDI system failure.
In addition to basic water distribution components, additional components allow the producers to monitor SDI system performance, allow flushing, and protect or maintain performance by injection of chemical treatments.
The injection equipment can also be used to provide additional nutrients or chemicals for crop production.
A backflow prevention device is required to protect the source water from accidental contamination if backflow should occur.
The actual characteristics and field layout of an SDI system vary from site to site, but irrigators often add additional capabilities to their systems.
For example, the SDI system in Figure 2 shows additional valves that allow the irrigation zone to be split into two flushing zones.
When the well or pump does not have the capacity to provide additional flow and pressure to meet the flushing requirements for the irrigation zone, splitting the zone into two parts may be an important design feature.
The American Society of Agricultural and Biological Engineers  recommends a minimum flushing velocity of 1 ft/s for microirrigation lateral maintenance.
This flushing velocity requirement needs to be carefully considered at the design stage, and may dictate larger sizes for submains and flushlines to assure that maximum operating pressures for the driplines are not exceeded.
Filter systems are generally sized to remove particles that are approximately 1/10 the diameter of the smallest emitter passageway.
However, small particles still pass through the filter and into the driplines, and over time, they can clump together.
Also, biological or chemical processes produce materials that need to be removed to prevent emitter clogging or a build-up of material at the outlet or distal end of the system.
Opening the flushline valves allows water to rapidly pass through the driplines, carrying away any accumulated particles.
A good design should allow flushing of all pipeline and system components.
The frequency of flushing is largely determined by the quality of the irrigation water and to a degree, the level of filtration.
A good measure of the need to flush is to evaluate the amount of debris caught in a mesh cloth during a flushing event.
When only a small amount of debris is found, the flushing interval may be increased.
Heavy accumulations of debris, however, mean more frequent flushing is needed.
Figure 2.
Layout for a well-designed SDI system.
In SDI systems, all water application is underground.
Because no surface wetting occurs in properly installed and operated systems, no visual cues of system operation are available to the manager.
Therefore, the flow meter and pressure gauges act as operational feedback cues.
The pressure gauges along the submain of each zone measure the inlet pressure to driplines.
Decreasing flow rates and/or increasing pressure may indicate clogging, and increasing flow rates with decreasing pressure may indicate a major line leak.
The inlet pressure gauges along with those at the distal ends of the dripline laterals at the flushline valve help establish the baseline performance characteristics of the system.
Good quality pressure gauges should be used at each of these measurement locations and the gauges should be periodically replaced or inspected for accuracy.
The flow rate and pressure measurements should be recorded and retained for the life of the system.
A time series of flow rate and pressure measurements can be used as a diagnostic tool to discover operational problems and determine appropriate remediation techniques, as illustrated in Figure 3.
Anomaly A: The irrigator observes an abrupt flowrate increase with a small pressure reduction at the Zone inlet and a large pressure reduction at the Flushline outlet.
The irrigator checks and finds rodent damage and repairs the dripline.
Anomaly B: The irrigator observes an abrupt flowrate reduction with small pressure increases at both the Zone inlet and the Flushline outlet.
The irrigator checks and finds an abrupt bacterial flare-up in the driplines.
He immediately chlorinates and acidifies the system to remediate the problem.
Anomaly C: The irrigator observes an abrupt flowrate decrease from the last irrigation event with large pressure reductions at both the Zone inlet and Flushline outlet.
A quick inspection reveals a large filtration system pressure drop indicating the need for cleaning.
Normal flowrate and pressures resume after cleaning the filter.
Anomaly D: The irrigator observes a gradual flowrate decrease during the last four irrigation events with pressure increases at both the Zone inlet and Flushline outlet.
The irrigator checks and find that the driplines are slowly clogging.
He immediately chemically treats the system to remediate the problem.
Figure 3.
Hypothetical example of how pressure and flowrate measurement records could be used to discover and remediate operational problems.
The heart of the protection system for the dripline emitters is the filtration system.
The type of filtration system depends on the quality characteristics of the irrigation water and the clogging hazards.
The illustration in Figure 1 depicts a pair of screen filters, while Figure 2 shows a series of sand media filters.
Screen filters are the simplest type of filtration and provide a single plane of filtration.
They are most often used in situations where the water source is relatively clean.
Sand media filtration systems, which consist of two or more large pressure tanks with specially graded filtration sand, provide three dimensional filtration and are well-suited for surface water sources.
Surface water supplies may require settling basins and/or several layers of bar screen barriers at the intake site to remove large debris and organic matter.
Another common type of filtration system is the disc filter which can also be considered as providing three dimensional filtration.
In some cases, the filtration system may be a combination of filtration components.
For example, a well that produces a large amount of sand in the pumped water may require a cyclonic sand separator in advance of the main filter.
Examples of the different types of filters are shown in Figure 4.
Figure 4.
Schematic description of various filtration systems and components..
Clogging hazards are classified as physical, biological or chemical.
Sand particles in the water represent a physical clogging hazard, and biological hazards are living organisms or life by-products that clog emitters.
Water sources that have high iron content are also vulnerable to biological clogging hazards, such as an iron bacteria flare-up within the groundwater well.
Control of bacterial growth generally requires water treatment in addition to filtration.
Chemical clogging hazards relate to the chemical composition or quality of the irrigation water.
As water flows from a well to the distribution system, chemical reactions occur due to changes in temperature, pressure, air exposure, or the introduction of other materials into the water stream.
These chemical reactions may form precipitates that result in emitter clogging.
In addition to the protection component, the chemical injection system injects nutrients or chemicals into the water to enhance plant growth or yield.
A variety of injectors can be used, but the choice of unit depends on the desired injection accuracy of a material, the rate of injection, and the agrochemical being injected.
When a wide variety of chemicals are likely to be injected, then more than one type of injection system may be required.
Also, state and federal laws govern the type of injectors, appropriate agrochemicals, application amounts, and required safety equipment that may be used in SDI systems, as illustrated by example in Figure 5.
Positive Displacement Pump Injection System
 Figure 5.
Layout of an Injection System with Safety Interlocks and Backflow Prevention Devices 
 Many different agrochemicals can be injected, including chlorine, acid, dripline cleaners, fertilizers, and some pesticides.
Producers should avoid injecting any agrochemical into their SDI system without knowledge of the agrochemical compatibility with irrigation water.
For example, various phosphorus fertilizers are incompatible with many water sources and may only be injected using additional precautions and management techniques.
All applicable laws and labels should be followed when applying agrochemicals.
The injection systems in Figures 1 and 2 have a single injection point located upstream of the main filter, but some agrochemicals may require an injection point downstream from the filter to prevent filter damage.
Care needs to be exercised in the location of the injection port to prevent system problems such as corrosion within the filters or chemical precipitation beyond the filter resulting in emitter clogging.
Chlorine is commonly used to disinfect the injection system and minimize the risk of clogging from biological organisms.
Acid injection can also lower the pH chemical characteristic of the irrigation water.
For example, water with a high pH clogs easily because minerals drop out of solution in the dripline after the water passes through the filter.
A small amount of acid added to the water lowers the pH to minimize to potential for mineral clogging.
Water quality also has a significant effect on SDI system performance and longevity.
In some instances, poor water quality causes soil and crop growth problems.
However, with proper treatment and management, water high in minerals, nutrient enrichment or salinity can be used successfully in SDI systems.
No SDI system should be designed and installed without first assessing the quality of the proposed irrigation water supply.
Clogging prevention is the key to SDI system longevity and requires understanding of the potential problems associated with a particular water source.
Table 1 details important water quality information that all designers and irrigation managers should consider in the early stages of the planning process.
With this information in mind, suitable management, maintenance plans, and system components, like the filtration system, can be selected.
Table 1.
Recommended water quality tests to be completed before designing an SDI system.
1.
Electrical Conductivity , a measure of total salinity or total dissolved solids, measured in dS/m or mmho/cm.
2.
pH, a measure of acidity, where a value of 1 is very acid, 14 is very alkali, and 7 is neutral.
3.
Cations include Calcium , Magnesium , and Sodium , measured in measured in meq/L,.
4.
Anions include Chloride , Sulfate , Carbonate , and Bicarbonate , measured in meq/L.
5.
Sodium Absorption Ratio , a measure of the potential for sodium in the water to develop sodium sodicity, deterioration in soil permeability and toxicity to crops.
SAR is sometimes reported as Adjusted  SAR.
The Adj.
SAR value better accounts for the effect on the HCO concentration and salinity in the water and the subsequent potential damage to the soil because of sodium.
6.
Nitrate nitrogen , measured in mg/L.
7.
Iron , Manganese , and Hydrogen Sulfide , measured in mg/L.
8.
Total suspended solids, a measure of particles in suspension in mg/L.
9.
Bacterial population, a measure or count of bacterial presence in # / ml, 
 10.
Boron* measured in mg/L.
11.
Presence of oil**
 Results for Tests 1 through 7 should be provided in a standard irrigation water quality test package.
Tests 8 through 11 are generally offered by Water Labs as individual tests.
The test for the presence of oil may be helpful in oil-producing areas of the state or if the well to be used for SDI has experienced surging, which causes existing drip oil in the water column to mix with the pumped water.
The fee schedule for Tests 1 through 11 varies from lab to lab and may total a few hundred dollars.
The cost is minor, however, in comparison to the value offered by the test in determining proper design and operation of the SDI system.
Burrowing mammals, principally of the rodent family, can cause extensive leaks that reduce SDI system uniformity.
Most rodents avoid digging into wet soil, so dripline leaks presumably are not caused by the animals looking for water.
Rather, rodents must gnaw on hard materials, such as plastic, to wear down their continuously growing teeth.
The difficulty in determining the actual location of a dripline leak caused by rodents is compounded by the fact that the leaking water may follow the burrow path for a considerable distance before surfacing.
Anecdotal reports from the U.
S.
Great Plains can be used to describe some of the typical habitat scenarios that tend to increase rodent problems.
These scenarios include the close proximity of permanent pastures and alfalfa fields, railroad and highway easements, irrigation canals, sandy soils, crop and grain residues during an extended winter dormant period, or absence of tillage.
Cultural practices such as tillage and crop residue removal from around SDI control heads and above-ground system apparatus seem to decrease the occurrence of rodent problems.
Some growers have tried deep subsoiling and/or applying poison bait around the SDI system field perimeters as a means of reducing rodent subsurface entry into the field.
Isolated patches of residue within a barren surrounding landscape will provide an "oasis" effect conducive to rodent establishment.
After the smaller rodents become established, other burrowing predators such as badgers can move into the field, further exacerbating the damage.
Caustic, odoriferous, pungent, and unpalatable chemical materials have been applied through SDI systems in attempts to reduce rodent damage, but the success of these trials has been varied.
Periodic wetting of the soil during the dormant period has been suggested as a possible means of reducing rodent damage.
Deeper SDI depths  may avoid some rodent damage.
Many of the burrowing mammals of concern in the United States have a typical depth range of activity that is less than 18 inches.
The decision to invest in an SDI system is ultimately up to the investor.
Good judgments require a thorough understanding of the fundamentals of the opportunities and challenges and/or the recommendations from a proven expert.
A network of SDI industry support is still in early development in the High Plains region, even though the microirrigation industry is over 40 years old and application in Kansas has been researched since 1989.
Individuals considering SDI should carefully determine if the system is a viable option for their situation by taking the following actions:
 1.
Getting educated before contacting a service provider or salesperson by
 C.
Visiting other producer sites that have installed and used SDI.
Most current producers are willing to show their systems to others.
2.
Interviewing at least two companies.
a.
Ask for references, credentials  and sites  of other completed systems.
b.
Ask questions about design and operation details.
Pay particular attention if the minimum SDI system components are not met.
If not, ask why?
System longevity is a critical factor for successful adoption of SDI.
C.
Ask companies to clearly define their role and responsibility in designing, installing and servicing the system.
Determine what guarantees are provided.
3.
Obtaining an independent review of the design by an individual that is not associated with sales.
This adds cost but should be minor compared to the total cost of a large SDI system.
Subsurface drip irrigation  offers a number of agronomic production and water conservation advantages but these advantages are only achieved with proper design, operation, and maintenance.
With proper care the SDI system can have an efficient, effective and long life.
One necessary change from the
 current irrigation systems, however, is the need to understand SDI's sensitivity to clogging by physical, biological and/or chemical agents.
Before designing or installing an SDI system, a comprehensive water quality assessment should be conducted on the source water supply.
Once this assessment is completed, the system designer can alert the manager of any potential problems that might be caused by the water supply.
The old adage "an ounce of prevention is worth a pound of cure" is very appropriate for SDI systems.
Early recognition of developing problems and appropriate action can prevent larger problems.
While the management needs may seem daunting at first, most managers quickly become familiar with the SDI system and its operational needs.
The SDI operator/manager also needs to understand the need for and function of the various components of the SDI system.
Many accessory options are available for SDI systems that can be included during the initial design and installation phases or added at a later time.
More importantly, minimum design and equipment features must be included in the basic system.
SDI is a viable irrigation system option, but it should be carefully considered by producers before making any financial investment.
The above discussion is a brief summary prepared from materials available through K-State.
The SDI related bulletins and irrigation-related websites are listed below:
 Related K-State Research and Extension Irrigation Websites:
 Contribution No.
09-241-A from the Kansas Agricultural Experiment Station.
ASAE.
2008.
Design and Installation of Microirrigation Systems.
ASAE EP405.1 APR1988.
ASABE, St Joseph, MI.
5 pp.
Harvesting 300 bu/acre field corn grown using SDI at KSU Northwest Research-Extension Center, Colby Kansas in 1998.
After the collapse of Tunnel No.
2 on the Goshen/Gering-Fort Laramie main canal in 2019, temporary repairs were made to Tunnels No.
1 and 2.
Steel ribs were installed inside the tunnels to give support to the concrete tunnel walls.
When extreme dry conditions occur in the fall, irrigators will usually water after the winter annual seeds have been sown.
Ideally, fall-drilled wheat and rye should have available soil water below the planted seeds.
When extreme dry conditions occur in the fall, irrigators will usually apply 1.0 to 2.0 inches of water following drilling season.
Precision mobile drip irrigation is an irrigation system where drip hoses are attached to a center pivot sprinkler and drug on top of the ground.
The placement of water by the hoses on the ground could potentially increase irrigation efficiency over a standard drop nozzle system.
In addition, problems associated with wet wheel tracks should be reduced.
However, drag hoses lying on the ground could cause more management concerns for farmers.
One example would be animal damage to the drip hoses which disrupts uniform water distribution.
The objectives of this study were to compare yield from corn irrigated using precision mobile drip irrigation  to sprinkler irrigation with drops.
The second objective was to discern if the emitters have a reduction in water flow over the season due to clogging.
Figure 1 is a sprinkler with the drag hoses attached.
The study was initiated on a center pivot sprinkler located seven miles north and three miles west of Hoxie, KS.
Cooperation from DLS Farms was very important to evaluating these two application methods.
Three spans, spans 4, 5, and 7, of an eight span center pivot sprinkler were divided into two sections.
Each section had either the PMDI system installed or the standard drop nozzle system.
With this configuration, three replications of each method were achieved for a total of six plots.
The center pivot sprinkler is nozzled to apply 300 gpm.
Drag hose spacing on the PMDI system was 60 inches while the spacing on the drop nozzle system was 120 inches.
The entire flow to the center pivot was screen filtered to 50 mesh.
For the 2004 growing season, the farmer strip-tilled the field the previous fall and applied 75 lbs/A of N as anhydrous ammonia and 7-25-0 lbs/A as 10-34-0.
The field was planted on May 2, 2004 in circular rows with Mycogen 2E685 treated with Cruiser at 26,000 seeds/A with 50 lbs/A of N as 32% UAN applied in a 2x2.
Appropriate pest management measures were taken to control weeds and insects.
For the 2005 growing season, manure was applied to the field, and then the field was strip-tilled in the fall.
On April 28, 2005 Mycogen 2E762 treated with Cruiser was seeded in straight noncircular rows at 26,000 seeds/A.
Appropriate pest management measures were taken to control weeds and insects.
Emitter water flow at the end emitter and then the 5, 10, and 15 emitter from the end of two drag hoses from each plot were captured for one minute on May 26, August 4, and September 13 in 2004 and May 27, July 29, and September 8 in 2005.
Water flow for the entire drag hose was also collected for the two drag hoses along with the water flow from two drop nozzles on the same span.
Corn yield was collected in two ways.
First, samples were hand harvested from forty feet of each plot.
Samples were then dried, threshed, weighed, and yield was calculated on a bu/a basis.
Yield was also collected at harvesting using a Green Star yield monitoring system for the entire field.
Weather conditions over the summer brought supplemental rainfall which allowed for respectable yields to be achieved at the site for both years.
When comparing hand harvest yields, there was no significant difference between the PMDI treatment and the drop nozzle treatment in either year or when combined across years.
When looking at the 2004 field map  or the 2005 field map  generated by a yield monitor, no discernable pattern was evident between the two systems.
Table 1.
Yield  as influenced by irrigation treatment 
 Treatment	2004	2005	Combined Results
 PMDI	233	239	236
 Drop Nozzle	236	236	236
 LSD 	NS	NS	NS
 Fig.
2 2004 Field Map DLS Farms
 Harvested Acres: 59.99 Date: 11/5/04 Yield: 234.58 bpa Moisture: 15.40% Harvest Hours: 4.33
 GREENSTAR JOHN DEERE AG MANAGEMENT SOLUTIONS
 Fig.
3 2005 Field Map
 Yield Map  Client: Owner Farm: Dave Up North Field: E PivotW/2 DLS-2 SE12-7-29 Harvested Acres: 61.89 Date: 10/5/2005-10/6/2005 Yield: 227.73 bpa Moisture: 15.73% Harvest Hours: 4.61
 GREENSTAR JOHN DEERE AG MANAGEMENT SOLUTIONS
 In 2004, the average emitter output over the summer declined from 214 ml/min.
on May 24 to 209 ml/min on August 4 to 180 ml/min on September 13.
Output from the emitters decreased by an average of 16% through the summer.
Output from the nozzles from span 4, 5, and 7 also decreased from an average of 2.51 gpm on May 26 to 2.48 gpm on August 4 to 2.28 gpm on September 13.
The average reduction in flow was 9%.
The 9% reduction in flow indicates that the overall pumping capacity of the well was reduced.
However, the additional 7% reduction in flow rate from the emitters is likely due to emitter clogging.
In 2005, the average emitter output over the summer declined from 180 ml/min.
on May 27 to 168 ml/min on July 29 to 158 ml/min on September 8.
Output from the emitters decreased by an average of 14% through the summer.
Output from the nozzles from span 4, 5, and 7 actually increased from an average of 2.13 gpm on May 27 to 2.17 gpm on July 29 to 2.49 gpm on September 8.
The average increase in flow was 17%.
Why there was an increase in flow over this time is difficult to explain, but it may be related to a difference in field evaluation for the locations where the sampling was conducted.
However, there was a greater difference in 2005 compared with 2004 in the flow between the average output of the emitters and the average output of the nozzles which implies increased clogging of the emitters.
In conclusion, as with any field evaluation, variability is inherently higher due to factors outside of the parameters that can be controlled by the investigators.
However, there was no positive or negative impact on yield from those plots that were irrigated with the PMDI system versus a standard drop nozzle system.
Emitter flow was decreased in both years when compared with nozzle flow which was likely due to emitter clogging.
Clogging of the emitters over the life of the system along with puncturing of the hoses from wildlife appear to be two negatives of the system, while one benefit of the system was the reduced wheel pivot tracks when the PMDI system is used to water crops near the pivot wheel.
The authors of this paper would again like to thank DLS farms for their cooperation on this project.
Fig.
5.
Emitter response from 2004 and 2005
 Fig.
6.
Nozzle Response from 2004 and 2005
Stormwater BMPs for Confined Livestock Facilities
 Steve Higgins and Sarah Wightman, Biosystems and Agricultural Engineering
 The U.S.
Environmental Protection Agency  states that agricultural sediment, pathogens, and nutrients account for more than 50 percent of water pollution in the United States.
Animal confinement facilities, widely used for holding, feeding, and handling animals, are potential sources of that pollution.
The pollution load of these facilities can be reduced by installing and maintaining best management practices.
The BMPs may be implemented as part of permit compliance or may be used to ensure that a permit is not needed.
Types of Animal Feeding Operations
 An animal feeding operation  is defined as a lot or facility where  animals have been, are, or will be stabled/ confined and fed/maintained for a total of 45 days or more in any 12-month period and  crops, vegetation, forage growth, or post-harvest residues are not sustained in the normal growing season.
AFOs are classified by size as large, medium, or small.
Some AFOs may also be classified as Concentrated Animal Feeding Operations.
A CAFO must meet the definition of a medium or large AFO and either  discharge pollutants into waters of the United States through a man-made ditch, flushing system, or other similar man-made device or  discharge pollutants directly into waters of the United States.
Water that does not infiltrate into the ground will run off, and on animal feeding operations, this runoff can become contaminated with manure, sediment, pathogens, and nutrients.
This polluted runoff then has the potential to move offsite and enter surface and groundwater resources.
Because of stormwater runoff and other pollution potential, the Kentucky Division of Water  considers confinement operations to be potential sources of pollutants, and therefore requires water quality permits for AFOs and CAFOs.
A Kentucky No Discharge Operational Permit  or a Kentucky Pollution Discharge Elimination system  permit may apply to animal feeding operations.
AFOs are not allowed to discharge to the waters of the United States, and either the KNDOP or KPDES permit can be used to ensure compliance.
CAFOs are required to obtain a KPDES permit.
Types of Confinement Facilities
 There are three general types of confinement facilities: totally enclosed, partially enclosed, and open.
Each is predisposed to a different kind of runoff pollution and requires different management strategies.
In totally enclosed facilities, the animals are managed completely under a roof.
Totally enclosed facilities generally do not produce runoff if designed correctly, although pollution can still originate from these facilities if stormwater is allowed to drain through the facility or if generated manure is not collected and managed properly and stormwater comes in contact with the manure or other waste.
In contrast, partially enclosed facilities may contain a roofed building that COVers a portion of the holding area, with the animals also having access to uncovered areas that may be paved or unpaved.
Open confinement facilities are unroofed corrals or holding areas where the animals are held, fed, and handled.
Partially enclosed and open facilities may be a significant source of pollution if stormwater runoff is not properly managed.
The surface used for partially open and totally open facilities affects runoff quantity and quality.
Generally, confinement facility surfaces are either paved
 Table 1.
Animal feeding operation  classification by animal type and number.
Animal Type	Small	Medium	Large
 Mature dairy COWS	<199	200 699	>700
 Veal calves	<299	300 999	>1,000
 Cattle (including heifers, steers, bulls,	<299	300 999	>1,000
 cows, or calf pairs)
 Swine 	<749	750 2,499	>2,500
 Swine 	<2,999	3,000 9,999	>10,000
 Horses	<149	150 499	>500
 Sheep or lambs	<2,999	3,000 9,999	>10,000
 Turkeys	<16,499	16,500 54,999	>55,000
 Laying hens or broilers	<8,999	9,000 29,999	>30,000
 Chickens2	<37,499	37,500 124,999	>125,000
 Laying hens2	<24,999	25,000 81,999	>82,000
 Ducks 	<9,999	10,000 29,999	>30,000
 Ducks1	<1,499	1,500 4,999	>5,000
 1 If the AFO uses a liquid manure handling system.
2 If the AFO uses other than a liquid manure handling system.
Figure 1.
Over the years, gravel has been added to this driveway, increasing its height so it now drains into the production area.
Figure 2.
This rock-lined channel diverts clean water away from the production area  and prevents erosion near the buildings.
with concrete or asphalt or left unpaved and lined with soil or heavy-use pads made of rock and geotextile fabric.
Paved surfaces usually generate more runoff than unpaved surfaces because they do not allow water to infiltrate the soil.
Unpaved surfaces allow water to infiltrate, but they also tend to become compacted, which can increase runoff.
By far, the best method for reducing the pollution potential of a confinement facility is stormwater BMPs.
Urban areas use these BMPs to reduce the "first flush," a high concentration of pollutants that is washed into streams, ponds, and lakes once a rainfall event begins.
Agricultural producers can use stormwater BMPs with the same concept in mind.
This document describes stormwater best management practices  that producers with confined livestock facilities should consider implementing to prevent pollution from discharging off-site.
Producers should carefully select appropriate practices to create a sustainable livestock operation.
The right BMPs depend on several factors, many of which are site specific.
No single BMP will prevent all types of pollution, and in many cases, multiple BMPs are needed to prevent a discharge of pollutants into the waters of the Commonwealth.
There are several BMPs that a livestock producer can implement to control stormwater pollution.
These BMPs fall into three main categories: structures, vegetation, and facilities management.
An ideal building site is one in which drainage is diverted away from the production area, but over time, topography can be altered with road creation, structure remodeling, and facilities additions, which can cause runoff to flow through the production area.
To keep clean runoff clean, diversion practices should be implemented if water enters the production facility from upland sources, such as streams or overland flow.
Headwater diversion entails installation of structures such as levees, dikes, drainage swales, and diversion ditches that carry the water away from the production area and to a natural drainageway.
Figures 3 and 4 show a before-and-after aerial photo of a production area in which headwater diversion techniques have been incorporated.
Diverting clean stormwater from the production area can reduce the water volume that must be managed and can increase storage capacity of holding ponds and lagoons, which is a management philosophy called "keeping clean water clean." In many cases, diverting clean runoff not only reduces the amount of water that needs to contained and managed, but it also creates a drier environment for the animals and reduces odors.
If a confinement facility has a roof that drains onto the production area, consider installing gutters with downspouts.
Placing gutters on the sides of buildings diverts clean rain water away from animal handling and holding areas and prevents the pollution of this otherwise clean and usable water.
Downspouts should be directed into diversion ditches, and guttered water should be carried away from animal containment areas.
Confinement areas have impervious surfaces that cause large volumes of water to flow quickly from the area.
The force created by the flow of this water can cause erosion, and although some erosion is natural, a lack of soil management accelerates the process and can become a significant problem.
To prevent severe erosion, hardened  structures should be installed.
To construct a hardened structure, simply line diversion ditches or swales with geotextile fabric and large rock.
It may be possible
 Figure 3.
Before clean water diversion methods were implemented, the production area drained into the liquid storage ponds.
Figure 4.
Installing clean water diversions increased capacity in the liquid storage ponds.
to line ditches that have a slope of 3% to 6% with vegetation, depending on the soil type.
Silty soils will erode more easily than clayey soils, SO in these instances, rock may be required to stabilize the soil.
To manage suspended sediments in runoff, small center-overflow dams made of stone, known as check dams, could be used.
Check dams reduce the velocity of runoff, allowing the sediment to settle out of suspension, thus serving as a sediment trap.
Multiple check dams located along the same channel should be spaced SO that the toe of the upper structure is at the same elevation as the top of the downstream dam.
Check dams should be installed to form a notch  to allow water to flow in the center of the channelnotches located on the side of the check dam contribute to erosion.
Slopes greater than 10% require heavy armoring and possibly grade stabilization structures.
A grade stabilization structure allows water to move to a lower elevation while reducing its energy and velocity SO that erosion can be controlled.
Unlike a weir or a dam, it is usually not meant for water impoundment, diversion, or raising the water level.
These structures typically consist of a series of closely placed posts and cattle panels that hold large rocks in place.
They are built on small or minor
 waterways that have steep channel gradients.
See University of Kentucky Cooperative Extension publication Building a Grade Stabilization Structure  for more information.
Runoff Collection, Treatment, and Application
 Water contaminated by manure and other wastes at the production facility must be appropriately managed.
The extent of collection and treatment will depend on the facility's size.
In a small-scale operation, settling channels or basins may be enough.
For larger operations, it may be necessary to install and manage holding ponds and/or lagoons, which should be managed based on Natural Resources Conservation Service  Standard Practice Code 590 Standard.
Wastewater should be tested for nutrient concentrations and land-applied as irrigation water to crops or forages based on soil test results, crop or forage nutrient requirements, and a realistic yield goal.
The producer will need to develop and implement a Nutrient Management Plan  or a Comprehensive Nutrient Management Plan.
The application of these wastes should be accomplished without edge-of-field losses.
The best way to prevent these losses is to adhere to manure setback criteria and install Riparian buffer size should be
 based on the distance between the water body and the next adjacent land use.
The more area available for a forested riparian buffer, the better, but even a buffer of 20 feet can provide some streambank protection.
Forvegetative buffers between fields and sensitive areas like streams, sinkholes, and wetlands.
Bioengineering solutions use vegetation to prevent water pollution.
Vegetation used typically consists of native grasses, shrubs, and trees.
The combination of different root sizes and depths holds soil in place and slows water flows, while also using and treating water.
Vegetative buffers can provide numerous benefits, including contaminant filtration, field separation, and soil stabilization.
Though the ecological goal of vegetative buffers is usually the same, their name and site-specific purpose may change according to their position on the landscape.
The three main types of conservation buffers used in livestock operations are filter strips, grassed waterways, and riparian buffers.
Filter strips are designed for sheet flow, grassed waterways for intermittent flow, and riparian buffers for ephemeral and perennial flow.
Figure 5.
Clogged driveway grate that allows a discharge from the production area.
Figure 6.
Functioning grate that forces polluted water to the proper waste storage facility.
Filter strips are areas of grass or other permanent vegetation that are maintained to reduce sediment, organic material, nutrients, pesticides, and other runoff contaminants in order to enhance water quality.
Filter strips slow the velocity of water, allowing the settling out of suspended soil particles and increased infiltration.
In most cases, filter strip efficiency is reliant upon flow length or filter width.
For more information about filter strips, see University of Kentucky Cooperative Extension Publication Vegetative Filter Strips for Livestock Facilities.
Grassed waterways are natural or constructed channels shaped to required dimensions and established in suitable vegetation.
While their main purpose is to transport runoff SO that erosion and flooding don't occur, proper planning and careful design can enhance these buffers SO that they also filter and divert runoff.
Grassed waterways must be constructed properly in order to de-
 crease the runoff's velocity.
In order to maximize the benefit of these waterways, a more hands-off approach than farm crews typically use is required.
No-mow zones should be established, and their width should be based on the amount and the speed of the runoff received by the grassed waterway.
Encouraging vegetation growth will prevent rutting of channels and encourage filtration of sediments and plant uptake of nutrients.
Riparian forest buffers consist of trees, shrubs, and grasses next to streams, lakes, ponds, and wetlands.
Riparian forest buffers perform many functions, including stream bank stabilization, shade, temperature moderation, and pollution filtration.
Riparian buffer size should be based on the distance between the water body and the next adjacent land use.
The more area available for a forested riparian buffer, the better, but even a buffer of 20 feet can provide some streambank protection.
For more information see the University of Kentucky Cooperative Extension publications Riparian Buffers: A Livestock Best Management Practice for
 Protecting Water Quality  and Planting a Riparian Buffer.
Several facilities management practices can reduce the potential for off-site movement of pollutants from a livestock production area.
The appropriate practice depends on the type of operation, equipment available, management skills, and amount of labor and capital available.
Management practices that control water pollution include:
 Installing a curb to contain liquid effluent
 Installing grates with large openings in driveways 
 Cleaning the manure from exposed surfaces at regular intervals appropriate to the amount of accumulation of manure
 Locating storage  and feeding areasaway from environmentally sensitive areas such as streams, sinkholes, and depression basins
 Installing heavy-use pads around feeding areas to reduce soil erosion
 Reducing the stocking to decrease the amount of manure produced
 Relocating the facility if natural drainage flows through the production area
 Converting open or partially open confinement facilities to closed facilities
 Cleaning manured or otherwise contaminated areas before rainfall events to reduce pollution of stormwater runoff
 Storing scraped manure in a covered stack pad area
 For more information on some of these practices, see the following University of Kentucky Cooperative Extension publications:
 Using Dry Lots to Conserve Pastures and Reduce Pollution Potential ,
 Using Soil-Cement on Horse and Livestock Farms ,
 High Traffic Area Pads for Horses , and
 Using Geotextiles for Feeding and Traffic Surfaces.
When it comes to the environment, producers need to consider not only whether the facilities can handle an operation of a certain size, but also whether the land can handle the pressures inherent in that operation's size.
For example, a producer should not only use the capacity of a barn to determine the size of an operation, but should also determine if their land area can support land applications of manure from the animals contained in that barn.
A producers considering building a new facility should also consider if the site's available drainage and soils can support a commercial building.
As a livestock producer, compliance with water quality regulations is not only encouraged, it is required by law.
Select BMPs carefully, because most of them are site specific.
In most cases, multiple BMPs will be needed to achieve regulatory compliance.
In some cases, there could be costshare assistance available to implement BMPs.
Check with your local conservation district about design criteria and cost-share availability.
The following Natural Resources and Conservation Service  practice codes are examples of practices that might be appropriate and eligible for funding under state or Environmental Quality Incentives Program  cost share:
 Comprehensive Nutrient Management Plan 
 Constructed Wetland 
 Filter Strip 
 Grade Stabilization Structure 
 Grassed Waterway 
 Heavy Use Area Protection 
 Lined Waterway or Outlet 
 Nutrient Management 
 Roof Runoff Structure 
 Sediment Basin 
 Structure for Water Control 
 Waste Storage Facility 
 Water and Sediment Control Basin 
More research is needed to conclude whether thermal sensing alone is sufficient to manage irrigation.
Additionally, more research needs to be conducted in different regions and climates to ensure these systems are optimized for different field and weather conditions.
Development of weather-, locationand crop-specific thresholds  would make the system more adaptable to new locations.
How to Interpret a Water Analysis Report
 This article outlines some of the major parameters you may see on the analysis and assists you in understanding the numbers on a water test report.
Whether your water causes illness, stains on plumbing, scaly deposits, or a bad taste, a water analysis identifies the problem and enables you to make knowledgeable decisions about water treatment.
Features of a Sample Report
 Once the lab has completed testing your water, you will receive a report that looks similar to Figure 1.
It will contain a list of contaminants tested, the concentrations, and, in some cases, highlight any problem contaminants.
An important feature of the report is the units used to measure the contaminant level in your water.
Milligrams per liter  of water are used for substances like metals and nitrates.
A milligram per liter is also equal to one part per million --that is one part contaminant to one million parts water.
About 0.03 of a teaspoon of sugar dissolved in a bathtub of water is an approximation of one ppm.
For extremely toxic substances like pesticides, the units used are even smaller.
In these cases, parts per billion  are used.
Another unit found on some test reports is that used to measure radon--picocuries per liter.
Some values like pH, hardness, conductance, and turbidity are reported in units specific to the test.
In addition to the test results, a lab may make notes on any contaminants that exceeded the PA DEP drinking water standards.
For example, in Figure 1 the lab noted that total coliform bacteria and iron both exceeded the standards.
Retain your copy of the report in a safe place as a record of the quality of your water supply.
If polluting activities such as mining occur in your area, you may need a record of past water quality to prove that your supply has been damaged.
Figure 1.
A sample water analysis report.
The following tables provide a general guideline to common water quality parameters that may appear on your water analysis report.
The parameters are divided into three categories: health risk parameters, general indicators, and nuisance parameters.
These guidelines are by no means exhaustive.
However, they will provide you with acceptable limits and some information about symptoms, sources of the problem and effects.
The parameters in Table 1 are some commons ones that have known health effects.
The table lists acceptable limits, potential health effects, and possible uses and sources of the contaminant.
Table 1: Standards, symptoms, and potential health effects of regulated contaminants.
Conservation Cost-Share for Farmers and Ranchers
 There are regional programs specially designed to help farmers and ranchers protect and improve the health of their land.
Southwest Florida Water Management District
 Southwest Florida Water Management District  was created in 1961 by a special act of the Florida Legislature after Hurricane Donna caused massive flood-related damage to southwest Florida.
When first created, SWFWMD focused solely on regional flood prevention.
Today, SWFWMD's scope encompasses water supply, flood protection, water quality management and natural systems management.
Farmers and ranchers in the sixteen counties served by SWFWMD are eligible for a number of cost-share programs.
These programs can help to cover the cost of FDACS Ag BMP projects and more.
Here is some information about two of SWFWMD's agricultural programs:
 Facilitated Agricultural Resource Management Systems 
 The FARMS cost-share can cover up to 75% of the cost of Ag BMP projects such as:
 Tailwater recovery/surface water irrigation pump stations, including pump, engine, fuel tank, filters and mainline pipe
 Irrigation system conversion to a more efficient system
 Weather stations, including rain gauge, anemometer and wireless telemetry
 Soil moisture sensors, including wireless telemetry
 Automated irrigation valves and pump start/stops
 Farmers and ranchers love their land.
Anyone who has ever made their living from the land knows that the health of your land affects the productivity of your land.
And at the end of the day, productivity is what makes or breaks a business.
Anyone who has ever made a living from the land also knows that making improvements to your land often comes with a hefty price tag.
If you are interested in learning how to improve the health and productivity of your land without breaking the bank, this series will help you do it.
There are federal, state, local, and independent programs specially designed to help farmers and ranchers protect and improve the health of their land.
The majority of the programs are federally funded and administered by the United States Department of Agriculture.
Contact the FARMS program:  985-7481, ext.
4413
 Mini-FARMS is a version of the FARMS cost-share program that is specially designed to fit the needs of agricultural operations of 100 acres or less.
Operations must be enrolled in FDACS Ag BMP program to be eligible.
The program reimburses producers for 75% of the cost of projects.
Commonly funded projects include but are not limited to:
 Weather stations with evapotranspiration measurements
 Irrigation pump station automation
 Irrigation pumps, controls, filtration and infrastructure
 Interesting facts about Water Management Districts in Florida:
 Over the last 20 years, Florida has invested $1.8 billion in phosphorus control programs that have significantly improved Everglades water quality.
Scientific monitoring shows at least 90 percent of the Everglades now meets ultra-clean water quality standards of 10 parts per billion or less of phosphorous.
Water Management Districts  don't just work with agricultural producers.
WMDs work with individual homeowners, municipalities, counties, and public and private land and business owners to improve water quality.
CORN PRODUCTION AS RELATED TO SPRINKLER IRRIGATION CAPACITY
 In arid regions, it has been a design philosophy that irrigation system capacity be sufficient to meet the peak evapotranspiration needs of the crop to be grown.
This philosophy has been modified for areas having deep silt loam soils in the semi-arid US Central Great Plains to allow peak evapotranspiration needs to be met by a combination of irrigation, precipitation and stored soil water reserves.
Corn is the major irrigated crop in the region and is very responsive to irrigation, both positively when sufficient and negatively when insufficient.
This paper will discuss the nature of corn evapotranspiration rates and the effect of irrigation system capacity on corn production and economic profitability.
Although the information presented here is based on information from Colby, Kansas  for deep silt loam soils, the concepts have broader application to other areas in showing the importance of irrigation capacity for corn production.
Corn evapotranspiration  rates vary throughout the summer reaching peak values during the months of July and August in the Central Great Plains.
Long term  July and August corn ET rates at the KSU Northwest Research Extension Center, Colby, Kansas have been calculated with a modified Penman equation  to be 0.268 and 0.249 inches/day, respectively.
However, it is not uncommon to observe short-term peak corn ET values in the 0.35 0.40 inches/day range.
Occasionally, calculated peak corn ET rates may approach 0.5 inches/day in the Central Great Plains, but it remains a point of discussion whether the corn actually uses that much water on those extreme days or whether corn growth processes essentially shut down further water losses.
Individual years are different and daily rates vary widely from the long term average corn ET rates.
Corn ET rates for July and August of 2003 were 0.344 and 0.263 inches/day, respectively, representing an
 approximately 15% increase over the long-term average rates.
Irrigation systems must supplement precipitation and soil water reserves to attempt matching average corn ET rates and also provide some level of design flexibility to attempt covering year-to-year variations in corn ET rates and precipitation.
Figure 1.
Long term corn evapotranspiration  daily rates and ET rates for 2003 at the KSU Northwest Research-Extension Center, Colby Kansas.
ET rates calculated using a modified Penman approach.
Simulation of corn irrigation schedules for Colby, Kansas
The event hosted more than 50 growers and ag businesses, and the agenda included funding sources for irrigation infrastructure at the local, state and federal levels.
Irrigation districts needing funding will have four different funding opportunities to meet their respective repair plans, including the Bureau of Reclamation WaterSmart grant.
Ashley Bandy, Earth and Environmental Sciences, and Carmen Agouridis, Biosystems and Agricultural Engineering
 G roundwater is an important water source for activities such as drinking, bathing, cooking, and crop irrigation.
Keeping our groundwater sources clean is becoming more challenging with an ever growing population.
In watersheds underlain with karst, such as many of those in Kentucky, the groundwater is more susceptible to contamination.
This is because surface waters, such as runoff and in some cases streamflow, travel into the subsurface of karst by way of fractures, sinkholes, swallow holes, conduits and caves.
Such direct paths into the groundwater mean that pollutants reach the aquifer much more quickly with little to no filtration.
Thus, while waters from springs and wells may look clean, they may actually contain unsafe levels of pollutants such as bacteria and nitrogen.
The following is a brief summary of the irrigation decisions made in each competition this year.
Sorghum: For the second year, the sorghum participants did not make irrigation decisions.
All 16 irrigated sorghum farms received the same amount of irrigation water throughout the season.
The total irrigation applied to the plots was 10 inches.
Cotton research personnel and growers have often observed that some insect pests are more abundant in parts of a cotton field or in entire fields where plant growth is rank and succulent.
The research reported here was initiated to test this observation.
Three different regimes of irrigation water and nitrogen, tested in factorial combinations brought about distinct differences in growth patterns between various plots.
Throughout the course of the study the lygus bug, Lygus hesperus Knight, was found significantly more abundant in plots with high irrigation and nitrogen levels, than in plots receiving minimum applications of either variable.
A complex relationship was found to exist between cotton lint production, vegetative plant growth, insect numbers, and water and nutritional management.
The implication of these tests is that cotton growers may reduce the threat from insect pests through management of their irrigation and fertilization practices.
INSECTS as affected irrigation fertilization
 THOMAS F.
LEIGH DONALD W.
GRIMES HIDEMI YAMADA
 W ATER AND FERTILITY MANAGEMENT influences the vegetative and fruiting growth of crops in arid climates and also influences the nutritional aspects of plants as hosts.
Since insects are known to respond differently to changes in environmental conditions, they should also be expected to respond to conditions in a crop ecosystem brought about by modification in the use of either water or fertilizer variables.
This progress report deals with an evaluation of the influence of irrigation water and nitrogen fertilizer variables on plant growth, the resultant insect populations in the crop canopy, and lint production.
The investigation is being carried out in field plots at the U.S.
Cotton Research Station, Shafter, and the University of California West Side Field Station, Five Points.
Soil at the Kern County location is classified as Hesperia sandy loam and at the Fresno County location as Panoche clay loam.
The results obtained at the two locations from the four years of study are similar and therefore only the 1968 experiment at the West Side Field Station is reviewed here.
In the 1968 experiment, treatments consisted of a factorial combination of
 three irrigation schedules and three levels of nitrogen application in a split-plot randomized complete block design with irrigation treatments as whole plots.
All plots were uniformly irrigated before planting to wet the soil profile to a depth of 6 ft.
Differential water availability was induced during the growing season by irrigating once , twice , and four times  as follows:
 Plot	applied	to pre-plant
 11-7/16 	10.3 inches
 1-7/1 , and 8/7 	18.0 inches
 1-6/17 , 7/9 ,
 7/31 , and 8/20 	27.2 inches
 Graph 1.
Soil water tension before irrigation for each of three irrigation treatments-Tension levels for the 12 and 13 treatments are an average of all irrigations for the specific treatment.
Graph 2.
Total lygus population found within plots receiving differential irrigation and nitrogen management.
gation and nitrogen fertilization levels.
On that date there were significantly fewer lygus in the I plots than in either the I2 or I3 plots.
The relationship between total lygus numbers and the amount of irrigation water and nitrogen applied during the growing season, , is shown in graph 2.
While the total amount of water indicated had not been added by July 24 when insect counts were made, plant growth differences reflecting these treatment differentials were well established.
An increase in water availability shows a striking increase in lygus abundance.
Increased lygus abundance was also noted with higher levels of applied nitrogen but this effect was not as great as with the increased water level.
By late summer, lygus numbers became more variable between irrigation and fertility differentials.
all fertility levels of the I and I3 plots than in any of the fertility levels of the I2 program.
The average number of spider mites  per leaf on August 20, 1968 in plots treated at three levels of irrigation and nitrogen fertilization was:
 IN COTTON by and practices
 Nitrogen treatment	1	l2	l3
 Average number per leaf
 No	112	79	102
 N1	166	48	201
 N2	116	89	166
 In the I and I3 programs, mites were most abundant at the N1 level of fertility and the lowest numbers were encountered in the N 1 fertility level of the I2 treatment.
Results obtained in other years of this study indicate there are distinct reproductive differences in the mite populations relative to nutrient composition of the leaves.
However, as with lygus, the abundance of predators may have a strong relationship to the numbers of mites present.
The big-eyed bug was present in sizeable numbers, particularly on the July 3 and July 24 sample dates.
Both total and nymphal numbers were greatest on July 3 in the I2 treatment which showed the lowest counts of lygus.
They were least abundant in the I3 plots which had the highest lygus counts, and were intermediate in abundance in the I1 plots.
By July 24, the big-eyed bug was most prevalent in the low water treatment  and least abundant in the wet  treatment.
On July 24, a significant negative correlation  between total lygus and big-eyed bug numbers was observed.
Nitrogen levels consisted of no added nitrogen , 75 lbs of nitrogen per acre , and 300 lbs of nitrogen per acre  sidedressed as ammonium sulfate in late May.
The nitrogen levels were selected with a knowledge of the response characteristics of the soil.
Where irrigation is optimum, maximum lint yields have been obtained from the highest level used while the 75-lb rate may be expected to produce a yield intermediate between no applied nitrogen and the maximum.
The frequency and amount of irrigation during the season was determined by the water-holding capacity of the soil and by the known water requirements of cotton.
Soil water tension levels attained immediately before irrigation for each of the three treatments are shown in graph 1.
DICK BASSETT JOHN R.
STOCKTON
 Cotton lint production resulting from individual treatments is shown in graph 3.
Addition of nitrogen increased lint production only at the lowest irrigation level I.
Lint production was depressed when nitrogen was added to the I2 and I3 irrigation treatments.
Increased irrigation water  improved yield over I only at low levels of added nitrogen.
The wet I3 irrigation treatment reduced yields at all levels of nitrogen fertilization.
Spider mite infestations developed late in the season.
Nevertheless, on August 21 they were significantly more abundant in
 The observed lint production trends from the various irrigation and nitrogen
 Insect and spider mite counts  insect sampler was used to sample the insect fauna; this provided a measure of all insects that were present in significant numbers in the upper portion of the plants.
While more than 20 species of insects were present, the comparative abundance of only two is reported here: the lygus bug, Lygus hesperus Knight, which is a major pest of cotton; and the big-eyed bug, Geocoris pallens Stal, a major predator.
Spider mites, Tetranychus pacificus McGregor, were also sampled by a chlorox-wash method and differences in abundance determined.
Typical plant growth is illustrated in the above photo with three plants selected from plots fertilized with 75 pounds of nitrogen per acre and from left to right: 1, 2, and 4 irrigations.
Total lygus bug numbers and nymphal numbers on July 3 were greatest in all fertility levels of the I3 plots, as indicated in the table.
This differential appeared to reflect the greater growth of plants irrigated at the earliest date.
By July 24, plant growth differences were evident among all plots receiving the varied irri-
 AVERAGE NUMBER OF LYGUS BUGS  AND BIG-EYED BUGS  PER 100 PLANT TERMINALS ON JULY 3 AND JULY 24 IN PLOTS TREATED AT THREE LEVELS OF IRRIGATION AND NITROGEN FERTILIZATION
 July 3	July 24
 TREATMENT	1	12	l3	1	12	13
 No	16	14	30	40	44	45
 N1	19	12	34	26	59	50
 N2	13	12	26	32	53	59
 No	0.0	0.8	5.0	4	23	15
 N1	2.3	1.3	6.8	7	28	19
 N2	1.3	2.0	2.8	10	23	23
 No	53	93	31	70	29	15
 N1	61	74	31	90	53	35
 N2	54	75	27	77	33	33
 No	6	22	1	15	6	6
 N1	7	15	2	29	8	10
 N2	9	12	4	20	6	8
 levels in this experiment differ considerably from the responses obtained when detrimental insect populations are controlled.
Under controlled conditions on this soil, optimum production has been obtained from approximately 20 inches of irrigation water, in addition to the water that was applied preplant, and from about 250 lbs of nitrogen per acre.
Where insect populations  are not controlled, a highly complex relationship was found to exist between cotton lint production, vegetative plant growth, insect numbers, and water and nutritional management.
This relationship accounts for the differential response characteristics where there was no control of insect populations.
The relation between lint production and plant
 growth  is illustrated in graph 4.
Increased lint production was associated with increased plant growth in a plant height range of from 100 cm to about 125 cm.
Increased plant growth and yield in this range were produced by added nitrogen in the dry  treatment or with no nitrogen at the I2 irrigation level.
Increased plant growth above approximately 125 cm was strongly associated with declining lint production and resulted from increased water and/or nitrogen availability.
At this point, a logical assumption might be that an increasing lygus population would be associated directly with declining lint production.
In considering the 1968 data, however, only a small nonsignificant negative correlation was observed.
However, a significant positive correlation was found to exist between lygus numbers on July 24 and final plant height.
The absence of an overall direct correlation between lygus numbers and lint production was accounted for by the fact that treatments which increased plant growth and lygus numbers also increased lint production to a certain point, but decreased yield thereafter.
Highly significant differences in the abundance of lygus bugs, big-eyed bugs, spider mites, and some of the other insects are evident for each of the years of this study.
Direct cause-and-effect relationships between lint production, plant
 growth, insect populations, and water and plant nutrition management were found difficult to identify.
Nevertheless, growers can reduce the likelihood of lygus attack on their cotton by utilizing "controlled" amounts of irrigation water and nitrogen-and could enable production of the most efficient crop with little or no use of insecticidal chemicals.
Manipulation of agronomic practices as a means of modifying insect populations and reducing pest problems is a continuing program in this approach to pest control.
Irrigation and fertilizer studies appear to offer great promise as a method of maintaining a more favorable level of insects in cotton.
These cultural manipulations can also add to the value of such additional pest management practices as varietal selection, host plant resistance, cultivation, and biological and chemical control.
Graph 3.
Cotton lint production from varied levels of irrigation and nitrogen fertilization under conditions of no insect control.
The indicated yields are averages of all replications.
Graph 4.
A relationship between cotton lint production and plant height.
Each point plotted on the graph is an average of four replications.
WATER ISSUES IN COLORADO
 I would like to cover two separate areas within Colorado that I thought would be of interest to the Central Plains region.
First, Colorado has been working on the development and implementation of an augmentation plan that was submitted to the Republican River Compact Administration in March 2008.
The augmentation plan is required to maintain compliance with the Republican River Compact and the Final Settlement Stipulation reached between Kansas, Nebraska and Colorado in 2002.
The presentation will include a discussion of the legal, physical and financial challenges that Colorado has faced in the development of this augmentation plan and the current status of negotiations between the three states regarding the request for approval by Kansas and Nebraska.
Additional information regarding our compact compliance efforts can be found at:
 Second, I promulgated new rules in the Arkansas River basin titled Irrigation Improvement Rules.
The Irrigation Improvement Rules are designed to allow improvements to the efficiency of irrigation systems in the Arkansas River Basin while ensuring compliance with the Arkansas River Compact.
I have determined that certain improvements to surface water irrigation systems, such as sprinklers and drip systems that replace flood and furrow irrigation, or canal-lining that reduces seepage, have the potential to materially deplete the usable waters of the Arkansas River in violation of the Compact.
The Irrigation Improvement Rules optimize use of the waters of the Arkansas River by allowing such improvements in a manner consistent with the terms of the Compact.
I submitted the Rules to the Water Court on September 30, 2009.
The Water Court approved the rules on October 25, 2010.
The effective date of the rules was January 1, 2011.
Additional information regarding the rules can be found at:
The last piece of information needed is the expected rainfall amounts between today and the date the crop matures.
While many parts of the state are very dry this year, one should still keep in mind the long-term average rainfall as shown in Figures 1 and 2.
Creating Urban Stormwater Control Ponds for Water Quality and Wildlife Habitat
 Thomas G.
Barnes, Extension Wildlife Specialist Lowell Adams, National Institute for Urban Wildlife
 Wellands are important wildlife habitats, and they provide numerous benefits and services to society.
Natural wetlands help replenish groundwater supplies, act as natural pollution filters, purify water, control erosion, lessen the impact of flooding, provide food and fiber for humans, and offer countless opportunities for education and recreation.
Because they are SO important to wildlife, wetlands have been called "nature's cities." Unfortunately, people have not valued wetland systems, and more than 80 percent of Kentucky's wetlands have been drained, filled, or destroyed.
Nationally, we have destroyed more than 50 percent of our wetlands.
Water is often a factor that limits the types, numbers, and abundance of wildlife in urban environments.
In the past, we destroyed natural wildlife water sources, such as wetlands and ponds, to make way for development.
Before land is developed, rainwater is intercepted by vegetation and infiltrates the soil.
After development, driveways, rooftops, and other impervious surfaces reduce the infiltration capacity of the soil.
Unable to percolate into the soil, rainwater moves over the area, with the potential to damage property and cause floods.
As water runs over roads, sidewalks, and parking lots, it picks up a number of pollutants including oil, grease, and heavy metals such as lead, zinc, copper, and mercury.
Rainwater that flows over lawns picks up nitrogen, phosphorous, and pesticides from lawn care products.
Stormwater runoff with its load of pollutants eventually reaches local streams where it deposits pollutants and increases the volume and velocity of stream water, resulting in greater stream contamination, channelization, erosion, and sedimentation.
As a result, fish and other aquatic life inhabiting these streams are often reduced in numbers or eliminated altogether.
In response to these problems, thousands of structures have been built throughout the United States for the purpose of controlling stormwater.
However, in the past, little consideration was given to structural designs that would also benefit wildlife and improve water quality.
The challenge to planners, engineers, and surveyors today is to design structures that will control stormwater and also improve water quality and provide wetland and wildlife habitat.
The purpose of this publication is to provide information for developers and government policy makers on creating a type of water source that will benefit wildlife and control stormwater discharge.
This information can also be used by developers when creating ornamental ponds at the entrances to new subdivisions and other public areas.
For specific en-
 gineering and hydrologic information, contact the local Natural Resources Conservation Service and ask for a copy of their publication, Ponds-Planning, Design, Construction.
You may also want to obtain a copy of Guidelines for Stream and Wetland Protection in Kentucky from the Kentucky Division of Water.
This publication compares detention and retention ponds, two of the most common stormwater control structures used today, and provides information on how to design these structures to benefit waterfowl and other wildlife.
The two types of structures most commonly used to control urban stormwater are "dry" ponds, also known as detention ponds, and "wet" ponds, also known as retention ponds.
As their names imply, the major difference is the length of time water stands in the pond.
Dry ponds are designed to collect water during a storm and then release this water at a predetermined rate to a nearby body of water.
They are generally dry between storms.
Wet ponds are designed to contain water on a year-round basis.
Although both types of structures control stormwater and reduce the risk of flooding, wet ponds are much better at improving water quality and providing wildlife habitat.
Some of the costs and benefits of creating a detention or retention pond are discussed below.
Feasibility for the Site
 The first step in choosing and designing a stormwater structure is to determine which designs are feasible for the site description, soil type, and local geology.
Wet ponds generally require more space than dry ponds, SO they are not recommended for small areas.
Soil permeability also influences which structures will be most successful.
For example, dry ponds work best in areas with extremely permeable sandy soils, but wet ponds are the better choice in areas with heavy clay soil where drainage is poor.
The local geology can also influence the design choice.
Wet ponds require extensive excavation and are more difficult to create in areas where the underlying bedrock is close to the surface.
Stormwater may contain many pollutants, including sediment and heavy metals that exist in particulate form and soluble pollutants such as nitrogen and phosphorus.
For a variety of reasons, wet ponds are much better than dry ponds at removing both types of pollutants and thereby improving water quality.
Sediment and particulate pollutants are removed from water when they are allowed to settle to the bottom of the pond.
Because water is present in dry ponds for relatively short periods of time, most of this sediment remains suspended in the water released from the pond.
However, wet ponds hold water for longer periods of time, allowing for greater settling of suspended sediments and nonsoluble pollutants, thus improving water quality in water bodies receiving this flow.
In addition, aquatic plants present in wet ponds are able to further improve water quality by using some of the soluble pollutants and incorporating them into plant tissue.
Groundwater recharge refers to water that infiltrates the soil surface and percolates into the groundwater reservoir.
Part of the water present in retention ponds infiltrates through the bottom and sides of the pond into the groundwater reservoir.
Detention ponds, on the other hand, usually allow less groundwater recharge because the water is only present a short period of time before moving into a receiving body of water.
Wildlife Habitat and Recreation Benefits
 Properly designed wet ponds can provide habitat for a number of species of wildlife and native plants that are dependent on wetlands.
Dry ponds, on the other hand, provide little opportunity for enhancing wildlife habitat.
Wet ponds will be used by various waterfowl species, furbearing animals, songbirds, and reptiles and amphibians.
Depending on their size and design, wet ponds can provide a number of recreational opportunities including birdwatching, fishing, boating, and ice skating.
Dry ponds do not typically provide such recreational values.
Construction and Maintenance Costs
 Construction costs are generally 30 to 60 percent higher for wet ponds than for dry ponds.
However, many studies have shown that homeowners are willing to pay more for houses near landscaped ponds, and developers are often able to make up this initial deficit.
In addition, landscaped ponds provide numerous other benefits that cannot be translated directly into dollar values, such as improved water quality and wildlife habitat.
Maintenance needs differ between the two structures.
For instance, dry ponds maintained as the law requires need more frequent mowing and removal of trash.
In addition, fertilizer used on the lawn contributes to the already excessive nutrient loads in downstream water.
Wet ponds require less routine maintenance; however, sediment removal is needed approximately every ten to twenty years, and this can be expensive.
Dry ponds require sediment removal much less frequently because they accumulate less sediment per storm.
Both types of structures should be inspected on a regular basis to ensure they are functioning correctly.
Wet Ponds as Community Assets
 In the past in the Northeast, dry ponds have been built more frequently than wet ponds.
This trend is beginning to change as citizen concern over water quality and availability continues to escalate and land planners and engineers become aware of the multiple values and benefits associated with well-designed and landscaped wet ponds.
Because wet ponds are far superior to dry ponds in improving water quality, providing wetland and wildlife habitat, and providing recreational and educational opportunities, these ponds should be built whenever they are feasible for available sites.
Wet ponds can be assets to a community because of these multiple benefits.
In addition, they enhance the quality of life by providing attractive and tranquil refuges in the midst of an urban environment.
Designing Stormwater Structures for Wildlife
 The opportunity exists for creating wetland and wildlife habitat in conjunction with stormwater management.
Design features that make a pond specifically attractive to wildlife are described below.
Each pond and site will be different, and not all of these recommendations will be possible for every pond.
However, the recommendations are guidelines to assist planners in designing multi-purpose ponds that not only control stormwater and improve water quality, but go one step further by providing wetland and wildlife habitat.
Stormwater regulations vary from location to location and should be consulted before developing a management plan.
In addition, it is beneficial to consult with a wildlife biologist for additional input on specific projects.
Water depth and bank slope
 To maximize wildlife habitat and pollutant removal, wet ponds should be shallow with gently sloping sides.
In general, 25 to 50 percent of the water surface area should be between two and three feet deep.
The shallow water areas provide habitat for tadpoles, small fish, and aquatic insects like dragonflies and mayflies.
These in turn provide food for waterfowl, wading birds such as great blue herons, and other
 wildlife.
Shallow areas are also necessary to establish aquatic plants that provide both food and cover for waterfowl and other wildlife.
A slope of 10:1  along the edge will provide shallow water habitat where aquatic plants can be established.
Studies have shown that shallow ponds beneficial for wildlife are also better for improving water quality and are safer for children.
If one objective of the pond is to maintain fish populations, part of the pond should be at least eight feet deep.
The edge between the terrestrial environment and the water is the shoreline.
This edge can be an extremely productive habitat for prey species such as insects, frogs, and crayfish, which in turn attract a diversity of birds and mammals.
When possible, the length of shoreline should be maximized.
This can be done by building ponds with irregular instead of circular shapes.
In large ponds, irregular shorelines having many coves enable pairs of birds to become visually isolated from one another.
That is, a pair of birds can set up a territory in one cove and not be seen by their neighbors in the next cove.
Research has shown that for many species the number of individuals that will breed on a pond is greatly increased when pairs are visually isolated from one another.
Mudflats, sandbars, and islands
 Providing exposed mudflats or sandbars is one of the best ways of making a pond attractive to shorebirds, wading birds, and waterfowl.
Shorebirds and wading birds feed in these nutrient-rich areas while the waterfowl use them for resting and loafing.
Mudflats or sandbars are established and maintained by fluctuating water levels that deposit nutrients into the soil and keep permanent vegetation from becoming established.
Mudflats and sandbars will develop naturally in shallow ponds with gradually sloped sides.
The sloped sides will be underwater during periods of heavy rainfall and exposed during dry periods.
Islands within the center of the pond provide a place for waterfowl to nest where they are protected from predators such as racoons or local dogs and cats.
This is particularly important in suburban and urban areas where populations of these predators are high.
Even if the pond is small, try to establish at least one island.
An island as small as 30 square feet will provide a nest site for a pair of ducks.
These islands should be above the high water mark and should have sloped sides SO water will drain.
Establishing grass on the island will prevent erosion and provide nesting cover.
Shrubs and trees along the edge of ponds and islands provide nest sites, perching sites, and cover for a variety of wildlife.
Aquatic plants within the pond provide food and cover for waterfowl and other wildlife.
Although a completely barren pond
 will eventually develop vegetation, it will do SO faster and become an attractive pond with both aesthetic and wildlife value when a landscape plan is developed and implemented.
The types of vegetation that can be established depend on the water depth and also on how frequently the area is inundated with water.
For landscaping purposes, Schueler  has divided stormwater ponds into six zones that relate to soil moisture and the types of vegetation that can be established.
The tables on pages 4-5 provide a representative list of plant species that can be planted in most zones.
Nest boxes along the edge of the pond and nesting platforms within the pond can be used to attract a variety of wildlife and will increase the visibility of wildlife to people visiting the pond.
Species that use nest boxes include the eastern bluebird, house wren, tree swallow, and purple martin.
A pond near woods may also attract wood ducks.
Canada geese, and mallards will nest on platforms in the pond, and turtles and ducks will use loafing platforms.
Nest boxes and platforms can be built or purchased from local lawn and garden stores or nature centers, or you can contact your local county Extension office or the Kentucky Department of Fish and Wildlife Resources for plans to construct your own.
Summary of Planning for Stormwater Control Ponds
 A summary of planning and design guidelines for optimizing the value of constructed urban stormwater control ponds as wetland reserves for wildlife is presented below.
Where possible, impoundments for stormwater control should retain water rather than merely detain it.
Pond design must meet applicable stormwater control criteria, including legal requirements.
Natural resources personnel, including biologists, should be consulted during the planning and design stages.
All potential pond locations should be evaluated to select the most suitable site in relation to the developed area and surroundings, and in recognition of physical, social, economic, and biologic factors.
There should be an adequate drainage area to provide a dependable source of water for the intended year-round use of the pond, considering seepage and evaporation losses.
The soil on site must have sufficient bearing strength  to support the dam without excessive consolidation and be impermeable enough to hold water.
The pond site should be located in an area where disturbances to valuable existing wildlife habitat by construction activities will be avoided or minimized.
Impoundments with gently sloping sides  are preferable to impoundments with steep slopes.
Gently sloping sides will encourage the establishment of marsh vegetation.
Vegetation will provide food and cover for wildlife and help to enhance water quality.
Impound-
 ments with gently sloping sides are also safer than steepsided ponds for children who might enter the impoundments, and gently sloping sides facilitate use by terrestrial wildlife.
Water depth should not exceed 2 ft.
for 25 percent to 50 percent of the water surface area, with approximately 50 percent to 75 percent having a depth not less than 3 1/2 ft.
An emergent vegetation/open-water ratio of about 50:50 should be maintained.
For larger impoundments , one or more small islands should be constructed.
The shape and position of islands should be designed to help direct water flow within the impoundment.
Water flow around and between islands can help to oxygenate the water and prevent stagnation.
Water quality can be enhanced by a flow-through system where water is continually flushed through the impoundment.
Islands should be gently sloping, and the tops should be graded to provide good drainage.
Appropriate vegetative cover should be established to prevent erosion and provide bird nesting cover.
Consideration should be given to including an overland flow area in the design of large impoundments.
Impoundments should be designed with the capacity to regulate water levels, including complete drainage, and with facilities for cleaning, if necessary.
Locating permanent-water impoundments near existing wetlands generally will enhance the wildlife values of impoundments.
Plants for Stormwater Control Pond Vegetation Zones
 Every effort has been made to fit wetland plants into appropriate zones.
However, many plants can be quite adaptable to a variety of zones and may spread or move after initial planting.
The following woody species may not need to be seeded because they may invade naturally: red maple , silver maple , box elder , green ash , sycamore , river birch , and cottonwood.
Zone 1: Deep Water 
 Common Name	Scientific Name
 Water Milfoil	Myriophyllum spp.
American Lotus*	Nelumbo lutea
 White Water Lily	Nymphea odorata
 These species are invasive and can cover the entire open * water portion of a pond.
To control the invasive nature of these plants.
grow them in containers.
Zone 2: Shallow Water 
 Cooper Iris	Iris fulva
 Southern Blue Flag Iris	Iris versicolor
 Pickerel Weed	Pontederia cordata
 Sweet Flag	Acorus calamus
 Lizard's Tail	Saururus cernuus
 Water Plantain	Alisma subcordatum
 Creeping Primrose	Ludwigia repens
 Marsh Millet	Zizaniopsis miliacea
 Swamp Privet	Forestiera acuminata
 Swamp Haw	Viburnum nudum
 Common Alder	Alnus serrulata
 Swamp Rose	Rosa palustris
 Rose Mallow*	Hibiscus moscheutos
 Swamp Mallow*	Hibiscus militaris
 Bald Cypress	Taxodium distichum
 Water Tupelo	Nyssa aquatica
 Water Hickory	Carya aquatica
 Swamp White Oak	Quercus bicolor
 Overcup Oak	Quercus lyrata
 Zone 3: Pond Shoreline.
Common Name	Scientific Name
 Marsh Violet	Viola cucullata
 Tickseed Sunflower	Bidens spp.
Cardinal Flower	Lobelia cardinalis
 Great Blue Lobelia	Lobelia siphilitica
 Monkey Flower	Mimulus ringens or 
 Joe-pye-weed	Eupatorium fistulosum or
 Red Milkweed	Asclepias incarnata
 Soapwort Gentian	Gentian saponaria
 Jewelweeds	Impatiens pallida or
 Cinnamon Fern	Osmunda cinnamomea
 Royal Fern	Osmunda regalis
 Soft Rush	Juncus effusus
 Frank's Sedge	Carex frankii
 Fox Sedge	Carex vulpinoidea
 Softstem Bulrush	Scripus atrovirens
 Dark Green Rulrush	Scripus validus
 Sweetshrub	Clethra alnifolia or
 American Elderberry	Sambucus canadensis
 Gray Dogwood	Cornus racemosa
 Silky Dogwood	Cornus amomum
 Stiff Dogwood	Cornus foemina
 Deciduous Holly	llex decidua
 Pin Oak	Quercus palustris
 Swamp Chestnut Oak	Quercus michauxii
 Cherrybark Oak	Quercus pagoda
 Bur Oak	Quercus macrocarpa
 Willow Oak	Quercus phellos
 Swamp White Oak	Quercus bicolor
 Shellbark Hickory	Carya laciniosa
 American Elm	Ulmus americana
 Zone 4: Riparian Fringe 
 Common Name	Scientific Name
 Eastern Gamagrass	Tripsacum dactyloides
 Prairie Cordgrass	Spartina pectinata
 Big Bluestem	Andropogon gerardii
 Wild Rye	Elymus virginicus
 New England Aster	Aster novae-angliae
 Dense Blazingstar	Liatris spicata
 Sweet Black-eyed Susan	Rudbeckia subtomentosa
 Branched Coneflower	Rudbeckia triloba
 Golden Alexanders	Zizia aurea
 Ironweed	Veronia altissima or
 False Dragonhead	Physostegia virginiana
 Shrubs (shrubs listed in Zone 3 will work in addition to the
 Smooth Sumac	Rhus glabra
 False Indigo	Amorpha fruiticosa
 Trees (all the trees listed in Zone 3 will work in addition to
 Northern Red Oak	Quercus rubra
 Shumard Oak	Quercus shumardii
 Black Walnut	Juglans nigra
 Red Elm	Ulmus rubra
 Yellow Poplar	Liriodendron tulipifera
 White Ash	Fraxinus americana
 American Basswood	Tilia americana
 American Hornbeam	Carpinus caroliniana
 Eastern Hophornbeam	Ostrya virginiana
 Downy Hawthorn	Crataegus mollis
 Zone 5: Floodplain Terrrace and Zone 6: Upland Slopes
 For woody plants suitable for Zones 5 and 6 , ask your county Extension office for a copy of the publication, Trees, Shrubs, and Vines That Attract Wildlife.
Figure 1.
Landscaping zones in stormwater areas.
Adapted from Wittans and Weiss, 1985, and Schueler, 1987.
Zone 1: Deep Water Areas
 This is the wettest zone; these areas are permanently under one to eight feet of water.
Plants in this zone require permanently saturated soils and are predominated by submergent aquatics  and floating plants such as duckweed, water lotus, spadderdock, waterlily, and eelgrass.
Zone 2: Shallow Water Areas
 This zone is permanently wet with an average water depth of less than one foot or semi-permanently inundated.
Ecological communities typified by this zone include bottomland hardwood forests, wet prairies and marshes, seeps, ponds and sloughs, and the margins of lakes.
Plants adapted to this zone prefer continuously wet soils and tolerate extended periods of flooding or inundation.
Examples of plants would include cattails, rushes, burreed, sweet flag, copper iris, southern blue flag iris, and cinnamon fern.
Zone 3: Pond Shoreline
 Plants in this zone must be tolerant of inundation during storms and exposure during dry periods.
Vegetation that can be established here includes sedges, buttonbush, and cattail.
Parts of the shoreline should be kept free of vegetation and maintained as mudflats or sandbars.
Zone 4: Riparian Fringe Area
 Plants in this zone must be able to tolerate both wet and dry soil conditions and periodic inundation.
Potential tree species include black willow, green ash, red maple, and sycamore.
Zone 5: Floodplain Terrace
 This zone includes most of the pond embankments.
Trees that grow in this zone prefer moist soil but can tolerate infrequent inundation.
These species include silky dogwood, elderberry, and spicebush.
When landscaping around the pond, avoid planting trees and shrubs on the embankment or along the dam because their roots can be destructive to the dam.
In general, a pond designed for waterfowl has only about 50 percent of this zone planted with trees and shrubs.
Zone 6: Upland Slopes
 This area is seldom inundated with water.
Trees that can be planted here include chokeberry, elderberry, and dogwood.
For woody plants suitable for Zones 5 and 6 , ask your county Extension office for a copy of the publication, Trees, Shrubs, and Vines That Attract Wildlife.
For Scenario 4, an end gun was placed on the end of the corner extension.
In this scenario the end gun functions only about 9 degrees out of each corner.
The size of the end gun determines how much energy could be conserved if the pump impeller speed is adjusted based on the need of the center pivot.
For Scenario 4 the energy cost savings when using a VFD averaged about $3.00 per hour.
How Much Nitrogen is in My Irrigation Water?
The amount of nitrate in water is measured as parts per million  or milligrams per liter , these are the same measure for nitrate.
Each ppm will add 0.227 pounds of nitrogen per acre with each inch of irrigation water applied.
Dean E.
Eisenhauer Derrel L.
Martin Derek M.
Heeren, General Editor Glenn J.
Hoffman
 Dean E.
Eisenhauer Derrel L.
Martin Derek M.
Heeren, General Editor Glenn J.
Hoffman
 Copy editing and layout by Peg McCann Cover design by Melissa Miller Cover photos: Drip lateral, photo courtesy of Toro Lake McConaughy, photo courtesy of Steve Melvin, Nebraska Extension Weather station, canal, furrow irrigation in corn, and center pivot photos by the authors
 This work is licensed with a Creative Commons Attribution 4.0 International License
 The American Society of Agricultural and Biological Engineers is not responsible for statements and opinions advanced in its meetings or printed in its publications.
They represent the views of the individual to whom they are credited and are not binding on the Society as a whole.
This book is dedicated to our wives and children for their love and support:
 Maria, Emily, and April
 JoAnn, Jennifer, and Kimberly
 Amber, David, Elizabeth, Nathan, and Joshua DMH
 Maria, Kimberly, Karen, and Sheryl GJH
CORN IRRIGATION MACROMANAGEMENT AT THE SEASONAL BOUNDARIES INITIATING AND TERMINATING THE IRRIGATION SEASON
 KSU Northwest Research-Extension Center 105 Experiment Farm Road, Colby, Kansas Voice: 785-462-6281 Fax: 785-462-2315
 Decisions about when to initiate and terminate the irrigation season are important irrigation macromanagement decisions that can potentially save water and increase net income when made correctly, but can have negative economic consequences when made incorrectly.
A combination of nine years of preanthesis water stress studies and sixteen years of post-anthesis water stress studies for corn was conducted at the Kansas State University Northwest Research-Extension Center in Colby, Kansas on a productive, deep, silt loam soil.
Overall, the pre-anthesis water stress studies suggest that corn grown on this soil type has great ability to handle early-season water stress, provided the water stress can be relieved during later stages.
A critical factor in maximizing corn grain yields as affected by pre-anthesis water stress is maximizing the kernels/area.
Maintaining a water deficit ratio  greater than 0.7 to 0.8 or limiting available soil water depletion in the top 4 ft of soil profile to approximately 30% maximized the kernels/area.
Overall, the post-anthesis water stress studies suggest that corn yield is nearly linearly related to the amount of crop water use during the post-anthesis period and that total crop water use amounts may average nearly 17 inches.
Producers should plan for crop water use during the last 30 and 15 day periods that may average nearly 5 and 2 inches, respectively, to avoid yield reductions.
Management allowable depletion during the postanthesis period should be limited to 45% of the available soil water for an 8-ft profile on the deep silt loam soils of this climatic region.
Definition of Macromanagement and Scope of the Problem
 Corn  is the primary irrigated crop in the U.S.
Great Plains.
There are a number of efficient methods to schedule irrigation for corn on a real-time, daily, or short-term basis throughout the season.
These scheduling methods essentially achieve water conservation by delaying any unnecessary irrigation
 event with the prospect that the irrigation season might end before the next irrigation event is required.
There are larger irrigation management decisions [i.e., irrigation macromanagement ] that can be considered separately from the step-by-step, periodic scheduling procedures.
Two important macromanagement decisions occur at the seasonal boundaries, the initiation and termination of the irrigation season.
Irrigators sometimes make these seasonal boundary determinations based on a traditional time-of-year rather than with sound rationale or science-based procedures.
However, a single, inappropriate, macromanagement decision can easily have a larger effect on total irrigation water use and/or crop production than the cumulative errors that might occur due to small, systematic errors in soil-, plant-, or climatic-based scheduling procedures.
This does not discount step-by-step irrigation scheduling.
To the contrary, it is an implicit assumption that improved macromanagement at the seasonal boundaries can only provide the potential for increased water conservation when used in conjunction with the step-by-step, periodic scheduling procedures.
Most of the established literature on irrigation management during the early and late corn growth stages is 35-45 years old and was written at a time when irrigated corn yields were much lower  than they are today.
It is quite possible that some of the numerous yield-limiting stresses  that were tolerable at the lower yield level are less tolerable today.
On the other side of the issue, there has been much improvement in corn hybrids during the period with incorporation of traits that allow water stress tolerance and/or water stress avoidance.
The corn vegetative stage is often considered the least-sensitive stage to water stress and could provide the opportunity to limit irrigation water applications without severe yield reductions.
The vegetative stage begins at crop emergence and ends after tasseling, which immediately precedes the beginning of the reproductive period when the silks start to emerge.
The potential number of ears/plant is established by the fifth leaf stage in corn.
The potential number of kernels/ear is established during the period from about the ninth leaf stage until about one week before silking.
Stresses during the 10 to 14 days after silking will reduce the potential kernels/ear to the final or actual number of kernels/ear.
Therefore, in research studies designed to examine water stresses during the first one-half of the corn crop season, both ears/plant and kernels/ear might be critical factors.
Additionally, there could be permanent damaging effects from the vegetative and early-reproductive period water stress that may affect grain filling.
Often, irrigators in the Great Plains, start their corn irrigation season after early season cultural practices are completed such as herbicide or fertilizer application or crop cultivation at the lay-by growth stage.
Crop evapotranspiration is increasing rapidly and drier weather periods are approaching, so often there is soil water storage that can be replenished by timely irrigation then for use later in the summer.
However, this
 does not always mean that the corn crop required the irrigation at that point-intime.
In contrast, the post-anthesis grain filling stage in corn is considered to be highly sensitive to water stress with only the flowering and early reproductive period being more sensitive.
Plant water stress can cause kernel abortion if it occurs early enough in the post-anthesis period but is more often associated with poor grain filling and thus reduced kernel weight.
Grain kernel weight is termed as a very loosely restricted yield component , meaning that it can be manipulated by a number of factors.
The final value is also set quite late, essentially only a few days before physiological maturity.
The rate of grain filling is linear for a relatively long period of time from around blister kernel to near physiological maturity.
Yield increases of over 4 bushels/acre for each day are possible during this period.
Providing good management during the period can help to provide a high grain filling rate and, in some cases, may extend the grain filling period a few days thereby increasing yields.
Availability of water for crop growth and health is the largest single controllable factor during this period.
However, the rate of grain filling remains remarkably linear unless severe crop stress occurs.
This is attributed to remobilization of photosynthate from other plant parts when conditions are unfavorable for making new photosynthate.
Irrigators in the Central Great Plains sometimes terminate the corn irrigation season on a traditional date such as August 31 or Labor Day  based on long term experience.
However, a more scientific approach might be that season termination may be determined by comparing the anticipated soil water balance at crop maturity to the management allowable depletion  of the soil water within the root zone.
Some publications say the MAD at crop maturity can be as high as 0.8.
Extension publications from the Central Great Plains often suggest limiting the MAD at season end to 0.6 in the top 4 ft of the soil profile.
These values may need to be re-evaluated and perhaps adjusted downward.
Lamm et al.
found subsurface drip-irrigated corn yields in northwest Kansas began to decrease rapidly when available soil water in the top 8 ft was lower than 5660% of field capacity for extended periods in July and August.
Lamm et al.
permitted small daily deficits to accumulate on surface-irrigated corn after tasseling, and subsequent analysis of those data showed declining yields when available soil water levels approached 60% of field capacity for a 5-ft soil profile at physiological maturity
 This presentation will summarize the results from several long term field studies at the KSU Northwest Research-Extension Center in Colby, Kansas on a productive, deep, silt loam soil where irrigation treatments were either initiated or terminated at various points-intime before and after anthesis, respectively.
The studies were conducted at the KSU Northwest Research-Extension Center at Colby, Kansas, USA on a productive, deep, well-drained Keith silt loam soil  during the sixteen-year period, 1993-2008.
In general, the 1990s were a much wetter period than the 2000s.
The summers of 2000 through 2003 would be considered extreme droughts.
The climate for the region is semiarid with a summer pattern of precipitation with an annual average of approximately 19 inches.
The average precipitation and calculated corn evapotranspiration during the 120-day corn growing period, May 15 through September 11 is 11.8 inches and 23.1 inches, respectively.
The corn anthesis period typically occurs between July 15 and 20.
The corn was planted in 2.5 ft spaced rows in late April to early May, and standard cultural practices for the region were used.
Irrigation was scheduled as needed by a climate-based water budget except as modified by study protocols that will be discussed in the sections that follow.
Calculated crop evapotranspiration  was determined with a modified Penman equation for calculating reference evapotranspiration  multiplied by empirical crop coefficients suitable for western Kansas.
Precipitation and irrigation were deposits into the crop water budget and ETc was the withdrawal.
Soil water was measured in each plot on a weekly or biweekly basis with a neutron probe to a depth of 8 ft.
in 1-ft increments.
These data were used to determine crop water use and to determine critical soil water depletion levels.
Water use values were calculated as the sum of the change in available soil water to the specified profile depth, plus the irrigation and precipitation during the specified period.
This method of calculating crop water use would also include any deep percolation or rainfall runoff that may have occurred.
Corn yield and yield components of plants/area, ears/plant, and kernel weight were measured by hand harvesting a representative 20-ft row sample.
The number of kernels/ear was calculated with algebraic closure using the remaining yield components.
Specific Procedures for Pre-Anthesis Water Stress Studies
 Data from two studies where the initiation date of the irrigation season was varied were combined in the analysis.
The first study consisted of five years of data  with the hybrid Pioneer 3162.
The second study during the four-year period  used two corn hybrids [Pioneer 32B33  and Pioneer 33B50 ].
Both studies utilized the same field site that had a subsurface drip irrigation  system installed in 1990 with 5-ft dripline spacing and an emitter spacing of 12 inches.
The 2.5-ft spaced
 corn rows were planted parallel and centered on the driplines such that each corn row would be 15 inches from the nearest dripline.
The nominal dripline flowrate was 0.25 gpm/100 ft, which is equivalent to an emitter discharge of 0.15 gal/h for the 12-inch emitter spacing.
The 2004-2007 study had six main irrigation treatments and the two corn hybrid split-plot treatments replicated three times in a randomized complete block  design.
The 1999-2003 study used the same experimental design without the split plot.
The whole plots were 8 rows wide  and 200 ft long.
The six irrigation treatments  were imposed by delaying the first normal irrigation either 0, 1, 2, 3, 4, or 5 weeks.
This typically resulted in the first irrigation for Trt 1 being between June 5 and June 15 and the first irrigation for Trt 6 being around July 10 to July 24.
In some years, excessive rainfall between two adjacent treatment initiation dates would negate the need for irrigation.
In that case, the later treatments would be delayed an additional week to provide an extended data set.
After the treatment initiation date occurred, SDI was scheduled to provide 0.4 inches/day until such time that the climate-based water budget fully eliminated calculated soil water deficits.
It should be noted that this irrigation capacity of 0.4 inches/day is much greater than the typical irrigation capacity in this region.
Additionally, the procedure of eliminating the severe irrigation deficits later in the season after the plants had been stunted may lead to excessive deep percolation.
The purpose of the study was not to optimize irrigation use within the study but rather to determine what capability the corn crop had to tolerate early season water stress.
Thus, the procedures were tailored to alleviate soil water deficits relatively quickly after the treatment initiation date.
Analysis of variance  of the yield and yield component data was performed for the 6 treatments for the 1999-2003 data set using a one-way AOV and using a split plot two-way AOV for the 2004-2007 data set.
Specific Procedures for Post-Anthesis Water Stress Studies
 Four separate studies were conducted over the years 1993 through 2008 to examine the effects of post-anthesis water stress on corn.
Prior to anthesis, all treatments in each of the studies were fully irrigated according to their need.
A two-year study  consisting of six irrigation treatments with three replications in a complete randomized block design was conducted in small level basins consisting of 6 corn rows each  approximately 90 ft long.
Surface irrigation was used to provide irrigation amounts for each event that were between 2.5 to 3 inches to help achieve higher distribution uniformity than smaller applications would have provided.
The six irrigation treatments were termination of the irrigation season on either August 5, 10, 15, 20, 25 or 30.
The corn hybrid was Pioneer 3183.
The year 1993 was an extremely poor corn production year
 characterized by very cool and wet conditions while 1994 was a good year for corn production.
A four-year study  consisting of nine irrigation treatments with four replications in a complete randomized block design was conducted in small level basins consisting of 8 corn rows each  approximately 90 ft long.
Surface irrigation was used in this study with event irrigation amounts of approximately 2.5 to 3 inches.
The nine irrigation treatments were termination of the irrigation season at either anthesis, anthesis plus 6, 12, 18, 24, 30, 36, 42 or 48 days.
The corn hybrid was Pioneer 3183.
Corn yields in 1995 were somewhat depressed due to a hail storm but were good in 1996 through 1998.
Another study was conducted from 1999 through 2001 using subsurface drip irrigation to more closely control soil water levels and distribution uniformity of irrigation water.
In this study, seven irrigation treatments were replicated three times in a complete randomized block with plot size of 8 corn rows  by approximately 280 ft.
In this study irrigation during the post-anthesis period was managed for two distinct periods.
Four of treatments began at anthesis with one treatment receiving no irrigation after anthesis and the other three treatments only receiving irrigation if the available soil water in the top 5 foot of profile fell below approximately 68, 48 or 27% of field capacity.
Three additional treatments were no irrigation after two weeks following anthesis and soil water maintenance level treatments of either 48 or 27% of field capacity beginning also at that time.
After anthesis, irrigation amounts were generally not greater than 0.5 inches for each required event and were conducted as needed to return the available soil water to the required treatment level.
The year 1999 had above normal precipitation but 2000 and 2001 were extreme drought years.
This study utilized an subsurface drip irrigation  system installed in 1999 with 5-ft dripline spacing and an emitter spacing of 24 inches.
The 2.5-ft spaced corn rows were planted parallel and centered on the driplines such that each corn row would be 15 inches from the nearest dripline.
The nominal dripline flowrate was 0.25 gpm/100 ft, which is equivalent to an emitter discharge of 0.30 gal/h for the 24inch emitter spacing.
The corn hybrid was Pioneer 3162.
The final post-anthesis water stress study  was conducted on the same SDI field site as the 1999 through 2001 study but the seven irrigation treatments were the irrigation season being terminated at one week intervals beginning one week after anthesis.
This typically meant that the first irrigation treatment ceased about July 20 to 27 and the last irrigation treatment ceased about August 31 to September 7.
The crop was fully irrigated until the irrigation termination date occurred and irrigation event amounts were generally not greater than 0.5 inches.
The seven irrigation treatments were replicated three times in a complete randomized block design.
The corn hybrid was Pioneer 3162.
Post
 anthesis water productivity was calculated as the crop yield in bu/acre divided by the post-anthesis crop water use.
Results for Pre-Anthesis Water Stress Studies
 Statistical and tabular data analysis for pre-anthesis water stress studies
 Delaying irrigation only statistically affected the yield components in three of the nine crop years and then only for the later irrigation dates.
Delaying irrigation until July 10, 2001, July 17, 2003 and July 27, 2005 significantly reduced the number of kernels/ear and the grain yield.
These three years had an average weather-based calculated July crop ETc rate of 0.32 inches/day.
In comparison the average July crop ETc rate value was 0.26 inches/day for the other six years.
It should be noted that the years 2000 through 2003 were extreme drought years in northwest Kansas.
Delaying irrigation also significantly reduced ears/plant in 2003 and 2005.
In 2003, the reduction in kernels/ear and ears/plant for Trt 6 was partially compensated for by a statistically higher kernel weight.
Overall, these results suggest that corn grown on this soil type has great ability to handle vegetative and early-reproductive period water stress provided the water stress can be alleviated during the later stages.
The hybrid selection affected yield in only one of the four years, 2006, with the longer season Pioneer 32B33 providing significantly greater yields for the later irrigation initiation dates.
This is probably because of earlier pollination for the Pioneer 33B50 prior to receiving irrigation.
Kernels/ear was significantly less for the shorter season Pioneer 33B50 hybrid in three of four years.
Hybrid selection did not affect ears/plant in any of the four years.
In 2004, kernel weight was significantly higher for Pioneer 33B50 for some irrigation treatments, probably because of the smaller number of kernels/ear for this hybrid in that year.
It should be noted that the results do not mean that irrigation can be delayed in the Western Great Plains until mid to late July.
These plots generally started the season with reasonably full soil profiles.
Most irrigators do not have irrigation systems with adequate capacity  to quickly alleviate severely depleted soil water reserves.
In addition, it is difficult to infiltrate large amounts of water into the soil quickly with sprinkler and surface irrigation systems without causing runoff problems.
Rather, look at these study results as describing the corn plant's innate ability to tolerate vegetative-period water stress.
Table 1.
Summary of yield component and irrigation data from an early season water stress study for corn hybrid Pioneer 3162, KSU-NWREC, Colby, Kansas, 1999-2003.
Year and Parameter	Trt 1	Trt 2	Trt 3	Trt 4	Trt 5	Trt 6
 1999 First Irrigation Date	22-Jun	29-Jun	6-Jul	13-Jul	20-Jul	27-Jul
 Total Irrigation 	11.2	11.2	11.2	10.0	10.0	7.6
 Yield 	253	a*	265 a	256 a	255 a	259 a	255 A
 Plant Pop.
31073 A	32234 a	31944 a	31653 a	32234 a	32234 A
 Ears/Plant	0.99 A	0.99 a	0.97 a	1.00 a	0.99 a	1.01 A
 Kernels/Ear	575 A	570 a	555 a	572 a	543 a	555 A
 Kernel Wt.
36.3 A	36.9 a	37.8 a	35.8 a	38.1 a	35.9 A
 2000	First Irrigation Date	5-Jun	12-Jun	19-Jun	26-Jun	3-Jul	10-Jul
 Total Irrigation 	19.7	19.7	19.7	18.9	18.9	18.9
 Yield 	225 A	235 a	225 a	227 a	216 a	217 A
 Plant Pop.
27878 A	28169 a	26717 a	26717 a	27007 a	27297 A
 Ears/Plant	1.02 A	1.04 a	0.99 a	1.03 a	1.02 a	1.01 A
 Kernels/Ear	544 A	553 a	568 a	544 a	548 a	529 A
 Kernel Wt.
36.9 a	36.8 a	38.0 a	38.4 a	36.4 a	37.8 A
 2001 First Irrigation Date	12-Jun	19-Jun	26-Jun	3-Jul	10-Jul	17-Jul
 Total Irrigation 	19.2	19.2	19.2	19.2	19.2	19.2
 Yield 	254 a	260 a	261 a	250 a	213 b	159 C
 Plant Pop.
33977 a	34993 a	35138 a	35284 a	34413 a	33831 A
 Ears/Plant	0.96 a	0.98 a	0.99 a	0.99 a	0.97 a	0.99 A
 Kernels/Ear	581 a	584 a	582 a	541 a	476 b	347 C
 Kernel Wt.
33.8 a	33.2 a	32.8 a	33.7 a	34.6 a	34.9 A
 2002	First Irrigation Date	12-Jun	19-Jun	26-Jun	3-Jul	10-Jul	17-Jul
 Total Irrigation 	18.5	18.0	18.0	18.0	18.0	18.0
 Yield 	233 a	232 a	217 a	219 a	222 a	223 A
 Plant Pop.
34558 a	34848 a	34558 a	35719 a	35719 a	34558 A
 Ears/Plant	0.98 a	0.97 a	0.98 a	0.99 a	1.00 a	0.99 A
 Kernels/Ear	454 a	443 a	407 a	435 a	391 a	422 A
 Kernel Wt.
38.6 a	39.8 a	40.3 a	36.6 a	40.5 a	39.2 A
 2003	First Irrigation Date	12-Jun	21-Jun	26-Jun	3-Jul	10-Jul	17-Jul
 Total Irrigation 	18.8	18.0	18.0	17.2	17.2	17.2
 Yield 	177 a	180 a	190 a	186 a	171 a	93	B
 Plant Pop.
32815 a	33396 a	34267 a	33106 a	34558 a	32815 A
 Ears/Plant	0.96 a	0.92 b	0.96 a	1.00 a	0.97 a	0.82 C
 Kernels/Ear	588 a	567 a	576 a	569 a	486 b	262	C
 Kernel Wt.
24.1	b	26.2 b	25.5 b	25.2 b	26.8 b	33.6	A
 Values followed by the same lower case letters are not significantly different at P=0.05.
Table 2.
Summary of corn yield component and irrigation data from an early season water stress study for hybrids Pioneer 33B50 and 32B33, KSU-NWREC, Colby, Kansas, 2004-2007.
Year and Parameter	Trt 1	Trt 2	Trt 3	Trt 4	Trt 5	Trt 6
 2004 First Irrigation	Hybrid	8-Jun	28-Jun	13-Jul	20-Jul	27-Jul	3-Aug
 Total Irrig.
12.8	11.6	10.8	10.8	10.8	10.8
 Yield 	33B50	220	aA*	213 aA	206 aA	233 aA	245	aA	210	aA
 32B33	226	aA	211 aA	209 aA	222 aA	229 aA	206	aA
 Plant Pop.
33B50	29040 aA	28169 aA	28169 aA	28169 aA	28750 aA	27878 aA
 32B33	28459 aA	29621 aA	29621 aA	28459 aA	29040 aA	28459 aA
 Ears/Plant	33B50	0.85 aA	0.91 aA	0.89 aA	0.93 aA	0.88 aA	0.84	aA
 32B33	0.88 aA	0.80 aA	0.79 aA	0.90 aA	0.83 aA	0.83 aA
 Kernels/Ear	33B50	595	aB	574 aB	589 aB	595 aA	648 aA	590	aB
 32B33	624	aA	616 aA	634 aA	600 aA	643	aA	612	aA
 Kernel Wt.
33B50	38.0	aA	36.8 aA	35.7 aA	38.2 aA	38.2 aA	38.6	aA
 32B33	36.8 aB	36.4 aA	36.2 aA	36.8 aB	37.6 aA	36.4	aB
 2005 First Irrigation	Hybrid	21-Jun	28-Jun	6-Jul	12-Jul	19-Jul	26-Jul
 Total Irrig.
13.2	13.2	13.2	13.2	13.2	13.2
 Yield 	33B50	254 aA	259 aA	256 aA	238 abA	227	bA	149	cA
 32B33	254 abcA	254 abcA	258 abA	264 aA	235	cA	162	dA
 Plant Pop.
33B50	28750 aA	28459 aA	28459 aA	28459 aA	29621 aA	28169	aA
 32B33	28459 aA	29040 aA	28459 aA	27848 aA	28750 aA	29621 aA
 Ears/Plant	33B50	0.99 abA	1.00 aA	0.99 abA	0.98 abA	0.96 bcA	0.95	cA
 32B33	0.98	bA	0.97 bcA	1.01 aA	1.00 abA	0.96 bcdA	0.94	dA
 Kernels/Ear	33B50	641	abA	653 aA	670 aA	604 bA	564	cA	422 dA
 32B33	638	bA	647 abA	644 abA	680 aA	654 abA	421	cA
 Kernel Wt.
33B50	35.4	aA	35.4 aA	34.5 aA	36.0 aA	35.9 aA	33.6 aA
 32B33	36.2 aA	35.4 aA	35.4 aA	35.5 aA	33.1 aA	35.1 aA
 2006 First Irrigation	Hybrid	8-Jun	15-Jun	26-Jun	29-Jun	6-Jul	14-Jul
 Total Irrig.
14.0	13.6	12.8	12.8	12.4	12.4
 Yield 	33B50	225	aA	230	aA	220	aB	220	aA	220	aB	206	aB
 32B33	229	aA	234 aA	246 aA	230 aA	241	aA	244	aA
 Plant Pop.
33B50	27588 aA	27007 aA	28169 aA	28169 aA	27588 aA	27297 aA
 32B33	28459 aA	27878 aA	28459 aA	27878 aA	28168 aA	28169 aA
 Ears/Plant	33B50	0.98 aA	0.98 aA	0.99 aA	0.99 aA	0.99 aA	0.96 aA
 32B33	0.96	aA	0.98 aA	0.98 aA	0.97 aA	0.98 aA	0.97 aA
 Kernels/Ear	33B50	561	aB	594 aAB	544 aB	547 aB	550	aB	519	aB
 32B33	597	aA	602 aA	618 aA	583 aA	585	aA	612	aA
 Kernel Wt.
33B50	37.8	aA	37.2 aA	36.8 aA	36.5 aA	37.4 aA	38.7 aA
 32B33	35.7 aA	36.2 aA	36.3 aA	37.1 aA	38.1 aA	37.2 aA
 2007 First Irrigation	Hybrid	7-Jun	21-Jun	28-Jun	4-Jul	12-Jul	19-Jul
 Total Irrig.
12.1	11.3	11.3	11.3	11.3	10.9
 Yield 	33B50	243	aA	252	aA	250 aA	245	aA	234	aA	213	aA
 32B33	259	aA	235 aA	252 aA	239 aA	255 aA	229	aA
 Plant Pop.
33B50	29040 aA	29621 aA	29331 aA	28459 aA	29040 aA	28169 aA
 32B33	29040 aA	28459 aA	28169 aA	27878 aA	28459 aA	28169 aA
 Ears/Plant	33B50	0.98 aA	0.99 aA	1.00 aA	0.99 aA	0.99 aA	1.00 aA
 32B33	0.98	aA	0.95 aA	0.99 aA	0.99 aA	0.99 aA	0.97 aA
 Kernels/Ear	33B50	668	aB	672 aB	693 aA	682 aA	645 aB	597	aB
 32B33	728	aA	724	aA	712 aA	712 aA	714 aA	674	aA
 Kernel Wt.
33B50	32.5	aA	32.5 aA	31.2 aA	32.4 aA	32.0 aA	32.2 aA
 32B33	31.6	aA	30.6	aA	32.3	aA	30.9 aA	32,3 aA	31.7 aA
 Irrigation treatment values within the same row followed by the same lower case letters are not
 significantly different at P=0.05, and hybrid treatment values within the same column followed by the
 same upper case letters are not significantly different at P=0.05.
Graphical data analysis for pre-anthesis water stress studies
 The tabular data do not give a mechanistic explanation of the results.
Attempts were made to relate yield component data to a large number of water factors in the broad categories of water use, evaporative demand, and critical profile soil water levels.
Relative values of yield and yield components were determined by normalizing each data point to the corresponding value for the earliest irrigation treatment in that year.
These relative values were used for comparisons between years.
Final grain yield was largely determined by the number of sinks or kernels/area  indicating there was little or no effect on the grain-filling stage imposed by the vegetative and earlyreproductive period water stress in these two studies.
The individual treatment values of corn grain yield and kernels/area were values compared to the irrigation treatment that had no initial delay in irrigation  to give relative values.
In a few cases, the Trt 1 values were not the highest value and, thus, relative values could be greater than one.
Deviations below the 1 to 1 unity line in Figure 1 would indicate a permanent negative effect on corn grain yield of early-season water stress because of reduced kernels/area.
Deviations above the line would indicate some grain yield compensation resulting from better grain filling of the reduced kernels/area.
Figure 1.
Relative corn grain yield as affected by relative kernels/area in an earlyseason corn water stress study, KSU-NWREC, Colby, Kansas, 1999-2007.
Relative kernels/area was found to be reasonably well related to relative July water use, the minimum available soil water in the top 4 ft of the soil profile during July and to the July 1 through July 15 water deficit.
Further analysis is needed to determine an improved overall relationship involving more than a single factor, but the individual factor results will be discussed here.
The 50% critical silking period for corn in this study ranged from approximately July 17 to July 22 during the study period.
The short-season hybrid in the latter study would typically silk approximately one week earlier.
A window of approximately two weeks on both sides around the silking period was used to compare the relative kernels/area to the relative July measured water use.
Actual soil water measurements were taken on an approximately weekly basis except for equipment problems or when excessive precipitation delayed measurements, so it was not possible with the data set to always have exactly 31 days of water use.
Dates used were those closest to July 1 through 31.
There tended to be some reduction in relative kernels/area when relative July water use was less than 80%.
Scatter at the lower end of relative July water use may be related to water-use differences occurring within the month or differences in evaporative demand between the years.
This relationship may not result in a very good signal for procedures to determine irrigation need because the relative July water use cannot be determined until it is too late to handle the reduction in relative kernels/area.
Figure 2.
Relative corn grain yield as affected by relative July water use in an earlyseason corn water stress study, KSU-NWREC, Colby, Kansas, 1999-2007.
The relative kernels/area tended to be reduced when July minimum available soil water in the top 4 ft  was below 0.6  in some years.
During years of less evaporative demand, water could be extracted from the soil profile to a further reduced level without much detriment to relative kernels/area, but severe reductions occurred for similar soil water conditions in years with large July evaporative demands.
The upper and lower envelope lines of Figure 3 were manually drawn to indicate the effect of evaporative demand of the given year on relative kernels/area.
These envelopes would match known theories of water stress and water flow through plants.
Figure 3.
Relative kernels/area as affected by July minimum available soil water in the top 4 ft of soil in an early-season corn water stress study, KSU-NWREC, Colby, Kansas, 1999-2007.
The upper  and lower  lines are manually drawn to illustrate years with larger and smaller July evaporative demand.
Water stress is greater both with reduced available soil water and with greater evaporative demand.
The kernels/area was most sensitive to the JASW in the top 4 ft of soil as compared to both smaller and greater profile depths.
This is reflecting the approximate rooting and soil water extraction depth of corn in July on this soil type.
There remains considerable unexplained scatter in this graph that does not appear to be related very well to differences in evaporative demand between the years.
For example, there was very little effect on relative kernels/area in 2002, although it had a moderately high evaporative demand.
The relationship of relative kernels/area to a critical level of available soil water can have some merit as a signal for determining the need for irrigation because available soil water can both be measured in real-time and the value can be projected a few days into the future.
The ratio of calculated well-watered crop ETc to the sum of irrigation and precipitation for July 1 through 15 was also related to the relative kernels/area.
The relative kernels/area tended to decrease when this water deficit ratio was less than 70 to 80%.
Attempts were also made in varying the timeframe of the ratio.
It appears that some of the remaining scatter in this graph is related to timing of irrigation and precipitation near the actual point of silking.
For example, the isolated point from 2002 near the vertical axis may be related to a significant precipitation event that occurred near silking, but later than July 15.
Further analysis should be conducted to allow the window to actually vary around the individual silking dates of each year.
This might be done by computing windows based on the number of thermal units  required for silking.
This relationship might also be a good signal in determining the need for irrigation because it can be determined in near real-time using the accumulated ratio to that point in time.
Figure 4.
Relative kernels/area as affected by the July 1 through 15 water deficit  in an early-season corn water stress study, KSU-NWREC, Colby, Kansas, 1999-2007.
Further analysis should focus on attempts to combine multiple factors  with a focus on developing irrigation signals that can be used in near real-time to make early season irrigation decisions.
Recommendations for managing pre-anthesis corn water stress
 Producers should use a good method of day-to-day irrigation scheduling during the pre-anthesis period.
To a large extent the information being used to make day-to-day irrigation scheduling decisions during the pre-anthesis period can also be used as in making the macromanagement decision about when to start the irrigation season.
This is because even though the corn has considerable innate ability to tolerate early season water stress, most irrigation systems in the Central Great Plains do not have the capacity  or practical capability  to replenish severely depleted soil water reserves as the season progresses to periods of greater irrigation needs.
However, there is some flexibility in timing of irrigation events within the vegetative growth period.
In years of lower evaporative demand, corn grown on this soil type in this region can extract greater amounts of soil water without detriment.
Timeliness of irrigation and/or precipitation near anthesis appears to be important in establishing an adequate number of kernels/area.
The strong linear 1:1 relationship that existed between the relative corn yield and the relative number of kernels/area  indicates that optimizing kernels/area is a key in optimizing grain yields.
Producers growing corn on deep silt loam soils in the Central Great Plains should attempt to maintain a water deficit ratio  during July of approximately 0.7 to 0.8 and not allow the available soil water within a 4-ft soil profile to decrease below 70%, particularly in years of greater evaporative demand.
Results for Post-Anthesis Water Stress Studies
 Tabular data analysis for post-anthesis water stress studies
 Results from 16 years  of studies indicate that anthesis for corn in Northwest Kansas varies from July 12 to July 24 with an average date of July 19.
Physiological maturity ranged from September 14 through October 10 with an average date of September 27.
The average length of the post-anthesis period was approximately 70 days.
Using the corn grain yield results from the study and the individual treatment irrigation termination dates responsible for those yields, Table 3 was created to indicate the problems with using inflexible dates for determining the irrigation season termination date.
Additionally, the corn grain yield results and the treatment irrigation dates were used to estimate the date when a specified percentage of maximum grain yield would occur.
Because there was not an unlimited number of irrigation treatment dates there are years when the date required for a specified percentage of maximum grain
 yield was the same as the date for the next higher percentage.
The average estimated termination date to achieve 80, 90 and 100% of maximum corn grain yield was August 2, 13, and 28, respectively, but the earliest dates were July 17, July 17 and August 12, respectively, while the latest dates were September 14, 21, and 21, respectively.
Irrigators that use average or fixed dates to terminate the corn irrigation season are not realistically considering the irrigation needs of the corn that may be greater or smaller in a particular year, and thus, often will neither optimize corn production, nor minimize water pumping costs.
Table 3.
Anthesis and physiological maturity dates and estimated irrigation season termination dates* to achieve specified percentage of maximum corn grain yield from studies examining post-anthesis corn water stress, KSU Northwest Research-Extension Center, Colby, Kansas, 1993-2008.
Note: This table was created to show the fallacy of using a specific date to terminate the irrigation season.
Note: Because there was not an unlimited number of irrigation treatment dates, there are years when the date required for a specified percentage of maximum grain yield was the same as the date for the next higher percentage.
Year	Date of	Date of	Irrigation Season Termination Date For
 Anthesis	Maturity	80% Max Yield	90% Max Yield	MaxYield
 1993	20-Jul	30-Sep	5-Aug	5-Aug	15-Aug
 1994	20-Jul	15-Sep	5-Aug	15-Aug	15-Aug
 1995	20-Jul	29-Sep	5-Aug	13-Aug	18-Aug
 1996	20-Jul	3-Oct	17-Jul	17-Jul	29-Aug
 1997	23-Jul	1-Oct	23-Jul	23-Jul	27-Aug
 1998	20-Jul	28-Sep	20-Jul	20-Jul	24-Aug
 1999	23-Jul	6-Oct	24-Jul	13-Aug	20-Sep
 2000	12-Jul	20-Sep	14-Sep	20-Sep	20-Sep
 2001	16-Jul	29-Sep	30-Jul	22-Sep	22-Sep
 2002	22-Jul	30-Sep	4-Aug	30-Aug	7-Sep
 2003	22-Jul	23-Sep	3-Aug	3-Aug	18-Aug
 2004	19-Jul	28-Sep	8-Aug	21-Aug	27-Aug
 2005	20-Jul	28-Sep	2-Aug	9-Aug	29-Aug
 2006	17-Jul	25-Sep	30-Jul	13-Aug	13-Aug
 2007	18-Jul	19-Sep	14-Aug	21-Aug	28-Aug
 2008	24-Jul	10-Oct	31-Jul	6-Aug	27-Aug
 Average	19-Jul	27-Sep	2-Aug	13-Aug	28-Aug
 Standard Dev.
3 days	6 days	13 days	19 days	13 days
 Earliest	12-Jul	14-Sep	17-Jul	17-Jul	12-Aug
 Latest	24-Jul	10-Oct	14-Sep	21-Sep	21-Sep
 *	Estimated dates are based on the individual irrigation treatment dates from each of
 the different studies when the specified percentage of yield was exceeded.
Maximum corn yields  during the 16-year period in the various studies averaged 258 bu/acre with a range of 154 to 298 bu/acre.
Extremely poor growing conditions  greatly reduced yields in 1993 and hail suppressed yield in 1995.
The post-anthesis water use that occurred for the irrigation treatment that maximized yield  averaged 16.9 inches with a range of 14.9 to 20.2 inches.
Assuming that yield formation for the corn crop started at anthesis, the average post-anthesis water productivity  was 15 bu/inch and the range of water productivity over the years was 8 to 20 bu/inch.
Table 4.
Maximum corn yields and post-anthesis water use data from studies examining post-anthesis corn water stress, KSU Northwest ResearchExtension Center, Colby, Kansas, 1993-2008.
Maximum	PAWU MY	PAWU	MY
 Year	Yield	PAWUMY*	PAWUMY	during last	during last 15
 			30 days	days
 1993	154	19.23	0.287	0.288	0.178
 1994	246	15.52	0.277	0.218	0.178
 1995	170	18.23	0.285	0.201	0.174
 1996	280	15.38	0.220	0.161	0.137
 1997	245	16.13	0.230	0.162	0.150
 1998	262	16.55	0.236	0.155	0.136
 1999	272	18.49	0.247	0.134	0.081
 2000	259	20.24	0.289	0.276	0.302
 2001	268	19.44	0.259	0.161	0.160
 2002	284	16.63	0.238	0.139	0.017
 2003	269	15.12	0.240	0.089	0.105
 2004	283	16.25	0.229	0.181	0.164
 2005	295	16.31	0.233	0.088	0.036
 2006	268	16.48	0.235	0.098	0.101
 2007	273	16.25	0.258	0.104	0.106
 2008	298	14.85	0.190	0.115	0.091
 Average	258	16.94	0.247	0.161	0.132
 Standard Dev.
40	1.65	0.027	0.061	0.066
 Minimum	154	14.85	0.190	0.088	0.017
 Maximum	298	20.24	0.289	0.288	0.302
 PAWUMY is the post-anthesis water use occurring for the irrigation treatment that
 achieved maximum corn grain yield within the specified year.
PAWUMY averaged 0.247 inches/day during the approximately 70-day period between anthesis and physiological maturity and remained at 65 and 53% of that value  during the last 30 and 15 days of the season, respectively.
This emphasizes that although crop water use is tapering
 off during the latter part of the season, due to maturing crop canopies and also due to lower reference evapotranspiration , therefore, it must be considered an important factor in late season crop management.
Producers should also be aware that irrigation systems with marginal or insufficient capacity may have allowed considerable soil water depletion  during the preanthesis period.
Graphical data analysis for post-anthesis water stress studies
 The corn grain yield results within a given year were normalized to the maximum value occurring in that particular year to give the relative yield.
The postanthesis water use within a given year was then normalized with respect to the water use that occurred for the irrigation treatment that maximized corn grain yield in that particular year.
This allowed treatments receiving excessive irrigation to have relative post-anthesis water use  values greater than one.
There was a strong relationship between relative corn yield  and relative post-anthesis water use  as shown in Figure 5.
Figure 5.
Relative corn grain yield  as affected by relative post-anthesis water use  for various studies examining the effect of post-anthesis water stress, KSU-NWREC, Colby, Kansas, 1993-2008.
The dotted line represents a unity relationship between RY and RPAWU MY.
Note: RPAWUMY values can exceed one because some treatments received irrigation water in excess of the amount required to maximize corn grain yield.
This excessive water may have been lost in deep percolation but would have been included in the calculation procedures of post-anthesis water use.
Although there are a number of curves that can be drawn through the data , there was a large portion of the data in the efficient range of RPAWUMY  that can be adequately characterized by a one-to-one relationship between RY and RPAWUMY.
The subtle differences between assuming a curvilinear or linear relationship in the efficient range of post-anthesis water use might become important when trying to optimize corn production using water resource and economic constraints.
There was a reasonably good relationship between relative corn grain yield  and the minimum post-anthesis available soil water  within the 8-ft soil profile  Corn yield tended to decrease for treatments having less than a minimum available soil water of approximately 55% of field capacity for any point-intime within the post-anthesis period.
Thus, the management allowable depletion  in these studies was approximately 45% as compared to the traditionally larger values often quoted in the literature.
However, the 45% MAD value is consistent with the results of Lamm et al.
and Lamm et al.
from irrigated corn studies on the same soil type.
Figure 6.
Relative corn grain yield  as affected by the minimum value of available soil water  within the 8 ft soil profile occurring during the postanthesis period.
Data are from various studies examining the effect of post-anthesis corn water stress, KSU-NWREC, Colby, Kansas, 19932008.
There was also a relatively good relationship between RPAWUMY and MPAASW.
RPAWUMY tended to decrease for treatments with MPAASW less than 55% of field capacity.
This is to be as expected because of the strong relationship between RY and RPAWUMY but does provide additional evidence and rationale for a MAD value of approximately 45% for this soil type in this region as compared to the higher values in the literature.
Mininum Post-Anthesis Available Soil Water
 Figure 7.
Relative post-anthesis water use  as affected by the minimum value of available soil water  within the 8 ft soil profile occurring during the post-anthesis period.
Data are from various studies examining the effect of post-anthesis corn water stress, KSU-NWREC, Colby, Kansas, 1993-2008.
Further data analysis should focus on determining the cause of increased scatter in the graph regions  where MPAASW is less than 0.55.
Additionally, further efforts are justified in comparing the MPAASW values for different soil profile depths to see which depth has the greatest correlation and also to determine the inaccuracy associated with choosing alternative depths.
Recommendations for managing post-anthesis corn water stress
 Producers should use a good method of day-to-day irrigation scheduling during the post-anthesis period.
The macromanagement decision about when to terminate the irrigation season should not be based on an average or fixed date.
Producers in the Central Great Plains should plan for postanthesis water use needs of approximately 17 inches and that water use during
 the last 30 and 15 days of the season might average nearly 5 and 2 inches, respectively.
This water use would need to come from the sum of available soil water reserves, precipitation and irrigation.
When irrigation losses are minimized, a percentage decrease in post-anthesis water use will result in nearly a one-to-one percentage decrease in corn grain yield.
Producers growing corn on deep silt loam soils in the Central Great Plains should attempt to limit management allowable depletion of available soil water in the top 8 ft of the soil profile to 45%.
Macromanagement decisions at the seasonal boundaries should always be made in the context of having implemented appropriate day-to-day irrigation scheduling.
Proper day-to-day scheduling will provide much-needed information about the crop and soil water status and evaporative demand being experienced within the given year.
Corn has greater than anticipated ability to withstand early season water stress provided that the water stress can be alleviated during the early-reproductive period.
However, it should be reiterated that these results are not suggesting that irrigation can be delayed until anthesis.
Most irrigation systems cannot quickly alleviate severely depleted soil water reserves as was accomplished in this pre-anthesis studies, but the results do indicate there is some flexibility in timing of irrigation events within the vegetative growth period.
Timeliness of appreciable amounts of irrigation and/or precipitation near anthesis appears to be very important in maximizing yield potential.
Corn yield formation was primarily linearly related to the water use during the post-anthesis period for cases when irrigation was limited to the amount required for maximum yield.
Limiting available soil water depletion to approximately 45% during the period is important in achieving maximum grain yields.
Contribution No.
09-240-A from the Kansas Agricultural Experiment Station.
Rhoads F.
M.
and J.M.
Bennett.
1990.
Corn.
Chapter 19 in Irrigation of Agricultural Crops.
pp.
569-596.
ASA-CSSA-SSSA, Mono No.
30, B.
A.
Stewart and D.
R.
Nielsen.
1218 pp.
Proper management of irrigated corn requires careful attention to crop water stress during both the pre-anthesis and post-anthesis growing periods.
Soil Sensor Install Tips: While other tasks may seem more pressing, early installation of sensors is critical to ensure their proper operation during the later critical growth phases.
Early installation helps to minimize root damage, allows time for sensors to acclimate to read actual soil water conditions instead of water within the sensor or slurry, and gives a better chance for proper soil contact.
Water Testing 1 Bacteriological Testing 1 Mineral and pH Testing 2 Chemical Testing 2
 Typical Problems 2 Hardness 2 Iron or Manganese 3 Acid Water  4 Total Dissolved Solids  5 Nitrates 5 Sulphates and Sulfides 6
 Home Water Treatment Equipment 7 Water Softeners 7 Reverse Osmosis  Units 8
 Pressure Filters 9 Manganese Greensand Oxidizing Filter 11 Taste and Odor Filter 12 Sand Filter to Remove Turbidity  12 Neutralizing Filter 12 Point-of-Use Filters 13
 Soda Ash Feeding 13 Calibration of Soda Ash 14
 Chlorination 14 Chlorine Demand 15 Contact Time 15 Continuous Chlorination 17 Chlorine Calibration 18 Shock Chlorination 18 Feeding Soda Ash and Chlorine Together 19
 Typical Problems and Possible Treatments 20 Hardness 20 Iron or Manganese  20 Iron or Manganese Bacteria 21 Acid Water  21 Hydrogen Sulfide Gas 21 Turbid Water  22 Nitrates 22 Total Dissolved Solids  22 Aggressive Water Aggressive Index  22
Total water use in Nebraska breaks down to approximately 81% groundwater irrigation, 13% surface water irrigation, 4% domestic water uses.
The remaining 2% comprises other uses such as livestock, industrial and mining.
After electrical concerns, the second biggest safety hazard with pivots is missing driveshaft covers.
Pivot Control Tools Providing Efficiency to Preserve, Conserve and Protect
 Monitoring and Control of Center Pivots
 The ability for producers to monitor and control center pivots has been available since the early 1990's.
This technology started with a direct access to the pivot through a land line phone connection on analog cell phone.
The technology has continued to evolve.
Today pivots and pumps can be controlled from the internet and phone anywhere in the world.
FieldNET was introduced by Lindsay Corporation three years ago.
FieldNET provides growers the ability to monitor and control center pivots from a secure user web site or via any telephone.
A key feature of FieldNET is that it can work for monitoring and start/stop controls on any brand of pivot.
The pivots are connected to the internet through cellular telemetry units or radio telemetry units, which connect to the internet through an internet bridge.
With this web based solution tool growers are able to create a network with all of their pivots and manage them at all times no matter where they are.
The user friendly web portal provides quick view of every pivot, providing information on pivot location, pivot status and water usage.
This encompassing view enables quick, effective decision making.
The portal provides a complete history log and the ability to create reports on water and chemical application.
FieldNET provides growers updates and alerts via phone, text message and email.
These notifications are set based upon the users information needs.
With this immediate information growers are able to react to various statuses when they occur rather than only when they are at the machine in the field.
This leads to greater efficiency and time resource savings.
Lindsay Corporation has just added FieldNET for pump controls.
Now FieldNET, with pump control, integrates the entire water delivery system from the well or surface water source to the center pivot.
It allows the industry-leading pumping solutions by Watertronics and Zimmatic center pivots to work together to automatically monitor and control the system to achieve maximum efficiency.
FieldNET Pump Control lets growers monitor and control several devices such as; pumps, pivots, and sensors.
Visual pressure settings on pumps with Variable Frequency Drives allow for management of pressure and flow for efficient energy savings.
Linking pump devises compares pump station capacity with pivot demand for informed irrigation decisions and alerts of any detected disparity.
Reports and charting allow for record keeping of total gallons pumped and electricity used.
FieldNET Irrigation Management Advantages
 There are many advantages to remote monitoring of pivots and pumps.
These include:
 Flexibility for current equipment
 Effective tool for professional service providers
 Development and use of Knowledge:
 Reduced risk and less downtime
 Enhanced best practices and stewardship:
Timing the Final Irrigation Using Watermark TM Sensors
 Chris Henry Ph.D., Associate Professor and Water Management Engineer Rice Research and Extension Center
 P.B.
Francis Ph.D., Professor University of Arkansas at Monticello
 L.
Espinoza Ph.D., Soil Scientist Crop, Soil and Environmental Science
 M.
Ismanov Ph.D., Program Technician Soils, Crop, Soil and Environmental Science
 Arkansas Is Our Campus
 This is the last in a series of three fact sheets on Watermark Soil Moisture Sensors.
The first fact sheet provides details on "How to Prepare, Test and Install Watermark Sensors." The second fact sheet discusses "How to Use Watermark Soil Moisture Sensors." This fact sheet provides a guide to using information from soil moisture monitoring to aid in irrigation termination decisions in corn and soybean production.
Timing the final irrigation of the season can be a challenging decision for crop managers.
The last irrigation should provide the water necessary to optimize yield.
It should IMPROVE profitability.
At times, rainfall can provide the last remaining water to carry the crop to maturity.
Irrigation is unnecessary.
Extending irrigation beyond what the crop requires is inefficient.
It also is costly because late season pumping typically is the most expensive due to increasing depth to groundwater after a long pumping season.
Prolonged irrigation also can delay harvest and exacerbate pest problems, which may reduce yield and quality.
For corn, the crop-based recommendation is to monitor ear maturity by examining the starch line development on kernels from the middle of the ear.
For furrow irrigated fields, irrigation termination is recommended when starch line movement is greater than 50%, and there is adequate moisture.
The final irrigation for soybeans is recommended to occur at growth stage R6 such that there is adequate moisture at R6.5.
are helpful, but they lack precision in specifying water needs to finish the crop or how to gauge how much soil moisture is available in the root zone.
This fact sheet provides a procedure to determine the amount of water available and needed to reach crop maturity.
Information in this fact sheet provides a crisp answer to when to stop irrigating.
Background: Monitoring Soil Moisture and Determining Allowable Depletion
 For irrigation termination decisions, one should determine crop stage and then gauge whether the soil has adequate plant available water or if additional water is needed via irrigation.
The calculation  is simply..
= Water needed to finish the crop
 Water available in the root zone effective rainfall
 If the plant water need value is positive, then irrigation or rain is needed.
If it is negative, no further irrigation will provide any benefit.
Irrigation is not completely effective due to application efficiencies.
Thus the amount of water that must be applied through irrigation must be adjusted for these efficiencies.
The amount of water  that should be applied through irrigation is determined by dividing the plant water need by the irrigation efficiency.
It is not necessary to perform this calculation during the season, only for the last irrigation.
Irrigation Application Depth 
 = Plant Water Need  Irrigation Efficiency
 When making soil moisture determinations, the full rooting profile should be used.
In most soil types in Arkansas, this will be 30 to 36 inches.
While visual inspection of roots can be done using soil probes or shovels, generally it is most practical to utilize changes in soil moisture sensor readings to assess the effective rooting depth.
For the last irrigation of the season for both center pivots and furrow systems, it is recommended to use either a 45% or 50% allowable depletion.
This will allow the crop to use all remaining soil water, and it will save on pumping costs.
Using an allowable depletion of up to 60% is considered acceptable for the last irrigation, SO using 50% has a factor of safety included.
Table 1.
Plant Available Water  for a Given Soil Matric Potential or Tension  at 50% Managed Allowable Depletion
 Soil Tension	Sand	Sandy Loam	with Pan	Silt Loam	Clay
 0	1.77	1.51	1.01	1.83	1.38
 5	1.72	1.51	1.01	1.83	1.36
 10	0.74	1.00	1.01	1.65	1.09
 15	0.35	0.74	1.01	1.53	0.91
 20	0.14	0.58	1.01	1.41	0.78
 25	0.02	0.46	0.88	1.29	0.68
 30	0.37	0.79	1.19	0.60
 35	0.29	0.76	1.14	0.53
 40	0.23	0.72	1.00	0.47
 45	0.18	0.64	0.89	0.42
 50	0.14	0.57	0.80	0.37
 55	0.10	0.49	0.71	0.33
 60	0.06	0.45	0.63	0.30
 70	0.01	0.35	0.50	0.23
 80	0.25	0.39	0.18
 90	0.21	0.29	0.13
 100	0.13	0.22	0.09
 120	0.03	0.09	0.02
 Source: Lab and model data of irrigated soils sampled and grouped from Arkansas farms.
Plant available water is dependent on soil texture.
The soil in the rooting zone has an upper and lower limit of storing water available to crop plants.
Water Holding Capacity  determinations have been done for groups of Arkansas soils.
Table 1 shows WHC for average Watermark readings for different generalized soil textures at a 50% allowable depletion or Managed Allowable Depletion.
Charts for 35% and 45% allowable depletions and in-season decision making is provided in the second fact sheet in this series.
These charts provide the plant available water in inches per foot for an average soil tension value.
Thus, for a one foot average reading of 45 centibars in a clay soil, there are 0.42 inches of plant available water.
For an effective rooting depth of 30 inches or 2.5 feet, there are 1.05 inches of plant available water.
Four Steps to Irrigation Termination Using Sensors
 Step 1.
Determine crop stage and water needed to finish the crop.
The amount of soil water typically required for plants to reach maturity varies with production region and system.
Crop water demand for corn is provided in Table 2 based on Nebraska research, and for soybean  based on research in Marianna, Arkansas.
For corn at R5 growth stage with kernel development at 3/4 milk line, the crop is approximately 7 days from maturity (black
 Table 2.
Crop Water Demand for Corn
 Crop Growth	Stage	Kernel Development	Days to maturity	to mature 	Water needed
 R4	Dough	34	7.5
 R4.7	Beginning dent	24	5
 R5	1/4 milk line	19	3.7
 R5	1/2 milk line to full dent	13	2.2
 R5	3/4 milk line	7	1.0
 R6	Maturity	0	0
 Table 3.
Crop Water Demand for Soybeans
 Crop Growth	Pod and plant	Days to maturity	Water needed
 Stage	development	to mature 2,3
 R4	End of pod elongation	50-60
 R5	enlargement	40-50	10.0
 End of seed enlargement to
 R6 R6.5	leaves beginning to yellow	30-40	4.71
 R6.5 R7	Leaves begin to yellow	20-30	2.9
 R7	Beginning maturity	10-15	0.75
 R8	Maturity	0	0.27
 layer).
That crop requires 1 inch of water in the soil profile to reach black layer.
To determine amount of water needed for the final irrigation, an irrigator should determine soil water availability.
If there is more than 1 inch available in the profile, then additional irrigation or rainfall is not needed.
For soybeans that have reached the R6.5 growth stage, there are 20 to 30 days left to reach maturity , and at that point approximately 2.9 inches of water are needed for optimal development.
Step 2.
Determine the amount of water available in the effective root zone.
It is recommended that irrigation managers deploy sensors at 6-", 12-", 18-" and 30-inch" depths to provide soil moisture information from different portions of the plant rooting zone.
These depths correspond to the top, middle and lower portions of the theoretical rooting profile.
The effective rooting zone can be determined from direct field sampling using a soil probe and inspecting roots.
However, estimating the effective rooting depth from the sensor responses from the season is more practical.
The upper 6and 12-inch sensors represent the most active area of the rooting profile.
Determining Plant Available Water : Use Table 1 and the following equation to convert readings from Watermark sensors to soil water holding capacity.
The calculations are simplified by using the UAEX Arkansas Soil Sensor Calculator mobile app.
Plant Available Water 
 = WHC X MAD  X Effective Rooting Depth 
 Example: Assume the average readings from four Watermark sensors is 40 cb.
For a silt loam soil with a hard pan at 50% MAD, the plant available water would be 0.72 inches/ft, as read from Table 1.
If the effective root zone is 3 feet, then the calculation would be:
 PAW = 0.72 in/ft ft = 2.4 inches of plant available water.
If this were a corn field, checking back to the information listed in Table 2, the PAW calculation would indicate that no further irrigations will be required because only 2.2 inches of water are needed to mature the crop.
If this were a soybean field at R6 , then the 2.4 inches PAW calculated value indicates that an addition irrigation would be required.
Step 3.
Account for any potential rainfall that may occur before the crop matures.
If rainfall occurs, this amount  can be added to the water balance.
For example, if 0.5 inches of water are needed to finish the crop, and that much or more falls on the field without runoff, then no additional irrigation need be applied.
Step 4.
Determine the irrigation need.
If rainfall does not provide enough to finish the crop, then a last
 Table 4.
Typical Irrigation Efficiencies for Arkansas Systems
 Furrow Irrigation	60-80%	70%
 Center Pivot	65-85%	80%
 irrigation is necessary.
The irrigation need is the difference between what is available in the soil and what is needed.
Irrigation is not 100% efficient.
Losses may be due to tail water runoff and deep percolation, or there may be uneven infiltration along the row.
All of the water applied to a crop does not reach all of the plants equally.
Furrow irrigation systems generally are only about 60-70% efficient, and center pivot systems are between 65-85% efficient depending upon condition and sprinkler package.
If the crop needs 1.0 inch of water to finish, and the irrigation system is only 70% efficient, then 1.4 inches of water  are needed to provide that inch of water.
Also, if only 1.0 inch of water is needed to finish out a furrow irrigated crop, then reduce the irrigation time or depth accordingly  rather than apply a full irrigation.
This should be adequate to provide an inch of water to the lower reach of the field.
For sprinklers, the irrigator should adjust the percent run time based on the pivot's operation chart to match the application depth needed.
Run time calculations should also account for irrigation efficiency.
Irrigation application efficiency is defined as Ea =  100.
A simplified net irrigation equation is below.
Applied Irrigation Depth = 
 Thus, to apply an inch of irrigation, using an irrigation system that is 70% efficient, it is necessary to apply 1.4 inches.
Table 5.
Applied Irrigation Depth  Needed for Plant Water Needs for Different Irrigation Efficiencies
 0.5	0.7	0.6	0.6
 1.0	1.4	1.3	1.1
 1.5	2.1	1.9	1.7
 2.0	2.9	2.5	2.2
 2.5	3.6	3.1	2.8
 3.0	4.3	3.8	3.3
 Readers are encouraged to use the mobile app designed for phones and tablets, "Arkansas Soil Sensor Calculator"  to determine the water available in the profile.
If the amount available is more than is needed, no additional irrigation is necessary.
The difference is the net irrigation required.
Crop Stage: Corn at R5 with the starch line at 50% and rooting depth of 3 ft.
Watermark sensor readings: 40, 63, 60, and 85 cb for 6-, 12-, 18and 30-inch depths.
Irrigation and soil: Furrow irrigated field with clay soil.
Rainfall: 0.15 inches rainfall occurred within 12 hours of making the readings.
Managed Allowable Depletion : 50%
 Step 1.
Determine crop stage and water needed to finish the crop.
Amount of water needed to finish the corn is determined from Table 2 = 2.2 inches.
Step 2.
Determine the amount of water available in the effective root zone.
The average of watermark
 Figure 1.
Apple version of Arkansas Watermark Tool, Soil Sensor Calculator result for the example.
The app does all of the calculations except adjusting for rainfall.
The app can be downloaded at the Apple App Store.
readings is 62cb [= 4 = 62 cb].
It is assumed the rooting depth is 3 feet because all the sensor readings moved during the season, and the irrigation manager used a shovel to visually inspect roots.
From Table 1, for a clay soil at 60 cb the plant available water per foot is 0.30 inches per foot.
PAW = 0.30 X 3 ft.
= 0.90 inches.
This is the plant available water in the effective rooting zone.
Step 3.
Account for any potential rainfall that may occur before the crop matures.
There were 0.15 inches of rainfall that occurred after the readings were taken, SO the total plant available water is 0.90 inches + 0.15 inches = 1.05 inches of plant available water.
Step 4.
Determine the irrigation need.
The irrigation need is 2.2 inches.
PAW is 1.05 inches.
The difference between PAW and the amount of water needed is  = 1.15 inches.
So, for this example, another irrigation is necessary to meet crop water demand.
This furrow irrigation system is at least 70% efficient, SO the depth to apply is 1.65 inches of water to get 1.15 inches.
If a normal irrigation is 2 inches, irrigation can be reduced after the advance has occurred about 20% earlier than a normal irrigation to finish the corn crop.
Figure 2.
Android version of Arkansas Soil Moisture Sensor Calculator result for the example.
The app does all of the calculations except adjusting for rainfall.
The app can be downloaded at the Google Play Store.
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Department of Agriculture, Director, Cooperative Extension Service, University of Arkansas.
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A REVIEW OF MECHANICAL MOVE SPRINKLER IRRIGATION CONTROL AND AUTOMATION TECHNOLOGIES
 ABSTRACT.
Electronic sensors, equipment controls, and communication protocols have been developed to meet the growing interest in using center pivot and lateral move irrigation systems to deliver different irrigation depths to management zones based on previous production levels, soil texture, or topography.
Onboard and field-distributed sensors can collect data necessary for real-time irrigation management decisions and transmit the information directly or through wireless networks to the main control panel or base computer.
Equipment controls necessary to alter water application depth to meet the management criteria for relatively small management zones are now commercially available from irrigation system manufacturers and after-market suppliers.
Communication systems such as cell phones, satellite radios, and internet-based systems are also available and allow the operator to query the main control panel or base computer from any location at any time.
Selection of the communications system for remote access depends on local and regional topography and cost relative to other methods.
Recent developments in the center pivot sprinkler industry have led to contractual relationships between after-market suppliers and irrigation system manufacturers that should support further development of technologies necessary to improve the management of water, nutrient and pesticide applications.
Although the primary focus of this article is center pivot sprinkler irrigation, much of the discussion could also apply to lateral move sprinkler irrigation systems.
Keywords.
Center pivot sprinkler, Distributed sensor networks, Site-specific irrigation, Variable rate irrigation, Wireless communication.
A gricultural fields are variable in terms of crop production for many reasons, including topographic relief, changes in soil texture, tillage and compaction, fertility differences, and localized pest distributions.
The effects of different sources of variability on management can be additive and interrelated.
Fortunately, recent advances in communications and microprocessors have enabled the general implementation of site-specific water applications by self-propelled center pivot and lateral move sprinkler irrigation systems.
The design of an irrigation system suitable for varying water application spatially based on a series of data inputs
 Submitted for review in August 2011 as manuscript number SW 9313; approved for publication by the Soil & Water Division of ASABE in March 2012.
Presented at the 5th Decennial Irrigation Symposium as Paper No.
9632-IRR10.
can be complex because of the need to address and integrate constraints imposed by the field site, irrigation system capabilities, and producer management.
The field site constraints may be the most difficult to address because they may be numerous and may be exhibited in varying extents from year-to-year.
Often, the underlying cause of crop performance variation is not fully understood.
Extreme fieldto-field variability further compounds selection of appropriate irrigation system capabilities required to achieve the desired objective.
The general management philosophy and operational preferences of the owner/operator must also be addressed through the use of decision support systems.
These issues are discussed in detail by Buchleiter et al.
, Evans et al.
, Sadler et al.
, Perry et al.
, Sadler et al.
, and McCarthy et al..
McCarthy et al.
developed a predictiveadaptive control model  for site-specific irrigation water application of cotton using a center pivot sprinkler, concluding that although the framework accommodated a range of system control strategies, further work was necessary for using data with a range of spatial and temporal scales.
Decision support systems should provide a holistic and robust approach to irrigated crop management.
After the irrigator defines the decision criteria and management
 guidelines to be used within the field, DSS must implement the approach through software and microprocessor-based control systems.
Results of geo-referenced grid sampling of soils, yield maps, and other precision agriculture tools can be major components in defining rules for these management systems.
These "rules" are used as the basis for analysis and interpreting data from real-time data networks, remote sensing, irrigation monitoring systems, agronomic, and other information used to provide direction and implement basic commands.
Decision support systems can also include instructions for chemigation  and provide alerts  to the grower based on output from established models using real-time environmental data.
In essence, DSS provide more management flexibility by implementing near term, routine commands to direct irrigation schedules and other basic operations, which frees the irrigator to concentrate on other management activities.
Successful DSS will require the integration of various sensor systems , irrigation system hardware and controllers to manage sprinkler application and hydraulics, accurate determination of field position , and ample computer processing speed and power.
The maximum benefits will be derived when DSS respond to actual crop conditions.
Crop conditions can be estimated from field-based or remotelysensed plant measurements , or inferred from soil water measurements or crop evapotranspiration estimates.
Ideally, the most robust monitoring system will be an integration of multiple approaches.
General, broad-based, and easily modified software for managing these DSS for a multitude of crops, climatic conditions, topography, and soil textures are not currently available from manufacturers, government agencies, or consultants.
Development and updating of management maps for these irrigation systems based on soils, soil water sensors, yield, or water availability is a highly specialized process that is currently done only once a year or less.
However, widespread implementation will require userfriendly data input capabilities that allow management maps to be adjusted much more frequently.
The objectives of this article are to provide a general discussion of the progression of sprinkler control and monitoring technologies to include: wireless sensor networks and communication protocols; available sensors and data management schemes; remote access for irrigation systems; their network and communication requirements; available sensors and data management schemes; and the current status of commercially available monitoring and control systems.
Mechanically-moved sprinkler irrigation systems, such as center pivot sprinklers and lateral move sprinklers, in current usage have a wide range of drive technologies.
These irrigation systems often operate on fields having both variable topography and soil textures.
In-field soil variability issues such
 as low water holding capacity or low infiltration rates present significant challenges to managers in decisions about how much water to apply to various areas of the field.
Each of these factors represents a reason for using some sort of monitor/controller to manage water applications based upon need.
Precision application, variable rate irrigation, and site-specific irrigation are terms developed to describe water application devices with the goal of maximizing the economic and/or environmental value of the water applied via a moving irrigation system.
Probably, the earliest center pivot sprinkler control was the methodology to alter the water application depth by mechanical adjustment of the speed of lateral travel.
Additional early developments provided a very limited set of controls to turn end guns on and off and to stop the center pivot sprinkler operation based on field position or completion of the irrigation cycle.
The development of programmable control panels allowed the speed of sprinkler travel to be adjusted multiple times during an irrigation event.
This approach was often used by producers when portions of the field were planted to a different crop, but these control panels generally lacked the flexibility necessary to supply water at rates required to meet the management objectives of relatively small field areas with irregular-shaped boundaries.
In the past few years, some companies have begun marketing control panels with an option to change irrigation system pivot travel speed in very small increments ranging from <1 to 10 as the lateral rotates around the field.
This tactic effectively changes application depths in each defined radial sector of the field, and generally no additional hardware is needed.
This technique is commonly referred to as speed or sector control, but could also be referred to as variable depth irrigation.
Nevertheless, field variability seldom occurs in long, narrow pie-slice shaped parcels  and because the sprinkler packages apply the same depth along the entire lateral length, adjusting speed of rotation may not provide a sufficient level of water application control.
A number of methods have been under development to address varying application depths along the moving lateral.
A variable flow sprinkler was developed for controlling irrigation water application by King and Kincaid  at Kimberly, Idaho.
The variable flow sprinkler uses a mechanically-activated pin to alter the nozzle orifice area which adjusts the sprinkler flow rate over the range of 35% to 100% of its design flow rate based on operating pressure.
The pin was controlled using either electric or hydraulic actuators.
The main concern with this approach is that the wetted pattern and water droplet size distribution of the sprinkler changed with flow rate which created water application uniformity issues due to a change in sprinkler pattern overlap.
Changes in water application depth can also be accomplished by using a series of on-off time cycles or "pulsing" individual or groups of sprinklers.
Management of the on-off of sprinklers can be used to manage the time-averaged water application rate.
Later efforts in Washington State involved equipping a center
 Figure 1.
Schematic diagram showing a soil survey map overlain by center pivot speed of travel settings changed every 12 or in 30 locations during a single revolution.
pivot sprinkler with a custom-built electronic controller to activate water operated solenoid valves in groups or banks of 2 to 4 sprinkler nozzles.
The use of normally-open solenoids protected the irrigation system from damage and ensured irrigation water was applied even if the control system failed.
Precise and accurate control of irrigation using a series of in-field and onboard wireless monitoring spread spectrum radios/sensors networks that pulsed individual sprinkler solenoid valves according to prescription maps was reported by Chvez et al..
In this research with two different lateral move systems, deviations related to positioning of sprinklers when irrigating were on average 2.5 H 1.5 m due mainly to the accuracy of the digital global positioning systems.
This level of accuracy is a vast improvement over systems not equipped with a GPS of any kind.
Controlling irrigation water application depth has also been accomplished through the use of multiple manifolds, each with different sized sprinkler nozzles to vary water and nitrogen application.
These systems often included two to three manifolds where simultaneous activation of one or more solenoid valves controlling individual manifolds adjusted the water application rate and depth.
When individual or groups of sprinkler nozzles are managed by on-off cycles or use the multiple manifolds, an irrigation system is termed to use zone control for sprinkler applications.
Zone control involves spatially defining irregularly-shaped management zones following specific guidelines , and differentially applying water to each management zone.
Most zone control systems vary water application depths by various forms of pulse modulation  for a given irrigation system speed, but zone control systems could potentially be combined with aspects of speed control to
 better balance water flow rates provided to the irrigation system.
Although the previously discussed speed control techniques are the most common site-specific sprinkler irrigation systems in use today, zone control systems probably have the largest potential for achieving the most efficient and economically viable management of water and energy.
Current uses of site specific, variable rate irrigation  on agricultural fields are generally on a fairly coarse scale.
Probably the most common use is limited to site-specific treatment of complex shaped, non-cropped areas such as waterways, ponds, roads, drainage ways, or rocky outcrops where some sprinkler nozzles are turned off.
However, SS-VRI also has application for animal production systems that wish to use the center pivot to apply liquid animal waste to field areas where there are legally required setbacks from wells, surface water impoundments, or other areas.
Similarly, setbacks may be required to meet water quality protection goals such as minimizing nitrate leaching or contamination of wildlife areas.
In these situations, normal cost recovery based on crop yield may be of secondary importance due to the potential for savings in product application cost.
Two main approaches to SS-VRI sprinkler controls  can have advantages and disadvantages depending on the desire to match infield management zones.
For example, the map presented in figure 2a is based strictly upon the soil mapping units presented in figure 1.
If the water management zones were defined strictly based on soil mapping units, grouping three to five sprinklers  together in blocks along the lateral might fit the contour at Position A quite precisely.
At Position B, since the grouping of sprinklers is fixed by the original installation, the same three to five sprinklers may need to irrigate more than one management zone.
Thus, the attempt to match water application depths to contour-shaped management zones using blocks of sprinklers may limit the number of effective management zones within a field.
The second approach is to control each individual sprinkler along the lateral independently.
Figure 2b presents the same map as in figure 2a.
The difference is that as the lateral travels around the pivot point individual sprinklers can be controlled in groups based on field position not on system plumbing.
At Position A, the same sprinklers included in blocks shown in figure 2a may be controlled as a block of individual sprinklers in figure 2b.
At Position B, a completely different sets of sprinklers can be combined together to match the zone contour at that location as precisely as was obtained at Position A.
The use of block or individual sprinkler types of control leads to areas of transition parallel and perpendicular to the travel direction of the irrigation machine.
The area impacted by the transition from one management zone to another is directly related to the wetted radius of the sprinklers installed on the system and the distance from the pivot point.
Although, several adjacent sprinklers may contribute to the application pattern and this may result is some application irregularities at various points of overlap, transition zones are more likely to conform to gradual changes in
 Figure 2.
Schematic drawings of a soil survey map showing the implementation of the sprinkler block  and individual sprinkler  control approach to SS-VRI.
field conditions such as soil texture, topography, or soil physical properties.
Consequently, implementation of management zones and the evaluation of the impact of changes in application must be undertaken with the knowledge that the change is not instantaneous in space but rather a gradual transition from one zone to another.
The potential impacts of implementing these two approaches has yet to be documented in the field and likely will depend on the level of variation exhibited within management zones.
However, if the desire is to precisely match variable-sized and shaped management zones, the approach with the maximum amount of flexibility in sprinkler control would be best able to capitalize on the field-based information used in developing the management zone map.
With sprinkler spacing ranging from 2 to 6 m, the magnitude of the difference in terms of crop area depends on the distance from the pivot point.
Further, it is anticipated that individual sprinkler controls will require additional components that will potentially increase maintenance requirements in the long run.
One of the largest factors limiting the use of SS-VRI is cost, often ranging from $2000 for a system monitor to over $20,000 for control of individual sprinklers along the entire system length.
In some cases, producers are treating symptoms of low crop production such as leaf yellowing, leaf curling, and stunted plants by substituting SS-VRI technology when improved management of other inputs might be more beneficial in improving crop production and water use efficiency at a lower overall cost.
DISTRIBUTED NETWORKS AND COMMUNICATION PROTOCOLS
 Site-specific variable-rate irrigation management allows producers to maximize their productivity while conserving water.
However, the seamless integration of sensors, data interface, software design, and communications for SS-VRI control using wireless sensorbased irrigation systems can be challenging (King et al.,
 2000).
Researchers have addressed the issues of interfacing sensors and irrigation control using several approaches.
Shock et al.
used radio transmission for soil water data from in-field data loggers to a central data management site where decisions were made and manually changed by the operator.
Miranda et al.
used a closed-loop control system and determined irrigation amount based on distributed soil water measurements.
Wall and King  explored various designs for smart soil water sensors and sprinkler valve controllers for implementing "plug-and-play" technology, and proposed architectures for distributed sensor networks for SS-VRI irrigation automation.
They concluded that the coordination of control and instrumentation data is most effectively managed using data networks and low-cost microcontrollers.
Adopting a standard interface for sensors and actuators allows reuse of common hardware and communication protocols such as communication interface and control algorithm software.
Instrumentation and control standards for RS232 serial  and RS485  communication protocols have been widely applied and well documented for integrating sensors and actuators, particularly in industrial applications.
However, these systems require direct wire connections to transmit data between the control panel or microprocessor and the sensors or actuators.
The need for direct connection between the control and data acquisition systems poses a problem when applied to pivot irrigation systems due to the potential for damage and the cost of installation.
Wireless network systems are an alternative to hardwired systems for data transport and have been used for infield sensor network systems.
Two wireless protocols that eliminate the need for direct wire connections are Bluetooth   and ZigBee .
Bluetooth and ZigBee  are designed for radiofrequency  telemetry applications that support a relatively low data rate, and provide solutions for long battery life and good network security.
ZigBee is a low-cost,
 nonproprietary wireless mesh networking standard, which allows longer life with smaller batteries, and the directsequence spread spectrum mesh networking provides high reliability.
Bluetooth is a faster but more expensive standard than ZigBee and uses spread spectrum modulation technology called frequency hopping to avoid interference and ensure data integrity.
ZigBee has lower power needs than Bluetooth, but it also transmits effectively over less distance.
Enhanced Bluetooth transmitters are available that can transmit up to 1 km.
Bluetooth wireless technology has been adapted in sensing and control of agricultural systems.
Zhang  evaluated Bluetooth radio in different agricultural environments, power consumption levels, and data transmission rates.
He observed 1.4 m as an optimal radio height for maximum 44-m radio range and reported limitations of significant signal loss after 8 h of continuous battery operation and 2 to 3 S of transmission latency with the increase of communication range.
Oksanen et al.
used a PDA with Bluetooth to connect a GPS receiver for their open, generic, and configurable automation platform for agricultural machinery.
Lee et al.
explored an application of Bluetooth wireless data transportation of moisture content of harvested silage and reported a limitation of 10-m short range.
However, the limitations of Bluetooth applications in agricultural systems can be solved or minimized by system design optimization.
The power shortage can be solved by using solar power that recharges the battery.
The radio range and transmission latency can also be extensively improved by using an upgraded power class and antenna.
These same techniques can be applied to Zigbee-based systems.
Drawbacks in using wireless sensors and wireless sensor networks include provision for ample bandwidth, existing inefficiencies in routing protocols, electromagnetic interference, interference by vegetation, radio range, sensor battery life , and synchronous data collection.
An immediate limiting factor in selfpowered wireless sensor network  operation is battery life, which can be addressed to some degree by decreasing the duty cycle of the sensor nodes, which is typically a significant method for improving battery longevity.
Power needs are often mitigated by using solar panels.
Other identified challenges specific to WSNs and agriculture include interference with radio propagation due to crop canopy height.
Signal obstruction issues relating to crop height and in-field equipment are inherently reduced when the moving sprinkler is used as the sensor platform; but infield sensors require manual adjustment above crop canopy.
In row crop production systems, the need to install and retrieve the sensors, data loggers, and radio transmission equipment from each measurement site on an annual basis requires trained labor to ensure the equipment is handled, installed and removed properly.
Few producers possess the knowledge base necessary and rarely hire personnel who could perform these tasks reliably.
Consequently, future developments in wireless technology will need to include the semi-permanent and below-ground installation of
 sensors and transmission equipment.
The addition of this requirement will require the development of WSNs with extended communication range  and battery life sufficient to limit the replacement frequency to the level required to gain acceptance by center pivot managers.
SENSORS AND INTEGRATED DATA MANAGEMENT SCHEMES
 One of the earliest and basic uses of sensors on a center pivot for management purposes was to determine alignment and lateral position.
Until recently, control systems based on the digital angle resolver typically had an accuracy of +0.5 to 1.5 of the first tower position.
Peters and Evett  found that resolver-determined position errors could be as great as 5 or over 30 m on a 390-m system.
Consequently, many center pivot sprinkler manufacturers now employ a Wide-Area Augmentation System  enabled GPS antenna option to identify the position of the end tower to an accuracy of less than 3 m.
With the WAAS enabled GPS antenna, accuracy of the outside tower position of less than 1 m can often be obtained because the long duration start-stop cycles of the system allow further buffering of GPS errors.
The net effect of being able to accurately determine the lateral location is that management zone size can be reduced without increasing the potential for a misapplication of water, nutrients, or pesticides.
Recent innovations in communication technologies combined with advances in internet technologies offer tremendous opportunities for development and application of real-time management systems for agriculture.
It is anticipated that DSS will increasingly rely on WSNs for real-time, automated recording of micro-meteorological instrumentation, or other sensors that are strategically distributed to provide continuous feedback of field conditions to center pivot control panels and field managers.
Sensors mounted on the irrigation lateral also can be used to provide real-time feedback for decision support as the system moves across a field.
Field-based data may also be integrated with various remotely sensed data to help differentiate between biotic and abiotic stresses.
Integrated data sources and networks provide needed information to recalibrate and check various simulation model parameters for on-the-go irrigation scheduling and adjustments.
Integration of these technologies into DSS can help determine when, where, and how much water to apply in real time, enabling implementation of advanced water conservation measures that can simultaneously address economic viability, crop production with limited water supplies, energy conservation, and enhanced environmental benefits.
Satellite and aerial imagery, GIS mapping services, and GPS are becoming commonplace throughout the agricultural industry around the world.
Remotely sensed information can be photometric , thermal, or multispectral and can be acquired by aircraft and satellites in a variety of formats and resolutions.
Multispectral data can be used to enhance water and energy conservation by helping to determine the causes of the non-uniform crop appearance and yield.
Advanced pattern-recognition software and other tools for multispectral or other remotely sensed data can be used to detect many problems in agriculture.
However, two barriers to the widespread adoption and use of these integrated technologies are the present cost of these services and the difficulty for producers to understand and use the output in a timely manner.
The timeliness of this type of information is critical to producers because it is much better for their farm profitability if they can make adjustments as the problems develop, not after the fact.
New analysis tools and interpretation aids as part of comprehensive DSS are needed for producers to take full advantage of these technologies.
Spectral and thermal ground-based remote sensors mounted on mechanical-move irrigation systems are capable of providing information to farmers in a timelier manner than aircraft or satellite sources.
Infrared thermocouple thermometers mounted on a moving lateral can provide radiometric temperature measurements of in-field crop canopies.
Software to control mechanical-move sprinkler systems has been integrated with this plant-feedback information and the Time-Temperature-Threshold  algorithm, patented as the Biologically Identified Optimal Temperature Interactive Console  for managing irrigation by the USDA under Patent No.
5539637.
Briefly, the TTT technique can be described as comparing the accumulated time that the crop canopy temperature is greater than a cropspecific temperature threshold with a specified critical time developed for a well-watered crop in the same region.
The TTT technique has been used in automatic irrigation scheduling and control of plant water use efficiency for corn in drip irrigated plots, and soybean and cotton in LEPA irrigated plots.
Peters and Evett  demonstrated that remote canopy temperatures could be predicted from a contemporaneous reference temperature and a pre-dawn temperature measurement.
Infrared canopy temperature measurements made from a mechanical-move sprinkler system can then be used to develop spatial and temporal temperature maps that correspond to in-field water stress levels of crops.
Many electromagnetic soil water sensors based on soil bulk dielectric permittivity are available  and can be incorporated into DSS for center pivot sprinkler irrigation systems.
Many resistance-based sensors  are also available and could also be used with DSS.
Recent discussions of these types of sensors, their
 accuracy and suitability for specific conditions have been provided by Evett et al.
and Chvez et al..
Integration of information collected at varying frequencies and spatial scales into DSS will be necessary to utilize all sources of information available for making improved irrigation management decisions.
The VARIwise model developed by McCarthy et al.
is a recent example of how data collected from a variety of sources can be incorporated into a DSS to manage center pivot water applications.
The Smart Crop system developed by Mahan et al.
is a recent commercial example of an in-field wireless system for canopy temperature monitoring.
Further development of this kind of management tool will be critical to the commercialization of DSS in the future.
REMOTE COMMUNICATIONS WITH IRRIGATION SYSTEMS
 Recent developments in the center pivot sprinkler industry have resulted in contractual arrangements with developers of after-market control and monitoring systems.
Categorical services provided include monitoring, control, communication systems for remote access, and data collection and reports to help summarize irrigation system performance, water and chemical applications, and ancillary data.
Of the five major manufacturers of center pivot and lateral move systems, all provide remote monitoring and control of position, speed of travel, water "on or off status, programmable stop and restart by position, and auxiliary components.
The number of type of auxiliary control items differs by manufacturer.
The benefits of remote monitoring for farmers are that they save time and fuel from driving out to fields where the irrigation systems are operating as expected.
All of the manufacturers provide guidance systems and some level of SS-VRI management.
Manufacturers also have the technical expertise on staff to provide the necessary equipment for remote system access.
Communication via cell phone allows a farmer to monitor multiple center pivots from any location, while RF communication and web-based posting provide the advantage of data overview and may help in making long-term decisions.
Successful implementation of advanced automation for mechanically-moved systems will depend on the integration of real-time automated data collection and hardware control capabilities.
Prices for the equipment vary among manufacturers and according to the amount of upgrades needed to satisfy the unique needs of each farmer and the amount of variability in each field.
Frequently, this equipment and services can be retrofitted onto existing pivot systems, in addition to being purchased for new installations.
Electronic sensors, equipment controls, and communication protocols have been developed to meet the growing
 Table 1.
Monitor, control, communication and data reporting capability of center pivot sprinkler control panels.
Center Pivot Sprinkler Manufacturer
 Pierce Reinke T-L Valmont Zimmatic
 Position in field and travel	Y	Y	Y	Y	Y
 Speed of travel	Y	Y	Y	Y	Y
 Wet or dry operation	Y	Y	Y	Y	Y
 Pipeline pressure	Y	Y	Y	Y	Y
 Pump status	Y	Y	Y	Y	Y
 Auxiliary components 	Y	Y	Y	Y	Y
 Stop-in-slot and auto restart	Y	Y	Y	Y	Y
 Wind speed	Y	Y	N	Y	Y
 Start and stop	Y	Y	Y	Y	Y
 Speed of travel	Y	Y	Y	Y	Y
 Auto restart and auto reverse	Y	Y	Y	Y	Y
 End gun operation	Y	Y	Y	Y	Y
 High and low pressure	Y	Y	Y	Y	Y
 High and low voltage	N/Y	N/Y	N/Y	Y/Y	Y/Y
 System stall shutdown	Y	Y	Y	Y	Y
 Auxiliary components 	Y	Y	Y	Y	Y
 System guidance	Y	Y	Y	Y	Y
 Maximum control points per	180	3600	180	180	180
 Sprinkler application	zones	8	2	3	30	No Limit
 Cell phone	Y	Y	Y	Y	Y
 Radio	Y	Y	Y	Y	Y
 Computer base station	Y	Y	Y	Y	Y
 Subscription required	Y	Y	Y	Y	Y
 Data Collection and Reports
 Soil water content	Y	Y	Y	Y	N
 Precipitation per season	Y	Y	Y	Y	Y
 Application date and depth	Y	Y	Y	Y	Y
 Irrigation events per season	Y	Y	Y	Y	Y
 Chemical application rate	N	N	N	N	Y
 Chemical application per	N	N	N	N	Y
 System position by date	Y	Y	Y	Y	Y
 [a] Y indicates that up to seven auxiliary components  can be controlled by the panel.
[b] N/Y indicates no automatic shutdown for high voltage is provided but the panel does provide automatic shutdown for low voltage.
[c] System guidance provided by above ground cable, below ground cable, furrow, or GPS.
[d] Number of positions in a single revolution where speed of travel and other set points may be changed.
[e] Number of sprinkler application zones along the irrigation lateral length where water application depth can be changed.
interest in SS-VRI using center pivot and lateral move sprinkler irrigation systems.
Onboard and field-distributed sensors can collect data necessary for real-time irrigation management decisions and transmit the information to the main control panel or base computer.
However, the need for semi-permanent soil water monitoring sites suitable for row crop production systems has only recently been initiated and will be necessary to gain widespread acceptance.
Manufacturers of center pivot and lateral move systems have long recognized the advantages of remote communication for system monitoring and control.
The major manufacturers offer communication systems such as cell phones, satel-
 lite radios, and internet based systems that allow a manager to query the main control panel or base computer from any location at any time.
This technology is largely mature and available to assist managers with operational management decisions by remote monitoring.
Equipment necessary to alter water application depth to meet the management criteria for specific and relatively small management zones is now commercially available from irrigation system manufacturers and after-market suppliers that should support further development of site-specific application of water, nutrients and pesticides.
However, DSS for automatic control of center pivots are largely not commercially available to irrigation managers.
In addition, with the availability of SS-VRI systems for center pivots comes the need of criteria for locating data acquisition systems in the field.
Alteration of the water application depth based on defined management zones will change the soil water balance during the growing season.
Managers of SS-VRI systems will need criteria for deciding whether and when the water management zone map needs to be changed, and remote access and monitoring of irrigation systems will play a vital role in the commercialization of SS-VRI management.
Field Evaluation of Container Nursery Irrigation Systems: Part 1: Measuring Operating Pressures in the Irrigation System
 Dorota Z.
Haman and Thomas H.
Yeager2
 Performance of sprinkler and microirrigation systems can be evaluated by measuring operating pressures, application rates, and uniformity of water application under nursery conditions.
Knowledge of these factors is important to determine the causes of poor system performance.
This publication will focus on operating pressure and will discuss application rates and uniformity in other publications.
Measuring Operating Pressures in the Irrigation System
 It is important to monitor pressures at critical points in an irrigation system.
A well-designed and correctly-installed system will have permanent pressure gauges at the critical points such as pump outlet, both sides of the filtration system , and at the inlet to each irrigation zone.
The gauges should be checked periodically and replaced as needed.
These pressure gauges allow the system manager to monitor the performance of the system and pinpoint any problems as soon as they occur.
For example, a drop in pressure at the inlet to the irrigated zone may indicate a broken pipe, too many zones running at the same time, or excessive discharge from the nozzles.
The difference in pressure between two sides of the filter can indicate the need for filter cleaning.
A significant decrease in pressure through the dirty filter can result in insufficient operating pressures at the irrigation zone.
Periodically, operating
 pressures within each zone should be tested to evaluate system performance.
Irrigation nozzles are designed to operate over a specific range of pressures.
The general rule is that the operating pressure of any nozzle in an irrigation system should not deviate by more than 15% from the nozzle pressure specified by the manufacturer.
That also means that the difference between the highest and the lowest pressure in the irrigated zone should not exceed 30%.
If operating
 2.
Dorota Z.
Haman, professor emeritus, Department of Agricultural and Biological Engineering; and Thomas H.
Yeager, professor, Environmental Horticulture Department; UF/IFAS Extension, Gainesville, FL 32611.
pressures are out of this range, irrigation system uniformity decreases and application rates may not be consistent.
Visual observation of irrigation water distribution during irrigation may give an indication that nozzle pressure is undesirable.
If operating pressure is too high, very small droplets are produced and fogging can be observed.
High pressure also results in irregular nozzle rotation and increased amounts of water applied near the sprinklers.
Conversely, operating pressures that are too low produce a doughnut-shaped water distribution pattern with very little water applied close to the sprinklers.
The pressure can be measured at the sprinkler nozzle using a pitot tube attached to a pressure gauge.
The pitot tube is placed about 1/8-inch from the nozzle and adjusted until the highest constant pressure can be read.
This procedure is illustrated in Figure 2.
A pitot tube can be purchased from an irrigation supply company.
Microirrigation or Low-Volume Irrigation
 Operating pressures of microirrigation or low volume systems can be measured using a portable pressure gauge equipped with a flexible tube and a fitting, which allows replacement of an emitter with the pressure gauge.
The pressure distribution in a lateral line with more than 10 emitters will not be significantly affected by blocking one emitter while others continue to flow.
Portable gauges can be purchased that are equipped with a needle on a flexible tube; for lateral lines constructed of flexible material at least 0.04 inch thick, the needle can be inserted directly into the lateral line.
The opening caused by the needle should close when the needle is removed.
Pressure should be measured at both ends of a lateral line to determine pressure losses along the line.
For most emitters, it is recommended that the pressure variation
 not exceed 20%  of the design pressure.
This also means that deviation from recommended pressure should be no more that 10% throughout the irrigated zone.
The exact percentage depends on the type of the emitter used.
Some emitters are more sensitive to pressure changes than others.
For example, pressure compensating emitter outputs are less sensitive to pressure changes, and are characterized by a constant flow rate at large pressure ranges.
The pressure changes in these systems are less critical as long as they are within the range specified by manufacturer.
Water Rights in Utah
 Chad R.
Reid, Agricultural Agent Iron County Keith H.
Christensen, Engineering Technician Division of Water Rights, Cedar City Robert W.
Hill, Extension Specialist Irrigation
 If you are connected to a municipal system, your water is probably categorized as "culinary or municipal water" and is used for everything from drinking and bathing to washing the car to watering tomatoes.
However the Utah Division of Water Rights takes a more itemized approach to water use when applied outside of a municipal system.
Water rights in Utah, as in other Western states are founded on the doctrine of "prior appropriation" and are administered by the State Engineer.
All waters are public property in Utah.
The State Engineer's office also directs the adjudication or re-adjudication of water rights, along with licensing of well drillers, dam safety, stream alteration, and water rights enforcement.
The "right" to use water is obtained through an application and permit issue process through the State Engineers office, if the basin in which your property is located is open to appropriation.
In brief, the steps are :
 Apply to appropriate water with the State Engineer.
Application is advertised, protests and rebuttals are heard if any are filed.
State Engineer evaluates application, protests, and other pertinent information and renders a decision on the application based upon principles established in State statute.
If approved the applicant begins developing water.
When fully developed the applicant files proof with the state engineer stating the details of development.
The State Engineer after reviewing proof issues a Certificate of Appropriation.
Most of the state is closed to new appropriations of
 water.
In closed areas, new development must be accomplished by securing an existing right and filing for a change application to accommodate the proposed development.
The three most basic beneficial uses of water are domestic, stockwatering and irrigation each with a specific annual requirement or "Duty." Other beneficial uses include municipal and industrial.
Domestic use is any use of water inside the home, and requires 0.45 acre foot of water right.
Stockwatering is quantified as 0.028 AF  per ELU.
An ELU is one horse and foal or cow and calf, or equivalent number of sheep, goats, pigs, chickens etc.
The beneficial use period for these uses is generally year round, but can vary with specific needs.
Irrigation is the act of applying water to any plant to obtain optimal growth and maintenance of that plant.
Lawns, gardens, shrubs, pastures and non-native trees and plants are all considered as irrigation, even though not all are harvested as crops.
The duty for irrigation ranges from 6.0 AF per irrigated acre in parts of the Virgin River drainage to 3.0 AF per irrigated acre in high mountain areas.
The average diversion duty is 4.0 AF per acre.
This "duty" is based on the highest water consuming crop, which is alfalfa, during the growing season of the region and surface irrigation practices.
Canal or Irrigation Company Water Rights
 The right to use water from a surface source, which is delivered through a canal, ditch, or pipeline by an irrigation company, is held by the company.
Some irrigation companies also own water rights in ground water wells in order to augment surface water supplies in times of shortage.
The individual "shareholders" in an irrigation company do not own the water right in a legal sense.
This right is allocated to the shareholders proportional to the number of shares owned by the individual shareholder.
The value or quantity of water allocated to a "share" of water is not constant through out the state and varies considerably from one irrigation company to another.
In some canal companies a share of water is allocated per acre, whereas in others, three or four shares may be needed to provide sufficient irrigation water for one acre of alfalfa.
Water is often delivered on the "turn" in most of Utah's canal systems.
This means that each shareholder is on a schedule of when they can take the water in rotation along the ditch.
The duration of the "turn" is proportional to the number of shares owned.
Thus, time of use is measured, not quantity of water.
It is essential to determine the appropriate number of shares needed to irrigate your property and to understand when the water is available.
The water rights process is a very complex part of any land development scenario and should be given early consideration when the planning process is started since the approval/rejection period for most change applications takes three to six months a substantial wait if you're out of water.
Before a parcel of property is purchased, several issues should be considered.
1.
Are the water rights currently perfected  on the property?
If so, do you want to leave them as is, or will a change application be required to make them fit your desired uses?
2.
If there is no water right appurtenant to the property, are there water rights being conveyed along with the property?
Is the amount being conveyed enough to fit your desired uses?
Is the water right being purchased in good standing?
Has the right been exercised, or beneficially used, during the last five years?
3.
In some cases a change in use will result in a reduction in the diversion allowance of the water right.
It is highly recommend that prior to purchasing a new property or water right you contact the Water Rights office in your area to discuss these and other issues to make sure you understand all the ramifications of your purchase.
Utah Division of Water Rights
 Utah has been subdivided into regions for water rights administration.
Also shown on the map are the watershed boundaries.
Regional offices are located in Cedar City , Logan , Price , Richfield , Salt Lake City (Weber River/Western.
Figure 1.
Utah water rights administration regions and watershed boundaries.
and Utah Lake/Jordan River), and Vernal  in addition to the Salt Lake City main office Specific contact information for the Division's regional offices follows:
 Northern Regional Office  Will Atkin, Regional Engineer 1780 North Research Parkway, Suite 104 North Logan, UT 84341 Phone:  752-8755 Fax:  752-0062 E-mail: willatkin@utah.gov
 Weber River/Western Regional Office  Ross Hansen, Regional Engineer 1594 West North Temple, Suite 220 P.O.
Box 146300 SLC, Utah 84114-6300 Phone:  538-7240 Fax:  538-7467 Email: rosshansen@utah.gov
 Utah Lake/Jordan River Regional Office  John Mann, Regional Engineer 1594 West North Temple, Suite 220 P.O.
Box 146300 SLC, Utah 84114-6300 Phone:  538-7240 Fax:  538-7467 Email: johnmann@utah.gov
 Eastern Regional Office  Bob Leake, Regional Engineer State and County Building 152 East 100 North Vernal, Utah 84078-2126 Phone:  781-5327 Fax:  781-8343 E-mail: bobleake@utah.gov
 Southeastern Regional Office  Marc Stilson, Regional Engineer 319 N.
Carbonville Road P.O.
Box 718 Price, Utah 84501-0718 Phone:  613-3750 Fax:  613-3755 E-mail: marcstilson@utah.gov
 Sevier River/Southern Regional Office  Kirk Forbush, Regional Engineer 130 North Main Street P.O.
Box 664 Richfield, Utah 84701-0563 Phone:  896-4429 Fax:  893-8114 E-mail: kirkforbush@utah.gov
 Southwestern Regional Office  Kurt Vest, Regional Engineer 585 North Main Street P.O.
Box 506 Cedar City, Utah 84721-0506 Phone:  586-4231 Fax:  586-2789 E-mail: kurtvest@utah.gov
Precision Irrigation: Where to Start?
As we enter the warm summer months, you might consider trialing the precision irrigation model on your farm to improve tree growth in your new plantings and maximize fruit size in your mature blocks.
Irrigation can be helpful in maximizing tree growth in the first few years of orchard establishment.
This is particularly important for trees planted with multiple large feathers in tall spindle plantings, as well-branched trees will have a disproportionally large leaf area that may not be adequately supplied with water by the trees' damaged roots.
Drip irrigation ensures the leaders can continue to grow to their full potential, leading to higher yields within the first five years of establishment in irrigated trees.
Irrigation can also increase fruit size in mature plantings.
While fruit thinning is one area where growers can affect fruit size, providing sufficient water is also critical.
Water stress, even temporarily, reduces the fruit growth rate.
Once the growth rate slows, this loss in size may be difficult to overcome, even when soil moisture levels return to normal during subsequent rain events.
This will then bring up a table, showing the current day in green, the previous week in blue, and the following predicted week in tan.
From here, you will have the option to adjust the numbers under the rainfall and irrigation columns.
The rainfall column is prepopulated with NEWA data, but you can change it if you know your site received an amount differing from what NEWA recorded.
You can also adjust the irrigation by gallons per acre.
Using this column and the one on the far right, the Cumulative Water Balance column, is how you can determine how much water you need to irrigate your blocks.
Looking at the Cumulative Water Balance Column, a positive number or a "0" indicates the field is saturated.
We generally begin applying irrigation when the field is at 80% water holding capacity, which for clay loam soils often begins at about -20,000 gallons per acre.
The other number you will want to determine is your application rate to know how many hours it will take for your system to put out a given GPA.
To determine this, you will need to know your emitters' flow rate in gallons per hour, and the number of emitters you have per acre.
Multiplying the number of emitters per acre by the flow rate will give you your application rate, which will be in gallons per hour per acre.
So, if you want to apply 5000 GPA, and your application rate is 622 Gallons per hour per acre, you can divide 5000 by 622, and determine you will need to irrigate for eight hours.
There are a few additional recommendations for practicing precision irrigation.
During the early season, apply the necessary irrigation once per week.
Then in mid-June switch to two applications per week in clay or loamy soils, and every other day in sandy soils.
When large rain events are predicted, do not irrigate the day before or three days after the rain event, as the upper layer of soil is likely to still be saturated.
So, if you would like to manage fruit size more precisely and maximize your tree growth in your new plantings, consider trialing the model on some of your irrigated blocks this season.
Nutrient Concentrations in Big Creek Correlate to Regional Watershed Land Use
 James Burke Program Associate
 Larry Berry Program Associate
 Stephen King Principal Scientist, Science and Technology Facilities Council, Rutherford Appleton Laboratory
 Arkansas Is Our Campus
 In the Ozark Mountain karst region, nutrient concentrations in streams of the Buffalo, Upper Illinois and Upper White River watersheds increase as the percent of land in pasture and urban use increases.
Averaged over the last three years, nutrient concentrations in Big Creek above and below the C&H Farm are similar to concentrations found in other watersheds where there is a similar amount of pasture and urban land use.
Land use within watersheds influences the quantity and quality of water draining from a watershed.
As land disturbance increases and use intensifies, there is a general increase in stormwater runoff and nutrient inputs that leads to a greater potential for nutrient discharge to receiving waters.
For instance, with urban growth, more impervious surfaces increase the flashiness of runoff, stream flows and wastewater treatment discharge.
Also, as areas of agricultural production grow, more fertilizer is applied to achieve optimum production.
Thus, as the percent of a watershed drainage area in pasture, row crop or urban use increases, there is a general increase in nutrient concentrations in storm and base flows.
In this fact sheet, we show the effect of land use on nitrogen  and phosphorus  concentrations in streams of the Ozark Highlands and Boston Mountains, northwest Arkansas, by combining previously published data for the Upper Illinois River Watershed , Upper White River Watershed  and ongoing
 monitoring in the Buffalo River Watershed.
The location of these watersheds is shown in Figure 1.
The relationships between stream nutrient concentrations and land use for the region are used to determine if a permitted concentrated animal feeding operation  in Big Creek Watershed, a sub-watershed of the Buffalo River Watershed, has affected stream water quality.
Land use in these watersheds is given in Table 1.
Nitrate-N, total N, dissolved P and total P concentrations have been measured over varying periods during base flow at the outlet of sub-watersheds in the Big Creek , Buffalo , Upper Illinois  and Upper White River Watersheds .
Data from Big Creek were paired with discharge available from a gaging station just downstream from the swine CAFO, where the USGS developed the rating curve; discharge information was only available from May 2014 through December 2017.
The data were then used to look at changes in flow-adjusted nutrient concentrations [A] in Big Creek.
[A] Concentration is defined as the mass of a substance , such as a nutrient, over the volume of water  in which it is contained, or C = M/V.
"Flow-adjusted nutrient concentrations" when looking at how concentrations change over time in streams, we have to consider how concentrations might also change with stream flow  and not just change in mass; nutrient concentrations often have some type of relation to flow, maybe increasing or even decreasing as stream flow increases.
We have to flow-adjust concentrations SO we can remove the variability in concentrations that flow might cause to see how things are changing over time.
Study Watersheds in the Ozark Highlands Ecoregion
 Upper Illinois River Watershed
 Upper White River Watershed
 Figure 1.
Location of the Big Creek, Buffalo River, Upper Illinois River and Upper White River watersheds in the Boston Mountains and Ozark Highlands ecoregion.
Information from U.S.
Geological Survey , Environmental Systems Research Institute  and National Aeronautics and Space Administration.
Table 1.
Percent of forest, pasture and urban land use in the Big Creek, Buffalo River, Upper Illinois and Upper White River watersheds.
Watershed	Forest	Pasture	Urban
 Upstream	89.5	8.0	2.6
 Downstream	79.5	17.0	3.5
 Buffalo River	52 99	0 25	0 1
 Upper White River	34 90	7 55	0 44
 Upper Illinois River	2 70	27 69	3 61
 * Up and downstream of CAFO operation and fields permitted to receive manure.
Putting Stream Nutrient Concentrations Into Context at Big Creek
 Geometric mean concentrations!
of stream P and N are related to the percent of watershed drainage area in pasture and urban land use for the Buffalo, Upper Illinois and Upper White River watersheds [C] The dashed lines on Figure 2 represent the upper and lower thresholds concentrations, where there is a 95 percent confidence that a stream draining a watershed with a specific percent pasture and urban land use will have a P and N concentration within those thresholds.
The relationship between land use and stream nutrient concentrations is not a model that can be used to predict concentration.
Given the large variability observed in these relationships, they simply show trends between two variables, land use and stream nutrient concentrations.
Continued monitoring of stream concentrations in Big Creek will continue to more reliably define trends.
As the percent pasture and urban land  increases, SO does stream P and N concentrations.
The general increase in nutrient concentrations is consistent with the fact that fertilizer  is routinely applied to pastures to maintain forage production, as well as deposition of nutrients by grazing cattle.
Beaver Reservoir Watershed Buffalo River Watershed A Illinois River Watershed
 Percent of land in pasture and urban use, %
 Figure 2.
Relationship between land use and the geometric mean N and P concentrations  in the Buffalo, Upper Illinois and Upper White River watersheds.
Dashed lines represent the 95 percent confidence intervals for the estimated mean.
Green points are geometric mean concentrations measured upstream of the CAFO on Big Creek and red points are geometric mean concentrations measured downstream of the CAFO on Big Creek.
In the Big Creek watershed, the percent of land influenced by human activities  doubles from ~10 percent to ~20 percent in the drainage area upstream and downstream of the CAFO.
In Big Creek itself, upstream of the swine production CAFO, the geometric mean concentrations of dissolved P, total P, nitrate-N and total N during base flow were 0.009, 0.030, 0.10 and 0.20 mg L-1, respectively, between September 2013 and December 2017.
Directly downstream of the CAFO, the geometric mean concentrations in Big Creek during base flow over the same period were 0.011, 0.030, 0.25 and 0.37 mg L-1, respectively.
Have Nutrient Concentrations Changed in the Short Term at Big Creek?
Geometric mean nutrient concentrations in Big Creek above and below the swine production CAFO and its current potential sphere of influence from slurry applications are similar to or lower than concentrations measured in rivers draining other subwatersheds in the Upper Illinois and Upper White River watersheds with similar proportions of agricultural land use.
Long-term  water quality data are needed to reliably assess how stream nutrient concentrations have changed in response to watershed management and climate variations.
The literature shows that stream nutrient concentrations can change relatively quickly in response to effluent management , but seeing a response  from landscape management can take decades or more.
A myriad of factors may influence observed nutrient concentrations in streams, including discharge, biological processes and climactic conditions , and dominant transport pathways.
Thus, we need to use caution when interpreting trends in water quality over databases that only cover a limited timeframe.
Flow-adjusted concentrations showed no
 Time since May 2014, days
 Figure 3.
Change in flow-adjusted concentration of  dissolved P,  total P,  nitrate-N and  total N over time since May 2014, when monitoring in Big Creek started.
statistically significant increasing or decreasing trends in dissolved P, total P, nitrate-N and total N ; where number of observations is 182) over the current monitoring period.
Nutrient concentrations at Big Creek upstream and downstream of the swine CAFO, and indeed most tributaries of the Buffalo River, are low relative to other watersheds in this ecoregion.
This provides a starting point to build a framework to evaluate changes in nutrient concentrations of streams as a function of land use and management.
The evaluation of flow-adjusted concentrations over time showed that nutrients in Big Creek were not increasing over the short duration of monitoring for which concentration and discharge data were
 available.
At this point in time, it is evident that nutrient concentrations in Big Creek have not increased at the monitored site.
However, flow and nutrient concentration data over a longer period are needed to reliably quantify water quality trends and characterize sources, and monitoring needs to continue for at least a decade to evaluate how discharge, season and time influence nutrient fluxes.
Stream nutrient concentration-land use relationships are not a predictive tool.
However, use of these relationships provides a method to determine if nutrient concentrations in a given watershed are similar to observed nutrient concentration-land use gradients in other watersheds of the Ozark Highlands and Boston Mountains.
Over time, tracking these relationships provides a mechanism to note and evaluate changes in nutrient concentrations.
In contrast, soybean maturity is dependent on day length.
Because soybeans may use more or less water than the averages listed in the table, and because it may be difficult to determine the actual correct growth stage, it is important to continue to monitor soil water until maturity.
This is where tools such as an ETgage and soil water sensors come into play.
An ETgage will give you potential crop water use and the soil water sensors will give you an idea of how much water is stored in the soil profile.
Then you will be able to determine how much water the crop will need in either irrigation or precipitation to finish out the year.
Since producers do not have time to do detailed work with large amounts of data often generated using SIS methods, the automation of SIS methods would likely provide incentives to producers by saving their time and, simultaneously, reducing the irrigation applications and producing optimal crop yield.
After cross-referencing the locations of the pivots with their groundwater concentrations, they found that none of the 76 wells feeding into the full-rust pivots contained nitrate above the 10 mg/L threshold established by EPA with the average nitrate concentration being 2.4 mg/L.
The reasons for that, Young said, are threefold.
Groundwater levels for the annual report are collected each spring, so data from some of the 5,000-plus wells measured throughout the state were collected prior to the mid-March floods.
Also, Young said, the floodwaters take time to seep into the states vast groundwater supply.
And in other cases, he said, wells that would typically be examined for the annual report could not be accessed, as they were completely submerged.
Selecting, Establishing & Maintaining the
 Seeding Sodding Care After Planting
 Primary Maintenance Practices	7
 Selecting a Fertilizer	9
 Fescue Fertilization Calendar	10
 Secondary Maintenance Practices	11
 Thatch and Its Development	11
 Slicing and Spiking	12
 Pests of Fescues	13
 Selecting, Establishing and Maintaining the Fescues
 Tom Samples, Associate Professor Ornamental Horticulture and Landscape Design
 Four fescue species are maintained as lawngrasses in Tennessee.
Originally from Europe, these perennial, cool-season lawngrasses are an integral part of many Tennessee landscapes.
They grow best in deep, well-drained soils at air temperatures from 60 to 75 F.
High temperatures and drought often slow their rate of growth during late spring and summer.
Species and varieties may vary in color, leaf texture, stand density, disease resistance and tolerance of shade, high temperature and drought.
Tall fescue  is adapted to a wide range of soil and climatic conditions.
This mediumto coarse-textured lawngrass tolerates high temperatures, drought and wear.
Tall fescue is usually best adapted in areas of the lawn receiving full sun or in light, open shade.
Turfgrass breeders continue to search for dark green, dense and disease-resistant tall fescue varieties.
Chewings , hard  and red  fescues are known collectively as fine fescues because of their narrow leaf blades.
Seeds of several fine fescue species are often mixed and marketed for use in shade.
Although they have excellent shade tolerance and good drought tolerance, the fine fescues are not particularly tolerant of high temperatures.
Tall and fine fescues establish from seed faster than Kentucky bluegrass.
They are also more tolerant of acid soil conditions, shade and drought.
Although tall fescue has short below-ground stems , most new leaves and tillers originate from the crown and not from nodes on rhizomes.
As a result, this lawngrass has very weak sod-forming characteristics and a bunch-type growth habit.
It may be necessary to broadcast seed over the lawn or slit-seed the lawn every two to three years to maintain a uniform,
 dense and weed-resistant turf.
Tall fescue is best adapted to fertile, moist soils but tolerates wet soils of low fertility.
Leaf blades are flat and rigid.
Seed of many Leaf Blade improved, turf-type tall fescue varieties is marketed in TennesRhizome see.
Several of these Daughter varieties are higher Plant in overall lawngrass quality and more Adventitious Roots disease resistant than 'Kentucky 31' tall fescue.
For more precise information
 Figure 1.
A lawngrass plant.
concerning tall fescue varieties, please contact your county Agricultural Extension office.
Table 1.
Drought, High Temperature, Shade, Soil Acidity and Wear Tolerances of Several Fescues.
Tolerance	Tall	Chewings	Hard	Red
 Drought	good	good	good	good
 High temperature	good	fair	fair	fair
 Shade	intermediate	excellent	excellent	excellent
 Soil acidity	excellent	good	good	good
 Wear	medium	medium	medium	medium
 Chewings fescue forms a very dense, finetextured and upright lawn.
Leaf blades of chewings fescue are thin, bristle-like and stiff.
This noncreeping, bunch-type lawngrass is well-adapted to acidic, infertile soils.
Chewings fescue does not usually tolerate wet, fertile soils or the high and low temperature extremes associated with sites exposed to full sun.
Hard fescue is a bunch-type lawngrass with tough, bluish-green leaves and an extensive root system.
Hard fescue forms a dense, somewhat tufted, low maintenance and low quality lawn.
Although hard fescue has limited high temperature
 tolerance, it is sometimes used alone or in grass and grass-legume mixtures for erosion control on ditch banks and along roadsides.
Often referred to as creeping red fescue, this lawngrass is similar in appearance to chewings fescue with one important exception it has a creeping growth habit.
Two distinct types of red fescue are F.
rubra ssp.
rubra, a relatively strong, sod-forming type and F.
rubra ssp.
trichophylla, with short, slender rhizomes.
Leaf blades are thin, bristle-like and deeply ridged above.
Red fescue forms a very dense, fine-textured lawn.
The rate of vertical growth of red fescue is slow compared to most cool-season lawngrasses.
The overall quality of a red fescue lawn often declines rapidly if an excessive rate of nitrogen is applied.
Red fescue is usually adapted to soil and climatic conditions favorable to chewings fescue.
Table 2.
Comparative Chart, Tall and Fine Fescues.
Characteristic	Tall	Chewings	Hard	Red
 Leaf texture	medium -
 coarse	fine	fine	fine
 Growth habit	bunch	bunch	bunch	sod-forming
 Level of care	medium	low	low	low
 establishment	seed/sod	seed/sod	seed/sod	seed/sod
 	good	good	good	good
 Density of aerial shoots	medium-low	high	high	high
 Tennessee is located within a transitional zone between temperate and subtropical climates.
Fescues maintained in this transition zone often experience high temperature and drought stresses during extended hot, dry periods in summer.
Tennessee can be divided into four climatic zones which favor the growth and persistence of
 certain lawngrasses.
Generally, the fescues are not well adapted in warm humid Zone IV.
Similarly, the moderately warm-to-cool humid climatic conditions in Zone III usually favor warm season  lawngrasses including bermudagrass and Zoysia.
The fescues are generally adapted in cool-to-warm humid Zone II and cool humid Zone I.
Figure 2.
Four lawngrass climatic zones in Tennessee.1
 Fescue lawns are commonly established from seed or by transplanting sod.
The preparation of a firm planting bed with appropriate fertility is critically important to the growth and performance of young seedlings or newly-transplanted fescue plants.
For best results:
 1.
Test soils six to eight weeks before the intended planting date to determine soil phosphorus, potassium and pH levels.
2.
Stockpile existing topsoil from new construction sites before excavation and construction begins.
3.
Control [i.e.
Roundup application according to instructions on the product label] troublesome perennial weed grasses and broadleaf weeds.
4.
Remove all debris (i.e.
wood, pipe, rock, discarded cement, brush and construction
 scrap) that may obstruct the growth of fescue roots and restrict soil water movement.
5.
Establish a rough grade which directs water away from the house.
6.
Install subsurface drainage and irrigation systems before final grading and smoothing.
7.
Redistribute the topsoil.
Topsoil should be free of troublesome weeds, including johnsongrass, thistle, etc., and should contain no stones, roots, trash or extraneous materials larger than 1 1/2 inches in diameter.
If suitable topsoil is not available on site, the existing soil may be modified.
Soil aeration and water drainage can be improved when proper amounts of coarse sand or loamy topsoil are incorporated into clay soils.
Mix 4 to 6 inches of sand or topsoil with the upper 2 to 4 inches of underlying soil.
If topsoil lacks organic matter, additives such as mature compost, well-rotted sawdust or decomposed manure may be mixed  with soil.
Determine pH, phosphorus and potassium levels in the soil by sampling after mixing sand, topsoil or organic materials.
8.
Uniformly apply nitrogen, phosphorus, potassium and lime according to soil test recommendations.
A general guideline for fertilizing a planting bed in lieu of a soil test is to apply 25 pounds of 6-12-12  fertilizer or equivalent per 1,000 square feet.
9.
Till the soil to a depth of 6 or more inches, thoroughly mixing lime and fertilizer with soil.
10.
Fine grade to smooth the soil surface before planting.
Hand raking is preferred for small areas.
A heavy steel drag mat, plank drag or tiller rake is effective on larger areas.
11.
If the soil is dry, water the planting bed to a depth of 5 or 6 inches several days before planting.
12.
Allow at least one week for settling of the soil before planting.
The planting bed should be firm enough to walk in, with the upper 1/2 inch of soil loosened.
If footprints are deeper than 1 inch, rolling or further watering is recommended.
Seed the fescues in late summer  just before most favorable climatic conditions.
Cool temperatures and moist soils during late summer, fall and early spring promote plant growth.
Fescues may also be seeded in early spring; however, spring plantings often result in greater susceptibility to heat and drought stresses.
Young fescue plants with limited root systems often do not survive the summer heat and dry conditions.
The recommended planting rate for establishing a tall fescue lawn from seed is from 5 to 8 pounds per 1,000 sq.
ft.
Plant chewings, hard or red fescues at a rate of 3 to 5 pounds of seed per 1,000 sq.
ft.
For best results, purchase high quality seed.
Tall fescue seed germination should be at least 85 percent; seed purity, 95 percent.
The minimum acceptable seed germination and purity of the fine fescues is 80 percent and 95 percent, respectively.
For more information regarding seed and the seed label, please refer to Extension PB1350,
 Straw is an effective mulch when uniformly
 broadcast over a seedbed after planting.
Eighty to 100 pounds of clean  mulching straw per 1,000 square feet usually protects the newly seeded lawn from seed washing and erosion.
Straw also conserves moisture and buffers emerging fescue seedlings from temperature extremes.
Spread the straw as evenly as possible to prevent layering, which can limit the amount of light reaching the young fescue plants.
When high-quality fescue sod is properly transplanted, it stabilizes soils and provides "instant" beautification.
Although sodding in September, October and March is preferred, fescue sod may be transplanted almost any time of the year.
Harvesting, installing and caring for fescue sod in mid-summer is especially challenging due, in part, to the potential damage from high temperatures, drought and disease activity.
Several weeks or months may be required before the newly-installed fescues root into the soil below and are capable of withstanding foot traffic.
Fescue sod produced and marketed in Tennessee is often harvested in 16-inch by 24-inch pieces with 5/8 inch  of soil.
Biodegradable netting, which improves the tensile strength and speeds harvest of the fescue sod, may be located near the soil surface.
One pallet containing about 50 square yards of fescue sod may weigh more than 2,000 pounds.
Transplant the first pieces of sod in a straight line along a driveway or sidewalk.
Work should progress toward the center of the lawn.
Place the pieces of sod in a pattern similar to bricks in a wall.
This will minimize the formation of long, straight lines and reduce the risk of dehydration of plants located near the edges.
Although they should fit together tightly, sod pieces should not be stretched or overlapped.
Figure 3.
Install sod in a pattern similar to bricks in a wall.
Begin irrigating the newly planted lawn area immediately after seeding or sodding.
Water frequently  to maintain adequate moisture in the upper 1 to 2 inches of soil.
Apply water slowly to prevent seed movement and runoff.
After seedlings are well developed  or the sod is well rooted, discontinue the practice of light, daily irrigations.
Apply more water less often to encourage deep rooting.
Mow the lawn when the tallest plants reach a height about 1 1/3 times the intended cutting height.
For example, if the cutting height is 2 inches, mow the lawn when the tallest plants reach a height of 2 2/3 inches.
Short grass clippings may be returned to the soil surface to provide nutrients and contribute organic matter to the soil.
Keep mower blades sharp.
Fescue seedlings may be easily torn or lifted from the soil by a dull mower blade.
Mowing, fertilization and irrigation are very important considerations when developing an effective lawn care plan.
For example, fescues perform best when they are mowed often at an appropriate cutting height.
Fertilizer applications can be timed to support active plant growth during favorable weather conditions.
The lawn can be watered to maintain active growth and to preserve the root system of fescues during extended periods of drought.
For best results, keep the mower blade sharp and mow when the lawn is dry.
Set the cutting height of the mower within the optimum range for the fescue being maintained.
The optimum cutting height range for tall fescue varieties is usually from 2 to 3 inches; the fine fescues, from 1 1/2 to 2 1/2 inches.
To determine the mechanically set cutting height , place the mower on a firm, level surface and measure the distance from the surface to the cutting edge of the blade.
The effective cutting height is the actual height of aerial shoots immediately after mowing.
The effective cutting height may be slightly higher than the bench setting when the soil is firm and the mower wheels ride on lawngrass shoots above the soil
 surface.
If the soil is soft or moist, the effective cutting height may be equal to or lower than the bench setting.
Raising the height of cut within the optimum cutting height range before extended periods of drought or high and low temperature stresses can be very beneficial.
Increasing the cutting height may promote deep rooting.
The additional vegetation may also insulate the soil against high and low temperature extremes.
Remove no more than one-third of the leaf tissue when mowing.
Scalping lawngrass plants back to their original height results in a weak and weedy lawn.
If the lawn grows too tall between mowings, gradually lower the cutting height over a period of two or three mowings.
Mowing patterns result from back-and-forth travel while mowing the lawn.
Try to alternate the mowing direction each time the lawn is mowed to distribute wear and soil compaction.
This may also encourage the fescues to grow upright.
Return small grass clippings to the lawn when mowing.
Small pieces of leaf tissue decompose naturally, recycling essential nutrients.
New mulching mowers and mower accessories are available to help evenly spread small clippings over the lawn.
Conventional sideor rear-discharge mowers may also be used to cycle clippings if the lawn is dry and no more than one-third of the aerial portion of the plants is removed when mowing.
For more information regarding clipping cycling, please refer to Extension PB1455, Lawn Care to Reduce Landscape Waste.
Figure 4.
New mulching mowers and mower accessories are available from some manufacturers to help evenly spread small clippings over the lawn.
Air and water supply the fescues with carbon, hydrogen and oxygen.
The soil provides 13
 essential mineral nutrients.
In Tennessee, soils usually contain adequate amounts of secondary nutrients  and micronutrients.
They seldom contain enough nitrogen to meet the needs of fescues.
Sometimes, additional phosphorus and potassium may also be required.
A fertilization program seldom delivers the desired results if the soil pH is not within the optimum range for plant growth.
Only a soil test can provide an objective assessment of the need for fertilization and liming, and the appropriate amounts of materials to apply.
For more information regarding collecting and processing a soil sample, please refer to Extension PB1061, Soil Testing.
The nutrient required by fescues in greatest amounts is nitrogen.
Nitrogen is mobile in the soil and is the nutrient most likely to be deficient in fescues.
Fescue lawns deficient in nitrogen appear yellowish to light green, are often thin and grow very slowly.
The application of too much nitrogen often results in rapid growth and reduces the lawn's tolerance of high and low temperature extremes, traffic and drought.
The monthly nitrogen requirement varies among the fescues.
Tall fescues require a medium level of nitrogen fertility  compared to the high level of nitrogen fertility most often required by Kentucky bluegrass (from 1/2 to 1 1/2 pounds of nitrogen per 1,000
 square feet per growing month).
Red and chewings fescues usually require from 1/5 to 3/5 pound of nitrogen per 1,000 square feet per growing month.
Some nitrogen sources may be very soluble in water and may release nitrogen for plant uptake very quickly.
Others may be relatively insoluble in water and release nitrogen slowly, over an extended period of time.
No more than 1 pound of quickly available nitrogen should be applied per 1,000 square feet of lawn surface at one time.
Ammonium nitrate [34-0-0, containing 34 percent nitrogen ] and urea  are examples of quickly available nitrogen sources.
Isobutylidene diurea , sulfur-coated urea , milorganite [6-2-0, containing 6 percent N and 2 percent available phosphate  and ureaformaldehyde  are sources of slowly available nitrogen.
Both mature fescue plants and developing seedlings need phosphorus.
Plants deficient in phosphorus may have red to reddish-purple leaves, and may grow slowly, due to low energy levels.
Fescues growing in soils testing low in phosphorus should receive more phosphorus each year than those maintained on soils testing medium or high.
Concentrated superphosphate (0-46-0, containing 46 percent P2O5 and diammonium phosphate (18-46-0, containing 18 percent N and 46 percent P2O5 are common sources of phosphorus.
Hydraulic Considerations for Citrus Microirrigation Systems
 Brian Boman and Sanjay Shukla
 Hydraulics is the study of the behavior of liquids as they move through channels or pipes.
Hydraulic principles govern the flow of water through irrigation pipes.
A basic understanding of these principles is necessary for understanding the design and operation of irrigation systems.
This publication provides an introduction to hydraulics as it relates to citrus microirrigation.
Important Basic Terminologies Head
 Head is the energy in water  expressed in terms of the equivalent height of a water column above a given reference.
Head at any point in the irrigation line is the sum of three components: static head, velocity head, and friction head.
Static or Elevation Head  e
 It is the vertical distance  between the water inlet and the discharge point.
It represents potential energy per unit mass of the water.
Velocity Head 
 It is the energy  needed to keep irrigation water moving at a given velocity.
It represents the kinetic energy per unit mass of water.
Friction head   is the energy needed to overcome friction in the irrigation pipes and is expressed in units of length.
It is the force per unit area.
It is expressed in pounds per square inch , Pascals, or Newtons per square meter.
A few basic hydraulic concepts related to water movement through pipes are particularly important to the design and proper operation of microirrigation systems.
1 ft3 of water = 62.4 pounds 
 1 gallon of water = 8.341
 Water weighs about 62.4 pounds per cubic foot.
This weight exerts a force on its surroundings, which is expressed as force per unit area or pressure.
The pressure on the bottom of a cubical container  filled with water is 62.4 lb/ft2.
Conversion to psi can be achieved as follows:
 Pressure on 1 ft2 = 62.41
 2.
Brian Boman, Emeritus professor, Department of Agricultural and Biological Engineering, UF/IFAS Indian River Research and Education Center; and Sanjay Shukla, professor, UF/IFAS Southwest Florida REC; UF/IFAS Extension, Gainesville, FL 32611.
Pressure in psi for 1 foot of water = 62.4 lb/1 ft2 = 62.4 lb/144 in2 = 0.433 psi.
Therefore to convert feet of water to psi and vice versa we can use:
 Head   = Pressure /0.433 = 2.31 = X pressure  Eq.
1
 The column of water does not have to be vertical.
To calculate the static pressure between two points resulting from an elevation difference, only the vertical elevation distance between the two points needs to be known.
However, other factors such as friction affect water pressure when water flows through a pipe.
If the pressure gauge at the bottom of a tank filled with water displays 10 psi, determine the height of water  in the tank.
H1 = Pressure X 2.31 = 10  X 2.31  = 23.1 ft
 Velocity  is the average speed at which water moves through a pipe.
Velocity is usually expressed in units of feet per second.
Water velocity in a pipe is greatest  in the middle of the pipe and smallest near the pipe walls.
Normally only the average velocity of water in the pipe is needed for hydraulic calculations.
To avoid excessive pressure losses due to friction and excessive potentially damaging surge pressures, a rule of thumb for pipe sizing for irrigation pipelines is to limit water velocities to 5 ft/sec or less.
Figure 1.
Typical velocity cross-section profile for full-flowing pipe.
The relationship between flow rate and velocity is given by the equation of continuity, a fundamental physical law.
This equation can be used to calculate flow by multiplying the velocity with the cross-sectional area of flow.
Q =AxV Eq.
2 or 7=Q/A Eq.
3 where,
 Q = flow rate in ft3/sec,
 A = cross-sectional area of flow in pipes in ft2 ,
 V = velocity in ft/sec, and
 D = pipe diameter.
If pipe diameters change in sections of the pipe without any change in flow rate, the relationship between flow and velocity can be calculated by:
 A1 V1 = A2 Eq.
4 where, A1 = cross-sectional area of flow for first section  = velocity in first section  A2 = cross-sectional area of flow for second section  V2 = velocity in second section 
 If the velocity is the same in a 2and a 4-inch diameter pipe , the flow rate with the 4-inch pipe would be four times as large as the flow rate from the 2-inch diameter pipe.
Note that the cross-sectional area is proportional to the diameter squared: 2 = 4 in., while 2 = 16 in2.
Therefore, doubling the pipe diameter increases the carrying capacity of a pipe by a factor of 4.
Figure 2.
Diameter  and velocity  relationships for adjoining pipe sections with a constant flow rate.
This principle is known as Bernoulli's Theorem and can be expressed as :
 Determine the flow rate  in a 4-in Class 160 PVC pipe if the average velocity is 5 ft/s.
Total head = =He+H,+ Eq.
H H Eq.
6 where, H = Static head or elevation head in feet above some reference point 
 The I.D.
for 4-in.
pipe is 4.154 ir 
 Q = AxV = 0.094 ft2x5 ft/s = 0.47 ft3/s 
 H = P/G  and G = specific weight  of water) 
 Q = 0.47 cfs X 448 gal/cfs = 211 gpm
 H = Velocity head  = V2/2g,
 V = velocity in ft/s,
 g = gravitational constant 32.2 ft/s2,
 H = friction head , and subscripts 1 and 2 refer to two points in the fluid system.
The pressure at the pump of an irrigation system is 30 psi.
A microsprinkler is located at another location, which is 10 ft higher than the pump.
What is the static water pressure at the microsprinkler ?
For convenience, the pump can be used as the elevation datum.
The friction head  can be calculated by the Hazen-Williams equation discussed in the next section.
Velocity head is usually a small fraction of the total hydraulic head in a pressurized irrigation system, therefore, for the purpose of design it can be ignored.
As water moves through any pipe, pressure is lost due to turbulence created by the moving water.
The amount of pressure lost in a horizontal pipe is related to the velocity of the water, pipe diameter and roughness, and the length of pipe through which the water flows.
When velocity increases, the pressure loss increases.
For example, in a 1-in.
schedule 40 PVC pipe with an 8 gpm flow rate, the velocity will be 2.97 fps with a pressure loss of 1.59 psi per 100 ft.
When the flow rate is increased to 18 gpm, the velocity will be 6.67 fps, and the pressure loss will increase to 7.12 psi per 100 ft of pipe.
The total energy at the pump is determined:
 where, H = energy head  P = pressure head  E = elevation 
 At any point within a piping system, water has energy associated with it.
The energy can be in various forms including pressure, elevation, velocity, or friction.
The energy conservation principle states that energy can neither be created nor destroyed.
Therefore, the total energy of the fluid at one point in the system must equal the total energy at any other point in the system, plus any energy that might be transferred into or out of the system.
C = conversion constant to convert psi to ft.
In this example, since there is no water flowing, the energy at all points of the system is the same.
Pressure at the microsprinkler is found by solving equation for P:
 Reorganization of Eq.
7 results in P=/c
 P =  / 2.31  = 25.7 psi = 25.7*2.31 = 59.37 ft
 Water flowing in a pipe loses energy because of friction between the water and pipe walls and turbulence.
In the above example, when the microsprinkler is operating, pressure will be less than the 25.7 psi due to friction loss in the pipe and the micro tubing.
It is important to determine the amount of energy  lost in pipes in order to properly size them.
The Hazen-Williams equation is extensively used for designing water-distribution systems.
The friction-loss calculations for most pipe sizes and water temperatures encountered under irrigation system conditions are shown in Table 1 and Table 2.
The values in Table 1 and Table 2 are computed using the Hazen-Williams equation.
A more accurate equation, Darcy-Weisbach, is sometimes used for smaller pipes or when heated water is being piped; however, the computations are more difficult.
The Hazen-Williams equation can be expressed as:
 H = friction loss 
 Q = flow rate )
 D = inside pipe diameter 
 L = length of pipe , and
 C = friction coefficient or pipe roughness
 For most irrigation systems a value of C=150  is used which reduces the above Equation to:
 The above Equation can also be expressed as:
 H=/D487 Eq.
10
 where all the terms and units are as defined except that Q has a unit of gallons per minute.
Friction loss in pipes depends on: flow , pipe diameter , and pipe roughness.
The smoother the pipe, the higher the C value.
Increasing flow rate or choosing a rougher pipe will increase energy losses, resulting in decreased pressures downstream.
In contrast, increasing inside diameter decreases friction losses and provides greater downstream pressure.
Determine the pipe friction loss in 1,000 ft of 8-inch Class 160 PVC pipe, if the flow rate is 800 gpm.
Hydraulics of Multiple Outlet System
 From Table 1, the I.D.
of 8-inch pipe is 7.961 inches.
From Equation 10:
 H1.85 x 1000)/7.961487) H = 9.39 ft
 Because of friction, pressure is lost whenever water passes through fittings, such as tees, elbows, constrictions, or valves.
The magnitude of the loss depends both on the type of fitting and on the water velocity.
Pressure losses in major fittings such as large valves, filters, and flow meters, can be obtained from the manufacturers.
To account for minor pressure losses in fittings, such as tees and elbows, Table 3 can be used.
Minor losses are sometimes aggregated into a friction loss safety factor  over and above the friction losses in pipelines, filters, valves, and other elements.
Although the HazenWilliams equation facilitates easy manual computations for pipe friction , more complex and accurate methods  are also available.
These complex equations are used in several of the currently available computer programs that are used to design microirrigation systems.
For a pipeline with multiple outlets at regular spacing along mains and submains, the flow rate downstream from each of the outlets will be effectively reduced.
Since the flow rate affects the amount of pressure loss, the pressure loss in such a system would only be a fraction of the loss that would occur in a pipe without outlets.
The Christiansen lateral line friction formula is a modified version of the
 Hazen-Williams Equation and was developed for lateral lines with sprinklers or emitters that are evenly spaced with assumed equal discharge and a single pipe diameter.
The Christiansen formula introduces a term known as multiple outlet factor "F" in the Hazen-Williams equation to account for multiple outlets:
 Hydraulic Characteristics of Lateral Lines
 The goal of a good irrigation system is to have high uniformity and ensure  that each portion of the field receives the same amount of water.
As water flows through the lateral tubing, there is friction between the wall of the tubing and the water particles.
This results in a gradual  reduction in the pressure within the lateral line.
The magnitude of pressure loss in a lateral line depends on flow rate, pipe diameter, roughness coefficient , changes in elevation, and the lateral length.
H = head loss due to friction in lateral with evenly spaced emitters 
 L = length of lateral 
 When a lateral line is placed up-slope, emitter flow rate decreases most rapidly.
This is due to the combined influence of elevation and friction losses.
Where topography allows, running the lateral line down-slope can produce the most uniform flow since friction loss  and elevation factors  cancel each other out to some degree.
F = multiple outlet coefficient 
 = [1/] + [1/2n] + [05/]
 m = velocity exponent ,
 Friction loss is greatest at the beginning of the lateral.
Approximately 50% of the pressure reduction occurs in the first 25% of the lateral's length.
This occurs because as the flow rate decreases, friction losses decrease more rapidly.
The lengths of laterals have a large impact on uniform application.
For a given pipe diameter and emitter flow rate, too long laterals is one of the most commonly observed sources of non-uniformity in microirrigation systems.
In general, longer lateral length results in less uniform application rate.
n = number of outlets on lateral,
 Q = flow rate in gpm,
 D = inside pipe diameter in inches,
 k = a constant 1,045 for Q in gpm and D in inches, and
 C = friction coefficient: 150 for PVC or PE pipe 
 Water hammer is a hydraulic phenomenon which is caused by a sudden change in the velocity of the water.
This velocity change results in a large pressure fluctuation that is often accompanied by loud and explosive-like noise.
This release of energy is due to a sudden change in momentum followed by an exchange between kinetic and pressure energy.
The pressure change associated with water hammer occurs as wave, which is very rapidly transmitted through the entire hydraulic system.
If left uncontrolled, water hammer can produce forces large enough to damage the irrigation pipes permanently.
Determine the friction loss in a 0.75-inch poly lateral that is 300 ft long with 25 evenly spaced emitters on each side of the riser.
Each emitter has a discharge rate of 15 gallons per hour.
H F x H  Eq.
11
 Flow rate into each half of the lateral is: 25 emitters X 15 gph each = 375 gph or 375 gph min = 6.3 gpm
 C = 130 for 0.75-inch poly tubing
 From Table 4, F = 0.355 
 From Table 2, the I.D.
of 0.75-inch poly is 0.824 inches
 For flow in gpm and diameter in inches the expanded form of the above Equation becomes:
 When water is flowing with a constant velocity through a pipe and a downstream valve is closed, the water adjacent to the valve is stopped.
The momentum in water creates a pressure head which results in compression of water and expansion of the pipe walls.
These pressures can be several times the normal operating pressure and result in broken pipes and severe damage to the irrigation system.
The high pressures resulting from the water hammer can not be effectively relieved by a pressure relief valve due to the high velocity of the pressure wave.
The best prevention of water hammer is the installation of valves that can not be rapidly closed, and the selection of air vents with the appropriate orifice which do not release air too rapidly.
Pipelines are usually designed to maintain velocities below 5 fps in order to avoid high surge pressures from occurring.
Surge pressures may be calculated by the following :
 P = {0.028  Eq.
12 where, Q = flow rate  D = pipe I.D.
P = surge pressure  L = length of pipeline  T = time to close valve 
 For an 8-inch Class 160 PVC pipeline that is 1,500 feet long and has a flow rate of 750 gpm, compare the potential surge pressure caused when a butterfly valve is closed in 10 seconds to a gate valve that requires 30 seconds to close.
From Table 1, diameter of 8 inch pipe is 7.961 inches
 Surge Pressure  = 0.028 X  /  = 49.7 psi
 Surge Pressure = 0.028 X  /  = 16.57 psi
 Head Losses in Lateral Lines
 From the above example, it is clear that increasing the closing time for valves can reduce the surge pressure.
Microsprinkler field installations typically have 10-20 gph emitters.
Emitters are normally attached to stake assemblies that raise the emitter 8-10 inches above the ground, and the stake assemblies usually have 2-3 ft lengths of 4-mm spaghetti tubing.
The spaghetti tubing is connected to the polyethylene lateral tubing with a barbed or threaded connector.
The amount of head loss in the barbed connector can be significant, depending on the flow rate of the emitter and the inside diameter of the connector.
The pressure loss in a 0.175 inch barb X barb connector is shown in Figure 3.
At 15 gph, about 1 psi is lost in the barbed connection alone.
Figure 3.
Pressure loss versus flow rate for 0.175 inch barb X barb connector.
In addition to the lateral tubing connection, there will be pressure losses in the spaghetti tubing.
Figure 4 shows the pressure required in the lateral line to maintain 20 psi at the emitter for various emitter orifices and spaghetti tubing lengths.
Note that with the red base emitters , an additional 25-30% pressure is required in the lateral tubing to maintain 20 psi at the emitter.
It is important to realize the hydraulic limits of irrigation lateral lines to efficiently deliver water.
Oftentimes when resetting trees, 2 or more trees are planted for each tree taken out.
If a microsprinkler is installed for each of the reset trees, the effects of increased emitters on the system uniformity and system performance can be tremendous.
Not only will friction losses increase and average emitter discharge decrease, but system uniformity and efficiency will decrease.
Figure 5 shows the maximum length of lateral tubing that is possible while maintaining + 5% flow variation on level ground with a 20 psi average pressure.
The discharge gradient is calculated by dividing the emitter flow rate  by the emitter spacing.
Figure 4.
Lateral line pressure required to maintain 20 psi at emitter for various emitter orifice sizes and spaghetti tube lengths.
Figure 5.
Lateral length allowable to achieve +/5% flow variation for level ground with 22 psi inlet pressure  for 1/2-, 3/4-, and 1-inch lateral tubing.
The maximum number of microsprinkler emitters and maximum lateral lengths for 0.75, and 1-inch lateral tubing is given in Table 5 and Table 6.
Similar information for drippers with 0.5, 0.75, and 1-inch lateral tubing is given in Table 7, Table 8, and Table 9.
All calculations are based on +5% allowable flow variation on level ground.
By knowing the emitter discharge rate, spacing, and tubing diameter, the maximum number of emitters and the maximum lateral length can be determined.
Determine the maximum allowable run length for 0.75inch lateral tubing with 10 gph emitters spaced at 12-ft intervals.
Discharge gradient = 10 gph / 12 ft = 0.83 gph/ft
 From Figure 5, maximum run length corresponding to 0.83 gph/ft gradient is about 380 ft.
Determine the maximum allowable run length for 0.75inch lateral tubing with 12 gph emitters spaced at 10-ft intervals.
For 12 gph and 10-ft spacing, :
 Maximum number of emitters: 31
 Maximum lateral length: 313 ft
 Alternatively, Figure 5 can be used to compute the maximum lateral length for +/-5% flow variations.
Discharge gradient = 12 gph/10 ft = 1.2 gph/ft
 Corresponding value for 1.2 gph/ft from Figure 5 is 300 ft.
Using Tables 7 to 9, determine the maximum allowable run length for 0.75-inch lateral tubing with 1.0 gph drip emitters spaced at 30-inch intervals.
From Table 8 for 1.0 gph at 30-inch spacing,
 Maximum number of emitters: 227
 Maximum lateral length: 568 ft
The last few irrigations of the season require some of the most important water management decisions of the year.
An extra irrigation may mean wasting 1 to 3 inches of water and 2 to 5 gallons of diesel fuel per acre.
Furrow irrigators may want to decide sooner due to the typical higher application amounts with flood, while pivot irrigators can delay the decision and take advantage of any rainfall that may occur.
The final criteria is that the impeller operate at near maximum efficiency.
Irrigated fields have some level of elevation change, but since the design is based on the worst case scenario most of the field will receive greater pressure and flow rate than needed.
Enter VFDs.
With pumping costs ranging from $6-15/acre-inch this year, any opportunity to save money by cutting back irrigation as early as possible sounds like a good strategy.
Correctly timing the last few irrigations of the season offers an excellent opportunity to save some water and money.
Daily information from the Dudley Ridge CIMIS weather station was used to estimate water requirements for mature walnuts, as well as irrigation timing and quantity.
Implementing CIMIS at the farm level: a grower's experience in walnuts
 The California Irrigation Management Information System  originated in 1982.
Its purposes were to provide estimates of crop water requirements as influenced by real-time weather conditions and to ensure reasonable use of limited water supplies for farming.
This study documents the effects of managing on-farm irrigation practices, with and without using CIMIS information, in a Kings County walnut orchard.
In this example, increased water use, increased production, and increased profits were experienced as a result of implementing CIMIS information.
It has been charged that existing irrigation practices on agricultural lands in California use limited water supplies inefficiently.
In partial response, the California Irrigation Management Information System  was initiated in 1982 to ensure reasonable use of limited water supplies on agricultural croplands.
Objectives of the CIMIS program have been to provide estimates of crop water requirements based upon real-time weather conditions and to promote adoption of CIMIS information into the irrigation scheduling practices of growers in California.
CIMIS consists of a network of about 65 automated weather stations located throughout the state.
Under the management of the California Department of Wa-
 ter Resources' Office of Water Conservation, hourly weather data is logged from each station onto a mainframe computer in Sacramento.
The public can obtain this information by calling the Department of Water Resources at  445-8259, by contacting public water agencies, or by referring to various publications.
Installation of the ribs restricted water flow to 80%-85% of full capacity, and water flow for the 2020 growing season was reduced to approximately 1,200 cubic feet per second.
How to Close an Abandoned Well Steve Higgins and Sarah Wightman, Biosystems and Agricultural Engineering
 A bandoned wells are often the only structures remaining after an old house or barn has been removed.
If left unmanaged in agricultural areas, these abandoned wells can pose a serious threat to livestock and human safety because of the large surface openings they often have.
Abandoned wells can also affect water quality, water as the shaft that forms bearing zone the well creates a conduit directly into groundwater resources.
If wells are not closed properly, pollutants present on the surface, including sediment, manure, and pesticides, can be transported through stormwater runoffin the groundwater through that conduit.
Water quality is also negatively impacted when livestock fall into these openings or the openings are used as a way to dispose of dead livestock.
Landowners can be held liable for groundwater contamination originating from a polluted well, just as they can for accidents caused by an abandoned well.
The goal of this publication is to provide information on the proper way to close an unused well, which will help prevent accidents and protect drinking water.
There are several types of wells that can be found on agricultural properties, including drilled wells, wells with multiple casings, bored and hand-dug wells, driven wells, and flowing artesian wells.
Figure 1.
This properly functioning well could become a hazard if abandoned.
To locate an abandoned well, search old photographs, fire insurance plan drawings, health department records, and water utility records.
Also, ask neighbors and former property owners for information.
Look for well casings, waterlines, pressure tanks, pumps, and electrical components such as wiring in the yard or basement or near old windmills or pump houses.
Metal detectors can help locate metal casings.
Figure 2.
This abandoned well has an open side, which makes it possible for pollutants to enter the aquifer unabated.
Figure 3.
This abandoned well is located in an agricultural area that is void of vegetation that could filter pollutants from stormwater runoff and reduce the amount of pollution entering groundwater resources.
Landowners in Kentucky are responsible for decommissioning abandoned wells within 30 days of deeming them unusable or unneeded.
Abandoned wells have clear guidelines for closure under the law , and all of the work needs to be accomplished by a Kentucky certified water well driller.
Figure 4.
This well's large opening could be hazardous for nearby livestock.
Before closing a well, measurements of the well depth, diameter, and its depth to static water level need to be taken and recorded in the Uniform Kentucky Well Maintenance and Plugging Record.
All obstructions must be removed from the well before closure.
If the pump or other equipment, such as casing, screens, or liners, is stuck in the well and cannot be removed, the certified driller should push the material to the bottom of the well.
Closing out a well requires that it must be disinfected in accordance with administrative regulation.
To disinfect a well, determine the correct amount of chlorine or hypochlorite granules to be used and pour it into the well.
Circulate the chlorine solution throughout the well for at least 30 minutes, ensuring that the chlorinated water contacts all parts of the well casing, borehole, discharge pipes, and all internal well components.
Allow
 Table 1.
Guidelines used to determine the amount of disinfectant that would provide a minimum chlorine concentration of 100 parts per million in the well.
of water)	of water)
 the chlorinated water to stand in the well for at least 30 minutes, then purge the well of all chlorinated water.
Make sure the chlorinated water is discharged to the ground and not to a drainage ditch, stream, pond, lake, or wetland.
Well Casing, Screen, and Liner Removal
 Well casing, screens, and liners must be removed from the well before sealing it.
If the well casing has been grouted in place and the certified well driller is unable to remove the casing, the certified well driller may cut off the casing a minimum of 5 feet below the ground surface.
For wells with multiple casings, the certified well driller should first remove the innermost well casing, screen, or liner.
The well should then be filled up to the bottom of the next outer casing before removing that casing, and SO on with any other casings.
If necessary to avoid borehole collapse, the well casing, screens, and liners may be removed at the same time sealing material is introduced.
The filling of the well is designed to prevent migration of surface water or contaminants to the subsurface and to prevent migration of contaminants along water-bearing zones.
Use Table 2 to determine what sealing material should be used to fill any type of well at a given depth.
These materials can be used singularly or in various combinations to properly abandon the well.
Under no circumstances should waste materials , or biodegradable wastes  be used to seal a well.
If you have questions concerning proper sealing material, please contact the Kentucky Division of Water.
If the well has a void, the certified well driller should fill the well with sealing materials or other inert materials from the bottom of the well to at least five feet below the void.
A packer, expansion bridge, or other support should then be placed at the top of the void, and a permanent bridge of at least 10 feet of sealing material should be placed above the expansion bridge.
After dealing with the void, filling can proceed as indicated in Table 2, using the top of the void as the new bottom of the well.
Flowing artesian wells are wells in which there is upward movement of water between aquifers.
Plug these wells with neat cement grout, which is generally formulated using a ratio of one 94-lb bag of portland cement to no more than gallons of water.
Pump the neat cement ground under pressure and mix with the
 Table 2.
Sealing materials recommended based on well type and depth.
From Bottom of Well	From 20 Feet Below Ground Surface
 Well Type	to 20 Feet Below Ground Surface	to 5 Feet Below Ground Surface	Top 5 Feet
 Drilled	Sealing materials, inert materials	Sealing materials	Sealing materials, clay, inert materials
 Multiple casings	suitable to proposed land use
 Bored and hand-dug	Sealing materials, dense grade aggregate limestone, sand, or native clay	Clay, impermeable materials suitable
 to proposed land use
 Note: Sealing materials commonly consist of natural rock fragments, sand, gravel, cement, bentonite, cement/bentonite mixtures, and in some cases, clean soils.
minimum quantity of water to facilitate handling.
The driller may restrict artesian flow if necessary.
After plugging the well with grout, the driller should place a well packer, cast-iron plug, or temporary bridge made of wood or neoprene at the bottom of the confining formation immediately over the artesian water-bearing horizon to seal off the flow.
Within 60 days of closing a well, the certified well driller must complete and submit a Uniform Kentucky Well Maintenance and Plugging Record to the well owner and to DOW.
in the Lower Rio Grande Valley
 Citrus is an important irrigated crop for South Texas.
Grown on 27,000 acres primarily in the Lower Rio Grande Valley, the citrus crop has been subject to freezes, market conditions and urbanization since 1950.
About 71 percent of the citrus area is planted with grapefruit and 29 percent with oranges.
Texas grapefruit varieties are 72 percent Rio Red, 17 percent Ruby Red, 11 percent Henderson/Ray and 1 percent other varieties.
The oranges are 59 percent Early, 28 percent Navel and 13 percent Valencias.
In the Lower Rio Grande Valley, reduced water supplies are a challenge to growers because citrus requires 35 to 48 inches of water each year and rainfall supplies only 22 to 26 inches.
Citrus growers in the Valley can increase fruit quality and production by scheduling irrigation according to soil moisture levels and crop needs and by using irrigation methods that are appropriate for local conditions.
Agronomic Characteristics of Citrus
 To manage irrigation properly, growers need to have a good understanding of how the soil type affects citrus growth.
Citrus trees start bearing fruit from the third year after planting, but economic breakeven is usually delayed until the eighth year.
Citrus trees flower in February and March, but less than 6 percent of the flowers produce mature fruits.
Fruits mature in 7 to 12 months after flowering, depending on such factors as the variety and water availability.
Harvest in the Lower Rio Grande Valley starts in late September or October and ends in May or June.
During maturation, the amount of acid in the fruit decreases while sugar and aromatic substances increase, improving fruit quality.
Because low temperatures increase the concentration of sugars within the fruit, many Valley growers do not begin harvest until after the first winter cold spell.
The color of the fruit is not an indicator of fruit maturity.
Fruit is usually harvested "green," depending on market demand and price.
Postharvest treatments can enhance ripening.
Citrus trees need a period of rest or reduced growth to flower.
In the subtropics, cool winters induce flowering, but without sufficient chilling, flowering can be induced by water deficits.
In the Valley, this chilling period generally occurs from November to January  when temperatures and rainfall decrease.
Juan Enciso, Julian W.
Sauls, Robert P.
Wiedenfeld and Shad D.
Nelson Associate Professor and Irrigation Engineering Specialist; Professor and Extension Horticulturist; Professor, Department of Soil and Crop Sciences; Associate Professor of Horticulture, The Texas A&M System
 Citrus Yield and Water Use
 Fruit yield is highly affected by the amount of water received in both current and previous growing seasons.
When the plants do not get enough water, growth is
 slowed, young fruits fall and the mature fruit lacks sugar and quality.
Also, vegetative growth is reduced, limiting the number of new fruitbearing branches.
The roots and leaves do not develop properly, which affects the number and size of the fruit and accentuates alternate bearing, which is high production one year followed by lower production the next year.
Figure 1.
Average monthly evapotranspiration , evaporation and rainfall between 1995 and 2003 in the Lower Rio Grande Valley.
Adequate water amounts are especially important during flowering and fruit set to achieve good production.
Yield is reduced when water deficits of more than 33 percent occur during bloom, fruit set and rapid vegetative growth in the spring; deficits of 66 percent can be tolerated during the summer, fall and winter.
Therefore, water stress should be avoided from February to June but can be somewhat tolerated from June through January.
According to research in 1986 by the Food and Agriculture Organization of the United Nations, good yields of citrus are:
 Oranges: 400 to 550 fruits per tree per year, corresponding to 10.1 to 16.1 tons per acre per year.
Grapefruit: 300 to 400 fruits per tree per year, corresponding to 16.2 to 24.3 tons per acre per year.
Lemons: 12.1 tons to 18.2 tons per acre per year.
Mandarin: 8.1 tons to 12.1 tons per acre per year.
Local conditions affect yields.
The Texas AgriLife Extension Service reported typical yields for three management levels in the Valley for an orchard density of 115 to 120 trees per acre.
Table 1.
Tons of citrus produced per acre under three levels of management in the Lower Rio Grande Valley.
Sauls, 2005.
Grapefruit	Early Oranges	Valencia
 	Age	Fair	Average	good	Very	Fair	Average	good	Very	Fair	Average	good	Very
 3	1	3	6	1	2	4	1	2	3
 4	3	6	10	2	5	7	2	3	4
 5	5	9	14	4	7	11	3	4	7
 6	7	14	19	5	10	13	4	7	10
 7	8	18	23	7	13	16	5	9	13
 8	10	20	26	8	15	19	6	11	15
 9	11	22	27	9	17	22	7	13	17
 10+	12	23	28	10	18	24	8	14	18
 Water is the most limiting factor for crop production.
A close relationship between production and water applied is called water use efficiency.
The Food and Agriculture Organization reported that water use efficiency for citrus is 428 to 1,070 pounds per acre-inch with a fruit moisture content of about 85 percent.
Impact of Water Requirements and Irrigation Scheduling
 Depending on weather conditions and ground cover, citrus requires from 35 to 48 inches of water per year; grapefruit requires more water than do oranges, lemons or limes.
Water is removed from a crop by evapotranspiration , which is the removal of water that evaporates or transpires from the plants and from the underlying soil.
In the Valley, more water is lost through this process than is gained through annual rainfall.
This means that supplemental irrigation is needed for citrus crops in the Valley.
A formula has been devised to estimate the amount of water needed by a particular crop under specific local conditions.
The formula uses the rate of evapotranspiration from a standard "reference" crop, such as grass that is actively growing.
This is called the reference evapotranspiration.
To calculate the evapotranspiration from a specific crop such as citrus, multiply the reference evapotranspiration  by the crop coefficient.
Crop coefficients for citrus are shown in Table 2.
The crop coefficient varies according to the crop's growth stage.
The reference evapo-
 Table 2.
Citrus crop coefficients.
Jan	Feb	Mar	Apr	May	June	July	Aug	Sep	Oct	Nov	Dec
 70% canopy	0.65	0.65	0.65	0.65	0.60	0.60	0.60	0.60	0.65	0.65	0.65	0.65
 50% canopy	0.60	0.60	0.60	0.60	0.55	0.55	0.55	0.55	0.60	0.60	0.60	0.60
 20% canopy	0.45	0.45	0.45	0.45	0.40	0.40	0.40	0.40	0.50	0.50	0.50	0.50
 Ground cover or weeds
 70% canopy	0.75	0.75	0.75	0.75	0.70	0.70	0.70	0.70	0.75	0.75	0.75	0.75
 50% canopy	0.75	0.75	0.75	0.75	0.75	0.75	0.75	0.75	0.75	0.75	0.75	0.75
 20% canopy	0.80	0.80	0.80	0.80	0.80	0.80	0.80	0.80	0.85	0.85	0.85	0.85
 Locally developed crop coefficients
 70% canopy	0.6	0.6	0.7	0.7	0.7	0.7	0.7	0.7	0.7	0.6	0.6	0.6
 Table 3.
Crop water requirements considering an average of 9 years of data  and using local crop coefficients in the Lower Rio Grande Valley.
Month		ET	ref	citrus	Kc		citrus		Rain		Rain
 Jan	3.4	0.6	2.1	0.2	1.9
 Feb	3.7	0.6	2.2	0.4	1.8
 Mar	5.0	0.7	3.5	1.5	2.0
 Apr	5.9	0.7	4.1	1.3	2.8
 May	7.1	0.7	5.0	1.3	3.7
 June	7.2	0.7	5.0	2.4	2.6
 July	7.8	0.7	5.5	1.9	3.6
 Aug	7.5	0.7	5.2	2.5	2.7
 Sep	5.8	0.7	4.1	5.0	0.0
 Oct	4.9	0.7	3.4	3.4	0.0
 Nov	3.8	0.6	2.3	1.8	0.5
 Dec	3.1	0.6	1.9	0.4	1.5
 TOTAL	65.3	43.8	22.1	23.1
 transpiration varies throughout the year.
Figure 1 shows the rainfall and evaporation during an average year in the Lower Rio Grande Valley.
If the soil has a ground cover such as grass or weeds, more water will be lost through evapotranspiration than that lost from bare soil, and the crop coefficient will rise.
Citrus in orchards with full grass cover can use 45 percent to 105 percent more water than can citrus in bare soil.
The crop coefficients are slightly lower at midseason than at the beginning and end of the season because the plants' stomata, or pores, close during periods of peak evapotranspiration (Table
 Table 3 lists irrigation guidelines for citrus that are based on average conditions for 9 years in the Lower Rio Grande Valley.
In an average year in the Valley, citrus crops with 70 percent canopy and ground cover require about 44 inches of water; about half this amount is supplied by rainfall.
To schedule effective irrigation, producers must know the properties of the soil and the amount of water stored in it.
A balance sheet approach similar to a check register can be used to keep track of the amounts added through rainfall and irrigation and removed through crop water use or evapotranspiration.
Depletion percentages can be measured directly or estimated.
Both methods require information about a crop's rooting depth and the soil's moisture holding capacity.
Citrus roots can extend to 6 feet and, in some cases, as much as 30 feet.
Roots extract most of the water in the first 2 feet; they grow better in sandy soils that have less clay.
Studies conducted in Spain found that citrus takes from 60 percent to 80 percent of its water from the upper 20 inches of the soil.
Table 4 shows the water-holding sandy loam capacities for the top 4 feet of differHidalgo sandy ent soils in the Lower Rio Grande clay loam Valley.
Water availability varies with Rio Grande soil depth.
For example, the Hidalgo silty loam sandy clay loam soil can hold up to 0.17 inches of water per inch of soil to a depth of 28 inches; it can hold up to 0.20 inches of water per inch of soil between depths of 28 and 80 inches.
The same soil can hold between 3.8 and 8.2 inches of water in 4 feet of soil.
Producers in the Lower Rio Grande Valley use various sensors to measure soil-moisture depletion levels.
The most commonly used are granular matrix sensors, such as Watermark soil moisture sensors from Spectrum Technologies, Inc., of Plainfield, Ill.; capacitance probes such as ECH2O probes from Decagon Devices, Inc., of Pullman, Wash., and EnviroSCAN soil moisture sensors from Sentek Sensor Technologies, Australia.
During 2004, two Valley farmers installed EnviroSCAN sensors, which relayed soil moisture information through a modem to the Internet.
After the sensors scanned the soil to a depth of 4 feet, the growers could monitor the soil water levels, enabling them to manage their drip and micro-irrigation systems more precisely.
These technologies are being evaluated and offer good potential for practical use.
The cost of these devices varies dramatically, with Watermark sensors at the low end and EnviroSCAN at the high end.
Table 4.
Properties of soils in the Lower Rio Grande Valley.
Other new technologies are less useful for growers.
Neutron probes and time domain reflectometry instruments are used to measure the volume of water in the soil.
These instruments have been used only for irrigation research in the Lower Rio Grande Valley.
They are impractical for most growers because they usually require calibration and are expensive and complicated to operate.
Also, neutron probes require radiation licensing and radiation monitoring for safety.
Soil	Available	Water available
 Soil series	horizons	water capacity	in the top 4 ft
 		
 Lyford sandy	0-11	0.18-0.24
 clay loam	11-48	0.16-0.21
 clay loam	15-65	0.10-0.18
 However, growers throughout the Valley have used sensors to measure soil moisture tension.
As soil moisture tension rises, plants have more difficulty extracting water.
Tools such as tensiometers and Watermark sensors are relatively inexpensive.
Watermark sensors can measure a wider tension range  than can tensiometers, which read only to 60 centibars.
Centibars measure the tension in which the water is held by the soil.
The higher the tension reading, the drier the soil.
Inexpensive sensors such as Watermark can be installed at different depths and in different locations to test soil variability.
Because moisture availability includes the effects of soil texture, the readings need not be adjusted for soil type; however, the readings can be affected by soil salinity.
Tension measurements tend to remain low for extended periods as plants absorb water from the soil, then rise rapidly as available moisture levels drop.
Irrigation becomes necessary when soil moisture tension in the root zone reaches between 30 and 60 centibars.
The Watermark sensor has been observed to be slow, sometimes taking about 12 hours to show from dry to wet.
Another potential problem can be caused by the placement of the sensor in relation to the trunk of the tree and the irrigation emitter.
Start irrigation when it is not yet completely dry to allow some time for the sensor to catch up and avoid tree stress.
To reliably measure conditions in the orchard, install the soil water sensors in several locations and at different depths, and record the sensor measurements regularly.
The responsiveness of the Watermark sensors can vary, depending on the irrigation method used.
These sensors respond faster to flood irrigation than to drip or microjet spray irrigation practices.
The management allowable depletion is the deficit point at which irrigation should be triggered.
In citrus, irrigation can be triggered when the crop depletes about 55 percent to 60 percent of the soil water stored in the root zone.
For example, for a Hidalgo sandy clay loam soil with waterholding capacity of 8.2 inches and a management allowable depletion of 60 percent, irrigation is needed at the point when 4.9 inches  has been used.
Table 5 shows the corresponding number of irrigations needed for a sandy clay loam in Hidalgo County with
 holding capacities of 8.2 inches and 60 percent allowable depletion.
Citrus growers in the Lower Rio Grande Valley commonly flood irrigate from five to seven times per year.
However, the number of irrigations will be affected by the weather, soil type and water availability.
The balance sheet approach assumes that a plant can equally access all available moisture between saturation and permanent wilting point.
This is an accurate assumption when soils are wet.
However, as soil dries, plants have more difficulty extracting water, which decreases growth rates.
Salinity and Crop Production
 Salinity is measured in millimhos per centimeter.
Water from the Rio Grande has moderate salinity, ranging between 1.0 to 1.65 mmhos/cm.
At Rio Grande City, the salinity is less than 1.2 mmhos/cm, with the highest values of 1.2 mmhos/ cm occurring between April and June.
The levels drop below 1.0 mmhos/cm  during the rest of the year.
Downstream, salinity levels increase: At the Mercedes Irrigation District, salinity ranges from 1.0 to 1.5 mmhos/ cm, reaching 1.6 mmhos/cm during part of November.
Good soil drainage minimizes the effects of salinity.
Heavy, slow-draining soils are poor for citrus production.
To help the salt leach from the soil and improve drainage, some Lower Rio Grande Valley producers practice deep chiseling between citrus rows.
Bad drainage also can cause the accumulation of sodium or other salts including boron and chlorine.
Citrus is sensitive to boron concentrations of 0.3 to 1.0 parts per million.
Citrus yields drop by 10 percent when soil salinity increases to 2.3.
The soil salinity is measured by extracting water from a soil saturated paste.
At higher soil salinity levels, the yields drop even more: by 25 percent at the 3.3 salinity level, 50 percent at the 4.8 level and 100 percent at 8 mmhos/cm.
Saline irrigation water also reduces citrus yields by 10 percent at 1.6 mmhos/cm.
Irrigation for Freeze Protection
 Citrus trees grow best when the temperature is 73.4 degrees F to 86 degrees F.
Growth
 Table 5.
Number of irrigations for citrus with 70 percent canopy in a Hidalgo sandy clay loam soil with 60 percent management allowable depletion and holding capacity of 8.2 inches in 4 feet of soil depth.
Figure 2.
Traditional irrigation with sloping borders and earth canals.
One of the main problems of earth ditches is that they can break, spilling water out of the area to irrigate.
slows in temperatures above 100.4 degrees F  and below 55.4 degrees F.
Active root growth occurs when soil temperatures are higher than 53.6 degrees F.
Most citrus species tolerate light frost for short periods only and can be injured by temperatures of 26.6 degrees F  over several hours.
Temperatures of 17.6 degrees F  cause branches to wither, and 14 degrees F  generally kills the tree.
Flowers and young fruits, which are particularly sensitive to frost, are shed after very short periods of temperatures slightly below freezing.
Dormant trees are less susceptible to cold injury.
Strong wind causes flowers and young fruits fall to easily; provide windbreaks when necessary.
Microsprinklers can protect young trees during freezing nights, especially when water is continuously applied to the lower part of the trunk, because as water freezes, heat is released.
When the application rate is high enough, the freezing water will maintain the trunk, the bud union and lower branches at temperatures near freezing.
To protect trees using microsprinklers, place the sprinklers 1 to 2.5 feet from the trunks in the upwind side of the trees.
Place insulating tree wraps around the trunks of young trees to slow the rate of temperature decline and protect the trunks; use the wraps in combination with sprinkler irrigation.
A microsprinkler irrigation rate of 20 gallons per hour is more effective for cold protection.
Turn on the water before the temperature reaches 32 degrees F , making sure the microsprinkler is placed correctly.
Continue running the microsprinkler all night during the freeze.
Evaporative cooling will cause greater damage if the irrigation system fails when the temperature is below freezing.
Therefore, do not to turn on the system if the pumping system is unreliable.
The system can be stopped once temperatures rise above 33.8 degrees F.
Irrigation Practices in the Lower Rio Grande Valley
 Historically, producers in the Valley have used flood irrigation to water citrus crops.
An extensive network of canals and large-diameter underground pipelines use
 gravity flow to deliver large volumes of water from the Rio Grande to fields over short periods of time.
Because the Valley generally slopes toward the northleast, away from the river, little pumping is necessary except to lift the water from the river to the canals.
Present water restrictions are causing interest in more efficient irrigation technologies.
Properly managed flood irrigation can be efficient.
During delivery, losses occur because of evaporation and leaks in canals and pipelines.
Irrigation canals that are unlined earthen ditches allow water to seep out.
Lining canals and using pipe to deliver water can reduce these losses and provide better control of the irrigation.
The most common irrigation method for citrus on the farm is flood irrigation with graded borders.
To irrigate efficiently with flood irrigation, level the land to the appropriate grade before establishing the orchard and control water applications with valves or structures.
Citrus groves that are bordered and properly graded do not produce runoff.
To distribute water faster and more efficiently, install alfalfa or orchard valves at different locations in the orchard use gated or flexible pipes.
Build permanent borders every two rows, with an irrigation valve between each pair.
Temporary borders may be single or double row, depending on the grower's preferences.
For better control and faster irrigation, build one border per row of trees.
The border edge is about 1 foot high.
To reduce the irrigated area, place temporary borders along one side of the rows of young trees.
This method, called strip flooding or narrow-border flood, allows faster water advancement.
A farmer can receive 1,346 gallons of water per minute or more to irrigate a field of 40 acres.
One "head" of water per outlet is equivalent to 3 cubic feet per second, or 1,346 gallons per minute.
Weed control methods affect the choice of irrigation method.
Permanent borders need trunk-to-trunk herbicidal weed control, while temporary border irrigation requires tillage to control weeds in the row middles.
In both cases, apply the herbicides beneath the tree canopies.
Use herbicides or tillage implements to control weeds in the row middles of orchards that are irrigated with microsprayer or drip irrigation systems.
Figure 3.
Border irrigation with alfalfa  valves.
Each valve covers one border with two rows of trees.
Figure 4.
Using a narrow-border flood can conserve more water than can traditional flood practices in the orchard.
Figure 5.
Irrigation of citrus crops with drip irrigation.
The top photo shows two drip lines per tree row and weeds that are climbing the tree.
The bottom photo shows an implement used to apply herbicide close to the tree to control weeds.
In deciding when to irrigate, producers also must consider the need to order water several days in advance and the wait for the water delivery.
Depending on the location and the irrigation district, a reservoir may be needed to store water for frequent irrigations using microsprinkler irrigation or drip irrigation systems.
Improving Citrus Irrigation Efficiency
 Periods of drought have reduced some water allocations in the Lower Rio Grande Valley.
Pressurized irrigation systems can be used to increase production per unit of water applied and to maintain orchards during droughts.
These pressurized systems have one or more emitters at each tree, which allows for the uniform injection of fertilizers and some agrochemicals.
This improves plant nutrition and increases productivity per unit of water applied, partly compensating for the higher initial cost of the system and the variable costs such as energy and maintenance.
The most common pressurized systems are drip and micro-irrigation.
On Lower Rio Grande Valley farms with drip irrigation systems, the most common method is to run the drip lines parallel to the tree rows.
Young orchards can be irrigated with a single line per row, but older trees require two lines-one on each side of the row-because they need more water.
The initial system design must allow for the additional line of emitters to ensure that enough water can be supplied to both lines in the future.
The drip emitters are generally spaced every 3 feet and apply about 1 gallon per hour per emitter.
Drip irrigation systems require filtration to prevent emitter clogging.
Many farms have settling ponds, where sediments and small particles from the pumped canal water can settle out.
The water is then filtered before entering the irrigation lines.
A drip irrigation system can save water because it wets only about 33 percent to 50 percent of the surface area.
In addition, a drip system can apply fertilizer quickly, efficiently and uniformly.
Weed control in the wetted area can be difficult because frequent irrigations cause the herbicides to leach below the soil surface, where they are needed.
Vines growing into and covering the tree are a serious problem.
A good
 herbicide program is especially vital with these systems, and growers should include less soluble herbicides in the weed control program.
Fortunately, some herbicides with reduced solubility can be applied through the irrigation system, placing the herbicide where it is most needed.
Micro-irrigation and Microsprayer Irrigation Systems
 A microsprinkler has moving parts, and it sprays one or two streams of water as it rotates.
Its deflectors move as they are hit by the water being sprayed.
In contrast, microsprayers have no moving parts; the water is deflected into several discrete streams as it is sprayed out.
In the Valley, moving parts have a tendency to clog when fine, wind-blown soil particles accumulate on the emitter.
Microsprayers are connected to a polyethylene lateral line through a micro-tube, often referred to as "spaghetti tubing," and are held in place by a plastic stake.
They can apply from 3 to 30 gallons of water per hour; the higher the flow rate and pressure, the larger the wetted diameter.
However, large orchards may need to be subdivided into two or more zones and irrigated separately.
Microsprayer irrigation sprays a fan of water over the soil.
The microsprayer can wet a diameter of 12 to 18 feet depending on the tree skirt.
The spray or mist is produced by a flat spreader and a small orifice operating at high pressure.
Popular microsprinklers can apply 24 to 28 gallons per hour at a pressure of about 30 psi.
These devices contain a deflector which allows water flow to be concentrated around young trees to a diameter of about 8 feet.
Without the deflector the wetted diameter can be up to 22 feet to irrigate larger trees.
The choice of irrigation technology and scheduling method depends on economic considerations as well as the location, situation and preferences of each grower.
Producers should also seek input from their irrigation district about the feasibility of installing a particular system in their fields.
The WaterSmart initiative has 14 different grant programs.
The two that apply to water districts are the water energy efficiency grants.
The larger grant would include funds for canal lining, piping, and other applications that apply to irrigation districts.
The smaller version of the same grant includes similar applications, but funding is $250,000.
The grants are being opened up in the summer of 2023.
The plot was kept free of weeds by spraying glyphosate in early February, and handweeding thereafter.
No water or fertilizer was provided.
Emergence of both blue and valley oak species averaged over 95% for this trial.
Only the March-sown blue oak acorns had less than 90% emergence by the middle of May.
However, sowing date greatly influenced the timing of seedling emergence.
The earlier the acorns were sown, the earlier they came up and started to grow.
Blue oaks emerged over a wider interval than valley oaks.
The average emergence date of blue oaks from the November SOWing was more than two weeks earlier than for valley oaks.
For the March sowing, valley oaks came up an average of 11 days later.
Only 50% of the blue oaks sown in March germinated, compared with 90% of valley oaks.
Blue oak planting trial
 In April 1987, one-year-old blue oak seedlings, raised in small plastic containers, were planted on a 5-foot spacing in a weed-free field.
Planting holes were dug 3 feet deep with a power auger, and 21-gram fertilizer tablets  were placed below the roots.
Seedlings were drip-irrigated from planting time until August, at 2 gallons of water once a week for the first 2 months, and 2 gallons every other week thereafter.
Screen cages were placed over the seedlings to protect them from grasshoppers, mice, and deer.
At the time of planting, the 120 seedlings were randomly divided into four groups of 30.
Each group received one of the following treatments: shade ; mulch 3-foot square of roofing felt around the seedling); shade plus mulch; and a control.
At the end of the first growing season, 95% of the seedlings had survived.
Growth varied greatly, ranging from dieback of the initial stem to more than 2 feet.
Average height growth of all surviving seedlings was over 10 inches.
There were no significant differences in either survival or height growth among the four treatments.
Growth of all seedlings in 1988 was even more rapid and vigorous, even though no irrigation was provided.
By late August.
seedlings averaged 44 inches tall and had grown, on average, 2.5 feet during their second season.
In general, seedlings that remained small and stunted during the first season also grew slowly the second year.
There were still no significant differences among treatments.
This research demonstrated that, with proper treatment and planting of acorns and seedlings, California blue and valley oaks can be successfully propagated.
If blue oaks are to be seeded directly, acorns should be collected during September or early October while they are still on the trees.
After collection, they should be refrigerated immediately (in 1.75-mil zip-lock
 Drainage reduction potential of furrow irrigation
 The most practical way to dispose of irrigation drainage water in the San Joaquin Valley is to reduce the volume of the water at its source through better irrigation management.
Upgrading furrow irrigation systems and cutting run lengths in problem areas reduced drainage 60% to 80%.
storage bags) to prevent drying and kept cold until they are planted.
Both blue and valley oak acorns can be planted from early fall  until midwinter.
Early sowing is favored.
In dry years, early initial growth may give seedlings a better chance to become established before soil moisture becomes limiting.
Subsurface drainage results from overirrigation  and nonuniform irrigation.
Because of nonuniformity, if the least-watered areas receive enough water to replace soil moisture de-
 These results have important implications for the production of native oaks in bareroot nurseries.
Early-season sowing should allow nursery operators to produce larger seedlings in a shorter time.
Blue oak seedlings can be successfully established by directly planting small container plants.
Excellent survival and vigorous growth can be achieved if seedlings are planted in deep augured holes and irrigated and fertilized during the first summer after planting, and if the area around them is kept free of competing vegetation.
Damage to seedlings from insects, mice, and deer can be prevented by caging with aluminum window screen.
Additional measures to protect seedlings from livestock may be necessary in grazed areas.
Research on the artificial regeneration of oaks is continuing.
Investigations include seedling container size, fertilization, effects of acorn size, direct-seeding acorns versus planting seedlings, and irrigation practices.
Douglas D.
McCreary is Natural Resources Specialist, Integrated Hardwood Range Management Program, University of California Sierra Footbill Range Field Station, Browns Valley.
pletion, other areas must receive more, and subsurface drainage occurs.
Keys to drainage reduction are thus to improve the uniformity of application and reduce the amount of water applied by improving application efficiency.
A source of nonuniformity in furrow irrigation is the advance time-the time it takes for water to flow from the upper end of the field to the lower.
Soil infiltration rate, length of run, furrow inflow rate, surface roughness, slope of the field, and furrow cross-sectional shape all affect advance time, but the infiltration rate has the greatest influence.
The advance time plus the time required for water to infiltrate to a desired depth at the end of the furrow is the set time.
Advance time is easily measured
 and is used to assess the effect of system changes on the uniformity of infiltrated water.
A second source of nonuniformity is variability of the soil intake rate in different areas of the field.
This includes differences in soil texture, random variability of the infiltration rate within a soil texture, and variability caused by differences between wheel and nonwheel furrows.
The extent of this variability is usually unknown.
For one soil texture, however, a UC study showed distribution uniformity  to be about 68%.
Nonuniformity can also result from different individual furrow inflow rates during a set, variability in the field inflow rate during
 irrigation, and slope variability within a field.
Different day and night set times also contribute to field-wide nonuniform water applications.
Ways to reduce drainage
 Subsurface drainage in furrow irrigation systems can be reduced by upgrading existing systems, converting to surge irrigation
 or level basin irrigation where appropriate, and changing set times.
Furrow irrigation systems can be upgraded by shortening the length of run, increasing the inflow rate, improving the slope uniformity, and reducing the surface roughness and infiltration rate by furrow compaction.
These measures cut down the advance time and improve uniformity.
TABLE 1.
Subsurface drainage, surface runoff, and set times for site ST
 Flow	Run	Subsurface	Surface	Set
 rate	length	drainage	runoff	time
 gpm	mile	inches	inches	hours
 37	0.5	2.5	1.1	22
 0.25	1.0	3.4	12
 0.125	0.4	8.4	9
 43	0,5	1.6	1,7	19
 0.25	0.7	4.4	11
 0.125	0.3	10.2	8
 56	0.5	1.4	2.0	15
 0.25	0.6	4.6	9
 0.125	0.3	11.5	7
 TABLE 2.
Performance characteristics, site ST
 Inflow	Run	Application	Distribution
 rate	length	efficiency*	uniformity
 gpm	mile	%	%
 37	0.5	76	78
 43	0.5	83	82
 56	0.5	86	84
 Assumes recirculation of surface runoff.
Does not account for soil variability.
TABLE 3.
Subsurface drainage, surface runoff, and set times for site BU
 Flow	Run	Subsurface	Surface	Set
 rate	length	drainage	runoff	time
 gpm	feet	inches	inches	hours
 18	1,440	3.3	0.2	17
 720	0.8	2.1	8
 480	0.4	4.3	6
 25	1,440	4.5	0	14
 720	0.9	1.9	6
 480	0.5	4.1	4
 34	1,440	4.3	0.1	10
 720	1.1	1.7	4
 480	0.6	3.5	3
 TABLE 4.
Performance characteristics, site BU
 Inflow	Run	Application	Distribution
 rate	length	efficiency'	uniformity
 gpm	feet	%	%
 18	1,440	58	69
 25	1.440	51	66
 34	1,440	54	67
 .
Assumes recirculation of surface runoff.
Does not account for soil variability.
Their effects on uniformity due to soil variability are unknown.
However, shorter run lengths may improve this uniformity if there are substantial differences in soil texture.
One UC study found that compaction of nonwheel furrows may reduce differences between wheel and nonwheel furrows.
The two-year study reported here entailed gathering irrigation data to field-verify computer models of the performance of a furrow irrigation system.
Information was collected for three furrow inflow ratesinflow and outflow, advance times, depth of flow and furrow cross-sectional shapes-and field length and slope.
This information, coupled with the computer model, was used to assess the potential of upgrading measures to reduce drainage.
This field, clay loam with a saline high water table, consisted of a half-mile run length with a 0.16% slope.
Furrow inflow rates used for the evaluation were 37 gpm , 43 gpm, and 56 gpm.
Data were collected for the preirrigation, first seasonal irrigation in June, and the last irrigation in August.
Smaller furrow inflow rates were used for the last irrigation.
Soil moisture depletion was about 6 inches, and there was about 2.5 inches of drainage at the normal inflow rate for the half-mile run.
Reducing the run to 1/4 mile lowered the drainage volume by 60% to about an inch.
A further reduction to 1/8 mile reduced drainage to about 0.4 inch, or 16% of normal.
Increasing the furrow inflow rate also reduced subsurface drainage.
For the halfmile run, the drainage volume for 43 gpm was about 64% of the normal, while that of 56 gpm was about 56%.
A key to drainage reduction when changing run lengths or furrow inflow rates is to reduce the set time, or overirrigation will occur.
Normally, it takes about 22 hours for water to infiltrate 6 inches in the lower end of the field.
About 12 hours are needed with a 1/4-mile run.
Set times have to be adjusted for increased furrow inflow rates or there will be more subsurface drainage and surface runoff.
A major problem with furrow irrigation is that losses as subsurface drainage and surface runoff are competitive: Reducing one increases the other.
Shortening the run increases the surface runoff, particularly for runs of less than 1/4 mile.
Surface runoff can be returned to the distribution system, recirculated on the field being irrigated, or used on downslope fields.
If the runoff is recirculated, it has to be used to irrigate for a set  independent of the district supply, or the surface runoff will become subsurface drainage.
Cutback irrigation, in which the inflow rate is reduced after advance to the end of the field, can reduce surface runoff.
It can present problems in dealing with surplus water, however, unless the district flow rate into the field can also be reduced.
The effect of these drainage reduction measures on performance characteristics is shown in table 2.
Uniformity due to intake time differences and application efficiency increased considerably when the run length was decreased to 1/4 mile.
Further decreases improved performance only slightly.
Analysis of the other irrigations showed that most of the subsurface drainage came from preirrigation.
Little drainage occurs after preirrigation because of the seasonal decrease in the soil infiltration rate.
The basic infiltration rate of the preirrigation was about 0.15 inch per hour, compared to 0.07 and 0.02 inch per hour for the June and August irrigations.
Run length at the BU site, a sandy loam soil with a high water table, was 1,440 feet with a 0.11% slope.
Furrow inflow rates of 18 gpm , 25 gpm, and 34 gpm were used during the evaluation.
Only the first seasonal irrigation was evaluated.
Soil moisture depletion was assumed to be 4 inches for this analysis.
Under normal conditions, subsurface drainage was about 3.3 inches.
Reducing the run length by half reduced subsurface drainage by 76% to about 0.8 inch.
Run lengths a third  of the original run reduced drainage by 88%.
As with site ST, surface runoff increased at an increasing rate as the run length decreased.
This site, however, required much shorter run lengths to substantially reduce drainage than site ST did, mainly because of its higher intake rate.
At 18 gpm, the set time must be reduced to about 8 hours when reducing the run by half.
Furrow inflow rates had little effect on subsurface drainage and surface runoff.
As the inflow rate rose, the intake rate became higher due to an increased wetted area of the furrow.
This behavior offset any drainage reduction benefits of a higher uniformity of intake times along the furrow.
Reducing run lengths increased the uniformity of the intake times from 69% to 86%, and the application efficiency from 58% to 89%.
The effect of the furrow inflow rate on the intake rate at site BU was not found at site ST.
There, the same intake relationship
 with time was found for all inflow rates, because most infiltration apparently OCcurred through cracks in the soil.
Thus, the intake rate appeared to be independent of wetted area.
Once the cracks sealed, there was little additional infiltration and any effect of different wetted areas on the intake rate could not be detected.
Surge irrigation is another way to reduce drainage in furrow irrigation systems.
This method, reported in the September-October 1987 issue of California Agriculture, requires about one-third less water for advance across the field than does continuous-flow furrow irrigation.
UC studies in the San Joaquin Valley revealed a potential reduction of 30% to 40% of current drainage volumes where the infiltration rates were relatively high.
Level basin irrigation has been successfully used to reduce drainage in Arizona's Wellton-Mohawk Valley.
A UC demonstration showed the method to have potential for substantial drainage reduction in areas where large district flow rates are available  and land leveling is economically feasible.
Basin lengths should not exceed 1/8 mile.
These results show a good potential for subsurface drainage reduction in furrow irrigation systems.
The most effective measure is to reduce run lengths.
Reductions of 60% to nearly 80% appear possible by cutting the run length in half.
The effect of increasing the furrow inflow rate depended on the soil type.
Reductions of 30% to 40% appear possible with surge irrigation.
At site ST, preirrigation was the major source of subsurface drainage, and reduction measures only needed to be carried out during that irrigation.
At site BU, however, the large amount of subsurface drainage during the first seasonal irrigation suggests that drainage may be generated throughout the irrigation season, requiring seasonal implementation of these measures.
First, there have to be good estimates of both soil moisture depletion and soil infiltration rates.
Depletion information is needed to know how much water to apply.
It can be estimated from evapotranspiration where high water tables do not exist.
With high water tables, depletion must be measured directly by soil sampling, tensiometers, or neutron probe methods, which may be time-consuming and expensive.
Estimates based on evapotranspiration between irrigations will be inaccurate because
 of the upward flow of water from a shallow water table.
The intake rate needs to be estimated to know how long to irrigate.
Unfortunately, the intake rates of many Valley soils are almost impossible to estimate by conventional means, such as ring or blocked furrow infiltrometers and inflow/outflow methods.
These are too time-consuming and unreliable in cracking soils.
However, relatively simple computer models, coupled with some advance time data, offer a potential for rapidly estimating infiltration rates.
Second, the short runs, such as those required in site BU, may cause problems with field-wide operations and may be relatively expensive.
Additional conveyance ditches or pipelines and surface runoff recovery systems will be needed, increasing capital costs.
Short runs can also interfere with farming practices.
Third, these drainage reduction measures may require set times incompatible with current labor limitations.
Normally, set times of 12 or 24 hours are used because of the ease of labor management.
Other set times may be difficult to implement.
Fourth, inflexibility in an irrigation district's distribution system in responding to frequent changes in demand may limit opportunities to change set times.
However, automation of furrow irrigation, using valves designed for surge irrigation, may overcome the problems of odd set times versus labor management and district inflexibility.
Fifth, leaching requirements under saline high water tables may limit the amount of drainage reduction to less than the potential.
There is a potential for substantial subsurface drainage reduction with properly designed and managed furrow irrigation sysitems.
Existing systems can be upgraded by cutting run lengths and set times, and/or converting to surge irrigation or level basin irrigation, where appropriate.
Major problems exist in achieving the
 However, labor management and cultural practices and the management of distribution systems will need to be changed considerably.
The limits imposed by these constraints and the reduced run lengths can only be assessed with field-wide demonstrations of drainage reduction measures.
Where these practices cannot be changed, other types of irrigation systems, such as drip/trickle irrigation or linear-move machines will need to be considered.
Blaine R.
Hanson is Irrigation and Drainage Specialist, Department of Land, Air and Water Resources, University of California, Davis.
How Economic Factors Affect the Profitability of Center Pivot Sprinkler and SDI Systems
 In much of the Great Plains, the rate of new irrigation development is slow or zero.
Since the 1970s there has been a dramatic shift in irrigation methods in the Great Plains region, as center pivot sprinkler irrigation systems have become the predominant technology, having replaced much of the furrow-irrigated base.
In addition, a small yet increasing amount of subsurface drip irrigation  has been installed.
Although SDI systems represent less than 1 percent of the irrigated area, producer interest still remains high because of their greater irrigation efficiency and irrigated water application uniformity.
As irrigation systems need to be upgraded or replaced, available irrigated water sources become more scarce, and farm sizes become larger, there will likely be a continued interest in and momentum toward conversion to modern pressurized irrigation systems.
Irrigation system investment decisions will be affected by both the physical characteristics of the irrigation systems being considered and the economic environment that irrigated crop enterprises are operating within.
Key assumptions about the physical characteristics of the irrigation systems include input-output efficiencies, life span, and system investment costs.
Key economic factors include commodity prices, costs of key crop inputs, irrigation energy costs, interest rates on operating expenses, the opportunity cost of capital investments, and overall inflation in production costs.
The economic factors affecting irrigation system choices can be strongly influenced by broader macroeconomic conditions and trends in the United States and world economies.
To the degree that the volatile patterns in agricultural, energy and financial markets since the early 1970s continue or even become more pronounced, economic decisions about irrigation system investments will become more riskprone and uncertain.
This paper will discuss how volatile economic conditions in key agricultural and financial markets affect expected relative profitability of center pivot sprinkler and subsurface drip irrigation systems under crop production conditions in the Great Plains.
This analysis will use a K-State center pivot sprinkler  and subsurface drip irrigation  comparison spreadsheet  to estimate the affect of various key economic factors upon investment decisions.
K-State Research and Extension introduced a free Microsoft Excel 1 spreadsheet template for making economic comparisons of CP and SDI in the spring of 2002.
The spreadsheet has been periodically updated since that time to reflect changes in input data, particularly system and corn production costs.
The spreadsheet also provides sensitivity analyses for key factors.
Lamm, et al.,  explains how to use the spreadsheet and the key factors that most strongly affect the returns comparisons.
The online accessible template has five worksheets , the Main, CF, Field size & SDI life, SDI cost & life, Yield & Price tabs.
Most of the calculations and the result are shown on the Main tab.
Critical field and irrigation system assumptions are illustrated.
This template determines the economics of converting existing furrow-irrigated fields to
 center pivot sprinkler irrigation  or subsurface drip irrigation  for corn production.
Field description and irrigation system estimates
 Total	Suggested	CP	Suggested	SDI	Suggested
 Field area, acres	160	160	125	125	155	155
 Non-cropped field area , acres	5	5
 Cropped dryland area, acres 	30	0
 Irrigation system investment cost, total $	$73,450	$73,450	$186,000	$186,000
 Irrigation system investment cost, $/irrigated acre	$587.60	$1,200.00
 Irrigation system life, years	25	25	21	20
 Interest rate for system investment, %	7.5%	8.0%
 Annual insurance rate, % of total system cost	1.60%	1.60%	0.60%	0.60%
 Production cost estimates	CP	Suggested	SDI	Suggested
 Total variable costs, $/acre 	$517.90	$517.90	$499.85	$499.85
 Additional SDI variable costs  or savings , $/acre	Additional Costs	$0.00	$0.00
 Yield and revenue stream estimates	CP	Suggested	SDI	Suggested
 Corn grain yield, bushels/acre	Suggested	220	220	220	220
 Corn selling price, $/bushel	$3.50	$4.00	KSTATE
 Net return to cropped dryland area of field 	$38.55	$36.00	Konsas State University
 Advantage of Center Pivot Sprinkler over SDI *	$/total field each year	$876
 * Advantage in net returns to land and management	$/acres each year	$5
 You may examine sensitivity to Main worksheet  assumptions on three of the tabs listed below.
Figure 1.
Main worksheet  of the economic comparison spreadsheet template indicating the 18 required variables  and their suggested values when further information is lacking or uncertain.
The scenario analyzed in this research is a comparison of whether a center pivot sprinkler irrigation system  is more or less profitable than a subsurface drip irrigation system on 160 acres of farmland.
The CP system would irrigate 125 acres of the 160 acres of farmland, with the remaining 35 acres divided between 30 acres of non-irrigated or "dryland" cropping systems and 5 acres of noncropped area.
The SDI system would irrigate 155 acres of the 160 acres of farmland, with the remaining 5 acres used for non-
 cropped roads and access areas.
Irrigation system design and cost information is available from the authors and the K-State Research and Extension publication Irrigation Capital Requirements and Capital Costs, MF-836.
Only information that is relevant to the comparison of returns for CP and SDI systems is included in this analysis.
This excludes such factors as cost of irrigated cropland which will not vary for those acres that are irrigated under either irrigation system investment scenario.
Non-irrigated cropland returns are included because of the inclusion of dryland acreage under the CP scenario.
Average cash rental rates are included as a market-based proxy for the returns expected from farming nonirrigated cropland.
For further discussion of the assumptions used in this analysis see Lamm, et al..
Actual values used in this analysis may vary from suggested values in the Main tab of the worksheet where current prices and market conditions warrant.
Key information from the Main tab for the following analysis is as follows.
2.
Interest rate for system investment, % = 7.5%
 3.
Total variable costs, $/acre: CP = $517.90
 4.
Total variable costs, $/acre: SDI = $499.85
 5.
Net return to cropped dryland area of field  = $ 38.55
 Production cost estimates and assumptions represented in the CF tab are based on K-State Research and Extension crop enterprise budget estimates for irrigated corn in western Kansas.
Seeding rate, seeds/acre	$/1000 S Suggested	34000	34000	34000	34000
 Seed, $/acre	$2.49	$2.24	$84.66	$84.66
 Herbicide, $/acre	$31.06	$28.68	$31.06	$28.68
 Insecticide, $/acre	$35.64	$35.30	$35.64	$35.30
 Nitrogen fertilizer, lb/acre	$/lb	Suggested	242	242	242	242
 Nitrogen fertilizer, $/acre	$0.24	$0.40	$58.08	$58.08
 Phosphorus fertilizer, lb/acre	$/lb	Suggested	50	50	50	50
 Phosphorus fertilizer, $/acre	$0.44	$0.35	$22.00	$22.00
 Crop consulting, $/acre	$6.50	$6.50	$6.50	$6.50
 Crop insurance, $/acre	$37.00	$37.00	$37.00	$37.00
 Drying cost, $/acre	$0.00	$0.00	$0.00	$0.00
 Miscellaneous costs, $/acre	$0.00	$0.00	$0.00	$0.00
 Custom hire/machinery expenses, $/acre	$143.79	$150.14	$143.79	$150.14 Assumes all tillage, cultural and harvesting operations.
Other non-fieldwork labor, $/acre	$0.00	$0.00	$0.00	$0.00 Assumed covered by custom hire.
Irrigation labor, $/acre	$6.50	$6.50	$6.50	$6.50
 Irrigation amounts, inches	17	17	13	13 Assumes approximately 25% savings with SDI.
Fuel and oil for pumping, $/inch	$3.75	$5.80	$3.75	$5.80 Assumes equal operating pressures at pump site.
Fuel and oil for pumping, $acre	$63.75	$48.75
 Irrigation maintenance and repairs, $/inch	$0.60	$0.60	$0.60	$0.60
 Irrigation maintenance and repairs, $/acre	Suggested	$10.20	$7.80
 1/2 yr.
interest on variable costs, rate	7.5%	8.0%	$18.72	$18.07
 Total Variable Costs	$517.90	$499.85	These values are suggested values on Main tab.
Figure 2.
CF worksheet  of the economic comparison spreadsheet template and the current production cost variables.
Sums at the bottom of the CF worksheet are the suggested values for total variable costs on the Main worksheet.
Corn enterprise cost of production information is available from the authors and the K-State Research and Extension publication Center Pivot Irrigated Corn Cost Return Budget in Western Kansas, MF-585.
Actual values may vary from suggested values in the worksheet where current prices and market conditions warrant.
Key assumptions represented on the CF tab that are relevant to this economic analysis are listed below.
1.
Nitrogen fertilizer, $/pound of 82-0-0 = $ 0.24 /pound
 2.
Phosphorus fertilizer, $/pound of 18-46-0 = $ 0.44 /pound
 3.
Fuel and oil for pumping, $/acre inch = $ 3.75 /acre inch
 4.
1/2 yr.
Interest on variable costs, rate = 7.5% interest
 5.
Total variable costs, $/acre: CP = $517.90
 6.
Total variable costs, $/acre: SDI = $499.85
 Lamm, et al.
provides a further explanation of sensitivity analysis of physical production factors critical to the CP versus SDI investment decision in spreadsheet tabs on a) Field size & SDI life, b) SDI cost & life, and c) Yield & Price tabs.
Economic Factors Affecting CP versus SDI Investments
 The key economic factors in this decision framework which are hypothesized to have an impact upon CP versus SDI investments include commodity prices, costs of key crop inputs, irrigation energy costs, interest rates on operating expenses, the opportunity cost of capital investments, and overall inflation in production costs.
Economic analysis typically relies upon "ceteris paribus" assumptions to determine the marginal impact of any particular factor in isolation.
The following analysis will first focus on the impacts of variability of key factors separately.
A final broader analysis will be conducted in which "low" versus "high" market product price and production cost regimes are examined to understand the systematic impact of these key factors.
This systematic perspective reflects the integrated, interdependent nature of agricultural, energy and financial markets.
Corn Price Variability Impact
 Over the October 2000-December 2009 period U.S.
corn prices have exhibited great variability, with corn upfront corn futures contract prices ranging from approximately $1.90 to $7.50 per bushel.
In this analysis, CP versus SDI investment returns will be analyzed for the base budget corn price , a low price  and a high price.
The low price of $1.95 per bushel represents the current U.S.
average commodity marketing loan program
 price for corn.
The high price of $6.00 per bushel represents a basis-adjusted estimate of cash prices that would be typically available to crop producers at the high end of the 2000-2009 corn futures trading range.
In this analysis, higher corn prices tended to favor SDI systems, while lower corn prices tended to favor CP systems.
These results can also be derived from the Yield and Price tab of the K-State spreadsheet.
Table 1.
Corn Price Variation Impact on SDI versus CP Returns
 Corn Price	CP	SDI	SDI Less CP	SDI Less CP
 Scenarios	Variable	Variable	Returns	Returns
 Cost 	
 Base: $3.50 per	$517.90	$499.85		
 Low: $1.95 per bu.
$517.90	$499.85		
 High: $6.00 per bu.
$517.90	$499.85	$15,624	$98
 Natural Gas Pumping Cost Variability Impact
 Just as for other agricultural and energy-related commodities, over the October 2000-December 2009 period U.S.
natural gas prices have exhibited great variability.
Lead contract natural gas futures contract prices have ranged from approximately $2.00 to nearly $16.00 per mcf..
In the irrigated crop enterprise budgets developed by K-State Research and Extension, natural gas is the energy source used to calculate irrigation pumping costs.
Center pivot sprinkler versus SDI investment returns will be analyzed for a base budget natural gas price of $5.53 per mcf., leading to a cost of $3.75 per acre inch of water applied for pumping-related fuel and oil.
The low natural gas price to be considered is $2.00 per mcf., leading to a cost of $1.55 per acre inch of water applied for pumping-related fuel and oil.
The high natural gas price is $12.00 per mcf., leading to a cost of $7.78 per acre inch of water applied for pumping-related fuel and oil.
Natural gas price variation does not have a large impact on net returns in this analysis, causing a variation of $2 to $3 per acre in the advantage of CP over SDI systems from the base scenario.
Table 2.
Natural Gas Price Variation Impact on SDI versus CP Returns
 Natural Gas Price	CP	SDI	SDI Less CP	SDI Less CP
 Scenarios	Variable	Variable	Returns	Returns
 Cost 	
 Base: $5.53 per	$517.90	$499.85		
 $3.75 per acre inch
 Low: $2.00 per	$479.10	$470.17		
 $1.55 per acre inch
 High: $12.00 / mcf.
$588.98	$554.20		
 $7.78 per acre inch
 Nitrogen and Phosphorous Fertilizer Cost Variability Impact
 Fertilizer prices for anhydrous ammonia or NH3  and diammonium phosphate or DAP  have also been extremely variable in the most recent decade.
Over the 1999-2008 period U.S.
fertilizer prices have trended higher, with 82-0-0 prices ranging from $211 to $755 per ton of nitrogen on average per year.
During the summer of 2008 anhydrous ammonia prices reached over $1,050 per ton of nitrogen.
During 1999-2008 di-ammonium phosphate prices ranged from $227 to $850 per ton, reaching up to $1,200 per ton in the summer months of 2008.
Although the prices for these two fertilizer products are not perfectly correlated in real world markets, the low and high price scenarios for anhydrous ammonia and di-ammonium phosphate will be analyzed together.
The base 82-0-0 price is $0.24 per pound of nitrogen, and the base price for 18-46-0 is $0.44 per pound.
The low 82-0-0 price is $211 per ton or $0.13 per pound of nitrogen, and $0.11 per pound for 18-46-0.
The high 82-0-0 price is $950 per ton or $0.57 per pound of nitrogen, and $0.85 per pound for 18-46-0.
Figure 5.
United States Annual Average Fertilizer Prices: 1999-2008.
Source: USDA Economic Research Service
 Fertilizer price variation does have some impact on net returns in this analysis, favoring SDI systems when fertilizer prices decline, and Center Pivot Irrigation systems when fertilizer prices increase.
High-low N and P fertilizer price variation in this analysis accounted for a $19 per acre change in the profitability of SDI and CP systems.
Table 3.
Fertilizer Price Variation Impact on SDI versus CP Returns
 Fertilizer	CP	SDI	SDI Less CP	SDI Less CP
 Price Scenarios	Variable	Variable	Returns	Returns
 Cost 	
 $0.24 / lb 82-0-0	$517.90	$499.85		
 $0.44 / lb 18-46-0
 $0.13 / lb 82-0-0	$473.16	$455.11	$466	$3
 $0.11 / lb 18-46-0
 $0.37 / lb 82-0-0	$571.81	$553.76		
 $0.85 / lb 18-46-0
 Interest Rate Variability Impact
 Interest rates in the United States have varied from almost 0% up to 20% since 1950.
Large swings in interest rates can have sizable impacts on the cost of borrowing money.
In this analysis interest rates affect variable operating costs and the cost of borrowing money for irrigation system investments.
Even if irrigation investments are paid for without credit and associated interest expenses on borrowed money, the opportunity cost of having capital invested in one enterprise as opposed to another are relevant to an investor's decision.
Figure 6.
United States Interest Rates: 1955-2010.
Source: St.
Louis Federal Reserve Bank.
In this analysis the base interest rate used is 7.5%.
The low interest rate scenario is calculated using a 5% rate on operating funds and capital investments.
The high interest rate was set equal to 75% of the top rate of 20% charged during the period of the late 1980s early 1990s, i.e., 15%.
Interest variation does have a large impact on relative returns in this analysis.
Low interest rates near 5% benefit SDI over CP systems by $4 per acre, while historically high 15% interest rates cause CP systems to become more profitable than SDI systems by approximately $35 per acre.
Table 4.
Interest Rate Variation Impact on SDI versus CP Returns
 Interest Rate	CP	SDI	SDI Less CP	SDI Less CP
 Scenarios	Variable	Variable	Returns	Returns
 Cost 	
 Base:	7.5%	$517.90	$499.85		
 Low:	5.0%	$511.66	$493.82	$685	$4
 High: 15.0%	$536.62	$517.91		
 Cost Inflation Variability Impact
 Since the early 1900s, inflation rates in the United States have varied from a negative 1.94%  during 1920-29 to a positive 8.7% during the 1913-1919 period.
Since World War II, the decade of the 1970s had the highest annual average rate of inflation at 7.09% per year.
Periods of high inflation in the cost of consumer goods raise consumer's cost of living and tend to diminish their real inflation-adjusted buying power and personal wealth.
In the same way, inflation in agricultural production costs tend to increase cost of production and diminish crop enterprise profitability if not accompanied by increases in agricultural product prices.
In this analysis, the impacts of one time inflations of 3% and 9% in the level of crop production costs are analyzed in comparison to the base scenario of no differential cost inflation.
For this scenario, the impact of inflation in seed, herbicide, insecticide, crop consulting, crop insurance, custom hire / machinery expenses, labor costs, irrigation maintenance and repair, and non-irrigated cropland rental rates are examined.
A more thorough multi-period analysis of inflation impacts over time is called for in future research.
Increasing inflation does not have a large impact on net returns in this analysis, causing increases of $3 to $8 per acre in the advantage of CP over SDI systems from the base scenario.
Table 6.
Interest Rate Variation Impact on SDI versus CP Returns
 Inflation Rate	CP	SDI	SDI Less CP	SDI Less CP
 Scenarios	Variable	Variable	Returns	Returns
 Cost 	
 Base:	0% Inflation	$517.90	$499.85		
 Low:	3% Inflation	$533.44	$514.84		
 High:	9% Inflation	$564.51	$544.83		
 Broader "Low versus High" Price Cost Scenario Impact
 Given the interrelated nature of agricultural and financial markets, it is judicious to examine the impact of broader "low price-low cost" and "high price-high cost" scenarios upon the profitability of SDI versus CP systems.
The various inputs into these two scenarios are given in Table 7.
Whether the "low" price cost or the "high" price cost regime is in effect has a large impact on the relative returns of a subsurface drip irrigation system as opposed to a center pivot sprinkler irrigation system.
"Low" prices and costs strongly favor CP systems while "high" price cost scenarios strongly favor SDI systems.
Table 7.
"Low" and "High" Price-Cost Scenario Inputs
 Key Crop	"Low" Price-Cost	"High" Price-Cost
 1.
Corn Price, $/ bu.
$1.95	$6.00
 2a.
Natural Gas $, $/mcf.
$2.00	$12.00
 2b.
Pumping Cost, $/acre in.
$1.55	$7.78
 NH3 , $/lb.
N.
$0.13	$0.37
 DAP , $/lb.
$0.11	$0.85
 4.
Interest Rates	5.0%	15.0%
 5.
Inflation Rate in Crop	3.0%	9.0%
 Table 8.
"Low"-"High" Price-Cost Impact on SDI versus CP Returns
 Price Regime	CP	SDI	SDI Less CP	SDI Less CP
 Scenarios	Variable	Variable	Returns	Returns
 Cost 	
 "Low" Price Cost	$442.00	$433.23		
 "High" Price -	$726.07	$686.60	$8,374	$52
 Variability in United States' agricultural and financial markets impacts irrigation investment decisions in general, and the decision to purchase a center pivot sprinkler or subsurface drip irrigation system in particular.
The levels of economic variability observed in U.S.
grain, energy, crop input and financial markets have been particularly heightened in recent years.
If the recent past is a reasonable predictor of the future, then volatility in these markets is likely to continue to add risk and uncertainty to irrigation investment decisions for the foreseeable future.
This analysis was based on a decision tool developed by Kansas State University to assist farmers in their irrigation system investment decisions particularly as they consider whether to invest in center pivot sprinkler or subsurface drip irrigation systems.
This analysis focused on the impact of broader economic factors whereas earlier efforts  focused more so on system physical efficiencies, design and life span in determining the most profitable system investment.
These results indicate that economic factors and forces that tend to either increase irrigated crop income or that tend to increase costs equally between the irrigation system alternatives tend to either favor subsurface drip irrigation or are neutral to the investment decision between the two options.
Higher corn prices distinctly favor subsurface drip irrigation system returns, while lower corn prices favor center pivot irrigation systems.
Changes in fertilizer prices, natural gas prices and associated irrigation pumping costs, and inflation in crop production costs tend to have neutral or small impacts upon the relative returns to each irrigation system.
Because of the higher investment cost required for subsurface drip irrigation systems, increases in interest rates on either borrowed capital or the on the opportunity cost of invested capital in irrigation systems tend to favor investment in center pivot sprinkler irrigation systems with their lower costs of initial investment.
When grouping economic factors into "low price cost" and "high price cost" scenarios, it turns out that "low price cost" scenarios tend to favor center pivot sprinkler irrigation cost investments.
Conversely, "high price cost" scenarios of economic factors favors subsurface drip irrigation investments.
Future analysis should focus on the multi-period impacts of inflation, interest, and variability in product revenues and crop input costs.
If farmers believe the hypothesis that higher levels of volatility will continue to exist in agricultural, energy and financial markets in the future, then their irrigation investment decisions will need to be all that much more informed in regards to the physical and economic uncertainties they are dealing with.
Use: utilize full pumping capacity as much as possible in systems with end guns or corner arms, VRI type: zone, Prescription type: n/a, management intensity: low.
For soybeans in R4 end of pod elongation stage of growth, there are approximately 37 days to maturity and 9.0 water use to maturity.
For soybeans in R5 Beginning seed enlargement stage of growth, there are approximately 29 days to maturity and 6.5 water use to maturity.
For soybeans in R6 end of seed enlargement stage of growth, there are approximately 18 days to maturity and 3.5 water use to maturity.
For soybeans in R6.5 leaves begin to yellow stage of growth, there are approximately 10 days to maturity and 1.9 water use to maturity.
For soybeans in R7 beginning maturity stage of growth, there are approximately 0 days to maturity and 0 water use to maturity.
Application of liquid manure to growing crops is often a convenient and agronomically acceptable means of land application.
Center pivots have been adapted to apply a broad range of fertilizers and pesticides.
Development of large animal production facilities has added manure application to the list of materials that can be applied via center pivots.
Al-Kaisi, et al.
reported on the impact of using a center pivot to apply dilute swine lagoon water to cropland in Colorado.
However, some producers have learned the hard way that manure contains some good and some bad materials.
Occasionally, crop damage occurs as a result of application of concentrated manure presumably because of high salt concentrations.
Sprinkler application of animal manure to growing crops is a different issue than most of the salinity research that has been conducted across the country.
Soluble salt levels in liquid manures are often higher than in the saline water used for irrigation in the western U.S.
When irrigating with saline irrigation water the major problem is buildup of salt over time due to removal of the water by the crop leaving the salts behind.
However, application of manure occurs at relatively low rates per acre and the annual rainfall or irrigation tends to leach the undesirable salts from the profile between applications.
An additional concern with center pivot application of concentrated swine manure is the potential for plant damage  due to high ammonia levels.
Crop damage due to sprinkler application of manure with high EC levels occurs because of the direct contact of the salt with plant leaves and potentially the roots.
Early research reporting the salinity thresholds for induced foliar injury concluded that since damage was caused by salt absorption into plant tissues, foliar application should be avoided in hot, dry, windy conditions that produce high potential evapotranspiration.
It was noted that species varied in the rate of foliar absorption of salts, such as: sorghum < cotton = sunflower < alfalfa = sugar beet < barley < potato.
However, the susceptibility to injury was not related to salt absorption, as injury varied as: sugar beet < cotton < barley = sorghum < alfalfa < potato.
They found that leaf absorption of salts may be affected by leaf age, with generally less permeability in older leaves, and by angle and position of the leaf, which may affect the time and amount of leaf salt exposure.
Producers need to know what the safe levels are and the effect of timing on potential plant damage for corn and soybeans.
The goal of the project was to establish the safe level of salt that could be applied to corn and soybean at different stages of growth.
To accomplish this goal, a range of swine manure concentrations was applied to a growing crop in a manner that simulated application via a center pivot.
Salt and ammonia concentration data from over 2700 manure samples were obtained from a private laboratory to determine the range in concentrations that should be evaluated in the field research.
The EC level is an indication of the salt concentration in the manure sample.
Figure 1 is a summary of the samples analyzed where the median EC level was 6.7 dS m 1 with a range from 0.1 to 70 dS m .
The median ammonia concentration was 497 ppm NH4-N with a range from 0.03 to 12646 ppm NH4-N.
The field research was conducted at the Haskell Agricultural Laboratory of the University of Nebraska located near Concord, Nebraska.
The soil was a Kennebec silt loam with a pH of 7.3, and 3.5% soil organic matter.
Corn  was planted on 16 May 2003 at 27,000 seeds per acre.
Soybean  was planted on 28 May 2003 at 189,000 seeds per acre.
Field plots were 8-30 inch rows wide and 35 feet long randomly arranged with three replications.
The experimental area was irrigated with a lateral-move sprinkler irrigation system equipped with low-pressure spray nozzles mounted on top of the pipeline.
The EC of the irrigation water was 0.6 dS m  Irrigation was applied as needed to maintain greater than 50% available water in the rootzone.
Irrigation supplied 8 inches of irrigation water to both crops, and precipitation supplied 14.4 inches between 1 May and the end of the season.
Figure 1.
Cumulative distribution of electrical conductivity of liquid manure submitted for analysis to a commercial laboratory in Nebraska.
The concentrations used in this study are also presented.
Swine manure from a commercial confined feeding operation was pumped from an under-building storage pit through a 2 mm screen to remove large solids.
The liquid manure was passed through a 0.4 mm screen and then pumped to transfer tanks equipped to continuously agitate the liquid.
Multiple screening was necessary to prevent the applicator nozzles from plugging during application.
The EC of the solutions was determined using a conductivity meter  calibrated with either a 1 or 10 dS m -1 solution.
Liquid manure samples for both applications were collected from the supply tank outlet between the tank and the applicator and sent to Ward Laboratories to determine EC and nutrient concentration.
The screened manure was diluted with fresh water to create four levels of EC in the liquid manure.
The original manure had an EC level of 20.3 dS m Fresh water was added to dilute the manure down to 6.4 and 11.7 dS m 1 Fresh water with an EC of 0.6 dS m -1 was used as a control treatment.
A portable applicator was developed and attached to the boom of a Hi-Boy sprayer.
The applicator consisted of 21 nozzles arranged in a 3nozzle wide by 7-nozzle long grid with a spacing of 3 feet between nozzles in each direction.
The liquid manure application treatments consisted of a single application of four soluble salt concentrations applied at one of two selected
 Table 1.
Chemical analysis of liquid manure applied to corn and soybean at Concord, Nebraska, in 2003.
EC Level (dS m  
 0.6	6.4	11.7	20.3
 Mean	SD	Mean	SD	Mean	SD	Mean	SD
 Organic N	0.04	0.04	23.8	3.1	63.6	22.0	179.2	41.0
 Ammonium N	0.5	0.1	78.6	9.6	170.4	6.0	365.7	15.9
 P as P2O5	0.6	0.4	33.7	4.6	112.8	61.3	301.0	72.9
 K as K2O	0.9	0.1	60.7	5.6	130.6	8.8	281.5	26.3
 S	3.5	0.5	12.2	1.8	25.5	4.5	53.4	7.1
 Ca	8.9	1.0	19.4	1.6	57.9	36.2	131.6	33.0
 Mg	2.0	0.1	8.9	0.9	23.2	10.6	57.9	13.4
 Na	2.5	0.1	13.8	1.2	27.7	1.2	59.7	3.6
 Soluble salts	37.0	1.3	412.4	43.6	753.5	24.2	1303.1	65.0
 EC (dS m	0.60	0.00	6.4	0.67	11.7	0.38	20.3	1.01
 pH	7.87	0.72	6.9	0.12	6.6	0.06	6.2	0.12
 Dry matter 	0.05	0.01	0.5	0.05	1.8	0.97	4.2	0.86
 Mean EC levels for the fresh water used as a control treatment and liquid manure dilutions applied to corn and soybean.
growth stages of corn and soybean.
The first application was applied on July 2when corn was at the V7 growth stage and soybean was in the V3 stage.
Air temperatures during application were in the upper 80's.
The second application was applied on July 24 when corn was at the V14 stage and soybean was at the R1 stage.
Air temperatures during application were again in the upper 80's.
Approximately 0.5 inches of liquid manure was applied over a 10-minute period to corn and soybeans at each EC level.
Figure 2.
Applicator used to apply liquid swine manure to corn and soybean.
Each of the production indices was decreased by the 20.3 dS m liquid manure for both application times.
Soybean plant population at harvest was less with the V3 application of 20.3 dS m liquid manure than with the 0.6, 6.4, or 11.7 dS m treatments, but the R1 application did not affect plant population.
Leaf area was damaged by the V3 application but the plants recovered due to less inter-plant competition from a reduced plant population.
Thus, the final plant LAI was not significantly different between application dates except for the 20 dS m application.
-1
 Table 2.
Effects of EC level of liquid manure and application time on soybean plant populations, leaf area, dry matter production, and grain yield for the 2003 growing season.
EC Level 
 0.6	6.4	11.7	20.3	Time	EC Level	T x R2
 V33	93800	102700	92000	24300	0.001*	0.003*	0.26
 R1 3	100900	106200	102700	104400
 P > F	0.67	0.82	0.55	<0.0001
 V3	4.6	4.5	2.2	0.3	0.85	0.0001*	0.03*
 R1 	3.5	4.1	2.5	1.5
 P > F	0.06	0.46	0.48	0.03*
 Whole-plant dry matter at maturity 
 V3	7447	7893	7395	1071	0.52	< 0.0001*	0.07
 R1 	6760	7400	7044	3909
 P > F	0.50	0.63	0.73	0.01
 V3	43	39	40	5	0.12	< 0.0001*	0.02*
 R1 	42	41	38	23
 P > F	0.57	0.40	0.32	<0.0001*
 1 Statistical significance of ANOVA main effects are given by the probability of the F-test ; significant differences are indicated by * *.
2 T X R is the timing X rate interaction.
3 V3 and V7 are leaf stage at the time of application.
R1 is the stage of growth, but V7 indicates that seven trifoliates were on the plant at the time of application.
When averaged over both application timings, grain yields were the same for the 0.6, 6.4, and 11.7 dS m 1 manure applications, averaging 41 bu/ac, as compared bu/ac for the 20.3 dS m  -1 application.
Soybean with the 20.3 dS m  to 14 -1 application at R1 had much higher grain yield  than with the 20.3 dS m  application at V3.
Thus, swine manure applied at EC levels less than 11.7 dS m  -1 have little impact on final yield despite causing plant damage at lower concentrations early in the growing season.
Corn growth was less affected than soybean, and damage was detected only with the V8 application at the 20.3 dS m 1 concentration.
The V14 application caused even less damage, likely due to salt tolerance of the fully developed cuticle on the corn leaves.
The V8 application of 20.3 dS m -1 concentration caused some stunting of plants but no plant death.
Overall, the manure increased the corn yields when applied at V14  compared to V8.
Table 3.
Effects of EC level of liquid manure and application time on corn plant populations, leaf area, dry matter production and grain yield for the 2003 growing season.
EC Level 
 0.6	6.4	11.7	20.3	Time	EC Level	T X R2
 Mature plant population 
 23522	24103	22216	24684	0.12	0.11	0.04*	*
 V14	22506	25410	25555	24394
 P > F	0.33	0.22	0.005*	0.78
 Leaf area (cm2 2 plant 
 V8	5161	5211	5149	4428	0.09	0.41	0.17
 V14	4899	5667	5326	5543
 P > F	0.53	0.29	0.67	0.02*
 Whole plant dry matter at maturity 
 V8	6987	7800	6883	5784	0.15	0.04*	0.35
 V14	6894	7654	7944	6874
 P > F	0.89	0.82	0.11	0.11
 Grain yield (Mg ha-1
 V8	175	181	154	149	0.02*	0.08	0.02*
 V14	164	186	179	185
 P > F	0.28	0.65	0.02*	0.003*
 1 Statistical significance of ANOVA main effects are given by the probability of the F-test ; Significant differences are indicated by *.
2 T X R is the Timing X Rate statistical interaction.
3 V8 and V14 are leaf stages at the time of application.
Weather conditions following liquid manure application may be important to crop tolerance.
Crop damage is expected to be more severe under dry, hot, and windy conditions  with more foliar absorption of salts at higher temperatures.
Although this study was conducted during one growing season, the weather conditions were within the range of most likely conditions for the time of application.
The liquid manure applications in this study were greater than typically applied by farmers in order to induce measurable damage.
Application through a center
 pivot may keep the foliage wet and the salts soluble longer than the approximate 10 min in our study, especially near the center of the pivot circle.
Our application rate was 0.5 ac-inches, but some pivots can apply as little as 0.2 ac-in), reducing the total amount of soluble salts applied and the potential for leaf damage.
Producers can use inexpensive EC meters to estimate the potential for damage with liquid manure application.
Application of liquid manure to corn and soybean through a sprinkler system is feasible with proper management.
The results support the hypothesis that growth stage and liquid manure soluble salt concentration  influence plant damage.
Based on the conditions of this study, liquid manure with EC levels greater than 6.4 dS m should not be applied to soybean during early vegetative growth.
Liquid manure with EC levels less than 11.7 dS m  can be applied to corn and to soybean after flowering.
If the soybean plants are not defoliated as a result of liquid manure application, yield is not likely to be reduced.
Crop tolerance to soluble salt application is greater during the reproductive growth stages of the season than during the early vegetative stages.
Applications of liquid manures that keep the foliage wet for longer periods than used in this study should be done on an experimental basis to make sure phytotoxicity is not increased by increased wetting periods.
An Assessment of Storm Water Runoff Issues in Pine Bluff, White Hall, the University of Arkansas at Pine Bluff and Jefferson County
 Cooperative Extension Program, University of Arkansas at Pine Bluff, United States Department of Agriculture, and County Governments Cooperating
 An Assessment of Storm Water Runoff Issues in Pine Bluff, White Hall, the University of Arkansas at Pine Bluff and Jefferson County
 Phase II Final Rule
 What Does This Mean?
Media Filters For Trickle Irrigation In Florida
 Dorota Z.
Haman and Fedro S.
Zazueta
 Trickle irrigation is the frequent application of small quantities of water on or below the soil surface.
This type of irrigation system delivers water, nutrients, and other chemicals directly to the root zone of the plant.
Applied quantities closely match evapotranspiration and nutrient demand.
Water is distributed through emitters placed along the water delivery  pipe in the form of drops, tiny streams, or miniature sprays.
Trickle methods include drip, bubbler, and spray irrigation.
In some cases the drip line may be buried under the soil surface and called subsurface irrigation.
Trickle irrigation systems operate at low pressure; therefore, they require less energy for water pumpage when compared to other irrigation systems.
Also, because of their precise application, they conserve water and nutrients when managed well.
Primary crops for trickle irrigation in Florida include citrus, vegetables and ornamentals.
Trickle emitters use small orifices or long flow paths with small diameters to deliver the small flow rates required.
Thus, they are subject to clogging by particulate matter, organic growth, or chemical precipitate from the irrigation water.
Effective and reliable filtration is required for successful trickle irrigation operation.
Water quality is a major concern in the management of trickle irrigation systems.
Clogging of emitters by physical, chemical, and biological contaminants may create a
 significant problem for the proper maintenance of these irrigation systems.
In Florida, water to be used in trickle irrigation requires filtration and often other forms of treatment.
Particulate matter and organic growths can be removed from the water supply using proper filtration.
Often, chemical treatment is required to prevent organic growths and/or chemical precipitation in the irrigation system.
A variety of filters is available for the removal of physical clogging agents from irrigation water.
The choice of filter depend on the origin and quantity of contamination anticipated in the system, as well as the size of the irrigation system.
Screen filters should be a primary choice when water is pumped from a well where the only filtration requirement is to remove mineral particulate matter.
They are sufficient in the absence of organic contamination.
In addition these filters are usually inexpensive and easy to maintain.
To remove both particulate matter and organic growths, media filters  may be used.
Media filters are recommended when large amounts of algae or other organic contaminants are present.
Structure Of The Media Filter
 Media filters are well suited for removal of either organic or inorganic particles.
Due to their three dimensional nature, media filters have the ability to entrap large amounts of contaminants.
They do not seal off as easily and therefore
 2.
Dorota Z.
Haman, professor emeritus; Fedro S.
Zazueta, professor emeritus.
Department of Agricultural and Biological Engineering; Publication contacts: Sandra Guzman, assistant professor, Department of Agricultural and Biological Engineering, UF/IFAS Indian River Research and Education Center, and Haimanote Bayabil, assistant professor, Department of Agricultural and Biological Engineering, UF/IFAS Tropical REC; UF/IFAS Extension, Gainesville, FL 32611.
will not clog as often as filters which trap particles on their surface, such as screen filters.
Media filters used in trickle irrigation systems are the pressure type of media filters shown in Figure 1.
They consist of fine gravel and sand of selected sizes placed in pressurized tanks.
The main body of the tank contains sand, which is the active filtering ingredient.
The sand is placed on top of a thin layer of gravel which separates it from an outlet screen.
Sharp-edged sand or crushed rock is recommended for the filtering media since the corners catch soft algal tissue.
Crushed granite or silica graded into specific sizes for a particular system are commonly used porous media.
The size of particles is very important.
Too coarse particles result in poor filtration and possible clogging of the emitting devices, while too fine particles trigger unnecessary frequent backwashing of the filter.
Figure 1.
Typical Pressure Filters.
Two factors describe the media used in the filter: Uniformity coefficient and mean effective size.
Uniformity coefficient reflects the range of sand sizes within the grade.
It is desirable to keep sand particles as uniform in size as possible.
The uniform size of filtering media assures better control of the filtration, since only particles large enough to clog the emitters should be retained by the filter.
Grading in size from fine to coarse causes premature clogging of the filter, since even small particles which can be tolerated by the emitters are retained by the nonuniform pores of the media.
The uniformity coefficient is represented by the ration of the size of the screen opening which will pass 60% of the filter sand to the screen opening which will pass 10% of the same sand.
For irrigation purposes a uniformity coefficient of 1.5 is considered adequate.
The mean effective sand size is the size of the screen opening which will pass 10% of the sand sample.
It is a measure of the minimum sand size in the grade and therefore an
 indicator of the particle size that will be removed by the media.
Some examples of sand media are shown in Table 1.
It can also be seen that the quality of filtration increases with a smaller effective size of filtering media.
Flow Through Media Filters
 The design flow capacity of a media filter is expressed in gallons per minute of flow per square foot of surface area of the media normal to the direction of flow.
The filter should be sized SO it can handle the poorest water quality at a given site and provide the required flow for the functioning of the irrigation system.
The quality of irrigation water before filtration may vary with the seasons and weather conditions.
This is especially true in regards to surface water, but it can also apply to well water in some cases.
Table 2 provides data on media filter flow rates for a range of design flow rates per square foot of sand surface.
A typical design flow rate for a trickle irrigation system is about 25 gallons per minute per square foot.
Most systems are designed to allow additional filters to be added, in parallel, to increase the filtering capacity if required.
The effectiveness of a filter is a measure of its ability to remove particles of a certain size.
As shown in Figure 2 the effectiveness of filtration increases with a decreasing size of filtering media grain size.
However, smaller media size will require more frequent cleaning.
Filtration effectiveness is also inversely proportional to the flow rate through the filter.
The higher the flow rate, the lower the effectiveness of the media filter.
For example Figure 2 shows that a filter with No.
11 media at a flow rate of 23 gpm/sq.
ft.
will effectively remove particles of 75 microns.
However, the increase in flow rate to 35 gpm will decrease the effectiveness of filtration to 100-micronsized  particles.
Figure 3 shows the increase in pressure differential with time for a typical system.
Notice that the pressure loss through a clean filter  varies between 3 and 8 psi depending on the size of the media and flow rate used.
The pressure differential increases with time as contaminants accumulate and partially plug the filter.
Figure 3 was developed from field data at one location, hence for a site-specific water quality.
Then this figure, should not be used as a guide for filter selection.
The slope of all three lines presented in the graph will change depending on the quality of the water.
Therefore, filter manufacturer's specifications and water
 quality samples should be used to select a filter based on the collected contaminants.
The backflush water is discharged
 Figure 2.
Filter effectiveness as a function of filtering media and the flow rate.
Figure 3.
An example of change in pressure differential with time for three media sizes.
Cleaning Of Media Filters
 Media filters are cleaned by backwashing.
This operation consists of reversing the direction of water flow in the tank.
Clean water is usually supplied from the second tank.
The upward flow fluidizes the media and flushes
 and does not enter the irrigation system.
The backwash flow must be carefully adjusted to provide sufficient cleaning without accidental removal of the media.
If flows larger than those recommended are used to backflush the media, it is very likely that the media will be flushed from the filter by the backflow water.
Only recommended flow rates for a given media should be used.
Table 3 provides the backflush flow rates that are sufficient to backwash a filter.
Figure 4.
Backwashing mode.
Most media filters are backflushed at prescheduled time intervals or by using automatic devices based on the pressure loss across the filter.
For systems in which low quality water requires frequent backflushing, automatic cleaning is necessary to avoid problems.
Since the filter is backflushed every time the pressure differential exceeds a predetermined value, large pressure drops in the irrigation system are avoided, maintaining the system's uniformity and efficiency.
The pressure differential triggering backflushing depends on the pressure required for the proper functioning of the irrigation system.
The irrigation system pump should be able to supply enough pressure to compensate for the pressure drop through the filter just before the filter is washed.
Pump capacity must also be adequate to supply enough pressure and flow rate to flush the filter.
Also, it is advisable in a large irrigation system to use a number of smaller tanks instead of a few large ones because of the higher backwash flow large tanks require for good cleaning.
Automatic backflush systems will eliminate sudden changes in water quality which can create problems if a filter is washed only at regular intervals.
This is especially important in systems using surface water supplies with changing contamination levels.
Filtering Standards for Trickle Irrigation
 The quality of water necessary for successful operation of an irrigation system depends on the type of trickle emitter used.
Emitter manufacturers' recommendations should be used to determine filtration requirements.
In the absence of manufacturers' recommendations, a rule of thumb is to filter the water to the equivalent of a 74-micron particle size for drip irrigation.
This corresponds to 200 mesh screen.
As shown in Table 1, a media filter with a No.
11, 16 or 20 can provide this degree of filtration.
The decision on the media designation number will depend on the emitter passage size and flow rate, water quality and economic considerations.
Water supplies for trickle irrigation in Florida often contain organic and inorganic materials that will clog the system if not filtered.
Media filters are an efficient form of filtration.
They are especially recommended when large amounts of algae or other organic materials are present.
Media filters have the ability to trap large quantities of contaminants and are specifically recommended for organic particles.
Proper sizing and design of media filters provide adequate water quality and good performance of the filter.
The system must provide a recommended backwash flow for cleaning.
Media filters may not be sufficient in some cases where water contains dissolved minerals or organic matter.
In these cases other forms of water treatment and/or additional filtering may be necessary.
Screen filters should be a primary choice when water is pumped from a well where the only filtration requirements are to remove mineral particulate matter.
They will be sufficient in the absence of organic contamination and in addition they are usually less expensive and easier to maintain then media filters.
Table 4 will assist in determining the cause of poor filter performance.
During the heart of the irrigation season, we recommend keeping the available soil water level above the 50% depletion level.
To do this we recommend irrigating as the soil water level approaches 35% depletion.
This will allow a few days for the irrigation to be completed before the crop experiences any stress.
As we near the end of the season, we can push the threshold to 60% depletion.
The crop is using water at a lower rate per day so that allows us to use more than the 50% depletion and from a deeper depth.
Grant West Program Associate
 Kent Kovacs Associate Professor
 Christopher Henry Associate Professor
 Isaac Engram Graduate Research Assistant
 Arkansas Is Our Campus
 Irrigation is a critical component of the agricultural economy of Arkansas.
Among the top five agricultural commodities by farm receipts in 2012 were soybean, rice and cotton.
All of these crops depend on irrigation to increase yields.
The information in the figures and tables below comes from the 2007 and 2012 Censuses of Agriculture and the USDA 2013 Farm and Ranch Irrigation Survey.
The purpose of this
 fact sheet is to indicate the trends and magnitude of irrigated agriculture in the state and to provide comparisons with other states that heavily depend on irrigation.
The Mississippi Alluvial Aquifer  lies beneath the states of Arkansas, Louisiana,
 Figure 1.
The Mississippi Alluvial Aquifer
 Mississippi, Missouri, Illinois, Kentucky and Tennessee.
The aquifer extends over roughly 19,000 square miles in Arkansas.
The depth to water in the aquifer varies from 1.7 to 150 feet at the deepest section.
The shallowest depths run along the Mississippi River, while the aquifer surface gets deeper further away from the river.
The deepest area is near the center of Arkansas.
Arkansas Critical Groundwater Areas
 Critical groundwater areas defined by the Arkansas Natural Resources Commission are areas determined to have "significant groundwater depletion or degradation."
 The critical groundwater areas are concentrated in the Delta and in South Central Arkansas.
Groundwater depletion in the Delta is most significant in the Grand Prairie and at the western edge of Crowley's Ridge.
This is where water-intensive rice production is the most prominent.
Farmers in critical groundwater areas receive higher priority to qualify for state and federal cost-sharing programs and tax credits for conservation practices.
Arkansas Is One of the Leading States in Irrigated Acres
 As of 2012, Arkansas has the third largest irrigated acres, totaling 4.8 million acres.
Figure 2.
Critical groundwater areas.
Between 2007 and 2012 agricultural census years, Arkansas' irrigated base expanded by 343,220 acres.
Out of the 55.8 million acres nationally under irrigation in 2012, about 8.6 percent are located in Arkansas.
Figure 3.
Top ten states in total irrigated acres.
About three out of five cropland acres in Arkansas are under irrigation.
Arkansas' irrigated acres expanded more than all other states, with the exception of Mississippi.
In general, the Western states saw a decline in irrigated acres over the five-year period due to water supply scarcity caused by drought.
Irrigation expanded in the Southern states where water is more readily available and prolonged drought conditions are less frequent.
The percentage of irrigated acres in Arkansas counties roughly corresponds to each county's proximity to the Mississippi Alluvial Aquifer.
Arkansas' irrigated acres lie mostly in the Delta region and along the Mississippi and Arkansas rivers.
This is because those farms typically have more productive soils and water availability.
Figure 4.
Total irrigated acres by county for 2012.
Source: NASS-USDA, 2012 Census of Agriculture
 There is also a substantial number of irrigated acres in the River Valley and along the Red River.
County Irrigation Changes, 2007-2012
 Between 2007 and 2012, 17 of the top 25 counties in Arkansas experienced an expansion of irrigated acreage.
While the overall net change in irrigated acres was positive, there was much variation in growth rate between different counties.
Table 1.
Irrigation Expansion, 2007-2012.
Change in Irrigated Acres
 Ranking	State	Acreage	Percentage
 1	Nebraska	-261,986	-3,1%
 2	California	-154,495	-1.9%
 3	Arkansas	343,220	7.7%
 4	Texas	-521,253	-10.4%
 5	Idaho	65,403	2.0%
 6	Kansas	118,544	4.3%
 7	Colorado	-351,172	-12.2%
 8	Montana	-110,148	-5.5%
 9	Mississippi	283,317	20.7%
 10	Washington	-102,346	-5.7%
 Source: NASS-USDA, 2012 Census of Agriculture
 Table 2.
Top 25 Arkansas counties in 2012 total irrigated acres.
Irrigated Acres	in Irrigated Acres
 County	2012	2007	Acres	%
 Arkansas	314,596	310,745	3,851	1%
 Poinsett	310,028	262,180	47,848	18%
 Mississippi	286,923	269,564	17,359	6%
 Craighead	271,621	244,365	27,256	11%
 Clay	235,621	227,000	8,621	4%
 Phillips	231,860	245,359	-13,499	-6%
 Cross	214,710	191,622	23,088	12%
 St.
Francis	209,256	144,804	64,452	45%
 Jefferson	207,481	200,247	7,234	4%
 Jackson	206,529	178,101	28,428	16%
 Desha	202,069	229,730	-27,661	-12%
 Lonoke	199,627	211,362	-11,735	-6%
 Monroe	199,486	163,211	36,275	22%
 Chicot	197,142	141,805	55,337	39%
 Woodruff	196,986	169,456	27,530	16%
 Prairie	179,147	176,263	2,884	2%
 Crittenden	173,321	138,102	35,219	26%
 Greene	165,966	164,615	1,351	1%
 Lee	157,999	174,518	-16,519	-9%
 Lincoln	135,047	99,861	35,186	35%
 Lawrence	130,317	130,983	-666	-1%
 Ashley	70,755	90,804	-20,049	-22%
 Drew	66,873	59,337	7,536	13%
 Randolph	56,920	67,301	-10,381	-15%
 White	39,358	43,243	-3,885	-9%
 Source: NASS-USDA, 2012 Census of Agriculture
 Figure 5.
Change in irrigated acres by county, 2007-2012.
Source: NASS-USDA, 2012 Census of Agriculture
 St.
Francis, Chicot and Poinsett counties were the leading contributors to the increase in irrigated acres.
Collectively these three counties account for 167,637 acres of increased irrigation acreage, a 34 percent increase over the five-year period.
Six counties, all in the Delta, had decreases of over 10,000 acres.
Water Application Rates by State
 Arkansas ranks third among states in total volume of water applied for irrigation.
The total water applied in 2013 to Arkansas irrigated acres was 6.45 million acre-feet.
The average irrigation water applied per acre in Arkansas in 2013 was 16 inches.
This is the same rate of application as Texas but less than the 37 inches in California and more than the 12 inches in Nebraska.
Percentage of Irrigation Water by Source Type
 Nebraska, Arkansas and Texas obtain over 80 percent of their irrigation water from groundwater sources.
At 13.9 percent, Arkansas has the highest percentage of on-farm surface water used for irrigation of the five states that irrigate most.
California and Idaho use off-farm water for over 45 percent of their irrigation needs, while Nebraska, Arkansas and Texas use less than 10 percent from off-farm sources.
Prominence of Gravity Application
 Gravity application systems make up 86 percent of the irrigated systems used in Arkansas.
This is due to the large number of rice acres in Arkansas under flood irrigation and the fact that furrow irrigation is typically less expensive than sprinkler irrigation.
Flow Meter Use by State
 States that use the alluvial aquifer have 6 percent or less of irrigated acres that use flow meters.
The percentage is likely higher in Mississippi now since their 2011 metering program.
Figure 6.
Top ten states in quantity of water applied.
Total Acre-Feet of Water Applied 
 Figure 7.
Percentage quantity of water applied by source: 2013.
Figure 8.
Arkansas irrigated acreage by type of system: 2013.
Figure 9.
Percentage irrigated acres using flow meters: 2013.
The four states that rank highest in the use of flow meters draw water primarily from the High Plains Aquifer.
Irrigation in Arkansas is expanding, especially in the northeastern part of the state and along the Mississippi River.
The vast majority of Arkansas irrigation is gravity flow sourced from the Mississippi Alluvial Aquifer.
Arkansas producers have more irrigated acres and apply more irrigation water than 47 other states.
The amount of water used by the plants during the tail end of the growing season changes from crop to crop.
With different crops, it is important to know how weather conditions affect crop water use.
For instance, weather conditions will affect the water use of the beans because they tend to mature based on daylength, as opposed to corn and sorghum that mature based on growing degree days.
Thus, for corn and sorghum, hotter conditions will result in more water use per day but will also mature the crop sooner.
On the other hand, beans may use more water during hotter weather conditions but wont mature quicker, resulting in greater total water use.
NITROGEN FERTILIZATION FOR CORN PRODUCTION WHEN USING LEPA CENTER PIVOT SPRINKLERS
 F.R.
Lamm and A.
J.
Schlegel 
 A four year study was conducted with LEPA  sprinklerirrigated field corn in western Kansas on a deep, well-drained, loessial silt loam to compare nitrogen  fertilization using preplant broadcast or in-season LEPA fertigation for five different applied-N amounts.
Residual soil N levels in the soil profile, corn yields, apparent nitrogen uptake , water use, and water use efficiency  were utilized as criteria for evaluating treatment differences.
In general, results were similar for both application methods, indicating that either method is acceptable for corn production.
Corn yield, ANU, and WUE all plateaued at approximately the same level of total applied N, 180 kg/ha.
Average yields at this level was 13.8 Mg/ha.
Soil nitrate concentrations to a depth of 2.4 m for this same treatment were below 5 mg/kg at the conclusion of the study.
The results emphasize that high-yielding corn production also can be efficient in nutrient and water use.
KEYWORDS.
Sprinkler irrigation, nutrient management, nitrogen application, water use efficiency
 Low energy precision application  sprinkler irrigation is a fast-growing irrigation technology in the U.S.
Great Plains.
This system applies water as a line source  at a height of approximately 0.45-0.6 m above the soil surface.
This can be very advantageous from a water conservation standpoint, reducing both evaporation due to wind and also reduced evaporation from wetting less of the soil surface.
However, it has the potential to be an advantage or disadvantage when used in combination with fertigation.
Using proper management it could result in reduction of fertilizer use similar to reductions applied to traditional banding of fertilizers.
Used with inappropriate management, it could increase the chances for groundwater contamination, because as fertilizer would be applied in a smaller zone and then "pushed downward" by the "slug" of irrigation water.
Irrigators are already investing heavily in LEPA sprinklers.
Fertigation in combination with LEPA also is likely to be a widely utilized technology, but some producers will continue to apply N fertilizer through traditional methods.
This study compared N fertigation with LEPA sprinklers to a more conventional preplant-broadcast application method.
This is contribution no.
00-271-A from the Kansas Agricultural Experiment Station.
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of Kansas State University or the US Department of Agriculture.
This research was partially funded by the Kansas Corn Commission.
The project was conducted with field corn from 1993-1996 at the KSU Northwest ResearchExtension Center at Colby, Kansas on a deep, well-drained, medium-textured loessial silt loam.
The continental climate was semi-arid with an average annual precipitation of 474 mm and annual lake evaporation of 1400 mm.
Irrigation was scheduled using a climatic water budget.
The study area accommodated 30 plots in a randomized complete block design of 2 whole-plot treatments  and 5 sub-plot treatments  with 3 replications.
The experimental treatments were applied during the 1993 corn-growing season to develop approximately equilibrium nitrogen levels in the soil profile and crop residue before the 1994 season.
No further discussion of the 1993 season will be made.
Each plot was approximately 12 m wide and 20 m long with circular row direction running parallel to direction of center pivot sprinkler travel.
Each LEPA sprinkler effectively irrigated 2 corn rows.
All N in the study was applied as an experimental variable except for the small amounts supplied by the spring starter fertilizer application  each).
The N source, urea-ammonium-nitrate  was either preplant broadcast in one application prior to corn planting or injected in weekly increments into the center pivot lateral for LEPA fertigation.
Weekly fractional amounts to be applied were estimated from a N-use curve developed at Iowa State University.
Fertigation was begun about mid-June with the final fractional amount of N  applied in mid-August.
Water use was calculated as the sum of seasonal changes in soil water between the first and last sampling dates, irrigation, and rainfall.
Furrow dams restricted runoff.
Available soil N  was determined for each plot at the initiation and conclusion of each cropping season to a depth of 2.4 m.
The apparent nitrogen uptake  was calculated from the field biomass levels and the whole-plant N content at physiological maturity.
Grain yield was determined from a hand-harvested sample at physiological maturity.
Water use efficiency  was obtained by dividing crop yield by water use.
Precipitation during the crop period was 277, 280 and 518 mm in the respective years 1994, 1996 and 1996 compared to the 25-year mean of 315 mm.
The cumulative calculated ET was slightly above the 25-year mean of 577 mm in 1994  and 1995  but significantly below the mean in 1996.
In this study, seasonal irrigation amounts were 373, 394 and 152 mm in 1994-96, respectively, compared to a long-term normal net irrigation requirement of 391 mm.
Although the climatic conditions for the three years varied, they did represent a good range of conditions.
Residual Nitrate-N in the Soil Profile
 After four years  of continuous application of the fertilizer treatments, nitrate-N levels in the soil increased with increasing rates of applied N under both preplant broadcast application and LEPA fertigation.
In general, the nitrate concentrations were less than 10 mg/kg.
An exception for the preplant broadcast application was a 17 mg/kg concentration near the soil surface for the 260 kg/ha applied N rate.
Elevated soil nitrate concentrations  also occurred for the 200 and 260 kg/ha LEPA fertigation treatments at the 0.6 to 0.9 m depth.
This actually may indicate fewer volatilization losses with this application method which resulted in more N available to move to the deeper depth.
The nitrate concentration at the end of the study did not exceed 5 mg/kg for N rates 145 kg/ha or less for either application method.
In terms of nitrate concentrations, a best management practice  would be to apply not more than 180 kg/ha of N.
The soil profiles for the 260 kg/ha N rate for the six different sampling periods indicates that leaching did not occur in every year even for the higher N rate.
If N runoff is a concern, these data indicate that LEPA fertigation with incremental applications can reduce the pool of N available for runoff.
5 10 15 Nitrate concentration 
 Figure 1.
Soil nitrate-N concentrations as a function of depth for the five applied-N rates for preplant broadcast and LEPA fertigation application methods.
Total applied N exceeded fertilization level shown in graph by N starter application of 35 kg/ha.
No significant differences  in corn yields occurred in any year as affected by application method.
However, corn yields were significantly  different among N rates in all three years but generally were similar at and above the 145 kg/ha applied N rate.
Overall yields were high  even when including 1995 yields that were lowered by hail and poor growing conditions.
This data would continue to support the BMP of 180 kg/ha  of N to optimize corn yields.
Figure 2.
Soil nitrate-N concentrations as a function of depth for six sampling dates for the 260 kg/ha N rate applied preplant broadcast or with LEPA fertigation.
Total applied N exceeded fertilization level shown in graph by N starter application of 35 kg/ha.
The amount of N in the aboveground biomass was significantly different  between application methods in only one year, being higher for the LEPA fertigation method in 1994.
Applied-N rate affected ANU in all three years with higher applied-N increasing ANU.
The three year average ANU exceeded the total amount of applied N for both application methods up to 235 kg/ha N rate , indicating good use of the applied N.
Water Use and Water Use Efficiency
 Water use was affected by application method only in 1995 with LEPA fertigation requiring less water.
Water use differed significantly  among N rates only in 1996 but tended to be higher for applied-N rates greater than 0 kg/ha in all three years.
Irrigation amounts were identical among treatments SO it can be concluded that adequate levels of fertilization can help better utilize available soil water.
WUE was not affected by application method in any year.
WUE was significantly different  among N rates  with a trend toward WUE maximization at a total applied-N rate of 180 kg/ha.
The plateauing of WUE coincided with plateauing of corn yield and ANU at approximately 180 kg/ha of total applied-N.
Figure 3.
Average  corn yield, apparent nitrogen uptake in the above-ground biomass, and water use efficiency as related to the total applied N.
In general, no appreciable differences occurred between preplant broadcast and LEPA N fertigation methods for corn production in terms of grain yields, nutrient uptake, residual soil N, water use or water use efficiency.
Increasing the applied-N rate to 200 kg/ha with an additional 35 kg/ha of starter N tended to increase nitrate concentrations in the soil profile above 5 mg/kg.
The lower 145 kg/ha N application rate was not appreciably different from the control treatment with no primary N application.
A primary application of 145 kg/ha of N using either application method with the addition of a 35 kg/ha N starter application optimized grain yields at approximately 13.8 Mg/ha.
Similarly, apparent nitrogen uptake and water use efficiency tended to plateau at the 145 kg/ha N level.
This emphasizes that high-yielding corn production also can be efficient in nutrient and water use.
Table 1.
Summary of corn yield, nutrient uptake, and water use data from a nitrogen fertilization study using LEPA sprinkler irrigation, 1994-96.
Nitrogen	N-	Yield	Apparent N uptake	Water use2	Water use efficiency3
 application	rate 	Mg/ha	kg/ha	mm	Mg/ha-mm
 199	199	199	Mea	199	199	199	Mea	199	199	199	Mea	1994	1995	1996	Mea
 4	5	6	in	4	5	6	in	4	5	6	in	in
 Preplant	0	10.25.5	7.9	7.9	12	8	8	96	75	73	70	732	0.01	0.00	0.01	0.01
 broadcast	+ 35	2	4	1	9	2	4	4	8	1	1
 90	13.6 10.7 13.9 12.7	25	16	15	193	83	71	74	764	0.01	0.01	0.01	0.01
 35	8	5	5	3	7	2	6	5	9	7
 145	15.112.315.1 14.1	24	19	23	222	78	80	71	766	0.01	0.01	0.02	0.01
 + 35	5	1	0	0	4	4	9	5	1	9
 200	14.011.8 14.913.5	24	22	25	238	84	81	76	808	0.01	0.01	0.02	0.01
 + 35	2	1	1	8	4	2	7	4	0	7
 260	14.511.414.813.5	25	23	27	257	82	80	73	787	0.01	0.01	0.02	0.01
 + 35	8	4	8	0	1	9	8	4	0	7
 LEPA	0	10.65.6	8.3	8.1	17	7	7	109	79	68	68	722	0.01	0.00	0.01	0.01
 fertigation	+ 35	5	5	7	5	9	1	4	8	2	1
 90	13.810.9 14.112.9	25	15	15	189	83	76	76	787	0.01	0.01	0.01	0.01
 + 35	7	6	4	1	5	7	7	4	8	6
 145	13.711.515.1 13.4	28	20	20	228	82	71	72	755	0.01	0.01	0.02	0.01
 + 35	0	4	0	3	4	6	7	6	1	8
 200	14.112.1 15.013.7	30	23	25	265	81	78	71	770	0.01	0.01	0.02	0.01
 + 35	3	8	4	8	2	1	7	6	1	8
 260	14.9 11.8 15.1 14.0	29	21	23	248	81	68	73	745	0.01	0.01	0.02	0.01
 + 35	1	4	9	5	3	7	8	7	0	9
 Preplant	13.5 10.313.3 12.4	22	17	19	201	80	77	73	771	0.01	0.01	0.01	0.01
 broadcast	5	9	9	8	4	2	7	3	8	6
 LEPA	13.4 10.413.512.4	26	17	18	208	81	72	72	756	0.01	0.01	0.01	0.01
 fertigation	1	7	5	6	7	4	7	4	9	6
 N rate	0	10.45.5	8.1	8.0	14	8	7	103	77	71	69	727	0.01	0.00	0.01	0.01
 + 35	9	0	9	7	0	2	4	8	2	1
 90	13.7 10.8 14.012.8	25	16	15	191	83	74	75	776	0.01	0.01	0.01	0.01
 + 35	7	0	5	2	1	4	7	5	9	7
 145	14.411.9 15.113.8	26	19	21	225	80	75	72	760	0.01	0.01	0.02	0.01
 + 35	3	7	5	1	9	0	8	6	1	8
 200	14.012.014.9 13.6	27	22	25	252	83	79	73	789	0.01	0.01	0.02	0.01
 + 35	2	9	3	3	8	7	7	5	0	7
 260	14.7 11.6 14.9 13.7	27	22	25	252	81	74	73	766	0.01	0.01	0.02	0.01
 + 35	5	4	8	8	2	8	8	6	0	8
 Applicatio	NS	NS	NS	NS	25	NS	NS	6	NS	46	NS	NS	NS	NS	NS	NS
 N-rate	1.2	0.9	1.0	0.8	36	41	31	24	NS	NS	41	38	0.00	0.00	0.00	0.00
 2	1	2	1
 N-rate with same method Method with same N-rate
 1 Applied nitrogen rate with preplant broadcast or LEPA fertigation method plus the 35 kg/ha nitrogen starter application.
2 Water use is defined as sum of irrigation, rainfall, and change in seasonal soil water in the 2.4 m soil profile.
3 Water use efficiency is defined as yield divided by water use.
Herbicides like Remedy, Tordon, Velpar or Cimarron Plus can control yucca, but only when each individual plant is sprayed directly.
General broadcast spraying to control yucca on rangeland is cost prohibitive, although small patches can and should be controlled before they expand.
Herbicides are most effective when applied in spring or summer.
Always touch high voltage equipment first with the back of your hand because if it is hot and you grab it with your fingers, you may not be able to let go.
SUBSURFACE DRIP IRRIGATION IN COLORADO
 Michael E.
Bartolo Vegetable Crops Specialist Colorado State University Arkansas Valley Research Center 27901 Road 21, Rocky Ford, Colorado 81067 Voice and Fax 254-6312 lichael.Bartolo@ColoState.EDU
 Drip irrigation is becoming increasingly popular in several irrigated production areas in Colorado.
As of 2004, there were approximately 2,000 acres devoted to drip irrigation, most of that being permanent systems where the drip tape is buried 6-8 inches below the soil surface.
Approximately 90% of the drip-irrigated acreage is being used to grow high-value vegetable crops including cantaloupe, watermelon and onions.
This paper will review some of the pros and cons associated with drip irrigation practices in Colorado, as well as issues that effect its future development.
Reasons for Conversion to Drip
 In Colorado=s Arkansas Valley, subsurface drip irrigation began to be adopted by commercial growers of cantaloupe in the early 1990's.
The primary reason for converting from furrow to drip irrigation was not water savings, but rather improved yield and quality.
In most cases, drip irrigation was used in conjunction with plastic mulch.
This plasticulture-based production system dramatically improved yield and quality and accelerated crop development thus giving growers access to more lucrative markets.
When cantaloupe were cultivated using furrow irrigation with no mulching, cantaloupe yields averaged about 300400 boxes  per acre.
Drip irrigation in combination with plastic mulch nearly doubled that figure for most growers and was even higher under experimental conditions.
Drip irrigation also made the use of row covers more practical which further advanced the earliness of the crop.
Plasticulture, with drip irrigation as the most critical component, made the production of other vegetables like onions, peppers, and tomatoes more practical.
Another notable example of a drip-irrigated specialty crop is seedless watermelon.
Seedless watermelons are relatively difficult to grow and seed is extremely expensive.
As a result, most seedless watermelons are established as greenhouse-grown transplants.
Without drip and plastic mulch, these transplants would have an extremely high mortality rate.
Overall, seedless watermelons grown with plasticulture can attain outstanding yields.
Table 1: Yield and earliness of Earligold , Gold Rush, and Nitro  cantaloupe grown with different plasticulture combinations including drip.
Variety and Seeding	Row Cover	First	Average Fruit	Market.
Yield
 or Transplanting Date	Harvest	Size 	
 Earligold	perforated	July 1	2.97	34,122
 Gold Rush	perforated	July 5	3.07	42,608
 Nitro	perforated	July 4	4.32	43,237
 Earligold	perforated	July 8	3.12	44,141
 Earligold	none	July 8	3.53	55,837
 Gold Rush	none	July 16	2.92	51,901
 Nitro	none	July 11	4.43	57,241
 Earligold	none	July 13	3.30	51,062
 LSD =	0.52	13,155
 Table 2.
Marketable yield, average fruit weight, and percent stand of seedless watermelon seeded or transplanted into plastic mulches and irrigated via drip.
Establishment	Mulch	%	Total Average	Total Mkt Yield
 Method	Color	Stand	Fruit Weight 	
 Seed	Black	50	12.5	34,321
 Transplant	Black	100	13.5	51,201
 Seed	Green	57	13.0	44,512
 Transplant	Green	100	13.0	58,796
 Seed	Clear	59	14.1	52,252
 Transplant	Clear	100	12.9	55,076
 Isd 	1.9	16,431
 As drought conditions persisted in Colorado during the 2001-2003 seasons, even more growers adopted drip irrigation.
This time the driving forces were not only improved production, but water savings as well.
Some of the most dramatic water savings were realized when growing onions.
Onions have a extremely shallow root system, with the majority of the roots located in the top 9 inches of soil.
Under furrow-irrigated conditions, a typical onion crop could require 14 or more irrigations during the course of the season with a total water application of 7 acre-ft/acre.
The vast majority of the total application amount is lost to evaporation, run-off at the end of the field, and deep percolation.
In contrast, drip-irrigation application rates have measured about 1.3 acre-ft/acre.
Barriers to Conversion to Drip
 Although subsurface drip irrigation has shown tremendous potential in Colorado, there remain sizeable hurdles for wider-scale adoption.
The first of these barriers is cost.
Most of the drip irrigation systems installed in Colorado cost in the range of $800$1300 per acre.
This huge investment is a hindrance to most growers, particularly those that do not grow high value crops.
Although some governmental assistance has been available, it is unlikely that growers of agronomic crops will install drip systems until a higher level of assistance can be offered.
Another sizable economic challenge is the need for specialized equipment for installation and tillage.
An additional barrier is the lack of a constant and reliable water supply.
Depending on the water right priority, waters originating from surface  flows may not be steady and constant.
In times of low river flows, some delivery canals may not have access to water for weeks.
This characteristic greatly diminishes the yield increase potential attributed to drip irrigation.
Well water would be another potential option in Colorado; however, since the Kansas vs.
Colorado conflict, well pumping has been greatly curtailed in the Arkansas River Basin and is following suit in other basins.
Future Concerns and Considerations
 One of the greatest concerns pertaining to drip irrigation is the ability to secure a constant and reliable water source.
Within the constraints of existing Colorado water laws, water saving methods of irrigation like drip are not justly compensated.
Given the costly and contentious nature of altering existing water laws, it may prove extremely challenging to foster the future development of drip irrigation in the state.
In some parts of the state particularly the Arkansas Valley, water quality is a concern.
The Arkansas River in southeast Colorado is one of the most saline rivers in the United States.
Average salinity levels increase from 300 ppm total dissolved solids  near Pueblo to over 4,000 ppm TDS near the ColoradoKansas border.
More than 200,000 acres along the river are irrigated with Class C4 water, the highest classification for salinity hazard.
Most surface waters also
 contain significant amounts of sediment.
Although they lack sediment, ground waters originating from shallow wells are typically even more saline than surface water.
It is not clear, if and how salts will accumulate in soils irrigated by drip.
Costly maintenance procedures may be needed to ensure that drip systems function properly under poor water quality conditions.
Yet another consideration for Colorado growers is the ability to design a drip system that is able to accommodate a wide variety of crops.
Most agronomic crops in the state are produced on a 30 inch row spacing making them amenable to a design containing drip lines spaced 60 inches apart.
Although some vegetable crops can be grown with this type of configuration, others, like onions, are not.
Since onions are planted in multiple rows per bed and are shallowrooted, a single drip line placed in the center of the bed at depths greater than 6 inches may not be sufficient to germinate the crop and provide adequate water to the outer rows.
In many instances, this design constraint has forced growers to drastically limit their rotation practices and thus, opens the possibility for severe pest problems.
Figure 1: Comparison of drip line placement for onion production; the standard single line placed 8 inches deep in the center of the bed and the more efficient configuration of two lines placed at a shallower depth.
Drip-irrigation has tremendous potential in Colorado if water law constraints can be ameliorated.
As more growers adopt drip irrigation, both research and educational programs will be needed to develop and promote practices that manage the movement of salts in the soil profile and ensure sustainable and profitable cropping patterns.
Drinking Water Problems: Perchlorate
 Monty C.
Dozier, Assistant Professor and Extension Specialist, Rebecca H.
Melton, Extension Assistant, Texas Cooperative Extension, The Texas A&M University System Michael F.
Hare, Senior Natural Resources Specialist, Pesticide Programs Division, Texas Department of Agriculture Dana O.
Porter, Associate Professor and Extension Agricultural Engineer, Bruce J.
Lesikar, Professor and Extension Agricultural Engineer, Texas Cooperative Extension, The Texas A&M University System
IRRIGATION AND TILLAGE MANAGEMENT EFFECTS ON CANOPY FORMATION IN CORN
 Effects of canopy formation and function are frequently represented in irrigation management models by crop coefficients, which can be used to calculate expected crop water requirements.
Soil tillage alters the micro-environment of a developing corn canopy.
The objective of this study was to evaluate irrigation capacity and tillage effects on seasonal changes in maize canopy and aboveground biomass productivity.
Leaf area index  and above-ground biomass  were quantified by non-destructive methods during four growing seasons for corn under two irrigation capacities  and three tillage regimes , strip till , or conventional till ).
Irrigation capacity and tillage effects were evaluated for each sampling period; seasonal trends were evaluated for year and treatment effects.
CT management resulted in earlier canopy formation and greater AGB accumulation during early vegetative growth in three of four years.
NT management resulted in extended canopy duration and greater AGB at tassel stage in two of four years; ST management resulted in greatest canopy duration in one year.
Evaluated over the four years, seasonal trends in LAI indicated earliest development under CT and delayed canopy development under NT management.
The intermediate rate of canopy development of corn under ST management, and favorable yield and water productivity, indicates utility of ST management for irrigated corn production.
The canopy of maize crops generates the structural biomass and carbohydrates which support grain yield formation.
Stomata embedded in leaves mediate the atmospheric demand which results in the transpiration component of evapotranspiration.
Effects of canopy formation are frequently represented in irrigation management models by crop coefficients, which can be combined with reference or potential ET to calculate expected crop water requirements.
The relationship of crop canopy formation and function to crop water requirements suggest the question: Can crop management alter canopy formation and subsequent productivity?
Soil tillage alters the micro-environment of a developing corn canopy, affecting crop residue distribution and soil physical properties in the tillage zone.
Full surface coverage by residue was required to reduce energy-limited evaporation by 50% or more, relative to bare soil with no shading by crop canopy; partial residue coverage  resulted in limited evaporation suppression relative to that of bare soil with no shading.
Corn grown under NT management required five to seven days longer to reach V6 development stage than corn under CT management in Ontario.
Corn yields were numerically greater under strip tillage  and no tillage management, relative to conventional tillage management.
The objective of this study was to evaluate irrigation capacity and tillage effects on seasonal changes in maize canopy and above-ground biomass productivity.
A corn hybrid of approximately 110-day relative maturity  was planted in 30" spaced circular rows on 8 May 2004, 27 April 2005, 20 April 2006, and 8 May 2007, respectively.
The two hybrids differ only slightly, with the latter hybrid having an additional genetic modification of corn rootworm control.
Three target seeding rates  were superimposed onto each tillage treatment in a complete randomized block design.
Irrigation was scheduled with a weather-based water budget but was limited to the three treatment capacities of 1 in.
every 4, 6, or 8 days.
This results in typical seasonal irrigation amounts of 12-20, 11-15, and 8-12 in., respectively.
The weather-based water budget was constructed using data collected from a NOAA weather station located approximately 600 yd.
northeast of the study site.
The reference evapotranspiration  was calculated using a modified Penman combination equation similar to the procedures outlined by Kincaid and Heermann.
The specifics of the ETr calculations used in this study are fully described by Lamm et al..
The basal crop coefficients were calculated for the area by assuming 70 days from emergence to full canopy for corn with physiological maturity at 130 days.
Leaf area index  was quantified, approximately bi-weekly, by a non-destructive light transmission technique.
Three sets of four below-canopy measurements were each referenced to an above-canopy measurement, minimizing sensor exposure to direct  irradiance.
Readings were screened against apparent transmittance ratios exceeding 1 using the manufacturer's software, FV2000.
An inverse solution to a model of light transmission through a vegetative canopy, provided by the manufacturer, was used to quantify apparent LAI.
Above-ground biomass  was quantified by non-destructive allometric measurements from V6 through early grain fill stages.
Three representative plants in each experimental unit were identified
 for repeated measure, commencing from V6 stage.
Stem measurements included diameter of the second internode and at the upper sheath of the youngest fully expanded leaf, distance from the ground to the base of the youngest fully expanded leaf, and number of fully expanded leaves.
For each sampling period, identical measurements were made for similar plants, outside the plot area but receiving similar management.
These plants were cut at ground level and dried, to determine above-ground biomass.
An allometric model was developed by regressing AGB against stem volume  and cumulative growing degree days.
Coefficients of this model were then applied to in-plot measurements to calculate apparent above-ground biomass.
Growing degree days  were calculated from daily temperature extremes  recorded at the NWREC weather station, using a mercury thermometer.
GDD = Tmax-Tmin Ty
 Upper and lower limits to temperature extremes were 30 C and 10 C , respectively.
Cumulative GDD was computed by summation of GDD, commencing from planting date.
Experimental design was randomized complete block, with some restrictions based on distance from the center pivot point.
Treatment design was split plot with irrigation capacity  as whole plot treatment and tillage method  as split plot treatment.
Population treatments were sampled for LAI and AGB at the mid-level  only.
Statistical analysis utilized analysis of variance , analysis of covariance  and regression techniques.
Repeated measure of LAI and maximum LAI observed in a year were analyzed by ANOV, using Proc GLM from SAS Institute.
Seasonal trends in LAI and AGB were analyzed by ANCOV using third order linear terms of cGDD or days after planting  as covariates.
A logistic model was also used to quantify changes in LAI through pollen shed stage, when all leaves were fully expanded.
A three parameter form of the logistic equation
 was fit to each set of LAI measurements from V6 through R1, for each set of treatment combinations of each year, using the non-linear feature of Statistix v9.1.
Coefficients for 'a', 'b', and 'c' terms were subjected to univariate analysis of variance, with year as a sampling environment.
A linearized form of the logistic equation  was also evaluated.
Here, Lo and Lm are initial and maximum leaf area, t represents days following emergence and k is a logistic coefficient for this linearized form.
Early season canopy formation occurred more rapidly under CT management in 2005, 2006 and 2007, as indicated by greater leaf area index.
End of season canopy persistence was favored by NT management in 2005 and 2006, and by ST management in 2007, as indicated by larger LAI values for later samplings.
Irrigation capacity affected LAI mid-season  in 2004; and late-season in 2006.
Maximum canopy formation, averaged among tillage treatments was greatest in 2007 , least in 2005  and intermediate in 2004  and 2006  see Table 1, Figure 1.
Figure 1.
Seasonal trends in leaf area index are shown in relation to cumulative growing degree days after planting, for corn grown in 2004 2007 seasons.
Seasonal trends in LAI, averaged over tillage and irrigation capacity effects, indicate delayed LAI development in 2006, relative to the other years.
Tillage effects were detected in the 'b' term of the three-term logistic model , when combined for the four years.
This term affects the rate of increase in the LAI function, indicating earliest canopy formation for CT , intermediate rate of canopy formation for ST  and latest canopy formation for NT.
No significant differences were detected for 'a'  or 'c'  terms, which scale final and initial LAI values, respectively.
The linearized form of the logistic equation indicated a negative linear relationship between maximum LAI and the logistic coefficient 'k'.
This 'k' term affects the rate of increase in the LAI function of Equation 3, similar to the 'b' term of Equation 2.
A smaller 'k' coefficient indicates a slower rate of canopy formation.
Table 1.
Leaf area index  of corn grown in no till , strip till  or conventional till  management in 2004-2007 growing seasons.
Crop year, 2004	Days after planting 
 37	51	65	86	97	110	121
 Cumulative Growing Degree Days 
 395	506	684	966	1098	1238	1364
 IC 1"/4d	0.60a	1.41a	3.25a	3.58a	4.49a	4.12a	2.97a
 IC 1"/8d	0.55a	1.31a	3.17a	3.58a	3.75b	3.81b	2.64b
 NT	0.56a	1.32a	3.41a	3.51a	4.00a	4.04a	2.79a
 ST	0.62a	1.36a	3.08a	3.63a	4.18a	3.95a	2.90a
 CT	0.55a	1.39a	3.14a	3.62a	4.18a	3.91a	2.74a
 Crop year, 2005	Days after planting 
 50	55	70	83	96	112	126	138
 Cumulative Growing Degree Days 
 377	446	641	818	985	1176	1349	1494
 IC 1"/4d	0.71a	0.97a	2.23b	3.18a	3.20a	3.38a	2.82a	2.08a
 IC 1"/8d	0.77a	1.12a	2.66a	3.28a	3.25a	3.31a	2.74a	2.09a
 NT	0.65b	0.89b	2.41a	3.24a	3.18a	3.41a	2.82a	2.20a
 ST	0.58b	0.96b	2.32a	3.28a	3.23a	3.34a	2.82a	2.16ab
 CT	1.00a	1.28a	2.60a	3.17a	3.26a	3.29a	2.70a	1.91b
 Crop year, 2006	Days after planting 
 47	61	76	90	104	118	132	147
 Cumulative Growing Degree Days 
 376	558	742	936	1109	1298	1453	1578
 IC 1"/4d	0.63a	1.29a	2.37a	4.05a	3.73a	4.40a	3.72a	3.88a
 IC 1"/8d	0.59a	1.17a	2.39a	3.96a	3.57a	4.20a	3.25b	3.60a
 NT	0.53a	1.04b	2.27a	4.00a	3.87a	4.46a	3.66a	3.64a
 ST	0.60a	1.29ab	2.26a	4.08a	3.55a	4.41a	3.54ab	4.00a
 CT	0.70a	1.35a	2.61a	3.94a	3.52a	4.04a	3.26b	3.58a
 Crop year, 2007	Days after planting 
 30	44	58	73	87	100	114	132
 Cumulative Growing Degree Days 
 260	4.23	596	790	989	1176	1363	1534
 IC 1"/4d	0.30a	1.38a	3.52a	4.65a	4.92a	4.00a	3.32a	2.71a
 IC 1"/8d	0.31a	1.39a	3.28a	4.65a	4.82a	3.80a	3.13b	2.58a
 NT	0.25b	1.16b	3.30a	4.51a	4.75a	3.77b	3.20b	2.49b
 ST	0.27b	1.35b	3.39a	4.61a	4.91a	4.14a	3.44a	2.83a
 CT	0.40a	1.64a	3.51a	4.83a	4.96a	3.80b	3.04b	2.62b
 Shaded items, within a column, are significantly different at P<0.05 when followed by a different lower case letter.
Figure 2.
Effects of tillage on seasonal trends in leaf area index are shown in relation to cumulative growing degree days after planting; results are a composite of 2004 2007 growing seasons.
Figure 3.
A linear relationship between the linearized logistic coefficient  and maximum leaf area index is shown for corn canopies observed in 2004 2007 growing seasons.
Increased irrigation capacity  resulted in greater early vegetative growth in 2004 and 2005, greater mid-vegetative growth in all years and greater biomass accumulation at maturity in all years but 2007, as indicated by larger values for AGB.
Early vegetative AGB accumulation was favored by CT management in 2005, 2006 and 2007, relative to NT management; ST management resulted in similar AGB values to CT management in 2006 and 2007.
By tassel formation, AGB was greater under NT management than for CT management in 2004 and 2007; at maturity, in 2004, AGB was greater under ST management than that under CT management.
Seasonal trends for AGB accumulation  indicate slightly greater AGB under CT but similar or greater AGB for NT and ST corn by early grain fill stage.
Figure 4.
Tillage effects on seasonal trends in apparent above-ground biomass of corn are shown in relation to cumulative growing degree days after planting, for corn grown under no till , strip till  or conventional till  management, derived from 2004 through 2007 growing seasons.
Table 2.
Irrigation and tillage effects on above-ground corn biomass, determined by a nondestructive allometric method, is shown for the 2004 2007 growing seasons.
Crop year, 2004	Days after planting 
 36	50	64	82	95	148
 Cumulative Growing Degree Days 
 367	490	652	901	1074	1643
 IC 1"/4d	350a	4,160a	8,600a	11,890a	12,570a	31,310a
 IC 1"/8d	280b	3,520b	7,780b	10,730b	11,590a	27,540b
 NT	300a	3,810a	8,120a	12,160a	12,550a	29,380ab
 ST	290a	3,980a	8,540a	11,400ab	12,380a	31,690a
 CT	350a	3,690a	7,890a	10,400b	11,330a	27,270b
 Crop year, 2005	Days after planting 
 40	54	68	82	95	153
 Cumulative Growing Degree Days 
 282	432	621	804	972	1507
 IC 1"/4d	1,210a	4,520a	14,460a	36,520a
 IC 1"/8d	1,300b	4,720a	13,540a	31,350b
 NT	1,170b	4,160b	14,340a	35,370a
 ST	1,180b	4,560ab	13,810a	32,610a
 CT	1,430a	5,190a	13,840a	34,210a
 Crop year, 2006	Days after planting 
 46	60	75	89	102	151
 Cumulative Growing Degree Days 
 364	544	730	921	1079	1622
 IC 1"/4d	2,910a	5,930a	12,700a	13,620a	14,510a	30,400a
 IC 1"/8d	2,900a	5,640a	12,160a	12,710b	13,450b	25,500b
 NT	2,800b	5,210c	11,360b	12,910a	14,170a	27,760a
 ST	2,850b	5,780b	12,750a	13,320a	14,100a	29,390a
 CT	3,070a	6,420a	13,250a	13,250a	13,660a	26,500a
 Crop year, 2007	Days after planting 
 29	43	57	75	85	132
 Cumulative Growing Degree Days 
 250	403	571	796	928	1504
 IC 1"/4d	140a	1,940a	9,830a	19,580a	19,090a	31,230a
 IC 1"/8d	140a	1,910a	11,070a	16,320a	17,850a	31,790a
 NT	90b	1,400c	10,270a	19,870a	20,600a	31,620a
 ST	160a	1,840b	10,830a	16,590a	18,990a	32,260a
 CT	190a	2,770a	10,200a	17,330a	16,080b	30,670a
 Shaded items, within a column, are significantly different at P<0.05 when followed by a different lower case letter.
Figure 5.
Tillage effects on seasonal trends in crop water use , above ground biomass accumulation  and canopy formation  are shown in relation to days after planting for corn grown under no till , strip till  or conventional till  management in the 2006 growing season; data are taken from the lowest irrigation capacity.
Early canopy formation and senescence for CT is evident , with delayed canopy formation for NT; maximum canopy occurred with ST management.
Similarly, more AGB accumulated during early vegetative growth under CT management  with similar AGB for ST by tassel and maximum AGB at maturity for NT.
Vegetative crop water use was similar among tillage treatments , but greater for NT and ST than for CT by maturity, reflecting differences in canopy senescence.
Earlier canopy formation and AGB accumulation under CT, detected in three of four years, is consistent with the report of more rapid corn development under CT management in Ontario.
This likely results from warmer soil conditions, early emergence, and more vigorous seedling growth under CT management.
Earlier canopy senescence and maturity also resulted from CT management in the same three growing seasons, indicating tillage management can cause a 'shift' in canopy formation and senescence.
The delayed canopy formation and extended canopy duration for NT, and, to a lesser extent ST, appears to be related to increased grain yield and increased water use.
This could result in extended water use during the late grain fill period, which may not be sufficiently represented in standard crop coefficients used in irrigation scheduling.
Vegetative water use was similar among tillage treatments.
Klocke et al.
reported that virtually 100% residue cover was required to achieve evaporation suppression with incomplete canopy closure.
Field observations on April 17, 2007 indicated 80%, 91% and 99% residue cover for CT, ST and NT, respectively.
However, greater seasonal water use for ST and NT treatments appear to be associated with delayed canopy senescence and with greater grain yields.
The two forms of the logistic equation  provide scaling tools with applications to functional representation of corn canopy formation.
In this regard, the tillage effect on the three term model provides a useful basis for simulating tillage effects.
Similarly, the linearized scaling relationship between LAI max and the 'k' coefficient could be useful for adjusting seasonal LAI values for remote sensing and GIS applications.
Reduced tillage delayed corn canopy formation and AGB accumulation during earlyto midvegetative growth, relative to conventional tillage management, in three of four growing seasons.
Delayed canopy senescence was also detected in the same three growing seasons.
Greater grain yield and crop water use was associated with this 'shift' in canopy formation.
Two forms of the logistic equation provide opportunity to functionally represent tillage effects on corn canopy formation and for use in remote sensing/GIS applications.
This work was partially supported by the Ogallala Aquifer Program, administered by the USDA-ARS, and also by the Monsanto Corporation.
Mention of tradenames is for informational purposes only and does not constitute endorsement by the i authors or by the institutions they serve.
Effect of Early Season Water Stress on Corn in Northwest Kansas
 Written for presentation at the 2011 ASABE Annual International Meeting Sponsored by ASABE Galt House Louisville, Kentucky August 7 10, 2011
 Abstract.
Decisions about when to initiate the irrigation season is an important irrigation macromanagement decision that can potentially save water and increase net income when made correctly, but can have negative economic consequences when made incorrectly.
A combination of nine years of pre-anthesis water stress studies for corn was conducted at the Kansas State University Northwest Research-Extension Center in Colby, Kansas on a productive, deep, silt loam soil.
Overall, the pre-anthesis water stress studies suggest that corn grown on this soil type has great ability to handle early-season water stress, provided the water stress can be relieved during later stages.
A critical factor in maximizing corn grain yields as affected by pre-anthesis water stress is maximizing the kernels/area.
Maintaining a water deficit ratio  greater than 0.7 to 0.8 or limiting available soil water depletion in the top 4 ft of soil profile to approximately 30% maximized the kernels/area.
Some of these results contradict traditional irrigation guidelines.
Keywords.
Irrigation management, water stress, kernel set, crop water use, corn
 Definition of Macromanagement and Scope of the Problem
 Corn  is the primary irrigated crop in the U.S.
Great Plains.
There are a number of efficient methods to schedule irrigation for corn on a real-time, daily, or short-term basis throughout the season.
These scheduling methods essentially achieve water conservation by delaying any unnecessary irrigation event with the prospect that the irrigation season might end before the next irrigation event is required.
There are larger irrigation management decisions [i.e., irrigation macromanagement ] that can be considered separately from the step-by-step, periodic scheduling procedures.
Two important macromanagement decisions occur at the seasonal boundaries, the initiation and termination of the irrigation season.
Irrigators sometimes make these seasonal boundary determinations based on a traditional timeof-year rather than with sound rationale or science-based procedures.
However, a single, inappropriate, macromanagement decision can easily have a larger effect on total irrigation water use and/or crop production than the cumulative errors that might occur due to small, systematic errors in soil-, plant-, or climatic-based scheduling procedures.
This does not discount step-by-step irrigation scheduling.
To the contrary, it is an implicit assumption that improved macromanagement at the seasonal boundaries can only provide the potential for increased water conservation when used in conjunction with the step-by-step, periodic scheduling procedures.
This paper will concentrate on the effect of water stresses during the period prior to corn anthesis.
Most of the established literature on irrigation management during the early growth stages is 3545 years old and was written at a time when irrigated corn yields were much lower  than they are today.
It is quite possible that some of the numerous yield-limiting stresses  that were tolerable at the lower yield level are less tolerable today.
On the other side of the issue, there has been much improvement in corn hybrids during the period with incorporation of traits that allow water stress tolerance and/or water stress avoidance.
The corn vegetative stage is often considered the least-sensitive stage to water stress and could provide the opportunity to limit irrigation water applications without severe yield reductions.
The vegetative stage begins at crop emergence and ends after tasseling, which immediately precedes the beginning of the reproductive period when the silks start to emerge.
The potential number of ears/plant is established by the fifth leaf stage in corn.
The potential number of kernels/ear is established during the period from about the ninth leaf stage until about one week before silking.
Stresses during the 10 to 14 days after silking will reduce the potential kernels/ear to the final or actual number of kernels/ear.
Therefore, in research studies designed to examine water stresses during the first one-half of the corn crop season, both ears/plant and kernels/ear might be critical factors.
Additionally, there could be permanent damaging effects from the vegetative and early-reproductive period water stress that may affect grain filling.
Often, irrigators in the Great Plains, start their corn irrigation season after early season cultural practices are completed such as herbicide or fertilizer application or crop cultivation at the lay-by growth stage.
Crop evapotranspiration is increasing rapidly and drier weather periods are approaching, so often
 there is soil water storage that can be replenished by timely irrigation then for use later in the summer.
However, this does not always mean that the corn crop required the irrigation at that point-in-time.
Two studies were conducted at the KSU Northwest Research-Extension Center at Colby, Kansas, USA on a productive, deep, well-drained Keith silt loam soil  during the sixteen-year period, 1993-2008.
In general, the 1990s were a much wetter period than the 2000s.
The summers of 2000 through 2003 would be considered extreme droughts.
The climate for the region is semi-arid with a summer pattern of precipitation with an annual average of approximately 480 mm.
The average precipitation and calculated corn evapotranspiration during the 120-day corn growing period, May 15 through September 11 is 300 mm and 587 mm, respectively.
The corn anthesis period typically occurs between July 15 and 20.
Both studies utilized the same field site that had a subsurface drip irrigation  system installed in 1990 with 1.5-m dripline spacing and an emitter spacing of 0.3 m.
The 2.5-ft paced corn rows were planted parallel and centered on the driplines such that each corn row would be 15 inches from the nearest dripline.
The nominal dripline flowrate was 0.25 gpm/100 ft, which is equivalent to an emitter discharge of 0.6 L/h for the 0.3 m emitter spacing.
The corn was planted in late April to early May, and standard cultural practices for the region were used.
Irrigation was scheduled as needed by a climate-based water budget except as modified by study protocols that will be discussed in the Specific Procedures section that follows.
Calculated crop evapotranspiration  was determined with a modified Penman equation for calculating reference evapotranspiration  multiplied by empirical crop coefficients suitable for western Kansas.
Precipitation and irrigation were deposits into the crop water budget and calculated ETc was the withdrawal.
Soil water was measured in each plot on a weekly or biweekly basis with a neutron probe to a depth of 2.4 m in 0.3-m increments.
These data were used to determine crop water use and to determine critical soil water depletion levels.
Water use values were calculated as the sum of the change in available soil water to the specified profile depth, plus the irrigation and precipitation during the specified period.
This method of calculating crop water use would also include any deep percolation or rainfall runoff that may have occurred.
Corn yield and yield components of plants/area, ears/plant, and kernel weight were measured by hand harvesting a representative 6 m row sample.
The number of kernels/ear was calculated with algebraic closure using the remaining yield components.
Specific Procedures for Pre-Anthesis Water Stress Studies
 Data from two studies where the initiation date of the irrigation season was varied were combined in the analysis.
The first study consisted of five years of data  with the hybrid Pioneer 3162.
The second study during the four-year period  used two corn hybrids [Pioneer 32B33  and Pioneer 33B50 ].
The 2004-2007 study had six main irrigation treatments and the two corn hybrid split-plot treatments replicated three times in a randomized complete block  design.
The 1999-2003 study used the
 same experimental design without the split plot.
The whole plots were 8 rows wide  and 600 m long.
The six irrigation treatments  were imposed by delaying the first normal irrigation either 0, 1, 2, 3, 4, or 5 weeks.
This typically resulted in the first irrigation for Trt 1 being between June 5 and June 15 and the first irrigation for Trt 6 being around July 10 to July 24.
In some years, excessive rainfall between two adjacent treatment initiation dates would negate the need for irrigation.
In that case, the later treatments would be delayed an additional week to provide an extended data set.
After the treatment initiation date occurred, SDI was scheduled to provide 10 mm/d until such time that the climate-based water budget fully eliminated calculated soil water deficits.
It should be noted that this irrigation capacity of 10 mm/d is much greater than the typical irrigation capacity in this region.
Additionally, the procedure of eliminating the severe irrigation deficits later in the season after the plants had been stunted may lead to excessive deep percolation.
The purpose of the study was not to optimize irrigation use within the study but rather to determine what capability the corn crop had to tolerate early season water stress.
Thus, the procedures were tailored to alleviate soil water deficits relatively quickly after the treatment initiation date.
Analysis of variance  of the yield and yield component data was performed for the 6 treatments for the 1999-2003 data set using a one-way AOV and using a split plot two-way AOV for the 2004-2007 data set.
Statistical and tabular data analysis for pre-anthesis water stress studies
 Delaying irrigation only statistically affected the yield components in three of the nine crop years and then only for the later irrigation dates.
Delaying irrigation until July 10, 2001, July 17, 2003 and July 27, 2005 significantly reduced the number of kernels/ear and the grain yield.
These three years had an average weather-based calculated July crop ETc rate of 8.1 mm/d.
In comparison the average July crop ET rate value was 6.6 mm/d for the other six years.
It should be noted that the years 2000 through 2003 were extreme drought years in northwest Kansas.
Delaying irrigation also significantly reduced ears/plant in 2003 and 2005.
In 2003, the reduction in kernels/ear and ears/plant for Trt 6 was partially compensated for by a statistically higher kernel weight.
Overall, these results suggest that corn grown on this soil type has great ability to handle vegetative and early-reproductive period water stress provided the water stress can be alleviated during the later stages.
The hybrid selection affected yield in only one of the four years, 2006, with the longer season Pioneer 32B33 providing significantly greater yields for the later irrigation initiation dates.
This is probably because of earlier pollination for the Pioneer 33B50 prior to receiving irrigation.
Kernels/ear was significantly less for the shorter season Pioneer 33B50 hybrid in three of four years.
Hybrid selection did not affect ears/plant in any of the four years.
In 2004, kernel weight was significantly higher for Pioneer 33B50 for some irrigation treatments, probably because of the smaller number of kernels/ear for this hybrid in that year.
It should be noted that the results do not mean that irrigation can be delayed in the Western Great Plains until mid to late July.
These plots generally started the season with reasonably full soil profiles.
Most irrigators do not have irrigation systems with adequate capacity  to quickly alleviate severely depleted soil water reserves.
In addition, it is difficult to infiltrate large amounts of water into the soil quickly with sprinkler and surface irrigation systems without causing runoff problems.
Rather, look at these study results as describing the corn plant's innate ability to tolerate vegetative-period water stress.
Table 1.
Summary of yield component and irrigation data from an early season water stress study for corn hybrid Pioneer 3162, KSU-NWREC, Colby, Kansas, 1999-2003.
Year and Parameter	Trt 1	Trt 2	Trt 3	Trt 4	Trt 5	Trt 6
 1999 First Irrigation Date	22-Jun	29-Jun	6-Jul	13-Jul	20-Jul	27-Jul
 Total Irrigation 	284	284	284	254	254	193
 Yield 	15.9 a*	16.6 a	16.1 a	16.0 a	16.3 a	16.0 a
 Plant Pop.
76781 a	79650 a	78934 a	78215 a	79650 a	79650 a
 Ears/Plant	0.99 a	0.99 a	0.97 a	1.00 a	0.99 a	1.01 a
 Kernels/Ear	575 a	570 a	555 a	572 a	543 a	555 a
 Kernel Wt.
36.3 a	36.9 a	37.8 a	35.8 a	38.1 a	35.9 a
 2000	First Irrigation Date	5-Jun	12-Jun	19-Jun	26-Jun	3-Jul	10-Jul
 Total Irrigation 	500	500	500	480	480	480
 Yield 	14.1 a	14.8 a	14.1 a	14.2 a	13.6 a	13.6 a
 Plant Pop.
68887 a	69606 a	66018 a	66018 a	66734 a	67451 a
 Ears/Plant	1.02 a	1.04 a	0.99 a	1.03 a	1.02 a	1.01 a
 Kernels/Ear	544 a	553 a	568 a	544 a	548 a	529 a
 Kernel Wt.
36.9 a	36.8 a	38.0 a	38.4 a	36.4 a	37.8 a
 2001	First Irrigation Date	12-Jun	19-Jun	26-Jun	3-Jul	10-Jul	17-Jul
 Total Irrigation 	488	488	488	488	488	488
 Yield 	15.9 a	16.3 a	16.4 a	15.7 a	13.4 b	10.0 C
 Plant Pop.
83957 a	86468 a	86286 a	87187 a	85035 a	83596 a
 Ears/Plant	0.96 a	0.98 a	0.99 a	0.99 a	0.97 a	0.99 a
 Kernels/Ear	581 a	584 a	582 a	541 a	476 b	347 C
 Kernel Wt.
33.8 a	33.2 a	32.8 a	33.7 a	34.6 a	34.9 a
 2002	First Irrigation Date	12-Jun	19-Jun	26-Jun	3-Jul	10-Jul	17-Jul
 Total Irrigation 	470	457	457	457	457	457
 Yield 	14.6 a	14.6 a	13.6 a	13.7 a	13.9 a	14.0 a
 Plant Pop.
85393 a	86109 a	85393 a	88262 a	88262 a	85393 a
 Ears/Plant	0.98 a	0.97 a	0.98 a	0.99 a	1.00 a	0.99 a
 Kernels/Ear	454 a	443 a	407 a	435 a	391 a	422 a
 Kernel Wt.
38.6 a	39.8 a	40.3 a	36.6 a	40.5 a	39.2 a
 2003	First Irrigation Date	12-Jun	21-Jun	26-Jun	3-Jul	10-Jul	17-Jul
 Total Irrigation 	478	457	457	437	437	5.8
 Yield 	11.1 a	11.3 a	11.9 a	11.7 a	10.7 a	93 b
 Plant Pop.
81086 a	82522 a	84674 a	81805 a	85393 a	81086 a
 Ears/Plant	0.96 a	0.92 b	0.96 a	1.00 a	0.97 a	0.82 C
 Kernels/Ear	588	a	567 a	576 a	569 a	486 b	262	C
 Kernel Wt.
24.1	b	26.2 b	25.5 b	25.2 b	26.8 b	33.6 a
 * Values followed by the same lower case letters are not significantly different at P=0.05.
Table 2.
Summary of corn yield component and irrigation data from an early season water stress study for hybrids Pioneer 33B50 and 32B33, KSU-NWREC, Colby, Kansas, 2004-2007.
Year and Parameter	Trt 1	Trt 2	Trt 3	Trt 4	Trt 5	Trt 6
 2004 First Irrigation	Hybrid	8-Jun	28-Jun	13-Jul	20-Jul	27-Jul	3-Aug
 Total Irrig.
(mm	325	295	274	274	274	274
 Yield 	33B50	13.8 aA*	13.4 aA	12.9 aA	14.6 aA	15.4 aA	13.2 aA
 32B33	14.2 aA	13.2 aA	13.1 aA	13.9 aA	14.4 aA	12.9 aA
 Plant Pop.
33B50	71758 aA	69606 aA	69606 aA	69606 aA	71041 aA	68887 aA
 32B33	70322 aA	73193 aA	73193 aA	70322 aA	71758 aA	70322 aA
 Ears/Plant	33B50	0.85 aA	0.91 aA	0.89 aA	0.93 aA	0.88 aA	0.84 aA
 32B33	0.88 aA	0.80 aA	0.79 aA	0.90 aA	0.83 aA	0.83 aA
 Kernels/Ear	33B50	595	aB	574 aB	589 aB	595 aA	648 aA	590 aB
 32B33	624	aA	616 aA	634 aA	600 aA	643 aA	612	aA
 Kernel Wt.
33B50	38.0	aA	36.8 aA	35.7 aA	38.2 aA	38.2 aA	38.6 aA
 32B33	36.8 aB	36.4 aA	36.2 aA	36.8 aB	37.6 aA	36.4 aB
 2005 First Irrigation	Hybrid	21-Jun	28-Jun	6-Jul	12-Jul	19-Jul	26-Jul
 Total Irrig.
335	335	335	335	335	335
 Yield 	33B50	14.2 aA	16.3 aA	16.1 aA	14.9 abA	14.2	bA	9.4	cA
 32B33	14.2 abc	14.2 ab	16.2 abA	16.6 aA	14.8 cA	10.2 dA
 Plant Pop.
33B50	71041 aA	70322 aA	70322 aA	70322 aA	73193 aA	69606 aA
 32B33	70322 aA	71758 aA	70322 aA	68812 aA	71041 aA	73193 aA
 Ears/Plant	33B50	0.99 ab	1.00 aA	0.99 abA	0.98 abA	0.96 bcA	0.95 cA
 32B33	0.98	bA	0.97 bc	1.01 aA	1.00 abA	0.96 bcd	0.94 dA
 Kernels/Ear	33B50	641	ab	653 aA	670 aA	604 bA	564	cA	422 dA
 32B33	638	bA	647 ab	644 abA	680 aA	654 abA	421	cA
 Kernel Wt.
33B50	35.4	aA	35.4 aA	34.5 aA	36.0 aA	35.9 aA	33.6 aA
 32B33	36.2 aA	35.4 aA	35.4 aA	35.5 aA	33.1 aA	35.1 aA
 2006 First Irrigation	Hybrid	8-Jun	15-Jun	26-Jun	29-Jun	6-Jul	14-Jul
 Total Irrig.
356	345	325	325	315	315
 Yield 	33B50	14.1	aA	14.4 aA	13.8 aB	13.8 aA	13.8 aB	12.9	aB
 32B33	14.4 aA	14.7 aA	15.4 aA	14.4 aA	15.1 aA	15.3 aA
 Plant Pop.
33B50	68170 aA	66734 aA	69606 aA	69606 aA	68170 aA	67451 aA
 32B33	70322 aA	68887 aA	70322 aA	68887 aA	69603 aA	69606 aA
 Ears/Plant	33B50	0.98 aA	0.98 aA	0.99 aA	0.99 aA	0.99 aA	0.96 aA
 32B33	0.96 aA	0.98 aA	0.98 aA	0.97 aA	0.98 aA	0.97 aA
 Kernels/Ear	33B50	561	aB	594 aA	544 aB	547 aB	550 aB	519 aB
 32B33	597	aA	602 aA	618 aA	583 aA	585 aA	612 aA
 Kernel Wt.
33B50	37.8 aA	37.2 aA	36.8 aA	36.5 aA	37.4 aA	38.7 aA
 32B33	35.7 aA	36.2 aA	36.3 aA	37.1 aA	38.1 aA	37.2	aA
 2007 First Irrigation	Hybrid	7-Jun	21-Jun	28-Jun	4-Jul	12-Jul	19-Jul
 Total Irrig.
307	287	287	287	287	277
 Yield 	33B50	15.3 aA	15.8 aA	15.7 aA	15.4 aA	14.7 aA	13.4	aA
 32B33	16.3 aA	14.8 aA	15.8 aA	15.0 aA	16.0 aA	14.4 aA
 Plant Pop.
33B50	71758 aA	73193 aA	72477 aA	70322 aA	71758 aA	69606 aA
 32B33	71758 aA	70322 aA	69606 aA	68887 aA	70322 aA	69606 aA
 Ears/Plant	33B50	0.98	aA	0.99 aA	1.00 aA	0.99 aA	0.99 aA	1.00 aA
 32B33	0.98	aA	0.95 aA	0.99 aA	0.99 aA	0.99 aA	0.97 aA
 Kernels/Ear	33B50	668	aB	672 aB	693 aA	682 aA	645 aB	597 aB
 32B33	728	aA	724 aA	712 aA	712 aA	714 aA	674 aA
 Kernel Wt.
33B50	32.5	aA	32.5 aA	31.2 aA	32.4 aA	32.0 aA	32.2	aA
 32B33	31.6	aA	30.6	aA	32.3 aA	30.9 aA	32.3 aA	31.7	aA
 Irrigation treatment values within the same row followed by the same lower case letters are not
 significantly different at P=0.05, and hybrid treatment values within the same column followed by the
 same upper case letters are not significantly different at P=0.05.
Graphical data analysis for pre-anthesis water stress studies
 The tabular data do not give a mechanistic explanation of the results.
Attempts were made to relate yield component data to a large number of water factors in the broad categories of water use, evaporative demand, and critical profile soil water levels.
Relative values of yield and yield components were determined by normalizing each data point to the corresponding value for the earliest irrigation treatment in that year.
These relative values were used for comparisons between years.
Final grain yield was largely determined by the number of sinks or kernels/area  indicating there was little or no effect on the grain-filling stage imposed by the vegetative and early-reproductive period water stress in these two studies.
The individual treatment values of corn grain yield and kernels/area were values compared to the irrigation treatment that had no initial delay in irrigation  to give relative values.
In a few cases, the Trt 1 values were not the highest value and, thus, relative values could be greater than one.
Deviations below the 1 to 1 unity line in Figure 1 would indicate a permanent negative effect on corn grain yield of early-season water stress because of reduced kernels/area.
Deviations above the line would indicate some grain yield compensation resulting from better grain filling of the reduced kernels/area.
Figure 1.
Relative corn grain yield as affected by relative kernels/area in an early-season corn water stress study, KSU-NWREC, Colby, Kansas, 1999-2007.
Relative kernels/area was found to be reasonably well related to relative July water use, the minimum available soil water in the top 1.2 mt of the soil profile during July and to the July 1 through July 15 water deficit.
Further analysis is needed to determine an improved overall relationship involving more than a single factor, but the individual factor results will be discussed here.
The 50% critical silking period for corn in this study ranged from approximately July 17 to July 22 during the study period.
The short-season hybrid in the latter study would typically silk approximately one week earlier.
A window of approximately two weeks on both sides around the silking period was used to compare the relative kernels/area to the relative July measured water use.
Actual soil water measurements were taken on an approximately weekly basis except for equipment problems or when excessive precipitation delayed measurements, so it was not possible with the data set to always have exactly 31 days of water use.
Dates used were those closest to July 1 through 31.
There tended to be some reduction in relative kernels/area when relative July water use was less than 80%.
Scatter at the lower end of relative July water use may be related to water-use differences occurring within the month or differences in evaporative demand between the years.
This relationship may not result in a very good signal for procedures to determine irrigation need because the relative July water use cannot be determined until it is too late to handle the reduction in relative kernels/area.
Figure 2.
Relative corn grain yield as affected by relative July water use in an early-season corn water stress study, KSU-NWREC, Colby, Kansas, 1999-2007.
The relative kernels/area tended to be reduced when July minimum available soil water in the top 1.2 m  was below 0.6  in some years.
During years of less evaporative demand, water could be extracted from the soil profile to a further reduced level without much detriment to relative kernels/area, but severe reductions occurred for similar soil water conditions in years with large July evaporative demands.
The upper and lower envelope lines of Figure 3 were manually drawn to indicate the effect of evaporative demand of the given year on relative kernels/area.
These envelopes would match known theories of water stress and water flow through plants.
Figure 3.
Relative kernels/area as affected by July minimum available soil water in the top 1.2 m of soil in an early-season corn water stress study, KSU-NWREC, Colby, Kansas, 1999-2007.
The upper  and lower  lines are manually drawn to illustrate years with larger and smaller July evaporative demand.
Water stress is greater both with reduced available soil water and with greater evaporative demand.
The kernels/area was most sensitive to the JASW in the top 4 ft of soil as compared to both smaller and greater profile depths.
This is reflecting the approximate rooting and soil water extraction depth of corn in July on this soil type.
There remains considerable unexplained scatter in this graph that does not appear to be related very well to differences in evaporative demand between the years.
For example, there was very little effect on relative kernels/area in 2002, although it had a moderately high evaporative demand.
The relationship of relative kernels/area to a critical level of available soil water can have some merit as a signal for
 determining the need for irrigation because available soil water can both be measured in realtime and the value can be projected a few days into the future.
The ratio of calculated well-watered crop ETc to the sum of irrigation and precipitation for July 1 through 15 was also related to the relative kernels/area.
The relative kernels/area tended to decrease when this water deficit ratio was less than 70 to 80%.
Attempts were also made in varying the timeframe of the ratio.
It appears that some of the remaining scatter in this graph is related to timing of irrigation and precipitation near the actual point of silking.
For example, the isolated point from 2002 near the vertical axis may be related to a significant precipitation event that occurred near silking, but later than July 15.
Further analysis should be conducted to allow the window to actually vary around the individual silking dates of each year.
This might be done by computing windows based on the number of thermal units  required for silking.
This relationship might also be a good signal in determining the need for irrigation because it can be determined in near real-time using the accumulated ratio to that point in time.
Figure 4.
Relative kernels/area as affected by the July 1 through 15 water deficit  in an earlyseason corn water stress study, KSU-NWREC, Colby, Kansas, 1999-2007.
Further analysis should focus on attempts to combine multiple factors  with a focus on developing irrigation signals that can be used in near real-time to make early season irrigation decisions.
Recommendations for managing pre-anthesis corn water stress
 Producers should use a good method of day-to-day irrigation scheduling during the pre-anthesis period.
To a large extent the information being used to make day-to-day irrigation scheduling decisions during the pre-anthesis period can also be used as in making the macromanagement decision about when to start the irrigation season.
This is because even though the corn has considerable innate ability to tolerate early season water stress, most irrigation systems in the Central Great Plains do not have the capacity  or practical capability  to replenish severely depleted soil water reserves as the season progresses to periods of greater irrigation needs.
However, there is some flexibility in timing of irrigation events within the vegetative growth period.
In years of lower evaporative demand, corn grown on this soil type in this region can extract greater amounts of soil water without detriment.
Timeliness of irrigation and/or precipitation near anthesis appears to be important in establishing an adequate number of kernels/area.
The strong linear 1:1 relationship that existed between the relative corn yield and the relative number of kernels/area  indicates that optimizing kernels/area is a key in optimizing grain yields.
Producers growing corn on deep silt loam soils in the Central Great Plains should attempt to maintain a water deficit ratio  during July of approximately 0.7 to 0.8 and not allow the available soil water within a 1.2 m soil profile to decrease below 70%, particularly in years of greater evaporative demand.
Macromanagement decisions at the seasonal boundaries should always be made in the context of having implemented appropriate day-to-day irrigation scheduling.
Proper day-to-day scheduling will provide much-needed information about the crop and soil water status and evaporative demand being experienced within the given year.
Corn has greater than anticipated ability to withstand early season water stress provided that the water stress can be alleviated during the early-reproductive period.
However, it should be reiterated that these results are not suggesting that irrigation can be delayed until anthesis.
Most irrigation systems cannot quickly alleviate severely depleted soil water reserves as was accomplished in this pre-anthesis studies, but the results do indicate there is some flexibility in timing of irrigation events within the vegetative growth period.
Timeliness of appreciable amounts of irrigation and/or precipitation near anthesis appears to be very important in maximizing yield potential.
if you plan to have nitrogen application this fall, consider the following to avoid over-application of nitrogen while reducing the potential of nitrogen loss.
Sample soil at 2or 3-foot depth to determine residual nitrate-N to be credited in nitrogen rate calculations.
Apply fertilizer-N  when the soil temperature is below 50F at the 4-inch soil depth and trending cooler.
Apply anhydrous ammonia rather than other N fertilizers.
Limit fall application of N to silt loams, silty clay loams, and finer textured soils.
Consider the use of nitrification inhibitors to slow the conversion of ammonium to nitrate, especially on coarse textured soils.
Avoid fall application on wet or flooding-prone soils.
Consider applying part of the nitrogen in the fall and applying the remaining in-season, preferably according to the results of pre-sidedress nitrate testing or canopy sensing.
Follow the UNL recommendations and plan to apply 5% more fertilizer-N with fall compared with spring application to compensate for the greater potential for N loss.
Water deeply, but infrequently.
Allowing the water to soak into the ground and letting the soil dry out between watering forces plants to produce strong, deep roots.
Mulch.
Mulch retains soil moisture, prevents erosion, controls weeds, and increases soil quality.
Install a rain sensor.
A rain senor turns the irrigation system off during and immediately after a rain event
 Don't water hardscapes.
Make sure sprinklers are watering the lawn and not the street or sidewalks.
Avoid heavy pruning.
Pruning stimulates growth and your plants will require more water.
Mature plants require less water.
Mature plants and trees have deep root systems and can be watered less frequently.
Use a rain gauge.
Typically, lawns requires 1 inch of water per week to stay healthy and up to 2 inches per week to stay green in the summer.
Take advantage of your downspouts.
Direct the downspout to your garden rather than draining towards the street.
Fix or replace broken sprinkler heads.
Take the broken irrigation head with you when buying a new one to ensure you get the right one.
Adjust your irrigation system.
Plants require less water in the fall and winter than in the spring and summer.
Check for leaks.
If you have a sudden increase in your water bill, dry or soggy areas in your yard, or overgrown turf areas you might have a leak.
The City of Oklahoma City has partnered with Oklahoma State University's Department of Horticulture and Landscape Architecture and Oklahoma Cooperative Extension Service to help promote outdoor water conservation.
The City of OKLAHOMA CITY UTILITIES DEPARTMENT
 Oklahoma Cooperative Extension Service Division of Agricultural Sciences and Natural Resources Oklahoma State University
 Oklahoma State University, in compliance with Title VI and VII of the Civil Rights Act of 1964, Executive Order 11246 as amended, Title IX of the Education Amendments of 1972, Americans with Disabilities Act of 1990, and other federal laws and regulations, does not discriminate on the basis of race, color, national origin, gender, age, religion, disability, or status as a veteran in any of its policies, practices or procedures.
This includes but is not limited to admissions, employment, financial aid, and educational services.
Not sure how much to water?
Homeowners often wonder how long they should irrigate their lawns, but the amount of water cannot be measured by time.
You can estimate how much water your yard is receiving by following a few simple steps.
1.
Gather 9 short, plastic rain gauges or use tuna cans to make your own.
2.
Place the rain gauges in a grid throughout the irrigated turfgrass areas in the lawn
 Start at the edge of the perimeter, set one rain gauge down and take 3 steps and place another cup.
Repeat until you have a grid.
3.
Irrigate the lawn for 20 minutes on a relatively non-windy day.
4.
After irrigating for 20 minutes, combine and measure the amount of water in all of the rain gauges, divide that by 9, then multiply by 3.
The answer is the average volume of water in 1 hour.
5.
At this point, the average volume can be measured against what is required to maintain a healthy lawn.
Table 1 shows the approximate average monthly irrigation needed for warm season and cool season grass
 Table 1: Average monthly evapotranspiration precipitation, and requirement for supplemental irrigation in Oklahoma County.
Month	Average	Average	Average
 ET	turf	Precipitation	Irrigation Need
 April	3.6	3.3	0.3
 May	4.0	3.8	0.2
 June	4.6	4.8	0.0
 July	5.4	3.0	2.4
 August	4.9	3.3	1.5
 September	3.4	3.3	0.1
 April	4.7	3.3	1.5
 May	5.3	3.8	1.5
 June	6.1	4.8	1.3
 July	7.2	3.0	4.1
 August	6.5	3.3	3.1
 September	4.5	3.3	1.2
 After completing this process, you'll have a very good estimate of average irrigation output in inches per hour.
Always adjust accordingly based on rainfall, temperature and wind.
While bermudagrass and buffalograss can be kept alive on lesser amounts, they may turn brown during extended droughts.
Strategies to Maximize Income with Limited Water
 Tom Trout Research Leader, Agricultural Engineer USDA-ARS Water Management Research Unit Ft.
Collins, CO 970-492-7419 Thomas.Trout@ars.usda.gov
 The best economic strategy for water limited agricultural production will often be maximizing income per unit of water available.
This requires information about the crop response  to water applied, ways to maximize the effectiveness of rainfall and efficiency of irrigation, forecasts of future weather, the costs and value of production, and strategies to optimally allocate the limited water supply.
Growers can make better decisions if they can predict at the beginning of the cropping season what crops and how many acres to plant.
Then during the season, they need to know where and when to apply their limited water supply for the next week and the remainder of the season.
They also could benefit from understanding the economic risks that result from inaccurate forecasts of irrigation water supply, weather, and crop and input prices.
This is a very complex problem best solved with the help of Decision Support Systems that incorporate simulation models of crop growth; projections of weather; and inputs of available irrigation water, production costs, and crop prices.
The core information required to best use limited water is the yield response of crops to water.
The Water Production Function, WPF , for a crop in terms of yield produced per unit of water applied, provides basic information needed to best allocate limited water supplies.
Yield response to water for numerous crops has been studied by many researchers for many years.
However, developing WPFs that are applicable to conditions different from the experimental conditions is difficult.
Response of a crop to applied irrigation water depends on rainfall amount, soil water storage and soil type, timing of irrigations, evaporative demand, irrigation method and efficiency, and crop cultivar.
Since it is impossible to include all of these variables in experimental trials, trials are often designed to mimic local conditions.
I believe a preferred approach is to base WPF trials on basic water balances so the information is most transferable to other conditions.
By basing the function on water consumed by the crop  rather than applied water, most of the effects of irrigation method and rainfall are eliminated.
The effects of irrigation method and efficiency, effective rainfall, and soil water storage can then be factored back in based on local conditions.
This method requires
 measurement of crop transpiration.
Crop water transpiration can be calculated by accurate measurement of water applied and stored in the root zone, measured changes in soil water storage, and estimates of soil evaporation.
This is most easily done with metered drip irrigation where small irrigations can be accurately and uniformly applied and surface evaporation is small.
Lysimeters can accurately measure transpiration, but are too expensive for most applications.
Transpiration can also be estimated with micrometeorological measurements such as Bowen Ratio or Eddy Correlation.
Navigable waters: The traditional view of this concept, was upheld in a Kansas case, State Ex Rel.
Meek vs.
Hays), which ruled that a stream must be navigable for commercial purposes to legally be considered navigable in fact.
If the stream or river was not used for commercial navigation at some point, then it is non-navigable.
Then the adjoining landowners therefore own to the thread  of the stream, and therefore no right of public recreation on the stream itself.
If the stream is navigable, the state owns the bed of the stream and the public has a right to recreate on the stream.
Water Restrictions: Sarasota County and Cities within County Boundaries
 All residents of unincorporated Sarasota County should follow landscape and irrigation water restrictions.
The restrictions apply to all sources of water including well, pond, or utility system.
Even numbered addresses  may water only on Tuesday.
Odd numbered addresses  may water only Thursday.
Common areas with no address, such as median or roadside plantings, clubhouse or recreation areas may be irrigated only on Tuesday.
The maximum amount of water applied is limited to three-quarters of an inch in each irrigation zone, on each allowable watering day.
Irrigation is prohibited between 10 a.m.
and 4 p.m.
on any allowable day.
Fountains and waterfalls may operate only eight hours per day.
No special watering allowances will be granted for verticutting or over-seeding.
New or replacement lawns: Watering may occur on the first day of installation any time of any day of the week.
After the first day, new lawns may be irrigated any day for another 29 days, before 10 a.m.
and after 4 p.m.
On days 31 through 60, new lawns may be irrigated up to 3 times a week, before 10 a.m.
and after 4 p.m.
Lawn watering is limited to twice per week.
Lawn watering days and times are as follows unless your city or county has a different schedule or stricter hours in effect.
Even addresses may water on Thursday and/or Sunday before 10 a.m.
or after 4 p.m.
Odd addresses may water on Wednesday and/or Saturday before 10 a.m.
or after 4 p.m.
Locations without a discernable address, such as rights-of-way and other common areas inside a subdivision, may water on Tuesday and/or Friday before 10 a.m.
or after 4 p.m.
Hand watering and micro-irrigation of plants  can be done on any day and at any time.
New lawns and plants: have a 30-30 establishment period, which allows any-day watering during the first 30 days.
During the second 30 days, watering is allowed three days per week: even-numbered addresses may water on Tuesday, Thursday and Sunday; odd-numbered addresses may water Monday, Wednesday and Saturday.
Reclaimed water is only subject to voluntary watering hours, unless restricted by the local government or utility.
City of North Port
 Addresses ending in even numbers Thursday and/or Sunday, before 10:00 a.m.
or after 4:00 p.m.
Addresses ending in odd numbers Wednesday and/or Saturday before 10:00 a.m.
or after 4:00 p.m.
No more than 3/4 inch of water may be applied to each irrigation zone on each allowable watering day.
There is no watering allowed during the hottest part of the day, 10:00 a.m to 4:00 p.m.
Non-lawn areas such as trees, flower beds and vegetable gardens may be hand-watered without restriction to day or time.
For newly-planted lawns and landscaped areas: New or Replacement Lawns: 30-30 establishment period, sixty days total, if needed.
Water any day during the first 30 days.
During the second 30 days, watering is allowed three days per week: even-numbered addresses may water on Tuesday, Thursday and Sunday; oddnumbered addresses may water Monday, Wednesday and Saturday; and locations without a discernable address may water on Tuesday, Friday and Sunday.
Other New Plant Establishment: Sixty days total, if needed.
Water any day during the first 30 days.
Even addresses may water only on Tuesday, Thursday and Saturday; Odd addresses may water only on Wednesday, Friday or Sunday during the next 30 days.
Time of day restrictions apply.
Watering is currently allowed one day per week regardless of the source water.
Addresses ending in odd numbers or letters AM may occur only on Sundays.
Addresses ending in even numbers or letters NZ may occur only on Tuesdays.
Irrigation may only take place during the hours of 12:01am to 10:00am or from 4:00pm to 12:00am; per Resolution 2001-12.
No matter where you live, use less when it comes to
 Be water wise and save the drops!
Venice residents may irrigate or hand water lawns and landscaping on the following days, if needed:
 Addresses ending in even numbers: Tuesday Addresses ending in odd numbers: Thursday
 Hand watering hot spots and microirrigation of other plants is allowed on any day at any time.
Car washing on residential property is limited to once a week.
Even-numbered addresses may wash on Tuesday or Saturday; oddnumbered addresses may wash on Wednesday or Sunday.
ALL WATERING MUST BE DONE BEFORE 8 A.M.
OR AFTER 6 P.M.
New lawns or landscape may be watered any day at anytime the day of installation.
During the first 60 days, they can be watered any day during the restricted hours.
Reclaimed or reuse water is not affected by the changes, but residents are asked to conserve water whenever possible.
Fig.
1.
Relationship between winter wheat grain yield and available soil water at wheat planting at Akron, CO.
FACTORS AFFECTING WATER STORAGE
 Time of Year/Soil Water Content The amount of precipitation that finally is stored in the soil is determined by the precipitation storage efficiency.
PSE can vary with time of year and the
 water content of the soil surface.
During the summer months air temperature is very warm, with evaporation of precipitation occurring quickly before the water can move below the soil surface.
Farahani et al.
showed that precipitation storage efficiency during the 2 1/2 months  following wheat harvest averaged 9%, and increased to 66% over the fall, winter, and spring period .
The higher PSE during the fall, winter, and spring is due to cooler temperatures, shorter days, and snow catch by crop residue.
From May 1 to Sept 15, the second summerfallow period, precipitation storage efficiency averaged -13% as water that had been previously stored was actually lost from the soil.
The soil surface is wetter during the second summerfallow period, slowing infiltration rate, and increasing the potential for water loss by evaporation.
Fig.
2.
Precipitation Storage Efficiency  variability with time of year.
Residue Mass and Orientation
 Studies conducted in Sidney, MT, Akron, CO, and North Platte, NE  demonstrated the effect of increasing amount of wheat residue on the precipitation storage efficiency over the 14-month fallow period between wheat crops.
Fig.
3.
Precipitation Storage Efficiency  as influenced by wheat residue on the soil surface.
As wheat residue on the soil surface increased from 0 to 9000 lb/a, precipitation storage efficiency increased from 15% to 35%.
Crop residues reduce soil water evaporation by shading the soil surface and reducing convective exchange of water vapor at the soil-atmosphere interface.
Additionally, reducing tillage and
 maintaining surface residues reduce precipitation runoff, increase infiltration, and minimize the number of times moist soil is brought to the surface, thereby increasing precipitation storage efficiency.
Fig.
4.
Precipitation Storage Efficiency  as influenced by tillage method in the 14-month fallow period in a winter wheat-fallow production system.
Snowfall is an important fraction of the total precipitation falling in the central Great Plains, and residue needs to be managed in order to harvest this valuable resource.
Snowfall amounts range from about 16 inches per season in southwest Kansas to 42 inches per season in the Nebraska panhandle.
Akron, CO averages 12 snow events per season, with three of those being blizzards.
Those 12 snow storms deposit 32 inches of snow with an average water content of 12%, amounting to 3.8 inches of water.
Snowfall in this area is extremely efficient at recharging the soil water profile due in large part to the fact that 73% of the water received as snow falls during non-frozen soil conditions.
Standing crop residues increase snow deposition during the overwinter period.
Reduction in wind speed within the standing crop residue allows snow to drop out of the moving air stream.
The greater silhouette area index  through which the wind must pass, the greater the snow deposition.
Data from sunflower plots at Akron, CO showed a linear increase in soil water from snow as SAI increased in years with average or above average snowfall and number of blizzards.
Typical values of SAI for sunflower stalks  result in an overwinter soil water increase of about 4 to 5 inches.
Fig.
5.
Influence of sunflower silhouette area index on over-winter soil water change at Akron, CO.
Silhouette Area Index (in2 in-2
 Because crop residues differ in orientation and amount, causing differences in evaporation suppression and snow catch, we see differences in the amount of soil water recharge that occurs.
The 5-year average soil water recharge occurring over the fall, winter, and spring period in a crop rotation experiment at Akron, CO shows 4.6 inches of recharge in no-till wheat residue, and only 2.5 inches of recharge in conventionally tilled wheat residue.
Corn residue is nearly as effective as no-till wheat residue in recharging soil water, while millet residue gives results similar to conventionally tilled wheat residue.
Fig.
6.
Change in soil water content due to crop residue type at Akron, CO.
Good residue management through no-till or reduced-till systems will result in increased soil water availability at planting.
This additional available water will increase yield in both dryland and limited irrigation systems by reducing level of water stress a plant experiences as it enters the critical reproductive growth stage.
Chapter 7: Insuring Corn in South Dakota
 Crop insurance is an important component for managing production and economic risks.
Crop insurance refers to the U.S.
Department of Agriculture's Risk Management Agency  programs that cover yield or revenue loss from multiple perils.
The coverage is sold to growers and landowners by private crop insurance companies and agents, although the policies are regulated and premium rates are established by the RMA.
The purpose of this chapter is to provide an overview of the common types and levels of crop insurance used in South Dakota corn production.
The cost of crop insurance can vary with changes in yield history, changes in price levels in the current year, and changes in the volatility for revenue products.
An understanding of the coverage types available is important because the premium cost varies with insurance type and because the insurance coverage should be matched to commodity marketing practices.
Knowledge of the coverage level is important because it may need to be adjusted to remain cost effective.
Insurance coverage for corn production was provided to 5.2 million South Dakota acres in 2015.
The statewide level of liability coverage for corn production was $2.2 billion, averaging $426 per insured acre in protection.
The liability was less than the expected value of the crop, reflecting the deductible.
The total premium averaged $73 per acre, but after subsidies the producer premium averaged $21 per acre.
The subsidy has led to a high adoption of insurance and coverage at higher levels than would otherwise be observed.
The adoption of coverage in South Dakota mirrors that in the Midwest, and a majority of corn acres have been insured in South Dakota since the late 1990s.
Information about crop insurance is commonly obtained from a crop insurance agent or the RMA website1.
Corn coverage details are outlined in the "Common Crop Insurance Policy," the "Coarse Grains Crop Provisions," and the "Commodity Exchange Price Provisions," or CEPP.
Yellow corn grown for grain on nonirrigated or dryland acres and using conventional production practices is the most common parameter used in South Dakota.
The RMA also has a fact sheet on corn for South Dakota.
Like for other crops, growers wanting farm-level coverage have to establish a production history.
Edwards  provides an overview of building a yield history and choosing among units when buying coverage.
Growers can use yield adjustments, where low yields for a unit can be replaced with 60% of the county transitional yield.
Units can be basic, optional, enterprise or whole-farm, and the premium subsidy is tied to the unit choice and coverage level.
In discussions with growers and agents, there has been a shift toward using enterprise units on corn.
This observation is consistent with the average observed premium subsidy that falls between that of basic/optional units and that of enterprise units.
Since 2012, many counties in South Dakota have had positive trend-adjustment factors for corn.
The factor is more heavily weighted for earlier years in a grower's production history, resulting in a higher approved yield.
The RMA reported that since 2012 there has been strong adoption of trend-adjusted yields in South Dakota.
The Agricultural Act of 2014 introduced other coverage options.
With the yield exclusion option, a yield year may be excluded from a grower's yield history if the county yield was sufficiently low.
For example, low yields  were common for corn in many central, south-central and southeast South Dakota counties in 2012 given the drought conditions that year.
The Supplemental Coverage Option  provides shallow-loss coverage, spanning the space between the farm-level election level of a policy and 86% of the county yield level or revenue level.
However, to be eligible for the SCO, a producer's base acres for the crop also need to be enrolled in Price Loss Coverage.
Based on data from the Farm Service Agency, less than 2% of the corn acres in South Dakota were enrolled in PLC.
Thus, adoption of SCO has been minimal.
Several dates are critical to assure the proper coverage is selected and in effect when needed.
For corn, the insurance must be purchased or changed by March 15 and the earliest planting date is April 10.
The final planting dates for full coverage vary slightly.
Corn for grain has a final planting date on irrigated and nonirrigated fields of May 25, except for counties in the southeast where the deadline is May 31.
For silage corn, the final planting date is May 31 regardless of the county or irrigation practice.
Silage has a price or value set by the RMA prior to the coverage deadline.
After the final planting date, there is a 25-day lateplanting period that provides reduced coverage.
The coverage is in effect until December 10.
Figure 7.1 Final planting dates of corn for grain in South Dakota with full insurance coverage.
Policy dates are aligned with the marketing patterns that are reported by the National Agricultural Statistics Service.
South Dakota corn planting dates generally range from April 30 through June 20, and the range of harvest dates is from September 30 through November 20.
Historically, corn has been marketed in October and November following harvest.
Claims can begin after the earliest planting date.
In the event of a loss, producers typically have 72 hours to notify their insurance agent of a potential claim.
After the final planting date, the most commonly used policies have prevented planting provisions, covering some of the expense of not growing the insured crop.
A grower may try to plant the insured crop in the late period or switch to a different crop.
Growers are responsible for using good farming practices, as defined in their policy, even after a partial loss, meaning they have to continue to take care of the crop.
Common reasons for insurance claims include: 1) drought, 2) natural causes , and 3) reduced corn quality.
Policy Types and Coverage Levels
 For corn production, the main policy types include: 1) Revenue Protection , 2) Yield Protection , 3) Revenue Protection with the Harvest Price Exclusion  and 4) Catastrophic Risk Protection.
These policy types are based on farm level yields.
Area Risk Protection Insurance  is also
 available in some counties to cover county-level yield or revenue loss, but it is seldom used.
Statewide in 2015, 97% of the insured corn acres were covered by RP.
The remaining acres were covered by YP, CAT, RP-HPE and ARPI.
With RP, there is a fixed guarantee level and either lower yields and/or lower prices may trigger an indemnity payment.
RP is designed to cover price increases and is ideal when producers use forward price contracts or hedge using futures contracts.
Note that there is a 200% limit on price changes by harvest, which is a feature specific to RP.
This caps the indemnity payment and could be managed by covering sales with call options.
With YP, a producer receives an indemnity payment at the fixed price per bushel if the resulting yield falls below the yield coverage level.
Harvest Price Exclusion 
 Figure 7.2 Counties in South Dakota with NAP and ARPI coverage.
RP-HPE is limited to downside revenue protection at a slightly higher cost than YP.
A price decline could trigger an indemnity payment with RP-HPE when YP would not have one.
RP-HPE costs less than RP and may be preferred if little forward pricing is expected.
Several counties in western South Dakota do not have grain coverage for nonirrigated acres: Butte, Custer, Fall River, Harding, Jackson, Lawrence, Meade and Pennington.
The Noninsured Crop Disaster Assistance Program  has been available in these counties with coverage for dryland grain.
In the Agricultural Act of 2014 the coverage for NAP was authorized to be available with buy-up to higher yield elections and with up to 100% of the price election level.
The cost is set at 5.25% of the liability.
Selecting Price Elections and Coverage Levels
 Once a policy type has been selected, a coverage level needs to be selected.
With RP and RP-HPE there is no price election option; one must use 100% of the projected price.
For YP, a producer can select less than 100% of the projected price.
To minimize the insurance premium, a producer could use a price election that closely aligns the insured price with the expected cash price.
For example, if the expected cash price is below the RMA's projected price, a price election of less than 100% may be appropriate.
Coverage level often refers to the yield coverage level or percent of the producer's production history.
Across policy types, the yield coverage level must be selected and can range from 50% to 85% coverage.
Between 2011 and 2015, most South Dakota corn producers selected 75% yield coverage.
However, the optimal level depends on a producer's willingness to be self-insured.
There is substantial variability in how much coverage is available across counties.
Specific to nonirrigated corn, the highest transition or "T" yield in 2015 was in Moody County at 156 bushels per acre and the lowest was in Todd County at 35 bushels per acre.
Producers may elect yield adjustments, yield exclusions, and trend-adjusted yields.
As a result, the approved yield can be much higher than T-yields.
Approved yields can be backed out of county data that includes irrigated and nonirrigated acres across policy types.
For example, the average approved yield in 2015 in Moody County was 178 bushels per acre for growers using RP with 75% coverage.
Observed average approved yields at the county level have been 10-40% higher than T-yields in recent years.
The RMA price discovery periods use the CBOT  December corn futures contract.
The projected price discovery period is from February 1 to February 28.
During this period, the average of the closing December corn futures contract prices is used to determine the Projected Price.
The Projected Price is used in YP to determine the price level at which indemnities are paid.
The Projected Price sets the minimum coverage level for RP and RP-HPE.
The harvest price discovery period is from October 1 to October 31.
During this period, the average of the closing December corn futures contract prices is used to calculate the Harvest Price.
The Harvest Price is combined with the actual yield to determine harvest revenue in RP-HPE.
The Harvest Price is also used in RP to determine whether higher coverage is relevant at harvest.
The unbiased nature of futures prices is evident based on the past 14 years.
The average change has been -$0.15 per bushel, which is not statistically different from zero.
Extreme moves are also evident as the price increased $1.82 per bushel in 2012 and decreased $1.27 per bushel in 2008.
The RP and RP-HPE insurance premiums are functions of the corn price volatility.
The volatility factor, as defined and measured by the RMA in late February for corn, has changed substantially through time and has ranged from 0.18 to 0.37.
Growers often respond to premium changes by adjusting yield coverage levels.
For planning purposes, knowing the volatility factor is useful to project premium costs.
Prior to the purchase deadline, the volatility factor can be estimated by finding the implied volatility  of the December futures price and adjusting it by 0.8 to adjust for the insurance period.
Implied volatility can be backed out of option prices or obtained from a market information provider.
Basis is the difference between the cash and future prices.
Basis is not factored into the projected nor harvest prices for crop insurance.
As such, the RMA prices likely exceed the expected and actual local cash prices.
For reference, the statewide price received by farmers  is shown for October along with the basis relative to the Harvest Price.
Basis variability is evident, ranging from -$0.13 per bushel in 2004 to -$1.44 per bushel in 2010, and this basis risk is not insurable.
Growers should be mindful that spot price changes may not correspond with indemnity payments.
The insurance settles during a fixed or static month , and therefore may not always line up with crop sales.
Thus, for growers hedging with futures or options, it may reduce the basis risk to use December
 Table 7.1.
South Dakota corn insurance and marketing factors.
Projected Price	Harvest Price	Change	Volatility Factor	October Cash	Basis 
 			Price 
 2002	2.32	2.52	0.20	0.18	2.21	-0.31
 2003	2.42	2.26	-0.16	0.20	1.95	-0.31
 2004	2.83	2.05	-0.78	0.21	1.92	-0.13
 2005	2.32	2.02	-0.30	0.21	1.60	-0.42
 2006	2.59	3.03	0.44	0.23	2.37	-0.66
 2007	4.06	3.58	-0.48	0.26	3.09	-0.49
 2008	5.40	4.13	-1.27	0.30	3.99	-0.14
 2009	4.04	3.72	-0.32	0.37	3.31	-0.41
 2010	3.99	5.46	1.47	0.28	4.02	-1.44
 2011	6.01	6.32	0.31	0.29	5.67	-0.65
 2012	5.68	7.50	1.82	0.22	6.61	-0.89
 2013	5.65	4.39	-1.26	0.20	4.22	-0.17
 2014	4.62	3.49	-1.13	0.19	3.09	-0.40
 2015	4.15	3.83	-0.32	0.21	3.37	-0.46
SOYBEAN IRRIGATION RESPONSE STUDY
 Evaluate the effects of various soil moisture levels and row widths on growth and yield of full season and double cropped soybeans.
Determine the optimal irrigation management strategy for full season and double cropped soybeans to maximize yield and profitability.
Determine the optimal row width for irrigated full season and double cropped soybeans to maximize yield and profitability.
Two studies will be conducted to determine the response of full season and double cropped soybeans to various soil moisture levels and row widths.
There will be a full season soybean and a double cropped soybean study.
The entire study area will be treated identically for all production inputs except irrigation.
Fertilizer will be applied based on the University of Delaware recommendations for soybean.
One soybean variety will be planted Mid-May for the full season study and one variety will be planted Mid-June for the double cropped study.
In both projects, plots will consist of soybeans planted in 7.5, 15, and 30 row widths.
Each plot will receive one of the following potential irrigation treatments and will be replicated five times.
Full season irrigation 
 No irrigation until flowering  then >50% soil moisture
 Limited irrigation  until flowering  then >50% soil moisture
 Limited irrigation  until pod development  then >50% moisture
 Limited irrigation  until seed development  then >50% soil moisture
 Limited irrigation  until flowering  then >50% soil moisture until pod development  then >70% soil moisture
 Evapotranspiration  based irrigation management using the Delaware Environmental Observing Systems weather station located on the research farm and the commonly accepted soybean crop coefficients
 Soil moisture will be monitored in each plot in the 15 in row width using Watermark soil moisture sensors placed at 4 in, 10 in, and 16 in below the soil line.
Soil moisture data will be transmitted wirelessly approximately 10 times daily from the field to a data logging receiver.
Moisture data will be viewed and interpreted daily to determine if any treatments require irrigation.
Irrigation in plots will be triggered whenever soil moisture reaches the specific treatment requirements at the 4 in or 10 in depth.
Weather data will be collected by a Delaware Environmental Observing System weather station located on the irrigation research farm.
The plant growth and development data will be analyzed to determine the effects of soil moisture levels and row spacing on plant growth and development.
In addition, soil moisture data will be analyzed to determine differences in soil moisture depletion between irrigation treatments.
Total water applied for each irrigation treatment will be determined and the economic implications of each irrigation management strategy will be calculated based on soybean yield.
A REVIEW OF MECHANIZED IRRIGATION PERFORMANCE FOR AGRICULTURAL WASTEWATER REUSE PROJECTS
 This paper will focus on a discussion of considerations and then some wastewater reuse projects which have failed, required significant changes to be successful or have succeeded.
An analysis will be presented of what leads to success and to failure of mechanized irrigation wastewater reuse projects both in the short and long run.
From the analysis a list of parameters will be discussed which are considered critical to a project's performance.
Only agricultural projects will be included in the discussion but many of the same drivers apply to industrial and municipal wastewater reuse projects.
Formerly on 'traditional' Midwest farms from the homestead days through the 1960's there typically were a variety of livestock maintained some for support of the farm family and some for market.
In most cases what livestock waste accumulated was handled primarily 'dry' or as a very thick slurry.
At different times of year the waste was applied to the fields with little to no regard for impact to ground or surface water or matching nutrient loading from the waste to nutrient use by the crop.
Numbers of animals per farm were relatively small and land fairly abundant.
With the introduction of the Clean Water Act in the early 1970's and other legislative action, combined with dramatic changes in the number of head of livestock per farm have lead us to a very different situation.
Today more and more the waste water producer does not own the land or sufficient land and must depend on working with neighboring farms to environmentally properly 'dispose' of their wastewater stream
 Land application of wastewater with mechanical move irrigation equipment both center pivot and linear has been successfully used for many years.
Since the early 1980's the equipment and techniques for irrigating with fresh water have changed dramatically and many of these changes have been incorporated into mechanized equipment used for land application.
While these changes have brought significant improvements, also in today's world we must take into account other issues and particularly public perception of land application systems.
Mechanical move irrigation equipment has been used for land application of waste water for reuse from municipal, industrial and
 agricultural sources.
Mechanized irrigation, due to its characteristics, is considered to have advantages with regards to applying waste water for reuse, particularly from a lagoon with large amounts of water to handle.
Some of these characteristics include limited labor input required, application uniformity, ease in handling large volumes of effluent and particularly the ability to apply to actively growing crops with minimal negative impact to the crop.
For our discussion we will focus on center pivots.
Pivots can also apply during periods of adverse climatic conditions which may prevent or prove challenging to conventional waste handling techniques requiring tractors and other equipment to move through the field..
Some concerns have been expressed include "Land application of wastes may be imposing in some locations, potentially dangerous conditions relative to environmental quality"..
Many projects choices are dictated by more than just the equipment to be used.
Also critically important is the project meets public scrutiny.
Some land application projects are very successful for many years and others are abandoned or shut down after a relatively short time.
In many cases the livestock operation producing the meat or milk has very little interest in crop production.
So they are looking for somewhere to go with their waste.
So what could be better than having a source of water and plant nutrients right next to your corn fields?
Many livestock operations today produce large volumes of nitrogen and water.
For example a 2,000 head dairy using flushing may produce in excess of 1000 acre inches of 'water' and 250,000 pounds of nitrogen.
Just considering the nitrogen, this has a potential value of $ 45,000 if it can be used to replace the purchase of commercial nitrogen fertilizers.
And on the flip side what could be better than having somewhere to go with all of the waste you are producing potentially saving you significant capital investment and operating cost each year.
So as a farmer near a facility what could possibly go wrong with agreeing to take waste water from a dairy, hog or beef operation or as a waste producer in sending it to an irrigator?
The answer is just about anything or everything!
Let us consider some specific potential issues.
This in itself may be a challenge.
Both partners must agree on nutrient management plan and crops need to match nutrient loading for the land area.
The farmer may be pushed to change his cropping plan by adding winter forage which may work well as long as the livestock operation is willing to buy but if not creates marketing challenges for the farmer.
To get everyone to agree on the same design is commonly a major issue -
 Fast delivery of large volumes
 May need to eliminate large volumes early in the season and/ or late
 May have chunks and trash
 Even volume over season
 Really only wants effluent when crop needs it
 Wants sprinkler package with good uniformity
 Construction cycle may interfere with crop production while installing pipelines and mechanical move irrigation equipment.
Delivery effluent when they want
 May deliver more 'objects' than anticipated Irrigator wants:
 -Take effluent when they want
 No need to clean nozzles
 The only thing they both agree on is they do not want any problems with neighbors and minimal labor required.
Let's now focus on some specific projects and their performance.
A review of the original choices considered, concerns, project developed, challenges and benefits will be considered.
1) Project for farrowing operation which was hydraulically challenged.
a.
Choices considered were direct injection or center pivots
 i.
Area needed for land application 125 acres
 b.
Concerns with using center pivot
 C.
Project developed with center pivots in 2001
 i.
Project expanded in 2003 with center pivots
 ii.
Project expanded in 2004 with center pivots
 iii.
Hog operation paid to install the pump, pipe and center pivot.
d.
Hog operation pays operating costs for the pumping
 ii.
Potential for getting pivots stuck
 ii.
Ability to apply during growing season
 Due to previous problems with being able to get into the fields to apply with a direct injection, center pivots were considered the preferred solution.
A farmer was identified early on and the design was developed to meet the hog and farm operations.
Getting stuck was a problem and early pivots commonly were not operated in complete circles due to wet spots.
Have added flotation options to specific drive units which as minimized the problem.
Livestock producer continued to identify possible farms for expansion and did a good job of explaining the benefits.
Hog operation happy Irrigator mostly happy
 2) Project for integrated hog production which was nutrient limited.
a.
Choices considered were direct injection or center pivots
 i.
Area needed for land application 195 acres
 b.
Concerns with using center pivot
 C.
Project developed with direct injection during 2000
 i.
Inability to apply during growing season
 ii.
Inability to apply early in the season when the fields were wet
 The hog operation was convinced center pivots would have the potential for too many odor issues.
They did not want to consider some of the advanced design sprinkler packages available.
Their vision was limited to impact sprinklers on top of the pipe.
In addition little effort was put into identifying a crop producer who might be interested in participating with a center pivot.
Hog operation ???
Land owners ???
3) Project for large dairy.
a.
Choices considered were direct injection or center pivots
 i.
Area needed for land application 325 acres
 b.
Concerns with using center pivot
 i.
Handling of sand 
 ii.
Neighbors wanted drops on pivot due to perception of odor
 C.
Project developed with center pivots during 2004 using existing pivots near the barns.
The dairy installed the pump station and piping to the pivots at their expense.
d.
Operating cost for pumping is paid by the dairy.
i.
Civil engineering design team 
 ii.
Plugging sprinkler packages
 iii.
Delivery of effluent early in the spring
 The dairy operation was convinced center pivots would have the potential to make things easy and keep their costs low.
They  did not complete the installation to the original design to remove sand and solids so many problems with sprinkler nozzles plugging plus wanted to pump when the farmer was trying to plant.
Farmer wanted to maintain good uniformity as was on loamy sand soils but due to narrow spacing of drops and small nozzle sizes has plugging problems.
The last time the participants met was not a happy experience!
Additional designs are being considered to resolve the issues.
Dairy not happy Irrigator not happy
 4) Project for large beef feedlot which was hydraulically challenged.
a.
Choices considered were traveling guns or center pivots
 i.
Area needed for land application 260 acres
 b.
Concerns with using center pivot
 ii.
Too much water at certain times
 C.
Project developed with center pivots during 2002 by piping to existing pivot irrigators at feedlots cost.
d.
Feedlot pays pumping costs.
i.
No even flow of effluent problems shifting between wastewater and freshwater
 ii.
Too much water early in the season and after storm events
 This situation uses the lagoons to control runoff from the pens.
The irrigator did not understand the effluent would primarily only be available after storm events and over winter.
The nutrient management plan made it appear there was equal distribution over the season.
Then even if there was water to be pumped as long as the lagoons were not near capacity, the feedlot does not want to spend the money for energy to pump and hope evaporation will take care of their problem.
The farmer becomes the last resort and does not have any dependable source of water.
Feedlot happy Irrigator not happy
 Land application using mechanical move irrigation equipment has proven very beneficial to many reuse projects and can be cost effective over the life of the project.
One of the keys to successful projects is an integrated approach to the design combining hardware, agronomic principles, management and neighbors together with the wastewater producer.
An analysis of the projects above would indicate the key parameters to be:
 Land application system should fit with the existing management and/or treatment processes.
Sufficient land must be available for the expected nutrient and hydraulic load with some allowance for the future.
Early identification of a potential farmer
 Design must be sensitive to the local concerns about odor, impact on visual landscape and other possible concerns.
Projects must be reviewed periodically to ensure operation is meeting the design basis and the participants' needs.
Continuing education must be kept up for consulting engineering firm's personnel so they understand the equipment, the concepts and agronomics of a land application water reuse system.
Key design considerations for the center pivots would be:
 Ability to apply very small depths to help manage lagoons
 High speed pivot operation
 Control and remote monitoring
 Packages such as Field Sentry, Pivot Alert, Tracker and others
 Control panels with sensor packages such as wind, rain and others
 Close attention to sprinkler packages
 Space as wide as possible to use larger nozzles
 Use of regulators or flow control nozzles
 Determine impact if no regulators used
 Review options available from sprinkler manufacturers
 Use of flotation technology
 Tracks on drive units
Soil water tension is a measure of how hard plants have to work to extract water from the soil.
Some advantages for resistance sensors are that they are relatively inexpensive and have been widely researched and calibrated for different soil types in Nebraska.
CENTER PIVOT AND LINEAR MOVE
 North Carolina,Cooperative Extension Service
 North Carolina State University
 Field Calibration Procedures for Animal Wastewater Application Equipment
 CENTER PIVOT AND LINEAR MOVE
 Land application equipment used on animal production farms must be field calibrated or evaluated in accordance with existing design charts and tables according to state rules that went into effect September 1, 1996.
Technical Specialist certifying waste management plans after September 1, 1996, must also certify that operators have been provided calibration and adjustment guidance for all land application equipment.
The rules apply to irrigation sysitems as well as all other types of liquid, slurry, or solid application equipment.
Information presented in manufacturers' charts are based on average operating conditions for relatively new equipment.
Discharge rates and application rates change over time as equipment ages and components wear.
As a result, equipment should be field calibrated regularly to ensure that application rates and uniformity are consistent with values used during the system design and given in manufacturers' specifications.
Field calibration involves collection and measurement of the material being applied at several locations in the application area.
This publication contains step-by-step guidelines for field calibration of center pivot and linear move irrigation systems.
Operating an irrigation system differently than assumed in the design will alter the application rate, uniformity of coverage, and subsequently the application uniformity.
Operating with excessive pressure results in smaller droplets, greater potential for drift, and accelerates wear of the sprinkler nozzle.
Pump wear tends to reduce operating pressure and flow.
With continued use, nozzle wear results in an increase in the nozzle opening, which will increase the discharge rate while decreasing the wetted diameter.
Clogging of nozzles or crystallization of main lines can result in increased pump pressure but reduced flow at the sprinkler.
Plugged intakes will reduce operating pressure.
An operating pressure below design pressure greatly reduces the coverage diameter and application uniformity.
Field calibration helps ensure that nutrients from animal waste are applied uniformly and at proper rates.
The calibration of a center pivot and linear move irrigation systems involves setting out collection containers, operating the system, measuring the amount of wastewater collected in each container,
 then computing the average application volume and application uniformity.
An in-line flow meter installed in the main irrigation line provides a good estimate of the total volume pumped from the lagoon during each irrigation cycle.
The average application depth can be determined by dividing the pumped volume by the application area.
The average application depth is computed from the formula:
 Average application depth  = Volume pumped  27,154  X Application area 
 The average application depth is the average amount applied throughout the field.
Unfortunately, sprinklers do not apply the same depth of water throughout their wetted area.
Under normal operating conditions, application depth decreases towards the outer perimeter of the wetted diameter.
Sprinkler systems are designed to have overlap to compensate for the declining application along the outer perimeter.
When operated at the design pressure, this overlap results in acceptable application uniformity.
When operated improperly, well-designed systems will not provide acceptable application uniformity.
For example, if the pressure is too low, the application depth will be several times higher near the center of sprinkler and water will not be thrown as far from the sprinkler as indicated in manufacturers' charts.
Even through the average application depth may be acceptable, some areas receive excessively high application while others receive no application at all.
When applying wastewater high in nutrients, it is important to determine the application uniformity.
Collection containers distributed throughout the application area must be used to evaluate application uniformity.
Many types of containers can be used to collect flow and determine the application uniformity.
Standard rain gauges work best and are recommended because they already have a graduated scale from which to read the application depth.
Pans, plastic buckets, jars, or anything with a uniform opening and cross section can be used provided the container is deep enough  to prevent splash and excessive evaporation, and the liquid collected can be easily transferred to a scaled container for measuring.
All containers should be the same size and shape.
All collection containers should be set up at the same height relative to the height of sprinkler nozzle.
Normally, the top of each container should be no more than 36 inches above the ground and no more than 36 inches below the sprikler or nozzler discharge elevation.
Collectors should be located SO that there is no interference from the crop.
The crop canopy should be trimmed to preclude interference or splash into the collection container.
Calibration should be performed during periods of low evaporation.
Best times are before 10 a.m.
or after 4 p.m.
on days with light wind.
On cool, cloudy days the calibration can be performed anytime during the day when wind velocity is less than 5 mph.
The volume  collected during calibration should be read as soon as the system completely passes over the row of collection containers to minimize evaporation from gauges.
Where a procedure must be performed more than once, containers should be read and values recorded immediately after each different setup.
Calibration Setup for Center Pivot and Linear Move Irrigation Systems
 Center pivot and linear move irrigation systems are calibrated by placing a row  of collection containers parallel to the system as shown in Figures 1 and 2.
Two or more rows increase the accuracy of the calibration.
For center pivot systems with multiple towers, place the first collection container beside the first moving tower ).
This will miss the area between the boss and first tower, but it is necessary to omit this area because too much time is required to operate the system through this zone.
The area missed will be less than 3 acres and will usually represent less than 10 percent of a typical sized system.
If the system has only one moving tower, place the first container 100 feet from the boss tower.
Place containers equally spaced to the end of the system.
For lateral move systems, place containers throughout the entire length of the system.
Containers should be spaced no further apart than one-half the wetted diameter of rotary impact sprinklers, 1/4 the diameter of gun sprinklers, or 50 feet, whichever is less.
On systems with spray nozzles, collection containers should be spaced no further than 30 feet.
A 20 to 25 foot spacing is generally recommended for all types of sprinklers which will result in 6 to 8 collection containers between each tower.
Collection containers should be placed such that they intercept discharge from a range of lateral distances from the sprinkler.
This can be accomplished by selecting a catch can spacing different from a multiple of the sprinkler spacing along the lateral.
Where end guns are used, the transect of collection containers should extend beyond the throw of the gun.
The system should be operated so that the minimum travel distance exceeds the sprinkler wetted diameter for the container closest to the boss tower.
Application volumes should be read as soon as all gauges stop being wetted.
1.
Determine the wetted diameter of the sprinkler, gun, or spray nozzle,
 2.
Determine the necessary spacing between collection gauges.
The spacing should not exceed 50 feet.
Twenty-five feet or less is generally recommended.
3.
Determine the number of gauges required.
Label gauges outward from the boss tower.
4.
Place gauges along a row as labeled and shown in Figure 2, equally spaced at the distance determined in item 2.
The row should be in the direction of system travel and at least one-half sprinkler wetted diameter from the sprinkler nearest the boss tower.
Note: The alignment of the row relative to the center pivot system does not matter as long as the system operates completely over each collection gauge.
For most setups, the gauges closest to the boss tower will control how long the system must be operated to complete the calibration.
5.
Operate the system for the time required for the sprinkler nearest the boss tower to completely pass the collection containers.
Record the time of operation  and distance traveled  at a reference point along the system.
6.
Immediately record the amounts collected in each gauge.
7.
Add the amounts in #6 and divide by the number of gauges.
This is the average application depth.
Sum of amounts collected in all gauges Average application depth = Number of gauges
 8.
Where an end gun is used, identify those gauges at the outward end where the depth caught is less than 1/2 the average application depth computed in #7.
The distance to the last usable gauge is the effective diameter of the system from which the effective acreage is computed.
Field Calibration Procedures for Animal Wastewater Application Equipment
 Figure 2.
Accounting for overlap when calibrating a hard hose traveler system.
9.
Recompute the average application depth for the "usable" gauges identified in #8 that fall within the effective width of the system.
Note: All gauges interior to the "effective width" of the system are included in the computations regardless of the amount caught in them.
Distance traveled  10.
Compute the reference travel speed and compare to the manufacturer's chart Time 
 11.
Calculate the deviation depth for each "usable" gauge.
The deviation depth is the difference between each individual gauge value and the average value of all gauges.
Record the absolute value of each deviation depth.
is dropped and all values are treated as positive).
The symbol for absolute value is a straight thin line.
For example, 2 means treat the number 2 as an absolute value.
It does not mean the number 121.
Because this symbol can lead to misunderstandings, it is not used with numbers in the worksheets at the end of this publication.
The symbol is used in formulas in the text.
Deviation depth = Depth collected in gauge i average application depth| "i" refers to the gauge number
 12.
Add amounts in #11 to get "sum of the deviations" from the average depth and divide by the number of gauges to get the average deviation.
Sum of deviations  Average deviation depth = Number of usuable gauges
 13.
Determine the application uniformity.
The application uniformity is often computed using the mathematical formula referred to as the Christiansen Uniformity Coefficient.
It is computed as follows: average depth  average deviation  U = 100 average depth 
 14.
Interpret the calibration results.
The higher the index value, the more uniform the application.
An index of 100 would mean that the uniformity is perfect -the exact same amount was collected in every gauge.
For center pivot and linear move systems operated in light wind, an application uniformity greater than 85 is common.
Application uniformity between 70 to 85 is in the "good" range and is acceptable for wastewater application.
Generally, an application uniformity below 70 is considered unacceptable for wastewater irrigation using center pivots and linear move systems.
If the computed Uc is less than 70, system adjustments are required.
Common problems include: clogged nozzles, sprinklers not rotating properly, inadequate system pressure, sprinklers installed in wrong order, end gun not adjusted properly, wrong end gun nozzle, and/or worn nozzles.
Contact your irrigation dealer or Certified Technical Specialist for assistance.
Table 1.
Example calibration data for a center pivot system operated with rotary impact sprinklers and an end gun.
Date: Landowner Farm No.
Sprinkler rated diameter 60 ft
 Gun wetted radius 120 ft
 Sprinkler spacing along lateral 9 feet or a mutiple thereof
 
 Gun distance from boss tower 600 ft
 Number of towers 3 Tower spacing 180 ft
 b.
Distance to first gauge 190 ft
 Spacing between collection containers Select 20 ft
 Calibration area length  Number of gauges =
 System length Distance tower one + end gun radius
 600 ft 190 ft + 120 ft
 + 1 = 27.5
 so use 28 gauges
 Table 1.
Example Calibration Data 
 d.
Start of irrigation event 7:15 a.m.
e.
End of irrigation event 8:30 a.m.
f.
Duration  75 minutes
 g.
Travel distance  415 feet
 h.
Operate the system, collect data, and record on the worksheet, opposite.
i.
Sum of all catches 8.09 inches
 j.
Average catch  0.289 inches
 k.
Usable catches  0.15 inches
 Adjusted average 
 = 7.98 inches / 26 containers = 0.307 inches
 I.
Sum of all deviations from the average catch 0.546 inches
 m.
Average deviation from average catch  0.021 inches
 n.
Uniformity coefficient 307 0.021 U = 0.307 = X 100 = 93 
 15 14 Wind direction 13 10 8 5 3 2 1 g
 Table 1.
Example Calibration Data 
 Gauge	Distance	Volume	Deviation
 No.
from Boss	Collected	from Average*
 1	190	.31	.003 
 2	210	.29	.017 
 3	230	.27	.037 
 4	250	.28	.027
 5	270	.33	.023
 6	290	.29	.017
 7	310	.30	.007
 8	330	.31	.003
 9	350	.30	.007
 10	370	.31	.003
 11	390	.34	.033
 12	410	.35	.043
 13	430	.31	.003
 14	450	.30	.007
 15	470	.36	.053
 16	490	.33	.023
 17	510	.32	.013
 18	530	.30	.007
 19	550	.30	.007
 20	570	.29	.017
 21	590	.28	.027
 22	610	.29	.017
 23	630	.32	.013
 24	650	.35	.043
 25	670	.32	.013
 26	690	.22	.087
 *Absolute value; treat all values as positive.
Irrigation System Calibration Data Sheet for Center Pivot and Linear Move Irrigiation System
 End gun wetted radius
 Sprinkler spacing along lateral
 End gun distance from boss tower
 b.
Distance to first gauge
 Spacing between collection containers
 Calibration area length  Number of gauges =
 System length Distance to tower + End gun radius
 d.
Start of irrigation event
 e.
End of irrigation event
 g.
Travel distance 
 h.
Operate the system and collect data
 i.
Sum of all catches
 j.
Average catch 
 k.
Usable catches 
 Adjusted average 
 I.
Sum of all deviations from the adjusted average catch
 m.
Average deviation from average catch 
 o.
Interpret the calibration data and make necessary adjustments.
Contact an irrigation dealer or Certified Technical Specialist if adjustments are needed.
Gauge	Distance	Volume	Deviation
 No.
from Boss	Collected	from Average*
 *Absolute value; treat all values as positive.
Prepared by R.O.
Evans, Biological and Agricultural Engineering Extension Specialist J.C.
Barker, Biological and Agricultural Engineering Extension Specialist J.T.
Smith, Biological and Agricultural Engineering Assistant Extension Specialist R.E.
Sheffield, Biological and Agricultural Engineering Extension Specialist
 2,500 copies of this public document were printed at a cost of $1,617, or $.65 per copy.
NORTH CAROLINA COOPERATIVE EXTENSION SERVICE
Overseeding Winter Grasses into Bermudagrass Turf
 David Kopec and Kai Umeda
 In the lower elevation desert of Arizona, the warm-season turfgrasses  become dormant and typically lose their green color during winter.
Overseeding bermudagrass with a cool-season grass provides a yearlong green lawn.
An oveseeded winter turf provides an aesthetic landscape and functionally provides a recreational turf.
Overseeding is the practice of seeding a cool-season winter grass into the existing bermudagrass lawn prior to it going into dormancy for the winter.
The most common winter grass, perennial ryegrass, is planted into the prepared bermudagrass turf and it becomes green from October through May.
St.
Augustinegrass and zoysiagrass generally are not suited for overseeding.
October is ideal for overseeding when daytime air temperatures are 80-85F and nighttimes are about 55F.
Overseeding too early when temperatures are warmer favors bermudagrass and prevents the winter grass from getting established.
Later overseedings may be threatened by frost when young seedling grasses may be damaged.
Cool-season grass choices for winter turf include:
 Annual ryegrass 
 Light green color, coarse leaves, and fast growing
 Inexpensive grass for home lawns and commercial landscapes where moderate turf quality is desired.
Perennial ryegrass 
 Deep green color, narrow leaves, and has improved frost tolerance with better resistance to diseases
 More expensive than annual ryegrass and produces a better quality winter turf
 Persists longer in the spring and competes with bermudagrass that is greening up
 Ahybrid between perennial and annual ryegrass with some desirable and undesirable qualities of each
 Roughstalk bluegrass 
 Fine-textured grasses commonly used for golf course greens
 Creeping bentgrass 
 Very fine-textured grasses used for golf course greens
 30 days before overseeding
 Stop nitrogen fertilization of the bermudagrass lawn
 14 days before overseeding
 Raise the mowing height 30 40%
 Decrease irrigation by 30%
 1 3 days before overseeding
 Mow at the "old" height that was before raising 3040%
 Just prior to overseeding, lower the mowing height another 25-30% and leave the clippings as mulch for the overseeded seed
 Do NOT scalp the bermudagrass to the ground level
 For dense bermudagrass hybrid varieties, perform shallow, vertical mowings or lightly dethatch to reduce thatch and promote adequate seed contact with soil
 
 Amount of seed to use
 Use ryegrass seed at 12 to 15 lb/1000 ft2
 Apply one-half of the seed by walking the spreader in one direction and the other half of the seed by walking in a pattern perpendicular to the first pass
 Drag or lightly rake the seed into the turf to ensure good soil contact or mow seeds into turf with a reel mower
 Table.
Sequence of activities to prepare and achieve successful overseeding for winter turf
 30 days before overseeding	Stop nitrogen fertilization of the bermudagrass lawn
 14 days before overseeding	Raise the mowing height 30 40%
 Decrease irrigation by 30%
 1 3 days before overseeding	Stop watering
 Mow at the "old" height that was before raising 30-40%
 Just before overseeding, lower the mowing height another 25 30% and leave the clippings as
 mulch for the overseeded seed
 Day of overseeding	Use ryegrass seed at 12 to 15 lb/1000 ft2
 Apply one-half of the seed by walking in one direction and the other half of the seed by walking in
 a pattern perpendicular to the first pass
 7-10 days after overseeding	Irrigate 3-4 times per day to keep germinating seed moist
 14 days after seedling emergence	Fertilize with ammonium phosphate  at 5 lb of product per 1000 ft2
 First mowing	When ryegrass height approaches 3 inches
 Irrigate 3 to 4 times per day for the first 7 to 10 days, until seedlings emerge.
Do not allow germinating seed to dry out.
When seedlings are established, gradually reduce watering interval to about once a week.
The top 6-inches of soil should remain moist.
If a long screwdriver easily penetrates the soil to a depth of six inches and comes out damp, no additional irrigation is needed
 At 2 weeks after seedling emergence, fertilize with ammonium phosphate  at lb/1000 ft2.
Always water after applying fertilizer.
Over fertilizing can increase likelihood of frost damage, disease occurrence, and necessitate extra mowing.
Grass should be mowed when dry and with a mower having sharpened blades.
Ryegrass should be first mowed when height reaches 23/4 to 3 inches
 A rotary mower can be set to mow at 21/4 to 23/4 inches
 reel mower on higher quality turf can mow the turf at 1 to 11/2 inches
 Bermudagrass resumes growth when spring nighttime temperatures remain above 60F for seven consecutive nights.
This generally occurs during April to May.
Encourage bermudagrass growth by lowering mowing heights by 35% and mow more often
 Apply nitrogen fertilizer weekly at a rate of 0.25 lb/1000 ft2
 Do not stop irrigating.
Any drying could slow bermudagrass growth
 Once 80% of the lawn is established as bermudagrass, complete the transition by lightly verticutting to remove the ryegrass, apply 0.25 0.50 lb N/1000ft2 and decrease watering for one week.
Repeat the fertilizer application and water cycle to put stress on the ryegrass.
Aerify bermudagrass during late June, July, through August
 During the summer, bermudagrass should grow for 100 days to establish and grow vigorous roots and rhizomes.
After 100 days of active growth, overseeding may be accomplished successfully.
COLLEGE OF AGRICULTURE & LIFE SCIENCES Cooperative Extension
 THE UNIVERSITY OF ARIZONA COLLEGE OF AGRICULTURE AND LIFE SCIENCES TUCSON, ARIZONA 85721
 DAVID KOPEC Extension Turfgrass Specialist KAI UMEDA Area Extension Agent
 CONTACT : KAI UMEDA KUMEDA@CALS.ARIZONA.EDU
MODELING COTTON GROWTH AND YIELD RESPONSE TO IRRIGATION PRACTICES FOR THERMALLY LIMITED GROWING SEASONS IN KANSAS
 Later planting and greater site elevation or latitude decreased seasonal growing degree days and cotton yield in Kansas.
Higher irrigation capacity  usually increased lint yield, which was probably due to increased early boll load.
Strategies for splitting land allocations between high irrigation rates and dryland did not increase production.
Cotton may reduce irrigation withdrawals from the Ogallala aquifer, but the Kansas growing season limits production.
ABSTRACT.
Precipitation in the western Great Plains averages about 450 mm, varying little with latitude and providing 40% to 80% of potential crop evapotranspiration.
Supplemental irrigation is required to fully meet crop water demand, but the Ogallala or High Plains aquifer is essentially non-recharging south of Nebraska.
Pumping water from this aquifer draws down water tables, leading to reduced water availability and deficit irrigation to produce an alternate crop such as cotton  with a lower peak water demand than corn.
Our objective was to compare simulated cotton yield response to emergence date, irrigation capacity, and application period at three western Kansas locations  with varying seasonal energy or cumulative growing degree days  and compare split center pivot deficit irrigation strategies with a fixed water supply.
We used actual 1961-2000 location weather records with the GOSSYM simulation model to estimate yields of cotton planted into soil at 50% plant-available water for three emergence dates  and all combinations of irrigation period  and capacity.
Simulated lint yield and its ratio to ET or water use efficiency , consistently decreased with delayed planting  as location elevation or latitude increased due to effects on growing season CGDD.
Depending on location, simulated cotton lint consistently increased  for scenarios with increasing irrigation capacity, which promoted greater early season boll load, but not for durations exceeding 4 to 6 weeks, probably because later irrigation and fruiting did not complete maturation during the short growing season.
Cotton WUE generally increased, with greater yields resulting from earlier emergence and early high-capacity irrigation.
We calculated lower WUE where irrigation promoted vigorous growth with added fruiting forms that delayed maturation and reduced the fraction of open bolls.
The irrigation strategy of focusing water at higher capacities on a portion of the center pivot in combination with the dryland balance did not increase net yields significantly at any location because the available seasonal energy limited potential crop growth and yield response to irrigation.
However, the overall net lint yield was numerically larger for focused irrigation strategies at the southwest Kansas location.
Based on lint yields simulated under uniform or split center pivot deficit irrigation, we conclude that cotton is poorly suited as an alternative crop for central western and northwestern Kansas because of limited grow-
 Submitted for review on 9 January 2020 as manuscript number NRES 13877; approved for publication as a Research Article and as part of the National Irrigation Symposium 2020 Collection by the Natural Resources & Environmental Systems Community of ASABE on 17 October 2020.
Mention of company or trade names is for description only and does not imply endorsement by the USDA.
The USDA is an equal opportunity provider and employer.
Keywords.
Cotton, Crop simulation, Deficit irrigation, Evapotranspiration, Irrigation capacity, Split center pivot irrigation, Water use efficiency, Yield limiting factors.
T he semiarid U.S.
High Plains physiographic region, extending from Texas to South Dakota, receives mean annual precipitation of approximately 450 mm, which provides 40% to 80% of the corresponding potential crop water demand for evapotranspiration .
To meet the balance of ETc, irrigation from the High Plains aquifer was developed
 during the 1950s with groundwater withdrawals that generally exceeded the negligible recharge.
The spatially weighted water-level change in the High Plains aquifer since pre-development  averages -4.8 m overall and -8 m in Kansas , in contrast to the limited variable changes of alluvial aquifers along the Colorado-Kansas border or central Kansas.
In western Kansas, the annual groundwater declines for the Ogallala region of the High Plains aquifer averaged 0.16 to 0.51 m over the past 20 years, with an average recommended pumping reduction of 30% to achieve irrigation sustainability, i.e., no change in the water table.
The declining water table has triggered a growing concern for the eventual depletion of the aquifer and reduction of irrigated areas in the central and southern High Plains by the year 2100, as estimated by Haacker et al..
The irrigated production levels in the southern and central Great Plains have been sustained, in part, by the development of additional wells to compensate for declining saturated thickness and reduced pumping capacities.
However, extending the longevity of the aquifer will require reduction in irrigated land area or some combination of increased irrigation efficiency and alternative crops.
Improved irrigation scheduling and application technologies that increase irrigation efficiency  have produced corresponding water savings of 1.96% and 3.91%, calculated as a fraction of the total irrigation demand, in the Texas High Plains.
Additional water savings averaging 8.26% of the irrigation demand could be achieved through the production of alternate crops that exhibit greater tolerance of water deficit stress.
For western Kansas, alternative crops gaining interest include grain sorghum  Moench.) and cotton , a potentially more profitable crop.
The median seasonal ETc estimated for the Texas High Plains with a calibrated Soil and Water Assessment Tool  model was 450 mm for cotton, or approximately 30% less than the ET for corn  of 635 mm.
On the merit of potential water savings when growing cotton rather than corn in the Ogallala region of Kansas, Gowda et al.
evaluated cotton production using the growing season energy expressed as cumulative growing degree days  calculated as the sum of the daily average of the minimum and maximum air temperatures minus a base temperature of 15.6C.
Their model used growing season energy to determine cotton growth and estimate lint yield assuming a typical plant density.
Gowda et al.
determined that cotton was a suitable alternative crop for conserving groundwater irrigation in the southwest Kansas Ogallala region despite any growing season energy limitations.
They also concluded that some irrigation strategies may be managed to extend cotton production to higher elevations and more northern U.S.
latitudes.
For example, by imposing water stress, Baumhardt et al.
induced cotton cutout and further flowering, which significantly reduced the number of green bolls while not reducing either the number of open bolls or lint yield.
Converting production of corn to cotton in western Kansas must confront challenges to identify suitable production practices for the alternative crop while promoting profitability and desirable yields under deficit irrigation.
Computer
 crop growth simulation has long been recognized as an efficient means of evaluating cultural practices  and evaluating some dryland cropping systems.
Cotton simulation has experienced increasing use by nontraditional crop modelers to gain production insights related to economics and climate issues.
Crop growth model guidance for improved management response to environmental factors increased growing season irrigation efficiency.
Modeling cotton growth, as concluded by Modala et al.
for the Texas Rolling Plains, may identify successful deficit irrigation strategies for producing a relatively new crop in western Kansas.
Using the GOSSYM cotton model, Baumhardt et al.
confirmed that cotton lint yield and water use efficiency , or the ratio of lint yield to ET, represented functionally as: WUE 
 increased with increasing initial soil water or greater irrigation capacity.
Application of a fixed water resource to a center pivot split 2:1 between irrigation at 3.75 mm d-Superscript and dryland and split 1:1 between dryland and 5.0 mm d-Superscript irrigated areas  or multiple spatial combinations  produced greater net cotton yields compared with uniform irrigation at 2.50 mm d-Superscript.
Although reducing irrigation duration from 8 weeks to 4 weeks decreased modeled yield of cotton irrigated at 2.5 mm d-Superscript by 14% at Bushland, Texas, increasing the irrigation capacity to 3.75 and 5.0 mm d-Superscript in 2:1 and 1:1 split center pivot applications increased the net yield after 4 weeks to 95% of the 8-week uniform irrigation that received double the water.
Grower-managed water availability for irrigation is often dictated by economic returns of competing crops and by well pumping capacity, which has led to cropping alternatives such as cotton.
While the CGDD analysis reported by Gowda et al.
demonstrated the impact of limited growing season energy to decrease the yield potential of full ETc irrigated cotton, the effect of deficit irrigation strategies to reduce applications or advance maturation  is not known for western Kansas.
The objective of this study was to develop irrigated cotton production information for the limited growing season energy conditions of western Kansas that improves water conservation through more efficient water application.
To achieve this goal, we compared simulated cotton yields having different emergence dates under various irrigation duration and pumping capacity combinations and evaluated net yields for applied split pivot irrigation strategies.
MATERIALS AND METHODS STUDY SITES
 Irrigation capacity and duration effects on the growth and yield of cotton with normal emergence  and two progressively later emergence dates  were evaluated for locations in southwest, west central, and northwest Kansas  with specific site locations and
 Figure 1.
Southwest, west central, and northwest Kansas sites used for modeling cotton response to irrigation application capacity and period.
elevations listed in table 1.
To do this, we used the mechanistic cotton growth simulation model GOSSYM  version 4, which simulates C, N, and water processes subject to stresses due to solar radiation, temperature, rainfall, wind, and soil conditions.
Related models  were developed without equating dewpoint and daily minimum temperatures, which led GOSSYM to underestimate ETc in arid climates.
However, Staggenborg et al.
concluded that leaf area index  caused more errors in calculated ET for semiarid climates.
CROPGRO-Cotton is another process-oriented model that simulates daily crop development and carbon, N, and soil water balances , but modeled yields did not consistently agree with observed 2005 and 2006 lint yields.
GOSSYM requires sitespecific climate input data, including observed daily solar irradiance , precipitation , and wind run.
These climate data were supplied from 1961-2000 weather records that predate the period when observed global warming was no longer indistinguishable from human-induced warming, according to the IPCC.
By confining weather data to a period with only random climate variability or a stationary series , the simulated cotton response to scenario emergence and the irrigation rate and duration were not confounded by climate change effects that biased the seasonal energy.
Although not the dominant soil at any site, we selected a nearly level  Ulysses silt loam  for the
 Table 1.
Georeferenced location, elevation , and mean growing season  of the modeled sites.
Modeled	Georeferenced	Elevation	Energy
 Site	Location	ASL)	
 Colby	39 23' N, 101 2' W	962	832
 Tribune	38 28' N, 101 45' W	1100	859
 Garden City	37 58' N, 100 51' W	865	945
 Hugoton	37 18' N, 101 W	940	1170[a]
 [a] Mean CGDD for the 2005-2012 Hugoton trials excludes 2008 and 2010 due to auxin herbicide damage.
simulations because it covers 11% to 25% of the county at all three locations.
Using a common soil eliminated any soil X location interaction and simplified interpretation of location crop performance differences due to irrigation rate and duration.
The Ulysses 1.9 m deep profile was divided into two layers that included a mollic epipedon  and underlying cambic horizons  with measured bulk density, texture, N, and hydrologic properties adapted from pedon ID 89P0734.
Each simulation began with an assumed initial soil water content of 50% plant-available water  uniformly distributed within the profile, although greater water would likely increase yield.
That amount of moisture is close to the ~170 mm of soil water measured for 0 to 1.9 m by Schlegel et al.
at the time of planting for deficit-irrigated  corn, sorghum, and soybean crops in western Kansas.
Modeled maximum rooting depth was unrestricted within the 1.9 m Ulysses soil profile and consistent with water extraction patterns to depths of 1.6 to 1.9 m reported for cotton grown in 2.2 m deep lysimeters at Bushland, Texas.
Cotton simulations were based on typical 0.76 m row spacing at 13 plants m-2 population using a stripper-type cultivar with a growth habit similar to All-Tex Atlas , as described in the variety file ST1 supplied with GOSSYM.
The variety files contain numerous parameters that modify the modeled plant growth and development through carbohydrate partitioning to reflect dry matter governing height, nodes, squares, bolls, and yield.
Sufficient N to maximize lint yield for available water up to 700 mm  or a yield equal to the variety trial 1200 kg ha-1 mean for desirable CGDD  was provided by Ulysses soil profile N of ~33 kg N ha-1  plus 110 kg fertilizer.
No other nutrient fertilizers were specified because GOSSYM does not simulate their effects on cotton growth.
Adequate infiltration of rain and irrigation into the Ulysses soil typically results in negligible runoff  and was not simulated.
All simulations began two weeks before the scenario emergence 10 d after a 15 May target planting date  plus sequential emergence delays of 1 and 2 weeks to DOY 152 and 159.
Growing season simulations continued from the prescribed emergence until plants reached physiological maturity  or the first freeze, when lint yield and growing season ET were determined.
Because cotton has been recognized as an alternative crop for Kansas , ongoing variety trials were conducted in southern Kansas, including about 15 km northeast of Hugoton  in southwest Kansas.
At that site, irrigated cotton variety trials following irrigated corn provided lint yield performance data from 2005 to 2012, excluding 2008 and 2010 due to auxin-type herbicide injury.
The annual variety trials, planted in 0.76 m row
 spacing at 13 plants m population on DOY 144 +2, varied in number of entries from 14 to 49, with few repeated >3 years.
We used the overall observed yield means from one dryland and six irrigated trials in assessing model performance independently of compared location, emergence, or irrigation duration and pumping capacity.
Cotton received customary crop protection chemicals and non-limiting irrigation and fertility applications from the cooperating producers who hosted these trials.
Cotton was sampled at maturity or following a killing freeze for lint yield and fiber quality at the Texas Tech Fiber and Biopolymer Research Institute, Lubbock, Texas.
Cotton yield was estimated by GOSSYM simulations for a stripper-type cultivar described in the variety file ST1 planted in 0.76 m row spacing at 13 plants m-2 population on DOY 145.
The model-required soil bulk density, texture, N, and hydrologic properties were specified for a 1.9 m Ulysses soil profile at a uniformly distributed initial soil water content of 50% plant-available soil water.
Nutrients specified for GOSSYM included the Ulysses profile 33 kg N ha-Superscript and 110 kg ha-Superscript fertilizer, or roughly double that recommended for irrigated cotton by Duncan et al..
Modeled lint yield was determined at plant physiological maturity  or the first freeze.
Cotton growth, lint yield, and water use were simulated under dryland conditions  or with decreasing deficit irrigation.
That is, irrigation, applied independently of crop growth stage, included three rates of 2.5, 3.75, and 5.0 mm d-Superscript that typify the variation in regional irrigation capacities of ~0.29, 0.43, and 0.58 L ha-1 and correspond to weak, declining, and strong producing irrigation wells.
Irrigation applications to supplement rainfall were on a 7 d interval beginning 37 d after emergence, or around first square, and continuing for incrementally increasing durations of 4, 6, 8, and 10 weeks to characterize cotton response to progressively later applications.
The cumulative irrigation depth resulting from the different combinations of irrigation capacity and period simulated over the growing season are shown in figure 2.
A total of 13 scenarios comprised of dryland, 0.0 mm d-1 plus all possible combinations of irrigation capacity 
 Figure 2.
Depth of irrigation applied using rates of 2.5, 3.75, and 5.0 mm dfor periods of 4 to 10 weeks showing incrementally greater application with increasing duration and similar or common amounts applied earlier in the growing season for higher irrigation rates.
and duration  for applications from 70 to 350 mm were evaluated for each of three emergence dates during 40 years of weather records at each of the three sites, amounting to 4,680 simulations.
Cotton growth, lint yield, and ET were simulated and WUE was calculated for each scenario emergence date by irrigation capacity and duration combination under the unique input weather conditions from 40 growing seasons at each location.
Normal climatic variability from the weather conditions, e.g., rainfall and temperature, unique for each growing season  supplied, as 40 replicates, the random experimental variability for comparing GOSSYM projected cotton performance.
We plotted by declining rank all growing season CGDD and yield values from the combined scenarios of irrigation practices and emergence dates at each location as a function of the nontransformed probability of being exceeded  according to Barfield et al..
We then compared the emergence date by irrigation capacity and duration fixed effects at each location according to a factorial arrangement of a completely randomized design replicated by years as random effects using the SAS mixed model ANOVA procedures.
Again using years as random effects, we subsequently isolated simulated cotton water use, growth, and lint yield at each location to compare scenario emergence date and irrigation capacity by duration fixed effects by location.
Unless otherwise specified, all statistical analysis effects were declared significant at the 0.05 probability level.
RESULTS AND DISCUSSION MODEL UNCERTAINTY
 Any cotton production insight using crop growth simulation largely depends on the validity of the simulation model to calculate plant performance under variable growing conditions.
For GOSSYM, previous model validation by Staggenborg et al.
demonstrated that the calculated daily water use was within one standard deviation of measured values and seasonal totals differed by ~10% for irrigated cotton under semiarid southern High Plains conditions.
Similarly, the observed and modeled dryland lint yields at Bushland, Texas, about 180 km north agreed well with observations, achieving an RMSE that was ~20% of the mean yield.
For Kansas, GOSSYM-estimated yields are plotted in figure 3 across overall means of as many as 49 cultivars from ongoing variety trials conducted near Hugoton, Kansas, 228 km NNE of Bushland.
Observed varietal mean yields + standard error generally agreed with the corresponding model-simulated yields and appear along the 1:1 line up to modeled yield estimates exceeding 1400 kg ha-1 where the observed yields averaged about 1700 kg ha-1.
Regressing observed on simulated yields through a 0.0 intercept produced R2 = 0.93 and a slope of 1.11 due to model underestimation of the higher 1600 to 1800 kg ha-Superscript observed yields.
We suggest that this yield underestimation was possibly because the N specified to meet crop needs for the expected 1200 kg ha yield was insufficient compared with the 33% to 50% higher actual
 Figure 3.
Mean lint yields of cotton cultivar trials in southwest Kansas from 2005 to 2012 plotted in relation to GOSSYM-simulated yields for corresponding emergence and irrigation conditions.
Error bars represent standard errors of mean observations and are plotted with both 1:1 and regression lines that intercept the origin.
yields.
Despite the possible N deficit, GOSSYM-simulated lint yields averaged ~90% of the mean observed yields of multiple cultivars, suggesting robust model performance that, taken in aggregate, shows reliable calculated yields.
Validation of GOSSYM using local soil parameters and weather has been consistently successful at sites spanning a ~400 km distance from Lubbock to Bushland  and on to Hugoton.
This suggests that model application for an additional ~250 distance north from Hugoton to Colby can provide reasonable management inferences despite no further validation in lieu of variety performance data.
GROWING SEASON CGDD AND LINT YIELD
 Growing season accumulated GDD beginning with emergence and continuing until first freeze often governs cotton performance and varies with elevation, latitude, and regional weather patterns.
For our three Kansas locations, the greatest CGDD averaged across all emergence dates was 945 GDD C at Garden City and ranged from a minimum of 753 GDD C to a maximum of 1288 GDD C.
In contrast, the corresponding CGDD averaged 859 GDD C for Tribune, ranging from 571 to 1116 GDD C, and averaged 832 GDD C for Colby, ranging from 598 to 1086 GDD C.
Each week of emergence delay decreased the CGDD by approximately 28 GDD C at Garden City, by 23 GDD C at Tribune, and by 22 GDD C at Colby, which reflected the declining seasonal CGDD accrual due to increasing elevation and, to a lesser extent, more northern U.S.
latitude.
The seasonal CGDD minimum of 750 GDD C at Garden City was, in fact, greater than that observed at Tribune for nearly 20% of the years and greater than that observed at Colby for about 25% of the years.
Although the median CGDD at Garden City exceeded 85% of the observations at Tribune and 69% of the observations at Colby, the corresponding energy maximums of about 1100 GDD C at Tribune and Colby exceeded all observed CGDD except the largest 7% to 10% of the growing seasons at Garden City.
To put growing season CGDD in perspective, Gowda et al.
specified crop failures when growing season CGDD did not exceed 800
 GDD C, which compares with the median growing season CGDD of 803 GDD C at Colby and 832 GDD C at Tribune.
Thorp et al.
noted that many crop models, including GOSSYM, use a growing degree day concept based on air temperature to simulate crop processes and development, which makes CGDD critical to yield.
The corresponding simulated lint yields for fully irrigated  and decreased by 20% to 25% with each week of delayed emergence.
In Kansas, the cotton lint yield, like growing season CGDD, was greatest for Garden City at 604 kg ha and decreased to 365 kg ha at Tribune and 314 kg ha at Colby with increasing latitude or elevation, which was similar to modeled dryland cotton yield trends in the Texas High Plains.
That is, Garden City lies at an elevation 235 m below and 55 km east of Tribune and 97 m below and 158 km south of Colby, thus contributing to the median lint yield at Garden City that exceeded 85% to 95% of the simulated lint yields at Tribune and Colby.
The minimum simulated lint yields at Garden City, which ranged from 145 to 445 kg ha-1, exceeded 30% to 40% of the simulated lint yields at Tribune and Colby for the corresponding planting dates.
Frequent 0.0 kg ha-1 lint yield estimates reflect the risk of crop failure and indicate the unsuitability of cotton as an alternate crop.
Gowda et al.
estimated crop failure for three out of four years in seven of eight northwestern counties from around Tribune, Kansas, to north of Colby, Kansas.
Our calculated yields of less than 100 kg ha-1 for Colby and Tribune likewise comprised 10% to 30% of simulated lint yields and may represent an undesirably large fraction for risk-averse producers.
Using a simple linear regression of growing season CGDD on simulated lint yield for the combined locations and emergence dates , we determined that a growing season CGDD not exceeding 700 GDD C was insufficient to produce minimal  lint yield, essentially a crop failure.
An overall simulated target lint yield of 500 kg ha was correlated  to a minimum CGDD of 900 GDD C, although yield increased by 100 kg ha-Superscript incrementally with each 50 GDD C additional CGDD during the growing season.
Our simulated yield conversion rate for accumulating growing season energy was very similar to the 42 GDD C used when estimating potential cotton yield for the southern and central High Plains.
For example, early  emergence cotton at Garden City had sufficient growing season CGDD for simulated lint yields exceeding 500 kg ha-1 during 85% of the years, as compared with 75% and 65% when emergence was delayed by 7 and 14 days, respectively.
Likewise, simulated lint yield of 500 kg ha-1 for irrigated cotton at Tribune and Colby decreased by ~20% after a 14-day emergence delay during more than one-third of the 40 growing seasons.
These cotton yields under full ET replacement irrigation revealed poor production with limited growing season CGDD in west central  or northwestern  Kansas.
However, the potential risk of growing cotton with insufficient growing season CGDD on a Ulysses soil has been shown to be
 Figure 4.
CGDD for the period 1961-2000 at the three locations considered  and simulated cotton lint yield  plotted as a function of exceedance probability for cotton emerging on day-of-year  145, 152, and 159.
manageable with deficit irrigation that limited water use to promote fruit maturation.
EFFECTS OF EMERGENCE, IRRIGATION CAPACITY, AND DURATION ON COTTON LINT YIELD
 Simulated mean cotton lint yields for the scenario irrigation capacities, durations, and emergence date combinations are summarized for main effects by location in table 2.
The overall average yield decreased significantly  from 604 kg ha-1 at Garden City to 365 kg ha 1 at Tribune and 314 kg at Colby because of location limited growing season CGDD that failed to mature bolls compared with Garden City.
Progressively later emergence dates likewise decreased both growing season length and, consequently, yield at all three locations  again due to reduced boll maturation.
Irrigation capacity and duration together determine the cumulative irrigation amounts that regulate potential yield depending on growing season CGDD.
As irrigation capacity increased from dryland or 0.0 mm d-1 to 5.0 mm d-1, cotton lint yield increased significantly from 229 to 697 kg ha-Superscript at Garden City, with a modest increase of ~250 kg ha at Tribune and Colby but no yield differences between the 3.75 and 5.0 mm di irrigation capacities.
The diminished irrigation capacity yield benefit for later crop emergence and resulting lower CGDD  was a significant interaction, although increasing irrigation capacity is a significant and logical benefit to yield.
Greater irrigation duration translates into increased water application and consequently larger plants and a greater boll load; however, our simulated yields never differed significantly for irrigation durations >8 weeks for any location.
While irrigation durations of 4, 6, and 8 weeks incrementally increased lint yield  at Garden City, simulated cotton yields for Tribune increased as
 irrigation duration increased above 4 weeks or increased from 6 to 10 weeks, suggesting that growing season CGDD limited crop response to irrigation.
This limited growing season CGDD effect on yield response to irrigation was further demonstrated at Colby by a non-significant 15 kg lint yield increase as the irrigation season duration increased from 4 to 10 weeks.
Earlier crop emergence combined with both decreased latitude and elevation limits growing season CGDD to interact with crop yield response to irrigation capacity and duration, as revealed in preliminary analyses and shown in figure 5.
That is, greater irrigation duration or capacity typically increased lint yield to a smaller extent as location elevation or latitude increased and as plant emergence was delayed.
The desirable incremental lint yield increases for the progressively longer 4 to 10 week durations of 2.5 mm d-Superscript irrigation diminished after the irrigation capacity increased to 5.0 mm d-Superscript, and yields did not differ for durations greater than 6 weeks.
Location-specific mean cotton water use ranged from 450 mm at Tribune up to 465 mm at Garden City with an overall average of ~460 mm, indicating that crop water use was largely independent of location, unlike either growing season energy for the dependent yield.
Not surprisingly, our simulated water use at all locations increased for the progressively earlier emergence dates due to the resulting longer growing season for maturing bolls.
The incrementally greater irrigation capacities, increasing from 0.0 to 5.0 mm d-1, also significantly increased simulated water use at Garden City and Colby, but water use at Tribune for the 3.75 and 5.0 mm d-Superscript irrigation capacities did not differ significantly.
Our calculated water use also increased  as irrigation duration increased incrementally from 4 to 10 weeks regardless of location.
For scenarios with either greater irrigation capacity or
 Table 2.
Main effects of emergence dates , irrigation capacity , and duration  on simulated cotton lint yield, ET, and WUE along with ANOVA test results.
Effect means within columns followed by the same letter are not significantly different.
Lint Yield	Water Use	Water Use Efficiency	Fraction of Open Bolls
 		
 Garden	Garden	Garden	Garden
 Effect	City	Tribune	Colby	City	Tribune	Colby	City	Tribune	Colby	City	Tribune	Colby
 145	710 a	465 a	397 a	480 a	463 a	481 a	0.147 a	0.099 a	0.083 a	67 a	46 a	38
 152	609 b	367 b	317 b	466 b	452 b	464 b	0.131 b	0.079 b	0.068 b	58	36	301 b
 159	493 c	263 c	227 c	448 c	436 c	440 c	0.111 c	0.060 c	0.051 c	46	25	20
 0.0 	229 d	149 c	180 c	278 d	271 c	305 d	0.070 c	0.049 c	0.055 c	66	49	37 a
 2.5	480 c	305 b	285 b	415 c	405 b	428 c	0.114 b	0.073 b	0.066 b	64 b	41	32b
 3.75	634 b	380 a	323 a	470 b	456 a	468 b	0.137 a	0.083 a	0.069 a	55 c	34	28 c
 5.0	697 a	409 a	334 a	509 a	490 a	490 a	0.139 a	0.082 a	0.067 ab	53	32	28c
 4	544 c	335 c	304 a	404 d	394 d	414 d	0.134 a	0.083 a	0.073 a	60 a	38	30 a
 6	603 b	364 b	314 a	447 c	434 c	449 c	0.135 a	0.082 a	0.069 b	57 b	361	29 a
 8	631 a	378 ab	319 a	485 b	469 b	479 b	0.130 b	0.078 b	0.066 c	56 b	35	29 a
 10	638 a	382 a	319 a	522 a	504 a	506 a	0.121 c	0.073 c	0.062 d	56b	34 b	29 a
 Significance 	Significance 	Significance 	Significance F)
 Emergence 	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01
 Irrig.
capacity 	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.02	<0.01	<0.01	<0.01
 ExC	<0.01	<0.01	0.67	0.77	0.23	0.97	<0.01	0.17	0.99	0.41	0.01	0.57
 Irrig.
duration 	<0.01	<0.01	<0.06	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01	0.06
 D x E	0.70	0.43	0.99	>0.99	0.99	0.99	0.98	0.98	0.88	0.99	0.99	0.99
 D x C	0.06	0.06	0.53	<0.01	<0.01	0.02	<0.01	<0.01	0.02	0.01	0.70	0.33
 DxCxE	>0.99	>0.99	>0.99	>0.99	>0.99	>0.99	>0.99	>0.99	>0.99	>0.99	>0.99	>0.99
 duration, the increased water available to the crop probably promoted greater evaporative losses and more vigorous plant growth that, consequently, increased cumulative water use.
The simulated water use means for the drought-tolerant alternative crop of cotton are comparatively lower than the reported ~650 mm ET for fully irrigated corn currently grown at these locations , the range of 635 to 677 mm for three different tillage systems and three plant densities in a four-year field study at Colby , and the 679 mm simulated for automatically irrigated corn at Garden City.
Although cotton water use for all locations typically increased with the earlier emergence and greater irrigation capacity and duration main effects, one significant interaction between irrigation capacity and duration was identified.
To illustrate this interaction, we plot simulated cotton water use at Garden City for each of the non-zero irrigation capacities and duration combinations within the three emergence dates, as shown in figure 6.
The simulated cotton water use for any emergence date incrementally increased with each additional 2-week water application up to 10 weeks, and the water use increment varied with irrigation capacity.
For example, simulated water use for the 2.5 mm d-Superscript irrigation capacity consistently increased by about 32 +2.5 mm with each 2-week, 35 mm irrigation increment ending on weeks 6, 8, and 10.
Cotton water use for the 3.75 mm d-Superscript irrigation capacity similarly increased by a near-uniform 42 +2.5 mm for each biweekly increment.
In contrast, the 5.0 mm d-Superscript irrigation capacity resulted in a declining water use from 52 mm during the initial 4 to 6 weeks, to 41 mm for the 6 to 8 weeks interval, and ended with 37 mm for weeks 8 to 10.
The declining biweekly water use may be due to meeting crop demand for initial vigorous growth and fruiting form development during the early to mid-growing season for the 5.0 mm d- irrigation capacity.
The WUE reflects both growing season CGDD and the effects of irrigation amount and timing on the cotton lint yield.
Due to the combined effects of decreased elevation and latitude in increasing the growing season energy, both simulated yields and the dependent WUE were significantly  greater for Garden City, averaging 0.13 kg m-3 compared with Tribune at 0.079 kg m-3 and Colby at 0.067 kg m-3.
For all locations, WUE increased significantly  with progressively earlier emergence dates as a predictable result of the corresponding higher growing season energy and yield, but emergence delays of only one week depressed WUE.
Mean WUE under lower-yielding dryland conditions was significantly  less than any simulation scenario with irrigation, regardless of location.
In contrast to Colby, where WUE with irrigation ranged from 0.066 to 0.069 kg m , WUE at Tribune and Garden City for the 2.5 mm d-Superscript irrigation capacity increased with either the 3.75 or 5.0 mm d-Superscript irrigation capacities that met crop water demand.
Similarly, the calculated WUE at Colby ranged from 0.073 to 0.062 as irrigation duration increased from 4 to 10 weeks, while WUE at Tribune and Garden City was optimized by shorter duration irrigation periods of 4 to 6 weeks compared with irrigations for 8 weeks or longer that progressively decreased WUE.
The significant interacting effects of irrigation duration and capacity on WUE, as shown in figure 7, exemplify a conditional benefit of short-duration irrigation at higher capacity.
That is, WUE was generally elevated at all locations and for all emergence dates as the number of weeks of irrigation at the 5.0 mm d-Superscript capacity decreased from 10 weeks to a minimum of 4 weeks.
Decreasing irrigation at the 3.75 mm d-Superscript capacity from 10 weeks to a minimum of 6 weeks at Garden City or to a minimum of 4 to 6 weeks for Colby and Tribune met crop water demand sufficiently to elevate WUE.
When irrigation capacity supplied 2.5 mm d-1, the duration to meet crop demand for higher WUE increased to a
 Figure 5.
Simulated  lint yields for cotton that emerged on day-of-year  145, 152, and 159 and was irrigated for 4, 6, 8, and 10 weeks at 2.5, 3.75, 5.0 mm d-Superscript in Garden City, Tribune, and Colby, Kansas.
Columns for common locations and emergence dates with the same letter are not significantly different  using Tukey.
minimum of 6 to 8 weeks at Tribune and Garden City, while the minimum 4-week duration maintained WUE at Colby.
The cotton lint yield WUE values at Garden City were similar to experimental values measured with disk tillage at Bushland during growing seasons accumulating average monthly GDD  but in the lower range reported by Zwart and Bastiaanssen.
Although simulated lint yields generally increased with irrigation amount, the calculated WUE values at Tribune and Colby were much lower by comparison because the limited CGDD was insufficient to mature the crop boll load acquired with the greater water use.
The crop consumed water less efficiently to expand biomass resulting from increased leaf area, and fruiting forms did not directly contribute to lint yield that was proportionately lower.
That is, in addition to adequately meeting crop water demand, longer duration and higher capacity irrigation scenarios promoted vigorous canopy growth and a greater simulated LAI, averaged across emergence dates, that exceeded 3.1.
Similarly, robust fruiting resulted in an overall average of 88 green and open bolls m-2 at Colby, which increased to 95 and 114 bolls m-2 at Tribune and Garden City, but generally varied less than 10% with earlier emergence or higher irrigation capacity and was practically unaffected by application period.
Our simulations revealed that the fraction of open bolls decreased as the location elevation and latitude increased, averaging 57% at Garden City while becoming significantly lower at Tribune and Colby.
For all locations, the percentage of open bolls also decreased significantly with the progressively later emergence due to the CGDD-limiting shorter growing season length, as well as decreasing when irrigation capacity increased to 5 mm d-Superscript at Garden City or to 3.75 mm d-Superscript at Tribune and Colby.
Except for Colby, the open boll fraction was significantly greater for irrigations lasting 4 weeks compared with longerduration scenarios with often larger fruit loads.
The significant location, emergence, and irrigation capacity and duration main factor effects on the percentage of open bolls and location-specific interactions between emergence and irrigation capacity at Tribune and irrigation capacity and duration at Garden City are shown in figure 8.
We observed a progressively larger fraction of open bolls at the more southerly
 Irrigation Capacity, mm d-
 Figure 6.
Simulated  water use of cotton emerging on day-of-year  145, 152, and 159 and irrigated for 4, 6, 8, and 10 weeks at 2.5, 3.75, 5.0 mm d-Superscript in Garden City.
Columns for common emergence dates with the same letters are not significantly different  using Tukey.
Figure 7.
Mean calculated water use efficiency  of cotton emerging on day-of-year  145, 152, and 159 that was irrigated for 4, 6, 8, and 10 weeks at capacities of 2.5, 3.75, 5.0 mm d-Superscript in Garden City, Tribune, and Colby, Kansas.
Columns for a specific location and emergence date with the same letter are not different  using Tukey.
locations of Tribune and Garden City with greater irrigation capacity and duration combinations.
Increasing irrigation capacity combined with duration or emergence produced a declining but small difference in the percentage of open bolls because the impacts of both factors overlap at locations with limited growing season energy.
These results suggest that WUE was governed more by factors limiting boll maturation, specifically seasonal CGDD, than the availability of water to support overall plant growth and fruiting.
Using modeled lint yield results for the Garden City, Tribune, and Colby locations, we compared three fixed water resource irrigation management strategies for the early emergence cotton that extends the growing season.
Figure 8.
Fraction of open bolls for cotton emerging on day-of-year  145, 152, and 159 that was irrigated for 4, 6, 8, and 10 weeks at capacities of 2.5, 3.75, 5.0 mm d-Superscript in Garden City, Tribune, and Colby, Kansas.
Columns for a specific location and emergence date with the same letter are not different  using Tukey.
Strategies included:  uniform full pivot deficit irrigation at 2.5 mm d-1,  splitting the center pivot at a 2:1 ratio with irrigation at 3.75 mm d-Superscript on the larger fraction and an unirrigated balance, and  evenly divided split-pivot irrigation at a 1:1 ratio with 5.0 mm d-Superscript on half and no irrigation on the balance.
Dryland lint yields were ~50% of the uniform 2.5 mm d-1 irrigation capacity with yields that averaged 550 kg ha-Superscript at Garden City and 389 kg ha-Superscript at Tribune.
As a result of diminished crop response to irrigation at Colby due to limited growing season energy, the dryland yields averaged 65% of the uniformly irrigated  yield of 363 kg ha-1.
Likewise, simulated lint yields increased by 36% to 51% over those for 2.5 mm d-Superscript irrigation capacity to 748 to 831 kg ha for irrigation capacities of 3.75 and 5.0 mm d-Superscript at Garden City.
In contrast, the corresponding lint yields for
 Table 3.
Garden City, Tribune, and Colby, Kansas, 40-year mean simulated lint yield for DOY 145 emergence cotton under dryland and uniform irrigation at 2.5, 3.75, and 5.0 mm d-Superscript capacities applied for 10 weeks and calculated weighted-average yields of split pivot irrigation strategies compared with uniform 2.5 mm d-Superscript irrigation capacity.
Split pivot application strategies used irrigated to dryland ratios of 2:1 at 3.75 mm d-Superscript and 1:1 at 5.0 mm d .
Irrigation	Corresponding	Fraction of	Weighted Yield by	Yield Fraction of
 Application	Capacity	Mean Yield[a]	2.5 mm d-Superscript Yield	Application Strategy{	Uniform Application
 Location	Strategy				
 Garden City	Uniform	2.50	550 c	100	550 c	100
 2:1	3.75	748 b	136	590 c	107
 Dryland	273 d	50
 1:1	5.00	831 a	151	552 c	100
 Dryland	273 d	50
 Tribune	Uniform	2.50	389 b	100	389 b	100
 2:1	3.75	481 a	124	381 b	98
 Dryland	183 c	47
 1:1	5.00	525 a	135	354 b	91
 Dryland	183 c	47
 Colby	Uniform	2.50	363 b	100	363 b	100
 2:1	3.75	408 a	112	350 b	96
 Dryland	235 c	65
 1:1	5.00	420 a	116	328 b	90
 Dryland	235 c	65
 [a] Location-specific yield means followed by the same letter are not significantly different.
higher irrigation capacities increased by modest amounts at Tribune and Colby, possibly due to the higher elevation effects at Tribune and more northern latitude at Colby.
That is, the increasingly limited growing season energy at Tribune and Colby decreased cotton lint yield response to the higher irrigation capacities, as corroborated by similar mean cotton yields for all emergence dates.
The mean weighted yields of the uniform, 2:1, and 1:1 application strategies are listed together with the corresponding yield fraction of the uniform 2.5 mm dirrigation in table 3 for each location.
At Tribune and Colby, yield means for the 2:1 and 1:1 irrigation strategies were 2% to 10% less than their respective 389 and 363 kg ha simulated yields with uniform irrigation, but they could not be differentiated at the p = 0.05 level.
Although the 2:1 split pivot application yields were competitive with the 2.5 mm d-Superscript uniform irrigation at Colby and Tribune, fewer than 20% of years had any yield increase with split pivot irrigation.
Compared with yields for the 2:1 split pivot application, uniform 2.5 mm d-Superscript irrigation increased lint yield by >50 kg ha-1 for Colby in 30% of the years and for Tribune in 20% of the years.
Fewer than 20% of the 1:1 split pivot application yields at Colby had any increase over the uniform 2.5 mm d-Superscript irrigation, while uniform irrigation increased yield by >50 kg ha-1 for about 33% of the years.
Tribune similarly had few years  in which the 1:1 split pivot irrigation had any increased yield over the uniform 2.5 mm d-Superscript irrigation, in addition to reduced yields with the 1:1 split pivot application than with uniform irrigation in 50% of the years.
Compared with the 550 kg ha-1 lint yield for uniform irrigation at Garden City, the lint yields with the 2:1 and 1:1 application strategies were not different.
However, the 2:1 strategy improved the weighted average by ~7% to a numerically greater simulated yield of 590 kg ha-1.
which is a similar to the findings of Baumhardt et al..
These findings contrast to net yield increases of 11% to 21% for similarly managed split center pivot irrigation of determinant crops such as grain sorghum.
For about half the years at Garden City, the 2:1 split pivot application resulted in numerically larger yields over
 the uniform 2.5 mm d-Superscript irrigation, with about 24% of lint yields being >50 kg larger.
As observed at Colby, the Garden City lint yields for uniform irrigation exceeded those for the 2:1 split pivot application by >50 kg ha-Superscript in about 30% of the years.
Although 1:1 split pivot irrigation at Garden City had some yield increase over uniform 2.5 mm d-Superscript irrigation in one-third of the years, uniform irrigation increased lint yield by >50 kg ha-Superscript over split pivot irrigation 40% of time.
Application strategies that resulted in greater irrigation amounts earlier in the growing season were beneficial, generally resulting in greater early boll formation and maturation that increased simulated lint yield.
We quantified the effects of irrigation capacity and duration plus split center pivot irrigation strategies on the simulated yield of cotton, an alternative crop with lower water use that may prolong irrigation from the non-recharging Ogallala aquifer in south, central, and northwestern Kansas.
Crop emergence date and location governed the long-term available growing season CGDD, which generally determines potential lint yield, as constrained by water and nutrient availability to meet plant demands.
Compared with Garden City, growing season CGDD decreased by an average of 10% for the increased elevation and latitude at Tribune and Colby, but the corresponding mean lint yield decreased by a more severe 44%.
Although cotton may be produced throughout western Kansas, the simulated crop performance illustrates that the risk associated with cotton production, regardless of commodity price or program support, is considerably less at Garden City in southwest Kansas compared with central western or northwestern Kansas.
Not surprisingly, the irrigation capacity and duration scenario elements that increased the amount of water applied also increased, at least numerically, both simulated ET and lint yield, although at a variable WUE.
That is, simulated WUE was consistently lower at 2.5 mm d-Superscript than for the 3.75 and 5.0 mm d-Superscript irrigation capacities when application durations did not exceed 4 to 6 weeks, depending on the
 interactive effects of location and emergence date.
In addition to the water savings expected by irrigating cotton instead of corn, we conclude that further savings may be possible at locations with higher WUE achieved by avoiding irrigations at 5.0 mm d-Superscript after 6 weeks in the limited growing season conditions of western Kansas.
However, the overall net lint yield for focused irrigation strategies at the southwest Kansas location  was numerically larger.
Based on both uniform and split center pivot deficit-irrigated lint yields, we conclude that cotton appears to be poorly suited as an alternative crop for central western or northwestern Kansas because of limited growing season CGDD.
Cotton appears better suited for southwestern Kansas and responded to irrigation strategies promoting early canopy development and fruiting.
This research was supported in part by the Ogallala Aquifer Program, a consortium between the USDA Agricultural Research Service, Kansas State University, Texas AgriLife Research, Texas AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
Sustainable Nursery Irrigation Management Series
 Part II.
Strategies to Increase Nursery Crop Irrigation Efficiency
 Amy Fulcher Assistant Professor Department of Plant Sciences, University of Tennessee
 Tom Fernandez Associate Professor Department of Horticulture, Michigan State University
 Part II discusses strategies to increase irrigation efficiency.
Because irrigation is SO critical to container production and most of the water associated with nursery production is applied to container plants, strategies are discussed largely in the context of container production.
N ursery irrigation management is a major concern for many nursery producers, especially container producers.
Extension publication, "W 278: Part I.
Water Use in Nursery Production," discussed competition for water and gave a general overview of water use in nurseries.
Part II discusses strategies to increase irrigation efficiency.
Because irrigation is SO critical to container production and most of the water associated with nursery production is applied to container plants, strategies are discussed largely in the context of container production.
Growers must make many irrigation management decisions on a daily basis, including when to irrigate, how much water to apply, which plants to irrigate and how to maximize efficiency.
They also must plan for and manage water supplies in order to meet local and state water regulations.
Increasingly, competition for water resources is affecting how these decisions are made.
Creating more efficient water-use systems can ease competition for water.
Many factors contribute to overall irrigation system efficiency.
Irrigation application efficiency is the proportion of total water applied that is intercepted and retained by the container.
Water loss to excessive leaching, evaporation, wind, container spacing, canopy
 Figure 1.
Often newly planted liners are the first plants to be irrigated.
Photo credit: Amy Fulcher
 shedding and poor irrigation system design can decrease irrigation application efficiency dramatically, whereas recovery and reuse of surface water runoff and subsurface flow can increase irrigation application efficiency.
Enhancing irrigation efficiency often increases crop water use efficiency.
Scheduling irrigation applications has been the focus of much agricultural research.
Scheduling can be relatively static and arbitrary, substrate/soil moisture-based, or plant-based.
The conventional container production practice is to irrigate once per day by automatic timers or manually.
Historically, these irrigation events were scheduled to begin predawn to minimize losses due to wind and evaporation and SO that most irrigation would occur before employees arrived.
However, applications are made commonly during daylight hours due to the number of hours needed to deliver water to the entire nursery every 24 hours.
The time that irrigation begins may be the same time every day using timer-based irrigation or may be completely arbitrary.
With static irrigation, application is not linked directly to plant or substrate moisture status.
Irrigation is not adjusted often for changes in evaporative demand due to weather changes, but rather is limited to gross changes when the seasons change.
A simple way to save water when using timer-based irrigation scheduling is to install a rain gauge that will prevent irrigation from being applied if a set amount of rainfall occurs.
Substrate moisture measurements consist of either substrate water potential or substrate moisture content and generally rely on moisture probes  or gravimetric 
 measurements.
Tensiometers reflect actual water potential but are difficult to use in coarse nursery substrates and may require regular maintenance.
Some companies are now developing tensiometers that are better suited for container substrates.
Capacitance probes and gravimetric techniques measure substrate water content.
They do not reflect water potential and, thus, the actual availability of water.
Advantages of using substrate moisturebased irrigation include the fact that it can reflect root-to-shoot signaling in response to substrate moisture conditions and can be relatively easy to automate.
Determining how to position a substrate moisture probe is challenging.
Scientists are still investigating the ideal probe number per container, number of containers with probes per crop, probe orientation and probe placement within containers.
However, studies at nurseries have shown that a very small number of probes involving modest financial investment can be effective in reducing water use without sacrificing plant quality or time to produce a crop.
A universal substrate moisture level on which to base irrigation  would facilitate adoption of this technology but may not be likely due to the variability in types of substrates used by the industry.
Therefore, growers will need to do some in-house experimentation to develop irrigation set points.
The set point may be affected by crop species, container size, temperature, root system size/time in current container, substrate and where the probe is placed in the container.
Plant-based irrigation systems, such as leaf temperature-based, allow for environmental influence but do not account for root-to-shoot signaling and are challenging to automate.
Plantbased systems can respond to the physiological changes that occur directly due to changes in plant water status, which make them very appealing to researchers and practitioners alike.
However, this response can be a disadvantage for conservative irrigation schedules in certain environments, because low plant water status induced by extreme mid-day conditions could trigger irrigation when substrate moisture is not limiting.
Leaf temperature, plant water potential and stem diameter fluctuations are some of the plant-based techniques that have been used to gauge water loss in horticultural crops.
Plantbased systems are not automated easily or widely commercially available at this time.
Figure 2.
Capacitance probes are currently used by researchers and a limited number of growers to schedule irrigation.
Photo credit: Amy Fulcher
 Figure 3.
Infrared temperature sensors are one plant-based technique for scheduling irrigation.
Photo credit: Amy Fulcher
 The approaches mentioned above address only when to irrigate.
Other approaches are needed to determine how much water to apply.
Growers commonly aim to apply 0.75 to 1 inch of irrigation water daily in the summer by irrigating for a set time period.
However, determining irrigation volume by a time period can lead to errors in application.
Research shows that due to variation in output  and distribution, application volume based on a time period can result in excess or inadequate irrigation.
For example, nurseries expecting to apply 1 inch of water in an hour may actually apply just 0.3 inch in 60 minutes, while other nurseries apply as much as 1.3 inches.
Over the course of a season, the amount of water applied within one irrigation zone in a 60-minute period can vary as much as half an inch.
Therefore, it is important to determine irrigation system application rates by measuring them periodically.
Several methods can be employed to determine how much water to use to prevent applying an excessive or deficient volume of water.
Irrigation volume can be based on the container leachate.
Leaching fraction is the percentage of water applied that leaches or drains out of the container.
A leaching fraction of 10 percent or less,
 allows for water and 24 nutrient conservation.
When irrigating at low leaching fractions , it is important to monitor substrates for soluble salts during production, especially during periods of low rainfall, as they can build up.
Water balance calculations are used to 20 estimate substrate moisture status and are calculated as the difference between water applied to the plant, both through irrigation and precipitation, and water lost through evapotranspiration.
Evapotranspiration is affected by many factors, including solar radiation, humidity and mulch layer.
Using an evapotranspiration model presents several challenges.
For instance, evapotranspiration models are often complex, requiring that several variables be measured.
A weather station and datalogger must be located on-site.
Additionally, a crop coefficient must be derived empirically for every species, perhaps even at the cultivar level and possibly for different stages of development, container sizes, plant  size and spacing.
Daily water
 replacement is a practical way to approach water balance calculations.
Daily water use measures how much water is lost during each 24-hour period and applies, or replaces, that volume of water minus rainfall.
Daily water use measurements may be made by measuring weight or using probes to measure volumetric water content every 24 hours.
Overhead irrigation is commonly used for plants in 5-gallon and smaller container sizes.
The water is delivered by sprinklers mounted on risers on rectangular, square or triangular patterns throughout the container pad.
While overhead sprinklers are easy and relatively affordable to set up, they are not efficient, because a lot of water lands between containers.
As linear spacing between plants increases, irrigation efficiency decreases considerably, with as little as 35 percent efficiency even at close spacing.
Microemitters are emitters that apply a small volume of water at low flow rates, generally to individual plants.
Microemitters are often used for 7-gallon
 Figure 4.
Overhead irrigation can vary significantly within an irrigation zone, across zones and over the course of a season.
Photo credit: Amy Fulcher
 Figure 5a.
This single-irrigation emitter is not supplying water to the entire root system of this 15-gallon container.
A different type of emitter, more than one emitter and/or different emitter placement is needed.
Photo credit: Amy Fulcher
 and larger container sizes.
Microemitters include microsprinklers, drippers and bubblers.
Microsprinklers, commonly called "spray stakes," are the most common type of microemitter in nursery production.
Sprinkler heads are mounted on a stake in the container.
The sprinkler head/ stake assembly is connected to the lateral line by a small diameter  flexible tube called spaghetti tubing.
Drip emitters and bubblers are not used often in nursery production because they do not apply the water to the surface of the substrate evenly, a problem that compounds the larger the container size.
Also, the single-point delivery of a drip emitter can lead to water channeling through the bark substrate due to its coarse nature.
Microemitters are very efficient; when properly installed, they apply water to the root system with no overspray or wasted water.
However, the particular spray patterns, placement in the container and juxtaposition to the trunk can affect the distribution of water.
Two or more emitters can be used to apply water more evenly and/or to increase the amount of water applied in a given amount of time, especially for very large containers.
Microirrigation systems have small orifices that can clog easily.
Appropriate filtration as well as regular maintenance and cleaning are required.
Ebb-and-flow is a subirrigation technique that is used most commonly in floriculture production.
An ebb-andflow irrigation system floods the production floor, or bench, periodically, slightly submerging the base of containers for a short period to allow the substrate to absorb water by capillary action.
A significant investment in infrastructure is required to develop an ebb-and-flow irrigation system.
Typically, the irrigation water is captured and sanitized for reuse, making it a highly efficient system.
A controlled water table also is a form of subirrigation and requires specialized infrastructure.
A CWT delivers water to plants via a capillary mat that pulls water from a reservoir  at the edge of the bench.
Like ebb-and-flow, CWTs are used most often in floriculture.
CWTs are very efficient but do require some maintenance.
Microemitters, ebb-and-flow systems and controlled water tables can be used to fertigate as well as irrigate.
Water-conserving Strategies for Nurseries
 Strategies to reduce water consumption in nurseries include grouping plants by relative water needs and container size and using cyclic irrigation.
Grouping plants by perceived irrigation needs  into irrigation zones is a common strategy employed by growers.
Grouping plants by water needs along with proper spacing can reduce water consumption tremendously.
Another conservative irrigation strategy is cyclic irrigation, in which the total daily volume of irrigation water is applied in multiple irrigation events with a minimum of one hour between irrigation events.
Using cyclic irrigation can reduce runoff by 30 percent, compared with conventional continuous irrigation.
Using
 Figure 5b.
Microemitters used in drip irrigation deliver water directly to the root zone, eliminating inefficiency due to evaporation and nontarget application.
Photo credit: Amy Fulcher
 amendments, such as calcined clay, to increase the substrate water-holding capacity also can reduce water use.
Growers have many options for increasing water-use efficiency in the nursery.
These include refining irrigation scheduling, irrigation volume and irrigation delivery.
The Extension publication, "W 280: Part III.
Strategies to Manage Nursery Runoff," discusses the significance of runoff from nursery production facilities, as well as strategies for minimizing and mitigating runoff.
Capacitance Probe Probe that measures volumetric content by measuring the dielectric permittivity of the surrounding soil or substrate.
A capacitance probe determines the dielectric permittivity of a medium by measuring the charge time of a capacitor, which uses soil or container substrate as a dielectric.
Continuous Irrigation Applying the total daily volume of water required by a crop in one irrigation event.
Controlled Water Table Form of subirrigation.
Delivers water to plants via a capillary mat that pulls water from a reservoir  at the edge of the bench.
Crop Coefficient  Calculation performed to estimate water use for a specific crop, sometimes at a particular growth or developmental stage.
Ratio of evapotranspiration of a specific crop relative to potential evapotranspiration.
Crop Water Use Efficiency Ratio of plant mass gained relative to the volume of water applied.
Cyclic Irrigation Applying the total daily volume of irrigation water in multiple irrigation events with a minimum of one hour between events.
Daily Water Replacement Method of refining irrigation volume by measuring how much water was lost in the previous 24hour period and applying that volume of water.
Ebb-and-Flow Subirrigation technique in which the production floor, or bench, is flooded periodically and then drained, slightly submerging the base of containers for a short period to allow the substrate to absorb water by capillary action.
Evapotranspiration Combination of water loss due to evaporation from the soil surface and transpiration from the plant.
Fertigate Applying water-soluble fertilizer in a low-volume irrigation system.
Gravimetric Measurement Using the weight of a container to measure substrate moisture content.
Irrigation Application Efficiency Portion of total water applied that is intercepted by the container.
Leaching Fraction Portion of water applied that drains from the container following irrigation.
Microemitters Irrigation emitters that apply a small volume of water at low-flow rates to individual containers.
Subirrigation Irrigation delivery method of providing water to the root zone from the bottom of the container rather than the top surface.
Glossary of Terms 
 Substrate Moisture Content How hydrated a substrate is, often expressed as volumetric water content.
Substrate Water Potential Measurement of how hydrated a soil or substrate is.
Water potential indicates the availability of water to plants.
Tensiometer Probe-like instrument used to measure the water potential of soil or substrate.
Volumetric Water Content Fraction of the total volume of soil or substrate that is occupied by the water contained in the soil or substrate.
Does not indicate the availability of water to plants.
Water Balance Calculations Used to estimate soil or substrate moisture status and are calculated as the difference between water applied to the plant  and water lost through evapotranspiration.
This publication was funded partially by the U.S.
Department of Agriculture's Specialty Crop Research Initiative project, "Impact and social acceptance of selected sustainable practices in ornamental crop production systems." The authors express their gratitude to Wanda Russell and Andrea Menendez for their skillful editing and Mark Halcomb, Brian Leib and Andrea Ludwig for their critical review, which strengthened the series.
THE UNIVERSITY of TENNESSEE UP INSTITUTE of AGRICULTURE
 W 279 4/13 13-0098
Soil water content is described using many different terms, including saturation, field capacity, permanent wilting point, excess or gravitational water, unavailable water, plant available water holding capacity, commonly known as available water, and minimum allowable balance.
For irrigated crop production in Nebraska, we usually focus on two of these terms, available water, and minimum allowable balance.
One of the main factors driving annual forage production in Nebraskas grazinglands is available moisture.
Both cooland warm-season grasses in the state rely heavily on spring and early summer precipitation at a time when the plant is rapidly growing.
This period of rapid growth varies by species and is driven by air temperature, day length and soil moisture.
Speed of spring growth and recovery after grazing depend on this.
Once optimal conditions have passed, getting significant growth even if it does rain is difficult.
Beans develop based on day length.
So with the same hot dry windy conditions, they will use more water per day and will still mature at about the same date resulting in more water use than predicted in the charts.
Thus, it is very important to monitor soil water in beans until they reach maturity.
For additional details and charts, see NebGuide Predicting the Last Irrigation of the Season.
Increasing the annual use of the module builder would reduce the total modulesystem cost to $6.42 per bale for 200 hours per year and to $6.14 per bale for 300 hours per year.
If 8-bale trailers were used only six times per year, the trailersystem cost would be $7.76 per bale.
These examples indicate that when module builders and transport trailers have reasonably high annual use, total picker-to-gin costs per bale can be significantly lower with the module system than with conventional trailers used only six to eight times per year.
Ricking, on the other hand, has been found to increase pickerto-gin costs by $3.50 to $5.00 per bale.
Cost summaries for 26 San Joaquin Valley gins  were analyzed as a basis for predicting the potential effects of seed cotton storage on ginning costs.
This analysis indicated that, with no change in total seasonal output, some gins could realize labor savings as great as $3.00 to $4.00 per bale if sufficient stored seed cotton were available to permit operating at a relatively constant daily output rate.
Storage probably would result in only minor labor savings for some other gins.
Increasing the total seasonal output from a given gin by operating more hours per year  would reduce plant overhead and administrative costs per bale.
The analysis indicated that in most of the 26 cases a 50% increase in seasonal output from a given gin might be expected to reduce the cost per bale by $2.00 to $4.50.
Doubling the seasonal output would reduce the cost per bale by $3.00 to $7.00.
A system involving module storage at the gin yard may have substantial added initial costs because of the relatively large, specially prepared storage area needed.
Tests and grower experience have indicated that seed cotton can be stored in covered ricks or modules up to about two months with no reduction in lint or seed quality if the seed and seed cotton moisture contents do not exceed 11% and the trash content is not excessive.
Longer storage periods may be satisfactory at lower moistures.
If a grower's trailers are still in good condition, the ricking system requires considerably less additional investment in equipment than does the module system.
GROWTH RETARDANT THROUGH CONTAINER IRRIGATION SYSTEMS
 TOK FURUTA W.
C.
JONES W.
HUMPHREY TOM MOCK
 S EVERAL DRIP AND SPRAY irrigation systems have been designed and successfully used to apply precise amounts of water and fertilizer to container-grown nursery plants.
The usefulness of these systems for application of smaller amounts of other chemicals had not been tested.
In these studies, tests were made of the possibilities for application of a growth retardant, ancymidol , through the irrigation system.
Two irrigation systems were tested.
The drip system utilized Drip Stick emitters, and the other system utilized the T-Spray nozzles.
In the check containers, the growth retardant was mixed with a known amount of water and then added to each container.
Only enough water was added to wet all the soil in each container.
The dosage of ancymidol for all treatments was 100 mg per plant.
The test plant was Eucalyptus globulus, growing in egg cans with a soil mix of 66% redwood sawdust and 34% sandy loam soil.
For both irrigation systems, the ancymidol was injected into the irrigation system just ahead of the sub main leading to the plants.
At the end of 28 days, the amount of growth and the number of nodes above the last elongating internode at the time of treatment was measured.
Only the central leader was used for measurement.
Application of ancymidol through the drip irrigation system seemed as effective
 GROWTH DIFFERENCES IN CONTAINER PLANTS FROM APPLICATION OF GROWTH RETARDANT ANCYMIDOL BY TWO METHODS OF IRRIGATION
 Treatment method	Nodes		Variability
 Drip irrigation system	8.8	28.3	10.9
 T-Spray irrigation system	8.6	36.4	8.4
 Hand application	7.5	25.3	5.6
 as the control when only the average elongation was considered.
However, considerably more variation between plants occurred when the growth retardant was applied through the drip irrigation system.
But modules can be taken from the field immediately and are then available for ginning at any time, regardless of the weather and field conditions.
The module system also has the potential for mechanized handling and automatic feeding at the gin.
Good management is more important with the module system than with the trailer system or ricking.
From the grower's standpoint, the ability to continue harvesting whenever the weather permits, rather than having to stop because no empty trailers are available, is the principal advantage of any
 These results indicate the possibility of applying growth retardants through container irrigation systems.
Greater variability should be expected between plants than would occur if the chemicals were accurately measured to each plant.
Refinement in application methods using the drip system may improve the uniformity of response.
Tokuji Furuta is Extension Environmental Horticulturist, and W.
C.
Jones is Staff Research Associate, University of California, Riverside.
Wes Humphrey is Farm Advisor, Orange County, Anaheim; and Tom Mock is Staff Research Associate, South Coast Field Station, Santa Ana.
The Drip Stick emitters, and T-Spray nozzles used in the irrigation systems tested were manufactured by the Aqua Data Company, Arcadia.
Chapter: 51 Corn Insect Pests
 Historically, the major corn insect pests in South Dakota have been northern and western corn rootworm, European corn borer and black cutworm.
Bt-corn hybrids are effective against most of these pests.
However, there are also minor or sporadic pests of corn in South Dakota including the bird cherry oat aphid, corn leaf aphid, fall armyworm, true armyworm and common stalk borer.
Although these pests are considered minor, each is capable of reducing corn yields under the appropriate conditions.
Issues faced: This chapter discusses the biology and management of important corn insect pests commonly observed in South Dakota.
Northern corn rootworm  and Western corn rootworm .
Northern corn rootworm and western corn rootworm can cause economic damage to corn in South Dakota.
Bt-corn hybrids that target corn rootworm are effective against corn rootworm larvae.
Crop rotation is an effective tactic in managing corn rootworms.
Corn rootworm larvae are currently the most damaging insect pests of continuous corn in South Dakota.
Figure 51.1 Color variation of northern  and western  corn rootworm adults.
Adult northern corn rootworm beetles are approximately 1/4-inch long and vary in color from yellow to green.
Western corn rootworm beetles are slightly larger with a black head and yellow thorax and abdomen.
The western corn rootworm adults have three black longitudinal stripes on their hardened forewings.
The stripes can vary in size and may appear as three distinct stripes or one broad stripe that covers the majority of the forewings.
The wormlike larvae of both species
  are white with a brown head and grow to approximately 5/8-inch in length.
Both the larvae and adults have chewing mouthparts.
Adult corn rootworm beetles feed on corn pollen, silks and leaves.
Feeding on the pollen and silks has the potential to reduce pollination and ear fill; however, significant injury from adult feeding occurs infrequently.
Adults may also feed on soybean, sunflowers and garden flowers but have not been reported as pests of these crops in South Dakota.
Adult female corn rootworms deposit eggs into the soil from late summer into the fall or until the females are killed by the first hard frost.
In South Dakota, rootworm eggs are primarily laid in cornfields where they overwinter in the soil.
Fields that are planted to corn following corn have an increased chance of being infested with corn rootworm eggs from the previous season.
Egg hatch occurs once the corn roots begin to grow.
Corn rootworm larvae feed on corn roots in June and July during active root growth.
Larvae transform into pupae in mid-July, and adult rootworm beetles emerge from the soil from late July through August  and mate rapidly after emerging.
The principal cause of yield losses associated with corn rootworm is larval feeding on corn roots during active root growth.
The damage to corn roots reduces water and nutrient uptake, and yield is reduced on average by 15% to 17% for each node of corn root pruned by rootworm larvae.
Furthermore, roots weakened by larval feeding can result in goose-necked plants  and lodged corn.
Lodged corn is difficult to harvest and decreases harvest efficiency and overall yields.
Typically, larval infestations are clustered within fields, and areas within the field that experienced higher infestation levels in a previous year tend to have higher infestations in the same areas when corn is planted the following year.
Corn rootworm larvae are generally unsuccessful when feeding on the roots of other crops including soybean, wheat, sunflower and alfalfa.
This specialization makes crop rotation an excellent management option.
Although Figure 51.4 Lodged corn is a symptom of corn multiple species of foxtail  grasses including rootworm larvae feeding on corn roots.
for corn rootworm larvae, the roots of these grasses are a poor nutritional substitute and produce smaller corn rootworm individuals.
Other management options include the use of Bt-corn hybrids that have rootworm-active toxins or in-furrow granular and liquid insecticides.
Figure 51.2 Life cycle of the NCR and WCR in South Dakota.
Figure 51.3 Goose-necked corn is a symptom of early season corn rootworm larvae feeding on corn roots.
Many genetically engineered Bt-corn hybrids are resistant to corn rootworm larvae.
These Bt-corn hybrids produce toxins derived from the soil-dwelling bacterium Bacillus thuringiensis that are toxic to rootworm larvae.
Although Bt corn reduces rootworm larval feeding injury, adult corn rootworm are not affected by Bt toxins.
Bt corn targeting corn rootworm became commercially available in 2003, and these hybrids produced only one Bt toxin that targeted rootworm.
More recently, Bt-corn hybrids have become commercially available that produce a pyramid of toxins  that target corn rootworm.
To delay the development of Bt-resistant rootworm, the EPA mandated that Bt-corn hybrids must be planted with non-Bt corn refuges, which depending on the Bt toxin produced, range in size from a 20% block of non-Bt corn to 5% refuge-in-the-bag.
However, reports of Bt-resistant corn rootworm already have been documented in Iowa, Nebraska and Illinois to Cry3Bb1 and mCry3A Bt toxins.
Table 51.1 Bt-corn genes that provide resistance to northern and western corn rootworm larvae.
Bt toxin	Trade name
 Cry3Bb1	YieldGard VT Triple
 Genuity VT Triple Pro
 Genuity VT Triple PRO RIB Complete
 Cry3Bb1 + Cry34/35Ab1	Genuity SmartStax
 Genuity SmartStax RIB Complete
 Refuge Advanced Powered by SmartStax
 mCry3A + eCry3.1Ab	Agrisure Duracade 5222 E-Z Refuge
 mCry3A + Cry34/35Ab1	Optimum Intrasect XTreme
 Cry34/35Ab1+eCry3.1Ab	Agrisure Duracade 5122 E-Z Refuge
 Management: Rootworm T-band/in-furrow Insecticides and Seed Treatments
 Many different insecticides are labeled for Table 51.2 Node-Injury Scale scores.
rootworm larval management.
Node-Injury score Root Description Granular or liquid insecticides are applied 0.00 No feeding injury observed in-furrow or very close to the seed furrow 1.00 One full root node pruned during planting.
Alternatively, systemic 2.00 Two full root nodes pruned insecticidal seed treatments are also available to corn growers for the management of 3.00 Three full root nodes pruned; scale maximum corn rootworm larvae.
It is not advised to use a Bt-corn hybrid that has more than one toxin targeting corn rootworm in combination with any conventional soil insecticide application.
The purpose of this recommendation is to reduce economic inputs and to reduce selection pressure on corn rootworm to adapt to two distinct management tactics.
For a list of T-band/in-furrow insecticides and also insecticide seed treatments that are currently labeled for the management of corn rootworm larvae, please refer to the current edition of the South Dakota Pest Management Guide: Corn.
Crop rotation has been an effective management tool against corn rootworm for over a century.
Adult rootworm lay eggs in cornfields during August, and larvae that hatch the following spring in fields rotated away from corn starve to death.
However, populations of both northern and western corn rootworm have adapted to crop rotation in parts of the corn belt.
Rotation-resistant northern corn rootworm are present in South Dakota.
These northern corn rootworm
 populations have adapted to crop rotation by having an extended diapause, and are sometimes referred to as "extended-diapause" rootworm.
Female rotation-resistant northern corn rootworm still lay eggs in cornfields; however, only a proportion of those eggs hatch the following year while another proportion will hatch two, three or even four years later.
Extended crop rotations that do not vary over time  can select for a greater percentage of eggs to hatch during years corn is planted, although this process would take many rotations cycles to build significant northern corn rootworm populations.
Rotation-resistant western corn rootworm are not presently found in South Dakota, these populations are typically found east of the Mississippi River.
Rotation-resistant western corn rootworm are commonly called the "soybean variant" rootworm, but this name can be misleading.
Western corn rootworm adapted to crop rotation by laying eggs not only in cornfields, but any other crop.
The name "soybean variant" emerged because rotation-resistant western corn rootworm first appeared in areas dominated by cornsoybean rotation.
Assessing Management Success through Rating Corn Roots
 Rating corn roots for rootworm feeding injury can assess whether rootworm populations have reached economically damaging levels within a field.
Rating roots for rootworm feeding injury is additionally advantageous because it measures the effectiveness of any rootworm management strategy that is presently being practiced within a field.
However, roots are rated within the planting season and there are no remediation treatments presently available to reduce yield loss if significant feeding has occurred.
To rate corn roots for injury, 10 roots should be dug from random areas within the field during July or August.
Use a spade and dig in a circular pattern approximately 4 5 inches away from the cornstalk.
Remove excess dirt without damaging the corn roots.
Soak the sampled roots in water for 24 48 hours, and remove any remaining soil using a high-pressure hose.
Allow the roots to dry prior to rating.
Corn roots are rated on the 0 3 Node-Injury Scale.
Only root nodes 4, 5 and 6 are rated for rootworm feeding injury.
The brace roots that emerge from the stalk above the soil line represent node 7, while node 6 roots emerge at the soil line.
To begin rating a corn root, count the total number of roots within a node for nodes 4, 5 and 6.
For example:
 Root sample #1: Node #4 has 10 roots Node #5 has 12 roots Node #6 has 10 roots
 Re-inspect each of the nodes and determine the number of roots that display rootworm larval feeding injury, typically referred to as "pruned" roots.
A root is considered pruned if the root has been eaten back to approximately 1.5 inches from the stalk.
In this example:
 Root sample #1: Node #4 has 5 / 10 roots pruned Node #5 has 4 / 12 roots pruned Node #6 has / 10 roots pruned
 Calculate the proportion of pruned roots for each node by dividing the number of pruned roots by the total number of roots.
In this example, node #4 has 5 pruned roots out of 10 total roots, SO the proportion of pruned roots for node #4 is 0.50.
Sum the proportion of pruned roots for nodes 4, 5 and 6 to get the Node-Injury score.
In this example, root sample #1 would score:
 0.50  + 0.33  + 0.20  = 1.03
 Rate all 10 sampled corn roots and then average the Node-Injury score to estimate the amount of root injury within a field.
Table 51.2 describes how root injury is scored on the Node-Injury Scale.
Depending on the cost of rootworm management and price of corn, economic loss from rootworm larval feeding may
 Node-injury Scale: 0.00 No apparent feeding
 Node-injury Scale: 0.1-0.9 One to nine roots pruned 
 Symptoms: May notice some lodging Yield Impact: Some economic loss could occur at or above a 0.5 rating, especially under dry  conditions.
Node-injury Scale: 1.0-1.9 At least one full node destroyed to within 1.5 inches of stalk
 Symptoms: Some lodging and goosenecking.
Yield Impact: Probably an economic loss in grain or silage, unless conditions are favorable for regrowth & lodging is minimal.
Note that regrowth can obscure damage, so care must be taken when rating roots later in the season
 Node-injury Scale: 2.0-2.9  Two or more nodes destroyed
 Symptoms: Severe lodging and goosenecking Beetles may be present and feeding on the silks and leaves.
Yield Impact Economic impact with loss in grain.
Expected to have poor ear fill if silks are fed on.
Difficulty in harvesting for both grain and silage.
Node-injury Scale: 3.0  Two or more nodes gone
 Symptoms: Severe lodging & goosenecking.
Numerous beetles may be present, feeding on leaves and silks.
Yield Impact: Severe.
Loss in grain, in addition to poor ear fill, if silks are fedon.
Difficulty in harvesting both grain and silage.
Figure 51.5 A visual guide of the Node-Injury Scale ratings used to determine the severity of corn rootworm larvae root pruning.
begin to occur above average Node-Injury scores of 0.25.
For Bt corn that targets corn rootworm, greater than expected injury is said to occur if average Node-Injury scores exceed 1.00 for Bt corn with only a single Bt toxin and 0.50 for Bt corn with a pyramid of Bt toxins.
Scouting and Economic Thresholds
 Scouting for adult rootworm during August can help assess the risk of injury to corn planted within a field the following year.
A simple method used to scout for adults are yellow sticky cards.
These cards are can be
 purchased through several retailers, and cost approximately $2 per card.
The cards have alternating yellow and white sides, with the yellow side being covered in a gluelike substance.
If yellow stick cards are being used to scout for corn rootworm populations, 10 cards should be placed randomly throughout the field in August.
The cards are then replaced on a weekly basis  throughout August.
For each card, count the total number of corn rootworm adults on the card and divide this total by the number of days the card was left in the field to calculate the number of rootworm adults captured per day.
If averages exceed two or more adults captured per day, the economic threshold has been reached.
European Corn Borer 
 South Dakota has univoltine  and bivoltine  ecotypes.
Bt-corn hybrids with toxins specific to the European corn borer provide effective management.
Univoltine corn borers can be more damaging and harder to manage than bivoltine corn borers.
Per-plant yield loss can range from 2% to 6% per larva in the absence of management.
European Corn Borer Description
 European corn borer larvae are light tan to pink in color with dark brown spots on each segment of their body.
Larvae have a dark brown head capsule, three pairs of true legs and four pairs of abdominal prolegs.
Mature larvae range in size from 3/4to 1-inch in length.
The female European corn borer moth is approximately 1/2-inch in length with triangular wings that have yellow to brown wavy markings.
The male moths are smaller and tend to be darker in color.
European Corn Borer Biology
 Within a single generation, European corn borer undergoes four developmental stages/forms: egg, larva, pupa, and adult.
During larval development, there are five instars or larval stages.
Each subsequent instar undergoes a period of growth followed by a molt.
When the larvae reach the fifth and final instar, they pupate and transition from a caterpillar to a moth.
Like all insects, the European corn borer life cycle is effected by the climate, resulting in a different number of generation per year occurring in different parts of the state.
In northern South Dakota, European corn borer is univoltine.
In central and southern South Dakota, European corn borer can be univoltine or bivoltine.
Univoltine European Corn Borer 
 European corn borer populations with only one generation per year are most commonly found in the northern counties of South Dakota.
Moths of these populations begin flying in mid-June, with peak populations occurring in mid-July.
Seasonal temperatures affect adult emergence, but moths generally lay eggs on the underside of corn leaves from June to July.
Eggs hatch within one week.
Newly hatched larvae feed on the leaf collars and may migrate toward the tassels to feed on pollen.
Young larvae often feed on the leaf surface and midribs, resulting in a "windowpane" type injury that is characterized by the removal of the surface layer of the leaf.
Secondand third-instar larvae will feed in the whorl, causing a
 "shot hole" type of injury.
Fourth-instar larvae tunnel into the stalk, molt into fifth-instar larvae and continue feeding until the end of the growing season.
Fifth-instar larvae overwinter in stalk residues left in the field, and transform into pupae and moths in the following spring.
Bivoltine European Corn Borer 
 In southern portions of South Dakota, European corn borer can have up to two generations per year.
Adult moths begin flying in mid-May and females lay eggs on the underside of the leaves when corn is between growth stages V6 to V9.
Similarly to univoltine populations, newly hatched bivoltine larvae also feed on the leaf surface and midribs, and may cause windowpane damage.
Secondand third-instar larvae feed in the whorl, causing a shot hole injury  that is visible when leaves unfurl.
Fourth-instar larvae tunnel into the stalk and then molt into fifth-instar larvae approximately 10 days later.
Larvae then transform into pupae after an additional 10 days.
The second generation of European corn borer moths emerge from the stalks about 8 days after pupating, and 5361221 lay eggs on the underside of leaves, leaf collars and on the ear husks during tasseling  and silking.
Approximately 1 week later, the second-generation eggs begin to hatch.
European corn borer larvae burrow into the stalks and ear shanks and feed on developing kernels.
Fifth-instar larvae overwinter in stalks and residue left on the field.
The winter survival potential of larvae is directly related to the amount of residue remaining in the field, with greater survival occurring with increased levels of residue.
Both the single  and two  generation European corn borer moths may visit fields that are located in the center of the state.
This phenomenon has been observed as far south as Lake, Minnehaha and Moody counties.
European Corn Borer Injury to Corn
 Tunneling injury attributed to European corn borer results in stalk breakage, Growth stage % Yield loss/larva/plant reduction in water and nutrient transport, V10  5.9 secondary infection with stalk rot fungi, and V16  5.0 ultimately yield loss.
Injury to ear shanks R1  4.0 and kernels can result in ear drop, loss of R2  3.1 grain quality and secondary infection of mycotoxin-producing fungi  2.4 46 for more information on mycotoxins).
Leaf feeding by early instar larvae causes "shot hole" and "windowpane" type injuries that are usually not serious enough to reduce photosynthesis.
However, leaf feeding injury can be used to indicate the presence of European corn borer larvae in the field.
The timing of larval infestation affects final yield , with northern parts of the state being
 Table 51.3 Estimated yield loss per corn borer larva at specific corn growth stages:
 
 more susceptible to economic losses because larval feeding occurs throughout the entire season.
The first generation of the bivoltine European corn borer tends to cause more injury than the second-generation because they occur during a more sensitive growth stage of the corn.
European Corn Borer Management: Bt-corn Hybrids, Scouting and Insecticides
 Bt-corn hybrids targeting European corn borer produce toxins in their leaves, stalks and ears that negatively effect larvae.
These Bt-corn hybrids have performed very well during outbreaks of the European corn borer.
However, the severity of corn borer infestations fluctuates from year to year.
The decision to deploy Bt-corn hybrids is made before planting and before the extent of this late-season problem is known.
Therefore, techniques to reduce the economic risk associated with decisions to choose treatments and varieties are needed.
Bt corn may be most suitable for planting Optimum Intrasect Xtra in areas with high previous history of Optimum Intrasect XTreme univoltine European corn borer populations Cry1A.105 + Cry2Ab2 + Genuity SmartStax.
Univoltine populations are Cry1F Genuity SmartStax RIB Complete less predictable than bivoltine European Refuge Advanced Powered by SmartStax corn borer.
In bivoltine areas, corn borer outbreaks often decline to levels below economic thresholds in a year after an outbreak.
When cornon-corn rotations are used, the increased risk of European corn borer may be great enough to warrant regular planting of Bt corn.
Refuges of non-Bt corn must be planted in or around fields with corn hybrids containing Bt toxins targeting European corn borer.
Scouting is needed to maximize the effectiveness of insecticides.
Insecticide treatments can be effective against this pest.
Table 51.4 Bt-corn toxins that provide resistance to European corn borer larvae.
Bt toxin	Trade name
 Genuity VT Double PRO
 Genuity VT Triple PRO
 Genuity VT Double PRO RIB Complete
 Genuity VT Triple PRO RIB Complete
 Agrisure 3122 E-Z Refuge
 Agrisure Viptera 3220 E-Z Refuge
 Agrisure Duracade 5122 E-Z Refuge
 Agrisure Duracade 5222 E-Z Refuge
 Table 51.5 Estimated timing for European corn borer scouting:
 1.
Look for egg masses, newly hatched larvae, and signs of injury on leaves in June and July.
2.
V8-R1  for univoltine corn borer.
3.
V8-V14  for first-generation bivoltine corn borer.
4.
R1-R2  for second-generation bivoltine corn borer.
Black Cutworm 
 Black cutworm larvae feed on corn seedlings early in the season.
Bt toxins Cry1P and Vip3A are effective against black cutworm.
Significant stand loss can occur if the seedlings are cut below the growing point.
Black cutworm does not overwinter in South Dakota.
Moths migrate into the state in early spring and are attracted to wet and weedy fields.
Black cutworm larvae vary in color from dark brown to black and are approximately 1 1/2-inches long
 when mature.
Their skin has a rough, pebbly texture.
Larvae have three pairs of true legs and four pairs of abdominal prolegs.
Adult black cutworm are dark brown in color with a dark mottling across each forewing.
Black Cutworm Biology and Injury to Corn
 Moths start migrating into South Dakota from the southern U.S.
in early April.
Strong southerly winds influence the transport, distribution and severity of black cutworm infestations.
Female moths deposit eggs onto weeds and crop residues prior to corn planting.
Upon hatching, black cutworm larvae feed on weeds and move to corn seedlings when they emerge in May and early June.
Black cutworm larval feeding results in cutting of corn seedlings, which may occur at or below the soil surface.
Feeding that occurs below the growing point can result in extensive seedling stand loss.
Black Cutworm Scouting and Management
 There are Bt-corn hybrids that produce toxins that are effective against black cutworm larval feeding.
Bt toxins Cry1F and Vip3A are resistant to black cutworm.
Many seed treatments are also labeled for management of black cutworm, including clothianidin and thiamethoxam.
Weed management can greatly influence black cutworm populations.
First, adult female black cutworm lay eggs on low-lying weeds and plant debris.
Fields with no-till or reduced-tillage management can attract egg-laying females.
Second, having weeds within a field can reduce the risk of injury to corn because black cutworm larvae develop better on many weed species than they develop on corn.
Black cutworm larvae should starve to death if weeds and plant residue are tilled into the soil more than 2 weeks before corn planting.
Conventional insecticides can be used in conjunction with scouting to manage black cutworm.
Black cutworm larvae are nocturnal and hide during the day.
Therefore, scouting focuses on larval feeding injury.
Scouting for black cutworm larval feeding injury should begin at the VE  stage and continue through the V5  stage.
Fifty plants should be examined throughout a field, with special attention given to areas of the field that have a history of increased moisture or weeds.
Look for plants that show signs of cutting or leaf feeding.
Measure the length of any black cutworm larvae found.
An insecticide treatment is recommended if 5%  of the seedlings scouted show signs of cutting or leaf feeding and if black cutworm larvae are less than 1 inch.
For a list of insecticides registered for black cutworm management on corn, please refer to the current edition of the South Dakota Pest Management Guide: Corn.
Figure 51.10 A black cutworm larva on a corn leaf.
Western Bean Cutworm 
 Western bean cutworm larvae feed on developing kernels late in the season.
Bt toxins Cry 1F and Vip3A are effective against western bean cutworm.
Western bean cutworm can reduce yields up to 40%.
Injured ears may be susceptible to mycotoxin-producing fungi.
Western Bean Cutworm Description
 Western bean cutworm larvae have a brown to gray body that is about 11/4-inch long at maturity.
Larvae have an orange-brown head with a black dorsal shield located directly behind the head.
The larvae have three pairs of true legs and four pairs of abdominal prolegs.
Western bean cutworm moths are approximately 3/4-inch long, brown in color, with a distinct white band on the leading edge of their forewings.
Western Bean Cutworm Biology and Injury to Corn
 In South Dakota, western bean cutworm moths begin flying in early July and reach peak flight populations during the third or fourth week of July or when corn is between the VT  and R1  stages.
Female moths lay eggs on top of the leaves in the upper canopy.
The eggs hatch within a week and the firstinstar larvae begin migrating toward the developing ears.
Larvae usually go through five instars.
The thirdthrough fifth-instar larvae feed on developing kernels for approximately one month before migrating to the soil, where they prepare to overwinter.
Once in the soil, the larvae construct earthen cells that are 5 to 10 inches below the surface.
Several western bean cutworm larvae can feed simultaneously on a single ear of corn, which can result in yield reductions by as much as 40% per plant.
Damaged ears may also be susceptible to infection from mycotoxin-producing fungi.
Western Bean Cutworm Scouting and Management
 Bt-corn hybrids that express either the Cry1F or Vip3A toxins provide resistance to western bean cutworm larvae.
Scouting for western bean cutworms should start at VT  stage and continue through the R3  stage.
Eggs and newly hatched larvae are usually found in the silks or leaves in the upper canopy.
At least 100 plants  per 40-acre field should be inspected to accurately gauge the infestation level.
Both the center and borders of the cornfield should be inspected.
Western bean cutworms should be managed if 8% of the scouted plants have eggs or newly hatched larvae.
For insecticides to be effective, they must be applied before the larvae enter the ears.
For a list of insecticides that are currently registered for western bean cutworm management on corn, please refer to the current edition of the South Dakota Pest Management Guide: Corn.
Fall Armyworm , and True Armyworm 
 Armyworms do not overwinter in South Dakota and are considered minor pests of corn.
Fall armyworms are attracted to late-planted corn and will feed on foliage and ears.
Corn near the field margins or fields with grass established prior to planting are at greater risk for true armyworm infestations.
Young corn  is more susceptible to true armyworms.
Fall armyworm larvae vary greatly in color, ranging from tan to green or even black.
The larvae have a characteristic white inverted "Y" on the front of their dark brown to black heads.
They also have three narrow, yellow-white lines that run the length of their bodies.
Each segment of their body has six black tubercles or spots.
Fall armyworm larvae have three pairs of true legs and four pairs of abdominal prolegs.
Adult fall armyworm moths have forewings that are dark grey with light-and dark-grey markings.
The tip of each forewing has a characteristic white spot.
Their hindwings are light grey in color.
Fall Armyworm Biology and Injury
 Fall armyworm moths migrate from the Gulf states and have one generation per year in South Dakota.
The female fall armyworm preferentially lays eggs in 5431825 late-planted corn from July to August.
Eggs generally hatch five to seven days after oviposition, and the larvae will begin feeding on corn.
Initially, larvae feed in protected areas, including the whorl.
As larvae mature they feed on the leaves with the exception of the tough midrib.
Feeding injury from fall armyworm results in jagged edges of leaves where defoliation has occurred.
During high levels of infestation, larvae may also feed on the ears where they consume developing kernels.
Fall Armyworm Scouting and Management
 Late-planted cornfields and corn near the margins should be scouted for fall armyworms.
Examine 20 plants in the field to determine whether fall armyworms are present.
Evidence of fall armyworm feeding includes leaves that have a ragged appearance from defoliation, and the presence of frass that resembles sawdust near the whorl.
The presence of fall armyworm feeding on corn ears is indicated by an entry hole in the husk and the presence of larvae.
When 80% of plants are infested with fall armyworm larvae, treatment may be necessary.
However, late-season infestations are difficult to manage with insecticides due to plant height and the location of the larvae within the whorl.
Insecticide management of this pest is frequently not economical.
For a list of insecticides registered for fall armyworm management on corn, please refer to the current edition of the South Dakota Pest Management Guide: Corn.
Bt corn may also manage fall armyworm injury.
Bt toxins that are efficacious against fall armyworm include Cry 1F, Vip3A, and Cry1A.105 + Cry2Ab2.
True armyworm larvae vary in color from tan to dark green to black.
They have a dull orange stripe on each side of their body, and a network of black lines present on their orange head.
True armyworm larvae have three pairs of true legs and four pairs of abdominal prolegs with dark bands.
True armyworm moths are tan to light brown in color with a small white spot in the center of each forewing.
True Armyworm Biology and Injury
 True armyworm is a migratory pest that overwinters in the southern U.S.
It may have as many as three generations per year in South Dakota, but only the first generation pose a risk to corn.
Female moths are attracted to and lay eggs in fields with living, grassy ground cover, including weeds or cover crops.
When eggs hatch, the larvae begin to preferentially feed on grassy hosts.
If initial hosts are consumed or destroyed, larvae will readily move to and feed on corn.
Early vegetative corn  is at greater risk for defoliation by true armyworm larvae.
Defoliation that occurs to corn after V8 is generally minimal, and does not require management.
For young corn, the larvae will begin feeding on the lower leaves of the plant, and work towards the whorl.
True armyworm larvae consume all leaf tissues, excluding the midrib.
There are instances during high infestations where entire corn seedlings will be removed by true armyworm larval feeding.
True armyworm larvae are nocturnal and will hide in the whorl of the plant during the day.
However, true armyworm larvae do not tunnel into the stalk, and on larger plants larvae do not feed on the growing point.
Feeding by true armyworm larvae results in jagged leaf edges, and in instances of severe defoliation only the leaf midrib will remain.
True Armyworm Scouting and Management
 Scouting for true armyworm should occur near the field margins and be intensified for fields that had grassy weeds or cover crops present prior to planting.
To reduce the potential for a true armyworm infestation, weeds and cover crops should be removed at least two weeks prior to planting.
To scout for true armyworm, examine 20 random plants for signs of defoliation.
Treatment is recommended for corn seedlings  if 10% or more of the plants are injured and the larvae that are less than 3/4-inch in length are present.
For corn that is in the 7-8 leaf stage  treatment is recommended if 25% or more of the leaf area is removed, there are more than eight larvae present per plant, and the larvae are less
 Figure 51.16 True armyworm larva feeding on a corn leaf.
Figure 51.18 True armyworm larva feeding on the whorl.
Figure 51.19 Defoliation caused by true armyworm.
than 3/4-inch in length.
Larvae that are smaller than 3/4-inch in length have the potential to feed for another
 week and may cause subsequent defoliation.
If treatment is necessary, please refer to the current edition of South Dakota Pest Management Guide: Corn for a list of insecticides that are currently registered for true armyworm management on corn.
At present, there are no Bt toxins or seed treatments labeled for true armyworm management.
Common Stalk Borer 
 Common stalk borer is an occasional pest in South Dakota.
Corn near field margins or fields with dense grassy weed history have the greatest risk of infestation.
Infested corn will have irregular holes in the whorl, and may be bent or stunted due to abnormal growth.
Young corn  is more susceptible to common stalk borer injury.
Common Stalk Borer Description
 Common stalk borer larvae are approximately 11/4-inch long and have three pairs of true legs and four pairs of abdominal prolegs.
Younger larvae have a characteristic purple saddle and cream-colored stripes on their abdomens.
The colors of the larvae fade as they mature.
Larvae have an orange head with a black stripe on each side.
Common stalk borer moths are redbrown in color.
In South Dakota, common stalk borer has one generation per year.
During the fall, female moths preferentially lay eggs on thin-stemmed, perennial grasses over annual, wide-leaved grasses or broadleaf plants.
Eggs overwinter and hatch between mid-April and early June the following year.
Maturing larvae initially feed in the stems of grasses and weeds until they outgrow their initial plant host.
Larvae will search for larger hosts, including corn.
Common stalk borer larvae primarily cause injury to corn by tunneling into the stalk but also feed on corn leaves.
When larvae feed on the whorls, new leaves appear ragged when they unfurl.
Larvae may also kill the plant by feeding on the growing point , resulting in stand loss and ultimately yield loss.
Common Stalk Borer Scouting and Management
 Infestations are more likely to occur near field margins where grasses or weeds are present.
Large-stemmed weeds, such as giant ragweed, are preferred, although the host range is as large as 176 plant species.
Minimum or no-till cornfields where grass or weeds are present prior to planting are also at an increased risk for infestation.
Corn is most susceptible to common stalk borer when it is between the V1-V5 growth stages, and field margins are at greater risk of injury.
Corn adjacent to grassy areas should be scouted by checking 30 plants from May to June.
Common stalk borer infestations can be detected by observing ragged holes in the newly emerged leaves and the presence
 Figure 51.20 Common stalk borer larva on a corn leaf.
Figure 51.22 Defoliation caused by common stalk borer larvae.
of frass that resembles sawdust near the center of the plant.
Table 51.6 contains threshold information for common stalk borer.
If an early infestation is detected, insecticides may be used to manage the common stalk borer.
However, applying insecticides to infested corn is generally not effective because larvae are protected within the plant.
Insecticide applications should target common stalk borer larvae as they migrate from weedy hosts to corn, which typically occurs from late May to approximately June 20 in South Dakota.
A list of insecticides registered for management of common stalk borer on corn can be found in the current edition of the South Dakota Pest Management Guide: Corn.
For fields with infestations occurring near field margins, the first 4-6 rows of corn should be treated with insecticide during larvae movement.
Removing weedy hosts from the field margins prior to corn planting may also reduce the populations of the common stalk borer.
However, this may increase infestation levels if corn seedlings are present when weeds and grasses are destroyed.
At present, only the Vip3A Bt toxin is labeled for management of common stalk borer.
Table 51.6 Economic threshold for common stalk borer larvae in corn expressed as the percentage of corn whorls infested1.
Plant	$3/Bushel	$4/Bushel	$5/Bushel
 Stage	150	175	200	225	150	175	200	225	150	175	200	225
 V1	5.8	4.9	4.3	3.8	4.3	3.7	3.2	2.9	3.5	3.0	2.6	2.3
 V2	7.1	6.0	5.3	4.7	5.3	4.5	4.0	3.5	4.2	3.6	3.2	2.8
 V3	9.3	8.0	7.0	6.2	7.0	6.0	5.3	4.7	5.6	4.8	4.2	3.7
 V4	9.9	8.5	7.4	6.6	7.4	6.4	5.6	5.0	6.0	5.1	4.5	4.0
 V5	11.3	9.7	8.5	7.6	8.5	7.3	6.4	5.7	6.8	5.8	5.1	4.5
 V6	19.8	17.0	14.9	13.2	14.9	12.8	11.2	9.9	11.9	10.2	8.9	7.9
 V7	54.7	46.9	41.1	36.5	41.1	35.2	30.8	27.4	32.8	28.2	24.6	21.9
 1 Assumes management cost of $10 per acre and 70% mortality of treated larvae.
2Economic threshold = Management cost /  Table adapted from Rice and Davis 2010 and Hodgson 2014.
Bird Cherry Oat Aphid  and Corn Leaf Aphid 
 Bird cherry oat aphids infest the stalk near leaf collars and the ear.
Corn leaf aphids mainly infest the whorl, tassel, and developing ears.
Maize dwarf mosaic virus can be transmitted by corn leaf aphids.
Heavy infestations may reduce photosynthesis, pollination, and ear development.
Black sooty mold is an indicator of large aphid populations.
Bird Cherry Oat Aphid Description and Biology
 The nymphs and adults of the bird cherry oat aphid are teardropor pear-shaped and dark green to olive in color.
These aphids can be identified by a characteristic rusty red-orange patch present at the end of their abdomens near their cornicles .
There are both winged and wingless forms of the bird cherry oat aphid.
These aphids prefer small grains, but can also be found on corn.
Corn Leaf Aphid Description and Biology
 The corn leaf aphids vary in color from green-olive to blue-green and have rectangular-shaped bodies.
There are both winged and wingless forms of the corn leaf aphid.
These aphids prefer sorghum but will readily feed on corn as well.
Bird Cherry Oat and Corn Leaf Aphid Scouting and Management
 The bird cherry oat aphids often feed on the stalk near leaf collars.
When ears are present, the bird cherry oat aphids can be found near the shank and also under the first few layers of the husk.
The corn leaf aphids often feed within the whorl but can also be found feeding on upper leaves.
The corn leaf aphid will also readily feed on the tassels and ears when present.
When scouting for both species of aphids stop at five locations throughout the field and randomly choose 20 plants at each location to inspect.
Examine the whorl and the underside of the leaves to determine whether either species of aphid is present.
The presence of black sooty mold, which grows on the honeydew produced by the aphids can be used as an indicator of aphid infestations.
The presence of ants foraging on the plant may also indicate the presence of aphids.
Current management recommendations indicate that treatment may be necessary if 50% of the inspected plants have more than 500 aphids on them during periods of sufficient moisture.
If the plants are drought-stressed, treatment may be necessary if 50% of the inspected plants have more than 100 aphids on them.
For a list of insecticides currently labeled for management of bird cherry oat aphids or corn leaf aphids on corn, please refer to the current edition of the South Dakota Pest Management Guide: Corn.
In order to help advance this particular irrigation scheduling technology, we conducted a research study focused on irrigation management of corn and soybean in a 140-acre research field at the Eastern Nebraska Research, Extension and Education Center.
The study included infrared thermometers  and multispectral sensors mounted on the center pivot.
The project utilized an irrigation management tool, the Irrigation Scheduling Supervisory Control and Data Acquisition  system, developed by the USDA Agricultural Research Service.
This tool automates data collection, interprets the data collected by the pivot-mounted IRTs and outputs an irrigation recommendation.
Chemigation training is offered at face-to-face events and online.
Either option can be utilized, regardless of whether you are seeking certification for the first time or renewing your certification.
Both training formats include an exam that you must pass to become certified.
There is no cost for chemigation training.
Grain Marketing Understanding Corn Moisture Content, Shrinkage and Drying
 In the United States, corn is marketed in bushels, which are measured in units of mass rather than units of volume.
For example, the industry standard for #1 yellow corn is 56 lbs per bushel, but may be bought and sold at many different % moisture contents.
Grain drying from higher to lower moisture content shrinks as water is lost.
Grain moisture shrinkage is an important concept in grain marketing as this impacts the buying price and discounts.
To optimize economic returns, understanding shrinkage and drying costs calculations are critical.
This chapter provides examples of how to determine the impact of variable grain moisture contents on grain mass.
Key facts about grain moisture content are provided in Table 35.1.
Table 35.1 Key facts about grain moisture content:
 1.
For long-term storage, grain moisture should be 13.1% to reduce disease and insect losses.
2.
Grain buyers post drying and shrink charges.
Know the product delivery specifications for these two factors.
Drying cost and shrink factors should be considered when deciding where to sell your corn.
a.
b.
Handling losses > 1% may be excessive.
3.
Grain moisture content is considered on a wet-weight basis, below are standard moisture contents for different grains.
a.
A bushel of corn at any moisture level weighs 56 lbs.
i.
A bushel of corn at 15.5% moisture contains 47.32 lbs of dry  corn and 8.68 lbs of water.
ii.
A bushel of corn at 13% moisture contains 48.72 lbs of dry corn and 7.28 lbs of water.
b.
A bushel of wheat at 13.5% moisture weighs 60 lbs.
C.
A bushel of soybeans at 13% moisture weighs 60 lbs.
Why is the Term Shrinkage Used for Grain?
Our forefathers developed the method for buying and selling grain.
Before large-scale weighing capability was available, grain was sold by volume.
The inside dimensions of a grain wagon were measured to determine its width, length, and height.
A bushelUnited States dry measure equals 2150.42 cubic inches.
A standard bushel
 of corn weighs 56 lbs at 15.5% final moisture content.
However, some grain buyers want to purchase even drier grain  and have a discount based on the % difference between the seller's grain moisture content and their posted moisture content.
The weight loss by drying is referred to as shrinkage.
When wet corn greater than the posted moisture content is purchased by the buyer and dried, the grain loses volume as water evaporates from the grain.
The grain test weight increases depending on the beginning and ending % moisture content, with a range of 0.25 to 0.50 lb/bushel-%point.
Thus, the term shrinkage was used to describe the phenomena of less volume due to moisture loss in a load of corn.
Today, volume  is not measured and grain transactions are based upon weight.
However, due to grainselling history before scales, the word shrinkage is still associated with moisture loss.
Economic Implications of Grain Moisture
 Grain discounts often consider shrinkage, handling losses, and drying costs.
Shrinkage is the loss of weight  when grain dries.
Handling losses are loss of weight due to grain respiration , loss of oils during drying, and the loss of materials when grain is transported or moved from one location to another.
Drying costs result from the amount of energy needed to dry corn to a storable moisture percentage to maintain quality.
To optimize the grain selling price, the farmer must understand the buyer's delivery specifications regarding: 1) shrinkage, 2) drying charges, and 3) final moisture content based on grain sale date.
In corn production, buyer discounts can substantially reduce the return.
For example, the buyer may have discounts for grain that has moisture contents different than their specifications.
Understanding these discounts can help farmers make sound economic decisions.
Grain moisture is measured with a sensor that usually requires, at the very least, annual calibration.
There are many companies that produce moisture sensors for grain, including real-time in line sensors for combines, sensors for bulk grain, and moisture probes.
When grain moisture content is measured, a sample is collected and analyzed.
As with all measurements, the analysis is only as good as the sample.
Accurate assessments require that a "good representative" sample be collected and that the sensor be precise and accurate.
To achieve a representative moisture value for grain from the field or in an on-farm bin, read and follow the instructions provided by the sensor manufacturer regarding sample collection.
Note that on-farm grain moisture sensors can be impacted by temperature of the grain.
Grain moisture meter errors typically increase once the temperature is less than 40F.
Bushels of corn based on corn weight: Bu = Amount of corn in wagon  56 lbs
 This equation does not take into account the moisture content of the grain.
Grain moisture equation:
 WW MC% = 100 X WW + wdc
 Where WW = weight of water WC = weight of wet corn wdc = weight of dry corn MC% = moisture content as a decimal
 The amount of water in wet grain is determined by the equation:
 WW = MC% X WC
 The grain moisture equation can be algebraically manipulated to determine the amount of water in grain based on the grain's dry weight:
 Equation [4] can be algebraically manipulated to determine the dry grain based on the wet weight of corn , the % moisture of the wet corn , and the % moisture of the dry corn.
100%-MC grain weight at 'dry' moisture % = WC X [5] 100%-dry%
 Dry weight of corn  can also be calculated using this equation:
 WDC = WC -WW
 When grain is dried, it loses moisture to the atmosphere.
The amount of loss is the shrink.
Moisture shrink  is determined with the equation:
 %Moisture shrink = 100 X original moisture content %-final moisture%
 This definition of shrinkage does not consider the amount of grain can also be lost at an elevator through dust and removal of foreign materials.
Typically, handling losses are 0.25 to 0.5%.
An alternative technique to solve this problem is to use equation 5: 100-20 = 16954 X = 15,590 100-13
 Finally, determine the number of bu of corn at 13% moisture, using equation [1]:
 Bushel corn '13% = 15,590 lbs 278.4 bushels 13%
 Based on these calculations, the amount of corn that the elevator will pay for is 278.4 bu.
Shrinkage is calculated by subtracting the initial weight from the final weight = 16,954-15,590 = 1,364 lbs
 The per bushel shrinkage is 1364/302.75 bushels = 4.505 lbs/bushel, and the shrinkage per bushel per each change in moisture percent is
 = 4.505 lbs/
 = 0.644 lbs /bu xpoint moisture].
This value is similar to Table 35.2
 This problem can also be solved by using Table 35.2.
In this table, the beginning and end moisture values are determined, and the water shrink factor value is multiplied by the difference.
For example, if the wet corn delivered has a % moisture content of 20% and the elevator docks for shrinkage at 13%, then 20-13 = 7% and the value for 1.149 from the table is multiplied by 7.
In this example, the elevator is using a grain moisture % of 13%.
In Table 35.2, the shrinkage value to 13% moisture is 1.149.
Step 1.
Determine the number of points difference from the wet grain delivered to the acceptable moisture content.
The difference between the initial moisture content  and final  is 7%.
This difference is the
 number of moisture points.
Step 2.
Percent water shrink is determined by:  X the water shrink factor.
Step 3.
The bushels lost due to water weight are calculated by multiplying the bushels at 20% moisture times the water shrink factor.
The water shrink factor is converted from a percent  to a decimal  by dividing the percent by 100.
First, bushels delivered at 20% moisture are calculated 16,954 lbs/ = = 303 bu at 20% moisture
 303 x0.0804 = 24 bushel shrink 20%
 Step 4.
Bushels at final moisture content = 13% is: 303 bu bu shrink = 279 20% 13%
 The same answer is achieved using both methods.
If you have access to a table with values, the calculations may take less time.
However, if the values for the water shrink factor are not available, the first method can be used.
What is the final $/bu paid to the farmer based on shrink discount?
If the corn had been delivered at 13% moisture and corn has a test weight of 56 lbs/bu, the paid amount would be: the number of bushels delivered X $/bushel.
In this example:
 Table 35.2 Relationship between the final moisture content, water shrink factor, and lbs water/bu-pt.
Final moisture	Water shrink	lbs water/
 Content 	factor 	Bu-pt
 Comparing Farm vs.
Elevator Drying Costs
 The elevator often charges for drying costs for grain that is delivered too wet to the elevator.
These charges are often expressed as a $ amount per point of moisture content between the wet  and dry.
The farmer must decide whether the drying cost is reasonable.
To calculate the on-farm drying costs, the fuel, capital, and labor costs must be considered.
Capital costs to own the dryer
 In this example, a 20 ft.
axial plenum grain dryer system costs approximately $77,000.
This system can dry corn up to about 750 bu/hour at full heat from 20% to 15% moisture.
The interest rate at the bank is 5% and depreciation is 8%.
The farm averages 750 acres of corn.
The average yield is 170 bu/acre.
The producer starts to harvest grain at 21% moisture desires a final dry moisture content of 15.5%.
Example 35.2 One thousand  lbs of grain at 22% moisture content are delivered to an elevator.
If the buyer's final moisture content is 13% moisture, determine shrinkage and the amount of grain at 13% moisture.
Method 1 100%-MC Using equation 5, grain weight at 'dry' moisture % = WC X 100%-dry% 100-22 = 1000 X =897 lbs 100-13
 Shrinkage was 1000-897= 103 lbs.
The load contains 16 bushels.
1.149% 9 shrink There were 17.86 bu corn at 22% moisture:
 17.86 bu X 0.101341 = 1.85 bu shrink 17.86 bu 1.85 bu = 16 bu,,
 Step 1.
First, the shrink value associated with the final moisture content of 15.5% must be determined.
Using Table 35.2:
 Final moisture	Water shrink	Lbs water/
 Content 	factor 	Bu-pt
 If the base price is $3.29 and the grain is aerated with high humidity air, the corn moisture content may potentially increase from 13% to 15.5%.
Water weight has been added to the grain to increase the moisture.
The resulting increase in grain price will be:
 Example 35.4 The elevator will dry each bushel of the 22% moisture corn to 13% moisture.
At delivery the corn had a moisture content of 22%.
For each bu of 56 lbs/bu 22% moisture corn dried, calculate is the lbs of dry corn at 13%.
Equation [5] is used to calculate the dry grain at the lower moisture content:  Dry grain weight=wet grain weight X 
 Substituting in the delivery moisture content  and the moisture content desired by the elevator , the dry grain weight is calculated:
 Grain weight at 13% = 56 =50.21 dry corn 100-13
 The elevator's actual shrinkage was from 56 lbs to 50.21 lbs, which is a loss of: 56-50.21 = 5.79 lbs water.
In this example the final corn moisture % is 15.5%.
At 15.5% final moisture content, a bushel point is 0.6627 pounds of water  :
 Final moisture	Water shrink	Lbs water/
 Content 	factor 	Bu-pt
 1.
Propane cost, amount needed per % point 0.6627 lbs water bu-pt X lb-water propane BTU 1 gal propane = bu-pt 3000 1 gal $1.45 $0.0315
 2.
Electricity cost for drying system and fans, amount needed per % point 0.6627 lbs water bu-pt X 0.03 kWh lb-water X $0.09 kWh $0.0018 bu-pt
 3.
Total cost on farm drying cost, energy $0.0315 $0.0018h $0.0333 propane
 Cost to own dryer per year  a.
X $77,000 = $10,010 100
 b.
Bushel points to dry:
 Cost to own on-farm dryer system C.
$10,010 $0.01427 701,250
 The total cost to dry grain on the farm considering energy, and interest and depreciation to own the systems is: $0.0333
 How fast does corn dry?
Typically in South Dakota it takes 15 to 30 growing-degree days  to reduce the corn moisture content from 30% to 29%.
After November 1, very little in-field drying occurs.
How efficient is your dryer?
Harvest Corn or Leave in the Field?
The cost of field drying is frequently viewed as being free; however, field drying has risks.
The longer corn is left in the field, the greater the potential for ear drop caused by wind, precipitation, or wildlife.
Drier corn  has been shown to exhibit greater combine harvest loss  than wetter corn.
To make the best decision for your operation, evaluate the costs of  on-farm drying VS.
local elevator drying charges.
The local elevator may be using natural gas rather than propane and this may result in both profit for the elevator and cost savings for the producer.
Method to Estimate Late-Season Crop Water Needs:
 To determine how much water from rain and irrigation will be needed to mature the crop, use the method described below and information from Table 1.
IRRIGATION SCHEDULING REMAINS IMPORTANT FOR LOW CAPACITY SYSTEMS
 Kansas State Research and Extension
 Many irrigators in the Central Great Plains region do not use science-based irrigation scheduling for a variety of reasons, many of which are not strongly related to the technical feasibility.
Evapotranspiration -based irrigation scheduling has been shown to be an acceptable irrigation scheduling method within the region.
Many irrigators have expressed the rationale that there is no need to implement irrigation scheduling because their marginal capacity irrigation must be ran continually throughout the season to meet corn irrigation needs.
ET-based irrigation schedules were simulated using 43 years  of weather data for Colby, Kansas to determine irrigation needs as affected by irrigation capacity, center pivot sprinkler system application efficiency and the initial soil water condition at corn emergence.
Adoption of ET-based irrigation scheduling with an initial soil water condition of 85% of field capacity and 95% application efficiency potentially could save on average 8.34 inches water for a 1 inch/4 days irrigation capacity and 2.80 inches for a severely deficit 1 inch/8 day irrigation capacity.
As application efficiency was decreased from 95% to 80% these savings for similar initial soil water conditions decreased from 6.93 to 2.64 inches for the greater and smaller irrigation capacities, respectively.
Potential irrigation savings using an application efficiency of 95% were reduced but still appreciable when the initial soil water condition was 60% of field capacity averaging 6.06 and 1 inches for the 1 inch every 4 or 8 days irrigation capacities, respectively.
Irrigators with marginal capacity systems should adopt sciencebased irrigation scheduling to make best use of their limited irrigation and should not discount their opportunity to save irrigation water even when their system restrictions are severe.
The most common definition of irrigation scheduling is simply the determination of when and how much water to apply.
Modern scientific irrigation scheduling uses a single approach or combination of weather-, soilor plantbased approaches.
Science-based irrigation scheduling has existed for approximately 60 years with one of the earlier discussions of the topic made by van Bavel  of using evapotranspiration to estimate soil water conditions and for timing of irrigation.
Although there is a wide body of literature on irrigation scheduling in reference books, journal articles, symposium proceedings, and extension publications, effective methods have not been well adopted by irrigators.
Lack of adoption was recognized many years ago as a key problem to advancing irrigation scheduling.
Behavior patterns and attitudes of irrigators were identified as more significant barriers to adoption than reliability and accuracy of scheduling methods.
The USDA-NRCS has offered cost-sharing for implementation of ET-based scheduling in several of the US Great Plains states.
When the accuracy of irrigation scheduling is perceived to be an issue, there is a great impediment to adoption since the economic penalty of over-applying water is usually many times less than that of under-applying water.
Lack of confidence by the irrigator can be the result of changes in cultural practices that affect the field water budget or introduction of new drought resistant varieties or hybrids that seem to indicate a change in the water use of the crop.
An example is drought resistance corn, which is often interpreted by irrigators as a corn that needs less water.
These examples suggest that some of the reasons for non-acceptance of irrigation scheduling are cultural and not strongly related to technical feasibility.
Figure 1.
Effect of irrigation inaccuracy on crop production points.
Adapted from discussion and graph in Lamm.
Additionally, irrigators, economists, and water planners often want to simplify the question of "How much irrigation water do I need?" to a single annual value when in reality there is no single answer.
Furthermore, as indicated in Fig.
2, averaging several years of data will result in a smooth yield/water response curve that has very little basis for obtaining good yields in a given
 year.
Fortunately, with science-based irrigation scheduling, irrigators do not need to use average values.
The Kansas USDA-NRCS officially adopted KanSched, developed at Kansas State University, as an approved ET-based irrigation scheduling program  and has offered cost share incentives to encourage irrigator adoption of ETbased scheduling and have required adoption as an eligibility requirement for other irrigation improvement cost-share programs.
Since 1997, approximately 730 contracts have been issued in Kansas.
Similar programs exist in other parts of the US Great Plains.
Figure 2.
Corn yield response to subsurface drip irrigation  amount in seven different years, KSU Northwest Research-Extension Center, Colby, Kansas.
The boldface curve is the average of all seven years emphasizing that average values are insufficient for irrigation management in an individual season.
All years were scheduled according to daily ET-based water budget with individual data points representing differences in available irrigation capacity.
Many irrigators have been unwilling to set aside much time to manage water.
They often feel that if their irrigation capacity is appreciably less than crop water needs, they need to operate their irrigation systems continuously during the growing season.
Although, there are a large number of marginal capacity irrigation systems in the region, there remains opportunities to delay unnecessary irrigations by using ET-based irrigation scheduling.
The possible savings attributable to adoption of ET-based scheduling can be estimated from simulation modeling, so the goal of this paper is to more fully quantify these savings for irrigators.
Weather data from 1972 through 2014  for Colby, Kansas , collected at the Kansas State University Northwest Research-Extension Center, was used to simulate annual ETbased irrigation scheduling water budgets for corn  production.
Briefly, the water budget model schedules a 1-inch irrigation event when two criteria are met.
The first criterion was that there is at least 22% depletion of plant available water in the 5-ft.
profile to allow storage of the irrigation event plus retaining some additional room for storage of precipitation.
The 22% depletion is equivalent to approximately 3.2 inches of soil water storage.
The second criterion is that there was sufficient irrigation capacity to conduct the event on that date.
Irrigation capacities of 1 inch for 4, 5, 6, and 8 days were simulated at application efficiencies of 95% and 80% representing a typical range of efficiencies for center pivot sprinklers in the region.
An irrigation capacity of 1 inch/4 days will typically approximate full irrigation on the deep silt loams and for the climatic conditions of this region.
The irrigation season was constrained to the 90-day period, June 5 through September 2 in all years which approximates the typical season for most irrigators in the region.
This results in potential maximum seasonal gross irrigation applications of 23, 18, 15, and 12 inches for the irrigation capacities of 1 inch for 4, 5, 6, or 8 days, respectively.
The irrigation scheduling water budget used in the simulations can be simplified to the following equation
 where Sc and Sp are the plant available soil water amounts in the soil profile on the current and preceding days, ET is daily crop evapotranspiration, R is irrigation runoff, P is effective precipitation, I is the irrigation water applied, and F is flux across the lower boundary of the control volume , all in any consistent unit of length.
Runoff was assumed to be controlled to negligible amounts by surface storage management with the exception of large rainfall events which were capped at a maximum infiltrated amount.
Complete details of the model and the specific parameters used in the simulations are described in Lamm et al..
Additionally, two initial soil water conditions at corn emergence were simulated, a wetter 85% of field capacity for the 5-ft soil profile and a drier 60% of field capacity.
Irrigation savings were calculated daily and accumulated throughout the season as the difference between full applications of the gross irrigation amount possible at a given capacity minus the gross irrigation amount predicted in the ET-based irrigation scheduling water budget for the same capacity.
The probability of needing a given amount of irrigation was computed using a normal distribution for the mean and standard deviation values of the 43 years.
It should be reiterated that the model assumed two criteria must be satisfied before an irrigation event would be scheduled: 1) specified soil water depletion or greater is reached; and 2) irrigation capacity is sufficient to cycle the event on that day.
Therefore, some of the marginal irrigation capacities examined here will not be sufficient during the greater water use periods towards the critical growth periods and crop yields would be reduced
 Irrigation capacity had a great effect on the amount of irrigation that could be saved as would be anticipated.
On average, the irrigation capacity of 1 inch/4 days had the potential of saving
 approximately 3 to 5 times more irrigation with ET-based irrigation scheduling than with the lowest 1 inch/8 day capacity for the range of application efficiencies and initial soil water scenarios evaluated.
A greater portion of these savings for the greater capacities occurred during the early part of the irrigation season, as indicated by the increased slope on this portion of the curves , when irrigation capacity and increased chances for precipitation greatly exceed corn evapotranspiration.
After that period, irrigation water savings are incrementally increased as the season progresses, increasing during cooler, more humid periods and decreasing during warmer and drier periods with a saw-tooth pattern as irrigation events occur.
This emphasizes the need to use season long day-to-day irrigation scheduling.
Table 1.
Calculated seasonal gross irrigation amounts  using ET-based irrigation scheduling for corn for the 90 day period  at various irrigation capacities using 43 years  of actual weather data from KSU Northwest Research-Extension Center, Colby, Kansas as affected by initial profile soil water conditions and sprinkler application efficiency.
Sprinkler irrigation events were gross 1 inch applications.
The 50% probability amount is equivalent to the actual average application due to the fact that a normal distribution was assumed in calculation of the probability.
Initial profile soil water condition, 85% of field capacity and sprinkler application efficiency of 95%
 Irrigation	Potential	Actual	Actual	75% Probability	50% Probability	25% Probability
 capacity	maximum	maximum	minimum	of needing to	of needing to	of needing to
 application	application	application	apply less than	apply less than	apply less than
 1 inch/4 d	23.0	20.0	6.0	17.0	14.6	12.3
 1 inch/5 d	18.0	17.0	6.0	14.9	13.1	11.3
 1 inch/6 d	15.0	14.0	6.0	12.9	11.6	10.3
 1 inch/8 d	12.0	11.0	5.0	10.1	9.2	8.3
 Initial profile soil water condition, 85% of field capacity and sprinkler application efficiency of 80%
 1 inch/4 d	23.0	21.0	7.0	18.3	16.1	13.8
 1 inch/5 d	18.0	18.0	6.0	15.4	13.8	12.2
 1 inch/6 d	15.0	15.0	6.0	13.4	12.1	10.8
 1 inch/8 d	12.0	12.0	6.0	10.2	9.4	8.5
 Initial profile soil water condition, 60% of field capacity and sprinkler application efficiency of 95%
 1 inch/4 d	23.0	23.0	7.0	19.7	16.9	14.2
 1 inch/5 d	18.0	18.0	8.0	17.0	15.2	13.3
 1 inch/6 d	15.0	15.0	9.0	14.7	13.6	12.4
 1 inch/8 d	12.0	12.0	7.0	11.9	11.0	10.2
 Initial profile soil water condition, 60% of field capacity and sprinkler application efficiency of 80%
 1 inch/4 d	23.0	23.0	10.0	21.5	19.2	16.8
 1 inch/5 d	18.0	18.0	10.0	17.8	16.4	14.9
 1 inch/6 d	15.0	15.0	10.0	15.0	14.0	13.0
 1 inch/8 d	12.0	12.0	8.0	12.0	11.3	10.5
 Figure 3.
Average savings of irrigation that could be obtained with ET-based irrigation scheduling as compared to maximum seasonal applications possible with various irrigation capacities for an application efficiency of 95% and an initial soil water condition of 85% of field capacity as determined in simulation modeling for 43 years of weather data, Colby, Kansas.
Greater irrigation system application efficiency  increases the possibility for saving irrigation with ET-based irrigation scheduling.
Potential irrigation savings for the 95% application efficiency compared to 80% at the 85% of field capacity initial soil water condition ranged from 6% for the 1 inch/8 day irrigation capacity  to 20% for the 1 inch/4 day irrigation capacity  emphasizing the importance of increasing application efficiency whenever it is economically and technically practical to do so.
The effect of increasing Ea from 80 to 95% for the drier initial soil water condition  was even greater, ranging from 31 to 58% across the range of irrigation capacities evaluated.
This increase occurs because the drier initial soil water condition results in greater irrigation needs during the season.
Figure 4.
Average savings of irrigation that could be obtained with ET-based irrigation scheduling as compared to maximum seasonal applications possible as affected by sprinkler application efficiency, Ea, for an initial soil water condition of 85% of field capacity for irrigation capacities of 1 inch every 4 or 8 days as determined in simulation modeling for 43 years of weather data, Colby, Kansas.
Greater initial soil water greatly increased the potential savings that could be obtained with adoption of ET-based irrigation scheduling  because of the opportunity to avoid some early season irrigation events with the greater soil water reserves at a time when evapotranspiration is reduced and chances for appreciable precipitation are greater.
When the initial soil water condition is only 60% of field capacity and the irrigation capacity is restricted to only 1 inch/8 days, then the average potential irrigation savings is essentially just a single 1-inch event.
However, when considering the range of 43 years examined there was one year where over 4 inches could have been saved even with this severely restricted scenario.
Considering the fact that most of the marginal system capacities are also related to groundwater wells with reduced and declining saturated thicknesses, saving any water in these restricted scenarios may extend the longevity of irrigation for those wells.
Additionally, one nearby area in Kansas has converted their fixed water application water rights to flexible five-year accounts, where water saved in one year might be utilized in a subsequent more water-stressed year.
Figure 5.
Average savings of irrigation that could be obtained with ET-based irrigation scheduling as compared to maximum seasonal applications possible with initial soil water conditions of 85% and 60% of field capacity for irrigation capacities of 1 inch every 4 or 8 days for an application efficiency of 95% as determined in simulation modeling for 43 years of weather data, Colby, Kansas.
Considerable water savings are possible when ET-based irrigation scheduling is adopted for marginal capacity irrigation systems.
Although these potential savings are increased for greater irrigation capacity systems, for systems with greater application efficiencies and for situations where initial soil water conditions are wetter, there are potential savings even under very restricted scenarios.
The importance of science-based irrigation scheduling should not be discounted by irrigators just because they typically are operating in a deficit condition.
Consistent, season-long use of science-based irrigation scheduling, such as the ET-based water budgets used in this study, can point out the opportunities and timing of when irrigation systems can be temporarily shut off.
Contribution no.
15-283-A from the Kansas Agricultural Experiment Station
Answer yes or no to all of the questions that apply to your operation.
For questions with a "yes" answer, pat yourself on the back for doing a good job.
If you answered "no" to any of the questions, you should develop an action plan to reduce your risk.
Use the information in this GAP education series and any of the resources listed below to help you develop your action plan.
If you use well water for spray irrigation, mixing pesticides, cooling fruit, or washing vegetables, is your well at least 100 feet from a:
 Do you have a maintenance schedule for your wells?
Septic system drainage field?
Discharge area for milk house wastewater?
Is the drinkable water/well water sources tested at least once per year?
Are records of all water tests on file?
Have you installed a backflow prevention device or other system to prevent contamination of clean water supplies by potentially contaminated water?
If you use surface water for irrigation and pesticide application:
 Do you used drip, under-tree or low volume spray irrigation to reduce water contact with fruit?
If you use overhead irrigation or evaporative cooling, do you test your irrigation water for fecal coliform concentrations during the growing season?
If livestock operations are located nearby the irrigation source, are animals excluded?
Are good management practices in place to protect the quality of irrigation water?
Do you use only potable water to apply foliar applications including pesticides, nutrients, and growth regulators?
In the barn or packing house?
Does water used to cool, clean and sanitize produce meet the EPA Drinking Water Standard?
Arkansas Water Primer Series: Arkansas Water Pollution Control Laws
 Dirty water compromises the chemical and biological integrity of Arkansas' waterbodies and poses a risk to public health.
The Arkansas General Assembly has enacted several laws that address the problem of water pollution.
The Arkansas Water and Air Pollution Control Act
 The Arkansas Water and Air Pollution Control Act of 1949 makes it unlawful to "cause pollution of any of the waters of this state," or to "place or cause to be placed any sewage, industrial waste or other wastes in a location where it is likely to cause pollution of any waters of this state."
 The Arkansas Pollution and Ecology Commission is the environmental policy-making agency for the state.
With guidance from the Governor, the General Assembly, the U.S.
Environmental Protection Agency and other stakeholders, the Commission establishes environmental policies for the state, which the Arkansas Department of Environmental Quality  implements.
The Commission is composed of seven members of the public who are appointed by the Governor and six representatives from the following agencies:
 Oil and Gas Commission
 Game and Fish Commission
 Citizens who suspect a water pollution law has been broken may file a complaint with ADEQ.
The agency's Water Division Inspection Branch, which has 13 District Field Inspectors and two Inspector Supervisors, investigates citizens' allegations against municipalities, industries, other citizens or agricultural facilities.
In 2007, ADEQ's staff responded to 933 water-related complaints and took 87 formal enforcement actions.
Violation of the Pollution Control Act
 The Commission may conduct administrative proceedings and institute civil enforcement actions in the proper court.
The Commission may not, except in emergencies, assess a penalty without the opportunity for a hearing.
Prior to a hearing, the agency must provide public notification and an opportunity for comments.
Administrative penalties may be no greater than $10,000 per day of violation.
Civil actions, as determined by the court, may result in:
 An order to abstain or desist and/or compel compliance
 An order for remedial measures and/or
 Recovery of all costs, expenses and damages.
Any violation of the Act is also a criminal misdemeanor, punishable by imprisonment for not more than one year, a fine of not more than $25,000, or both.
A purposeful, knowing or reckless violation that "creates a substantial likelihood of adversely
 affecting" human health or the environment is a felony, punishable by imprisonment for not more than five years, a fine of not more than $50,000, or both.
A purposeful, knowing or reckless violation that "places another person in imminent danger of death or serious bodily injury" is punishable by imprisonment of not more than 20 years, a fine of not more than $250,000, or both.
In addition, if the court finds that the violator made money from the offense, the state may seek an additional fine of double the amount of the gain.
Additional Water Pollution Laws
 Arkansas' Solid Waste Management Act makes it unlawful to "sort, collect, transport, process or dispose of solid waste in such a manner or place as to cause or be likely to cause water pollution within the meaning of the Arkansas Water and Air Pollution Control Act." The penalties are the same as for violations of the Water and Air Pollution Control Act.
The Litter Control Act makes it unlawful to "drop [or] discard litter into any river, lake, pond or other stream or body of water within this state." There is no violation of the Act if the:
 Property is designated as a permitted disposal site
 Litter is deposited in such a manner as to prevent it from being carried away or the person is the owner or tenant in lawful possession of the property and
 Litter does not create a public nuisance, health or fire hazard.
A violation of the Act is a misdemeanor.
First-time offenses are subject to a $100 fine or 100 hours of community service.
Fact Sheet 109  Glossary of WaterRelated Terms contains a comprehensive list of terms used in the Arkansas Water Primer Fact Sheet Series.
The Arkansas Water Primer Fact Sheet Series was funded by a grant from the U.S.
Department of Agriculture with additional financial assistance from the University of Arkansas Division of Agriculture.
Original research for the Series was provided by Janie Hipp, LL.M., and adapted by Tom Riley, associate professor and director of the University of Arkansas Division of Agriculture's Public Policy Center, and Lorrie Barr, program associate, University of Arkansas Division of Agriculture's Public Policy Center.
Irrigation rates and frequency based on turfgrass species selection, soil type and evapotranspiration  rates.
Appropriate turfgrass genus and species for your geographical region.
Regional variations in soil type and evapotranspiration rates.
Turfgrass species evapotranspiration replacement requirements.
Best timing of irrigation applications.
Introduction to turfgrass species
 When trying to minimize irrigation inputs, the best turfgrass species for the Oregon climate include perennial ryegrass  in Western Oregon, Kentucky bluegrass  in Central/Eastern Oregon and tall fescue  in Western, Central or Eastern Oregon.
Bentgrass, including creeping, colonial, velvet and highland are well-adapted to areas of little or no irrigation.
However, they typically are not planted in lawns because of heavy thatch accumulation and lower mowing height recommendations.
Fine fescue is well-adapted to low fertility and shady environments.
It is capable of persisting with little or no irrigation.
Still, it requires the most frequent summer irrigation to prevent visible drought stress and summer dormancy  from developing.
All of these turfgrass species can be maintained without irrigation in Western Oregon if summer dormancy and the presence of drought-tolerant weeds
 Alyssa Cain, graduate assistant, Department of Horticulture; Alec Kowalewski, turfgrass specialist and associate professor, Department of Horticulture; Brian McDonald, senior faculty research assistant II, Department of Horticulture; Clint Mattox, research associate , all of Oregon State University
 Photo: Alec Kowalewski,  Oregon State University
 Figure 1: Regularly irrigated turgrass  compared to unirrigated turfgrass  in Corvallis, Oregon in 2019.
like dandelion, crabgrass and spurge is acceptable.
In Central/Eastern Oregon, irrigation will be required for turfgrass to persist.
Residents of Western Oregon, where winter weather is cool and wet, will likely prefer perennial ryegrass.
Perennial ryegrass is a fine-textured turfgrass species that provides a dark green, visually pleasing lawn when maintained with frequent mowing, fertilization and regular irrigation.
Perennial ryegrass may be injured in Central/Eastern Oregon because of its poor cold tolerance.
For high-quality, aesthetically pleasing lawns in Central/Eastern Oregon, Kentucky bluegrass is the best turfgrass species.
During periods of snow cover, Kentucky bluegrass goes dormant.
But it recovers in the spring with an aggressive, rhizomatous growth habit.
When maintained with frequent mowing, fertilization and irrigation, this species provides a lush, dark-green lawn capable of recovering well from foot traffic.
In
 Western Oregon, however, it is susceptible to coolweather pathogens, and will not persist as a major component of the lawn.
Tall fescue provides a drought-tolerant option for those hoping to use less water.
Tall fescue is adapted to warm weather and does well in the summer months with minimal irrigation.
Its deep root architecture helps tall fescue tolerate droughts.
A mowing height of 3 inches encourages deeper rooting.
It is well-adapted to low fertility levels.
Breeding has improved the texture of tall fescue, but its leaves are coarser than perennial ryegrass and Kentucky bluegrass, and often will not achieve the visual aesthetics these species possess.
In Western Oregon, tall fescue tends to go semidormant in the winter and is susceptible to leaf spot  and Microdochium patch  diseases, especially the first winter after planting.
Because of its weak rhizomatous growth habit, tall fescue persists in Eastern/Central Oregon and may be an option for those who want to save water.
Photo: Alec Kowalewski,  Oregon State University Figure 2: Turfgrass species from fine to coarse leaf texture, left to right: fine fescue, perennial ryegrass, Kentucky bluegrass and tall fescue, Corvallis, Oregon.
Photo: Alyssa Cain,  Oregon State University
 Figure 3: Irrigation applied at 1/4" depth four times per week  and irrigation applied at 1" once per week , Sept.
3, 2019, Corvallis, Oregon.
While the species plays a large role in the amount of irrigation required for turfgrasses, soil also plays a critical role.
Sandy soil, for instance, drains water faster than clay soil.
The type of soil affects irrigation frequency, but not total amount.
Sandy soils need to be watered more frequently, but with less water with each application.
Excessively watering a sandy soil allows water to move beyond the root zone of the grass.
Knowing the texture of a soil is critical for making effective, long-term irrigation schedules.
Soils in Western Oregon are often high in clay content, hold onto water longer and drain slowly.
Irrigation can be less frequent on these soils.
Conversely, soils in Central/Eastern Oregon typically have less clay and more sand.
These soils have low water-holding capacity, drain rapidly and require morefrequent irrigation.
The loss of water from a vegetative canopy to the atmosphere also known as evapotranspiration, or ET and precipitation are major factors to consider when developing an irrigation program.
In summer when
 precipitation is minimal, irrigation is required to keep turfgrass green.
Different turfgrass species require different irrigation amounts.
For instance, research conducted in Western Oregon determined that fine fescues  require the most water 58% to 96% ET replacement to achieve high quality.
Kentucky bluegrass requires 45% to 50% ET replacement, perennial ryegrass requires 32% to 49% and tall fescue requires 26% to 43%.
Evapotranspiration rates increase as summer temperatures increase.
Because Oregon receives very little summer rain, turfgrasses depend on irrigation for ET replacement.
Irrigation rates and frequencies
 Cool-season turfgrass species are inherently shallowrooted and in Oregon require relatively frequent irrigation to prevent summer dormancy.
In Western Oregon, irrigate twice per week for tall fescue and every two to four days for perennial ryegrass.
Apply a quarterinch to half-inch of water to maintain green color in the summer.
In Western Oregon, fine fescues will require irrigation every other day or daily.
Apply a quarter-inch to half-inch of water to maintain acceptable green color during peak drought stress.
In Central and Eastern Oregon, irrigation frequency should be increased to compensate for sandy soil, prolonged periods of low precipitation and higher ET rates.
Tall fescue in Central/Eastern Oregon will require irrigation several times per week.
Kentucky bluegrass will require frequent  irrigation in June and July.
Fine fescues will require daily irrigation throughout the summer months to prevent dormancy.
The best time to irrigate is at dawn; few people are using the landscape and wind levels are likely at their lowest.
As temperature and wind increase, irrigation efficiency decreases.
Irrigating at dawn also provides the plant with water and sunlight at a relatively cool time of day for maximum photosynthesis.
Irrigation requirements vary greatly according to turgrass species, soil type and ET rates across the state of Oregon.
Turfgrass is inherently shallow-rooted, so onequarter to a half inch of water should be applied per application.
Apply irrigation to cool-season turfgrass at relatively frequent intervals to prevent summer dormancy.
In Western Oregon, turfgrass can be maintained without irrigation if summer dormancy and weed encroachment is acceptable.
However, summer irrigation is necessary for turfgrass to persist in Central/Eastern Oregon.
Tall fescue will require the least frequent irrigation and lowest ET replacement, and will grow well in all areas of the state.
Perennial ryegrass in Western Oregon requires irrigation every two to four days depending on the month.
Kentucky bluegrass in Eastern Oregon will require frequent irrigation to prevent summer dormancy.
Fine fescues will require the most frequent irrigation and greatest amount of ET replacement to prevent drought stress.
Photo: Alec Kowalewski,  Oregon State University
 Figure 4: Irrigation application rate of a 1/2" depth, determined using a rain gauge, Corvallis, Oregon.
Table 1: Average monthly evapotranspiration  in Western Oregon and Central/Eastern Oregon
 Western Oregon	Mar.
Apr.
May	June	July	Aug.
Sept.
Oct.
Total
 Astoria	1	2.3	4	4.8	5.8	4.8	2.9	1.3	26.9
 Bandon	1.4	2.2	3	3.8	3.9	3.1	2.5	1	20.9
 Brookings	1.4	2.8	3.4	4.5	3.7	3	2.9	2.4	24.1
 Corvallis	1.2	3.2	5.3	6.9	8.6	7.7	4.6	2.3	39.8
 Forest Grove	1	2.6	4.4	5.3	6.8	5.5	3.1	1.3	30
 Medford	1.3	3.1	4.9	6.5	7.7	6	4	2	35.5
 Oregon	Mar.
Apr.
May	June	July	Aug.
Sept.
Oct.
Total
 Baker	0	1.8	4.5	5.4	6.9	6.3	3.8	0	28.7
 Christmas Valley	0.1	5.1	5.1	6	7.4	6.2	4.1	0	34.1
 Hermiston	1.5	6.8	6.8	8	9.2	8.5	6.5	2.5	49.9
 Klamath Falls	0.1	5.4	5.4	6.6	7.7	6.7	4.3	0	36
 Madras	0.5	5.2	5.2	7.5	8.5	7.6	4.6	0.8	40
 Ontario	1.8	6.3	6.3	7.7	9.3	7.8	5.3	1	45.4
 Trade-name products and services are mentioned as illustrations only.
This does not mean that the Oregon State University Extension Service either endorses these products and services or intends to discriminate against products and services not mentioned.
Nonpoint Source Pollution in the Poteau River Watershed
 The Poteau River Watershed is located on the Arkansas-Oklahoma border and includes communities in Polk, Scott and Sebastian counties.
A "watershed" is an area of land where all of the water that drains off of it goes to the same place, SO rainwater or snowmelt in communities in this watershed eventually drain to the same place.
This watershed is named for the Poteau River, whose headwaters begin in Arkansas but wind into Oklahoma.
Arkansas has a smaller portion of the overall watershed, but its 1,889 square miles of land and water are no less important when it comes to preventing or reducing pollutants that enter streams and rivers in runoff water after it rains or snow melts.
This fact sheet is intended to provide a better understanding of the Poteau River Watershed and its role on the state's priority list of 10 watersheds impacted by nonpoint source pollution.
Water pollution that comes from diffused points of discharge, such as runoff from parking lots, agricultural fields, lawns, home gardens, construction, mining and logging, is known as nonpoint source pollution.
As runoff water moves across the landscape, it carries natural and manmade substances that can build up in waterways.
Potential pollutants include bacteria, nutrients, sediment, toxic or hazardous substances and trash.
1 These pollutants are not easily traced back to their source.
Poteau River Watershed Data source: GeoStor.
Map created March 2011.
Major streams: Hawes Creek, Jones Creek, Poteau River , Riddle Creek and Ross Creek.
Poteau River Watershed Water Quality Issues
 In 2006, environmental officials in Arkansas determined the maximum amount of phosphorus, copper, zinc and suspended sediments the Poteau River can receive and still meet water quality standards.
This determination is a calculation called a Total Maximum Daily Load, or TMDL.
2
 Past water testing has shown that a short section of the Poteau River below the city of Waldron has not been able to support aquatic life because of excessive levels of various metals and nutrients such as phosphorus, according to the state's Nonpoint Source Management Plan.
Arkansas' Priority Watershed List for Nonpoint Source Pollution
 Arkansas has used a watershed-based approach to nonpoint source pollution management, allowing the public to guide plans for addressing water quality issues.
The Arkansas Natural Resources Commission, or ANRC, administers the Nonpoint Source Pollution Management Program.
The program exists to reduce water pollution through the funding of watershed planning and restoration activities, adoption of voluntary best management practices and the development of technologies that assist in water pollution reduction in Arkansas.
Based on public input and the use of a qualitative risk assessment matrix, ANRC has designated 10 priority watersheds as needing the greatest attention.
The current risk matrix3 identifies the following priority watersheds: Bayou Bartholomew, Beaver Reservoir, Cache River, Illinois River, L'Anguille River, Lake Conway-Point Remove, Lower Ouachita-Smackover, Poteau River, Strawberry River and Upper Saline.
Metals and phosphorus come from natural and manmade sources.
Metals present in the water can be naturally occurring from geologic formations, deposited from the atmosphere or discharged from industrial or city water treatment plants.
Phosphorus can threaten water quality when people don't follow best management practices, such as applying the right amount of phosphorus as a fertilizer or using grassy buffers to prevent it from
 entering runoff water or nearby waterways.
Phosphorus can also enter waterways as part of discharge from water treatment plants, which are regulated by the state and have permits that allow specific amounts of nutrients to be discharged.
According to the state's Nonpoint Source Management Plan, there are municipal and industrial discharges near this section of the Poteau River.
Another section of the Poteau River just before it meets the Arkansas River was also found to not support aquatic life because of excessive turbidity, which means the water is murky from a variety of materials such as soil particles, algae, microbes and other substances.
Turbidity is a measure of the clarity of water.
These issues and its border state status led to the watershed being designated as a priority by the Arkansas Natural Resources Commission in the state's 2006-2011 Nonpoint Source Pollution Management Plan.
The watershed remains a priority in the 2011-2016 Plan.
4
 To encourage continued public input, the University of Arkansas Division of Agriculture's Public Policy Center facilitated a water quality stakeholder forum for the Poteau Watershed in Waldron in September 2014.
Participants identified unpaved roads and flooding as concerns that needed to be addressed in their watershed.
Other identified concerns included erosion, excessive nutrients and sediment.
All of these concerns can have an impact on water quality.
The University of Arkansas Division of Agriculture's Public Policy Center provides timely, credible, unbiased research, analyses and education on current and emerging public issues.
Looking forward, water scarcity is even a bigger concern for maintaining a high level of agricultural production in the Great Plains.
However, the adaptation and innovation that led to significant advances in the past will likely continue to be helpful in fostering food production while managing water resources.
A healthy balance between the use of water for irrigation and conservation of these resources will be key to sustainable use in the future.
With potential for continued increases in CWP, water supplies will likely be stretched further than what might be expected based on past rates of water use.
Saving Water and Energy Crop Residue Management
 In many instances, such as for planning purposes, estimates of percent cover may be adequate.
For example, it may be desirable to determine if eliminating a certain operation from a tillage and planting system is likely to result in adequate residue cover to meet the level called for in a conservation plan.
The calculation method of estimating residue cover can be useful for such a determination.
The calculation method involves first determining or estimating the amount of residue cover present after harvest.
This value is then multiplied by estimates of the percentage of cover that will remain following weathering, tillage, and any other residue-disturbing operations.
This article discusses many of the factors that influence the reduction of residue cover, and presents estimates of the amount of residue cover expected to remain following tillage and other residuedisturbing operations.
RESIDUE COVER AFTER HARVEST
 Determining the amount of residue cover after harvest is the first step in the calculation method.
This is most accurately done by measurements in the field using the line-transect method.
If this is not possible, an average value can be used.
Table 1 presents typical after-harvest percent residue cover values for various crops.
Use these values with caution, as the actual amount of cover in a particular field can vary considerably depending on crop variety and yield, conditions throughout the growing season, and other factors.
For all crops, the residue should be uniformly distributed at harvest, not left in windrows, clumps, or bunches.
FACTORS INFLUENCING RESIDUE REMAINING
 Fragile or Non-Fragile Residue
 Crop residues have been classified as fragile or non-fragile, Table 1.
This classification is based on factors such as plant characteristics , total amount of plant material produced, and ease of residue decomposition or breakdown when the residue is disturbed or exposed to the weather.
Soybean residue would be an example of a fragile residue, whereas corn and grain sorghum residues are classified as non-fragile.
Estimates of the percentage of residue cover remaining after various residuedisturbing operations are listed in Table 2.
For a given implement, the actual amount of residue remaining will be influenced by many factors, including implement design, adjustments, speed, depth of soil disturbance, previous residue disturbance, and soil and residue condition.
The ranges of values given for both fragile and non-fragile types of residue account for some of these factors.
Be conservative and use careful judgement when selecting values from the table.
Do not use all high values; the result is usually overestimation of final cover.
This is especially true on land that is designated as highly erodible.
For these areas, values near the lower end of the range usually result in better estimates of actual cover.
However, if all implements are designed, adjusted, and operated with the specific goal of preserving residue cover, values near the middle or upper end of the range may be appropriate.
Biological processes cause a general deterioration of residue condition.
Moisture and warmer temperatures increase the rate at which this occurs.
One way that residue cover is affected by moisture and climate is an actual reduction of percent cover due to decomposition or decay of the residue, particularly the leaves and small pieces.
In a study of soybean residue, a 31 percent loss of cover occurred between measurements taken after harvest and again before spring field operations in southeast Missouri.
Approximately 25
 inches of rainfall was received between these two measurements.
In northwest Missouri, with cooler temperatures and about eight inches of rainfall during the same time period, losses averaged 12 percent.
Conditions in southeast Nebraska and northeast Kansas are generally similar to those in northwest Missouri, and some actual residue cover loss is likely over the winter.
However, in much of Nebraska, over-winter losses do not appear to be a significant factor.
For example, in a northeast Nebraska study, the amount of soybean residue cover was comparable both after harvest and in the following spring.
Even though actual decreases in percent cover may be minimal, with exposure to the weather, residue becomes more fragile over time.
This is most pronounced for residue that has been tilled or otherwise disturbed, but it also occurs with undisturbed residue.
Because of less annual precipitation, this change takes place more slowly in western Nebraska than in the eastern part of the state.
Weathering and when the residue-disturbing operations are performed are closely related.
If residue is disturbed in the fall by grazing, tillage, stalk chopping, manure incorporation, or knifing-in fertilizer, subsequent spring operations reduce cover more than if all operations are conducted in the spring.
This is because fall tillage and knifing operations cut or break the residue into smaller pieces, mix soil and residue, and speed over-winter weathering, thus making the residue more susceptible to decomposition and burial in the spring.
University of Nebraska research showed that for the same sequence of field operations used in corn residue, residue cover measured after planting averaged 12 percent less when one or more operations were conducted in the fall, compared to performing all operations in the spring.
For operations that are done in the fall, use values towards the lower end of the ranges in Table 2 or include an additional weathering reduction factor for fall operations, also listed in Table 2.
In contrast, when operations are conducted with little elapsed time between them, less reduction of residue occurs.
In these cases, values near the upper end of the range are generally appropriate.
For example, when disking and field cultivating on the same day, the field cultivator may cause little additional loss of cover.
The field cultivator simply redistributes the residue that is on the soil surface.
Under certain conditions, the field cultivator may also bring buried, coarse residue to the surface, resulting in a slight increase in cover, perhaps up to five percentage points.
However, if there are more than a few days and it rains between disking and field cultivation, field cultivation generally results in reduced levels of cover.
Results from a residue grazing study provide an example of the effects of prior residue disturbance on the amount of cover reduction.
No-till planting into ungrazed corn residue reduced the cover by 10 percent, from 83 percent cover to 75 percent; whereas no-till planting into residue that had been grazed reduced the cover by 16 percent, from 62 percent cover to 52 percent.
A winter wheat/fallow rotation provides an illustration of the combined effects of weathering and timing of tillage operations.
Shortly after harvest, the wheat residue often appears to be quite resistant to breakup and burial by tillage.
But, by late the next summer at the end of the fallow period, the residue has become quite fragile.
Percent residue cover following a tillage operation near the end of the fallow period is likely to be less than what it would have been following the same tillage operation done shortly after harvest.
However, when additional
 operations are conducted, greater cover reductions will typically occur for the system where tillage was first done shortly after harvest and the disturbed residue was exposed to the weather, compared to the system where the residue remained undisturbed during much of the fallow period and operations were delayed until near the end of the fallow period.
Use values at or near the upper end of the ranges listed in Table 2 when an operation is performed within two or three days of the previous operation.
Use values near the middle of the range if a week or more elapses between operations, especially if more than about one-half inch of precipitation or irrigation also occurs.
Use values near the lower end of the ranges if operations are conducted over a month apart.
Chopping or Shredding of Residue
 Chopping or shredding the residue may result in reduced amounts of cover.
In University of Nebraska research on corn residue, tillage and planting systems that included a stalk chopping operation had an average of 22 percent less cover after planting than when the residue was not chopped.
Although percent cover appeared to increase immediately after chopping because the residue had been cut into smaller pieces and was redistributed, the chopped residue deteriorated more from the weather and subsequent field operations than non-chopped residue.
If the residue is chopped, this additional reduction needs to be included in the calculations to estimate the amount of cover that is expected to remain.
For small grains, if a rotary combine or a combine with a straw chopper is used, the residue should be considered to be fragile.
In these cases, use the values in Table 2 that are for fragile residue.
Livestock grazing will reduce the amount of residue cover.
The amount of reduction depends on factors that include stocking density , animal size, length of the grazing period, whether the residue is from irrigated or dryland crops, how much ear drop or other losses occurred during harvest, how much supplemental feed is supplied, and weather conditions.
As an approximation, the Natural Resources Conservation Service estimates that each 1000 pound cow will remove 15 percent of the available cover per acre per month; or 0.5 percent cover removed per cow per acre per day.
Although estimates of cover reduction can be used, the best procedure for grazed residue is to use the line-transect method to measure the amount of cover at the end of the grazing period.
This value can then be used for the calculations instead of percent cover after harvest.
Under certain conditions, residue cover may remain on the soil surface for more than one cropping year.
Carry-over is most likely to occur under dry climatic conditions when residue that is classified as non-fragile has received only minimal disturbance, such as with no-till planting.
In a long-term experiment using a grain sorghum/soybean rotation, residue cover measured after planting grain sorghum averaged approximately 15 percentage points less for a no-till planting system with row cultivation than no-till without cultivation.
Some grain sorghum residue remained on the soil surface during the year that soybeans
 were grown and was also present the following spring.
However, residue cover carry-over is highly variable, and generally should not be relied on to provide significant amounts of cover.
ESTIMATING PERCENT RESIDUE COVER
 An approximation of the percent residue cover after planting can be obtained by multiplying the percent residue cover after harvest by the appropriate values from Table 2 for weathering and for each residue-disturbing operation that is conducted or planned.
Selecting appropriate values to use in the calculation method is a key to obtaining reasonably accurate results.
All operations and other factors that affect residue cover need to be accounted for.
Think in terms of a complete sequence of operations.
For each operation, evaluate how the residue will be affected by both prior and subsequent operations and by weathering.
The following examples illustrate how to use information from Table 2 to estimate residue cover by the calculation method.
Assume that a tillage and planting system used in a field of irrigated corn residue in southeast Nebraska consists of three field operations:
 1) anhydrous ammonia application in the fall using a knife-type applicator with rigid shanks;
 2) tandem disking in the spring; and
 3) planting soon after disking using a conventional planter with double disk openers and no coulters.
95%	X	0.75	X	0.90	X	0.60	X	0.95	=	37%
 initial	knife	winter	disk	planter	final
 cover	applicator	weathering	residue
 Using the same tillage and planting system in soybean residue would result in only about nine percent cover, which is not enough for effective erosion control.
70%	0.45	X	0.85	X	0.40	0.85	=	9%
 initial	knife	winter	disk	planter	final
 cover	applicator	weathering	residue
 If the corn residue example was changed to dryland production on highly erodible land in northeast Nebraska, and rainfall occurred between the disking and planting operations, less than 20 percent cover would remain after planting.
80%	X	0.75	X	0.99	X	0.35	X	0.85	=	18%
 initial	knife	winter	disk	planter	final
 cover	applicator	weathering	residue
 Consider the calculation method to be only a rough estimate since the variables involved prevent accurate determination of percent residue cover.
However, this method can be useful in residue management planning by offering a general idea of how much residue cover will remain after a specific sequence of operations.
There are also computer programs available to predict percent residue cover.
However, these programs use the calculation method and average values for residue cover reduction, and as such should be used only when a rough estimate is satisfactory.
Crop residue management, or maintaining residue on the soil surface, is the most cost-effective method of reducing soil erosion available to Nebraska farmers.
Accurate estimates of percent residue cover are necessary to determine if sufficient cover is available to adequately reduce erosion and to comply with conservation plan specifications.
When accurate estimates are needed, percent cover should be measured using the line-transect method.
When only rough estimates of percent cover are adequate, the calculation method is often useful and appropriate.
This method can be used for initial planning purposes to evaluate certain crop residue management goals and/or to compare potential residue cover remaining for a variety of tillage and planting systems.
Table 1.
Crop residue classification and typical percent residue cover after harvest of various crops in Nebraska.
Actual percent cover can vary substantially from these values.
Use these values for estimation purposes only when the percent cover for a particular field cannot be more accurately determined using the line-transect or photo-comparison method.
Alfalfa or Other Hay Crops
 Immediately after cutting	35
 60 to 120 bu/ac grain yield	80
 120 to 200 bu/ac grain yield	95
 Harvested for silage	15
 Immediately after cutting	25
 30 to 60 bu/ac grain yield	50
 60 to 100 bu/ac grain yield	85
 Dry edible beans	15
 For small grains, if a rotary combine or a combine with a straw chopper is used, or if the straw is otherwise cut into small pieces, consider the residue to be fragile.
Table 2.
Estimated percentage of residue remaining on the soil surface after specific implements and field operations.
1 
 Percentage of Residue Remaining
 Moldboard plow	0-10	0-5
 Disk plow	10-20	5-15
 Machines that fracture soil:
 	60-80	40-60
 Straight spike points	35-75	30-60
 Twisted points or shovels	25-65	10-30
 Coulter chisel plows with:
 Straight spike points	35-70	25-40
 Twisted points or shovels	25-60	5-30
 Disk chisel plows with:
 Straight spike points	30-60	25-40
 Twisted points or shovels	20-50	5-30
 Stubble-mulch sweeps or blade plows with:
 V-blades greater than 30" wide	75-95	60-80
 with mulch treader attached	60-90	45-80
 V-blades 20" to 30" wide	70-90	50-75
 with mulch treader attached	55-85	40-70
 Heavy plowing	25-50	10-25
 Primary tillage	30-60	20-40
 Secondary tillage	40-70	25-40
 Light tandem disk after harvest,	70-80	40-50
 Field cultivators: 
 Used as primary tillage:
 Sweeps 12" to 20" wide	60-80	55-75
 Sweeps or shovels 6" to 12" wide	35-75	50-70
 Duckfoot points	35-60	30-55
 Used as secondary tillage:
 Sweeps 12" to 20" wide	80-90	60-75
 Sweeps or shovels 6" to 12" wide	70-80	50-60
 Duckfoot points	60-70	35-50
 Combination finishing tools with:
 Disks, shanks, and leveling attachments	50-70	30-50
 Spring teeth and rolling basket	70-90	50-70
 Springtooth 	60-80	50-70
 Spike tooth	70-90	60-80
 Flex-tine tooth	75-90	70-85
 Roller harrow 	60-80	50-70
 Packer roller	90-95	90-95
 Plain rotary rod	80-90	50-60
 Rotary rod with semi-chisels or shovels	70-80	60-70
 Runner openers	85-95	80-90
 Staggered double disk openers	90-95	85-95
 Double disk openers	85-95	75-85
 Smooth coulters	85-95	75-90
 Ripple or bubble coulters	75-90	70-85
 Fluted coulters	65-85	55-80
 2 or 3 fluted coulters	60-80	50-75
 Row cleaning devices	60-80	50-60
 (8" to 14" wide bare strip using brushes,
 spikes, furrowing disks, or sweeps)
 Ridge-till planter	40-60	20-40
 Hoe opener drills	50-80	40-60
 Semi-deep furrow drill or press drill	70-90	50-80
 
 Deep furrow drill with 12" spacing	60-80	50-80
 Single disk opener drills	85-95	75-85
 Double disk opener drills	80-95	60-80
 Drills with the following attachments used in residue laying on the soil surface:
 Smooth coulters	65-85	50-70
 Ripple or bubble coulters	60-75	45-65
 Fluted coulters	50-70	35-60
 Drills with the following attachments used in standing stubble:
 Smooth coulters	85-95	70-85
 Ripple or bubble coulters	80-85	65-85
 Fluted coulters	50-80	40-70
 
 
 Row cultivators: 
 Single sweep per row	75-90	55-70
 Multiple sweeps per row	75-85	55-65
 Finger wheel cultivator	65-75	50-60
 Rolling disk cultivator	45-55	40-50
 Ridge-till cultivator	20-40	5-25
 Rigid shanks	75-85	45-70
 with coulters	80-90	50-75
 Coil shanks	70-80	40-65
 with coulters	75-85	45-70
 Closing disks	55-70	30-50
 Chisel or sweep injectors	30-65	5-15
 Disk-type applicators	40-65	15-40
 Coulter-type applicators	80-95	65-80
 Rotary hoe	85-90	80-90
 Bedders, listers, and hippers	15-30	5-20
 Furrow diker	85-95	75-85
 Mulch treader	70-85	60-75
 Climatic effects of over winter weathering:
 Summer harvested crops	70-90	65-90
 Fall harvested crops	80-100	75-100
 Fall operations 	85-95	80-95
 Weathering losses are highly dependent on precipitation and temperature.
In winters with long periods of snow cover and frozen conditions, weathering may reduce residue levels only slightly.
In warmer winters without much snow or during wet years, weathering losses may reduce residue levels significantly.
Estimate reduction of residue cover for either fragile or non-fragile residue at 15 percent per 1000 pound cow per acre per month, or 0.5 percent per cow per acre per day.
Use the following formulas to estimate residue cover reduction due to grazing and the percentage of residue remaining factor.
Percent Grazing =  X  X  X   1000
 Percentage of Residue =  Remaining Factor
 1 Adapted from the pamphlet "Estimates of Residue Cover Remaining After Single Operation of Selected Tillage Machines, published by the Soil Conservation Service and Equipment Manufacturers Institute, February 1992.
Values adjusted based on University of Nebraska research and field observations.
Every irrigator can make excellent irrigation scheduling decisions by getting the right information and polishing their skills in analyzing the data.
Today it is easier than ever to install equipment that will automatically record and help analyze the data before sending it to your computer or smartphone.
Your diligence will be rewarded with higher profitability and protecting the environment.
Vegetable production is increasingly popular for Tennessee residents.
Growing vegetables at home provides financial and nutritional benefits through the bounty of a fresh harvest, and the activity enhances personal health and well-being.
However, a basic understanding of soils, site selection and crop maintenance is required before backyard growers can take full advantage of the benefits of home food production.
To meet these needs, this series of fact sheets has been prepared by UT Extension to inform home gardeners and propel them to success in residential vegetable production.
SITE CHALLENGES FOR HOME VEGETABLE GARDENS
 SITE CHARACTERISTICS LIGHT, ACCESSIBILITY AND WATER
 Many who are interested in vegetable gardening may not have suitable land to plant a traditional garden.
Some live in apartments or condominiums where they have no access to soil, while others may have small lots or restrictions on planting in their residential areas.
In these situations, raised beds can provide a great alternative.
However, other site considerations are still important.
Productive vegetable crops generally require 6 to 8 hours of full sunlight per day while a few leafy crops  may be grown with 4 to 6 hours of sunlight.
The best method of estimating sunlight is to observe potential sites throughout the day and track sunlight hours.
Nearby trees can block light, compete with crops for water, or even produce compounds  that are toxic to some plants.
It would likely be preferable in the long run to build a raised bed and use amended soil in an area with good light but poor soil than to choose a site with good soil quality but more shade than is desirable.
Additionally, a nearby, highquality water source will enhance the productivity of your garden and reduce maintenance time.
Figure 1.
Raised beds can be appropriate for a variety of crops and sites.
Soil that is easily workable and allows water to soak in  and drain easily is best.
In some residential areas, there may be a scarcity of highquality soil.
Common issues include topsoil removal or compaction during neighborhood development and soil that is high in clay or rocks or drains poorly.
Be aware of any previous uses or structures on the site that may have added heavy metals, debris or other undesirable materials to the soil.
The home gardener has several choices if soil conditions are not ideal, but the first step is completing a soil test as discussed in UT Extension publication W 346-A "The Tennessee Vegetable Garden Site Selection and Soil Testing." This test can help determine the pH and nutrient levels of the soil as well as the organic matter content.
Over time, organic matter additions, fertilizer applications, and pH management can improve the workability and productivity of native soil.
OPTIONS FOR SITES WITH POOR QUALITY OR DEGRADED NATIVE SOIL
 Some home gardeners enjoy the process of improving the soil on their site over time.
Soil can be brought to the site or cover crops and organic matter can be used to improve soil characteristics.
But many gardeners may prefer to have alternatives to provide faster return on their efforts.
Raised beds are one of the most common options to grow residential food and flower crops.
They can be constructed to take advantage of the best lighting and water access and allow garden size to be tailored to family needs.
Raised beds allow more control over substrate , drain more easily, and warm up faster in the spring than traditional in-ground gardens.
Containers also can be used by gardeners with limited
 space on on balconies and patios.
Raised beds and containers enable gardeners who may not be able to handle the equipment or the labor of traditional gardening to stay active and continue to produce edible crops.
POTENTIAL DRAWBACKS OF RAISED BEDS
 Mechanical tillage equipment is difficult to use in raised beds.
Bed must be carefully constructed to withstand the weight of substrate plants and management over time.
Close spacing can reduce air flow and increase the opportunity for disease infection or shading.
The growing substrate will drain faster and require more frequent watering.
Large vining plants like many squash and pumpkin selections are generally not well-suited to raised beds.
Figure 2.
A raised bed that accommodates standing or seated gardeners.
INTRODUCTION TO RAISED BED GARDENING
 RAISED BED MATERIALS AND CONFIGURATION
 Temporary raised beds using soil can be constructed without side support, although these are mostly used in traditional gardens.
A range of materials can be used to construct permanent raised beds including wood, stone, brick, block or composite materials.
Prior to December 2003, chromated copper arsenate  was used as a preservative in lumber for residential uses.
So, use caution because this older treated lumber as well as railroad crossties can contain metals that can leach into garden soil.
Each gardener should select and use materials he or she is comfortable with for a home vegetable production.
See additional resources listed below for more details on using treated materials.
Gardeners can line raised beds with plastic to reduce leaching concerns or chose cedar or redwood lumber that is more resistant to decay.
Additionally, boards made from recycled plastic used for decking are a more expensive but long-term option for constructing raised beds.
It is important to select a material that will allow construction of a stable bed that will support itself, the growing substrate and plants.
Taller and longer beds will contain more substrate and weight and require more substantial construction, support and bracing.
Small beds may be constructed of 1-inch-wide lumber, but it is more common to use lumber that is at least 2 inches wide.
A common bed width is 4 feet if accessed from both sides, and 2 to 3 feet if accessed from one side.
Beds are generally constructed 6 inches to 12 inches in height but can be deeper.
Shallow-rooted crops such as lettuce, spinach, kale and other leafy crops may be produced in beds that are
 only 4 inches to 6 inches in depth.
Taller and deeper rooted crops such as tomatoes, peppers, okra and corn often require deeper beds for root exploration and stability.
A smaller substrate volume will retain lower amounts of water and nutrients.
Since raised beds drain more rapidly than nearby level soil, deeper beds with more substrate can decrease watering frequency.
An additional consideration in bed construction is the ability to accommodate those who may not be able to work at ground level.
RAISED BED INSTALLATION AND CONSTRUCTION
 If the site has usable soil, there may be no concern with leaving the bottom of the bed open and letting the roots of plants grow into native soil.
However, hand dig or till to combine the raised bed substrate with the upper layer of native soil to avoid creating an abrupt gradient between amended and native soil.
If native soil is of poor quality or
 the garden is on a non-soil surface, a wooden or porous ground cloth bottom can be installed under the raised bed.
Newspapers or cardboard also can be used as a barrier to prevent weed or plant growth from underlying soil and sod, but they will be less effective if weed pressure is severe.
IMPORTANT CONSIDERATIONS IN RAISED BED GARDENING
 If the native soil is of high quality, raised beds can be filled with topsoil from the site.
If constructing a taller  raised bed, be cautious of reduced drainage when using only native soil.
Often soilless mixes are used as a substrate to increase drainage, aeration and optimize nutrition.
Soilless mixes usually consist of peat moss, compost, vermiculite and perlite.
A common mix is equal volumes  of 1) peat moss, 2) compost and 3) vermiculite.
Purchased components also can be mixed with high-quality native soil to decrease costs.
A common mixture would be equal volumes of 1) garden soil, 2) peat moss or compost, and 3) vermiculite or perlite.
Keep in mind that testing is important when preparing substrate for a raised bed to determine if lime or fertilizer is required.
If compost is used in the substrate, it can provide plant nutrients but should still be tested to account for variation.
Use caution when introducing any material into your substrate  that could add weed seeds.
If compost heating is insufficient, weed seeds can still be viable.
The two most important considerations in selecting crops for raised bed include seasons best suited for growth and space needed for production.
The most common way to classify vegetables is according to their temperature requirements.
Cool-season crops are more productive and of higher quality when they are grown and mature under cooler spring and fall season temperatures.
They tend to be shallower rooted and more sensitive to periods of low moisture.
Many cool-season crops can be wellsuited to raised beds because they can be closely spaced and sequentially planted.
Raised beds, because of their potential for higher spring soil temperatures and excellent drainage, can often be planted earlier than inground gardens.
Earlier planted coolseason crops are more likely to mature under preferred cooler temperatures.
The opportunity to plant earlier is especially useful in many parts of Tennessee where spring temperatures may quickly rise to levels that are higher than ideal for cool-season crops.
Warm-season crops are damaged or killed by frost and should be planted after the threat of spring frosts and freezes are passed.
These crops produce optimally under warmer temperatures and also tend to have a deeper root system that is better able to withstand drier, hotter conditions that are typical of Tennessee summers.
Cool-season vegetables	Warm-season vegetables
 Beet, broccoli, cabbage, cauliflower, carrot,	Bush, pole, and lima beans, muskmelon,
 kale, collard, kohlrabi, leaf and head lettuce,	sweet corn, cucumber, eggplant, okra, pea
 mustard, onion, English and snap pea, Irish	, pepper, pumpkin, Malabar
 potatoes, radishes, spinach, Swiss chard,	spinach, squash, summer and winter, sweet
 turnip	potato, tomato, watermelon
 The second important consideration in selecting crops is space.
Often beginning gardeners make the mistake of planting too closely, which creates competition for water, light and nutrients.
Even if these factors are not limiting, close spacing can reduce air movement and increase disease risk.
The chart below provides estimates of spacing for vegetable crops in typical raised beds.
An increasing number of space efficient cultivars are being introduced.
One of the benefits of raised beds is that no walking space is needed, so often seeds or plants are placed in a grid rather than in rows.
Table 1.
Vegetable crops categorized by broad temperature requirements.
2 to 4 inches between	6 to 8 inches	12 to 18 inches between	More than 18
 seeds or plants	between seeds or	seeds or plants	inches between
 Snap bean, beet,	Basil, Swiss chard,	Cabbage, collard, broccoli,	Winter squash,
 carrot, radish,	pak choy, small	cauliflower, eggplant, pep-	watermelon,
 onion, pea, turnips,	head lettuce,	per, compact or determinate	many tomatoes
 garlic, spinach, leaf	strawberry, kale	tomato, compact cucumber
 lettuce	and summer squash
 Table 2.
Vegetable crops categorized by typical spacing in traditional raised beds.
Raised beds often have better drainage and aeration than traditional gardens, but usually will dry out faster due to elevation and greater substrate porosity.
Close spacing in raised beds also may mean plant roots do not have as much substrate volume from which to draw water.
So, water management is especially important in raised beds.
Typically garden vegetables require 1 inch to 1.5 inches or more of water per week.
Raised beds would require at least this much moisture, and likely more during warm or hot weather.
Overhead watering can be used, but do not allow leaves to remain wet overnight because of disease risk.
It is especially important in the close spacing of raised beds to keep leaves as dry as possible to prevent infection and spread of diseases.
Irrigation involving drip tape or soaker hoses is often preferable to overhead irrigation because it keeps leaves dry and efficiently delivers water to the substrate and roots.
Drip irrigation also allows more thorough watering because water can be provided slowly and has the opportunity to spread evenly through the substrate.
Fertilization in raised beds can be similar to managing nutrients in traditional gardens.
If using compost in preparing growing substrate , be sure to consider any nutrients that are contained in the compost when calculating fertilizer needs.
One of the greatest advantages of raised beds is that the smaller growing area and close plant spacing can reduce time spent weeding compared to traditional gardens.
Care in selecting a substrate without weed seeds can also prevent problems before they start.
Mulching also can be an excellent way to reduce weed issues.
Natural mulches such as compost or straw can be a good way to improve the growing substrate over time while reducing weed pressures.
Black plastic mulches block light to prevent weed growth and increase soil temperatures, especially in the spring, by absorbing solar radiation and transferring heat to the soil beneath.
Most plastic mulches block moisture, so drip irrigation is required under the mulch.
Woven black or white ground covers are a mulch option that is permeable to water and air and can be reused.
Both natural and plastic mulches reduce the rate of evaporative water loss from soil, so
 they can help conserve soil moisture and reduce watering needs.
It is best to cycle different types of crops in raised beds to reduce the buildup of pests and diseases.
It is common to group crops in terms of fruiting , vining , Brassica crops , and root crops.
These different types of crops have varied nutrient needs and sometimes different pest and diseases complexes, so rotating them through your beds can increase production and reduce disease risks.
Providing support for vegetable plants can improve their ability to intercept light to support photosynthesis and make sugars needed for leaf and fruit growth.
It also can improve air movement and reduce disease risk.
In addition to these benefits, raised bed gardeners should consider training and supporting their crops because of space efficiency.
Vertical supports can consist of trellises, stakes, cages, twine or a combination.
It is common to plant vining crops (cucumbers, winter squash, pole beans,
 Require support for space efficient	Could benefit from support	Do not need support
 use in raised beds
 Vining cucumber, pole bean, tomato,	Bush bean, compact cucumber and winter	Lettuce, beet, spinach, cabbage, broccoli,
 watermelon, muskmelon, winter squash,	squash cultivars, pepper, eggplant, okra,	cauliflower, kale, radish, carrot, Swiss chard,
 snap and shell pea	compact pea	bush summer squash
 Table 3.
Vegetable crops categorized by their need for vertical support in raised beds.
1 plant/2	1 plant/ft2	2 plants/ft2	4 plants/ft2	8-9 plants/ft2	16 plants/ft2
 Muskmelon, vining	Broccoli, cabbage,	Cucumber	Swiss chard, corn,	Large beets, peas,	Small beets,
 squash (bush types	cauliflower, eggplant,	lettuce, basil, parsley,	beans, spinach	carrots, onion,
 9 ft2	okra, pepper, vine	potato, strawberry	radish, chives
 Table 4.
Spacing for crops in the SFG method 
 Figure 3.
This image illustrates the use of agricultural fabrics both floating on the top of a raised bed crop and supported by hoops to form a low tunnel.
etc.) on the north side of the raised bed so that a trellis can be installed that will not shade the shorter crops.
Tomatoes, peppers and eggplants are more commonly supported individually using stakes or cages.
They also can be attached to twine and suspended from an overhead support.
Tomatoes, especially indeterminate crops that continue to grow both from the primary growing point and side shoots, may be more manageable if some side shoots are removed.
PRACTICES THAT CAN COMPLEMENT RAISED BED PRODUCTION
 SQUARE FOOT GARDENING 
 Square foot gardening, a concept first introduced by Mel Bartholomew, has helped introduce many to small-scale home gardening.
While the principles of square foot gardening are similar to other raised bed methods, there
 are some specifics.
The SFG method is based on raised beds with dividers that create 1-square-foot plots within the larger raised bed.
A common size is a 4-by-4-foot bed that creates 16 square foot units.
Common crops are planted at set densities within each square foot unit for clarity and productivity.
SFG typically uses a mix of equal volumes of peat moss, compost and vermiculite in a 6-inch-deep raised bed.
Due to compost in the substrate, SFG gardeners are encouraged to rely on the nutrients from the compost, which is added at the end of each cropping cycle to resupply nutrients.
Season extension methods combine well with raised beds.
Several techniques can be used to provide increased temperatures and longer growing seasons for vegetable garden crops, and two of the most common are described below.
Floating row covers, or agricultural fabrics, form a lightweight cover that allows light, air and moisture to pass
 through.
These covers can be simple to install because they do not need a support system.
However, for some crops with sensitive growing points, like tomatoes and peppers, floating row covers can cause abrasion under windy conditions.
There are a range of row cover weights that differentially alter temperatures.
Greater temperature increase will occur during sunny days as the covers trap sunlight.
The lightest covers may provide 1-2 F temperature buffer overnight while the heaviest covers can provide 4-8 F protection.
Heavier covers reduce light much more than the lighter covers.
While the light covers can allow around 90 percent of ambient light to reach the plants, the heaviest covers will block over 50 percent.
These heavy covers often are removed in the morning and replaced in the late afternoon to provide nighttime temperature protection while still enabling light to reach the crops during the day.
Trapping heat can be detrimental under warm and sunny conditions.
So, season extension methods are typically used in the spring, fall and winter and are removed when warm conditions
 persist.
They also block pollinating insects, so vine crops like pumpkins, squash, muskmelons and watermelons must have the covers removed when flowering begins.
An added benefit is that the covers also can protect plants from some insect damage if installed early enough and tightly.
Low tunnels can be made of agricultural fabrics used for floating row covers or clear polyethylene plastic.
Either material is stretched over wire hoops to form miniature greenhouses typically 2 to 3 feet tall.
Like floating row covers, they are generally applied in the spring and fall and removed during the warmest part of the growing season.
Low tunnels made
 of polyethylene are often perforated or vertical slits are made to allow air movement and prevent overheating in bright sunlight.
The downside of polyethylene low tunnels is that they do not allow rain to reach the crops, so irrigation will probably be necessary.
Low tunnels made of floating row cover material are permeable to water, so irrigation needs will depend on precipitation.
UMA INSTITUTE OF AGRICULTURE THE UNIVERSITY OF TENNESSEE Real.
Life.
Solutions.
TM
 W 346-E 6/16 16-0143
In the Central Plains area of Colorado, Kansas and Nebraska, approximately 10.6 million acres of cropland are irrigated by center pivot irrigation systems.
Existing systems span the generations of center pivot technology evolution from water to electric and hydraulically driven machines.
Standard sprinkler system designs seek to apply water as uniformly as possible.
Due to their operating flexibility, center pivots are operating on varying topography, and often have a range in soil textures present under a single machine.
Field anomalies such as perched water tables, surface drains, and rock outcroppings challenge managers of standard machines with the need to deliver different depths of water to specific areas of the field.
Each of these factors provides some justification for using a monitor and control system to manage water applications based upon a predetermined management scheme.
On a more basic front, farming operations often include an average of 3 center pivot systems with some operations including 15 or more.
Without a controller, the producer must physically be on site to determine the status of the center pivot.
With new technology, producers can obtain knowledge of whether the system is operating on a real-time basis by communicating with the machine to determine operating status.
The purpose of this article is to present some of the research that has been conducted to evaluate system controllers for use in monitoring and controlling center pivots and discuss how these systems could be used in a site-specific irrigation system.
Center pivot manufacturers have developed proprietary means of monitoring and controlling center pivots using a variety of technologies.
Computerized control panels provide center pivot operators with the potential to monitor and control center pivots using telephones, radio telemetry, internet connections and satellite communication.
In addition, there are a few private venture monitor and/or
 controllers that are available under the trade names: FarmScan, AgSense, and PivoTrac.
Table 1 provides a summary of the current monitor and control capability of programmable panels marketed by the four major center pivot manufacturers.
The first requirement of a controller is to know the system position.
If a producer queries the control panel during the course of an irrigation event, knowledge of where the system is lets the producer determine if problems have occurred and also how soon the system will reach stop-in-slot  positions.
Standard machines utilize a resolver located at the pivot point to report the position of the first tower.
In nearly all cases, the main component of new controllers is a Wide Area Augmentation System  enabled GPS unit that is mounted near the last tower of the center pivot.
The WAAS is a publicly available GPS system that provides a differentially corrected signal to increase the accuracy of the unit at a relatively low cost.
With the WAAS system, the position of the last tower is provided with + 11foot accuracy.
However, due to the pivot speed of travel and stop-start motion of the machine, + 3 foot accuracy is possible.
Part two includes monitoring the center pivot control circuitry.
This is accomplished directly at the main pivot panel.
The main panel houses control circuitry for the end gun, system speed of travel and direction, and on/off controls.
Since most of this circuitry terminates at the end tower, some aftermarket center pivot monitors and controllers are mounted near the last tower control box.
At the pivot point additional components can be monitored and/or controlled such as auxiliary chemical injection pumps, system operating pressure and flow rate.
Likewise, weather sensors can be monitored to provide wind speed and direction, temperature and rainfall information if desired.
Options also exist to continuously monitor soil water sensors in the field.
Recent field research is aimed at developing decision support tools for using center pivot mounted infrared thermometer  or spectral sensors to help manage irrigation water, fertilizer, and pesticide applications.
Part three of the system includes a communication link between the controller and the end user whether that be cell phone, land line phone, radio or internet connection.
Cell phone links are accomplished using an on-board modem.
This arrangement requires cell phone service from the pivot location and from the user location.
Despite the addition of many cell towers, there are still a few locations in the Central Plains where communications are not possible.
Some systems transmit GPS coordinates and system monitor information via radio to a satellite which is transmitted back to a ground-based facility where it is distributed via the internet and made accessible by phone using IVR solutions developed specifically for center pivot controls.
Table 1.
Monitor, control, communication, and data reporting capability of center pivot control panels.
Reinke	T-L	Valmont	Zimmatic
 Position in field and travel direction	Y	Y	Y	Y
 Speed of travel	Y	Y	Y	Y
 Wet or dry operation	Y	Y	Y	Y
 Pipeline pressure	Y	Y	Y	Y
 Pump status	Y	Y	Y	Y
 Auxiliary components B	Y 	Y 	Y 	Y 
 Stop-in-slot and auto restart	Y	Y	Y	Y
 Wind speed	Y	N	Y	Y
 Start and Stop	Y	Y	Y	Y
 Speed of travel	Y	Y	Y	Y
 Auto restart and auto reverse	Y	Y	Y	Y
 End gun	Y	Y	Y	Y
 High and Low pressure shutdown	Y	Y	Y	Y
 High and Low voltage shutdown2	N/Y	N/Y	Y/Y	N/Y
 System stall shutdown	Y	Y	Y	Y
 Auxiliary components	Y	Y	Y	Y
 System guidance	Y	Y	Y	Y
 Maximum control points per circle	3600	360	180	180
 Sprinkler application zones 	2	3	30	NL
 Cell phone	Y	Y	Y	Y
 Radio	Y	Y	Y	Y
 Computer	Y	Y	Y	Y
 Subscription required	Y	Y	Y	Y
 Data Collection and Reports
 Soil water content	Y	Y	Y	N
 Precipitation per season	Y	Y	Y	Y
 Application date and depth	Y	Y	Y	Y
 Irrigation events per season	Y	Y	Y	N
 Chemical application rate	N	N	N	Y
 Chemical application per season	N	N	Y	Y
 System position by date	Y	Y	Y	Y
  N/Y indicates no automatic shutdown for high voltage is provided but the panel does provide automatic shutdown for low voltage.
B Y indicates that up to 7 auxiliary components  can be controlled by the panel.
System guidance provided by above ground cable, below ground cable, furrow or GPS.
II Number of positions in a revolution where set points may be changed.
Number of banks of sprinklers that can be controlled along the pivot pipeline.
Line-of-sight radio telemetry is another means of transmitting information from the field to the office or phone.
However, since the radios are line-of-sight buildings, trees, and hills impede communications over long distances.
Most radio communication links employ radios operating in the 900 MHz range to
 communicate over distance less than 15 miles.
For longer distances, a bridge or repeater is positioned on a tower or other structure to communicate over longer distances.
Recent developments in the center pivot industry have resulted in contractual arrangements with developers of after-market control and monitor systems.
These additions to the existing onboard control capabilities of center pivot panels make site-specific irrigation a reality for irrigation zones of 1000 ft2 or larger.
The main considerations remaining include the development of decision support systems that maximize the value of the applied water or chemical based on fieldbased information, the cost recovery potential of the cropping system, and the verification of water savings and/or improved productivity when there are a large number of management zones within the field area.
Precision agriculture technologies are based upon the premise that crop growth and/or yield is not uniform across a field.
It further assumes that the field average yield would increase if inputs of water and/or nutrients could be differentially applied to small field areas based upon a predefined management scheme.
Sitespecific water application technologies make it possible to vary both water and chemicals to meet the specific needs of a crop in each unique zone within a field.
The hypothesis is that the total water and nutrients applied could potentially be reduced on a per field basis and/or crop yield or quality will be greater.
One project comparing site-specific irrigation to conventional uniform irrigation was conducted in Idaho on potatoes.
They found that while statistical differences in yield were not recorded, a trend toward greater yield using site-specific irrigation was noted.
The mean yield increase would allow the equipment costs to be recovered in a 2-3 year time frame.
With a uniform application, the questions are 'when' to irrigate and 'how much' to apply.
The implementation of site-specific irrigation adds a third question of 'where' to the irrigation scheduling decision.
Answering the question about where requires that specific management zones be identified in some fashion.
Early efforts to develop methods for identifying where zones should be located and why included using soil survey maps, field topography, landscape position, and bulk soil electrical conductivity.
Missouri research concluded that the number of zones necessary in each field is dependent of the availability of water and the type of crop planted in the field.
Over the last two decades research has been conducted by public and private groups seeking to development methodology and decision support tools necessary for application of water and plant nutrients based upon the physical limitations of a tract of land.
In essence this work has added center pivot irrigation systems to the list of variable rate applicators.
As the technology has
 evolved so has the list of terminology used to help lay claim to unique ways that standard center pivot controls are replaced and/or enhanced to allow variation in the center pivot's application depth and/or water application rate.
Definitions for some of the terminology are included at the end of this paper.
Initial steps to define decision making tools used for site-specific irrigation began in the early 1980's.
Sadler, et al  stated one of the issues with site-specific irrigation is that "most of these technologies have been developed without considering the knowledge levels, skills and abilities of farmers and service providers to effectively and economically manage these tools.
In addition, the equipment is often expensive and the economic returns from adopting these technologies have not been easy to consistently demonstrate.
Nevertheless, the economics are improving and there is little doubt that at least some of the emerging precision agriculture technologies will be part of future crop production systems in American agriculture".
Technologies such as Low Energy Precision Application  were developed based on the early efforts to define optimum flow rates for sprinkler heads operating within inches of the soil surface.
A series of control manifolds were used to deliver different flow rates.
Later work by Roth and Gardner  sought to use the irrigation system to apply different amounts of nitrogen fertilizer with irrigation water.
Fully site-specific irrigation research was initiated in earnest in the early 1990's at four USDA-ARS research lab locations across the US.
Reports of this work were published beginning in 1992 based upon work conducted the USDA-ARS researchers located in Fort Collins, CO , Moscow, ID , Florence, SC , and Pullman, WA.
These efforts have helped to shape the technologies used to control moving sprinkler systems and individual sprinklers.
The major addition needed to convert center pivot irrigation systems to allow sitespecific water application is a means of controlling water flow to individual sprinklers.
Individual sprinkler flow control can be accomplished by using a series of on-off cycles or as it has become known as 'pulsing' the sprinkler.
Changing the sprinkler on time is effective at reducing both the application depth and the water application rate.
This is accomplished using either direct-acting or pilot-operated solenoid valves.
Direct acting valves have a linkage between the plunger and the valve disc while the pilot-operated solenoid uses irrigation pipeline pressure to activate the valve.
A second method for controlling irrigation water application was developed by King and Kincaid  at Kimberly, ID.
The variable flow sprinkler uses a mechanically-activated needle to alter the nozzle outlet area which can adjust the sprinkler flow rate over the range of 35 to 100% of its rated flow rate based upon operating pressure.
The needle can be controlled using electrical and hydraulic actuators.
The main issue is that the wetted pattern and water droplet size
 distribution of the sprinkler changes with flow rate which creates potential water application uniformity issues due to a change in sprinkler pattern overlap.
A third method of controlling irrigation water application is to include multiple manifolds with different sized sprinkler nozzles.
In this case, activation of more than one sprinkler manifold can serve to increase the water application rate and depth above that for a single sprinkler package.
Control of each manifold is accomplished using solenoid valves similar to those described for the pulsing sprinkler option above.
These new systems have been installed in various locations across the country, but few site-specific systems have been installed in the northern High Plains area.
As with any new technology, there are positives and negatives associated with each of these three methods of controlling sprinkler flow rates.
Certainly long term maintenance could be an issue.
Water flow rates to 13 water application zones were monitored on a center pivot with results indicating most were within 10% of the target flow rate.
Application uniformity of sprinkler pulsing type site-specific systems has been addressed by Dukes, et al.,  who found coefficient of uniformities in excess of 90% regardless of the system travel speed and cycling rate.
An additional concern is verification of results which can be difficult since it requires that comparable areas of the field where site-specific irrigation and uniform irrigation methods have been employed over a series of years.
Selecting the method of sprinkler control may be the easiest decision to make since the main factor of concern is: Will it pay to install the controls?
However, once the decision is made to use a variable rate sprinkler application system and the management zones have been defined, design of the remaining portions of the irrigation system becomes interdependent.
How will the pumping plant respond to changes is system flow rate requirements?
And how much additional pressure can the distribution system safely take before a pipeline breaks?
As sprinklers turn on and off, the flow rate required by the system varies.
The response of a standard pumping plant is that the pump output will follow the pump curve to the right or left depending on whether more or fewer sprinklers are operating.
More significant is that sprinklers near the end gun have flow rates that are significantly greater than sprinklers near the pivot point.
Consequently, turning off sprinklers on the third span of the system will have much less effect than turning off the sixth span.
The correct design response is to install a pumping plant with variable revolutions per minute  so that as more sprinklers are added, the pumping RPM is increased and visa versa.
In this way the pumping plant can supply water at the design pressure regardless whether 50 or 150 sprinklers are in operation.
The difficulty arises when the motor used to supply power to the pump is the same one used to supply power to the center pivot.
Changes is pump RPM require changes in engine RPM.
Engines operating at too high of an RPM will provide too much power to the center pivot while engines with too low of an RPM will not deliver enough power to the pivot.
So a separate energy supply may be required for the center pivot should the system be converted to site-specific irrigation applications.
New installations would be best served by installing a variable frequency drive electric motor with a pressure sensor to control the motor RPM.
How do I adjust the chemical injection system to apply different chemical amounts ?
Application of variable chemical rates can be achieved by simply maintaining a design injection rate and let the difference in water application depth control the chemical application rate.
However, we have a problem if our management decisions require high application of a plant nutrient to an area that is to receive little or no water?
A second factor is that the time of travel for chemicals to be transported from the pivot point to a position on the pivot lateral varies with the velocity of water in the pipeline.
As the number of sprinklers in operation changes so does the water flow velocity.
Thus, chemical could enter the system with a velocity of 6 feet per second when all sprinklers are on and 3 feet per second when a large number of sprinklers are turned off.
This factor will determine when a change in injection rate will reach different positions along the pivot pipeline.
How accurately can I determine system position if application rate changes are desired?
Center pivot position on most systems  is determined by the resolver that is located at the pivot point.
Alignment systems typically have an accuracy of +1.5 of where the first tower is located.
Thus, at a distance of 1320 feet from the pivot point, the position of the last sprinkler could be off by 34 feet or more.
Research conducted by Peters and Evett  found that resolver determined position errors could be up to 5 degrees or over 100 feet on a 1320 foot long center pivot.
Installation of a WAAS enabled digital GPS system is needed to ensure water and chemical are applied accurately.
The net effect of the WAAS system is that management zone size can be reduced without increasing the potential for a misapplication.
From an engineering perspective these are not trivial questions particularly if changes in water, nutrient and energy use efficiency are to be accomplished simultaneously.
In the end, it is the accuracy of the data used to make decisions that is critical.
And so another question must be answered: Will the increase in water application to Management Zone 25 increase yields enough to pay for the application?
To make full use of site specific irrigation techniques, site-specific field information is needed for variables that will be used in making irrigation management decisions.
Field soil texture and fertility will be needed to help isolate field areas where plant available water is indeed the single most important factor.
Yield maps could show areas with reduced yields that are due more to soil nutrient levels than plant available water or a combination of the two.
The difficult factor is to have production functions that give accurate information about what will happen to yield if water or plant nutrients are altered.
Acquiring this information may require a 3-5 years of in-field testing while harvesting with a yield monitor.
Private companies are becoming more active in providing a service of collecting and summarizing the field data.
Field maps of each of these variables  represent information that make up levels in a Graphic Information System  analysis.
It is important that these maps provide information with enough resolution to delineate the desired number of management zones.
Limitations in the ability to collect point measurements due to cost or response time of sensors all impact the spatial resolution of the application map.
For example, an 8-row combine operating at 6 mph and collecting yield estimates every 3-seconds provides a different spatial resolution than a center pivot with control of banks of 5 sprinkler heads.
Consequently, variable rate irrigation controls will typically be at a lower resolution than any of the other crop production inputs.
Ultimately, mathematical models will be needed to utilize the different sources of information to produce a water application map.
Center pivot controllers and monitors are available to help producers manage water application on a whole or part of field basis.
The combination of knowledge of current system status and location in the field help ascertain if the irrigation application is proceeding as planned.
By recording other field based information water applications can be adjusted due to different crops, field topography, soils and productivity levels.
Ultimately, the complete control of crop water inputs on an IMZ basis could save between 10-20% of the water applied per season.
Lower installation costs and further development of decision support systems for use by producers are needed before site-specific technology will receive widespread use by row crop producers in the Central Plains area.
Listed below are general definitions for the acronyms that are used in the discussion of center pivot monitors and controls.
GIS Geographic Information Systems is a system that allows for sets of georeferenced variables  to be analyzed, managed, displayed, and used to develop site-specific maps for the application of water, pesticides, or plant nutrients.
GPS Global Position Systems is a satellite system means of determining field positions, speed of travel, and time with sufficient precision to allow site specific application of irrigation water, pesticides, or plant nutrients in response to productivity indices.
IMZ Individual Management Zone is an individual area of an irrigated field for which the technology exists to alter the application of water, pesticides, or plant nutrients in response to productivity indices.
IRT Infra-Red Thermometry is the use of an infrared thermometer to record plant leaf temperature as an indicator of plant stress.
IVR Interactive Voice Response is technology that enables users to retrieve or deliver information on time critical events and activities from any telephone.
LEPA Low Energy Precision Application is a water, soil, and plant management system for uniformly applying small frequent irrigations near the soil surface to field areas planted in a circular fashion and accompanied by soil-tillage to increase soil surface water storage.
PA Precision Agriculture, or site-specific farming is the precise delivery of water, pesticides and plant nutrients based upon suspected deficiencies in or need for water, pesticides, or plant nutrients.
PLC Programmable Logic Controller is a digital computer used for automation of electromechanical processes and is designed for multiple inputs and outputs, and is not affected by temperature, electrical noise, or vibration.
VRI Variable Rate Irrigation is the delivery of irrigation water to match the needs of individual management zones within an irrigated field.
VRT Variable Rate Technology is the process of applying irrigation water, pesticides, or plant nutrients at rates which are based on defined crop production indices.
WAAS Wide Area Augmentation System is a navigation aid developed by the Federal Aviation Administration to augment the accuracy, integrity and availability of the GPS for use in aircraft flight monitoring and control.
Karmeli, D and G.
Peri.
1974.
Basic principles of pulse irrigation.
Journal of Irrigation and Drainage Division, ASCE 100:309-319.
McCann, I.R., B.A.
King, and J.C.
Stark.
1993.
Site-specific crop management using continuous-move irrigation systems.
IN: Proceedings of the International Irrigation Exposition and Technical Conference, San Diego, CA: Irrigation Association.
pp 232-236.
Minimum allowable balance refers to the soil water content where plants usually start showing stress, which is typically 50 percent of the available water.
With full irrigation, applications of water should be started before we get to this point, with 35% depletion often used as a trigger point.
With deficit or limited irrigation, stress is tolerated at vegetative growth stages, when little or no yield loss is expected and late grain fill when stress impacts yeild at minimum levels.
CENTER PIVOT SPRINKLER APPLICATION DEPTH AND SOIL WATER HOLDING CAPACITY
 Advanced irrigation technologies, including center pivot irrigation, are excellent tools that make it possible to meet crop water requirements with a high level of water and energy efficiency and distribution uniformity.
Within constraints of available water capacity and other site-specific limitations, a well designed, maintained and managed irrigation system provides for a high level of flexibility and precision to meet crop water requirements with minimal losses.
The key to optimizing center pivot irrigation is management, which takes into account changing crop water requirements and the soil's permeability and water holding capacities.
LOW PRESSURE CENTER PIVOT IRRIGATION SYSTEMS
 Center Pivot irrigation systems are used widely throughout the Central High Plains, including the Texas High Plains where most of the systems are low pressure systems, including Low Energy Precision Application ; Low Elevation Spray Application ; Mid-Elevation Spray Application  and Low Pressure In-Canopy.
Low pressure systems offer cost savings due to reduced energy requirements as compared with high pressure systems.
They also facilitate increased irrigation application efficiency, due to decreased evaporation losses during application.
Considering high energy costs and in many areas limited water capacities, high irrigation efficiency can help to lower overall pumping costs, or at least optimize crop yield/quality return relative to water and energy inputs.
LEPA irrigation applies water directly to the soil surface through drag hoses  or through "bubbler" type applicators,  Notably LEPA involves more than just the hardware through which water is applied.
It involves farming in a circular pattern  or straight rows.
It also includes use of furrow dikes and/or residue management to hold water in place until it can infiltrate into the soil.
LEPA irrigation generally is applied to alternate furrows; reducing overall wetted surface area, and hence reducing evaporation losses immediately following an irrigation application.
Because a relatively large amount of water is applied to a relatively small surface area, there is the potential of runoff losses from LEPA, especially on clay soils and/or sloping ground.
Furrow dikes and circular planting patterns help reduce the runoff risk.
Still, LEPA is not universally applicable as some slopes are just too steep for effective application of LEPA irrigation.
Low pressure spray systems LESA, MESA and LPIC offer more flexibility in row orientation, and they may be easier for some growers to manage, especially on clay soils or sloping fields.
Objectives with these systems include applying water at low elevation  to reduce evaporation losses from water droplets ; applying water at a rate not exceeding the soil's infiltration capacity ; and selecting a nozzle package that provides good distribution uniformity and appropriate droplet size and wetting pattern.
A well designed, maintained and managed center pivot irrigation system can provide a high level of irrigation application efficiency and distribution uniformity.
It offers the ability to apply a range of application rates to meet changing crop water requirements, and it can be re-nozzled if needed to adapt to changing irrigation capacities.
A key to efficient irrigation management through center pivot application is optimizing irrigation scheduling  to meet the crop water demand with an application rate  to match soil permeability.
1 The mention of trade names of commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the Texas AgriLife Extension Service or Texas AgriLife Research.
IRRIGATION SCHEDULING: WHEN AND HOW MUCH?
Good irrigation management provides sufficient water to the crop to avoid drought stress, while avoiding over-irrigation which can lead to runoff and/or deep percolation losses as well as poorly aerated  conditions.
In meeting crop water demands, it is helpful to keep in mind how plants use water.
Without addressing the specifics of plant physiology, plants draw water and dissolved nutrients from the root zone through their roots, xylem, plant tissues and eventually through stomata.
Generally speaking, roots grow best in moist soil, since dry or saturated conditions limit root growth.
Contrary to popular belief, roots do not grow in dry soil.
Managing soil moisture conditions that encourage an expansive root system can in effect maximize the plant's ability to extract water and dissolved nutrients from a greater volume of soil, therefore potentially increasing nutrient use efficiency as well as water use efficiency.
Pre-season and Early Season Irrigation Management
 Where water resources and/or irrigation system capabilities are insufficient to meet full irrigation demand, and where soil moisture at planting is insufficient to ensure crop germination, it is common practice to apply a pre-season or "preplant" irrigation.
The decision of when to apply a pre-season irrigation and how much to apply can be challenging.
Research conducted at Halfway, Texas  indicated that in this area known for its dry windy spring conditions, pre-season irrigation losses can be very high, with total water losses from irrigation and rainfall exceeding 47% in the 30-45 days preceding planting.
In the same study, however, yield reductions were observed in fields where pre-plant irrigation was limited.
Hence although starting irrigation applications too early can result in excessive losses of applied water, insufficient stored soil moisture limits crop productivity, particularly where irrigation capacities are insufficient to meet crop water requirements.
Pre-season irrigation considerations include:
 What is the soil moisture?
Consider the seedbed as well as the crop's potential root zone.
Soil moisture is field-specific and can be greatly affected by the crop previously grown in that field as well as off-season precipitation and atmospheric conditions.
What is the capacity of the irrigation system and water resource?
Low  capacity systems require more time to apply a given amount of water to the field.
Table 1 relates approximate irrigation application rates according to irrigation system capacity.
What is the target pre-season soil moisture?
Consider the soil's water holding capacity, and whether the soil is to be wetted to field capacity, or if allowance should be made for the storage of anticipated rainfall before planting.
Keep in mind that through the early part of the crop season  crop water requirements may be relatively low; hence there may be opportunity to continue to build soil moisture reserve after planting.
Table 1.
Approximate depths of application  as related to irrigation system capacity.
Relating irrigation system capacity to depth of application
 
 Note: these values do not take into account irrigation efficiency.
In-season irrigation scheduling generally involves meeting crop water demand, including peak water demand, if possible.
Long-term averages and researchbased water use curves can be very useful in irrigation planning, and many of
 Late Season Irrigation Management
 Irrigation termination decisions involve predicting how much water will be needed by the crop from the last irrigation until physiological maturity or harvest.
Longterm "average" crop water use curves from local experience or published literature; estimates of stored soil moisture; anticipated rainfall and other climate considerations; economic considerations ; and irrigation system capabilities are all factors that should be considered.
Irrigation termination recommendations are often based upon local applied research programs.
Especially where irrigation capacities are insufficient to meet crop water demand, stored soil moisture is relied upon to help make up the difference.
Soil moisture monitoring is a very useful complement to evapotranspiration -based information.
In many semi-arid areas, including the Texas Southern High Plains, pre-season irrigation or excess early season irrigation is used to provide moisture for crop establishment and to fill soil moisture storage capacity to augment often deficit irrigation during peak crop water use periods.
Pre-season irrigation water losses through evaporation and deep percolation can be quite high.
Hence it is important for growers to understand how much water their soil root zone will hold, taking into account the effective root zone depth and soil moisture storage capacity per foot of soil.
Applying more water than the soil can hold can result in deep percolation losses or runoff; starting irrigation too early increases opportunity for evaporation losses.
These risks need to be balanced with irrigation system capacity.
The Root Zone and Soil Water Holding Capacity
 The potential root zone depth is determined by the crop; however effective root zone depth is often limited by soil conditions.
Soil compaction, caliche layers, perched water tables, and other impeding conditions will limit the effective rooting depth.
Roots are generally developed early in the season, and will grow in moist  soil.
Most crops will extract most  of their water requirement from the top one to two feet of soil, and almost all of their water from the top 3 feet of soil, if water is available.
Deep soil moisture is beneficial primarily when the shallow moisture is depleted to a water stress level.
Commonly reported effective root zone depths by crop are listed in Table 2.
Table 2.
Effective root zone depths reported for selected crops.
These values represent the majority of feeder root as reported by various sources.
Deep percolation losses are often overlooked, but they can be significant.
Water applied in excess of the soil's moisture storage capacity can drain below the crop's effective root zone.
In some cases, periodic deep leaching is desirable to remove accumulated salts from the root zone.
But in most cases, deep percolation losses can have a significant negative impact on overall water use efficiency even under otherwise efficient irrigation practices such as low energy precision application  and subsurface drip irrigation  irrigation.
Leaching of nutrients and agricultural chemicals through deep percolation can reduce efficiency and efficacy of these inputs and present groundwater contamination risks.
Coarse soils are particularly vulnerable to deep percolation losses due to their low water holding capacity.
Other soils may exhibit preferential flow deep percolation along cracks and in other channels formed under various soil structural and wetting pattern scenarios.
Runoff losses occur when water application rate  exceeds soil permeability.
Sloping fields with low permeability soils are at greatest risk for runoff losses.
Vegetative cover, surface conditioning , and grade management  can reduce runoff losses.
Irrigation equipment selection  and management can also help to minimize runoff losses.
A soil's capacity for storing moisture is affected by soil structure and organic matter content, but it is determined primarily by soil texture.
Field capacity is the soil water content after soil has been thoroughly wetted when the drainage rate changes from rapid to slow.
This point is reached when all the gravitational water has drained.
Field capacity is normally attained 2-3 days after irrigation and reached when the soil water tension is approximately 0.3 bars  in clay or loam soils, or 0.1 bar in sandy soils.
Permanent wilting point is the soil moisture level at which plants cannot recover overnight from excessive drying during the day.
This parameter may vary with plant species and soil type and is attained at a soil water tension of 10-20 bars.
Hygroscopic water is held tightly on the soil particles  and cannot be extracted by plant roots.
Plant available water is retained in the soil between field capacity and the permanent wilting point.
It is often expressed as a volumetric percentage or in inches of water per inch of soil depth or inches of water per foot of soil depth.
Approximate plant available water storage capacities are 0.6 1.25 inches water per foot of soil depth for fine sandy soils; 1.2 1.9 inches water per foot of soil for loam soils; and 1.5 2.3 inches water per foot of soil for clay loam soils.
To avoid drought stress, a management allowable depletion is often imposed as a trigger for irrigation applications.
Management allowable depletion is often in the range of 50-60% of plant available water for many agronomic crops, but may be as low as 20-30% of plant available water for drought sensitive crops.
Permeability is the ability of the soil to take in water through infiltration.
A soil with low permeability cannot take in water as fast as a soil with high permeability; the permeability therefore affects the risk for runoff loss of applied water.
Permeability is affected by soil texture, structure, and surface condition.
Generally speaking, fine textured soils  have lower permeability than coarse soils.
Surface sealing, compaction, and poor structure  limit permeability.
Soil Moisture Monitoring and Soil Water Measurement
 Methods used to measure soil water are classified as direct and indirect.
The direct method refers to the gravimetric method in which a soil sample is collected, weighed, oven-dried and weighed again to determine the sample's water content on a mass percent basis.
The gravimetric method is the standard against which the indirect methods are calibrated.
Some commonly used indirect methods include electrical resistance, capacitance and tensiometry.
Electrical resistance methods include gypsum blocks or granular matrix sensors  that are used to measure electrical resistance in a porous medium.
Electrical resistance increases as soil water suction increases, or as soil moisture decreases.
Sensors are placed in the soil root zone, and a meter is connected to lead wires extending above the ground surface for each reading.
For most on-farm applications, small portable handheld meters are used; automated readings and controls may be achieved through use of dataloggers.
Capacitance sensors measure changes in the dielectric constant of the soil with a capacitor, which consists of two plates of a conductor material separated by a short distance.
A voltage is applied at one extreme of the plate, and the material that is between the two plates stores some voltage.
A meter reads the voltage conducted between the plates.
When the material between the plates is air, the capacitor measures 1.
Most solid soil components , have a dielectric constant from 2 to 4.
Water has higher dielectric constant of 78.
Hence, higher water contents in a capacitance sensor are indicated by higher measured dielectric constants.
Changes in the dielectric constant provide an indication of soil water content.
Sensors are often left in place in the root zone, and they can be connected to a datalogger for monitoring over time.
Tensiometers measure tension of water in the soil.
A tensiometer consists of a sealed water-filled tube equipped with a vacuum gauge on the upper end and a porous ceramic tip on the lower end.
As the soil dries, soil water tension  increases; in response to this increased suction, water is moved from the tensiometer through the porous ceramic tip, creating a vacuum in the sealed tensiometer tube.
Water can also move from the soil into the tensiometer during or following an irrigation.
Most tensiometers have a vacuum gauge graduated from 0 to 100.
A reading of 0 indicates a saturated soil.
As the soil dries, the reading on the gauge increases.
The useful limit of the tensiometer is about 80 cb.
Above this tension, air enters through the ceramic cup and causes the instrument to break suction with the soil and fail reading on the gauge.
Therefore, these instruments are most useful in sandy soils and with drought-sensitive crops because they have narrower operational soil moisture ranges.
Alternately, a soil's moisture condition can be assessed by observing its feel and appearance.
A soil probe, auger, or spade may be used to extract a small soil sample within each foot of root zone depth.
The sample is gently squeezed manually in the palm of a hand to determine whether the soil will form a ball or cast, and whether it leaves a film of water and/or soil in the hand.
Pressing a portion of the sample between the thumb and forefinger allows one to observe whether the soil will form a ribbon.
Results of the sample are compared with guidelines described by the USDA-NRCS.
Soil water monitoring methods have advantages and limitations.
They vary in cost, accuracy, ease of use, and applicability to local conditions  Most require calibration for accurate moisture measurement.
Proficiency of use and in interpreting information results from practice and experience under given field conditions.
Crop water requirements are crop-specific, and they vary with weather and growth stage.
Water management is especially important for critical periods in crop development.
Knowledge of the root zone should be applied to optimize irrigation management taking into account the crop's effective rooting depth, the soil moisture storage capacity, and field-specific conditions.
In the use of irrigation scheduling, soil moisture monitoring, evapotranspiration information, and/or plant indicators can be used to fine-tune water applications to meet crop needs.
Bordovsky, James P.
and Dana O.
Porter.
2003.
Cotton response to pre-plant irrigation level and irrigation capacity using spray, LEPA and subsurface drip irrigation.
ASAE Paper No.
032008.
Presented at: 2003 Annual International Meeting of the American Society of Agricultural Engineers, Las Vegas, Nevada, July 27-30, 2003.
Enciso, Juan, Dana Porter, and Xavier Peries.
2007.
Irrigation Monitoring with Soil Water Sensors.
Fact Sheet B-6194.
Texas AgriLife Extension Service, Texas A&M System, College Station, TX.
Klocke, Norman L., Loyd R.
Stone, Gary A.
Clark, Troy J.
Dumler, and Steven Briggeman.
2005.
Crop water allocation for limited groundwater.
ASAE Paper No.
052187.
Presented at: 2005 Annual International Meeting of the American Society of Agricultural Engineers, Tampa, Florida, July 17-20-2005.
USDA-NRCS.
1998.
Estimating soil moisture by feel and appearance.
United States Department of Agriculture Natural Resources Conservation Service Program Aid Number 1619.
MISSOURI WATER RESOURCES PLAN 2020 UPDATE
 1.2 Missouri Department of Natural Resources
 1.3 Participating Water Institutions
 1.3.1 State Water Institutions
 1.3.2 Federal Water Institutions
 1.4.1 Interagency Task Force
 1.6 Water Resources Plan Approach
After being postponed from the original date due to a spring storm, the Testing Ag Performance Solutions  program hosted its 2023 Kickoff Event on March 21, 2023, in Doniphan, Nebraska.
In addition to the rich variety of sessions, there will be special events to facilitate networking among participants, including two evening receptions; tours of the Water Sciences Lab and the Greenhouse Innovation Center; optional site tours of a University of Nebraska research center, a working farm and a feedlot; and a student poster competition.
EM 8912 Revised January 2013
 Drip Irrigation Guide for Potatoes
 O regon State University Malheur Experiment Station at Ontario, Oregon, has evaluated drip irrigation on potato.
We have investigated crop response to drip tape flow rate, bed conformation, drip tape placement with respect to potato rows, microirrigation criteria, and potato plant population.
When compared to furrow irrigation, drip irrigation of potato reduces water use, nitrate leaching, erosion, and deep percolation, while increasing marketable yield.
Drip irrigation of potato uses less water than sprinkler irrigation for comparable yield.
Drip systems should be designed for each crop and field.
Growers have many options for custom fitting a drip system to their specific situation.
It is difficult to describe in a brief publication all of the factors that affect irrigation.
Thus, this publication provides a framework, general recommendations, and rationales to aid potato growers interested in maximizing their land use and crop yield through drip irrigation.
Consult your local Extension agent or other agricultural professional for additional information.
Clearwater Supply, Ontario, OR: Jim Klauzer
 Center for Agricultural Water Research in China, China Agricultural University, Beijing: Feng-Xin Wang, associate professor
 In 1984 and 1985, the potato industry in the Pacific Northwest faced a crisis.
Potato tuber quality was inadequate to meet the needs of potato processing companies.
A condition called "sugar ends" or "dark ends" was common in fried slices of tubers grown on stressed plants, but the stresses aggravating the condition were poorly defined.
Growers lost contracted acres.
Malheur Experiment Station, Oregon State University: Clint C.
Shock, director and professor; Rebecca Flock, former research aide; Eric Eldredge, faculty research assistant; Andre Pereira, visiting professor.
In 1989, northern Malheur County was declared a groundwater management area due to groundwater nitrate contamination.
The groundwater contamination was linked, at least in part, to furrow irrigation.
In arid regions, all irrigation systems require some leaching fraction to avoid salt accumulation.
However, the high nitrogen  fertilizer rates used through the 1980s, combined with heavy water applications by furrow irrigation, allowed nitrate and other mobile compounds to be readily lost to deep percolation.
Irrigation-induced soil erosion was also a problem.
Figure 1.
Cross section of a drip-irrigated, flat-topped bed in which the drip tapes are placed offset above the plant rows.
In an effort to find an alternative method of irrigating crops with high water demand in an arid region, both sprinkler and drip irrigation were considered.
This guide discusses drip irrigation.
Drip irrigation is the slow, even application of lowpressure water to soil and plants using plastic tubing, called drip tape, placed directly in the plants' root zone.
Emitters are evenly spaced along the tape's length to allow the water to drip into the crop root zone.
This method allows for very little evaporation and zero runoff, saves water by directing it more precisely, reduces the transmission of pathogens, and wets less of the soil surface, thus producing fewer weeds.
When designing a drip system, first identify irrigation zones.
Irrigation zones are based on factors such as topography, field length, soil texture, optimal tape run length, and filter capacity.
A drip system supplier will have design software that takes these factors into consideration.
Once the zones are identified and the drip system
 designed, it is possible to schedule irrigations to meet the unique needs of each zone.
The traditional bed conformation for potato is a hilled row.
This design is common throughout England, Ireland, and Wales, where furrows are used both to irrigate crops and to drain off water in these high rainfall environments.
The Malheur Experiment Station carried out experiments with bed conformation that may be more suited to the arid climate of the Treasure Valley and may provide a cooler environment for tuber growth.
One of the simplest bed conformations that had a high yield of U.S.
No.
1 grade is two rows of potatoes 36 inches apart on a 72-inch flat bed.
Two drip tapes are used; each is placed offset above a row of seed pieces.
When potato seeds are planted directly in line with the drip tape, the tubers are in the best irrigated part of the soil, but may pinch off the drip tape as they grow.
In preliminary trials, this conformation outperformed sprinkler-irrigated potato on
 conventional beds.
However, conventional 36-inch hilled rows equipped with subsurface drip tapes directly above the seed piece did not fare as well as potatoes in sprinkler-irrigated hills.
Plant population for drip irrigation
 Research at the Malheur Experiment Station showed no significant economic advantage to increasing plant population per acre.
The standard planting rate  was compared to a rate increased by 30 percent.
The additional seed did not increase the percentage of U.S.
No.
1 tubers harvested per acre, but did increase the percentage of undersized tubers.
Several varieties and numbered clones have been identified as genotypes that express fewer tuber defects than Russet Burbank when subjected to stress.
These varieties may be further distinguished by their response to irrigation method.
For example, the varieties Ranger Russet and Umatilla Russet produce nearly equal yields under sprinkler irrigation.
Nevertheless, Ranger Russet has outperformed Umatilla Russet under drip irrigation.
When Ranger Russet is grown on flat beds with a single drip tape for each row of plants, marketable yield is higher than on comparable sprinkler-irrigated conventional beds.
An ineffective or improperly managed filter station can waste a lot of water and threaten a drip system's fitness and accuracy.
In the western U.S., sand media filters have been used extensively for drip irrigation systems.
Screen filters and disk filters are common alternatives, or are used in combination with sand media filters.
Sand media filters provide filtration to 140 to 200 mesh, which is necessary to clean water from
 open canals for drip irrigation.
These water sources pick up fine grit and organic material, which must be removed before the water passes through the drip tape emitters.
Sand media filters are designed to be selfcleaning through a "back flush" mechanism.
This mechanism detects an increase in the pressure differential between input and output of the filter due to the accumulation of filtered particles.
It then flushes water back through the sand to dispose of clay, silt, and organic particles.
Some back flush mechanisms are based on elapsed time rather than on pressure differential.
Sand used for filters should be between size 16 and 20 to prevent excessive back flushing.
It may be better to use several smaller sand media filters rather than a few larger tanks SO that clean water is available for the flush.
In addition to a sand media filter, a screen filter can be used as a prefilter to remove larger organic debris before it reaches the sand media filter, or as a secondary filter before the irrigation water enters the drip tape.
For best results, screens should filter out particles four times smaller than the emitter opening, as particles may clump together and clog the emitters.
Secondary screen filters often are omitted if the drip tape is replaced annually.
Screen filters can act as a safeguard if a problem occurs with the main filters.
They also may act as the main filter if a sufficiently clean underground water source is used.
However, some groundwater contains enough particulate matter to require a sand media filter.
A water flow meter should be an integral part of the system, and each zone's total flow should be recorded regularly.
This provides a clear indication of how much water was applied to each zone.
Water flow records can be used to detect deviations from the standard flow, which
 may be caused by leaks in the system or by clogged lines.
Leaks can occur unexpectedly as a result of damage by insects, animals, hand weeding, or cultivation tools.
Systematically monitor the lines for damage.
It is important to fix holes as soon as possible in order to maintain system uniformity.
Some insect damage to the drip tape can be avoided through preventive insecticide applications or by running the irrigation system as soon as the drip tape is installed.
Chlorine clears clogged emitters
 If the rate of water flow progressively declines during the season, the tape may be slowly
 plugging, resulting in severe damage to the crop.
In addition to maintaining the filter stations, flush the drip lines once a month by opening a portion of the tape at a time and allowing the higher velocity water to wash out the sediment.
The application of chlorine through the drip tape will help minimize clogging.
In the northern U.S., because algae growth and biological activity in the tape are especially high during June, July, and August, chlorine usually is applied at 2-week intervals during these months.
If drip lines become plugged in spite of maintenance, a cleaning product may be available through irrigation system suppliers.
Choose a product appropriate for the specific cause of the clogging.
Figure 2.
Drip irrigation system with a prefilter, pump station with backflow prevention, and chemical injection site.
A pressure control valve is recommended to adjust the water pressure as desired before it enters the drip lines.
A water meter can be placed after the pressure control or between a solenoid valve and each zone.
An air vent provides vacuum relief.
Vacuum relief is necessary between the solenoid valve and the drip tapes to avoid suction of soil into the emitters when the system is shut off.
Daily crop water use
 Irrigation application must reflect crop water use.
Therefore, it is crucial to plan how much water to apply and when to apply it to optimize potato crop performance.
Water applied at any one irrigation should not exceed the soil's water-holding capacity.
Different combinations of duration, frequency, and flow rates can be customized to meet varying irrigation needs within a field.
During each irrigation, the wetting pattern needs to effectively rewet the root zone.
The first irrigation of the season establishes the wetting pattern and can be longer than subsequent irrigations.
Initial irrigations are commonly 24 hours, or 48 hours in dry years.
Fine particles or salts in the soil can be moved laterally with the initial wetting front, and they stop moving when the water ceases to move outward.
Expanding a wetting pattern beyond this initial boundary can require an excessive amount of water.
Once growers monitor for the desired wetting pattern during the initial irrigation, subsequent irrigation sets should maintain the previously established wetting pattern.
The drip tape emitters determine the flow rate of water into the root zone.
Drip tapes with lower water application rates make low-intensity, highfrequency irrigations more feasible by improving wetting pattern and uniformity.
Low flow  and ultra-low flow  are two of the
 emitter options commercially available for silt loam.
There was no difference in potato production between low-flow and ultra-low-flow tapes on silt loam.
Growers can expect to irrigate drip fields more frequently than furrow-irrigated fields.
One reason for the need for more frequent irrigation is simply that less water is applied per irrigation.
Also, moisture may be wicked away from the root zone as the irrigated soil and surrounding dry soil equilibrate.
Drip irrigation permits greater control and precision of irrigation timing and the amount of water applied.
This flexibility to manage a schedule based on root zone soil water tension , thus precisely matching crop needs, may be the greatest advantage of drip irrigation.
Automated irrigation cycling between drip zones can aid in providing the right amount of water to each zone.
Why measure soil water tension?
SWT is economically and environmentally important because it is the measure of how strongly water is held in the soil.
Potatoes have a relatively shallow root system and little tolerance for water stress or irrigation errors.
Tuber yield and grade are related to the amount of energy needed for the roots to remove water from the soil.
Viewed in graphical form, the SWT clearly indicates the relative condition of the root zone of the crop over time.
The use of granular matrix sensors and tensiometers to determine crop water needs is discussed in Irrigation Monitoring Using Soil Water Tension, EM 8900.
These principles are applied to potato in Successful Potato Irrigation Scheduling, EM 8911.
Potato is a water-stress-sensitive crop.
Potato plants are more productive and produce higher quality tubers when watered precisely using SWT than if they are underor overirrigated.
Tuber
 market grade, specific gravity, and French fry processing quality are all negatively affected by excessive water stress during tuber bulking.
Conversely, oversaturating the soil reduces aeration of the root zone and may result in increased potato decay in storage.
For drip-irrigated potatoes on silt loam, tuber growth and grade are maximized if plants are irrigated when SWT at the 8-inch depth reaches 30 centibars .
Note that lower numbers indicate wetter soil.
This recommendation is based on several factors.
After tuber initiation, even small amounts of water stress can result in decreased tuber grade, decreased specific gravity, or increased incidence of dark-end fry colors.
Delaying drip irrigation until the soil dries to 45 cb has been shown to reduce tuber yield and grade.
With sprinkler irrigation, a single episode of water stress  can reduce tuber grade and specific gravity and increase the occurrence of dark-ends at harvest.
Overly dry soil, especially during the early stages of tuber development, also favors common scab.
Average readings at the 8-inch depth must remain below 60 cb in order to avoid permanent damage to developing potato tubers.
Irrigation at 15 cb on silt loam results in excessive use of water and swollen lenticels.
Yield reductions due to overirrigation can be attributed to poor soil aeration, increased susceptibility to rots and diseases, and leaching of N from the shallow root zone.
Irrigation and fertilization should be managed together to optimize efficiency.
Chemigation through drip systems efficiently deposits chemicals in the root zone of the receiving plants.
Because of its
 precision of application, chemigation can be safer and use less material than spray applications.
Several commercial fertilizers and pesticides are labeled for delivery by drip irrigation.
Injection pumps with backflow prevention devices are necessary to deliver the product through the drip lines.
These pumps allow for suitable delivery rate control.
Backflow prevention protects both equipment and the water supply from contamination.
Other safety equipment may be required; contact a drip-irrigation system supplier for details.
Soil microorganisms convert N fertilizers to nitrate.
Nitrate is water soluble, available to plants, and subject to leaching loss.
Since nitrate loss management was one of the initial reasons for exploring drip irrigation in the Treasure Valley, it is appropriate that we revisit this topic.
Research conducted at Malheur Experiment Station showed that high-quality tubers can be produced with far lower inputs of N fertilizer  than growers had used in the past.
Optimum yield responses have even been obtained with rates ranging from 120 lb N/acre to no additional N following alfalfa.
If excess irrigation is avoided, N rates over 120 lb N/acre are rarely economically beneficial.
Principles of N fertilization for drip-irrigated potato in silt loam soil in the Treasure Valley include the following.
Nitrogen fertilizer application is needed only when potatoes have the greatest opportunity to absorb N.
Nitrogen may be applied efficiently via the drip system at this time.
Careful irrigation management produces little to no nitrate leaching.
In silt loam soils, it also can reduce N fertilization requirements.
Potatoes with the lowest fertilizer application rates have the highest tuber specific gravity,
 providing an additional advantage to moderate N application.
The best way to determine N fertilizer needs is through regular petiole sampling.
Proper irrigation scheduling also affects pest management strategies.
Soil water decreases the mobility of cutworms and potato tuber moth, protecting the tubers from attack.
Systemic insecticides sometimes are used in drip systems for enhanced insect and nematode control.
Normally, the product is introduced during the middle of the irrigation set, allowing a clean water period to push the product out of the drip tape and closer to the crop.
Alkaline irrigation water decreases the effectiveness of some insecticides.
Consequently, acid sometimes is needed to reduce the pH of the water.
A second injection pump is needed for the acid.
Excessively wet soil is conducive to many tuber-rotting pathogens, and excessive moisture on the crop canopy encourages the incidence of foliar blights and wilts that can limit potato performance.
Drip irrigation can be managed to provide adequate water without creating excess moisture, thus potentially requiring fewer fungicide applications.
Shallow-set tubers exposed by erosion in sprinklerand furrow-irrigated fields are subject to greening or sun scald and are more susceptible to early and late blight pathogens.
Drip irrigation is an effective way to prevent tuber exposure since water application is more gentle.
Funding to help prepare this publication was provided by an Oregon Watershed Enhancement Board grant.
Drip irrigation is the slow, even application of low-pressure water to soil and plants using plastic tubing placed directly in the plants' root zone.
Drip irrigation systems facilitate water management in fields that are difficult to irrigate due to variable soil structure or topography.
Potato yield and grade respond very sensitively to irrigation management.
For drip-irrigated potato grown on silt loam, recommended soil water tension for irrigation onset is 30 centibars.
Seasonal water needs for drip-irrigated potato are 16 to 24 inches at Ontario, OR, depending on the year.
Drip systems require careful design and maintenance.
2013 Oregon State University.
As described in the video, walking and visually observing an irrigation system when it is running often can help locate where there are mechanical causes for poor uniformity.
In some cases, obvious or easily noticeable issues can be identified, such as the broken gooseneck shown in the video.
However, other instances such as stuck sprinklers or clogged nozzles may be less noticeable, especially if the sprinklers are on drops in a tall crop canopy.
Diana G.
Helsel and Zane R.
Helsel Department of Agronomy
 The PDF version of this publication includes illustrations.
Missouri's growing season is characterized by excessive moisture in the spring followed by inadequate moisture during the middle of the growing season.
Because of the lack of moisture during the crops' peak demand, some producers have invested in irrigation systems.
The cost of maintaining and using these systems is high, SO it is imperative to manage moisture in the most efficient way possible.
The following discussion should help Missouri soybean producers understand the crop's need, the soil's ability to hold and supply water, and the agronomic practices that can result in maximum economic yields under irrigation.
Soybean response to irrigation
 Irrigation usually improves soybean yields on drought-prone soils and in exceptionally dry seasons.
The amount of increased yield  fluctuates, depending on variety, geographic location, soil type and fertility.
An eight-year study of irrigated VS.
nonirrigated soybean yields in southeast Missouri indicates yield increases are greater for short-season varieties under irrigation.
Full-season varieties show almost no yield response, and medium-season varieties show an intermediate response to irrigation.
Responses of soybeans to irrigation in southeast Missouri, 1967-1974
 Maturity	Average of three sites
 Early	27.1 bushels per acre	33.8 bushels per acre	6.7 bushels per acre
 Medium	32.0 bushels per acre	35.7 bushels per acre	3.7 bushels per acre
 Late	32.9 bushels per acre	33.7 bushels per acre	0.8 bushels per acre
 Adapted from Shannon and Duclos.
In central Missouri, a survey indicates that over a 10-year period, soybean growers obtained an average increase of 13 from irrigating full-season soybeans.
In research sponsored by the grower check-off program, yields of 10 varieties grown in southwest Missouri during the dry years of 1983 and 1984 averaged 29 and 13 bushels more per acre respectively under irrigation.
In 1985, when plentiful rains occurred during the seed-fill period, yields increased by only about 1 bushel per acre.
The economics of achieving these yield increases are of paramount importance.
The type of irrigation system and the water source greatly affect cost.
Flood or furrow irrigation with a cheap water source may cost as little as $25 per acre per year, while a center pivot system with a deep well could cost as much as $100.
Prospective irrigators should weigh potential costs against returns they can expect from the increased yields and reduced risks created by irrigation.
In addition to influencing yields, irrigation may alter other characteristics of importance to soybean growers, such as maturity and lodging.
Irrigation delays the maturity of shortor midseason varieties only a few days.
Full-season varieties usually show no difference in maturity unless extended drought or charcoal rot infection occurs.
Plant height normally increases under irrigation, which increases the chance of lodging.
However, proper variety selection may reduce this problem.
Weather patterns and crop water use
 Missouri rainfall patterns are characterized by sufficient winter and early spring rainfall that maintains the soil at or near saturation capacity until almost the first of June.
During late June, July and August, the crop's need for moisture usually exceeds that available from either the soil or rainfall.
Water requirements are a function of the plant's metabolic needs, the quantity needed for transpiration , and the quantity lost by evaporation from the soil.
This combined demand is called "evapotranspiration."
 The peak water use period for soybeans occurs during reproductive growth, when they may need as much as 2.5 inches of water per week.
The average rainfall during this period is less than 0.6 inches per week.
Available soil moisture is depleted by the time reproductive growth begins, so unless you provide supplemental irrigation, the plant will be subjected to moisture stress.
Short-season varieties complete flowering and pod filling during the period of greatest evapotranspiration.
This results in decreased yields if you don't irrigate.
Full-season varieties normally reach their critical growth period after the period of the highest evapotranspiration passes.
Soybeans are most sensitive to moisture deficits during the late pod development/early bean filling periods.
Figure 1 depicts the yield response of northern soybeans relative to the time at which moisture stress develops.
Lack of water during flowering and podding causes flower and pod abortion.
Stress during pod development and early seed fill reduces the number of seeds per pod.
Drought conditions
 during seed fill reduce seed size and thus final yield.
The critical period of water need for indeterminate varieties occurs from late flowering through mid pod fill.
For determinate varieties, such as those grown in the Bootheel, the period of greatest water need begins earlier in flowering.
The new determinate semidwarf  varieties often show critical water needs through most stages of growth.
The effect of a moisture stress on soybean yield at various growth stages.
From Shaw and Laing, 1966.
lowa State University
 Availability of soil moisture
 Specific soil types have varying abilities to hold moisture.
The available soil moisture, in terms of inches of water held per foot depth of a soil, is described in Table 2.
Sandy soils retain the least amount of water, while silt loam and clay loam soils hold the most.
Note that clay soils have less available water than do clay loam soils.
Clay soils hold more water, but less of that water is available for plant growth because water adheres strongly to the clay particles.
Table 2 Potential available water storage capacity for various soil types
 Soil type	Available soil moisture per foot of depth
 Loamy sands	1.0 inch
 Sandy loam, clay loam	1.5 inches
 Loams, silty clay loam	1.8 inches
 Silt loams	2.5 inches
 Adapted from Kiniry, Scrivner, and Keener, 1983.
You must also consider the rooting depth of the crop in a particular soil.
The effective rooting depth of soybeans ranges from a few inches after emergence to 2 to 3 feet during the early reproductive stages.
However, some Missouri soils are compacted and some acid sublayers restrict the effective rooting depth to that depth of topsoil above the compacted layer.
In these soils, it is wasteful to supply more water than is necessary to wet the upper zone.
You can measure or estimate soil moisture by a variety of methods.
Each has its advantages and limitations.
Irrigators who use soil moisture measurements for scheduling purposes usually establish an allowable soil moisture depletion level.
For soybeans, the limit is about 70 percent depletion in the vegetative stages and 50 percent for reproductive stages.
You should irrigate if you reach these levels.
To maintain the soil moisture content above the allowable depletion level, you should start irrigating sooner on sandy soil, which has a lower moisture storage capacity.
One of the quickest and most popular methods of determining soil moisture is based on feel and appearance of the soil.
Charts to aid inexperienced irrigators are available.
The method is not quantitative and requires individual judgment.
Thus, it lacks the precision of other methods.
Electrical resistance instruments, commonly called moisture blocks, measure the moisture content of the soil indirectly.
They sense a change in electrical properties of the blocks which correlates with block moisture content and, in turn, the soil moisture.
These devices consist of two electrodes mounted in blocks made of plaster-of-paris, fiberglass, gypsum or other materials.
Wires from the electrodes attach to a meter that measures electrical conductivity, a function of the water content of the soil.
To install moisture blocks, dig a hole with a soil auger and place the block in it.
Pack soil around the block to ensure good capillary action between the sensor and the soil.
Calibrate blocks in each field to ensure accurate prediction.
Moisture blocks are not recommended for sandy soils.
Tensiometers are well adapted to sandier soils.
Tensiometers measure the soil moisture tension how tightly the soil particles hold the water.
This is directly related to the tension required for plant roots to extract water from the soil.
Tensiometers consist of a tube with a porous ceramic cup at one end and a gauge at the other.
To install, place in the soil to the depth of plant rooting.
Fill with water.
The water will move from the cup into the soil until the water content reaches equilibrium.
As the soil dries, the tension increases, indicating water is more difficult to extract from the soil.
Although tensiometers indicate when you should begin to irrigate, they do not indicate how much water you should apply.
Missouri irrigation scheduling charts
 MU Extension centers can provide irrigation scheduling charts for soybeans and other crops.
A computer develops a customized chart  for each field depending on crop, soil type, planting date, variety , location in the state, and any moisture deficit at planting time.
Use this chart to develop an irrigation schedule
 The chart projects the cumulative minimum and maximum amounts of water you should provide  to optimize crop yield, assuming average weather conditions for the site.
You use the scheduling chart to maintain the total water added  during the season between the minimum and maximum water needs.
Usually, a 1to 2-inch range exists between the minimum and maximum cumulative totals of needed water application, depending on the available water holding capacity of the soil.
Thus the chart is well suited for sprinkler irrigation because sprinklers usually apply less than 2 inches of water per application.
A planned linear depletion of two-thirds of the total soil moisture storage by crop maturity is planned with a starting date of June 1, at which time the profile is assumed full.
For years when temperatures exceed the normal, you can modify charts to account for increased evapotranspiration.
The charts should minimize irrigation operating costs and water use and reduce runoff and leaching.
Plant response to timing of irrigation
 If you can irrigate only once during the growing season, do so during the late pod development to early seed-filling period if soil moisture levels are low.
This timing maximizes seed yield and seed size and minimizes lodging problems and maturity delays.
A detailed study of irrigation timing with indeterminate soybeans was conducted in Nebraska.
Irrigation was applied in single applications  and in split applications.
Researchers evaluated plants and their responses in height, lodging, and yield.
Plant height and, in turn, lodging increased the most by multiple applications of water.
The addition of water allowed the plants to prolong their vegetative growth, thereby increasing plant height.
Delays in maturity were progressively longer as the frequency of irrigation application increased.
The greatest maturity delay, however, was six days, which is unlikely to cause crop loss from early frost.
Figures 3 through 8.
These charts show the response of various soybean plant and seed characteristics to timing of irrigation application.
Figure 3 shows plant height; 4, lodging; 5, maturity; 6, seed yield; 7, seeds per plant; and 8, 100-seed weight..
Several irrigation treatments produced comparable yield.
Irrigating at flowering did not result in optimum water use.
At flowering, soybeans use water to produce flowers which they usually abort.
They don't use the water to fill the beans.
In the Bootheel where determinate varieties are grown, however, adequate water during flowering is important because of the shorter duration of this initial reproductive period.
Seeds per plant were greatly enhanced with all irrigation treatments.
However, the greater numbers of seeds did not result in higher yields for some treatments.
This component of yield indicates irrigation promotes the retention of pods and perhaps increases the number of seeds per pod compared to a nonirrigated situation.
The recommendation to irrigate during late pod development and early seed filling is largely based on its impact on seed size.
Seed sizes resulting from irrigation during seed-filling were clearly superior to those achieved when water was supplied at other times during reproductive development.
This occurs because of the plant's enhanced ability to completely fill the seeds with photosynthetic products.
When attempting to maximize yields under irrigation, consider four factors.
Because lodging is frequently a problem, you should select genetically lodging resistant varieties.
In the north, the new determinate semi-dwarf varieties are useful for high-yielding environments, such as those that exist under irrigation where lodging is a severe problem.
Second, consider reducing plant populations by 10 to 15 percent.
This allows the plants to develop more branches and sturdier stems which reduces lodging.
Again, the goal is to reduce yield losses associated with down plants at harvest.
Less seed also reduces seed cost per acre.
Third, because yields are higher with irrigation, the soil needs more fertilizer to accommodate the greater demands plants make on it.
On average, increase fertility to about 20 percent more than the amount you would apply under nonirrigated conditions.
You can get more specific recommendations by matching soil test results to yield goals.
Finally, monitor soybeans closely.
Irrigation provides a better growing environment not only for soybeans but for weeds, insects, and some diseases as well.
Research at the MU indicates that when soybeans have adequate water, little if any yield loss occurs as long as the tops of the weeds are shorter than the tops of the soybeans.
Insects may increase because of the lush vegetation that develops.
However, these insects normally cannot keep up with the rapid growth of the plant.
By adequately watering plants, you can greatly reduce the number of insects like grasshoppers and spider mites, which are severe pests in dry years.
Root rots and leaf diseases may increase if soybeans receive too much water, particularly early.
However, the effects of many soybean diseases are abated because irrigated plants are healthier.
Increased input costs for irrigation necessitate the need for careful monitoring and management if you are to realize positive net returns.
Soil Sensor Install Tips: As plants mature, later installation can lead to poorer readings as a result of root damage, residual water in the sensor or slurry, and more challenging installation given soil conditions.
Because of these disadvantages, early installation of sensors is highly recommended.
Nebraska Extension, the Ogallala Water Project and the Nebraska Water Balance Alliance will host a water and crops field day on Aug.
23 at the West Central Research and Extension Center, 402 W.
State Farm Road, North Platte.
Partnering with producers & industry  tackling todays challenges and tomorrows opportunities is the theme for this educational event which will focus on innovative and practical crop management solutions.
What if the stream bed is private property but the public has the right of recreational navigation?
In this case, the public will often have the right to incidentally touch the bed and will have an additional right of portage  the ability to take a boat or other watercraft around any obstructions in the stream.
But generally, the public will not have the right to  cross private property to get to the stream without the owners permission  to leave the canoe and picnic, etc.
on private property without the owners permission.
If they do, they have committed trespass.
The public never has an automatic right of way across private property to gain access to a public stream for recreational purposes.
University of Nebraska irrigation scheduling recommendations encourage irrigators to allow the crop to continue using more and more of the stored soil water starting in August and continuing into September when the crop matures.
The recommendation is to lower the soil water level from the usual summer watering condition of 50% plant available water to 40% plant available water in the top four feet of soil.
Thus, the stored soil water content should be significantly lower when the crop matures in September than earlier in August.
However, as the data shows in Table 1, many irrigators are applying more water late in the season than is needed.
Some years, a significant rain can cause the soil to be wetter in September, but it is usually due to applying more irrigation water than needed.
WATER WITHDRAWAL REGULATIONS EVERY AGRICULTURAL USER IN SOUTH CAROLINA SHOULD KNOW
 Published: Oct 2, 2020 |  Printable Version  | Peer Reviewed
 Ethan Barnette, Calvin B.
Sawyer and Dara Park
 South Carolina has important regulations to protect and conserve its water resources.
This article should provide producers with a better understanding of state water quantity regulations that potentially impact their operation, estimating their farm water use, and helping them avoid possible penalties.
The flowcharts and tables included assist producers in understanding relevant regulations and for estimating water usage.
On average, South Carolina experiences between forty-five to fifty-five inches of rainfall annually.1 Even with such abundant rainfall, the state will still sustain dry periods with sporadic rainfall, especially during the summer months.
During these times, agricultural producers may rely on irrigation to maintain adequate soil moisture and promote crop growth.
Depending on the amount of water applied, surface water or groundwater users can strain the states water resources.
Beginning in 1962, concerns of overuse and resource degradation led to a legislative declaration of state water regulation policy.
The declaration states, The General Assembly declares that the general welfare and public interest require that the groundwater resources of the State be put to beneficial use to the fullest extent to which they are capable, subject to reasonable regulation, in order to conserve and protect these resources, prevent waste, and to provide and maintain conditions which are conducive to the development and use of water resources, and gave regulating authority to the SC Department of Health and Environmental Control.2 Since this declaration, the state has enacted several regulations to promote wiser water use.
These regulations have a broad impact, and proper understanding of the regulation scope and framework can help agricultural water users make sure they are within compliance with the regulations.
Water use in South Carolina is an important and complex issue.
Currently, the primary consumptive water uses by volume include residential, power production, and irrigation.
SCDHEC separates the primary consumptive uses into the following categories:
 General water supply use3
 Since enacting the 1962 Groundwater Use Reporting Act, South Carolinas first water quantity regulation, the state has continually strengthened water resource conservation efforts.
Protecting and conserving the states water resources ensures environmental and economic benefits such as ecosystem resilience, a quality drinking water supply, and tourism.
Any agriculture water user in South Carolina withdrawing more than three million gallons in any single month  is required to either register the withdrawal or obtain a permit, depending on the operations geographic location and whether the withdrawal is from a surface water or groundwater source.3
 A significant volume of the states water use results from agricultural irrigation and comes from ground and surface water withdrawals.
Most producers use a center pivot, traveling gun, linear move, or similar irrigation systems.
According to the 2018 SCDHEC Water Use Report, agricultural irrigation use exceeded 54 billion gallons for the reporting period and accounted for 14% of the states total reported water use .3
 A pie chart describing the reported consumptive water use for South Carolina in 2018.
Water supply: 57%, Aquaculture: 0%, Golf Course Use: 1%, Industrial: 27%, Mining: 1%, Agricultural Irrigation: 14%, and Other: 0%.
Figure 1.
South Carolina reported consumptive water use for 2018.3 Image credit: Ethan Barnette, Clemson University.
Additionally, both the volume and the number of reporting facilities withdrawing water for agricultural irrigation purposes have increased over the last five years.
The growth in the number of registered agricultural water users includes an increase of 46.7% for groundwater withdrawals and 6.5% for surface water withdrawals.3,4
 Two bar graphs  describing the trend in volume and registered agriculture facilities reporting water withdraws.
Top: displays the constant upward trend in agricultural water volume use  from 2014-2018.
Bottom: displays the constant upward trend in registered agricultural withdrawal facilities from 2014-2018.
Figure 2.
Agricultural irrigation water use trend from 20142018 for  the volume of water used for agricultural purposes and  the number of agricultural facilities withdrawing water.3-7 Image credit: Ethan Barnette, Clemson University.
Groundwater withdrawal capacity varies throughout the state and is largely based on underlying soil composition.
Soils in the Piedmont tend to be less permeable, contain underlying bedrock, and require finding fractures in the bedrock to access larger volumes of groundwater easily.
Such soil conditions generally make Southern Piedmont soils unsuitable for high capacity wells.
Soils of the Midlands and Coastal Plain of the state  have higher permeability since they are typically comprised of a higher percentage of sand.8 The Midlands and Upper Coastal Plain regions are typically characterized by shallower, more accessible underlying aquifers that contain little bedrock, making them more suitable for high capacity wells.
The common factor separating these areas is the states fall line.
This line signifies the geologic shift in soil types from the Piedmont region to the Coastal Plain region and runs southwest to northeast, approximately following Interstate Twenty.
An approximation of the fall line overlaid on figure 3 provides a visual representation of where geologic change occurs.
The necessity to obtain a withdrawal permit or register use will depend on both the wells geographic location and volume of monthly use.
Groundwater in South Carolina is regulated through areas designated as capacity use.
According to SCDHEC, a Capacity Use Area is an area where excessive groundwater withdrawal presents potential adverse effects to the natural resource or poses a threat to public health, safety, or economic welfare or where conditions pose a significant threat to the long-term integrity of a groundwater source, including saltwater intrusion.9 The Board of SCDHEC creates a Capacity Use Area in a region of the state where groundwater withdrawal volume is large and without monitoring and regulation, the groundwater resources have a high potential to become degraded and their use unsustainable.
If a user plans to withdraw more than 3 MGM of groundwater in a capacity use area, they must apply for and obtain a groundwater withdrawal permit from SCDHEC.9 The full registration and permitting process is detailed in SCDHEC Regulation 61-113.
Title: South Carolina Groundwater Capacity Use Area Map.14 Pee Dee CU Area : Marlboro, Darlington, Dillon, Marion, Florence, and Williamsburg counties.
Waccamaw CU Area : Horry and Georgetown counties.
Trident CU Area : Berkeley, Dorchester, and Charleston counties.
Low Country CU Area : Colleton, Beaufort, Hampton, and Jasper counties.
Western Capacity CU Area : Aiken, Lexington, Calhoun, Orangeburg, Barnwell, Bamberg, and Allendale counties.
Notice of Intent  Counties: Chesterfield, Kershaw, Lee, Richland, Sumter, and Clarendon.
Registration Counties: Oconee, Pickens, Greenville, Cherokee, York, Lancaster, Fairfield, Newberry, Saluda, Edgefield, McCormick, Greenwood, Laurens, Union, Chester, Spartanburg, Anderson, and Abbeville.
Figure 3.
Map of South Carolina groundwater capacity use areas.12 Image credit: SC Department of Health and Environmental Control.
If a user is constructing a new well or replacing an existing well for drinking water or irrigation, a general permit must be obtained before the work may commence.10 This permitting process involves submitting a Notice of Intent  to SCDHEC for their review and approval or denial, which must come within forty-eight hours.
The permittee must also give notice of the location, time, and date of the well construction, forty-eight hours prior to construction.10 The full process for applying and obtaining a well installation or replacement permit is found in SCDHEC Regulation 61-44.
Users requiring registration or a permit must submit an annual water use report to SCDHEC.
Penalties for violating this law and regulation include a $1,000 per day fine for each day of violation and potential for a criminal misdemeanor charge.11
 Complete versions of these regulations can be found by searching Water Regulations on SCDHECs website or using the URLs in the citations at the end of the article.
Producers can use the flowchart in figure 4 to understand the groundwater regulation process and how it might affect their operation.
The flowchart helps guide users in determining if their withdrawals are in compliance with SCDHEC regulations and direct them to the specific regulatory documents for any questions.
Title: Groundwater Regulation Flowchart Top of chart begins Q: is the withdrawal greater than three million gallons in any one month?
1.
If yes to withdrawal amount, then Q: is the withdrawal in a capacity use area?
a.
If yes to capacity use area, then an approved withdrawal permit is required.
i.
If permit is required, then consult SCDHEC Reg 61-113 sections C-I for permitting and annual reporting process.
b.
If no to capacity use area, then only registration and reporting of the withdrawal is required.
i.
If only registration and reporting required, then consult SCDHEC Reg 61-113 sections D-I for registration and reporting process.
2.
If no to withdrawal amount, then: no permit or registration is required for the withdrawal.
a.
If no permit is required, then: consult SCDHEC Reg 61-44 for Well permitting process.
Figure 4.
Flowchart detailing the groundwater regulation process and when to consult SCDHEC regarding registration and permitting.
Image credit: Ethan Barnette, Clemson University.
Many agricultural producers in South Carolina withdraw and irrigate from surface water sources.
Withdrawing surface water requires a different registration process; this process is outlined in SCDHEC Regulation 61-119, which can be found on SCDHECs website or by using the URL in the citation at the end of the article.
This regulation is derived from the South Carolina Surface Water Withdrawal, Permitting, Use and Reporting Act [49-4-10].
The surface water and groundwater withdrawal volume thresholds are the same.
Those exceeding this level of surface water withdrawal for agricultural uses are required to register and report their use to SCDHEC.13 If the withdrawal volume was reported before January 1, 2011, the user is considered registered and can continue withdrawing up to the greatest level previously reported or to the intakes design capacity.12 If the surface withdrawal is new or is an expansion, the user must file the registration application with SCDHEC.
The requirements for the application are found in SCDHEC Regulation 61-119, section L-4.
If the surface water withdrawal is only for agricultural purposes and  originates from a farm pond owned or leased by the user or  if the pond is on private property across multiple parcels and all owners agree to the water use, then the withdrawal is exempt from registration and reporting requirements.12
 An annual quantity use report must be submitted to SCDHEC no later than the February 1 of each year by all non-exempted registered agricultural surface water withdrawals.12 The report must detail the quantity of water withdrawn and describe how the quantity withdrawn was determined.
Approved methods can be found in Regulation 61-119, section N-2.
Penalties for violating this law and regulation include a $10,000 per day fine for each day of violation and possibly a criminal misdemeanor charge.13 Producers can use the flowchart in figure 5 to understand the surface water regulation process and how it might affect their operation.
The flowchart will guide the user in determining if their withdrawals are in compliance with SCDHEC regulations and direct them to the specific regulatory documents for more information.
Title: Surface water Regulation Flowchart Top of chart begins Q: is the withdrawal greater than three million gallons in any one month?
1.
If yes to withdrawal amount, then Q: Is the withdraw from a farm pond only used for ag purposes; owned or leased by withdrawer or on private property owned by several and all agree to the withdraw?
a.
If yes to purpose and ownership, then Withdrawal registration and reporting is exempt via Section C-1-c of SCDHEC Reg 61-119.
b.
If no to purpose and ownership, then Q: was the withdrawal being reported before January 1, 2011?
i.
If yes to reporting date, then the withdrawal is considered registered and can continue withdrawing at the highest level previously reported.
1.
If withdrawal is considered registered, then consult SCDHEC Reg 61-119 for any questions or for the annual reporting process.
ii.
If no to reporting date, then the withdrawal is considered new/expansion and requires registration and reporting.
1.
If withdrawal is new, then consult SCDHEC Reg 61-119 sections L-4 and N for registration and reporting process.
2.
If no to withdrawal amount, then: no registration is required for the withdrawal.
Figure 5.
Flow chart detailing the surface water regulation process and when to consult SCDHEC regarding the registration and reporting process.
Image credit: Ethan Barnette, Clemson University.
All water users in the state should strive to comply with relevant regulations.
To help determine if agricultural water usage is in compliance at an operation, use the tables below.
The tables provide information to help producers understand if irrigation applications may exceed SCDHEC threshold volumes  by visualizing the > 3 MGM threshold across different acreage using varying application rates.
Table 1.
Water usage application guide in inches applied per one-month basis.
The y signifies that water usage is less than the 3 MGM threshold.
The x represents water usage that exceeds the 3 MGM threshold.
At first glance, exceeding the 3 MGM withdrawal limit may seem unreachable for many agricultural users.
However, the 3 MGM volume is quickly attainable, and users may exceed the threshold without even being aware of any regulatory ramifications.
For example, common agronomic crops grown and irrigated in South Carolina are corn, cotton, and soybeans.
To optimize yield, each of these crops would require 0.3 inches of water per day per acre during their peak growth period.14 If a grower irrigated at this daily rate or at the equivalent application rate of 2.1 inches per week for one month, across just fifteen acres, they would exceed the monthly threshold and trigger either the registration or permitting requirements set forth in the regulations.
By helping agricultural producers understand and comply with relevant regulations, more informed conservation plans can be established, and South Carolinas water resources can be safeguarded for future use.
Robert E.
Sojka Lewis H.
Stolzy
 that as the ODR of a soil decreases, stomata close, independently of other factors like soilwater status or light intensity.
Leaf diffusive resistance  is an indicator of stomatal aperture.
When Rs is high, stomata are closed; when Rs is low, stomata are open.
Figure 1 shows the effect of ODR on Rs for wheat grown in soil at equilibrium with gas mixtures of 0, 4, and 21 percent O2.
Soil temperatures were varied also to give 9, 15, and 21 C treatments.
These two factors combined to create a range of ODRs.
At low ODRs Rs increases sharply, indicating stomatal closure.
This occurs despite the maintenance of uniformly favorable soil water status in all treatments.
Similar responses have also been found in tomato, cotton, sunflower, and jojoba.
Figure 2 demonstrates the Rs increases of sunflower and jojoba in an experiment similar to the wheat experiment.
Evidently, the Rs of both sunflower and jojoba responds to soil temperature.
At high soil temperatures, the respiration rate of roots  increases, as does competition for soil O2 by soil microorganisms.
Higher soil temperatures thus induce an oxygen shortage, which results in greater stomatal closure.
Interestingly, crop damage caused by excessive soil water is usually more severe in warm weather than in cool weather.
This follows from our results since stomatal closure due to flooding would prevent the normal transpirational cooling of plant tissues.
These findings have practical implications.
When stomata are closed, we can expect not only heat stress to occur, but also photosynthesis to be reduced.
These data may promote rethinking of the practice of flood-irrigating some crops, particularly on fine-textured soils, or when excessive canopy temperatures are likely.
They also help us to better understand one mechanism of crop damage resulting from unwanted soil flooding.
Simplified but scientific irrigation scheduling
 Elias Fereres Patricia M.
Kitlas Richard E.
Goldfien
 William O.
Pruitt Robert M.
Hagan
 the past, when irrigation water was ample and its cost negligible, the obvious management strategy was to eliminate water as a limiting factor in producing crops at the lowest possible cost.
As irrigated agriculture competes for the limited water supplies and costs of both energy and water rise, effective on-farm water management programs are needed to maximize irrigation efficiency.
This report describes a new approach to developing and disseminating irrigation scheduling information among California's agricultural water users.
In designing their seasonal water-management programs, farmers are confronted with three essential questions:  how often should each field be irrigated;  how much water should be applied at each irrigation; and  which irrigation management techniques should be used to efficiently apply the needed amounts of water at the appropriate levels?
Although we address only the first two questions here, the answers may be academic without evaluating the adequacy and efficiency of individual irrigation practices.
Among the many procedures commonly used to schedule irrigations, the water-budget method is the most prevalent.
In the water budget the crop root zone is visualized as a reservoir of crop-available water.
Water is withdrawn from the reservoir through evapotranspiration  or drainage and added through rainfall and irrigation.
If the volume of the reservoir and the amount that can be used without stressing the plant  are known, along with the depletion rate , the date of the next irrigation can be predicted.
Effectiveness of the method hinges on an accurate determination of AD and ET.
Research over
 many years has established the ET requirements of several crops in California and made possible the day-by-day prediction of ET.
Water retention properties of the principal soils are also well known, as are typical rooting depths of many crops.
What is now needed is to make this information available in a form that the average farmer or irrigator can use.
A useful characteristic of summer weather in California's interior valleys is the constancy in evaporative demand.
The absence of rainfall and the small year-to-year variations in summer weather make long-term averages of weather parameters attractive for use in prediction.
Early studies conducted by the University of California at Davis and the State Department of Water Resources in several locations throughout the Central Valley documented the variability in ET rates during the irrigation season, indicating that 90 percent of the time, 10-day to 2-week forecasts of ET based on long-term averages are within 10 percent of actual ET.
The relative constancy in ET demand during a good part of the irrigation season and the availability of long-term ET records and accurate crop coefficients for many crops in the Central Valley make it possible to use average or normal year crop ET to predict irrigation dates and amounts for management purposes.
Recently, many large-scale irrigation scheduling programs have been implemented by various agencies and private consultants.
Computer programs based on the water-budget concept are now being used to help provide irrigation scheduling services in large areas of the western states.
Field verification of computer predictions is necessary, however, because of uncertainty
 about the depth of water actually applied at each irrigation; uncertainties in evaluating the crop rooting depth, soil water storage capacity, and allowable depletions; the spatial variability of soil water-holding characteristics within each field; uncertainties in computations of crop ET, particularly in the early growth stages; and the need to evaluate the effective rainfall on each farm.
This need for field checks and frequent calculations is perhaps one of the most important factors limiting broad acceptance of irrigation scheduling techniques among farmers.
Although in some parts of the Central Valley, irrigation scheduling services may be contracted for, in many other areas where the apparent economic benefits do not justify the cost of such services, farmers do not have the time or expertise to make detailed water budget calculations and field checks.
Therefore, despite significant efforts by various agencies and the University, adoption of detailed water budgeting techniques by farmers has not been widespread so far.
A simplified approach to scheduling irrigations is needed that, at the same time, will have predictive value.
If the ET data for a normal year are combined with the water-holding characteristics of a particular soil, an irrigation management program  may be designed that indicates when to irrigate and how much to apply under average or normal-year conditions.
The example presented in figure 1 shows cumulative ET for any time after planting.
The vertical distance between two adjacent horizontal lines represents the allowable depletion for each irrigation cycle.
The irrigation date is determined by drawing the horizontal line to intersect the ET curve, and then a vertical line to the date line at the base of the graph.
This IMP, presented in tabular form or on a graph, is an easy-to-use, predictive tool that requires much less effort for irrigation programming by the farmer than do detailed water-budget calculations.
If more accuracy is desired, the normal-year IMP provides an excellent base for irrigation scheduling: the ET curve is simply updated periodically with values from the current year and the irrigation dates changed accordingly.
Once the appropriate IMP has been designed for a given soil-crop combination, it can then be used as a rational basis for irrigation scheduling with only periodic checks.
In California these checks must be made more frequently at the start and end of the irrigation season, when unpredictable weather conditions may cause large year-to-year variations in ET rates.
The IMPs are valuable aids in predicting requirements for water, labor, and other essential inputs.
They are also helpful in planning the date of the last irrigation so that expected winter rainfall will be stored within the root zone of next year's crop.
And although they are based on the crop's being fully supplied with water, they are helpful in
 Fig.
2.
Operation of IMP computer program.
adjusting cropping patterns, planting dates, and other strategies when the preseason prediction is for a less-than-normal water supply.
It should be pointed out that under any irrigation scheduling method there are uncertainties in evaluating crop ET, the soil waterholding capacity, allowable depletion, and the volume of water applied at each irrigation and stored within the root zone, as well as its variability throughout the field.
Thus the need for precise estimates of other parameters, including crop ET, may be questioned.
Where soil water-holding capacity is low, water costs high, or crops very sensitive to water stress, the use of more sophisticated techniques for scheduling irrigations may be justified, however.
Therefore, a computer model was developed SO that IMPs could be designed for any crop-soil-management condition.
The irrigation scheduling model used in designing IMPs requires input of two parameters: crop evapotranspiration and allowable soil moisture depletion.
Once these are
 known, a water budget is used to determine irrigation dates and amounts.
The flow chart  illustrates the sequence followed by the computer program in designing an IMP.
A.
Estimating crop evapotranspiration.
ET is computed by using long-term pan evaporation data for either the Sacramento or the San Joaquin Valley.
Crop ET is calculated as:
 ETcrop = Epan Kp
 where Epan is the evaporation from a class A pan, and Kp is an experimentally or empirically determined crop coefficient that varies with time after planting.
In this program the Kp values for a given crop and planting date are fitted to a cubic spline function, which draws a smooth curve through the data points allowing for interpolation at any required time interval.
B.
Estimating allowable soil moisture
 depletion.
Allowable soil moisture depletion, AD, is estimated for any given time in the growing season as follows:
 AD = AW RD %AD
 where AW is the available water-holding capacity of the soil, RD is the rooting depth at the time of the estimate, and %AD is the percentage of available soil water that can be extracted from the root zone without reducing crop yield.
The AD level depends on plant factors , soil factors , and atmospheric factors.
The extensive body of literature and current knowledge of crop responses to water stress were used to select appropriate AD levels in designing the IMPs.
To estimate the extent of the root zone in an annual crop as it develops, a simple root growth model based on the functional balance between shoot and root growth was developed.
In this model, the rate of vertical root growth into the soil profile is assumed to be proportional to the rate of vegetative growth above the soil surface.
Using the crop coefficient, Kp, as a quantitative measure of vegetative growth, the change in root depth with time is correlated directly to the change in the crop coefficient with time.
Whenever the crop coefficient reaches a maximum , root depth, limited by either soil depth or the crop's growth characteristics, is also a maximum.
Although the root development model may be too simple to work under all situations, it provides a needed approximation in the absence of data on root development under field conditions.
Several management options may be included in the design of the IMPs.
Soil intake rate or system considerations may limit the
 depth of water that may be applied during a single irrigation, regardless of the storage capacity of the soil.
The program can be modified to impose irrigations at fixed time intervals under situations where water delivery to the farms is on a rotation cycle.
The need to supply the ET losses since last irrigation then becomes the main emphasis.
Test of the IMP
 A number of tests were carried out using the computer program to first design IMPs for a given year and then compare the predicted irrigation dates for that year with those obtained using the long-term average Epan data as input.
Four crops, four years, three locations, and several soil types in the Central Valley were used to compare actual with normal-year irrigation dates.
There was good agreement between predicted and actual irrigation dates calculated with current-year ET data.
Most of the discrepancies occur for the first irrigation where year-to-year variations in ET are generally greatest.
These tests support our hypothesis that long-term average ET may be safely used in designing the IMPs.
IMPs for many important crops of the Central Valley are now being developed based on different planting dates and a wide range of allowable soil-water depletion levels.
Leaflets containing the IMP and a simple form to update it will be made available.
The farmer, assisted by a farm advisor, Soil Conservation Service engineer, or consultant, will evaluate
 the water-holding capacity, crop rooting depth, and soil depth to select the appropriate IMP.
The IMP can then be adjusted to the farmer's method of irrigation and other cultural operations.
The IMP is a simplified, practical approach, which we are optimistic will receive much greater acceptance than past efforts to involve farmers in using technical data to schedule irrigations.
It isready-to-use, precalculated irrigation program that takes into account evaporative conditions, the crop and its stage of growth, and soil factors determining water availability.
By selecting the IMP developed for a particular crop and adjusting for the planting date and allowable depletion expected in the specific soils, the farmer can much more easily make technically sound irrigation decisions.
When evaporative conditions depart from the normal pattern, the IMP can be readily corrected to adjust the irrigation schedule or depth of water to be applied, or both.
Use of these IMPs will help meet the need to achieve a high level of efficiency in agricultural consumption of the state's limited water resources.
Elias Fereres is Irrigation and Surface Water Specialist, Cooperative Extension; Patricia M.
Kitlas is Research Assistant, Department of Land, Air, and Water Resources ; Richard E.
Goldfien is Post-Graduate Researcher, LAWR; William O.
Pruitt is Lecturer in Water Science and Agricultural Engineering and Irrigation Engineer, LAWR; and Robert M.
Hagan is Water Specialist, Cooperative Extension.
All are with the University of California, Davis.
For alfalfa, daily water use drops significantly in the fall to less than one-fourth-inch per day due to cooler days.
Overall, alfalfa requires six to seven inches per cutting for optimum production.
More Nebraska Extension fall crop irrigation publications are available on our website: NebGuide G1778 Irrigation Management and Crop Characteristics of Alfalfa and EC731 Producing Irrigated Winter Wheat.
For dry edible beans in the emergence crop growth stage the estimated water use during the previous week of May 29 June 4, 2023 is 0.07 inches and the estimated water use during the week of June 5-11, 2023 is 0.20 inches.
Developing a Farm Digital Strategy 2  Precision Technology and Data Generation
 John Fulton, Professor and Extension Specialist, Department of Food, Agricultural and Biological Engineering, Ohio State University
 Jenna Elleman, Integrated Solutions Consultant at Ag-Pro
 Elizabeth Hawkins, Field Specialist, Agriculture and Natural Resources, Ohio State University Extension
 Data is nothing new to agriculture and, specifically, farming operations.
Historically, hand-written notes have represented the data used by farmers to evaluate their operation and yield.
With the arrival of precision agriculture  in the early 1990s, however, farmers began using technology to collect site-specific, electronic data.
As PA technology has evolved, internet connectivity and cloud technology have enhanced the access and portability of data collected on farm machinery and through mobile applications.
Most farm machinery today comes from the manufacturer connected to the internet using telematics or wireless technologies, allowing data to be moved on and off machinery easily.
Furthermore, original equipment managers , agriculture technology providers , and retailers provide software platforms to store, visualize and analyze farm data.
Additionally, mobile applications  are widely used on farms.
This technological access allows farmers and their consultants to use data to support decisions within farm operations on a field-by-field basis.
Today, machines and other on-farm technologies can generate large volumes of data, coupled with cloud platforms that allow the data to be stored, accessed, visualized, and shared.
These advances make it necessary for farm operations to develop a digital strategy, which is important from legal and data usage perspectives.
This fact sheet, the second in a series of three  to look at digital strategies, details the information a farm needs to get started on developing its unique digital strategy.
The first steps for developing a digital strategy involve documentation:
 Identify the PA technologies  being used on the farm.
Identify the types and format of the data collected by these technologies.
Most, if not all, site-specific data files have geo-referenced points with attributes or variables that relate to field operations or characteristics of the field.
Most of these points have more information than can be visualized in one single map.
Elements collected at each point often include date/time, GPS location, application rate, elevation, ground speed, product, and more.
PA data can be placed in one of several types of data categories including agronomic, machine, prescription, remote sensed imagery, production, and others.
Figure 1 gives examples of the data that would be included in each category.
Figure 1.
Different types of precision ag data that can be collected at the farm.
Hand holding ear of corn broken in half	Colored map	Tractor pulling sprayer in field	Colorful digital representation of a field	Combine dumping corn in a cart in the field.
Developed by the Ohio State University Extension Digital Ag Team
 A digitized overhead map of a farm field that is mostly lime green , and gray in a few places.
Figure 2.
An example of agronomic data.
This map was generated from as-planted data and indicates the planted population of a cornfield.
Agronomic data represents data compiled at the field level that is related to agronomy-based information.
Types of this data include hybrid , planted population , yield, soil type, soil texture, soil fertility, pesticides applied, fertilizer applied, scouting information, and more.
Data generated from a yield monitor connected to a GNSS receiver can document yields spatially across a field.
As-applied and as-planted data represent agronomic data that can be collected during field operations.
Soils data can be used to support fertilizer and regional environmental compliance decisions.
Scouting data can be used to track pest and disease pressures and help make spraying decisions.
Many farm machines in use today collect crop and soil data in new and notable ways.
Sensors, imagery, and other technologies work collaboratively to provide farmers with details about soil nutrients, moisture, weeds, insects, sunlight, shade, and other factors.
When analyzed, the data can help farmers adjust their practices during the planting season, thus providing a more rewarding harvest.
Several agriculture companies provide services that collect data from farm machines and pair it with other data sets, such as weather, productivity potential, harvest yields and satellite imagery.
Soil moisture sensors, for example, can help farmers monitor the need for irrigation and, in some cases, automate the process.
These types of sensors allow companies to advise farmers on inputs, application rates and practices that can maximize yields and profits.
Recommendations are then provided to the farmer in the form of a prescription file for input into the machines display.
An overhead digitized map of a green farm field with red, yellow and lime green stripes across it.
The stripes represent machine and planting data.
Figure 3.
Illustration of ground speed  as an example of machine data during planting.
Machine data is compiled using multiple sensors and communication networks located on agricultural machinery.
Most of this data relates machine data to the information that can be collected from the controlled area network  on machines and implements.
These include fuel usage, engine RPM, engine load, ground speed, slip, gear selection, and much more.
Machine data can also indicate whether the autosteer is engaged, GPS location, machine heading, implement status, 3-point hitch status, and hydraulic pressure and flow rate.
Machine data can be an effective tool to evaluate operating costs and field capacity  when coupled with telemetry/wireless technology.
Figure 3 illustrates a map of ground speed as an example of machine data.
If you have a new tractor, combine, cotton picker or sprayer, machine data can most likely be collected, especially if using a telemetry option on the machine.
With the recent surge in drone use, imagery of fields has become relatively easy to collect.
Imagery gathered in the visible light spectrum can be used to view soil patterns, drainage patterns, subsurface tile locations, and more.
However, relying on visible imagery alone limits farmers to what they can see with the naked eye.
By also collecting light outside the visible spectrum, such as infrared, a new perspective on the field can be viewed and analyzed.
One of the more commonly used imagery examples in agriculture includes the normalized difference vegetation index.
NDVI is a numerical indicator that is useful for distinguishing vegetation from soil by recording the reflective light that falls on it.
One of the benefits of using imagery is the ability to develop variable rate prescription maps for seeding in the absence of a yield map.
Additionally, remote sensed imagery can help identify man-made variability, aid in the collection of data for on-farm research, provide yield estimates, and direct scouting activities.
Production data includes all other data, including farm data, notes, weather data, application dates, planting dates, etc.
Production data is useful to support and supplement other forms of digital agriculture.
Hurdles with Farm Data
 The data learning curve can be steep for farmers.
Two major issues include data compatibility and file formats, and both should be considered in a farms digital strategy.
Additional details are outlined below.
Data Compatibility Enables any data from any compatible data system to be simply integrated with the data from any other compatible data systems.
More simply, it allows data to read or be translated by any system.
File Formats A standard method for data to be stored in an electronic file.
File formats can be either proprietary or free, and either unpublished or open.
Metadata  A set of data that describes and gives information about other data.
File Elements  Elements  that make up an electronic file.
Simply, it is the information stored within the file
 A current focus within the digital agriculture community is achieving interoperability  the ability of a system or a product to work with other systems or products without special effort on the part of the user.
One example would be connecting the data stream between a Brand A tractor and a Brand B planter.
Many companies have their own proprietary standards and formatting for data.
Efforts should thus be focused on standardizing, formatting, and developing ways to transport information so it can be used to its fullest potential.
Currently, lack of interoperability is a major limiting factor for digital agriculture.
A variety of data formats are commonly used by companies.
Many are proprietary, requiring specialized software to view and use.
Proprietary formats  are used for storing and exchanging data between field machinery and farm management software but can be an obstacle to on-farm data use.
Some open-source file formats such as.txt,.shp, and.xml are available and can make it easier to use data stored in these formats.
But many commonly-used data formats are not interchangeable, making it a challenge to view and analyze data within ones software package.
The tables below list many of the common file formats that can be used for storing agricultural data.
The volume and variety of data that can be generated by farm machines and PA technologies for an individual field today is significant.
In fact, annual data can easily exceed one terabyte  per acre for farmers who have invested heavily in PA technologies and who use digital tools such as APPs and remote sensing.
It is therefore crucial for a farms digital strategy to outline the technologies that generate data.
Clearly identifying what data is being collected, while also understanding the file format in which it is being stored, is important.
Many technologies store data in a proprietary file format, requiring the use of either the companys software or a farm management software package to upload, read, and use the data.
Listing the types of data and file formats within a farms digital strategy helps make data usable and valuable to a farm.
Soil water monitoring data is easier to analyze once the crop has taken up water at the 16to 24-inch depth during the vegetative growth stage.
This drier zone can then be monitored with sensors to see if the area gets wetter or drier.
If it keeps getting drier, the irrigation system needs to keep running.
However, if it starts to get wetter, then stop irrigating for a few days.
Ideally, the drier zone should slowly expand deeper with the crop using most of the subsoil water by the time the crop matures.
For more information on this scheduling strategy, watch the Advanced Irrigation Scheduling Techniques video.
REDUCING THE COST OF PUMPING IRRIGATION WATER
 Energy Use in Irrigation
 Irrigation accounts for a large portion of the energy used in Nebraska agriculture.
Analysis of data from the 2003 USDA Farm and Ranch Irrigation Survey shows that the average energy use for irrigating crops in Nebraska was equivalent to about 300 million gallons of diesel fuel annually.
A number of irrigation wells have been installed since 2003, thus energy use today is even higher.
While use varies depending on annual precipitation, average yearly energy consumption is equivalent to about 40 gallons of diesel fuel per acre irrigated.
The cost to irrigate a field is determined by the amount of water pumped and the cost to apply a unit  of water.
Factors that determine pumping costs include those that are fixed for a given location  and those that producers can influence.
The four factors that producers can influence include: irrigation scheduling, application efficiency, efficiency of the pumping plant, and for center pivots the pumping pressure required for the system.
Pumping costs can be minimized by concentrating on these factors.
Figure 1.
Diagram of factors affecting irrigation pumping costs
 Irrigation scheduling can minimize the total volume of water applied to the field.
Demonstration projects in central Nebraska have indicated that 1.5-2.0 inches of water can be saved by monitoring soil water content and estimating crop water use rates.
The general idea is to maximize use of stored soil water and precipitation to minimize pumping.
Maximizing the efficiency of water application is a second way to conserve energy.
Water application efficiency is a comparison between the depth of water pumped and the depth stored in the soil where it is available to the crop.
Irrigation systems can lose water to evaporation in the air or directly off plant foliage.
Water is also lost at the soil surface as evaporation or runoff.
Excess irrigation and/or rainfall may also percolate through the crop root zone leading to deep percolation.
For center pivots, water application efficiency is based largely on the sprinkler package.
High pressure impact sprinklers direct water upward into the air and thus there is more opportunity for wind drift and in-air evaporation.
In addition, high pressure impact sprinklers apply water to foliage for 20-40 minutes longer than low pressure spray heads mounted on drop tubes.
The difference in application time results in less evaporation directly from the foliage for low pressure spray systems.
Caution should be used so that surface runoff does not result with a sprinkler package.
Good irrigation scheduling should minimize deep percolation.
Energy use can also be reduced by lowering the operating pressure of the irrigation system.
One must keep in mind that lowering the operating pressure will reduce pumping cost per acre-inch, but reducing the pressure almost always results in an increased water application rate for a center pivot.
The key is to ensure that the operating pressure is sufficient to eliminate the potential for surface runoff.
Field soil characteristics, surface roughness, slope and tillage combine to control how fast water can be applied to the soil surface before surface runoff occurs.
If water moves from the point of application, the savings in energy resulting from a reduction in operating pressure can be eliminated by the need to pump more water to ensure that all portions of the field receive at least the desired amount of water.
Finally, energy can be conserved by ensuring that the pumping plant is operating as efficiently as possible.
Efficient pumping plants require properly matched pumps, systems and power sources.
By keeping good records of the amount of water pumped and the energy used, you can calculate if extra money is being spent on pumping water and how much you can afford to spend to fix components that are responsible for increased costs.
This document describes a method to estimate the cost of pumping water and to compare the amount of energy used to that for a well maintained and designed pumping plant.
The results can help determine the feasibility of repairing the pumping plant.
The cost to pump irrigation water depends on the type of energy used to power the pumping unit.
Electricity and diesel fuel are used to power irrigation for about 75% of the land irrigated in Nebraska.
Propane and natural gas are used on about 8 and 17% of the land respectively.
Very little land is irrigated with gasoline powered engines.
The cost to pump an acre-inch of water depends on:
 The amount of work that can be expected from a unit of energy.
The distance water is lifted from the groundwater aquifer or surface water.
The discharge pressure at the pump,
 The efficiency of the pumping plant, and
 The cost of a unit of energy.
Figure 2.
Percent of land irrigated in Nebraska by type of energy source.
The amount of work produced per unit of energy depends on the source used to power the pump.
For example one gallon of diesel fuel provides about 139,000 BTUs while propane provides about 95,500 BTUs/gallon.
Clearly, more propane would be required to pump an acreinch of water even if diesel and propane engines were equally efficient.
The Nebraska Pumping Plant Performance Criteria was developed to provide an estimate of the amount of work that can be obtained from a unit of energy by a well designed and managed pumping plant.
Values were developed from testing engines and motors to determine how much work (expressed as
 water horsepower hours) could be expected from a unit of energy for pumping plants that were well designed and maintained.
The values reflect the amount of energy available per unit and how efficiently engines, motors and pumps operate.
Table 1.
Amount of work produced per unit of energy used for a well designed and maintained pumping plant.
Source	Value	Work Per Unit of Energy
 Diesel	12.5	whp-hours / gallon
 Gasoline	8.66	whp-hours / gallon
 Propane	6.89	whp-hours / gallon
 Natural Gas	61.7	whp-hours / 1000 ft 3
 Electricity	0.885	whp-hours / kilowatt hour
 whp stands for water horsepower
 Figure 3.
Diagram of pumping lift and discharge pressure measurements needed to assess pumping plant efficiency.
The discharge pressure depends on the pressure needed for the irrigation system, the elevation of the inlet to the irrigation system relative to the pump discharge, and the pressure loss due to friction in the piping between the pump and the irrigation system.
It is best to measure the discharge pressure with a good gage near the pump base.
The amount of energy required for a properly designed and maintained pumping plant to pump an acre-inch of water can be determined from Tables 2 and 3.
For example, a producer who has a system with a pumping lift of 150 feet and
 Table 2.
Gallons of diesel fuel required to pump an acre-inch at a pump performance rating of 100%.
Lift	Pressure at Pump Discharge, psi
 feet	10	20	30	40	50	60	80
 0	0.21	0.42	0.63	0.84	1.05	1.26	1.69
 25	0.44	0.65	0.86	1.07	1.28	1.49	1.91
 50	0.67	0.88	1.09	1.30	1.51	1.72	2.14
 75	0.89	1.11	1.32	1.53	1.74	1.95	2.37
 100	1.12	1.33	1.54	1.75	1.97	2.18	2.60
 125	1.35	1.56	1.77	1.98	2.19	2.40	2.83
 150	1.58	1.79	2.00	2.21	2.42	2.63	3.05
 200	2.03	2.25	2.46	2.67	2.88	3.09	3.51
 250	2.49	2.70	2.91	3.12	3.33	3.54	3.97
 300	2.95	3.16	3.37	3.58	3.79	4.00	4.42
 350	3.40	3.61	3.82	4.03	4.25	4.46	4.88
 400	3.86	4.07	4.28	4.49	4.70	4.91	5.33
 Table 3.
Conversions for other energy sources.
Energy Source	Units	Multiplier
 Natural Gas	1000 cubic feet	0.2026
 Table 4.
Multiplier when pumping plant
 performance rating is less than 100%.
Rating, %	100	90	80	70	50	30
 Multiplier	1.00	1.11	1.25	1.43	2.00	3.33
 operates at a pump discharge pressure of 60 pounds per square inch  would require 2.63 gallons of diesel fuel to apply an acre-inch of water.
If the producer uses electricity the value of 2.63 should be multiplied by the factor in Table 3 to convert energy units.
So,  = 37 kilowatthours would be needed per acre inch of water.
The amount of energy required for an actual pump depends on the efficiency of the pump and power unit.
If the pumping plant is not properly maintained and operated, or if conditions have changed since the system was installed, the pumping plant may not operate as efficiently as listed in Table 2.
The energy needed for an actual system is accounted for in the performance rating of the pumping plant.
Table 4 can be used to determine the impact of a performance rating less than 100%.
For a performance rating of 80% the multiplier is 1.25, so the amount of energy used would be 25% more than for a system operating as shown in Table 2.
The amount of diesel fuel for the previous example would be  = 3.29 gallons per acreinch of water.
Producers can use Tables 2-4 and their energy records to estimate the performance rating of the pumping plant and the amount of energy that could be saved if the pumping plant was repaired or if operation was adjusted to better match characteristics of the pump and power unit.
Producers can also use hourly performance to estimate how well their pumping plant is working.
For the hourly assessment an estimate of the pumping lift, discharge pressure, flow rate from the well and the hourly rate of energy consumption are required.
The acre-inches of water pumped per hour can be determined from in Table 5.
Table 5.
Volume of water pumped per hour.
Pump	per hour,	Pump	per hour,
 Discharge,	acre-	Discharge,	acre-
 gpm	inch/hr	gpm	inch/hr
 250	0.55	1250	2.76
 300	0.66	1300	2.87
 350	0.77	1350	2.98
 400	0.88	1400	3.09
 450	0.99	1500	3.31
 500	1.10	1600	3.54
 550	1.22	1700	3.76
 600	1.33	1800	3.98
 650	1.44	1900	4.20
 700	1.55	2000	4.42
 750	1.66	2100	4.64
 800	1.77	2200	4.86
 850	1.88	2400	5.30
 900	1.99	2600	5.75
 950	2.10	2800	6.19
 1000	2.21	3000	6.63
 1050	2.32	3200	7.07
 1100	2.43	3400	7.51
 1150	2.54	3600	7.96
 1200	2.65	3800	8.40
 100 Value from Table 2 100 x 2.63 R = Pp
 The performance of the pumping plant  in terms of energy use per acre-inch of water is then the ratio of the amount of energy used per hour divided by the volume of water pumped per hour:
 For this case the performance rating is 85 meaning that the system uses about 17% more diesel fuel than required for a system at the Nebraska Criteria.
The
 fueluserate  Pp= V, W 
 For example, suppose a pump supplies 800 gallons per minute and the diesel engine burns 5.5 gallons of diesel fuel per hour.
A flow rate of 800 gpm is equivalent to 1.77 acre-inches per hour.
The pumping plant performance is computed as 5.5 gallons of diesel per hour divided by 1.77 acreinches of water per hour.
This gives a performance of 3.11 gallons of diesel per acre-inch.
Suppose that the pumping lift is 150 feet and the discharge pressure is 60 psi.
If the system operates at the Nebraska Pumping Plant Performance Criteria only 2.63 gallons of diesel per acre-inch would be required.
The pumping plant performance rating  would be:
 multipliers in Table 2 can also be used with the hourly method for other energy sources.
Energy savings from repairing the pumping plant should be compared to the ability to pay for the repairs.
The money that can be paid for repairs is determined by the length of the repayment period and the annual interest rate.
These values are used to compute the series present worth factor.
The
 Table 6.
Series Present Worth Factor
 6%	7%	8%	9%	10%	12%
 3	2.67	2.62	2.58	2.53	2.49	2.40
 4	3.47	3.39	3.31	3.24	3.17	3.04
 5	4.21	4.10	3.99	3.89	3.79	3.60
 6	4.92	4.77	4.62	4.49	4.36	4.11
 7	5.58	5.39	5.21	5.03	4.87	4.56
 8	6.21	5.97	5.75	5.53	5.33	4.97
 9	6.80	6.52	6.25	6.00	5.76	5.33
 10	7.36	7.02	6.71	6.42	6.14	5.65
 12	8.38	7.94	7.54	7.16	6.81	6.19
 15	9.71	9.11	8.56	8.06	7.61	6.81
 20	11.47	10.59	9.82	9.13	8.51	7.47
 25	12.78	11.65	10.67	9.82	9.08	7.84
 breakeven investment that could be spent is the value of the annual energy savings times the series present worth factor.
The series present worth factor represents the amount of money that could be repaid at the specified interest rate over the repayment period.
For example, for an interest rate of 7% and a repayment period of 10 years each dollar of annual savings is equivalent to $7.02 today.
Only $4.10 could be invested for each dollar of savings if the investment was to be repaid in 5 years rather than 10 years.
Some examples will illustrate the procedure to estimate potential from improving a pumping plant.
Suppose a pivot was used on 130 acres to apply 13.5 inches of water.
The pumping lift was about 125 feet and the discharge pressure was 50 psi.
Energy use records for the past season show that 5500 gallons of diesel fuel were used.
The average price of diesel fuel for the season was $3.00 per gallon.
The analysis of this example is illustrated in the worksheet in Figure 4.
An efficient pumping plant would require about 3843 gallons of diesel fuel for the year.
If a
 producer's records show that 5500 gallons were used to pump the water, then the performance rating would be  X 100 = 70%.
This shows that 1657 gallons of diesel fuel could be saved if the pumping plant performance was improved.
The annual savings in pumping costs would be the product of the energy savings times the cost of diesel fuel; i.e., $3/gallon times 1657 gallons/year = $4971/year.
If a 5-year repayment period and 9% interest were used, the series present worth factor would be 3.89.
The breakeven repair cost would be $4971 X 3.89 = $19,337.
If repair costs were less than $19,337 then repairs would be feasible.
If costs were more than $19,337 the repairs may not be advisable at this time.
This example represents a center-pivot field irrigated with a pump powered by electricity.
Details of the system are also included in Figure 4.
In this case the pumping lift is 175 feet which is not listed in Table 2.
The lift of 175 feet is half way between 150 and 200 feet so the amount of diesel fuel per acre-inch of water is estimated as 2.44 gallons per acre-inch.
Since electricity is used to power the pumping plant the multiplier of 14.12 is used in row M of Figure 4.
The calculations for the second example are similar to the first example for the rest of the information in Figure 4.
This pumping plant has a performance rating of 88% and given the cost of electricity only about $3,770 could be spent for repairs.
This example illustrates the application of the hourly method for a propane powered pumping plant.
This system has a performance rating of 88% and based on Table 4 13% of the annual energy cost could be saved if the pumping plant was brought up to the Nebraska Criteria.
This publication demonstrates a method to estimate the potential for repairing pumping plants to perform at the Nebraska Pumping Plant Performance Criteria.
Producers frequently have several questions regarding the procedure.
First they want to know "Can actual pumping plants perform at a level equal to the Criteria".
Tests of 165 pumping plants in the 1980s indicated that up to 15% of the systems actually performed at a level above the Criteria.
So producers can certainly achieve the standard.
The second question is "What level of performance can producers expect for their systems?" Tests on 165 systems in Nebraska during the 1980s produced an average performance rating of 77% which translates to an average energy savings of 30% by improving performance.
Tests on 200 systems in North
 Dakota in 2000 produced very similar results.
These values illustrate that half of the systems in the Great Plains could be using much more energy than required.
The simplified method can help determine if your system is inefficient.
The third issue focuses on "What should I do if the simplified method suggests that there is room for improving the efficiency?" You should first determine if the irrigation system is being operated as intended.
You need to know if the pressure, lift and flow rate are appropriate for the irrigation system.
For example, some systems were initially designed for furrow irrigation systems and are now used for center-pivot systems.
If the conditions for the current system are not appropriate for the system you need to work with a well driller/pump supplier to evaluate the design of the system.
Sometimes the system is simply not operated properly.
An example occurred where a center-pivot sprinkler package was installed that used pressure regulators with a pressure rating of 25 psi.
However, the end gun on the pivot was not equipped with a booster pump so the main pump was operated at a pressure of 75 psi to pressurize the entire system just to meet the needs of the end gun.
Since end guns only operate about half of the time the pump was actually pumping against the pressure regulators half of the time, wasting a significant amount of energy.
The problem here was not the pump or the power unit but the sprinkler design and its operation.
We recommend that you periodically arrange with a well drilling company to test the efficiency of your pump.
They conduct a test that determines pumping lift, discharge pressure and the efficiency of the pump for a range of conditions that you would expect for your system.
They also use equipment to measure the power output of your engine or electric motor.
While they don't usually measure the energy consumption rate the results of the test will tell you if the pump is performing efficiently.
This provides an excellent reference for future analysis.
Hourly	Propane	Example	250	55	130	Propane	$1.80	3.44	1.814	700	1.55	9.65	11.0	88
 Annual	Electric	Example	175	40	128	13	65,000	Electric	$0.07	7	10	2.44	1664	4060	14.12	57,327	88	7673	$537	7.02	$3,770
 Annual	Diesel	Example	125	50	130	13.5	5500	Diesel	$3.00	9	5	2.19	1755	3843	1	3843	70	1657	$4,971	3.89	$19,337
 Figure Worksheet Pumping Cost 4.
Information Known 1.
lift, feet Pumping	discharge, Pressure psi at pump	field, Size irrigated of the acres	inches of irrigation applied, Depth	field of for irrigate used the the Amount to energy year	of Type used to water energy pump source	of $/kwh,  energy a	interest % Annual rate,	period, Repayment years	Performance 2.
Annual	of fuel  Table @ acre-inch to pump an	 Volume of pumped, acre-inches: C water X row row	K) Performance Gallons of fuel Rating diesel  for  100% used rating Energy at pump	 Performance rating pump	 Potential kWh, with gallons, savings repair, etc.: energy	$  savings, Annual cost	factor Series  worth present	R) , acre-inches/hour hour pumped water per	 if Performance Rating Energy hour 100% at use per	kWh/hr) feet/hr, 1000 cubic  performance Pumping plant rating
 A	B	C	D	E	F	G	H	I	J	K	L	M	N	o	P	Q	R	S	T	U	V	W	X
Tiffany Maughan, Dan Drost, and L.
Niel Allen
 Proper irrigation is critical for onion production.
Optimal irrigation management leads to steady plant growth, uniform bulb size, maximum yields, and superior bulb quality.
Under-irrigation results in a reduction of yield, single centeredness, and quality.
However, overirrigation increases disease susceptibility, nutrient leaching, and inefficient water use.
For ideal bulb development, a consistent moisture supply throughout the season is necessary.
Onions are extremely sensitive to water stress with the most critical time being during bulb swelling.
Different irrigation methods are commonly used to irrigate onions, each with different management considerations.
Historically, furrow irrigation was the method of choice.
Furrow irrigation results in large fluctuations in soil moisture, nutrient leaching, and low water use efficiency.
Drip irrigation is becoming more widely used to grow onions.
The advantages of drip include better fertilizer management, reduced water use, improved pest and weed control, and increased onion bulb size, uniformity, and marketable yield.
Regardless of the irrigation system used, there are some basic principles to understand that will help ensure proper irrigation.
This fact sheet will discuss these basic principles.
Drip irrigation being used for onions.
Properly managing irrigation is analogous to managing money.
In addition to knowing your current bank balance , it is important to track both expenses  and income.
Bank Balance 
 How big is my bank account?
Water holding capacity First, some terminology:
 Field Capacity is the amount of water that can be held in the soil after excess water has percolated out due to gravity.
Permanent Wilting Point is the point at which the water remaining in the soil is not available for uptake by plant roots.
When the soil water content reaches this point, plants die.
Available Water is the amount of water held in the soil between field capacity and permanent wilting point.
Allowable Depletion  is the point where plants begin to experience drought stress.
Depending on soil type, the amount of allowable depletion for onions is about 25 to 30% of the total available water in the soil.
The goal of a well-managed irrigation program is to maintain soil moisture between field capacity and the point of allowable depletion, or in other words, to make sure that there is always readily available water and that plants do not experience water stress.
The amount of readily available water is related to the effective rooting depth of the plant, and the water holding capacity of the soil.
The effective rooting depth depends on soil conditions and variety, but in general onions are a shallow-rooted crop.
About 70% of onion roots are in the top foot of soil, with 25% in the second foot and some roots extending deeper.
The water holding capacity within that rooting depth is related to soil
 texture, with coarser soils  holding less water than fine textured soils such as silts and clays.
A deep sandy loam soil at field capacity, i.e., would contain 0.6 to 0.75 inch of readily available water in an effective rooting depth of 1 foot.
Figure 1.
Soil water content from saturated to dry.
Optimal soil moisture levels for plant growth are between field capacity and allowable depletion.
What's in the bank?
-Measuring Soil Moisture
 In order to assess soil water content, one needs to monitor soil moisture.
Monitors should be placed in the primary root zone.
One of the
 most cost effective and reliable methods for measuring soil moisture is by electrical resistance block, such as the Watermark TM sensor.
These blocks are permanently installed in the soil, and wires from the sensors are attached to a handheld unit that measures electrical resistance.
Resistance measurements are then related to soil water potential, which is an indicator of how hard the plant roots have to "pull" to obtain water from the soil.
Figure 2.
For onion, the amount of allowable depletion, or the readily available water, represents about 25 percent of the total available water.
Table 1.
Available water holding capacity for different soil textures, in inches of water per foot of soil.
Total available water is the amount of water in the soil between field capacity and permanent wilting point.
Allowable depletion  is the amount of water the plant can use from the total available before experiencing drought stress.
Allowable depletion for onion is approximately 25% of total available.
inch/foot	In top1'	In top 1.5'
 Sands and fine sands	0.5 0.75	0.13	0.19	0.19	0.29
 Loamy sand	0.8 1.0	0.2	0.25	0.30	0.38
 Sandy loam	1.2 1.5	0.3	0.38	0.45	0.57
 Loam	1.9 2.0	0.48	0.5	0.72	0.75
 Silt loam, silt	2.0 2.1	0.5	0.53	0.75	0.79
 Silty clay loam	1.9 2.0	0.48	0.5	0.72	0.75
 Sandy clay loam, clay loam	1.7 2.0	0.43	0.5	0.65	0.75
 The handheld unit reports soil moisture content in centibars, where values close to zero indicate a wet soil and high values represent dry soil.
The relationship between soil water potential and available water differs by soil type.
The range of the sensor is calibrated to 0 to 200 centibars , which covers the range of allowable depletion in most soils.
The sensors are less effective in coarse sandy soils, and will overestimate soil water potential in saline soils.
Remember that allowable depletion is about 25 to 30% of available water, which roughly corresponds to soil water potentials of 14 centibars for a loamy sand soil, and 20 centibars for a silt loam.
Table 2.
Recommended WatermarkTM sensor values at which to irrigate.
Soil Type	Irrigation Needed
 Silt loam, silt	20-22
 Clay loam or clay	22-24
 TMWatermark is a registered trademark of Irrometer, Co., Riverside, CA.
Table 3.
Daily total reference evapotranspiration  for six Utah cities expressed in  inches per day,  gallons per acre per day, and  drip-irrigated gallons per 100 feet per day.
Month	Tremonton	Corinne	Brigham City	Ogden	Layton	Farmington
  Inches per day
 Mar	0.11	0.11	0.10	0.10	0.11	0.11
 Apr	0.16	0.18	0.16	0.17	0.17	0.17
 May	0.22	0.24	0.22	0.22	0.22	0.22
 Jun	0.28	0.30	0.27	0.28	0.28	0.28
 Jul	0.34	0.33	0.32	0.32	0.31	0.31
 Aug	0.29	0.29	0.28	0.29	0.29	0.28
 Sep	0.22	0.21	0.20	0.20	0.20	0.20
 Oct	0.13	0.11	0.12	0.12	0.12	0.12
  Gallons per acre per day.
Irrigation amounts need to be adjusted by Crop Coefficient and Irrigation
 Mar	2987	2987	2716	2716	2987	2987
 Apr	4345	4888	4345	4617	4617	4617
 May	5974	6517	5974	5974	5974	5974
 Jun	7604	8147	7332	7604	7604	7604
 Jul	9233	8961	8690	8690	8418	8418
 Aug	7875	7875	7604	7875	7875	7604
 Sep	5974	5703	5431	5431	5431	5431
 Oct	3530	2987	3259	3259	3259	3259
  Drip-irrigated gallons per 100 feet of bed length per day based on 3.25 foot bed spacing.
Irrigation
 amounts need to be adjusted by Crop Coefficient and Irrigation Efficiency.2	2
 Mar	22.3	22.3	20.3	20.3	22.3	22.3
 Apr	32.4	36.5	32.4	34.4	34.4	34.4
 May	44.6	48.6	44.6	44.6	44.6	44.6
 Jun	56.7	60.8	54.7	56.7	56.7	56.7
 Jul	68.9	66.9	64.8	64.8	62.8	62.8
 Aug	58.8	58.8	56.7	58.8	58.8	56.7
 Sep	44.6	42.5	40.5	40.5	40.5	40.5
 Oct	26.3	22.3	24.3	24.3	24.3	24.3
 Conversion to gallons per acre per day  =  X 7.481 * 43560 / 12.
2Calculation for drip-irrigation:  =  X 3.25 ft.
/ 435.6.
If different bed spacing is used, adjust calculation accordingly.
Table 4.
Description of stages of growth and crop coefficient estimates for onion crops.
Growth Stage Indicator 1
 12-13	1.5 inch	Last
 Planting	Emergence	leaves	bulb size	Irrigation	Lifting
 Crop coefficient	0.3	0.5	1.0	1.0	1.0	0.5
 1 From AgriMet Cooperative Agricultural Weather Network with alfalfa as the reference crop
 Some weather stations in Utah are programmed to calculate and report the ET estimates for alfalfa as a reference crop  that is specific to your crop and its stage of development.
Note: Some publications use ET which is a grass reference ET instead of ETr.
ET uses a different set of Kcrop values.
You can multiply ET by 1.25 to get a good estimate of ETr.
ETcop = ET, x Kerop
 The Kcrop for onions are shown in Table 4.
The Kcrop varies depending on current growth stage.
Water use increases gradually as the crop develops until the full canopy is established.
For onions, irrigation is stopped a few weeks before harvesting to allow curing and improve storability.
Income Irrigation and Rainfall
 In Utah's high elevation desert climate, rainfall only contributes a small fraction of the in-season water requirements of the crop.
Therefore, regular irrigation is needed to supply plant water needs.
Onion irrigation is supplied by furrow or drip irrigation.
Furrow irrigation has historically been used to irrigate onion crops in Utah and the infrastructure for flood irrigating is already in place.
However, in areas prone to water shortages, furrow irrigation may be a poor choice due to lower efficiency.
Onions are commonly furrow irrigated once per week with irrigation sets of 12 hours or more.
Drip irrigation is expensive to install.
However, with the potential water savings, combined with advantages of water uniformity and fertilizer applications many growers have been able to justify the material costs.
Whichever irrigation system you utilize, it is important to know precisely how much water is being applied.
Drip irrigation tape comes with recommended operating pressures, a variety of emitter spacings, and various flow rates.
Most drip tapes operate at 10 psi.
Emitters may be spaced from 4 to 36 inches apart and come in a variety of flow rates.
Flow rates are commonly reported in gallons per100 feet of tape per hour  or gallons/emitter/hr.
For a tape with a 12-inch emitter
 spacing , 24 gallons/100ft/hr = 24/100 = 0.24 gallons/emitter/hr.
Pressure compensating emitters  provide the best uniformity.
Flow rate from each emitter and emitter spacing can be used to calculate rate per area.
Drip irrigation systems are usually operated every day or every few days to maintain optimal soil moisture.
The uniformity of your system is a measure of how much you have to over-water the wetter areas in the field to get adequate water to the drier areas.
Efficiency is related to the uniformity of application, scheduling of irrigations, and the amount of evaporation from the soil.
A well-designed drip system can be 90 to even 95% efficient, while furrow irrigation of onion is typically about 50% efficient due to difficulty of applying frequent light irrigations.
If your water supply is limited, a more efficient system can make a large difference in water savings and crop productivity.
Following is an example of how to calculate water needs for an onion crop in August with a full canopy in Corinne, Utah.
The soil is a loam with drip irrigated rows every 3.25 feet.
o Water use 
 ETr values are 0.29 inches per day.
Crop coefficient is 1.0.
ETcro = ETr X Kcrop
 = 0.29 inches/day * 1.0 = 0.29 inches/day
 Soil storage capacity 
 The total storage capacity for readily available water over the 1.5-foot effective rooting depth is 0.7 inches.
0.7 inches / 0.29 inches per day = 2.4  days between irrigations.
In 2 days replace 0.58 inches.
Restated, the soil moisture in the root zone will go from field capacity to plant stress levels in 2.4 days.
To recharge the soil profile, you will need to add a net of 0.58 inches of water every 2 days.
Assuming a drip irrigation system with an efficiency of 90%, 0.64 inches of water application will be required for each watering.
If you are operating your drip system
 Good irrigation management requires:
 1.
An understanding of the soil-plant-water relationship
 2.
A properly designed and maintained irrigation system, and a knowledge of the efficiency of the system
 3.
Proper timing based on
 a.
Soil water holding capacity
 b.
Weather and its effects on crop demand
 C.
Stage of crop growth.
Each of these components requires a commitment to proper management.
Proper management will lead to the maximum yields per applied irrigation water, and will optimize the long term health and productivity of your crop.
Surface Irrigation  Inches/hour = cubic feet per second  / acres Example: 4 cfs/ 5 acres = 0.8 inches/hour
 Drip Irrigation  Inches/hour=1.6 *gallons per hour /emitter spacing  Example: 1.6*0.5 gph /  = 0.25 inches/hour
 Irrigation Set Times Set time  = Gross Irrigation Need  / application rate  Example: 3 inches / 0.28 inches/hour = 10.7 hours
 Conversions 1 cfs= 448.8 gpm 1 gpm 60 gph 1 acre = 43,560 feet2 
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In about 50% of the field sites studied the best pressure sensor location was near Tower 8.
For 20% of the systems the best place was near Tower 7 and for 15%, it was near Tower 6.
Results point strongly to evaluating each center pivot installation separately to determine where the sensor should be placed on the center pivot.
Although irrigation has had an impact on water resources, it has also improved how effectively water is used to produce a crop.
The article defines crop water productivity  as the crop yield divided by the seasonal crop water use.
In general, irrigated crops in the Great Plains have a CWP approximately double that of crops grown with rainfall alone because of crop water stress between rains or the crop running out of water before maturity.
Tensiometers for Soil Moisture Measurement and Irrigation Scheduling 1
 Allen G.
Smajstrla and Dalton S.
Harrison 2
 Tensiometers are instruments that are used to measure the energy status  of soil water.
That measurement is a very useful one because it is directly related to the ability of plants to extract water from soil.
Irrigators often use tensiometers for irrigation scheduling because they provide direct measurements of soil moisture status and they are easily managed.
In addition, tensiometers can be automated to control irrigation water applications when the soil water potential decreases to a predetermined critical value.
A tensiometer consists of a porous cup, connected through a rigid body tube to a vacuum gauge, with all components filled with water.
The porous cup is normally constructed of ceramic because of its structural strength as well as permeability to water flow.
The body tube is normally transparent SO that water within the tensiometer can easily be seen.
A Bourdon tube vacuum gauge is commonly used for water potential measurements.
The vacuum gauge can be equipped with a magnetic switch for automatic irrigation control.
A mercury
 manometer can also be used for greater accuracy, or a pressure transducer can be used to automatically and continuously record tensiometer readings.
Figure 1 illustrates the components of one model of a commercially available tensiometer using a vacuum gauge.
Tensiometer cost depends on its length, or the depth at which it will be installed.
In general, prices of standard, manually-read instruments range from about $60 each for the 6-inch size to about $75 for the 4-ft size.
Automatic switching tensiometers cost about $30 more.
Vacuum gauge tensiometers are manufactured by several companies and are available at most irrigation supply businesses.
2.
Allen G.
Smajstrla and Dalton S.
Harrison, Professor and Professor emeritus, respectively, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.
Tensiometers are placed in the field with the ceramic cup firmly in contact with the soil in the plant root zone.
The ceramic cup is porous SO that water can move through it to equilibrate with the soil water.
A partial vacuum is created as water moves from the sealed tensiometer tube.
The vacuum causes a reading on the vacuum gauge which is a direct indication of the attractive forces between the water and soil particles.
This reading is a measure of the energy that would need to be exerted by the plant to extract water from the soil.
Because the porous ceramic cup is permeable to both water and dissolved salts, tensiometers do not record the water potential due to dissolved salts.
The actual total potential that plants would need to overcome to extract water from soils includes the osmotic potential.
If soils are saline, or if poor quality irrigation water is being used, the osmotic potential will be a large portion of the total potential.
In those cases, osmotic potential should also be measured using soil salinity sensors.
As the soil dries, water potential decreases  and the tensiometer vacuum gauge reading increases.
Conversely, an increase in soil water content  decreases tension and lowers the vacuum gauge reading.
In this way, a tensiometer continuously records fluctuations in soil water potential under field conditions.
Rapid and accurate tensiometer response will occur only if air does not enter the water column.
Air expands and contracts with changes in pressure and temperature, thus causing inaccurate tensiometer readings.
Even if instruments do not have leaks, dissolved air enters with water flow through the ceramic cup during normal operation of the instrument.
When a significant amount of air enters the instrument, it must be expelled and the tensiometer refilled with water before it will operate reliably again.
The tensiometer measures water potential or tension.
Water potential is commonly measured in units of bars  or kilopascals.
One bar is approximately equal to one atmosphere (14.7 lb/in 2 of pressure.
One centibar is equal to one kilopascal.
Because water is held by capillary forces within unsaturated soil pore spaces, its water potential is negative, indicating that the water is under tension and that work must be done to extract water from the soil.
A water potential reading of 0 indicates that the soil is saturated, and plant roots may suffer from lack of oxygen.
As the soil dries, water becomes less available and the water potential becomes more negative.
The negative sign is usually omitted for convenience when soil water potentials are measured with tensiometers.
The negative sign will be omitted in this publication, and readings will be reported as soil water tensions.
Figure 2 The gage illustrates the dial face of a typical tensiometer vacuum gauge.
Divisions are in units of centibars , with a range of 0-100 cb.
Recently, one company began to manufacture a "Florida" tensiometer with a range of 0-40 cb.
The expanded scale in this range is ideal for irrigation scheduling in typical Florida sandy soils.
Because of the vaporization of water at low pressure, the range of operation of a tensiometer is limited to 0 to about 85 cb.
Above 85 cb the column of water in the plexiglass tube will form water vapor bubbles , and the instrument will cease to function.
This range represents only a fraction of the water tension range that is normally considered to be available for plant growth.
Many plants can survive to a water tension of 15 bars.
However, plant growth and productivity cease well before this point.
In sandy soils, tensiometers measure the entire range of soil water tension of interest for irrigation.
Thus, the tensiometer is an excellent instrument for irrigation management in Florida.
Research has shown that to optimize production, irrigation should be scheduled when soil water tension reaches 10-20 cb in sandy soils.
The exact values to be used depend on soil hydraulic properties, crop suscept-ibility, and production objectives.
These water tensions are well within the tensiometer range of application.
Tensiometers measure soil water tension in only a small volume of soil immediately surrounding the ceramic cup.
Therefore, the ceramic cup must be placed in the active root zone of the crop for which irrigations are being scheduled.
Depending upon crop type, two or more tensiometers may be required at a measurement site.
Figs.
3 and 4 illustrate proper depths of installation for row crops and tree crops, respectively.
Because of differences in soil and plant characteristics, several measurement sites may be required to adequately assess the water status of large areas.
For more valuable or more sensitive crops, more tensiometers should be used.
For uniform soil types fewer tensiometers may be adequate.
The sites selected for installation should be representative of the surrounding field conditions.
Isolated low, wet areas or high, dry areas should be avoided.
Tensiometers should be placed within the plant canopy in positions where they will receive typical amounts of rainfall and irrigation.
Placement
 of tensiometers with depth is critical.
For shallow-rooted  crops such as some vegetables, only one tensiometer may be required with depth.
It should be centered in the crop root zone, but at least 4-6 inches below the surface.
The ceramic cup should not be exposed to the atmosphere.
For crops with deeper root zones such as most field crops, two tensiometers should be used at each measurement site.
The shallower one should be placed in the zone of maximum root concentration.
This is normally at 6 inches or about one-third of the active rooting depth.
In tree crops, depths of 6 to 24 inches are often used.
Other depth combinations may be used where appropriate.
When multiple instruments are used, most irrigations will be scheduled to replenish the upper part of the root zone monitored with the shallow instrument.
The deeper instrument will indicate when less frequent larger irrigations are needed to replenish the entire root zone.
The tensiometer can be a useful instrument for irrigation scheduling only if it is properly installed.
In general, proper installation requires that the instruments be in good hydraulic contact with the surrounding soil SO that water can move into and away from them as efficiently as possible.
In addition, tensiometers must be properly located in the crop root zone as discussed in the previous section on site selection.
Before field installation, each tensiometer should be tested to verify that it is operating properly.
Fill each tensiometer with clean water  and allow it to stand in a vertical position for at least 30 minutes SO that the ceramic tip will saturate.
A plastic squeeze bottle and small diameter plastic tube can be used to fill the tube from the bottom to help eliminate air bubbles.
When its tip is thoroughly wetted, it can be refilled and capped.
The tensiometer will not be serviceable immediately because of air bubbles in the vacuum gauge.
A small hand vacuum pump , obtainable from tensiometer manufacturers, can be used to remove air bubbles and
 test for air leaks.
This service will be necessary before installation as well as periodically in the field.
Tensiometers are installed in previously cored holes in the field.
Manufacturers sell coring tools of the proper dimensions for tensiometer installation.
In sandy soils, the access holes can be cored by hand, while on heavier
 soils it may be necessary to use a hammer to aid the installation.
If commercially available coring tools are not available, a length of standard water pipe or other tubing of the proper diameter can be used with acceptable results.
It is critical, regardless of the installation method used that the ceramic cup be in intimate contact with soil in order for the tensiometer to function properly.
If a rock or other obstacle is encountered, the tensiometer should be moved to another location to avoid possible damage when it is placed in the cored hole.
The tensiometer should not be driven into place with a hammer or other object.
Although adequate for normal use, the mechanical strength of the ceramic cup is not adequate to allow it to be hammered into place.
In very loose cultivated soils, such as frequently encountered in commercial row crop production, it is possible to push shallow tensiometers into place without coring a hole.
This method of installation is acceptable when applicable.
Again, the surface soil must be firmly packed around the instrument after installation.
After installation, several hours may be required before the tensiometer reads the correct soil water potential value.
This is because of the disturbance to the soil caused by the installation procedure, and because of the need for water to move through the ceramic cup before equilibrium is reached.
The correct reading will be reached more quickly in moist soils than in dry soils.
After this initial equilibrium period, the tensiometer will accurately indicate the soil water tension, and it will closely follow changes in tension as they occur in the soil.
Tensiometers are delicate instruments and should be protected from harm both before and after installation.
They should be handled carefully and protected from impact by equipment or animals in the field.
Also freezing conditions will damage
 tensiometers.
They should not be left filled with water during freezing conditions.
To operate properly, tensiometers must be serviced in the field periodically.
This is because with normal use, air is extracted from water under tension.
The air becomes trapped within the tensiometer and reduces response time progressively until the instrument fails to operate.
If the soil in which the tensiometer has been installed is moist, soil tensions will be low and very little air will accumulate.
If, however, the tensiometer is installed in drier soils, with water potentials in the range of 40 to 60 cb, air will accumulate more quickly.
The body tube should be inspected for accumulated air each time the tensiometer is read.
If over 1/4 inch of air has accumulated beneath the service cap, the cap should be removed and the tube refilled with water as shown in Figure 9
 In wet soils, the tensiometer will probably need to be serviced approximately every 2 weeks.
In dry soils, servicing may need to be more frequent, perhaps as often as every time the tensiometer data is collected.
Tensiometer measurements are useful in deciding when to irrigate because they give a continuous indication of soil water status, but they do not indicate how much water should be applied.
The decision to irrigate is made when the average tensiometer reading exceeds a given critical value.
To optimize production the critical value is normally in the range of 10 to 20 cb for typical Florida sandy soils.
The critical values are different for specific soil types, crops, and stage of crop growth.
At critical stages of crop growth, lower values are used, resulting in irrigations being scheduled more frequently.
The critical values are also functions of economic considerations, with higher values set if the irrigated commodity price drops or if the cost of irrigation increases.
A tensiometer indicates only when irrigation should be scheduled, and not how much water should be applied.
To determine the amount of water to be applied, a moisture characteristic curve specific for the irrigated soil must be used.
Figure 10 is a moisture characteristic curve for Lake Fine Sand, a typical deep sandy soil of central Florida.
The depth of irrigation water to be applied should be adequate to restore only the root zone to field capacity.
Excessive water will be lost to deep percolation below the crop root zone, carrying nutrients with it.
The data illustrates tensiometer field data and irrigations scheduled by the tensiometer method.
In this illustration, timing and amount of irrigation were controlled with tensiometers at two depths.
When the major root zone  depth became as dry as desired, small irrigations were scheduled to rewet the 12-inch zone, but not the 24-inch depth which was still sufficiently wet.
When, eventually, the 24-inch zone also reached the desired degree of dryness, a larger irrigation was scheduled to rewet the entire soil profile.
A major advantage of tensiometers is that they can be instrumented to provide automatic control of irrigation systems.
A modification is required to
 allow a tensio-meter to be used as an irrigation controller.
The vacuum gauge is equipped with a magnet and a magnetic pick-up switch SO that, when a desired  water tension occurs, the switch closes, starting the irrigation pump.
The pump operates for a preset period of time, lowering the tensiometer reading, after which the tensiometer is again monitored until the critical water tension again occurs.
A schematic of such an automatically controlled irrigation system is shown in Figure 12
 The schedules in Table 5 are for a typical season's duration and may need to be adjusted depending on specific cultural practices and growing season conditions.
Some factors that might lead to
 Tensiometers for Soil Moisture Measurement and Irrigation Scheduling
 expanding or compressing the injection schedule are described in this section.
Crop development rate can be increased by transplanting in contrast to direct seeding.
For example, watermelons can produce earlier fruit by about 7 to 10 days from transplants compared to seeds.
Transplanted crops will require slightly greater amounts of nutrients early in the season than seeded crops.
Injection rates can be increased by 0.5 lb per acre per day for the first 4 to 6 weeks compared to a seeded crop.
Since transplanted crops mature faster than seeded crops, the rates of injection can be reduced or discontinued earlier than for seeded crops.
Although the scheduling may change slightly for seeded and transplanted crops, the total amount of nutrients injected by the end of the crops should be similar.
The crops and schedules detailed in this publication are for vegetables produced on polyethylene mulch.
Mulch has a growth enhancing effect on crop development.
Some growers desire to use drip irrigation without mulch.
In these situations, the growth season might be increased by 7 to 10 days where the mulch is absent.
Therefore, injection schedules can be expanded by reducing the amount injected in the early weeks.
For a given crop, growth in the fall is usually faster than spring growth.
The difference can be one week for a crop such as squash or two weeks for tomato or pepper.
Therefore, fall injection schedules would need to be compressed compared to spring schedules.
Amounts of nutrients injected can be
 increased during the first few weeks by 0.5 lb per acre per day.
Total seasonal fertilizer amounts for spring and fall crops should be similar.
The schedules in this publication are for situations where all N and K will be injected.
It is usually best to place some nutrients in the bed before mulch application.
The general rule-of-thumb is 20% of N and K as a starter.
For most crops, this results in about 25 to 30 lb N per acre in the bed.
Under these situations, the first injection can be delayed by one or two weeks.
The length of harvest period can have an effect on extending the injection schedule.
In some of the southern winter-growing regions, the production season for pepper might encompass 4 to 6 months.
In these situations, the injection schedule will be considerably longer than for a typical 3to 4-week harvest season.
Where the crop will be continued through the winter with approximately biweekly harvests, growers can inject 1 to 1.5 lb of N per acre per day as a maintenance program for these extra months.
The exact amount of N and K should be determined by plant tissue analysis.
Finally, the cultivar  can affect the crop development rate.
In a given season, early cultivars might mature as much as 2 weeks ahead of later-maturing cultivars.
The schedules in this publication are for the standard cultivars presently recommended.
In general, most cultivars currently being grown will do well under these injection schedules.
For situations where a particular cultivar may mature significantly earlier or later than currently grown cultivars, an adjustment in the schedule might be needed.
Use: reduced application rate to avoid runoff in part of a field, VRI type: zone, prescription type: static, management intensity: medium.
The Arkansas portion of the Lower QuachitaSmackover Watershed is located in south central Arkansas and includes communities in Bradley, Calhoun, Cleveland, Columbia, Dallas, Nevada, Quachita and Union counties.
A "watershed" is an area of land where all of the water that drains from it goes to the same place, SO rainwater or snowmelt in this watershed eventually drains to a common location.
The Lower Ouachita-Smackover Watershed covers 1,797 square miles of land that is made up of predominantly forestland.
1 The population has been declining in this watershed, to about 38,000 people in 2011.2
 This fact sheet is intended to provide a better understanding of the Lower Ouachita-Smackover Watershed and its place on the state's priority list of 10 watersheds impacted by nonpoint source pollution.
Water pollution that comes from multiple sources spread over an area, such as runoff from parking lots, agricultural fields, residential lawns, home gardens, construction, mining and logging, is known as nonpoint source pollution.
As runoff moves across the landscape, it carries natural and manmade substances that can accumulate in waterways and make them uninhabitable for aquatic species or unusable by people.
Potential pollutants include bacteria, nutrients, sediment, hazardous substances and trash.
Given the number of potential sources and variation in their potential contributions, these pollutants are not easily traced back to their source.
Nonpoint Source Pollution in the Lower OuachitaSmackover Watershed
 Lower Ouachita-Smackover Watershed Data source: GeoStor.
Map created March 2011.
Major streams: Camp Creek, Champagnolle Creek, Moro Creek, Quachita River, Smackover Creek
 Lower Ouachita-Smackover Watershed Water Quality Issues
 Through water quality monitoring, environmental officials in Arkansas have determined that the main areas of concern for the Lower Ouachita-Smackover Watershed include mercury, ammonia, nitrates, minerals, turbidity, total dissolved solids and waste water discharge.
4 The Lower Ouachita River, Champagnolle and Moro creeks have fish consumption advisories due to mercury contamination.
Mercury is found in area rock formations and was previously mined in the region.
In addition, high levels of ammonia, nitrates, minerals and metals have been found in waterways near El Dorado where numerous oil and brine processing and storage facilities exist.
Metals can come from natural or manmade sources, including a single or dominant rock type, air pollution, runoff/leaching from mining operations and discharges from industrial or city water treatment
 plants.
High concentrations of metals can be hazardous to the environment because of how they accumulate in aquatic species and build up in soils.
Turbidity is a measure of the clarity of water and is often the result of excess silt or sediment entering a stream.
High turbidity levels mean the water is murky from a variety of materials, such as soil particles, algae, microbes and other substances.
Turbidity can affect aquatic life in
 Arkansas' Priority Watershed List for Nonpoint Source Pollution
 Arkansas has used a watershed-based approach to nonpoint source pollution management, allowing the public to guide planning to address water quality concerns.
The Arkansas Natural Resources Commission, or ANRC, administers the Nonpoint Source Pollution Management Program.
The program exists to reduce water pollution through the funding of watershed planning and restoration activities, adoption of voluntary best management practices and the development of technologies that assist in water pollution reduction in Arkansas.
Based on public input and the use of a qualitative risk assessment matrix, ANRC has designated 10 priority watersheds as needing the greatest attention.
The current risk matrix5 identified the following priority watersheds for 2011-2016: Bayou Bartholomew, Beaver Reservoir, Cache River, Illinois River, L'Anguille River, Lake Conway-Point Remove, Lower OuachitaSmackover, Poteau River, Strawberry River and Upper Saline.
waterways.
Total dissolved solids can originate from natural geological sources such as dissolving rocks.
These concerns led to the Lower Ouachita-Smackover Watershed being designated as a priority by the Arkansas Natural Resources Commission in the state's 2011-2016 Nonpoint Source Pollution Management Plan.
6
 To encourage continued public input, the University of Arkansas Division of Agriculture's Public Policy Center facilitated a water quality stakeholder forum for the Lower Ouachita-Smackover Watershed in June 2015.
People who attended the forum identified lack of education about water quality, erosion from forestry practices and concerns about drinking water as local priorities.
People who live, work or recreate in this watershed are encouraged to consider these community priorities when addressing water pollution.
The public is also welcome to attend an annual stakeholder meeting where priority watersheds and nonpoint source pollution are discussed.
For more information about nonpoint source pollution and its impact on the Lower OuachitaSmackover Watershed, contact the Cooperative Extension Service, Arkansas Natural Resources Commission or the Arkansas Department of Environmental Quality.
The Arkansas Watershed Steward Handbook is also a good source of information about basic water quality concerns and how the public can get engaged in addressing water pollution.
This fact sheet is one in a series of 10 fact sheets on nonpoint source pollution in priority watersheds.
The University of Arkansas Division of Agriculture's Public Policy Center provides timely, credible, unbiased research, analyses and education on current and emerging public issues.
The Arkansas Cooperative Extension Service offers its programs to all eligible persons regardless of race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
SELECTING SPRINKLER PACKAGES TO MINIMIZE POTENTIAL RUNOFF
 The state and county were selected in his example.
You can also directly enter the legal description of the field.
You can then zoom to your field using the magnifying glass icon.
Once you have zoomed so that the field is visible in the map you then need to use the area of interest icon  to draw a rectangle around your field.
After you have defined the area of interest you can then click on the Soil Map tab.
This will bring up the soil map for your field as illustrated in the second figure below.
The Soil Map includes information about the soil series in the field along with the fraction of the field represented by each mapping unit.
This is the information that will be used to help select appropriate sprinkler devices for the conditions in your field.
The important characteristics for the mapping units are the general soil texture.
We also need the slope for the mapping unit.
While the slope is only a generalization of slope categories it helps classify the soil.
If you have better slope information you should certainly use that data.
Figure 1 Selection of general area of interest in Web Soil Survey.
Platte County, Nebraska 	R
 Map Unit	Map Unit Name	Acres	Percent of
 Symbol	in AOI	AOI
 3951	Fillmore silt loam,	7.0	4.0%
 6628	Belfore silty clay	128,4	73.4%
 loam, 0 to 2 percent
 6778	Nora-Crofton	13.3	7.6%
 complex, 6 to 11
 6812	Moody silty day	26.3	15.1%
 loam, 2 to 6 percent
 Totals for Area of Interest	175.0	100.0%
 Figure 2.
Soil map produced for the area of interest selected for your field.
We have developed some general guidelines for some typical sprinkler devices that commonly used.
Table 2 shows the amount of surface storage that is required to avoid runoff for general soil textures when one inch of water is applied with the pivot.
Results in Table 2 for the silty clay loam texture class shows that about 0.49 to 0.62 inches of surface storage for any devices suspended on drops while storage would have to be from 0.38 to 0.53 inches for devices installed on top of the center pivot lateral.
Clearly, the silty clay loam soil will require significant residue cover to avoid runoff for even mild soil slopes.
Applying smaller applications per irrigation can help reduce the runoff potential.
Results in Table 3 are for an application of 0.75 inches per irrigation.
As the table illustrates the amount of surface storage required to avoid runoff for applications of 0.75 inches drops to a range from 0.37 to 0.47 inches for devices installed on drops and from 0.29 to 0.40 inches for installation on top of the pivot lateral.
Thus smaller applications may allow for steeper slopes and less residue.
Table 1.
Surface storage available due to residue and slope.
Percent	Storage Due to
 Residue Cover	Residue, inches
 0.5	1	1.5	2	2.5	3	3.5	4	5
 0	0.00	0.50	0.44	0.38	0.30	0.26	0.20	0.16	0.10	0.00
 10	0.01	0.51	0.45	0.39	0.31	0.27	0.21	0.17	0.11	0.01
 20	0.03	0.53	0.47	0.41	0.33	0.29	0.23	0.19	0.13	0.03
 30	0.07	0.57	0.51	0.45	0.37	0.33	0.27	0.23	0.17	0.07
 40	0.12	0.62	0.56	0.5	0.42	0.38	0.32	0.28	0.22	0.12
 50	0.18	0.68	0.62	0.56	0.48	0.44	0.38	0.34	0.28	0.18
 60	0.24	0.74	0.68	0.62	0.54	0.5	0.44	0.4	0.34	0.24
 70	0.35	0.85	0.79	0.73	0.65	0.61	0.55	0.51	0.45	0.35
 Table 2.
General guidelines of surface storage  needed to avoid runoff for 1-inch application for common sprinkler devices.
Device Installed on Top of Lateral	Device Suspended on Drops
 White	10 psi	Pad	Rotator @ 20	White Pad	psi	Impact	Vane	with	Spray @ 10 psi	Trajectory	Multi	Concave	10 psi -	LDN @	@ 15 psi	Spinner	@ 10 psi	I-Wob	@ 15 psi Multi	Trajectory	Rotator
 NR	NR	NR	NR	NR	NR	NR	NR
 Loamy Sand	NR	NR	NR	NR	NR	NR	NR	NR
 Sandy Loam	NR	NR	NR	NR	NR	NR	NR	NR
 Loam	0.07	NR	NR	0.22	0.17	0.10	0.10	0.01
 Silt Loam	0.11	0.00	NR	0.25	0.22	0.15	0.15	0.05
 Sandy Clay Loam	0.40	0.28	0.21	0.52	0.49	0.43	0.43	0.34
 Clay Loam	0.54	0.44	0.38	0.63	0.60	0.56	0.56	0.49
 Silty Clay Loam	0.53	0.44	0.38	0.62	0.60	0.56	0.56	0.49
 Sandy Clay	0.67	0.60	0.56	0.74	0.72	0.69	0.69	0.64
 Silty Clay	0.70	0.64	0.59	0.76	0.74	0.72	0.72	0.67
 Clay	0.77	0.72	0.68	0.81	0.80	0.78	0.78	0.74
 Table 3.
Guidelines of surface storage  needed to avoid runoff for 0.75-inch application for common sprinkler devices.
Device Installed on Top of Lateral	Device Suspended on Drops
 Xi-Wob	Rotator	Impact	Spray	LDN	Rotator
 @ 10 psi White @ 20 psi White	with	@ 10 psi -	@ 10 psi -	Spinner	I-Wob	@ 15 psi Multi
 Multi	@ 15 psi	@ 10 psi
 Texture Class	Pad	Pad	Vane	Trajectory	Concave	Trajectory
 Sand	NR	NR	NR	NR	NR	NR	NR	NR
 Loamy Sand	NR	NR	NR	NR	NR	NR	NR	NR
 Sandy Loam	NR	NR	NR	NR	NR	NR	NR	NR
 Loam	0.05	NR	NR	0.16	0.13	0.08	0.08	0.01
 Silt Loam	0.08	0.00	NR	0.19	0.16	0.11	0.11	0.03
 Sandy Clay Loam	0.30	0.21	0.16	0.39	0.37	0.32	0.32	0.26
 Clay Loam	0.40	0.33	0.29	0.47	0.45	0.42	0.42	0.37
 Silty Clay Loam	0.40	0.33	0.29	0.47	0.45	0.42	0.42	0.37
 Sandy Clay	0.50	0.45	0.42	0.55	0.54	0.52	0.52	0.48
 Silty Clay	0.53	0.48	0.45	0.57	0.56	0.54	0.54	0.50
 Clay	0.57	0.54	0.51	0.61	0.60	0.58	0.58	0.56
 Chapter 2	Soils	Part 652
 NIG National Irrigation Guide Part 652
 NEBRASKA SUPPLEMENTS TO NIG:
  Soil and Irrigation Parameters	NE 2-35
  Use of Irrigation Design Groups	NE 2-36
 Table NE2-16	Available Water Holding Capacities	NE 2-37
  Alphabetical list of irrigable soils in Nebraska	NE 2-38
 and the applicable irrigation design group
  Irrigation design group description including	NE 2-53
 applicable soils.
intake rates & water holding capacities
 Figure 3.
Copy of a portion of the table of contents for Nebraska Irrigation Guide.
The USDA-NRCS has categorized soil series as shown in the Soils Map above into general soil intake families.
We generally find that three intake familes  are appropriate for many soils.
Generally these intake families represent most soils that pivots are adapted to and that express some runoff potential.
You can refer to the file from the NRCS if your soil is not listed on the following tables.
Table 4.
Soil Series in the INTAKE FAMILY 0.3
 Deep soils with a clay loam, silty clay loam, or sandy clay loam surface layer and moderate or moderately slow permeability in the subsoil.
Aksarben Silt clay loam	Haverson Silt clay loam	Nora variant Silt clay loam
 Alcester Silt clay loam	Hobbs Sandy loam	Norrest Clay loam
 Bazile Silt clay loam	Holder Silt clay loam	Norrest Silt clay loam
 Belfore Silt clay loam	Holder variant Silt clay loam	Nuckolls variant Silt clay loam
 Betts Clay loam	Holdrege Silt clay loam	Onita Silt clay loam
 Blake Silt clay loam	Holdrege variant Silt clay loam	Paka Sandy clay loam
 Blyburg Silt clay loam	Hord Silt clay loam	Pohocco Silt clay loam
 Boel Silt clay loam	Judson Silt clay loam	Ponca Silt clay loam
 Buffington Silt clay loam	Kanorado Silt clay loam	Reliance Silt clay loam
 Bufton Clay loam	Kennebec Silt clay loam	Roxbury Silt clay loam
 Bufton Silt clay loam	Kenridge Silt clay loam	Rusco Silt clay loam
 Burchard Clay loam	Lamo Clay loam	Rusco variant Silt clay loam
 Coleridge Silt clay loam	Lamo Silt clay loam	Salix Silt clay loam
 Colo Silt clay loam	Lawet Silt clay loam	Salmo Silt clay loam
 Cortland Loam	Lohmiller Silt clay loam	Saltine Silt clay loam
 Cozad Silt clay loam	Manvel Silt clay loam	Savo Silt clay loam
 Deroin Silt clay loam	Marshall Silt clay loam	Sharpsburg variant Silt clay loam
 Geary Silt clay loam	McCook Silt clay loam	Shelby Clay loam
 Geary variant Silt clay loam	Merrick Sandy clay loam	Shell Silt clay loam
 Gibbon Silt clay loam	Minnequa Silt clay loam	Shell Variant Silt clay loam
 Gibbon Variant Silt clay loam	Moody Silt clay loam	Skilak Silt clay loam
 Gymer Silt clay loam	Morrill Clay loam	Steinauer Clay loam
 Hall Silt clay loam	Muir Silt clay loam	Steinauer Loam
 Hastings Silt clay loam	Nodaway Silt clay loam	Trent Silt clay loam
 Hastings variant Silt clay loam	Nora Silt clay loam	Uly variant Silt clay loam
 Yutan Silt clay loam
 Table 5.
Soil Series in the Intake Family 0.5
 Deep soils with a silt loam or loam surface layer and moderate or moderately slow permeability in the subsoil.
Alliance Loam	Holdrege Silt loam	Moody Loam
 Alliance Silt loam	Humbarger Loam	Moody Silt loam
 Belfore Silt loam	Humbarger variant Silt loam	Nuckolls Silt loam
 Betts Loam	Janise Loam	Nuckolls variant Silt loam
 Burchard Loam	Janise Silt loam	Nunn Silt loam
 Burchard Silt loam	Johnstown Loam	Onita Silt loam
 Calco Silt clay loam	Judson Silt loam	Ord Variant Silt loam
 Calco Silt loam	Kadoka Silt loam	Paka Loam
 Calco Sandy loam	Keith Loam	Ree Loam
 Caruso Loam	Keith Silt loam	Ree Silt loam
 Caruso variant Loam	Keya Loam	Reliance Silt loam
 Clarno Loam	Kuma Loam	Richfield Loam
 Coleridge Silt loam	Kuma Silt loam	Richfield Silt loam
 Colo Silt loam	Lamo Loam	Rusco Silt loam
 Geary Silt loam	Lamo Silt loam	Salix Silt loam
 Goshen Loam	Lamo Variant Loam	Salmo Silt loam
 Goshen Silt loam	Lawet Loam Lawet	Satanta Loam
 Hall Silt loam	Silt loam Lawet	Satanta Very fine sandy loam
 Harney Silt loam	variant Loam Leisy	Thirtynine Loam
 Hastings Silt loam	Loam	Thirtynine Silt loam
 Hastings variant Silt loam	Loretto Loam	Tomek Silt loam
 Hemingford Loam	Mace Silt loam
 Holder Loam	Marshall Silt loam
 Holder Silt loam	Maskell Loam
 Table 6.
Soil Series in the Irrigation Intake Family 1.0
 Deep soils with a silt loam, loam, or very fine sandy loam surface layer and a moderately permeable, medium-textured subsoil.
Ackmore Silt loam	Graybert Very fine sandy loam	Napier Silt loam
 Alcester Silt loam	Grigston Silt loam	Nimbro Silt loam
 Angora Very fine sandy loam	Haverson Loam	Nodaway Silt loam
 Aowa Silt loam	Haverson Silt loam	Nodaway variant Silt loam
 Benkelman Very fine sandy loam	Haynie Silt loam	Nora Silt loam
 Bigbend Loam	Haynie Very fine sandy loam	Nora variant Silt loam
 Blackwood Loam	Haynie variant Silt loam	Norwest Loam
 Blackwood Silt loam	Hobbs Silt loam	Oglala Loam
 Blyburg Silt loam	Hobbs Sandy loam	Oglala Very fine sandy loam
 Bridget Loam	Hord Silt loam	Olmitz Loam
 Bridget Silt loam	Hord Very fine sandy loam	Olney Loam
 Bridget Very fine sandy loam	Ida Silt loam	Omadi Silt loam
 Bushman Very fine sandy loam	Janude Loam	Pohocco Silt loam
 Colby Loam	Kenesaw Silt loam	Ponca Silt loam
 Colby Silt loam	Kennebec Silt loam	Ralton Loam
 Coly Silt loam	Kezan Silt loam	Roxbury Silt loam
 Cozad Loam	Laird Fine sandy loam	Rushcreek Loam
 Cozad Silt loam	Leshara Silt loam	Saltine Loam
 Cozad variant Loam	Malcolm Silt loam	Saltine Silt loam
 Cozad variant Silt loam	McCash Very fine sandy loam	Shell Silt loam
 Craft Loam	McConaughy Loam	Sidney Loam
 Craft Very fine sandy loam	McCook Loam	Sulco Loam
 Creighton Very fine sandy loam	McCook Silt loam	Sulco Silt loam
 Crofton Silt loam	McCook variant Loam	Sulco Very fine sandy loam
 Duroc Loam	McPaul Silt loam	Sully Loam
 Duroc Silt loam	Merrick Loam	Sully Silt loam
 Duroc Very fine sandy loam	Merrick variant Loam	Trent Silt loam
 Eltree Silt loam	Mitchell Silt loam	Tripp Loam
 Eudora Loam	Mitchell Very fine sandy loam	Tripp Very fine sandy loam
 Eudora Silt loam	Mitchell variant Silt loam	Uly Silt loam
 Gates Silt loam	Modale Silt loam	Ulysses Loam
 Gates Very fine sandy loam	Modale Very fine sandy loam	Ulysses Silt loam
 Gibbon Loam	Monona Silt loam	Yockey Fine sandy loam
 Gibbon Silt loam	Morrill Loam	Yockey Loam
 Gosper Loam	Moville Silt loam	Yockey Silt loam
 Grable Silt loam	Muir Silt loam	Yockey Very fine sandy loam
 Grable Very fine sandy loam	Munjor Loam
 Grable variant Silt loam
 Sandy soils that are classified into soil intake families with larger infiltration rates such as Intake Family 1.5 or higher seldom have serious runoff problems with most sprinkler devices.
We have developed a graphical procedure to estimate the required wetted diameter of a sprinkler packages for selected application depths, available surface storage and system capacity expressed as the system flow rate divided by the size of the field.
To use the chart you should determine which intake family for the most runoff prone areas in the field.
Those soils should include enough area to be significant and should be located at the outer end of the pivot lateral where the water application rate is the highest.
The next step is to select your typical application depth per irrigation and move horizontally across the chart until the horizontal line intersects the available surface storage for your field.
Move vertically downward to the lower portion of the graph until the vertical line intersects the system capacity of your system.
Move horizontally to the right from that intersection point to read the required wetted diameter for sprinkler devices located near the end of a traditional center pivot with a lateral that is about 1300 feet long.
You can then compare the required wetted diameter to the value produced by an array of sprinkler devices that are installed at various heights above the crop.
You can obtain sprinkler performance data directly from the web page for most sprinkler manufacturers.
The analysis is illustrated in Figures 4-6 for the three soils when the available surface storage is 0.3 inches and the system capacity is 6 gallons per minute per acres.
The results in Figure 4 show that sprinkler devices at the end of a traditional lateral would need to produce a wetted diameter of about 70 feet for the 0.3 Intake Family such as found in the Soil Map for the field in Platte County.
The required wetted diameter drops to about 45 feet for the 0.5 Intake Family Soils and to about 25 feet for the 1.0 Intake Family Soils.
Obviously, the correct sprinkler choice will vary a great deal for these conditions.
Choices are fairly limited for the 0.3 Intake Family and efforts to increase residue cover and enhance the infiltration rate would be strongly recommended.
Figure 4.
Graphical procedure to estimate the wetted diameter of the sprinkler devices to avoid runoff at the end of a traditional pivot that is 1300 feet long for soils that are categorized in the 0.3 Intake Family.
Figure 5.
Graphical procedure to estimate the wetted diameter of the sprinkler devices to avoid runoff at the end of a traditional pivot that is 1300 feet long for soils that are categorized in the 0.5 Intake Family.
Figure 6.
Graphical procedure to estimate the wetted diameter of the sprinkler devices to avoid runoff at the end of a traditional pivot that is 1300 feet long for soils that are categorized in the 1.0 Intake Family.
THE IMPACT OF IRRIGATED AGRICULTURE ON A STABLE FOOD SUPPLY
 Irrigated agriculture is one of the most critical human activities sustaining civilization.
The current world population of 6.8 billion people is sustained in a large part by irrigated agriculture.
USDA statistics show that 17% of cultivated crop land in the United States is irrigated.
Yet this acreage produces nearly 50% of total US crop revenues.
According to the FAO the approximate 1,260 million ha under rainfed agriculture, corresponding to 80% of the world's total cultivated land, supply 60% of the world's food; while the 277 million ha under irrigation, the remaining 20% of land under cultivation, contribute the other 40% of the food supplies.
On average, irrigated crop yields are 2.3 times higher than those from rainfed ground.
These numbers demonstrate that irrigated agriculture will continue to play an important role as a significant contributor to the worlds food supply.
Water is increasingly in the headlines and irrigated farmland is often to blame for shortages and quality issues.
Government subsidized "cheap water" from century old dams and water projects are not viewed a foresight but as taxpayer subsidies to farmers dismissing the positive effect on food supply and prices.
Farmers are blamed for maximizing yield at the expense of natural resources, as much a criticism of capitalistic philosophy as agriculture.
The fact is that today's farmers are producing more food on less land than ever before.
Given current trends in population growth and the loss of prime agricultural land to development this trend must continue if we are to maintain an adequate food supply for the world.
The critical environmental vagary farmers have to deal with is precipitation.
Other environmental factors such as temperature, sunlight even insects and disease are far more regular.
Thus Irrigation is a powerful mitigator of main environmental risk associated with farming.
To this end farmers in drought prone areas make large investments in irrigation.
The risk mitigation provided by irrigation goes beyond simple economic advantage to the farmer.
Irrigation allows for a more consistent food supply and higher productivity.
Recent studies have shown increased CO2 sequestration, reduced N2O emissions and more efficient fertilizer use associated with irrigation.
The evidence that irrigated farming has a positive effect on society and even the environment is compelling.
The causes of famine in the world are complex, often involving economic, political, and biological factors.
Each of these factors paints the cause of famine with its own perspective.
Economically, famine is the failure of the poor to command sufficient resources to acquire essential food.
The great famine in Ireland which began in 1845 occurred even as food was being shipped from Ireland to England because the English could afford to pay higher prices.
The 1973 famine in Ethiopia also occurred as food was being shipped out of Wollo, the center of the famine, to Addis Abba because the capital city could afford to pay more.
Political causes of famine occur because of war, violence or poor public policy.
The citizens of the social dictatorships of Ethiopia and Sudan in the 1970's and early 1980's suffered huge famines while the democracies of Zimbabwe and Botswana avoided them in spite of having worse drops in the national food production.
This was done through the simple step of creating short term employment for the worst affected groups.
Biologically, famine is caused by the population outgrowing its regional carrying capacity to produce food resources.
The failure of a harvest or the change in conditions such as drought can create a situation whereby large numbers of people live where the carrying capacity of the land has dropped radically.
Interestingly, at a time when "industrial agriculture" is perceived as a villain, even portrayed as destroying the planet, famine due to crop failure is most often associated with subsistence agriculture, that is where most farming is aimed at simply supplying enough food energy to survive.
This means that for farming to provide sufficient food it must be economically satisfying to the farmer not just in good years but year in and out.
Famine records indicate that farm programs that subsidize production may have a positive effect on famine reduction.
Europe and the United States have not faced widespread famine due to crop failure in the past 200 years.
Even during the dust bowl in the 1930's the United States did not face widespread famine and the famine that did occur was mostly economic, people not being able to afford food due to the great depression.
Up until the middle of the 20th century Africa was not considered to be famine prone.
Famine in Africa increased as the economics of agricultural pursuits has become less profitable.
Africa does have an ample share of drought, soil problems, crop diseases and especially civil unrest and associated land issues.
This has resulted in agrarian life to be uneconomic, and in some regions, fatal.
It is the lack of this security that holds most of the blame for African food issues.
Long term land and crop security could do much to relieve this.
Crop failures, whether due to natural or man made conditions, have been associated with famine since recordkeeping began.
Manmade conditions most frequently include war, particularly attacks on land and farmers meant to starve the local populations.
Natural crop failure occurs because of plant disease, such as occurred during the great potato famine, insects such as locusts and, most frequently, drought.
Irrigated agriculture provides a buffer against crop failure due to drought.
Figure 1.
USDA corn yields data for Nebraska and Illinois.
In the year 2007 Nebraska had over 80% irrigated corn acres while Illinois had less than 5% irrigated corn acres.
To investigate the effect of irrigation on agricultural productivity corn yields from 1900 to 2008 was compared for the rain irrigated state of Illinois averaging over 30 inches per year rainfall and the dryer state of Nebraska with less that 15 inches rainfall on average.
To make up for the lack of rainfall, over the last 30 years irrigation has increases in Nebraska from 30% of planted corn in 1966 to over 80% of planted corn in 2008.
The yield data in Figure 1 can be roughly divided into three distinct segments.
The relatively constant yields of 30 to 40 bushels/ acre that occurred from 1900 to 1933 covers the period when corn varieties were open pollinated.
The rise in corn yields from the 1930's until the 1960's occurs concomitantly with the increased use of double cross hybrids during this time.
The more rapid increase in yields from the 1960's until present day roughly corresponds to the introduction of single cross hybrids.
A closer look at each segment offers some insight into the factors affecting corn yields in these two different environments.
The trends from 1900 to 1930 when farmers only had access to open pollinated corn varieties are illustrated in figure 2.
During this period there was some flood irrigation in Nebraska but it accounted
 Figure 2.
USDA statistics of corn yields in Illinois and Nebraska from 1900 to 1930.
for less than 10% of total corn acreage.
During this period the total acreage planted to corn in these states was some 20% higher than that planted today, over 9 million acres in Nebraska and 13 million acres in Illinois.
On average Illinois yielded about 10 bushels more per acre than Nebraska.
It is clear from the data that the yields from Nebraska are more variable than the yields from Illinois.
It is not possible to correlate yield to specific rainfall events because the timing of the rain is critical to corn yields but it can be said that greater variability in yields observed in Nebraska as opposed to Illinois can be related to the greater variability in rainfall found in this region.
The general downward trend in yields during this time period is often associated with lack of sophisticated fertilization practices
 The period from 1930 to 1935 corresponds to the drought that caused the dust bowl in the Great Plains.
The collapse of corn yield in Nebraska is evident in Figure 1.
The drought during this time did impinge upon yields in Illinois but was much less severe in this region.
Following this period yields began to increase
 due to advanced genetics and better crop practices particularly fertilization practices developed by the land grant universities.
Interestingly, the approximate 10 bushel higher yield observed for corn grown in Illinois compared to Nebraska was maintained during this period.
Yield reductions due to a significant drought from 1952 to 1957 are obvious in this data.
As was seen in the period 1930-1935, the effect was more pronounced in Nebraska relative to Illinois due to more variable precipitation in the more western state.
The period from 1965 to present is marked by a massive increase in irrigation in Nebraska.
In 1966 there were 3 million irrigated acres while in 2002 there were 8 million acres.
Over this time the area devoted to corn in the state of Nebraska was constant at a little over 9 million acres.
This period also marked the largest increase in yields in both irrigated Nebraska and non-irrigated Illinois.
This yield increase is often attributed to the "green revolution" of better fertilization methods along with improved varieties and crop protection chemicals.
The reality is that the green revolution started as early as the turn of the century and started to take off in the 1930's.
The large yield increases seen since the 1960's was the mainstreaming of the yield increasing technologies due to increased farm investment.
Figure 3.
USDA statistics of corn yields in Illinois and Nebraska from 1935 to 1965.
The data in Figure 4 indicate that the average yield for the state of Nebraska is for the first time approaching the yield for Illinois.
This suggests that irrigation, or the lack of it, was entirely responsible for the difference in yields between the two states.
In addition over this time period the variability in yields is more pronounced in Illinois.
A regression analysis confirms this giving an R squared for Nebraska of 0.85 while for Illinois a 0.68.
This suggests that irrigation also reduces variability in yield.
Figure 4.
USDA statistics of corn yields in Illinois and Nebraska from 1965 to 2009.
Productivity of Irrigated land
 According to the FAO, average crop yields for irrigated acres are 2.3 times those from rainfed areas.
The actual yield increases vary according to the region and the crop.
In Nebraska the yield boost attributed to irrigation between 1992 and 2007 ranged from 10% for sorghum in 1998 to 268% for corn grown in 2002  Corn wheat and alfalfa exhibited the greatest response to irrigation while sorghum and soybeans had a lower positive response.
The high productivity of irrigated agriculture allows fewer acres to feed a larger proportion of the global population.
Increasing productivity per acre is critical as farmland acreage continues to be converted to residential property.
The need for increasing yields on increasingly poor quality land is becoming more pressing as land development for housing increases.
The United States looses two acres of prime farmland every two minutes.
From 1992 to 1997, six million acres of agricultural land was converted to developed uses.
This represents an area the size of Maryland.
Much of this land is prime land.
Yield per Acre of Major Crops in Nebraska
 Corn for Grain 	Sorghum Grain 	Wheat 	Soybeans 	Alfalfa Hay 
 irrigated	non-irrigated	irrigated	non-irrigated	irrigated	non-irrigated	irrigated	non-irrigated	irrigated	non-irrigated
 1992	144	117	101	93	49	29	45	41	4.5	3.4
 1993	111	90	70	58	56	28	41	34	4.1	3.2
 1994	153	113	109	97	55	34	53	45	4.5	3.2
 1995	130	73	74	57	62	40	42	29	4.4	3.2
 1996	156	115	106	94	53	35	50	43	4.8	3.3
 1997	151	99	101	80	48	36	51	37	4.5	2.8
 1998	161	119	104	94	68	45	51	41	4.8	3.4
 1999	159	111	102	91	66	47	51	38	4.6	3.4
 2000	154	84	98	69	63	34	50	30	4.5	2.6
 2001	173	110	106	83	59	35	53	39	4.7	3
 2002	166	62	83	48	63	30	51	29	4.4	2.3
 2003	186	82	117	56	67	44	54	31	4.8	2.9
 2004	186	134	110	78	66	33	54	40	4.7	2.9
 2005	185	108	113	84	60	37	59	43	na	2.4
 2006	185	101	109	77	67	32	59	42	na	2.1
 2007	181	125	117	96	58	40	55	47	na	2.4
 Table 1.
Yield of irrigated and non-irrigated crops in Nebraska 1992 to 2007
 The rate of conversion of prime land was 30% faster than for non prime land.
This results in more marginal land being put into production.
In addition, most of the development is occurring in areas that receive significant natural rainfall.
Of the top 12 states losing prime farm land only one, Texas, significantly relies on irrigation.
This development forces more production into irrigated lands increasing the pressure on water supplies.
Development is also pushing agriculture to more marginal lands.
Flat, well drained land is considered prime land for farming.
It is also the least expensive to develop into housing and commercial properties.
The San Joaquin Valley in California averages 10 to 15 inches of rainfall a year while the coastal valley including Watsonville and Salinas averages twice that amount.
Yet housing is pushing vegetable production out of the relatively wet coastal valley to the dryer central valley where more irrigation is required.
In another example, most of the best farmland in New Jersey is now covered by houses.
This is occurring at a time when "buy local" is being promoted as the most sustainable food option.
Loss of arable land is increasing as the world population gets wealthier.
The general fact is that agricultural land and water use cannot compete economically with industrialized or residential uses.
As discussed earlier farming must result in economic benefit for the farmers or crop production will not keep up with demand
 and food shortages will result.
Water use policy must also include land use policy as part of the conversation.
Irrigated Agriculture and Environmental Quality
 Researchers are beginning to consider the effect of irrigated agriculture on greenhouse gasses and air quality.
Researchers in Idaho looked at the organic
 State	87-92	92 -97
 carbon stored in soils having long-term cropping histories of various crops.
They found that irrigated pasture and irrigated reduced till cropping sequestered more carbon in the soil than native rainfed vegetation.
Full tillage irrigated crops sequestered the least carbon.
The authors concluded that if worldwide irrigated acreage were expanded 10% and the same amount of rainfed land were converted to native grassland that 5.9% of the total carbon emitted in the next 30 years could be sequestered.
Studies of the effects of irrigation on the environment are new but show promise.
WI 54,200 91,900 Another study compared drip and furrow NY 36,900 89,100 irrigation relative to CO2 and N2O emissions.
The CO2 emissions were SC 52,600 86,200 lower in drip irrigated compared to flood CA 73,800 85,200 irrigated treatments but the differences were small.
More significantly, of the 100 pounds of N/acre added as fertilizer 18% was lost as N2O in the furrow irrigated treatments compared to only 4% in the drip irrigated treatments.
Although both gases are significant contributors to global warming N2O is 300 times more potent than CO2.
Other studies indicate a positive relationship between irrigation and fertilization efficiency, supporting the conclusion that efficient irrigation reduces N2O emissions.
Table 2 Farm acres lost by state
 Rainfall leaches nutrients from the soil.
This is why, even in areas of high rainfall such as Florida, many growers practice plasticulture, the practice of using plastic mulch and drip irrigation to better manage the soil environment.
Strawberries and tomatoes are often grown in beds that are covered with plastic mulch.
In addition to creating a clean surface for the fruit, this mulch prevents the natural heavy rains from saturating the soil and leaching out the applied nutrients.
Irrigation is then used to supply the necessary water.
Studies conducted in West Texas from 2000 to 2007 revealed that recovery efficiency of added N fertilizer ranged from a minimum of 12% in furrow irrigated
 fields to a maximum of 75% in fertigated fields.
The relationship of total N uptake  relative to yield in bales for all irrigation systems indicates that a bale of yield requires 40 pounds N per acre regardless of the treatment.
Thus a furrow system that is only 12% efficient must apply 300 lbs N/bale/acre compared to 53 lbs N/bale/acre for a drip system that is 75% efficient.
This saves money, potential runoff and N2O emissions.
Irrigated Agriculture and Business planning
 The risk associated with Agricultural production can be divided into three components
 1) Systemic Risk this is the risk associated with lost production most often associated with the weather, particularly rainfall but also insects and disease
 2) Market risk that associated with crop prices
 3) Credit risk usually associate with the low value of farm land relative to the cost of production.
The systemic risk is mitigated through the implementation of a crop insurance program, crop protection program, nutrient management program and irrigation program.
The first three are usually treated as variable expenses while the irrigation system is a capital expense.
The United States offers an excellent laboratory for considering the systemic risk associated with irrigated agriculture.
In the Western arid states most crops cannot be grown without irrigation so irrigation is a necessary component of production.
As you move least to the high plains, most crops can be successfully grown using natural rainfall but irrigation is necessary to obtain maximum yields.
In this case there are measurable benefits and risks to choosing or not choosing to irrigate.
The actual choice is many times dictated by incentives and subsidies but the result is more consistent high yields.
Table1 indicates the risk for dryland farming of corn in Nebraska ranges from a minimum of 21 bushels to a maximum of 102 bushels per acre.
The average difference is 58 Bu.
This yield increase significantly reduces the risk associated with production in this region which is why over 80% of Nebraska farmland is irrigated.
Moving east of the Mississippi, rainfall is usually adequate for crop product except for exceptionally dry years.
The decision then is whether to invest in irrigation as an insurance against 2 or 3 out of 10 dry years.
This type of irrigation insurance is strongly dependent on the price of the irrigation system.
Market risks are mitigated through various selling contracts, futures, cash sales and hedge contracts.
These instruments, while complicated, add significant upside potential to the farmer.
The credit risk of farming is usually associated with lenders but can affect farmers looking for funds to make significant investment in equipment such as irrigation systems.
In addition to risk mitigation, irrigation also allows for a more consistent yield year after year.
This was shown to be true in irrigated Nebraska compared to Illinois.
More consistent yields allow for more consistent application of market risk management tools such as futures and hedges.
Also, the regular income associated with more consistent yields also improves the credit risk position of farmers seeking credit.
This results in lower rates and better profitability.
Finally consistent yields and revenues contribute to better business planning on a longer time scale, resulting in increased resource efficiencies.
Irrigated agriculture is critical to maintaining and growing the world's food supply as population grows.
Analysis of yield data from Nebraska and Illinois indicates that irrigation mitigates the effects of drought, the number one environmental factor reducing yields.
In addition irrigation results in more consistent yields which allow for better business planning particularly with regard to market dynamics.
Prime agricultural land is being lost to development at an astonishing rate.
Irrigation improves agricultural productivity particularly on marginal ground.
This is necessary to meet future food needs in the face of reduced growing area.
Irrigation may also help sequester carbon dioxide, reduce N2O emissions from the soil and reduce fertilizer needs.
This is not to say that water supplies, both ground and surface, need not be managed.
Water must be available for people, industry, nature and food.
Food is critical because it is the abundance of food that sustains people and industry and allows us the freedom to consider and preserve nature.
A new NebGuide addresses this need by providing a clear presentation of the topic of consumptive use in the context of irrigated crop production.
In the NebGuide, guidelines are given for determining whether a new irrigation technology that may reduce water withdrawals for irrigation will also reduce consumptive use of water, resulting in more water stored in the watershed, available to other water users or for later use.
There was some limited relief to the persistent dry conditions that have encompassed Nebraska this growing season across parts of southwest, south-central and central Nebraska.
NERain observations indicated that the southern tier of counties from McCook to Red Cloud received 1.50-2.50 inches of moisture for the month.
Monthly totals of 2.504.00 inches were reported in pockets of central and south-central Nebraska.
Unfortunately, a large portion of the east-central Nebraska failed to receive an inch of moisture for the month of September.
Chapter: 45 Scouting for Corn Diseases
 The purpose of scouting and having field records is to provide information, from which economically and environmentally sound recommendations are developed.
The economic-based pest threshold is the severity level at which the yield loss equals the cost of the controlling the plant disease.
Field scouting is conducted to: 1) diagnose disease problems; 2) determine disease severity; 3) determine the need for applying fungicides; and 4) assess the effectiveness of previously applied control strategies.
The purpose of this chapter is to discuss the basics of field scouting.
Table 45.1 Key factors to consider when field scouting:
 Note the current and forecast weather conditions.
Provide information when pest population thresholds/severity are nearing or exceeding the cost of control.
Base the frequency and intensity of field scouting on the crop, crop growth stage, pest of concern, and timing and frequency of control practices.
Provide site-specific data by noting location, intensity, and extent of pest problem.
Avoid costly mistakes by checking field records and the corn trait package.
Put the information into your field records.
Use pest-specific sampling protocols.
Preparing to Scout a Field
 Understand the pathogen biology and control approaches.
Have an idea when certain diseases occur in the season.
Start with the big picture the entire field look for stunted, yellowing plants, or areas that raise suspicion.
If you see a problem, ask: Are the infected plants in any pattern ?
Scouting
 Table 45.2 Useful tools to use when scouting production fields:
 Clipboard or notebook	Clear plastic Ziploc bags or screw-top vials
 Scouting sheet	Paper bags
 Plastic bucket	Camera/video recorder
 Hand lens 	Trowel or hand spade
 Sharp pocket knife or single-edge razor	Soil sampling probe
 Marker/sharpie	Pest ID guides
 for diseases should be done periodically, starting with assessing plant-stand establishment , then assessing for early season diseases , midseason diseases , and finally, late-season diseases.
If a remote-sensed image is available, scout areas that are anomalous  first.
If no imagery is available, then start scouting the field by first walking into the field at least 30 ft  from the edge of the field and assessing 10 plants.
This assessment should include the percentage of the entire plant that is covered by the disease.
Do this for at least 10 stops in a zigzag pattern to cover the large portion of the field while avoiding the edges of the field.
If the field has rolling topography, make sure to include scouting points at each landscape position , as stress conditions and disease incidence may differ.
The average of all the points assessed will indicate the severity of the disease.
Figure 45.1 Sampling plan.
Walk in the field at least 10 steps from the field edge and examine 10 plants at every black dot.
Collecting an accurate and reliable estimate of disease intensity  is important in making disease-management decisions.
Inspect the infected plants to assess what parts of the plant are infected: the entire plant , lower leaves, midcanopy, top.
For example, bacterial stalk rot usually infects the top part of the plant.
Specific activities include:
 1.
Splitting the stalk and looking for any discoloration of the stalk or pith disintegration.
2.
Distinguishing between fungal, bacterial, viral, and nematode diseases.
a.
Fungal leaf spots and blight diseases usually are smaller in size.
The spots could be irregular in shape, as in northern corn leaf blight, or could have a regular shape, such as gray leaf spot.
Bacterial blights could have larger lesions, such as Goss's and Stewart's wilts, or small lesions, such as Holcus spot.
b.
Yellowing and stunted growth are usually symptoms of virus and nematode infection.
Take samples of diseased plants and send to the South Dakota State University Plant Diagnostic Clinic to obtain or confirm diagnosis.
Every county 4-H office has self-addressed envelopes for mailing samples to the clinic.
Finding only two or three plants with disease does not justify applying fungicides.
Disease intensity can be measured as incidence or severity.
Incidence is the percentage of units assessed with disease.
For example, three diseased plants out of 10 sampled plants would have a 30% disease incidence.
Severity, on the other hand, is the amount of unit area that is covered by disease lesions.
This can be on the leaf basis or on the plant basis.
For example 30% severity on whole plant basis would mean that 30% of the plant's total area is
 covered by lesions.
Usually severity is more informative.
Create and implement a management plan.
The in-season rescue treatment for foliar fungal diseases is fungicide application.
However, little research has been done on corn foliar disease threshold for individual foliar diseases partly because of the difficulty in keeping other stresses from interfering with yield response to disease.
Additionally, diseases differ in the minimum amount of severity/incidence that can occur before significant yield loss is observed.
For instance, for northern corn leaf blight, a 10% severity may cause similar yield loss as 30% eye spot severity.
In sweet corn, common rust incidence threshold was found to be 80%.
The general consensus for fungal disease threshold to justify fungicide application is fungal diseases  occurring on 3rd leaf below ear leaf and higher on 50% of plants.
The best timing for fungicide application is between VT  and R2.
However, depending on the disease pressure, a fungicide can be applied until R5.
Earlier fungicide application has not been associated with consistent yield gain, except for corn-on-corn rotations and in no-till situations.
Scout for diseases at V6 to determine the need for early fungicide application.
If fungal diseases are developing on lower leaves on 50% of the plants, an early fungicide application may be beneficial.
Scout again at tasseling and note the different diseases beginning to develop and which leaf positions are affected.
If no disease is observed on the 3rd leaf below ear leaf and higher leaves at this stage, scout again at R2 growth stage.
If the current weather is wet and warm, scout every four days.
The most critical period for yield protection is between R2 and R5.
Diseases occurring past R5 will cause minimal yield loss.
Protection of ear leaf and leaves above the ear from fungal infection protects against yield loss.
Scout early and continue scouting for foliar fungal diseases every 4-5 days until R3 to decide the need for fungicide application.
A proactive management plan might include cultural methods ; preventative treatments ; and possible fungicide treatments.
The goal of the Nebraska Chemigation Act is to protect the groundwater and surface waters of Nebraska from contamination by fertilizers or pesticides.
To accomplish this goal, the Act provided the legal requirements for the future use of chemigation as a means of nutrient or pesticide application.
A more modern view  is that if a stream can be used for recreational purposes, then it is considered navigable, and the public has a right to recreate on the stream.
The report on Discount on Cash Rent per Acre When Tenant Owns Pivot for Irrigation System in Nebraska shows the discount given to the tenant as credit for their ownership of the pivot in the lease agreement.
Table 1 shows the estimated discount range and percentage of respondents associated with each estimated amount.
The University of NebraskaLincoln has not conducted additional surveys on this topic since the 2018 report.
Approximately 55% of the center pivots evaluated had a pressure below the required regulator inlet pressure for at least 5% of the time.
Approximately 19% of the center pivots evaluated had a pressure within the ideal range.
Approximately 25% of the center pivots evaluated had a pressure above the required regulator inlet pressure for more than 10 psi above the required pressure.
Chapter: 47 Corn Diseases in South Dakota and Their Management
 There are several fungal pathogens that can infect corn and may cause significant yield losses in South Dakota if the right conditions occur.
Yield reductions are related to hybrid susceptibility, cultural practices, inoculum presence, weather conditions, and timing of infection.
Because most fungal pathogens are residue-borne unlike rusts that must be blown up on southerly winds fungal disease management includes residue management through crop rotation and tillage , hybrid selection, and fungicide application.
Anthracnose infection tends to be high in continuous cornfields and plants that are potassium deficient.
This disease is most prevalent on young corn plants when leaves are closer to the soil surface.
Anthracnose of corn is caused by the fungus Colletotrichum graminicola and overwinters on infected corn residues.
Splashing rain and wind carry the conidia spores to young corn plants where primary infection takes place.
Disease development is favored by warm, moist weather  and high humidity.
The symptoms are oval-shaped lesions that are approximately ~ -1/2-inch long with a dark brown border, which is surrounded by a yellow halo.
Under magnification , small, black spines  may be observed on the dead tissue/lesion.
1.
Select resistant varieties.
Scout and keep records of diseases occurring in your field and select hybrids with good tolerance or resistance to the diseases in your area.
2.
Consider residue management.
If high levels of infection were present in the current year, consider doing a tillage operation to bury residue.
Burying residues will help reduce the amount of inoculum in the field.
The anthracnose pathogen survives on infested cornstalk residue.
3.
Practice crop rotation.
Rotating away from corn allows the residue to break down and therefore helps to reduce the inoculum level in the field.
For fields with a history of severe corn diseases, longer rotations  out of corn can reduce the risk of disease development.
Figure 47.1a Anthracnose leaf blight.
Figure 47.1b Anthracnose top dieback caused by Colletotrichum graminicola.
Notice the black spots on the rind, which are a sign of the pathogen.
Common rust of corn is caused by the fungus Puccinia sorghi.
Urediniospores of the fungi are blown north from Mexico and the Gulf states on the wind currents where they are deposited into South Dakota cornfields.
Common rust prefers cool temperatures  and approximately six hours of moisture  for optimal infection.
Common rust occurs very frequently in South Dakota.
The symptoms of common rust are small raised spots  that are a dark, reddish-brown color and are oval to elongate in shape.
These pustules are scattered over both the upper and lower surface of the corn leaves.
Because this pathogen does not overwinter in South Dakota, rotations and tillage are not effective control methods.
The management for common rust includes:
 1.
The use of resistant hybrids.
Resistance ratings may not be available for all hybrids as common rust is rarely economically damaging.
2.
Scout for early detection.
Fungicides can be used to control common rust if the disease is rapidly increasing.
Fungicides can be economical especially on seed corn production fields.
Figure 47.2  Common rust on resistant hybrids forms a few scattered pustules.
Common rust can reach yieldreducing levels on susceptible hybrids.
Figure 47.3  Southern rust on corn.
The pustules are clustered.
Southern rust held against light showing yellow halo around the pustules.
Usually southern rust reaches South Dakota when corn is around dent growth stage and rarely does it develop to reach yield-reducing levels.
Southern rust is caused by the fungus Puccinia polysora.
Urediniospores of the fungus are blown north from Mexico and the Gulf states on the wind currents where they are deposited into South Dakota cornfields.
Southern rust prefers warmer temperatures  and approximately six hours of moisture  for optimal infection.
The symptoms include small raised spots that appear primarily on the upper leaf surface, orange to light brown in color, round, and are usually densely packed on a leaf surface.
Southern rust can be differentiated from common rust by color , distribution on the leaf surface , halo around pustules  , and the rapturing of the leaf surface by pustules.
Corn smut is commonly observed in corn  in South Dakota.
However, corn smut is not usually an economically damaging disease.
Corn plants generally are infected early in the growing season.
Yield losses have been reported to be as high as 20% some years.
Common smut of corn is caused by the fungus Ustilago maydis.
Immature corn smut galls  are treated as a delicacy in Mexico.
Spores from the common smut galls overwinter in the soil.
These overwintering spores are called teliospores.
Teliospores can be blown long distances with soil particles or carried into a new area on unshelled seed corn, and in manure from animals that are fed infected cornstalks.
Spores germinate with moisture and air temperatures between 50-95F.
Common smut is most severe when young, actively growing plant tissues are wounded.
Figure 47.4  Common smut on corn ear.
Common smut can also develop on leaves.
The symptoms for common smut include the development of a smut gall.
A smut gall is composed of a mass of black, greasy, or powdery spores enclosed by a smooth, greenish-white to silvery-white membrane.
As the spores mature, the outer covering of the gall becomes dry and papery and disintegrates, releasing the spores.
Any portion of the corn plant located above ground can become infected, including, tassels, ears, leaves , and areas near the stem nodes and aerial roots.
Management of common smut includes:
 1.
Maintain appropriate soil fertility levels.
2.
Avoid injury to roots, stalks, and leaves during cultivation.
3.
Use smut-resistant hybrids.
Dent corn tends to be more resistant to corn smut than popcorn or sweet corn.
4.
Seed treatment for grain harvested from cornfields with moderate incidence of common smut.
5.
Use rotations and tillage to reduce spore populations.
Young corn plants subjected to saturated soil conditions are prone to crazy top infection.
This is a rare disease on corn in South Dakota but is observed occasionally on a few scattered corn plants along a field edge.
Crazy top is caused by the soil-borne fungus Sclerophthora macrospora.
This fungus attacks all types of corn and a number of wild Figure 47.5 Crazy top of corn.
Proliferation of what would have been the tassel grasses.
Infected grasses at and  chlorotic stripes on the leaf caused by crazy top pathogen.
as an additional inoculum source.
Crazy top develops when soils have been flooded shortly after planting or before plants are in the fourto five-leaf stage.
The crazy top pathogen survives in the soil as oospores.
These germinate into sporangiospores.
It is the sporangiospores that produce zoospores that swim in a film of water and infect young developing corn plants.
The most common characteristic of this disease is proliferation of the tassel, where instead of a normal tassel a mass of leafy structures develops.
Sometimes infected plants may have excessive tillering and multiple small ears.
Leaves of severely infected plants may show chlorotic striping.
The management for crazy top includes:
 1.
Providing adequate soil drainage.
This will reduce the risk of flooding and subsequent infection.
2.
Do not plant corn in low, wet spots especially if the disease has occurred in the area before.
3.
Control grassy weeds.
This fungus attacks corn and grassy weeds; controlling the weeds will reduce the inoculum buildup.
4.
Seed treatment will not control crazy top of corn.
Eye spot is a residue-borne disease and can be a problem in continuous cornfields and in reduced-tillage systems.
Eye spot is caused by the fungus Aureobasidium zeae.
The spores produced by this fungus are widely distributed by wind.
Infection takes place during cool, wet weather.
The fungus overwinters on corn residue.
In the spring, the fungus produces spores that are carried to the new corn crop.
The fungus may also be seed-borne, but this source of fungal inoculum
 is negligible when compared to the number of spores produced on infested crop residues.
Eye spot symptoms include small circular spots  about 1/8-inch in diameter.
The central area of the spot dies, leaving a tan to cream-colored center surrounded by a distinct brown to purple border.
The border is frequently encircled by a yellow halo that is easily seen when the leaf is held to the light.
Eye spot can be most severe in reduced-tillage systems where the crop residues are left on the soil surface.
Management for eye spot includes:
 1.
Plant corn hybrids that have resistance to eye spot.
Resistant hybrids are the main line of defense against this disease.
2.
Practice crop rotation.
Rotating away from corn helps to reduce the inoculum level in the field.
3.
Consider residue management.
Burying residues will help reduce the amount of inoculum in the field.
Figure 47.6 Eye spot on corn.
Notice the yellow halo around the lesion.
4.
Fungicide can be used to control eye spot.
Fungicides can be economical especially on seed corn production fields.
Hybrid susceptibility and weather strongly influence gray leaf spot development.
Gray leaf spot can develop to reach economically damaging levels especially in no-till corn-after-corn fields.
Gray leaf spot is caused by the fungus Cercospora zeae-maydis.
The fungus overwinters on infected corn residue at the soil surface.
Infection takes place during prolonged warm  and humid conditions  with leaves remaining wet  for twelve hours or more.
Gray leaf spot early infection symptoms are small, pinpoint lesions.
Early symptoms can be easily confused with those of other diseases such as eye spot, anthracnose, and mature common rust lesions with no pustules.
As lesions mature, they elongate and turn brown to gray in color.
These lesions are often bound by the veins on the leaf.
Under favorable conditions, lesions can coalesce to form large, irregular areas of dead tissue on the leaves.
Figure 47.7 Gray leaf spot on corn.
Gray leaf spot can reduce corn yields.
Hot, dry weather will slow disease spread.
Management of gray leaf spot includes:
 1.
Planting resistant cultivars.
2.
Practice residue management.
Burying the residues will help reduce the amount of inoculum from building up in the field.
3.
Use crop rotations.
4.
Scout the field from VT to R1 and use fungicides if the infestation is greater than the economic threshold  and if a susceptible hybrid was seeded.
Under moderate disease pressure, timely fungicide applications can greatly minimize the impact on yield.
Northern Corn Leaf Blight
 New northern corn leaf blight lesions can produce spores in as little as 1 week, allowing northern corn
 leaf blight to spread much faster than many other corn leaf diseases.
Spores of the fungus are spread by wind and rain splash.
Northern corn leaf blight is caused by the fungus Exserohilum turcicum, previously called Helmithosporium turcicum.
The fungus overwinters as mycelia and conidia on corn residues left on the soil surface.
During warm, moist weather in early summer, new conidia are produced on the old corn residue, and the conidia are carried by the wind or rain to lower leaves of young corn plants.
Infection by germinating conidia occurs when free water is present on the leaf surface for 6to 18-hours and the temperature is between 65F and 80F.
Lesions develop within 7-12 days.
Secondary spread within fields occurs by conidia produced on the leaf tissues.
Conidia can be carried by wind over long distances where infection can occur in other fields.
In this case, lesions may develop in the midto upper canopy.
The symptoms associated with northern corn leaf blight are often referred to as cigar-shaped lesions.
They are typically 1to 6-inches long, graygreen to tan-colored, and often observed on the lower leaves.
As the disease develops, the lesions spread to all leafy structures, including the husks.
The lesions may become SO numerous that the leaves are eventually destroyed causing major reductions in yield due to lack of carbohydrates available to fill the grain.
The leaves then become grayish-green and brittle, resembling leaves killed by frost.
Yield losses can reach as high as 30-50% if the disease establishes itself before tasseling.
Management systems that leave corn residues on the soil surface can have a high risk of this disease.
The fungus prefers wet areas in production fields.
Hot, dry weather slows disease growth.
Management for northern corn leaf blight includes:
 Figure 47.8 Northern corn leaf blight symptoms.
Note the "cigar" shape of the lesion.
1.
Planting resistant hybrids to northern corn leaf blight.
This is the most effective form of northern corn leaf blight control.
2.
Utilizing fungicide application when warranted.
Numerous fungicide trials across the Midwest have found that products that contain a triazole are usually more effective than those that do not contain this chemistry.
3.
Practicing crop rotation.
Rotating away from corn helps to reduce the inoculum level in the field.
The longer the rotation, the more benefits from rotation.
Physoderma brown spot is of minor importance on corn in South Dakota but occasionally can develop in corn when rainfall is abundant in spring and the mean temperature is high.
Physoderma brown spot is caused by the fungus Physoderma maydis.
The fungus overwinters as thick-walled sporangia in infected tissue or soil that germinate under moisture and light to produce zoospores.
Zoospores swim in water and when in contact with leaf surface of young corn leaves, infection is initiated.
Corn plants are most susceptible 50to 60-days after germination and they become resistant with age.
Standing water in the leaf whorls for at least 24 hours and high temperatures are required for infection to take place.
Corn plants infected with Physoderma maydis develop very small oblong to round, yellowish spots on lead blade, leaf sheath, stalk, and sometimes on the outer ear husk and tassels.
Infected tissues turn chocolate brown to reddish brown and coalesce to form large irregular blotches.
Stalks infected at the nodes beneath the sheaths often break and result in heavy lodging 
 This disease can survive for 3 years on corn residue and in soil.
Management should include the use of crop rotations to reduce inoculum, and the use of tillage to bury crop residues.
Figure 47.9  Physoderma leaf spot symptoms on a corn leaf.
Damage caused by Physoderma infection on the stalk rind.
Corn stalk lodging on the second node caused by Physoderma infection early in the season.
Stalk rots are among the most common and damaging of the corn diseases.
Yield losses  result from premature plant death and lodged plants.
Stalk rot diseases are primarily caused by fungi that commonly occur in the field.
Typical stalk rot symptoms include wilting plants with leaves that turn color , pith discoloration , and roots that may decay.
Anthracnose stalk rot of corn is caused by the fungus Colletotrichum graminicola, which overwinters on infested corn residues.
This is the same fungus that can cause anthracnose leaf blight.
However, presence of the leaf blight phase does not necessarily lead to stalk rot phase.
The fungus produces Figure 47.10  Outer anthracnose stalk rot symptoms.
Corn plants killed by reproductive structures, called anthracnose stalk rot.
acervuli, which contain setae.
Conidia, fungal reproductive spores, are produced in large quantities in the acervuli and infect new plants.
Splashing rain and wind carry the conidia spores to young corn plants where primary infection takes place.
Disease development is favored by warm, moist weather  and high humidity.
Anthracnose stalk rot is one of the most important stalk rot diseases in the United States.
The symptoms for anthracnose stalk rot are stalks that often have shiny, black lesions on the stalk's outer rind.
Anthracnose stalk rot management should include:
 1.
The use of resistant hybrids.
If available, resistant hybrids are effective at managing anthracnose stalk rot.
2.
The use of a balanced soil fertility program.
Ensure optimal levels of nitrogen  and potassium  are maintained in the soil.
3.
Consider lowering the plant populations.
High plant populations tend to have an increased severity of stalk rots.
4.
Tillage to reduce surface residues.
Burying crop residues can reduce the fungus survivability in the soil.
5.
Control foliar diseases.
High foliar disease severity may weaken the stalk making it more prone to stalk rot development.
This pathogen also causes stalk and stem rot of alfalfa, sorghum, and soybean.
Although this disease has been found on corn in South Dakota, its incidence and severity remain very low.
Charcoal rot is caused by the fungus Macrophomina phaseolina, and it is often called the dry weather wilt.
Charcoal rot typically affects prematurely senescing plants that are under drought stress.
Disease development is ideal when soil is dry and soil 5447501 temperatures are 90F or higher.
The signs of charcoal rot include sclerotia, which are tiny, black, round, survival structures produced by this fungus.
When sclerotia are produced inside the stalk it gives the appearance of charcoal dust.
Rotating the field into soybeans may not help with disease control because soybeans generally support a higher microsclerotia population than corn.
Seed treatments may not be effective against this disease.
Figure 47.11 Charcoal rot on corn.
Management should include the use of resistant hybrids, if they are available, and adjusting planting date to coincide with greater moisture availability.
Diplodia used to be one of the most common and damaging stalk rots found in corn, but now anthracnose and Fusarium stalk rots have increased in incidence and exceed Diplodia in the Midwest.
Corn is the only host of this pathogen.
Infection is favored by wet, warm conditions shortly after pollination.
The fungus, Diplodia maydis , causes both Diplodia stalk and ear rot of corn.
The fungus overwinters on crop residue.
Conidia  can be splashed onto other areas of the plant.
Infection at the nodes below the ear results in stalk rot, whereas infection of the silks and husks will cause ear and kernel rot.
Injury by birds and insects also favor infection.
Figure 47.12 Diplodia stalk rot.
The symptoms for Diplopia stalk rot are wilted plants with shredded pith tissues.
On the outside of the stalk, minute, dark brown/black pycnidia  are embedded in the rinds.
The pycnidia feel rough and cannot be easily dislodged from the surface.
Infected plants may have stalks that are easily broken.
Diplopia stalk rot can result in low test weights, high harvest losses, and reduced harvest speeds.
Management should include: 1) the planting of corn hybrids with corn borer resistance and high scores for stalk strength as planting these hybrids minimizes wounds caused by insects; 2) crop rotation and tillage to reduce corn residue on the soil surface, and a 3) balanced fertility program.
Gibberella stalk rot is one of the most common stalk rots in the corn belt.
Gibberella stalk rot is caused
 by the fungus Gibberella zeae, which is called Fusarium graminearum in its asexual stage.
This fungus is also a common seedling pathogen of corn and soybeans, and the causal pathogen of Fusarium head blight  of wheat, barley, oat, and rye.
The symptoms are a pinkishred discoloration of the inside the cornstalk.
Perithecia  may be observed on the surface of the stalk rind as small, round, black specks often near a node and are easily scratched off.
Perithecia overwinter on the crop residue and act as the primary inoculum for the next growing season.
This pathogen causes both ear rot and stalk rot of corn.
Disease development is favored by warm, wet conditions.
Stalk breakage and lodging often occur due to this disease.
To harvest based on stalk strength.
manage Gibberella stalk rot, plant hybrids with good stalk strength and corn borer resistance, rotate crops, control the surface residues, use management practices that minimize yield limiting factors, and schedule
 Figure 47.13 Gibberella stalk rot.
Fusarium stalk rot is one of the most difficult diseases to diagnose.
This pathogen is usually suspected after the diagnostic characteristics of the other stalk rot pathogens have been ruled out.
This fungus infects sorghum, sugarcane, wheat, cotton, pineapple, and tomato.
It overwinters on the infected surface residues.
Corn borer adults can spread the disease in the cornfield.
Fusarium stalk rot is caused by many different Fusarium species, including F.
verticillioides, F.
proliferatum, and F.
subglutinans.
Fusarium stalk rot is favored by dry weather prior to silking and warm, wet weather after silking.
The symptoms are white fungal growth on the outside of the stalk.
Infected plants may have poor kernel quality and test weights.
Figure 47.14 Fusarium stalk rot on a corn plant  compared with a healthy plant.
The management for Fusarium stalk rot includes using a hybrid with good stalk strength and disease resistance, crop rotation, tillage to facilitate the breakdown of crop residues, planting at an appropriate seeding rate, soil tests, and application of appropriate amounts of K and N, insect control, and scouting to assess stalk conditions.
If conditions are favorable for stalk rot development, field scouting is critical for determining which fields should be harvested first to avoid or minimize plant lodging and ear drop.
Scouting for stalk rots
 The most common method used while scouting for stalk rots is the Push or Pinch Test.
For this test, walk through a cornfield and randomly select a minimum of 100 plants representing a large portion of the field.
To test for stalk rot:
 1.
Push the plant tops approximately 30 degrees from vertical.
If plants fail to snap back to vertical, the stalk has been compromised by stalk rot.
2.
Pinch or squeeze the plants at one of the lowest internodes above the brace roots.
If the stalks crush easily by hand, their integrity has been reduced by stalk rot.
If > 10% of plants exhibit stalk rot symptoms, harvest that field first to reduce the potential for plant lodging and yield loss.
Fungi cause several ear and kernel rots in corn that may result in yield loss, both in quantity and grain quality.
In terms of quality, many ear rot pathogens also produce mycotoxins  that can affect feed value and marketability of the grain.
Development of ear and kernel rots is enhanced by stalk lodging, and insect and bird injury.
Weather also plays a major role in what type ear rot is likely to develop.
Gibberella ear rot, also called red rot, is quite common in corn especially under prolonged rainy weather late in the growing season.
Its symptoms are characterized by a reddish mold that appears at the tip and grows down the ear.
If infected early, the entire ear may rot and be covered with a pinkish mycelium that causes the husk to tightly adhere to the ear.
Gibberella ear rot is caused by Gibberella zeae.
This pathogen overwinters on corn debris and has a wide host range including small grains.
In wheat, this pathogen results in Fusarium head blight.
The fungus infects the ear through silks and Figure 47.15 Gibberella ear rot on corn.
wet weather just after silking.
Corn following corn is more prone to Gibberella ear rot development.
This fungus produces mycotoxins  and zearalenone) in infected grain.
This disease reduces yield, test weight, and storage life.
If grain is contaminated with mycotoxins, it may be unsuitable for many uses.
Management of this pest includes:
 1.
Select resistant hybrid, husk tightness and hybrids that dry-down rapidly.
2.
Scout fields prior to harvest to identify high-risk areas.
3.
Adjust the combine to minimize kernel damage.
4.
Dry infected corn to 15% moisture or less.
5.
Use residue management through tillage and rotation to reduce inoculum load.
Fusarium ear rot develops under hot dry weather and occurs at and after flowering.
Infection can occur through the silks but damage by birds, insects, or hail increase chances of infection.
Several Fusarium species cause ear rot, but the most common species are F.
verticillioides and F.
proliferatum.
These Fusarium species overwinter in corn residue from corn and other plants.
The fungus infects corn ear through silk and wounds, and it can enter the ear through hail damage or wounds from feeding insects.
Occasionally, Fusarium stalk rot can develop systemically and cause ear rot.
These Fusarium species also produce mycotoxins.
The symptoms vary greatly depending on the genotype, environment, and disease severity.
Individual infected kernels can be scattered in the ear, and under severe conditions, the fungus may consume the entire ear.
Infected kernels have whitish pink to lavender fungal growth.
Figure 47.16 Corn ear with Fusarium ear rot.
This disease reduces yield and grain quality.
The kernel can be completely consumed by fungus and be contaminated with mycotoxins , which can be fatal to
 livestock.
Management for this disease includes:
 1.
Selection of resistant hybrids.
The relative rating should be based on previous history.
If this has been a problem in past years, select hybrids with high scores for ear rot resistance.
2.
The use of tillage and rotation to reduce pest populations and overwintering.
3.
The control of insects that can cause wounds.
4.
Store infected grain separately to avoid infecting the entire bin.
5.
Dry grain to < 15% moisture if grain is to be stored through the next summer.
Diplodia ear rot develops in cornfields with history of this disease and when weather is wet and warm around the silking time.
Diplodia ear rot is caused by Diplodia maydis.
Infected corn residue is the main source of inoculum.
Ears are most prone to infection about three weeks after flowering when the silk dies off.
Conidia are spread through splashing rain during wet weather.
Corn is the only known host of this disease.
The infected ears have husks that appear bleached to straw-colored and can be seen from a distance with dead ear leaf.
Unlike Gibberella ear rot, Diplodia ear rot starts at the base of the cob.
Infected kernels are dull gray to brown.
If infection occurs several days after flowering, the ears do not show external symptoms, but white fungal mycelium may be seen between the kernels.
This disease reduces yields, kernel size, and test weight.
The management of Diplodia ear rot includes the selection of resistant hybrids.
In fields with previous history of this disease, select hybrids with greater resistance.
1.
The use of crop rotation and tillage to reduce inoculum.
2.
Grain from infected fields should be dried to a moisture content < 15% as quickly as possible.
3.
Grain from infected fields should be cleaned to remove damaged kernels.
Aspergillus ear rot is most important ear disease because of the production of aflatoxins that are dangerous to humans and animals.
Two common species Aspergillus flavus and A.
parasticus infect corn.
Of these, A.
flavus is the most predominant species.
The fungus overwinters in the soil and debris and infection is favored by hot, dry weather.
The fungus is spread to silk by wind or insects.
This disease can be important under drought conditions.
Insect damage predisposes the kernels to infection and consequent Aspergillus ear rot development.
In most cases only a few kernels on an ear are infected.
Infected kernels have masses of olive to yellowgreen spores on and between them.
Usually the tip of the ear is where infected kernels tend to concentrate but any other part of the ear may be infected.
Sporulation of the fungus is most evident on kernels that were injured.
However the fungus can also be present on kernels without showing symptoms.
Figure 47.17a Diplodia ear rot on corn.
Notice the dead ear leaf.
If Aspergillus ear rot is present in a field, the grain needs to be tested for aflatoxins.
If concentrations are > 20 ppb the grain cannot be sold or transported across state lines.
The blending of corn to reduce concentrations is prohibited for interstate trade.
If the grain is used for ethanol production, the distillers
 Figure 47.17b Corn ear with late Diplodia ear rot infection.
Notice the white mycelia between kernels.
grain will have elevated aflatoxin levels.
The risk of this disease can be reduced by:
 1.
Selecting appropriate hybrids.
Most seed corn companies do not rate hybrids for Aspergillus ear rot resistance.
Hybrids with good drought resistance should provide some protection.
2.
Use management techniques that increase water use efficiency, such as a balanced soil fertility program, and seeding at appropriate rates and dates.
3.
Control insects to prevent injury to ears.
4.
Practice tillage to reduce the inoculum.
5.
If the grain is harvested from infected fields, use techniques that minimize kernel damage, harvest the grain separately, screen the grain to remove broken kernels, control insects, and maintain low temperatures and moisture during storage.
Bacterial diseases can be destructive if infections are severe and widespread.
The selection of resistant hybrids and the use of other integrated pest management strategies are the cornerstones for controlling bacterial diseases.
There are four bacterial diseases that occur on corn in South Dakota: Goss's wilt, Holcus leaf spot, bacterial stalk rot, and Stewart's wilt.
Figure 47.18 Aspergillus ear rot symptoms.
Goss's Bacterial Wilt and Leaf Blight
 Goss's wilt has increased in occurrence in South Dakota.
Continuous corn production especially under irrigation increases the spread of this disease.
Additional hosts for this pathogen include green foxtail, shattercane, barnyardgrass, and other common grass species.
Goss's bacterial wilt and leaf blight of corn  is caused by the bacterium Clavibacter michiganensis subsp.
nebraskensis.
The bacteria overwinter on infested crop residue on the soil surface from which they are splashed onto growing corn plants.
The bacteria enter the plants either through their natural plant openings or wounds created by hail, heavy rainfall, sand blasting, high winds, and insect feeding.
Disease development is favored by high humidity  and temperatures of 80F.
The symptoms for Goss's bacterial wilt and leaf blight are foliar  blight  and a systemic wilt.
Leaf blight is more common than systemic wilt.
Lesions may be gray to tan in color with wavy, irregular margins that follow the leaf veins.
The most obvious characteristics are the dark green to black water-soaked lesions often called "freckles" that appear on the infected area.
Another characteristic of Goss's wilt is the bacterial ooze that may be found on the leaf surface.
On the leaf surface, dry bacterial
 Figure 47.19a Characteristic lesion of Goss's wilt showing the black freckles  within the lesion.
Figure 47.19b Corn wilt caused by early infection of Goss's wilt bacteria.
ooze may appear to shine and glisten in the sunlight.
An easy technique to use when looking for the freckles is to use a lighted flashlight on the underside of the lesion or hold the leaf up to the sunlight SO it is backlit.
The dark freckles will appear translucent.
The risk of this disease is greater in corn-on-corn fields with high residues on the soil surface.
The management of this bacterial disease includes:
 1.
The use hybrids tolerant of Goss's wilt.
Check with your seed dealer for Goss's wilt ratings.
2.
The use of rotations and tillage to reduce inoculum.
Any type of tillage that buries infested residues and encourages residue decomposition will help reduce the inoculum level in the field.
Rotating to a nonhost crop such as soybean, small grains, alfalfa, or dry bean will help reduce primary inoculum in the corn residues, but rotation will not completely eliminate the bacteria.
3.
Control grassy weeds.
Grassy weeds serve as additional hosts for Goss's wilt SO weed control is important for disease control.
4.
Fungicide applications are not effective against this bacterial disease.
There are no in-season control measures available for the prevention or spread of Goss's wilt.
Holcus spot symptoms can resemble chemical injury to leaves, similar to paraquat drift.
Holcus spot is occasionally observed in South Dakota and typically does not reduce yield or reduce grain quality.
The pathogen is caused by a bacterium called Pseudomonas syringae pv.
syringae, which overwinters in crop debris.
Wounds caused by hail, blowing soil or wind can increase chances of infection.
Warm , wet, windy conditions early in the season favor infection and the development of Holcus leaf spot.
The pathogen has a wide host range including many grasses and dicots.
It can have ice nucleating activity that may enhance frost injury to corn leaves.
Holcus spot symptoms first appear as water-soaked, dark green lesions near the tips of lower leaves.
They then develop into round or elliptical, tan to white spots that are 1/8 to 1/2" in diameter.
Red to brown margins develop around the spots, which may be surrounded by yellow halos.
The management for this bacteria should include the use of crop rotations and tillage to bury the crop residue.
The use of fungicides will not be effective against this bacteria.
Figure 47.20 Holcus spot in corn.
Stewart's Disease or Stewart's Wilt
 This disease is somewhat unique because its spread depends almost completely on an insect vector, the corn flea beetle.
Stewart's wilt is occasionally observed in South Dakota.
The use of seed treatment insecticides has reduced the occurrence of the disease.
Infection occurs in plant tissues that are wounded during feeding by the corn flea beetle.
The corn flea beetle is the overwintering host and vector of the bacterium Pantoea stewartii, formerly called Erwinia stewartii, the bacterium that causes Stewart's wilt.
There are two phases of Stewart's wilt that occur on corn: the seedling wilt phase  and the leaf blight phase.
In either case, symptoms appear as leaf lesions originating from flea beetle feeding scars.
The bacteria overwinter in the insect gut.
Leaf tissue surrounding feeding wounds initially become watersoaked.
Pale-green to yellow linear streaks with irregular or wavy margins develop parallel to leaf veins.
These lesions become necrotic with age and may extend to the entire length of the leaf on susceptible cultivars.
When plants are infected systemically, symptoms appear on new leaves emerging from the plant whorl, and cavities may form in the stalks near the soil line.
Bacteria spread throughout the vascular system of infected plants and occasionally infect kernels.
Foliar symptoms of the leaf blight phase are similar to those of the seedling wilt phase.
Chlorotic or necrotic tissues may extend the entire length of leaves, or symptoms may be limited to a few inches depending on the susceptibility of the cultivar.
Premature leaf death due to Stewart's wilt may predispose the weakened plant to stalk rot resulting in reduced yields.
The bacteria will reduce yields for several reasons.
First, early season infection reduces the plant population.
Second, the disease reduces leaf area and sugar production, and consequently, the risk of stalk rot is increased.
Management for this disease includes:
 1.
The use of resistant varieties.
Stewart's wilt is controlled effectively by planting resistant corn hybrids.
2.
The control of corn flea beetles.
This should include scouting and the application of appropriate insecticides, if needed.
3.
Use of pathogen-free seed.
The bacterium can be excluded from areas where it does not already occur by ensuring that the seed is pathogen-free.
4.
Fungicides are not effective against this bacterial disease.
Bacterial stalk rot typically develops midseason rather than at the onset of senescence.
It is more common in irrigated corn when an open well as the source of irrigation water.
Bacterial stalk rot is caused by the bacterium Erwinia chrysanthemi pv.
zeae.
Infection is associated with warm temperatures  and high humidity.
This pathogen overwinters only in stalk tissues above the soil surface.
Infection can initially take place at the top or bottom of the plant.
Early symptoms consist of plant lodging and dark brown, water-soaked lesions that progress to soft or slimy stalk tissues, which appear at stalk internodes located above the ground.
A foul odor often accompanies infected plant tissues.
The management for bacterial stalk rot should include the use of tillage to bury surface residues and soil drainage to reduce disease incidence.
Fungicides are not effective against this disease.
Figure 47.21 Bacterial stalk rot symptoms on corn.
This disease affects the top part of the plant.
Corn nematodes are microscopic, unsegmented roundworms that either feed inside the corn roots  or feed outside the corn roots.
Nematodes feed on root cells by puncturing the cell walls with their hollow stylets, which resemble minute hypodermic needles.
Nematodes cause yield losses in corn in two ways: directly, by injuring cells and using up cell metabolites; and indirectly, by creating wounds that become entry points for bacterial, fungal, and viral pathogens.
Over a dozen nematodes have been found to infect corn in South Dakota and the extent of yield loss will depend on the type of nematode, the population density in the soil, soil type , and other stresses such as fertility and moisture stress.
The most common groups of plant parasitic nematodes found on corn are lesion , dagger , lance , needle , stubby root , and stunt  nematodes.
Figure 47.22 Severe damage caused by sting nematodes on corn.
Although several nematodes can be found infecting corn, few are of major concern in South Dakota.
However, producers are encouraged to sample and test soil from low-yielding spots for corn nematodes.
Diagnosis of nematodes should not be based solely on plant symptoms because these can be caused by other problems such as low fertility, poor drainage, drought, herbicide injury, or other pathogens, including fungi and viruses.
Under high nematode population density, the following symptoms may be displayed:
 Stunted plants and uneven plant height along the rows.
Root necrosis and stubby roots.
Management for corn nematodes includes:
 Figure 47.22 Severe damage caused by sting nematodes on corn.
1.
Test soil for corn nematodes, especially if corn plants are stunted, yellowing , and have necrotic roots.
Carefully dig up affected corn plants and send them to the South Dakota State University Plant Diagnostic Clinic for nematode extraction before corn reaches the V6 stage of development.
2.
Practice crop rotation to check or reduce nematode population density.
3.
Use nematicide seed treatment in areas where nematode population density is high.
Though several reports show no consistent yield benefit with a nematicide seed treatment in corn, these may reduce high nematode population densities.
4.
Avoid plant stress.
Use proper fertility management, drainage, and weed control.
There are three viruses that are occasionally found infecting corn in South Dakota: wheat streak mosaic virus , maize dwarf mosaic virus , and brome mosaic virus.
Viruses are obligate pathogens that cannot be grown in artificial culture, cannot be seen with the naked eye, and must always pass from living host to living host in what is referred to as a "living or green" bridge.
Managing corn viruses requires that the living bridge of hosts be broken.
Fungicides and bactericides cannot be used to manage viral problems in corn.
Wheat Streak Mosaic Virus
 Wheat streak mosaic virus  was first observed in Nebraska in 1922.
WSMV has been observed in varying degrees in South Dakota.
WSMV is the most important endemic  viral disease in wheat but it rarely is observed or causes measureable yield loss in corn.
The pathogen causing this disease is Wheat streak mosaic virus.
WSMV is transmitted by the wind-blown wheat curl mite.
Both the mites and virus survive South Dakota winters on seeded and volunteer winter wheat and perennial grasses.
Corn serves as a host for the mites after wheat harvest until a new crop of wheat emerges.
The symptoms for wheat streak mosaic virus include a red streak in the kernel.
This streak is a response to a toxin that is found in the mites' saliva.
The management of wheat streak mosaic virus includes:
 1.
The control of grassy weeds and volunteer wheat.
Break the living bridge by controlling the grassy weeds and volunteer winter wheat.
This prevents the mites from spreading the virus as the mites and virus cannot survive more than a day without a living host.
Figure 47.24 Red stripe on kernels caused by a toxin produced by wheat curl mites.
2.
The use of resistant varieties/cultivars.
If planting wheat, use the most tolerant/resistance cultivars/ hybrids available in your area.
Maize Dwarf Mosaic Virus
 Maize dwarf mosaic virus  is rarely observed in South Dakota.
MDMV is vectored by many species of aphids, most commonly the corn leaf aphid, the greenbug, and the green peach aphid.
MDMV can also infect Johnson grass and sorghum.
The symptoms include small, chlorotic spots that are observed on green, young leaves that later develop into a mottle or a mosaic pattern along the veins of leaves, leaf sheaths, and husks.
As infected plants continue to grow and the temperature rises, the mosaic symptoms may disappear while the young leaves become more yellow.
Plants may be stunted, excessive tillering may occur, and poor seed set may take place.
Management should include the use of tolerant hybrids, the control of the insect vector, and the control of Johnson grass.
Brome mosaic virus  is transmitted by nematodes in the Longidoridae family.
BrMV infects several grass species, and tillage along the field edges may move nematodes to the field.
This virus is not common, but sometimes corn plants near field edges can be infected.
Infected plants are stunted and leaves have mosaic, chlorotic streaks on the entire leaf.
Infection is systemic  and infected plants do not produce an ear.
Sometimes infected plants die or are outcompeted by healthy plants.
BrMV can be managed by using tolerant hybrids, avoiding movement of soil from the field edges, and controlling grassy weeds especially at the field edges.
Figure 47.25 A close-up of brome mosaic virus symptoms.
Notice the chlorotic mosaic streaks on the corn leaf.
Figure 47.26 A stunted corn plant infected with brome mosaic virus between healthy plants.
Such plant will not produce any ears.
Chadron wells average about 350 feet deep, and the majority  are used for domestic supply, but livestock and irrigation wells account for 15% and 12% of the wells, respectively.
The biggest challenge to using the Chadron aquifer is poor water quality.
Roadside Guide to Clean Water: Riparian Buffers
 A riparian buffer involves planting or retaining trees, shrubs, or tall grasses along the banks of rivers, streams, lakes, and ponds.
Riparian Buffers at a Glance
 The word "riparian" is used to describe the area alongside a river or other body of water.
A riparian buffer involves planting or retaining trees, shrubs, or tall grasses along the banks of rivers, streams, lakes, and ponds.
Riparian buffers exist in both urban and rural areas and can be planted along any body of water capable of supporting plants.
How Riparian Buffers Work
 When plants like meadow grasses and trees are allowed to grow or new trees and shrubs are planted, the soil becomes more porous and allows water to soak in more easily.
Riparian buffers act like sponges along a waterway, soaking in precipitation and water running off the land.
They also capture sediment, nutrients, and other pollutants that are carried with the water runoff.
In addition to helping absorb water and pollution, the deep roots of these plants are very good at holding streambanks in place.
This further reduces water pollution by preventing the land from caving in and washing downstream.
Another benefit of trees and shrubs in a riparian buffer is the shade and wildlife habitat created by the leaves and branches.
The wider the riparian buffer extends from the water's edge, the more effective it is at improving water quality.
Community Benefits of Riparian Buffers
 Climate Change: Promotes climate change resiliency
 Landscape: Beautifies the landscape
 Habitat: Provides wildlife habitat
 You can expect to find riparian buffers in urban, suburban, and rural settings.
How to Recognize Riparian Buffers
 Riparian buffers can be as simple as a no-mow zone along a water body.
Photo by Kristen Kyler
 Very young, native, wet-area-loving trees and shrubs are often planted to grow a forested riparian buffer.
Photo by Kristen Kyler
 Tubelike shelters are often used to protect trees from deer and other animals.
Nets on top of each shelter prevent birds from falling inside and becoming trapped.
Photo by Kristen Kyler
 Many dairy and livestock farmers install fencing to exclude their herd from the riparian area.
Photo by Kristen Kyler.
Learn more at "Stream Bank Fencing: Green Banks, Clean Streams."
 Mowing, herbicide application, and other forms of weed control are common to help trees  outcompete weeds when getting established.
Photo by Jennifer Fetter
 It only takes a few years before the trees grow out of their tubes and a forest will be growing next to the stream.
Photo by Kristen Kyler
 Planting trees along streets and other locations in urban areas provides similar benefits to  riparian buffers.
Visit the Urban and Suburban Trees webpage to find out more.
Sprinkler systems, primarily center pivot systems, are widely used in the Great Plains of the United States.
Methods of irrigation application using sprinklers vary considerably and include high-angle, high-pressure impact sprinklers, low-angle, mediumto low-pressure impact sprinklers, mediumto low-pressure spray nozzles, mediumto low-pressure rotary nozzles, ground-level LEPA  bubblers or drag socks or multi-mode LEPA devices , and various LESA  or LPIC  application systems.
Graded furrow irrigation, typically from gated pipelines, is still widely used in the Great Plains.
Some of these systems utilize tailwater recovery to recirculate field runoff water.
Microirrigation, especially SDI , is growing in use in the Great Plains, although still not a widely adopted application technology, but one that can fit many situations with a high potential for effective irrigation.
To achieve effective applications, the irrigation technology must fit the soil, crop, and irrigation water supply.
Optimum irrigation water management must then be coupled with the chosen irrigation application technology to achieve effective applications to the crop.
Effective application is the terminology chosen to describe efficiency both in terms of water applications and crop productivity.
In prior Central Plains Irrigation conferences , concepts of irrigation efficiency and water use efficiency were described and discussed.
The purpose of this paper is to briefly outline choices for irrigation application technology and irrigation water management that can lead to effective applications that minimize inefficient uses of water and that can lead to near optimum crop profitability.
The outline concepts from Purcell and Currey  provide a useful tool in evaluating likely processes to achieve "effective applications." Figure 1 illustrates the water flow pathway from its source to the crop and then through the process
 of obtaining a yield from the crop.
In order to calculate the differences between water inputs, losses and uses, all the items in Fig.
1 must have compatible temporal and spatial scales.
Determining some of the water pathway components may be difficult or highly uncertain for some time and space situations.
In broad terms, this concept of effective water use is often described as "water use efficiency"  although Howell  and Lamm  point out the differences between WUE and irrigation efficiency  or irrigation application efficiency.
For many reasons as discussed in Purcell and Currey , WUE and either E or E cannot individually determine effective applications, but collectively they can distinguish irrigation technology and management that will have "effective applications."
 Figure 1.
Illustration framework of water flow pathway from source to crop for producing yield adapted from Purcell and Currey.
Traditional concepts of irrigation efficiency  are based on engineering concepts of the fraction of water being diverted that is then available for useful and beneficial needs of the crop.
Of course, the catch in these engineering definitions is characterizing what constitutes a "required" and/or "beneficial" use of the water , which may be determined by outside institutions  and/or other societal issues.
Figure 2 illustrates several of the water transport
 components involved in ET defining various irrigation Rain Irrigation performance measures.
Transpiration The spatial scale can Interception vary from a single Plant Evaporation irrigation application device  to Runoff an irrigation set  Depth Soil Uptake to broader land scales Water.
Groundwater Flow The time scale can vary Percolation and may include periods from as short as a single application , to a part of the crop components needed to characterize irrigation season , or the irrigation season, crop season, or a year, partial year , a water year , or even a period of years.
Irrigation efficiency affects the economics of irrigation, the amount of water needed to irrigate a specific land area, the spatial uniformity of the crop and its yield, and the amount of water that might percolate beneath the crop root zone.
It can also affect the amount of water that can return to surface sources for downstream uses or to ground water aquifers that might supply other water uses, and the amount of water lost to unrecoverable sources.
Return flow of water is not a loss in terms of the larger scale  and will not reduce overall efficiency unless the water quality is unsuitable for irrigation use or the returned water is not available within the irrigation season under consideration.
Spears and Snyder  discuss the added energy needed to recover this return water and the concepts of efficiency on the basin scale.
The volumes of water for the various irrigation components are typically expressed in units of depth  or simply the volume for the
 area being evaluated.
Irrigation water application volume is difficult to measure; so, it is usually computed as the product of water flow rate and time.
This places emphasis on accurately measuring the flow rate.
The accurate measurement of water percolation volumes, ground water flow volumes, and water uptake from shallow ground water remain nearly impossible under most circumstances.
We are prone to speak and characterize some water components as losses, although they are not lost but just unavailable for use.
From the water supply , water can be a lost due to evaporation , transpiration , vertical seepage or horizontal flow beyond the "control boundaries" , and any operational losses or leakages from the source that can't be recovered.
From the source to the farm, there may be conveyance losses which might be evaporation from any open water conveyances , leakages , operational spills, as well as transpiration by phreatophytes or weeds along the water route.
There could be gains in water from the release point to the farm if water is recovered from drainage ditches, groundwater inflows, as well as regional surface water recovery from runoff.
Each of these water sources is subject to various State, water district, and environmental laws or regulations that might restrict their use either by permit, custom, or legal restrictions.
In the Great Plains, we find limited on-farm storage of water because the majority of irrigation water is supplied directly to the farm through wells into a aquifer [usually the High Plains Aquifer or Ogallala Aquifer although some alluvial aquifers are of major importance.
In some cases, small holding reservoirs are utilized with larger center pivot systems or with some microirrigation systems for short-term storage and flow regulation when several wells are needed to supply water to the field at a rate that exceeds an individual well's flow rate.
In these cases, a submersible turbine pump  or a centrifugal pump will be used to lift the water from the shallow storage reservoir  to the irrigation system and to provide the system operating pressurization.
These on-farm storage ponds have similar potential water loss components as those discussed above for conveyance and water supply.
On the farm or field, the net irrigation supply is augmented by water sources that are specific to individual regions  and available soil water.
The amount of irrigation water required by the crop is the net difference between the crop evapotranspiration  and the net "effective" precipitation during a specific period, and "readily" available soil water.
The available water is generally a property of the soil texture (its
 physical particle size distribution, bulk density, mineralogy, chemical characteristics, etc.).
This "net" Irrigation requirement is typically expressed as
 where I is the "net" irrigation requirement for period i, ET is the evapotranspiration during the period, Pe is the "effective" precipitation during the period, and SW is "available" soil water used  during the period with all parameters expressed in units of depth.
Equation 1 neglects or ignores percolation below the root zone and possible water table uptake, too.
Various procedures are used to estimate Pe, and for simplicity at a given location  SW might be assumed to be a constant value dependent on the soil texture at the site, the ET rate, and the length of specific period "i".
The "gross" irrigation requirement is simply estimated as the "net" requirement  divided by an estimated or known irrigation application efficiency.
Although E  is a widely used concept , it also quite suspect and often difficult to know precisely.
Ea is generally defined as the fraction of the "gross" irrigation amount that is stored in the root zone.
It is determined by measuring or estimating
 "gross" application 
 off-target water 
 percolation below the root zone
 evaporation from applied water 
 change in water stored in the root zone
 all of which are difficult to quantify precisely.
In addition, the exact crop root zone may not be known precisely.
The "gross" irrigation application may not be known with great precision owing to the myriad techniques utilized to either measure flow rate or volume or indirect measures.
Measuring soil water is nearly a complete science unto itself.
If one assumes that off-target losses are minimal, we are left with what many call the "Big Three" losses:
 D or percolation  from the root zone
 E or evaporation, and
 Effective applications must minimize these, so called "Big Three," losses, particularly where irrigation water costs are directly linked to the volume of water diverted.
As Lamm  emphasized, Ea is often misused and incorrectly used in comparing or ranking irrigation application technologies.
It certainly has its place in irrigation science as a performance measure, but it is, perhaps, better utilized as a tool to indicate means to improve specific irrigation systems rather than a tool to judge systems.
Certainly, specific irrigation application technologies will have a "potential" to be more efficient than other technologies.
But, a conversion from one technology to another solely to improve efficiency is usually "suspect", as far as "saving water", without a concurrent irrigation water management technology or training investment.
Percolation losses are more easily controlled with the smaller, more frequent applications from center pivot systems or SDI  compared with the typically larger, less frequent surface irrigations.
However, even SDI can have significant percolation losses from the root zone if not managed carefully.
Surge flow furrow irrigation has been one of the more effective technologies to reduce excessive infiltration and percolation with graded furrow systems.
Furrow packing or "slicking" has been used effectively with graded furrow irrigation to reduce excessive infiltration.
PAM  polymers have been effective in reducing graded furrow percolation losses.
Even if no apparent percolation loss is perceived from smaller, frequent applications, surface redistribution from higher application rate technologies  can result in "potential" percolation losses in lower lying areas that might accumulate runoff.
Besides the loss of water available to the crop, percolation losses invariably also include nutrient leaching that can reduce available crop nutrients within the root zone, which increases costs for crop nutrients  and has water quality and environmental concerns.
Evaporation losses are reduced by not irrigating bare soil, using alternate furrow irrigation, lowering center pivot system applicators nearer the ground to reduce wind effects together with utilizing various choices of spray/rotator plate deflectors , sprinkler applicators, spacing,
 etc.
together with optimum operating pressure for the nozzle size to reduce small droplets.
Sprinkler evaporation losses, particularly for center pivot systems, are generally perceived to be greater than measurements indicate [see Howell et al.
for a current review up to that time, and Schneider  for a later review].
Tolk et al.
and Thompson et al.
discuss measurements and modeling of center pivot system water losses from evaporation in more detail.
However, for "gross" applications of 25 mm , evaporative losses from center pivot systems with sprinklers or spray heads can as large as 10 to 20% of the applied water depending on the specific circumstances of the application.
LEPA applications under "optimum" cases  may be less than 5-6% of the application amount.
The main evaporation loss from most sprinkler or spray technologies is the "net" canopy evaporation, which is influenced by the wetting duration.
The wetting duration depends on distance from the center pivot point and "gross" application amount, and on the wetted diameter of the application technology.
Of course, end guns will have a much greater "potential" evaporation loss  due to both the larger wetted diameter of the end gun and the greater droplet transit times and greater exposure to the wind/atmospheric factors.
In order to spread evaporative losses evenly around the field, the center pivot irrigation frequency  is generally desired to be a non day integer , but a fraction of an even day integer so the system will irrigate differing zones of the field at the same time of the diurnal cycle.
Crop residues effectively reduce evaporation from the soil.
They also improve soil tilth and, generally, increase infiltration if the residue mass amount is significant.
Ridge till or strip till has been effective in preserving soil cover using previous crop residues while utilizing a reduced or conservation tillage system.
Runoff from graded furrow systems can exceed 30 to 60% of the applied water.
PAM  polymers have been effective in reducing the runoff fraction of surface irrigation  but sometimes at the expense of increased percolation losses.
Runoff with surface irrigation and center pivot systems  can be a significant loss of water and cause ineffective applications.
Generally, no irrigation runoff should occur with SDI or microirrigation unless a pipeline leaks or breaks.
LEPA requires surface storage from furrow dikes or dammer diker implements to provide temporary surface storage for application volumes that exceed the soil infiltration capacity (Kincaid et al., 1990; Kranz and
 Eisenhauer, 1990; Coelho et al., 1996; Howell et al., 2002).
Furrow diking and dammer diking serve dual purposes in storing irrigation applications as well as rainfall  for infiltration and reducing/eliminating runoff from the field.
It is a well known practice in dryland cultures.
Furrow diking can be particularly important with center pivot systems when deficit irrigation is planned or water deficits result from regional/local droughts when irrigation capacity  is insufficient to meet the crop irrigation need.
Figure 3 illustrates the potential surface storage needed for impact sprinklers and LESA/LPIC with center pivot systems.
Systems with high instantaneous application rates, particularly LEPA, LESA, or LPIC systems, must utilize a surface storage tillage technology or an effective conservation tillage system  to minimize surface water redistribution and possible runoff or percolation from down slope areas.
Irrigation water management is the integration of irrigation scheduling or automation with the application technology.
Basically, irrigation scheduling is making decisions on irrigation timing and irrigation amount subject to the irrigation supply constraints  in concert with the operational constraints.
The goal is often to produce the greatest profit within the land, labor, capital, and water restrictions of the farm or operation.
Most irrigation scheduling involves the application of Eqn.
1 to estimate the irrigation amount needed to refill a portion of the soil water reservoir.
The irrigation amount is constrained by both the irrigation capacity  [also considering the irrigation frequency or interval] and the irrigation application technology.
Most irrigation timing decisions are based on estimated  or measured soil water.
By recognizing that in Eqn.
1 that
 SW=0k-0j, Eqn.
1 can be rearranged as follows:
 where O is the mean or total "available" soil water within the root zone
 on the end day "k" of period "i", 0 is the mean or total "available" soil water on the beginning day "j" of the period, and Pej, lj, and ETi were previously defined.
All
 terms in Eqn.
2 are in depth units.
Typically, O is taken as O fc  minus a desired soil water storage term to allow intermediate rainfall storage to minimize runoff and/or percolation.
The
 Figure 3.
Illustration of runoff or surface water redistribution potential for impact sprinkler and spray  center application packages for an example soil.
represents the start of the irrigation,  is the peak application rate , and  is the completion of the irrigation.
The first intersection point of the infiltration curve and the application rate curve represents the first ponding on the soil surface.
goal of most irrigation decisions is to maintain the root zone soil water within the defined limits given as
  2020.
[3]
 where C is the allowed storage for intermediate rainfall and Oc C is a "critical" lower
 limit of soil water that will reduce yield or crop quality.
The value of O C depends on the soil texture and other factors such as crop growth stage, atmospheric water demand, etc..
For lighter textured soils , C may be very small or impractical to utilize due to the lower "available" soil water content.
Martin et al.
defined the irrigation dates in the terms of "earliest date" [irrigation depth typically applied will just refill the root zone without excessive runoff or percolation] and the "latest date" [amount if irrigation was delayed until O was near Oc].
Both of these irrigation dates bracket the optimum irrigation timing decision date expressed as De Do D1, where the subscripts denote "e" for early, "o" for optimum, and "I" for latest.
The decision to postpone irrigations from De to D considers rainfall forecasts, ET rates, labor and farm operation decisions and the risk assumed by the producer.
As the date is postponed to near D1, some reduction in yield may be anticipated.
Effective irrigations must consider the application technology and the irrigation water management.
Table 1 gives an outline of technologies that can be effective in achieving irrigations that are aimed to achieve high profits within producer constraints.
No single irrigation application technology or management technology will insure "effective applications", but an integration of "Best Management Practices"  involving technology and management can offer pathways to achieve "effective applications" and wise utilization of our limited water supplies for profitable irrigated agriculture.
Table 1.
Example irrigation concepts for "effective applications" emphasizing "Big
 Three" water loss components.
Percolation	+	Reduced by more uniform infiltration
 Surge Flow	Runoff	+	Reduced by runoff flows and "cut-back"
 This technology has relatively low costs and can be easily
 adopted into most existing gated pipe systems.
Percolation	+	Reduces field percolation but greater
 seepage losses from reservoir.
Recovery	Runoff	+	Recycles runoff water.
This technology can be adopted for most furrow systems,
 but it adds additional pumping and capital costs to return the
 Percolation	+	Reduced by more uniform infiltration
 PAM	Runoff	+	Reduced by reduced flows and "cut-back"
 This technology is relatively low cost, although repeated
 applications may be required, and is easily adopted to most
 Center Pivot Sprinkler Irrigation
 Percolation	+	Reduced by lowered application amounts.
Low-Angle Impact	Evaporation	+	Reduced by lowered wind effects.
Sprinklers	Runoff	+	Reduced by usually having a lower peak
 Easily adopted to existing high angle sprinkler systems.
Percolation	In some cases, can have significant
 Evaporation	+	Reduced by having smaller wetted
 diameter and selection options for spray
 applicators, plate grooves, and groove
 Applicators	Runoff	-	Increased if reduced wetted diameter and
 higher peak application rate exceed soil
 infiltration and surface storage capacity.
Moderate capital costs if retrofitting older machines with
 wider drop spacing and greater number of heads that are
 t The "+" symbols indicate a generally recognized practice to reduce losses for that component
 and the "-" symbol indicates either no improvement or possibly greater loss for that component.
Table 1.
Part II.
Center Pivot Sprinkler Irrigation, continued
 Percolation	+	Reduced by lowered application amounts.
Evaporation	+	Reduced by reduced wetted area (minimal
 Runoff	+	Reduced if furrow dikes retain all applied
 water.
Can be a significant water loss if
 dikes can't contain the applied water.
Easily adapted to newer pivots with closely spaced outlets.
Can add increased costs for the greater number of
 applicator heads and diking machinery.
Requires furrow
 diking and circular planting to be most effective.
Percolation	+	Reduced by lowered application amounts.
Evaporation	+	Reduced by reduced wetted area.
Runoff	Can be a significant water loss if reduced
 wetted diameter and higher peak
 application rate exceed soil infiltration and
 LESA / LPIC	surface storage capacity.
Easily adapted to newer pivots with closely spaced outlets.
Can add increased costs for the greater number of
 applicator heads and diking machinery, if needed.
Easily
 compatible with conservation tillage systems when diking not
 required or furrow dikes used with ridge till.
Percolation	+	Reduced by lowered application amounts,
 but can be a significant loss if water profile
 is maintained at a high soil water content.
Evaporation	+	Reduced by smaller wetted area (only
 water that moves upward readily can
 Runoff	+	Reduced by lowered application amounts.
Technology is rapidly advancing.
It remains relatively
 expensive but is easily automated.
Adaptable with ridge till
 and/or strip till systems.
Fits odd or irregular shaped fields.
Evaporation	+	Reduced by crop residues shading the soil
 and by reduced heating of the soil.
Runoff	+	Reduced by crop residues enhancing soil
 Ridge Till	infiltration rates ad increasing surface
 Requires planting and cultivating machinery retrofitting or
 changing.
May require some individual equipment
 adoptions.
Adapted to SDI as well as LEPA/LESA/LPIC.
Table 1.
Part III.
Evaporation	+	Reduced by crop residues shading the soil
 and by reduced heating of the soil.
Runoff	+	Reduced by crop residues enhancing soil
 infiltration rates ad increasing surface
 Requires planting and cultivating machinery retrofitting or
 changing.
May require some individual equipment
 adoptions.
Well adapted to LESA/LPIC but can be used
 Percolation	+	Reduced by decisions to time and size
 events to match soil water holding
 Evaporation	+	Reduced by using a later day scheduling
 timing to lengthen event cycles.
Runoff	+	Reduced by using timing to consider
 Easily adapted to all irrigation application technologies.
Requires training and field observations and measurements.
Can be contracted through private consultants.
Percolation	+	Reduced by decisions to time and size
 events to match soil water holding
 capacity.
Can actually monitor lower root
 Evaporation	+	Reduced by using a later day scheduling
 timing to lengthen event cycles.
Based	Runoff	+	Reduced by automated irrigation shut-
 Easily adapted to all irrigation application technologies.
Requires modest to significant capital investment and some
 training.
Can be contracted through private consultants.
Can be easily integrated with center pivots or SDI into
 Evaporation	+	Reduced by using a later day scheduling
 timing to lengthen event cycles.
Based	Easily adapted to most irrigation application technologies.
Requires modest capital investment and some training.
Can
 be contracted through private consultants.
Can be
 integrated with center pivots or SDI into automated controls.
Research Report Sensor-based management of Nitrogen of irrigated durum wheat in Arizona, 2013
 Pedro Andrade-Sanchez and Michael J.
Ottman Extension Agricultural Engineer and Extension Agronomist University of Arizona, College of Agriculture and Life Sciences
 Nitrogen use efficiency  in irrigated high-input wheat production is an area of concern due to N losses associated with fertility, irrigation, and tillage management.
Restricted use of N fertilizer may improve NUE but yield potential would be compromised.
An improved management option will make use of new sensing technology capable of detecting in-field variation of plant size and nutritional status and enable site-specific management of fertility inputs.
Field-ready hardware can provide for automatic variable-rate dispensing of fertilizers, but a computer algorithm needs to be developed in order to provide instructions to the rate controller.
Commercial-grade technology is being tested in Maricopa as part of this study and includes active-light canopy reflectance and displacement sensors, as well as GPS-based rate controllers for application equipment.
Experimental data on sensor output and corresponding plant conditions are being used to develop an algorithm specific to the conditions and yield goals of Central Arizona.
The irrigated farming systems in the semi-desert are highly productive and require substantial amounts of production inputs to sustain this productivity level.
For durum wheat production in Arizona, Nitrogen fertilizer is an essential component of fertility management.
It is needed to ensure the crop will reach adequate protein levels in the grain.
On the other hand, Nitrogen use efficiency  in wheat production can be an area of concern since wheat, as the case of most cereals, tends to have low NUE due to N released from the plant tissue and other losses associated with fertility, irrigation, and tillage management.
Nitrogen fertilizer is an energyintensive, expensive material that should be carefully managed to ensure high productivity within economical limits and with the minimum environmental footprint possible.
This project targeted the use of new technology in sensing crop needs and dispensing prescribed rates of N fertilizer.
There are three basic components of this technological package: a) improved application technology, which is commercially available and includes GPS, in-cab multi-function computer displays and electronic variable-rate controllers; b) crop biomass/vigor monitoring sensors such as active-light spectral sensors; and c) the mathematical algorithms that determine the rate to use according to the crop condition and location in the field.
This experiment was established in 3 acres of loamy-clay texture soil at the Maricopa Agricultural Center.
This land was sown with Sudan grass in the summer months of 2012 in
 order to enhance the response of the crop to nitrogen fertilizer.
Durum wheat of Kronos variety was planted on dry ground at a rate of 150 Ib/A on December 12, 2012, followed by next-day irrigation.
The treatments were a combination of total amounts of nitrogen fertilizer and the application timing which created total cumulative amounts of 0, 100, 150, 250, and 325 Ib/A of applied nitrogen fertilizer.
Every combination was replicated three times to generate a total number of 36 experimental plots which were randomly allocated in three blocks.
The harvestable area of each experimental plot was 2,000 ft2.
Table 1 contains a compilation of treatments in this study.
Table 1.
Experimental fertility treatments showing nominal values of nitrogen fertilizer rates  arranged by time of application.
Maricopa, AZ.
2013.
Treatment ID	Pre-planting	Tillering	Stem elongation	Heading
 			
 1	0	0	0	0
 2	0	150	0	0
 3	0	150	100	0
 4	0	150	100	75
 5	50	0	0	0
 6	50	100	0	0
 7	50	100	100	0
 8	50	100	100	75
 9	100	0	0	0
 10	100	50	0	0
 11	100	50	100	0
 12	100	50	100	75
 Nitrogen fertilizer applications were carried out using a ground rig with a rear boom with special nozzles for low-pressure, high-flow application.
This rig was instrumented with Raven flow and section control sensors, along with GPS receiver and active-light "Green-Seeker" spectral sensors.
These sensors were connected to a Trimble FMX on-board computer with variable-rate unlock to handle the application function and control the flow to keep constant application rates as demanded by the experimental design.
The liquid fertilizer used in this study was UAN-32 and this material was applied in top-dressing mode with no injury to the crop canopy.
Figure 2 shows the sprayer setup used in this project to deliver the target application rates of nitrogen fertilizer.
combine with a 20 ft.
header and instrumented with a GPS-based yield monitor.
Grain samples were taken for quality analysis using percent protein at 12% moisture content.
Figure 1.
Ground rig during field deployment of application equipment.
Maricopa, AZ.
2013.
The soil sampling at the time of planting showed an average concentration of 7.9 ppm of Phosphorous and 3.3 ppm of Nitrates.
With these findings we expected to have a strong response to nitrogen fertilizer applications.
Phosphorous levels were adequate for crop development, since it was uncertain if the crop would respond to P applications it was decided not to apply and avoid confounding responses to a mixed fertility management.
Tables 2 and 3 present a compilation of crop yield and grain quality, as well as crop response parameters measured during the season.
Plots in figure 2 show the response of fertility treatments that received the maximum amount of nitrogen fertilizer  and therefore reported the highest yields in these trials.
These N-rich treatments resulted in similar protein levels but with significant differences in yield.
The dynamics of change in sensor readings suggest that sensor readings can be used to apply rates based on the crop response to light.
Statistical analyses are being carried out and will be completed at the time of submitting the final report.
Table 2.
Average values of yield and grain protein content.
Maricopa, AZ.
2013.
Treatment ID	Yield	Grain protein
 Table 3.
Average values of spectral sensors, biomass production, and Nitrates concentration in soil and plant.
Maricopa, AZ.
2013.
Normalized-Difference Vegetation Index 	Above ground biomass 
 Treatment ID	1/24/2013	3/1/2013	4/1/2013	4/10/2013	2/5/2013	3/1/2013	4/5/2013
 1	0.25	0.53	0.39	0.37	15.50	27.69	64.18
 2	0.26	0.73	0.58	0.52	15.50	50.46	103.84
 3	0.25	0.73	0.60	0.51	15.50	50.46	100.17
 4	0.26	0.72	0.64	0.57	15.50	50.46	100.17
 5	0.26	0.60	0.52	0.48	15.12	33.98	75.93
 6	0.27	0.70	0.69	0.63	15.12	46.11	98.03
 7	0.27	0.72	0.72	0.67	15.12	46.11	97.64
 8	0.26	0.70	0.69	0.64	15.12	46.11	97.64
 9	0.25	0.65	0.55	0.53	16.49	39.10	85.97
 10	0.26	0.68	0.54	0.52	16.49	44.23	105.13
 11	0.26	0.67	0.55	0.50	16.49	44.23	107.16
 12	0.25	0.68	0.58	0.53	16.49	44.23	107.16
 Soil Nitrates concentration 8-in 	Plant lower stem Nitrates concentration 
 Treatment ID	12/8/2012	1/24/2013	3/1/2013	3/30/2013	4/9/2013	1/24/2013	3/1/2013	3/30/2013	4/9/2013
 1	3.23	3.12	0.86	0.23	3.72	0.16	0.16
 2	3.23	3.12	4.93	3.21	3.72	8.81	8.31
 3	3.23	3.12	4.93	9.96	8.11	3.72	8.81	20.98	19.01
 4	3.23	3.12	4.93	9.96	23.65	3.72	8.81	20.98	21.43
 5	3.23	10.13	1.21	0.19	12.55	0.29	0.08
 6	3.23	10.13	6.01	0.84	12.55	7.83	4.34
 7	3.23	10.13	6.01	7.33	1.60	12.55	7.83	20.58	17.95
 8	3.23	10.13	6.01	7.33	12.54	12.55	7.83	20.58	18.93
 9	3.23	10.27	1.66	0.15	16.62	1.57	0.21
 10	3.23	10.27	3.72	0.35	16.62	5.60	5.91
 11	3.23	10.27	3.72	10.44	7.31	16.62	5.60	18.90	15.72
 12	3.23	10.27	3.72	10.44	32.64	16.62	5.60	18.90	15.84
 Figure 2.
Dynamics of crop vegetation growth and nitrogen use.
Maricopa, AZ.
2013.
The crop water stress was found to be small soon after a rainfall/irrigation event and drastically increased three to four days after a wetting event.
For example, the crop water stress data for corn in 2020 is shown in Figure 2 where the crop water stress was low for all irrigation levels but increased after two days from a wetting event.
It was noted from the figure that the rainfed had the highest water stress while the fully irrigated levels had least stress on a specific day.
In the Central Plains area of Colorado, Kansas and Nebraska, approximately 9 million acres of cropland are irrigated by center pivot irrigation systems.
Existing systems span the generations of center pivot technology evolution from water to electric and hydraulically driven machines.
Due to their design, center pivots are operating on varying topography, and often have a range in soil textures present under a single machine.
Perched water tables challenge managers of standard machines with the need to provide little or no irrigation water to some areas while fully irrigating others.
Each of these factors represents a reason for using some sort of monitor/controller to manage water applications based upon need.
In the process, altering machine speed of travel and irrigation cycles is the first step in site specific irrigation.
Precision application and site specific irrigation are techniques to maximize the value of the water applied via a center pivot.
On a more basic front, farming operations often include an average of 3 center pivot systems with some operations including 15 or more.
Without a programmable controller, the producer must physically being on site to determine the status of the center pivot.
With new technology, producers can now obtain knowledge of whether the system is operating on a real-time basis by communicating with the machine to determine operating status.
The same technology provides to change operation settings from a remote location.
The purpose of this article is to present some of the research that has been conducted to evaluate system controllers for use in monitoring and controlling center pivots and discuss how these systems could be used in a site-specific irrigation system.
Over the last two decades research has been conducted by public and private groups seeking to development methodology and decision making tools necessary for application of water and plant nutrients based upon the physical
 limitations of a tract of land.
In essence this work was adding center pivot irrigation systems to the list of variables that can be considered on a site-specific basis.
As the technology has evolved so has the list of terminology used to help lay claim to unique ways standard center pivot controls are replaced and/or enhanced to allow variation in the center pivot's application depth and water application rate.
Initial steps to define decision making tools used for site-specific irrigation began in the early 1980's.
Technologies such as Low Energy Precision Application  were developed based on the early efforts to define optimum flow rates for sprinkler heads operating within inches of the soil surface.
A series of control manifolds were used deliver different flow rates.
Later work by Roth and Gardner  sought to use the irrigation system to apply different amounts of nitrogen fertilizer with irrigation water.
Fully site-specific irrigation research was initiated in earnest in the early 1990's at four locations across the US.
Reports of this work were published beginning in 1992 based upon work conducted the USDA-ARS researchers located in Fort Collins, CO , Moscow, ID , Florence, SC , and Pullman, WA.
These efforts have helped to shape the technologies used to control moving sprinkler systems and individual sprinklers.
Individual sprinkler control of water application depth can be accomplished by using a series of on-off time cycles or as it has become known as 'pulsing' the sprinkler.
Reducing the on time is effective and reducing both the application depth and the water application rate.
This is accomplished using either direct-acting or pilot-operated solenoid valves.
Direct acting valves have a linkage between the plunger and the valve disc while the pilot-operated solenoid uses irrigation pipeline pressure to activate the valve.
A second method for controlling irrigation water application was developed by King and Kincaid  at Kimberly, ID.
The variable flow sprinkler uses a mechanically-activated needle to alter the nozzle outlet area which lowers the sprinkler flow rate over the range of 35 to 100% of its rated flow rate based upon operating pressure.
The needle can be controlled using electrical and hydraulic actuators.
The main issue is that the wetted pattern and water droplet size distribution of the sprinkler changes with flow rate which creates water application uniformity issues due to a change in sprinkler pattern overlap.
A third method of controlling irrigation water application is to include multiple manifolds with different sized sprinkler nozzles.
In this case, activation of more than one sprinkler manifold can serve to increase the water application rate and depth above that for a single sprinkler package.
Control of each manifold is accomplished using solenoid valves similar to those described for the pulsing sprinkler option above.
As with any new technology, there are positives and negatives associated with each of these three methods of controlling sprinkler flow rates.
Certainly long term maintenance is an issue.
However, the biggest factor limiting their use is installation cost that ranges from around $2000 for a system monitor to over $20,000 for control of individual sprinklers.
Center pivot manufacturers have developed proprietary means of monitoring and controlling center pivots using a variety of technologies under the trade names:, OnTrac IPAC, Tracker, and Grow Smart.
The computerized control panels provide center pivot operators with the potential to monitor and control center pivots using telephones, radio telemetry, internet connections and satellite communication.
In addition, there are a few private venture monitors and/or controllers that are available under the trade names: Farmscan, AgSense, and Pivotrac.
Farmscan is the only company providing equipment for total VRI at this time.
The first requirement is to know the system position.
If a producer queries the control panel during the course of an irrigation event, knowledge of where the system is lets the producer determine if problems have occurred and also how soon the system will reach stop-in-slot  positions.
Standard machines utilize a resolver located at the pivot point to report the position of the first tower.
In nearly all cases, the main component of new controllers is a Wide Area Augmentation System  enabled GPS unit that is mounted near the last tower of the center pivot.
The WAAS is a publicly available system that provides a differentially corrected signal to increase the accuracy of the unit at a relatively low cost.
Part two includes monitoring the center pivot control circuitry.
This is accomplished directly at the main pivot panel.
But can also be done using a Programmable Logic Controller  device.
The main panel houses control circuitry for the end gun, system speed of travel and direction, and on/off controls.
Since most of this circuitry terminates at the end tower, center pivot monitors and controllers also can be mounted near the last tower control box.
At the pivot point additional components can be monitored and/or controlled such as auxiliary chemical pumps, system operating pressure and flow rate.
Likewise, weather sensors can be monitored to provide wind speed and direction, temperature and rainfall information if desired.
Options also exist to continuously monitor soil water content in the field.
Current research is aimed at developing decision support tools for using a center pivot mounted infrared thermometer  to help manage irrigation water applications.
Part three of the system includes a communication link between the controller and the end user whether that be cell phone, land line phone, radio or internet connection.
Cell phone links are accomplished using an on-board modem.
This arrangement requires cell phone service from the pivot location and from the user location.
However, there are few locations in the Central Plains where communications are not possible.
Some systems transmit GPS coordinates and system monitor information via satellite radio to a satellite which is transmitted back to a ground-based facility where it is distributed via the internet and made accessible by phone using IVR solutions developed specifically for center pivot controls.
Radio telemetry is another means of transmitting information from the field to the office or phone.
However, radios are line of site communication devices so buildings, trees, and hills can impede communications over long distances.
Most radio communication links employ radios operating in the 900 MHz range to communicate over distance less than 15 miles.
For longer distances, a bridge or repeater is positioned on a tower to communicate over longer distances.
Selecting the method of sprinkler control may be the easiest decision to make since the main factor of concern is: Will it pay to install the controls?
However, once the decision is made to use a variable rate sprinkler application systembased upon some predetermined management zone size, design of the remaining portions of the irrigation system become interdependent.
How will the pumping plant respond to changes is system flow rate requirements?
As sprinklers turn on and off, the flow rate required by the system varies.
The response of a standard system is that the pump output will follow the pump curve to the right or left depending on whether more or less sprinklers are operating.
More significant is that sprinklers near the end gun have flow rates that are significantly greater than sprinklers near the pivot point.
Consequently, turning off sprinklers on the first 200 feet of the system will have much less effect than turning off a 200 foot section near the end gun.
The correct design response is to install a pumping plant with variable revolutions per minute  so that as more sprinklers are added, the pumping RPM is increased and visa versa.
In this way the pumping plant can supply water at the design pressure regardless whether 50 or 150 sprinklers are in operation.
The difficulty arises when the motor used to supply power the pump is the same one used to supply power to the center pivot.
Changes is pump RPM require changes in engine RPM.
So a separate energy supply may be required for the center pivot.
How do I adjust the chemical injection system to apply different chemical amounts ?
Application of variable chemical rates can be achieved by simply maintaining a design injection rate and let the difference in water application depth control the chemical application rate.
However, what if our management decisions require high application of a plant nutrient to an area that is to receive little or no water?
A second factor is that the time of travel for chemicals to be transported from the pivot point to a position on the pivot lateral varies with the velocity of water in the pipeline.
As the number of sprinklers in operation changes so does the water flow velocity.
Thus, chemical could enter the system with a velocity of 6 feet per second when all sprinklers are on and 3 feet per second when a large number are turned off.
This factor will determine when a change in injection rate should start.
How accurately can I determine system position if application rate changes are desired?
Center pivot position on most systems  is determined by the resolver that is located at the pivot point.
Alignment systems typically have an accuracy of +1.5 of where the first tower is located.
Thus, at a distance of 1320 feet from the pivot point, the position of the last sprinkler could be off by 34 feet or more.
Research conducted by Peters and Evett  found that resolver determined position errors could be up to 5 degrees or over 100 feet on a 1320 foot long center pivot.
Installation of a WAAS enabled digital GPS system can increase the accuracy of determining the location of the pivot lateral to errors of less than 10 feet.
The net effect of being able to accurately determine the pivot lateral location is that management zone size can be reduced without increasing the potential for a misapplication.
From an engineering perspective these are not trivial questions particularly if changes in water, nutrient and energy use efficiency are to be accomplished simultaneously.
In the end it is the accuracy of the data we use to make decisions that is critical.
And so another question must be answered: Will the increase in water application to management Zone 25 yield enough forage or grain to pay for the application?
To make full use of site specific irrigation techniques, geo-referenced field information is needed for variables that will be used in making irrigation management decisions.
Field soil texture and fertility will be needed to help isolate field areas where plant available water is indeed the single most important factor.
Yield maps could show areas with reduced yields that are due more to soil nutrient levels than plant available water or a combination of the two.
The difficult factor is to have production functions that give accurate information about what will happen to yield if water or plant nutrients are altered.
Acquiring this information may require a few years of in-field testing while harvesting with a yield monitor.
Field maps of each of these variables  represent information that make up levels in a Graphic Information System  analysis.
It is important that these maps provide information on a management zone size basis.
Limitations in the ability to collect point measurements due to cost or response time of sensors all impact the spatial resolution of the application map.
For example, an 8-row combine operating at 6 mph and collecting yield estimates every 3-seconds provides a different spatial picture than a center pivot with control of banks of 5 sprinkler heads.
Consequently, variable rate irrigation controls will typically be at less resolution than any of the other crop production inputs.
Center pivot controllers and monitors are available to help producers manage water application on a whole or part of field basis.
The combination of knowledge of current system status and location in the field help ascertain if the irrigation application is proceeding as planned.
By recording other field based information water applications can be adjusted due to different crops, field topography, soils and productivity levels.
Ultimately, the complete control of crop water inputs on a IMZ basis could save between 10-20% of the water applied per season.
Lowe installation costs and further development of decision support systems for use by producers are needed before variable rate technology will receive widespread use by row crop producers in the Central Plains area.
Listed below are general definitions for the acronyms that are used in the discussion of center pivot monitors and controls.
GIS Geographic Information Systems is a system that allows for sets of geo-referenced variables  to be analyzed, managed, displayed, and used to developed sitespecific maps for the application of water, pesticides, or plant nutrients.
GPS Global Position Systems is a satellite system means of determining field positions, speed of travel, and time with sufficient precision to allow site specific application of irrigation water, pesticides, or plant nutrients in response to productivity indices.
IMZ Individual Management Zone is an individual area of an irrigated field for which the technology exists to alter the application of water, pesticides, or plant nutrients in response to productivity indices.
IRT Infra-Red Thermometry is the use of an infrared thermometer to record plant leaf temperature as an indicator of plant stress.
IVR Interactive Voice Response is technology that enables users to retrieve or deliver information on time critical events and activities from any telephone.
LEPA Low Energy Precision Application is a water, soil, and plant management system for uniformly applying small frequent irrigations near the soil surface to field areas
 planted in a circular fashion and accompanied by soil-tillage to increase soil surface water storage.
PA Precision Agriculture, or site-specific farming is the precise delivery of water, pesticides and plant nutrients based upon suspected deficiencies in or need for water, pesticides, or plant nutrients.
PLC Programmable Logic Controller is a digital computer used for automation of electromechanical processes and is designed for multiple inputs and outputs, and is not affected by temperature, electrical noise, or vibration.
VRI Variable Rate Irrigation is the delivery of irrigation water to match the needs of individual management zones within an irrigated field.
VRT Variable Rate Technology is the process of applying irrigation water, pesticides, or plant nutrients at rates which are based on defined crop production indices.
WAAS Wide Area Augmentation System is a navigation aid developed by the Federal Aviation Administration to augment the accuracy, integrity and availability of the GPS for use in aircraft flight monitoring and control.
Karmeli, D and G.
Peri.
1974.
Basic principles of pulse irrigation.
Journal of Irrigation and Drainage Division, ASCE 100:309-319.
Managing Your Well During Drought
 Groundwater levels in wells vary over time.
Water conservation and pump adjustments can help manage your water well during drought.
Droughts can be stressful for the three million rural residents in Pennsylvania who rely on private wells for their water supply.
These individual wells tap groundwater aquifers that cannot easily be seen or monitored.
The invisible nature of groundwater leads to an uneasy feeling among homeowners relying on wells that their water supply could dry up without warning during a drought.
The Normal Cycle of Groundwater Levels
 The water level in a groundwater well will fluctuate naturally during the year.
Groundwater levels tend to be highest during March and April in response to winter snowmelt and spring rainfall.
The movement of rain and snowmelt into groundwater is known as recharge.
Groundwater levels usually begin to fall in May and continue to decline during the summer.
Figure 1.
Natural groundwater fluctuation during the year in a typical Pennsylvania water well.
Groundwater recharge is limited during late spring and summer because trees and other plants use the available water to grow.
Natural groundwater levels usually reach their lowest point in late September or October.
In late fall, after trees and plants have stopped growing and before snow begins to fall, groundwater levels may rise in response to rainfall and recharge.
Groundwater recharge persists through the fall until cold temperatures produce snowfall and frozen soil that limit the ability of water to infiltrate into the ground.
Groundwater levels during winter may be stable or fall slightly until spring snowmelt and rainstorms start the annual cycle again.
Given this natural cycle of groundwater, most problems with wells tend to occur in late summer or early fall when groundwater levels naturally reach their lowest levels.
The natural fluctuation of groundwater levels illustrated in Figure 1 tends to be most pronounced in shallow wells.
As a result, shallow wells are usually more susceptible to drought than deeper wells.
Shallow, hand-dug wells, for example, are often the first wells to dry up during drought.
Although deeper wells may be slower to suffer from drought conditions, they may also take longer to recover after a drought has occurred.
Can Land Use Changes Affect the Susceptibility of My Well to Drought?
Dramatic changes have occurred to the landscape in many rural areas of Pennsylvania.
Increasing development and rural population growth will likely continue in the future in parts of Pennsylvania.
Existing rural residents often worry that these changes may create competition for groundwater that might increase the susceptibility of their well to drought.
It is unlikely that small numbers of new homes will cause significant changes in groundwater levels.
However, more dramatic changes in land use that tap large amounts of groundwater or prevent recharge from occurring over a wide area could make existing wells more susceptible to drought.
This is especially true in areas where mining is occurring or where large paved areas prevent rainfall and snowmelt from recharging groundwater.
How Can I Monitor Groundwater Levels?
Direct determination of the groundwater level in your well is difficult and usually requires the use of a water level meter.
These meters are comprised of an electrical probe attached to the end of a measuring tape.
The probe is lowered into the well until a display or light indicates that it has reached water.
The depth to water is then read directly from the measuring tape.
These instruments generally cost $300 or more depending on the anticipated length of tape needed.
There are other less direct but more practical methods to determine the status of your well water supply.
The U.S.
Geological Survey  provides a simple website which compiles the various drought measurements  into one county-based graphic at the USGS website.
The circular graphic in each county provides more information about the current status of drought indicators in that county.
By clicking on the groundwater tab , you can access more information about the current status and trends of groundwater in your county.
You may also be able to learn more about your local groundwater conditions by contacting local well drillers and neighbors.
Well drillers are continually drilling new wells and, therefore, may have knowledge of groundwater levels near your well.
They may also have installed new submersible pumps in nearby wells that would allow them to document the existing groundwater level.
Similar discussions with neighbors that have had new pumps installed or had new wells drilled may provide valuable information about the groundwater level.
How Can I Conserve Water?
Water conservation measures become critical during times of drought.
Homeowners relying on private wells should begin to conserve water as soon as drought conditions occur.
Water use within the home can be significantly reduced through changes in habits and by installing water-saving devices.
In emergency situations, changes in water use habits can provide quick reductions in water use.
Examples might include flushing the toilet less often, taking shorter showers, only washing full loads of dishes or laundry, and collecting water from roof gutters for outside use.
It is also important to note that certain drought declarations may also require water use reductions or restrictions on water use.
For example, a "drought emergency" declaration bans the nonessential use of water such as car washing and lawn watering.
These regulations apply to everyone, including homeowners with private wells.
For more information on ways to save water around the home, consult 20 Ways to Save Water in an Emergency and Household Water Conservation.
What Can I Do If My Well Runs Dry?
There are a number of reasons why a well may quit producing water.
The most frequent cause is a malfunctioning or worn-out submersible pump.
Other electrical problems such as a malfunctioning electrical switch at the pressure tank may also cause a loss of water.
Pressure tanks also need to be replaced from time to time.
Water quality problems like iron bacteria and sediment may also clog the well and severely restrict water flow from the well.
A well driller or competent plumber should be consulted to determine the exact cause of the problem.
Under persistent dry weather conditions, the water level in your well may drop below the submersible pump, causing a loss of water.
In some cases, the water level may only temporarily drop below the pump when water is being frequently pumped from the well during showers or laundry.
Under these conditions, you may be able to continue using the well by initiating emergency water conservation measures and using water only for essential purposes.
If the water level permanently drops below the submersible pump, it may be possible to lower the submersible pump within the existing well.
In most cases this will only provide a short-term solution to the problem.
More permanent solutions require either deepening the existing well or drilling a new well.
Be aware that deepening an existing well may not increase the well yield and could produce water of different water quality characteristics.
You should consult with a local well driller or a professional hydrogeologist to determine the best solution for your situation.
Proper management of private wells during droughts will become more important as competition for water in rural areas of Pennsylvania increases.
By monitoring nearby groundwater levels online you may be able to detect potential problems early and implement water conservation strategies that may prevent your well from going dry.
The amount of available water in a soil is determined primarily by soil texture and organic matter content.
Sandy soils, with large soil particles and low organic matter levels, hold less water than a silt or clay soil, which have smaller particles and higher organic matter levels.
This difference in available water is the reason sandy spots show crop stress much sooner than surrounding soils.
Agriculture irrigation accounts for approximately 80 percent of the consumptive ground and surface water use in the United States.
Recently, acreage of irrigated land for row crop production has increased in humid regions , leading to the need for optimizing water use in these systems to conserve water resources and bring economic benefit to producers.
Soybean water use varies with growth stage.
Soil water sensors are one tool that can be utilized to better assess soil water availability in the soil profile and schedule irrigation appropriately during soybean growth stages.
Soil water sensors should be installed as soon as the crop is established but before plants get too large.
Carefully place sensors in the row using a soil probe or auger to achieve correct depth.
One thing to consider when placing and installing the sensors/logger stations is to select representative areas of the whole field.
Typical sensor depth can be 6 to 36 inches which may vary depending on sensor and crop types.
Source: USDA, National Agricultural Statistics Service, Map Atlases for the 2012 Census of Agriculture.
Figure 1.
Change in acreage of irrigated cropland, 2007-2012   Tennessee and West Tennessee, 1930-2012.
Figure 2.
Soybean water use across growth stages.
Objective: The objective of this study was to determine the latest effective soybean growth stage to initiate irrigation and maximize yield for soybean plants.
Large plots  accommodated a variable rate irrigation  equipped center pivot at the Milan AgResearch and Education Center, in Milan, Tennessee,  in 2017, 2018 and 2019.
Soil water loggers  equipped with Teros-21 soil water sensors and rain gauges were used to monitor precipitation and guide irrigation decisions.
The soil type at the study location was a silt loam, a Providence silt loam soil.
A maturity group  4.8 variety  was planted in early to mid-May and subjected to three irrigation initiation timings , one irrigation termination timing  , and one rainfed  treatment; irrigation was withheld if soil matric potential was greater than -65 to -70 cb , based on soil water sensor readings.
Treatments were replicated four times.
Soybean plots were harvested with a Case IH combine equipped with a yield monitor; yield data were excluded from an area 10 feet from the edges of each plot to remove the irrigation transition zones.
Yield data were analyzed with JMP Pro 13.2 and means were separated using the student's t-test.
Differences were considered significant for a = 0.05.
Figure 3.
Irrigation zones on a VRI equipped center pivot  and plots layout showing yield points, trimmed plot, and water loggers/ sensors station  areas  in Milan, Tennessee.
precipitation events.
The precipitation events for August 4 and 5 represent the irrigation that was applied.
measured logger.
Example graph  of the graph illustrates 2020 growing season soil water potential and precipitation Meter Inc.
sensor ZL6  , a screenshot of ZENTRA-Cloud app , and a soybean large plot equipped with Figure 4.
Monitoring soil water and water usage to aid irrigation strategies.
Teros 21 matric potential sensor , 10 HS soil moisture via soil water sensors.
The blue bars represent the
 SOYBEAN GROWTH STAGING GUIDE
 Pods are 1/4-inch long at one of the four uppermost nodes on the main stem
 Pods are 3/4-inch long at one of the four uppermost nodes on the main stem
 R5 Beginning seed Seeds are 1/8-inch long in the pod at one of the four uppermost nodes on the main stem
 R6 Full seed Pods contain green seeds that fill the pod to capacity at one of the four uppermost nodes on the main stem
 Majority of pods are yellow
 main stem has reached its
 95% of the pods have reached
 and at least one pod on the
 The study site received 7.24 inches and 7.41 inches more rain from June through August in 2017 and 2019, respectively, compared to 2018.
In 2017 and 2019, no significant difference was observed between the yield of irrigated or rainfed treatments, and this was attributed to the high amount of rainfall received at the site.
An early irrigation initiation at soybean growth stages , such as beginning bloom  or beginning pod , would be expected to promote bloom or pod retention, while a late irrigation initiation at early seed  should increase seed number and size.
In 2018, all irrigated plots yielded similarly to each other but had significantly higher yields than rainfed plots.
Based on results from two wet years and one drier year, delaying irrigation initiation until R5 was as effective as an early initiation at either R1 or R3.
Overall, using soil water sensors for real time monitoring of the soil water status enables more informed irrigation decisions and potential water and energy savings, and prevents potentially negative effects of overwatering if irrigation is begun too early in the season.
Irrigation decisions are based on the needs of the crop and may vary from one year to the next.
Furthermore, environmental factors such as diverse rainfall patterns, soil type, soil water availability, heat waves and high evaporative demand need to be considered.
For example, in sandy soils, soybeans are more likely to require irrigation in the late vegetative and early reproductive stages , and providing adequate soil water in the later reproductive stages  is even more critical.
Table 1.
The rainfall and amount of water added  to each treatment at AgResearch and Education Center at Milan
 Month	May	4.01	3.00	2.50
 June	4.84	4.37	3.48
 July	6.93	3.06	7.47
 August	4.80	1.90	5.79
 September	4.41	11.27	0.34
 October 	1.01	4.36	3.37
 Treatment	R1R6	2.35	6.56	2.87
 R3R6	2.05	5.33	2.05
 R5R6	2.05	3.28	0.82
 No irrigation	0.00	0.00	0.00
 Figure 6.
Soybean yield for each irrigation treatment  in 2017, 2018 and 2019.
Means of the same year followed by the same letter are not significantly different.
Where do we go from here?
The distribution of rainfall within a growing season was an important factor in determining the efficacy of irrigation timing.
In our study, the site received adequate rainfall early and mid-season that supported yields that were similar to our R5R6 irrigation regime.
An explanation for significantly lower soybean yield under R1R6 and R3R6 irrigation treatments in 2017 compared to rainfed  is prolonged periods of saturation which likely reduced the production.
Further study during years with both above and below average rainfall is necessary in order to refine our soybean irrigation recommendations.
Soil type also affects plant-soil-water relations, and in 2017, experimental plot layout resulted in within field variation of soil  texture and fertility that may have resulted in no differences between irrigation timing reflected in the data.
Soil types with different water-holding capacities will require different irrigation strategies.
Our work was conducted using a late MG 4 soybean variety, which reflects a large percentage of planted acres in Tennessee.
Ongoing studies with MG 3 and 5 varieties will indicate whether MG should be a consideration when timing irrigation in soybean.
UTIA.TENNESSEE.EDU Real.
Life.
Solutions." TM
As a rule of thumb, during the growing season the 50% allowable water depletion is used to avoid yield loss.
Irrigators with an older system prone to break downs or are on electric load control may want to select 30 or 40% depletion as a target.
CHAPTER 2: Growth Stages of Soybean
 Angela McClure, Professor Emeritus Department of Plant Sciences
 The purpose of this chapter is to describe basic growth and development of the soybean plant in order to enable accurate staging of a soybean field during scouting.
Herbicide application, timing and termination of irrigation, and insecticide and fungicide timing decisions are based on key growth stages.
Therefore, understanding how the soybean plant develops and what some of those key growth stages are is critical to managing the crop effectively.
"Staging" a soybean field means to determine current crop growth progress.
Crop staging should be part of the scouting process along with checking leaves for diseases or using a sweep net to gauge insect populations.
Staging involves evaluating growth of about 10 plants in three or more representative locations of the field.
If at least 50 percent of plants checked are at one specific stage, then the entire field is considered to be at that stage.
Soybean growth occurs in a series of vegetative and reproductive development phases.
Following emergence, soybeans are considered to be vegetative while leaves are produced on the main stem until the initiation of flowering, at which time they are considered to be reproductive for the duration of the season.
The soybean plant is a "short day" plant, meaning flowering is triggered when plants are exposed to shorter days with longer nighttime or dark periods of a critical length.
The actual trigger date when flowering starts will depend on the planting date, temperature and the maturity of the variety.
This response to daylength allows soybeans planted on different dates to reach physiological maturity before a hard freeze in the fall.
Mid-April planted soybeans need five months or longer to fully mature; however, mid-June planted soybeans mature in about four months.
The soybean plant is a dicot meaning two cotyledon or "seed" leaves emerge first.
The growing point or apical meristem is located above ground at the top of the main stem.
New leaves develop at the apical meristem on main stem nodes.
Each leaf attaches to the main stem by a petiole.
An axillary bud develops where petioles connect to the main stem and is the source of flowering racemes, pods and branches.
Fig.
2-1.
Source: Pedersen, 2009.
The soybean root system consists of a branched taproot and lateral roots.
The soybean is a legume, and it forms a symbiotic relationship with soil Bradyrhizobium japonicum or "rhizobia" that results in the formation of nodules on the roots.
Three to four weeks after emergence, nodules begin converting atmospheric nitrogen  into a form used by the plant, which eliminates dependency on N-containing fertilizer.
Tiny nodules grow and fix N for about 2 months, then die and are replaced by new nodules throughout the season.
Nodules that are actively fixing N are pink to red on the inside.
Soybean growth habit or growth type is either determinate or indeterminate and describes the amount of overlap between vegetative growth and reproductive
 Fig.
2-2.
Example of a V3 soybean plant.
Plant 3 has fully developed trifoliates and 4 nodes.
Source: McClure, 2022.
development.
Most varieties in maturity group  00 through 4 are indeterminate; early MG 5 varieties may be indeterminate or determinate; and late MG 5 through MG 8 varieties are primarily determinate.
Maturity groups 00 through 4 were bred for production in northern states.
Northern-adapted MGs grown at southern latitudes will bloom before the summer solstice in response to the daylength and warmer nights at more southern latitudes.
Determinate soybeans produce trifoliate leaves at alternating nodes on the main stem until day length triggers flowering, whereupon the production of at terminal raceme  at the top of the main stem ceases new leaf production and the plant enters reproduction.
For determinate growth habit beans, vegetative growth on the main stem overlaps very little with reproductive development.
Indeterminate soybeans produce trifoliate leaves for a period of time until flowering is triggered by daylength
 and temperature.
Upon flowering, the plant continues to produce new nodes and leaves from the growing point while also producing blooms and pods at the older  nodes.
For indeterminate varieties grown in Tennessee, there is strong overlap between vegetative and reproductive development and a potentially wider flowering and pod set window.
Both determinate and indeterminate varieties can recover from short-term drought events during flowering and early pod stages by replacing blooms aborted during stress with new flowers when conditions improve.
The wider flowering window for indeterminate varieties means they can potentially do this longer.
The resource section contains links to publications that describe in detail the process of seed germination and seedling emergence.
Staging soybeans begins when seedlings have emerged.
Table 2-1 contains vegetative growth stage descriptions beginning at emergence of the seedling  through leaf development on main stem nodes.
A soybean plant can produce as few as 12 to more than 20 nodes on the main stem.
Full season soybeans growing under good conditions have more nodes  than June-planted double crop beans or soybeans growing under frequent stress.
New nodes appear about every 4 days under favorable conditions, but production slows down considerably if temperatures are too cold and will cease while plants are growing under drought stress.
A fully developed leaf is one in which leaf or leaflet edges have unrolled to where the edges do not touch one another.
At VC, a pair of unifoliate leaves are unrolled and are opposite at the first node of the main stem.
All leaves that follow are single trifoliate leaves  that are produced at a node on alternate sides up the length of the main stem.
After VC, a "V" number is assigned to each fully developed trifoliate leaf node.
A soybean field is at V3 stage when 50 percent
 Table 2-1.
Descriptions of soybean vegetative stages and their importance for timing management decisions.
Source: Adapted from Pedersen, 2009.
VE	Emergence	Cotyledons appear above the soil surface.
VC	Cotyledon	Unifoliate leaves unrolled so that the leaf edges do not touch.
V1	1st trifoliate leaf	Fully developed  trifoliate leaf.
V2	2nd trifoliate leaf	Two fully developed trifoliate leaves.
Early N-fixing root nodules becomes functional.
V3	3rd trifoliate leaf	Three fully developed trifoliate leaves.
V3 is the cutoff stage for some post herbicides.
V	 trifoliate leaf	"n" number of fully developed trifoliate leaves.
'Note: Although the descriptive term for soybean leaves is "unifolioate" and "trifolioate," the more commonly used "unifoliate" and "trifoliate" will be used in this publication.
Table 2-2.
Description of soybean reproductive stages and importance for timing management decisions.
Source: Adapted from Pedersen, 2009.
R1	Beginning bloom	One flower opens at any node on the main stem.
A flower opens at one of the top two nodes on the main stem with a fully developed
 R2	Full bloom	trifoliate.
Beginning of rapid nutrient accumulation to vegetative parts.
Pod 3/16 inch long at one of the four uppermost nodes with fully developed trifoliate.
R3	Beginning pod	Fungicide application timed at R3-R4.
R4	Full pod	Pod 3/4 inch long at one of the four uppermost nodes with fully developed trifoliate.
Seed 1/8 inch long in a pod at one of the four uppermost nodes with fully developed
 R5	Beginning seed	trifoliate.
Apply insecticide when economic thresholds are reached.
Green seed fills pod cavity in a pod on one of the four uppermost nodes with fully
 R6	Full seed	developed trifoliate.
Irrigation terminated at R6.5.
R7	Early maturity	One normal pod on main stem turns mature brown color.
R8	Full maturity	95 percent pods on main stem reach mature brown color.
of the scouted plants contained three fully developed trifoliate leaf nodes.
Branching is also vegetative growth, but it is not considered when staging a field.
A branch contains nodes, leaves and meristems capable of producing blooms and pods.
Side branches sprout from lower main stem axillary buds following damage to the growing point.
At lower populations, more sunlight reaches lower leaves and can stimulate branching.
All soybean plants can branch; however, genetics and the environment control the intensity of branching.
Varieties with a bushy type canopy will branch extensively at low populations compared to a straight line or medium canopy variety.
Branch pods usually add very little to yield as sunlight is limited in the lower canopy.
Consider only plants with intact main stems when staging soybean reproductive development.
Stages R1-R2 describe flowering, R3-R4 describe pod development, R5-R6 describe seed development and R7-R8 describe plant maturation.
Soybeans become reproductive at first bloom or R1 when 50 percent or more of plants in a field have at least one flower somewhere on the main stem.
Flowers develop on "racemes" or flowering structures at the apical meristems.
For indeterminate varieties, flowering usually begins on the third to sixth trifoliate node of young beans, while determinate varieties begin blooming on the upper third of the main stem of mostly fully grown plants.
The soybean plant will produce many more blooms than actually develop into pods, as a means to overcome short-term stress.
In general, the last flowers produced are those at the very top of the main stem and the tip end of any branches.
Both indeterminate and determinate varieties reach full bloom or R2, when flowers appear on one of the two uppermost nodes with a fully developed trifoliate leaf.
The time difference between R1 to R2 varies between 3 to 10 days depending on maturity group and planting date.
After flowering begins, indeterminate plants continue to grow vegetatively, producing new nodes on the main stem and branches.
Under drought conditions, indeterminate varieties may remain at R2 for two or more weeks.
Once a field reaches full bloom, monitor pod and seed development by focusing on the top four nodes with a fully developed trifoliate leaf node until the onset of maturity.
This means ignoring the lower nodes on indeterminate varieties where pod and seed development may be more advanced compared to the top of the plant.
By returning each time to the upper four nodes, management for diseases and insects becomes about protecting
 Fig.
2-3.
Soybean pod example at R3, R4 and R5 stage.
Source: Photographer unknown, 2022.
Fig.
2-4.
Seed size difference between soybean stages R5, R5.5 and R6.
Source: Pedersen, 2009.
the middle and upper canopy pods that contribute the most to yield.
Scout soybeans regularly for pod-feeding insects and diseases beginning at R3 with regular checks made through seed fill.
The number of days between R2 and R3 or early pod depends on planting date and growth habit as well as temperature and environmental stress.
Full season indeterminate varieties growing under stress may cease main stem growth for a period of time, then resume node and leaf production, sometimes making field appear to "go backward" in development.
At R3 or early pod, a tiny pod 3/16 inch long is visible on at least one of the top four fully developed trifoliate nodes of half the plants checked during staging.
At early R3, new pods, new flowers and dying flowers can be found at the same node.
Under stress, R3 pods may abort or lengthen slowly when plants lack adequate moisture to elongate pods, meaning plants sometimes remain at R3 for several days.
Pod loss at R3 has a lesser impact on yield, as the plant can still generate new pods or make adjustments to seed numbers per pod or seed weight during later stages.
At R4 or full pod, a pod has elongated to 3/4 inch  on at least one of the top four fully developed trifoliate leaf nodes.
Rapid pod growth and the initiation of seed occurs during R4, making this stage critical for seed yield determination.
Pods normally reach their full length and width before seeds begin to develop.
With stress at R4, there may be some impact on seed number per pod, and plants are less able to produce new pods to compensate for aborted pods, potentially reducing total pod numbers.
At R5 or early seed, rapid seed growth and seed fill begins with tiny 1/8 inch seed "shapes" that can be seen through the pod wall  on at least one of the four upper trifoliate leaf nodes.
At early R5, it is possible to find a few
 flowers and young pods on the plant as well as pods with seed.
By late R5, plants have usually reached maximum height and leaf area, and flowering has ceased.
During R5, the soybean plant mobilizes water and nutrients to the developing seed from the leaves and stems.
In Tennessee, irrigation is typically initiated at early R5 if soil moisture is lacking in order to meet the demands of the developing seed.
Seed weight and therefore yield is strongly impacted by stress during R5.
Stress can shorten the rate and duration of seed fill as well as reduce pod and seed number per pod.
At R6 or full seed, seed reaches maximum size in one or more pods on at least one of the upper four trifoliate leaf nodes of half the plants checked during staging.
By mid R6  about 80 percent of seed dry weight has accumulated and irrigation may be terminated.
At R6.5, a few leaves may be turning, and some pods may be lighter in color.
Upon examining the upper four nodes, seed should separate fairly easily from the pod wall when a pod is pulled apart on about half of the plants that are checked.
Stress during R6 impacts the seed size/weight component of yield.
At R7 or early maturity, maximum seed dry weight is reached.
Leaves are turning, seed begin to reduce in size, turning mature light brown color, and at least one healthy pod has turned its mature brown color on at least 50 percent of the plants in the field.
At R8 or full maturity, 95 percent of pods have turned their normal brown color.
Seed moisture is still high, but the field is typically 10-12 days away from harvest.
Moisture or heat stress during reproduction will affect yield components differently.
During R1 through R5, a soybean plant can adjust the number of flowers, pods or seeds according to amount and duration of stress.
Plants at R1 through R3 have a greater ability to compensate for flower and pod loss than plants at R5.
Stress during R1 through R4 could reduce the total number of pods.
Stress at R4 through R6 may cause beans to abort in the pod and stress at R5.5 to R6.5 can affect seed size at harvest.
Fig.
2-5.
At R6.5, upper node pods may be light green to slightly yellow, seed shrink down slightly and pull apart from pod wall.
Source: McClure, 2022.
DAYS BETWEEN GROWTH STAGES
 There is no perfect alternative to routine checking of fields; however, when time is limited, a crop development model can provide an estimate for when key soybean growth stages are likely to occur.
Crop development models  use long-term weather data for a specific geographic area to estimate soybean development when the MG and planting date are known.
Nevertheless, most data used to create crop growth models are from irrigated studies and therefore predict optimal rate of development.
Dryland fields may be a few days to weeks earlier depending on the timing and duration of seasonal moisture stress.
Table 2-3 includes approximate days from planting to key growth stages for different MG soybeans planted in April, May and June under irrigated Tennessee conditions.
More planting dates and MG are at UT's Soybean Development Estimator web tool.
Planting date and MG determine the number of days from planting to reach key growth stages.
Planting date alters the daylength hours and the temperature to which plants are exposed, which will impact rate of development.
Within a MG, soybeans planted in April and early May, true "full season beans," tend to maximize the amount of time spent at each stage.
Soybeans planted in June have shorter intervals between growth stages as a way to hasten maturity before a freeze.
Nothing replaces boots in the field when managing a soybean crop.
Periodic checking of beans is critical to monitor growth, time herbicide application and identify
 insect and disease problems.
Remember the 50 percent rule that a field progresses in development when at least half the plants checked during staging have moved into the next stage.
Know where on the plant to look when staging flowering plants versus plants that are at pod or seed stages, and always remember that drought will affect the rate of development compared to what crop models might predict.
Table 2-3.
Approximate days to key reproductive  stage for irrigated soybean MG1 planted on different dates.
Source: Soybean Development Estimator, McClure and Verbree, 2016.
MATURITY	PLANTING	DAYS FROM PLANTING TO "R" STAGE
 GROUP	DATE	R1	R3	R5	R6	R8
 Apr 24	47	63	82	103	142
 3.9	May 8	35	55	73	91	125
 June 17	33	51	60	78	110
 Apr 24	48	65	85	108	144
 4.2	May 8	40	63	74	97	135
 June 17	38	52	64	81	117
 Apr 24	47	68	90	107	144
 4.8	May 8	34	66	78	103	132
 June 17	35	55	68	82	114
 Apr 24	50	68	85	111	147
 5.3	May 8	41	67	76	98	132
 June 17	39	53	67	83	123
 1 Note: All varieties were indeterminate growth habit.
INSTITUTE OF AGRICULTURE THE UNIVERSITY OF TENNESSEE
 UTIA.TENNESSEE.EDU Real.
Life.
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Benchmarking Irrigation Water Use on Mixed Vegetable Farms in Northern Colorado: 2010-2018
 Fact Sheet #4.724 Crops Irrigation
 It is crucial to meet vegetable crop water needs in the semi-arid west for optimal plant health, yield and produce quality that consumers demand.
Vegetable crops in Colorado require supplemental irrigation to meet these goals.
However, before the time of this publication, Colorado growers and agriculture professionals lacked baseline water use data for mixed vegetable farms in our region.
Our objective was to quantify the amount of irrigation water in acre inches/acre applied by mixed vegetable farms in Boulder County, Colorado.
This factsheet describes the results of a mixed vegetable farm irrigation water application study over nine field growing seasons and the use of local weather station data as means to benchmark mixed vegetable farm water use.
These results and tools can be used by mixed vegetable producers with similar environmental conditions to understand how their water use compares to a group of producers in the Colorado high plains and how to reference weather data as an additional decision factor when scheduling irrigations.
Vegetable crop types vary in their tolerance of water depletion from the root zone.
We speculate that in these mixed vegetable fields, growers typically defer irrigation management decisions to the crop with the highest water demands, meaning there was no way to irrigate to the water needs of individual crop types.
Given that there are multiple vegetables grown with different water use characteristics in most small, mixed vegetable farm fields, irrigation efficiencies are not the same as would be anticipated when only one vegetable type is in an irrigation zone.
Additionally, irrigation efficiency is highly dependent on the management practices of the irrigator.
In this study, some farm managers incorporated soil moisture monitoring technology to determine soil moisture deeper than four inches in the soil profile, however many did not consistently utilize this technology.
As such, it is likely that some over-irrigated or under-irrigated some or all the vegetable crops in an irrigation zone in order to meet the water needs of crops perceived to have the highest water demand.
Evapotranspiration , or the collective water loss from the soil surface and plant leaves in the form of water vapor, can be influenced by air temperature, solar radiation, crop canopy, natural or plastic mulch, soil cultivation/tillage events, leaf surface area, wind velocity, and relative humidity.ET amounts are typically reported in inches.
Water use from 9 farms for 9 years averaged 21.5 inches per acre  and ranged from 11.3 inches 24.2 inches per acre.
Subtract field level effective precipitation from turf grass evapotranspiration  to create a rough guideline as inches of soil water to replace during the middle to end of a vegetable crop's lifecycle.
Actual farm water use coupled with ET minus EP form the basis of benchmarking mixed vegetable farm water use in Northern Colorado.
Conversions: 325,851 gallons/acre foot, 27,154.25 gallons/acre inch, 43,850 sq ft per acre
 Adrian Card, Boulder County Agriculture Agent; Sharon Bokan, Boulder County Small Acreage Coordinator; Tyler Mason, CSU PhD Candidate, Department of Horticulture and Landscape Architecture; Joel Schneekloth, Extension Regional Water Resources Specialist
 The United Nations Food and Agriculture Organization  indicates that the ET rate for vegetable crops is similar to that of turf grass.
Thus, turfgrass ET  is a surrogate that can be used to estimate vegetable crop water use.
Use of the abbreviation ET in this factsheet refers to turf grass ET.
ET varies based on stage of crop development.
For example, vegetable crops consume from 40 70% of ET during their initial establishment period then progressively move to 100 115% of ET during their middle growth and/or fruit set period, then end at 55 95% of ET during their fruit fill and finish period.
Rainfall also factors into vegetable crop irrigation scheduling.
Effective precipitation  events drop 0.10 inch or more of rainfall and contribute to soil water in the root zone.lt is important to understand that the measured EP may not always be effective.
In raised bed production systems using plasticulture, for instance, the plastic mulch may prevent EP from entering the plant root zone.
Similarly, measured rainfall with significant run-off, without infiltration into the soil, may overestimate the actual EP.
Growers with turf grass ET available from an online source can use this data to develop a running total of inches of water consumed by vegetable crop production.
Irrigation science uses the abbreviation ETo for turf grass ET and online sources will report it as ETo.
Subtracting field level EP from ET  creates a rough guideline for determining inches to replace through irrigation during the middle to the end of a vegetable crop lifecycle  and, along with actual farm water use reported here, is the basis in this factsheet for benchmarking water use on mixed vegetable farms in Northern Colorado.
While field-specific EP rainfall data may vary, ET is highly representative of field conditions when a weather station is accurately reporting this data at a similar latitude and elevation as the field of interest.
Turf grass ET varies, but during the peak ET months for vegetable crops of June, July and August, turf grass ET is typically 0.20 0.33 inches per day in Northern Colorado.
Daily ET and tipping bucket rainfall data were imported from the Northern Colorado Water Conservancy District weather station, Longmont South, near the intersection of highway 287 and highway 52.
This location was chosen as a reference point because it was generally a central location to all the farms included in this study and in an area with less urban environmental impacts to ET.
From 2010 through 2018 staff from the CSU Extension, Boulder County office installed totalizing water flow meters  delivering irrigation water to drip and/or sprinkler systems on mixed vegetable fields in the county and took measurements May October of acres irrigated, as a total of acres in drip irrigation plus acres in sprinkler irrigation, and gallons used as reported at the flow meter.
Flow meters served one or more irrigation zones.
Each fall flow meters, measuring raw ditch water, were cleaned to ensure measurement accuracy.
Field areas ranged from 1.4 20.8 acres irrigated during the mixed vegetable crop irrigation season studied.
Data from nine farms, comprising 17 mixed vegetable fields, produced 78 observational units used in this study.
The total amount of irrigation provided  was normalized to a per day usage by accounting for the length of time that irrigation was provided.
For comparison purposes, all data presented is based on a 160-day irrigation season.
These fields had either multiple vegetable crop types from the same plant family  or several plant families within the field.
Within the field, irrigation zones, if present, seldom had only one vegetable crop type.
Water use across all farms and all years averaged 21.5 inches per acre and ranged from 11.3 inches 24.2 inches per acre.
There was no statistical difference between sprinkler or drip irrigation.
Figure 1: Irrigation applied  by nine mixed vegetable production farms in Boulder County ; solid black line indicates average  water usage.
Figure 2: Irrigation applied  to seventeen mixed vegetable production fields in Boulder County ; solid black line indicates average  farm level water usage.
Figure 3: Comparison of irrigation needs to meet turf grass irrigation demands  by month and inches of irrigation water per acre applied  to vegetable crops on nine mixed vegetable farms in Boulder County.
Figure 3 shows that growers in this study were meeting crop water needs or potentially under irrigating during crop establishment in June  while likely over irrigating in September.
Although irrigation applied in June is less than the predicted ET, this generally represents the time period of establishment for most vegetable crops when vegetable ET is less than turf grass ET.
However, irrigation in September and October was greater than turf grass ET.
This would represent an opportunity for producers to reduce irrigation applied in excess of turf grass ET during those late season months.
Figure 4: The blue line shows average reference irrigation water applied per year for all fields in this data set as a percent of annual benchmark ET.
Annual benchmark ET  equals 1.
The red bars show effective precipitation in inches per year.
The average EP for the Longmont South weather station is approximately 7 inches during the growing season.
In Figure 4 the average water use  of all fields cited in the research closely matches the ET EP benchmark in years 2012 2017.
Years below "1" indicate average water use of all farms was less than ET EP and years above "1" indicate average over irrigation by farms in this model.
In drought years of 2012 and 2016  growers applied 70% or more of vegetable crop water needs predicted by the ET EP benchmark.
However, in drought year 2010, growers in this study applied the least amount of predicted crop water needed during a drought at just under 60%.
In September of 2013 Boulder County experienced a 1000-year flood event, which explains the high amount of EP during that year.
The 2011 growing season shows high EP but a 60% underirrigation as an average of all fields in the study.
This may support the need for soil moisture monitoring in a wet year, when periodic rain storms give the appearance of ample moisture in the top 4 inches while soil below that depth may have exceeded a management allowable depletion.
2010	2011	2012	2013	2014	2015	2016	2017	2018
 Predicted irrigation water requirement
 Turf grass ET	33.4	32.8	35.5	32.0	30.9	30.2	32.7	30.5	30.2
 Effective	4.5	9.1	1.7	12.4	6.0	8.5	3.5	8.4	10.5
 ET minus EP	28.9	23.7	33.8	19.5	24.9	21.7	29.2	22.1	19.7
 Actual irrigation water applied in acre inches per acre
 Minimum	7.9	7.6	6.3	13.4	11.8	6.4	14.2	11.3	8.8
 Median	19.6	9.1	25.0	21.1	22.8	17.7	22.1	22.4	20.2
 Maximum	22.6	11.2	39.2	36.9	50.5	31.6	41.4	51.2	60.8
 Avg 	16.3	9.4	24.3	21.9	26.0	17.6	22.9	23.3	25.7
 Actual irrigation water applied in gallons per acre
 Minimum	215,605	206,915	170,257	363,867	320,420	173,516	385,590	306,843	238,686
 Median	532,223	246,018	678,856	572,955	619,117	480,630	600,109	608,255	548,516
 Maximum	613,686	304,128	1,064,447	1,001,992	1,371,290	858,074	1,124,186	1,390,298	1,650,978
 Avg 	441,584	255,476	660,277	595,462	704,811	477,343	622,605	633,035	697,714
 Table 1.
Comparison of turf grass reference ET demand, effective precipitation , the difference between ET and effective precipitation, then minimum, median, maximum and average acre inches per acre applied and gallons per acre applied to all fields by year for nine mixed vegetable farms in Boulder County.
Although this study cannot represent the actual crop water needs by growth stage of the multiple crops planted in the same irrigation zone with multiple planting dates, it does offer a reference benchmark from the research findings presented here, allowing growers to assess mixed vegetable farm water use retrospectively against a range and average of historical water use.
Produce growers can also utilize the ET minus EP benchmark to calculate a daily or weekly estimate of vegetable crop water needs during the season as well as to conduct a similar retrospective analysis of farm water use.
By installing and maintaining flow meters serving one or more fields, gathering seasonal acre inches or gallons of water used, compiling ET and EP data , and comparing actual farm water applied to the research summary presented here and to their estimate from the ET minus EP model, mixed vegetable farmers have new benchmarking tools for understanding how much irrigation water should be applied  and applying amounts to match crop water demand.
Additionally, those seeking to convert fields to mixed vegetable crop production now have a water volume benchmark for securing appropriate water supply to fulfill that goal.
Measuring Seepage Losses from Canals Using the Ponding Test Method
 Eric Leigh and Guy Fipps*
 S eepage losses from canals can be significant.
The Texas AgriLife Extension Service has measured seepage loss rates ranging from 23 to 1,690 acre-feet per mile  in the Lower Rio Grande Valley of Texas.
Measuring seepage loss rates is one of the best ways to prioritize canals for maintenance and rehabilitation and determine the effectiveness of canal improvements quantified through preand post-rehabilitation testing.
Table 1.
Results of canal seepage loss tests in the Lower Rio Grande River Basin.
Test ID	Width 	Depth 
 LF1	12	5	1.77	152.9
 LF2	10	6	4.61	369.1
 MA4	12	5	8.85	529.7
 SJ4	15	4	1.17	111.2
 SJ5	14	5	1.38	145.5
 UN1	12	6	2.32	217.7
 UN2	8	3	2.09	121.2
 BR1	60	11	3.14	794.6
 MA3	19	5	13.9	1690.1
 RV1	38	4	0.15	23.0
 SB4	16	4	0.64	68.3
 SB5	18	3	1.67	188.3
 SB6	20	5	1.44	189.0
 SB7	16	4	0.42	47.4
 SB8	20	5	0.83	104.0
 There are several methods of estimating and measuring seepage losses from canals.
One way is to use typical seepage loss rates such as those shown in Tables 1 and 2, combined with your "best professional judgment" on the condition of the particular canal.
Another method involves measuring the flow in a canal at an upstream and downstream location and attributing any flow reductions to seepage loss.
The accuracy of this method depends on the type of flow meter and measuring technique used, the size of the canal and the volume of water.
Table 2.
Canal seepage rates reported in published studies.
Lining/Soil type	Seepage rate 
 Brick masonry lined3	2.23
 'DeMaggio 2U.S.
Bureau of Reclamation  3Nayak, et al.
Nofziger 
 The Ponding Test Method
 The ponding test method is considered to be the most accurate, and is often used as the standard of comparison for other methods.
In this method two ends of a
 canal segment are closed or sealed  to create a ponded pool of water.
The change in water level is measured over 24 to 48 hours and used along with the canal dimensions to calculate the seepage loss rate for the canal.
Ponding tests are classified as either "seepage loss tests" or "total loss tests" depending on the characteristics of the canal segment and the presence of leaking valves, gates and other structures.
Seepage loss tests measure the seepage losses through the bottoms and sides of canals.
Short canal segments are often used to avoid valves, gates or other structures that can leak.
Thus, all water loss is due to seepage through a canal's bottom and sides.
Total loss tests are conducted in canal segments that contain valves, gates and other structures that might contribute to the losses measured.
It may be important to account for losses from leaky control structures when considering canal improvements, but these types of leaks are often hard to notice and difficult to measure separately from canal seepage.
Figure 1.
Ponding test.
Factors Affecting Water Loss
 Many factors can affect seepage and total water losses in canals.
Documenting and recording these factors can help in selecting canals and comparing test results.
Soil type-texture, compaction and permeability 
 Type and condition of lining material-permeability, condition , erosion, construction methods, etc.
Control structures-leaks through wooden gates and rusty and/or broken steel valves
 Wildlife-holes and erosion caused by animal traffic and rodents
 Shallow groundwater table-depth to groundwater
 Sedimentation-Silting can help seal the canal bottom, but breaking the silt seal on unlined canals during reshaping and routine maintenance increases seepage.
Evaporation-temperature, wind speed, relative humidity, wind blocks, etc.
Roots can crack a canal lining and create holes through canal levees.
Plant transpiration accounts for some loss.
Cleaning out and reshaping unlined canals can often break the seal caused by sedimentation.
Heavy machinery used to clean out lined canals can crack the concrete.
Length of time the canal has been in operation before testing-level of saturation and absorption of water into canal walls
 Depth of water in canal-Generally, the higher the water level, the higher the losses.
Selecting the Canal for a Ponding Test
 The selection process can be as easy or as complex as you want to make it.
In most cases, canals are pre-selected for testing because of known problems and rehabilitation plans.
A more systematic approach is to rank canals using certain parameters.
Table 3.
Important parameters for prioritizing canals for testing.
Earthen Construction preparation and methods used Material type of levee Compaction Soil type inside the canal Erosion Lined Construction preparation and methods used Material type of levee Compaction Type of lining materials Size and frequency of cracks Current condition Visible leaks Water and vegetation in drain ditch Vegetation Annual use/Area served
 Any documentation on the original construction methods used will be helpful.
Unlined canals obviously have higher seepage rates in more porous soils.
Canals built in clay soils or with clay linings may be subjected to shrinking and swelling, which can cause cracks in the canal floor if the canal is allowed to dry out.
Unreinforced concrete/shotcrete is more apt to crack and break in a shorter period of time.
A synthetic membrane under-liner can reduce or eliminate seepage, but if the synthetic liner is improperly installed and then covered with concrete/shotcrete, the liner may tear and cause continual seepage.
An exposed lining material can be vulnerable to cuts, holes and abrasions from many sources.
In unlined canals, seepage losses often are proportional to soil texture, with sandy soils having higher loss rates than clays.
If there is no documentation of the soils used in construction, general soil series maps can be helpful in identifying canal segments with higher seepage rates, as canals usually are constructed with surrounding materials.
These maps are available from the USDA Natural Resources Conservation Service.
While appearances can be deceiving, it is often true that the worst looking canal will have the highest loss rate.
Visually rating the condition of canals can help you
 prioritize them for testing.
In our studies, the characteristics and numerical rating scales in Table 4 have accurately predicted the magnitude of seepage loss rates of canals.
Other indicators of significant water loss include yearround aquatic vegetation and standing water in the drainage system, large stands of vegetation around or on canal levees, and cropland adjacent to canals that has become waterlogged or salted out because of a rising water table level.
Current and future use
 Other factors in selecting test canals involve current water usage in the district and how that is expected to change over time.
Priority is usually given to those areas that have the most annual water use and that are expected to stay in production for years to come.
5.
Consult soil maps to select an area representative of a certain soil type.
6.
Choose areas accessible to trucks and other vehicles used for testing or constructing the test sections.
7.
Check the levee for leaks from large holes and cracks that are not representative of the test segment, unless your intent is to specifically measure this problem area.
8.
Generally, the longer the test section, the better; 600 feet long is typical.
However, it is better to shorten the length of the segment than to include sections with gates and valves.
If such control structures cannot be avoided, seal and back-fill with soil around the structure to minimize leakage.
Table 4.
Canal rating by observation.
2.
More then 10 feet apart
 3.
5 feet to 10 feet apart
 4.
3 feet to 5 feet apart
 5.
Less than 3 feet apart
 Aquatic vegetation growing from bottom
 % aquatic vegetation in water 
 Types of aquatic vegetation in water
 Canal sidewall lining vegetation growing in canal lining
 Drainage ditch vegetation in drainage ditch and along the outer level embankment base
 1.
Normal; rain-fed weeds only
 2.
Moderate; bushes and some trees 
 3.
Dense; more bushes and larger trees and/or standing water with little or no aquatic vegetation
 4.
Dense and lush; bushes, trees and/or lots of aquatic vegetation with standing water
 Selecting the Test Segment
 The next step is to select the specific canal segment for testing, using the following guidelines:
 1.
Avoid curves and select straight canal sections.
2.
Avoid sections on steep slopes.
3.
For seepage loss tests, avoid segments containing turnouts, valves, gates and other flow control structures.
4.
Select segments with minimal changes in canal dimensions.
9.
Beware of areas that might be vandalized easily to avoid damage to equipment and dams; or provide security 24 hours a day.
Planning: Have you thought about
 When can the canal be shut down?
How long can the canal be shut down?
Who will this affect?
Do I need to tell or send out notices to the users ?
How much time in advance will I need to send out the notices?
Is maintenance needed on the test segment?
Preparing for the Test
 Measuring and flagging the test segment
 Use a measurement wheel or survey instrument to measure the length of the test segment.
Determine the staff gauge locations and place flag markers or stakes at the locations of the dams and the staff gauges.
Staff gauges are placed in the canal test segment to measure the fall in water level during the test.
Use a minimum of three staff gauges.
Space them evenly throughout the test segment, or place one in the center and two at the ends located at least 20 feet from the dams.
The longer the test segment, the more staff gauges you should use.
Using several will help you compare and evaluate readings and will reduce errors in the event a staff gauge should fall over or be moved.
Walk the test segment and check both sides of the canal levee for leaks from large holes and cracks, valves and gates.
When conducting total loss tests, if a leak is not representative of the test section, try to fill it in with soil or seal it some other way.
Usually a bucket or two of dirt from a backhoe will be sufficient.
Smaller leaks can be filled in with shovels using the surrounding soil from the levee.
Note any leaks on the test data form and record whether you needed to seal them.
While clay soils are desirable, the type of soil used for constructing the dams is usually determined by availability and location.
Some water districts prefer to have
 the soil brought in by truck , while others will use a backhoe and take it directly from the canal levee.
This should be done only when there is an adequate amount of soil so as to not cause damage.
Dams can be built with or without water in the canal.
When the canal is full of water, more soil is usually needed to build the dam because the soil spreads out as it falls through the water column.
This is especially true in a deep canal.
Don't completely drain the canal.
Having some water in the canal during construction of the dams helps saturate and stabilize them.
As the dams are built up, the soil should be compacted with a backhoe , taking care not to push away uncompacted soil.
Compaction will help reduce water movement through the dam and provide better stability.
No matter how good the compaction is, some water will probably seep through the dams.
To prevent this, cover the interior sides of the dams with 4to 8-ml sheets of plastic.
The size of the dams should be proportional to the size of the canal.
The water pressure on the dams will be significantly greater in deeper canals.
The tops of the finished dams should be at least 2 feet higher than the testing water depth.
Dams should be at least 3 feet wide and stable enough to walk on.
If you don't feel safe walking across the dam, it is not finished.
Measurement Equipment and Installation
 To measure the changes in water level you will need to manually read staff gauges and/or electronic water level sensors.
While there are advantages and disadvantage to both, we suggest always using staff gauges even if other devices are used.
The staff gauge provides a quick and easy visual indicator of water level and is often more reliable than electronic sensors.
Most districts have a limited opportunity to perform tests and you don't want to get to the end of the test and realize you have no usable data.
Staff gauges are available in a variety of styles and materials.
Use ones with large numbers and line markers that are easy to see from a distance.
Figure 10 shows a staff gauge scaled to 0.01 foot.
Electronic water level sensors, such as pressure transducers and float and pulley encoders, can be programmed to record measurements at set intervals throughout the testing period.
This reduces manpower and the number of trips to the testing site.
Disadvantages include the cost  and the possibility of power failure, programming errors, vandalism and theft.
When constructing or buying stands for the staff gauges, be sure they are heavy enough to withstand some water movement but not top heavy.
Figure 11 shows a simple tripod stand that is easy to construct and performs very well in both lined and unlined canals.
Stainless steel is a good material for stands that will be used often.
in the center of the canal, just make sure that the markings will cover the full change in the water level.
Waders or a small boat may be useful during installation.
After the staff gauge stand is set, use a small bubble level to level the staff gauge.
When placing the measurement equipment in the canal, be sure it is stable.
Avoid areas where the canal bottom is uneven or has debris that will cause the staff gauge stand to be unsteady.
It is not necessary to put the staff gauge
 One or more rain gauges should be placed along the test section to measure any rain that falls during the test.
The amount of rainfall is subtracted from the staff gauge readings.
Canal Measurements and Shapes
 Measure the canal dimensions at every staff gauge location.
Also take measurements to determine the relationship between the staff gauge readings and the actual depth of the canal.
Measuring or surveying can be done before the canal water level is raised or after the test is completed and the water has drained.
When taking measurements after the test, be sure to dismantle the downstream dam slowly to
 prevent high flow rates that could move the staff gauge stands.
Canal measurements are taken to define its shape.
Then water loss can be calculated using one of two methods:
 Method 1 basic shapes.
The cross-section of the canal was originally built using one of these common shapes: rectangular, trapezoidal, triangular or parabolic.
Measure the basic canal cross-sectional dimensions, including the top width, depth, side slopes and bottom width, as illustrated in Figures 16-19.
Determine which shape best represents the canal.
Over time, earthen  canals will likely take on a parabolic shape.
Method 2 irregular shapes.
For irregularly shaped or eroded canals, or if it is difficult to determine canal shape or take the standard dimensions, more elaborate surveying techniques must be used.
One method is to
 determine the top width of the canal, then take depth measurements every 1 to 2 feet as shown in Figure 20.
Alternatively, ten depth measurements can be taken at equal spacings across the canal.
These depth-width measurements are then used to create a cross-sectional profile.
Spanning and staking a tape measure across the top of the canal will help measure the distance from each surveyed point, and will also help to keep your surveyed points in a straight line.
Filling the Test Segment
 After the downstream dam is in place, there are two methods for establishing the pond:
 1.
Raise the water level in the test segment to the desired level, usually the normal or maximum operating level.
Then build the upstream dam.
2.
Build the upstream dam, then use portable pumps to fill the test segment, or begin pumping while the upstream dam is being built.
Figure 15.
A staff gauge being referenced in accordance with actual water level of the canal.
Figure 16.
Rectangular cross section, basic dimensions and area equation.
Figure 17.
Trapezoidal cross section, basic dimensions and area equation.
Figure 18.
Triangular cross section, basic dimensions and area equation.
Figure 19.
Parabolic cross section, basic dimensions and area equation.
Figure 20.
A basic survey method for determining the shape of the cross section by measuring the depth at marked intervals.
After both dams have been built and the pond has been filled to the desired test level, inspect again and make sure any control structures are sealed.
If additional leaks are found during the test, write down a description of them to help you with estimating water loss later.
The testing period is usually 24 to 48 hours, with time added at the beginning for the stabilization and saturation period.
The staff gauge readings should be taken on a pre-determined schedule.
However, you may need to adjust the schedule if it appears that the ponded segment will be empty before the end of the test.
The exact time of each staff gauge reading should be recorded.
For each time interval, record the level for each staff gauge.
Record the first staff gauge readings about 30 minutes after pretest preparations have been completed.
The first set of readings probably will not be used for the final calculations, but will help you determine when the water level in the canal stabilizes.
Continue taking readings every hour for the next 3 to 4 hours.
This will help you determine the rate of loss during the canal's startup period.
During the following day, continue to take at least three readings per day and two readings at the end of the test.
Tables 5 and 6 give suggested schedules for 24and 48-hour test periods.
In the appendix there is a Data Collection Form you can use to record staff gauge readings.
Table 5.
48-hour test.
Day 1	1	12:00
 Day 2	5	9:00
 Day 3	8	9:00
 Table 6.
24-hour test.
Day 1	1	12:00
 Day 2	5	8:00
 Calculating Water and Seepage Loss Rates
 Method 1 basic shapes
 To determine the loss rate from ponding tests, the wetted perimeters  and the cross-sectional area  must be calculated using the appropriate equations shown in Figures 16-19.
Note: For parabolic-shaped canals, WP and A can not be calculated directly, but must be done using a trial and error process.
Or, search the Web for interactive calculators that perform these computations.
Step 1: Calculate the initial cross-sectional area  using the appropriate equation  based on canal shape.
Use initial water depth  in place of total depth.
Step 2: Calculate the final cross-sectional area  using the appropriate equation based on canal shape.
Use the final water depth  reading in place of total depth.
Tip: Starting the test early in the day will ensure that you have plenty of light to see the staff gauge markings.
Step 3: Calculate the rate of water loss in terms of gallons per day using this equation.
iA = initial cross-sectional area fA = final cross-sectional area t = duration of test  7.48 = conversion factor rWL = rate of water loss
 Step 4: Calculate the wetted perimeter at the initial water depth  reading.
Step 5: Calculate water loss in terms of volume per area  per linear foot of the canal.
Gal ft2/day iWP = Initial Wetted Perimeter 
 A 600-foot long, trapezoidal, concrete canal section was selected and sealed for a ponding test.
The dimensions of the cross section are as follows:
 W = top width 
 B = bottom width 
 D = total depth 
 e = ?
can be calculated using the equation in Step 1 below.)
 The canal section was filled to normal operating level or initial depth  of 5 feet.
After 48 hours, the water depth had dropped by 0.5 feet, for a final depth  of 4.5 feet.
Step 1: Calculate the side slope  of the canal using the equation for a trapezoidal canal.
E Z = 10At-5A 0.42
 Step 2: Calculate the total cross-sectional area  using
 A = B x D + Z x D2 45 ft2 = ftx6ft+0.42x62
 Step 3: Calculate the initial cross-sectional area  using the starting water level or initial depth  reading of the test using the trapezoidal equation.
iA = B x iD + Z x iD 2 35.42 ft2 = f t x 5 ft + 0.42x52
 iD : initial depth at the start of the test 
 iA = initial cross-sectional area
 Step 4: Calculate the final cross-sectional area  using the ending water level or final depth  reading of the test using the trapezoidal equation.
iA = B x iD + Z i D 2 30.94 f ft2 = 5 ft 4.5 ft + 0.42 x 4.52  fD = final depth at the end of the test fA = final cross-sectional area
 Step 5: Calculate the change in cross-sectional area  during the test.
AA = iA fA AA = 35.42 ft2 -30.94 ft2 AA = 4.48 ft2
 The change in area  times 1 linear foot of the canal is the volume of water loss , or 4.48 ft3.
Step 6: Convert the volume of water loss , 4.48 ft3, to gallons of water loss.
vWL = vWL x 7.48 WLgal = 4.48 ft3 x 7.48 WLgal = 33.5 gal 
 Step 7: Calculate rate of water loss  in terms of gallons per day.
The total test time was 48 hours or 2 days.
vWL rWL = 33.5gal rWL = 2 days rWL = 16.75 gal/day
 Step 8: Calculate the wetted perimeter  using the initial depth  and using the wetted perimeter equation for a trapezoid.
+ ft X 0.5
 Step 9: Calculate the rate of water loss  in terms of gallons per day per square foot.
rWL per ft2
 16.75  15.83 ft2
 Step 10: Calculate water loss in terms of acre feet per mile per year.
X 365 days =
 
 Method 2 irregular shapes
 In calculating water loss from ponding tests, it is necessary to determine the wetted perimeter and the change in cross-sectional area during the test.
In canals of irregular shape, the standard equations cannot be used.
But there are several methods that can be used to determine these parameters.
One method is to graph the coordinates and then use graphic means to estimate the wetted perimeter and cross-sectional area.
Another method is to fit an equation through the coordinates defining the canal's shape, and then integrate the equation to determine the area.
Corrections for Rainfall and Evaporation
 If it rains during the test, rain gauges at the test site can be used to adjust the change in water level or ending depth for the amount of rainfall.
Loss to evaporation is usually insignificant and does not affect seepage loss rate, SO it is usually ignored.
To make this adjustment, pan evaporation or ETo  rates can be used.
However, the evaporation out of a canal will be less than either ETo or pan evaporation.
Usually an adjustment factor of 0.6 to 0.8 is used depending on the size of the canal, the height of canal banks and similar factors.
Once the wetted perimeter and change in cross-sectional area are computed, the calculations are the same as given above.
For more information, contact your county Extension office or your engineering consultant.
Field Guide for Performing a Ponding Test
 Site Inspection and Preliminary Survey
 1.
Inspect the test segment by walking both sides to check for leaks from large holes or cracks, valves and gates.
Mark leak locations with flags.
Fill in with soil or seal if you determine that a leak is not representative of the test section.
2.
Set a flag marker at one of the locations where the earth dams will be built.
With a measurement wheel, start from the flag and walk off the desired length of the test segment.
3.
Determine the spacing of the staff gauges according to the test segment length.
4.
Use the measurement wheel to place flag markers at the staff gauge locations.
5.
Start building the downstream earth dam.
Equipment required: backhoe, truck load of soil.
6.
Place staff gauges in the test segment.
Equipment required: boat , waders, staff gauges.
7.
Survey the canal's cross sections at each staff gauge location and reference each staff gauge's height with the survey.
Equipment required: transit and rod, or survey grade GPS unit.
If the canal is too full for the survey, drain the canal and survey after the test has been completed.
8.
Raise water in the test section to the desired level, usually to the normal or maximum operating water level.
9.
Build the upstream earth dam.
If you need to raise the water level after the dam has been built, use portable pumps.
10.
After filling the test segment, wait 30 minutes and take the first staff gauge readings and water span measurements.
11.
Record the next water level measurements according to your schedule.
Try to take each round of readings from the staff gauges within 2 minutes of the next.
12.
Record the rain gauge level if rain has occurred.
13.
Drain the canal, removing the downstream dam first.
If you still need to survey the cross-sections and staff gauges, drain the test segment slowly so the staff gauges won't be disturbed.
14.
After surveying, remove the staff gauges and download any information from data loggers if electronic water level sensors were used.
15.
Remove the upstream dam.
Portable gas-powered water pump
 Survey grade GPS equipment used to determine the cross-section of the canal
 Stake or flag markers
 Measuring tape, non-metallic fiberglass 
 Staff gauges and stands
 Standard hand tools are used to install and maintain the testing equipment: drill, 1/16-inch drill bit, adjustable wrenches, rubber mallet, and standard and Philip's screw drivers.
Signs may be used around the test site area to warn people of danger and to inform them that testing is in progress.
Signs may include a phone number, company, contact, and danger or warning labels.
Sample Ponding Test Data Form
 Test ID	ID-97	Top width	15.77 feet 
 Canal	Lateral-11	Total depth	5.7 feet 
 Lining type	Geo liner/ shotcrete	Test length	802 feet
 Survey type	GPS Survey-Grade
 Location	Off of 'l' Road, south of Military Hwy.
Measurements: Staff gauge readings
 Readings	Time	Readings	Time	Readings	Time
 1	27-July	1.92	15:20	2.39	15:22	5.55	15:24
 2	1.92	17:23	2.39	17:25	5.55	17:27
 3	28-July	1.89	09:17	2.36	09:19	5.52	09:21
 4	1.89	11:19	2.36	11:21	5.52	11:23
 5	1.89	13:23	2.36	13:25	5.52	13:27
 6	1.89	15:18	2.36	15:20	5.52	15:22
 7	29-July	1.89	17:15	2.36	17:17	5.52	17:20
 Water level	Staff gauge	True height	Staff gauge	True height	Staff gauge	True height
 adjustment	2.00	4.00	3.00	4.00	6.00	4.00
 Notes: Test segment has two major cracks.
Ponding Test Data Form
 
 Test ID	Top width
 Lining type	Test length
 Measurements: Staff gage readings
 Readings	Time	Readings	Time	Readings	Time
 Water level	Staff gauge	True height	Staff gauge	True height	Staff gauge	True height
Educators and specialists from Nebraska Extension and the Midwestern states, including Kansas, Colorado and Texas, will be on hand to address water issues that may affect your farming operation.
Topics will include information on water management, economics and agronomic principles.
Approximately 30 commercial vendors will be on hand throughout the day to provide live product demonstrations.
as guides to irrigation practices
 The moisture sensing unit-a porous tensiometers must be reached by the irrigation water if the moisture measuring instruments are to be of practical value as guides to irrigation practices.
In most soils a good location for a tensiometer station is often next to the furrow, but it may be necessary to locate the porous cup under the furrow in orchard soils with little or no lateral movement of water during irrigation.
In sprinkler-irrigated orchards the cup must be in soil that is re-wetted by the sprinkler at each irrigation but is not shielded by a low hanging branch nor is flooded by runoff from a branch.
Also the porous cup should be in areas of active feeder roots as determined by root density studies, or by digging at different sites until a general pattern of root densities is apparent.
Some traffic between the tree rows is necessary in most orchards, so the soil moisture measuring instrument must be in a protected spot reached by irrigation water and where feeder root density is average for the tree.
In general, a good location for a tensiometer is at the drip line on the tree side of the first furrow, south or west of the tree.
Usually instruments are put at two depths at each selected station.
In an orchard with an average root system, a tensiometer in the soil depth gives information on moisture availability sufficient for irrigation timing.
A tensiometer with the porous cup 24"36" deep shows the minimum depth of soil which is re-wet at each irrigation.
If the instrument does not respond following irrigation, a visual check-made by digging-will show that the water did not penetrate to the porous cup.
A tensiometer placed deeper than 36" in a citrus orchard seldom gives much functional information except in special cases, such as in a leaching program or where more than 3' of coarse sandy soil overlies a silt layer that supplies the tree roots with a disproportionate share of moisture and nutrients.
Successive readings of tensiometerswhen plotted on a graph-indicate certain soil characteristics to be considered in an irrigation program.
As an example, a citrus orchard on Ramona loam was on a monthly irrigation schedule with three days of water delivery for each irrigation.
The graph on the left, prepared from tensiometer readings shows the
 soil in this part of the orchard to be very slowly permeable below the 24" depth.
Following irrigations the tensiometer at the 24" depth registered zero readings for several days.
However, some of the irrigation water eventually moved out of the 24" depth by moving through the slowly permeable soil or by root activity.
The graph on the right shows a relatively steep curve following irrigations at the 24" depth, indicating water was moving downward through the soil as well as being used by the tree.
A comparison of the plotted tensiometer readings from the two stations in the orchard revealed that the 12" depth shown in the graph to the left changed in suction values--measurement of the energy holding water in rapidly than the 12" depth shown in the second graph.
The reverse was true of the 24" depth.
Root activity was at a minimum at the 24" depth in the first graph, indicating that the saturated condition of the soil after each irrigation caused the roots to disappear, probably due to root rot fungi.
Also, the readings showed over-irrigation during the monthly 3-day irrigation period.
Furthermore, high suction values existed between irrigations for long periods during July, August, and September when moisture from winter rains had been depleted in all soil areas where roots were present, except in the irrigated soil.
Where the energy holding moisture in soil is relatively stronghigh suction values-in the irrigated areas, production is apt to be reduced by the moisture stress on the trees.
A pipe line in the middle of this particular or-
 Concluded on next page
 Left.
Soil moisture conditions in a mature navel orange orchard located on a Ramona loam soil furrow-irrigated monthly for a 3-day period.
Tensiometers installed at dripline of third tree in a 36-tree irrigation run.
Flat-top portions of curves caused by inability of tensiometers to read above 80 centibars, reflect a very low soil water availability.
Right.
Soil moisture conditions in the same orchard and tree row but at lower end of the irrigation run.
Increased activity at the 24" depth indicates better subsoil drainage and a greater concentration of healthy roots.
CALIFORNIA AGRICULTURE, MARCH, 1960
 Inadequate drainage was the cause of a soil salinity problem on 25,000 acres of Tulelake land during a five-year study of water tables and soil salinity.
The predominant crop in the Tulelake area is barley, a crop that can stand higher soil salt concentration than most other crops.
However, when the salinity level exceeds four millimhos-unit of measurement of electrical conductivity of saline-a reduction in barley yield begins.
At eight millimhos the yield is reduced about 20% and at 16 millimhos there is a 50% reduction in yield.
A field examination of the salinity problem in Tulelake was initiated in 1955 and during the growing season water table heights were measured by continuous recorders and observation wells.
Soil samples were taken adjacent to the recorders three times during the growing season-at the start, the middle, and the end-and analyzed for total salts.
Because of the limited number of sampling sites included in the study, the salinity readings are merely indicative of the general situation.
Undoubtedly there are many salty areas not sampled, and some of the salty land may include areas of low salt.
Soil samples from several locations at the end of the growing season were examined to determine the vertical distribution of salt in the soil profile.
One representative analysis showed a high concentration of salt in the surface soil layers.
The top inch of soil contained about twice as much salt as the second half foot.
Soil samples taken at the end of the growing season clearly indicated that the salinity problems in the land studied were the result of the high water table.
JAMES N.
LUTHIN AND KENNETH BAGHOTT
 Water moves upward from the water table level by capillary action to the soil surface and evaporates, leaving the salts in the soil.
However, the water table must be close to the soil surface for long periods of time for the upward movement and evaporation of the water to take place.
Poor soil drainage and inadequate
 Salt Content in Surface
 Salt Content at Same Location with
 control of irrigation water contribute to the salinity problem.
The following spring more soil samples were taken to determine the effect of the winter rains in soil leaching.
There was considerable leaching of the salt and the average salinity was below the levels found at the start of the field examination.
The amount of leaching by winter
 rains depends on the total seasonal rainfall, the amount of each storm, the level of the water table during the rainy season, and on the adequacy of field drains for rapid removal of water from the soil.
When the water table is close to the soil surface, the winter rains are not effective for leaching.
However, when the water table is kept 4' or 5' below the soil surface by a system of drains, winter rains will wash out an appreciable amount of salt.
To keep the water table sufficiently below the soil surface, some sort of drainage-tile lines or open ditches-must be provided at a depth of at least 4 and spaced close enough together to lower the water table rapidly.
Water must move through and out of the soil to get rid of the salts, so ponding water on the soil without adequate drainage accomplishes little in the way of leaching.
Flooding land lacking drainage prior to the growing season, as has been the practice for many years in the Southwest Sump of the Tulelake lands, has resulted in a continued increase in the soil salinity problem.
James N.
Luthin is Associate Professor of Irrigation, University of California, Davis.
Kenneth Baghott is Farm Advisor, ModocSiskiyou Counties, University of California.
Continued from preceding page
 chard would reduce the number of trees in an irrigation run and give more flexibility in the irrigation practices of the two areas.
A three-week irrigation schedule with a reduced amount of water would prevent excessive saturated soil conditions and benefit the orchard.
Another orchard on Ramona sandy loam appears to have a very active root system at both the 12" and 24" soil depths.
A slowly permeable subsoil restricts the downward movement of water and forces it to move laterally until the whole soil area around the tree is saturated.
A three-week irrigation schedule
 with not more than 24 hours of water applied at one time would be a better irrigation program than a monthly program for a three-day period.
A third orchard-on a Hanford sandy loam-has a deep root system and root activity causes the soil suctions to increase more rapidy at the 24" and 36" soil depths than at the 12" depth.
Apparently some restriction in the soil between the 12" and the 24" depths prevents the soil suction values at the deeper depths from reaching saturation.
The recovery from saturated conditions at the 12" depth makes a favorable condition for feeder roots.
Tensiometer readings indicate a good irrigation program in the orchard.
Citrus trees are conditioned by cultural practices and a shallow-rooted orchard might not stand a sudden change to longer intervals between irrigations.
Citrus trees under sprinkler irrigation tend to develop root systems that are shallower than those of furrow-irrigated trees.
Also, sprinkler irrigated citrus trees wilt at much lower suction values, for comparable depths, than trees under furrow irrigation.
L.
H.
Stolzy is Assistant Irrigation Engineer, University of California, Riverside.
A.
W.
Marsh is Extension Irrigation and Soil Specialist, University of California, Riverside.
Puffer is Farm Advisor, San Bernardino County, University of California.
D.
C.
Baier is Farm Advisor, Orange County, University of California.
There is increasing pressure on our water resources.
Concerns about natural ecosystems and the sustainability of groundwater withdrawals are heightening.
Domestic and international competition for water between different users is increasing.
Agricultural demand by a global population growing both in number and in wealth is rising.
B.C.
SPRINKLER IRRIGATION MANUAL
 Prepared and Web Published by
 BRITISH COLUMBIA Ministry of Agriculture
 LIMITATION OF LIABILITY AND USER'S RESPONSIBILITY
 The primary purpose of this manual is to provide irrigation professionals and consultants with a methodology to properly design an agricultural irrigation system.
This manual is also used as the reference material for the Irrigation Industry Association's agriculture sprinkler irrigation certification program.
While every effort has been made to ensure the accuracy and completeness of these materials, additional materials may be required to complete more advanced design for some systems.
Advice of appropriate professionals and experts may assist in completing designs that are not adequately convered in this manual.
All information in this publication and related materials are provided entirely "as is" and no representations, warranties or conditions, either expressed or implied, are made in connection with your use of, or reliance upon, this information.
This information is provided to you as the user entirely at your risk.
The British Columbia Ministry of Agriculture and the Irrigation Industry Association of British Columbia, their Directors, agents, employees, or contractors will not be liable for any claims, damages or losses of any kind whatsoever arising out of the use of or reliance upon this information.
PIPE SELECTION DESIGN AND INSTALLATION
 Proper design, installation and operation of piping systems will increase the effective life of the pipe and ensure a reliable water supply to an irrigation system.
Mainline design must take into account the total system flow rate, total pressure requirement, terrain, and pipe material to be used.
Lateral pipe lines must be designed to ensure that the pipe friction losses are not excessive and allow all sprinklers along the lateral to operate within an appropriate pressure range.
Appendix B provides additional information on pipe properties, such as friction loss characteristics for pipe generally used in the irrigation industry.
Pipe material should be selected on the basis of site conditions, pressure required and material cost compared to alternatives.
The following pipe types are usually used for irrigation purposes.
Aluminum is lightweight, easy to assemble, and used extensively for above ground portable irrigation systems.
Aluminum pipe is not buried unless protected with a coating.
Pipe size used range from 2 inch to 10 inch with recommended working pressures not exceeding 130 to 140 psi.
Working pressures for aluminum are indicated in Table A.1.
The pipe is generally available in 30 and 40 foot lengths.
Steel is commonly used for irrigation pipe larger than 8 inch where high working pressures are desired.
Steel is susceptible to corrosion and requires corrosion protection if buried.
Steel mainlines for irrigation are usually laid above ground to reduce corrosion and allow for periodic inspection.
The pipe is usually available in 20 or 40 foot lengths.
Poly Vinyl Chloride 
 PVC pipe is available in numerous classes and schedules depending on the working pressures desired.
It is lightweight, durable, easy to install and has excellent resistance to most chemicals.
PVC deteriorates when exposed to sunlight and becomes quite brittle at freezing temperatures making it impractical for most exposed work.
For irrigation purposes, the operating pressure of PVC pipe should not exceed 72% of the pipe pressure rating.
Pipe sizes typically range from 1/2 inch to 12 inch.
The pipe is available in 20 foot lengths with either a solvent weld or gasket bell end.
Polyethylene pipe has similar characteristics to PVC except that it is more flexible.
It is not commonly used for high pressure, large pipe installations primarily due to cost.
PE pipe is most often used for small solid set sprinkler or trickle irrigation systems.
For irrigation purposes, the operating pressure of polyethylene pipe should not exceed 72% of the pipe pressure rating.
The typical size range is 1/2 inch to 2 inch.
The pipe is available in coil lengths of 100, 200, 300, 400, 500 feet or reel lengths of 1,000 feet.
High Density Polyethylene Pipe 
 HDPE pipe more ridged than regular PE pipe.
It still has some flexibility and can curve around gentle corners.
It is often used when an open ditch is converted to buried pipe.
HDPE is available in a large range of sizes and tends to be more expensive than PVC pipe.
Higher pressure ratings are available and it can be used as mainline and laterals.
The larger pipe sizes come in 40 foot lengths and are joined by heat fusion.
8.2 Pipe Rating Systems
 Many different systems are used to rate the pipe that is used for irrigation.
Steel pipe uses a gage or schedule system.
Aluminum tubing is rated by wall thickness.
PVC pipe uses a schedule or class system.
Polyethylene pipe uses a maximum working pressure rating system.
HDPE pipe uses a pressure rating system and a Surface Dimension Ratio  system.
An understanding of the pressure rating systems is useful in selecting the type of mainline required for an irrigation system.
Straight seam pipe is often available in a gage rating.
The gage number refers to a standard wall thickness as specified by the Burmingham or Stub's Iron Wire Gage.
The working pressure for each gage number varies with the pipe size.
Table A.2 indicates the wall thickness and pressure rating for various gage number and pipe size.
Irrigation pipe is often grouped under headings of schedule 40 or schedule 80.
It is the familiar designation of pipe for which the outside diameter, wall thickness, and inside diameter are fixed by specification.
The dimensions of plastic or steel pipe produced to these schedules are identical.
Working pressures vary for different pipe diameters within any schedule.
Table A.3 provides the working pressure of various PVC pipe sizes manufactured to "schedule" specifications.
Class, Series or "SDR" System
 Polyethylene and PVC pipe are often manufactured to a "class" or "series" system.
This system classifies pipe to a pressure rating.
It is a system in which the working pressure for all pipe in a given series is the same, having the same safety margin and operating at the same fibre stress.
The pipe is grouped according to its standard dimension ratio.
SDR is the relationship of pipe wall thickness and outside diameter.
Equation 8.1 Standard Dimension Ratio 
 Outside Diameter SDR = Wall Thickness
 SDR = standard dimension ratio Outside Diameter = outside diameter of pipe [in] Wall Thickness = wall thickness of pipe [in]
 The wall thickness and inside diameter vary with the pressure rating or class of pipe.
The number after the class or series indicates the pipe maximum working pressure.
Table B.3 provides information on PVC pipe specifications for class or series pipe.
8.3 Calculating Pipe Size
 Water flowing through pipelines is always accompanied by a pressure loss due to friction.
The amount of friction loss that occurs will depend on:
 the pipe dimensions 
 the type of pipe 
 quantity of water flowing through the pipe
 When an irrigation pipe mainline or lateral is designed, the pipe size is selected based on a maximum water velocity of 5 feet per second.
If the velocity is too high the pressure rating of the pipe can be exceeded with sudden valve closure causing water hammer.
For agricultural irrigation design water hammer problems are avoided by ensuring that flow velocities do not exceed 5 ft/sec.
Equation 8.2 Flow Velocity 
 Q V = 2.45D 2
 V = velocity [ft/s] Q = flow rate [US gpm] D = inside pipe diameter [in]
 The friction loss tables in Appendix B have a dotted line in the size columns to indicate a velocity of 5 ft/s.
When using the tables, stay above this line to ensure safe velocities which minimize friction loss and reduce the problems that can be caused by water hammer.
See section 8.4.
Helpful Tips Lateral Pipeline Design
 The allowable friction loss in a lateral line should not exceed more than 10 % of the sprinkler operating pressure whenever possible.
Therefore a sprinkler operating at a nominal pressure of 50 psi would limit the pressure loss along the lateral to 5 psi or less.
Keeping the friction losses within this range will provide improved system uniformity which in turn improves system performance.
Using the 5 ft /sec rule to initially select lateral pipe sizes often results in a friction loss for the lateral line that is within this tolerance.
If the range is exceeded then larger pipe sizes should be selected for portions of the lateral line.
See the lateral friction loss calculations in Example 8.5.
Example 8.1 Flow Velocity Check
 Question: For a travelling gun system having a flow rate of 250 US gpm would a 4-inch PVC mainline be large enough?
Farm location Flow rate  pipe diameter Inside pipe diameter  
 250	2	US gpm
 Check to see if the velocity is below 5 ft/s.
Since this velocity is greater than 5 ft/s, the 4-inch pipe is too small.
The next larger size mainline should be looked at, i.e., 5 inch.
The parameters for this pipe are:
 Inside pipe diameter   5.033 6 in
 Since this velocity for 5 inch mainline is below 5 ft/s, this is the minimum size mainline that should be used.
Most manufacturers do not make 5 inch PVC pipe therefore 6 inch may be required.
Pipe friction loss is calculated based on properties of the pipe, diameter of the pipe, and flow in the pipe.
The most commonly used formula is the Hazen-Williams illustrated in Equation 8.3.
Equation 8.3 Friction Loss
 where Hf  = friction loss  Q = flow rate [US gpm] C = coefficient of retardation based on pipe material D = inside pipe diameter [in] Source: Design and Operation of Farm Irrigation Systems, 2nd Edition, ASABE
 Coefficient of Retardation 
 This coefficient is different for the types of pipe materials being used.
The smoother the inside wall of a pipe is, the higher the C factor.
Table 8.1 C Factor
 Type of Pipe	C Factor
 Aluminum with couplers	120
 Helpful Tips Friction Loss for Steel Pipes
 For agricultural irrigation systems, old steel pipes are more commonly used than new steel pipes due to lower cost.
If new steel pipes are used, Appendix Table B.2  should be used to calculate friction losses.
New steel pipes are generally used for many decades, and will become aged.
Therefore, using friction losses of old steel pipes when designing the system is recommended to ensure the friction losses are compensated for.
Example 8.2 Mainline Friction Loss Calculation
 Question: What is the friction loss, Hf  for a 6-inch PVC mainline delivering 250 US gpm water?
Farm location Flow rate 
 Since the mainline is to be buried, PVC pipe will be used.
A travelling gun operating at 110 psi will often require Class 200 PVC.
For a 6-inch Class 200 PVC pipe,
 Coefficient of Retardation  Inside pipe diameter  
 150 3 5.995 4 in
 Method 1: Using Hazen-Williams Equation
 Method 2: Using Friction Loss Tables From Appendix B.7 for PVC 6" Class 200 PSI PVC Pipe, with a flow rate of
 Example 8.3 Mainline Friction Loss of Wheeline System in Armstrong
 From Example 5.1, each wheelline in the sprinkler system operates at 46 psi with a flow rate of 231 US gpm.
The entire system flow rate is 693 gpm.
The mainline length required from the pump house to the first hydrant is 600 feet.
The remaining hydrants are 120 feet apart.
The farmer wishes to use a buried mainline.
What type and sizes mainline are required?
What is the pipe friction loss?
Farm location Flow rate  System operating pressure
 Since the farmer wants a buried line, PVC pipe will be used.
With friction loss and elevation change added to the system pressure, select: Pressure rating  160 4 psi
 1.
Determine flow rates through each mainline section
 When looking at the farm plan, start from the furthest wheeline and measure back to the pump.
Wheelines #2 and #3 should start on opposite ends of the field and move towards each other.
This allows for lower flow rate and potentially smaller pipe size for the second half of the mainline.
Keep in mind that section X1 X2 must be sized to handle the combined flow rate of the two wheelines when they meet at mid-point.
2.
Select pipe size based on the 5-feet-per-second rule
 In the case of wheeline #1, the flow rate would have been under 5 ft/sec for a 5-inch mainline.
The product is difficult to obtain with a 160 psi rating, and in some locations may not be available.
Therefore, 6-inch pipe was selected.
If the flow rate was in between two choices on the table, interpolation could be used to achieve a more accurate number.
When estimating flow rate, always select the larger value.
Refer to Helpful Tips below for interpolating friction loss.
3.
Add friction loss for each pipe size, and calculate section loss 
 Section	Pipe	Flow Rate	Length	Pipe	Diameter	Pipe	Pipe Length	per 100 ft	X	Friction Loss per	100 ft	=	Friction Loss for	Section
 Q [US gpm]	L [ft]	D [in]	L per 100 ft	Hf  [psi]	Hf  [psi]
 X0 X1	693	600	8	6.0	X	0.33	=	1.98
 X1 X2	693	660	8	6.6	X	0.33	=	2.18
 X2 X3	462	660	8	6.6	X	0.15	=	0.99
 X3 X4	231	1,320	6	13.2	X	0.16 *	=	2.11
 * Refer to Helpful Tips below for interpolation of friction loss.
The mainline friction loss is 7.26 psi.
Helpful Tips Interpolation of Friction Loss
 Interpolation is required especially with high friction loss or long pipes where the total friction loss difference can become significant.
In the above example, interpolation was required to determine the friction loss for the 6-inch mainline with 231 US gpm flow rate.
From Appendix Table B6 for 6-inch Class 160 PSI PVC pipe,
 H at 200 US gpm = 0.12 psi Hf  at 250 US gpm = 0.18 psi The difference in flows on the table = 250 US gpm 200 US gpm = 50 US gpm The difference in friction loss = 0.18 psi 0.12 psi = 0.06 psi
 The friction loss of the extra flow of 31 US gpm needs to be added to friction loss at 200 US gpm.
This can be calculated by cross multiplication.
31 US 50 US f = 0.037 psi
 This amount of friction loss  must be added to the friction loss for the 8-inch pipe with a 200 US gpm flow rate.
Therefore, the friction loss of a 6-inch Class 160 PVC pipe at 231 US gpm is:
 Hf = 0.12 psi + 0.037 psi
 Fitting and Miscellaneous Losses
 When calculating mainline friction loss the length of the pipe line and the fittings losses must be taken in to account.
Fitting friction loss is determined by equivalent length of straight pipe.
In Appendix Table B.9 has equivalent lengths for steel fittings and Appendix Table B.10 has equivalent lengths for plastic fittings.
Example 8.4 Fitting Friction Loss of Wheeline System in Armstrong
 In Example 8.3, there are two 45-degree elbows and two 90-degree elbows before the first hydrant.
There is also a reducer coupling from the larger to the smaller mainline.
What would the friction loss of the fittings be?
1.
From Appendix Table B.10, the equivalent pipe lengths for the various fittings required for the system are as follows:
 Pipe	Equivalent Pipe	Friction	Total Friction
 Diameter	Fitting Type	Length	X	Quantity	X	Loss per	=	Loss
 [in]	[ft]	[ft/100 ft]	100 ft	[psi]
 8	45 elbow	20	0.20	X	2	X	0.33	=	0.132
 8	90 elbow	45	0.45	X	2	X	0.33	=	0.297
 8 6	coupling	24	0.24	X	1	X	0.33	=	0.0792
 Total Fitting Friction Loss, Hf 	=	0.508
 The fitting friction loss is 0.508 psi.
Helpful Tips Friction Loss for Miscellaneous Fittings
 If fitting losses are not accurately calculated then a 20% miscellaneous loss should be added to the pipe friction loss calculation.
Keep in mind that the total friction loss in the system should not exceed 10 % of the operating pressure.
Example 8.5 Lateral Friction Loss of Undertree Solid Set System in Osoyoos
 From Example 5.2, the apple farmer in Osoyoos is using an undertree solid set sprinkler system with Class 200 PVC pipe.
The sprinkler operating pressure is 34 psi.
The lateral line is split in the middle by the mainline.
What pipe sizes should be used for the laterals?
What is the lateral friction loss?
Sprinkler spacing  Sprinkler flow rate   Number of sprinklers Sprinkler operating pressure
 1.
In order to properly determine the lateral friction loss, each section along the lateral line would have to be calculated.
For the last sprinkler, the flow rate in the lateral section is 2.0 gpm.
From Table B.7, 1-inch pipe is the smallest listed size with the flow rate well below 5 feet per second.
For the second to the last sprinkler, the flow rate in the lateral section is for 2 sprinklers and therefore 4.0 US gpm.
The 1-inch pipe size would still be adequate for the velocity to stay below 5 feet per second.
2.
Add friction loss for each pipe section, and calculate lateral friction loss.
Interpolation between friction loss values listed in the Table may be required.
Section	Pipe	Flow Rate	Pipe Length	Diameter	Pipe	Pipe Length	per 100 ft	X	Friction Loss per	100 ft	=	Friction Loss for	Section
 Q [US gpm]	L [ft]	D [in]	L per 100 ft	Hf  [psi]	Hf  [psi]
 1	20	30	1-1/4	0.30	X	1.51	=	0.45
 2	18	30	1-1/4	0.30	X	1.24	=	0.37
 3	16	30	1-1/4	0.30	X	1.00	=	0.30
 4	14	30	1	0.30	X	2.43	=	0.73
 5	12	30	1	0.30	X	1.83	=	0.55
 6	10	30	1	0.30	X	1.30	=	0.39
 7	8	30	1	0.30	X	0.86	=	0.26
 8	6	30	1	0.30	X	0.51	=	0.15
 9	4	30	1	0.30	X	0.24	=	0.07
 10	2	30	1	0.30	X	0.07	=	0.02
 Total =	3.29 psi
 The total lateral friction loss is 3.29 psi.
If fitting losses of 20% are included the total loss is 4.0 psi.
To maintain 34 psi at the end of the lateral line, the start of the lateral line needs to have 38 psi, assuming the lateral is flat with no elevation change.
This lateral has been designed to stay close to an allowed pressure variation of 10% of the sprinkler operating pressure to improve uniformity.
To accomplish this section 3 was designed with 1 1/4 " pipe instead of 1" pipe even though 1 " pipe was within the flow velocity rules.
This reduced friction losses by 0.63 psi.
Example 8.6 Mainline Friction Loss of Undertree Solid Set System in Osoyoos
 Continuing from Example 8.5, the undertree solid set sprinkler system on the orchard in Osoyoos requires a mainline with four 90 elbows, two 45 elbows, one tee and a gate valve.
The water source is 240 feet from the edge of the field.
What pipe sizes are required for the mainline and what is the mainline friction loss?
Sprinkler spacing  Sprinkler flow rate   Number of sprinklers per lateral Number of laterals operating at a time Total number of laterals
 1.
Determine the system flow rate.
2.
To allow both laterals to be operated at the end of the field, the same pipe size will be used for the mainline.
From Appendix Table B.7, the friction losses along each section of the mainline are as follows:
 Section	Pipe	Flow Rate	Length	Pipe	Diameter	Pipe	Pipe Length	per 100 ft	X	Friction Loss per	100 ft	=	Friction Loss for	Section
 Q [US gpm]	L [ft]	D [in]	L per 100 ft	Hf  [psi]	Hf  [psi]
 X1	80	240	3	2.4	X	0.52	=	1.25
 X1 X3	80	465	3	4.65	X	0.52	=	2.42
 Total =	3,67	6
 3.
From Appendix Table B.10, the equivalent pipe lengths for the various fittings required for the system are as follows:
 Pipe	Equivalent Pipe	Friction	Total Friction
 Diameter	Fitting Type	Length	X	Quantity	X	Loss per	=	Loss
 [in]	[ft]	[ft/100 ft]	100 ft	[psi]
 3	90 elbow	17	0.17	X	4	X	0.52	=	0.3536
 3	45 elbow	8	0.08	X	2	X	0.52	0.0832
 3	tee	36	0.36	X	1	X	0.52	=	0.1872
 3	gate valve	1.4	0.014	X	1	X	0.52	=	0.00728
 Total Fitting Friction Loss, Hf 	=	0.63	7
 Total Mainline Friction Loss
 Mainline Friction Loss + Fitting Friction Loss
 3,67	6	psi +	0.63	7	psi
 When designing an irrigation system the overall pressure requirement must be calculated.
In some cases, using a larger pipe to reduce friction loss could allow for a smaller horsepower pump to be used.
This would then lower the annual operating costs and help offset the extra expense in purchasing the larger pipe.
In Example 8.5, lateral friction loss was determined by calculating loss for each section of pipe.
If the pipe size is the same, a factor may be used to determine the lateral frictioin loss.
The general friction loss  assumes that all of the water is carried to the end of the pipe.
If sprinkler outlets are discharging the same amount of water and the spacing is consistant, a factor can be used to calculate the friction loss in a lateral.
Factor F is for laterals that start with a full length on the first sprinkler.
Factor is for laterals that start with half spacing on the first sprinkler.
Equation 8.4 Lateral Friction Loss
 Hf  = Lateral friction loss [psi] F = Lateral friction loss correction factor Hf  = Total friction loss [psi]
 Table 8.2 Lateral Friction Loss Correction Factor, F
 F = first section full length, F = first section half length
 # Spr	1	2	3	4	5	6	7	8	9	10	14	20	25	30	40
 F	1	0.64	0.53	0.49	0.46	0.44	0.43	0.42	0.41	0.40	0.39	0.38	0.37	0.37	0.36
 F	1	0.52	0.44	0.41	0.40	0.39	0.38	0.38	0.37	0.37	0.36	0.36	0.36	0.36	0.36
 Example 8.7 Lateral Friction Loss of Microsprinkler System
 Question: For the microsprinkler system in Example 5.3, each lateral has 20 outlets at 0.65 gpm for a total of 13 US gpm.
The selected pipe size is 1 inch Class 200 PVC.
What is the lateral friction loss, Hf ?
8.4 Calculating Pipe Pressure Requirement
 The pipe selected must have a pressure rating that exceeds the total pressure that can be exerted on the system.
The total pressure head consists of the following components:
 The pressure required to operate the sprinkler.
The maximum elevation difference between the mainline intake and operating point in the field.
The pressure loss occurring by water flowing through pipes.
Friction loss for the lateral line and mainline must be considered.
Appendix B provides additional information on pipe friction loss.
The sudden closure of a valve or quick pump start up or shut down will create pressure surges in the irrigation line.
This is often referred to as water hammer.
Agricultural irrigation systems are designed to limit flow velocities in irrigation piping at 5 ft/sec.
A flow velocity of 5 ft/sec allows friction loss to remain at an acceptable level and limits surge pressures to tolerable levels.
Appendix B can be used to determine the suggested maximum flow capacities of various pipe types and sizes.
All values below the dark lines in the friction loss tables are in excess of 5 ft/sec and should therefore be avoided.
Water hammer, recognized by a pressure surge, develops when water under pressure in a pipeline is subjected to a change in its flow rate.
The rate at which the water velocity is altered determines the water hammer intensity.
Mainline design must give consideration to these potential surge pressures that may develop during system operation.
Water velocity in a pipe of constant cross-sectional area will change due to:
 opening or closing a valve
 starting or stopping a pump
 movements of air pockets along a pipeline
 sudden release of air from a pipeline
 The pressure increase in a pipeline flowing full of water due to a change in water velocity can be determined by:
 P= pressure increase  where W = 62.4 lb/ft3 C = =0.0135 g = 32.2 ft/sec2 a = velocity of pressure wave  AV = velocity change 
 Table 8.3 provides values for pressure wave velocities of different pipe types.
To minimize water hammer pressure surges it is recommended that the flow velocity in the pipe be limited to 5 ft/sec.
For irrigation purposes, the operating pressure of PVC and polyethylene pipe should not exceed 72% of the pipe pressure rating.
Table 8.3 can be used to determine the maximum pressure rise anticipated by operating irrigation mainlines at a flow velocity of 5 ft/sec.
The maximum pressure rise possible occurs when the valve closure time is less than system critical time.
Table 8.4 indicates the maximum operating pressure for different classes of PVC pipe and the maximum flow velocity recommended for systems operating at the maximum operating pressure.
Exceeding these flow velocities when the system is operating at the maximum recommended operating pressures will create pressure surges that cause the total system pressure to exceed the pipe pressure rating.
The flow velocity in a pipe can be calculated by using Equation 8.2.
Table 8.3 Maximum Pressure Rise for an Instantaneous Valve Closure at a Flow
 Velocity of 5 ft/sec
 Type of Pipe	Class or	Nominal Size	Outside	Wall	Pressure	Maximum
 Schedule		Diameter	Thickness	Wave	Pressure
 		Velocity	Rise 
 Steel	Sch.
40	4	4.500	.231	4390	295
 6	6.625	.280	4320	290
 8	8.625	.322	4270	287
 10	10.750	.365	4230	285
 Steel	14 Gauge	4	4	.083	3910	263
 6	6	.083	3630	244
 8	8	.083	3400	229
 Steel	12 Gauge	4	4	.109	4110	277
 6	6	.109	3870	260
 8	8	.109	3670	247
 Steel	10 Gauge	4	4	.134	4230	285
 6	6	.134	4020	270
 8	8	.134	3840	258
 4	4	.050	2730	184
 Aluminum	4	4	.072	3070	207
 6	6	.058	2490	168
 6	6	.083	2830	190
 8	8	.064	2320	156
 8	8	.072	2430	164
 PVC	Sch.
40	4	4.500	.231	1350	91
 5	5.563	.258	1280	86
 6	6.625	.280	1220	82
 8	8.625	.322	1150	77
 10	10.750	.365	1090	73
 PVC	Sch.
80	4	4.500	.337	1640	110
 5	5.563	.375	1550	104
 6	6.625	.432	1530	103
 8	8.625	.500	1440	97
 10	10.750	.593	1400	94
 PVC	Class 125	All Sizes	1040	70
 Class 160	All Sizes	1165	78
 Class 200	All Sizes	1300	87
 Class 315	All Sizes	1630	110
 The time for a pressure wave to travel from the valve to the pressure source and back is given as the critical time.
Critical time can be determined from the following equation:
 Equation 8.6 Critical Time
 where	Tc = system critical closure time 
 L =	length of pipeline 
 a =	velocity of pressure wave 
 Table 8.4 Maximum Recommended Operating Pressure and Flow Velocity for PVC
 Class or	Nominal Pipe	Pressure	Maximum	Allowable	Maximum Flow
 Schedule	Size 	Rating 	Recommended	Pressure Surge	Velocity
 Operating	Rise 	 *
 Sch.
40	3	260	186	74	3.71
 4	220	157	63	3.46
 5	190	136	54	3.13
 6	175	125	50	3.04
 8	160	114	46	2.97
 10	140	100	40	2.72
 Sch.
80	3	370	264	106	4.47
 4	320	229	91	4.12
 5	290	207	83	3.97
 6	280	200	80	3.88
 8	250	178	72	3.71
 10	230	164	66	3.50
 Class 125	All Sizes	125	89	36	2.57
 Class 160	All Sizes	160	114	46	2.92
 Class 200	All Sizes	200	143	57	3.25
 Class 315	All Sizes	315	225	90	4.10
 Maximum flow velocities suggested are for systems operating at the maximum recommended operating pressures
 only.
If systems are operating well below the maximum recommended operating pressure, a maximum flow rate
 of 5 ft/sec is suggested.
The water hammer pressure increase is maximum and constant for valve closure times less than the critical time.
Water hammer pressure surges can be reduced by slowing the closure time to less than the system's critical time.
Table 8.5 can be used to determine the minimum valve closure times for PVC systems at maximum operating pressures and a flow velocity of 5 ft/sec.
Table 8.5 Minimum Valve Closure Time for PVC Pipelines at Maximum Operating
 Minimum Valve Closure Times [sec]
 Class or	Nominal Pipe	Pressure	Length [ft]
 Schedule	Size 	Rating 
 500	1,000	2,000	5,000	10,000
 Sch.
40	3	186	1.8	3.6	7	18	36
 4	157	2.1	4.2	8	21	42
 5	136	2.3	4.6	9	23	46
 6	125	2.5	5.0	10	25	50
 8	114	2.8	5.6	11	28	56
 10	100	3.0	6.0	12	30	61
 Sch.
80	3	264	1.2	2.4	5	12	24
 4	229	1.5	3.0	6	15	30
 5	207	1.6	3.2	6	16	32
 6	200	1.7	3.4	7	17	34
 8	178	1.9	3.8	7	19	37
 10	164	2.0	4.0	8	20	40
 Class 125	All Sizes	89	3.4	6.8	14	34	68
 Class 160	All Sizes	114	2.8	5.6	11	28	55
 Class 200	All Sizes	143	2.2	4.4	9	22	45
 Class 315	All Sizes	225	1.5	3.0	6	15	30
 Example 8.8 Operating Pressure and Surge Pressure of a Travelling Gun
 A travelling gun has a connection pressure requirement of 110 psi with an elevation lift of 40 ft from the intake to the top of the field.
The mainline is 1,500 ft long and a 6-inch Class 200 PVC pipe is used with a flow rate of 210 US gpm.
What is the total system operating pressure and maximum surge pressure allowed?
Travelling gun pressure	110	1	psi
 Elevation	40	2	ft
 Mainline length	1,500	3	ft
 Mainline pipe diameter	6	4	in
 Mainline pipe pressure class	200	5	psi
 Conversion factor from feet to psi	0.433	6	psi/ft
 System flow rate	210	7	US gpm
 1.
Operating System Operating Pressure.
a).
Determine the maximum system operating pressure.
Max.
System Pipe Pressure Class X 72% = Op.
Pressure = 200 5 psi X 72% = 144 8 psi
 b).
Determine the elevation pressure loss.
Elevation Loss = Elevation Loss in Feet X Conversion Factor
 c).
Determine the mainline friction loss.
At a system flow rate of 210 US gpm with 6-inch Class 200 PVC pipe,
 Mainline Mainline Length X Friction Loss per 100 ft = Friction Loss
 d).
Determine the miscellaneous loss.
Friction loss 
 e).
Determine the total system operating pressure.
Travelling gun pressure	110	1	psi
 Elevation loss	17.3	9	psi
 Mainline friction loss	2.0	11	psi
 +)	Miscellaneous loss	0.4	12	psi
 Total system operating pressure	130	13	psi
 Since the total system operating pressure is less than the maximum suggested for Class 200 PVC, this pipe class and size are appropriate.
2.
Maximum Allowable Surge Pressure.
a).
Determine allowable maximum pressure surge.
Pa = Pipe Pressure Class Total System Operating Pressure
 b).
Determine the flow velocity.
Pipe inside diameter  5.995 1 in
 c).
Determine pressure increase due to an instantaneous valve closure
 Since the pressure generated due to instantaneous valve closure does not exceed the maximum allowable surge pressure, the valve may be closed quickly.
To reduce pressure surge, care should be taken to ensure velocity changes occur slower than the system critical time.
d).
Determine the system critical time
 8.5 Pipeline Design Considerations
 As discussed in Section 8.3 and 8.4, the pipe selected must he capable of withstanding the total possible pressure that can be exerted on the system.
The following points should be considered in designing mainline systems:
 The flow velocity in the pipe should be limited to 5 ft/sec.
For PVC pipe systems the operating pressure should not exceed 72% of the stated pipe pressure rating.
An air-vacuum release valve should be installed at all summits of the pipeline.
These valves release air during start up which reduces potential surge pressures.
It also allows air to re-enter the pipeline during shut down which prevents the possibility of vacuum collapsing the pipe.
Suggested minimum sizes for air-vacuum release valves are shown in Table 8.6, for pipe lines operating with a flow velocity of 5 ft/sec or less.
Table 8.6 Air-Vacuum Release Valve Sizing
 Pipe Diameter	Minimum Air-Vacuum Release Valve Diameter
 up to 4"	1 1/2"
 On gravity fed irrigation systems, a vent should be installed at the intake to allow entry of air should the intake become blocked.
Drains or pump outs should be installed at all low points in regions where freezing is a hazard.
Check valves should be used to prevent back flow through the pump.
Spring loaded check valves are suggested as they will close before flow reversal begins, reducing possible pressure surges.
If water hammer pressures are excessive, gasket joints should be used to allow for pipe expansion.
If multiple laterals are being operated at the same time the designer should calculate friction loss at the furthest point.
The pipe should be snaked moderately between fixed supports to allow for expansion and contraction.
Temperature problems can be minimized by installing pipe when it is within a few degrees of the expected operating temperature.
Anchoring of the pipe is required whenever excessive movement due to temperature changes or steep slopes are likely to occur.
Buried pipe should be backfilled  to a one foot depth shortly after laying.
This tends to distribute thermal expansion or contraction evenly over the pipe.
It also keeps the pipe in alignment during the final backfill process.
The pipe should be pressure tested after being partially back filled SO that all joints and fittings can be observed.
Irrigation trenches should have the following characteristics:
 free from rocks and frozen earth
 deep enough to protect pipe from surface loads or below frost level if drains are not provided.
Recommended pipe depths, assuming frost not to be a factor are given in Table 8.7.
the bedding material on the trench bottom should support the pipe uniformly over its entire length.
trenches should be free from water.
trenches should not curve faster than the recommended rate for the specific pipe to be buried.
Table 8.7 Recommended Pipe Installation Depths Excluding Frost Requirements
 Nominal Pipe Diameter	Pipe Depths
 [in]	[mm]	[ft]	[m]
 1/2 2	12 63	1.5	0.45
 2 4	63 100	2.0	0.60
 > 4	> 100	2.5	0.80
 Thrust blocks may be required at all changes in pipe direction or where the flow rate changes significantly.
The thrust block must support the pipe against forces caused by water pressure and changes in momentum.
This is done by increasing the soil bearing area for buried pipe or by the weight of a block or anchoring for surface pipe.
The size and location of the thrust block depends on the pipe size, line pressure, and type of fitting, soil type and degree of bend.
PVC pipe less than 3" that is solvent welded will usually not require thrust blocking.
The following tables can be used to determine the thrust block size.
Table 8.8 Pipeline Thrust Factors
 Nominal Pipe Diameter	Pipeline Thrust [Ib/psi]
 [in]	[mm]	Dead Ends	Tees	Elbows	90	Elbows	45	Elbows	22.5
 1.5	38	2.94	4.16	2.25	1.15
 2	50	4.56	6.45	3.50	1.80
 2.5	63	6.65	9.4	5.10	2.60
 3	75	9.80	13.9	7.51	3.80
 4	100	16.2	23.0	12.4	6.31
 5	127	24.7	35.0	19.0	9.63
 6	150	35.0	49.2	26.7	13.5
 8	200	59.0	83.5	45.2	23.0
 10	250	91.5	130.0	70.0	35.8
 12	300	129.0	182.0	98.5	50.3
 16	400	201.1	284.4	153.8	78.6
 Source: ASAE Standards 1987
 Table 8.9 Bearing Strength of Soils
 Soil Type	Safe Bearing Load [Ib/ft2]
 Medium clay can be spaded	2,000
 Coarse and fine compact soil	3,000
 Cemented gravel and sand difficult to pick	4,000
 Source: ASAE Standards 1987
 Example 8.9 Thrust Block Sizing
 Question: An 8" PVC pipe operating at 125 psi is buried in a compact sand type soil.
For a 90 elbow, what size thrust block will be required?
Pipeline thrust 
 A pipeline under pressure exerts an outward thrust at each deflected coupling.
Usually well tamped soil is sufficient to prevent any side movement in the pipe.
However, if soft soil conditions exist then thrust blocks may be required, especially for gasket joints.
Table 8.10 can be used to calculate the thrust block size to limit side thrust.
Table 8.10 Pipeline Thrust Factors
 Nominal Pipe Diameter	Side Thrust
 [in]	[mm]	[lb/psi/degree deflection]
 Source: ASAE Standards 1987
 For example, the side thrust for an 8" pipe operating at 125 psi with a 10 degree deflection is 1.03 lb/psi/deg X 10 degree X 125 psi = 1,287 lb.
The soil conditions should be evaluated to determine if thrust blocking will be required for the side thrust calculated in this example.
Table 8.11 can be used as a guide to determine the need for thrust blocking in-line valves.
Table 8.11 Anchoring of In-Line Valves
 Valve Size Requiring Anchorage
 50 100	12" and up
 100 150	8" and up
 150 200	all sizes
 Recommended thrust blocking consists of concrete having a calculated compressive strength of at least 2,000 psi.
The concrete mixture suggested is one part cement, two parts washed sand and four parts gravel.
Figure 8.1 indicates how thrust blocks are used for above ground mainline installations.
Figure 8.2 provides details on thrust block positioning for buried pipes.
Thrust block at Vertical Bend.
The thrust block must be heavier than the thrust force by at least 50% for vertical bends.
Thrust pad at vertical bend.
Figure 8.1 Thrust Block Positioning for Above Ground Irrigation Pipelines
 Figure 8.2 Thrust Block Positioning for Underground Irrigation Pipelines
With pivots, special consideration must be taken to prevent clogging of sprinklers with the solids.
Traveling guns have larger sprinklers, so they can accommodate up to approximately 5 percent solids whereas center pivots can only handle about 3 percent solids.
Table II.
Total available water in top 4 feet if soil is at field capacity and minimum balances at physiological maturity.
For loam, very fine sandy loam, or silt loam topsoil which is silty clay loam or silty clay subsoil, the available water in 1 foot of soil at 100% of available water is 2.0 in/ft, the available water in top 4 feet at 100% of available water is 8.0 in/4 ft, and minimum balance in top 4 feet at 40% of available water is 3.2 in/ft.
For loam, very fine sandy loam, or silt loam topsoil which is medium textured subsoil, the available water in 1 foot of soil at 100% of available water is 2.5 in/ft, the available water in top 4 feet at 100% of available water is 10.0 in/4 ft, and minimum balance in top 4 feet at 40% of available water is 4.0 in/ft.
Drip irrigation in California
 D rip irrigation first appeared in California agriculture in 1969 or 1970.
Enthusiasm rose rapidly because of the attractive newness of the method and because of high hopes for substantial water saving.
With water in California both costly and scarce, the prospect seemed inviting.
Before its introduction in California, no research on drip irrigation had been conducted by the University.
The first such research project, initiated by Cooperative Extension, was an avocado trial in San Diego County, which has been observed by a large number of growers, industry representatives, and scientists from around the world.
Since then, many drip-irrigation research projects have been conducted throughout the state on a variety of crops.
These have mainly been directed at methods of water and fertilizer management for various crops grown in different soil conditions.
Meanwhile, industry has worked on equipment problems, including emitter performance, clogging, and water cleaning to avoid clogging.
Expansion of drip irrigation was rapid during the first five years, but has slowed slightly in the last one or two years.
A mail survey in 1976 by C.D.
Gustafson, San Diego County farm advisor, revealed that drip irrigation is presently used in California on 60,000 to 65,000 acres.
Estimates by the same respondents show a potential acreage of about 100,000 by 1981.
Drip irrigation is used on many crops, mostly in four groups: orchards, vegetables, vineyards, and ornamentals.
Because the systems are costly, they are feasible mainly on such high-value crops and not on close-growing field crops, which would require more tubing and
 emitters and generally are of lower value.
Drip irrigation has been used to irrigate soils and terrain that could not have been watered by other methods.
In San Diego County there are areas having ideal climate for growing avocados but with shallow soils on steep, rocky, mountain slopes.
Drip irrigation has made avocado growing possible in these areas that would otherwise remain rough mountain brushland.
Vegetables grow well in some coastal valleys where irrigation efficiency has been poor because of the sandy soil.
Drip irrigation has improved both efficiency of irrigation and crop performance.
In the Central Valley of California, many soils have such poor infiltration rates that irrigation water fails to penetrate to the lower root zone except in the winter and spring.
In some tests, drip irrigation applied slowly and very frequently has been able to penetrate.
Drip irrigation also has been able to save substantial amounts of water in some cases and a significant amount in all -which is particularly important where water is expensive and limited.
The amount of savings has varied widely depending on the efficiency of the system with which it is compared.
Important water savings have occurred with new crops that have small root systems and do not need water in the surrounding soil not yet occupied by crop roots.
Crops have generally responded favorably to drip irrigation where it has been well managed.
This is particularly true of young plants that have a small root system and respond to high frequency of irrigation.
Crops also respond well to the injection of nitrogen fertilizer in the irrigation water.
The fertilizer is applied frequently in small amounts directly to the concentrated feeder-root zone near the emitters, which promotes efficient absorption by the roots.
Application of fertilizers other than nitrogen has not always been successful and is not being recommended as yet.
New mechanical devices have problems that are solved in time.
For drip irrigation, the most common and difficult problem is clogging of the small orifices of the emitters by mineral or organic matter in the water.
Even with careful filtration, some clogging can occur.
Fine silt, clay particles, and organic slimes are difficult to remove, and some waters have to be treated with chlorine or other chemicals to control organic slimes.
To make emitters less susceptible to clogging, manufacturers have evolved methods for automatic or manual flushing, which enlarge the orifice tempo-
 rarily so clogging material can pass through and leave the orifice clear.
Others have used larger orifices that are less likely to clog, increasing the length of the flow channel to achieve the reduction in pressure needed for flow control.
When irrigation is converted to the drip method, which may wet only 50 percent rather than all of the soil, a new cluster of feeder roots must grow to replace those that are in soil no longer wetted.
A mature tree may be subject to stress if hot weather arrives before the new roots have developed.
To avoid this stress, the system should be converted during fall and winter.
Drip irrigation potentially can produce large savings in labor, because water distribution is entirely mechanical, systems are easily automated, and fertilizers can be applied in the irrigation water.
However, labor requirements often have not actually been reduced, because of the need to patrol lateral lines to clear clogged emitters.
The potential for savings in labor needed for weed control also has not been entirely realized.
Although in new plantings weed growth is limited to the vicinity of the emitters, mechanical control around emitters is difficult, and chemical control is still inadequate.
After six years of use in the field in California, it is evident that drip irrigation is here to stay.
Because of the high cost of installed systems, the method will be limited to high-value crops or to situations where special problems exist that only drip irrigation can solve.
As performance of emitters improves so that efficiency of application increases, drip irrigation will find wider use because of increasing cost and scarcity of water and pressures to conserve water.
With improved performance, the labor requirement will decrease.
This also will serve to promote use of drip irrigation as farm labor costs escalate.
With a method still so young, many new ideas, modifications, and applications can be expected.
Drip irrigation generally uses lower water pressure than sprinklers, an advantage where energy costs have increased rapidly.
New developments may result in systems that operate similarly to drip irrigation while using no more pressure than that available in low head pipelines supplying water for flood irrigation.
New developments in drip irrigation may help solve problems of vandalism and of water spilling on traffic surfaces in landscaped areas.
Albert W.
Marsh is Soils and Water Specialist, Cooperative Extension, University of California, Riverside.
Chapter 4: Importance of Using Field Records for Corn Management Recommendations
 Field records provide information needed to avoid future problems.
Field records are created by combining your field-specific information into a single document.
This chapter discusses what should be included in your field records and how to integrate this information into the decision process.
Importance and Federal Regulations
 The time spent maintaining careful records can help to improve profits and overall efficiency of your enterprise.
Records provide information needed to identify successes and failures, and they should be as detailed and complete as possible.
Field record information may include field location, crop type, hybrid number, genetic enhancements, soil type, previous crops and yields, tillage, planting information, maps showing problem areas, soil test results, and any fertilizer/manure applications or pesticide applications.
Scouting maps and the results of soil and manure tests should be attached or included in the records.
If available, daily or monthly weather records should be attached to the yearly record.
Federal law requires that all private applicators keep records of applications of all restricted-use pesticides.
These records must be kept for a minimum of 2 years.
Restricted-use pesticides will be clearly labeled for "restricted use," and they can be purchased or applied only by a certified applicator.
Additional
 Figure 4.1 Field records of current and prior pest populations can be used to assess current and future risks.
This image shows a cornfield with very few pests.
Corn production costs can exceed $500/acre or $80,000 for a quarter section.
To ensure that these resources are well-invested, fields are routinely scouted to identify problems.
This information is compiled can be used as a benchmark for identifying successes and failures.
Although rarely discussed in achieving high yields, we believe that maintaining accurate records is a critical step in optimizing yields.
Field records should include information about field productivity, previous soil test information and fertilizers applied, historical information, and insect and weed pest management history.
Figure 4.2 Scouting a field.
Many decisions come down to the expected cost and return from each investment.
An economic analysis can be based on a single or multiple years.
A critical component when conducting an economic analysis is knowing your input costs and expected returns.
Examples of these costs are available in Chapter 54.
Input production costs are associated with the cost of the seed, fertilizer, herbicide, or insecticide, whereas the financial return is the expected yield times the selling price.
Expected yields can be estimated from longterm field records.
If long-term productivity information is not available, it may be possible to assess yield improvements using archived Landsat images or soil survey information.
If the data suggests that yields have not increased, then the land may not have been managed properly.
Yield data is a valuable tool for evaluating management strategies.
Difference between the observed and expected yields can be used to identify problem areas.
Soil Fertilizers and Test Results
 A periodic assessment of your corn soil fertility program will help determine whether you are applying the right fertilizer, at the right rate, at the right time, and at the right location.
This assessment would reveal if changes in the soil nutrient levels had occurred.
This assessment requires that historical soil test results and yields be available.
Details on conducting this assessment are available in Chapter 29.
Historical information is a valuable source of information.
When South Dakota was homesteaded, most quarter sections had a farmstead where livestock were maintained.
Even though many of these homesteads were removed over 50 years ago, their location can still be located in soil nutrient maps.
Depending on prior management, the size of area with high nutrient concentration can be small or large.
These areas should be sampled separately from the rest
 Figure 4.3 Influence of farmstead and feedlot on soil test P levels.
of the field.
Old aerial photographs may be available in the local USDA-NRCS office.
Field records and record keeping are critical components of an integrated pest management program.
Field pressure from weeds, plant diseases, nematodes, and insects is affected by tillage and crop management practices.
Historically, tillage was used to bury the surface residues, which reduced disease pressures.
Each of these pests is discussed throughout the manual.
The weed-control management history provides a picture of previous and potential problems.
Past records of weeds and their associated control reveal information about what worked and what did not work.
Weed records can also be used to identify herbicide resistance.
Increasingly, chemical companies are reformulating old chemistry into "new" products.
Therefore, record the trade name as well as the common name of the active ingredients and mode of action.
To reduce the risk of developing pest resistance, avoid using compounds with similar modes of action.
Figure 4.4 Cornfield with high weed pressure.
A complete history of each field should include any insect and disease infestations, and the effectiveness of the different control practices.
Records of the crop rotation, tillage, planting dates, insect identification, insect scouting reports, and economic losses can be used to predict future risks.
When assessing insects, scout the borders of your field.
Many insects overwinter in plants found outside of the field boundaries.
Keep records of insecticides used, including genetically modified organism  traits, for insect control.
Refuge areas should be maintained or refuge-in-a-bag planted to reduce resistant insect populations.
Volunteer corn in soybeans can increase corn rootworm problems in the following corn crop.
Detailed field records can provide a wide variety of valuable information.
The use of yield monitors provides an opportunity to build a profile for every field.
The gathering of field information and data from the past, present, and future is the basis of productivity and economic efficiency.
Accurate, concise field records and data provide information to creatively minimize risks and maximize profits.
1) Pumping Plants Electric motors account for the majority of the pumping plants in Nebraska, about 55% according to 2013 NASS Irrigation Survey.
They are relatively maintenance free but still need to be looked over.
It is a good idea to change the oil in the unit every year.
Next, open up the junction box and make sure the connectors are tight and have a good ground.
Also check for frayed wires and damage from rodents.
NITROGEN AND IRRIGATION MANAGEMENT FOR SORGHUM IN SOUTH CAROLINA
 Published: Apr 18, 2021 |  Printable Version  | Peer Reviewed
 Udayakumar Sekaran, Bhupinder Singh Farmaha, Michael W.
Marshall and Jose O.
Payero
 Sorghum is a drought-tolerant crop suitable for growing in South Carolina.
Although it can survive well under adverse conditions, nitrogen  insufficiency and water stress can reduce sorghum grain yield.
This publication summarizes how the negative impacts of water stress and N insufficiency can be mitigated with supplemental irrigation  and N fertilization.
Potential shifts in precipitation patterns due to climate change could alter how crops fulfill water requirements, reduce water availability and crop productivity, and increase the costs of water access across the agricultural landscape.
Adopting alternative crops with lower water requirements and increased crop yield per unit of water applied is important for agricultural sustainability.
Grain sorghum  is an ideal grain crop suitable for growing in regions drier than those for corn 1,2 In many humid regions, corn is usually a better choice than sorghum.
However, interest in sorghum production has increased because of recent climate changes resulting in hotter and drier conditions which creates water scarcity.
Although sorghum can survive and produce yield under adverse conditions, environmental stress and improper management can reduce yield considerably.
This is because drought conditions decrease the plants ability to utilize solar radiation, and plant growth depends on water availability during different growth stages.
Adequate water supply increases the photosynthetic rate and gives plants extra time to translate carbohydrates into grains.3 According to the 2012 US Census of Agriculture report, US producers planted grain sorghum on approximately 5.2 million acres with 0.50 million acres irrigated.
Sorghum can be an alternative to corn in the southeastern United States, especially in South Carolina.
However, poor and uneven rainfall distribution and marginal soil fertility of South Carolinas humid region can affect crop production.2,4
 In many regions where sorghum is grown, farmers use irrigation to supplement rainfall.
Previous research studies have found that integrated irrigation and fertilization can improve biomass and grain production in cereal crops.5 Irrigation methods affect the distribution, content, and movement of soil water, strongly influencing plant growth, and root system development, and water uptake.6 Increased N content can enhance root density and contribute to increased shoot biomass and grain yield.
In 2013, in Arizona, Texas, and North Carolina, sorghum growers applied an average of approximately 43, 14, and 2.4 inches of irrigation water to grain sorghum, respectively.7 Deficit irrigation is a common practice for sorghum grown in the Texas Southern High Plains region because precipitation rates are below well-watered crop requirements.
In Mississippi, Bruns 8 concluded that supplemental irrigation did not significantly increase the sorghum grain yields in the Mid-South under normal seasonal conditions.
However, limited information is available on providing supplemental irrigation to sorghum in humid regions like South Carolina.
Understanding the optimum supplemental irrigation level and N fertilization will help farmers achieve sorghum grain or silage yield or sorghum in South Carolina.
Nitrogen and Supplemental Irrigation Effects on Sorghum Aboveground Biomass
 Sigua et al.
9 observed in South Carolina to determine the combined effects of N fertilization at rates of 0 lb, 76 lb, and 152 lb N ac-1 and supplemental irrigation applied at rates of 0%, 50%, and 100% of the full irrigation rate in South Carolina.
The researchers measured the effect on aboveground biomass  for two grain sorghum varieties  grown in South Carolina.
Supplemental irrigation combined with the N fertilizer application at the rates of 76 lb and 152 lb N ac-1 increased the sorghum aboveground biomass, N use efficiency, and N uptake in this research study.
On the other hand, the application of 76 lb and 152 lb N ac-1 produced a statistically similar yield.
These results confirm that the application of supplemental irrigation along with optimum N fertilization  mitigated the impact of water stress and N deficiency in sorghum grown in South Carolina.
The results also implied that sorghum grown under N deficient conditions  slows the rate of accumulation of dry matter accumulation.
Reducing the N content below the threshold level may lead to vegetative tissue death and restrict the sorghum crops growth, productivity, and grain yield.
Table 1.
Aboveground biomass  as influenced by supplemental irrigation and N fertilization in 2013 and 2014 cropping.9
 Treatments	Average aboveground biomass 
 1.
0% Irrigation	2723b
 2.
50% Irrigation	2941b
 3.
100% Irrigation	3472a
 1.
0 N 	2660b
 2.
76 N 	3251a
 3.
152 N 	3336a
 Irrigation x N 	*
 Values within the same column followed by letters are significantly different at p<0.05 within the treatments.
*p<0.01.
Combining supplemental irrigation  with 76 lb N ac-1 resulted in significantly higher aboveground biomass in this grain sorghum study.
The study demonstrated that sorghum growers could mitigate the negative impacts of water stress and N deficiency by providing supplemental irrigation and optimum N fertilization.
On-farm research trials conducted near Lawrence, Nebraska over three years 10 showed that in two out of three years, sorghum had the highest crop water use efficiency  followed by corn and soybean.
10
 Table 2a.
Crop evapotranspiration  of corn, soybean, and sorghum in on-farm trials conducted near Lawrence, Nebraska, 2009-2011.10
 Ways to Improve Crop Productivity Under Water-Scarce Conditions
 There are two fundamental approaches to improve and sustain crop productivity under water-scarce conditions:
 Selecting and planting varieties that are well-adapted to drought conditions.
Providing supplemental irrigation and reducing soil water loss by managing the soil environment.
Improving water use efficiency can be achieved by using efficient irrigation systems , using proper irrigation scheduling techniques , and using site-specific irrigation technologies ) to apply water when, where, and in the amount needed to meet crop requirements while minimizing water losses.
Application of these technologies enables water to stay in the crop root zone, available to the crop, minimizing water losses by runoff, surface evaporation, and deep drainage.
The USDA Environmental Quality Incentives Program  website provides information about financial opportunities for growers to implement some of these water conservation technologies.
Poor and uneven rainfall distribution and soil fertility in humid coastal plain regions like South Carolina may affect the production of grain crops.
A crop with lower water requirements, like grain sorghum, is well adapted to various adverse environmental conditions and can replace corn in areas where soil fertility is low and water supply is limited.
The use of supplemental irrigation  along with optimum N fertilization  to sorghum could mitigate the negative impacts of water stress and nutrient deficiency.
This study concludes that effective use of irrigation water and maintaining soil N level will improve the biomass of grain sorghum in South Carolina.
The article, entitled Past, Present and Future of Irrigation on the U.S.
Great Plains and published by the American Society of Agricultural and Biological Engineers , also put irrigation in the context of its impact on water resources.
Today, irrigation in the region is primarily dependent on groundwater , although surface water sources continue to be significant.
In some locations, the rate of water withdrawal for irrigation has exceeded the rate of aquifer recharge, resulting in declining water levels in the High Plains Aquifer.
Data used to compile the annual Groundwater-Level Monitoring Report are collected by 30 different state and local agencies, and Young leads a University of NebraskaLincoln effort to process the data, plot it and then hand draw maps that are published in the report.
The goal, Young said, is to provide annual analysis of one of Nebraskas most vital resources.
All this water is essential to our agricultural economy, he said.
Without this, growing crops would be next to impossible in many parts of the state.
End of Corn Irrigation Season Study, 2003
 A study is underway at the KSU Northwest Research-Extension Center at Colby Kansas to develop improved criteria for decisions about terminating the irrigation season for field corn.
Currently, 7 treatments are being examined consisting of 7 different dates to shut off irrigation.
In 2003, these dates increased in 1 week increments beginning one week after silking.
The actual shutoff dates were July 29, August 5, 12, 19, 26, September 2 and 9.
Prior to treatment initiation, all treatments received the same amount of irrigation.
Additionally, all treatments were fully irrigated up until the point of their respective termination date.
Seasonal irrigation amounts were 11.35, 14.90, 18.10, 20.20, 21.95, 23.00, and 24.00 inches for the 7 respective termination dates.
It should be strongly noted that the purpose of this study is not to establish a given shutoff date or a given irrigation requirement and that the results are not meant to be interpreted in that fashion.
Rather, the dates and irrigation amounts were used to impose differing levels of water stress during the period of grain filling.
This is to provide information about how grain filling is affected.
Further analysis and additional study will be necessary to incorporate this and other information into an improved season termination criteria.
The results from 2003 are provided here primarily to emphasize that the grain filling stage is a very important period in corn production and that grain filling rates can be altered by water stress.
In 2003, heavy spider mite damage probably lowered the ultimate yields of the adequately irrigated treatments.
The results show that a grain filling rate of 3 to 3.5 bushels/day was achieved during the 28 day period  for the treatments that were adequately irrigated.
In 2003, the yields for the heaviest irrigated treatments  were lower due to spider mite damage.
For the treatments  with higher water stress, grain filling rates for the 28-day period averaged only 1.5 to 2.4 bushels/day.
The results do show that large yield differences can occur just due to improper irrigation management during the grain filling stage.
More analysis and more years of study are needed to incorporate these results into new criteria.
Figure 1.
Corn yield for different dates  as affected by 7 different irrigation termination dates and amounts at Colby, Kansas.
Note: Physiological maturity was on September 23.
the leaves differed as to the time of peak larval densities in August.
Thus, as previously mentioned, in the leaf samples larval abundance and leaf damage were greatest the week of August 8 to 15 when 75% of the larvae found were small; however, the net sweeps recorded the highest number of larvae the following week, August 15 to 22.
The sweep-net method apparently did not collect sufficient numbers of small worms to accurately reflect larval densities of cabbage looper when the majority of larvae present were less than 1/2 inch in length.
An assessment of the field populations of bollworm eggs and larvae was made by examining terminals, squares, and both small and large bolls at weekly intervals.
In each treatment, 400 structures of each category were examined-a total of 1600 plant parts per week.
There was good correlation between the field counts of bollworm eggs and larvae and the mean number of moths collected in the two light traps.
The upward trend in moth abundance began the week of August 15 to 22, and an increase in egg and larval numbers was found in the field counts made the week of August 29 to September 5.
Thereafter, the numbers of eggs and larvae recorded increased until the end of the test period.
Two light traps located 3.75 miles apart and each situated about 1 mile from a test field were used effectively to trap moths of cabbage looper and bollworm, and reflected similar patterns in timing, magnitude, and duration of moth flights.
Increased collections of moths in the traps were followed by a rise in egg and larval populations in the field.
Through a combination of light-trap information and adequate field sampling procedures, a more effective means for detecting the onset of infestations and assessing the population levels of cabbage looper and bollworm in cotton appears possible.
DUAL-USE RETURN-WATER IRRIGATION SYSTEM
 F.
K.
ALJIBURY J.
W.
BROWN C.
E.
HOUSTON
 This study indicates that where tailwater is a necessity to provide an appreciable increase in production of a relatively highvalue crop, a large investment in the irrigation return-water system can still be economically feasible.
R ECENT STUDIES in the surface-irrigated citrus areas of southern California have shown that insufficient water application at the lower ends of orchards has sometimes decreased fruit production.
To overcome this problem without a prohibitive increase in irrigation labor, it has been necessary to irrigate for a longer period of time-resulting in excess tailwater.
With Colorado River water costs as high as $30 per acre foot, it is imperative that the tailwater be reused.
Gener-
 The installation costs (including $3,500
 for material) were approximately	$7,000
 Value of land and trees removed for the
 Yearly depreciation cost $8,100
 	486
 Total annual cost	$1,486
 Estimated annual cost per acre $6.30
 1.5 box increase in orange production
 per tree (30 trees affected per acre,
 or 45 boxes per acre)
 At $1 per box, value of system per acre $45.00
 Cost for return-flow system per acre	6.30
 Return per acre	$38.70
 Annual value of tailwater reused	$4,050
 About 150 acre-feet at $27.00
 ally when this tailwater is reused, the high content of suspended solids creates silting problems when the water is introduced directly into an irrigation pipeline.
The study reported here is of a dual system constructed for conservation of tailwater and removal of suspended solid material.
Applying sufficient water to replenish soil water in the entire orchard resulted in an increase in orange production of about 1.5 boxes per tree on the lower third of the orchard, with tailwater amounting to about 25% of the water applied.
Irrigation water applications at a rate of 100 gallons per minute per acre for 24 hours produced about 11/3 acre-
 Intake for return-flow irrigation system at Irvine Ranch, Orange County.
TAILWATER REUSE SYSTEM-THE IRVINE COMPANY
 1.
Reservoir large enough to give the retention time required for settling the suspended solids.
2.
Reservoir settling area below inlet and outlet pipes is large enough to require cleaning once a year and still not require cleaning close to the plastic.
3.
Discharge ties into an existing gravity irrigation main for reuse.
4.
Manhole on inlet pipe to permit cleaning pipes if required.
inches of tailwater at each irrigation.
Laboratory tests indicated optimum settlement of silt and clay occurred in about 10 hours.
A reservoir was designed for this system to accommodate a flow of 300 gallons per minute or 18,000 gallons per hour.
For the 10 hours needed for settlement, the reservoir capacity necessary was 180,000 gallons or 24,000 cubic ft.
The reservoir constructed averaged 105 feet long, 34 feet wide, and a depth above the outlet pipe of 7 feet, making a total volume of 25,000 cu ft available.
Analyses of tailwater samples indicated silt and clay in suspension of 0.131% by weight.
This amounts to 4710 lbs per day
 for a flow of 300 gallons per minute or about 47 cu ft of settlement per day.
The dimensions of the reservoir below the outlet pipe were 100 X 25 X 4 ft or a volume of 10,000 cu ft.
If the settlement occurred at the same rate throughout the volume of the reservoir, it would need to be cleaned every 213 days, or 7 months.
A trial operation for four months indicated that 40 acre feet at a flow of 90 gallons per minute into the reservoir settled silt and clay near the inflow pipe rather than equally throughout the reservoir.
This required removal to prevent interference with the inflow.
The removal and maintenance cost for the period was
 about $250.
Assuming the reservoir is operated at the rate of 150 acre-feet per year, it is estimated that three to four cleanings will be required per year or a $1000 total maximum maintenance cost.
During the period of peak use of water, 21 days should be the maximum time between irrigations.
The dual system can serve 12 acres a day or 250 acres during the peak use period.
Irrigation return-water system reservoir, is shown in photo below, and check gate, photo to right.
Economics of Irrigation Ending Date for Corn: using field demonstration results.
Troy J.
Dumler, Danny H.
Rogers, and Kent Shaw
 Extension Agricultural Economist, SW Research-Extension Center, Garden City, KS; Professor, Kansas State University, Manhattan, KS; and Mobile Irrigation Lab Program coordinator, SWREC, Garden City, KS, respectively.
Written for presentation at the 18th Annual Central Plains Irrigation Conference & Exposition sponsored by CPIA
 Colby, Kansas February 21-22, 2006
 Abstract: The results from a field study indicate that corn growers of western Kansas may cut back last one or two irrigation events of the season without appreciable loss in production.
This will improve the economic return by reducing input cost from water.
Recent increase in energy cost for pumping water has necessitated this study to compare the benefits of continuing irrigation until black layer formation.
With the decline of Ogallala aquifer groundwater level and rising fuel cost, any reduction of pumping makes economic sense.
The first irrigation ending date around August 10-15, corresponding to denting and starch layer formation of 1/4 to 1/2 towards the germ layer resulted in an yield reduction of 17 bushels averaging for four years of data for a silty loam soil as compared to second ending date around August 21-22, which corresponded to starch layer at 1/2 to 3/4 towards the germ layer.
However, continuing irrigation until September 1, corresponding to the start of black layer formation, improved yield by only 2.5 bushels per acre.
Economic sensitivity tests show that irrigating until the formation of starch layer at 1/2 to 3/4 towards germ layer is feasible with a corn price of $2 per bushel and $8 per inch pumping costs.
However, irrigating past this stage of grain development is not feasible even with $2.75 / bushel of corn and pumping costs as low as $4 / inch.
Keywords.
Ogallala aquifer, corn
 Crop production in western Kansas is dependent on irrigation.
The irrigation water source is groundwater from the Ogallala aquifer.
The water level of the Ogallala aquifer is declining causing the depth of pumping to increase.
The additional fuel consumption required for greater pumping depths and higher energy costs have resulted in higher pumping costs in recent years.
Because of declining water levels and higher pumping costs, it is necessary to conserve water
 by adopting efficient water management practices.
Irrigation scheduling is an important management tool.
Farmers are interested in information on optimum timing for ending the irrigation season.
There are some misconceptions regarding the optimum irrigation ending dates.
Some farmers believe that the corn crop must continue to have water to avoid eardrop.
Over application at the end of season based on this thought cause waste of water, increases cost of production, and may even cause degradation of quality of the grain due to high humidity or disease.
Most of all, the excess use of water may reduce the useful life of the Ogallala aquifer which is a confined aquifer with little or no recharge.
Depletion of the Ogallala aquifer will impact irrigated agriculture and the present economy of the area.
The objective of the study was to determine the affect that irrigation ending date had on corn yield and economic return.
A producer's center pivot sprinkler irrigated field was selected for the study.
A silty loam soil of Ulysses series was selected and the study was conducted for four years.
Two sets of six nozzles were shut progressively after the formation of starch layer in the corn grain.
The first closure was done when the starch layer was 1/4 to 1/2 to the germ.
This corresponded to August 10th to 15th, depending on growing degree units.
The second closure was done when the starch layer was 1/2 to 3/4 to the corn germ.
This corresponded to August 21 to 24.
The third closure occurred when the producer ended irrigation for the year.
This happened during the first week of September.
Four random plots of 30 ft.
by 30 ft.
were identified within the center pivot sprinkler circle over which the selected nozzles would pass during an irrigation event.
Ridges were built around the plots to prevent entry of water from the adjacent areas.
Gypsum block soil water sensors were buried in the plots at three different depths  below the soil surface.
The soil of the test field is Ulysses silt loam series.
It is relatively dark with a deep profile and good water holding capacity.
The soil surface, however, cracks when dry.
Corn ears were hand harvested.
Four contiguous rows measuring ten feet each were harvested at the middle of each plot to remove any border effect.
Grain yields were adjusted to 15.5% moisture content.
In 2005, the study was moved to a field with loamy fine sand soil  to evaluate irrigation ending date for a light textured soil with lower water holding capacity.
The hypothesis is that the sandy soil may require continuation of irrigation and irrigation ending date may be delayed compared to a silty loam soil with higher water holding capacity.
The procedure followed was similar to the earlier study where two sets of six nozzles were closed progressively as the grain formed starch layer.
Continuation of irrigation from the first ending date in early August  to the second ending date in the beginning of the fourth week  gave an increase of average 19.5 bushels of grain per acre.
The additional irrigation application amounted to 2.1 inches.
The yield difference from the August 22 ending date to the first week of September ending date, as normally practiced, was only 2.5 bushels per acre on average for four years.
The additional irrigation quantity for the period from the first ending to last irrigation date amounted to 4.6 inches  as an average for four years.
The yearly yields are shown in figure 1.
Figure 1: Yield of corn grain as affected by irrigation ending date at different growth stage on a silty loam soil, Stevens County, Kansas, 2000 -2003.
The tool used to determine the optimum irrigation ending date was the marginal value VS.
marginal cost analysis.
In this analysis corn price ranged from $2.00 to $2.75 per bushel, while pumping cost ranged from $3.00 to $8.00 per inch.
Positive returns indicate that the marginal benefit of continuing irrigation was greater than the cost of applying water.
Figure 2 shows that under nearly all scenarios, irrigation remains profitable until the second ending date.
However, irrigation past this growth stage may not be profitable.
Return becomes negative at pumping cost of $4.00 per inch for corn even at $2.75.
Figure 2: Returns at different levels of input cost and price of corn for difference between 1st and 2nd ending dates
 Figure 3: Returns at different levels of input cost and price of corn for difference between 2nd and 3rd ending dates
 Kansas State University water management bulletin No.
MF-2174 presents a table showing normal water requirements for corn between stages of growth and maturity.
Corn grain, at full dent, will use 2.5 inches of water for the remaining 13 days before reaching physiological maturity.
The available water holding capacity of the soil in the study field is estimated to be approximately six inches or more per 3 feet of root zone.
It is expected that at a 50 percent management allowable depletion level this soil will provide about 3 inches of water.
This may be the reason that there was no appreciable benefit from continuing irrigation past August 21 or after the starch layer has moved past 1/2 to 3/4 towards germ layer.
The soil water sensors indicated that the soil water condition was adequate to carry the crop to full maturity.
Soil water status monitored by gypsum block sensors is presented in Figure 4-6.
Figure 4: Soil water status for 1st irrigation ending date.
Figure 4 shows that the soil water at first and third feet depths were falling below Management Allowable Depletion  level for the first ending date that caused reduction in yield.
Figure 5 shows that soil water in first foot started to go down in the plots of second ending date, but there was enough in second and third foot to carry the crop to maturity.
It is also seen that at this site for some reason the moisture level at 1-2' feet were at MAD level in the very beginning of the season.
However, this changed as irrigation started.
Figure 5: Soil water status for 2nd irrigation ending date.
Figure 6: Soil water status on 3rd irrigation ending date.
Figure 6 shows soil water readings taken until September 11 at the area where irrigation continued until September 1 under producers practices, indicate that soil water was almost at Field Capacity, except for the first foot of the profile.
The crop was already mature and there was no more water use.
The profile was left with high water content over the winter.
Most of the irrigated cornfields in western Kansas reflect this situation and have little room to store winter and early spring precipitation.
This causes double loss from not taking advantage of natural precipitation and leaching of nutrient with the deep percolation of excess water.
A three-year study by Rogers and Lamm  also indicated that the irrigation practices of corn producers of western Kansas leave approximately 1.4 inches of available soil water per foot of soil profile.
Irrigated agricultural producers are continuously being educated on irrigation scheduling.
Kansas State University Biological and Agricultural Engineering developed computer software called KanSched to provide the producers with an easy to use tool for irrigation scheduling.
The irrigation events, rainfall, and crop water use  data were entered to track soil water depletion pattern, which is presented in Figure 8.
Tracking of crop water use and irrigation application show that the soil profile was pretty full at the end of the season when irrigation was continued until September 1.
Figure 7: Chart showing water balance between soil water storage at field capacity and permanent wilting point.
The dashed line in the middle represents management allowable depletion.
It would be worthwhile to mention that there was no appreciable eardrop observed in the field within the circular area with the first irrigation ending.
However, the plants were dryer as compared to the rest of the field at the time of harvest.
Results of 2005 trial on Vona loamy fine sand needs to be continued to establish a trend.
However, the first year results do indicate that the return remains in the positive at pumping cost of $5.00 per inch although the rate of return has been greatly reduced, Figure 9-10.
Figure 8: Returns at different levels of input cost and price of corn for difference between 1st and 2nd ending dates.
Figure 9: Returns at different levels of input cost and price of corn for difference between 2nd and 3rd ending dates
 A four-year field study indicates that the present practice of irrigating until the formation of black layer in corn grain may not be economical.
An earlier ending date for irrigation corresponding to the starch layer at 1/2 to 3/4 of the grain may help improve the economic return and best utilize the soil profile water in a silt loam soil.
Using KanSched or Soil water monitoring by other means may help in the decision process.
However, this may require more cautious evaluation in a sandy soil for its low water holding capacity.
Minimum Number of Soil Moisture Sensors for Monitoring and Irrigation Purposes
 Lincoln Zotarelli, Michael D.
Dukes, and Marcelo Paranhos
 Managing soil moisture properly through irrigation is key to increasing crop yield and conserving water.
By understanding soil moisture variability, growers can better manage their irrigation systems to apply the right amount of water at the right time.
Soils are known to be heterogeneous across fields, and this plays an important role in soil moisture variability.
By knowing the spatial variability of soil moisture on an irrigated field, localized and precise irrigation scheduling can be performed, thus avoiding underand over-irrigation, which can result in plant water stress or nutrient leaching.
Improved irrigation scheduling techniques that use soil moisture sensors to control irrigation events can greatly increase irrigation water use efficiency.
Capacitance-based soil moisture measurement devices are relatively accurate in the sandy soils common to Florida.
This publication proposes guidelines for soil moisture sampling that account for spatial variability, which helps to determine the minimum number of soil moisture sensors required to survey and monitor a specific area for irrigation.
Soil moisture can be directly evaluated using commercially available portable soil moisture sensor devices.
Specific zones of the field can be easily identified and managed when soil moisture sensing technology includes global
 positioning systems  and geographic information systems  for producing soil moisture maps.
For the purposes of this publication, near-surface  volumetric soil moisture content was sampled using a commercially available portable time domain reflectometry  probe.
The equipment has a published error of +2% vol/vol or less.
The soil probe consists of two parallel 0.25-inch-thick and 8-inch-long stainless steel rods.
The TDR unit was connected to a GPS for georeference of each sampling point.
The georeferenced soil moisture data were stored in the TDR unit's datalogger.
Soil Moisture Sampling Plan
 After determining the boundaries of a given area, a soil moisture sampling plan should be developed.
The initial sampling should be performed in a small grid; however, it is important to maintain a minimum of twenty sampling points per acre for a good soil moisture characterization, covering the entire area.
Subsequent soil moisture sampling can be conducted using a grid-based system; however, the sampling density can be reduced to half of the distance beyond which soil moisture is no longer spatially dependent .
A temporal distribution of the sampling is also recommended in order to capture the spatial soil moisture variability of the area with regard to overall soil moisture
 2.
Lincoln Zotarelli, assistant professor, Horticultural Sciences Department; Michael D.
Dukes, professor, Agricultural and Biological Engineering Department; and Marcelo Paranhos, research assistant, Horticultural Sciences Department; UF/IFAS Extension, Gainesville, FL 32611.
conditions.
Sampling should be taken under at least three soil moisture conditions: high soil moisture ; medium soil moisture , and low soil moisture.
Figure 1.
Example of soil moisture sampling distribution map in an 8.2-acre-field.
Each cross represents a soil moisture sampling point.
Axes are represented by coordinates.
The X-axis represents longitude, and the Y-axis represents latitude.
Credits: M.
Paranhos, UF/IFAS
 Determining Soil Moisture Scale and Preparing Soil Moisture Map
 Table 1.
Soil moisture scale for soil moisture variability analysis.
Volumetric soil water content	Soil moisture condition
 Basic Components of Geostatistics, Variogram Interpretation, and Data Interpolation
 Geostatistical procedure provides a set of tools for incorporating the spatial coordinates of soil moisture observations in data processing.
This allows for better description and modeling of spatial patterns and better prediction of soil moisture at unsampled locations.
Detailed descriptions of geostatistical estimation can be found in specific texts, such as Goovaerts.
This publication explains important parameters of geostatistical analysis in a more simplistic language to help with interpretation of observed results.
This publication does not aim to teach the reader how to perform geostatistical analysis or data interpolation.
The first product obtained from a geostatistical analysis is the variogram.
The variogram is a measurement of how quickly the measured parameters, in this case sampled soil moisture, change according to their distance from one another.
The underlying principle is that, on average, two observations closer together are more similar than two observations farther apart.
The variogram model mathematically specifies the spatial variability of the data set and the resulting grid file.
The interpolation weights, which are applied to data points during the grid node calculations, are direct functions of the variogram model.
The variogram includes two independent variables and one dependent variable: sill, range, and nugget, respectively.
Figure 2 shows the variogram's components.
Figure 2.
Example of exponential variogram and its parameters.
Credits: M.
Paranhos, UF/IFAS
 Nugget effect: The nugget effect is the distance on the Y-axis between the origin and at the point where the fitted model intersects the Y-axis at a positive value.
It quantifies the
 sampling and assaying errors and the short variability.
The units of the nugget effect are the units of the observation squared.
Range: The range is the distance beyond which the deviation in the values does not depend on distance; hence, values are no longer correlated.
Sill: The sill is the total scale of the variogram , and is also the plateau of bounded variograms.
The linear, logarithmic, and power variogram models do not have a sill.
If there is spatial autocorrelation between the sampled points, it should expect the variogram values to increase as the separation distance  increases.
In most situations, the variogram stops increasing at a given distance, called the range, which can be interpreted as the distance of dependence or the zone of attribute's influence.
The nugget effect or discontinuity at the origin of the variogram  arises from measurement errors, sources of spatial variation at distances smaller than the shortest sampling interval, or both.
For instance, very high nugget effect indicates a very high variance between close samples.
This might be attributed to the soils' natural variability or to management that needs to be further investigated.
The parameters obtained from the variogram mentioned above are used to provide confidence in the performed analysis.
Identifying Areas with Homogenous Soil Moisture for Soil Moisture Sensor Placement
 The minimum number of soil moisture sensors for irrigation or monitoring of a given area can be estimated by using the range value obtained from the geostatistical analysis.
The range value  is where the variogram stops increasing at a given distance, which is interpreted as the maximum distance between sampled points where there is correlation of distance dependence, in this case for soil moisture content.
In other words, the range value  can be translated as the maximum distance between soil moisture sampling points.
After the initial soil moisture sampling characterization, future sampling can be conducted on a grid system, where the grid should be half of the range value distance.
The range value should
 be determined for the three predominant soil moisture conditions , and then the values can be compared to each other considering the homogeneity of the area, based on soil moisture maps.
The prediction of unsampled areas  and mapping preparation can be performed by using kriging, which allows the estimation of soil moisture values at an unsampled location, given the soil moisture measured values at neighboring sampled locations.
Detailed descriptions of kriging procedures can be found in specific texts, such as Goovaerts , and can be performed with specific software.
Practical Example of Soil Moisture Sensor Determination for Agricultural Areas
 For this example of soil moisture sensor number determination, 26.6 acres of perennial pasture located in Hillsborough County, Florida, was chosen.
Figure 3 shows the aerial photograph of the area and identifies the soil series.
Figure 4 shows the soil moisture distribution map for three different soil moisture conditions.
The dry condition  was characterized by the percentage of the sampled points below 7.9% volumetric water content.
In this case, 94.7% of the points were below the VWC threshold, while only 5.3% of the sampled points were between 8% and 15% VWC range.
For the medium soil moisture condition evaluation , about 20% of the area sampled was characterized by medium soil moisture conditions.
The sampling was performed 2 days after 1.4 inches of precipitation.
Another soil moisture variability evaluation was performed after
 3.43 inches of rainfall in the 3 previous days, characterizing a wet soil moisture condition.
Figure 4.
Soil moisture distribution maps under different conditions for pasture in Hillsborough County, Florida.
The graphs represent soil moisture spatial distribution using the kriging interpolation method: a)  dry conditions; b)  medium conditions; and c)  wet conditions.
The X-axis represents longitude, and the Y-axis represents latitude.
Credits: M.
Paranhos, UF/IFAS
 For the area of this example, three soil moisture conditions were evaluated in terms of spatial soil moisture distribution patterns.
For irrigation and crop management purposes, the soil moisture maps were used to identify homogenous area.
These areas are called management zones, and they should be managed independently for irrigation based on soil moisture and crop water requirements.
For those areas, the fixed soil moisture sensors located in the management zones could be used to periodically monitor the soil moisture or automatically drive the irrigation valves.
Based on graphs of soil moisture distribution, three management zones were identified  for the studied area.
Because of their soil moisture characteristics, the three zones should be managed independently for irrigation purposes.
Zone I was characterized by drier soil moisture conditions than Zones II and III.
The estimated area of Zone I was 16 acres, followed by 9.4 and 1.2 acres for Zones II and III, respectively.
Zones I and II could be monitored by one or two soil moisture sensors placed at convenient points within each management zone.
Because of its small area, a single moisture sensor could monitor Zone III, or alternatively, area drainage could be improved and,
 depending on a future soil moisture characterization, the area could be incorporated into Zone I or II accordingly.
Figure 5.
Suggested distribution of management zones according to soil moisture homogeneity.
Credits: L.
Zotarelli, UF/IFAS
 When determining irrigation management zones, one should also consider irrigation method and design.
Irrigation management zones with irregular shapes may not be practical and could be hard to manage.
Therefore, adequate distribution of irrigation management zones within irrigation design may be crucial to irrigate the crops according to the soil moisture holding capacity of each zone.
Datasets of soil moisture can be investigated from a geostatistical point of view in relation to spatial soil water distribution in different predominant soil moisture conditions.
Repeated soil moisture measurements over several drying/wetting cycles are necessary to access spatial soil moisture patterns and confidently evaluate the required number of soil moisture sensors for a given area.
For the TDR measurement procedure, the first sampling should be performed under a high density of measured points using small-grid sampling.
Further moisture sampling plans can be developed based on the first sampling.
Sampling can be conducted on a grid system, where the grid should be half of the range value distance.
After the homogenous soil moisture areas are mapped, these areas can be identified as management zones and managed independently for irrigation based on soil moisture and crop water requirements.
For those areas, the fixed soil moisture sensors could be used to periodically monitor soil moisture or for automated irrigation systems.
RESPONSE OF IRRIGATED SUNFLOWERS TO WATER TIMING
 With declining water supplies in the Central Great Plains Region, conservation of water is an important issue for producers.
Many areas have reported declining groundwater levels for 20 or more years within Colorado, Kansas and Nebraska.
As groundwater levels decline, well output has declined in some regions to the point that systems are limited in their capability to fully irrigate a single crop under the entire system.
When producers are faced with this situation, they are faced with only being able to limit irrigate a single crop or they must irrigate two or more crops under a single system and properly time the water needs of each crop.
Sunflowers are a crop that has been proven to be beneficial to dryland producers because of its drought tolerance.
However, little is known about the responsiveness of sunflowers to limited water and the timing of water needs for that crop.
The experimental site was at the U.S.
Central Great Plains Research Station at Akron, CO.
Soil was a Weld silt loam  with a plant available water holding capacity of 2 inches per foot.
The previous crop was rainfed corn in 2003.
The irrigated sunflowers were planted May 25, 2004 no-till into the corn stubble.
The varieties planted were Triumph 658 NuSun for oil and Triumph 765C for confectionary.
Planting rates were 26,000 seeds per acre for oil and 24,000 for confectionary in 30 inch rows.
Fertilizer application was 100 lbs/acre of nitrogen and 30 lbs/acre of phosphorous.
Furadan was applied at 1 quart per acre in-furrow at planting for stem weevil control.
Herbicide application was Spartan at 2 oz/acre, prowl at 2 pt/acre and Round-up at 20 oz/acre applied two weeks before planting and hand weeding for escape weeds.
A split-plot design was used for this experiment with timing of water application being the main plot with sunflower type  as the sub-plot.
Main
 plots were 15 ft  by 130 feet with sub-plots 65 feet long.
Water was applied with a surface drip system on 60 inch centers.
The application rate of the system was 0.08 inches per hour and operated to apply 0.8 to 1.0 inches per application.
Soil moisture was monitored weekly with the neutron attenuation method to a depth of 5 feet in 1 foot increments for each treatment.
Plots were hand harvested on October 7, 2003.
The middle two rows were harvested for a total row length of 20 feet.
Weather and Irrigation Amounts
 Precipitation during the three year period ranged from excessively dry in 2002 to slightly above normal in 2003.
Precipitation for the cropping year of 2004 was characterized by normal precipitation for the cropping season.
Precipitation for the cropping year was 84% of average.
Precipitation from Oct 2003 to June 2004 was 63% of average.
Precipitation during June 200 to September 2004 was 103% of average.
Precipitation during 2002 was below normal during the entire growing season.
Non-growing season precipitation was 33% of normal with growing season precipitation being 80% of normal.
Precipitation during 2003 was typified by above normal precipitation during the non-growing season and below normal precipitation during the growing season.
Irrigation amounts for 2002 to 2004 are reported in Table 2.
Total irrigation in 2004 was the greatest due to a 3 inch pre-irrigation to increase beginning soil moisture.
Irrigation amounts in 2002 and 2003 were similar although total precipitation was less in 2002.
Grain yields for confection and oil sunflowers are reported in Table 3 and 4.
Grain yields for confection and oil generally increased as the amount of water applied increased.
Maximum yields for confection sunflowers occurred with irrigation prior to the R5 growth stage.
Yields for Full Water, R1-R5, and R4-R5 irrigation strategies were similar in 2003 and 2004.
However, in 2002, lack of beginning soil moisture reduced yields for the R4-R5 irrigation strategy as compared to the full water or R1-R5 irrigation strategies.
Withholding irrigation until after the R5 growth stage resulted in reduced grain yields as compared to irrigation early but was greater than dryland management.
During years with adequate soil moisture such as 2003, irrigating during any early reproductive growth stage had similar years with a tendency for irrigation during the R1-R5 growth stages being advantageous.
During years with marginal soil moisture, irrigation during the vegetative growth stages increased yields slightly, but no significantly.
However, during years with inadequate soil
 moisture such as 2002, irrigation during the vegetative or early reproductive growth stages increased yields.
Grain yields for full water oil sunflowers were greater than all other strategies two of three years.
Only in 2003, when stored soil moisture was adequate, were grain yields for all irrigation strategies equal.
Grain yields for the R1-R3 irrigation strategy were significantly lower than all other irrigation strategies in 2004.
Irrigating during the early reproductive growth stages had a tendency to create unfavorable growing conditions for the plant later in the growing season that resulted in the lower yields.
Irrigation management strategies of R1-R5 and R4R5 had equal yields which were slightly greater than the R6-R7 growth stage.
Withholding irrigation until the R6 growth stage was after the yield determination growth stage for irrigated oil sunflower.
Irrigation Water Use Efficiency
 How efficient each irrigation strategy was is important in limited water management.
Irrigation water use efficiency  is defined as the following:
 IWUE = Irrigated Yield Rainfed Yield Irrigation Amount
 The IWUE shows how efficient irrigation water applied during each growth stage was converted to grain yield.
A higher IWUE indicated each inch of irrigation applied was converted to more grain production.
Maximum IWUE for oil sunflowers occurred when the crop was irrigated during the R4-R5 growth stages.
Each inch of water applied at this growth stage was converted to approximately 244 lbs/acre-in of seed for 2002 to 2004.
Only in 2002 did the R4-R5 growth stage not have the greatest IWUE.
Irrigation during the R6-R7 growth stage had the next highest IWUE with Full Water management having the lowest IWUE for 2002 to 2004
 Maximum IWUE for confection sunflowers occurred when the crop was irrigated during the R4-R5 growth stages.
Irrigation water use efficiencies for R1-R5 and R1-R3 strategies were similar with approximately 130 lbs/acre-in increase in yield.
Full water and R6-R7 management strategies resulted in the lowest IWUE on average.
Irrigation after the R6 growth stage was to late to significantly increase yields while irrigation during the vegetative growth stage was not as efficient as waiting until the reproductive growth stages.
The lower IWUE for full water management for both oil and confection sunflower would indicate that irrigation during the vegetative growth stages was not an efficient irrigation strategy for limited water supplies.
Irrigation timing significantly impacted seed size of confection sunflower.
Irrigation earlier in the growth stages resulted in greater large and jumbo seed size as compared to irrigating after the R5 growth stage.
Seed size for the R6-R7 strategy was lower than the early strategies but similar to dryland each of the three years.
Seed size for the R4-R5 strategy was similar to full water and R1-R5 strategies in 2003 and 2004 but significantly less in 2002.
Stopping irrigation after the R3 growth stage resulted in lower seed size two of the three years.
Only in 2003 when soil moisture was adequate did withholding irrigation after the R3 growth stage not reduce seed size.
Oil Content and Production
 Oil content of sunflower was significantly affected by irrigation timing.
Delaying irrigation until the R6 growth stage significantly increased oil content each of the three years as compared to the other irrigation strategies.
Irrigating during the R4-R5 growth stages increased oil content two of three years.
Only in 2004 was oil content of this irrigation strategy significantly lower than full water or dryland oils.
Irrigation management strategies that applied water during the early reproductive growth stages generally had lower oil contents.
However, ending irrigation at the R3 growth stage significantly reduced oil content as compared to full water management.
Oil contents were greatest in 2002 which was a hot and drier year as compared to 2003 and 2004.
Oil contents in 2004 were the lowest in each of the three years with oil contents less than 40% for most strategies.
Temperatures during 2004 were lower than average with low temperatures less than 40 degrees F several days.
Total production of oil per acre incorporates yield and oil content.
Average production of oil per acre for 2002 to 2004 was greatest for full water management.
If 2002 was not used for the average due to the excessive drought and lack of beginning soil moisture, oil production for full water and R4-R5 management strategies were similar.
Although yields for the R6-R7 irrigation strategy were reduced as compared to the full water, R1-R5 and R4-R5 management strategies, oil production was reduced by approximately 150 lbs/acre.
The R1-R3 irrigation management strategy produced the lowest amount of oil per acre of the irrigated strategies and oil slightly more than dryland production.
Total yields of oil and confection sunflower generally increased as irrigation applied increased.
However, several water saving strategies have been
 identified.
Irrigated during the early reproductive growth stage had similar yields and seed sized for confection sunflower as compared to full water management.
However, irrigating during the R1-R5 growth stages reduced the amount of irrigation applied by approximately 3.6 inches as compared to full water management.
Irrigating during the vegetative and late reproductive growth stages did not significantly increase yields or seed size components.
However, irrigation must be continued through the R5 growth stages.
Ending irrigation prior to that growth stage reduced grain yield and seed size.
Full water management for oil sunflowers produced the greatest yield and total lbs of oil per acre as compared to all other irrigation strategies.
However, the irrigation strategy of R4-R5 produced only slightly less yield and lbs of oil per acre.
The irrigation strategy of R4-R5 required approximately 6 inches less irrigation.
If water is limited, this irrigation strategy may be economically viable due to the potential of increasing irrigated acres.
Table 1.
Growing year precipitation from October to September 2002 to 2004.
Oct.
Nov.
Dec.
Jan.
Feb.
Mar.
Apr.
May Jun.
Jul.
Aug Sep.
2001-02	0.63	0.78	0.00	0.09	0.06	0.08	0.50	0.55	1.71	0.10	3.44	1.50
 2002-03	1.04	0.39	0.03	0.22	0.41	2.34	2.47	4.05	4.34	0.90	1.54	0.26
 2003-04	0.00	0.12	0.20	0.32	0.39	0.69	1.37	1.89	2.50	1.74	2.85	1.67
 Average	0.90	0.55	0.40	0.33	0.34	0.83	1.64	2.96	2.45	2.67	2.08	1.23
 Table 2.
Irrigation amount for irrigation strategies.
Dryland	R6-R7	R4-R5	R1-R3	R1-R5	Full Water
 Year	Inches of Water
 2002	0	2.6	3.7	4.5	6.4	9.0
 2003	0	1.8	3.0	3.8	5.3	9.3
 2004	3.0	7.0	6.7	6.0	9.3	13.5
 Average	1.0	3.8	4.5	4.8	7.0	10.6
 Table 3.
Confection Sunflower grain yields.
Average Grain Yields	2002-2004	2003-2004
 2002	2003	2004	Overall Avg	Overall Avg
 lbs/acre	lbs/acre	lbs/acre	Lbs/acre	Lbs/acre
 Dryland	299d	2550ab	1193c	1347	1871
 R6-R7	688c	2249b	1778b	1572	2014
 R4-R5	883bc	2875ab	2063ab	1940	2469
 R1-R3	1137ab	2847ab	1797b	1927	2322
 R1-R5	1192a	3139a	2173ab	2168	2656
 Full Water	1335a	2617ab	2463a	2138	2540
 Table 4.
Oil Sunflower grain yields.
Average Grain Yields	2002-2004	2003-2004
 2002	2003	2004	Overall Avg	Overall Avg
 lbs/acre	lbs/acre	lbs/acre	Lbs/acre	Lbs/acre
 Dryland	468d	2387b	967d	1274	1677
 R6-R7	771cd	2540ab	1956bc	1756	2248
 R4-R5	1022bc	3031a	2297bc	2117	2664
 R1-R3	1327b	2530ab	1803c	1887	2166
 R1-R5	1287b	2701ab	2411bc	2133	2556
 Full Water	1981a	2728ab	3147a	2619	2938
 Table 5.
Irrigation Water Use Efficiency for oil sunflowers.
Average Oil Yield	2002-2004	2003-2004
 2002	2003	2004	Overall Avg	Overall Avg
 lbs/acre-in	lbs/acre-in	lbs/acre-in	lbs/acre-in	lbs/acre-in
 R6-R7	117	88	250	174	200
 R4-R5	150	215	361	244	295
 R1-R3	191	37	283	163	144
 R1-R5	128	59	231	143	152
 Full Water	168	37	207	140	127
 Table 6.
Irrigation Water Use Efficiency for confection sunflowers.
Average Oil Yield	2002-2004	2003-2004
 2002	2003	2004	Overall Avg	Overall Avg
 lbs/acre-in	lbs/acre-in	lbs/acre-in	lbs/acre-in	lbs/acre-in
 R6-R7	150	-172	148	81	50
 R4-R5	158	108	236	171	179
 R1-R3	186	78	204	154	133
 R1-R5	140	111	157	137	135
 Full Water	115	7	120	82	67
 Table 7.
Seed size and oil content for confection and oil sunflowers.
Confection Seed Size	Oil Content
 2002	2003	2004	2002	2003	2004
 Irrigation	% Large	% Jumbo	% Large	% Jumbo	% Large	% Jumbo	%	%	%
 Dryland	0.4d	0.0d	70.3b	30.9b	29.5c	3.6c	48.5ab	43.9b	36.8b
 R6-R7	9.5d	0.2d	70.8b	31.8b	32.8bc	6.5c	49.7a	47.3a	41.4a
 R4-R5	22.9c	0.5d	75.0ab	44.7ab	78.0a	35.9b	47.2b	47.7a	35.1c
 R1-R3	55.0b	16.6c	80.9ab	43.5ab	45.5b	14.4c	43.3d	41.3c	34.5c
 R1-R5	64.2ab	30.2b	82.1ab	49.6ab	85.7a	60.1a	45.2c	43.4bc	34.8c
 Full Water	72.2a	48.5a	85.6a	61.8a	78.3a	50.7a	45.3c	42.5bc	37.9b
 Table 8.
Oil yield for oil sunflowers.
Average Oil Yield	2002-2004	2003-2004
 2002	2003	2004	Overall Avg	Overall Avg
 Lbs oil/ac	Lbs oil/ac	Lbs oil/ac	Lbs oil/ac	Lbs oil/ac
 Dryland	227	1047	356	543	702
 R6-R7	383	1202	809	798	1006
 R4-R5	483	1446	806	911	1126
 R1-R3	574	1045	621	747	833
 R1-R5	581	1171	839	864	1005
 Full Water	897	1160	1193	1083	1176
CROP SELECTIONS AND WATER ALLOCATIONS FOR LIMITED IRRIGATION
 Irrigators choose crops on the basis of production capabilities, economic returns, and crop adaptability to the area, government programs, crop water use, and their preferences.
When full crop evapotranspiration demand cannot be met, yield-irrigation relationships and production costs become even more important inputs for management decisions.
Under full irrigation, crop selection often is driven by the prevailing economics and production patterns of the region.
Crops that respond well to water, return profitably in the marketplace and/or receive favorable government subsidies are usually selected.
These crops still can perform in limited irrigation systems, but management decisions arise as water is limited: should fully watered cops continue to be used; should other crops be considered; what proportions of land should be devoted to each crop; and finally, how much water should be apportioned to each crop?
The outcome of these questions is finding optimal economic return for the available inputs.
Determining the relative importance of the factors that influence the outcome of limited-irrigation management decisions can become complex.
Commodity prices and government programs can fluctuate and change advantages for one crop relative to another.
Water availability, determined by governmental policy or by irrigation system capacity, may also change with time.
Precipitation probabilities influence the level of risk the producer is willing to assume.
Production costs give competitive advantage or disadvantage to the crops under consideration.
The objective of this project has been to create a decision tool with user interaction to examine crop mixes and limited water allocations within land allocation constraints to find optimum net economic returns from these combinations.
This decision aid is for intended producers with limited water supplies to allocate their seasonal water resource among a mix of crops.
But, it may be used by others interested in crop rotations and water allocation choices.
CWA calculates net economic return for all combinations of crops selected for a rotation and water allocated to each crop.
Subsequent model executions of landsplit  scenarios can lead to more comparisons.
Individual fields or groups of fields can be divided into in the following ways: 50-50; 25-75; 33-33-33; 25-25-50; 25-25-25-25.
The number of crops eligible for consideration in the crop rotation could be more than the number of land splits under consideration.
Optimum outcomes may recommend fewer crops than selected land splits.
Fallowing part of the field is a valid option.
Irrigation system parameters, production costs, commodity prices, yield maximums, annual rainfall, and water supplied to the field were held constant for each model execution, but can be changed by the user in subsequent executions.
The model examines each possible combination of crops selected for every possible combination of water allocation by 10% increments of the water supply.
The model has an option for larger water iteration increments to save computing time.
For all iterations, net return to land, management, and irrigation equipment is calculated:
 Net return =  
 commodity prices were determined from user inputs, crop yields were calculated from yield-irrigation relationships derived from a simulation model based on field research, irrigation costs were calculated from lift, water flow, water pressure, fuel cost, pumping hours, repair, maintenance, and labor for irrigation, and production
 costs were calculated from user inputs or default values derived from Kansas State University projected crop budgets.
All of the resulting calculations of net return are sorted from maximum to minimum and several of the top scenarios are summarized and presented to the user.
Field research results have been used to find relationships between crop yields and amounts of irrigation.
Yields from given irrigation amounts multiplied by commodity prices are used to calculate gross income.
Grain yields for corn, grain sorghum, sunflower, and winter wheat were estimated by using the "Kansas Water Budget" software.
Software development and use are described in Stone et al.
, Khan , and Khan et al..
Yield for each crop was estimated from irrigation amount for annual rainfall and silt loam soils.
The resulting yield-irrigation relationship for corn  shows a convergence to a maximum yield of 220 bu/ac from the various combinations of rainfall and irrigation.
A diminishing-return relationship of yield with irrigation applied was typical for all crops.
Each broken line represents normal annual rainfall for an area.
Figure 1.
Yield-irrigation relationship for corn with annual rainfall from 11-21 in.
Reducing income risk is often an irrigator's motivation for switching crops as water availability declines.
The Crop Water Allocator , in its present form, ranks alternative planting patterns based on mean income alone, without considering outcomes associated with changes in input variables.
This risk arises from a variety of factors that are uncertain at the time of planting; the most important of these is weather conditions during the growing season.
For example, although corn often generates the highest mean income, it is also likely to have a highly uncertain yield because its growth is sensitive to water stress during critical stages of the growing season.
Adding trend analysis to CWA can project net returns over a range of input variables.
Years with above normal, below normal and average rainfall can be simultaneously examined to find trends in net returns.
The same methods can be used to project income trends for ranges of commodity prices, maximum yields, production costs, irrigation costs, and irrigation efficiency.
Ranges of user input variables can be entered with ranges of net economic returns as the output.
These results indicate the income risks when rainfall, irrigation costs, crop production costs, irrigation efficiencies, commodity prices, or crop maximum yields vary.
Trend analysis allows the user to find net returns over a range of possible inputs: rainfall, irrigation efficiency, commodity prices, maximum crop yields, irrigation costs, and crop production costs.
For example, the program user may be interested in the response of net returns if annual precipitation varies from 13 to 21 inches and corn price ranges from $2 to $4/bu.
CWA executes a series of calculations over the range of irrigation costs, producing the corresponding range of net returns.
Two input ranges can be simultaneously processed in fixed trend analysis to find the influence of both inputs on net return.
Table 1.
Net returns for $2 to $4/bu corn and 13-15 inches of annual precipitation.
Crop Price Corn 	13	15	17	19	21
 2	$-197 /ac	$-190 /ac	$-183	$-176/ac	$-172/ac
 3	$-76 /ac	$-50 /ac	$-25 /ac	$-4 /ac	$10 /ac
 4	$46 /ac	$89 /ac	$132/ac	$168 /ac	$192 /ac
 5	$168 /ac	$229/ac	$289 /ac	$341 /ac	$375 /ac
 6	$289 /ac	$369/ac	$447 /ac	$513 /ac	$557 /ac
 Table 2.
Inputs for example in table 1.
Total Production Costs:	$389/ac
 Maximum Yield:	200 bu./ac
 Irrigation Costs:	$94 /ac
 Irrigation System Efficiency:	85%
 This work was partly supported by the US Department of Interior, Kansas Water Resources Institute, and the USDA-ARS Ogallala Aquifer Research Initiative.
Deciding on the Final Irrigation
 In deciding on the timing of the last irrigation, the best thing to follow is the crop first and the calendar second.
In this sense, the best thing to watch for is the progression of the crop towards, and into cut-out.
Counting the number of nodes above the top  white flower  provides an easy and reliable estimate of crop maturity and the onset of cutout.
Generally, as the NAWF becomes 5 or less, the crop is progressing directly into cut-out.
Timing of cut-out can be estimated by tracking heat units accumulated after planting.
Table 2 provides the range of HUAP required for cut-out for the three general variety types.
The range in HUAP for cut-out is due to a number of factors including the variety, the position of the first fruiting branch, fruit retention levels, crop stresses, etc.
When the NAWF approaches 5 or less, it is a good time to assess the overall situation in terms of general crop condition, as well as current pest pressures.
If a more indeterminate  variety is being grown, the grower has an option of pushing the crop on towards a top-crop.
If the variety is a medium or short season type, the top-crop potential is more limited in this respect and decisions concerning the last irrigation need to be made.
In general, a reasonable topcrop potential exists when a) total fruit retention is about 40% or less, b) the variety is a long-medium or full season type, and c) the crop has plenty of vigor.
From recent research in Arizona, with common Upland and Pima varieties, it takes about 600 heat units  for a bloom to develop into a full-sized, hard boll.
In July, August, and early September, the accumulation of 600 HU translates roughly to 21 days for most cotton growing areas of Arizona.
An easy and direct approach for determining the final irrigation for a crop can start with a good field evaluation to determine the last set of blooms that one intends realistically to take to harvest.
When that decision is made, the last set of blooms should be given at least three weeks of good plant-water conditions, or available soil moisture to complete their development to a full sized boll.
In this regard, actual HU accumulations should be fol-
 lowed as well as the development of the last bolls intended for harvest.
The number of irrigations that this will require will depend upon the soil texture , the amount of water applied in an irrigation, and the soil water depletion rate.
Since irrigation water is often one of, if not the most expensive item in many Arizona cotton production systems, making the last irrigation can be a very important economic decision.
Additional irrigations in the late season may not be necessary and may be expensive.
For example, two irrigations may result in the application of an additional an acre-foot of water.
The best approach to terminating irrigations for cotton includes identification of the last bolls intended for harvest; selecting a cut-off date that provides at least 600 HU  of good soil moisture for final boll development; and a consideration of the insect pest pressures that are present.
Therefore, selecting the last set of blooms intended for harvest is a key point of consideration, irrespective of whether you are trying to terminate a crop early or push for a top-crop.
This represents an important management decision that can impact final profits and system efficiencies for cotton farms throughout the region.
THE UNIVERSITY OF ARIZONA COLLEGE OF AGRICULTURE AND LIFE SCIENCES TUCSON, ARIZONA 85721
 Jeffrey C.
Silvertooth Cotton Extension Agronomist
 Table 1.
Relationships between cotton growth stage and the number of nodes above the top white flower.
* NAWF, first position fruiting site on mainstem fruiting branches.
Table 2.
General (ut-outoccurrences for cotton variety types commonly grown in Arizona.
Vareity Type	HU at Cut-out*
 *Heat Units  accumulated after planting.
Fig.
1.
NAWF example
Iowa soils hold 1.5-2.5 inches per foot of effective rooting depth.
Root depth in Iowa has been found at depths greater than six feet.
The importance of proper early root development cannot be underestimated.
Crops with deep root systems explore a greater volume of soil are able to withstand drought conditions better.
RO-DRIP R User Manual
 WHAT IS DRIP IRRIGATION?
Drip irrigation is about delivering water, nutrients and chemicals where you want them, when you want them.
Using a network of pipes and drip laterals, a drip system releases water and nutrients uniformly, through precision manufactured emitters, directly into the root zone.
Near-optimum soil moisture levels are maintained and rapid response can be made to a variety of crop needs.
The precise delivery of water and nutrients made possible by drip irrigation gives you a level of control over the soil environment that is not possible with traditional sprinkler or furrow irrigation.
This means better control of crop health, water and fertilizer usage, harvest time and your bottom line.
Following are some of the many benefits reported by growers who have converted from sprinkler and furrow irrigation to drip irrigation:
 Improved crop yield, quality, and uniformity
 Better control over harvest time and market timing
 Reduced cost of chemicals and fertilizer
 Better utilization of uneven terrain
 More land can be utilized if water is a limiting factor
 Reduced environmental impact from runoff and percolation of chemicals, fertilizers, and salts
 This is a remarkable set of benefits for any single technology to deliver.
However, it is only with careful attention and commitment to the unique requirements of your drip irrigation system that you can enjoy its many potential benefits.
The Roberts Difference: Roberts Irrigation Products, Inc.
has been bringing the benefits of efficient irrigation to growers for over thirty years.
An ongoing commitment to tradition, integrity, and innovation have made Roberts Irrigation Products one of the world's leading producers of micro and drip irrigation products, including RO-DRIP and RO-DRIP XL drip irrigation tapes.
We have spent enough time in the field to recognize the practical needs of row crop growers like you, and have applied the latest precision manufacturing methods to produce a drip tape system that meets these needs.
Our RO-DRIP and RO-DRIP XL drip tapes represent the practical application of today's latest technologies to the long-felt needs of growers.
Throughout this manual you will find short captions titled "The Roberts Difference" located in the margins of each section.
These captions describe some of the unique benefits of RO-DRIP products for drip irrigation users.
IS DRIP IRRIGATION FOR YOU?
Each year large numbers of growers around the world convert from traditional irrigation methods to drip irrigation.
Some are attracted by the promise of higher yields, some by the promise of higher profits, and some by the simple appeal of using the latest technology.
Drip irrigation is capable of delivering on each of these promises.
However, you should carefully consider your unique goals and situation when deciding whether drip irrigation will work for you.
A drip irrigation system requires a significant investment in time and money.
The first step in this investment begins here, by taking time to become fully informed before initiating your drip irrigation project.
Your goals for this "initial investment" in time should be to:
 Develop awareness about what it takes to design, install, and operate a system
 Determine your ability financial and otherwise to proceed
 Assess the level of commitment you are willing to make to develop a properly designed and managed drip irrigation system
 Locate a qualified irrigation dealer with drip experience
 You are the most important component in the success of your drip irrigation system.
CULTIVATING A LONG-TERM VIEW
 Growers are naturally inclined to take a long-term view on things.
This common-sense wisdom is especially valuable when applied to the planning of a drip irrigation system.
Your initial investment in terms of equipment and know-how may take 2 or more years to recover.
However, your investment should be seen not only in terms of crop quality and yield, but as an intelligent response to global trends in diminishing natural resources, reduced government subsidies, and increased environmental regulation.
If you are like most growers, you have vast experience with traditional sprinkler or furrow irrigation practices.
You recognize the value of this accumulated expertise and probably would not think of irrigating your fields without applying that knowledge to get the best result.
If you are new to drip irrigation, you can be sure there is a great deal to learn from quick tips and techniques to fundamental changes in your procedures.
Until you reach a comfortable level of expertise in drip irrigation, it makes sense to get in touch with someone who can share their expertise with you.
Specifically, you should be prepared to contact qualified experts in hydraulic engineering, filtration, chemical treatment, pest control and installation.
What you learn from these experts in one season will pay off for years to come.
In a recent survey of experienced growers, all confirmed the value of becoming fully informed, especially by consulting experts, before initiating their own drip irrigation program.
MANAGING NEW CULTURAL PRACTICES
 Drip irrigation allows precision response to changes in crop need, environmental conditions,
 and even market timing.
All of these benefits require a well-functioning system.
Unlike traditional irrigation methods that use fewer, larger applications of water, successful drip irrigation is based on many small applications.
This requires a new way of thinking: collecting and recording better and more frequent information on your crop status and water quality,, monitoring system performance, and making minor adjustments whenever needed.
Fortunately, there is now a full line of products, know-how, and automation equipment available to help you in this process.
While drip irrigation can deliver significant savings on labor and resources, you should expect some increase in management time, especially in the first year as you learn to operate the system.
There is no substitute for a competent farm manager who fully understands the drip irrigation system and is available to make adjustments as needed.
This guide covers all the basic requirements for drip tape irrigation in row crop, nursery and greenhouse operations.
It has been written to be a useful reference for almost any drip irrigation question you may have, regardless of what drip tape you decide to use.
However, since Roberts Irrigation considers RO-DRIP the most advanced and cost effective drip tape available, special sections are included that describe features and requirements unique to RO-DRIP and RO-DRIP XL wherever applicable.
NOTE: This guide is intended to provide information about RO-DRIP and generally accepted knowledge in drip irrigation and crop production.
Roberts Irrigation Products, Inc.
is not engaged in rendering engineering, hydraulic, agronomic, or other professional advice in this guide.
Consultation with qualified local irrigation dealers and agronomists is recommended.
This guide is specifically written for irrigation with drip tape thin walled collapsible emitting hose.
While many of the concepts are applicable to other forms of drip irrigation such as hard-wall hose with inserted or in-line emitters, this guide does not specifically address such products.
All of the steps involved in assembling and managing a successful drip irrigation system are covered in the following sections: Planning, Design, Installation and Startup, Management, and Retrieval.
We recommend that you read the guide completely before beginning your drip irrigation program.
At a minimum, review the following summary of Important Cautions and Notes.
Also consider reviewing the Key Concepts listed at the beginning of each section.
IMPORTANT CAUTIONS AND NOTES
 Observe the following important cautions and notes when designing, installing, and managing your drip irrigation system:
 Carefully design and engineer all parts of your drip irrigation system before installation and use.
Consult specialists in irrigation, water quality, pest control, agrochemicals and other areas as necessary.
Always use proper filtration for your water source.
Inadequate filtration or filter maintenance may severely damage your drip irrigation system.
Where ground pests are a potential problem always implement pest controls before installing drip tape.
Do not step on drip tape or drag it across the soil surface.
Ensure that all installation equipment is free of burrs and other sharp edges.
When using clear plastic over drip tape, always bury the tape.
Operate all systems before any planting begins.
Chemicals used in irrigation, fertigation, and water treatment can be extremely hazardous.
Use extreme caution when mixing, handling, and injecting any chemicals.
The Roberts Difference: Roberts Irrigation has set up a special system of support-after-sale to help you use and maintain your drip irrigation system.
Our in-house technical staff, our network of competent dealers and our library of drip irrigation publications and referrals are all at your disposal to help you get the job done.
Before you begin a design, you need to identify clear and specific goals based on the answers to questions such as: What crops will you grow?
How often will you rotate?
Will the system deliver fertilizer and chemicals, or only water?
Will you use plastic mulch?
These are the starting points for gathering the information you will need to properly plan your system.
It is also important to know what you have to work with and what other factors will affect the design.
Soil type, climate, water quality and availability, field topology, crop water requirements, and indigenous pests can all influence system design, as can legal concerns such as environmental and land-use regulations.
Finally, proper planning will help you design a system that makes maximum use of your existing infrastructure to reduce both capital and labor costs.
Your drip system design should reflect a careful consideration of soil type, water quality, evapotranspiration, topography, crop choice, and indigenous pests.
Collect all of the necessary information before starting.
Know the look, feel, and soil moisture content that corresponds to field capacity.
Your drip irrigation system should be designed to keep the soil moisture close to this value.
Obtain a chemical and physical analysis of your irrigation water from an independent laboratory.
This information will be critical in determining filtration, water treatment and fertigation requirements.
Have a soil sample tested to determine the nutrient content of your soil.
This will be the first step in developing your fertigation program.
Make use of your existing infrastructure whenever possible.
The Roberts Difference: The broad RO-DRIP product line has been successfully used with a diverse variety of crops and field conditions.
Soil type, both texture and structure, influences your system design by determining field water requirements and, in some cases, by limiting your choice of crops.
Soil type has a great effect on water movement and therefore on root development, plant growth, and, ultimately, crop yield and profits.
Because of its effect on water movement, soil type has a major influence on the emitter spacing, tape placement depth, and flow rates of a good system design.
Inadequate drainage leads to inadequate aeration of soil, increased incidence of disease, limited root zone size and limited ability to leach salts away from the root zone.
Drainage problems can be caused by perched water tables, compaction layers, and stratified soils.
Adding gypsum or organic amendments to heavy soils can improve drainage, although amendments that contain salt should be avoided when possible.
Where drainage is poor, deep  subsoiling and chiseling every 1 to 4 years may be necessary.
In some cases, deep plowing can maintain good drainage for longer periods of time.
If a high water table inhibits drainage, drainage channels or subsurface drain systems may be required.
Water availability and quality are central factors in the design of your drip system.
Unlike traditional sprinkler and furrow irrigation, drip irrigation places very specific demands on the quality and availability of your water source.
It is important to design your system so that optimum soil moisture is maintained throughout the growing season.
The system must be capable of supplying your crop's peak needs plus any additional amounts needed for flushing.
Although drip irrigation may use less water than required by other irrigation methods, it requires it on a consistent and reliable basis.
Typical drip systems irrigate several times a week, or even several times a day.
In addition, because drip irrigation promotes more localized root growth, even a short lapse in water availability can cause serious crop damage.
It is important to confirm that your water source will be available whenever you need it, throughout the growing season.
If necessary, arrange for a supplementary water source that can be used in the event that your primary source becomes unavailable.
If a supplementary water source is required, confirm that your system design includes filtration appropriate for the additional water source.
Water quality refers to the physical and chemical composition of your irrigation water.
It has important effects on the type of filtration to use, chemical water treatment that may be necessary, the frequency of cleaning and line flushing, and the management of salt and chemical buildup in the soil.
The effect of water quality on your system's performance should not be underestimated.
System designs that do not account for the quality of their specific water source can become completely debilitated by emitter plugging and can result in serious crop damage.
These problems can be easily prevented through proper filtration and/or water treatment.
Before designing your system, order a complete physical and chemical analysis of your water source.
This analysis should quantify the amounts of the following matter commonly found in water sources:
 Since all of these factors interact in complex ways to affect the operation of your drip system, consult a water quality specialist and an irrigation engineer when designing your drip system.
Also, because water sources can change with time, perform water quality tests periodically and make adjustments as necessary.
See appendix A for tables to assist you in understanding your water quality report.
Inorganic matter found in water sources includes sand, pipe scaling, and other large particles, all of which can lead to plugged emitters and other damage to your system.
Since these particles are usually heavier than water, they can often be removed using a centrifugal sand separator.
Smaller inorganic particles, such as silt and clay, can become cemented together by bacteria and algae which results in a slimy buildup that can clog emitters.
Since these smaller particles are more difficult to remove, media filters and/or settling basins may be required to protect your system.
Organic matter found in water sources includes algae, slime, plants, and particles from other living organisms.
While some of these can be removed by standard filtration equipment, chemical treatment of the water and lines is usually required for more complete control of organic matter.
Since organic matter is typically lighter than water, it cannot be removed by a centrifugal sand separator.
Sand media filtration is the most effective method for removing most forms of organic matter.
Dissolved minerals are found in most water sources and, since they are dissolved, would not be expected to cause emitter plugging However, there are a number of factors that can cause these solids to "precipitate" or settle out.
These include changes in pH, changes in temperature, and reactions with commonly used fertilizers and chemicals.
The most common cause of precipitation-induced plugging is calcium carbonate  precipitation.
Iron or manganese, which may be dissolved in well water, will precipitate when exposed to air or chlorine; these precipitates are troublesome because they can lead to bacterial growth that can readily clog filters and emitters.
Sulfides can lead to similar bacterial growth and emitter plugging.
Interaction of dissolved solids with your drip irrigation system can be highly complex, and can change throughout the season.
In addition to their effects on the performance of your drip system, dissolved ions can be both beneficial and detrimental to soil properties and plant health.
Perform a careful assessment of the dissolved solids in your water before designing your system and especially before adding any chemicals or fertilizer to your water.
Table 2.1 Soil Solution Salinity Level
 to Cause 10% Yield Reduction.
Lettuce, Pepper, Raddish, Onion, Carrot	2.0
 Cabbage, Cucumber, Muskmelon, Potato	3.0
 Corn, Artichoke, Sweet Potato	2.5
 Sugar Cane 	2.6
 Cotton 	4.7
 Most water sources and many fertilizers carry some level of dissolved salt that accumulates in the soil during regular irrigation.
In arid regions where salinity is a significant problem, this buildup can affect the health of your plants.
In such cases, your system design and operation must account for and properly manage salt buildup.
Your water quality analysis should include a report of the salt content and type.
See appendix A for tables to assist you in interpreting a water quality report.
Table 2.1 gives the salt tolerance of several popular crops in terms of the salinity of the soil solution.
The Roberts Difference: RO-DRIP drip tape is manufactured to exacting technical specifications to produce a uniform wall thickness, which means less breakage on installation and retrieval.
NOTE: In areas with low rainfall, salinity of the soil solution is typically higher than the salinity of your irrigation water.
Even with good irrigation management, soil solution salinity can be 1.5 to 3 times the irrigation water salinity.
The initial effects of salt buildup can be subtle.
It is important to understand that salt damage to your crop may not be apparent until it is too late to prevent.
Fortunately, proper drip irrigation practices include ways to manage salinity and to keep it out of the root zone.
See MANAGEMENT: Managing Soil Salinity for guidance on monitoring and managing salt buildup in the soil.
Your system must be designed to supply enough water to exceed your crop's water requirements during the hottest day of the season, while also providing enough water for line flushing and salt leaching where needed.
Water requirements are influenced by the following factors:
 Ambient temperature and humidity
 System operations 
 Fertilizers and chemicals used
 The interaction of these factors can be complex.
However, by making a few measurements, and by referring to standard formulas and tables, it is relatively easy to calculate your actual irrigation requirements and develop a proper irrigation schedule.
Most crops reach their full potential if the soil in the root zone is at all times maintained at a moisture content that is near the soil's maximum water holding capacity.
The goal of a drip irrigation system throughout most of the growing season is to maintain this level by replacing soil water as it is lost to evapotranspiration.
With some adjustments to account for local weather, minor crop differences, salinity, and system inefficiency you can develop a good prediction of water requirements.
Note: Applying more water than is needed can increase root disease and operating cost, while applying less than needed can stress or burn your crop and cause your soil to dry, destroying its ability to move water.
A properly designed and managed irrigation system will deliver just enough water to maximize both yield and profit.
The Roberts Difference: The highly plug-resistant design of RO-DRIP makes it the right choice when water quality is a concern.
Field capacity is an estimate of the amount of water that is held by the soil after it has been completely drained by gravity.
Field capacity is dependent on soil type, and represents optimum soil moisture conditions for most crops because of its ideal balance between aeration and available water.
In order to keep soil moisture conditions ideal for crop growth, you must be able to determine when your soil is at field capacity.
If you have a moisture-sensing device available, you can obtain a quantitative measurement of field capacity with the following procedure:
 1.
Determine the proper monitoring depth for your crop.
2.
Prepare the field and install the moisture sensor at the proper depth.
More accurate results can be obtained by installing 4 sensors in a 10 X 10 ft  test area.
3.
Irrigate until the soil under the moisture sensors is saturated.
If tensiometers are used, this should produce a reading of 0 cb.
4.
Monitor the sensor readings daily.
When the readings level off , read and record the displayed values.
The result is the measured water content at field capacity.
If your sensor measures soil water tension the reading will generally be between 10 cb and 25 cb depending on soil type.
If your sensor measures moisture content, the field capacity reading may range from 10% to 50% depending on soil type.
The optimum soil moisture level for most crops during vegetative growth stages is at or slightly below field capacity.
In general, your system must be capable of replacing all water used by the crop since the last irrigation and must be used frequently enough to minimize depletion below field capacity.
Evapotranspiration  is a measure of how much water is used by your crops for transpiration and how much is lost through evaporation from the plant and soil surface; it is expressed in inches  of water used per day or inches  of water used per month.
ET measurements allow you to anticipate how the weather in your area will interact with your crop to determine water requirements.
ET values based on a reference crop for your region are usually available from local water resource and agricultural agencies.
ET is affected by:
 Size of leaf canopy
 Stage of growth cycle
 Size of wetted area
 Research has shown that, for vegetative crops, yield is generally proportional to transpiration.
For given weather conditions, transpiration is maximized when the water content in the root zone is near field capacity at all times.
Therefore it is important that, as water leaves the root zone as a result of ET, your irrigation system is able to replace it as soon as possible.
The ability to keep the root zone near field capacity at all times is an important benefit of drip irrigation.
To realize this benefit, your system design must be capable of supplying water at the rate of ET at all times during the growing season.
You can anticipate what peak demand will be by referring to historical ET data, and use this information to design a system that can supply enough water under any conditions.
If ET information is not available for your area, refer to MANAGEMENT: Scheduling, Determining your crop's daily requirement for methods of estimating ET.
Since filtration cannot remove all contaminants, silt and clay may settle in drip laterals and, if not removed, may build up and plug emitters.
In areas where water quality is a problem or when drip tape laterals will be used for multiple growing seasons, your system design must allow for periodic flushing of the laterals.
If flushing is necessary, the system should be designed so that the ends of the laterals are accessible.
Consider using end caps or flushing manifolds.
In systems where flushing is necessary, the capacity of the upstream components is often determined by the flushing requirement alone.
It is recommended to maintain a minimum flushing velocity of 1 foot per second in the laterals, which requires flow rates at the end of laterals to be at least 1 GPM  in standard 5/8-in.
drip tape, or 2 GPM  for 7/8-in.
drip tape.
Substantially higher flow rates at the beginning of the laterals are required to achieve these flow rates at the end of the laterals.
The crops you grow will have a great effect on system design and cultural practices.
Any and all crops can be grown under drip irrigation, but your choice of crops and their planting method  will have an important impact on your drip system design.
An important question about your crops is whether they will be direct seeded or transplanted.
The germination of seeds places special requirements on your drip system design and management.
If these requirements are not met, sprinklers will be required for germination and initial plant
 growth.
See MANAGEMENT: Germinating Seeds.
While topography clearly influences system design, it can also be a motivating factor in the decision to implement a drip irrigation program.
Drip irrigation allows cultivation of uneven terrain that cannot be cultivated using furrow irrigation or certain types of sprinklers.
Drip irrigation is uniquely suited to growing on uneven terrain due to its flexibility in placement and its use of pressure to move water directly where it is needed.
Consider performing a survey to document your field's geometry and topography since this information will be useful in developing a complete system design.
Insects such as ants, crickets and wire worms; and animals such as rodents and coyotes can all cause damage to drip tape laterals.
Pest control should be initiated before placing drip tape laterals in the field, and periodically thereafter as needed.
Where pests are a significant problem, consider using thicker drip tape and/or buried placement.
Consult a pest control advisor for guidance on controlling the specific pests found in your region.
Chemigation refers to the combination of irrigation and chemical water treatment into a single process, and is recommended to maintain a well-functioning drip irrigation system.
Chemical treatment includes the use of chemicals to prevent plugging of the drip tape emitters.
For example, chlorine and/or acid may be injected to kill microorganisms and to prevent precipitation of dissolved minerals.
Chemical treatment may also include injection of pesticides, herbicides or systemic fungicides to improve the health of your crops, or gypsum or acid to improve the physical characteristics of your soil.
MANAGEMENT: Water Treatment describes how to use chemical injection to prevent emitter clogging by organic matter and precipitates.
Caution: all personnel who use or otherwise come in contact with fertilizers and chemicals should be thoroughly trained and qualified in the safe and effective storage, use and application of these potentially dangerous substances.
CAUTION: all personnel who use or otherwise come in contact with fertilizers and chemicals should be thoroughly trained and qualified in the safe and effective storage, use and application of these potentially dangerous substances.
One of the outstanding benefits of a well-designed drip irrigation system is the ability to precisely control the nutrient environment in the root zone of your plants for optimum yield and quality.
Drip fertigation can apply N, P, K and minor nutrients exactly where and when they are needed, throughout the season.
To take advantage of this high level of control, it is necessary to closely monitor the nutrient level in the soil and plant tissue, and make adjustments as necessary.
Before installing your drip irrigation system, have a soil sample tested to determine its nutrient content.
This should include nitrogen, phosphorus, potassium and minor nutrients.
The nutrient requirements of your plants change throughout the season, and your fertigation program should reflect this.
If possible, obtain data on the nutrient requirements of your crop at each growth stage.
In combination with tissue testing throughout the season , this information will allow you to maximize the efficiency of your fertigation program.
Installing a drip irrigation system inevitably requires changes in equipment, training, and cul-
 tural practices.
However, a new system design does not always require completely new infrastructure.
In fact, a good system design should identify and make use of as much existing infrastructure as possible, such as the existing water source, distribution systems, electrical supply, and access roads.
The term "plasticulture" refers to methods of growing under plastic using drip tape.
Drip irrigation is uniquely suited to cultural practices that use plastic mulch.
For some crops, the combination of drip tape and plastic mulch results in optimum yield and water usage through improved control of soil temperature and moisture level.
While growing under plastic has been a barrier to water delivery using traditional sprinkler and furrow irrigation, plastic mulches and crop tunnels do not present a problem with drip irrigation.
Plasticulture is used for a number of reasons, including:
 Control of soil temperature
 Control of weeds, pests, and erosion
 Control of production timing
 Improved processing of nutrients by beneficial microbes
 Control of the wetted area
 Protection of fruit from soil moisture
 Prevention of nutrient leaching due to rainfall
 If you plan to use clear plastic mulch or crop tunnels, your system design should specify buried drip tape, since the heat trapped by these plastics may cause wandering of the tape as a result of increased expansion and contraction.
Note that plastic mulch is not optimal or even practical for all crops see appendix B for information on specific crops.
Figure 2.1 Plastic Mulch
 Drip irrigation delivers the highest efficiency and uniformity of any commonly used form of irrigation.
This can directly result in reduced consumption of water, chemicals, and fertilizer.
High uniformity in combination with the low application rates of drip irrigation makes possible the precise control of soil water content at the root zone which leads to more effective application of nutrients, better salinity control, and increased yields.
Only by designing, installing and maintaining an efficient system can you achieve all of the benefits of drip irrigation.
Selecting the right drip tape product, properly sizing supply manifolds, and selecting appropriate filtration components are all necessary to maximize efficiency and to meet the irrigation needs of your crops under any field conditions.
This section will help you design a high-efficiency drip irrigation system that meets the unique needs of each of your crops.
It starts by defining irrigation efficiency and explaining how it is affected by your choice of drip tape and other system components, and how it can change with time.
After developing this background, the section takes you through the steps of specifying components and designing the right system for your field.
Have a laboratory analysis of your irrigation water performed before beginning your system design.
Select a high quality drip tape.
This is a key decision in your drip system design.
To design drip laterals it is necessary to specify length of run, emitter spacing, placement depth, position relative to plant rows, and flow rate.
All of these decisions require in-depth knowledge of your growing operation.
Your design must provide enough water to meet the needs of your crop under any conditions, and must not require more than your water supply can deliver.
Proper filtration is crucial to prevent plugging of your drip system-don't skimp on filtration components.
A good design includes pressure gauges, flow meters, and other instrumentation at key locations.
The Roberts Difference: Precision-manufactured RO-DRIP products provide the quality and consistency needed for high uniformity and efficiency.
NOTE: The guidelines in this section are general recommendations and are not intended to suggest complete design or production practices.
Please consult your local Roberts Irrigation Products dealer for specific design applications.
The Roberts Difference: RO-DRIP employs an advanced emitter design which delivers unparalleled discharge uniformity and resistance to plugging.
Before designing your drip irrigation system, use the information collected in the PLANNING section to establish clear design goals.
Because of the conflicting requirements of a drip irrigation system, some of the following goals may need to be adjusted after you begin the design process.
Uniformity.
Define the minimum uniformity your design will need to achieve, keeping in mind that higher uniformity designs may result in higher cost.
See Irrigation Efficiency, in this section.
Application Rate.
Know what the application rate requirements will be to replace peak ET.
System Life.
Decide whether your drip tape laterals will be used for a single season or for several years.
Also determine how long the other system components should last.
System Cost.
Know your sensitivity to cost, which may influence your decisions about target uniformity and system life.
Your challenge will be to design a system that meets these conflicting goals.
You will need to make tradeoffs between uniformity, system life, and system cost.
System cost encompasses both one-time installation costs and ongoing operating costs, which also may conflict.
While there are many differences in individual drip systems, most have the components shown in figure 3.1.
Components of a Typical Drip Irrigation System :
 3.
Back flow prevention valve
 6.
Butterfly valve or ball valve
 Figure 3.1 Components of a Typical Drip Irrigation System
 8.
Mainline control valve
 11.
Air vents at high points, after valves and at ends of lines
 12.
Pressure relief valve
 13.
Field control valve
 14.
Submain secondary filters
 15.
Pre-set pressure regulator
 What is Irrigation Efficiency?
The Irrigation Efficiency  of your system is a measure of the proportion of water used for intended purposes.
If your system is 90% efficient, then 90% of the water it applies is used by your plants, or for other intended purposes, and 10% of the water is not used productively.
Irrigation Efficiency is affected by both the design and management your irrigation system.
Distribution Uniformity  is a measure of how uniformly your irrigation system applies water to all parts of your field.
A non-uniform irrigation system delivers less water to some parts of the field and more to others.
Drip irrigation can deliver very high uniformity and this is one of the keys to its high potential efficiency.
A well-designed drip system can achieve DU of 90% or higher.
Poor distribution uniformity leads to non-uniform crop growth and poor irrigation efficiency.
Poor uniformity can be caused by:
 Drip emitters becoming plugged with dirt, algae or other material
 Pressure variations caused by uneven terrain
 Pressure variations caused by friction losses
 Excessive drip tape run lengths
 Use of poor quality drip tape
 All of the above factors can be controlled with careful design and management.
Drip Emitters and their Effects on Distribution Uniformity [fig.
3.2]
 A drip tape emitter consists of an inlet, a flow channel, and an outlet.
The inlet allows water into the flow channel from the main chamber of the drip tape.
The flow channel is a narrow path with a complex shape designed to slow down the flow of water and create turbulence, which prevents contaminants from settling.
The emitter outlet is a small opening at the end of the flow channel through which the water drips into the soil.
A well-engineered emitter does three things very well:
 It emits water at a predictable and consistent rate
 It emits water at nearly the same rate for a range of supply pressures
 Two important numbers quantify how well a drip tape emitter does its job: the Coefficient of
 flow channel molded into RO-DRIP
 Variation  and the Discharge Exponent.
Most drip tape manufacturers publish Cv and X values for all of their products or will provide them upon request.
Several independent test labs also rate emitters and publish this information.
See appendix C for definitions of Cv and X and explanations of how they affect system performance.
Figure 3.2 Anatomy of a Drip Emitter
 The Roberts Difference: RO-DRIP is manufactured with an advanced, high-precision process that results in an emitter coefficient of variation of 0.03 or lower.
This translates to better distribution uniformity and higher irrigation efficiency in your field.
The Roberts Difference: The RO-DRIP emitter has a unique expanding flow channel which can open up to pass trapped debris.
If a clog occurs it can often be removed by temporarily increasing the supply pressure until the expanding flow channel flexes open and allows it to pass.
The Roberts Difference: The comprehensive RO-DRIP product line provides a broad selection of wall thickness, emitter spacing, flow rate and diameter that will allow you to select the right drip tape for your application.
The Roberts Difference: The advanced emitter design and smooth inside walls of RO-DRIP products allow long lateral runs with high uniformity.
RO-DRIP performance charts are available in the Roberts Irrigation Products publication RO-DRIP PERFORMANCE SPECIFICATIONS.
Drip tape can become non-uniform to a point where it is completely debilitated in the midst of a growing season if emitters become plugged.
This can result from any of the following:
 Organic or inorganic sediment in the irrigation water
 A vacuum condition inside of the drip tape causing dirt to siphon back in through the outlet
 Mineral buildup in the flow channel or at the outlet
 The primary features of an emitter that determine its likelihood of plugging are the cross-sectional area of its flow channel and the amount of turbulence created within the flow channel.
A large cross-section gives plenty of room for contaminants to pass through without accumulating into clogs.
A highly turbulent channel keeps dirt particles suspended as they move through the emitter.
Other emitter features also play important rolls in plugging resistance.
Some drip tape products have emitter outlets that resist root intrusion.
The design of the emitter inlet can also affect clog resistance.
Finally, some emitters provide mechanisms that help to remove clogs if they should occur.
To design your drip laterals, you need to specify the following:
 Placement of laterals 
 Drip tape wall thickness
 Table 3.1 summarizes these parameters and their effect on performance.
Each is discussed in greater detail in the remainder of this section.
Lateral Run Length and its Effect on Uniformity
 Length of run has a direct effect on the uniformity  of each drip lateral.
If laterals are too long, pressure losses cause a higher application rate at the beginning of the run than at the end.
In general, longer run lengths with good uniformity are possible with low flow rate and/or large diameter drip tapes, although all drip tapes have their limits.
The DU of a single lateral is determined by its length, slope, operating pressure, flow rate, X, and Cv.
Performance Charts published by most drip tape manufacturers summarize all of these effects, and tell you how long your drip tape runs can be for a given set of conditions.
Consult the Roberts Irrigation performance charts for all RO-DRIP products.
You plan to use a 13 mil RO-DRIP product with a performance chart in appendix D to irrigate cotton.
There is a 0.5% downhill slope, and the distance from the supply manifold to the end of the field is 1000 ft.
You require a DU of 85% for each lateral, and the average pressure of the supply manifold is 8 PSI.
Pressure = 8-PSI  Target EU = 85% Run Length = 1000-ft  Slope = -0.5% Soil: Sandy loam Using the charts in appendix D, RO-DRIP 13-12-24 has a DU of slightly more than 80% for a
 Table 3.1 Drip Tape Design Parameters and their Effect on Performance
 thicker walls improve resistance to	Thicker drip tape is more costly and is
 damage from pests and/or	usually used where the field is rough,
 installation	for sub-surface placement, and for
 Wall thickness	thicker walls allow higher operating	long-term placement.
Thick tape is
 and flushing pressures	also used for better pest resistance.
Thinner tape is used for single-season
 thicker walls make longer-term instal-
 closer emitter spacings result in high-	Choice of spacing is based on planting
 er flow rates	method ,
 closer emitter spacings are	soil texture, and crop selection.
sometimes required for seed
 closer emitter spacings can provide a
 Emitter spacing	better wetting pattern in some light
 larger emitter spacings can deliver low
 flow rates without increasing the risk
 higher flow rates result in more	Choice of flow rate depends on water
 lateral movement of water in sandy	availability, ET requirements, length of
 soils	drip tape laterals, soil
 higher flow rates reduce the risk of	texture, and crop selection.
Nominal flow rate	emitter plugging
 lower flow rates allow longer lateral
 lower flow rates allow improved
 infiltration of water in heavy soils
 large diameters allow longer lateral	Standard drip tape is 0.625-in diame-
 Diameter	runs	ter.
Larger diameter drip tape products
 allow longer lateral runs, but are more
 1000-ft  run at 8-PSI , which does not meet your requirements.
RO-DRIP 13-24-17 has a DU over 85%, and 13-12-24XL has a DU over 90%, both of which meet your requirements.
RO-DRIP 13-12-24 XL will work well in this application.
You may be able to save cost by using the smaller diameter 13-24-17, but it may be difficult to achieve sufficient lateral movement of the wetted pattern with a 24-in  emitter spacing in sandy loam soil.
Try a small test area first.
You can also realize initial cost savings by lowering your uniformity target to 80%, which allows you to use 13-12-24, also with a 5/8-in ID.
However, the initial savings may be offset by increased water usage to compensate for the lower uniformity.
The correct answer depends on the specifics of your growing operation.
The placement of drip tape defines its depth and distance from the plants, and the distance between laterals.
In all cases, the drip tape must be oriented with the emitters facing up to resist plugging from sediment settling.
Proper placement is determined by several factors, including:
 Soil texture and structure
 Use of plastic mulch
 Each field situation has many variables, and the best solutions come from experience.
Experiment with small trial plots to find the best lateral placement and application rates to meet the needs of your crop.
Refer to the crop examples in appendix B to see how experienced drip tape users have made lateral placement decisions.
Following are a few general guidelines.
The placement of drip tape relative to each plant row depends on the amount of lateral movement of water allowed by your soil type and the requirements of your plants.
In general, lateral movement of water in light  soils is difficult to achieve, SO drip tape should be placed close to the plant row.
Conversely, larger distances  are acceptable for high clay content soils, which promote easy lateral water movement and which may result in ponding due to low infiltration rates.
Drip tape should also be placed close to the plant row if plants are direct seeded.
This provides the high soil moisture required by the seeds, as well as additional salt leaching which may be necessary during the early, salt-sensitive growth stages.
When direct seeding in sandy soil, laterals should be placed as close as possible to the plants.
See MANAGEMENT: Germinating Seeds.
The spacing between laterals is determined to a large extent by the distance between centers of your crop rows.
Depending on your soil type and ET requirements, however, it may be possible to irrigate more than one row with each lateral, resulting in reduced system cost and lower application rates.
Other combinations, such as using three laterals to irrigate a four-row bed, are also possible.
In such cases it is important to be sure that the edge of the wetting pattern from each lateral does not coincide with the position of the plant row.
Salts that accumulate at the edge of the wetting pattern can damage or kill plants.
To calculate the total length of drip tape, L, which will be required to cover your field at a given spacing between laterals, use the following formula:
 Figure 3.3 Lateral Placements
  L  = X  
  L =  X  
 If your field is flat, set "number of tape rows per bed" to 1, and use the lateral spacing in place of "bed spacing" above.
Surface VS.
subsurface 
 There are four common methods of depth placement for drip tape:
 Surface placement on flat ground
 Shallow sub-surface: 1-4 in 
 Deep sub-surface: deeper than 5 in 
 Depending on your specific situation and crop, any of the above placement methods may be appropriate.
Table 3.2 presents some typical applications for each.
NOTE: When drip tape is installed deep enough that the wetted area does not reach the surface, salt buildup may occur just under the surface of the soil.
This can create a situation in which rain can leach salt into the root zone and stress or even kill the crop.
Refer to MANAGEMENT: Managing Soil Salinity for information on managing salt buildup.
NOTE: Depth of laterals is critical if they are used to germinate crops.
Depending on soil type, deep subsurface laterals may not be able to supply the water to the surface required by the seeds.
In such cases, sprinklers are required.
[fig.
3.4]
 Raised beds are not necessary in drip applications.
However, they should be considered where salinity or drainage around the plants is a serious problem.
Raised beds can also facilitate harvesting of short stature crops such as strawberries.
Finally, raised beds can increase soil temperature, resulting in increased yield and earlier harvest.
Where possible, consider a large bed width of 60 or 80 inches  and use 2 drip laterals per bed to increase the percentage of production area and yield potential.
NOTE: When two laterals are used, the middle of the bed should be left open for salt accumulation.
Laterals should not be placed so that the edge of the wetting pattern is under the center of a row.
Figure 3.4 Lateral Depth Placement
 Drip tape in hillside applications should be placed on the uphill side of the plant row to ensure a balanced wetted area in the root zone.
On steep slopes, the laterals should be placed parallel to the contour lines of the terrain to minimize pressure differences caused by uphill or downhill runs.
Table 3.2 Typical Applications for Drip Tape Placement Depths
 Placement	Application	Advantages	Disadvantages	Notes
 Single season	Easy, low-cost	Increases risk of	Requires anchoring of
 Retrieval and re-use	installation	mechanical damage	tape
 Applications where	Easy to confirm	Tape may wander due	Should not be used
 installation equipment	uniformity and	to heat or wind	with clear plastic COV-
 Surface	field is small	is unavailable or the	Easy to locate and	operation	Surface wetting	increases weed	erings to avoid burn-	ing or overheating of
 	repair damage	growth and may	tape
 Easy to retrieve	promote disease
 Same as surface place-	Easy, low-cost	More exposure to	A compromise
 ment	installation	damage than with	between the charac-
 Easy to confirm	sub-surface place-	teristics of surface
 V-Ditch	uniformity	ment	and shallow sub-
 Easy to locate and	Increased weed	surface placement
 5-8 cm deep)	(2-3 in deep,	Reduced runoff	repair damage	Increased	growth	Mechanical or	manual installation is
 Single or	Prevents tape	More difficult to visu-	Usually requires
 multi-season	wandering from heat	ally detect	mechanical installa-
 or wind	damage	tion via tractor and
 evaporation	Rodent and insect
 Reduced damage from	problems are
 cultural	greatest in new fields
 sub-surface	Reduced pest	adequate control
 	damage	been used
 Multiple year	Can be used for	Salt accumulates just	Requires careful
 several seasons with-	below the soil surface	design and
 out retrieval	and may be carried	maintenance
 Reduced damage from	into the root zone by	The system should be
 cultural	rain	designed for easy
 sub-surface	Deep	operations	More difficult to	flushing of
 Reduced pest	repair damaged tape	laterals
 (deeper than 5	damage	Installation	Operation of system
 in, 13 cm)	Reduced weed growth	equipment required	during light rain may
 Reduced loss to evap-	oration	Sprinklers may be	required to	be required to	prevent salt from
 germinate crops or to	leaching into the root
 leach salt from the	zone
 Selection of Emitter Spacing
 Common drip tape emitter spacings are 4, 8, 12, 16 and 24 inches.
Narrowly spaced emitters are useful in sandy soil, or where high flow rates are desired.
Wider spacings provide lower flow rates that make longer lateral runs possible.
See table 3.3 for guidelines on selecting emitter spacing.
These are general descriptions only.
Table 3.3 Guidelines for Emitter Spacing
 EMITTER SPACING	APPLICATIONS AND FEATURES	CROPS*
 greenhouse and field flower applications	Flowers
 short lateral runs	Potted plants
 4 inch	10 cm
 results in good wetting patterns in sandy soils
 very high flow rate
 results in good wetting patterns in sandy soils	Flowers
 aids in germination of seeds	Potted plants
 8 inch	20 cm
 provides a relatively high flow rate	Strawberries
 crops in most soils	Potted plants
 lower flow rate than 8-in  spacing	Strawberries
 longer runs are possible due to lower flow rates	Most vegetables
 12 inch	30 cm
 lower flow rate for improved infiltration of heavy soils	Melons
 longer runs possible than with 8 or 12in 	Corn
 16 inch	41 cm	spacing	Cotton
 may not effectively germinate seeds in light soils	Sugar cane
 provides lower flow rate for improved infiltration of heavy soils	Corn
 24 inch	61 cm	very long runs are possible	Cotton
 may not effectively germinate seeds in light soils	Sugar cane
 General guidelines only.
Actual spacing will depend on soil type, run length and other specifics of your operation.
*
 Selection of Flow Rate
 As illustrated in the previous section, drip tapes with narrow emitter spacing deliver higher flow rates due to the larger number of emitters per unit of length.
In addition, many drip tape products are available with two flow rates for each emitter spacing, referred to as Standard Flow and Low Flow products.
Table 3.4 provides a comparison of Standard Flow and Low Flow emitters.
Examples of Standard Flow and Low Flow RO-DRIP products are given in table 3.5.
Consult the RO-DRIP Product Data Sheets for a complete listing of flow rates and emitter spacings.
When you select a drip tape flow rate, emitter spacing, and lateral spacing, you need to ensure that, during irrigation,
 The system does not require a higher flow rate than your water supply can provide
 The system can sustain the application rate required by your field
 Table 3.4 Standard Flow and Low Flow Emitters
 provides a better wetting pattern in some light soils
 Standard Flow	higher application rate for a given emitter spacing
 less susceptible to emitter plugging than low-flow products
 improved infiltration on heavy soils
 longer lateral run lengths are possible
 more susceptible to emitter plugging
 Table 3.5 Standard Flow and Low Flow RO-DRIP Products
 UNITS	EMITTER SPACING	STANDARD FLOW	LOW FLOW
 US	8-in	40 GPH/100 ft	20 GPH/100 ft
 Metric	20-cm	497 LPH/100m	248 LPH/100m
 US	12-in	24 GPH/100 ft	15 GPH/100 ft
 Metric	30-cm	298 LPH/100m	186 LPH/100m
 US	16-in	20 GPH/100 ft	10 GPH/100 ft
 Metric	41-cm	248 LPH/100m	124 LPH/100m
 If your system requires a higher flow rate than your water supply can provide, it will not work.
It will be necessary to divide your field into smaller zones that can be irrigated independently, or reduce the number of acres you are irrigating.
Use the following formula to calculate the total flow rate, Q, each zone of the system will require of your water supply, or use the tables in appendix E:
  X   X  Q = 6000 6000
 If US units are used in the above formula, Q will be in gallons per minute.
If metric units are used, Q will be given in liters per minute.
Calculate the application rate, AR, of your system as follows, or use the tables in appendix E:
 rate, GPH / 100')  AR ) 62 
 If US units are used, AR will be in inches per hour.
If metric units are used, AR will be in mm per hour.
The application rate delivered by your system must be capable of replacing water lost to ET during the peak months of the season.
It is good practice to apply a safety factor when estimating your peak water requirements, to account for system inefficiency as well as the possibility of equipment failure or extreme weather conditions.
You plan to increase the output of your quarter-section  corn field by replacing an existing center pivot with drip irrigation.
The corn is planted on 36-in  centers and you will use one RO-DRIP 13-24-17 lateral for every two rows, resulting in a 6-ft  lateral spacing.
The peak ET for corn in your area is 8.5-in  in the month of July.
The capacity of your water supply is 1200 GPM.
43,560 160 43,560 = 1,161,600 feet 
 The system will be capable of delivering an application rate of
 AR 100').046 inches per hour  = mm
 or 1.1 in per day.
The required flow rate will be
  X  N  = 1.67 X 
 From the above, the system is capable of delivering more than three times the application rate required during peak ET, but it requires a higher flow rate than your water supply can provide.
A possible solution to this problem is to divide the field into three equally sized zones, and irrigate one zone at a time.
Doing this, the maximum application rate to the field will be 1.1 / 3 =.37 in per day , and 1097 GPM  will be required of your water supply.
See Dividing Your Field Into Independent Zones, in this section.
Table 3.6 Guidelines for Selecting Wall Thickness for Drip Tape
 THICKNESS	APPLICATION AND FEATURES
 minimum number of rocks and pests
 5 mil	0.127 mm
 applications where installation cost is very important
 first time drip tape users who desire a thin-walled drip tape
 6 mil	0.152 mm
 experienced drip tape users in multiple season applications
 first time drip tape users
 8 mil	0.200 mm
 experienced drip tape users in multiple season applications
 portable applications 
 10 mil	0.254 mm
 multiple year buried applications
 portable applications 
 13 mil	0.325 mm	multiple year buried applications
 maximum resistance to pests and mechanical damage
 portable applications 
 15 mil	0.375 mm	multiple year buried applications
 maximum resistance to pests and mechanical damage
 The Roberts Difference: RO-DRIP XL is a premium quality 7/8 in-diameter drip tape product designed for long lateral runs.
It is available in several emitter spacings and flow rates and has been successfully used for lateral runs over 1/4 mile  long.
Selection of Wall Thickness
 Drip tape products are available with a variety of wall thicknesses ranging from 4 mil to 25 mil.
The thinnest walled products are lower cost, but are more susceptible to mechanical and pest damage.
They are typically used in single season applications by experienced growers.
The thicker walled products are more resistant to damage and can be used for multiple seasons.
Their higher tensile strength also makes them well suited for retrieval and re-installation in the field.
See table 3.6 for general guidelines on selecting wall thickness.
Run-Length and Selection of Diameter
 For a given flow rate, larger drip tape diameters allow longer lateral runs.
The standard diameter of most drip tape products is 5/8 in.
Most manufacturers also offer largerdiameter drip tape for applications requiring extremely long lateral runs.
RD3.12
 Table 3.7 Considerations for Selecting Drip Tape Diameters
 lower cost than 7/8-in  diameter products
 run lengths are sufficient for most field layouts
 larger variety of emitter spacings and flow rates are available
 very long lateral runs with high uniformity are possible
 less problems with high water application at head of field on heavier soils
 Large Diameter	allows use of fewer submains, possibly resulting in cost savings
 	fewer submains may also result in fewer tractor turns
 higher cost than standard diameter
 fittings and other components may cost more than with standard diameter
 Table 3.7 provides background on the selection of tape diameter.
Actual design decisions may require run length information from performance charts and price information from your irrigation dealer.
See the Roberts Irrigation Products publication RO-DRIP PERFORMANCE SPECIFICATIONS.
Figure 3.5 Typical Field Layout
 The previous section explained how to use performance charts to select a drip tape product and run length that meet your uniformity goals along the length of each lateral.
It is equally important to select mainlines, submains, and other components to ensure that the supply pressures to all of the laterals are consistent so the distribution uniformity over the entire field will meet your goals.
Figure 3.1 shows the major components of a typical field layout.
The function of a submain or supply manifold is to distribute water uniformly to a number of laterals.
For surface or shallow subsurface systems, submains are commonly made of polyethylene hose or reinforced flexible PVC  on the surface, or buried PVC.
The submains for a deep subsurface system should be PVC.
When PVC is installed on the surface, use a light cover of soil to protect it from UV degradation and algae growth within the pipe that can result from exposure to sunlight.
Table 3.8 summarizes the features of each type of submain.
Each submain in your system should supply consistent pressures to all of the laterals attached to it.
Consult a qualified irrigation designer to specify submain diameters that can meet this requirement as cost effectively as possible.
If your system is used for multiple seasons, or water quality is poor, it may be necessary to periodically flush the laterals by opening the ends to remove sediment with the resulting water flow.
If flushing is infrequent, this may not require any special consideration in the design stage, although removable end caps can make the procedure easier.
In large systems that require frequent flushing, flushing manifolds, as shown in figure 3.6, can save time and labor.
Several laterals terminate to a single flushing manifold, and a valve can be opened or an end cap can be removed to flush them all simultaneously.
If flushing manifolds are used, their diameters must be large enough to allow sufficient flow velocity from the ends of the laterals.
In addition, the connection from each lateral to the flushing manifold should not significantly restrict flow.
Figure 3.6 Design for Lateral Flushing
 To effectively remove sediment, the flushing velocity should be at least 1 ft/sec at the end of each lateral.
This translates to approximately 1 GPM  for a 5/8-in  lateral or 2 GPM  for a 7/8-in  lateral.
Depending on run length, this may require 2 to 3 GPM  from the supply manifold to flush a single 5/8-in lateral, or 3 to 5 GPM  for a 7/8-in lateral.
When designing a manifold to
 Table 3.8 Types of Submains
 Material	Description	Advantages	Disadvantages
 Rigid PVC pipe	Long life, if buried	Degrades if exposed to sun-
 light; should be buried
 PVC	More difficult to work with
 than PE hose or layflat
 Flexible polyethylene hose	Long life  in above	Requires more storage space
 with round or	or below-ground applica-	than vinyl layflat
 oval-shaped cross-section	tions	Thermal expansion and con-
 Polyethylene Hose	Easy to install simply	traction can cause movement
 unroll from coil	Can flatten in a buried trench
 Easy to attach laterals and
 Collapsible vinyl hose which	Very compact for	Shorter life than poly hose or
 inflates under water pres-	shipping and storage	buried PVC
 sure	Relatively long life in	Often moves due to
 Vinyl Layflat	applications 	above-ground	internal water velocity
 Easy to install simply
 flush several laterals simultaneously, it is important to ensure that the capacity of your water supply will not be exceeded.
If it is, the flow requirements during flushing can be reduced by using several smaller flushing manifolds at the end of the field, which can be opened individually.
Submains on Uneven Terrain
 When drip laterals are in a level orientation across a steep slope, the submains run up or down the slope.
Pressure variations will occur within the submains if they are long and/or the
 Table 3.9 Minimizing the Effects of Submain Pressure Variations
 If submains are short, the elevation change along each is less than 5 feet , and a pres-
 Short submains	sure regulator is installed at the beginning of each submain, pressure
 variations will be within acceptable limits.
A flow restriction is installed on the submain at each 5-foot  change in elevation.
The
 flow restriction can be an in-line valve on a PVC or poly hose submain, or a clamp on a layflat
 submain.
This method requires some trial and error to adjust the restrictions properly.
Submains are carefully sized so that pressure lost due to friction offsets pressure gained due
 to elevation change.
This results in larger diameter pipe at the top of the slope, "telescoping"
 Telescoping submains	down to smaller diameters further down the slope.
Telescoping submains can also be used on
 flat ground to reduce cost of pipe.
If small-diameter transfer tubes are used to connect laterals to submains, their lengths can be
 set to vary the amount of flow restriction they provide.
Short tubes are installed at the top of
 Variable length transfer	the slope and long tubes are installed at the bottom.
Charts and formulas are available that
 give the friction loss caused by a given length of transfer tube, or trial and error can be used.
slope is severe.
Every 5 feet  of elevation change will cause approximately 2 psi  pressure change, which is enough to affect uniformity.
There are several ways to minimize the effects of slope on uniformity.
The submain should run downhill, with the water supply at or near the top.
Refer to table 3.9 for methods to minimize the effect of submain pressure variations.
Air/vacuum relief at the high points of sloping submains is critical to prevent vacuum conditions that can suck dirt particles into the emitters and cause plugging when the system is drained.
Mainlines distribute water from the source to one or more submain risers which supply the individual submains in the system.
They are most commonly made from buried PVC, although poly hose or layflat can be used in small or portable installations.
Do not use metal pipe  because it can react with chemicals that are injected through the system and plug emitters.
Important considerations in the design of mainlines include the following:
 Mainlines should be carefully laid out to minimize both material cost and pumping cost.
Tradeoffs between initial material cost and ongoing pumping cost must be made when sizing mainlines.
Thrust blocks should be installed on large mainlines at points where flow changes direction.
Mainline sizes should be specified such that flow velocities do not exceed 5 ft/sec m/sec).
Up to 8 ft/sec  is acceptable in some cases where water is free of sand and care is taken to open and close valves slowly.
Pressure relief valves should be installed at low points and at the end of mainlines.
Air/vacuum relief valves should be installed at high points and downstream of any valves.
Flush valves should be included at the end of mainlines.
Consult a qualified irrigation designer to design mainlines that meet these requirements as
 cost effectively as possible.
Connection of Mainlines to Submains
 A pressure regulator at the start of each submain can improve distribution uniformity in many cases.
In addition, the submain connection to the mainline  may include a control valve, an air relief valve and, if necessary, a secondary screen filter.
DIVIDING YOUR FIELD INTO INDEPENDENT ZONES
 Most large drip irrigation systems are comprised of several zones that can be independently scheduled.
Each zone typically has one or more submains, and a control valve that allows it to be turned on and off.
Automatic irrigation controllers are helpful if several zones are implemented, each with a different schedule.
More than one independent zone may be required if one of the following situations apply:
 The capacity of your water supply is not sufficient to irrigate your entire field at the flow rate and lateral spacing specified in your design 
 Fields are staggered for different planting and harvesting dates
 Several different crops are being irrigated with different water requirements
 Topography varies throughout your operation
 Drainage or soil texture vary throughout your operation
 The maximum size of any one zone is determined by the capacity of your water supply:
  X  N  = 7.26 X 
  X  N  = 1.67 X 
 Ideally, each zone should be sized to fully utilize your water supply, although this is not always practical.
In some cases it is desirable to irrigate more than one zone at a time, but it is never possible to simultaneously irrigate more acres  than the number given above.
Filtration Requirements for Drip Irrigation The main purpose of filtration is to keep your emitters clean and working properly.
Maintaining clean emitters is as important to your drip system as water is to your crops.
Two common sources of emitter clogs, in-line particulate  and chemical precipitates, can and should be prevented by proper filtration and water treatment.
NOTE: Filtration equipment is a crucial component of your drip system.
Resist the temptation to save money on unreliable or inappropriate filtration equipment-it is the heart of your system and should be the right equipment for your farm water source.
In addition to filtration, chemical water treatment may be necessary to control pH or to remove algae, bacterial slime, and mineral participates that can clog emitters.
See MANAGEMENT: Water Treatment for more on water treatments.
Filter Types and Filter Selection
 There are several types of filter systems available.
Your choice among them should be based on careful consideration of the following factors:
 A thorough analysis of your water supply including particle size and concentration
 Filtration requirements of the drip irrigation tape
 Seasonal or other changes in potential contaminants
 Potential for precipitation of dissolved solids due to chemical reactions
 Consultation with a qualified irrigation specialist
 Table 3.10 summarizes the filter types and their proper use.
There are a variety of pump types available.
Each has a performance profile represented by a pump performance curve.
Pump lift, capacity, and discharge pressure are all factors to consider.
The particular balance of these factors will be determined by the pressure and flow rate required by your system, and by the type and location of your water source.
Table 3.10 Filter Types
 Filter Type	Application	How it Works	Specifications	Notes
 Required for any open	Fine sand particles with-	Filtration to 74 microns	Cleaned by backflush-
 or surface water source	in pairs of closed tanks		ing
 where large amounts of	create a three-dimen-	Sizes: 12-48 in	Available in carbon
 organic matter are pre-	sional filtering surface.
steel, stainless steel,
 Sand Media Filter	Frequently used for well	water	sent	solids.
Filters are back-	and fine suspended	Removes algae, slime,	Use at least 3 tanks if	possible to avoid back-	.A settling basin may be	and fiberglass
 flushed one at a time,	flushing	required if large
 while remaining units	problems	amounts of silt or clay
 continue filtration.
particles are
 Several tanks can be
 used in parallel for
 Usually a secondary fil-	Fine-meshed screen	Available screen mesh:	Clean by flushing
 ter, as a back-up for a	enclosed in a	50 to 200 (300 to 74	Easily clogged by organ-
 Screen Filter	media filter	pressurized tank traps	micron)	ic matter
 May be used as a	organic and inorganic	Available sizes 0.75-10
 primary filter for very	particulate.
in 
 Used to remove sand,	Centrifugal action	Removes particles heav-	Self cleaning
 well casing and other	creates a vortex that	ier than water, down to	Low maintenance
 Centrifugal Sand	Separator	Can be used as a	inorganic material	pre-filter to reduce	ier than water.
Removes	pushes away	particulate that is heav-	Works with 5-7 psi	74 microns 	pressure loss	Does not remove organ-	ic matter
 backflushing of main fil-	well casing scale, sand,	Not 100% effective -
 ters	and other inorganic par-	usually used as a pre-
 For low or medium	Water falls on a screen	Available from 100-200	Cleaned by water flow
 levels of particulate	separator which catch-	mesh	and additional spray
 Gravity-Flow	Used to deliver a large	es particulate.
nozzles
 Filters	volume of water at a	Particulate is washed	Booster pump is
 low pressure	into a collection tank.
usually necessary after
 Primary filtration	Filters water through	Available from 20-600	Cleaned by backflush-
 Used in many of the	microscopic grooves on	mesh	ing
 same applications as	densely packed discs.
Can handle high flow
 Disc Filter	media filters	conditions by installing
 several banks of disk
 Not for use with large
 Suction Screen	Used for pre-filtration at	Relatively coarse	Available in 10-30	Cleaned by rotating
 Filter	pump intake	screen traps debris.
mesh	water jets
 Pre-filtration to remove	Allows suspended parti-	Sized according to peak	Cleaned by draining
 silt or other inorganic	cles to settle.
Removes	water requirement and	and removing buildup
 particles	high quantities of silt	particulate type	Care must be taken to
 and clay particles.
Also	control algae growth
 Settling Pond	provides aeration to	Inlet must be away
 Your choice among pump types and sizes should be determined by the optimum operating pressure and flow rate of your system.
Once you have determined the requirements of your system, you can choose the most efficient combination of pump and power source by consulting catalogs of pump performance curves.
Pump specification is an in-depth topic that is not covered in detail here.
Many pump manufacturers provide detailed guidelines on sizing pumps for irrigation applications.
Connecting laterals to submains
 Three basic methods used to connect drip tape laterals to submains are:
 Direct connection using twist-lock connectors
 Connection via transfer tubes and fittings
 Connection via transfer tubes without fittings
 Each of these methods is described in detail in INSTALLATION AND STARTUP: Connecting Laterals to Submains.
Refer to the Accessories section of the Roberts Irrigation Product Catalog for information on the fittings and tubing that are available from Roberts Irrigation Products, Inc.
Table 3.11 summarizes the advantages and disadvantages of each connection method.
Laterals can be terminated into flushing manifolds , or they can be individually terminated with or without fittings.
The best method of terminating laterals is usually determined by the flushing requirements of your system.
The lowest cost method of terminating an individual lateral is to fold it over and use a short length of drip tape as a sleeve to slip over the fold.
This method is described in detail in INSTALLATION AND STARTUP.
Threaded end cap fittings can be used to simplify flushing of laterals.
Automatic flushing end caps are also available, although they should not be used in place of a regular flushing program because they do not allow sufficient flushing velocity.
See the Accessories section of the Roberts Irrigation Catalog for more information on the end-caps available from Roberts Irrigation Products, Inc.
Valves and Pressure Regulators
 Drip systems rely on uniform emission rates from all emitters.
While pumps provide a basic level of pressure and flow volume, many more minor adjustments are required to keep your system operating at optimum efficiency and safety.
The following types of valves may be required for your system:
 Pressure-regulating valves keep downstream pressures constant in the presence of varying upstream pressures.
They do not affect water flow directly.
They can be of great value in limiting pressure differences across the field, especially when installed at the beginning of each submain.
Pressure regulators must be sized according to the flow rates they will be subjected to, and not according to submain size.
Be careful when installing pressure regulators since they can be damaged by water hammer.
Avoid low cost units that do not regulate downstream pressure but only maintain a pressure drop.
Use pressure-relief valves when the pressure in your system has the potential to increase beyond a safe level.
Temporary high pressure conditions may occur with sudden opening or closing of valves or air vents, or may occur due to water hammer.
The optimal location for pressure relief valves can be difficult to establish.
They generally should be included at low points and at the end of lines, but also at any other point that can be subjected to large pressure surges.
Table 3.11 Lateral Connections to Submains
 Simple and reliable only one fitting per lateral
 Twist-Lock fitting	Most common in surface applications
 In subsurface applications, laterals must be buried at the same depth as submains
 Allows surface placement of laterals with buried submains
 tube using fittings	Small diameter transfer tubes may result in pressure losses
 Requires up to two fittings and a transfer tube for each lateral
 Lowest cost method of connecting a lateral to a submain
 Small diameter transfer tubes may result in pressure losses
 Greater risk of leaks
 A field control valve is usually included at the beginning of each submain.
Gate valves, butterfly valves, and globe valves are commonly used, and field control valves may be automatically controlled.
Field control valves are usually used as on/off valves, with in-line pressure regulators or pressure reducing valves used to control the pressure in each submain.
Control valves used on mainlines may be simple on/off valves, or may be used to partially restrict flow or reduce pressure.
Gate valves and butterfly valves are commonly used, with globe valves sometimes used in smaller systems.
Gate valves should only be used for for on/off operation and not to partially restrict flow, since the valve may wear while partially open and may not seat properly when closed.
Air vent/vacuum relief valve
 Air that accumulates in mainlines and submains can restrict flow and lead to damage from water hammer.
Vacuum conditions, which can occur in drip laterals when the system is shut down, can cause contaminants to be sucked into the emitters and lead to plugging.
In addition, the vacuum that forms downstream of control valves when they are suddenly closed can damage pipes or the valves.
Install air/vacuum relief valves
 At all high points on mainlines and submains
 At the ends of mainlines and submains
 Downstream of all control valves
 Upstream of pump check valves
 Check valves only allow flow in one direction.
If chemical injection is used, a check valve should be installed at the output of the chemical holding tank to prevent irrigation water from flowing into the tank.
Check valves are also installed downstream of pumps to prevent water from flowing in the wrong direction when the pump is turned off.
A backflow prevention valve prevents water from flowing back into the supply from the irrigation system.
There are several types of backflow prevention valves that use different mechanisms to operate.
Backflow prevention valves prevent chemicals and other contaminants from entering the water supply.
They should be installed in drip systems that are used for
 chemigation and/or fertigation, and are required by law in many areas.
The two most important devices for measuring water movement between the water source and your field are flow meters and pressure gauges.
Close monitoring and accurate record keeping with these devices will allow you to make the most fundamental adjustments to your system operations and detect problems before they can have serious effects on your crop.
Flow meters allow you to directly measure application rates, and can help you detect problems such as clogging or line breakage.
Install at least one flow meter on the main supply line to indicate the total amount of water being applied to the field.
Read this meter and record the information for the new system a regular basis thereafter.
Flow meters are available that show total and instantaneous flow rates.
There are several types of flow meters to choose from, the most popular being the propeller-type flow meter due to its reliability and low cost.
The reliability of flow measurements is highly dependent on the flow meter location.
Propeller flow meters should be located downstream from a straight, unobstructed length of pipe at least eight times the diameter in length.
For accurate readings, the pipe must flow full.
The performance of your system depends on consistent control of water pressure.
Regardless of how well your system is designed, or how well your drip tape is manufactured, operating pressures must remain at design specifications to maintain the desired distribution uniformity.
Changes in pressure can indicate a variety of problems.
A pressure drop may indicate a leak, a component or line break, a blocked filter, or a malfunctioning pump.
A pressure increase usually indicates a block in the filters, valves, or lines.
Install pressure gauges on the mainline both before and after the filters.
You can obtain additional information by installing a pressure gauge directly downstream of each pressure regulator to indicate the actual pressure supplied to the submains.
As with flow meters, read all pressure gauges and record the information when the system is new and on a regular basis during operation
 Controlled injection of chemicals and fertilizers may be the most important benefit of your drip irrigation system.
Substances commonly injected into drip systems include chlorine, acids, fungicides, herbicides, pesticides and fertilizers.
This section describes the design aspects of chemical injection.
Use of your injection system for treating your irrigation water and fertilizing your crops is described in MANAGEMENT: Maintenance, Water Treatment, and MANAGEMENT: Fertigation.
Precision application of high quality fertilizers is especially important and can improve crop response to essential nutrients, while using less fertilizer than traditional irrigation methods.
Drip fertigation can also efficiently fertilize crops that are covered by plastic mulch.
Locate injection equipment downstream of your pump and upstream of your filters, which aid in mixing and can prevent emitter plugging due to particulate buildup or chemical precipitation.
The only exception to this rule is strong acids, which may corrode filter components, and should be placed downstream of the filters.
When specifying and/or installing injection equipment, always do the following:
 Include a backflow prevention device to prevent backflow of chemicals into the water source and a check valve to prevent flow of irrigation water into chemical tanks
 Use injector pumps and components that resist corrosion from fertilizers and acids
 If using an electric injection pump, include an interlock circuit to ensure the injection pump automatically turns off when the system pump shuts down
 Select an injector that is easy to operate and adjust during system operation
 Confirm that the injector you specify is capable of low flow rates; rates as low as 0.1% of the total irrigation flow may be required
 Check with regulatory agencies for specific requirements regarding backflow prevention
 It may be necessary to use several injectors to achieve desired flow rates and to allow separate injection of incompatible chemicals.
Before adding anything to your pipelines, test its compatibility with your water using a jar test, which is a simple test of precipitation risk.
See MANAGEMENT: Fertigation for instructions on performing a jar test.
There are many types of injectors to choose from.
Table 3.13 summarizes the features of some common injection equipment.
Highly concentrated acids and other corrosive chemicals are commonly injected into drip irrigation systems.
Be sure the components of your injection system, including tubing and fittings, are made from suitable materials.
While PVC and other commonly used materials are highly resistant to diluted acids, concentrated acids can degrade them over time.
Injection should be into the center of the water flow in the mainline or in a mixing chamber, so the chemical is diluted before it makes contact with the inside wall of the pipe.
Tubing and fittings made from Kynar"  plastic are resistant to concentrated acids and other chemicals used in irrigation systems.
Kynar is a registered trademark of Elf Atochem North America.
CAUTION: Never inject acid into aluminum pipe.
One of the primary benefits of drip fertigation over other fertilizer application methods is the accurate control of application rate.
In addition the effectiveness of chlorine, acid, and other chemicals depends heavily on concentration.
As a result, it is important to design an injection system that allows good control over injection rates.
Pressure differential tanks, in particular, are not recommended where accurate control of injection rate is required.
If you inject fertilizer or chemicals into your system it is essential, and in some cases is required by law, to install a backflow prevention device upstream of the injection point.
Depending on local your regulations, this may require a pressure-reduced backflow preventer or a double check valve assembly.
Figure 3.12 Common Injector Types
 Table 3..12 Common Injector Equipment and Their Features
 Type	How it Works	Notes
 A pressure differential caused by a	Simple
 valve or other restriction is used to	Does not allow control of injection
 Pressure Differential Tank	Batch or	force water into a tank containing the	chemical.
The chemical then mixes	er than the final concentration	rates: the initial concentration is high-
 with the water, exits the tank, and re-
 enters the water flow downstream of	Causes a pressure drop in the main
 A tank stored above the water flow	Allows control of injection rates
 Gravity Tank	drips the chemical into the water at a	constant rate.
Simple
 Requires a float valve and a
 Water passing over a narrow	Allows control of injection rates
 opening causes a vacuum which pulls	There is a 10-30% pressure drop
 the chemical into the water path.
caused by friction in the venturi
 Can be used in conjunction with a
 small pump to reduce pressure loss
 Many types available; all require power	Allows precise control of injection
 to push liquid forward.
rates
 Drip tape installation methods range from manual placement of single laterals without the use of tractors or other equipment, to automated injection of several laterals simultaneously in combination with other operations such as bed shaping and mulch laying.
The right method for your operation depends on a variety of factors including the size of your field, lateral placement depth, and the equipment available to you.
Careful installation and startup of your system can reduce initial cost and enhance long term performance.
Experience has shown that most damage to drip irrigation systems occurs during tape installation.
If you use mechanical tape laying equipment, it should be carefully designed and free of burrs, sharp edges, mud, sticks and stones.
Whatever method you use to install your system, following a few well-tested procedures can help you avoid expensive and time-consuming repairs.
Accurate placement of laterals can result in increased water distribution uniformity and better movement of water through the soil, allowing you to take advantage of the full potential of your system.
This section explains how to install drip laterals, how to connect them to submains, and how to properly start up and check your system for trouble-free operation over the long run.
Precise installation of your system can result in more uniform performance and easier retrieval.
Always install drip tape with the outlets facing up to prevent plugging by sediment that may settle during operation.
The installation shank is the main tool used for mechanized drip tape installation.
All equipment that makes contact with the drip tape during installation must be free of burrs and other sharp edges.
Before irrigating, test the entire system to confirm proper functioning.
The Roberts Difference: RO-DRIP's unsurpassed uniformity, simple installation and retrieval, reduced infrastructure, and lower cultivation costs make it the performance leader for any length of run in the field.
Table 4.1 summarizes several important guidelines for proper installation.
Table 4.1 Installation Guidelines
 Store drip tape in a protected area and leave wrapping in	Begin installation before carefully planning and
 place until ready to install	engineering your system
 Prepare soil and beds before planting.
Particle size should	Step on laterals or drag drip tape across soil surface
 be small and uniform	Apply uneven tension or jerks that can stretch tape and alter
 Install laterals with emitters facing up	flow rates
 Maintain a low constant tension on drip tape roll	Handle drip tape using any tools or equipment with burrs or
 Test the system before irrigating	other sharp edges
 Note: Always install tape with the emitters facing up, in both surface and subsurface applications.
This prevents sediment from settling to the bottom of the tape and clogging the emitters.
INSTALLING DRIP TAPE LATERALS
 Manual drip tape installation is common in small fields and greenhouses where laterals are placed on the surface, because it is often the most cost-effective choice.
Manual installation is less practical in large fields or in subsurface applications.
It is generally not practical to manually install deep subsurface drip systems.
Use PVC, vinyl layflat or poly hose for submains.
If using PVC submains above ground, protect them from sunlight with a light covering of dirt.
Do not use steel or aluminum pipe.
Use the following steps to install drip laterals.
Figure 4.1 Pulling Drip Tape Along a Row
 1.
Mount the spool on a low stand at the front end of the row.
2.
Pull the lateral along the row, taking care not to drag it on the soil surface.
Lay the drip tape with the emitters facing up.
Note: If the ground is rocky or there is stubble in the field, install the drip tape by carrying the spool down the row.
This avoids damage caused by dragging the drip tape.
3.
Place a shovel full of dirt on the drip tape every 10 to 15 ft  to prevent twisting or wandering.
Avoid stretching or jerking the lateral during installation.
4.
Leave extra length at both ends of each lateral to allow for expansion and contraction and to connect to the manifolds.
Figure 4.2 Walking Spools Along a Row
 Installation equipment: an overview The basic component used in all mecha-
 Figure 4.3 Placing Dirt on a Lateral
 nized installation is the injection shank.
Its purpose is to accurately locate the drip tape to the point of installation, either on or below the surface and, in subsurface installations, to dig a trench for the lateral.
One or more spools and injection shanks can be mounted together on a tool bar.
Figure 4.4 shows a Tube Type injection shank, which is popular because of its simple and functional design.
Simple injectors such as the Tube Type Shank are easy to build, although extreme care must be taken to eliminate all sharp surfaces.
More advanced injectors, which allow high-speed installation of thin-walled tapes, can be pur-
 chased from a number of suppliers.
Pay attention to the following important factors when you design or purchase an injection shank:
 The installation tube should have a flared opening and should be free of burrs, nicks, sharp edges, weld lines or seams that can cause damage to the drip tape
 The diameter of the installation tube should be as small as possible.
1-in Schedule 40 steel for standard 5/8-in drip tape or 1.25-in for 7/8-in drip tape
 The bottom of the installation tube should be at the same depth as the bottom of the shanking tool
 The drip tape spool should be positioned close to the injection tube directly above it if possible
 The drip tape spool should be mounted on a shaft that can spin freely; stationary shafts will be damaged by the spool hubs, or can damage spool hubs
 The shaft should have a braking system that can provide drag to prevent overspinning of the spool when the tractor stops
 Wood or metal disks should be used to support the cardboard drip tape spools
 The injection shank can be mounted on a toolbar with other equipment to perform several
 Figure 4.4.
Tube-type injection shank, Courtesy of Andros Engineering
 tasks simultaneously.
In fact, it is possible-and now fairly common-to shape beds, install drip tape laterals, install plastic mulch, and even side dress beds with fertilizer all in a single pass.
These operations are often performed on several rows at once.
Packaged systems that install drip tape while performing other operations are available from a number of vendors.
Tape installation procedure subsurface
 Figure 4.5 Combination Bed Shaper, Plastic Layer, and Drip Tape Installer
 For shallow subsurface systems, mainlines and submains can be above ground vinyl layflat, poly hose, or buried PVC.
Deep subsurface systems should use PVC for mainlines and submains.
If using PVC submains above ground, protect them from sunlight with a light covering of dirt.
Do not use steel or aluminum pipe.
Use the following steps to install drip laterals.
1.
Mount the spool on the shaft that feeds the injection shank.
2.
Setup and align the shanking tool so that, when installed, the drip tape emitters face upward.
The Roberts Difference: RO-DRIP spools utilize an industry standard bore for a 1-in shaft, making it an easy fit for all commercially available injection equipment.
3.
Secure the beginning of the lateral with a weighted object or a stake.
4.
Start and stop the tractor smoothly to prevent stretching or jerking of the drip tape through the installation tube.
Do not apply excessive drag on the spool.
Avoid stretching the drip tape.
5.
Leave extra length at both ends of the laterals to allow for expansion and contraction and for connection to the manifold.
6.
After the first lateral is installed, evaluate it for excess drag set on the spool.
Check the tension of the lateral by hand.
Periodically re-evaluate drag throughout the installation.
Tape installation procedure surface
 Use the same basic procedure as with subsurface installation.
With surface installation, however, the means of securing the laterals are different.
Place a shovel full of dirt over each laterals every 10-15 ft  to minimize their movement by wind or thermal expansion and contraction as shown in figure 4.3.
Installation of Tape with Plastic Mulch
 For many crops, the combination of drip irrigation and plastic mulch gives the greatest degree of control over the root zone environFigure 4.6 Mechanical Installation of Tape ment, and results in higher yields and more efficient use of water and chemicals.
Injection shanks can be mounted on tool bars along with plastic layers and bed shapers.
Packaged systems are available from several vendors that lay plastic and inject tape.
Some of these systems also shape beds.
Note:Drip tape should be buried if it is used with clear plastic mulch.
Water droplets on the surface of the plastic act as magnifying lenses which can focus sunlight to burn and damage drip tape.
The Roberts Difference: RO-DRIP is available with the wide variety of emitter spacings required for nursery and greenhouse applications.
This includes a 4-in emitter spacing for closely spaced plants.
Figure 4.7 Simultaneous Installation of Drip Tape and Plastic Mulch
 Drip tape is an effective method of irrigating nursery and greenhouse plants.
It is commonly used to irrigate both potted plants and field plants.
The increased level of control made possible with drip tape results in higher quality crops with reduced incidence of disease.
To irrigate potted plants, drip tape is laid across pots or containers and secured tightly at each end.
In some installations it helps to string a wire over the containers and fasten the drip tape to the wire rather than laying it directly on the containers.
Emitters should face to one side , to prevent water from running along the tape and missing the pots.
In field nursery applications, drip tape is either laid on the surface or buried 2-3 in  below the surface.
Figure 4.8 Direct Use of Dip Tape for Potted Plants
 CONNECTING LATERALS TO SUBMAINS
 Figure 4.9 Field Nursery Installation
 Drip tape laterals can be connected to submains using fittings and/or transfer tubes.
Connect laterals to the submains as part of an integrated startup procedure that includes flushing mains and submains.
Drip tape laterals can connect to rigid PVC, layflat, or polyethylene hose submains with a few basic fitting types See the Roberts Irrigation Product Catalog for a complete list of Roberts fittings and tubing.
Connecting to PVC submains
 Drip laterals can be connected to PVC submains either directly with fittings or through transfer tubing.
Both glued fittings and gasketed fittings can be used.
In either case, fittings are available that directly connect PVC submains to the following:
 Drip tape using a lock-sleeve fitting
 Transfer tubing using an external compression fitting
 Transfer tubing using an internal barb
 See Connecting a Transfer Tube to a Lateral below for instructions on connecting a transfer tube to a drip tape lateral once it has been connected to the submain.
Figure 4.10.
Common Fittings for PVC Submains
 For either fitting type, an appropriately sized hole must be drilled that is free of gaps, cracks or splits.
Only clean holes will allow a proper connection.
Use the procedure shown in figure 4.12 to connect a fitting or 4.13 to directly connect a transfer tube to a PVC submain.
Figure 4.11 Creating a Hole in a PVC Submain
 Figure 4.12c-d Connecting a Glued Fitting to a PVC Submain
 Figure 4.12a-b Connecting a Gasketed Fitting to a PVC Submain
 Figure 4.13 Directly Connecting a Transfer Tube to a PVC Submain
 Connecting to Polyethylene Hose Submains
 There are 2 basic methods for connecting a drip lateral to a poly hose submain: using a direct transfer tube or using a fitting.
Fittings are available that directly connect polyethylene hose submains to the following:
 Drip tape using a lock-sleeve fitting
 Transfer tubing using an external compression fitting
 Transfer tubing using an internal barb
 Figure 4.14 shows several fittings available for connecting laterals to poly hose submains.
Figure 4.14 Common Fittings for Poly Hose Submains
 Create a hole in the poly hose submain that is slightly smaller than the outside diameter  of the transfer tube or barb fitting.
Use the procedure shown in figure 4.16 to connect a fitting to a poly hose submain or figure 4.17 to directly connect a transfer tube.
See Connecting a Transfer Tube to a Lateral below for instructions on connecting the transfer tube to a drip tape lateral once it has been connected to the submain.
Figure 4.15 Creating a Hole in a Poly Hose Submain
 Figure 4.16 Connecting a Fitting to a Poly Hose Submain
 Figure 4.17 Connecting a Transfer Tube to a Poly Hose Submain
 Connecting to Layflat Hose Submains
 There are 2 basic methods for connecting a drip lateral to a layflat hose submain: using a direct transfer tube or using a fitting.
Figure 4.18 shows some common fittings for connecting a layflat hose submain to a transfer tube or lateral.
Figure 4.18 Common Fittings for Layflat Submains
 Use the procedure shown in figure 4.19 to connect a fitting to a layflat submain or figure 4.20 to directly connect a transfer tube.
See Connecting a Transfer Tube to a Lateral below for instructions on connecting the transfer tube to a drip tape lateral once it has been connected to the submain.
The Roberts Difference: Roberts Irrigation Products manufactures a premium quality line of polyethylene hose products which are available in all of the sizes commonly used for drip irrigation transfer tubes.
Figure 4.19 Connecting a Fitting to a Layflat Submain
 Figure 4.20 Directly Connecting a Transfer Tube Layflat Submain
 CONNECTING A TRANSFER TUBE TO A LATERAL
 Transfer tubes connect submains to laterals.
Smaller transfer tubes  can be directly connected to laterals.
Larger tubes  are connected using wire ties.
Finally, a lateral can be connected to a transfer tube with a barbed lock sleeve fitting.
Use the procedure shown in figure 4.21 to directly connect a small-diameter transfer tube to a lateral.
Figure 4.21 Steps for Connecting a Lateral to a Transfer Tube Without Fittings
 Use the procedure shown in figure 4.22 to connect a transfer tube to a lateral using a wire tie.
Figure 4.22 Steps for Connecting a Lateral to a Transfer Tube Using a Wire Tie
 Use the procedure shown in figure 4.23 to connect a transfer tube to a lateral using a lock sleeve fitting.
Figure 4.23 Steps for Connecting a Lateral to a Transfer Tube with a Fitting
 The Roberts Difference: The unique polyethylene material blend used to make RO-DRIP provides strength as well as flexibility and memory.
The result is reliable, leak-free connections to transfer tubes and fittings.
Drip tape laterals can be spliced using tubing  and wire ties , or by using a locking sleeve fitting.
Figure 4.24 Splicing a Lateral Using Poly Hose and Wire Ties
 Figure 4.25 Splicing a lateral Using a Locking Sleeve Fitting
 Figure 4.26 Closing a Lateral Using a Closing Band
 Drip tape laterals can be terminated using a closing band  or a lock sleeve end cap fitting.
Figure 4.27 Closing a Lateral Using an End Cap
 Before you begin irrigating it is important to thoroughly flush the system, check for leaks or breaks, and ensure that all components are working properly.
Make sure you have gone through all of the following steps before you use your drip system to irrigate your field.
1.
Open mainline flushing valves with submain valves closed until discharge water runs clear for 5 minutes.
Close the mainline flushing valves.
In large systems, dye can be added in the filter station when the dye is no longer visible at the end of the line, flushing is complete.
2.
Connect laterals to the submains, without terminating the ends.
3.
For each submain, open the control valve until the discharge water at the end of each lateral runs clear.
If the capacity of your water supply is not high enough to flush all laterals simultaneously, it may be necessary to terminate some of the laterals so that you can flush only a few laterals at a time.
Close the submain control valves.
4.
Close the laterals or connect the ends of the laterals to the flushing manifold, if used.
5.
Operate the system until it is fully pressurized and all air is discharged.
6.
Check the system for leaks and repair them if necessary.
7.
Re-flush after all leaks are repaired.
8.
Check all pressure gauges and adjust pressure regulators or regulating valves, if necessary.
9.
Check for proper operation of all system components: pumps, controllers, valves, air vents, pressure regulators, pressure gauges, flow meters, filters, and chemical injectors.
10.
Record readings from all pressure gauges and flow meters.
The three critical components of a drip system management program are scheduling, monitoring, and maintenance.
Each has requirements that differ from traditional furrow and sprinkler irrigation.
Scheduling must be carefully planned to keep the soil in the root zone near field capacity, providing ideal conditions for plant growth.
Monitoring of pressures, flow rates, and soil moisture is necessary to continually fine tune your irrigation schedule.
Finally, a regular maintenance program is required to keep the drip emitters clean and free of clogs that can reduce efficiency and damage your system.
This section tells you how to schedule, monitor, and maintain your drip irrigation system for years of successful operation.
Emphasis is placed on diligent planning and adjustment of your program to maximize crop performance and avoid potentially costly problems.
The section finishes with management and maintenance issues associated with chemical/fertilizer injection and salinity management.
Take the time to learn, train and implement some new ways of irrigation management.
The three components of a successful drip irrigation management program are scheduling, monitoring, and maintenance.
The goal of drip irrigation scheduling is to replace soil moisture as it is lost to evapotranspiration.
Small amounts of water are applied frequently, often daily.
Regularly monitor pressures, flow rates, soil moisture, and other factors to take full advantage of the high level of control that drip irrigation offers.
The central goal of a drip irrigation maintenance program is to keep the emitters clean, so they will continue to deliver water and nutrients uniformly to your plants.
The Roberts Difference: RO-DRIPand RO-DRIP XL provide the most reliable, cost-effective solution for subsurface and above ground irrigation.
The goal of drip irrigation scheduling is to select an irrigation duration and frequency that results in a properly sized wetted area around plants and keeps the soil in the root zone at or near field capacity.
The right schedule for your system depends on your specific crop requirements, soil texture, field preparation and weather conditions.
Adjustments throughout the season based on monitoring of field conditions allow you to fine-tune the irrigation schedule to the needs of your crop.
NOTE: Deficit irrigation can be used to increase the soluble solid content of fruits or vegetables by deliberately maintaining soil moisture below field capacity.
This is usually done at the end of the growing season, shortly before harvest, and is common with grapes, sugar cane, tomatoes, cotton and several other crops.
Precise control of application rates make drip irrigation ideally suited for deficit irrigation when necessary.
To determine how much water to apply during irrigation, first calculate the amount needed by your crop for evapotranspiration, and use this as a starting amount.
After irrigating, you will be able to fine-tune the schedule by examining the wetted pattern, measuring soil moisture, and making adjustments accordingly.
Determining Your Crop's Daily Requirements
 For most crops, the soil in the root zone should be kept near field capacity at all times.
This means that irrigation should be frequent, and the amount of water applied each time should be equal to the amount used by the plants since the last irrigation.
Therefore, it is important to know the rate at which water is lost to Evapotranspiration.
The ET rate of a reference crop for you area is usually available from a local agricultural agency or, in some areas, through the Internet.
Portable weather stations are also available which can be more accurate, since ET can vary from field to field.
Use the following formula to calculate the ET rate of the specific crop in your field:
 where ETo is the reference crop evapotranspiration and Kc is a crop factor, or crop coefficient that depends on the specific crop you are irrigating.
The value of the crop factor varies throughout the season as your crop matures.
You can estimate it by starting with the value shown in table 5.1 and multiplying it by the percent of ground covered by your plants.
If the resulting number is less than 0.2, use a value of 0.2.
Calculate the percent ground coverage as the distance across the bed that is covered by the crop divided by the bed spacing times 100.
For example, cucumbers early in the season which cover 50% of the ground surface will have a crop coefficient of 0.5 X 0.9 = 0.45.
Table 5.1 Estimated Peak Crop Factors for Various Plants
 ESTIMATED PEAK CROP FACTORS  FOR VARIOUS PLANTS
 Crop	KC	Crop	KC
 Cabbage	.95	Pepper	.95
 Cantaloupe	.95	Potato	1.05
 Carrot	1.00	Strawberry with plastic mulch	1.05
 Celery	1.00	Strawberry without plastic mulch	1.10
 Cotton	1.05	Sugar cane	1.05
 Corn	1.00	Squash	.90
 Cucumber	.90	Tomato	1.05
 If you do not find your crop in table 5.1, you can estimate Kc as the percentage of ground covered.
Both crop coefficients and reference ETo values are now available on the Internet for many areas.
These web sites provide both real-time and historical information and can be very useful design and management tools.
If a reference evapotranspiration  rate is not available for your area, use a potential
 Table 5.2 Potential Evapotranspiration 
 Climate	in per Day	mm per Day
 Cool humid	0.10 0.15	2.5 3.8
 Cool dry	0.15 0.20	3.8 5.1
 Warm humid	0.15 0.20	3.8 5.1
 Warm dry	0.20 0.25	5.1 6.4
 Hot humid	0.20 0.30	5.1 7.6
 Hot dry	0.30 0.45	7.6 11.4
 evapotranspiration rate  from table 5.2 as an approximation of ETo.
Developing and Maintaining a Proper Wetted Area
 In general, short irrigation cycles with high application rates help promote lateral movement of water, resulting in better wetting patterns for light soils.
"Pulse irrigation," where the system is operated several times a day for short durations, can further widen the wetted pattern.
Long duration at a low application rate results in better infiltration of water in heavy  soils.
The right irrigation cycle depends on the specifics of your field experiment to find out what works best.
Determining Your Irrigation Schedule
 How often to irrigate 
 The irrigation frequencies used in drip irrigation are typically quite different from those used in other methods of irrigation.
The increased control offered by drip systems allows you to apply small amounts of water daily or several times a week without significant loss to evaporation or surface runoff.
As a result, irrigation can be scheduled to replace water as it is used by the plant on a daily basis.
This ability to use frequent irrigation to keep the soil moisture level near field capacity is a unique advantage of drip irrigation.
In most cases, irrigation can take place several times a day, once a day, or several times a week.
Research has shown that there is little difference between these as long as enough water is applied each time, although there are some exceptions.
During consecutive days of hot dry weather, or when young seedlings are grown in coarse textured soil, daily irrigation is good practice to ensure your plants are not stressed.
Irrigating several times daily may result in reduced distribution uniformity, since the repeated filling and draining of submains and laterals with each irrigation results in heavier irrigation at the low points of the field.
As described above, however, "pulse irrigating" can help with the development of a good wetting pattern, making it a good choice in some cases.
NOTE: Drip irrigation only wets soil near the plants.
Roots only develop in the wetted area and, as a result, can be more localized than with other irrigation methods.
This normally does not cause problems, but it makes irrigation frequency critical.
Because the water holding capacity in the root zone is smaller, an extended period of time without irrigating can easily cause plant stress.
During hot weather conditions, daily irrigation may be necessary to avoid crop damage from water stress.
How long to irrigate 
 The Roberts Difference: Roberts Irrigation manufactures several high flow rate products with close emitter spacings that are specially designed to form good wetted patterns in soils with high sand content.
These include 8-in 40 GPH RO-DRIP  and 4-in 60 GPH RO-DRIP.
The Roberts Difference: Roberts Irrigation manufactures several low flow rate products with wider emitter spacings which are specially designed to form good wetted patterns in heavy soils with high clay content.
These include 12-in 15 GPH RO-DRIP , 16-in 10 GPH RODRIP  and 24-in 17 GPH RO-DRIP.
Once you have determined an irrigation frequency, you must determine the duration of each
 Table 5.3 The Effect of Wetted Area on Crops
 Small Wetted Area	Large Wetted Area
 Restricts roots to a small volume of soil	Wastes water and fertilizer
 Reduces uptake of needed minor nutrients from soil	Increases the number of weeds
 Increases potential for plant water stress during	Does not improve crop performance
 periods of high temperature and wind
 The ideal wetted area is shaped as shown
 Sandy Soil	Clay Soil
 The wetted area should be maintained at the same size
 throughout the season to prevent salts near the edges from
 Soil type and field preparation affect the shape of the cross
 irrigation that will apply enough water to replace evapotranspiration  and compensate for system inefficiency.
Use the following steps to determine the proper irrigation duration:
 1.
Estimate the amount of water used by your crop between irrigation cycles by multiplying the daily ET rate  by the number of days between irrigation cycles.
2.
Compensate for irrigation inefficiency by dividing the resulting application amount by the irrigation efficiency.
Estimate IE as being equal to the distribution uniformity  that you have designed for.
3.
Divide the amount of water to be applied by your system application rate.
The resulting irrigation duration, given in hours, is a starting estimate for your irrigation schedule.
After irrigating, it will be necessary to make adjustments as described later in this section.
Cantaloupes will be irrigated every other day using a drip irrigation system with the following specifications:
 ET 0.19 in/day Spacing between laterals: 60 in  Emitter spacing: 12 in  Drip tape flow rate: 24 GPH per 100 ft  Distribution uniformity: 90%
 Determine the required irrigation duration.
Since irrigation is performed every other day,.19 x =.38 in  of water must be replaced at each irrigation.
The distribution uniformity is 90%, so.38/.9 =.42 in  must be applied by the drip system at each irrigation.
Using the formula in DESIGN: Lateral Design, the application rate  of the system is calculated as:
 AR =   24.077 in per hr  62 X  62  62x5
 The required duration, T, is the amount of water to be applied at each irrigation divided by
 A mount to be applied.42 in.42 T = = = 5.45 hr AR.077 in per hr.077
 or approximately 51/2 hours.
Adjusting your irrigation schedule
 Confirming the amount of water applied
 It is important to verify your irrigation schedule by taking direct readings from flow meters.
Confirm that the system is applying the amount of water each day that you intended it to in your schedule, as described in Monitoring, below.
Make adjustments as necessary.
Since ET can vary from day to day and even from field to field within the same geographic area, it is always necessary to adjust your schedule based on observations of the wetted pattern and measurements of soil moisture.
The section below: Monitoring, Soil Moisture, describes how to use moisture sensing devices to measure the amount of water in your soil.
If soil moisture measurements in the middle of the root zone indicate the water level is consistently below field capacity or the soil is consistently saturated, adjust your irrigation schedule by changing the irrigation duration as shown in table 5.4.
Try making small modifications over several cycles before making any drastic revisions to the schedule.
Table 5.4 Adjusting Your Schedule with Soil Moisture Response
 Sensor Response	Cause	Scheduling Change
 Consistent high moisture 	Too much water applied	Decrease duration
 readings indicating field is saturated
 Moisture level does not return to field	Too little water applied	Increase duration
 capacity after each irrigation
 To achieve the high yields and water savings possible with drip irrigation, it is necessary to monitor your system and make adjustments to fine tune the amount of water and nutrients applied.
In addition, careful system monitoring gives advance warnings of potential problems.
Monitor the performance of your system by taking readings from all of the flow meters and pressure gauges at regular intervals.
There should be at least one flow meter installed on the mainline to indicate the total amount of water being applied to the field.
Once your irrigation schedule has been determined, read the flow meter to confirm that the system is applying the amount of water it was designed to apply.
Because of the large number of variables at play in an irrigation system, the measured application rate cannot be expected to be exactly the same as the predicted rate.
However, a large difference indicates either a problem in your calculations or a physical system problem such as a broken or clogged line.
If the results are not what you expect, identify and fix the problem.
Flow meter readings can also indicate problems that can occur mid-season.
To make use of this valuable information, to measure and record flow meter readings for the new system, and on a regular basis thereafter.
Table 5.5 shows some of the problems that can be diagnosed by keeping track of system flow rates.
Any of these problems should be addressed immediately to
 avoid serious crop damage.
Note: Tables 5.5 and 5.6 are intended to present examples of problems that can be diagnosed through regular monitoring.
They are not a comprehensive list of problems that can occur with your specific drip irrigation system.
Most flow meters provide instantaneous readings of flow rate, as well as a reading of total flow.
The totalized reading is more accurate than the instantaneous reading and can be used to calculate the average flow rate or application rate over a given time.
This reading can also be used to indicate the total water usage during an entire season.
Table 5.5 Problems Diagnosed from System Flow Rates
 Gradual decrease in flow rate	Could indicate pump wear or filter clogging check
 Stuck or plugged control valve
 Sudden decrease in flow rate	Other flow restriction check pressures
 Water supply failure check pressures
 Incremental damage to laterals from insects or other pests
 Gradual increase in flow rate
 Damaged or broken lateral
 Damaged or broken submain
 Sudden increase in flow rate
 Damaged or broken mainline
 Table 5.6 Problems Diagnosed from System Pressures
 Debris buildup in filters
 Large pressure drop across filters
 Inadequate flushing of filters
 Gradual pressure decrease at filter input
 Other water supply problems
 Damaged or broken lateral
 Damaged or broken submain
 Sudden pressure decrease at filter output	Damaged or broken mainline
 Water supply failure check flow rates
 Gradual pressure increase at filter output
 Other flow restriction check flow rates
 Sudden pressure increase at filter output
 Other flow restriction check flow rates
 Sudden pressure decrease at submain	Damaged or broken lateral check flow rates
 Pressure gauges, or ports for a pressure gauge, should be installed on the mainline both before and after the filters.
The pressure gauge or port after the filters should be located near the mainline flow meter, since flow and pressure changes can work together to reveal a variety of potential problems.
Additional information can be obtained by installing a pressure gauge at each submain riser.
As with flow meters, all pressure gauges should be read and recorded for the new system, and on a regular basis thereafter.
Table 5.6  shows some of the problems you can diagnose by keeping track of system pressures.
Act on any of these problems immediately to avoid serious crop damage.
Note: Table 5.6 is intended as an example of some problems that can be diagnosed through regular monitoring.
It is not a comprehensive list of problems that can occur with your specific drip irrigation system.
Soil moisture measurements should be made at the following times:
 Before the first use of the system to determine field capacity 
 After the first few irrigation cycles to verify your irrigation schedule and to make necessary adjustments
 Periodically throughout the season to make schedule adjustments as the water requirements of your plants change
 Soil moisture content and tension
 Most commercial moisture sensors provide a reading either of tension  or moisture content.
Tension is a measure of the work a plant must do to remove water from the soil and is usually expressed in bar or centibar.
The drier the soil is, the more work plants must do to remove water, and the higher the tension.
Tension is a useful measurement, since it is the aspect of soil moisture that directly affects your crops.
Moisture content is a measurement of the water contained in the soil as a percentage of the volume of the entire soil solution.
Moisture content can directly indicate how much water you need to apply at the root zone to return it to field capacity.
Measure soil moisture at several depths and locations in the field.
With a portable moisture sensor, you can accomplish this by taking a number of measurements with the same sensor.
If you are using a low-cost sensor such as a tensiometer or gypsum block, you can install several
 Table 5.7 Important Soil Moisture Levels
 Condition	Tension	Moisture Content
 Saturation	0-3 cb	15-60% depending on soil type
 Field Capacity	10-25 cb depending on soil type	10-50% depending on soil type
 Permanent Wilting	15 bar 	2-30% depending on soil type
 sensors in the field, each at a different depth and location.
Take readings in sets of three measurements just below the surface, in the middle of the root zone, and below the root zone in the row between plants.
Use two or more sets within an irrigation block to verify that measurement sites are representative.
Additional sites may be helpful in non-uniform soil.
A variety of sensors are commercially available for measuring soil moisture.
Each sensor either measures moisture content or tension directly.
Table 5.9 summarizes several types of moisture sensors.
Numerous other types are available .
Table 5.8 Sensor Depth
 Depth below surface*	Result
 Reflects soil moisture conditions in the root zone during early plant growth or
 6 in 	throughout the season for shallow rooted crops.
Monitors the root zone as plants mature and their roots enlarge.
Use this depth to monitor
 12 in 	irrigation during most of the plant's life.
Monitors the degree of leaching below the root zone should not change during
 18 or 24 in	normal irrigation.
* Actual depth may vary depending on crop type and rooting depth.
Even with low-salinity water, salt can accumulate in the soil unless some leaching occurs.
In addition to the salts that are part of almost all irrigation water, fertilizers can also add to salt content.
Relatively low concentrations can damage some crops by making the soil water less available to the plant root system.
By the time the effects of salinity are actually seen in the plants, damage to yield has already occurred.
In problem areas, periodically send samples of the soil solution to a lab for analysis of salt concentration.
Several commercial EC sensors are also available that can give reasonably accurate results in a short amount of time.
Maintenance of your drip irrigation system is critical.
Drip systems require more diligent attention than other forms of irrigation, and failure to properly maintain all components can lead to system failures that result in expensive repairs or even crop damage.
The purpose of most maintenance functions is to keep emitters clean, although other functions such as pest control and repair of damaged laterals are also important.
Keeping the emitters clean
 Great care must be taken to prevent drip emitters from plugging with dirt, organic matter or precipitates.
A slight plugging problem will eventually result in greatly reduced distribution uniformity.
A serious plugging problem can result in complete failure of your drip irrigation system.
Such a failure can occur mid-season when it is not possible to make repairs or replacements.
Include the following steps in your maintenance program to prevent this from happening.
The importance of proper filtration was discussed in the DESIGN section.
Once your filters
 Table 5.9 Moisture Sensors
 Method or Device	How it works	Advantages	Disadvantages	Notes
 With experience it is	No instrumentation cost	Cannot be automated	Currently the most
 possible to learn, with a fair	Observation of soil and	Will yield inconsistent	common method
 degree of accuracy, how your	plants may reveal prob-	results if several
 "BY FEEL"	soil looks and feels when it	lems that could be	people are taking mea-
 	is at field capacity.
Look and	missed with	surements
 feel includes observation of	automatic sensors
 the soil as well as the crops
 for signs of stress.
TENSIOMETER	Soil capillary action removes	Low cost	Not accurate in dry soil	Accurate in the
 	water from a cup through a	Reliable for tension		moisture range of
 porous material creating a	below 80 cb	Relatively high mainte-	interest to
 vacuum that is equal to the	tension of the soil matrix.
A	Not affected by salinity	nance requirement	Can use electronic	irrigation
 vacuum gauge gives tension	vacuum transduc-
 readings in bar or centibar.
er for remote
 Soil water permeates a	Very low cost	Poor accuracy in wetter	Provides a qualita-
 porous block of gypsum with	Can easily be read	soil 	tive reading of
 two embedded	remotely	Readings can be affect-	"wet" or "dry"
 GYPSUM BLOCK	electrodes that measure	ed by salinity	Limited effective-
 	meter is calibrated to give	readings of tension in bar or	resistance.
A resistance	High maintenance	requirement	gation, since soil	is kept near field	ness for drip irri-
 Measures the dielectric con-	High accuracy	Relatively high cost	Cost is becoming
 stant of the soil	Fast measurement time	Readings can be affect-	lower
 time required for an	solution by measuring the	Can easily be read	ed by salinity
 electrical pulse to travel	remotely	Calibration required
 	through a spike or probe.
Low maintenance
 Uses this measurement,	requirement
 along with the known dielec-
 tric constant for water, to
 Measures the dielectric con-	High accuracy	Relatively high cost	Cost is becoming
 stant of the soil solution by	Readings not affected	Calibration required	lower
 measuring the change in fre-	by salinity
 quency of an RF pulse.
Uses
 FDR SENSOR	this measurement, along with	Can easily be read
 	the known dielectric constant	remotely
 for water, to report percent-	Low maintenance
 age moisture content.
requirement
 Uses measurements of the	High accuracy	High cost	Generally too
 permeation of soil by a	Non-destructive	Calibration required	expensive and
 	NEUTRON PROBE	which is proportional to mois-	determine hydrogen content,	radioactive source to	Tests a relatively large	volume of soil	Must be installed in	field for each reading	practical farm use	complex for
 ture content.
Radioactive requires
 The Roberts Difference: RO-DRIP employs the largest emitter cross-section available on the market to deliver unmatched resistance to plugging.
While this does not eliminate the need for maintenance, it can mean the difference between success and expensive failure in applications where water quality is a problem
 are operational, it is critical that you maintain them properly.
This includes a regular program of backflushing and/or cleaning filters to keep contaminants out of your drip laterals.
Regular monitoring of pressure differentials across filters is important to indicate whether your backflushing program is adequate.
In addition, sand media should be replaced periodically as it becomes worn.
Check the owners' manual of your specific filter.
Algae, bacteria, and mineral deposits can build up inside of laterals and eventually plug emitters, even if a very high level of filtration is used.
The rate at which this occurs depends on your water source and climate.
In many cases, buildup of organic matter and minerals can be reduced or eliminated with regular injection of chlorine or acids, or both.
The best defense against buildup of algae and many types of bacteria is chlorine.
Chlorine is available in three forms: sodium hypochlorite , calcium hypochlorite , and gas chlorine.
Sodium hypochlorite and calcium hypochlorite are high in salts and must be used carefully with salt-sensitive plants or in soils that are already high in salt.
Gas chlorine is an extremely hazardous substance and must be contained and used with great care.
Use chlorine as follows:
 To control algae, iron bacteria, and sulfur, add chlorine until a concentration of 2-10 ppm free chlorine is achieved at the end of the furthest lateral from the injection point.
Maintain this level for 30-60 minutes.
This can be done once every two to three weeks or as frequently as after each irrigation cycle, depending on the chlorine concentration used and level of organic material in the irrigation water.
Alternatively, chlorine can be applied continuously to obtain concentrations of 0.5 to 1 ppm at the ends of the furthest lateral.
Use higher concentrations if the organic material content of the irrigation water is high.
Use higher concentrations of chlorine if the pH of the water is 7.5 or greater, or lower pH by injecting acid.
To eliminate severe algae growth, consider using a one-time "superchlorination" of up to 50 ppm for 4-6 hours at elevated pressure and pH below 6.5, followed by thorough flushing with clear water.
Chlorine is more effective at killing algae and bacteria when the pH of the water is 6.5 or lower.
Alkaline water should be acidified for effective chlorination.
NOTE: Always inject chlorine and other chemicals upstream of filters to avoid problems from chemical precipitation and to clean filter elements.
CAUTION: Inject acid and liquid chlorine through two different injection ports.
Mixing acid and chlorine in the same tank will release dangerous chlorine gas.
Acids and chlorine should never be mixed together.
It may be necessary to add acid to irrigation water to lower its pH to prevent the precipitation of calcium carbonate , calcium phosphatic compounds, or iron oxides  that can plug emitters.
In addition, low concentrations of acid can increase the effectiveness of chlorine in alkaline water.
The three acids generally used are sulfuric, muriatic, and phosphoric.
Extra care
 should be taken when using phosphoric acid because precipitation of minerals in the water can occur.
Care should also be take with muriatic acid, which is high in salt.
NOTE: When adding acids for extended periods of time  inject them downstream of filters to avoid corrosion of metal filter components.
Always perform a "jar test" before injecting chemicals into your system to ensure they do not precipitate when added to your irrigation water.
This is particularly important with acids that are injected downstream of any filtration.
NOTE: Some filters, such as stainless steel media filters, are specifically designed to resist corrosion from acids.
These filters are ideal because they allow acids to be injected upstream.
Consult your filter supplier.
NOTE: Some filter media materials can buffer back acids and reduce their effectiveness.
NOTE: Inject acid into the center of the mainline flow or into a mixing chamber to prevent it from damaging pipe walls before it becomes diluted in the irrigation water.
CAUTION: Never inject acid into aluminum pipe.
Injecting acids in high concentrations can sometimes correct problems that have occurred due to poor quality irrigation water or mismanagement of a drip system.
See Clearing Clogs if they Occur, below.
NOTE: Acid is heavier than water.
When high concentrations are added, it can "lay down" and remain in your drip system after injection is complete.
If high pH fertilizers are later added, precipitation can occur.
Even when a properly designed filtration system is used, fine silt and clay particles can get past the filters and settle in the laterals.
If they are allowed to build up, they can eventually plug emitters and damage the system.
In multiple year subsurface applications, the system should be run with the ends of the laterals open after each season, in order to flush these particles out.
In areas where water quality is a problem, lateral flushing may be required more often.
Systems using extremely dirty water may require flushing as often as every 2 weeks or even after each irrigation.
Paying extra attention to prevention of plugging is always less costly than having to replace an entire system once it becomes plugged.
Flush laterals by opening the ends and running the system until the discharge water runs clear.
Opening the ends is easier if removable end caps or flushing manifolds were specified in the design stage.
The flow velocity at the end of each lateral should be at least one foot per second  which is achieved with a flow rate of 1 GPM  at the end of each 5/8-in  lateral or 2 GPM  at the end of each 7/8-in lateral.
A rule of thumb that has been successfully used by many growers is that a stream of water should squirt 2 to 3 feet from the end of the lateral.
You can flush several laterals simultaneously as long as your water supply capacity is sufficient.
Clearing clogs if they occur
 You can almost always avoid emitter plugging through proper system design and maintenance.
In the event that plugging does occur, however, it is sometimes possible to dislodge or dissolve clogs by adding chemicals.
Injecting acids in higher concentrations can sometimes correct plugging problems caused by
 The Roberts Difference: The emitters of RO-DRIP drip tape incorporate a unique expandable flow channel  which provides a second line of defense against plugging during high-contaminant conditions.
If plugging occurs, increase the supply pressure to the maximum recommended pressure  for several minutes.
In most cases the channel will expand open to purge obstructions and restore flow.
Figure 5.2.
Open Laterals and a Flushing Manifold in Action
 algae and bacterial growth or mineral deposits.
High acid concentrations can also kill roots that have grown into lateral outlets.
Note: acid is very dangerous and extreme care must be taken.
Always add acid to water.
Never add water to acid.
When possible, have your chemical company mix acids for you.
Note: Many states require permits for the use and storage of concentrated acids.
Storage, labeling and safety equipment requirements are often specified by law.
Use the following procedure to correct plugging problems with acid.
Only use this procedure between crops.
Figure 5.3.
RO-DRIP's Expandable Flow Channel
 1.
Flush all mains, submains, and laterals with clear water before injecting acid.
2.
Inject sufficient sulfuric, phosphoric, or muriatic acid to achieve a pH below 4.0 for a period of 30-60 minutes.
3.
Leave the acid solution in the system for 24 hours.
4.
Increase the system pressure to the maximum pressure allowed for your drip tape for several minutes.
5.
Flush mains and submains first.
Close mains and submains and flush laterals.
6.
Run the system for one hour at elevated pressure.
7.
Repeat the procedure if plugging or contamination is severe.
Pests and small animal populations must be controlled.
Ants, crickets, wire worms, other insects, rodents, coyotes, and other small animals can cause severe damage to drip tape laterals.
Irrigating as soon as drip tape is buried can often reduce damage from wire worms by keeping the soil moist enough that they do not seek out the tape.
Injecting certain pesticides can also help reduce insect damage consult a pest control advisor.
Damage from larger pests such as coyotes is more difficult to avoid.
Often a bucket of water placed in the field for animals will help keep them away from the drip tape.
Burying drip tape can also reduce damage from animals.
If pests are present in the field, consult a pest control advisor before installing and using your drip system.
Laterals that are damaged by pests, equipment, or inexperienced field workers can be repaired by cutting out the damaged portions and splicing the ends together.
This can be done with twist-lock couplings or with polyethylene hose and wire ties, as described in INSTALLATION AND STARTUP: Splicing Laterals.
System Shut-Down Between Crops 
 When a drip system is shut down between crops, extra maintenance is required to kill the
 roots of the crop.
If the roots of the previous crop are not killed, they will seek the water remaining in the laterals and may plug emitters, making them unusable in the future.
In addition, laterals should be opened and thoroughly flushed at the end of each season.
If you plan to use your laterals for more than one crop, use the following procedure to shut down your subsurface drip irrigation system at the end of each season.
Follow the procedure whether the laterals are permanently installed or are to be removed and re-installed.
1.
As soon as the crop is no longer in production, inject a soil fumigant to kill roots around the drip tape to prevent root intrusion.
2.
If algae is present in the system, inject chlorine at a concentration of 50 ppm.
If algae and mineral deposits are both present, inject a concentration of acid that is sufficient to lower the pH to 4.0 at the ends of the laterals.
3.
Allow the chlorine or acid to remain in the system for 4-6 hours.
4.
Run the system for at least 1 hour with clear water.
5.
Open the ends of the laterals and flush the system thoroughly, or open the flushing valve if a flushing manifold is used.
6.
Close the ends of the laterals.
The successful use of your drip irrigation system for seed germination depends on your soil texture, soil structure, soil salinity, the depth of your laterals, the emitter spacing, and the preparation of your beds.
To germinate seeds, enough water must reach the surface for the individual seeds or plants to receive water.
In addition, salt buildup must be kept away from the seeds or plants.
Drip tape can generally be used to germinate seeds of salt-tolerant crops under the following conditions:
 The laterals are less than 8-in deep
 The emitter spacings are 12-in or less
 The soil is not excessively coarse or sandy
 Salinity is not a major problem
 The seedbed is uniform and clod free several inches deep
 Conditions are further improved if there is at least 6 in  of effective rainfall per year to leach salt away from the surface.
When using drip tape to germinate a crop, irrigate frequently enough and with adequate run times to assure that near field capacity conditions are maintained around the seed at all times.
Over irrigation, however, can lead to fungal disease and "damping-off" of seedlings.
If laterals are buried deeper than 8 in, emitter spacings are greater than 12 in, or the soil has a high sand content, water may not make it to the surface where it can be used by the seeds.
In these cases, sprinklers must be used for germination.
Even under ideal water movement conditions, some growers prefer sprinklers because of their physical impact that drives air out of the soil and results in favorable germinating conditions for some crops.
One of the principal advantages of drip irrigation is the direct access it provides to the root zone for injection of fertilizer and other chemicals.
This allows frequent, accurate, and economical application of nutrients to field crops-even those grown with mulch-throughout the growing season.
With proper monitoring and testing, drip irrigation allows you to quickly adjust nutrient levels with precision that is not possible with furrow or sprinkler irrigation.
Fertilizers are widely available in liquid form that can be directly injected into your drip
 irrigation system.
Many fertilizer dealers provide liquid fertilizer blends specifically for drip fertigation, which may include N, P, K and minor nutrients.
These blends can be region and/or crop specific.
While some fertilizer blends can be expensive, drip fertigation maximizes their benefits by applying them precisely and efficiently.
Most clear, liquid fertilizers can be injected directly into drip irrigation systems.
Only apply a fertilizer through your drip system after testing its compatibility with your local irrigation water.
Water Soluble Dry Fertilizers
 Non-liquid fertilizers must be mixed with water to form a solution before they are injected.
Dry fertilizers must be water-soluble, and it is necessary to consider how they will react with the minerals contained in your water or other fertilizers which are injected.
Only apply a fertilizer through your drip system after testing its compatibility with your local irrigation water.
NOTE: Some dry fertilizers, which are described as being water soluble, are coated with clay or wax to prevent clumping.
This coating material is not water-soluble and can plug filters and drip emitters.
It can be removed through a "decanting" process by thoroughly mixing the fertilizer with water and allowing it to settle for 12-18 hours.
Pour the clear solution through a 200-mesh screen taking care not to allow the sediment or precipitate to enter the system.
Figure 5.4 Jar Test
 Performing a simple test of your irrigation water and fertilizer mixture before injection can help you avoid the high cost of cleaning or replacing your drip system if precipitation occurs.
Perform a jar test as follows:
 1.
Fill a clear, 1-quart  glass container with your irrigation water and add an appropriate amount  of the fertilizer mixture you intend to apply through the drip system.
2.
Mix thoroughly and let it sit overnight.
3.
If the mixture is cloudy the next day, or if there is a precipitate in the jar, do not use the fertilizer.
It will plug filters and/or emitters.
Most nitrogen fertilizers are soluble in water and can be injected into drip systems with minimal problems.
Precipitation may occur, however, if they are mixed with other fertilizers.
For example, injecting both calcium nitrate and ammonium sulfate into the same irrigation water will result in an insoluble gypsum precipitate that can readily plug emitters.
In many cases, phosphorus is applied before planting.
Phosphorous is especially important for seed emergence and healthy transplant growth, and soluble phosphorus fertilizers can be expensive.
Growers often broadcast apply phosphorous before planting, then supplement it later in the season through drip fertigation.
Most dry phosphorus fertilizers for general farm use are insoluble and cannot be injected into irrigation water.
Applying soluble phosphorus fertilizers through drip fertigation is challenging because they often react with other nutrients to form precipitates that can clog emitters.
In particular, most phosphate fertilizers will form precipitates when injected into water containing calcium or magnesium.
Reducing the pH of the irrigation water through acidification or by using
 phosphoric acid can usually control precipitation.
White phosphoric acid can be safely injected into most irrigation water as long as the pH of the solution is low.
Soluble potassium is a positively charged ion that easily binds to negatively charged clay particles.
As a result, when it is applied from the surface, it usually only penetrates the top few inches where it can not always be used by the plants.
Subsurface drip irrigation can help solve this problem by delivering potassium directly to the active part of the root zone.
In some cases, foliar sprays of potassium are more effective.
All potassium fertilizers are water soluble, and precipitation problems are infrequent.
Minor nutrient availability to plants is highly pH dependent.
Metal micro-nutrients  become less soluble in high pH soils, while S, Mo, B, C and M become less soluble in low pH soils.
Chelated micro-nutrient metals are a convenient way of making metal ions available to the plant root zone.
Chelates are expensive, but they can be very effective both at delivering injected metal micro-nutrients to the plant root zone, and at making metal ions already resident in the soil available to plants.
The ability to utilize expensive fertilizers such as chelated metals as efficiently as possible is one of the many benefits of drip fertigation.
NOTE: Fertilizers containing calcium should be flushed from all tanks, pumps, filters and tubing prior to injecting any phosphorus, urea-ammonium nitrate, urea sulfuric fertilizer, or any sulfate form of fertilizer to avoid precipitation which can cause severe emitter plugging.
Always test the compatibility of fertilizers with each other and with your irrigation water before mixing them in your system.
Drip irrigation allows fertilizer to be applied as frequently as your plants need, even daily if necessary.
This flexibility allows you to quickly make adjustments to your fertigation program to respond to changes in your plant needs, and use expensive fertilizers as efficiently as possible.
Inject fertilizer during the latter part of the irrigation cycle to reduce the possibility of leaching some of it past the root zone.
However, be sure to operate the system long enough to completely purge fertilizer from the laterals to avoid algae and bacteria growth.
Plugging is likely to occur if algae and bacteria are allowed to grow and feed on the residual fertilizer left in the laterals.
The "travel time" required to transport chemicals to the end of a long  drip lateral can be up to 60 minutes depending on slope and flow rate.
Travel times through mainlines and submains must also be considered.
Several software packages are available which calculate travel time within laterals.
Consider using the "25% rule" of fertilizer injection.
During the first 25% of the irrigation cycle, only clear water is delivered through the laterals.
Fertilizer is injected for the next 50% of the cycle then clear water is again used for the final 25%.
Note: Always inject fertilizers into the water stream before the filter.
Note: Only inject fertilizer if a proper backflow prevention device has been installed upstream of the injector to prevent flow of fertilizer into the water source.
Drip fertigated fields require less fertilizer than those using sprinkler or furrow irrigation.
Fertilizer is only applied to the root zone, and used as efficiently as possible.
Drip fertigation allows you to optimally use your fertilizers by adjusting the application rates throughout the season as the needs of your plants change.
To take full advantage of this feature, you will need to know the nutrient levels of your soil and plants throughout the season to make the necessary
 The first step in determining which nutrients to apply and how much of each to apply is to have a soil test performed at the beginning of the season.
Use your drip system to make up the difference between what is available in the soil and what your plants need.
Additional information such as the soil pH, EC and base saturation will help you determine which fertilizers can be readily used by your plants when they are injected into the root zone, and what can be done to make existing nutrients more available.
Plant tissue tests can be performed throughout the season to determine the nutrient levels within your plants.
These tests are particularly useful because they directly indicate nutrient deficiencies that can be made up through fertigation.
"Quick Tests" for soil nutrient levels are now available and are becoming popular.
These tests can be used to monitor soil nutrient levels on-farm and use the information to immediately make adjustments to your fertigation program.
Many laboratories can now perform soil sample tests, tissue tests and/or sap tests with a one-day turnaround, also allowing you to make necessary adjustments exactly when they are needed.
In arid regions such as the western US, salinity management is important with all fruit and vegetable crops, and is critical with strawberries.
Depending on water quality and soil type, many other crops also require active salinity management, especially during germination.
With good management, the salinity of the soil solution can be 1.5 to 3 times the salinity of your irrigation water.
If salt is not managed properly, the salinity of the soil extract can reach levels that are lethal to plants.
Symptoms of Salinity Problems
 Salt is added to the soil during each irrigation.
Adding fertilizers can further increase salinity.
Excess salt must be removed from the root zone before it increases to a level that seriously affects yield.
Symptoms of excess salinity depend on the type of crop and the types of salts involved.
Mild salinity problems are frequently overlooked because the plant size reduction and change in color are uniform across the field.
Excess salinity initially causes a subtle change in color.
As salinity stress increases, stunting becomes apparent and leaves are eventually burned at the tip and around the edges.
It is important to recognize that yield loss from excess salinity occurs well before the symptoms are visible in your plants.
Patterns of Salt Buildup in the Soil
 Most salts are readily soluble and move with water in the soil.
The salt content of the root zone varies with depth and distance from the point in the soil where water is applied.
Salinity near the application point of irrigation water is usually low.
Salt builds up at the outer edges of the wetted area.
Figure 5.5 shows salt patterns caused by different lateral placements.
If the drip lateral is installed near the soil surface and the wetted area brings the soil near the surface and plant row to above field capacity, then the salt layer will move away from the seed line or plants.
If the lateral is placed deep enough so that the wetted
 Figure 5.5 Salt Patterns
 area does not reach the surface, salt can build up just under the surface of the soil.
During periods of light rain, deep subsurface drip systems for salt-sensitive crops must be left running to prevent the rain from leaching salts into the root zone.
If rain is heavy enough, salts will be leached below the root zone where they will not cause problems.
NOTE: Where salt buildup is a problem, a surface or shallow subsurface placement will give the best results.
Do not move drip laterals after water application has started on salt-sensitive crops.
Moving the laterals will cause the salt buildup to move.
If the salt buildup moves into the root zone, it will stress or even kill plants.
Also, do not allow the soil in the root zone to dry between irrigation cycles.
This can result in reverse movement of soil water, and transfer salt from the perimeter back into the rooted area of the soil.
To minimize salt buildup in the root zone, keep the wetted area at or near field capacity at all times.
For optimal salinity control, maintain a nearly continuous, slow downward movement of water and salts.
This requires more water than is necessary to maintain field capacity.
The additional water added to leach salts away from the root zone is commonly referred to as the leaching requirement and, in problem areas, can be as much as 10-20% of the total application rate.
Place drip laterals as close as possible to salt-sensitive plants to continuously leach salts outward from the root zone.
Monitor the soil salinity throughout the season to help maintain proper levels and avoid plant stress, which can easily go unobserved.
Flood or sprinkler irrigating between crops can be very effective in removing salts and, may be necessary, in some cases.
Apply excess water for leaching early in the season, since it may be difficult to apply adequate water during the peak of the irrigation season.
In many cases you can save money by irrigating more than one crop row with each lateral.
In multiple row beds, however, be careful not to place a row directly between two drip laterals.
The salts at the edge of the wetted pattern of each lateral can accumulate under the center row and can damage or kill salt-sensitive plants.
Figure 5.6 illustrates proper and improper methods of avoiding salt buildup when irrigating multiple rows with a lateral.
Figure 5.6 Proper and Improper Placement of Laterals for Multiple Rows
 Soil permeability is affected by texture, structure, organic material content and chemical content.
Good soil preparation and addition of organic amendments can reduce permeability problems caused by compaction.
Several permeability problems are caused by the quality of your irrigation water and can often be avoided through chemical water treatment or chemical soil amendments.
The first step in managing permeability is to have a chemical analysis of your irrigation water performed.
Table 5.10 shows how to manage certain water quality problems that can lead to problems with soil permeability.
Observe the following cautions when injecting gypsum into a drip irrigation system:
 Only inject high purity gypsum.
Only inject finely ground gypsum.
98% should pass through a 200-mesh screen.
Always locate the injector before filtration equipment.
Do not inject at excessively high rates that exceed the solubility limit of gypsum in water.
Table 5.10 Permeability Problems Caused by Poor Water Quality
 Water Quality Problem	Description	Possible Solutions
 As proportion of sodium attached to	Increase calcium content of water by
 clay particles increases, soil tends to	injecting gypsum
 High SARa resulting from high	"run together", resulting in reduced	If damage to soil is already done, soil
 Na/Ca ratio	water penetration rates.
In extreme	amendment with gypsum may be
 cases  soil can no longer be	required
 HCO3 removes calcium from the soil by	Reduce HCO3 in water by injecting sul-
 binding with it to form CaCO3 (calcium	furic acid, sulfur dioxide, or other acid
 High SARa resulting from high	carbonate).
The calcium removed from	If damage to soil is already done, soil
 bicarbonate  content	the soil complex is replaced with sodi-	amendment with sulfur or gypsum may
 um, and the soil becomes sodium-rich.
be required
 Interaction between the salinity of	Injecting or ammending with gypsum
 water and various ions has an effect on	can improve permeability of pure
 permeability.
Appendix B shows that	water both by increasing EC and by
 high SARa can cause more of a prob-	increasing calcium content
 Pure irrigation water	lem if EC is low.
Very pure (EC < 0.2
 dS/m) water can cause severe prob-
 lems even if there is a high proportion
 of calcium in the irrigation water.
Your drip irrigation system, or at least the laterals, will ultimately be retrieved from your field.
This may be after several years in a subsurface system, or after a single crop in a surface or shallow buried application.
In some cases the laterals may be retrieved and disposed of.
In other cases they may be re-installed in your field after being stored for a period of time.
Still in other cases, they may be moved to another location and re-installed.
The best method of retrieval depends on the specifics of your growing operation.
The choice is affected by cultural practices, drip lateral placement, residual crop material, soil moisture and economics.
This section helps you evaluate the important variables and decide whether to re-use or dispose of your drip tape after removing it from the field.
The basic procedures and equipment used for drip tape retrieval are also described for each method.
The best retrieval method for you depends on whether you will re-use or dispose of the drip tape after it is removed from the field.
If you plan to dispose of drip tape, it should be compacted and baled as tightly as possible.
The retrieval head is the main tool used for mechanized drip tape retrieval.
The two common retrieval methods are over-the-row retrieval using a tractor and end-of-row retrieval using a fixed retrieval head.
The most common problem encountered during retrieval is damage to the drip tape from stretching.
Ensure tape is free of entanglements, and water has been removed.
If possible, perform retrieval in the morning before the sun heats up the drip tape.
The following options are available at the end of the growing season:
 Retrieval and disposal of drip tape
 Retrieval and re-use of drip tape
 Leaving drip tape installed for the next season
 Retrieval and disposal is currently the most common method used, although the other options are becoming more popular.
The replacement cost of drip laterals, in combination with ever-increasing disposal costs, weigh in favor of using laterals for more than one season.
Multiple year installations, which are not retrieved and re-installed after each season, are usually buried deep below the surface  SO cultural operations can be performed without causing damage.
Table 6.1 summarizes the advantages and disadvantages of each option.
Table 6.1 Disposal VS.
Re-use of laterals
 Method	Advantages	Disadvantages	Notes
 Simple	Recurring cost of drip tape	Currently the most common
 Low-cost, thin-walled drip	Cost of disposal	use
 Single season	tape can be used	Environmental impact	Can be retrieved with or with-
 Re-using drip tape may save	Retrieval and re-	Proper maintenance is impor-
 Retrieve and re-use	money	installation can damage	tant
 Reduced disposal require-	tape	Requires a motorized
 Potential for very long-term	Requires heavy-gauge drip	Proper maintenance is
 Retrieval and re-	Between-crop cultural prac-
 Multi-season buried	installation is not	tices require more care
 necessary during most sea-
 Retrieval operations are faster and simpler if the drip tape is disposed of.
Stretching and other damage is not important as long it does not interfere with the retrieval.
In most cases, the drip tape must be disposed of in landfills, which are placing stricter requirements on what they will accept.
If you are retrieving drip tape onto spools, they should be compact and tightly wound.
If not, loose drip tape should be tightly baled and tied.
Many landfills will not accept loose drip tape because of the damage it causes to their equipment.
Drip tape is designed to last many years without degrading or decomposing.
Disposal issues are likely to become more important as landfill space becomes increasingly scarce.
Any steps that can be made to reduce this trend will have a long-term positive impact on the environment.
Several steps must be taken to ensure that drip tape intended for re-use is in good condition at the beginning of each season.
For best results when re-using drip tape, observe the following important guidelines:
 Follow a proper shutdown procedure  to ensure the drip tape is clean and free of roots, bacteria, and algae before it is removed from the ground.
Avoid jerking or excess tension while retrieving drip tape from the ground.
Any stretching of the drip tape will result in uneven flow rates and decreased distribution uniformity.
Always store drip tape in a dry, pest free, protected area.
Retrieval for re-use is a more delicate process than retrieval for disposal.
In general, it is easier to retrieve thicker-gauge drip tape without damage.
Use a great deal of care when retrieving any tape less than 10-mil thick.
When drip tape is retrieved for re-use it should be rolled onto a suitable spool.
Commercial plastic spools are available for retrieving drip tape.
Many growers choose to make their own spools by placing wood or metal side plates on the ends of a large-diameter section of PVC pipe, which acts as the core of the spool.
When the roll is full, the side plates can be removed and the drip tape can be stored on the PVC core.
When in-field splices are made, either for repairing damaged laterals or splicing rolls together, special consideration should be taken if the laterals will later be retrieved for re-use.
Twist-lock couplings are convenient for making splices, but will not easily go through retrieval equipment and will not roll smoothly on a retrieval spool.
Figure 6.1 Manual Retrieval of Drip Tape
 When making an in-field splice, use a piece of 0.510"x0.610" polyethylene hose and two wire ties as described in INSTALLATION AND STARTUP: Splicing Laterals.
Be sure to tightly wrap the wire ties around the spliced lateral and remove all sharp points so they will not hang up on installation equipment or damage the drip tape.
Wrap the splice with black electrical tape for further protection.
Alternatively, several heat-seal splicers are available now for drip-tape.
Surface and shallow buried  drip tape is easily retrieved for disposal without the use of mechanical equipment.
If the drip tape is to be re-used, it can be economically retrieved using an "end of row" operation as described below in Mechanized Retrieval.
To manually retrieve drip tape for disposal, simply pull it from the field and bale it together.
As described in the previous section, make the bales as tight as possible, and tie them together with string or drip tape for easy disposal.
Figure 6.2 Retrieval Head 
 The main tool used for mechanized drip tape extraction is the retrieval head.
The retrieval head consists of a driven shaft onto which the spool is mounted, and a guide to bring the drip tape to the spool.
A means of tension control is usually provided to avoid damage to the tape during momentary hang-ups or during rapid speed changes of the tractor.
Some retrieval heads incorporate a level-wind mechanism that places the drip tape evenly on the spool as it rolls These mechanisms make the roll more compact and easy to re-use.
Retrieval heads and complete retrieval systems are available from several
 The Roberts Difference: The RO-DRIP product line includes several heavygauge products with high tensile strength which are well-suited for retrieval and re-use.
These include products with wall thicknesses of 10, 13, and 15 mil.
suppliers.
Retrieval heads can either be mounted over-the-row on a tractor tool bar, or end-of-row where the head is stationary and the drip tape is pulled out of the row from one end after it has been picked up and placed on top of the crop.
Surface and Shallow Subsurface Drip Systems
 Surface and shallow subsurface  laterals are the simplest to remove, either for re-use or disposal.
When laterals are placed on the surface, either end-of-row or over-the-row techniques can be used.
End-of-row extraction is the most common method of retrieval due to several advantages, including
 End-of-row extraction is not limited by the speed of a tractor, so it can be done faster
 When multiple retrieval heads are used, if one head needs to be stopped for any reason, the others can continue operating
 Pulling the tape along the row provides cleaning and water removal action which results in less damage and better spooling
 After disconnecting the laterals from the manifolds, remove water by blowing them out with compressed air.
Pull the tape out using one or more retrieval heads mounted on a trailer at the end of the field.
If laterals are buried, they need to be manually removed from the ground before retrieval.
This is usually simple if the burial depth is less than 3 in.
In some cases it helps to soften the soil around the laterals by irrigating for a period of time before removal.
If the drip tape will be re-used, avoid stretching it or scraping it on rough soil or field stubble.
It sometimes helps to lift the drip tape off the ground and place it on top of the plants before retrieving it.
Several retrieval heads can be mounted on a single fixture to retrieve from several rows simultaneously.
Figure 6.3 End of Row Retrieval
 NOTE: The most common problem encountered during drip tape retrieval is damage from stretching.
Ensure tape is free of entanglements, and water has been removed.
In hot climates, if possible, perform retrieval in the morning before the sun heats up the drip tape.
TIP: If the spool is spinning faster than the tape appears to be coming off of the ground, the tape is stretching.
Another way to check for stretching is to stop the retrieval head and unlock the spool.
If it backspins, the tape is stretching.
Over-the-row extraction is not as common as end-of-row extraction, but it is sometimes the best choice when laterals are buried.
In over-the-row extraction, one or more retrieval heads are mounted to a tractor tool bar.
A system of guides brings the tape to the spool as it is pulled off the surface.
Over-the-row extraction is less prone to damaging the drip tape by stretching or scraping, but it can be more costly and time consuming than end-of-row extraction.
If the drip tape is buried less than 3-in deep, and is a suitably heavy gauge, it can usually be pulled through the soil.
In some cases it helps to soften the soil around the laterals by irrigating for a period of time before removal.
Figure 6.4 Over-the-Row Retrieval
 Deep subsurface drip laterals can be removed over-the-row by using an appropriate tool to open the bed above the tape.
Use a furrower or a disc-type opener to open the bed down to a depth of 2-3 in  above the lateral and pull the tape through the remaining soil in the same operation.
Retrieval is easier if the drip tape was installed accurately at the beginning of the season.
A reliable and consistent burial depth allows you to place the opening tool close to the buried lateral and minimize the amount of soil through which it must be pulled.
Retrieval is simpler if the soil above and around the laterals is loosened and softened beforehand.
If possible, turn the last crop and wait a few days for subsurface plant matter to decompose and soften.
Immediately before retrieval, soften the soil around the laterals by irrigating for a period of time.
Disrupt the bed on either side of the laterals with picks or chisels.
The following tables summarize the information that may be presented in your water quality report and give guidelines to help you interpret how it will affect your operations.
Table A.
1 Quantities Measured in Your Water Quality Analysis
 Determination	Symbol	Units1	Typical Range
 Electrical Conductivity	ECW	dS/m	0 3
 Total Dissolved Solids	TDS	ppm	0 2000
 Calcium	Ca++	me/l	0 20
 Magnesium	Mg++	me/l	0 5
 Sodium	Na+	me/l	0 40
 Carbonate	CO3++	me/l	0 0.1
 Bicarbonate	HCO3-	me/l	0 10
 Chloride	CI-	me/l	0 30
 Sulfate	SO4-	me/l	0 20
 Nitrate Nitrogen	NO3-N	ppm	0 10
 Ammonium Nitrogen	NH4-N	ppm	0 5
 Phosphate-Phosphorus	PO4-P	ppm	0-2
 Potassium	K+	ppm	0 2
 Boron	B	ppm	0 2
 Acidity	SAR	pH	6.0 8.5
 Sodium Adsorption Ratio	0 15
 1 dS/m = deciSiemen per meter  me/l = milliequivalent per liter
 2 NO3-N is nitrogen in the form of nitrate.
NH4-N is nitrogen in the form of ammonia.
Both may be reported as N.
3 SAR is calculated from the reported Na, Ca and Mg:
 Table A.2 Guidelines to Interpret Your Water Quality Report
 Restriction on Water Use
 SALINITY 
 ECW 	ECw 0 7.7	0.7 < ECw < 3.0	ECw> 3.0
 TDS 	TDS < 450	450 < TDS < 2000	TDS > 2000
 INFILTRATION 
 if SARa = 0-3	ECw>0.7	0.2 < ECW < 0.7	ECW <.2
 SARa = 3-6	ECw> 1.2	0.3 < ECW < 1.2	ECw <.3
 SARa = 6-12	ECw>1.9	0.5 < ECw < 1.9	ECw <.5
 SARa = 12-20	ECw>2.9	1.3 < ECW < 2.9	ECW 1.3
 SARa = 20-40	ECw>5.0	2.9 < ECW < 5.0	ECw 2 2.9
 ION TOXICITY 
 Sodium 	SAR 3	3 < SAR < 9	SAR 9
 Sodium 	me/ 3	3 < me/l < 9	me/l 9
 Chloride 	me/l <4	4 < me/l < 10	me/l > 10
 Boron 	ppm < 0.7	0.7 < ppm < 3	ppm > 3
 OTHER EFFECTS 
 Nitrogen, NO3-N 	ppm < 5	5 < ppm < 30	ppm > 30
 Bicarbonate, HCO3, me/l	me/l < 1.5	1.5 < me/l < 8.5	me/l > 8.5
 PH	Normal Range: 6.5 8.5
 1 High SARa accompanied with high ECW allows water penetration, but is unacceptable for production of salt-sensitive crops.
Table A.3 Guidelines for Potential Emitter Plugging from Water Contaminants
 Suspended solids	50 ppm	50-100 ppm	>100 ppm
 pH	7.0	7.0-8.0	>8.0
 Salt	500 ppm	500-2000 ppm	> 2000 ppm
 Manganese 1	0.1 ppm	0.1-1.5 ppm	> 1.5 ppm
 Total iron	1	0.2 ppm	0.2 1.5 ppm	> 1.5 ppm
 Hydrogen Sulfide	0.2 ppm	0.2 2.0 ppm	> 2.0 ppm
 Bacterial population	2,500/gal	2,500-13,000/gal	>13,000/gal
 1 When testing for iron and manganese, acidify
 There are many variables involved in specifying a drip irrigation system design, which can interact with each other in complex ways.
Coming up with the right combination of lateral placement, drip tape wall thickness, emitter spacing and flow rate is a complex process where experience plays an important role.
This appendix provides examples of how experienced growers have made design decisions for their specific crops.
Each page covers one crop, and gives a description of general practices for growing that crop with drip irrigation.
The description includes a specific example of how one experienced grower in one geographic region has grown that crop.
Due to differences in climate and soil type the best practice for your field may be different, but the examples can give you an idea of what is required.
It always helps to learn from the experience of others.
The crops described in this appendix are:
 All of the crops that are irrigated with drip tape could not possibly be included in this appendix.
If you do not find your crop listed above, contact Roberts Irrigation we may have it on file.
Onions are usually direct seeded on four row beds, spaced 42-in  between centers.
Rows are spaced 6 to 12-in  apart with 1 to 4-in  in-row spacing.
Spacing is closer and populations are higher for smaller bulbing varieties.
Onions are extremely shallow rooted and need an easily crumbled, medium texture soil that maintains moisture well.
Onions should never be stressed for water once bulbs start to enlarge, or splitting may result.
Avoid salty, hard, or weed-infested soils.
In the example below, the grower used a short row length of 328-ft.
Using RO-DRIP 8-12-24, good uniformity can be maintained with run lengths of up to 800-ft  on flat ground.
Crop fresh market onion Location Baja California, Mexico Field size 150-acres  Plants per acre 197,885  Season Feb-March Planting method direct seeded Soil type sandy loam Maximum ET.0.35 in  per day Water Source deep well Ground cover.none Crops rotated with broccoli, cauliflower Time to maturity 180 days Average yield.60 tons/acre  Duration of tape installation.6 months
 Primary filtration	sand separator
 Irrigation duration	4-10 hours
 Irrigation frequency	3-5 days
 Line flushing	at startup
 Drip Tape: RO-DRIP 8-12-24  
 Strawberry plants are extremely salt sensitive.
Strawberry production with relatively salty water is a remarkable success story that illustrates the ability of drip irrigation to manage salinity and meet the needs of row crops under adverse conditions.
Transplants are usually planted in the early fall, three or four rows per bed.
Beds are spaced 60 to 64-in  between centers, with two drip laterals per bed placed between rows.
In-row spacing of 9 to 10-in  is frequently used.
Polyethylene mulch is typically used to increase bed temperature and maintain winter growth.
Strawberry plants must be protected from frost.
Excessive salinity decreases root development, water uptake, growth rate, and fruit yield.
Where salts are a problem, it is important to leach with solid set sprinklers before bed preparation or after transplanting, and prior to putting plastic mulch over the beds.
Rain water can be helpful in decreasing salinity around plants during early growth, but only if the holes in the plastic near the plant are large enough to permit infiltration of the rain water.
Location	Central Coast, California, USA
 Field size	.40 acres 
 Plants per acre	150,000 
 Soil type	sandy loam
 Maximum ET	0.30 in  per day
 Crops rotated with	celery
 Time to maturity	.60 days
 Average yield	3,500-5,000 cartons/acre
 Duration of tape installation	9-10 months
 Primary filtration.sand media Secondary filtration screen Submains layflat Mulch plastic mulch
 Irrigation frequency 1-3 times per week Irrigation duration 2-4 hours Chemigation yes Fertigation.yes Line flushing 2-4 times per season Filter back-flushing automatic
 Melons are typically direct seeded 3 to 4-in  from the drip lateral in single rows at 12-in  in-row spacing with 60 to 84-in  between rows.
Watermelons will generally have an in-row spacing of 24 to 36-in  with 72 to 108-in  between rows.
Laterals are usually placed on or near the surface.
Two laterals placed 4 to 6-in  on either side of the seed line may be required in lighter soil if there is difficulty is achieving an adequate wetted area for deep-rooted melon crops.
Heavy watering late in the season can lead to soft, poor-quality melons.
This is especially true in heavier soils.
Irrigation, as a general rule, should be reduced to about one-half of ET  2 weeks before harvesting is expected to begin.
Continue reduced irrigation immediately after each harvest to support subsequent production.
The best time to begin reducing irrigation and the amount to cut back depends on soil type, rooting depth, total wetted area, and the usable water reserve in the soil.
Crop watermelons Location.North Central Florida, USA Field size 150 acres  Plants per acre 1,440  Season mid Feb end of June Planting method direct seeded Soil type sandy Maximum ET.0.35 in  per day Water Source well Ground cover.rye in off-season Crops rotated with.rye, peanuts Time to maturity 100 days Average yield 25 tons/acre  Duration of tape installation 1 year
 Irrigation duration	1-4 hours
 Filter back-flushing	based on well
 Iceberg and mixed lettuce are typically direct seeded on double-row 40 to 42-in  beds.
Rows are spaced 8 to 12-in  apart with a single drip lateral in between the plant rows, placed on or near the surface.
Seed is normally planted at 2 to 3-in  spacing using pelleted seed and precision planters.
Germinating lettuce in hot weather can lead to thermodormancy of the seed and irregular stands.
Keep the soil around the seed moist during warm weather germination to provide cooling, and start the germination process in the evening so the seed imbibes water during the coolest part of the day.
Plants are thinned to an in-row spacing of 8 to 12-in  depending on the type of leaf lettuce.
Plant spacing and fertilization can be varied to control head size.
Location	Baja California, Mexico
 Field size	90 acres  ha)
 Plants per acre	37,100 
 Planting method	direct seeded
 Soil type	sandy loam
 Maximum ET	0.35 in  per day
 Water Source	deep well
 Crops rotated with	broccoli, cauliflower
 Time to maturity	50-60 days
 Ave.
yield	500 boxes/acre 
 Duration of tape installation	.60 days
 Primary filtration	sand separator
 Irrigation frequency	3-5 days
 Irrigation duration	4-10 hours
 Line flushing	at startup
 Drip Tape: RO-DRIP 5-12-24  
 Celery is usually transplanted on single-row 24 to 30-in  beds or double-row 32 to 40-in  beds.
In double-row plantings rows are spaced 10 to 12-in  apart with a singe drip lateral on or near the surface between the plant rows.
Plants are spaced 7 to 10-in  apart within each row.
Celery is a biennial that normally produces foliar growth in the first year and seed stalks in the second year.
However, celery plants can form seed stalks  the first year if exposed to temperatures below 55F  for 7 days or longer.
Some varieties are more susceptible to bolting than others.
Celery planted early in the year in cooler climates is usually covered with plastic tunnels to increase daytime temperatures and prevent induction of bolting by low night temperatures.
Celery is a shallow-rooted crop; most roots are in the upper 18-in  of soil.
It is, therefore, very susceptible to drought.
Hot, dry periods without water reduce growth and may induce blackheart.
EXAMPLE: Celery Baja California, Mexico
 Crop celery Location Baja California, Mexico Field size 100 acres  Plants per acre 120,000  Season Mar-Apr/Sep-Oct Planting method direct seeded Soil type sandy loam Maximum ET 0.35 in  per day Water Source deep well Ground cover.none Crops rotated with Time to maturity 50-60 days Average yield.500 boxes/acre  Duration of tape installation.60 days
 Primary filtration	sand separator
 Irrigation frequency	1-3 days
 Irrigation duration	6-12 hours
 Line flushing	at startup
 Sugar cane is a 2-year crop in some parts of the world and a 1-year crop in others.
It is typically grown from a mechanically planted stalk every 48-in  in the row.
Rows are spaced in pairs 36-in  apart with the drip lateral in the center.
The pairs of rows are 72-in  apart, resulting in a between-lateral spacing of 108-in.
After a crop has been harvested and the ground prepared for the next crop, the soil is very dry.
With newly planted stalks, irrigate for 48 to 72 hours to wet the entire area between rows to a depth of 60-in.
After the first long irrigation, irrigate every other day.
Gradually increase the length of the irrigation cycle during the first 6 months.
After 6 months irrigate the cane for 24 hours every other day  until maturity.
Upon maturity, cease irrigation and begin harvesting when the sugar content is at its maximum.
In many areas, including Hawaii, phosphates are applied in granular form at planting time.
A typical granular fertilizer would be 10-30-10.
A typical liquid nitrogen fertilizer would be Ammonium Nitrate 32%.
Fertilizer is generally applied through the system only during the first 10 months.
This is necessary to build sugar content.
NPK and trace elements can also be applied through the drip irrigation system.
Some varieties of sugar cane are salt tolerant, and brackish water with up to 1500 ppm of total dissolved salts can be used for irrigation.
Sugar cane is also relatively drought-resistant; if you miss an irrigation cycle, you can usually apply extra water during the next cycle without much adverse effect.
Field size	10,400 acres 
 Plants per acre	27,000 
 Soil type	sandy loam
 Maximum ET	0.28 in  per day
 Water Source	deep well
 Crops rotated with	none
 Time to maturity	.30 days
 Average yield	46 tons/acre 
 Duration of tape installation	8 years
 Primary filtration	.sand media
 screen & sand separator
 Irrigation frequency	.3-4 days
 Irrigation duration	24 hours
 Potted flowers and other plants can be irrigated with drip tape either directly or with the use of a capillary mat.
For direct irrigation, lay heavy-gauge drip tape across pots or containers and secure it tightly at each end.
In some installations it is advantageous to string a wire over the containers and fasten the drip tape to the wire rather than laying it directly on the containers.
Install the drip tape with the outlets facing out to one side.
Alternatively, pots or containers can be placed on a capillary mat that is irrigated with drip tape.
The water moves laterally across the mat and is drawn up into the container as it is used by the plant.
In the following example the grower successfully uses RO-DRIP drip tape to irrigate potted flowers in a greenhouse.
EXAMPLE: Potted Flowers  Sacramento Valley, California, USA
 Crop mums  Location Sacramento Valley, California, USA Size.3.5 acres  Plants per acre 35,000  Season non-seasonal Planting method transplanted Soil type pot mix Water Source municipal Ground cover.none Crops rotated with.none Time to maturity.60 days Average yield 35,000/acre  Duration of tape installation 2 years
 Irrigation frequency	every 3 days
 Irrigation duration	15-30 min
 Line flushing	every crop
 Tomato transplants are typically planted on single-row beds spaced 60 to 72-in  center-to-center, with 18 to 20-in  in-row spacing.
Stakes are placed between every three or four plants.
Twine is tied to the stakes and around the tomato plants to support their heavy fruit crop.
Tomatoes can be grown on almost any moderately well-drained soil, from deep sand to clay loam.
The highest production is usually achieved from well-drained loamy soil types.
You can also use plastic mulch to achieve better control of soil conditions and produce higher yields.
In the following example the grower uses plastic mulch and RO-DRIP drip tape to successfully grow fresh market tomatoes.
Location	Coastal Virginia, USA
 Field size	.250 acres 
 Plants per acre	3630 
 Soil type	.sandy loam
 Maximum ET	0.3 in  per day
 Water Source	surface water pond
 Crops rotated with	soybeans
 Time to maturity	.80 90 days
 Average yield	.20 tons/acre 
 Duration of tape installation	5 months
 Primary filtration	.sand media
 Mulch	plastic, 60" X 1.25 mil
 Irrigation duration	1-3 hours
 Drip Tape: RO-DRIP 8-12-24  
 Potato production requires good water penetration and aeration.
The soil must also be worked properly for correct tuber formation and growth.
Potatoes are seeded on 34 to 40-in  single-row beds.
In-row plant spacing is regulated by the placement of the individual seed pieces.
Seed piece spacing ranges from 6 to 7-in  for the red varieties, and 8 to 12-in  for the White Rose and Russet varieties.
Proper irrigation scheduling is critical to maintain the root zone at the proper moisture level.
When stressed for water between cycles, potatoes tend to develop cracks and become "knobby" and rough.
When red varieties are water stressed they tend to develop poor color.
When exposed to soil moisture levels above field capacity for extended periods of time, potatoes frequently develop enlarged lenticels and root or tuber diseases.
Proper soil moisture during tuber development reduces the severity of scab and is usually adequate to control disease.
During tuber initiation and early tuber growth  maintain available soil moisture between field capacity and 20% depletion.
Avoid planting potatoes in fields with severe scab problems.
Crop sweet potatoes Location Central Valley, California, USA Field size 50 acres  Plants per acre 13,000  Season Apr-Oct Planting method transplant Soil type sandy to sandy loam Maximum ET 0.35 in  per day Water Source well Ground cover.fallow with grain Crops rotated with.2-3 yrs, melons/grain Time to maturity 90-150 days Ave.
yield 11-25 tons/acre  Duration of tape installation 1 year
 Primary filtration	sand media
 Irrigation duration	4-6 hours
 Cotton is a deep-rooted crop  with a 6 to 8 month growing season.
Cotton is typically planted in beds spaced 30 to 40-in  apart.
Seeds are typically planted 3 to 4-in  apart in single rows.
A carefully managed drip irrigation system will allow you to grow cotton using saline water.
However, the seeds should be germinated and the stand established using water of at least average quality.
After the stand is established, poor quality water  can be used until maturity.
After harvest, the salt must be leached from the soil before planting the next crop.
If there is inadequate rainfall to accomplish leaching, a heavy flood or sprinkler irrigation will be required.
When using salty water, lay drip tape on or near the surface to keep buildup away from the plants.
With higher quality water, the laterals can be buried up to 18-in  deep and, on heavy soil, can be spaced up to 80-in  apart.
On sandy soils, space the laterals 40-in  apart.
When using a deep buried drip system, it is necessary to use a supplemental irrigation system to germinate.
Cotton should not be grown for more than 2 to 3 years on the same land without rotating in another crop such as wheat, sugar beets, process tomatoes, or melons.
Drip irrigation can increase yields with all crops and, since you can use the same drip system with successive crops, a well-planned system will allow you to offset the initial installation cost.
Location	Central Texas, USA
 Field size	100 acres 
 Plants per acre	19,000 
 Planting method	direct seeded
 Soil type	silt clay loam
 Maximum ET	.0.35 in  per day
 Ground cover	winter wheat
 Crops rotated with	.none
 Average yield	2.25 bales/acre
 Duration of tape installation	multi-year
 Primary filtration	.sand media
 Irrigation frequency 1-2 times per week Irrigation duration.4 hours Chemigation yes Fertigation yes Line flushing.3 times per year Filter back-flushing automatic
 Corn is typically seeded on 30-in  row spacings with 6 to 10-in  in-row spacing.
One drip lateral is placed between every other pair of rows, resulting in a 60-in spacing between laterals.
Twelve-inch emitter spacings are common, at either 15 or 24 GPH per 100-ft.
Since RO-DRIP XL drip tape can deliver good uniformity on runs up to mile long, it is often used in grain applications where large filed sizes are common.
Drip irrigation is becoming a method of choice in applications such as corn, which have traditionally been served by center pivots.
Center pivot irrigation cannot provide the same per-acre yield or complete utilization of rectangular fields that is possible drip irrigation.
In fields where there is already a significant investment in center pivot hardware, yield can be increased by using drip tape to irrigate the corners.
Crop.corn Location Kansas, USA Field size 80 acres Plants per acre 28,000 Season Spring Planting method direct seeded Soil type clay loam Maximum ET 0.4 in per day Water Source well Ground cover none Crops rotated with soybeans Time to maturity 120 days Ave.
yield 200 bushels/acre  Duration of tape installation 5+ years
 Irrigation frequency	.3 days
 Irrigation duration	16 hours
 Outside field flowers are usually grown in single or double rows either on level ground or in beds.
The most commonly used tape is 8-mil wall thickness with 8-in emitter spacing.
Cut flowers are grown in greenhouses on multiple-row beds.
Use three laterals for a typical 36 to 48-in  bed in a greenhouse.
For a single or double row of flowers, or for outside bulbs, use a single lateral with an 8 or 10-mil wall thickness and an 8-in emitter spacing.
EXAMPLE: Field Flowers Central Coast, California, USA
 Crop field flowers Location Central Coast, California, USA Field size 50 acres  Plants per acre 175,000  Season.year round Planting method direct seeded and transplanted Soil type clay to clay-loam Maximum ET 30 in  per day Water Source well Ground cover none Crops rotated with none Time to maturity 20-60 days Average yield depends on market Duration of tape installation.3-6 months
 Primary filtration.sand media filters Secondary filtration.none Submains layflat Mulch.none
 Irrigation frequency 1-3 times per week Irrigation duration 1-2 hours Chemigation fungicides Fertigation yes Line flushing monthly Filter back-flushing automatic
 Peppers are a warm-season crop.
Pepper plants can be injured or killed by frost and grow best in soil temperatures above 65F  and in air temperatures of 70 to 80F.
Transplanted peppers root only to a depth of about 2-ft , but use soil moisture efficiently.
Young pepper plants are relatively resistant to water stress but may show slower development and reduced yields.
Peppers are usually transplanted in single rows on 36-in  beds with 12-in  in-row spacing; or on 72-in  beds with double rows spaced 12 to 18-in  apart and staggered on either side of the drip lateral, with 12 to 18-in  in-row spacing.
Plastic mulch in combination with drip irrigation can be used to increase yields.
EXAMPLE: Peppers Pennsylvania, USA
 Crop peppers Location Pennsylvania, USA Field size 25 acres 10 ha) Plants per acre 12,000  Season.summer Planting method transplant Soil type silty loam Maximum ET 0.30 in  per day Water Source deep well Ground cover plastic mulch Crops rotated with cabbage, corn, tomato Time to maturity.60 days Average yield.
22.5 tons/acre  Duration of tape installation 120 days
 Primary filtration	screen filter
 Irrigation frequency	1-2 times per week
 Irrigation duration	4-6 hours
 Drip Tape: RO-DRIP 8-12-24  
 COEFFICIENT OF VARIATION AND EMITTER DISCHARGE EXPONENT
 If you randomly select several emitters from a section of drip tape, apply the same water pressure to each, and measure the discharge rate from each, the Coefficient of Variation  is a measure of how consistent the results will be.
If the emitters were manufactured with a high precision production process and good quality control, the discharge rates of all of the emitters will be nearly identical and the Cv will be low.
On the other hand, emitters made from a poor design, an inconsistent manufacturing process, or with little or no quality control will have wide variations in discharge rate and a high Cv.
Cv can be calculated by measuring the discharge rate from each emitter in a sample of drip tape , then using the following formula:
 where Sq is the standard deviation of the discharge rates measured in the sample, and q is the average discharge rate of the sample.
Most drip tape manufacturers publish the Cv of their products.
Several independent labs also test Cvs, and compare them among manufacturers.
A perfect manufacturing process is impossible, so emitters with zero Cv  do not exist.
However, since good Distribution Uniformity is impossible if emitter flow rates are not consistent, you should select a drip tape with a low Cv.
Table C1 gives an idea of Cv values you can expect and what they mean.
Table C1 Emitter Cv Values and their Classification
 *As designated by American Society of Agricultural Engineers ASAE EP405.1 DEC94
 The Roberts Difference: RO-DRIP is manufactured with an advanced, highprecision process which results in an emitter coefficient of variation of 0.03 or lower.
This translates to better distribution uniformity and higher irrigation efficiency in your field.
It is important to realize that the Cv values published by manufacturers are for new product; and that long-term performance of your installed drip system can be as much affected by how well the emitters resist plugging as by the Cv.
Emitter discharge exponent :
 When a drip tape emitter is operating at its recommended pressure, it generally discharges water at its published rate.
If you increase pressure from that point, the discharge rate will increase.
If you decrease pressure, the discharge rate will decrease.
The quality of the emitter determines how much the discharge rate changes in response to pressure changes.
The Discharge Exponent  of an emitter is a measure of how much its discharge rate varies as supply pressure varies.
An X of 1 means that the discharge rate varies directly with pressure.
A low X means that the discharge rate does not vary greatly when pressure varies.
Most high-quality drip tape products have X values in the range of 0.4 to 0.7.
Some lower-quality products have X values greater than 1.
The discharge exponent of a drip emitter can be calculated by measuring its discharge rate at two different pressures.
The equation which relates pressure to discharge rate for a drip emitter is
 where Pis the pressure applied to the emitter, q is the discharge rate, X is the discharge exponent and K is a constant.
By measuring discharge rates at two different pressures, you can calculate the exponent as follows:
 where q1 is the discharge rate measured at pressure P1 and q2 is the discharge rate measured at pressure P2.
Most drip tape manufacturers publish the discharge exponent of their products.
Several independent labs also test discharge exponents, and compare them among manufacturers.
This user guide tells you how to design your drip system to have minimal pressure variations from elevation changes and friction losses.
Even a well-designed system, however, can have higher pressures in some parts of the field than in others.
If you select a drip tape product with a low X value, you can avoid the problems of higher discharge rates in some parts of the field than in others and low distribution uniformity.
Following are sample performance charts for three RO-DRIP products, XX-12-24 , XX-24-17 and XX-12-24 XL.
The "XX" term denotes the wall thickness, and can be 5, 8, 10, 13 or 15 mil.
For a complete set of performance charts for all RO-DRIP products, see the Roberts Irrigation Products publication RO-DRIP PERFORMANCE DATA.
Table D.1 Sample Performance Charts
 Maximum Run Length, feet
 RO-DRIP XX-12-24	RO-DRIP XX-24-17	RO-DRIP XX-12-24 XL
 Cv 0.03	q=0.40	Cv 0.03	q=0.28	Cv = 0.03	q = 0.40
 X 0.52	X 0.52	k=115311	X = 0.52	k x =.081396
 Slope	Inlet Pressure psi	Inlet Pressure psi	Inlet Pressure psi
 EU	6	8	10	12	EU	6	8	10	12	EU	6	8	10	12
 80%	1078	1088	1088	1081	80%	1335	1355	1363 1366	80%	1830	1896	1928	1939
 -1.5%	85%	936	941	939	930	85%	1153	1177	1183	1178	85%	1551	1632	1664	1677
 90%	735	754	754	750	90%	872	935	947	944	90%	304	1240	1306	1333
 80%	1076	1069	1056	1044	80%	1349	1349	1339	1328	80%	1871	1895	1898	1894
 -1.0%J	85%	929	921	907	898	85%	1169	1167	1157	1143	85%	1615	1640	1643	1634
 90%	747	740	731	720	90%	940	939	934	917	90%	1260	1308	1313	1311
 80%	1022	1001	986	973	80%	1298	1273	1256	1239	80%	1805	1788	1766	1749
 -0.5%J	85%	877	857	845	833	85%	1119	1092	1077	1063	85%	1557	1534	1514	1499
 90%	701	686	676	662	90%	900	872	856	846	90% 1248 1227 1211 1193
 80%	834	843	850	852	80%	1039	1052	1057	1063	80%	1370	1393	1412	1430
 0.0%	85%	717	721	729	734	85%	897	902	905	911	85%	1172	1192	1209	1222
 90%	566	574	577	578	90%	708	713	717	724	90%	920	938	949	959
 80%	605	656	689	716	80%	702	771	823	857	80%	831	939	1018	1078
 +0.5%1	85%	510	556	586	610	85%	591	655	700	729	85%	682	784	854	909
 90%	379	419	445	471	90%	431	489	531	556	90%	477	564	621	675
 80%	465	530	577	614	80%	514	600	667	715	80%	560	678	773	851
 +1.0%1	85%	382	441	486	519	85%	413	494	551	601	85%	441	548	627	699
 90%	264	315	354	380	90%	281	346	403	436	90%	287	367	428	484
 Cv = coefficient of variation q = discharge rate, GPM/100' ; X = emitter exponent ; k = flow constant ; required filtration: 140 mesh.
LENGTH, APPLICATION RATES, AND FLOW RATES
 The tables in this appendix summarize the results of the equations given in DESIGN: Lateral Design for several drip tape flow rates and lateral spacings.
Lateral spacings and flow rates must be specified for an application rate sufficient to meet irrigation requirements during peak ET  without exceeding the capacity of the water supply.
Table E.1 Length and Flow Rate Requirements, US Units
 Drip Tape Flow Rate per 100 ft at 8 PSI
 Between	Drip Tape	40 GPH	24 GPH	20 GPH	17 GPH	15 GPH
 Laterals		per Acre		.67 GPM	.40 GPM	.33 GPM	.28 GPM	.25 GPM
 GPM Required per Acre
 30	17,424	117	70	58	49	44
 32	16,335	109	65	54	46	41
 34	15,374	103	62	51	43	38
 36	14,520	97	58	48	41	36
 38	13,756	92	55	45	39	34
 40	13,068	88	52	43	37	33
 42	12,446	83	50	41	35	31
 44	11,880	80	48	40	33	30
 46	11,363	76	46	28	32	28
 48	10,890	73	44	36	31	27
 54	9,680	65	39	32	27	24
 60	8,712	58	35	29	24	22
 66	7,920	53	32	26	22	20
 72	7,260	49	29	24	20	18
 84	6,223	42	25	21	17	16
 96	5,445	37	22	18	15	14
 120	4,356	29	17	14	12	11
 Table E.2 Length and Application Rates, US Units
 Drip Tape Flow Rate per 100 ft at 8 PSI
 Between	Drip Tape	40 GPH	24 GPH	20 GPH	17 GPH	15 GPH
 Laterals		per Acre		.67 GPM	.40 GPM	.33 GPM	.28 GPM	.25 GPM
 Application Rate 
 30	17,424	0.258	0.155	0.131	0.108	.096
 32	16,335	0.242	0.145	0.123	0.101	.090
 34	15,374	0.228	0.136	0.115	0.095	.085
 36	14,520	0.215	0.129	0.109	0.090	.080
 38	13,756	0.204	0.122	0.103	0.085	.076
 40	13,068	0.193	0.116	0.098	0.081	.072
 42	12,446	0.184	0.110	0.093	0.077	.069
 44	11,880	0.176	0.105	0.089	0.074	.066
 46	11,363	0.168	0.101	0.085	0.070	.063
 48	10,890	0.161	0.093	0.082	0.067	.060
 54	9,680	0.143	0.086	0.073	0.060	.054
 60	8,712	0.129	0.074	0.065	0.054	.048
 66	7,920	0.117	0.070	0.059	0.049	.044
 72	7,260	0.107	0.064	0.055	0.045	.040
 84	6,223	0.092	0.055	0.047	0.039	.034
 96	5,445	0.081	0.048	0.042	0.034	.030
 120	4,356	0.064	0.039	0.033	0.027	.024
 Table E.3 Length and Flow Rate Requirements, Metric Units
 Drip Tape Flow Rate per 100 m at.55 bar
 Between	Drip Tape	497 LPH	298 LPH	248 LPH	211 LPH	186 LPH
 Laterals		per Acre		8.3 LPM	5.0 LPM	4.1 LPM	3.5 LPM	3.1 LPM
 M3/hr Required per Acre
 80	12,500	62	38	31	26	23
 90	11,110	55	33	27	23	21
 100	10,000	50	30	25	21	19
 110	9,090	45	27	22	19	17
 120	8,333	42	25	21	18	16
 130	7,692	38	23	19	16	14
 140	7,143	36	21	18	15	13
 150	6,667	33	20	16	14	12
 160	6,250	31	19	15	13	12
 170	5,882	29	18	15	12	11
 180	5,556	28	17	14	12	10
 190	5,263	26	16	13	11	10
 200	5,000	25	15	12	11	9
 210	4,762	24	14	12	10	9
 220	4,546	23	14	11	10	9
 230	4,348	22	13	11	9	8
 240	4,167	21	13	10	9	8
 Table E.4 Length and Application Rates, Metric Units
 Drip Tape Flow Rate per 100 m at.55 bar
 Between	Drip Tape	497 LPH	298 LPH	248 LPH	211 LPH	186 LPH
 Laterals		per Acre		8.3 LPM	5.0 LPM	4.1 LPM	3.5 LPM	3.1 LPM
 Application Rate 
 80	12,500	6.25	3.75	3.12	2.61	2.30
 90	11,110	5.55	3.31	2.77	2.34	2.06
 100	10,000	5.00	2.98	2.50	2.11	4.86
 110	9,090	4.54	2.71	2.27	1.91	1.68
 120	8,333	4.16	2.48	2.08	1.76	1.55
 130	7,692	3.84	2.29	1.92	1.62	1.43
 140	7,143	3.57	2.13	1.78	1.51	1.33
 150	6,667	3.33	1.99	1.66	1.41	1.24
 160	6,250	3.12	1.86	1.56	1.32	1.16
 170	5,882	2.94	1.72	1.47	1.24	1.09
 180	5,556	2.77	1.66	1.38	1.17	1.03
 190	5,263	2.63	1.57	1.31	1.11	0.99
 200	5,000	2.50	1.49	1.25	1.06	0.93
 210	4,762	2.38	1.42	1.19	1.01	0.89
 220	4,546	2.27	1.35	1.13	0.96	0.85
 230	4,348	2.17	1.30	1.08	0.92	0.81
 240	4,167	2.08	1.24	1.04	0.88	0.78
 APPENDIX F ENGINEERING CONVERSION FACTORS
 To Convert	To	Multiply by	To Convert	To	Multiply by
 Miles	inches	63,360	kilometers	meters	1,000
 miles	feet	5,280	kilometers	feet	3,280.8
 miles	yards	1,760	kilometers	yards	1,093.6
 miles	nautical miles	0.87	kilometers	miles	0.6214
 miles	meters	1,609.34	kilometers	nautical miles	0.54
 miles	kilometers	1.609	meters	centimeters	100
 feet	meters	0.3048	meters	inches	39.37
 feet	centimeters	30.48	meters	feet	3.281
 inches	centimeters	2.54	meters	yards	1.094
 inches	millimeters	25.4	centimeters	inches	0.3937
 inches	mils	1,000	millimeters	inches	0.03937
 mils	microns	25.4	millimeters	microns	1,000
 To Convert	To	Multiply by	To Convert	To	Multiply by
 sq miles	acres	640	sq kilometers	hectares	100
 sq miles	hectares	259	sq kilometers	acres	247.1
 sq miles	sq kilometers	2.59	sq kilometers	sq miles	0.3861
 acres	sq feet	43560	hectares	sq meters	10,000
 acres	sq yards	4840	hectares	acres	2.471
 acres	hectares	0.4047	sq meters	sq centimeters	10,000
 sq feet	sq inches	144	sq meters	sq feet	10.764
 sq feet	sq yards	0.111	sq centimeters	sq inches	0.1549
 sq feet	sq meters	0.0929
 sq inches	sq centimeters	6.452
 APPENDIX F ENGINEERING CONVERSION FACTORS
 To Convert	To	Multiply by	To Convert	To	Multiply by
 Acre Feet	Gallons	325851	Cubic Meters	Liters	1000
 Acre Inches	Cubic Feet	3630	Cubic Meters	Gallons	264.2
 Cubic Yards	Cubic Meters	0.765	Cubic Meters	Cubic Feet	35.32
 Cubic Yards	Liters	769	Cubic Meters	Cubic Yards	1.308
 Cubic Yards	Cubic Feet	27	Liters	cubic Meters	0.001
 Cubic Yards	Cubic Inches	46656	Liters	Cubic Yards	0.0013
 Cubic Yards	Gallons	200	Liters	Cubic Feet	0.035
 Cubic Feet	Gallons	7.48	Liters	Gallons	0.264
 Cubic Feet	Cubic Inches	1728	Liters	Cups	4.22
 Cubic Feet	Cubic Yards	0.037	Liters	Quarts	1.057
 Cubic Feet	Cubic Centimeters	28317	Liters	Pints	2.11
 Cubic Feet	Cubic Meters	0.0283	Liters	Cubic Inches	61
 Cubic Feet	Liters	28.32	Liters	Cubic Centimeters	1000
 Cubic Feet	Acre Inches	0.000275	Cubic Centimeters	Cubic Feet	3.53x10-5
 Cubic Feet	Acre Feet	0.0000230	Cubic Centimeters	Gallons	0.000264
 Gallons	Acre Feet	0.00000307	Cubic Centimeters	Pints	0.00211
 Gallons	Cubic Feet	0.134	Cubic Centimeters	Cubic Millimeters	1000
 Gallons	Cubic Inches	231	Cubic Centimeters	Cubic Inches	0.061
 Gallons	Cubic Yards	0.005	Cubic Centimeters	Liters	0.001
 Gallons	Cubic Centimeters	3785	Cubic Centimeters	Quarts	0.0011
 Gallons	Cubic Meters	0.0038	Cubic Centimeters	Ounces	0.0338
 Gallons	Liters	3.785	Cubic Centimeters	Tablespoons	0.067
 Gallons	Quarts	4	Cubic Centimeters	Fluid Ounces	0.0333
 Gallons	Pints	8	Cubic Millimeters	Cubic Centimeters	0.001
 Quarts	Cubic Centimeters	946.4
 Quarts	Cubic Inches	57.75
 Pints	Cubic Centimeters	473.2
 Pints	Cubic Inches	28.88
 Cubic Inches	Cubic Feet	0.00058
 Cubic Inches	Cubic Yards	2.14x10-5
 Cubic Inches	Cubic Centimeters	16.4
 Cubic Inches	Gallons	0.00433
 Cubic Inches	Liters	0.0164
 Cubic Inches	Quarts	0.0173
 Cubic Inches	Pints	0.0346
 Fluid Ounces	US Gallons	0.00781
 Fluid Ounces	Pints	0.0625
 Fluid Ounces	Cubic Centimeters	30
 Tablespoons	Cubic Centimeters	15
 To Convert	To	Multiply by	To Convert	To	Multiply by
 Ounces	Grams	28.35	Grams	Ounces	0.0353
 Ounces	Pounds	0.0625	Grams	Pounds	0.0022
 Ounces	Kilograms	0.0284	Grams	Kilograms	0.001
 Pounds	Grams	453.6	Kilograms	Grams	1000
 Pounds	Ounces	16	Kilograms	Ounces	35.21
 Pounds	Kilograms	0.454	Kilograms	Pounds	2.205
 Pounds	Tons 	0.0005	Kilograms	Tons	0.0011
 Pounds	Tons 	0.00045	Kilograms	Metric Tons	0.001
 Pounds	Metric Tons	0.000454	Metric Tons	Kilograms	1000
 Tons 	Tons 	0.907	Metric Tons	Pounds	2205
 Tons 	Tons 	0.893	Metric Tons	Tons 	0.984
 Tons 	Kilograms	907.2	Metric Tons	Tons 	1.1
 Tons 	Pounds	2000
 Tons 	Metric Tons	1.02
 Tons 	Tons 	1.12
 Tons 	Pounds	2240
 To Convert	To	Multiply by	To Convert	To	Multiply by
 Metric Tons per Hectare	US Tons per Acre	0.446	US Tons per Acre	Metric Tons per Hectare	2.24
 Kilograms per Hectare	Pounds per Acre	0.892	Pounds per Acre	Kilograms per Hectare	1.12
 Cubic Meters per Hecare	Bushels per Acre	11.48	Bushels per Acre	Cubic Meters per Hectare	0.087
 To Convert	To	Multiply	by	To Convert	To	Multiply	by
 Acre Inches per 24 Hours	Gallons per Minute	18.86	Cubic Meters per Hour	Liters per Second	0.278
 Cubic Feet per Second	Gallons per Minute	448.8	Cubic Meters per Second	Cubic Feet per Second	35.31
 Cubic Feet per Second	Acre-in per Hour 	1	Cubic Meters per Second	Gallons per Minute	15850
 Cubic Feet per Second	Acre-Ft per Day 	2	Liters per Minute	Cubic Feet per Second	5.89x10-4
 Cubic Feet per Second	Liters per Second	28.32	Liters per Minute	Cubic Gallons per Second	4.40x10-3
 Cubic Feet per Second	Liters per Minute	1699	Liters per Minute	British Gallons per Minute	13.2
 Cubic Feet per Second	Cubic Meters per Second	0.0283	Liters per Second	Cubic Meters per Hour	3.6
 Gallons per Minute	Cubic Meters per Second	6.39x10-5	Liters per Second	Cubic Feet per Second	0.0353
 Gallons per Minute	Liters per Second	0.0631	Liters per Second	Gallons per Minute	15.85
 Gallons per Minute	Cubic Feet per Second	0.00223
 Gallons per Minute	Acre Inches per 24 Hours	0.053
 Gallons per Second	Liters per Minute	0.0631
 British Gallons per Minute	Liters per Minute	0.0757
 APPENDIX F ENGINEERING CONVERSION FACTORS
 To Convert	To	Multiply	by	To Convert	To	Multiply	by
 Miles per Hour	Feet per Second	1.467	Kilometers per Hour	Feet per Minute	54.68
 Miles per Hour	Feet per Minute	88	Kilometers per Hour	Feet per Second	0.91
 Miles per Hour	Meters per Second	0.447	Kilometers per Hour	Meters per Second	0.28
 Miles per Hour	Centimeters per Second	44.7	Kilometers per Minute	Meters per Second	16.67
 Miles per Hour	Meters per Minute	27.0	Meters per Minute	Miles per Hour	0.037
 Miles per Minute	Feet per Minute	5280	Meters per Second	Kilometers per Hour	3.6
 Miles per Minute	Meters per Second	26.82	Meters per Second	Kilometers per Minute	0.06
 Miles per Minute	Centimeters per Second	2682	Meters per Second	Miles per Hour	2.237
 Feet per Minute	Kilometers per Hour	0.0183	Meters per Second	Miles per Minute	0.037
 Feet per Minute	Meters per Second	0.00508	Meters per Second	Feet per Minute	196.8
 Feet per Minute	Miles per Hour	0.0114	Meters per Second	Feet per Second	3.281
 Feet per Minute	Miles per Minute	0.000189	Centimeters per Second	Miles per Hour	0.0224
 Feet per Second	Meters per Second	0.305	Centimeters per Second	Miles per Minute	0.000373
 Feet per Second	Miles per Hour	0.68
 Feet per Second	Kilometers per Hour	1.10
 Feet per Second	Miles per Minute	0.0114
 To Convert	To	Multiply	by	To Convert	To	Multiply	by
 Pounds per Square Inch	Kg per Square Meter	703.1	Atmospheres	Pounds per Square Inch	14.7
 Pounds per Square Inch	Bar	0.0689	Atmospheres	Inches of Mercury	29.9
 Pounds per Square Inch	Atmosphere	0.068	Atmospheres	Feet of Water	33.9
 Pounds per Square Inch	Pounds per Square Foot	144	Atmospheres	Bar	0.9869
 Pounds per Square Inch	Feet of Water	2.31	Bar	Pounds per Square Inch	14.5
 Pounds per Square Inch	Inches of Mercury	2.036	Bar	Atmosphere at Sea Level	1.013
 Pounds per Square Inch	Inches of Water 	27.68	Kg per Square Meter	Inches of Mercury	0.0029
 Pounds per Square Foot	Pounds per Square Inch	0.00694	Kg per Square Meter	Pounds per Square Foot	0.2048
 Pounds per Square Foot	Kg per Square Meter	4.88	Kg per Square Meter	Pounds per Square Inch	0.00142
 Inches of Mercury	Atmosphere at Sea Level	0.0334
 Inches of Mercury	Kg per Square Meter	345.3
 Inches of Mercury	Feet of Water	1.13
 Inches of Mercury	Inches of Water 	13.60
 Inches of Mercury	Pounds per Square Inch	0.491
 Feet of Water	Inches of Mercury	0.883
 Feet of Water	Pounds per Square Inch	0.4335
 Feet of Water	Atmosphere at Sea Level	0.0295
 Inches of Water 	Inches of Mercury	0.0736
 Inches of Water 	Pounds per Square Inch	0.0361
 APPENDIX F ENGINEERING CONVERSION FACTORS
 To Convert	To	Multiply	by	To Convert	To	Multiply	by
 Horsepower	Foot-Pounds per Second	550	Calories per Second	Horsepower	0.0056
 Horsepower	Watts	745.7	Calories per Second	Kilowatts	0.00419
 Horsepower	Kilowatts	0.7457	Watts	Kilowatts	0.001
 Horsepower	Calories per Second	178.1	Watts	Horsepower	0.00134
 Foot-Pounds per Second	Kilowatts	0.000738	Kilowatts	Watts	1000
 Foot-Pounds per Second	Horsepower	0.00182	Kilowatts	Foot-Pounds per Second	1356
 Foot-Pounds	Calories	0.3239	Kilowatts	Calories per Second	238.9
 Foot-Pounds	BTUs	0.00129	Kilowatts	Horsepower	1.341
 Foot-Pounds	Kilowatt-Hours	3.7710-7	Calories	Foot-Pounds	3.09
 BTUs	Foot-Pounds	778	Kilowatt-Hours	Calories	8.60x105
 BTUs	Calories	252	Kilowatt-Hours	BTUs	3413
 BTUs	Kilowatt-Hours	0.00029	Kilowatt-Hours	Horsepower Hours	1.341
 Horsepower-Hour	Kilowatt-Hours	0.7457	Kilowatt-Hours	Foot-Pounds	2.66x106
 APPENDIX F ENGINEERING CONVERSION FACTORS
 To Convert	To	Multiply	by	To Convert	To	Multiply	by
 Milligrams per Liter	Parts per Million	1	Millimho per Centimeter	Decisiemens per Meter	1.00
 Milligrams per Liter	Grams per Cubic Meter	1	Millimho	Milliequivalents per Liter	10
 Decisiemens per Meter	Millimho per Centimeter	1	Milligrams per Liter	Parts per Million 	1
 Decisiemens per Meter	Parts per Million Salt	640	Grams per Cubic Meter	Parts per Million 	1.00
 Parts per Million 	Milligrams per Liter	1
 Parts per Million 	Grams per Cubic Meter	1
 Parts per Million 	Tons per Acre Foot	0.00136
 Parts per Million 	Grains per Gallon	0.0584
 Parts per Million Salt	Decisiemens per Meter	0.00156
 Tons per Acre Foot	Parts per Million 	735
 Grains per Gallon	Parts per Million 	17.1
 To Convert	To	Formula	To Convert	To	Formula
 Degrees Celcius 	Degrees Fahrenheit 	1.8xC+32	Degrees Fahrenheit 	Degrees Celcius 	/1.8
Salvatore S.
Mangiafico, Environmental and Resource Management Agent Christopher C.
Obropta, Extension Specialist in Water Resources Elaine Rossi-Griffin, Program Coordinator, Environmental Science
 Rainwater harvesting is used as a primary source of domestic or irrigation water in less-developed countries and arid climates.
This is often the case where water infrastructure is limited or rain is insufficient for crop production.
However, rainwater harvesting is used increasingly in developed nations for the irrigation of crops and landscaped areas and other non-potable uses.
Users include owners of municipal buildings, businesses, plant nurseries, and individual homes.
In New Jersey, there is interest in harvesting rain water from the roofs of buildings and greenhouses at businesses and farms.
Benefits of harvesting rain water may include:
 reducing runoff during rain events
 having a source of relatively high quality water for supplemental irrigation
 avoiding state permits for additional water allocations
 Reducing runoff and conserving potable water contribute to a wider goal of sustainable development, particularly in densely populated areas.
The most basic form of rainwater harvesting is simply diverting roof runoff away from stormwater infrastructure and onto permeable areas like lawns and landscaped areas.
Small-scale storage of rain water can be accomplished with a rain barrel (See Bakacs and
 Haberland [2010]), which is suitable for homeowners or for demonstrations at businesses.
While rainwater can be harvested in a variety of vessels including stone cisterns or open basins, most commonly closed tanks are used.
Plastic tanks in a variety of sizes and shapes are available commercially.
Plastic tanks for above-ground use should be made from plastic that is resistant to ultraviolet light and opaque in color.
For underground use, tanks manufactured for this application should be used.
Larger commercially-available tanks are made from fiberglass, galvanized steel, or a variety of other materials when a plastic liner is used.
If collection vessels are recycled from other uses, those used to store toxic materials must be avoided.
Matrix systems which consist of modular milk-crate-like plastic forms are also available.
They are pieced together to provide an underground storage space without the need for a single large open tank.
These systems provide flexibility in size and shape of the reservoir area, and can be used where a load-bearing vessel is desired.
Pre-packaged and modular systems are available commercially, and some manufacturers have certified contractors for their installation.
Collection tanks are often fitted with some method to facilitate draining and to remove any debris that may collect in the tank.
A drain or manhole opening can be used for this purpose.
For maximum collection efficiency, a spare tank can be connected to collect
 water while the main tank is taken offline for cleaning.
The ability to drain or pump out stagnant water is also helpful.
Tanks may need to be vented to allow filling with water, but all openings should be screened to prevent access by mosquitoes or small animals.
Tanks should be located both as close to the collection surface and as close to where water will be used as is practical.
The capacity of a rainwater harvesting system can range from a single 55-gallon barrel to a series of cisterns capable of storing thousands of gallons.
The desired capacity for a collection system will depend on many factors including:
 Anticipated demand How much water is needed or desired for irrigation or other uses?
What portion of that demand is to be satisfied by collected rainwater?
In New Jersey, where rainwater harvesting is primarily for supplemental irrigation and stormwater management, matching collection capacity to demand may be less critical.
The ability to use collected water for a specific purpose Larger tanks will provide a greater capacity for storage.
If only a small portion of collected water will be used, a smaller tank would achieve the same efficiency in the long run.
Available collection area Determine the roof area that is available and practical to be used as a collection surface.
Table 1.
Average rainfall for select locations in New Jersey.
Average monthly rainfall 	Average annual
 Apr.
May	Jun.
Jul.
Aug.
Sep.
Oct.
total precipitation
 Atlantic City	3.25	3.16	2.46	3.36	4.16	3.02	2.71	38.37
 Audubon	3.95	4.38	3.81	4.52	4.37	4.11	3.26	45.95
 Belvidere	3.93	4.28	4.22	4.46	3.65	4.30	3.55	45.15
 Cape May	3.31	3.65	3.01	3.39	3.78	3.31	3.41	41.39
 Millville	3.53	3.94	3.27	3.59	4.35	3.47	3.04	43.20
 Morris Plains	4.64	5.09	4.40	5.29	4.37	5.33	4.17	53.67
 Sandy Hook	3.69	4.01	3.53	4.10	4.03	3.42	3.36	43.58
 Somerville	4.00	4.34	3.98	4.63	4.39	4.58	3.69	47.71
 Sussex	4.44	4.46	4.57	4.22	4.23	4.45	3.72	48.03
 Toms River	4.02	4.17	3.52	4.56	5.00	3.95	3.55	48.81
 Wanaque	4.23	4.54	4.34	4.31	4.25	4.58	3.67	48.78
 * Adapted from NOAA 2002.
Data are from 1971-2000.
Note that local areas may receive more or less rain than indicated.
Note that annual variations include periods of droughts or unusually wet weather, so that the indicated rainfall may not estimate actual rainfall for any given year.
Water conservation or runoff management goals Tanks could be sized to meet a specific need, for example capturing 10% of roof runoff, or collecting enough water to irrigate a specific garden.
Water Quantity and Demand
 Average annual rainfall for New Jersey ranges from 38 to 54 inches, with an overall average of about 48 inches .
While droughts and unusually wet weather occasionally occur, on average rain is relatively equally distributed across months.
It should be remembered, though, that some months may have significantly more or less rain than average.
Collection systems should be designed with regard to expected monthly rainfall.
When designing rainwater harvesting systems, the possibility of periods of drought and wet weather should be considered.
Additionally, the seasonality of water demand should be considered, particularly if the water will be used for supplemental irrigation, as irrigation demand is generally greater in summer months.
Finally, it should be remembered that in winter months precipitation may fall as snow, which may or may not be collected with the rainfall harvesting system.
There are simple formulas that can be used to calculate the potential volume of rain water harvested from a storm.
The volume of rainwater is equal to the area of the roof from which the rain is being collected multiplied by the depth of the rainfall, then multiplied by a unit correction factor:
 volume  = roof area  x depth of rainfall  x 0.623 or volume  = roof area  x 10
 A 1-inch rain falling on a 1000-sq-ft.
roof would yield 623 gallons.
Or, a 3-cm rain falling on a 100-m roof would yield 3000 L.
It is important to note that the roof area should be calculated as the footprint of the roof, or the area of the roof surface in the horizontal plane.
In other words, the roof over a house with a 1200-square-foot footprint would have an "area" of 1200 square-feet for this calculation, no matter the pitch of the roof.
There may also be losses of water along the collection path.
It is estimated that 75-95% of the total water falling on the catchment surface will make it to the
 collection vessel.
This should be factored into calculations of how much water will be collected.
If the collected water is going to be used for irrigation, similar calculations can be used to determine how large a crop area can be irrigated with harvested water.
The depth of irrigation water that can be applied is equal to the volume of water collected divided by the crop area, with a factor to correct for units:
 depth of irrigation  = volume  crop area  x 1.605 or depth of irrigation  = volume  crop area  x 0.1
 For every 1000 gallons of collected water applied to a 500-square-foot garden would give 3.2" of applied irrigation.
Or, 4000 L of collected water applied to a 50m garden would give 8 cm of applied irrigation.
Rain Harvesting System Components
 A basic rainwater harvesting system consists of:
 The catchment surface.
For roof collection systems, this is the roof surface.
A water delivery system.
This may be a simple spigot and hose on a rain barrel or a pump system that supplies an irrigation system.
Leaf screens may be useful to keep debris out of the collected water.
These may be simple mesh screens over the gutters.
Such screens will need maintenance to prevent clogging as they collect leaves and other debris.
Additionally, a first-flush diverter may be useful to remove the first flush of water after runoff begins.
At the beginning of runoff from the collection surface, the initial volume of water may have elevated contaminant levels.
One recommendation is to divert 10-20 gallons for each 1000 square foot of collection surface.
Firstflush diverters can have a variety of designs, including standpipes or boxes with baffles.
See Texas Water Development Board  and Council on the Environment NYC  for more details on system design.
Other Design Considerations and Components
 Overflow.
Consideration should be given to the disposition of water that overflows the collection tank during large rain events.
Because water flow may be concentrated, care should be taken that overflow does not cause erosion or negatively impact neighbors or nearby waterways.
Overflowing water should not be diverted to septic drain fields.
Consultation with a qualified engineer may be advisable.
If harvested rain water will be used for critical irrigation, it may be necessary to use municipal water or well water as a back-up source of water.
This is sometimes called a dual supply system.
In this case, caution should be taken to prevent cross-connection, and the use of proper anti-siphon procedures will prevent the possibility of collected rain water being siphoned into the potable water supply lines.
Inspections or permits may be necessary for these connections.
Cross connection and backflow prevention.
Crossconnection refers to any case where a water system with non-potable water is connected to a potable water system, and such connections can constitute a serious threat to public water supplies.
Backflow occurs when an unexpected decrease in water supply pressure allows contaminated water to be siphoned into the potable water supply.
The potential for backflow can be prevented by leaving a physical air gap between the potable water supply outlet and the potentially contaminated water or by installing anti-siphon devices such double check valves or vacuum breakers.
It should be remembered that collected rainwater may have bacteria, heavy metals, or contamination by other substances, and SO any potential of rainwater entering potable water supplies should be avoided.
Additionally, it should be remembered that wells and groundwater also constitute potable supplies, and methods should be taken to prevent their contamination as well.
Winterizing.
During the design phase, accommodations for winter conditions must be considered.
Modifications may include a method to divert water from being collected during winter months and a valve to drain water from the tank before the onset of freezing temperature.
Depending on location, local conditions, and materials used, tanks and their plumbing may not need any special preparations for winter weather.
Valves may need testing the following spring as they are susceptible to damage by freezing water.
Local Regulations.
In all cases, building codes, health department stipulations, and water supply company
 requirements should be followed in order to prevent cross connection.
Obtaining permits, using certified plumbers, or allowing inspections of completed installations may be required.
It should be remembered that a gallon of water weighs more than eight pounds, SO a 55-gallon drum of water will weigh over 400 pounds, and a 500-gallon cistern would weigh over 4,000 pounds.
Any water collection vessel should be installed on a level and solid surface to prevent the possibility of anyone being crushed or trapped by an unstable tank.
A base of soil, sand, or pea gravel may be a suitable platform for a collection vessel, but a concrete pad may offer a more stable surface less susceptible to erosion.
Consulting a professional engineer to be sure of the stability of the soil or constructed base is advisable.
For sites serviced with municipal or well water, pergallon savings of using harvested water are unlikely to offset the costs for the installation and maintenance of a rainwater collection system in the short-term.
Instead, the most valuable benefits may be the environmental gains of water conservation and stormwater management, and, for businesses, the demonstration of good environmental stewardship.
Additionally, rain water harvesting may be a good solution for sites without ready access to municipal or well water.
The costs of building a rainwater collection system will depend on the size of the system and collection vessel, the materials used, if labor for installation must be paid for, and if the system requires running pumps or other equipment.
Some estimates are given by Council on the Environment NYC.
Self-installation of modular systems or custom-designed set-ups may be less expensive than installation by certified contractors.
lead to an increased sodium hazard when used for irrigation because these residual carbonates will bind with available calcium and magnesium in the soil, eliminating some of the effect those minerals could have in neutralizing any sodium surplus.
High residual carbonates have the effect of adjusting the effective SAR to even higher levels than actually measured.
RSC is reported in units of milliequivalents per liter.
Table 1.
Irrigation Water Suitability.
Water Quality	Degree of Problem
 Factor	None	Moderate	Severe
 EC 	750	750-3000	>3000
 SAR	<6	6-9	>9
 Boron 	<0.75	0.75-2.0	>2.0
 Chloride 	<92	92-230	>230
 RSC 	<1.25	1.25-2.5	>2.5
 Your irrigation water test report will have printed recommendations based on the measured levels of total salt, sodium, and boron.
There are a number of different ways of classifying the suitability of water for irrigation use.
The suitability is often the accumulation of several different factors, most importantly total salinity, sodicity, boron, chlorides and residual carbonates.
Moderate hazards in several factors may be tolerable, while a severe hazard in one area may be enough to make water unusable for irrigation.
An online interactive water test interpretation is available at: soiltesting.okstate.
edu/water-test-interpretation-program.
Nitrate  in irrigation water is not a quality problem for plants.
It can be a health concern in drinking water, however.
To avoid the possibility of leaching excess nitrates to ground water, it is a good practice to account for any nitrate added through irrigation water when calculating how much nitrogen fertilizer to apply to achieve your yield goal.
Applying 1 inch of irrigation water with
 a nitrate content of 1 ppm NO 3 as N adds 0.23 pounds of nitrogen per acre to your crop.
PSS-2912 Drinking Water Testing L-256 Understanding Your Livestock Water Test Report L-296 Understanding Your Household Water Test Report MWPS-14 Private Water Systems Handbook.
Midwest Plan Service, Ames, IA.
PSS-2401 Classification of Irrigation Water Quality
 Hailin Zhang Director, SWFAL Laboratory
 Understanding Your Irrigation Water Test Report
 Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30.
1914, in cooperation with the U.S.
Department of Agriculture, Director of Oklahoma Cooperative Extension Service, Oklahoma State University, Stillwater, Oklahoma.
This publication is printed and issued by Oklahoma State University as authorized by the Vice President for Agricultural Programs and has been prepared and distributed at a cost of 42 cents per copy.
Revised 0716 GH.
Oklahoma Cooperative Extension Service
 Division of Agricultural Sciences and Natural Resources
 UNDERSTANDING YOUR IRRIGATION WATER TEST REPORT
 The OSU Soil, Water and Forage Analytical Laboratory  provides an inexpensive but comprehensive analysis of water to evaluate its suitability for irrigation of crops and landscape plants.
Water testing is an important first step in irrigation development to determine if your water source contains salts which could damage your soil, reduce crop yields, or even kill your plants.
One pint of water is enough for testing.
It can be collected in any clean plastic container.
Take the sample to your county Extension office.
They will collect your payment and send your sample to the laboratory.
Results of the test are normally returned within one week.
Your water will be tested for the following factors:
 1.
Sodium  10.
Bicarbonate 
 2.
Calcium  11.
Hardness
 3.
Magnesium  12.
Alkalinity
 4.
Potassium  3.TotalDissolvedSolids
 5.
Nitrate  4.ElectricalConductivity
 6.
Chloride  15.
pH
 7.
Sulfate  16.
Percent Sodium 
 8.
Boron  17.ResidualCarbonate
 9.
Carbonate  18.
Sodium AdsorptionRatio 
 The most important factors to consider in irrigation water quality are:  total salt content as measured by electrical conductivity  or total dissolved solids ;  sodium hazard as measured by sodium adsorption ratio  or sodium percent sodium ; and  boron.
Pure water is a poor conductor of electricity.
Water with increasing amounts of salt conducts electric current more and more effectively.
The SWFAL reports electrical conductivity  in units of micromhos/cm.
Other laboratories may report conductivity in units of millimhos/cm  or deciSiemens/m , which are 1000 times larger than umho/cm.
Total dissolved solids  are an indication of the total salt content of water.
It is measured in units of milligrams per liter  or parts per million.
Both EC and TDS evaluate the overall effect of salinity and do not indicate the concentration of individual salts.
The effect of total salt content makes it more difficult for growing plants to take up water from the soil.
The additional energy the plant must exert to overcome the pull of the salt on the water in the soil around its roots reduces the performance of the plant, leading to stunted growth, lower yields and in extreme cases, death of the plant.
The severity of salinity effects vary widely among plant species.
Plants such as Bermudagrass and cotton are very tolerant, being unaffected until the electrical conductivity of soil water reaches about 7,000 umho/cm.
In contrast, strawberries and green beans are saltsensitive, experiencing yield reductions when the electrical conductivity reaches 1,000 umho/ cm.
Sodium  is one mineral that requires special attention in irrigation water.
Sodium can become toxic to many plants at high concentrations.
Sodium toxicity usually is seen as a burning along the edges of mature plant leaves.
The toxic effects of sodium accumulate over time, SO the burning effect in older leaves will eventually move toward the center of the leaf as the leaf ages.
Woody perennial plants like citrus, deciduous fruits and nuts are normally most sensitive to sodium.
Another serious problem of sodium in irrigation water is its dispersive effect on soil clays.
In soils with significant clay content, sodium will cause the clay particles to separate from each other.
Dispersion in soil is the reverse process to aggregation.
As a result of clay dispersion, soils will have poor
 physical properties.
This results in a massive or puddled soil with low water infiltration, poor tilth and surface soil crust formation.
The clay will clog the soil pores, causing a thin layer of slowly permeable material near the soil surface.
This dramatically reduces the rate at which soil can absorb water.
This sodicity hazard is most serious in fine-textured soils, especially those with expanding clays.
Sodicity hazard is measured by SAR or by sodium percentage.
The effect of sodium can be counteracted or reversed by adding calcium to the soil.
Calcium, usually in the form of gypsum, is added to the soil when the SAR of the topsoil reaches a critical threshold level.
Boron  is another mineral of particular importance in irrigation water.
It is an essential micronutrient to plants, but it can become toxic at very low concentrations.
Sensitive plants, such as nuts, deciduous fruits, and grapes experience toxic effects when the boron concentration in the soil reaches 1 ppm.
Even the most tolerant plants, such as asparagus and alfalfa are affected once the soil boron concentration is 4 ppm.
Boron toxicity symptoms are similar to those of sodium, with the burning effect beginning at the edges of older leaves.
Woody perennial plants are generally most sensitive to boron.
High concentrations of chloride ions  can cause injury to woody perennials, burning the edges of mature leaves.
Other plants can also be injured by high-chloride water, especially if leaves are wet by sprinkler irrigation when the air temperature is high and humidity is low.
Water with high concentrations of carbonate and bicarbonate relative to the concentrations of calcium and magnesium has a high residual carbonate level.
This type of water can
2009 IRRIGATION CROPLAND LEASE ARRANGEMENTS
 Grain price volatility and changing crop input costs have affected the equitability of existing irrigated cropland leasing arrangements during the 2006 through 2009 period.
It has been challenging for tenants and landowners to maintain equitable cropland leasing arrangements in response to both the historic increases and the following decrease that have occurred in agricultural commodity and crop input prices over the last 3-4 years.
This paper utilizes western Kansas crop enterprise cost of production estimates in the KSU Lease.xls program to estimate equitable cropland leasing arrangements for 2009.
Cost of production estimates for irrigated corn, sunflowers, grain sorghum, soybeans and wheat were taken from K-State Farm Management Guide budget projections and Kansas Farm Management Association Farm Enterprise budgets.
Non-irrigated cost of production estimates for wheat and other crops were used from the same sources.
The KSU Lease.xls program is a spreadsheet budgeting program developed by Kansas State University Extension Specialists Kevin Dhuyvetter and Terry Kastens that can be used to determine equitable crop share and cash lease rental arrangements.
Information on common irrigated and nonirrigated crop leasing arrangements were taken from K-State surveys of irrigated and nonirrigated crop leasing arrangements published in November-December 2008.
SCENARIO #1: CENTER PIVOT OWNED BY LANDOWNER, SHARING OF SELECTED CROP INPUT EXPENSES
 The first analysis of how equitable a common irrigated cropland leasing arrangement is focused on the scenario in which the Landowner owns the center pivot irrigation system and shares the cost of selected crop input expenses.
On a 160 acre field, it is assumed that a center pivot irrigation system is used covering 125 acres of irrigated corn.
For the nonirrigated corners  it was assumed that a wheat-fallow rotation was used.
In this scenario the tenant owned and paid 100% of the cost of the irrigation power unit used.
The landowner shared 33% of the cost of fertilizer, herbicides, insecticides, and crop insurance with the tenant.
The tenant paid 100% of all other expenses, including seed, crop consulting, machinery, labor, and energy costs.
The opportunity cost of farmland ownership for 125 acres of irrigated farmland and 35 acres of nonirrigated farmland  was calculated to be a 5% rate of return.
Farmland values were assumed to be those reported in the August 2008 Kansas Farmland Values publication from Kansas Agricultural Statistics.
The grain prices used represent bids for the Colby Goodland area on January 21, 2009.
Following are the 2009 crop budgets used for this 160 acre scenario on which irrigated corn is grown.
CROP BUDGETS SHOWING TOTAL COSTS AND RETURNS	Link to KSU Farm Management Guides 
 Crop/System	Corn	Soybean	Oil SF	Milo	Wheat	Wht-Flw	Total	Per	Per
 Planted acres of each crop	125.0	0.0	0.0	0.0	0	17.5	142.5	Acre	Acre
 Tillable acres per planted acre	1.00	1.00	1.00	1.00	1.00	2.00	160.0	Planted	Tillable
 A.
Yield per acre	200.0	55.0	22.0	120.0	70.0	45.0	--	--	--
 B.
Price per unit	$3.57	$9.15	$14.25	$2.83	$5.38	$5.38	--	--	--
 C.
Net government payments	$32.53	$32.53	$32.53	$32.53	$32.53	$16.26	$4,351	$30.53	$27.19
 D.
Indemnity payments	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0	$0.00	$0.00
 E.
Miscellaneous income	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0	$0.00	$0.00
 F.
Returns/acre 	E)	$746.53	$258.36	$97,838	$686.58	$611.48
 1.
Seed	$67.20	$10.40	$8,582	$60.22	$53.64
 2.
Herbicide	35.54	12.07	4,653	32.65	29.08
 3.
Insecticide/Fungicide	35.30	0.00	4,412	30.96	27.58
 4.
Fertilizer and Lime	247.64	73.37	32,239	226.24	201.49
 5.
Crop Consulting	6.50	6.25	6.50	6.25	6.00	0.00	813	5.70	5.08
 6.
Crop Insurance	50.00	20.00	20.00	20.00	20.00	12.50	6,469	45.39	40.43
 7.
Drying	0.00	0.00	0	0.00	0.00
 8.
Miscellaneous	10.00	10.00	10.00	10.00	10.00	5.50	1,346	9.45	8.41
 9.
Machinery Expense	148.38	103.98	20,367	142.93	127.30
 10.
Non-machinery Labor	16.77	11.70	2,301	16.15	14.38
 11.
Irrigation	210.33	0.00	26,291	184.50	164.32
 12.
Land Charge /	80.00	83.00	11,453	80.37	71.58
 G.
SUB TOTAL	$907.65	$312.51	$118,926	$834.57	$743.29
 13.
Interest on 1/2 Nonland Costs	27.38	7.79	3,559	24.97	22.24
 H.
TOTAL COSTS	$935.03	$320.30	$122,484	$859.54	$765.53
 I.
RETURNS OVER COSTS 					
 J.
TOTAL COSTS/UNIT 	$4.68	$7.12	--	--	--
 K.
RETURN TO TOTAL COST /G	-17.75%	-17.33%	-20.12%	-20.12%	-20.12%
 Delete inputs in columns not being used!
M.
Breakeven price 	$3.89	-$2.87	-$7.17	-$1.31	-$2.25	$3.97
 N.
Breakeven yield 	220.4	7.0	3.1	18.7	5.7	32.6
 Base crop for breakeven analysis	1	0	0	0	0	1
 1 All "blue values" are inputs, black values are calculated from those inputs
 TABLE 1.
Production Inputs Used for Budgets
 ITEM	Corn	Wht-Flw	$/unit
 Seeding rate 	30	150	23.4	6.5	90	65
 Seed price, $/unit	$2.24	$0.25	$0.91	$3.16	$0.16	$0.16
 82-0-0	270	0	120	150	122	79	$0.570 /lb
 N 	0	0	0	0	0	0	$0.850 /lb
 P	86	48	44	53	39	26	$1.090 /lb
 K	0	0	0	0	0	0	$0.620 /lb
 Lime	0	0	0	0	0	0	$0.010 /lb
 RT3	44	$0.40 /oz
 + Bicep Lite II Magnum	1.5	1.5	$11.29 /qt
 + Additives	1	$1.00 /ac
 Prowl	3.6	$3.65 /oz
 Glyphosate + Adjuvants	2	$9.64 /ac
 Prowl H2O	3	$4.19 /pt
 Spartan	4	$3.53 /oz
 Marksman	2	$4.26 /pt
 Ally  + Banvel 	1	1	$2.85 /ac
 RT3  + 2, 4-D 	1	$9.22 /ac
 Force 3G	5.4	$4.64 /lb
 Capture 2EC	0.08	$128.00 /lb
 Warrior 1 EC	0.05	$258.46 /lb
 Tilt	4	$3.00 /OZ
 Irrigation water, inches/acre	18	15	10	12	10	0	$5.80 /in
 Irrigation repairs, $/acre-inch	$0.33 /in
 Drying cost, $/unit 	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00
 Delete inputs in columns not being used!
8:38 AM	01/23/09
 TABLE 2.
Machinery and Land Resources Used for Budgets
 ITEM	Corn	Wht-Flw	$/unit
 Drill/Plant, $/acre	$12.48	$12.52	$12.39	$12.18	$10.91	$10.91
 Tillage and Chemical Applications:
 Chisel	1	1	1	1	0	0	$11.04 /ac
 Disk	1	1	1	1	2	0	$9.07 /ac
 Field cultivate	1	1	1	1	1	1	$8.29 /ac
 Sweep	0	0	0	0	0	3	$7.62 /ac
 Anhydrous application	1	0	1	1	1	1	$9.68 /ac
 Fertilizer application	0	0	0	0	0	0	$4.80 /ac
 Herbicide application	2	2	1	2	1	4	$5.15 /ac
 Insecticide application	1	0	2	0.5	1	0	$5.14 /ac
 Base charge, $/acre	$25.33	$25.87	$23.89	$19.96	$19.28	$19.28
 Charge for high yields, $/unit	$0.188	$0.181	$0.002	$0.182	$0.183	$0.183
 High yield	71	28	14	36	21	21
 Hauling, $/unit	$0.164	$0.164	$0.003	$0.175	$0.177	$0.177
 Non-machinery labor, hr/acre	1.29	0.79	0.80	1.04	0.85	0.90	$13.00 /hr
 Irrigation labor, hr/acre	0.50	0.50	0.50	0.50	0.50	0.00	$13.00 /hr
 Average land value, $/acre /A	$1,600	$1,600	$1,600	$1,600	$1,600	$830
 Annual return to land, % /A	5.0%
 Interest on capital, %	8.0%
 Irrigation Equipment	Total	$/wet ac	Years	value, %
 Well, pump and gearhead value	$53,000	$424	25	0%
 Power unit and meter	$12,250	$98	7	0%
 Irrigation system	$59,500	$476	20	25%
 Price scenarios to consider	Corn	Wht-Flw	Use 
 Long-run prices 	$3.36	$7.36	$13.33	$3.02	$5.02	$5.02	0
 Short-run prices 	$4.44	$8.39	$13.33	$4.10	$5.86	$5.86	0
 2009 bids 	$3.57	$9.15	$14.25	$2.83	$5.38	$5.38	1
 /A -The annual cost associated with land can either be entered as a Land Value X Rent-to-Value OR as a Cash Rent X 100% For example, if cash rent in region is $42 per acre, this can be entered as $42 in row 94 and 100% in cell K95 OR as $840 in row 94 and 5% in cell K95 [$42 X 100% = $840 X 5%].
The operator's share of production inputs are shown.
Here, "-100%" indicates that an expense is equitably shared in the same % as resource contributions.
Landowner	Landowner, Northwest KS, 123-456-8888	01/23/09
 Operator	Tenant, Northwest KS, 123-456-9999	8:38 AM
 Basis for equitable share calculations: For the entire rotation , Crop-by-crop 	0
 OPERATOR'S share of production inputs 
 Crop/System	Corn	--	--	--	Wht-Flw	Total
 Planted acres	125.0	--	--	--	17.5	142.5
 Seed	100%	100%	100%	100%	100%	100%
 82-0-0	67%	67%	67%	67%	67%	67%
 N 	67%	67%	67%	67%	67%	67%
 P	67%	67%	67%	67%	67%	67%
 K	67%	67%	67%	67%	67%	67%
 Lime	67%	67%	67%	67%	67%	67%
 RT3	67%	67%	67%	67%	67%	67%
 + Bicep Lite II Magnum	67%	67%	67%	67%	67%	67%
 + Additives	67%	67%	67%	67%	67%	67%
 Prowl	67%	67%	67%	67%	67%	67%
 Glyphosate + Adjuvants	67%	67%	67%	67%	67%	67%
 Prowl H2O	67%	67%	67%	67%	67%	67%
 Spartan	67%	67%	67%	67%	67%	67%
 Marksman	67%	67%	67%	67%	67%	67%
 Ally  + Banvel 	67%	67%	67%	67%	67%	67%
 RT3  + 2, 4-D 	67%	67%	67%	67%	67%	67%
 Force 3G	67%	67%	67%	67%	67%	67%
 Capture 2EC	67%	67%	67%	67%	67%	67%
 Warrior 1 EC	67%	67%	67%	67%	67%	67%
 Tilt	67%	67%	67%	67%	67%	67%
 Crop consulting	100%	100%	100%	100%	100%	100%
 Crop insurance	-100%	-100%	-100%	-100%	-100%	-100%
 Drying cost	-100%	-100%	-100%	-100%	-100%	-100%
 Operator's equitable share 	68.0%	60.7%	67.7%
 Crop/System	Corn	--	--	Wht-Flw	Total
 Planted acres	125.0	--	--	---	17.5	142.5
 OPERATOR'S share of machinery, labor, irrigation, and land 
 Drill/Plant	100%	100%	100%	100%	100%	100%
 Tillage and Chemical Applications:
 Chisel	100%	100%	100%	100%	100%	100%
 Disk	100%	100%	100%	100%	100%	100%
 Field cultivate	100%	100%	100%	100%	100%	100%
 Sweep	100%	100%	100%	100%	100%	100%
 Anhydrous application	100%	100%	100%	100%	100%	100%
 Fertilizer application	100%	100%	100%	100%	100%	100%
 Herbicide application	100%	100%	-100%	-100%	-100%	-100%
 Insecticide application	100%	100%	100%	100%	100%	100%
 Harvest	100%	100%	100%	100%	100%	100%
 Hauling	100%	100%	100%	100%	100%	100%
 Miscellaneous	100%	100%	100%	100%	100%	100%
 Non-machinery labor	100%	100%	100%	100%	100%	100%
 Labor	100%	100%	100%	100%	100%	100%
 Fuel and oil	100%	100%	100%	100%	100%	100%
 Repair and maintenance	100%	100%	100%	100%	100%	100%
 Well, pump and gearhead	0%	0%	0%	0%	0%	0%
 Motor	0%	0%	0%	0%	0%	0%
 Irrigation system	0%	0%	0%	0%	0%	0%
 Land	0%	0%	0%	0%	0%	0%
 Cash payment to landowner, $/acre	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0
 Operator's equitable share 	68.0%	60.7%	67.7%
 Landowner's equitable share 	32.0%	39.3%	32.3%
 Pre-defined operator's share for income  1
 Operator's share 	0.0%
 1 By entering a pre-defined share for the operator , the calculated equitable share percentage (cell
 L70) will be over-ridden and not used in the Lease Budgets tab.
Operate KEAR the available subject.
Extension Agricultural Economists, Kansas State University
 This analysis indicates that the operator is contributing 67.7% and the landowner 32.3% of total resources in this example where the landowner also owners the center pivot.
The operator's and landowners costs and returns for this particular crop share leasing arrangement are shown below.
CROP BUDGETS SHOWING OPERATOR'S COSTS AND RETURNS
 Tenant, Northwest KS, 123-456-9999	8:38 AM	01/23/09
 Equitable share 	67.7%	67.7%	67.7%
 Crop/System	Corn	Wht-Flw	Total	Per	Per
 Total tillable acre	160.0	Planted	Tillable
 Planted acres of each crop	125.0	17.5	142.5	Acre	Acre
 Harvested yield per acre	200.0	45.0	--	--	--
 A.
Yield per acre	135.3	30.4	--	--	--
 B.
Price per unit	$3.57	$5.38	--	--	--
 C.
Net government payments	$22.01	$11.00	$2,944	$20.66	$18.40
 D.
Indemnity payments	$0.00	$0.00	$0	$0.00	$0.00
 E.
Miscellaneous income	$0.00	$0.00	$0	$0.00	$0.00
 F.
Returns/acre  + C+D E)	$505.11	$174.81	$66,198	$464.55	$413.74
 1.
Seed	$67.20	$10.40	$8,582	$60.22	$53.64
 2.
Herbicide	23.81	8.08	3,118	21.88	19.48
 3.
Insecticide/Fungicide	23.65	0.00	2,956	20.74	18.48
 4.
Fertilizer and Lime	165.92	49.16	21,600	151.58	135.00
 5.
Crop Consulting	6.50	0.00	813	5.70	5.08
 6.
Crop Insurance	33.83	8.46	4,377	30.71	27.36
 7.
Drying	0.00	0.00	0	0.00	0.00
 8.
Miscellaneous	10.00	5.50	1,346	9.45	8.41
 9.
Machinery Expense	148.38	97.32	20,251	142.11	126.57
 10.
Non-machinery Labor	16.77	11.70	2,301	16.15	14.38
 11.
Irrigation	116.84	0.00	14,605	102.49	91.28
 12.
Land Charge / Rent	0.00	0.00	0	0.00	0.00
 G.
SUB TOTAL	$612.90	$190.62	$79,948	$561.04	$499.68
 13.
Interest on 1/2 Nonland Costs	22.53	6.32	2,927	20.54	18.29
 H.
TOTAL COSTS	$635.43	$196.94	$82,875	$581.58	$517.97
 I.
RETURNS OVER COSTS 					
 J.
TOTAL COSTS/UNIT 	$4.70
 K.
RETURN TO TOTAL COST 	-20.51%	-11.24%	-20.12%	-20.12%	-20.12%
 CROP BUDGETS SHOWING LANDOWNER'S COSTS AND RETURNS
 Landowner, Northwest KS, 123-456-8888	8:38 AM	01/23/09
 Equitable share 	32.3%	32.3%	32.3%
 Crop/System	Corn	Wht-Flw	Total	Per	Per
 Total tillable acre	160.0	Planted	Tillable
 Planted acres of each crop	125.0	17.5	142.5	Acre	Acre
 Harvested yield per acre	200.0	45.0	--	--	--
 A.
Yield per acre	64.7	14.6	--	--	--
 B.
Price per unit	$3.57	$5.38	--	--	--
 C.
Net government payments	$10.52	$5.26	$1,407	$9.87	$8.79
 D.
Indemnity payments	$0.00	$0.00	$0	$0.00	$0.00
 E.
Miscellaneous income	$0.00	$0.00	$0	$0.00	$0.00
 F.
Returns/acre  + E)	$241.42	$83.55	$31,639	$222.03	$197.74
 1.
Seed	$0.00	$0.00	$0	$0.00	$0.00
 2.
Herbicide	11.73	3.98	1,536	10.78	9.60
 3.
Insecticide/Fungicide	11.65	0.00	1,456	10.22	9.10
 4.
Fertilizer and Lime	81.72	24.21	10,639	74.66	66.49
 5.
Crop Consulting	0.00	0.00	0	0.00	0.00
 6.
Crop Insurance	16.17	4.04	2,092	14.68	13.07
 7.
Drying	0.00	0.00	0	0.00	0.00
 8.
Miscellaneous	0.00	0.00	0	0.00	0.00
 9.
Machinery Expense	0.00	6.66	117	0.82	0.73
 10.
Non-machinery Labor	0.00	0.00	0	0.00	0.00
 11.
Irrigation	93.49	0.00	11,686	82.01	73.04
 12.
Land Charge / Rent	80.00	83.00	11,453	80.37	71.58
 G.
SUB TOTAL	$294.75	$121.90	$38,978	$273.53	$243.61
 13.
Interest on 1/2 Nonland Costs	4.85	1.47	632	4.44	3.95
 H.
TOTAL COSTS	$299.61	$123.36	$39,610	$277.96	$247.56
 I.
RETURNS OVER COSTS 					
 J.
TOTAL COSTS/UNIT 	$4.63	--	--	--
 K.
RETURN TO TOTAL COST 	-19.42%	-32.27%	-20.12%	-20.12%	-20.12%
 KSU Lease.xls -Developed by Kevin C.
Dhuyvetter and Terry L.
Kastens Extension Agricultural Economists, Kansas State University
 The final summary comparison of alternative estimates of equitable irrigated crop leasing arrangements are shown below.
ALTERNATIVE METHODS OF ESTIMATING CASH RENT	8:38 AM	01/23/09
 Crop/System	Corn	Wht-Flw	Total	Per	Per
 Total tillable acre	160.0	Planted	Tillable
 Planted acres of each crop	125.0	17.5	142.5	Acre	Acre
 Land	$80.00	$83.00	$11,453	$80.37	$71.58
 Irrigation equipment	$93.49	$0.00	$11,686	$82.01	$73.04
 Total	$173.49	$83.00	$23,139	$162.38	$144.62
 B.
Landowner's EQUITABLE SHARE RENT	risk adj factor	3.0%
 Total income	$746.53	$258.36	$97,838	$686.58	$611.48
 Landowner's share	32.3%	32.3%	32.3%	32.3%	32.3%
 Landowner's income	$241.42	$83.55	$31,639	$222.03	$197.74
 Landowner operating expense	126.12	40.36	16,471	115.58	102.94
 Income less operating expense	$115.30	$43.18	$15,168	$106.44	$94.80
 Less risk adjustment	3.46	1.30	455	3.19	2.84
 Cash rent equivalent	$111.84	$41.89	$14,713	$103.25	$91.96
 C.
Amount tenant CAN AFFORD TO PAY
 Total income	$746.53	$258.36	$97,838	$686.58	$611.48
 Total operating expense	$761.54	$237.30	$99,345	$697.16	$620.91
 Return to land and irr equip		$21.06			
 Comparison of alternative cash rent methods
 Low		$21.06			
 Average	$90.11	$48.65	$12,115	$85.02	$75.72
 High	$173.49	$83.00	$23,139	$162.38	$144.62
 Returns above all costs 					
 Part A of this table shows that the landowner's costs for this land, including both the cash and opportunity cost of the irrigation equipment and the opportunity cost of farmland ownership  amount to $144.62 per acre.
Part B indicates that for this example in which the landowner owns the center pivot irrigation system and contributes a 1/3 share of selected crop input costs , with a 3% risk adjustment factor, the landowner's equivalent share rent is $91.96 per tillable acre.
Part C shows that the amount the tenant can afford to pay if all resources are valued at their full economic opportunity cost is actually negative.
That said, full economic opportunity costs for irrigation equipment, labor and farmland are often not fully covered in such leasing arrangements.
In a comparison of the alternative cash rent calculation methods, the average rent per tillable acre is $75.72 for the full 160 acre field, with an average of $90.11 on the irrigated corn acres and of $45.38 per acre on the dryland acres.
SCENARIO #2: CENTER PIVOT OWNED BY OPERATOR, SHARING OF SELECTED CROP INPUT EXPENSES
 The second analysis of how equitable a common irrigated cropland leasing arrangement is focused on the scenario in which the Operator  owns the center pivot irrigation system and shares the cost of selected crop input expenses.
All other aspects of the lease are unchanged from the first scenario.
OPERATOR'S share of machinery, labor, irrigation, and land 
 Drill/Plant	100%	100%	100%	100%	100%	100%
 Tillage and Chemical Applications:
 Chisel	100%	100%	100%	100%	100%	100%
 Disk	100%	100%	100%	100%	100%	100%
 Field cultivate	100%	100%	100%	100%	100%	100%
 Sweep	100%	100%	100%	100%	100%	100%
 Anhydrous application	100%	100%	100%	100%	100%	100%
 Fertilizer application	100%	100%	100%	100%	100%	100%
 Herbicide application	100%	100%	-100%	-100%	-100%	-100%
 Insecticide application	100%	100%	100%	100%	100%	100%
 Harvest	100%	100%	100%	100%	100%	100%
 Hauling	100%	100%	100%	100%	100%	100%
 Miscellaneous	100%	100%	100%	100%	100%	100%
 Non-machinery labor	100%	100%	100%	100%	100%	100%
 Labor	100%	100%	100%	100%	100%	100%
 Fuel and oil	100%	100%	100%	100%	100%	100%
 Repair and maintenance	100%	100%	100%	100%	100%	100%
 Well, pump and gearhead	0%	0%	0%	0%	0%	0%
 Motor	0%	0%	0%	0%	0%	0%
 Irrigation system	100%	100%	100%	100%	100%	100%
 Land	0%	0%	0%	0%	0%	0%
 Cash payment to landowner, $/acre	$0.00	$0.00	$0.00	$0.00	$0.00	$0.00	$0
 Operator's equitable share 	72.7%	60.7%	72.2%
 Landowner's equitable share 	27.3%	39.3%	27.8%
 Pre-defined operator's share for income 
 Operator's share 	0.0%
 1	By entering a pre-defined share for the operator.
the calculated equitable share percentage (cell
 L70) will be over-ridden and not used in the Lease Budgets tab.
Operator and Landowner's income shares are based on the equitable concept.
Part A of the following table shows that the landowner's costs for this land, including both the cash and opportunity cost of the irrigation equipment and the opportunity cost of farmland ownership  amount to $112.08 per acre.
Part B indicates that for this example in which the operator owns the center pivot irrigation system with the landowner contributing a 1/3 share of selected crop input costs , with a 3% risk adjustment factor, the landowner's equivalent share rent is $67.14 per tillable acre.
Part C shows that the amount the tenant can afford to pay if all resources are valued at their full economic opportunity cost is actually negative.
As in the previous illustration, full economic opportunity costs for
 irrigation equipment, labor and farmland are often not fully covered in such leasing arrangements.
In a comparison of the alternative cash rent calculation methods, the average rent per tillable acre is $45.75 for the full 160 acre field, with an average of $52.21 on the irrigated corn acres and of $45.38 per acre on the dryland acres.
ALTERNATIVE METHODS OF ESTIMATING CASH RENT	11:46 AM	01/23/09
 Crop/System	Corn	Wht-Flw	Total	Per	Per
 Total tillable acre	160.0	Planted	Tillable
 Planted acres of each crop	125.0	17.5	142.5	Acre	Acre
 Land	$80.00	$83.00	$11,453	$80.37	$71.58
 Irrigation equipment	$51.84	$0.00	$6,480	$45.47	$40.50
 Total	$131.84	$83.00	$17,933	$125.84	$112.08
 B.
Landowner's EQUITABLE SHARE RENT	risk adj factor	3.0%
 Total income	$746.53	$258.36	$97,838	$686.58	$611.48
 Landowner's share	27.8%	27.8%	27.8%	27.8%	27.8%
 Landowner's income	$207.73	$71.89	$27,225	$191.05	$170.15
 Landowner operating expense	123.77	38.82	16,151	113.34	100.94
 Income less operating expense	$83.96	$33.07	$11,074	$77.71	$69.21
 Less risk adjustment	2.52	0.99	332	2.33	2.08
 Cash rent equivalent	$81.45	$32.08	$10,742	$75.38	$67.14
 C.
Amount tenant CAN AFFORD TO PAY
 Total income	$746.53	$258.36	$97,838	$686.58	$611.48
 Total operating expense	$803.19	$237.30	$104,552	$733.70	$653.45
 Return to land and irr equip		$21.06			
 Comparison of alternative cash rent methods
 Low		$21.06			
 Average	$52.21	$45.38	$7,320	$51.37	$45.75
 High	$131.84	$83.00	$17,933	$125.84	$112.08
 Returns above all costs 					
 These illustrations of equitable leasing arrangements are intended for general illustration purposes.
They may or may not be representative of a particular farm or equitable farmland leasing relationship, depending on the degree to which that a particular field, irrigation system, or set of production costs does or does not accurately fit other situations.
Alternative leasing scenarios can be calculated for the irrigated crops, including sunflowers, soybeans, grain sorghum and wheat.
In this session at the 2009 Central Plains Irrigation Conference, we will give closer scrutiny to the cost estimates used in these examples, and show the effect of using alternative crops and cropping systems upon the bottom line equitable lease returns.
We will also show a number of nonirrigated / dryland crop leasing arrangement examples, and discuss some relevant irrigated equipment related tax planning issues.
Scaling smallholder irrigation and supporting entrepreneurs in small-scale agriculture.
Western rivers, a changing climate and the role of irrigated agriculture.
The impacts of drought and water-related health issues on human health.
New techniques for irrigation water management.
Gender diverse institutions for water security.
Making the business case for climate-resilient WASH for the food and beverage sector.
Transitioning from a linear to a circular bioeconomy.
Resilient and sustainable agri-food systems.
Addressing water scarcity in agriculture and the environment through partnerships and innovation.
A view from the field  how farmers from different parts of the world are using technology and best practices to increase yields.
The dates and locations for the six-part series include:
 Jan.
14 and 15, 2022  Kearney, Nebraska 
 Feb.
21, 2022  Kearney, Nebraska 
 March 8-9, 2022  North Platte, Nebraska 
 June 21, 2022  North Platte, Nebraska 
 Aug.
24, 2022  North Platte, Nebraska 
 Dec.
13, 2022  North Platte, Nebraska
 Attendance at all sessions is important because of the sequential nature of the curriculum.
Participants must attend at least five of the six sessions to receive a Certificate of Completion.
B.C.
SPRINKLER IRRIGATION MANUAL
 Prepared and Web Published by
 BRITISH COLUMBIA Ministry of Agriculture
 LIMITATION OF LIABILITY AND USER'S RESPONSIBILITY
 The primary purpose of this manual is to provide irrigation professionals and consultants with a methodology to properly design an agricultural irrigation system.
This manual is also used as the reference material for the Irrigation Industry Association's agriculture sprinkler irrigation certification program.
While every effort has been made to ensure the accuracy and completeness of these materials, additional materials may be required to complete more advanced design for some systems.
Advice of appropriate professionals and experts may assist in completing designs that are not adequately convered in this manual.
All information in this publication and related materials are provided entirely "as is" and no representations, warranties or conditions, either expressed or implied, are made in connection with your use of, or reliance upon, this information.
This information is provided to you as the user entirely at your risk.
The British Columbia Ministry of Agriculture and the Irrigation Industry Association of British Columbia, their Directors, agents, employees, or contractors will not be liable for any claims, damages or losses of any kind whatsoever arising out of the use of or reliance upon this information.
Farmers in British Columbia may pump their own water from a number of sources including surface water such as lakes, rivers and streams, groundwater and canals or ditch systems that are supplied by a municipality or other water purveyor.
In addition there are some water purveyors that provide pressurized water in pipelines to the farm gate.
Issues with respect to water supply and irrigation include both quality and quantity.
Water of poor quality may impact the operation of an irrigation system, can affect irrigation practices with respect to soil quality and may also affect food safety.
The Canadian Water Quality Guidelines outline the recommended levels of waterborne chemicals and pathogens for various uses including agriculture, irrigation and livestock.
Provincial jurisdictions may develop their own guidelines or criteria.
Check the internet for the most recent water quality standards in the province as the numbers shown here may change.
11.1 Water Quality Concerns
 The primary activities concerning water quality are:
 Cross-connection among water supply lines carrying contaminants that pollute the water supply.
Well construction , location , or abandoned wells that cause groundwater pollution.
Disturbances to watercourses during installation and maintenance of intake screens that may result in water pollution and habitat loss.
Irrigation with water of poor quality that contaminates edible crops with pathogens, or causes salt build-up in the soil.
Application of fertilizers and other chemicals that may lead to water or soil pollution.
Water containing silt and algae or chemicals dissolved in the water that may clog micro-irrigation systems
 Use of petroleum fuels for pumps adjacent to a watercourse.
Excessive irrigation can cause contaminants to enter the watercourse or aquifers by leaching through the soil or by overland runoff.
Heavy soils that have low infiltration rates are susceptible to runoff if the irrigation system applies water at a rate greater than the infiltration rate of the soil.
Contaminants from the soil or plants can be carried by the irrigation water to surface water sources or groundwater.
Ammonia  plus ammonium  is referred to as total ammonia, and both exist in urine, manure, fertilizer and compost.
Water containing elevated levels of total ammonia may be toxic to fish and other aquatic organisms.
The ammonium form is more harmful to aquatic organisms compared to ammonium.
KEY CONSIDERATIONS FOR A SUCCESSFUL SUBSURFACE DRIP IRRIGATION  SYSTEM
 Subsurface drip irrigation  systems are currently being used on about 15,000 acres in Kansas.
Research studies at the NW Kansas Research and Extension Center of Kansas State University begin in 1989 and have indicated that these systems can be efficient, long-lived, and adaptable for irrigated corn production in western Kansas.
This adaptability is likely extended to any of the deep-rooted irrigated crops grown in the region.
Many producers have had successful experiences with SDI systems; however most have had to experience at least some minor technical difficulties during the adoption process.
However, a few systems have been abandoned or failed after a short use period due to problems associated with either inadequate design, inadequate management or combination of both.
Both research studies and on-farm producers experience indicate SDI systems can result in high yielding crop and water-conserving production practices, but only if the systems are properly designed, installed, operated and maintained.
SDI systems in the High Plains must also have long life to be economically viable when used to produce the relative low value field crops common to the region.
Design and management are closely linked in a successful SDI system.
A system that is not properly designed and installed, will be difficult to operate and maintain and most likely will not achieve high irrigation water application uniformity and efficiency goals.
However, a correctly designed and installed SDI system will not perform well, if not properly operated and is destined for early failure without proper maintenance.
This paper will review important considerations for a successful SDI system.
IMPORTANT SDI SYSTEM CONSIDERATIONS
 Design considerations must account for field and soil characteristics, water quality, well capabilities, desired crops, production systems, and producer goals.
It is difficult to separate design and management considerations into distinct issues as the system design should consider management restraints and goals.
However, there are certain basic features that should be a part of all SDI systems, as shown in Figure 1.
Omission of any of these minimum components by a designer should raise a red flag to the producer and will likely seriously undermine the ability of the producer to operate and maintain the system in an efficient manner for a long period of time.
Minimum SDI system components should not be sacrificed as a design and installation cost-cutting measure.
If minimum SDI components cannot be included as part of the system, serious consideration should be given to an alternative type of irrigation system or remaining as a dryland production system.
Figure 1.
Schematic of Subsurface Drip Irrigation  System.
K-State Research and Extension Bulletin MF-2576, Subsurface Drip Irrigation  Component: Minimum Requirements
 The water distribution components of an SDI system are the pumping station, the main, submains and dripline laterals.
The size requirements for the mains and submains would be similar to the needs for underground service pipe to center pivots or main pipelines for surface flood systems.
Size is determined by the flow rate and acceptable friction loss within the pipe.
In general, the flow rate and acceptable friction loss determines the size  for a given dripline lateral length.
Another factor is the land slope.
Theoretically, but totally unwise, a drip system could be only a combination of pumping plant, distribution pipelines and dripline laterals.
However, as an underground system, there would be no method to monitor system performance and the system would not have any protection from clogging.
Clogging of dripline emitters is the primary reason for SDI system failure.
The remaining components outlined in Figure 1, are primarily components that allow the producers to protect the SDI system, monitor its performance, and if desired, provide additional nutrients or chemicals for crop production.
The backflow preventive device is a requirement to protect the source water from accidental contamination should a backflow occur.
The flow meter and pressure gauges are essentially the operational feedback cues to the manager.
In SDI systems, all water application is underground.
In most properly installed and operated systems, no surface wetting occurs during irrigation, so no visual cues are available to the manager concerning the system operating characteristics.
The pressure gauges at the control valve at each zone, allows the proper entry pressure to dripline laterals to be set.
Decreasing flow and/or increasing pressure can indicate clogging is occurring.
Increasing flow with decreasing pressure can indicate a major line leak.
The pressure gauges at the distal ends of the dripline laterals are especially important in establishing the baseline performance characteristics of the SDI system.
The heart of the protection system for the driplines is the filtration system.
The type of filtration system needed will depend on the quality characteristics of the irrigation water.
In general, clogging hazards are classified as physical, biological or chemical.
The Figure 1 illustration of the filtration system depicts a pair of screen filters.
In some cases, the filtration system may be a combination of components.
For example, a well that produces a lot of sand may have a sand separator in advance of the main filter.
Sand particles in the water would represent a physical clogging hazard.
Other types of filters used are sand media and disc filters.
Biological hazards are living organisms or life by-products that can clog emitters.
Surface water supplies may require several layers of screen barriers at the intake
 site to remove large debris and organic matter.
Another type of filter is a sand media filter, which is a large tank of specially-graded sand and is well-suited for surface water sources.
Wells that produce high iron content water, can also be vulnerable to biological clogging hazards, such as when iron bacteria have infested a well.
Control of bacterial growths generally requires water treatment, in addition to filtration.
Chemical clogging hazards are associated with the chemical composition or quality of the irrigation water.
As water is pulled from a well and introduced to the distribution system, chemical reactions can occur due to changes in temperature, pressure, air exposure, or the introduction of other materials into the water stream.
If precipitants form, they can clog the emitters.
The chemical injection system can either be a part of the filtration system or could be used as part of the crop production management plan to allow the injection of nutrients or chemicals to enhance plant growth or yield.
The injection system in Figure 1 is depicted as a single injection point, located upstream of the main filter.
In many cases, there might be two injection systems.
In other cases, there may be a need for an injection point downstream from the filter location.
The injection system, when it is a part of the protection system for the SDI system, can be used to inject a variety of materials to accomplish various goals.
The most commonly injected material is chlorine, which helps to disinfect the system and minimizes the risk of clogging associated with biological organisms.
Acid injection can also be injected to affect the chemical characteristic of the irrigation water.
For example, high pH water may have a high clogging hazard due to a mineral dropping out of solution in the dripline after the filter.
The addition of a small amount of acid to lower the pH to slightly acid might prevent this hazard from occurring.
As with most investments, the decision as to whether the investment would be sound lies with the investor.
Good judgments generally require a good understanding of the fundamentals of the particular opportunity and/or the recommendations from a trusted and proven expert.
While the microirrigation  industry dates back over 40 years now and its application in Kansas as SDI has been researched since 1989, a network of industry support is still in the early development phase in the High Plains region.
Individuals considering SDI should spend time to determine if SDI is a viable systems option for their situation.
They might ask themselves:
 What things should I consider before I purchase a SDI system?
1.
Educate yourself before contacting a service provider or salesperson by
 C.
Visit other producer sites that have installed and used SDI.
Most current producers are willing to show them to others.
2.
Interview at least two companies.
a.
Ask them for references, credentials  and sites  of other completed systems.
b.
Ask questions about design and operation details.
Pay particular attention if the minimum SDI system components are not met.
If not, ask why?
System longevity is a critical factor for economical use of SDI.
C.
Ask companies to clearly define their role and responsibility in designing, installing and servicing the system.
Determine what guarantees are provided.
3.
Obtain an independent review of the design by an individual that is not associated with sales.
This adds cost but should be minor compared to the total cost of a large SDI system.
SDI can be a viable irrigation system option, but should be carefully considered by producers before any financial investment is made.
The above discussion is a very brief summary from materials available through K-State.
The SDI related bulletins and irrigation related websites are listed below.
Related K-State Research and Extension Irrigation Websites:
 This paper was presented at the 17th annual Central Plains Irrigation Conference, Sterling, Nebraska, Feb 17-18, 2005.
The correct citation is:
 This paper is Contribution Number 05-206-A from the Kansas Agricultural Experiment Station.
The broken gooseneck on this pivot, as shown in the video, is one cause of non-uniform water application.
Walking the irrigation span to visually inspect it can help identify issues before crop yield is affected.
WHEELMOVE SPRINKLER IRRIGATION OPERATION AND MANAGEMENT
 Robert W.
Hill, Extension Specialist Irrigation
 Wheelmove sprinklers water about 336,000 acres in Utah.
This is more than one fourth of Utah's 1.3 million acres of irrigated land.
There are nearly four and one half times as much wheelmove irrigated area than that watered by center pivots in Utah.
Utah is the number one state in proportion of wheelmove to total irrigated acres.
The reason for this is that many of Utah's field or farm units are usually smaller than 40-80 acre blocks or are odd-shaped.
Economics also may be a factor, particularly with regard to initial capital outlay costs.
Often times, one wheel move is placed on a 40 acre 1/4 mile by 1/4 mile field.
An 11 or 22 day irrigation interval is possible depending on whether 12 hour or 24 hour set-times are used.
The soil type, crop, rooting depth, and design evapotranspiration rate are all factors to be considered SO that the system application does not exceed either the root zone soil water storage capacity or the soil surface infiltration rate.
These factors also determine whether a 12 hour or 24 hour move cycle should be used.
WHAT Is A WHEELMOVE?
The term "wheelmove" seems to be the industry preferred label for what are also known as wheel-line, sideroll, or lateral-roll irrigation machines.
A wheelmove consists of the mover, lateral pipe, wheels, sprinklers, couplers, and connectors to the mainline supply.
The lateral pipe conveys water along the line to sprinklers typically spaced 30 to 40 feet apart.
While system lengths vary, most are 1280 feet long to match a quarter mile wide field.
The lateral pipe also acts as an axle for wheels midway between the sprinklers.
The lateral pipe is typically either 4 inch or 5 inch diameter, with some systems using 5 inch close to the mover and 4 inch further away.
The 5 inch pipe is desirable as a stronger axle where the system operates on a side hill or on undulating ground.
The wheels vary in diameter from five feet  to ten feet.
The most common wheel diameter in Utah is 7 foot  which moves the line 60 feet laterally with 3 revolutions.
Five foot  wheels are often used to give a 50 foot move with three
 revolutions.
Probably a significant majority of wheelmoves have 7 feet diameter wheels with 5 inch pipe.
The height of lateral line/axle limits the crops which are adapted to wheelmove systems to approximately half the wheel diameter.
It is not likely to see a wheelmove in a corn field except, perhaps, for one or two early irrigations.
Nor would it be used in orchards or any other similar tall crops.
This is not a serious limitation in Utah as only six percent of the irrigated land is in corn and orchard crops.
Nearly 80% is in perennial forages including alfalfa, hay, and pasture.
The couplers connect the lateral pipe sections together and transmit the axle torque.
They also include a drain and an outlet for the sprinkler.
In fields of varying width, such as those at an angle to a roadway, the ease of dropping or adding lateral sections is important.
Thus, a clamp type coupler may be desirable.
Also, the use of a leveler on the sprinkler is not only recommended but is an essential requirement for any wheelmove system.
The joint of pipe making up the lateral pipeline serve as the axle for the wheelmove system and are supported above the ground by wheels mounted midway along their length.
Sprinklers are located at the connections and ends of the lateral pipe, positioning a sprinkler head midway between each well and at the ends of the lateral pipeline.
Normally, a wheelmove system has impact sprinkler heads with levelers to keep the sprinklers in an upright position.
Located adjacent to each sprinkler is a drain that automatically empties the lateral pipeline when water pressure drops off.
The couplers between the pipe joints provide a watertight connection and also transmit torque, produced by the power mover, to the entire length of the system.
The power mover is mounted in the center of the wheelmove system and provides the power to move or drive the irrigation system.
One end of the lateral line is connected via a flexible hose to a pressurized mainline pipe with risers at suitable intervals.
At periodic intervals  the system is rolled 50 or 60 feet laterally by a small single cylinder gasoline or diesel engine power unit.
The power unit,  operates through a combination of hydraulics, gears, and chains located at the middle or end of the lateral.
All the water must be drained through the automatic drains from the line prior to moving.
The move usually takes 20 to 30 minutes, including draining, which is considerably less time than required for a hand move line.
Prior to moving the line it should be straight.
Then the mover will be slightly ahead of the line, which will be tight without slack when moving.
If the line migrates to one end in moving, the opposite end should be "trailed" back manually.
This unbalance will tend to shift the line in the desired direction.
The end should be realigned after the line position is corrected.
It is important to keep the wheels from getting ahead of the mover SO as to prevent serious misalignment.
When the wheel line operates crosswise on a slope, the line may migrate down slope.
If the mover is situated off center towards the downhill side, the extra "pull" from the longer uphill line will tend to offset this downward migration.
A typical wheelmove in Utah uses impact sprinklers with levelers and has 3/16" diameter nozzles operating at 45 to 50 psi pressure.
Unfortunately, some systems are operating at pressures somewhat below this which lead to problems with distribution uniformity.
Several years back, in a program funded in part by the Utah Department of Agriculture and the Utah Agricultural Experiment Station, we evaluated numerous sprinkler irrigation systems around the state.
Irrigation application efficiencies  for wheel moves varied from 39% to 75%.
With reasonable
 Figure 1.
Wheelmove water distribution, no offset, CU of 62%.
Figure 2.
Wheelmove water distribution with 20 foot offset in 2nd irrigation.
good management, the wheelmove application efficiencies averaged nearly 70%.
The lower application efficiencies were from lower pressures than designed or, perhaps, a greater distance in the move than is desirable.
One such system we evaluated had a coefficient of uniformity  of 62% on the 40 foot by 60 foot sprinkler spacing.
The uniformity improved to 87% when a 20 foot offset  was used on alternate irrigations.
The 20 foot offset, in this case, was equivalent to one revolution of the wheel move to either the right or the left of the previous irrigation lateral position.
The objective of the moving sequence is to maintain adequate soil water for best crop growth, while not causing excess deep percolation.
Deep percolation is detrimental to water conservation and salinity reduction goals.
Various wheel move sequencing scenarios have been tried and/or suggested:
 A.
Irrigate every move across the block and then roll it back empty.
This move sequence is similar to the way hand move lines were used.
But a major disadvantage is the long distance the empty line is rolled back.
B.
Skip irrigate every other move across the block and then on return irrigate the skipped sets on the way back instead of rolling back empty.
C.
Irrigate every set across and then start, say twelve hours later, and irrigate every set coming back.
This avoids rolling the line empty all the way back, it also avoids some of the concern about the skip irrigation having alternating unirrigated spots on either side that may bother people.
However, irrigating SO soon after the previous irrigation causes extra deep percolation losses on the wet side of the field.
There is also a longer than needed interval between irrigations on the opposite  side.
This mode is not recommended due to the alternate over irrigation followed by soil water shortage.
D.
Irrigate every set across, roll the line empty for about three sets back and then irrigate the rest of the way back.
Roll the line empty for three sets or SO and then irrigate across again.
This reduces the effect mentioned in Part C above, but does not eliminate it.
E.
Other possible variations exist and depend upon soil, crop and field characteristics.
Much of the maintenance is related to the single cylinder air-cooled engine and associated hydraulics, gears, and chain drive for moving the system.
It is important to follow the engine manufacturers' recommendations for oil viscosity and change intervals and for air filter, spark plug, and other service requirements.
The wheelmove manufacturers provide adequate operation and maintenance instructions to fit their particular drive system.
It is important that the owner/operator read and be familiar with and follow the instructions that match the equipment he/she is using.
Check all nozzles and impact sprinklers for plugging, mismatched sizes, breakage, corrosion or other damage caused by wear or winter weather.
Couplers and connections should be checked for leaks and repairs/replacements should be done early.
It is a good practice to identify problem components at the end of the previous irrigation season and to have the replacement parts on hand for spring installation.
If water leaks occur at joints or drain plugs during irrigation, check the gaskets and pipeline connections for wear or cracks and replace them as needed.
Check and tighten the couplers and connectors as required.
In those places where an open ditch water supply is used, adequate screening and sediment removal are essential for minimum trouble operation This is particularly a problem in the spring and early fall with more trash in the ditches and canals at those times.
There are quite a few anecdotal stories about runaway wheelmoves in high winds.
Anytime the wheelmove is empty, and particularly during the off season, it is essential that it be anchored to prevent wind damage.
Often this is as simple as moving the system over to a fence and tying it down in three or four places to sturdy posts.
However, special wind anchors are available which attach to the lateral pipe and act like a brace to prevent movement.
Wheelmoves are used on almost all of the more than 300 gravity pressurized sprinkler systems in Utah.
Utah's mountain valley topography is favorable to developing gravity pressurized pipelines.
Much of our irrigated area is in mountain valleys in close proximity to canyon streams.
Thus, it is often economic to install a pipeline up the canyon to gain about 110 feet or SO of elevation induced head.
This also has the advantage of reducing open channel water
 seepage losses in the canyon mouth alluvium and extends the available water supply.
Many previously surface irrigated systems  have converted over to gravity pressure wheelmove irrigation.
This switch from the traditional  surface irrigation to gravity pressurized sprinkler has created some interesting situations.
The value of "head end" water access opportunities in preference to a "tail end" location in multiple user surface irrigation systems is well known.
However, when a conversion to gravity pressure sprinklers occurs, the historically "tail end" irrigators become switched to the "head end" position in that they now have the highest pressure.
For some, this is the first time ever that they have had access to abundant water instead of the tail end dribble they are used to.
These advantages are often short-lived as the irrigation company board of directors have responded by requiring pressure or flow regulated nozzles and strict adherence to water deliveries proportionate to water stock shares owned.
While there are similarities in available wheelmove systems, prices and features vary considerably.
Some of these companies manufacture the wheels, fittings, couplers, etc., and ship to dealers who then press couplers on aluminum pipe for the purchaser.
One or two make their own pipe and ship complete systems from the factory.
Presently there are six U.S.
wheelmove manufacturers:
 Rain Dance Irrigation  14402 Chambers Road Tustin, CA 92780  832-3400
 Travis Pattern & Foundry E.
1413 Hawthorne Road Spokane, WA 99207  466-3545
 Representatives of each of the wheelmove manufacturers provided information which was used in writing this fact sheet.
I also appreciate the helpful information from Bill Bullen of Bullen's Inc., of Logan, UT; and from Intermountain Farmers Association of Salina, Utah.
WHERE CAN YOU GET HELP?
Utah State University Extension Service
 Robert W.
Hill, Professor and Extension Irrigation Specialist, Biological and Irrigation Engineering Department, Utah State University, Logan, UT, 84322-4105.
Utah State University Extension is an affirmative action/equal employment opportunity employer and educational organization.
We offer our programs to persons regardless of race, color, national origin, sex, religion, age or disability.
WATER MANAGEMENT IN DRIP-IRRIGATED VEGETABLE PRODUCTION
 Department of Vegetable Crops University of California, Davis, CA 95616 May 1999
 Additional Index Words: trickle irrigation, irrigation scheduling
 Many factors influence appropriate drip irrigation management, including system design, soil characteristics, crop and growth stage, environmental conditions, etc.
The influences of these factors can be integrated into a practical, efficient scheduling system which determines quantity and timing of drip irrigation.
This system combines direct soil moisture measurement with a water budget approach using evapotranspiration estimates and crop coefficients.
Drip  irrigation offers the potential for precise water management and divorces irrigation from the engineering and cultural constraints that complicate furrow and sprinkler irrigation.
It also provides the ideal vehicle to deliver nutrients in a timely and efficient manner.
However, achieving high waterand nutrient-use efficiency while maximizing crop productivity requires intensive management.
Central to that management is appropriate irrigation scheduling, both in terms of timing and volume applied.
This discussion focuses on the practical aspects of drip irrigation management for commercial vegetable production.
There are two basic approaches to scheduling drip irrigation: soil-moisture-based scheduling and a water-budget-based approach that estimates crop evapotranspiration.
There are limitations to both methods, but when used together they are a reliable way to determine both quantity and timing of drip irrigation.
The amount of water evaporated from the soil surface and lost through transpiration of the crop is collectively called evapotranspiration.
With drip irrigation, evaporation from the soil is minimized, particularly in plastic mulch production systems, leaving crop transpiration as the main component of water loss.
Wayne K.
Clatterbuck Associate Professor Forestry, Wildlife & Fisheries
 Water is the most limiting factor for tree survival and growth.
Trees use water during photosynthesis and lose water during transpiration.
Water shortages affect both young and old trees.
Drought conditions can lead to tree decline, making the tree more susceptible to pest problems.
Supplemental watering can greatly assist trees during stressful drought periods in the summer and in the dormant season when soil moisture is limited.
Desiccating winds and lack of precipitation can increase transpiration in evergreens  and create soil moisture deficits even during the winter.
Ideally, watering should begin when soil moisture reaches some critical level.
However, most homeowners do not have the instrumentation to measure soil moisture.
Thus, precipitation events should be monitored and the soil observed to evaluate when watering is needed.
Trees should be watered before they show symptoms of leaf curling or leaf detachment due to a lack of moisture.
The best way to water trees is gradually with a soaker hose or by trickle or drip irrigation.
Sprinklers are less efficient, but they are easy to use.
Use an organic mulch to conserve moisture and apply water over the top of the mulch.
Do not concentrate the water at the base of the tree.
Most of the fine feeder roots of trees are located several feet from the trunk.
Excessive watering at the base of the tree can lead to pest problems and root diseases.
Deep watering a tree with a pipe wedged 12 or more inches in the soil
 Larry Tankersley Extension Forester Forestry, Wildlife & Fisheries
 is not recommended.
Since most of the absorbing roots are located in the upper 12 inches of the soil, surface applications are more beneficial.
Deep watering misses these roots and allows water to drain away from the more active root zone, wasting water and watering efforts.
Surface soaking allows tree roots more opportunity to absorb the water.
Watering should take place beneath the crown of the tree and extending a few feet beyond the drip line of the crown.
Trees need not be watered closer than 3 feet to the base of the trunk and not much beyond the drip line.
These are the areas generally beneath the foliage and shaded by the tree.
Be sure that the water slowly soaks into the soil and does not run off.
Use mulch and slow application rates
 Example of mulched areas free of vegetation under the drip line of trees.
Watering should be concentrated in these areas.
on slopes, heavy  soils and compacted soils.
Grass and other landscape plants adjacent to trees will also benefit from deep-soaking water.
Young, recently planted, ball-and-burlap trees also require frequent watering.
Since water moves downward more than sideways, application of water should be directly over the planting area or the root ball.
The best time to water is during the evening hours and at night.
Trees have a chance to replenish their moisture during these hours when they are not as stressed by hot temperatures.
Watering at night allows effective use of water and less evaporative loss.
Water use by trees increases with increasing temperatures.
Trees surrounded by pavement or adjacent to other energy-absorbing, increased-temperature surfaces can be 20 to 30 degrees F warmer than normal soil surfaces.
For every 18to 20-degree increase in temperature, the amount of water lost by a tree nearly doubles.
Supplemental watering should be part of the tree-maintenance plans, especially during periods of water deficits and in areas where surface temperatures are escalating.
How Much Water and How Often?
The amount of water used in irrigation will depend on soil texture and structure, temperatures and the amount and timing of previous precipitation.
Trees in limited rooting areas , in containers or pots, on slopes, adjacent to warmer surfaces and in sandy soils will probably need more water.
Trees in heavier soils with greater water-holding capacity will require less water.
Overwatering these sites often leads to anaerobic soil conditions, leading to root diseases or death.
Trees should be watered once or twice a week in the growing season if there is limited rainfall.
A few, high-volume waterings are more beneficial than many light and shallow waterings.
Light waterings encourage shallow rooting, which can lead to more damage during lengthy drought.
Once watering begins, it should be continued throughout the drought period when precipitation is limited.
Light watering tends to benefit turf more than trees, especially with in-ground irrigation systems.
Watering with irrigation tends to be shallow, usually at short, cyclic intervals  every day or two.
Greater volume and deeper watering at less-frequent intervals is recommended for tree roots.
Other plants  near the tree compete for available water.
The competition for water can be severe.
Removing some of this competing vegetation from around the tree will reduce moisture stress.
Use mulch to conserve soil moisture and prevent weed competition.
Late in the growing season  as the days get shorter and the temperatures get cooler, trees are preparing themselves for the winter.
Many of the leaves look unhealthy as they curl, become spotty in appearance and begin to change color or discolor.
This is a normal part of the aging process as leaves begin to senesce.
Watering during this time may be necessary when soils are excessively dry.
However, the amount of water and the frequency of watering should be curtailed as the tree does not require as much water for transpiration and photosynthesis.
More long-term planning and research is needed to develop moisture-efficient landscapes to conserve water.
Some species are more adaptable to drought and other environmental stresses than others.
Refer to UT Extension publication SP570 for examples of trees that are more droughttolerant.
Landscapes with more drought-tolerant vegetation will be better able to survive stressful environmental conditions and still provide a functional and aesthetically pleasing landscape.
Adapted from: K.D.
Coder.
1999.
Watering Trees.
University of Georgia, Warnell School of Forest Resources, Athens, GA
 Printing for this publication was funded by the USDA Forest Service through a grant with the Tennessee Department of Agriculture, Division of Forestry.
The Trees for Tennessee Landscapes series is sponsored by the Tennessee Urban Forestry Council.
Irrigation has been part of agriculture in the Great Plains, which Nebraska is right in the middle of, as far back as we have records and probably much longer than that.
The region has productive soils and a good climate to grow crops but does not receive enough rain to produce top yields.
In addition, the rain that is received is inconsistent, thus irrigation can supplement the water the crops need between rains allowing farmers to produce a good crop every year.
The increased yields and year-to-year yield stability has led to a better economic environment in the region as well.
Irrigation Water Quality Criteria
 Fact Sheet No.
0.506
 Salt-affected soils develop from a wide range of factors including: soil type, field slope and drainage, irrigation system type and management, fertilizer and manuring practices, and other soil and water management practices.
In Colorado, perhaps the most critical factor in predicting, managing, and reducing salt-affected soils is the quality of irrigation water being used.
Besides affecting crop yield and soil physical conditions, irrigation water quality can affect fertility needs, irrigation system performance and longevity, and how the water can be applied.
Therefore, knowledge of irrigation water quality is critical to understanding what management changes are necessary for longterm productivity.
Corn plant damaged by saline sprinkler water.
*T.A.
Bauder, Colorado State University Extension water quality specialist; R.M.
Waskom, director, Colorado Water Institute; P.L.
Sutherland, USDA/ NRCS area resource conservationist; and J.G.
Davis, Extension soils specialist and professor, soil and crop sciences.
10/2014
 Irrigation Water Quality Criteria
 Soil scientists use the following categories to describe irrigation water effects on crop production and soil quality:
 Salinity hazard total soluble salt content
 Sodium hazard relative proportion of sodium to calcium and magnesium ions
 pH acid or basic
 Alkalinity carbonate and bicarbonate
 Specific ions: chloride, sulfate, boron, and nitrate.
Another potential irrigation water quality impairment that may affect suitability for cropping systems is microbial pathogens.
Table 1.
General guidelines for salinity hazard of irrigation water based upon conductivity.
*dS/m at 25 C = mmhos/cm
 1Leaching required at higher range.
Good drainage needed and sensitive plants may
 have difficulty at germination.
The most influential water quality guideline on crop productivity is the water salinity hazard as measured by electrical conductivity.
The primary effect of high EC water on crop productivity is the inability of the plant to compete with ions in the soil solution for water.
The higher the EC, the less water is available to plants, even though the soil may appear wet.
Because plants can only transpire "pure" water, usable plant water in the soil solution decreases dramatically as EC increases.
The amount of water transpired through a crop is directly related to yield; therefore, irrigation water with high EC reduces yield W
 Knowledge of irrigation water quality is critical to understanding management for long-term productivity.
Irrigation water quality is evaluated based upon total salt content, sodium and specific ion toxicities.
In many areas of Colorado, irrigation water quality can significantly influence crop productivity.
Table 2.
Potential yield reduction from saline water for selected irrigated crops.
Crop	0%	10%	25%	50%
 Barley	5.3	6.7	8.7	12
 Wheat	4.0	4.9	6.4	8.7
 Sugarbeet	4.7	5.8	7.5	10
 Alfalfa	1.3	2.2	3.6	5,9
 Potato	1.1	1.7	2.5	3.9
 Corn 	1.1	1.7	2.5	3.9
 Corn 	1.2	2.1	3.5	5.7
 Onion	0.8	1.2	1.8	2.9
 Dry Beans	0.7	1.0	1.5	2.4
 Adapted from "Quality of Water for Irrigation." R.S.
Ayers.
Jour.
of the Irrig.
and Drain.
Div., ASCE.
Vol 103, No.
IR2, June 1977, p.
140.
2E = electrical conductivity of the irrigation water in dS/m at 25C.
Sensitive during germination.
EC...
should not exceed 3 dS/m for garden beets and sugarbeets.
mg/L	milligrams per liter
 meq/L	milliequivalents per liter
 ppm	parts per million
 dS/m	deciSiemens per meter
 mmho/cm	millimhos per centimeter
 TDS	total dissolved solids
 Table 4.
Guidelines for assessment of sodium hazard of irrigation water based on SAR and EC 2
 Component	Convert	By	Obtain
 Water nutrient or TDS	mg/L	1.0	ppm
 Water salinity hazard	1dS/m	1.0	1mmho/cm
 Water salinity hazard	1mmho/cm	1,000	1 umho/cm
 Water salinity hazard	ECw 	640	TDS 
 for EC <5 dS/m
 Water salinity hazard	ECw 	800	TDS 
 for EC >5 dS/m
 Water NO3N, SO4-S, B applied	ppm	0.23	lb per acre inch
 Irrigation water	acre inch	27,150	gallons of water
 Potential for Water Infiltration Problem
 water SAR	Unlikely	Likely
 0-3	> 0.7	< 0.2
 3-6	> 1.2	< 0.4
 6-12	> 1.9	< 0.5
 12-20	> 2.9	< 1.0
 20-40	> 5.0	< 3.0
 Modified from R.S.
Ayers and D.W.
Westcot.
1994.
Water Quality for Agriculture, Irrigation and
 Drainage Paper 29, rev.
1, Food and Agriculture Organization of the United Nations, Rome.
Table 3.
Conversion factors for irrigation water quality laboratory reports.
Table 5.
Susceptibility ranges for crops to foliar injury from saline sprinkler water.
Na or CI concentration  causing foliar injury
 Na concentration	<46	46-230	231-460	>460
 CI concentration	<175	175-350	351-700	>700
 Apricot	Pepper	Alfalfa	Sugarbeet
 Plum	Potato	Barley	Sunflower
 Foliar injury is influenced by cultural and environmental conditions.
These data are presented only as general guidelines for daytime irrigation.
Source: Mass  Crop salt tolerance.
In: Agricultural Assessment and Management Manual.
K.K.
Tanji.
ASCE, New York.
pp.
262-304.
potential.
Actual yield reductions from irrigating with high EC water varies substantially.
Factors influencing yield reductions include soil type, drainage, salt type, irrigation system and management.
Beyond effects on the immediate crop is the long term impact of salt loading through the irrigation water.
Water with an EC of 1.15 dS/m contains approximately 2,000 pounds of salt for every acre foot of water.
You can use conversion factors in Table 3 to make this calculation for other water EC levels.
Other terms that laboratories and literature sources use to report salinity hazard are: salts, salinity, electrical conductivity , or total dissolved solids.
These terms are all comparable and all quantify the amount of dissolved "salts"  in a water sample.
However, TDS is a direct measurement of dissolved ions and EC is an indirect measurement of ions by an electrode.
Although people frequently confuse the term "salinity" with common table salt or sodium chloride , EC measures salinity from all the ions dissolved in a sample.
This includes negatively charged ions.
Another common source of confusion is the variety of unit systems used with EC.
The preferred unit is deciSiemens per meter , however millimhos per centimeter  and micromhos per centimeter  are still frequently used.
Conversions to help you change between unit systems are provided in Table 3.
Although plant growth is primarily limited by the salinity  level of the irrigation water, the application of water with a sodium imbalance can further reduce yield under certain soil texture conditions.
Reductions in water infiltration can occur when irrigation water contains high sodium relative to the calcium and magnesium contents.
This condition, termed "sodicity," results from excessive soil accumulation of sodium.
Sodic water is not the same as saline water.
Sodicity causes swelling and dispersion of soil clays, surface crusting and pore plugging.
This degraded soil structure condition in turn obstructs infiltration and may increase runoff.
Sodicity causes a decrease in the downward movement of water into and through the soil, and actively growing plants roots may not get adequate water, despite pooling of water on the soil surface after irrigation.
The most common measure to assess sodicity in water and soil is called the Sodium Adsorption Ratio.
The SAR defines sodicity in terms of the relative concentration of sodium  compared to the sum of calcium  and magnesium  ions in a sample.
The SAR assesses the potential for infiltration problems due to a sodium imbalance in irrigation water.
The SAR is mathematically written below, where
 Na, Ca and Mg are the concentrations of these ions in milliequivalents per liter.
Concentrations of these ions in water samples are typically provided in milligrams per liter.
To convert Na, Ca, and Mg from mg/L to meq/L, you should divide the concentration by 22.9, 20, and 12.15 respectively.
For most irrigation waters encountered in Colorado the standard SAR formula provided above is suitable
 to express the potential sodium hazard.
However, for irrigation water with high bicarbonate  content, an "adjusted" SAR  can be calculated.
In this case, the amount of calcium is adjusted for the water's alkalinity, is recommended in place of the standard SAR.
Your laboratory may calculate an adjusted SAR in situations where the HCO is greater than 200 mg/L or pH is greater than 8.5.
The potential soil infiltration and permeability problems created from applications of irrigation water with high "sodicity" cannot be adequately assessed on the basis of the SAR alone.
This is because the swelling potential of low salinity  water is greater than high EC waters at the same sodium content.
Therefore, a more accurate evaluation of the infiltration/ permeability hazard requires using the electrical conductivity  together with the SAR.
Many factors including soil texture, organic matter, cropping system, irrigation system and management affect how sodium in irrigation water affects soils.
Soils most likely to show reduced infiltration and crusting from water with elevated SAR  are those containing more than 30% expansive  clay.
Soils containing more than 30% clay include most soils in the clay loam, silty clay loam textural classes and finer and some sandy clay loams.
In Colorado, smectite clays are common in areas with agricultural production.
The acidity or basicity of irrigation water is expressed as pH 7.0 acidic; > 7.0 basic).
The normal pH range for irrigation water is from 6.5 to 8.4.
Abnormally low pH's are not common in Colorado, but may cause accelerated irrigation system corrosion where they occur.
High pH's above 8.5 are often caused by high bicarbonate  and carbonate  concentrations, known as alkalinity.
High carbonates cause calcium and magnesium ions to form insoluble minerals leaving sodium as the dominant ion in solution.
As described in the sodium hazard section, this alkaline water could intensify the impact of high SAR water on sodic soil conditions.
Excessive bicarbonate
 concentrates can also be problematic for drip or micro-spray irrigation systems when calcite or scale build up causes reduced flow rates through orifices or emitters.
In these situations, correction by injecting sulfuric or other acidic materials into the system may be required.
Chloride is a common ion in Colorado irrigation waters.
Although chloride is essential to plants in very low amounts, it can cause toxicity to sensitive crops at high concentrations.
Like sodium, high chloride concentrations cause more problems when applied with sprinkler irrigation.
Leaf burn under sprinkler from both sodium and chloride can be reduced by night time irrigation or application on cool, cloudy days.
Drop nozzles and drag hoses are also recommended when applying any saline irrigation water through a sprinkler system to avoid direct contact with leaf surfaces.
Table 6.
Chloride classification of irrigation water.
Chloride  Effect on Crops
 Below 70	Generally safe for all
 70-140	Sensitive plants show
 Above 350	Can cause severe
 Chloride tolerance of selected crops.
Listing in order of increasing tolerance:  dry bean, onion, carrot, lettuce, pepper, corn, potato, alfalfa, sudangrass, zucchini squash, wheat, sorghum, sugar beet, barley.
Source: Mass  Crop Salt Tolerance.
Agricultural Salinity Assessment and Management Manual.
K.K.
Tanji.
ASCE, New York.
pp 262-304.
Boron is another element that is essential in low amounts, but toxic at higher concentrations.
In fact, toxicity can occur on sensitive crops at concentrations less than 1.0 ppm.
Colorado soils and irrigation waters contain enough B that additional B fertilizer is not required in most situations.
Because B toxicity can occur at such low concentrations, an irrigation water analysis is advised for groundwater before applying additional B to irrigated crops.
Table 7.
Boron sensitivity of selected Colorado plants 
 Sensitive	Moderately Sensitive	Moderately Tolerant	Tolerant
 0.5-0.75	0.76-1.0	1.1-2.0	2.1-4.0	4.1-6.0
 Peach	Wheat	Carrot	Lettuce	Alfalfa
 Onion	Barley	Potato	Cabbage	Sugar beet
 Sunflower	Cucumber	Corn	Tomato
 Source: Mass  Salt tolerance of plants.
CRC Handbook of Plant Science in Agriculture.
B.R.
Cristie.
CRC Press Inc.
*Maximum concentrations tolerated in soil water or saturation extract without yield or vegetative growth reductions.
Maximum concentrations in the irrigation water are approximately equal to these values or slightly less.
The sulfate ion is a major contributor to salinity in many of Colorado irrigation waters.
As with boron, sulfate in irrigation water has fertility benefits, and irrigation water in Colorado often has enough sulfate for maximum production for most crops.
Exceptions are sandy fields with <1 percent organic matter and < 10 ppm SO in irrigation water.
Nitrogen in irrigation water  is largely a fertility issue, and nitrate-nitrogen  can be a significant N source in the South Platte, San Luis Valley, and parts of the Arkansas River basins.
The nitrate ion often occurs at higher concentrations than ammonium in irrigation water.
Waters high in N can cause quality problems in crops such as barley and sugar beets and excessive vegetative growth in some vegetables.
However, these problems can usually be overcome by good fertilizer and irrigation management.
Regardless of the crop, nitrate should be credited toward the fertilizer rate especially when the concentration exceeds 10 ppm NO3-N.
Table 3 provides conversions from ppm to pounds per acre inch.
The quality of irrigation water available to farmers and other irrigators has a considerable impact on what plants can be successfully grown, the productivity of these plants, and water infiltration and other soil physical conditions.
The first step in understanding how an irrigation water source can affect a soil-plant system is to have it analyzed by a reputable lab.
The Colorado State University Extension factsheet 0.520, Selecting an Analytical Laboratory can help you locate a lab in your area that is familiar with irrigation water quality.
Additional information on understanding and managing for saline and sodic conditions is found in Colorado State University factsheets 0.503, Managing Saline Soils and 0.504, Managing Sodic Soils.
Leave Room for Storing Rainfall
 Monitoring soil moisture and leaving it moderately dry during the vegetative growth states also leaves room for the soil to store any rainfall that may come.
Too wet and youll lose that rainfall as runoff or deep percolation.
Each inch of rainfall you store saves irrigation, input costs and prevents nitrate leaching.
COMPARISON OF SOIL WATER SENSING METHODS FOR IRRIGATION MANAGEMENT AND RESEARCH
 S.R.
Evett*, T.A.
Howell, and J.A.
Tolk Soil and Water Management Research Unit USDA-ARS, Bushland, TX *Voice: 806-356-5775, Fax: 806-356-5750 Email: isrevett@cprl.ars.usda.gov
 As irrigation water resources decrease and deficit irrigation becomes more common across the Great Plains, greater accuracy in irrigation scheduling will be required.
With deficit irrigation a smaller amount of soil water is held in reserve and there is less margin for error.
Researchers investigating deficit irrigation practices and developing management practices must also have accurate measures of soil water content in fact, the two go hand in hand.
New management practices for deficit irrigation will require more accurate assessments of soil water content if success is to be ensured.
This study compared several commercial soil water sensing systems, four of them based on the electromagnetic  properties of soil as influenced by soil water content, versus the venerable neutron moisture meter , which is based on the slowing of neutrons by soil water.
While performance varied widely, the EM sensors were all less precise and less accurate in the field than was the NMM.
Variation in water contents from one measurement location to the next was much greater for the EM sensors and was so large that these sensors are not useful for determining the amount of water to apply.
The NMM is still the only sensor that is suitable for irrigation research.
However, the NMM is not practical for on-farm irrigation management due to cost and regulatory issues.
Unfortunately, our studies indicate that the EM sensors are not useful for irrigation management due to inaccuracy and variability.
A new generation of EM sensors should be developed to overcome the problems of those currently available.
In the meantime, tensiometers, electrical resistance sensors and soil probes may fill the gap for irrigation management based on soil water sensing.
However, many farmers are successfully using irrigation scheduling based on crop water use estimates from weather station networks and reference ET calculations.
When used in conjunction with direct field soil water observations to avoid over irrigation, the ET network approach has proved useful in maximizing yields.
For most uses and calculations in irrigation management and research, soil water content (Ov, m m-3 is expressed as a volume fraction,
 volume of soil water [1] total volume of soil
 Soil texture is quantified by the relative percentages by mass of sand, silt, and clay after removal of salts and organic matter.
Both texture and structure determine the soil-water characteristic curve, which quantifies the relationship between soil water content and soil water potential, which is the strength with which the soil holds water against removal by plants.
This relationship differs largely according to texture , but can be strongly affected by organic matter and salt contents.
The range of plant-available water  possible for a given soil is determined by two limits.
The upper limit, also know as the field capacity, is often defined as the soil water content of a previously saturated soil after 24 h of free drainage into the underlying soil.
The field capacity can be viewed as the water content below which the soil does not drain more rapidly than the crop can take up water.
In heavier textured  soils, this limit is often characterized as the water content at -0.10 kPa soil water potential.
In more sandy  soils, the upper limit may be more appropriately placed at -0.33 kPa soil water potential.
The difference in soil water potentials that are related to the upper limit of PAW is due to the relatively large conductivities for water flux in lighter soils near saturation, which means that lighter soils will drain more rapidly.
The lower limit of PAW, also known as the permanent wilting point, is often defined as the soil water content at which the crop wilts and cannot recover if irrigated.
The soil water potential associated with the lower limit varies with both the crop and the soil; but is often taken to be -1500 kPa.
The amount of PAW differs greatly by soil texture.
For example, as illustrated in Figure 1, a clay soil may have a plant available water content range of 0.19 to 0.33 m m -3 ,
 or 0.14 m 3 m -3 PAW; whereas a silt loam may have a larger PAW content range or 0.21 m 3 m -3 PAW.
Sandy soils tend to have small of 0.08 to 0.29 m 3 m -3 , amounts of PAW, such as the 0.04 m m -3 for the sandy loam illustrated in Fig.
1 or the 0.06 m m -3 reported by Morgan et al.
for an agriculturally important fine sand in Florida.
Thus, irrigation management often focuses on applying smaller amounts of water more frequently on sandy soils.
Figure 1.
The soil water content VS.
soil water matric potential relationship for three soil textures as predicted by the Rosetta pedotransfer model.
Horizontal lines are plotted for the field capacity, taken as -333 cm , and for the wilting point, taken as -15 000 cm.
Crops differ in their ability to extract water from the soil, with some crops not capable of extracting water to even 1500 kPa, and others able to extract more water, reaching potentials even more negative than -1500 kPa .
Confounding this issue is the soil type effect on rooting density and on the soil hydraulic conductivity, both of which influence the lower limit of PAW for a particular crop.
The fact that soil properties vary with depth means that the lower limit of PAW may be best determined from field, rather than laboratory, measurements.
The available soil water holding capacity  is a term used to describe the amount of water in the entire soil profile that is available to the crop.
Because water in the soil below the depth of rooting is only slowly available, the AWHC is generally taken as the sum of water available in all horizons in the rooting zone, calculated for each horizon as the product of the horizon depth and the PAW for that horizon.
For example, for a crop rooted in the A and B horizons of a soil the AWHC is the product of the PAW of the A horizon times its depth plus the PAW of the B horizon times the rooted depth in the B horizon.
Figure 2.
Deviation of the lower limit of water extraction, OLL, measured in the field using a neutron probe, from that measured at -1500 kPa in the laboratory on soil cores taken at several depths in the soil.
Data are for corn, sorghum and wheat crops grown in a Ulysses silt loam.
Table 1.
Example calculation of available water holding capacity  in the rooting zone of a crop rooted to 0.95-m depth in a soil's A and B horizons, each with a different value of plant available water.
range	depth	depth	PAW	AWHC
 Horizon				
 A, silt loam	0 to 20	0 to 20	20	x	0.21	=	4.2
 B, clay	20 to 100	20 to 95	75	X	0.14	=	10.5
 For irrigation scheduling using the management allowed depletion  concept , irrigation is initiated when soil water has decreased to the OMAD level.
The OMAD value may be chosen such that the soil never becomes dry enough to limit plant growth and yield, or it may be a smaller value that allows some plant stress to develop.
Choice of the OMAD value needs to consider the irrigation capacity , which determines how quickly a given irrigation amount can be applied to a specified sized field.
It is common to irrigate at some value of water content, OMAD+, that is larger than OMAD.
This is done to ensure that the error in water content measurement, which may cause inadvertent over estimation of water content, is not likely to cause irrigation to be delayed until after water content is actually smaller than OMAD Minimizing the difference, d = OMAD+ OMAD, allows the irrigation interval to be increased.
It is desirable to know the number of samples required to estimate the water content to within d of OMAD at the  probability level.
Knowing the sample standard deviation, S, of soil water content measurements, the required number of samples, n, can be estimated as
 where Ua/2 is the  value of the standard normal distribution, and  is the probability level desired.
Equation [2] is valid for normally distributed values that are independent of one another and for the population standard deviation estimated from the sample standard deviation, S, of a large number of samples.
Figure 3.
Illustration of the soil profile indicating fractions of the total soil volume  that are occupied by water at four key levels of soil water content.
For this silty clay loam, the soil is full of water at saturation , drains easily to field capacity , and reaches the permanent wilting point  at 0.18 m m water content.
To avoid stress in a crop such as corn, irrigations are scheduled when the soil water content reaches or is projected to reach 0.25 m 3 m -3 , the value of OMAD for this soil and crop.
Because this analysis depends on the sample standard deviation determined by repeated readings with a particular device, it encapsulates the variability of readings from that device; but it does not include bias  that may be present in the device readings due to, for example, inaccurate calibration.
Aside from large-scale spatial variability, the calibration is a potentially large source of error; and this error is not reduced by repeated sampling.
Thus, careful field calibration is essential to minimize such bias.
In most cases, this analysis may be applied to values of soil profile water storage that are calculated on the basis of samples at multiple depths.
For example using the data for the three soils in Fig.
1, the differences between the values of water content at field capacity, OFC, and at the permanent wilting point, OPWP, are the plant available water, OPAW.
Assuming that the management allowed depletion is 0.6 of OPAW, the allowable ranges of water content during irrigation scheduling are 0.126, 0.085, and 0.022 m m for silt -3 loam, clay, and loamy sand, respectively , a specific sensor must still provide an acceptably precise mean value of field readings.
Table 2.
Example calculation of management allowed depletion (MAD, m m-3 in three soils with widely different textures.
The small range of MAD severely tests the abilities of most soil water sensors, particularly for the loamy sand soil.
OFC	OPWP	OPAW	MAD	MAD
 Horizon	(m m-3	(m  3	(m  3	fraction
 silt loam	0.086	0.295	0.209	X	0.6	=	0.126
 loamy sand	0.066	0.103	0.037	X	0.6	=	0.022
 clay	0.190	0.332	0.142	x	0.6	=	0.085
 The ability to provide an acceptably precise mean value of field readings using a cost-effective number of access tubes or sensors in the soil is where some sensors are lacking.
In particular, the capacitance sensors appear to be very sensitive to small-scale variations in soil water content, and thus require many more access tubes to attain a precision equal to that attained with much fewer NMM or gravimetric samples.
Another example is data from Australia showing that the standard deviation of profile water contents reported by the EnviroSCAN system was 12.36 cm compared with S of 0.93 cm for the NMM in the same flood irrigation basin.
If no other information were available about soil water variability, sampling a field for profile water content would typically require many profiles to be sampled, either directly or using water content sensor in access tubes.
However, distribution of profile water content tends to be temporally stable in some fields, at least over a growing season.
This means that there are locations in the field where the profile water content is usually very representative of the mean for the field, or of the extremes .
Irrigators recognize this when they observe the crop in a field for water stress or when they probe the soil for water content.
For example, an irrigator may ignore drier crops at the edge of a field, or a low, wet corner of the field when assessing the need to irrigate.
The tendency is to make observations in places that show the mean behavior of the field.
This is not an adequate way of choosing observation locations for a scientific experiment for which blocking,
 randomization, replication and other considerations are required for statistical validity.
But, for irrigation management in production agriculture, the choosing of measurement locations on the basis of observed soil and plant properties that are representative of the field may be the most cost effective and efficient method.
Table 3.
Calculation using Eq.
[2] of the number of access tubes  needed to find the mean profile water storage in a field to a precision d  at the  probability level  for a given field-measured standard deviation  of profile storage.
Data are from ten access tubes for each device, spaced at 10-m intervals in transects that were 5-m apart.
a =	0.05	0.10
 d  =	1	0.1
 Method	condition	S 	N	N
 Diviner 2000+	Irrigated	1.31	6.6	464
 Dryland	2.42	22.5	1584
 EnviroSCAN	Irrigated	1.52	8.9	625
 Dryland	2.66	27.2	1914
 Delta-T PR1/6+	Irrigated	2.72	28.4	2002
 Dryland	12.16	568.0	40006
 Sentry 200AP	Overall	3.78	54.9	3866
 Trime T3	Irrigated	0.75	2.2	152
 Dryland	2.38	21.8	1533
 Gravimetric by	Irrigated	0.45	0.8	55
 push tube	Dryland	0.70	1.9	133
 CPN 503DR	Irrigated	0.15	0.1	6
 NMM	Dryland	0.27	0.3	20
 t Capacitance type sensors + Estimated from data of Evett and Steiner 
 The previous paragraph not withstanding, the scheduling of irrigations on the basis of a single profile water content measurement in a field is prone to large errors.
Also, there is strong evidence that actively growing vegetation can reduce or eliminate the temporal stability of water content, particularly in the root zone  and in fields with little topographic relief.
A reasonable minimum for the NMM or gravimetric sampling is three to four profile water content measurements at locations chosen to be representative of the field.
For other methods, such as the capacitance sensors, that sense smaller volumes resulting in larger values of S, the number of profile measurements needed may be much greater.
Figure 4.
Ranking of locations by their average relative difference from the field mean profile water content.
Vertical bars indicate the range of values observed over the course of the experiment.
Location 21 in particular was close to the mean profile water content at all times.
Electromagnetic  soil water sensing systems are rapidly entering the soil water sensor market.
Common systems use sensors based on capacitance or time domain reflectometry  principles.
For three capacitance soil water sensing systems , the Trime T3 quasi-TDR soil water sensing system, and the neutron moisture meter , we developed soil-specific calibrations for the A, Bt, and calcic Bt horizons of the Pullman soil at Bushland, TX.
We applied these calibrations to data acquired in a wheat field in 2003 in order to investigate the variability of soil water estimates without the confounding factor of inaccurate factory calibrations.
There were ten access tubes for each system, arranged in linear transects.
After the first three measurement cycles, half of the winter wheat field  was irrigated to see how the five systems were able to sense the differences in water content.
Access tubes were spaced 10-m apart.
In addition to the five soil water sensing methods, gravimetric samples were taken with an hydraulic push probe  in transects on some of the sampling dates.
Sampling points were spaced 10-m apart; and samples were 10-cm in height and had a volume of 75.5 cm 3 The data in Table 3 are from this study.
Profile water contents reported by the six methods differed considerably , particularly in the degree of water content variability and the shape of the profile, which is influenced by over and under estimation of water content at different depths.
The smallest variability of water content was reported by the NMM; and the NMM data matched the direct gravimetric data better than any other sensor.
Variability of gravimetric measurements was only slightly larger than that of the NMM; and variability of Trime T3 results was somewhat more variable, but still representative of the profile water content in much the same way as the NMM.
In this field, the depth to the CaCO3-enriched  layer was ~120 cm.
As shown by the NMM and gravimetric results, inherent soil water variability was larger in the caliche horizon below 120 cm than in the Bt and A horizons above 120 cm.
The larger variability below 120 cm is due to the presence of prairie dog burrows that are present in the softer caliche soil.
These are invariably found in soil pits dug at the Bushland research station.
The burrows contain soil that has washed in from the overlying Bt and A horizons; and they typically exhibit smaller bulk density than the overlying and surrounding soil.
Depending on the presence or absence of macropore flow, typically occurring in soil cracks in the overlying A and Bt horizons of this soil, the soil in burrows may exhibit larger or smaller water content than surrounding soil.
While all of the EM sensors exhibited more variability than the NMM, the three capacitance sensors exhibited the most variability as well as a tendency to severely underestimate water content in the A horizon above 50-cm depth.
This could be indicative of a weakness in the soil-specific calibrations of Evett et al.
, or it might be due to poor contact of the plastic access tubes in this soil after more than seven months in the soil.
Particularly near the top of the access tubes, vibration from repeated instrument insertion and extraction can cause small annular air spaces to develop between the soil and access tube.
Also, shrinkage and swelling of the soil could create air space around the tubes near the surface where the soil is unconstrained.
The NMM is not sensitive to such small air gaps, but they can permit water movement down the outside tube walls.
The under estimation by the capacitance sensors was so consistent that we think it is due to a very strong dependency of the calibration equation coefficients on clay content of the soil, which increases strongly with depth in this soil.
The variability in water contents illustrated in Fig.
5 is reflected in the values of S in Table 3.
A second study was done in a drip irrigated sweet pepper field near Five Points, CA, in the San Joaquin Valley on a Panoche clay loam soil in 2005.
Data are presented for two periods in the season.
The first period was during the irrigation season as pepper fruits were developing; and the second period was during field dry down after irrigation had been suspended, but the crop was still transpiring.
Sensors studied were the NMM, and three capacitance sensors: the Delta-T PR2/6 , the Sentek Diviner 2000 and the Sentek
 EnviroSCAN.
Data from the NMM showed that, below the surface, the soil water content profile was nearly uniform with depth at both dates, though the decrease in water content during dry down was evident.
Gravimetric data  from the same field showed the same uniformity of water content with depth as did the NMM.
Data from the PR2/6 indicated that the water content was much more variable, and that water content increased with depth during the dry down period.
Neither indication is true.
What is true is that this soil becomes increasingly saline during the irrigation season, and that salinity increases with depth in the profile at the end of the season.
Thus, the increasing water contents with depth from the PR2/6 are the result of this sensor being sensitive to salinity, not an indication that water content increased with depth.
Data shown are using the factory calibration for clay soils for the PR2/6, which resulted in both over and under estimation of water contents, depending on the depth.
Data for the EnviroSCAN and Diviner 2000 for the same two periods are similar.
They show more variability than actually existed at the scale of crop water uptake; and similar to the PR2/6, they showed a false increase of water content with depth late in the season, probably due to salinity increasing with depth.
Again, the use of factory calibrations resulted in some large over and under estimations of water content.
Figure 5.
Profile water contents for ten transect locations for each of five sensor systems, in a winter wheat field on 5 November, 2003, compared with gravimetric measurements.
Half of the field  was irrigated.
Sensing methods were frequency domain , quasi-TDR , and the neutron moisture meter.
Photograph of the Pullman soil profile to 2-m depth showing the lighter colored caliche horizon.
Figure 6.
Water content data from two periods for each sensor during a 2005 study in California.
The first period was during the irrigation season as pepper fruits were developing; and the second period was during field dry down after irrigation had been suspended, but the crop was still transpiring.
Sensors studied were the NMM and the Delta-T PR2/6 , and the Sentek Diviner 2000 and EnviroSCAN.
World wide, 20% of irrigated soils are salt affected.
Sensitivity to soil salinity, measured as the bulk electrical conductivity , limits the applicability of frequency domain or power loss sensors in many irrigated soils in which BEC varies across the field  and with time.
Variations of BEC of as much as 12 dS m 1 can occur over distances of less than one meter , and differences equally as large can occur from year to year or even within an irrigation season in one location.
Abdel gawad et al.
measured periodic soil solution EC variations of 5 to 6 dS m 1 under drip irrigation in Syria.
Mmolawa and Or  measured a BEC change from 0.3 to 2.3 dS m -1 in a few hours under drip irrigation of corn.
While it is possible to calibrate most sensors for a particular BEC, in these situations of temporally and spatially variable BEC, such a calibration is not applicable.
From the available data, it is clear that errors larger than 50% in soil water content at a single location, and errors similarly large in soil profile water content are possible given the range of BEC values measured.
Spatial and temporal variations of BEC are not confined to drip irrigation, but are present under furrow, flood, and sprinkler irrigation as well.
ECe color scale 
 Figure 7.
Variations in EC of saturation paste soil extracts  in two dimensions of a pistachio plantation that was drip irrigated in California.
Figure 8.
Variations in EC from saturation paste soil extracts from a single location in a drip-irrigated tomato field in California in two different years.
No yield variation was found.
Sensors based on electromagnetic principles are often also sensitive to clay content and type even in non-saline soils.
This is because clays exhibit varying degrees of charge and are associated with cations or anions in the soil solution to varying degrees.
Commonly, clays exhibit negative charge and are associated with cations to a degree that is evaluated as the cation exchange capacity.
As the soil content of high CEC clay increases, the soil becomes more electrically lossy, that is, more capable of affecting the movement of electrical fields.
This affects the frequency of oscillation of capacitance systems and the power loss of power loss systems in a way that is separate from, but not completely independent of, the soil water content.
Examples include the much different calibration equations developed for the several soils existing under one center pivot irrigation system in France  , and the different calibration equations reported by Baumhardt et al.
at Lubbock, TX, and Morgan et al.
for the Sentek EnviroSCAN system.
Figure 9.
Calibrations of the model CS615 soil water probe from Campbell Scientific, Inc.
in nine different soil layers of three different soils , illustrating the wide variance in calibration equations for different layers in a particular soil and among soils.
Several types of granular matrix sensors  are on the market.
The sensor consists of a porous medium in which are embedded two wires, often connected to wire mesh electrodes inside the sensor.
The reading is of the electrical resistance in the medium between the wires or mesh electrodes.
Often, a quantity of gypsum  is included to buffer the soil water solution and decrease effects of salinity on the resistance.
The greater the soil water tension, the less water is in the porous medium, and the greater the electrical resistance.
Calibration may be done in a porous medium covering a pressure plate, which is subjected to several values of pressure in a pressure chamber.
Calibrations are soil specific, so it is wise to use the soil to be measured as the porous medium.
Installation and contact problems are similar to those for a tensiometer or gypsum block, including contact problems in coarse sands and shrink/swell clays.
At tensions less than 30 kPa, Taber et al.
found that tensiometers responded more rapidly than GMS sensors in silt loam, loam, and coarse sand.
As with gypsum blocks, reading requires an alternating current to minimize effects of capacitive charge build up and ionization.
Lack of precision and calibration drift over time may limit use of GMS for determining soil water potential gradients.
The useful range of readings is approximately 10 to -200 kPa matric potential, though Morgan et al.
were able to use GMS sensors to -5 kPa in a fine sand.
Sensors may be manually read or data logged.
Some
 hysteresis is noted with these sensors; and they are temperature sensitive.
Like gypsum blocks, GMS may be installed to practically any useful depth, limited only by wire length.
Fewer problems with soil contact are noted with GMS.
The usefulness of GMS systems for irrigation scheduling has been illustrated by work done with onions, potato , alfalfa, and sugar beet in the Malheur Valley of Oregon.
Because of soil and irrigation variability, at least six sensors should be used to provide data for irrigation scheduling.
For irrigation science, the GMS can be useful if calibrated for the soil over a range of temperatures and soil water potentials, and if soil temperature is measured at the location of each sensor so that calibration corrections for temperature can be applied.
Automatic irrigation scheduling has been successfully implemented using GMS for high-value row crops  and for landscapes.
Figure 10.
Soil water potential in a sprinkler-irrigated potato field as sensed with six granular matrix sensors datalogged using a Hansen model AM400 data logger, showing very good control of soil water potential.
Note the dry-down period at the end of the irrigation season 
 Direct observations can be very useful in guiding irrigation management.
The soil feel and appearance method involves squeezing a ball of soil in the hand and comparing its feel and appearance to photographs that show the appearance of different soil textures at various water contents.
The USDA-NRCS publishes a handy guide with the photographs and descriptions of how the soil feels in the
 Another method of direct observation common in irrigated Great Plains soils is the push probe.
The probe consists of a 3/8 or 1/2-inch diameter steel rod with a T handle at the top and a ball bearing of slightly larger diameter welded to the bottom end.
The ball bearing makes a hole larger than the diameter of the rod so that most of the resistance to penetration into the soil is at the ball, not due to friction between the soil and the rod.
An experienced irrigator can fairly quickly assess variability in irrigation infiltration depth across a field, and perhaps most importantly can identify deep wetting of the profile that can result in deep percolation losses.
Water lost to deep percolation carries with it costly fertilizers, the loss of which can reduce yield appreciably.
Indeed, among farmers who have been over irrigating in the past, it is a common observation that reduction in water application is accompanied by increase in yield.
T handle of same material
 Push-probe, shovel insertion, etc.
Fairly accurate for depth of wetting
 front important for assessing
 Inaccurate for water content, but
 useful in experienced hands
 Push probe allows quick evaluation of
 irrigation uniformity over the field
 Approx.
10 mm steel rod
 Approx.
12 mm ball bearing welded to end
 Figure 11.
The push probe, a useful device for assessing irrigation penetration depth and relative water content.
Compared on Four Continents.
17th World Congress of Soil Science, August 14-21, 2002, Bangkok, Thailand, Transactions, pp.
1021-1 1021-10..
Howell, Terry, Marek, Thomas, New, Leon, and Dusek, Don.
1998.
Weather network defends Texas water tables.
Irrig.Business & Technology VI:16-20.
Managing High Water Tables in Corn Production
 Poorly drained areas frequently require drainage to optimize crop growth.
In these areas, high water content can drown crops, delay seeding, increase N fertilizer loss, increase crop disease, and slow seed germination.
These areas often are small depressional zones in large, relatively flat fields or lower elevational areas in fields with rolling topographies.
Individualized drainage systems need to be developed based on a field's topography.
In addition, many poorly drained fields have high salt concentrations.
This chapter addresses high water table management.
Lowering High Water Tables with Subsurface Drainage
 Approximately 25% of the farmable acres in the U.S.
have some form of artificial drainage.
Subsurface  drainage is used to remove excess soil water and salts using drainage pipes or tiles installed below the soil surface.
Since the 1970s, perforated polyethylene tubing has become the most popular material for drainage pipes.
Historically, cylindrical clay or concrete sections, or "tiles," were used, SO the customary terms "tiling" and "tile drainage" are still used to describe subsurface drainage.
Drains typically are installed below the root zone at depths ranging from 2.5to 4-feet.
The drain line outlets generally are streams or open ditches.
Figure 30.1 Water flowing from the outlet of a subsurface drain.
Subsurface drainage is used to enable timely planting, harvesting, and other field operations, and to increase crop yields.
Many South Dakota soils have poor natural drainage, and without artificial drainage, they would remain waterlogged for extended periods from excess precipitation.
By removing excess water from the root zone , salts are flushed from the root zone, and the risk of soil compaction from field operations is reduced.
Since soils with subsurface drainage dry out and warm up faster in the spring than undrained soils, subsurface drainage can enhance the ability to implement notill and minimum-tillage systems.
Along with improved yield, subsurface drainage tends to reduce surface runoff and peak flows by
 encouraging increased water infiltration into soil.
Zucker and Brown  reported that subsurface drainage reduced surface runoff from 29% to 65%, and peak flows were reduced from 15% to 30%.
The impacts of subsurface drainage on water quality can be both positive and negative.
Because subsurface drainage reduces surface runoff, sediment and nutrient losses from surface runoff are also reduced.
Sediment loss reductions range from 16% to 65%, and phosphorous losses may be reduced up to 45%.
However, subsurface drainage can increase nitrate export.
The nitrate concentration in drainage water frequently exceeds the drinking water standard.
There are several emerging practices designed to maintain the benefits of drainage, while reducing negative environmental impacts.
South Dakota drainage law currently  delegates regulatory authority of drainage to the county level.
Therefore, a first step in any drainage project is to consult with the county drainage board  about permitting requirements.
Note that other states have different governing authorities for regulating drainage activities.
In addition to county regulations, the Swampbuster provisions introduced in the 1985 Food Security Act  discourage the drainage of wetlands for agricultural use.
Therefore, local USDA Farm Service Agency and Natural Resources Conservation Service offices also must be consulted about drainage plans.
Draining wetlands can result in the loss of farm program benefits.
When preparing a drainage plan, it is useful to gather background information from county soil surveys, topographic maps, aerial photos, climate data, local water management authorities, and drainage guidelines from neighboring states.
Figure 30.2 Subsurface drainage removes excess water from the root zone via pipes or "tile" buried beneath the soil surface.
A primary goal of subsurface drainage is increased profit for the producer.
Because installing a subsurface drainage system involves a significant investment, an economic feasibility study should be conducted before installation.
Factors that should be considered are expected yield response, impact on equipment and material costs, and cost of the drainage system over its lifetime.
Although the actual lifetime of a welldesigned drainage system may be 50 to 100 years, its economic lifetime often is assumed to be 20 to 30 years.
Estimating values to use in the economic analysis, particularly yield response, is difficult.
Comparisons of combine yield monitor data from poorly drained and adequately drained areas of a field may provide some indications of potential yield response when drainage improvements are made.
Other potential sources of information include neighboring producers who have installed drainage systems, and drainage contractors.
As examples of yield increases following drainage, results from an 11-year study in Ohio indicated that subsurface drainage increased corn yields by 20 to 30 bushels per acre , and data based on 20 years of yield records from Ontario showed yield increases of 26 bushels per acre  on average for corn.
Additional information is available in Hofstrand.
Subsurface drainage systems perform only as well as the outlet, SO good drainage design should begin by ensuring there is a suitable outlet.
Typically, the drainage outlet is the lowest point in the drainage system.
At the outlet, water is delivered to a natural or manmade open channel that is deep enough SO that the bottom of the outlet is at least 1 foot above the normal low-water level in the waterway.
Proper
 maintenance is needed to prevent drainage ditches from becoming clogged by sediment and/or vegetation.
Consequently, erosion and weed control are essential to ensure that these systems continue to function effectively.
Any existing drainage outlet should be checked to see whether it can handle additional water, and if it is deep enough to allow the planned additional field drains to be placed at the desired depth.
Pumped outlets may be considered where there is an otherwise adequate outlet that is not deep enough to allow for gravity drainage.
The outlet should be protected from rodents or other small animals, washout, and erosion.
In addition to the physical requirements for an outlet described above, the outlet also must meet all legal and regulatory requirements for drainage outlets.
In general, the drainage should occur through a natural or established watercourse and should not alter substantially the flow such that it causes unreasonable harm downstream.
In many cases, downstream notification or approval may be required as part of the regulatory process.
Regardless, drainage problems often are not limited to a single property, SO working with neighbors to address drainage problems can result in more effective solutions and less potential for disputes.
Surface intakes traditionally have been used to remove ponded water from closed depressions or potholes through a subsurface drainage system.
By providing a direct connection to water at the surface, however, these intakes serve as a shortcut for sediment, nutrients, or other pollutants to travel to downstream surface water bodies.
Several alternative practices exist for removing ponded surface water that can eliminate the need for traditional surface intakes.
Often a more intense set of closely spaced laterals or a buried coil of tile in the low spot will drain water quickly enough that a surface intake is not needed.
A rock or "blind" inlet is another option that eliminates the need for a riser and filters out sediment before it enters the drain.
Open intakes that are flush with the soil surface, in particular, should be avoided because they provide no protection from sediment entering the system.
Commercial low-velocity inlets with wicks are available that filter out sediment before it enters the drainage system.
More traditional slotted or perforated risers allow for some settling of sediments before water enters the intake.
A permanent grass buffer should be established around the riser to trap sediment and other pollutants before they reach the intake.
If surface intakes are added to a subsurface drainage system, the system should be large enough to accommodate the concentrated flow entering from the surface.
Surface intakes can be a source of weakness in the drainage system because hitting an intake with farm implements can damage the connecting line.
Offsetting the intake on a short lateral line helps protect the main line.
The drainage system should be designed to remove excess water from the active root zone within 24 to 48 hours of excess precipitation to prevent crop damage.
The rate at which the drainage system removes water from the soil is commonly called the drainage coefficient and is a measure of the system capacity.
The drainage coefficient typically is expressed as the depth of water removed in a 24-hour period.
Because drain spacing and sizing will be determined by the drainage coefficient, the choice of a drainage coefficient is an economic, as well as, an agronomic decision.
Table 30.1 Typical drainage coefficients for humid regions.
No Surface	Blind Surface	Open Surface
 Mineral Soils			
 Field crops	3/8 1/2	1/2 3/4	1/2 1
 High value crops	1/2 3/4	3/4 1	1 1/2
 Field crops	1/2 3/4	3/4 1	1 1 1/2
 High value crops	3/4 1/2	1/2 2	2 4
 Typical drainage coefficients for humid regions are shown in Table 30.1.
Skaggs  developed
 equations for estimating a drainage coefficient to maximize profit based on growing-season rainfall.
Based on these equations, design drainage coefficients for eastern South Dakota range from 1/6 to 1/2 inches per day.
In addition to this guidance, the choice of an appropriate drainage coefficient should be made based on local conditions, experience, and judgment.
If surface inlets will be used to directly drain water from the surface through the drain pipes, a larger drainage coefficient should be used to account for the additional water coming from the surface.
Drain Depth and Spacing
 The depth and spacing of parallel drains necessary to achieve a certain drainage coefficient are determined, in large part, by the hydraulic conductivity  of the soil and the depth to a low permeability barrier.
For single targeted drains, the hydraulic conductivity and depth to the barrier will determine the effective distance from the drain that will be adequately drained given the depth of the drain.
Depth and spacing should be considered simultaneously when trying to achieve a desired drainage coefficient.
As shown in Figure 30.2, the water table will be highest midway between two parallel drains and lowest at the drains themselves.
The depth and spacing are chosen to maintain a minimum depth to the water table midway between the drains.
The height that the water table will reach above the drains will be less for drains spaced more closely together.
Table 30.2 Typical drain spacing and depths for parallel drains for various soils.
Drain Spacing  for:
 Soil Type	Permeability	Fair	Good	Excellent	Depth
 Drainage	Drainage	Drainage	
 		
 Clay loam	Very low	70	50	35	3.0-3.5
 Silty clay loam	Low	95	65	45	3.3-3.8
 Silt loam	Moderately low	130	90	60	3.5-4.0
 Loam	Moderate	200	140	95	3.8-4.3
 Sandy loam	Moderately high	300	210	150	4.0-4.5
 Drains typically are placed 3to 4-feet deep.
If possible, drains should be placed above shallow lowpermeability layers.
The minimum depths to avoid damage from heavy equipment are 2 feet for laterals with 3to 6-inch diameter pipes and 2.5 feet for mains with pipes 8-inches or more in diameter.
Ideally drainage systems would have uniform depth, but field topography and the layout design will determine actual drain depths.
The layout of the drainage system, along with the design decisions made above, will determine the uniformity of drainage for the field or area.
Drainage system layout is chosen to best match field topography, outlet location, and drainage needs of the field.
Topography will dictate what layout options are practical.
There are several layout options available for drainage systems.
Main lines are run through natural low areas toward the outlet, and lateral lines may be added to provide drainage for larger wet areas.
The layout may be complex or as simple as a single drain line from a wet spot in the field.
Parallel drainage systems are used to drain large areas or entire fields of regular shape and uniform soils.
Herringbone systems are typically used in relatively narrow depressions such as those along shallow drainageways.
Double main systems are used where a larger or deeper drainageway divides the field.
Targeted drainage systems are used where there are isolated wet areas that require drainage.
For any layout pattern, a general guideline to follow when laying out the system is to align lateral lines along the field contours to the extent possible.
This allows the lateral lines to act as interceptors of water as it moves down the slope.
Collectors or main lines are then placed on steeper grades or in swales to allow for a more uniform lateral grade line.
Drain Grades and Envelopes
 Drainage systems should be designed such that both minimum and maximum grade recommendations are followed.
This is to ensure that flow velocities are within an acceptable range.
The grade should be sufficient to prevent sediments from accumulating in the drains and shallow enough to prevent excessive pressure that could result in erosion of soil around the drain.
Drains in stable soils  can be placed on shallower grades.
Soils lower in clay, with more fine sands and silt, require steeper grades.
Table 30.3 lists the minimum recommended grades for various pipe sizes depending on whether fine sands and silts are likely to be a problem.
In addition to minimum grades, the use of drain envelopes should be considered for soils high in fine sands and silts, particularly if shallower grades must be used.
Materials used for drain envelopes include gravel, synthetic fiber membranes, and pre-wrapped geotextiles.
To prevent problems with excessive pressures and velocities, mains should not be placed on grades 4 0.07 0.05 0.55 greater than 2% where practical.
When steeper 5 0.05 0.04 0.41 grades must be used, additional precautions should 6 0.04 0.03 0.32 be taken, which may include the use of pressurerelief wells.
Large changes in grade, particularly steep to flat, should be avoided to prevent the risk of blowouts.
Humps or dips in the pipe from reversals in grade must always be avoided.
The recommended size of drainage pipe depends on the area to be drained, the chosen drainage coefficient, the grade on which the pipe is laid, and the pipe material.
To determine the required flow that the pipe must handle the following equation can be used:
 Table 30.3 Minimum recommended grades  for drainage pipes where CPE is corrugated polyethylene plastic pipe and smooth refers to smoothwall plastic pipe or concrete or clay tile.
Drains not subjected	Drains subjected
 Inside	to fine sand or silt	to fine sand or silt
 diameter of	(min.
velocity of 0.5	(min.
velocity of 1.4
 drain 	ft/s)	ft/s)
 CPE	Smooth	CPE	Smooth
 3	0.10	0.08	0.81	0.60
 Q Area lacres/  DC  23.8
 Where Q is the required flow rate  in cubic feet per second , the area to be drained is in acres, and the drainage coefficient  is in inches per day.
For example, the flow capacity needed to drain 40 acres with a 3/8-inch drainage coefficient is: 40 acres X 0.375 inch/day 23.8 = 0.63 cfs.
To size the outlet, the total area to be drained by that outlet should be used.
For sizing individual laterals,
TRENDS IN PLANT AVAILABLE SOIL WATER ON PRODUCER FIELDS OF WESTERN KANSAS
 ABSTRACT.
Residual soil water after harvest and prior to planting was measured to a depth of 2.4 m with neutron attenuation techniques for approximately 45 irrigated corn and 45 dryland wheat fields annually from 2010 through 2012 in the western one-third of Kansas.
The sampling locations were in three-county transects in northwest, west central and southwest Kansas with generally five fields for each crop type for each county.
Residual plant available soil water  in corn fields was generally much greater than in wheat fields  for any given sampling period illustrating the residual influence of irrigation.
Although weather conditions varied between regions and years there was not a strong effect on PASW in irrigated corn fields but there was an effect in dryland wheat fields.
Annual differences in fall irrigated corn PASW for the 21 individual fields that were available for sampling in all three years varied less than 50 mm/2.4 m soil profile implying considerable stability in an individual producer's response  to changing weather conditions as evidenced by the similar year-to-year PASW values.
Drought conditions existed for much of the total period  in southwest Kansas, yet the irrigated corn PASW was still relatively high.
So, the presence of drought may not be a good indicator of the amounts of residual soil water producers are leaving after irrigated corn harvest.
Although differences in irrigated corn PASW varied greatly among producers , there were much smaller differences between regions and years with a variation from 8% to 22%.
Irrigation system capacity  had very little effect on residual fall PASW in the corn fields possibly indicating that producers with deficit capacity are pumping earlier and later into the season to help mitigate their lower irrigation capacity.
Irrigated corn grain yields began to plateau when PASW reached a value of approximately 200 mm/2.4 m profile which would represent a water storage of approximately 56% of.
field capacity.
The residual PASW in irrigated corn fields decreased about 1 mm for each 2 mm decrease in irrigation and cropping season precipitation illustrating the difficulties that can arise in managing for a target residual PASW.
These results suggest that producers should be scheduling irrigation with science-based methods, rather than habits and previous experiences.
Keywords.
Corn, Field capacity, Soil moisture content, Soil water, Volumetric water content, Wheat.
W later shortage is the primary factor limiting crop production in the USA's west-central Great Plains, and agricultural sustainability depends on efficient use of water resources.
Submitted for review in May 2017 as manuscript number NRES 12452; approved for publication as a Technical Note by the Natural Resources & Environmental Systems Community of ASABE in August 2017.
Precipitation is limited and sporadic with mean annual precipitation ranging from 400 to 500 mm across the region, which is only 60% to 80% of the seasonal water use for corn.
Precipitation increases from west to east in the Great Plains and in Kansas the average increase is approximately 0.9 mm for each kilometer.
Yields of dryland crops are limited and variable and some producers have used irrigation to mitigate these effects.
Continued declines within the Ogallala Aquifer will result in a further shift from fully irrigated to deficit or limited irrigation strategies or even a return to dryland production in some areas.
As this occurs, producers will desire to maintain crop production levels as great as possible while balancing crop production risks imposed by constraints on water available for production.
Efficient utilization of plant available soil water  reserves is important for both dryland and irrigated summer crop production systems.
In western Kansas, dryland grain sorghum yield was linearly related to PASW at emergence and sorghum yields increased 22.1 kg/ha for each additional mm of PASW.
When the experimental effects of tillage were considered, grain sorghum yield response to water supply  was greater with no-tillage than with conventional tillage.
Grain sorghum yield with conventional tillage at Bushland, Texas, increased 17.0 kg/ha-mm of PASW at planting.
Careful management of soil water can make a great difference in crop production.
Annual cropping of summer crops and oilseed crops with wheat, instead of using an 11-month fallow period prior to drilling wheat reduced crop water productivity by 31%.
The water productivity slope above the dry matter threshold  for corn and grain sorghum in western Kansas have been reported as great as 41.6 and 30.1 kg/ha-mm, respectively.
Evaporative demands increase from north to south  in the Great Plains and this can reduce overall yield response to water.
Preseason irrigation  is a common practice in central and southern sections of the western Great Plains on the deep soils with large water-holding capacity that are prevalent.
The residual soil water left in irrigated corn fields has a strong effect on the amount of preseason irrigation and precipitation that can be stored during the dormant period.
Although preseason irrigation is common, research has shown it is often an inefficient water management practice.
Measured water losses from borderline insufficient preseason irrigation capacities during the 30 to 45 day period prior to planting in a Texas study were extremely high, ranging from 45% to 70%.
While several reasons are given by producers for the use of preseason irrigation, Musick et al.
stated its primary purpose is to replenish soil water stored in the plant root zone.
From an analysis of soil water data from producer fields with silt loam soils near Colby, Kansas, Rogers and Lamm  concluded that irrigation above the amount required to bring soil water to 50% PASW would have a high probability of being lost or wasted.
They found in a three-year study  of 82 different fields that on average producers were leaving residual PASW in the top 1.5 m of the soil profile at 70% of the PASW associated with field capacity water content.
Since that time, groundwater levels have continued to decline and more irrigation systems have marginally insufficient capacity and as a result producer fields currently may be drier than in this previous period.
When soil profiles are less than 50% of field capacity there may be advantages in applying some preseason irrigation.
Corn grain yields in west central Kansas increased an average of 1 Mg/ha for preseason irrigation amounts of 75 mm with a decreasing positive response as irrigation capacity increased from 2.5 to
 5 mm/day.
A slow late season depletion of the water in the soil profile might be advantageous in allowing more overwinter accumulation and less nutrient leaching but this strategy is difficult to successfully implement without crop yield suppression.
In a comparison in northwest Kansas of three irrigation regimes , small daily deficits after tasseling  decreased corn grain yields and did not increase crop water productivity.
Research is needed to both assess the current amounts of residual PASW producers are leaving in the field after irrigated corn harvest and how much PASW is replenished during the period before spring planting of the next corn crop.
The research results can be used to develop better cropping recommendations for producers based on their geographical location within western Kansas when used with information about their anticipated summer precipitation.
The primary objectives of this project were 1) to characterize the fall residual profile PASW after irrigated corn production and in the subsequent spring, and 2) to characterize the PASW in dryland wheat stubble following early summer harvest and prior to the next summer's crop in producer fields in three distinct regions of western Kansas [southwest , west central  and northwest ].
A three year study was initiated in the fall of 2010 and concluded in the winter of 2012 on the deep silt loam soils of western Kansas.
Fifteen commercial producer fields from each of the three regions  were sought  for each crop residue type  for sampling of PASW.
In general, five fields of each residue type were selected in each county.
In a few cases, additional fields  were selected when it was deemed useful in gaining a better geographical distribution.
Another selection criterion for the irrigated corn fields was irrigation system capacity.
Attempts were made to find one or two fields in each county with irrigation capacities equivalent to <25, 25 to 38, and >38 L/s for a 50 ha field.
Strip-tillage was the predominate tillage practice employed in the irrigated corn fields following harvest, but there were a few producers performing no tillage between harvest and subsequent harvest.
A very few producers may have performed conventional disk tillage in the spring prior to planting but subsequent to our spring soil water measurements.
All the dryland producers were practicing chemical fallow  for the after wheat harvest period through the following spring up through our spring soil water measurements.
It is likely they continued with no tillage prior to planting since the wheat residue is managed relatively well with modern row planters.
Although a broad geographical representation was a primary desire (fig.
an attempt was made to select producers using good management practices and for which realistic
 Figure 1.
Example geographical distribution of soil water measurement location in producer fields for western Kansas in 2010.
Each symbol represents a GPS-referenced producer field.
weather conditions could be obtained from public sources.
Fields in NW Kansas were selected in Sheridan, Thomas, and Sherman counties.
Fields in WC Kansas were selected in Scott, Wichita, and Greeley counties.
There was increased difficulty finding producers with continuous  irrigated corn fields in WC Kansas, particularly in Wichita and Greeley Counties.
The Ogallala aquifer in this region of Kansas is severely depleted, SO producers appear to be using more crop rotation to better utilize residual soil water, thus maintaining crop productivity and conserving aquifer water for future years.
Fields in SW Kansas were selected in Haskell, Grant, and Stanton counties.
There were 96 total fields in the 2010 fall sampling and 91 fields in fall 2011.
It was not possible to sample the same wheat residue fields in each year because there is little continuous annual cropping of wheat in this region of Kansas , SO new fields were obtained each year.
The dryland wheat field portion of the study was not conducted in the summer of 2012.
There were 33 total irrigated corn fields sampled for soil water content in the fall of 2012.
There were 31 irrigated corn fields that were sampled in both 2010 and 2011 and there were 21 fields that were made available for soil water sampling in all three years.
The annual availability of previously-sampled continuous corn fields was negatively
 affected by persistent drought conditions during a large period of the study.
For example, producers might choose to harvest the corn early as ensilage and then subsequently plant irrigated wheat for fall and spring livestock grazing.
GPS-referenced soil water access tubes  were installed in an equilateral triangular-shaped pattern  in a representative area of the field that also was easily accessible from nearby roads.
Initial volumetric soil water content in 0.3 m increments to a depth of 2.4 m was determined by neutron attenuation techniques in the fields after installation of tubes and again in late spring prior to summer crop planting.
The access tubes were removed from the fields prior to spring cropping.
The same general sampling area  was selected for irrigated fields repeating in subsequent years.
Published soil type and soil characteristics for the prevalent regional silt loam soils were used to estimate PASW in mm/2.4 m within the profile.
These soils will hold approximately 440 mm of PASW in the 2.4 m profile at field capacity.
The data from the three sampling points was examined for uniformity between readings and to remove any anomalies.
A few tubes were lost due to damage by producer field operations between the fall and spring measurement periods.
Less than 1% of the data was lost due to measurement anomalies or damaged tubes.
Annual irrigation amounts for the corn fields were obtained where possible from the Kansas Water Information Management and Analysis System.
The reported water use values in this system are associated with a given parcel of land which in some cases was larger than the single field selected for the soil water sampling.
In summarizing the irrigation amounts, the average amount for the whole parcel was used.
However in some cases, data that appeared to be unrealistic and was excluded from analysis.
It should be noted that this data set of annual values does not allow separation of inseason and dormant season irrigation amounts.
County-wide monthly precipitation for the period January 1981 through December 2015 was obtained from the PRISM dataset maintained by Oregon State University.
These data were used to examine soil water trends between the sampling years  as affected by precipitation and to determine the long-term  mean monthly values of precipitation.
In addition, cumulative May through September precipitation amounts were added to annual irrigation amounts for correlation with the resultant fall PASW for the irrigated corn fields.
Corn grain yield samples at physiological maturity were hand-harvested from a 6 m length of row near the irrigated field soil water sampling points in 2011 and 2012 to examine the corn yield correlation to fall PASW.
Some samples were not obtained due to earlier harvest prior to the site visit.
Corn yield results from fields exhibiting heavy insect damage  and for fields with low plant density  were excluded from analysis.
As a result there were 25 and 17 corn yield samples in 2011 and 2012, respectively.
Statistical separation of means was conducted with pooled two-sample t-tests using Microsoft Excel  and linear regression in Microsoft Excel was used to determine functional relationships.
Figure 2.
Monthly precipitation for the nine counties in the three western Kansas regions for 2010-2012 and the long term  mean monthly precipitation.
RESULTS AND DISCUSSION PRECIPITATION CONDITIONS
 Weather conditions in nearly all of western Kansas were excessively dry from early August 2010 through mid-April 2011.
The western portion of WC and NW Kansas began to get more normal precipitation in late April 2011 and ended the cropping season with normal amounts of precipitation or greater.
However, SW Kansas remained under severe drought conditions through the summer and much of the fall of 2011.
For example, Grant County received less than 30% of normal annual precipitation for the period 1 September 2010 through 1 September 2011.
In SW Kansas in 2011, dryland summer crops resulted in almost total failure and even many irrigated crops were severely stressed.
The western edge of WC Kansas  and nearly all of NW Kansas experienced nearto above-normal precipitation for most of the 2011 summer period.
A particularly wet multi-day weather period in early October 2011 tracked across some counties in WC Kansas and the eastern half of NW Kansas with those areas receiving between 50 and 100 mm of precipitation.
Because of the multi-day nature of this precipitation, much of the water infiltrated into the soil profile.
Precipitation amounts ranging from 49 to 93 mm occurred in April 2012 in the selected counties and this lessened the drought conditions temporarily and improved the potential for summer crop germination and establishment.
However, the summer and fall periods of 2012 were generally excessively dry and even irrigated crop yields were negatively affected.
The extended drought resulted in some producers performing some dormant season irrigation which may have increased some of the residual fall PASW values and may have further affected the spring PASW values.
For this reason and the lack of field-to-field specificity for precipitation due to only having county-wide average precipitation, overwinter precipitation storage efficiency will not be reported here.
SOIL WATER AS AFFECTED BY LOCATION AND RESIDUE TYPE
 In general, sprinkler irrigated corn fields had greater PASW than the dryland wheat fields  as would be anticipated.
Additionally, it should be noted that in some cases, some fall dormant season irrigation  had been practiced prior to the soil water measurements to facilitate easier strip tillage operations.
However, generally these amounts prior to strip tillage were between 25 and 40 mm.
Soil water was measured in the dryland wheat and irrigated corn fields between October and 30 December as producer preferences, weather conditions, and work schedules allowed.
Some changes in soil water storage may have occurred between harvest and soil water measurement depending on weather conditions, particularly for the wheat fields since harvest was most likely in early July when precipitation amounts are greater than in the fall months.
In 2010, NW Kansas had slightly more PASW  in wheat fields  than in the other two regions.
The coefficient of variation  of PASW in wheat fields was least in NW Kansas and greatest in SW Kansas, probably reflecting the higher evaporative demand and worse drought conditions affecting SW Kansas.
The irrigated corn fields residual PASW averaged 160% that of the dryland wheat fields which was statistically significant at P<0.0001  and also had less variability.
The average PASW in irrigated corn fields for the three regions varied by only 21 mm  and with an average value of 262 mm/2.4 m that would approximate a profile at 60% of FCASW, which would suggest overall adequate irrigation management.
However, there was a large amount of field to field variation.
The greatest measured PASW for the irrigated corn fields of the three regions averaged 416 mm/2.4 m which would be very wet unless there was considerable late season precipitation or fall dormant season irrigation before sampling.
At the other end of the spectrum, the lowest measured average PASW of the three regions was approximately 109 mm/2.4 m, which would be only about 25% of FCASW.
There was on average slight losses or very small accumulations in the dryland wheat residue fields by late spring 2011 , with the exception of NW Kansas which saw
 Table 1.
Plant available soil water  in producer fields in western Kansas in fall 2010.
Residue Type	No.
of	Fields	Average	Greatest	Least	CV
 Northwest Kansas, Sheridan, Thomas, and Sherman Counties
 Dryland Wheat	Sheridan 	194	290	114	0.33
 Thomas 	218	281	156	0.19
 Sherman 	139	210	98	0.31
 All 3 Ctys 	188	290	98	0.30
 Irrigated Corn	Sheridan 	267	282	218	0.06
 Thomas 	274	395	172	0.22
 Sherman 	212	296	167	0.24
 All 3 Ctys 	254	395	167	0.24
 Irrigated to	Sheridan	1.37	0.97	1.91	0.19
 Dryland Ratio	Thomas	1.26	1.40	1.10	1.12
 Sherman	1.52	1.41	1.70	0.77
 All 3 Ctys	1.35	1.36	1.70	0.79
 West Central Kansas, Scott, Wichita, and Greeley Counties
 Dryland Wheat	Scott 	130	228	63	0.50
 Wichita 	130	236	77	0.48
 Greeley 	156	281	53	0.53
 All 3 Ctys 	138	281	53	0.48
 Irrigated Corn	Scott 	304	421	208	0.27
 Wichita 	236	299	166	0.20
 Greeley 	223	270	101	0.32
 All 3 Ctys 	255	421	101	0.29
 Irrigated to	Scott	2.34	1.85	3.31	0.54
 Dryland Ratio	Wichita	1.83	1.27	2.16	0.42
 Greeley	1.43	0.96	1.91	0.60
 All 3 Ctys	1.85	1.50	1.91	0.60
 Southwest Kansas, Haskell, Grant, and Stanton Counties
 Dryland Wheat	Haskell 	137	259	38	0.72
 Grant 	87	154	43	0.50
 Stanton 	276	366	188	0.29
 All 3 Ctys 	167	366	38	0.66
 Irrigated Corn	Haskell 	249	433	60	0.61
 Grant 	230	352	160	0.37
 Stanton 	351	424	292	0.14
 All 3 Ctys 	275	433	60	0.41
 Irrigated to	Haskell	1.82	1.67	1.58	0.84
 Dryland Ratio	Grant	2.64	2.28	3.69	0.74
 Stanton	1.27	1.16	1.56	0.47
 All 3 Ctys	1.65	1.18	1.58	0.62
 [a] Coefficient of variation is defined as the standard deviation of PASW divided by the mean PASW.
an average increase of 52 mm of PASW in the soil profile.
This reflects some appreciable late April 2011 precipitation events in NW Kansas that the other regions had missed or had lesser amounts.
In contrast, NW Kansas had only minimal increase in PASW in the irrigated corn fields while PASW in the WC and SW Kansas fields increased approximately 45 mm/ 2.4 m.
This reflects that many of the WC and SW Kansas fields had received additional dormant season irrigation to better cope with the drought before spring planting.
The greatest measured PASW for the sprinkler-irrigated corn fields averaged 399, 510, and 474 mm/2.4 m for NW, WC, and SW Kansas, respectively.
These values in WC and SW Kansas would be considered extremely wet  and
 Table 2.
Plant available soil water  in producer fields in western Kansas in spring 2011.
Residue Type	No.
of	Fields	Average	Greatest	Least	CV
 Northwest Kansas, Sheridan, Thomas, and Sherman Counties
 Dryland Wheat	Sheridan 	245	319	198	0.19
 Thomas 	246	291	186	0.13
 Sherman 	223	274	180	0.20
 All 3 Ctys 	240	319	180	0.16
 Irrigated Corn	Sheridan 	285	309	271	0.05
 Thomas 	280	399	209	0.22
 Sherman 	222	301	162	0.24
 All 3 Ctys 	264	399	162	0.21
 Irrigated to	Sheridan	1.16	0.97	1.37	0.26
 Dryland Ratio	Thomas	1.14	1.37	1.12	1.69
 Sherman	1.00	1.10	0.90	1.21
 All 3 Ctys	1.10	1.25	0.90	1.28
 West Central Kansas, Scott, Wichita, and Greeley Counties
 Dryland Wheat	Scott 	159	277	95	0.46
 Wichita 	129	183	92	0.30
 Greeley 	164	289	62	0.50
 All 3 Ctys 	150	289	62	0.43
 Irrigated Corn	Scott 	369	510	246	0.27
 Wichita 	282	352	191	0.23
 Greeley 	269	345	114	0.34
 All 3 Ctys 	307	510	114	0.30
 Irrigated to	Scott	2.32	1.84	2.59	0.58
 Dryland Ratio	Wichita	2.20	1.92	2.07	0.78
 Greeley	1.65	1.20	1.84	0.67
 All 3 Ctys	2.04	1.77	1.84	0.70
 Southwest Kansas, Haskell, Grant, and Stanton Counties
 Dryland Wheat	Haskell 	159	280	53	0.64
 Grant 	102	176	58	0.45
 Stanton 	223	303	134	0.34
 All 3 Ctys 	161	303	53	0.54
 Irrigated Corn	Haskell 	307	474	145	0.43
 Grant 	292	400	179	0.30
 Stanton 	346	410	260	0.18
 All 3 Ctys 	315	474	145	0.31
 Irrigated to	Haskell	1.94	1.69	2.73	0.67
 Dryland Ratio	Grant	2.86	2.28	3.10	0.67
 Stanton	1.56	1.35	1.94	0.53
 All 3 Ctys	1.95	1.56	2.73	0.56
 [a] Coefficient of variation is defined as the standard deviation of PASW divided by the mean PASW.
would be subject to considerable losses from deep percolation.
Close examination of the individual field data revealed that these high PASW values in spring 2011 also were very wet on the same fields in fall 2010 , suggesting that these irrigators should cut back on late and/or dormant season irrigation.
In contrast, the lowest values of PASW in spring 2011 on the producer fields averaged only 140 mm in the 2.4 m profile.
These producers with such low values of PASW might have greatly benefited had they used more dormant season irrigation, particularly prior to dry summers.
The irrigated corn fields had approximately 160% of the PASW of wheat fields which was statistically significant at P<0.0001, somewhat similar to the results from fall 2010, and again with less variability in PASW.
Fall soil water measurements were conducted between 30 September and 12 December.
In fall 2011, because of the continuing drought in SW Kansas, it was anticipated that producer fields would be much drier than in 2010.
Although this turned out to be true for SW Kansas for dryland wheat fields , overall the irrigated corn fields were wetter  in 2011, with only SW Kansas having slightly drier irrigated fields in fall 2011.
The wetter summer period in portions of WC Kansas  and NW Kansas no doubt had some effects on the amounts of residual PASW.
The October 2011 multi-day wet period resulted in some very wet wheat
 residue fields in Sheridan County in northwest Kansas.
The irrigated corn fields were significantly wetter than the wheat fields  having approximately 150% of the PASW of the wheat fields, similar to the results from the fall of 2010 and again with less variability in PASW.
Spring 2012 soil water measurements were conducted between 29 February and 8 May.
The improvement in spring precipitation in 2012 as compared with 2011 resulted in an average fall 2011 to spring 2012 PASW increase in the dryland wheat fields of 48 mm/2.4 m profile across the three regions with the SW region having an average increase of 73 mm.
Table 3.
Plant available soil water  in producer fields in western Kansas in fall 2011.
Residue Type	No.
of Fields	Average	Greatest	Least	CV
 Northwest Kansas, Sheridan, Thomas, and Sherman Counties
 Dryland Wheat	Sheridan 	354	452	179	0.29
 Thomas 	181	232	157	0.16
 Sherman 	174	221	96	0.31
 All 3 Ctys 	236	452	96	0.46
 Irrigated Corn	Sheridan 	350	396	265	0.14
 Thomas (5	332	428	227	0.22
 Sherman 	211	297	151	0.28
 All 3 Ctys 	301	428	151	0.28
 Irrigated to Dry-	Sheridan	0.99	0.88	1.49	0.49
 land Ratio	Thomas	1.84	1.84	1.44	1.32
 Sherman	1.21	1.34	1.58	0.89
 All 3 Ctys	1.27	0.95	1.58	0.61
 West Central Kansas, Scott, Wichita, and Greeley Counties
 Dryland Wheat	Scott 	205	278	138	0.25
 Wichita 	212	255	164	0.20
 Greeley 	218	273	168	0.18
 All 3 Ctys 	212	278	138	0.20
 Irrigated Corn	Scott 	330	453	248	0.23
 Wichita 	320	361	273	0.11
 Greeley 	298	311	279	0.04
 All 3 Ctys 	316	453	248	0.16
 Irrigated to	Scott	1.61	1.63	1.79	0.90
 Dryland Ratio	Wichita	1.50	1.41	1.66	0.57
 Greeley	1.37	1.14	1.66	0.22
 All 3 Ctys	1.49	1.63	1.79	0.80
 Southwest Kansas, Haskell, Grant, and Stanton Counties
 Dryland Wheat	Haskell 	152	262	69	0.46
 Grant 	83	171	4	0.90
 Stanton 	141	207	118	0.26
 All 3 Ctys 	125	262	4	0.52
 Irrigated Corn	Haskell 	264	396	75	0.59
 Grant 	223	419	80	0.66
 Stanton 	282	363	220	0.20
 All 3 Ctys 	258	419	75	0.46
 Irrigated to	Haskell	1.74	1.51	1.08	1.30
 Dryland Ratio	Grant	2.69	2.45	19.02	0.74
 Stanton	2.00	1.75	1.87	0.76
 All 3 Ctys	2.06	1.60	17.84	0.88
 Coefficient of variation is defined as the standard deviation of PASW divided by the mean PASW.
Table 4.
Plant available soil water  in producer fields in western Kansas in spring 2012.
Residue Type	No.
of	Fields	Average	Greatest	Least	CV
 Northwest Kansas, Sheridan, Thomas, and Sherman Counties
 Dryland Wheat	Sheridan 	356	477	125	0.32
 Thomas 	211	304	166	0.19
 Sherman 	202	346	90	0.33
 All 3 Ctys 	254	477	90	0.41
 Irrigated Corn	Sheridan 	368	433	268	0.13
 Thomas 	356	478	248	0.18
 Sherman 	245	314	163	0.17
 All 3 Ctys 	326	478	163	0.23
 Irrigated to	Sheridan	1.03	0.91	2.14	0.41
 Dryland Ratio	Thomas	1.69	1.57	1.49	0.95
 Sherman	1.21	0.91	1.81	0.52
 All 3 Ctys	1.28	1.00	1.81	0.56
 West Central Kansas, Scott, Wichita, and Greeley Counties
 Dryland Wheat	Scott 	277	377	166	0.26
 Wichita 	257	404	144	0.29
 Greeley 	262	320	156	0.17
 All 3 Ctys 	265	404	144	0.24
 Irrigated Corn	Scott 	399	526	244	0.18
 Wichita 	391	475	350	0.10
 Greeley 	342	372	284	0.07
 All 3 Ctys 	377	526	244	0.15
 Irrigated to	Scott	1.44	1.40	1.47	0.69
 Dryland Ratio	Wichita	1.52	1.17	2.43	0.34
 Greeley	1.30	1.16	1.82	0.41
 All 3 Ctys	1.42	1.30	1.69	0.63
 Southwest Kansas, Haskell, Grant, and Stanton Counties
 Dryland Wheat	Haskell 	223	378	119	0.33
 Grant 	132	216	65	0.47
 Stanton 	226	328	145	0.28
 All 3 Ctys 	198	378	65	0.39
 Irrigated Corn	Haskell 	391	523	214	0.30
 Grant 	332	521	217	0.35
 Stanton 	363	492	235	0.18
 All 3 Ctys 	362	523	214	0.28
 Irrigated to	Haskell	1.76	1.38	1.79	0.91
 Dryland Ratio	Grant	2.52	2.41	3.36	0.74
 Stanton	1.61	1.50	1.62	0.64
 All 3 Ctys	1.83	1.38	3.31	0.72
 Coefficient of variation is defined as the standard deviation of PASW divided by the mean PASW.
Overwinter PASW profile increases in the irrigated corn fields averaged 63 mm across the three regions with the resulting PASW averaging 355 mm/2.4 m in the spring, which would be approximately 80% of FCASW.
Profile PASW values were greater in WC and SW as compared with the NW region , probably reflecting both greater spring precipitation  and prevalence of more dormant season irrigation due to the drought conditions of 2011.
The greatest PASW for the sprinkler irrigated corn fields averaged 478, 526, and 523 mm/2.4 m for NW, WC and SW Kansas, respectively, which indicate soil water contents greater than field capacity and the likelihood of considerable deep percolation.
In contrast, the lowest values of PASW in spring 2012 on the producer fields averaged 207 mm in the 2.4 m profile  and were 47% greater PASW than spring 2011.
The irrigated corn fields were significantly wetter  having approximately 150% of the PASW of the wheat fields, slightly less than the results from spring 2011 and again with less variability in PASW.
Fall 2012 soil water measurements were conducted 19-26 October.
Despite the widespread severe drought in 2012 in all of western Kansas, residual PASW in the 2.4 m profile still averaged 275 mm  or approximately 62% of FCASW for the irrigated corn fields.
The wettest profiles were located in the SW region which received greater than normal precipitation in late-summer and early fall  near the time of the fall soil water sampling.
Fall 2012 soil water profiles across the three regions averaged 275 mm/2.4 m of PASW, 22% drier  than the spring 2012 profiles probably reflecting the prevalent inability of marginally insufficient irrigation system capacities to match the evaporative demands of the severe drought.
In contrast, fall 2011 PASW and spring 2011 PASW values were not significantly different  and were nearly equal at approximately 295 mm/2.4 m.
Table 5.
Plant available soil water  in producer irrigated corn fields in western Kansas in fall 2012.
Residue Type	Fields	Average	Greatest	Least	CV
 Northwest Kansas, Sheridan, Thomas, and Sherman Counties
 Irrigated Corn	Sheridan 	281	418	187	0.33
 Thomas 	261	421	182	0.33
 Sherman 	206	304	112	0.47
 All 3 Ctys 	258	421	112	0.34
 West Central Kansas, Scott, Wichita, and Greeley Counties
 Irrigated Corn	Scott 	319	408	255	0.25
 Wichita 	259	275	241	0.07
 Greeley 	201	276	151	0.33
 All 3 Ctys 	260	408	151	0.28
 Southwest Kansas, Haskell, Grant, and Stanton Counties
 Irrigated Corn	Haskell 	313	494	130	0.54
 Grant 	332	485	131	0.55
 Stanton 	262	316	209	0.29
 All 3 Ctys 	308	494	130	0.46
 [a] Coefficient of variation is defined as the standard deviation of PASW divided by the mean PASW.
ANNUAL DIFFERENCES IN CORN RESIDUAL PASW
 Although record or near-record drought conditions exlisted in southwest Kansas for the entire period from the middle of summer 2010 through fall 2011 and for all of western Kansas in 2012, there were only minimal annual differences in fall irrigated corn PASW for the 21 individual fields that were available for sampling in all three years.
The slope of the lines in figure 3 are not significantly different from unity, nor is the intercept significantly different from zero  Overall, 2012 averaged less than 25 mm greater PASW than 2010, and 2011 averaged approximately 50 mm greater PASW than 2010.
It appears there was considerable stability in an individual producer's response  to changing weather conditions as evidenced by the similar year-to-year values.
Part of the rationale might be that drought conditions existed for much of the total period.
However, the irrigated corn residual soil water was still relatively high on the average for SW Kansas.
So, the presence of drought may not be a good indicator of the amounts of residual soil water left after irrigated corn harvest.
Sometimes, crop yield reductions are caused by system capacity  at the critical stages, rather than what total irrigation amount can be applied during the season.
Insect damage, such as from spider mites, is exacerbated by high canopy temperatures and drought.
Producers recognizing the drought and anticipating crop damage may have continued irrigating hoping to mitigate further crop damage and this sometimes increases profile PASW as the damaged crop is no longer transpiring typical amounts of water.
One caveat, in some cases the PASW results are probably reflecting the effects of some fall dormant season irrigation that occurred before the PASW sampling.
However, in most cases the fall irrigation amounts were not large.
Figure 3.
Similarity of fall residual plant available soil water  in the 2.4 mm soil profile in irrigated corn fields after harvest for the years 2010, 2011, and 2012 in western Kansas producer fields.
These data represent 21 fields that producers made available for PASW measurements in all three years of the study.
The solid line is the unity line, the dashed line is the Fall 2011 data and the dotted line is the Fall 2012 data.
EFFECT OF REGIONAL CHARACTERISTICS ON CORN RESIDUAL PASW
 Although intuition might suggest that less saturated thickness of the Ogallala and more marginally insufficient irrigation system capacities  would result in less average residual PASW and lower PASW values in the irrigated corn fields of WC Kansas, there was no strong evidence from the data of 2010 through 2012 that would support that theory.
This might be because producers with lower capacity irrigation systems have adjusted to their limitation by using longer pumping periods.
Their goal, by pumping later into the crop season, would be to minimize crop yield loss, but sometimes those later irrigation events also increase residual PASW.
There was greater variation in PASW values in SW Kansas  as compared with the other two regions probably reflecting greater evaporative demand to some extent and also more variation in producer irrigation management.
EFFECT OF FIELD TYPE ON OVERWINTER CHANGE IN PASW
 Overwinter accumulation or loss of PASW could be affected by precipitation, initial PASW, residue type, and any applied dormant season irrigation, SO the following results are being discussed in terms of field type, rather than just crop residue type.
During the overwinter period 2010 through 2011, corn fields on average accumulated approximately 50 mm of soil
 Figure 4.
Effect of western Kansas region on average, greatest, lowest, and coefficient of variation of measured plant available soil water  in the 2.4 m soil profile in irrigated corn fields after harvest for the fall periods in 2010-2012.
water overwinter when the fall PASW was very low and less than 25 mm of accumulation when the fall PASW was high.
The slope of the corn data line was not significantly different from unity.
In contrast, the wheat fields accumulated only about 40 mm of soil water overwinter when the fall 2010 PASW was very low and tended to lose approximately 40 mm of PASW when fall 2010 PASW was higher.
Additionally, the slope of the wheat line was significantly different from unity.
These small differences are probably due to dormant season irrigation slightly increasing PASW in the corn fields while the drought conditions were not favorable for much overwinter accumulation in the dryland wheat fields.
Overwinter accumulation of PASW was greater for the fall 2011 through spring 2012 period for both field types  and the slopes of both the wheat and corn data lines were significantly different from unity.
Normal to wetter than average April conditions in the region  contributed to increased spring 2012 PASW for many of the fields.
In addition, many irrigated producers had practiced some dormant season irrigation due to the persistent, continuing drought.
Figure 5.
Effect of field type  on accumulation of plant available soil water  in the 2.4 m soil profile for the period fall 2010-spring 2011 for producer fields in western Kansas.
Figure 6.
Effect of field type  on accumulation of plant available soil water  in the 2.4 m soil profile for the period fall 2011 through spring 2012 for producer fields in western Kansas.
Irrigated corn and dryland wheat fields had 130 and 80 mm/2.4 m greater spring PASW when soil profiles were very dry in the fall.
However when fall soil profiles were on the wetter range , overwinter PASW accumulation for both field types was approximately 20 mm/2.4 m.
Less overwinter PASW accumulation when soil profiles are wetter is consistent with the soil water recharge model of Lamm and Rogers.
EFFECT OF SYSTEM CAPACITY ON FALL PASW IN IRRIGATED CORN FIELDS
 There was very little correlation of residual PASW with irrigation system capacity  despite the hypothesis that lower capacities would result in drier fall soil profiles.
In two years , the greatest capacity  had slightly greater average PASW  while in 2010 the greatest capacity was 22 mm/2.4 m drier than the lowest capacity.
The rationale for these results is probably similar to the rationale for results from west central Kansas where low saturated thickness did not have a large effect on PASW relative to the other regions.
In both cases, producers may have increased the length of the irrigation season in attempting to mitigate irrigation deficiencies and ended up with similar PASW to the systems where irrigation was less restrictive.
There tended to be less variability for the lower capacity systems and this probably just reflects less variance in producer management when capacity is low.
RELATIONSHIP OF CORN GRAIN YIELD TO FALL PASW
 Corn grain yield was somewhat correlated  with the fall PASW, increasing sharply up until about 200 mm and nearing a plateau at about 250 mm.
Although a fall PASW of 250 mm corresponds to a water storage value approximately 56% of field capacity, which is greater than most current extension publication recommendations  for an after harvest residual PASW of around 40%, this greater value corresponds well with results from Lamm and Aboukheira  who found corn yields beginning to
 Figure 7.
Effect of irrigation system capacity  on residual plant available soil water  in the 2.4 m soil profile for the period fall 2011-spring 2012 for producer fields in western Kansas.
Fall PASW 
 Figure 8.
Relationship of corn grain yield to residual plant available soil water  in the 2.4 m soil profile for 2011 and 2012 for producer fields in western Kansas.
decrease at PASW values corresponding to less than 55% of field capacity.
Corn yields varied greatly across a wide range of fall PASW values suggesting that irrigation scheduling for good crop yields, while targeting a lower residual fall PASW, in practice has not been easy for irrigators to achieve.
EFFECT OF CUMULATIVE IRRIGATION AND CROP SEASON PRECIPITATION ON FALL PASW IN IRRIGATED CORN FIELDS
 The residual fall PASW was reasonably well correlated  with the total of May through September precipitation and applied irrigation.
The slope of relationship was 0.49 which means that to decrease fall PASW by one mm it was necessary to decrease seasonal precipitation and irrigation by over two mm.
In an earlier research study in western Kansas, Lamm et al.
found that to reduce fall PASW by one unit, irrigation had to be reduced four units.
This further emphasizes that targeted management of fall PASW is not easily achieved.
Figure 9.
Effect of cumulative irrigation and precipitation amount on residual plant available soil water  in the 2.4 m soil profile for 2010-2012 for producer fields in western Kansas.
These results suggest a few very important aspects for irrigated crop production in western Kansas and the central Great Plains.
Irrigation not only increases the water available for crop production, but also reduces the variability in profile available soil water in the field.
An average residual available soil water value may not be indicative of an individual field, SO it is wise for producers to check each field prior to the next crop year to plan water use strategies for that year.
Each year is different, SO irrigating to average conditions is risky and will likely be less profitable.
Science-based irrigation scheduling  should be able to help producers better manage water resources in-season and between seasons.
There was considerable stability in annual values of residual soil water in western Kansas corn fields with relatively little effect of weather differences and irrigation system capacity.
Considerable amounts of residual soil water are left in producers' fields annually reducing the need for dormant season irrigation to replenish the soil profile.
This research was supported in part by the Ogallala Aquifer Program, a consortium between USDA Agricultural Research Service, Kansas State University, Texas AgriLife Research, Texas AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
Contribution no.
17-365-J from the Kansas Agricultural Experiment Station.
Center Pivot Operating Pressure: Checking the pressure regularly  or monitoring continuously can help maintain optimum efficiency and minimizes irrigation costs.
Operating pressure can deviate above or below the required pressure for a number of reasons, such as changes in groundwater level overtime, topography, and leaks along the irrigation system.
For example, Figures 2 and 3 illustrate the fluctuation of pressure at the end of a pivot overtime and across a field , respectively.
For more information, contact your local extension educator or irrigation dealer.
Also, the articles below provide more depth on specific components of a system evaluation:
 Nebraska Extension: Irrigation System Evaluation
 Checklist for Winterizing Your Center Pivot
 Sprinkler Irrigation System Maintenance for Improved Uniformity and Application Efficiency
 Problems Regarding Operating Pressure & Uniformity
 Center Pivot Irrigation Handbook
Common Terms In Water Recycling And Agricultural Irrigation
 Jessica Dery, Channah Rock, Jean E.
McLain, and Daniel Gerrity
 All water is used and reused naturally in what is called the water, or hydrologic, cycle.
There are also many ways to reuse our water supplies using advanced treatment technologies and processes that allow for the safe reuse of water in diverse ways, such as in agricultural irrigation.
Thoughtful integration and management planning of all our valuable water resources can minimize environmental impacts and contribute to economic and social endurance, through a concept called One Water.
The following glossary covers some of the common terms and concepts used in water reuse and agriculture, technologies and processes, policy and laws, and reflects current regulations in Arizona.
Core Terms And Concepts
 ACRE-FOOT: A volume of water equal to one foot in depth covering an area of one acre, or 43,560 cubic feet; approximately 325,851 gallons.
AGRICULTURE: The science, art, and business of cultivating the soil, producing crops, and raising livestock.
Rock et al., 2012
 AQUIFER: An underground geological formation, or group of formations, containing water.
Are sources of groundwater for wells and springs.
Environmental Protection Agency , 2009
 BENEFICIAL REUSE: The use of recycled water for purposes that contribute to the water needs, economy and/or environment of a community.
WateReuse, 2015
 BEST MANAGEMENT PRACTICE : A practice or combination of practices established as the most practicable means of increasing water use efficiency.
AWE, 2016
 CONTAMINANTS OF EMERGING CONCERN : Broadly defined as any synthetic or naturally occurring chemical or any microorganism that is not commonly monitored in the environment but has the potential to enter the environment and cause known or suspected adverse ecological and human health effects.
In some cases, release of emerging chemical or microbial contaminants to the environment has likely occurred for a long time but may not have been recognized until new detection methods were developed.
In other cases, synthesis of new chemicals or changes in use and disposal of existing chemicals can create new sources of emerging contaminants.
United States Geological Survey , 2016b
 CENTRAL ARIZONA PROJECT  CANAL: A canal structure that delivers water to various municipalities  from the Colorado River to Central and Southern Arizona.
Central Arizona Project , 2016
 COVERED PRODUCE: Produce that is a raw agricultural commodity  is covered by the Produce Safety Rule.
RAC are any foods that are in their raw and natural state.
This includes a produce RAC that is grown domestically, for import, or offered for import in any State or territory of the United States, the District of Columbia, or the Commonwealth of Puerto Rico.
This includes fruits, vegetables, and mixes of intact fruits and vegetables.
Produce Safety Alliance , 2016
 CLIMATE: The long-term average of the weather in a given place.
While the weather can change in minutes or hours, a change in climate is something that develops over longer periods of decades to centuries.
Climate is defined not only by average temperature and precipitation but also by the type, frequency, duration, and intensity of weather events such as heat waves, cold spells, storms, floods, and droughts.
EPA, 2016
 DAM: A structure built to hold back a flow of water.
Barrier built across a watercourse to impound or divert water.
EPA, 2017a
 DROUGHT: Along period of below average precipitation.
USGS, 2016a
 ECOSYSTEM: The biotic community and abiotic environment within a specified location and time, including the chemical, physical, and biological relationships among the biotic and abiotic components.
EPA, 2017a
 ENDOCRINE DISRUPTING COMPOUNDS : Chemicals that can interfere with the normal hormone function in humans and animals.
Columbia Analytical Services , 2011
 water water).
One thousand parts per billion is equal to one part per million.
PARTS MILLION : A unit of measure for contamination concentration.
One part per million is equal to one milligram per liter.
ENVIRONMENTAL REUSE: The use of reclaimed water to create, enhance, sustain, or augment water bodies including wetlands, aquatic habitats, or stream flow.
EPA, 2012
 ESTUARY: Region of interaction between rivers and near-shore ocean waters, where tidal action and river flow mix fresh and salt water.
Such areas include bays, mouths of rivers, salt marshes, and lagoons.
These brackish water ecosystems shelter and feed marine life, birds, and wildlife.
EPA, 2009
 PHARMACEUTICALLY-ACTIVE COMPOUNDS : A group of compounds that include hormones, antibiotics and painkillers that can pass into the environment.
Rock et al., 2012
 PHARMACEUTICALS AND PERSONAL CARE PRODUCTS : Products include pharmaceuticals; personal care products like shampoo, dish soap, perfume, and baby wipes; plastic products; and a host of other household products.
As a result of human use, these compounds make their way into wastewater at generally minute concentrations.
Rock et al., 2012
 RESERVOIR: A body of water used to collect and store water, or a tank or cistern used to store potable water.
Any natural or artificial holding area used to store, regulate, or control water.
Rock et al., 2012; EPA, 2009
 REUSE: Treating water to sufficient levels to allow it to be used more than once.
WateReuse 2011; EPA, 2012
 TOTAL DISSOLVED SOLIDS : A measure of the residual minerals dissolved in water that remain after evaporation of a solution.
Usually expressed in milligrams per liter.
Rock et al., 2012
 SEAWATER INTRUSION: The movement of salt water into a body of fresh water.
It can occur in either surface water or groundwater basins.
USGS, 2016a
 TOTAL SUSPENDED SOLIDS : A measure of the suspended solids in wastewater, effluent, or water bodies, determined by tests for "total suspended non-filterable solids." Usually expressed in milligrams per liter.
EPA, 2009
 INTEGRATED RESOURCE PLANNING : A method for looking ahead using environmental, engineering, social, financial, and economic considerations; includes using the same criteria to evaluate both supply and demand options while involving customers and other stakeholders in the process.
Rock et al., 2012
 EUTROPHICATION: The deterioration of an aquatic ecosystem due to high nutrient loads that lead to algal blooms, oxygen depletion, noxious odors, and a loss of biodiversity.
Rock et al., 2012
 TURBIDITY: A measure of suspended solids in water; cloudiness.
Usually expressed as NTUs.
Rock et al., 2012
 RUNOFF: Surface flow of water from a specific area.
AWE, 2016
 IRRIGATION: The beneficial use of water or reclaimed water, or both, for growing crops, turf, or silviculture, or for landscaping.
Arizona Department of Environmental Quality , 2017
 URBAN RUNOFF: Water from an urban area that neither infiltrates the soil nor is consumed, but flows into a storm sewer or open waterway.
Stormwater from city streets and adjacent domestic or commercial properties that carries pollutants of various kinds into the sewer systems and receiving waters.
Rock et al., 2012; EPA, 2017a
 MILLIGRAMS PER LITER : A measurement describing the amount of a substance  in a liter of water.
One milligram per liter is equal to one part per million.
SALINITY: Generally, the concentration of mineral salts dissolved in water.
Salinity may be measured by weight , electrical conductivity, or osmotic pressure.
Where seawater is known to be the major source of salt, salinity is often used to refer to the concentration of chlorides in the water.
Rock et al., 2012
 NANOGRAMS PER LITER : A measurement describing the amount of a substance  in a liter of water.
One nanogram per liter is equal to one part per trillion.
WATER CONSERVATION: The US Water Resources Council defines water conservation as activities designed to  reduce the demand for water,  improve efficiency in use
 MAXIMUM CONTAMINANT LEVEL : Maximum level of a contaminant allowed in water delivered to any user of a public water system.
EPA, 2017a
 MICROGRAMS PER LITER : A measurement describing the amount of a substance  in a liter of water.
It is expressed in terms of weight per volume.
One ug/Lis equal to one part per billion.
MILLION GALLONS PER DAY : A measure of water flow.
ONE WATER: Integrated and inclusive approaches to water resource management that exemplify the view that all water has value and should be managed in a sustainable, inclusive, integrated way.
The aim is to integrate planning and management of water supply, wastewater, and stormwater systems in a way that minimizes the impact on the environment and maximizes the contribution to social and economic vitality.
Howe & Mukheibir, 2015
 PARTS PER BILLION : A unit of measure for contamination concentration (parts of contamination per billion parts of
 PATHOGENS: Disease-causing organisms, such as some bacteria, viruses, or protozoa.
EPA, 2017a
 and reduce losses and waste of water, and  improve land management practices to conserve water.
Sometimes called "end-use efficiency" or "demand management".
AWE, 2016; Rock et al., 2012
 AGRICULTURAL WATER REUSE: 1).
FOOD CROPS: The use of reclaimed water to irrigate food crops that are intended for human consumption.
2).
PROCESSED FOOD CROPS AND NON-FOOD CROPS: The use of reclaimed water to irrigate crops that are either processed before human consumption or not consumed by humans.
EPA, 2012
 WATER  CYCLE: Describes how water moves on the Earth.
Water evaporates from water bodies , forms clouds, and returns to earth as precipitation.
The amount of water that evaporates each year and the amount that falls back to the ground are virtually constant, meaning that the amount of water on Earth does not change.
Water reuse solutions essentially use technology to mimic the natural cycle and create clean water faster and more efficiently than it would otherwise be available.
WateReuse, 2015
 BRACKISH WATER: Distastefully salty but less saline than seawater.
In addition to certain surface water settings such as estuaries, brackish water can be found in aquifers.
-National Ground Water Association , 2010
 WATER STORAGE: Water held in a reservoir for later use.
Rock et al., 2012
 WETLANDS: Areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support a prevalence of vegetation typically adapted for life in saturated soil conditions.
Wetlands generally include swamps, marshes, bogs, and similar areas.
USGS, 2016a
 XERISCAPE: Landscaping that involves seven principles: proper planning and design; soil analysis and improvement; practical turf areas; appropriate plant selection; efficient irrigation; mulching; and appropriate maintenance.
Vegetation is suited to soils and climate and requires less water than traditional landscaping.
EPA, 2017a; Rock et al., 2012
 DESALINATED WATER: Saline water that has had its dissolved salts removed.
USGS, 2017
 WATERSHED: The land area from which water drains into a stream, river, or reservoir.
EPA, 2012
 CLASS A+ RECYCLED/RECLAIMED WATER: Wastewater that has undergone the most treatment of a minimum secondary treatment, nitrogen removal treatment, and high levels of disinfection.
It is the highest quality of recycled water and can be used for food crop and landscape irrigation, fire protection systems, snowmaking, toilet flushing, vehicle and equipment washing, and commercial closed loop air conditioning systems.
ADEQ, 2017; ADEQ, 2016
 DEVELOPED WATER: Water that has been captured in reservoirs, diverted from rivers/streams, or accessed by wells for use by society.
AWE, 2016
 DIRECT POTABLE REUSE : Involves putting recycled water directly into a potable water supply distribution system downstream of a water treatment plant or into the source water supply.
WateReuse, 2015
 FINISHED WATER: Water that has been treated and is ready to be delivered to customers.
Considered safe and suitable for delivery to consumers.
EPA, 2017a; Rock et al., 2012
 ADVANCED PURIFIED WATER OR PURIFIED WATER: Water that has passed through proven treatment processes and has been verified through monitoring to be safe for augmenting drinking water supplies.
The source water for advanced treatment is often clean water from a wastewater treatment or resource recovery plant.
Purification processes can involve a multistage process such as microfiltration, reverse osmosis and advanced oxidation, as well as Soil Aquifer Treatment.
Any of these options are capable of producing water quality that has been verified through monitoring to be safe for augmenting drinking water supplies.
WateReuse, 2015 AGRICULTURAL WATER: Water used on produce [agronomic purposes; to sustain livestock], normally consumed raw in activities such as growing , harvesting, packing, and holding.
Agricultural water is intended or likely to contact produce normally consumed raw or food-contact surfaces.
Food and Drug Administration , 2013
 GRAY WATER: Wastewater that has been collected separately from a sewage flow and that originates from a clothes washer or a bathroom tub, shower or sink but that does not include wastewater from a kitchen sink, dishwasher, or toilet.
ADEQ 2017
 Types Of Water And Water Reuse
 GROUNDWATER: Water that has seeped beneath the earth's surface and is stored in the pores and spaces between alluvial materials.
AWE, 2016
 GROUNDWATER RECHARGE: Naturally occurring as part of the water cycle and may be enhanced by using constructed facilities to add water into a groundwater basin.
WateReuse, 2015
 IMPORTED WATER: Water that has originated from one hydrologic region and is transferred to another hydrologic region.
Rock et al., 2012
 INDIRECT POTABLE REUSE : The blending of recycled water with other environmental systems such as a river, reservoir or groundwater basin, before the water is reused for drinking water.
WateReuse, 2015
 INDUSTRIAL WATER: Water used for fabrication, processing, washing, and cooling in industries including but not limited to chemical, food, mining, paper, petroleum refining, and steel industries.
USGS, 2016a
 IRRIGATION WATER: Includes water that is applied by an irrigation system to sustain plant growth in all agricultural and horticultural practices.
Irrigation also includes water that is used for preirrigation, frost protection, application of chemicals, weed control, field preparation, crop cooling, harvesting, dust suppression, and leaching salts from the root zone.
USGS, 2016a
 TAILWATER RECOVERY: An irrigation system in which all facilities utilized for the collection, storage, and transportation of irrigation tailwater for reuse have been installed.-USDA Natural Resources Conservation Service, 2008.
UNPLANNED WATER RECYCLING: Occurs when cities draw their water supplies from rivers that receive wastewater discharges upstream from those cities.
Water from these rivers has been reused, treated, and piped into the water supply a number of times before the last downstream user withdraws the water.
EPA, 1998
 NONPOTABLEWATER: Recycled water for purposes other than drinking purposes, such as irrigation and industrial uses.
WateReuse, 2015
 WASTEWATER: Is the used water of a community or industry that contains dissolved and suspended matter.
There are different types of wastewater: domestic, commercial, and industrial.
WateReuse, 2015
 NONTRADITIONAL WATER: Any water source other than groundwater including agricultural runoff, treated wastewater, recycled water, produced water, untreated surface water**, and brackish surface and groundwater.
USDA, 2017a
 DOMESTIC WASTEWATER/SEWAGE: The used water from washing our food, dishes, clothes and bodies, and toilet flushing.
The used water that goes down the drain or is flushed down the toilet is called sewage.
Because a considerable amount of water is used to carry away only a small quantity of waste, domestic sewage is mostly water.
It is referred to as "wastewater" in most places.
WateReuse, 2015
 POTABLE WATER: The water is purified sufficiently to meet or exceed federal and state drinking water standards and is safe for human consumption.
WateReuse, 2015
 POSTHARVEST WATER: Water used during or after harvest of produce usually eaten raw.
Includes water used in the field as well as packing and holding activities.
PSA, 2016
 INDUSTRIAL WASTEWATER AND COMMERCIAL WASTEWATER/ SEWAGE: The liquid waste generated by industries, small businesses and commercial enterprises and can be discharged to a sewer upon approval of a regulating authority.
Some industrial wastewater may require pretreatment before it can be discharged into the sewer system, while other industrial and commercial wastewaters are explicitly excluded.
Controlling the release of harmful chemicals into the wastewater collection system is known as source control.
WateReuse, 2015
 PROCESS WATER: Water used by industrial water users for producing products.
Can include water used in manufacturing processes, water used for testing, cleaning and maintaining equipment and water used to cool machinery or buildings used in the manufacturing process.
AWE, 2016
 PLANNED WATER RECYCLING: Projects developed with the goal of beneficially reusing a recycled water supply.
EPA, 1998
 PRODUCTION WATER: Water that contacts produce usually eaten raw during growth.
Irrigation, fertigation, foliar sprays, and frost protection.
PSA, 2016
 PROCESS WASTEWATER: Water that comes into contact with a raw material, product, or byproduct including manure, litter, feed, milk, eggs, or bedding and water directly or indirectly used in the operation of an animal feeding operation for any or all of the following: a.
Spillage or overflow from animal or poultry watering systems; b.
Washing, cleaning, or flushing pens, barns, manure pits, or other animal feeding operation facilities; C.
Direct contact swimming, washing, or spray cooling of animals; or d.
Dust control.
ADEQ, 2017
 RAW WATER: Surface or groundwater that has not gone through an approved water treatment process.
WateReuse, 2015
 RECLAIMED WATER: Water that has been treated or processed by a wastewater treatment plant or an on-site wastewater treatment facility.
If it is appropriately treated by an advanced reclaimed water treatment facility to become potable water, it is not considered "reclaimed water".
ADEQ, 2017
 Treatment Technologies, Processes, And Products
 RECYCLED WATER: A processed water that originated as a waste or discarded water, including reclaimed water and gray water, for which the Department has designated water quality specifications to allow the water to be used as a supply.
Grey water, industrial water, and reclaimed water are separate and unique categories of recycled water.
ADEQ, 2017
 ADVANCED OXIDATION: Process that can be used as a safety barrier in the water purification process.
Hydrogen peroxide, ultraviolet  light and other processes are used in combination to form a powerful oxidant that provides further disinfection of the water and breaks down the remaining chemicals and microorganisms and provides further disinfection of the water.
WateReuse, 2015
 ADVANCED TREATMENT: Additional treatment provided to remove suspended and dissolved substances that persist through conventional secondary treatment.
Often this term is
 RETURN FLOW: Surface and subsurface water that leaves a field after the application of irrigation water.
EPA, 2017a
 SURFACE WATER: Water located on the Earth's surface.
All water open to the atmosphere  and all springs, wells, or other collectors that are directly influenced by surface water.
PSA, 2016.
TAIL WATER: The runoff of irrigation water from the lower end of an irrigated field.
EPA, 2009
 used to mean additional treatment after tertiary treatment for the purpose of further removing contaminants of concern to public health.
In many cases, this includes membrane filtration, reverse osmosis , and advanced oxidation/disinfection with ultraviolet light  and hydrogen peroxide.
-Rock et al., 2012
 size of a microfiltration filter has a pore size of 0.1 micron.
WateReuse, 2015
 MULTI-BARRIER PROCESSES: Purification processes that consist of several barriers to ensure sufficient reduction elimination of the various substances that need to be controlled.
As in all processes, monitoring is important in order to check that the processes are working properly and efficiently.
Membrane filtration, reverse osmosis, advanced oxidation, riverbank filtration, soil aquifer treatment, and constructed wetlands all may be parts of a multi-barrier purification process.
Not all of these processes are needed in all situations.
WateReuse, 2015
 NANOFILTRATION: A filtration process that utilizes membranes that is used most often with low total dissolved solids water such as surface water and fresh groundwater, with the purpose of softening  and removal of disinfection by-product precursors such as natural organic matter and synthetic organic matter.
It is commonly used in conjunction with desalination.
The pore size of a nanofiltration filter has a pore size of 0.001 micron.
BACKFLOW PREVENTION: The prevention of contamination to potable water supplies from the reverse flow of water from an irrigation system or other customer activity back into the potable distribution system.
AWE, 2017
 BIOCHEMICAL OXYGEN DEMAND : A measure of the amount of oxygen consumed in the biological processes that break down organic matter in water.
Used as an indicator of the amount of organic material in the waste stream.
Usually expressed in milligrams per liter.
CAS, 2011
 NEPHELOMETRIC TURBIDITY : A unit of measure related to the individual particles suspended in water.
Measured by the amount of light that is deflected through a sample.
AUGMENTATION: Process of adding recycled water into an existing raw water supply.
WateReuse, 2015
 OZONATION: Process of applying ozone  for the disinfection of water/wastewater.
Ozone is a strong oxidant.
WateReuse, 2015
 ADVANCED WATER TREATMENT FACILITY: A facility that treats and purifies Class A+ or Class B+ reclaimed water to produce potable water suitable for distribution for human consumption.
Potable water produced by an advanced water treatment facility is not considered reclaimed water.
ADEQ, 2017
 PRETREATMENT: A process in wastewater treatment where metal screens are used to remove large objects and chunks of debris.
Rock et al., 2012
 SECONDARY TREATMENT: Process where dissolved and suspended biological matter is removed to a nonpotable level SO that the water may be disinfected and discharged into a stream or river, or used for irrigation at controlled locations.
WateReuse, 2015
 REVERSE OSMOSIS: Method of removing dissolved salts, ions and other constituents from water.
Pressure is used to force the water through a semi-permeable membrane that transmits the water but stops most dissolved materials from passing through the membrane.
This treatment method is commonly used in desalination, a process that takes salt out of seawater.
The pore size of a reverse osmosis filter has a pore size of 0.001 micron.
WateReuse, 2015
 SOIL AQUIFER TREATMENT: When water, including recycled water, soaks into the ground and is purified by the physical, chemical, and biological processes that naturally occur in soil.
WateReuse, 2015
 DUAL MEDIA FILTRATION: Filtration method that uses two different types of filter media, usually sand and finely granulated anthracite.
WateReuse, 2015
 DISINFECTION: A process that destroys or inactivates potentially harmful bacteria.
-Rock et al., 2012; EPA, 2017
 FILTRATION: A process that separates small particles or microorganisms from water by using a porous barrier to trap the particles while allowing water to pass.
Rock et al., 2012
 GRANULAR ACTIVATED CARBON: Process used to remove chemicals that are dissolved in the used water with activated carbon.
WateReuse, 2015
 MICROFILTRATION: A physical separation process where tiny, hollow, straw-like membranes separate particles from water.
It is used as a pretreatment for reverse osmosis.
The pore
 RETROFIT: The process of constructing and separating potable and recycled water pipelines that allow recycled water to be used for non-drinking purposes.
This also includes the process of preparing customer use sites for recycled water use.
WateReuse, 2015
 BIOFOULING: The formation of bacterial film  on fragile reverse osmosis membrane surfaces.
The accumulation of undesirable organisms, including bacteria, fungi, diatoms, algae, plants or animals, causing surfaces to become encrusted, clogged or otherwise degraded.
Rock et al., 2012; USDA, NAL, 2017b
 PRIMARY TREATMENT: Process where solid matter is removed.
The remaining liquid may be discharged or subjected to further treatment.
WateReuse, 2015
 CHLORINATION: The process of adding chlorine gas or chlorine compounds to wastewater for disinfection.
EPA, 2004
 DIRECT INJECTION: Injecting recycled water through an injection well directly into a groundwater basin.
If the water will later be used for drinking, the recycled water will receive advanced treatment prior to injection.
Rock et al., 2012
 DISCHARGE: The release of effluent, which meets regulatory standards, and designated by a regulatory permit to be safely discharged into the environment without causing harm.
WateReuse, 2015
 TERTIARY TREATMENT OR ADVANCED WATER TREATMENT: Processes that purify water for uses such as irrigation or for water blended with other environmental systems such as a river, reservoir, or groundwater basin prior to reuse.
It can also include treatment processes to remove nitrogen and phosphorus in order to allow discharge into a highly sensitive or fragile ecosystem.
WateReuse 2015
 ULTRAFILTRATION : A membrane filtration process that falls between reverse osmosis  and microfiltration  in terms of the size of particles removed.
The pore size of ultrafiltration filter is 0.01 micron.
Rock et al., 2012
 ULTRAVIOLET TREATMENT : The use of ultraviolet light for disinfection or as part of an advanced oxidation process.
This usually renders the pathogens inactive.
WateReuse, 2015
 ZERO-VALENT IRON  BIOSAND FILTERS: Iron hydroxides, oxides and oxyhydroxides are formed from ZVI's reactions with dissolved oxygen and protons in water.
The hydroxides, oxides and oxyhydroxides have high pHpzc  that strongly adsorb viruses and negatively charged microorganisms.
Unlike other chemical treatments, ZVI does not create potentially harmful by-products.
Ingram et al., 2012.
Laws, Regulations, & Policies
 CLEAN WATER ACT : The federal law that establishes how the United States will restore and maintain the chemical, physical, and biological integrity of the country's waters.
Regulates the discharges of pollutants into these water systems.
Rock et al., 2012; EPA, 2017b
 ENDANGERED SPECIES ACT: The federal law that sets forth how the United States will protect and recover animal and plant species whose populations are in dangerous decline or close to extinction.
The law protects not only threatened and endangered species but also the habitat upon which those species depend.
Rock et al., 2012
 ENVIRONMENTAL IMPACT STATEMENT : Detailed analysis of the impacts of a project on all aspects of the natural environment required by federal National Environmental Policy Act for federal permitting or use of federal funds.
Rock et al., 2012
 FOOD SAFETY MODERNIZATIONA  PRODUCE SAFETY RULE: Signed into law on January 4, 2011, to ensure food safety in the U.S.
It focuses on responding to contamination rather than simply responding to it.
Establishes science-based minimum standards for the safe growing, harvesting, packing, and holding of produce grown for human consumption to minimize contamination.
FDA, 2017
 NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM : A federal permit authorized by the Clean Water Act, Title IV, which is required for discharge of pollutants to navigable waters of the United States, which includes any discharge to surface waters-lakes, streams, rivers, bays, the ocean, wetlands, storm sewer, or tributary to any surface water body.
Rock et al., 2012; EPA, 2017b
 SAFE DRINKING WATER ACT : Federal legislation passed in 1974 that regulates the treatment of water for human consumption and requires testing for and reduction and/or elimination of contaminants that might be present in the water.
Rock et al., 2012
 WATER AUDIT: 1) An on-site survey of an irrigation system or other water use setting to measure hardware and management efficiency and generate recommendations to improve its efficiency.
2) For water distribution systems, a thorough examination of the accuracy of water agency records and system control equipment to identify, quantify, and verify water and revenue losses.
AWE, 2016
 *The term "nontraditional water" defined by the USDA includes untreated surface water to emphasize that its quality can be impacted by external environmental factors such as runoff.
The agricultural community  already uses surface water to irrigate, and considers surface water to be a "traditional water" source.
Conserving Water in the Garden
 Most of us take for granted the seemingly unlimited water that comes out of the hose or tap.
Although New Hampshire has an abundant fresh water supply, it is still a decidedly finite resource.
Anyone whos been gardening for years knows that the weather patterns in New Hampshire are changing.
Were seeing more extremes throughout the year, most notably an increased number of droughts and dry spells in the hot summer months.
At many homes, more water goes to gardening and landscaping than any other purpose.
Our desire for lush flower beds and jewel green lawns leads us to use vast amounts of water.
Knowing what we do about the anticipated scarcity and uncertainty of freshwater resources in the coming decades, the way we look at water in the garden needs to change.
By making a few simple adjustments, we can create beautiful landscapes that ultimately need less maintenance and are more ecologically sound.
Designing a water efficient garden
 Mid-summer is not the time to be making big changes in the garden.
High temperatures and dry soils are not a recipe for landscaping success.
However, there are still a number of things you can do.
July and August is a great time to pay attention to which plants thrive in the heat and which suffer.
If a certain plant is always wilting and requiring frequent watering and attention, its either not a great fit for your garden or would perform better if moved to a different location.
Try sketching out your landscape on graph paper, noting where all of the important landscape features are and keeping track of sun and wind exposure.
Mark how much sun each area gets as well as soil type and drainage.
Make lists of the plants that are struggling and plan to move those to wetter parts of the garden or replace them with more drought tolerant species.
Perhaps the most important thing when it comes to water conservation is plant selection.
Plants will always perform best in sites that suit their needs.
Choose trees, shrubs, and perennials that are compatible with soils and sun exposure in your garden.
There are many drought tolerant choices available, many of which are native.
More often than not, native plants are some of the best choices for low maintenance landscapes, as they are adapted to grow in local climate and soil conditions.
Its also not a bad idea to minimize the amount of area you have planted as lawn.
Lawns are the thirstiest part of most landscapes.
Planting ground covers or groupings of trees and shrubs in place of turf grass can help save a significant amount of water.
Remember, even if a perennial or shrub is drought tolerant, it will still need a good deal of water to become established.
Watering deeply is the key to making sure new plants develop resilient and self-sufficient root systems.
Moistening the soil to a depth of eight inches or more will encourage plants to develop deep roots that can access water lower in the soil profile during periods of dry weather.
Before you pull out the hose or start running the sprinkler, you should always check to make sure your garden does indeed need water.
Natural rainfall quantity can be determined with a rain gauge or with a straight sided can and a ruler.
Its also a good idea to measure the amount of water being emitted by sprinklers by setting out coffee cans beneath them.
Run the sprinklers for 15 minutes, shut them off, then measure the result and calculate how much water would be applied in an hours time.
Most gardens benefit from an inch of water a week.
In terms of water efficiency, sprinklers are not the best way to go.
They tend to waste a fair amount of water by spraying non-target areas and plant foliage.
They should only be used in the morning and on non-windy days to limit evaporative losses and plant disease issues.
Delivering water directly to the soil is much more effective and can be easily achieved with soaker hoses or a customized drip irrigation system.
Collecting rainfall is also a great opportunity to lessen water consumption.
Use rain barrels to save water that can be used when needed at a later date.
Rainwater also had the added benefit of being free from any chlorine, fluorine, or softening salts.
Although water scarcity is seldom an issue we have to deal with in New Hampshire, that doesnt mean we shouldnt make an effort to slow the drain on municipal and well water supplies.
At the very least, consider adopting some water conserving practices to lower your water bill!
CROP GROWTH AND DEVELOPMENT FOR IRRIGATED CHILE 
 Jeffrey C.
Silvertooth, Paul W.
Brown, Stephanie Walker
 Plants vary tremendously in their physiological behavior over the course of their life cycles.
As plants change physiologically and morphologically through their various stages of growth, water and nutritional requirements will change considerably as well.
Efficient management of a crop requires an understanding of the relationship between morphological and physiological changes that are taking place and the input requirements.
Heat units  can be used as a management tool for more efficient timing of irrigation and nutrient inputs to a crop.
The thermal environment impacts the development of all crop systems including chiles.
Plants will develop over a range of temperatures which is defined by the lower and upper temperature thresholds for growth.
Heat unit systems take into account the elapsed
 Figure 1.
Typical relationship between the rate of plant growth and development and temperature.
Growth and development ceases when temperatures decline below the lower temperature threshold  or increase above the upper temperature threshold.
Growth and development increases rapidly when temperatures fall between the lower and upper temperature thresholds.
time that local temperatures fall within the set upper and lower temperature thresholds and thereby provide an estimate of the expected rate of development for the crop.
Heat units systems have largely replaced days after planting in crop phenology models because they take into account day-to-day fluctuations in temperature.
Phenology models describe how crop growth and development are impacted by weather and climate and provide an effective way to standardize crop growth and development among different years and across many locations.
The first step in developing a phenological guideline for chiles would be to look for critical stages of growth in relation to HU accumulation.
Figure 2 describes the basic phenological baseline for New Mexico chile and was developed from field studies conducted in New Mexico and Arizona between 2003 and 2010.
Use of HUs to predict chile development is considered superior to using days after planting due to the simple fact that the crop responds to environmental conditions and not calendar days.
This approach, using phenological timelines or baselines, works best for irrigated conditions where crop vigor and environmental growth conditions are more consistent than in non-irrigated or dryland situations where irregularity in year-to-year rainfall patterns can alter growth and development patterns significantly.
Phenological guidelines can be used to identify or predict important stages of crop development that impact physiological requirements.
For example, a phenological guideline can help identify stages of growth in relation to crop water use  and nutrient uptake patterns.
This information allows growers to improve the timing of water and nutrient inputs to improve production efficiency.
For some crops or production situations HU based phenological guidelines can be used to project critical dates such as harvest or crop termination.
Many other applications related to crop management  can be derived from a better understanding of crop growth and development patterns.
New Mexico Type Chile Plant Development as a Function of Heat Units
 Figure 2.
Basic phenological guideline for irrigated New Mexico-type chiles.
Irrigation allows crops to grow close to their potential yield, in which case the crop functions more optimally and produces more yield for each inch of water consumed.
Advances in crop genetics and production practices, including drought-tolerant and high-producing hybrids, have also led to increases in CWP over time.
A report from the Daugherty Water for Food Global Institute estimates that CWP for corn and soybean in Nebraska has increased by approximately 75% over 24 years.
Summary of Current University of Tennessee Institute of Agriculture Research Evaluating Urea-Nitrogen-Fertilizer Additives or Coatings
 H.J.
Savoy, Associate Professor, and Michael Essington, Professor Department of Biosystems Engineering and Soil Science Xinhua Yin, Associate Professor, and Angela McClure, Associate Professor Department of Plant Sciences
 Loss of nitrogen through ammonia volatilization  has been of concern to growers for some time.
The problem is primarily associated with the use of urea as a nitrogen source in conservation tillage systems where urea-containing fertilizer materials are broadcast or banded onto the soil surface and not quickly incorporated by tillage, rainfall or irrigation.
Urea nitrogen when applied to a soil is hydrolyzed by the urease enzyme  and converted first to ammonium carbonate [CO3] and then to ammonia gas.
Urease is everywhere in the environment and can be found in soils, manures, on plants and plant residues.
Within the soil, this ammonia gas becomes the ammonium cation through a reaction with the soil water and is held onto the soil cation exchange complex instead of being lost.
Four factors of major importance when considering potential for nitrogen volatilization are temperature, soil pH, soil moisture and nitrogen rate.
In general for a moist soil as soil temperature, soil pH and nitrogen rate increase, losses of nitrogen as ammonia gas increase from surface applied non-incorporated urea-containing-fertilizers.
This fact sheet briefly summarizes the results of current University of Tennessee field research evaluating the effects of urea-nitrogen fertilizer treated with various chemical additives or coatings on corn grain yield.
These yields were compared to yields obtained with ammonium nitrate  and untreated urea.
Some initial work was completed in 2011 and after 2012, more studies were conducted at two locations each year as shown in Table 1.
Table 1.
Locations and Soil Types for Tennessee Nitrogen
 Fertilizer Additive/Coating Studies 2011-2015
 West TN Region	Middle TN Region
 Year	Location	Soil Type	Year	Location	Soil Type
 2011	Milan	Loring silt loam	2011	No study	No study
 2013	Milan	Loring/Henry silt loam	2013	Springfield	Hamblen silt loam
 2014	Jackson	Memphis/Loring silt loam	2014	Springfield	Staser silt loam
 2015	Jackson	Memphis silt loam	2015	Springfield	Hamblen silt loam
 The studies were set up in an experimental design so that yield and other results could be evaluated using commonly accepted statistical procedures.
Corn was planted in six row plots that were 30 feet long, and the middle two rows of each plot were harvested for yield determinations.
Generally at planting we tried to achieve a plant population of about 32,000 per acre.
Lower nitrogen rates of 110 and 150 pounds of nitrogen per acre were used to better ensure the separation of products that may not have any effect in reducing volatilization.
The nitrogen fertilizers and additives/coatings evaluated are shown in Table 2.
Products were applied to the urea as suggested on the product label.
Product effects on yield were looked at over the combined nitrogen fertilizer rates for each product.
Table 2.
Nitrogen Fertilizers and Additives/Coatings Used in This Study
 Fertilizer	Stabilizer active ingredient	Stabilizer trade name
 Urea	NBTP*	Agrotain 
 Urea	NBTP*	Agrotain 
 Urea	Ca salt of Maleic polymer	Nutrisphere-N 
 Polymer	Semipermeable Polymer	Environmentally Smart Nitrogen 
 coated	coating of the urea granule	
 * N butyl thiophosphoric triamide
 Yield results for all seven site years are shown in Table 3.
Ammonium nitrate appears to be the best product for avoiding volatilization loss of nitrogen in these no-till corn systems studied.
The NBTP products and ESN also give better results than untreated urea but not always as good as ammonium nitrate.
Table 3.
Average Corn Yield Results 
 by Product Used, Location and Year
 Product used	West Tennessee Locations	Middle Tennessee Locations
 2011	2013	2014	2015	2011	2013	2014	2015
 nitrate	176 a	198 a	207 a	163 a	NA	206 a	212 ab	204 a
 2.
Untreated Urea	149 b	126 d	147 C	111 d	NA	143 d	223 a	144 C
 3.
Nutrisphere Urea	149 b	134 d	152 C	121 C	NA	159 cd	211 ab	143 C
 4.
Agrotain 	175 a	159 C	170 b	140 b	NA	202 ab	224 a	172 b
 5.
Agrotain ultra	NA	170 bc	166 b	138 b	NA	180 bc	217 ab	163 b
 6.
Environmentally	NA	178 b	175 b	147 b	NA	179 bc	198 b	165 b
 Numbers followed by the same letter are not significantly different P 0.05
 NA	No data obtained
 Evaluation of corn grain yield at each site for seven site years produced the following summary results:
 Ammonium nitrate use resulted in the highest corn grain yields in seven of seven site years.
Untreated Urea use gave the lowest corn grain yields in six of seven site years.
Ca salt treated Urea product  resulted in corn grain yields similar to untreated Urea corn grain yields for all seven site years.
NBPT product  equaled Ammonium nitrate three of seven site years and exceeded untreated Urea for six of those seven site years.
Agrotain ultra  performed similarly to Agrotain.
Polymer coated urea  yields equaled Ammonium nitrate one out of six site years, equaled NBTP products six of six site years and exceeded untreated Urea yields five of six site years.
ESN was not included in the test conducted in 2011.
UMA INSTITUTE OF AGRICULTURE THE UNIVERSITY OF TENNESSEE Real.
Life.
Solutions." TM
Simple Irrigation Checkup for Home Sprinkler Systems
 Justin Quetone Moss Research and Extension Specialist
 Joshua Campbell Extension Associate
 A simple irrigation checkup may reduce outdoor water use by helping identify problems with your irrigation system.
An efficient, properly designed and properly installed irrigation system can help to keep landscapes and turfgrasses healthy and attractive.
However, irrigation systems not kept in proper operating condition or managed well can waste water.
An irrigation system should be maintained and will fall into disrepair without regular checkups.
This fact sheet is not intended to provide information on sprinkler system repair or operation but serves to help homeowners identify problems with irrigation systems so a professional irrigation contractor can be contacted for repairs.
For information on specific irrigation system repairs, consult the manufacturer manuals or contact a professional irrigation contractor in your area.
The simple irrigation checkup is a three-step process:
 Step 1.
Check controller settings: Specific watering days may be established by your municipality.
Check the controller settings to ensure they are set to water on the appropriate days and times.
Most water waste is due to unnecessary or improper tarttimes and lengthy run times.
Watering in the heat of the day will result in water that is lost to evaporation.
Set the controller to water early in the morning or in the evening.
Record current controller settings on the irrigation checkup form  and then make necessary changes.
Appropriate controller settings reduce water waste and save money.
Step 2.
Run each irrigation zone: Turn on each irrigation zone one at a time or set your controller to run through each zone using a test cycle setting.
If choosing to run a test cycle of each zone, set a time limit long enough to observe each zone and mark needed repairs, about three minutes.
Step 3.
Identify problems and make repairs: While each zone is running, walk through the yard and check each sprinkler head, noting any that require attention.
Flag or mark problems to make them easier to identify when making repairs.
Simple Definitions of Common Irrigation Terms:
 Controller A "timer" used to set scheduled run times and turn an automatic irrigation system on and off.
Zone A grouping of irrigation heads in the landscape where irrigation is controlled by a single control valve.
Start time The time of day an irrigation system is set to begin watering.
Run time The length of time an irrigation zone is set to water.
Valve A device that responds to electrical currents from the controller to turn water flow on and off.
Spray head An irrigation head that puts out water in a fixed stationary pattern.
Rotor An irrigation head that puts out water in a large rotating stream.
Nozzle The part of a sprinkler the water exits.
In most cases, the nozzle is removable so it can be easily cleaned or replaced.
Nozzle shape, size and placement have a direct effect on the distance, watering pattern and distribution of irrigation water.
Rain/Freeze Sensor A device connected to the controller that prevents automatic sprinkler systems from watering during rain or freezing temperatures.
Irrigation Simple Checkup System
 Settings: Some of schedules.
programmed landscapes determine number through of operation At and number settings controller, the the the in to zones your go and determine indicated of of Next, schedule schedules length B, is A, time each time have the time the day is each etc.
start two set to set to or or more zone run as may visible if municipality irrigation applicable.
morning Mark night Many knowing schedules late for established when early they watering days not at water.
set are are or your efficiently.
help schedule will system manage you your your Controller
 Checkup: through Walk Irrigation landscape provided head for Look Label is by while issues running.
in the each the using the the key.
type system zone zone zone your listed of needed problems below section make and repairs.
the to notes use
 Abbreviation fixed Spray, Head Mix including S= of Rotor, Key: R= head sprinkler rotating M Type and nozzles.
nozzle apply such types at rotors water sprays spray as = different distribution of Mixing head will lead in and rates.
water types to waste.
zone uneven cause an a
 following  the issues: 1
 Sprinkler heads sidewalk, driveway road spraying or a
 Sprinkler  of with heads cloud operating mist a
 Sprinkler adjustment heads tilted of that out or are
 Sprinkler leaking broken, heads base popping the not at or up
 different heads sprinkler of rotors) (sprays, A mix the same zone on
 failing Rotors in stuck position, to turn one
 wind speeds clogged Dry low high due nozzle water to pressure, areas or a
 blocking Grass, shrubs sprinkler trees patterns spray or
 Electrical  issues valves wire, turning controller not error on,
 1	2	3	4	5	6	7	8	9	10	11	12
 Figure 1.
Sprinkler head spraying a sidewalk.
Figure 2.
Sprinkler heads with excessive or high pressure causing misting of irrigation water.
Figure 3.
Sprinkler head tilted and out of alignment.
Figure 5.
An irrigation zone with a mix of rotors and fixed spray sprinklers.
Figure 6.
Sprinkler head stuck and failing to fully pop up above the ground.
Figure 7.
A dry area due to poor sprinkler distribution and uniformity.
Figure 4.
Sprinkler head leaking and causing ponding at the base.
Figure 8.
Plants blocking a sprinkler head causing an uneven spray pattern.
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Director of Oklahoma Cooperative Extension Service, Oklahoma State University, Stillwater, Oklahoma.
This publication is printed and issued by Oklahoma State University as authorized by the Vice President for Agricultural Programs and has been prepared and distributed at a cost of 30 cents per copy.
0517 GH.
Controlling Bacteria, Algae, and Weeds in Irrigation Ponds
 Craig A.
Storlie, Ph.D., Extension Specialist in Agricultural Engineering
 Ponds are used as reservoirs for irrigation water in many areas of New Jersey.
Where pond water is used for drip irrigation, controlling bacteria, algae, and weeds is essential to prevent clogging of drip irrigation systems.
Where sprinkler irrigation is used, controlling pond vegetation is required only if the growth is SO dense that it effects the performance of the irrigation system.
Screen and/or media filtration is usually all that is required to provide excellent water quality where groundwater is used as a water source.
Pond water often requires additional treatment in order to keep irrigation lines free of biological materials.
Bacteria, algae, and weed growth in an irrigation pond complicate drip irrigation water treatment.
Uncontrolled growth of these organisms can overload media filters, causing excessive backwashing and can lead to clogging of the media and, in severe cases, filtration system failure.
Algae and weeds can also clog the intake pipes leading to pumps.
Algae are primitive plants that are observed as hair-like strands or as tiny, floating single cells that give the water a clouded, "soupy" appearance.
Higher plants have roots and leaves and live above or below the water.
In this fact sheet, higher plants will be referred to as "weeds" because they are undesirable.
Bacteria are also present in ponds and can cause drip irrigation clogging if other water conditions favor bacteria growth.
The best way to control algae and weed growth is to prevent it from occurring.
If these pests are present, there are two effective methods of eliminating them.
The first is by mechanical means.
Raking or dragging weeds out of the pond may be practical for very small ponds or where weed growth is confined to the edge of the pond.
In the majority of ponds, however, chemical control is the safest, easiest, most effective, and most economical control method.
Controlling Algae and Weeds with Copper Sulfate
 Granular copper sulfate is an excellent herbicide which is available for control of bacteria, algae, and weeds in ponds.
The amount needed to provide effective control is influenced by  the kind and amount of vegetation to be destroyed,  pond size,  water temperature,  water hardness, and  the amount of water flowing through the pond.
Control is easiest and most effective if made shortly after plant growth has started.
Control with copper sulfate is most effective when water temperature is above 60F.
Low water temperatures are generally not a problem in New Jersey where pond vegetation problems occur in midto late-summer.
However, if water temperature is below 60F, a greater amount of copper sulfate will be required to provide effective control.
If higher than necessary amounts of copper sulfate are used, fish, insects, and other pond animals may be endangered.
Dying weeds and algae will use oxygen in the water, and possibly suffocate fish.
If the pond is heavily infested, treat only a portion of it at a time.
Again, the best method of preventing a build up is to treat early, in May or June, after water temperature has risen above 60FF.
Applications should be repeated as necessary, and typically may be required every two to four weeks.
Applying the proper amount of copper sulfate requires that the volume of the pond be estimated.
In Table 1, the pounds of copper sulfate required to obtain a given copper sulfate concentration are listed.
In this table, pond volume is given in acre-feet and gallons.
A pond with a 1 acre-foot volume has a surface area of one acre and a depth of one foot.
When treating ponds with outlets, these should be closed during treat-
 ment and for several days following treatment.
Generally, a dose of between 1/4 and 1 ppm of copper sulfate is sufficient and safe for treatment of algae.
Heavily infested ponds will require higher concentrations, as will "hard" water.
In most cases, the single cell, "soupy" type of algae can be controlled with 1/4 ppm of copper sulfate.
For the stranded, "pond scum" variety of algae, 1/2 ppm is usually adequate.
Certain weeds will require much higher concentrations of copper sulfate, sometimes as high as 40 ppm.
At these concentrations, aquatic life is endangered.
In most cases, it is not necessary to control weeds if algae can be controlled with lower copper sulfate concentrations.
Media filtration is probably sufficient for minor algae problems.
Floating inlet pipes will also reduce the amount of treatment necessary by reducing the amount of algae and trash drawn from a pond.
Where a floating inlet is used, it is important to draw water from a foot or two below the water surface.
A simple floating inlet can be constructed by strapping the irrigation system inlet pipe to the bottom or side of a sealed 55-gallon drum.
Controlling Bacteria With Chlorine
 Waters which are free of algae and weeds may contain bacteria.
Both surface and groundwater sources can contain bacteria if water pH is 4.5-6.5, temperature is above 45F, iron is present at concentrations of 0.21.0 ppm or hydrogen sulfide is present at concentrations of 0.1 ppm or greater.
Under these conditions, bacteria secrete a slime which can plug emitters.
Chlorination is the most common and efficient treatment for bacteria.
Chlorine is available in several forms.
Liquids containing between 5-15% sodium hypochlorite are commonly used.
Gaseous chlorine is more economical, but is extremely dangerous to use.
Solid forms of chlorine containing 65-75% calcium hypochlorite are also available.
It is important to note that both liquid and solid forms of chlorine will cause water pH to rise.
This is critical because chlorine is most effective in acidic water.
If water pH is above 7.5, it must be acidified for chlorine injection to be effective.
Several options are available for chlorine treatment of irrigation water.
Since most bacteria grow and multiply when the system is not running, an effective control method is to fill the irrigation system with chlorinated water during the end of each irrigation cycle.
For this treatment method 10-20 ppm of chlorine  are recommended.
Another possibility is to inject higher concentrations , during the last 15-30 minutes of irrigation cycles once or twice each month.
Chemical treatment of irrigation water will prevent many of the clogging problems that can seriously disable drip irrigation systems.
Keep in mind that the injection of chlorine and copper sulfate require that labeled products be used, and that the operator possess a New Jersey Private Applicators License.
New Jersey legislative code also requires that a functioning backflow prevention device be used where chemicals are injected into an irrigation system.
An Aquatic Use Permit is required where copper sulfate is added to ponds with outlets, such as a pond which is fed by a stream.
TABLE 1.
Pounds of copper sulfate required to achieve desired concentration in various size ponds
 Pond volume	Desired copper sulfate concentration 
 acre-feet	gallons	1/4	1/2	3/4	1
 0.2	65,000	0.14	0.27	0.4	0.5
 0.4	130,000	0.27	0.54	0.8	1.1
 0.6	195,000	0.41	0.82	1.2	1.6
 0.8	261,000	0.54	1.09	1.6	2.2
 1.0	326,000	0.68	1.36	2.0	2.7
  2004 by Rutgers Cooperative Research & Extension, NJAES, Rutgers, The State University of New Jersey.
Desktop publishing by RutgersCook College Resource Center
Effects on soybean during grain fill
 Drought effects on soybean are generally not as severe as corn.
This is a result of overlapping of development stages.
When short-term drought stress results in flower or pod abortion, new flowers and pods will set when conditions improve.
During prolonged drought stress, or when the stress occurs during pod set and seed filling stages, the compensatory ability is not as likely to occur.
Drought can reduce pod number by up to 20 percent as a result of flower and pod abortion.
Seeds per pod and seed size can also be affected by drought stress but to a lesser extent than the number of pods.
Drought stress often results in earlier maturity or shortening of the grain filling period resulting in lower seed weights and yields.
Soybean yield loss from drought stress is compounded by the lack of nitrogen mineralization and nitrogen fixation.
In dry conditions, nodules cease nitrogen fixation because of a lack of soil moisture and lack of carbohydrate supply from the soybean plant.
If water deficits are short lived, nodule nitrogen fixation can resume.
Calculating Horsepower Requirements and Sizing Irrigation Supply Pipelines
 Pumping costs are often one of the largest single expenses in irrigated agriculture.
Table 1 shows typical fuel use and costs of pumping in Texas as measured in irrigation pumping plant tests conducted by the Texas Agricultural Extension Service.
Properly sizing pipelines for the particular situation will help minimize these costs.
This publication outlines how to calculate the horsepower requirements of irrigation pumps and how to use this information in sizing supply pipelines.
An irrigation pumping plant has three major components:
 1.
a power unit,
 2.
a pump drive or gear head, and
 For electric powered plants, the pump lineshaft and the motor shaft are usually directly connected, making a pump drive or gear head unnecessary.
The overall pumping plant efficiency is a combination of the efficiencies of each separate component.
Individual pumping unit components in good condition and carefully matched to the requirements of a specific pumping situation can have efficiencies similar to those given in Table 2.
However, many pumping units operate at efficiencies far below acceptable levels.
Additional details on pumping plant efficiency are given in L-2218, "Pumping Plant Efficiency and Irrigation Costs,".
There are two commom methods of determining the efficiency of pumping plants.
One is to measure the efficiency of each component of the plant.
Once the efficiencies of the components are
 known, the overall efficiency is easily calculated.
This requires specialized equipment and considerable expertise.
Another method is to calculate the load on the motor or engine and then measure how much fuel is used by the power unit.
The fuel usage can then be compared to a standard.
The most widely used standards were developed by the Agricultural Engineering Department of the University of Nebraska.
The fuel consumption rates in Table 4 indicate the fuel use which can be reasonably expected from a properly engineered irrigation pumping plant in good condition.
The actual fuel usage of a new or reconditioned plant should not be larger than that shown in Table 4.
Horsepower is a measurement of the amount of energy necessary to do work.
In determining the horsepower used to pump water, we must know the:
 1.
pumping rate in gallons per minute , and
 2.
total dynamic head  in feet.
The theoretical power needed for pumping water is called water horsepower  and is calculated by:
  = TDH 
 Since no device or machine is 100 percent efficient, the horsepower output of the power unit must be higher than that calculated with equation 1.
This horsepower, referred to as brake horsepower , is calculated by:
 whp  bhp = 
 Total Dynamic Head 
 TDH may be viewed as the total load on the pumping plant.
This load is usually expressed in feet of "head" (1 psi, or pound per square inch = 2.31 feet of
 head).
TDH can be calculated with the following equation:
  TDH =  +  +  + 
 Pumping lift: "Pumping lift" is the vertical distance from the water level in the well to the pump outlet during pumping.
In areas of falling water table, often the maximum depth to the water table expected during the pumping season is used.
Friction loss: Water flowing past the rough walls in a pipe creates friction which causes a loss in pressure.
Friction losses also occur when water flows through pipe fittings, or when the pipe suddenly increases or decreases in diameter.
Tables with values for friction loss through pipe and fittings similar to Tables 6 and 7 are widely available.
Operating pressure requirements: Manufacturers provide recommended operating pressures for specific water applicators in irrigation systems.
Operating pressure in psi is converted to feet of head by the relationship:
 1 psi =2.31 ft
 Elevation change: Use the total change in elevation from the pump to the point of discharge, such as the end of the pipeline or sprinkler head.
This elevation change may be positive  or negative.
Use only the difference in elevation between these two points, not the sum of each uphill or downhill section.
Do not forget to add the distance from the ground to the point of water discharge, particularly for center pivot systems.
For center pivots, elevation differences caused by slopes in the field usually are accounted for in the computer printout of the design, and are included in the operating pressure requirements.
If not, then the elevation change from the pivot point to the highest point in the field should be added to the total elevation change.
In sizing irrigation water supply pipelines, two factors are important: friction losses and water hammer, both are influenced by the relationship between flow rate  and pipe size.
When moving water is subjected to a sudden change in flow, shock waves are produced.
This is referred to as water hammer or surge pressure.
Water hammer may be caused by shock waves created by sudden increases or decreases in the velocity of the water.
Flow changes and shock waves can occur when valves are opened, pumps are started or stopped, or water encounters directional changes caused by pipe fittings.
To control surge pressure in situations where excessive pressures can develop by operating the pump with all valves closed, pressure relief valves are installed between the pump discharge and the pipeline.
Also, pressure relief valves or surge chambers should be installed on the discharge side of the check valve where back flow may occur.
Air trapped in a pipeline can contribute to water hammer.
Air can compress and expand in the pipeline, causing velocity changes.
To minimize such problems, prevent air from accumulating in the system by installing air-relief valves at the high points of the pipeline, at the end, and at the entrance.
Other general recommendations for minimizing water hammer include:
 1.
For long pipelines sloping up from the pump, install "nonslam" check valves designed to close at zero velocity and before the column of water above the pump has an opportunity to move back.
2.
In filling a long piping system, the flow should be controlled with a gate valve to approximately three-fourths of the operating capacity.
When the lines have filled, the valve should then be slowly opened until full operating capacity and pressure are attained.
5 Feet per Second Rule
 To minimize water hammer, especially for plastic  pipe, water velocities should be limited to 5 ft/s  unless special considerations are given to controlling water hammer.
Most experts agree that the velocity should never exceed 10 ft/s.
Also, the velocity of flow in the suction pipe of centrifugal pumps should be kept between 2 and 3 ft/s in order to prevent cavitation.
Table 5 lists the maximum flow rates recommended for different ID  pipe sizes using the 5 ft/s rule.
Many friction loss tables give both the friction loss and velocity for any given gpm and pipe size.
Velocity  in feet per second  can be calculated based on the flow rate in gallons per minute  and pipe internal diameter in inches as:
 Flow   V  = 
 Pumping plants must provide sufficient energy to overcome friction losses in pipelines.
Excessive friction loss will lead to needlessly high horsepower requirements and correspondingly high fuel usage for pumping.
Often the extra cost of a larger pipe will be recovered quickly from lower fuel costs.
Both undersized and oversized pipe should be avoided.
Smooth pipe produces less friction loss and has lower operating costs than rough pipe.
Plastic pipe, such as PVC, is the smoothest, followed by aluminum, steel and concrete, in that order.
Table 6 lists typical friction losses in commonly used pipe.
The friction
 losses shown are for pipes of these internal diameters.
This table is presented for information purposes only.
Actual pipe diameters vary widely and more precise figures from manufacturers' specifications should be used for design purposes.
Polyvinyl chloride  or thermoplastic pipe is exactly manufactured by a continuous extruding process which produces a strong seamless pipe that is chemically resistant, lightweight, and that minimizes friction loss.
PVC pipe is produced in many sizes, grades and specifications.
Low pressure pipelines underground thermoplastic pipelines with 4to 24-inch nominal diameter used in systems subject to pressures of 79 psi or less.
High pressure pipelines underground thermoplastic pipelines of 1/2to 27-inch nominal diameter that are closed to the atmosphere and subject to internal pressures (including surge pressures, from 80 to 315 psi.
Class or PSI designation refers to a pressure rating in pounds per square inch.
Schedule refers to a plastic pipe with the same outside diameter and wall thickness as iron or steel pipe of the same nominal size.
SDR  is the ratio of the outside pipe diameter to the wall thickness.
Table 9 gives the pressure rating for pipes of various SDR.
IPS refers to plastic pipe that has the same outside diameter as iron pipe of the same nominal size.
PIP is an industry size designation for plastic irrigation pipe.
Tables 8 and 9 show the recommended maximum operting pressures of various classes and schedules of PVC pipe.
Actual operating pressure may be equal to these pressure ratings as long as surge pressures are included, but be sure to account for all surges.
To determine which pipe to use, simply combine the total head in the pipe with the surge pressures, and select the closest larger class.
However, surge pressures should not exceed 28 percent of the pipe's pressure class rating.
When surge pressures are not known, the actual operating or "working" pressure should not exceed the maximum allowable working pressures given in Table 11.
As discussed above, keeping the velocity at or below 5 ft/s will help minimize surge pressure.
However, the sudden opening and closing of valves will produce a surge pressure, which increases with higher velocities.
The maximum surge pressure that will be produced in a PVC pipe with the sudden opening or closing of a valve can be determined with Table 10.
For example, the surge pressure from a sudden valve closure with a water velocity of 7 ft/s in a SDR 26 PVC pipe is:
 7 14.4 = 100.8 psi
 This pressure then is added to the operating pressure to determine which class of PVC pipe to use.
Example Problem #1 Complete Analysis
 Determine the difference in horsepower requirements and annual fuel costs for 6-inch and 8-inch mainlines  for the following system:
 1.
type of power plant	diesel
 2.
cost of energy	$0.65 per gal.
3.
pumping lift	250 ft.
4.
pump column pipe	8-in.
steel pipe
 distance to pump in column pipe	350 ft.
5.
system flow rate	750 gpm
 6.
yearly operating time	2000 hrs.
7.
distance from pump to pivot	4000 ft.
8.
required operating pressure	45 psi
 9.
elevation change from pump to pivot	+37 ft.
10.
types of fittings in system	check valve, gate valve, two standard elbows
 Step One Calculate Total Dynamic Head 
 TDH =  +  +  + 
 1.
Pumping lift  = 250 ft.
2.
Elevation change (item = + 37 ft.
3.
Operating pressure  = 45 psi X  = 104 ft.
4.
Friction loss: Pump column pipe
 a.
friction loss in 8-in.
well casing  = 1.8 ft./100 ft.
b.
total friction loss = 1.8 x 3.5 = 6.3 ft.
5.
Friction loss in plastic mainline 
 a.
friction loss in pipe  = 3.4 ft./100 ft.
X 40 = 136 ft.
C.
total friction loss = 136 + 2.2 = 138.2 ft.
6.
Friction loss in plastic mainline 
 a.
friction loss in pipe  = 0.8 ft./100 ft.
X 40 = 32 ft.
C.
total friction loss = 32 + 0.6 = 32.6 ft.
7.
TDH  =  +  +  +  +  = 250 + 37 + 104 + 6.3 + 138.2 = 535.5 ft.
8.
TDH  =  +  +  +  +  = 250 + 37 + 104 + 6.3 + 32.6 = 429.9 ft.
Step Two Calculate Water Horsepower 
  whp =  X  = 101 whp 3,960
  whp =  X  = 82 whp 3,960
 Note: The output of the power plant must be larger than the water horsepower due to the pump's efficiency.
Usually a pump efficiency of 75 percent is used in design.
However, actual pump selection is based on pump performance curves available from manufacturers.
Do not buy a pump on the basis of its horsepower rating alone.
For more information see L-2218, "Pumping Plant Efficiency and Irrigation Costs," available from your county Extension agent.
Brake horsepower 
  bhp = 101/.75 = 135 bhp
  bhp = 81/.75 = 108 bhp
 Step Three Calculate Annual Fuel Use
 Note: The Nebraska Performance Standards  may be used to estimate annual fuel use.
From Table 4, each gallon of diesel fuel will provide 12.5 water horsepower-hours.
fuel use = whp X 1 X    fuel use = 101 whp X gal.
X 2,000 hrs.
= 16,160 gals.
12.5 whp hrs.
yr.
yr.
fuel use = 81 whp X gal.
X 2,000 hrs.
= 12,960 gals.
12.5 whp hrs.
yr.
yr.
Step Four Calculate Annual Fuel Costs
  16,160 gals.
X $0.65 = $ 10,504 per year for diesel fuel yr.
gal.
12,960 gals.
X $0.65 = $ 8,424 per year for diesel fuel yr.
gal.
DIFFERENCE = $10,504 $8,424 = $2,080
 Step Five Calculate Total Water Pumped per Year
 Note: The conversion rate used is 325,851 gal.
= 1 ac.-ft.
750 gals.
X 60 mins.
X 2,000 hrs.
= 90 million gals.
= 276 acre-feet of water min.
hr.
yr.
Example Problem 2: Simplified Analysis
 In the above example, we found that the friction losses in the pump column pipe and through the fittings are minor.
The only other difference between Case 1 and Case 2 was the friction loss in the pipeline.
Thus, the difference in horsepower requirements and annual fuel costs between the 6-inch and 8-inch pipelines in the above example can be approximated by considering only the friction loss in the pipe.
Step One Calculate Pipeline Friction Loss Difference
   = 136 32 ft.
= 104 ft.
Step 2 Calculate Increase in Horsepower and Annual Fuel Use
 whp = 750 x 104 = 19.7 whp 3,960
 fuel use = 19.7 whp X gal.
X 2,000 hrs.
= 3,151 gals.
12.5 whp hrs.
yr.
yr.
Note: This means that 3,151 more gallons of diesel would be required if a 6-inch mainline was used instead of an 8-inch mainline.
Drawn By Ed Wilson
 Table 1.
Pumping costs in the Texas High Plains  and in South/Central Texas  per acre-inch of water at 100 feet total head from irrigation pumping plant efficiency tests conducted by the Texas Agricultural Extension Service.
Type and price	Region2	Cost  per ac.-in.
per 100 ft.
head
 Natural Gas	THP	0.40	3.93	0.81
 @ $3.00 MCF	SCT	0.31	1.96	0.76
 Electricity	THP	0.49	3.10	1.35
 Diesel	THP	0.57	1.91	0.77
 1 Assumed price-actual prices varied in each region.
2THP  results are from more than 240 efficiency tests.
SCT  results are from 240 efficiency tests.
Table 2.
Irrigation pumping equipment efficiency.
Pumps 	75-82
 Right-angle pump drives 	95
 Table 4.
Nebraska performance criteria for pumping
 plants.
Fuel use by new or reconditioned plants
 should equal or exceed these rates.
Energy source	per unit of energy	units
 Natural gas	66.73	1,000 ft.
1Based on 75 percent efficiency.
2Includes drive losses and assumes no cooling fan.
natural gas content of 1,000 btu per cubic foot.
Table 3.
Typical values of overall efficiency for represen-
 tative pumping plants, expressed as percent.*
 Power source	as acceptable	field tests
 Natural gas	18-24	9-13
 Butane, propane	18-24	9-13
 * Ranges are given because of the variation in efficiencies of
 both pumps and power units.
The difference in efficiency for
 high and low compression engines used for natural gas,
 propane and gasoline must be considered especially.
The
 higher value of efficiency can be used for higher compression
 t	Typical average observed values reported by pump efficiency
 Table 5.
Approximate maximum flow rate in different
 pipe sizes to keep velocity 5 feet per second.
Pipe diameter	Flow rate 
 Table 6.
Friction losses in feet of head per 100 feet of pipe.
4-inch	6-inch	8-inch	10-inch	12-inch
 Pipe size	Steel Alum.
PVC	Steel Alum.
PVC	Steel Alum.
PVC	Steel Alum.
PVC	Steel Alum.
PVC
 100	1.2	0.9	0.6	---	---	---	---
 150	2.5	1.8	1.2	0.3	0.2	0.2
 200	4.3	3.0	2.1	0.6	0.4	0.3	0.1	0.1	0.1
 250	6.7	4.8	3.2	0.9	0.6	0.4	0.2	0.1	0.1	0.1	0.1
 300	9.5	6.2	4.3	1.3	0.8	0.6	0.3	0.2	0.1	0.1	0.1
 400	16.0	10.6	7.2	2.2	1.5	1.0	0.5	0.3	0.2	0.2	0.1	0.1	0.1
 500	24.1	17.1	11.4	3.4	2.4	1.6	0.8	0.6	0.4	0.3	0.2	0.1	0.1	0.1	0.1
 750	51.1	36.3	24.1	7.1	5.0	3.4	1.8	1.3	0.8	0.6	0.4	0.3	0.2	0.1	0.1
 1000	87.0	61.8	41.1	12.1	8.6	5.7	3.0	2.1	1.4	1.0	0.7	0.5	0.4	0.3	0.2
 1250	131.4	93.3	62.1	18.3	13.0	8.6	4.5	3.2	2.1	1.5	1.1	0.7	0.6	0.4	0.3
 1500	184.1	130.7	87.0	25.6	18.2	12.1	6.3	4.5	3.0	2.1	1.5	1.0	0.9	0.6	0.4
 1750	244.9	173.9	115.7	34.1	24.2	16.1	8.4	6.0	4.0	2.8	2.0	1.3	1.2	0.9	0.6
 2000	313.4	222.5	148.1	43.6	31.0	20.6	10.8	7.7	5.1	3.6	2.6	1.7	1.5	1.1	0.7
 NOTE: Flow rates below horizontal line for each pipe size exceed the recommended 5-feet-per-second velocity.
Table 7.
Friction loss in fittings.
Friction loss in terms of equivalent length of pipe  of same diameter.
Inside pipe diameter 
 Type of fitting	4	5	6	8	10	12
 45-degree elbow	5	6	7	10	12.5	15
 Long-sweep elbow	7	9	11	14	17	20
 Standard elbow	11	13	16	20	25	32
 Close return bend	24	30	36	50	61	72
 Gate value 	2	3	3.5	4.5	5.5	7
 Gate value 	65	81	100	130	160	195
 Check valve	100	110	30	40	45	35
 Table 8.
Pressure rating for class and SDR non-threaded PVC pipe.*
 Pipe designation	Maximum working pressure
 *For pipes of standard code designation: PVC 1120, PVC 1220,
 Table 10.
Maximum surge pressures associated with
 sudden changes in velocity in psi per ft./s.
water velocity (for 400,000 psi modulus of
 SDR	Maximum surge pressure 
 per each ft./s.
of water velocity
 Example: The surge pressure from a sudden valve closure with
 a water velocity of 7 ft./s.
in a SDR 26 PVC pipe is 7 X 14.4 =
 Table 9.
Pressure rating for schedule 40 and schedule 80 PVC pipe.*
 Diameter 	Maximum operating pressure 
 Schedule 40	Schedule 80
 *For Type I, Grade I at 73.4 degrees F.
Table 11.
Maximum allowable working pressure for
 non-threaded PVC pipe when surge pressures
 are not known and for water temperatures of
 SDR	Maximum working pressure 
While there has been a lot of work linking farm management practices with soil health or water quality, few have looked at the connection to both soil and water quality, notes Cates.
Generally, management systems that lead to better soil health result in decreased risk to water quality, but that is not the case in all conditions or for all management systems.
What works in one field for both soil health and water quality might not be the best option for another field.
This whitepaper explores those intricacies so educators can better recognize and communicate when the relationship isnt positively correlated.
Center pivots have been adapted to operate on many different soils, to traverse extremely variable terrain, and to provide water to meet a number of different management objectives.
Consumers have access to an array of different sprinkler types.
For some fields, many packages will perform adequately.
Other fields will have a limited number of to choose from.
Sprinkler package selection should be based upon accurate field based information, and careful consideration how the package will interact with cultural practices and system management.
The system flow rate determines how a number of factors impact system operation.
For example, if the flow rate is greater than necessary, the peak water application rate may cause runoff toward the outer end of the pivot lateral but the system can recover from unplanned system downtime.
If the flow rate is too low, runoff may be eliminated, but unexpected breakdowns can result in significant yield losses.
There are three important considerations when estimating flow rate requirements: a) environmental factors; b) system downtime; and d) the soil water holding capacity.
The most important environmental considerations are the likelihood of rainfall and the peak crop water use rate.
NebGuide G89-932 Minimum Center Pivot Design Capacities in Nebraska presents a procedure for the determining the minimum net system capacity for Nebraska conditions.
A similar procedure can be used for Colorado and Kansas.
Estimated crop water use rates, soil water holding capacity and rainfall data were evaluated for different locations in Nebraska.
The analysis identified areas where the system flow rate should be increased to account for lower annual precipitation and greater peak ET rates.
Our best estimate is that systems
 located west of the 20-inch annual precipitation line should have greater flow rates.
Table 1 presents the estimated minimum net system capacity required to meet crop demands 90% of the time for regions in Nebraska.
The last line in the table provides the system capacity necessary to meet peak water demands 100% of the time.
That calculation is based on Equation 1:
 Qp = irrigation system flow rate, gpm 18.9 = units conversion constant ETp = peak water use rate, in/day A = irrigated area, acres ti = irrigation interval, days Ej = irrigation efficiency, decimal tf = irrigation time per event, days
 Table 1.
Minimum net system capacities to meet crop water demands 90% of the time for the major soil texture classifications and regions in Nebraska .
AWC	Region 1	Region 2
 Soil Texture	In/ft	gpm/ac	gpm/ac
 Loam, silt loam or very fine sandy loam	2.5	3.85	4.62
 Sandy clay loam, loam	2.0	4.13	4.89
 Silty clay loam, fine sandy loam	2.0	4.24	5.07
 Silty clay	1.6	4.36	5.13
 Clay, sandy loam	1.4	4.48	5.19
 Loamy sand	1.1	4.83	5.42
 Fine sand	1.0	4.95	5.89
 Peak ET	5.65	6.60
 Data taken from NebGuide G89-932 Minimum Center Pivot Design Capacities in Nebraska.
The values in Table 1 need to be adjusted for system downtime and the water application efficiency of the center pivot.
Downtime can result from regularly scheduled maintenance, load control, system failure, or labor restrictions.
The downtime experienced due to system failure depends on the current age of the components and how frequently the system is checked.
Operators with a shutdown phone alarm will have immediate knowledge when the system shuts down while others may not be aware that the system is down for 8 hours or more.
If the system is operated 24/7, each 12 hours of down time requires a flow rate increase of 6%.
Once the net capacity has been adjusted for down time, the gross flow rate required is determined by dividing by the estimated water application efficiency.
The system water application efficiency depends on the sprinkler package.
Some potential water application efficiencies are provided in Table 2.
They are listed as potential efficiencies because they assume that runoff does not occur.
Thus, the field conditions will determine the actual water application efficiency.
Table 2.
Potential water application efficiencies for different sprinkler packages.
Sprinkler/ Nozzle Type	Potential Application Efficiency
 High Pressure Impact	80-85
 Low Pressure Impact	82-85
 Low Pressure Spray up top	85-88
 Low Pressure Spray at truss	87-92
 Low Pressure Spray at 3-7 feet	90-95
 Low Pressure Spray Bubble mode	95-98
 The Soil Survey provides one source of estimates for average water infiltration rates, field slopes and soil water holding capacities.
Request that the NRCS provide the soil intake family, and record the average field slope, infiltration rate and the soil water holding capacity information on each mapping unit from the local soil survey book.
Record them in a table similar to Table 3.
Some sprinkler packages are selected and installed without a site visit by the sprinkler system provider.
Though soil mapping units give some indication of average field conditions, the data may not be sufficiently accurate to make a decision.
Therefore, a rough grid topography map  will determine if areas mapped as 7 to 11% slopes are closer to 7% or 11%.
Finally, the site visit can provide valuable information related to tillage and planting practices.
A field farmed on the contour can safely use a sprinkler package that would be unsuitable if farmed up-and-down hill.
Crop residues left on the soil surface can absorb the impact energy of rainfall and irrigation.
Thus, the soil infiltration rate would be more consistent throughout the season.
Each of these factors may cause you to make a slightly different decision.
Sprinkler packages should be selected that do not result in runoff.
Too often the desire to reduce pumping costs clouds over selecting the most appropriate sprinkler package.
The zero runoff goal requires that the sprinkler package be carefully matched to field conditions and to the operator's management scheme.
This requires that the water application pattern of the sprinkler be compared to the soil infiltration rate.
Table 3.
Summary of soil characteristics for each mapping unit in a quarter section of land in Pierce County, NE.
1
 Mapping	Drainage	Soil Water	Field Slope	Intake	Land Area
 Unit	Group	Capacity		Family	
 Co	Moderately Slow	2.4	0-1	0.3	42.1
 He	Well	2.4	0-1	1.0	23.9
 CsC2	Well	2.4	1-7	1.0	11.0
 HhC	Well	2.4	1-7	1.0	36.8
 MoC	Well	2.3	1-7	0.5	5.3
 CsD2	Well	2.4	7-11	1.0	28.0
 NoD	Well	2.4	7-11	1.0	1.8
 CsE2	Well	2.4	11-17	1.0	11.1
 Data taken from Pierce County Soil Survey
 The CPNOZZLE computer program was converted to Visual Basic to provide an opportunity to estimate of how well suited the sprinkler is to field soils and slopes.
The program is useful in predicting how much the design criteria should be changed to eliminate a potential runoff problem.
For example, if a sprinkler package with a 40-foot wetted diameter produces runoff, the program can be used to determine a wetted diameter that produces no runoff.
If you are in the process of retrofitting an old system with a new sprinkler package, the program can be used to select an appropriate system flow rate and sprinkler wetted radius.
Based upon research conducted at the University of Nebraska, the program develops an elliptical shaped water application pattern depending upon the position on the system, wetted diameter of the package, and the system flow rate.
The program uses the NRCS Intake Family to estimate the weighted potential runoff for various positions along the system.
Data inputs include: 1) system length in feet; 2) system capacity in gpm; 3) application amount in inches; 4) wetted diameter of the sprinkler in feet; 5) soil intake family; 6) field slope in %; and 7) percent residue cover in %.
The data inputs can be saved to a file or they will be printed with the output information.
When all inputs are entered, the program output can be viewed by clicking on results.
Figure 1.
Sample input table for the CPNOZZLE program.
File View Options Help
 Figure 2.
Sample output table and graph from the CPNOZZLE program.
Program output includes a table presenting potential runoff for 10 positions along the system and the weighted potential runoff for the entire field.
Output generated for a system with inputs of 1320 foot system, 800 gpm, 1.0 inch
 application, 60 foot wetted diameter, 0.3 intake family, 10% slope, and 40% residue cover are presented in Table 4.
In addition to the inputs listed above, the program also prints results for the same system with a flow rate of 100 gpm more and 100 gpm less than 800 gpm.
Results indicate that approximately 18 % of the water applied could move from the point of application or run off the field.
By clicking on the intake family button below the output table, the user can view output from one intake family higher and one lower than the original inputs.
The purpose of the additional output is to allow comparisons between different soil intake families and flow rates because few fields have soils that fit into a single intake family.
Any of the input information can be changed to perform a 'what if' style of analysis.
Additional output can include a graphical presentation of the comparison between the water application pattern and the soil infiltration rate curves.
By clicking on any of the potential runoff estimates in the table, a graph will appear on the right side of the screen.
For example, if the user moves the computer mouse and clicks on the number 25.0 under the 800 gpm column, a graph will appear specifically for the position on the system.
In the best-case scenario, the two curves do not intersect.
Table 4.
Output table from the CPNOZZLE program for a site in Platte Co., NE
 length	diameter	storage	700 gpm	800 gpm	900 gpm
 132	60	0.07	0.0	0.0	0.0
 264	60	0.07	0.0	0.0	0.0
 396	60	0.07	0.0	0.0	0.0
 528	60	0.07	0.0	3.1	6.9
 660	60	0.07	6.0	10.3	14.1
 792	60	0.07	11.8	16.1	19.8
 924	60	0.07	16.8	20.9	24.5
 1056	60	0.07	20.9	25.0	28.4
 1186	60	0.07	24.5	28.4	31.7
 1320	60	0.07	27.6	31.4	34.6
 Weighted Average Percent	14.7	18.1	21.1
 Hours per revolution	81.2	71.1	63.2
 Peak Water Application Rate	2.2	2.5	2.8
 Water Application Time	0.58	0.52	0.46
 Agency and irrigation distribution companies may wish to develop a series of graphs to represent conditions in their area.
For example, Figure 3 presents weighted potential runoff comparisons for a range of NRCS intake families when the water application depth increases from 0.5 inches to 2.0 inches per revolution for a 1320 foot center pivot.
Inputs of flow rate, sprinkler wetted diameter, field slope, and residue cover were consistent and are presented under the table heading.
Note that as application depth increases the potential for runoff increases.
However, fields with greater than 5% slope, the application depth cannot be reduced to eliminate runoff without surface storage for soils in the 0.1 to 1.0 NRCS intake family.
Should runoff be predicted, one option is to reduce the system flow rate.
Figure 4 presents results for reducing the system flow rate from 800 gpm to 600 gpm.
Increasing the wetted diameter of the sprinkler from 40 to 60 feet also helps reduce the potential for runoff.
However, though not shown in graphical format, when slopes are above 5% and no crop residues are present, the potential for runoff from low infiltration rate soils is great for the 0.1 to 0.5 Intake Family soils.
Impact sprinklers are a better option for fields with steep slopes and low infiltration rate soils.
Estim ated Potential Runoff 800 g p m , 40 foot diam eter, 10% slope, 0% residue
 Figure 3.
Effect of soil intake family and water application depth on weighted potential runoff for a 1320 foot center pivot with a sprinkler package wetted diameter of 40 feet and a flow rate of 800 gpm.
Center pivot buyers have a vast array of sprinkler packages to choose from.
Selecting the most appropriate sprinkler package for an individual field should be based upon collection of accurate field based information for soils, slopes, and cropping practices.
The final selection should not be based on energy costs alone.
Rather the system should first apply water uniformly without generating runoff.
The new Visual Basic version of the CPNOZZLE computer program provides an opportunity to perform 'what if?' sort of analyses prior to making a sprinkler package purchase.
600 gp m , 40 foot diameter, 10% slope, 0% residue cover
 Figure 4.
Effect of soil intake family and water application depth on weighted potential runoff for a 1320 foot center pivot with a sprinkler package wetted diameter of 40 feet and a flow rate of 600 gpm.
Kranz, Bill, Lackas, Greg, and Derrel Martin.
1989.
Minimum center pivot design capacities in Nebraska.
NebGuide G89-932-A.
UNL Cooperative Extension.
important to know whether initial wetting is sufficient, or if a long-term residual effect is needed.
In general, if initial wetting is required to prevent erosion and increase infiltration, the most efficient nonionic would be one of the ether group.
If long-term efficiency is required, the ester group would be better.
There are
 many requirements between these limits and the selection of the wetting agent will depend on which is the most important.
GRAPH 2.
WETTING EFFICIENCY OF VARIOUS WETTING AGENTS.
HOLLOW BAR REPRESENTS THE EFFICIENCY FOR FIRST TEST PERIOD.
SOLID BAR REPRESENTS THE EFFICIENCY AT THE END OF THE THREE YEAR PERIOD.
GRAPH.
3.
WETTING EFFICIENCY OF VARIOUS WETTING AGENTS.
HOLLOW BAR REPRESENTS THE EFFICIENCY FOR FIRST TEST PERIOD.
SOLID BAR REPRESENTS THE EFFICIENCY AT THE END OF THE THREE YEAR PERIOD.
K.
URIU P.
E.
MARTIN R.
M.
HAGAN
 Trunk growth studies of almonds at Davis have given new information about the need for spring irrigation.
A lever-type dendrometer developed at the University of Idaho was used to follow trunk growth patterns for four consecutive years under widely varying conditions of soil, water, and crop density.
The study has shown that the need for early irrigation increases when there is a heavy crop.
In the spring, trunk growth rates were increased by irrigation even when as much as 40 per cent available water still remained in the top 4 ft of soil.
After mid-season, trunk growth rates were not increased by irrigation unless the soil water content had dropped to the plant wilting percentage before irrigation.
These studies also showed that trunk growth rates were reduced as the crop density increased.
T HIS IRRIGATION study began in the spring of 1963 and was conducted for four seasons in a 20-year-old almond orchard at University of California, at Davis.
Lever-type dendrometers were installed, one instrument per tree, in four differentially irrigated rows.
End trees were not instrumented, leaving eight instrumented trees per row.
Two guard rows separated the irrigation treatments.
Dendrometers always show maximum trunk expansion attained since the last
 IRRIGATION, CROP DENSITY ON ALMOND TRUNK GROWTH
 reading.
As the trunk expands , the lever of the dendrometer is pushed outward.
When expansion stops, the lever remains stationary and does not retract with trunk shrinkage.
Readings were taken every two days.
The data from trees in each treatment row were averaged.
There were four irrigation treatments:  trees irrigated every two weeks during the growing season  ;  trees irrigated when the water content average of the top 3 feet of soil was still about 3 per cent above the wilting point 
 GRAPH 2.
AVERAGE SOIL WATER CONTENT , 1964.
GRAPH 1.
CUMULATIVE RADIAL TRUNK GROWTH  AND CROP DENSITY  FOR 1964.
TREATMENT A HAD NINE IRRIGATIONS DURING THE SEASON; TREATMENTS B, FOUR; C, TWO; AND D, NONE.
SYMBOLS ON CURVES INDICATE IRRIGATION DATES.
GRAPH 3.
CUMULATIVE RADIAL TRUNK GROWTH  AND CROP DENSITY  FOR 1965.
TREATMENT A HAD NINE IRRIGATIONS DURING THE SEASON; TREATMENTS B, FOUR; C, TWO; AND D, NONE.
SYMBOLS ON CURVES INDICATE IRRIGATION DATES.
-four irrigations;  trees irrigated when the average water content in the top 3 feet of soil reached WPand  trees that were not irrigated.
Irrigation water was applied in rectangles enclosing two trees each.
Water was applied to a depth calculated to return the soil moisture to field capacity throughout the root zone.
Samples for gravimetric determination of soil water were obtained in foot increments down to 6 ft before each irrigation, and once a month in the unirrigated plot.
Soil water percentages from the top 4 ft were averaged and plotted.
Yields per tree, and nut sizes, were determined at harvest, and an estimate of the total number of nuts per tree was calculated.
Trunk circumference was measured at the end of each year, trunk cross-sectional area calculated, and a crop density figure obtained.
The tendency of almonds to bear in alternate years was quite evident during the four years of this study; 1963 was a moderately light crop year, 1964 heavy, 1965 very light, and 1966 again heavy.
Also, preseason winter rainfall was above normal prior to the 1963 and 1965 seasons and below normal for 1964 and 1966.
Thus, rainfall and crop conditions and subsequent trunk growth results were very similar in alternate years.
Trunk growth curves for 1964 are therefore used to illustrate both the 1964 and 1966 results, and 1965 curves to illustrate 1963 and 1965 results.
In the winter and spring of 1963-64 there was about 11 inches of rainfall.
This resulted in a relatively low reserve of soil water in the spring.
In the dry plot  the soil was wet to a depth of only 4 ft, and the soil below was at the wilting point.
The crop load was heavy, ranging from 11 to 15 nuts per cm2 of trunk cross-sectional area.
The average crop for this orchard is about six to 10 nuts per cm.
The total cumulative radial trunk growth at the end of the season  was greatest in treatment A.
Treatment B had slightly less growth even though the crop load was slightly less than in A.
Treatment C, with a higher crop density, had considerably less
 GRAPH 4.
AVERAGE SOIL WATER CONTENT , 1965.
growth than in A or B.
Treatment D, with the highest crop density, had the least growth.
In the beginning of the season, treatments A and B, with practically the same crop density, were growing at about the same rate until A was irrigated in late April.
Then the growth rate of A exceeded that of B even though the soil water was well above the wilting point in both treatments.
Around mid-May, the growth rate was considerably higher in B than in C although the soil water level at this time was the same in both treatments.
Neither had been irrigated yet.
The crop density, however, was considerably higher in the C plot.
Since the soil water conditions were the same in both, it can be assumed that the growth rate was lower in C than in B because of the heavier crop.
Likewise, the growth rate was the lowest in treatment D which had the highest crop density.
In June, growth was suddenly reduced in both treatments C and D when the soil water content neared the wilting point.
Growth resumed in the C plot when an irrigation was applied in late June, but it did not resume in the unirrigated D treatment.
The first irrigation of the season in treatment A was followed by a growth response, although at the time of irrigation 30 to 40 per cent available water still remained within the top 4 ft of soil.
Irrigations later in the season did not further increase the rate of growth.
Also, the rate of growth in A, from late June on, was no greater than in B even though A was given twice as many irrigations as B.
In C, the last irrigation 
 did not bring about an increase in growth rate although soil water content was close to the wilting point.
Unlike in 1964, the preseason rainfall in 1965 was approximately 19 inches.
Average rainfall for the area is about 16 inches.
Therefore, soil water was abundant down to 6 ft in all plots prior to spring growth.
The crop was extremely light-only two to four nuts per cm2 of trunk area.
With a very light crop and adequate soil water, trunk growth did not differ much between treatments until late in the season.
As treatments D and C approached WP in mid-July and late August, respectively (graph trunk growth rates were markedly reduced.
Treatments A and B, in contrast, had sufficient irrigations so that growth was not restricted by soil water deficits.
Total growth in B was greater than in A although B had fewer irrigations.
However, crop density was higher in A, indicating that the heavier crop suppressed trunk growth.
Even in the waterdeficient plots , the plot with the lower crop density  had the greater total trunk growth.
Also in the early part of the season, when all plots had abundant soil water, trunk growth rate correlated inversely with crop density: growth rates decreased in order from treatments D to A, while the crop loads increased.
After irrigations were started, however, this order was not maintained.
Thus, treatment A, whose early growth was the slowest , by mid-June  was growing as fast as the un-
 irrigated treatment D, which had initially been growing twice as rapidly.
Later, as the soil water content in D decreased and approached the wilting point, growth in D slowed while A maintained its rate.
A temporary increase in growth rate of D in late July was associated with a period of unseasonably cool weather which diminished the effect of the soil water deficit on the water balance in the tree.
However, with the return of higher temperatures the growth rate in D was again markedly reduced.
In each of the four years of the study, both the soil water supply and crop load, whether in a high crop or a low crop year, influenced rate of trunk growth and total seasonal growth.
Trunk growth was primarily influenced by soil water and secondarily by crop load.
This was apparent in the low-rainfall years of 1964 and 1966, during which and D reached the wilting point in midseason.
Trunk growth was stopped and resumed only after irrigation of treatment C in late June.
Even then growth in C never equaled the rate in plots A and B which were irrigated much earlier in the season.
This indicates that irrigations applied late in mid-season have much less effect on current rates of trunk growth than those applied early in the irrigation season.
In all four years, early irrigations  increased trunk growth rate in treatments A and B, even though the average soil water content through the top 4 ft of soil was well above the wilting point  at time of irrigation.
Later irrigations in plots A and B, whether at intervals of two or four weeks, did not increase growth rate further, but merely maintained the rate established earlier.
This study indicates that high crop density in almonds increases the need for irrigation, especially early in the season.
During years of low crop density, trunk growth rates may be maintained with a schedule of less frequent irrigations.
K.
Uriu is Associate Pomologist, Department of Pomology; P.
E.
Martin is Laboratory Technician IV; and Robert M.
Hagan is Irrigationist, Department of Water Science and Engineering, University of California, Davis.
HONEY BEE POLLINATION OF ALFALFA SEED
 improved by supplemental feeding
 BOB SHEESLEY BERNARD PODUSKA
 Results of these Fresno County experiments indicate possible advantages to both alfalfa seed growers and beekeepers from the use of supplemental feeding, and requeening of bee colonies used in alfalfa pollination.
ALFALFA SEED GROWERS in Fresno County produced 22 per cent of the United States' alfalfa seed on 10 per cent of its seed acreage in 1967.
Pollination of this crop in Fresno County requires 150,000 honey bee colonies during the three-month period of June, July, and August.
Seed growers are continually looking for practical management procedures to improve seed yields.
Pollination during the 10-to-12-week alfalfa seed setting period depends upon a continuing supply of new bees to replace worn out or dead field workers.
Colonies entering seed alfalfa for pollination need actively laying queens with brood of all stages and enough workers to serve the colony and to pollinate the alfalfa flowers.
Recent tests have demonstrated that a January feeding of natural pollen mixed with drivert sugar mixed with 1 per cent natural pollen stimulated egg laying.
This food supplement was fed before natural pollen was available, and resulted in larger bee populations in time for almond pollination.
Another experiment was conducted recently in Fresno County to explore
 answers to the following questions:  can pollination of alfalfa blossoms be increased by feeding honey bees prior to bloom or during bloom?; and  what happens to the strength of brood, and pollen collecting abilities of honey bee colonies while in seed alfalfa?
Results reported here are from this single experiment conducted under one set of conditions.
The consistency of results does suggest they are valid for this set of conditions.
However, there are many variables in field experiments of this type.
For this reason it is unlikely that the same results will be obtained with extremely different bee populations, or different environmental and pesticide situations.
Sixty colonies of bees were divided into four test treatment groups of 15 colonies each.
Each test group included five strong colonies, five of medium strength, and five weaker colonies.
These original strength ratings were based on actual brood area measurements on May 28, two weeks before they were moved to the alfalfa seed field.
Natural pollen had been available to all colonies since January 13.
The colonies were further assigned to five equal replications to determine any pollen collection differences due to the effect of physical locations in the alfalfa seed field.
The four treatment groups in the experiment were:  the control group of bees, receiving no food;  those receiving 11/2 lbs.
of drivert sugar with 1 per cent pollen fed dry on May 29, two weeks before they entered the alfalfa seed field;  those receiving the same
If you suspect a problem with the equipment, fix it right away by calling your dealer if you are not qualified to do the work yourself.
Slugged fuses will kill people.
A slight electrical tingle today may indicate a problem that may be fatal under different conditions tomorrow.
The conclusion is that many irrigators could save money, water and nitrogen by using data from irrigation scheduling systems to make data-driven decisions to help them feel confident they are getting optimal yields without putting on extra water just for insurance purposes.
Otherwise, irrigators follow their natural tendencies to put on about the same amount of water as in the past and just slightly adjust it for dry or wet years.
For more information on yield losses, take time to read the following NebGuide: Plant Growth and Yield as Affected by Wet Soil Conditions Due to Flooding or Over-Irrigation.
Public Drinking Water Quality and Regulatory Guidelines That Impact Human Health
 Edmund Buckner, Ph.D.
Interim Dean/Director, School of Agriculture, Fisheries and Human Sciences, University of Arkansas at Pine Bluff
 Michael Daniels, Ph.D.
Professor, University of Arkansas Cooperative Extension Service
 William Torrence, Ph.D.
Associate Professor, University of Arkansas at Pine Bluff
 During the early twentieth century, scientists discovered that by providing safe drinking water infectious diseases could be avoided.
Worldwide, nearly 2 million people die each year from diarrheal waterborne diseases.
Of those 2 million deaths, 88 percent can be attributed to drinking unsafe water, inadequate sanitation and poor hygiene.
About 1.1 billion people worldwide do not have access to an adequate supply of drinking water, and some 2.4 billion have no access to basic sanitation.
Approximately, 80 percent of all infectious diseases in the world are transmitted through drinking water that has been contaminated either at its source or during transportation and storage.
On a global scale, 1.8 million people die every year from diarrheal diseases, and of those deaths 90 percent are children under five.
Federal regulations were enacted to improve drinking water quality to address these concerns in the U.S.
Prevention of diseases in drinking water has included removal
 of harmful pollutants.
The Safe Drinking Water Act  passed by Congress in 1974 required the U.S.
Environmental Protection Agency  to establish health-based goals to safeguard the nation's public drinking water supplies against both man-made and natural pollutants.
Drinking Water Regulatory Issues and Safety Guidelines
 National drinking water standards apply to public water systems that receive their drinking water supply from treatment plants.
However, there are no federal laws that require those who receive drinking water from a public water system to assess their water quality on a regular basis.
Failure to monitor the quality of drinking water at destination sites may result in unsafe drinking water, especially in older buildings that have older plumbing and/or fixtures.
The EPA National Primary Drinking Water Regulations provide federal guidelines for enforceable drinking water standards of the
 acceptable levels of various contaminants in drinking water.
The Arkansas Department of Health enforces these regulatory guidelines in the state of Arkansas.
The EPA National Secondary Drinking Water Regulations provide additional drinking water guidelines that are non-enforceable for contaminants that may cause minor effects to humans.
TABLE 1.
EPA National Primary Drinking Water Regulatory Standards for acceptable maximum contaminant levels  of arsenic, copper, lead, E.
coli and total coliform in drinking water are shown in this table.
Target EPA MCL goal levels are also shown.
These MCL goal levels represent EPA public health goals of levels for the potential contaminants shown.
National Primary Drinking Water Regulatory Standards
 Milligrams Per Liter mg/L
 Contaminant	MCL	Public Health
 E.
coli	0	0
 Total	5.0% positive samples	0
 Coliform	limit for water systems
 that collect 40+ samples
 -one positive sample limit
 for water systems that
 collect less than 40
 Source: Environmental Protection Agency 
 TABLE 2.
Environmental Protection Agency  National Secondary Drinking Water Regulatory Standards for acceptable maximum contaminant levels  of copper and iron in drinking water are shown in this table.
These standards are not enforced by EPA, and EPA does not require states to comply.
National Secondary Drinking Water Regulatory Standards
 Milligrams Per Liter mg/L
 Source: Environmental Protection Agency 
T his tale is based on real events.
I've just changed the names, details of the water right, the specific facts of the dispute, and the location to avoid undue embarrassment to anyone.
In 2002, Michael Hartman looked at a ranch for sale on a major tributary in the upper Missouri river basin.
It was IIOO acres with frontage on a trout stream, and it had an active sprinkler-irrigated hay operation on 160 acres.
When Hartmann was negotiating the deal, the realtor produced a water rights document entitled "Statement of Existing Water Right Claim".
It included a water right number, identified a flow rate of IO cubic feet per second , and 320 irrigated acres, complete with a legal description of the acres irrigated.
It seemed like a great deal-nice property right on a famous trout stream, and a whole lot of water rights to work with.
What's not to like?
So he bought it.
After moving on to the land, Hartman looked at the acres claimed for irrigation in the Statement of Claim, located the 16o acres that weren't currently being irrigated, and embarked on plans to start irrigating them.
When he walked the land, he didn't notice any sign of ditches or headgates on the quarter section he wanted to irrigate, but he figured, "Hey, it's listed on the water right, SO I have the water for it." He approached the Natural Resources Conservation Service  about cost sharing a new center pivot on the land and putting a pump into the ditch serving the other 160 acres, and they seemed interested.
Well, his little valley was a small town and word got out about what he had planned.
Some downstream irrigators, who were having particular difficulty getting their water that year, contacted a lawyer.
The lawyer wrote to Hartman, telling him that the property he wanted to irrigate had no history of irrigation, and that if he didn't cease-and-desist , his clients would take Hartman to court.
Hartman was stunned.
"But, my water right says I can irrigate this land," he thought.
So he called his lawyer, who specialized in real estate law, but had taken a course in water law at the University of Montana 20 years before.
The lawyer, after perusing Hartman's Statement of Claim, assured his client it was okay to irrigate that property.
To shorten this up a bit, Hartman started to install his pivots and the downstream irrigators sued to stop him from using the pivot because he did not have a water right for the acreage he wanted to irrigate.
Several thousands of dollars later, the court ordered Hartman to cease and desist because Hartman could produce no evidence that the land had been irrigated and, notwithstanding the language in the Statement of Claim, he did not have a water right to irrigate those acres.
The moral of this tale?
First, don't necessarily believe everything you read on that Statement of Claim-due diligence in searching water rights in Montana requires more than simply looking at your paper "water right" as Hartman did.
And, by the way, don't hire just any old lawyer to advise you on water law-hire one that specializes in water law.
W elcome to Montana water law.
To the casual observer, water law appears arcane, internally contradictory, illogical, and generally inaccessible to anyone not fully immersed in it.
At one time or another it can indeed be all those things.
Happily, however, you don't have to be a water-law expert to avoid Hartman's fate.
The purpose of this guide is simple-to help you, the prospective buyer of Montana land, determine if any real water rights go with the land you want to buy.
One thing this guide won't do is make you an expert.
But it should help you ask some of the right questions when you're looking at a piece of land with water rights.
Montana Water Law in a Nutshell
 Performing Due Diligence on the Existence of a Water Right
 Township, Range, and Quarter Quarter Quarter Section: A Quick And Dirty Guide to Reading Legal Descriptions
 Streamflow Restoration Options for Landowners
 Profile of a Water Lease: A Little Bit of Water Can Go a Long Way
 Flood VS.
Sprinkler: Which Consumes More Water?
The Statewide Adjudication: What Is It, and What Does It Have To Do With My Water Rights?
Resource Guide for Researching Water Rights
 The Language of Water Law A Glossary of Key Terms
 The conventional wisdom is to put the glossary at the back of a report.
Because so much of the philosophical underpinning of western water law is expressed in its jargon, it makes sense to provide terminology at the front end of the discussion.
Read through these definitions now, and even though it won't all immediately fall into place, you'll find the rest of this guide easier going.
At the very least, you'll have a few water law terms that you can throw around to impress your friends.
ABANDONMENT.
Abandonment is the intentional, prolonged, non-use of a water right, resulting in the loss of the right.
See more under "Montana Water Law in a Nutshell" below.
ABSTRACT.
This is a term that you may hear used.
It is another way to describe the "Statement of Existing Water Right Claim." So if you hear the term used elsewhere, that is what it refers to.
continued on page 4
 First in Time, First in Right
 L ike most of the western United States, Montana operates under what is known as the doctrine of "prior appropriation." Simply stated, this doctrine says that those who first put water to beneficial use get to continue using it first when water is scarce.
This "first in time, first in right" priority system ensures that water users whose forebears first put water to use-so-called "senior users"-can rightfully demand that their needs from a stream be fulfilled before the interests of junior users.
Some senior water rights in Montana go back to the late 1860s.
In years when water is too scarce to satisfy all water rights, senior users get water and junior users often don't.
So the first take-home lesson is that not all water rights are created equal.
In a dry year, a 1910 water right for IO cfs may not provide as much water to the user as an 1875 water right for 2 cfs.
Not all water rights are created equal.
In a dry year, a 1910 water right for 10 cfs may not provide as much water to the user as an 1875 water right for 2 cfs.
Beneficial Use-A Moving Target
 Another key provision of this doctrine of prior appropriation is that water must be put to a beneficial use.
When this system evolved in the arid west in the 19th century, "beneficial use" was largely defined by the act of diverting waters from the stream.
Water left instream was widely considered to be waste.
A well-managed stream was a dry one.
The idea of water left instream serving a beneficial use didn't begin to surface in Montana law until the late 1960s.
Now, in specific circumstances, it is possible to acquire a legal water right for instream use for such things as the benefit of fisheries, wildlife, and water quality.
The key to protecting your claim to a water right is to apply it to a beneficial use.
In the case of irrigation, for instance, that means actually irrigating something other than the bottom of a ditch.
Likewise, pouring enough water on fifty acres to irrigate 400 acres doesn't establish a beneficial use in the excess water.
Your beneficial use is limited by the reasonable need of the particular use.
A Water Right is a Property Right.
One cautionary note about diversions and beneficial use-some water right holders believe that simply diverting water, even if they don't apply it to a beneficial use, protects their water right from a claim of abandonment.
It doesn't.
While it may seem contradictory at first blush, the State of Montana owns all the water in the state-the owners of water rights possess only the right to use some of that water.
Here's the crucial language in Article IX of the Montana Constitution:
 ACRE-FOOT.
This is a term used to describe a volume of water.
An acre-foot equals 325,851 gallons, or enough to cover one acre in one foot of water.
An acre-foot is also enough water to meet the demands of a family of four for a year.
"All surface, underground, flood, and atmospheric waters within the boundaries of the state are the property of the state for the use of its people and are subject to appropriation for beneficial uses as provided by law."
 Just because water arises on your land, you don't have an automatic right to use it.
You must have a water right.
USE IT OR LOSE IT.
So the state owns it, but we get to use it.
Your right to use the water-your water right or appropriation right-has been recognized as a form of property right.
But it's not like a piece of real estate or a new car: you have to use it.
If you don't use it-usually over a long period of time-you can lose it.
This concept of "use it or lose it" doesn't mean it has to be used every year-a really junior right may only find available water every few years, and then only for a small part of the year-it's still a valid water right; just not a very reliable one.
Disuse, coupled with some outward sign of intent to no longer use the
 ADJUDICATION.
In the context of Montana water law this refers to the statewide judicial proceeding to determine the type and extent of all water rights claimed before July I, 1973.
See the sidebar below on the adjudication.
ADVERSE EFFECT.
In water rights, something that impedes the ability of a water user to make use of water.
Change in use must avoid an adverse effect to other water users.
The key to protecting your claim to a water right is to apply it to a beneficial use.
water, can lead to abandonment
 of a water right.
APPROPRIATE.
The acts necessary to create a water right.
Keep this concept of abandonment in mind as you consider the water rights claimed for the property you're examining.
If you see an abstract that shows a claim for irrigated acres where there is no sign of any irrigation system or, if what is there looks like it hasn't been used since the advent of the internal combustion engine, it should send up a warning flag.
APPROPRIATION RIGHT.
A long-winded way of saying water right.
A water right is a right to put water to a beneficial use.
APPROPRIATOR.
One who applies water to a beneficial use.
An appropriator owns a water right.
BENEFICIAL USE.
A use of water for the benefit of the appropriator, other persons, or the public, including but not limited to agricultural , domestic, fish and
 wildlife, industrial, irrigation, mining, municipal, power, and recreational uses; a use of water to maintain and enhance streamflows to benefit fisheries pursuant to conversion or a lease of a consumptive use right.
Note: simply diverting water down a ditch and letting it run back to the stream is not a "beneficial use."
 In a similar vein, a declaration of intent to use a water right, by itself, does not establish a water right.
A water right has to be perfected by actually putting it to a beneficial use.
In the 19th and early 20th century, it was possible to file a notice of a water right in the county clerk's office.
Miners, often with an excess of wishful thinking, were particularly fond of doing this.
In many cases, that is all that ever happened-no ditches were dug or water diverted.
To put it kindly, the validity of those water rights is highly suspect.
Just because water arises on your land, you don't have an automatic right to use it.
You must have a water right.
WATER RIGHTS ARE TRANSFERABLE.
A lot of water rights traditionalists repeat a common refrain, "Water runs with the land." The statement is only partly true.
If you own a piece of real estate, and it has water rights on it, when you sell that real estate, if you don't mention the water rights in the conveyance, the water rights automatically transfer to the buyer of the real estate.
Some old timers want to believe that this means the water right can never be severed from the land.
That isn't true, and hasn't been true since at least 1895.
Water rights can be transferred to new places of use totally unrelated to the original real estate.
But there's a catch.
A change in the place of diversion, the place of use, the purpose of use, or the place of storage of a water right.
These changes need the approval of the Department of Natural Resources and Conservation  to assure that the change will cause no adverse effect to other water users.
ANY CHANGE IN THE PURPOSE, PLACE OF USE, OR PLACE OF DIVERSION OF A WATER RIGHT MUST FIRST BE APPROVED BY THE MONTANA DEPARTMENT OF NATURAL RESOURCES AND CONSERVATION.
Prior to 1973, if you wanted to change the place of use, purpose, or point of diversion, you just did it.
While you had an obligation not to do anything that would adversely affect the water rights of others, you didn't have to seek any prior agency approval to do the change.
If you harmed somebody, they had the option to sue you after the deed was done.
In 1973 however, with the passage of the Montana Water Use Act, that all changed.
Now, if you want to change the point of diversion, place of use, or purpose of use of
 CHANGE IN APPROPRIATION RIGHT.
DNRC.
The Montana Department of Natural Resources and Conservation, the state agency responsible for permitting new water rights and changes in appropriation rights.
continued on page 6
 I.O CFS = 448.8 GPM = 40 MINER'S INCHES I.O CFS X 24 HRS : 1.98 ACRE FEET
 CUBIC FEET PER SECOND.
448.8 gallons per minute.
Cfs is a measurement of flow.
flow of 1.0 cfs over 24 hours will yield a volume of 1.98 acre feet.
CONSUMPTIVE USE.
A beneficial use of water that reduces the source of supply, such as irrigation or municipal use.
your water right, you have to first secure DNRC's approval, and the burden is on you to prove that you won't adversely affect the water rights of anyone
 else.
And step one in providing that proof?
Historic use of a water right-not what an abstract, or even what a court decree says-is key to establishing the extent of a water right.
Documenting historic use.
Ultimately, it's
 a bit more complicated than that-there is
 some hydrology involved-but a key part of
 FLOW RATE.
A measurement of the rate at which water flows are diverted, impounded, or withdrawn from the source of supply for beneficial use, and commonly measured in cubic feet per second  or gallons per minute.
Put in every day terms, when you turn on the faucet in your kitchen sink, the water comes out at a certain rate of flow.
granting a change is assuring that there won't
 be any expansion of use over what historically
 occurred.
So, back to our cautionary tale at the beginning, any proposed
 change which will expand the amount of water diverted or consumed might
 have an uphill battle getting DNRC's approval if there are any downstream
 Historic use of a water right-not what an abstract, or even what a court decree says-is key to establishing the extent of a water right.
So, when you embark on due diligence research of a water right, one fundamental goal is get a handle on what the actual historic use was.
INSTREAM FLOW OR USE.
Water left in a stream or river for nonconsumptive uses such as a fishery use.
JUNIOR APPROPRIATOR.
A secondary user on a water course.
One who does not have the most senior rights.
MINER'S INCH.
An archaic description of flow rate that you'll occasionally hear.
In Montana, one cfs equals 40 minor's inches.
Or one miner's inch equals 11.22 gallons per minute.
One caveat for the strict constructionists among you-a miner's inch in Montana isn't necessarily the same a miner's inch in another state.
Why?
Go figure.
NONCONSUMPTIVE USE.
A beneficial use of water that does not reduce quantity, quality, or timing of water in the source of supply, such as an instream use.
NRCS.
The Natural Resources Conservation Service.
This is the federal agency that implements the federal farm
 continued on page 8
 W readily accessible to an interested prospective buyer.
There are a number of useful single aspect of a ue-diligence inquiry, but rather those things that are hat follows in this section is a step-by-step guide to researching the validity of water rights claims attached to a piece of land.
This does not cover every steps omitted here-examination of tax records, close examination of 19th century filing documents, comparison of claimed flow rates with measured ditch capacity, or a review of electrical records where irrigation is powered by electricity, to name a few-that in are better done by a trained professional.
But if you follow the suggestions rights that attach to a property and help you decide whether you need professional advice on the water rights aspect of your purchase.
this section, it should substantially improve your understanding of the water
 Page of 1 General Abstract
 April 10.
2006 76F 3917-00
 DEPARTMENT OF NATURAL RESOURCES AND CONSERVATION STATE OF MONTANA 1424 AVENUE O.BOX 201601 HELENA MONTANA
 Water Right Number: geizer ORIGINAL STATEMENT RIGHT OF CLAIM Status: ACTIVE Owners: KOURRA MY JUNE 26, 1932 Priority Date: Enforceable Priority Date: JUNE 26, 1932 Type of Historical Right: DECREED IRRIGATION Purpose : Maximum Flow Rate: 15.00 CFS Maximum Volume: 117.60 AC-FT Maximum Acres: 60.00 Source: Source Name: ROCK CREEK SURFACE WATER Source Type:
 established few most water rights of any early priority are long since dead, and because very their irrigators actually measured the amount of water they diverted and applied to fields, establishing historic use can be a challenge.
The most accessible approach been to establish the existence of an irrigation claim  is to look at acres historically irrigated.
There is
 if consider the right claims are a key part of a parcel's value, you should conduct hiring a consultant or attorney who specializes in water rights seriously to While water much of this can be easily be done by the prospective purchaser, the search.
ID	Govt Lot	SWSWNW	Qtr Sec	See	5	Twp	14N	11W	Rge	County	POWELL
 Diversion	Means:	MULTIPLE	SWNE	5	14N	11W	POWELL
 2	Diversion Means:	UNKNOWN
 MAY to SEPTEMBER 1
 Purpose :	Irrigation Type:	SPRINKLER
 Volume:	MAY to SEPTEMBER
 Period of Use:	Place of Use:	1	Acres	60.00	Govt Lot	NW	NE	Sec	6	5	Twp	14N	14N	11W	11W	Rge	County	POWELL	POWELL
 Point of Diversion and Means of Diversion:
 I) Get Copies of the Statement of Claim.
Remarks: THE FOLLOWING ELEMENTS WERE AMENDED BY THE CLAIMANT ON 03/10/2006: POINT OF DIVERSION, PLACE OF USE.
OWNERSHIP UPDATE RECEIVED OWNERSHIP UPDATE ID x28541 RECEIVED 12/09/2005.
irrigated-don't necessarily accurately represent the extent of the water right.
This is just what a prior owner has asserted as a claim-it may or may not be accurate.
In many instances-especially when the adjudication has progressed beyond an initial filing-you may find text at the bottom of the abstract that can provide some hints as to the validity of the historic use claims.
These are called "issue remarks." DNRC, after examination of the claim, has placed them on the abstract.
For example, a common issue remark is "THIS CLAIM PRESENTS ISSUES OF LAW AND FACT THAT MAY BE ADDRESSED AT THE OBJECTION STAGE.
IT APPEARS THAT ACRES [instead of the acres claimed on the abstract] ARE ACTUALLY IRRIGATED, AND PROBLEMS COULD EXIST WITH THE FLOW RATE AND PLACE OF USE." If you see a comment like this, you'll want to see what claims examination was done to prompt such a comment, and that information should be available in the regional DNRC office.
2) Review the original 1982 water right claim file and the material submitted in support of it.
The statement of claim that you obtained at step I shows what the water user claimed for the water right in 1982 as part of the statewide adjudication.
As of 2006, that adjudication has yet to be completed in any basin.
The information on the abstract likely also includes any adjustments to the original claim made as a result of any proceedings in the adjudication.
You can see the detail behind the abstract by going to the records on file at the DNRC headquarters in Helena , at the State Water Court Offices in Bozeman , or at the regional DNRC Water office that covers the water right in question.
The file might include the claim document, supporting evidence, maps, or air photos.
It might also include DNRC claims-review documents and field reports.
At times, the claims review notes can be a bit cryptic-if you have trouble understanding
 bill, and has local and regional offices around the state.
It is a source of information and assistance on agricultural irrigation practices, soil types, weed control, grazing practices, and other ranch management issues.
It also has a variety of programs providing partial funding for irrigation improvements and some habitat restoration.
PERFECTED.
A water right claim is perfected when it is actually put to use.
Under the traditional system one could file a notice of a claim in the county clerk and recorder's office without first having put the water to use.
And under the modern permitting system , an applicant for a water use permit must get DNRC approval before putting the water to use.
In either instance, if the water is not subsequently put to use, then the water right has not been perfected, and it may not be valid.
Remember, a water right is defined by its actual beneficial use.
Good intentions don't count for much.
PLACE OF USE.
The place at which a water right is put to use.
POINT OF DIVERSION.
The place on a water source at which water is diverted.
SENIOR APPROPRIATOR.
As between two or more users on a source, the water user with the earliest priority date.
RETURN FLOW.
Part of a diverted
 flow that is applied to irrigated land and is not consumed and returns underground to its original source or another source of water, and to which other water users are entitled to a continuation, as part of their water right.
them, ask for help from DNRC personnel.
Often the detail you find is not of much help, but it's still worth a look.
When you visit any of these offices, the office can give you an update on the status of the adjudication and how it might affect the claims you are examining.
One useful item that may surface as part of this inquiry is an old court decree.
Historically, if people had a water rights dispute, parties would sue in district court to resolve it.
Many-but far from all-streams have some historic water rights decree that apportions water use among the water users on that stream.
While it is not conclusive evidence of historic use, it is another helpful piece of evidence that the water right was indeed put to use at some time in its claimed history.
VOLUME.
On the Statement of Claim, the volume of the water right is indicated in acre-feet.
This indicates the total amount of water that can be diverted from the stream at the specified flow rate.
In many cases, you may see this comment on the "maximum volume" line on the Statement of Claim: "The total volume of this water right shall not exceed the amount put to historical and beneficial use."
 3) Review the current deed to the property to assure that no water rights have been reserved  from the land.
WASTE WATER.
That part of a diverted flow which is not consumptively used and which returns as surface water to any surface water source, and which other water users can appropriate, but have no legal right to its continuance.
For example, if an irrigator puts so much water on his field that some of it flows off his land as surface flow, that surface flow is waste water.
Remember, In Montana, unless expressly stated otherwise, water rights attached to land will pass with the conveyance of the land, unless the water right holder expressly exempts the water right from the conveyance.
So notwithstanding anything else you have heard, it's good to peruse the deeds to the land to make sure none of the water rights have been reserved from conveyance to the current owner.
4) If the water rights are represented by shares in a ditch company or irrigation district, check with the ditch company or irrigation district to confirm status of the shares.
WATER COURT.
Located in Bozeman, the Water Court's primary function is to carry out the state-wide adjudication.
Disputes between water right holders are still handled in local district court, and the local district courts still oversee any water commissioners in their area.
If the current owner indicates that the water for the land you are looking at is provided by an irrigation district or ditch company, ask to see the owner's records concerning those shares.
And get the name and address of the ditch company, along with any key personnel or phone numbers, SO you can conduct your own examination of the shares that attach to your
 land.
Among other things, you'll want to make sure that any annual assessments have been paid.
5) Review the Montana Water Resources Survey Maps for the township and range in which the water right claims a place of use.
Irrigation activity is often readily identifiable on aerial photos.
NRIS photo.
6) Look at other aerial photos.
their particular region); and  the water rights website for the water rights claim in question.
By clicking on the "use count" box in the water rights list, you can generate a water rights map that can then be converted to an aerial photo  that can provide some guidance as to recent use.
There are a number of other sources of aerial photography, but if you need to go to that much effort and level of detail, you may want to consider hiring a consultant.
Part of due diligence is establishing that there has been some continuity of use of a water right-not that it has just been used for one year  and never again.
One way to do this is to look at other aerial photos.
Two sources of aerial photos are  the DNRC regional offices (they will have aerial photos for
 7) Look at topographical maps.
One useful exercise is to look at a topographical map of the ground claimed to be irrigated.
Most irrigation claims, even if they are now perfected through some kind of pump and sprinkler system, started as flood irrigation.
Flood irrigation relies on gravity.
For a flood system to work, the water has to flow downhill.
And that's where the topographical map comes in handy.
If a parcel that has been claimed to be flood irrigated sits higher than the source claimed to irrigate it, that claim of irrigated land is, to put it kindly, suspect.
And, indeed, such claims have been filed.
In addition, many topographical maps will show some evidence of irrigation canals.
8) Ask the seller for a map that highlights the property for sale and then compare that map to the irrigated acres described in the Statement of Claim.
Over the years, if the property has been split, part of the land irrigated may not be on the parcel you are considering, and that may not necessarily have been reflected in the conveyances.
It is possible that there may be more than one person claiming the right.
9) Check the legal descriptions of the points of diversion against the legal description on the land that you are considering buying.
If the points of diversion and ditches are not on the prospective property, you will want to check for any easements on the property where the points of diversion and ditches reside.
If you see an abstract that shows a claim for irrigated acres where there is no sign of any irrigation system, it should send up a warning flag.
IO) Do a site visit.
If you're serious about purchasing land, you will no doubt be visiting the site.
In a perfect world, you will have read this guide, done your office homework on the water rights, and come prepared to closely scrutinize any evidence of water use at that first visit.
If not, plan a second visit and
 If the place of use is in section 1  and the point of diversion is in section 11 , Section 1 couldn't be flood-irrigated from section 11.
in heavily-used drainages, they might not always-and sometimes not often-get the full amount of the claim satisfied  The other limiting factor may be the source itself.
So it's important to focus some inquiry on the seniority of the right and on the reliability of flow in the stream that provides the water.
Good sources for this information include not only the landowner, but other water users on the source.
If there was a court decree on the stream, there may be a court appointed water commissioner who knows who gets what, and who is typically an unbiased source of information.
So make sure to ask if there is a water commissioner on the stream.
come with a camera, a topographical map, copies of the water rights abstracts, the Water Resources Survey map, and a note pad.
When you' re on the ground, make sure you see any current irrigation operations, and try to correlate them to the legal descriptions of irrigated ground found on the claim abstract.
Ask to see any old diversion sites, ditches or other irrigation works, even if they are not currently in operation.
Take pictures.
Ask questions about the historic use-what was irrigated, what crops were grown.
Determine if there are any old timers around who can talk about what the irrigation practices were.
Ask about any historic records-jour nals, irrigation records, etc.that might shed light on the historic water use.
12) Check the seniority of the right.
As to seniority, there are a number of things that can be done.
First, when reviewing the abstract at the online site described in item I, also look at a list of the other water rights on the stream in question.
This provides you an opportunity to see what the relative priority is of the water rights in question.
If there are a lot of water rights senior to the rights in question, they may not provide much access to the water claimed.
This may trigger some additional questions of the previous owners as to how often the water right gets satisfied, and how far into the season they get water.
Don't hesitate to ask questions of either DNRC or water court personnel about the claims you are looking at.
One key question-ask if a district court has appointed a water commissioner to the stream in question.
If so, get the name of the commissioner, contact the commissioner and find out if, or when, water rights of the priority date in question cease getting water during the irrigation season because of their relatively junior status.
For example, on the
 One of the great limitations of junior rights is that,
 Look for signs of historic irrigation, such as old ditches or headgates.
II) Inquire into reliability of the right and how often it is satisfied.
West Gallatin, water rights with a priority date of 1890 or later are considered SO junior as to only be able to get water during spring runoff.
If you can't find the commissioner, the clerk of court should have his report of his work that he must file to get paid.
This can often have useful information about the actual use of the water right.
15) If, after doing the first fourteen things on this list, you're still not sure about the water right, consult an expert.
Diversions aside, many streams in Montana have extremely low flows, or even dry up, naturally.
Yet water rights on those streams might be expressed in flow rates and acres irrigated to suggest otherwise.
So it is important to ask questions about whether the stream is perennial or intermittent.
In fact, a late-season site visit  might be the best way to assess that.
13) Check the reliability of the source.
14) For any Water Use Permits  make sure the Permit has been perfected.
Once you have compiled this kind of evidence, it should give you a realistic picture of what the extent of the water right is.
It is rare that a claimed water right is completely false.
But it is not unusual for there to be some variance between what is claimed and what can actually be documented as historically used.
This is the difference between a "paper water right" and a real water right.
In the case of Mr.
Hartman and my cautionary tale, Hartman had paper claiming 320 acres, but a real water right only to 160 acres.
A reasonable due diligence effort such as described here can go a long way toward providing a reasonable expectation about the water right available for use, and avoiding the kind of shock that Mr.
Hartmann encountered.
While water use permits, because of their junior priority dates, may not be the most powerful water rights, sometimes they may be all you get-and in some locations, they may be plenty reliable.
So if you see statements of claim with a priority dates of July I, 1973 or later, make sure they have actually been put to use.
Also, check with DNRC to make sure the required notice of completion has been filed for the permit, or if any extensions on the filing of that notice have been granted.
When on your site visit, compare the permit with what you see on the ground.
If there is no evidence of beneficial use, the right may not be valid.
CHECKLIST DILIGENCE DUE IV.
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 Check for Remarks Issue
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 file of original right claim material it 1982 in submitted Review the and the support water
 Check for claim aerial photos, used support etc.
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 Check for claims materials examination any
 files office interpreting for assistance Ask in personnel
 for of evidence Look district decree court a
 of have Review rights been that make deeds property to current to water no sure owner from  land the reserved
 If ditch district, irrigation check rights represented by shares the in water company or are a of district confirm ditch the shares irrigation the with to status company or
 Resources Montana Review the for which Water Maps Survey the in township and the range right of claims place water use a
 Statement if land Claim claimed the of Survey the Map in is be See irrigated shown to as on irrigated.
historic for of evidence aerial Look photos at use
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 Look topographical at maps
 of Compare of elevations diversion between claimed the the and places point use
 of for Look evidence ditches irrigation
 land legal of offered Compare irrigated description described the for the in sale the the to acres Claim-do fully of Statement overlap?
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 descriptions legal of Check the legal of diversion land against description the the points the on buying.
considering that are you
 visit Do site a
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 Check claims abstract irrigation operations, current to compare
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 of Inquire right satisfied how often is it reliability and the into
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Township, Range, and Quarter Quarter Quarter Section A Quick And Dirty Guide to Reading Legal Descriptions
 If you haven't spent a lot of time reading legal descriptions-and most of us, happily, haven't-it can be a bit confusing the first time you try it.
Water rights-both point of diversion and place of use-are described by reference to township, range, and section numbers.
So what's a section, and what on earth has that got to do with a township and a range?
A SECTION is a tract of land that measures one mile by one mile-it contains 640 acres.
A TOWNSHIP is a tract of land made up of thirty-six sections-six across and six down-in reference to a given baseline.
So a description of T3N identifies a township that is the third township north of a baseline.
A RANGE sets the east/west location of a township from reference point known as a "principal meridian." So a a description of R2W indicates the east west location of a township as being two ranges to the west of a principal meridian.
A typical legal description, down to the section level, would look like this:
 TIS R15W, section 32, Beaverhead County.
So you would look on the map  for Township I South, Range I5 West, Section 32 in Beaverhead County.
But you'll find water rights described down to the quarter quarter quarter section.
640 Acres-1 Mile Square
 The quarter section descriptions are based on dividing a section into 4 equal quarters of 160 acres each-moving clockwise, a northwest  quarter,
 a northeast  quarter, a southeast quarter, and a quarter section.
So the description of the northwest quarter
 southwest  quarter.
If you see this description: NE 1/4 section 32, It is describing this:
 A quarter quarter section simply divides the quarter section into quarters of 40 acres each.
If you want to describe the northeast quarter of the northeast quarter of section 32 it will look like this: NE 1/4 NE 1/4 section 32.
And that will describe the blue shaded portion of Figure 3.
The description of a quarter quarter quarter section, which is IO acres, simply looks at one fourth of a quarter
 of the southwest quarter of the northeast quarter of section 32 would look like this: NW 1/4 SW 1/4 NE 1/4 section 32.
And that will describe the yellow shaded portion of Figure 3.
That's all pretty straightforward.
Now try it out.
When you come upon the description of NW 1/4 SW 1/4 NW 1/4 section 32, read it from the back to the front  and mark it on Figure 4:
 Find section 32; Then find the NW 1/4 of section 32; Then find the SW 1/4 of the NW 1/4; Then find the NW 1/4 of the SW 1/4 of the NW 1/4, And you' re there!
Pretty easy, huh?
What happens when you have purchased a ranch, and want to restore its streams?
Until recently, it wasn't possible for an irrigator to simply let water flow in a stream instead of diverting it.
If he did, he risked abandoning his right.
Above: Rock Creek before flow and habitat restoration.
Below: Rock Creek one year after restoration.
Montana, however, now has a statutory "water leasing" program to provide water for fish in streams.
As the Mannix Brothers Ranch did in partnership with TU to keep water in Wasson Creek , it is possible to voluntarily convert an irrigation use to an instream use in Montana to benefit fisheries.
A water user in Montana has three options:  convert all or part of a consumptive-use water right to an instream use by seeking a change in purpose and place of use without use of a lease;  lease a water right to the Montana Department of Fish, Wildlife and Parks; or  lease a water right to a private entity such as Trout Unlimited.
So what does it mean to convert a consumptive use to an instream use under this law?
Well, first, it keeps the priority date intact.
For example, if you had an 1865 priority date on irrigation right and you converted it to an instream use, the instream use would retain the 1865 priority date.
Second, the ownership of the water right remains the same.
The Mannix Brothers Ranch still owns its entire water right, it is just temporarily leasing the right to TU to provide flows in Wasson Creek.
There are limitations on your ability to convert a water right to an instream use.
The biggest one is that, in most cases, a conversion can only be done for a period of ten years.
You can renew use for successive ten-year periods ad infinitum, but you cannot make a "permanent" conversion to instream uses.
In some instances, if there is the construction of some kind of conservation measure, such as the replacement of a ditch with a pipeline, it is possible to extend the life of an instream lease or conversion to 30 years.
Restoring streamflows through a water lease can be a critical piece of a more comprehensive restoration effort.
This was the case on Wasson Creek, where the water lease was a key component of restoring native westslope cutthroat trout, but its success depends on the channel and riparian restoration work that had been done on Wasson Creek to create good habitat conditions.
If you decide you want to explore an instream option, a good first step is to talk to either Trout Unlimited or the Montana Department of Fish, Wildlife and Parks about water leasing.
Wasson Creek is tiny.
As you drive over it on Highway 141 near Helmville, Montana, you likely wouldn't recognize it as a C1 serpentine swath of willows and cottonwoods that mark its course.
The vegetation encroaches enough that you most definitely woul you were whizzing along at highway speed.
Despite its humble appearance, Wasson Creek has become a key piece in the effort to restore fisheries in the middle reach of the Blackfoot River.
Years of human activity have seriously compromised the fisheries of lower Nevada Creek, which in turn has reduced fisheries in the Blackfoot for several miles below its confluence with Nevada Creek.
There are several challenges ranging from low flows to high temperatures to nutrient pollution from irrigation runoff.
Complete restoration will involve work on several fronts over many years.
But the efforts of landowners on two tributaries to Nevada Creek-Spring Creek and its tributary, Wasson Creek-mark a promising start on the larger restoration effort.
Spring Creek was restored from a livestock-damaged, shallow, warm stream in the first five years of this century-it now sends a clean, cold pulse of water into the lower reaches of Nevada Creek yearround.
But, left to its own devices, it wasn't growing many fish as the restoration progressed.
That's where Wasson Creek comes in.
Like Spring Creek, Wasson Creek has taken its share of knocks.
The creek has suffered from straightening, irrigation depletions, and grazing.
But the reach above the irrigation diversion is home to a robust population of pure-strain westslope cutthroat trout.
Those native fish represent a promising seed source for Spring Creek, Nevada Creek and eventually the Blackfoot.
The problem is that, until recently, irrigation diversions have de-watered lower Wasson creek by mid-summer SO much that those cutthroats had not been able to migrate down to repopulate the newly restored Spring Creek.
But over the past few years, the Mannix Brothers Ranch, the primary owner on Wasson Creek, has partnered with TU, the downstream landowners, and a variety of state and federal agencies, on a comprehensive restoration effort.
An integral part of that work has been to restore stream flows in the lower two miles.
According to David Mannix, the ranch operations rely heavily on the contributions of Wasson Creek to provide pasture grass for its cattle.
Working with TU, however, the ranch has come up with a solution that allows them to continue much of their irrigation while keeping flows in the lower reach in late summer.
The Mannix Brothers Ranch experimented for a couple of summers with one-year agreements with TU to not irrigate after flows in the lower reach
 dropped to 0.5 cfs.
TU paid the ranch for its reduction in pasture grass.
Under this arrangement, the ranch could maintain its early-season irrigation while providing water for fish in the important late-summer period.
For Randy Mannix, it's a question of balance.
"As ranchers who believe in stewardship, the challenge for us is to protect these stream resources while still maintaining an economically viable agricultural operation," he said.
"This lease gives us a chance to find part of that balance and, to also demonstrate that agricultural interests and fisheries interests could work together to each other's benefit."
 The results of this experiment were immediate.
In the fall after the first season of the agreement, a population check in the Spring Creek documented the presence of westslope cutthroat in the stream for the first time in decades.
In the wake of this success, the ranch and TU have entered into a ten-year lease to maintain a minimum flow in Wasson Creek, helping to restore the native trout fishery.
Answer from page 17.
There is a widely held belief that spans almost every segment of the Montana community-irrigators, anglers, biologists, federal farm subsidy programs-that the key to making our water go further is to reduce the amount of flood irrigation that occurs by replacing it with sprinkler irrigation, especially sprinkler irrigation by center pivots.
The basic premise is that because sprinkler irrigation is more efficient, we'll save more water.
As with SO many things involving water, however, the devil in this myth lies in the details.
First, sprinkler irrigation can have some very real benefits both for the irrigator and for water quality.
For irrigators, increased productivity is often a significant benefit.
Many irrigators report a much higher yield of crop with sprinklers than they got with flood irrigation.
Second, center pivots in particular can save an irrigator a substantial amount of time.
Flood irrigation is labor-intensive, hard work.
With a properly operating center pivot, you hit the "On" button, and the center pivot pretty much does the rest.
In many places flood irrigation can leach salts, chemical fertilizers, and other pollutants from the soil into groundwater and eventually back into the streams that they came from.
Sprinkler irrigation can reduce that leaching, substantially benefiting water quality.
But sprinklers as a "water saving" device?
Well, the benefits aren't nearly SO straight forward.
Consider increased productivity.
If an irrigator can grow four tons of hay with sprinkler irrigation where he used to grow only two tons-well, four tons consume  up to twice as much water over the course of an irrigation season.
What the crop drinks and evaporates doesn't go back into the stream.
Often people will say, but "I don't have to divert SO much water with a sprinkler system, so how can I be using more water?" First, flood irrigation systems often don't provide what is known as "full service" irrigationirrigation throughout the entire irrigation season, resulting in maximum
 crop production.
In many cases, as streamflows drop throughout the irrigation season, irrigators are unable to divert enough water to effectively flood irrigate, SO they quit diverting.
A sprinkler system fed by a pump and pipeline, however, may be able to divert water and irrigate throughout the entire season, because it can effectively utilize low stream flows.
So while a sprinkler may divert less in the early season, they may actually divert more in the late season, when flood irrigation would have ended.
And, if late-season low flows are a problem for fish, sprinklers may aggravate the problem.
Second, irrigated land coverage within a field boundary by a sprinkler system is effectively 100%.
In contrast, many flood-irrigated fields are not capable of achieving full coverage due to uneven terrain.
The difference results in higher crop production for sprinkler irrigation, which translates into higher water consumption.
Third, flood irrigation provides "return flows," or those streamflows that were diverted from the stream but not consumptively used by the crop.
These "return flows" are sub-surface flows that follow the hydrologic gradient and emerge again as stream or river flows downstream.
The timing and amount of return flows are particular to each stream reach and irrigation practice, SO it is difficult to generalize other than to say that flood irrigation provides more return flows than sprinkler irrigation.
These return flows can be critical in sustaining fisheries later in the season.
At times, sprinklers may allow irrigation without as much early season diversion as flood irrigation.
For some native species, that may be a critical period.
In those cases, sprinklers may actually prove beneficial to fish.
The bottom line on sprinklers is that they do not offer a silver bullet for water conservation and stream flows.
Their relative benefit-or detriment-is site specific, and people engaged in streamflow enhancement need to view them carefully and critically before adopting a conversion to sprinkler as part of a conservation plan.
Sooner or later, anyone who acquires water rights in Montana will hear about the "adjudication." In an effort to secure Montana water rights from claims by downstream states, and in an effort to get some kind of accurate accounting of water use in Montana, the 1979 legislature passed a bill that required Montana to initiate a statewide adjudication of all water rights with priority dates prior to July I, 1973, and established a statewide Water Court to preside over the adjudication.
Under the auspices of that 1979 law, everyone who claimed a pre-July I, 1973 water right had to file a statement of claim with the Montana Water Court by April 30, 1982 or lose their water rights.
By April 30, 1982, claimants had filed over 200,000 claims.
When you look at a water rights claim abstract on the internet at the state website, you are looking at a dressed-up version of the original claim as filed in 1982.
In some cases there may have been modifications to those claims that will be reflected in the abstracts, in others, they appear pretty much as they were filed.
The bottom line?
Those official looking abstracts don't necessarily reflect your actual water right.
So if everybody filed claims way back in 1982, the adjudication must be complete and all those claim abstracts represent that final adjudication, right?
Well, no.
Since the filing of those claims, the adjudication has moved with might kindly be termed "deliberate speed." Which is to say, at a glacial pace.
The 2005 Montana Legislature, recognizing that there is yet to be a final decree from the Water Court in any river basin, passed a new law to add funding to the adjudication by imposing a fee on all water rights.
With luck, the entire adjudication could be completed by 2020.
With luck.
The good news is that even while we await the completion of this seemingly endless process, irrigators can still irrigate, fish can still swim, and we can still change water rights from one use to another, working together to find ways to make Montana's glorious rivers and streams serve many needs.
The following resources can assist a prospective land purchaser in performing due diligence on water rights.
Montana Department of Natural Resources Water Resources Division, Water Rights Bureau, 406-444-6610
 Regional Offices: Regional offices have some aerial photos of the lands covered by their offices and also have current information on the status of the statewide adjudication in its region.
BILLINGS: AIRPORT INDUSTRIAL PARK, 1371 RIMTOP DR., BILLINGS, MT 59105-1978 PHONE: 406-247-4415 FAX: 406-247-4416 SERVING: Big Horn, Carbon, Carter, Custer, Fallon, Powder River, Prairie, Rosebud, Stillwater, Sweet Grass, Treasure, and Yellowstone Counties
 LEWISTOWN 613 NORTHEAST MAIN ST., SUITE E, LEWISTOWN, MT 59457-2020 PHONE: 406-538-7459 FAX: 406-538-7089 SERVING: Cascade, Fergus, Golden Valley, Judith Basin, Meagher, Musselshell, Petroleum, and Wheatland Counties
 BOZEMAN: 273 Boot Hill Court, Suite IIO, BOZEMAN, MT 59715 PHONE: 406-586-3136 FAX: 406-587-9726 SERVING: Gallatin, Madison, and Park Counties
 MISSOULA: 1610 S 3RD ST WEST, SUITE 103, PO BOX 5004, MISSOULA, MT 59806-5004 PHONE: 406-721-4284 FAX: 406-542-1496 SERVING: Granite, Mineral, Missoula, and Ravalli Counties
 GLASGOW: 222 6TH STREET SOUTH, PO BOX 1269, GLASGOW, MT 59230-1269 PHONE: 406-228-2561 FAX: 406-228-8706 SERVING: Daniels, Dawson, Garfield, McCone, Phillips, Richland, Roosevelt, Sheridan, Valley, and Wibaux Counties
 HAVRE: 2IO 6TH AVENUE, PO BOX 1828, HAVRE, MT 59501-1828 PHONE: 406-265-5516 FAX: 406-265-2225 SERVING: Blaine, Chouteau, Glacier, Hill, Liberty, Pondera, Teton, and Toole Counties
 HELENA: 1424 9th Ave., PO BOX 201601, HELENA, MT 59620-1601 PHONE: 406-444-6999 FAX: 406-444-9317 SERVING: Beaverhead, Broadwater, Deer Lodge, Jefferson, Lewis and Clark, Powell, and Silver Bow Counties
 KALISPELL: IO9 COOPERATIVE WAY, SUITE IIO, KALISPELL, MT 5990I-2387 PHONE: 406-752-2288 FAX: 406-752-2843 SERVING: Flathead, Lake, Lincoln, and Sanders Counties
 TROUT UNLIMITED, MONTANA WATER PROJECT: Works on instream leases and water rights issues related to instream flows.
321 East Main St., Bozeman, MT 59715.
phone: 406-522-7291.
The publication of A Buyer's Guide to Montana Water Rights would not have been possible without generous donations from the following sponsors.
Thank you!
Outlandish Conservation Land Brokerage & Consulting
 Trout Unlimited is a non-profit, tax-exempt charitable organization under Section 501 of the Internal Revenue Code.
Donations are tax-deductible.
Stan Bradshaw works as a staff attorney for Trout Unlimited's Montana Water Project.
His responsibilities include working with irrigators to change water rights from consumptive uses to instream uses.
All of the photos in this handbook were taken by Stan unless otherwise credited.
Many people have contributed their thoughts, suggestions, edits, and common sense to make this guide much better that it was in its first draft.
Amy Kelley has given us an inspired design and layout, not to mention a seemingly endless reservoir of patience in working with us.
My colleague Julie Eaton not only gave me invaluable critical comments from a lay perspective, but she also worked closely with Amy on the presentation of the information and in finding key photos and illustrations.
Jamie Morin, Mike McLane, Ryan McLane, Matt Williams, Scott Irvin, and Andy Brummond have all provided the benefit of their considerable practical water rights experience in their review and suggestions.
Greg Neudecker, Paul Roos, Dave Johnson, and Dave and Randy Mannix all applied not only their discerning eyes, but a considerable dose of common sense to their review of the manual.
Glenda Bradshaw and Kate Wright both had an important hand in proof-reading and copy-editing the text.
Thanks to Bob Kiesling for telling me he thought this project was a good idea when I had just about talked myself out of it.
Two organizations, the Montana Association of Land Trusts and the Blackfoot Challenge, made important early commitments to help distribute this guide, both through their websites and through their member organizations.
Thanks, finally, to my boss, Laura Ziemer, for her constant encouragement and wise counsel.
Whatever flaws remain after the good efforts of everyone mentioned above are mine alone.
Trout Unlimited, Montana Water Project 321 E.
Main Street, Suite 411 Bozeman, MT 59715 406-522-7291
How To Make A
 Ready for the Fair
 The Master Gardeners would like to invite you to show a plant or two  in the fair this year.
While October is still some time away, don't let the time get away from you-start preparing your plants now using the tips on page 4.
This is a fun, learning experience and nothing like a professional plant show.
So whether you have something rare or common-if it is special to you, they want to see it in the show!
Best Regards, alicia Alicia R.
Lamborn Horticulture Extension Agent Baker County Extension Service
 Like us on Facebook
 Dripline Irrigation and the Landscape Friday, October 2nd Choose your session: 10am or 3pm
 Drip irrigation is a great way to cut costs on water.
It is also more effective at providing water directly to the root zone of plants.
This workshop discusses the importance of protecting Florida's water resources and will show you how to install a system at home.
Workshop is free but seating is limited; RSVP by calling  259-3520.
Butterfly Garden Expansion Project
 Over several years, the Baker County Extension Butterfly Garden has been spreading its wings and is now soaring to new heights.
Originally planted in 2010 by 4-H members and expanded in 2011 by Master Gardener Volunteers, the garden generates much interest from visitors who enjoy learning about low maintenance plant species that attract butterflies with their colorful flowers.
With over 200 people viewing the garden each year, the need for further improvements was identified by three volunteers who took charge of the project.
Over a one month period, Master Gardeners created their ideal butterfly garden design and each presented their work to the group.
With guidance from the agent, project leaders created a final plan for the garden using features from each of the designs and began preparing the area for the transformation.
While the old garden had approximately 25 plants of 11 species, the new garden features over 100 plants of 28 species and includes both nectar and host plants.
New edging with gentle curves gives the garden a nice shape while easing maintenance for mowers.
Two species of vines now use the chain link fence as a trellis and will one day provide a more attractive backdrop for the garden.
A new stone path guides visitors through the garden allowing for a closer look at both flowers and pollinators, while a stool positioned opposite from a puddling dish serves as an invitation to sit and watch as butterflies stop to take a drink of water.
Butterfly-shaped plant markers compliment the garden theme and help visitors identify plant species.
Looking north, Master Gardener Mary Ann Ray is busy planting the new section of the garden.
Project leaders strategically placed evergreen perennials towards the outer edges of the garden to mask the cold damaged perennials that die back in winter.
The growing number of flowering plants has attracted the attention of many species of butterflies, bees, wasps, and other insects, as well as gardeners.
If you would like to visit the garden yourself, the Extension Office welcomes you.
Just check in at the front office and we'll provide you with a butterfly garden plant guide so you can learn more about the plants you see in the garden.
Looking southwest, the garden now contains flowering perennials planted in masses for added interest.
How To Make A Puddling Station for Your Butterfly Garden
 Water is an important component of a butterfly garden and you can attract butterflies to your garden just by providing a puddling station that collects rain or irrigation water and entices them to stop for a drink.
Butterflies can not drink free-standing water.
Instead they sip liquids and minerals from mud and wet sand through their proboscis.
Therefore, your puddling station should consist of a shallow dish with sand and pebbles to create an ideal landing pad for butterflies.
A large, plastic plant saucer  works great as a dish, as it will hold water longer, enable butterflies to find it easily, and allow room for more butterflies.
Once you've filled your dish with sand you may cover the top with pebbles.
To make your puddling dish more attractive to butterflies, sprinkle a pinch of table salt over the top before adding water, and occasionally add a capful of natural fish emulsion.
An alternative to fish emulsion is to add a thin layer of composted manure or compost to the top.
This creature is known as a Sweat Bee.
Did you know?
"Puddling" or "Puddle-clubs" is when butterflies are seen grouped together around a puddle or muddy area.
These butterflies are "drinking" minerals, such as salt, from the soil.
Most puddling butterflies are males getting the extra nutrients they need for mating.
Males of the species are approximately 11mm long and have a metallic green head and thorax with a yellow and black-striped abdomen.
Females are only slightly smaller and their entire body is a brilliant metallic green color.
These bees cover a wide range: from North Dakota to Maine, south to Texas and Florida.
Where we live, they are most commonly seen from April to October visiting several families of plants in search of pollen.
Flowers that attract them include Aster, Brassica, Coreopsis, Gaillardia, llex, Ligustrum, Prunus, Solidago, Stokesia, Vaccinium, Verbena, and many more.
The male Sweat Bee above was photographed in the Baker County Extension Butterfly Garden while visiting the many Gaillardia plants growing there.
It's Time to Get Your Plants Ready for the Fair!
The horticulture exhibit at the Baker County Fair gives local gardeners of all ages a chance to show off their plants.
Adult and youth entries follow the same judging procedures but are judged separately, and it doesn't cost anything to participate.
In fact, you can earn some cash for each plant you show plus you'll receive a free entrance pass to come see what you've won.
All types of plants are accepted but only qualified entries receive a ribbon and cash prize.
It's easy to qualify, but now is the time to get your plants ready to show.
To qualify: All plants must have been grown by you, and in your possession for at least three months prior to the fair.
All plants must be free from disease and insects.
Other helpful tips: Remember to rotate your plant regularly so that it looks full and symmetrical.
Grooming your plants to remove leaves with holes and dead tips is usually necessary before the show.
Entries: You may enter up to 25 plants, but not more than one of the same cultivar or variety of plant.
Categories include: Flowering/Fruiting , Foliage Plants , Special Display , Bonsai, Cacti & Succulents, Hanging Plants , and Patio Plants.
IMPORTANT INFORMATION FOR HORTICULTURE ENTRIES:
 Judging procedures: If you are intimidated about showing plants at the fair, don't be!
Showing plants at the fair is a fun, learning experience.
Here's how the judging works: Round 1: Judges look at each plant individually, judging it based on health of the plant and general appearance when compared to the standard for that particular plant species.
Plants are awarded a 1st , 2nd , or 3rd  place ribbon and judges may write comments on your entry tag that they believe might help you score higher next year.
Round 2: Judges select plants worthy of an 'Award of Merit' ribbon, and may compare blue ribbon plants to each other since they are looking for plants of exceptional quality.
Round 3: The judges select a 'Best in Show' plant from all the 'Award of Merit' winners.
Premiums for Ribbons: Blue $3 Red $2 White $1 Award of Merit $5 Best of Show $10 4-H Members: Receive an extra $1 premium from Ms.
Shaina
 UNIVERSITY of FLORIDA IFAS Extension Baker County Extension
 Baker County Extension Service 1025 West Macclenny Avenue Macclenny, FL 32063
 UF FLORIDA UNIVERSITY of IFAS Extension Baker County Extension
Grid Sampling Soils to Improve Understanding of Soil Variability
 ariability in soil land landscape characteristics reduces yield response to management techniques, particularly regarding seeding rates and fertilizer additions.
Yield maps provide a spatial map of yield, which can be associated with drainage issues, soil nutrient holding, or nutrient concentrations.
One method to uncover soil variability and crop response is to use precision soil sampling, including either grid or zone methods.
Both increase the cost of taking soil samples, and each have their value depending on the desired outcomes.
For grid sampling, prior work in other states has shown advantages of grids no larger than 2.5-acres, with increased accuracy at 1-acre.
To observed how accurate grids must be on the Delmarva peninsula, the Maryland Grain Producers sponsored a project at the University of Delaware Warrington Irrigation Research farm.
This farm has variable rate pivot and variable rate linear irrigation.
A Veris was used to map soil EC on 90-foot centers , and then the field was sampled on a 0.25 acre grid spacing.
These grid samples match up with the center of our 90 by 90 foot treatment plots, outlined on our center pivot and linear plots.
Soil samples were taken from the upper 8-inches of soil from the center of each grid in April 2022 and submitted to the University of Delaware Soil Testing lab for analyses.
Figure 1: a) Plot layout for the variable rate center pivot  and variable rate linear irrigation  and the b) Veris EC map of the research plots.
The densest sampling scheme  was strongly correlated with soil characteristics and nutrient contents at the next densest sampling of  acres.
The  acre sampling was not as strongly related to 1   or 3-acre sampling schemes, particularly for organic matter and CEC measurements.
This is important, considering that organic matter and the CEC are unlikely to change over the long term, so a more accurate map could last a longer period.
The 3-acre grid  also had moderate to weak correlations to the  and 1   acre grids.
In some cases correlations were not significant , so the relationships to general soil characteristics are again better represented by a denser grid, while nutrients like P and K have moderate relationships based on grid size.
Grid Sampling Average Plot Levels
 Using our 9090 foot plot maps , we averaged soil nutrient levels based on each grid sampling density.
It is important to know that grid density was changed by deleting points from the  acre grids, and different placement of points would also change these results.
For example, the average CEC was greatest based on 1.5 acre grids but was similar across the other treatments.
However, if the sampling point location changes, these averaged may also change.
Organic matter also averaged higher in our plot maps in the 1   and 3-acre grids, but was lower in  and  acre grids.
So in this study, lower resolution  increased OM estimates when averaged across small areas, similar to setting up zones in the field.
There were no differences observed in plot pH based on sample size, but K, Ca, and Mg were all higher in the 1  acre grids, and Ca was lowest in the 3-acre grids.
However, the differences were minor in terms of determining fertilizer application.
Interpolated Maps of Different Soil Properties and Nutrient Concentrations
 Maps of soil properties can be visually striking, without any additional analyses.
When comparing CEC by sampling density , the loss in resolution is clear when you drop to grids above  acre.
On the coastal plain, where CEC can range from extremely low values , accuracy could help with variable rate management of leachable nutrients, particularly potassium in these soils.
Figure 2: Grid sampling for a)  acre CEC, b)  acre CEC, c)1  acre CEC, d) 3-acre CEC.
Green is higher CEC.
Results for soil pH are similar , where pH is most accurate at  density, but with a large loss in resolution when grids reach 1  acres.
What is particularly striking about the pH map for the  grids is the blocked pattern on the lower half of the pivot, following the shape of the research plots, indicating past management.
This pattern is not present in the lower density sampling.
Grid sampling is often described as best at finding past management issues but may miss the smallest details above  acre grids.
The high density sampling also produces the most accurate lime rate map , which has a range of 1-6 tons per acre, based on UD recommendations.
Figure 3: Grid sampling for a)  acre soil pH, b)  acre soil pH, c) 1  acre soil pH, d) 3-acre soil pH.
Blue is higher pH.
Figure 4: Estimate lime rates  based on University of Delaware recs.
The  acre grid had similar relationships to the  in both nutrient correlations and plot average extractions.
This project reveals interesting patterns and corroborates that grid sizes should be less than 2.5 acres, and preferably less than an acre.
Future analyses will include the response to variable rate lime and K application, as well as variation in micronutrients.
When properly calibrated, soil water sensors can give irrigators an accurate measurement of how much water is currently available, and how much has been depleted, in the soil for the crop.
When used along with weather data and crop water use data, this accurate measurement of soil water can help irrigators make a more informed decision on when irrigation should start, how much to apply, and when to quit irrigating.
When looking at sensors, be sure to have an understanding of soil water content and how they actually measure soil water.
State law requires an applicator who does not recertify their license before it expires to retake  their certification exams to regain a valid license.
Predicting how much rain the field will receive is difficult, but if you do not plan for the possibility of rain, it is easy to apply too much irrigation water.
Figures 2 and 3 show the long-term weekly average rainfall for August and September in Nebraska.
Concrete Pipe Irrigation successful water distribution systems can be improved further by more adequate designs and installations
 Plain concrete pipe systems carry most of southern California's irrigation water but still can be improved in design and installation.
Improvement is possible in four general areas: water regulation can be simplified; expansion and contraction failures reduced; concrete qualities improved; and hydrant capacity increased.
The widely used open systems on steeper slopes have been unsatisfactory because of surge problems, regulation difficulties, inflexibility of deliveries, and the necessity of providing for tail water wastage.
It is doubtful whether any opentype system will ever be fully satisfactory where grades are steep enough to require drop structures.
The alternative is to design a semiclosed system, with float valves replacing the overpour features of the periodic stands of the open system.
Semi-closed float valve systems on farms, though limited in number, have proved their value on the steeper slopes.
There is no tail water; pressure and rate of flow is always controlled; any change in any portion of the system causes completely automatic adjustments all the way upstream; and pressures are kept within the allowable limits for plain pipe.
Concrete pipe is well on its way to supersede use of canals and ditches on new district systems, and drop structures will be common.
The semi-closed system-untried for district distributionshould be given a thorough trial before such design proceeds further.
It would give the farmers much more flexibility in handling the water and should result in higher application efficiencies.
The fact that wet concrete expands and drying concrete contracts has a vital effect upon pipe.
When pipe is moistened after laying and backfill, longitudinal or axial wetting expansion is almost completely restrained.
Compressive stresses develop, which are partially the cause of pipe ripping.
Experiments in a testing machine proved that failure from axial stresses invariably took the form of longitudinal cracks.
Open pot hydrants being installed for a future vineyard.
These hydrants permit small flows in single furrows along each side of the row.
The vines will soon require that more soil area be wet.
A new water supply is available but it contains almost four times the concentration of salines.
The farmer must flood in strips almost 10 feet wide to control salinity.
For this, the open pot hydrants are inadequate.
But longitudinal wetting compression would not alone cause ripping.
Accompanying it are bending stresses set up by differences in wetting around the circumference of the pipe.
Such circumferential bending stresses account for the rips being in the top and sometimes also in the bottom of the pipe, and for the fact that large pipe sizes are more susceptible to failure than smaller sizes.
Axial compression tends to reach a peak in about two weeks after wetting, and circumferential stresses apparently after a much shorter period.
Also, no possibility can be foreseen that pipe once laid and covered can ever be as dry as before laying.
Therefore, rips probably always occur within a few days to two weeks after laying.
Lines may rip before water is turned in.
The moisture to cause expansion then comes from the joint mortar or from moisture in the soil.
Moisture in the soil probably is transferred in the vapor phase.
This possibility was investigated by measuring length changes in concrete pipe placed in a constant temperature room where relative humidity could be varied between 32% and 100%.
The results showed that rate of length change increased with increasing humidity.
Humidity was increased in steps, one following immediately after the
 other, then decreased in one big step, after which the pipe was immersed.
Expansion was much more rapid with immersion but it can be estimated that expansion from a single jump change in humidity-as from 45% to 95%-might have been at about one third the immersion rate.
Obviously relative humidity has a marked effect on expansion.
When weather is dry just prior to laying, and the initial backfill soil is dry, pipe will be subject to excessive wetting expansion.
If any moisture is present, it will probably be around the invert where there is more joint mortar, and in the trench bottom soil.
These are prime conditions favoring ripping.
Effect of Cold Water
 Pipe systems often develop bad leaks when cold water is run through them in winter.
Usually the breaks are circumferential cracks caused by thermal contraction, but a few are old rips that previously did not open up.
Contraction leaks appear more serious where the pipe line is empty and was dried out prior to being filled with cold water.
Because of danger of such leaks, as much longitudinal compression as possible should be retained in a line.
Low temperatures will then merely tend to relieve this thrust rather than to open up cracks.
There is one more condition which affects expansion and contraction: the drying out caused by a draft of air circulating through a line.
Experiments showed that the intrados-inside surface-dries quickly, and that the extrados-outside surface-also dries and
 Continued on page 12
 Two types of stands which, on small farm systems, have been fairly successful in eliminating surges by giving the air more opportunity to escape.
PIPE Continued from page 3
 shrinks, even when it is in contact with somewhat moist soil.
Generally, rips and cracks can be largely prevented by always using moist soil for the initial backfill, following two to five lengths behind laying; designing systems so that air can not circulate through the pipes, and preventing air circulation during installation; and constructing all stands before the pipe is laid, and tying the pipe into such structure promptly after laying.
Prompt filling of a new line with water is also desirable to prevent cracks.
General experiences and experimental studies point to the importance of density in concrete toward making for permanence.
Even if high strength is not needed in thin shelled plain concrete pipe, emphasis should be placed on high quality-density and imperviousness.
Good grading of the mix, good compaction, and good lubrication of the mix-possibly through air entrainment-are important.
Farmers can use the absorption test to check the quality of pipe they are purchasing.
Simply, in this test a fragment of pipe is boiled five hours in water, weighed wet, then dried to constant
 Orchard valve hydrants-left-are commonly installed where alfalfa valve hydrants-right-should be installed for flooding irrigation.
With the same size riser, the latter may permit almost three times the maximum flow of the former.
weight in a 110 C oven.
The weight loss should not exceed 8% of the dry weight.
Experiments showed that this simple test correlates absorption with bulk density of the concrete.
Of the two common hydrants for flooding irrigation, the alfalfa valve and the orchard valve type, the latter is neaterthere is less erosion around the hydrant.
However, this hydrant may have as little as one third the capacity of the alfalfa valve type of comparable size.
If the alfalfa valve is placed low-several inches below the soil surface-erosion is usually not too severe.
In easily eroded soils old tires or a short length of larger pipe can
 be buried around the hydrant and provide protection.
Normally, the entire capacity of the pipe line should be available from each hydrant, and it would be shortsighted and false economy to underdesign hydrants.
Large capacity is becoming increasingly important as the trend is away from furrow and toward flooding irrigation to provide more water and avoid salinity problems.
In arid regions rainfall is often inadequate to accomplish sufficient leaching, so irrigation must be used to control salinity.
A.
F.
Pillsbury is Associate Professor of Irrigation, University of California College of Agriculture, Los Angeles.
The above progress report is based on Research Project No.
860.
Continued from page 6
 more mature the legumes-higher in moisture than the grasses-increased proportionately as the clippings became less frequent.
This about offset the expected differences in dry matter with increasing maturity.
The protein percentage was highest in alfafa-grass mixtures, lowest in the trefoil-grass, with ladino ranking in between.
All mixtures showed a considerable decline in protein content as the clipping intervals became greater.
This is not too significant because even the
 lowest protein percentage for the infrequent clippings is large enough to supply far more than the requirements of the grazing animal.
As the drop in protein percentage is associated with an increase in fiber content, the digestibility of the feed may be lowered.
The question of how far yield should be sacrificed to increase quality is still unanswered.
It is not known at this time how livestock will gain under a rotation scheme which allows a considerable amount of topgrowth.
The concentration of enough stock on each pasture to graze it down quickly
 and evenly is an essential part of a rotation grazing system.
If grazed down too slowly, much of the pasture's grass will be trampled and fouled by manure droppings.
Overgrazing will reduce pasture yield; undergrazing will permit some of the grass to become more mature, and this will result in losses in feed quality and livestock gain.
M.
L.
Peterson is Assistant Professor of Agronomy, University of California College of Agriculture, Davis.
The above progress report is based on Research Project No.
1407.
Clover grazed at intervals of four or five weeks will attain a height of 12 to 15 inches.
The stake in the picture is 15 inches tall.
T HETEMPERATURE OF WATER released from large reservoirs is of concern to irrigated agriculture in California as well as other parts of the world, including Japan and northern Italy.
Water is usually released from the bottom of the large, deep reservoirs, where the temperatures are low throughout the year At Shasta Dam in California, the temperature of reservoir water averages 45 F at the outflow.
The completion of such large reservoirs can cause a major change in the water temperature of the rivers downstream.
pipeline distribution systems, especially when used alternately with warmer water.
Water sports are also adversely affected by cold water.
Warm-water gamefish are less numerous, but salmon and other fish preferring cooler water may increase.
The influence of low water temperatures presently concerns agriculture along the Sacramento River downstream from Shasta Dam.
Similar problems, perhaps on a more intensive basis, were predicted downstream from Oroville Dam on the Feather River.
Possibly some portions of the area to be served by this water in the
 EFFECTS OF IRRIGATION ON SOIL AND CROP
 The effects of this colder water, as San Joaquin Valley will also be affected.
observed in recent years, have included a As the result of experience gained in decrease in rice yields in the Sacramento the operation of Shasta Dam, plus measValley-primarily in fields directly irriurements of water temperatures in the gated from large irrigation canals.
Cold Feather River System and its service area, water may also be beneficial, however, and information on possible detrimental especially when used to cool soils planted effects from releasing cold water, the to crops sensitive to high soil temperaState Department of Water Resources is tures at certain stages of growth.
Cold building a multi-level inlet structure for water can be detrimental to underground Oroville Dam.
This will permit some con-
 P.
J.
WIERENGA ROBERT M.
HAGAN
 Graph 1.
Air and soil temperatures measured before, during, and after irrigation of alfalfa-at 40 ft from the intake in two parallel border checks.
Temperature of irrigation water was 52F during irrigation of border check 1 and 56F during irrigation of border check 2.
trol of the temperature of outflow water.
For optimal use of this multi-level intake structure, more complete information on water temperature requirements for rice and other crops grown in the service area is needed.
The possible extent and effects of delivering cooler irrigation water to areas of the San Joaquin Valley will also need more complete study.
Investigation should also be made along the western part of the Sacramento Valley-which will receive relatively cold water from Shasta Dam through the Tehama-Colusa Canal.
Information gained about water temperatures from reservoirs in the Sacramento Valley also raises the question of whether water discharged from reservoirs along the east side of the San Joaquin Valley may be cold enough to influence crop production there.
DAY July 31 August 1 August 2 August 3
 Since 1962, the Department of Water Science and Engineering at the Davis campus has cooperated with the State Department of Water Resources in their measurements of the water temperature in the Feather River, and in canals of the Feather River service area, using 12 thermograph stations along the principal distribution canals.
Data now available show that daily maximum and minimum temperatures, when averaged over five-day periods, fluctuate for all stations in the service area.
This is due apparently to changes in weather conditions and in the rate of flow of water in the canals.
Although there is no well-defined relationship between the gain in water temperature in the district canals and the distance
 COLD WATER TEMPERATURE GROWTH
 Limited studies with water temperatures, as reported in this article, indicate soil temperatures are reduced for short periods of time with possible effects on yield where crops are irrigated frequently with cold water.
Graph 2.
Per cent decrease in yield of Red Kidney beans given periodic cold treatments  for 72 hours, compared with control plants at a constant soil temperature of 77 F.
from the intake on the Feather River, the average monthly gain in different canals ranges from 0.05 F to 1.0 F per canal mile.
Thus, the average increase in temperature of water flowing through district canals may be as low as 0.5 F per 10 miles of canal length or as high as 10 per 10 miles of canal.
These differences in temperature increases are caused mainly by differences in canal dimensions and flow rates.
rate and at a relatively high initial soil temperature, a drop of 9 F was recorded at the 24-inch depth.
Very little information has been available on changes in soil temperatures resulting from irrigation.
To obtain such information, a soil temperature measurement program was set up in the Anderson Irrigation District south of Redding, where the irrigation water temperature averages a low 50 to 55 F the year around.
Fields planted to alfalfa, mixed pasture, and corn were selected.
Soil temperatures were measured and recorded at hourly intervals with thermocouples at 0, 4, 12, 18 and 24 inches below the soil surface and located 20, 40, 80, 160 and 320 feet from the head ditch.
A typical set of soil temperature data taken during irrigation of an alfalfa field is given in graph 1.
From these, and other soil temperature data, it was found that at 4-inch soil depth the temperature drops to within 2 to 3 F above that of the applied irrigation water.
Changes in soil temperature due to irrigation decreased at lower depths.
At the 24-inch depth in most soils, these changes were minor-usually less than 3 F.
However, in a dry, sandy-loam soil with a rapid infiltration
 Changes in soil temperature were generally of short duration.
Within 24 hours after irrigation, the soil temperature at the 4-inch depth tended to return to its pre-irrigation level.
Temperature changes at greater depths persisted longer.
At least 48 hours were required to regain the original temperature level at the 12-inch depth.
The warming of the irrigation water as it moved down the field caused the soil temperatures to drop less at 320 feet from the head ditch than close to the water intake on the field.
The extent of changes in soil temperature caused by irrigation was found to depend upon many factors in addition to the water temperature-including the amount of irrigation water applied, soil type, distance from the irrigation ditch, and time of day.
The influences of these factors on resultant soil temperatures have not yet been evaluated.
More detailed laboratory studies are underway to provide information that may allow prediction of changes in soil temperature.
gave more reliable results than the thermographs.
These and earlier experiments were conducted using either thermographs, or thermocouples and a multipoint recorder for measuring soil temperatures.
Thermographs must be properly installed and frequently calibrated, preferably in place.
The thermocouple system proved to be very useful for field measurements and
 The effects of lowered soil temperatures on plant growth were studied in greenhouse experiments set up to simulate the effects of irrigation with cold water under field conditions.
Previous studies of Caloro rice showed that it matured only when water temperatures remained above 70F.
In later greenhouse experiments, it was reported that a drop in root temperatures from 77 to 59F for a period of only five days had a depressing effect on yield of Caloro rice, particularly when the low temperature occurred during tillering and flowering.
Some interaction between changes in soil temperature and rate of fertilization was also observed in these previous studies.
Increased phosphate fertilization in some cases minimized the detrimental effects of a lowered soil temperature.
Studies with beans were started in the summer of 1964.
Red Kidney and Sutter Pink beans were grown at constant soil temperatures of 59, 68, 77, 86, and 95F.
Yields of shoots and roots increased gradually with increasing soil temperature reaching a maximum of 86F for shoots and 77F for roots.
Yields decreased sharply at root temperatures above the optimum values.
In a subsequent experiment, Red Kidney beans were grown at a constant soil temperature of 77F.
At various stages of the growth cycle, the temperature of the soil was lowered to 50F for three days.
The yield of shoot and root material was
 decreased by 17% when plants were given a single cold treatment early in the growing cycle  and by 14% when chilled at the 6-leaf stage.
Lowering the soil temperature at the 9-leaf stage did not affect vegetative growth, but the yield of beans was 15% below that of the plants grown at a constant 77F soil temperature.
Repeated cold treatments-lowering root temperature for three days carly in the growing cycle  and during two additional 3-day periods at 10-day intervalscaused the greatest yield reductions 
 The effect of cold water on crop growth was also studied under field conditions.
Plots of undisturbed soil 3 ft X 3 ft were insulated from the surrounding soil by rigid foam walls 2 inches thick and 20 inches deep.
Red Kidney beans and pickling cucumbers were planted in two successive experiments.
Treatments consisted of irrigating with water of 50, 59, 68, and 77F for beans and of 41, 50, 59, and 68F for cucumbers.
Resulting differences in soil temperature patterns between treatments were minor, however, due to warming of the irrigation water on the soil surface before infiltration.
No significant differences in growth or yield of shoots or fruit were found between treatments, indicating that possible shock effects of cold irrigation water may not be very important.
Because of the slow infiltration of the irrigation water into the soil in this experiment, and the resultant warming of the water, extrapolation of these field plot data to predict effects on yield under field conditions must be done with caution.
These temperature studies were too limited to provide general conclusions.
However, results indicate that yields of crops other than rice may also be reduced under field conditions, particularly if each of frequent irrigations with cold water causes an appreciable lowering of the soil temperature for several days.
On the other hand, certain crops (including
 Peter J.
Wierenga is Postgraduate Research Water Scientist, and Robert M.
Hagan is Professor and Irrigationist, Department of Water Science and Engineering, University of California, Davis.
This research has been supported by the University of California Water Resources Center under contract with the California State Department of Water Resources.
potatoes, lettuce and strawberries) have been reported to benefit from a decrease in soil temperature.
Both detrimental and beneficial effects would presumably de-
 Penalty for private use to avoid payment of postage, $300 University of California Division of Agricultural Sciences, Agricultural Experiment Station.
Berkeley, California 94720 c.
7.
Killy Director Free--Annual Report or Bulletin or Report of Progress Permit No.
1127
 pend on type of crop, on the stage of growth at the time cold water is applied, and on what part of the plant is to be harvested.
DONATIONS FOR AGRICULTURAL RESEARCH
 Contributions to the University of California, Division of Agricultural Sciences
 California Cedar Products Company	$ 500.00
 Forest Products Laboratory research in wood machining
 Chemical control of plant pathogens-entomological
 L.
R.
Hamilton, Inc.
500.00
 For continuing research on integrated control of
 Penick Company	Ryanicide  100
 For field tests against oriental fruit moth
 The Upjohn Co.
$2,500.00
 To continue support in plant pathology for
 Vincent B.
Zaninovich & Sons, Inc.
500.00
 For continuing research on integrated control of
 Peter A.
Ekstein Original drawings of a dairy complex For Agricultural Engineering
 Arthur Korpela $ 25.00 Sheep foot rot research in animal husbandry
 Lake County Pear Association 500.00 For pomology research on Lake County pear orchards
 Mr.
Mervyn LeRoy Services of Thoroughbred stallion For animal husbandry research
 Major C.
C.
Moseley Services of Thoroughbred stallion For animal husbandry research
 American Cocoa Research Institute $2,500.00 For study of Phytophthora palmivora in relation to black pod of cacao.
Chevron Chemical Company-Ortho Division 2,500.00 To study effects of spray oils on citrus insects; yield, quality of citrus fruits For research in control of vegetable crop insects 1,000.00 For study of control of stored product insects 750.00 Eli Lilly and Company 1,500.00 In support of studies on control of postharvest decay in citrus fruits
What Is a Wireless Sensor Network?
Clyde Fraisse, Janise McNair, and Thiago Borba Onofre2
 A wireless sensor network  is a system designed to remotely monitor and control a specific phenomenon or event.
WSNs are mostly used in agriculture to monitor environmental conditions and control irrigation.
The WSN has the following advantages over traditional stand-alone sensors and controllers.
Site specificity: Sensors can be positioned close to production fields.
Target specificity: Network nodes can be customized to monitor only the variables of interest, reducing the number of sensors deployed and the cost of the network.
High spatial resolution: Multiple nodes can be used to increase the number of sensors and controllers per unit area.
WSNs consist of nodes, routers, and a gateway.
There are two types of nodes: sensor nodes  and actuator nodes .
Routers are used to extend the communication range or circumvent an obstacle.
The gateway is the device that allows the management  of the network and aggregates the information received from the nodes to send real-time or near real-time data to a user platform.
When the gateway is connected to a local laptop, the user can locally control and monitor the WSN.
Adding a
 cellphone modem or an Internet modem to the gateway guarantees remote management.
Figure 1.
WSN components.
Credits: Thiago Borba Onofre, UF/IFAS
 Power Consumption and Conservation
 When a sensor node or a router runs out of power, it will disconnect from the WSN and negatively impact the application.
In order to extend the network lifetime, energy conservation techniques must be used.
Solar panels are the most popular solution for recharging the batteries of WSN components.
Another approach to save energy is a technique called sleeping, which allows nodes, routers, and gateways to sleep during their idle times.
The gateway is important because it coordinates the communication aspect of the WSN as well as its sleeping protocol.
At a given time, the gateway wakes up nodes and routers.
Data are exchanged, and then the nodes and
 2.
Clyde Fraisse, associate professor, Department of Agricultural and Biological Engineering; Janise McNair, associate professor, Department of Electrical and Computer Engineering; and Thiago Borba Onofre, PhD student, Department of Agricultural and Biological Engineering; UF/IFAS Extension, Gainesville, FL 32611.
routers go back to sleep.
Sleeping is necessary for WSNs to save power.
A sensor node generally spends 90% of its time sleeping.
A communication protocol defines the rules of how data are exchanged.
The most popular communication protocols for WSNs are Wi-Fi, Bluetooth, and ZigBee.
Wi-Fi is excellent for data exchange and is ideal where the power supply is not a problem, like in household devices.
Bluetooth is also popular and is present in many battery-powered devices, such as watches, mice, keyboards, and other electronics.
Bluetooth is a good option with low power consumption, short communication range, and high data rate.
ZigBee requires even less power than Bluetooth and has a longer communication range, but it is quite slow.
ZigBee would not be suitable for surfing the Internet or transmitting photos from a wireless camera, but it is well-suited for transmitting data from sensors in a field.
In a very fast data-logging event, sensors and controllers usually report a simple dataflow  each minute.
Table 1 summarizes the three technologies accordingly with communication range and typical applications.
ZigBee radios can operate at 2.4 GHz, 900 MHz , and 868 MHz , while Wi-Fi and Bluetooth operate at 2.4 GHz.
The lower the radio frequency, the larger  the communication range.
For example, commercial wireless radios that use the ZigBee protocol operating in 900 MHz can communicate up to 14 miles , while the 2.4 GHz radios have a communication range of 650 meters .
Increased water vapor in the atmosphere during rainy or foggy days as well as in metal structures such as cars and buildings negatively impacts the communication range, resulting in temporary network communication failure.
This happens because water and metal absolve, reflect, and attenuate wireless waves.
Routers must be used to overcome these obstacles and guarantee a successful signal link between gateways and nodes.
Table 1.
Wireless technologies comparison.
A good WSN design will provide the gateways with smooth Internet connectivity.
A dependable range of communication is essential to establish and maintain autonomy within the WSN.
If communication is lost due to power failures in the nodes, the WSN has self-healing and self-organization capabilities, which guarantee an autonomous setup once power is reestablished.
This can provide researchers and decision makers with better real-time data quality to make in-time crop management adjustments, saving natural and economic resources while increasing production efficiency.
WSN technology has a vast potential to improve resource use efficiency, irrigation management, and frost protection in agriculture and facilitate site-specific weather monitoring as well as monitoring of plant disease risk levels.
Step 1: Based on the current crop growth stage , look up the approximate days to maturity in column 3 and the water use to maturity in column 4.
Step 2: Add the approximate days to maturity to todays date to estimate the crop maturity date.
Step 3: Subtract the water use to maturity from the remaining available water.
If the number is positive, it indicates adequate soil water to mature the crop; however, if the number is negative it indicates the additional amount of water the crop will need from rain and irrigation to reach maturity.
Chapter 8: Corn Seeding Rates in South Dakota
 Optimum seeding rate depends upon the variety, the yield potential, the grain selling price, and seed cost.
Generally, seeding rates increase with rainfall and yield expectations.
Optimal corn target populations in South Dakota vary from ~ 15,000 to 36,000 plants per acre.
Highly productive soils with sufficient drainage and available water can support higher populations.
New corn planters provide the option to vary the seeding rate across the field.
This chapter provides directions for calculating a seeding rate and guidelines for optimizing seeding rates are provided in Table 8.1.
Table 8.1 Guidelines for optimizing seeding rates:
 1.
Set seeding rates higher than target population to account for less than 100% germination and seedling mortality.
Different tillage systems may have different germination rates.
2.
Match the seeding rate to your yield potential.
3.
Increase seeding rate by = 2000 seeds/acre in no-till systems.
4.
Increase the desired populations by approximately 10% for silage crops.
5.
Consider seeding lower populations in lower-yielding areas and higher populations in more productive areas.
The optimal seeding rate for corn grain production is ultimately determined by the interplay of nutrient and water availability and competition between the developing plants.
The relationship between corn yield and plant population follows a nonlinear response and generally yield increases with population until it levels off.
At this point, additional increases in population can reduce yields.
The economic optimum rate is the point where seed inputs equal the economic increase in yield.
Yield decreases at very high population levels may result from increased lodging or increased yield reductions resulting from increased abiotic  and biotic  stressors.
Determining the Corn Seeding Rate
 Determining the Ratio Between the Seed Cost and Commodity Price
 1000 kernels and the selling price per bushel is 0.94.
This value when combined with the yield response function and expected yield is then used to calculate the seeding rate.
Table 8.2 The ratio between the cost of seed and the value of corn as a commodity.
Seed Cost 
 200.00	250.00	300.00	350.00
 Seed Cost 
 2.50	3.13	3.75	4.38
 Corn Commodity Price 	Ratio of Seed Cost to Commodity Value 
 3.00	0.83	1.04	1.25	1.46
 4.00	0.63	0.78	0.94	1.10
 5.00	0.50	0.63	0.75	0.88
 6.00	0.42	0.52	0.63	0.73
 7.00	0.36	0.45	0.54	0.63
 Estimating the Yield Potential
 Corn yields are a function of many factors, including the location in a field and where the farm is located in the state.
In many fields, yields routinely vary across the field.
Topography has a large effect on yield in a relatively short distance.
To account for this variability, seeding rates can be selected for the whole field or portions of the field.
When selecting a single rate, planting a high population in the lowest-yielding areas can reduce the yields, and planting a low population in the highest-yielding areas can result in lower yields.
The analysis of yield monitor data can provide information needed to account for this variability.
When selecting a yield, it is important to consider regional variability.
Yield generally decreases from east to west across South Dakota.
This variability is predictable.
For example, in the east-central region, the average yield was 162 bu/acre in 2014, whereas in the west-central region of South Dakota the yield was 81 bu/acre.
Figure 8.1 Corn yields in a South Dakota field in 2006 
 Table 8.3 Average regional corn yields in 2014 in South Dakota.
The South Dakota regions were southeast , east-central , northeast , south-central , central , north-central , southwest , westcentral , and northwest.
SE	EC	NE	SC	C	NC	SW	WC	NW
 165	162	156	102	132	145	99	81	91
 Determining the Seeding Rate
 Once the cost-to-return ratios and yield potentials are calculated, the optimum plant population can be determined based on data provided in Table 8.4.
The seeding rate is then determined by accounting for germination.
For example, if the optimum seeding rate is 29,000 plants per acre, then the seeding rate should be 32,000 plants per acre  if the germination rate is 90%.
Table 8.4 The optimum plant population based on ratio between seed cost and selling price of corn and the yield estimate.
The cost of seed/seed cost per bushel is provided in Table 8.2.
These seeding rates need to be adjusted for the germination rate.
The seeding rates were based on coefficients developed using the equation: seeding rate = [1000.yield.
A ].
The coefficients for this equation are provided.
The values of n and A are defined below.
$ cost seed/$ per bu
 0.5	0.75	1.0	1.5
 coefficient	n	A	n	A	n	A	n	A
 -0.00383	0.377919	-0.00357	0.346804	-0.00329	0.316176	-0.00261	0.256593
 Optimum planting rate /acre
 50	15.6	14.5	13.4	11.3
 100	25.8	24.3	22.8	19.8
 150	31.9	30.4	29.0	26.0
 200	35.1	33.9	32.8	30.5
 250	36.2	35.5	34.8	33.4
 Defining Seeding Rates Based on Soil Characteristics
 Seeding rates can also be defined using soil characteristics.
Generally, highly productive soils with adequate drainage and available water can support higher populations.
In the drier, western portion of the state, hybrids with a longer maturity rating  are a risky choice.
A rule of thumb is that 1 inch of rain is needed for a four-day increase in hybrid maturity.
For example, a hybrid with a relative maturity of 100 days would require 3 additional inches of water than an 88-day hybrid.
In South Dakota, 8-11 inches of water is the minimum requirement to produce a corn crop.
Table 8.5 Relationship between the yield potential and soil characteristics on the target population in notilled and tilled systems.
Influence of soil type and yield potential on target population and seeding rate.
These calculations were based on corn seed selling for $240/bag and corn grain selling for $6/bu.
Yield potential by soil type		Target population	
 High Yield Potential 
 deep loams	33-35	35 37	34-36
 Moderate Yield Potential 
 clays sandy loams	27-29	30 32	28 30
 well-drained to moderately well-drained
 Low Yield Potential 
 somewhat poorly drained to poorly	19-22	21-24	20-23
 1 Increase population by 10% for silage corn.
Corn Hybrid Specific Responses
 Different corn hybrids have different yield VS.
plant population responses.
When possible, use hybridspecific information.
Over the past 50 years, genetic changes have produced plants that have the capacity to increase yields in response to intense crowding.
However, in response to increasing populations, per plant yields are lower.
Lower per plant yields with increasing
 population are the result of the down expression of many critical genes.
A plant's ability to respond to increasing crowding generally decreases as the plant matures, which in turn accounts for corn's weed-free period.
Hybrids are being developed with improved water-use efficiency.
Many of these hybrids increase yields only under water-stressed conditions.
These hybrids have been developed using traditional and transgenic techniques.
The impact of improved water-use efficient hybrids on South Dakota seeding rates has yet to be determined.
Example 8.1 Use the data in Tables 8.2 and 8.4 to calculate the economically optimum seeding rate if corn is selling for $5/bu, the desired yield is 200 bu/acre and a bag of seed costs $300.
From Table 8.4 the optimum plant population is 33,900 plants/acre.
If the germination rate is 95%, then the germination-adjusted seeding rate should be 35,700 seeds/acre.
Corn Seeding Rate for Silage
 Generally, corn-seeding rates are 10% higher for silage than grain seeding rates.
It may be possible to increase silage yields further by planting narrow rows.
See Chapter 18 for more information.
The conference, scheduled for Monday, May 8 to Thursday, May 11, at Nebraska Innovation Campus in Lincoln, will focus on innovative ways to improve water and food security by increasing farmers resiliency to a changing landscape.
A discount of $100 is available to those who register on or before March 13.
Conference details, including how to register, are available here.
VARIABLE RATE IRRIGATION ON CENTER PIVOTS.
WHAT IS IT?
SHOULD I INVEST?
B.
Molaei, IAREC, Washington State University
 M.
Flury, Professor, Ph.D., Washington State University
 Variable rate irrigation , also sometimes referred to as 'precision' or 'site-specific' irrigation, is the ability of an irrigation system to apply different amounts of water to different areas of the field.
This paper discusses the various VRI options for center pivots, when they might save water, energy, or create higher crop yields, and when it might be unreasonable to expect these kinds of improvements.
Some of the remaining challenges associated with VRI are discussed, and a simple soil-water balance model is used to illustrate water savings estimates from various soils and how VRI might be used to take advantage of significant, in-season rainfall events.
Variable Speed Irrigation vs.
Variable Zone Irrigation
 Recently center pivot manufacturers and some third-party equipment dealers have been offering variable rate irrigation  as an option or upgrade on their pivots in a couple ways: variable speed irrigation, and variable zone irrigation.
Variable Speed Irrigation often does not require additional hardware on the pivot.
It simply uses a more sophisticated control panel that will slow down or speed up the pivot to apply more or less water in different areas of the field.
Many of the newer pivot control panels already have this ability built into them.
After-market solutions from third-party equipment dealers usually mount on the last tower of the pivot, have an integrated GPS receiver to determine field position, and interrupt and re-send the movement control signal to the last tower to vary the speed of the pivot in different areas of the field.
Despite variable speed irrigation's obvious limitations to apply only in pie-shaped wedges , variable speed irrigation is fairly low cost  since the only modifications to the pivot are to the pivot electronic controls.
These costs will likely decrease over time.
The overall pivot flow rate remains constant.
Some additional useful applications for variable speed technology:
 On pivots that are not full circles  it is possible to vary the speed going into or coming out of the hard stops  to avoid running the pivot in overly wet areas in an attempt to reduce wheel-tracking issues.
For example: if the wiper is applying 0.5 inches in a pass , the pivot might speed up to apply 0.2 inches of water in the 20 degrees of angle before the hard stop SO the field stays drier.
Then after reversing, slow down to apply 0.8 inches until it reaches the 20-degree mark again where it speeds up slightly again to return to applying 0.5 inches.
In areas of the field where infiltration is an issue due to tight soils or steep slopes, it is possible to speed up to wipe back and forth across that area of the field to allow additional time between water applications for water to infiltrate and move deeper into the soil before water is again applied to the surface.
For example: If there is always runoff on a slope between 20 and 40 degrees, and the grower is applying 0.75 inches of water in a clockwise rotation, the pivot could speed up at 20 degrees to apply 0.25 inches over the trouble spot, then reverse at 40 degrees to apply 0.25 inches, travel back to 20 degrees where the pivot would again reverse to apply 0.25 inches.
The pivot would then slow down at 40 degrees to apply 0.75 inches to the rest of the field.
The same total amount of water was applied to the trouble spot, but the back-and-forth movement gives more time between water applications for the water to move into the soil in that spot hopefully increasing infiltration and reducing runoff.
Pivot tires sometimes slip slightly when climbing hills or when going down steep slopes.
This makes the pivot panel think it is moving further than it is.
The pivot speed can be altered slightly to account for the difference in tire rotations compared to actual ground travel speed.
Variable Zone Irrigation includes the ability to vary the speed of the center pivot as it moves in a circle and vary the application rate along the pivot lateral.
Variations in the application rate along the lateral works in conjunction with variations in the pivot speed creating the ability to apply a wide variety of irrigation depths to different areas of the field.
The
 application rate along the lateral is usually varied by pulsing sprinklers on and off for various amounts of time.
In some cases, zones of sprinklers are controlled independently, in other cases every sprinkler is controlled independently.
Because additional hardware must be mounted on the pivot, and it requires a more sophisticated control technology, variable zone irrigation is significantly more expensive than variable speed irrigation.
These costs will also likely decrease over time.
Variable zone irrigation is much better at responding to the spatial variations in the field.
Turning sprinklers on and off varies the overall flow rate of the pivot.
Therefore, a water delivery system that can absorb these variations is necessary.
Is It Worth It?
Is variable rate irrigation right for your pivot?
It depends.
The upfront costs of VRI, especially variable zone systems, can be substantial.
The ongoing management costs can also be high.
In many cases, modifying the management of existing soils can eliminate the perceived need for VRI.
On the other hand, in certain instances it may save substantial amounts of water in the long run.
A discussion of when water savings should and should not be expected follows.
Variable Rate Irrigation in Response to Variable Soils
 The water use of healthy crops with access to sufficient water and nutrients will not be significantly dependent on what kind of soil they are grown in.
Crops grown in sandy soils will not use significantly more or less water than crops grown in silt or clay soils.
So, for example, even in a field with highly variable soils, all areas of the field will be using 1/4 inch of water every day.
Because of this, applying different amounts of water to different areas of the field only makes sense if the crops are getting water from another source besides where the center pivot irrigation system is applying it, or if the crops are using less water in some areas of the field due to disease or pest pressure.
More discussion on this follows below.
"I apply more water to the sandier areas of my field during each irrigation.
Sandy soils do not need more water.
They cannot hold the extra water.
If they are watered more each time, then the additional water will be lost to deep percolation.
They need to be watered in smaller amounts more frequently.
Because of this, if the entire field is managed as a whole to prevent water stress and water losses to deep percolation in the sandy areas of the field then all other areas of the field will be fine.
Figure 3.
Soil serves as a reservoir for water and nutrients.
The size of the reservoir depends on the soil's water holding capacity , and the rooting depth of the soil or crop.
Irrigation or precipitation that infiltrates into the soil when there is space in the soil to hold that water is stored for later use by the crop.
If more water is applied to the soil than the soil can hold, then that extra water is lost  out the bottom of the root zone.
Crop water use, or evapotranspiration , is largely independent of the soil type.
Figure 4.
If the same field has areas that are both silt and sand, then if they both started full, then after a given amount of time the sandy areas will be getting dry and exhibiting crop water stress, while the silty areas will appear fine.
If the entire field is managed for no stress, or no water losses to deep percolation in the sand , then the silty areas will also be fine.
If more water is applied to the sand when refilling the soil, that additional water will be lost to deep percolation.
"I have runoff on the steeper slopes, and the crop is water stressed in that area of the field so I apply more water to those slopes.
If water is already running off a slope, applying more water will result in all of the additional water also running off, possibly causing erosion, and that additional runoff water may pond in the low spots of the field, making the overall irrigation and crop uniformity problems in the field worse.
If the water is running off, then less water, not more, needs to be applied to slopes in a pass to ensure that the applied water infiltrates into the soil.
But to ensure that these areas of the field do not fall behind the rest of the field, this means speeding the pivot up on the entire field as spatial variation would result in these areas falling permanently behind.
The "wiping" method described above can help to reduce or eliminate runoff.
As an alternative to speeding the pivot up, or as an additional runoff-prevention measure, runoff in these steep sloped areas can be mitigated by changing the tillage methods, and possibly the crop row orientation.
Modifying the sprinkler system SO that it applies water at a slower rate can also help improve infiltration.
This might include physically offsetting every-other sprinkler to spread the sprinkler pattern out using boombacks  or draping every other sprinkler around the outside of the truss rods , or using sprinklers with a much larger wetted radius.
If the soil is hydrophobic  then using soil surfactants may also help with infiltration.
Because of these things, in low rainfall areas purchasing VRI in response to highly variable soils has little opportunity to increase profitability in comparison to optimally managing the entire field uniformly for the problem soils.
Situations Where VRI can Conserve Water and Improve Profitability
 Avoid Irrigating Non-Cropped Areas
 VRI can save water, agrochemicals, and reduce maintenance problems by completely shutting the water off in areas of the field that should not be irrigated.
These might include rock piles, ponds, or streams, waterways or roads that cross through the field or areas under the irrigation system that are otherwise not farmable.
Sometimes pivots overlap.
Shutting the water off on one of these pivots in the overlapped areas will reduce overwatering those areas.
These constant, unchanging prescriptions where the water is turned off completely will result in the largest water and power savings at the lowest long-term management costs.
Consequently, most VRI systems being sold are primarily being used in this application.
Avoiding off-target application of agrichemicals or liquid wastes is another large driver for the adoption of VRI.
Figure 5.
Pivots that could benefit from VRI to avoid irrigating non-cropped areas.
The 2017 growing season started with warm dry planting conditions, followed by significant rain delays in May in many parts of the state, and a summer of intermittent weeks of hot and cool temperatures.
The net result is that crops may mature over a longer period than usual this fall.
Fortunately, the following procedure for making end-of-season irrigation decisions is based on crop maturity stage rather than the calendar.
Pre-Plant Nitrogen Response in Irrigated Corn
 Jason Warren Associate Professor, Soil and Water Conservation
 Brian Arnall Associate Professor, Precision Nutrient Management
 Saleh Taghvaeian Assistant Extension Specialist, Water Resources
 Cameron Murley Senior Station Superintendent
 A 2018 study was initiated at the McCaull Research and Demonstration farm in the Oklahoma Panhandle to evaluate corn yield response to pre-plant applied nitrogen with different irrigation rates based on evapotranspiration  replacement.
The irrigation rates were 1 inch , 1.25 inches , and 1.5 inches  approximately every five days.
The resulting yield data was used to provide estimates of economic returns as a function of gross revenue and variable costs.
This large, field scale project provides valuable insight into the benefits of optimizing N and irrigation management to improve profitability and sustainability of irrigated corn production in the Panhandle.
In 2018 a large scale field trial was initiated at the McCaull Research and Demonstration Farm located in northern Texas County, OK near Elkhart KS.
The study was conducted on a 125-acre pivot where pre-plant nitrogen was applied at rates of 100, 150, 200, 250 pounds nitrogen per acre-1 as anhydrous ammonia plus 100 pounds of a blended fertilizer containing 12 percent nitrogen, 40 percent P2O5 5' 10 percent sulfur and 1 percent zinc.
These treatments were applied in three replicated strips around the pivot between wheel tracks 4 and 7.
A 16-row commercial strip till applicator, with 20-inch row spacing was used to apply these treatments March 23.
This allowed for the five nitrogen rates to be located between pivot tracks.
The zero anhydrous ammonia check strips received 100 pounds per acre-1 of the blended fertilizer and were located towards the center of the pivot instead of within the replicated area to allow for more replicated fertilizer nitrogen treatments within the main study for a higher resolu-
 Figure 1.
Orientation of pre-plant fertilizer strips, replicated 3 times between pivot wheel tracks.
The zero anhydrous ammonia check strips are in lime green near center of pivot.
tion assessment of nitrogen response at the top of the yield curve.
Irrigation was applied at 1-inch, 1.25-inch and 1.5-inch application rates such that the 1.25-inch treatment served to replace 100 percent crop ET with a minimum return interval of 4.9 days to simulate 3.8, 4.8 and 5.8 gallons per minute acre-1 irrigation capacities.
The amount of irrigation water applied was manipulated for each treatment by adjusting pivot speed.
These irrigation treatments were applied in 18-degree slices of the pivot overtop of the nitrogen rate strips to provide four replicates of each irrigation treatment.
The cumulative in season rainfall at this location was 12.4 inches, which is above the typical average of 10 inches during this time of year in the Panhandle region.
Figure 3 shows the cumulative ET as estimated using the Mesonet irrigation planner, as well as the cumulative rainfall + irriga-
 Figure 2.
Placement of the 1" , 1.25" , and 1.5"  irrigation treatments using pivot telemetry and speed control.
Figure 3.
The cumulative ET as estimated from the Mesonet irrigation planner  and the cumulative rainfall + irrigation resulting from each irrigation treatment.
tion applied with each treatment.
The final irrigation event was applied September 2.
The 1.25-inch irrigation treatment was successful in replacing crop ET as estimated from the Mesonet.
The 1-inch, 1.25-inch and 1.5-inch irrigation treatments resulted in 17, 21 and 24.5 inches of irrigation during the growing season, respecively.
Figure 4 shows the nitrogen response curves for corn yield produced under the three irrigation regimes.
The data shows no difference in yield response among the irrigation treatments.
Yields in the fertilized strips ranged from 210 bushels per acre-1 with 100 pounds nitrogen acreto 245 bushels per acre-1 with 300 pounds nitrogen per acre-1 The check strip which received no nitrogen except for 12 pounds nitrogen per acre-1 in the blended fertilizer produced an average yield of 168 bushels per acre-1.
The data show that optimum yield could be achieved with the 17 inches of irrigation applied in the 1-inch treatment,
 Figure 4.
Corn grain yield response to pre-plant anhydrous ammonia applications under three irrigation regimes at McCaull R&D farm in 2018.
which supplied approximately 80 percent of crop ET.
The ET reported at the Eva station for this corn crop was below the 15-year average ET reported at the Goodwell station.
This, combined with in-season rainfall, which was 2.4 inches above average, can further explain the relatively low amount of irrigation required to optimize yield.
Furthermore, many research findings in the regions have shown that 75 to 85 percent of ET replacement is sufficient to optimize irrigated corn yields.
Figure 5 shows the revenue based on $4 corn price minus the variable costs.
The data show that there was very little or no return on investment for nitrogen fertilizer at nitrogen rates above 200 pounds nitrogen per acre-1.
Furthermore, it shows that the 1-inch treatment, which supplied 80 percent of crop ET provided for optimum revenue over variable costs with $300 revenue-variable cost, whereas the 1.25-inch treatment provided $260 revenue-variable cost per acre.
It is important to note that this research was limited because only the speed of the pivot could be changed to alter the irrigation applied.
This is why the different depths were used.
A similar financial outcome could have most likely been achieved by reducing the frequency of the 1.25-inch application so it provided for 80 percent of ET replacement.
Figure 5.
Revenue  minus variable costs as a function pre-plant anhydrous ammonia applications under 3 irrigation regimes at McCaull R&D farm in 2018.
It is interesting to note that the 1.5-inch treatment did not decrease yield response to nitrogen in the fertilized treatments.
This suggests that in this one year of data, the irrigation applied in excess of ET did not cause sufficient leaching to decrease availability of the pre-plant applied anhydrous ammonia.
Corn yield response was unaffected by the amount of irrigation water applied in this study.
In fact, yield was unresponsive to irrigation treatments imposed because the 1-inch treatment provided irrigation capacity sufficient to supply 80 percent of ET which was sufficient to optimize grain yield.
The excess water supplied by the 1.5-inch  irrigation treatment apparently did not cause detrimental leaching of the pre-plant anhydrous nitrogen applied in this
 study.
Economic returns were optimized with the 1-inch irrigation treatment receiving 200 pounds nitrogen acre-1: first because of reduced pumping cost; and secondly because the added revenue resulting from the yield maximized with 300 pounds nitrogen per acre-1 was insufficient to pay for the additional nitrogen and harvest costs associated with this fertilizer treatment.
Traditional irrigation decision-making relies heavily on experience and requires frequent visits to the field.
The process is time consuming and labor demanding, while the results are not quantitative and prone to error.
ENSURING EQUAL OPPORTUNITY SPRINKLER IRRIGATION
 Terry A.
Howell Research Leader and Agricultural Engineer USDA-ARS CPRL Bushland, Texas tahowell@cprl.ars.usda.gov
 Equal opportunity to water applied by sprinkler irrigation to each plant must be carefully considered by crop producers, irrigation consultants, and the industry that supplies the irrigation equipment.
Equal opportunity can be negated by improper marketing, design, and installation of equipment, as well as through improper farming operations, and irrigation mismanagement.
These issues have greater significance when the irrigation is applied within or near the crop canopy.
Key issues that must be addressed to ensure equal opportunity to sprinkler irrigation applications are irrigation application symmetry, spatial orientation of sprinkler travel with respect to crop rows, and the seasonal longevity of the sprinkler pattern distortion caused by crop canopy interference.
There are both producer and industry roles in providing equal opportunity for the crop to the applied sprinkler water.
Mechanical-move sprinkler irrigation systems are typically designed to uniformly apply water to the soil at a rate less than the soil intake rate to prevent runoff.
In the U.
S.
Great Plains, there is a growing use of in-canopy and nearcanopy sprinkler application because of reduced evaporative losses, however these application devices introduce a much greater potential for irrigation non-uniformity and run-off and/or run-on.
Some of the earliest descriptions of in-canopy sprinkler irrigation  discuss the importance of all crop plants having equal opportunity to water, yet irrigators, designers and equipment manufacturers do not always follow this guideline.
This paper will discuss the issue from a conceptual standpoint using both research and on-farm examples.
The objective is attaining greater acceptance of this design criteria so that irrigator's can avoid the reduced crop production and runoff that occur when equal opportunity is violated.
SYMMETRY OF SPRINKLER APPLICATION
 Uniformity of water application and/or infiltration is an important attribute in ensuring equal opportunity sprinkler irrigation.
Increased uniformity will often result in increased yields, decreased runoff, and decreased percolation.
Improved sprinkler uniformity can be desirable from both economic and environmental standpoints.
Their study
 shows irrigation non-uniformity can result in nutrient leaching from over-irrigation and water stress from under-irrigation.
Both problems can cause significant economic reductions.
Returning to the first sentence of this paragraph, the careful wording can be noted of "uniformity of water application and/or infiltration".
This wording suggests that the primary goal is for the plants to have equal opportunity to root-zone soil water.
Sprinkler irrigation does not necessarily have to be a uniform broadcast application to result in each plant having equal opportunity to the irrigation water.
Equal opportunity can still be ensured using a low energy precision application  nozzle in the furrow between adjacent pairs of crop rows provided runoff is controlled.
Figure 1.
LEPA concept of equal opportunity of plants to applied water.
LEPA heads are centered between adjacent pairs of corn rows.
Using a 5-ft nozzle spacing with 30-inch spaced crop rows planted circularly results in plants being approximately 15 inches from the nearest sprinkler.
After Lamm.
Some sprinkler application non-uniformity can also be tolerated when the crop has an intensive root system.
When the crop has an extensive root system, the effective uniformity experienced by the crop can be high even though the actual resulting irrigation system uniformity within the soil may be quite low.
Additionally, when irrigation is deficit or limited, a lower value of application uniformity can be acceptable in some cases  as long as the crop economic yield threshold is met.
Some irrigators in the U.S.
Great Plains are using wider in-canopy sprinkler spacings  in an attempt to reduce investment costs.
Spray heads which perform adequately at a 10 ft interval above bare ground have a severely distorted pattern when operated within the canopy.
Figure 2.
Differences in application amounts and application patterns as affected by sprinkler height that can occur when sprinkler spacing is too wide  for in-canopy application.
Center pivot sprinkler lateral is traversing parallel to the circular corn rows.
Data are from a fully developed corn canopy, July 1996, KSU Northwest Research-Extension Center, Colby, KS.
Data are mirrored about the centerline for display purposes.
Although Figure 2 indicates large application non-uniformity, these differences may or may not always result in crop yield differences, but they should be considered in design.
Hart  concluded from computer simulations that differences in irrigation water distribution occurring over a distance of approximately 3 ft were probably of little overall consequence and would be evened out through soil water redistribution.
Some irrigators in the Central Great Plains contend that their low capacity systems on nearly level fields restrict runoff to the general area of application.
However, nearly every field has small changes in land slope and field depressions which do cause field runoff or percolation when the irrigation application rate exceeds the soil infiltration rate.
In the extreme drought years of 2000 to 2003 that occurred in the U.
S.
Central Great Plains, even small amounts of surface water movement affected sprinkler-irrigated corn production.
Figure 3.
Large differences in corn plant height and ear size for in-canopy sprinkler application over a short 10-ft.
distance  as caused by small field microrelief differences and the resulting surface water movement during an extreme drought year, Colby, Kansas, 2002.
The upper stalk and leaves have been removed to emphasize the ear height and size differences.
Mechanical-move sprinkler system manufacturers do not always provide nozzle spacings that ensure equal opportunity to the water.
There are a host of nozzle outlet spacings available from industry, 30, 57, 90, 108 inches and the multiples of these spacings, but often a particular manufacturer will have their own limited selection which may be further limited in some span lengths.
The industry may have valid reasons for this limitation related to overall inventory and international marketing but that does little to accommodate the various crop row spacings  that are commonly used in the United States.
Since irrigation is primarily a tool to increase crop production, maybe ensuring equal opportunity to the sprinkler irrigation water should be more important than marketing issues.
After market suppliers have provided some solutions to this problem through furrow-arm goosenecks and hose draping devices but these "fixes" can be cumbersome to adjust and maintain in the proper position.
The direction of travel of the mechanical-move sprinkler lateral with respect to crop row direction can affect the equal opportunity issue when in-canopy application is used.
It has been recommended for center pivot sprinkler systems that crop rows be planted circularly so that the rows are perpendicular to the sprinkler lateral.
Matching the direction of travel to the row orientation satisfies the important LEPA Principles 2 and 5 noted by Lyle  concerning water delivery to one individual crop furrow and equal opportunity to water by for all plants.
Some producers have been reluctant to plant row crops in circular rows because of the cultivation and harvesting difficulties of narrow or wide "guess" rows.
However, using in-canopy application for center pivot sprinkler systems in non-circular crop rows can
 pose two additional problems.
In cases where the CP lateral is perpendicular to the crop rows and the sprinkler spacing exceeds twice the crop row spacing, there will be non-uniform water distribution because of pattern distortion.
When the CP lateral is parallel to the crop rows there may be excessive runoff due to the great amount of water being applied in just one or a few crop furrows.
There can be great differences in in-canopy application amounts and patterns between the two crop row orientations.
Figure 4.
Two problematic orientations for in-canopy sprinklers in non-circular rows.
Figure 5.
Differences in application amounts and application patterns as affected by corn row orientation to the center pivot sprinkler lateral travel direction.
Dotted lines indicate location of corn rows and stemflow measurements.
Data are from a fully developed corn canopy, July 23-24, 1998, KSU Northwest Research-Extension Center, Colby, KS.
Data are mirrored about the centerline.
PATTERN DISTORTION AND TIME OF SEASON
 Drop spray nozzles just below the center pivot sprinkler lateral truss rods  have been used for over 25 years in northwest Kansas.
This configuration rarely has had negative effects on crop yields although the irrigation pattern is distorted after corn tasseling.
The reasons are that there is only a small amount of pattern distortion by the tassels and this distortion only occurs during the last 30 to 40 days of growth.
In essence, the irrigation season ends before a severe soil water deficit occurs.
Compare this situation with spray heads at a height of 1 to 2 ft that may experience pattern distortion for more than 60 days of the irrigation season.
Yield reductions might be expected for some corn rows in the latter case because of the extended duration of the pattern distortion.
Lowering an acceptably spaced  spinner head from 7 ft further into the crop canopy  can cause significant row-to-row differences in corn yields.
Figure 6.
Row-to-row variations in corn yields as affected by sprinkler height for 10 ft.
spaced in-canopy sprinklers.
Sprinkler lateral travel direction was parallel to crop rows.
Data was averaged from four irrigation levels for 1996 to 2001, KSU Northwest Research-Extension Center, Colby, KS.
Short and long term water supply problems in the U.
S.
have forced those involved with irrigation to look for cost-effective, water saving techniques.
Sprinkler irrigation is now the predominant irrigation method in the U..S.
Great Plains because of both water and labor savings.
Ensuring equal opportunity of crop plants to the applied water has long been recognized as an important tenet of irrigation, yet there continues to be a lack of appropriate attention to this rule particularly with the newer in-canopy and near-canopy sprinkler application techniques.
Both end-users and industry have important roles in
 solving this problem.
Neglecting this equal opportunity issue can easily waste more water and cause more crop yield reductions than other irrigation problems producers and industry are trying to avoid.
This paper was first presented at the 28th Annual International Irrigation Association Exposition and Technical Conference, San Diego, California, December 9-11, 2007.
Paper No.
IA07-1013.
Proceedings available on CD-Rom from Irrigation Association, Falls Church, Virginia.
This is a joint contribution from Kansas State University, USDA-ARS and the Texas Agricultural Experiment Station.
Contribution No.
08-138-A from the Kansas Agricultural Experiment Station.
The authors are supported in part by the Ogallala Aquifer Program, a consortium between USDA-Agricultural Research Service, Kansas State University, Texas Agricultural Experiment Station, Texas Cooperative Extension, Texas Tech University, and West Texas A&M University.
Chapter: 38 Estimating Corn Yields
 Corn yield estimates can be used for a variety of purposes including: marketing; planning storage requirements; organizing harvest equipment; and making decisions about pests.
The purpose of this chapter is to provide guidance and examples on how to convert field measurements into estimated corn yields.
Table 38.1 Basic steps to estimate yields:
 1.
Yield estimates start with tracking seed germination, assessing planter effectiveness, and determining your plant density.
Many of these measurements can occur shortly after seedling emergence.
2.
As you approach plant maturity, grain yields can be estimated by assessing the number of kernels/ear and kernel weight.
The basic steps include:
 a.
Estimating the ears/acre.
b.
Estimating the kernels/ear.
C.
Calculating kernels/acre =.
d.
Estimating kernel size.
e.
Calculating bu/acre = [/],
 Estimating Yield after Emergence
 As the corn plant grows, it is important to identify problems that could reduce yields.
This requires that the fields be routinely scouted  and calculations conducted to convert point measurements to common yield units, usually bushels/acre.
To estimate yield following emergence, you need to make many assumptions, which include:
 1.
The number of rows of kernels on an ear.
2.
The number kernels in each of the rows.
3.
The number of kernels per bushel.
Example 38.1 provides steps for determining yield estimates.
These estimates are based on plant population and do not consider how yield may be reduced due to planting date, or pest or nutrient stresses.
For example, Carter et al.
and Nafziger et al.
reported that a 1.5-week delay from the "normal" planting date decreased yield 5% and that a 3-week delay reduced yield 12%.
Example 38.1 Calculations for yield potential based on seedling number or plant population prior to the reproductive growth stages.
This calculation is based on the assumptions that: 1) the average grain contained on an ear is 0.28 lb/ear and 2) there is one ear per plant.
Estimated yield= plants acre X plants ear X ear
 35,000 plts 0.28 bu 175 acre plt ear 56 lbs acre
 This calculation is based on kernels per ear and assumes that there are 90,000 kernels in 56 lbs of grain.
Estimated acre #kernels kernel
 Estimated yield= 16rowx28 kernel/row
 Both approaches make assumptions about the size of the ear.
Different assumptions will influence the expected yields.
The number of rows on the ear is impacted by the plant's genetic capacity, whereas the number of kernels in a row is impacted by the environment and population density.
Yield Estimates During the Early Reproductive Stages of Corn Growth 
 As the season progresses, the yield estimates become more accurate.
The R1 growth stage occurs when silks are visible outside the husk.
At this growth stage, the silks catch the falling pollen grains and fertilization occurs after the pollen moves down the silk to the ovule.
Each ovule has the capacity to become a kernel.
Yield is estimated by measuring the plant population and then estimating the number of kernels per ear.
An approach similar to Example 38.1 can also be used to estimate yield.
Yield Estimates from R4-R6 Growth Stages
 The R4 growth stage is called the dent growth stage and the R6 stage is physiological maturity .
At these growth stages, yield estimates become more accurate.
Step 1.
Determine the number of ears per acre.
Measure off 1/1000 of an acre.
A tape measure is the most accurate way of measuring off the indicated length of row.
A faster way, but less accurate method, is to step off the row length.
With practice and calibration, it is possible to step off the indicated length with an accuracy of plus or minus a few inches.
As an example, if you are working in 30-inch rows, the plants are counted along a length of row measuring 17 feet, 5 inches.
Then, estimate the plant population per acre by multiplying the number of plants per row length by 1000.
Note: Across a field, you may want to take several estimates and average them, or if population is variable by area, each area may need its own estimate.
These estimates would then be averaged based on the percent area that is expected to have a similar population.
Table 38.1 The length of row to count for 1/1000 of an acre depending on row width 
 Step 2.
Determine the number of kernels/ear by counting the number of kernels/row and the number of rows/ear.
If the ear size in the field appears
 Row width	Row length
 Figure 38.1 Example of an ear used to calculate the number of kernels per row.
Only fully filled kernels along fully filled rows should be counted.
The lines indicate the kernels that should be included in the count.
This ear contains ~34 rows of kernels.
Example 38.2 Based on a plant population of 35,500 plants/acre, estimate your yield at the tasseling  stage of development.
Step 1.
Estimate your plant population by:
 1.
Counting the number of plants in 1/1000 of an acre.
2.
Multiplying your count by 1000.
Step 2.
Estimate the yield by multiplying your plant population by the estimated weight of grain per ear, and dividing the lbs grain/acre by 56 lbs/bu.
This example assumes that each ear weighs 0.4 lbs.
35,500 ears X 0.4 lbs X bu 254 bu acre 1 ear 56 lbs acre
 Note: Reduce your estimate if you know the crop has been stressed.
For example, weeds present during the weed-free period can reduce yield from 5% to 100% depending on species present and density.
Similar yield reduction calculations can be conducted for nutrient deficiencies, or insect and disease damage.
Examples for estimating yield losses are available in Clay et al..
At the early reproductive growth stages, yield estimates are not accurate and typically overestimate actual yield.
As the crop matures, kernel-based assessments become more accurate.
uniform, select 4 or 5 "average ears" and count the number of kernels/row.
Include only the kernels and rows that are fully filled.
This ear contains ~36 kernels/row.
Count the number of rows/ear.
For this step break the ear in half, which makes it easier to count rows.
The count for the ear below is ~ 18 rows/ear.
The rows/ear will almost always be an even number.
The number of kernels/ear can be calculated or determined using Table 38.2.
If the number of kernels/row is highly variable, we suggest that at least 10 ears be counted from each area.
Step 3.
Calculate the kernels/a from the data collected in Steps 1 & 2.
To determine the number of kernels/a, the calculations are shown below.
Assume that the number of plants counted along the 17'5" length = 35 plants.
Therefore, 35 X 1000 = 35,000 plants  per acre.
ears Kernels X plant acre 35,000 Ears 648 Kernels 22,680,000 Kernels acre acre
 Step 4.
Estimate the number of kernels/bu.
The mass/kernel of corn varies greatly.
The number of kernels/bu can range from 70,000 kernels/bu to 105,000 kernels/bu.
The kernel weight is very sensitive to climatic conditions between August and September.
During wet conditions, a bushel may contain 70,000 kernels, whereas if August and September are hot
 Figure 38.2 Count the number of rows.
On this ear, there are ~20 kernels per row.
Table 38.2 A table for estimating the number of kernels/ear.
In the above example, the number of kernels/row was 36 and number of rows/ear was 18.
Using this table, the value would be estimated to be 630 kernels/ear, whereas the calculated value was 648.
Because there was 1 kernel/row extra  = 630 + 18 = 648.
Rows/ear	20	25	30	35	40	45
 12	240	300	360	420	480	540
 14	280	350	420	490	560	630
 16	320	400	480	560	640	720
 18	360	450	540	630	720	810
 20	400	500	600	700	800	900
 22	440	550	660	770	880	990
 24	480	600	720	840	960	1080
 26	520	650	780	910	1040	1170
 28	560	700	840	980	1120	1260
 Example 38.3 Determine the number of corn kernels per bushel if 200 field dry kernels weigh 56.3 g.
In this example, it is assumed that the kernels are at 15.5% moisture and that 1 bushel weighs 56 lbs.
1000 grams = 1 kilogram; 1 kg = 2.21 lbs; 16 ounces/lb.
200 kernels X 1 kg X 56 lbs_90,000 kernels 200 0.0563 kernels kg 2.21 16 lbs 56 bu lbs 90,000 kernels OR OZ X = bushel 2 OZ 1 lb bu
 Example 38.4 Using Tables 38.2 and 38.3, what is the estimated yield if the plant population is 29,000 ears/ acre and 30 kernels/row and 22 rows/ear.
Based on Table 38.2, each ear contains 660 kernels.
Based on Table 38.3, 29,000 plants containing 650 kernels/ear will yield 209 bu/a and 29,000 plants/acre containing 700 kernels/ear will yield 226 bu/a.
Therefore, the yield would be estimated to be between 209 and 226 bu/a.
To calculate the "exact" value:
 660 X 209 bu = 212 bu 650 acre acre
 and dry, a bushel may contain 105,000 kernels.
The producer's management  also impacts the number of kernels/bu.
The kernel weight per bushel can be estimated by weighing a known number of kernels that are representative of the kernels 
 Step 5.
Calculate the bu/acre.
The estimated yield per acre can be determined by calculating the bu/a  or by using a Table 38.3.
kernel bu bu X = acre kernel acre 22,680,000 kernels bu X 90,000 acre
 Using Table 38.3, the information needed includes: 35,000 plants/acre and 648 kernels/ear.
At 650 kernels/ ear and 35,000 plants/a, the value from Table 38.3 is 253 bu/a.
Table 38.3 Table for converting kernels/ear and ears/acre to corn yield in bu/a.
In this calculation, it was assumed that a bushel contains 90,000 kernels.
acre	250	300	350	400	450	500	550	600	650	700	750	800
 15	42	50	58	67	75	83	92	100	108	117	125	133
 17	47	57	66	76	85	94	104	113	123	132	142	151
 19	53	63	74	84	95	106	116	127	137	148	158	169
 21	58	70	82	93	105	117	128	140	152	163	175	187
 23	64	77	89	102	115	128	141	153	166	179	192	204
 25	69	83	97	111	125	139	153	167	181	194	208	222
 27	75	90	105	120	135	150	165	180	195	210	225	240
 29	81	97	113	129	145	161	177	193	209	226	242	258
 31	86	103	121	138	155	172	189	207	224	241	258	276
 33	92	110	128	147	165	183	202	220	238	257	275	293
 35	97	117	136	156	175	194	214	233	253	272	292	311
 37	103	123	144	164	185	206	226	247	267	288	308	329
Irrigation Management Options for Containerized-Grown Nursery Crops
 Gladis Zinati, Ph.D., Extension Specialist in Nursery Management
 Growing nursery plants in containers is a unique system compared to field-grown plants.
Container plants are grown in substrates that contain a limited amount of water, retain smaller quantities of nutrients, and confine roots in a limited volume.
Consequently, production inputs such as irrigation and nutrients require precise and properly timed applications in quantities that result in maximum benefit to the container plant production system.
Irrigation is a very important aspect of nursery crop production because nutrient and pesticide runoff are related to irrigation practices.
There are several means by which to supply a crop with irrigation water: overhead sprinkler, hand-watering, drip or trickle irrigation systems.
The first two irrigation systems are typically more wasteful delivery sysitems, and wet the foliage, increasing the potential for diseases.
Drip or trickle irrigation systems are more efficient and provide greater control over the amount of water applied.
No matter which irrigation system is used, it is important that the system be well-designed hydraulically to assure high uniformity and distribution of water efficiently.
Efficiency of water application depends on the system, design, management skills, and irrigation scheduling.
Irrigation Management and Water Quality
 Irrigation management involves a combination of interrelated practices that improve irrigation efficiency, reduce runoffs, and protect, improve, and maintain water quality.
Managing runoff at production sites reduces soil erosion from irrigation and rainfall, and minimizes contaminant carryover into surface and ground waters.
Indeveloping an irrigation management plan it is important to determine what is present in runoff or leached water and in what concentrations.
High amounts of nitrate, phosphorus, salts, pesticides, and pathogenic organisms are the common problems.
The simple tests for nitrates and other nutrients are relatively inexpensive.
However, detailed nutritive and chemical tests  will be more costly.
Each grower or manager should make a list of the common chemicals and their concentrations they use in their nursery operations, especially those that have the potential to end up in the water supply.
Seasonal analysis is the best plan.
Occasional analysis for trace elements is necessary to determine their trends.
It is important to follow the analytical laboratory instructions on sampling and handling of water samples.
If the sample cannot be sent immediately after collection, then freeze it until sent to the laboratory.
The following are irrigation management options that can be adopted to improve irrigation efficiency, reduce and conserve water usage and quality.
Irrigation efficiency can be expressed relative to three aspects of water application: 1) uniformity of application, 2) amount of water retained in substrate media following irrigation, and 3) amount of water that enters containers compared to that which falls between containers.
Irrigation application efficiency is the ratio of the volume of irrigation water stored in the root zone and available for crop use  to the volume delivered from the irrigation system [Eq.
1].
This ratio is always less than 1.0 because of losses due to evaporation, wind drift, and leaching, which may occur during irrigation.
Improved irrigation efficiency can lead to reductions in water and energy consumption, more effective nutrient use and disease management, better yields, and improved crop quality and erosion control management systems.
[Eq.
1] Volume of water applied
 Irrigation uniformity refers to how evenly water is distributed across the production beds.
No irrigation is perfectly uniform.
In all cases, some parts of the production beds receive more water than others.
The degree of uniformity however, can be highly variable depending on the selected irrigation system and its management.
While some irrigation systems are more efficient than others , it is important to realize that poor management of a relatively efficient system can greatly reduce or negate system efficiency and increase pollutant discharge to runoff or percolating waters.
It is recommended that the irrigation manager perform irrigation system maintenance regularly.
The manager should check for leaks and clogged nozzles, measure operating pressures, do simple tests to measure application rate and distribution uniformity.
Distribution uniformity can be measured using a grid of collection format with straight-sided containers and placing them in the defined area.
The sprinkler system is run for a set period of time; the water volumes in the containers are collected and
 measured.
Additionally, using an anemometer  and a pressure gauge provides information on whether the sprinkler heads in the test area are operating under the same water pressure.
Distribution uniformity tests must be repeated several times to conduct an accurate evaluation.
Irrigation distribution can be affected by pressure, wind speed, and distance from the pumping water source.
In addition, test well water regularly for potential contamination , check and record results of back-flow prevention devices at least once a year.
available water in the medium and hence, for root absorption, than if the plants are grown in a mix that contains only bark and sand.
Additionally, the grower will benefit from reducing water consumption, less irrigation frequency, runoff, and leaching.
On the other hand, with plants that require less irrigation and more air space, it is advisable to incorporate more coarser particles in the medium to ensure oxygen availability to plants' roots.
Water holding capacity =  X 100 [Eq.2 Container volume Percent air space =  X 100 [Eq.3] Container volume
 The amount of water that enters the containers depends on plant spacing and plant structure.
It is estimated that 50% to 75% of the water applied, through overhead irrigation systems, falls outside and missing the containers completely.
The Interception Efficiency  is a theoretical measure of the amount of applied water that is captured by the containers during an overhead irrigation event excluding the amount of water that falls onto the land around the containers.
It is expressed as a percentage of the applied water but, in terms of area, it is the "container top area" divided by the "land area  allotted to one container".
The "container top area" is the open area of the top of the container through which irrigation water enters the container.
Land area is defined by the container spacing.
The percentage of irrigation water or fertigation solution  that falls directly onto the land is calculated as 100 IE,% and that contributes more directly to nutrient runoff.
The value is particularly important in those operations that "fertigate", i.e., apply soluble nutrients in the irrigation water.
Containers placed closely have a higher interception efficiency compared to spaced "unjammed" containers.
Properly installed drip irrigation should have 100 percent interception efficiency.
On the other hand, not all intercepted water is held within the container.
The irrigation water in excess leaches out through the bottom openings of the container.
Optimize Leaching Fraction 
 Leaching fraction is a measure of the excess water that is applied during an irrigation event.
It is the amount of water that drains out the bottom of the container divided by the total amount of water applied to the container.
Leaching factor is mainly affected by the physical properties of the soilless media used for growing plants, plant growth stage, and the volume of water applied per irrigation.
The goal is to manage water applications more accurately and reduce the leaching that contributes to runoff.
A LF between 10 and 15 is considered safe for plant growth and environmentally friendly.
However, care should be practiced when LF is below 5, especially because soluble salts build up in the soilless media and may injure roots of sensitive plants to salts.
Irrigate plants with fresh water from time to time with LF about 20 to reduce soluble salt levels and to protect plants from salt injury.
When fertilizer concentrations are reduced, less leaching will be needed and conversely, if leaching is reduced you will need to use less fertilizer to avoid buildup of salts in the medium.
Interception efficiency and leaching fraction provide a means of assessing potential runoff, which is the excess water that flows out of the growing area being irrigated and moves toward off-site surface water.
For overhead irrigation, runoff is made up of water that leaches through containers plus the water that is not intercepted by individual containers.
For drip irrigation, runoff is measured by leachate.
Interception Efficiency, IE Square Container Spacing
 Figure 1.
Interception Efficiency
 Figure 2.
Leaching Fraction
 Irrigation scheduling is the process of determining when to irrigate and how much water to apply per irrigation.
Proper irrigation scheduling improves crop production and/or quality, conservation of water and energy, and lower production costs.
Several methods used to successfully reduce irrigation volume and runoff, include micro-irrigation and pulse  irrigation.
Pulse irrigation refers to the practice of alternating small volume irrigations and resting intervals.
Pulsing can work with sprinkler, or drip irrigation.
Thus, the opportunity exists to make sure the appropriate management strategies are used, recognizing the site-specific nature of nursery production facilities.
If you do not have a control irrigation system, a simpler method can be used to determine when and how much to water.
A target weight for watering must be set.
The target weight can be determined in a simple method.
Check the weight of container at full water holding capacity, and then at the plants' point of wilting.
The goal is to water most plants when approximately 60-70% of the available water has been used and re-water to full water holding capacity and not beyond unless salt build up is a problem.
The target weight may have to be increased as the crop grows.
Adjusting irrigation frequency through scheduling and irrigation efficiency can reduce water use and
 reduce water pollution.
Some growers tend to rely on the "eyeball" method to determine when plants need water.
As a result, many crops get more water than they need, creating excess runoff.
Also, EC levels in leachates can be used as an indicator on whether more irrigation time to reduce salt build up in the growing media or fertilization is required.
For example, collected leachate from containers with EC levels in the range of 1.8-2.0 mmhos/cm indicate that more irrigation is necessary in the next week's irrigation to reduce the excess soluble salts and conversely, an EC in the range of 0.2-0.3 mmhos/cm indicates less irrigation is needed because excess irrigation is leaching out nutrients.
Consider Using Indicator Plants
 Choose indicator plants that help trigger the decision to irrigate.
For example, Japanese Barberry may be used as an indicator plant for plants with low water requirement.
Japanese Boxwood and Crape Myrtle can be indicator plants for plants with medium and high water requirement, respectively.
Drooping leaves and a change in leaf color are signs of wilting.
Adopt New Irrigation Technologies
 A variety of computers and irrigation scheduling software is available.
The cost of such a system can be a worthwhile investment.
Install rain sensors to ensure irrigation does not occur during rain events.
To lower costs and runoff, irrigate plants when needed based on media moisture content.
This can be assessed by a) appearance or feel, b) remote sensor tensiometers, c) weight of media moisture, d) light accumulators, and e) moisture conductivity.
Several devices relate media moisture to electrical conductivity.
When the growing media dries to a preset level, the electronic circuit activates the solenoid valve.
Plan and Install Irrigation Systems That Provide Efficient Water Use
 Do careful research to install the most appropriate system for your operation.
Types of plants, soil/ container media, and location of the site to water
 bodies should be included in the decision making.
Growers producing nursery crops that are sensitive to water molds and to pathogens that cause leaf diseases should consider using drip irrigation system versus overhead irrigation system, where amounts can be better controlled and leaf tissue is not wetted frequently.
Select Appropriate Growing Medium
 Growers are recommended to choose components of container substrates that are best adapted to plants and management.
Recommended physical characteristic values for nursery container substrates after irrigation and drainage are : total porosity 50 to 85%, air space 10 to 30%, available water content 25 to 35%, and bulk density 0.19 to 0.70 g/cc.
A container medium with a high proportion of coarse particle size has a high air space and a relatively low water holding capacity.
Consequently, leaching of pesticides and nutrients is likely to occur if not managed well.
Humic substances such as peat moss, will enhance water and nutrient-holding capacity substantially.
Consider the Use of Wetting Agents
 Research showed that wetting agents increase water absorption of many peat-based media, when using drip irrigation.
Wetting agents not only allow quicker wetting and uniform water distribution, but also allow more water to be held by the peat and reduce channeling of water down the sides of containers, which consequently can result in reducing leaching.
Select a quality product designed for horticultural use and do not over use wetting agents, as they can be toxic to plants.
Group Plants with Similar Water Needs
 Establishing irrigation zones improves irrigation efficiency.
Prioritize water use on plants of most value and least drought-tolerant.
For example, the water requirements of evergreens are usually less than those of deciduous shrubs during summer and should
 not be placed in the same irrigation zone.
Similarly, conifers have lower water requirements than broadleaf evergreens and should be grouped separately.
Plants can be categorized into three categories, those with high, medium, or low water requirement.
Refer to Table 1 for list of plants that are grouped according to water needs.
Collect and Recycle Irrigation Water
 Monitor recycled water for pH, salts , nutrients, pathogens, and pesticide content before application to nursery plants at least three times a year.
Simply, in clean darkcolored plastic bottles, collect 3-5 water samples from tail-water recovery system early in the morn-
 Manage Solubility of Pesticides
 Monitor Pathogen Levels in Recycled Water
 Some diseases that attack nursery crops are in what is known as the "water mold" group of fungi, such as Pythium and Phytophthora.
These pathogens thrive in high moisture.
Runoffs collected in water recovery systems may carry these pathogens.
Water can be sampled at different points and sent to any local plant disease diagnostic laboratory to determine pathogen presence and levels.
Treat recycled water for disease organisms with any decontamination system such as retention and dilution, filtration, chlorination, ozonation, and or UV light.
The selection of a decontamination system depends on the nursery size: volume of runoff to be captured, topographic features that determine the number of collection basins needed to capture runoff water, value and susceptibility of plant species to major diseases, and types of applied pesticides.
Chlorine and bromine can be used to treat recycled runoff water.
Chlorination involves the use of granular calcium chloride or gaseous chlorine, although the latter should be used only for larger operations.
The key is having enough free chlorine  in the water long enough  to kill pathogens.
If you choose to work with chlorine, remember that chlorine gas is very hazardous and must be handled with adequate safeguards.
Another agent available to control water borne pathogens is a bromine biocide, commonly known as Agribrom.
The concentration required is higher , than chlorine, it is safer to handle than chlorine and is equally effective.
Manage Storm Water Runoff
 Storm water runoff is water flowing over the land, during and immediately following a rainstorm.
Storm water storage systems can reduce peak runoff rates, provide settling and dissipation of pollutants, lower probability of downstream flooding, stream erosion and sedimentation, and provide water for other beneficial uses.
Develop a system to deal with storm water retention and runoff from
 the nursery.
Invest in planting vegetated grassed waterways, wetlands, and vegetative buffer.
These components increase infiltration and evaporation, allow suspended solids to settle and remove potential pollutants before they are introduced to other water resources.
Constructed wetlands serve as a biological filter for removing chemical pesticides and fertilizers.
In addition, the extra water surface of the wetland area increases the oxygen available to decompose organic compounds and to oxidize dissolved metals in the water.
For references on filter strips, contact the local office of the Natural Resources Conservation Service.
Alternative techniques improve irrigation and nutrient management on dairies
 Larry Schwankl Carol Frate
 Many of the dairies in California's Central Valley use a water flush system for manure handling; the manure water is eventually mixed with freshwater and applied to cropland during irrigation.
Good performance during irrigation applications is important due to the nutrients in the manure water.
This project evaluated alternative management techniques  for improving irrigation practices on dairies.
All three techniques reduced the amount of water required for irrigation.
The project also investigated the impact of changing the timing of manurewater additions to the fresh irrigation water.
Delaying the addition of manure water until the advancing fresh irrigation water had reached approximately 80% of the distance down the field improved nutrientapplication uniformity and reduced nutrient applications.
M any of the more than 1,600 dairies in the Central Valley of California use a water flush system to clean manure from free-stall barns.
This flush water is collected and held in ponds until it can be mixed with freshwater and applied to cropland as part of surface irrigation practices.
The application of manure-water nutrients in excess of agronomically appropriate rates can result in loss of nutrients, often to deep percolation below the crop's root zone.
Due to the high levels of nutrients in manure water, high efficiency and uniformity are important to assure a uniform distribution of nutrients during irrigation and
 Researchers measured water discharge into the field by placing plastic hydrants over alfalfa valves with a Doppler flow meter attached.
to minimize the deep percolation of nitrates, which can pollute groundwater.
Furrow and border irrigation systems are commonly used with manurewater applications on dairies in the San Joaquin Valley.
Sprinkler irrigation with manure water is seldom used due to odor and air pollution concerns, and is prohibited in some counties.
Furrow and border irrigation systems are often inefficient due to over-irrigation and poor application uniformity.
Tailwater irrigation water that runs off the end of a field that is not reused is one source of inefficiency.
Tailwater containing manure cannot leave the grower's property, and the standard practice on dairies is to minimize its generation during irrigation.
If tailwater is generated, a return system is often used to collect it for reuse.
Deep percolation is the major contributor to irrigation inefficiency on dairies, and over-irrigation often results when fields are too long.
A certain quantity of irrigation water is required simply to advance water to the end of the field.
This is the minimum amount of water applied per irrigation event, which often exceeds the amount of water required to refill the crop's
 root zone and results in inefficient irrigation.
A field project was undertaken during the summers of 2001 and 2002 to evaluate techniques for improving the irrigation and nutrient management of flood irrigation systems that apply manure water.
Improved irrigation systems should apply water and the nutrients carried in water  more evenly on the field and allow application of the correct amount of water to match crop needs.
Three irrigation-water management techniquesfurrow torpedoes, surge irrigation and field-length reductions were investigated on a Tulare County dairy.
Another management strategy, manipulating the timing of manurewater additions to the fresh irrigation water, was evaluated on the same dairy.
Furrow torpedoes are steel cylinders, often filled with concrete, which are dragged in the furrow to break up soil clods and smooth the surface.
They can allow water to advance across a field more quickly, resulting in improved irrigation uniformity and efficiency.
Torpedo use is beneficial after field preparation or cultivation, but it is not
 The application of manure-water nutrients in excess of agronomically appropriate rates can result in loss of nutrients, often to deep percolation below the crop's root zone.
effective if there is no cultivation to disturb the furrow between irrigations.
The impact of torpedo use for manure-water irrigations was evaluated by comparing three irrigation blocks of 25 torpedoed furrows each, with the same number of blocks and furrows that were not torpedoed.
All furrows were 1,250 feet long.
Water was supplied at the head of the field using an underground pipeline with alfalfa valves.
Each block of 25 furrows centered on an alfalfa valve was bordered by berms running the length of the field.
These berms kept the water from each alfalfa valve constrained to flow down the 25 furrows supplied by that valve.
This is a common irrigation system for dairies in the San Joaquin Valley.
The preseason irrigation event was monitored.
This irrigation is often inefficient because the soil has been extensively worked and has a high infiltration rate.
A PVC hydrant with a discharge pipe out its side was placed over the alfalfa valve during irrigation.
A Doppler flow meter was attached to the hydrant's discharge pipe to measure the flow rate and volume applied to each monitored block of furrows.
The flow rates from the valves supplying areas being compared were kept as similar as possible, and records of total volume applied versus irrigation time were collected.
There was some variation in inflow between furrows being
 supplied by a common alfalfa valve, but the water advance was fairly consistent between furrows.
The rate that water advanced along the furrow was also monitored.
Information on the advance rate and irrigation set-time was used to determine the intake opportunity times and the infiltrated water at locations within the field.
The irrigation set was changed soon after water reached the end of the field.
Without a return system, care was taken to minimize tailwater runoff.
Tailwater generated by furrows in which water advanced faster to the end of the field flowed a short distance into the tail end of "dry" furrows, which had not yet completed their water advance.
Torpedo use was effective in reducing the applied water from 12.9 to 9.4 inches a 27% reduction from continuous-flow irrigation (table Water advanced faster across the field, resulting in a shorter irrigation set-time and less water applied.
Torpedo use is not widespread in the San Joaquin Valley, primarily due to the difficulty and cost.
The torpedoes are dragged behind a tractor and it is often difficult to turn at the end of the field with the torpedoes attached.
Some growers have solved this problem by connecting the torpedoes to a sled SO that they can be hydraulically lifted at the ends of fields.
Because of these complications, furrows are often torpedoed as a separate equipment pass through the field an added cost.
Surge irrigation on dairies
 Furrow torpedoes are attached to a sled to ease turning at the end of the field.
Surge irrigation is the on-off cycling of water during irrigation.
Water is allowed to run down a group of furrows and at some point , the water is moved to another group of furrows.
While water is running in the second group of furrows, water in the first group of furrows is infiltrating and the furrows are "de-watering." When water in the second group of furrows has advanced to the same distance as the first group, water is switched back to the first group.
As water is reintroduced to the first group of furrows, it advances across the wetted portion of the field very quickly and then slows down appreciably as it starts to advance across the dry soil.
This on-off cycling of water is continued until water reaches the end of the field.
This practice can improve irrigation efficiency by advancing water across the field using less water as compared to continuous-flow irrigation due to an infiltration reduction on soil wetted by a previous surge cycle.
This infiltration-rate reduction is likely due to a sealing of the soil surface.
Surge irrigation has not been previously investigated on fields irrigated with manure water.
Manure water contains a substantial amount of fine solids, which was thought to have a significant positive impact on surge-irrigation performance.
Surge irrigation was evaluated by comparing two blocks of 25 furrows each irrigated with continuous flow; and four blocks of 25 furrows each surge-irrigated.
Four surge cycles were used.
Water was allowed to advance about one-quarter of the way down the field , and then the water was transferred to another section of furrows.
By the time the water was transferred back to the original section, water had infiltrated into the furrow.
During the second surge, water was allowed to advance another one-quarter of the field.
Water was again transferred to another set of furrows.
This continued for the third surge  and fourth surge.
TABLE 1.
Effects of surge irrigation, furrow torpedoes and field length on furrow-irrigation performance
 Block	Torpedoed	Flow	at 1,250 ft.
at 600 ft.
1	No	Continuous	12.9	7.1
 2	No	Surge	9.1	5.4
 3	No	Surge	8.4	5.2
 4	Yes	Surge	7.8	5.0
 5	Yes	Surge	10.5	4.8
 6	Yes	Continuous	9.4	4.3
 Surge irrigation was effective in reducing the amount of water required to irrigate nontorpedoed furrows.
Applied water was reduced from 12.9 to 9.1 inches a 30% decrease, or from 12.9 to 8.4 inches a 35% decrease.
For torpedoed furrows that were surgeirrigated, results were mixed.
Applied water on one section of furrows was reduced from 9.4 to 7.8 inches a 17% decrease.
On another block of 25 furrows, the torpedoed/surgeirrigated furrows required more water, 9.4 versus 10.5 inches a 12% increase.
Surveying the field slope on the monitored blocks revealed that block 5 had an uneven slope, which likely affected the amount of applied water required.
From these results, it is not conclusive that using surge irrigation on torpedoed furrows is beneficial.
It is likely that the excess applied water avoided by using surge irrigation or torpedoes would go to deep percolation, which could leach nitrates.
Sulfur fertilizer has been added to this advancing front of water, to act as a visual tracer.
The tracer has not been added to water in the furrows at the top and bottom
 Irrigations occur day and night.
Using surge irrigation at night is more complicated than during the day, when advance rates can be more easily observed.
However, once an irrigator determines the advance times on a field, surge-irrigation switches could be made on an irrigation-time basis.
This assumes a constant irrigation flow-rate to each block of a field, which can be difficult to achieve since many ranches irrigate multiple fields at the same time.
Evaluation of irrigation-system performance for shorter field lengths was relatively simple since the applied water, advance time and other necessary information was available as a subset of the field-evaluation data that was collected as part of the continuous/surge flow evaluations.
The 1,250-foot furrows were evaluated to see how much water would be required if field length was reduced to 600 feet.
Applied irrigation amounts could be reduced by 35% to 55% when field lengths were reduced from 1,250 to 600 feet.
San Joaquin Valley field lengths vary widely, but one-quarter mile is common.
This is often too long to allow water applications that match the water needs of the crop.
The minimum irrigation-application amount is determined by the amount of water needed to advance water to the end of the field.
For example, if 6 inches of water is required but the crop water use since the last irrigation has been 4 inches, at least 2 inches of water would be lost to deep percolation.
If nutrients are available to be leached, the excess water could be the vehicle for carrying them below the crop's root zone.
Shortening the field length allows a lesser irrigation amount to be applied during an irrigation set and allows that amount to more closely match the water depleted from the crop's root zone, thereby increasing irrigation efficiency.
Irrigation uniformity is also improved in shorter fields.
Surge irrigation would therefore seem to be a natural practice for growers to adopt, but the furrow systems on most dairies do not lend themselves to it.
Surge irrigation using freshwater alone is done using gated pipe and an automatic surge valve.
Dairies seldom use gated pipe because the manure solids and trash  in the manure water clog the discharge openings.
Instead, dairies often use alfalfa valves, which discharge water into a block of furrows.
An added complication is that the automatic surge valve has an internal, motorized, butterfly valve that could become entangled with trash in the water.
To use surge irrigation on dairies now would require irrigators to manually open and close alfalfa valves a significant increase in labor and management costs.
Reductions in field length have the greatest impact on irrigation performance, but they are also the most costly and inconvenient to implement.
To reduce a one-quarter-mile-long field to two one-eighth-mile fields would require a new pipeline , a new road  and possibly new tailwater-collection facilities.
Shorter field lengths are also a significant inconvenience when equipment is moved through the field, with consequent impacts on field preparation, cultivation, pest and weed control, and harvest activities.
Timing of manure-water additions
 Field tests were done to manipulate the timing of manure-water additions to irrigation water.
The objectives were:  to improve the uniformity of nutrient applications, and  to provide a
 method for applying smaller amounts of nutrients per irrigation event as compared to adding manure water during the entire irrigation event, which is currently the most common practice.
This strategy of changing the timing of manure-water additions hinges on infiltration characteristics, which vary during irrigation.
The infiltration rate is high when water first comes into contact with a dry soil and then decreases, often significantly, until a final, relatively constant intake rate is reached.
Due to the time required for water to advance across the field, water is in contact with the soil  at the head of the field for a significantly greater time than at the field's tail end.
The result is more infiltrated water at the head of the field than the tail.
The same is true of nutrient applications if manure water is added continuously to the irrigation water.
To apply a lower nutrient amount during a continuous irrigation by using manure water with a high nitrogen concentration, a smaller flow-rate of manure water must be added to the irrigation water.
This is often incompatible with the large manure pumps and pipelines designed for high flow-rates that dairies currently have.
Running small flow-rates of manure water through large pipelines can result in settling and clogging of the pipeline.
We evaluated multiple irrigation events at the Tulare County commercial dairy.
For an initial visual evaluation, a tracer  was added to the irrigation water at various delayed times during the irrigation event.
The sulfur fertilizer turns the irrigation water milky in appearance and can be visually tracked as it moves down the furrow.
The sulfur fertilizer was not used to trace infiltrated nutrients into the soil profile.
From monitoring the tracer, it became evident that nutrient additions to the irrigation water could begin quite late in the irrigation set and still have time to advance to the end of the field before the end of the irrigation set.
TABLE 2.
Irrigation evaluation results of manure-water irrigation strategies 
 From these tracer tests, we determined that the addition of manure water would start when clean irrigation water had advanced approximately 900 feet along the 1,250-foot-long field.
Nutrient application	Average	Irrigation	Avg.
manure	Manure-water	Nitrogen
 strategy	irrigation	uniformity 	water infiltrated	uniformity 	applied
 inches	%	inches	%	Ib/ac
 during entire irrigation	7.1	64	7.1	64	242
 = 900 ft.; shut-off when
 advanced to end of field	7.1	64	2.5	69	86
 = 900 ft.; shut-off = end of
 field advance + 1 hr.
7.6	70	3.0	69	102
 = 1,000 ft.; shut-off when
 advanced to end of field	7.1	64	0.9	91	31
 = 1,000 ft; shut-off = end of
 field advance + 1 hr.
7.6	70	1.4	88	49
 As a result, the advancing front of the manure-water/freshwater mix caught the advancing front of the freshwater at the 1,050-foot furrow distance.
It took the clean irrigation water 4 to 5 hours to advance to 1,050 feet, but it took the delayed manure-water advancing front less than 1 hour to reach the 1,050-foot mark.
Water samples were collected at frequent intervals  and at multiple locations along the furrow.
These water samples traced the movement of the manure water along the furrow and provided the spatial and temporal distribution of water quality during the irrigation event.
RBC flumes were placed in furrows to monitor furrow flow-rate.
The field was surveyed and its slope was determined.
Advance-recession measurements were also gathered.
The results from the irrigation evaluation were used to provide inputs to a two-point Volume Balance furrow-irrigation model , to determine infiltrated water amounts along the furrow and the irrigation uniformity.
The results of delaying additions of manure water to the irrigation water were promising: not only could a lesser amount of nutrient be applied using the existing manure-water application
 equipment, but the nutrients could also be applied more uniformly.
Nitrogen and ammonium are found in manure water and can pollute groundwater if applied at levels too high and then leached through the soil profile.
The fresh irrigation water/ manure-water mix used for irrigation had approximately 100 milligrams per liter  ammonium  and 150 mg/l total nitrogen.
For example, nitrogen samples taken 30 minutes after manure water traveled 900 feet along the field recorded the following ammonium  and total nitrogen  levels: head of field, 101 and 155; 300 feet along field, 106 and 155; 600 feet along field, 107 and 131; and 900 feet along field, 101 and 139.
There was little change in ammonium content and a slight change in total nitrogen of the water along the furrow.
As is common with dairy manure-waters, there was no nitrate in the manure water because manure ponds are anaerobic.
The manure water used for irrigation was relatively low in solids since the dairy had a solids separator and a multipond manure-handling system.
For this manure water, the majority of the nitrogen nutrients were tied up in the ammonium form and in the organic form as small particles that stay
 in suspension.
The constant nitrogen content of the irrigation water along the furrow may not hold for manure water high in large particles, which settle out at the head of the field.
In such cases, it is possible that the organic nitrogen content of the water would decrease more significantly as it moves down the furrow.
In order to gauge infiltration and irrigation uniformity, we monitored an early-season irrigation event following a cultivation.
Water advanced across the field in approximately 5.5 hours.
The average irrigation depth applied was 7.1 inches with a distribution uniformity  of 64%.
As with many dairies in Tulare County, the irrigation system was operated to minimize tailwater runoff.
Therefore, once water advanced to the end of the field, it was allowed to run only a short time before the irrigation set was switched.
As a result, the top end of the field received substantially more infiltrated water than the tail end.
For the monitored irrigation event, the head of the field received approximately 9.4 inches of infiltrated water while the tail end received approximately 3.1 inches.
If manure water had been added to the irrigation flows during the entire irrigation event, the uniformity of nitrogen application would have been the same as the water application uniformity 64%.
The top end of the field would have received significantly more nitrogen than the tail end.
Adding manure water during the entire irrigation event would have resulted in the field receiving an average of 242 pounds of nitrogen per acre, which is generally considered to be excessive for a single irrigation event.
When manure water was added to the irrigation water after freshwater had advanced 900 feet along the furrow, the manure-water application uniformity was increased from 64% to 69%.
However, at least as importantly, the average nitrogen application to the field was reduced from 242 to 86 pounds per acre , a level more appropriate for nutrient management.
With the field data available for model verification, the following simulations
 of other irrigation and manure-timing strategies were investigated using a two-point Volume Balance model.
Simulation 1.
Manure-water additions began when freshwater reached 900 feet along the furrow.
Irrigation water was shut off 1 hour after it reached the end of the field.
This strategy would result in a nutrient application uniformity nearly the same as the irrigation uniformity  , but the average nitrogen application amount is reduced from 242 pounds per acre for the continuous manure-water addition strategy to 102 pounds per acre for this delayed manure-water addition practice.
Simulation 2.
Freshwater was allowed to advance 1,000 feet along the furrow before manure water was added to the irrigation water.
The irrigation supply was shut off shortly after water reached the end of the field.
The result of this practice would be a small amount of nitrogen  applied to the field very uniformly.
This is a good strategy if frequent, small applications of nitrogen are desired.
Simulation 3.
In this delayed manurewater addition strategy, manure water was added to the irrigation water after freshwater had advanced to 1,000 feet.
Irrigation was allowed to continue for 1 hour after water advanced to the end of the field.
This strategy allows the application of a limited amount of nitrogen to the field  while applying it with a high uniformity.
Of all the strategies evaluated, this is preferable since it increases both the irrigation and nutrient application uniformities  compared to adding manure water during the entire irrigation event, which is stopped when water reaches the end of the field.
Delayed addition of manure water holds promise as a means of improving nutrient application uniformity and of applying less nitrogen during an irrigation, while still using existing highflow-rate manure-water pumps and pipelines.
One disadvantage of delaying manure-water applications is that there is a delay between when manure-water pumps are turned on and when manure water reaches the irrigated field.
For the field evaluated in this study, that delay was approximately 20 minutes.
Furthermore, it is quite common for dairies to
 irrigate multiple fields at the same time, often at different locations on the dairy and utilizing complex piping systems, to deliver the water.
This makes delayed manure-water additions, as well as any form of manure-water nutrient management, a complex task.
Reducing applied irrigation water
 The three irrigation water-management techniques furrow torpedoes, surge irrigation and shortening field lengths were all effective in reducing the amount of applied water per irrigation.
Furrow torpedoes reduced the applied water by approximately 25% and surge irrigation by 15% to 35%.
Field-length reductions were also effective.
Splitting a one-quarter-mile field into two oneeighth-mile fields could reduce the applied irrigation water by 35% to 55%.
The normal practice for applying manure water to a field is to add it to the freshwater during the entire irrigation event.
Delaying addition of manure water until the advancing freshwater has reached 900 feet along a 1,250-foot field resulted in an increase in distribution uniformity  of the manurewater application and a decrease in applied nitrogen  as compared to the continuous addition of manure water.
Simulation of other delayed manure-water addition strategies indicated that nutrient application uniformity could be increased to nearly 90% while applying 30 to 50 pounds per acre of nitrogen during an irrigation event.
L.
Schwankl is Irrigation Specialist, UC Cooperative Extension, UC Davis; and C.
Frate is Farm Advisor, UC Cooperative Extension, Tulare County.
The authors would like to thank the UC Center for Water Resources-Prosser Trust Fund for support of this work.
ACHIEVING A SUSTAINABLE IRRIGATED AGROECOSYSTEM IN THE ARKANSAS RIVER BASIN: A HISTORICAL PERSPECTIVE AND OVERVIEW OF SALINITY, SALINITY CONTROL PRINCIPLES, PRACTICES, AND STRATEGIES
 Nature of Agricultural Salt Problems
 Salinity is defined as the concentration of dissolved mineral salts in waters and soils.
The concentration can be expressed either on a mass, volume, or chemical equivalent basis.
Expressed on a mass basis, readers are probably most familiar with the units of parts per million , while on a volume basis the typical unit is milligrams per liter.
Another very useful way of expressing the dissolved mineral concentration is on an equivalent basis since many chemical composition calculations involve equivalence calculations.
The unit that is commonly used is milliequivalents per liter  which is also the same as millimoles of charge per liter, abbreviated as mmol/l.
A dissolved mineral constituent expressed in either ppm or mg/l is converted to its equivalence.
For any reported value the chemical equivalent  and the anions.
Sometimes the term hypersalinity will be encountered.
Here, reference is being made to the concentration of not only the dissolved minerals listed above, but also include other constituents that may include manganese, boron, lithium, fluoride, barium, strontium, aluminum, rubidium, and silica and specifically describes land salt sources found in enclosed, inland water bodies that have solute concentration well in excess of sea water.
Salinity is often expressed as one of two coalesced parameters representing the aggregated concentration of the dissolved minerals.
The first parameter that most people are familiar is either the electrical conductivity or specific conductance.
Sometimes hydrologists like to distinguish specific conductance from measured electrical conductivity.
In this case, the electrical conductivity hereby referred to, as EC is the reciprocal of the solution resistance measured between two electrodes and the specific conductance  is then the value accounting for variations in the conductivity cell used in the laboratory or field.
For our discussion EC and SC are used interchangeably; both have been multiplied by the appropriate "cell constant" and corrected for
 temperature and normalized to 25 degrees centigrade.
From hereinafter the of the applied irrigation water will be referred to as ECw.
Soil salinity is typically measured in a saturation soil extract , a saturated paste , or in situ by electroconductmetric methods by measuring the apparent bulk conductivity, ECa.
The units for can sometimes be confusing.
The unit for the conductivity per unit volume of 1 cm is siemens per centimeter  but this unit is much too large.
Consequently, the most common working units are the millisiemen per cm , the decisiemen per meter  which is equal to the traditional millimhos per cm  unit dimension for expressing EC.
The second parameter is the gravimetric measure of the aggregated concentration of the dissolved minerals commonly known as the total dissolved solids, or just TDS expressed in units of ppm or mg/l.
Knowledge of the gravimetric content of salts is particularly important in determining loading.
One of the overall effects of salinity and the degradation of soils is the special case where excessive sodium in irrigation water is a contributing factor to infiltration problems.
This is referred to as "sodicity." The two factors that influence the infiltration of water into the soil are  the salinity of the water, and  the amount of sodium relative to the amount of calcium and magnesium.
The index that has been used most commonly to determine the contributing potential of sodium to infiltration problems is the Sodium Adsorption Ratio.
The SAR can be expressed in two ways; it's original form as:
 or it's "adjusted" form accounting for changes associated with calcium dissolution/precipitation at the soil surface:
 Source of Agricultural Salt Problems
 The primary origin of salts is the chemical weathering of geological materials and anthropogenic processes.
Congruent, incongruent dissolution, and redox reactions are responsible for salt accumulation in soils and waters by chemical weathering.
The anthropogenic salinization processes are driven by evapotranspiration which are discussed briefly as follows.
The concentrations of soluble salts increase in soils as the soil water is removed to meet its atmospheric demand by evaporation and transpiration.
The salts, which are left behind concentrate in the shrinking soil-water volume with each successive applied irrigation; passing through the soil profile.
Furthermore, soils with shallow, saline water tables can become salinized as the result of the upward flux of water and salt into the rootzone.
It is these soluble salts that if not managed, will eventually build up in irrigated soils to the point that crop yield is adversely affected.
PHYSIOGRAPHIC FEATURES AND AGROECOLOGY OF THE ARKANSAS RIVER BASIN
 The Arkansas Valley originates upstream from Leadville, Colorado, at an elevation of more than 14,000 feet.
A notable feature of the Arkansas River Drainage Basin, which encompasses about 26,150 square miles including the Cimarron River watershed, is that its headwaters are at the highest point  in Colorado.
The river leaves the state downstream at the lowest point in Colorado of less than 3,400 feet elevation.
Between these two points the river flows about 360 miles through Colorado.
The river's transition from the mountains to the plains is near Canon City, 36 miles west of Pueblo.
West of this transition the river gradient averages about 40 feet per mile; least of this point the river gradient is reduced to a little less than nine feet per mile.
The Sawatch Mountain Range separates the basin from the Colorado River Drainage Basin on the northwest; the Rio Grande Drainage Basin by the Sangre de Cristo, and Culebra Ranges on the southwest.
There are 23 peaks in these three mountain ranges that have elevations greater than 14,000 feet above sea level.
On the north, the Mosquito Mountain Range and Monument Divide also referred to as the Palmer Lake Divide or Palmer ridge separates the northern boundary from the South Platte River Drainage Basin.
The basin is typically divided into two physiographic provinces; to the west is the Southern Rocky Mountain Province while to the least is the Great Plains Province.
The division between the two provinces is approximately at the 105-degree parallel.
The Southern Rocky Mountain Province consists primarily of the mountain area underlain by Precambrian igneous and metamorphic rock formations.
Late Cretaceous marine shales and limestones underlie the Great Plains Province.
The Great Plains Province can be further divided into the "Colorado Piedmont" and the "Raton Section." A parallel line divides them approximately 25 miles south of the Arkansas River representing the elevated plain north of the line and the trenched peneplain south of the line.
Surface and groundwater irrigation water, return flows, and irrigation ditch overflow are the primary water sources.
Surface water supplies consist of both direct-diverted, native waters and transmountain diverted water imported in to the Arkansas River Basin.
Since 1996 all diversions of tributary groundwater  for irrigation including those within the proposed project area are subject to specific augmentation requirements.
Based on whether the groundwater source is used as supplemental or sole source water supply for irrigation purposes, a percentage of the total water pumped is to be replaced to the Arkansas River.
This replacement of these so-called presumptive stream depletions are placed to prevent material injury to senior surface water rights and depletions to the Colorado-Kansas stateline flows under the Colorado-Kansas Compact.
Settlers arriving in the area relied on cultivated irrigated crops.
As early as 1853 it was recorded that in addition to corn and wheat, the potato, rutabaga, and beet were easily cultivated.
Other crops that drove the early production system of the region were alfalfa, watermelon, first grown in 1878; and cantaloupe, first grown in 1884.
In 1896, the Rocky Ford Melon Growers Association
 was organized to bring producers together into one marketing group.
Melons were shipped with the brand name "Rocky Ford" cantaloupe, a name that remains widely known across the country.
By 1905, four seed companies had developed businesses in Rocky Ford.
By 1907, one of these, the Rocky Ford Seed Breeders Association, was selling 30 tons of cantaloupe seed per year to growers in the Imperial Valley of California.
By 1925 ninety percent of the cucumber seed and 75 percent of the cantaloupe seed planted in the United States were grown in Otero County.
However, the perishability of these commodities and price fluctuations led farmers to seek a more diversified irrigated agriculture.
The crop introduced to fill the void turned out to be the sugar beet.
Much of the original irrigation development has been tied to the sugar beet industry.
At the peak of the industry, 22 sugar beet processing facilities operated in southeastern Colorado.
Ultimately, the valley had more factories than the farmers and land were able to support.
This coupled with lower yields, caused by poor quality irrigation water, sugar-pricing problems, and outbreaks of beet blight  resulted in sharp decline and elimination of profits.
All but one of the factories had closed by 1967 and all are presently closed.
Another key crop in the development of the agricultural heritage was Pascal celery.
It was through the efforts, in part, of the Pierce Seed Company of Pueblo that the "Pueblo celery" became recognized as high quality celery surpassing that of the products produced in Michigan and California.
The Pueblo Pascal celery, which was characterized by its crispness, whiteness, and distinctive nutty flavor, soon became the preferred choice over the Golden celery grown elsewhere.
By 1919, shipments amounted to 500 refrigerated railcars, each carrying 40,000 pounds.
The celery grown from what were called the Booth Gardens fields near Pueblo was being served on the tables of hotels in New Orleans and St.
Louis during the early 1900's.
The celery was served in the dining cars of the Missouri Pacific and Santa Fe railroads.
Between 1923 and 1927 it was this celery grown near Pueblo, Colorado, that President Coolidge and his wife wanted for their holiday White House dinners.
One of the most notable celery producers by the name of Charley Barnhart became the largest celery producer in the area.
He was considered the leader in celery production, overcoming the many cultural problems including the method of planting the stalks back three times during the year.
Although most of the crop went to market during the Thanksgiving and Christmas holidays, Barnhart advanced the storage technique of placing celery in trenches covered with straw and soil.
Under favorable conditions this allowed the celery to be kept as late as April of the following year and marketed when prices were high.
Celery met a similar fate to that of the sugar beet.
The sugar beet leafhopper and the aster yellows virus proved disastrous to the local celery industry.
The last celery crop was grown in 1981.
Although the "Rocky Ford" cantaloupe, sugar beet, and the "Pueblo Pascal" celery were two of the earliest crops critical to development of the valley, other crops have proved to be adaptable to the area.
Crops currently grown include corn, grain sorghum, alfalfa, soybean, dry bean, wheat, onions, tomato, potato, watermelon, honeydew, cucumber, cabbage, cantaloupe, chile, wine grapes, cabbage, apples, sweetcorn, raspberries, pumpkins, black-eyed peas, green beans, squash, cherry, plum, okra, barley, parsnip, winter turnip, garlic, turf, and zinnia flowers for seed.
One will find a cornucopia of fresh vegetables in today's roadside markets including a host of chile pepper varieties, spelled "chile" not "chili".
The first pepper to be grown was the cherry pepper.
In 1961 just a year later, Denver's Dreher Pickle Packing Co.
contracted three acres.
By 1996, the acreage grew to almost 800 acres and has come to include many of the pungent as well as non-pungent chile peppers with household names such as 'Big Jim', and 'Anaheim'.
Just as the "Pueblo celery" dominated the early 20th century, the "Pueblo chile", is becoming a recognized important part of the agricultural commodity system.
A mirasol  chile, it is a preferred pungent type for many culinary uses including salsas.
Two seed companies remain as leaders in the development, culture, and marketing of curcurbit and other specialty seeds worldwide.
Melon development continues as well.
The "Rocky Sweet," a cross between a cantaloupe and honeydew was grown commercially for the first time in 1985 and is steadily becoming a favorite for the melon connoisseur.
A part of the special agricultural production heritage of the middle reach of the basin relates to the dominance of the small farmer many of who are of southern European decent.
Most came to the United States during the early 1900's to work in the Colorado Fuel and Iron  steel mill.
Looking for alternate income sources during mill slowdowns, they started small truck farms and developed roadside markets.
Although the farms have tended to become larger over time the small truck farm operations still play a very important role in today's production system.
A HISTORIAL PERSPECTIVE OF IRRIGATION DEVELOPMENT AND ITS CURRENT STATUS
 Much of the interesting irrigation history in the southwest surrounds the debate that all puebloan groups including the Rio Grande Valley of New Mexico practiced irrigation before the Coronado expedition.
It has been asserted without a great deal of evidence that these puebloans learned to irrigate from the Chacoan Anasazi.
It is important to note though that protohistoric Sonorant irrigated agriculture was observed by both the Coronado and Ibarra expeditions.
However, the records of Coronado did not mention anything about the engagement of Rio Grande puebloans in irrigated agriculture.
This other side of the debate suggests that not all puebloan groups inherited the knack for irrigation; that it were the encomenderos and missionaries that imposed the irreversible reliance on irrigated culture  on the native peoples of this region that would eventually become Colorado and New Mexico.
One substantial piece of evidence to support the push of intensive agriculture came out of the Espejo expedition starting in 1582.
The expedition included visits to a number of pueblos including those of the Piro and Salinas Provinces in the vicinity of present-day Socorro, New Mexico.
It was reported that corn was being irrigated with dams and canals apparently from the Rio San Jose or Rio Cubero Rivers that looked to have been built by the Spaniards.
Just previous to the Espejo expedition, reports from the RodriguezChamuscado expedition in 1581 provided positive evidence of puebloan irrigation just north of present-day Bernalillo.
Cornfields were being irrigated from what is assumed to be Las Huertas Creek that drains the north slopes of the Sandia Mountains.
In a region that neither Espejo nor the
 Chamuscado expeditions had explored, Gasper Castano de Sosa reported all six pueblos in the Sante Fe area that his expedition visited in 1591 had canals for irrigation.
The generally accepted beginning of Spanish irrigation in the region, however, was marked by the construction start of an irrigation ditch or Acequia madre  for the Tewa Pueblo in 1598.
Under the Spanish repartimiento and encomienda system the demands compelled the Puebloans to intensify agricultural production through irrigation during the seventeenth century.
The demanding system for labor, the inclination for Puebloans to hunt rather than farm; economic exploitation and religious persecution as history recounts, led to the Pueblo Revolt of 1680 which decimated the Spanish settlements.
This brings us to the Spanish Colonial New Mexico period following the Reconquest of New Mexico.
This period was ushered in with a new economic regime; one that focused on land grants rather than encomiendas.
With the exception to Diego de Vargas himself, the Spanish settlers were required to support themselves by their own labors.
Rehabilitation and development of new acequia madres was of primary consideration.
Much of Colorado's irrigation history is centered in the Arkansas River Basin.
The richness of the agricultural heritage as related to irrigation is significantly enhanced from the geographic setting where the Arkansas River divided the future state.
This was the border separating Mexico and the United States between the years 1803  and 1848 , which signaled the end of the Mexican-American War.
The first known attempt at modern irrigation within this region of the Spanish Territory is documented to have been near Pueblo.
In the summer of 1787 ten years after his appointment, Juan Bautista de Anza, the Governor of the Spanish New Mexico Province entered into a treaty with the Jupe tribe of the Comanche Indians.
It was one of the outcomes of this treaty that led to the establishment of the first recorded irrigation system.
Leading up to the treaty there were hit-and-run raids by the Comanche Indians on the Ute villages, Spanish hamlets, and pueblos along these northern regions of the territory.
Previous attempts to squash the Jupe Commanche raids were unsuccessful.
The Spanish would advance over Raton Pass or Sangre de Cristo Pass only to have the Jupe Comanche Indians spot dust clouds and campfires of Spanish soldiers and then perspicaciously retreat to western Kansas to safety.
The raids, led primarily by Chief Cureno Verde , tormented and menaced the Spanish settlers and villagers to the point that in 1779, Governor Anza led a military party to the Jupe Comanche hunting grounds on Greenhorn Creek.
It was a location on Greenhorn Creek, a tributary to the St.
Charles River where Verde was engaged in battle and killed.
An ancestor of Anza's cartographer has recently disputed the original marked site of this battle.
Because of the original mistranslation of the Spanish word "zanja" coupled by retracing the mileage in Anza's diary it is now thought that the battle was fought near the intersection of Water Barrel Road and Burnt Mill Road.
Greenhorn Peak, the highest within the Wet Mountains, just southwest of present-day Pueblo and readily visible from the proposed project area is named in honor of this battle.
Anza had not only demonstrated his leadership abilities as a military leader but also as an expert frontiersman.
He had already founded San Francisco  and Mission
 Dolores in 1776 and earned the name "Great Colonizer." As a part of the treaty that Governor Anza had orchestrated with the Jupe Comanche following the untimely death of Verde, Anza sent about 20 Spanish farmers and artisans to settle a colony with the tribe who had given in to the Spaniards and were willing to settle in villages.
This colony was built on the banks of the San Carlos  River at the confluence of the Arkansas River.
It was named "San Carlos de Jupes." Provided with seeds to plant and sheep and cattle, the Spaniards with their Comanche counterparts constructed a ditch that took water from the San Carlos  to irrigate a large tract of land that had been sodbroken and put into cultivation.
The Colony was eventually abandoned.
There are at least two accounts for the lack of success of the venture.
The lack of leadership by the successor to Governor Anza who died in 1788 coupled with the Commanche's lack of enthusiasm for the manual labor required for irrigated farming and homes contributed to the Colony's demise.
Another account suggests that the death of a woman who had been admired by Chief Paruanarimuco contributed to abandonment; that the Comanche viewed the woman's death as a divine sign of disapproval.
As a result they deserted the settlement and other Spanish colonists weren't interested in moving to San Carlos.
There are accounts of several early unsuccessful attempts of irrigation and farming in the basin following the Louisiana Purchase.
These include a ditch that was built near Bent's Fort in 1832 in which about 40 acres of corn, beans, squash, and melons were planted.
However, Indian ponies grazing on the growing crops thwarted any kind of productive harvest.
Probably the first record of what could be considered a successful irrigation venture was the establishment of the settlement in 1841 of what would become known as "El Pueblo".
Along with the trading post there was extensive acreage cultivated until Ute and Apache Indians killed the Mexican inhabitants in 1854.
An irrigation enterprise was established in 1846 where the Taos Trail crossed Greenhorn Creek.
The location became known as John Brown's Store near present day Rye.
In the same area a settlement of French-Canadian hunters and their Indian wives were reported farming in the Greenhorn Valley in 1847 by G.F.
Ruxton.
In the same year, the Bent Brothers under the guidance of John Hatcher, downstream of present day Trinidad on the Purgatoire River  dug an irrigation ditch.
In 1853 a report by Lieutenant Beckwith traveling with Gunnison's exploration party showed that six Mexican families were diverting water out of Greenhorn Creek using the ditches previously constructed by John Brown.
It was also in 1853 that a ditch was dug for purposes of irrigation by Charles Autobees on the west bank of the Huerfano River.
In 1859, at the same location where Beckwith reported the diversion of water from Greenhorn Creek, Zan Hicklin and his wife Estefana who was Charles Bent's daughter established one of the largest irrigated farming operations.
Using the ditches originally dug by John Brown and employing large numbers of Mexican laborers, the Hicklin's cultivated a total of 380 acres.
This water right associated with the appropriation of this water was the earliest adjudicated appropriation in the basin  in the name of Hicklin Ditch on Greenhorn Creek.
The first two water rights on the main-stem of the Arkansas were decreed 30 days apart in 1861; the second to be that of the Bessemer ditch.
By the middle 1880's the main-stem and tributaries of the Arkansas were fully appropriated.
Water right decrees later than 1887 are little more than flood rights providing water only during snow melt and after summer rainstorm events; the last decreed right is 1933.
Major irrigation development required large scale financing to enlarge the very early diversions.
Most of the systems were constructed between 1874 and 1890.
Historically, the area of land irrigated in the Arkansas Valley has remained relatively stable.
In 1969 the U.S.
Bureau of Reclamation  estimated the land-irrigated equal to about 415,000 acres.
In the mid 1980's the estimated number of irrigated acres was cited to be about 411,000 acres, of which 56,000 acres are located in the upper portions of the basin.
The seasonal water supply in the basin is subject to considerable fluctuation.
Waters native to the Arkansas River, its tributaries, and water imported into the basin via the Frying Pan Arkansas Project, are used and reused.
The basin also includes a number of storage reservoirs.
Institutionally Arkansas River Drainage Basin  is divided into 13 Water Districts.
For a complete description of the operations of the various water systems, the reader is referred to Abbott.
Arkansas River Mainstem.
In the upper reach of the Arkansas River above Pueblo Reservoir  water is diverted to irrigate alfalfa, hay, or irrigated pasture, and serves small orchards.
Major conveyance systems include the South Canon Ditch, Pump Ditch and the Crooked Ditch, Canon City Hydraulic Ditch, Fruitland Ditch, Grandview Ditch, Canon City and Oil Creek  Ditch, Fremont County Ditch, Union, Hannenkratt ditch, and the Lester and Atteberry ditch.
Below Pueblo Reservoir Major irrigation conveyances diverting from the main stem of the Arkansas River in Water District 14 are the Bessemer Ditch, Colorado Canal, Rocky Ford Highline Canal, and Oxford Farmers Ditch.
There are also several small irrigation ditches including the Hamp-Bell, West Pueblo, Riverside Dairy, Excelsior, and Collier.
Above John Martin Reservoir the Otero, Catlin, Holbrook, Fort Lyon Storage, Rocky Ford, Fort Lyon, and Las Animas Consolidated Canals headgates are all in Water District 17.
The canal and ditch systems on the mainstem below John Martin Reservoir are in Water District 67; these include the Fort Bent Canal, Keesee, Amity Canal, Lamar Canal, Hyde, Manvel, X-Y Canal and Graham Ditch, Buffalo Canal and Sisson Ditch.
Although the diversion of the Frontier Ditch is physically located in Colorado just west of the state line it irrigates cropland in Kansas and therefore considered a Kansas ditch.
Arkansas River Tributaries.
There are a number of significant water conveyance systems that divert water from Arkansas River tributaries.
Included in the Wet Mountain Valley, located in Custer and Fremont County is the DeWeese-Dye ditch; located on Fourmile, Hardscrabble, and Beaver Creeks are Park Center, Hardscrabble ditch, and Brush Hollow Supply Ditch.
Other tributaries with minor diversions include Fountain Creek and the Apishapa River.
Serving the terrace lands on Fountain Creek between Colorado Springs and Pueblo are the Fountain Mutual ditch and the Chilicott Canal.
Limited water is diverted for irrigation In the upper reach of the Apishapa River from the Escondito, Salisbury and Widderfield ditches
 As previously mentioned the main tributary of the St.
Charles River, is Greenhorn Creek the location of the earliest priority in the Arkansas River basin: the Hicklin ditch, with a water right from spring 1859.
Smaller ditches include St.
Charles Flood, Tucker, Fairhurst,, McDowell, Chase, Wagner, Eagle, Fisher,Bryson and Anderson.
Diversions on the upper Huerfano River include the Medano Ditch and small direct diversions on Pass, Williams, and Turkey Creeks convey water to a number of ranches near Red Wing, Colorado.
Other diversions include the Orlando Ditch, Huerfano Valley, Farmers Nepesta, and Welton Ditch.
Also there are waters used for irrigation supply from the Cucharas River, tributary to the Huerfano River.
These are Middle Creek, Wahatoya Creek, Abeyta Creek, Bear Creek, and Santa Clara Creek, and the Gomez Ditch.
The other tributary supplying significant water for irrigation is the Purgatoire River.
Diverted through eight structures on the Purgatoire River's, water is delivered to 11 ditch companies and entities from the Bureau of Reclamation's "Trinidad project." Diverting water from the north side of the river include the Salas, Burns and Duncan, Hoehne, Model Inlet/Johns Flood, El Moro, and Picketwire.
The Lewelling-McCormick, South Side, Victor Florez, and Chilili Ditches divert water from the south side of the Purgatoire River.
Downstream from the Purgatoire Canyon and above the confluence with the Arkansas River are the headgates of the Ninemile and the Highland Canals.
RELATIONS OF SALINITY TO SELECTED PHYSIOGRAPHIC FEATURES IN THE ARKANSAS RIVER BASIN
 The areal and seasonal salinity characteristics within the Arkansas River Basin have been studied extensively.
The information has included data for both the surface and groundwater resources.
The information has emphasized electrical conductivity , its areal spatial, temporal variability and relationship to streamflow.
Concentrations of dissolved solids and major ions have also been examined.
One of the first comprehensive studies was that conducted by Miles.
A key finding of this study was that an estimated 14 percent of the total salt load within the basin can be attributed to irrigation; industrial and municipal uses contributes about 8 percent with the remaining 78 percent resulting from natural sources.
For the period studied  approximately 1.4 million tons of salt were diverted annually in the irrigation water from Canon City to the Colorado-Kansas stateline.
Areal and Temporal Distribution of Salinity and Relationship to Streamflow
 The median electrical conductivity  of the Arkansas River increases with increasing distance downstream.
The lowest values occur in the upper reach.
Small increases occur above Canon City.
At Canon City the median EC is 0.3 dS/m or about 240 ppm.
Between Canon City and Pueblo the salinity nearly doubles.
The largest increases occur between La Junta and Las Animas.
From the headwaters of the river to the Colorado-Kansas State line the salinity increases nearly 30 fold.
The median salinity at the stateline is about 4.1 dS/m.
The maximum salinity is about 6.5 dS/m.
The total electrolyte concentration within the basin  ranges from about 0.97 meq/l  to 61 meq/l.
In terms of the TDS the gravimetric salt content ranges between 76 mg/l to 4058 mg/l
 The distribution of the dissolved chemical constituents and relationships of to dissolved solids are also very important particularly in evaluating waters suitability and calculating mass balances.
The waters of the Arkansas River are primarily gypsiferous.
The sulfate concentration ranges from about 40 percent  of the total anions  in the headwaters to 85 percent  at the stateline.
In terms of cations, there occurs almost 6 times as much dissolved calcium  as sodium  in the upper reaches.
The ratio of calcium to sodium decreases with increasing distance downstream.
The concentrations become almost equal below John Martin Reservoir.
As expected the lowest salinity occurs during late spring and the irrigation season ; the periods of high snowmelt and flow.
Conversely, the greatest salinity occurs during the winter months and the non-irrigation season  in periods of low surface flow.
As such there is strong correlation between salinity and streamflow.
Seasonally and spatial log-log relations have been shown to best represent the inverse relation between salinity and streamflow.
These relationships can be used to accurately estimate ECw  from measured or simulated streamflows.
Figure 1.
Spatial variation of surface water salinity in the Arkansas River Drainage Basin.
Looking closer in Figure 4 the relationship between river streamflow and specific conductance comparing the irrigation season and non-irrigation season is significantly different for an upstream location  as compared to a downstream location.
During the non-irrigation season and low native surface flow the higher proportion of groundwater return flow to the river accounts for the overall streamflow and high specific conductance at the downstream location.
Figure 4.
Relationship between river streamflow and specific conductance during periods of the year for an upstream location  as compared to a downstream location.
MANAGING FOR SUSTAINED CROP PRODUCTIVITY AND WATER RESOURCE PROTECTION
 As an anthropogenic cause of salinity, irrigation has a profound effect on introducing soluble salts into irrigated agroecosystems.
There are four rules regarding irrigation and salinity that need to be understood:
 RULE #1: ALL waters used for irrigation contain salts of some kind in some varying amount.
RULE #2: Salinization of soil and water is inevitable to some extent.
RULE #3: An irrigated agroecosystem cannot be sustained without drainage, either natural or artificial.
RULE #4: Rules 1 through 3 can't be changed.
Figure 2 illustrates the salinization process in irrigated terrestrial system and is described as follows.
The anthropogenic salinization process by irrigation is driven by evapotranspiration.
The concentrations of soluble salts increase in soils as the soil water is removed to meet its atmospheric demand by evaporation and transpiration.
The salts, which are left behind as a consequence of plant uptake of nearly pure water concentrate in the shrinking soil-water volume are added to the existing quantity of salt in the root zone with each successive irrigation that is applied and passed through the soil profile.
As an example, an irrigation source with a salt content of 850 ppm is introducing 1.16 tons of salt for every acre-foot of water applied.
Drains empty into a collector system that transports the drainage water to a discharge point.
LEGEND Indicates salts Indicates flow of water
 Figure 5.
Mechanics of the salinization process in irrigated cropland systems.
Furthermore, soils with shallow, saline water tables can become salinized as the result of the upward flux, probably more familiarly known as capillary rise, of water and salt into the rootzone.
Simply stated, these shallow water tables result when the natural discharge is less than the irrigation-induced recharge.
There is a very close correlation between the level of salt accumulation in the soil with the water table depth, the salt content of the groundwater, and the soil's hydraulic properties.
It is these soluble salts, that, if not leached, managed, and disposed of properly with drainage, will eventually build up in irrigated soils to the point that crop yield is adversely affected.
There is not usually a single prescription for an effective salinity management strategy.
Rather, different practices and approaches need to be combined into a management scheme that is satisfactory in addressing an existing salinity problem or preventing one from manifesting itself into the terrestrial system.
A given solution to a salinity problem can be complex.
Not only are there the hydrogeology and edaphic, factors but economic and social factors to be carefully considered.
The following discussion outlines an important guiding principle and its elements in the development and adoption of appropriate management strategies.
Since it's the chemical composition of the irrigation water that creates the adverse soil condition to begin with it seems logical to form a problem-solving framework starting with assessing the given water's suitability for use.
In this regard perhaps the one overarching guiding principle that the practitioner needs to understand in order to develop the most effective salinity control strategy for a given situation should be evaluated on the basis of the potential use of a given source of water.
Simply stated the principle is as follows:
 "Water has no intrinsic quality, except in the resource setting for which it is to be used.
The suitability of any given water source relies strictly on what can be done with it under the specific conditions of use."
 In as much there are several important elements in the development and adoption of appropriate management strategies within this cornerstone principle.
These essential elements are  grow suitable salt tolerant crops,  use planting and tillage procedures that prevent excessive salinity accumulation in the seedbeds,  deliver irrigation water to fields efficiently,  apply irrigation water in an efficient manner that minimizes the leaching fraction and resulting deep percolation,  provide adequate drainage, and  monitor irrigation adequacy and soil profile salinity.
Grow Suitable Salt Tolerant Crops
 The adverse effects of salts on plants are generally divided into three parts; 1) the osmotic effect , 2) specific ion effects, and 3) the indirect effects caused from soil dispersion due to excess sodium.
The emphasis of this section is directed at the first two categories; osmotic effects and to lesser importance the tolerance of plants to foliar salt injury caused by specific ion effects.
The indirect soil dispersion effect and the management of infiltration problems will be addressed in a later section.
Osmotic Effect.
The plant extracts water from the soil by exerting an absorptive force in response to a gradient along the soil-plant-atmospheric-continuum one that is greater than that adsorptive force that holds water within the soil matrix.
When the plant cannot exert enough energy to extract sufficient water from the soil matrix the plant develops water stress.
Similarly, as the salt concentration of the water within the soil matrix increases, the energy that the plant needs to exert also increases.
Increased salt concentrations narrows the gap between the soil water and internal plant energy potential.
This is referred to as the osmotic effect caused by the increase in the osmotic potential of the root-zone soil solution.
In order to maintain a suitable energy gradient for water uptake to occur, non-halophytes  require additional expenditure of metabolic energy.
This additional energy expenditure shift would normally go to building dry matter and other plant functions.
For our purposes here, soil salinity is expressed as the mean electrical conductivity of a saturatedsoil extract of the root zone, ECe.
The SI unit expressing electrical conductivity is decisiemens per meter.
The osmotic potential  of the root zone soil water at field capacity can be approximated with the relation, OPfc= -0.725ECe100.
All crop plants do not respond to salinity in the same way; some produce acceptable yields at higher soil salinity levels than others do.
Each crop species has an inherent ability to make the needed osmotic adjustments enabling them to extract more water from a saline soil.
This ability for some crops to adjust to salinity is extremely useful.
In areas where the accumulation of salinity within the soil profile cannot be controlled at acceptable levels, an alternative crop can be selected that is more tolerant resulting in the production of better economical yields.
Yield Response Functions.
The relative salt tolerance of most agricultural crops is known well enough to provide general guidelines about salt tolerance for making management decisions.
The salt tolerance of any given crop can best be illustrated by plotting the potential yield, sometimes referred to as the relative yield, as a function of soil salinity.
The potential yield  or relative yield, expressed as a percent, is defined as the yield under saline conditions  relative to the yield under non-saline conditions :
 Although it has been shown that the relation between potential yield and soil salinity follows a sigmoidal curve, a piece-wise linear response function is used to easily describe the potential yield/soil salinity relation for acceptable crop yields.
Two intersecting straight-line segments represent this linear piece-wise response function.
One of the segments has a slope of zero.
This means that the yield potential is constant across a range of soil salinity.
The second line segment is a salinity-dependent line whose slope describes the yield reduction per unit increase in soil salinity.
The point where the two line segments intersect specifies the threshold soil salinity ) or the maximum average root zone soil salinity at which yield reductions will not occur.
Yield reductions will occur when soil salinity levels exceed this threshold value.
Mathematically, this piece-wise function can be represented as follows:
 When, ECe is greater than or equal to ECe, Yr= b-ECe)
 and when, ECe is less than ECe, Yr= 100
 where b is the slope of the second line segment expressed as the percent yield decrease per unit increase in soil salinity, ECe.
Figure 6.
Yield response to soil salinity for tomato.
Rearranging Equation 2 the soil salinity at which a given yield potential can be obtained may also be calculated:
 ECe= -Yr)/b  Likewise, the slope  of the line can also be calculated by rearranging Equation 2, b= 100/[0 Yield]-ECe [100% Yield]) 
 where ECe [0% Yield] and ECe[100% Yield] are soil salinities at 0 yield potential and 100% yield potential, respectively.
The analysis of tolerance field data shows that crops with similar tolerances form groups.
The upper boundaries and relative tolerance rating have been assigned to these groups as shown by the thick-segmented lines.
The four  regions between the lines define specific divisions for relative crop salt tolerance.
These groups are classified as
 sensitive , moderately sensitive , moderately tolerant , and tolerant.
Field soil salinity values that fall beyond the dotted line are considered to be unsuitable for most crops of economic importance.
Figure 7.
Crop yield response to salinity and categories for classifying salinity tolerance.
Although these groups are arbitrary, they are particularly useful in those instances where insufficient field data for a crop is available, but a relative rating can be assigned based on field experiences and local observations.
The yield response of a crop that has been given a relative tolerance can be then be described.
Table 1.
Relative crop salt tolerances.
Relative Crop Salinity	Slope 
 Tolerance Rating	ECe [0% Yield]	ECe	[100% Yield]	[Equation 5]
 dS/m	-% per dS/m -
 Sensitive 	7.0	1.3	17.5
 Moderately Sensitive 	16.0	3.0	7.7
 Moderately Tolerant 	24.0	6.0	5.6
 Tolerant 	32.0	10.0	4.6
 Appendix 1 lists the salinity thresholds ) and slopes,  for the most common crops and plants.
In addition, these species have been rated as sensitive , moderately sensitive , moderately tolerant , and tolerant.
The reader is referred to Maas  for an expanded list of crops and their salinity tolerance.
It has been suggested that using the piece-wise linear relation is somewhat flawed.
The reasons cited are that  there's a significant error in evaluating the slope near the threshold, that few studies include treatments to accurately determine the threshold value, and  the slope decreases with increasing soil salinity at the upper end of the curve.
One of the more popular sigmoidal models for quantifying crop salt tolerance has been the logistic model that incorporates the parameter representing the salinity  at which the yield is reduced by 50%, designated as C50 as presented by van Genuchten and Hoffman.
The general logistic model numerical expression takes the form, then, as:
 Yr = 1/P) X 100  where C is the soil salinity expressed as ECe.
When too few data points are available to precisely evaluate the salinity threshold, the value of C50 and p, a crop dependent constant determining the curves shape, provides a more definitive and stable characterization of the yield response to salinity.
However, the values of C50 and p have been evaluated for a limited number of crops.
It is important to note that for the most part the threshold soil salinity values that are cited were established from field studies where chloride was the predominant anion.
In preparation of saturated-soil extracts in the laboratory, gypsum  will be dissolved.
For soils that are dominated by gypsum, the ECe may range from 1 to 3 dS/m higher than non-gypsiferous soils at the same moisture content and electrical conductivity of the soil water, ECsw.
This means that values of ECe for crops grown on soils dominated by gypsum may exceed table values by as much as 2 dS/m.
If the soil salinity levels greatly exceed the tolerance of all of the crop selections options and yield potentials of less than 100 percent are not acceptable, "reclamation" leaching may be necessary prior to any cropping.
There are two conditions where reclamation leaching are most likely to be neccesary.
The first condition is where an inverted soil salinity profile  has developed.
This condition is most familiar where salts have accumulated in the presence of a shallow water table.
The second condition is where a regular soil salinity profile  exists at excessive levels caused by inadequate leaching.
The goal of reclamation leaching must be to reduce the salt concentration in the upper portion of the root zone to a level that approaches the crop tolerance.
Susceptibility of Crops to Foliar Salt Injury Due to Sprinkler Irrigation.
Foliar salt injury has been observed on a number of crop species.
Similarly to the varying response of crops to soil salinity, species vary widely in their response to this injury from sprinkler irrigation utilizing saline waters.
The foliar injury, commonly referred to as "salt burn", is caused by leaf absorption of excess concentrations of sodium and chloride.
Of all crop species evaluated, citrus and deciduous fruit trees, like apricot, plum, and almond, are the most susceptible to foliar injury.
The extent of the injury may go beyond considerable leaf
 necrosis and may also include leaf defoliation.
Among the herbaceous crops, plants' belonging to the Solonaceae family is generally the most sensitive.
This would include potato, tomato, and peppers.
Table 2 provides some general guidelines for determining the susceptibility of crops to foliar salt injury from sprinkler irrigation based on the concentrations of sodium or chloride.
These data represent field studies where the sprinkling occurred during daytime hours.
There appears not to be a correlation between a crops tolerance to soil salinity and its susceptibility to foliar injury.
Two examples include strawberry and avocado; both are very salt sensitive crops, but field data shows the risk of foliar injury to be negligible.
Changes in management have been shown to reduce the risk of foliar salt injury.
These include irrigating at night, avoiding periods of hot, dry winds, increasing sprinkler droplet size, and increasing rates of application.
Table 2.
Tolerance of crops to foliar salt injury from water applied using sprinkler irrigation methods.
Critical Sodium  or Chloride  Concentrations 
 >20	10-20	5-10	<5
 Cauliflower	Alfalfa	Grape	Plum
 Sugarbeet	Sorghum	Pepper	Citrus sp
 Cotton	Safflower	Tomato	Almond
 Sunflower	Barley	Potato	Apricot
 Stages of Growth.
The soil salinity/crop tolerance relations in Appendix 1 apply primarily to responses from the late seedling growth stages to maturity.
Field data on the variable crop tolerance during the early stages of growth  are extremely limited.
As a general rule most plants are tolerant during germination.
After germination, plants may then become sensitive during emergence and the development of the seedling.
Past studies have shown that increased salt concentrations may delay emergence, but does not affect final emergence.
However, secondary conditions such as soil crusting could result in reduced crop stands.
A general recommendation is that a soil salinity level of 4 dS/m in the seed zone will delay emergence seedling growth.
Use Planting and Tillage Procedures that Prevent Excessive Salinity Accumulation in the Seedbed
 A number of crops tend to be sensitive to salinity during germination and seedling establishment.
Stand losses can occur particularly when raised beds or ridges are employed.
These losses can be significant even when the average salinity levels in the soil and in the irrigation water are moderately low particularly under furrow irrigation.
Since salts move with the water, the salt accumulates progressively towards the surface and center of the raised bed or ridge.
Thus the
 greatest damage occurs when a single row of seeds is planted in the middle of the bed.
This is SO because salts tend to accumulate under furrow irrigation in those regions of the seedbed where the water flows converge and evaporate this problem is magnified when saline waters are used for irrigation.
Seedbed planting systems and furrows need be designed to minimize this problem.
This can be accomplished by considering alternative bed-furrow configurations and irrigation practices that involve seedbed shape, seed placement and irrigation techniques including alternate furrow irrigation.
Figure 3 illustrates typical salt patterns in flat and sloping beds.
Figure 8.
Salt accumulation patterns of flat and sloping beds as influenced by irrigation practice.
With the expansion of the use of subsurface drip irrigation in the Arkansas River basin, it is important to consider the distribution of salts within the root zone and bed.
The patterns that form under subsurface irrigation are distinct and differ significantly from the pattern where the drip tubing is on the soil surface.
Common to both cases salinity gradually increases as the horizontal distance from the line increases and the greatest salinity occurs at the leading edge of the wetting front very high salinity levels can occur near the soil surface.
While adequate leaching occurs below the buried tubing, the accumulation of salts above the drip tubing presents a dilemma.
A salinity hazard can develop if insufficient non-crop season precipitation occurs and moves the surface soil accumulated salts back into the immediate seed zone that can be detrimental to the subsequent year's crop.
One strategy is to leach the salts with sprinkler irrigation.
Figure 9.
Root zone salt distribution with subsurface drip irrigation system.
Deliver Irrigation Water to Fields Efficiently
 Unmistakably, the strategy for sustaining crop productivity and reducing the risk of salinity hazards of irrigated lands requires good irrigation management.
The basis for good irrigation management for salinity control is timely uniform irrigations, applied in an adequate quantity to meet the crop's consumptive use  and at the same time satisfy the leaching requirement.
In addition, the causal and interacting elements of good irrigation water management include the delivery system and the method and manner of irrigation.
For example water delivery based on predetermined amounts or preset periods without consideration of seasonal variations generally encourages over-irrigation.
A consequence of these institutional constraints is limited adoption of higher efficient irrigation such as sprinkler and drip.
The optimum water delivery infrastructure is one that can provide metered, controlled water nearly on a continuous basis SO that the soil water content in the rootzone can be kept within prescribed limits.
The other two factors that must be considered as an overall strategy are controlling  seepage losses and  maintaining drainage systems.
Excessive loss of irrigation water from canals constructed in permeable soil contributes to not only the mineral dissolution of the underlying geologic materials, but contributes significantly to the manifesting of high water tables and soil salinization.
Every effort should be taken to minimize these seepage losses.
The maintenance of the drainage system is also a key factor.
Both in-field tile lines and open drains should be kept in working order.
As far as sustaining irrigated agriculture it may well be necessary to reactivate many of the drainage districts in the basin.
Apply Irrigation Water in an Efficient Manner that Minimizes the Leaching Fraction and Resulting Deep Percolation
 As discussed earlier some salt accumulation is inevitable attributed to two processes.
Salt loading occurs from mineral weathering and dissolution of soluble salts.
Moreover, salt concentration occurs from plant uptake of water driven by evapotranspiration, thus leaving the salts behind.
When the accumulation of salts in the soil root zone becomes excessive to the point of affecting crop yield, they can easily be leached in the absence of a water table.
The goal is to move a portion of the salts below the root zone  by passing irrigation water through the root zone.
The ability to pass a specific volume of water through and passed the root zone is dependent on sufficient water-entry at the soil surface or infiltration.
The negative effect of salinity, specifically the amount of calcium and magnesium, relative to the amount of sodium is the interference in the normal infiltration rate and subsequent percolation of the infiltrated water  through the vadose zone.
When an infiltration problem results from the deleterious effect of the adsorbed sodium it is most commonly referred to as a sodium hazard or "sodicity".
This section discusses the leaching fraction , the proper calculation of the LF and assessing sodium hazards.
Leaching and Deep Percolation.
Clearly, if the volume of water applied can be minimized in a quantity not to exceed a crop's requirement, then the amount of salt added to the soil can be minimized.
For example, water immediately below John Martin Reservoir contains about 3.3 tons of salt for every acre-foot of water diverted.
Leaching, as the key factor in controlling the soluble salts, is accomplished by applying an amount of water that is in excess of the crops seasonal evapotranspiration and runoff.
This excess amount of water is called the leaching fraction , normally expressed in the decimal form.
As an example, a LF of 0.5 means that 50% of the water infiltrating into the soil profile passes through and out of the root zone.
The strategy is to optimize the leaching fraction to an acceptable minimum.
The basis for attaining a minimum LF is two-fold.
First as the LF decreases the precipitation of the dissolved salts applied in the irrigation water increases.
The precipitation of salts consists of calcium, bicarbonate, and sulfates as carbonates and gypsum.
The salt precipitation results in a decrease of the amount of salt in the soil and subsequent discharge from the rootzone.
Second, reducing the amount of water passing through the root zone reduces the risk of additional dissolution of weathered minerals from substrata from the percolating water.
The extent to which the LF can be minimized is limited by  the irrigation system,  a crop's tolerance to an increase in the root zone salinity.
To demonstrate the effect of leaching fraction on soil profile salinity, an example is given using the expected dissolved salt constituents of water diverted at two different landscape positions and six
 different leaching fractions.
Figures 10a and 10b compare the soil profile salinity distribution and the precipitation-dissolution of gypsum when irrigated with water composition expected of that below John Martin Reservoir compared to that expected between John Martin and Pueblo Reservoirs.
Figure 10.
Soil profile salinity distribution as a function of the leaching fraction for the  lower reach and  middle reach of the Arkansas River basin.
Below John Martin Reservoir  the leaching fraction increases as the average expected soil ECe in the absence of a water table decreases ranging from 6.9 dS/m at a 3 percent LF to an ECe of 2.5 dS/m at LF equal to 40 percent.
[Note that the ECe is about half of the EC of the soil water.] Above John Martin  the average expected soil ECe in the absence of a water table ranges from 3.1 dS/m at a 3 percent LF to an ECe of 1.2 dS/m at LF equal to 40 percent.
This illustrates the greater potential of reducing the leaching fraction of waters within the middle reach.
To keep the salts balanced SO that the soil profile ECe is equal to 2.5  we can minimize the LF to 40 percent and 5 percent using water diverted below and above John Martin Reservoir, respectively.
Leaching Fraction Estimation.
In order to estimate the LF and the amount of water required, only three pieces of information are needed;  the crop threshold soil salinity, ECe,  the salinity of the irrigation water, ECw, and  seasonal maximum evapotranspiration  of the crop.
Figure 7 shows the relation between the leaching fraction, LF, and the ratio, Fc.
Figure 11.
Relationship between the allowable rootzone salt concentration factor, Fc, and the leaching fraction, LF.
This ratio  is the crop threshold salinity divided by the irrigation water salinity /ECw).
This relation shows that for any particular crop, the LF exponentially increases as the salinity of the water increases.
Knowing the threshold salinity, ECe, for a given crop and the electrical conductivity of the irrigation water, ECw, the necessary leaching fraction  can be graphically determined from Figure 11.
For a more accurate LF estimation the exponential relations shown in Figure 11 can be simplified for any particular crop.
The "classical" method  of determining the LF is described by the following equation:
 where ECse is the average ECe at which the yield potential is 90% or greater.
In recent years  it has been shown that the LF is affected by the net water application.
To account for this effect an alternative method of determining the LF has been developed based on the allowable root zone concentration factor, Fc.
Since the net water application can be related to the irrigation system these relations are divided into two categories, namely  conventional and  high frequency.
Under "conventional irrigation" where there are relatively large net water applications, a higher leaching fraction is required at the same value of Fc as compared to high frequency irrigation.
Conventional irrigation scenarios where net water applications are relatively large include deep rooted crops grown under surface irrigation.
High frequency irrigation scenarios include shallow rooted crops under surface irrigation or where sprinkler or drip irrigation systems are used.
The exponential relations for the conventional irrigation  and high frequency irrigation  can be calculated as follows:
 The net annual depth of irrigation water  that is required to meet both the crop evapotranspiration  and the leaching requirement, Dsw'  is equal to:
 Dw = ETm + Dsw' 
 Relative to the crop's total annual evapotranspiration the net annual depth of irrigation water can then be calculated:
 Dw = ET/  where the ET and Dw are expressed in inches.
From Equation 10, the portion of water that is applied for the leaching can then be calculated as:
 Dsw' = Dw ET or,
 Field studies and observations have shown that as a general rule the timing of leaching is not critical as long as the crop tolerance threshold is not exceeded during critical periods or extended time periods.
Alternative timings include every irrigation, at selected seasonal irrigations or less frequently.
It must be noted that water losses attributed to deep percolation that occur during the season, particularly with surface irrigation systems, are often in excess of the leaching fraction.
A careful analysis must be done to determine whether or not the amount of water required for salt leaching will be satisfied by the field's irrigation inefficiency.
Infiltration and the Sodium Hazard.
Salinity and sodicity affect soil structure in which the aggregate stability provides a network of conducting pores or optimum infiltration and permeability to take place.
As previously introduced, a negative effect of salinity and the amount of sodium is the interference in the normal infiltration rate and subsequent percolation of the infiltrated water  through the vadose zone.
In the presence of sodium surface crusting, swelling, and dispersion are the primary processes responsible for an infiltration problem occurring In the presence of sodium which is reflected in the reduction in the soils hydraulic conductivity.
The soil's sodicity can be described based on the exchangeable sodium ratio  or the more familiar term; the exchangeable sodium percentage  which is the percentage of the total exchange complex  saturated with sodium.
Although the sodium hazard is a direct function of the soils exchangeable sodium percentage  the sodium adsorption ratio  of the soil solution is the variable that is used to describe the sodic condition since the SAR is more easily ascertained.
Figure 12.
Soil permeability hazard as influenced by salinity of infiltrating water and sodium and SAR.
In review, we said that the two factors that affect water infiltration are the  water's salinity and,  its sodium content in relation to the content of calcium and magnesium.
The following general precepts are good few rules of thumb to remember:
 High salinity water  increases infiltration
 Conversely, low salinity water  decreases infiltration
 Water with a high sodium content relative to the calcium and magnesium content  decreases infiltration.
The principle to keep in mind is that both factors, the salinity of the water and sodium content, operate at the same time.
In other words, just because a certain water's electrical conductivity  is low or the water's SAR is high doesn't necessarily mean that an infiltration problem will be manifested.
This can be thought of in another way.
That is to say that if there is sufficient calcium to offset the dispersing effect of the excessive sodium and that the total electrolyte concentration of the applied water is above the critical flocculation concentration, the soil pore sealing and soil dispersion causing reduced infiltration is unlikely.
Since the SAR is the criterion for describing the sodium dispersing effect and the ECw can be used as the criterion for describing the electrolyte concentration of the infiltrating water, one may guess then that the SAR and ECw can be considered together in properly assessing a potential infiltration problem.
That is indeed the case; a very useful relationship has been established that the conservation planner can use.
In Figure 12, the SAR at the soil surface is plotted on the y axis and the electrolyte concentration or the salt content of infiltrating water on the X axis.
Since the SAR at the soil surface is very near the same as the SAR of the infiltrating water the SAR of the water being applied is used while the salt content of the infiltrating water is merely the specific conductance or electrical conductivity of the water.
There are two areas separated by the line that is the threshold electrolyte concentration.
The area to the left of the line represents the combinations of SAR and ECw where a permeability hazard is likely to occur.
Conversely the area to the right of the line represents the combinations of SAR and ECw of stable permeability where it is unlikely for a permeability hazard to occur.
The third rule of salinity control and its management is that if a field is to be irrigated it must be drained.
The lack of adequate drainage leads to  waterlogging,  secondary soil profile salinization resulting from the upward capillary flux, and  impaired movement and operation of farm equipment.
In order to reduce the risk of waterlogging and secondary soil profile salinization, drainage should be provided.
In the absence of natural drainage artificial drainage will be needed.
There are fundamentally two purposes of drainage.
First, sufficient drainage is required to discharge the excess precipitated salts that have accumulated from previous irrigation and those salts of the infiltrated water into the soil which are in excess of the crop evapotranspiration demand.
Second, the water table, if present needs to be kept at the proper depth.
This permits adequate root development by minimizing the net flux of salt-laden groundwater upwards into the rootzone.
Monitor Irrigation Adequacy and Soil Profile Salinity
 A very important consideration in achieving a sustainable irrigated agroecosystem susceptible to salinity hazards is to monitor rootzone soil salinity levels and distributions.
The periodic assessment and inventory can serve as critical means to guide management including the adequacy of leaching and drainage.
On a large-scale or regional basis temporal and spatial information can be useful to delineate regions of drainage problem areas and salt-loading areas.
The proper framework to guide management practices in controlling salnity can be best outlined as follows :
 1) Adequate knowledge of the temporal trends in the level, extent, magnitude and spatial distribution of rootzone soil salinity within irrigated cropland fields.
2) Ability to ascertain the impact of changes in management practices and provide a course of action for evaluating irrigation and drainage system adequacy and effectiveness.
3) Ability to pinpoint salinity hazards and analyzes the inherent causes, whether managementinduced.
4) Capability to isolate parts of individual fields and areas of large-scale irrigated regions where excessive deep percolation is occurring.
If the outcomes identified within this framework are to be achieved traditional observation methods are no longer appropriate.
The framework requires the need for repeated measurements in both time and space that accurately describe salinity patterns.
Obtaining the needed information using conventional soil sampling and laboratory-analysis procedures is not practical and cost prohibitive.
A set of practical salinity assessment procedures and in situ techniques for measuring soil salinity in the field has been developed.
Large intensive and extensive data sets can be collected using these techniques and methodologies; they provide a systematic means for describing salinity condition both spatially and temporally.
Most importantly it allows practitioners to evaluate management effects.
These salinity assessment procedures involve the geospatial measurement of the bulk soil electrical conductivity  directly in the field.
The methodology and instrumental techniques can be integrated into a system that is rapid and mobile.
Several variations of the mobile apparatus, including what has become known as the "Salty-Dawg", and the "Salt-Sniffer", are currently being utilized.
These self-propelled units are comprised of commercially available components.
Figure 13.
Example map produced showing the spatial pattern of soil salinity.
An example of the application of this technology in the Arkansas River Drainage Basin is shown in Figure 13.
In order to assess alternative conservation treatment the field-scale soil salinity conditions where characterized and mapped using the dual pathway parallel conductance model.
The description of the model, its theory, mechanization, and example applications are provided elsewhere.
ALTERNATIVE STRATEGIES FOR CONTROLLING SALINITY OF WATER RESOURCES
 Interception, Isolation of Drainage Water and its Subsequent Reuse
 One alternative strategy to control the salinity is to intercept drainage waters before they are returned to the river.
These waters are then substituted for the less saline water of the original water supply.
The drainage waters that have been intercepted and isolated from can then be applied during the irrigation season to the more salt-tolerant crops grown in the rotation.
The process is repeated with the continued successive resuse of the drainage water and its application to the increasingly salt tolerant crops.
Once the water's capacity has been depleted and become too saline for any of the crops in the rotation the water can be discharged or treated.
This kind of irrigation scheme was been shown to be extremely successful.
Another alternative is one that removes land from irrigation that has been shown to adversely affect receiving water supplies.
There may be circumstances where irrigation is occurring on hydrogeologic landscapes, where the salt-loading and degradation of the water resource is severe enough, that warrants the consideration of eliminating irrigation of those lands.
McHendrie, A.W.
1952.
The early history of irrigation in Colorado, and the doctrine of appropriation.
In: A Hundred Years of Irrigation in Colorado: 100 Years of Organized and Continuous Irrigation, 1852-1952, Colorado Water Conservation Board and Colorado Agricultural and Mechanical College, Fort Collins, CO.
So, if we want to apply 8.5 gallons/acre of 32% UAN  with a pivot irrigating 5.7 acres/hour, the pump would need to be set to pump 48.5 gph.
8.5 g/acre x 5.7 acre/hr = 48.5 gph
 The pump would need to be set to deliver 48.5 gph to apply the planned 30 lbs/acre.
The biggest safety hazard is not having the 4th wire present or correctly connected all the way back to the power grid or generator.
Having the grounding rod correctly installed and connected is important, but is not a foolproof personal safety device by itself.
Grounding rods can be installed in situations where it is of little good because of soil type or after a lightning strike.
Some dealers have meters to check the rod installation for its resistance level.
IMPACT OF WIDE DROP SPACING AND SPRINKLER HEIGHT FOR CORN PRODUCTION
 Bill Kranz Northeast Research and Extension Center University of Nebraska Norfolk, NE 68701
 Freddie Lamm Northwest Research-Extension Center Kansas State University Colby, KS 67701-1697
 Derrel Martin Biological Systems Engineering Department University of Nebraska Lincoln, NE 68583
 Jose Payero West Central Research and Extension Center University of Nebraska North Platte, NE 69101
 Using center pivot sprinkler nozzles below the top of the corn crop canopy presents unique design and management considerations.
Distortion of the sprinkler pattern can be large and the resultant corn yield can be reduced.
In many areas, water available for irrigation is being limited due to reduced supply of both ground and surface water.
During periods of drought, uniformity problems associated with center pivot irrigation become quite visible.
Many times water stress on the crop is not evident until late in the season when the crop has nearly matured.
In many cases aerial observations of fields have revealed concentric rings that corresponded to sprinkler spacing.
Figure 1a.
Height reduction in corn caused by drops spaced too wide.
Figure 1b Concentric rings in corn field caused by having drops spaced too wide.
The impact of sprinkler spacing on water distribution and corn yield was the focus of University of Nebraska and Kansas State research studies.
Researchers conducted field experiments along with on-farm evaluations to gain a better understanding of operating sprinkler devices within the corn canopy.
The results from these experiments will be discussed.
Field Evaluation of Changes in Soil Water Content
 In a Nebraska study soil water content was measured as a method to evaluate the uniformity of water distribution.
Soil water content was measured in the top 12 in.
of soil before and after irrigation.
Spinners 1 were spaced 12.5 ft apart and located at a height of 42 inches in a mature corn crop.
Sprinklers were moving parallel to the corn rows but not necessarily between the corn rows.
Figure 2 shows the location of the sprinklers in the corn rows and the change in soil water content measured before and after irrigation.
Soil water content increased nearly 12% in the rows nearest the sprinkler device.
Soil water content averaged less than a 2% increase at locations directly between the sprinkler devices.
The small change in soil water content indicates the rows between the sprinkler devices received little or no water during the irrigation event.
In-Canopy Water Distribution Pattern
 Figure 2.
Changes in water content following irrigation with sprinkler nozzles located in a corn canopy.
Variation in Corn Yield as Affected by Sprinkler Height
 When the sprinkler pattern is distorted and the nozzle spacing is wide enough to prevent some corn rows from getting equal opportunity to water, yields can be reduced.
A study was conducted at the KSU Northwest Research-Extension Center from 1996-2001 to examine the effect of irrigation capacity and sprinkler height on corn production when the spray nozzle spacing was too wide for adequate in-canopy operation.
Performance of the various combinations was examined by measuring row-torow yields differences  Corn rows were planted circularly allowing the nozzle to remain parallel to the corn rows as the nozzle traveled through the field.
As might be expected, yield differences were greatest in dry years and nearly masked out in wet years.
For the purpose of brevity in this report, only the 6 year average results will be reported.
Even though the average yield for both corn rows was high, there is a 16 bu/acre yield difference between the row 15 inches from the nozzle and the corn row 45 inches from the nozzle for the 2 ft nozzle height and 10 ft nozzle spacing.
At a four ft nozzle height the row-torow yield difference was 9 bu/acre and at the 7ft height the yield difference disappeared.
This would be as expected since pattern distortion was for a shorter period of time for the higher nozzle heights.
It should be noted that the circular row pattern probably represents the least amount of yield reduction, since all corn rows are within 3.75 ft of the nearest nozzle.
For straight corn rows, the distance for some corn plants to the nearest nozzle is 5 ft.
KSU-NWREC, 1996-2001 Spinner Nozzle with 10ft spacing Note: 10 ft spacing not recommended
 Figure 3.
Row-to-row variation in corn yields as affected by sprinkler height in a study with a nozzle spacing too wide  for in-canopy irrigation, Colby, Kansas.
Data averaged across 4 different irrigation levels.
Note: The average yield for a particular height treatment would be obtained by averaging the two row yields.
On-Farm Evaluation of Sprinkler Spacing
 Many center pivot sprinkler systems are designed with wide sprinkler spacing as a method to reduce equipment cost.
For outer spans closer sprinkler spacing is needed in order to meet the water application requirements.
Although concentric rings were showing up in Nebraska fields, the outer portions of the fields showed no such pattern.
To evaluate the rings, a series of samples were collected to determine crop yield and soil water content.
Samples were collected from both sprinkler spacings where the spacing transition occurred to insure similar soil type and cultural conditions.
The location of sprinklers were first identified in relation to the wheel tracks.
Then the location of sprinklers were superimposed in that area of the field where the center pivot sprinkler devices run nearly parallel with the planted rows of corn.
All corn rows between two sprinkler devices were sampled to determine soil water content and grain yield.
Yield was determined by harvesting 10 feet of row.
Soil water content was measured to a depth of 4 feet at one location in each row.
The results given are the average of two yield and soil water content samples.
Field measurements were collected for two different center pivot fields represented in figures 4 and 5.
Sprinklers were located at a height of 7 ft.
and at either a 9 or 18 ft.
spacing.
Corn rows were planted 30 in.
apart.
Figures 4a and 5a shows the results for the narrow spacing of the two fields while figures 4b and 5b show results for the wide sprinkler spacing.
Generally, there were no reasonable patterns for either yield or soil moisture content for the 9 ft.
sprinkler spacing in figures 4a and 4b.
However, corn yield did decline when the sprinkler spacing increased to 18 ft.
in figures 5a and 5b.
Because soil water data was collected at the end of the season when the crop was mature, some of the difference, or lack of difference, in soil water content may have been eliminated with late season precipitation or added irrigation.
It should also be noted that soil water content is extremely low and most likely approaching wilting point.
Figure 4a.
Corn yield and soil water content for sprinkler devices spaced 9 ft apart at 7 ft height.
Figure 4b.
Corn yield and soil water content for sprinkler devices spaced 18 ft apart at 7 ft height.
Figure 5a.
Corn yield and soil water content for sprinkler devices spaced 9 ft.
apart at 7 ft height.
Figure 5b.
Corn yield and soil water content for sprinkler devices spaced 18 ft.
apart at 7 ft height.
Effect of sprinkler height and type on corn production
 Another study conducted from 1994-95 at the KSU Northwest ResearchExtension Center examined corn production as affected by sprinkler height and type and irrigation capacity.
Spray nozzles on the span , spray nozzles below the truss rods  and low energy precision application  nozzles  were compared under irrigation capacities limited to 1 inch every 4, 6, 8 or 10 days.
Corn yields averaged 201, 180, 164, and 140 bu/a for irrigation capacities of 1 inch every 4, 6, 8, or 10 days, respectively.
No statistically significant differences in corn yields, or water use efficiency were related to the sprinkler package used for irrigation.
There was a trend for the  package to perform better than spray nozzles at limited irrigation capacities and worse than the spray nozzles at the higher irrigation capacities.
Figure 6.
Corn grain yields as affected by sprinkler height and type at four different irrigation levels, KSU Northwest Research-Extension Center, Colby, Kansas, 1994-1995.
The first observation is supported by research from other locations, which shows that LEPA can help decrease evaporative water losses and thus increase irrigation efficiency.
The second observation indicates that LEPA may not be suited for higher capacity systems on northwest Kansas soils, even if runoff is controlled as it was in this study.
It should be noted that this study followed the true definition of LEPA with water applied in bubble mode to every other row.
The term LEPA is often misused to describe in-canopy spray nozzle application.
The reason that LEPA is not performing well at the higher irrigation capacities may be puddling of the surface soils, leading to poor aeration conditions.
However, this has not been verified.
In 1995 with a very dry late summer, LEPA performed better than the other nozzle orientations at the lower capacities and performed equal to the other orientations at the higher capacities.
Averaged over the two years, the trend continued of LEPA performing better at the lower irrigation capacities.
Overall, spray nozzles just below the truss rods performed best at the highest two capacities, but LEPA performed best when irrigation was extremely limited.
As the cost of pumping increases and water supplies become more restricted, irrigation schedules that more closely match water application to water use will exaggerate the nonuniform application of water due to sprinkler spacing and incanopy operation of sprinkler devices with similar results to what we have shown here.
It has been a common practice for several years to operate drop spray nozzles just below the center pivot truss rods.
This results in the sprinkler pattern being distorted after corn tasseling.
This generally has had relatively little negative effects on crop yields.
The reasons are that there is a fair amount of pattern penetration around the tassels and because the distortion only occurs during the last 30-40 days of growth.
In essence, the irrigation season ends before severe deficits occur.
Compare this situation with sprinklers operated within the corn canopy that may experience pattern distortion for more than 60 days of the irrigation season.
Assuming a 50% distortion for sprinklers beginning 30 days earlier, it would result in irrigation for some rows being approximately 40% less than the needed amount.
These experiments have shown that significant yield reductions do occur because of the extended duration and severity of water stress.
Welcome news at the conference included the snowpack/snowmelt runoff estimates delivered by the U.S.
Bureau of Reclamation in Mills, Wyoming, for the upper North Platte River basin.
The forecasted runoff is currently 1.43 million acre-feet with an estimated irrigation demand of 1.1 million acre-feet.
The total storage for all reservoirs/water holders in Wyoming is 1.3 million acre-feet.
These numbers do not account for a large amount of snowfall in the central Wyoming area last week.
That runoff will impact the lower North Platte River basin, and the runoff will be stored in the Glendo Reservoir.
WATER WORKS WITH EXTENSION From the Ground Up
 The Mississippi State University Extension Service brings practical, research-based education to Mississippians who manage water issues, including water conservation, crop irrigation, water recreation, wastewater management, public water systems, and private wells.
RISER-Row-Crop Irrigation Science E Extension Research
 RISER is a science-based approach to identifying, evaluating, and demonstrating irrigation best management practices.
RISER assists producers in maintaining yields and profitability while reducing water use.
For every $1 invested in RISER, Mississippi producers earn approximately $2.
RISER personnel conduct hands-on training and learning opportunities with producers; promote adoption of irrigation water management practices; and continue to offer assistance to producers who already use integrated water management practices.
REACH-Research E Education to Advance Conservation E Habitat
 Producers working with Extension's REACH program discover the benefits that adopting conservation practices can have for conserving water resources and improving water quality.
REACH combines research with outreach to help landowners document the environmental benefits of integrating waterconservation practices into production systems.
The goal of REACH is to identify conservation practices that help farmers build resiliency and sustainability into their operations and maintain farm profitability.
KEEPING OUR WATER SAFE
 When Mississippi residents rely on household wells to meet their water needs, they can participate in the Mississippi WellOwner Network.
Well owners discover how to maintain their private wells, and they learn about water quality, groundwater resources, and water treatment.
Participants may have their water screened for total coliform and E.
coli bacteria, too.
This program equips well owners to monitor their wells and ensure that their water is safe.
Agricultural Water Management and Waste Pesticide Disposal
 Producers are learning and applying strategies that help conserve water and improve its quality, including using on-farm water storage systems and low-cost soil moisture sensors for better irrigation timing.
Extension offers waste pesticide disposal days SO landowners can safely dispose of unneeded or expired agricultural pesticides, at no cost to them.
This program ensures these waste products do not contaminate water resources.
Produced by Agricultural Communications.
Extension Service of Mississippi State University, cooperating with U.S.
Department of Agriculture.
Published in furtherance of Acts of Congress, May 8 and June 30, 1914.
GARY B.
JACKSON, Director
When dealing with solid  manure type, the applicator options include a solid spreader and side-slinger spreader.
When dealing with semi-solid  manure type, there are no applicator options because the material is too wet to handle as solid and too dry to handle as a slurry.
When dealing with slurry  manure type the applicator options are tanker spreader with or without injection toolbar, side-slinger spreader, and towed-hose applicator.
When dealing with effluent  manure type, the applicator options are tanker spreader with or with an injection toolbar, towed-hose applicator, traveling gun, and center pivot.
Use: apply water treatments to on-farm research plots, VRI type: both, prescription type: both, management intensity: medium/high.
An electric motor  requires practically no maintenance compared to diesel  and propane  engines, but the high cost of electricity now makes the internal combustion engines cheaper overall for irrigation pumping.
Cost comparison: engines vs.
electric motors for irrigation pumping
 Farmers may save money in the long run by switching from electric to diesel, natural gas, or propanepowered irrigation pumps, but fuel cost trends are hard to predict.
A new computer program can help growers compare potential costs of all four irrigation power sources.
Electric rate increases and resulting high pumping costs have prompted some growers to consider switching from electric motors to internal combustion engines for irrigation pumping.
Time-of-use electric rates offer reduced electric power costs for off-peak use, but many growers are unable to restrict their pumping to offpeak periods without also making major modifications to increase the capacity of their irrigation systems.
Cost is the primary reason for the increasing interest in engines; however, operational and convenience factors must also be considered.
The electric motor provides flip-the-switch convenience along with minimal service and attention requirements.
It also maintains its power output level year after year, whereas engines tend to lose power over time because of wear.
An engine, on the other hand, permits the operator to vary its speed within certain limits and thereby vary the pump output.
An engine also makes it possible to operate the irrigation system 24 hours a day without regard for the schedules associated with time-of-use rates.
The cost data presented here compare the electric motor with three types of engine: diesel, natural gas, and propane.
Of these three engine types, diesel is the most commonly used for irrigation pumping in California.
It should be pointed out that engines used for irrigation pumping in California may be subject to additional costs resulting from exhaust emission regulations.
Local air pollution districts have the authority to levy annual permit fees on offroad engines of any type.
Local air pollution districts also have authority to require that engines be retrofitted to meet the latest and best emission control technology,
 but they cannot set emission standards for engines.
Emission standards for off-road engines are being developed by the Environmental Protection Agency  and the California Air Resources Board.
CARB is working on regulations covering all off-road engines from 25 to 175 horsepower ; however, amendments to the Federal Clean Air Act of 1990 have preempted the state's power to regulate engines of less than 175 hp if they are used in construction or farm equipment.
In 1992, CARB adopted regulations for off-road, heavy-duty diesel engines of 175 hp and up.
The regulations are scheduled for implementation in 1996  and 2000.
The EPA is also working on regulations that will cover offroad diesel engines including those used
 Fig.
1.
Energy costs for pumping irrigation well water of crops, 1954 to the present.
Data for four likely energy sources are presented as the dollar cost of pumping one acre-foot of water one foot up the well shaft.
Fig.
2.
Dollar costs per kilowatt-hour  of pumping water with electric power at four annual rates of use and two daily schedules: 18 hours per day with 12% of the pumping during "on-peak" hours, and 18 hours per day with no pumping during "on-peak" hours.
in construction and farm equipment, plus clarification of definitions for these two use categories.
There has been discussion of requirements to retrofit existing engines; it now appears, however, that proposed regulations by CARB, EPA, or both will apply only to new engines.
Fuel and electricity costs
 Figure 1 shows, in a general way, how the costs for electricity and engine fuels for irrigation pumping have increased and fluctuated over a 27-year period dating back to 1954.
Energy costs, shown as dollars per acre-foot of water per foot of lift, increased rapidly after the oil embargo of 1973-1974.
Engine fuel costs surged ahead of electricity costs during the early 1980s, but dropped appreciably and fell below electricity again in about 1987.
The Persian Gulf crisis pushed engine fuel prices upward again, and the major effect was on diesel fuel.
The cost differential that has developed between electricity and engine fuels shows clearly.
Energy prices and resulting costs to growers vary according to individual circumstances.
For electricity, the price per kilowatt hour  under time-of-use rate schedules depends upon several factors, including the electric rate, hours of operation per season, and daily or weekly operating schedule.
Operating schedules determine the amount of energy used during on-peak periods when energy costs are significantly higher.
Figure 2 is an example in which a 50-hp electric motor is operated 18 hours per day for 500, 1,000, 1,500, and 2,000 hours per year on the lowest-cost 1991 Pacific Gas and Electric Company summer rates.
The bottom curve represents the cost per kWh when there is no on-peak use.
The top curve represents the cost per kWh when the pump is operated during 4 of the 6 onpeak hours each weekday, or 12% of the total operating time on-peak.
Cost per kWh shown in figure 2 includes energy, demand, and customer charges.
In this example, the cost of electricity ranges from a high of 17 cents to a low of 8 cents per kWh, depending on annual usage and operating schedule.
Diesel and propane fuel prices vary according to location within California and the quantity purchased per load.
For example, a fuel price survey in early 1991 showed a price range of 79 to 98 cents per gallon for diesel.
The same survey indicated an estimated 1991 summer price range of 35 to 50 cents per gallon for propane.
Natural gas core prices for 1991 were in the range of 50 to 57 cents per therm.
Southern California Gas Company also had non-core gas available in 1991 at prices ranging from 34 to 38 cents per
 TABLE 1.
Total cost of owning and operating an electric motor for irrigation pumping, at various prices
 per kilowatt-hour 
 Dollars per year in total cost*
 Acre-	Pump	Operating	At	At	At	At	At	At	At
 pumped	Lift	power	per year	kWh	kWh	kWh	kWh	kWh	kWh	kWh
 92	100	35	500	1,579	1,873	2,167	2,461	2,755	3,048	3,342
 92	214	75	500	2,768	3,381	3,994	4,607	5,220	5,832	6,445
 92	314	110	500	3,812	4.705	5,598	6,491	7,384	8,277	9,170
 276	100	35	1,500	3,436	4,317	5,198	6,079	6,960	7,842	8,723
 276	214	75	1,500	6,603	8,442	10,280	12,118	13,957	15,795	17,634
 276	314	110	1,500	9,381	1,2060	14,739	17,418	20,097	22,775	25,454
 460	100	35	2.500	5,324	6,792	8,261	9,730	11,198	12,667	14,135
 460	214	75	2,500	10,489	13,553	16,617	19,681	22,745	25,809	28,873
 460	314	110	2.500	15,022	19,486	23,951	28,416	32,880	37,345	41,809
 *Costs shown include fixed, energy, repairs, and maintenance.
TABLE 2.
Total cost of owning and operating a diesel engine for irrigation pumping, at various prices per gallon of diesel fuel 
 Dollars per year in total cost*
 Acre-	Pump	Operating	At	At	At	At	At	At	At
 pumped	Lift	power	per year	gal.
gal.
gal.
gal.
gal.
gal.
gal.
92	100	35	500	1,712	1,927	2,141	2,356	2,571	2,785	3,000
 92	214	75	500	2,559	3,001	3,443	3,885	4,327	4,769	5,211
 92	314	110	500	3,300	3,940	4,581	5,221	5,861	6,502	7,142
 276	100	35	1,500	3,675	4,319	4,963	5,607	6,251	6,895	7,539
 276	214	75	1,500	5,658	6,984	8,310	9,636	10,962	12,288	13,614
 276	314	110	1.500	7,392	9,313	11,235	13,156	15,077	16,999	18,920
 460	100	35	2,500	5,692	6,765	7,839	8,912	9,985	11,059	12,132
 460	214	75	2,500	8,838	11,048	13,258	15,468	17,678	19,888	22,098
 460	314	110	2.500	11,587	14,789	17,992	21,194	24,396	27,599	30,801
 Costs shown include fixed, energy, repairs, and maintenance.
TABLE 3.
Total cost of owning and operating a propane engine for irrigation pumping, at various prices per gallon of propane fuel 
 Dollars per year in total cost
 Acre-	Pump	Operating	At	At	At	At	At	At	At
 pumped	Lift	power	per year	gal.
gal.
gal.
gal.
gal.
gal.
gal.
92	100	35	500	1,959	2,260	2,561	2,861	3,162	3,462	3,763
 92	214	75	500	3,459	4,074	4,689	5,303	5,918	6,533	7,148
 92	314	110	500	4,771	5,660	6,550	7,439	8,329	9,218	10.108
 276	100	35	1,500	4,160	5,062	5,964	6,866	7,767	8,669	9,571
 276	214	75	1.500	7,347	9,191	11,035	12,879	14,723	16,567	18,412
 276	314	110	1.500	10,135	12,803	15,472	18,140	20,809	23,477	26,146
 460	100	35	2,500	6,436	7,939	9,442	10,945	12,448	13,951	15,454
 460	214	75	2,500	11,376	14,449	17,522	20,595	23,669	26,742	29,815
 460	314	110	2.500	15,696	20,143	24,591	29,038	33,486	37,933	42,381
 *Costs shown include fixed, energy, repairs, and maintenance.
TABLE 4.
Total cost of owning and operating a natural gas engine for irrigation pumping, at various prices per therm 
 Dollars per year in total cost*
 Acre-	Pump	Operating	At	At	At	At	At	At	At
 pumped	Lift	power	per year	therm	therm	therm	therm	therm	therm	therm
 92	100	35	500	1,844	2,095	2,346	2,598	2,849	3,101	3,352
 92	214	75	500	3,224	3,738	4,252	4,766	5,280	5,794	6,308
 92	314	110	500	4,430	5,174	5,918	6,661	7,405	8,149	8,893
 276	100	35	1,500	3,815	4,569	5,323	6,077	6,831	7,585	8,339
 276	214	75	1,500	6,641	8,183	9,725	11,266	12,808	14,350	15,892
 276	314	110	1,500	9,113	11,344	13,575	15,806	18,036	20,267	22,498
 460	100	35	2,500	5,862	7,118	8,374	9,631	10,887	12,144	13,400
 460	214	75	2,500	10,200	12,769	15,338	17,907	20,477	23,046	25,615
 460	314	110	2,500	13,994	17,712	21,430	25,148	28,866	32,584	36,302
 *Costs shown include fixed, energy, repairs, and maintenance.
therm; however, the non-core rate is interruptible and requires a back-up fuel supply.
A key question is: What will energy prices be in the future?
It seems fairly certain that electricity prices will continue to escalate for agricultural customers.
The California Public Utilities Commission has determined that revenues from the agricultural class are substantially below the level required to put them on an equal percentage of marginal costs basis with other classes.
It is probable that a major portion of this difference will be made up over a 5-year period ending in 1995.
Additional increases may also occur as a result of energy cost adjustments.
The long-term trend in diesel and propane prices will undoubtedly be up, but we may see a period of somewhat stable prices unless there is another international oil supply crisis.
In 1987, the authors made a study of irrigation power unit costs that included a survey of equipment dealers throughout California.
These costs were updated in early 1991.
The resulting cost calculations were written into a computer program  for comparing total costs of electric motors and diesel, natural gas, or propane engines.
These total costs include fixed costs, fuel or electricity, repairs, and maintenance and service.
Income tax considerations are not included in this analysis.
Costs are calculated in terms of current dollars.
Included with the cost program is another program that can be used to derate  engine horsepower and fuel consumption for differences in altitude, temperature, and engine accessories or equipment between manufacturer's test conditions and actual conditions of use.
Failure to properly derate an engine when necessary can significantly affect actual horsepower output and fuel consumption.
Figure 3 compares the total cost per year to operate a 75-hp pump 1,500 hours per year with an electric motor or an engine.
Energy costs used for this comparison are electricity , diesel , natural gas , and propane.
It should be emphasized that the energy cost of 10 cents per kWh for the electric motor represents the average cost per kWh for the year, including demand charges, customer charges, and the like.
This example shows that, at the energy prices listed above, all three types of engine cost less to operate than the electric motor.
Diesel and natural gas costs are about equal.
The bar graph also breaks down the total costs for each power plant
 into fixed costs, repairs, energy, and maintenance and service.
This breakdown shows that energy cost is about 90% of the total cost for the electric motor, versus about 75% of the total cost for the engines.
Tables 1 through 4 show total annual costs for an electric motor and for diesel, propane, and natural gas engines, when pumping a given number of acre-feet of water under specific conditions of lift in feet.
Each table represents three hp sizes , three annual operating periods , and a range of fuel or energy costs.
If the decision is made to use an engine instead of an electric motor, the engine must be properly matched to the pump.
A properly matched engine will provide the necessary horsepower to operate the pump at the desired revolutions per minute.
Proper matching is also necessary to optimize fuel efficiency and engine life, and to keep repair costs low.
Engine manufacturers provide data on hp and fuel consumption based on laboratory tests.
Most manufacturers provide both maximum and continuous hp test data.
The continuous hp test is run at a level that the engine can sustain on a continuous basis, 24 hours per day, and is usually about 25% less than maximum hp.
An engine should be matched to a pump by starting with the manufacturer's continuous hp data and derating  that data to reflect any differences between the manufacturer's test conditions and actual conditions of use.
Factors to be considered in derating are altitude and ambient temperature conditions; engine accessories, such as an alternator or muffler; and auxiliary equipment, such as the gear drive for operating a pump.
Some of these factors, such as an alternator and gear drive, consume power and affect both hp and fuel consumption.
Other factors, such as a muffler and ambient temperature conditions, are oxygenlimiting and only affect hp consumption.
Fig.
3.
Total annual costs to operate a 75horsepower irrigation power plant 1,500 hours per year using an electric motor or a diesel, natural gas, or propane engine.
It is a good idea to further derate the continuous hp test data to allow for loss of power due to engine wear over time, and to provide a factor of safety against engine overload.
Manufacturers' engine data obtained in the cost survey were derated for a typical set of conditions that covered altitude, temperature, and accessories and equipment.
They were further derated by 10% to provide a margin of safety against overload.
In general, engines become more cost competitive with the electric motor as size  and annual hours of use increase.
This is because fuel efficiency increases as engine hp increases, and the labor required to service and attend to an engine in the field is nearly the same for a small engine as for a large engine.
Although fixed costs are higher for an engine than for an electric motor, they have less effect on total cost if they are spread over more hours of use.
It should be emphasized that the comparisons shown here are based on generalized cost data and are intended to provide approximate values.
Specific costs will vary, depending on the particular situation.
Anyone considering a change from an electric motor to an engine should make a careful analysis.
The computer program developed for these comparisons is written SO that the user can provide the input data or utilize default data stored in the program.
Default data include typical values for fuel or electricity consumption, power unit prices, repairs, maintenance and service, and expected lifespan.
The cost comparisons in figure 3 and tables 1 through 4 were made with the computer program using default values for these inputs.
Output from the program shows total costs in dollars per year, plus a breakdown of the costs for energy, repairs, fixed costs, and maintenance and service.
It also shows the break-even energy prices for the power units being compared.
G.
Curley is Extension Agricultural Engineer Emeritus, and D.
Knutson is Associate Development Engineer, Agricultural Engineering Department, UC Davis.
The computer program, Power Plant Costs for Irrigation Pumping, is available at a nominal price from the Agricultural Engineering Department, UC Davis.
To order the program, contact Shirley Hickman, Agricultural Engineering Extension, University of California, Davis, CA 95616.
Phone:  752-0120.
Species Selection and Establishment for Irrigated Pastures in New Mexico
 Species Selection and Establishment for Irrigated Pastures in New Mexico
 Using animals to harvest forage crops, such as irrigated pastures, requires much less labor and equipment than hay and feeding operations and allows for an increase in net farm income.
But there are numerous other uses for irrigated pastures that are not driven by generating income.
In many areas, small tracts are used to pasture horses or hobby livestock.
Ranchers use irrigated pastures as holding sites, calving pastures, horse pastures, hay sources or supplemental rangeland grazing.
To assist New Mexico's irrigated pasture producers with selecting and establishing pasture species, New Mexico State University's Agricultural Experiment Station has conducted research throughout the state and accumulated information from other states and producers.
That information is presented here as a guide to developing productive, irrigated pastures in New Mexico.
These recommendations might change as more data and improved species become available.
Several factors must be considered in pasture species selection that fall into two broad categories-local adaptation and intended use.
Within those two categories, there are some questions producers should answer before developing their forage program.
How long will this land be in pasture?
Pasture cropping systems generally fall into three categories: permanent, annual and rotational.
Permanent pastures usually consist of perennial species that remain on the site indefinitely.
Benefits of permanent pastures include establishment costs prorated over a longer period, soil and water conservation and soil improvement, particularly on marginal land.
Annual pastures are planted for seasonal use.
They can be used to supplement permanent pastures during times of low forage productivity, or they may constitute the entire forage program.
Many producers prefer to use a combination of annual species year-round for pastures, because they provide a valuable source of high-yielding, nutritious forage.
While annual species generally yield more than permanent pastures, the additional cost of land preparation, seed and planting each year could more than offset any differences in production.
Irrigated pastures that will be rotated with row crops are part of a rotational cropping system.
The forage species used in
 this situation, whether annuals or perennials, cool-season or warm-season, depends on the length of the rotation, season of the year and the desired amount of forage produced.
What kind of animals will graze the pasture?
Different animal species and classes of animals within each species have different nutrient requirements.
Animals that have high nutritional demands, such as working horses, lactating COWS or growing steers, need greater amounts of higher-quality forage.
But, in the case of horses, if quality is too high and fiber too low, colic can be a problem.
Also, if the pasture will be managed only for aesthetics or as a low-maintenance turf, less productive pasture species might be more desirable.
Additionally, different animal species apply different kinds of grazing
 pressure to pastures.
Some, like beef cattle, graze uniformly across a pasture.
Others, such as horses, spot graze, leaving some areas to become overmature and overgrazing other areas.
Finally, while legumes usually are higher in yield and quality than grasses, some legumes cause bloat in ruminants, which can lead to death.
Producers need not avoid legumes entirely, but they do need to manage pastures with legumes to lessen the likelihood of the occurrence of bloat.
More information about bloat and protecting animals against bloat is presented in Circular 586.
What forage crop species can be grown?
New Mexico has vast differences in elevation and latitude.
The wide range of climatic conditions allows for a broad range of species that may be adapted when irrigated.
Pasture
 Normal forage availability by months
 species discussed later in this publication are known to be well-adapted to the state and have value as livestock feed.
The description of each species includes limitations on adaptation.
Other considerations in determining adaptability are the types of insects and weeds found in the area to be used for pasture.
Not many pesticides are labeled for pasture use.
Soil type also plays a key role in selecting pasture species.
Species performance can be affected greatly by poor or excessive drainage, soilborne diseases and nematodes, soil depth, soil pH and salinity.
The U.S.
Department of Agriculture soil survey and a soil analysis will help determine the soil constraints on your property that should be considered when selecting irrigated pasture species.
Once the pasture species are selected, variety selection also can be a critical decision based on the same criteria as that
 used for species selection.
Contact your local county Cooperative Extension Service for more information.
DESCRIPTION OF PASTURE SPECIES
 Species types.
Forage species usually are classified by their growth characteristicswhen they grow, how long they live and how they spread.
Cool-season species grow best between 60 and 80F.
Warm-season species grow best between 80 and 95F.
Most warm-season species are killed when temperatures consistently fall below 10F.
Annual species complete their life cycle in one year or less, biennials need two growing seasons or years to complete their life cycle.
Species that persist for three or more years are considered perennial.
Generally, cool-season species are higher in quality than warmseason species, annuals are higher in quality
 than perennials, and legumes are higher in quality than grasses.
Seasonal yield distribution is another factor to consider when making species selections SO that forage production will match animal demand.
Coolseason perennial species generally have their highest production in the spring, followed by a summer slump and another growth period in the fall.
If irrigation water is available only during the growing season, alfalfa yields will be lower early in the season and sustained during the summer.
Cool-season annuals grow some in the fall, followed by a period of dormancy or minimal growth in the winter and highest production in the spring.
Generally, warm-season annuals and perennials grow actively from mid-May until a hard freeze in the fall.
Peak production generally is in midsummer.
Most species will spread by seed.
Otherwise, some species have a bunch-type growth habit and spread by tillering or crown expansion.
Other species reproduce vegetatively, with lateral stems either belowground  or aboveground  that can form new plants by rooting at nodes.
In addition to spreading by seed, Johnsongrass  spreads by rhizomes; buffalograss spreads by stolons.
Bermudagrass can spread by rhizomes, stolons and seed.
Forage crops described in this publication include grasses and legumes.
All forage crops need nitrogen for maximum productivity, but legumes live in cooperation  with certain nitrogen-fixing bacteria , which form nodules on the roots and convert atmospheric nitrogen into a form the plant can use.
For this reason, little or no nitrogen fertilizer is necessary for legumes.
Grasses do not have this capability and must have their nitrogen requirement met by other means.
Another difference between most grasses and legumes is their potential to cause frothy
 Figure 4.
Seasonal yield distribution  of alfalfa and tall wheatgrass pastures at NMSU's Agricultural Science Center at Tucumcari, 1999-2001.
bloat in ruminants.
Cool-season, annual grasses, such as small grains and most legumes, can cause bloat; animals grazing pastures including these species should have a bloat preventive available at all times.
Finally, grass tetany, caused by magnesium deficiency, can occur if soils are low in magnesium.
This disease is most common in monoculture grass pastures during periods of rapid growth from fall through spring.
Some grass species are more likely to cause grass tetany, generally because they are poor magnesium accumulators or they have a period of extremely rapid growth in the spring.
More information on grass tetany is given in Circular 586.
Mixtures.
Grass-legume mixtures generally are preferred over monocultures.
Because forage yield and quality usually increase, seasonal distribution can become more uniform.
And the legume supplies nitrogen to the grass, reducing fertilizer costs.
Also, if the grazed material from the pasture is at least 50 percent grass, the incidence of bloat is reduced.
Furthermore, using grass-legume mixtures can reduce the likelihood of grass tetany mixtures, because legume forage generally is higher in magnesium.
With few exceptions, the legumes described in this publication should be used in pastures as mixtures rather than monocultures.
Simple mixtures  are better than complex mixtures, because complex mixtures present several problems.
Differences in requirements for cultural practices ; grazing management; and ability to compete for light, water, nutrients and space make it difficult to maintain all species in the stand.
Additionally, animals will selectively graze more palatable species and eliminate them from the stand, leaving less palatable species to become overmature.
While mixing perennial cooland warm-season grasses in the same pasture has not been successful in most irrigated areas, including perennial cool-season legumes in warm-season grass pastures
 has been successful in the Southeast and some testng has been done in New Mexico.
Overseeding dormant, warm-season pastures, such as bermudagrass, with annual cool-season grasses like annual ryegrass or legumes also has been successful.
However, in these mixtures, the warm-season grass needs to be going dormant prior to planting in the late summer, and the cool-season species should be grazed or killed before the warm-season grass greens up in the spring.
The availability of irrigation water for establishment and early spring production might be a concern in many areas of the state.
grazed.
Alfalfa is a high-yielding, nutritious, palatable species, but the possibility of bloat in ruminant animals exists, even in grazingtolerant varieties.
Alfalfa  is a long-lived species that continues to be the legume of choice in most irrigated pasture situations.
The plant grows erect with shoots rising from the crown.
Grazing might damage the crown, providing an entry for disease organisms.
However, grazing pressure has been used to develop many newer varieties.
These varieties have a crown located below the soil surface where it is protected from trampling effects.
They also have broader crowns and taproots that maintain a higher carbohydrate reserve and shoots that produce leaves below the grazing horizon, SO that the plants can continue to photosynthesize while being
 Most of the forage crop species listed in this publication have demonstrated adaptation and are prominently used in irrigated pastures in New Mexico.
A few are included that have not yet been widely used but show promise.
Other species might be well-adapted, but are not included because of low productivity, insurmountable antiquality factors or they simply might not be as well-adapted as the species listed in this publication.
Specific varieties are not listed because of differences in seed availability and local adaptation.
Alfalfa is adapted to most regions of New Mexico.
It grows best on loamy, fertile, well-drained soils, but it grows on most soil types.
Once established, it can tolerate a considerable amount of salt and has more heat tolerance than most coolseason forage legumes.
Alfalfa produces high yields as a monoculture but also performs well when mixed with many grasses.
If planted as a monoculture, use 15 to 20 pounds per acre.
For mixtures, use only 4 to 5 pounds per acre.
Alfalfa is allelopathic.
That is, when a stand is more than a year old, a compound is released into the soil that kills or stunts newly germinated alfalfa seedlings.
This toxic compound remains in the soil for approximately one year after all the alfalfa is gone.
So, once alfalfa is no longer contributing enough to pasture yield and quality, renovation with another legume, such as birdsfoot trefoil or red clover, is advisable.
After one year, alfalfa can be reestablished successfully.
Otherwise, the entire pasture should be rotated to an annual crop for at least one complete growing season, SO that tillage and irrigation practices can help dissipate the toxic compound.
Birdsfoot trefoil  is a biennial or short-lived perennial with a semierect to prostrate growth habit.
It is adapted only to the state's cooler regions or higher elevations, because it lacks heat tolerance.
Birdsfoot trefoil is adapted to most soil types and can be grown on heavy, poorly drained or swampy soils unsuited for most
 other legumes.
Birdsfoot trefoil has good tolerance to flooding and salinity.
It is considered nonbloating, but bloat can occur on rare occasions.
Birdsfoot trefoil does not have the yield potential of alfalfa and other legumes.
While it is best-suited for mixing with grass, yield of the mixture is usually similar to that of a properly fertilized monoculture of the associated grass.
Birdsfoot trefoil should be sown at 4 to 6 pounds per acre in mixtures.
It should be managed to permit natural reseeding at least every other year SO that new plants can replace those that die.
Cicer milkvetch  has a creeping, rhizomatous growth habit.
It is drought-tolerant, but must be irrigated to maintain stands in most of New Mexico.
Cicer milkvetch is nonbloating, but it does cause photosensitivity  in livestock.
Seedling emergence and growth is slower than either alfalfa or sainfoin.
It generally does not perform well in mixed pastures and should be used only as a monoculture in which it will produce approximately half the yield of alfalfa.
Additionally, persistence of cicer milkvetch under grazing has been questioned.
However, for low-maintenance situations or rotational stocking with a longer rest  period, cicer milkvetch might perform satisfactorily.
The seeding rate for monoculture cicer milkvetch is 5 to 8 pounds per acre.
Kura clover  is rhizomatous and long-lived.
It is very similar in appearance to white clover, but plants are larger.
Kura clover establishment is directly related to the number of plants that nodulate, but it does not nodulate well in the field.
Therefore, when seeding kura clover, it is crucial to use properly inoculated seed  or to use seed that has been factory treated within the previous year.
This species is slower to establish than most other legumes.
However, once established, kura clover is an aggressive spreader.
It even overtook tall fescue sown at the same time in a trial in north-central New
 Mexico at NMSU's Sustainable Agriculture Science Center at Alcalde.
In that study, it yielded as well as alfalfa after four years and was still maintaining stand and yield after eight years when the trial was concluded.
In trials in eastern New Mexico, at the Agricultural Science Center at Tucumcari, kura clover did not perform as well as it had in north-central New Mexico, indicating that its adaptation area might be limited to the higher elevations of northern New Mexico.
Like white clover, most of the grazed material is leaf and, therefore, higher in quality than alfalfa.
But it can cause bloat.
Kura clover establishes well when sown in mixtures.
It is likely that drilling the kura clover in rows  and broadcasting the associated grass on the soil surface would help enhance stand establishment.
Data indicates that initial yields will be mostly grass that will provide grazing until the kura clover is established.
Once established, kura clover will become dominant in the stand.
Bloat preventives should be provided to animals grazing pastures that include kura clover, even in the early years when the stand is greater than 50 percent grass.
Although high-yielding, kura clover does not tolerate frequent defoliation and should be rotationally stocked with a long rest interval.
Red clover  generally is a biennial or short-lived perennial that might act as an annual in some areas.
It has an erect growth habit.
The leaves usually are covered with hair.
Red clover does not tolerate frequent close grazing.
However, in a rotational stocking system similar in frequency to that of hay management , it can perform quite well.
Red clover does best on fertile, well-drained soils with a moderate pH range.
It is adapted to the state's cooler regions.
Diseases common to red clover contribute to its short life span in other areas
 but might not be prevalent in New Mexico's well-drained soils.
Four-year-old stands of red clover at NMSU's Agricultural Science Center at Tucumcari still yielded comparably to two-year-old stands without reseeding.
Bloat is a severe problem with red clover, but it is compatible with several cool-season grasses.
Although red clover usually is a shortlived species, stands can be maintained by allowing it to reseed naturally approximately every other year.
Use 8 to 12 pounds per acre when seeding monoculture red clover or 4 to 6 pounds for mixtures.
Sainfoin  has a growth habit similar to that of alfalfa, but production has been limited to early to midspring.
Sainfoin's stand persistence has been questionable in many situations, especially when grown under intense irrigation.
Sainfoin's crown is weak and will not tolerate trampling by grazing animals, SO it should be planted in rows to reduce trampling, if used in pastures.
Sainfoin requires a well-drained soil and is adapted to calcareous and sandy or cobbly soils that might be unsuitable for other forage legumes.
It is resistant to the alfalfa weevil.
But is susceptible to many other alfalfa pests as well as Lygus bugs.
Sainfoin also is susceptible to root and crown diseases.
It is nutritious, highly palatable and nonbloating.
These qualities make sainfoin susceptible to overgrazing if not managed properly.
It is compatible with many cool-season grasses but also makes an excellent pasture as a pure stand.
Sainfoin is not an efficient nitrogen fixer and might suffer a midseason slump in production due to nitrogen deficiency.
Seeding rates for sainfoin are 35 to 40 pounds per acre as a monoculture and 20 pounds per acre in mixtures.
Strawberry clover  is a long-lived, stoloniferous perennial.
Because it is a very low-growing species, it is well-suited for grazing, but not for hay production.
While strawberry clover is adapted best to the state's cooler
 regions, it has fair heat tolerance.
It also has good salt tolerance and prefers wet soils with high pH.
Strawberry clover is not used widely for irrigated pastures in New Mexico, but it has potential for lowmaintenance areas and is compatible with many cool-season grasses.
Use 2 to 3 pounds per acre when seeding strawberry clover as a monoculture or in mixtures.
Sweetclover  includes species that are coolseason biennials or annuals with a very erect growth habit.
Plants in these species usually grow to heights of more than 2 feet with stems that are coarse and become woody toward maturity.
Sweetclover not only causes bloat, but also contains a chemical called coumarin, which has an undesirable taste, affecting palatability.
Coumarin can be converted to a toxic substance that reduces the blood's clotting ability, causing animals to bleed to death from slight wounds or internal hemorrhaging.
Sweetclover also has a very low leaf-to-stem ratio, which affects both quality and yield.
Although it is adapted to most soil and climatic conditions in the state and is an excellent green manure crop, sweetclover generally is not recommended as a pasture species because of its antiquality factors.
White clover , a biennial or short-lived perennial has a creeping, stoloniferous growth habit.
White clover tolerates frequent close grazing and trampling by livestock.
It is adapted to a wide variety of soil types and will grow on poorly drained soils, but it does not tolerate salinity.
Stolon and root rot diseases can deplete white clover stands.
It also is susceptible to leaf diseases and root knot nematodes, although some varieties have tolerance to nematodes.
Like alfalfa, white clover can cause bloat.
It can be grown in most areas of New Mexico, but it is best-adapted to the northern half of the state and higher elevations in the southern half.
The various white clover
 types are well-adapted to grazing.
But because of their prostrate growth habit, they are not well-suited for hay.
White clover is compatible with most cool-season bunch grasses and should be sown at 2 to 3 pounds per acre in mixtures.
All perennial cool-season grasses described in this publication are compatible with legumes.
Unless otherwise specified, seeding should be 15-20 pounds per acre rates for monocultures and 12-14 pounds per acre for mixtures.
Altai wildrye  is a rhizomatous species that looks like a bunchgrass.
Tests at Tucumcari, have shown it to be widely adapted to well-drained and poorly drained, high saline soils.
It was among the highest-producing, cool-season grass species, giving greater summer and lateseason yields than tall wheatgrass and tall fescue.
Leaf blades are wide, similar to tall fescue, and coarse like tall wheatgrass with a sharp point.
However, cattle grazing plots that included several cool-season grasses appeared to have a similar preference for altai wildrye as for tall wheatgrass.
Because this species holds promise for increasing lateseason, cool-season grass pasture productivity, more research is needed to determine how broadly adapted it is to New Mexico and the best management practices for its use here.
Orchardgrass  has a bunch-type growth habit.
It is adapted to New Mexico's cooler regions and tolerates a wide range of soil conditions, but prefers fertile, well-drained soils.
Orchardgrass is palatable when fertilized well and grazed frequently.
It is one of the more widely used pasture grasses at the higher elevations in northern New Mexico, but it is not as hardy or long-lived as tall fescue or tall wheatgrass and is not very salt-tolerant.
Orchardgrass also is a poor accumulator of magnesium, and grass tetany can be a problem (see
 Perennial ryegrass  is a short-lived perennial with a bunch-type growth habit that can reseed when managed properly.
However, ergot can reduce seed yield and quality and limit reseeding.
Of all the cool-season grasses used in New Mexico, perennial ryegrass appears to be the most sensitive to cold, heat and drought.
Best adapted to New Mexico's cooler regions, it prefers fertile, well-drained, medium-textured soils with nearly neutral pH.
Perennial ryegrass generally is not recommended for New Mexico pastures.
Russian wildrye  is a long-lived, bunchgrass.
In tests at Tucumcari, it was the most drought-tolerant of the coolseason grasses and responded quickly to precipitation.
Russian wildrye is a lowgrowing species that produces seedheads early and remains vegetative for the rest of the year, maintaining fine leaves that are palatable and high in quality.
Because it is low-growing, it is not well-suited for hay production.
This species might have value in low-input, low-stocking density systems in the northern half of New Mexico, but production can be increased with irrigation and fertilization.
Smooth bromegrass  is a rhizomatous perennial with an erect growth habit.
It has an adaptation area similar to that of orchardgrass and is used mainly in the higher elevations of northern New Mexico.
Smooth bromegrass might tolerate periods of drought, temperature extremes and salt better than orchardgrass.
But it tends to become sod-bound because of heavy rhizomes, which can reduce productivity.
To overcome this, stands may need to be renovated by disking or chiseling every three to five years to improve air, water and fertilizer infiltration.
Tall fescue  is a long-lived species with a bunch-type growth habit, although it is weakly rhizomatous and
 can form a dense sod over time.
Tall fescue can be grown throughout New Mexico, but it performs best in the northern half of the state, particularly along the Rio Grande and Pecos corridors.
It is adapted to a wide variety of soil types and pH, tolerating wet, poorly drained soils as well as moderate drought, heat and shade.
Tall fescue is quite tolerant to grazing and management stresses.
Although it might be less palatable than some cool-season grasses, livestock will graze it and perform well, when it is fertilized properly and grazed frequently.
Tall fescue is compatible with most cool-season legumes in mixtures.
Tall fescue endophyte.
Poor animal performance on tall fescue pasture has been linked to a fungus, Acremonium coenophialum, found within the plants  that is only transmitted through the seed.
This endophyte causes tall fescue plants to make alkaloids that are associated with their ability to withstand mismanagement and other stress factors.
But the alkaloids also have been linked to poor animal performance.
Producers who want to know the endophyte status of their tall fescue pastures can submit a plant sample for analysis.
Contact your county Cooperative Extension Service office about the sampling technique and laboratories that conduct analysis.
Because the endophyte is more active in reproductive tillers, declines in animal performance can be reduced or avoided by maintaining the tall fescue in a vegetative state.
This can be accomplished by grazing until approximately early May, when seedstalk elongation begins, and clipping after grazing to remove the seedstalks.
Additionally, anytime the tall fescue is stressed from heat or drought, the endophyte's negative effects will be magnified.
Endophyte-free varieties that perform as well as the older, endophyte-infected varieties are available.
These cultivars might not stand
 up as well under mismanagement, such as overgrazing or drought.
One variety that has a beneficial endophyte has not been shown to cause poor animal performance.
Tall wheatgrass  is a long-lived bunchgrass that, like tall fescue, can form a dense sod.
While most perennial cool-season grasses decline in quality and palatability when mature, tall wheatgrass does more SO than other species.
It is adapted to a wide range of soil types and has the best salt tolerance of most perennial cool-season grasses described in this publication.
Tall wheatgrass can withstand frequent grazing but not overgrazing.
Although it is adapted to most of New Mexico, its primary use will be in the lower elevations of the state's northern two-thirds.
Timothy  is a biennial bunchgrass adapted to the higher elevations of northern New Mexico.
It exhibits perennial characteristics by vegetative reproduction.
Timothy provides high-quality forage for hay or pasture but will not persist under close, continuous grazing; is not heator drought-tolerant; and recovers slowly under limited moisture.
Because it is a biennial, managing timothy is critical to stand maintenance.
To allow sufficient storage of carbohydrates important to vegetative reproduction, the first harvest each year should occur between flowering and the soft-dough stage.
This is in contrast to most other cool-season grasses, which should be harvested at the early head stage to maximize yield and quality.
Additionally, even more crucial than for all other cool-season grasses, nitrogen should be applied to timothy more frequently, but in lesser amounts.
This species produces two generations of tillers each year, the second of which overwinters and becomes the primary growth for the following year.
To encourage second generation growth in both years, nitrogen needs to be available in the fall and early spring.
Without split applications, poor
 fall growth will occur and even poorer regrowth the next spring.
Management similar to that which maximizes yield and quality of other cool-season forage grasses, namely higher applications of nitrogen and early harvest, will consistently reduce timothy stands.
The seeding rate is 8 to 14 pounds per acre for monoculture timothy and 4 to 6 pounds per acre for mixtures.
There are no perennial, warm-season legumes known to be suitable for use in New Mexico's irrigated pastures.
Sericea lespedeza  and perennial peanut  are examples of perennial warm-season legumes used elsewhere.
However, sericea lespedeza performs poorly in calcareous soils, such as those prevalent in New Mexico.
Additionally, production potential by perennial peanut is reduced after long, cool spells and it winterkills at 15F.
Perennial, Warm-Season Grasses Bermudagrass  establishes rapidly compared with most perennial warm-season grasses and forms a dense sod, spreading by both rhizomes and stolons.
It favors mediumto light-textured soils and is very saltand drought-tolerant.
Bermudagrass responds well to fertilizer and can stand heavy applications of animal waste.
It has poor shade tolerance and is not compatible with many other grasses or legumes, but might mix well with alfalfa.
Bermudagrass is sensitive to cold; growth slows or ceases when night temperatures fall below 60F.
Therefore, bermudagrass grows best at the lower elevations found in the southern two-thirds of New Mexico.
While winterkill has been a problem for bermudagrass in New Mexico, newer varieties are available that are more cold-tolerant.
Bermudagrass can be established either vegetatively  or by seed.
Sprigging is more expensive than
 seeding but might give quicker fill, even when sprigs are placed on 3-foot centers.
Some bermudagrass varieties are available only as sprigs, because they do not produce large quantities of seed or the seed is not true to the variety.
Most of these are ecotypes that might be well-adapted and productive near their area of origin.
However, the farther away from their point of origin they are grown, the less productive they tend to be with the same level of fertilizer and water inputs.
The Natural Resources Conservation Service has plant materials centers located around the country.
These centers, including one located at NMSU's Agricultural Science Center at Los Lunas and another in Woodward, Okla., have tested many bermudagrass ecotypes and can provide information about the adaptation area of many varieties, as well as many other forage crop species.
As is the case with all forage crops, some companies have not had their bermudagrass varieties independently tested by universities over a broad range of environments.
Before buying planting material  of any bermudagrass variety, always ask if university data is available for that variety.
Sprigged bermudagrass varieties should be planted at 15 to 20 bushels per acre.
If a seeded type is selected, plant 5 to 10 lb per acre.
Harvest frequency and fertility management, particularly of taller-growing cultivars, can influence forage bermudagrass yield and quality.
Blue grama  is a native range bunchgrass that has been improved for use in irrigated pastures.
Because of its rangeland background, improved blue grama is probably better suited for limited irrigation and limited nitrogen situations than the other perennial warm-season grasses, which are all introduced species, listed in this publication.
Although some seedstalks can be 1 to 3 feet
 tall, blue grama leaves remain closer to the ground, SO it is not well-suited for hay production.
Additionally, blue grama quality will likely be better maintained in low-input systems and after the growing season.
Productivity also will be lower.
Blue grama can grow throughout New Mexico.
It should be sown at 1 to 1.5 pounds pure live seed  per acre, using a drill with a fluffy seed box.
Kleingrass  is a bunchgrass introduced to the United States from Africa.
It is fine-stemmed and leafy and grows to a height of 3-4 feet.
Kleingrass spreads by tillering and short rhizomes.
It also can establish roots at nodes on the stems that come in contact with the soil, an effect called layerage.
Kleingrass is adapted to a fairly wide range of soil and climatic conditions.
However, there are some concerns about its cold tolerance.
Although it has been grown successfully during a period of mild winters at Tucumcari, it currently is recommended for use only in the southern half of the state.
Kleingrass can cause photosensitization  in white-faced sheep.
The seeding rate for kleingrass is 1.5 to 2 pounds PLS per acre.
Old world bluestem  is a bunchgrass that was introduced from eastern Europe and Asia.
This species is not as salt-tolerant as bermudagrass and prefers well-drained soils.
Growth is initiated later in the spring than bermudagrass and is sustained later in the summer, when other species are not as productive or are dormant.
Establishment can be slow, but good stands can be achieved in one season under good management and optimum conditions.
Initially, old world bluestem does not compete well with weeds or other species when sown in mixtures.
Once established, it is very competitive, spreading by crown expansion and seed.
During peak production periods, livestock might not be able to prevent old world
 bluestem from forming seedheads.
Concentrating animals in a smaller part of the pasture and harvesting excess forage as hay might help resolve this problem.
When seeding old world bluestem, plant 2 to 3 pounds PLS per acre using a drill with a fluffy seed box.
Berseem clover  has been grown at Tucumcari, even though it was originally not known to be a winterhardy species and has not been previously used in New Mexico.
It has an erect growth pattern and is very tolerant of alkalinity, salinity and poor drainage.
Berseem clover produces highquality forage that is nonbloating.
It can be grazed when it reaches 10 inches and will continue producing new growth if a 3to 4-inch stubble is maintained.
Although berseem clover did not produce viable seed in the planting at Tucumcari, newer varieties have been managed for natural reseeding in other areas by removing animals during the bud stage.
Once seed is produced, grazing can resume to remove all standing residue and to form good seed-to-soil contact for latesummer germination.
The seeding rate for berseem clover is 20 pounds per acre.
Hairy vetch  is widely adapted to New Mexico's climate.
It has a vinelike growth habit and can be grown as a monoculture or overseeded into dormant, perennial, warm-season grasses.
Hairy vetch does not yield well in the fall, but it can provide four to six weeks of grazing in the early spring before the warm-season grasses break dormancy.
Hairy vetch will reseed naturally if cattle are removed prior to the bud stage.
As with berseem clover, once the seed is produced, grazing can begin on new growth of the warm-season companion grass or residue from the hairy vetch.
Initial seeding rate for hairy vetch is 20 to 40 pounds per acre.
Annual  ryegrass  is similar to perennial ryegrass, except it completes its life cycle in one season.
Annual ryegrass has been used successfully as a winter annual pasture in southern New Mexico.
This species performs well in the southeastern United States, when sown into dormant, warm-season grass pastures.
Use a no-tillage drill when overseeding dormant, warm-season grass pastures to achieve good seed-to-soil contact, which promotes germination and establishment.
Seeding rates of 20 to 30 pounds per acre should be used for monocultures or overseeding operations.
Small grains include barley , oats , rye , wheat  and triticale.
Barley and oats are somewhat more susceptible to cold temperatures and historically have been recommended only for southern New Mexico.
But newer varieties of both have been grown successfully for pasture and hay in recent years at Tucumcari.
Rye, wheat and triticale are more cold-tolerant and have been used more in the cooler regions.
Barley and rye generally produce more forage than wheat or oats in the fall.
Barley appears to be the most salt-tolerant of these crops, while rye generally performs better than the others on sandy or poor land.
Mixtures of smallgrained species are not desirable, because selective or spot grazing is likely to occur.
In grazing preference trials at Tucumcari, oats were selected over other small-grained species.
Performance by animals grazing monocultures will likely be similar across small-grained species.
Some newer varieties of spring oats also have survived winters at Tucumcari and are very productive in the fall.
A mixture of those varieties and winter oats might increase fall productivity without the selective grazing problem.
A better option is to plant a pasture
 with spring oats for fall grazing, a second pasture with winter oats for spring grazing and a third pasture with rye as a rescue pasture for winter and early spring grazing.
Small grains should not be grazed until they are 5 to 6 inches tall, allowing the plants to establish a good root system.
Grazing too soon or too close to the ground slows root development and decreases the plant's ability to survive the winter and be productive in the spring.
Animals should be removed when the forage has been grazed to a height of 2 inches.
Small grains can provide grazing in both the fall and the spring and still produce a grain crop if grazing is halted in mid-March or at the first sign of stooling.
If the crop is not to be harvested for grain, grazing can continue until forage becomes limiting, which can be well into May.
Rotational stocking or deferred  grazing might be valuable for providing higher levels of high-quality feed during periods of low productivity  and to extend grazing beyond midMay.
Two pastures with two-month rest periods might be satisfactory for stand recovery and productivity.
Seeding rates for smallgrained species in irrigated pastures should be 60 to 100 pounds per acre.
Nitrate toxicity, which will be discussed in more detail later, can be a problem when using small grains pastures.
Bloat is another concern, especially after a freeze or during rapid growth in the spring.
Grass tetany also can be a problem during rapid spring growth.
Warm-season annual legumes have not been tested broadly in New Mexico for use in irrigated pastures.
But a few, such as cowpea , lablab  and tepary bean , might have value when mixed with a warm-season annual grass and intensively, rotationally stocked to maximize productivity.
Seeding rates for warm-season annual legumes are 60 to 100 pounds per acre as monocultures or mixtures.
Sorghums and sorghum X sudangrass hybrids  provide valuable temporary pasture in lower elevations throughout New Mexico.
These forages respond well to nitrogen fertilization and irrigation, producing high yields of palatable forage.
Sorghum forage quality has been improved by including the brown midrib and photoperiod sensitivity traits.
Brown midrib  varieties have a lower lignin concentration that increases available energy and digestibility.
Heading in photoperiod sensitive varieties is not initiated until approximately mid-September when day length decreases.
This broadens the harvest window, allowing for higher yields of highquality vegetative forage.
Seeding rate also can affect quality.
Plants from higher seeding rates have finer stems than those seeded at lower rates.
Lower seeding rates are recommended for BMR varieties, because finer stems coupled with lower lignin concentrations increase the likelihood of lodging.
Sorghums should not be sown until the soil temperature reaches 60F, which normally occurs by mid-May in most of New Mexico.
Recommended seeding rates for pastures are 20 to 40 pounds per acre.
at least three days after the plants are completely frozen down to protect livestock from new growth.
Prussic acid is short-lived in stored sorghum forage, dissipating from hay or silage within a month after harvesting.
NMSU has more information on prussic acid in Guide B-808, "Livestock Poisoning from Prussic Acid."
 Antiquality factors associated with sorghums.
Prussic acid poisoning is caused when animal are fed immature sorghum forage ; by regrowth after harvest or grazing; or when plants are stressed by cool weather, herbicide injury, drought stress and frost.
Death can occur within 15 minutes.
Avoid grazing sorghums until plants are 24 to 30 inches tall.
After plants recover from stress, check their base to see if new growth, less than 24 inches tall, is present.
Rapid, immature growth is more palatable to grazing livestock, but it also is highly toxic.
It is best not to graze sorghums in the fall until
 Nitrate toxicity is another concern for sorghum pasture and hay but not as much for silage.
Actually, any plant can accumulate toxic nitrate levels, although it is most common with annual grasses.
Sorghums are prone to accumulate nitrates, because they grow rapidly and typically receive high rates of nitrogen fertilizer.
Drought stress also is commonly associated with toxic forage nitrate levels.
When moisture is limiting, plants continue to take nitrogen up from the soil, but they are not able to convert it from nitrate to protein.
Thus, nitrate accumulates in older and less photosynthetically active plant parts, which usually are lower to the ground.
Additionally, plants that grow rapidly due to recent irrigation or precipitation might take up nitrogen faster than they can assimilate it, particularly during cool, overcast weather.
In grazing situations, livestock prefer the newer growth near the top of the plant.
However, hungry animals are not as discriminating and might consume older plant parts that are toxic.
While the ensiling process can reduce nitrate levels by as much as 60 percent, nitrates do not dissipate from forage stored as hay.
Feeding greenchop is most dangerous because animals cannot avoid less palatable parts  like they can when grazing or feeding on hay.
Suspect forage should be tested and, if toxic levels are found, diluted with hay having low protein content and/or fed with a concentrated energy supplement, such as grain.
High nitrates in forage harvested for hay or
 greenchop can be avoided somewhat by raising the cutting height to leave lower stem portions in the field.
Nitrate toxicity generally is not a problem for monogastric animals.
But levels greater than about 3,000 parts per million  on a dry matter basis can be toxic for ruminants , particularly if they are under stress from illness, hunger, pregnancy or lactation.
Healthy animals can be slowly acclimated to higher forage nitrate levels.
Concentrations above 6,000 ppm are potentially toxic and should never be the only feed source.
Concentrations of 9,000 ppm and above often will lead to death.
Finally, sorghums also cause sorghum cystitis-ataxia syndrome in horses.
The same compounds that are precursors to prussic acid are thought to cause cystitis-ataxia.
Affected horses might exhibit urinary incontinence due to nerve damage in the urinary tract.
Prolonged exposure leads to posterior ataxia or incoordination and numbness in the hindquarters.
Further, urinary stasis  can result in urinary tract infections that may lead to kidney infection.
Horses exhibiting symptoms can be treated with antibiotics for urinary tract infections, but if ataxia is present, recovery is very unlikely.
Guide B-704, "Sudangrass and Sorghum Sudan Hybrid Poisoning of Horses" provides more information.
Pearl millet  is another choice for lower elevations, but it does not perform well on soils high in calcium.
This species will not yield as much as the sorghums, but it is safe for horses and does not cause prussic acid poisoning.
Foxtail, German or Italian millet  might provide temporary summer pasture in New Mexico's higher elevations.
Foxtail millet is less productive than pearl millet and its shallow root
 system makes it easy for grazing animals to uproot.
As plants mature, they can accumulate setarian, a compound that acts as a diuretic in horses, causing excessive urination.
This compound can lead to kidney problems and also has been implicated in liver, bone and joint damage, especially if the foxtail is the only hay source for the horses.
If symptoms are observed early, removing millet hay from the diet might correct the problem.
More information on all species of millet can be found in Guide A-414, "Millet Production."
 Crop residues.
Other forage sources for grazing include plant residues after grain harvest or cotton harvest that can be used to defer grazing on small grains or stockpiled pastures.
Except for the seed found in cotton remnants, these materials generally are lower in quality, because they are no longer actively growing.
They also are overmature and weathered.
In the case of grain crops, the energy was removed by previous harvest.
Thus, some supplementation might be necessary, particularly for actively growing or producing livestock.
Establishing Irrigated Pastures Seed and plant stock selection.
When establishing an irrigated pasture, use the best quality seed or planting stock available to improve your chances of obtaining a uniform, productive and persistent stand.
Once a species or combination of species is chosen, variety selection is critical to get the best genetics for your irrigated pasture system.
Use certified or plant variety protected seed stocks to ensure the genetics in the bag are true to the variety name.
Read the seed label , because several factors listed involve seed quality and directly affect the pasture species performance.
The test date on the label must be within the previous nine
 months for the seed to be sold legally in New Mexico.
Seed purity affects seeding rate and stand uniformity as well as establishment of weeds and undesirable crop species.
High inert matter, which includes stems, chaff, dirt and rocks, usually is due to inefficient or poorly developed seed-cleaning techniques.
Higher seeding rates must be used, increasing seed costs.
Excessive inert matter also interferes with seed distribution, because it can plug planting equipment or restrict seed flow.
Weeds and other crop species compete for water, space and nutrients and reduce forage production and quality.
A relatively weed-free field can be contaminated with weeds, if seed containing weed seeds is sown.
Be sure that no noxious weeds are listed on the label.
Germination also is important for determining the seeding rate and obtaining a uniform stand.
Seeding rate of many species is given as pure live seed.
Seeding rates for many warm-season grasses are given as PLS values because they generally are very chaffy  and have low germination rates.
Germination is affected by crop species and seed dormancy, age, damage, weathering and storage conditions.
However, even seeds that will germinate might not have enough energy to produce viable plants.
Seedling vigor might be affected by the same factors as germination.
Seed treatments are beneficial to seed delivery, legume inoculation and protection from seedling diseases and insects.
Preplant fertility and legume inoculation.
Before ground is broken for a new pasture, a soil sample should be taken and submitted for analysis.
Guide A-114, "Test Your Soil" gives information about soil sampling and testing.
If sowing a monoculture grass pasture, apply 20 to 25 pounds per acre of starter nitrogen to help the grass get established.
If planting a grass-legume mixture, pay attention to the phosphorus and potassium recommendations.
Legumes have the ability to fix nitrogen from
 the atmosphere.
If inoculated with the proper bacteria, they can meet their own nitrogen requirement and provide nitrogen to the companion grass.
Adding excessive nitrogen at establishment will inhibit nitrogen-fixing nodule formation.
Without good nodulation, legumes will produce stunted, yellow plants typical of nitrogen deficiency, necessitating the addition of supplemental nitrogen.
Natural inoculation can occur if the legume has been grown in the field within the previous five years.
However, if there is any doubt, it is best to inoculate and not use any preplant nitrogen.
Different legume species need different bacteria, and the cost of inoculum is relatively low compared to the cost of nitrogen fertilizer.
Commercially available seed of many legumes will be pretreated.
The treatment date should be within the previous year.
If untreated seed is purchased, inoculate the seed just before planting.
Be sure to use the inoculant strain labeled specifically for the legume to be planted.
Apply the inoculum evenly to the seed.
Be sure to follow the instructions on the inoculum package, including those related to using a sticker to ensure uniform contact between the seed and the inoculant.
Beware of using carbonated soft drinks, 10 percent syrup mixtures or other homemade stickers, because they might be too acidic or alkaline and kill the bacteria.
When adding a liquid sticker, don't get the seed too wet or it will become clumpy.
Alfalfa seed should just feel sticky, and it must be uniformly moist.
Mixing by hand in a large bucket, using a hoe in a larger pan or using a cement mixer are equally effective for a uniform treatment.
More information about legume inoculation can be found in Guide A-130, "Inoculation of Legumes."
 Land preparation.
Proper land preparation is important for establishing and maintaining an irrigated pasture.
The field
 Figure 5.
Effect of seeding depth on alfalfa emergence.
should be prepared SO it provides for the best use and uniform distribution of water.
The type of irrigation system and soil condition determines how much land preparation is necessary.
With sprinkler systems, the land need only be level enough to allow easy operation of the sprinklers and other equipment.
Flood and furrow irrigation, on the other hand, require the land to be level across the flow pattern, with the proper slope for water to flow freely, while allowing sufficient time for infiltration.
Another aspect of land preparation involves developing a firm, smooth seedbed SO that planting depth can be regulated and good seed-to-soil contact can be achieved.
Most perennial forage crops have small seeds and should be planted no deeper than onehalf inch in heavy soil or up to an inch in sandier soils.
Uneven ground will cause some seeds to be planted too deep, and the new seedlings will not have enough energy to emerge and begin photosynthesis.
It also is difficult to regulate planting depth in loose or cloddy seedbeds.
Seed sown at the
 surface of loose seed beds can be displaced by irrigation water, leaving unsown areas for weed infestation.
Additionally, seed might be at the correct depth, but poor contact with soil particles limits access to water and nutrients and decreases root-anchoring strength when seedbeds are loose.
Planting time.
Time of seeding is determined largely by soil temperature and species to be sown.
Warm-season plants germinate and emerge most rapidly when soil temperature is above 55F; cool-season plants germinate and emerge when the soil temperature reaches 45F.
Warm-season species should be planted from spring to midsummer.
This allows sufficient time for the crop to establish a good root system before freezing temperatures occur.
While cool-season perennial species can be sown in the spring, several factors make late summer planting  more desirable.
Late summer seedings give the plants time to establish fully and be ready to graze the following
 spring.
Also, there usually is less weed competition in fall than in spring; more time is available to control weeds that germinate during summer.
And, while some summer weeds might germinate after planting, not many will have time to produce seed before frost.
Finally, evapotranspiration and wind generally are less in the fall, allowing for lower water requirements.
Late summer seedings need to be early enough to allow plants to establish before freezing.
Generally, six to eight weeks are needed for fall establishment.
Planting methods.
Most pasture species are established by seeding.
But certain crops like some of the improved bermudagrasses must be established vegetatively.
Vegetative planting requires special operations and equipment.
The sprigs  must be vigorous and healthy.
Plant them as soon as possible after harvesting, because they do not store well.
Sprigs may be scattered and covered by light disking or rototilling, or they can be planted with a sprigging machine.
Sprigging machines provide more uniform sprig distribution and covering, but they might not always be readily available.
Sprigging and then irrigating are a common practice to improve sprig-to-soil contact.
When possible, seeding is more desirable than vegetative planting because of availability and equipment and planting material costs.
With conventional tillage, many pasture species can be sown either by drilling or broadcasting.
Both methods provide uniform seed distribution, but properly set drills and air-seeders with packer wheels provide better seed coverage in the same operation.
Seed left on the surface can be displaced by wind and water, removed by birds or rodents, or die due to lack of seedto-soil contact.
Broadcast plantings must be covered with a harrow or roller but neither provides covering as well as packer wheels on a drill or air-seeder.
Generally, harrowing or rolling is done in a second
 operation, but equipment is available that will broadcast and harrow or roll in one operation.
Broadcast seeding is easier and takes less time than drilling, but this advantage can be more than offset through seed loss by displacement and the need for secondary operations.
Hydroseeding also might be an option for establishing smaller pastures.
Hydroseeders are available at many larger landscaping companies.
If land reconstruction is not needed to improve conditions for irrigation, no-tillage or minimum-tillage planting can save time and money as compared with conventional tillage operations.
These practices also improve moisture conservation, because the soil is mulched with plant residue.
No-till planting does require a seed drill especially designed for penetrating untilled ground, SO be sure the equipment is heavy enough to place the seed at the proper depth.
Existing vegetation must be controlled to prevent competition and allow new seedlings to establish.
Initial chemical applications should be made two weeks before planting to remove the established insects' food sources and to encourage them to migrate to another area SO that they won't feed on the seed.
Insecticide seed treatments help overcome this problem.
Also, if the same forage species is reseeded, disease pressure on seedlings might escalate, especially for legumes.
Metalaxyl seed treatment is relatively effective for protecting seedlings from many diseases.
For no-till planting, use the highest recommended seeding rate.
Established grass pastures can be renovated with legumes by either of two methods, no-till in late summer or frostseeding in late winter.
In either situation, apply a chemical to burn down the grass or remove as much top growth as possible by grazing.
Grazing probably is the best option, and animals can remain in the pasture until they begin biting or uprooting the new seedlings.
Once that happens, remove
 Figure 6.
Relative effectiveness of using different seeding equipment and methods to achieve a forage crop stand.
the animals and allow the new seedlings to establish by reaching 25 percent bloom.
Irrigation.
Preplant irrigation can help overcome some problems with land preparation and seed movement caused by post-planting irrigation.
Wetting the soil breaks down clods and firms the seedbed, improving seed-to-soil contact at planting time.
Soil crusting, which inhibits new seedlings from emerging, also can be prevented with pre-irrigation.
But this method also has disadvantages.
Planting must be done before the soil has dried too much for satisfactory germination.
If the soil is too wet, there can be excessive soil compaction and crusting.
Knowing when the soil is moist enough to plant, yet dry enough to drive equipment over the field, is largely a matter of experience.
Also, because most perennial forage crop seeds are small and must be planted shallowly, desiccation of new seedlings must be prevented by keeping the top inch or SO moist until emergence.
Crusting also must be prevented, possibly requiring more frequent irrigation just for establishment.
This should not be much of a problem when using sprinkler irrigation, which can apply lesser amounts of water more frequently.
But flood and furrow irrigation systems are not as efficient and small amounts of water cannot be applied.
Pre-irrigating might cause water to be in short supply at another time during the growing season.
Companion crops.
Sometimes an annual crop, usually a small-grained species, is planted with a perennial pasture species as a companion  to protect it until it becomes established.
This practice is discouraged except under special circumstances, such as when seedlings need protection from wind or the soil is highly erodible.
The companion crop might protect the pasture species from the wind and provide an early hay or grain crop, but it competes directly with the pasture species for
 water, nutrients, light and space, delaying stand establishment drastically and possibly resulting in a less uniform stand.
Seeding early enough in the late summer for plants to establish a good root system and some top growth is the best management option.
Producers also can consider no-till seeding into residue from the previous crop to protect the new seedlings.
Completing establishment.
Once seedlings have emerged from the soil, they need special care to become established as a productive, persistent pasture.
Management during the first growing season determines the perennial pasture stand's uniformity and longevity.
Adequate nutrients are essential.
Follow preplant soil test recommendations for the species.
Irrigation management also is critical.
There must be a compromise between providing enough moisture for the plant to rapidly grow and forcing the plant to develop a good root system as it searches for water.
Too little irrigation causes the plant to use too much energy for root system development rather than top growth.
Desiccation also can lead to plant death.
Too much irrigation also is detrimental, because some nutrients can be leached, root system development is inhibited, and seedling diseases are encouraged.
Weed control still will be a concern because weeds compete for nutrients, water, light and space.
The best weed control begins with a weed-free seedbed, assisted by a uniform stand of the pasture plants that can quickly establish ground cover.
It still might be necessary, however, to mow weeds or control them with a herbicide labeled for the weed and the forage crop.
Be sure to mow high enough to avoid clipping the desirable species.
Grazing pastures too soon also can cause problems.
New pasture plants should be allowed to become reproductive before being harvested or grazed the first time.
Allow grasses to reach the early heading stage and legumes to reach approximately 25 percent
 bloom.
Manage grass-legume mixtures for the legume.
If a companion crop is sown to protect the new seedlings, use grazing as with a frost-seeding.
Otherwise, harvest the companion crop as hay to reduce shading and competition.
In either case, manage the pasture to protect the new seedlings by not grazing or clipping them until they are mature enough.
New Mexico State University is an equal opportunity/affirmative action employer and educator.
NMSU and the U.S.
Department of Agriculture cooperating.
The tendency should not be a surprise, because humans are creatures of habit.
We get out of bed every day on the same side, we sit at the same place at the table for breakfast, etc.
Farmers are no different  they tend to plant about the same number of seeds per acre each year, they apply about the same amounts of fertilizer each year, they plant the rows the same direction, etc.
Well, you get the point, and without any compelling reasons, why make changes, right?
However, irrigation scheduling should be an exception to this approach because the rainfall amounts and their timings are different each year.
In 1945 the Water Appropriation Act was passed by the Kansas Legislature that set forth a number of provisions, including: "All water within the state of Kansas is hereby dedicated to the use of the people of the state, subject to the control and regulation of the state.
In the late 1960's people in the rapidly developing groundwater areas of the state became concerned over declining water levels and the lack of state policy to address the resource concerns.
There was strong interest in more local control of the water issues and implementation of water law.
This led to the establishment of the Groundwater Management Act in 1972, which set forth the state policy recognizing local management as the best approach.
In 1976 the Southwest Kansas Groundwater Management District No.
3 was established.
Today, GMD3 covers all or parts of the 12 counties in southwest Kansas.
GMD3 is the largest district in Kansas covering 8425 square miles that include over 10,000 active non-domestic wells with an average of just under 2 million acre feet of water use reported annually.
IMPLEMENTATION OF FLOWMETERS IN GMD3
 Information is the key to good management.
In 1992, GMD3 started a flowmeter program which required that all active, non-domestic wells be equipped with an approved water flowmeter.
This was done on a four year rotational basis with all wells located in the SE quarter of each section required to have a flowmeter installed in 1992.
That was then followed by the NE quarter in 1993, NW quarter in 1994 and the SW quarter in 1995.
Flowmeters are required on all nondomestic wells that are active.
If the well/land is in a conservation program, it is not required to have a flowmeter installed, but the flowmeter is required prior to the well being put back into service.
The flowmeters must be on the State's list of acceptable flowmeters.
In the beginning, it was required that the flowmeter either have sufficient spacing from pipe obstructions or have straightening vanes.
But spacing could be waived if the flowmeter installation was verified to be accurate.
A main issue on the installation was measurement of all the water pumped from a point of diversion.
It remains to this day the responsibility of the well owner to insure the flowmeter continues to operate satisfactorily.
The operator was required to report the meter readings on the annual water use reports submitted to the state that are required by statute.
EARLY MONITORING AND COMPLIANCE
 In the early stages of the metering program, we would do random inspection or a full inspection of a particular instillation if there was a compliance issue.
We tried a self monitoring method with the producers.
If they found their meter was not working correctly they were to notify our office and we would issue a "Safety" tag that would be placed at the location while the meter was removed.
This allowed us to track the flowmeters and gave inspectors a visual sign that the meter had permission to be taken off for service.
The tags were good for 15 working days.
We would schedule follow up visits to ensure that the service had corrected any problems and the meter was now working correctly.
In 2003 GMD3 implemented a seasonal meter inspection program.
Our office would hire three to four seasonal employees and assign them hundreds of wells to inspect.
The program was to visit two thousand or more wells a year.
The information they collected was submitted to our office bi-monthly.
This type of program has continued to today.
If a problem or a noncompliant meter is found, our office is notified within 24 hours.
This starts the process to have the noncompliance corrected in a timely manner.
The data taken from these inspections also allows us to monitor the pumping rates and supply changes across the District.
The flowmeter is a mechanical device that can be prone to malfunctions and be cause for unreliability if they are not properly installed and maintained, or have faulty parts or instillation.
Through the years of the GMD3 metering program we have seen a lot of different issues, but we will discuss the most common.
The most common issue we see is that the flowmeter is just not working which could be due to a variety of reasons.
There could be something lodged in the propeller preventing it to spin.
It could also, for example, have impeller bearings that locked up or any of several other mechanical failures.
The operators do not always catch these failures, because the instantaneous reading could still be working, but the totalizer, which is the accurate part of the mechanics, may fail.
These two functions, on certain flowmeters, sometimes work independently of each other.
Since it is the totalizer that must be reported every year, it is critical to make sure that mechanism is always functioning.
Meters that are found not working, must be repaired right away and the operator must then submit a flowmeter repair/replacement report to our office or the State.
We have also recently begun to ask for a copy of the invoice as documentation of the repairs
 We do see quite a few cases in the field where the meter register is not readable.
The biggest reason for this is moisture inside the lens.
We have talked to most of the manufacturers and have been told that if there is moisture inside the meter, it is not reliable and could fail at any time.
This is another case where the operator will need to send the meter in for repair and report to us when it is fixed and installed.
A requirement of the State is that all flowmeters must have a manufacturer's seal on it.
The seal indicates the manufacturer's warranted reliability.
And, the lack of a seal can sometimes indicate that the meter was tampered with.
Unfortunately, over time, the seal can just fall off from exposure.
In this case the operator has two alternatives.
If they believe that the meter is working properly and it is just missing the seal, our office can perform a flow verification test.
If the installed meter is within +/6%, we will put our seal on the meter, and that is acceptable.
If the operator has any concern about how the flowmeter is operating, the meter must be sent to a certified repair person and they will put a seal on it after confirming accuracy.
We also see cases when the flowmeter is not installed properly in the pipe.
This can mean it is on backwards, not installed where it will measure all of the water being diverted or does not meet current meter installation requirements.
Today, if a well is redrilled or if the operator installs a new flowmeter, it must have at least 5 pipe diameters upstream and 2 diameters downstream of unobstructed straight run from the meter sensor.
This rule applies unless the manufacturer has more stringent requirements.
The meter must also have straightening vanes and be installed in a manufacturer approved measuring chamber.
If spacing is not met the operator will have to make adjustments to the installation to make
 sure it meets current regulations.
These regulations are intended to assure that in most cases, the flowmeter will function properly and an accurate measurement will likely occur.
In many areas within the District, the wells can no longer pump at the rate they were originally certified as producing.
This can lead to a flowmeter not having a full flow of pipe across the measuring device.
The operator will again need to make the proper corrections to ensure that there is a full flow of pipe across the meter or the meter performance will be compromised.
Our office continues to work with operators to achieve the best records are maintained in order to managing the water in our District.
We can't manage the resource without good information.
There are several services that we provide to assist water users.
In order to give the operators the best information on flowmeters, our office is constantly in contact with meter manufacturers.
We try to keep up to date with the new technology in flowmeters and have a good understanding of how the meters work.
This allows us to help operators determine what the problems might be for their installed meters and provide the best solution to the operator.
We continue to stress the importance of maintaining a properly working flowmeter.
A good way to look at it is that the flowmeter needs to be treated just like any other equipment the operator uses.
It is always good to do routine inspections and maintenance on the flowmeter.
A well maintained meter will be more able function properly and most of the time, require less costly repairs.
GMD3 has staff that is certified by the State to perform flow verification tests on installed flowmeters to determine accuracy.
We are also required to have our non-intrusive meters certified every year for accuracy traceable to NIST standards.
We also perform random tests across the District throughout the year and at the request of the operators.
The best and sometimes most difficult thing to do is education of the operators on how to maintain the flowmeters and use them to their full potential.
We are constantly encouraging people to time their meters and do simple, easy inspections on the flowmeters.
If the operators would do self-inspections on the meters they could avoid the more expensive repairs.
We also try to let people
 see the advantage of taking ten minutes to calculate what the meters are actually registering.
This is a good way to keep track of how much they have pumped and can give the operator the ability to determine if the meter is not totalizing correctly
 If you have a properly working meter, it can help you monitor your water usage, which could prevent water right enforcement actions later on.
The best example we can give the operators is to look at their water rights as a checking account.
The can start the year out with a full allocation in their account.
As they pump the well, they are withdrawing from the account.
The flowmeters can indicate how much is withdrawn and how much is left.
It is also a good comparison to say that if you overdraw your checking account, there can be severe penalty.
This is the case if you overpump your water right.
In this day and age, it is easy to get information out to a lot of people by using the internet.
We offer a lot of different types of assistance from our webpage, and soon will offer even more.
If the operator has to repair their flowmeter they can get the report that they will need to turn into our office.
There are instructions of how to time your meters, perform quick inspections, and spreadsheets that will help them keep track of their water account.
A new program we are working with is the installation of temperature loggers used in the shipping industry to track groundwater well operations.
We have done some testing in the last couple of years with installing inexpensive temperature loggers on the discharge pipe to record the temperature of the pipe every 15 to 30 minutes.
When the well is pumping, the discharge pipe will maintain a fairly constant 60-65 degrees.
This allows us to calculate how many hours the well operates.
If we know the flow rate, we can estimate the amount of water pumped and when.
This is a relatively easy way to back up the flowmeter data and gives our office valuable information about the timing of water applications.
Currently we have the loggers installed on all of the wells that we are required to monitor by contract each year, as well as on some wells that have had noncompliance issues and need added supervision regarding well operations.
Give us a call if you have questions or would like to discuss this information further.
Method of irrigation affects sour skin rot of onion
 Beth L.
Teviotdale R.
Michael Davis John P.
Guerard Dennis H.
Harper
 Sour skin rot of onion was controlled successfully by substituting furrow irrigation for overhead sprinkler irrigation.
Fresh weight of bulbs and percentage soluble solids were not affected by the irrigation method or the volume of water delivered.
Sour skin is a serious bacterial disease of processing onions in California's Central Valley.
The bacteria  enter plants through wounds in young leaves and progress down the leaf to rot the corresponding scales in the bulb.
The infected leaf develops a watery rot in the onion neck, which turns light brown and can be removed easily from the plant.
In advanced stages, infected scales discolor and separate from healthy portions of the bulb.
Severe outbreaks may result in the rejection of entire lots of onions at the processing plant.
Although details of the survival and spread of P.
cepacia are not well understood, the pathogen is known to be soilborne or
 present in decaying plant tissue, and moved in irrigation water.
It has not been reported on onion seed.
Bacteria, including P.
cepacia, are readily transported in water, and many bacterial diseases depend upon rain or sprinkler irrigation for their spread.
Our dry California climate serves as a natural control for many bacterial diseases, outsprinkler irrigation may create conditions that favor disease.
Careful management of sprinkler irrigation can limit the infection of crops subject to bacterial disease.
The objective of this study was to determine the influence of the irrigation method and the amount of water applied by sprinkler irrigation on the incidence of sour skin rot and yield in processing onions.
South Port White Globe onions were direct-seeded at the University of California West Side Field Station, Fresno County, in January 1987 and 1988.
When the plants developed three to four leaves in mid-April of each year, the fields were divided lengthwise into four sections of 16 beds each.
Sprinklers were placed between the center two rows of each section and gated pipe was laid transversely across the field, creating 16 sections.
These sections accommodated four
 Onions irrigated by sprinkler too late in the season tend to develop sour skin rot.
Affected leaves turn light brown and scales discolor and separate from healthy portions.
When harvested, infected onions are rotted and discolored within.
replications of four irrigation regimes: furrow irrigation all season; sprinkler irrigation until bulbing and furrow irrigation for the remainder of the season; sprinkler irrigation to 30 days past bulbing and furrow irrigation for the remainder of the season; and sprinkler irrigation all season.
In this study, bulbing, which occurred in late May in both years, is defined as the time when the bulb diameter is about twice that of the neck.
Each week included two 6-hour sprinkler sessions and one furrow irrigation.
The final irrigation came in the first week in July each year.
The total seasonal water applications for treatments 1 through 4, including furrow irrigations, were 24.9, 24.3, 21.9, and 19.3 inches in 1987 and 38.0, 37.2, 36.5, and 36.0 inches in 1988.
Variations in pump pressure and an increase in the number of irrigations because of weather conditions accounted for the differences in totals for the two years.
Plots were centered between risers and located in the second beds on both sides of sprinkler lines and on the corresponding two beds in the furrow-irrigated sections.
Both beds in each section were divided into 10-foot subplots, which were either inoculated or noninoculated.
The inoculum consisted of a water suspension of P.
cepacia, approximately 1 million bacteria perml, and was applied to runoff using a compressedair sprayer during two regularly scheduled sprinkler irrigations in the first and third weeks of June in both years.
Disease incidence was evaluated in midJuly.
All bulbs in the subplots were cut just below the shoulder, and disease incidence was expressed as the percentage of bulbs with internal discoloration.
Pseudomonas cepacia was recovered in culture from representative diseased bulbs.
Yield data were collected in August 1987 and July 1988.
Fresh weights of all bulbs from 20 feet of the third  bed on both sides of the sprinkler line and the
 TABLE 1.
Effect of sprinkler and furrow irrigation
 on sour skin rot incidence in onion, Fresno
 Irrigation	Innoc.
innoc.
Innoc.
innoc.
all season	0.3at	0.1a	6.7a	4.4a
 of season	1.2a	0.2a	6.6a	1.2a
 of season	9.5b	1.6b	17.4b	1.1a
 all season	29.9c	4.6b	42.9c	13.5b
 *Values are means of four replications of about 200 onions each.
Onions were inoculated by spraying a water suspension of Pseudomonas cepacia twice on leaves in June.
tMeans in each column followed by the same letter do not differ significantly according to Duncan's Multiple Range Test, P 0.05.
Bulbing occurred in late May of both years.
TABLE 2.
Yield of onions that were sprinkler-irrigated with three sizes of nozzle orifice, Kern County
 weight per 10 feet*
 diameter	1987	1988	A	B	C
 3/32	51.4a	34.8a	40.6a	24.9a	22.4a
 7/64	52.2a	38.7a	44.7a	32.2b	30.1b
 1/8	50.6a	33.3a	45.9a	34.2b	33.2b
 *Four replications of each treatment.
Fresh market onions used in 1987.
all others are processing on ions.
+Identical experiments located in three fields designated A.
B.
and C.
corresponding beds in the furrow-irrigated plots were recorded in 1987.
Identical measurements were taken from 10 feet per plot in 1988.
The percentage of soluble solids in a sample of about 30 macerated onions taken from each plot was measured with a refractometer.
#Means followed by the same letter do not differ significantly according to Duncan's Multiple Range Test.
P 0.05.
The incidence of sour skin was significantly less in the two treatments employing furrow irrigation for most or all of the season than in the two treatments irrigated by sprinkler for most or all of the season.
The highest percentage of rot occurred in plots irrigated by sprinkler all season.
Rot found in uninoculated checks was attributed to natural spread and infection.
There were no significant differences in fresh weight of bulbs or percentage soluble solids among the four irrigation systems in either year.
Yields ranged from 2.8 to 3.4 and 5.9 to 6.6 pounds per bed foot in 1987 and 1988, respectively.
Percentage soluble solids varied from 22.5 to 23.7 in 1987 and 13.6 to 15.0 in 1988.
Volume of overhead irrigation
 We tested the influence of variations in the amount of water applied by sprinklers on disease incidence and yield by altering the nozzle orifice size in five commercial onion fields.
The experiment was conducted in fields of fresh-market and processing onions in Kern County in 1987 and 1988, respectively, and in three fields of processing onions in 1989 in Fresno County.
Plots were established between two adjacent sprinkler lines 16 beds apart.
Two opposite pairs of sprinklers, forming a square, werefitted with nozzles having orifices 3/32, 7/64, or 1/8 inch in diameter.
These nozzles delivered 0.10, 0.20, and 0.26 inches water per hour, respectively.
There were four replications of each treatment.
Irrigation schedules varied, but most were every to days and 2 to 6 hours long.
One of the center beds in each plot was inoculated with P.
cepacia as described above during regularly scheduled irrigations in June.
Plots were inoculated twice in 1987 and 1988 and once in 1989.
All bulbs in the center 10 feet of each inoculated bed in the 1987 Kern County trial and 100 bulbs in each plot in the other trials were cut and evaluated for disease in mid-July.
Fresh weights of bulbs in 10 feet in each treatment were determined and soluble solids were measured as described above.
The volume of water delivered by the three nozzle orifice sizes increased with increasing orifice diameter.
However, there was no correlation between the amount of water delivered and the percentage of rotted onions.
The incidence of sour skin was low in four trials , but high in the other trial.
The fresh weight of bulbs was significantly lower in two experiments during 1989 in which onions were irrigated using 3/32-inch nozzles than with either 7/64or 1/8-inch nozzles.
No significant differences in the fresh weight of bulbs were found among treatments in the 1987 or 1988, or in one of the 1989 experiments.
Percentage soluble solids was not affected significantly by the variable amounts of water in any trial.
Method of irrigation has a substantial impact on the incidence of sour skin of onions.
Season-long overhead irrigation provided a favorable environment for sour skin rot, whereas furrow irrigation resulted in almost complete control of the disease.
Only treatments in which sprinkler irrigation was used after bulbing resulted in high levels of the disease.
The final four or five sprinkler irrigations were accompanied by a 150 to 300% increase in disease.
Where sour skin is a potential problem, a change from sprinkler to furrow irrigation at least from bulbing to the end of the season is advisable.
The possibility that disease incidence could be lowered by reducing the volume of water delivered was not substantiated by our experiments.
Varying the amounts of water with different sizes of nozzle orifice did not reduce the incidence of sour skin in lotsirrigated with even the smallest volume of water.
Thus, growers opting for seasonlong overhead irrigation may not be able to reduce the volume of sprinkler irrigation enough to reduce disease while maintaining optimum yields.
Percentage soluble solids of the bulbs was not affected by differing amounts of water delivered by the three nozzle sizes.
However, yield as measured by fresh weight of bulbs was reduced in two experiments in 1989 where the 3/32-inch-diameter orifice sprinklers were used.
This may also have been true for the third 1989 experiment, but the test for significance failed by a slight margin.
The 3/32-inch nozzle size offers no advantage for disease control, and may be deleterious to yield.
The 7/64-inch appears to be a better choice than the 1/8-inch nozzle because the former delivers significantly less water, but does not reduce the yield of fresh bulb weight or the percentage soluble solids content of bulbs.
Beth L.
Teviotdale is Extension Plant Pathologist and Dennis H.
Harper is Staff Research Associate, Kearney Agricultural Center, Parlier; R.
Michael Davis is Extension Plant Pathologist, Department of Plant Pathology, University of California, Davis; and John Guerard is Farm Advisor, UC Cooperative Extension, Kern County.
This research was supported by a grant from the American Dehydrated Onion and Garlic Association.
Low Energy Precision Application  in the Pacific Northwest
 Troy Peters, Howard Neibing, and Richard Stroh
 Low Energy Spray Application  is sprayed on.
Additional hardware costs can be offset by the pumping power savings due to lower pumping pressure requirements and improved irrigation efficiency.
Costs/year.
Equipment	$	902.16	$ 768.85
 Labor/Maintenance	$ 617.72	$ 284.15
 Annual Pumping Costs	$ 3,344.17	$ 5,115.60
 Total/year	$ 4,864.05	$ 6,168.60
 LESA gives less time for water to infiltrate into the soil.
Therefore it may not be suitable to tight soils or steep slopes where infiltration and runoff can be an issue.
Double Goosenecks and truss-rod hose slings spread the water out to help offset shorter infiltration times.
Inadequate outlet spacing can be overcome with simple attachments and large hose clamps.
The sprinkler head can irrigate below the top of the canopy without problems.
However, it can limit the ability to chemigate.
Double goosenecks and truss-rod hose slings also decrease drop spacing.
LESA worked well in corn.
The narrow spacing eliminates typical uniformity issues on wider spacings due to the canopy disrupting the application pattern.
It didn't hang up too much in the canopy.
No need to plant in a circle.
LEPA/LESA sprinklers are easy to maintain.
You don't get as wet!
We can test your field to determine if LEPA/LESA will work for you.
Please contact us  if you are interested in having us come test your infiltration rates.
It works!
So far, all demonstration field owners are expanding its use on their farms.
Overview of LEPA/LESA Challenges
 High application rates.
If you have no trouble getting water into the soil, then you might benefit!
If you have tight soils and/or steeps slopes, the LEPA/LESA is probably not for you.
Chemigation.
The sprinklers can go into the canopy.
The canopy won't get wet when this happens.
Can raise the drops slightly.
Can switch to chemigation spray plate that sprays upwards.
This is inexpensive and easy to do..
Smaller nozzle sizes.
This may lead to additional plugging if you have dirty water.
Finer filter screens may be required.
Overview of LEPA/LESA Advantages
 Irrigation Efficiency is much higher.
You will need less water.
Low pressure!
Save pumping energy.
Less variation in application efficiency (less daynight differences in applied depths, less difference between windy VS.
calm days.
Less lodging.
Heavy and wet crops can fall over.
Wheel tracks.
It's easier to keep them dry.
Dry canopy.
Possibly less crop diseases.
Maintenance is easier.
No ladders.
Stay drier.
Better uniformity in corn.
Contact Us for More Information!
Irrigation System Maintenance, Groundwater Quality, and Improved Production
 Lack of irrigation system maintenance can waste water, nitrogen, and energy and can lead to degradation of groundwater.
Simply replacing nozzles on sprinklers can go a long way toward having efficiently operating systems.
The Connection between Poor Irrigation and Poor Groundwater Quality
 S uppose that a farmer takes pure water from an aquifer and applies it to her land, but she applies a bit too much or applies it unevenly.
How can this common event contaminate the aquifer?
We first need to note that the soil nitrogen that makes plants green is primarily in the form of nitrate, and this nitrogen is accessible to plants specifically because it stays dissolved in the soil water.
In a typical corn field, where the bulk of the roots are in the top 18 inches of soil and the soil has a water-holding capacity of 25 percent, the corn root zone can hold 4.5 inches of water.
If the farmer adds an extra 4.5 inches of water during the year on top of what is needed to wet the soil, essentially all the soluble nitrogen will be pushed out of the root zone.
Four and one-half inches of water is about 15 percent of the annual water requirement of corn in the Willamette Valley, SO overwatering by only this much over the entire growing season is a very easy error to make.
Figure 1 shows how nitrate concentrations
 John Selker, professor of bioengineering, Oregon State University.
below the root zone responded to irrigation-driven percolation as mint fields were irrigated.
Similar data were obtained under row crops.
If a farmer overirrigates each year, he will think that to keep the crop green requires much more nitrogen than anticipated.
It's not surprising, then, that many farmers apply more nitrogen than the crop would require under controlled irrigation.
Thus, overirrigation leads to excess nitrogen applications and at the same time drives the mobile nitrate to the aquifer.
Figure 1.
Observed average nitrate  concentrations in percolating soil water at a 3-foot depth under seven commercial mint fields in Lane County, OR.
The drinking water standard is 10 ppm.
Excess irrigation is not only applying too much water to the whole field.
What about a farmer who is applying just enough to keep the field well watered: could this farmer have a problem?
Yes, if the irrigation system is applying water unevenly.
It is not unusual to see one section of a line sprinkler applying 20 percent more than the average output and another section applying 20 percent less than the average.
To get full production on all parts of the field, the farmer will set the system at a 20-percent higher rate to compensate for the section that's underapplying water.
That means the overirrigated area will get 40 percent too much water, and even the part of the field that was receiving the average amount will get 20 percent too much water.
The farmer is wasting large amounts of water and energy; furthermore, this excess water flushes the nitrate out of the root zone.
So, to get full yield off the most overirrigated area, the farmer must apply additional nitrogen during the season.
Given the poor irrigation system, this farmer is doing only the absolute minimum in irrigation and nitrogen application sufficient to get full yield.
Thus, it is clear that nonuniform water application is at least as problematic as overirrigation in requiring excess nitrogen application.
Figure 3.
Patterns of water application by sprinklers with correct, excess, and insufficient water pressure.
The conical pattern at left overlaps with neighboring sprinklers to create a nearly uniform pattern.
Figure 2.
Sprinkler output before  and after  nozzle replacements on a typical commercial farm in the Willamette Valley.
What Happens When Nozzles Wear Out?
Why would a well-designed irrigation system apply water irregularly?
One would hope that on the first day of operation the spray was acceptably uniform, but let's consider how this system might evolve.
Each year, some components will be used more hours than others, and some components will fail and be replaced.
In addition, a successful farmer often adds new land to the production area and may add new, compatible components to an older system.
As water shoots through a nozzle, it enlarges the orifice, letting more water out and reducing the pressure in the system.
A system with a mix of nozzle ages therefore will not apply water uniformly.
Even if all nozzles are the exact same size, if the openings wear to a size much larger than when installed, the system pressure drops too quickly along the line as it goes farther from the water source, which also leads to poor uniformity.
Of 12 systems studied, half were operating below the pressure required for uniform application, and every one of them showed significant improvement in uniformity with new nozzles.
A poorly functioning or poorly managed irrigation system wastes water, wastes energy, wastes nitrogen, and reduces crop production.
We recommend:
 Replacing all nozzles at least every 4 years 
 Check system operating pressures periodically.
If below optimal range, check that the pump is working correctly, that the number of sprinklers is not in excess of pump capacity, and that nozzles are not worn.
Make sure that sprinklers are discharging at the correct angle and that impact sprinkler heads are rotating properly.
A riser that is tilted rather than vertical or a rotating sprinkler head that spends more time discharging in one direction over another will result in nonuniformity.
Schedule irrigation using climate and direct observation.
First, look at how much the crop should demand and then check weekly that the soil is neither too wet nor too dry.
For more information, refer to publications listed below under "About irrigation scheduling."
 Have everyone who works with the irrigation system understand the importance of correct function to the farm's productivity.
Drive train: Drain water from gearboxes and top off with the proper lubricant.
Check knuckles for wear and make sure shields are in place.
Check tire pressure.
Irrigation Monitoring with Soil Water Sensors
 Juan M.
Enciso, Dana Porter, Steven R.
Evett, Xavier Pris, and Troy Peters*
 Monitoring the water content of your soil will help you decide how much water to apply and when to apply it.
Soil water sensors can give the information you need to:
 Monitoring the soil's moisture will help you schedule irrigation in order to avoid applying too little or too much water; which under irrigation will reduce crop yields.
Overirrigation can also:
 increase water and energy costs
 leach fertilizers below the root zone
 move soil particles and chemicals to drainage ditches
 result in unnecessary labor costs
 By understanding basic soil water concepts, the strengths and weaknesses of different types of soil water sensors, and methods of installing them, you can irrigate crops more efficiently, improve water conservation, and make your farm more profitable.
To figure out when and how much to water, you need to know your field's: field capacity, plant available water, and the permanent wilting point.
These levels of soil water content can be expressed in inches of water per foot of soil  as well as in bars.
Field capacity is the amount of water in the soil when water draining from a heavy irrigation changes from fast to slow.
This is the point when all the gravitational water has drained.
Medium to heavy  soils normally reach field capacity 2 to 3 days after irrigation.
In these soils, the soil water tension at field capacity is about 0.3 bars  of tension.
In sandy soils, which drain more quickly, field capacity measures about 0.1 bar.
Permanent wilting point is the soil water content from which plants cannot recover overnight after drying during the day.
This parameter has been determined in greenhouse experiments, and can vary with plant species and soil types.
The permanent wilting point occurs at water tensions between 10 and 20 bars.
An average of 15 bars is generally used.
The water in the soil at and below the permanent wilting point is called hygroscopic water.
Hygroscopic water is held tightly on the soil particles below permanent wilting point and cannot be extracted by plant roots.
Plant available water is the soil water content between field capacity and the permanent wilting point.
This level of water content, usually expressed in inches of water per foot of soil depth, depends on the soil's bulk density, texture, and structure.
Again, the approximate amount of plant available water varies in different soil textures.
Volumetric water content  is another measure used to describe the amount of water in the soil.
This is the direct measurement used to calibrate other soil water sensing techniques.
Volume of water O = Volume of soil
 Values of 0 are always less than 1 and can be expressed a depth of water per unit depth of soil.
For
 Table 1.
Soil water content parameters for different soil textures.
Soil	Field	Plant	Permanent
 Texture	Capacity	available	wilting
 Sand	1.2 *	0.7 	0.5 
 Loamy sand	1.9 	1.1 	0.8 
 Sandy Loam	2.5 	1.4 	1.1 
 Loam	3.2 	1.8 	1.4 
 Silt loam	3.6 	1.8 	1.8 
 Sandy clay	4.3 	1.9 	2.4 
 Sandy clay	3.8 	1.7 	2.2 
 Clay loam	3.5 	1.3 	2.2 
 Silty clay loam	3.4 	1.6 	1.8 
 Silty clay	4.8 	2.4 	2.4 
 Clay	4.8 	2.2 	2.6 
 *Numbers in parentheses are volumetric water contents expressed as foot of water per foot of soil.
Source: Hanson 2000.
Figure 1.
Soil water parameters and classes of water.
example, it can be expressed as foot per foot, and used to calculate irrigation depth.
Assume, for example, that the current volumetric water content is 0.20 ft/ft and the field capacity is 0.30 ft/ft.
If we want to bring the top 2 feet to field capacity, the required irrigation depth to bring the soil to field capacity is calculated as follows:
 Irrigation depth =  X 2 feet = 0.1 X 2 feet =0.1 X 24 inches = 2.4 inches
 If we want to know how much water the soil contains at 0.20 ft/ft plant available soil water, the available water depth can be calculated accordingly:
 Water depth = 0.20 x 2 feet = 0.20 X 24 inches = 4.8 inches
 Water storage capacity of soils
 The degree to which water clings to soil is often expressed as soil moisture tension.
Soil moisture tension is commonly expressed in units called bars or centibars.
Soil that is saturated has a soil moisture tension of about 0.1 centibar, or less; under this condition plants use little energy to draw moisture from soil.
As the soil dries out, the tension increases, requiring plants to must use more energy to draw water from the soil.
A soil water characteristic curve  describes the relationship between soil water content and the tension at which the water is held in the soil.
The relationship varies from soil to soil.
In saturated soil, the tension is 0; as the soil dries, tension increases.
Sandy soils do not hold as much plant-available water; they generally drain faster and need to be irrigated more often than do clay or loam soils.
Management allowable depletion  is the percent depletion of the plant available water beyond which the soil water content should not be depleted.
Depletion beyond this limit will create excessive water stress on the plant and reduce production.
Figure 2.
Soil water characteristic curves for typical sandy and clay soils.
The management allowable depletion, or allowable deficit, depends on the plant species and varies between growing seasons.
Recommended MAD levels for many field crops are near 50 percent, though it may be as low as 25 percent for some vegetable and other drought-sensitive crops.
Table 2 shows typical values of allowable depletion and root zone depth for selected crops.
Soil conditions such as compacted layers, shallow water
 Table 2.
Allowable soil water depletions  and root depths  for selected crops.
Crop	Allowable	Root depth*
 Barley and oats	55	3.3-4.5
 Grazing pastures	60	1.6-3.3
 Cool season	40	1.6-2.2
 Warm season	50	1.6-2.2
 Apricots, peaches	50	3.3-6.6
 70% canopy	50	4.0-5.0
 50% canopy	50	3.6-5.0
 20% canopy	50	2.6-3.6
 Conifer trees	70	3.3-4.5
 Walnut orchard	50	5.6-8.0
 and watermelons	40-45	2.6-5.0
 Sweet Peppers	30	1.6-3.2
 Zucchini and cucumbers	50	2.0-4.0
 *Note: Root depths can be affected by soil and other conditions.
Effective root zone depths are often shallower.
Source: Allen et al., 1996.
Table 3.
Example calculationt using management allowed depletion percentatge to calculate the allowable water content change (OMADI m m 3 in three soils with widely different textures.
Soil type	O field	-	O permanent	plant-	MAD/100	=	maximum
 capacity	wilting point	available	allowable
 silt loam	0.295	-	0.086	=	0.209	X	0.6	=	0.126
 loamy sand	0.103	-	0.066	=	0.037	X	0.6	=	0.022
 clay	0.332	-	0.190	=	0.142	X	0.6	=	0.085
 t OFC, OPWP, and OPAW are the soil water content at field capacity and the permanent wilting point and the plant-available water.
tables, and dry soil can limit root zone depth.
In general, vegetables have relatively shallow root systems; the soil water storage they can access is limited.
Crops with lower allowable depletion levels and shallower root depths must be irrigated more often.
Examples of how to determine 60 percent of MAD are shown in Table 3.
In loamy sand, the soil water content at field capacity is 0.103 ft/ft and the permanent wilting point is 0.066 ft/ft, resulting in a plant available water content range of 0.037 ft/ft.
If only 60 percent of this water can be used before yield or quality declines, the amount of water that can be safely extracted from the soil is 0.022 ft/ ft.
Subtract OMAD from OFC to find that water content at which irrigation should be initiated.
The small range of O MAD severely tests the abilities of most soil water sensors, particularly for the loamy sand soil.
Another criterion often used to trigger irrigation applications is soil water tension.
This method of irrigation scheduling is very well suited to sprinkler irrigation or microirrigation  systems because they can apply water frequently and precisely.
The soil water tension method can also be used with surface irrigation methods as well.
Soil water tension can be measured indirectly with a sensor such as the Watermark granular matrix sensor or with a tensiometer.
The soil water tension at which irrigation is required will vary with soil type, the depth at which the sensor is placed, and the crop.
Calibration and site-specific experience will help you get the best results from moni-
 Table 4.
Recommended allowable soil moisture tensions for selected crops.
Vegetative growth stage	40-50
 Source: Hanson et al.
2000.
toring soil water tension in irrigation scheduling.
Table 4 lists suggested soil water tension values for selected crops.
The water content of soil water can be measured directly or indirectly.
The direct method uses weight to determine how much water is in a sample of soil.
A soil sample is collected, weighed, oven dried, and weighed again to determine the sample's water content either by mass  or by volume.
The volume of water in soil as determined by weight is the standard against which the indirect methods are calibrated.
Several indirect methods can also be used to sense soil water content or tension.
Studies comparing direct and indirect methods have found that:
 All soil water sensing methods must be calibrated, despite the efforts of manufacturers to provide calibration curves.
Only the neutron probe and conventional time domain reflectrometry , are accurate enough for scheduling irrigation using the MAD procedure.
The capacitance methods are sensitive to soil temperature, salinity, clay content and type, and microscale soil structure.
This makes them unreliable for MAD irrigation scheduling.
They may be used to follow wetting and drying patterns over time and they allow you to detect wetting fronts from irrigation at the depths of sensor installation.
The sensors that respond to soil water tension also require calibration except for the tensiometer, which is a direct method.
The case examples here are intended for instruction only and are not a recommendation.
Gypsum blocks and granular matrix sensors
 Gypsum block sensors measure the water content of soil at whatever depth they are set.
They do this by measuring the electrical resistance between two circles of wire mesh that are embedded in a porous block of gypsum.
Granular matrix sensors work in essentially the same way, but their block is made of different sized sand particles rather than of gypsum.
While sand is inert, gypsum dissolves over time and changes the block's porosity.
This change causes the gypsum block's sensors to respond differently to soil water tension.
Electrical resistance increases as soil water content decreases.
Although the electrical resistance is measured in ohms, the handheld meter converts the reading and displays it in centibars.
The Watermark sensor  is a granular matrix sensor.
It does contain a small amount of gypsum, but that is to buffer the conductivity of the water in the pores of the sensor
 against undue influence by soil salinity.
It is more durable in the soil than a gypsum block and may be more responsive to changes in soil water suction.
The handheld meter for the Watermark sensor  indicates soil water tension over the range of 0 to 199 centibars.
The tension should be interpreted carefully, considering the soil properties.
Watermark sensors should be calibrated to the soil it will be used in.
These sensors are affected by temperature and salinity.
The sensor in Figure 4 can be adjusted for soil temperature.
Figure 3.
Watermark sensor before installation.
Figure 4.
Using handheld meter for Watermark sensor.
How to install and read a Watermark sensor
 To get an accurate water tension reading, install Watermark sensors in several locations within a field, especially if the field includes several soil types.
Place them in representative areas, such as within the plant row for row crops, in the bed for vegetable crops or in wetted areas under drip irrigation.
Depending on the effective root zone depth of the crop, each station should often have three sensors placed at multiple depths in order to read the effective root zone.
This will help evaluate water movement and depletion within the root zone over time and to detect depth of wetting following an irrigation event which may indicate deep percolation losses.
1.
Soak the sensors in water and install them wet to improve the sensor response to the first irrigation.
2.
Use a 7/-s-inch auger to drill a hole in the soil to the desired depth.
3.
Push the sensor in with a stick.
4.
Add water and soil to backfill the hole, leaving the wire leads accessible above the ground.
5.
Place a flag or other marker at each site to make it easier to find the sensor leads for subsequent readings.
Sensors can be reused for several seasons.
If you move them, remove the sensors carefully then clean and dry them for relocation or storage.
Once you are ready to install them again, ensure that they are reading properly; soak them in water overnight and then make sure that the submerged sensors read between 0 and 5 cb.
If they read more than 5 cb, discard them.
Connecting the sensor leads to a Watermark digital meter will give you an instant reading.
Regular readings will show how fast the soil water is depleting and help you know when you need to irrigate.
There are several data loggers like the one in Figure 5 that read the sensors and record the water level continuously.
This information can be downloaded to a portable computer.
Figure 5.
Watermark sensors connected to a 3-port WatchDog data logger.
Figure 6 tracks the changing soil water tension at different soil depths  in an orange orchard.
In this application, subsurface drip irrigation was triggered when the sensor located at a soil depth of 18 inches reached approximately 40 cb.
An irrigation application of about 0.7 inches  saturated the soil.
Note that the soil dried first in the top of the root zone and later in the deeper portion of the root zone.
Sensors such as these that are connected to devices that read and record soil moisture, can track irrigation and indicate soil water trends.
Rainfall  allowed the manager to delay irrigation.
This type of sensor measures changes in the dielectric permittivity of the soil by using two metal electrodes.
There are a wide variety of these types of sensors and they come in many shapes and configurations.
The electrodes are inserted or buried in the soil, or are cylindrical rings inside a plastic access tube that is inserted vertically into the soil.
Sometimes the electrodes, such as the ECH2O sensors are covered in plastic.
An electronic oscillator circuit energizes the electrodes with high frequency alternating current.
The resonant frequency decreases as water content increases.
By measuring the changes in the sensor frequency, the soil water content is sensed indirectly.
Unfortunately, certain soil properties affect soil's dielectric permittivity, and make capacitance sensors inaccurate.
These include: clay content and type, soil temperature, and the bulk electrical conductivity of soil which increases with soil water 6-inch  18-inch  content, salinity, and tempera30-inch  ture.
Measuring capacitance is Irrigation  highly sensitive to the condiRainfall  tions immediately next to the electrodes.
Consequently, small air gaps or soil structure anomalies next to the sensor can greatly affect the reading.
Because of this, these types of sensors are most accurate and repeatable in sandier soils, and
 Figure 6.
Watermark sensors soil water readings of rainfall and irrigation for oranges under drip irrigation.
soils that won't pull away from the sensor  as they dry.
Several dielectric permittivity sensors have been introduced that do not depend on capacitance measurements alone.
Two examples are the model CS616 from Campbell Scientific and the HydraProbe from Stevens.
Both of these sensors are temperature sensitive and over-predict water content in clayey soil.
Soil-specific calibration will prevent the over prediction, but cannot overcome the temperature sensitivity.
Also, these sensors give different water content readings at the same soil water content; there are sensor-to-sensor differences between CS616 sensors and also between HydraProbes.
A sensor that is less temperature sensitive, but still requires soil-specific calibration, is the Acclima.
It uses a measurement method that is equivalent to that of the accurate but expensive time domain reflectometry method.
When calibrated for a specific soil, the TDR and Acclima sensors are accurate sensors for irrigation management because they show little sensor-to-sensor variability and little sensitivity to soil salinity and temperature.
Time domain reflectometry systems are used primarily for research because they are complicated and expensive.
However, the Acclima sensor is an affordable consumer alternative for irrigation scheduling.
After digging a hole to the
 Fig.
7.
CS616 water contents from calibration for sandy clay loam with bulk electrical conductivity = 0.75 ds m-1 at saturation ; and Hydra Probe water contents using Seyfried et al.
general calibration.
All were installed at the same depth in a uniformly wetted soil.
This soil cannot become wetter than the 0.42 ft/ft water content marked with the dashed line because that is the porosity of the soil.
Fig.
8.
Conventional time domain reflectometry  water contents ; and Acclima sensor water contents , both using soil-specific calibrations.
They were installed at the same depth and in the same soil as the sensors illustrated in Fig.
7.
Two irrigations are illustrated.
desired depth, the Acclima sensor is buried in the soil and connected by insulated wires to a weather-tight case were data are Figure 9.
Acclima sensor and cable.
recorded and stored.
Data including the soil temperature can be transmitted by radio to a pivot point or to the edge of a field and viewed.
A tensiometer measures tension to determine soil water content.
This instrument consists of a sealed water-filled tube equipped with a vacuum gauge at the top end and a porous ceramic cup on the bottom.
As soil dries, water will move from the tensiometer tube through the ceramic cup into the soil in response to soil water suction.
Water can also move from the soil into the tensiometer during or following irrigation.
As the soil dries, the tensiometer loses water, a vacuum forms in the tube and is measured by the gauge.
Most tensiometers have a vacuum gauge that registers from 0 to 100 centibars.
During irrigation, water returns to the tensiometer, and the gauge reading approaches 0 and indicates the soil is saturated.
The useful limit of the tensiometer is about 80 cb.
Above this tension, air sometimes enters through the ceramic cup and causes the instrument to fail.
Therefore, these instruments are most useful with drought-sensitive crops because they have narrower allowable soil water loss ranges.
Fig 10.
Tensiometer components and two tensiometers installed at different soil depths.
Fig.
11.
Station of 3 tensiometers installed at different soil depths.
Tensiometers are useful in intermediate-texture soils and in non-cracking clays.
In cracking clays and sandy soils, contact problems often cause measurement errors.
After several wetting and drying cycles, some air may be drawn into the tensiometer and collected below the reservoir.
Some tensiometers are equipped with small water reservoirs to replace this water and reduce the service required.
How to install and read a tensiometer
 1.
Soak the instruments in a bucket of water for 2 or 3 days before you plan to install them.
This eliminates air trapped in the porous cup.
2.
Fill the tube with distilled water you have colored and treated with algaecide.
Gently tap the top of the reservoir to remove air bubbles
 from the tube and the vacuum gauge by tapping the top of the reservoir gently.
3.
Apply a strong vacuum with the hand vacuum pump until the gauge reads 80 to 85.
4.
Seal the cap properly.
5.
Check the reading when the ceramic tip is immersed in water.
6.
Install the ceramic cup in the active root zone of the soil.
Two tensiometers are recommended at each site.
For shallow-rooted crops, such as vegetables, install one tensiometer 6 inches deep and one 12 inches deep.
Install one tensiometer 12 inches deep and another at 24 or 36 inches deep for deeper rooted field crops.
7.
Use a 7-inch auger that has the same diameter as the tube to dig a hole to the desired depth.
To measure the exact depth, subtract the height of the ceramic tip obtain that exact depth.
Finish the prehole with a smaller diameter probe, and push the tensiometer into place.
To obtain accurate readings, the ceramic tip must have good contact with the soil.
8.
Backfill with dirt and pour water around the tensiometer to improve soil contact.
Pack a 3to 4-inch mound of soil around the tube.
You can also use a clay slurry to pack the tip of the tensiometer.
Use the smallest amount of water possible to make the mud flow just enough to push in the cup.
Neutron scattering is a time-tested technique for measuring total soil water content by volume.
This apparatus estimates the water content of soil by sensing the amount of hydrogen that is present in the soil.
Though organic matter in the soil contains hydrogen, only soil water content changes quickly and makes it possible to calibrate the probes to measure water content.
The neutron probe consists of a unit that includes a source of high-energy neutrons and a detector.
The probe is lowered down a plastic, steel or aluminum access tube to the desired depth, where it is held in place by clips attached to its cable.
A control and counting unit is connected to the cable above ground.
Fast neutrons are emitted from the source and pass through the access tube into the surround-
 Table 5.
Advantages and disadvantages of selected soil water monitoring systems.
Gravimetric	Very accurate	Destructive
 Results are not immediately available
 Watermark sensors	Good accuracy in medium to fine soils	Slow response to changes in soil water content, rainfall or
 because their fine-sized particles are similar	irrigation
 to the sensor's inner granular matrix	Lack of accuracy in sandy soils
 Affordable (about $40-50 per sensor, $250	Problems getting adequate soil contact in clayey and sandy soils
 for the meter)	Time consuming to determine what sensor reading is best
 Easy to use (light weight, pocket-sized, easy	suited for irrigation
 installation and direct reading)	Affected by soil salinity and temperature
 Greater water measuring range than	Small sample area
 Requires intensive labor to collect data regularly (unless you
 Reusable for several seasons with proper	connect the Watermark sensors to a data logger, collect data
 care 
 year)	Must be calibrated for best accuracy
 Continuous measurements at same location
 Capacitance sensors	Reports volume of soil water content directly	Expensive-requires a computer and $95 for the software
 Requires no special maintenance	or about $300 for the manual meter; The HOBO data logger
 Measures continuously at same location	needed to connect several sensors costs $200.
EC ECH2O probes
 cost $100 for up to 10 units; $70 each for 11 or more.
Affected by soil temperature, salinity, and clay content
 Very sensitive to proper installation, which can be difficult
 Highly sensitive to the small soil area immediately next to the
 Affected by soil salinity and temperature
 Requires calibration for each soil type, yet may be inaccurate
 even with soil-specific calibration
 Tensiometers	Low cost	May require periodic service
 Direct water tension reading for irrigation	Operates only to 80 cb soil water suction; not useful in drier soil
 Continuous measurements at same location
 Neutron Probe	The most accurate methods for measuring	Requires a depth control stand for readings nearer to the
 soil water content when properly calibrated	surface than 8 inches
 Able to measure soil water at different	Very expensive, about $4500
 depths several times during the growing	Radiation safety regulations require special licensing, regular
 season	training for the operator, and special handling, shipping and
 Samples a relatively large soil volume	storage procedures
 Needs to be calibrated against gravimetric measurements
 by selecting a wet and a dry spot; and for calibrating to the
 different soil types and depths
 Figure 12.
Neutron probe used at a citrus orchard.
ing soil where they lose their energy to collisions with other atomic nuclei.
These neutrons collide with soil water  and are slowed down by the hydrogen nuclei.
Slow neutrons are counted when they bounce back to the detector.
This count is linearly related to the total volumetric water content in the soil.
A
 higher count indicates higher soil water content.
While the relationship is linear, it must be calibrated for each particular soil.
To calibrate the neutron probe, you need a dry and a wet site for each soil type.
Neutron probe readings at each site are correlated with measured soil water contents using the gravimetric method to determine a calibration line with these two end points.
The calibration converts the neutron gauge readings to volumetric water contents.
Although this method is well accepted as highly accurate, the high equipment cost, licensing requirements and regulatory burden limits its application to research, consultants, or to areas where extensive sampling is needed.
Advantages and disadvantages of selected soil water sensors
 Table 5 describes some of the advantages and disadvantages of the gravimetric method, the Watermark sensors, ECH2O Sensors, tensiometers, and neutron probe.
Several methods are available for monitoring soil moisture.
Each has advantages and disadvantages, but when installed and calibrated properly, they all can be effective tools measuring soil water content.
Knowing the soil moisture content will enable you to manage irrigation effectively based on plant moisture needs, on soil water storage capacity, and
 on root zone depth and characteristics.
Timely and adequate-but not excessive-irrigation promotes water conservation and profitability.
Decreased water application uniformity is often offset by applying extra water to satisfy needs in under-watered areas, which drives up operational expense and may result in surface runoff and topsoil erosion as well as leaching of plant nutrients in overwatered areas.
Young said that some pockets of the state, predominantly in southwestern Nebraska and the Panhandle, saw minor groundwater level declines.
But a map in the latest Groundwater-Level Monitoring Report that shows the changes in groundwater supply from spring 2018 to spring 2019 is mostly bathed in hues of green and blue, indicating a wealth of increases in groundwater across the rest of Nebraska.
On average, wells measured in spring 2019 saw a 2.63-foot increase in groundwater levels statewide.
Image 2.
Irrigation water flows through Tunnel No.
2 on the Goshen/Gering-Fort Laramie supply canal in 2021; this is the tunnel where the collapse occurred in 2019.
Alternatively, if the pivot has regulators, the pressure should be at least 5 psi above the pressure rating of the regulators when checking it at the outer end of the pivot when it is on the highest point of the field.
If the pressure is lower than usual, it may indicate that there is a leak in the system or that the pump is not pumping sufficient water/pressure for the current nozzle package.
Chapter 13: Preparing a Corn Seedbed and Managing Crop Residues
 Crop residues that are not uniformly distributed can cause uneven soil temperatures and soil moisture levels that impact seed germination and stand variability.
A goal in residue management and seedbed preparation is to minimize this variability.
The purpose of this chapter is to provide a checklist of residuemanagement options.
Residue Removal and Crop Yields
 In a continuous corn rotation, harvesting corn residues can produce a short-term yield increase in the following corn crop that often diminishes with time.
This increase is attributed to many factors including warmer soils, improved germination, and reduced variability of the distance between adjacent plants.
However, the practice may also produce a long-term yield decrease that is attributed to a gradual decline in soil health and organic C.
The organic C is important because it builds soil resilience and provides important nutrients to the plant.
Clay et al.
reported that 22%, 63%, and 36% of the increases in corn, soybean, and wheat yields, respectively, from 1974 to 2012, could be linked to soil health improvements.
They also reported that improved soil health had a $1.1 billion impact on the South Dakota economy in 2012.
Removing the surface residue can place these gains in jeopardy.
Residue Management and Seedbed Preparation
 Table 13.1 Checklist for preparing for seeding:
 Since 1970, the corn harvest index [harvest index = lbs of grain / ] has remained stable at about 0.5, while statewide corn yields have been increasing at a rate of 2.9 bu/acre.
This means that as yield increased from 75 to 150 bu/acre, the amount of surface residue increased from 3550 pounds of biomass/acre to 7400 pounds of biomass/acre.
This residue contains nutrients required by the plant and helped South Dakota farmers increase their soil organic matter content 24% over the past 25
 1.
Seedbed preparation starts by evenly distributing crop residues during harvest.
2.
A good residue-management plan can reduce pest problems.
However, it does not replace the importance of using an appropriate seed treatment or using preand post-plant herbicide treatments.
3.
Removing corn residue is not generally recommended in South Dakota for disease management.
Options for improved disease management are tillage, use of residue manager, rotations, seed treatments, and foliar fungicide applications, if warranted.
4.
Review the seeder owner's manual.
5.
On the planter, replace worn parts, calibrate seed meters, calibrate planter fertilizer and pesticide applicators, check down-pressure springs, maintain even and recommended tire pressure, and lubricate bearings and other moving parts.
6.
Do not plant if soil is too wet.
years.
However, the increased crop residue has complicated preparing a "good" seedbed and slowed soil warming in the spring.
Good residue management starts in the fall during harvest and continues through planting.
The residuemanagement plan should consider both the chaff and straw.
Chaff is discharged from the cleaning unit, whereas straw consists of corncobs, husks, and cornstalks.
A chaff spreader uses spinning discs to distribute the fine materials, whereas a straw chopper uses knives to break or cut residue prior to distribution.
Additional information for individual combines is available in Butzen et al..
A corn combine that chops the stalks can be used to evenly spread the residue on the soil surface.
If the combine does not have the equipment to uniformly distribute residue, an aftermarket purchase may be needed.
Recommendations for improving residue distributions include:
 1.
Visit with your dealer and refer to the owner's manual.
2.
Check the distribution pattern and add residue-spreading attachments if needed.
3.
Check residue distribution pattern periodically during harvest.
4.
Do not overcorrect for windrowing problems.
5.
Adjust the speed of the straw spreaders by changing the pulleys.
6.
Inspect, sharpen, and replace chopper blades when needed.
A good residue-management plan can also reduce disease and insect problems, while improving stand uniformity and yields.
A poor residue-management plan can:
 1.
Push residue into the seed furrow.
2.
Slow soil warming.
3.
Cause toxic impact on the germinating seed.
5.
Increase overwintering of insects and diseases.
Plant at Appropriate Soil Moisture Content
 Planting a field when it is too wet can cause emergence and compaction problems.
When planting, the top 4 inches of soil should be dry enough that it crumbles easily and does not form a ribbon when compressed in your hand.
The soil moisture content should be below field capacity to avoid sidewall compaction, which can lead to a shallow root system.
Field capacity is the amount of water remaining in the soil after gravity has removed the gravitational water.
Most soils approach field capacity 2 or 3 days after a rainfall.
If the soil is too wet, the disc openers can cause sidewall compaction, which produces variable emergence.
Compaction can also be reduced by lowering the tire pressure to the minimal allowable pressure, using flotation tires, and installing larger diameter tires.
High residue can shelter germinating pests from chemical pesticides.
In high-residue systems, consider using a variety of control strategies.
Since early planting is recommended, a fungicide and insect seed treatment is also suggested.
Producers are encouraged to combine practices such as including residue cleaners on planters, using strip-tillage to devoid the planting zone of residue, or incorporating genomic and cultural options with chemical solutions for weed, insect, and disease control.
Planter Maintenance and Preparation
 A corn planter is a piece of precision equipment that requires all of the components to be adjusted correctly.
Research suggests that the uniform spacing of seed can increase yields up to 20 bu/acre.
Although plant spacing and density are conducted too late to correct an in-season problem, stand counts and planter variability information is useful in assessing whether a new planter or refurbishing is needed.
Examples for determining emergence rates are available in Chapter 34.
Growing conditions should also be evaluated to assess whether soil crusting, compaction, temperature, or moisture could be responsible for nonuniform stands.
Information for assessing compaction is available
 in Chapter 14.
Potential yield losses due to uneven stands can be estimated.
If planter calibration is necessary, always follow the manufacturer's instructions for calibrating seedmetering equipment.
Assistance is available from local Extension educators, crop consultants, seed dealers, and the equipment manufacturer.
Different adjustments may be required for different tillage systems.
For example, the downward pressure of the planter should be higher for no-tillage VS.
a tilled seedbed.
During planting, it is important to place seed at the proper depth and ensure that the opener does not smear the walls of the furrow.
Down-pressure tension should be adjusted if the seed is not placed at the desired depth.
Closers or packing wheels should apply enough pressure for "good" seedto-soil contact; too much pressure will compact the seedbed, whereas too little will provide poor soil-toseed contact.
Adjust down-pressure tension in consideration of soil moisture and residue conditions.
As no-till and reduced-till systems become increasingly popular, the planter takes on the added responsibility of assisting in residue management.
Hence, there are more parts to wear out and maintain.
Residue managers can help cut residue and clear a path for the planting unit.
If residue is not managed appropriately, it can interfere with seed placement, delay germination, produce a physical barrier to the emerging seedling, slow plant growth, increase pest problems, and reduce nutrient efficiency.
The spring planting window generally ranges from late April to mid-June.
Historically, 90% of the corn acres in South Dakota are seeded by mid-May and completed by mid-June.
Seed germination depends on soil moisture and temperature.
Care should be taken to avoid tillage and planting operations when the soil is wet.
As a general rule, corn should not be planted until the soil temperature  approaches 50F.
In cold soil conditions , seeds will readily absorb water but will not initiate root or shoot growth.
This can lead to seed rots and poor emergence.
If circumstances force planting before soil temperatures reach 50F, it is recommended to use a seed treatment and consult with a reputable seed dealer or agronomist to select an appropriate hybrid.
Delaying seeding can reduce corn grain yields.
Use of a Packer Wheel
 High germination rates require good soil-to-seed contact.
Packer wheels can improve soil-to-seed contact, nutrient uptake, and stand uniformity in dry soil, whereas in wet soil, packer wheels can increase soil compaction and crusting.
The use of packer wheels should be based on the soil conditions at the site when planting.
Delayed Planting and Replanting Considerations
 Delayed planting reduces the number of growing-degree units  accumulated during the season, hindering the crop from maturing before the first fall killing frost.
Corn killed by frost before maturity will have lower yields and higher drying costs.
If planting is delayed, late-maturing hybrids can lose up to 1.1 bu/acre per day compared with earlier-maturing hybrids.
Often, the trade-off is that earlier hybrids have a lower yield potential.
The number of GDUs that a hybrid needs to reach physiological maturity is related to maturity ratings.
Hybrids with an 80-day maturity rating often require 1900 growing-degree days , whereas a 95day hybrid requires approximately 2200 GDD.
Additional information is available in Chapter 10.
A rule of thumb is to plant 20% of your acres with a full-season hybrid, 60% with a mid-season hybrid, and the remaining 20% with a short-season hybrid.
When you are developing a seeding strategy, you should also develop a harvest strategy.
If planting is delayed, growers are urged to consult their seed dealer to determine whether an earlier-maturing hybrid is warranted or available.
Depth and Planting Operations
 Under optimal conditions , seed placement is 1 1/2 to 2 inches below the soil surface.
However, in dry soil it may be advantageous to plant deeper.
Planting deeper than 3 inches is not recommended because seed emergence is very low.
Although soil conditions may be dry, consider the probability of rain in the near future.
Rain can seal the soil surface, resulting in soil crusting and reduced emergence rates.
Seeds should be placed at shallower depths  if rain is likely.
When planting into areas with heavy residue, seed depth should be at least 1.25 inches but not deeper than 1 1/2 inches if soil moisture conditions are favorable.
High residue can result in seeds being left on the surface and variable soil temperature and emergence.
Seed left on the soil surface or in the residue layer will not properly develop.
To ensure that seeds are placed at the proper depth, check seed depth in highresidue situations.
These measurements should not include any surface residue.
If residue is problematic, consider residue management planter attachments.
VFDs are electronic monitor and control systems that alter the speed of pump rotation by adjusting the frequency of the electricity delivered to the motor.
It turns out that the motor cares little about what frequency the power is and the speed of the motor changes linearly with the change in frequency.
For corn in the V4 crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.21 inches and the estimated water use during the week of June 19-25, 2023 is 1.30 inches.
For corn in the V6 crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.41 inches.
For corn in the V8 crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.60 inches.
For soybeans in the V1 1st Node crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.24 inches and the estimated water use during the week of June 19-25, 2023 is 1.30 inches.
For soybeans in the V2 2nd Node crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.47 inches.
For soybeans in the V3 3rd Node crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.71 inches.
during a rainfalldeficient year
 F.
J.
Veihmeyer and A.
H.
Hendrickson
 MANY FARMERS ARE CONCERNED about the moisture needs of their crops.
Lack of water cannot be overcome by any practice other than irrigating.
There are, however, some things which may be done to use water economically and which may aid in reducing its loss.
Farmers who contemplate raising annual crops this year, of course, will consider the adequacy of the supply of water in their area which will be available and may wish to defer planting this season if it seems likely there will not be enough water to mature the crops.
Growers who have permanently rooted crops such as orchards, vineyards, alfalfa.
and others, and have a limited supply of water, should plan a schedule of irrigating which best serves the needs of the plants without seriously injuring them.
Early-season irrigation of deciduous fruit orchards may be needed this year.
maintain the permanently rooted crops for very long, and water should be applied before growth starts.
ing when the soil moisture in the upper layers is exhausted.
The grower then has advance notice that the entire soil-reservoir soon may be dry.
When only a small stream of water is available, the time necessary to cover the orchard may be so long that trees which are irrigated last may be decidedly affected unless irrigation is started before it is really necessary.
If soils are wet to a depth of about six feet, there should be enough water stored in them, especially in sandy loam, clay loams and clays, to take care of the needs of trees and vines until the latter part of June, and economy in the use of water may be made by delaying application until that time.
Since the weeds ordinarily are not so deep rooted as the trees, they give warn-
 A guide as to the probable need for water for deciduous fruit trees may be taken from the following tabulation in which the water loss from the soil through evaporation and transpiration has been measured at Davis from orchards in which readily available water was maintained throughout the growing season.
A portion of the water used, of course, comes from rain which is stored in the soil and the amount of irrigation needed is the difference between the total used and stored rainfall.
The elimination of all weeds will conserve water since plant transpiration is the chief cause of the soil drying.
The loss of water by evaporation directly from the soil is largely confined to a shallow surface layer and very little loss occurs below the top foot.
Once the weeds have been removed.
nothing will be gained by subsequent cultivation because stirring the soil for the purpose of maintaining a mulch will not affect the loss of moisture from the surface of the soil.
Water Needed in Early Season
 Every time water is applied, there is unavoidable waste by evaporation, in conveyance to the place of use, and frequently by deep seepage.
In many deciduous fruit and vineyard sections on deep soil, if the soil is wet to Continued on page 16
 It is best to delay irrigation until the soil-reservoir is nearly dry before irrigating.
Where the water supply is insufficient to maintain readily available water throughout the season, the grower must decide which is the best time to apply it.
The appearance of the soil when at the permanent wilting percentage is sometimes misleading.
Frequently, soils may be moist enough to retain their shape when pressed into a ball by the handsthe method frequently used to judge the wetness of the soil-but actually the soil may be at the permanent wilting percentage, and consequently too dry for plant growth.
Amount of water	Amount of water
 Month	used, inches	Month	used, inches
 March	0.5	July	7.7
 April	2.5	August	5.4
 May	4.0	September	3.4
 June	7.2	October	1.8
 Total = 32.5 inches
 It will help to understand irrigation requirements if the soil is considered as a reservoir which contains varying amounts of water at different times during the year.
Generally, at the beginning of the growing season, the soil will hold all the water it can, except in localities where the winter rain is insufficient or where cover crops have used some of the water.
Usually, the soil is wet to a considerable depth at this time, due to the rain or because of irrigation during the previous fall.
This year the scanty rainfall has wet the soil only to a shallow depth, and in many sections the soil is dry below the first foot.
This is not enough wet soil to
 Another method of anticipating the time the first irrigation is needed is by watching some of the broad-leaved weeds which may be left as indicator plants in various places in the orchard.
These weeds generally are deep rooted enough to indicate by the wilting-usually a decided drooping of the leaves-a depletion of the readily available moisture in the parts of the soil occupied by the roots of the weeds.
IRRIGATION Continued from page 3
 a depth of about six feet, the trees and vines probably will come through the season without serious damage, but the current season crop may be reduced.
We suggest that the first irrigation be applied now if the rainfall has not been enough to wet the soil to a depth of about six feet.
If water for only one additional irrigalion is available, a second watering, for fruit trees, should be given about the latter part of June.
Our experiments show that it is best to keep the trees and vines supplied with water early in the season.
Lack of water is more injurious in early season than in the fall, although a continuous supply of readily available water at all times is most desirable.
Economy in the use of water by annual crops may also be obtained by applying the principle that satisfactory returns can be obtained by delaying irrigation until the soil moisture is reduced close to the permanent wilting percentage.
For example, in the Sacramento Valley it is possible to raise as large a crop of sugar beets with three irrigations of eight acre-inches each as with more frequent applications, provided the soil is wet to a depth of about six feet by rains.
Cotton usually is irrigated very frequently, but good crops may be obtained with one or two irrigations in addition to the preplanting irrigation.
Watermelons on deep loam or clay soils may not need irrigation if the soil is wet deeply before planting, but cantaloupes which are not so deep rooted as watermelons, probably will need irrigation during the growing season.
Tomatoes, a deep rooted crop, likewise may be raised with one or two irrigations on deep fine textured soil.
The suggestions made may be summarized briefly as follows: Do not plant annual crops unless an assured supply of water is available.
Remove all weeds, but do not waste time and effort cultivating in their absence.
Put water on in one application to wet to the full depth of rooting rather than giving frequent applications with shallower wetting, thus reducing waste.
Delay irrigation until the soil moisture is reduced to about the permanent wilting percenlage, taking into consideration the size of the stream available and the acreage to be irrigated.
With a limited supply of water, irrigate in the first part of the season to keep the
 crops supplied with readily available moisture, because lack of water is more injurious in early summer than late in the fall.
Find out how much water in depth of application is required and how frequently it should be applied for each crop.
Material savings may be made by reducing the frequency of irrigations.
Farm advisers have bulletins and detailed information concerning the depth of rooting and irrigation of various crops.
J.
Veihmeyer is Professor of Irrigation and Irrigation Engineer in the Experiment Station, Davis.
A.
H.
Hendrickson is Pomologist in the Experiment Station, Davis.
QUICK DECLINE Continued from page 12
 all probability, be found to be carriers of the quick decline virus.
Progress has been slow because symptoms do not appear on oneto two-yearold trees until 15 months or longer after inoculation.
Smaller trees are now being used in certain experiments.
A sweet orange top is grafted onto sour orange seedlings having trunk diameters of from one-eighth to one-quarter inch.
Such trees can be prepared in a relatively short time and it is hoped that after being inoculated they will show symptoms quicker than the larger trees.
In the late summer of 1946, grafttransmission experiments, started in June of 1945, showed conclusively that quick decline is a virus disease.
A study, commenced two years before it was known that quick decline was a virus disease, discovered that more than 225 different species of sucking insects were present in affected areas.
Perhaps not more than one species will be found to be capable of transmitting the virus.
Extensive experimental studies are thus necessary to determine the role of insects in the spread of quick decline.
In order to establish ideal conditions for experiments involving insect carriers of virus, the Riverside Experiment Station erected a "screen house" at one of the experimental plots within the quick decline area.
The screen is small enough to filter out practically all insects that could cause infection.
Controlled inoculation tests are now being conducted by entomologists of the Citrus Experiment Station.
Similar Disease in South America
 Experiments in Brazil have indicated an aphid to be the virus carrier of the
 disease, Tristeza, which is similar to the California orange tree quick decline.
An aphid closely related to the Brazilian carrier is present in California and efforts being made to determine if this insect may be causing spread of the quick decline virus.
Other insects, particularly several other aphids and leaf-hopper species, are also being tested as carriers.
L.
D.
Batchelor is Director of the Citrus Experiment Station, Professor of Horticulture, and Horticulturist in the Experiment Station, Riverside.
J.
M.
Wallace is Associate Plant Pathologist in the Experiment Station, Riverside.
PUNJAB FLAX Continued from page 10
 To windrow the flax and later thresh with combine equipped with pick-up attachment, or to combine the standing grain direct, is a question on which there is divided opinion among growers and threshermen alike.
Naturally, there are both advantages and disadvantages to each method.
Both methods are extensively used.
In many cases, circumstances force the decision, for if the flax contains any appreciable amount of green weeds it cannot be threshed standing.
Only clean fields of mature dry flax, or ones in which the weeds and flax are both dry, can be direct combined.
If conditions are favorable to direct combining, the cost of windrowing is avoided.
On the other hand, dry standing flax is susceptible to loss by wind damage which in many cases more than offsets the cost of windrowing.
If windrowed, the flax should be cut as soon as the seeds are botanically ripe.
This occurs several weeks before the plants are dry enough to permit direct combining.
At this stage, no loss of seed from shattered bolls will have occurred.
Windrowing also permits harvesting early enough to destroy most summer-growing weeds before they mature their seeds to infest the soil.
Other advantages of windrowing are the more favorable weather conditions-less humidity-for threshing early in the season, and earlier use of the land for the summer rotation crop.
L.
G.
Goar is Associate in Agronomy Experiment Station, and is Superintendent of the Imperial Valley Field Station, Meloland.
Improvement in the technology of preservation of fruit juices by freezing, particularly control of the enzymes responsible for the curdling of frozen juice, is under study by the Division of Food Technology.
Irrigation Scheduling by the Checkbook Method
 Thomas F.
Scherer Extension Agricultural Engineer
 Dean D.
Steele Associate Professor of Agricultural Engineering
 W 'ith variable rain events and a mixture of soil types, determining when to irrigate and how much water to apply during the growing season can be a challenge.
With too little water, the crop is stressed, while with too much water, crops are stunted and fertilizer is leached below the root zone, and pumping costs are increased.
Either way, the crop suffers and reduces the yield.
North Dakota State University Fargo, North Dakota
  Standard S526.4, used with permission)
 Available soil water, more commonly called available water capacity : The portion of soil water that plant roots of most crops can absorb readily; expressed in millimeters  of water per mm of soil  for a specific soil depth.
It is the amount of water stored in the soil between field capacity  and permanent wilting point.
It typically is adjusted for salinity  and rock fragment content.
In some texts it also is called available waterholding capacity.
Crop evapotranspiration : The amount of water used by the crop in transpiration and building of plant tissue, and that evaporated from adjacent soil or was intercepted by plant foliage.
It is expressed as depth in mm  and can refer to daily, peak, design, monthly or seasonal quantities.
Sometimes referred to as consumptive use.
Crop water use: Calculated or measured water used by plants; expressed in mm per day.
Same as ETc except it is expressed as daily use only.
Deficit irrigation: An irrigation water management alternative where the soil in the plant root zone is not refilled to field capacity in all or part of the field.
Field capacity : Amount of water remaining in a soil when the downward water flow due to gravity becomes negligible.
An estimate of field capacity ranges between soil water contents at matric potentials of minus 10 to minus 33 kilopascal .
Irrigation scheduling: The process of determining when to irrigate and how much water to apply based upon measurements or estimates of soil moisture or water used by the plant.
Management-allowed depletion : The desired soil-water deficit at the time of irrigation.
Permanent wilting point : Soil water content below which plants cannot readily obtain water and permanently wilt.
Sometimes called "permanent wilting percentage," or WP.
Often estimated as the water content corresponding to a matric potential of minus 1.5 megapascal .
Soil-water deficit: Amount of water required to raise the soil-water content of the crop root zone to field capacity.
It is measured in mm  of water.
Also called soil-water depletion.
Water application efficiency: Ratio of the average depth of water infiltrated and stored in the root zone to the average depth of water applied.
Water-holding capacity : Total amount of water held in a freely drained soil per increment of depth.
It is the amount of water held between field capacity and the oven-dry moisture level; expressed in centimeters/centimeters  , centimeters/meter   or total centimeters  for a specific soil depth.
Sometimes called total waterholding capacity.
Adapted from Steele et.al.
2010, Applied Engineering in Agriculture with permission from ASABE
 A system for scheduling irrigation using the "checkbook" method is outlined in this publication.
It's called the checkbook method because it operates just like a bank checking account.
Rain and irrigation are deposits to the soil and the crop withdraws water from the root zone.
During the critical growth periods, the checkbook requires almost daily updates by the irrigator and, if used properly, it is a proven tool for irrigation scheduling.
Quick Start to Using the Checkbook
 To use the checkbook method, the irrigation manager needs to obtain the maximum daily air temperature and have at least one and preferably two accurate rain gauges in or near the field being irrigated.
Using the maximum daily air temperature, crop water use can be estimated from tables in this publication.
The daily water use is entered into a soil water balance sheet to determine the amount of soil water removed from the root zone and the soil water deficit.
Crop water use increases the deficit, but rain and irrigation reduce the deficit.
When a predetermined soil water deficit is reached, irrigation should be started.
To start, study the example soil water balance sheet and then begin your own checkbook using the blank copies at the end of this publication.
The checkbook method is a root-zone soil-water accounting method.
The amount of water plant roots can extract is a soil's available water capacity.
This is the difference in water content between a wet soil at field capacity and a dry soil at the permanent wilting point.
Soil texture is the major factor affecting soil waterholding capacity.
Texture refers to the relative amounts of sand, silt and clay particles in the soil.
The available water-holding capacity of the soil must be determined prior to the start of irrigation scheduling.
The available water capacity of soils in the field can be estimated using the values shown in Table 1.
If more than one soil type is present in the field, the soil with the lowest water-holding capacity should be used for scheduling irrigations.
However, if that soil type covers a relatively small area, the soil type covering the largest area should be used.
Table 1.
Range of plant-available water for different soil textures.
Inches of Water	Inches of Water
 Soil Texture	per Inch of Soil	per Foot of Soil
 Coarse sand and gravel	0.02 to 0.06	0.2 to 0.7
 Sands	0.04 to 0.09	0.5 to 1.1
 Loamy sands	0.06 to 0.12	0.7 to 1.4
 Sandy loams	0.11 to 0.15	1.3 to 1.8
 Fine sandy loams	0.14 to 0.18	1.7 to 2.2
 Loams and silt loams	0.17 to 0.23	2.0 to 2.8
 Clay loams and silty clay loams	0.14 to 0.21	1.7 to 2.5
 Silty clays and clays	0.13 to 0.18	1.6 to 2.2
 Assuming no subsurface restrictions, at maturity, each crop has a typical fully developed root zone depth.
The root zone determines to what depth the plant can extract water from the soil.
The root zone of annual crops may not fully develop until eight weeks after the crop emerges.
However, established perennials such as alfalfa and forage grasses will start with deeper roots.
Plant roots extract the greatest amount of soil water from the upper part of the root zone, and each crop is different.
Generally, for all the crops shown in Figure 1, more than 90 percent of the water extracted from the root zone during the growing season will come from the depth shown as shaded.
Therefore, a depth less than a fully developed root zone can be used for irrigation management purposes.
Fully developed root zone depths, along with irrigation management depths, are shown in Table 2.
At the beginning of crop emergence and growth, having the soil water-holding capacity in the total root zone at or near field capacity is important.
Moist soil is necessary for germination and proper root development.
However, low previous autumn rainfall, no winter snow accumulations and less spring rain may result in dry subsoil below about 2 feet.
Under these conditions, irrigating prior to or after planting to store water in the lower part of the root zone may be necessary.
Roots will not grow through or into a dry layer of soil, and a reduced root depth will result.
Thus, checking the soil moisture to at least the 3-foot depth prior to or at planting time is important.
Table 2.
Typical range of crop root depths in deep soils, along with the recommended irrigation water management depth.
Depth of Fully	Root Zone for
 Potatoes	24 to 30	18
 Soybeans, dry edible	30 to 36	24
 Wheat, barley, oats	42 to 48	36
 Corn, sugar beets,	48 to 54	36
 Established alfalfa	60 to 72	48
 Figure 1.
Typical fully developed root zone depths for the commonly irrigated crops in North Dakota.
The shaded area is the irrigation water management depth.
During a particular day, water use is dependent on the type of crop, stage of growth, air temperature, solar radiation , wind speed, relative humidity and soil water content in the root zone.
These are a lot of variables, and determining water use may seem complicated.
However, based on many years of research, the estimation of crop water use has been simplified for North Dakota conditions.
This publication includes tables for estimating each crop's water use based solely on daily maximum air temperature and stage of growth.
Tables 6 through 14 give the estimated water use in inches per day for the most commonly irrigated crops in North Dakota.
The daily crop water use can be obtained by recording the maximum daily air temperature to within 10 F and knowing the date of crop emergence.
The date of crop emergence is when you can see about half the plants have emerged.
Critical crop growth stages also are indicated on the lower part of the tables.
Sometimes, due to variable weather conditions, the critical crop growth stage should determine the number of weeks past emergence, rather than the calendar.
Table 3.
System pumping capacity in gallons per minute per acre for common irrigated areas under center pivots for various pumping rates assuming no evaporation or wind drift losses.
Pumping	Irrigated Area 
 	80	100	125	132	154
 400	5.00	4.00	3.20	3.03	2.60
 500	6.25	5.00	4.00	3.79	3.25
 600	7.50	6.00	4.80	4.55	3.90
 700	8.75	7.00	5.60	5.30	4.55
 800	10.00	8.00	6.40	6.06	5.19
 900	11.25	9.00	7.20	6.82	5.84
 1,000	12.50	10.00	8.00	7.58	6.49
 1,100	13.75	11.00	8.80	8.33	7.14
 1,200	15.00	12.00	9.60	9.09	7.79
 The pumping capacity determines the application rate of the irrigation system.
Pumping capacity often is referred to in units of gallons per minute  per irrigated acre.
For example, a 750 gpm pumping rate used to irrigate 125 acres has a 6 gpm/acre pumping capacity.
A 500 gpm pumping rate used to irrigate 100 acres has a 5 gpm/acre pumping rate.
Sprinkler irrigation is not 100 percent efficient.
Due to evaporation and wind drift, not all pumped water gets into the soil for plant growth.
The amount of water that does not infiltrate into the soil determines the application efficiency of the system.
For example, if the irrigation system is set to apply 1 inch of water but only 0.85 inch infiltrates into the soil, the application efficiency is  X 100, or 85 percent.
However, application efficiency can vary from about 50 percent during a hot, windy afternoon to more than 95 percent with calm winds after dark.
For good irrigation water management, the pumping capacity should match the average peak water use of the crop.
For example, the seasonal average peak water use of corn is about 0.27 inch per day, although the daily peak water use may exceed 0.30 inch per day.
Therefore, the minimum pumping capacity should be able to apply the seasonal average peak amount of water with the understanding that on some days, the crop water use will be greater.
Replacing 0.27 inch used by the corn in one day requires a pumping rate of 6 gpm/acre, assuming 85 percent application efficiency.
With sprinklers mounted on the top of the center pivot span pipe, the average annual application efficiency is about 85 percent when applying 1 inch of water or more, but it drops to 80 percent when applying 1/2 to 3/4 inch.
Why?
Because most of the pumped water that doesn't get to the soil is lost to water that wets the plants and evaporates.
The same amount is lost whether 1 inch or 1/2 inch is applied.
With sprinklers mounted on drop pipes, the application efficiency can be greater than 85 percent because less foliage is wetted.
The pumping capacity shown in Table 3 can be translated into equivalent daily infiltrated depths for the various application efficiencies shown in Table 4.
For example, a center pivot with a 5.5 gpm/acre pumping capacity has an application efficiency of 85 percent.
If the percent timer on the center pivot is set to apply 0.9 inch, making a revolution will take slightly more than three days.
But only 85 percent of 0.9 inch, or 0.76 inch, actually will infiltrate into the soil for plant use.
Thus, the net applied amount is 0.76 inch, or approximately 0.25 inch/day, as shown in the 85 percent column in Table 4.
Table 4.
Pumping capacity represented as an equivalent daily infiltrated depth assuming 24-hour-per-day pumping.
Capacity	80%	85 %	90	95%	Loss to
 	Efficiency	Efficiency	Efficiency	Efficiency	Evaporation
 4	0.17	0.18	0.19	0.20	0.21
 4.5	0.19	0.20	0.21	0.23	0.24
 5	0.21	0.22	0.24	0.25	0.26
 5.5	0.23	0.25	0.26	0.28	0.29
 6	0.25	0.27	0.29	0.30	0.32
 6.5	0.28	0.29	0.31	0.33	0.34
 7	0.30	0.31	0.33	0.35	0.37
 7.5	0.32	0.34	0.36	0.38	0.40
 8	0.34	0.36	0.38	0.40	0.42
 Determining Soil Water Deficit
 The checkbook expresses the soil water content in terms of deficit, which is the difference between the soil water content at field capacity and the current soil water content in the root zone.
It is presented as inches of water deficit or as a percentage of the available water capacity.
Think of it as the amount of water required to fill the root zone to field capacity or the point of zero deficit.
One way to picture this concept is to imagine a tube that contains 4 inches of water when full, but if it only contains 3 inches of water, then it is one-fourth low, or it has a deficit of 1 inch of water, or 25 percent.
To fill the tube, 1 inch must be added.
To begin the checkbook method of scheduling, you must determine the soil water content in the field at the start of the growing season.
The initial soil water content can be determined with soil moisture sensors, but the easiest way is to use a soil probe to obtain samples from several areas of the field.
Pay particular attention to areas with the coarsest soil textures.
Estimate the soil water deficit using the "Feel Method" outlined in Table 5.
Soil samples should be taken in 6-inch increments to the depth used for water management.
Brochures with pictures showing the feel method for various soil textures can be found on the internet by doing a search using "soil water by the feel method" or go to the website listed in the section titled Additional Irrigation Scheduling Resources for North Dakota
 Standard soil probe.
Testing soil moisture in the top 6 inches with a soil probe.
Wet soil that forms a tight ball and indicates more than 75 percent available water.
water.
Dry soil with less than 50 percent of available
 The total root zone deficit is computed by adding the deficits for each foot.
The example below shows the procedure to estimate the soil water deficit in a 3-foot root zone.
This should be done at the start of the growing season and about every two weeks after emergence, depending on rain events.
Estimating Soil	Corn was planted and has a 3-foot water management root zone
 Water Deficit	.
Soil Water-holding Capacity at One Location in the Field
 Soil Depth	Soil Texture	Average Water-holding Capacity 
 0 to 1 foot	Fine sandy loam 	0.16 inch per inch
 1 to 3 feet	Loamy sand 	0.09 inch per inch
 Soil Depth			Deficit 
 0 to 6 inches	6 in X 0.16 in/in = 0.96	X 50 %	= 0.48
 6 to 12 inches	6 in X 0.16 in/in = 0.96	X 40 %	= 0.38
 12 to 24 inches	12 in X 0.09 in/in = 1.08	X 30 %	= 0.32
 24 to 36 inches	12 in X 0.09 in/in = 1.08	X 20 %	= 0.22
 Table 5.
Guide for judging how much water has been removed from the soil.
The numbers in each box are approximate inches of water deficit in 1 foot of soil depth.
Divide the numbers by 2 for 6-inch soil layers.
Note: A ball is formed by firmly squeezing a handful of soil.
A ribbon is formed by squeezing some soil between the thumb and forefinger and pushing forward.
Fine Sands and	Sandy Loams and	Loams, Silt Loams,	Clay Loams, Silty Clays
 Soil Water Deficit	Loamy Sands	Fine Sandy Loams	Silty Clay Loams	and Clay
 0% to 5% 	Upon squeezing, no	Upon squeezing, no	Upon squeezing, some	Upon squeezing, some
 	free water appears on	free water appears on	free water appears on	free water appears on
 soil but wet outline of	soil but wet outline of	soil with wet outline of	soil with wet outline of
 ball is left on hand, 0.0	ball is left on hand, 0.0	ball left on hand, 0.2	ball left on hand, 0.3
 5-25% Wet	Forms a weak ball	Forms a weak ball and	Forms a ball; very	Forms a ball, ribbons
 under pressure with	makes a weak ribbon	pliable that ribbons	easily and has a slick
 water staining on	that breaks easily, 0	easily, 0.0 to 0.5	feeling, 0 to 0.6
 fingers, 0 to 0.2	to 0.4
 25-50% Moist	Forms a weak ball; will	Forms a ball under	Forms a ball that is	Forms a smooth ball
 not ribbon but some	pressure with light	somewhat plastic and	and ribbons, 0.6 to 1.2
 water staining on	staining on fingers, 0.4	forms a weak ribbon,
 fingers, 0.2 to 0.5	to 0.8	0.5 to 1.0
 50-75% Slightly	Appears to be dry but	Forms a weak ball	Forms a weak ball but	Forms weak ball;
 Moist	will form a weak ball	with finger marks but	holds together with	somewhat pliable but
 when squeezed, 0.5	not much staining on	pressure and no water	no water stains on
 to 0.8	fingers, 0.8 to 1.2	staining on fingers, 1	hand, 1.2 to 1.9
 75-100% Dry	Dry, loose and single	Forms a very weak ball	Dry and sometimes	Baked hard; clods are
 (100% soil water	grains flow through	and soil grains break	slightly crusted; clods	hard to crumble with
 deficit results in	fingers, 0.8 to 1	away easily, 1.2 to 1.5	crumble with pressure,	pressure, 1.9 to 2.5
 permanent wilting)	1.5 to 2
 The soil water balance uses a checkbook like accounting procedure to show the amount of water removed from the soil profile.
Crop water use removes water from the soil and increases the deficit on a daily basis, while irrigation and/or rain add water to the soil and decrease the deficit.
The purpose of irrigation scheduling is to:
 Prevent the soil water deficit from becoming excessive, causing plant stress
 Restrict irrigation when the deficit is very small
 The amount of irrigation should not be greater than the deficit amount because this leads to leaching of nutrients and deep percolation below the root zone.
Also, you must leave some room for rain to reduce runoff potential.
An important aspect of scheduling irrigations is to look several days into the future to determine when irrigation may be needed.
For example, a center pivot can take three days or more to make a complete revolution and cover a field.
The checkbook can be used to project and estimate what the soil water deficit will be on the last irrigated sector of the field to help determine when to start the irrigation system.
Irrigation Trigger Points Based on Soil Water Deficit
 In general, annually planted crops are most sensitive to water stress in the reproductive stage of growth.
They are less sensitive to water stress early in the growing season and later when approaching physiological maturity.
The most common scheduling guideline is to prevent the soil moisture deficit from exceeding 50 percent in the root zone.
This is a general recommendation and applies to most agronomic crops such as corn, soybean, alfalfa and dry bean.
However, potato quality is very sensitive to water stress, and most growers do not want the deficit to be greater than 35 to 40 percent.
On the other hand, sunflower and some forage crops can withstand a slightly higher deficit than 50 percent.
Corn and soybean can withstand deficits up to 60 percent during vegetative growth, but with the onset of tasselling or blossoms, they should be irrigated to maintain a deficit of 50 percent or less.
Soil Water Balance Sheet
 A completed soil water balance sheet example and blank copies are included in this publication.
The irrigation manager should keep a balance sheet for each individual irrigated field.
Keeping a soil water balance between zero and the allowable deficit for the specific crop in the field is the goal of irrigation scheduling.
Recording Rain and Irrigation Amounts
 To use the balance sheet, the dates and measured amounts of irrigation and rain must be recorded.
Rain is so variable over the landscape that two easily accessible rain gauges should be located in or near each irrigated field.
Ideally, rain gauges should be located as shown in Figure 2.
The rain gauges should be at least 3 inches in diameter for accuracy.
The standard 4-inch-diameter National Weather Service rain gauge that records rain events to 0.01 inch is highly recommended.
Figure 2.
Ideally, each center pivot should have two rain gauges, one in the dryland corner and one along the access road about halfway to the pivot point.
Soil moisture deficit should be measured near the starting point of the center pivot  and near the last part of the field to be irrigated.
Daily Crop Water Use Estimates
 Tables 6 through 14 provide estimates of water use for the major irrigated crops in North Dakota.
To use the tables, you need to know the daily maximum air temperature and the number of weeks after emergence.
To make the process easy, the maximum air temperature for a day has to be only within a 10-degree range.
As an illustration, on the example soil water balance sheet, the maximum temperature on July 11 was 85 degrees.
To obtain a crop water use estimate for corn, look on Table 6 under the ninth week after emergence in the row for the range of 80 to 90 degrees to find a crop water use estimate of 0.25 inch.
Estimating alfalfa water use is different because alfalfa is cut several times during the growing season and water use is reduced after cutting.
The additional tables that accompany Table 14 can be used to estimate alfalfa water use the first three weeks after cutting.
To use the balance sheet, enter the estimated water use and add this to the previous day's soil water deficit.
For the first day after emergence, enter the estimated deficit from the field measurements.
Subtract rain and/ or irrigation for that day and record the new soil water deficit amount.
Compare this to the 50 percent deficit point shown at the top of the balance sheet  to determine when irrigation is needed.
Of course, check weather reports to see if rain is forecast for the area where the field is located.
Remember, the soil water deficit never can be less than zero because zero indicates the soil is at field capacity.
If a negative deficit is calculated for a particular day, enter zero in the deficit column.
To ensure the checkbook is tracking the soil water deficit accurately, the field should be probed to root zone depth about every two weeks at several locations.
If the checkbook is different from the field measurements, enter the measured deficit value for that day.
Standard 4-inch-diameter National Weather Service rain gauge
 Additional Irrigation Scheduling Resources for North Dakota
 The first version of this publication was authored by Darnell R.
Lundstrom and Earl C.
Stegman in 1976, reprinted in 1983 and revised in 1988.
This publication is a revision and update of the 1988 version.
We are indebted to these gentlemen for coining the term "Checkbook Method," which is used throughout the U.S.
to refer to soil water accounting methods for irrigation scheduling.
Sample Soil Water Balance Sheet
 Soil Water Balance Sheet
 Crop	Corn	Field name	SW 23	Emergence date	5/15/18
 Table 4	Pumping capacity	6.0	gpm/ac	App.
efficiency	85	%	Net irrig.
0.27	in/day
 Table 2	Root zone depth	3	ft.
AWC in root zone	4.1	in.
50% of AWC	2.05	in.
Alfalfa cut dates:	1st	2nd	3rd
 Add	Subtract	Add	Subtract
 Week after	6/12	72	0.12	0.12	0.0	16	17	80	82	0.24	0.24	0.94	1.18
 emergence	5	13	79	0.12	0.24	18	84	0.24	1.42
 14	86	0.15	0.39	19	80	0.24	0.52	1.14	Soil water
 16	15	75	85	0.12	0.15	0.19	0.47	0.54	20	21	78	77	0.19	0.19	1.33	1.52	deficit is
 17	70	0.14	0.61	22	81	0.23	1.75	corrected by
 Add 0.61	to 0.14	20	19	18	79	78	75	0.14	0.14	0.14	0.89	0.75	1.03	11	24	25	23	74	78	81	0.23	0.18	0.18	1.0	X	1.34	1.93	1.16	field using	probing the
 to get 0.75	21	84	0.19	1.22	26	70	0.18	X	1.52	the soil feel
 22	86	0.19	0.20	1.20	27	75	0.18	X	1.70	method
 24	23	76	78	0.17	0.14	0.35	1.35	1.17	28	29	79	78	0.17	0.18	1.0	1.05	1.88	
 25	78	0.17	1.34	30	82	0.22	X	1.27
 7	26	27	85	82	0.22	0.22	1.78	1.56	12	8/1	31	89	67	0.13	0.22	X	X	1.49	1.62	2.1
 28	89	0.22	2.00	2	80	0.22	184
 29	80	0.22	0.47	1.75	3	88	0.22	1.0	1.32
 air temp is	Maximum daily	7/1	30	81	76	0.24	0.17	X	0.75	1.17	1.41	4	5	80	89	0.22	0.21	X	X	1.75	1.54	Rain and
 water use is	recorded and	estimated crop	8	3	4	5	2	77	77	83	83	0.24	0.24	0.19	0.19	0.48	0.42	X	1.65	1.47	1.37	1.18	13	9	8	7	6	88	88	88	79	0.21	0.17	0.21	0.21	1.0	X	X	X	1.13	1.92	1.55	1.34	from previous	irrigation are	subtracted
 taken from	6	82	0.24	0.43	1.18	10	91	0.26	X	1.81	days deficit
 Table 6	8	7	84	92	0.25	0.30	0.11	1.48	1.62	12	11	93	99	0.25	0.26	X	1.0	1.32	1.07
 9	82	0.25	1.87	13	84	0.20	X	1.52
 9	10	//	85	86	0.25	0.25	4.93	0.0	0.25	14	15	14	71	81	0.16	0.20	X	1.68	1.88	Checkbook
 12	81	0.25	0.50	16	is up to date
 13	87	0.25	0.75	17
 14	89	0.25	1.00	18
 Rain amount exceeds	Irrigation is started SO deficit
 previous days deficit	does not exceed 50% of AWC.
plus today's crop water use	The pivot timer is set to apply
 0.75 inches in 3 days
 Soil Water Balance Sheet
 Crop Field name Emergence date Pumping capacity gpm/ac App.
efficiency % Net irrig.
in/day Root zone depth ft.
AWC in root zone in.
50% of AWC in.
Alfalfa cut dates: 1st 2nd 3rd
 Add	Subtract	Add	Subtract
 conditions	Date	all	Chap	water	vse	informa	Soli	etter	Date	art	Chap	water	use	Sol	walter	detet
 Soil Water Balance Sheet
 Crop Field name Emergence date Pumping capacity gpm/ac App.
efficiency % Net irrig.
in/day Root zone depth ft.
AWC in root zone in.
50% of AWC in.
Alfalfa cut dates: 1st 2nd 3rd
 Add	Subtract	Add	Subtract
 Media	atitic	Date	all	Chap	water	ver	Raimall	informa	Sol	water	delet	Medi	etten	Date	art	Chop	water	use	Rental	informa	Sol	documento	delicit
 Water Use Estimates for Irrigated Crops in North Dakota
 Table 6.
Average Corn Water Use 
 Emergence	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17
 50-59F	0.01	0.02	0.03	0.04	0.05	0.06	0.07	0.08	0.08	0.08	0.08	0.08	0.07	0.07	0.06	0.04	0.03
 60-69F	0.02	0.03	0.05	0.06	0.08	0.10	0.12	0.14	0.14	0.13	0.13	0.13	0.12	0.11	0.09	0.07	0.06
 70-79F	0.03	0.04	0.06	0.09	0.12	0.14	0.17	0.19	0.19	0.19	0.18	0.17	0.17	0.16	0.13	0.10	0.08
 80-89F	0.04	0.06	0.08	0.11	0.15	0.19	0.22	0.24	0.25	0.24	0.23	0.22	0.21	0.20	0.17	0.13	0.10
 90-99F	0.05	0.07	0.10	0.14	0.18	0.23	0.27	0.30	0.30	0.29	0.29	0.27	0.26	0.25	0.20	0.16	0.12
 I	|	I	I	I	|	I
 3	12	Silk	Blister	Early Dent	Black
 Leaf	Leaf	Kernel	Dent	Layer
 Table 7.
Average Wheat Water Use 
 Emergence	1	2	3	4	5	6	7	8	9	10	11	12	13	14
 50-59F	0.01	0.03	0.04	0.06	0.07	0.08	0.08	0.08	0.08	0.08	0.07	0.06	0.04	0.03
 60-69F	0.02	0.04	0.07	0.10	0.12	0.13	0.14	0.14	0.14	0.14	0.12	0.10	0.07	0.04
 70-79F	0.03	0.06	0.10	0.13	0.17	0.19	0.19	0.19	0.19	0.19	0.17	0.14	0.10	0.06
 80-89F	0.04	0.08	0.12	0.17	0.22	0.24	0.24	0.25	0.25	0.25	0.22	0.17	0.12	0.08
 90-99F	0.05	0.10	0.15	0.21	0.26	0.29	0.30	0.30	0.30	0.30	0.27	0.21	0.15	0.09
 I	I	I	I	I
 2	Joint	Heading	Early	Early
 Table 8.
Average Barley Water Use 
 Emergence	1	2	3	4	5	6	7	8	9	10	11	12	13
 50-59F	0.02	0.03	0.05	0.06	0.08	0.08	0.08	0.08	0.08	0.07	0.06	0.04	0.02
 60-69F	0.03	0.05	0.08	0.10	0.13	0.13	0.13	0.14	0.14	0.12	0.09	0.06	0.03
 70-79F	0.04	0.07	0.11	0.14	0.18	0.18	0.19	0.19	0.19	0.17	0.13	0.08	0.04
 80-89F	0.05	0.09	0.13	0.19	0.23	0.23	0.24	0.24	0.25	0.22	0.17	0.11	0.05
 90-99F	0.06	0.10	0.16	0.23	0.28	0.29	0.29	0.30	0.30	0.27	0.20	0.13	0.06
 Water Use Estimates for Irrigated Crops in North Dakota
 Table 9.
Average Soybean Water Use 
 Emergence	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16
 50-59F	0.01	0.02	0.03	0.04	0.05	0.06	0.07	0.08	0.08	0.08	0.08	0.07	0.07	0.06	0.05	0.04
 60-69F	0.02	0.03	0.05	0.07	0.09	0.11	0.12	0.13	0.13	0.13	0.13	0.12	0.11	0.10	0.08	0.06
 70-79F	0.03	0.05	0.07	0.09	0.12	0.15	0.17	0.19	0.19	0.18	0.17	0.17	0.16	0.14	0.11	0.08
 80-89F	0.04	0.06	0.09	0.12	0.15	0.19	0.22	0.24	0.24	0.23	0.22	0.21	0.20	0.18	0.14	0.10
 90-99F	0.05	0.07	0.11	0.15	0.19	0.23	0.27	0.29	0.29	0.29	0.27	0.26	0.25	0.22	0.17	0.13
 Table 10.
Average Sunflower Water Use 
 Emergence	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15
 50-59F	0.01	0.03	0.05	0.06	0.08	0.08	0.08	0.08	0.08	0.08	0.08	0.07	0.06	0.04	0.03
 60-69F	0.02	0.05	0.08	0.10	0.12	0.14	0.14	0.14	0.13	0.13	0.13	0.12	0.10	0.07	0.04
 70-79F	0.03	0.07	0.11	0.15	0.17	0.19	0.19	0.19	0.19	0.18	0.17	0.16	0.13	0.10	0.06
 80-89F	0.03	0.09	0.14	0.19	0.22	0.25	0.25	0.25	0.24	0.23	0.22	0.21	0.17	0.13	0.07
 90-99F	0.04	0.11	0.17	0.23	0.27	0.30	0.30	0.30	0.29	0.29	0.27	0.26	0.21	0.15	0.09
 Bud	Ray	100%	Ray Petal	Maturity
 Table 11.
Average Potato Water Use 
 Emergence	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15
 50-59F	0.02	0.03	0.04	0.05	0.07	0.08	0.08	0.08	0.08	0.08	0.08	0.07	0.06	0.05	0.04
 60-69F	0.03	0.04	0.07	0.09	0.11	0.13	0.14	0.14	0.14	0.13	0.13	0.12	0.10	0.09	0.07
 70-79F	0.04	0.06	0.09	0.12	0.15	0.17	0.19	0.19	0.19	0.19	0.18	0.17	0.14	0.12	0.10
 80-89F	0.05	0.08	0.12	0.16	0.19	0.22	0.25	0.25	0.25	0.24	0.23	0.21	0.18	0.16	0.13
 90-99F	0.06	0.10	0.14	0.19	0.24	0.27	0.30	0.30	0.30	0.29	0.29	0.26	0.23	0.19	0.16
 Water Use Estimates for Irrigated Crops in North Dakota
 Table 12.
Average Pinto Bean Water Use 
 Emergence	1	2	3	4	5	6	7	8	9	10	11	12	13
 50-59F	0.02	0.03	0.04	0.05	0.06	0.08	0.08	0.08	0.08	0.08	0.08	0.07	0.05
 60-69F	0.04	0.05	0.06	0.08	0.11	0.13	0.14	0.14	0.13	0.13	0.13	0.11	0.08
 70-79F	0.05	0.06	0.09	0.12	0.15	0.18	0.19	0.19	0.19	0.18	0.17	0.15	0.11
 80-89F	0.06	0.08	0.11	0.15	0.19	0.23	0.25	0.25	0.24	0.23	0.22	0.19	0.14
 90-99F	0.08	0.10	0.14	0.18	0.23	0.28	0.30	0.30	0.29	0.29	0.27	0.24	0.17
 4 Leaf	Flower	Podding	Initial	Leaf	Maturity
 Table 13.
Average Sugar Beet Water Use 
 Emergence	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20
 50-59F	0.02	0.02	0.03	0.04	0.05	0.06	0.07	0.08	0.08	0.08	0.08	0.08	0.08	0.07	0.07	0.06	0.06	0.05	0.05	0.05
 60-69F	0.02	0.04	0.05	0.06	0.08	0.10	0.11	0.13	0.14	0.14	0.13	0.13	0.13	0.12	0.11	0.10	0.10	0.09	0.08	0.08
 70-79F	0.03	0.05	0.07	0.09	0.11	0.14	0.16	0.18	0.19	0.19	0.19	0.18	0.17	0.17	0.16	0.15	0.14	0.13	0.12	0.11
 80-89F	0.04	0.06	0.09	0.12	0.15	0.17	0.20	0.23	0.24	0.25	0.24	0.23	0.22	0.21	0.20	0.19	0.17	0.16	0.15	0.14
 90-99F	0.05	0.08	0.11	0.14	0.18	0.21	0.25	0.28	0.30	0.30	0.29	0.29	0.27	0.26	0.25	0.23	0.21	0.20	0.18	0.17
 Table 14.
Average Alfalfa Water Use 
 May 1	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22
 50-59F	0.04	0.05	0.06	0.07	0.08	0.08	0.08	0.08	0.08	0.08	0.08	0.08	0.08	0.08	0.08	0.07	0.07	0.06	0.06	0.05	0.05	0.05
 60-69F	0.07	0.09	0.11	0.12	0.13	0.13	0.13	0.14	0.14	0.14	0.14	0.14	0.13	0.13	0.13	0.12	0.11	0.10	0.10	0.09	0.08	0.08
 70-79F	0.09	0.12	0.15	0.17	0.18	0.18	0.19	0.19	0.19	0.19	0.19	0.19	0.19	0.18	0.17	0.17	0.16	0.15	0.14	0.13	0.12	0.11
 80-89F	0.12	0.16	0.19	0.22	0.23	0.23	0.24	0.24	0.25	0.25	0.25	0.25	0.24	0.23	0.22	0.21	0.20	0.19	0.17	0.16	0.15	0.14
 90-99F	0.15	0.19	0.23	0.27	0.28	0.29	0.29	0.30	0.30	0.30	0.30	0.30	0.29	0.29	0.27	0.26	0.25	0.23	0.21	0.20	0.18	0.17
 Use these tables for the first three weeks after cutting.
1st and 2nd Cut	1	2	3
 50-59F	0.05	0.06	0.08
 60-69F	0.08	0.11	0.13
 70-79F	0.11	0.15	0.18
 80-89F	0.15	0.19	0.23
 90-99F	0.18	0.23	0.28
 3rd Cut	1	2	3
 50-59F	0.04	0.05	0.07
 60-69F	0.07	0.09	0.11
 70-79F	0.10	0.13	0.15
 80-89F	0.13	0.16	0.20
 90-99F	0.15	0.20	0.24
 Worksheet to Estimate the Soil Water Deficit at One Location in the Field 
 Water Deficit	Crop	Root zone	
 Soil Water-holding Capacity at One Location in the Field
 Soil Depth	Soil Texture	Average Water-holding Capacity 
 Soil Depth		and Table 5	Deficit 
 0 to 6 inches
 6 to 12 inches
 12 to 18 inches	X	=
 18 to 24 inches
 24 to 30 inches	X	=
 30 to 36 inches
 EXTENDING KNOWLEDGE >> CHANGING LIVES
 NDSU Extension does not endorse commercial products or companies even though reference may be made to tradenames, trademarks or service names.
To determine the actual cost, we would recommend the use of the IrrigateCost app.
The app, which is available for both Apple and Android products, allows users to input their specific information such as acres irrigated, pumping lift, system PSI, pump and pivot life, and inches applied as well as related costs such as for the well and engine, labor, energy, district fees, and taxes.
The app then calculates total irrigation cost as well as total ownership and total operating costs.
It also breaks down costs by irrigation well, pump, gear head, pump base, diesel engine and tank and system and calculates per acre annual cost and per acre-inch annual cost.
Mitigating Irrigation Fatigue and Drought Stress in 2022
 Christopher G.
Henry, Professor and Water Management Engineer
 When the spring 2022 rains shut off this year, it really compressed the workload for managing irrigation.
Our minds need to shift from "I can't keep up" to "where does the water I have, need to go." The next 30 days will be critical for many irrigators, as fatigues sets in, and many crops are still at or entering high water demand.
However, there are things that farmers can do to mitigate the both the human and plant stress being experienced.
The following are recommendations for reducing stress and extending the capacity of irrigation systems.
Computerized Hole Selection such as Pipe Planner, Rice Irrigation or PHAUCET help plan water distribution across the field.
These programs reduce pump time usually between 10% and 50%.
Plan for it taking longer: Most crops need between 0.25 and 0.35 inches per day to meet peak water demand.
What happens is that as wells are drafted and reservoirs are withdrawn, our pumps reduce capacity because they must lift water further as groundwater declines and reservoirs are drawn down.
Thus, irrigation sets we designed with computerized hole selection were planned to irrigate in 24 hours take longer.
Some alluvial wells can drop off as much as 50% and its not uncommon for relifts to fall off 30% as we get to the bottom.
Expect to take longer to irrigate a set or flood up a field, and adjust accordingly.
Flowmeters aid in predicting how much longer sets will take.
For irrigation sets that are planned for 24 hours, that are taking longer because pump capacity are reduced by 30%, those sets may now require 30 hours.
Additionally, if the normal application depth of 2 inches was used, but now require 3 inches because the soil is SO dry and the furrow flow rates are reduced, the 24 hour set is now a 47 hour set.
In addition to heat and drought stress, water stress is now being introduced since water may be standing on some of the field for more than 40 hours.
Time irrigation for when it will yield the most profit: Deficit irrigation is when irrigation water supply is inadequate to meet full crop demand, and we are using the water to maximize yield.
In general, to do this effectively provide just enough water during the vegetative phase of growth and then apply irrigation during the reproductive phase, and if it's going to be short, do it at the very end.
So, for soybeans, provide irrigation sparingly until R3 and use the remaining irrigation supply and capacity until termination.
The last irrigation needs to well before maturity.
For example, on soybeans we need 2.9 inches to finish at R6.5 SO apply any irrigation before then because if any extra may not contribute to yield.
In a limited situation, put the last irrigation on by R6  where the risk of yield penalty is greater than at R6.5.
Thus, in water limited situations, refrain from irrigation as much as
 possible until R3 and apply at R6 to maximize yield if for example only adequate water exists for two irrigations.
For corn, once the starch line develops, increase the frequency of irrigation until 50% starch, make last irrigation at this time if water is limited.
Soil moisture sensors save profitability: Irrigators who are using soil moisture sensors, surge irrigation and computerized hole selection should be more efficient and have an assessment of the soil water balance.
Its not necessary to have soil moisture sensors in every field, even just a few can help to understand how many days we can wait between irrigations.
In generally stress does not accumulate until after 50% allowable depletion, the average of all sensors in the profile where stress would begin to occur is shown in Table 1.
Table 1.
Soil Tension where no readily Plant Available Water Remains 
 Sand	Sandy Loam	Silt Loam with Pan	Silt Loam	Clay
 				
 	25	70	123	134	120
 Most important, doing this will allow for stopping unnecessary irrigation, its now possible to easily plan out if you have enough water for the crop or if measures need to be taken to preserve profitability.
Even with a handful of sensors, put the sensors in a field, then read two days later, remove and move to the next field.
This technique can be used to assess several fields in a week with one set of sensors.
Use the sensor readings and the mobile app to predict how much water will be needed to finish out the season.
This is a low-cost investment and considerable help is available to aid in doing this through Extension and NRCS irrigation technicians.
Deep Irrigate: Instead of flushing water across fields, put a full 2 to 3 ac-in/ac across the field, try to fill the profile when you do irrigate.
This will force the roots to go deeper for water and extract the subsoil moisture later.
Focus on doing a good irrigation SO it will be a while before you need to come back.
In sealed up silt loams, where it is not uncommon to only put on 0.5 inches in an irrigation, try irrigating and then irrigating again the next day to get more into the soil.
It can have mixed results, but can allow more time between irrigations.
How to estimate irrigations remaining?
The top quartile average total water use efficiencies,  observed in the Most Crop per Drop Contest are 6, 10 and 4 bu/in for rice, corn and soybeans are used in Table 2 to provide an estimate of total water needs for drought planning.
To estimate how much additional water or the number of irrigations needed to finish out the season, take the yield goal time the WUE.
For example, for a farm with a yield goal  of 225 bu corn, take 10 bu/in divided by the yield goal of 225 bushels, which yields 22.5 inches of total water.
Then subtract effective rainfall since emergence, if rain since emergence was 8 inches, the subtract from 22.5 inches 8 inches = 14.5 inches.
Most apply 2 inches per irrigation so, divide 14.5 inches by 2 inches per irrigation, which equals 7 irrigations.
If there have been 5 irrigations SO far, then plan 2 additional irrigation between now and 50%-75% starch.
Table 2.
Target Water Use Efficiencies of Crops for Drought Planning maintain fully irrigated yields.
Crop	Target Total Water Use Efficiency  [yield/]
 Water demand  =
 Irrigation Needed to finish = Water demand rainf all
 14.5 inches = 22.4 inches 8 inches
 # of total irrigations = 14.5 inches 2 inches per irrigation = 7 irrigations total needed
 For those with soil moisture sensors and the Arkansas Watermark tool mobile app, the water needed by the crop is automatically calculated and this estimate can be used to predict the amount of water remaining.
Tables 3, 4 and 5 for corn, soybeans and rice report the amount of water to finish a crop out can be estimated.
These tables can be used to estimate how many irrigations are needed to finish out the growing season.
Soil moisture sensors can be used to estimate the amount of water remaining in the soil, using the app or the factsheet.
Those without sensors will have to estimate how much water is still available in the soil using the feel method.
Subtract any rain experienced at the field.
These tables can be used to estimate irrigations, even without sensors and the feel method.
For example, if corn is at R5 50% milk, even without sensor data, if the soil is really dry, it will take a full 2 inch irrigation to finish out the crop, at R5 and 25% milk line, 3.7 inches is required, SO two irrigations will be needed.
For soybeans at R6.5, if the soil is dry at this stage, 4.7 inches are required, SO at least 2.5 irrigations of 2 ac-in/ac, will be needed.
If there is still moisture in the soil at this point, then 2 may be adequate.
Table 3.
Crop Water Demand for Corn
 Crop Growth	Water needed to mature
 Stage	Kernel Development	Days to Maturity	
 R4	Dough	34	7.5
 R4.7	Beginning dent	24	5
 R5	1/4 milk line	19	3.7
 R5	1/2 milk line to full dent	13	2.2
 R5	3/4 milk line	7	1.0
 R6	Maturity	0	0
 Table 4.
Crop Water Demand for Soybeans
 Crop Growth Stage	Pod & Plant Development	Days to Maturity	mature 2,3
 R4	End of Pod Elongation	50 60
 R5	Beginning of seed enlargement	40 50	10.0
 End of seed enlargement to
 R6 R 6.5	leaves beginning to yellow	30 40	4.71
 R6.5 R7	Leaves begin to yellow	20 30	2.9
 R7	Beginning Maturity	10 15	0.75
 R8	Maturity	0	0.27
 Table 5.
Crop Water Demand for Rice
 Days to	Water to
 Crop Growth Stage	Plant Development	Maturity	finish
 VF-1 to VF-2	Pre-flood	2	14.9
 VF-3 to VF-4	Flood	19	14.7
 VF-4 to Flag Leaf 	Flag Leaf 	29	11.9
 R2	Pre-boot	6	6.7
 R3  R5	Boot and panicle development	7	6.1
 R6 R7	At least one yellow hull	11	5.0
 R8	Prior to drain time for rice	10	3.3
 R9	All grains have brown hull, near drain time	24	1.8
 Source: M.
Reba, USDA ARS Delta Water Management Center, Jonesboro, Arkansas
 Reservoir Dilemma: Reservoirs are only designed to supplement 10 ac-in/ac of irrigation water.
Thus in years or in time of drought it may be prudent to estimate how much water is needed by crops and how much remains in the reservoir.
To estimate how many irrigations may be available in a reservoir first make an estimate of the area and depth.
For a 40 acre reservoir that has 10 feet remaining, 400 acre feet are available or 4,800 acre inches.
For a 750 acre farm, 4,800 divided by 750 acres leaves 6.4 inches of water or about 3 irrigations at 2 ac-in/ac.
If the farm is half rice at boot and half soybeans at R1, the soybeans will need 12.7 inches to finish and the rice will need 6.1 inches to finish.
So there is enough water in the reservoir for rice, but only half of what will be needed for soybeans.
So if a well can provide the extra 1,125 acre inches.
In this case if a 500 gpm well can provide 26 acre inches in 1 day.
Thus 375 acres of beans times 6 acre inches is 2,250 acre inches and it will take 2,250/26 = 86 days to make up.
There is only about 30 or 45 days left in the season, SO the well could only make up half of the remaining water.
In this situation, it would be wise to delay irrigation on the soybeans as much as possible SO that there is enough water in the reservoir for the R5 and R6 growth stages where stress will have less yield impact.
Use the feel method: NRCS has a published method on how to estimate soil water using the feel method.
Download the publication for Estimating Soil Moisture Content by Feel and Appearance on the USDA NRCS website.
If sensor data is not available, use the feel method and a soil probe to estimate soil water.
It will be necessary to probe at least 24 inches down to estimate the moisture in the subsoil.
Managing Rice with Limited Water: For rice, Alternating Wetting and Drying , drying down to mud is safe AWD, but data from Mississippi indicated one can go as far as 2-4 inches below the surface before we would experience yield penalty.
This is using a panni pipe, or perforated PVC pipe installed in the ground.
However, a spade can be used instead to see how wet the soil is below the surface, and if one can still see water just below the surface you can go this far between re-floods.
Use DD50 to plan to predict the drain date, the strategy should be to have the field at mud consistency at that DD50 date.
Plan to stop irrigating before this date to get to have the soil at this condition on the DD50 drain date SO water is not wasted that could be used on other crops.
For row rice, data on silt loams that suggests a 40% allowable depletion will not result in yield penalty.
This equates, in general, to about 7 days between irrigation, before a significant yield penalty.
However even irrigation every 14 days irrigation only resulted in a yield penalty of 25 bpa.
At least for hybrids, even though they may look stressed, the yield penalty may not be as much as it appears.
From our water stress research 30 total inches of water  would be a target for any rice field before water stress would likely impact yield.
For comparison the rice verification program normally measures 32 ac-in/ac of irrigation on average, SO when water is scarce, acceptable yields are still achievable.
There are several apps available to track rainfall in fields.
Don't overlook the obvious: Irrigation pumps in Arkansas operate just under 800 hrs per year, but the drought is going to push way past that normal run time.
For diesel power units, oil changes, greasing propeller shafts may seen obvious, but changing the oil in the gear head is often overlooked.
For electric motors, greasing the bearings, often requires grease specific for electric motors, and on vertical hollow shaft motors, there is a dry plug that should be removed then 3-4 pumps max, grease
 should come out of the dry port.
Don't over lubricate an electric motor, or the grease will fill up the housing and get into the windings.
The top bearing in a hollow shaft motor runs in oil, and should be changed annually.
Obtain the proper lubricants for electric motors from your well driller or pump dealers.
If the oil in the sight window is black or white, there is a high risk of bearing failure.
Drip oil should be set in the morning, 6-8 drips per minute, when it is cool as the oil expands during the day.
Setting the dripper in the heat of the day, could stop the drip when the temperature cools in the morning.
For poly pipe, there are zipper repair patches and a press-on patch that are good to keep on hand in addition to repair couplers for pipe repairs.
Heat stress and heat exhaustion awareness are real threats to safely sustaining irrigation, keep ample water to employees and yourself and don't get in a hurry, it may take more time to do things safely.
Take care not to slip near drive shafts.
Understanding how each type of sensor achieves this estimate will help you when selecting a sensor for use in irrigation management.
While there are many different types of sensors, for this article we are going to focus on the two main types being used for irrigation management in Nebraska; electrical resistance sensors and capacitance probes.
VISUAL GUIDE TO SOYBEAN GROWTH STAGES
 Published: Apr 29, 2022 |  Printable Version  | Peer Reviewed
 Michael Plumblee and Bennett Harrelson
 Identifying soybean growth stages is essential for proper crop management of pests, irrigation, and fertility.
This guide will help growers, consultants, extension, and research personnel correctly identify soybean growth stages in both determinate and indeterminate soybean varieties.
Generally, soybean growth and development can be divided into vegetative  and reproductive  growth stages.
However, soybean can be broken into two different growth habits: indeterminate and determinate.
Indeterminate cultivars continue vegetative growth even after reproductive growth has been initiated and are classified as maturity groups  000IV.
In contrast, determinate cultivars cease vegetative growth once reproductive growth begins and are classified as MGs VX.
Each growth stage starts when at least 50% of plants in the field or area are at that stage.
Vegetative growth stages start with soybean emergence, and reproductive growth stages begin with the first flower for all soybean cultivars.
Vegetative  Growth Stages
 Vegetative growth stages of soybean progress through four or more stages of maturity prior to initiation of reproductive growth stages.
Pictures of each stage and a description of that stage are presented below.
The soybeans vegetative growth stages begin with the VE stage of seedling emergence.
Prior to germination, soybean seed absorbs water equal to approximately 50% of its weight.
Hypocotyl elongation brings the cotyledons out of the soil, starting the soybean plant emergence process.
After emergence, unifoliolate leaves on the first node unroll in addition to cotyledons and start the VC stage.
Soybean plant emerging from soil.
Figure 1.
VE  depends on soil temperature and moisture.
Image credit: Clemson University.
VC two unifoliate leaves unrolled in addition to cotyledons.
Figure 2.
VC   two unifoliolate leaves unrolled in addition to cotyledons.
Image credit: Clemson University.
V1, V2, V3 to V Stages
 Stages following VC are designated numerically from V1, V2, V3, through V.
For example, the V1 stage starts with one fully developed trifoliolate leaf on the second node.
The V2 stage occurs when one additional trifoliate leaf is fully developed on the third node.
The  represents the number of the last fully developed trifoliolate leaf.
A fully developed trifoliolate leaf has unrolled or unfolded leaflets.
V1 unrolled trifoliolate leaf on soybean plant.
Figure 3.
V1  one unrolled trifoliate leaf above unifoliate leaves.
Image credit: Clemson University.
V2 two unrolled trifoliate leaves above the unifoliate leaves
 Figure 4.
V2two unrolled trifoliate leaves above the unifoliate leaves.
Image credit: Clemson University.
Reproductive  Growth Stages
 The reproductive stages of soybean progress through eight growth stages before reaching physiological maturity.
Pictures of each stage and a description of that stage are presented below.
R1 and R2 Stages
 In both determinate and indeterminate soybean, the reproductive stages begin with the R1  stage when at least one open flower is present on the main stem.
The R2  stage begins when an open flower is present at any of the top two nodes with a fully developed trifoliate.
R1 one open flower on the main stem of a soybean plant.
Figure 5.
R1  Beginning bloom.
One open flower on the main stem.
Image credit: Michael Plumblee, Clemson University.
Seed pod with a full bloom flower on soybean plant.
Figure 6.
R2  Full bloom.
Open flower at any of the top two nodes with a fully developed trifoliate.
Image credit: Michael Plumblee, Clemson University.
R3 and R4 Stages
 The R3  stage begins when pods are 3/16-inch long at one of the top four nodes with a fully expanded trifoliate.
The R4  stage begins when pods are 3/4-inch long at one of the top four nodes and with the presence of a fully expanded trifoliate.
New seed pods on a soybean plant.
Figure 7.
R3  Beginning pod.
Pods are 3/16-inch long at one of the top four nodes.
Image credit: Michael Plumblee, Clemson University.
Seed pods on a soybean plant.
Figure 8.
R4  Full pod.
Pods are 3/4-inch long at one of the top four nodes.
Image credit: Michael Plumblee, Clemson University
 R5 and R6 Stages
 The R5  stage begins when seeds are 1/8-inch long on one of the top four nodes with a fully expanded trifoliate.
The R6  stage begins when pods are filled with a green seed on one of the top four nodes with the presence of a fully expanded trifoliate.
Small seeds in a soybean pod.
Figure 9.
R5  Beginning seed.
Seeds are 1/8-inch long on one of the top four nodes.
Image credit: Michael Plumblee, Clemson University.
Soybean seed pods with three full pods.
Figure 10.
R6  Full seed.
Pods are filled with a green seed on one of the top four nodes.
Image credit: Michael Plumblee, Clemson University.
R7 and R8 Stages
 The R7  stage begins when one pod per plant has reached mature color, normally brown or tan.
The R8  stage begins when 95% of the pods have reached their mature color.
Figure 11.
R7  Beginning maturity.
One pod per plant has reached mature color, normally tan or brown.
Image credit: Bennett Harrelson, Clemson University.
Figure 12.
R8  Full maturity.
95% of pods have reached their mature color.
Image credit: Gerald Holmes, Cal Poly, Bugwood.
Rain Gardens and Stormwater
 Katie Teague County Extension Agent Agriculture/Water Quality
 Mike Daniels Professor Water Quality and Nutrient Management
 John Pennington County Extension Agent Agriculture/Water Quality
 Mark Brown County Extension Agent Water Conservation
 Arkansas Is Our Campus
 When precipitation falls to the ground or snow melts, it either percolates into the soil or moves across the land or an impervious surface as stormwater until it reaches a creek or stream, eventually flowing to a natural storage area such as a pond, a lake or a reservoir.
In some cases, stormwater is stored temporarily in small depressions until it can infiltrate or evaporate.
Stormwater runoff is a natural process, but it can be greatly altered by development, which creates large areas of impervious surfaces such as parking lots, roofs, buildings, roads, sidewalks and driveways.
Impervious surfaces prevent infiltration and create greater volumes and flow velocities of stormwater runoff for a given area.
This, in turn, increases the potential for stormwater to collect and transport pollutants such as sediment, nutrients, bacteria and petroleum-based products to streams and ultimately to lakes and oceans.
It also creates greater potential for flooding in urban areas when small natural drainage areas can no longer accommodate stormwater flows due to increased runoff volume and flow velocities.
To protect our waterways from polluted stormwater, the United States Environmental Protection Agency now has laws in place that require certain municipalities to manage and control stormwater runoff through measures such as bio-retention basins, bioswales,
 constructed wetlands, open space conservation and land development ordinances.
Homeowners and property managers can also manage stormwater in a manner that is relatively inexpensive, pleasing to the eye and beneficial to the environment through the use of rain gardens.
What is a rain garden?
As their name implies, rain gardens are cultivated areas created to collect stormwater runoff.
A rain garden is a landscaped depression that collects rainfall from impervious areas such as roofs, driveways or parking lots and blends in seamlessly with other landscaping.
Thus, they are really smaller-scale bio-retention basins that fit perfectly around houses and lawns.
The garden's flat bottom and porous soil help distribute rain water evenly across the planted area, allowing the water to slowly soak into the ground within 48 hours after the rain stops.
Appropriately designed rain gardens will not increase mosquito populations since mosquitoes cannot complete their breeding cycle in this length of time.
While they are beautiful, lowmaintenance additions to your yard, rain gardens also provide important environmental benefits.
Landscaped with native plants, rain gardens provide habitat that attracts local wildlife, including butterflies and birds.
By catching and allowing rainwater to slowly percolate into the soil, rain gardens recharge groundwater supplies and decrease stormwater
 runoff.
Rain gardens are designed and constructed in such a way that the soil in the garden can filter and remove any pollutants from the captured stormwater, thereby protecting the quality of our groundwater.
Rain gardens can vary in size and shape and contain an infinite arrangement of plants and colors to fit into any landscape.
Rain gardens have been used at businesses, in neighborhoods, schools and parks.
They can be placed virtually anywhere where runoff can be collected.
How do rain gardens work?
Rain gardens are designed to capture stormwater and to hold it long enough to allow interaction with soil but not long enough to create habitat for mosquitoes.
Rain gardens capture stormwater by being placed downslope of drainages from impervious surfaces.
Once stormwater is collected, it is stored temporarily in the rain garden where it interacts with plants and soil before draining to groundwater or evaporating.
In this manner, rain gardens can function like temporary, miniature wetlands.
Wetlands can remove pollutants by slowing the flow of stormwater to allow soil to filter pollutants via adsorption and entrapment, while plants can uptake some pollutants such as nutrients and metals in a process known as phyto-remediation.
Also, oxygen imported into the soil by wetland plants can help microbes transform and degrade pollutants before the water drains to groundwater or is released to natural drains.
In this manner, rain gardens become more than a beautiful landscape feature, they become an effective way of capturing, reducing and remediating stormwater runoff.
What are the environmental benefits of rain gardens?
Rain gardens provide a number of relatively low-cost benefits to the environment including:
 Removing pollutants including sediment, fertilizers, pesticides, automotive fluids and metals from stormwater.
Increasing water infiltration and recharging groundwater supplies.
Enhancing the beauty of yards, neighborhoods and businesses through beautiful landscaped areas.
Providing habitat for birds, butterflies and beneficial insects.
Reducing flooding and drainage problems in yards and communities.
Sustaining creek flows during dry periods.
Reducing the flow intensity of creeks during storm events.
How do you build a rain garden?
The first step to constructing a rain garden is to develop a plan that includes location, size and shape , porous media selection, mulch selection and plant selection.
Rain gardens can be placed just about anywhere but must be placed at a lower elevation than the runoff entrance and the surrounding land.
The installation of a rain garden will most likely require some shallow excavation.
To avoid damage to underground utility lines and serious injury, contact
 Figure 1.
Examples of rain gardens.
Figure 2.
Schematic cross section of a typical rain garden.
your local utilities to ensure your location does not coincide.
Other tips for locating rain gardens include:
 The rain garden should be at least 10 feet from the house to avoid interaction with the foundation.
Do not place rain gardens directly over septic systems or lateral lines.
Avoid areas where water already ponds as this indicates poor infiltration.
Place rain gardens in full or partial sun.
Selecting gently sloping land will reduce excavation efforts.
An extremely important consideration for determining the suitability of your site is to ensure that you have adequate infiltration and water movement through the soil.
You can do a simple percolation test to determine how quickly water moves through your soil.
Dig a hole about 12 inches deep and about 6 inches in diameter.
A post-hole digger is good for this.
Fill the hole with water three times and allow it to thoroughly saturate the surrounding soil.
Fill the hole with water a
 fourth time and observe how long it takes the water to soak out of the hole.
If the soil is already saturated from rain, you may not have to fill it three times.
Use the following guidelines to determine suitability:
 Rapid percolation: Water drains out of the hole within an hour; soil may not hold water long enough for establishment of vegetation.
Organic matter amendments such as compost or peat moss needed.
Moderate percolation: Water drains out of the hole within eight hours; ideal for effective rain garden establishment.
Slow percolation: Water does not completely drain within 24 hours; site may be too wet, clayey or low for effective rain garden.
Additional digging and soil amendments necessary.
Once you have determined a location that is free of utility lines, then determining the size and shape should follow.
Rain gardens can be any size and
 shape, but here are a few guidelines that can improve performance:
 Total area should be at least 10% the size of the impervious area from which runoff is being collected, such as a roof or driveway, with 30% being optimum.
The depression area of the garden should be excavated to six to eight inches below the original soil surface or deeper with greater slope.
The bottom of the garden should be flat.
If the percolation test indicated slow water movement, then dig four to six inches deeper and remove that soil and save for berm construction.
Break up the soils on the bottom of the bed with a rototiller, shovel or pitchfork.
Backfill with soil mixture described below.
A berm four to eight inches above the top of the planting bed should be constructed around the perimeter of the garden.
As far as shape, rain gardens can be any shape including kidney, crescent, rectangular, circular or square.
Its shape can be constructed to uniquely fit your landscape and be pleasing to your eye.
The results of your percolation test can help guide you on how to amend the soil that is used as backfill.
For rapid infiltration, mix removed soil with equal mixture of an organic amendment such as compost or peat moss.
For moderate percolation, you may not have to amend for water movement.
However, adding 25% to 40% compost or peat moss may be advantageous to the long-term soil fertility and plant life.
For slow percolating soils, remove and use the soil collected from the additional digging for the berm.
Mix equal parts sand, organic material and original topsoil  and backfill to desired garden depth.
Rain gardens can be as colorful, beautiful and unique as your creativity allows.
Hundreds of plants can work in rain gardens.
However, native perennial flowers, grasses and shrubs that can tolerate both drought or moist soil conditions should thrive in your garden.
They'll also entice butterflies, hummingbirds and other nectar and berry feeders to visit and provide better disease resistance.
These local plants tend to be welladapted to a range of regional conditions and will flourish without chemical fertilizers and pesticides.
A list of select native plants for Arkansas is listed in Table 1.
Table 1.
Native Arkansas plants for rain gardens.
Plants shown in gray either can take a good amount of shade or need afternoon shade.
Allium cernuum	Nodding onion
 Amsonia tabernaemontana	Willow leaf blue star
 Andropogon geradii	Big bluestem
 Andropogon glomeratus	Bushy bluestem
 Asclepias incarnata	Swamp milkweed
 Aster oblongifolius	Fragrant aster
 Aster paludosus	Prairie aster
 Aster sagittifolius	Arrow leafed aster
 Aster turbinellus	Violet prairie aster
 Baptisia sphaerocarpa	Yellow wild indigo
 Carex species	Many sedges
 Chasmanthium latifolium	Northern sea oats or Indian
 Chelone species	Turtle head
 Eupatorium species	Joe Pye weed
 Gelsemium sempervirens	Carolina jessamine
 Helianthus angustifolius	Narrowleaf sunflower
 Hibiscus coccineus	Texas star hibiscus
 Hibiscus mos.
V.
lasiocarpus	Red eye mallow
 llex verticillata	Winterberry holly
 Iris fulva	Copper iris
 Iris virginica	Blue flag
 Lobelia cardinalis	Cardinal flower
 Lobelia siphilitica	Blue cardinal flower
 Malvaviscus arb.
Turk's turban
 Muhlenbergia capillaris	Pink muhly grass
 Osmunda cinnamomea	Cinnamon fern
 Osmunda regalis V.
speciosa	Royal fern
 Parthenium integrifolium	Wild quinine
 Penstemon tenuis	Gulf Coast penstemon
 Physostegia species	Obedient plant
 Polemonium reptens	Jacob's ladder
 Polygonatum biflorum	Solomon's seal
 Rudbeckia maxima	Giant coneflower
 Schizachyrium scoparium	Little bluestem
 Sisyrinchium angustifolium	Blue eyed grass
 Tripsacum dactyloides	Eastern gamma grass
 Vernonia arkansana	Arkansas ironweed
 Vernonia lettermanii	Letterman's ironweed
 Vernonia missurica	Missouri ironweed
 Veronicastrum virginicum	Culver's root
 Alnus serrulata	River alder
 Amorpha fruticosa	Evening primrose
 Aronia arbutifolia	Red chokeberry
 Aronia melanocarpa	Black chokeberry
 Betula nigra	River birch
 Callicarpa americana	Purple beauty berry
 Chionanthus virginicus	Fringe tree
 Cornus drummondii	Rough leaf dogwood
 Cornus racemosa	Gray dogwood
 Itea virginica	Virginia sweet spire
 Magnolia virginiana	Sweet bay magnolia
 Myrica cerifera	Southern wax myrtle
 Nyssa sylvatica	Black gum
 Quercus michauxii	Swamp white oak
 Rosa palustris	Swamp rose
 Sambucus canadensis	American elderberry
 Taxodium distichum	Bald cypress
 Viburnum nudum	Shonny haw
 Viburnum prunifolium	Blackhaw viburnum
 Rain gardens are becoming a popular landscape feature in Arkansas because they are relatively inexpensive, beautiful and provide many environmental benefits.
They are a great way for homeowners, businesses, neighborhoods and communities to address stormwater runoff and ensure that our surrounding creeks and streams are clean, healthy and functional.
Printed by University of Arkansas Cooperative Extension Service Printing Services.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Director, Cooperative Extension Service, University of Arkansas.
The Arkansas Cooperative Extension Service offers its programs to all eligible persons regardless of race, color, national origin, religion, gender, age, disability, marital or veteran status, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
Percent of fields that became wetter moving from August to Sept.
15.
The dry years 2020, 21 and 22 fields are much drier than the other years in the fall.
In the weighted average dry years, 2020, 2021, 2022, 42% of fields with soil in the 15-25 in zone became wetter from August to Sept.
15, 30% of fields with soil in the 25-36 in zone became wetter from August to Sept.
15, and 19% of fields with soil in both zones became wetter moving from August to Sept.
15.
INFLUENCE OF NOZZLE PLACEMENT ON CORN GRAIN YIELD, SOIL MOISTURE AND RUNOFF UNDER CENTER PIVOT IRRIGATION
 Maximizing irrigation efficiency is of enormous importance for irrigators in the Central Great Plains to conserve water and reduce pumping costs.
High temperatures, frequently strong winds and low humidity increase the evaporation potential of water applied through sprinkler irrigation.
Thus, many newer sprinkler packages have been developed to minimize water losses by evaporation and drift.
These systems have the potential to reduce evaporation losses as found by Schneider and Howell.
Schneider and Howell found that evaporation losses could be reduced by 2-3% as compared to above canopy irrigation.
Many producers and irrigation companies have promoted placing sprinklers within the canopy to conserve water by reducing the exposure of the irrigation water to wind.
However, runoff losses can increase due to the reduced wetted diameter which increases the application rate greater than soil infiltrate capacity.
Schneider and Howell  found that furrow dikes were necessary to prevent runoff with in-canopy irrigation.
In 2003 and 2004, a study was conducted comparing sprinkler nozzle placement near Burlington, Colorado in cooperation with a local producer.
The objective of this study was to determine the impact of placing the sprinkler devices within the canopy upon soil moisture, runoff and crop yield.
A secondary objective was to determine the usefulness of in-season tillage on water intake and preventing runoff.
For this study, the current configuration of a center pivot irrigation system owned by our cooperating farmer was utilized.
This configuration included drops with spray heads at approximately 1.5 feet  above the ground surface.
The sprinkler heads on the seventh and outside span of the center pivot were raised to approximately 7 feet above ground level.
This nozzle height allowed for an undisturbed spray pattern for a majority of the growing season.
The sprinkler heads on the sixth span of the center pivot remained at the original height.
In 2003, the nozzles were raised by attaching the
 flexible drop hose using truss rod slings.
Because the farmer decided not to irrigate this field in 2004, the study was moved to an adjacent pivot in 2004.
The pivot nozzles were raised by replacing the drop hoses and 'j-tubes' on this system.
In 2004 the nozzle heights in the outside span were left at 1.5 feet above ground level and the next span into the field were raised to 7 feet.
Spacing was 5-feet between nozzles for both site-years.
For the 2003 growing season, three in-season tillage treatments were replicated three times under each of the sprinkler heights.
The three tillage treatments were cultivation, inter-row rip and basin tillage.
The cooperating farmer implemented the tillage treatments when the corn was at the V6 growth stage.
The tillage treatments were implemented in strips running the length of the field.
The field was planting perpendicular to the sprinkler direction.
In 2004, the cooperating farmer chose to use grow the corn crop using no-till and planted in a circular pattern.
In-season tillage was was to be implemented, inter-row rip and basin tillage operations, it was prevented by wet weather in June..
Thus, the only tillage in 2004 was no-till.
The cooperating farmer conducted all field operations  during 2003 and 2004.
Runoff was measured on cultivation and basin tillage for 2 replications and both sprinkler heights in 2003.
Four-inch, V-notch furrow weirs installed at the bottom of the 8-row plots.
The runoff for two 30-inch rows for the entire length of the pivot span  was directed into the weir by the tillage treatment and soil berms where needed.
The water level height in the stilling-wells of the weirs was recorded using auto-logging pressure transducers.
Because the cooperating farmer chose no-till for the 2004 season, two 10-foot by 38-foot runoff plots using landscape edging were installed.
Furrow weirs were installed on the lower end of the plots to measure runoff.
The soil type at both sites was Kuma Silt Loam.
The slope was approximately 1 to 1.5 percent and was fairly uniform across treatments.
We measured soil moisture from mid-June through early September using a Troxler neutron probe at one-foot increments to five feet of soil depth.
A neutron access tube was installed in each tillage and nozzle height treatment in 2003 and six access tubes were installed in each nozzle height treatment in 2004.
The study was repeated in 2005 but the results are not published.
Problems associated with the bowls created surging and resulted in sections of sprinklers not outputting water.
These sprinklers were generally the above canopy sprinklers.
In 2006, yields were taken from each sprinkler height.
No soil moisture or runoff measurements were taken.
Grain yields in 2003 were not significantly different for in-canopy and above canopy irrigation.
Statistically significant difference between tillage treatments were not found.
However the yields for above canopy irrigation were consistently 4 bushels per acre greater than in-canopy irrigation within each tillage treatment.
This would indicate that moisture stress did not occur under either above canopy or in-canopy irrigation.
Grain yields for above canopy sprinkler placement were not statistically greater than in-canopy placement in 2004 or 2006 as well.
However, grain yields averaged over the three year period indicate a trend where above canopy placement of sprinklers has greater yields than that of in-canopy placement.
Soil moisture was measured for both above canopy and in-canopy sprinklers during the 2003 growing season.
When comparing above canopy to in-canopy irrigation, changes in soil moisture were greater for in-canopy irrigation than above canopy.
The depletion of soil moisture was significantly higher for the in-canopy sprinkler placement than with above canopy sprinklers.
With similar yields, this would indicate that greater runoff losses occurred with incanopy irrigation since soil moisture usage offset reduced infiltration.
The greatest difference in change in soil moisture between above and in canopy irrigation occurred during early August when the difference was greater than 3 inches of soil moisture between the two sprinkler placements.
Differences in soil moisture usage at physiological maturity were 1.7 inches greater for in-canopy irrigation than above canopy irrigation.
Changes in soil moisture between tillage treatments in 2003 were not significantly different from each other within a sprinkler height during the growing season.
This would indicate that sprinkler height was the dominant factor in soil moisture content.
Contrary to 2003, soil moisture initially increased early in the 2004 growing season, declining after drier weather and higher ET rates began in July.
Soil moisture content initially showed a greater increase for in-canopy placement as compared to above canopy placement.
Much of this was due to the incanopy placement being drier at the beginning of the season and above canopy placement reaching field capacity in mid-July.
Most likely, deep percolation occurred in the above canopy placement while stored soil moisture increased for the in-canopy placement.
Changes in soil moisture for both in-canopy and above canopy placement were similar after July 27.
This was after the above canopy and in-canopy placement reached maximum stored soil moisture during the growing season.
Due to inconsistent and unreliable readings from one replication of the data loggers installed on the weirs recording runoff, only one replication of the 2003 measurements was used for this paper.
Runoff was greater with in-canopy irrigation than above canopy for the conventional cultivation and basin tillage treatments.
Changes in soil moisture between sprinkler placement treatments agree with runoff results collected for each placement.
Greater amounts of runoff between sprinkler packages were offset by greater soil moisture loss.
Runoff amounts were less for basin tillage as compared to cultivation.
The reduction in runoff was due to the increase in surface storage created by the implanted basins.
Although not measured, no or little runoff or signs of runoff was observed in the inter-row ripping tillage plots.
Only two significant runoff events due to irrigation, 1.1 and 0.89 inches of runoff, were recorded in 2004.
This was due to management changes made by the producer.
Irrigation depths in 2003 were 1.5 to 2 inches per application.
In 2004, application amounts were reduced to 0.7 inches per application.
This reduction in application depth reduced runoff in all but two irrigations where the producer applied higher amounts  per application.
Results from this study suggest that above canopy irrigation was more efficient at increasing stored soil moisture and reducing runoff as compared to in-canopy irrigation.
Less runoff from above canopy irrigation in 2003 resulted in more stored soil moisture and similar to slightly more grain yield than in-canopy irrigation.
In-season tillage such as basin tillage decreased runoff as compared to conventional cultivation.
Yields between tillage treatments were not significantly different, but a trend of yield increases was observed when soil intake rates were modified by tillage.
No statistically significant yield differences were observed within a year when irrigation sprinkler nozzles were placed above the canopy and soil moisture differences between above canopy and in-canopy placement reflected the differences in runoff.
The results of this project suggest that sprinkler placement above a corn canopy would be preferable to placing sprinklers in-canopy unless significant changes in irrigation management practices occur.
However, when averaged over the three years of this study, sprinkler placement near truss level  had significantly greater yields than compared to in-canopy placement.
PLUGGED EMITTERS IN DRIP IRRIGATION
 Drip emitters can become plugged with fine particles, mineral deposits, or biofilms.
When emitters become clogged, the plants nearest the clogs will receive less water and have more water stress and grow less or be stunted.
This is seen most commonly in higher density planted crops such as peppers.
A common cause of plugged emitters is water containing high levels of dissolved iron.
This can cause a proliferation of iron utilizing bacteria.
These bacteria form heavy biofilms on the inside of the drip tube.
They also oxidize the iron in the water  and leave behind iron precipitates that can plug emitters.
Chlorination of drip lines is needed to control iron bacteria.
From the Mid-Atlantic Commercial Vegetable Recommendations:
 Periodic treatment before clogging develops can keep the system functioning efficiently.
The frequency of treatment depends on the quality of the water source.
Generally, two or three treatments per season is adequate.
Irrigation water containing high concentrations of iron  can also result in clogging problems due to types of bacteria that feed on dissolved  iron.
The bacteria secrete a slime called ochre that may combine with other solid particles in the trickle tubing and plug emitters.
The precipitated  form of iron, known commonly as rust, can also physically clog emitters.
Treating water containing iron with chlorine will oxidize the dissolved iron, causing the element to precipitate so that it can be filtered and removed from the system.
Chlorine treatment should take place upstream of filters in order to remove the precipitated iron and microorganisms from the system.
Take care when adding chlorine to trickle irrigation systems, however, since concentration at or above 30 ppm can be toxic to growing plants.
For managing dissolved iron and microbes in the water source, one of the following basic strategies is suggested as a starting point:
 Inject liquid sodium hypochlorite continuously at a rate of 1 ppm for each 1 ppm of iron in irrigation water.
In most cases, 3 to 5 ppm is sufficient.
Inject liquid sodium hypochlorite continuously at a rate of 5 to 10 ppm where the biological load is high or
 Inject 10 to 20 ppm during the last 30 minutes of each irrigation cycle or
 Inject 50 ppm during the last 30 minutes of irrigation cycles one to two times each month or
 Super chlorinate  once per month for the length of time required to fill the entire system with this solution and shut down the system.
After 24 hours, open the laterals and flush the lines.
Another common problem in some aquifers, is well water with high levels of calcium and magnesium.
In high water pH conditions, these can precipitate out as calcium or magnesium carbonates that will clog emitters.
If you look inside the drip tubing you will see a white or chalky film.
In addition, if soluble phosphorus fertilizers are put into water with high levels of dissolved calcium or magnesium salts, they can precipitate out as calcium or magnesium phosphates, also plugging emitters.
Acidification of water can reduce or eliminate this problem.
Also, avoid running phosphorus through the drip if you have hard water.
Inadequate filtering is another possible cause of plugged emitters.
While this is most common when using surface water from ponds, ditches or streams it can also occur in wells that have fine particles in the water.
The key to knowing the correct setting for the chemigation pump is to determine how many acres per hour the pivot will cover at the desired irrigation application depth or rate.
Chemigation injection pumps are calibrated in gallons per hour.
So, if you know how much product you want to apply per acre e.g., 10 gallons/acre  and how many acres the pivot will irrigate per hour  e.g., five acres/hour  then you will know how many gallons per hour the pump will need to deliver.
Troy A.
Bauder Extension Specialist, Department of Soil and Crop Sciences, Colorado State University
 Reagan M.
Waskom Director Colorado Water Institute, Colorado State University
 Assistant Extension Specialist, Department of Soil and Crop Sciences, Colorado State University
 In association with: Colorado Department of Agriculture and the Agricultural Chemicals and Groundwater Protection Advisory Committee
 Colorado Department of Public Health & Environment USDA Natural Resources Conservation Service Colorado State Office Colorado State University Department of Soil and Crop Sciences
 Cover design by: Jessica Potter, Colorado Department of Agriculture
 Layout design by: Kierra Jewell, Department of Soil & Crop Sciences, Colorado State University
 Cover photo: Noland Farms, Inc.
BEST MANAGEMENT PRACTICES FOR NITROGEN FERTILIZER
 Nitrogen  is the essential plant element that most frequently limits crop production.
Commercial N fertilizers, manure and compost, are a costeffective means of supplementing soil supplied N for plant growth and are typically necessary for sustaining high crop yields.
However, it has been documented that improper or excessive use of N sources can lead to nitrate pollution of ground or surface water.
Both urban and rural fertilizer applicators can minimize this problem by implementing Best Management Practices  for N use.
Nitrate in Drinking Water
 Managing the amount, form, placement, and timing of N application are the most practical and acceptable approaches to minimizing ground and surface water contamination resulting from fertilizer use.
In Colorado, the use of fertilizers by both urban and rural applicators may be regulated under the Agricultural Chemicals and Groundwater Protection Act  if the Colorado Department of Agriculture finds voluntary measures insufficient to protect groundwater.
Therefore, applicators need to evaluate the nitrate leaching potential of fields where fertilizer is used and voluntarily adopt BMPs to protect water quality.
While fertilizer use efficiency has greatly improved in U.S.
agriculture the last 30 years, it is estimated that about 30% of N applied to crops is lost through leaching, volatilization, or denitrification.
These losses are estimated to be even higher during wet years.
Leaching is the major problem on coarsetextured soils, while denitrification is the primary pathway on poorly drained clay soils.
While a certain amount of loss is unavoidable, producers can gain economic and environmental benefits by minimizing losses and maximizing crop uptake.
To fully understand the transformation and movement of N in the environment, some knowledge of the N cycle is needed.
Nitrogen in the soil is commonly found in the form of organic N in the soil humus, ammonium , nitrate , or in a gaseous form.
Nitrogen in soil organic matter may be converted to the ammonium form
 The Colorado Legislature passed C.R.S.
25-8-205.5 in 1990, which established authority for the Agricultural Chemicals and Groundwater Protection Program.
The mandate of this program is: "to protect groundwater and the environment from impairment or degradation due to the improper use of agricultural chemicals while allowing for their proper and correct use".
The approach is to promote the voluntary adoption of Best Management Practices.
Voluntary adoption of BMPs by agricultural chemical users will help prevent contamination of water resources, improve public perception of the agricultural industry, and perhaps eliminate the need for regulation and mandatory controls.
BMPs are recommended methods, structures, or practices designed to prevent or reduce water pollution.
Implicit within the BMPs concept is a voluntary, sitespecific approach to water quality problems.
Development of BMPs in Colorado has been accomplished largely at the local level, with significant input from chemical applicators and other local experts.
Many of these methods are already standard practices, known to be both environmentally and economically beneficial.
Figure 1.
The nitrogen cycle in soils.
Nitrogen is dynamic in the soil environment and can exist in many forms.
by a biological process called mineralization.
The ammonium form is converted to nitrate by another biological process called nitrification.
Fertilizer N, whether organic or inorganic, is biologically transformed to nitrate, which is highly leachable.
The speed of this transformation is determined by soil temperature and moisture, but will eventually occur in any well-drained agricultural soil.
Plants will absorb and utilize both ammonium and nitrate.
Therefore, producers need to match N applications to crop uptake patterns to minimize nitrate leaching and maximize efficiency.
Nitrate in Colorado Groundwater
 Nitrate  is a naturally occurring form of N that is highly soluble in water and may cause health problems if ingested in large amounts.
A number of sources of nitrate exist, including manure, septic and municipal effluent, decomposing soil organic matter, and N fertilizer.
High nitrate levels in drinking water can cause methemoglobinemia, or
 "blue baby syndrome," a condition primarily seen in very young infants and farm animals.
Although reports of methemoglobinemia are extremely rare, the U.S.
EPA has established a safe drinking water standard of 10 parts per million  of nitratenitrogen for community drinking water supplies.
Colorado's highly varied geography, land use, geology, climate and soils make predicting nitrate contamination of groundwater difficult.
Therefore, the Agricultural Chemicals and Groundwater Protection Program  has sampled groundwater in Colorado since 1992.
As of December 2016, the Groundwater Program has collected over 3,600 samples from nearly 1,300 wells.
Most of these samples were collected in areas of the state with extensive irrigated agricultural production.
Wells in urban, suburban, and nonagricultural rural areas have also been sampled, but at a lower frequency.
The Groundwater Program samples wells that are used for domestic, livestock, and irrigation purposes, and wells that were installed
 Figure 2.
Groundwater nitrate detections in Colorado from monitoring conducted by the Groundwater Program.
Detections in yellow are nitrate at levels from 0.1 to 9.9 ppm nitrate-nitrogen.
Nitrate above the Maximum Contamination Level  are samples exceeding 10 ppm nitrate-nitrogen.
specifically for groundwater monitoring.
Groundwater Vulnerability to Nitrate Leaching
 Groundwater monitoring has also shown that there is significant variability in Colorado's groundwater with respect to nitrate concentration.
This variability is partially due to the extreme spatial differences in the application of N containing fertilizers, biosolids, and manures in Colorado and in the location and quantity of groundwater resources.
Thus, certain combinations of land use and hydrogeologic factors cause some areas to be more vulnerable to nitrate leaching than others.
Figure 3 was produced using five factors that influence aquifer vulnerability to nitrate on a regional scale: aquifer locations, depth to water, soil drainage class , land use, and recharge availability.
The validity of the map was checked using data similar to Figure 2.
Vulnerability is commonly described as the relative ease with which a contaminant can migrate to an aquifer under a given set of agronomic management practices and aquifer sensitivity
 Figure 3.
Vulnerability of Colorado's groundwater to nitrate contamination as mapped by Ceplecha, et al, 2004.
nature of these properties, applicators should determine the relative leaching hazard of each application site in order to select the appropriate BMPs.
conditions.
Areas where groundwater is less vulnerable to nitrate contamination may not require the same level of management as areas with high vulnerability.
Figure 3 shows these vulnerability differences and areas that may need higher levels of N management to prevent contamination of groundwater.
A quick comparison of Figures 2 and 3 shows that many of the areas mapped as highly vulnerable are also regions with significant nitrate contamination.
However, nitrate contamination can and has occurred in places where groundwater is not mapped as vulnerable and not all highly vulnerable groundwater is contaminated.
These discrepancies can be partially explained by the management of N fertilizer and manure, which is why it is important to assess leaching hazard at the field scale and adjust management practices accordingly.
Determining Field Scale Leaching Hazard
 Leaching potential of a given site depends upon soil properties, management, irrigation, and climatic factors.
Depth to groundwater and the overlying geologic material determine the contamination potential of an aquifer.
Due to the site-specific
 Leaching hazard can be ranked as severe, moderate, or slight by simultaneously considering soil characteristics, irrigation method, and aquifer vulnerability.
Those operators with sites that have a severe leaching potential and a shallow water table  should select appropriate BMPs to decrease leaching hazard.
Operators working Moderate High under moderate leaching conditions should assess what particular practices may cause future groundwater contamination and make the necessary changes to reduce any groundwater quality problems.
Operators with uncontaminated groundwater and slight leaching hazard should continue observing good management practices.
Table 1 can help operators evaluate the potential leaching hazard of their particular sites.
Information on the depth to the water table and water quality can be obtained through several sources, if not currently known.
All rural well owners are strongly encouraged to periodically have a water sample analyzed by a qualified laboratory.
The website provided on the previous page provides localized groundwater quality and depth in some cases, as well as the nitrate vulnerability map in Figure 3.
Experienced local well drillers also have knowledge of local groundwater conditions.
Agencies such as the Natural Resources Conservation Service , CSU Extension, and others can frequently provide information to help you evaluate groundwater vulnerability at your site.
In some cases, soil type and a shallow water table combine to create a very high leaching potential.
For example, if the soil at a given site is coarse
 Table 1.
Potential leaching hazard as predicted by soil type1 aquifer depth, and irrigation method *
 Aquifer Depth and Condition
 Irrigation method	Shallow or contaminated	Deep or	Aquifer properties
 Flood or	Coarse soil: Severe	Coarse soil: Moderate	Coarse soil: Severe
 conventional furrow	Fine soil: Moderate	Fine soil: Slight	Fine soil: Moderate
 with efficiency < 60%
 Sprinkler or	Coarse soil: Moderate	Coarse soil: Moderate	Coarse soil: Moderate
 surge furrow with	Fine soil: Slight	Fine soil: Slight	Fine soil: Slight
 Dryland or drip	Coarse soil: Moderate	Coarse soil: Slight	Coarse soil: Moderate
 irrigation	Fine soil: Slight	Fine soil: Slight	Fine soil: Slight
 Severe leaching hazard: Operators should implement all appropriate BMPs.
Moderate leaching hazard: Operators should evaluate fertilizer use and apply appropriate BMPs.
Slight leaching hazard: Operators should continue to use fertilizers according to recommendations and good management procedures.
1 Soil texture breakdown: Coarse soil is soil with > 35% sand and <30% clay including sand, loamy sand, sandy loam, sandy clay loam, or loam soil.
If greater than a third of the field contains these coarse-textured soils, the entire field should be considered coarse in this rating scale.
Fine-textured soil includes all soils not listed above.
2 Shallow groundwater is defined here as <25 feet below the soil surface.
Contaminated refers to aquifers yielding water with > 10 ppm nitrate-nitrogen or any detection of pesticide.
* For more detailed information about your site and soils, contact your local USDA Natural Resources Conservation Service office.
textured, and depth to the water table is less than 10 feet, it is recommended that shallow-rooted crops not be grown under conventional furrow irrigation.
Deeper rooted crops and higher efficiency irrigation methods are necessary for these conditions.
Nitrogen in Surface Water
 forms and attached to sediment and organic matter.
Reducing irrigation and precipitation induced runoff and sediment losses from fields can significantly reduce N movement and potential contamination concerns.
Nitrogen Management Practices to Protect Water Quality
 While soil, climatic, and geologic characteristics of the site strongly influence leaching potential, management practices ultimately determine the amount and extent of N leaching.
Proper nutrient management includes:
 Correct accounting for crop N needs according to a realistic yield goal; and
 applying appropriate inputs as determined by N budget  ; and
 applying N when  and where  it can be used most efficiently by the crop; and
 applying the right form of N fertilizer or organic source for the crop and soil conditions.
These practices will assure that residual soil NO is minimized.
The following management practices
 will help producers and fertilizer applicators maximize economic returns from fertilizer dollars while protecting water quality.
Soil testing is a very important BMP for determining plant nutrient needs.
Yearly sampling of each field is necessary to make accurate N fertilizer recommendations.
The key to good soil test results is proper sampling protocol.
Each sample should contain 12 to 20 cores of soil from a reasonably uniform area of approximately 40 acres.
Large fields should be broken into sampling units based upon crop, yield, and fertilizer histories.
Deep soil sampling for residual nitrate is requisite to precise fertilizer recommendations and provides producers season end information regarding crop N use and N remaining for next year's crop.
Depending upon crops, sampling to a depth of two to three feet is recommended for all soil types.
Setting realistic yield goals is also a very important BMP.
N Fertilizer recommendations are based upon a yield goal submitted by producers with their soil samples.
Overestimating yield goals results in excess N applications, leading to loss of farm income and potential groundwater contamination.
For example, applying enough fertilizer for a 200 bu/A corn crop, when other conditions such as limited irrigation water will only allow a 150 bu/A yield, can result in 60-70 Ib/A of excess N being applied.
Rather than project a yield goal, it is recommended that producers establish a yield expectation based upon historical yield averages.
Yield expectations must be established on a fieldby-field basis.
The five most recent yield averages for each field should represent an obtainable yield.
If a recent crop has been lost to hail or other disaster, that year's yield should be omitted from the average.
Colorado State University suggests that a producer add 5% to the five-year yield average and use this value as the yield expectation.
If the crop season and growing conditions appear to be above average, producers can adjust N rates upward at sidedressing or by applying N through irrigation water.
In-season soil or plant tissue analysis may
 Table 2.
Nitrogen credits for crop requirements
 Crop	lb N/A credit*
 Alfalfa	> 80% stand	100 140
 60 80% stand	60 100
 0 60% stand	0 60
 Sweet clover and red	80% of credit for alfalfa
 Manure	lb N/ton credit***
 Beef	10	5 (at 70% DM
 Dairy	15	7 12 
 Poultry	25	25 
 Swine	2 8 
 Sheep	5 10 
 Irrigation Water	2.7 X ppm NO3-N X AF
 *For the second year, use 1/2 of the first year N credit.
Sugar beets are included due to the incorporation of beet tops.
They are not a legume crop.
*** For the second and third years, use 1/2 and 1/4 of the first year N credits, respectively.
Dry matter.
****
 Calculation 1.
Irrigation water N credit
 Example: 30 inches of water applied containing 7 ppm NO-N 12 ppm NO3 N X 2.7 lb N/AF X 15 inches applied/A = 40.5 lb N/A 
 be used to determine if additional N is required.
The key to setting realistic yield expectations is to base them on actual field averages plus a modest increase for improved management and good growing conditions.
Chapter: 48 Corn Foliar Fungicides
 Foliar diseases can lead to premature leaf senescence, and predispose stalks to rotting, poor grain quality, and reduced yields.
Common fungal diseases found on corn include common rust, northern corn leaf blight, gray leaf spot, eye spot, anthracnose leaf blight, and Physoderma brown spot.
Management of foliar diseases involves managing the surface residue , selecting resistant hybrids, and performing in-season fungicide application.
Corn residue on the surface of the soil can increase certain foliar disease problems, such as gray leaf spot and northern corn leaf blight.
Although the severity of these diseases varies from year to year, application of foliar fungicides may provide effective control in years of high disease pressure.
The purpose of this chapter is to provide guidance on the use of fungicides.
Figure 48.1 Northern corn leaf blight symptoms on corn.
Fungicides are an effective in-season management tool for fungal leaf diseases, and sometimes can reduce chances of stalk rot development.
A number of fungicide products that are effective against fungal pathogens on corn are available for use.
However, some are more effective on certain pathogens than others.
Most of the fungicides available are preventive in nature and stop the fungus from infecting or advancing within the plant.
Therefore, timing of a fungicide treatment is critical.
If fungicides are applied when the severity is already high, the benefit will be limited.
When deciding whether to apply a foliar fungicide, consider the following:
 The level of disease.
Is there a significant amount of disease showing up on the leaves below the ear leaf?
The current weather.
For example, has it been warm and humid?
Does the forecast predict continued hot conditions?
If yes, disease severity may worsen, SO application is advised.
If no, disease outbreaks may not reach a critical stage and scouting should continue until corn has passed dent growth stage.
The corn growth stage.
How far along is the corn?
If corn is at R5 , diseases most likely will not
 influence yield or will be minimal.
Susceptibility of hybrid.
For example, most the hybrids have moderate resistance to common rust and therefore, no treatment may be needed.
Potential yield.
If yield is predicted to be low , chances of an economic gain due to fungicide treatment will be low.
Grain price.
When prices are high, it takes only a few bushels to pay for the cost of applying a fungicide.
Once a fungicide treatment is deemed to be necessary, growers should ensure the sprayer is calibrated to deliver the recommended rate , and that weather conditions are not too windy  or too hot.
Table 48.1 The number of corn bushels needed to break even for the cost of fungicide and its application.
Price of	Application cost 
 corn 	12.0	15.0	20.0	25.0	30.0	40.0	50.0
 1.5	8.0	10.0	13.3	16.7	20.0	26.7	33.3
 2.0	6.0	7.5	10.0	12.5	15.0	20.0	25.0
 3.0	4.0	5.0	6.7	8.3	10.0	13.3	16.7
 4.0	3.0	3.8	5.0	6.3	7.5	10.0	12.5
 5.0	2.4	3.0	4.0	5.0	6.0	8.0	10.0
 6.0	2.0	2.5	3.3	4.2	5.0	6.7	8.3
 7.0	1.7	2.1	2.9	3.6	4.3	5.7	7.1
 8.0	1.5	1.9	2.5	3.1	3.8	5.0	6.3
 9.0	1.3	1.7	2.2	2.8	3.3	4.4	5.6
 Proactive Fungicide Treatments Economic Benefit
 Several research studies have shown that when a fungicide is applied in the absence of disease or very low disease severity, the probability of increasing yield to pay for the treatment decreases significantly.
For example, Mueller and Wise  analyzed data from 613 treatment comparisons of strobilurin-treated and nontreated plots over a 10-year period in the Corn Belt region.
The fungicides were applied between V14 and R5  with a majority of treatments being applied between tasseling  and R2.
They reported that when disease severity was less than 5% on the ear leaf at the end grain fill period, the fungicide treatment increased yields 1.5 bu/acre, and when the disease severity was > 5% the yield gain averaged 9.6 bu/ acre.
These results suggest that there may be some benefit from proactive fungicide applications.
The yield enhancement has been linked to improved crop health  and reduced fungal populations.
However, these benefits must be balanced against the long-term risk of the fungal pathogens developing resistance.
Therefore, to avoid problems associated with unnecessary application of fungicides , growers should always scout to determine the need for a fungicide application.
Fungicide Efficacy for Control of Corn Diseases 2016
 The South Dakota State University Plant Pathology Extension is a member of the Corn Disease Working Group  and has participated in the fungicide efficacy trials.
The group has developed the following information on fungicide efficacy for management of major corn diseases in the United States.
Efficacy ratings for each fungicide listed in the table were determined by committee members field-testing the materials over multiple years and at multiple locations.
Efficacy ratings are based upon level of disease control achieved by product and are not necessarily reflective of yield increases obtained from product application.
Efficacy depends upon proper application timing, rate, and application method to achieve optimum effectiveness of the fungicide as determined by labeled instructions and overall level of disease in the field at the time of application.
Differences in efficacy among fungicide products were determined by direct comparisons among products in field tests and are based on a single application of the labeled rate as listed in Table 48.2.
Fungicide	 Class	ingredient	Active		Product/Trade	name	Rate/a		Anthracnose	leaf blight	Common	rust	spot	Eye	Gray	spot	leaf	Northern	blight	leaf	Southern	rust	Restriction2	Harvest
 22.9%	6.0-15.5	VG	E	VG	E	G	G	7 days
 Pyraclostrobin	23.6%	Headline 2.09	EC/SC	6.0-12.0	VG	E	E	E	VG	VG	7 days
 Picoxystrobin	SC	3.0-12.0	VG	VG-E	VG	F-VG	VG	G	7 days
 41.8%	Multiple	2.0-4.0	NL	VG	E	G	G	F-G	30 days
 41.0%	Proline 480 SC	5.7	U	VG	E	U	VG	G	14 days
 38.7%	Multiple	4.0-6.0	NL	U	NL	U	VG	F-G	36 days
 20.5%	ME	4.0-6.0	U	U	U	E	U	G	R3 
 2.2 SE	Quilt Xcel	10.5-	14.0	VG	VG-E	VG-E	E	VG	VG	30 days
 Azoxystrobin	0.83	A 4.0	7 days 
 13.5%	U	U	U	E	VG	E
 + Trivapro B	B 10.5	30 days 
 3.4-6.8	U	U	U	E	VG	G-VG	30 days
 4.0-6.0	U	U	U	E	VG-E	VG	R4 
 4.0-8.0	U	VG	U	VG	U	G	21 days
 Fungicide	 Class	ingredient	Active		Product/Trade	name	Rate/a		Anthracnose	leaf blight	Common	rust	spot	Eye	Gray	spot	leaf	Northern	blight	leaf	Southern	rust	Restriction2	Harvest
 Headline AMP	1.68 SC	10.0-	14.4	U	E	E	E	VG	G-VG	20 days
 4.18 SC	4.0-5.0	VG	E	VG	E	VG	G-VG	14 days
 Affiance 1.5 SC	14.0	U	U	U	U	U	G	7 days
 Additional fungicides are labeled for disease on corn, including contact fungicides such as chlorothalonil.
Certain fungicides may 1 be available for diseases not listed in the table, including Gibberella and Fusarium ear rot.
Applications of Proline 480 SC for use on ear rots requires a FIFRA Section 2 and is only approved for use in Illinois, Indiana, Iowa, Louisiana, Maryland, Michigan, Mississippi, North Dakota, Ohio, Pennsylvania, and Virginia.
2Harvest restrictions are listed for field corn harvested for grain.
Restrictions may vary for other types of corn , and corn for other uses such as forage or fodder.
Clean up vegetation: Around pivot point and well.
Make the space less inviting to rodents.
Effects of Irrigation on the Grc
 amounts and timing of applications influence lint grade and staple length
 J.
R.
Stockton and L.
D.
Doneen
 The following preliminary reports cover are not final but are an indication of tr proved irrigation practices in rela
 Studies on the irrigation of cottonthe relation of soil moisture to growth, physiological development, and yield of the plant-were started in 1954 at the U.
S.
Cotton Field Station at Shafter.
Changes in the variety of cotton grown, in cultural practices, and information on irrigation practice gained since the last extensive investigations on irrigation prompted the new studies.
The soil used in the tests is Hesperia sand loam of recent alluvial origin, well drained and alkali free.
At field capacity it will hold approximately 4" of available water in the surface 3'.
The soil was preirrigated in early March and the cotton planted April 7.
The temperature was above normal for April 1954, so the seeds germinated readily and there was rapid growth during the seedling stage.
The stand was approximately 39,000 plants per acre, The soil was moderately nematode infested, and it was soon evident they interfered with normal root development.
Much nematode injury occurred in the seedling stage, when the tap root had reached a depth of 8" to 10".
This usually resulted in the development of a
 branched system without a strong deep tap root and caused a retarded growth in depth early in the season.
However, as the season progressed, the plants showed an improved root development and extraction of available soil moisture to a depth of 3', with some moisture used from the 4' and 5' depths.
Water consumed by the plant was calculated from the soil moisture record.
When the plants were small and the temperature cool, moisture use was very small, only a few hundredths of an inch a day.
As the plants developed in sizewith increasingly warmer temperaturesthe rate of use increased to approximately 0.15" per day for June, 0.20" for the first part of July, and 0.30" or more in later July and through August, with a rapid decline in September.
The total use for treatments having a good vegetative growth was approximately 22" of water for the season.
The August temperatures in 1954 were below normal, and these moisture records may not reflect the consumptive use in a normal or warmer season.
In this first year's work, the main irrigation treatments-each consisting of
 Average plant heights from differential irrigation treatments, 1954.
Response of cotton to dry and to W growth
 four randomized plots-were identified as A, B, C, D, and E.
Some of the data collected from these irrigation treatments are given in the table in the first column on page 10.
Treatment C utilized the irrigation water most efficiently.
To the 26.2" applied, approximately 4" of available water from the preirrigation should be added.
The difference between the 22" consumptive use by the plant and that applied is the loss by deep percolation.
Most of this loss occurred in the early part of the growing season when the plants were small and had a limited root system.
Treatment A also used the water efficiently, but yields were reduced.
Treatments B, D, and E showed no signs of water stress, but Treatment Cprior to each irrigationshowed definite signs as evidenced by a distinct color change of the foliage and OCcasional transient wilting the afternoon before irrigation.
This observed color change in foliage is due primarily to the lack of new terminal growth.
Comparison of mature leaves from Treatment C with those of the wetter plots showed no difference in plant color.
The main irrigation these studies to : of frequency of in levels of soil ml sponse, yield and fiber were:
 A.
Under treatment ment-the test pk proximately two signs of water sin severe wilting prit
 B.
A wet treatment irrigated as frequi for July and Aug ered normal prod on light sandy soil todes.
C.
Irrigated at th for water.
This we tinch color change transient wilting
 D.
Irrigated prior and was intermed irrigation between
 E.
An extremely tain a very high in the root zone < ment was irrit every four days gust.
G.
A wet treatme week during Ju which was the season.
82.
The regular last irrigation f gust 31.
1.
A wet treatment week for July, with the last im September 27
 Concluded on page 10
 Continued from page 8
 The checking of new terminal growth -so-called change in color-appears to be the key to soil moisture stress because yields were not reduced.
If this approach can be developed to a practical application, it will integrate many factors of soil and climate, such as varying soil type, hardpans, claypans, nematodes, saline conditions, and varying seasonal temperatures.
The difference in yields for the four wetter treatments is small and is not statistically significant.
Even the slight checking in growth immediately before each irrigation-Treatment C-did not reduce yields.
The yields for the wettest
 next two periods of drought caused a wider discrepancy between A and the other treatments,
 Does not Include the preirrigation.
A	8	C	D	E
 irrigations*	3	12	7	10	21
 inches*	15.4	33.9	26.2	30.0	52.5
 bales/acre	2.15	2.97	2.90	2.92	2.81
 Trash, %	8.1	8.3	8.2	8.3	8.1
 ciency, %	93.9	95.1	94.0	95.6	95.3
 treatment-E-were slightly less than for Treatments B, C, and D, but not significantly so.
The only significant reduction in yield occurred in the dry Treatment A.
The plots were machine-picked on November 9.
The plants had been killed by frost and no chemical defoliant was used.
Under this condition there was no essential difference in per cent trash or in picker efficiency for any of the irrigation treatments.
The effect of these various irrigation practices on vegetative production for the growing season was obtained by measuring main stem height at periodic intervals.
The results of these measurements are given in the graph on page 8.
The vegetative height was in the same order as the increase in frequency of irrigation.
Treatment A produced the smallest plants.
At the first irrigation June 14, there was less growth than for the other treatments.
Although the plants grew rapidly after this irrigation, they did not recover the loss in growth due to the two weeks of water stress, and the
 Treatment C with temporary checking of growth before irrigations was not affected by the first two irrigations, but after the third on July 6, a difference between this treatment and the wetter ones began to appear.
The frequently irrigated Treatment E showed a marked increase in height which was also evident from a general observation of the plots.
As noted in the table in column 1, the yields did not follow the vegetative growth of the plant.
Final plant heights and weight of the stalks, leaves and cotton removed, are reported in the table in column 2 for each irrigation treatment.
The final plant heights are in agreement with those listed in the graph on page 8, but the weight of stalks does not follow this trend, especially the wet Treatment E, which produced the tallest plants but not the greatest weight.
From this data and observation of the plots, it would appear that the high soil moisture condition of Treatment E produces a tall, spindling plant but does not increase yield.
A study of leaf area and boll set in August was made for Treatments A, B,
 Vegetative Measurements of the Cotton Plant
 A	B	C	D	E
 inches	28.7	37.4	35.6	36.9	40.5
 tons per acre	1.17	1.89	1.86	1.98	1.88
 sq.
inches	8.7	9.5	10.1
 boll, sq.
inch	41.1	46.1	46.5
 and C, and the pertinent information is given in the last two items of the table in column 2.
The dry Treatment A had smaller leaves than either B or C, and the temporary checking of terminal growth did not affect leaf size.
The leaf area per boll was smaller on the dry Treatment A than for either of the other two treatments, indicating these smaller plants were very efficient in producing cotton.
Three treatments-G, B2, I-were used in a study of the effect of the timing of the last irrigation.
All treatments followed the irrigation schedule of Treatment B, which is considered normal
 Effect of Various Irrigation Frequencies on Cotton Fiber and Yarn Properties
 TREATMENT	E	8	D	C	A
 Irrigations	21	12	10	7	3
 Fiber Grade	M*	M*	M*	M'	SM
 Staple length, inches	1%3	1 1/8	1 1/8	11/2	1 1/42
 Yorn strength, lbs.
122	124	126	129	127
 Nep count	17	24	24	19	13
 Yorn appearance index	95	95	95	95	105
 practice for the area until the final irrigation.
The treatments and dates of the last irrigation are summarized in the table below.
The timing of the last irrigation had considerable effect on vegetative growth.
Slightly shorter plants were obtained with a smaller stalk weight for Treatment G, with the last on August 10.
A
 Results of Timing the Last Irrigation, 1954
 Date of last Irrigation	Aug.
Avg.
Sept.
Number of irrigations	9	12	15
 Water applied, inches	25.4	33.9	41.4
 Final plant height, inches	36.2	37.4	37.8
 per acre	1.58	1.89	2.16
 Yield lint, bales per acre	2.58	2.97	3.02
 Trash, %	6.8	8.3	8.8
 Picker efficiency, %	95.2	95.1	94.8
 large degree of natural defoliation or leaf fall occurred in this treatment.
Prolonging the irrigation schedule, as in Treatments B2 and especially I, gave a pronounced late growth and is reflected by the increase in weight of stalks.
Lint yields Significantly reduced for Treatment G, but no significant differences occurred between Treatments B2 and I.
Treatment G had a smaller trash content, probably a reflection of the natural defoliation.
Picker efficiency was lower for Treatment / and may have been influenced by the late vegetative growth and lodging of the plant.
In late September this lodging was quite serious and would have hampered an early machine picking.
The lodging, in part, was caused by delayed boll opening and excessive weight of green bolls and leaves.
Irrigation practice has been popularly associated with fiber quality.
Soil moisture and its availability during the period of development may influence many fiber properties such as length, strength, fineness, and maturity.
Since the cotton is bought on the basis of lint grade and staple length, these items will be of most interest, but the reputation that fiber from irrigated cotton makes at the spinning mills is most important in maintaining a good demand for western-grown cotton.
The effect of irrigation practices on fiber properties and spinning quality was evaluated by the following tests:
 Lint grade is based on the amounts of leaf trash and other impurities and on the color of the ginned cotton.
Staple length refers to the length of fibers in a sample of ginned cotton and may be influenced by certain environmental factors during the period of fiber elongation.
Yarn strength is a measure in pounds of the weight required to rupture a given size yarn.
Variation in yarn strength is closely associated with fiber strength, but
The Use of Technology in Mechanized Irrigation
 The development of electronic technology has impacted all of us.
It allows better communication, better access to information, and innumerable things that make our lives easier.
It is only natural that these new tools are being put to use to enhance the operation of irrigation equipment as well.
As in other applications this manifests itself primarily in two ways.
First, as a means to improve the ability to monitor and control equipment.
Second, as way to improve the performance and efficiency of the equipment itself.
Unlike most other farm equipment, irrigation systems typically operate unattended.
Most farming operations have multiple irrigation installations and often times these are distributed over a large area.
In the critical growing season timely management is very important.
Interrupted operation at a time of high crop stress can be costly.
Monitoring used to require an individual visual checking each system.
This required a lot of time and if a system failed just after being checked it would set idle until the next scheduled "drive by", wasting valuable time.
Satellite and cell phone networks are now available to us for communication with systems regardless of their accessibility.
Devices have been developed that are easily retrofitted to pivots in the field.
In their simplest form they can be used for monitoring the system only.
More sophisticated units add the ability to control at least the basic functions of the system.
Improved performance and efficiency
 To improve the efficiency with which water is applied it is often desirable to "program" a pivot or linear move system to alter its operation either by time of day or location in the field.
For instance half of a pivot might be planted to corn and the other half to soybeans, or the operator might want to irrigate only at night.
Early computerized control panels allowed these things to be accomplished but with a marked increase in the complexity of operation.
Alpha numeric displays manipulate by a key pad could be very confusing resulting in limiting the utilization of the systems capability.
Touch screen technology provides a much more intuitive and efficient operator interface.
Visual representation of the system as programmed is one facet.
Another is the ease of moving through several screens that provide direct feed back to the operator.
One of the main bits of information needed for effective management of an irrigation system and its functions is location.
For center pivots, several devices have been used to mechanically measure the angular location of the pivot center.
The accuracy and reliability of such devices is suspect because relatively small angle changes represent large displacement of the out end of a system.
A GPS device located on or near the end of a system provides the accuracy needed.
Crop water use will vary across the Panhandle due to variations in temperature and precipitation events.
Crop water use will assist growers with irrigation scheduling and efficient water use.
The other thing to keep in mind is expected rainfall through crop maturity.
While many parts of the state are dry, keep in mind the long-term average rainfall for this time of year as shown in Figures 1 and 2.
Operating pivots below the required regulator inlet pressure can lower pivot performance  and may result in overor under-irrigating.
It was expected that fields with a greater range in topography would be more likely to have a low pressure ; however, this was not observed.
It is also expected that center pivots with wells where the water table declines significantly through the growing season may be more likely to have low operating pressures.
Understanding Cotton Irrigation Requirements in Oklahoma
 Jason Warren Soil and Water Conservation Extension Specialist
 Seth Byrd Cotton Extension Specialist
 Saleh Taghvaeian Extension Specialist in Water Resources
 Making the most of available water is critical in modern production agriculture.
Crop physiologists and irrigation engineers use the term water use efficiency  to describe crop response to this critical resource.
In its simplest form, cotton WUE is the amount of lint produced per quantity of water and is typically expressed as pounds of lint per inch of water available to the crop, including rainfall, irrigation and stored soil moisture.
In contrast, irrigation water use efficiency refers to the lint produced per unit of irrigation water applied.
Irrigation WUE can vary widely as function of rainfall, soil water-holding capacity and irrigation system efficiency.
When salinity is not an issue, cotton responds well to moderate levels of deficit irrigation.
This can be defined as irrigating less than the full crop need, typically based on evapotranspiration models.
If a high efficiency delivery system is used, deficit irrigation can result in higher irrigation WUE with similar yields to those achieved when full evapotranspirational demand is met, if properly managed.
It should be noted that cotton yields are sensitive to heat unit availability.
Studies show that yield and
 WUE are negatively affected by reductions in heat units below the required thresholds.
Cotton Water Use Patterns
 Based on long-term Mesonet data from Altus, seasonal water use for adequately watered and otherwise healthy cotton is approximately 30 inches in southwestern Oklahoma.
Figure 1 illustrates the typical seasonal water use pattern for cotton produced for select locations in Oklahoma.
Cotton water use, also known as evapotranspiration , can be defined as the sum of evaporation and transpiration, and is both crop-species and growth-stage dependent.
Evaporation is water loss from plant and soil surfaces.
Transpiration means water taken up by roots and is transpired through the stomata in leaves.
From planting to square initiation , ET is generally less than 0.1 inch per day.
Plant water requirements are low due to the limited leaf area.
Most of the water used in transpiration is extracted from the top foot of soil.
The transpired amount of water from planting to square initiation is fairly small and most water loss during this period is due to evaporation.
ET increases to 0.1 to 0.3 inch per day during the square to early bloom stage.
Dur-
 Figure 1.
The 15-year  average rate of water use in relation to cotton development in Altus, Blackwell, Chickasha and Goodwell, based on long term data from the Mesonet Irrigation Planner.
ing this period, leaf canopy and roots develop rapidly, and transpiration exceeds evaporation.
Moisture extraction occurs mainly from the top 2 feet of soil, although the taproot and some feeder roots extend to deeper depths if unrestricted by soil depth, hard pans, plow pans, etc.
From early bloom to the opening of the first bolls , ET values of 0.25 to 0.35 inch per day are common.
At this stage, plants have reached their maximum leaf canopies and root densities.
Because the root system is fully developed, moisture can be extracted from deeper in the entire soil profile at this stage.
ET values may exceed 0.4 inch per day during the peak bloom period.
During extreme stress , crop ET values can be as high as 0.55 inch per day.
Following the opening of the first bolls until crop termination, ET generally declines from about 0.25 inch per day to as little as 0.1 inch per day.
Actual water use will vary with the condition of the plant, soil moisture status and general growing conditions.
Fruit production, retention and shedding are closely related to availability of soil moisture.
Production is optimized with an available moisture status that allows uninterrupted development of fruiting positions while avoiding excessive vegetative development on the one hand, or fruit shedding on the other.
Many producers believe it is appropriate to allow cotton to stress the plants before applying the first irrigation in order to slow vegetative growth, force root system expansion and enhance early fruit development.
While it is true that excessive soil moisture during this time can cause excess vegetative growth and limit root expansion, it is important not to limit water to a point of excessive stress.
In contrast, it is more accurate to say that it is best to challenge cotton to expand its root system, while providing adequate water under drought conditions to allow for adequate rates of growth and maturity development.
Research has shown that excessive stress prior to the first irrigation may reduce main-stem node development and result in fewer nodes above white flower at first bloom, which can ultimately reduce yield potential.
Severe moisture stress during the peak flowering period can have a pronounced negative effect on yield and fiber quality.
However, stress either early or late in the blooming period results in significant yield reductions.
Ideally, moisture stress should be avoided throughout the crop development period.
Early irrigations may be justified to maintain adequate, but not excessive vegetative growth.
Matching the lower water demand late in the season is key to achieve timely cutout and optimize fiber quality; i.e.
minimize the number of immature bolls present that contribute to low micronaire.
Micronaire is a measure of the air permeabilty of compressed cotton fibers.
It is often used as an indication of fiber fineness and maturity.
Irrigation application efficiency can be described as the amount, typically in percent, of water delivered by an irrigation system that contributes to transpiration of a crop.
Application
 efficiency for furrow typically ranges from 40 percent to 80 percent, center pivot sprinkler/spray ranges from 65 percent to 90 percent, center pivot low energy precision application  ranges from 85 percent to 95 percent and sub-surface drip ranges from 85 percent to 99 percent.
The theoretical goal is to be 100 percent efficient.
If using a spray system, make sure to use nozzle applicators that generate large droplet sizes.
This should help reduce evaporation losses during application.
Apply at least 1 inch per application, if it can be done without causing runoff.
Larger applications will increase the depth water infiltrates into the soil, which will decrease evaporation from the soil surface.
Be thoughtful not to over-apply and cause drainage.
The likelihood of drainage can be better estimated if an irrigation planner or soil moisture probes are used to estimate soil moisture status.
Evaporation replacement Tables 1 and 2 provide information concerning ET replacement for 60-acre and 120-acre center pivots with various pumping capacities and delivery efficiencies.
This analysis shows that an ET of 0.35 inch per day  will require 400 gallons per minute for a 60-acre pivot or 800 gallons per minute for a 120-acre pivot at 100 percent application efficiency.
In contrast, if the application efficiency is 85 percent, then the capacity required for 0.35 inch per day increases to 500 and 1,000 gallons per minute for the 60and 120-acre pivots.
These irrigation pumping system capacities will ensure sufficient water is supplied to the crop to maximize water use efficiency, regardless of rainfall.
However, these irrigation capacities assume that all of the water is supplied through irrigation.
Rainfall in southwest Oklahoma will generally supplement these irrigation requirements and reduce the irrigation capacity requirements to 200 and 400 gallons per minute for the 60and 120-acre pivots.
During periods of limited rainfall, high temperatures and wind; irrigation capacity requirements can dramatically increase, as illustrated by the irrigation capacities required when the maximum daily ET is 0.55 inch.
This was experienced in western Oklahoma in 2011.
In fact, maximum daily ET values as high as 0.58 inch were experienced with no rainfall leading to reduced crop performance with irrigation capacities that were sufficient in other years.
Irrigation water quality should not be overlooked.
High salinity water and/or saline soils can adversely affect crop performance.
If high salinity water is the sole source of water input for the crop, there is a high risk the crop will ultimately suffer.
These effects can vary with seasonal rainfall, soil type and soil salinity, however this discussion is beyond the scope of this fact sheet.
OSU Extension Fact Sheet PSS-2401, Classification of Irrigation Water Quality provides classification of irrigation water quality, describes how irrigation water quality is determined and the conditional use of low-quality water for various crops including cotton.
If you are concerned about water quality, contact the local county Extension office.
Educators can send a water sample in for analysis at the OSU Soil, Water and Forage Analytical Laboratory.
Table 1.
Amount of cotton evapotranspiration replacement for various 60-acre center pivot irrigation pumping capacities and delivery efficiencies.
Pumping capacity delivered to center pivot	Acre-In/acre/day	Irrigation application efficiency 
 at 100%	(Low elevation
 GPM	GPM/acre	Gal/day	Acre-ft/day Acre-in/day	efficiency		spray)	
 100	1.7	144,000	0.44	5.3	0.09	0.08	0.08	0.07
 200	3.3	288,000	0.88	10.6	0.18	0.17	0.15	0.13
 300	5.0	432,000	1.33	15.9	0.27	0.25	0.23	0.20
 400	6.7	576,000	1.77	21.2	0.35	0.34	0.30	0.27
 500	8.3	720,000	2.21	26.5	0.44	0.42	0.38	0.33
 600	10.0	864,000	2.65	31.8	0.53	0.50	0.45	0.40
 700	11.7	1,008,000	3.09	37.1	0.62	0.59	0.53	0.46
 800	13.3	1,152,000	3.53	42.4	0.71	0.67	0.60	0.53
 900	15.0	1,296,000	3.98	47.7	0.80	0.76	0.68	0.60
 1,000	16.7	1,440,000	4.42	53.0	0.88	0.84	0.75	0.66
 Table 2.
Amount of cotton evapotranspiration replacement for various 120-Acre center pivot irrigation pumping capacities and delivery efficiencies.
Pumping capacity delivered to center pivot	Acre-In/acre/day	Irrigation application efficiency 
 at 100%	(Low elevation
 GPM	GPM/acre	Gal/day	Acre-ft/day Acre-in/day	efficiency		spray)	
 100	0.8	144,000	0.44	5.3	0.04	0.04	0.04	0.03
 200	1.7	288,000	0.88	10.6	0.09	0.08	0.08	0.07
 300	2.5	432,000	1.33	15.9	0.13	0.13	0.11	0.10
 400	3.3	576,000	1.77	21.2	0.18	0.17	0.15	0.13
 500	4.2	720,000	2.21	26.5	0.22	0.21	0.19	0.17
 600	5.0	864,000	2.65	31.8	0.27	0.25	0.23	0.20
 700	5.8	1,008,000	3.09	37.1	0.31	0.29	0.26	0.23
 800	6.7	1,152,000	3.53	42.4	0.35	0.34	0.30	0.27
 900	7.5	1,296,000	3.98	47.7	0.40	0.38	0.34	0.30
 1,000	8.3	1,440,000	4.42	53.0	0.44	0.42	0.38	0.33
 The Oklahoma Cooperative Extension Service WE ARE OKLAHOMA
 The Cooperative Extension Service is the largest, most successful informal educational organization in the world.
It is a nationwide system funded and guided by a partnership of federal, state, and local governments that delivers information to help people help themselves through the land-grant university system.
Extension carries out programs in the broad categories of agriculture, natural resources and environment; family and consumer sciences; 4-H and other youth; and community resource development.
Extension staff members live and work among the people they serve to help stimulate and educate Americans to plan ahead and cope with their problems.
Some characteristics of the Cooperative Extension system are:
 The federal, state, and local governments cooperatively share in its financial support and program direction.
It is administered by the land-grant university as designated by the state legislature through an Extension director.
Extension programs are nonpolitical, objective, and research-based information.
It provides practical, problem-oriented education
 for people of all ages.
It is designated to take the knowledge of the university to those persons who do not or cannot participate in the formal classroom instruction of the university.
It utilizes research from university, government, and other sources to help people make their own decisions.
More than a million volunteers help multiply the impact of the Extension professional staff.
It dispenses no funds to the public.
It is not a regulatory agency, but it does inform people of regulations and of their options in meeting them.
Local programs are developed and carried out in full recognition of national problems and goals.
The Extension staff educates people through personal contacts, meetings, demonstrations, and the mass media.
Extension has the built-in flexibility to adjust its programs and subject matter to meet new needs.
Activities shift from year to year as citizen groups and Extension workers close to the problems advise changes.
EVALUATION OF MOBILE DRIP IRRIGATION  AND OTHER SPRINKLER PACKAGES
 The Ogallala aquifer has been a major driver of agriculture in the U.S.
High Plains for the past six decades.
However, this agricultural productivity led to the decline of the aquifer.
As a result of drastic aquifer drawdown, well capacities in some regions of the High Plains are no longer sufficient to sustainably irrigate crops.
Irrigators have converting their flood irrigation systems to a relatively more efficient center pivot systems  which has now become the most widely used system in Kansas.
However, there are still efforts to further improve irrigation efficiency by focusing on the different water application packages.
The producers are looking for visible proof as to which application packages are going to work for their particular location and cropping management.
These water application packages include new mobile drip irrigation , bubbler nozzle package and sprinkler nozzle package.
Evaluation of these application packages were based on the studies done on the research plots at KState Southwest Research-Extension Center and at select Water Technology Farms  in western Kansas.
WTFs are demonstration farms that allow the installation and testing of the latest irrigation technologies on a whole field scale.
K-State Research Extension  and Kansas Water Office, along with private and non-governmental entities, monitor and provide support to these WTFs.
Proceedings of the 31st Annual Central Plains Irrigation Conference, Kearney, NE Feb.
26-27, 2019 Available from CPIA, 760 N.
Thompson, Colby, Kansas
 Figure 1.
The location of the five research water technology farms in south central and southwest Kansas and the Northwest Kansas Technical College farms for workforce development.
The Garden City Co./Roth Farm and South of it is the T&O Farm in Finney County, the ILS Farm in Pawnee County, Circle C farm straddling Scott and Lane Counties, and Hatchers Farm in Seward County.
The concept of using driplines on center pivot  system is not new.
T-L Irrigation, Inc.
experimented with this idea in the early 2000s, calling it precision mobile drip irrigation.
However, based on the studies of Olson and Rogers , no yield differences between the PMDI and CP were found.
They associated the lack of discernible impact to the relatively wet years of the study and inherent high variability in the field caused by factors beyond the control of the investigators.
The MDI was developed with the concept of combining the high efficiency but expensive subsurface drip irrigation  technologies and the relatively low-cost simple operation and maintenance of center pivot irrigation technologies.
Although, MDI should increase irrigation efficiency, a previous study on a similar product found more negative management issues than positive efficiency advantages.
However, a recent study using new MDI product lines in corn reported no significant differences in yield between MDI and in-canopy spray nozzles but better soil water storage under MDI.
In addition to potential irrigation efficiency improvement with MDI, there is producer interest in MDI as a potential water application system to help alleviate wheel track rutting issues,  which in turn would reduce erosion and improve field conditions.
The Water Technology Farms
 T&O Farms, LLC in Finney County  consists of 10 sprinkler systems, four equipped with MDI, and four equipped with low pressure spray nozzles.
There are four circles planted to sorghum and alfalfa that are set-up as paired field comparison of MDI and spray nozzles.
Each field has a soil water sensor.
The systems are fully automated with water use, groundwater levels, moisture sensor data and weather station data tied to a real-time website.
Other notable set-up and technology in the farm includes
 sorghum seeding rate plots, application of soluble polyacrylamide on soybean and corn, circular planting and the use aerial imageries for thermal and plant health assessment.
The Garden City Company/Dwane Roth Farm in Finney County  north of Holcomb consists of a circle with multiple modes and spacing of water application packages on its four outer spans.
These application packages include MDI on 30and 60-in spacing, i-Wob spray nozzle, and bubbler on 30and 60-in spacing.
The farm is unique as the water source is both ground and surface water.
The circle is planted circle to corn managed with a precision soil zoning package, uses soil water sensors and has aerial imageries for thermal and plant health assessment.
The WaterPACK/ ILS Farm in Pawnee County  is comparing MDI with regular spray nozzles on a higher utilizing volume irrigation wells than those wells being studied in Finney County.
Two corn circles are involved with the spray nozzles planted in typical straight rows with the other field is planted in circle.
Irrigation scheduling using weather-based and soil water sensors was utilized at this farm.
The Hatcher Farm in Seward County  is made up of two fields that have had field mapping completed to identify management zones and locate where soil moisture probes were to be installed.
The farm utilizes soil moisture probes, aerial imagery, center pivot controllers, iWob nozzles, Bubbler nozzles, MZB soils map.
One pivot is the site of water application comparisons with different nozzle packages.
Another field has plant-based sensors being used to manage plant stress.
Aerial imagery is being collected to monitor the results and then evaluate the impacts of different water management strategies.
The Circle C Farm that straddles in the boundaries of Scott and Lane Counties  is comparing several technologies including EC soils mapping of all fields, soil moisture probes, variable rate irrigation, iWob and Bubbler nozzles, and aerial imagery.
The goal of the farm is to maintain production while increasing water use efficiency with the use of the technology together with cover crops.
Figure 2.
Location of the Water Technology Farms with different water application packages
 MDI, Bubbler and Spray Packages at SWREC Research Plots
 The yield data in 2016 at the SWREC plots showed that there was barely any difference between the MDI treatments, bubbler and sprays at the higher well capacities.
Interestingly, at the 600 gpm, spray seem to have a significant advantage with the MDI with 2gpm hose.
However, at the 150 gpm well capacity, the spray did show a significant disadvantage or yield penalty compare with the most of the other treatments.
Table 1.
Yield data for 2016 from the different application packages at the SWREC research plots.
on 125 ac	600	300	150
 Drip 2 gpm	245 b	271 a	243 ab
 Drip 1 gpm	294 ab	263 a	268 a
 Bubbler	275 ab	256 a	239 ab
 Spray	265 a	240 a	212 b
 Irrigation 	11	6	4
 MDI VS Spray at T&O Farms, LLC
 In 2016, the center pivots in the fields incurred substantial repair costs particularly related to wheels and wheel drive train.
The costs of these repairs were included in a partial budget analysis  for that year on four of the ten fields.
If one considers the profit above variable expenses, there is slight advantage in using the MDI  compared with spray nozzles.
However, if you consider the water use in the computation, then the profit per acre-inch per acre now becomes favorable for spray.
A couple of caveats on this data that this this the first year of the alfalfa and that this is only based on one year of data.
Table 2.
Partial budget analysis of fields with comparable systems at T&O Farm for the cropping year 2016
 Pivot Designation	NE20	SW20	SE20	NW20
 Technology	MDI	Spray	MDI	Spray
 Crop	Alfalfa	Alfalfa	Sorghum	Sorghum
 Acres	123	123	123	122
 Yield per Acre	2.97	3.13	140.04	145.25
 Price	$161.48	$161.48	$4.46	$4.46
 Gross Profit 	$479.19	$505.45	$624.58	$647.80
 Seed	$74.63	$96.59	$8.45	$9.00
 Herbicide	$13.18	$13.18	$60.68	$59.37
 Fertilizer	$25.06	$40.88	$77.69	$91.69
 Drive Train Repairs	$0.00	$3.86	$0.00	$12.88
 Variable Expenses	$112.87	$154.51	$146.82	$172.94
 Profit Above	$366.31	$350.94	$477.76	$474.86
 Water Use 	4.46	3.77	9.65	9.36
 Profit per ac-in/ac	$82.14	$93.10	$49.53	$50.71
 Yield per ac-in/ac	0.67	0.83	14.52	15.51
 Several Sprinkler Packages at The Garden City Company/Dwane Roth Farm
 The yield comparisons for the different sprinkler packages on this farm are presented in Figure 3.
It shows the hose has consistently had the lowest yield while the bubbler had consistently higher yields.
For some reason in 2018 the hose had a slightly higher population rate than over the other treatments.
The differences in each package did not show in the yield monitor of the combine harvester.
The producer claims that given no major differences in the packages, his preference may now be based on ease of use and management of these sprinkler packages.
Proceedings of the 31st Annual Central Plains Irrigation Conference, Kearney, NE Feb.
26-27, 2019 Available from CPIA, 760 N.
Thompson, Colby, Kansas
 Figure 3.
Two years of yield and plant population data under each sprinkler packages at The Garden City Company/Roth Farm.
MDI VS Spray at the WaterPACK/ ILS Farm
 The farm received a total of 17 inches of rainfall during the 2016 cropping season.
The total depth of irrigation they applied was 13.5 inches to the South field and 14.1 inches to the North field.
The yields from both fields and treatments were not significantly different  whose values ranged from 222 bu/ac in the South field and 235 bu/ac for the MDI in the North field.
The average yield from the tractor combine was 200 bu/ac for both fields.
In 2017 cropping season, a very similar yield results were observed, no significant differences.
The farm cooperators decided that on its last year of the project they would like to test the limits of the MDI.
They decided to reduce the application rates in the MDI by 20 and 30 percent while maintaining a full rate at the nozzle spray packages.
Table 2 summarizes the yield data and the water use efficiencies of each treatments in the farm.
With the reduction in the application rate, the MDI did suffer yield losses of about 20 bu/ac.
However, the water use efficiency was greater in the MDI compared with the spray considering that the MDI had as much as four inches difference compared with what the spray treatments applied.
Available from CPIA, 760 N.
Thompson, Colby, Kansas
 Figure 4.
Corn yields at the different treatments at the ILS farm.
Table 3.
Yield and water use data for 2018 cropping season at the ILS Farm.
FIELD	TREATMENT	YIELD	YIELD	IRRGN	WATER USE
 		APPLIED 	EFFICIENCY
 NORTH 16	ALL	234	244	13.1	18.62
 MDI 	243	9.8	24.8
 MDI 	237	11.2	21.2
 SPRAY 	249	259	14.0	18.5
 SOUTH 15	SPRAY	232	237	15.3	15.5
 Moving Plates, Fixed Plates and LEPA/Bubbler Packages at Hatcher Farm
 Hatcher farm was not interested about MDI but rather was interested at evaluating other different types of nozzle packages, namely I-Wob, Bubbler and Spray.
For the two years and two fields, the bubbler package did have the lowest yield and the fixed spray had the highest yield in most instances.
However, when the producer got the combine yield spatial data, there was a noticeable ring of higher yielding section in the field.
Upon further investigation, the ring is around the fourth span which a moving plate package and that the ring was very apparent around the southeast section of the field.
This section of the field has about 10% slope towards the southeast.
Based on field observation and this information, we think that the water applied from the third span with bubbler is running-off to the fourth span, thus the yield increase on the fourth span and the relatively low yield on bubblers.
Proceedings of the 31st Annual Central Plains Irrigation Conference, Kearney, NE Feb.
26-27,2019 Available from CPIA, 760 N.
Thompson, Colby, Kansas
 Figure 5.
Yield and plant population of corn in the different application packages at Hatcher's farm.
Figure 6.
Combine yield map at the eastern part of Hatcher's farm
 Moving Plates, Fixed Plates and LEPA/Bubbler Packages at Circle Farm
 The spray nozzle treatments in the Circle Farm have consistently been low in the last two years.
In 2017, there the difference was not significant.
However, in 2018 both the spray and iwob nozzle packages was significantly different from the bubbler.
Upon talking with the farmer, the yield map from the combine did not pick-up this difference.
Unlike the Hatcher's farm, the fields in Circle farm are very flat and we did not notice any movement of the water in all of the nozzle packages.
Figure 7.
Yield and population data for the different nozzle packages installed in Circle C farm.
There are many ways of improving the water use efficiency in irrigated fields.
This paper looked at the performance of some water application packages.
These are just preliminary data and analysis since we plan to look at the other parameters that may be affecting these yield differences and similarities.
In general, performance of the different application devices depends on several factors, one of which is the topography or slope, then the wetted area of the application.
Where there is in-field movement of water away from the target area, yields are usually suppressed.
But if the runoff is minimal, then the wetted area of application become more critical.
The less water lost through drift and canopy evaporation, the better is the performance of the nozzle package as reflected in the yields.
material support for this project.
The authors would also like to thank Mr.
Kent Shaw and Mr.
Bruce Niere for their help in implementing this project and for monitoring, data collection and processing.
Donors to the water technology farms: Kansas Water Office; United Sorghum Check-Off Program; Kansas Corn Commission; Seaman Crop Consulting, SW KS GMD No.
3; Kansas Department of Agriculture; Conestoga Energy Partners; Teeter Irrigation; MDI; Helena; Kansas Geological Survey; Ogallala Aquifer Program; Syngenta; Hortau; Servi-Tech Expanded Premium Services, LLC; Kansas Farm Bureau; KSU Mesonet; K-State Research and Extension; AquaSpy; Kansas Grain Sorghum Commission; Crop Metrics; Netafim; Valley Irrigation; Garden City Coop; American Irrigation; WaterPACK; Pioneer HiBred International; Western Irrigation Supply House and Ag Systems, Inc.; and Presley Solutions.
Leaves showing boron toxicity symptoms in soybean varieties: Clark, left, Chippewa, center, and Wayne, right.
Effects of Irrigation CHEMICAL In the
 TABLE 1.
CHEMICAL ANALYSES OF SOYBEAN LEAVES* FROM DIFFERENT LOCATIONS ON PLANTS SAMPLED JULY, 1966 
 on plant	8	No	CI	K	P
 ppm	%	%	%	%
 West Side Field Station
 Chippewa	Upper	175	0.11	0.21	1.96	0.26
 Lower	262	0.04	0.58	1.18	0.18
 Clark	Upper	129	0.10	0.36	2.20	0.26
 Lower	325	0.03	0.63	1.18	0.18
 Wayne	Upper	125	0.14	0.18	2.15	0.26
 Lower	300	0.07	0.31	0.88	0.18
 Chippewa	Upper	72	0.14	0.01	0.92	0.21
 Clark	Upper	75	0.05	0.04	1.70	0.22
 20 leaves per plot.
T RECENT CUTBACKS in acreage allotments in the San Joaquin Valley have caused cotton ranchers with interests in oil-processing facilities to recognize the need for a supplemental oil crop, such as soybeans, to allow continued use of the facilities at or near capacity.
Projected population increases in many parts of the world also indicate that a protein crop such as soybean could have increasing importance in meeting future food needs.
Review of early tests
 Results of earlier tests at Davis, where seed was sown in a mulch in pre-irrigated plots, showed that, whereas 10 irrigations increased lodging but not yield, four irrigations did not have these effects.
There were indications, however, that two properly spaced irrigations following preirrigation may produce reasonably good yields.
Tests were also conducted at Brawley, based on the number and timing of irrigations, with special attention to the tim-
 ing of the final irrigation.
Results there indicated that, while nine to 10 irrigations gave the highest yields at this location, an irrigation after the lower leaves began turning yellow , did not increase yield.
These tests also indicated that, whereas excessive irrigation should be avoided during the flowering period, severe moisture stress at that time would decrease yield.
Because soybeans appear to be sensitive to saline conditions, tests were also initiated at Brawley to study the salt tolerance of the plants.
It was found that some soybean varieties were more tolerant of salt than others.
Chemical analysis of plant parts from many soybean varieties showed that all plant roots contained about the same chloride concentration, but the stems and leaves of salt-tolerant varieties had much lower chloride concentrations than varieties susceptible to salt damage.
Soybean varieties were
 found to be salt-tolerant either in the germination stage, in the later growth stage, or in both.
Indications are that separate mechanisms may control tolerance or susceptibility during each stage.
Investigations were begun in 1966 at the West Side Field Station with the following objectives:  to determine the yield responses of three soybean varieties to three levels of irrigation, and  to study the effects of the irrigation treatments on the oil and protein content of the soybeans.
Seed of three soybean varieties, Chippewa, Clark, and Wayne, were inoculated and planted in pre-irrigated beds on May 26, 1966.
Three different irrigation treatments  were set up and readings were obtained from gypsum blocks located at the 18-inch soil depth.
Block readings corresponded to an estimated 2.2, 2.5, and 3.0 inches of total moisture per foot of soil at that depth at the start of irrigation treatments I1, I2,
 the San Joaquin Valley
 Clark soybean variety, left, and Wayne variety, right, in test plots during study of irrigation management in San Joaquin Valley,
 and I3, respectively.
The total moisture content of the soil at field capacity and at the permanent wilting point at this depth was calculated to be 4.0 and 2.0 inches, respectively, Gypsum blocks were also installed at the 36-inch soil depth in order to determine deeper soil moisture changes during the growing season.
Moisture block readings indicated that the Clark variety required more moisture than either of the other two soybean varieties.
The Clark soybeans also grew considerably taller and had a larger leaf area than the other varieties.
All varieties reduced the soil moisture content at the 36inch depth to a lower level under irrigation I1 than they did under irrigations I2 and I3.
Total inches of water applied in the 12-inch preplanting irrigation and subsequent irrigation treatments were: I1 = 17, I2 = 27, and I3 = 34 inches.
Treatment I consisted of one 5-inch irrigation; I2, three irrigations of 5, 4, and 6 inches; and I3, five irrigations of 5, 3, 5, 4, and 5
 inches, following the pre-planting irrigation.
Soybean yields  obtained from the irrigation treatments are shown in graph 3.
The Wayne variety appeared to be more responsive than Chippewa or Clark to the selected irrigation treatments in this study.
Good quality soybeans were obtained from all varieties with irrigation treatments I2 and I3.
Under irrigation treatment I1 the beans were shriveled and small.
Graphs 4 and 5 show the relationships between the irrigation treatments and pounds of protein and oil produced per acre for the three soybean varieties.
The Wayne variety produced considerably more protein and oil per acre than the other two varieties at the two higher irrigation levels.
Relationships between the irrigation treatments and percentage of protein and oil are shown in graphs 1 and 2 for the three soybean varieties.
Although seed yield of the Chippewa variety was generally lower than Wayne and Clark, it was
 somewhat higher in percentage of protein at all irrigation levels.
The percentage of oil was considerably lower for Clark than for Chippewa and Wayne at the more frequent irrigation levels.
Earlier reports have shown an inverse relationship between the oil and protein percentage in soybean seeds.
Now it appears that irrigation practices may influence this relationship.
Yields were apparently limited in this area by the moderately high amount of boron in the irrigation water and soil.
Previous work at the West Side Field Station  indicated that leaching reduces the concentration of this element in the soil, at least temporarily.
However, under conditions of this test, there was considerable damage to the lower  leaves due to boron accumulation by the plants.
Table 1 shows the chemical composition of soybean leaves from the upper and lower part of the plants sampled at the WSFS in July, 1966.
Chemical analy-
 ses of leaf samples showed that the boron  content ranged from 125 to 325 ppm.
Previous research suggests that these eoncentrations may be expected to reduce yields by as much as 25%.
Marked differences were observed in the boron as well as chlorine  content of the leaves at the WSFS when compared with those sampled at the Corcoran location.
Yields at Corcoran for the varieties Chippewa and Clark were 7 to 8 bushels per acre higher than at the WSFS.
The difference in plant concentrations of boron and perhaps chloride at the two locations may have been a big factor in the yield differences obtained.
Sodium , potassium , and phosphorus  contents of the leaves appeared to be at tolerable or satisfactory levels in the leaves analyzed, ex-
 Inches of water applied following 12" pre-irrigation
 Relationships of irrigation treatments with three soybean varieties on percentage of protein in soybean seed, graph above, and percentage of oil in soybean seed, below.
Inches of water following 12" pre-irrigation
 TABLE 2.
SOIL AND WATER ANALYSES FROM SOYBEAN EXPERIMENT AT THE WEST SIDE FIELD STATION IN 1966 Soil 
 depth	B	No	Ci	ECXIO
 0 to ft	1.1	5.8	1.2	0.86
 1 to ft	1.5	5.1	1.2	0.75
 2 to ft	1.4	5.8	1.6	0.81
 1.4	8.3	3.3	1250
 cept for the potassium content of Chippewa from Corcoran, which appeared to be low and was approaching a deficiency level.
Table 2 shows soil and water analysis at the WSFS in 1966.
The boron content of both the soil extract and the irrigation water were probably above the safe level for soybeans.
Soil and water analyses from the Corcoran location were not available.
The relationship between gross value per acre and irrigation treatments was similar to that found between yield and irrigation shown in graph 1.
With the higher levels of irrigation, the value from the increase in percentage of protein was more than enough to offset the decrease in percentage of oil, and accounted for more of the average gross value per acre.
However, considering the cost of well water at this location, the I2 irrigation treatment was the most profitable of the three treatments used in this study.
A wider range of irrigation treatments and fewer soybean varieties are being tested in the 1967 study.
Varietal plot size has been increased to facilitate harvesting with larger equipment.
Plant leaf samples are being collected during the growing season for chemical analyses, especially for boron and chlorine content.
RELATIONSHIP BETWEEN SOYBEAN YIELDS AND IRRIGATION TREATMENTS 
 Inches of water applied following 12" water as pre-irrigation
 RELATIONSHIP BETWEEN PROTEIN PER ACRE AND IRRIGATION TREATMENTS 
 Inches of water following 12" pre-irrigation
 RELATIONSHIP BETWEEN OIL PER ACRE AND IRRIGATION TREATMENTS 
A number of partnering technology companies, as well as seed dealer representatives, were on hand at the kickoff to visit with participants about the opportunities that they will have to use their products and platforms in the 2023 competition.
Irrigation season has wrapped up here in Nebraska.
Now is a good time to evaluate you center pivot to make sure it is ready for winter and for another growing season.
Here is a quick list of things to look at before winter sets in.
METHODS OF MEASURING FOR IRRIGATION SCHEDULING-WHEN
 Proper irrigation management requires that growers assess their irrigation needs by taking measurements of various physical parameters.
Some use sophisticated equipment while others use tried and true common sense approaches.
Whichever method used, each has merits and limitations.
In developing any irrigation management strategy, two questions are common: "When do Irrigate?" and "How much do I apply?" This bulletin deals with the WHEN.
One method commonly used to determine when to irrigate is to follow soil moisture depletion.
As a plant grows, it uses the water within the soil profile of its rootzone.
As the water is being used by the plants, the moisture in the soil reaches a level at which irrigation is required or the plant will experience stress.
If water is not applied, the plant will continue to use what little water is left until it finally uses all of the available water in the soil and dies.
When the soil profile is full of water, reaching what is called field capacity , the profile is said to be at 100% moisture content or at about 0.1 bars of tension.
Tension is a measurement of how tightly the soil particles hold onto water molecules in the soil: the tighter the hold, the higher the tension.
At FC, with a tension of only 0.1 bars, the water is not being held tightly and it is easy for plants to extract water from the soil.
As the water is depleted by the plants, the tension in the soil increases.
Figure 1 shows three typical curves for sand, clay and loam soils.
As Fig.
1 shows, the plants will use the water in the soil until the moisture level goes to the permanent wilting point.
Once the soil dries down to the PWP, plants can no longer extract water from the soil and the plants die.
Although there is still some moisture in the soil below the PWP, this water is held SO tightly by the soil particles that it cannot be extracted by the plant roots.
The PWP occurs at different moisture levels depending on the plant and soil type.
Some plants, which are adapted to arid conditions, can survive with very little moisture in the soil.
With most agronomic crops, PWP occurs when the tension in the soil is at 15 bars.
This means that the soil is holding on very tightly to the water in its pores.
In order for plants to use
 Figure 1.
A diagram of typical tension and water amounts for sand, clay and loam..
this water, they must create a suction greater than 15 bars.
For most commercial crops, this is not possible.
At 15 bars, most plants begin to die.
The difference between field capacity and PWP is called the plant available water.
Irrigation targets are usually set as a percent depletion of the PAW.
This depletion level is referred to as Management Allowable Depletion.
The bulk of irrigation research recommends irrigating row crops such as grain or cotton when the MAD approaches 50%.
For vegetable crops, the MAD is usually set at 40% or less, because they are more sensitive to water stress.
These defined amounts insure that water stress will not be SO severe as to cause any appreciable yield losses.
Careful monitoring of the PAW needs to be done throughout the season SO that the appropriate point of irrigation can be anticipated.
The following approaches can be used to determine soil moisture content.
Determining soil moisture by feeling the soil has been used for many years by researchers and growers alike.
By squeezing the soil between the thumb and forefinger or by
 squeezing the soil in the palm of a hand, a fairly accurate estimate of soil moisture can be determined.
It takes a bit of time and some experience, but it is a proven method.
Table 1 gives a description of "how the soil should feel" at certain soil moisture levels.
In this table soil moisture information is given using inches per foot.
This term  refers to how many inches of water are available in a foot of soil.
For example, looking at sand  we can see that the wilting point is about 1.0 in.
/ft.
This implies that sand holds one inch of water per foot of soil.
As the soil dries, it becomes harder to make a soil ball; soon the soil is crumbling in your fingers.
Irrigation should occur somewhere in the shaded area, earlier for crops sensitive to water stress.
Sandy loam soil makes a good ball at 0.6 in.
/ ft.
deficit  but will not make a ball at all and only sticks together at 1.0 in.
/ ft..
Once you become familiar with the feel of the soil, it becomes easier to estimate soil moisture content.
However, it takes time to become familiar with the feel of the soil and this method requires a great deal of experience.
Table 1.
Description of the soil texture parameters used to determine soil moisture using the feel method.
Moisture Deficiency	Coarse	Light	Medium	Fine	Moisture Deficiency
 Inches/ft					Inches/ft
 			
 0.0	Leaves a wet outline	Leaves wet outline on	Leaves wet outline on	hand; will ribbon out	0.0
 on hand when	hand; makes a short	hand; will ribbon out	about 2 inches
 squeezed	ribbon	about 1 inch
 Appears moist	Makes a hard ball
 0.4	Makes a weak ball	Forms a plastic ball,	Will slick and ribbon	0.4
 Slicks when rubbed	easily
 0.6	Sticks together	Makes a good ball.
Makes a thick ribbon	0.6
 0.8	Very dry; loose, flows	Makes a weak ball	Forms a hard ball	0.8
 Makes a good ball
 1.0	Wilting point	1.0
 Sticks together	Forms a good ball	Will ball but won't
 but will not ball	ribbon.
Small clods
 1.2	Forms a weak ball	1.2
 1.4	Wilting Point	Clods crumble	1.4
 1.8	A "Ball" is formed by	Wilting Point	1.8
 2.0	A "Ribbon" is formed	2.0
 2 The University of Arizona Cooperative Extension
 Figure 2.
Diagram of a neutron moisture gauge.
The neutron probe has been used extensively in research situations to determine soil moisture.
A neutron probe or neutron moisture gauge contains a radioactive source that sends out fast neutrons.
These fast neutrons are about the size of a hydrogen atom, a critical component of water.
When fast neutrons hit a hydrogen atom, they slow down.
A detector within the probe measures the rate of fast neutrons leaving and slow neutrons returning.
This ratio can then be used to estimate soil moisture content.
However, because every soil has some background hydrogen sources that are not related to water, calibration is important for each soil.
To measure soil moisture with a neutron probe, an access tube is installed into the ground.
Then, the probe  is lowered to the desired depth.
Probes are quite expensive , and because they contain radioactive material, require an operating license.
Another method that has been used for several years to determine soil moisture content is electrical resistance.
Devices such as gypsum blocks and Watermark sensors use electrical resistance to measure soil moisture.
The principle behind these devices is that moisture content can be determined by the resistance between two electrodes embedded in the soil.
The more water in the soil, the lower the resistance.
In the early stages of development, it was discovered that a salt bridge can form between the two electrodes, giving false readings.
Today, electrodes are embedded in more stable material and are not as susceptible to salt bridging.
The practical use of these devices is limited as they operate best in the high range of soil moisture.
To measure soil moisture, the blocks are buried in the ground at the desired depth, with wire leads to the soil surface.
A meter  is connected to the wire leads and a reading is taken.
Retrieval of these instruments is difficult in clay soils, but they are relatively inexpensive.
Figure 3.
Diagram of resistance blocks.
Here, three blocks are anchored by a stake in the field.
Figure 4.
Diagram of a tensiometer.
In some cases, the gauge is replaced with a connection for a transducer that measures suction.
As previously mentioned, as soil dries out, the soil particles retain the water with greater force.
Tensiometers measure how tightly the soil water is being held.
Most tensiometers have a porous or ceramic tip connected to a water column.
The tensiometers are installed to the desired depth.
As the soil dries, it begins to pull the water out of the water
 column through the ceramic cup, causing suction on the water column.
This force is then measured with a suction gauge.
Some newer models have replaced the suction gauge with an electronic transducer.
These electronic devices are usually more sensitive than the gauges.
Tensiometers work well in soils with high soil-water content, but tend to lose good soil contact when the soil becomes too dry.
Like the resistance blocks, they are difficult to remove from clay soils.
Costs range from $30 for small tensiometers with gauges to $2000 for the electronic meters.
New devices and methods become available to growers every year.
Two new techniques for soil moisture determination are instruments using Time-Domain Reflectometry  and Capacitance.
TDR instruments work on the principle that the presence of water in the soil affect the speed of an electromagnetic wave.
The TDR sends an electromagnetic wave through a guide  placed into the ground at the desired depth.
It then measures the time it takes the wave to travel down the guide and bounce back  up the guide.
The time is recorded and converted to a soil moisture reading.
The wetter the soil, the longer it takes for the electromagnetic wave to travel down the guide and reflect back.
C-Probes and FDRs use an AC oscillator to form a "tuned" circuit with the soil.
After inserting probes that are either parallel spikes or metal rings into the soil, a tuned circuit frequency is established.
This frequency changes depending on the soil moisture content.
Most models use an access tube installed in the ground.
TDR, FDR and C-Probes have all worked well, but have their limitations.
They read only a small volume of soil surrounding the guides or probes.
FDR and C-Probes are also sensitive to air gaps between the access tube and the soil.
Many of these newer instruments require professional installation to operate properly.
In soils where caliche and other hard pan layers exist, installing these probes may be difficult.
This type of problem is compounded when the soil is dry.
Cost for the probes range from $5,000-$10,000.
Also useful in determining WHEN to irrigate are plant indicators.
Plant indicators enable the grower to use the plant directly for clues as to when to irrigate, not an indirect parameter such as soil or evaporative demand.
Observing a plant characteristic can a good indication of the status of the soil's moisture content.
An infrared  thermometer measures the thermal temperature of the plant leaves or a crop canopy.
Similar to humans perspiring to keep cool, plants transpire through
 Figure 5.
Diagram of an infrared sensor.
This is a hand-held model.
openings called stomata.
Once plants go into water stress, they begin to close their stomata and cease to transpire, causing the plant to "heat up" and the canopy temperature to rise.
Infrared readings can detect this increase in plant temperature.
When using this method, baseline temperatures need to be taken prior to measurements.
The baseline temperature should be taken in a well-watered field, free of water stress.
On days when the air temperature is very high, some plants will stop transpiring for a brief period.
If infrared readings are being taken at that time, they may read that there is a water stress when, in fact, it is just a normal shutdown period.
Compare readings with the well-watered readings to make a decision.
IR also requires taking temperature readings on clear days at solar noon.
This normally occurs between noon and 2:00 p.m.
This is to assure that the measurement is taken at maximum solar intensity.
During the monsoon season, this may be difficult to achieve due to cloud cover.
Early in the season, IR readings will often measure soil temperature when canopy cover is sparse.
These readings usually result in higher temperature readings since the soil tends to heat up quickly.
Figure 5 is a diagram of a hand-held IR gun.
The use of computer programs to help schedule irrigation was introduced in the 1970's.
However, only recently with the introduction of fast, personal computers have they begun to gain wider acceptance.
Several methods can be used to determine crop water use and help growers schedule irrigation.
The most common is to use an equation to calculate the water use or evapotranspiration  for a reference crop and relate that to other crops.
ET refers to water loss from soil evaporation and plant transpiration.
In the beginning of a crop's growing season, the plants are small and most of the
 Table 2.
List of equations used to calculate reference ET..
RESIDUAL SOIL WATER IN WESTERN KANSAS AFTER CORN HARVEST
 Norman L.
Klocke Water Resources Engineer Kansas State University, 
 Water shortage is the primary factor limiting crop production in the USA's westcentral Great Plains, and agricultural sustainability depends on efficient use of water resources.
Precipitation is limited and sporadic with mean annual precipitation ranging from 16 to 20 inches across the region, which is only 6080% of the seasonal water use for corn.
Yields of dryland crops are limited and variable and some producers have used irrigation to mitigate these effects.
Continued declines within the Ogallala Aquifer will result in a further shift from fully irrigated to deficit or limited irrigation or even dryland production in some areas.
As this occurs, producers will desire to maintain crop production levels as great as possible while balancing crop production risks imposed by constraints on water available for production.
Efficient utilization of plant available soil water  reserves is important for both dryland and irrigated summer crop production systems.
In western Kansas, dryland grain sorghum yield was linearly related to PASW at emergence and sorghum yields increased 501 lbs/acre for each additional inch of PASW.
When the experimental effects of tillage were considered, grain sorghum yield response to water supply  was greater with no-tillage than with conventional tillage.
With conventional tillage at Bushland, Texas, grain sorghum yield increased 385 lbs/acre-inch of PASW at
 planting.
Evaporative demands increase from north to south  in the Great Plains and this can reduce overall yield response to water.
Precipitation increases from west to least in the Great Plains and in Kansas the average increase is approximately 1 inch for each 18 miles.
Research is needed to characterize the amounts of PASW available to producers in the spring before planting of summer crops.
The research results can be used to develop better cropping recommendations for producers based on their geographical location within western Kansas when used with information about their anticipated summer precipitation.
Preseason irrigation  is a common practice in central and southern sections of the western Great Plains on the deep soils with large water-holding capacity that are prevalent.
The residual soil water left in irrigated corn fields has a strong effect on the amount of preseason irrigation and precipitation that can be stored during the dormant period.
Although preseason irrigation is common, research has shown it is often an inefficient water management practice.
Measured water losses from marginal preseason irrigation capacities during the 30-45 day period prior to planting in a Texas study were extremely high, ranging from 45 to 70%.
While several reasons are given by producers for the use of preseason irrigation, Musick et al.
stated its primary purpose is to replenish soil water stored in the plant root zone.
From an analysis of soil water data from producer fields with silt loam soils near Colby, Kansas, Rogers and Lamm  concluded that irrigation above the amount required to bring soil water to 50% PASW water would have a high probability of being lost or wasted.
They found in a three-year study  of 82 different fields that on average producers were leaving residual PASW in the top 5 ft of the soil profile at 70% of field capacity.
Since that time, groundwater levels have continued to decline and more irrigation systems have marginal capacity.
Research is needed to both assess the current amounts of residual PASW producers are leaving in the field after irrigated corn harvest and how much PASW is replenished during the period before spring planting of the next corn crop.
The primary objectives of this project were to characterize the fall residual profile PASW after irrigated corn production and the PASW in dryland wheat stubble following the winter period and prior to dryland summer crop production in producer fields in three distinct regions of western Kansas [southwest , west central  and northwest ].
Secondary objectives were to characterize aspects of the overwinter precipitation storage for the two crop residues.
This paper will focus only on the irrigated corn fields.
A three year study  was conducted on the deep silt loam soils in western Kansas.
Fifteen fields from each of the three regions  were sought for each crop residue type  for sampling of PASW.
In general five fields of each residue type were selected in each county.
In a few cases, additional fields  were selected when it was deemed useful in gaining a better geographical distribution.
Another selection criterion for the irrigated corn fields was irrigation system capacity.
Attempts were made to find one or two fields in each county with capacities equivalent to less than 400, 400 to 600, and over 600 gpm for a 125 acre field.
++	Shermant	+	+	Thomas	+	*	Sheridan
 +	Greeley	+	+	Wichita	+	+	Scott	++	Lane
 + + +	+	+	+++
 +	+	+	+
 +	Stanton	+	+	+	#	Grant + +	Haskell	+	+
 Figure 1.
Geographical distribution of soil water measurements in producer fields in western Kansas, 2010.
Each symbol represents a GPS-referenced producer field.
Although a broad geographical representation was a primary desire , an attempt was made to select producers using good management practices and for which realistic weather conditions could be obtained from public sources.
Fields in NW Kansas were selected in Sheridan, Thomas and Sherman counties.
Fields in WC Kansas were selected in Scott, Wichita and Greeley counties.
There was increased difficulty finding producers with continuous  irrigated corn fields in WC Kansas, particularly in Wichita and Greeley Counties.
The Ogallala aquifer in this region of Kansas is more marginal and severely depleted, so producers appear to be using more crop rotation to utilize residual soil water better, thus conserving more aquifer water for future years.
Fields in SW Kansas were selected in Haskell, Grant and Stanton counties.
There were 96 total fields in 2010 fall sampling and 91 fields in 2011.
The GPS-referenced neutron access tubes  were installed in an equilateral triangular-shaped pattern.
Initial volumetric soil water content was determined in these fields after installation of tubes and again in late spring prior to summer crop initiation in one-foot increments to a depth of 8 feet.
Published soil type and soil characteristics were used to estimate PASW within the profile.
The data from the three sampling points was examined for uniformity between readings and to remove any anomalies.
A few tubes were lost due to damage by producer field operations between the fall and spring measurement periods.
Less than 1% of the data was lost due to measurement anomalies or damaged tubes.
As time progressed into the third year, fewer fields were available for fall sampling due to extreme drought in western Kansas because producers had changed plans mid-summer often relegating their crop for ensilage production and replanting to winter wheat.
In 2012, corn grain yields were obtained from 26 irrigated fields by hand harvesting a representative sample in the vicinity of the soil water sampling tubes  to observe how fall PASW was correlated with yield.
The analysis is still ongoing and some of the more complex interrelationships of producer practices with residual soil water have not been quantified or evaluated yet.
Although it should be noted that the results may vary widely from what may be occurring on your or other fields located within these counties, the soil water results may still be indicative of some of the irrigation capacities and practices, climatic, soil, and cropping conditions of these three distinct regions of western Kansas.
Weather conditions in nearly all of western Kansas were excessively dry from early August 2010 through mid-April of 2011.
The western portion of WC and NW Kansas began to get more normal precipitation in late April 2011 and ended
 the cropping season with normal amounts of precipitation or greater.
However, SW Kansas remained under severe drought conditions through the summer and much of the fall.
For example, Grant County received less than 30% of normal annual precipitation for the period September 1, 2010 through September 1, 2011.
In SW Kansas, dryland summer crops resulted in almost total failure and even many of the irrigated crops were severely stressed.
The western edge of WC Kansas  and for nearly all of NW Kansas experienced nearto above-normal precipitation for most of the summer period.
A particularly wet weather multi-day period in early October 2011 that tracked across some counties in WC Kansas and the eastern half of NW Kansas with those areas receiving between 2 and 4 inches of precipitation.
Because of the multi-day nature of this precipitation, much of the water infiltrated into the soil profile.
Exceptional drought conditions were generally the case for all of western Kansas in 2012.
Soil Water as Affected by Location
 It should be noted that in many cases in SW Kansas, some fall dormant season irrigation  had been practiced prior to the soil water measurements to facilitate easier strip tillage operations.
However, these dormant season irrigation amounts were relatively small, just being used to facilitate easier tillage.
The average PASW in irrigated corn fields for the three regions only varied about 1 inch  and with an average value of 10.30 inches/8ft would approximate a profile at 60% of field capacity, which would suggest overall adequate irrigation management.
However, there was a large amount of field to field variation.
The maximum PASW for the irrigated corn fields averaged nearly 16.4 inches/8ft which would be very wet unless there was considerable late season precipitation or fall dormant season irrigation.
At the other end of the spectrum, the minimum average PASW was approximately 4.3 inches, which would be only about 25% of field capacity.
In fall of 2011, because of the continuing drought in SW Kansas, it was anticipated that producer fields would be much drier than in 2010.
However, overall the irrigated corn fields were wetter  in 2011, with only SW Kansas having slightly drier irrigated fields in fall 2011.
The wetter summer period in portions of WC Kansas  and NW Kansas no doubt had some effects on the amounts of residual PASW.
The drought continued in western Kansas in 2012 and actually was more severe in NW and WC Kansas than in the southwest though it was only marginally better.
It should be noted that SW Kansas was still experiencing precipitation
 shortfalls that had been very severe in 2011.
On average, NW Kansas irrigated corn fields were the driest with a range of 5.95 to 16.86 inches/8 ft and an average of 10.16 inches/8 ft which would approximate a profile at 60% of field capacity, similar to 2010 values.
The average irrigated corn field PASW in SW Kansas was 12.12 inches/8 ft or approximately 70% of field capacity.
These difference may reflect the increased severity of the drought in NW Kansas or some early fall rains that occurred near harvest in SW Kansas
 Discussion of Annual Differences in Corn Residual PASW
 Although record or near-record drought conditions existed in southwest Kansas for the entire period from the middle of the summer of 2010 through the fall of 2011, there were only minimal differences in fall irrigated corn PASW for the 31 fields that were available for PASW measurements in both years.
Part of the rationale might be that drought conditions were similar between the two years.
However, the irrigated corn residual soil water is still relatively high on the average for SW Kansas.
So, the presence of severe drought may not be a good indicator of the amounts of residual soil water left after irrigated corn harvest.
Sometimes, crop damage is caused by system capacity  at the critical stages, rather than what irrigation amounts can be applied during the total season.
Insect damage such as spider mites is exacerbated by high canopy temperatures and drought.
Producers recognizing the drought and crop damage may continue to irrigate hoping to mitigate further crop damage and this sometimes increases profile PASW as the damaged crop is no longer transpiring typical amounts of water.
One caveat, in some cases the PASW results are probably reflecting the effects of some fall dormant season irrigation that occurred before the PASW sampling.
However, in most cases the fall irrigation amounts were not large.
There were a total of 21 irrigated corn fields in the region that were available for fall soil water sampling in all three years.
Generally, there was considerable similarity in the fall PASW for a particular field  with an overall difference for the 21 fields averaging 3.1 inches.
The similarity suggests that fall PASW for irrigated corn is much stronger related to the irrigation management conducted on a particular field than it is to weather conditions.
That management may either be reflecting the preference of the irrigator or the irrigation system capacity or a combination of both aspects.
Effect of Regional Characteristics on Corn Residual PASW
 Although intuition might suggest that less saturated thickness of the Ogallala and more marginal irrigation system capacities  would result in less residual PASW in the irrigated corn fields of WC Kansas, there was no strong evidence of that in the results averaged over 2010 through 2012.
This might be because producers with lower capacity irrigation systems have adjusted to their limitation by using longer pumping periods.
Their goal by pumping later into the crop season would be to minimize crop yield loss, but sometimes those later irrigation events also increase residual PASW.
Table 1.
Plant available soil water  in producer fields in western Kansas in fall 2010.
Residue Type	number of fields	Average	Maximum	Minimum	CV*
 Northwest Kansas, Sheridan, Thomas and Sherman Counties
 Irrigated Corn	Sheridan 	10.50	11.10	8.57	0.06
 Thomas 	10.79	15.55	6.76	0.22
 Sherman 	8.35	11.64	6.56	0.24
 All 3 Ctys 	9.99	15.55	6.56	0.24
 West Central Kansas, Scott, Wichita and Greeley Counties
 Irrigated Corn	Scott 	11.98	16.57	8.20	0.27
 Wichita 	9.31	11.78	6.54	0.20
 Greeley 	8.78	10.63	3.96	0.32
 All 3 Ctys 	10.02	16.57	3.96	0.29
 Southwest Kansas, Haskell, Grant and Stanton Counties
 Irrigated Corn	Haskell 	9.82	17.06	2.37	0.61
 Grant 	9.06	13.86	6.28	0.37
 Stanton 	13.83	16.71	11.50	0.14
 All 3 Ctys 	10.84	17.06	2.37	0.41
 * Coefficient of variation is defined as the standard deviation of PASW divided by the mean PASW.
Table 2.
Plant available soil water  in producer fields in western Kansas in fall 2011.
Residue Type	number of fields	Average	Maximum	Minimum	CV*
 Northwest Kansas, Sheridan, Thomas and Sherman Counties
 Irrigated Corn	Sheridan 	13.77	15.60	10.45	0.14
 Thomas 	13.07	16.86	8.94	0.22
 Sherman 	8.31	11.69	5.95	0.28
 All 3 Ctys 	11.85	16.86	5.95	0.28
 West Central Kansas, Scott, Wichita and Greeley Counties
 Irrigated Corn	Scott 	13.00	17.85	9.75	0.23
 Wichita 	12.59	14.21	10.74	0.11
 Greeley 	11.73	12.25	10.98	0.04
 All 3 Ctys 	12.46	17.85	9.75	0.16
 Southwest Kansas, Haskell, Grant and Stanton Counties
 Irrigated Corn	Haskell 	10.40	15.58	2.94	0.59
 Grant 	8.76	16.49	3.13	0.66
 Stanton 	11.11	14.30	8.65	0.20
 All 3 Ctys 	10.15	16.49	2.94	0.46
 * Coefficient of variation is defined as the standard deviation of PASW divided by the mean PASW.
Table 3.
Plant available soil water  in producer fields in western Kansas in fall 2012.
Residue Type	number of fields	Average	Maximum	Minimum	CV*
 Northwest Kansas, Sheridan, Thomas and Sherman Counties
 Irrigated Corn	Sheridan 	11.06	16.46	7.37	0.33
 Thomas 	10.29	16.56	7.18	0.33
 Sherman (3	8.11	11.97	4.40	0.47
 All 3 Ctys 	10.16	16.56	4.40	0.34
 West Central Kansas, Scott, Wichita and Greeley Counties
 Irrigated Corn	Scott 	12.55	16.06	10.02	0.25
 Wichita 	10.19	10.84	9.50	0.07
 Greeley 	7.92	10.86	5.94	0.33
 All 3 Ctys 	10.22	16.06	5.94	0.28
 Southwest Kansas, Haskell, Grant and Stanton Counties
 Irrigated Corn	Haskell 	12.32	19.45	5.11	0.54
 Grant 	13.06	19.10	5.14	0.55
 Stanton 	10.33	12.44	8.22	0.29
 All 3 Ctys 	12.12	19.45	5.11	0.46
 * Coefficient of variation is defined as the standard deviation of PASW divided by the mean PASW.
Fall 2010 PASW 
 Figure 2.
Similarity of plant available soil water  in the 8 ft soil profile in irrigated corn fields after harvest for the fall periods in 2010 and 2011 in western Kansas producer fields.
These data represent 31 fields that producers made available for PASW measurements in both years.
Figure 3.
Similarity of plant available soil water  in the 8 ft soil profile in irrigated corn fields after harvest for all three fall periods 2010 through 2012 in western Kansas producer fields.
These data represent 21 fields that producers made available for PASW measurements in all three years.
Effect of System Capacity on Fall PASW in Irrigated Corn Fields
 There were only small differences in PASW  as affected by low , medium  or high  irrigation system capacity  in 2011.
Further analysis of the effect of capacity on fall PASW will be done by incorporating more precise information about system capacity and also from information to be provided by the producers about actual aspects of their irrigation cropping season and irrigation schedule.
Corn Grain Yield as affected by Fall PASW
 Corn yields were related yields were related to fall PASW , increasing sharply up until approximately a PASW of 8 inches/8 ft.
and then plateauing at approximately 10 inches/8 ft..
This suggests that many of the irrigators have determined from experience that they cannot severely deplete soil water reserves without encountering corn grain yield reductions.
Figure 4.
Effect of western Kansas region on average, maximum and minimum measured plant available soil water  in the 8 ft soil profile in irrigated corn fields after harvest for the fall periods in 2010 and 2011.
Fall ASW 
 Figure 5.
Corn yield as related to fall 2012 PASW in western Kansas irrigated fields.
These results suggest a few very important aspects for irrigated crop production in western Kansas:
 1.
Irrigation not only increases the water available for crop production, but also reduces the variability in ASW in the field.
2.
Average PASW may not be indicative of an individual field, so it is wise to check your each field after harvest.
3.
Each year is different, so irrigating to average conditions is very risky and may be less profitable.
4.
Science-based irrigation scheduling can help to better manage your water resources in-season and between seasons.
Cost-sharing programs may be available to help individuals implement science-based irrigation scheduling.
This research was supported in part by the Ogallala Aquifer Program, a consortium between USDA Agricultural Research Service, Kansas State University, Texas AgriLife Research, Texas AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
Chapter 9: Crop Rotations Can Increase Corn Profitability and Reduce Pests
 This chapter provides a brief overview on how rotations can increase long-term sustainability and resilience against climate variability for South Dakota producers.
Crop rotation is a complex subject where biological factors, farm management resources, and market forces all interact to influence rotation effectiveness.
Crop rotations are long-term plans that improve sustainability and profitability.
A producer considering crop rotation should examine:
 Profitability, equipment, and labor availability.
Climate and market variability.
Short-term gains VS.
long-term sustainability.
The impact on weed, insect, and disease problems.
Pest resistance to various control mechanisms.
Matching crop production requirements with available resources.
Crop rotations are a foundational element of sustainability and long-term profitability.
For example, the introduction of the "Norfolk Rotation"  by Sir Charles Townshend in England played a large role in nearly tripling England's agriculture output in the 1700s in a sustainable manner.
This technology improvement provided food and the labor required for England's Industrial Revolution.
Opposite results can occur if the production systems adopt extractive rather than sustainable techniques.
For example, it is thought that the ancient inhabitants of Easter Island deforested their island leading to soil erosion, a loss of productivity, and societal collapse.
Although in a different environment, similar loss of soil resources occurred in the Mediterranean 1500 years ago.
One way to consider sustainable production systems is to look at natural systems as a model to mimic.
Natural systems tend to maximize resource capture and biomass production while minimizing nutrient loss.
Natural systems keep the soil covered and protect the soil from erosion.
As natural systems develop, they follow a "succession" process where one set of species modifies the environment to the benefit of the next set of species.
In a similar manner, a good rotation program should be productive, minimize nutrient loss, cover the soil, provide resilience against pests and stress, and each crop should benefit of the next crop.
Rotations should be adaptable to local conditions and challenges.
There are many factors that must be considered when designing a rotation.
Producers need to look at rotations as one tool for optimizing longterm profitability and reducing risk.
Achieving these goals is complicated, as one management practice may have negative implications on other practices.
For example, reducing tillage intensity without use of a sustainable rotation can increase the risk of plant diseases.
Table 9.1 Some corn diseases that can be influenced by rotations.
Disease	Pathogen and Environment	Inoculum source
 Goss's wilt	Clavibacter michiganensis ; associated with injury	Overwinters on residue; also some
 from violent weather ; favored by	grassy weeds act as alternate hosts;
 moderate temperatures, and can overwinter on some weeds.
moves with rain.
Gray Leaf Spot	Cercospora zeae-maydis ; favored by moderate to	Overwinters on residue; moves with
 warm temperatures and high humidity.
wind and rain.
Anthracnose leaf blight	Colletotrichum graminicola ; favored by warm	Overwinters on residue; moves with
 and stalk rot	termperatures and long periods of cloudy, humid weather.
wind and rain.
Eyespot	Kabatiella zeae ; favored by cool, wet weather.
Overwinters on residue; moves with
 Northern Corn Leaf	Exserohilum turcicum ; favored by moderate	Overwinters on residue; moves with
 Blight	temperatures and humid weather.
wind.
Rotations and Plant Diseases
 Rotation is a very valuable tool for breaking disease cycles, particularly in no-till and conservation tillage systems.
Crop residue acts as an inoculum source for many important diseases in corn.
Hence, rotations that use nonhost crops or resistant hybrids/varieties provide an opportunity for the residues to decompose, which should decrease pest risks.
Because certain pests persist in the soil, there are some diseases, such as seedling damping off  and root rots , that can be managed only by combining the rotation with other techniques.
Additional methods might include using appropriate seed treatments, delaying seeding, and installing tile drainage.
Rotations and Weed Management
 Rotation can have large impacts on weed pressure.
Rotations provide the opportunity to rotate the herbicide mode of action, which should reduce the risk of creating herbicide-resistant weeds.
A "stacked" rotation can be effective in reducing this risk.
In a stacked rotation, the same or very similar crops are grown two years in a row and then skipped for four or more years , allowing for the use of herbicides with long residuals in the first year of each crop while maintaining a long period  where the land is rotated to other crops.
Alfalfa can also be used for this purpose.
Similarly, an advantage can be gained by a rotation between warmand cool-season crops, where each cycle is held for two seasons .
Holding the given pattern for two years disrupts weed life cycles such that the weed seeds have to survive for three years
 Figure 9.1 Average weed density after 10 years of different sequences of warm-season  and coolseason  crops from three trials.
The lowest weed density was found where the warmand cool-season crops were each grown in two-year blocks two years of cool-season crops followed by two years of warmseason crops  
 before they get the opportunity to grow and multiply.
Rotation, Residue, and Nutrient Availability
 Corn produces more residue than either soybeans or small grains.
For example, a 150 bu/acre corn crop will produce about 8400 lbs reside/acre, whereas a 45 bu/acre soybean crop generates about 2500 lbs residue/acre, much of this being leaves which quickly decompose.
A 60 bu/acre wheat crop will produce about 3600 lbs residue/acre.
The large amount of residue from corn is an asset in building soil organic matter and protecting the soil from erosion.
If current climate projections, i.e., more intense storms, hold true , then the value of the residue becomes increasingly important.
However, large amounts of residue can also pose challenges in creating a "good" seedbed, controlling pests, and recycling nutrients.
The high level of corn residue is a concern for wheat because it acts as a host for the fungi Fusarium graminearum, which causes wheat head scab.
For this reason, it is not a good idea to follow a corn crop with a wheat crop.
Soybeans tend to tolerate high-residue situations better than many other crops.
The persistence of corn residue may slow nutrient recycling and the release of N from decaying stover.
Following corn with a legume crop such as soybeans can be used to overcome this problem.
The use of cover crops before and following corn is a topic that needs additional investigation.
Research at the SDSU Southeast Research Farm suggests that corn yields are higher following fall-planted, cool-season broadleaves  than grass-dominated cover crops.
Benefits of cover crops on corn yields is attributed to improved nutrient recycling and increased plant diversity.
Impacts on Yield in a Corn-Soybean System
 Studies in South Dakota, Minnesota, Wisconsin, and Nebraska have reported a 10% to 22% yield benefit for corn grown in rotation with soybeans versus a continuous corn cropping pattern .
Similar results were observed for soybeans where there was an 8% to 10% yield advantage when grown in rotation with corn rather than a continuous soybean rotation.
The rotational effect is attributed to many factors including enhanced root growth.
Crop rotations can impact profitability.
A 15-year Wisconsin study compared the corn-soybean rotation with continuous corn and rotations that contained oats and alfalfa.
This study reported that the corn-soybean rotation was more profitable than continuous corn and rotations that include oats and alfalfa.
While a corn-soybean rotation has been shown to be superior to continuous corn, it is still not a very diverse system.
In many fields, there is a corn yield decrease of about 5% to 15% for second-year corn relative to first-year corn.
The greatest yield reductions are typically measured between firstand second-year corn but can also be high when weather is unfavorable.
Yield reductions generally stabilize after the third-year corn.
Soybeans have similar responses and generally yield 5% to 8% more when following two or more years of corn.
Crookston et al.
conducted a 9-year study looking at corn and soybean yields in
 Figure 9.2 Average corn yields, at the end of six years, in three rotational sequences.
Even after just two cycles, yield differences were apparent.
Data shown are averages across three tillage regimes from the final year of the study.
These plots received 145 lbs/acre of N.
southwestern Minnesota.
They concluded that "a superior cropping sequence would include at least three crops and possibly more." Additional benefits from diverse rotations include reduced development of pest resistance, improved ability to manage variable weather conditions, and increased economic diversification.
Rotations and Water Use
 Rotations can be used to improve water management.
For example, rotations provide protection from summer droughts by distributing the critical water-use periods across the growing season.
Research conducted by the author shows that corn, wheat, and soybeans have different critical periods for water stress.
Wheat partially avoids drought-stress by flowering and completing its lifecycle earlier in the growing season than either corn or soybeans.
Soybean flowering is spread over several weeks SO that it can better avoid the effects of drought.
The corn crop, on the other hand, flowers and sets seed at one point in time and does this during the warmest part of the year, when evaporative demand  is at its peak.
High temperatures and drought stress can reduce corn kernel set by decreasing pollen viability and delaying silking.
By seeding hybrids of different maturities, the length of the pollination period for the farm can be expanded.
A worksheet for calculating agricultural intensity for different rotations is available at the South Dakota Lakes website.
This calculator can be used to determine water harvesting from the different crops in a rotation.
Along with water-use timing, crop rooting depth should be considered.
Crops with deep extensive root systems that grow late into the season  are likely to leave less reserve moisture than shallower-rooted, earlier maturing crops.
Cropping more frequently with high water-use crops increases the cropping system intensity.
Barley, winter wheat, field peas, and canola are low water-use crops, whereas corn, soybean, and alfalfa are high water-use crops.
When considering diversity, crop rotations can increase diversity and reduce problems with labor, equipment, disease, weeds, and insects.
Diversity assessments should consider the type of plant.
In South Dakota, commonly grown crops can be classified as:
 1.
Cool-season grass: spring wheat, winter wheat, barley, durum wheat, oat, and winter rye.
2.
Warm-season grass: corn, sorghum, sudangrass, and millet.
3.
Warmand cool-season broadleaf plants such as field pea, lentil, canola, mustard, crambe, flax, safflower, chickpea, sugar beet, sunflower, dry edible bean, soybean, and alfalfa.
When selecting a crop rotation it is important to avoid potential conflicts between the seeding and harvest times of different crops.
Rules of Thumb for Increasing Diversity in Semi-arid Regions
 1.
Use soil survey information to evaluate soil water storage.
Determine the appropriate cropping intensity based on this information.
2.
Manage crop residues to facilitate soil water storage.
3.
Manage crop nutrients to optimize yields while minimizing competition with weeds.
4.
Utilize legume crops and animal manure to increase energy efficiency and improve soil quality.
5.
Adopt techniques that minimize wind and water erosion.
6.
Anticipate equipment and/or labor requirements for growing new crops.
7.
Use cover crops to increase crop rotation intensity and diversity.
8.
Consider a perennial crop, such as grass or alfalfa.
They provide excellent weed suppression in a rotation, particularly if the crop following perennial plant is planted with minimal soil disturbance.
9.
Consider the marketability of the commodity prior to planting a crop.
10.
Avoid using crops with the same pests after each other.
For example, soybeans should not follow field peas.
Importance of Linking Tillage and Crop Rotations
 Crop rotation and tillage should be considered simultaneously.
Designing appropriate crop rotations is a mix of art and science.
For any given situation, there will be a range of rotations that are appropriate.
Within this range, there are rotations and tillage practices that reduce or increase risks.
Additional information on tillage systems is available in Chapter 11.
YIELDS AND ET OF DEFICIT TO FULLY IRRIGATED CANOLA AND CAMELINA
 Deficit irrigation applies less water than is required to meet full ET.
The goal is to manage irrigation timing such that the resulting water stress has less of a negative impact on grain yield.
Previous NE research on limited irrigation  has looked at a range of crops but not canola and camelina.
Currently, a program for managing limited irrigation water , enables producers to evaluate what crops to grow, how many acres to irrigate and how much water to apply during a given year, field by field.
However, this program did not include potential biofuel crops and deficit irrigation.
Over a fouryear period , University of Nebraska researchers, with funding from
 the USDA Risk Management Agency, conducted research to develop additional capabilities in Water Optimizer to expand its application to other crops and geographic areas.
The focus of this report is to present results related to irrigation and water use production functions that will provide additional management tools for predicting springplanted camelina and canola yields under limited and full irrigation for western NE.
Camelina  and Canola  were planted under linear irrigation systems at the Panhandle Research and Extension Center, Scottsbluff, NE  and the High Plains Ag Lab, Sidney, NE.
Canola was planted under a center pivot irrigation system on the Dan Laursen Farm, near Alliance, NE.
Camelina and canola were planted at rates of 3 and 5 pounds per acre , respectively.
Soils were: Scottsbluff  ~ 6 to 7 in); Alliance  ~ 5 to 6 in); and Sidney  ~ 9 to 11 in.).
Management and cultural practices for experimental plots were adapted from limited tillage/limited irrigation cropping systems and/or relevant research findings, including planting requirements, fertilization recommendations, herbicide/insecticide applications, and harvesting.
Roundup@-ready canola was used.
Plots were routinely scouted during the summer for insect problems.
Helix seed treatment was required for canola to protect against flea beetle but no other insects were a problem.
Because of the crop rotation there were no major insect problems in the other crops.
During the wetter years of 2009 and 2010, there was a downy mildew problem on both canola and camelina that was treated with fungicide.
Cumulative irrigation treatments had targeted amounts of 0, 4, 8 and 12 inches of water; however, if insufficient soil moisture or soil crusting was present, all treatments received light irrigations  to enhance and ensure uniform seed germination and plant emergence.
Treatments were replicated three times in a randomized complete block design and applied to subplots within main plots of each crop.
Irrigation was based on estimated crop use and/or critical growth stages.
Rain gauges were placed within plot areas to accurately record irrigation and rainfall amounts.
Soil water content from 0-6 inches was determined gravimetrically, while water contents at soil depths of 1, 2, 3, 4 and 5 feet were determined from neutron probe measurements.
Cumulative water use  was calculated from the water balance equation.
These calculations assume negligible rainfall and irrigation loss by deep percolation and runoff.
However, observed runoff losses, resulting from significant/intense rainfall events, were estimated from differences in neutron probe readings taken prior to and after such events.
Irrigation/seed yield production functions
 Rainfall at the different sites was drastically different over the four years.
This provided an excellent range of conditions from drought to above average precipitation to develop production functions.
Table 1.
Growing season precipitation.
Location	2007	2008	2009	2010	30 yr avg.
Alliance	5.7	6.6	___*	6.4	8.3
 Scottsbluff	2.6	5.3	12.4	9.3	8.0
 Sidney	10.5	7.5	15.1	9.6	8.6
 Irrigation versus seed yield production functions for camelina and canola are depicted in Figures 1 and 2, respectively.
Data for Sidney camelina  and canola  are not reported due to significant crop losses from downy mildew  and adverse harvesting conditions, respectively.
Data for Alliance canola  is not reported due to severe crop loss from hail.
Seed yield for both camelina  and canola  increased curvilinearly in response to increases in cumulative irrigation.
The data suggest that at least two  functions can be fitted to the data, herein referred to as upper and lower production functions.
In general, for both crops, location years associated with the upper production functions are characterized by relatively high amounts of precipitation and/or stored soil moisture during the growing season whereas years associated with the lower production functions are characterized by relatively low precipitation and/or stored soil moisture.
Seed yields for the upper and lower camelina production functions increased linearly, at the rate of 150-160 pounds per acre per inch of irrigation, until cumulative irrigation amounts of approximately 8 to 10 inches were applied, respectively.
Thereafter, the respective functions predict incremental seed yield increases of 50 to 70 and 80 to 100 pounds per acre for each additional inch of irrigation.
Maximum seed yields of 2390 and 2560 pounds per acre were produced at the respective maximums of cumulative irrigation water for each function.
Data for both camelina functions exhibit "plateaus" in seed yield at or near the respective maximums of cumulative irrigation water.
These "plateaus" are significant since they represent the cumulative irrigation water required to meet full evapotranspiration crop demand.
Based on water use data  and phenology data , these "plateaus" correspond to a total water use of 18 to 20 inches when stored soil water, rainfall and irrigation are considered.
Seed yields for the upper and lower canola functions increased linearly, at the rate of 200 to 220 pounds per acre per inch of irrigation, until cumulative irrigation amounts of 4 and 8 inches were applied, respectively.
Thereafter, corresponding incremental seed yield increases of 20 to 30 and 80 to 100 pounds per acre for each additional inch of irrigation are predicted.
Maximum seed yields of 2900 and 2930 pounds per acre were produced at the respective maximums of cumulative irrigation water for each function.
As with camelina, "plateaus" exhibited by both canola production functions indicate that full evapotranspiration crop demand was attained at or near the respective maximums of cumulative irrigation water.
Figure 4 shows these "plateaus" correspond to a total water use of 20 to 22 inches when stored soil water, rainfall and irrigation are considered.
Water Use/Seed Yield Production Functions
 Figures 3 and 4 present water use versus seed yield functions for camelina and canola, respectively.
Each function is described by a linear regression, the slope and x-intercept corresponds to a water use efficiency and threshold water use value.
The water use/seed yield production functions for camelina and canola predict water use efficiencies of 158 and 172 pounds of seed for each inch of cumulative water use, respectively.
In addition, the corresponding production functions predict threshold water use values of 4.8 and 4.9 inches or, in other words, approximately 5 inches of cumulative water would be required for any production of camelina or canola seed.
Camelina seed yields ranged from 520 to 2560 pounds per acre with 8.1 and 20.7 inches of cumulative water use, respectively.
On the other hand, canola seed yields ranged from 400 to 2930 pounds per acre with 6.5 and 22.9 inches of cumulative water use, respectively.
Nielsen  reported a water use/seed yield production function for canola that predicted a threshold water use of 6.2 inches and a water use efficiency of 175 pounds of seed per acre for each inch of water use.
These reported values were based on soil moisture contents to a depth of 65 inches and a maximum water use of 20.5 inches.
Growing Season Water Use
 The effect of the different irrigation levels was highlighted well for both canola and camelina during the 2008  season.
Figure 5 shows the effect of different irrigation levels on the extent and duration of crop ET as affected by
 water stress for camelina.
The true dryland treatments advanced through flowering and seed fill more rapidly than well-watered treatments  and the maximum water use varied considerably as did the time period of high water use.
Maximum water use approached values for corn during the hot and dry conditions of 2008.
Maturities were significantly different due to water effects.
In contrast, 2009 was an above average rainfall year and there was no significant difference between any of the irrigation levels for water use, crop development, maturity and yield.
Disease did limit yields even though fungicide was applied to control downy mildew.
Weekly water use was maximized near 1.7 inches per weeks versus a higher value in a dry year.
Camelina seed yields produced typical curvilinear responses to increasing irrigation.
In drier years the full irrigation requirement ranged from 11 to 13 inches whereas 6 to 8 inches of irrigation produced optimum yields in wetter years.
Maximum ET for fully irrigated camelina in dry years approached 2.4 inches per week for a total water use of 18-20 inches, when stored soil water, rainfall and irrigation are considered.
Maximum seed yields of 2300 to 2500 lbs/ac are attainable with current cultivars.
Non-irrigated yields ranged from 500 to 1200 lbs/acre.
Soil water was extracted from at least 4 feet.
Canola has a higher yield potential than camelina with maximum seed yields of 2900 to 3000 pounds per acre.
This is likely a result of more years of genetic improvement in canola versus camelina.
Non-irrigated yields ranged from 700 to 1900 lbs/acre.
In drier years the full irrigation requirement ranged from 11 to 13 inches whereas 6 to 8 inches of irrigation produced optimum yields in wetter years.
Maximum ET was similar to camelina, however, canola showed soil moisture extraction to at least the 5 foot level.
Both crops required a minimum of 5 inches of ET to produce the first pound of seed.
Our research did not show major differences in drought tolerance or water productivity (172 VS.
160 lbs/inch for canola VS.
camelina.) Both crops need sufficient soil moisture for germination and stand establishment.
Stress during the reproductive stage can significantly reduce yield.
Data suggest that spring camelina and canola would be suitable crops for biofuel production with limited water supplies in the northern High Plains.
Council for Agricultural Science and Technology.
2008.
Convergence of Agriculture and Energy: III.
Considerations in Biodiesel Production.
CAST Commentary QTA2008-2.
CAST, Ames, lowa.
Settling Basins for Trickle Irrigation in Florida
 Dorota Z.
Haman and Fedro S.
Zazueta
 Trickle irrigation systems deliver water, nutrients and other chemicals at low rates and high frequency directly to the root zone of the plant.
Water is distributed through an extensive network of pipes and delivered in the form of drops, tiny streams, or miniature sprays by emitters.
Well-managed trickle irrigation systems result in water and nutrient savings due to application of water into or near the root zone, and energy savings due to low operating pressure.
However, trickle irrigation systems usually require a higher level of management than other irrigation systems.
Water quality is a major concern in the management of trickle irrigation systems.
The potential for the emitters to become plugged by physical, chemical or biological contaminants creates significant problems to be addressed in everyday maintenance.
By far, the most common problem is blockage of the emitter passage by solid particles in the irrigation water.
therefore, effective and reliable water treatment is mandatory for the successful operation of trickle irrigation systems.
Generally, groundwater requires less treatment and causes fewer clogging problems for trickle irrigation systems than surface water.
However, groundwater containing high levels of iron and sulfur, which is often the case here in Florida, can cause bacterial growth and severe clogging problems if the water is not properly treated.
Often, the most economical source of irrigation water is from a river, canal, stream, or irrigation ditch.
Water from
 these sources the greatest potential for clogging problems, due to the organic contaminants that are usually present.
Nevertheless, if organic growth can be eliminated and all debris filtered out, surface water can be successfully used for trickle irrigation.
Settling basins can provide an effective and economical solution for two water treatment problems:  high levels of turbulence  in surface waters, and  high levels of dissolved iron in groundwaters.
A settling basin can serve as the primary filtration unit, increasing the efficiency of secondary filters in the irrigation system and decreasing the frequency of required filter cleanings.
However, settling basins should not be used unless one of these problems is present, since a basin can easily introduce other problems, particularly if the water supply is from a well.
The basin can catch windblown contaminants, and algal growth in the pool may create greater filtration problems than those caused by sand and silt from the well.
Frequent chemical treatment of the basin water and media filtration may be necessary to remove this organic contamination.
Settling basins can remove suspended inorganic particles ranging from sand  to silt , depending on basic design.
The finer sediments
 2.
Dorota A.
Haman, assistant professor; and Fedro S.
Zazueta, assistant professor; Department of Agricultural Engineering; UF/IFAS Extension, Gainesville, FL 32611.
require longer settling times and, hence, longer water transit times through the basin.
The size of the basin is a function of the flow rate of water that must be treated, the size of the sediments in the water, and the water quality required at the outlet.
It is usually not practical to remove small silt and clay particles , unless they are flocculated using alum and/or polyelectrolites.
Without chemical coagulation, the sedimentation time required is extremely long.
These particles are small enough not to cause any problem, and chemical treatment may be too costly for an irrigation system.
For a trickle irrigation system, it is generally assumed that the smallest particles that need to be removed have equivalent diameters of 75 microns, which corresponds to 200-mesh filtration.
Particles of this size can be satisfactorily removed in a well-designed settling basin.
However, a screen filter at the entrance to the irrigation system is also recommended as a safety device to filter any debris picked up by the pump.
Sedimentation is the removal of suspended particles that are heavier than water by gravitational settling.
Where sedimentation employs only the natural force of gravity and natural particle aggregation, it is called plain sedimentation.
Plain sedimentation includes two types of processes.
One type is called free settling, a process by which relatively large particles such as sand and silt settle individually.
This usually happens in suspensions with low concentrations of solids and where particles are large.
The other type of settling is preceded by natural flocculation of the particles, which forms aggregated, larger particles that can settle faster due to their increased mass.
An example of this type of sedimentation is the oxidation and flocculation of iron.
When chemicals or other substances are added to induce aggregation and settling of fine suspended particles, the process is called coagulation.
The most common coagulants used are alum, sodium aluminate, ammonium alum, copperas , ferric sulfate and pulverized limestone.
Coagulation can be expensive and uneconomical for irrigation purposes.
Determination of Settling Velocity
 When discrete, nonflocculating particles such as sand and larger particles of silt are settling due to the force of gravity
 , sedimentation velocity can be determined from Stokes' law.
The velocity of sedimentation depends upon particle size, shape and density.
Settling velocity of spherical, smooth and rigid particle varies with the square of its diameter according to Equation 1: For inorganic soil particles, SG is typically taken as 2.6, the specific gravity of quartz.
Equation 1 assumes that the settling particle is spherical, smooth and rigid, which is hardly true of typical soil particles.
However, the concept of particle equivalent diameter allows use of Equation 1 to estimate the settling velocity of soil particles.
A particle's equivalent diameter is the diameter of a sphere made from the same material, which would fall with the same velocity as the particle of interest.
Frequently, a plate-shaped soil particle will be larger than its equivalent diameter.
Figure 1 gives settling velocities for different particle sizes.
From this graph it can be found that the settling velocity for 75-micron particles is 12.7 inches per minute.
Note, however, that the actual size of 75-micron equivalent diameter particles may be larger than 75 microns.
Vp = 0.00135 X d2 X  where : Vp = settling velocity of particles in water  d = particle diameter  SG = specific gravity of particle
 Figure 1.
Graphical representation of Stokes' law for a particle with specific gravity  2.67.
Where natural flocculation occurs, the settling velocity of the aggregated particles must be measured in a settling column under laboratory conditions before a settling basins can be designed.
It is difficult to estimate this velocity theoretically, since the extent of flocculation depends on empirical factors such as particle shape and surface geometry, the range of particle sizes present in the water, velocity gradients in the system, and the depth of the basin.
ensure that this condition is met.
In practice, the minimum required detention time for the particles to be removed for irrigation purposes is so short, that the basin depth can be selected to suit topography or other convenience considerations.
Area = 1.604 X  where: Area = surface area of settling basin  Vp = settling velocity of design particle size 
 The surface area required for a settling basin is determined from the calculated settling velocity and the water inflow rate, or according to Equation 2: The settling basin length should be approximately five times its width.
Where construction area is limited, a U-shape design may be recommended.
If cross sections of the settling basin are trapezoidal, the mean width and mean length should be considered in the design.
Whenever the basin length  equals five times the width , they may each be determined from the area as shown in Equation 3: The time required for a unit of water to flow through the settling basin is called the detention time.
This time should be long enough SO that all particles of the chosen size will settle at the bottom of the basin.
The basin depth  and detention time  are related to the design settling velocity of the chosen particle size  according to Equation 4: It is the ratio of basin depth to detention time that is important, not just basin depth or detention time alone.
Theoretically, as long as the ratio of basin depth to detention time is less than or equal to the settling velocity, the basin will operate properly.
Sizing the basin according to equation  or equation  will
 The height of the laboratory settling column should be equal to the depth of the proposed settling basin, since the depth of the basin will influence the extent of flocculation and, as a result, the settling time.
The diameter of the settling column does not influence settling velocity, SO a column of any diameter can be used.
It is important that at the beginning of the experiment the number and sizes of suspended particles are uniformly distributed from the top to the bottom of the column.
The particle settling velocity is calculated by dividing the settling distance by the time required to obtain clean water in the column.
Area W = and L = 5.0 X W where: L = basin length W = width
 The first step in the design of a settling basin is to decide what size particles should be removed from the irrigation water to prevent the emitters from clogging.
Assuming that Stokes' law holds for the suspended material, the settling velocity of the chosen particle can be easily determined from Equation 1.
where: D = basin depth  t = detention time  Vp = settling velocity of design particle size 
 Area = 1.604 where: Area = surface area of settling basin  F = storage or safety factor  Q = flow rate  Vp = settling velocity of design particle size 
 As sediment accumulates on the bottom of the basin, the depth decreases.
Therefore, an allowance must be made for sediment storage in the design.
The minimum amount of storage required will depend on how much sediment is carried by the water and on how often the basin is cleaned.
Storage and other factors-such as turbulence at the inlet to and from the outlet to the basin, and differences in velocities of water in various parts of the basin are usually
 included in the storage factor F , which results in the overdesign of the basin to make sure that the desired particles will be removed.
A value of F = 2 is often used.
With this safety factor, Equation 2 will have the form as shown in Equation 5:
 outlet should be below the water surface to avoid floating contaminants.
If the water level in the basin can fluctuate, the best solution is a floating type of entrance.
In a basin where an irrigation pump is used at the outlet, the pumping levels should be controlled by floats.
In the case of continuous operation, the rate of pumping must not exceed the rate of production of clean water.
The turbulence effects of the inlet and outlet are included in the safety factor F.
Figure 3.
Relative locations of settling basin inlet and outlet.
First, organize all necessary design parameters:
 A settling basin will require periodic sediment removal.
The frequency of cleaning will depend on the amount of suspended solids in the water and on the F factor which was assumed in basin design.
A large F value allows for more sediment and less frequent cleaning of the basin.
1.
The flow rate into the settling basin  is 900 gpm.
This is also the rate at which clean water will be produced.
Example-Design of a Typical Settling Basin
 An irrigation ditch with a high load of suspended mineral particles  will be used in this example of a design of a typical settling basin for a trickle irrigation system.
The system requires 900 gpm, and all soil particles larger than 75 microns  should be removed in the basin during sedimentation.
The basin will have trapezoidal cross sections and a depth of 24 inches.
The safety factor  is assumed to be 2.0.
The inlet to a settling basin should minimize entrance velocities, create very little turbulence, and distribute water across the basin as uniformly as possible.
Diffusion structures or baffles  are usually used for this purpose at the entrance.
The most important consideration for the outlet is its position.
Water should be removed high enough above the bottom to be free of sediments.
At the same time, the
 Figure 2.
Disign drawing for a settling basin with trapezoidal cross sections.
Basin Inlet and Outlet
 2.
The design settling velocity for the smallest particle to be removed  is 12.7 inches per minute.
Remember that this is the settling velocity for the equivalent diameter, and it is likely that not all particles larger than 75 microns will be removed.
3.
A storage factor  F of 2.0 is assumed.
This safety factor should be adequate to allow particles which are larger than 75 microns but have equivalent diameter smaller than 75 microns to settle.
4.
The depth of the basin will be 24 inches, or 2 feet.
Second, use Equation 5 to calculate the mean surface area of the settling basin as shown in Equation 6.
Area = 1.604 Area 1.604 2.0 X 12.7 900 = X Area = 227 ft2 where : Area = surface area of settling basin  Q = flow rate  Vp = settling velocity of design particle size 
 Third, using the mean surface area in square feet  and mean width  from Equation 3 as shown in Equation 7.
Finally, using Equation 4, the calculated detention time is approximately 1.9 minutes for a settling velocity of 12.7 inches per minute and the selected depth of 2 feet.
This is the time required to allow proper sedimentation of the particles in this basin.
Actual detention time in this basin is almost 4 minutes, due to the safety factor used in Equation 5.
The design drawing of the basin is presented in Figure 2.
This is the minimum basin size with a safety factor of F = 2.
A larger basin will have an improved efficiency or a larger safety factor.
Fig.
1.
Relationship between winter wheat grain yield and available soil water at wheat planting at Akron, CO.
FACTORS AFFECTING WATER STORAGE
 Time of Year/Soil Water Content The amount of precipitation that finally is stored in the soil is determined by the precipitation storage efficiency.
PSE can vary with time of year and the
 water content of the soil surface.
During the summer months air temperature is very warm, with evaporation of precipitation occurring quickly before the water can move below the soil surface.
Farahani et al.
showed that precipitation storage efficiency during the 2 1/2 months  following wheat harvest averaged 9%, and increased to 66% over the fall, winter, and spring period .
The higher PSE during the fall, winter, and spring is due to cooler temperatures, shorter days, and snow catch by crop residue.
From May 1 to Sept 15, the second summerfallow period, precipitation storage efficiency averaged -13% as water that had been previously stored was actually lost from the soil.
The soil surface is wetter during the second summerfallow period, slowing infiltration rate, and increasing the potential for water loss by evaporation.
Fig.
2.
Precipitation Storage Efficiency  variability with time of year.
Residue Mass and Orientation
 Studies conducted in Sidney, MT, Akron, CO, and North Platte, NE  demonstrated the effect of increasing amount of wheat residue on the precipitation storage efficiency over the 14-month fallow period between wheat crops.
Fig.
3.
Precipitation Storage Efficiency  as influenced by wheat residue on the soil surface.
As wheat residue on the soil surface increased from 0 to 9000 lb/a, precipitation storage efficiency increased from 15% to 35%.
Crop residues reduce soil water evaporation by shading the soil surface and reducing convective exchange of water vapor at the soil-atmosphere interface.
Additionally, reducing tillage and
 maintaining surface residues reduce precipitation runoff, increase infiltration, and minimize the number of times moist soil is brought to the surface, thereby increasing precipitation storage efficiency.
Fig.
4.
Precipitation Storage Efficiency  as influenced by tillage method in the 14-month fallow period in a winter wheat-fallow production system.
Snowfall is an important fraction of the total precipitation falling in the central Great Plains, and residue needs to be managed in order to harvest this valuable resource.
Snowfall amounts range from about 16 inches per season in southwest Kansas to 42 inches per season in the Nebraska panhandle.
Akron, CO averages 12 snow events per season, with three of those being blizzards.
Those 12 snow storms deposit 32 inches of snow with an average water content of 12%, amounting to 3.8 inches of water.
Snowfall in this area is extremely efficient at recharging the soil water profile due in large part to the fact that 73% of the water received as snow falls during non-frozen soil conditions.
Standing crop residues increase snow deposition during the overwinter period.
Reduction in wind speed within the standing crop residue allows snow to drop out of the moving air stream.
The greater silhouette area index  through which the wind must pass, the greater the snow deposition.
Data from sunflower plots at Akron, CO showed a linear increase in soil water from snow as SAI increased in years with average or above average snowfall and number of blizzards.
Typical values of SAI for sunflower stalks  result in an overwinter soil water increase of about 4 to 5 inches.
Fig.
5.
Influence of sunflower silhouette area index on over-winter soil water change at Akron, CO.
Because crop residues differ in orientation and amount, causing differences in evaporation suppression and snow catch, we see differences in the amount of soil water recharge that occurs.
The 5-year average soil water recharge occurring over the fall, winter, and spring period in a crop rotation experiment at Akron, CO shows 4.6 inches of recharge in no-till wheat residue, and only 2.5 inches of recharge in conventionally tilled wheat residue.
Corn residue is nearly as effective as no-till wheat residue in recharging soil water, while millet residue gives results similar to conventionally tilled wheat residue.
Fig.
6.
Change in soil water content due to crop residue type at Akron, CO.
Good residue management through no-till or reduced-till systems will result in increased soil water availability at planting.
This additional available water will increase yield in both dryland and limited irrigation systems by reducing level of water stress a plant experiences as it enters the critical reproductive growth stage.
Unfortunately, the rate of adoption for SIS methods has been fairly low.
For example, soil moisture probes are used in only 7-12% of fields, while traditional methods of irrigation scheduling such as plant and soil appearance remain very popular.
Unfortunately, these methods leave farmers feeling uncertain about whether the crop has enough water, which leads to putting on extra irrigation for insurance purposes.
A REVIEW OF IN-CANOPY AND NEAR-CANOPY SPRINKLER IRRIGATION CONCEPTS
 center pivot irrigation ASABE tech transfer
 ABSTRACT.
The use of in-canopy and near-canopy sprinkler application with mechanical-move systems is prevalent in the U.S.
Great Plains.
These systems can reduce evaporative losses by nearly 15%, but they introduce a much greater potential for irrigation non-uniformity and other water losses.
This article is a review of these application technologies for mechanical-move sprinkler irrigation systems that have been widely adopted in the region, where irrigation capacities are typically less than those required to meet "fully irrigated" crop water demand and there is limited seasonal precipitation.
Close attention to the design, installation, management, and operating guidelines for these systems can prevent many of the nonuniformity and water loss issues that reduce system performance and crop water productivity.
Keywords.
Center pivot, In-canopy sprinkler application, LEPA, LESA, LPIC, MESA, PARM, Sprinkler irrigation.
I n the U.S.
Great Plains, center-pivot  sprinkler irrigation is the predominant irrigation method.
There are far fewer linear lateral-move  sprinkler irrigation systems, and together with CP systems they are jointly termed mechanical-move  sprinkler irrigation systems.
Windy and semi-arid conditions in the region during the growing season affect MM irrigation uniformity and evaporative losses.
As a result, many producers have adopted MM sprinkler systems and methods that apply water at a lower height within or near the crop canopy height, thus avoiding some of the application nonuniformity caused by wind and droplet evaporative losses.
However, these sprinkler systems are often adopted without appropriate understanding of the requirements for proper water management, and thus other problems occur, such as runoff and poor soil water redistribution.
This article discusses in-canopy and near-canopy MM sprinkler irrigation from a conceptual standpoint with supporting data from research studies conducted in the U.S.
Great Plains region and beyond.
Submitted for review in November 2018 as manuscript number NRES 13229; approved for publication as an Invited Review and as part of the Center-Pivot Irrigation Tech Transfer Collection by the Natural Resources & Environmental Systems Community of ASABE in February 2019.
Contribution No.
19-220-J from the Kansas Agricultural Experiment Station.
GUIDELINES, DEFINITIONS, AND DESCRIPTIONS
 Traditionally, MM sprinkler irrigation systems have been designed to apply water uniformly to the soil at a rate less than the soil intake rate to prevent runoff from occurring.
These design guidelines need to be either followed or intentionally circumvented with appropriate design criteria and other cultural practices for managing a MM system that applies water within the canopy or near the canopy height where the sprinkler application pattern is intercepted by the plant canopy.
Peak application rates can easily be 5 to 30 times greater for in-canopy sprinklers than for above-canopy sprinklers.
Peak application rate is a direct function of the system length, the irrigation capacity , and the application technology's wetted di-
 Figure 1.
Typical application rates for various sprinkler systems to apply an equivalent irrigation depth.
Curves from highest to lowest are LEPA, LESA, MESA, rotating spray, and impact sprinkler.
ameter and is independent of the application depth.
A number of sprinkler systems have been developed that apply water in the crop canopy or near the canopy height.
They should be and are classified as systems because they involve sprinkler irrigation hardware as well as installation and management guidelines.
Low-energy precision application  was probably the earliest in-canopy application system for MM irrigation, although there had been earlier attempts with traveling drip irrigation systems.
A prototype LEPA system was developed as early as 1976 by Bill Lyle at Texas A&M University.
Jim Bordovsky joined the development effort in 1978 , and the first scientific publication of their work was in 1981.
Although LEPA was originally used in every furrow, subsequent research  demonstrated the superiority of alternate-furrow LEPA.
The reasons for this superiority are not always evident, but they may be due to the deeper irrigation penetration , possible improved crop rooting and deeper nutrient uptake, and less surface water evaporation.
Seven guiding principles  necessary for successful LEPA were given by Lyle.
There are overlaps in definitions among in-canopy and near-canopy sprinkler irrigation systems, as well as differences in their focus.
LEPA and LPIC were both initially developed when there was an intense focus on irrigation energy costs, SO they both emphasize aspects of energy within their name.
LPIC was partially developed as an alternative to LEPA for tighter soils and steeper topography, where preventing runoff was difficult with LEPA.
Irrigators using LPIC systems often have difficulties strictly adhering to LEPA principles 2, 3, 5, and 6 , but many irrigators still believe that they are obtaining most of the benefits of LEPA.
In fact, many LPIC systems are inaccurately called LEPA systems in the U.S.
Great Plains.
In a worthwhile attempt to clarify and prevent misuse of in-
 Figure 2.
Relative heights of MESA, LESA, LPIC, and LEPA systems in tall and short crops.
There can be overlapping definitions.
Table 2.
Seven guiding principles of LEPA.
1	Use of a moving overhead tower-supported pipe system (lin-
 ear-move or center-pivot travel).
2	Capable of conveying and discharging water into a single crop
 3	Water discharge very near the soil surface to negate evapora-
 tion in the air.
4	Operation with lateral end pressure no greater than 70 kPa
 when the end tower is at the highest field elevation.
5	Applicator devices are located SO that each plant has equal op-
 portunity to the water.
The only acceptable deviation is where
 nonuniformity is caused by nozzle sizing and topographic
 6	Zero runoff from the water application point.
7	Rainfall retention that is demonstrably greater than conven-
 tionally tilled and managed systems.
canopy and near-canopy irrigation technologies, the USDAARS at Bushland, Texas, developed two new terms, MESA and LESA, that can essentially replace LPIC.
MESA and LESA both emphasize spray application at a relative height above the ground but not necessarily relative to the crop or to the MM lateral.
Although the terms do not emphasize pressure in their names, MESA and LESA can both have operating pressure requirements similar to LPIC or
 Table 1.
Near-canopy and in-canopy sprinkler systems and their general installation and management guidelines.
Sprinkler System and Hardware	Tillage and Crop Row Orientation	Height
 MESA :	Any tillage system and row orientation.
Controlled traffic desired.
Basin tillage	1.2 to 2.5 m,
 180 or 360 spray head; stationary,	with ridge-till or reservoir tillage desirable, with or without beds.
Compatible	above crop canopy
 rotating, or oscillating plates.
with no-till, ridge-till, or conservation tillage.
for most of season
 LESA :	Any tillage system with circular crop rows desired for CP systems.
Controlled	0.3 to 0.6 m,
 180 or 360 spray head; stationary,	traffic desired.
Basin tillage with ridge-till or reservoir tillage desirable, with	within crop canopy
 rotating, or oscillating plates.
or without beds.
Compatible with no-till, ridge-till, or conservation tillage.
for most of season
 LPIC :	Any tillage system and row orientation.
Controlled traffic desired.
Basin tillage	0.3 to 0.6 m
 180 or 360 spray head; stationary,	with ridge-till or reservoir tillage desirable, with or without beds.
Compatible
 rotating or oscillating plates.
with no-till, ridge-till, or conservation tillage.
LEPA :	Circular rows required with CP systems.
Controlled traffic desired.
Basin tillage	0.3 to 0.6 m,
 bubbler nozzle.
with ridge-till or reservoir tillage required, with beds on non-level landscapes.
within crop canopy
 Adjustment of irrigation interval is allowable to prevent runoff.
for most of season
 LEPA with drag sock:	Circular rows required with CP systems.
Controlled traffic desired.
Basin tillage	0 m,
 any nozzle within drag sock.
with ridge-till or reservoir tillage required, with beds (basin tillage is more effec-	within crop canopy
 tive) on non-level landscapes.
Adjustment of irrigation interval is allowable to	for entire season
 PARM (precision application, residue man-	Circular rows should be used with CP systems.
A no-till or strip-till system with	<0.5 m,
 aged): bubbler nozzle or large droplet	"flat planting" with at least 75% irrigated high-residue crops.
Runoff of applied	within crop canopy
 dome pattern using a shroud or shield.
irrigation is not allowed.
Nozzles in every interrow are recommended.
for most of season
 LEPA.
PARM is an emerging type of in-canopy sprinkler application described by the USDA-NRCS , and there has been little, if any, research published on it.
PARM requires 75% irrigated crop residue to control excessive translocation of applied water and recommends sprinklers between every pair of rows.
This latter recommendation runs counter to the earlier recommendation of alternate-row spacing for LEPA.
LEPA is often used in the Texas High Plains with lowcapacity wells and on relatively level fields, whereas LPIC, LESA, and MESA are predominately used in Kansas and the Colorado High Plains.
The worldwide annual benefit of LEPA has been estimated to be $1.1 billion, with a $0.477 billion benefit to consumers in the U.S..
The other types of in-canopy and near-canopy sprinkler irrigation do not necessarily require adherence to all seven of the LEPA principles listed in table 2.
However, it is unfortunate that there has been a lack of knowledge or a lack of understanding of the importance of these principles, because many of the problems associated with in-canopy and near-canopy sprinkler irrigation can be traced back to a failure to follow or effectively work around one or more of these principles.
EFFECTS OF SPRINKLER SYSTEMS ON WATER LOSSES
 There are numerous water loss pathways for CP sprinklers, and each sprinkler system has advantages and disadvantages, as outlined by Schneider  and Howell , that must be balanced against the risk of water loss.
In-canopy and near-canopy application systems can reduce evaporative losses , but these water sav-
 ings must be balanced against runoff, deep percolation, and other soil water nonuniformity problems that can occur when the systems are improperly designed and managed.
Net sprinkler evaporative losses from solid set sprinklers in Spain ranged from 14% to 18% of the applied water during the day, but during the night sprinkler evaporative losses were lower, at approximately 10%, and were a function of wind speed.
The researchers concluded that a reduction in ET and transpiration during daytime irrigation moderately increased the resulting sprinkler application efficiency.
Similar results were reported from simulation modeling by Thompson et al.
, who reported that evaporative losses were reduced to a range of 2% to 6% of the total irrigation depth, primarily because transpiration and water evaporation from the soil surface would have occurred even without irrigation.
Sprinkler height can also affect water losses, as reported by Ortiz et al..
In their study, a 1 m sprinkler height, when compared to 2.5 m sprinkler height, reduced evaporation and drift losses by as much as 33% and 45% for daytime and nighttime periods, respectively.
They also reported that fixed-plate spray sprinklers had 18% greater evaporative losses than rotating-plate spray sprinklers, which they attributed to the smaller drop sizes for the fixed-plate sprinklers.
SURFACE WATER REDISTRIBUTION AND RUNOFF WATER LOSSES
 Although evaporative losses are typically reduced with in-canopy and near-canopy sprinkler application, other serious water problems, such as surface water redistribution and runoff, can be exacerbated due to the reduction in the wetted radius of sprinklers operating in or near the canopy.
Some amount of surface water redistribution can be tolerated, particularly if variations in soil infiltration rates and soil water redistribution smooth out the applied water.
Simulation modeling by Hart  indicated that
 Table 3.
Typical water loss components associated with various sprinkler systems.
These descriptions assume that water losses are not exacerbated by excessively poor management.
Water Loss Component	Overhead{a	MESA	LESA	LEPA
 Droplet evaporation	Yes	Yes	Yes	No
 Droplet drift	Yes	Yes	No	No
 Canopy evaporation	Yes	Yes	Yes 	No 
 Impounded water evaporation	No	Yes	Yes	Yes 
 Wetted soil evaporation	Yes	Yes	Yes	Yes 
 Surface water redistribution	No 	Yes 	Yes	Yes (not major unless
 surface storage is not used)
 Runoff	No 	Yes	Yes	Yes (not major unless
 surface storage is not used)
 Percolation	No (if managed	No (but possible with	No (but possible with	No (but possible with
 carefully)	excessive redistribution	excessive redistribution	excessive redistribution
 of surface water)	of surface water)	of surface water)
 [a] Includes impact sprinklers and rotating or fixed spray applicators.
Table 4.
Partitioning of sprinkler irrigation evaporation losses with a typical 25 mm application for various sprinkler systems.
Air Loss	Canopy Loss	Ground Loss	Total Loss	Application Efficiency{
 Sprinkler System					
 Impact sprinkler 	3	12	-	15	85
 MESA 	1	7	-	8	92
 LEPA 	2	2	98
 [a] Ground runoff and deep percolation are considered negligible in these data.
differences in irrigation water distribution occurring over an approximate distance of 1 m are probably of little overall consequence and will be evened out through soil water redistribution.
Summarizing his own field research, with additional work from Stern and Bresler , Li  illustrated that the Christiansen uniformity  of soil water content averaged an acceptable 90% to 94%, while the CU of sprinkler water application ranged from approximately 67% to 83%.
In another field study, Li and Kawano  reported that soil characteristics , sprinkler application uniformity, total amount of sprinkler-applied water, and initial soil water content were all important variables in the resulting soil water redistribution, with the latter two factors being most important.
Some irrigators in the U.S.
Central Great Plains contend that their low-capacity systems on nearly level fields restrict runoff to the general area of application.
However, nearly every field has small changes in slope as well as field depressions that cause field runoff on medium to heavy textured soils, in-field redistribution, or deep percolation in ponded areas when the irrigation application rate exceeds the soil infiltration rate.
In the extreme drought years of 2000 to 2003 that occurred in the U.S.
Central Great Plains, even small amounts of surface water movement affected sprinkler-irrigated corn production.
Although surface water redistribution may or may not result in a direct loss in crop production, field runoff  is a water loss to crop production that also has environmental consequences, including soil erosion and offsite agrochemical losses.
Buchleiter  reported that LEPA on 1% sloping silt loam soils in northeastern Colorado had no runoff, while runoff exceeded 30% on a 3% slope.
Runoff from LEPA with basin tillage was approximately 22% of the total applied water and twice as great as MESA  for grain sorghum production on a clay loam in Texas.
Basin tillage created by periodic diking  of crop furrows , rather than reservoir tillage created by pitting or digging small depressions , is often more effective for time-averaging of LEPA application rates, and thus preventing runoff.
Increasing the irrigation frequency, and thus lowering the irri-
 gation amount per event, is also used to reduce in-canopy and near-canopy sprinkler application runoff and deterioration of furrow dikes.
LEPA performed sufficiently well when coupled with reservoir tillage  with field slopes less than 1% to 2% on silt loam soils in Kansas.
However, in that study, the flat spray mode  was more effective in maintaining soil water and ultimately corn yields, probably due to the greater wetted radius as compared to LEPA.
Decreasing the irrigation application rate is the most effective way to prevent field runoff losses and surface redistribution within the field , and numerous resources are available to help irrigators appropriately address this topic.
When runoff and surface redistribution occur using in-canopy sprinklers because of a reduced wetting pattern, one easy solution is to raise the sprinkler height, which increases the wetted radius, but of course moves away from the concept of in-canopy and near-canopy sprinkler application.
However, raising the sprinklers can be applied strategically only to the portion of the MM lateral where runoff is a problem.
Further discussion of how sprinkler application can be affected by the crop canopy is presented later in this article.
EQUAL OPPORTUNITY OF ACCESS TO SPRINKLER APPLICATION
 The previous section emphasized that water loss pathways must be carefully managed and balanced to achieve the greatest level of success with in-canopy and near-canopy sprinkler applications.
Perhaps the most useful guideline for successful in-canopy and near-canopy sprinkler application refers back to LEPA principle 5 in table 2 , which can be paraphrased as "provide each plant equal access to applied water." Using this paraphrase as a working principle, five topics need more extensive discussion:  partitioning of the applied sprinkler irrigation amount,
  symmetry of sprinkler application,  spatial orientation,  seasonal duration of sprinkler pattern distortion, and  combinations of poor design, installation, maintenance, and management aspects.
Figure 3.
Large differences in corn plant height and ear size for in-canopy sprinkler application over a short distance  as caused by small differences in field microrelief and the resulting surface water movement during an extreme drought year.
The upper stalks and leaves have been removed to emphasize the ear height and size differences.
Figure.
4.
Runoff and surface water redistribution potential for impact and LESA sprinkler application on an example soil.
PARTITIONING OF APPLIED SPRINKLER IRRIGATION AMOUNT
 The sprinkler application amount that reaches the crop canopy is partitioned into three major components: stemflow, throughfall, and interception storage.
Stemflow is the amount of irrigation water that flows down the leaves to the leaf-stem node and then down the stem to the soil surface.
Throughfall represents any irrigation water that reaches the soil surface by falling directly or indirectly through the plant leaf structure.
Interception storage is the amount of water temporarily remaining on the plant after irrigation, including both water on the leaf and stem surfaces and water trapped in the leaf-sheath area.
Although interception storage is eventually lost as evaporation, crop transpiration is temporarily reduced during the evaporative process.
Stemflow is the predominant flow path to the soil after the corn canopy is fully developed, averaging 55% of the total irrigation amount for corn with a within-row plant spacing of 0.18 m.
Throughfall averages approximately 42% for the same plant spacing, and interception storage  is approximately 2 mm for each irrigation event.
This interception storage value matches well with previously reported values.
When averaged over the entire field, there are very few differences in the partitioning process between above-canopy impact sprinklers and MESA at a height of 2.2 m.
However, because of MESA pattern distortion by the crop canopy, there are large partitioning differences between corn rows near and far from the applicator head.
The ratio of stemflow to throughfall also increases with increased in-canopy applicator height, effectively allowing the corn plant to serve as a larger funnel.
SYMMETRY OF SPRINKLER APPLICATION
 The importance of uniform water application and/or infiltration has been documented by numerous studies (Zaslav-
 Figure 5.
Partitioning of 25 mm of applied sprinkler irrigation by a fully developed corn canopy  as affected by sprinkler type and row location.
Impact sprinklers spaced at 12 m were at 4.1 m height, and MESA sprinklers spaced at 3 m were at 2.2 m height with 0.76 m row spacing and 0.18 m plant spacing.
MESA pattern distortion resulted in different stemflow and throughfall values for rows that were 0.38 and 1.14 m away from the nozzle.
Fixed interception storage estimates are provided only for the two sprinkler types and were not evaluated for individual rows with MESA.
Calculated values used equations from Lamm and Manges.
sky and Buras, 1967; Seginer 1978, 1979; von Bernuth, 1983; Feinerman et al., 1983; Letey, 1985; Duke et al., 1992; Li and Kawano, 1996; Li, 1998).
Increased uniformity can increase yields and decrease percolation.
Improving the uniformity of MM systems is highly desirable for economic and environmental reasons.
Duke et al.
showed that irrigation nonuniformity, such as over-irrigation resulting in nutrient leaching or under-irrigation resulting in water stress, can cause significant economic reductions.
An excellent conceptual discussion of the need to consider the extent of crop rooting in irrigation design is presented by Seginer.
Although the effective uniformity of in-canopy and near-canopy sprinkler irrigation may be sufficient as experienced by the crop, the actual uniformity of the applied water on the soil surface may be quite low.
In some cases where irrigation is deficient or limited, a lower value of application uniformity can be acceptable (von
 Figure 6.
Hypothetical relationship of relative crop yield and relative water needs for nonuniform deficit irrigation  and for uniform deficit irrigation.
The average relative water need is the same for both irrigation schemes, and consequently the average relative yield is also the same.
Bernuth, 1983).
For example, when the maximum water application depth falls on the upward sloping line of the yield production function, a crop area that is deficient in water will be compensated for by an area receiving a larger amount of water.
The overall production for uniform and nonuniform irrigation is identical because the production function is linear over the range of water applications.
In-canopy and near-canopy sprinkler irrigation does not necessarily result in nonuniform application that is detrimental to crop production.
Using a LEPA sprinkler in the furrows between adjacent pairs of crop rows obeys the guiding principle of each plant having equal opportunity to water.
Some irrigators in the U.S.
Great Plains are experimenting with wider in-canopy sprinkler spacing  to reduce sprinkler investment costs.
Spray heads that perform adequately at these intervals above bare ground have a severely distorted pattern when operated within the canopy.
This problem is widespread in portions of the U.S.
Great Plains.
In a transect survey of eight western Kansas counties in 2006 that
 Figure 7.
LEPA concept of equal opportunity of plants to applied water.
LEPA heads are centered between adjacent pairs of corn rows.
A 1.5 m sprinkler spacing with 0.75 m circular row spacing results in plants approximately 0.38 m from the nearest sprinkler.
Figure 8.
Approximate differences in application depths and patterns for a rotating-plate sprinkler as affected by sprinkler height when the sprinkler spacing is too wide  for in-canopy application with 0.76 m spaced corn rows.
The CP lateral traverses parallel to circular rows.
Dotted lines indicate locations of corn rows and stemflow values.
Areas under curves do not match due to the coarseness of sampling locations and the difficulty of jointly displaying stemflow  and throughfall.
Unpublished data from fully developed corn canopy, July 23-24, 1998, KSU Northwest Research-Extension Center, Colby, Kansas.
Data are mirrored about the centerline for illustrative purposes only.
observed 385 CP sprinklers with nozzle height less than 1.2 m, only 131  of the systems had nozzle spacings less than 2.4 m.
Although figure 8 shows large application nonuniformity, these differences may or may not always result in yield differences, but they should be considered in irrigation system design.
Pattern distortion will result in over-irrigation in some areas, which may cause runoff or deep percolation, and under-irrigation in other areas, which may cause crop yield reductions.
Sometimes the symmetry problem of excessively wide spacing of sprinklers for in-canopy application is not obvious and is only revealed under drought conditions  when water deficits are not obfuscated by precipitation.
When using in-canopy sprinkler application with CP systems, circular planting of the crop rows is recommended SO that the crop rows are always perpendicular to the sprinkler lateral.
Matching the direction of sprinkler travel to the row orientation satisfies LEPA principles 2 and 5 in table 2  concerning water delivery to individual crop interrows and each plant's equal access to water.
However, producers are often reluctant to plant row crops in circular rows because of the agronomic difficulties.
Circular planting can be difficult, resulting in narrow or wide "guess" rows.
This problem further manifests itself during in-season cultural practices, such as weed cultivation and harvesting.
The "guess" row planting problem can be effectively solved with modern planting systems that use global positioning systems  and for either type of MM system with wheel spacing that matches the planting equipment and crop row geometry.
A circular harvesting problem may still exist when the combine harvester and tractor/grain cart must be coordinated over greater distances.
Figure 9.
Irregularity of sprinkler-irrigated corn performance in southwest Kansas in 2011 under extreme drought conditions thought to be related to excessively wide nozzle spacing  for in-canopy application.
Figure 10.
Two problematic orientations for in-canopy sprinklers when crops are not planted in circular rows.
Using in-canopy application for CP sprinkler systems in non-circular crop rows can pose two additional problems.
In cases where the CP lateral is perpendicular to the crop rows and the sprinkler spacing exceeds twice the crop row spacing, there will be nonuniform water distribution because of pattern distortion.
When the CP lateral is parallel to the crop rows, there may be excessive runoff due to the large amount of water applied in just one or a few crop interrows.
There can be great differences in the amount and pattern of in-canopy application between the two crop row orientations.
The application differences shown in figure 11 are best considered as point estimates because the coarseness of the sampling locations becomes a critical problem for stemflow and throughfall measurements when the crop row orientation to the CP lateral changes from parallel to perpendicular.
The overall observation from figure 11 is that parallel circular rows impose less distortion of the application pattern than perpendicular straight rows.
SEASONAL DURATION OF SPRINKLER PATTERN DISTORTION
 Drop spray heads just below the CP lateral truss rods  at a height of 2.1 to 2.7 m have frequently been used for over 35 years for corn production in northwest Kansas.
This irrigation method has had relatively little negative effect on corn yields, even though the MESA pattern is distorted after corn tasseling, because there is only a small
 Figure 11.
Approximate differences in application amounts and patterns as affected by row orientation to the CP lateral travel direction.
Dotted lines indicate stemflow values  for both row orientations, although there could have been additional stemflow values for the perpendicular rows.
Areas under curves do not match due to the coarseness of sampling locations and the difficulty of jointly displaying stemflow  and throughfall.
Unpublished data from fully developed corn canopy, July 2324, 1998, KSU Northwest Research-Extension Center, Colby, Kansas.
Data are mirrored about the centerline for illustrative purposes only.
amount of pattern distortion due to the tassels, and the distortion occurs only during the last 30 to 40 days of growth.
In essence, the irrigation season ends before a severe soil water deficit occurs.
Compare this situation with LESA at a height of 0.30 to 0.60 m, which may experience pattern distortion for more than 60 days of the irrigation season.
Yield reductions might be expected for some corn rows in the latter case because of the extended duration of the pattern distortion.
Under dry and elevated evapotranspiration conditions in 1996, row-to-row corn height differences developed rapidly for 3 m spaced sprinklers at a 1.2 m sprinkler height following a single 25 mm irrigation event on a silt loam soil in Kansas.
A long-term  study at the same location found that lowering an acceptably spaced  spinner head from 2.1 m farther down into the crop canopy  caused significant row-to-row differences in corn yields.
COMBINATIONS OF POOR DESIGN, INSTALLATION, MAINTENANCE, AND MANAGEMENT ASPECTS Sometimes poor design, installation, maintenance, and
 Figure 12.
Crop height difference that developed rapidly under a widely spaced  in-canopy sprinkler  following a single 25 mm irrigation event at the KSU Northwest Research-Extension Center, Colby, Kansas.
Photo taken on July 6, 1996.
Figure 13.
Row-to-row variations in corn yield as affected by sprinkler height for 3 m spaced in-canopy sprinklers.
Sprinkler lateral travel direction was parallel to crop rows.
Unpublished data were averaged from four irrigation levels for 1996 to 2001, KSU Northwest ResearchExtension Center, Colby, Kansas.
management problems can exist for years before they are observed in irregular corn performance under sprinkler irrigation.
Severe drought conditions may be necessary for some of these subtle effects to combine throughout the season to such an extent that noticeable crop irregularity and yield loss occur.
In addition, smaller row-to-row differences in crop yield cannot be measured with the yield monitors on commercial-sized harvesters.
An example of combining several of these subtle effects was observed during the severe drought of 2002 in northwest Kansas.
The sprinkler height difference allowed at least three effects to combine and reduce corn performance:
 The height difference resulted in unequal flow rates for these low-pressure sprinklers with no pressure regulators.
With one sprinkler within the canopy while the other two sprinklers were above the canopy, there was incorrect overlap of the sprinkler patterns due to the height difference.
Evaporative losses would be greater for the sprinklers above the crop canopy.
Figure 14.
Irregular performance of in-canopy and near-canopy sprinkler-irrigated corn near Colby, Kansas, during extreme drought year of 2002.
Nozzle on the left is within the canopy and not visible.
Short-term and long-term water supply problems in the U.S.
have forced those involved with irrigation to look for cost-effective water-saving techniques.
Sprinkler irrigation is now the predominant irrigation method in the U.S., particularly in the Great Plains, because of both water and labor savings.
Ensuring equal opportunity of crop plants to the applied water has long been recognized as an important tenet of irrigation, yet there continues to be a lack of appropriate attention to this rule, particularly with the newer in-canopy and near-canopy sprinkler application techniques.
Important aspects of ensuring equal opportunity include symmetry of the sprinkler application, the spatial orientation of the sprinkler with respect to the crop rows, and the temporal aspects of any pattern distortion by the crop canopy.
Engineers, scientists, water agency staff, industry personnel, and irrigators all have important roles in solving this problem.
Neglecting the equal opportunity of crop plants to applied irrigation water can easily waste more water and cause more crop yield reductions than the other irrigation problems that irrigators are trying to avoid.
Appreciable portions of this article have been presented over the years in proceedings papers at various national and regional conferences, including the American Society of Civil Engineers, the Irrigation Association, and the Central Plains Irrigation Conference.
The updated version presented here is a more complete summary intended to be more widely accessible to the scientific community.
This article is part of a center-pivot irrigation technology transfer effort supported by the Ogallala Aquifer Program, a consortium of the USDA Agricultural Research Service, Kansas State University, Texas A&M AgriLife Research, Texas A&M AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
of root zone.
Irrig.
Sci., 1, 89-96.
Other secondary aquifers in eastern Nebraska include the Niobrara aquifer , the Codell aquifer , and the Western Interior Plains Aquifer System.
Only one active well is currently installed in the Western Interior Plains Aquifer System in Nebraska, but the aquifer system was a historic source of water to the Omaha area, and still supplies huge volumes of water to Iowa and other states to our east.
Efficient Irrigation of Perennial Forages with Wheel Lines in the Pacific Northwest
 lan McGregor, Mara Isabel Zamora Re, Gordon Jones and Troy Peters
 The impact of leaks
 Management considerations to promote efficiency
 Wheel lines are commonly used to irrigate forages in the Pacific Northwest.
Credit: Gordon Jones,  Oregon State University
 Forage-based industries are essential to food supply and local economies across the Pacific Northwest.
Wheel lines are commonly used to irrigate forages in the Pacific Northwest.
A substantial decline in snowpack levels in the western United States will force many agricultural irrigators to work with a less-than-ideal water supply and use water-efficient strategies to maintain satisfactory production levels.
Aside from the water shortage, irrigators should consider how mismanaged irrigation can reduce profits.
Every gallon of water pumped results in higher energy bills.
Mismanaged irrigation is also likely to prevent crops from reaching their optimal yields, encourage nutrient leaching and runoff, and lead to a less-than-optimal cost-to-return ratio.
Managing water resources efficiently greatly benefits irrigators and other community water users.
Wheel lines consist of moveable irrigation systems, usually stationary for 12or 24-hour sets.
These systems have unique management challenges.
It can take several days to water an entire field.
Irrigators must consider the rate at
 which moisture is depleted from the soil and the rate at which the wheel line applies water across the field.
These considerations determine optimal irrigation set times, how many wheel lines are needed to adequately irrigate a field, and an irrigation schedule throughout the growing season.
This publication provides step-by-step guidance to help irrigators design an irrigation program tailored to their scenario, as well as other general tips for enhancing wheel-line irrigation efficiency.
Saturation: Soil water status in which the soil pore spaces are filled with water.
Excess water is lost through drainage.
Field capacity : After a rainfall or irrigation event, soil water status in which the excess water has drained and the rate of downward water movement has decreased.
Permanent wilting point : Soil water status in which the water is no longer available for plant uptake.
Available water: Total amount of water that can be stored in a soil profile, typically defined as the range between FC and the PWP.
Maximum allowable depletion : The amount of water  that can be depleted before irrigation is required to prevent crop water stress.
This value varies across crops and crop growth stages.
Soil water holding capacity : The amount of water that can fit into the soil profile before runoff occurs.
Illustration of saturation, field capacity and permanent wilting point.
Credit: Maria Zamora Re,  Oregon State University
 Irrigation application rate: step-by-step calculations
 Each irrigation event should apply enough water to prevent crop water stress until the next irrigation event while minimizing water loss through deep percolation.
In other words, irrigators must maintain soil moisture levels between maximum allowable depletion  and field capacity.
Step 1.
Determine the rate at which your wheel line can apply water.
Step 2.
Determine how many inches of water the soil can hold in the rooting depth of the forage crop.
Step 3.
Determine how much water  is pulled out of the soil  each day by the forage crop based on values from a nearby AgriMet weather station.
Figure 1.
Irrigation management can be simplified into three basic values: irrigation application rate , water holding capacity within the root zone  and crop evapotranspiration.
These three values can determine how much water should be applied to meet the crop needs without excess water being lost through deep percolation beyond the root zone.
Note: Stand-alone calculations can be found in Appendix A.
Credit: Gordon Jones,  Oregon State University
 Step 1: Determine the rate at which your wheel line can apply water
 1A: Calculate the amount of water  applied per irrigation set: Fixed run times for wheel lines are typically 12 or 24 hours.
The goal in selecting a run time is to time your wheel-line positioning so that the amount of water the soil profile can hold is similar to what your irrigation system can apply in a 12or 24-hour set.
In other words, the goal is to reach field capacity in a fixed irrigation time.
Field capacity occurs when the soil holds as much moisture as it can after drainage ceases following an irrigation or rainfall event.
If the sprinklers on a wheel line apply water at a rate of 6 gallons per minute , the amount of water leaving the sprinklers for a 12and 24hour set can be calculated:
 Sprinkler water application rate in GPM X minutes in an hour = gallons applied in an hour per sprinkler
 6 GPM x 60 minutes/hour = 360 gallons applied per hour per sprinkler 360 gallons/hour X 12 hours = 4,320 gallons applied per sprinkler in a 12-hour set 360 gallons/hour X 24 hours = 8,640 gallons applied per sprinkler in a 24-hour set
 The impact of leaks
 The picture on the right shows a leak in a wheel line that was leaking at a rate of 8 gallons per minute.
This means you have to compensate for this leak by pumping more water.
See the example below.
We account for 5 sprinklers on this line
 With the leak, we now have to pump enough water for 6.3 sprinklers to apply the water we wanted with 5 sprinklers
 We must pump an extra 26% water to account for the leak.
6.3 5 = 1.26
 A leaking wheel line.
Credit: lan McGregor,  Oregon State University
 1B: Determine how much water is being applied, considering wheel-line inefficiencies: Given the nature of wheel-line sprinklers, water droplets spend a considerable amount of time in the air after leaving the sprinkler.
Water droplets suspended in the air are susceptible to evaporation and wind drift.
It has been estimated that wheelline irrigation system efficiency is between 60% to 75%, with 70% generally used as a season-long average.
This means that only 70% of the water leaving the sprinkler of the wheel line is making it to the ground.
Therefore, only 3,024 gallons of water are efficiently applied with a 12-hour set, and 6,048 gallons of water are efficiently applied with a 24-hour set, using the previous example with sprinklers that run at 6 GPM.
1C: Convert the total amount of water applied  to inches by considering the area where sprinklers apply water: If risers from the main line are 48 feet apart, then the wheel line is responsible for irrigating 24 feet on both sides of the wheel line at any given position.
If sprinklers on the wheel line are 30 feet apart, each sprinkler would be responsible for irrigating 15 feet on either side of the sprinkler laterally along the wheel line.
The area the wheel line is responsible for irrigating can be calculated by:
 Sprinkler application area = length X width
 
 30 feet X 48 feet = 1,440 square feet
 The area an individual wheel-line sprinkler is responsible for applying water to is 1,440 square feet.
Since there are 144 square inches in a square foot, one wheel-line sprinkler applies water to 207,360 square inches.
Since a gallon of water is 231 cubic inches of water, it would take 898 gallons of water to apply 1 inch of water to this area.
This means that in a 12-hour set, considering the previous example, an individual sprinkler applies 3.4 inches of water to the ground and 6.8 inches in a 24-hour set.
Another option for determining wheel-line application rates is a direct measurement using catch cans.
This approach requires a few empty cans and a ruler.
Place several straight-walled cans  underneath your wheel line, with the cans centered between two sprinklers.
Ensure the cans are level and the crop canopy will not intercept the irrigation water.
Back the wheel line up to the previous riser and run the system for an hour.
Move the wheel line back over the catch cans and run the system in that position for another hour.
Finally, move the wheel line to one riser beyond the catch cans and run for a third hour.
Now measure the water depth per can and find the average depth.
Multiply this average application rate by your set time to determine inches of irrigation application.
Figure 2.
Grid of catch cans.
Credit: Rob Wilson,  University of California, Davis
 A local Natural Resource Conservation Service or Soil and Water Conservation District office can help determine your wheel line's application rate.
Step 2: Determine how much water the soil can hold within the rooting depth of forages 
 The effective rooting depth for most established perennial forage grasses is approximately 3 feet.
However, alfalfa is a noteworthy outlier, with rooting depth often exceeding 5 feet.
Sometimes, if the soil is shallow or a hardpan is present, the rooting depth might be less than 3 feet.
For this article, a 3-foot rooting depth is used, but beware of the various parameters in your pasture or hayfield that warrant using a number more or less than 3 for your own irrigation calculations.
To find out where the bulk of the crop roots are, dig a hole using a backhoe or shovel and see how deep most of your forage roots extend into the soil.
2A: Determine the total available water in your soil: Soil texture the proportion of sand, silt and clay determines how much water your soil can hold.
Larger soil particles, like sand, have less surface area on which water can cling than silt and clay.
For this example, we assume the soil is sandy loam holding roughly 2 inches of water per foot of soil.
If we have a rooting depth of 3 feet, and the soil can hold 2 inches per foot of soil depth, then we can calculate how much water the soil can hold for forage roots to access.
Total Available Water  = SWHC ft of soil * Effective root zone 
 inches of water Total Available Water ft soil * 3ftsoil Total Available Water = 6 inches of water
 The formula for calculating how much water the soil can hold and that forage roots have access to.
Credit: lan McGregor,  Oregon State University
 Table 1.
Average water holding capacity per 1 foot of root zone depth 
 Table 1.
Average water holding capacity per 1 foot of root zone depth
 (assuming uniform soil properties throughout the profile.
Average soil water holding
 Step 3: Use AgriMet crop water-use data to determine when your crop needs irrigation.
This information can also help determine set times or if you need to buy another wheel line, etc.
With this in mind, we can set up some trigger dates to assess moisture levels and pasture conditions, informing the implementation of a drought management plan.
April 15 to May 10: Smooth bromegrass pastures with below-average precipitation, annual production may be reduced 25-50%.
CONVERTING REFERENCE EVAPOTRANSPIRATION INTO TURF WATER USE
 Paul Brown and Dave Kopec
 Accurate estimates of turf water use are required to effectively manage a turf irrigation system.
In Volume I of this series entitled "Basics of Evaporation and Evapotranspiration ," we indicated that actual turf water use  is rarely measured in the real world.
Instead, we use meteorological data and a mathematical model known as the Penman-Monteith Equation to estimate reference evapotranspiration  the ET from a tall, cool-season grass that is supplied with adequate water.
In the lower elevations of Arizona the ETos value would seem of limited value since we rarely grow turf that is equivalent to the reference surface.
However, we get around this problem by adjusting the ETos value to account for differences in turf type, quality and stage of development.
This document describes the procedures used to adjust ETos for use on managed turf surfaces in Arizona.
Estimating Turf ET From ETos
 An adjustment is necessary to convert ETos values to estimates of turf ET.
The adjustment process is actually quite easy and consists of multiplying ETos by an adjustment factor known as a crop coefficient :
 ETT = Kcx ETos
 The procedure can be completed in seconds with spreadsheet software or a hand calculator provided you have access to an ETos value and an appropriate Kc value for your turfgrass.
Lets look at an example.
If we have a pivot that is 1,300 feet long with an end gun having a throw of 100 feet, how much slower should the pivot travel when the end gun is operating to cover the same acres per hour as when the end gun is off?
First, we need to figure the ratio of the end gun throw  to the pivot length.
Ratio of the end gun throw to the center pivot length:
 100ft / 1,300ft = 0.0769
 Rounded to = 0.08
 Table 1 shows how the ratio of Rg/R relates to the pivot speed with the end gun on  compared to the speed with the end gun off.
Therefore, rounding to 0.08, we can look in Table 1 to find our speed ratio of 0.86.
Using the ratio, multiply the pivot speed by the number in the table to get the speed when the end gun is on.
So, for example, if the pivot is set to operate at a 90% timer setting when the end gun is off, it should only operate at 0.86 of that speed when the end gun is on.
Calculate the speed when the end gun is on:
 90% x.086 = 77.4%
Divided ownership of a center pivot irrigation system may come about from one of three situations:
 The transition of dryland to irrigated cropland.
The addition of a center pivot system may provide higher rental income for the landowner.
For the tenant, it could imply higher yields.
The transition from gravity irrigated ground.
Arguments for transitioning to a center pivot is the potential for higher rental income and reduced annual ownership costs for the landowner.
For the tenant, the transition could mean higher water use efficiency and decreased labor.
The replacement of an outdated or aged center pivot system.
Typically, the update of an existing pivot has only a small effect on rental rates.
The first freezing temperatures of the fall were reported in the Alliance area the morning of Sept.
12 when the Airport reached 31F.
Scattered light frost was reported across the Panhandle and north-central Nebraska Sept.
25-26 when air temperatures dropped into the low 30s.
There may have been some scattered light frost across northeast Nebraska the morning of Sept.
28 with the Wayne airport reporting a low of 33F.
Preliminary data suggest that hard freeze conditions  was observed at the Whitman 5NE Nebraska Mesonet station on Sept.
26.
AGREEMENT FOR SINGLE FAMILY WATER USE EFFICIENCY PROJECT Landscape Irrigation Rebate Program
 The Miami-Dade Water and Sewer Department's  Landscape Irrigation Rebate Program provides financial incentives for homeowners in Miami-Dade County to modify their irrigation systems to use water more efficiently.
Improved efficiency will reduce the amount of water used and create healthier landscapes.
Applicants must have a functioning irrigation system on the property to qualify for the rebate program.
Approved applicants will receive an irrigation assessment before and after the system is retrofitted.
Assessments are free and provide information to homeowners on appropriate, cost effective retrofits to their landscape and irrigation system.
A pre-assessment of the property must be completed for program qualification.
Invoices and proof of payment verifying retrofit installation must be submitted within six months from date of post evaluation assessment conducted by UF/IFAS Extension Miami Dade County Florida Friendly Landscaping TM  Program's Urban Conservation Unit  or by August 31st, whichever comes first.
Rebates are available for the retrofits and/or modifications approved by UCU listed below:
 List of Approved Irrigation Retrofits
 Rebates are available for the following irrigation retrofits :
 Item #	Qualified retrofit	possible rebate
 1	Purchase and installation of a rain sensor	$120
 2	Purchase and installation of an EPA Water Sense labeled smart irrigation	$400
 controller or soil moisture sensor  if system is already digital
 3	Removal of irrigation where determined not needed or obstructed, or relocate	$200
 sprinklers for better coverage
 Installation of plants that are drought tolerant combined with removal of	$400
 4	irrigation.
Plants must be listed in publication titled "Low Maintenance
 5	Redesign of irrigation system to create hydrozones (i.e.
grass on a separate zone	$400
 6	Modification and installation of multi-stream, multi-trajectory nozzles to provide	$400
 matched precipitation or better coverage 
 7	Installation of micro-irrigation  in ornamental	$400
 8	Conversion of mechanical system to EPA Water Sense labeled smart irrigation	$500
 controller /electric system 
 9	Purchase and installation of a rainwater collection system (rain barrel must be 70	$400
 10	Purchase and installation of flow sensor	$400
 All costs to be reimbursed must be documented.
Participants must provide original receipts/invoices to UCU.
Receipts/invoices must be itemized showing the cost for labor and individual parts installed and show payment in full in order to qualify for the rebate.
Proof of payment can be in the form of a cancelled check, money order, in-store sales receipt or credit card statement.
A maximum of $500.00 is available for each participant, per program year for up to five years.
Rebates shall be granted on a first-come first-serve basis until program funds are expended.
This agreement is entered into on / /20 by and between WASD, the UCU and , Single Family Homeowner hereinafter referred to as the SFH for the Landscape Irrigation Rebate Program under the following TERMS:
 1.
A functioning irrigation system is located on the property.
The SFH will be contacted to schedule an onsite pre-evaluation of the property's irrigation system and landscaping by the UCU.
Following the preevaluation inspection, the UCU will provide the SFH with a written report with recommendations on how to make the landscape and irrigation system more water efficient.
2.
The WASD will reimburse the SFH up to but not exceeding five hundred dollars  for retrofits made to the existing irrigation system.
Only modifications that are on the "List of Approved Irrigation Retrofits"  or a modification that is approved by the UCU prior to retrofit will be reimbursable.
3.
After retrofits are completed, the SFH must schedule a post-retrofit evaluation of the system by the UCU to ensure retrofits are operating properly.
To receive a rebate each SFH must:
 a.
Receive a pre-retrofit evaluation of their irrigation system;
 b.
Receive a post-retrofit evaluation of their irrigation system;
 C.
Provide itemized receipts and approved payment for parts and labor used in retrofits.
4.
Retrofits must be completed, and invoices and proof of payment submitted within six months from date of post evaluation inspection conducted by UCU or August 31st, whichever comes first.
5.
The undersigned is solely responsible for permitting and retention of a licensed contractor to perform the installation work.
6.
Failure to maintain a scheduled appointment or failure to reply to UCU requests for an appointment will result in dismissal of the application.
7.
The SFH will be informed of other water conservation programs available from WASD through the UCU and will receive information about FFL.
8.
The SFH will allow the UCU to release copies of both pre and post evaluation reports to FFL, WASD, and the South Florida Water Management District.
9.
The SFH agrees to hold harmless WASD, FFL and the UCU for any loss or damage to SFH property or landscaping.
10.
The SFH may participate in the program up to, but not exceeding 5 times.
The SFH may apply in each program year  and must complete retrofits, submit invoices and proof of payment within six months of initial assessment or August 31st of the program year, whichever comes first in accordance with this Agreement.
Have you previously enrolled in this program?
If so, what year?
Sustainable Nursery Irrigation Management Series
 Part I.
Water Use in Nursery Production
 Amy Fulcher Assistant Professor Department of Plant Sciences, University of Tennessee
 Associate Professor Department of Horticulture, Michigan State University
 Part 1 of the three-part series, "Sustainable Nursery Irrigation Management," is devoted to responsible practices for watering nursery-produced crops and focuses primarily on the general importance of proper irrigation practices and some of the issues that lead to water competition in this country.
W later is essential to plant life and is a critical input to nursery crop production.
For plants, water is used in temperature regulation, as a carrier for nutrients and plant hormones, and is the hydraulic force behind growth.
Water is taken up by plant roots and is lost to the environment through the stomates and the leaf cuticle.
A water deficit can negatively affect plant growth, plant health and the amount of time needed to grow a crop to a marketable size.
Irrigation can shorten the production period for field nursery crops and increase quality, which has a positive impact on nursery profitability.
Because the nursery industry has shifted from primarily field-produced crops to container-produced crops, the need for irrigation is increasing.
Over 75 percent of nursery crop value  in 17 of the major nursery producing states is currently grown in containers.
Container nursery production is not possible without the use of irrigation.
The demand for fresh, high-quality water is increasing across the U.S.
and the world.
In eight of the 10 most populous states and in the top 10 nursery-producing states (based on farm gate
 Figure 1.
Because nursery containers have limited volume and coarse, soilless substrate is used, daily irrigation during the growing season is almost always necessary to prevent plants from desiccating.
Photo credit: Diana Cochran
 value), competition between human, industrial and agricultural water use is becoming a major issue.
Most wholesale nurseries require relatively large amounts of water for irrigation.
A container nursery with 70 percent of the land in production under overhead irrigation could use between 14,000 to 19,000 gallons of water per acre per day during the peak growing season.
ability to use lower-quality alternative water sources depends on the type and quantity of contaminants in the source water and the sensitivity of specific species to those contaminants.
Overhead irrigation is commonly used to produce small containers.
Inefficient application can occur easily with overhead irrigation due to a lack of delivery uniformity, which can be
 Figure 2.
Container nurseries require large volumes of water.
Photo credit: Amy Fulcher
 Scientists and industry leaders anticipate that there will be less water available for agricultural production in the future.
U.S.
municipalities in California, Delaware, Florida, Maryland, Michigan, North Carolina, Oregon and Texas already have responded to competition for water and/or concerns regarding water quality and runoff by creating legislation to monitor or regulate irrigation practices.
Growers and researchers are exploring novel ways to alleviate this concern.
Nurseries have two main strategies for alleviating competition for water: improved irrigation efficiency and use of alternative, possibly lower-quality water from nontraditional sources.
Many practices can improve efficiency, including irrigation scheduling, refining irrigation volume, irrigation system selection and delivery, substrate composition, plant spacing, and plant grouping within irrigation zones.
The
 caused by inappropriate system design or clogged or damaged emitters.
This leads to overor under-irrigation of part or all of the target crops.
In addition to poor delivery uniformity contributing to inefficient irrigation application, container spacing plays a substantial role in application efficiency.
Up to 80 percent of overhead irrigation misses the intended target depending on pot spacing.
The potential consequences of inefficient irrigation
 include wasted water; increased nutrient and pesticide leaching ; increased water runoff and movement of contaminants in runoff; increased biotic and abiotic stresses; reduced plant growth; increased plant death; and increased production duration.
The potential consequences of under-irrigation include the latter four.
Water is necessary for industrial, municipal and agricultural purposes.
Nursery crop production, especially container production, is dependent on water to grow healthy crops in a reasonable time period.
Nursery crop production is often located in or near populated regions of the U.S., which can create competition for water.
Growers can use several strategies covered in the UT Extension publications, "W 278: Part II.
Strategies to Increase Nursery Crop Irrigation Efficiency" and "W 279: Part III.
Strategies to Manage Nursery Runoff," to increase irrigation efficiency and manage nursery runoff.
Figure 3.
Overhead irrigation often provides nonuniform water delivery within an irrigation zone.
Here, water is being released unevenly from the emitter.
Also, the irrigation zone is irrigating beyond the production block, thus wasting water.
Photo credit: Amy Fulcher
 Figure 4.
Overand under-irrigation can lead to unmarketable plants due to poor plant quality, disease and death.
Photo credit: Amy Fulcher
 Cuticle Protective waxy layer on the outside of leaves.
Irrigation Efficiency Calculation that can refer to one of the three following aspects of nursery crop irrigation: 1.
amount of water beneficially used divided by amount of water extracted, 2) amount of water retained in pot  divided by amount extracted or 3) amount of yield increase  divided by amount of water extracted.
Stomates/Stoma Small openings, generally on the lower leaf surface, that permit gas exchange for photosynthesis and loss of water vapor.
Water Deficit Condition in which less water than is needed is available to a plant.
This publication was funded partially by the U.S.
Department of Agriculture's Specialty Crop Research Initiative project, "Impact and social acceptance of selected sustainable practices in ornamental crop production systems." The authors express their gratitude to Wanda Russell and Andrea Menendez for their skillful editing and Mark Halcomb, Brian Leib and Andrea Ludwig for their critical review, which strengthened the series.
THE UNIVERSITY ofTENNESSEE UP INSTITUTE of AGRICULTURE
 W 278 4/13 13-0098
Irrigation Scheduling For Corn: Macromanagement
 Freddie R.
Lamm Danny H.
Rogers Gary A.
Clark
 Corn irrigation scheduling issues such as initiation and termination of the irrigation season, determining the need for dormant season irrigation, and non-crop water decisions are defined as macromanagement in this discussion.
Macromanagement can have a significant effect on water conservation and production.
The water conservation and crop production advantages of efficient step-by-step irrigation scheduling using the crop water balance can be greatly reduced by inappropriate macromanagement.
Irrigators should use sound rationale for macromanagement.
In some cases, researchers need to develop, re-evaluate or update macromanagement procedures.
Keywords: Irrigation strategies, Irrigation management, Water conservation, Zea mays L., Maximum allowable deficit 
 Corn  is a major irrigated crop in the Central Great Plains.
Any realistic attempt to reduce irrigation withdrawals from the Ogallala Aquifer must address this fact.
A number of excellent irrigation scheduling methods for corn can be used to schedule irrigation on a real time, daily, or short-term basis throughout the season.
These methods of irrigation scheduling achieve water conservation by delaying any unnecessary irrigation event with the prospect that the irrigation season might end before the next irrigation event is required.
However, larger irrigation management issues can have a greater impact on water conservation than the step-by-step, periodic scheduling procedures.
These include strategies for initiation and termination of the irrigation season, determining the need for dormant-season irrigation, and noncrop water issues.
Macromanagement strategies can provide the potential for increased water conservation when used in conjunction with the step-bystep periodic scheduling procedures.
This paper will discuss macromanagement using research-based rationale for corn irrigated with groundwater in the semi-arid Central Great Plains, but has implications for other regions and other crops.
An implicit assumption of the concepts is that efficient irrigation scheduling based on the crop water balance is used throughout the irrigation season.
INITIATION OF IRRIGATION SEASON
 The date for the first irrigation can usually be effectively determined by comparing the daily calculated rootzone soil water balance to a preset maximum allowed deficit.
The MAD is often assumed to be 50% of the available soil water in the active crop rootzone, but soil and climate conditions and irrigator judgment may dictate other criteria.
The soil water balance is initialized with a measured or assumed initial soil water condition.
The initial measurements or assumptions
 must be appropriate for the given year.
For example, excessive temperatures can limit early season root growth and thus limit the rootzone available to the corn crop.
Similarly, if irrigation with discrete application has been used, such as furrow or line-source drip irrigation, measurements or assumptions need to be based on the active rootzone, not the wetted portion of the soil.
In some cases, additional irrigation may be required to satisfy this early-season rootzone distribution.
This event can have a low application efficiency due to increased percolation and due to applications to nonrootzone areas.
Furrow irrigators may initiate the first irrigation following the last cultivation or furrowing process to eliminate water stress associated with root pruning and to help seal soft furrows, rather than an irrigation need dictated by the crop water balance.
Irrigators should carefully evaluate the need for these additional or early irrigations which are not dictated by the soil water balance if water conservation is important.
This is particularly true in areas with a continental climate where there is a high probability of precipitation exceeding the early season corn evapotranspiration.
Simulations of sprinkler irrigation schedules for corn  at Colby, Kansas indicate the first 25 mm irrigation event occurs between June 5 and July 5, with most years between June 10 and June 15.
Some irrigators with low capacity irrigation systems start irrigation sooner than normal.
The simulations indicate that usually there is no need to start irrigating in northwest Kansas before June 10 unless the soil profile is extremely dry from the previous crop or from a dry overwinter period.
Crop water stress problems associated with decreased irrigation capacity in July and August is not alleviated by the excess system capacity in June, when the soil profile is already relatively full of water.
An overall point of the simulations that should not be missed is the variability in initial irrigation dates.
An objective of step-by-step irrigation scheduling is to delay irrigation until necessary in hopes of replenishment by natural precipitation.
Proper determination of the first irrigation date is an important step in water conservation.
Irrigators should use-crop water balances and/or soil water measurements to establish the first irrigation date and not rely on traditional calendar dates.
TERMINATION OF IRRIGATION SEASON
 Conceptually, the irrigation season is terminated when the marginal cost of additional irrigation equals the marginal benefits of the harvested economic yield of the crop.
Two noteworthy points of wording in the previous statement should be made.
First, in many cases, the cost of deep percolation caused by additional late-season irrigation has not been assessed.
If groundwater contamination due to excessive percolation is a concern, then the marginal cost of irrigation must reflect that fact.
The second point is that the marginal costs must be balanced against the harvested economic yield.
For example, if the termination decision  affects harvesting,  then the actual economic yield could be reduced in a way not traditionally considered.
From a practical standpoint, termination of the irrigation season is most effectively determined by comparing the anticipated soil water balance at physiological maturity to the MAD.
It should be noted that the MAD for the end of the season may not be the same as at other growth stages during the season.
Doorenbos and Kassam  indicate the MAD may approach 80% near physiological maturity for corn.
The MAD point should be established according to crop sensitivity and the maximum daily ET during the period in question.
They list MAD values of 0.8, 0.6 and 0.5 for maximum corn ET values of 3, 5 and 7 mm/day, respectively.
Extension publications from the Central Great Plains often suggest limiting the MAD at the end of the season to 0.6 in the top 1-1.2 m.
These values may need to be re-evaluated and perhaps adjusted downward.
Lamm et al.
found subsurface, drip-irrigated corn yields in northwest Kansas to begin to decrease rapidly when available soil water in the top 2.4 m was lower than 56-60% of field capacity for extended periods in July and August.
Lamm et al.,  permitted small daily deficits to accumulate on surface-irrigated corn after tasseling, and subsequent analysis of those data showed declining yields when available soil water levels
 approached 60% of field capacity for a 1.5-m soil profile at physiological maturity.
Current high corn yield levels may require greater available soil water levels than were used in earlier studies.
The anticipated soil water balance at physiological maturity is projected from historical ET and precipitation data.
Irrigators should time the last irrigation to ensure a reasonable probability of remaining above the chosen MAD level at physiological maturity.
In the absence of good historical estimates of ET, extension publications are available that give crop water use values for the latter part of the season.
Available soil water 
 Figure 1.
Corn yields as related to available soil water  in a 1.5-m soil profile at harvest in an irrigation-scheduling study where slight deficits were allowed to occur after tasseling.
Data analyzed from Lamm et al.,.
The advantages of preseason irrigation  are to 1) provide water for seed germination; 2) delay the initiation of seasonal irrigation; 3) improve tillage and cultural practices associated with crop establishment; and 4) more fully utilize marginal irrigation systems on additional land area.
The disadvantages are that it may 1) increase production costs; 2) increase irrigation requirements; 3) lower overall irrigation efficiencies; and 4) lower soil temperatures.
Preseason irrigation for crops such as corn has been advocated for the semi-arid Great Plains for most of the 20th century, and the practice has been debated for nearly as long.
Knorr  found that at Scottsbluff, Nebraska, fall irrigation normally increased corn yields.
Farrell and Aune  found opposite results at Belle Fourche, South Dakota.
Knapp  recommended winter irrigation for most of western Kansas with the exception of sandy soils.
Off-season labor utilization was seen as an important factor, along with avoiding conflicts with busy summer schedules.
Power
 et al.
in a North Dakota study found that when fall irrigation was practiced, nearly all the winter precipitation was lost.
On dryland plots, significant amounts of soil water were stored during the winter.
Adding fall irrigation to normal seasonal irrigation did not significantly affect yields of barley or of corn silage.
Hobbs and Krogman , finding that storage efficiency of winter precipitation decreased as fall irrigation increased, concluded that fall irrigation to bring soil water in the profile to 50% of field capacity would be advisable.
Stone et al.
, at Tribune, Kansas, reported that the net benefit of additional irrigation decreased linearly with increases in soil-water content in the fall.
There were no significant differences in corn yields  between fields irrigated in the fall and those not irrigated in the fall.
They concluded that fall irrigation to bring soil water in the profile to approximately 50% of field capacity was an efficient practice.
Willis et al.
observed that fall irrigation subsequently increased runoff during natural precipitation, thus contributing to inefficient water storage.
Stone et al.
concluded irrigation water should be reserved for inseason application unless needed for stand establishment.
Despite considerable controversy over preseason irrigation for corn, it remains a common practice in parts of the Great Plains.
Greb  advocated it as an efficient practice in much of the Central Great Plains, and Hay and Pope  reported that preseason irrigation should always be considered as a management tool in corn production in western Kansas.
Elimination of unnecessary preseason irrigation could result in the largest single water savings an irrigator might obtain in a season.
Musick and Lamm  indicated that for surface irrigation systems the preseason irrigation is normally the largest event and may be as much as 25% of the total irrigation applied for corn.
Lamm and Rogers  developed an empirical model to aid in decisions concerning fall preseason irrigation for corn production in western Kansas.
Available soil water at spring planting was functionally related to overwinter precipitation and initial available soil water in the fall.
An extension of this simple model by incorporating precipitation probabilities is presented in Fig.
2.
Using probability and the model, the irrigator can determine the need for preseason irrigation and the irrigation amount necessary to reach a desired soil-water content at planting.
Procedures used to develop this model could be used in other regions, even though the coefficients are likely to be site specific.
In most years, fall preseason irrigation for corn is not needed to recharge the soil profile in northwest Kansas, unless residual soil water remaining after corn harvest is excessively low.
Rogers and Lamm  found in a post-corn harvest survey of 82 randomly selected fields in northwest Kansas that the available soil water in the 1.5-m soil profile averaged 70% of field capacity.
Available soil water was similar for center pivot sprinklerand surface-irrigated fields, but within-field variation was higher for surface-irrigated fields.
A number of low-capacity sprinkler irrigation systems exist in the Great Plains region, and many irrigators assume they must compensate with dormant-season irrigation.
However, even though an irrigation system may have insufficient capacity during a critical period, an irrigator may try to catch up with irrigation later in the season, which builds soil-water reserves but may not affect yield.
The survey results indicate irrigators should evaluate their conditions prior to initiating preseason irrigation.
DORMANT-SEASON SOIL WATER MANAGEMENT
 Drier soil profiles at harvest result in greater opportunity for capturing winter precipitation and also reduce the potential for overwinter drainage losses and leaching of chemicals to groundwater.
Research in Kansas by Rice  found nitrate leaching during the growing season was minimal, and the overwinter period was of greater concern because evapotranspiration is usually lower than the precipitation.
One method of obtaining drier soil profiles and conserving water is to mine the plant-available soil water gradually during the irrigation season in anticipation of recharge from precipitation during the off season.
This concept of irrigation scheduling with planned soil water depletion was developed by Woodruff et al.
under semi-humid conditions in Missouri.
Further experimental testing of the concept  found it could be used successfully
 on deep soil profiles with high water holding capacity, provided irrigation frequency was sufficient to maintain adequate soil water in the most active zone of water and nutrient uptake.
Martin et al.
reported that mining of 50% of the soil water may be acceptable if off-season precipitation is sufficient to fully recharge the crop rootzone.
Figure 2.
Probability of reaching specified percentage of field capacity by June 1 with a specified value of fall  available soil water  in the 1.5-m soil profile on a Keith silt loam soil at Colby, KS.
After Lamm and Rogers.
Lamm et al.
found in a surface-irrigated study that irrigation scheduling with planned soil water depletion for corn was not justified for water conservation.
Reductions in soil water at harvest were accompanied by reductions in corn yields.
Water use efficiencies were similar across treatments.
Mining plant-available soil water to a low level would be acceptable, and even desirable, if corn yields could be maintained.
However, deficit irrigation of corn is difficult to implement successfully without incurring yield reductions.
After reviewing numerous studies, Rhodes and Bennett  reported that water stress imposed at any growth stage on corn will generally lower the efficiency of the water used in transpiration.
Lamm et al.
found irrigation needed to be reduced about 4 units for each unit reduction in available soil water at harvest.
They concluded that irrigation scheduling with planned soil water depletion was not justified for use with surface irrigation , but might be successful with surge, sprinkler or drip irrigation.
Stegman et al.,  reported that an irrigation interval of seven days or less should be used when scheduling irrigation with planned soil water depletion.
Figure 3.
Available soil water  at maturity in the 1.5-m soil profile as related to seasonal irrigation on a Keith silt loam soil at Colby, KS.
After Lamm et al.,.
Traditional step-by-step, periodic irrigation scheduling using the crop water balance has been used successfully for many years.
Conceptually, these methods attempt to minimize the number of irrigations and the total seasonal irrigation amount by providing irrigation "just-in-time." Macromanagement for irrigation scheduling attempts to provide the seasonal boundaries and governing parameters that provide the framework for conducting the step-by-step irrigation scheduling.
The seasonal boundaries are the initiation and termination of the irrigation season.
Irrigators sometimes make these seasonal boundary determinations based on a traditional time-ofyear rather than with sound rationale or procedures.
In some cases, researchers need to develop, evaluate, or update the procedures used in these determinations.
Dormant-season irrigation and dormant season water quality management are governing parameters instituted by the irrigator, but will affect in-season, step-by-step irrigation scheduling.
Inattention to irrigation scheduling macromanagement or practice of traditional macromanagement without adjustment for the conditions  can lead to inefficient use of irrigation water and/or decreased corn yields.
A single, inappropriate macromanagement decision can easily have a larger effect on total irrigation water use and/or crop production than the cumulative errors in stepby-step irrigation scheduling that might occur due to small systematic errors in the crop water balance.
This does not discount step-by-step irrigation scheduling.
To the contrary, the use of it has been an implicit assumption of this entire discussion.
Using rational macromanagement strategies and step-by-step irrigation scheduling closely together offers the best opportunities to conserve irrigation and maintain high production levels.
Measuring Pump Capacity for Irrigation System Design
 D.Z.
Haman and F.
S.
Zazueta
 Proper design of an irrigation system requires that the pumping system be precisely matched to the irrigation distribution system.
Then the pressure and flow rate required can be efficiently provided by the pumping system.
When an irrigation system is designed or modified to use an existing pumping system, it is necessary to measure the capacity of the existing pump.
The irrigation system can be properly designed only if the flow rate and pressure of the pump are accurately measured.
It is not adequate to visually estimate pump capacity or to use the manufacturer's specifications to determine current pump capacity.
Visual estimates are normally not accurate, and manufacturer's specifications do not include the effects of site-specific factors such as well characteristics or suction and discharge pipe sizes.
Manufacturer's specifications also do not include the effects of age and wear on pumping system performance.
The capacity of a pump has two components, the pump discharge rate and the discharge pressure.
The discharge rate is normally measured in gallons per minute  in English units or liters per second  in metric units.
Pressure is normally measured in pounds per square inch  in English units or kiloPascals  in metric units.
It is necessary to measure both discharge rate and pressure under normal operating conditions in order to determine how the pumping system will operate as a part of an irrigation system.
The discharge rate can be measured using one of the following three methods.
A flow rate meter is the most direct method because it measures the flow rate directly in gpm or lps.
The cost of flow rate meters varies widely.
Costs range from about $50 for small pitot meters which measure only flow rate, to several hundred dollars for impeller meters which measure flow rate and totalize the flow through the meter.
Pitot meters are inserted through a hole drilled into an irrigation pipe.
They divert a small stream of water through the meter and float a ball or disk flow indicator.
The flow rate is read from a graduated scale at the height of the flow indicator.
One type of commercially-available pitot flow rate meter is shown in Figure 1.
An impeller flow rate meter measures both the flow rate and the total flow through the meter.
The flow rate is read directly from a needle similar to a car speedometer, and the total flow is registered on a meter similar to the odometer  on a car.
An impeller meter is used as a component of the pump capacity measuring apparatus shown in Figure 2.
* MINIMUM ACCEPTABLE DIMENSIONS Figure 1.
Pitot tube flow rate meter.
Figure 2.
Pump capacity measuring apparatus, including a pressure gauge, flow meter, and regulating valve.
A totalizing flow meter measures the total volume of water that has passed through the meter in gallons  or liters.
Totalizing water flow meters are relatively inexpensive because they are commonly used for many applications ranging from metering homeowner's water use to metering agricultural irrigation systems.
Their costs range from about $50 for 1/2-inch meters which have capacities up to 10 gpm to $2,000-3,000 for large meters with capacities of several thousands of gpm.
To determine pump discharge rates with a totalizing flow meter, a stop watch or other watch with a second hand is needed.
The volume of water metered must be divided by the time during which the volume was measured to determine the flow rate.
For example, the meter register reads 200.0 gal at the beginning and 395.0 gal at the end of a 10 minute measurement period.
Then the flow rate is  gal / 10 min = 19.5 gpm or 1.23 lps.
Flow rates can be measured using a container of known volume and a stop watch.
For example, flow is directed into a 50-gal graduated tank for 10 minutes.
The volume of water collected is 47 gal.
Then the flow rate is 47 gal / 10 min = 4.7 gpm or 0.30 lps.
The discharge pressure can be measured easily and inexpensively using a standard pressure gauge.
Standard pressure gauges are available in 15, 30, 60 and 100 psi  ranges for about $10.
Select a pressure gauge that is accurate within the range of pressures that the pump can produce.
For example, if your pump can produce a maximum pressure of 50 psi  select a 60-psi  gauge as the next-largest commercially-available size.
For centrifugal and turbine irrigation pumps, the discharge rate depends on the pressure that the pump operates against.
If the pressure is high, the discharge rate will be low, and conversely, if the pressure is low, the discharge rate will be high.
The relationship between pressure and discharge rate is known as the head-discharge curve for the pump.
The head-discharge curve may be different for each pump because of the pump characteristics and many site-specific factors.
An apparatus which can be used to measure a pump head-discharge curve is shown in Figure 2.
The apparatus consists of a pressure gauge, flow meter, and regulating valve installed on a section of straight pipe.
The pipe must be long enough SO that the flow meter works properly.
Many flow meters require certain minimum lengths of straight pipe upstream and downstream of the meter for accuracy.
See the flow meter manufacturer's specifications.
Common straight pipe lengths required are 10 pipe diameters upstream and 6 pipe diameters downstream of the meter, although these lengths may be reduced if the flow meter is equipped with straightening vanes.
Straightening vanes are installed inside the meter tube and help improve meter performance by reducing extreme turbulence as water is directed through the meter.
A pipe fitting or connecting hose is needed SO that the head-discharge measurement apparatus can be connected to the pump discharge.
All components must be sized and pressure-rated to permit the measurement of the complete range of pressures and discharge rates that the pump produces.
1.
Measure the head-discharge curve in the following steps:
 2.
Connect the head-discharge apparatus to the pump discharge with sufficient lengths of straight pipe to obtain an accurate flow rate measurement.
3.
Operate the pump to remove air from the pump and pipelines and to reach normal operating conditions.
4.
Slowly close the regulating valve and measure the shut-off head..
The shut-off head is the maximum pressure that the pump delivers when there is no flow.
Record this pressure.
5.
Do not leave the pump operating under no-flow conditions for long periods of time, as this may overheat and damage some pumps.
6.
Open the regulating valve a small amount and measure the pressure and flow rate at this valve setting.
7.
Repeat Step 4 at other valve openings until the valve is completely open.
Valve adjustments should be made to produce at least 6 to 8 pressure-discharge data points over the flow range from completely closed to wide open.
8.
It is convenient to use the pressure gauge to uniformly distribute the measured data points over the range that the pump can produce.
For example, assume that the pump shut-off head was 45 psi.
Then, for convenience, adjust the regulating valve to set 5 psi changes in pressure as the valve is opened.
First, open the valve until the pressure drops to 40 psi and measure the discharge rate at that pressure.
Then, open the valve until the pressure drops to 35 psi, etc., until the valve is completely open and the final pressure is 0 or nearly 0 psi.
The final pressure may not reach 0 depending on the specific design of your head-discharge measurement apparatus.
An example set of head-discharge data is shown in Table 1.
These data were developed following the previous example in which the shutoff head was assumed to be 45 psi , and flow rates were measured at 5 psi  increments until the regulating valve was completely open.
This measurement strategy produced a total of 10 data points.
Figure 3 is a graph of the data shown in Table 1.
Notice that the relationship between pressure and discharge rate is a curve rather than a straight line.
This is the reason that at least 6 to 8 data points are necessary to accurately describe this relationship.
From the data shown in Table 1 and Figure 3, the designer can read the information needed to properly design an irrigation system using this pump.
For example, if a sprinkler
 irrigation system requires 35 psi  at the pump, then 13.0 gpm  is the maximum flow rate that is available from this pump.
If the system requires more than 13.0 gpm, then it will need to be designed and operated in zones SO that no zone requires more than 13.0 gpm.
Table 1.
Example pump head-discharge data.
Pressure 	Discharge 
 Figure 3.
Example pump capacity curve using the data from Table 1.
As another example, if a drip irrigation system requires 20 psi  from the pump, then this pump can deliver 25.2 gpm  at this pressure.
Factors Affecting Head-Discharge Curves
 Many factors affect the pump head-discharge curves measured, including the design of the pump and the size of the pump and power unit.
Other factors include worn impellers or other components, speed at which the pump is operated, size of well, aquifer characteristics, depth to water table or surface water level, and size of suction and discharge pipes.
The size, design, and maintenance of intake screens and check valves also affect pump capacity.
The measurement procedures described in this publication allow the effects of all of these factors to be included, and the results are valid only when the same conditions exist
 during the operation of the irrigation system.
If operating conditions change greatly from the test conditions, then the pump may produce much different outputs when connected to an irrigation system.
In the following paragraphs, several examples are given to illustrate changes in pumping conditions that could cause changes in pump capacity.
If water is being pumped from a pond, and the pond water level drops greatly during the irrigation season, the pump output will be reduced as the water level drops.
Likewise, if the water level in a well drops, then the pump output will also drop.
Thus, pump capacity tests should be scheduled when water levels are low SO that the minimum pump output can be measured, or tests should be made at both high and low water levels SO that the effects of water levels can be measured.
If the pump is driven by an internal combustion engine, its output will be greatly affected by the engine speed.
Therefore, pump capacity tests must be run at the same RPMs that will be used during irrigation.
If the intake strainer on the suction pipeline becomes partially clogged by debris in a pond, the pump capacity will be reduced.
Thus, pump capacity tests should only be conducted after strainers have been cleaned and other maintenance has been performed.
Likewise, routine maintenance is required SO that the pump capacity is not reduced for this reason during irrigation.
When an existing pumping system will be used as a component of an irrigation system, it is necessary to measure the capacity of the pump SO that the irrigation system can be designed to operate efficiently using the available flow rate and pressure.
This requires measuring pump discharge rates and pressures at several points over the available range.
Flow meters or volumetric methods can be used to measure discharge rates, while pressures are easily measured with pressure gauges.
Procedures for measuring pump capacity were presented, and factors affecting pump capacities under field conditions were discussed.
While low operating pressure may occur occasionally throughout an irrigation event , frequent low pressure can be attributed to either leaks developing along the system or low well capacity relative to the irrigation system.
Use: reduce application in wet areas to avoid water logging or leaching, VRI type: both, prescription type: both, management intensity: low.
Sprinkler irrigation can involve frequent wetting of the soil surface.
Once to twice per week wetting is common.
The largest rates of soil water evaporation occur when the soil surface is wet.
At this time soil water evaporation rates are controlled by radiant energy.
The more frequently the surface is wet, the more time that the evaporation rates are in the "energy" limited phase.
Crop residues have the capacity to modify the radiant energy reaching the soil surface and reduce the soil water evaporation during the "energy" limited phase of evaporation.
As the soil surface dries, the evaporation rate is controlled by soil properties.
However, with high frequency sprinkler irrigation the soil may remain in the "energy" limited phase.
This produces the opportunity for crop residues to impact soil evaporation rates.
Evapotranspiration, consisting of two processes, consumes the water applied by irrigation.
The two processes are transpiration soil water evaporation.
Transpiration, the process of water evaporating near the leaf and stem surfaces, is a necessary function for plant life.
Transpiration rates are related atmospheric conditions and by the crop's growth stage.
Daily weather demands cause fluctuations in transpiration as a result.
It is literally the process that causes water to flow through plants.
It provides evaporative cooling to the plant.
Transpiration relates directly to grain yield.
As a crop grows, it requires more water on a daily basis until it matures and generally reaches a plateau.
Soil water begins to limit transpiration when the soil dries below a threshold which is generally half way between field capacity and wilting point.
Irrigation management usually calls for scheduling to avoid water stress.
Limited irrigation management requires management to limit plant water stress in critical growth periods and allow more stress during less critical growth periods.
Evaporation from the soil surface may have an effect on transpiration in the influence of humidity in the crop canopy.
However, the mechanisms controlling evaporation from soil are independent of transpiration.
The combined processes
 of evaporation from soil  and transpiration  are measured together as evapotranspiration  for convenience.
Independent measurements of E and T are difficult but independent measurements are becoming more important for better water management.
Field research in sprinkler irrigated corn has shown that as much as 30% of total evapotranspiration is consumed as evaporation from the soil surface.
These results were from bare surface conditions for sandy soils.
For a corn crop with total ET of 30 inches, 9 inches would be going to soil evaporation and 21 inches to transpiration.
This indicates a window of opportunity if the unproductive soil evaporation component of ET can be reduced without reducing transpiration.
Evaporation from Soil Trends
 Evaporation from the soil surface after irrigation or rainfall is controlled first by the atmospheric conditions and by the shading of a crop canopy if applicable.
Water near the surface readily evaporates and does so at a rate that is only limited by the energy available.
This so-called energy limited evaporation lasts as long as a certain amount of water that evaporates, 0.47 inches for sandy soils and 0.4 inches for silt loam soils.
The time it takes to reach the energy limited evaporation depends on the energy available from the environment.
Bare soil with no crop canopy on a sunny hot day with wind receives much more energy than a mulched soil under a crop canopy on a cloudy cool day with no wind.
After the threshold between energy limited and soil limited evaporation is reached, evaporation is controlled by how fast water and water vapor can move through the soil to the soil surface.
There is a diminishing rate of evaporation with time as the soil surface dries.
The soil surface insulates itself from drying as it takes longer for water or vapor to move through the soil to the surface.
The challenge for sprinkler irrigation is the high frequency that the soil surface is put into energy limited evaporation.
With twice-weekly irrigation events it is likely that the soil surface will be in the higher rates of energy limited evaporation during the entire growing season.
Only during the early growing season with infrequent irrigations and little canopy development would there be a possibility for lower rates of soil limited evaporation.
Evaporation and Crop Residues
 For many years, crop residues in dryland cropping systems have been credited for suppressing evaporation from soil surfaces.
Evaporation research dates back into the 1930's when Russel reported on work with small canister type lysimeters.
Stubble mulch tillage and Ecofallow have followed in the progression of innovations with tillage equipment, planting equipment, and herbicides to allow for crop residues to be left on the ground surface.
These
 crop residue management practices along with crop rotations have increased grain production in the Central Plains.
Water savings from soil evaporation suppression has been an essential element.
In dryland management, saving 2 inches of water during the fallow period from wheat harvest until planting corn the next spring was important because in meant an increase of 20 to 25 bushels per acre in the corn crop.
This difference came from the presence of standing wheat stubble during the fallow period versus bare ground.
North Platte, Ne Study
 The question is to what extent water savings could be realized from crop residue management in sprinkler irrigation?
A research project  was conducted near North Platte, NE during the mid 1980's to begin to address this question.
Four canister type lysimeters were placed across the inter-row of sprinkler irrigated corn.
The lysimeters were 6 inches in diameter and 8 inches deep and were filled by pressing the outer wall into the soil.
The bottoms were sealed and the lysimeters were weighed daily to obtain daily evaporation from changes in daily weights.
Half of the lysimeter treatments were bare soil and half were covered with flat wheat straw mulch at the rate of 6000 pounds/acre or the equivalent to the straw produced from a 60 bu/acre wheat crop.
The other variable was irrigation frequency: dryland, limited irrigation, and full irrigation.
The sprinkler irrigation system was a solid set equipped with low angle impact heads on a grid spacing of 40 ft X 40 ft.
The corn population varied with the irrigation variable and was appropriate with the expected water application and yield goal for that treatment.
The resulting leaf area, shading, and biomass followed accordingly.
The results are summarized in Tables 1 and 2.
Evaporation measurements with the mini-lysimeters were not taken during days of irrigation or rainfall.
Data were collected from June 10 to September 13 in 1986 with 78, 75, and 75 days of collection from dryland, limited irrigation, and full irrigation, respectively.
In 1987, data were collected from May 28 to August 20 with 65, 64, and 59 days of collection, for dryland, limited irrigation, and full irrigation, respectively.
To understand the possible full season implications of this study, the average daily evaporation rates were applied to the missing days of data during the respective time periods.
These evaporation values may still be conservative since evaporation rates are highest immediately after wetting.
Only six rainfall events were more than 0.4 inch of precipitation.
After these significant rainfall events occurred, the bare soil in the dryland treatment showed brief periods of energy limited evaporation.
When the straw covered and bare soil dry land treatments were paired together, they had nearly the same evaporation both with and without the crop canopy.
This implied that the crop canopy had some effect on evaporation, but the wheat straw did not for dryland management.
Soil limited evaporation was more of the controlling factor.
The limited irrigation added three irrigation events of, 2.0, 2.0, and 1.75 inch.
The cumulative evaporation for bare soil unshaded treatment showed the classic patterns of energy limited-soil limited evaporation.
These patterns were suppressed in the other treatments indicating that the canopy and residue prolonged the transition from energy limiting to soil limiting evaporation.
During the last 40 days of the season, the mulched unshaded treatment and bare treatment under the canopy closely tracked one another and ended with similar cumulative evaporation.
The singular contribution of the straw mulch and crop canopy, each acting alone, were the same.
However, in limited irrigation straw mulch added a benefit to the canopy effect that was not evident in dryland management.
The reduction in evaporation by the straw compared with the bare soil was more under the canopy than without the canopy.
The straw mulch contributed to reducing energy limited evaporation more days under the canopy than in the unshaded treatment.
The evaporation probably shifted from energy to soil limited sooner after wetting in the unshaded than the canopy treatment.
Full irrigation included nine irrigation events, seven of which were at weekly intervals and two that were at two-week intervals.
The pattern of cumulative evaporation from the unshaded bare soil treatment indicated periods of both energy and soil limited evaporation.
These patterns were more subtle early in the bare soil treatment under the crop canopy.
The magnitude of unshaded bare soil evaporation was larger in the fully irrigated treatment, but the unshaded mulched and bare soil evaporation under the canopy was similar to the limited values.
These latter two treatments also tracked each other closely as they did in they limited management.
The reduction in evaporation from the wheat stubble was even more in the fully irrigated management than the limited and dryland management.
This effect started early and carried on throughout the growing season.
Table 1.
Projected growing season soil water evaporation including irrigation and rainfall days.
Year	Bare	Straw	Bare	Straw
 1986	7.6	7.6	5.2	5.2
 1987	8	7.1	6.1	5.7
 1986	10.4	8.5	7.6	5.2
 1987	11.3	9.4	8.5	5.7
 1986	15.1	8.5	7.6	3.8
 1987	14.6	9.4	8.5	4.7
 Table 2.
Full season soil water evaporation savings from straw cover compared with bare soil..
Year	Unshaded	Corn Canopy-
 Garden City, KS Study
 A similar study was conducted in Garden City, Kansas during 2004 in soybean and corn canopies.
Two twelve inch diameter PVC cylinders that held 6-inch deep soil cores were placed between adjacent soybean or corn rows.
The crop rows were spaced 30 inches apart.
These mini-lysimeters, which had been cored into natural field settings, were either bare or covered with corn stover or standing wheat stubble.
The treatments were replicated four times in plots that were irrigated once or twice weekly.
Soil water evaporation measurements began on June 2 and June 9 for corn and soybean, respectively.
The early season measurements were taken in an unshaded location out of the field setting and continued until June 30 and July 13 for corn and soybean, respectively.
At these times, the lysimeters measurements were initiated in the field.
Soil water evaporation measurements were recorded on 60 of 83 days between June 30 and September 20 for the corn canopy and 51 of 70 days between July 13 and September 20 for soybeans.
The missing days were due to rainfall and irrigation.
Average daily evaporation from measured data during vegetative and full canopy growth periods were used to fill the data gaps.
Growing season irrigation and rainfall event totals are in Table 3.
The irrigation amounts for fully watered corn and soybean were approximately half of normal.
Rainfall was above normal and timely and the soil profile was filled at the beginning of the season.
Table 3.
Growing season irrigation and rainfall events and accumulation for Garden City site during 2004.
Events	Inches	Events	inches
 Once/Week	3	3	4	4
 Twice/Week	7	7	9	9
 Rain	23	12.8	24	14.3
 Results in Table 4 are the total evaporation amounts for the growing season and the percentages of evapotranspiration.
The development of the crop canopy affected evaporation rates as the season progressed.
Evaporation rates and E as percentage of ET decreased as the canopy developed.
The results in Table 5 give the same possibilities for reductions in evaporation as the results from the previous Nebraska corn study.
Also, the roles of corn stover and standing wheat straw are shown.
The corn stover in the lysimeters covered 87% of the soil surface, which is equivalent to very good no-till residue cover.
These results reflect the maximum capability of the residue for evaporation suppression.
Table 4.
Projected growing season  soil water evaporation from soybean and corn crops with bare soil, corn stover, and wheat stubble surface treatments.
June 9-Sept.
20-	June 2-Sept.
20-
 Cover*	Soil E	% of ET	Soil E	% of ET
 Bare 1	6.50	33	5.78	32
 Bare 2	7.90	32	6.59	35
 Corn 1	3.80	19	3.10	17
 Corn 2	3.66	15	3.77	19
 Wheat1	3.37	17	2.72	15
 Wheat2	4.07	17	3.74	19
 * 1=weekly and 2=twice weekly irrigation frequency
 Table 5.
Growing season  soil water evaporation savings with corn stover and wheat stubble compared with bare soil.
June 9-Sept.
20--	June 2-Sept.
20-
 Cover*	Soil E	Soil E
 Corn 1	2.70	2.68
 Corn 2	4.24	2.82
 * 1=weekly and 2=twice weekly irrigation frequency.
No matter how efficient sprinkler irrigation applications become, the soil is left wet and subject to evaporation.
Frequent irrigations and shading by the crop leave the soil surface in the state of energy limited evaporation for a large part of the growing season.
Research has demonstrated that evaporation from the soil surface is a substantial portion of total consumptive use.
These measurements have been 30% of ET for E during the irrigation season for corn on sandy and silt loam soils.
It has also been demonstrated that crop residues can reduce the evaporation from soil in half even beneath an irrigated crop canopy.
The goal is to reduce the energy reaching the evaporating surface.
We may be talking about seemingly small increments of water savings in the case of crop residues.
The data presented here suggests the potential for a 2.5 to 3.5 inch water savings due to the wheat straw during the growing season.
Dryland research would suggest that stubble is worth at least 2 inches of water savings in the non growing season.
In water short areas or areas where water allocations are below full irrigation, 5 inches of water translates into possibly 20 and 60 bushels per acre of soybean and corn, respectively.
The pivot can be automated to run without water application for acquisition of data.
This can eliminate the labor requirements and save time for producers.
The SIS methods can be programmed to compute an irrigation recommendation based on the data collected.
However, research is needed to test different types of sensors mounted on the pivot and their use for irrigation management with SIS methods.
Irrigation Tests with Oranges effects of various irrigation practices on growth and production of citrus trees subject of studies
 M.
R.
Huberty and S.
J.
Richards
 Improper irrigation can reduce navel orange yields by 30% to 40%-under conditions where tree growth and vigor are only slightly influenced-according to results obtained in a long-term experiment at Riverside.
Irrigation requirements and methods vary throughout the citrus-growing sections; so results of experimental work carried on at one location may not be applicable to another.
Nevertheless, it is desirable to know the effects of various irrigation practices on growth and production of citrus trees.
A Washington navel orange grove of approximately 10 acres, planted in June, 1930, has been under various irrigation treatments since 1934.
Half of the trees are on sour and half on sweet rootstocks.
The soil is a Ramona sandy loam having a slightly consolidated subsoil.
Both winter and summer cover crops were grown during the first three years, and then only winter crops until 1948.
Summer weeds were controlled by cultivation, usually disked.
Under this practice, a marked cultivation pan developed.
Since 1948, the grove has been under nontillage, with oil spray for weed control.
The normal traffic in the grove has compacted the surface soil, but in the furrows nearest the trees where this compaction has not occurred, infiltration of irrigation water is good.
Furrow irrigation has been practiced with some variation in the number of furrows used.
The furrows are 200' long and are on an average grade of about 2%.
Irrigation water is from the Santa Ana River and ground water basin, and is of good quality, with less than 600 ppm-parts per million-of dissolved salts.
While the local growers have irrigation water supplied only at scheduled intervals, water storage facilities on the Citrus Experiment Station made it pos-
 Average Production for All the Plots of Test Field S-3.
sible, with few exceptions, to have water available on demand for the irrigation of plots.
Throughout the life of the orchard, the amounts of fertilizer applied have been relatively low.
Organic matter was applied whenever it was available.
In the early years of the experiment, the treatments were designed to study the effect of timing the irrigation applications and, with another series of plots, to measure the effect of irrigating so as to wet different amounts of the soil occupied by the root systems.
The table in this column gives the results of a series of treatments based on average yields from selected tree rows over a ten-year period.
The first two treatments show the effects of the frequency of irrigation.
The plots receiving frequent irrigation applications-an average of 6.5-were irrigated when the surface foot of soil had reached the wilting percentage as based on periodic soil moisture samplings.
The guide for timing the infrequent applications was not always the same but, in general, it was based on soil moisture and some measure of tree response such as fruit size or leaf water deficit.
As a soil moisture guide, the soil was allowed to reach the wilting percentage to a depth of three feet.
The timing of irrigations for the treatments labeled 40% and 80% was also determined when the surface foot of soil reached the wilting percentage.
An attempt was made to wet 40% and 80% of the root zone of the trees.
This was accomplished by increasing the number of furrows and running the water longer in the center furrows for the 80% treatment.
It was evident that the most efficient use of water was made when the water
 Average Yields of Selected Rows and Water Used Over a 10-year Period.
Treatment	lbs./tree	Yield	Surface	Irriga-
 frequent	221	34.7	6.5
 infrequent	182	27.4	3.3
 40%	219	20.5	6.7
 80%	198	29.5	5.3
 was confined to the smaller volume of soil.
As between the plots said to be frequently irrigated-average 6.5 irrigations-and the infrequently irrigated plots-3.3 irrigations-the difference in yield was highly significant.
The reduction in yield was relatively large compared with the other tree growth measurements.
Under the conditions of this experiment, relatively large water applications in the 80% treatment did not result in increased production.
A study of the root distribution made in 1951 showed that only about 15% of the feeder roots were below a depth of 30", and less than 4% of the roots were found below 42".
Rate of soil moisture absorption, as measured by soil sampling, showed a higher percentage of roots in the lower depths in 1940 than those reported above.
This indicates that water moving beyond a depth of three feet is largely wasted.
Had these experimental plots been located in an area where soil salinity is a problem-or where the irrigation water was high in soluble material-it is very likely that on plots where water Concluded on page 15
 Effects of Irrigation Interval on Yields for Navel Oranges.
Year	Root-	stock	2	7	3	6
 1948 sweet	63%	71%	100%	105%
 sour	69	80	107	104
 1949 sweet	93	98	106	110
 sour	91	93	103	109
 1950 sweet 66	61	94	128
 sour	65	87	112	159
 1951 sweet	99	121	53	85
 sour	98	113	74	106
 1952	swt.
109	145	67	71
 sour	95	113	76	76
 1953 swt.
108	131	108	124
 sour	100	122	112	120
 The plot yields are given as per cent of the yearly average for an entire 10-acre block.
Continued from page 8
 was maintained for three years-1948 to 1950.
During this period, the yields were greater for the plots on the three-week schedule.
In order to have a better comparison of the relative effects of irrigation during the 1951 and 1952 seasons, the irrigation schedules were reversed, and in 1953, the treatments were reversed to those of the 1948-1950 period.
It is generally recognized that irrigation is only one of the factors influencing crop production.
The table in column one on page 8 gives the average production for the entire 10-acre block, including all of the irrigation treatments and both sweet and sour stocks.
was added in excess of the amount used by the trees, the trees would have shown a favorable response.
Under such conditions, the excess water would remove undesirable salts which would otherwise accumulate in the root zone.
There is no significant difference between yield of sweet and of sour rootstock in the long-run experiment, even though significant differences did appear in the early analysis.
This is due to the superiority of trees on sweet rootstock in the early years, with trees on sour rootstock being the better yielders in later years.
Many growers have irrigation water supplied at scheduled intervals only.
In recognition of this, the plots which were under the frequent treatment were later watered on a three-week schedule, and the plots which were infrequent were changed to a six-week irrigation interval.
More water was added per irrigation on the six-week plots so that the seasonal total did not differ by more than 25%.
The calendar schedule for these plots
 in a considerably lower yield, yet the trees responded and produced up to the grove average on the first year that the irrigation schedules were reversed.
For the years 1949 and 1953, some factor other than interval of irrigation-possibly climatic conditions-was such that 3.
and 6-week irrigation intervals did not result in significant yield differences.
During the crop years 1948 to 1950, there were no planned changes in any of the irrigation treatments or grove management practices, yet these years included the greatest variation in crop production.
To show the relative effects of changing the irrigation practices, the plot yields resulting from the various irrigation practices are given in the table in column three on page 8.
Plots No.
2 and No.
7 had a history of 16 years where infrequent irrigation schedules resulted
 In addition to yield records, trunksize measurements were made annually as an index to tree growth.
In 1950, the records show that after 15 years of differential treatments, the average crosssectional areas of the trees on plots No.
3 and No.
6-frequently irrigated-were only 9% larger than for plots No.
2 and No.
7-infrequently irrigated.
This difference in size did not limit the yield of the trees of plots No.
2 and No.
7, since their production was greater for 1951 and 1952 when the irrigation treatments were reversed.
M.
R.
Huberty is Professor of Irrigation, University of California, Los Angeles.
S.
J.
Richards is Associate Irrigation Engineer, University of California, Riverside.
The above progress report is based on Research Project No.
904-D.
DONATIONS FOR AGRICULTURAL RESEARCH
 BERKELEY	Gulf State Asphalt Co.
37 sheets asphalt canal lining;
 100# hot asphalt; 15 gais.
adhesive
 American Cyanamid Co.
3 15# drums 2% exp.
insecticide	For studies on canal linings
 For tomato insect investigations
 California Cedar Products Co.
Copper pressure vessel	Ipsen Manufacturing & Supply Co.
For experimental poultry housing	200 12" cages
 For research in wood chemistry
 Chemagro Corporation	For melon insect investigations	1 gal.
Meta-Systox spray concentrate	Kalmbach-Burckett Company, Inc.
For Field Station experiments	120# soybean seed
 Dow Chemical Company	100# Ovotran wettable	National Canners Association	$500.00
 For melon insect investigations	For experimental packing of pears for taste tests
 Mrs.
Alice Eurich	Surgical instruments	National Science Foundation	$2,300.00
 For poultry husbandry research	For cytogenetic studies in the genus Lycopersicon
 Pacific Molasses Co...
3 drums 10% protein-equivalent "Promol" molasses
 DAVIS	For application to oat hay to test palatability for sheep
 Agriform Co., Inc.
5 gal.
sulfuric acid	Shell Chemical Corporation	For taste evaluation of crops grown with insecticides	$1,200.00
 For Field Station experiments
 A.
M.
Andrews Co.
For studies to determine flow characteristics of tubing	25 ft.
6 inch supported vinyl sheet tubing	Stockton Tallow Works Co.
For nutritional experiments with swine	1200# stabilized tallow
 Bakelite Co.
For studies with canal linings	80 yd.
polyethylene film	Sugar Research Foundation, Inc.
For research on effect of various types of sugars on canned cling peaches		$2,500.00
 California Beet Processors	For sugar beet research	$3,000.00	Public Health Service	For detection and identification and differentiation of	$3,611.79
 California Committee on Relation of Electricity to Agriculture $4,125.00	the virus of vesicular disease viruses
 For investigations of electrical applications to agriculture	The Upjohn Company	$400.00
 California Tree Fruit Agreement	$1,250.00	For field and laboratory studies of mastitis ointments and
 For Bartlett pear maturity studies	research on mastitis in dairy cattle
 Calord Corporation	Plastic Home Watering System, 100' unit	complete with fittings	Western Condensing Co.
For research on use of soybean products in animal feeds	$1,200.00
 For experimental use of poultry watering system in cage houses
 Canners League of California	$1,500.00	LOS ANGELES
 For continuation of tomato breeding work	Brea Chemicals, Inc.
100# ammonium sulfate
 Citrus Industry Research Association	$750.00	For turfgrass culture research
 For field expenses in connection with bulk-handling	studies involving citrus fruit	Calavo Growers of California	For subtropical horticulture research	1000 Nabal avocado seeds
 Dewey and Almy Chemical Company	Cry-O-Vac Aluminum Clips	standard size-10#-4,000	California Planting Cotton Seed Distributors	$10,000.00
 For experimental packaging of poultry products	For defoliation research in cotton
 Dow Chemical Company	For Field Station experiments	1 gal.
Kuron weed killer	Geigy Agricultural Chemicals	For entomological experiments in avocado grove	48# DDT wettable powder
 E.
I.
du Pont de Nemours Co.
4# Karmex W.
Herbicide	6 1/2 gals.
Quilon	Wilson & George Meyer & Co.
For turfgrass culture research	100# Hi-Press peat moss
 For experiments of seepage loss in irrigation canals	Concluded on next page
 Gifts to the University of California for research by the Division of Agricultural Sciences accepted in August, 1954
Figure 1.
A hypothetical map of soil properties , possible speed control zones , and conceptual average soil properties for each management zone.
Speed control may be sufficient to account for variability in some fields.
2017-2018 Irrigated Soybean Seeding Rates
 Over the last ten years, several Universities have reported that planting soybeans at lower populations doesnt necessarily reduce yield, but can increase margins.
Studies at Ohio State between 2014-2016 indicated better returns with reduced seeding rates and an agronomic optimum planting rate of 150,000 seeds/acre.
Both Iowa State and Nebraska have observed that a final stand of 100,000 plants  does not always reduce yield, but does improve margins due to lower seed costs.
Regionally, Virginia Tech recommends higher planting rates for poor ground , while fields with yield of 55-70 bu/acre could go as low as 90,000 seeds/acre.
In order to test lower seeding rates locally, a study was conducted at the University of Delaware Warrington Research farm in 2017 and 2018.
Soybeans were planted at four rates  with and without irrigation in a field with a corn-soy rotation.
Asgrow 4135 soybeans were planted on May 18, 2017 and Dynagrow S40LL35 were planted on May 10, 2018.
In both years, seeds were planted in 15 rows with a monosem vacuum planter equipped with variable rate seeding technology.
Stand counts were taken to determine final population each year.
Actual stands were 81-90% of the planting rate, with lower emergence and survival as seeding rate increased.
No significant differences were observed  in soybean yield in 2017, 2018, or when both years were combined.
When potential income across both years was calculated, the lowest seeding rate of 80,000 seeds per acre had the greatest income.
The use of irrigation improved yields by 19 bu/acre in 2018, while there was a 7 acre/bu averaged across both years.
No advantage was measured in 2017, which may be due to adequate rainfall balancing the need for irrigation.
Compared to the previous summer, rainfall was lower during a critical reproductive stage, potentially lower yields in non-irrigated plots.
Normalized difference vegetation index  was used to monitor plant growth over the summer 2018.
Plot borders are present on June 12 and July 3, by July 13 most variability in NDVI appears to be soil related rather than planting rate.
On August 27th most plots under irrigation have reached full canopy, which is reflected in the NDVI.
Alternatively, the non-irrigated plots typically have lower NDVI values, with soil variability  present.
Our results are consistent with those from other parts of the US, where lower seeding rates dont necessarily result in a lower yield.
This study was only performed on one soil type though, and may not have similar results across the state.
Achieving good stands at lower planting rates will require proper planting depths and good seed to soil contact.
Irrigation during dry periods will, at a minimum, protect yields.
Water for Beef Cattle
 Shane Gadberry Associate Professor Animal Science
 Livestock require the proper balance of water, carbohydrates , protein, vitamins and minerals for optimal levels of performance.
Of these nutrients, water is the most critical for all classes of livestock.
Cattle have little ability to adapt to water restriction, and feed intake will be greatly reduced following only short periods without water.
Because of this, a plentiful supply of good quality water is necessary for profitable beef production.
Many factors influence the amount of water required by cattle.
Table 1 shows average water needs for various classes of beef cattle.
Note that water consumption varies considerably, depending on the temperature and stage of production.
These allowances are not absolute requirements and should only be used as a guide in developing water sources or as a starting point for supplying water to penned cattle.
Water consumption is influenced by other factors, such as moisture and protein level of the feed, salt intake,
 relative humidity and the breed of cattle.
When high-moisture feeds such as silage or fresh forages are used, water intake as drinking water is reduced.
Because of the need to excrete more urine, high levels of salt or protein in the feed increase water needs.
In areas with high humidity, animals require somewhat less water because of lower losses to evaporation.
Brahman cattle have a greater ability to adapt to hot, dry conditions than the temperate breeds of cattle, so they better withstand short-term water restriction.
Because of the importance of water to body function and the difficulty in estimating requirements, cattle in all circumstances should have free access to all the quality water they will consume.
Arkansas Is Our Campus
 Quality of drinking water for both humans and livestock is a growing national issue.
Some water supplies have been contaminated by agricultural chemicals or contain naturally occurring contaminants that interfere with animal performance.
The purpose of this fact sheet is to provide an outline for maximum tolerable levels
 Table 1.
Estimated Daily Water Intake of Cattle, Gallons/Day 
 Daily	Cows	Dry and	Growing and Finishing Cattle
 Temp	Calves1	Cows	Bulls	400 lb	600 lb	800 lb	1,000 lb
 35	11	6	7	4	5	6	8
 50	13	7	9	5	6	7	9
 65	16	8	11	6	7	9	11
 80	18	11	13	7	9	10	14
 95	20	15	20	11	15	17	19
 1First four months of lactation.
of contaminants in water and to promote practices that help to maintain water quality and prevent pollution of water sources by beef cattle.
Salinity.
Waters that contain high levels of dissolved salts  can result in depressed performance of beef cattle.
These waters are normally found in wells in coastal regions of the southeast.
The following guidelines should be used with water high in TDS.
In general, the type of salt  has little influence on the acceptable levels.
Cattle prefer water containing some salt, but increasing levels to about 5,000 ppm TDS reduces intake and average daily gain by about 10 percent for feedlot cattle.
Water containing from 5,000 to 7,000 ppm TDS is safe for cattle in most cases but likely results in depressed performance.
Water containing from 7,000 to 10,000 ppm TDS is safe only for dry cows under low levels of environmental stress, and water containing more than 10,000 ppm TDS should not be used for cattle.
When use of a water source high in TDS is necessary, gradually adapt animals rather than rapidly switch water sources.
It is also important to consider the fact that consumption of salty feeds, such as a salt-limited protein or mineral supplement, is influenced by TDS in drinking water.
When animals are fed salt-limited supplements and the water supply is highly saline, intake of the supplement is reduced and protein or mineral deficiency could result.
Individual salt compounds may be measured to determine TDS, or electrical conductivity may be used to estimate salinity of water.
Nitrates.
Nitrate in drinking water can be a problem for livestock in the southeastern United States.
A guide to evaluating water contaminated with nitrates is given in Table 2.
Water test results generally have nitrates and nitrites combined and may report levels as nitrate nitrogen, nitrate ion or sodium nitrate.
This can greatly affect interpretation of the results.
Levels in Table 2 are expressed in the three major forms that may be reported.
Nitrate is not poisonous to livestock, but it can be converted in the gastrointestinal tract to nitrite, which impairs oxygen transport by the blood.
Nitrite converts the hemoglobin  in red
 blood cells into methemoglobin, which is brown in color and does not bind oxygen.
Excessive nitrate intake  may result in a lethargic animal and sudden death.
Animals may adapt to high levels of nitrate if levels are raised gradually, but chronic exposure either in feed or water may result in depressed feed intake, depressed growth rate and abortions.
In some situations, nitrate levels in water will be below maximum tolerable levels, but because of substantial levels of nitrate in forages, the water may contribute to a nitrate toxicity problem.
Nitrates in runoff from agricultural fields are quickly dissipated from rapidly flowing surface waters through volatilization, so nitrate is normally a problem met when using well water, especially shallow wells in agricultural areas.
Avoid ditches and ponds as water sources because ditches and ponds on poorly drained land can collect runoff from cropland which may contain high levels of nitrates as well as other agrochemicals.
Failure to test soil over many years results in excessive nitrogen fertilization in some areas.
The nitrogen then leaches into the soil and enters shallow groundwater.
The leaching of nitrate from improper waste management facilities around livestock, especially heavy concentrations of swine operations on sandy soils, may contaminate shallow surface water.
When planning a forage system that may lead to high forage nitrate levels, it is strongly recommended that cattle drinking water be tested for nitrates.
Blue-green algae.
Stagnant waters may contain excessive levels of blue-green algae, which may be toxic and result in death of cattle.
Because of their stagnant, nutrient-rich nature, small ponds and streams in late summer can have toxic algae blooms.
Toxicity is most common following a rapid bloom in late summer when cattle are consuming a substantial amount of the algal surface scum.
The problem is difficult to predict, and the first sign may be sudden animal death.
Because of this, it is advisable to restrict cattle access to stagnant waters, especially when a substantial amount of algae scum is visible.
Algae blooms can be controlled in ponds through the use of copper sulfate , but the rapid dieoff of algae may result in a fish kill.
Table 2.
A Guide to the Use of Waters Containing Nitrate for Cattle 
 Form of Nitrogen Reported 
 Acceptability	Nitrate Nitrogen	Nitrate lon	Sodium Nitrate
 Safe	Less than 100	Less than 443	Less than 607
 Questionable	100-300	443-1329	607-1821
 Unsafe	Over 300	Over 1329	Over 1821
 1 Water analysis labs will report values in one of these three ways.
Values are reported in parts per million.
2 These waters should be used with caution.
High nitrate in forages, or high temperatures , could result in problems.
3 Cattle should not have access to these waters.
The best method to control algae is to eliminate the source of nutrients entering the pond.
If copper sulfate is used, the recommended application rate to water depends on the alkalinity  of the water.
Copper ions can kill fish if the water's total alkalinity is below 40 ppm.
Copper sulfate treatment may be ineffective if alkalinity of the water is greater than 300 ppm.
The maximum tolerable level of copper sulfate in water is 2.7  and 6.8  pounds of copper sulfate per acre-foot.
The formula to calculate the pounds of copper sulfate needed is as follows:
 Total alkalinity  100 X 2.04 X acre-foot volume = Pounds of copper sulfate needed
 Do not exceed the application limits for livestock, especially sheep.
Livestock  should not be watered for at least five days after the last visible evidence of the algae bloom.
Care should be taken to avoid water that has algae cells, either from treatment with algicide or natural aging of the bloom, because most toxin is freed in the water only after breakdown of the intact algae cells.
Substances in water.
Other substances in water that may cause problems for beef cattle are listed in Table 3, along with maximum safe levels.
Problems that are common are high or low pH or excessive levels of sulfates, hydrogen sulfide, iron or manganese.
These factors may result in decreased water intake because of off-flavors.
In addition, excessive levels of some minerals may interfere with normal trace mineral absorption, especially of copper and zinc, and lead to nutritional deficiencies.
In some situations, shallow groundwater or surface water may be contaminated with agricultural chemicals such as pesticides.
Any shallow well, stream or pond adjacent to cropland with a long history of agricultural chemical use should be tested for major chemicals before being used as the water source for cattle.
Guidelines for pesticides and herbicides in water for beef cattle have not been established, so allowable levels in drinking water for humans are given in Table 4.
Because of the possibility that these chemicals in water could lead to residues in meat, take every effort to prevent water contamination.
Sampling water for analysis.
Water supplies should be taken for analysis if a producer suspects water is causing a problem or when a new source of water is developed.
If sampling will be done only once, take samples when water is at its lowest quality.
Quality shouldn't vary much for springs and wells, but ponds and streams will normally be lowest in quality during late summer.
Test streams and ponds when water is highest  and lowest  in quality.
Care should be taken to get a sample representative of what the cattle are drinking.
Water analysis can be evaluated for abiotic  and biotic  components.
In Arkansas, water samples can be submitted to the Arkansas Water Resources
 Table 3.
Recommended Limits for Some Potentially Toxic Substances in Drinking Water for Beef Cattle
 Nitrate nitrogen	See Table 2
 Salinity 	3000
 Total dissolved solids	2500
 pH	Range 5.5 to 8.5
 No upper limit established because of limited experimental data.
Table 4.
Maximum Allowable Concentrations of Pesticides in Human Drinking Water 
 Center, Water Quality Laboratory through local county Extension offices.
Maintaining water quality and preventing water pollution.
Because of the importance of highquality water to beef production, producers should do everything possible to maintain the quality of their water sources.
If a well is used as the primary water source, it should be properly graded and capped to prevent contamination by runoff surface water, and fertilizer and other chemical applications to adjacent pasture or cropland should be closely controlled.
Apply nitrogen fertilizers only according to soil test results.
Forage systems decreasing the need for added nitrogen should be used.
In addition, keep waterers as clean as possible.
A waterer with excessive algal growth or other filth can decrease water
 intake and performance, even though the water is apparently of high quality.
Cattle should not have unlimited access to ponds and streams.
In addition to using these water sources for drinking, cattle will also loaf in water, especially in hot weather.
This results in both fecal and urinary contamination.
In ponds and slow-flowing streams, this results in deteriorating water quality as summer progresses.
Cows can also contract diseases such as mastitis and leptospirosis from lounging in dirty water.
When cattle have recently been sprayed with insecticides or tagged with fly tags, they should not be allowed to loaf in water.
Allowing free access to ponds can result in fish kills, or possibly complete sterilization of a pond.
Ponds can be kept clean and provide good-quality water if they are fenced, and cattle have access to only a small area in one corner, or if water is run through a pipe to a tank at the base of the dam.
Quality of the pond for recreational uses such as swimming and fishing will also be improved by keeping the cattle out.
Weeds and algae may be a problem in ponds, especially if they get drainage water from cropland, or if cattle have free access to the ponds.
To control such problems, first find and eliminate the source of nutrients if possible.
Herbicides can be used to kill off the weeds, and copper sulfate can be used to control algae.
When open streams are the water source, cattle cause stream bank erosion and contaminate the water with manure and urine.
The sediment and nutrient-polluted water then flows to the next farm and eventually enters rivers and lakes where it can cause algae blooms and fish kills.
Likewise, water contaminants may enter the farm from upstream, and the contaminated water can result in spread of diseases such as leptospirosis.
For these reasons, preventing cattle access to streams is advisable to protect the producers and their neighbors, as well as the general public.
Mike Daniels Professor and Environmental Management Specialist Agriculture
 Brian Haggard Associate Professor Water Quality
 Andrew Sharpley Professor Crop, Soil and Environmental Sciences
 Arkansas Is Our Campus
 During the last two decades, there has been a tremendous increase in efforts to protect the quality of our nation's water resources.
This stems from the recent changes in philosophy of addressing impaired water bodies by trying to find and treat the source rather than the problem, which became increasingly expensive.
Many of these efforts, especially local ones, have begun utilizing the concept of watersheds as a basis for defining the geographical scope of protection activities.
Watersheds provide the natural catchment boundaries for isolating geographical areas with similar hydrological influence.
Watershed protection efforts range from federal regulations to voluntary efforts such as local watershed organizations consisting of concerned citizens.
Future water quality protection efforts will be implemented on a watershed basis.
For example, the Arkansas Natural Resource Commission's Title 22  defines nutrient-sensitive watersheds where residents must meet certain requirements before applying nutrients to land.
A nutrient-sensitive watershed is defined as "an area in which the soil concentration of one or more nutrients is SO high or the physical characteristics of the soil or area is such that continued application of the nutrient to the soil could negatively impact soil fertility and the waters within the state." Thus, monitoring efforts are aimed increasingly at determining the status of soil and water resources within an entire watershed and establishing a better understanding of how land use within the watershed affects
 the quality and biodiversity of water in streams and rivers.
Everyone lives in a watershed, and everyone can play a part in watershed protection.
It is important to understand the concepts associated with watersheds: how they are designated and named, how their boundaries differ from political boundaries and why they are important to the protection of water resources.
This fact sheet will address these items as well as provide information on the watersheds of Arkansas.
What Is a Watershed?
The United States Environmental Protection Agency  defines a watershed as "the area of land where all of the water that is under it or drains off of it goes into the same place." A watershed, catchment or drainage basin catches precipitation that falls within its boundaries and funnels it to a particular creek, stream, river or groundwater formation.
Figure 1.
Graphical representation of a watershed.
Watershed boundaries divide one drainage area from another.
Some characteristics of watersheds include:
 Boundaries are defined by natural hydrology.
For surface drainage boundaries, physical geographic features such as elevation and relief can be used to define the location of boundaries.
Surface drainage boundaries can be estimated from a topographical map.
Surface drainage within the watershed boundaries is to a central outlet or collection point unique to that drainage area.
While it is easy to observe surface drainage in many watersheds, most water  can move below ground and thus be more difficult to measure and influence.
Larger watersheds can be divided into smaller sub-watersheds.
Boundaries can cross political boundaries such as county or state lines.
No two watersheds are the same.
Watersheds have unique topographic and geologic properties which define water flow pathways and the quantity and quality of water moving within them.
Because watersheds are defined by natural hydrology, they represent the most logical basis for managing water resources.
Basically, any land use activity within a watershed, be it large or small, can impact water resources.
Some activities can improve or maintain water quality, increasing biological diversity, wildlife habitat, recreational value, fish production, drinking water supply, etc.
On the other hand, we know other activities can negatively impact or damage these resources.
A key issue in addressing these
 activities and keeping watersheds healthy is protecting the economic and environmental sustainability of both land and water resource users in a watershed.
These resources become the focal point, and managers are able to gain a more complete understanding of overall conditions in an area and the stressors that affect those conditions.
In this manner, water quality issues can be addressed in a more systematic, comprehensive approach that may be unique to an individual watershed.
Because surface drainage is to a unique, central outlet, the potential source area for pollutants derived from the landscape  can be defined by the watershed boundaries.
Even though the exact location of the origin of nonpoint source pollutants within a watershed may not easily be determined, knowing the watershed area helps foster understanding of the land use relationships to in-stream water quality conditions.
This understanding can help watershed managers develop better, more applicable solutions to the issue.
In this manner, addressing water quality issues can be more efficient in terms of resource protection and resource allocation.
For example, upgrading water treatment facilities in New York City was going to cost $10 billion.
However, upon considering the condition of the watershed of the city's drinking water source, it was determined that spending $20 million helping watershed stakeholders improve certain aspects of watershed management could achieve the same benefit as the more costly alternative.
How Are Watersheds Identified?
Because larger watersheds are made up of smaller subwatersheds, it can be difficult to identify or separate watersheds from one another.
A watershed is
 usually identified by its name, which is usually based on the major drainage or collection feature of the area such as a stream, river or lake.
But names alone do not tell us much about the characteristics of a watershed.
Drainage basins, or watersheds, come in all shapes and sizes, with some only covering an area of a few acres while others are thousands of square miles.
To overcome this, the United States Geological Survey has developed a classification scheme known as Hydrologic Unit Code.
This system is a way of identifying all of the watersheds in the United States in a nested number arrangement from largest  such as the Mississippi River to smallest watersheds.
The United States is divided and subdivided into successively smaller hydrologic units which are classified into four major levels: regions, sub-regions, basins and sub-basins.
Each hydrologic unit is identified by a unique HUC consisting of digits ranging from two to eight digits based on the four levels of classification.
What Do the Numbers in a HUC Represent?
The first level of classification divides the nation into 21 major geographic areas or regions.
Eighteen of the regions occupy the land area of the conterminous United States.
Alaska is region 19, the Hawaii Islands constitute region 20 and Puerto Rico and other outlying Caribbean areas are region 21.
These numbers represent the first two digits of the HUC.
The second level of classification divides the 21 regions into 222 sub-regions.
A sub-region includes the area drained by a river system, a reach of a river and its tributaries in that reach, a closed basin or a group of streams
 forming a coastal drainage area.
The sub-region is represented by the third and fourth digits on the HUC.
The third level of classification subdivides many of the subregions into basins.
These 352 hydrologic basins nest within the sub-regions.
They are represented by the fifth and sixth digits of the HUC.
For HUC purposes, basins are referred to as accounting units.
The fourth level of classification is the sub-basin, the smallest element in the hierarchy of hydrologic units.
A sub-basin unit is a geographic area representing part or all of a surface drainage basin, a combination of drainage basins or a distinct hydrologic feature.
There are 2,150 subbasins in the nation, and they are represented by the seventh and eighth digits in the HUC.
Sub-basins are often called "eight-digit watersheds." For HUC purposes, basins are referred to as accounting units.
The eight-digit watershed is the most widely used hydrological unit in water resource planning, management and policy.
Hydrologic unit codes can contain more than eight digits; however, until recently, the techniques to easily delineate watershed boundaries beyond eight digits were impractical.
With the advent of geographic information systems , efforts are now underway by state and federal agencies to delineate eight-digit watersheds into twelveand fourteen-digit watersheds.
Arkansas Hydrologic Unit Codes
 In Arkansas, there are only two major hydrologic regions : the Lower Mississippi  and the Arkansas-Red-White Rivers  drainage systems.
This
 Figure 3.
The twenty-one hydrologic regions of the United States.
Arkansas has two hydrologic regions: the Lower Mississippi  and the Arkansas-White-Red.
Source: The United States Geological Survey
 means all hydrologic unit codes  begin with either the digits 08 or 11.
Sometimes the "0" in 08 is left out of the HUC.
The two hydrological regions in Arkansas contain nine subregions or nine four-digit watersheds.
Arkansas contains five river basins.
The hydrological unit code for basins contains six digits.
In Arkansas, the HUC for basins will begin with one of the nine
 four-digit codes listed in Table 1 and end in the two-digit accounting code assigned to the basin.
Arkansas has 57 eight-digit watersheds.
These watersheds serve as a good starting point for knowing the watershed in which you live and for local water resource protection planning.
The Arkansas Natural Resources Commission used eight-digit watersheds as the basis for defining inutrient-sensitive
 watersheds in Title 22, Rules Governing the Arkansas Soil Nutrient and Poultry Litter Application and Management Program.
They also used eightdigit watersheds as a basis for determining the state's priority watersheds for nonpoint source abatement as required by the Environmental Protection Agency under the Federal Clean Water Act.
The Arkansas Department of Environmental Quality  has used eight-digit watersheds as the structure for defining impaired waters within the state, which it is required to report to Congress every two years to fulfill its obligation to federal regulations defined under the Clean Water Act.
The eight-digit watersheds have been used by concerned citizens as the local geographical basis for organizing nonprofit groups whose goals are to protect the water resources in their watershed.
Two examples include the Bayou Bartholomew  Alliance and the Little River Watershed  Coalition.
Figure 4.
Sub-regions of Arkansas
 Figure 5.
Basins of Arkansas.
Watersheds and Water Quality
 Water quality standards for nutrients have been set on a watershed basis by the U.S.
EPA Office of Water as part of its National Regional Nutrient Criteria Program.
To do this, reference conditions or background
 levels found in pristine streams, lakes, reservoirs and other surface waters in a given geographical area have been identified.
Waters where there is the least amount of human impact were monitored for total P, total N, chlorophyll-a and clarity.
These values become a benchmark against which similar watercourses in the area can be compared.
The difference between the reference condition for a given
 nutrient and current measurement indicates the relative extent of management required to protect or restore the nutrient quality of that water to an approximately "natural" state.
Pristine waters of the type existing before European settlement are almost impossible to achieve, but a reasonably natural condition reflecting reduced cultural impacts of human activities can be identified.
The reference condition approach makes it possible to demonstrate
 that such minimally impacted waters do in fact exist for that type and locale, so that management efforts are based on realistic background conditions for a watershed in each geographic  area.
The significance of these regional nutrient criteria to watersheds and their management is that resource managers and concerned farmers have an attainable target of nutrient
 reduction to aim for in planning conservation farming practices within a watershed.
While these criteria have application to the regulatory function of EPA, in that nutrient standards and permit limits can be derived, criteria values are also suitable for voluntary watershed planning programs and evaluation purposes.
With these target values in mind, a given watershed can be divided into constituent subwatershed land units and the goal of a particular nutrient level parceled out among the tributary systems.
Subsequently, individual farmers can target nutrient load amounts as their equitable share of the water quality protection
 objective.
This, of course, is subject to considerable variability including an understanding of watershed hydrology as it influences water flow pathways, the nutrient delivery rate from soils and slopes draining to those streams as well as seasonal changes in precipitation.
Table 1.
Sub-regions in Arkansas and their associated four-digit Hydrologic unit code.
Hydrological Region 	Sub-Region	HUC
 Lower Mississippi 	Lower Mississippi-Hatchie	0801
 Lower Mississippi-St.
Francis	0802
 Arkansas-White-Red 	Lower Arkansas	1111
 Figure 7.
Draft aggregations of level III ecoregions for the National Nutrient Strategy.
Table 2.
Arkansas eight-digit watersheds  by region.
Lower Mississippi River Region	Arkansas-White-Red Region
 HUC	Watershed Name	HUC	Watershed Name
 08010100	Lower Mississippi-Memphis	11010001	Beaver Reservoir
 08020100	Lower Mississippi-Helena	11010003	Bull Shoals Lake
 08020203	Lower St.
Francis	11010004	Middle White
 08020204	Little River Ditches	11010005	Buffalo
 08020205	L'Anguille	11010006	North Fork White
 08020301	Lower White-Bayou Des Arc	11010007	Upper Black
 08020302	Cache	11010008	Current
 08020303	Lower White	11010009	Lower Black
 08020304	Big Creek	11010010	Spring
 08020401	Lower Arkansas	11010011	Eleven Point
 08020402	Bayou Meto	11010012	Strawberry
 08030100	Lower Mississippi-Greenville	11010013	Upper White-Village
 08030207	Big Sunflower	11010014	Little Red
 08030209	Deer-Steele	11070206	Lake O' The Cherokees
 08040101	Ouachita Headwaters	11070208	Elk
 08040102	Upper Ouachita	11070209	Lower Neosho
 08040103	Little Missouri	11110103	Illinois
 08040201	Lower Ouachita-Smackover	11110104	Robert S.
Kerr Reservoir
 08040202	Lower Ouachita-Bayou De Loutre	11110105	Poteau
 08040203	Upper Saline	11110201	Frog-Mulberry
 08040204	Lower Saline	11110202	Dardanelle Reservoir
 08040205	Bayou Bartholomew	11110203	Lake Conway-Point Remove
 08040206	Bayou D'arbonne	11110204	Petit Jean
 08050001	Boeuf	11110205	Cadron
 08050002	Bayou Macon	11110206	Fourche La Fave
 08010100	Lower Mississippi-Memphis	11110207	Lower Arkansas-Maumelle
 08020100	Lower Mississippi-Helena	11140105	Kiamichi
 08020203	Lower St.
Francis	11140106	Pecan-Waterhole
 08020204	Little River Ditches	11140108	Mountain Fork
 08020205	L'Anguille	11140109	Lower Little
 08020301	Lower White-Bayou Des Arc	11140201	Mckinney-Posten Bayous
 Water resource protection is increasingly being done on a watershed basis.
This will only continue to expand.
Understanding how watersheds function will be vital to more efficient and effective protection efforts.
New technology is allowing us to separate eight-digit watersheds into progressively smaller sub-watersheds
 that will be easier to characterize and manage.
This move to smaller watersheds will allow for better understanding of those factors that degrade watershed resources and, in turn, more targeted watershed protection approaches.
The University of Arkansas Division of Agriculture has announced plans for a Watershed Research and Education Center to help all of us better understand what
 watersheds are, how they function, how they can be managed to everyone's benefit and, most importantly, that everyone can contribute to watershed protection.
The Watershed Research and Education Center will be created to specifically target a variety of stakeholder groups from cow/broiler/pasture producers to urban dwellers and stakeholders
 from ages K-12 to adult.
The Center will serve as a forum to transfer evolving and innovative sustainable management strategies to these groups.
A key component of the Center will involve a stakeholder Executive Council to ensure stakeholder input to WREC activities.
The Council will advise the project director and co-investigators on which Best Management Practices  should be implemented, demonstrated and educated.
educational activities and demonstrations.
This involvement will facilitate stakeholder ownership in evolving WREC as a nationally recognized forum for technology transfer to this underserved clientele.
Once BMPs are established, the Council will guide the focus of field days, walking tours,
In this drought year, many irrigated fields have very little subsoil moisture, while other portions of Nebraska have experienced significant rains over the last month.
With irrigation, any grower can can over-irrigate early and create a wet spring.
The most reliable method to know when and how much to irrigate is to monitor soil moisture at multiple depths.
Keep in mind that when irrigation is applied with a center pivot an inch at a time on the soil surface, the top foot will stay very wet all summer.
Tiffany Maughan, Dan Drost, Niel Allen and Brent Black
 Proper irrigation is essential to growing a healthy and productive melon crop.
For ideal fruit development, a consistent moisture supply throughout the season is necessary.
Too little irrigation will result in weak plants with under-sized fruits and reduced quality.
Over irrigation can lead to disease problems and nutrient leaching.
There are a number of irrigation systems that can be used to irrigate a melon crop, each with different management considerations.
Regardless of the irrigation system used, there are some basic principles to understand that will help ensure proper irrigation.
This fact sheet will discuss these basic principles.
Properly managing irrigation is analogous to managing money.
In addition to knowing your current bank balance , it is important to track both expenses  and income.
Bank Balance 
 How big is my bank account?
Water holding capacity First, some terminology:
 Field Capacity is the amount of water that can be held in the soil after excess water has percolated out due to gravity.
Permanent Wilting Point is the point at which the water remaining in the soil is not available for uptake by plant roots.
When the soil water content reaches this point, plants die.
Available Water is the amount of water held in the soil between field capacity and permanent wilting point.
Allowable Depletion  is the point where plants begin to experience drought stress.
Depending on soil type, the amount of allowable depletion for melons is about 50% of the total available water in the soil.
The goal of a well-managed irrigation program is to maintain soil moisture between field capacity and the point of allowable depletion, or in other words, to make sure that there is always readily available water and that plants do not experience water stress.
Figure 1.
Soil water content from saturated to dry.
Optimal soil moisture levels for plant growth are between field capacity and allowable depletion.
The amount of readily available water is related to the effective rooting depth of the plant, and the water holding capacity of the soil.
The effective rooting depth depends on soil conditions and variety.
About 70% of melon roots are in the top foot of soil, with 30% in the second foot and the tap roots extend down to 3 feet.
The water holding capacity within that rooting depth is related to soil texture, with coarser soils  holding less water than fine textured soils such as silts and clays.
A deep sandy loam soil at field capacity, i.e., would contain 0.6 to 0.75 inch of readily available water in an effective rooting depth of 1 foot.
What's in the bank?
-Measuring Soil Moisture
 In order to assess soil water content, one needs to monitor soil moisture at several depths, from just below the soil surface , to the bottom of the effective rooting depth.
One of the more cost effective and reliable methods for measuring soil moisture is by electrical resistance block, such as the Watermark sensor.
These blocks are permanently installed in the soil, and wires from the sensors are attached to a handheld unit that measures electrical resistance.
Resistance measurements are then related to soil water potential, which is an indicator of how hard the plant roots have to "pull" to obtain water from the soil.
Figure 2.
The amount of allowable depletion, or the readily available water, represents about 50 percent of the total available water.
Table 1.
Available water holding capacity for different soil textures, in inches of water per foot of soil.
Total available water is the amount of water in the soil between field capacity and permanent wilting point.
Allowable depletion  is the amount of water the plant can use from the total available before experiencing drought stress.
Allowable depletion for melons is approximately 50% of total available.
inch/foot	In top1	In top 1.5'
 Sands and fine sands	0.5 0.75	0.25 0.38	0.38 0.57
 Loamy sand	0.8 1.0	0.4 0.5	0.6 0.75
 Sandy loam	1.2 1.5	0.6 0.75	0.9 1.13
 Loam	1.9 2.0	0.95 1.0	1.43 1.5
 Silt loam, silt	2.0 2.1	1.0 1.05	1.5 1.58
 Silty clay loam	1.9 2.0	0.95 1.0	1.43 1.5
 Sandy clay loam, clay loam	1.7 2.0	0.85 1.0	1.28 1.5
 The handheld unit reports soil moisture content in centibars, where values close to zero indicate a wet soil and high values represent dry soil.
The relationship between soil water potential and available water differs by soil type.
The range of the sensor is calibrated to 0200 centibars , which covers the range of allowable depletion in most soils.
The sensors are less effective in coarse sandy soils, and will overestimate soil water potential in saline soils.
Remember that allowable depletion is 50% of available water, which roughly corresponds to soil water potentials of 50 centibars for a loamy sand soil, and 70 centibars for a loam.
Water is lost from the field through surface runoff, deep percolation , evaporation from the soil surface, and transpiration through the leaves of the plant.
Of these, the biggest losses are
 Table 2.
Recommended WatermarkTM sensor values at which to irrigate.
Soil Type	Irrigation Needed
 Loamy sand	40 50
 Sandy loam	50 70
 Silt loam, silt	70 90
 Clay loam or clay	90 120
 TMWatermark is a registered trademark of Irrometer, Co., Riverside, CA.
Some weather stations in Utah are programmed to calculate and report the ET estimates for alfalfa as a reference crop  that is specific to your crop and its stage of development.
ETcrop = ET, x Keno
 The Kcrop for cantaloupe and watermelons are shown in Table 4.
The Kcrop varies depending on current ground cover relative to the row width, which provides an estimate of percent ground cover.
Ground cover can be estimated by placing a yard stick under the canopy of the plant and counting the number of inches that are shaded.
Measurements should be taken when the sun is directly overhead.
When the vine covers 20% of the ground, a field of cantaloupes is using about 30% of the amount of water used by the alfalfa reference crop.
Water use increases gradually as the canopy develops until the full canopy is established.
For melons, reducing the amount of water applied in the last week before harvest by about 10 to 15% will improve flavor and quality.
However, it is important to remember that melon fields may be harvested over several weeks, SO sustained water reduction may affect later developing fruit size and yield.
Table 3.
Daily total alfalfa reference evapotranspiration  for seven Utah cities expressed in  inches per day,  gallons per acre per day, and  drip-irrigated gallons per 100 feet of bed length per day.
Month	Logan	Farmington	Spanish Fork	Salt Lake City	Green River	Moab	St.
George
  Inches per day
 Mar	0.09	0.12	0.12	0.11	0.15	0.12	0.15
 Apr	0.15	0.19	0.16	0.17	0.23	0.19	0.22
 May	0.2	0.25	0.21	0.22	0.29	0.24	0.28
 Jun	0.24	0.3	0.26	0.28	0.32	0.3	0.32
 Jul	0.29	0.27	0.28	0.30	0.32	0.29	0.31
 Aug	0.26	0.23	0.25	0.27	0.25	0.26	0.28
 Sep	0.18	0.19	0.18	0.19	0.2	0.2	0.21
 Oct	0.09	0.12	0.1	0.11	0.12	0.13	0.14
  Gallons per acre per day.
Irrigation amounts need to be adjusted by Crop Coefficient and Irrigation
 Mar	2444	3259	3259	2987	4073	3259	4073
 Apr	4073	5160	4345	4617	6246	5160	5974
 May	5431	6789	5703	5974	7875	6517	7604
 Jun	6517	8147	7061	7604	8690	8147	8690
 Jul	7875	7332	7604	8147	8690	7875	8418
 Aug	7061	6246	6789	7332	6789	7061	7604
 Sep	4888	5160	4888	5160	5431	5431	5703
 Oct	2444	3259	2716	2987	3259	3530	3802
  Drip-irrigated gallons per 100 feet of bed length per day based on 6-foot bed spacing.
Irrigation amounts
 need to be adjusted by Crop Coefficient and Irrigation Efficiency.2 2
 Mar	33.7	44.9	44.9	41.1	56.1	44.9	56.1
 Apr	56.1	71.1	59.8	63.6	86	71.1	82.3
 May	74.8	93.5	78.6	82.3	108.5	89.8	104.7
 Jun	89.8	112.2	97.3	104.7	119.7	112.2	119.7
 Jul	108.5	101	104.7	112.2	119.7	108.5	116
 Aug	97.3	86	93.5	101	93.5	97.3	104.7
 Sep	67.3	71.1	67.3	71.1	74.8	74.8	78.6
 Oct	33.7	44.9	37.4	41.1	44.9	48.6	52.4
 Table 4.
Description of growth  and crop coefficient estimates for melons grown in a plasticulture system.
Crop	Crop coefficient	20	40	60	80	100
 Cantaloupe	Kcrop	0.24	0.48	0.60	0.68	0.72
 Watermelon2	Kcrop	0.32	0.52	0.64	0.80	0.60
 1.
Grattan, et al., 1998.
2.
Ministry of Agriculture and Food.
October 2001.
Income Irrigation and Rainfall
 In Utah's high elevation desert climate, rainfall contributes a small fraction of the in-season water requirements of the crop.
Therefore, regular irrigation is needed to supply plant water needs.
This irrigation water can be supplied by furrow, impact sprinklers, drip lines or microsprinklers.
Whichever irrigation system you utilize, it is important to calibrate your system SO that you know precisely how much water is being applied.
With sprinklers and microsprinklers, the simplest way to do this is to place catch cans in multiple locations in your planting and collect water for a set period of time.
The amount of water collected over time will give you an application rate , and differences in water collected among the catch cans will tell you how uniform the application is within your planting.
When trying to determine application uniformity, it is best to measure output at both ends of your irrigation system.
Also, if your planting is on a slope, you should measure output at the highest and lowest points of your field.
Elevation differences and the distance the water travels through the irrigation lines both affect water pressure, and consequently the flow rate at the nozzle.
Drip irrigation tape comes with recommended operating pressures, a variety of emitter spacings, and various flow rates.
Most drip tapes operates at 10 psi.
Emitters may be spaced from 4 to 36 inches apart and come in a variety of flow rates.
Flow rates are commonly reported in gallons per 100 feet of tape per hour  or gallons/emitter/hr.
For a tape with a 12-inch emitter spacing, 24 gallons/100ft/hr = 24/100 = 0.24 gallons/emitter/hr.
Pressure compensating emitters  provide the best uniformity.
Flow rate from each emitter and emitter spacing can be used to calculate rate per area.
Drip irrigation systems are usually operated every day or every few days to maintain optimal soil moisture.
The efficiency of your system is a measure of how much you have to over-water the wettest spots in the field to get adequate water to the dry spots.
Efficiency is related to the uniformity of application and to the amount of evaporation that occurs before the water can move into the soil.
A well-designed microsprinkler or drip system can be 70 to 90% efficient.
Overhead sprinkler systems are typically 60 to 75% efficient, while flood and furrow irrigation is typically 30 to 50% efficient.
If your water supply is limited, a more efficient system can make a large difference in water savings and crop productivity.
Following is an example of how to calculate water needs for a cantaloupe crop with a full canopy.
The soil is a deep sandy loam with drip irrigated rows every 6 feet.
ETr values are 0.30 inches per day.
Crop coefficient is 0.80.
ETcrop = ET, Kcrop
 ETcrop = 0.30 inches/day * 0.8 = 0.24 inches/day
 Soil storage capacity 
 The total storage capacity for readily available water over the 2-foot effective rooting depth is 1.1 inches.
1.1 inches / 0.24 inches per day = 4.6  days between irrigations.
In 4 days replace 0.96 inches.
Restated, the soil moisture in the rootzone will go from field capacity to plant stress levels in 4.6 days.
Good irrigation management requires:
 1.
An understanding of the soil-plant-water relationship
 2.
A properly designed and maintained irrigation system, and a knowledge of the efficiency of the system
 3.
Proper timing based on
 a.
Soil water holding capacity
 b.
Weather and its effects on crop demand
 C.
Stage of crop growth.
Each of these components requires a commitment to proper management.
Proper management will lead to the maximum yields per applied irrigation water, and will optimize the long term health and productivity of your crop.
Surface Irrigation  Inches/hour = cubic feet per second  / acres Example: 4 cfs/ 5 acres = 0.8 inches/hour
 Sprinkler Irrigation  Inches/hour=96.24 gallons per minute /area  Example: 96.24*7 gpm /  = 0.28 inches/hour
 Drip Irrigation  Inches/hour=1.6 *gallons per hour /emitter spacing  Example: 1.6*.5 gph /  = 0.32 inches/hour
 Irrigation Set Times Set time  = Gross Irrigation Need  / application rate  Example: 3 inches / 0.28 inches/hour = 10.7 hours
 Conversions 1 cfs= 448.8 gpm 1 gpm= 60 gph 1 acre = 43,560 feet^2
 Utah State University is committed to providing an environment free from harassment and other forms of illegal discrimination based on race, color, religion, sex, national origin, age , disability, and veteran's status.
USU's policy also prohibits discrimination on the basis of sexual orientation in employment and academic related practices and decisions.
Utah State University employees and students cannot, because of race, color, religion, sex, national origin, age, disability, or veteran's status, refuse to hire; discharge; promote; demote; terminate; discriminate in compensation; or discriminate regarding terms, privileges, or conditions of employment, against any person otherwise qualified.
Employees and students also cannot discriminate in the classroom, residence halls, or in on/off campus, USU-sponsored events and activities.
This publication is issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Kenneth L.
White, Vice President for Extension and Agriculture, Utah State University.
Arkansas Water Primer Series: Water Basics
 Water is a finite, non-renewable resource.
Although water covers approximately 75 percent of the Earth's surface, only 3 percent is fresh water that can be consumed and used.
Of that fresh water, two-thirds is frozen in glaciers, polar ice caps and icebergs.
It is vital that citizens and policy makers understand the importance of water and how to ensure its use for future generations.
An overview of water, where it comes from and how it's used is fundamental to understanding how and why water policies, laws and regulations have been established.
It is also key to the development of proper water resource management tools.
The water we use today is the same water that has been used for millions of years.
It is continuously circulating and being recycled through a process called the hydrologic cycle.
There are five processes at work in the cycle:
 Evaporation from the Earth's surface and evapotranspiration from plants that introduce water into the atmosphere
 Condensation of water vapor
 Infiltration water that seeps into the ground
 Runoff water that ends up in waterbodies, including streams, rivers, lakes and oceans
 The hydrologic cycle controls the amount of water available for use and where.
All of the processes influence water availability at a specific location at a particular point in time.
The speed with which water moves among stages in the cycle and the amount of time it spends in storage at any stage affect water availability.
Population increases, rising living standards and industrial and economic growth are contributing to changes in the hydrologic cycle.
Not only is the world using more water, it is discharging more wastewater.
Urbanization and poor irrigation practices are also factors that influence the availability of usable water.
These variables are among the many that affect the amount of usable surface and groundwater.
Surface water is the most visible part of the hydrologic cycle.
It refers to bodies of water above the ground such as streams, rivers, lakes and reservoirs.
The bulk of surface water is naturally replenished by precipitation such as rain and snow.
Approximately 30 percent of surface water comes from groundwater percolating up to the top.
Surface water is lost through discharge to the oceans, evaporation, evapotranspiration and sub-surface seepage.
The Importance of Surface Water
 Surface water is the largest source of fresh water.
Streams and reservoirs supply approximately 50 percent of the nation's drinking water, primarily in urban
 areas, according to the U.S.
Geological Survey.
Streams, reservoirs, lakes and downstream estuaries are also vital aquatic ecosystems that provide important environmental and economic benefits.
Surface water is abundant in Arkansas.
According to the 2014 Arkansas Water Plan, more than 92 million acre-feet of water flows through the state's major river basins each year.
However, supply fluctuates depending on the season, SO there are times when supply is low and demand is high.
A drainage basin is a geographical area which contributes surface water runoff to a particular point.
There are five major drainage basins within Arkansas.
The principal rivers in these drainage basins are:
 Almost 4 billion gallons of surface water are used in Arkansas daily, with most of the water going toward irrigating crops, thermoelectric power generation and municipal water supplies.
Many of the largepopulation counties rely on surface water for drinking water supplies.
Water stored below the Earth's surface is called groundwater.
The water is the result of past precipitation or from seepage that infiltrated downward from surface waterbodies.
Where water infiltrates the
 Source: U.S.
Geological Survey, Estimated Water Use in Arkansas 2010
 ground, gravity pulls the water down through the pores until it reaches a depth where all of the spaces are filled with water.
At this point, the soil or rock becomes saturated.
The upper surface of this saturated layer is called the water table.
The water table is not always at the same depth below the land surface.
During periods of high precipitation, the water table can rise.
Conversely, during periods of low precipitation and high groundwater use, the water table can fall.
Groundwater is found in aquifers, which consist of relatively porous layers of rock, sand or gravel below the water table where water can easily move.
In areas where aquifers are shallow enough and penetrable, wells are drilled and water is pumped out.
There are two types of aquifers.
Unconfined aquifers are found close to the surface, with the water table acting as the upper boundary for the aquifer.
Water must be pumped out in wells accessing these types of aquifers.
Confined aquifers are found deep below the surface and are enclosed by impermeable layers of rock or impermeable materials such as clay.
Because of the impermeable layers above and below, water in a confined aquifer is normally under pressure and can cause the water level in a well to rise above the water table.
If the water rises above the ground surface, it is designated as a flowing artesian well.
In the hydrologic cycle, aquifers act as a storage facility and filter for water.
When water enters an aquifer through seepage, this is called recharge.
Later in the cycle, when water moves from an aquifer and enters a stream or lake, the water is called groundwater discharge.
In Arkansas, groundwater typically discharges from aquifers to replenish rivers, lakes or wetlands.
An aquifer may receive recharge from these sources, an overlying aquifer or, more commonly, from precipitation followed by infiltration.
The recharge zone is an area either at the surface or below ground that provides water to an aquifer.
Because surface and groundwater flow paths are not the same, a recharge zone may encompass one or more watersheds.
The Importance of Groundwater
 Groundwater is an important resource.
It replenishes Arkansas' streams, rivers and habitat.
It is also an important source of fresh water for drinking, irrigation and industry.
Groundwater serves as a source for more public water systems than surface waterbodies, according to the U.S.
Environmental Protection Agency.
In Arkansas, 71 percent of statewide water demand is supplied from groundwater sources, according to the Arkansas Water Plan.
Arkansas is the second-largest user of groundwater in the U.S., behind only California,
 The average Arkansan uses 155 gallons of water each day.
Dairy cattle require 30 gallons of water per day.
What is poured on the ground today can end up in the drinking supply many years later.
Source: U.S.
Geological Survey
 according to 2010 U.S.
Geological Survey data.
This is significant considering California is the most populous state in the country.
Nearly 95 percent of the groundwater withdrawals in Arkansas are used for irrigation.
A majority of the groundwater consumption in Arkansas comes from two major aquifers the Mississippi River Valley alluvial aquifer  and the Sparta-Memphis Aquifer.
The Alluvial Aquifer is the most productive aquifer within Arkansas.
It provides most of Arkansas' groundwater used for irrigation and fish farming; the Sparta-Memphis Aquifer provides most of the groundwater for industry and public supply.
Fact Sheet FSPPC109 Glossary of Water-Related Terms contains a comprehensive list of terms used in the Arkansas Water Primer Fact Sheet Series.
One visual observation of a non-functioning regulator is when water is spraying out of the side of the regulator.
If you have concerns that your regulators are approaching their usable life, contact your irrigation equipment dealer to have your regulators tested.
We are excited to learn more about irrigation and nitrogen management in the growing of popcorn more sustainably, commented Chuck Burr, Water and Integrated Cropping Systems specialist and TAPS team member.
The data does not give any insight into why so many fields get wetter, but it could be because the irrigation routine is set in July when the plants are in top condition transpiring at their peak level, the days are long, and the temperatures are high.
Then as we move later into the summer as the daylight shortens and the temperatures get lower, we keep irrigating like we were in July even though crop water use for corn has gone from an average of 0.30 inches/day at silking to 0.18 inches/day at full dent.
Other crops have a similar dramatic drop in crop water use, as well.
CORN AND GRAIN SORGHUM PRODUCTION WITH LIMITED IRRIGATION
 Soil water management during the growing and non-growing season can be enhanced with crop residues.
Capture and retention of soil water plus irrigation at critical growth stages can maximize limited irrigation resources.
This research quantified the water use and irrigation requirements of corn and grain sorghum grown with optimum water management using water conservation techniques.
Corn grain and forage yields declined with less than full irrigation, but sorghum grain and forage yields remained nearly constant.
Net economic returns increased as more irrigation was applied to corn, but decreased with additional irrigation on sorghum.
When irrigation was reduced in corn and sorghum production, there was less impact on grain and forage yield from the same proportional decrease in irrigation.
For example, a 50% reduction in full irrigation caused a 20% reduction in corn grain yields.
Sorghum grain yields were reduced by 8% with a 72% reduction in irrigation.
However, net economic return from corn production increased at the same rate with additional irrigation.
Additional irrigation decreased annual net returns from sorghum production.
Irrigators, responding to economic returns form their irrigation practices, would tend to fully irrigate corn and reduce irrigation for sorghum.
The overall goal of the project was to conduct cropping systems field research with the emphasis on crop yield response to full and limited irrigation.
The objectives were to:
 1.
Measure grain and forage production of corn and grain sorghum with deficit irrigation and no-till management.
2.
Measure grain yield and irrigation to develop production functions for corn and grain sorghum in no-till management with irrigation inputs from 2 to 3 inches to full irrigation.
3.
Determine soil water during the growing-season and non-growing season to assess the impacts irrigation on soil water storage and use.
4.
Find the net economic returns of corn and grain sorghum receiving irrigation from deficit to fully irrigated management.
The cropping systems project was located at the Kansas State University's Southwest Research-Extension Center near Garden City, KS.
Deficit irrigation strategies and no-till management strategies were used to test crop responses to limited water supplies.
The experimental field was subdivided into strips, oriented east to west, that were irrigated by a 4-span linear move sprinkler irrigation system.
Six irrigation treatments, replicated four times, ranged from 3 to 12 inches for corn and 2 to 8 inches for sorghum.
If rainfall was sufficient to fill the soil profile to field capacity, irrigation was not applied.
Irrigation treatments were the same for each plot from year to year so the antecedent soil water carried over to the next year.
The days between irrigation events increased as irrigation decreased.
The same net irrigation  was applied for each irrigation event.
Soil water was measured once every two weeks with the neutron attenuation method in increments of 12 inches to a depth of 8 feet.
These measurements along with effective precipitation , net irrigation, and soil water use were used to calculate evapotranspiration for each two-week period during the season.
Ending season and beginning season soil water measurements were used to calculate soil water accumulations during the nongrowing season and soil water use during the growing season.
The soil was a Ulysses silt loam with an available water capacity of 2 inches/ft and volumetric water contents of 33% at field capacity and 17% at permanent wilting.
Cultural practices, including hybrid selection, no-till planting techniques, fertilizer applications, weed control, were the same across irrigation treatments.
Yieldirrigation relationships were used with current commodity price and crop production costs to determine net economic returns from corn and sorghum crops across irrigation treatments.
Table 1.
Days between irrigation events for irrigation treatments.
1 High	4.5	4.9
 Low 6	13.8	15.7
 Relative yields were calculated as the ratio of irrigation treatment yields and fully irrigated yields for corn and sorghum.
Relative yield results were expressed as percentages of yields for the fully irrigated treatment.
In the same fashion, relative irrigation was calculated as the ratio of irrigation amount of each treatment and the fully irrigated treatment.
For example, the corn treatment that
 received 9 inches of water produced 92% of the yield of fully irrigated treatment with 74% of the irrigation.
Corn grain yields decreased at a decreasing rate as irrigation was reduced.
Sorghum yields from the driest irrigation treatment produced only 5 bu/acre less that the fully irrigated treatment.
The driest irrigation treatment produced 96% of full yield with 28% of the water.
Table 2.
Average grain yields, relative grain yields, irrigation, and relative irrigation for corn after corn and sorghum after wheat for 2004-2007.
Corn after corn 2004-2007	Sorghum after Wheat 2004-07
 Average	Relative	Annual	Relative	Average	Relative	Average	Relative
 Yield	Yield	Irrigation	Irrigation	Yield	Yield	Irrigation	Irrigation
 bu/ac	%	inches	%	bu/ac	%	inches
 205	100	12	100	122	100	7	100
 199	99	10	85	125	100	6	86
 185	92	9	74	124	100	5	72
 163	81	6	52	117	100	4	48
 141	70	5	39	117	96	3	34
 119	59	3	29	117	96	2	28
 Results for forage yields from corn and sorghum mimicked grain yields.
Corn was planted at rates for predicted yield potential from each irrigation treatment, which were 19,500 plants/ac for the driest treatment to 32,000 plants/ac for the driest treatment.
Sorghum was planted with 107,000 plants/ac for all irrigation treatments.
Table 3.
Average forage yields  and relative forage yields for corn after corn and sorghum after wheat for 2004-2007.
Corn after corn 2004-2007	Sorghum after Wheat 2004-07
 Average	Relative	Annual	Relative	Average	Relative	Average	Relative
 Yield	Yield	Irrigation	Irrigation	Yield	Yield	Irrigation	Irrigation
 T/ac	%	inches	%	T/ac	%	inches
 9.6	100	12	100	7.6	100	7	100
 8.2	85	10	85	7.2	98	6	86
 7.9	82	9	74	7.5	96	5	72
 5.7	59	6	52	6.8	90	4	48
 6.2	64	5	39	7.5	92	3	34
 5.7	61	3	29	6.7	92	2	28
 Results in tables 2 and 3 are four-year averages for each irrigation treatment.
Variation in crop yields from year-to-year is important to evaluate income risk.
Data for each irrigation treatment each year of the study are in figures 1 & 2.
Regression of corn relative yields  show decreasing yields as irrigation decreased, but sorghum relative yields remained constant.
The distance of the data points from the trend line indicates the variation in yields from year-to-year.
Corn yield variation increased for less than 10 inches of irrigation.
Variation in sorghum yields remained constant from the most to least irrigation.
Yield variation can influence crop rotation choices.
Fig.
1.
Trend and variation in relative Fig.
2 Trend and variation in relative yields for corn.
yields for sorghum.
Cropping season evapotranspiration  was calculated from the summation of net irrigation  effective precipitation , and the stored soil water used during the growing season.
Corn ETc  was from 25.5 the wettest irrigation treatment to 19 inches for the driest treatment for a difference of 6.5 inches.
Productivity was calculated as the ratio of grain yields and ETc.
Corn yields decreased relatively more than ET causing productivity to decrease with less irrigation.
Plant population may have decreased potential yields for the drier treatment in 2004, which had above normal growing season precipitation.
Sorghum ET  was 24.2 to 20.8 inches.
Field observation and forage yields showed that the wetter treatments developed more dry matter, but the uniform plant populations did not restrict yield potential in the drier plots.
Sorghum productivity increased with less irrigation causing better use of available water for grain production.
Table 4.
Cropping season ETc, yield, and productivity for corn.
Irrigation	SW Use	Rainfall	ET	Yield	Productivity
 Inches	inches	inches	inches	bu/ac	bu/ac-in
 12	1.8	11.7	25.5	205	8.0
 10	2.3	11.7	24.0	199	8.3
 8	3.2	11.7	22.9	185	8.1
 6	2.9	11.7	20.6	163	7.9
 4.5	3.9	11.7	20.1	141	7.0
 3	4.3	11.7	19.0	119	6.3
 Soil water accumulated during the non-growing season and some of this water was used as component of ETc during the following growing season.
As irrigation decreased, the crop developed roots deeper into the soil and extracted more soil water creating more room to store water during the following non-growing season.
There was a correspondence between
 Table 5.
Cropping season ETc, yield, and productivity for sorghum.
Irrigation	SW Use	Rainfall	ET	Yield	Productivity
 inches	inches	Inches	inches	bu/ac	bu/ac-in
 8	4.3	11.9	24.2	122	5.0
 6.7	4.7	11.9	23.3	125	5.4
 5.3	5.5	11.9	22.7	124	5.4
 4	5.8	11.9	21.7	117	5.4
 3	6.3	11.9	21.2	117	5.5
 2	6.9	11.9	20.8	117	5.6
 water stored and water used during the following season.
More water soil water use followed more water storage.
More water accumulated prior to sorghum than corn because soil water extraction was deeper into the soil in the sorghum crop.
Table 6.
Stored soil water  gains during the previous non-growing season and stored soil water use during the growing season for corn following corn and sorghum following wheat.
Irrigation	Gain	SW Use	Irrigation	SW Gain	SW Use
 Corn	Corn	Corn	Sorghum	Sorghum	Sorghum
 inches	inches	inches	inches	inches	inches
 12	3.3	b	1.8	d	8	6.8	bc	4.3	d
 10	4.9	ab	2.3	cd	6.7	6.4	C	4.7	d
 8	4.9	ab	3.2	ab	5.3	7.5	ab	5.5	C
 6	5.9 a	2.9	abc	4	7.8	ab	5.8	bc
 4.5	5.7 a	3.9	ab	3	8.0 a	6.3 b
 3	6.0 a	4.3 a	2	7.9 a	6.9	a
 LSD0.05	1.7	1.1	1.1	0.5
 Fallow efficiency was calculated as the ratio of stored soil water and precipitation during the non-growing season.
The time between wheat harvest and sorghum emergence was almost 11 months, but 7 months elapsed between corn harvest and emergence of the next corn crop.
Soil water accumulations nearer to the time of use were more effective than early water storage.
There was more time to store water in the wheat stubble that preceded sorghum planting, which refilled more of the soil profile, but there was more time for drainage.
The small difference in stored soil water between the wettest irrigation treatment and the driest treatment was 1.1 inches, probably contributed to smaller differences in sorghum grain yields.
Yield results from the field study and crop prices were used to calculate gross income for corn sorghum.
Net income was calculated as the difference in gross income and production costs including irrigation costs.
These commodity prices and production costs can vary over time and from one producer to the next.
In this example corn could be planted on the entire field or
 Table 7.
Non-growing season fallow efficiency and drainage.
--Fallow Efficiency	---ET + Drainage--	Drainage
 Corn	Sorghum	Corn	Sorghum	Corn	Sorghum
 %	%	inches	inches	inches	inches
 33	32	6.7	14.2	3.7	7.2
 49	30	5.1	14.6	2.1	7.6
 49	36	5.1	13.5	2.1	6.5
 59	37	4.1	13.2	1.1	6.2
 57	38	4.3	13	1.3	6.0
 60	38	4.0	13	1.0	6.0
 or planted on half the field and rotated with sorghum.
Irrigation pumping capacity can limit the irrigation amount that can be delivered to the crop.
If 9 inches of irrigation were available during the growing season, the net return would be approximately $280/ac or $36,400 for a 130 ac field.
If corn was rotated with sorghum and 12 in of irrigation were applied to corn, the net return would be $350/ac for corn.
Sorghum would receive 6 inches of water for a net return of $125/ac.
The combined net return for 130 acres would be $30,800.
The difference in net return between continuous corn and the rotation is not the only consideration.
Income variability from one year to the next would be less for the rotation because the corn yield would be less variable.
Table 8.
Net returns  for corn after corn.
Net	Corn	Grain	Gross	Irrigation	Production	Return
 Irrigation	Price	Yield	Income	Cost	Costs*
 inches	$/bu	Bu/ac	$/ac	$/ac-in	$/ac	$/ac
 11.5	4	205	820	9	471	349
 9.8	4	199	796	9	507	289
 8.5	4	185	740	9	474	266
 6	4	163	652	9	427	225
 4.5	4	141	564	9	380	185
 3.3	4	119	476	9	344	132
 Table 9.
Net returns  for irrigated sorghum.
Net	Sorghum	Grain	Gross	Irrigation	Production	Return
 Irrigation	Price	Yield	Income	Cost	Costs*
 inches	$/bu	bu/ac	$/ac	$/ac-in	$/ac	$/ac
 7.3	3.5	119	416	9	301	115
 6.3	3.5	116	406	9	286	120
 5.3	3.5	114	400	9	270	131
 3.5	3.5	107	376	9	253	123
 2.5	3.5	109	382	9	246	136
 2.0	3.5	109	381	9	235	146
Drip-Irrigation Systems for Small Conventional Vegetable Farms and Organic Vegetable Farms1
 Eric Simonne, Robert Hochmuth, Jacque Breman, William Lamont, Danielle Treadwell, and Aparna Gazula
 A drip-irrigation system-when properly designed, maintained and operated-can be a production asset for a small farm.
Using drip irrigation for profitable vegetable production requires an understanding of several basic engineering and horticultural concepts and their application.
The goals of this publication are to present the principles behind drip irrigation and some practical guidelines for successful and profitable use of drip irrigation.
1.
Overview of Drip Irrigation
 1.1 What is drip irrigation?
Drip irrigation  is an irrigation method that allows precisely controlled application of water and fertilizer by allowing water to drip slowly near the plant roots through a network of valves, pipes, tubing, and emitters.
Plasticulture is the combined use of drip irrigation, polyethylene mulch and raised beds.
Greatest productivity and earliness may be achieved in vegetable production by combining plasticulture with the use of transplants.
1.2 Is drip irrigation adapted to all operations?
Drip irrigation is not a silver bullet; it may not be applicable to all farms.
Yet, when properly managed, it is a valuable production technique that may reduce labor and production costs while improving productivity.
Small farmers considering the use of drip irrigation should evaluate both the advantages and disadvantages of this system to determine the benefits of drip irrigation for their operation.
1.3 What are the main advantages of drip irrigation?
Reduced water use: Because drip irrigation brings the water to the plant root zone and does not wet the entire field, drip irrigation typically requires half to a quarter of the volume of water required by comparable overheadirrigation systems.
2.
Eric Simonne, professor, Horticultural Sciences Department, and Northeast district Extension director; Robert Hochmuth, regional specialized Extension agent IV vegetables and assistant center director UF/IFAS North Florida Research and Education Center; Jacque Breman, emeritus Extension Agent IV, UF/IFAS Extension Columbia County; William Lamont, professor, Penn State University; Danielle Treadwell, associate professor, Horticultural Sciences Department; Aparna Gazula, small farm advisor, University of California Cooperative Extension Santa Clara County; and Charles Barrett, regional specialized agent water resources; UF/IFAS Extension, Gainesville, FL 32611.
The use of trade names in this publication is solely for the purpose of providing specific information.
UF/IFAS does not guarantee or warranty the products named, and references to them in this publication does not signify our approval to the exclusion of other products of suitable composition.
All chemicals should be used in accordance with directions on the manufacturer's label.
Use pesticides safely.
Read and follow directions on the manufacturer's label.
The Institute of Food and Agricultural Sciences  is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations.
For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.
U.S.
Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating.
Nick T.
Place, dean for UF/IFAS Extension.
Joint management of irrigation and fertilization: Drip irrigation can improve the efficiency of both water and fertilizer.
Precise application of nutrients is possible using drip irrigation.
Hence, fertilizer costs and soluble nutrient losses may be reduced with drip irrigation.
Nutrient applications may also be better timed to meet plant needs.
Reduced pest problems: Weed and disease problems may be reduced because drip irrigation does not wet the row middles or the foliage of the crops as does overhead irrigation.
Simplicity: Polyvinyl chloride  and polyethylene parts are widely available in several diameters and are easy to assemble.
Many customized, easy-to-install connectors, endcaps, and couplers are available in different diameters.
Cutting and gluing allows for timely repairs.
Low pumping needs: Drip systems require low operating pressure  compared to overhead systems.
Many existing small pumps and wells may be used to adequately irrigate small acreage using drip systems.
Automation: Drip-irrigation application may be simply managed and programmed with an ACor battery-powered controller, thereby reducing labor cost.
Adaptation: Drip systems are adaptable to oddly shaped fields or those with uneven topography or soil texture, thereby eliminating the underutilized or non-cropped corners and maximizing the use of available land.
Production advantages: Combined with raised beds, polyethylene mulch, and transplants, drip irrigation enhances earliness and crop uniformity.
Using polyethylene mulch also increases the cleanliness of harvested products and reduces the risk of contamination with soil-born pathogens.
Reflective mulches further help reduce the incidence of viral diseases by affecting insect vectors, such as thrips, whiteflies, or aphids.
1.4 What are the disadvantages of drip irrigation?
Drip irrigation requires an economic investment: Dripirrigation systems typically cost $500-$1,200 or more per acre.
Part of the cost is a capital investment useful for several years, and another part is due to the annual cost of disposable parts.
Growers new to drip irrigation should start with a relatively simple system on a small acreage before moving to a larger system.
Drip irrigation requires maintenance and high-quality water: Once emitters are clogged or the tape is damaged, the tape must be replaced.
Water dripping from an emitter and the subsequent wetting pattern are hard to see, which makes it difficult to know if the system is working properly.
Proper management of drip irrigation requires a learning period.
Water-application pattern must match planting pattern: If emitter spacing  does not match the planting pattern, root development may be restricted and/ or plants may die.
Safety: Drip tubing may be lifted by wind or may be displaced by animals unless the drip tape is covered with mulch, fastened with wire anchor pins, or lightly covered with soil.
Leak repair: Drip lines can be easily cut or damaged by other farming operations, such as tilling, transplanting, or manual weeding with a hoe.
Damage to drip tape caused by insects, rodents, or birds may create large leaks that also require repair.
Drip-tape disposal causes extra cleanup costs after harvest: Planning is needed for drip-tape disposal, recycling, or reuse.
1.5 How does my drip-irrigation system affect organic certification?
The design and maintenance of a drip-irrigation system should be clearly outlined in the Organic System Plan , including any inputs that will be delivered through the drip-irrigation system.
In all cases, contact your certifying agency before using a product
 to confirm that use of that product will not jeopardize organic certification.
Drip-irrigation water.
In most cases, groundwater, surface water, rainwater, and potable water may be used in certified organic production.
In some instances, the certifying agency may request a water analysis.
Products for drip-irrigation maintenance.
Within stated restrictions , CFR 205.601 of the NOP lists the following substances as allowable as synthetic algaecide, disinfectant, and sanitizers:  alcohols, including  ethanol and  isopropanol;  chlorine materials [except that residual chlorine levels in the water shall not exceed the maximum residual disinfectant limit under the Safe Drinking Water Act], including  calcium hypochlorite,  chloride dioxide,  sodium hypochlorite;  hydrogen peroxide; and  soap-based algaecide/demisters.
Additionally, under NOP Rule CFR 205.105, citric acid is allowed when irrigation water needs to be acidified.
However, other compounds commonly found in ready-to-use dripirrigation cleaners and maintenance products and typically used in conventional systems  are prohibited in certified organic production.
Fertilizers and pesticides.
No specific ruling prohibits NOP-compliant products from being distributed through a drip-irrigation system.
Plans to use drip irrigation to distribute fertilizers and/or pesticides should be clearly outlined for approval in the Organic System Plan.
When in doubt, consult first with your certifying agency.
All growers are obligated to follow state and federal guidelines for injecting inputs through irrigation systems.
1.6 Is drip irrigation considered a Best Management Practice?
Yes.
Best Management Practices  are cultural practices that help reduce the environmental impact of production while maintaining or increasing productivity.
The BMP program for vegetables grown in Florida is described in "Water quality/quantity best management practices for Florida vegetable and agronomic crops".
The BMP manual describes all the BMPs that apply to vegetable production, as well as a decision-tree to identify the BMPs that apply to each operation and guidelines for completing and submitting the Notice of Intent to Implement.
Participation in the Florida BMP program and the organic certification program are two separate processes.
Vegetable growers who are enrolled in the statewide BMP program receive three statutory benefits:  a waiver of liability from reimbursement of cost and damages associated with the evaluation, assessment, or remediation of nitrate contamination of groundwater ;  a presumption of compliance with water-quality standards ), and  eligibility for cost-share programs ).
Specific vegetable BMPs that address drip irrigation include BMP 33 "Optimum fertilization application/ management", BMP 34 "Chemigation/fertigation", BMP 39 "Irrigation system maintenance and evaluation", and BMP 47 "Plasticulture farming".
Additional BMPs involving drip irrigation include BMP 26 "Soil testing/soil pH", BMP 36 "Water supply" and BMP 40 "Irrigation scheduling".
BMP implementation requires record keeping.
When properly implemented, all BMPs that apply to drip irrigation help to increase efficiency in the use of water and nutrients.
1.7 What is the best way  to express irrigation rates when drip irrigation is used?
For irrigation systems that entirely wet the field , irrigation rates are typically expressed in inches.
This unit of measurement represents a vertical amount of water.
The actual "volume" of water is calculated by multiplying the height of water by the field surface.
For example, 1 acre inch is the volume of water present on a 1-acre field with a 1-inch depth: 1 acre inch = 27,154 gallons.
Because drip irrigation does not wet the entire field, expressing drip-irrigation volumes as a height of water poorly represents reality.
Instead, drip-irrigation volumes should be expressed in gallons-per-100-linear-foot-of-drip-tape In some cases, drip-irrigation volumes can be converted to and from water heights by considering the relative surface of the field under plastic mulch.
For example, the relative surface under plastic mulch of a 1-acre field with 30-inchwide beds of 4-ft centers is 62.5%.
Hence, if 0.5 acre inch needs to be applied to that field through a drip-irrigation system, the total volume of water needed is 8,484 gallons.
Because in a 1-acre field with beds of 4-ft centers there are 10,890 linear-bed-feet of plastic, the drip-irrigation rate should be reported as 78 gallons/100 ft.
If a drip tape with a
 24-gal/100-ft/hr flow rate is used, it will take 3 hours and 15 minutes to apply this amount of water.
In heavy soil, it is reasonable to assume that a drip tape installed in the middle of the bed will be sufficient to wet the entire bed width.
However, research has shown that, on Florida's sandy soils, the wetted width seldom exceeds 18 inches -is not correct for most drip-irrigation systems in Florida.
The actual wetted width should be used in place of the bed width.
2.
Components of a Drip-Irrigation System
 The type and sequence of components in a drip-irrigation system are typically the same for all field sizes.
Yet, based on field size , component sizes  may vary.
Larger components tend to be more expensive.
The backflow-prevention devices-comprised of two check valves and the lowpressure drain, also known as "anti-siphoning device"-are the only components required by Florida law  when fertilizer or chemicals are injected into the system.
The actual selection of a specific component  generally needs to be made on a case-by-case basis.
The following is a brief description of the main components of a typical drip-irrigation system.
Common water sources for drip irrigation are surface water , groundwater, and potable water .
Use the water source that will provide the largest amount of water of greatest quality and lowest cost.
Potable water is of high, constant quality, but is by far the most expensive.
The role of the pumping system is to move water from the water source to the field through the distribution system.
Pumping systems may be classified as electric powered systems, gas/diesel powered systems, and gravity systems.
Gas/diesel pumps offer the greatest versatility in isolated fields.
Figure 1.
This pond provides surface water for the irrigation of strawberry.
Credits: Eric Simonne.
Figure 2.
Diesel engines mounted on a trailer offer the greatest flexibility of use.
Credits: Eric Simonne.
The role of the distribution system is to convey the water from the source to the field.
Distribution systems may be above ground  or underground.
Pipes are most commonly made of PVC or polyethylene plastics.
Aluminum pipes are also available, but are more difficult to customize, cut, and repair.
The size and shape of the distribution system may vary widely from field to field and from farm to farm.
2.4 Drip Tape 
 The drip-irrigation system delivers water to each plant through a thin polyethylene tape  with regularly spaced small holes, called emitters.
Selection of drip tape should be based on emitter spacing and flow rate.
The typical emitter spacing for vegetables is 12 inches, but 8 inches
 or 4 inches may be acceptable.
Dry sections of soil may develop between consecutive emitters when a wider emitter spacing  is used on sandy soils.
Flow rates are classified into low flow , medium flow  and high flow.
The risk of emitter clogging is generally higher with the lower-flow drip tapes.
The following equivalent units are commonly used to report flow rates: gal/100 ft/hr or gallons/emitter/hr.
For example, with a 12-inch emitter spacing, 24 gal/100 ft/hr = 24/100 = 0.24 gal/emitter/hr.
In the field, drip-irrigation tape should be installed with emitters upward  to prevent clogging from sediment deposits settling in the emitters between irrigation events.
Drip tapes are widely available from several manufacturers
 Figure 3.
Drip tapes can be distinguished and recognized by their features.
Note the emitter  and the turbulent flow channels.
Credits: Eric Simonne.
Injectors allow the introduction of fertilizer, chemicals, and maintenance products into the irrigation system.
Florida law requires the use of an anti-siphoning device  when fertilizer, chemicals, or any other products are injected into a drip-irrigation system.
Backflow-prevention devices ensure the water always moves from the water source to the field.
The devices prevent chemicals in the water from polluting the water source.
The most common injectors used with small drip-irrigation systems are the Venturi  injector  and the Dosatron.
Because Venturi injectors involve no moving parts and are less expensive, they are commonly used on small farms.
The injector is typically located as close as possible to the irrigation zone, but before the filter.
Figure 4.
Back-flow prevention made of two ball valves and a vacuum breaker are placed upstream of the Venturi injector.
Credits: Eric Simonne.
Figure 5.
Injection made possible with a Dosatron.
Credits: Eric Simonne.
Because drip-irrigation water must pass through the emitters, the size of the particles in the water must be smaller than the size of the emitter to prevent clogging.
Nearly all manufacturers of drip-irrigation equipment recommend that filters be used.
The manufacturer generally will not honor warranties unless filters are used.
The filtration system removes "large" solid particles in suspension in the water.
Different types of filters are used based on the type of particles in the water.
Media filters  are used with surface water when large amounts of organic matter  need to be filtered out.
Screen filters or disk filters may be used with groundwater.
A 200-mesh screen or equivalent is considered adequate for drip irrigation.
When the water contains sand, a sand separator should be used.
Figure 6.
Disk filters are made of stacked disks with small openings.
They are usually color coded to indicate the filtration mesh.
Credits: Eric Simonne.
Rapid clogging may occur when no filter or the incorrect type of filter is used.
A filter needs to be cleaned when the difference in pressure across the filter  is greater than 5-8 psi.
A drip-irrigation system should never be operated without a filter even if the filter requires frequent cleaning.
Failure to use a filter will result in clogged drip-tape emitters, often resulting in poor uniformity and sometimes in crop loss.
The filter should be cleaned as often as needed.
Efforts should be made to understand the cause of the rapid clogging, and remediation for the problem should be developed.
The presence of the filter after the point of fertilizer injection means totally soluble fertilizers must be used.
Otherwise fertilizer particles may contribute to filter clogging.
Conventional growers may use two types of fertilizer materials: ready-to-use true solutions or dissolved granular fertilizer.
Ready-to-use solutions are easily injected.
However, granular fertilizers are sometimes coated with a thin layer of oil to prevent dusting.
Upon dissolution of the fertilizer granules, an oily film may form at the surface of the solution.
Injecting the oily film together with the fertilizer may contribute to filter and emitter clogging.
Certified organic fertilizers are seldom true solutions , and may also contribute to filter clogging.
Consequently, the actual fertilizer rate applied may be reduced by the amount of fertilizer particles trapped by the filter.
In both cases, small-scale trials may be needed to assess the clogging risk of each fertilizer material used.
System controls are devices that allow the user to monitor how the drip-irrigation system performs.
These controls help ensure the desired amount of water is applied to the crop throughout the growing season.
Pressure regulators, installed in-line with the system, regulate water pressure at a given water flow , thereby helping to protect system components against damaging surges in water pressure.
Pressure surges may occur when the water in the pipe has a velocity >5 feet t/second  or when water flowing in the pipe has no avenue for release due to a closed valve or a clog in the pipe.
Figure 7.
Pressure regulators are installed side-by-side in this system to allow a greater flow rate.
Note the small injection port for chemical injection.
Credits: Eric Simonne.
Water meters monitor and record the amount of water moving through a pipe where the water meter is installed.
When a stopwatch is used together with a water meter, it is possible to determine the water flow in the system in terms of gallons-per-minute.
Figure 8.
Water meters installed near the field.
Credits: Eric Simonne.
Pressure gauges monitor water pressure in the system and ensure operating pressure remains close to the recommended or benchmark values.
Based on where the pressure gauge is installed, it will measure water pressure in a various ranges, from 0-100 psi near the pump to 0-20 psi at the end of drip tape.
Pressure gauges may be installed at set points.
They can also be mounted as portable devices and installed temporarily at the end of a drip tape.
Figure 9.
A portable pressure gauge measures pressure at the end of the drip tape.
Credits: Eric Simonne.
Figure 10.
A fixed pressure gauge.
Note the needle bathing in oil to prevent needle vibration and damage.
Credits: Eric Simonne.
Soil-moisture-measuring devices  are used to measure soil moisture in the root zone of the crop.
The Florida Extension Service recommends maintaining soil-water tension between 8 and
 12 centibars 6 inches away from the drip tape and at the 12-inch depth.
Electrical timers connected to solenoid valves  may be used to automatically operate a drip-irrigation system at pre-set starting and ending operating times of day.
Figure 11.
Solenoid valves connected to a timer allow sequential irrigation of different zones.
Credits: Eric Simonne.
3.
Tips for Design and Layout
 Irrigation engineers are trained and certified to properly design drip-irrigation systems.
Relying on their expertise will pay off in the long run.
Many small-scale growers abandon drip irrigation because of poor performance of flawed designs or inadequately modified designs.
Do not hesitate to ask for professional help when designing your drip-irrigation system or when planning major modifications to an existing system.
The following section presents the basics of system design, but is not a substitute for the professional services of a qualified engineer.
3.1 Planning a Drip Irrigation System: Horticultural Considerations
 The goal of drip irrigation is to bring water to the crop.
The main parameters that determine crop water use are the type of crop planted and row spacing.
A drip irrigation system should be able to supply 110%-120% of crop water needs.
In other words, the system should be slightly oversized.
In designing a drip-irrigation system, it is common to consider that vegetable crops ordinarily need approximately 1.5-acre-inches of water for each week of growth or approximately 20-acre-inches of water per crop.
Actual crop water use will be more or less than this amount, depending on weather and irrigation efficiency.
3.2 Planning a Drip Irrigation System: Design Considerations
 Start with what is already available-the water source or the field.
If a water source is already available , the amount of water available may be used to calculate the maximum size of each irrigation zone.
If no water source is available, the amount of water needed by the crop-based on the size of the planted area-may be used to calculate the type of well or pond size needed.
Lay out of beds and rows.
Because differences in altitudes affect water pressure, it is preferable to lay out beds perpendicular to the slope.
This arrangement of rows is called "contour farming".
Figure 12.
In contour farming, rows are laid perpendicularly to the natural field slope, which allows each drip tape to be parallel to each other and contour.
Credits: Eric Simonne.
Pipe sizing.
Larger-diameter pipes are more expensive than smaller-diameter pipes, but larger-diameter pipes carry more water.
All delivery mains and secondary lines should be sized to avoid excessive pressure losses and velocities and should be able to withstand a pressure of 80 psi.
Excessive pressure losses result in a large difference in pressure from the pressure level at the beginning of the line compared to the pressure level at the end of the line.
Since the flow rate of the emitters is usually a function of water pressure, the water application at the beginning of the line may be very different from the water application at the end of the line.
This difference will result in irregular water application on the crop.
Excessive water velocities  in the lines-the result of a too-small diameter-are likely to create a water hammer , which can damage the delivery lines.
Growers should be aware of the maximum acreage that can
 be irrigated with different pipe sizes at a water velocity of 5 feet/second.
The maximum length of drip tape should be based on the manufacturer's recommendation and the actual terrain slope.
Typically 400-600 feet are maximum values for driptape length.
Excessive length of laterals will result in poor uniformity and uneven water application.
When the field is longer than 400-600 feet, consider placing the secondary  line in the middle of the field-rather than at the end-and connect drip tape on both sides.
A Y-connector is convenient on a drip system connected to a hose bibb because a garden hose can be connected to the other side.
To evaluate source flow rate, run water full force from an outside faucet and note the number of seconds required to fill a bucket of known volume.
Calculate the gallons of flow per hour  by dividing the bucket size in gallons by the number of seconds required to fill it, then multiply by 3600 seconds for gallons-per-hour:
 System flow rate  = Bucket volume  / time needed to fill  X 3,600 seconds per hour
 The maximum flow is considered to be 75% of the flow-rate measure above.
Maximum flow is the largest number of gallons available for use at one time while operating a drip-irrigation zone.
Use goof plugs to plug holes in the mainline that are no longer needed due to system modification.
Common setup mistakes include not installing a filter or a pressure reducer, using excessively high lengths of mainline, and/or adding too many drip emitters.
Zones should be approximately the same size throughout your drip-irrigation system.
Variation in zone sizes will reduce the efficiency of pump operation.
When all zones are of the same size, pipe sizes and system cost will normally be minimal.
The length of the mainline should not exceed 200 feet in a single zone.
Pressure regulators may be required if the pressure produced by the pump is too large or if zones vary greatly in size.
If the pump was sized for a previously existing sprinkler system, it would likely operate at pressures that are excessive for the components of a drip system.
If the system consists of different size zones, the pump must
 deliver the amount of water required in the largest zone at the pressure required by the tape used for lateral lines.
If some zones are significantly smaller, the pump will produce higher pressure at the smaller discharges required by these zones.
This pressure must be reduced by pressure regulators to the pressure-level required by the drip tape in the lateral lines.
4.
Drip System Maintenance and Operation
 The goal of drip-irrigation maintenance is to preserve the high uniformity of water application allowed by drip irrigation.
A successful program of maintenance for a drip-irrigation system is based on the prevention-is-thebest-medicine approach.
It is easier to prevent a drip tape from clogging than to "unclog" it or replace it.
See Table 11 for additional readings on this topic.
4.1 Water Sampling for Drip Irrigation
 4.2 The Prevention-Is-the-Best-Medicine Maintenance Program for Drip Irrigation
 This maintenance program is based on filtration, chlorination/acidification, flushing, and observation.
Filters were described in section 2.5, above.
Chlorination and acidification go together.
Chlorination consists of the introduction of a chlorinating compound  that produces hypochlorous acid.
In its non-dissociated form, hypochlorous acid oxidizes organic matter and precipitates iron and manganese.
The chlorination point should be placed before the main filters SO the precipitates that form by the chlorination can be removed from the water.
In Florida, most groundwater is alkaline.
The proportion of hypochlorous
 acid in the non-dissociated form  is significantly greater at lower pH.
Hence, acidification makes chlorination more efficient.
In conventional production, hydrochloric acid , sulfuric acid, or phosphoric acid may be used.
The amount of acid and chlorine needed to achieve a 1or 2-ppm free chlorine concentration at the end of the line may be calculated by following the direction provided in EDIS Publication CIR1039 Treating Irrigation System with Chlorine.
When applied correctly, the small amount of chlorine needed for drip-tape maintenance will be harmless to the crop grown in the soil.
Water acidification may be a challenge in certified organic production because NOP standards allow only acetic acid, citric acid, peracetic acid, and other natural acids for use as a cleaner for drip-irrigation systems.
It may take large, unpractical, and expensive amounts of these acids to significantly reduce water pH.
Certified organic growers have three alternative options for drip-tape maintenance.
First, chlorination may be done without acidification although this is less efficient and will require more product.
Second, when economical and feasible, certified organic growers can choose to use potable water for drip-tape maintenance.
Potable water may have a lower pH than well water, but analyses of both waters are needed to make this assessment.
Third, non-chlorine-based products-such as natural chelating agents, hydrogen peroxide, or ozone-may be used to oxidize organic matter in the water.
When in doubt, however, consult with your certifying agency for an acceptable plan for maintenance of your drip irrigation system.
Flushing may be accomplished automatically at each irrigation cycle when self-flushing end caps are used.
Additional labor is required for flushing when the drip tape is tied or capped.
Flushing may also be achieved by increasing pressure SO to temporarily increase water velocity in the drip tape to 4-6 ft/sec.
Flushing takes all the precipitates and slime that may develop outside of the drip tape.
Observation and record keeping are needed throughout the season to ensure that the performance of the drip-irrigation system does not change.
Measure pressure and flow, including how these change throughout the season.
4.3 Scheduling Drip Irrigation
 An adequate method of irrigation scheduling is needed to reduce water needs, maximize crop yield and uniformity, and reduce nutrient movement below the root zone.
Scheduling irrigation consists of knowing when to start irrigation and how much to apply.
A complete irrigationscheduling program for drip-irrigated vegetables includes a target rate of water application adjusted to weather demand and plant age , as well as a measurement of soil moisture, an assessment of rainfall contribution, a rule for splitting irrigation, and detailed record keeping.
The actual size of the wetted zone may be visualized by injecting a soluble dye into the water and digging the soil profile.
Because drip irrigation does not wet the entire field, the best unit for expressing crop water needs and irrigation amounts is volume-of-water-per-length-of-row such as gallons-per-100-feet , which is the most commonly used unit.
Vertical amounts of water  are commonly used with overhead and seepage irrigation, but should not be used for drip irrigation.
4.4 Fertigation and Chemigation
 Conventional growers have a wide array of soluble-fertilizer sources to choose from.
Important characteristics of liquid fertilizers are the fertilizer content  and the ratio among elements.
When all the P,O, is applied pre-plant, most vegetables require a 1:0:1 type of liquid fertilizer.
However, certified organic growers have fewer choices for liquid fertilizers.
The NOP rule limits the use of sodium nitrate  to 20% of the total N.
For example, if the seasonal N rate is 150 lbs/A-as for watermelon or cantaloupe , 20% of the seasonal N represents 30 lbs N/A/season.
If the seasonal N rate is 200 lbs/A-as for tomato and bell pepper, 20% represents 40 lbs N/A/ season.
Some formulations of seaweed or fish emulsions
 may be allowed by the NOP, but the use of these fertilizers in a drip-irrigation system may increase the risk of emitter clogging.
5.
Glossary of Terms
 Acid: A compound that releases H+ ions when dissolved into solution.
Compounds such as hydrochloric acid  or acetic acid  are acids.
Acidification: The introduction of an acid-such as phosphoric, sulfuric, or hydrochloric  acid-into an irrigation system.
This practice is mostly done in maintenance to improve the effectiveness of chlorination.
Algicide: A substance toxic to algae.
Anti-siphon device : A safety device used to prevent back flow of irrigation water into the water source by back-siphonage.
Application efficiency: The percentage of water applied by an irrigation system and stored in the root zone available for water use.
Application rate: The average rate at which water is applied by an irrigation system.
For drip irrigation, rate is expressed as gallons/hour/100 ft or gallons/minute/emitter.
Backflow-prevention device : A device required by Florida law and preventing contaminated water from being sucked back into the water source should a reverse-flow situation occur.
Bactericide: A substance that kills bacteria.
Base: A compound that produces OH ions when dissolved into solution.
Compounds such as potassium hydroxide  or sodium hydroxide  are bases.
Best Management Practices : A set of cultural practices known to increase the efficiency of the irrigation and fertilization program while minimizing the environmental impact of production.
Certifying agency: An independent, accredited third party that verifies that a certified-organic operation is compliant with the regulations described in the National Organic Standards as appropriate for their farming system.
Chelate: A compound that binds polyvalent metals at two or more cation-exchange sites.
Chelate is often a component of ready-to-use formulations for drip-irrigation
 cleaning.
The use of synthetic chelates is not allowed in certified-organic production for cleaning drip-irrigation systems, but synthetic chelates may be used in certifiedorganic production to correct a documented micronutrient deficiency.
Chemigation: A general term referring to the application of water-soluble chemicals into the drip-irrigation system.
Chemigation includes  the application of fertilizers, acids, chlorine and pesticides.
Chlorination: The introduction of chlorine-at a calculated rate-into an irrigation system.
Chlorination can use liquid sodium hypochlorite  or chlorine gas.
Some chlorinating agents are allowed in certified organic production.
Cleaning agent: A substance used to remove dirt, filth, and contaminants.
Control valve: A device used to control the flow of water.
Control valves turn on and off water to the individual zones.
Detergent: A synthetic substance that is not a soap and that is used to change the surface tension to remove oil and grease and other substances relatively insoluble in water.
Detergents are not allowed in certified organic production.
Disk filter: A stack of round, grooved disks used to filter water in a drip-irrigation system.
As the size of the groves decreases, the more the water is filtered.
Each disk has groves on both sides.
Sediments and organic matter accumulate on the disks as water passes through the groves.
Disks are reusable.
Once taken apart, they can be easily cleaned with pressured water and/or a detergent solution.
Drip irrigation: A method of irrigation using the slow application of water under low pressure through tube openings or attached devices just above, at or below the soil surface.
Emitter: A dispensing device or opening in a microirrigation tube that regulates water application.
An emitter creates a controlled flow expressed in gallons/minute/ emitter or gallons/100 ft/hr.
Emitter spacing: Distance between two consecutive emitters.
Typical emitter spacings for vegetable crops are 4, 8, and 12 inches.
Evapotranspiration : The combined losses of water by evaporation from the soil and transpiration from the plant.
Fertigation: The application of soluble fertilizer  through a drip irrigation system.
Fertigation is allowed in certified-organic systems provided the fertilizer sources used are allowed by NOP standards.
Field capacity: The water content of the soil after all free water has been allowed to drain by gravity.
Filter: A canister device containing a screen or a series of disks of a specified mesh or filled with a coarse solid medium and designed to catch solid particles large enough to clog emitters.
Fittings: The array of coupling and closure devices used to construct a drip system and including connectors, tees, elbows, goof plugs, and end caps.
Fittings may be of several types, including compression, barbed, or locking.
Flow: The amount of water that moves through pipes in a given period of time.
For micro-irrigation , flow is expressed in gallons-per-hour  or gallons-perminute.
Flow meter: A device used to measure changes in flow in a drip-irrigation system over the course of a crop cycle.
Goof plug: An insertable cap used to plug holes in mainline and microtubes where drip devices have been removed or are no longer needed or when an accidental hole needs to be plugged.
Hole punch: A device that makes round holes in the pipes SO to connect drip tape with laterals.
Hydrochloric acid : An acid often used to lower the pH of water to increase the efficiency of chlorination.
Use of HCI is prohibited in certified organic production.
Hypochlorous acid : The weak acid generated by chlorinating products.
Hypochlorous acid destroys organic matter.
Use of HOCI is restricted in organic production.
Irrigation schedule: The watering plan and procedures that determine the proper amount of water to apply, the operating time, and the frequency of an irrigation event.
Mainline: The tubing used in the drip system.
Mainline is sometimes called lateral line.
It may be made of hard PVC or soft polyethylene material and comes in diameters ranging from 0.5 to 4 inches.
Mazzei injector : Patented T-shaped, venturi-type injector that does not involve moving parts.
Media filter: A pressurized tank filled with fine gravel and sand.
The sand is placed on top of the gravel.
Sharp-edged sand or crush rock are more efficient in catching soft algal tissue than round particles.
Media filters should be used for filtering water that contains high levels of organic matter.
Micro-irrigation: Synonym for drip irrigation.
Muriatic acid: Another name for hydrochloric acid.
Overfertigating: Applying more fertilizer than the recommended rate.
Overfertigating may result in nutrient leaching below the root zone.
Overwatering: Applying more water than necessary to meet the crop needs and/or applying water in excess of soil water-holding capacity.
Overwatering potentially results in nutrient leaching below the root zone.
Part-per-million : The ratio of one in one million: 1 ppm = 1/1,000,000.
The "ppm" measurement may also represent concentrations: 1 ppm = 1 mg/L.; 1% = 10,000 ppm.
Peracetic : A mixture of acetic acid  and hydrogen peroxide  in an aqueous solution that can be used in certified organic
 production as a substitute for prohibited chlorination products.
Permanent wilting point: The water content of the soil in the plant root zone when the plant can no longer extract water from the soil.
pH: A number between 0 and 14 that represents the amount of acidity  in solution and calculated as: pH = -log[H+].
pH can be simply measured with a pH-meter.
A solution is acidic when pH<7, neutral when pH = 7, and basic when pH>7.
pH affects the solubility and ionic forms in solution.
pH is the single most important chemical parameter for water or soil.
Phosphoric acid : An acid often used to lower the pH of water SO to increase the efficiency of chlorination.
Use of phosphoric acid is prohibited in certified organic production.
Pressure: The "force" propelling water through pipes.
Common static  pressure in irrigation systems is 20-70 psi.
Irrigation systems operate under dynamic  water pressure, which is reduced with elevation gain and friction loss caused by the water rubbing on the sides of pipes.
Pressure due to gravity : This measurement may be calculated as gain  or loss  by multiplying the height of the water column in feet by 0.433.
For example, if a 200-foot drip tape is laid on a field with a downhill slope of 3 ft/100 ft , the gain in pressure due to gravity will be 200 X 0.03 X 0.433 = 2.59 psi.
Pressure loss: The loss of water pressure under flow conditions caused by debris in a filter, friction in pipes and parts, and elevation changes.
Pressure rating: The maximum pressure a pipe or dripsystem component is able to handle without failing.
For example, Class 160 PVC pipe refers to plastic irrigation pipe with a pressure rating of 160 pounds per square inch.
Aluminum irrigation pipe has a pressure rating of 145-150 psi.
These pressure ratings will normally be adequate for mainlines in drip-irrigation systems.
Pressure-relief valve: A valve that opens and discharges to the atmosphere to relieve the high pressure condition when pressure in a pipeline exceeds a pre-set point.
Pressure-compensating emitter: An emitter designed to maintain a constant output  over a wide range of operating pressures and elevations.
Pressure-sensitive emitter: An emitter that releases more water at the higher pressures and less at lower pressures, which are common with long mainlines or terrain changes.
Pressure regulator: A device that reduces incoming water pressure for lowpressure drip systems.
Typical household water pressure is up to 50-60 psi while drip systems are designed to operate SO not to exceed 8-12 psi in the drip tape.
Due to friction losses, pressure in the delivery pipes may be 20-30 psi, thereby requiring a pressure regulator.
The important ratings of a pressure regulator are the diameter, the downstream pressure and the maximum flow allowed by the pressure regulator.
Root zone: The depth and width of soil profile occupied by the roots of the plants being irrigated.
Sand separator: A device also called hydrocyclone that utilizes centrifugal force to separate sand and other heavy particles out of water.
It is not a true filter, but could be considered a pre-filter.
Screen filter: A type of filter using a rigid screen to separate sand and other particulates out of irrigation water.
Self-flushing end cap: A spring-loaded device that lets water go out at the end of the drip tape when the water pressure is less than the threshold of the cap.
Sulfuric acid : An acid often used to lower the pH of water SO to increase the efficiency of chlorination.
Use of sulfuric acid is prohibited in certified organic production.
Sulfur, powdered: Elemental sulfur  in the yellow powder form is allowed in certified organic production.
It is commonly used to decrease soil pH, but this requires chemical conversion by soil microorganisms.
Powdered sulfur should not be used for chlorination purposes.
Soap: Alkaline salts of fatty acids used to remove hydrophilic particles.
Strong acid: An acid that is totally dissociated in water.
Common strong acids are hydrochloric acid  and sulfuric acid.
Tape-to-lateral connector: A device sometimes called a barbed adapter and that is placed at the end of the drip tape  to connect it with the lateral.
Tape-to-tape connector: A device used to repair or replace a leaking section of drip tape.
The tape-to-tape connector allows two pieces of drip tape to be connected together.
Trickle irrigation: Synonym for drip irrigation.
Turbulent-flow emitter: Emitters with a series of channels that force water to flow faster, thereby preventing particles from settling out and plugging the emitter.
Uniformity of water application: A measure of the spatial variability of water applied or stored in an irrigated field down a row and across several rows.
Uniformity of water application is usually expressed as a percentage, 100% representing perfect uniformity.
Venturi injector: A tapered constriction which operates on the principle that a pressure drop accompanies the change in velocity of the water as it passes through the constriction.
The pressure drop through a venturi must be sufficient to create a negative pressure , relative to atmospheric pressure.
Under these conditions, fluid from the tank will flow into the injector.
Water applied: The amount of water actually applied during an irrigation cycle.
For drip irrigation, it is expressed in gallons/100 feet of drip tape.
Water hardness: The sum of multi-valent ions-such as calcium, magnesium, aluminum, or iron-in solution.
Hardness is expressed in mg/L of calcium carbonate equivalent, and its value is used to classify the water as soft , moderately soft , slightly hard , moderately hard , hard , or very hard.
Water alkalinity: Ability of water to neutralize acids.
Water alkalinity is based on the content of hydroxide , carbonate  ions.
Water velocity: The speed at which water travels inside a pipe, usually expressed in feet/second.
Water hammer: Pressure surge that occurs because of sudden stoppage or reduction in flow or because of a change in direction of flow.
Water hammer may be reduced by slowly turning water on and also by an irrigation-system design in which water velocity is less than 5 feet/second.
Weak acid: An acid that is only partially dissociated in water.
Common weak acids are phosphoric acid , boric acid , acetic acid , and citric acid -CH2-COOH].
Zone: A section of an irrigation system that can be operated at one time by means of a single control valve.
Given the drought conditions that Nebraska experienced in 2022, it is likely that many pastures will have an abundance of spring and summer weeds this year.
Chapter: 19 Precision Farming Opportunities
 Precision farming is the site-specific implementation of management practices that will economically optimize yields while maintaining the soil, water, atmospheric, plant, and animal natural resources.
Precision farming can involve the use of integrated pest management , precision conservation, site-specific nutrient management, site-specific pest management, global positioning systems , geographic information systems , remote sensing, and detailed landscape analysis.
In the past, the adoption of precision systems was limited by barriers related to complexity, economic returns, equipment breakdowns, incompatible software and hardware products, and time demands during critical periods.
Today, many of these barriers have been resolved and adoption is mainly limited by the difficulty of converting locally collected information into practical solutions.
The goal of this chapter is to provide an introduction to precision farming.
In precision farming, a wide variety of location-based information layers are used to develop better decisions.
These layers include yield, remote sensing, scouting, soil nutrients, elevations, weeds, insects, and disease population information.
Precision farming may or may not lead to variable-rate treatments.
Over the past several years there have been many technological advances that simplify precision farming.
Some of these include:
 1.
Equipment improvements that simplify precision farming.
Figure 19.1 Image of a soybean field collected by a UAV on September 15 flying at 400 ft.
This field contains a large reflectance variability.
In areas that are white, the soybean leaves have senesced and fallen to the soil.
The moisture content in these soybeans is less than the green areas on the image.
Table 19.1 General guidelines for precision farming:
 1.
Precision farming is the site-specific implementation of management practices that will economically optimize yields while maintaining the soil, water, atmospheric, plant, and animal natural resources.
2.
Many tools are available to implement precision farming.
3.
Precision farming includes identifying the goal, assessing the potential economic impact, and field testing the technique using on-farm research.
Figure 19.2 Corn yield, soil P, and ragweed maps superimposed on totpography map 
 2.
Electronics improvements that improve communication.
3.
The development of Unmanned Aerial Vehicles/ Systems  that collect high-resolution images.
4.
The wide-scale availability of digital databases, making highly accurate elevation information publicly accessible.
5.
Training is available that reduces adoption barriers.
Spatial information contains longitude , latitude , elevation, and one or more measured values.
The longitude and latitude values can be identified with a differentially corrected global positioning system.
When using GPS it is important to remember that complex mathematics is used to solve very difficult problems.
The complexity of the mathematics has resulted in slightly different techniques that are based on a projection and datum, to convert a curved surface to a flat map.
Two commonly used projections are UTM and Geographic, and two common datum are NAD-83 and WGS-84.
The latitude and longitude values can be different for different projections.
When using geographic information system 
 Figure 19.3 The use of remote sensing superimposed on totpography map to identify area that needed to be scouted.
Remote-sensing layer is near infrared  band taken from airplane in 1997.
Weed patches were identified by field scouting.
Table 19.2 The types and formats of spatial data that are used for precision agriculture.
Data	Point	Line	Polygon	Images
 Formats	Text , Shape	Shape	Shape	tif, jp2, sid, img, las
 Data sets	Yield monitor data, Soil	Soil survey data	Satellite image, Aerial image, Elevation
 test data, Veris Cart EC	data 
 software, the projection and datum for each spatial data set needs to be specified.
Geospatial information can also be stored in a wide range of formats , which are often unique for each collection system or data type.
Yield monitor, elevation, soil nutrient and pest maps, remote sensing, soil electrical conductivity, and soil maps are information layers that can be used to produce useful site-specific implementation maps.
However, each data layer may have unique characteristics that influence its usefulness.
Combines equipped with yield monitors can be used to collect yield data.
Each collection system has unique characteristics.
For example, Ag Leader's PF3000 / PF Advantage / YM2000 models have *.yld format and INTEGRA VERSA / COMPASS have *.agdata format.
John Deere's Greenstar 2 or 3 have * *ver format and Greenstar GSY or GSD have.gsy or *.gsd formats.
To ensure that the data is correct, the monitors must be calibrated.
Yield-monitor data can be used to identify yield goal management zones, nutrient removal maps, and variable seeding maps.
Elevation information can be obtained from several different sources, including combine GPS data collected when harvesting a field, a topographic survey that you have conducted, or a publically available digital elevation model.
More recently, elevation maps are being created from LiDAR data.
Light Detection and Ranging  technology uses a pulsed laser to measure distance between the sensor and the surface of a target.
Based on this information, accurate 3-D maps and images can be created.
Other information layers such as yield, remote sensing, and electrical conductivity maps can be overlaid onto LiDAR elevation maps.
LiDAR has a vertical error of less than 1 foot.
Spatial Soil Nutrient and Pest Information
 In the past, spatial soil-nutrient and pest information was expensive to obtain.
Within a field, soil-nutrient maps were created by collecting soil samples from grid points, management zones, or grid cells.
These samples were then analyzed for the nutrient of interest.
Spatial pest maps were obtained by walking a field and counting the number of pests at a number of sampling points.
In the future, it is likely that scouting will be augmented by remote sensing collected by satellite, aircraft, or UAV.
Disadvantages of satellite and aircraft data include cost, resolution, timeliness, and availability.
They also rely on illumination from the sun, which introduces variability from one pass of a satellite to the next.
In the past, many agronomists used Landsat images, which are multi-spectral images with a 30 m  resolution.
Images are captured every 16 days, and the information from different wavelengths  can be combined  to calculate the normalized difference vegetation index  and the green normalized difference vegetation index  values.
These indices have been used to identify stress in crop plants.
These indices are related to plant stress and the values are calculated with the equations:
 NDVI =  /  GNDVI =  / 
 Figure 19.4 Different resolutions that can be collected by different sensors.
Figure 19.5 The relationship between the wavelengths and bands as well as the influence of vegetation on the reflectance within a band.
The recent availability of UAVs has the potential to increase the use of remote sensing for management decisions.
UAVs have the potential to collect high-resolution information quickly when you need it.
Some UAV systems collect geometrically corrected data.
Soil Electrical Conductivity 
 High salt areas can be identified by conducting a visual survey or an apparent electrical conductivity survey, using a Geonics EM38  or the Veris Soil EC Mapping System manufactured by Veris Technologies.
Maps produced by these systems are quick to collect and provide information that can be used to identify management zones.
The electrical conductivity is the ability of a material to transmit  an electrical current and high values are often correlated with poor drainage.
STATSGO2  has a scale of 1:250,000 and is designed for broad-based planning and management at the regional, state, and multi-state areas.
The database is maintained and distributed as spatial and tabular data sets by the USDA-NRCS.
The original STATSGO data for South Dakota was published in 1995.
SSURGO  is mapped and described at a smaller scale than STATSGO2.
The intended use of SSURGO is for natural resource planning and management by landowners, townships, and counties.
Details for accessing this data layer are available in Chapters 16 and 17.
Figure 19.6 Soil EC map  taken by Veris Cart and sampling points for EC measurement.
Like STATSGO2, SSURGO consists of polygons called map units that may be composed of several soil components.
Map units have defined spatial boundaries but components have discrete boundaries.
Components have unique properties, interpretations, and productivity ratings that map units do not.
Map unit properties are derived from aggregating component properties and can be different depending on the method of aggregation.
STATSGO2 and SSURGO provide information about soil types, drainage classes, soil textures, and slope.
The soil survey maps can be used to make management zones.
The management-zone approach separates fields into unique areas where it is assumed that a common management strategy can be implemented.
Digital information obtained from the Web Soil Survey search engine is based on this concept.
Within a management zone, it is assumed that a given problem is uniform and that a single treatment should be implemented across the zone.
For example, in high-yield areas, corn will be seeded at a rate of 38,000 seeds/acre, whereas in low-yield areas corn will be planted at a rate of 29,000 seeds/acre.
Preparing data for mapping is beyond the scope of this manual.
There are multiple software packages available for this purpose.
Making good management-zone maps with given data set requires a skilled agronomist.
Prescriptions Based on Contour Maps
 For some information layers, continuous information was collected.
Examples of this type of data are remote sensing, LiDAR elevation, and yield-monitor data.
This data can be used to create application maps using geographic information systems  software.
The resolution of the prescription maps is dependent on the operator, equipment used to implement the prescriptions, and the given field.
A prescription map tells the system controller how much product to apply based on the location in the field.
Each controller needs the data in a different structure.
For example, a prescription map written for an Ag Leader PF3000 Pro requires the *.tgt format, and a Raven Viper can read the *.shp format.
Most agricultural GIS packages can create prescription maps in multiple formats.
The prescription is written to a compact flash , PCMCIA card , USB hard drive, or other type of data storage device, which is then uploaded to the computer within the machine cab.
Wireless transfer of prescription and as-applied maps are also available in many newer systems.
Precision farming is in its infancy and the technologies are rapidly changing.
Across the US, scientists are developing and testing algorithms that seek to improve yields and reduce costs.
Software companies are making prescription maps easier.
We believe that implementing precision farming next year will be easier than implementing it today, and today it is much easier than it was 10 years ago.
During the heart of the irrigation season, we recommend keeping the available soil water level above the 50% depletion level.
To do this, we recommend irrigating as the soil water level approaches 35% depletion.
This will allow a few days for the irrigation to be completed before the crop experiences any stress.
As we near the end of the season, we can push the threshold to 60% depletion.
D EMANDS ARE continually increasing for water from the Colorado River, which is the source of irrigation for the Imperial Valley.
This series of experiments was designed to investigate the possibility of greater efficiency in utilization of the water supply through sprinkler irrigation.
The conventional furrow system now in use for row crops requires one or more days to adequately irrigate the 42-inch beds.
When lettuce is planted, water is allowed to flow in the furrows for varying periods, as long as 21 days.
The continuous flow serves both to cool and moisten the beds and is continued until the desired stand emerges.
The first experiment, initiated on October 29, 1964, compared sprinkler and furrow irrigation on precisionand conventionally seeded plots.
Seeding rates were 3.0, 0.7 and 0.5 lb of seed per acre.
The 0.5-lb rate was placed at 2-inch intervals using a Clow Vac Jet planter; and the other rates were applied with a Planet Jr.
seeder.
Results showed irrigation by sprinklers caused no observable damage to plants due to salt concentration on the leaves, and no humidity-induced pathogen developed.
In addition, the sprinklerirrigated, precision-planted plots matured at a uniform rate sufficient to allow 71% of the heads to be harvested at one time.
The other seed rates and furrow irrigation required three harvest periods at weekly intervals.
Furthermore, the 71% yield was from one to two weeks earlier than those of other treatments.
The favorable results from sprinkler irrigation were associated with the maintenance of low surface-salt accumulation in the seed rows.
The second experiment, initiated on January 18, 1965, compared carrot growth on conventional 41-inch beds with growth on an 82-inch bed-under both furrow and sprinkler irrigation.
This experiment showed that a significantly greater number of plants emerged in the wide beds where salt had been removed from the soil surface by sprinkling resulting in a significantly higher yield on the 82-inch, sprinkled, beds.
This carrot experiment demonstrated the salt-
 The Colorado River water used for irrigation contains approximately 1.3 tons of salt per acre foot.
As the water evaporates, a deposit of salt accumulates on the surface of the beds.
The salt concentration sometimes falls on the seed rows along the shoulder of the beds, preventing germination of the seeds.
removal advantage of sprinkler irrigation in allowing great flexibility in bed size and shape, and leading to more efficient utilization of existing crop acreage.
An auxiliary greenhouse experiment established that the cause of carrot forking observed in the test program was the conventional broadcast-placement of ammonium nitrate pellets prior to bedding up.
This left a planar configuration of pellets 1 inch below the germinating seedlings.
The probability of a direct hit upon one of these high concentrations of fertilizer by a tender radical was greatly increased by the placement configuration.
The forking could be avoided by mixing the pellets in the soil before bedding.
The effect of increased carrot density
 upon the growth rate of carrots sprinkler irrigation is also under i gation, and should lead to recomi tions of proper seeding rates.
The third experiment examin microclimatic-modifying effects of kler irrigation.
This experiment wa ated on August 30, 1965 with p sugar beet seed.
Seeds were place per foot of row by using an Intern Harvester 185 precision planter.
irrigation regimes were compare cluding  a continuous furrow water until the seeds emerged;  sprinkler application for on followed by three hours per day first week.
The daily application
 Photo below shows carrot beds with spotty stand in foreground resulti furrow irrigation, in contrast to solid stand of larger plants in backgrou had been sprinkler irrigated.
Sprinkler Irrigation Imperial Valley
 F.
E.
ROBINSON O.
D.
MC COY G.
F.
WORKER, JR.
Photo above shows solid stands of onions under sprinkler irrigation in experiment four.
Photo below shows one-sided stands of onions as affected by salt accumulation resulting from furrow irrigation in experiment four.
vented entrapment of the emerging seedlings by soil crusting.
Both the furrow and sprinkler irrigations lowered temperatures approximately 20F with the sprinkler plots being 2F cooler than the furrow plots, at the half-inch depth.
Soil salinity in the seed rows was approximately one-third as high as that in the furrow areas.
The emergence of seedlings was 78% in the sprinkler plots, 44% in the intermittent furrow plots, and 32.5% in the continuous furrow plots.
Greenhouse experiments disclosed that the inhibiting effect of the continuous furrow irrigation resulted from the exclusion of air by water in the soil.
The significantly higher emergence rate of pelleted sugar beet seed under sprinkler irrigation was attributed to lower salinity, cooler temperature, and better soil aeration.
The fourth experiment-conducted with lettuce, cabbage, carrots, and onions -was begun October 14, 1965, and compared sprinkler and furrow irrigation at
 Sprinkler irrigation reduced surface salt accumulation, increased water use efficiency, and cooled the soil surface more effectively than conventional furrow irrigation in recent tests.
No detrimental effects were observed on lettuce, cabbage, carrots, onions or sugar beet seedlings from sprinkler application of Colorado River water.
Emergence of seedlings was significantly higher with cabbage, sugar beets, carrots, and onions-and in some cases with lettuce-when sprinkled, as compared with furrow irrigation.
When combined wth precision planting, sprinkler irrigation resulted in earlier maturity of lettuce as well as highest yields obtained from a single harvest.
Further studies will be needed to re-evaluate cultural practices involved in changing from furrow to sprinkler irrigation.
Photo above shows solid stands of lettuce and cabbage under sprinklers in experiment four.
Photo below shows one-sided stand of lettuce and cabbage resulting from accumulation of salts during furrow irrigation.
three intervals of application.
Stands were first established and then the irrigation intervals were imposed, based on the rate of evaporation from a class A US Weather Bureau pan.
The wettest interval involved an irrigation for each 11/2 inches of water evaporation; the intermediate treatment, for each 2 inches; and the dry treatment, for each 3 inches of evaporation.
Results of this experiment showed that the sprinkler irrigation removed soil-surface salt, producing a higher rate of emergence of cabbage, carrots and onion seedlings.
The driest treatment significantly reduced onion bolting on early plantings.
The intermediate treatment on carrots produced a significantly higher yield of carrots than the dry treatment, and used less water than the wet treatment.
Both carrots and onions were shown to have growth rates dependent upon plant population density.
These results indicate that in changing from furrow to sprinkler irrigation, either rates of seeding should be reduced, or a longer time allowed for the crops to mature.
Water use under furrow irrigation was 21/2 times greater than that required by sprinkler irrigation.
Additional experiments are under way to adjust herbicide and insecticide applications in changing from furrows to sprinklers.
A series of experiments with precision planting of lettuce resulted in the achievement of 84% of a perfect stand of lettuce from a 12-inch spacing of raw lettuce seed placed with the UC-Giannini precision planter.
During September and October of 1966, growers germinated more than 1,000 acres of lettuce by sprinkler irrigation for the first time in the Imperial Valley.
Rainfall caused a soil crust to develop on one field, but where sprinkler irrigation had been used, an acceptable stand was obtained.
Where furrows had been used no stand was obtained and replanting was necessary.
Results from sprinkling on lettuce were generally favorable and it is anticipated that considerably more acreage will be put under this method of irrigation in coming years.
Frank E.
Robinson is Assistant Water Scientist; Orval D.
McCoy is Associate Specialist in Vegetable Crops; and George F.
Worker, Jr., is Associate Specialist in Agronomy, University of California, Imperial Valley Field Station, El Centro.
Assistance with this project was received from Rain for Rent , Rainbird Sprinkler Corporation, Perma Rain Irrigation Company, Henning Produce Incorporated, Clow Seed Company, Vessey and Company Incorporated, and Holly Sugar Corporation.
H.
YAMADA B.
B.
FISCHER C.
R.
POMEROY
 To obtain maximum yields of barley in the San Joaquin Valley, a normal  pre-irrigation and at least one supplemental crop irrigation are required, according to these studies.
When a heavy pre-irrigation is applied, the soil may be wetted below the potential rooting depth of the barley, in which case the moisture would not be available to the plants.
B ARLEY IS PLANTED on more irrigated acres in the San Joaquin Valley than any other single crop.
Yields fluctuate greatly from season to season, and from area to area-from a low of 1800 lbs per acre to 5800 lbs per acre.
This great fluctuation in barley yields can be attributed mostly to moisture availability during critical times of the growing seasonalthough soil-fertility levels, planting dates, and the disease situation can also play key limiting roles.
Pre-irrigation with 12 to 14 inches of water and one additional irrigation in late February or early March  produced the most economical returns in earlier, non-replicated, trials.
A 1964 study demonstrated that pre-irrigation without supplemental irrigations, a common practice of many barley growers in the San Joaquin Valley, resulted in production of yields that were uneconomical and below optimum levels.
In the study reported here, an irrigation experiment was conducted on a Panoche clay loam soil to determine yield responses to varying amounts of water applied by pre-irrigation and crop irrigations on barley.
The experiment was conducted on a grower's field , and included four treatments with three replications.
The treatments were as follows: B1, heavy pre-irrigation only; B2, normal pre-irrigation plus two crop irri-
 gations  B3, normal pre-irrigation plus one crop irrigation  B4, normal pre-irrigation only.
Plots were 25 ft wide and 640 ft long.
All plots were uniformly fertilized, prior to the preirrigation, with NH3 gas injected in the soil to a depth of 9 inches with 16-inch spacing, at the rate of 80 lbs of nitrogen per acre.
Following pre-irrigation in midOctober, 70 lbs per acre of California Mariout barley were drilled into the plots on December 4.
Plots were machine harvested  on June 23.
Rainfall between planting and harvest was approximately 2.5 inches.
The amount of water applied in preirrigation and in each crop irrigation was measured through siphon tubes for each plot.
The amounts applied to the treatments were as follows: B1, 22.1 inch preirrigation; B2, 12.2 inch pre-irrigation plus 7.6 inch early boot stage and 4.8 inch at flowering stage  B3, 12.6 inch pre-irrigation plus 7.8 inch early boot stage  B4, 14.5 inch pre-irrigation.
Soil samples were taken from each foot to a depth of 8 ft from eight locations in the field, prior to pre-irrigation, to determine the initial moisture content of the field.
All treatments were sampled at two locations after pre-irrigation and after harvest.
The bulk density, averaging 1.4 gm/cm3 at 8 ft, was determined from two pits dug in the field after harvest, with a back hoe.
Using the density figure of 1.4 gm/cm and the oven-dried weight of the soil sample, calculations were made of the total inches of water for each treatment at the time of sampling.
From the soil samples collected before and after pre-irrigation, it was found that 29% of the 22.1-inch pre-irrigation in B1 percolated below the 8-ft depth of sampling.
Evapotranspiration rates for treatment B1, B2, B3, and B4  were 47%, 72%, 74% and 72% respectively, of
to Reduce Nitrogen Loads from Drained Cropland in the Midwest
 UNIVERSITY OF ILLINOIS EXTENSION
 Issued in furtherance of Cooperative Extension Work Acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture.
George F.
Czapar, Director, University of Illinois Extension, University of Illinois at Urbana-Champaign.
University of Illinois Extension provides equal opportunities in programs and employment.
Published in collaboration with Purdue University Extension, South Dakota State University Extension, the Iowa Soybean Association-Environmental Programs and Services, Iowa State University Extension and Outreach, and University of Minnesota Extension.
Laura Christianson, Crop Sciences, University of Illinois Jane Frankenberger, Department of Agricultural and Biological Engineering, Purdue University Chris Hay, Department of Agricultural and Biosystems Engineering, South Dakota State University ; Iowa Soybean Association  Matt Helmers, Department of Agricultural and Biosystems Engineering, Iowa State University Gary Sands, Department of Bioproducts and Biosystems Engineering, University of Minnesota
 Dan Jaynes, USDA ARS National Laboratory for Agriculture and the Environment, Ames, Iowa Tom Kaspar, USDA ARS National Laboratory for Agriculture and the Environment, Ames, Iowa Jeff Strock, Department of Soil, Water, and Climate, University of Minnesota, and Southwest Research and Outreach Center, Lamberton, Minnesota
 Factors Affecting Nitrate Loads from Drained Cropland	7
 Practices that Reduce Nitrate in the Plant Root Zone
 1.
Improved Nitrogen Management	11
 2.
Winter Cover Crops	14
 3.
Increasing Perennials in the Cropping System	17
 Practices that Reduce Delivery of Nitrate to the Field's Edge
 4.
Drainage Water Management 	21
 5.
Reduced Drainage Intensity	24
 6.
Recycling Drainage Water	27
 Practices that Remove Nitrate at the Edge of the Field or Downstream
 9.
Alternative Open-Ditch Design	35
 10.
Saturated Buffers	38
 Economic Considerations of the Ten Strategies	40
This article  investigated the use of soil water sensors for VRI management.
If VRI will be used to meet the crop water needs in each part of the field, a combination of soil water sensors and remote sensing will likely be needed.
The Brule sand-sandstone aquifer and the Upper Cretaceous aquifer are the other two secondary aquifers in western Nebraska.
The Brule sand-sandstone aquifer is distinguished from wells installed in Brule siltstone.
The Upper Cretaceous aquifer supplies water to only about 13 wells, mostly in western Scotts Bluff County, although it is heavily used in the Denver area.
The Upper Cretaceous aquifer has high sodium, and sometimes high chloride concentrations in Nebraska.
Historic annual increases in global carbon dioxide  concentration are expected to continue; increased global temperatures are forecast as well.
Crop productivity can benefit from increased ambient CO2 as similar assimilation rates can be maintained with smaller canopy conductance, resulting in modestly reduced crop water requirement.
Cool-season grass crops and broadleaf crops will likely gain photosynthetic efficiencies with elevated CO2 levels.
When elevated temperatures exceed optimal conditions for assimilation, stress responses can include damage to the light-harvesting complex of leaves, impaired carbon-fixing enzymes, thereby reducing components of yield including seed potential, seed set, grain fill rate, and grain fill duration.
Field studies conducted under conditions of elevated CO2indicate that benefits of elevated CO2 are reduced by heat-induced stress responses.
Crop cultural practices can be adapted to avoid stress, genetic advances may yield germplasm capable of tolerating or resisting stress factors.
Climate change forecasts for the central High Plains, pertinent to crop growth, indicate increases in ambient carbon dioxide  concentration, average annual temperatures, and intensity of hydrologic events .
Field and controlled environment studies document substantial effects of these expected climate changes on factors affecting crop yield formation.
Briefly, transpiration efficiency tends to increase with elevated ambient CO2; elevated temperatures can impair yield formation by damaging photosynthetic capacity, reducing enzyme activity, impairing seed-set and grainfill rates, increasing respiratory losses of assimilates, and reducing radiation capture due to accelerated crop development.
Climate change forecasts indicate greater temperature increases in the High Plains relative to eastern regions.
Though the High Plains may encounter greater impacts, qualitatively similar effects may be expected in the eastern Great Plains.
Opportunities to mitigate these effects may require discovery and utilization of genetic resources to
 provide tolerant/resistant cultivars as well as revised crop cultural practices.
A summary of critical processes is outlined below.
EXPECTED CLIMATE CHANGE FACTORS
 Increased atmospheric CO2 concentrations recorded at Mauna Loa are a matter of historic record.
Forecasts for continued increases in ambient CO2 depend on expected rates of fossil fuel combustion.
Increased global temperatures are a more recent phenomenon  and are associated with greenhouse gas effects.
Forecasts for continued global warming depend on the rate of greenhouse gas accumulation and modeled effects on global surfaceatmosphere exchange processes.
This review will focus on the expected impacts of increased atmospheric CO2 and increased temperatures on crop productivity and yield formation, considering current knowledge of plant physiology.
Figure 1.
Global surface temperature forecast from climate change model experiments from 16 groups  and 23 models collected at PCMDI.
Committed warming averages 0.1C per decade for the first two decades of the 21st century; across all scenarios, the average warming is 0.2C per decade for that time period.
Source: IPCC  Ch.
10, Fig.
10.4, TS-32; after Feddema.
Crop yield  can be related to water use , considering the transpiration  component of ET, biomass productivity relative to T  and the grain fraction of biomass.
Each component of this relationship can be altered by genetic, environmental and/or crop management effects.
Tanner and Sinclair  provided evidence that transpiration efficiency approaches a constant value, kd, when adjusted for daily vapor pressure deficit  effects.
This intrinsic transpiration efficiency is greater for crops, such as corn, which utilize C4 physiology , relative to that of crops, such as soybean, with C3 physiology.
An analogous relationship  can be developed between yield  and biomass productivity relative to photosynthetic electron supply , considering the fraction of absorbed radiation used to drive assimilatory processes , intercepted photosynthetically active radiation , photosynthetically active radiation  and HI.
IPAR = RUE PSII.
PAR PAR HI [2]
 Krall and Edwards  demonstrated a direct linear relationship between gross photosynthesis and absorbed photosynthetically active radiation, when corrected for quantum yield of photosystem II.
Kiniry et al.
reported a linear relationship between RUE and VPD, analogous to that observed for TE.
Equations [1] and [2] indicate that crop yield can be related to either the transpiration component of water use or the interception component of solar radiation, considering conversion efficiencies to biomass and yield formation factors.
Rochette et al.
demonstrated a linear relationship between the ET and net photosynthesis flux for well-watered corn after canopy closure when ET was adjusted for VPD effects.
This supports interpretation of equations [1] and [2] as analogous.
Together, these equations provide a framework for evaluating expected climate change effects on crop productivity and grain yield.
CROP RESPONSES TO EXPECTED CLIMATE CHANGE FACTORS
 Crop productivity, with respect to water use, is expected to increase as ambient CO2 increases.
Elevated CO2 increased productivity of plants with C3 physiology-with increased yield as well.
As an example, Figure 2 shows effects of ambient CO2 concentration  on water vapor efflux and CO2 influx across a leaf stoma.
Calculations of leaf conductance assume identical assimilation rates  and a constant ratio of CO2 within the sub-stomatal cavity  to ambient : 0.5.
In this example, stomatal conductance would be 16% smaller under current conditions of elevated ambient CO2, relative to that around 1965.
Associated with less stomatal conductance is reduced transpiration and a warmer canopy temperature.
These results are expected for plants with both C3 and C4 physiology, though a greater relative increase in CO2 fixation is expected for plants with C3 physiology due to inefficiencies associated with the carboxylating enzyme, Rubisco.
Figure 2.
Schematic depicts CO2 diffusion through stomatal aperture of a leaf, into the sub-stomatal cavity.
Carbon fixation  can be calculated as the product of stomatal conductance  and the gradient between ambient  and sub-stomatal  CO2 concentrations.
In this hypothetical example, the increase in atmospheric CO2 concentrations, from 1965 to 2005, results in identical assimilation rates, with a smaller gs.
Smaller gs tends to reduce evaporative loss of water, though canopy temperatures tend to increase.
The photosynthetic efficacy of Rubisco, e.g.
in fixing CO2 into six-carbon sugars, is limited by the relative concentrations of CO2 and O2 at the reaction site.
Typically, plants with C4 physiology sequester Rubisco in bundle sheath cells, where O2 concentrations are small, hence the
 superior productivity of plants with C4 physiology.
Rubisco occurs in mesophyll cells of C3 plants, exposed to near-ambient O2 concentrations, resulting in approximately one third of enzyme activity diverted from CO2 fixation.
Because of this difference, the increased assimilation response of plants with C3 physiology, to increased CO2 concentration can generally be attributed to increased Rubisco efficacy in mesophyll cells, though plant acclimation to elevated CO2 can introduce further complexities.
The relative impacts of elevated CO2 on photosynthesis, growth and yield formation of plants with C3 and C4 physiology is somewhat controversial.
Long et al.
reported that Free-Air CO2 Enrichment  technologies indicate ~ 50% less yield benefits from elevated CO2 than earlier studies of crop responses to elevated CO2, based on enclosure techniques.
The FACE studies indicate plants with C4 physiology have little increase in assimilation with CO2 enrichment  but stomatal conductance is reduced for these plants, thereby reducing water consumption.
Wall et al.
reported, for well-watered sorghum, that under FACE, stomatal conductance decreased 37% and assimilation increased 9%, and leaf water potential increased  by 3%; however, no change in final shoot biomass was detected.
Long et al.
found increased productivity for plants with C3 physiology with CO2 enrichment, but the yield increase was less than that projected from earlier enclosure studies.
These studies show that, though assimilation capacity increased by 36%, the increase in canopy assimilation was 20%; biomass increase was 17% and yield increase was 13%.
The limited yield response, relative to increased productivity potential, could result from plant acclimation to elevated CO2 conditions.
The FACE studies indicate that opportunities to realize the potential benefits of elevated CO2 for C3 crops will require further development.
Table 1.
Percentage increases in yield, biomass, and photosynthesis of crops grown at elevated CO2  relative to ambient CO2 in enclosure studies summarized by Cure and Acock.
Percentage increases for FACE studies were generated by meta-analysis of Long et al..
Taken from Long et al..
Source	Wheat	Soybean	C4 Crops
 Cure and Acock 	19	22	27
 FACE studies	13	14	0*
 Cure and Acock 	24	30	8
 FACE studies	10	25	0*
 Cure and Acock 	21	32	4
 FACE studies	13	19	6
 *Data from only one year in Leakey et al..
Evidence is emerging that plants adjust, or acclimate to elevated CO2 conditions.
Watling et al.
reported changes in the carbon-fixing potential for sorghum grown at elevated CO2, relative to the current condition.
These changes included increased leakage of CO2 from bundle sheath cells to mesophyll, requiring further metabolic processing, decreased activity of PEP carboxylase , resulting in reduced carboxylation efficiency and assimilation potential.
Comparative analysis of gene expression in soybean  under current and elevated CO2 indicated that respiratory breakdown of starch, promoting cell expansion and leaf growth, was accelerated with elevated CO2.
Controlled environment and FACE studies confirm that increased ambient CO2 can increase biomass productivity for C3 crops, reduced crop water use, and elevated canopy temperatures for C3 and C4 crops.
Realizing potential benefits of elevated CO2 conditions will require discovery and utilization of adaptive traits as well as adaptive crop management.
Increased atmospheric CO2 can alter crop-pest interactions.
Zavala et al.
found that soybean could be more susceptible to coleopteran herbivores  under elevated CO2 due to down-regulation of genes coding for production of cysteine proteinase inhibitors; these inhibitors are deterrents to coleopteran herbivores.
Other unexpected consequences could involve enhanced growth of plant pests, with C3 physiology, and reduced herbicide efficacy-further aggravating climate change impacts.
Heat stress on crops can impair assimilation by damaging light-harvesting apparatus and by reducing carbon-fixing enzyme capacity.
Yield formation processes, including seed set and grain fill rate, can be impaired at elevated temperatures.
The duration of growing season-and subsequent radiation capture-can be reduced by increased temperatures, as indicated by the growing degree day concept.
Muchow et al.
found greatest grain yield potential of corn occurred in a cool, temperate environment, due to increased growth duration and increased radiation capture; under warmer sub-tropical conditions growth duration, light absorption, and grain yields were reduced.
Factors affecting intensity of heat stress and crop responses to heat stress are briefly discussed.
Canopy temperatures are generally linked to ambient temperatures, but can increase with radiative loading and decrease with evaporative cooling.
Canopy productivity can be damaged when temperatures exceed critical levels.
Optimum temperatures for photosynthesis  and carbon-fixing enzymes are approximately 30 to 38 C  for corn ; 25 to 30 C  for winter wheat  and 32 C  for soybean.
Net
 photosynthesis in corn was inhibited at leaf temperatures exceeding 38 C , though severity of inhibition decreased with acclimation.
The temperature acclimation process is thought to involve a protein known as Rubisco activase, which maintains the Rubisco enzyme in an active state when under heat stress.
Rubisco activation in corn decreased for leaf temperatures greater than 32.5 C , with near-complete inactivation at 45 C.
Acclimation of photosynthesis to temperature for winter wheat, in the range of 15 to 35 C , involved the light-harvesting apparatus.
Thermotolerance of C3 crops was increased by growth under elevated CO2 conditions, but decreased for C4 crops.
Ristic et al.
reported a rapid, low-cost technique to detect heat tolerance of light-harvesting apparatus, indicated by chlorophyll content, in wheat, corn, and possibly other crops.
Elevated temperatures can impair light-harvesting apparatus and inactivate critical carbonfixing enzymes, thereby reducing assimilation rates and ultimate yield potential.
The specific mechanisms affected by heat stress remain a subject of active investigation.
Seed number and seed weight are commonly critical components of grain yield formation.
Heat stress can impair both aspects of yield potential.
Potential seed number, commonly determined during ear, panicle, head, or pod formation, is influenced by assimilate supply at the end of juvenile development, which can be reduced by heat stress.
Pollen viability and the pollination process can be impaired by heat stress, reducing seed set and yield potential.
Grain fill rate can be related to canopy productivity-particularly productivity of leaves in the upper canopy-during this developmental stage.
Thus effects of heat stress on radiation capture and carbon fixation  may reduce the grain-fill/seed weight component of yield potential.
Direct effects of heat stress on pollen viability, pollination and seed set can reduce seed number; indirect effects of heat stress on canopy productivity can reduce seed weight during grain fill.
Muchow and Sinclair  simulated effects of increased temperatures on corn yield; they reported a 10% yield decrease with 4 C  average temperature increase, despite an assumed 33% increase in normalized transpiration efficiency.
These effects are expected for plants with either C3 or C4 physiology.
Adaptive traits to increase transpiration efficiency could aggravate heat stress effects.
Increasing canopy resistance under conditions of large evaporative demand can increase transpiration efficiency.
Hall and Hoffman  reported decreased leaf conductance of sunflower and pinto bean with increased VPD, independent of leaf water potential.
Teare et al.
compared canopy behavior of sorghum and soybean following a stress period.
Canopy resistance
 of sorghum canopy was nearly three times that of soybean; relative air temperature above the sorghum canopy was 3 C greater than that above soybean, despite a larger root system and more water in the soil profile for the sorghum crop.
Sloane et al.
reported a slow-wilting soybean cultivar; this cultivar was later found to reduce water use, under conditions of large evaporative demand, by limiting maximum transpiration rates.
Controlled environment studies demonstrated that leaf xylem conductivity limited water supply to evaporative surfaces, reducing transpiration rates when VPD exceeded 1.9 kPa.
A simulation study  indicated that, under favorable conditions, grain sorghum yields were reduced for cultivars with the canopy trait of limited maximum transpiration but yields increased by 9-13% when yield potential was less than 450 kg ha  The limited transpiration trait is expected to improve yield potential under water deficit conditions.
However, this trait could increase likelihood of heat stress, as elevated VPD tends to correspond with radiative loading-particularly for irrigated crops in semi-arid regions.
Other consequences of elevated temperatures in crop production systems can include greater respiratory losses of photosynthate and shifts in crop-pest interactions.
Warm night temperatures can result in increased loss of assimilates due to greater respiration rates, which can increase with temperature.
Tropically adapted sorghum lines maintain productivity by restricting respiratory losses, while temperate-adapted sorghum lines fail to accumulate significant biomass under conditions of warm nights, due to accelerated respiratory losses.
Other production factors which could be affected by warmer global temperatures include increased survival of insect and disease pests , increased productivity of weeds, and corresponding reduced efficacy of pesticides.
YIELD FORMATION FACTORS AFFECTED BY EXPECTED CLIMATE CHANGE
 Productivity for crops with C3 physiology is expected to benefit from increased atmospheric CO2; the corresponding yield formation factors would be TE for [1] and PSII for [2].
Secondary effects would include accelerated canopy formation, increasing the transpiration fraction of ET [1] and the intercepted fraction of PAR [2].
Though HI may have reached an upper limit by extensive breeding, for some crops, HI might be expected to increase, for other crops, to the extent that potential seed number, seed-set, and grain fill rate can be increased.
In contrast, warmer ambient temperatures and stress-augmented increases in canopy temperatures would likely reduce crop productivity and components of yield for crops with C3 or C4 physiology.
Increased VPD would effectively reduce the TE factor of [1] while reduced efficacy of light-harvesting apparatus and carbon-fixation could combine to reduce the OPSII factor of [2].
Reduced canopy formation would tend to decrease the transpiration fraction of ET [1] and the
 interception fraction of PAR [2]; similarly, decreased harvest index could result from reduced potential seed number, seed-set, and grain fill rate.
Benefits of increased CO2 could readily be offset by increased heat stress.
Field studies comparing crop growth at ambient and elevated CO2 levels indicate gains from elevated CO2 levels were less than anticipated; the reduced level of benefits were attributed to stress responses to factors including elevated canopy temperature.
Realizing full benefits of increased atmospheric CO2 would require avoidance or tolerance of stress associated with rising global temperatures.
Hubbert et al.
found that photosynthesis in rice can be affected by breeding strategy; photosynthetic capacity and stability under heat stress could be a useful target when yield is limited by biomass accumulation rather than harvest index.
Sloane R.J., R.P.
Patterson and T.E.
Carter, Jr.
Field drought tolerance of a soybean plant introduction.
Crop Sci 30:118-123.
Grazing Management Affects Runoff Water Quality and Forage Yield
 John Pennington County Extension Agent Agriculture
 Andrew Sharpley Professor Crop, Soil and Environmental Sciences
 John Jennings Professor Forage
 Mike Daniels Professor Water Quality and Nutrient Management
 Philip Moore, Jr.
USDA/Agricultural Research Service
 Tommy Daniel Professor Crop, Soil and Environmental Sciences
 Arkansas Is Our Campus
 In 2008, most of the 30,000 beef farms in Arkansas were family owned , averaged about 30 head per farm and accounted for about 1.8 million cows and calves, worth $432 million.
The total economic impact of the Arkansas beef industry is well over $1.4 billion.
Part of the beef industry's success is attributed to its symbiotic relationship with the broiler industry.
In fact, the two industries experienced paralleled growth with the broiler industry, providing litter to grow the forage on otherwise unproductive soils and terrain.
While both industries are well established and will continue to thrive, preserving and maintaining good water quality is becoming an ever-increasing priority for land owners, citizens, state/federal agencies and the legal community.
Stream water quality in established pasture regions is generally high as runoff and erosion are minimized because the soil is protected from raindrop impact by the forage.
However, uncontrolled grazing management can result in overgrazed pastures and lead to high runoff volumes, increased erosion and poor water quality.
Overgrazed pastures have low vegetative surface cover and forage yield, increased soil compaction and lower water infiltration, which can lead to increased erosion and runoff.
When litter or any other fertilizer is applied to such pastures, the risk of nutrient loss in runoff increases, especially for phosphorus.
Too much P in our lakes and streams accelerates the natural aging process, called eutrophication, resulting in excessive aquatic weeds and algae, reduced recreational use and taste and odor problems in drinking water supplies.
Water quality is a national concern, especially in Northwest Arkansas, where some streams flow into bordering states.
There are many sources of runoff from agricultural and urban areas like those in Northwest Arkansas.
One of the more prominent agricultural sources is runoff from pastures.
Although pasture management is known to affect the quantity and quality of runoff, the effects of grazing management are neither fully understood nor quantified in terms of P loss.
While studies are limited, researchers have shown a close correlation between P loads in runoff  and land use.
For example, some studies have shown that potential P losses from forested areas are much less than from agricultural areas which are much less than from urban areas.
For pastures, P losses have been shown to vary depending on watershed conditions and management.
For example, runoff loadings within the Illinois River Watershed were shown to
 range from 0.2 to 1.2 lb P/ac/yr with annual loads of 0.6 lb P/ac/yr attributed to pasture watersheds not influenced by point source discharge.
A study in the southern grasslands of Oklahoma found that the highest  and lowest  loads were associated with poor and well managed pasture, respectively.
What Do Studies in Arkansas Indicate?
Recent research at the USDA-ARS Dale Bumpers Small Farm Research Center in Booneville and the University of Arkansas Research and Extension Center in Fayetteville is addressing the question "How does grazing management affect runoff water quality and forage yield?" One study utilized replicated pasture watersheds.
In both studies, runoff under different grazing management practices was monitored for total solids , total P , dissolved P  and forage yields.
For every runoff event, runoff volume and concentrations of TS, TP and DP were measured.
Event loads or loss of TS, TP and DP were calculated from runoff volumes and concentrations.
Total solids  represent the amount of erosion or sediment lost during the event, while TP loss is a measure of the total amount of P lost.
How much of the TP is available to aquatic algae?
Not much, maybe 5 percent, but all of the P in the DP parameter is available and can, if conditions are ideal, produce rapid algae blooms in receiving lakes and reservoirs.
The USDA-ARS study was located on soils with ~8 percent slope.
Pastures were a mix of common bermudagrass and annual ryegrass and received poultry litter as fertilizer at ~2 ton/ac annually in the spring.
Forage yields were measured monthly.
Treatments for the USDA-ARS watersheds in Booneville included hayed only, overgrazed, rotational grazed and rotational grazed with a buffer.
Hayed only watersheds were hayed three times annually, in April, June and again in the fall.
The grazed watersheds varied in grazing intensity as defined by the number of animal units  per acre combined with the grazing time.
Overgrazed is defined as a stocking rate of ~3 AUs/ac with a grazing period of several months at a time, whereas rotational grazed is defined as a higher stocking rate of ~6 to ~12 AUs/ac but with a shorter grazing period of only ~3 to ~4 days with a two-week or more rest/regrowth period for the forage.
The rotational with buffer treatment included the same rotational grazing regime plus a 50-foot buffer  at the base of the watershed.
The University of Arkansas study in Fayetteville examined runoff from similar treatments of hayed, overgrazing and rotational grazing in tall fescue pastures with ~5 percent slopes.
Nutrient loadings from these land uses were compared to those from a typical Ozark natural hardwood forest, which was used to represent background/natural levels.
Runoff Water Quality Results
 Percent cover and sediment loss.
Generally, the higher the surface cover, the better the soil is protected from raindrop impact, resulting in less runoff and erosion.
Percent soil surface cover provided by the forage and sediment loss as a function of grazing type are shown in Figure 1.
While surface cover for all treatments was high , hayed watersheds were significantly higher in percent cover than other treatments.
Typical of most pasture situations, erosion losses from all treatments were very low because of the high surface cover.
Even though the losses were low, erosion from the overgrazed was roughly four times greater than the other treatments, which were not different.
Soil compaction and runoff.
The more dense or compacted the surface soil, the greater the risk the rainwater will runoff rather than infiltrate into the soil.
Figure 2 shows the effect of grazing type on soil compaction.
Overgrazing resulted in the highest compaction and the highest amount of runoff, being nearly two to five times higher than the other
 Figure 1.
Effect of grazing on soil surface cover and sediment loss.
Different letters represent significant differences in the same parameter.
treatments, which were not different in either compaction or runoff volume.
The hayed watershed was the lowest both in amount of runoff and compaction, with the rotational-grazed treatment in between, showing no difference with or without a buffer.
Figure 2.
Effect of grazing on runoff and soil compaction.
Different letters represent significant differences in the same parameter.
Figure 3.
Effect of grazing on total and dissolved runoff P concentrations.
Different letters represent significant differences in the same parameter.
Total and dissolved phosphorus runoff losses.
There was no difference in the concentration of TP and DP in runoff with overgrazed, hayed and rotational grazed.
However, significantly lower concentrations of both TP and DP occur with the rotational-plus-buffer watershed.
Other pasture studies, particularly when manure is applied, have shown that most of the TP in runoff is in the DP form, probably because the P in manure is water soluble and therefore at a high risk of being transported in runoff water.
Presence of the 50-foot vegetative buffer reduced P concentration in runoff considerably by having the runoff travel relatively short distances through vegetative material.
While P concentrations are important, P loads are probably more meaningful because this parameter combines both concentration and runoff volume.
Figure 4 depicts the effect of grazing on loads of TP and DP.
While the concentrations of both TP and DP from several treatments  were the same, the runoff volume between treatments was very different.
These factors are combined and demonstrated in Figure 4, with overgrazing being significantly higher than the other treatments because the soil was more compacted, producing higher runoff volumes.
Hayed was one of the lowest ranking treatments for P load because of the low runoff volume, even though P concentrations were high.
Rotational grazed with a buffer had low P concentrations as well as low runoff, making it again one of the lowest ranking treatments.
Figure 4.
Effect of grazing on total and dissolved P runoff loads.
Different letters represent significant differences in the same parameter.
Similarly, the study at Fayetteville showed the overgrazing treatment produced the highest runoff and TP loads, followed by hayed and rotational grazed watersheds.
In addition, when compared to the traditional Ozark hardwood forest representing natural/background levels, the overgrazed treatment was ~5 times higher both in runoff and TP loads.
Figure 5.
Effect of grazing on runoff and total P loads compared to forest/background levels.
From the UA demonstration project.
Figure 6.
Effect of grazing on forage yield.
Different letters represent significant differences in the same parameter.
Forage Yield and Management
 Forage yield.
The hayed watersheds produced significantly higher forage yield than all other treatments and were over 50 percent higher compared to the overgrazed treatment.
These results are similar to other pasture studies in the literature which attribute increased soil moisture to the hayed treatment due to increased infiltration of rainwater.
Due to increased moisture and rest periods for the forage, rotational grazing management can potentially increase forage production as compared to an overgrazing management system.
Other commonly observed benefits of rotational grazing are increased AU carrying capacity of the farm and the opportunity to harvest excess forage as hay for sale or later use and reduced fertilizer input costs.
Management.
It's a given that there isn't one particular grazing management system that is the best fit for every single producer.
Likewise, every grazing system has its own strengths and weaknesses.
Overall, the most important aspect of any successful grazing management system is for a producer to match farm resources, goals and management availability with a particular grazing system in order to optimize profits while also achieving environmental and economic sustainability.
With improved grazing management, cool-season forages may be stockpiled in the fall for winter grazing and warm-season forages can be hayed in the summer to be fed in drought periods or winter.
Improved grazing management should be designed to extend the grazing season for both warmand cool-season forages.
This will result in better utilization of forages, which will reduce the number of days that hay must be fed.
In many cases, improving a grazing system makes it possible to graze in Arkansas for 300 days, or more, out of the year.
It is true that a controlled grazing management system will require increased cost initially because of additional fencing supplies, watering facilities and labor.
However, with time, controlled grazing management is more productive, flexible and sustainable.
Additionally, although it is possible, there is no need to fully implement a controlled grazing system at once.
In many cases it may be better in terms of finance and management time to increase control of grazing management one fence and one pasture at a time.
Results from these and other studies clearly show that grazing management affects forage yield and runoff water quality.
Inherent in the different grazing techniques is the potential to reduce compaction and improve vegetative surface cover , which has a dramatic impact on runoff, erosion and P loss.
Unfortunately, the less management intensive and more traditional grazing practice
 of overgrazing ultimately results in lower forage production and increases conditions for runoff and erosion, which can degrade water quality.
While it is clear that better grazing management can indeed benefit production as well as the environment, inclusion of BMPs, such as buffers, can have even a more dramatic impact on nutrient concentration in runoff water.
For example, the inclusion of the 50-foot buffer on the rotational-grazed treatment reduced P loading three to four times.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Director, Cooperative Extension Service, University of Arkansas.
The Arkansas Cooperative Extension Service offers its programs to all eligible persons regardless of race, color, national origin, religion, gender, age, disability, marital or veteran status, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
The description of a speed control VRI system is that its application rate is varied by changing the speed of the pivot and that the irrigation management zones are pie slice shaped.
Considerations for the speed control VRI system are that it is relatively inexpensive many picot panels are capable without additional investment.
It also needs no special hardware on the sprinklers.
Example uses of it are if spatial variation lines up well with pie slices, varying application based on topography  if it lines up pie slices, multiple crops or varieties under one pivot, and on-farm research.
September 2022 Mesonet Extremes
 Highest air temperature: Big Springs 8NE, 106F, Sept.
8
 Lowest air temperature: Whitman 5NE , 28F, Sept.
26
 Highest heat index temperature: Cook 4SW, 105F, Sept.
20
 Max wind gust : Bushnell 12SE, 45 mph, Sept.
9
 Highest daily precipitation: Decatur 7S, 1.63 inches, Sept.
18
 Highest four-inch soil temperature: Dickens 1NE, 99F, Sept.
6
If you want to learn more about using an ETgage, feel free to contact me at the Extension office or you can download this publication off the UNL website.
Using Modified Atmometers  for Irrigation Management
Total dissolved solids and sodium concentrations are uniformly high, but other aspects of water chemistry vary from place to place.
Arsenic and uranium concentrations have both been documented to exceed their recommended maximum contaminant levels in places, and Chadron well owners should consider testing their wells for these compounds.
How Soils Hold Water: A Home Experiment
 Brian Leib, Associate Professor, Irrigation Systems and Management Tim Grant, Extension Assistant, Soil and Water Resources Department of Biosystems Engineering and Soil Science
 Financial support from the Tennessee Soybean Promotion Board, Cotton Incorporated, and a USDA NRCS Conservation Innovation Grant
 The short answer to how soils hold water is pores and the tension or suction that pores exert to retain water.
The pores or openings between the soil particles provide space for water to reside and surface area on which water can adhere.
The interactions between soil and water can be complex, but it is possible to run a simple home-based experiment to better understand how a porous media like soil and soil pores behave in the presence of water.
Yes, this experiment is safe for children to try at home.
The porous media to be studied is the common but extraordinary paper towel.
First, submerge the paper towel in a bowl of water.
Participants should agree that all pores are now filled with water.
In the same way, a soil can have all its pore space filled with water, a status known as saturation.
Saturation is good for forming wetlands, but most agricultural crops will not grow in a soil devoid of air, and tractor performance is less than desirable in this soupy condition.
Next, remove the paper towel and hold it above the bowl for one minute.
Participants will observe water draining out of the pores and should agree that drainage will stop before all of the moisture is removed from the paper towel.
Similarly, the larger pores in a saturated soil will drain progressively until only the smaller pores are able to hold their water against the force of gravity, a status known as field capacity.
All soils will drain to field capacity unless a restrictive layer or water table prevent the downward movement of water.
In well-drained fields, the condition of field capacity is usually reached in one or two days after a heavy rain.
One goal of irrigated agriculture is to keep soil moisture at or below field capacity.
Over-irrigation and excess rainfall can increase soil water above field capacity.
The excess water above field capacity can percolate past the bottom of root zone and leach agricultural fertilizer and chemicals toward groundwater.
After the paper towel has finished draining, proceed to squeeze it firmly and then squeeze a second time as tightly as you can.
Participants should note that at first a lot of water is released with little effort, then little water is released with a lot of effort, and finally, there is water remaining in the paper towel that cannot be squeezed out.
In a similar way, plant roots exert their own tension forces to remove water from soil pores.
Plants can extract water from soil until the remaining soil water is held too tightly by the smallest pores, a status known as permanent wilting point.
The range from field capacity to wilting point is known as the available soil water holding capacity.
Even though water is available to plants as soil moisture decreases to wilting point, the goal of irrigated agriculture is usually not to stress the plant.
For each crop, a management allowable depletion  has been established as the percentage of available soil water holding capacity that can be removed without unduly stressing the crop.
Traditionally, the goal of irrigation scheduling has been to irrigate before reaching MAD and to return the soil moisture to field capacity, an approach known as full irrigation.
However, in a humid region, the goal should be to irrigate before reaching MAD but not return soil moisture to field capacity, allowing for the capture of rainfall, a method referred to as Managed Depletion Irrigation.
The MDI approach has been specifically applied to cotton and soybean2 in University of
 Tennessee Institute of Agriculture experiments and publications.
The soil water continuum for an MDI approach is illustrated in Figure 1.
General values for available soil water holding capacity by texture are shown in Table 1 and MAD values for row crops are illustrated in Table 2.
The Tennessee specific water holding capacity by soil type can be found in the NRCS Soil Surveys3 and a study conducted by the University of Tennessee Institute of Agriculture.
The MAD values for most crops can be found at United Nations Food and Agriculture  Website.
5
 As a final note, marketing would have us believe that some paper towels can absorb more moisture than others.
This is definitely true of soils.
A loamy sand will hold around 1 inch of water per foot of soil, while a silt loam will hold more than 2 inches per foot.
If lettuce with a 1.5-foot root zone and a MAD of 35 percent are grown on loamy sand, the effective storage of soil water will only be around half an inch.
In contrast, cotton  grown in silt loam could effectively store more than 5 inches of water.
The combination of soil and crop can significantly affect the soil water reservoir and the need to irrigate in terms of initiation timing, frequency and the amount of water applied.
Therefore, knowing soil type and its corresponding water holding capacity is an integral part of every irrigation decision.
Table 1: Available Soil Water Holding Capacity
 Soil Texture	Capacity 
 Clay	1.20 to 1.50
 Silty Clay	1.50 to 1.70
 Silty Clay Loam	1.80 to 2.00
 Silt Loam	2.00 to 2.50
 Fine Sandy Loam	1.50 to 2.00 in/ft
 Sandy Loam	1.25 to 1.40 in/ft
 Loamy Sand	1.10 to 1.20 in/ft
 Fine Sand	0.75 to 1.00 in/ft
 Course Sand	0.25 to 0.75 in/ft
 Figure 1: Soil Water Continuum.
Table 2: Management Allowable Depletion*
 *Percent of available water that can safely be depleted from the soil before yield loss is expected.
AG.TENNESSEE.EDU Real.
Life.
Solutions.
To properly maintain the system:
 Periodically inspect plants for signs of overor underwatering, such as wilting and/or changes in leaf color; adjust emitters or timer/controller as necessary.
Check soil wetting patterns around individual plants to ensure that at least half of the root zone area is covered.
Whole root zone coverage is preferable.
Inspect and clean filters and emitters on a regular basis.
Flush the system every two months to discharge debris.
As plants grow, inspect emitters and move them away from the original planting area.
Reset irrigation controller seasonally to adjust to changes in plant water needs.
Replace battery in automatic timer twice a year.
When replacing parts, use only parts specified by the equipment manufacturer.
Monitor irrigation times to prevent overwatering.
If standing water or excessive runoff occurs, reduce irrigation time and/or frequency.
Use a multi-program controller on automatic systems that will enable micro-irrigation zones to run on their own program.
Add a timer to manually controlled systems to avoid the possibility of forgetting to turn the system off.
Install a rain shutoff device to avoid unnecessary watering.
TAMPA BAY WATER Supplying Water To The Region
 Republished with permission from the Tampa Bay Water's Conservation Coordination Consortium.
For more information on landscapes that conserve water and protect the environment, contact your local county Extension office.
UF FLORIDA UNIVERSITY of Yards & Florida IFAS Extension Neighborhoods
 Designed and printed by: Southwest Florida Water Management District
 The Southwest Florida Water Management District is responsible for maintaining a balance between the water needs of current and future users without damaging the environment.
This information will be made available in accessible formats upon request.
Please contact the Communications Department at  796-7211 or 1-800-423-1476 , ext.
4757; TDD only at 1-800-231-6103.
A Guide to the Basics of Micro-Irrigation
 below the soil surface) is an effective way to determine if a plant needs water.
Many plants may require 3/4 to 1 inch of water per week during the growing season.
Your irrigation system's operating schedule should be adjusted based on the type of micro-irrigation* and according to the following conditions:
 Micro-Sprays Irrigate more area per emitter than other types of microirrigation.
These devices come in a variety of nozzle sizes and spray patterns.
Generally visible in the landscape.
Micro-irrigation, commonly referred to as "drip" or "low-volume" irrigation, offers a way to improve landscape quality while saving water.
When designed and used correctly, this approach can improve the efficiency of landscape irrigation through the precise application of water.
Microirrigation emitters have a maximum flow rate of 30 gallons per hour , or 0.5 gallons per minute.
In contrast, traditional spray and rotor sprinklers can apply water at a rate of over 3 gpm.
Generally used for landscape irrigation and potted plants, micro-irrigation is not recommended, and in some places prohibited, for use on Florida lawns.
Plants grown in sandy soils may require more frequent watering and/or closer emitter spacing than those in loam or clay soils.
Sun and Shade Patterns
 Drip Emitters Used for precise applications, such as in potted plants, hanging plants or where plant materials are spaced far apart.
May or may not be visible in the landscape.
Due to lower evapotranspiration rates, plants in shady areas may require less frequent irrigation than those planted in sunny areas of the landscape.
Reduce irrigation frequency during periods of slow plant growth  and frequent rain events.
When watering newly installed plants, irrigate frequently for short durations to promote root development.
Over time, gradually decrease watering frequency while increasing the duration to promote a deeper, more drought-tolerant root system.
Once the plant has developed a substantial root system, watering can be reduced to an "as needed" basis.
Minimized pest problems, such as weeds and diseases, by applying water to the root area of the plant.
Decreased water loss from evaporation, wind and runoff.
Increased water application efficiency when retrofitting in-ground sprinkler systems.
Easy connection to hoses or outdoor spigots.
Flexibility in meeting variable water needs of new, maturing and established plants.
Minimized erosion when watering plants on steep slopes.
Compliance with local water conservation codes and ordinances.
Plants are grouped into one of three water-use categories, or hydrozones: oasis , drought-tolerant  or natural.
When watering plants, irrigate according to specific hydrozone requirements.
In-Line Drip Tubing Used where plants are installed in rows or close together.
Typically placed below the mulch, reducing its visibility.
*Please note: Micro-irrigation emitters deliver water at rates between 0.5 and 30 gallons per hour, and application rates applied  will also vary.
Adjust irrigation operating schedules appropriately.
With proper design, operation and maintenance, micro-irrigation systems can have many benefits, including:
 Landscapes generally should be irrigated as needed.
A visual plant check  combined with a soil check (feel for moisture
Irrigators wanting to purchase equipment should keep in mind that many NRDs across the state offer incentives to purchase irrigation scheduling equipment.
Pumps for Florida Irrigation and Drainage Systems
 The primary function of a pump is to transfer energy from a power source to a fluid, and as a result to create flow, lift, or greater pressure on the fluid.
A pump can impart three types of hydraulic energy to a fluid: lift, pressure, and velocity.
In irrigation and drainage systems, pumps are commonly used to lift water from a lower elevation to a higher elevation and/or add pressure to the water.
The classification of pumps used in this publication first defines the principle by which energy is added to the fluid, then identifies the means by which this principle is implemented, and finally, distinguishes among specific geometries commonly used.
Under this system of classification, all pumps may be divided into two major categories: 1) dynamic pumps, where continuously added energy increases velocity of the fluid and later this velocity is changed to pressure, and 2) displacement pumps where periodically added energy directly increases pressure.
This publication will discuss only dynamic pumps which are commonly used for pumping water in agricultural applications such as irrigation and drainage.
Displacement pumps have limited capacities and are not suitable for pumping large amounts of water required for irrigation or drainage.
They are used mainly for chemical injection in agricultural irrigation systems.
Displacement pumps are discussed in another publication.
Dynamic pumps described in this publication can be classified as one of several types of centrifugal pumps and a group of special effect pumps.
In centrifugal pumps, energy is imparted to a fluid by centrifugal action often combined with propeller or lifting action.
Centrifugal pumps can be classified by impeller shape and characteristics.
Impellers are grouped according to the major direction of flow with respect to the axis of rotation.
A continuous range in impeller types can be found.
They vary from the radial-flow type , through mixed-flow types, to the axial flow type.
2.
Dorota Z.
Haman, associate professor, Department of Agricultural and Biological Engineering; UF/IFAS Extension, Gainesville, FL 32611.
With respect to type of impeller, all centrifugal pumps can be classified into the three following groups:
 In addition, a centrifugal pump can be classified in one of four major groups depending on its design and application :
 Table 1 presents advantages and disadvantages of various centrifugal pumps.
This comparison may be helpful in selecting a centrifugal pump for a particular application.
Further subclassification of centrifugal pumps distinguishes among the number of water inlets to the impeller.
There are single suction impellers and double suction impellers.
Finally, the mechanical construction of the impeller itself provides an additional classification.
The impeller can be:
 Enclosed with shrouds or side walls
 Open with no shrouds
 Most irrigation pumps use enclosed or semi-enclosed impellers.
Pumps with open impellers are usually used for pumping liquids with large particles and may be advantageous in drainage or when animal waste is applied through an irrigation system.
Open impellers require frequent adjustments since the clearance between the impeller and the housing is critical.
Basically, a centrifugal radial-flow pump has two main parts: 1) a rotating element  and 2) a stationary element.
Water enters the pump near the axis of the high-speed impeller, and by centrifugal force is thrown radially outward into the pump casing.
The velocity head imparted to the fluid by the impeller is converted into pressure head by means of a volute  or by a set of stationary diffusion vanes  surrounding the impeller.
The centrifugal volute pump is the most common type of radial-flow centrifugal pump.
It has an impeller housed in a progressively widening spiral casing as shown in Figure 2.
Water enters the eye of the impeller and is thrown radially outward.
This type of pump does not have diffuser vanes to reduce the velocity of the water.
Instead, velocity is reduced by the shape of the volute itself.
This design creates an unequal pressure distribution along the volute which may result in a heavy thrust load on the impeller, creating deflection of the shaft, and increasing the probability of its failure.
Volute pumps can be single-suction or double-suction pumps.
A single-suction pump impeller is exposed to a
 large axial hydraulic thrust resulting from the unbalanced hydraulic pressures on the impeller.
In a double-suction pump, water is fed from both sides of the impeller, significantly improving its hydraulic balance.
As a result, double-suction volute pumps can produce higher pressures than single-suction pumps.
Volute pumps are commercially available as single-stage  or multistage  pumps.
The main reason for the multistage configuration is to increase the head produced by the pump.
If a multistage pump has single suction impellers, the impellers are usually arranged with equal numbers discharging in opposite directions to counteract the hydraulic imbalance on each of the impellers.
Volute pumps are used where irrigation water is obtained from depths generally less than 20 ft.
The exact value of possible lift is determined by the net positive suction head required by the pump and other factors as discussed later in this publication.
In a diffuser-type centrifugal pump, the impeller is surrounded by a ring of fixed diffuser vanes that provide enlarging passages in which the velocity of the water leaving the impeller is reduced, and as a result pressure is increased.
The diffuser vanes provide a more controlled flow and allow a more efficient conversion of velocity into pressure than volute pumps.
Shock losses are small since the change from velocity to pressure takes place gradually.
Diffuser pumps, especially large ones, often have efficiencies over 90 percent.
Diffuser pumps have the additional advantage of a balanced radial loading on the impeller, which reduces the chance of shaft failure due to fatigue.
Diffuser pumps are usually selected for high head applications.
As with volute pumps, diffuser pumps can be single or multistage depending on pressure requirements.
Axial-flow pumps, also called propeller pumps, produce flow by the lifting action of the propellers.
Axial-flow pumps are designed for conditions where the capacity is relatively high and the head developed by the pump is low.
An axial pump does not produce high pressure or lift, but can have significant flow capacity if the pump is large enough.
Most axial-flow pumps operate on installations where suction lift is not required.
Generally, these pumps are mounted vertically or on an incline from vertical since it is necessary to submerge the impeller of an axial-flow pump.
In some applications where high volumes of water are required and ample submergence above the pump is available, it is possible to mount an axial-flow pump in a horizontal position.
Mixed-flow centrifugal pumps use both centrifugal force and some lifting action to move water.
Water is discharged both radially and axially into a volute-type casing.
The process is a combination of processes occurring in volute and axial-flow types of pumps.
Mixed-flow impellers are often used in deep-well turbine and submersible turbine pumps.
Under this category are grouped all types of pumps that are suspended by the discharge column within which the drive shaft is located.
The name, deep-well turbine pump, is applied only to pumps operating on the centrifugal principle and having diffuser vanes within the bowl or case.
They can be single-stage or multistaged for higher pressure applications.
Pump bowls which contain impellers and diffusers are located below the water surface, and they should be submerged under pumping conditions.
The drive shaft is located in the center of a discharge pipe and it can be either oil or water lubricated.
A submersible turbine pump is a turbine pump that is close-coupled to a submersible motor which is attached to the lower end of the pump.
This eliminates the long shaft required for deep-well turbine pumps.
Submersible pumps are primarily deep-well pumps; however, they are sometimes used under conditions where the depth of water changes significantly during the season and may drop below the level required for the centrifugal volute or diffuser pump.
Important Concepts for Centrifugal Pumps
 Important concepts associated with the operation of centrifugal pumps include pump efficiency, net positive suction head, specific speed, affinity laws, cavitation, and priming.
Good design, efficient operation, and proper maintenance require understanding of these concepts.
The efficiency of a pump is a measure of its hydraulic and mechanical performance.
It is defined as the ratio of the useful power delivered by the pump  to the power supplied to the pump shaft.
The efficiency of the pump is expressed in percent and can be calculated using Equation 1: To calculate water horsepower the flow rate in gpm and the total dynamic head  in feet must be known.
Water horsepower can be calculated using Equation 2: The efficiency of a pump is determined by actual test.
All parameters required for the determination of water horsepower are recorded while brake horsepower is measured.
Then, equations  and  are used to calculate the efficiency of the pump.
The efficiency range to be expected varies with the pump size, type and design.
However, it is normally between 65 and 80 percent.
A pump should be selected for a given application SO that it will operate close to its point of maximum efficiency.
E = X 100% bhp
 whp = water horsepower bhp = brake horsepower Equation 1.
whp = gpm X TDH 3960
 The absolute pressure on the water at the water source is the driving force for the water moving into the eye of the impeller.
Theoretically, if a pump could create a perfect vacuum at the eye of the impeller, and if it were operating
 at sea level, the atmospheric pressure of approximately 14.5 psi would be the driving force pushing water into the eye of the impeller.
This pressure could lift water a distance of 34 ft..
In practice, this lift is much smaller due to lack of perfect vacuum in the impeller and friction losses in the intake pipe.
The practical value of maximum lift differs between pumps, but it is usually no greater than 20 ft.
If the pump is submerged under water, static water pressure is an additional driving force pushing water into the eye of the impeller and it must be added to the atmospheric pressure.
Each foot of water above the eye of the impeller will add 0.43 psi of pressure to the driving force.
Net Positive Suction Head
 Net positive suction head available  is the absolute pressure of the water at the eye of the impeller.
It is atmospheric pressure minus the sum of vapor pressure of the water, friction losses in the intake pipe, and suction head or lift.
Since any variation of these four factors will change the NPSHa, NPSHa should be calculated using Equation 3: Suction head  must be added instead of subtracted if the water source is located above the eye of the pump impeller.
An accurate determination of NPSHa is critical for any centrifugal pump application.
The NPSHr  is a measure of the head necessary to transfer water into the impeller vanes efficiently and without cavitation.
The NPSHr required by a specific centrifugal pump depends on the pump design and flow rate.
It is constant for a given head, flow, rotational speed and impeller diameter.
However, it changes with wear and different liquids since it depends, respectively, on the impeller geometry and on the density and viscosity of the fluid.
For a given pump NPSHr increases with increases in pump speed, flow rate, and water temperature.
The value of NPSHr is provided by the manufacturer for each specific pump model and it is normally shown as a separate curve on a set of pump characteristic curves.
To
 avoid cavitation NPSHa must be always equal to or greater than NPSHr.
Two pumps are geometrically similar when the ratios of corresponding dimensions in one pump are equal to the same ratios of the other pump.
Specific speed is a constant for any geometrically similar pump.
It is an index number correlating pump flow, head and speed at the optimum efficiency point which classifies pump impellers with respect to their geometric similarity.
Specific speed is usually expressed as shown in Equation 4: It should be noted that for a double suction impeller the flow  is taken as half of the total flow.
Ns = pump specific speed
 N = rotational speed of pump at optimum efficiency 
 Q = flow at optimum efficiency 
 H = head at optimum efficiency 
 The specific speed is an index which is used when selecting impellers to meet different conditions of head, capacity, and speed.
Knowing this index is very helpful in the determination of the maximum permissible suction lift, or minimum suction head, which is necessary to avoid cavitation under different capacities, heads and pump speeds.
For a given head and capacity, suction lift is greater for a pump with lower specific speed.
The calculation of specific speed allows for determination of the pump type required for a given set of conditions to be determined.
Usually high head impellers have low specific speeds and low head impellers have high specific speeds.
There is often an advantage in using pumps with high specific speeds since, for a given set of conditions, their operating speed is higher, and the pump is therefore smaller and less expensive.
However, there is also some trade-off since pumps operating at higher speeds will wear faster.
A set of formulas called affinity laws governs the performance of a given pump and the performance of geometrically similar pumps.
Basically, affinity laws state
 that for a given pump, the capacity will vary directly with a change in speed, the head will vary as the square of speed, and the required horsepower will vary as the cube of speed or, mathematically, as shown in Equation 5: Assuming that impeller diameter is held constant, the mathematical relationships between these variables can be expressed as shown in Equation 6: Basically, the above relationships mean that an increase in pump speed will produce more water at a higher head but will require considerably more power to drive the pump.
These calculated values are very close to actual test results, provided pump efficiency does not change significantly.
However, when conditions are changed by speed adjustment, usually there is no appreciable change in efficiency within the range of normal pump operation speeds.
Q = pump capacity in gpm H = pump head in feet BHP = required brake horsepower N = rotational speed of pump
 For increase in pump speed the NPSHr increases but it cannot be determined from the affinity laws.
Also the laws do not say anything about how the efficiency of the pump will change with speed, but generally this is not a significant change.
NPSHr and efficiency changes must be obtained
 from the pump manufacturer's data.
The above equations assume that the diameter of the pump impeller is constant.
In some cases the size of the impeller can be changed.
Often a pump is very precisely matched to a specific application by trimming the impeller.
It is not feasible to increase impeller diameter.
There is a second set of affinity laws , which describes the relationships between the same variables when the impeller size is changed under constant speed conditions.
These laws relate the impact of impeller diameter changes to changes in pump performance.
Since change of impeller diameter changes other design relationships in a pump, therefore, this second set of affinity laws does not yield the accurate results of the first three laws discussed above and must be applied with caution.
Law 1b: Q1_D1 Q2 D2 Law 2b: Law 3b: BEFORE where: D = initial diameter of impeller D2 = diameter of impeller after trimming
 This second set of affinity laws strictly applies only to radial-flow pumps.
They are only approximate for mixedflow impellers.
In addition, these equations only hold for small changes in impeller diameter.
Calculations for a trim of more than 10 percent of the original diameter can be significantly in error.
Pump cavitation is defined as the formation of cavities on the back surface of an impeller and the resulting loss of contact between the impeller and the water being pumped.
These cavities are zones of partial vacuum which fill with water vapor as the surrounding water boils due to the reduced pressure in the cavities.
The cavities are
 displaced with the flowing water along the pump impeller surfaces toward the outer circumference of the impellers.
As they move toward the circumference, the pressure in the surrounding water increases, and the cavities collapse against the impellers with considerable force.
The force created by the collapse of the cavities often causes erosion and rapid wear of the pump impellers as well as a characteristic noise during pump operation.
The process of cavitation is caused by the reduction in pressure behind the impellers to the point that the water vaporizes.
Thus, it can be caused by any combination of factors which allow pressure to drop to that point, including inadequate submergence or excessive suction lift so that little pressure is available to move water into the pump, high impeller speeds which cause extremely low pressures to be generated behind the impellers, restricted pump intake lines which prevent water from moving readily into the pump, and high water temperatures which decrease the pressure at which water vaporizes.
Cavitation can occur in all types of pumps and it can create a serious problem.
In some cases of mild cavitation, the only problem may be a slight drop in efficiency.
On the other hand, severe cavitation may be quite destructive to the pump and result in pitting of impeller vanes.
Since any pump can be made to cavitate, care should be taken in selecting the pump for a given system and planning its installation.
Pump manufacturers specify the Net Positive Suction Head required  for the operation of a pump without cavitation.
Pump cavitation can be avoided by assuring that the net positive suction head available  is always greater than that required  by the pump.
CAVITATION IN RADIAL FLOW AND MIXED FLOW PUMPS
 In radial-flow and mixed-flow types of centrifugal pump, when the water enters the eye of the impeller, an increase in velocity takes place.
As a result of this velocity increase, water pressure is reduced as the water flows from the inlet of the pump to the entrance to the impeller vanes resulting in cavitation.
A concentrated transfer of energy during cavitation creates local forces capable of destroying metal surfaces.
The more brittle the material which the impeller is constructed of, the greater the damage.
In addition to causing severe mechanical damage, cavitation causes a loss of head, reduces pump efficiency, and results in noisy pump operation.
If cavitation is to be prevented, volute or diffuser pumps must be provided with water under absolute pressure which exceeds the NPSHr.
The following conditions should be avoided in volute and diffuser pump installations:
 Heads much lower than head at peak efficiency of pump.
Capacity much higher than capacity at peak efficiency of pump.
Suction lift higher or submergence head lower than recommended by manufacturer of the pump.
Water temperature higher than that for which the system was originally designed.
Speeds higher than manufacturer's recommendation.
CAVITATION IN AXIAL-FLOW PUMPS
 In axial-flow pumps cavitation cannot be explained in the same way as for radial-flow and mixed-flow pumps.
The water enters an axial-flow pump in a large bell-mouth inlet and is guided to the smallest section, called the throat, immediately ahead of the propeller.
The capacity at this point should be sufficient to fill the ports between the propeller blades.
When the head is increased beyond a safe limit, the capacity is reduced to a quantity insufficient to fill up the space between the propeller vanes, creating cavities of almost a perfect vacuum.
When these cavities collapse the water hits the propeller vane with a force sufficient to pit the surface of the vane.
The first two cavitation prevention rules listed for volute and diffuser pump are different for an axial-flow pump.
Avoid:
 Heads much higher than head at peak efficiency of pump.
Capacity much lower than capacity at peak efficiency of pump.
The last three rules are the same for all centrifugal pumps.
Priming of Centrifugal Pumps
 All centrifugal pumps must be primed by filling them with water before they can operate.
The objective of priming is to remove a sufficient amount of air from the pump and suction line to permit atmospheric pressure and submergence pressure to cause water to flow into the pump when pressure at the eye of the impeller is reduced below atmospheric as the impeller rotates.
When axial-flow and mixed-flow pumps are mounted with the propellers submerged, there is normally no problem with repriming of these pumps because the submergence pressure causes water to refill the pumps as long as air can readily be displaced.
On the other hand, radial-flow pumps are often located above the water source, and they can lose
 prime.
Often, loss of prime occurs due to an air leak on the suction side of the pump.
Volute or diffuser pumps may lose prime when water contains even small amounts of air or vapor.
Prime will not be lost in a radial-flow pump if the water source is above the eye of the impeller and flow of water into the pump is unrestricted.
In some cases pumps are primed by manually displacing the air in them with water every time the pump is restarted.
Often, by using a foot valve or a check valve at the entrance to the suction pipe, pumps can be kept full of water and primed when not operating.
If prime is lost, the water must be replaced manually, or a vacuum pump can be used to remove air and draw water into the pump.
A self-priming pump is one that will clear its passages of air and resume delivery of liquid without outside attention.
Centrifugal pumps are not truly self-priming.
So called self-priming centrifugal pumps are provided with an air separator in the form of a large chamber or reservoir on the discharge side of the pump.
This separator allows the air to escape from the pump discharge and entraps the residual liquid necessary during repriming.
Automatic priming of a pump is achieved by the use of a recirculation chamber which recycles water through the impeller until the pump is primed, or by the use of a small positive displacement pump which supplies water to the impeller.
Special Effect Pumps Jet Pumps
 A jet pump is a combination of a volute centrifugal pump and a nozzle-venturi arrangement.
The driving force lifting the water in this type of pump is provided by a high pressure nozzle which creates a low pressure region in a mixing chamber.
This low pressure causes water to flow into the pump.
A diffuser following the mixing chamber slows down the water and converts velocity head into pressure head.
The jet nozzle is installed in the
 pipe conveying the water.
For a shallow well the nozzle is frequently located outside the well next to the centrifugal pump.
However, for a deep well, the nozzle can be placed inside the well in the intake line.
This location increases the jet pump lift capability considerably beyond that which is practical for the volute centrifugal pump.
The role of the centrifugal pump in a jet pump is to produce the flow to the nozzle and maintain the combined flow through the intake pipe beyond this point.
Jet pumps are self-priming, have no moving parts and do not require lubrication.
Their efficiency is typically low  and they provide low flows at high pressure.
Because of this characteristic, they are not suitable
 for large scale irrigation.
However, they are frequently used for home water supplies and irrigation of lawns and gardens.
Air-lift pumps operate on the principle that a mixture of air and water will rise in a pipe surrounded by water.
An air-lift pump basically consists of a vertical pipe partially submerged in water and an air supply tube allowing compressed air to be fed into the pipe at a considerable distance below the static water surface.
The mixture of water and air is lighter than the water outside the pipe and it rises in the pipe (Figure The head which can be produced depends on the depth of submergence of the air tube.
Air-lift pumps are relatively inefficient.
Typical efficiencies range between 30 and 50 percent.
Generally, air-lift pumping is most efficient when the static water level is high, the casing diameter is relatively small, and the well depth is not excessive in relation to the pressure capability of the compressor.
The volume of air needed to lift the water depends on the total pumping lift, the submergence, the length of air line, and the casing length and diameter.
A useful rule of thumb for determining the proper compressor capacity for air-lift pumping is to provide about 3/4 cfm  of air for each 1 gpm of water at the anticipated pumping rate.
Air-lift pumps have some advantages over the other pumps discussed above.
They do not have any moving parts, can be used in a corrosive environment, and are easy to use in irregularly shaped wells where other deep well pumps cannot fit.
Air-lift pumps are not available from suppliers, but they are very simple to build.
The main disadvantages of air-lift pumps are their low efficiencies and requirement of a very large submergence as compared to other pumps.
A hydraulic ram pump is a motorless low flow rate pump.
It uses the energy of flowing water to operate.
It is suitable for use where a large flow rate is not required.
The flow rate of typical commercially available units is limited to approximately 14 gallons per minute or 20,000 gallons per day.
The head produced by the pump depends on quantity and velocity of water flow at the pumping source.
Water can be lifted up to 400 feet depending upon the quantity and velocity of water flow in the delivery pipe.
Hydraulic ram pumps can be used for domestic water supply or livestock watering.
Usually, their flow rates are too small to consider them for other applications, such as irrigation.
For more information on operation and selection of hydraulic ram pumps see Agricultural Engineering Fact Sheet AE-19.
Why use irrigation over other methods?
Farmers have multiple options when applying manure to their fields as shown in the table to the right.
All options  require manned vehicles moving back and forth across the field, which may cause compaction and use more fuel compared to irrigation.
USING AN INTEGRATED APPROACH TO UTILIZING CENTER PIVOTS FOR LIVESTOCK WASTE MANAGEMENT
 The title says it all using an integrated approach to utilizing center pivots for livestock waste management.
What does integrated mean?
It means considering the entire system from waste source to the application in the field.
To achieve this, the discussion will focus not on center pivots, or separators, or pumps, or lagoon design or any one element of a livestock waste management system, but all of them together integrated into one package so all parts work together and no one part is a constraint.
Consideration will be given to planning for a new or updated system and what to do with an existing system.
Land application of wastewater with mechanical move irrigation equipment both center pivot and linear has been successfully used for many years.
Since the early 1980's the equipment and techniques for irrigating with fresh water have changed dramatically.
Many of these changes have been incorporated into mechanized equipment used for land application.
While these changes have brought significant improvements, we must take into account other issues and particularly public perception of land application systems.
Today, too often phone calls are received by consultants, dealers and manufacturers from a farmer that goes something like this "My pivot is plugged and I need it fixed." So how does one start when responding?
Is the problem the sprinkler package, the pivot or something else?
Where does one begin to look for a solution to the farmer's problem?
And better yet how does one ensure this does not happen again?
Today it is very common that the wastewater producer does not farm or own sufficient farmland.
They rely on working with the irrigator who has little or no experience with confined livestock so collecting information from the irrigator may be a challenge.
And if the wastewater producer does own the irrigation equipment they still may treat it as a separate enterprise and commonly will have separate management focused on crop production and meeting the grain and forage needs of the animal unit.
Whether looking at a new installation or trying to resolve an existing situation like the phone call, it is imperative that one considers the complete system and not just one specific component.
There are a number of ways to look at a system.
One example of how the system may be broken down into components is as follows:
 Waste source hog, beef, dairy, other
 Collection how is the waste collected
 Storage how is the waste stored
 Pumping how is the waste pumped and distributed
 Land application unit for our discussion we will use the center pivot and its sprinkler package.
Briefly before we go into a more detailed discussion, let's consider what each party  wants out of the system:
 The wastewater producer wants:
 Fast delivery of large volumes
 Particularly important to beef feedlots after a rainfall event to ensure they have the capacity to contain another event
 The possibility to eliminate large volumes early in the crop growing season and at the end of the season
 Storage may be full after the winter and may need to be lowered as much as possible prior to winter
 To 'dispose' of chunks and trash
 The nutrient management plan to work as planned
 Waste water only when crop needs it
 A sprinkler package with good uniformity
 No problems eliminating sprinkler plugging is at the top of the list
 Back to the situation of the phone call and how to proceed.
Whether you are a farmer, consultant, dealer or manufacturer, there are suggested steps to follow to determine how well the system is integrated and how to proceed.
Typically the irrigator is asked to describe the system.
Often there are long periods of silence as he does not know:
 The waste source not critical but helps to know what to expect
 He knows the species of livestock, but:
 Farrowing, feeder or finisher Important as farrowing units usually have plenty of water and is a dilute stream while feeder and finishers need to have a higher level of solids
 Type of bedding if any Important for bedding is if sand is used is it collected and recycled or how will it be handled
 Type of collection system in the confinement unit Importance of collection is if flushing should have plenty of water for dilution and if scraping may have challenge of high solids content
 Collection 
 How the waste stream is moved to storage
 Pipeline or open channel
 Important to understand if trash can get into the stream
 Sand recovery for use as bedding
 Important to help understand what solids potentially could be expected at the center pivot.
If lots of solids are coming to the pivot and a separator is being used would indicate a problem in this area
 He knows there is storage, but not sure of:
 Which unit his waste stream comes from Important as if multiple cells should be pumping from the last cell which should have the least solids.
He knows there is a pump, but:
 Does not know the waste producer's plan to send to the field?
If a single cell is the pump close to where the waste stream comes into the storage?
Important moving away from where the waster stream comes into the lagoon can help minimize solids
 Type of pump commonly the irrigator will say he thinks it is a solids handling pump not knowing that this means the
 pump will deliver big chunks.
This is good for the waste producer but bad for the irrigator.
Position of the inlet to the pump in the lagoon one of the big issues
 Is it a floating inlet
 Important as where the inlet is positioned generally relates to the waste producers expectations as to the solids they plan to pump.
He knows the center pivot, but may not be well aware of how it applies wastewater
 Says he has pressure regulators
 Uses spray nozzles Important to guide the change to the sprinkler package to minimize the problems
 At this stage the consultant, dealer, or manufacturer needs to really dig into what is happening.
There are some questions that must be answered.
The most important questions to get answered are :
 1) What is the sprinkler package and where is it plugging?
a.
If the irrigator has pressure regulators this needs to be evaluated to determine if regulators are really needed or if an alternative such as flow control nozzles would be a solution.
Or if the pump intake is moved would that minimize the amount of solids in the liquid stream so regulators could be used?
b.
If the nozzles are plugging in the first spans of the center pivot consider a wider spacing even if the uniformity may not be optimum.
Remember the uniformity of plugged nozzles is poor!
C.
If the plugging is occurring on the pad consider a different pad configuration that provides less opportunities for trash to 'catch'.
2) What type of pump is being used?
a.
A solids handling pump is going to send large chunks to the center pivot.
Consider the location of the inlet to minimize chunks getting into the pump
 3) Intake to the pump location
 a.
Position so it is not on the bottom or top of the storage in a zone that is as free of trash and solids as possible unless the overall plan is to pump high amounts of solids.
4) What are the waste producer's expectations of what is sent to the field?
a.
Percent of solids
 b.
Size of solids
 e.
There may be a complete mis-match of ideas as to what is going to happen.
On an existing system the costs to fix can be substantial.
f.
If the irrigator and wastewater producing cannot agree the producer will need to find another area to use and amend the nutrient management plan.
When one is starting a new wastewater system it is necessary to integrate  all of the following items to meet the overall system needs.
Hopefully the wastewater producer and the irrigator can work together in a partnering that is mutually beneficial to both.
If these items are not integrated, it could jeopardize one partner or the other or only meet one partner's needs.
Permitting Both partners must agree on a nutrient management plan and crops need to match nutrient loading for the land area.
The farmer may be pushed to change his cropping plan by adding winter forage.
This may work well as long as the livestock operation is willing to buy the forage, but if not, it creates marketing challenges for the farmer.
Design Waste producer may want rapid disposal of large volumes any time during the season while the irrigator wants even volume over the season and no plugging.
Both want no problems.
The design is critical to identify and outline the solutions to try to satisfy both parties.
Construction The construction cycle may interfere with crop production while installing pipelines and mechanical move irrigation equipment.
Operation If the design was balanced to meet both parties' needs, there should not be operational issues.
If however the design is oriented to meet only one, then someone is going to be unhappy.
For a land application project to be successful, all parts of the project need to be integrated together planning, design, collection, storage, pumping and the land application equipment.
Mechanical move irrigation equipment can be beneficial to the reuse of wastewater if it is integrated with the entire project.
Both the wastewater producer and the irrigator need to understand the needs and expectations of the other.
When problems arise within a system, one needs to look at the entire stream from where it is produced to the land application equipment to determine the best course of action.
Often several different parts of the system will need to be reviewed and changes considered to meet both the irrigator and livestock producer's expectations.
Now is the time to get the probes in the ground.
While other tasks may seem more pressing, early installation of sensors is important to ensure proper operation during the later critical growth phases.
Early installation helps to minimize root and leaf damage and makes it easy to get around the field with the pickup or ATV to install the equipment.
Extension Agricultural Engineer The Texas A&M University System
 Surge flow irrigation has the potential to increase furrow irrigation efficiencies to levels usually associated with sprinkler and drip irrigation systems.
This is possible because surge irrigation is more often efficient and can achieve faster water advance down the furrow than conventional furrow irrigation.
In some cases, you can-with the same amount of waterirrigate twice the area at the same time by using an automatic surge valve.
In many situations, surge allows you to apply more precise levels of water.
Instead of applying 4 to 6 inches, as you may with conventional furrow irrigation, you can put out as little as 1 to 2 inches.
For most soil types, surge reduces the volume of water needed during the first few irrigations following tillage.
Its effectiveness on subsequent irrigations has varied.
Surge typically improves efficiencies from 8 to 30 percent.
However, it is difficult to predict whether it will work for a particular field and situation.
Adequate furrow stream  is also necessary to see benefits.
So how does surge work?
In surge, water is applied in a series of on-off cycles or watering periods.
Applying the water in timed cycles:
 increases the rate of water advance down the furrow
 reduces deep percolation losses
 increases the uniformity of the wetting front along the furrow
 produces a more even depth of water penetration into the soil
 Why does alternating on-off cycles of water increase furrow irrigation efficiencies?
The prevailing view is that there are two factors involved: surface sealing and intake rate.
In many soils, once wetted, a surface seal forms as it dries out.
Also during irrigation, the soil intake or infiltration rate decreases as the soil moisture level increases.
Soil roughness is also a factor.
The largest benefits of surge irrigation occur during the first few irrigations following tillage when the soil is still rough.
Air entrapment during the wetting cycle may also contribute to the faster advance times seen with surge.
Surge system components, configuration, and operation
 In a typical surge irrigation setup, a surge valve is used to alternate water between 2 sets of gated or poly pipe in a series of on-off cycles or watering periods.
Figure 1 shows the internal operation of a surge valve to alternate water to the right or left side of the valve.
A typical surge irrigation setup is shown in Figure 2.
Single butterfly type valve
 Figure 1.
Surge flow valve.
Diagram of a split-set gated pipe system used in surge flow irrigation.
Flow is alternated from side to side.
Supply pipeline 
 Figure 2.
Typical surge flow set up as a split-set gated pipe system used for surge irrigation.
Flow is alternated from side to side in on-off "cycles."
 There are two major manufacturers of automatic surge flow valves in the USA.
Automatic surge valves are simple devices that consist of a valve, a programmable controller, a battery, and solar cell recharging panel.
Figure 4 shows the base unit of the surge valve.
Each manufacturer has several different controllers with varying capabilities which sit on top of the base unit.
Surge valves come in several sizes as shown in Table 1.
You should size your surge valve according to the flow that you have available.
The larger valves can be quite heavy.
Table 1.
Size, capacity, and weight for US manufactured surge valves.
Pipe size	Max GPM	Weight
 4"	300	19 lbs
 6"	700	31-37 lbs
 8"	1200	44-46 lbs
 10"	2000	50-54 lbs
 12"	2600	67-90 lbs
 Figure 3.
One of two automatic surge valves manufactured in the US shown in use with plastic gated pipe during start-up.
Figure 4.
Several different controllers with varying capabilities are available which sit on top the surge valve base.
Gated pipe and poly pipe
 Surge is used with gated aluminum, plastic and poly pipe.
With gated pipe, it is easy to balance flow to all furrows by simply adjusting each gate to the correct opening size.
For poly pipe, it is important that the holes be punched precisely to achieve the targeted furrow stream size.
Poly pipe manufacturers have on-line guides and soft-
 Figure 5.
Recommended adjustable plastic gates that can be inserted into polypipe to balance flows in rows to improve the uniformity of furrow irrigation.
Figure 6.
Insertion gate shown with sleeve used to reduce erosion at the head of the furrow.
ware and sell special hole punchers that will allow you to do this.
The Natural Resources Conservation Service's  Phaucet software is an example of a well-supported furrow irrigation help tool that is available on-line.
When using poly pipe you can also use insertion gates which pop into the punch holes.
These can be adjusted like aluminum-gated pipe.
Sleeves are available with connecting insertion gates and are effective at reducing soil erosion at the head of the furrow.
The terms used for surge flow irrigation share many of the ones used in furrow irrigation.
Terminology shared between furrow and surge flow irrigation
 Advance phase	The phase or phases in which
 the dry furrow is wetted.
Out time	The time required for water to
 reach the end of the furrow.
Soaking phase	The phase in which the required
 application depth is infiltrated.
Soaking time	The time it takes for the required
 application depth to infiltrate.
Recession phase	The phase that starts when
 application of water to the fur-
 row is stopped, and ends when
 water disappears from the soil's
 Opportunity time	The total time that water is pres-
 ent at each point in the furrow.
On-time	The time water is applied to one
 side of the surge valve before it is
 switched to the other side
 Off-time	The time water is not applied to one
 side of the surge valve (usually the
 Cycle-time	The time required to complete one
 on/off cycle ("on-time" plus "off-
 Cycle-ratio The ratio between the "on-time" and the "cycle-time" 
 The advance phase of surge irrigation consists of a series of surges or cycles to get the water to the end of the furrow.
Once the advance is complete, the soaking  phase consists of the cycles needed to fill the root zone with the targeted amount of water.
Determining surge cycle times
 1.
The advance phase should be completed in 4 to 6 surges.
2.
The next to the last advance phase should stop just short of the end of the field.
3.
Cycle times should be such that individual surges do not overlap or coalesce.
4.
Furrow stream  should be near the maximum non-erosive value.
Once the water has reached the end of the furrow, the on-time for the soaking phase will normally be shorter than for the advance phase.
As a starting point, set the soaking phase at about 75 percent of the advance on-time.
The goal is to minimize tailwater loss while still allowing sufficient soaking at the lower end of the furrow.
Soaking on-times that are too long create excessive runoff; soak cycles that are not long enough, put too much water on the upper end of the furrow and not enough on the lower end.
Once you achieve the best soaking on-time, continue the surges until you reach the desired application depth.
A soil probe is useful for measuring application depth.
The USDA Natural Resources Conservation Service  uses two basic approaches for managing surge irrigation.
Automatic valves allow you to experiment with both approaches.
You can update the valve's programing based on the time or distance that the advance reaches certain points along the furrow.
The controller can also automatically calculate variable cycle times based on such factors as soil type, length of furrow and slope.
As with continuous furrow irrigation, NRCS recommends using the maximum non-erosive furrow stream size with the following two approaches:
 I.
The variable-distance, constant-time method.
You select an on-time which is usually the amount of time it takes for the first surge to advance a quarter of the furrow length.
This on-time is repeated until the advance is complete.
When the advance reaches the end of the furrow, NRCS recommends reducing the on-time for the post-advance surges SO the wetted advance reaches 75 to 80 percent of the furrow length by cutoff.
This allows the irrigation water to roll-on to the end of the furrow and minimizes tailwater losses.
II.
The constant-distance, variable-time method.
The on-time during the advance phase is set so that the advance progresses a set distance during every surge.
The post-advance phase is dealt with as in I above.
Cycle times in surge irrigation will vary depending upon soil texture, slope, and furrow length.
Surge works better on leveled fields and furrows with only small slopes.
On soils with low intake rates such as heavy clays or compacted soils, surge is unlikely to reduce advance times below those of continuous flow.
It may, however, provide a more uniform application of water.
Surge is typically the most beneficial during the first few irrigations following tillage.
Later in the season when the furrows are smooth, there tends to be less difference between surge and continuous flow.
As in conventional furrow irrigation, the largest stream  that does not cause serious erosion will give the best results.
You need a minimum of 15 to 25 gpm per furrow to see benefits from surge irrigation.
For surge irrigation to succeed, you also need a constant flow rate.
If you take water from irrigation canals, be aware that fluctuating water levels in the canal will, in turn cause the flow rate to fluctuate as well and give you poor results.
In irrigation districts, the term "head" is commonly used to refer to the flow of water at the farm turn-out.
While in general, one head of water is equal to 450 gpm, this is not a precise number and is often just estimated.
Your flow rate should be measured directly.
Some irrigation districts and NRCS offices have portable propeller test meters  and will measure the flow rate for you.
Figure 7.
Potable propeller test meter equipped with a pressure gage, quick-connects and handles for insertion into existing water supply pipelines for measuring flow rates.
These portable test meters are available with handles and a pressure gauge, and come equipped with "quick-connects" allowing for simple insertion into exiting alfalfa valves and water supply pipelines.
Straightening veins improved accuracy when measuring flows in pipelines with shorter straight sections.
Straight sections of pipelines are needed equal to at
 Figure 8.
Saddle flow meter which can be installed into an existing pipeline by cutting a hole in the top of the pipe.
Meter shown has an optional digital output for use with irrigation control and monitoring systems.
least 10 pipe diameters downstream and 5 pipe diameters upstream of the meter for accurate flow measurement.
It is usually best to use a test meter that is a smaller diameter than the existing pipeline to ensure the test meter flows full.
If you want surge to succeed, don't guess your flow rate-measure it.
Saddle meters are available and recommended for installation in existing pipelines for continuous flow measurement.
Will surge work for you?
A simple test is to run a few furrows of continuous flow alongside furrows in which flow is interrupted and reapplied.
If the rate of advance is greater with the interrupted streams, surge would work on your soils.
Keep in mind that the soil in wheel rows is typically compacted which slows the infiltration rate and speeds the advance time.
Do not use these rows for testing.
A more effective test would be to irrigate one block of land using surge and another block with continuous flow, then measure the depth of water penetration on both with a soil probe or soil moisture sensors.
If the depth of water penetration at the lower and upper sections of the furrows is more uniform with surge, then surge would work for you.
Surge flow is not magic, and it is difficult to predict whether it will work for a particular situation.
However, where it does work, there are significant benefits.
Texas A&M AgriLife Extension Service
 Educational programs of the Texas A&M AgriLife Extension Service are open to all people without regard to race, color, sex, religion, national origin, age, disability, genetic information, or veteran status.
No-Till Management Case Study: Stoneyvale Farm
 Farmer: Bob and Travis Fogler
 Farm Type: Dairy & Forage
 Size: 1000 milking cows + 1350 acres of corn, alfalfa, and grasses
 Soil Type: Mixture of Bangor, Thorndike, and Dixmont
 Crops: Corn, alfalfa, potatoes
 Cover Crops: Mixture of annual rye, winter rye, tillage radish, and crimson clover seeded after corn planting.
Winter rye seeded post-harvest.
Weed Management: Mixture of cover cropping and chemical 
 No-till since: Scaling up since 2008
 Current equipment setup: Yetter row-cleaners, opening disks.
Removed no-till coulters.
Advantages to using no-till management:
 Increased soil moisture and improved soil drainage
 Improvement in soil health and tilth
 Speed of getting corn planted, which allows for harvesting first crop of haylage when at peak quality
 Saving money on equipment, time, and fuel: estimated savings of $50 per acre of corn planted
 Challenges to using no-till management:
 Planting windows can be narrow in wet conditions  on dewy mornings, row cleaners can cause mud to stick to plants and implements, and it is best to wait until the ground dries out later in the day to plant.
Conversely, no-till fields themselves are markedly easier to work on when wet than conventional fields.
Advice to growers new to no-till:
 Be prepared to change your management style and planting schedule.
Pay close attention to your planting implement, and understand that you may have to make frequent adjustments as you plant.
Make sure your double disk openers are sharp and not worn, and your planter well maintained.
Begin with a fall killed sod and always use cover crops.
Start slowly!
Try the system out on a small part of your farm, and expand gradually if and when you get positive results.
The Foglers and No-Till
 Bob and Travis Foglers transition to no-till production started by accident.
The Foglers, whose 1000 dairy cows are fed by forage crops grown on site, planted no-till corn for the first time into a field of fall-killed sod in 2008.
Hoping simply to break up the sod in time for a fall planting, they planned to harrow in August what they were sure would be a failed corn crop.
They were surprised and delighted when an outstanding crop of corn emerged, and were encouraged over time to transition nearly all of their 750+ acres of forage crop land to no-till management.
Rather than jump in all at once, the Foglers first experimented with no-till on their poorer soils: rocky sods that had not been worked in decades, and potato fields where the soil health was degraded from decades of production..
Their soil has responded well to the shift, becoming more resistant to erosion and less likely to dry out in the hottest part of the summer.
Best of all, theyve experienced increased yields while simultaneously saving money on tillage parts, time, and fuel.
At this point, they are firm believers in the no-till system.
Cover Crops: Boost Yields and Control Weeds to Aid The Transition
 The Foglers believe cover crops to be vital to the success of their no-till system, helping to control weeds, improve soil health, and build soil structure.
Some growers experience a decrease in yield in their first several years using a no-till management system, especially with crops like corn that require significant nitrogen.
To make up for this potential yield loss, many no-till growers incorporate cover crops into their planting rotation.
Currently, most prefer to plant winter rye after corn harvest, which grows well in the fall and is green and actively growing in the spring.
The cover crop also creates a thick mulch on the soil surface when terminated.
Bob and Travis have shifted to a more species-rich cover crop mixture, including annual and winter rye, triticale, tillage radish, turnip, and crimson clover.
Using lower grade  seed, accompanied by a decrease in seeding rate, will make it easier to plant, improving the efficiency of their cover cropping system.
While they still use chemical herbicides to manage weeds, especially in potato fields, they hope to see a tremendous decrease in chemical usage as their new management system takes hold.
Developing a Suitable Planter Setup
 Its taken the Foglers a number of years to refine their planting implement setup to fit their needs as no-till growers.
Over time, they removed their no-till coulters, which they found were making it difficult to reach uniform seed depth.
By reducing the number of opening disks on the planter, less pressure is required to get the double disk openers to cut into the surface residue to prepare for planting.
They keep those opening disks very sharp, and replace them about once every two years, a process that costs about $1600.
This expense is more than made up for, they say, by the amount they save on conventional tillage parts.
Travis notes that a bit more attention must be paid to the planter while in action in order to make adjustments that might ease and improve the planting process.
[On] tilled land, you pretty much get on and start plantingand never get off and look all day.
With no-till, he says, the planter requires a little more babysitting.
In addition to the opening disks, a pair of row cleaners have likewise helped ensure successful planting.
Bob and Travis have recently invested as well in a tractor with GPS and auto-steer to aid in precise mechanical work.
A Big Reward: Soil Health
 While it could take years for significant yield gains under no-till to become truly apparent, the Foglers have already delighted in what is perhaps an even greater reward: soil that is visibly healthy and teeming with life.
I can find earthworms [in] every spade-full nowits an incredible change in just three years, says Bob.
The lack of continual soil disturbance encourages increased biological activity.
For the Foglers, the result has been soil that drains and stores water effectively, nourishes healthy crops, and is easy to work with from planting to harvest.
In addition, the partner potato farm has also noticed increased yields and less need for irrigation during the potato rotation.
Thoughts for New No-Till Growers
 When asked how he addresses no-till management with new or interested growers, Bob Fogler is reluctant to push anyone into making a decision too soon.
I tell them to start slow, because I think there is a learning curve to it.
Changing management styles, the timing of planting, and establishing the correct equipment setup takes time.
He makes sure to tell them, though, that our experiences have been outstanding.
Subsurface Drip Irrigation  for Enhanced Water Distribution: SDI-Seepage Hybrid System
 Lincoln Zotarelli, Libby Rens, Charles Barrett, Daniel J.
Cantliffe, Michael D.
Dukes, Mark Clark, and Steven Lands2
 In Florida, in agricultural production areas with a high water table due to a shallow impermeable layer, vegetable crops have been intensively cultivated with irrigation by adjusting the water table level.
This type of irrigation system is commonly called seepage irrigation or subirrigation  and relies on groundwater as the main source of irrigation water.
However, the system can benefit from rainfall.
The seepage system is characterized by low implementation, maintenance, and operation costs.
In terms of water use efficiency, seepage systems are one of the most inefficient methods of irrigation because they require large volumes of water to raise the water table up to the crop root zone.
Proper irrigation is achieved by maintaining the water table just below the crop root zone and allowing the capillarity of the soil to bring the water up into the range of the roots.
A major disadvantage of these systems is the inability to wet the soil surface.
Without rainfall, soil emergence of shallow seed crops can be greatly impeded.
A traditional seepage system in Northeast Florida uses PVC pipes to transport water from pumps to irrigation furrows.
These irrigation furrows are spaced 60 ft apart and range in length from 250 to 2,000 ft or more.
The furrows are also used for rainfall runoff drainage.
The furrows empty into an outlet ditch equipped
 with water retention structures  that are used to retain and control the water table at the appropriate water level.
Figure 1.
Traditional seepage irrigation system used to manage the water table for a potato crop in Hastings, Florida.
Credits: L.
Zotarelli
 The challenge of a seepage irrigation system is to maintain the water table just below the root zone to provide the crop with enough soil moisture to meet the evapotranspiration requirements, while at the same time avoiding root zone saturation, which may negatively impact the crop.
Field evaluations of soil moisture content in the crop root zone
 Figure 2.
Left: Seepage irrigation systems rely on a drainage system with ditches around the cultivated area.
Right: Water retention structures are used to back up the water to raise the water table level.
Credits: L.
Zotarelli
 Soil moisture at surface in seepage irrigation systems
 Figure 3.
Map of volumetric soil moisture content  at potato root zone 0-8 in.
deep in a potato hill.
Sampled with a time domain reflectometry  probe in a seepage irrigation system during potato season in spring of 2012 in Hastings, Florida.
Credits: Libby Rens
 The variability of soil moisture in the root zone can be explained by the dynamics of the water table during the processes of irrigation and drainage through the furrows.
During these processes, the water table does not rise and fall in a level line across the field; rather, it responds as shown in Figure 4.
The middle of the field is slower to drain and irrigate, and water table levels rise in these areas first during rain events compared to areas closer to the irrigation furrows.
The different water table levels across the field
 Figure 4.
Representation of the water table depth under seepage irrigation.
Top: water table during irrigation.
Bottom: water table during drainage process.
Credits: L.
Zotarelli
 and the oscillation of the water table during the irrigation/ drainage processes directly affect the soil moisture in the root zone.
It is important to understand that the behavior of the water table across the field during irrigation and drainage directly affects the soil moisture content in the crop root zone.
This also has implications with regard to crop yield because nutrient availability, photosynthesis, and plant growth and development are dependent on proper soil moisture.
The depth of the impermeable soil layer also plays an important role in the efficiency of seepage irrigation and soil moisture distribution.
For example, areas with very shallow impermeable soil layer depth  would make the seepage irrigation very difficult because it would require closer  in-furrow spacing, which can be impractical for a commercial operation.
To improve water table management, alternative irrigation designs can contribute to the improvement of water distribution across a field-especially in areas with shallow impermeable soil layers or in small or irregular fields-in which the conventional seepage irrigation practice is almost impossible.
The subsurface drip irrigation system , which is the application of water below the soil surface by microirrigation , can be considered as an alternative to improve the water distribution and time required to raise the water table for seepage irrigation.
However, because the principle of the irrigation system still is subirrigation/seepage , this system should still be called seepage irrigation or subirrigation.
Description of the First SDI Test in Hastings
 In the 1990s, UF/IFAS Research proposed the use of SDI tape with emitters to apply water directly into the plant beds in sufficiently large quantities to establish and maintain shallow water tables.
A 3-year research trial comparing the traditional seepage irrigation management with SDI showed no differences in potato yield; however, there was a consistent 36% reduction in the volume of water applied using drip compared to traditional seepage.
In the proposed system, all irrigation water was applied through the buried drip system  and the furrows were maintained to drain excess rainfall.
Figure 5 shows the expected water table level when the irrigation water is applied through the drip.
With the drip system, it is expected that the water table would be more evenly distributed across the bed compared to the water
 table with irrigation water being applied through the furrows.
Figure 5.
Expected water table level with subsurface drip irrigation for water table management.
Credits: L.
Zotarelli
 The system tested by Smajstrla et al.
consisted of microirrigation tubing with 1 gph emitters spaced every 4 ft.
Figure 6 shows an overview of the system tested in Hastings, Florida.
Three drip tapes per bed  were buried to a depth of 20 in..
The drip tapes were connected to a polyethylene manifold pipeline at each inlet end.
The water was supplied from a continuously pressurized main pipeline to each manifold through an automatic solenoid valve, pressure regulator, flow meter, and vacuum breaker.
The downstream end consisted of an automatic flush valve at the end of each drip tape.
The operating pressure was defined according to the drip tape specifications.
For this particular example, a 30 psi pressure regulator was used.
Figure 6.
Overview of the subsurface drip irrigation systems for water table control tested by Smajstrla et al..
Credits: L.
Zotarelli
 Figure 7.
Installation of subsurface drip tape at a depth of 24 in.
below the soil surface in a potato field, Hastings, Florida.
Upper figures: subsurface drip tape positioning after the installation.
Lower left: detail of the manifold.
Lower right: chisel plow adapted for subsurface drip installation.
Credits: L.
Zotarelli
 The system was equipped with an injection system for chemical treatment to clean the drip system.
The design also included a filtration system with a Y-strainer, media filters, and screen filters.
Another important point to be considered when designing, planning, and budgeting the SDI system is energy consumption.
Because SDI operates on higher pressure, energy consumption is 70% greater than seepage, despite smaller water applications with drip irrigation.
The subsurface drip emitters were operated at 25 psi, which required a manifold pressure of 30 psi.
The seepage system required a manifold pressure of only 5 psi.
Points to Consider before Adopting SDI for Seepage Irrigation Management
 Little information is available about the design, installation, and operation of SDI for water table control in Florida.
However, there are several similarities in terms of maintenance and operation between SDI and conventional drip irrigation.
The similarities and challenges are discussed in this section.
1.
Design and Installation
 The design of an SDI system for water table management is very similar to that of a conventional drip irrigation system, except that the drip irrigation tapes should have high flow and are generally buried 6 in.
below the soil.
Even though the SDI industry has grown significantly in the United States in the last decade, little research has been conducted and few professionals have provided design, installation, and guidelines for operating SDI for water table management.
In several instances, the grower is responsible for system design and installation.
Although few references have been published about the best depth of placement of the drip tape for subsurface irrigation, installing the drip tape above the impermeable soil layer is important.
Where possible, positioning the tape below the level of cultivation helps prolong the longevity of the system.
Therefore, a field survey is required to determine the average depth of the impermeable layer before determining the drip installation depth.
2.
Drip Tape Specification and Number of Drip Tapes Required Per Area
 The number of drip tape lines required for SDI to manage the water table is still not defined.
Only one reference exists for Florida  in which the authors successfully tested three drip lines installed per bed with 16 potato rows.
In this system, the operating pressure was set at the inlet of each bed at 30 psi, which resulted in an application equivalent to 0.45 in.
per day.
The drainage furrows were maintained , but more research is required to evaluate the possibility of wider furrow spacing, which will result in greater available land for planting.
For shallow impermeable soil layers, short distances between furrows are not recommended.
Several factors should be considered for drip tape selection, including wall thickness, emitter spacing and flow, and operational pressure.
Drip tape wall thickness can range from 4 to 15 mil.
Thinner drip walls  are recommended for surface drip systems for short-season crops; intermediate drip walls  are recommended for general use and average soil condition; and 10-15 mil wall thickness is designed to be more resistant to adverse conditions, such as rocky soils, and for more than a season.
For subsurface drip systems, thicker walls are recommended  because they are less subject to damage, and it is expected that the system will last longer than traditional surface drip tape.
For crop irrigation, emitter spacing generally changes according to the plant spacing, soil type, and desired flow
 rate.
A wide range of emitter spacing, ranging from 4-6 in.
to 20-24 in.
are regularly available.
For SDI to manage the water table, wider emitter spacing and high flow rate are recommended.
In general, flow rates above 25 gph/100 ft are recommended.
4.
Filtration System and Water Treatment
 For any drip irrigation system, filtration of the irrigation water is essential for proper system operation and longevity.
This is critical, especially for SDI, because there are no opportunities to clean the emitters manually.
The filtration system prevents the emitter from plugging up with foreign material.
In the trial conducted by Smajstrla et al.
to address the risk of emitter plugging by preventing chemical precipitates and microbial growth, irrigation water was treated with commercially available irrigation line chemical treatment , which was continuously injected at a rate of 4 ppm.
However, after the growing season, the system was turned off for approximately 3 months, and the emitter flow rates dropped by 21% the following season.
To avoid a drop in flow rate, the system needs to be periodically run and chemicals, such as phosphoric or sulphuric acid or chlorine, need to be injected to avoid plugging and further loss of the drip tape.
5.
Irrigation Management and Monitoring
Over the past year or so, a team of extension educators and specialists has been working to update the curriculum for chemigation training.
A new manual has been implemented and new videos are currently being developed to enhance the training program.
Crop Production in Western Kansas as Related to Irrigation Capacity
 Daniel M.
O'Brien, Area Director and Agricultural Economist, PhD
 Contribution No.
06-319-A, Kansas Agricultural Experiment Station
 Written for presentation at the 2006 ASABE Annual International Meeting Sponsored by ASABE Oregon Convention Center Portland, Oregon 9 12 July 2006
 Abstract.
Crop production and economics of irrigated corn, grain sorghum, soybean and sunflower were simulated for 34 years of weather data in Northwest Kansas at irrigation system capacities ranging from dryland production up to 8.5 mm/day.
The simulated net irrigation requirements for corn, grain sorghum, soybean and sunflower for the 34-year period were 375, 272, 367, and 311 mm, respectively.
Assuming a 95% application efficiency , the average long term crop yield is approximately 12.9, 8.2, 4.4 and 3.2 Mg/ha for corn, grain sorghum, soybean and sunflower, respectively.
Although corn is currently the predominant irrigated crop in western Kansas, current projections indicate soybean is a more profitable alternative.
Soybean net irrigation requirements are only about 2% lower than corn, so a shift to soybean will not result in significant water conservation.
In arid regions, it has been a design philosophy that irrigation system capacity should be sufficient to meet the peak evapotranspiration needs of the crop to be grown.
This philosophy has been modified for areas having deep silt loam soils in the semi-arid US Central Great Plains to allow peak evapotranspiration needs to be met by a combination of irrigation, precipitation and stored soil water reserves.
The major irrigated summer crops in the region are corn, grain sorghum, soybean and sunflower.
Corn is very responsive to irrigation, both positively when sufficient and negatively when insufficient.
The other crops are less responsive to irrigation and are sometimes grown on more marginal capacity irrigation systems.
This paper will discuss the simulated irrigation requirements rates and the effect of irrigation system capacity on summer crop production and net returns.
Although the results presented here are based on simulated irrigation schedules for 34 years of weather data from Colby, Kansas  for deep silt loam soils, the concepts have broader application to other areas in showing the importance of irrigation capacity for summer crop production.
Weather data from 1972 through 2005 for Colby, Kansas  was used to calculate reference evapotranspiration, ETr, using a modified Penman equation.
The reference evapotranspiration was further modified with empirical crop coefficients for the region  to give the crop evapotranspiration, ETc.
Figure 1.
Alfalfa-based crop coefficients used in the simulated irrigation schedules and crop yield modeling.
Irrigation schedules  for the major summer crops  were simulated with a daily time-step for the same 34 year period using precipitation and calculated ETc.
Typical emergence, physiological maturity, and irrigation season dates were used in the simulation.
The 1.5 m soil profile was assumed to be at 85% of field capacity at corn emergence  in each year.
Effective rainfall was allowed to be 88% of each event up to a maximum effective rainfall of 57.2 mm/event.
The application efficiency, Ea, was initially set to 100% to calculate the simulated full net irrigation requirement, SNIR.
Center pivot sprinkler irrigation events were scheduled if the calculated irrigation deficit exceeded 25.4 mm.
Table 1.
Parameters and factors used in the simulation of irrigation schedules and crop yield modeling.
Parameter	Corn	Grain Sorghum	Soybean	Sunflower
 Emergence date	May 15	June 1	May 25	June 15
 Physiological maturity date	September 11	September 13	September 16 September 11
 Crop season, d	120	105	115	100
 End of irrigation season	September 2	September 4	September 7	September 2
 Irrigation season, d	110	95	105	90
 Factors for crop yield model
 Vegetative period, d	66	54	38	53
 Susceptibility factor 	36.0	44.0	6.9	43.0
 Flowering period, d	9	19	33	17
 Susceptibility factor 	33.0	39.0	45.9	33.0
 Seed formation period, d	27	22	44	23
 Susceptibility factor 	25.0	14.0	47.2	23.0
 Ripening period, d	18	10	-	7
 Susceptibility factor 	6.0	3.0	-	1.0
 Slope on yield model, Mg/ha-mm	0.0416	0.0301	0.0121	0.0096
 Intercept on yield model, Mg/ha	-11.55	-5.32	-2.40	-1.33
 The irrigation scheduling model was coupled with a crop yield model to calculate crop grain yields as affected by irrigation capacity.
In this case, the irrigation level is no longer full irrigation but was allowed to have various capacities.
Irrigation was scheduled according to climatic needs, but was limited to these capacities.
Crop yields for the various irrigation capacities were simulated for the same 33 year period  using the irrigation schedules and a yield production function developed by Stone et al..
In its simplest form, the model results in the following equation,
 Yield =  + Yldintercept
 with yield expressed in Mg/ha, yield intercept and slope as shown in Table 1 and ETc in mm.
As an example, the equation for corn would be,
 Yield =  -11.55 Mg/ha
 Further application of the yield model reflects crop susceptibility weighting factors for specific growth periods.
These additional weighting factors were incorporated into the
 simulation to better estimate the effects of irrigation timing for the various system capacities.
The weighting factors and their application to the model are discussed in detail by Stone et al..
Soybean weighting factors were developed by use of yield response factors of Doorenbos and Kassam.
The economic component of this analysis estimates economic returns from crop production over annual variable cash production costs.
The 2006 cost estimates used here  include variable cash crop production costs for seed, herbicides, insecticides, fertilizer, crop consulting and custom harvest.
Also included are annual irrigation fuel, oil, repair and irrigation labor costs, as well a custom rates-based estimate of machinery expenses.
Crop price, farm program revenue, interest cost, and other crop production enterprise assumptions in this study are consistent with 2006 Farm Management Guide Crop Production Budgets for irrigated and dryland crops developed by K-State Research and Extension.
In this analysis, cost items that do not vary across the alternative crop enterprises were not considered.
These include land charges, depreciation and interest on irrigation equipment, a $ 25/ha miscellaneous crop expense charge, and non-machinery labor charges.
Crop insurance was not included in these budgets.
Table 2.
Economic Parameters Varying by Crop
 Corn	Grain Sorghum	Soybean	Sunflower
 Crop Price, $/kg	$0.1012	$0.0894	$0.2065	$0.2575
 Herbicide.
$/ha	$75.48	$66.98	$36.74	$46.60
 Insecticide, $/ha	$95.63	$0.00	$0.00	$35.40
 Consulting, $/ha	$16.06	$15.44	$15.44	$16.06
 Custom Rates Machinery, $/ha	$74.67	$66.53	$62.56	$74.15
 Yield Threshold for Extra Harvest
 Charge, Mg/ha	4.77	2.26	1.75	NA
 Extra Charge for Yield, $/Mg	$6.06	$5.71	$5.33	NA
 Crop Hauling Cost, $/Mg	$5.00	$5.59	$5.10	$4.96
 Interest Rate Used On 1/2 Production Costs, All Crop and Irrigation Scenarios, 8%
 Table 3.
Economic Parameters Varying by Crop and Irrigation Capacity
 8.5	6.4	5.1	4.2	3.2	2.5	Dryland
 Corn Seeding Rate, 1000
 p/ha	84.0	79.1	74.1	69.2	64.2	59.3	44.5
 Corn Seed Cost, $/ha	$125.18	$117.82	$110.45	$103.09	$95.73	$88.36	$66.27
 kg/ha	286	280	263	252	224	202	112
 Corn N Fertilizer Cost, $/ha	$182.73	$179.15	$168.40	$161.23	$143.32	$128.99	$71.66
 kg/ha	95	90	84	78	73	67	34
 Corn P Fertilizer Cost, $/ha	$52.51	$49.42	$46.33	$43.24	$40.15	$37.07	$18.53
 Rate, kg/ha	7.3	7.3	7.3	7.3	7.3	6.7	3.4
 Grain Sorghum Seed Cost,
 $/ha	$42.88	$42.88	$42.88	$42.88	$42.88	$39.59	$19.79
 Grain Sorghum N-Rate at
 Grain Sorghum N Fertilizer
 Cost, $/ha	$75.24	$75.24	$75.24	$71.66	$71.66	$64.49	$43.00
 Grain Sorghum P-rate at
 Grain Sorghum P Fertilizer
 Cost, $/ha	$33.98	$33.98	$33.98	$33.98	$30.89	$27.80	$18.53
 1000 p/ha	371	371	371	358	346	334	297
 Soybean Seed Cost, $/ha	$77.84	$77.84	$77.84	$75.24	$72.65	$70.05	$62.27
 Soybean P Fertilizer Cost,
 $/ha	$33.98	$33.98	$33.98	$33.98	$30.89	$27.80	$18.53
 1000 p/ha	43.5	43.5	43.5	43.5	43.5	43.5	39.5
 Sunflower Seed Cost, $/ha	$58.28	$58.28	$58.28	$58.28	$58.28	$58.28	$52.98
 Sunflower N Fertilizer Cost,
 $/ha	$100.32	$100.32	$96.74	$93.16	$85.99	$82.41	$57.33
 Sunflower P Fertilizer Cost,
 $/ha	$30.89	$30.89	$29.03	$27.80	$25.95	$24.71	$18.53
 Summer Crop Evapotranspiration Rates
 Crop evapotranspiration  rates varied throughout the summer reaching peak values during the months of July and August in the Central Great Plains.
Long term  July and August corn ET rates at the KSU Northwest Research Extension Center, Colby, Kansas were calculated to be 6.8 and 6.3 mm/d, respectively.
However, it is not uncommon to observe shortterm peak corn ET values in the 9 to 10 mm/d range.
Occasionally, calculated peak corn ET rates may approach 13 mm/d in the Central Great Plains, but it remains a point of discussion whether the corn actually uses that much water on those extreme days or whether corn growth processes essentially shut down further water losses.
Individual years are different and daily rates vary widely from the long term average corn ET rates.
Irrigation systems must supplement precipitation and soil water reserves to match average corn ET rates and also provide some level of design flexibility to attempt covering year-to-year variations in crop ET rates and precipitation.
The mean simulated net irrigation requirement  for corn, grain sorghum, soybean and sunflower for the 34-year period was 375, 272, 367, and 311 mm, respectively.
The maximum SNIR for the crops was in 1976, ranging from 432 for grain sorghum to 533 mm for corn and soybean.
The minimum SNIR occurred in 1992, ranging from 76 mm for grain sorghum to 127 mm for corn and soybean.
This emphasizes the tremendous year-to-year variance in irrigation requirements.
Good irrigation management will require the irrigator to use effective and consistent irrigation scheduling.
July and August required the highest amounts of irrigation for all four summer crops with the two months averaging 86% of the total seasonal needs.
However, it might be more appropriate to look at the SNIR and seasonal distribution in relation to probability, similar to the probability tables from the USDA-NRCS irrigation guidebooks.
In this sense, SNIR values will not be exceeded in 80 and 50% of the years, respectively.
The minimum gross irrigation capacities  generated using the SNIR values are 6.7, 4.8, 6.1, and 5.4 mm/d  for corn, grain sorghum, soybean and sunflower, respectively, using center pivot sprinklers operating at 85% Ea.
It should be noted that this simulation procedure shifts nearly all of the soil water depletion to the end of the growing season after the irrigation season has ended and that it would not allow for the total capture of major rainfall amounts  during the irrigation season.
Thus, this procedure is markedly different from the procedure used in the USDA-NRCS-Kansas guidelines.
However, the additional inseason irrigation emphasis does follow the general philosophy expressed by Stone et al.
, that concluded inseason irrigation is more efficient than offseason irrigation in corn production.
It also follows the philosophy expressed by Lamm et al.
, that irrigation scheduling with the purpose of planned seasonal soil water depletion is not justified from a water conservation standpoint, because of yield reductions occurring when soil water was significantly depleted.
Nevertheless, it can be a legitimate point of discussion that the procedure used in these simulations would overestimate full net irrigation requirements because of not allowing large rainfall events to be potentially stored in the soil profile.
In simulations where the irrigation capacity is restricted to levels significantly less than full irrigation, any problem in irrigating at a 25-mm deficit becomes moot, since the deficit often increases well above 25 mm as the season progresses.
Table 4.
Simulated net irrigation requirements, mm, for four major irrigated summer crops for Colby, Kansas, 1972-2005.
Year	Corn	Grain Sorghum	Soybean	Sunflower
 1972	229	152	203	178
 1973	381	279	381	305
 1974	432	330	432	356
 1975	330	254	356	305
 1976	533	432	533	457
 1977	254	178	254	203
 1978	483	356	483	432
 1979	203	127	203	203
 1980	483	356	483	381
 1981	381	279	356	279
 1982	279	229	254	254
 1983	533	406	533	483
 1984	483	381	483	432
 1985	406	254	356	254
 1986	432	330	406	330
 1987	406	305	406	356
 1988	483	356	483	406
 1989	356	254	356	279
 1990	432	330	406	356
 1991	406	305	406	356
 1992	127	76	127	102
 1993	203	127	203	127
 1994	406	279	381	356
 1995	406	305	406	381
 1996	178	102	178	102
 1997	330	203	305	229
 1998	305	178	279	229
 1999	254	178	279	229
 2000	508	356	483	381
 2001	508	381	483	406
 2002	508	356	483	381
 2003	457	330	457	406
 2004	330	229	330	330
 2005	381	279	381	356
 Maximum	533	432	533	483
 Minimum	127	76	127	102
 Mean	375	272	367	311
 St.
Dev.
110	92	109	100
 Table 5.
Average  monthly distribution, %, of simulated net irrigation requirements for four major irrigated crops at Colby, Kansas.
Crop	June	July	August	September
 Corn	13.7	42.6	41.9	1.8
 Grain Sorghum	6.0	38.9	50.5	4.6
 Soybean	10.0	43.2	40.5	6.4
 Sunflower	2.3	25.5	53.2	19.1
 Table 6.
Simulated net irrigation requirements  of 4 summer crops not exceeded in 80 and 50% of the 34 years 1972-2005, associated July through August distributions of SNIR, and minimum irrigation capacities to meet July through August irrigation needs, Colby, Kansas.
Corn	G.
Sorghum	Soybean	Sunflower
 Criteria	SNIR	August	July-	SNIR	August	July-	SNIR	August	July-	SNIR	August	July-
 SNIR value not exceeded	483	93.8%	356	100.0%	483	88.9%	381	84.2%
 in 80% of the years	mm	452 mm	mm	356 mm	mm	429 mm	mm	342 mm
 requirement	7.3 mm/d	5.7 mm/d	6.9 mm/d	5.5 mm/d
 Minimum gross capacity at
 85% application efficiency	8.6 mm/d	6.7 mm/d	8.1 mm/d	6.5 mm/d
 Minimum gross capacity at
 95% application efficiency	7.7 mm/d	6.0 mm/d	7.3 mm/d	5.8 mm/d
 SNIR value not exceeded	406	87.5%	279	90.9%	381	84.2%	356	80.0%
 in 50% of the years	mm	355 mm	mm	254 mm	mm	321 mm	mm	285 mm
 requirement	5.7 mm/d	4.1 mm/d	5.2 mm/d	4.6 mm/d
 Minimum gross capacity at
 85% application efficiency	6.7 mm/d	4.8 mm/d	6.1 mm/d	5.4 mm/d
 Minimum gross capacity at
 95% application efficiency	6.0 mm/d	4.3 mm/d	5.4 mm/d	4.8 mm/d
 Simulation of Crop Yields as Affected by Irrigation Capacity
 Although crop grain and oilseed yields are generally linearly related with ETc from the point of the yield threshold up to the point of maximum yield, the relationship of crop yield to irrigation capacity is a polynomial.
This difference is because ETc and precipitation vary between years and sometimes not all the given irrigation capacity is required to generate the crop yield.
In essence, the asymptote of maximum yield in combination with varying ETc and precipitation cause the curvilinear relationship.
When the results are simulated over a number of years the
 curve becomes quite smooth.
Using the yield model, the 34 years of irrigation schedules and assuming a 95% application efficiency , the average maximum yield is approximately 12.9, 8.2, 4.4 and 3.2 Mg/ha for corn, grain sorghum, soybean and sunflower, respectively.
Estimates of crop yields as affected by irrigation capacity at a 95% application efficiency can be calculated from the polynomial equations in Table 7.
Corn has a much steeper slope than the other 4 crops up to about the 6.5 mm/d irrigation capacity.
Figure 2.
Simulated summer crop yields in relation to irrigation system capacity for the 34 years, 1972 to 2005, Colby, Kansas.
Table 7.
Relationship of crop yield, Mg/ha, to irrigation capacity for four summer crops at Colby, Kansas for 34 years  of simulation at a 95% application efficiency.
Crop	irrigation capacity  in mm/d	Crop yield relationship  to	R2	Standard	Error
 Corn	Y = 4.85 + 1.9507IC-0.0915 IC2 0.0031 IC3	1.000	0.027
 Grain Sorghum Y = 4.76 + 1.1730 IC-0.1232 IC2 + 0.0038 IC3	0.999	0.041
 Soybean	Y = 1.62 + 0.6173 0.0137 IC2 0.0025 IC3	0.999	0.024
 Sunflower	Y = 1.75 + 0.3973 IC 0.0291 IC2 + 0.0002 IC3	1.000	0.010
 Simulation of Economic Net Returns as Affected by Irrigation Capacity
 Similarly, the net returns for the four summer crops can be estimated for the different irrigation system capacities.
Although corn is currently the predominant irrigated crop in western Kansas, current projections indicate soybean is a more profitable alternative.
Production costs which are typically tied to energy costs  are much greater for corn than soybean, so during these times of rapidly increasing energy costs, corn is less competitive.
Soybean net irrigation requirements are only about 2% lower than corn , so a shift to soybean will not result in significant water conservation.
Figure 3.
Simulated net returns above direct cash costs for four summer crop yields in relation to irrigation system capacity for the 34 years, 1972 to 2005, Colby, Kansas.
Sunflower and grain sorghum are better economic alternatives than corn under dryland and extremely deficit irrigation, but with current yield projections and prices, they are noncompetitive at the higher irrigation capacities.
They do offer the opportunity for stable production at a wider range of irrigation capacity.
This analysis shows that dryland grain sorghum is more profitable than any level of irrigated grain sorghum.
This is reinforced by the fact that irrigated grain sorghum is also not chosen by producers in the area.
This may be related to the fact that higher elevations and the resulting cool nights in the region limit higher grain yields from occurring.
Estimates of the economic net returns above direct cash costs as affected by irrigation capacity at a 95% application efficiency can be calculated from the polynomial equations in Table 8.
Table 8.
Relationship of net returns above direct costs, $/ha, to irrigation capacity for four summer crops at Colby, Kansas for 34 years  of simulation at a 95% application efficiency.
Crop	Crop net return relationship  to	irrigation capacity in mm/d	R2	Standard	Error
 Corn	NR = 7.58 + 62.614 IC 3.0145 IC2 0.1552 IC3	0.999	3.03
 Grain Sorghum NR = 136.46 2.713 IC + 0.0112 IC2 0.0036	0.726	4.43
 Soybean	NR = 122.77 + 46.32 IC + 0.1101 IC2 0.3117	0.996	4.58
 Sunflower	NR = 109.61 + 22.112 IC 2.3911 IC2 + 0.0463 IC2 3	1.000	0.010
 Crop Yield and Net Return Penalties for Insufficient Irrigation Capacity
 The crop yield and net return penalties for insufficient irrigation capacity at a 95% Ea can be calculated for various irrigation capacities by using the yield relationships in Table 5 and 6 and comparing these values to the maximum yield and net returns.
Table 9.
Penalty to crop yields for center pivot irrigated crop production at 95% application efficiency when irrigation capacity is below 8.5 mm/d.
Negative net return penalties indicate a more economically favorable capacity than 8.5 mm/d.
Results are from simulations of irrigation scheduling and yield for the 34 years, 1972 to 2005, Colby, Kansas.
capacity	Penalty to crop yield, Mg/ha	Penalty to economic net returns, $/ha
 mm/d	Corn	Sorghum	Grain	Soybean	Sunflower	Corn	Sorghum	Grain.
Soybean	Sunflower
 8.5	0	0	0	0	$0.00	$0.00	$0.00	$0.00
 6.4	0.19	0.02	0.04	0.01	-$13.70	-$1.72	-$2.00	-$6.34
 5.1	0.90	0.12	0.26	0.10	-$2.88	-$12.82	$11.32	-$14.51
 4.2	1.66	0.35	0.55	0.22	$20.37	-$15.79	$33.20	-$12.78
 3.2	2.90	0.85	1.01	0.44	$59.87	-$10.91	$75.66	-$3.87
 2.5	3.75	1.21	1.31	0.58	$81.86	-$16.72	$100.81	$7.84
 Dryland	8.06	3.43	2.74	1.40	$220.14	-$23.93	$211.29	$44.22
 The results indicate there is not much yield advantage and no economic advantage on average for planning for the higher 8.3 mm/d irrigation capacity and it's associated higher crop production inputs.
The most profitable design capacity for corn, soybean and soybean is 6.4 mm/d, 4.2 mm/d for sunflower, and dryland production for grain sorghum.
Discussion of the Simulation Models
 The results of the simulations indicate corn yields decrease when irrigation capacity falls below 6.4 mm/d.
The argument is often heard that with today's high yielding corn hybrids it takes less water to produce corn.
So, the argument continues, we can get by with less irrigation capacity.
These two statements are misstatements.
The actual water use  of a fully irrigated corn crop really has not changed appreciably in the last 100 years.
Total ETc for corn is about 585 mm in this region.
The correct statement is we can produce more corn grain for a given amount of water because yields have increased not because water demand is less.
There is some evidence that modern corn hybrids can tolerate or better cope with water stress during pollination.
However, once again this does not reduce total water needs.
It just means more kernels are set on the ear, but they still need sufficient water to ensure grain fill.
Insufficient capacities that may now with corn advancements allow adequate pollination still do not adequately supply the seasonal needs of the corn crop.
It should be noted that the yield model used in the simulations was published in 1995.
The model may need updating to reflect yield advancements.
However, it is likely that yield improvements would just shift the curves upward in Figure 2.
Differences in yield improvements between crops could also affect the relative net returns position of the crops.
Opportunities to Increase Deficient Irrigation Capacities
 There are many center pivot sprinkler systems in the region that this paper would suggest have deficient irrigation capacities.
There are some practical ways irrigators might use to effectively increase irrigation capacities for crop production:
 Plant a portion of the field to a winter irrigated crop.
Remove end guns or extra overhangs to reduce system irrigated area
 Clean well to see if irrigation capacity has declined due to encrustation
 Determine if pump in well is really appropriate for the center pivot design
 Replace, rework or repair worn pump
 The question often arises, "What is the minimum irrigation capacity for an irrigated crop?" This is a very difficult question to answer because it greatly depends on the weather, your yield goal and the economic conditions necessary for profitability.
These crops can be grown at very low irrigation capacities and these crops are grown on dryland in this region, but often the grain yields and economics suffer.
Evidence is presented in this paper that would suggest that it may be wise to design and operate center pivot sprinkler irrigation systems in the region with irrigation capacities in the range of 6.4 mm/d for corn and soybean.
In wetter years, lower irrigation capacities can perform adequately, but not so in drier years.
It should be noted that the entire analysis in this paper is based on irrigation systems running 7 days a week, 24 hours a day during the typical 90 day irrigation season if the irrigation schedule  demands it.
So, it should be recognized that system maintenance and unexpected repairs will reduce these irrigation capacities further.
For soybeans in the VC Cotyledon crop growth stage the estimated water use during the previous week of May 29 June 4, 2023 is 0.12 inches and the estimated water use during the week of June 5-11, 2023 is 0.85 inches.
For soybeans in the V1 1st Node crop growth stage the estimated water use during the previous week of May 29 June 4, 2023 is 0.24 inches.
For soybeans in the V2 2nd Node crop growth stage the estimated water use during the previous week of May 29 June 4, 2023 is 0.48 inches.
Chapter: 20 Corn Nitrogen Timing
 To optimize uptake of nitrogen  fertilizer efficiency and to minimize the adverse impact of N on the environment, we recommend that N be applied at the right time, in the right form, at the right place, and in the right amount.
This chapter specifically addresses applying N at the right time.
A corn plant takes up a large percentage of its N between the V6  and R1  growth stages.
During this period, newer hybrids require as much as 8 lbs/day to maintain maximum production.
When N is applied earlier than it is needed by the plant, it can be lost through a variety of mechansims including leaching and denitrification.
Table 20.1 Advantages and disadvantages of various fertilizer timing.
N Timing	Advantage	Disadvantage
 N loss off-field can be through several
 Weather permitting, time is typically not a	Applied prior to crop demand.
Often has lower
 constraint.
efficiency than spring and split applications.
If excessive spring rainfall, N loss off-field can
 Preplant spring	Reduced N losses relative to fall.
still be significant.
Salts and ammonium/ammonia in the fertilizer
 At planting pop-up	Applied with or near the seed.
can inhibit germination.
For pop-up use, only low rates required.
Applied prior to crop demand.
Volatilization losses may be high when surface
 Rainfall required to move N into the soil when
 to standing crop after
 emergence and when	Reduces losses relative to fall or preplant spring.
surface broadcast.
corn is < 6 inches	Leaching/denitrification losses may be high
 following spring rainfalls, but inhibitors may
 Accounts for early spring rainfall, however,
 Sidedressed, applied	Applied when plant needs N.
rainfall is required to move the N into the soil.
<12 inches tall	Accounts for rainfall.
Can be delayed by excessive rainfall conditions.
Improved N efficiency.
Time demands due to weed control requirements.
+ sidedressed 	Accounts for rainfall, can have high efficiency.
Time required to apply the sidedressed N.
The advantages and disadvantages associated with N fertilizer timing in corn production are summarized in Table 20.1.
Corn producers need to consider weather, N fertilizer source, placement, and cultural practices such as tillage, pest, weed, and disease pressure.
The ultimate goal of an N fertilization program is to supply N when it is most needed.
While economic and logistic factors make fall N applications more convenient, the practice has risks that may not be worth the trade-offs.
In years with a wet spring a significant amount of N may be lost, making spring and split N applications preferable.
This chapter provides management guidelines for fall, spring, and split N applications.
With the high cost of N fertilizer and an awarenes of adverse effects of N on the environment, there is an increased interest in adopting techniques that improve N fertilizer efficiency.
Recent research has strengthened the case that in humid or irrigated environments, a split application is more effective at meeting corn N demands than a single application applied either in the fall or early spring.
However, in rainfed corn production systems, delaying the N application increases the risk that surface-applied N will not be incorporated and available for uptake from crop roots.
When this happens, the yield loss can also be substantial.
Fall Broadcast Applications of Urea
 Broadcast-applied urea is most susceptible to environmental loss through volatilization.
It is not recommended to fall apply N before the soil cools to less than 50F or to sandy soil.
Moreover, research from Montana found that application to snow-covered soil still maintained fairly high volatilization rates, particularly during periods of snowmelt.
Additionally, application to soil with high pH, generally above 7.5, increases volatilization.
Ammonia volatilization is reduced by incorporating the urea granual into the soil either by cultivation or rainfall.
Starter and Pop-up Fertilizers
 Starter fertilizer is generally placed 2 inches to the side and 2 inches below the seed.
By separating the fertilizer and seed, the risk of salt injury is reduced.
However, this risk is not eliminated and it is recommended to apply less than 70 lbs of N + K2O if the band is within 2 inches of the seed.
In a split-N application system, N is applied at multiple times during the season.
It can be applied in the fall, with the seed as a starter, in a band next to the seed , or between the rows as a sidedressed application.
One of the greatest strengths with the split-N approach is that it allows the grower to account for early season N losses and changes in the grain yield potential.
When a preseason nitrogen test shows adequate soil N, a producer may benefit economically by reducing preplant or starter N rates.
Research in South Dakota indicates that splitting N applications between preplant and V6 can increase corn grain yield over fall application of N.
However, the amount of N to apply at V6 is dependent on the amount of nitrate-N contained in the soil.
The pre-sidedress nitrate test  is one tool that can be used to estimate the sidedress N application rate.
For PSNT, randomly collect 16 to 24 soil cores from the surface 12 inches when the plants are between V3 to V5.
Sample collection and handling should follow good sampling protocols.
Determine the N rate based on the NO concentration.
Table 20.2 Relationship between the amount of in-season soil test N in the surface 12 inches and the sidedressed N rate.
In-season soil test	Sidedressed
 One of the problems with applying N at the V6 growth stage is that rainfall is needed to move the fertilizer into the soil where it can be absorbed by the roots.
This problem can be avoided by injecting the N into the soil.
However, if the in-season N application is delayed due to high rainfall or logistical issues, recent research from Missouri suggests that "rescue N" applications can be applied as late as tasseling.
However, growers must take precautions to minimize leaf burn.
Summary of N Timing
 Nitrogen is typically lost through volatilization, leaching > 25 0 and/or denitrification.
A single, fall application of N represents a gamble on whether N will be available in late June and early July when it is most needed by the crop.
There are cases where it has been found acceptable.
However, fall applications on sandy soils are not recommended, and it is not recommended on other soils until temperatures decrease below 50F.
The potential losses from early-applied N and the yield advantage from in-season application are well-defined.
After accounting for N in the soil, a broader set of recommendations would include N application through a combination of applying some N  early in the growing season, with the remainder being applied in the mid-vegetative stages.
Protecting the N with urease and nitrification inhibitors can also prolong the time period when N is safe from loss.
Where possible, adding N through irrigation water is an effective approach.
What is the Buffalo River Watershed Management Plan?
A watershed management plan for the Buffalo River Watershed, a tributary of the White River in north central Arkansas, was completed in 2018 as part of a state-led approach to identify and address potential issues of concern in the watershed.
Watershed management plans are voluntary and not regulatory, which means no state agency or land-owner is required to use the strategies or steps identified in the document.
The existence of a plan is not the same thing as a regulation being in place.
The Buffalo River Watershed Management Plan states it is a "framework for landowners, communities, and organizations to voluntarily undertake water quality projects in the watershed and improve their ability to solicit and secure funding and assistance for these projects from various government and private sources."
 These types of non-regulatory plans typically describe watershed features, include water quality data, and identify concerns and voluntary strategies to address them.
Stakeholders people who live, work or have some other interest in an area often provide input on what concerns exist and recommendations to address them.
In this case, a series of public meetings were led by FTN Associates, an environmental consulting firm, to gather input from stakeholders.
This fact sheet is an attempt to provide people with an increased understanding of the Buffalo River Watershed Management plan, how it was developed, and the recommendations included.
What is a Watershed?
A watershed is any area that drains to a common location, such as a stream or a lake.
The stormwater drains from watersheds into local waterways.
Water that does not run off mostly soaks into the ground but can also flow sideways beneath the surface or vertically into the groundwater.
This moving water can encounter and move pollutants with it on its way to streams
 and rivers as it flows across or under places such as streets, yards, construction sites, pastures, and forests.
Pollutants delivered to streams and lakes from runoff is known as nonpoint source  pollution.
Nonpoint source pollution is difficult to predict and manage due to the diffuse nature of the source and variability in landscapes, climate, land use and many other factors.
Ultimately, the pollutants delivered to streams can degrade or impair water quality to the extent the waterway no longer meets its designated uses such as swimming, supporting wildlife, fishing, drinking, or using for agricultural or industrial water supply.
Understanding Watershed Management Plans 
 Many communities, non-profit organizations, agencies, and local governments have created plans for how to manage the watersheds that provide their drinking water or receive their stormwater and wastewater discharges.
The common goal of these plans sometimes called by the acronym WMP is to limit pollution into nearby waterways.
In Arkansas, watershed management plans have been used to identify voluntary strategies for achieving water quality goals.
A watershed management plan typically follows the same format and includes:
 A description of how land is used in the watershed 
 Results of water quality studies
 Concerns and problems identified by local residents, property owners and government officials
 Strategies for reducing or resolving water quality concerns through land management practices and educational public outreach programs
 A time frame for when actions should take place
 The document creates a shared starting point for communities and organizations interested in working on water quality issues and can increase the likelihood for project funding from various government agencies.
Multiple watershed management plans have been developed in Arkansas.
Plans exist for Bayou Bartholomew, Cache River, Illinois River, Lake Fort Smith, L'Anguille River, Lee Creek, Lower Little,
 Strawberry River, and the Upper White River.
The Arkansas Department of Agriculture Natural Resources Division  coordinates the drafting of these plans in Arkansas and submits them to the U.S.
Environmental Protection Agency for review.
The federal agency's acceptance increases the likelihood water quality projects in those watersheds could qualify for and receive funding from government agencies.
The Development of the Buffalo River Watershed Management Plan
 In response to concerns voiced about the water quality of the Buffalo River, a committee established by the governor called for the creation of a watershed management plan.
The Beautiful Buffalo River Action Committee originally included staff from the Arkansas Department of Environmental Quality , Arkansas Department of Health, Arkansas Agriculture Department, Arkansas Department of Parks and Tourism, and the Arkansas Natural Resources Commission.
The Natural Resources Division was tasked with creating the plan and submitting it to the EPA.
The general approach for developing the plan placed emphasis on building partnerships, characterizing the watershed, establishing management goals, identifying solutions, and designing an implementation framework.
The process included four public meetings, which sought to inform stakeholders about the development of the plan and solicit their input and feedback throughout its creation.
The Buffalo River Watershed
 The Buffalo River watershed is located in north central Arkansas and crosses the borders of nine counties.
The watershed covers 1,342 square miles.
About 80% of the watershed is forested land that is difficult to access, another 14% is pastureland, and the remaining portion is a mix of herbaceous/grassland and urban land use.
An estimated 15,545 people live in the watershed, according to the management plan.
The Buffalo River
 was designated as a National Park in 1972 and attracts 1.7 million visitors a year.
Counties Making Up the Buffalo River Watershed
 Major tributaries, or subwatersheds, in this watershed are Bear Creek, two Big Creeks, Calf Creek, Cave Creek, Cecil Creek, Clabber Creek, Davis Creek, Little Buffalo River, two Mill Creeks, Richland Creek, Tomahawk Creek, Water Creek, Thomas Creek, Spring Creek, and Sellers Creek.
The Buffalo River and its tributary Richland Creek are considered an Extraordinary Resource Water and Natural and Scenic Waterway by the state, which are designations that recognize the scenic beauty, scientific value, recreation potential and value the waterway has among its users.
Portions of the Buffalo River also have been designated as critical habitat for the threatened Rabbitsfoot mussel.
The watershed also includes habitat for endangered bat species.
Eleven species in the overall watershed are listed as threatened or endangered by the state and federal government.
Four of these species are bats, two are mussels, and five are plants.
The Division of Environmental Quality  keeps a list of waterbodies in the state that do not support their intended use such as drinking water, swimming, fishing, or irrigation.
Bear Creek is the only waterway in the Buffalo River Watershed that is on DEQ's 2016 list.
Water quality monitoring found that Bear Creek had high levels of total dissolved solids, most likely a result of treated wastewater discharged into the creek near Marshall.
Buffalo River Watershed Management Plan
 Despite this, the popularity of the Buffalo River and concerns over a hog farm then operating in the watershed have prompted discussions about the impact of human activities that introduce potential pollutants such as bacteria, sediment, trash, and nutrients on water quality in the entire watershed.
The Buffalo River Watershed Management Plan attempts to address water quality concerns by providing a series of voluntary recommendations that can be acted upon by anyone.
The document encourages partnerships and teamwork to accomplish the goal of maintaining and improving water quality.
The recommendations involve land management practices, water quality monitoring, studies to help identify sources of erosion and bacteria, creation of watershed teams, and monitoring of trash levels.
The 794-page plan focuses on six subwatersheds: Bear Creek, Big Creek , Brush Creek, Calf Creek, Mill Creek  and Tomahawk Creek..
What the Buffalo River Watershed Plan Includes:
 Basic information on how land is used in the watershed
 Results of past water quality testing in the watershed
 Recommendations for reducing nitrogen and bacteria levels in the watershed
 An overview of water quality concerns voiced by stakeholders at public meetings
 General voluntary land management practices producers could use to reduce nutrient and sediment loss
 Recommendations for continued water quality monitoring and testing
 Studies that should be undertaken to identify eroding streambanks and microbial sources of E.
Coli
 Recommendations for continued educational outreach and the formation of volunteer watershed teams
 What the Buffalo River Watershed Plan Doesn't Include:
 Regulations or new laws that require property owners to use land management practices recommended in the plan
 Funding for implementing the recommendations
 What does the plan recommend?
The Buffalo River Watershed Management Plan recommends actions unique for each of these subwatersheds across five categories:  management practices,  monitoring,  studies,  awareness and education, and  teams.
Management practices to reduce pathogens, nutrients, erosion, and sediment are recommended to greater or lesser amounts for each subwatershed depending on their characteristics and water quality.
When it comes to land use or landcover, recommendations involve using best management practices for pastureland, forests, unpaved roads, riparian areas along waterways, and on-site wastewater.
Some examples of recommendations include rotating cattle grazing, using cover crops, constructing ponds to help trap sediment in runoff water, on-site waste water system improvements and management, and unpaved road improvements.
While these are recommendations to maintain and improve water quality in the watershed, landowners in the watershed are not required to follow any of the recommendations.
The plan's existence is not the same as there being a regulation or a requirement created by law.
Some potential sources of funding are included in the plan, but a new source of funding through the Beautiful Buffalo River Committee for the watershed was created after the plan was developed.
What Can I do as an Individual Stakeholder?
Individuals can play a major role in voluntary implementation of watershed protection including:
 Removing all trash when using the river for recreation such as canoeing, swimming, fishing and camping
 Organizing an Arkansas Game and Fish Stream Team where a portion of the river is adopted to clear trash and report any potential pollutant concerns
 Undertaking septic system/on-site wastewater management improvements
 Following all park recommendations on proper disposal of human wastes
 Promoting good stewardship to others in a respectful manner
 Volunteering for water quality improvement activities
 Increasing and maintaining streamside vegetation
 For more information about how you can help protect this treasured natural resource and participate in watershed protection, contact your local County Extension Office for educational resources such as the Arkansas Watershed Stewardship Program and Streamside Management for Landowners.
The University of Arkansas System Division of Agriculture's Public Policy Center provides timely, credible, unbiased research, analyses and education on current and emerging public issues.
This fact sheet was written by Kristin Higgins, program associate in the Public Policy Center; John Pennington, water quality educator; and Adam Willis, Newton County extension agent.
Surge VS.
continuousflow irrigation
 David A.
Goldhamer Mohammad H.
Alemi Rebecca C.
Phene
 A primary goal of good irrigation management is to minimize deep percolation of water  while replenishing soil water in the plant root zone along the entire length of the field.
Deep percolation losses depend directly on irrigation system performance, which, in turn, depends mainly on how evenly water infiltrates across the field.
Furrow and border irrigation, the primary methods used in the drainage problem area of the San Joaquin Valley's West Side, usually have relatively low uniformities because of  unequal infiltration opportunity times for water across the field, and  spatial variability in soil water transport proper-
 ties.
Properly designed and managed sprinkler and drip irrigation systems, on the other hand, commonly achieve a better uniformity, since the amounts infiltrated depend primarily on application rates and system design rather than on soil infiltration properties.
Changing from surface to sprinkler or drip irrigation systems to improve the uniformity of infiltrated water and decrease drainage volumes may not be economically feasible for many growers.
Even though the best-managed surface systems may not equal the application efficiencies possible with sprinkler or drip systems, enhancing the performance of existing surface systems by improved
 Irrigation specialist Dave Goldhamer sets the solar-powered flow control valve of a surge irrigation system, in which water is applied in a series of pulses.
management or innovative irrigation strategies may be an alternative until long-term solutions to the drainage water disposal problem are found.
Surge irrigation, the application of water as a series of pulses rather than conventional continuous inflow, has been proposed as a means of improving the uniformity of surface methods.
The principles of this technique are not new to California; "bumping," or noncontinuous application, has been used when attaining water advance to the end of the field has been a problem.
Research conducted primarily in Utah, Colorado, and California has shown that the surge method can increase the rate of stream advance, thereby decreasing differences in infiltration opportunity times across the field.
The improvement in advance has been attributed to a reduction in the infiltration rate due to wetting and drying cycles created by the pulse application.
Suggested mechanisms responsible for this behavior include surface sealing due to soil particle rearrangement, surface layer consolidation, a more diffuse wetting front, and air entrapment in the soil.
While accelerated advance rates with surge are clearly documented, other studies have found it to provide little or no improvement.
Lack of positive results with surge appears to occur most often on fine-textured, cracking soils, which are the type most often found in the drainage problem areas of California.
Since field evaluation of surge irrigation on these and other soils in California has been limited, we undertook a study to compare the performance of surge and continuousflow irrigation on different California soil types.
This work was conducted with grower cooperators in Kern and Fresno counties.
We studied numerous fields, but report here on results from two sites, one with a Wasco sandy loam and the other a Panoche clay loam.
Each field was 1,200 feet long and had graded furrows.
Evaluations were made during preplant irrigation or the first postplant irrigation, when infiltration rates are relatively high.
Randomized plots, usually replicated four times, were established for both irrigation methods.
Each plot contained at least one of the four furrow "types" found in each tractor implement pass through the field:  traffic ,  nontraffic ,  nontraffic guess , and  nontraffic belly.
Each furrow type be-
 TABLE 1.
Operational data for each case evaluated
 Item	sandy loam clay loam
 Field length 	1,200	1,200
 requirement 	8	8
 Advance 1	24	27
 Post advance	42	45
 haves differently with respect to advance, and we have limited our presentation here to data only for the nontraffic  furrows.
Two parallel gated pipelines were positioned at the top of the field, one equipped with a Tee-type  surge valve and the other set to operate continuously.
The surge valve had a controller and internal program that allowed for variable surge "on-times" during the irrigation.
A cycle ratio of 0.5 was used, resulting in equal onand off-times.
High, non-erosive inflow rates were selected.
Equal instantaneous inflow rates for each method were compared, although slight differences sometimes existed.
Flow rates were monitored with flumes or orifice plates at the inlet and the end of field throughout the irrigation.
Steady state  intake rates were determined by taking the difference in inflow and runoff just before the end of the irrigation.
Advance and recession were monitored by recording the arrival and
 disappearance of water at increments of 50 or 100 feet across the field.
Intake opportunity times were calculated as the difference between the advance and recession values.
Hydraulic cross-sectional area was measured at various distances from the inlet during stream advance in each monitored furrow.
A "two-point" volume balance model was used with the continuous-flow data to determine the parameters necessary to describe the infiltration function.
The two-point technique has proved to be quite accurate in previous continuous-flow furrow evaluations based on predicted and measured runoff.
We used the infiltration data, along with the measured intake opportunity times, to calculate the distributions of infiltrated water under both irrigation methods.
Predicting the distribution of infiltrated water under surge is more complex than under continuous flow, in that multiple infiltration functions must be used to account for the intermittent wetting.
Several researchers have presented models that include descriptions of infiltration under surge.
These mathematical descriptions allow for adjusting the normal infiltration function based on the immediate wetting history of the soil.
The following three zones  are identified for computing infiltration:
  dry zone soil wetted only by the current surge.
transition zone soil wetted by one or two previous surges.
wet zone soil wetted by two or three previous surges.
Researchers have chosen different wetting regimes associated with the transition and wet zones.
Our choice of the appropriate transition and wet zone descriptions used in each comparative evaluation reported here was based on the predicted cumulative infiltration and the
 measured cumulative inflow during the advance phase differing by no more than 5 percent.
Operational data for each of the field sites evaluated appear in table 1.
The two soil types had different infiltration characteristics, as reflected by steady state  intake rates of 0.91 inch per hour for the Wasco sandy loam and 0.53 inch per hour for the Panoche clay loam.
We chose to use the "variable on-time/constant advance distance" approach to surge management in our studies.
By increasing the on-time for each successive surge, the advance of water over dry soil is nearly constant.
This approach is opposed to "constant on-time/variable advance distance," in which dry advance is progressively less for each surge.
The surge advance and recession data for the Wasco sandy loam show that water traveled rapidly over the soil wetted by previous surges but then slowed dramatically once dry soil was encountered.
This behavior results in the trajectories having a "knife" shape, except at the head end of the field, where the recession was relatively fast.
More time was required for the surge irrigation to reach a given distance across the field than with continuous flow.
With surge, however, water was applied to the test furrows for only one half of the elapsed irrigation time.
Thus, if the continuous advance trajectory just touched the tips of each of the surge "knives," equivalent advance would have been achieved with 50 percent less water than required with continuous flow.
The conditions at the Wasco site under which the comparison of infiltration distributions was made a high infiltration rate and a small irrigation requirement  made it difficult to achieve good irrigation performance.
Much less infiltration occurred with surge; the maximum amount infiltrated
 Distance from inlet 
 Fig.
1.
Measured advance and recession trajectories for the six surges required for full advance at site with Wasco soil.
Continuous flow advance is also shown.
Fig.
2.
Calculated distributions of infiltrated water at water application times  when the irrigation requirement  at the end of the field was satisfied.
TABLE 2.
Irrigation performance parameters
 Appl.
Volume	Amount	Deep	Appl.
Distri.
Case	time	ratio*	stored	percolation	Runoff	effic.
unfrmty
 Surge	270	0.61	2.75	2.54	0.03	60.4	55.6
 Continuous	440	0.61	2.75	4.87	0.10	35.5	57.2
 Surge	492	0.57	7.87	2.41	1.44	67.1	81.4
 Continuous	868	0.57	7.87	5.69	0.65	55.4	70.8
 * Volume Volume continuous
 was 7.1 inches compared with 10 inches for the continuous flow.
However, the calculated distribution uniformities, based on infiltration near the end of the field relative to the average amount infiltrated, were 55.6 for surge and 57.2 for continuous flow.
Deep percolation was much greater with continuous flow, which was largely responsible for an application efficiency  of 35.5 percent compared with 60.4 percent for surge irrigation.
Even though the calculated uniformity was lower, the surge technique improved irrigation performance.
One measure of the relative performance of surge and continuous flow is the ratio of the volumes of water required to attain a given advance distance.
Advance times used to generate this infor-
 mation were always less than or equal to the on-time for each surge.
Values of the volume ratio less than one indicate that less water was required for surge than for continuous advance.
Both cases show that the volume ratio was always less than one.
Volume ratios decreased with distance from the inlet at the Wasco site but generally increased with distance at the Panoche site.
While the reason for this behavior is not clear, it apparently involves the number of advance surges used six and eight for the Wasco and Panoche sites, respectively and associated on-times.
The volume ratios at the end of the field were similar, averaging 0.59.
Field-measured full advance volume ratio data collected at other sites had similar values.
The calculated distributions of infiltrated water at the Panoche site shown in figure 4 are, again, for when the irrigation requirement at the end of the field  had just been satisfied.
This case represents a typical preplant irrigation situation on the West Side of the San Joaquin Valley.
Under surge, 942 minutes of water application were needed to meet the irrigation requirement, compared with 1,190 minutes for continuous flow.
The resulting distribution uniformities were 81.4 and 70.8 percent for surge and continuous, respectively.
More than twice as much deep percolation occurred under continuous flow, although cumulative runoff was less.
Fig.
3.
Advance volume ratios with distance across the field.
It should be noted that total surge runoff was greater at the Panoche site because of the longer elapsed irrigation time required by the intermittent water applications.
Cumulative runoff hydrographs for the Panoche soil show that the time-averaged runoff rate over the period during which runoff occurred for each irrigation method was lower with surge.
This result suggests that there was no large reduction in the basic soil intake rate with surge, a situation that could present a water management problem in attempting to refill the soil moisture reservoir in a timely manner.
In other words, the surge influence appears to occur during the early stages of infiltration when the intake rate is relatively high.
Using linear slopes of the hydrographs over the period that runoff took place, the surge runoff rate was approximately 75 percent that of continuous.
Recent research has shown that using a shorter post advance  surge cycle or using continuous flow during post advance  can further decrease the runoff rate, minimizing tail-
 Fig.
4.
Calculated distributions of infiltrated water for the Panoche soil site when the irrigation requirement at the end of the field was satisfied.
Fig.
5.
Cumulative runoff hydrographs showed that the runoff rate was lower with surge irrigation.
water.
One of the problems in the past in using relatively high inflow rates with continuous flow to achieve good distribution uniformity has been excessive runoff.
Surge irrigation appears to offer a partial solution by using rapid post advance cycling or continuous inflow at a relatively low rate.
Surge irrigation accelerated water advance rates in the two field situations reported in this study.
Other evaluations  yielded similar results.
The results were presumably due to the influence of the wetting and drying cycles on soil infiltration characteristics.
The full  advance volume ratio of surge to continuous flow averaged 0.59.
This resulted in generally improved distributions of infiltrated water and consequently lower drainage volumes.
Timeaveraged runoff rates were lower under surge, although cumulative runoff was greater because of longer irrigation set times required to apply a given amount of water.
Based on this study, surge irrigation appears to be a promising short-term alternative for decreasing drainage volumes in California while using existing surface irrigation systems, especially for early-season irrigations where high infiltration rates can result in low application efficiencies with continuous flow.
Improving poor efficiencies associated with surface-irrigated, shallow-rooted crops also appears to be possible using surge irrigation.
More information is needed to establish best management practices, including the optimum combination of inflow rates, cycle times, and number of surges.
David A.
Goldhamer is Irrigation and Soil Specialist, Cooperative Extension, University of California Kearney Agricultural Center, Parlier; Mohammad H.
Alemi is Visiting Soil and Water Scientist, Department of Land, Air and Water Resources, UC Davis; and Rebecca C.
Phene is Staff Research Associate, Cooperative Extension, Kearney Agricultural Center, Parlier.
The authors thank the following for help in this study: Kater Hake, Kern County Farm Advisor; Christine Peterson, Kern County Research Assistant; and Zeferino Cervantes, Research Assistant.
They also appreciate the cooperation of growers Gary Wilson, John Diener, and Air-Way Farms, Inc.
Surge irrigation, in which water is released into furrows intermittently instead of as a continuous flow, may reduce irrigation water needs by a third, substantially reducing drainage requirements.
UC researcher Dave Goldhamer  and visiting Japanese scientist Tomoo Inaba check the flow of water from the main feeder line through RBC flumes that measure in-furrow flow rates.
Percent of fields that became wetter moving from August to Sept.
15.
The dry years 2020, 21 and 22 fields are much drier than the other years in the fall.
In 2022, 36% of fields with soil in the 15-25 in zone became wetter from August to Sept.
15, 20% of fields with soil in the 25-36 in zone became wetter from August to Sept.
15, and 18% of fields with soil in both zones became wetter moving from August to Sept.
15.
One thing to note is that the time needed for corn to mature is dependent on growing degree days.
If corn needs five inches of water to reach maturity and we receive some hot windy days in late August, the corn will still use five inches  it will just finish up a few days quicker.
Using Physical Soil Amendments, Irriga
 Among the soil amendments, peat has the advantages of promoting a very good top growth and dense root system, when properly irrigated to avoid poor aeration.
It has the disadvantages of not being able to withstand compaction and can become excessively wet if proper irrigation practices are not followed.
Lignified wood has the advantages of withstanding compaction, providing high infiltration rates, allowing good aeration, maintaining an extended supply of nitrogen under leaching conditions, and promoting a good root system under a high oxygen diffusion rate.
It has the disadvantages of contributing to soil salinity, and apparently requires a higher ODR for maximum root growth.
Calcined clay has the advantages of withstanding compaction, providing high infiltration rate and allowing for good aeration.
Its disadvantage is that although it promotes deep roots, they are rather sparse with few roothairs.
Better results were obtained with irrigation based upon tensiometer records than by irrigation according to a set calendar schedule.
Advantages over the set program chosen for this experiment included a savings in water, improvement in soil aeration, and reduction in soil compactability.
One requirement in irrigating by tensiometer records is that excess water must be applied periodically to cause leaching, if salinity becomes too high.
The wetting-agent treatment , increased the infiltration rate of the unamended soil, reduced compactability of peatamended soil, and also resulted in some other effects of minor significance.
Other research in progress indicates that the relationships between wetting agents and plant growth are extremely complex, and no general conclusions are likely for some time.
W.
C.
MORGAN J.
LETEY S.
J.
RICHARDS N.
VALORAS
 T URFGRASSES ARE GROWN for their beauty and durability under recreational uses.
They are subject to soil compaction by foot traffic and equipment used in management operations.
Soil compaction may adversely affect root growth, elongation, soil-water relationships, and soil aeration.
This report resulted from a greenhouse experiment at the Riverside campus to determine the effect of  physical soil amendments,  compaction,  irrigation, and  wetting agents on growth of turfgrasses.
Soil with poor structural stability was amended  with sphagnum peat moss, lignified wood, and calcined clay.
Special containers were constructed from plexiglass for use in this experiment.
They were 4 inches in diameter and 17 inches high.
Tensioneter cups were inserted through holes on the side of the containers at depths of 3 inches and 8 inches.
A hole was drilled at the bottom of each container for drainage, and a short piece of plexiglass tubing was sealed in the hole.
Rubber tubing was used to conduct drainage effluent from the containers to bottles placed directly beneath the containers.
A 2-inch layer of coarse sand was placed in the bottom of the containers.
The soil mixes were placed in the containers over the sand layer.
Since the lignified wood contained 1% nitrogen, equivalent amounts of nitrogen were added to the other soil materials in the form of calcium nitrate in the water used for the initial wetting.
Twenty common bermudagrass sprigs  were planted in each container and top dressed.
Replanting was done as necessary to maintain uniformity in all containers.
The cylin-
 ders were wrapped with black polyethylene sheeting to keep light from the roots.
Two compaction treatments, two wetting agent treatments and two irrigation programs were superimposed on each of the soil materials for a total of 32 treatments.
Each treatment combination was duplicated in randomized block design.
The compaction tests consisted of an untreated check compared with compaction accomplished by placing a circular hardwood plug cut to fit inside the cylinder on top of the grass.
A spring-loaded tube requiring about 70 lbs to move it to the end of a stop was pushed down three times on top of the wooden plug.
This was done daily for the first five weeks of the experiment and then four times a week for the remaining three weeks of the experiment.
On days that water was required, compaction was done before water was added.
The wetting agent treatments consisted of a check without wetting agents and a wetting treatment of the dry soil initially with water containing 3 ppm wetting agent.
The two irrigation programs used were a set calendar schedule and irrigation guided by the tensiometer readings.
Onehalf surface inch of water was applied three times a week under the set irrigation program.
Water was applied to the containers receiving tensiometer-guided irrigation only when the soil water suction was between 30 and 40 centibars.
If the shallow tensiometer indicated need for water but the lower one didn't, only water sufficient to wet the upper part of the soil column was applied.
When the lower tensiometer indicated water need, additional water was applied to reach the lower parts of the container.
Water was never added in quantities sufficient to cause drainage from the bottom of the container under the tensiometer-guided irrigation program.
Midway through the experiment, fertilizer was added equivalent to lb N per 1,000 sq ft in the form of a
 tion, and Wetting Agents in Turfgrass Management
 dissolved in 90 ml of Hoagland's solution.
Containers with lignified wood received Hoagland's solution but no nitrogen.
The experimental period extended from May 25 to July 20.
The infiltration rate was highest in the calcined-clay.
and lignified-woodamended soils, next highest in peat, and lowest in the soils without amendments.
The compaction treatment decreased the infiltration rate of peat and unamended soil but had no significant effect on the other two treatments.
The wetting-agent treatment increased the infiltration rate of unamended soil, but had no effect on the physically amended soils.
The compaction treatment caused the soil mixes to become compact in this order  : unamended soil, peat, lignified wood, and calcined clay.
For each soil material, the compaction was greater when the irrigating was done on a set schedule as compared with the tensiometer-guided irrigation.
The wetting agent caused the peat-amended soil to become less compact, but had no effect on the other soil materials.
The evapotranspiration was higher under set, as compared with tensiometerguided, irrigation.
This result is probably due to the surface remaining much
 wetter under set irrigation.
The only effect of soil mix was that the evapotranspiration was less in lignified-woodamended soil than the others when tensiometer-guided irrigation was used.
This probably resulted from less top growth under this treatment.
Evapotranspiration was less when the soil mixes were compacted as compared with no compaction.
This is also probably due to reduced top growth resulting from soil compaction.
These results closely follow the results on evapotranspiration.
The irrigation program had the biggest effect on evapotranspiration and number of irrigations.
These results are strictly applicable to the calendar irrigation program adopted,
 Typical root systems of grass grown under the various irrigation and compaction treatments in the different soil mixes.
The abbreviations on the photographs are:  unamended soil,  peat,  lignified wood, and  calcined-clay-amended soil.
and the environmental conditions of the experiment.
Had a set schedule of oncea-week irrigation, rather than three times a week-or higher environmental evaporative demands--existed, the results could have been different.
The set schedule was chosen because it is similar to programs commonly followed in turf irrigation in southern California.
Tensiometers can be installed to guide irrigation SO that the soil will not become too dry before watering.
Moreover, field experience with turf, citrus, and avocados indicates that the general effect of tensiometer-guided irrigation, as compared with prevailing irrigation programs, is to decrease the amount of water used for irrigation.
Dry weight of clipppings
 Measurements of clippings from the first half of the experiment showed top growth was greater when the soil was amended as compared with no amendment, when irrigated on the set program.
When irrigation was based on tensiometer records, the lignified-wood-amended and the unamended soil produced less top growth than the other two soil mixes.
In comparing the two irrigation programs, there was less top growth on the lignified wood treatment, when watered according to tensiometer records, than the set program.
This was in contrast to the other soil materials which had higher average dry weight  when irrigated on the tensiometer program.
Compaction significantly reduced the top growth as compared with no compaction.
The effect of irrigation programs on top growth over the last half of the experiment was the same as for the first half-except that differences were large enough to be statistically significant.
Lignified wood provided the most top growth when much water was used, as under the set irrigation program.
When tensiometers were used to guide irrigation, amendment with lignified wood was no better than unamended soil for producing top growth.
Of all treatment combinations, peat under tensiometer-guided irrigation produced most top growth.
Whereas compaction treatment affected the top growth during the first half of the experiment, it had no significant effect over the last half.
Wetting agents had no effect on top growth.
The electrical conductivity  of the leachate caused by set irrigation is pre-
 sented as a function of time for the various soil materials in the graph.
The electrical conductivity is related to the concentration of salt in the water.
Salts from the unamended, the peat, and the calcined-clay-amended soils were leached out during the first 18 days.
The EC thereafter remained fairly constant and equal for these three soil materials.
The EC of the leachate from lignifiedwood-amended soil was, in general, higher than the others and particularly so over the last part of the experiment.
These data suggest that the lignified wood has a source of ions which are slowly released and therefore not immediately removed by leaching.
The increase in EC from lignified wood after the twenty-fifth day was probably caused by a change in the weather which, up to that date was fairly cool and cloudy, then became clear and hot.
A smaller fraction of the water added came through as leachate and therefore was more concentrated.
The original saturated-soil-extract EC of the various soil mixes was 1.30, 1.97, 2.16, and 4.12 mmho cm-1 for unamended soil, calcined clay, peat, and lignified-wood-amended soil respectively.
Under tensiometer-guided irrigation there was no leaching so these values represent the approximate salinity of the various soil mixes.
7.6, 7.1, 5.9, and 5.2 for the unamended soil, calcined clay, lignified wood, and peat, respectively.
The pH of leachates from unamended soil and calcined-clayamended soil did not change much through the course of the experiment.
The leachates from the peat-amended soil during the latter part of the experiment had a higher pH than for the first part of the experiment.
The opposite was the case for lignified-wood-amended soil where the higher pH values were measured in the first part of the experiment.
The better top growth of grass grown on lignified-wood-amended soil when the soil was subjected to much leaching-as was the case with set irrigation-is most likely due to the retention and slow release of nutrients.
The failure of the grass to grow well on lignified wood under tensiometer-guided irrigation was due to high salinity.
The average pH of the leachate was
 The mineral concentrations in the clippings analyzed were influenced by the treatments  : the levels of concentration were higher than have been considered as deficient for grass growth, except nitrogen, which was borderline.
The concentration of nitrogen was highest in grass grown in lignified-woodamended soil.
The concentration of nitrogen was lower when the soil materials were irrigated on a set schedule, as com-
 ELECTRICAL CONDUCTIVITY OF LEACHATE FROM CONTAINERS IRRIGATED ON SET SCHEDULE AT VARIOUS TIMES AFTER START OF EXPERIMENT
 CALIFORNIA AGRICULTURE, JANUARY, 1967
 pared with tensiometer-guided irrigation-except for the lignified wood which was not affected by irrigation treatment.
The lower concentration of nitrogen in plants grown under set irrigation in soil, peat, and calcined clay was probably because the nitrogen was leached from the soil.
The slow release of nitrogen from lignified wood kept adequate nitrogen available for the plant in spite of leaching.
These results help explain the good growth of grass on lignified-woodamended soil when irrigated under the set irrigation program.
ODR and root growth
 The measured oxygen diffusion rate  values from containers receiving irrigation based upon tensiometer readings were all higher than 0.40 ug cm-2min- These values are not expected to be deficient for plant growth.
It is possible that, if ODR measurements had been taken daily, ODR might have been in the deficient range for certain treatments for a period of time after irrigation.
In general, the ODR values under set irrigation were lowest in the unamended soil.
Peat-amended soil was next lowest with the other two amendments providing an environment of fairly high ODR.
Oxygen diffusion rate values measured in the noncompacted soil materials were higher than in the compacted unamended soil and peat-amended soil.
The ODR values in the other amended soils were not greatly affected by compaction.
The root growth was, in general, correlated with ODR measurements.
The lower ODR limit for root growth was about 0.15 cm-2min-.
The photographs illustrate the roots grown in the various soil mixes for various compaction and irrigation treatments.
It can be noted that the lignified wood and calcined clay tended to eliminate the effects of overirrigation and compaction on root growth.
Tensiometerguided irrigation tended to reduce the ill effects of compaction on root growth in unamended soil.
W.
C.
Morgan is Turfgrass Farm Advisor, Los Angeles County; J.
Letey is Associate Professor of Soil Physics; S.
J.
Richards is Professor of Soil Physics; and N.
Valoras is Laboratory Technician in Department of Soils and Plant Nutrition, University of California, Riverside.
The Emery Corporation, Southern California Turfgrass Council, and Loamite Division of Pope and Talbot Corporation assisted in financing this project.
Comparison of Two Soil Amendments for Carnation Production
 S.
T.
BESEMER D.
H.
CLOSE
 C ARNATION GROWERS utilize any of several bulky organic materials for amending greenhouse soils to improve aeration, drainage, and moisture retention.
Redwood sawdust has been the standard material used in San Diego County.
The trial reported here compared plant growth and flower production of carnations grown with two soil amendments-10 and 20% by volume of Redwood sawdust, and 10 and 20% by volume of processed lignin particles, replicated three times.
They were conducted at Hillside Floral Company, Encinitas, and the amendents were incorporated in a Carlsbad sandy loam in raised benches prior to planting.
The greenhouse soil had not been previously amended.
Each series of replications was planted to a Sims carnation variety  in mid-July, 1963.
The plant spacing was 3.15 plants per sq ft of bench area.
First blooms were cut in late October.
Daily harvest records of blooms were recorded for each treatment for one year.
Grades were not recorded.
Periodic checks were made for differences in growth and bloom quality.
Based on the conditions of this experiment, a 20% addition of processed lignin particles to a previously unamended soil, produced about 31/2 additional carnation flowers per sq ft of bench in 12 months of flower production as shown below:
 FLOWER PRODUCTION, AVERAGE OF THREE REPLICATES FOR ONE YEAR
 ment	per sq	per
 Lignin 20%	54.80*	17.14
 Lignin 10%	51.50	16.45
 Redwood 20%	51.23	16.38
 Redwood 10%	51.02	16.13
 *Significantly different.
If this difference could be obtained in commercial practice, a 20% addition of processed lignin particles would produce an economic gain despite its higher initial cost.
From observation as well as data recorded, it appeared that the gain in production with addition of 20% lignin was due to a more rapid early growth of the plants and more rapid crop cycling.
Flowering of the first crop was about two weeks early where the 20% lignin treatments were applied.
It was also apparent that a 10% lignin addition was insufficient to produce a measurable production response.
Redwood at 10% and 20%, and lignin at 10% were statistically the same.
Soil amending is but one of many cultural factors affecting flower production.
Response may vary considerably depending on the type of soil to be amended.
Economic extrapolations are particularly difficult in flower-producing enterprises because of the many differences in grower practices, such as plant spacing variations, percentage of greenhouse area in production, the area involved in replanting, the time of year that flowers are produced, average price received, and flower grades.
Growers interested in comparing redwood sawdust and processed lignin particles for amending soils for carnation production should compare the two materials, each at 20% by volume of soil, on a trial basis.
Accurate flower harvest records should be kept with occasional quality grade-outs.
Additional data will also be needed to determine relative responses in the second year of production.
Seward T.
Besemer and Daniel H.
Close are Farm Advisors, University of California, San Diego County.
The processed lignin amendment used in these tests is a product of the Loamite Division of Pope and Talbot Corporation.
COST OF PRODUCTION ESTIMATE PER SQ FT OF BENCH
 Redwood	Redwood	Lignin	Lignin
 10%	20%	10%	20%
 Basic costs	$1.0000	$1.0000	$1.0000	$1.0000
 Soil amendmentsb	.0037	.0074	.0222	.0444
 Flower handling	.5102	.5123	.5150	.5480
 $1.5139	$1.5197	$1.5372	$1.5924
 Cost 	2.9673	2.96644	2.9849	2.9058
 Based on a 1958 Carnation Cost Study, San Diego County, Agricultural Extension Service, University of California.
b Based on costs of $2.00 per CU yd for Redwood sawdust and $12.00 per CU yd for processed lignin particles.
Flower handling is that portion of production costs, such as disbudding, banding, cutting, grading, and bunching, that is accrued per flower, and increases with the number produced.
Table I.
Normal water requirements for corn, grain sorghum, soybeans, and dry beans between various stages of growth and maturity in Nebraska.
For Dry Beans R5 crop stage, the stage of growth is known as early seed fill, the approximate days to maturity is 35, and the water use to maturity is 7.0 inches.
For Dry Beans R6 crop stage, the stage of growth is known as mid-seed fill, the approximate days to maturity is 25, and the water use to maturity is 4.2 inches.
For Dry Beans R7 crop stage, the stage of growth is known as beginning maturity, the approximate days to maturity is 15, and the water use to maturity is 2.0 inches.
For Dry Beans R8 crop stage, the stage of growth is known as harvest maturity, the approximate days to maturity is 0, and the water use to maturity is 0.0 inches.
Nebraska has approximately 9 million irrigated acres of cropland , making it the top state in irrigated acres.
The amount of water applied per irrigated acre is approximately 10 inches, ranking fourth nationally.
Weed control under drip and low-volume sprinkler irrigation
 Bill B.
Fischer David A.
Goldhamer Thomas Babb Roger Kjelgren
 D rip and other types of low-volume microsprinklers and misters are being used in some orchards and vineyards as an alternative to conventional irrigation methods.
Water and energy costs, as well as the development of agricultural areas where the topography and soil type limit furrow or basin irrigation, have stimulated the use of low-volume frequent applications of water.
Low-volume emitters also have the potential to improve uniformity of water application.
A serious drawback, however, is that vigorous weed growth occurs in the wet areas.
Weed control is often shorter lived in frequently wetted soil than under gravity or conventional impact sprinkler irrigation methods.
The poor performance of preemergence herbicides is related to the water management strategies associated with drip and low-volume systems strategies fundamentally different from those used in surface gravity irrigation.
Under conventional methods, such as furrow, flood, basin, and impact sprinklers, water applications are at intervals of less than 10 days to 20 days or more during the season, depending on crop, climate, and soil conditions.
Water is applied much more frequently under drip and low-volume irrigation, however usually daily with drip and two to three times a week with low-volume sprinklers.
Degradation of preemergence herbicides appears to be related to high soil water levels and length of time these levels remain in the soil.
High-frequency irrigation can thus cause these chemicals to perform poorly.
In frequently wetted soil, summer annual grasses and broadleaf weeds, especially barnyardgrass , crabgrass , pigweed , purslane
 , and cudweed , grow vigorously and are difficult to control.
It has been reported that weeds, such as sprangletop  and purple ammannia , that commonly occur in rice fields have become prevalent in many orchards.
Soil-persistent herbicides applied preemergence, such as napropamide  and oryzalin  do not provide adequate long-lasting control.
Therefore, the application of contact or systemic herbicides, such as paraquat, dinoseb, and glyphosate , may be necessary Some orchardists have found it necessary to treat the area around drip emitters four to eight times a year to control weeds an expense that possibly could be eliminated or minimized.
We investigated weed growth and control under different irrigation methods in a vineyard and a deciduous orchard at the University of California Kearney Agricultural Center in Fresno County, California.
The vineyard study used 15 rows of mature Thompson Seedless vines divided into three, five-row plots.
One plot had low-volume sprinklers suspended from raised laterals; the sprinklers were 2 feet above the ground midway between the vines.
Both 360and 40-degree spray patterns directing the water along the vine rows were evaluated.
In another plot, two drip emitters per vine, spaced 2 1/2 feet from either side of the trunk, were installed.
Automatic controllers permitting different durations of water application were installed in both the drip and sprinkler plots.
Volumetric discharge rates
 Vigorous weed growth in frequently wetted areas is a serious drawback of drip and low-volume sprinkler systems.
were 1 and 5 gallons per hour through the emitters and sprinklers, respectively.
The vines were irrigated daily in the drip and twice a week in the low-volume plots.
A third plot was basin-flood irrigated on the average of once every 20 days.
A strip of raised soil  approximately 3 feet wide under the vines confined the water to a 7-foot-wide basin between the vine rows.
The herbicides were applied in midFebruary with a commercial-type sprayer to a 41/2-foot-wide area centered on the vine row.
The native vegetation between the rows was mowed periodically during the season.
Eight herbicide regimes plus a nontreated control were tested under each irrigation method.
In the deciduous tree study, we evaluated drip and low-volume sprinkler irrigation on young bareroot Flavorcrest peach, Nubiana plum and Nonpareil and Mission almonds planted in early 1982 Two almond varieties were used because they differ significantly in their susceptibility to some herbicides.
For each irrigation method, 27 plots, each containing four trees, one of each variety, spaced 17 feet apart were established in a randomized block design.
Herbicide applications were limited to a 31/2foot strip on each side of the tree rows.
Therefore, the herbicide-treated area in each plot was 7 by 68 feet.
Eight herbicide regimes, plus a nontreated control, were replicated three times.
The herbicides were applied with an experimental sprayer in early March 1982, and the treatments were repeated in succeeding years in mid-January.
We rated weed control in the vineyard and orchard four or five times each year and, after each evaluation, sprayed weeds in all plots with glyphosate or sulphosate.
Hence, on each evaluation date, only newly emerged weeds were rated.
This system allowed assessment of the effectiveness of the herbicides on numerous weed species and their persistence under the different methods of water application.
The net amount of applied water available for crop use was the same under each irrigation method in both the vineyard and orchard plots.
In planning the irrigation schedule, we estimated crop water use from long-term historical daily evapotranspiration estimates and published crop coefficient values for grapes and deciduous trees.
Adjustment for immature tree canopy size was based on the shaded area of the orchard floor mea-
 TABLE 1.
Performance of herbicides under different irrigation methods in a vineyard
 Weed control in wetted areat
 Herbicides*	Ratest	flood	emitters	emitter
 lb ai/A	%	%	%
 Diuron  + simazine 	1.5 + 1.5	98	35	55
 Oryzalin  + simazine	4 1	100	25	50
 Napropamide  + simazine	4 1	85	25	40
 Oryzalin + simazine + oxyfluorfen 	2 + 1 + 2	100	35	60
 Napropamide + simazine + oxyfluorfen	2 1 + 2	98	50	65
 Napropamide + simazine	4 2	90	35	40
 Oryzalin + simazine	4 2	85	35	50
 Oxyfluorfen + simazine	2 1	80	0	30
 NOTE: No symptoms of phytotoxicity were observed.
Glyphosate  or sulphosate  added to all treatments at 2 pounds active ingredient per acre as a tank mix to control emerged weeds.
t Rates: lb ai/A = pounds active herbicide applied per treated acre.
+ Herbicides applied March 5, 1982, and February 18, 1983.
Evaluated November 19, 1984.
TABLE 2.
Performance of herbicides under drip and low-volume sprinklers in a deciduous orchard
 Weed control in wetted area
 Herbicide*	Rates	Drip	Sprinkler	Drip	Sprinkler
 Ib/ai/A	%	%	%	%
 Napropamide + simazine	4 1	96	98	22	88
 Oryzalin + simazine	4 1	100	100	42	85
 Napropamide + oxyfluorfen	4 2	97	94	65	93
 Oryzalin	4	97	97	37	84
 Napropamide + simazine + oxyfluorfen	2 1 + 2	100	96	65	93
 Oryzalin + simazine + oxyfluorfen	2 1 + 2	99	90	58	93
 Oxyfluorfen	3	98	95	15	96
 Untreated	-	39	28	22	28
 Weed control in wetted areas
 Herbicide*	Rates	Drip	Spkir	Drip	Spkir	Drip	Spklr
 lb ai/A	%	%	%	%	%	%
 Napropamide + simazine	4 1	57	93	85	90	66	81
 Oryzalin + simazine	4 1	97	100	78	99	73	86
 Napropamide + oxyfluorfen	4 2	93	97	87	97	78	90
 Oryzalin + oxyfluorfen	4 2	96	93	80	99	76	93
 Napropamide + simazine + oxyfluorfen	2 + 1 + 2	97	99	90	99	85	93
 Oryzalin + simazine + oxyfluorfen	2 1 + 2	100	98	78	99	90	96
 Oxyfluorfen	2	90	98	88	98	75	83
 Oxyfluorfen + simazine	2 1	99	99	87	99	76	90
 Untreated	0	30	87	83	26	35
 NOTE: No evidence of phytotoxicity was seen through 1984 on any trees.
Glyphosate or sulphosate added to all treatments as a tank mix at 3 ponds active ingredient per acre to control emerged.
weeds.
sured at midday during the summer.
Application efficiencies were estimated at 70 percent for the drip and low-volume sprinkler irrigated trees in 1983 and 90 percent in 1984.
For the vineyard, application efficiency estimates were 75 percent for the basin-flood and 90 percent for the drip and low-volume sprinkler irrigated vines.
Weed control in both the vineyard and deciduous orchard reflected the susceptibility of the weeds to the applied herbicides and their persistence under the different irrigation methods.
In both studies, all herbicide treatments were very effective through mid-May regardless of the irrigation method.
In the orchard, however, later evaluation indicated that all herbicide treatments under the low-volume sprinklers provided better weed control
 than they did under drip.
As the season progressed, the differences in effectiveness became greater, as illustrated by the October evaluation in 1983.
In the vineyard study, the most effective and longest residual weed control occurred under basin-flood irrigation, where no water was applied over the herbicidetreated area.
Unlike the orchard, the vineyard showed no appreciable difference in weed control between the drip and lowvolume sprinklers throughout the season.
We attribute this result to disruption of the sprinkler's spray pattern by low-hanging canes of the vines.
Deposition of the water directly beneath the point of spray interception caused a wetted surface area similar to that associated with drip emitters.
Soil wetness beneath the vines was prolonged by the vine canopies, which limited surface evaporation and promoted high humidity.
It should be noted that
 mechanical cane cutting  is practiced in the production of certain grape varieties.
This cutting allows an uninterrupted spray pattern and could presumably improve herbicide performance with low-volume sprinklers.
In the orchard, the most effective weed control under low-volume sprinklers throughout the 1983 season was in areas treated with oxyfluorfen.
Oxyfluorfen under drip irrigation, however, showed poor seasonal performance.
Generally, more effective weed control with drip irrigation was obtained where oxyfluorfen was applied in combination with other herbicides.
Under low-volume sprinklers, the same herbicide combinations resulted in substantially better weed control.
In both studies, we observed shifts in weed populations in 1984.
Species that are tolerant of or marginally susceptible to certain herbicides or combinations of herbicides became dominant.
For example, in the oxyfluorfen-treated plots, cudweed, horseweed , and flaxleaved fleabane  predominated.
As a result, in both the drip and low-volume sprinkler plots, superior weed control was obtained in areas treated with combinations of three herbicides:  oryzalin, simazine , and oxyfluorfen or  napropamide, simazine, and oxyfluorfen.
These studies demonstrated that preemergence herbicides give more effective and longer residual weed control with low-volume sprinklers than with drip emitters.
This effect is presumably due to the more rapid microbiological and chemical  degradation of herbicides in the continually wetted soil associated with high-frequency drip irrigation.
It thus appears that low-volume sprinklers, while having most of the advantages of drip emitters, also offer the potential of better preemergence herbicide performance because of less frequent and concentrated water applications However, since the management of unwanted vegetation continues to be troublesome and expensive in orchards and vineyards under localized irrigation, research is planned to evaluate the effectiveness and selectivity of certain herbicides introduced in the irrigation system through drip emitters and low-volume sprinklers.
Bill B.
Fischer is Farm Advisor, Fresno County, and David A.
Goldhamer is Soil and Water Specialist, Kearney Agricultural Center, Parlier, both with University of California Cooperative Extension.
Thomas Babb, formerly Research Associate, Fresno County, is now Agronomist, Amstar Corp.
and Roger Kjelgren, formerly Research Associate, Kearney Agricultural Center, is now a graduate student, University of Washington, Seattle.
Dilshad Brar, a graduate student in the UNL Biological Systems Engineering Department, looked at 1000 center pivot installations in 10 Nebraska counties to determine if placing a VFD on the system would be economical.
A standard length center pivot with eight towers was superimposed on each fields digital elevation map.
The hydraulics of the systems were calculated for a set flow rate and diameter of pivot pipeline.
The repairs of the equipment are divided according to the ownership.
If the scenario above holds true, the landowner is responsible for the underground repairs.
The tenant would be responsible for all above ground repairs and maintenance.
This shifts the bulk of the annual maintenance expense from the landowner to the tenant.
PERFORMANCE EVALUATION OF SELECTED SOIL MOISTURE SENSORS
 Irrigation water management practices could greatly benefit from using soil moisture sensors that accurately measure soil water content or potential.
Therefore, an assessment on soil moisture sensor reading accuracy is important.
In this study, a performance evaluation of selected sensor calibration was performed considering factory-laboratoryand field-based calibrations.
The selected sensors included: the Digitized Time Domain Transmissometry  which is a volumetric soil water content sensor, and a resistance-based soil water potential sensor.
Measured soil water content/potential values, on a sandy clay loam soil, were compared with corresponding values derived from gravimetric samples.
Under laboratory and field conditions, the factory-based calibrations for the TDT sensor accurately measured volumetric soil water content.
Therefore, the use of the TDT sensor for irrigation water management seems very promising.
Laboratory tests indicated that a linear calibration for the TDT sensor and a logarithmic calibration for the watermark sensor improved the factory calibration.
In the case of the watermark, a longer set of field data is needed to properly establish its accuracy and reliability.
Soil moisture is an important factor used in irrigated agriculture to make decisions regarding irrigation scheduling and for land managers making decisions concerning livestock grazing patterns, crop planting, and soil stability for agricultural machinery operations.
Many methods of determining soil moisture have been developed, from simple manual gravimetric sampling to more sophisticated remote sensing and Time Domain Reflectometery  measurements.
One common technique is to measure dielectric constant, that is, the capacitive and conductive parts of a soil's electrical response.
Through the use of appropriate calibration curves, the dielectric constant measurement can be directly related to soil moisture.
However, there are several different types of sensors commercially available which present different levels of
 soil water content/potential readings' accuracy.
Hignett and Evett  indicated the following: "in general, a manufacturer's calibration is commonly performed in a temperature controlled room, with distilled water and in easy to manage homogeneous soil materials  which are uniformly packed around the sensor.
This calibration procedure produces a very precise and accurate calibration for the conditions tested.
However, in field conditions variations in clay content, temperature, and salinity may affect the manufacturer's calibration."
 Sensor accuracy needs to be assessed in order to do a better job managing water and to realize the reliability of the sensor.
In addition, appropriate sensor calibration curves can be developed during the sensor evaluation process.
This study evaluates the performance of a Digitized Time Domain Transmissometry  soil water content sensor developed by Acclima, Inc.
, and of a resistance-based  soil water potential sensor on a sandy clay loam soil from an agricultural field near Greeley, CO.
This study took place during the 2010 corn growing season in eastern Colorado.
The field was an experimental field cooperatively operated by the United States Department of Agriculture Agricultural Research Service  and Colorado State University  near the City of Greeley, CO.
Corn was grown at this location and was irrigated using furrows.
Geographic coordinates, dry bulk density, porosity and soil texture of the soil can be found in Table 1.
Bulk density was obtained using a Madera Probe.
The porosity was estimated using the sampled bulk density from each field and an assumed particle density of 2.65 g/cm.
Soil textures were determined in the Laboratory by a particle size analysis.
Table 1.
Site Name, Geographic Coordinates, Dry Soil Bulk Density , Porosity , and Soil Texture in the 10 30 cm soil layer.
Site	Lat.
Long.
Pb		Q	Sand			Silt	Clay		Class
 Greeley,	CO	4026'	10438'	1.46	45	65	10	25	Sandy clay	loam
 The TDT soil water content sensor is provided with a calibration by the sensor manufacturer, which enables the sensor to give a direct reading of volumetric soil water content , soil temperature , and electrical conductivity.
According to the Cut Sheet TDT soil moisture sensor , the volumetric
 water content accuracy of the sensor is +1%  under temperature conditions of 0.5 to 50 C and EC of 0 to 3 dS/m.
Laboratory and field tests were conducted to test this claim of accuracy.
The Watermark sensor directly measures voltage excitation  which is converted to electrical resistance  through the datalogger's internal program.
Soil water potential  is then estimated using the electrical resistance through another internal correction.
The equations used in the dataloggers are shown as Equations 1 and 2.
where Vr  is the ratio of the measured voltage divided by the excitation voltage, Rs  is the measured resistance, T  is the soil temperature measured by the TDT sensor, and SWP  is the soil water potential.
SWP is directly related to Ov through water retention  curves, which vary by soil type.
The manufacturer of the Watermark sensor recommended relating the SWP to volumetric water content through curves for general soil types published by Ley et al..
This curve was generalized using equation 3.
Ov = aX  3
 where a and are coefficients and X is the sensor-based soil water potential.
The a and coefficients for the soil in this study are 104.63 and 0.19, respectively.
Laboratory calibrations were performed using soil samples collected from the upper 0-30 cm layer.
The laboratory calibration for the TDT sensor was based on the procedure proposed by Starr and Paltineanu  and Cobos.
Soil collected from each field was air-dried until it could pass through a 2-mm sieve.
It was then packed in a 19 L container to approximate field bulk density.
The sensor was then inserted vertically into the soil, and several soil water content readings were taken every 20 minutes.
After each sensor reading, soil gravimetric samples were taken from the container and were oven-dried at 105 C for 24 hours.
The volumetric water content was then computed by multiplying the gravimetric water content by the soil bulk density obtained from field core soil samples.
The soil from the container was then wetted with 500 mL of water and was mixed thoroughly.
The above procedure was repeated several times, each time repacking the container, taking multiple readings and adding another 500 mL of water.
A total of sixty data points  were used in the analysis of the soil moisture.
The volumetric water contents of the soil moisture samples ranged from 10.7 to 35.9%.
Fangmeier et al.
reported values of permanent wilting point  and field capacity  for the same type of soil as the one used in this study as being 16 to 26%.
Therefore, the range of soil water content sampled in the laboratory covered the PWP to FC range.
A linear calibration equation was developed by plotting the sensor probes' readings  versus the volumetric water content derived from the gravimetric method.
The linear regression equations were developed using Microsoft Excel Regression Analysis.
The equations take the form of equation 4, below.
4
 where ao is the slope of the of the curve while A1 is the intercept of the curve with the Y-axis.
Ov.
S is the sensor-based Ov.
During these tests, the average EC recorded by the TDT sensor was 0.69 dS/m.
The soil temperature was nearly constant  throughout the entire study.
The laboratory calibration procedure using the Watermark sensor was different from that of the TDT because water tension in the Watermark sensor must equilibrate with that of the surrounding soil before an accurate reading can be taken.
Therefore the sieved soils from the previous tests were separated into multiple smaller buckets of different water contents.
One Watermark sensor was placed in each bucket and left for three days to equilibrate with the soil.
Gravimetric samples were then taken from each bucket, oven-dried and converted into Ov using the dry soil bulk density obtained from field samples.
A total of seven samples  were used in the analysis.
Two types of calibration equations were developed by plotting 0v_g versus the SWP sensor output.
The logarithmic equation is shown in equation 5 below.
where a and are coefficients and X is the sensor-based soil water tension.
To assess the accuracy of the developed calibration equation obtained from the laboratory procedure, the 'laboratory equations' were applied to the field sensors' readings and results were compared with the field-sampled Ov.
During July of 2010 TDT and Watermark sensors were installed at the study site.
This site had three differing irrigation treatments and each treatment contained one TDT sensor and one Watermark sensor.
In each irrigation treatment the
 sensors were installed under the crop row/bed, roughly 0.25 m apart from each other, at a depth of 10-12 cm below the average level of the corn beds.
These sensors were installed by digging a shallow trench and inserting the sensors horizontally into the wall, then backfilling the trench.
Data collection for each TDT sensor began in the mid July.
Data collection for the Watermark sensor in treatment 1 also began in mid-July, while the sensors in treatments 2 and 3 began operating in the middle of September.
From the time of installation until the first week of October, 2010, automated sensor readings were recorded every five minutes.
Readings were compared with periodic gravimetric measurements, totaling eleven from each irrigation treatment.
Since the Watermark sensors in treatments 2 and 3 did not begin operating until September, only two gravimetric samples were collected for each treatment for these sensors.
The gravimetric samples were taken using a soil auger approximately 1-2 meters away from each sensor location.
These samples were immediately placed in sealed containers inside a cooler and taken directly to a laboratory to be weighed , oven-dried, and weighed again.
The gravimetric samples were then converted into Ov using the dry soil bulk density field value.
During the times of gravimetric field sampling, soil temperatures ranged from 15 22 C in irrigation treatment 1, 15 24 C in treatment 2, and 16 30 C in treatment 3.
EC ranged from 0 1.23 dS/m in treatment 1, 0 1.31 dS/m in treatment 2, and 0 2.12 dS/m in treatment 3.
Sensor-specific linear calibration equations were developed for the TDT sensors based on the Ov read by the sensor.
This equation is shown in equation 4, above.
For the Watermark sensors, the logarithmic equation  was derived.
Generalized equations were developed to incorporate the readings from all of the Watermark sensors in that field.
Four statistical measures were computed to compare and evaluate each modelpredicted  equation with the observed  gravimetric samples taken from the field and laboratory soils.
These include the coefficient of determination , mean bias error , root mean square error , and index of agreement  as defined by Willmott.
where n is the sample size, P and O O.
The units for MBE and RMSE are volumetric water content , and K is dimensionless.
Hignett and Evett  point out that in most agricultural and research applications the measurement accuracy needs to be within 0.01 to 0.02 m 3 m-Superscript.
Therefore MBE under 2.5% and RMSE less than 5% fit this criterion.
The scale of K ranges between 0-1, with higher numbers representing greater correlation between the model prediction and observations.
In general, under laboratory and field conditions, the factory-based calibrations of Ov did not consistently achieve the required accuracy within the PWP to FC range of water contents.
For the TDT sensor, the factory calibration performed well in most cases.
For the Watermark sensors, on all tests the sensor did not achieve the required accuracy.
Table 2 and Table 3 show low MBE and RMSE and high K values for the TDT sensor.
This result indicates that the TDT's factory calibration was within the previously-described limits and thus performed very well.
The MBE values for the Watermark's factory calibration in Table 2 show that this sensor overestimated measured Ov in average 20.5+21.1% in the laboratory test.
This is a large overestimation and in part it may be due to lack of appropiate equilibrium of water tension between the the sensor cap and soil during the three days that the probe was left in the container at a given soil water level.
Table 2.
Comparison of the Factory Calibration-Based Ov  with Laboratory Measurements of Ov.
Soil Type	Size 	Sample	R2	MBE		RMSE		K
 TDT	60	0.94	-1.2	3.9	0.95
 Watermark	7	0.93	20.5	21.1	0.32
 Table 3.
Comparison of the Factory Calibration-based Ov  with Field Measurements of Ov.
Soil Type	Location	Size 	Sample	R2	MBE		RMSE		K
 1	11	0.73	2.1	3.0	0.85
 TDT	2	11	0.83	1.8	2.9	0.92
 3	12	0.77	-1.8	3.3	0.90
 Watermark	Composite	15	0.87	11.2	12.6	0.48
 *One equation represented readings from all field sensors.
However, in the field, the Watermark's factory calibration overestimation of Ov was much less, i.e.
11.2+12.6%.
This seems to confirm that the Watermark sensor needed a longer time to attain equilibrium of soil water tension under laboratory conditions.
Soil-specific calibration equations developed in the laboratory yielded high levels of accuracy, well within the targeted statistical parameters, for both sensors.
The MBE, RMSE and K parameters, shown in Table 4, were each better than the parameters representing the factory calibrations.
Table 4.
Comparison of the Laboratory-based Calibration of Ov  versus Laboratory Measurements of Ov 
 Soil Type	Eqn.
Type	Size		R2	MBE		RMSE		K
 TDT	Linear	60	0.94	0.0	1.8	0.98
 Watermark	Logarithmic	7	0.94	0.0	1.1	0.98
 Table 5 displays the results of comparing the use of the laboratory-derived calibration equations with field-measurements of Ov.
For both sensors, applying the laboratory-derived equations to the field sensors' data yielded larger MBE, RMSE, and smaller K values than when compared to measured data at the laboratory.
With respect to the TDT sensor, the laboratory equations resulted in levels of accuracy that were very similar to the factory calibrations.
However, applying the soil-specific calibration equation developed in the laboratory to the Watermark sensor installed in the field resulted in an average underestimation of 4.3+5.0%.
Table 5.
Comparison of the Laboratory-based Calibration of Ov  versus Field Measurements of Ov 
 Soil Type	Location	Eqn.
Type	Size		R2	MBE		RMSE		K
 1	Linear	11	0.73	2.0	2.8	0.83
 TDT	2	Linear	11	0.83	1.8	2.6	0.90
 3	Linear	12	0.77	-1.8	3.1	0.89
 Watermark	Composite	Logarithmic	15	0.79	-4.3	5.0	0.73
 *One equation represented measurements from all field sensors.
The field-based calibration equations developed for both sensors, within the PWP to FC range of water contents, showed higher levels of accuracy than the
 factoryor laboratory-derived equations.
As shown in Table 6, the RMSE values were consistently low  for both sensors and errors well within the ideal statistical targets.
Table 6.
Comparison of the Field-based Calibration of Ov  versus Field Measurements of Ov.
Soil Type	Depth 	Location /	Eqn.
Type	Size		R2	MBE		RMSE		K
 1	Linear	11	0.73	0.0	1.9	0.91
 TDT	2	Linear	11	0.83	0.0	1.9	0.95
 3	Linear	12	0.74	0.0	2.4	0.93
 Watermark	Composite	Logarithmic	15	0.81	0.0	1.6	0.94
 *One equation represented measurements taken with all field sensors.
The different derived equations were applied to the field data from the TDT sensor in treatment 1, results are shown in Figure 1.
This treatment was fully irrigated.
It is assumed that right after irrigation the soil around the soil moisture sensors reached complete saturation.
Considering a porosity of 45%, the TDT's factory calibration measured levels of water content that were larger than porosity while the laboratoryand field-derived equations indicated complete saturation.
It is evident in Figure 1 that the TDT responded well to small amounts of rainfall , and all calibration equations resulted in water content levels similar to values derived from gravimetric field measurements.
Figure 1.
TDT soil water content sensor calibration curves for Treatment 1.
This research evaluated the performance of Watermark soil water potential and TDT soil water content sensors under laboratory and field conditions in a sandy clay loam soil.
Sensor measured soil water content values were compared with corresponding values derived from gravimetric samples.
Soil potential  values from the watermark were converted to volumetric soil water content for the evaluation.
Linear calibration equations were developed for the TDT sensor while a logarithmic calibration equation was developed for the Watermark sensor.
According to laboratory tests, the TDT's factory-recommended calibration performed very well with errors less than 1.2+3.9%.
In the case of the Watermark sensor, the factory-recommended equation, evaluated with measured soil water content from a corn irrigated field, in average overestimated soil water content by 11.2+12.6%.
Finally, field-derived calibration equations developed for both sensors resulted in higher accuracy than the factoryor laboratory-derived equations.
The resulting mean bias error  and root mean square error  for the TDT sensor was 1.8+2.6% and for the Watermark sensor -4.3+5.0%, respectively.
These results indicate that the TDT soil water content sensor was accurate and consistent in measuring soil moisture.
In the case of the watermark sensor the accuracy was less than expected.
However, more field data still are needed to further conclude on the accuracy and reliability of the watermark sensor.
NEBRASKA WATER POLICY TASK FORCE
 Ann Salomon Bleed Deputy Director Nebraska Department of Natural Resources Lincoln, Nebraska Voice:  471-0569 Fax:  471-2900 Email: ableed@dnr.state.ne.us
 In 2002 the Nebraska Legislature created a Water Policy Task Force to evaluate the effectiveness of and make recommendations on any needed changes to the law governing the integrated management of surface water and hydrologically connected ground water.
The Legislature also asked the Task Force to make recommendations on water transfers, leasing and banking and on how to address inequities between surface water and groundwater users.
The 49 Task Force members were appointed by Governor Johanns to represent specific interests as required by statute.
The first Task Force meeting took place on July 29, 2002; a total of eight full task force meetings were held prior to completion of Task Force work in December 2003.
A 14 member Task Force Executive Committee met 18 times over the course of the effort.
Interest in Executive Committee efforts was sufficiently strong that most of its meetings were heavily attended by other Task Force members.
These meetings were all advertised and open to the public.
A number of non-Task Force members also faithfully attended meetings and actively participated in the Task Force deliberations.
In addition subcommittees were formed to address: surface water transfers, groundwater transfers, funding, data requirements, equities between surface water and groundwater users, and presentation of the Task Force recommendations.
Consensus Based Decision Making
 The recommendations of the Water Policy Task Force are the result of a consensus-based decision-making process.
A consensus is the strongest form a group decision can take, because it is a settlement or solution that all participants in the decision making process accept.
The consensus by members of the Water Policy Task Force was built by identifying and exploring all parties' interests, and assembling a package agreement that satisfied these interests to the greatest extent possible.
Achieving consensus involved, but did not require, unanimous support by all Task Force members for all elements of the settlement.
In its consensus decisions, some parties strongly endorsed particular solutions for issues while others accepted them as workable settlements or compromises.
At the end of discussions and deliberations of the Water Policy Task Force, consensus was reached, and no one blocked the approval of the package.
In
 addition to the agreement package, some participants in the Water Policy Task Force wanted to have a section of the document where issues that need additional discussion and attention could be listed.
Some of these issues were discussed by the Task Force and others were mainly mentioned as items that need future attention.
Providing these comments, however, does not take away from the recommendation that the proposals be accepted by the Legislature as a package.
If any one piece is changed in substance or deleted, this could change any given Task Force member's willingness to support the package and break apart the consensus that was achieved by the Task Force.
The Water Policy Task Force presented its report to the Governor on schedule on December 18, 2003.
The Task Force recommends that the basic components of existing surface water and groundwater law be left in place, but that Nebraska adopt a stronger, more proactive approach to the integrated management of surface water and hydrologically connected groundwater.
Key goals of the Task Force recommendations were to address potential problems between groundwater and surface water users before conflicts arise and to manage the water resources of the State to sustain a balance between hydrologically connected water uses and water supplies.
"The Task Force recommendations represent a major step forward in addressing equitable management of Nebraska's interrelated groundwater and surface water; with this step we have really bitten the bullet."
 -Clayton Lukow, Task Force member
 "I was skeptical of the consensus process at first, but it worked very well.
The Task Force met its goal in developing a mandate for the future." Jim Meismer, Task Force member
 Key components of the Task Force Recommendations are that the State:
 Maintain the basic framework of the existing laws.
The Task Force, in formulating its recommendations, chose to work within the state's existing basic institutional and legal framework governing the use of surface and groundwater and its recommendations are intended to build and improve upon this framework.
Modify existing law to be more proactive and require certain management actions be taken by NDNR and the NRDs when a basin is determined to be over appropriated or fully appropriated.
Identify the Platte River Basin above Elm Creek, Nebraska as being over appropriated.
The Task Force recommends that the NDNR and NRDs develop a basin-wide plan that will guide the plans of individual NRDs that will incrementally reduce the difference between the present level of development and the fully appropriated level of development in that basin.
Provide adequate funding to develop a sound scientific basis for management decisions and fair implementation of the integrated management plans.
The Task Force believes that adequate funding is essential if the proposed program is to be successful both in avoiding such conflicts and in addressing current inequities between surface water and groundwater users.
Allow temporary and permanent transfers or leases of surface water and groundwater.
Key Provisions of the PROACTIVE PLAN
 NDNR and the NRDs will be required to make an annual determination of which basins, sub-basins or river reaches are fully appropriated and,
 If a basin is declared over appropriated or fully appropriated there shall be an immediate suspension of all new uses until the NDNR or the NRD decide more can be allowed.
In basins declared over appropriated or fully appropriated, NDNR and NRDs are required to jointly develop and implement an integrated surface water and groundwater management plan within 3 to 5 years of the determination.
One goal of the Integrated Management Plan shall be to manage all hydrologically connected groundwater and surface water to sustain a balance between water uses and water supplies so that the economic viability, social and environmental health, safety and welfare of the basin, sub-basin or reach can be achieved and maintained for both the near and long term.
The Integrated Management Plan may use a number of voluntary measures as well as the controls in current law, such as allocation of withdrawals, rotation of use, reduction of irrigated acres, and other measures.
Any disputes between the NDNR and NRDs over the development or implementation of the joint action plan will go to a dispute resolution process.
If the dispute is still unresolved, the disputed issues will be presented to a five member Interrelated Water Review Board, which will make the final decision on which components to put into the plan or how the plan shall be implemented.
The Board will consist of five members including the Governor or his or her appointee, one additional member of the Governor's choosing and three additional members appointed by the Governor from a list of at least six persons nominated by the Nebraska Natural Resources Commission.
Key Recommendations on SURFACE WATER TRANSFERS
 Transfers of water rights from one location to another will continue to be allowed.
In specified instances authorize NDNR to issue temporary and permanent permits that either change the purpose for which water is used or change from one type of permit to another.
No permanent transfers or changes are allowed if it involves a change to a different preference category.
Add safeguards to ensure changes in type of permits or changes in use will not adversely impact existing users.
Some of those include:
 Temporary transfers and changes are for a minimum of one year or a maximum of thirty years, with the possibility of renewal for another 30 years after the midpoint of the term of the transfer or change.
Temporary transfers will retain the same priority date as the original permit and shall revert to the original location and use at the end of the permit period.
Only the historic consumptive use can be transferred or changed to a new use.
Transfers for irrigation can be on an acre for acre basis.
The number of acres irrigated as a result of the transfer can be increased if:
 a) The applicant can show there is not an increase in consumptive use as a result of the increase in acres involved in the transfer, or b) In basins that are not over appropriated or fully appropriated, the increase in the number of acres irrigated is not more than 5% of the existing permit or greater than 10 acres, whichever is less.
Such increases must be on the same or an adjacent quarter section as the original permit.
Such increases in acreage can only be done once for any given permit.
If the transfer or change involves land served by an irrigation district, the district must approve the transfer or change.
Development of a banking system is not necessary at this time.
The development of a banking process should occur if and when there appears to be a need for such a system in the future.
Key Recommendations on SURFACE WATER ADJUDICATIONS
 Extend the period of allowable nonuse before cancellation without excuses from 3 years to 5 years.
If there are excusable reasons for nonuse, extend the allowable period of nonuse without cancellation from 10 up to 15 years.
Extend the period of allowable nonuse before cancellation when water unavailability is the reason from 10 years to up to 30 years or, upon petition by the appropriator, even longer if the permit is in a basin that has been determined to be over appropriated or fully appropriated and water is expected to be restored for use in accordance with an integrated management plan.
When an appropriation held in the name of an irrigation district or company is cancelled, the district shall have up to 5 years to assign the right to another use.
After adjudication, allow a rate of diversion to be greater than one cubic foot per second for 70 acres if the higher rate is necessary, using good husbandry, to meet a full crop irrigation requirement.
However, the total amount of the new diversion rate could not be greater than the total amount of the permitted rate before adjudication.
Key Recommendations on GROUNDWATER TRANSFERS
 Allow a Natural Resources District to require as a Management Area Control: 1) District approval of transfers of groundwater off the land where it is withdrawn, and 2) District approval of transfers of rights to use groundwater that result from District allocations imposed under the Groundwater Management and Protection Act.
Require the District to deny or condition the approval of transfers if needed to: 1) ensure consistency of the transfer with the purposes of the Management Area, 2) prevent adverse impacts on groundwater users, surface water appropriators, or the state's ability to comply with an interstate compact, decree, or agreement, and 3) otherwise protect public interest and prevent detriment to the public welfare.
Empower Natural Resources Districts to grant groundwater transfers off the overlying land to augment supplies in wetlands or natural streams for the purpose of benefiting fish or wildlife or producing other environmental benefits.
The determination of whether to grant a permit is to be based upon stated factors, including whether the use is a beneficial use, the availability of alternative supplies, negative effects of the proposed withdrawal, cumulative effects of the proposed withdrawal, and consistency with groundwater management plans and integrated management plans.
"The proposal is good for wildlife because it provides for greater flexibility in addressing their water needs." Dave Sands, Task Force member
 "It is a doable plan that recognizes everyone's interests; it would be a shame if we lose this opportunity.
Changes in the adjudication statutes will streamline the process and help both NDNR and the irrigators." -Al Schmidt, Task Force member
 The Task Force believes that water is so essential to agriculture, the environment, industry, human health and well being and to the overall economic viability of the state that leaving it to the fluctuation and uncertainty of the annual appropriations process seems unwise.
The Task Force recommends a dedicated funding source.
Funding needs include data gathering and organization, modeling/analysis, and local specialized studies necessary to ensure decisions are based on sound scientific data.
Without such data, the plans and regulations will not be acceptable to the public.
Funding is also needed to prepare and implement the plans.
Finally funding is needed to address the inequities between surface and groundwater users in over appropriated basins.
Inequities could be addressed by such activities as developing alternative water supplies and providing incentives for decreasing water use.
A Water Resource Trust Fund should be created to provide grants for interrelated water management activities.
Grants from the fund to local NRDs would require a 20% match from local funding.
$4.7 million will be necessary to fund the Task Force recommendations for planning/management and to address inequities between surface and groundwater users.
Also recommended for inclusion would be $6.3 million of current appropriations to the Nebraska Resources Development Fund, the Nebraska Soil and Water Conservation Fund and the Small Watersheds Flood Control Fund.
NRD groundwater management activities should be exempt from the statutory 2 1.2% budget lid placed on local subdivision budgets.
The NRDs also should be able to supplement the funds they can raise through their maximum 4 1.2 C property tax levy with an additional levy, imposed only in groundwater management areas.
Without additional funds, some NRDs will not be able to implement Integrated Management Plans.
"An historic effort that is starting to bear fruit." Jack Maddux, Task Force member
 "In all the 30+ years I have had the honor working on water isues, this has been one of the most intense 18 months, and hopefully one of the most successful undertakings in looking at water changes that need to come about." Dick Mercer, Task Force member
Nitrate leaching loss rates typically range from five to 10 pounds of nitrogen for every inch of water lost to deep percolation or drainage in Nebraska.
Leaching losses can be even larger in sandy soil, with values as large as 30 lb/ac for every inch of over-irrigation measured in a loamy sand soil.
Over-irrigation is very expensive and something that needs to be avoided.
Why do farmers apply manure to their crops?
Using manure as a fertilizer recycles nutrients.
Crops are fed to animals to meet their nutritional needs.
Any nutrients that are fed and not utilized by the animal are excreted in the manure.
Thus, manure contains many nutrients that crops need, so it makes a very good fertilizer.
It also has other benefits, including reduced erosion and runoff and aggregate stability in soils.
Now is the time to get the probes in the ground.
While other tasks may seem more pressing, early installation of sensors is important to ensure proper operation during the later critical growth phases.
Early installation helps to minimize root and leaf damage and makes it easy to get around the field with the pickup or ATV to install the equipment.
Keep in mind that the plants next to the probes are an integral part of the sensor and must be protected so they can represent all of the other plants in the field.
Do not install the sensors when the soil is wet and make as few footprints as you can to prevent soil compaction.
IRRIGATED SUNFLOWERS IN NORTHWEST KANSAS: PRODUCTIVITY AND CANOPY FORMATION
 Gerald J.
Seiler Research Botanist Sunflower & Plant Biology Research Unit USDA-ARS, Northern Crop Science Laboratory Fargo, North Dakota Voice: 701-239-1380 Fax: 701-2391346 Email: Gerald.Seiler@ARS.USDA.GOV
 Sunflower was grown in a three year study  at the KSU Northwest ResearchExtension Center at Colby, Kansas under a lateral move sprinkler irrigation system.
Irrigation capacities were limited to not more than 1 inch every 4, 8, or 12 days but were scheduled only as needed as determined with a weather-based water budget.
Achene  yields and oil yield generally plateaued at the medium irrigation level.
Dormant preseason irrigation increased achene yield and oil yield by 2% with most of this increase occurring in the extreme drought year, 2012.
The optimum harvest plant population for sunflower in this study in terms of achene yield and oil yield was approximately 19,000 to 20,000 plants/acre.
Sunflower is a crop of interest in the Ogallala Aquifer region because of its shorter growing season and thus lower overall irrigation needs.
Sunflowers are thought to better withstand short periods of crop water stress than corn and soybeans and the timing of critical sunflower water needs is also displaced from those of corn and soybeans.
Thus, sunflowers might be a good choice for marginal
 sprinkler systems and for situations where the crop types are split within the center pivot sprinkler land area.
Center pivot sprinkler irrigation , the predominant irrigation method in the Ogallala region, presents unique challenges when used for deficit irrigation.
Center pivot sprinkler irrigation cannot be effectively used to apply large amounts of water timed to a critical growth stage as can be done with surface irrigation methods.
The CP systems also cannot efficiently use small frequent events to alleviate water stress as is the case with subsurface drip irrigation.
Thus with CP systems, it is important that available soil water in storage be correctly managed temporally in terms of additions and withdrawals so that best crop production can be achieved both economically and water-wise.
Three easy ways to control irrigation water additions are irrigation capacity, preseason management, and the season initiation date.
Withdrawals can be partially managed by plant population.
This study examined sunflower production using the three methods of controlling irrigation additions for three different targeted plant populations.
The study was conducted from 2009 through 2012 at the KSU Northwest Research-Extension Center at Colby, Kansas under a lateral move sprinkler irrigation system.
However, data from 2011 is excluded due to a devastating hail storm that destroyed the crop.
Key agronomic characteristics of the annual tests are shown in Table 1.
Table 1.
Agronomic characteristics of an irrigated sunflower study conducted at the KSU Northwest Research-Extension Center, Colby, Kansas, 2009-2012.
Data from 2011 are excluded due to devastating hail storm.
Characteristic	2009	2010	2012
 Hybrid	Triumph S671	Triumph S671	Triumph S671
 Planting date	June 18	June 16	June 13
 Emergence date	June 25	June 24	June 26
 Harvest date	October 16	October 13	October 8
 Rainfall, emergence to maturity 	9.89	7.32	5.25
 Preseason irrigation 	5.0	5.0	9.2
 First seasonal irrigation	July 27	July 25	July 25
 Last seasonal irrigation	September 15	September 15	September 23
 Whole plot treatments were sprinkler irrigation capacities of 1 inch every 4, 8, or 12 days as limited by ET-based water budget irrigation scheduling.
An additional whole plot irrigation factor was the addition or no addition of dormant preseason irrigation resulting in a total of 6 different irrigation treatments.
The target preseason irrigation amount for those plots receiving it was 5 inches, but in 2012 a total of 9.2 inches of preseason irrigation was applied due to an application error.
Three targeted plant populations 18,000, 23,000, or 28,000 plants/acre were superimposed on the whole plots for a grand total of 108 subplots.
Irrigation amounts were 1 inch applied as needed, but limited by the imposed capacity and the water budget irrigation schedule.
The whole plots  were in a randomized complete block  design.
Soil water was measured periodically in each plot each crop season with a neutron probe to a depth of 8 feet in one foot increments.
Crop water use was calculated as the sum of changes in soil water between emergence and physiological maturity, precipitation and irrigation amount.
Crop water productivity  was calculated as the achene yield in lbs/acre divided by the total crop water use in inches.
At R6 development stage and to maturity , sunflower achene moisture content, dry mass and oil content were measured by collecting six achenes from each of five representative plants, semi-weekly.
At maturity, sunflower heads were hand harvested from a representative sample area and threshed for yield and yield component determinations.
Leaf area index  was quantified, approximately bi-weekly, by a non-destructive light transmission technique.
Three sets of four belowcanopy measurements were each referenced to an above-canopy measurement, minimizing sensor exposure to direct  irradiance.
Readings were screened against apparent transmittance ratios exceeding 1 using the manufacturer's software, FV2000.
An inverse solution to a model of light transmission through a vegetative canopy, provided by the manufacturer, was used to quantify apparent LAI.
Growing degree days  were calculated from daily temperature extremes  recorded at the NWREC weather station, using a mercury thermometer.
GDD = Tmax-Tmin Tb
 Upper and lower limits to temperature extremes were 34 C and C , respectively.
Cumulative GDD  was computed by summation of GDD, commencing from planting date.
Statistical analysis utilized analysis of variance  and analysis of covariance.
Repeated measure of LAI and maximum LAI observed in a year were analyzed by ANOV, using Proc GLM from SAS Institute.
Seasonal trends in LAI and were analyzed by ANCOV using third order linear terms of cGDD or days after planting  as covariates.
The crop year 2009 was very cool and wet and irrigation needs were low.
In-season irrigation amounts for the 1 inch every 4 and 8 days treatments were 7.68, 6.72, and 4.80 inches, respectively.
During the period April through October every month had above normal precipitation and between crop emergence and crop maturity the total precipitation was 9.89 inches.
The early portion of the crop year 2010 was wet and irrigation needs were lower than normal.
However, later in season, it was extremely dry with only 1.08 inches of precipitation occurring between August 4 and crop maturity on October 11.
Precipitation during the sunflower growing period totaled 7.32 inches.
In-season irrigation amounts were 11.52, 6.72, and 4.8 inches for the irrigation capacities limited to 1 inch/4 days, 1 inch/8 days, and 1 inch/12 days, respectively.
The 2010 sunflower irrigation amounts appear to be approximately 1 inch less than normal as estimated from long term  irrigation scheduling simulations conducted at Colby, Kansas.
Extreme drought conditions existed for all of 2012 and only 5.25 inches of precipitation occurred during the sunflower growing period.
Additionally, temperatures of 100F or greater occurred on 20 days between June 26 and August 15.
Crop establishment may have been negatively affected by excessively hot temperatures  that occurred for the entire period between planting and emergence even though small amounts of irrigation kept sufficient amounts of water in the seed zone.
Sunflower plant populations at harvest in 2012 averaged approximately 75% of levels that occurred in 2009 and 2010.
In-season irrigation amounts were 13.94, 8.18, and 6.26 inches for the irrigation capacities limited to 1 inch/4 days, 1 inch/8 days and 1 inch/12 days, respectively.
Summarizing the weather conditions, the crop year 2009 was cooler and wetter than normal, the crop year 2010 was approximately normal though a severe drought began in early August, and the crop year 2012 was extremely hot and dry.
Crop Yields and Yield Components
 The addition of dormant preseason irrigation did not significantly increase yields in any of the three years , but did increase achene yield and oil yield by 2%, when all years were analyzed together.
Most of the increase in yield for preseason irrigation occurred in the extreme drought year, 2012.
Preseason irrigation did significantly increase heads/plant in 2009 and harvest plant population in 2010, but these differences were only about 3% greater.
There were no statistically significant differences in yield attributable to irrigation capacity in 2009 and 2012, but increased irrigation capacity did increase achene yield in 2010.
Increased irrigation capacity tended to numerically increase achene and oil yield in all three years up through the 1 inch/8 day irrigation capacity but tended to have less or no response above that level..
Achene yields were lower in 2010 than in 2009 and 2012, but still were towards the upper range of yields for the region.
There were no plant population effects on achene yield in 2009, but increased plant population decreased achene yield in 2010 and increased achene yield in 2012.
The difference between 2010 and 2012 responses is probably related to the differences in harvest plant populations between the two years.
As indicated in earlier section, crop establishment was poor in 2012.
Harvest plant populations in 2010 averaged 19,263, 23,426, and 26,257 plants/acre for the three respective targets as compared to the much lower 2012 values of 14,452, 17,530, and 19,781 plants/acre.
Increasing plant population significantly decreased achenes/head in both 2009 and 2010 but had no consistent effect in 2012, once again probably because harvest plant populations were so low.
Increasing plant population significantly decreased achene mass and significantly increased achene oil content  in all three years.
Within a given year average differences in oil content ranged from 1 to 2% as affected by plant population.
Harvest plant populations above 19,000 to 20,000 plants/acre resulted in reduced achene yields and oil yields, but oil content was greatest at the greatest plant population in all three years.
Crop Water Use and Water Productivity
 In-season crop water use was significantly increased by increased irrigation in all three years.
However, crop water productivity  was significantly reduced by increased irrigation in all three years.
Irrigation amounts ranged from 4.80 to 7.68 inches in 2009, 4.80 to 11.52 inches in 2010, and 6.26 to 13.94 inches in 2012.
Soil water depletion decreased with irrigation capacity.
Figure 1.
Achene yield and oil yield as related to irrigation amount and total crop water use in a sprinkler irrigated sunflower study, KSU Northwest Research-Extension Center, Colby, Kansas, 2009-2012.
Note: Irrigation responses in blue unbroken lines and crop water use responses in green dashed lines.
Figure 2.
Achene yield, oil content, and oil yield as related to harvest plant population in a sprinkler irrigated sunflower study, KSU Northwest Research-Extension Center, Colby, Kansas, 2009-2012.
Table 2.
Summary of sunflower yield components and water use parameters for a sprinkler irrigated study, 2009, KSU Northwest Research-Extension Center, Colby Kansas.
Irrigation	capacity	Preseason	irrigation	population		plant		Yield	population	plant		/plant	Heads Achenes	/head	Achene	Mass		Achene	Oil%		Water	use	Productivity		Water
 18	3266	16262	0.94	2114	46.6	45.6	21.94	149
 23	3324	20183	0.92	2043	40.2	46.2	22.49	148
 28	3109	23813	0.93	1720	37.2	46.6	22.10	141
 1 in/4 d	Mean	3233	20086	0.93	1959	41.3	46.2	22.18	146
 	18	3229	16553	0.94	2155	44.3	45.7	22.06	146
 23	3326	20328	0.93	1919	42.0	46.3	22.24	150
 28	3246	22942	0.99	1728	39.3	46.8	22.96	141
 Mean	3267	19941	0.95	1934	41.9	46.2	22.42	146
 Mean 1 inch/4 days	3250	20013	0.94	1947	41.6	46.2	22.30 C	146 b
 18	3376	16698	0.95	2259	43.4	45.7	21.08	161
 23	3189	20183	0.95	1893	40.4	46.0	21.29	150
 28	3081	22506	0.96	1790	37.5	46.5	21.89	141
 1 in/8 d	Mean	3215	19796	0.95	1981	40.4	46.1	21.42	151
 	18	3427	16553	0.99	2214	42.8	45.0	21.56	159
 23	3208	19312	0.96	1934	40.6	46.1	21.21	151
 28	3332	22506	1.01	1766	38.4	46.6	22.01	152
 Mean	3322	19457	0.99	1971	40.6	45.9	21.60	154
 Mean 1 inch/8 days	3269	19626	0.97	1976	40.5	46.0	21.51 b	152 a
 18	3158	16408	0.93	2198	42.8	45.7	20.38	155
 23	3186	19457	0.96	1923	40.3	45.9	20.75	154
 28	3168	24103	0.91	1728	38.3	46.5	20.75	153
 1 in/12 d	Mean	3171	19989	0.93	1950	40.5	46.0	20.63	154
 	18	3100	16117	0.97	2127	42.3	46.1	20.36	152
 23	3345	19166	0.96	1985	41.9	45.6	20.41	164
 28	3279	23522	0.94	1758	38.4	46.2	20.68	159
 Mean	3241	19602	0.96	1957	40.8	45.9	20.48	158
 Mean 1 inch/12 days	3206	19796	0.95	1953	40.7	46.0	20.56 a	156 a
 Study-Wide Mean	3242	19812	0.95	1959	40.9	46.0	21.45	151
 Preseason	None	3206	19957	0.94 a	1963	40.7	46.1	21.41	150
 Irrigation	5 inches	3277	19667	0.97 b	1954	41.1	46.0	21.50	153
 18	3260	16432 a	0.95	2178 a	43.7 a	45.6 C	21.23	154 a
 population 	23	3263	19771 b	0.95	1950 b	40.9 b	46.0 b	21.40	153 a
 28	3203	23232 C	0.96	1748 C	38.2 C	46.5 a	21.73	148 b
 Shaded items within a column are significantly different at P<0.05 when followed by a different lower-cased letter.
Table 3.
Summary of sunflower yield components and water use parameters for a sprinkler irrigated study, 2010, KSU Northwest Research-Extension Center, Colby Kansas.
Irrigation	capacity	Preseason	irrigation	population		plant		Yield	population	plant		/plant	Heads Achenes	/head	Achene	Mass		Achene	Oil%	 	Water	use	Productivity	Water
 18	3172	20038	0.94	1916	40.4	44.2	22.69	141
 23	2919	23668	0.89	1631	38.6	44.7	22.74	128
 28	2946	27007	0.85	1570	37.4	45.0	23.32	127
 1 in/4 d	Mean	3012	23571	0.90	1706	38.8	44.6	22.92	132
 	18	3000	19166	0.93	1845	42.3	43.8	20.99	143
 23	3062	23958	0.95	1646	37.3	44.7	21.15	146
 28	2987	25265	0.95	1597	36.1	45.3	20.72	145
 Mean	3172	20038	0.94	1916	40.4	44.2	22.69	141
 Mean 1 inch/4 days	3014 a	23184	0.92	1701	38.7	44.6 a	21.93 a	138 C
 18	3043	19602	0.92	1893	41.0	44.5	19.63	157
 23	2989	23377	0.98	1668	36.1	44.6	20.01	150
 28	3004	25700	0.97	1563	35.7	45.3	19.36	156
 1 in/8 d	Mean	3012	22893	0.96	1708	37.6	44.8	19.66	154
 	18	3091	18440	0.98	1912	40.6	44.3	19.01	164
 23	2892	23087	0.93	1647	37.2	44.7	19.31	151
 28	2951	25410	0.98	1506	36.3	45.3	19.58	152
 Mean	3043	19602	0.92	1893	41.0	44.5	19.63	157
 Mean 1 inch/8 days	2995 a	22603	0.96	1698	37.8	44.8 a	19.48 b	155 b
 18	2983	19312	0.96	1868	39.4	43.2	17.25	175
 23	2886	23522	0.96	1715	34.4	43.6	16.85	175
 28	2705	27588	0.88	1480	34.4	44.0	17.10	159
 1 in/12 d	Mean	2858	23474	0.93	1688	36.1	43.6	17.07	170
 	18	3059	19021	0.95	1983	39.0	43.7	18.12	170
 23	2831	22942	0.94	1613	37.0	43.6	17.99	158
 28	2833	26572	0.91	1511	35.5	44.1	17.67	162
 Mean	2908	22845	0.93	1702	37.2	43.8	17.93	163
 Mean 1 inch/12 days	2883 b	23159	0.93	1695	36.6	43.7 b	17.50 C	167 a
 Study-Wide Mean	2964	22982	0.94	1698	37.7	44.4	19.64	153
 Preseason	None	2961	23313 a	0.93	1700	37.5	44.3	19.88	152
 Irrigation	5 inches	2967	22651 b	0.95	1695	37.9	44.4	19.39	155
 Target plant	18	3058 a	19263 C	0.94	1903 a	40.5 a	43.9 C	19.61	158 a
 population	23	2930 b	23426 b	0.94	1653 b	36.8 b	44.3 b	19.67	151 b
 	28	2904 b	26257 a	0.92	1538 C	35.9 b	44.8 a	19.62	150 b
 Shaded items within a column are significantly different at P<0.05 when followed by a different lower-cased letter.
Table 4.
Summary of sunflower yield components and water use parameters for a sprinkler irrigated study, 2012, KSU Northwest Research-Extension Center, Colby Kansas.
Irrigation	capacity	Preseason	irrigation	population		plant		Yield	population	plant		/plant	Heads Achenes	/head	Achene	Mass		Achene	Oil%		Water	use	Productivity		Water
 18	3145	14956	1.00	1555	61.6	39.4	24.82	126
 23	3265	16988	0.99	1497	59.6	39.8	25.89	126
 28	3315	21635	0.87	1750	52.9	41.6	24.86	133
 1 in/4 d	Mean	3242	17860	0.95	1601	58.0	40.3	25.19	129
 	18	3183	14985	1.00	1666	58.1	39.1	25.33	126
 23	3448	17424	0.99	1572	58.2	40.3	25.64	134
 28	3662	19689	0.99	1599	53.7	40.3	26.79	137
 Mean	3431	17366	0.99	1612	56.6	39.9	25.92	132
 Mean 1 inch/4 days	3328	17635	0.97	1606	57.4	40.1	25.52	130 C
 18	3191	13939	1.00	1717	62.6	38.9	20.45	157
 23	3160	16698	0.99	1494	58.8	39.6	20.23	156
 28	3423	19747	1.00	1439	55.3	40.8	20.80	165
 1 in/8 d	Mean	3258	16795	1.00	1550	58.9	39.7	20.49	159
 	18	3148	14375	1.00	1544	65.2	39.2	18.61	172
 23	3310	17569	0.98	1495	59.4	40.1	18.37	181
 28	3480	19747	1.00	1414	58.0	41.5	18.75	187
 Mean	3313	17230	0.99	1484	60.9	40.3	18.58	180
 Mean 1 inch/8 days	3286	17013	0.99	1517	59.9	40.0	19.54	169 b
 18	3237	14462	1.00	1610	63.8	39.1	17.41	188
 23	3126	17772	0.98	1280	64.9	39.9	17.18	183
 28	3121	18121	1.00	1490	54.5	40.0	17.43	180
 1 in/12 d	Mean	3161	16785	0.99	1460	61.0	39.7	17.34	183
 	18	3074	14084	1.00	1440	70.1	38.4	18.52	168
 23	3487	18992	0.99	1478	57.5	39.8	18.47	191
 28	3417	19457	0.97	1410	59.3	40.5	18.47	186
 Mean	3316	17424	0.99	1440	62.6	39.5	18.49	181
 Mean 1 inch/12 days	3244	17125	0.99	1450	61.9	39.6	17.95	182 a
 Study-Wide Mean	3286	17251	0.99	1525	59.7	39.9	20.99	161
 Preseason	None	3224	17168	0.98	1541	59.2	39.9	21.22	156
 Irrigation	9.2 inches	3350	17337	0.99	1508	60.2	39.9	20.75	166
 Target plant	18	3160 b	14452 C	1.00	1586	63.7 a	39.0 C	20.83	156
 population	23	3294 ab	17530 b	0.99	1472	59.7 b	39.9 b	21.01	161
 28	3404 a	19781 a	0.97	1515	55.7 C	40.8 a	21.13	165
 Shaded items within a column are significantly different at P<0.05 when followed by a different lower-cased letter.
Seasonal changes in sunflower canopy are shown in Figure 3.
Preseason irrigation amounts of 9" resulted in greater leaf area from mid-vegetative growth through mid-seed fill in 2012.
Canopy formation and senescence occurred relatively earlier in 2010 than 2009 and 2012, which were similar.
Canopy formation was greatest in 2010 and least in 2012.
Figure 3.
Seasonal trends in canopy formation and senescence are shown in relation to days after planting for a sprinkler irrigated sunflower study, KSU Northwest Research-Extension Center, Colby, Kansas, 2009-2012.
Note that symbols represent field observations and lines represent a trend model.
Preseason irrigation effects  were detected in 2012.
Achene water content, oil content, and dry mass changes during the season are shown in Figure 4.
Achene water contents were greatest for the initial sampling dates and declined throughout the seed fill period.
In 2010, achene water content was slightly greater for the largest irrigation capacity.
Oil content of achenes increased from the R6 to R8 development stage, remaining consistent through maturity; slightly greater oil contents were observed for the smallest irrigation capacity in 2010.
Oil contents from late-season samples appeared similar, though the harvest samples from a larger sampling area  indicate greatest oil content in 2009
  and smallest oil content in 2012.
The change in achene mass in 2012, relative to the initial sampling date, was approximately twice that observed in 2009 and 2010; this likely reflected effects of the reduced stands discussed earlier.
Preseason irrigation resulted in larger achenes in 2009, but smaller achenes in 2012, likely reflecting differences in achenes per head.
Cumulative growing degree days appears to provide an inconsistent measure of time relative to onset and completion of the yield formation periods, as indicated by the staggered onset and duration of sampling intervals over the three growing seasons.
Cumulative Growing Degree Days 
 Figure 4.
Trends in sunflower achene water content , oil content  and dry achene mass  are shown in relation to cumulative growing degree days from planting.
This sprinkler irrigated sunflower study was conducted at KSU Northwest Research-Extension Center, Colby, Kansas, 2009-2012.
Preseason irrigation  and irrigation capacity  effects, which were detected in the study, are indicated.
Sunflower was grown under sprinkler irrigation in Colby, Kansas for three very different crop years.
Irrigation capacities were limited to not more than 1 inch every 4, 8, or 12 days but irrigation events were scheduled only as needed as determined with a weather-based water budget.
Seasonal trends indicated earlier canopy formation, greatest canopy extent, and earliest senescence in 2010; least canopy extent developed in 2012.
Seasonal trends were similar for achene water content , oil content, and achene mass.
Achene yield was only statistically increased by irrigation in 2010, but tended to increase numerically up through the medium irrigation level  in all three years.
Similarly, oil yield plateaued at the medium irrigation level.
Dormant preseason irrigation increased achene yield and oil yield by 2%.
The optimum harvest plant population for sunflower in this study in terms of achene yield and oil yield was approximately 19,000 to 20,000 plants/acre.
This work was partially supported by the Ogallala Aquifer Program administered by the USDAARS and also by the National Sunflower Association.
i Mention of tradenames is for informational purposes only and does not constitute endorsement by the authors or by the institutions they serve.
Dealing with Iron and Other Micro-Irrigation Plugging Problems1
 Tom Obreza, Ed Hanlon, and Mongi Zekri2
 This publication targets agricultural and horticultural producers, homeowners, Extension agents, industry or governmental staff, land managers, other professionals, youth and interested citizens.
This publication is part of a series of documents dealing with proper installation, maintenance, and operation of micro-irrigation systems.
These systems save water, reduce the potential for offsite loss of nutrients and agrochemicals, and directly contribute to yield and quality of many commercially-produced citrus and vegetables in Florida.
The objective of this document is to describe problems with emitter plugging and discuss management strategies to overcome and correct causes of plugging in micro-irrigation systems.
This publication focuses, in particular, on iron scaling, documenting recent successes in treating this common problem in Florida.
Information in this document should be of interest to vegetable and citrus producers, fertilizer and irrigation equipment dealers, Certified Crop Advisors, and other parties involved in the operation of micro-irrigation.
Causes of Micro-Irrigation Plugging Particulate Matter
 The primary cause of emitter plugging is foreign material, such as particulate matter  from soil and/or the water source.
These small inorganic particles may pass through filters and cause plugging at the microemitter.
If the size of the particles exceeds the diameter of the emitter orifice, or if smaller particles stick together to form a much larger mass, then emitter plugging is likely.
Filters are the primary defense against particles entering the micro-irrigation system.
The most economical solution is to buy the best filtration system you can afford, and then maintain that system according to the manufacturer's instructions.
Screen filters are the first line of defense for removing particles from the water source BEFORE particles are distributed throughout the irrigation system.
This type of filter is designed to trap predominantly inorganic materials and will clog if elevated levels of organic materials enter the upstream side of the filter.
Thus, if the water source has both particulate matter and organic materials, screen filters should be placed in the system after filtration of the organic constituents.
This multiple filter arrangement is often recommended for surficial water
 2.
Tom Obreza, senior associate dean for Extension and professor, Office of Dean for Extension and Florida Cooperative Extension Office; Ed Hanlon, professor emeritus, Department of Soil and Water Sciences; and Mongi Zekri, multi-county citrus Extension agent, UF/IFAS Extension Hendry County; UF/IFAS Extension, Gainesville, FL 32611.
Filtration can greatly reduce plugging problems; however, algae and other small plants and animals that live in, or seek, the water can still pass through the filters.
Microbes that pass through the filters can continue to grow inside the system.
Some organisms can build up in numbers, often forming clumps within the tubing at the point where water enters the emitter.
Additionally, arthropods like ants may enter the emitter from the outside when the irrigation system is idle and become stuck in the tubing as they seek water, particularly when the system is turned on.
The least expensive treatment to control living organisms is injecting free chlorine into the micro-irrigation system to obtain 1 part per million  of free chlorine at the end of the system.
To be effective, the amount of chlorine needed to achieve 1 ppm concentration at the far end should be injected EACH time the irrigation system is used.
This technique is called continuous chlorine injection.
The intent is to continuously introduce free chlorine at a relatively low concentration to prevent organic growth in the irrigation system.
Super-chlorination-th so-called "shock" treatment-does not require continuous free chlorine injection because it is usually done on a weekly basis.
With this method, a much higher concentration of free chlorine is injected so that as much as 500 ppm free
 Scaling may be caused by calcium or iron.
These elements, usually associated with limestone or iron oxides, are often dissolved in the irrigation water source.
Using this water for irrigation without treatment for calcium or iron can lead to scaling and ultimately plug the emitters or even irrigation system pipes.
CALCIUM SCALING AND TREATMENT
 Calcium is dissolved in water originating from groundwater aquifers, which are formed from limestone.
Once brought to the surface, the calcium enters the irrigation system and may precipitate in the tubing or around and in emitters as calcium carbonate if the concentration is high enough or if the water pH changes.
Preventing calcium from forming scale within the irrigation system is preferable to treating scale that has already formed.
Calcium scale may be easily prevented with the injection of an appropriate concentration of acid, allowing the calcium to remain in solution and to exit the irrigation system harmlessly.
IRON SCALING AND TREATMENT
 Scaling caused by iron is more difficult to deal with than scale formed by calcium, and shall be explored in some detail.
Iron is abundant throughout the earth, composing up to 5% of the earth's crust.
Hence, iron compounds are common.
Given Florida's sandy soils and geologic time, iron compounds move through the soil and enter the shallow groundwater.
Much of the rust or brownish red color found in many Florida soils is due to the presence of iron oxides and related compounds.
Irrigating with ironrich water may result in staining, not only of equipment, but also on foliage in contact with the water source.
Within the irrigation system itself, iron scaling can reduce flow in pipes and clog emitters.
When iron concentrations exceed
 0.3 ppm, staining and scaling conditions exist.
A review of groundwater concentrations in southwest Florida indicates that iron concentrations range from 0.1 to 7.0 ppm.
Iron chemistry is complex because ionic Fe can exist in two forms.
The reduced cationic form, exhibiting two plus charges, is the ferrous form.
The ferrous form may be introduced into the irrigation system with the source water because this form of iron is soluble.
Chemical conditions may change within the irrigation system itself, resulting in formation of a highly insoluble oxidized form with three positive charges.
It is the ferric form that causes scale within the irrigation system.
The maximum amount of ferric iron that can be retained in solution as ferric oxide is 0.6 parts per billion , considerably less than the iron concentrations reported above  found in southwest Florida groundwater.
The conversion from ferrous  to ferric  form is affected by several chemical parameters, the most important of which are oxygen content and water pH.
The ferrous form results when oxygen content of the water is low, such as in groundwater of many aquifers.
When water is pumped from these locations into the irrigation system, it moves from an anaerobic condition to an aerobic condition with much higher levels of oxygen.
When the ferrous form is exposed to oxygen, the result is a rapid conversion to the ferric form, with subsequent precipitation.
The pH of the water has an effect on the rate of this conversion.
Since many of the aquifers in Florida are limestone, the initial pH of water pumped from those aquifers is alkaline, often at or more than 8.0.
Scale at this pH can form quickly once sufficient oxygen is present.
Usually, sufficient oxygen is usually introduced throughout the irrigation system, and scale forms within the system, especially at or near oxygen sources such as leaking pipes or emitters.
The first step in controlling scaling of any type is to have field and laboratory tests completed on the irrigation water source.
If a Mobile Irrigation Lab, typically associated with the local Soil and Water Conservation District, is operating in your area, lab personnel can test your water for plugging potential.
Laboratory and field measurements are helpful in determining the plugging hazard associated with the water source.
This document shall primarily focus on problems with iron only.
After identifying that the irrigation water source
 does contain sufficient iron to cause scaling , several preventative strategies are available.
Use of a Sedimentation Pond
 A sedimentation pond allows the oxygenation of the source water, and hence the precipitation of ferric iron, before the water is introduced into the irrigation system.
Well water is pumped into a pond allowing equilibration of the water with the atmosphere.
As oxygen enters the water, ferric iron is formed and precipitates.
Factors affecting the time needed for precipitation include water temperature, wind speed, depth and mixing of the water, aeration and wave action.
A good first estimate for the minimum time required is several hours, especially if the water is aerated.
After the iron precipitates, water is removed from the pond and conveyed into the irrigation system for subsequent filtering and distribution.
Advantages of a Sedimentation Pond
 A sedimentation pond permits the removal of iron from the system without any chemical treatment, leaving behind iron scale in the pond itself.
Since most Florida aquifers are composed of limestone, initial water pH from these aquifers is quite high.
The sedimentation pond, in addition to oxygenating the water to remove ferric iron, also allows time for the equilibration of the water with Earth's atmosphere and the dissipation of carbonates and bicarbonates.
As the carbonates and bicarbonates dissipate from the water source, the initial high water pH is lowered 1 to 2 pH units, improving water quality for irrigation.
Disadvantages of a Sedimentation Pond
 Unfortunately, while the sedimentation pond improves water quality with respect to both iron and the high pH caused by carbonates, it is an open water source.
The pond is likely to introduce organic materials and living organisms into the irrigation system.
A second disadvantage is that an additional pumpage is required between the pond and the irrigation system.
The introduction of water to the pond from the well source and its subsequent withdrawal for use in irrigation system must be considered when designing the size of the sedimentation pond to minimize turbidity and the introduction of grit into the irrigation system.
A sedimentation pond requires two pumps as described above.
Additionally, a properly sized sedimentation pond
 requires sufficient land surface, which may take a substantial tract of land out of production.
Oxygenation and Filter Systems
 The next alternative in iron scaling prevention is much more high tech.
This system includes a gas chlorinator, hydro-cyclone filters, sand media filters, and backup disk filters.
The gas chlorinator  introduces chlorine gas into the water system, which causes the iron to oxidize.
The filtering system traps the scale that has formed before the scale is introduced into the remaining portions of the irrigation system.
Figure 1.
Diagram of a vacuum-type gas chlorinator used to treat irrigation water.
Advantages of Oxygenation and Filtration
 Chlorine gas is relatively inexpensive.
Using chlorine to oxidize iron from ferrous to ferric also provides active chlorine within the irrigation system to control microbial activity.
This system also requires considerably less land area compared with the sedimentation pond system.
Disadvantages of Oxygenation and Filtration
 Safety precautions for workers and equipment must be in place and followed correctly when handling chlorine gas.
Because sand media filters are normally used to remove the scale, they require frequent backwashing.
Irrigation Line Maintenance Chemicals
 In situations where iron has already formed, or as a preventive measure in situations where iron scale has been problematic for other users of the same water source, scale can be controlled by appropriate injection rates of chemicals, which can be grouped according to their reactions.
Inorganic acids react quickly with water and solids to help prevent scale formation.
The reaction is partially controlled by regulating the strength of the acid through dilution with water.
In some cases, these acids may also supply nutrients after they have reacted in the irrigation system.
Chelating agents are organic compounds that sequester or occlude iron from further reactions by binding sufficiently tightly to the iron, removing it either as a free agent in solution or as scale.
The iron is held by the chelating agent and the combined molecule flows out of the irrigation system.
In some cases, the iron and other elements chelated by this group of chemicals may later serve as a nutrient source for the crop.
The last chemical group is of the reducing agents.
These chemicals cause ferric iron to revert to ferrous iron, greatly increasing the solubility of the iron, which may then exit the irrigation system in solution.
This group of chemicals can be quite reactive and yet can be handled and stored safely for agricultural purposes.
Some of these chemicals are the byproducts of industrial processes, contributing to a so-called green re-use in the treatment of scale.
SCALE REMOVAL FROM IRRIGATION LINES
 In addition to preventing iron scaling, many of these chemicals may help remove iron scale from irrigation tubing.
The irrigation manager should understand that preventing scaling from forming in the first place is usually much more effective than trying to restore an iron scaleimpaired system.
Research using selected chemicals indicates that some chemicals are much more effective at removing the iron scale from tubing than others.
Figure 2.
Efficacy of selected chemicals in removing iron scale from irrigation tubing.
Sodium hydrosulfite proved to be quite effective at removing scale.
This reducing agent is also used to bleach paper and can present handling and safety issues for agricultural use that should be built into the farm safety program.
However, this chemical is readily available from many sources, and proved to be the best chemical for removing scale in this study.
The next best chemical was a chelating agent, citric acid, which is readily available from many sources and does not pose the same level of handling problems as sodium hydrosulfite.
The discharge water from systems treated with sodium hydrosulfite, a reducing agent, and citric acid, a chelating agent, turns different colors as scale is being removed from the system.
The water from the sodium hydrosulfite contains ferrous iron, which is relatively colorless, while the chelated iron from the citric acid treatment remains in the ferric state, imparting a rust or reddish brown color to the flush water.
Figure 3.
Flush water from treatment of scale using sodium hydrosulfite  and citric acid.
Sulfuric acid is a strong inorganic acid, often produced as a byproduct of many industrial processes.
While sulfuric acid was the least effective chemical in this study, sulfuric acid is relatively inexpensive and can be safely handled with the proper equipment.
As with many of the other chemicals,
 spill kits must be available and personal safety gear must be worn when handling sulfuric acid.
Sulfuric acid may be most useful in situations where it is injected frequently in low concentrations.
This acid may also be helpful in controlling microbial activity within the irrigation system through the appropriate regulation of water pH.
In field trials, iron scale was removed to a greater or lesser degree based upon the selected chemical and the concentration with which that chemical was introduced into the scale-affected tubing.
The reddish brown iron scale  decreases as the concentration of the selected chemical is increased.
Any one of the three chemicals at the higher treatment concentrations successfully treated this moderate scale problem.
Figure 4.
Treatment of iron scale formed within irrigation tubing with sulfuric acid, citric acid, and a proprietary product at selected concentrations.
Iron scale on the inside of the tubing is evident by the reddish brown/rust color.
POTENTIAL PROBLEMS FOR TREATING EXISTING IRON SCALE IRRIGATION SYSTEMS
 When any of these chemicals are introduced into a system that has been affected by iron, scale on the tubing walls may be removed.
However, it is likely that some scale may flake off as a result of the treatment process, rather than being completely dissolved.
The resulting iron scale flakes may in turn cause plugging at the emitter as the small particles build up.
After flushing, the irrigation system should be treated with the desired chemical concentration, letting the system sit idle for at least one day.
This technique gives the chemical
 time to react with the iron scale, and yet does not move the iron scale particles to the emitters, preventing possible clogging of the emitters.
Before using this system to irrigate, a second flush of the system will move iron scale particles out of the system and not adversely affect the emitters.
USING SCALE-MONITORING DEVICES TO EVALUATE CLEANING
 A scale-monitoring device is a clean, non-scaled surface like a standard glass microscope slide within a PVC coupling  or short section of new tubing  that is spliced into an irrigation lateral line.
These devices may be installed across the irrigation system network, from laterals close to the pump to those at the far end of the system.
After installation, the irrigation system should be operated normally for several weeks or months, followed by periodic inspection of the devices for new scale deposition.
When trying a new water treatment chemical, leave untreated at least one irrigation zone that draws from the same water source as the treated zones, and install scale monitoring devices in each.
After a 4to 6-week trial period of irrigation in treated and untreated zones, examine the scale-monitoring devices to see if less scale was deposited in the zone where the water treatment chemical was used.
Figure 5.
A 3/4-inch PVC coupling found in plumbing-supply stores serves well as in-line glass slide holder.
Observing the amount, type, and rate of scale deposition occurring on a clean side  can help determine the scaling potential of the irrigation water and the effect of injected scale-inhibiting chemicals.
Figure 6.
A short section of new plastic tubing "inserted" into an irrigation lateral can serve as a scaling indicator.
After sufficient water has passed through the line, the insert can be removed and cut open to observe newly-deposited scale.
The amount, type, and rate of scale deposition occurring on the tubing wall can help determine the scaling potential of the irrigation water and the effect of injected scale-inhibiting chemicals.
The effect of an injected purge chemical can be evaluated by installing a section of scaled tubing prior to treatment and observing the inside walls following system flushing.
Summary and Concluding Remarks
 Proper filtration equipment is available to address many of the irrigation water quality problems faced by southwest Florida growers.
Iron scaling is a common problem in some areas, and pre-treating the water before it enters the irrigation system is the most reliable way to avoid iron-related problems.
However, if the system has already been impaired by iron scaling, chemicals and management strategies are available to at least partially remediate the irrigation system.
Treatment of existing scaling problems may increase the problems with plugged emitters due to particles of scale migrating to the emitters as the scale is removed from the tubing.
Flushing, subsequent chemical treatment, and additional flushing may also ameliorate some of the existing scale problems.
Avoiding iron scale through the pretreatment of irrigation water is by far the best solution.
Table 1.
Conversion of iron from ferrous to ferric forms in the presence of 2 ppm oxygen at 70 Fahrenheit.
Table 2.
Interpretations to be used with laboratory water testing results, indicating the potential hazard from plugging of microirrigation systems.
Plugging hazard based on concentration
 Measurement	Units	Slight	Moderate	Severe
 Suspended solids1	ppm	< 50	50-100	> 100
 pH	< 7.0	7.0-7.5	> 7.5
 Total dissolved solids1	ppm	< 500	500-2000	> 2000
 Iron1	ppm	< 0.1	0.1-1.5	> 1.5
 Manganese	ppm	< 0.1	0.1-1.5	> 1.5
 Calcium	ppm	< 40	40-80	> 80
 Alkalinity as CaCO	ppm	< 150	150-300	> 300
 Hydrogen sulfide	ppm	< 0.2	0.2-2.0	> 2.0
 Bacteria	#/mL	< 10,000	10,000-50,000	> 50,000
 1 Concentration as mg/L or parts per million.
Factors in italics: Measure in the field if at all possible.
Table 3.
List of irrigation line treatment chemicals, grouped by chemical reaction.
Inorganic acids	Chelating agents	Reducing agents
 Hydrochloric acid	Citric acid	Sodium sulfite
 Phosphoric acid	Glycolic acid	Sodium hydrosulfite
 Sulfuric acid	Malic acid	Sodium metabisulfite
 Nitric acid	Gluconic acid
 Sulfamic acid	Oxalic acid
 Italics indicate readily available products that were included in a recent iron scale study in southwest Florida.
Chemical agent	Where to purchase	Handling	Notes
 Sodium hydrosulfite, Na2S2O4	Industrial chemical supply	Strong reducing agent;	A sodium hydrosulfite solution must be
 	outlets	Safety precautions are	use immediately because the chemical
 required	decomposes in water.
Citric Acid, CHO	Farm or industrial chemical	No special precautions
 Sulfuric Acid, H2SO4	Industrial chemical supply	Strong acid; Safety
 outlets	precautions are required
Effect of irrigation frequencies on alfalfa seed yield
 Robert W.
Hagemann Carl F.
Ehlig Mikeal J.
Huber Richard Y.
Reynoso Lyman S.
Willardson
 Alfalfa, at full bloom, in the furrow Irrigation study.
Alfalfa, before flowering, in the subsurface drip Irrigation study.
M aximum alfalfa seed set in the Imperial Valley is achieved through slight water stress, which is sufficiently high to suppress vegetative growth but not so high as to reduce pollination and seed development.
Alfalfa seed yields were maximized in a previous experiment by maintaining an average of 50-centibar soil water tension at 9 inches below surface drip irrigation lines.
Average soil water tensions of 10, 100, and 200 centibars produced lower yields.
Daily water applications and 12-inch orifice spacings were used.
When plastic drip irrigation lines were placed underground to reduce sunlight and mechanical damage, yields decreased with greater orifice intervals, from continuously porous to 36-inch intervals.
In our present study, we compare water application frequencies for subsurface drip and furrow irrigation systems in the Imperial Valley.
Several conditions and procedures were common to both experiments although each experiment was conducted separately.
A Holtville silty clay soil was used, the upper 2to 3-foot layer of which has a fine texture and a relatively high water-holding capacity.
All treatments within each experiment were irrigated the same, as for hay production, except during the seed-production period.
Phosphorus was applied at the beginning of each seed-setting period at 50 pounds P per acre, in the acid form, through drip lines or sidedressed, as super phosphate, in the furrow study.
Honeybees were provided, at a minimum quantity of eight colonies per acre, for pollination during the seed-setting period.
Insecticides were applied as needed
 for controlling aphid, lygus, stinkbug, and cricket.
Continuously porous drip tubing was installed in 12 plots.
Each plot was 20 feet long and contained six parallel lines placed 6 inches deep on 40-inch centers.
Drip lines were connected through a control panel of flow valves and time clocks to provide three irrigation treatments randomly arranged within four replicates.
The experimental area was flat.
Moapa 69 seed was planted in rows 6 inches to each side of the drip tubing and 1/3 inch deep.
Sprinklers were used on October 23, 1974, and on several occasions until February 1, 1975, for seed germination and to establish a uniform seedling stand.
The drip irrigation system was started on December 2, 1974, to supply water daily, or several times a week, in amounts necessary to maintain a soil water tension of 10 to 30 centibars 9 inches deep in the plant row.
Seedlings were thinned to a 6-inch spacing.
Because of leaks after one year of service, the original tubing was replaced with bi-wall tubing with 12-inch orifice spacing.
The new tubing was placed 2 inches below the soil surface and the old tubing was left in place.
The tensiometer location was changed to 7 inches below the new drip lines.
The alfalfa was cut on May 15, 1975, and April 23, 1976, to start the seed production periods.
Irrigation frequencies of once daily, twice weekly, and once weekly were started at the early bloom stage on June 2, 1975 , and May 13, 1976.
All treatments received the same total amount of water per week.
The amount of water per application for the twiceand once-weekly frequencies was determined by the amount required to maintain a 50+ 20centibar soil water tension at the reference location in the once-daily frequency.
The daily water requirement was usually between 7100 and 8700 gallons per acre per day (0.26
 TABLE 1.
Subsurface Drip Irrigated Clean
 Seed Yields Harvested on
 August 22, 1975 and September 1, 1976
 Once daily	461	355
 Twice daily	612	402
 Once weekly	540	308
 *Yields are not significantly different at P=
 0.05, in either year.
to 0.32 inches per day) during June, July, and August.
During April and May, when plants were treated uniformly for hay production, water applications usually varied between 4000 and 6500 gallons per acre per day.
The plots used for the once-daily and once-weekly frequencies were exchanged in the spring of 1976.
Clean seed yields obtained during the two years of the experiment are shown in table 1.
In October 1975, seed of UC Salton alfalfa was planted at 2 pounds per acre on double row beds spaced 40 inches between centers.
Seed rows were 12 inches apart on the beds.
Seedlings were not thinned.
Thirty plots were arranged for randomizing five treatments within six replications.
Individual plots were six rows wide and 60 feet long.
Plots were separated by a bare area of two beds within replicates and 30 feet between replicates to assist bees in identifying their preferred plots.
Tensiometers were placed at 12and 18-inch depths midway between the plant rows in the center of one of the two center beds in the treatments; gypsum blocks were placed at a 12-inch depth adjacent to the tensiometers.
The alfalfa was cut on May 14, 1976, to start seed production.
The last common irrigation was applied to all plots on June 4.
Five irrigation treatments included irrigation of:  every furrow every 7 days,  alternate furrows every 7 days with the dry furrows alternated between successive irrigations,  every furrow every 9 or 10 days,  alternate furrows every 9 or 10 days with the dry furrows alternated between successive irrigations, and  the same alternate furrows every 9 or 10 days.
With a 24-hour irrigation, the soil wetted about three-quarters of the distance across the beds with alternate furrows irrigated and beds wetted entirely with every furrow irrigated.
Soil water tension at both depths usually exceeded the tensiometer range for 1 to 2 days before irrigation of treatments  and  and several days before irrigation of treatments , , and.
The gypsum blocks did not perform satisfactorily within their laboratory-determined calibration curves.
Clean seed yields are shown in table 2.
Clean seed yields were highest with furrow irrigation at 7-day intervals and were lower with furrow irrigation at 9or 10-day intervals and with subsurface irrigation at all frequencies.
Every-furrow and alternate-furrow applications yielded
 equally when the dry furrows were alternated between successive irrigations.
With alternate furrow irrigation always in the same furrows, plants in rows adjacent to the dry furrow received insufficient water and produced low seed yields.
Irrigation frequencies of once daily, twice weekly, and once weekly produced equally low alfalfa seed yields with the subsurface drip system.
Drying winds prevented seed production during periods in both experiments.
In the furrow experiment, plants were in full bloom between June 14 and 28, 1976, but very little seed was set.
Afternoon winds, estimated at 5 to 10 miles per hour, caused flowers to dry and be shed, although morning counts indicated excellent bee visitations.
A heavy seed set occurred during the succeeding two-week period when winds did not occur and bee visitations were fewer.
During the windy period, seed set was negligible in the subsurface drip experiment, where plants had already set much of their final seed yields.
Strong winds also prevented seed set in the subsurface drip experiment during early June 1975.
Because winds may occur at any time in the Imperial Valley, a farmer cannot effectively plan or select a wind-free period for seed setting.
Data from these and the previously cited experiments indicate that planting alfalfa on beds may be important for maximum seed yield on clay soils in the Imperial Valley.
Yields were higher with drip and furrow irrigation on beds than on the flat.
Low seed yields in fields previously used in hay production support this conclusion.
R.
W.
Hagemann is Farm Advisor, Imperial County; Ehlig and R.
Y.
Reynoso are Plant Physiologist and Agricultural Research Technician, respectively, USDA, Science and Education Administration, Brawley, California; M.
J.
Huber is Maintenance Supervisor, USDA, Science and Education Administration, Riverside, California ; L.
S.
Willardson is Professor of Agricultural and Irrigation Engineering, Utah State University, Logan, Utah.
TABLE 2.
Furrow Irrigated Clean Seed Yields Harvested on September 1, 1976
 Every furrow	7	953a*
 Every furrow	10	596b
 *Yields significantly different at 0.05 if not
 followed by the same letter.
Using the 40% recommendation, the data shows many irrigators are applying more water late in the season than is needed.
Some years, a significant rain can cause the soil to be wetter in September, but it is usually due to applying more irrigation water than needed.
The data shows that in 2017, 72% of fields were over-irrigated late in the season, and even in the drought year of 2022, 36% of fields were over-irrigated late in the year.
SALINITY AND PLANT TOLERANCE
 Jan Kotuby-Amacher, Director, Utah State University Analytical Labs Rich Koenig, Extension Soils Specialist Boyd Kitchen, Uintah County Extension Agent
 Soil salinity is a measure of the total amount of soluble salt in soil.
As salinity levels increase, plants extract water less easily from soil, aggravating water stress conditions.
High soil salinity can also cause nutrient imbalances, result in the accumulation of elements toxic to plants, and reduce water infiltration if the level of one salt element-sodium-is high.
In many areas throughout Utah, soil salinity is the factor limiting plant growth.
Salt-affected plants are stunted with dark green leaves which, in some cases, are thicker and more succulent than normal.
In woody species, high soil salinity may lead to leaf burn and defoliation.
High salinity causes alfalfa yield to decrease while the leaf-to-stem ratio increases, influencing forage quality.
Grasses also appear dark green and stunted with leaf burn symptoms.
Salinity tolerance is influenced by many plant, soil, and environmental factors and their interrelationships.
Generally, fruits, vegetables, and ornamentals are more salt sensitive than forage or field crops.
In addition, certain varieties, cultivars, or rootstalks may tolerate higher salt levels than others.
Plants are more sensitive to high salinity during seedling stages, immediately after transplanting, and when subject to other  stresses.
Climate and irrigation also influence salinity tolerance.
As soil dries, salts become concentrated in the soil solution, increasing salt stress.
Therefore, salt problems are more severe under hot, dry conditions than under cool, humid conditions.
Increasing irrigation frequency and applying water in excess of plant demand may be required during hot, dry periods to minimize salinity stress.
SOURCES OF SOIL SALINITY
 Salts are a common and necessary component of soil, and many salts  are essential plant nutrients.
Salts originate from mineral weathering, inorganic fertilizers, soil amendments , and irrigation waters.
An additional, important source of salts in many landscape soils comes from ice melters used on roads and sidewalks.
The addition of virtually any soluble material will increase soil salinity.
It is only when salts are present in relatively high amounts that plant growth is adversely affected.
Soil salinity is determined by measuring the electrical conductivity of solution extracted from a water-saturated soil paste.
Salinity is abbreviated as EC  with units of decisiemens per meter  or millimhos per centimeter.
Both are equivalent units of measurement and give the same numerical value.
The Utah State University Soil Testing Lab charges $5.00 per sample to test for soil salinity.
This is a small investment relative to the cost of seed and vegetation planted in fields and landscapes.
In principle, soil salinity is not difficult to manage.
The first requirement for managing soil salinity is adequate drainage, either natural or man-made.
Determine salinity level by collecting a representative soil sample to a 12 inch depth and having it analyzed by a lab.
If the salinity level is too high for the desired vegetation , remove salts by leaching the soil with clean  water.
Application of 6 inches of water will reduce salinity levels by approximately 50%, 12 inches of water will reduce salinity by approximately 80%, and 24 inches by approximately 90%.
The manner in which water is applied is important.
Water must drain through the soil rather than run off the surface.
Internal drainage is imperative and may require deep tillage to break up any restrictive layer impeding water movement.
Sprinkler irrigation systems generally allow better control of water application rates; however, flood irrigation can be used if sites are level and water application is controlled.
Test another soil sample after leaching the site to determine whether salinity level is now suitable for planting.
PLANT RESPONSES TO SOIL SALINITY
 Table 1 describes general plant responses to different soil salinity ranges.
Due to economic and/or environmental limitations , it may not be possible to leach salt from soil.
In these situations, select plants that are tolerant of the salinity level in soil.
Tables 2 through 8 describe the salt tolerances of common agricultural, horticultural, and ornamental plants grown in Utah.
Tolerance values should be used as a guide when selecting vegetation.
Varietal differences and environmental conditions may make plants more or less salt tolerant than indicated in the tables.
For harvested crops, threshold values indicate soil salinity levels where plants begin to experience yield-reducing effects.
Above the threshold, salinity levels associated with expected yield losses of 10%, 25% and 50% are indicated.
Ornamental plants are grouped according to their relative salinity tolerance  with EC ranges indicated for each category.
With the exception of turf, relatively little research has been done on landscape and ornamental plant salinity tolerance.
Most research conducted on ornamentals has addressed tolerance to salt spray deposited on foliage.
A high tolerance to salt spray, however, may indicate a high tolerance to salinity in the root zone.
Table 1.
General guidelines for plant response to soil salinity.
Salinity 	Plant response
 0 to 2	mostly negligible
 2 to 4	growth of sensitive plants may be restricted
 4 to 8	growth of many plants is restricted
 8 to 16	only tolerant plants grow satisfactorily
 above 16	only a few, very tolerant plants grow satisfactorily
 Table 2.
Salinity tolerance of common field crops grown in Utah.
Crop	Threshold value	10%	25%	50%
 Barley	8.0	9.6	13.0	17.0
 Beans 	1.0	1.5	2.3	3.6
 Canola	2.5	3.9	6.0	9.5
 Corn 	2.7	3.7	6.0	7.0
 Oats 	5.2	6.7	9.0	12.8
 Rye 	5.9	7.7	12.1	16.5
 Safflower	5.3	8.0	11.0	14.0
 Sorghum	4.0	5.1	7.1	10.0
 Sugarbeets	6.7	8.7	11.0	15.0
 Sunflower	2.3	3.2	4.7	6.3
 Triticale 	6.1	8.1	12.0	14.2
 Wheat	4.7	6.0	8.0	10.0
 Table 3.
Salinity tolerance of common forages grown in Utah.
Crop	Threshold value	10%	25%	50%
 Alfalfa	2.0	3.4	5.4	8.8
 Barley 	5.3	7.4	9.5	13.0
 Beardless Wild Rye	5.0	10.0	14.0	20.0
 Bermuda Grass	6.9	8.5	10.8	12.0
 Birdsfoot Trefoil	4.0	6.0	7.5	10.0
 Brome, Meadow	3.0	4.0	6.0	8.0
 Brome, Smooth	2.5	3.1	4.0	5.0
 Clovers 	1.5	3.2	5.9	10.3
 Clovers 	5.0	8.0	10.0	12.0
 Clovers 	1.3	2.3	3.6	5.7
 Corn 	1.8	2.7	6.8	8.6
 Field Peas	1.3	2.0	3.1	4.9
 Harding Grass	4.6	5.9	7.9	11.0
 Newhy/Hoffman	4.8	6.4	8.0	16.0
 Lovegrass	2.2	3.2	5.0	8.0
 Meadow Foxtail	1.3	2.0	3.5	6.5
 Oats 	2.6	3.2	4.1	6.8
 Orchard Grass	1.5	3.1	5.5	9.6
 Perennial Ryegrass	5.6	6.9	8.9	12.0
 Rye 	2.5	3.5	5.1	7.2
 Sweet Clover	4.0	6.0	7.5	10.0
 Sudangrass	2.8	5.1	8.6	14.0
 Tall Fescue	3.9	5.8	8.6	15.0
 Timothy	2.0	2.7	3.8	5.0
 Triticale 	6.1	8.1	10.4	13.6
 Vetch 	3.0	3.9	5.3	7.6
 Crested Wheatgrass	3.5	6.0	9.8	12.0
 Tall Wheatgrass	7.5	9.9	13.0	19.0
 Table 4.
Salinity tolerance of common vegetables grown in Utah.
Crop	Threshold value	10%	25%	50%
 Asparagus	5.0	8.0	11.0	13.0
 Beans	1.0	1.5	2.3	3.6
 Beets	5.3	8.0	10.0	12.0
 Broccoli	2.7	3.5	5.5	8.2
 Cabbage	1.8	2.8	4.4	7.0
 Cantaloupe	2.2	3.6	5.7	9.1
 Carrot	1.0	1.7	2.8	4.6
 Cauliflower	2.7	3.5	4.7	5.9
 Celery	1.8	3.5	5.8	10.1
 Corn, Sweet	1.7	2.5	4.0	6.0
 Cucumber	2.5	3.3	4.4	6.3
 Lettuce	1.3	2.1	3.2	5.2
 Onion	1.2	1.8	2.8	4.3
 Peas	0.9	2.0	3.7	6.5
 Pepper, Bell	1.3	2.2	3.3	5.1
 Potato	1.7	2.5	3.8	5.9
 Radish	1.2	2.0	3.0	8.0
 Spinach	3.7	5.5	7.0	8.0
 Squash/pumpkins	3.9	4.9	5.9	7.9
 Sweet Potato	1.5	2.4	3.8	6.0
 Tomato	2.5	3.5	5.0	7.6
 Turnips	0.9	1.9	3.1	4.9
 Watermelon	2.0	2.5	3.5	4.5
 Table 5.
Salinity tolerance of common fruit and nut crops grown in Utah.
Crop	Threshold value	10%	25%	50%
 Apple	1.7	2.3	3.3	4.8
 Almond	1.5	2.0	2.8	4.1
 Apricot	1.5	2.0	2.6	3.7
 Blackberry	1.0	2.0	2.6	3.8
 Boysenberry	1.3	2.0	3.0	4.0
 Cherries, Sweet and Tart	0.9	1.9	2.2	3.1
 Grape	1.5	2.5	4.1	6.7
 Nectarines	1.6	2.0	2.6	3.7
 Peach	1.7	2.2	2.9	4.1
 Pear	1.7	2.3	3.3	4.8
 Pecan	1.9	2.5	3.5	4.9
 Plum	1.5	2.1	2.9	4.3
 Raspberry	1.0	1.4	2.1	3.2
 Strawberry	1.0	1.3	1.8	2.5
 Walnut	1.7	2.3	3.3	4.8
 Table 6.
Salinity tolerance of selected flowers grown in Utah.
Low tolerance	Moderate tolerance	High tolerance
 EC less than 2.0 dS/m*	EC = 2.0 to 3.0 dS/m*	EC = 3.0 to 4.0 dS/m*
 China Aster	Carnation	Rose
 Approximate tolerance ranges.
Very little research has been done on the salinity tolerance of flowers.
*
 Table 7.
Salinity tolerance of common turfgrasses grown in Utah.
The following represents electrical conductivity levels at which the species begin to show a reduction in growth and quality.
Low tolerance	Moderate tolerance	Mod.
to High tolerance	High tolerance
 EC e = less than 3.0	EC e = 3.0 to 6.0	EC e = 6.0 to 9.0	EC e = 9.0 to 12.0
 Kentucky bluegrass	Fairway crested wheatgrass	Tall fescue	Alkaligrass
 Annual bluegrass	Creeping red fescue	Bermudagrass
 The Western Fertilizer Handbook, 8th edition.
1995.
Interstate Publishers, Danville, Illinois.
Diagnosis and improvement of saline and alkali soils.
1954.
USDA.
Table 8.
Salinity tolerance of ornamental and shade trees grown in Utah.
Low tolerance	Moderate tolerance	High tolerance
 EC less than 2 dS/m*	EC = 2 to 3 dS/m*	EC = 3 to 4 dS/m*
 Alders	Boxelder	Maples 
 Beech	Ohio Buckeye	Honeylocust
 Norway Spruce	Catalpas	Cottonwoods
 Giant Sequoia	Birchs 	Ash 
 Dawn Redwood	Kentucky Coffeetree	Flowering Crabapple
 Scots/Scotch pine	Ginkgo	Poplars
 Japanese Arborvitae	London Planetree	Goldenraintree
 Maples 	Hackberry	Horsechestnut
 Filbert/Hazel	Hawthorn	Joshua Tree
 Littleleaf Linden	American Holly	Tamarack
 American Linden	Silver Linden	Paper Birch
 Eastern Redbud	Magnolia	Willows
 European Hornbeam	Firs	Junipers/ E.
Redcedar
 Yellow-Poplar	Mountainash	European Larch
 Oaks 	Locust (Black, Idaho, New
 American Sycamore	Austrian Pine
 Walnut 	Chinese Date
 Pines (Bristlecone, Limber,	Oaks (English, Northern Red,
 For a more complete listing of ornamental tree tolerances to salinity and other conditions, see the Utah State University Extension Bulletin #HG460, Selecting and Planting Landscape Trees.
Utah State University Extension is an affirmative action/equal employment opportunity employer and educational organization.
We offer our programs to persons regardless of race, color, national origin, sex, religion, age or disability.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Robert L.
Gilliland, Vice-President and Director, Cooperative Extension Service, Utah State University, Logan, Utah.

Further, monitoring of total water pumped from the wells and registration of existing and new wells was made mandatory by the NRDs.
Since surface water and groundwater are connected, various needs for instream flows have had an impact on how groundwater is managed.
IRRIGATION RESEARCH PROJECTS AND STUDIES
 Corn plots planted with the pivot
 One of the first tasks assigned to the irrigation research team by Delaware farmers was to answer the decades old question of how to best irrigate corn on sandy soils for maximum yield.
Our initial research began using an evapotranspiration  based schedule to determine when the crop should be irrigated, and looked at applying the water in varying amount per application.
The application rates during peak water use were 0.33 per day vs.
0.66 every other day vs.
1 every three days.
The results of the initial work was rather inconclusive as soil type appeared to make more of a difference than application method.
At this point, it became obvious to begin looking at varying amounts of irrigation across a range of soil types.
For the Summer 2012 study, we were fortunate enough to acquire a variable rate irrigation control for the four tower center pivot located at the Warrington Farm.
This controller permits the individual control of each nozzle on the pivot  based on field location.
With this new equipment capability, we are now able to apply very specific irrigation amounts to to relatively small  plots.
The field was then divided into five tiers of ranked  soil types based on historical aerial images.
These tiers were used as the five individual replications of each irrigation treatment.
Various levels of crop stress
 Within each soil type tier, 9 irrigation treatments were maintained throughout the season.
The treatments included:
 Evapotranspiration based schedule using a 50% managed allowable depletion.
Soil moisture triggered at 20 centibars for the full season.
Soil moisture triggered at 30 centibars for the full season.
Soil moisture triggered at 40 centibars for the full season.
Soil moisture triggered at 50 centibars for the full season.
Soil moisture triggered at 20 cb from emergence to V16; 40 cb from V16 to R3; and 20 cb from R3 to maturity.
Soil moisture triggered at 40 cb from emergence to V16; 20 cb from V16 to R3; and 40 cb from R3 to maturity.
Soil moisture triggered at 30 cb until R5.
Soil moisture triggered at 30 centibars until half milkline.
All of the plots were planted with a Kinze 3660 12 row 30 vaccum planter at using Dekalb 63-14 at 34,000 seeds per acre.
3 tons/acre of broiler litter and 90lbs/acre of Potash  was applied prior to chisel plowing the field.
An additional 35 lbs of nitrogen was applied in a 2 x 2 band at planting followed by a 50 lbs/acre sidedress application and 3   25 lbs/acre applications through the irrigation system.
The soil moisture levels in each of the 45 plots will be continuously monitored by a Watermark 950T  wireless soil moisture monitoring transmitter.
Each transmitter will collect soil matric potential values from three Watermark matric potential sensors placed at 6, 12, and 18  and transmit the data to a central logger approximately 15 times per day.
For each treatment, irrigation will be initiated when soil moisture at  6 reaches a specific threshold soil matric potential.
Soil matric potential at the 12 and 18 depths will determine the volume of irrigation applied.
The volume of water applied to each plot was  recorded and summed over the whole season and during each applicable growth period.
Corn grain was harvested from each plot at maturity.
Grain yield from each plot was determined using a weigh wagon and the on-board combine yield monitor.
Grain weight was adjusted for moisture content prior to analysis.
Data is currently being analyzed using appropriate statistical methods to determine the effects of irrigation schedules on the amount of water applied and grain yield.
Results from this study will be used to adjust UD soil matric potential recommendations for irrigation management with the results of the first year of study becoming available in January.
All of the plots were planted with a Kinze 3660 12 row 30 vaccum planter at using Dekalb 63-14 at 34,000 seeds per acre.
Three tons/acre of broiler litter and 90lbs/acre of Potash  was applied prior to chisel plowing the field.
An additional 35 lbs of nitrogen was applied in a 2 x 2 band at planting followed by a 50 lbs/acre sidedress application and 3-25 lbs/acre applications through the irrigation system.
The soil moisture levels in each of the 45 plots will be continuously monitored by a Watermark 950T  wireless soil moisture monitoring transmitter.
Each transmitter will collect soil matric potential values from three Watermark matric potential sensors placed at 6, 12, and 18  and transmit the data to a central logger approximately 15 times per day.
For each treatment, irrigation will be initiated when soil moisture at 6 reaches a specific threshold soil matric potential.
Soil matric potential at the 12 and 18 depths will determine the volume of irrigation applied.
The volume of water applied to each plot was recorded and summed over the whole season and during each applicable growth period.
Corn grain was harvested from each plot at maturity.
Grain yield from each plot was determined using a weigh wagon and the on-board combine yield monitor.
Grain weight was adjusted for moisture content prior to analysis.
Data is currently being analyzed using appropriate statistical methods to determine the effects of irrigation schedules on the amount of water applied and grain yield.
Results from this study will be used to adjust UD soil matric potential recommendations for irrigation management with the results of the first year of study becoming available in January.
Soybean Irrigation Response Study
 Soybeans planted in 7.5, 15 and 30 rows following pivot.
Evaluate the effects of various soil moisture levels and row widths on growth and yield of full season and double cropped soybeans.
Determine the optimal irrigation management strategy for full season and double cropped soybeans to maximize yield and profitability.
Determine the optimal row width for irrigated full season and double cropped soybeans to maximize yield and profitability.
Watermark 950T Soil Moisture Wireless Transmitter monitoring moisture levels at 4, 8 and 18.
Two studies will be conducted to determine the response of full season and double cropped soybeans to various soil moisture levels and row widths.
There will be a full season soybean and a double cropped soybean study.
The entire study area will be treated identically for all production inputs except irrigation.
Fertilizer will be applied based on the University of Delaware recommendations for soybean.
One soybean variety will be planted Mid-May for the full season study and one variety will be planted Mid-June for the double cropped study.
In both projects, plots will consist of soybeans planted in 7.5, 15, and 30 row widths.
Each plot will receive one of the following potential irrigation treatments and will be replicated five times.
Variable Rate Irrigation  nozzle controller applying varying irrigation rate to each plot.
Full season irrigation 
 No irrigation until flowering  then >50% soil moisture
 Limited irrigation  until flowering  then >50% soil moisture
 Limited irrigation  until pod development  then >50% moisture
 Limited irrigation  until seed development  then >50% soil moisture
 Limited irrigation  until flowering  then >50% soil moisture until pod development  then >70% soil moisture
 Evapotranspiration  based irrigation management using the Delaware Environmental Observing Systems weather station located on the research farm and the commonly accepted soybean crop coefficients
 Harvesting the research plots
 Soil moisture will be monitored in each plot in the 15 in row width using Watermark soil moisture sensors placed at 4 in, 10 in, and 16 in below the soil line.
Soil moisture data will be transmitted wirelessly approximately 10 times daily from the field to a data logging receiver.
Moisture data will be viewed and interpreted daily to determine if any treatments require irrigation.
Irrigation in plots will be triggered whenever soil moisture reaches the specific treatment requirements at the 4 in or 10 in depth.
Weather data will be collected by a Delaware Environmental Observing System weather station located on the irrigation research farm.
The plant growth and development data will be analyzed to determine the effects of soil moisture levels and row spacing on plant growth and development.
In addition, soil moisture data will be analyzed to determine differences in soil moisture depletion between irrigation treatments.
Total water applied for each irrigation treatment will be determined and the economic implications of each irrigation management strategy will be calculated based on soybean yield.
Irrigated Lima Bean Yield & Quality
 Corn plots planted with the pivot
 Research will be performed to determine the ideal irrigation management strategy for lima beans.
An automatic irrigation control system will be utilized to schedule irrigation based on actual soil moisture levels.
Yield and quality differences will be compared across 4 irrigation treatments and the economics of each intensity level will be determined and shared with producers.
Irrigation research for baby lima beans will be performed on the University of Delaware, Research and Education Center farm in Georgetown.
The field trials will have 4 replications of two varieties of baby limas  with four irrigation treatments.
Plots will be two rows, 25 in length.
Irrigation will be provided by two lines of low flow  drip tape per plot.
Irrigation treatments will consist of:
 Treatment 1  No Irrigation
 Treatment 2  Irrigation will be triggered when the plant available water  reaches 50% of capacity throughout all crop stages; irrigation will be interrupted when the soil reaches field capacity.
Treatment 3  Irrigation will be triggered when the PAW reaches 35% of capacity throughout all crop stages; irrigation will be interrupted when the soil reaches field capacity.
Treatment 4  Irrigation will be triggered during vegetative growth stages at 35% of PAW followed by a 50% PAW trigger during reproduction.
Watermark 950T matric potential sensors will be placed at 4, 12 and 18 depth within each plot and will be hard wired to a Campbell CR 1000 data logger.
The data logger will collect and record the real time soil moisture content every half hour.
The data logger control ports will energize a 24VAC solenoid valve to initiate irrigation whenever the measured soil moisture levels are below the set point.
Each plot will be evaluated for plant effects, harvestable yield, and quality.
Plots will be harvested as close to ten percent dry pods as possible.
Plants will be cut off at soil level and weighed for fresh weights.
To determine maturity at harvest, pods will be stripped from five harvested plants from each plot and counted as full, flat or dry.
The plants and pulled pods will be fed into a stationary FMC viner to shell.
After cleaning of any trash, shelled beans will be weighed to determine yield.
Plant stress measurements such as canopy temperature or spectral reflectance will also be collected at points throughout the growth cycle.
Presentations were made at the 2014 and 2015 Delaware Ag Week to present the results of this three-year study.
Corn plots planted with the pivot
 Given the broad potential impact of SDI technology on Delaware agriculture, a cooperative project to create a SDI research facility was initiated in 2011.
Project partners include the University of Delaware with USDA-NRCS, Delaware Department of Agriculture, Toro Ag, John Deere Water, Sussex Irrigation and Vincent Farms.
The installation of a 42 zone sub-surface drip irrigation research station on a 20-acre parcel of the University of Delawares Warrington Irrigation Research Farm in Harbeson, DE, began in December 2012.
This facility will enable the University of Delaware to research specific questions regarding the installation, maintenance and management of these systems for 15 to 20 years and generate localized recommendations for Delaware producers.
As is typical with the introduction of a technology new to a region, several questions have arisen regarding the best ways to implement and manage SDI technology for Delaware conditions.
Questions involving installation parameters such as drip tape row spacing, depth of placement and flow rates can be partially addressed utilizing research experience from other regions combined with a site specific soil profile.
However, most of the unanswered questions involve management strategies such as, determining crop water needs, ideal soil moisture sensor placement, planting configuration, pulsed irrigation and crop establishment.
These strategies are more difficult to address and require intensive local field research.
The sole purpose for the creation of this SDI research facility is to develop the management recommendations essential to continue the successful adoption of this technology.
Corn plots planted with the pivot
 1  450 gallon per minute well with submersible pump controlled by a variable frequency drive to maintain constant pressure over varying flowrates.
42 individual computer controlled irrigation zones.
1  2 zone, tape placement study with tape installed at 10 & 16 depths on 30 and 60 row spacings.
2  20 zone irrigation management study areas; each capable of randomizing four replications of five different irrigation treatments in two different crops.
The tape will be installed at the typical Delaware SDI installation parameters of 16 deep on 60 rows.
Average zone dimensions will be 60 x 300.
Soil moisture monitoring utilizing an extensive Irrometer Watermark 950T and 950R wireless data logger network.
Average percent of fields by year fitting into the six categories.
The dry years 2020, 21 and 22 are different than the other years.
In 2017, out of 86 reports, 28% were ranked good, 10% were fair, 13% were wet late, 13% were wet early, 22% were wet all season, and 14% were very wet all season.
A person should always check wires with his meter before the electricity is turned off to make sure the meter is working, then turn the power off and recheck the wire to make sure the right switch is turned off.
A History of National Water Legislation
 Clean water is of vital importance to sustaining public health, maintaining a strong economy and preserving a thriving ecosystem.
Laws and regulations have played a major role in protecting the country's environment.
To better understand water quality and quantity legislation, it is important to examine the history of the federal government's role as well as the states' in regulating this important resource.
The Cornerstone of Environmental Law
 The National Environmental Policy Act of 1969  is considered the nation's first comprehensive environmental legislation.
NEPA applies to almost all actions taken by or approved by federal agencies.
The first part of NEPA establishes broad environmental goals for the nation.
The second part contains the statute's requirements for agency actions.
The Act is based on the principle that federal agencies should "look before they leap." Thus, NEPA requires federal agencies to conduct an environmental assessment  before taking any major action.
An EA allows the agency to decide if its proposal may have significant impacts.
If the agency decides that the proposal will not have significant impacts, then the agency can end the process by issuing a "finding of no significant impact".
If the agency finds that a proposed action might have significant impacts, then it must do a full environmental impact statement.
The full NEPA process can be lengthy and complicated.
It requires agencies to seek public comment at many points in the EIS process.
However, the federal courts have ruled
 that NEPA is a purely procedural statute.
Even after preparation of a full EIS, NEPA does not mandate any particular decision.
It simply requires that agencies do the analysis and reporting required by law.
NEPA requirements apply to all agencies of the federal government, but not to Congress, the courts or the president.
Federal water legislation dates back to the 19th century with the passage of the River and Harbor Act of 1899.
The purpose of the Act was to protect the nation's waters and promote interstate commerce.
Almost 50 years went by before Congress enacted the Water Pollution Control Act of 1948.
The legislation provided federal technical assistance and funds to states interested in protecting their water quality.
In 1965, Congress passed the Water Quality Act , which charged states with setting water quality standards for interstate navigable waters.
Navigable waters are waters of the United States that have been used historically or are now used for interstate commerce or foreign commerce, including, but not limited to, interstate waters, interstate wetlands, intrastate lakes, rivers and streams.
The Clean Water Act
 In 1972, the Federal Water Pollution Control Act  strengthened WQA's water quality standards protocol and established a regulatory structure for controlling discharges of pollution into the nation's waters.
FWPCA made it illegal to discharge a toxic or non-toxic polluting substance without a permit, encouraged the use of the best available technology for pollution control and provided federal funding for constructing sewage treatment plants.
The Act also directed states to set water quality standards
 for waters other than those designated as interstate navigable waters and to implement wetlands protection programs.
In 1977, FWPCA was amended by the Clean Water Act.
The Act authorizes water quality programs, requires state water quality standards and permits for discharges of pollutants into navigable waters and authorizes funding for wastewater treatment works, construction grants and state revolving loan programs.
CWA identifies two sources of pollution:
 Point source pollution from clearly discernible discharge points such as pipes, wells, containers, concentrated animal-feeding operations, boats or other watercraft.
Nonpoint source pollution coming from diffused points of discharge such as runoff from parking lots, agricultural fields, lawns, home gardens, construction, mining and logging operations.
CWA established federal restrictions on discharges.
No one may discharge a pollutant from a point source into navigable waters of the U.S.
without a National Pollution Discharge Elimination Systems  permit, which is issued by the U.S.
Environmental Protection Agency.
There are considerable administrative penalties, fines and/or criminal prosecution both at the state and federal levels for people or organizations that do not have a NPDES permit.
1
 Federal and State Oversight of CWA
 The U.S.
Army Corps of Engineers , EPA and the states are charged with enforcing various provisions of CWA.
Under CWA, states are charged with protecting and restoring the quality of the nation's waters:
 It is the policy of the Congress to recognize, preserve and protect the primary responsibilities and rights of States to prevent, reduce and eliminate pollution, to plan the development and use  of land and water resources
 States engage in a number of activities to fulfill the requirements of CWA, including assessment, identification of total maximum daily loads and implementation.
Assessment is the process of determining the status and condition of a state's water resources and the progress being made to restore and protect these waters.
States are required to submit assessment reports to EPA.
These include but are not limited to:
 Section 305 reports comprehensive biennial inventories of the conditions and trends of waters within the state
 Section 314 reports information about clean lakes within the state and
 Section 319 reports information about waters within the state that are threatened by nonpoint source pollution.
EPA has three basic tools for enforcing CWA:
 Administrative orders requiring compliance
 Civil actions to collect penalties or obtain an injunction.
Separate enforcement provisions apply to dredging and filling activities and oil discharges that require a permit from the Corps.
EPA has almost complete discretion to negotiate and settle its civil or administrative enforcement actions.
Fines are calculated according to specific penalty policies or guidelines, which typically emphasize the severity, frequency and duration of the violation.
Settlements also typically include a consent order creating a specific timetable for compliance and stipulated penalties for violations of the consent order.
The Safe Drinking Water Act
 Another significant water law is the Safe Drinking Water Act.
Passed by Congress in 1974 and amended in 1986 and 1996, SDWA regulates the nation's public drinking water supply in order to protect public health.
SDWA authorizes EPA to set national health-based standards for the presence of contaminants in drinking water.
It also allows EPA, states and drinking water systems to work together to implement these standards.
SDWA gives EPA authority to regulate all public water systems in the U.S.
that provide piped water for human consumption for at least 60 days a year to at least 15 service connections or 25 people.
Systems that do not meet this definition are classified as private
 water systems and are not subject to federal regulation.
EPA has established Primary Drinking Water Regulations.
States are responsible for enforcing the regulations, which require identifying contaminants that may pose a risk to human health and that occur in drinking water at potentially unsafe levels.
EPA specifies a Maximum Contaminant Level Goal  for each contaminant.
The goals are set at levels below which there are no predicted health risks.
The agency also creates a legally enforceable Maximum Contaminant Level , which is the greatest amount of contaminant that will be allowed in the public water supply.
The Act originally stressed treatment as the primary means of providing safe drinking water.
The 1996 amendments greatly expanded the law's scope by recognizing the need for:
 Funding for water system improvements.
It also required source water assessment programs  for all U.S.
public drinking water supplies.
These source water assessments determine a drinking water system's potential susceptibility to contaminants.
In addition, public water suppliers are required to inform customers about the source and quality of their tap water with an annual consumer confidence report.
The Arkansas Department of Health's  Division of Engineering is charged with the regulation and oversight of the state's public water systems.
According to the ADH's Drinking Water Program Annual Report, there were 1,094 public water systems in operation during 2006.
Of those, 714 were community water systems, 35 were non-transient non-community water systems and 345 were transient non-community water systems.
Arkansas' public water systems serve 91.8 percent of the population.
The Division's mission is to protect the health of all of Arkansas' citizens and visitors by providing technical assistance, analytical services, training, regulation and public education for the purpose of ensuring that public water systems provide adequate quantities of safe, palatable water and that community sewage systems dispose of domestic wastes in a safe manner.
Specifically, ADH's Division of Engineering:
 Reviews plans of new water system facility construction
 Inspects water system facilities
 Troubleshoots water treatment and distribution problems
 Collects and analyzes samples to determine water quality
 Reviews plans of new sewer system construction
 Inspects proposed cemetery sites
 Community Water System a public water system that serves the same people year-round.
Reviews plans of public swimming pools and
 Non-Community Water System a public water system that serves the public but does not serve the same people year-round.
There are two types of non-community water systems:
 Trains and certifies water system operators.
Non-Transient Non-Community Water System a noncommunity water system that serves the same people more than six months per year, but not year-round.
An example would be a school with its own water supply.
Transient Non-Community Water System a noncommunity water system that serves the public but not the same individuals for more than six months.
An example would be a rest area or a campground.
Drinking water standards for public water systems are based on their type and size:
 Drinking Water State Revolving Fund Program
 A 1996 amendment to SDWA authorized the Drinking Water State Revolving Fund  Program to help public water systems finance infrastructure improvements needed to protect public health and ensure compliance with SDWA.
Arkansas Act 772 of 1997 created the Safe Drinking Water Fund Program.
Types of projects which can be funded include compliance, water supply, public health, treatment, distribution storage, plan and design, consolidation and restructuring.
Entities eligible for funding include cities, towns, counties, public facilities boards, improvement districts, regional water distribution districts, community water systems and regional development authorities.
Types of assistance approved under the program include low-interest loans up to 20 years or the life of the project, whichever is less, or up to 30 years or the life of the project for disadvantaged communities,
 whichever is less.
The Arkansas Natural Resources Commission  is the lead agency for the Safe Drinking Water Revolving Loan Fund Program.
ANRC works with ADH to identify eligible projects.
In order for a project to receive funding it must be listed on the federal DWSRF project priority list.
Through an interagency agreement, the Arkansas Development Finance Authority  serves as the financial manager for the program.
ADFA is responsible for investing and disbursing funds as authorized by ANRC, servicing loans, preparing and submitting monthly financial reports and annual financial statements and procuring audit services.
ADFA and ANRC use a priority system for funding projects based on three criteria from the Act.
Priority is given to projects that:
 Address the most serious risk to human health
 Are necessary to ensure compliance with the requirements of SDWA and
 Assist systems most in need, on a per-household basis, according to state-determined affordability criteria.
The federal government annually provides money to states, which, in turn, negotiate loans at belowmarket interest rates to pay for qualifying improvements to drinking water system infrastructure.
Each state's grant allotment is proportional to the total state need identified in the most recent national assessment of drinking water infrastructure needs.
States use the principal and interest payments received from loan recipients to provide more loans.
According to EPA, Arkansas' appropriation was $10.33 million for fiscal year 2007.
States are allowed to make loans for eligible
 projects to publicly owned, privately owned and nonprofit community water systems and noncommunity water systems.
There are five basic categories of eligible projects:
 Items specifically excluded from DWSRF eligibility include:
 Expenditures for monitoring, operations and maintenance
 Projects whose primary purpose is to facilitate growth
 Projects to construct or rehabilitate dams and reservoirs
 Projects to obtain water rights and
 Projects needed primarily for fire protection.
Fact Sheet 109  Glossary of WaterRelated Terms contains a comprehensive list of terms used in the Arkansas Water Primer Fact Sheet Series.
1 33 U.S.C.
Section 1342  and ; States with approved programs may administer permit requirements and issue and enforce permits; 33 U.S.C.
Section 1342; 40 CFR Section 122 et seq for provisions regarding activities required to obtain permits; activities not requiring permits; modification; revocation and reissuance of permits; schedules of compliance.
The University of Arkansas Division of Agriculture's Public Policy Center provides timely, credible, unbiased research, analyses and education on current and emerging public issues.
The Arkansas Water Primer Fact Sheet Series was funded by a grant from the U.S.
Department of Agriculture with additional financial assistance from the University of Arkansas Division of Agriculture.
Original research for the Series was provided by Janie Hipp, LL.M., and adapted by Tom Riley, associate professor and director of the University of Arkansas Division of Agriculture's Public Policy Center, and Lorrie Barr, program associate, University of Arkansas Division of Agriculture's Public Policy Center.
Here is an example of how to figure ET.
I have an ET gage in a field located in Valley County, Nebraska.
The reading over the past week was 1.8.
This is a corn field at the V6 growth stage.
We refer to the chart of Kc values and find that it is 0.35.
We then multiply 1.8 X 0.35 and get 0.63.
Divide this figure by seven days in the week and we have 0.09 of water used per day this past week.
So as you can see, when the crop is early in its development, it is not using much water each day.
Kyle Egbert, Matt Yost, Bryce Sorensen, Grant Cardon, Niel Allen, and Ryan Larsen
 Fertigation is the application of fertilizer through an irrigation system.
It can be implemented in surface, sprinkler, and drip systems.
In the 2013 agriculture census, nearly 135,000 acres of irrigated cropland in Utah utilized fertigation.
Utah growers most commonly fertigate corn  and orchards , but it is also used to a lesser degree on small grains, alfalfa, and other hay.
In most cases, fertilizer used for fertigation is available in liquid solutions or in a soluble form.
Liquid fertilizer such as Urea Ammonium Nitrate , Ammonium Thiosulfate , Ammonium Polyphosphate , and Anhydrous Ammonia  are most commonly used due to their convenience, and are currently the primary forms sold by fertilizer companies for fertigation in Utah.
In addition to the liquid fertilizers, soluble fertilizers are an additional option for supplementing crops during the growing season.
A variety of soluble products are available at local agronomic retailers.
The purpose of this fact sheet is to provide general information on forms of fertigation for primary plant nutrient, fertigation timing, and fertigation economics.
The most common nutrient that is applied by fertigation in Utah is nitrogen.
Nitrogen
 fertilizers have a high solubility, which makes them relatively easy and effective to apply with an irrigation system.
Because of its high solubility, N is also extremely susceptible to leaching.
There are several different forms of N that can be used for fertigation.
One of the most commonly used in Utah is UAN.
The nitrogen in UAN is in three forms 50% urea, 25% ammonium, and 25% nitrate.
Anhydrous Ammonia  is commonly used in surface irrigation systems because it can be bubbled into the irrigation water.
Anhydrous Ammonia is less expensive than soluble liquid nitrogen per unit of N, and is a common option for surface irrigators.
Be aware that anhydrous ammonia typically increases the pH of the water around the application site, and that N losses from volatilization can be as high as about 30-50% of the
 Figure 1.
Center pivot fertigation.
Photo credit: Kyle Egbert.
Figure 2 Anhydrous ammonia being bubbled into surface irrigation water.
Photo credit: California Department of Food and Agriculture.
N applied, which can also cause poor application uniformity.
Great caution must be taken when using NH3 because of its high reactivity with water on the skin and organs.
Because there are many different forms of N fertilizers it is important to pick the correct one for your application.
Keep in mind that not all forms of nitrogen will be immediately available to the plant.
Nitrate and ammonium are the predominate forms used by plants and are usually rapidly available after application.
Urea is not readily accessible and must be converted into ammonium and nitrate by soil bacteria before uptake can occur.
Conversion may take several days depending on soil conditions and temperature.
These conditions should be considered when deciding fertigation timing.
When choosing a N fertilizer, look for forms that are highly soluble, less corrosive, and will meet the nutrient needs of your crop at the correct time.
The most common form of phosphorus  that is fertigated in Utah is APP.
Most irrigation water in Utah is hard water containing high amounts of calcium  and magnesium.
When liquids containing APP are injected into high pH water, CaP precipitates may form.
The resulting precipitates may plug irrigation lines and emitters, decrease the life of nozzles, and increase maintenance costs.
Applying phosphoric acid instead of APP is a less
 practiced method because it may increase wear and tear on irrigation systems; but it can usually resolve the issue of precipitates forming in the irrigation system.
Due to the challenges Utah's hard water presents, and the fact that phosphorus is not easily leached from the soil, broadcasting and incorporating  solid forms of phosphate fertilizers before the growing season is a more common practice.
When potassium  is needed according to soil tests, fertigation is an option.
Liquid potassium  fertilizer is rare.
However, most K fertilizers are soluble in water and can be used for fertigation in the right applications.
The two most common used for fertigation are potassium chloride  and the more expensive potassium nitrate .
Potassium can precipitate when combined with other fertilizers SO be sure to test small mixtures in a jar or container prior to fertigation.
Although feasible, K will rarely be economic to fertigate as a stand-alone fertilizer.
Fertigation of K may be suitable in instances su ch as intensely hayed cropping systems, sandy soils , high-value crops, and depleted soils.
With that being said, potash is one of the most inexpensive fertilizers and is easily broadcasted at the beginning of the growing season.
Water Chemistry and Fertigation Compatibility
 Water chemistry can have an adverse effect on the ability to deliver liquid fertilizers through an irrigation system.
For example, aqueous ammonia injected as an N source can increase the pH of the water to an extent that dissolved salts in the water may precipitate, forming solid crystals that can clog nozzles and drip emitters.
High bicarbonate in waters, most commonly found in shallow groundwater well sources, can cause rapid precipitation of calcium and magnesium in fertilizer sources such as calcium nitrate or CAN 17.
Phosphate fertilizers  are particularly sensitive to precipitation when irrigation water is high in dissolved calcium and magnesium, especially at a water pH of 7.5 or higher.
Sulfate forms of various nutrients can also
 form gypsum or Epsom salt precipitates in high pH, high dissolved calcium and magnesium content waters.
Potassium fertilizers  rarely have issues with precipitation when injected in irrigation waters.
A simple jar test can be performed prior to fertigation injection to test for irrigation water incompatibility with liquid fertilizers.
This is done by filling a glass jar with irrigation water directly from the source and at the temperature it is normally delivered to the irrigation system, and then mixing in liquid fertilizer at the desired concentration.
Vigorously shake and aerate the solution for one minute and then let stand for 15 minutes.
If any cloudiness in the solution forms, or one notes any solid precipitates settling to the bottom, suspended, or floating, there is significant likelihood of nozzle or emitter plugging with the chosen combination of water and fertilizer.
Timing of Fertilizer Application and Nutrient Uptake
 One of the most important benefits of fertigation is the increased control over application timing, which allows for in-season nutrient applications that can be split and applied to better match rapid nutrient uptake periods.
In addition to timing, fertigation can be an important management practice in soils that are prone to leaching or other nutrient loss pathways.
Therefore, when planning fertigation amount and timing, it is important to account for the crops total nutrient needs, timing of the need, estimated nutrition provided by the soil, and leaching potential.
Crops use different amounts of nutrients at different growth stages.
For example, less than half the total N and P uptake occurs prior to the reproductive corn stages, whereas nearly 80% of the K uptake occurs prior to reproductive stages.
Uptake of N, P, and K is more consistent for small grains and the majority of the uptake occurs during tillering and stem elongation.
Information of this sort will help to determine optimal fertigation timing.
Soil and tissue testing can help specify the crops nutrient requirements.
Matching fertigation to major crop uptake periods will help maximize nutrient efficiency and increase crop yields and quality.
Figure 3 Nutrient uptake of corn from Heard, 2006.
Figure 4 Small grain nutrient uptake from Malhi, Johnston, Schoenau, Wang, and Vera, 2006.
In high nitrogen loss scenarios, more frequent applications at lower rates of leachable nutrients may enhance your nutrient use efficiency, and save fertilizer costs.
For example, Nebraska and other states recommend applying about 20-30 lb N/acre per irrigation for corn, starting with the first irrigation and ending when nitrogen uptake ceases.
Economics of Fertigation vs.
Broadcast Applications
 Few economic comparisons of fertigation VS.
broadcast application of fertilizers have been conducted because of the difficulty in comparing total fertigation prices among agronomic companies.
In addition to fluctuating prices of product, each agronomic company will charge
 differently for the various components of fertigation and the fertilizers.
Agronomic companies often attempt to outbid one another and develop different pricing structures when it comes to fertilizer and fertigation services and sales.
A simple method to evaluate the two methods is to use a partial budget approach.
A partial budget simply evaluates the change due to the use of either fertigation or broadcast spreading.
In the case below, broadcast application would be the base case and we will compare that to utilizing fertigation application.
The table below provides a framework:
 Table 1.
Partial Budget Framework for Fertigation Application.
Key	Fertigation Application	Impact
 Yield	Does fertigation provide a	+ or -
 Change	change in yield to offset
 Cost	Evaluate the cost per acre	+ or -
 Change	for each application
 method.
This includes the
 cost of fertilizer, appli-
 Overall	Add up the changes to	+ or -
 Change	provide an overall
 It is important to note that fertigation applications are only as uniform as the irrigation applications.
Windy conditions can significantly decrease the uniformity of fertigation applications from overhead sprinklers.
Thus, it is not recommended to use pivots for fertigation in windy conditions if it can be avoided.
Fertigation in furrow/flood irrigation systems is generally riskier and not as efficient as in pressurized systems.
This is due to the risk of fertilizer loss in run-off water and because application uniformity can be low.
Loss of fertilizer in runoff water not only represents a direct economic loss to the farmer, but also poses the risk of environmental pollution.
Effective fertigation requires careful monitoring of fertigation timing, crop growth stages, irrigation system operation, rates, and additional equipment maintenance.
Keep in mind that using fertigation to apply fertilizers will require more setup procedures than simply hooking up the fertilizer cart and broadcasting across the field, and potentially more monitoring and maintenance of equipment.
However, once a fertigation system is setup, subsequent fertigations throughout the growing season should require much less effort.
For more information on setup and equipment involved in fertigation see the companion USU Extension publication titled "Chemigation Guide".
The use of fertigation for field and horticultural crops is increasing in Utah.
Fertigation can be an effective method for improving nutrient stewardship and improving crop yield and quality.
Keys to successful fertigation include irrigation system maintenance and uniformity, proper fertigation setup and management, and timing nutrient applications to match crop needs.
Getting the crop off to a great start is essential for a successful season.
On dry years, it is sometimes necessary to start irrigating in May and June.
However, it is critical to monitor soil moisture to balance crop needs with the risk of losing nitrogen and other valuable crop inputs.
Monitoring will also help prevent unnecessary irrigation expenses, and if you have a water allocation, avoid using up water that is critical for later growth stages.
Texas Managing Groundwaten Resources
 Through Groundwater Conservation Districts
 Priority Groundwater Management Areas
 Current Extent of Groundwater Districts
 Powers and Responsibilities of GCDs
 Creation of Groundwater Conservation Districts
Drought last year also has led to the general recommendation of delaying turn out to pasture, but early flash grazing can be an option to capitalize on growth of some of those weeds.
Flash grazing is the process of quickly rotating through pastures early, before they are scheduled for their main summer grazing period.
Jennifer Richards, Assistant Professor, Department of Agricultural Leadership, Education and Communications
 Tennessee 4-H Youth Development
 Irrigation Challenge STEM Camp
 The learner will be able to:
 Identify the steps of the Engineering Design Process.
Use the engineering design process to build a marshmallow tower.
Create a plan to solve a real-world problem following the steps of the Engineering Design Process.
Learners will be successful if they:
 Complete the Ask, Imagine and Plan stages of the Engineering Design Process.
Time Needed 90 Minutes
 Irrigation Challenge Handout STEM Challenge Planning Sheet Toothpicks Mini Marshmallows Pens or Pencils Large Chart Paper and Markers Painter's Tape
 This lesson introduces the concept of irrigation and the Engineering Process.
Students will compare and contrast design ideas to find the strongest and most effective design.
They will also focus on solving real-world problems.
Students will first receive a quick lesson about the purposes and practices of irrigation, as well as an introduction to thinking like an engineer.
Students will then be split into small groups to explore design ideas for their own irrigation system model.
Before making their final product, students will have the opportunity to practice using the engineering process within their small groups with a short activity.
Richards, Jennifer.
Curriculum Specialist, Tennessee 4-H Youth Development.
Terms and Concepts Introduction
 Irrigation: The process of moving water from one place to another to help plants grow.
Concept of photosynthesis and plant care.
Engineering Process: Ask, Imagine, Plan, Create and Improve.
Setting the Stage and Opening Questions
 Introduce the need for water when growing crops by engaging students in a discussion.
Ask students:
 Divide students into groups of mixed ability, age and gender to make the groups stronger through their diversity.
What are some things that plants need to grow?
What happens to plants if they don't get enough water?
What are some ways that people get water to plants if they don't get enough water from rain?
Tell students: This week we are going to learn about a process called irrigation.
Does anyone know what "irrigation" means?
Allow students to share their guesses.
Ask students if they have seen any examples of irrigation in their village and allow them to share examples.
Direct the discussion to include the following important points:
 Irrigation is moving/controlling the movement of water.
Irrigation is used to water crops/plants.
Irrigation techniques include tunnels, canals, aqueducts, tanks, pumps, ditches, hoses, pipes, etc.
Tell students: In this lesson, you are going to pretend to be engineers.
What is an engineer?
You and a team of your fellow engineers are going to work with a small group to figure out how to build an irrigation system to water crops in your school garden.
By the end of this lesson you will be able to:
 Identify the steps of the Engineering Design Process.
Use the Engineering Design Process to build a marshmallow tower.
Create a plan to solve a real-world problem following the steps of the Engineering Design Process.
Divide students into teams of three.
Pass out the Irrigation Challenge Sheet and ask teams to take three minutes to read the challenge sheet to identify:
 What are you being tasked with accomplishing?
Develop and build a plan to move 250mL water over 1 meter.
What are the criteria ?
Maximize the speed at which the water moves while minimizing the loss of water along the way.
What are the constraints ?
Use everyday items to build your irrigation system.
Ask students to use the back of the Challenge Sheet to make a list of all the things they need to know to accomplish their task.
Give students three minutes to compile their list, then aggregate responses on chart paper.
Tell students: In this lesson, you are going to work in your teams to solve the challenge of moving water across a distance.
Before you get started trying to solve this challenge, I want to share with you a problem-solving tool called the Engineering Design Process.
Introduce the Engineering Design Process through the following important points.
Incorporate examples of each step along the way.
The Engineering Design Process is a series of steps that engineers use to guide them as they solve problems.
It is a process that is cyclical, meaning you can begin at any step or move back and forth between steps numerous times.
There are five steps:
 What is the issue or problem you need to solve?
What are the criteria and constraints?
Develop solutions by brainstorming ideas.
Consider all options, then choose the best one.
Develop a plan that meets the criteria and constraints.
Test the prototype Does it work?
Evaluate the prototype Does it solve the problem?
How could it be better?
Modify the prototype to address weaknesses.
Retest the solution to see if it works better now.
Gather relevant information for decision-making 
 As part of a group, identify and agree on a common task.
Practice the Engineering Design Process.
Tell students: Before we dive into your big challenge as engineers to see if you can build a simple irrigation system out of everyday materials, let's practice with some other fun materials.
Distribute supply bags to students with marshmallows and toothpicks.
Tell students: In your bags, you all have the same materials.
Take a quick look and see what you have.
If you eat your materials now, you won't have what you need to win this challenge!
Allow students about one minute to explore their bags.
Ask students to share what they found.
Tell students: Now, here is your challenge: In your team, I'd like you to build the tallest freestanding  tower you can, using only the materials provided, in just two minutes.
But before you just jump right in, let's remember what we just learned about the Engineering Design Process.
Lead students through an exploratory process that follows the Engineering Design Process:
 What is your challenge?
What are the criteria?
What are the constraints?
What shapes can you make with the marshmallow and toothpicks?
Which do you think are the strongest?
Which do you think will NOT work?
Decide as a group how you will build your structure.
What roles will all the group members play?
For the purpose of time, combine the test and improve steps here.
Instruct each group to release their towers SO they are freestanding.
Make sure each group's tower stands for at least 10 seconds.
Then use a measuring tape to see which is the tallest.
Give a prize to the group with the tallest tower.
Lead students through a quick debrief:
 Which shapes were the strongest?
What building strategies did not work well?
How did your final designs differ from your initial plans?
What did you learn about using the Engineering Design Process in this challenge?
Students will now create an irrigation design and identify materials.
Tell students: Now that you've had a chance to learn about and practice the Engineering Design Process, let's return to your irrigation challenge.
We've already identified the challenge, criteria and constraints, so we've already worked through the first step.
Distribute the Irrigation STEM Challenge Planning Sheet to students and ask them  to record the important information in the Ask section.
Review the challenge, criteria and constraints.
What step is next in the Engineering Design Process?
What sorts of things does you team need to do in the Imagine step?
Allow students about five minutes to complete this step.
Encourage them to take notes on their planning sheet.
Give students a chance to share the ideas that their group developed.
What step is next in the process?
What does your team need to do in this step?
Give students about five minutes to use their planning sheets to create a plan.
Remind students that this is the critically important step to complete today because they will need to gather their everyday materials before you meet again tomorrow!
Encourage them to build their plans around materials they can actually find at home or in nature.
Ask students to share the types of materials they are going to scavenge to use tomorrow.
Ask them how they will improvise if they cannot find the materials they need.
We started today by working in teams.
We also established that by the end of the day, you would be able to :
 Identify the steps of the Engineering Design Process.
Use the Engineering Design Process to build a marshmallow tower.
Create a plan to solve a real-world problem following the steps of the Engineering Design Process.
Who can remind me of the steps in the Engineering Design Process?
You have all created your plan for developing an irrigation system.
Tomorrow, we will continue working on your plan to build and test it as well as try out another fun challenge!
Remind students to gather their everyday materials before you meet again tomorrow.
Supplemental Information Educational Standards Met
 EVSC.LS2.6.
Evaluate the interdependence among major biogeochemical cycles  in an ecosystem and recognize the importance each cycle has in maintaining ecosystem stability.
4.ETS1.1 Categorize the effectiveness of design solutions by comparing them to specified criteria for constraints.
4.ETS2.2.
Determine the effectiveness of multiple solutions to a design problem given the criteria and the constraints.
5.ETS1.1.
Research, test, re-test, and communicate a design to solve a problem.
5.ETS1.2.
Plan and carry out tests on one or more elements of a prototype in which variables are controlled and failure points are considered to identify which elements need to be improved.
Apply the results of tests to redesign the prototype.
Tennessee 4-H Youth Development
 Irrigation Challenge STEM Camp
 The learner will be able to:
 Apply the steps of the Engineering Design Process to solve a real-world problem.
Learners will be successful if they:
 Materials for building irrigation system Water measured in 250mL increments Meter stick
 This lesson reinforces the concept of irrigation and the engineering process.
Students will work in groups to utilize their creativity and problem-solving skills to finalize the designs of their irrigation systems.
This lesson is Day 2 of the Irrigation Challenge STEM Camp lesson plan.
In this lesson, students will work in teams to execute the designs they brainstormed the previous day.
Students will have the opportunity to experiment with trial and error as they continue to search for their best design for the task.
Richards, Jennifer.
Curriculum Specialist, Tennessee 4-H Youth Development.
Terms and Concepts Introduction
 Irrigation: The process of moving water from one place to another to help plants grow.
Concept of photosynthesis and plant care.
Engineering Process: Ask, Imagine, Plan, Create and Improve.
Setting the Stage and Opening Questions
 Tell students: Yesterday, your team of engineers was presented with the challenge of using everyday materials to build an irrigation system that can move 250mL of water over 1 meter.
You worked with your team to move through the Ask, Imagine and Plan stage.
Today, we are going to work on the Create stage.
By the end of our time together, you will be able to:
 Apply the steps of the Engineering Design Process to solve a realworld problem.
Show that you can work effectively in a team.
Remind students of the important points in Create:
 Test the prototype Does it work?
Evaluate the prototype Does it solve the problem?
How could it be made better?
Tell students: Yesterday, you identified the everyday materials you would need to find to build your prototypes.
If you were able to find all of your materials, you are ready to start building.
If you weren't able to find materials from around your home, take some time now and take a walk around the school to see what you can find that might be useful.
Encourage students to record notes about their progress on their Challenge Planning Sheet from yesterday.
Tell students that when they believe they are ready to test their irrigation system, they should come to you.
While students are working, ask them questions about their plans, particularly to explain their rationale for why they made certain choices.
After students have been working for about 20 minutes, have all groups stop working and engage the whole group in a "check-in." Ask each group to share their answers to the following questions:
 Circulate around the room to observe the students working.
Answer questions and facilitate problemsolving as students run into barriers and problems.
Tell us a bit about your progress so far.
What are you working on now?
What problems have you encountered?
How have you addressed those problems?
What will your next steps be?
Tell students they will have another 15 minutes to work today.
During this time, they should wrap up their tests and finalize their designs.
Tell students: We've spent our time together working in teams on a STEM engineering challenge.
We also established that by the end of today you would be able to:
 Apply the steps of the Engineering Design Process to solve a real-world problem.
Show that you can work effectively in a team.
What do you have left to finish up tomorrow?
What step is left in the Engineering Design Process?
While you are at home this afternoon and tonight, see if you can find examples of other real-world problems at home or in your village where you might use the Engineering Design Process to find a solution to the problem.
Tomorrow, you will finish up your designs and each team will test their design in front of the whole group.
Gather relevant information for decision-making.
As part of a group, identify and agree on a common task.
Supplemental Information Educational Standards Met
 EVSC.LS2.6.
Evaluate the interdependence among major biogeochemical cycles  in an ecosystem and recognize the importance each cycle has in maintaining ecosystem stability.
4.ETS1.1 Categorize the effectiveness of design solutions by comparing them to specified criteria for constraints.
4.ETS2.2.
Determine the effectiveness of multiple solutions to a design problem given the criteria and the constraints.
5.ETS1.1.
Research, test, re-test, and communicate a design to solve a problem.
5.ETS1.2.
Plan and carry out tests on one or more elements of a prototype in which variables are controlled and failure points are considered to identify which elements need to be improved.
Apply the results of tests to redesign the prototype.
Tennessee 4-H Youth Development
 Irrigation Challenge STEM Camp
 The learner will be able to:
 Apply the steps of the Engineering Design Process to solve a real-world problem.
Use strong communication skills to explain your design plan to others.
EVSC.LS2.6 4.ETS1.1.
4.ETS2.2 5.ETS1.1 5.ETS1.2
 Learners will be successful if they:
 Complete the Improve stage of the Engineering Design Process.
Prototypes from Day 2 of this lesson
 This lesson reinforces the concept of irrigation and the engineering process.
Students will work in groups to utilize their creativity and problem-solving skills to finalize the designs of their irrigation systems.
Students will then reflect on their successes and failures in this activity.
This lesson is Day 3 of the Irrigation Challenge STEM Camp lesson plan.
In this lesson, students will reflect on the experimentation process for their irrigation system designs and settle on a final design idea.
The ideas will then be shared with the rest of the class.
Students will be given an opportunity to reflect on the similarities and differences of the designs and the role of the Engineering Process throughout the week's activities.
Richards, Jennifer.
Curriculum Specialist, Tennessee 4-H Youth Development.
Terms and Concepts Introduction
 Irrigation: The process of moving water from one place to another to help plants grow.
Concept of photosynthesis and plant care.
Engineering Process: Ask, Imagine, Plan, Create and Improve.
Setting the Stage and Opening Questions
 Lead students through a quick review of what you did yesterday:
 What steps in the Engineering Design Process did we use yesterday?
Before you left yesterday, I asked you to see if you could find examples of other real-world problems at home or in your village where you might use the Engineering Design Process to find a solution to the problem.
What examples did you find?
Tell students: This week, your team of engineers has been working with everyday materials to build an irrigation system that can move 250mls of water over 1 meter.
You worked with your team to move through the Ask, Imagine, Plan and Create stages.
Today, we are going to finalize the Improve stage and present your final design to the whole group.
By the end of our time together, you will be able to:
 Apply the steps of the Engineering Design Process to solve a real-world problem.
Use strong communication skills to explain your design plan to others.
Write sample questions on chart paper as models for students to use for their own questions.
Remind students of the important points in Improve:
 Modify the prototype to address weaknesses.
Retest the solution to see if it works better now.
Allow students about 10 minutes to finish testing and final designs.
Invite students to present their final products to the whole class.
Encourage the other students to ask questions about why certain design elements were included, why they chose particular materials, etc.
Lead the whole group in a debrief discussion:
 How were the designs from one group similar to another?
How were they different?
Was there one design that worked better than the others?
In what ways did using the Engineering Design Process allow you to work as a team to meet your challenge?
Ask students to reflect on what they have learned by using the Engineering Design Process to build their marshmallow towers and their irrigation systems.
Ask them to share with a neighbor where they might use this process in their everyday lives.
Encourage volunteers to share their reflections with the class.
Gather relevant information for decision-making.
As part of a group, identify and agree on a common task.
Supplemental Information Educational Standards Met
 EVSC.LS2.6.
Evaluate the interdependence among major biogeochemical cycles  in an ecosystem and recognize the importance each cycle has in maintaining ecosystem stability.
4.ETS1.1 Categorize the effectiveness of design solutions by comparing them to specified criteria for constraints.
4.ETS2.2.
Determine the effectiveness of multiple solutions to a design problem given the criteria and the constraints.
5.ETS1.1.
Research, test, re-test, and communicate a design to solve a problem.
5.ETS1.2.
Plan and carry out tests on one or more elements of a prototype in which variables are controlled and failure points are considered to identify which elements need to be improved.
Apply the results of tests to redesign the prototype.
Imagine you are an engineer and part of a team that has been asked to build an irrigation system to water your school garden.
Your challenge is to build a prototype or a model using everyday items you can find at home or in nature.
Your model will be successful if it is able to move of 250mL of water over 1m.
Make sure your prototype moves the water as quickly as possible  while losing water along the way.
Imagine you are an engineer and part of a team that has been asked to build an irrigation system to water your school garden.
Your challenge is to build a prototype or a model using everyday items you can find at home or in nature.
Your model will be successful if it is able to move of 250mL of water over 1m.
Make sure your prototype moves the water as quickly as possible  while losing water along the way.
Ideas: Best Idea: Pros: Cons:
 What do we need to change?
Calculating the amount of water needed from rain and irrigation for the crop to reach maturity becomes important after early August.
The objective is to leave the field as dry as possible without lowering the yield.
Chapter: 17 Online Soil Survey Information SoilWeb Application 
 Figure 17.2 Opening page of SoilWeb application.
Note the drop-down options in the upper left-hand corner of the page when the Menu button is clicked.
moved  by holding down the left button on your mouse and moving the cursor to the location of your study site.
The map background can be changed by selecting Map Settings from the Menu.
Another drop-down list appears, offering the following map types: 1) satellite image, 2) a highway-only image, 3) a hybrid  view, or 4) a terrain image.
Selections can be saved for the next session.
The Menu's Help tab provides a list of soil survey terms employed in the website and their definitions.
Once the image background and location is determined, the latitude and longitude values of specific points are determined by moving the mouse cursor  to the desired location.
You can zoom in or out by using the features  of your mouse.
At the bottom right-hand corner of the image the latitude and longitude information for the + is provided.
To obtain soils information for a specific study area, double-click the cursor and a red circle with a white will appear, and the soil mapping unit  information at that specific location is displayed on the X left side of the image.
The soil  information available incudes: MU name; MU symbol and surface texture; MU composition ; MU slope and flooding or ponding; and MU data.
Additional information on a soil term or property can be obtained by clicking on a blue button containing a question mark.
Click on a soil name under the Map Unit Composition tab to obtain specific information about a map unit component.
A drop-down list appears with additional information about each soil.
The soils information available under the soil series selected  tab includes:
 1.
Soil Data Explorer this link provides soil series information for the selected soil.
The information available includes: official series description, available lab data {e.g., % sand, % silt, % clay, bulk density, % total carbon, % organic carbon, % organic matter, pH, base saturation, CEC [cation exchange capacity], % gypsum, % CaCO 3 [lime], SAR [sodium adsorption ratio], and others} , component and series associations , block diagrams of typical landscapes , a listing of the soil mapping units where the selected soil is dominant , and a visual map of where the selected soil is found in the US.
a) Profile sketch visual image of the typical profile including horizons and depths.
b) Selected soil property values are graphically shown by soil depth: % organic matter , % clay, % sand , Ksat , K factor , pH by water, EC , SAR , % CaCO2 , % gypsum, CEC , linear extensibility % , and data source.
Additional information about the selected soil can be found in the Soil Taxonomy, Land Classification, Hydraulic and Erosion Ratings, and Soil Suitability Ratings sections in the drop-down list.
The information available under the Soil Taxonomy tab includes: order, suborder, great group, subgroup, family, series, and source of the data.
The information available in the Land Classification tab includes: Land Capability Class , Ecological Site Description , and Forage Suitability Group.
In the Soil Suitability Ratings tab  information can be obtained about Waste Related , Engineering , Irrigation , Urban Recreational , Wildlife, and Runoff.
NOTE Not all states, counties, or areas will have data for all options within a category.
Figure 17.3 Zoom To Location options available from the Menu in SWA.
Figure 17.4 Map Settings options accessed via the SoilWeb Menu.
Figure 17.5 Soil Survey Definitions accessed via the Help tab in the SoilWeb Menu.
Figure 17.6 SoilWeb application image for Section 24, T110N, R50W, Brookings County, SD.
The cross  location  is shown in lower righthand corner.
Figure 17.7 Soil Mapping Unit drop-down list for site located  in SoilWeb application.
Figure 17.8 Soil profile sketch in the drop-down list for Brandt soil in map unit Z181A in SoilWeb application.
Soil Data Explorer BRANDT
 Lab Data Component Association Series Association Block Diagrame Map Units Extent
 Figure 17.9 Soil Data Explorer page for Brandt soil in map unit Z181A in SoilWeb application.
The page opens with the Official Series Description.
Figure 17.11 Soil Series Association profile sketches for the Brandt series in map unit Z181A in SoilWeb application.
Map units named for the BRANDT series
 Figure 17.13 List of soil map units in the United States where Brandt soil series is dominant using the SoilWeb application.
Figure 17.10 Lab data available for Brandt soil in map unit Z181A in SoilWeb application.
There are three pedons of data available.
Figure 17.12 Sample block diagram available from SoilWeb, Soil Data Explorer option.
Figure 17.14 Series extent map in the United States for the Brandt soil in map unit Z181A using the SoilWeb application.
Figure 17.15 Soil organic matter levels data for the Brandt soil in map unit Z181A using the SoilWeb application.
Figure 17.16 Example of help information for Brandt soil organic matter data in map unit Z181A using the SoilWeb application.
Figure 17.17 Percent sand data for the Brandt soil in map unit Z181A using the Soil Web application.
Figure 17.18 Additional soil information available in the drop-down sections for the Brandt soil in map unit Z181A using the SoilWeb application.
Figure 17.19 Example of the Ecological Site opening page for the Brandt soil in map unit Z181A using the SoilWeb application.
Figure 17.20 Irrigation Ratings for the Brandt soil in map unit Z181A using the SoilWeb application.
SEE: Soil Series Extent Explorer Application
 The Soil Properties application is an interactive map that allows you to visually explore soil properties aggregated on a regional and statewide basis.
This app is currently available only for California.
Use and Limitation of SoilWeb Application  Information
 SoilWeb application  information is useful in understanding how soils differ and will perform under various land-management systems.
Producers can integrate SWA data with yield-monitor information and other data to improve seeding, fertility, pest management, water/erosion conservation, tillage, and other crop-related management decisions.
It is important to point out that the SWA maps are based on NRCS soil maps, which were originally prepared in South Dakota at scale of 1:20,000 or 1:24,000.
As a result, the smallest delineation that can be shown on a South Dakota soil survey maps is about 2 acres.
Soils located in areas less than 2 acres are generally noted in the unit descriptions as inclusions.
If higher resolution is needed, a more detailed soil map is required.
This chapter outlines how to use SWA to obtain soil and land attributes for making land-use and management decisions.
Samples of output and the SWA website use are presented to demonstrate the potential and capabilities of SWA.
There are numerous useful, credible, and user-friendly websites providing soil and natural resource information.
Explore the sites and see the incredible wealth of information available to you online.
Abbreviations are provided in Chapter 16.
EM 8902 Revised January 2013
 Drip Irrigation Guide for Growers of Hybrid Poplar
 Figure 1.
Two-month-old hybrid poplars grown from 8-inch cuttings  and 7-yearold hybrid poplars.
Malheur Experiment Station, Oregon State University: Clint C.
Shock, director and professor; Rebecca Flock, former research aide; Erik Feibert, senior faculty research assistant; Andre Pereira, visiting professor 
 New Mexico State University: Mick O 'Neill, associate professor and superintendent, Agricultural Science Center, Farmington, New Mexico
 O ver the past 15 years, the Oregon State University Malheur Agricultural Experiment Station in Ontario, Oregon, and New Mexico State University Agricultural Science Center at Farmington, New Mexico, have evaluated hybrid poplar production, including irrigation criteria, irrigation amounts, irrigation systems, cover crops, and pruning.
This research has found distinct advantages for water use and wood productivity when drip irrigation is used.
Drip irrigation provides control and precision of irrigation timing, as well as the amount of water applied, while assuring high yield.
As a result, drip irrigation causes significantly less erosion, less deep percolation, and less leaching than furrow irrigation.
Drip irrigation can be managed to protect the environment, avoiding off-site losses of fertilizer and water.
Drip systems can be tailored to each crop and field.
Growers have many options for custom fitting drip irrigation to their specific situation.
It is difficult to describe in a short publication all of the factors that affect irrigation.
Thus, this publication provides a framework, general recommendations, and rationales to aid growers interested in maximizing their land use and wood production through drip irrigation.
Consult your local Extension agent or other agricultural professional for additional information.
As native timber supplies become less available, alternative sources of wood products are needed.
Hybrid poplar wood has proven to have desirable characteristics for many nonstructural timber products.
Growers have made experimental plantings of hybrid poplar for saw logs, peeler logs, and other uses.
Poplar is the common name given to all species of the genus Populus.
Conventional hybridization among poplar species has resulted in trees that combine desirable characteristics of different species.
Hybrid poplars are grown as short-rotation woody perennials.
Oregon State Extension Service UNIVERSITY
 Hybrid poplars grow best in fertile, productive agricultural soils.
Poplars need adequate moisture.
The best sites have annual precipitation close to the water use of the trees or access to groundwater or irrigation.
Poplar prefers a soil pH of 5.5 to 8 and does not do well in excessively acid or alkaline soils.
Poplar clones vary in their growth rates and tolerance to alkaline soils.
Select clones based on their adaptation to soil pH and climate.
Medium-texture soils are preferred.
Avoid soils subject to flooding during the summer growing season.
While it is not always possible to use the best site, avoid very poor sites because they result in low productivity and high operating costs.
Also consider operational factors such as the plantation location in relation to markets and easy access within the field for efficient operations and harvest.
Consider field shape, topography, and drainage for efficient mechanization.
Plant population and planting
 It is difficult to predict the optimum tree population.
Generally, as tree population decreases, tree size increases.
High tree populations, as used for pulp production, produce high yields of very thin trees.
In the Treasure Valley, hybrid poplar grown for saw logs is planted at a 14-foot by 14-foot spacing.
The minimum marketable tree size for saw logs is 12-inch diameter at breast height.
In the Treasure Valley, poplar trees normally are planted at leaf-out in mid-April as 8-inch dormant sticks.
Some producers find that 13to 14-inch sticks result in young trees with stronger root systems that are less subject to being uprooted by wind.
The ideal small-end diameter of sticks is 1/2 to 11/2 inches.
Leave one leaf bud of the stick above ground.
Irrigate the
 newly planted sticks immediately, and keep the soil wet until after bud break and rooting.
Rather than planting sticks, some producers plant poles.
Poles are grown on a "stool bed" of stumps.
One-year-old poles are 9 to 12 feet tall.
Two-year-old poles are 15 to 18 feet tall.
Before planting, all side branches are trimmed from the poles.
Only very straight poles are used.
The poles are inserted into vertical holes three feet deep.
Starting trees from poles is more expensive but has the advantage of developing very straight trunks.
Keep the plantation free of weeds or other vegetation.
Weeds or crops growing between the tree rows can significantly reduce tree growth, especially during the first 3 years.
Getting started with drip irrigation
 When designing a drip system, first determine the different irrigation zones.
Irrigation zones are based on factors such as topography, field length, soil texture, optimal tape run length, and filter capacity.
An irrigation engineer and system supplier may need to determine these factors and design the drip system.
Once the zones are assigned and the drip system designed, it is possible to schedule irrigation to meet the unique needs of each zone.
Daily crop water use
 Irrigation application must reflect crop water use.
Therefore, it is crucial to plan how much water to apply and when to apply it to optimize efficiency.
Water applied at any one irrigation should not exceed the soil water-holding capacity.
Customize irrigation intensity, frequency, and flow rates to meet the specific water needs of the crop and soil water-holding capacity of each field.
Typically, poplar plantations use drip tubing laid on the ground along the tree row.
Do not bury the drip tubing because roots can grow into the emitters and cause plugging.
The drip tubing emitters determine the flow rate of the water onto the soil.
Ideal emitter flow rates depend on the soil type.
Coarser soils usually require higher emitter flow rates.
At the Malheur Experiment Station, poplar research is conducted on silt loam with a slope of about 3 percent.
The drip irrigation system uses two drip tubes along each tree row, with emitters spaced 12 inches apart.
Low-flow emitters  provide uniform wetting without runoff.
This system applies 0.03 acre-inch/hour.
In the Columbia Basin of Oregon, commercial plantings on sandy soils use one drip tube along each tree row, with emitters spaced 3.75 feet apart.
This system applies 0.03 to 0.06 acre-inch/hour using 0.42 to 0.75 gal/hour emitters.
With older trees, drip tubing can be moved between the rows of trees to stimulate the growth of wider root systems.
Wide root systems help avoid uprooting of trees during windstorms.
Why measure soil water tension?
Soil water tension  is economically and environmentally important because it is the measure of how strongly water is held in the soil.
Tree growth is related to the amount of energy needed for plant roots to remove water from the soil.
SWT indicates the best moment to irrigate to maximize yield.
SWT also provides information on soil saturation, which can help growers avoid saturating the soil, thereby maintaining aeration of plant roots and reducing leaching losses of water or nutrients.
Viewed on a graph, the SWT readings clearly indicate the relative soil moisture condition in the tree root zone.
The use of granular matrix sensors and tensiometers to determine crop water needs is discussed in Irrigation Monitoring Using Soil Water Tension, EM 8900.
Based on a 3-year study at the Malheur Agricultural Experiment Station , it is recommended that drip-irrigated hybrid poplar in the Treasure Valley of eastern Oregon and southwestern Idaho be irrigated when SWT at an 8-inch depth reaches 25 cb.
This threshold for irrigation onset prevents yield reductions under the experimental conditions of the Malheur Experiment Station.
Growers can expect to irrigate drip-irrigated fields more frequently than furrow-irrigated fields.
One reason is simply that less water is applied per irrigation cycle with drip irrigation.
Poplar drip-irrigation systems inherently have low water application rates because of the wide spacing of the drip tubing and because water application is calculated based on the whole area between trees.
Installing more drip tubes along the tree row would raise the system cost, and water application could exceed the intake rate of the soil.
Installing more drip tubes between the tree rows would also complicate equipment traffic.
In research plots at the Malheur Experiment Station, optimum tree growth is achieved if 1 inch of water is applied when the soil water tension reaches 25 cb.
With this schedule, the interval between irrigations (the time between the end of one irrigation and
 the start of the next) is about 1 to 3 days during July and August.
In the Columbia Basin, with systems using one drip tube per row of trees, plantations are irrigated daily, applying the amount of water used the previous day.
With an application rate of 0.03 acre-inch/ hour, it takes 17 hours to apply 0.5 acre-inch of water.
Every trickle counts when you are battling a water shortage.
An ineffective or improperly managed filter station can waste a lot of water and threaten a drip system's fitness and accuracy.
In the West, sand media filters have been used extensively for microirrigation systems.
Screen filters and disk filters are common as alternatives or for use in combination with these filters.
Sand media filters provide filtration to 140 to 200 mesh, which is necessary to clean surface water and water from open canals for drip irrigation.
These water sources pick up a lot of fine grit and organic material, which must be removed before the water passes through the drip tape emitters.
Sand media filters are designed to be selfcleaning through a "back flush" mechanism.
This mechanism detects the drop in pressure due to the accumulation of filtered particles.
It then flushes water back through the sand to dispose of clay, silt, and organic particles.
Sand used for filters should be between mesh size 16 and 20 to prevent excessive back flushing.
To assure enough clean water for back flushing, several smaller sand media filters are more appropriate than a single large sand media filter.
In addition to a sand media filter, a screen filter can be used as a prefilter to remove larger organic debris before it reaches the sand media filter, or as a secondary filter before the irrigation water enters the drip tube (Figure 2,
 page 5).
For best results, filters should remove particles four times smaller than the emitter opening, as particles may clump together and cause clogs.
Screen filters can act as a safeguard if the main filters fail, or may act as the main filter if a sufficiently clear underground water source is used.
The drip hose should be lifted periodically SO that leaves, soil, and debris do not cover the hose.
If the drip hose is not lifted, roots will grow over the hose, anchor it to the ground, and eventually pinch off the flow of water.
Place a water flow meter between the solenoid valve and each zone and record its gauge daily.
This provides a clear indication of how much water is applied to each zone.
Records of water flow can be used to detect deviations from the standard flow of the system, which may be caused by leaks or by clogged lines.
Leaks can occur unexpectedly as a result of damage by insects, animals, weeding crews, or farming tools.
Systematically monitor the lines for physical damage.
It is important to fix holes as soon as possible to prevent uneven irrigation.
Chlorine clears clogged emitters
 If the rate of water flow progressively declines during the season, the tubes may be slowly plugging, resulting in severe damage to the crop.
In addition to maintaining the filtering stations, regular flushing of the drip tube and application of chlorine through the drip tube will help minimize clogs.
Once a month, flush the drip lines by opening the far ends of a portion of the tubes at a time and allowing the higher velocity water to wash out the sediment.
Because algae growth and biological activity in the tape are especially high during June, July, and August, chlorine usually is applied at
 2-week intervals during these months.
Buffering the irrigation water to below pH 5.0 increases chlorine activity significantly.
If drip lines become plugged in spite of maintenance, many cleaning products are available through irrigation system suppliers.
Choose a product appropriate for the specific source of contamination.
Manage irrigation and fertilization together to optimize efficiency.
Chemigation through drip systems efficiently delivers chemicals in the root zone of the receiving plants.
Because of the precision of application, chemigation can be safer and use less material.
Several commercial fertilizers and pesticides are labeled for delivery by drip irrigation.
Injection pumps with backflow prevention devices are necessary to deliver the product through the drip lines.
These pumps allow for suitable delivery rate control, while backflow prevention protects both equipment and the water supply from contamination.
Remember that in Oregon, water belongs to the public, not the landowner.
Other safety equipment may be required; contact a drip-irrigation system supplier for details.
Fertilizer can be injected through the drip system.
Typically, less nitrogen fertilizer is needed with drip irrigation than with furrow irrigation because the fertilizer is spoon-fed to the root system and little is lost to leaching.
Leaf tissue analysis performed by a qualified agricultural lab can help determine poplar nutrient needs during the season.
Figure 2.
Drip irrigation system with a prefilter, pump station with backflow prevention, and chemical injection site.
A pressure control valve is recommended to adjust the water pressure as desired before it enters the drip lines.
A water meter can be placed after the pressure control or between a solenoid valve and each zone.
An air vent provides vacuum relief.
Vacuum relief is necessary between the solenoid valve and the drip tapes to avoid suction of soil into the emitters when the system is shut off.
Funding to help prepare this publication was provided by an Oregon Watershed Enhancement Board Grant.
Drip irrigation is the slow, even application of low-pressure water to soil and plants using plastic tubing placed directly at the plants' root zone.
Drip irrigation causes little evaporation or runoff, saves water by directing it more precisely to the root zone, reduces the transmission of pathogens, and produces fewer weeds.
Drip irrigation systems facilitate water management in fields that are difficult to irrigate due to variable soil structure or topography.
Poplar wood productivity responds very sensitively to irrigation management.
Recommended soil water tension at an 8-inch depth for irrigation onset for dripirrigated poplar is 25 centibars.
"Soil water potential" is the negative of "soil water tension." A soil water potential of -20 cb is the same as a soil water tension of +20 cb.
Also, cb is the same as kPa.
Drip systems require careful design and maintenance.
Extension work is a cooperative program of Oregon State University, the U.S.
Department of Agriculture, and Oregon counties.
Oregon State University Extension Service offers educational programs, activities, and materials without discrimination based on age, color, disability, gender identity or expression, genetic information, marital status, national origin, race, religion, sex, sexual orientation, or veteran's status.
Oregon State University Extension Service is an Equal Opportunity Employer.
Trade-name products and services are mentioned as illustrations only.
This does not mean that the Oregon State University Extension Service either endorses these products and services or intends to discriminate against products and services not mentioned.
IRRIGATION MANAGEMENT S E R I E S
 EFFICIENCIES AND WATER LOSSES OF IRRIGATION SYSTEMS
 Danny H.
Rogers, Freddie R.
Lamm, Mahbub Alam, Todd P.
Trooien, Gary A.
Clark, Philip L.
Barnes and Kyle Mankin, Kansas State University, Research and Extension Engineers
 Efficiency ratings receive a lot of attention.
We like efficient engines, air conditioners, water heaters and furnaces.
Conservationists like efficient water systems that deliver water for its intended use without loss due to leakage, spills or contamination.
Since irrigation is the largest appropriated water user in Kansas, irrigation systems also receive merit based on how efficient they are reported to be.
While this might sound straightforward and simple, there is room for confusion because there are different ways to define efficiency.
Efficiencies also vary in time and with management.
Very "efficient" systems by some definitions can be very poor performers by other definitions, for example, if distribution uniformity and delivery amount are inadequate to fulfill crop need.
This bulletin will define and explain several common efficiency terms in use for irrigation systems and show how these terms apply to some common irrigation situations.
Water Conveyance Efficiency : The percentage of source water that reaches the field.
E = 100 (W f / W = Water delivered to field W, = Water diverted from source S
 Conveyance efficiency is generally a concern for irrigation districts that supply a group of farmers through a system of canals and open ditches.
Since most Kansas irrigation water pumped and carried in closed conduits, conveyance efficiency should be nearly 100 percent.
Water Application Efficiency : The percentage of water delivered to the field is used by the crop.
E=100 WC = Water available for use by the crop W = Water delivered to field
 Water application efficiency gives a general sense of how well an irrigation system performs its primary task of getting water to the plant roots.
However, it is possible to have a high E but have the irrigation water a SO poorly distributed that crop stress exists in areas of the field.
It is also possible to have nearly 100 percent E
 but have crop failure if the soil profile is not filled sufficiently to meet crop water requirements.
It is easy to manipulate W SO that E, can be nearly 100 percent.
Any irrigation system from the worst to the best can be operated in a fashion to achieve nearly 100 percent E, if W is sufficiently low.
Increasing E, in this manner totally ignores the need for irrigation uniformity.
For E to have practical meaning, a W needs to be sufficient to avoid c undesirable water stress.
Water application efficiency sometimes is incorrectly used to refer to the amount of water delivered to the surface of the soil in an irrigated field by a sprinkler system.
Water losses can occur after reaching the soil surface, leading to overestimation of the application efficiency.
E a is often confused with water storage efficiency , which is the fraction of an irrigation amount stored in the crop root zone.
The use of this term is discouraged because of the difficulty in determining the crop root zone and because E can be very low while sufficient water is provided to the crop.
Water losses include surface runoff and deep percolation.
If a center pivot is equipped with a properly designed nozzle package and operated using best management practices and irrigation scheduling, these losses can be negligible.
However, for many systems, these losses can be large and result in poorly distributed or nonuniform irrigation.
Irrigation Efficiency : The percentage of water delivered to the field that is used beneficially.
Wb = Water used beneficially Wf Water delivered to field
 Irrigation efficiency is more broadly defined than water application efficiency in that irrigation water may have more uses than simply satisfying crop water requirements.
Other beneficial uses could include salt leaching, crop cooling, pesticide or fertilizer applications, or frost protection.
However, most Kansas irrigation systems are single-purpose, that is to supply water for crop use, which allows water application efficiency and irrigation efficiency to be used interchangeably.
Water lost to percolation below the root zone due to nonuniform application or over-application water runoff from the field, wind drift and spray droplet evaporation all reduce irrigation efficiency.
For a better insight of the system performance, water distribution should also be considered.
application depth delivered to the least-watered part of the field.
Water Distribution Efficiency : The percentage of the average
 Ed = 100 [ 1 ] y = Average absolute numerical deviation in depth of water stored from average depth stored during the irrigation
 d = Average depth of water stored during irrigation
 The water distribution efficiency indicates the degree of uniformity in the amount of the water infiltrated into the soil.
It also could be defined as the uniformity in depths applied at the surface based on catch-can measures for sprinkler systems.
This concept for uniformity was originally developed by Christiansen in 1942 for sprinkler systems.
Figure 1.
Application, E and distribution, Ed, efficiencies and the effect on crop production illustrated by two-dimensional soil profiles.
For these examples, E estimates are made assuming no runoff.
Generally, high uniformity is associated with the best crop growth conditions since each plant has an equal opportunity to access applied water.
Non-uniformity results in areas that are under-watered or overwatered.
Distribution Uniformity : The percentage of average application amount received in the least-watered quarter of the field.
q Average low-quarter depth of water infiltrated  Xm = Average depth of water infiltrated 
 The distribution uniformity gives an indication of the magnitude of the distribution problem.
It can be defined as the percent of average application amount in the lowest quarter of the field.
U is less tedious to calculate than the Ed.
Irrigation efficiency examples are shown in Figure 1 for surface and sprinkler irrigation.
Examples ,  and  show a series with increasing application depth for a field with the heaviest application occurring at the top of the field.
The dashed line in the profile represents the depth of water needed to meet crop requirements until the next irrigation event.
When the shaded application depth does not reach this line, that portion of the field would be under water stress.
Example  illustrates how a portion of a crop can be under stress with 100 percent application efficiency, while example  shows a crop with no stress but a low application efficiency.
Notice crop vigor is represented as less than optimum for areas with heavy deep percolation.
Excess water can leach needed nutrients or cause waterlogged growing conditions.
The application efficiencies in Figure 1 are made using a no-runoff assumption, although for the surface irrigation example , , and , this might be better represented as complete tailwater capture and reuse.
Example ,  and  could be
 Figure 2.
Illustration of sprinkler package water distribution uniformity versus infiltrated water distribution uniformity in soil.
Table 1.
Range of Application Efficiencies for Various Irrigation Systems
 System Type	Application Efficiency Range* 
 Traveling Gun	60 70
 Center Pivot & Linear	70 95
 Solid Set	70 85
 Point source emitters	75 95
 Line source emitter	70 95
 * Efficiencies can be much lower due to poor design or management.
These values are intended for general system type comparisons and should not be used for specific systems.
thought of as blocked-end or diked surface irrigated fields.
Blocking the end of the field generally results in the driest portion of the field being about 2/3 to 4/5 of the length of run with wettest conditions and the potential for deep percolation losses split between the upper and lower portion ends of the field.
Sprinkler irrigation illustrations are shown in examples , , and.
Example  is the desirable situation while  illustrates crop stress due to under-irrigation and  shows overirrigation.
Center pivot sprinkler packages, even if properly designed, do not have perfect distribution uniformity.
Each nozzle outlet progressively has to cover a larger land area (concentric
 circles) with increasing distance from the center pivot point.
Each outlet has a unique and specific discharge rate requirement.
However, nozzle outlets are not manufactured in an infinite number of sizes.
For a specific nozzle outlet, the designer will select the nozzle outlet size that most closely matches the design specification.
Sprinkler spacing must also be consistent with the manufacturer's recommendations to avoid distribution problems.
Good designs should have distribution uniformities of approximately 90 percent.
In Figure 2, the average design application depth is represented by the solid green line above the soil surface.
The dotted black line that moves above and below the design depth represents what actual measured results might look like.
Figure 3.
Irrigation water loss and storage locations.
Table 2.
Estimated Sprinkler Water Loss Components for a 1-inch Irrigation.
Ground evaporation, runoff, and deep percolation were negligible 
 Air	Canopy	Surface	Total	Application
 System	Loss	Loss	Loss	Loss	Efficiency
 Impact	0.03	0.12	-	0.15	85%
 Spray Head	0.01	0.07	-	0.08	92%
 LEPA	-	-	0.02	0.02	98%
 *Runoff within field, distribution, or deep percolation loss are not considered.
Table 3.
Surface Irrigation Loss Estimates*
 Loss	Estimate Method	Irrigation Applied
 Evaporation	 = 0.08 inches**	2.00
 Evaporation	** = ac-in/day	0.28
 Evaporation	 = 0.60 ac-in/day	0.94
 Leakage	 = 0.5 ac-in/day	0.78
 * Distribution or deep percolation loss not considered Same rate as LEPA.
8 hours represents watered furrow conditions during advance and recession.
Every other row irrigation.
*** 20 ft.
strip, 1320 ft.
long.
If the soil surface is sloped and the application rate exceeds the soil intake rate and surface storage capability, then water movement in the field will occur.
If this water moves off the field as runoff, water application efficiency is reduced.
Within the field, water movement can cause nonuniform storage, resulting in under-watering on slopes and overwatering in flat areas.
This illustrates why application efficiency alone does not always indicate the irrigation condition in a field.
Slope, surface condition, and infiltration capacity all affect the depth and uniformity of water delivery to the roots.
Determination of application efficiency of a specific irrigation system is generally time consuming and often difficult.
One difficulty is that efficiency varies in time due to changing soil, crop and climatic conditions.
Table 1 lists typical ranges of reported application efficiency.
Of course, poorly designed or operated systems can have efficiencies even lower than the shown values.
In general, sprinkler systems in Kansas are operated at higher application efficiency than surface flood systems.
Although a well designed and managed surface system
 can be quite efficient, in general these systems have lower efficiency due to length of runs that are too long and incorrect set times.
Most set times, in order to minimize labor input, are fixed at 12 or 24 hours intervals.
Irrigation water losses, illustrated in Figure 3, include air losses, canopy losses, soil and water surface evaporation, runoff, and deep percolation.
The magnitude of each loss is dependent on the design and operation of each type of irrigation system.
Table 2 shows an estimate of the application efficiency of three sprinkler packages, assuming ground evaporation, runoff and deep percolation are negligible.
Ground evaporation may be an important component early in the season, before the crop canopy covers the surface.
Air losses include drift and droplet evaporation.
Air losses can be very large if the sprinkler design or excessive pressure produce a high percentage of very fine droplets.
Drift is normally considered to be water particles that are removed from the target area, while droplet evaporation would be the loss of water by evaporation directly from the drop of water while in flight.
Direct movement and droplet evaporation vary, but the general estimate of droplet evaporation is small, probably less than 1 percent of the output.
Total air loss under properly-operating sprinklers and low wind conditions is likely to be in the 1 to 3 percent range, although some older publications, have much higher values.
Table 2 assumes 3 percent for the impact sprinkler and 1 percent for the spray head at a 5 foot height.
Air losses were assumed to be negligible for the bubble mode LEPA head.
Canopy losses include losses due to water held on the plant  and canopy evaporation during the irrigation.
Water evaporation from the wetted surface of the plant does reduce transpiration by the plant.
However, evaporation from a free water surface is faster than
 transpiration through plant stomates.
Net canopy evaporation loss estimates range from 0.02 to 0.04 inch per hour.
Two hours of wetting was assumed for the impact sprinkler and 45 minutes for the spray nozzle.
Plant interception loss estimates range from 0.04 to 0.08 inches.
The 0.04 inches loss estimate was used in Table 2.
The only loss shown for the bubble mode LEPA nozzle is surface water evaporation.
Since the LEPA system uses an application rate in excess of soil intake capabilities, the free water surface must be held on the soil surface until it can be infiltrated.
The surface water evaporation loss estimate is 0.01 inch/hour over the two hours estimated for intake to be complete.
In all examples of Table 2, water movement as runoff or redistribution of the surface water, deep percolation, and ground evaporation were considered to be negligible.
Any runoff from the field or deep percolation would reduce application efficiency by a percentage of the total application amount.
Runoff of up to 60 percent of the application amount has been measured for in-canopy sprinkler heads on sloping ground.
Surface irrigation losses include runoff, deep percolation, ground evaporation and surface water evaporation.
Runoff losses can be significant if tailwater is not controlled and reused.
Although use of tailwater reuse pits could generally increase surface application efficiency, many surface irrigators use a blocked furrow to prevent runoff.
Usually the lower portion of the field is leveled to redistribute the tailwater over that portion.
While runoff may be reduced to near zero, deep percolation losses may still be high with this practice.
Surge irrigation can accomplish faster furrow advances.
To further improve an advance time, large furrow flows may be used.
However, care should be taken to avoid furrow erosion.
Some chemicals  have been reported to be useful in reducing erosion.
Rapid advance allows better water distribution efficiency and smaller application
 amounts, which can reduce deep percolation losses and improve overall irrigation efficiency.
Evaporation loss percentages from a surface irrigated field are small.
The components of the loss are furrowwater evaporation , tailwater evaporation  and tailwater pit evaporation, and are dependent on system operation.
Loss estimates are shown in Table 3 assuming a 4-inch gross application depth is applied to a 160-acre surface irrigated field using 12-hour sets on a 10-day irrigation interval.
Some loss components were estimated on a daily basis, SO the percent loss was dictated by the daily application amount.
Tailwater pit leakage is also a potential loss and is shown in Table 3.
Various terms exist to describe how efficiently irrigation water is applied and/or used by the crop.
Incorrect usage of these terms is common and can lead to misrepresentation of how well an irrigation system is performing.
Reporting of both application efficiency and water distribution uniformity would provide a better indication of overall irrigation system performance.
However, these values are often difficult to measure in the field.
They also vary over time and with operating conditions.
OTHER AVAILABLE IRRIGATION PUBLICATIONS
 Predicting the Final Irrigation for Corn, Grain Sorghum, and Soybeans MF2174 Scheduling Irrigations by Electrical Resistance Blocks L901 Soil Water Measurement: An Aid to Irrigation Water Management L795 Soil, Water and Plant Relationships L904 Sprinkler Package Effects on Runoff L903 Subsurface Drip Irrigation for Field Corn: An Economic Analysis L909 Surge Irrigation L912 Tensiometer Use In Scheduling Irrigation L796
 Using Evapotranspiration Reports for Center Pivot Irrigation Scheduling L915 Using Evapotranspiration Reports to Schedule Irrigation on Furrow Irrigated Ground L914 Water Measurement as a Management Tool L878
 Packages on Center Pivots	L908
 Guidelines for Use of Propeller-Type
 Irrigation Water Methods	L869
 Irrigation Water Measurement	L877
 for Center pivots	L907
 and Flat Sprays on Corn	L879
OREGON STATE UNIVERSITY EXTENSION SERVICE
 WATER SYSTEMS: Taking Care of a Precious Resource
 Stan Dean and Rachel Werling
 E veryone needs high-quality water, but water is a limited resource.
These best practices for wells, ponds and other water systems can help you secure a safe, reliable water supply adapted to your needs.
These practices also help to ensure that we protect our streams, lakes and groundwater.
The useful life of a well can extend for decades with little or no trouble, but a variety of factors can lead to problems.
These steps can help:
 Periodically check the flow of the well to make sure that it remains good.
A well casing projects above ground so no water can enter the top.
Note the identification tag issued by the Oregon Department of Water Resources.
Periodically test for contaminants in wells used for potable water.
The quality of the water can change over time.
Regulations require that well owners test for coliform bacteria, arsenic and nitrate during real estate transactions.
It may be important to test for other contaminants as well.
Make sure wells are sited appropriately.
Wells may need maintenance at any time of
 Stan Dean, OSU Extension Land Steward and civil engineer, and Rachel Werling, coordinator, OSU Land Steward program.
Photo: Rachel Werling,  Oregon State University Ron and Pam Hillers check out their rainwater collection system in Ashland, Oregon.
Pipes underneath the tank move water through an irrigation system.
Use this document to evaluate and improve your own water systems
 1.
Read Water Systems: Taking Care of a Precious Resource.
2.
Use Worksheet 1: Resource Assessment for Water Systems, page 8, to assess your resource.
3.
Use Worksheet 2: Management Activity Assessment for Water Systems, page 11, to assess your current management practices and identify areas for improvement.
If you have questions, contact your local Extension office, Soil and Water Conservation District, or regulators, such as the watermaster from the Department of Water Resources or the Department of Environmental Quality.
About the Rural Resource Guidelines
 This is one of a series developed for private landowners with little or no technical background by the Land Steward program of Oregon State University's Southern Oregon Research and Extension Center.
This guide covers general terms and helps users assess resources and manage property in a responsible manner.
This guide was developed for use in Jackson and Josephine counties, but many of the practices are applicable to other areas.
year.
Consider the consequences if a well fails and you can't get to it in snowy conditions or when dry grass creates a fire hazard in the summer.
Periodically check the flow of your spring and test for contaminants.
The performance of a spring can change seasonally and from year to year.
Maintain the integrity of spring boxes.
Developing a spring means constructing facilities to help get the water from the ground into your delivery system.
Most spring boxes gather water in an enclosed structure, preventing contact with rodents and mosquitoes.
Consider installing treatment systems if the water is used for potable purposes.
This depends on the quality of the spring water and the security of the spring box and other parts of the system.
Use water wisely.
Whether water is supplied from surface water, an irrigation district, or from wells, a
 Screen surface water intakes to keep fish out.
Intakes located in the watercourse should be screened wherever surface water diversions are used.
Reduce contamination.
Excess water moving off farmed areas can be a significant source of contaminants to our streams, rivers and groundwater.
Consider these steps to cut down on contamination:
 Practice farming techniques that minimize soil loss and keep sediments out of waterways.
Practice techniques that minimize the amount of percolation to groundwater to help keep groundwater clean.
Apply the least amount of fertilizer necessary.
Excessive fertilizer can run off to surface waters or seep into the groundwater and become pollutants.
Exercise caution when using herbicides and pesticides.
Do not allow these products to enter surface or groundwater.
Herbicides and pesticides should not be used as an automatic first choice; use them only as one part of an Integrated Pest Management strategy that considers multiple management tactics.
key management practice is efficient delivery that minimizes waste.
Water conservation in agricultural applications has the potential for large savings.
Ponds offer enjoyment and can serve a variety of purposes, but they commonly fail over time for a number of reasons.
They can cease to hold water due to burrowing animals, pond liner failure and erosion.
Inlet, outlet and overflow facilities can also fail.
Ponds accumulate silt and other debris over time, decreasing their capacity.
Ponds can develop water quality problems, including stagnation and odors.
They can be havens for mosquitoes, and submerged and floating aquatic vegetation can become a nuisance.
Here are some steps that can help:
 Prevent stagnation.
If stagnant water is not acceptable, try aerating the water, harvesting excessive weeds and removing accumulated sediments.
Dredge responsibly.
If sediments are dredged, check with the Department of Environmental Quality regarding proper disposal of dredged material.
It may also be necessary to control pests such as mosquitoes.
Photo: Rachel Werling, Oregon State University This pond located near animal pastures shows an excess of algae growth.
Such an "algae bloom" can be an indication that there is too much nutrient runoff from fertilizer or manure in nearby agricultural lands.
Prevent runoff and manage nutrients.
Excessive nutrients, such as nitrogen and phosphorous, often cause water quality problems.
Excess nutrients are difficult to remove from ponds, since these nutrients will continue to be cycled through the water column and sediments.
Dredging sediments and removing vegetation can help, but these efforts could fall short.
One key management practice is to prevent runoff from lands receiving fertilizer applications from entering ponds.
Avoid invasives.
Exotic species of plants and animals can create serious problems in our natural waterways.
When ponds overflow and come into contact with other surface waters, invasive plants like parrot feather, yellow flag iris and purple loosestrife can spread.
If the pond is suspected of being contaminated or of having warm water, check with the Department of Environmental Quality for guidelines on proper removal or release of the water.
When constructed and maintained in accordance with state standards, septic tanks and drain fields are usually reliable and safe for the environment.
However, in certain situations, they can contribute excessive nitrate to groundwater.
Failure that results in surfacing of
 Graphic  Oregon State University A septic system is a safe, reliable way to break down wastes.
Keep harmful chemicals out.
wastewater can lead to odor, nuisances and pollution.
Septic tanks rely on bacteria to break down wastes, and it is important to keep the bacteria healthy.
Keep harmful chemicals and materials from entering the system.
Avoid or reduce the use of bleach.
Small amounts of cleaning bleach will do little harm, but putting a large amount in the system could affect its biology.
Avoid fats, oils, grease and excessive food waste (typically associated with heavy use of in-sink garbage
 disposals).
While food wastes will not harm the biology in the septic tank, the wastes will cause the tank to fill up faster than necessary.
Keep recreational vehicle waste out of septic tanks.
Keep plastics and other wastes that don't decompose out of the system.
Carefully consider the use of additives.
Some additives promise to enhance septic systems but are typically unnecessary.
Pump the solids out of the septic tanks every few years, depending on use.
If tanks fill with too many solids, they will not work properly.
Keep trees and woody vegetation off drain fields because their roots can damage parts of the system.
Encourage grasses on drain fields.
Paving, vehicular traffic, structures, and large animals should also be kept off the drain fields.
Site septic systems appropriately.
Note that these systems can need maintenance at any time of year.
Don't put a septic tank in a location that would make it difficult to pump out every few years.
Photo: Rachel Werling, Oregon State University In this rainwater harvest system, water runs off the roof, is collected in gutters, and goes through pipes into a storage tank.
Not shown are pipes running from the bottom of the tank underground to a pump, which moves the water through an irrigation system.
recommendations in this manual are using good management practices.
These practices address ways to keep the water free of debris and mosquitoes, allow the rainwater systems to be easily cleaned, and prevent freezing problems in the winter.
Consult Oregon Smart Guide: Rainwater Harvesting, published by the Oregon Department of Consumer and Business Services.
Systems that meet the
 Most rainwater harvest systems are not intended to provide potable water, but it is possible for misunderstandings to happen.
Nonpotable systems should be clearly identified with signs, or by painting pipes purple.
To Subsurface Drip Irrigation
  Oregon State University Graywater systems move drainage from household waste through irrigation systems.
Keep harmful chemicals out of graywater systems.
Depending on the uses of the graywater and the configuration of the system, chemical-free practices may be even more critical to graywater systems than they are to septic systems.
Generally, graywater systems are highly regulated, and following the regulations results in excellent management practices.
The way in which stormwater moves through and away from structures and developed areas can be critical.
Use pipes and ditches to convey stormwater away from buildings.
Water can damage structures.
Control water velocity to prevent erosion of soils.
Use retention basins, berms and drop structures to control velocity as water is conveyed.
Photo: Jason Johnson, USDA-NRCS A rain garden can clean storm water before it enters waterways.
It also allows water to percolate into the ground, adding to the groundwater supply.
Make sure that stormwater doesn't pick up contaminants.
The flow should not be routed through areas that contain stored manures, chemicals, or fuels.
Keep waste out of stormwater.
Encourage stormwater to percolate into the ground through facilities such as permeable pavement.
Try a rain garden.
Vegetative systems can enhance water quality, slow the movement of water and encourage percolation.
Examples of vegetative systems include rain gardens, bioswales and buffer strips.
These management practices apply to all of the above water facilities.
Practice conservation.
Surface water and groundwater are precious resources, and it is important to conserve water.
At home, use watersaving appliances, along with low-flow showers, faucets and toilets.
Outdoors, consider using drip irrigation systems.
Conduct inspections.
Water systems contain working parts, such as pipes, pumps, and a variety of mechanical and electrical equipment.
To keep the systems functioning properly, periodically inspect parts of the systems and maintain them in good working order.
Document the location of underground pipes, tanks and other facilities.
It is easy to forget where things are buried years after the work is done.
Marked maps and photos are good tools.
When installing new systems, try using metallic tracer wire with plastic
 Keep operation and maintenance instructions.
One good management practice is to organize a comprehensive set of instructions for the systems.
The instructions should include published information supplemented with site-specific needs.
Develop contingency plans.
For critical systems, it is important to know how to respond in the event of a failure.
For example, if a home is served by a single well and has no other source of potable water, the homeowner should know how to respond in the event of a well failure.
pipe so that metal detectors can locate pipes in the future.
In general, water systems are highly regulated by a variety of state and local agencies.
Here are some regulatory highlights for the different types of systems.
Water wells are permitted by the Oregon Department of Water Resources in accordance with specific standards.
Approval for construction of domestic wells is nondiscretionary; as long as the well meets state standards, it is allowed.
The standards address where wells can and cannot be located, and how they must be constructed.
Wells must be constructed by a licensed and bonded well driller or by a landowner who has applied for and received a Landowner's Water Well Permit, as well as a landowner bond.
Landowners or drillers must also follow reporting requirements during construction.
Single-family residences served by wells can use up to 15,000 gallons per day for domestic purposes; those wells can also be used to irrigate up to a half-acre of noncommercial crops.
Wells can also be used for up to 5,000 gallons per day for commercial purposes other than irrigation.
Use of more water requires a water right permit, which may be difficult to obtain.
The uses from a well that are allowed without a water right permit are limited per parcel  or well system..
Within incorporated areas such as cities, ordinances generally prohibit private wells and require hookup to the municipal water supply system.
Landowners can use springs under certain limited conditions.
If, under natural conditions, flow from the spring would normally leave the property, it is considered water of the state.
In that case, spring water can only be used with a water right permit from the Department of Water Resources.
Surface water diversions require water rights permits issued through the Department of Water Resources.
Water rights laws are complicated.
Obtaining new water rights can be difficult and sometimes impossible.
Irrigation district deliveries are typically made under an agreement between the district and the landowner.
The agreements specify the amount of water that can be used, the times it is available and the location where it is available.
Watermasters also have oversight of irrigation district deliveries.
Ponds are regulated by the Department of Water Resources.
Pond regulations include:
 A primary water right permit is required for construction of ponds and to hold water in ponds.
Larger ponds  must have the dam/levee designed by a licensed engineer to ensure that the facilities are constructed in a safe manner.
Smaller ponds also require a primary water right permit, but the dam does not need to be engineered.
A secondary water right permit can be required to actually use the water in ponds unless the water is only used for purposes that are exempt.
Stock watering is an example of an exempt use that does not need a secondary permit.
Another exemption is the collection and use of rainwater as long as it is collected from artificial impervious surfaces.
Ponds holding rainwater collected from artificial impervious surfaces do not need a primary or secondary water right permit as long as the storage facility is designed in a way that prevents any other type of surface water from entering the pond.
Bulge ponds that temporarily store irrigation water may also be exempt from needing a permit.
Consult with your local watermaster.
Septic systems are permitted by Oregon Department of Environmental Quality in accordance with state standards.
The standards address where facilities can
 be located and design requirements.
In certain situations, owners must have maintenance contracts with certified professionals.
Most cities prohibit septic systems wherever is it possible to connect to a municipal wastewater collection and treatment system.
Rainwater can be collected and used as long as it has not touched the earth's surface and is captured from an artificial impermeable surface.
Once it comes in contact with the earth it becomes property of the state.
State requirements for rainwater harvest systems vary depending on how the water is used:
 If rainwater is for potable use, plumbing standards govern design of the system, and proper treatment is required.
Another set of plumbing standards applies if the water is used for nonpotable, nonirrigation purposes, such as flushing toilets or cooling water.
If the rainwater is used for irrigation only, it is not regulated by the state under the plumbing code; however, local building officials may have special requirements, and your project may need to meet building and electrical standards.
Graywater systems are subject to a stringent set of requirements by the Oregon Department of Environmental Quality.
The extent of the requirements depends on the uses of the graywater.
Permits and annual reporting and fees are required.
Stormwater regulations originate at the federal level under the Clean Water Act, which is administered by the U.S.
Environmental Protection Agency.
One set of requirements applies to municipalities that collect stormwater in piping systems and discharge to water courses.
In Oregon, responsibility for municipal stormwater systems is delegated to the Department of Environmental Quality and then to the local municipalities.
The cities of Medford and Ashland manage their own stormwater program, while Rogue Valley Sewer Services oversees the program on behalf of the cities of Phoenix, Talent, Central Point and urbanized parts of Jackson County.
These programs have elements that address public education and outreach, control of illicit discharges and management of large construction projects.
Stormwater programs typically require compliance through implementation of management practices.
While these programs are not required for rural homeowners, the principles and practices for managing stormwater are good for everyone.
For information on public drinking water systems, contact the Oregon Health Authority and the Oregon Department of Environmental Quality.
OHA regulates drinking water systems, and DEQ has a source water protection program to help protect the quality of drinking water supplies.
More OSU Extension publications
 United States National Institute Department of of Food and Agriculture Agriculture
 Sustainable Agriculture Research & Education
 This material is based upon work supported by the National Institute of Food and Agriculture, under award number EW18-015 through the Western Sustainable Agriculture Research and Education program.
USDA is an equal opportunity employer and service provider.
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author and do not necessarily reflect the view of the U.S.
Department of Agriculture.
This series was developed by the Oregon State University Land Steward working group: Rachel Werling, Land Steward coordinator; Max Bennett, Extension Forestry and Natural Resources faculty and associate professor; Clint Nichols, rural planner, Jackson County Soil and Water Conservation Service; and Land Stewards Stan Dean, Jack Duggan, Don Goheen, Scott Goode and Cat Kizer.
2019 Oregon State University.
Extension work is a cooperative program of Oregon State University, the U.S.
Department of Agriculture, and Oregon counties.
Oregon State University Extension Service offers educational programs, activities, and materials without discrimination on the basis of race, color, national origin, religion, sex, gender identity , sexual orientation, disability, age, marital status, familial/parental status, income derived from a public assistance program, political beliefs, genetic information, veteran's status, reprisal or retaliation for prior civil rights activity.
Oregon State University Extension Service is an AA/EOE/Veterans/Disabled.
Worksheet 1: Resource assessment for water systems
 Use this checklist of characteristics to assess your water systems.
Use extra paper if necessary.
Yes	No	sure	Not	N/A
 Do you have documented water rights or agreements?
Water rights may be required for wells and are
 required for stream diversions.
Agreements with irrigation districts are usually required.
Do you understand the requirements and limitations of the water rights or agreements?
Potable water 
 Find out how much water the well produces.
Is this enough?
Is the quality of the water adequate?
pH, bacteria, nitrates, other chemicals, sand, etc.
Does the system function properly?
No leaks, mechanical and electrical equipment works, water pressure is
 Potable water 
 Does the spring produce enough water?
Is the quality of the water adequate?
pH, bacteria, nitrates, other chemicals, debris, etc.
Does the system function properly?
No leaks, equipment is working, water pressure is adequate, etc.
Is there a spring box that protects the water from vectors?
Find out how much water is available.
Is it enough?
Is the time when water is available suitable?
Is the quality of the water adequate?
Bacteria, nutrients, chemicals, algae and debris, etc.
Does the system function properly?
No leaks, equipment is working, water pressure is adequate, etc.
Is the type of irrigation system suitable for the use?
Flood, drip, spray, etc.
Is the source of the water for the pond known?
Does the pond hold water as intended?
Do dikes and overflow facilities appear adequate to contain and release water?
Are nuisance conditions present ?
Worksheet 1: Resource assessment for water systems
 Use this checklist of characteristics to assess your water systems.
Use extra paper if necessary.
Yes	No	sure	Not	N/A
 Does the system function properly?
No odors present, no backups or overflows, no soggy soils, no seepage
 that comes back to the surface, working mechanical and electrical equipment, etc.
Identify the uses of the rainwater.
Are the uses appropriate?
Does the quantity of available rainwater match needs?
Does the system function properly?
No leaks, debris kept out of system, freeze protection works, water pres-
 sure is adequate, mechanical and electrical equipment works
 Identify the uses of the graywater.
Are the uses appropriate?
Does the quantity of available graywater match needs?
Does the system function properly?
Odors not present, no leaks, mechanical and electrical
 After significant rain, is water left standing in undesirable areas (such as adjacent structures, wells and
 Do roof downspouts direct stormwater in desirable directions?
Does stormwater drainage contribute to soil erosion?
Does stormwater drainage move through areas where it can pick up contaminants?
Do water systems prevent waste through water conservation?
Are systems in good working order?
Are locations of underground facilities known?
Are operations and maintenance instructions available?
Are there contingency plans for failure of parts of the system?
Given your responses above, how would you characterize your current water systems?
Check one description.
What actions are required, if any?
A.
Potable water	Excellent	Fair	Poor	Not sure
 List actions you can take to improve or maintain potable water.
B.
Irrigation water	Excellent	Fair	Poor	Not sure
 List actions you can take to manage irrigation water.
C.
Ponds	Excellent	Fair	Poor	Not sure
 List actions you can take to improve or maintain ponds.
D.
Wastewater 	Excellent	Fair	Poor	Not sure
 List actions you can take to improve or maintain wastewater systems.
E.
Rainwater harvest	Excellent	Fair	Poor	Not sure
 List actions you can take to manage rainwater.
F.
Graywater	Excellent	Fair	Poor	Not sure
 List actions you can take to manage graywater.
G.
Stormwater	Excellent	Fair	Poor	Not sure
 List actions you can take to manage stormwater.
Worksheet 2: Management activity assessment for water systems
 Use the checklist of management practices below to	PRACTICE ASSESSMENT
 identify activities you incorporate in your water systems
 management.
Use extra paper if necessary.
Ongoing	Completed	Need to do	Consider	N/A
 Potable supply with well water
 Well flow is periodically checked.
Well water quality is periodically checked.
The system components are accessible in all seasons.
Potable supply with spring water
 Spring flow is periodically checked.
Spring water quality is periodically checked.
A secure spring box or equivalent means of protection is in
 place such as water treatment.
Surface water diversions are screened.
Farming techniques minimize soil loss.
Runoff amount is minimized.
Fertilizers, pesticides, and herbicides are used appropriately.
Mechanisms for keeping ponds from getting overgrown with
 vegetation and becoming stagnant are available, if desired.
Mosquitoes and other pests are controlled.
Excessive nutrient loads are kept from entering ponds.
Exotic plants and animals are not put in ponds than can
 overflow and connect with other surface waters.
Harmful wastes are not put into the system.
Septic tank is pumped at appropriate intervals.
Trees and woody vegetation are kept off drain field areas.
Pavement, vehicles, structures, and heavy animals are kept
 off the drain field.
The system components are accessible in all seasons.
System has good mechanisms for control of debris,
 mosquitoes, and freezing conditions.
Systems that do not provide potable water are clearly
 Harmful wastes are not put in the system.
Water is deliberately conveyed away from structures.
Worksheet 2: Management activity assessment for water systems
 Use the checklist of management practices below to	PRACTICE ASSESSMENT
 identify activities you incorporate in your water systems
 management.
Use extra paper if necessary.
Ongoing	Completed	Need to do	Consider	N/A
 Velocity of conveyed water is controlled.
Stormwater does not pick up contaminants.
Stormwater is encouraged to percolate into groundwater
 .
Vegetative systems such as rain gardens, bioswales, and
 buffer strips are used to enhance water quality.
Infrastructure 
 Water conservation practices are followed.
System components are periodically inspected and
 Location of underground facilities is known and documented.
Written operation and maintenance instructions are kept
 and updated when system changes are made.
Contingency plans are in place in the event of loss
 Know the rules 
 Owner is familiar with applicable regulations.
Facilities have all required permits and agreements.
Facilities are built, operated and maintained in accordance
 Review the results of Worksheets 1 & 2.
Consider any resource concerns and healthy conditions identified in Worksheet 1, and practices that you checked in the "Need to do" and "Consider" columns in Worksheet 2.
What are the most important potential follow-up actions?
List and briefly describe these below.
Reduce Spray Drift by Choosing the Right Nozzle
 Josh A.
McGinty Assistant Professor and Extension Agronomist, The Texas A&M University System
 Paul A.
Baumann and Gaylon D.
Morgan Professors and Extension Weed and Cotton Specialists, The Texas A&M University System
 Spray drift is the lateral movement of pesticide droplets away from the target area before they reach the plant or soil.
Reducing spray drift is vitally important because applicators are legally liable for any damage that drifting pesticide spray causes to off-target plants.
Reducing drift is also important because drift effectively reduces the amount of pesticide that is applied to the intended area.
Do not confuse spray drift with vapor drift.
Vapor drift occurs when a pesticide evaporates or volatilizes after it has reached the target plant or soil.
This discussion focuses specifically on spray drift.
Spray drift is influenced by wind speed, air temperature, and relative humidity.
You must consider these factors day-to-day or even hour-to-hour, however, spray equipment has to be selected and set up well before reaching the field.
The nozzle, operating pressure, and boom height you chose can all potentially contribute to spray drift.
Of these variables, nozzle selection is the most important factor in reducing spray drift.
Nozzle size and design directly influence the size of spray droplets.
Though all spray droplets exit the nozzle at the same velocity, smaller droplets take longer to fall to the target because they lose velocity more quickly.
The longer a droplet takes to reach the target, the more susceptible it is to lateral drift.
Manufacturers frequently provide color-coded tables with their products to describe the spray droplet sizes for specific nozzles and operating pressures.
Droplets are commonly measured in micrometers  one um equals 1/25,400 of an inch.
This classification system uses the volume mean diameter  to define categories of droplet size.
The VMD is the size  at which half of the spray volume droplets are larger than the VMD, and half are smaller than the VMD.
This classification is shown in Table 1.
Table 1.
ASABE S572.1 droplet size classification.
Category	Symbol and color	Approximate
 Extremely fine	XF	<60
 Very fine	VF	61-144
 Very coarse	VC	404-502
 Extremely coarse	XC	203-665
 Ultra coarse	UC	>665
 *Estimated from sample reference graph provided for ASABE S572.1 nozzle design
 Modern spray nozzles have several different design features that significantly influence the size of the spray droplets they produce.
Many standard flat-fan nozzles such as the TeeJet Extended Range  nozzle use a simple design with a single orifice.
This single orifice regulates the flow of the spray solution and produces the spray pattern.
Nozzles like the XR can provide excellent COVerage, but can also be quite drift-prone.
The TeeJet Drift Guard  nozzle is a an improvement over the single orifice design.
This nozzle combines a preorifice to regulate the flow, with a second orifice to produce the spray pattern.
This design significantly reduces spray drift while still providing excellent coverage.
The TeeJet Air Induction  and Air Induction Extended Range  nozzles incorporate further improvements.
In addition to a pre-orifice, these nozzles have air inlet ports that draw air in to the spray solution.
This additional disturbance to the spray solution causes the droplet size to increase.
Nozzles such as the Turbo TeeJet Induction  nozzle increase the droplet size even more.
This nozzle includes pre-orifice and air induction technology in addition to a turbulence chamber.
This is simply a small chamber inside the nozzle body that helps absorb some of the energy of the spray solution by forcing it to change direction twice before exiting the nozzle.
Research conducted by the Texas A&M AgriLife Extension Service in cooperation with USDA-ARS Aerial Application Technology Research Unit in College Station, TX, has demonstrated how the nozzle designs mentioned above affect droplet size.
Researchers used precision laser diffraction analysis to measure droplets of various pesticides produced by these different nozzles.
Although this research tested only TeeJet nozzles, other manufacturers such as Greenleaf Technologies, Pentair Hypro, and Hardi International produce nozzles with similar features.
Figure 1 shows the effect of these nozzles operated at both 30 and 60 pounds per square inch  on VMD.
As Figure 1 shows, nozzle design plays a major role in determining the droplet sizes of the spray.
For
 example, changing from an XR to a TTI nozzle at 30 psi causes a nearly 5-fold increase in droplet size.
Note also that Figure 1 data shows that droplets get smaller as operating pressure increases.
Next, the researchers analyzed these same sprays to determine what portion was prone to drift.
Figure 2 shows the percentage of spray droplets measuring 100 um or less, at 30 and 60 psi.
Droplets of 100 um are roughly the same diameter as a human hair and can be used as a partial indicator of how much of the spray is likely to drift.
This figure shows drift-prone droplets can be reduced by more than 50 percent
 by changing from a single-orifice nozzle  to a pre-orifice nozzle such as the DG.
You can reduce drift-prone spray even further by changing to a nozzle such as the TTI.
Spray produced with his nozzle's pre-orifice and air induction technology contains only a fraction of a percent of drift-prone droplets.
As expected, sprays produced at 60 psi contained more drift-prone droplets than sprays at 30 psi.
For pesticide applications to be accurate and effective, the applicator must do everything under his or her control to ensure that the pesticide stays in the intended area.
Research shows that nozzle selection is one of the most important factors for reducing spray drift potential.
Finally, if you require higher nozzle output, consider using nozzles with a larger orifice rather than increasing operating pressure.
This will help reduce the number of smaller droplets that are caused by increased pressure.
Texas A&M AgriLife Extension Service
For pasture grass in the actively growing crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 1.00 inches and the estimated water use during the week of June 19-25, 2023 is 1.50 inches.
U D G E T
 CONVENTIONAL IRRIGATED CORN FOR GRAIN, GOSHEN COUNTY, WYOMING
 Brian Lee, Assistant Research Scientist, SAREC
 John Ritten, Associate Professor, Department of Agricultural and Applied Economics
 Tom Foulke, Senior Research Scientist, Department of Agricultural and Applied Economics
 T his crop budget models a representative irrigated corn operation in southeast Wyoming.
The operations described in this budget are typical for a southeast Wyoming operation.
Irrigated corn harvested for grain is a typical crop in southeast Wyoming.
The budget contains one year of corn production and its representative operations.
Operations and values in the budget represent the best estimates from multiple sources in southeast Wyoming and the Nebraska Panhandle, including University of Nebraska state crop budgets.
University of Minnesota machinery cost estimates were used to establish use-related and total costs.
Many different corn varieties are planted to mostly irrigated acres in Wyoming.
Almost all of the corn planted in the state, and in the nation, are considered biotech varieties.
Biotech varieties would include any type of glyphosate resistant  or Bacillus thuringiensis enabled  corn.
Combining modified biotech seed with compatible herbicide and pesticide regimes is common in commercial U.S.
corn production.
This budget assumes the land base is owned by the producer.
Real estate opportunity cost is assumed at 4 percent per acre.
Real estate taxes are assumed to be 1 percent per acre.
The per-acre land value is estimated as the average value of irrigated cropland in the state of Wyoming, according to the most current Wyoming Agricultural Statistics Service survey.
This budget assumes labor is provided by the landowner at a rate of $25 per hour for all field operations except the custom application of fertilizer, assumed at $6.50 per acre by a chemical supply company or $3.96 per acre if done by the landowner.
Interest on operating capital is included at 5.5 percent.
This percentage represents interest paid to a lending institution on loaned capital.
Interest is charged on operating capital for cash expenses for a 6-month window.
This percentage should be adjusted based on the individual producer's situation.
The enterprise budget is based on an assumed yield of 150 bushels per acre.
No crop insurance is assumed for this budget, but there are various options available.
Three fertilizer applications are included in the budget, a pre-plant 32-0-0 application, a 10-34-0 pop-up fertilizer, and post-plant application with a coulter rig..
Center pivot irrigation is assumed, and we consider the use of an electric motor and 50-foot well depth.
Pivot costs
 Conventional Irrigated Corn for Grain, Southeast Wyoming, 2017
 Conventional Corn, 150 bushel/acre goal Pivot irrigated, 50 foot well, 13 acre inches
 Field Operations	Cost/Acre	Cost/Acre
 Deep Rip	$11.16	$14.07
 Field Cultivation	$4.87	$6.24
 Pre Plant Spray	$3.03	$3.96
 Row Crop Cultivation	$6.15	$7.73
 Post Plant Spray	$3.03	$3.96
 Pivot Irrigation, 50'	$58.50	$145.55
 Harvest Corn	$32.03	$37.78
 Grain Cart	$13.11	$15.99
 Stalk Chop	$10.80	$13.39
 Total Conventional Corn Field Operations	$163.57	$276.10
 Materials and Services	Type	Rate	Unit	Per Unit Price	Total Cost
 32-0-0 Fertilizer	125	lbs N	$0.47	$58.75
 Pre-Plant	Balance Flexx Herbicide	4	ounce	$6.00	$24.00
 Bicep II Magnum Herbicide	2.1	quart	$12.50	$26.25
 At Plant	10-34-0 Fertilizer	8	gallon	$2.80	$22.40
 Corn SmartStax RIB Complete Seed	36.8	k seed	$3.81	$140.30
 Liquid Fertilizer	32-0-0 Fertilizer 	40	lbs N	$0.47	$18.80
 Spray	1	acre	$7.00	$7.00
 Custom Herbicide	Glyphosate with Surf	32	ounce	$0.13	$4.00
 Dicamba	12	ounce	$0.59	$7.03
 Harvest	Haul Grain Bushels	150	bushel	$0.36	$54.00
 Dry 2 Points Removed	150	bushel	$0.09	$13.50
 Total Field Operations	$376.03
 Listed Operations, Materials, and Services	$652.13
 Annual Interest on Operation Capital	Cash Related/Non Ownership	5.50%	$539.60	$29.68
 Total Operations, Materials, and Services	$681.81
 Overhead	Insurance, vehicles, office	$20.00
 Real Estate Opportunity Cost	Wyoming Irrigated	$2,200.00	acre	4.00%	$88.00
 Real Estate Taxes	$2,200.00	acre	1.00%	$22.00
 Total Cost Including Overhead	$811.81
 Cost per Bushel	$5.41
 Cash Cost per Bushel	$3.94
Sergio M.
Abit Jr.
Extension Specialist for Soils under Non-agricultural Uses
 John William Jones Graduate Research Associate
 In areas with deep and medium textured soil, onsite wastewater  treatment systems that rely heavily on the soil for wastewater treatment such as the Conventional System are preferred.
However, systems that provide more advanced treatment prior to soil dispersal of wastewater are required in areas that have limitations concerning soil texture  and/or soil depth.
An advanced system that has gained popularity in Oklahoma during the last decade is the aerobic treatment unit/system.
ATUs are proprietary devices that aerate the septic wastewater to enhance microbial decomposition of dissolved and solid constituents and to reduce the population of microorganisms that can cause diseases to humans.
It is essentially a scaled-down version of a centralized activated sludge wastewater treatment plant, which attains treatment by channeling the sewage through a series of tanks designed for solid-liquid separation, aeration, static clarification and
 disinfection prior to effluent dispersal.
Sewage purification by an ATU is accomplished by the following components :
 A Trash Tank where the effluent is primarily separated from the solids.
An Aeration Tank where the wastewater is aerated  with an air pump connected to diffusers submerged in the effluent.
A Clarifier where undecomposed particulates and microbial masses are given time to settle in calm conditions.
In most systems used in Oklahoma, the Clarifier is a chamber built into the Aeration Tank.
A final treatment and dispersal component where wastewater is disinfected and pumped for the ultimate dispersal of the effluent to the soil either by surface spray or subsurface drip irrigation.
This bulletin focuses on the installation of ATUs, the processes taking place in each ATU component, as well as maintenance tips to keep the system in working order.
Figure 1.
Schematic illustration of an aerobic treatment system treatment train.
Note: the pump system includes a Pump Tank -not included in figure because no treatment takes place in it.
In Oklahoma, National Sanitation Foundation  Standard 40 aerobic treatment systems may be installed in lot sizes of at least 3/4 acre if drinking water is drawn from a private well onsite.
If water is from a public water system, the minimum lot size requirement is 1/2 acre.
In addition, it can only be installed for treatment of sewage from residential units and cannot be used when the average daily flow is less than 100 gallons per day  or greater than 1,500 gpd.
If the daily flow fluctuates such that daily flow occasionally exceeds the unit's daily capacity, an ATU may still be used if a flow equalization tank is installed between the trash tank and the aeration tank.
The type of soil used for treated wastewater dispersal is another consideration.
Areas with soils that do not meet minimum requirements for simpler systems  can have an ATU provided that minimum requirements for ATUs, as summarized in Table 1, are met.
Table 1 also shows that for a given soil group; vertical separation requirements  for ATUs are shorter than for conventional systems.
This is because effluent coming out of the ATU had been pre-treated more effectively and can be finally purified by a shorter thickness of soil.
Once installed, the top of each tank  should have no more than one inch variation in elevation from side to side and end to end.
In addition, the top of all components of the aerobic treatment system, excluding the trash tank and the dispersal field should be covered with no more than 24 inches of soil.
The installer of any aerobic treatment system in Oklahoma is required to maintain the system for a period of two years following the date of installation at no cost to the owner.
Dur-
 ing this mandatory two-year maintenance period, the installer shall be responsible for the following:
 1.
repairing, adjusting and replacing of any broken or malfunctioning parts;
 2.
measuring and recording the depth of the sludge in the trash tank at least once every six months;
 3.
measuring and recording the volume of sludge in the aeration tank at least once every six months;
 4.
notifying the owner in writing of any repairs, adjustments and replacements, the sludge depth measurements and the possible need for the sludge to be pumped-out.
Trash tanks permitted for installation should meet requirements of the American National Standards Institute / NSF Standard 40.
The trash tank must have a minimum liquid capacity of 300 gallons or the average daily flow, whichever is greater.
The main function of the trash tank is to separate the effluent from the solids that settle and from the oil and grease that float.
This clarifies the effluent before it flows into the succeeding tank in the treatment train.
Minimal treatment of contaminants occurs in the trash tank.
Ammonium  is the main dissolved form of nitrogen, while much of the phosphorus in the sewage is locked in the settled solids.
Wastewater in the trash tank is anaerobic causing anaerobic and facultative  microorganisms to dominate.
This leads to two things:
 1.
The rate of the decomposition process under anaerobic conditions is slow causing the solids to accumulate;
 2.
Minimal disturbance of the activity of pathogenic bacteria.
Table 1.
Minimum vertical separation requirements for conventional system and aerobic treatment systems.
Source: DEQ, 2012.
Prevalent Soil Group	Conventional System Subsurface	With Aerobic Treatment Units
 in Vertical Separation1 Range	Absorption Field	Drip Irrigation Field	Spray Irrigation Field
 (coarse sand, loamy	NOT ALLOWED	at least 18"
 coarse sand)	vertical separation
 (sand and loamy sand	at least 24"	at least 14"
 excluding loamy coarse sand)	vertical separation	vertical separation
 	at least 21"	at least 12"	Allowed for all
 vertical separation	vertical separation	Soil Groups
 (sandy clay loam, loam,	at least 18"	at least 10"
 silt, silt loam with < 20% clay)	vertical separation	vertical separation
 (sandy clay w/o slickensides,	at least 14"	at least 8"
 silt loam with > 20% clay)	vertical separation	vertical separation
 	at least 10" vertical separation	at least 6" vertical separation
 (sandy clay with slickensides,	NOT ALLOWED	at least 6" vertical separation
 1 Vertical Separation: The vertical distance between the bottom of a subsurface trench or the wastewater application depth and the limiting subsurface layer which could either be an impervious rock layer or a water-saturated layer.
The aeration tank must meet the most current ANSI/ NSF Standard 40 and accommodate the projected daily flow.
It also must have an opening of sufficient size to allow for maintenance.
Since atmospheric air is forced into the chamber by a compressor or aerator, a venting mechanism for proper airflow through the aeration tank is required.
The main function of the aeration tank is the removal of the organic matter and the reduction in activity of pathogenic microorganisms.
Treatment in the aeration chamber is a biological process in which microbes consume the waste and transform it into non-polluting or relatively lesshazardous by-products.
When atmospheric air  mixes with the wastewater, conditions become aerobic leading to a higher rate of microbial activity inside the chamber.
This promotes decomposition  of the solids and dissolved organic constituents in the wastewater including antibiotics, pharmaceuticals and household chemicals.
In addition to increasing the decomposition rate, the aerobic condition in the tank also results in the following:
 1.
Dissolved NH is converted to nitrate (NO no considerable change in speciation of dissolved phosphorus is expected.
2.
Pathogenic bacteria may be killed or weakened under aerobic conditions.
In addition, aerobic bacteria will dominate and could out-compete the bacterial pathogens.
It is important to keep in mind that microorganisms in the aeration tank need to be constantly fed to maintain an active and diverse population, so they can effectively decompose a variety of materials.
Microorganisms in the aeration tank will not thrive in situations with an extremely low food supply such as in a seasonal-use facility or vacation home.
Clarifier or Settling Chamber
 Treated wastewater exiting the aeration chamber enters the clarifier or the settling chamber.
For most systems in Oklahoma, the clarifier is in the same tank as the aeration chamber.
The effluent entering the clarifier contains suspended solids.
The solids must be removed to prevent clogging caused by carryover of the solids to the orifices or nozzles of
 Figure 2.
Schematic illustration of a tank with both aeration and settling chambers.
the dispersal lines.
Calm conditions in the clarifier allow biomass suspended in the wastewater to settle.
Sludge collected in the clarifier should be returned to the aeration chamber.
If spray irrigation is used as the mode of dispersal, then the effluent needs to be disinfected.
If the effluent is dispersed by subsurface drip irrigation, disinfection is not required.
Disinfection is performed after the effluent has gone through the clarifier, but before it is pumped for dispersal.
The most common method of disinfection is by chlorination.
Manufacturer instructions about chlorination must be followed.
Ultraviolet irradiation is an option, but seldom used.
Effluent from the clarifier flows into a pump tank, where it is channeled through subsurface lines and eventually landapplied by either surface spray or subsurface drip irrigation.
No biological treatment process takes place in the pump tank.
The pump tank should meet ANSI/NSF Standard 40 and have a minimum liquid capacity of 700 gallons or, for systems with an average flow capacity of 350 gpd, have a liquid capacity of at least twice the average daily flow.
A sampling port at the discharge outlet or in the treated effluent line following the pump tank is required for monitoring access.
In Oklahoma, pump tanks are also required to have a high-water alarm set to alert the owner/operator if the tank is more than half full.
For systems with subsurface drip irrigation, the drip lines should be buried eight to ten inches deep and installed according to manufacturer specification.
Emitters should be spaced one foot apart for soil groups 1, 4 and 5; and two feet apart for soil groups 2, 2a, 3 and 3a.
The emitter should be set to wet 4 square feet, and be pressure compensating to deliver uniform distribution regardless of the pressure entering the drip line.
The required length of the drip line will depend upon the soil group  and the number of bedrooms in a residence as shown in Table 2.
Systems with spray irrigation require a dispersal area that is vegetated and landscaped, and/or terraced to prevent runoff.
At least two spray heads are required to disperse the
 Table 2.
Minimum drip line trench length  of individual drip irrigation fields.
Source: ODEQ, 2012.
Number of Bedrooms in Residence1
 Soil	Two or	Each Additional
 Group	Fewer	Three	Four	Bedroom
 1	125	165	205	40
 2	160	210	260	50
 2a	250	330	410	80
 3	340	450	550	100
 3a	500	665	830	165
 4	660	880	1,100	220
 5	1,000	1,330	1,660	330
 1 Based on average flow of 6,000 gallons per month for a two-bedroom residence with an additional 2,000 gallons per month for each additional bedroom.
The size of the system should be increased if the actual or anticipated water usage exceeds this average.
The aerobic treatment system has components requiring regular maintenance.
Maintenance starts by following manufacturer's guidelines.
Take the following as suggestions to keep your system in working order:
 1.
Know your installer.
Know your installer and request that you be oriented to the operation and maintenance of your system.
If you bought a used house, determine if the warranty can be transferred to you.
Knowing the installer will at least point you to the person who is familiar with your system whom you can call for future maintenance and repairs.
2.
Work within the daily treatment capacity of your system.
A family in a three-bedroom home should not exceed the treatment capacity of a system designed to treat 266 gallons of wastewater per day.
However, sometimes you may have visitors, causing daily water use to possibly double.
During these times, a homeowner needs to make adjustments.
An example adjustment would be to stagger significant use of water in the house.
It would be unwise to use the bath tub, clothes washer and dishwasher at around the same time.
3.
Monitor the accumulation in the trash tank and in the aeration tank.
The best way to prevent overwhelming of the trash tank is to monitor the amount of solid accumulated at least every six months.
This can simply be done by dipping a long stick into the tank to measure the thickness of the accumulated solids at the vicinity of the outlet baffle.
The tank should be pumped if the sludge layer has built up to within 40 percent of the liquid capacity of the tank.
Follow manufacturer suggested methods of testing the sludge accumulation in the aeration tank.
4.
Be familiar with your system.
Keep a record of the diagram of the tank, the location of the access ports and check wells, soil treatment area and repair area locations.
It would even be better if there are markers of actual locations in the field.
Knowing the location of various components makes it easier to implement measures to protect them from being disturbed/ destroyed and easier to locate them for maintenance/ monitoring purposes.
5.
Maintain the dispersal field.
Properly maintaining the dispersal field starts with knowing the location of the buried lines and/or nozzles.
To ensure proper functioning of the soil in your dispersal field, you have to do the following:
 Maintain adequate grass cover over the area.
Deeplyrooted shrubs and trees should not be allowed to grow within the dispersal field.
Divert surface waters  away from the tanks and dispersal field.
Keep heavy traffic like automobiles and heavy equipment off the dispersal field.
6.
Perform regular simple checks on your system.
Listen to your system.
You should hear the compressor running indicating that the equipment is forcing air into the aeration tank.
Check chlorine levels often making sure that adequate chlorine  should be present.
Check for foul odor often.
Foul odor  could be an indication that the system is not working properly.
Check the nozzles/spray heads regularly.
Faulty spray heads is a common problem of ATUs with spray irrigation.
7.
If an alarm sounds, call your maintenance provided.
Do not try to repair the system yourself.
Until the problem is fixed, reduce nonessential water use in the house.
8.
Be aware of what NOT to put in your drain.
There are materials, that if disposed in the drain or toilets, may limit the functioning and the lifespan of your system.
Grease and used cooking oils should not be poured into the kitchen sink drain.
Use of household chemicals such as bleach and other cleaning agents should be regulated.
Pharmaceuticals, especially unused antibiotics, as well as pesticides, paint thinners, and solvents should never be disposed through the drain because they can adversely affect the microorganisms that help treat the sewage.
9.
Allow the microbial population to recover.
Not using the system for a few weeks will lower the microbial population in the tank because of the lack of food.
When you use the system again, consciously reduce the amount of household water use for at least two days.
Washing a dozen loads of laundry immediately after arriving from a vacation can washout what population is left in the aeration tank.
Low-Pressure Drip Irrigation for Small Plots and Urban Landscapes
 Water purveyors in the western U.S.
are developing management plans that include incentives to help conserve available water supplies for essential needs.
Many cities in New Mexico  have implemented inclining block water rate structures in which the cost per unit of water increases with increased water use.
Other measures taken to help curb outdoor domestic water use include irrigation restrictions, penalties for obvious water waste, rebates for removal of turfgrass, and building codes  or rebates  to stimulate the use of rainwater catchment sysitems.
In response to these water conservation incentives, drip  irrigation is becoming more popular for irrigating small farm plots, vegetable gardens, and landscapes in and around urban centers.
Since drip irrigation applies small volumes of water and can operate under low pressure, it represents an effective method of distributing irrigation to plants by gravity from elevated rainwater catchment systems or other tanks.
The purpose of this paper is to share information gained while conducting low-pressure drip irrigation research at New Mexico State University's Agricultural Science Center at Farmington.
Drip irrigation uses piping and small outlets  to apply water near the base of plants at very low application rates.
Flexible polyethylene  or vinyl piping is usually used.
Plastic emitters may be built into the pipe at a regular spacing by the manufacturer , or they can be independent of the pipe, inserted at selected locations along the pipe by the user.
Line source drip lines are usually used in gardens or orchards where plants are in rows at a consistent spacing
 Figure 1.
Examples of point source and line source emitters.
within the row.
The lines may have rigid walls , which are usually sold in rolls of less than 1,000 feet, or thin walls that allow the line to lie flat , and which are sold in coil lengths of over 5,000 feet.
Emitter spacing may range from 8 to 48 inches or more, and the tubing or tape may be laid above or below the soil surface.
The flow rate of individual line source emitters is usually 1 gallon per hour  or less, but flow rate is often expressed as gph per 100 feet, in which case the flow rate per emitter is determined by dividing the flow rate per 100 feet by the number of emitters per 100 feet.
Example: 15 gph per 100 ft / 30 emitters per 100 ft = 0.5 gph per emitter
 Point source emitters  are more suitable for irrigating widely or irregularly spaced plants, such as in landscapes or diversified gardens where a number of different plant species are grown.
Point source drip systems are usually more expensive than line source sys-
 items, but they are much more versatile.
The PE tubing can be snaked around a landscape or garden in various configurations, and emitters of varying flow rates can be installed to satisfy the specific water requirement of each plant.
Many other components, such as multiport manifolds and micro fittings for feeding 1/8to 1/4-inch spaghetti distribution tubing , can also be used with point source systems.
The mainline valve, the closest component to the water source, can be a gate valve , ball valve, or faucet, and is used to manually open and close water flow to the irrigation system.
Secondary valves, either manual or electronic solenoid, are commonly used downstream of the main valve, but should not be used in place of the manual mainline valve.
A backflow prevention device is required in drip systems connected to a municipal or other potable water source.
It prevents irrigation water from being siphoned back into, and potentially contaminating, the potable water if there is a sudden loss of pressure.
In most urban areas, regulations specify what particular backflow prevention devices and installation procedures are required to legally comply with local building codes.
Before designing or installing any irrigation system that will use domestic water, contact the local building inspector or water purveyor to ensure compliance with the correct backflow prevention requirements.
A simple check valve  might be the only requirement to prevent backflow in some cases, but more fail-safe methods are usually required, such as anti-siphon valves or pressure vacuum breakers.
A filter must be installed in the mainline  to prevent clogging of the emitters.
It is an essential component of the system and should be used in all systems, regardless of the water source.
There are two types of filters used in small drip systems: screen and disk.
Screen filters have mesh sizes that range from about 50 to 200.
Disk filters consist of a stack of closely spaced disks, rather than screens, but their filtering capacity is still rated as a mesh size equivalency.
A filter mesh size of about 150 is recommended for drip emitters that have flow rates between 0.5 and 10 gph.
For the drip system to operate effectively, the filters must be regularly cleaned or flushed.
If the water comes from an irrigation ditch and has a heavy silt load, filters may require cleaning after every irrigation or even during irrigation.
Disk filters are better at filtering organic matter (e.g., algae
 cells) than screen filters and, based on experience at ASCF, seem to function better, with less clogging than screen filters.
If sediments in the water are excessive, a sand filter or series of settling tanks may be required to pre-filter the water.
Drip irrigation systems are generally designed to operate in the pressure range of 10 to 30 pounds per square inch , but domestic water is usually delivered to households at pressures above 30 psi.
These higher pressures can blow out point source emitters and have an erosive effect on drip lines and other components.
Therefore, a pressure reducer  should be used if the water delivered to the drip system comes from a domestic, or pump-driven, source.
A pressure reducer  lowers the pressure to a specified level.
A pressure regulator is more expensive than a pressure reducer, but the outlet pressure can be adjusted by turning a bolt on the regulator.
For pressure reducers and regulators to function properly, there must be a minimum water pressure differential between the inlet and outlet of the reducer/regulator.
This information should be available from the manufacturer or distributor.
When installing components of the manifold , it is important that the arrows stamped on check valves, pressure reducers, filters, and other components match the direction of water flow.
Headers, end caps, footers, and flush valves
 Downstream of the mainline, the header pipe distributes water directly to the drip laterals.
Additional manual or electronic solenoid valves can be installed at various locations in the system to supply water to different zones or to individual laterals.
Zoning is needed if available water flow is insufficient to satisfy the flow requirements of the entire system.
Zoning is also used to separate plants with different water requirements SO that each plant type receives the appropriate amount of water.
Various methods can be used to cap the ends of the drip laterals, but whatever is used, it should allow for easy periodic flushing and draining of the laterals.
In the crimping method, special "figure 8" fittings, or short pieces of 1or 1 1/4-inch PE or PVC, can be used to hold a crimp at the end of 1/2-inch drip tubing.
The ends of drip tape can be capped in the same manner by folding the tape at the end and holding the fold in place with a short  piece of tape.
Small plastic ball valves, which make lateral flushing and draining much easier than the crimp method, can also be used.
They require clamping in high-pressure systems and are more costly than crimping.
Figure 2.
Spaghetti tubing for transporting water from point source emitter to plant.
Figure 4.
Example of types of filters used in small plot, drip-irrigation systems.
In lieu of separate caps on each lateral, a footer pipe that connects the ends of all the drip laterals in a zone can be used.
A single flush valve can then be installed at the lowest end of the footer to periodically flush and drain each zone.
This option adds cost to the system since additional tubing and fittings are required, but it saves flushing time and helps equalize pressure throughout the zone.
Other fittings, Teflon tape, and clamps
 Various plastic fittings  are used to join drip lines.
The appendages of barbed fittings  fit inside the drip lines and are held tightly to the drip line with stainless steel clamps.
Compression fittings fit tightly to the outside of drip lines  and do not require clamps.
Barbed fittings create a flow restriction at the pipe joint since they decrease the inside diameter of the pipe, but they are readily available at most hardware stores and are usually cheaper than compression fittings.
In high-pressure sysitems, however, cost savings are neutralized by the addi-
 Figure 3.
Example of components used in the mainline manifold of a high-pressure drip system.
Figure 5.
Example diagram of a simple, two-zone drip system.
tional expense of clamps required for the barbed fittings.
Compression fittings do not restrict water flow, but they are not as readily available as barbed fittings and they are more difficult to disassemble once installed.
To prevent water leakage at threaded joints , all male threads should be wrapped  with a couple of layers of Teflon tape prior to assembly.
Too much Teflon tape can create a leakage problem once the connectors are screwed together.
For vegetable gardening, a fertilizer injector is essential if the gardener's goal is high yields of good quality produce.
Liquid fertilizers and other soluble chemicals are easily applied regularly into the water stream, which carries them to the soil around the base of each plant.
With careful management, fertilizer efficiency is very high because it is applied frequently in low doses and there is no overspray or application to off-target areas.
A simple, low-cost fertilizer injector  is suitable for small,
 Figure 6.
Examples of barbed and compression fittings, clamp, and Teflon tape.
Figure 7.
Example of a fertilizer injector for small drip systems.
Figure 8.
Four-zone manifold with electronic solenoid valves.
high-pressure drip systems.
If irrigation water has high levels of calcium , fertilizers with high phosphorus concentrations should be avoided because calcium phosphate  precipitates can form and clog emitters.
An electronic controller and solenoid valves, or in-line battery operated timers with built-in valves, can be used to automatically turn the water flow on and off at pre-programmed times.
This automation is particularly useful if there are several different irrigation zones in the system and/or no one is available to manually control the system.
Figure 8 shows an example of a four-zone manifold with electronic solenoid valves.
Air relief valves should be installed at high points in above-ground systems if the ground is excessively uneven or sloped , and in the above-ground manifolds of all buried systems.
These valves are used to burp trapped air from the system.
Water flow and pressure gauges, which can help indicate problems such as leaks or clogged filters or emitters, can also be installed in the water delivery lines of the system.
Pressure and flow rate
 When designing a drip irrigation system, the required operating pressure of the emitter  and the flow rate of water in each section of distribution line or lateral that services the emitter must be considered.
The greater the flow rate, which is determined by the sum of the flow rates of all outlets downstream of a particular pipe section, the greater the required inside diameter  of that pipe section to minimize pressure differences between outlets caused by friction.
Unlike sprinkler or flood irrigation systems, which require large ID piping  to satisfy the high gallon per minute  flow rates of the outlets, drip line IDs are usually less than 1 inch since flow rates are very low.
For example, the flow rate of one brass Rainbird model 30H impact sprinkler operating at 50 psi is equivalent to the flow rate of more than 500 1-gph emitters.
Table 1 shows the relationship between pressure loss and flow rate for different PE pipe sizes commonly used in drip irrigation systems.
Note that the nominal  size of pipe does not necessarily equal the pipe's ID.
In fact, as shown in the top row of Table 1, there are three different IDs associated with nominal 1/2-inch PE pipe available from this manufacturer: 0.520, 0.600, and 0.620 inch.
It is
 Table 1.
Pressure Loss Per 100 Feet for Selected Sizes of Polyethylene  Pipe  at Various Flow Rates
 PE pipe less than 3/8 inch	PE pipe greater than 3/8 inch
 Nominal size	1/4 inch	5/16 inch	3/8 inch	1/2 inch	1/2 inch	1/2 inch	5/8 inch	3/4 inch	1 inch	1 1/4 inches
 Pipe ID 	0.170	0.250	0.375	0.520	0.600	0.620	0.720	0.830	1.060	1.39
 Pipe OD 	0.250	0.307	0.455	0.620	0.700	0.710	0.830	0.940	1.200	1.55
 	0.040	0.028	0.040	0.150	0.050	0.045	0.055	0.055	0.070	0.080
 Flow 	Pressure loss per 100 feet 	Flow 	Pressure loss per 100 feet 
 2.0	0.49	0.08	0.01	30	0.32	0.16	0.14	0.07	0.03	0.01	0
 2.5	0.75	0.11	0.02	45	0.68	0.34	0.29	0.14	0.07	0.02	0.01
 3.0	1.05	0.16	0.02	60	1.17	0.58	0.50	0.24	0.12	0.04	0.01
 3.5	1.39	0.21	0.03	75	1.76	0.88	0.75	0.36	0.18	0.06	0.01
 4.0	1.78	0.27	0.04	90	2.47	1.23	1.05	0.51	0.25	0.08	0.02
 4.5	2.22	0.34	0.05	105	3.29	1.64	1.40	0.67	0.34	0.10	0.03
 5.0	2.69	0.41	0.06	120	4.21	2.10	1.79	0.86	0.43	0.13	0.04
 6.0	3.78	0.58	0.08	135	5.23	2.61	2.22	1.07	0.54	0.16	0.04
 7	5.03	0.77	0.11	150	6.36	3.17	2.70	1.31	0.65	0.20	0.05
 8	6.44	0.99	0.14	165	7.59	3.78	3.22	1.56	0.78	0.24	0.06
 9	8.00	1.23	0.17	180	8.91	4.44	3.79	1.83	0.92	0.28	0.07
 10	9.73	1.49	0.21	195	5.15	4.39	2.12	1.06	0.32	0.09
 12	2.09	0.29	210	5.91	5.04	2.43	1.22	0.37	0.10
 14	2.78	0.39	225	6.72	5.73	2.77	1.38	0.42	0.11
 16	3.56	0.49	240	7.57	6.45	3.12	1.56	0.47	0.13
 18	4.42	0.62	270	9.41	8.03	3.88	1.94	0.59	0.16
 20	5.38	0.75	300	9.76	4.71	2.36	0.72	0.19
 22	6.42	0.89	330	5.62	2.81	0.86	0.23
 24	7.54	1.05	360	6.61	3.31	1.01	0.27
 26	8.74	1.22	390	3.84	1.17	0.31
 28	10.03	1.39	420	4.40	1.34	0.36
 30	1.58	450	5.00	1.52	0.41
 Table adapted from Handbook of Technical Irrigation Information, produced by Hunter Industries
 very important to identify the actual ID of the nominal 1/2-inch pipe that is being used for the drip system for a couple of reasons.
First, the pressure loss due to friction per 100 feet of the 0.520-inch ID pipe is about double that of the 0.600-inch ID pipe and about 2.3 to 2.4 times that of the 0.620-inch ID pipe.
While the 0.520-inch ID may be more than adequate for short drip laterals with low flow rates , the larger ID sizes should be used for longer laterals with higher flow rates.
Second, compression or barbed fittings are generally not interchangeable between the different  1/2-inch pipe sizes.
If the actual ID and outside diameter  are known, the proper fittings can be obtained for constructing a new system or for repairing an existing system.
In the absence of a pump, static pressure  at any point in a drip system is created by the height of the water surface above the emitter.
Pressure is measured in psi, and each 2.31 feet of water  above an emitter or other point in the
 irrigation system provides 1 psi of static pressure at that point.
On a sloped or uneven field, static pressure changes with elevation.
In a perfectly level field, the difference in dynamic pressure  from one point to another along the drip line will be due to friction only.
Ideally, drip laterals should be kept as short as practical to minimize pressure loss due to friction, and should be laid slightly downslope  on sloped plots to help neutralize friction loss with pressure gain created by the increased head from the water surface to the downslope emitters.
On very steep slopes, it is best to lay the drip lines along the contour of the slopes rather than upslope or downslope to avoid excessive pressure variability between emitters.
Pressure compensating  emitters are designed to emit the same flow rate within a wide range of pressures  and should be used on terrain that is excessively undulated or uneven.
Another suggestion when obtaining components for a point source drip system is to use utility or irrigation
 Figure 9.
Example of the flow rate of a pressure compensating  emitter at different water pressures.
grade PE pipe rather than drinking water grade.
Drinking water grade PE is more expensive than utility grade PE, and its greater wall thickness makes fittings and point source emitters much more difficult to install.
ADVANTAGES OF DRIP OVER SPRINKLER OR FLOOD IRRIGATION
 Early in the growing season, water losses through direct soil surface evaporation are less with drip irrigation, which wets only a small area around the base of each plant, than with sprinkler or flood irrigation, which wets the entire soil surface.
Unlike sprinkler or flood irrigation, surface runoff of water is virtually non-existent in drip irrigation.
Water application uniformity, a measure of irrigation efficiency, is usually much better in drip irrigation than in sprinkler or flood irrigation because drip is not affected by wind  and water is not applied down furrows between rows.
Since each plant theoretically receives the same volume of water in a well-designed drip system, plant growth and yield should be relatively uniform over the entire irrigated area.
Weed and disease control
 A major advantage of drip irrigation over other methods in the dry climate of the Southwest is reduced weed growth between crop rows.
When the entire soil surface is continuously wetted, as in sprinkler or flood irriga-
 tion, weed seeds in the soil between the rows continue to germinate throughout the growing season.
Even if preplant herbicides are used, their effectiveness may be diminished if the active ingredients are diluted or leached by excessive sprinkler or flood irrigation.
Because herbicide use and hand hoeing are reduced with drip irrigation, money spent on weed control is saved and crop yield and quality are not as adversely affected by weed competition as they can be in sprinkler and flood irrigation.
The potential for foliar diseases is also reduced compared to sprinkler irrigation since the leaves and stems of the crop are not being wetted.
As mentioned previously, liquid fertilizers  can be injected directly into the irrigation stream and applied to the soil right at the base of each plant.
It can be applied frequently and at very low doses to "spoon feed" the plants throughout the growing season.
With careful management, fertilizer losses are minimal and fertilizer efficiency is very high.
The small-diameter PE pipe used in drip irrigation is flexible and can easily conform to the garden or landscape configuration and topography.
Crops do not need to be planted in straight rows, but can instead be planted along contours of the land.
With point source systems, plant spacing can be highly variable, and the number and flow rates of emitters can be selected to sat-
 isfy the specific water requirements of each plant within an irrigation zone or landscape.
DISADVANTAGES OF DRIP OVER FLOOD OR SPRINKLER IRRIGATION
 Because of the small, but localized, volumes of water applied to plants under drip irrigation, the water must be applied frequently  and for relatively short durations  depending on the crop, the crop's growth stage, the absorptive capacity of the soil, and the flow rates of the emitters.
While this may not be a limiting factor when using a municipal, water-ondemand system, particularly if the drip system is automated, it can be problematic for irrigators using water from canals, ditches, and acequias where water availability may be restricted by specific, predetermined schedules set by the water purveyor or district.
If water can only be obtained once per week for a 24-hour period, for example, drip irrigation management becomes very difficult unless water can be stored in a pond or tank for use on demand.
Another common problem with drip irrigation is the perception by irrigators accustomed to sprinkler or flood irrigation that not enough water is being applied.
There can be a tendency to apply more water than required for adequate plant growth to make up for the perceived water deficit.
This excess water, along with essential, readily soluble nutrients in the soil  may be lost from the plant root zone through deep percolation.
This results in water and fertilizer waste and potential reduction in crop yield.
In areas with saline soil or water, salts can reduce soil quality and adversely affect plant growth by accumulating at the perimeter of the area wetted by emitters.
Periodic sprinkler irrigations may be required if natural precipitation is insufficient to leach this accumulated salt into the soil below the plant root zone.
Contraction and expansion of PE laterals
 Since PE drip line is flexible, it contracts and expands with temperature changes.
Consequently, it may be necessary to lay out the drip laterals and fill them with cool irrigation water either before planting  or before installing emitters.
This is of particular concern if the drip lines are very long  and the emitters are widely spaced.
If the lines are laid out when they are warm, which is preferable because they are more pliable and easier to work with, they
 will be expanded.
If transplants or seeds are planted next to an emitter on a warm, expanded line, water may not be applied directly to the plants or seeds when it is filled with cool water and it contracts.
Because of this, line source drip lines should be filled with water and run for a while to create wet spots where the transplants or seeds should be planted.
With a point source drip line, planting can be done before laying out the PE line next to the plants, but the line should be filled with water prior to installing the emitters SO their placement will be in close proximity to the plants.
If the chosen point source emitters can accommodate spaghetti tubing, it can be used to distribute water from the emitter outlet closer to the base of the plant if necessary.
The small plastic components of drip systems are fragile and are easily damaged by equipment, animals, or humans.
Cheap, thin-walled drip tape and other exposed components can deteriorate when exposed to weathering and the ultraviolet rays of the sun.
In subsurface drip systems, buried lines can incur significant damage from pocket gophers and other burrowing rodents.
These problems can be overcome by selecting highquality materials, by covering above-ground components with mulch, and by avoiding subsurface drip where burrowing rodents are common.
Water quality and emitter clogging
 Clogging of drip emitters by particulate matter can usually be prevented with proper filtration and lateral flushing.
If the irrigation water is high in calcium and bicarbonates, chemical clogging by precipitates of calcium carbonate  may occur.
Additionally, if the water source is a pond or open irrigation canal, algae or other organic material may clog filters and emitters.
Chemical clogging can be prevented by adding an acid  to the water, while adding chlorine  can help remediate biological clogging.
Considering the initial costs for components and installation, drip irrigation is more expensive than flood irrigation , and drip upkeep costs may be greater than upkeep costs for sprinkler systems.
Over time, however, if components are well maintained and used for many years, these higher initial costs will be recovered by reduced labor costs, reduced inputs of fertilizers and pesticides, higher quality and yields of produce, and lower water use compared to flood or sprinkler irrigation.
In this paper, low-pressure drip irrigation will be defined as water supplied through piping and emitters from an elevated reservoir  to a garden or landscape at a head of less than 20 feet, or 8.7 psi of pressure , to the emitters.
Advantages of low-pressure drip compared to high-pressure drip
 Only two primary components are required in the mainline manifold of a low-pressure, gravity system: a valve and a filter.
Since the water reservoir surface is elevated above the emitters and there is a break between water inflow and outflow, a backflow prevention device is not required.
Pressure is already low, SO a pressure regulator is not needed, and since fertilizer can be added directly to the elevated tank, a fertilizer injector is not required.
Unlike high-pressure systems, which require tight-fitting compression fittings or clamped barbed fittings to prevent blowouts and leaks, a friction fit between PE tubing and barbed fittings is usually sufficient to hold connections together in a lowpressure system.
Short  pieces of an old 1/2or 5/8-inch garden hose, rather than clamps or specialized fittings, can sometimes be used to clamp drip tape to barbed fittings.
Disadvantages of low-pressure drip compared to high-pressure drip
 One major disadvantage of a low-pressure system is that emitter flow rates are lower than those specified by the manufacturer at their recommended operating pressure.
Consequently, on-site measurements are required to identify the actual flow rate of emitters and to determine the application uniformity  at these lower pressures.
Determining emitter flow rate and application uniformity.
Average emitter flow rate and system application uniformity  can be determined by placing a small container  into depressions dug into the soil under selected emitters along laterals and recording the volume of water caught in each container during a specified period of time.
Each lateral should be of the desired length , and in the case of point source laterals, all emitters of the zone should be installed.
If all laterals fed by a header are similar , the irrigated area is level, and the header is of sufficient size to minimize friction loss between laterals , measurements from one lateral should represent measurements from all laterals fed by the header.
Measurements should be taken from emitters near the header, midway between the header and footer, and close to the footer  of the farthest lateral from the mainline to
 Figure 10.
Example of components used in the manifold of a low pressure drip system.
determine flow rate variability between emitters.
While it is preferable to measure the volume of water caught in each can with a graduated cylinder that has a milliliter  scale, a tablespoon or small measuring cup with a fluid ounce scale can be used.
The following conversion factors and equation can be used to convert flow rate from ml/second to gallons per hour :
 1 fluid ounce = 30 ml 1 tablespoon = 0.5 fluid ounce  1 gallon = 3,785 ml
 Flow rate  =  X 0.95
 As a general rule, emitter flow rates taken from different emitters should not differ by more than 20%.
If it appears that emitter flow rate is decreasing with increased distance from the header, laterals may be too long and should be shortened.
If plant rows to be irrigated with low pressure are more than 100 feet long, AU may be improved by positioning the header across the center of the garden  and connecting the laterals to the header SO they distribute water down the rows in both directions from the central header.
An experiment was undertaken at ASCF in 2010 to determine which components might be suitable for use in low-pressure, rainwater catchment systems.
Flow rates were measured for seventeen different point source emitters, two line source tubings, and one  drip tape at a low pressure of 2.5 psi.
The average flow rates and AUs of one line source drip
 Table 2.
Measured Application Uniformity, Flow Rate, and Percent of Manufacturer's Specified Flow Rate at Recommended Pressure of Five Point Source and Two Line Source Emitters When Operated at Low Pressure 
 Emitter Model	Uniformity	Flow Rate 	MRMPd,
 Cat.
No.)	b	Measured	% MSFR	MSFR	psi
 D012	0.957	0.336	33.6	1.0	20
 D006	0.940	0.519	51.9	1.0	ns
 D023	0.913	0.991	24.8	4.0	20
 D002	0.894	1.174	58.7	2.0	ns
 D013	0.871	0.723	36.1	2.0	20
 Drip Tape 	0.958	0.104	39.0	0.27	10
 Drip Tube 	0.940	0.315	31.5	1.0	10
 tape, one line source drip tubing, and five different models of point source emitters are shown in Table 2.
Each flow rate value  represents the mean of several measurements taken from emitters located at various distances along replicated 50-foot and 100-foot laterals.
The uniformity  is expressed as 1 CV , where CV is the standard deviation divided by the average of all measurements for a given emitter model.
The closer uniformity is to 1, the less difference there is in the flow rate between emitters.
Table 2 shows only those emitters  for which uniformity was greater than 0.85.
The measured flow rate is also expressed as a percentage  of the manufacturer-specified flow rate  at the recommended pressure range.
The manufacturer's recommended minimum pressure  is shown in column 6.
Average flow rate per emitter ranged from 0.104 gph for the drip tape to 1.174 gph for the D002 emitter.
The drip tape and the emitter D012 provided the best application uniformity of all emitters tested , but the flow rates were very low.
It is important to identify the actual emitter flow rates and the system AU under these low-pressure conditions SO irrigations can be scheduled effectively and efficiently.
If the drip system cannot provide the maximum daily water requirements of the plants being irrigated, plant growth and yields  or plant quality  may be unacceptably reduced.
Crop water use or evapotranspiration
 Seasonal crop coefficient  curves have been formulated for many different crops , and if appropriate weather data are available to calculate ETr, they can be used to estimate the water use of these crops when grown in large monocultures.
A modification of the technique  can be used to estimate the irrigation requirement  of individual plants in small, drip-irrigated vegetable gardens and landscapes.
To calculate IR, measurements of the plant's canopy diameter  and ETr , which vary during the growing season, are multiplied by an adjustment factor  and a constant  that converts D to plant canopy area  and IR from inches to gallons.
To prevent overirrigation, effective precipitation  between irrigations is subtracted from ETr.
To calculate effective precipitation , measured rainfall events less than 0.2 inch are ignored, and only 75%  of the amounts in excess of 0.2 inch are considered.
To help prevent under-irrigation of plants,
Pressure data has been analyzed in an ongoing study from 66 pivots across Nebraska with either AgSense FieldCommander or Lindsay FieldNET remote monitoring equipment.
Of these systems, 34 pivots  are operating below their pressure requirement for at least 5% of the time.
This indicates that low pressure is likely to be a more common problem than what we realize.
Screen Filters in Trickle Irrigation Systems1
 Dorota Z.
Haman and Fedro S.
Zazueta
 Trickle irigation is a system by which water is applied at low rates and high frequency to the root zone of a crop.
In addition, water soluble nutrients and other chemicals can be delivered with irrigation water at rates close to the plant requirement.
When well managed, trickle irrigation will result in water, nutrient, and energy savings due to its low operating pressure and high emission uniformity.
However, trickle irrigation usually require a higher level of management than other irrigation systems.
Water quality is a major concern in the management of trickle irrigation systems.
Emitters plugged by physical, chemical, or biological contaminants may create significant problems in everyday maintenance.
Therefore, effective and reliable filtration is mandatory for successful operation of trickle irrigation systems.
There are different types of filters available for the removal of physical contaminants from irrigation water.
Selection of a filter depends on the type and amount of contaminants in the irrigation water, as well as the size of the irrigation system and the desired management practices.
Various types of screen filters are commonly used in irrigation systems.
Screen filters are simple and economical filtration devices of various shapes and sizes, most frequently used for the removal of physical contaminants.
They can be made
 of metal, plastic or synthetic cloth enclosed in a special housing.
Screen filters are recommended for the removal of very fine sand or larger-sized inorganic debris.
It is normally not effective to use screen filters for the removal of heavy loads of algae or other organic material, since filters clog rapidly, requiring too frequent cleaning to be practical.
Figure 1.
Screen filter.
When surface water is used for trickle irrigation, screens are often used as secondary filters, after organic matter has been removed with media filters.
In this capacity they prevent washed out media from entering the irrigation system.
When well water is used for irrigation, a screen filter may be used as a primary filter, or it may be secondary to a vortex sand separator, depending on the mineral particle load in the water.
Filtering screens are classified according to the number of openings per inch, with a standard wire size given for each screen size.
The minimum size of particle retained by a screen filter with a certain mesh can be determined from Table 2.
A 200 mesh screen is used often in trickle irrigation.
Water filtered with a 200 mesh screen will contain
 2.
Dorota Z.
Haman, assistant professor; and Fedro S.
Zazueta, associate professor; Department of Agricultural and Biological Engineering; UF/IFAS Extension, Gainesville, FL 32611.
only particles of very fine sand or particles of even smaller sizes.
Generally, it is recommended to remove particles down to a size four times smaller than the emitter's passageway SO that grouping and bridging of particles will not cause clogging.
The maximum tolerable particle size for a given emitting device should be provided by the manufacturer.
Organic particles with a density approaching the density of water tend to group and bridge more easily.
Particles heavier than water, typically mineral particles, may settle and collect in the low flow zones of the irrigation system.
Selecting a Screen Filter
 When estimating the appropriate size of filter for a specific application, one should consider the quality of water needed, volume of water required to be passed through the filter between consecutive cleanings, filtration area of the filter screen, and allowable pressure drop through the filter.
A screen filter can handle a large range of discharges.
However, discharges that are large in relation to the filtering surfaces will result in greater pressure losses, shorter life of the filter, and the requirement for frequent cleaning.
The size of the filter is specified by its effective area, which is the area of the openings in the screen.
It is specified in relation to cross-sectional area of the man pipe.
A desirable ration is 2 or more.
The mesh size of the filter  will depend on the smallest particle size to be removed from the irrigation water.
If the irrigation water contains large amounts of sand or other inorganic contaminants, it is advisable to use vortex sand separators before the screen filters.
Vortical water flow separates heavier particles away from the fine mesh cartridge.
They collect at the bottom of the filter, where they can be periodically flushed away.
Gravity screen filters operate on the principle of gravity force, not water pressure.
Because only atmospheric pressure is used, soft organic material is not forced through the screen.
Gravity screen filters are often used where an elevated water source from the canal or reservoir is available.
Since the pressure loss through a gravity screen filter is very small, they are often used in systems where such losses must be minimized.
Gravity screens are easy to install and maintain.
Usually, these filters are constructed as two chambers separated by a fine mesh screen, which can be cleaned manually or automatically.
However, most of them incorporate self-cleaning water jets.
Figure 2.
Gravilty filter.
If water is pumped from a surface source , aquatic plants, fish, and animals should be kept away from the intake pipes.
This can be accomplished with an intake screen.
The design of the screen must allow for the separation of the debris from the water without pulling the debris against the screen.
Use a horizontal screen placed below the water surface or an intake basket-type filter.
Figure 3.
Intake screen.
Figure 4.
Permanent horizontal-screen structure for debris control for water obtained from irrigation ditches.
The efficiency of pumping may be reduced by debris in the water entering the suction pipe.
The problem can be solved by using intake screens.
Some of these screens are self-cleaning and require very little maintenance.
Small amounts of larger particles, such as limerock flakes from the Florida aquifer, can be removed using a Y-type strainer with replaceable screens and with clean-out faucets or valves.
They can be flushed while in use if the required high flow for flushing is provided.
Figure 5.
Y-type strainer.
Blowdown filters operate in the same way as other types of pressure screen filters.
They are designed for easy cleaning, which is done by opening a valve that diverts the water flow through the screen, releasing trapped particles.
Occasionally, blowdown filters require manual cleaning to eliminate particles that have become lodged in the screen.
Figure 6.
Blowdown screen filters.
Screen filters can be cleaned manually by removing the screen and washing it with clean water.
However, dismantling is not very practical for use with waters containing
 high levels of contaminants, since it must be done often.
Blowdown screen filters greatly simplify the cleaning process.
They are cleaned with the water diverted through the screen by opening a valve.
This operation does not require disassembling.
The screen does not have to be removed for routine cleaning of the filter, but it must be removed for occasional cleaning of the particles which become lodged in the screen.
The most convenient method for cleaning screen filters is automatic screen flushing triggered by critical pressure differential across the filter, which increases with buildup of debris on the screen.
Automatic cleaning can also be set on a time schedule.
It is very important to prevent particles from entering the irrigation system during cleaning.
Even small amounts of organic or inorganic contamination may be sufficient to clog a trickle irrigation system.
Filtered water is recommended for washing and backflushing.
Additional safety devices such as secondary screen filters at the entrance to each irrigation system subunit are highly recommended.
Disk filters are relatively new types of filters which can replace screen filters in trickle irrigation systems.
The filtration element consists of a stack of grooved metal disks coated with epoxy and placed on a telescopic shaft inside the housing.
Water flows through the disks from the outside inwards along the radii of the disks.
Particles suspended in the water are trapped in the grooves of the disks, and clean water is collected in the center of the disks.
Figure 7.
Epoxy-coated metal filter with grooved disc elements.
Disk elements can be manually or automatically cleaned.
During manual cleaning, the housing is removed, the telescopic shaft is expanded, and the compressed disks separated for easy cleaning.
They are normally cleaned by rinsing with a water hose.
The telescopic shaft prevents the individual disks from falling off the shaft during rinsing.
Automatic backflushing is triggered by the preset pressure differential.
This pressure differential opens the exhaust valve and water flows backwards through the disks, removing trapped particles from the grooves.
Screen filters are the most popular filtering devices used in irrigation systems.
They are commercially available in many shapes, sizes, and screen meshes.
Screen filters are primarily recommended for the removal of inorganic material, such as sand and scale.
They should not be used as the only filtration system in the presence of organic contamination.
In that case they should be used as secondary filters following media filters.
EVALUATION OF ADWR WATER DUTIES FOR LARGE TURF FACILITIES
 The Arizona Department of Water Resources  limits the amount of groundwater large turf facilities  may use for irrigation in the Tucson and Phoenix Active Management Area.
Current ADWR regulations effectively cap groundwater use at 4.6 and 4.9 acre-feet per acre per year  for turfgrass grown within the Tucson and Phoenix AMAs, respectively.
Operators of LTFs have expressed concerns that ADWR regulations  are too stringent and provide insufficient water to: 1) produce acceptable quality turfgrass and 2) sustain leaching requirements necessary to avoid problems with salinity.
University of Arizona research appears to support the concerns of LTFs.
Brown et al.
conducted a three-year study to develop crop coefficients  for the typical desert turf system consisting of bermudagrass in summer and overseeded ryegrass in winter.
Crop coefficients are adjustment factors that when used in conjunction with weather-based estimates of reference evapotranspiration  provide accurate estimates of turf water use.
When the Kcs developed by Brown et al.
were applied to long term averages of ETo available from the Arizona Meteorological Network , annual ETt was projected to approach 4.9 af/a/yr in both the Tucson and Phoenix AMAs, indicating annual evaporative demand equals  or exceeds  the water duties in the two AMAs.
If these projections prove to be true, operators of LTFs would have to rely on precipitation  to offset soil water deficits resulting from the duties and facilitate deep percolation required to remove  salts from the turf root zone.
In an effort to help clarify this issue, a study was initiated on the large weighing lysimeters located at the University of Arizona Karsten Turf Research Facility in Tucson.
The objective of the three-year study was to determine if the ADWR turf water duty for the Tucson AMA provided sufficient water to: 1) sustain acceptable quality turfgrass and 2) support acceptable levels of leaching when turfgrass was irrigated using the Kcs recommended by Brown et al.
This report first summarizes the results of this Tucson study, then concludes with a discussion of how to translate the study results to LTFs in both the Tucson and Phoenix AMAs.
The study was conducted between 1 October 1997 and 30 September 2000 at the University of Arizona Karsten Desert Turf Research Facility located in Tucson, AZ.
Two large weighing lysimeters, centrally located within a 5 acre  field research area, were used to monitor the water balance of a desert turf system, consisting of 'Tifway' bermudagrass in summer and overseeded 'Froghair' intermediate ryegrass in winter.
The lysimeters are cylindrical in shape with diameter and depth equal to 8.2'  and 13.2' , respectively.
The lysimeter soil is uniform with depth and is classified as a Vinton fine sand.
Each lysimeter rests on a modified truck scale which is connected to a load cell.
An automated data logger is used to monitor the output signals from the load cells.
The data logger is programmed to sample load cell outputs every 2 seconds and compute 10-minute averages of lysimeter mass.
Scale accuracy is about lb  which is equivalent to a depth of 0.0024" of water.
Water draining to the bottom of the lysimeters is removed using a vacuum pump that is attached to a series of suction candles.
Drainage water is stored in onboard tanks until removed and quantified by lysimeter technicians.
During periods of rainfall, irrigation amount was determined by subtracting rainfall from EToa during the previous 24-hr period.
Irrigations were eliminated on days when rainfall exceeded EToa.
Rainfall amounts in excess of EToa were assumed stored in the soil and used to offset future evaporative demand with the proviso that stored rainwater could never exceed 0.5".
Irrigation was resumed once this stored supply of rainwater was depleted.
The turf received N at a rate of approximately 31 lb/a/ month  from irrigation water and chemical fertilizer.
Monthly applications of fertilizer N were adjusted based on the irrigation rate and N concentration in the irrigation water.
Potassium  and phosphorus  were applied every six weeks at rates of 21.6 and , respectively.
Granular K,SO4 4  and Ca2  served as fertilizer sources for K and P, respectively.
The turf was mowed two to three times per week during the summer and one to two times per week during the winter with a reel mower.
Mowing height was set at 0.875"  in summer and 1.0"  in winter.
Turf evapotranspiration  was determined daily in units of mm/d for the 24-hr period ending at midnight using the soil water balance equation:
 where I is the amount of irrigation, P is precipitation, S is the daily change in soil moisture storage and D is the amount of drainage.
Irrigation was applied on most days during a 15-minute period before sunrise.
The gain in lysimeter mass during this period was set equal to the amount of irrigation.
Precipitation was measured in two ways: 1) from the increase in lysimeter mass during precipitation events, and 2) using a tipping bucket rain gauge.
The greater of the two precipitation measurements was set equal to P.
The change in lysimeter mass for the day was assumed equal to S, and D was obtained by multiplying the volume of drainage water in liters  by a specific gravity of 1.0 kg/L.
Tifway bermudagrass, established on the lysimeters and the surrounding 10000 ft2  area by sprigging during the summer of 1994, served as the turf surface during the summers of 1998,1999 and 2000.
Froghair intermediate ryegrass was overseeded into the bermudagrass at a rate of 600 lb/a  on a pure live seed basis in mid-October
 of each year and served as the turf surface during the winter.
Dates of overseeding were 13,15 and 13 October of 1997, 1998 and 1999, respectively.
The lysimeter facility allows one to accurately quantify the water balance of the standard desert turf system consisting of bermudagrass in summer and overseeded ryegrass in winter.
Components of the water balance include precipitation and irrigation as inputs, and evapotranspiration  and deep percolation  as losses.
The difference between inputs and losses represents the change in soil moisture storage over the course of the year.
For this study, a "turf year" begins on 1 Oct and concludes on 30 Sep of the following year.
The abbreviations TY98, TY99, and TY00 are used to designate the periods 1 Oct 1997 30 Sep 1998, 1 Oct 1998 30 Sep 1999, and 1 Oct 1999 30 Sep 2000, respectively.
Tables 1-3 provide a numerical summary of the water balance components by year while Figures 2-4 present these same results in a graphical format.
Average values of the water balance components over the course of the study  are provided in Table 4 and Figure 5.
The tables provide the components for the individual lysimeters as well as average values of each component.
The figures simply present the average values for each component.
Turf performance over the period of study was rated as acceptable or higher with the exception of some finite periods of weaker turf performance associated with spring and fall transition.
Early June proved to be the period where poor turf performance was observed in the spring.
Spring transition is often delayed at the study location due to cool night temperatures.
Poorer turf performance was also evident in late October and early November during the period of overseed establishment.
Given that turf performance is commonly inferior during these spring and fall transition periods, it was concluded that the irrigation regime utilized in this study did not negatively impact turf performance.
Turf ET varied from 56.2"  in TY98 to 62.4"  in TY00 and averaged 59.2" yr  over the period of study.
The ETt values recorded from the two lysimeters were remarkably consistent and varied by less than 2" / yr  over the course of the study.
Turf ET exceeded the Tucson water duty  in each year of the study, providing clear evidence that the quantity of water available from the Tucson duty is insufficient in most years to fully offset evaporative demand.
Over the course of this study, ETt exceeded the water duty by an average of 4.0" / yr  which represents the average water deficit that must be made up from precipitation.
Table 5 provides ETt, EToa and the ratio of ETt to EToa for each year of the study.
Figure I.
Graphical depiction of the soil water balance for a turf system.
Precipitation and irrigation serve as inputs of water into the system.
Water is lost from the system through deep percolation and turf evapotranspiration.
Figure 2.
Components of the soil water balance for TY98.
The arrow indicates the quantity of water provided in ADWR's water duty for LTFs in Tucson.
Figure 3.
Components of the soil water balance for TY99.
The arrow indicates the quantity of water provided in ADWR's water duty for LTFs in Tucson.
Figure 4.
Components of the soil water balance for TY00.
The arrow indicates the quantity of water provided in ADWR's water duty for LTFs in Tucson.
Figure 5.
Components of the soil water balance for the period I Oct 1997 to 30 Sep 2000.
The arrow indicates the quantity of water provided in ADWR's water duty for LTFs in Tucson.
Table I.
Summary of turf water balance components for TY98.
Individual components consisting of irrigation, precipitation, drainage, ETt, and change in soil moisture storage are presented in units of inches and mm for each lysimeter.
Mean values for each component are presented in the last two columns of the table and represent the average of the two lysimeters.
Components of	LYSIMETER IRRIGATED WITH	Mean Values
 Water Balance	Groundwater	Effluent
 Inputs of Water	In	mm	In	mm	In	mm
 Irrigation	51.0	1296.7	50.9	1292.6	51.0	1294.6
 Precipitation	17.6	448.4	17.8	451.0	17.7	449.7
 Total Inputs	68.7	1745.1	68.6	1743.6	68.7	1744.3
 Drainage	16.4	417.6	12.5	317.0	14.5	367.3
 ETt	55.2	1402.5	57.2	1453.6	56.2	1428.0
 Total Losses	71.7	1820.1	69.7	1770.6	70.7	1795.3
 Change in Storage	-3.0	-75.0	-1.1	-27.0	-2.0	-51.0
 Table 2.
Summary of turf water balance components for TY99.
Individual components consisting of irrigation, precipitation, drainage, ETt and change in soil moisture storage are presented in units of inches and mm for each lysimeter.
Mean values for each component are presented in the last two columns of the table and represent the average of the two lysimeters.
Components of	LYSIMETER IRRIGATED WITH.
Mean Values
 Inputs of Water	In	mm	In	mm	In	mm
 Irrigation	51.9	1319.3	50.1	1272.8	51.0	1296.0
 Precipitation	15.2	384.9	15.1	384.5	15.1	384.7
 Total Inputs	67.1	1704.2	65.2	1657.3	66.2	1680.8
 Drainage	10.2	257.9	7.4	187.2	8.8	222.6
 ETt	59.1	1500.0	59.0	1499.5	59.0	1499.8
 Total Losses	69.3	1757.9	66.4	1686.7	67.8	1722.4
 Change in Storage	-2.2	-53.7	-1.2	-29.4	-1.6	-41.6
 Table 3.
Summary of turf water balance components for TY00.
Individual components consisting of irrigation, precipitation, drainage, ETt and change in soil moisture storage are presented in units of inches and mm for each lysimeter.
Mean values for each component are presented in the last two columns of the table and represent the average of the two lysimeters.
Components of	LYSIMETER IRRIGATED WITH.
Mean Values
 Water Balance	Groundwater	Effluent
 Inputs of Water	In	mm	In	mm	In	mm
 Irrigation	61.6	1563.6	61.1	1552.6	61.3	1558.1
 Precipitation	8.6	218.4	8.7	220.0	8.6	219.2
 Total Inputs	70.2	1782.0	69.8	1772.6	70.0	1777.3
 Drainage	7.7	196.4	5.6	142.7	6.7	169.6
 ETt	61.9	1573.1	62.8	1595.6	62.4	1584.4
 Total Losses	69.7	1769.5	68.4	1738.3	69.1	1754.0
 Change in Storage	0.5	12.5	1.4	34.3	0.9	23.3
 Table 4.
Summary of turf water balance components for the three year period from I October 1997 to 30 September 2000.
Individual components consisting of irrigation, precipitation, drainage, ETt and change in soil moisture storage are presented in units of inches and mm for each lysimeter.
Mean values for each component are presented in the last two columns of the table and represent the average of the two lysimeters.
Components of	LYSIMETER IRRIGATED WITH	Mean Values
 Water Balance	Groundwater	Effluent
 Inputs of Water	In	mm	In	mm	In	mm
 Irrigation	54.8	1393.2	54.0	1372.7	54.4	1383.0
 Precipitation	13.8	350.6	13.8	351.8	13.8	351.2
 Total Inputs	68.6	1743.8	67.9	1724.5	68.3	1734.2
 Drainage	11.4	290.6	8.5	215.6	10.0	253.1
 ETt	58.7	1491.9	59.7	1516.2	59.2	1504.0
 Total Losses	70.2	1782.5	68.2	1731.9	69.2	1757.2
 Change in Storage	-1.5	-38.7	-0.3	-7.4	-0.9	-23.0
 Table 5.
Turf evapotranspiration , reference evapotranspiration , and the ratio of ETt to EToa for TYs 98, 99, and 00.
In	mm	In	mm
 TY98	56.2	1427.5	74.5	1892.3	0.75
 TY99	59.0	1498.6	78.4	1991.4	0.75
 TY00	62.4	1585.0	82.8	2103.1	0.75
 Mean	59.2	1503.7	78.6	1996.4	0.75
 While annual values of ETt and EToa differed by as much as 6.2"  and 8.3" , respectively, the ratio of ETt to EToa averaged a consistent 0.75.
This ratio is by definition a crop coefficient; thus, it appears that 0.75 serves as an excellent annual Kc value for a bermudagrass turf system that is overseeded in winter with ryegrass.
Amount of Applied Irrigation and Precipitation
 The amount of irrigation water applied ranged from 51.0"  in both TY98 and TY99 to 61.3"  in TY00 and averaged 54.4"  over the period of study.
During two years of the study and on average over the course of the study, the amount of irrigation water applied was less than the water duty of 55.2".
Similar amounts of irrigation water were applied to each lysimeter during individual turf years and over the course of the study.
The large difference in the level of irrigation water applied between TYs 98 and 99, and TY00 results from differing levels of precipitation.
Above normal precipitation was recorded at the study site in both TYs 98 and 99 and helped to lower irrigation demand.
In contrast, precipitation was below normal during TY00 when irrigation demand was highest.
It is also interesting to note the impact of precipitation on evaporative demand as indicated by EToa.
EToa totaled 74.5" , 78.4"  and 82.8"  during TYs 98, 99 and 00 when precipitation totaled 17.7" , 15.1"  and 8.6"  respectively.
A more in-depth evaluation of the relationship between precipitation and EToa was performed using 15-17 years of data available from AZMET.
This analysis confirmed an inverse relationship between annual values of precipitation and EToa exists in both the Tucson and Phoenix areas, suggesting precipitation impacts the amount of applied irrigation water in both a direct and indirect manner.
The direct impact is obvious as precipitation replaces water that would otherwise come from irrigation.
The less obvious indirect impact is that precipitation with its associated cloudiness and higher humidity lowers EToa.
Drainage and Leaching Fractions
 Drainage or water lost to deep percolation serves as the final important component of the water balance.
Drainage is required to minimize the accumulation of soluble salts in the root zone and thereby avoid salinity problems.
Drainage ranged from 6.7"  during TY00 to  during TY98 and averaged 10.0" / yr  over the course of the study.
The high rates of drainage in TY98 appear to include some residual drainage from the previous study where higher rates of irrigation maintained soil moisture at higher levels.
Changes in stored soil moisture suggest this residual drainage totaled -2.0"  in TY98.
Proper assessment of drainage requires one to convert drainage values to leaching fractions and then assess for a given turfgrass and irrigation water quality whether the leaching fraction is adequate.
The leaching fraction is defined as the fraction of applied water that passes through the entire root zone and is lost to deep percolation.
Leaching
 fractions for TYs 98, 99, and 00 were 0.21, 0.13, and 0.096, respectively, and averaged 0.15 during the entire period of study.
Bermudagrass is rated as tolerant to salinity while ryegrass is rated as moderately tolerant; both grasses therefore have a low leaching requirement when irrigated with good quality water.
The electrical conductivity of the irrigation water used in this study averaged 0.4 dS/m for the lysimeter irrigated with groundwater and 1.0 dS/ m for the lysimeter irrigated with effluent.
The resulting leaching requirements for bermudagrass irrigated with groundwater and effluent were 0.012 and 0.03, respectively.
The leaching requirements for ryegrass equal 0.014 and 0.037 when using groundwater and effluent, respectively.
Leaching was clearly adequate to avoid salinity problems in this study.
Changes in Soil Moisture Storage
 Stored soil moisture remained fairly constant over the course of the study.
Over the three years of study, moisture storage declined 0.9".
Annual changes in soil moisture storage ranged from -2.0" in TY98 to +0.9" in TY00.
It is important to realize that these changes in soil moisture pertain to the entire lysimeter soil profile which has a depth of 12.3' ; thus, the annual changes in soil moisture storage represent no more than 12% of soil moisture at field capacity.
The largest decline in soil moisture storage occurred at the beginning of TY98 and may reflect some residual drainage from the previous study where higher rates of irrigation maintained soil moisture at higher levels.
Translation of Results to Large Turf Facilities
 The results presented in the previous section of this report appear to provide good evidence that ADWR water duties when combined with normal to above normal levels of precipitation provide sufficient water to support year round green turf while preventing future problems associated with excessive soil salinity.
However, such a conclusion may be called into question when one attempts to transfer these results to LTFs.
One important issue impacting the translation of these results to LTFs pertains to the procedures used to quantify the amount of applied irrigation water in this study.
The daily gain in lysimeter mass during the brief  early morning irrigation window was used as the daily irrigation rate.
In effect, this methodology measures the amount of water reaching the turf, not necessarily the total amount of water used in the irrigation process.
This is an important distinction since ADWR monitors water used at the well head or diversion point, not water that reaches the turf.
The amount of irrigation water reaching turf is always less than the water used at the well head or diversion point due to system leaks, evaporation while the water is in transit from the irrigation head to the turf, and drift off target.
These losses of water along with other losses associated with runoff and deep percolation represent the main factors impacting irrigation efficiency which can be
 defined as the percentage of total applied water that is put to beneficial use.
Another irrigation related factor that may impact the translation of these results to LTFs relates to irrigation nonuniformity.
No irrigation system applies water over an area in a perfectly uniform manner.
This non-uniformity is assessed via an irrigation audit which involves setting out an array of catch cans prior to an irrigation event to quantify the variation in precipitation resulting from system operation.
Irrigation audits were run on the lysimeter irrigation systems and non-uniformity averaged 0.93 using Christiansen's Uniformity Coefficient.
While it is common to increase irrigation run time to offset non-uniform irrigation, such a strategy was not employed in this study.
Given that we did not observe any serious problems with turf performance in this study, it is tempting to assume that the results of this study are valid for irrigation systems exhibiting CU values approaching 0.90.
However, it is questionable whether one can directly extrapolate the relationship between turf performance and irrigation non-uniformity found in small plots such as the lysimeters to LTFs.
One reason such an extrapolation is unreasonable is that the high CU values obtained in this study are difficult  to replicate for LTF irrigation systems.
A second reason such an extrapolation is questionable is that in small plots, turf root systems may be able to exhibit sufficient horizontal growth to offset the apparent limitations associated with non-uniform irrigation.
For example, if 10% of the lysimeter received insufficient irrigation to support optimal growth, the total area under watered would be 5.3 ft2 If the entire under watered area was located in one square block of turf, the dimension of the block would be 2.3' X.
Presumably, the turf in this small block could extend its roots outward in an horizontal manner and pick up water from adjacent areas receiving higher watering rates and turf performance would not greatly suffer.
If however this same scenario is used on a 4-acre golf fairway, the area under watered is 17424 ft2.
If this under watered area were divided into 10 blocks of equal size.
In this case, it is unlikely turf in the middle of the block would be able to extend its root system into adjacent areas for supplemental water and thus would remain stressed and exhibit a lower visual quality.
One final issue that may impact translation of study results to LTFs involves topography and soil type.
The lysimeter facility provides an experimental setup consisting of a level turf surface combined with a soil that supports a high water infiltration rate.
This combination provides a best case scenario for infiltration of both irrigation water and precipitation.
Often, LTFs must contend with one or both of the following features: 1) complex topographical features that include areas with steep slopes, and 2) soils with either fine textured or compacted surface layers that do not support high rates of water infiltration.
These real world topographical and soil infiltration characteristics will lead to higher rates of runoff during irrigation and rainfall events with the overall impact being a reduction in available water supply for turf.
The previous paragraphs present what appears to be a conflict between what the study results indicate is possible in small plot studies versus the practical realities of translating these results to LTFs.
To help clarify this conflict, a simple model was devised to assess the overall water balance of a unit area of turf in a LTF setting in the Tucson and Phoenix areas.
The model estimates the net water balance of a turf area subjected to three scenario climate regimes  when irrigation system performance and runoff limit the amount of water that infiltrates the soil supporting the turfgrass.
Input data required to run the model are presented in Table 6 and include precipitation, ETt, and the amount of water available from ADWR water duties.
Wet and dry years were assigned precipitation values equal to 133% and 67% of normal, respectively.
Annual values of ETt were assumed equal to 75% of EToa.
EToa for the three precipitation regimes was determined from least squares regression lines relating annual EToa to annual precipitation for the Tucson and Phoenix areas.
The model projects the net water balance for the turf system when various percentages of the available water supply  infiltrate the soil supporting the turf.
Runoff from precipitation events was allowed to range from 0 50% of the annual precipitation amount in increments of 10%.
The model assumes a LTF applies 100% of its allotted duty through the irrigation system but varies the percentage of this water that infiltrates into the unit area of turf from 75-100% in 5% increments.
The output from the model is the net water balance  for the turf system which is defined as the amount of irrigation  and precipitation  water that enters the turf system minus the ETt for the year:
 where: WB is the annual water balance of the unit turf area 
 f, is the fraction of irrigation water duty that infiltrates into the turf area
 I is the amount of water applied via irrigation 
 f is the fraction of precipitation that infiltrates into the turf area
 P is the annual amount of precipitation 
 ETt is the annual rate of turf evapotranspiration 
 Positive water balance values indicate a surplus of available water.
This surplus water, if actually applied, would be lost to deep percolation and thus assist with control of soil salinity.
Negative balances indicate an insufficient water supply which may generate less acceptable turf and inadequate leaching to prevent the buildup of soil salinity.
Table 6.
Input data used to model turf water balances at LTFs in the Tucson and Phoenix AMAs.
Water	Precipitation Regime	Turf Evapotranspiration
 Dry	Normal	Wet	Dry	Normal	Wet
 In	mm	In	mm	In	mm	In	mm	In	mm	In	mm	In	mm
 Tucson	55.2	1402	8	203	12	305	16	404	59.4	1509	57.3	1455	55.2	1402
 Phoenix	58.8	1494	5	127	7.5	190	10	254	58.3	1481	57.6	1463	56.9	1445
 Turf Water Balance Estimates: Tucson
 The results of this modeling effort for the Tucson area are presented in Table 7.
Model scenarios that generated surpluses in the water balance are presented in blue text while scenarios generating deficits in the water balance are presented in red text.
One immediate observation from Table 7 is the impact of precipitation on the water balance of the turf.
During dry years, the water balance of the turf system is negative under nearly all water supply scenarios with the exception of situations where a LTF irrigation system can deliver 95-100% of the water duty to the turf.
As indicated earlier in this report, evaporation, drift off target, runoff and leaks ensure that a facility will not be able to apply 100% of the water duty to the turf system.
The water balance improves substantially when precipitation is normal for the year.
LTFs irrigation systems that can deliver a high percentage of the water duty to the turf and are not subjected to severe problems with runoff would be able to maintain a positive water balance in years with near normal precipitation.
Facilities that can not deliver a high fraction of the water duty to the turf or have significant problems with infiltration would likely encounter a soil moisture deficit in normal years.
The soil water balances are generally positive in wet years.
Presumably, most LTFs could maintain a positive water balance in these wet years.
Only LTFs with very difficult infiltration problems or problem irrigation systems would be expected to run a deficit in wet years.
Turf Water Balance Estimates: Phoenix
 The results of this modeling effort for the Phoenix area are presented in Table 8.
The scenario precipitation regimes did not impact the Phoenix turf water balance estimates to the same degree as was observed for the Tucson area.
Two factors explain why the Phoenix estimates are not as responsive to the precipitation regimes: 1) the difference in precipitation between regimes was just 2.5" compared with 4.0" for Tucson; and 2) the impact of annual precipitation on ETt is not as large in Phoenix as in Tucson.
Nevertheless, the trend at Phoenix still follows the general trend observed for
 Tucson.
During dry years, only LTFs with irrigation systems that can deliver 95-100% of the water duty would be able to maintain a positive water balance.
The additional 2.5" of precipitation expected in a normal year in Phoenix improves the water balances only slightly.
LTFs with irrigation systems that can deliver 90% of the water duty to the turf and are not prone to severe runoff problems would be added to the group of LTFs that could sustain positive turf water balances.
Wet years produce further improvements in turf water balances, but the results suggest LTFs that can not deliver in excess of 80% of the water duty to the turf, or are subject to severe problems with infiltration would continue to run a water deficit in wet years.
It is important to note when examining the results of this modeling exercise that the model does not directly address the issue of irrigation non-uniformity.
The results are for turf areas receiving irrigation at the mean precipitation rate of the irrigation system  or 4.9  af/a/yr).
In reality, approximately half the area would receive more than the mean precipitation rate and would produce a more positive water balance while the other half of the area will receive less than this mean rate, thus generating a less favorable balance.
A common engineering approach to this non-uniformity problem is to obtain a measure of non-uniformity from an irrigation audit and then increase the irrigation rate in a manner that minimizes the amount of area that is under watered.
This approach generates very high levels of water use and often produces excessive wetness which can limit the usefulness or "playability" of turf.
Many sports related LTFs do not use this approach to address irrigation non-uniformity because of: 1) playability issues and 2) water supply limitations.
Instead, these facilities "pull hoses" and hand water or extend run times on selected heads or zones to add moisture to drier areas.
The water used in such "unscheduled" irrigations would count against the water duty and would lower the amount of water that could be applied via the irrigation system.
If for example 5% of a LTF's total water duty was applied via unscheduled irrigations, then only 4.37 af/a  to 4.66 af/a  could be applied
 Table 7.
Projected turf water balances in inches and millimeters for LTFs in the Tucson AMA, assuming: I) the indicated percentages of the annual water duty infiltrate the soil and 2) the indicated percentages of annual precipitation are lost to runoff.
Results assume a LTF applies its entire water duty each year.
See Table 6 for assumptions regarding annual rates of turf evapotranspiration  and precipitation.
Positive water balances are presented in blue text; negative water balances are presented in red text.
Projected Turf Water Balances: Tucson
 % of Duty	% of Precipitation Lost to Runoff 
 Infiltrating	0	10	20	30	40	50
 In	mm	In	mm	In	mm	In	mm	In	mm	In	mm
 100	3.8	97.5	3.0	77.1	2.2	56.7	1.4	36.3	0.6	15.8	-0.2	-4.6
 95	1.1	27.4	0.3	7.0	-0.5	-13.4	-1.3	-33.8	-2.1	-54.3	-2.9	-74.7
 90	-1.7	-42.7	-2.5	-63.1	-3.3	-83.5	-4.1	-103.9	-4.9	-124.4	-5.7	-144.8
 85	-4.4	-112.8	-5.2	-133.2	-6.0	-153.6	-6.9	-174.0	-7.7	-194.5	-8.5	-214.9
 80	-7.2	-182.9	-8.0	-203.3	-8.8	-223.7	-9.6	-244.1	-10.4	-264.6	-11.2	-285.0
 75	-10.0	-253.0	-10.8	-273.4	-11.6	-293.8	-12.4	-314.2	-13.2	-334.7	-14.0	-355.1
 % of Duty	% of Precipitation Lost to Runoff 
 Infiltrating	0	10	20	30	40	50
 In	mm	In	mm	In	mm	In	mm	In	mm	In	mm
 100	9.8	249.9	8.6	219.5	7.4	189.0	6.2	158.5	5.0	128.0	3.8	97.5
 95	7.1	179.8	5.9	149.4	4.7	118.9	3.5	88.4	2.3	57.9	1.1	27.4
 90	4.3	109.7	3.1	79.2	1.9	48.8	0.7	18.3	-0.5	-12.2	-1.7	-42.7
 85	1.6	39.6	0.4	9.1	-0.8	-21.3	-2.0	-51.8	-3.2	-82.3	-4.4	-112.8
 80	-1.2	-30.5	-2.4	-61.0	-3.6	-91.4	-4.8	-121.9	-6.0	-152.4	-7.2	-182.9
 75	-4.0	-100.6	-5.2	-131.1	-6.4	-161.5	-7.6	-192.0	-8.8	-222.5	-10.0	-253.0
 % of Duty	% of Precipitation Lost to Runoff 
 Infiltrating	0	10	20	30	40	50
 In	mm	In	mm	In	mm	In	mm	In	mm	In	mm
 100	16.0	405.4	14.4	364.8	12.8	324.3	11.2	283.8	9.6	243.2	8.0	202.7
 95	13.2	335.3	11.6	294.7	10.0	254.2	8.4	213.7	6.8	173.1	5.2	132.6
 90	10.4	265.2	8.8	224.6	7.2	184.1	5.7	143.6	4.1	103.0	2.5	62.5
 85	7.7	195.1	6.1	154.5	4.5	114.0	2.9	73.5	1.3	32.9	-0.3	-7.6
 80	4.9	125.0	3.3	84.4	1.7	43.9	0.1	3.4	-1.5	-37.2	-3.1	-77.7
 75	2.2	54.9	0.6	14.3	-1.0	-26.2	-2.6	-66.8	-4.2	-107.3	-5.8	-147.8
 Table 8.
Projected turf water balances in inches and millimeters for LTFs in the Phoenix AMA, assuming: I) the indicated percentages of the annual water duty infiltrate the soil and 2) the indicated percentages of annual precipitation are lost to runoff.
Results assume a LTF applies its entire water duty each year.
See Table 6 for assumptions regarding annual rates of turf evapotranspiration  and precipitation.
Positive water balances are presented in blue text; negative water balances are presented in red text.
Project Turf Water Balances: Phoenix
 % of Duty	% of Precipitation Lost to Runoff 
 Infiltrating	0	10	20	30	40	50
 In	mm	In	mm	In	mm	In	mm	In	mm	In	mm
 100	5.5	140.2	5.0	127.4	4.5	114.6	4.0	101.8	3.5	89.0	3.0	76.2
 95	2.6	65.5	2.1	52.7	1.6	39.9	1.1	27.1	0.6	14.3	0.1	1.5
 90	-0.4	-9.1	-0.9	-21.9	-1.4	-34.7	-1.9	-47.5	-2.4	-60.4	-2.9	-73.2
 85	-3.3	-83.8	-3.8	-96.6	-4.3	-109.4	-4.8	-122.2	-5.3	-135.0	-5.8	-147.8
 80	-6.2	-158.5	-6.7	-171.3	-7.2	-184.1	-7.8	-196.9	-8.3	-209.7	-8.8	-222.5
 75	-9.2	-233.2	-9.7	-246.0	-10.2	-258.8	-10.7	-271.6	-11.2	-284.4	-11.7	-297.2
 % of Duty	% of Precipitation Lost to Runoff 
 Infiltrating	0	10	20	30	40	50
 In	mm	In	mm	In	mm	In	mm	In	mm	In	mm
 100	8.6	219.5	7.9	200.6	7.2	181.7	6.4	162.8	5.7	143.9	4.9	125.0
 95	5.7	144.8	5.0	125.9	4.2	107.0	3.5	88.1	2.7	69.2	2.0	50.3
 90	2.8	70.1	2.0	51.2	1.3	32.3	0.5	13.4	-0.2	-5.5	-1.0	-24.4
 85	-0.2	-4.6	-0.9	-23.5	-1.7	-42.4	-2.4	-61.3	-3.2	-80.2	-3.9	-99.1
 80	-3.1	-79.2	-3.9	-98.1	-4.6	-117.0	-5.4	-135.9	-6.1	-154.8	-6.8	-173.7
 75	-6.1	-153.9	-6.8	-172.8	-7.5	-191.7	-8.3	-210.6	-9.0	-229.5	-9.8	-248.4
 % of Duty	% of Precipitation Lost to Runoff 
 Infiltrating	0	10	20	30	40	50
 In	mm	In	mm	In	mm	In	mm	In	mm	In	mm
 100	11.9	301.8	10.9	276.5	9.9	251.2	8.9	225.9	7.9	200.6	6.9	175.3
 95	8.9	227.1	7.9	201.8	6.9	176.5	6.0	151.2	5.0	125.9	4.0	100.6
 90	6.0	152.4	5.0	127.1	4.0	101.8	3.0	76.5	2.0	51.2	1.0	25.6
 85	3.1	77.7	2.1	52.4	1.1	27.1	0.1	1.8	-0.9	-23.5	-1.9	-48.8
 80	0.1	3.0	-0.9	-22.3	-1.9	-47.5	-2.9	-72.8	-3.9	-98.1	-4.9	-123.4
 75	-2.8	-71.6	-3.8	-96.9	-4.8	-122.2	-5.8	-147.5	-6.8	-172.8	-7.8	-198.1
 through the irrigation system.
Because the hand watering would be targeted for areas receiving less than the mean precipitation rate, the water balances presented in Tables 7 & 8 would be less favorable by an amount approaching 2.5".
The results of this study provide additional evidence that ADWR turf water duties provide significant challenges for LTFs that wish to maintain a year round green turf surface.
Turf ET over the course of the three year study averaged 59.2" yr  or 4" yr  above the current water duty for the Tucson area.
The amount of water supplied via irrigation averaged 54.4" yr ) or 0.8"  less that the ADWR water duty.
Precipitation supplied the additional water required to: 1) prevent to development soil moisture deficits and 2) support deep percolation required to minimize the buildup of salinity.
While the study results suggest that ADWR water duties supply adequate water to sustain year round turf in the Tucson area, when the study results are adjusted to accommodate runoff during precipitation events and the inefficiencies in LTF irrigation systems , precipitation becomes the critical factor that determines whether the ADWR water duty is adequate to support year round turf.
Results from a simple water balance model suggest the water duties will prove inadequate for nearly all Tucson and Phoenix LTFs in dry years.
The adequacy of the water duties in normal years appears to be "facility dependent" in both locations.
LTFs with efficient irrigation systems and soils that support high rates of infiltration could get by with the water duty in years with normal precipitation.
Facilities with less efficient irrigation systems and/or soil with poor infiltration characteristics would likely find the duties inadequate in normal years.
In wet years, modeling efforts indicate the water duties should be adequate for most LTFs in the Tucson area, but remain "facility dependent" in the Phoenix area.
The modeling effort used to translate the results of this study to LTFs reveals several important issues that must be resolved to make a more definitive statement regarding the adequacy of ADWR water duties for turfgrass.
One issue pertains to the fraction of pumped or diverted water that reaches the turf surface in a well managed and maintained irrigation system.
As stated earlier, leaks, drift off target and evaporation  are the potential causes for such losses.
The modeling results in Tables 7 and 8 indicate such losses play a critical role in determining the adequacy of the water duties.
Results from some preliminary UA studies and comments from other researchers in turf irrigation indicate losses approaching 20% are not uncommon.
If such losses do approach 20%, then the water duties would prove inadequate in most circumstances.
Studies that can accurately quantify these losses represent an important area
 of future research.
Salinity represents the second importantissue of importance for the future.
The modeling results presented in Tables 7 & 8 indicate whether the annual balance between water supply and water use is positive or negative.
A positive balance would support deep percolation and minimize problems with soil salinity.
Model scenarios that predict a negative water balance would indicate deep percolation is inadequate, thus leading to future problems with salinity.
As indicated earlier in this report, irrigation non-uniformity will ensure that close to half of the turf at a LTF will receive less than the mean rate of irrigation indicated in Tables 7 and 8.
Such areas should be more vulnerable to the buildup of soil salinity and will likely exhibit higher levels of soil salinity.
An assessment of soil salinity at LTFs should therefore provide additional important information regarding the adequacy of ADWR turf water duties.
If these assessments reveal evidence of salinity problems  at LTFs employing efficient irrigation practices, such results would indicate the water duty is inadequate to support year round turf.
For a state located in the middle of the continent, Nebraska has an abundance of water.
Chapter: 22 Matching Remote Sensing to Problems
 Remote sensing can provide useful information for a variety of problems.
However, there is not a universal solution for all situations because each problem has unique data requirements.
Different problems may have different data requirements.
For example, the use of remote sensing to scout for pests has a different data requirement than developing an N recommendation.
Remote sensing can provide a flexible structure for collecting information that can be analyzed using a variety of approaches.
This chapter provides examples of matching remote-sensing information to problems.
Remotely sensed images are composed of individual pixels that have a specified spatial resolution.
For each information layer  that is monitored, a pixel has one value assigned to that spatial location.
For a different information layer, a pixel will likely have a different value assigned to it.
For example in a healthy plant, the relative pixel value for the blue band might be 7%, whereas in the near infrared  band, a healthy plant might reflect 60% of the incoming light.
An unhealthy plant may have very different reflectance characteristics.
The main advantages of remote sensing are:
 1.
Rapid analysis.
2.
Assessment of a large area within a single image.
3.
Easy identification of differences within an image.
4.
Improved field scouting efficiency.
6.
Information from areas difficult to access.
7.
Data that can be analyzed using a number of different analysis approaches.
8.
Remote data collection.
9.
Relatively inexpensive data collection that provides a permanent benchmark.
10.
Ability to use sensors aboard a UAV  to overcome problems associated with resolution, rapid
 data collection and analysis.
11.
Potential ability to convert crop reflectance into variable-rate N application maps.
1.
Multiple stresses can have similar impacts on reflectance.
2.
Adverse climatic conditions  or temporal changes can influence interpretation of findings.
3.
Spectral signature of a plant may be different for each plant growth stage.
4.
Ground scouting may be required to confirm problem.
5.
Different problems may require different spatial resolution.
6.
Pixel values are not acquired by direct measurement.
7.
The spatial resolution may be inadequate.
8.
Data analysis and collection need trained and experienced person.
9.
Geometric and radiometric correction may be required.
10.
Image data may be difficult to convert into variablerate maps.
Application of Remote-sensing Technique to Farming
 Application of remote sensing to precision farming can be separated into 4 unique steps : 1) determine whether remote sensing can help, 2) develop a stress map, 3) identify the yield-limiting factors, and 4) develop a corrective management solution.
Remote-sensing data can be visualized and processed in a variety of ways.
For example, a true color composite image can be made by displaying the blue, green, and red bands as blue, green, and red colors, respectively.
However, a false color composite image is produced when the green, red, and NIR bands are displayed as blue, green and red colors, respectively.
In a true color image, healthy plants appear green whereas in a false color image, a healthy plant appears bright red.
Images from satellites are useful for identifying problem areas that are not time-sensitive.
For example, images of hail-damaged corn fields can be important for crop insurance and for estimating grain yields.
Figure 22.3 shows normalized difference vegetation index  images derived from Landsat data acquired before and after a hailstorm.
The images are useful for identifying the damaged areas and calculating the acreage of the damage.
Grain yields can be reduced by nutrient deficiencies, water stress, weeds, insects, and diseases.
Information
 Figure 22.2 The concept of remote-sensing technique for crop management.
about the extent of problems can be identified by scouting the field from the air, scouting the field from the ground, or collecting satellite images.
Technical Note for Remote Sensing
 Remote-sensing indices have been used for making N fertilizer recommendations.
The two most commen indices are NDVI [/] and GNDVI [/] For NDVI calculations, reflectance in the near infrared and red bands must be collected, whereas reflectance information in the near infrared and green bands must be collected for GNDVI calculations.
In some fields, GNDVI has a stronger relationship to N stress than NDVI.
Either index can help a farmer switch from a single preplant N recommendation to a split N recommendation, which in turn can reduce fertilizer costs and improve profitability.
Across the corn belt, research is being conducted in the development of N management N-based algoriths.
Remote-sensing imagery can be collected using various platforms, including handheld, manned aircraft, UAV , and space-based.
Each platform has different advantages and disadvantages.
Understanding the benefits and limitations of various platforms and sensors is critical for selecting the appropriate remote-sensing system.
In a general sense, resolution is directly related to cost.
Table 22.1 Advantages and disadvantages of various platforms for remote-sensing data collection.
Hand or ground	Can be used to identify the reflectance	Collect the reflectance characteristic from a
 characteristics of an individual leaf, plant, or	single point, not creating image.
Useful for real-time spraying applications.
UAV	Flexible availability.
Relatively unstable platform can create blurred
 Relatively low cost.
images.
Very high spatial resolution.
Geographic distortion.
Changeable sensors.
May require certification to operate.
May be limited in height above ground.
Processing the data into field images may be
 Aircraft	Relatively flexible availability.
High cost.
Relatively high spatial resolution.
Availability depends on weather condition.
Satellite	Some free images.
High cost for high spatial resolution images.
Clear and stable images.
Clouds may hide ground features.
Large area within each image.
Fixed schedule.
Good historical data.
Data may not be collected at critical times.
May need to sort through many images to
 Nonimaging portable sensors such as CropScan, Greenseeker, and many others have been used to identify reflectance characteristics for a variety of problems.
For example, these sensors have been used to develop a stress index of corn plants and to sense weeds between corn rows.
Sensors mounted on a tractor are used for real-time, variable-rate fertilizer/herbicide applications.
Aerial sensors can be mounted on manned and unmanned aerial platforms.
The primary advantages of aerial sensors are that the high-resolution images are collected quickly and the data can be used for a variety of problems.
However, the cost can be very high.
It may be possible to reduce sample collection costs by using a UAV, commonly known as a drone.
UAVs
 can fly any time and take images under cloudy conditions if there is no rain and the wind is under 25 mph.
Currently restrictions are in place to prevent flying UAVs higher than 400 feet above ground level.
Drone restrictions, however, are under review.
The primary limitations of UAVs are vibrations, unstable attitude , and variable wind speeds and directions.
A wide variety of satellite and sensor choices are available.
In general, each sensor collects data within different wavelength intervals and at different resolutions, and each satellite has different revisit times.
The spatial resolution of the panchromatic band  is generally higher than the resolution for the multispectral  bands.
Spatial resolution is the ground area of each pixel within an image.
For example, a resolution of 1.84 m means that the pixel has the dimensions of 1.84 by 1.84 m on the ground.
Problems with space-based images are that clouds can prevent data collection, the atmosphere can distort reflectance values, and the platforms may have a long revisit time.
The data cost can range from free to high.
Table 22.2 Characteristics of sensors mounted on satellites that can be used for agriculture.
Pan represents panchromatic  images, and resolution is minimum size of one side of square pixel within an image.
Spatial Resolution 	Temporal
 Multi-Spectral Bands	Relative Cost
 Pan	Multi	Revisit days
 High Spatial Resolution Images
 GeoEye-1	0.46	1.84	B, G, R, N	2.1 to 8.3	High
 WorldView-1	0.55	1.7 to 5.9	High
 WorldView-2	0.52	2.4	B, G, R, N, R-edge, 3 others	1.1 to 3.7	High
 WorldView-3	0.34	1.38	B, G, R, N, R-edge, 23 others	1 to 4.5	High
 Pleiades-1A	0.5	2	B, G, R, N	Daily	High
 Pleiades-1B	0.5	2	B, G, R, N	Daily	High
 QuickBird	0.73	2.9	B, G, R, N	1 to 3.5	High
 IKONOS	1	4	B, G, R, N	3	High
 SPOT-6	1.5	6	B, G, R, N	1 to 5	High
 SPOT-7	1.5	6	B, G, R, N	1 to 5	High
 RapidEye	5	B, G, R, N, R-edge	1 to 6	High
 Moderate Spatial Res.
Images
 Sentinel-2	10	B, G, R, N, R-edge, 5 others	5 to 10	Free
 SPOT-5	5	10	G, R, N, Shortwave IR	2 to 3	Free
 LANDSAT 7 ETM+	15	30	B, G, R, N, 3 others	16	Free
 LANDSAT 8 OLI	15	30	B, G, R, N, 6 others	16	Free
 B: Blue; G: Green; R: Red; N: NIR; R-edge: Red-edge; IR: Infrared
To allowing producers to get hands-on experience in existing and new technologies to manage nitrogen more efficiently, UNL launched a precision nitrogen management project in 2020.
Producers interested in this project would be able to compare their current N management practice against canopy sensing, images, crop models-based tools, and inhibitors with the support of UNL extension educators and specialists.
In contrast, soybean maturity is dependent on day length.
Because soybeans may use more or less water than the averages listed in the table, and because it may be difficult to determine the actual correct growth stage, it is important to continue to monitor soil water until maturity.
Center pivots often use a 480-volt power supply.
In order to minimize risk of accidents, it is important to ensure proper wiring at the center pivot, at the pump, and connections to the power supply.
Determine how much water from rain and irrigation will be needed to reach crop maturity assuming the field is located in central Buffalo County, the date is August 10, and the corn crop is at the R4  stage.
For this example the remaining available water is 2.25 inches if the top 4 feet of soil is allowed to dry to 40% of available water-holding capacity.
Referencing Table 1, corn at the R4 stage should take approximately 34 days to mature and will use about 7.5 inches of additional water to reach maturity.
Add 34 days to todays date to get the approximate day of maturity, using Aug.
10 as the example.
34 days from Aug 10 is Sept 13.
Subtract the water required to reach maturity from the remaining available water.
Subtracting 7.50 inch  from 2.25  gives us 5.25 inches.
The calculation shows that 5.25 inches of water will be needed from rain and irrigation to mature the crop without limiting yield.
GLOBAL CLIMATIC CHANGE EFFECTS ON IRRIGATION REQUIREMENTS FOR THE CENTRAL GREAT PLAINS
 Change is inevitable, but variability is certain in weather, especially in the Great Plains.
The Great Plains is considered the U.S.
bread basket and certainly is critically important to national and even world agricultural productivity.
The Great Plains agricultural crop productivity is dependent upon water, both from precipitation and groundwater.
Groundwater from the vast Ogallala Aquifer in the Central Plains is predicted to continue to decline as long as irrigation remains viable considering escalating energy costs and farm production costs.
Water right transfers from agriculture to urban and industrial requirements will further exacerbate this inevitable resource strain.
Labor or farm skills for the rapidly escalating advances in agricultural technology may become a limiting factor in the future, too.
Weather directly affects the water requirements of crops and thus their irrigation requirement.
Climate change is controversial, as to warming or cooling and especially the cause, but the world data on increased atmospheric carbon dioxide  and green house gases  is incontrovertible.
The impact of rising CO2 is generally considered 'positive' in terms of photosynthesis and its effects on plant control of transpiration through stomatal regulation.
GHGs likely impact only atmospheric solar transmittance both for short-wave  and long-wave radiation.
Many believe that GHGs contribute to the earth temperature rise from the so called 'green house effect,' but many leading scientists also believe that any warming cycle is potentially derived from plasma bursts or "sun spot activity' on the sun and part of longer-term historical weather trends.
Average SST Anomalies 7 DEC 2008 3 JAN 2009
 MADE 15 JAN 2009
 Figure 2.
NOAA National Center for Environmental Predictions for May-JuneJuly 2009 temperature from January 15, 2009 predictions using the ENSO SST using procedures from Saha et al..
Figure 3.
NOAA National Center for Environmental Predictions for May-JuneJuly 2009 precipitation from January 15, 2009 predictions based on the ENSO SST using procedures from Saha et al..
CLIMATE CHANGE AND VARIABILITY
 Increasing concentrations of GHGs in the earth's boundary layer make the earth's atmosphere opaque to long-wave radiation preventing long-wave radiation from escaping through the atmosphere.
The trapped long-wave radiation in the earth's atmosphere is believed to alter the earth's radiation energy balance and thereby increasing the surface temperature.
GHGs include carbon dioxide, water vapor, methane, nitrous oxide, chlorofluorocarbons, and other gases.
Carbon dioxide  concentration in the atmosphere has increased since the industrial revolution from the burning of carbon-based fuels.
Neftel et al.
estimated that the preindustrial global atmospheric CO2 concentration was in the range of 265-290 ppm  based on ice core samples from the Siple Station.
The longest CO2 records are from the Mauna Loa Observatory, Hawaii  from NOAA and the Scripps Institution of Oceanography, University of California, San Diego.
Carbon dioxide concentrations have increased from 315 ppm in 1958 to 385 ppm in 2008.
This increase in atmospheric CO2 is generally attributed to deforestation and the burning of fossil fuels such as fuel oil, natural gas, and coal.
The atmospheric CO2 concentrations are expected to double from the preindustrial concentrations at some point in the 21st century.
The annual mean CO2 concentration growth rate has approximately doubled from 1 ppm yr-1 in the 1950s to about 2 ppm yr 1 since 2000.
Water vapor is also a GHG that is highly variable both spatially and temporally.
Atmospheric water vapor is the result of evaporation from lakes, rivers, and oceans and evapotranspiration  from land surfaces.
'Green house' warming should result in an increase in evaporation and ET because of increased surface temperature.
However, the increased atmospheric water vapor will likely increase cloudiness.
Exact prediction of cloudiness at a specific location is imprecise due to local elevation, position , and global winds.
Increased clouds in some areas may increase the likelihood of convective and/or influence orographic precipitation.
The clouds also reflect direct solar irradiance and scatter short-wave irradiance  reaching the earth's surface.
Most expect at many global locations that net radiation, one of the most important surface energy balance parameters determining crop water use rates, will possibly be reduced with a feed-back effect to reduce 'green house' warming.
Ramirez and Finnerty  reviewed the large uncertainties in the global 'green house' warming hypothesis.
To summarize their review, they cited research results based on data from remote sensing during the 1979 to 1988 years that showed no obvious trend in atmospheric temperature over the 10-yr period; some statistical evidence that supported a 0.4C decrease in temperature
 Atmospheric CO2 at Mauna Loa Observatory
 for the northern hemisphere from the years 1940-1980; a global temperature rise less than 0.4C from 1880 to 1970; and according to the statistical analysis of climate records and from an analysis of global climate records from land and the oceans around the world, a temperature increase over the past 90 years that was in the range of 0.4-0.6 C.
Singer and Avery  cited studies from 450 peerreviewed authors and co-authors that found reason to doubt the 'global warming hypothesis'.
Avery  indicated that these concerns did not mean that fossil fuels use and other GHG sources shouldn't be reduced , but that additional engineering solutions including greater efficiency in transportation, energy efficient buildings, and greater planning for droughts and shifting patterns in water availability should be included.
CO2 and Plant Response to Climate Change
 Rising atmospheric CO2 has been called 'atmospheric fertilization' because greater concentrations in CO2 will lead to greater rates in photosynthesis.
Bisgrove and Hadley  provide a useful review of global warming on plant responses.
Because rising CO2 and a possible temperature increase and possible decrease in precipitation could dramatically alter future climatological records, the increased frequency of extreme weather events  is widely speculated but nearly impossible to quantify.
Global climate change will impact other factors of irrigated agriculture, too, like weeds  and diseases.
Current carbon dioxide concentrations limit plant photosynthesis based upon the following photosynthesis equation:
 6 CO2  + 6 H2O   [1] C6H12O6 12  + 6 O2 
 Green house growers of horticultural crops have raised the concentration of CO2 in the enclosed greenhouses to increase crop growth and yield for many years.
Research has shown that doubling of CO2 concentrations will lead to approximately a 40-50% increase in the growth of plants.
Kimball  reported that doubling CO2 concentrations increased biomass productivity on average by 33% in vegetal species studied with a decrease in evapotranspiration.
Poorter's  review reported that herbaceous crop plants produced more biomass than herbaceous wild species , and potentially fast growing wild species had greater biomass than slow growing species.
In addition, he found that leguminous species capable of symbiosis with nitrogen fixing organisms had larger responses to CO2 compared with other species.
Poorter  also indicated that there was a tendency for herbaceous dicotyledons  to show a larger response than monocotyledons like grasses.
Plants, however, adapt to elevated CO2 concentrations, and the long-term exposure to elevated CO2 is much less than short-term elevated CO2 exposure.
In addition, it has been reported that some species in an elevated CO2 environment have a lower stomata density.
Nonetheless, the effect of increased CO2 remains a significant factor in increasing photosynthesis and increasing water use efficiency.
Carbon dioxide concentration is a main mechanism that plants use to regulate the respiration rate and the rate of absorption of CO2 for photosynthesis by changing the stomatal resistance.
An increase in atmospheric CO2 will increases the leaf's internal CO2 absorption rate mainly for C3 species.
The plant will respond by increasing its stomatal resistance , which reduces the CO2 absorption rate to maintain a desired internal substomatal CO2 concentration.
Kimball and Idso  reported stomata responded to increased CO2 by regulating photosynthesis in more than 50 species.
Transpiration is reduced by this increased stomatal resistance and leaf
 temperature is increased.
An increase in stomatal resistance will reduce the plant transpiration rate, thereby increasing the plant water use efficiency.
Most agricultural plants are categorized by their photosynthetic mechanisms that control the chemical processes in their glucose manufacture from CO2 and H2O  [eqn.
1] as C3 and C4 species because of their photosynthetic pathways [for a more thorough review of the impacts of elevated CO2 and temperature on photosynthesis see Sage  and Ainsworth and Rogers ].
Other plants are called CAM that stands for Crassulacean Acid Metabolism after the plant family in which it was first found  and because the CO2 is stored in the form of an acid before use in photosynthesis.
CAM species are mainly succulents such as cactuses and agaves.
Common C3 species include wheat, cotton, soybean, and most legumes like alfalfa while common C4 crop species include sorghum, corn, and sugarcane.
Some grass species are either C3 or C4 types.
C3 plants fix atmospheric CO2 directly onto 5 carbon sugar RuBP  and thus into glucose.
C4 plants first fix atmospheric CO2 into 4-carbon acids in the mesophyll of the leaf and decarboxylate the 4-carbon acids in the bundle sheath cells where the CO2 is then fixed by RuBP carboxylase.
CAM plants first fix atmospheric CO2 into malic acid and other 4C-acids at night.
During the day, malic acid is decarboxylated and the CO2 released is then fixed by rubisco.
Generally, the C4 photosynthetic pathway is considered more water efficient than C3 species.
However, C3 species typically are more sensitive to elevated CO2.
The carbon-fixing efficacy of Rubisco depends on the ratio of CO2:O2.
For C3 plants, this is closely coupled to ambient conditions, and efficacy is approximately 2/3 while for C4 plants, the CO2:O2 ratio is much greater and carboxylation efficacy is nearly 100%.
Therefore, increased CO2 in air should directly increase assimilation for plants with C3 physiology.
For C4 plants, the elevated CO2 effects are indirect due to increased stomatal resistance and reduced transpiration.
EFFECTS OF CLIMATE ON IRRIGATION REQUIREMENT
 Two main modes have been used to estimate long-term climate change on crop water requirements and irrigation requirement.
The earlier and simpler ones used were sensitivity analyses of regular ET equations and/or crop simulation models to estimated climate scenarios based on projections of weather scenarios.
Several examples are illustrated: Warrick  used 1930s weather data with a statistical yield model that showed a 50% wheat yield decline in the Great Plains; Terjung et al.
used a yield model with four climate scenarios for air temperature, solar irradiance, and precipitation to find that ET and total applied irrigation were sensitive to the climatic scenarios and locations used; Liverman et al.
reported lower dryland yields under cloudy, hot, and dry climates; and Rosenzweig  suggested that in the Southern Great Plains spring wheat varieties might be required to replace winter wheat cultivars due to colder winter temperatures with a doubling of CO2.
Most recent attempts to investigate climate change on irrigation have used GCMs as a climate basis.
Many GCMs were simulations under 2 X CO2 concentrations that result in global temperature increases of 2-5C, with regional temperature changes from -3C to +10C.
Precipitation fluctuates in the range of -20% to +20% from current regional averages.
GCMs generally are limited in resolution to a 0.5 X 0.5 grid.
The 'predicted' weather represents that whole grid.
They simplify the spatial and temporal scales of global fluid dynamics as well as the complex physics that drive the exchanges of water, heat, and energy between the earth's atmosphere, oceans, and continental land masses on those grids; however, in most cases GCMs still require near 'super' computers to make all the complex computations necessary.
Hence, they are typically operated at major universities and/or governmental agencies.
GCMs' spatial scales are considered too large to accurately capture smaller scale terrain and other heterogeneities on the local and regional climate scale.
Different GCMs use different modeling strategies and often produce different model climates.
Therefore, there is a rather large uncertainty associated with the predicted potential climate changes.
Two widely used GCMs are the BMRC   and the UIUC.
Table 1 illustrates the GCM simulation climate scenarios used by Smith et al.
in their series of papers by the two above GCMs.
The BMRC model temperatures changes were slightly larger than the 'global' scenarios while the precipitation was reduced over the U.S.
For the UIUC model without sulfates, the temperatures matched the 'global' scenarios well, but the precipitation was increased considerably compared with the BMRC model.
For the UIUC + Sulfates model runs, the simulated temperatures were lower than the BMRC scenarios and the precipitation increased as a mean over the conterminous U.S.
Figure 5 shows the predicted annual mean temperatures for the conterminous U.S.
from Smith et al..
The Australian model  predicts a slightly warmer Central Great Plains for the +1C GMT scenario and a smaller temperature change for the western parts of the Central Great Plains,
 except the eastern portions and the southern parts.
It predicts a significantly drier trend  for the Central Great Plains region for both scenarios.
The Univ.
of Illinois model without sulfates  predicted a warmer Central Great Plains for both scenarios and an
 Table 1.
Annual mean change in temperature and precipitation over the conterminous United States by the GCM climate change scenarios.
Source: Smith et al..
GCM	GMT	Change	Change
 BMRC	1.0	1.5	-39
 UIUC	1.0	0.9	98
 UIUC + Sulfates	1.0	0.4	132
 1	GMT is global mean temperature
 increased precipitation in the Central Great Plains.
When sulfates were included in the UIUC model, it predicted a more modest temperature change with only a small precipitation increase for the +2.5C scenario.
Climate change  would likely lead growers to change crops, cultivars, and management practices, including irrigation, to mitigate any adverse effects or to take advantage of more favorable conditions.
Peterson and Keller  suggested that higher temperatures and reduced precipitation could increase crop water demand in some areas and prompt the development of irrigation in regions previously devoted to dryland or rainfed cropping.
They reported that the percentage of cropland irrigated in the western U.S.
increased when global mean temperature  exceeded 3C and a decline in production resulted from inadequate water for irrigation.
Tung and Douglas  found in a study of crop response to GCM projected climate change with double atmospheric CO2 concentrations that the higher ET effects outweighed the effects of CO2 fertilization in some areas of the U.S., and they suggested that irrigation could mitigate effects of climate change.
In another simulation study of CO2 induced climatic changes, Allen et al.
reported higher ET demand and irrigation water requirement for alfalfa, but decreases for winter wheat and corn, although the GFDL  model had increased corn irrigation requirement , in the Great Plains due to higher temperatures and changes in precipitation patterns.
Allen et al.
used CGMs from Princeton Univ.
and the GISS .
Figure 5.
Annual mean temperature change from baseline for three GCMs for two global mean temperature scenarios.
Source: Smith et al..
Note: 5C change = 9F change.
Figure 6.
Annual precipitation change from baseline for three GCMs for two global mean temperature scenarios.
Source: Smith et al..
Note: 200 mm change = 7.88 in.
change.
Brumbelow and Georgakakos  used GCMs from the Canadian Centre for Climate Modeling and Analysis Global Coupled Model 1  and some from the UK Meteorological Office Hadley Climate Model version 2  together with crop simulation models and USDA soils data   to estimate climate change impacts on crop productivity and irrigation in the conterminous U.S.
They are one of the few simulation studies that validated
 model outputs with U.S.
county yield data for a 19yr calibration period.
Table 2 summarizes Region their mean irrigation requirement changes in four Great Plains regions and for three crops.
Figure 8 illustrates their predicted change in corn yield and irrigation requirement for the conterminous U.S.
The predicted mean change in irrigation requirement in most of the Central Great Plains had a 'neutral' change.
The western portions of the Central Great Plains had a more pronounced decrease in irrigation requirements from -40 to -11 mm.
Predicted irrigated corn yields decreased 600 to 1,200 kg ha -1.
Table 2.
Regional mean changes in irrigation requirement in mm and % change  for three crops in the Great Plains.
Source: adapted from Brumbelow and Georgakakos.
Strzepek et al.
modeled water supply and demand for irrigation in the U.S.
Corn Belt with climate change using a suite of GCMderived scenarios of climate change.
They found that producers
 Northwestern GP	nal 1	-25.9 	-15.1 
 Northeastern GP	2.5 	-16.0 	-0.8  2
 Southwestern GP	30.6 	28.1 	-15.7 
 Southeastern GP	23.9 	16.1 	-4.0 
 1, na' region was not simulated.
2 Percent appears large due to the small value of the 'baseline' irrigation requirement.
Figure 7.
Projected percent change in seasonal irrigation requirement from 'baseline'  for four Great Plains states for five levels of simulated increase in bulk stomatal resistance from increased CO2 for  alfalfa [top];  corn [center]; and  winter wheat [bottom].
Source: Allen et al..
Figure 8.
Changes in mean corn irrigation requirements  and crop yield.
Source: adapted from Brumbelow and Georgakakos.
would benefit from utilizing irrigation, but they also indicated a concern in the spring for excessive soil water perhaps requiring more subsurface drainage.
In the near term, they suggested that the relative abundance of water for U.S.
agriculture can be maintained.
They suggested that progressively greater changes in agricultural production and practices from climate change impacts were expected by 2050 and beyond in agreement with Reilly et al..
Accurately predicting global climatic change impacts on the Great Plains remains largely uncertain.
Nevertheless, future environments in the Central Great Plains will have elevated CO2 and GHGs in the atmosphere that will impact the surface energy balance, photosynthesis, water use efficiency, cloudiness, and precipitation, and likely extreme weather phenomena.
These all have some
 degree of uncertainty and probably more variability than past climatic patterns.
Most reports indicate few impacts immediately; however, in the out-years  we should begin seeing significant shifts in weather in the Great Plains.
Some will be 'positive'  while others might be more 'adverse'.
Undoubtedly, some changes in Great Plains agriculture will be necessitated, e.g., crop hybrid changes, crop species adjustments, crop management, etc., and irrigation will continue to be a significant factor, especially in the Central Great Plains, for mitigating global climate change impacts and providing national food security.

Water Use Patterns Differ Between Pad and Sprinkler Cooling
 Yi Liang Associate Professor Air Quality
 Tom Tabler Professor, Mississippi State University Extension Service
 Arkansas Is Our Campus
 Modern commercial poultry houses in the United States employ tunnel ventilation and evaporative cooling systems, where evaporation takes place in the buildings or in inlet air.
Evaporative pads are most often chosen because of their high efficiency, while foggers  are often installed as auxiliaries due to their limited cooling potential.
Fogging systems, when used after cool cell pads, further increase the humidity inside the chicken house, making it increasingly difficult to provide bird cooling.
This inability to effectively cool themselves can result in a large number of heat losses, even though the air temperature in the chicken house may only be in the low 80s.
Low-pressure sprinkler systems have been installed as an alternative to foggers to provide bird cooling during hot weather.
The sprinkler system uses a different mechanism than the evaporative pad system for bird cooling sprinkling coarse water droplets on the birds and taking advantage of immediate evaporation
 locally on the chicken surface.
As a result, the pattern and quantity of water use of pad and sprinkler systems are different.
By incorporating a sprinkler system into tunnel-ventilated houses, the demand for water during hot weather can be reduced without affecting live performance.
What Factors Determine Cooling Water Use in Pad Systems?
The amount of water used by evaporative cooling pads is dependent on three factors the amount of air being drawn through the pads, outside temperature and outside humidity.
The drier the air, the more water the pads evaporate in the inlet air, the more cooling they produce  and more overall cool cell water is used.
By assuming a typical cooling efficiency of 75% for a 6-inch evaporative pad, the amount of water used can be predicted based on the hourly outside
 Table 1.
Cooling water usage  for a 40' x 400' broiler house with 160,000 cfm fan capacity under various outdoor conditions
 30%	40%	50%	60%	70%	80%	90%
 70F	-	-	-	2.6	1.9	1.2	0.6
 75F	-	4.4	3.6	2.8	2.0	1.3	0.6
 80F	5.3	4.8	3.9	3.0	2.1	1.4	0.7
 85F	5.7	5.3	4.2	3.2	2.3	1.4	-
 90F	6.1	5.7	4.4	3.3	2.3	-	-
 95F	6.5	6.1	4.7	3.5	-	-	-
 100F	6.9	6.5	5.0	-	-	-	-
 105F	7.2	6.9	-	-	-	-	-
 temp and humidity.
Figure 1 shows hourly water use by cool cell pads in a 40' X 400' house ranging from 100 to 280 gallons per hour as ambient temperature rises from 85F in the morning to 98F in midafternoon on a typical summer day.
Daytime cooling water adds up to 3,000 gallons in each house on such a summer day.
Figure 1.
Hourly cooling water with temperature of outside air and air exiting pads on a summer day in a 40' x 400' broiler house with 160,000 cfm fan capacity.
Water use by pads is not directly correlated with bird age once birds reach approximately 4 weeks old.
The same amount of water can be consumed at 35 d age or at 45 d age when weather gets that hot.
This is because during summer months almost all tunnel fans operate continuously on full capacity, making the daily water usage depend only on how dry the outside air is and, therefore, has little to do with the age of the birds.
Instead, pad water usage increases as the number of operating tunnel fans increases over the course of a hot summer day.
The high capacity of tunnel ventilation that delivers 600 or 700 feet per minute  air speed in newer broiler houses, though providing benefits of convective cooling, inadvertently consumes a large quantity of cooling water, reaching 5,000 gallons or more per day.
Adding tunnel fans and increasing tunnel inlet areas during retrofit on farms will inevitably increase cooling water usage.
Cooling water demand
 Figure 2.
Cooling water of fiveand six-week growout could exceed that from drinkers in a summer flock of 19,000 birds.
could exceed daily drinking water for older birds during some extended hot and dry periods.
Sprinkler Water Use Depends on the Age of the Birds
 In sprinkler cooling, direct evaporation of water from surfaces of birds releases metabolic heat to ventilation air.
Sprinkler cooling attempts to cool individual birds not the environment the birds are living in, as cool cell systems do.
There is no need to cool a large mass of ventilation air with cooling pads in order to increase convective cooling.
The phase change from liquid to water vapor taking place on surfaces is much more efficient than convective heat transfer between chicken bodies and warm surroundings with a small temperature gradient.
This seemingly subtle difference in mode of cooling has big implications.
First, because houses are hotter and drier, water evaporates more readily, alleviating wet litter conditions commonly seen at pad areas.
Second, because bigger birds need higher metabolic heat dissipation than younger birds , sprinkler controllers ramp up sprinkler rates with birds' ages to meet the increased heat production demand.
This guarantees
 Figure 3.
Sprinkler water rates increase positively with house temperature and weight of birds in a 40' x 400' poultry house.
Figure 4.
Higher sprinkler water rates with higher heat demands either at older flock age or at higher house temperatures in a trial conducted in a 40' x 400' commercial production house.
precise and more efficient use of cooling water.
Third, birds thrive better in a lower humidity environment, due to their being heavily dependent on latent heat loss as the house temperature rises above the thermoneutral zone.
Birds can withstand higher air temperatures if the humidity is lower.
The combination of heat and humidity tends to cause heat losses.
Research has demonstrated that faster water evaporation translates to higher metabolic heat dissipation.
Notice the overall lower sprinkler cooling water use  compared to that in an adjacent pad cooling house  at equivalent daytime temperatures.
Sprinkler Cooling Requires Drier Environment
 Sprinkler cooling is most effective when the surrounding air is dry.
Dry air means more moisture can be absorbed before being saturated , regardless of whether the moisture is from the respiratory tract of an animal, a wet chicken or litter surface.
Table 2 shows the vapor pressure deficit  values, which is a measure of how much additional moisture  air can absorb before reaching saturation.
The dryness of air cannot simply be represented by relative humidity.
For example, 40% RH at 95F is a lot drier than 40% RH at 85F and is, therefore, more "deficit"  than air at 85F.
Apparently, hot air can hold more moisture  and more readily "grabs"  moisture from moist sources in the environment.
This includes litter in broiler houses, receiving more than 60% of drinking water as manure, or the wet surface of birds after each sprinkling.
Consequently, a sprinkler system in the house should operate before cool cells are wetted in early flock age and during morning hours.
Once the cool cells are wetted, reduce sprinkling rates to avoid adding excessive water in a nearly saturated environment or restrict the operation of cool cells only at higher offset from set point in the program.
The vapor pressure deficit values in Table 2 help explain litter conditions in houses with pad cooling systems.
Relatively high humidity occurring in the low 80s has limited drying power  and likely encourages retention of moisture in the litter.
Air of 80% relative humidity does not give much chance for the moisture from drinker leaks and manure to escape resulting in wet bedding, especially near the pad area where air temperature is lowest and vapor pressure deficit is lowest.
In most cases, drier air is hotter air, and hot air inside a chicken house with big chickens scares most people.
The higher temperatures in the chicken house take some getting used to, but this is when the sprinkler is most efficient and bird performance does not suffer.
As long as air flow down the house is adequate, chickens may actually feel more comfortable  at 90F and 40% humidity  than at 82F and 90% humidity.
The higher temperature and lower humidity help keep the litter drier and make it easier for the birds to dissipate heat.
A sprinkler cooling system needs less cooling water with younger birds than with older birds in the growout cycle under equivalent weather conditions.
On the contrary, water usage from a pad cooling system is not sensitive to bird age but only to weather condition and air exchange through the house.
As a result, sprinklers use less water than pad cooling systems.
A sprinkler system requires a drier house environment to maximize its benefit of evaporative heat loss, both from birds and any other moist surface such as litter on the floor.
Evaluating the Success of N, K, and P Fertilizer Applications
 To assess whether the fertilizer investment is adequate, it is important to conduct a periodic assessment of your corn soil fertility program.
This assessment could consider changes in the soil nutrient level or the amount of nutrients harvested by the crop.
This chapter discusses and provides examples on how to conduct P, K, and N assessments.
Table 29.1 Steps for improving a fertilizer program:
 1.
Collect soil samples from your field following appropriate protocols.
2.
Conduct a visual scouting of the production field.
Consider collecting plant samples and soil samples from problematic areas.
Have these samples been analyzed for a.
the nutrients in question?
Compare your nutrient concentration with optimum plant nutrient concentrations.
If the sample nutrient concentration is below the critical level, this does not necessarily mean that your plants are nutrient-limited.
The critical levels were defined many years ago and they should be used only as a benchmark for comparison.
Plant nutrient concentrations should be compared with soil test results and previous yields.
3.
Assess the N rate by measuring stalk nitrate and the residual N content at the end of the growing season.
4.
Calculate changes in soil N by converting soil organic matter contents to organic N.
5.
Track changes in soil P and K over the past several years.
How do your soil P and K nutrient levels compare with the optimum soil nutrient levels?
6.
Develop a P and K budget.
In this calculation, consider removal and additions.
7.
Based on your results, revise the N, P, and K recommendations.
Preparing to Conduct N and P Fertility Assessments
 1.
Soil Sample Collection
 The goal for a nutrient assessment is to provide information for a valid comparison over time.
This requires that the samples be collected in the same location and relative date.
Due to plant uptake during the growing season, N, P, and K soil test results are often lower in following harvest than prior to planting.
To the best of our knowledge, an appropriate sampling time for
 Figure 29.1 An aerial image and field soil test P contour map.
Very high P levels can be found in old homestead sites.
long-term fertilizer assessments has not been reported.
Our recommendation is to use either spring or fall samples for assessments, not both.
Sample Preparation for Shipping
 After the samples are collected they should be prepared for shipping to an appropriate laboratory.
When selecting a soil testing laboratory, consider the reliability of the results as well as the turnaround time.
Selection of a precise and accurate laboratory is essential in terms of data quality and reliability.
Precision and accuracy represent two different terms.
Precision is a measure of repeatability, while accuracy is a measure of correctness of the reported value.
Laboratories can be precise and inaccurate as well as imprecise and inaccurate.
Where possible, select laboratories that are precise and accurate.
The Soil Science Society of America sponsors the North American Proficiency Testing  program that provides a certification of laboratories.
A list of certified laboratories is available online at naptprogram.
org.
Ask your laboratory if it participates in a sample exchange program.
Once a laboratory is selected, follow its recommendations for submitting samples.
Many soil testing laboratories recommend that the samples be cooled and submitted for analysis as soon as possible.
Do not leave moist soil samples in the truck for several days or in direct sunlight.
Check with the laboratory about its recommendations for sample preparation.
When scouting the field, it is important to note the date, determine the plant growth stage, visually inspect the plants for nutrient deficiencies , measure the plant population, and travel beyond the field boarders.
Different protocols may be adopted for N, K, and P assessments, and in many situations, problems can be remediated only in next year's crop
 Once the analytical and scouting results are obtained, the data should be stored for future reference.
To facilitate this analysis, yield data, associated cultural practices, images, pest problems, personal notes, sampling dates, sampling protocols, and soil test results should be placed into long-term storage.
Choices for long-term storage include:
 Printed hard copies of all data from a given field.
On-farm storage of digital records.
This is complicated by computer systems that routinely change.
Off-farm storage by a data management company.
Routinely update data to current data storage formats.
Tissue sampling can be used for in-season assessment of nutrient shortages.
Tissue samples collected from a prescribed location and different protocols are used for different plants and crop growth stages.
For example, in soybeans at the seedling growth stage, collect the entire plant, whereas for plants between the R1 to R3 growth stages, collect 30 to 50 of the most recently mature trifoliates.
Figure 29.2 During scouting, walk in the field at least 10 steps from the field edge and examine 10 plants at every black dot.
For corn at the seedling growth stage, 15 to 20 whole plants should be collected, whereas for plants between 12 inches tall  to tasseling, 15 to 20 of the first fully developed leaves from the top of the plant should be collected.
For plants between tasseling and silking, collect 12 to 20 of the leaves directly below the ear.
Again, care should be followed to make sure the plants do not mold.
The expected ranges for selected nutrients are provided in Tables 29.3 and 29.4.
Table 29.2 General plant deficiency symptoms that can be observed when scouting a field.
Nutrient	Symptom	Plant part	Solution
 Nitrogen	General yellowing.
Older parts first.
In legume, treat seed with
 Bradyrhizobium or apply N
 Phosphorus	Dark green or reddish purple leaves.
Older parts first.
Apply P fertilizer, check soil P level.
Potassium	Wilting, interveinal chlorosis, and	Older parts first.
Apply K fertilizer, check soil K
 scorching of leaf margins starting at	levels.
the edge.
Sulfur	General yellowing.
Younger leaves first.
Apply S fertilizer, check soil S level.
Iron	Yellowing of veins of the leaves	Younger leaves first.
Use Fe efficient cultivars and treat
 generally found in high pH soils.
seed with Fe.
Whole leaf may turn white.
Zinc	Pale green plants; interveinal	Younger leaves first.
Apply Zn fertilizer.
mottling (or interveinal chlorosis in
 drybean) of older leaves leading to
 bronze necrosis; green veins.
Table 29.3 Expected ranges for soybean trifoliates collected between R1 and R3.
Plant Nutrient	Unit	Expected Range
 Table 29.4 Expected ranges of selected nutrients for corn collected at three growth stages.
Images of corn growth stages are available in Chapter 5.
Nutrient	Unit	Seedling	Vegetative	to Silking
 Nitrogen	%	4.0-5.0	3.5-4.5	2.76-3.75
 Phosphorus	%	0.4-0.6	0.35-0.50	0.25-0.50
 Potassium	%	3.0-5.0	2.0-3.5	1.75-2.75
 Calcium	%	0.51-1.6	0.20-0.80	0.30-0.60
 Magnesium	%	0.3-0.6	0.20-0.60	0.16-0.40
 Sulfur	%	0.18-0.40	0.18-0.40	0.16-0.40
 Iron	ppm	40-500	25-250	50-250
 Zinc	ppm	25-60	20-60	17-75
 Boron	ppm	6-25	6-25	5.1-40
 Manganese	ppm	40-160	20-150	50-250
 Copper	ppm	6-20	6-20	3-15
 Conducting an N Assessment
 Assessing the effectiveness of the N fertilizer rate is more difficult than assessing the phosphorus fertilizer program.
The differences between the nitrogen and phosphorus assessment approaches are that nitrate is rapidly lost from soil, whereas phosphate is retained by soil.
Annual N fertilizer assessments can be conducted by using a stalk nitrate test to determine the amount of nitrate-N contained in stalks 2 or 3 weeks prior to black layer.
4.
Stalk Nitrate Test Annual Assessment
 The cornstalk nitrate test has been used as an end-of-season tool to assess the N program.
However, it is important to point out that many external values may influence the interpretation.
For example, a drought can result in elevated values.
In this test, 2 or 3 weeks prior to black layer, the section of the plant between 6 and 14 inches above the ground collected and analyzed.
Previous research has shown that high nitrate concentration is the result of N availability exceeding the plant requirement.
Research conducted in Indiana suggests that a concentration < 450 ppm represents low availability, between 450 and 2000 ppm represents optimal availability, and > 2000 ppm excessive availability.
Slightly different values are suggested for Minnesota, where the adequate levels are defined between 700 and 2000 ppm.
Stalk nitrate-N concentrations for South Dakota have not been defined.
5.
Changes in Soil C and N Long-term Assessment
 Long-term changes in the soil organic C and N can be used to assess temporal changes in soil health and the N supplying power.
Increases in soil organic matter have been linked to increased plant-available water and N mineralization.
Sample calculations are provided in Example 29.1.
This assessment shows that 488 lbs of organic N/acre have been added to the soil.
There have been numerous attempts to develop a soil chemical test that will predict how much of the organic N will be available to the growing crop in the next growing season.
In spite of these efforts, a simple chemical test is not available.
Different states have integrated soil organic matter into the N recommendation differently.
For example, in Nebraska soil organic matter is integrated into the calculation.
However, in South Dakota soil organic matter is not integrated into the calculation.
Nitrogen contained in the soil organic matter can be made available to the plant only through N mineralization.
Example 29.1 If your soil organic matter in the surface 6 inches  has increased from 2% to 2.5%, how much additional C and N is stored in the soil?
In this calculation, assume that the surface 6 inches contains 1,673,000 lbs of soil/acre, and the C/N ratio is 10.
This soil has a bulk density of 1.25 g/cm.
Step 1.
Determine the amount of soil organic matter  in the soil.
In this calculation, it was assumed that 1 acre of soil 6 inches deep contained 1.68 million lbs soil.
1,680,000 lbs soil	8,400	lbs	SOM
 lb soil	acre	acre
 Step 2.
Convert SOM to organic C
 8400 lbs SOM	acre	X	1 lb organic matter	0.58 lbs C	4870 lbs C	c/acre
 Step 3.
Calculate change in soil N
 4870 lbs C	acre	X	0.1 lbs N	1 lb	488 lbs N	/acre
 Determining P and K Removal
 6.
Temporal Changes in Soil Nutrients Nutrient assessments are based on comparing changes in the soil test value with fertilizer additions and the amount of nutrient removed in harvested crops.
Factors that influence the effectiveness of these
 1.
That soil test values are often lower in the fall following harvest than the spring.
Temporal differences resulting from overwinter recharge increase soil nutrient concentrations.
2.
Field-moist samples often have lower K concentrations than dried and ground samples.
3.
Soil test P can increase under anaerobic conditions and decrease under aerobic conditions.
This change is attributed to changes in the oxygen concentration and associated changes in the relative amounts of Fe+2  and Fe+3  contained in the soil solution.
Yield monitor data, when combined with average nutrient levels in grain and tissue samples, can be used to track P removal.
The basic approach for converting yield monitor data to nutrient removal maps is to use data in Table 29.5.
Because the yield monitor data contains erroneous information, it must be cleaned prior to analysis.
Several approaches for cleaning yield monitor data are provided in Pierce and Clay.
Table 29.5 Estimates of nutrient removal of N, K2O, Mg, and S by major South Dakota crops.
Crop	Plant Part	Unit	N	P2O5	K2O	Mg	S
 Corn	Grain	lbs/bu	0.9	0.38	0.27	0.09	0.08
 Stover	lbs/ton	16	5.8	40	5	3
 Soybean	Grain	lbs/bu	3.8	0.84	1.3	0.21	0.18
 Stover	lbs/ton	40	8.8	37	8.1	6.2
 Wheat	Grain	lbs/bu	1.5	0.6	0.34	0.15	0.1
 Straw	lbs/mt	14	3.3	24	2	2.8
 When developing a P budget, all crops used in the rotation must be considered.
Removal rates for selected crops are provided in Table 29.5.
The amount of nutrient removed from a field is determined by summing the amount of nutrients removed over several years, while additions are determined by summing the nutrient additions, including manure.
Removal can be converted from P to P2O5 by dividing the removal value by 0.436 and K can be converted to K2O by dividing the removal value by 0.83.
7: Determine Nutrient Inputs
 Nutrient inputs are determined by summing all of the nutrients contained in the fertilizer and the manure.
For example, if 100 lbs/a of diammonium phosphate  is applied every other year, then over a 6-year period 300 lbs of DAP will be applied.
Based on a fertilizer grade of 18-48-0 , 144 lbs of P2O5/a or 62.9 lbs P/acre have been applied.
If 115 lbs P2O5 are removed annually then more P is removed than added.
Under these conditions, the soil test value should decrease.
An additional example is provided below.
If analysis suggests that mining has occurred  and soil test values have decreased below the critical nutrient level, consider increasing the fertilizer rate.
If the soil value is much higher than the critical level, consider reducing the fertilizer rate.
In some situations, environmental considerations necessitate decreasing or eliminating additional P applications.
The potential impact of increasing or decreasing the fertilizer rate can be tested by placing side-by-side fertilizer strips in the field.
Meeting Environmental and Production Goals
 Figure 29.3 A conceptual relationship between relative yield and relative soil nutrient level.
This chart shows the relationship between the critical soil nutrient level, maintenance fertilizer applications, and where not to apply any additional fertilizer.
In the past, fertilizer recommendations were based on the plants economic responses to specific nutrients.
Agronomists are now asked to consider both production and environmental goals simultaneously.
Achieving this goal may require that fertilizer Best Management Practices become aligned with the 4-R program.
The 4-R program is the application of fertilizers using the right source, at the
 Example 29.2 Estimating crop P and K removal in a corn and soybean rotation.
1.
Calculate the amount of P2O5 and K2O removed by 60 bu/acre soybean crop and 200 bu/acre corn crop.
Pounds of P2O5 /acre removed by a 60 bu/a soybean crop
 Pounds of P2O5 /acre removed by a 200 bu/acre corn crop
 200 bu acre 0.38 lbs bu
 Total removal is 126 pounds of P2O5 /acre
 Pounds of K2O /acre removed by a 60 bu/a soybean crop
 Pounds of K2O /acre removed by a 200 bu/acre corn crop
 Example 29.3 Determine the amount of N and P205 harvested in a 200 bu/acre corn crop.
A 200 bu corn crop produces approximately 9464 lbs of dry stover [xx].
This calculation assumes a harvest index [HI= dry grain/] = 0.50
 N and P2O5 in the grain stover
 Example 29.4 Calculate the amount of P2O, added to a soil if 50 gal/acre of ammonium polyphosphate  are applied annually for 3 years.
Determine the amount of K2O that has been applied if 125 lbs of potassium chloride  is applied annually for 3 years.
years X 125 acre lbs 100
 right rate, at the right time, and at the right place.
This basic concept is designed to increase yields while having a minimal impact on the environment.
Worldwide research is being conducted to achieve this goal.
To further improve fertilizer recommendations, new knowledge, new diagnostic techniques, routing scouting, and improved record keeping needs to be integrated into our assessment and recommendation protocols.
A critical component of improving fertilizer efficiency may include changing our conceptual understanding of fertilizer response and converting static fertilizer algorithms to dynamic algorithms that consider changes in climatic conditions.
Sample Budget for Large-Scale Bell Pepper Operations and the Impact of Phytophthora Blight on Farm Revenue and Costs 2022 -
 Margarita Velandia, Department of Agricultural and Resource Economics Zachariah Hansen, Department of Entomology and Plant Pathology Annette Wszelaki, Department of Plant Sciences Ty Wolaver, Department of Agricultural and Resource Economics
 At the end of this document, we provide some instructions on how to use the Excel version of this sample budget.
The budget presented here is an example; therefore, users should modify numbers to estimate their net farm revenue.
Every farm is unique; hence, estimated costs and revenue will vary depending on soil conditions, pepper varieties, production practices used, pest and disease pressure and other factors.
Bell Pepper Production in Tennessee
 According to the U.S.
Department of Agriculture  2017 Census of Agriculture, there were 434 farms growing bell peppers in Tennessee on 235 acres.
The number of operations growing bell peppers and the number of acres of bell pepper production in Tennessee increased by 280 percent and 8 percent, respectively, between 2012 and 2017.
Although many alternative production methods exist, this publication focuses on conventional plasticulture, which is the most common method of pepper production in Tennessee.
Generally, the fall goal is to have adequate stored moist in the upper two feet of soil profile while leaving enough storage room to take full advantage of off-season precipitation.
For sandy soils, it may require two inches of water to fill the top two feet of soil, while clay soils may need four inches of water to fill the two-feet profile.
Sensor Sprayers for Specialty Crop Production
 Due to intense pressure from pests and diseases, specialty tree crops such as fruits, nuts, and ornamentals currently rely on regular applications of pesticides to produce marketable varieties.
Many of the pesticide application technologies used today are based on airassisted sprayers, also known as air-blast sprayers.
These sprayers are versatile, reliable, and can be modified to fit many types of crops, all of which are reasons for their continued popularity.
But despite their popularity, air-blast sprayers have long had a reputation for inefficient application.
These sprayers were first developed in the 1950s when orchard trees were commonly 20 feet  tall or more; today, trees are typically 6.5 to 13 feet  tall.
Losses to the ground of 30% to 50% of spray and off-target drift from 10% to 20% are common for airblast sprayers.
Current trends such as limited labor and negative public opinion of pesticide use in agriculture
 have pressured farmers to improve the efficiency of pesticide applications.
Sensor-controlled spray systems were first designed in the 1980s as a way to reduce labor costs and pesticide waste.
Sensor sprayers can help growers use fewer chemicals and less water while maintaining good pest control.
Sensor-controlled spray systems are receiving renewed interest as their reliability has improved and more options have become available.
This publication provides an overview of current sensor sprayer technology specifically for use in perennial crop systems, such as nurseries, orchards, and vineyards.
Types of sensor sprayers
 There are three basic types of sensor sprayers :
 1.
Standard sprayers manually controlled with constant spray volume output.
2.
Sensor sprayers that are actuated  by canopy presence and output a constant spray volume.
3.
Canopy adapting sprayers for which the sensors actuate the spray  and actively modulate sprayer outputs  in real time according to crop canopy characteristics.
Figure 1.
Illustration of the different sensor sprayer types.
Standard air-blast sprayers with constant spray output and manual operation.
Canopy actuated  sensor sprayer with constant outputs: nozzle sections are automatically turned on and off as plant material is sensed.
Canopy modulated sprayer: individual nozzles apply a volume of pesticide proportional to the canopy sensed using a single sensor.
In each drawing, blue and white lines around the sprayer perimeter indicate flow control; red ovals indicate sensors, with grey shapes illustrating emitted waves.
Brent W.
Warneke, faculty research assistant; Jay W.
Pscheidt, Extension plant pathology specialist and professor; both of Department of Botany and Plant Pathology; Robin R.
Rosetta, Extension horticulturist, nursery crop pest management; Lloyd L.
Nackley, assistant professor; both of North Willamette Research and Extension Center; all of Oregon State University
 Standard sprayers are controlled by the driver, who manually turns the sprayer on when spraying a crop area and off when exiting a row or crop area.
On/off sensor sprayers operate by using an "automatic" mode on the spray controller that automatically turns individual nozzles or sections of nozzles on or off depending on whether an object is sensed in the sensor zone.
Crop adapting sprayers are similar to on/off sensor sprayers but also change spray flow rate, air flow volume, air flow direction, or a combination of these variables in response to crop canopy characteristics such as leaf density and canopy volume.
Most on/off sensor sprayers and crop adapting sensor sprayers can also be operated in manual on/off mode if the sensor is malfunctioning and spraying needs to continue.
On/off sensor sprayers are available in a variety of configurations through many sprayer manufacturers.
Canopy adapting sensor sprayers are available, but currently there are not many options.
Market pressure to decrease chemical use in specialty crops will continue to improve and expand sensor sprayer options.
Although there is a wide range of sensor sprayer brands and configurations, almost all have the same components.
Components of the sensor system are designed to input data such as ground speed and crop characteristics and actively modify spray output to match the crop shape.
Crop sensing systems are the "eyes" of the sprayer; they determine crop shape by emitting and receiving signals.
Commercially available crop sensing systems emit either infrared, near-IR beams, or ultrasonic waves.
Generally, many signals per second are emitted.
Some
 of these signals bounce off a physical object  and return to the sensor receiver.
The time of flight  is the duration between when the signals are emitted and received.
TOF is used to calculate the distance from the sensor to the physical object.
The individual signals can be put together to measure the plant shape.
These plant measurements are then used in real time to apply pesticide precisely where it is needed.
Sensors vary in viewing angle width, so sometimes multiple sensors are needed to control all the nozzles on a sprayer.
Infrared  sensors used in commercial spray systems detect IR radiation emitted from plants.
Atmospheric conditions such as humidity and temperature have little impact on IR sensing accuracy.
However, light intensity, plant and leaf appearance, and driving speed can affect the accuracy of these sensors.
Light conditions during dawn and dusk, when red wavelengths are more abundant, are known to interfere with IR sensor functioning.
Applicators can operate IR sprayers in standard mode during dawn and dusk if they are forced by other conditions to spray during these times of day.
Currently, IR sensors have a relatively short sensing distance and narrow viewing width.
For example, a commercially used IR sensor  detects a 2.4-inch  diameter zone 10 feet  away from the sensor.
The inability to resolve characteristics of plant structure makes IR sensors more suited to straightforward applications, such as triggering the sprayer on and off at a plant.
Figure 2:  Infrared sensor used in sensor sprayer applications  LiDAR sensor  used in the "Intelligent Spray System".
Even with their limitations, the low cost of IR sensors makes them economically viable for commercial sprayers.
IR systems are used on air-blast systems for foliar applications of pesticides.
An example of a commercially available IR system is the Banner Eye System  that uses a single IR sensor on each side of the sprayer to trigger the release of spray.
Ultrasonic sensors emit high-frequency sound waves to measure objects.
A sonic emitter generates an ultrasonic sound wave, a sensor detects the returning sound wave, and a chronometer measures the time of flight of the wave.
The TOF of the wave gets translated into the distance of the object from the sensor.
This technique is similar to how bats echolocate to navigate and search for food.
When arranged in an array, ultrasonic sensors can detect objects that are 4 inches  or larger.
This accuracy allows for a calculation of canopy volume that is similar in accuracy to taking manual measurements.
Typically, many ultrasonic sensors are mounted on each side of the sprayer to control sections of nozzles independently.
Individual sections of nozzles are then turned on and off to match sprayer output to crop architecture.
Bumps and swaying from rough driving conditions can change the accuracy of the ultrasonic sensor because movement affects the angle of signal detection.
Ultrasonic systems can be used effectively for foliar applications of pesticides in small fruit orchards, other orchards, and nursery fields.
The initial patents on ultrasonic sensors expired decades ago; continued off-patent development has improved their quality and capability while reducing costs.
Comparatively, ultrasonic sensors are more expensive than IR sensors but less expensive than laser sensors.
Examples of currently available systems are Smart Spray  and Sonic Spray.
Most laser sensors used in agriculture emit light beams in a two-dimensional plane around the sensor using a mechanical scanner.
These are called LiDAR sensors, which is an acronym for "light detection and ranging." LiDAR sensors have been used for decades in the forestry sector to determine canopy structure and forest density.
Compared to other sensors, LiDAR most accurately measures crop characteristics.
LiDAR sensors  send out many laser pulses per second in a wide field of view  and measure the TOF to plants and other objects.
These measurements are called a point cloud.
The point cloud can then be further processed to produce three-dimensional scans of the field, which can be used in variable rate spraying.
LiDAR sensors emit waves that are thinner and that diverge less from their point of emittance than ultrasonic sensors, allowing for millimeter resolution of plant structures.
LiDAR sensors are enclosed in waterproof casing because they have delicate moving parts inside the scanning apparatus.
There are many LiDAR sensors available for industrial applications, including agriculture.
An example of a commercially available sensor sprayer system using a LiDAR sensor is the Intelligent Spray System.
Maintaining accurate ground speed sensing is critical to ensure correct functioning of sensor sprayers because the computer directly controls the release of spray material based on this input.
Sensor spraying systems are not directly connected to the speedometer on the tractor, so a separate speed sensor is needed.
Sensor sprayers sense and accommodate for speed in various ways.
Ground speed sensors are used in combination with crop sensors to sync spray release to plant characteristics as the sprayer moves through the field.
In systems without a speed sensor, spray timing can be improved by adjusting the position of the sensors and the delay triggers to have a direct effect on when the sprayer turns on and off after objects are sensed.
Other spray systems derive speed measurements from tractor wheel attachments or with speed sensors that use radar waves similar to Doppler technology to measure ground speed without moving parts.
All sensor sprayer systems have a controller that allows the operator to customize the characteristics of the system.
Some control systems are adjusted mechanically, with potentiometers that modify the sensor-spray delay, and a spray controller that allows the operator the choice to spray or avoid targets.
Other systems have an operator interface with an LCD screen and buttons that allow for more precise adjustments of
 Table 1: Pros and cons of sensors used in sensor-based spraying systems
 Sensor type	Measurement method	Pros	Cons
 Infrared	Detection of infrared	Little impact of	Red light intensity and
 waves emitted or reflected	temperature and humidity	driving speed affect
 from plants	on sensing accuracy	sensing ability
 Low cost	Narrow field of view and
 Unable to determine plant
 Ultrasonic	Measurement of the	Ability to determine plant	Limited resolution of plant
 distance to objects using	structure characteristics	structure
 Relatively easy to	Need multiple sensors to
 Uses time of flight concept	implement	detect plant structure
 LiDAR	Measurement of the	Rich data acquisition	Data acquisition affected
 distance to objects using	capability	by tractor bouncing, which
 laser beams	Fine resolution of plant	requires correction
 Uses time of flight concept	structure	Delicate moving parts
 High speed of measurement
 1Modified from Zhang et al., 2018.
the sensor settings.
For example, the operator can turn off zones of the sprayer that would be pointed at the ground and trunks when their spray target is the canopy.
Other settings that the operator can adjust include the maximum distance the sensor will detect and the lag time from when the sensor sees something to when the nozzles turn off.
Some systems also have flow control and GPS mapping components.
Spraying with sensor sprayers
 Pesticide material savings are most significant when sensor sprayers are used in areas with sparse foliage or irregularly shaped crops.
Variability in the size of plants across a field is common in some perennial cropping systems.
Variability can be due to multiple plant varieties, the death of plants or limbs, and replanting.
For example, orchards where sick trees are removed and replaced have a mosaic of different age classes and sizes of canopies.
This can also occur in tree nursery production systems where different age classes are planted in close proximity to one another.
Pest and disease control with sensor sprayers is similar to that of standard sprayers.
In a nursery, it was shown that powdery mildew on flowering dogwood  was controlled to a similar extent with a canopy adapting sprayer as with a standard air-blast
 sprayer.
This was accomplished in addition to a 56% reduction in spray volume.
When ultrasonic sensors were used to actuate nozzles in one-, three-, and seven-yearold apple orchards, apple rust mite  and pear psylla  were both controlled with similar efficacy to standard sprayers.
Pear psylla lives on young shoots located at the perimeter of the plant, next to gaps where the sprayer turns on and off.
Similar control of pear psylla with standard and sensor sprayers shows that the sensing technology adequately covers small plant tissues with spray.
Apple scab  and apple powdery mildew  also were controlled to a similar extent using sensor sprayers or standard sprayers.
Figure 3.
Illustration of a spray controller for a sensor sprayer system.
The upper switch pair controls whether the sprayer turns on  or off  when an object is sensed.
The lower switch pair controls whether the sprayer will use the sensors  or be fully on.
Other spray controllers can have more options.
Economic and labor savings
 The most direct savings from sensor sprayers come from a reduction in the cost of spray materials required to treat an area.
Many years of research have demonstrated that sensor sprayer systems reduce pesticide volumes, resulting in less pesticide used and lost to the environment.
The savings in the volume of pesticides, adjuvants, and surfactants is proportional to the area sprayed.
A reasonable range for many operations to expect is 10% to 33% pesticide volume savings, meaning fewer trips to refill the sprayer tank.
While sensor sprayers are generally more efficient in operation, the amount of infield crop variability and the type of sensor used will influence how much the application efficiency is increased.
Generally, in crops with a uniform canopy, such as grape vineyards or densely planted orchards, sensor sprayers result in less savings compared to crops with a more variable canopy.
For example, pesticide savings were 15% in a dense and uniform planting and 40% in a less dense planting of mature prune trees in California.
That study used axial fan air-blast sprayers with ultrasonic sensors.
When there is a uniform canopy, on/off sensor sprayers will be on for a large proportion of the time and will mainly act as a standard sprayer.
Canopy adapting technology can be more effective at increasing application efficiency in these uniform systems.
One study used pulse width modulation paired with ultrasonic sensors to make a canopy adapting system.
That system applied a volume of pesticide proportional to canopy width based on a sensor measurement of tree row volume.
The canopy adapting sprayer achieved pesticide savings of 70%, 28%, and 39% in olive, pear, and apple orchards, respectively.
In the study, the olive trees were 13 feet  apart, resulting in gaps between canopies, while the pear trees were 5 feet  apart.
Another aspect of sensor sprayers that can save time and money is automatic adjustment of nozzles as plant growth progresses during the season.
Early in the season when there is not much foliage, a sensor system automatically adjusts which nozzles are on to apply the product to the place where it is needed.
This can save the operator the time it takes to manually adjust nozzles.
Labor savings from using a sensor sprayer will be more significant for a farm with more acreage because efficiencies from sensor sprayers result in fewer trips to refill spray tanks.
For example, a 100-acre orchard gets
 air-blast sprayed at a target rate of 2 acres per hour.
At 60% efficiency , the sprayer would cover 1.2 acres per hour, with the whole field taking 83 hours of work to complete.
Using a sensor sprayer, the efficiency could increase to 80%, and the area covered would increase to 1.6 acres per hour.
In this scenario, the field could be sprayed in 62 hours, about 20 hours less.
If an operator is paid $15 an hour this would result in labor costs per acre of $12.50 for the 60% efficient sprayer and $9.30 for the 80% efficient sprayer.
Therefore, using the 80% efficient sprayer could result in $315 savings for the farm per application.
A larger orchard with more than one sensor sprayer would accumulate savings more quickly due to incremental increases in overall operational efficiency for each sprayer as it is added.
In addition to monetary savings, driver fatigue is reduced as the number of hours the tractor is in operation goes down.
Also, fewer sprayer fill-ups lower labor and fuel costs, and reduce wear and tear on the tractor.
When spray operations can be completed more quickly, then it can also be easier to fit sprays into windows of good weather.
Critical application windows, such as when a plant pathogen or pest is reproducing, are also easier to cover when applications take less time.
While using sensor sprayers has demonstrated savings of pesticide and time in a wide variety of systems, ultimately the decision to adopt a new technology depends on projections of economic returns specific to each operation.
Investing in sensor sprayers
 Different sensor sprayer technological levels are more profitable over the sprayer's life span, depending on the type, size, and crop grown on a farm.
Assuming a single commodity is grown, the larger the farm, the higher the cost of plant protection products, labor, and equipment.
Therefore, larger farms could potentially recover the cost of an investment in a sensor sprayer more quickly than a smaller farm that applies less pesticide.
Also, with crops that require a large number of pesticide applications throughout a season, the increased efficiency of each application using a sensor sprayer can more quickly pay off its purchase price.
An analysis of the profits related to increasing technological levels of sensor sprayers was done in wine grape vineyards and apple orchards.
Standard air-blast, on/off sensor sprayers and canopy adapting sensor sprayers were compared to find the most profitable option.
In the analysis, all operational costs were taken into account over an assumed six-year sprayer lifespan.
For wine grape vineyards, standard air-blast sprayers were the most profitable option in operations less than 24.7 acres , on/off sensor sprayers were most profitable from 24.7 to 247 acres , and canopy adapting sprayers were most profitable for vineyards larger than 100 hectares.
In apple orchards, standard air-blast sprayers were the most profitable in farms less than 42 acres ; for farms larger than that, on/off sensor systems were most profitable.
Canopy adapting systems were never the most profitable sprayer option in the apple scenario, likely due to the lower cost of the pesticides used in the apple plant protection program compared to the wine grape program.
While the profit from using a sensor sprayer is the most important long-term aspect of the system, the payback period on the initial investment also plays a vital role in the decision to adopt the technology.
The payback period is often one of the most important considerations when thinking of implementing new technology.
The payback period for a sensor sprayer is most closely tied to the cost of plant protection treatments applied on the farm.
To investigate this, researchers looked at the payback period for an on/off air-blast system  in orchard crops.
These researchers based their calculations on the assumption that an ultrasonic sensor sprayer would cost $15,000.
They determined that pesticide material cost savings of $57, $47, and $30 per acre were achieved in peaches, almonds, and prune field trials, respectively.
Therefore, fully recouping the sprayer investment would take 2.6, 3.2, or 5 years with a 100-acre farm of peaches, almonds, or prunes, respectively.
A farm smaller than 100 acres would have a more extended payback period, and a larger farm would have a shorter payback period.
Sensor sprayer systems can also provide significant value when used in a supplemental role for specific tasks: for example, an IR system used to spray green suckers on trunks in hazelnut orchards.
In a scenario for a 100-acre orchard and four sucker-spray events with pesticide and material costs of $11.39 per acre each, a $5,000 IR system could potentially save a grower 50% on each sucker spray and could pay for itself in just over 2 years.
Another consideration that could influence the payback period of a sensor sprayer is the degree of diversification of crops present on a farm.
When transitioning from crop to crop, the operator spends less time optimizing sprayer nozzles when a sensor can automatically open nozzles in the canopy area and close them above the canopy.
This could result in a quicker payback period for both small and large, diversified farms.
Environmental benefits of using sensor sprayers
 The major environmental benefit of using a sensor system is a reduced chemical load on the nontarget crop environment, including beneficial organisms and workers.
Sprayer drift can be broadly defined as any spray that does not get deposited on the intended target.
Drift can be deposited on the ground near the intended target or can be carried farther, eventually landing on nontarget plants.
Ground-deposited drift is especially common in gaps between trees, which can result in significant pesticide load on the environment.
In almond orchards, on/off sensor sprayers reduced ground deposition by 72% compared to a standard axial fan air-blast system.
Airborne drift from over-application is another significant source of nontarget pesticide load from air-blast sprayers.
In apple orchards, 23% to 45% of the applied pesticide volume has been observed to drift off target.
Canopy adapting sprayers can be particularly effective at reducing spray drift.
A study looking at three different canopy stages in an apple orchard from early to late season showed reductions in spray drift of 70% to 100% using a canopy adapting sprayer.
Lower nontarget chemical loads also help decrease the rate of development of pesticide resistance because there is less pesticide residue on nontarget locations.
Other considerations include less pesticide contamination of surface and groundwater and lower chances of exposure to nontarget organisms such as beneficial insect populations and livestock.
These benefits incrementally improve the vitality of the agricultural landscape and should not be overlooked when thinking of implementing a sensor sprayer.
Obtaining a sensor sprayer
 In most cases, sensor sprayers are standard sprayers that have sensor components connected to the spray controller.
There are two general ways to obtain a sensor sprayer:
 1.
Purchase a sensor system integrated into a new sprayer.
2.
Purchase a retrofit kit for an existing sprayer through a sprayer manufacturer or from the sensor manufacturer.
Many sprayer manufacturers include sensor systems as optional components to add on to new sprayers at the time of the order.
If purchased directly from a sprayer manufacturer as an integral component on a new sprayer, a sensor sprayer can be customized for the specific
 application.
For example, ducting can be hooked up to pull air from the sprayer fan and redirect it across the sensors if the system will be used in dusty environments.
Also, more sensors can be added to increase the sprayer's sensitivity to changes in plant structure.
Consult the sprayer manufacturer about the sprayer's intended use to ensure optimum sprayer design for the intended purpose.
Many manufacturers offer sensor systems as retrofits for existing sprayers.
Retrofitting can facilitate more rapid adoption of sensor systems.
Depending on the system desired, the cost of an IR system retrofit can range from $2,500 to $5,000.
An IR system can be put on a sprayer that makes most of the foliar applications on the farm.
Ultrasonic sensor-controlled system retrofits cost from around $12,000 to $16,000.
These systems are typically meant for foliar air-blast type sprayers used in orchards where there are gaps between plants.
Companies that sell sensor systems
 Rears Manufacturing in Coburg, Oregon sells IR and ultrasonic systems as integral components on new sprayers.
They also provide a wide variety of customization services for specific sprayer demands.
Gillison's Variety Fabrication in Benzonia, Michigan manufactures the Sonic Spray ultrasonic system and offers it as an integral component or retrofit on a variety of sprayers.
Their Sonic Spray system is available through several sprayer manufacturers, such as Ag Tec sprayers and Rears Manufacturing.
On request, other spray manufacturers may be able to integrate their system as well.
Smart Spray is a similar ultrasonic system manufactured by Durand Wayland in LaGrange, Georgia, available as an integral component on Durand Wayland or John Bean brand sprayers.
AgOtter  is a sprayer retrofit that includes software integrated with sensors to record and map where pesticide was applied.
The AgOtter system uses GPS, flow tracking, and a variable rate valve to maintain a consistent application rate across a range of ground speeds.
Many sprayer manufacturers offer a wide range of customization that could be done at a customer's request, so sensors can sometimes be integrated or retrofitted onto sprayers even if it is not explicitly listed as an option.
Check with the manufacturer for availability.
Sensor sprayers as a service
 Some companies specialize in retrofitting sensor spraying systems onto existing spray equipment as a service to provide agricultural businesses with the benefits of using a sensor system.
This minimizes the liability of equipment failure a grower may have when outright purchasing a system.
Smart Guided Systems  offers the Intelligent Spray System as a retrofit service on air-blast type sprayers, with kits available for sprayers that have up to 39 nozzles.
When using the AgOtter system, farmers can buy a software service called AgHippo Live to allow real-time monitoring of the location, flow rate, and ground speed of each equipped AgOtter sprayer.
Government incentives to implement sensor sprayer systems
 The Conservation Stewardship Program  is funded through the USDA Farm Bill.
It offers financial assistance to farm businesses implementing conservation techniques on agricultural land.
Agricultural operations approved to participate in the CSP are typically already implementing some conservation practices  on their land.
Adopting precision spray technology  to reduce off-target pesticide waste is one management activity for which CSP can provide incentive funds.
Funds are granted annually to the farm to assist with implementing its conservation practices and provide a way to help offset the costs of purchasing a sensor sprayer.
Applications for CSP are accepted throughout the year, but there are deadlines associated with ranking applications and awarding funds for a given year.
The Natural Resources Conservation Service  administers the CSP.
Contact a local NRCS office for more information on applying to the program.
Treating Irrigation Systems with Chlorine 1
 Kati W.
Migliaccio, Brian Boman and Gary A.
Clark2 2
 Irrigation systems can become partially or completely clogged from biological growths of bacteria or algae which are often present in surface water and ground water.
Bacteria and algae use chemical elements such as nitrogen, phosphorus, sulfur, or iron as nutrient sources to grow and develop .
Thus, irrigation systems that also receive nutrients  may experience greater rates of clogging.
While all irrigation systems should have some type of filtration system, this alone cannot effectively remove microorganisms.
Microorganism growth can result in clogged pipes, fittings, and emission devices , decreasing water application amounts and reducing application uniformity and efficiency.
The results of these are generally reduced agriculture productivity.
A chemical method for removing microbial growth is chlorination.
Proper injection methods and amounts
 Figure 1.
Irrigation emitter clogged with algal growth.
Credits: Brian Boman UF/IFAS
 of the chlorine chemical must be used to provide an effective water treatment program without damaging the irrigation system or the agricultural crop.
This publication provides a guide for using chlorine to treat inhibiting microorganism buildup in irrigation systems.
2.
Kati W.
Migliaccio, assistant professor, Department of Agricultural and Biological Engineering, Tropical Research and Education Center --Homestead FL; Brian Boman, professor, Department of Agricultural and Biological Engineering, Indian River REC--Ft.
Pierce FL; Gary A.
Clark,associate professor, Department of Agricultural and Biological Engineering, KansasState University ; Originally written with Allen G.
Smajstrla, professor, Department of Agricultural and Biological Engineering; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.
Treating Irrigation Systems with Chlorine
 Figure 2.
Drip emitter covered with sulfur slime that was blocking irrigation flow.
Credits: Brian Boman UF/IFAS
 Chlorine, no matter the form, is a toxic and corrosive substance.
Safety precautions should be observed at all times when handling chlorine.
Appropriate protection equipment should be used  to minimize the chance of direct contact with the chemical.
A clean container should be used when chlorine is mixed with water.
It is particularly important to ensure that no fertilizer residue is in the container as chlorine and fertilizer can create an exothermic reaction resulting in violent mixing of the contents.
It is also important to remove any combustible materials from the area where chlorine will be stored or handled, and to keep fresh water available in case of accidental contact with the chlorine.
Chlorine may react with some metal and plastic components of irrigation systems.
Therefore, always check with the manufacturer or supplier of system components to identify any potential problems before beginning a chlorine injection program.
Chlorine should be injected before  the system filter SO that any precipitates that form can be trapped in the filters.
Filters should be cleaned on a regular basis to maintain their operational capabilities.
The chlorine injection point should be far enough upstream of the filters to provide thorough mixing of the chlorine and irrigation water before it passes through the filter.
This is required to ensure the removal of precipitates resulting from chlorine reactions.
Elbows in the injection line may assist with the mixing process allowing for quicker mixing in less irrigation line length.
Chlorine deteriorates over time and when exposed to heat and sunlight, therefore on-site storage should be kept at a minimum.
Chlorine is sold in different forms: solid, liquid, or gas.
Solid  chlorine forms, typically calcium hypochlorite, are commonly used to chlorinate swimming pools.
Calcium hypochlorite is used to treat swimming pool water because the solid chlorine form is inexpensive, easy to store, and easy to use.
It generally has 65 to 70 percent of available chlorine.
Dissolving calcium hypochlorite in water will result in the formation of hypochlorous acid  and hydroxyl ions , a reaction that raises the pH of the water.
Approximately 1.5 lb of calcium hypochlorite will treat 1,000,000 lb  of water with a 1 ppm concentration of Cl,.
2 It is important to note the rise in pH as chlorine is most effective under acidic conditions.
Calcium hypochlorite injectors are available for small irrigation systems, are simple to use, and may be an alternative for low flow rate systems.
Figure 3.
HOCI concentration at different pH for 25 C.
One drawback to using calcium hypochlorite to clean a clogged irrigation system is that the calcium may react with other elements in irrigation water to form precipitates which could clog micro-irrigation emitters and thus defeat the purpose for chlorination.
Thus, solid chorine is not recommended.
An alternative to solid chlorine is liquid chlorine.
Liquid chlorine  should be used in irrigation systems, especially when the irrigation water source is high in minerals.
Treating Irrigation Systems with Chlorine
 Liquid chlorine  is most commonly used as laundry bleach.
Mixing liquid sodium hypochlorite in water results in the formation of hypochlorous acid  and hydroxyl ions , a reaction that raises the pH of the water.
It is important to note the rise in pH as chlorine is most effective under acidic conditions.
Unlike the calcium added in the solid chlorine form, the sodium added in this liquid form does not contribute to clogging problems.
The portion of active chlorine in sodium hypochlorite is generally 10% to 15%.
The gas form of chlorine is commonly used in municipal water treatment systems.
As chlorine gas reacts with water, hypochlorous acid , hydrogen , and chloride  are formed.
This reaction lowers the pH of the water.
The change in pH depends on how much chlorine gas is injected and on the buffering capacity of the water.
Chlorine gas is 100% available active chlorine.
Only 1 pound  of chlorine gas  is required to provide a 1 ppm concentration of Cl, to 1,000,000 lb  of water.
Similarly, an injection of 1 lb of chlorine gas per hour will provide a 1 ppm concentration of Cl, to a water supply with a flow rate of about 2,000 gallons per minute.
Extra precautions should be taken when using chlorine gas because it is a respiratory irritant which affects the mucous membranes.
It can be detected as an odor at a concentration of 3.5 ppm and can be fatal after a few breaths at 1,000 ppm.
Thus, maximum air concentrations should not exceed 1 ppm for prolonged exposure.
Chlorine gas should only be used in well-ventilated areas SO that any leaking gas cannot concentrate.
The potential hazards associated with chlorine gas limit its application to experienced or licensed users and require the facility to abide by governmental reporting requirements.
To ensure safety, manufacturers have developed chlorine gas injectors for irrigation systems that work on a vacuum principle.
A venturi injector is used to create a vacuum which actuates the injector.
This design prevents chlorine gas from being injected unless the irrigation system is operating SO that the
 gas is immediately dissolved in the irrigation water.
For safety, only vacuum injectors should be used with chlorine gas.
Hypochlorous acid  is the effective agent in chlorination disinfection that controls bacterial growths.
The amount of HOCI that will be present in solution, and thus active, will be larger at lower pH levels .
If the irrigation water pH is high , the effectiveness of chlorine may be enhanced by injecting an acid to reduce the pH of the water before injecting chlorine.
In addition to increasing the effectiveness of chlorine, acid injection can also prevent the precipitation of minerals which may plug micro-irrigation systems.
Chlorination is most effective when pH is at or below 7.2.
Note that it is very important to store chlorine and acid sources separately.
Most microorganisms will be inactivated and controlled at free residual chlorine concentrations of 1 ppm.
However, higher concentrations must be injected due to the inherent chlorine demand of different water sources.
As a start, use 2 ppm of chlorine for each ppm of hydrogen sulfide, plus 0.6 ppm of chlorine for each ppm of ferrous iron.
A chemical water test can be used to determine the levels of hydrogen sulfide or ferrous iron present in solution.
Test kits are available from a variety of online sources and are easy to use.
Water from surface sources such as lakes, ponds, or canals should be treated with approximately 5 to 10 ppm of chlorine.
Higher levels may be needed for water with high amounts of microbial activity such as may occur during the warmer months of the year.
The chlorine injection rate should be checked by testing the treated water at the most distant part of the irrigation system using a test kit designed to measure "free" residual chlorine.
Residual concentrations of 1
 Treating Irrigation Systems with Chlorine
 to 2 ppm at this location indicate that active chlorine still exists after the water and system parts have been appropriately treated.
Test for active chlorine using a diethyl-p-phenylene diamine  color indicating test kit that measures "free" residual chlorine.
Do not use a test kit that only measures total chlorine.
While levels of total chlorine may appear to be adequate, the active "free" residual form may not be adequate.
Therefore, ask for a DPD test kit from either a swimming pool or irrigation supply company.
After determining the desired chlorine concentration , the proper amount to be injected must be determined.
The amount of chlorine to apply per gallon of irrigation water will depend on the desired concentration in the irrigation system and the concentration or strength of the chlorine source.
Liquid sodium hypochlorite is the most convenient and generally safest form of chlorine available to inject into irrigation systems.
Stock solutions can be bought with concentrations of 5.25, 10, or 15 percent available chlorine.
Table 1 or Equations 1-3 may be used to determine the chlorine solution injection rate in gallons per hour  for different desired ppm injection levels and irrigation system flow rates.
Equations 1 3 are specific for liquid chlorine injection and are designed for stock solution chlorine concentrations of 5.25, 10, and 15 percent, respectively.
For more information on chemical injection, see Haman et al.
and Clark et al..
Equation 1 can be used to determine the injection rate  of a 5.25% available chorine liquid with ppm referring to the desired chlorine concentration.
gph =  971
 Equation 2 can be used to determine the injection rate  of a 10% available chorine liquid with ppm referring to the desired chlorine concentration.
Equation 3 can be used to determine the injection rate  of a 15% available chorine liquid with ppm referring to the desired chlorine concentration.
gph = Irrigation_flow_rate,gpm) 2775
 For example, an irrigation system has a flow rate of 500 gpm and the water is to be treated with 8 ppm of available chlorine using a stock solution with 10% available chlorine.
Using Equation 2, the injection rate of the stock solution is:
 The same information can be determined using Table 1.
For example, a treatment level of 8 ppm with a 10% available chlorine concentration corresponds to an injection rate of 0.43 gph.
Note that this is the required injection rate for each 100 gpm.
Thus, for 500 gpm, the injection rate would be five times as large, or 2.2 gph.
Another example is provided by equation 5 where a stock solution concentration of 5.25% available chlorine was used with a 500 gpm irrigation system.
The goal was to have an 8 ppm active chlorine concentration in the irrigation system:
 Calculations can also be completed for the same scenario illustrated in equation 5 using information from Table 1.
For a treatment level of 8 ppm and a 5.25% available chlorine source concentration, the corresponding injection rate of 0.82 gph per 100 gpm of irrigation flow rate can be read from Table 1.
The chlorine injection rate for a 500 gpm irrigation system would be five times as large as the 100 gpm value, or 4.1 gph.
Some chemical injection pumps may not provide settings low enough to deliver the estimated chlorine rates to the irrigation system.
In these cases, the chlorine stock solution can be diluted with water.
A 10% chlorine stock solution could be diluted with 1 part water and 1 part 10% chlorine solution to create a
 Treating Irrigation Systems with Chlorine
 5% available chlorine solution.
Likewise, a 10% stock solution can be diluted with 4 parts water and 1 part 10% chlorine solution to make a 2% available chlorine solution.
Injection pumps should also be calibrated before use and periodically during use to determine actual injection rates.
For more information on injection pump calibration see Chemigation Equipment and Techniques for Citrus.
Continuous, intermittent, and shock treatments
 Chlorine may be injected using different management strategies depending on the desired outcome.
Continuous chlorine treatments may be injected at very low concentrations to maintain a clean system.
Intermittent injection of chlorine would be at a higher concentration than continuous injection.
Continuous and intermittent injections are considered a preventative maintenance measure.
Alternatively, a shock treatment would be at a very high concentration  and be considered a corrective measure.
Injection of chlorine using continuous treatments should occur after the irrigation system has been pressurized.
For intermittent or shock treatment a different process is advised.
For this method, flush irrigation lines by pressurizing the system and alternating opening different lines to obtain a vigorous flush.
This would be followed by a chlorine injection with irrigation.
The chlorine should be allowed 30 to 60 minutes of contact time in the irrigation lines; the lines should then be flushed with irrigation water.
A critical consideration when using chlorine to clean irrigation systems is the sensitivity of the irrigated crop to chlorine.
Some crops that have been shown to be sensitive to chloride are starch potatoes, tomatoes, tobacco, strawberries, peppers, cucumber, melon, lettuce, and flowers and ornamentals.
The sources of chlorine used to treat water for microorganisms include chlorine gas, powder or tablets of calcium hypochlorite , and liquid sodium hypochlorite.
The concentration of available chlorine ranges from 5.25-15% in liquid sodium hypochlorite.
Therefore, the amounts of these products to be injected will depend on the stock solution concentration used.
The user should check with the chlorine supplier to ensure that the material is labeled for injection into irrigation systems.
In addition, safety and proper backflow prevention are always required when injecting chemicals into an irrigation system.
Crop Residue and Soil Physical Properties
 Soil physical properties such as bulk density, porosity, water sorptivity, and aggregation dictate the water infiltration characteristics of the soil.
Most important are the physical properties of the surface soil as this layer is the initial soil-water interface.
Crop residue and tillage management may affect surface soil physical properties important to water capture and infiltration.
Management practices that minimally disturb the soil and produce, return, and leave more residue biomass on the soil surface  have the potential to decrease soil bulk density, increase porosity, and increase sorptivity in the soil over time.
Also, systems that produce, return, and leave the largest amounts of crop residue in the soil have the highest potential for increased root activity, soil aggregation, and channels that can increase water infiltration.
A study was conducted to determine the effect of crop residue on soil physical properties after 12 years of dryland no-till cropping management in eastern Colorado.
Although the study was conducted under dryland conditions the principles behind crop residue and its effect on soil physical properties hold under irrigated condition as well.
The objectives of the study were:  determine how differing amounts of crop residue affect bulk density, soil porosity, and soil aggregation in the surface 1 inch of soil after 12 years.
And,  determine how these soil physical properties affect water sorptivity.
Crop Residue: Annual post-harvest above ground crop residue samples were collected across 3 cropping systems of increasing production intensity  using a 39.4 inch quadrant for 12 years.
Samples were sifted to remove any soil, dried, and weighed.
The cropping systems created a gradient of crop residue returned to the system, from relatively low, to relatively high.
The overall amount of residue returned to each system over a 12 year period was then tabulated.
Soil Bulk Density and Porosity:
 Bulk density was determined using a modified core method.
Exact procedures for determining bulk density are listed in Shaver et al..
Samples were collected across 3 cropping systems of increasing production intensity.
Soil total porosity was then calculated using bulk density and particle density figures.
Sorptivity is defined as the cumulative infiltration proportionality constant and is essentially a measure of the amount time it takes a given head of water to infiltrate.
Sorptivity measurements were collected across all positions using rings pushed into the soil surface by hand.
Any debris or plant material that could be removed without disturbing the surface was removed.
Water was poured into the ring to a depth of 1 cm.
A stopwatch was used to measure the time it took for the water to infiltrate.
Sorptivity was calculated using the following equation :
 Sorptivity  = It Where: 1 = head of water  t = time 
 Aggregation and Organic Carbon:
 Soil samples from each position were collected and then analyzed in the lab to determine aggregate stability.
Organic carbon content was also determined from these samples.
A detailed synopsis of the procedures are listed in Shaver et al..
Regression analysis was performed to determine the linear relationship between crop residue and soil bulk density, soil porosity, soil aggregation, and aggregate organic carbon.
Similar analysis was performed to determine the linear association between sorptivity and the aforementioned soil physical properties.
Bulk density is an important soil property because it affects soil porosity, which in turn affects water infiltration.
Systems that produce and return more crop residue to the soil surface should reduce its bulk density because under no-till conditions the residue accumulates in the surface soil.
This accumulation should do three things: 1) Residue is lighter than mineral matter, and therefore bulk density should decrease by dilution; 2) Residue decomposition products should promote more aggregation and thus reduce bulk density; and 3) The root activity in the surface should increase because of the improved water conditions and the root activity in turn favors aggregation.
Our results indicate that increased quantities of crop residue decrease soil bulk density over time and that 72% of the variability observed in bulk density was explained by the amount of crop residue returned to the system over the 12 year period.
As soil bulk density decreases with crop residue addition, water sorptivity increases linearly with bulk density  meaning water enters the soil more quickly as bulk density decreases.
Results also show that 77% of the variability observed in sorptivity can be explained by bulk density.
These results suggest that increased amounts of crop residue coupled with no-till management can lead to beneficial soil properties that can increase levels of water sorptivity and infiltration.
Porosity is directly related to bulk density because as bulk density decreases, porosity increases.
As aggregates form and increase in size, inter-aggregate and intra-aggregate cavities form and increase.
These cavities connect with other cavities creating conduits for fluid transport.
By utilizing management practices that increase the porosity we should be able to increase water capture as well.
Our results show that porosity was related to crop residue production.
As crop residue increased, so did soil porosity and nearly 72% of the variability in porosity was explained by biomass production.
Our results also show that sorptivity is highly related with soil porosity.
This is to be expected as the pores are how the water moves into and through the soil.
These results again suggest that increased crop residue can lead to the development of soil physical properties that increase the potential for water getting into the soil.
Aggregation is an important soil physical property because it affects water infiltration, wind and water erosion, and crop yield.
Aggregation is affected by many factors, but most importantly by organic matter  and soil texture.
Aggregation is also a dynamic factor that is affected  by tillage.
Increasing aggregation is important because of its affects on bulk density, porosity, and subsequently, infiltration and water use efficiency
 of the system.
It is also important in decreasing soil erosion.
All of these factors are important to crop production and sustainability.
Aggregates are generally placed in one of two categories, macroaggregates, and microaggregates.
Microaggregates form first, and then combine to form larger and larger aggregate structures eventually building into macroaggregates.
Microaggregate stability itself is not affected by management practices or soil organic matter content.
Aromatic humic materials associated with amorphous Fe and Al compounds and polyvalent metal cations are thought to be responsible for microaggregate stability.
Macroaggregate stability has been correlated to sterols, lipids, organic carbon and many other organic matter structures  that bind and stabilize macroaggregates.
Thus, macroaggregates should increase as these binding agents increase with increased residue production and decomposition.
Our study confirms past findings showing that as organic carbon increases so too did
 macroaggregation , and organic carbon is directly related to crop residue quantities.
Macroaggregation is important for water infiltration.
As macroaggregates form larger channels and pores in the soil also form allowing for greater water capture.
This is shown in Figure 3b.
As macroaggregation increased sorptivity increased as well.
Overall, the results of systems that create and return higher levels of crop residue to the soil are positive.
Soil physical properties are directly related to crop residue and by decreasing the bulk density and increasing porosity there is increased potential for rapid capture of water , greater infiltration, and increased water use efficiency for the system.
The decreased bulk density and increased porosity and macro-aggregation also decrease the potential for runoff, erosion, and evaporation by increasing the potential for faster water capture leaving more water available for plant use.
This ultimately leads to a more efficient, sustainable, and economically viable system.
The conference theme is Cultivating Innovation: Solutions for a Changing World, focusing on the next generation of research, smart technology, policy development and best practices that are achieving breakthroughs in the vitally important mission of water and food security.
Throughout the conference, experts will share research results, case studies and perspectives on how we can achieve global food and water security.
Solutions discussed will be sustainable, scalable and adaptable to local contexts, involving all stakeholders in the decision-making process.
Looking forward, mounting sensors on the center pivot shows promise as an important component of automating irrigation.
The sensors on the pivot used in this study were able to accurately detect crop water stress in different irrigation levels using the ISSCADA system.
Mounting sensors on the pivot worked well to manage irrigation; additional types of sensors/imagers can be mounted to retrieve specific crop-related data.
Kansas State Research and Extension
 Grain Sorghum is one of the major irrigated crops in Kansas.
Irrigators are faced with the problem of declining well capacities due to water withdrawals from the Ogallala aquifer for irrigation exceeding mean annual recharge.
In addition to limited well capacities, public policy may also impose limits on total amounts of water that can be pumped.
For example the 20% reduction in pumped water that is being implemented as part of a Local Enhanced Management Area  policy in parts of Groundwater Management District  4 and several Water Conservation Areas  that have been implemented in GMD 3.
The drought tolerance attributes of grain sorghum make it a good choice for limited irrigation.
However, increase in grain sorghum irrigated area has lagged those of other irrigated crops in Kansas mainly corn and soybean.
One of the major challenges facing irrigated grain sorghum producers in Kansas is how to increase yields under declining well capacities or limited water supplies.
To develop limited irrigation management strategies for grain sorghum, we evaluated yield response under well-watered conditions as well as under very limited water supplies.
The purpose of the study was to determine the top-end grain sorghum yield potential under well-watered conditions  at three locations in western Kansas  and the effect of growth stage based irrigation timing on grain sorghum yields, water productivity and yield components with water supplies limited to 6 or 10 inches total.
The study was conducted at three locations in western Kansas including; 1) the Kansas State University, Southwest Research-Extension Center  near Garden City, 2) SWREC, near Tribune and 3) the Northwest Research-Extension Center , near Colby.
The soil type at Tribune and Garden City is Ulysses silt loam while that at Colby is a Keith silt loam.
The climate at
 the three locations is semi-arid with mean annual rainfall of 17, 18, and 19 inches for Tribune, Garden City, and Colby respectively.
Cumulative rainfall and reference evapotranspiration during the 2015 and 2016 growing seasons at each location are shown in Figure 1.
The experimental design was a randomized complete block design with four replications at each location.
Figure 1.
Cumulative rainfall and reference evapotranspiration at Colby, Garden City and Tribune, Kansas during the 2015 and 2016 grain sorghum growing seasons.
At each of the three locations, the study was conducted under a lateral move sprinkler irrigation system modified to apply irrigation water in any desired treatment combination.
The irrigation treatments included the following:
 1.
Full irrigation 100%ET
 2.
50% ET prior to booting of grain sorghum and 100% ET after boot and total irrigation limited to 10 inches
 3.
100% ET limited to 10 inches
 4.
50% ET prior to booting of grain sorghum and 100% ET after boot and total irrigation limited to 6 inches
 5.
100% ET limited to 6 inches
 6.
Dryland 
 As a case study, two limitations on total irrigation, 6 and 10 inches  were compared to full irrigation.
The fully irrigated treatment was managed as a non-water limiting crop with 100% ET replenishment.
Soil water in the 8.0 feet soil profile was measured as a check for adequacy of the ET-based irrigation scheduling and for determination of crop water use.
Soil water measurements were made using neutron scattering technique.
In-season irrigation events were adjusted to account for rainfall amounts received during the growing season.
Irrigation application dates and amounts at each location during the 2015 and 2016 grain sorghum growing seasons are shown in Tables 1 to 3.
Table 1.
Sorghum Commission Study Irrigation at Tribune, KS, 2015 and 2016.
1	2	3	4	5
 26-Jun-2015	1.58	1.58	1.58	1.58	1.58
 6-Jul-2015	1.48	1.48	1.48
 13-Jul-2015	1.48	1.48	1.48
 23-Jul-2015	1.48	1.48	1.48
 31-Jul-2015	1.47	1.47	1.47	1.47
 8-Aug-2015	1.80	1.80	1.80	1.80
 26-Aug-2015	0.92	0.92	0.92	0.92
 TOTAL-2015	11.74	7.30	10.21	5.77	6.02
 13-Jul	2.02	2.02	2.02
 29-Jul	1.14	1.14	1.14
 11-Aug	1.52	1.52	1.52	1.52	1.52
 20-Aug	1.54	1.54	1.54	1.54	1.54
 02-Sep	1.48	1.48	1.48	1.48	1.48
 12-Sep	1.56	1.56	1.56	1.56	1.56
 TOTAL-2016	9.26	6.10	9.26	6.10	9.26
 1 = 100% ET 2 = 50% ET to boot then 100% ET to 10" total 3 = 100% ET to 10" total
 4 = 50% ET to boot then 100% ET to 6" total 5 = 100% ET to 6" total
 Table 2.
Sorghum Commission Study Irrigation at Garden City, KS, 2015 and 2016.
1	2	3	4	5	6
 07-Apr-2015	0.75	0.75	0.75	0.75	0.75	0.75
 5-Aug-2015	1.00	1.00	1.00	1.00	1.00
 10-Aug-2015	1.00	1.00	1.00	1.00	1.00
 24-Aug-2015	1.00	1.00	1.00	1.00	1.00
 31-Aug-2015	1.00	1.00	1.00	1.00	1.00
 10-Sep-2015	1.00	1.00	1.00	1.00	1.00	1.00
 18-Sep-2015	1.00	1.00	1.00	1.00	1.00
 TOTAL-2015	7.75	6.75	6.75	6.75	6.75	1.75
 19-May-2016	0.75	0.75	0.75	0.75	0.75	0.75
 28-Jul-2016	1.00	1.00	1.00
 01-Aug-2016	1.00	1.00	1.000
 15-Aug-2016	1.00	1.00	1.00	1.00	1.00
 18-Aug-2016	1.00	1.00	1.00	1.00	1.00
 22-Aug-2016	1.00	1.00	1.00	1.00	1.00
 29-Aug-2016	1.00	1.00	1.00	1.00	1.00
 01-Sep-2016	1.00	1.00	1.00	1.00
 06-Sep-2016	1.00	1.00	1.00	1.00
 09-Sep-2016	1.00	1.00	1.00
 TOTAL-2016	9.75	7.75	9.75	6.75	7.75	0.75
 1 = 100% ET 2 = 50% ET to boot then 100% ET to 10" total 3 = 100% ET to 10" total
 4 = 50% ET to boot then 100% ET to 6" total 5 = 100% ET to 6" total 6 = Dryland
 Table 3.
Sorghum Commission Study Irrigation at Colby, KS, 2015 and 2016.
1	2	3	4	5	6
 07-Jul-2015	0.96	0.96	0.96
 12-Jul-2015	0.96	0.96	0.96
 01-Aug-2015	0.96	0.96	0.96
 04-Aug-2015	0.96	0.96	0.96	0.96	0.96
 10-Aug-2015	0.96	0.96	0.96	0.96	0.96
 17-Aug-2015	0.96	0.96	0.96	0.96	0.96
 20-Aug-2015	0.96	0.96	0.96	0.96
 24-Aug-2015	0.96	0.96	0.96	0.96
 29-Aug-2015	0.96	0.96	0.96	0.96
 02-Sep-2015	0.96	0.96	0.96
 TOTAL-2015	10.56	7.68	9.60	5.76	5.76	0.00
 23-Jun-2016	0.56	0.56	0.56
 25-Jun-2016	0.96	0.96	0.96
 12-Jul-2016	0.96	0.96	0.96
 22-Jul-2016	0.96	0.96	0.96	0.96	0.96
 24-Jul-2016	0.96	0.96	0.96
 29-Jul-2016	0.96	0.96	0.96	0.96	0.96
 2-Aug-2016	0.96	0.96	0.96	0.96	0.96
 5-Aug-2016	0.96	0.96	0.96	0.96
 11-Aug-2016	0.96	0.96	0.96	0.96
 17-Aug-2016	0.96	0.96	0.96	0.96
 25-Aug-2016	0.96	0.96	0.96
 TOTAL-2016	11.12	7.68	10.16	5.76	6.32	0.0
 1 = 100% ET 2 = 50% ET to boot then 100% ET to 10" total 3 = 100% ET to 10" total
 4 = 50% ET to boot then 100% ET to 6" total 5 = 100% ET to 6" total 6 = Dryland
 The hybrid used at all the three locations was Pioneer 84G62 because it is full season and well adapted under both irrigated and dryland environments.
Grain sorghum was planted at seeding rate of 100,000 seeds per acre on June 04, 2015, June 04, 2015 and June 02, 2015 at Tribune, Garden City, and Colby respectively.
In 2016, grain sorghum was planted on June 01, 2016, May 23, 2016, and May 25 at Tribune, Garden City, and Colby, respectively.
Best management practices for fertilizer and weed control for high yielding grain sorghum were followed.
For example, at planting 10:34:0 was applied at a rate of 10 gal/ac and at least 160 lb N/a was applied.
Some of the
 herbicides used for weed control included Atrazine 4L at rate of 32 oz/ac and Lumax EZ at a rate of 80 oz/ac.
Grain Sorghum was hand harvested on November 12, 2015, October 20, 2015 and October 20, 2015 at Tribune, Garden City and Colby respectively.
In 2016 grain sorghum was harvested on October 19, October 13, and October 6 at Tribune, Garden City, and Colby respectively.
At Tribune the previous crop was fallow , at Garden City the previous crop was corn  at Colby the previous crop was sunflower.
In 2016, at Tribune the previous crop was grain sorghum, at Garden City the previous crop was corn and at Colby the previous crop was sunflower.
Grain sorghum yield and yield components
 There were no significant differences in grain yield between irrigation treatments at Tribune, Garden City and Colby for the 2015 grain sorghum growing season.
This is probably due to the above normal rainfall received during the 2015 grain sorghum growing season.
In 2015, it was shown that the top-end yield potential could exceed 190 bu/ac.
The grain yield results are within range of K-State variety trials data that have shown grain sorghum to have a potential yield of higher than 200 bu/ac.
The highest grain sorghum yields were recorded at Tribune, followed by Garden City and Colby as shown in Tables 4 to 9.
Kernels per head, which greatly influences yield, was highest at Tribune.
There were more heads per acre at Garden City and Colby compared to Tribune, but Tribune had higher yields implying the effect of kernel number per head, which was highest at Tribune, might exert a strong influence on grain yield compared to heads per acre.
Kernel weight was similar between the three locations in 2015.
The study was repeated in 2016, grain yield was not significantly different across all irrigation treatments in Tribune, but yields were significantly different among treatments in Garden City and Colby locations as shown in Tables 7 and 9.
Averaged across treatments, grain yields were 17.9%, and 5.3% lower in Tribune and Garden City in 2016 compared to 2015.
Averaged across treatments, grain yields were 18.4%, higher in Colby in 2016 compared to 2015.
The differences could be attributed to seasonal variations in weather such as rainfall amount and distribution, environment and management.
It is worth noting that the fully irrigated treatment  was not significantly different from deficit irrigated treatments in both years at the three locations.
In addition, there is no substantial differences in yield between irrigation management limited to 6 and 10 inches of water per season and between growth stage based irrigation treatments.
Dryland treatments resulted in yield reduction of more than 25 bu/ac in Colby in 2016, which was drier than normal.
In fact at Colby in 2016 all irrigated treatments produced significantly higher yield than the dryland treatment.
At Garden City dryland treatment resulted in yield reduction ranging from 2 to 21 bu/ac.
Grain sorghum appears to be a suitable crop for limited irrigation with very little water needed to obtain maximum yield in a normal to wet year like 2015 and 2016.
However, in drought years of 2011 and 2012 Klocke et al.
showed that there was a strong relationship between in grain yield and irrigation applied.
Table 4.
Sorghum Commission Study.
Crop parameters as affected by irrigation timing and amount at Tribune, KS, 2015.
Treatment	yield,	bu/a	Ib/a-in.
WUE1,	Heads,	Seeds /lb	1000 seed,	OZ	Kernels	/head	Kernels /ft2	Heads /ft2
 100% ET	190	422 b	69.0	16119	0.99	2497	3931	1.6
 50/100%ET to 10"	181	447 ab	71.9	16691	0.96	2346	3847	1.7
 100%ET to 10"	186	419 b	70.6	15937	1.00	2352	3800	1.6
 50/100%ET to 6"	185	479 a	67.4	16198	0.99	2508	3832	1.5
 50/100%ET to 10"	182	478 a	69.7	16341	0.98	2383	3803	1.6
 LSD 0.05	17	50	10.7	834	0.05	354	379	0.2
 ANOVA  Trt.
0.738	0.046	0.918	0.417	0.431	0.766	0.945	0.918
 1WUE = water use efficiency 250% ET to boot then 100% ET until seasonal limit of 6 or 10 inches is reached
 Table 5.
Sorghum Commission Study.
Crop parameters as affected by irrigation timing and amount at Tribune, KS, 2016.
Treatment	yield,	bu/a	lb/a-in.
WUE1,	Heads,	10 //a	Seeds /lb	1000 seed,	OZ	Kernels	/head	Kernels /ft2	Heads/ft2
 100% ET	154	347 ab	108	17840	0.90	1911	3540	1.79
 50/100%ET to 10"	153	379 b	104	17693	0.91	1961	3475	1.79
 100%ET to 10"	149	334 a	104	18122	0.89	1933	3455	1.79
 50/100%ET to 6"	153	379 b	110	17799	0.90	1866	3502	1.89
 50/100%ET to 10"	150	328 a	104	17710	0.90	1911	3408	1.78
 LSD 0.05	16	38.8	10.9	1183	0.06	315	346	0.19
 ANOVA  Trt.
0.94	0.03	0.67	0.94	0.94	0.94	0.94	0.67
 Superscript-WUE = water use efficiency 250% ET to boot then 100% ET until seasonal limit of 6 or 10 inches is reached
 Table 6.
Sorghum Commission Study.
Crop parameters as affected by irrigation timing and amount at Garden City, KS, 2015.
Treatment	yield,	bu/a	Ib/a-in.
WUE1,	Heads,	Seeds /lb	1000 seed,	OZ	Kernels	/head	Kernels /ft2	Heads/ft2
 100% ET	157	426	89.7	17971	0.89	1826	3835	2.1
 50/100%ET to 10"	157	436	90.6	16676	0.96	1640	3445	2.1
 100%ET to 10"	150	403	88.0	16434	0.97	1541	3236	2.1
 50/100%ET to 6"	160	461	88.9	16393	0.98	1623	3373	2.1
 50/100%ET to 10"	149	444	86.2	16505	0.97	1579	3156	2.0
 Dryland	145	490	88.2	18120	0.88	1661	3321	2.0
 LSD 0.05	19	63	13.6	3152	0.13	464	977	0.3
 ANOVA  Trt.
0.59	0.095	0.997	0.492	0.409	0.844	0.756	0.997
 1WUE = water use efficiency 250% ET to boot then 100% ET until seasonal limit of 6 or 10 inches is reached
 Table 7.
Sorghum Commission Study.
Crop parameters as affected by irrigation timing and amount at Garden City, KS, 2016.
Treatment	yield,	bu/a	lb/a-in.
WUE1,	Heads,	10 //a	Seeds /lb	1000 seed,	OZ	Kernels	/head	Kernels /ft2	Heads /ft2
 100% ET	144	346 ab	69	17089	0.94	2006	3158	1.6
 50/100%ET to 10"	148	367 ab	74	17102	0.94	1923	3254	1.7
 100%ET to 10"	156	379 a	74	16517	0.97	1954	3317	1.7
 50/100%ET to 6"	137	338 b	66	16776	0.96	1976	2959	1.5
 50/100%ET to 10"	149	355 ab	72	17457	0.92	2021	3347	1.7
 Dryland	135	410 C	71	17993	0.90	1932	3100	1.6
 LSD 0.05	14.2	39.0	10.4	1484	0.08	286	433	0.3
 ANOVA  Trt.
0.047	0.01	0.48	0.40	0.40	0.97	0.44	0.997
 1WUE = water use efficiency 250% ET to boot then 100% ET until seasonal limit of 6 or 10 inches is reached
 Table 8.
Sorghum Commission Study.
Crop parameters as affected by irrigation timing and amount at Colby, KS, 2015.
Treatment	yield,	bu/a	Ib/a-in.
WUE1,	Heads,	Seeds /lb	1000 seed,	OZ	Kernels	/head	Kernels /ft2	Heads/ft2
 100% ET	132	284 a	91.9	18116	0.88	1482	3112	2.1
 50/100%ET to 10"	159	363 b	88.2	16846	0.95	1690	3380	2.0
 100%ET to 10"	147	312 ab	95.4	16694	0.96	1426	3137	2.2
 50/100%ET to 6"	152	360 b	91.3	16116	0.99	1505	3161	2.1
 50/100%ET to 10"	129	295 a	84.7	16902	0.95	1434	2725	1.9
 Dryland	151	402 ab	91.3	17150	0.93	1603	3366	2.1
 LSD 0.05	29	64.5	15.7	1497	0.07	480	631	0.36
 ANOVA  Trt.
0.221	0.008	0.788	0.127	0.17	0.836	0.398	0.788
 Superscript-WUE = water use efficiency 250% ET to boot then 100% ET until seasonal limit of 6 or 10 inches is reached
 Table 9.
Sorghum Commission Study.
Crop parameters as affected by irrigation timing and amount at Colby, KS, 2016.
Treatment	yield,	bu/a	Ib/a-in.
WUE1,	Heads,	10 //a	Seeds /lb	1000 seed,	OZ	Kernels	/head	Kernels /ft2	Heads/ft2
 100% ET	176 a	447 ab	118	14596 a	1.10 a	1214	3295	2.7
 50/100%ET to 10"	178 a	480 ac	121	14899 a	1.08 a	1231	3416	2.8
 100%ET to 10"	172 a	426 b	112	14613 a	1.10 a	1261	3233	2.6
 50/100%ET to 6"	178 a	496 C	119	15603 b	1.03 b	1311	3573	2.7
 50/100%ET to 10"	176a	458 ab	115	14741 a	1.09 a	1264	3332	2.6
 Dryland	150 b	490 a	118	16950 C	0.95 C	1209	3266	2.7
 LSD 0.05	13.9	46.6	10.1	690	0.05	113	302	0.23
 ANOVA  Trt.
0.003	0.008	0.56	0.001	0.001	0.836	0.24	0.56
 1WUE = water use efficiency 250% ET to boot then 100% ET until seasonal limit of 6 or 10 inches is reached
 Crop yield response to water
 There were significant differences in grain sorghum crop water use in 2015 growing season.
Treatments that received more irrigation water had the higher crop water use.
Crop water use ranged from 25.2 to 21.3, 20.7 to 16.7, and 25.6 to 20.7 inches at Tribune, Garden City and Colby respectively.
In 2015, there were significant differences in crop water use between irrigated and the non-irrigated treatments at Garden City and Colby.
In 2016, irrigation treatments that limited irrigation to 50% ET prior to booting used less water and consequently had higher WUE compared to other treatments at Colby and Tribune.
Crop water use for irrigated treatments averaged 24.1 inches and dryland crop water use was 19.4 in Garden City.
In Colby crop water use for irrigated treatments averaged 21.4 in and dryland crop water use was 17.2 in.
There is strong year-to-year variations in crop water use as shown in Tables 10 to 15.
Water productivity also known as water use efficiency was significantly different between treatments at Colby and Tribune but not at Garden City in 2015.
Water productivity was comparable between Tribune and Garden City but somewhat lower at Colby.
Averaged across treatments water productivity was 448 lb/ac-in at Tribune and Garden City and 336 lb/ac-in at Colby.
In 2016, water productivity was significantly different between treatments.
Averaged across treatments water productivity reduced by 21% in Garden City in 2016 compared 2015 while it increased by 39% in Colby in the same period.
Production functions are shown in Figs.
2 & 3, in a wet to normal rainfall years such as 2015, there was low to moderate response to evapotranspiration.
However, in 2016, Colby received below normal rainfall, and there was strong response to crop water use as shown by an r2 of 0.9.
At Garden City, there was a stable moderate response to irrigation with r2 of about 0.40 to 0.42.
These preliminary results indicate no substantial difference in yield for irrigation application amounts between 6 and 10 inches and between growth stage based irrigation treatments.
This implies that in a normal year producers might only need to allocate at least 6 inches of irrigation to obtain maximum yield.
However, in a drought year this might increase to more than 10 inches under soil conditions and climatic environment of western Kansas.
Table 10.
Available water in profile , at Tribune, KS, 2015.
Treatment	6/10	10/20	Water use 
 100% ET	16.70	12.27	25.19 a
 50-100% ET to 10"	14.90	8.69	22.54 b
 100% ET to 10"	15.01	9.46	24.78 a
 50-100% ET to 6"	14.50	7.77	21.53 b
 100% ET to 6"	15.44	9.17	21.31 b
 LSD 0.05	1.66	3.27	1.98
 ANOVA  Trt.
0.104	0.095	0.02
 Planted on June 4  and harvested on November 12.
In-season rainfall  was 9.02".
In-season irrigation  was 1 = 11.74"; 2 = 7.30"; 3 = 10.21"; 4 = 5.77"; = 6.02".
150% ET to boot then 100% ET until seasonal limit of 6 or 10 inches is reached
 Table 11.
Available water in profile , at Tribune, KS, 2016.
Treatment	6/01	10/20	Water use 
 100% ET	16.31 a	13.31 a	24.87 a
 50-100% ET to 10"	14.21	10.29 b	22.64 ab
 100% ET to 10"	14.72 b	11.65 b	24.93 a
 50-100% ET to 6"	13.78 b	9.87 b	22.63 ab
 100% ET to 6"	14.98 b	12.27 b	25.58 a
 LSD 0.05	2.1	0.13	1.4
 ANOVA  Trt.
0.001	0.001	0.001
 Planted on June 1,  and harvested on October 20,.
In-season rainfall  was 12.61".
In-season irrigation  was 1 = 9.26"; 2 = 6.10"; 3 = 9.26"; 4 = 6.10"; 5=9.26".
150% ET to boot then 100% ET until seasonal limit of 6 or 10 inches is reached
 Table 12.
Available water in profile , at Garden City, KS, 2015.
Treatment	6/22	10/13	Water use 
 100% ET	9.9 a	5.6 a	20.7 a
 50-100% ET1 to 10"	10.8 a	6.1 a	20.1 b
 100% ET to 10"	12.8 b	7.2 a	20.9 a
 50-100% ET to 6"	14.5 b	10.1 b	19.5 ab
 100% ET to 6"	8.5 a	5.1 a	18.6 b
 Dryland	14.3 b	7.8 a	16.7 C
 LSD 0.05	1.99	2.59	1.26
 ANOVA  Trt.
0.001	0.009	0.001
 Planted on June 3  and harvested on October 18.
In-season rainfall  was 13.18".
In-season irrigation  was 1 = 7.0"; 2 = 6.0"; 3 = 6.0"; 4 = 6.0"; 5 = 6.0", 6 = 1.0".
150% ET to boot then 100% ET until seasonal limit of 6 or 10 inches is reached
 Table 13.
Available water in profile , at Garden City, KS, 2016.
Treatment	6/23	10/11	Water use 
 100% ET	8.7	4.9	24 a
 50-100% ET1 to 10"	7.9	2.6	24 a
 100% ET to 10"	8.1	4.5	24 a
 50-100% ET to 6"	9.7	3.5	24 a
 100% ET to 6"	12.1	5.8	25 a
 Dryland	10.0	2.2	19 b
 LSD 0.05	3.1	2.8	2.0
 ANOVA  Trt.
0.29	0.03	0.001
 Planted on May 24  and harvested on October 13.
In-season rainfall  was 15.06".
In-season irrigation  was 1 = 9.0"; 2 = 7.0"; 3 = 9.0"; 4 = 6.0"; 5 = 7.0", 6 = 0.0".
Plus 0.75 preplant irrigation
 150% ET to boot then 100% ET until seasonal limit of 6 or 10 inches is reached
 Table 14.
Available water in profile , at Colby, KS, 2015.
Treatment	6/10	10/20	Water use 
 100% ET	17.0	10.9 a	25.59 a
 50-100% ET to 10"	15.8	8.2 b	24.13 b
 100% ET to 10"	16.3	8.9 b	25.91 a
 50-100% ET to 6"	16.4	7.8 b	23.28 b
 100% ET to 6"	17.5	8.2 b	24.00 b
 Dryland	16.1	4.2 C	20.76 C
 LSD 0.05	1.14	1.30	1.01
 ANOVA  Trt.
0.05	0.001	0.001
 Planted on June 4  and harvested on October 20.
In-season rainfall  was 8.12".
In-season irrigation  was 1 = 10.56"; 2 = 7.68"; 3 = 9.60"; 4 = 5.76"; 5 = 5.76", = 0.00".
150% ET to boot then 100% ET until seasonal limit of 6 or 10 inches is reached
 Table 15.
Available water in profile , at Colby, KS, 2016.
Treatment	10/5	Water use 
 100% ET	14.1	10.3 a	22.0 ab
 50-100% ET1 to 10"	14.6	8.5 b	20.9 ab
 100% ET to 10"	15.0	9.6 a	22.6 b
 50-100% ET to 6"	14.7	7.4 bc	20.2 C
 100% ET to 6"	14.4	6.4 C	21.5 ab
 Dryland	14.2	4.1 e	17.2 d
 LSD 0.05	2.2	1.7	1.4
 ANOVA  Trt.
0.96	0.001	0.001
 Planted on May 25  and harvested on October 6.
In-season rainfall  was 7.11".
In-season irrigation 6-23-9-09) was 1 = 11.12"; 2 = 7.68"; 3 = 10.16"; 4 = 5.76"; 5 = 6.32", 6=0.00".
150% ET to boot then 100% ET until seasonal limit of 6 or 10 inches is reached
 Crop Water Use 
 Figure 2.
Grain sorghum yield versus crop water use  at Colby, Garden City and Tribune, Kansas during the 2015 growing season.
Figure 3.
Grain sorghum yield versus irrigation at Colby, Garden City and Tribune, Kansas during the 2015 and 2016 growing season.
Grain sorghum yield under full and limited irrigated was evaluated at three locations in western Kansas.
The top-end yield under full irrigation was 190 bu/ac measured at Tribune in 2015.
However, there was no significant differences among irrigation treatments at all the three locations due to the above normal rainfall received during the 2015.
In 2016, the fully irrigated treatment  was not significantly different from deficit irrigated treatments  in both years at the three locations.
However, dryland yields were lower than irrigated grain sorghum yields at Garden City and Colby.
These preliminary results also indicate that there is potential to improve grain sorghum yields and that management that constrains irrigation to replenish only 50% ET prior to boot enhanced water productivity.
It is worth noting from this preliminary data that there is no substantial differences in yield between irrigation management limited to 6 and 10 inches of water per season in a normal to wet years, which makes grain sorghum a suitable crop choice for limited irrigation.
Management of Natural Turf Sports Fields
 Bradley S.
Park, Sports Turf Research and Education Coordinator James A.
Murphy, Extension Specialist in Turfgrass Management
 Maintaining a dense turf cover with enough vigor to outgrow damage from play should be the primary focus of a sports field management program.
Damage from overuse of natural turf fields is a common challenge.
Programs to control traffic  are needed to prevent severe loss of natural turf from year-long, unregulated play.
Soil cultivation  and overseeding practices in addition to mowing, fertilization, and irrigation are essential to the health and vigor of natural turf sports fields receiving intense play.
Partitioning school and municipal grounds into management zones with specific pest thresholds is an effective Integrated Pest Management  technique to minimize pesticide use and identify areas where pesticides may not be needed.
An attractive natural turf sports field appeals to spectators and enhances community pride.
Of greater importance, however, is the stable, resilient turf surface that provides the footing needed for athletic play and the cushion to protect athletes against injury.
Overused sports fields often lose turf cover and degrade to a bare soil surface within the high play zones of fields.
Bare soil on a sports field becomes very hard and dusty when dry, and muddy and slippery when wet.
Properly managed natural turf can withstand a significant amount of play without wearing out and losing its turf cover.
Abuse, however, can cause permanent damage that cannot be overcome by even the best maintenance program.
For example, the use of fields when the turf and soil are extremely wet is likely to result in severe damage that will require costly procedures to repair.
Field conditions will steadily degrade if the repair is not properly timed or not performed at all.
Maintaining a dense cover of turfgrass with vigorous growth is essential to producing high-quality playing surfaces on intensively used sports fields.
Unfortunately, there is not an exact answer to the question of how many events a sports field can tolerate per year.
This question is difficult to answer because of the numerous factors that affect the ability of natural turf to tolerate traffic including the sport, age of athletes, season, duration of play, wetness during play, soil type, construction design, variety of turfgrass, weather during recovery, and regime of maintenance practices.
This bulletin describes the concepts employed in the proper management of natural turf sports fields.
A traffic control program should regulate field use and allow field maintenance programs to keep pace with damage from play.
One common approach is the designation of game and practice fields.
Game fields are
 obviously the most important fields and are provided the most protection and greatest use restrictions compared to practice fields.
Accordingly, practice fields may actually have the greatest need for maintenance inputs and repair.
Field use permitting is another approach to control traffic to sustainable levels.
Develop a use permit system that only allows fields to be used a specific number of times at a specific time of the year.
Schedule time for routine maintenance as well as rest periods to allow the field to reestablish turf cover and density by way of recovery or repair efforts.
Field use permitting also provides a structure to collect user fees for those situations where it is appropriate/necessary.
Signage, fencing, and flagging are very useful for educating and alerting users that fields are either open or closed to play.
The most effective signs are easy to understand yet informative to users.
Informed users are more likely to abide with field use restrictions if they understand the program.
Signs should inform users about why fields are closed and what to expect when fields re-open.
Fencing and flagging can be used to reinforce signage that fields are open or closed.
If feasible, establish at least one alternate field that is always open to users when other fields are periodically closed.
Not unexpectedly, "always open" fields will not have ideal conditions but it provides users an option when the higher priority fields are closed.
In communities where the demand for sports fields is great, many grounds managers have found that installation of a synthetic turf field helps to manage traffic on natural turf sports fields.
Synthetic fields are durable over a wide range of weather conditions and better withstand intense, prolonged use scheduling over a short time span.
Natural turf fields can be protected by scheduling sporting events that require frequent day and night  play onto a synthetic field.
This type of field rotation is especially helpful during early spring and late fall when natural turf fields have low vigor  during cold weather.
Synthetic turf fields have high installation costs and require routine maintenance during their lifespan.
Long-term budgeting needs to include costs for removal, disposal  and surface replacement of worn out synthetic surfaces.
Recognize that some community members may be opposed to development of synthetic fields as replacement of, or supplement to, a more natural landscape.
Investments in the establishment, renovation, or reconstruction of sports fields can be wasted unless an appropriate maintenance program is implemented.
A sound maintenance program requires a well-thought out budget to properly allocate materials, equipment, and personnel as well as a conscientious and knowledgeable grounds manager being available to implement and oversee the program.
In cases where natural turf maintenance tasks are outsourced to contractors, the owner  should retain at least one employee with a thorough knowledge of sports field management to authorize appropriate bid specifications and provide oversight of contractor performance.
The primary goal of a maintenance program is to produce conditions favorable to the growth and development of a vigorous healthy turf.
Unregulated access/traffic to a recreational area that has destroyed the turf cover.
Signage, fencing and flagging system that is a highly effective method of controlling field activity and preventing unsustainable use/traffic.
Periodic assessment of soil conditions with profiling tools is effective at identifying hidden problems.
Movable goals are effective traffic management tools for highly used natural turf sports fields.
All natural turf fields do not require exactly the same maintenance practices, however, any maintenance program should include attention to the following cultural practices: mowing, fertilization, irrigation, overseeding, and soil cultivation.
Mowing once or twice per week is an acceptable frequency for many sports fields that are cut at a height of 2.0 to 2.5 inches.
Mowing as often as three times per week may be necessary during periods of rapid growth  or when the sport requires mowing below 2.0 inches.
Natural turf fields used for sports such as field hockey, soccer and baseball are often mowed lower than 1.5 inches and require the most frequent mowing.
Reel mowers are the best type of equipment for mowing at low cutting heights.
Rotary mowers set below 2 inches can scalp  turf rather than mow it, especially if the field has an uneven surface.
Mow sports field as often as needed SO that no more than 1/3rd the height of the turf is cut off in a single mowing.
This will allow return of leaf clippings without interfering with play.
Returning clippings to the turf also recycles fertilizer nutrients to the turf  and eliminates clipping disposal issues.
Regular sharpening and adjustment of mower blades, reels, and bedknives ensures that mowers will cut cleanly rather than tear and bruise leaf blades.
Mowers that are operated every day will probably need weekly sharpening of the cutting edges.
Similarly, mowers cutting turf grown on sandy soil will need more routine sharpening of dulled blades, reels, and bedknives than turf grown on loamy soils.
Employees should be thoroughly trained on the proper operation of mowing equipment and the ability to recognize the need for mower adjustments.
Lime.
Properly managed soil does not require annual liming.
Apply limestone only when soil test results indicate it is necessary.
Lime is applied to neutralize excess soil acidity and adjust the soil pH into a range of 6.0 to 6.7, which renders many essential nutrients more available to plant roots.
Do not guess at the need for liming; excess liming can harm plant growth by tying up essential plant nutrients such as phosphate, manganese, iron, and others.
Soil test results are used to determine whether calcitic or dolomitic limestone is needed and the amount of limestone that needs to be applied.
Greater amounts of lime will be needed in soil containing more organic matter and clay, which can be assessed in a soil test.
Liming is more effective after it is incorporated into the soil, SO it useful to apply before any soil cultivation, especially during late summer and fall.
Details on liming during the establishment of natural turf sports fields can be found in the Rutgers Cooperative Extension Bulletin E300 Turfgrass Establishment Procedures for Sports Fields njaes.rutgers.
edu/pubs/publication.asp?pid=E300
 Nitrogen.
Nitrogen is the nutrient that has the greatest impact on turf vigor and growth.
Unfortunately, N recommendations cannot be developed solely from soil test results.
Other important factors need to be considered including the age and vigor  of the turf, soil organic matter content, mowing , and availability of irrigation.
For example, older turfs growing on high-quality soil will not require as much
 Table 1.
Sample nitrogen  fertilization program based on the intensity of play  and maintenance on a sports field.
Intensity of Play &	Approximate Timing of Nitrogen  Fertilization	Annual
 Maintenance	March-April	May-June	August-September	October-November
 pounds of N per 1000 square feetb
 Low	0.5	0.5	0.5	0.5	2.0
 Moderate	0.8c	0.8	0.8	0.8	3.2
 High	1.0	1.0	1.0	1.0	4.0
 Time the application of N fertilization to increase turf vigor immediately before and recovery immediately after intense periods of play
 .
Uptake of N fertilizers by turfgrass is most efficient when soil temperatures are warm and light-to-moderate rain or irrigation
 occurs soon after application.
New Jersey law prohibits application of N  fertilizer after December 1st and before March 1st.
bAdjust the amount  of N to increase or decrease turf vigor based on the expected amount of damage or need for more or less recov-
 ery of turf cover and density.
Multiply by 44 to convert number to pounds per acre.
Use fertilizer containing slow release N at application rates greater than 0.7 pounds of N per 1000 square feet.
N fertilization as a new field constructed of poor soil.
Additionally, more N is needed as the playing intensity  increases on a field.
Nitrogen application guidelines outlined in Table 1 can be used to develop a bimonthly N fertilization program based on the intensity of play  and maintenance on a sports field.
Deviations from the suggestions in the table should be based on the condition of the turf and soil and quality expectations of the playing field.
The following are some generalized relationships between N fertilization and sports field management and use expectations.
For low maintenance sports fields, older turfgrass stands, and/or sports fields subjected to minimal traffic intensity, apply N fertilizer one to two times per year at an N rate of 1 pound per 1000 square feet per application.
Use a fertilizer with at least 30% slow-release-N.
For spring sports such as baseball, applications during early spring followed by a midto late spring application are generally appropriate.
For sports fields that have intense traffic events and receive regular overseeding, apply the maximum amount of N  allowed by New Jersey law.
Nitrogen fertilization should be timed to mirror those periods of intense field use and overseeding.
Greater fertilization is needed when recuperation of turf and development of new seedlings  is expected.
For example, sports fields used for fall sports should have N applied several weeks before  the start of season.
Make the first N fertilizer application in midto lateAugust followed by a second application in September or October to encourage turf recovery during the season as well as after fall play.
Apply N at a rate of 0.5 to 1 pound per 1,000 square feet.
Additional N fertilizer should be applied in early spring if the turf has not completely recovered from the damage incurred during the previous fall play.
Apply N at a rate of 0.5 to 1 pound per 1,000 square feet.
If there is adequate recovery of turf, spring fertilization can be delayed until the turf shows signs of reduced growth and vigor in midto late spring.
Fields with intense use during summer  will need some N fertilization during the summer to maintain turf vigor and encourage recovery from damage.
Irrigation will often be required as well.
Apply N at rates between 0.3 and 0.7 pounds per 1,000 square feet as-needed to maintain turf vigor and density during summer play.
Time the application to precede rain or irrigation which will enhance turf response to the fertilization.
Avoid excessive applications of N fertilizer  during summer which can have detrimental effects on turf and may encourage diseases such as brown patch and Pythium blight.
This discussion of N fertilization is intended to provide a reference from which to design a fertilization program.
Modifications will be necessary to accommodate the varying site and environmental conditions encountered at individual facilities.
Phosphate and Potassium.
Soil test results should be used to determine the necessity and quantity of phosphate and K applied to sports fields.
Per New Jersey Law, phosphate may not be applied as maintenance fertilization without justification of need provided by soil testing.
Phosphate may be applied in lieu of soil testing if turf is being established for the first time or being repaired.
Organic Fertilizers.
Organic fertilizers are fertilizers that are permissible for use in organic production systems per United States Department of Agriculture  National Organic Program  standards.
Synthetic fertilizers and fertilizers that contain sewage sludge  should not be used where a claim of organic management is being made.
Organic fertilizers typically contain a small percentage of N compared to synthetic counterparts.
Thus, organic fertilizers need to be applied in large quantities of product to apply a modest amount of N.
Also, organic fertilizers often contain phosphate and use of these fertilizers may result in the application of phosphate even if it is unnecessary per soil test results.
New Jersey Law allows up to a 0.25 pound of per 1,000 square feet to be applied in lieu of soil testing if the fertilizer source is derived from a natural organic source.
Organic Matter Additions.
A soil test for organic matter content is the primary criterion for determining whether organic matter should be added to a soil.
The Rutgers Soil Testing Laboratory can determine percent organic matter for submitted samples and subsequently characterize the organic matter level  relative to soil texture.
Ideally, organic matter  should be incorporated into soils during the sports field construction process.
Composts can be applied to the surface  of established sports fields, however, repeated applications are needed over time to avoid the development of an excessive layer at the surface.
Light applications of compost applied as topdressing  followed by core cultivation  will assist in compost incorporation and minimize layering potential.
Where an irrigation system is available, apply water as infrequently as necessary to maintain proper growth and avoid drought-stress of the turf.
Soil texture and degree of compaction will control how much water can infiltrate and be stored in the soil, affecting the quantity and rate at which water can be applied through irrigation.
For example, turf grown on sandy soil needs to be watered more often than turf grown on loamy or clayey soils.
However, sandy soils hold less water and require smaller amounts of water applied per irrigation event.
In contrast, turf growing on a loamy or clayey soil should be irrigated less often but with larger quantities of water per irrigation event.
Excess irrigation wastes water to evaporation, runoff and leaching.
Excess irrigation can also increase the amount of weeds that will invade a sports turf.
As a general rule, thorough watering once or twice a week during drought periods is often preferable to light daily sprinkling.
The exception is very sandy soil which may need irrigation three times per week during hot dry conditions.
Apply sufficient water in a single irrigation event to wet the entire root zone.
Do not apply irrigation too rapidly, otherwise water may runoff and collect in small depressions  on the field.
If this occurs, adjust the irrigation SO that only the amount of water that does not cause ponding is applied.
Move the sprinkler or switch to another station  before water starts to pond.
If this is not enough water to completely wet the root zone, allow the applied water to soak into the soil before apply the remaining portion of water.
Repeat this cycling of irrigation and soaking until all the water is applied.
Use a soil probe to assess the need for irrigation as well as how deeply the root zone needs to be wetted.
Place small rain gauges or tin cans on the turf to catch and measure the amount of water applied during irrigation.
Quantify the amount  of water applied during a specific time to calculate a precipitation rate  for the irrigation system.
This information is needed to know how long an irrigation system should run to deliver the required amount of water.
Under moderate temperatures, sports turf will need about one-inch of water per week to maintain growth.
Thus,
 when it rains less than one-inch in a week, subtract the amount of rain that occurred from one-inch to estimate how much should be applied.
Use the soil probe to confirm that the root zone has been adequately wetted after irrigation.
Keep in mind that irrigation is of little or no value if liming, fertilizing, mowing and other practices are neglected or done improperly.
Turf cover in goal creases, field centers, and penalty kick areas will inevitably thin out at some point during an intense playing season.
It is essential to preemptively overseed those areas of fields that will thin out from play and potentially lose turf cover.
Initiate overseeding prior to the beginning of the playing season and repeat overseeding wherever thinning of the turf is observed during the playing season.
It is far more difficult to recover or repair natural turf fields with overseeding if high-wear areas have completely lost turf cover.
Overseeding is easily done with a rotary spreader before and during the playing season.
Seed-to-soil contact is achieved by athletes' shoes "cleating-in" the seed during play.
Repeated scattering of seed with a rotary spreader is preferred over a slit-seeder.
The vertical blades on a slit-seeder will cause too much injury to the existing turf as well as the new seedlings from previous overseeding.
Choosing the appropriate seed for an overseeding program is critical.
Perennial ryegrass seed is the best choice for routine overseeding of the high traffic zones of sports fields.
Perennial ryegrass seed will germinate faster and at cooler soil temperatures than Kentucky bluegrass and tall fescue making it the best choice for overseeding during fall and early spring.
Seed blends  of perennial ryegrass that have good tolerance to gray leaf spot disease are recommended.
See the RCE publication FS1048 at njaes.rutgers.
edu/pubs/publication.asp?pid=FS1048 for more information on this disease problem.
There are numerous suppliers specializing in turfgrass seed for the sports turf market.
Be cautious with seed mixtures marketed as "sports turf mixtures".
Many of these mixtures contain Kentucky bluegrass and tall fescue and are better suited for new establishment where there is ample time to fully establish a turf.
Applying a sufficient quantity of seed is important for overseeding to be successful.
As an example, apply a perennial ryegrass blend at 6 pounds per 1,000 square feet to the area between the hash marks of a football field before every home game.
The area between the hash marks on a football field is 16,000 square feet, which
 will require 96 pounds  of seed.
Take notice of the high play areas after several games, if new seedlings are not keeping up with damage and turf cover is diminishing, increase the overseeding rate by one or more 50-lb bags of seed.
Regular cultivation of the turf and soil is necessary on sports fields subjected to intense traffic, especially when the soil is very susceptible to compaction.
Spring and fall are typically the best time for cultivation.
At minimum, the high traffic areas of a sports field should be cultivated  at the end of each playing season.
Core cultivation or coring refers to equipment capable of extracting 0.5 to 1 inch diameter cores of soil to a depth of 2 or more inches.
Objections to the soil cores brought to the turf surface after coring can be avoided by either removing the soil cores or working the cores back into the turf.
Soil cores can be broken-up and returned to the turf through verticutting  or drag-matting the cores.
Soil cores dried to the proper water content  will be easier to break up and work back into the turf.
Cultivation can also be performed using a machine that creates similar-sized holes with a solid tine , which enables cultivation during the playing season.
Some machines use solid tines to horizontally shatter the soil and can be equipped with a seeding box SO that cultivation and seeding can be done simultaneously.
Soil that is deeply compacted should be first cultivated with a deep  tine and/or rotary decompaction machines.
Treatment with deep cultivation equipment has sufficiently improved many older sports turfs and, as a result, helped avoid the high costs of reconstruction.
It should be noted that deep cultivation will not solve compaction problems associated with improper construction practices.
There are numerous contractors capable of providing these services if the cost of purchasing cultivation equipment is deemed too expensive.
Frequency of cultivation is determined by the intensity of field use and severity of compaction.
High-priority fields that receive intensive play will benefit from two or more cultivation treatments per season.
Targeting cultivation to only the high-traffic zones of a field rather than treating the entire field will allow you to treat problem areas more frequently.
Core cultivation can be used in conjunction with overseeding and fertilization to repair badly damaged turf on fields or areas of a field using the following steps:
 1.
Core cultivate to a 2-inch depth or more in late summer ;
 2.
Break-up and re-incorporate the cores using a towbehind drag mat;
 3.
Seed with a blend of two-to-five perennial ryegrass varieties using a slit-seeder in two directions at a minimum of 5 pounds of seed per 1,000 square feet per direction.
If a slit-seeder is not available, a rotary spreader can be used.
However, it would be best to apply seed prior to core cultivation  to achieve better seed-to-soil contact;
 4.
Apply a starter fertilizer; and
 5.
Irrigate to maintain a moist seedbed.
Integrated Pest Management  is a management system that helps grounds managers anticipate and prevent pest problems from reaching damaging levels by using a wide range of control tactics.
IPM strategies use control measures only when necessary, which saves time, minimizes costs, conserves energy resources, and results in the judicious use of pesticides that minimizes any adverse effects on the function and quality of landscapes.
Growing a healthy, dense, and vigorous turf is one of the best methods for reducing potential pest problems.
Implementing the management practices discussed above will help maintain healthy turf and reduce pest activity on sports fields.
Unfortunately, even the best implementation of management practices can sometimes fail to suppress pest activity below levels  that negatively affect the playability and safety of sports fields.
Pest control products may be needed whenever other actions fail to adequately manage weed, insect, and disease problems.
Pesticide applications on New Jersey school grounds must be made in accordance with the New Jersey School Integrated Pest Management  Law.
A major emphasis in an IPM program is determining  where action is needed to reduce pest problems, which can be daunting for a multi-acre facility with numerous natural turf sports field and grounds with varying uses and varying tolerances to pest problems.
Examples of different uses for turf include sports fields, practice fields, physical education, school recess, passive recreation, lawns, and other general common areas.
Each of these uses typically has a unique management level and threshold for pest activity.
A threshold defines the point at which pest-specific actions are taken.
Subdividing a multi-acre facility into management zones based on turf use and threshold for pest activity helps grounds managers to prioritize scouting, actions, and allocation of resources.
For example, management zones can be defined as:
 A.
Grounds that have the lowest threshold for pest activity and highest expectations for use such as safe footing and cushion for play or high aesthetic quality;
 B.
Turfs and grounds that have a moderate threshold for pest activity and moderate expectations for use such as a persistent ground cover or moderate aesthetic quality; and
 C.
Grounds that have the primary function of soil stabilization , greatest threshold for pest activity, and minimal expectations for aesthetic quality.
Examples of Zone A grounds include sports and practice fields, particularly those used by high school-aged athletes and older.
Relatively low thresholds  of weed, disease and insect activity can adversely affect the ability of these turfs to provide safe footing and cushion for play as well as a reliable surface for ball bounce and roll.
Very good to excellent turf cover from cool-season perennial turfgrass is demanded.
Another example includes high-value ornamental lawn and garden landscapes.
Examples of Zone B grounds include sports fields, passive recreation areas, and lawns where stakeholders have moderate expectation levels for playing surfaces and aesthetic quality of landscape plants.
A greater threshold for weeds, diseases, and insect activity can be tolerated as the nature of the recreational activity, age of athletes, or aesthetic importance dictates.
High-visibility lawns and landscape grounds and sports fields used by middle school-aged athletes may fall under this category.
Examples of Zone C grounds might include sports fields primarily used by elementary school-aged athletes, "alternate fields" that are always open to users when high value fields are closed, and naturalized landscapes.
These uses typically have very high thresholds for pest activity and low expectations for aesthetic quality.
Soil stabilization is the primary management concern for these grounds.
Grassy weeds  and broadleaf weeds  are highly opportunistic plants that can invade sports fields after play has reduced turfgrass cover and exposed bare soil.
Midfields, goal creases, and other high traffic areas are very susceptible to the
 encroachment of these weeds.
Practices that control traffic and maintain a dense turfgrass cover, as described previously, will significantly reduce the encroachment of weeds.
When broadleaf weed infestations exceed a threshold for a specific management zone, selective herbicides  can be used to reduce weed populations below the threshold.
Fall and spring are the most appropriate times to apply herbicides for broadleaf weeds.
For those sports fields receiving regular overseeding, new seedlings should be mowed 2 to 4 times before applying a broadleaf herbicide.
Always carefully read and follow pesticide labels.
Sports fields and grounds with a history of crabgrass or goosegrass indicate there is a problem with maintaining adequate turf density and cover during the spring.
A management program review should be performed to determine if adjustments can be made to improve turf cover.
Preemergence herbicides  can be applied to control crabgrass and goosegrass before these weeds germinate in the spring.
Corn gluten meal is a by-product of corn milling and is generally considered to be an organic product with preemergence herbicidal activity that can be applied in a manner similar to conventional preemergence herbicides.
Corn gluten meal will be more effective under low weed pressure; expect only suppression of crabgrass and goosegrass when weed pressure is great.
Preemergence herbicides  should not be used in early spring on a sports field where large areas of turf cover have been lost.
Instead, improve turfgrass cover using either seed or sod.
If applied, conventional preemergence herbicides and corn gluten meal will damage or kill new seedlings and sod and greatly limit your ability to restore turfgrass cover on bare soil.
Postemergence herbicides can be used to control crabgrass  and goosegrass  if these weeds threaten to ruin a spring seeding.
A number of nonselective weed control products contain active ingredients defined as "low impact pesticides" by the NJ School IPM Law.
These active ingredients include citric acid, clove oil, eugenol, lauryl sulfate, 2-phenethyl propionate, and sodium lauryl sulfate.
These materials can be used for nonselective control of young  weed seedlings.
Potential uses include "trimming" along fences lines and turf border edges.
These products are most effective if used in spring when the weeds are small and are not recommended for the control of large, mature perennial weeds.
Use of these active ingredients for spot treatment of weeds in turf will cause unac-
 ceptable injury/discoloration  to the established turfgrass unless care is taken to only treat the undesirable vegetation.
This is especially important in newly seeded turfgrass; immature turfgrass seedlings have limited potential to recover from damage by these materials.
White grubs are the insect pest of greatest concern for sports turf in New Jersey.
White grubs are soil inhabiting pests that feed on plant roots during summer, fall and spring.
Root system damage on a sports turf greatly compromises the footing needed for athletic play.
Furthermore, secondary damage from raccoon, skunk and other vertebrate predators foraging on grubs will destroy the turf and render a sports field unplayable.
As a result, fields used for late summer and fall play have a very low threshold for white grub populations.
Preventative applications of insecticides are typically used to avoid serious damage to sports field turfs with a low threshold for white grub damage.
Curative applications of insecticides are possible but have risks.
Timing of curative applications is less flexible and will overlap with play on late summer and fall sports increasing exposure risk for athletes.
Soil insecticide applications never work overnight SO white grub and predator foraging damage will continue for some time after the application.
Products containing insect parasitic nematode species or milky disease-causing bacteria provide biological control  options for white grubs but these products have limitations.
The level of control will depend on the white grub species , availability of water, air and soil temperature, and the method used to apply the nematodes.
These products may be expensive compared to conventional insecticides and need to be used soon after delivery.
Nematodes tend to work better against larvae of the Japanese beetle than the other species.
And the product based on milky disease-causing bacteria only affects Japanese beetle larvae.
Yet, the most common white grub species in New Jersey is the oriental beetle.
Turfgrass seed that contains endophytes will produce turf more or less resistant to billbugs, chinch bugs, sod webworms and some other leaf and crown feeding insects.
Endophytes are beneficial  fungi growing within a turfgrass plant, which provides
 the turf with biological control of many foliar feeding insects.
The seed of many new varieties of perennial ryegrass, tall fescue, and fine fescues contain endophytes.
These varieties are strongly recommended for the establishment or overseeding of turf.
Seed containing endophytes should be stored under cool dry conditions because the endophytes in seed are lost  when stored under hot, humid conditions for an extended period of time.
Selecting turfgrass species and varieties with improved tolerance to important diseases is an effective approach to managing disease pests.
Always consider this when selecting grass seed for a new seeding or overseeding.
Important examples of this approach include the use of seed blends  of perennial ryegrass that have good tolerance to gray leaf spot or Kentucky bluegrass with enhanced resistance to summer patch.
Several biological disease control products, often referred to as microbial inoculants, are registered for use in turf.
These products contain microorganisms  that suppress the populations of disease causing microorganisms.
They are most effective when used on a preventive basis in areas with a history of disease and when disease activity is low to moderate.
Efficacy of these products is usually poor when used on a curative basis or where disease pressure is high.
To be effective over long periods, biocontrols products usually need to be reapplied periodically to maintain populations of the beneficial microbes at disease suppressive levels.
The term "compost t refers to a liquid derived from steeping compost in water.
Compost teas should not be viewed as fungicides, but are more accurately described as soil or foliar inoculants intended to promote soil and plant health.
Although compost teas have been shown to occasionally reduce the severity of foliar diseases in the field, research has not shown them to consistently prevent or control turfgrass diseases.
Table 2.
Biological products with turfgrass disease suppressive activity.
Product name	Organism	Diseases suppressed
 Companion Biological Fungicide	Bacillus subtilis GB03 strain	Summer patch, brown patch
 EcoGuard R	Bacillus licheniformis SB3086 strain	Dollar spot
 Prestop R Biofungicide	Gliocladium catenulatum J1446 strain	Foliar diseases
 Rhapsody R	Bacillus subtilis QST 713 strain	Summer patch, brown patch
 Organic Materials Review Institute  Listed
 Actinovate SP	Streptomyces lydicus WYEC 108 strain	Soilborne diseases
 Regalia R PTO Biofungicide	Reynoutria sachalinensis	Anthracnose, brown patch, dollar spot
 TurfShield R PLUS	Trichoderma harzianum	Brown patch, dollar spot
 This bulletin describes sports field management strategies meant to produce favorable conditions for the development and growth of a vigorous healthy turf.
All too often, however, only certain aspects of turf management receive attention due to budget limitations or personnel unable to identify the best practices needed to manage a specific field.
The implementation of a suitable sports field maintenance program requires a trained sports field manager who has the ability to both anticipate future problems and provide solutions to existing problems.
Furthermore, the program must be done within a budget that supports the necessary materials, equipment, and additional trained personnel.
Types of Drive Systems
 Wheel and Drive Options
 The center pivot is the system of choice for agricultural irrigation because of its low labor and maintenance requirements, convenience, flexibility, performance and easy operation.
When properly designed and operated, and equipped with high efficiency water applicators, a center pivot system conserves three precious resources-water, energy and time.
Manufacturers have recently improved center pivot drive mechanisms , control devices, optional mainline pipe sizes and outlet spacings, span lengths, and structural strength.
The first pivots produced in the 1950s were propelled by water motors.
They operated at high pressures of 80 to 100 psi and were equipped with impact sprinklers and end guns that sprayed water toward the sky, resulting in significant evaporation losses and high energy use.
Today, pivots are driven by electric or oil hydraulic motors located at each tower and guided by a central control panel.
Pressures as low as 10 to 15 psi  are usually adequate for properly designed LESA  and LEPA  pivots that are 1/4 mile long operating on level to moderately sloping fields.
Water application efficiency with such systems is 85 to 98 percent.
When purchasing a center pivot system one must select:
 mainline size and outlet spacing;
 length, including the number of towers;
 application rate of the pivot; and
 the type of water applicator.
These choices affect investment and operating costs, irrigation efficiency, and crop production.
Wise decisions will result in responsible water management and conservation, flexibility for future changes, and low operating costs.
Switching from furrow to pivot irrigation can save water and money.
For example, on the Texas High Plains, field measurements show that corn is irrigated an average of 16 to 17 hours per acre per year with furrow irrigation.
With center pivot MESA irrigation , similar corn yields are pro-
 duced with 12 to 13 hours per acre per year.
LEPA and LESA applicators further reduce irrigation to an average of 10 to 11 hours per acre per year.
A quarter-mile  system that irrigates about 120 acres typically costs $325 to $375 per acre excluding the cost of groundwater well construction, turbine pumps and power units.
Longer systems usually cost less on a per-acre basis.
For example, half-mile systems  that irrigate approximately 500 acres cost about $200 to $250 per acre.
This relatively high cost is often offset by a number of advantages, including reduced labor and tillage, improved water distribution, more efficient pumping, lower water requirements, more timely irrigation, and convenience.
Programmable control panels and remote control via phone lines or radio can start and stop irrigations, identify location, increase or decrease travel speed, and reverse direction.
Fertilizers and certain plant protection chemicals can be applied through the center pivot, which increases the value and use of the system.
Programmable injection unit control, monitoring, and safety are compatible with center pivot control sysitems.
Towable pivot machines are available, so that additional tracts of land can be irrigated with the same machine.
When considering a towable machine, remember that sufficient water is needed to irrigate all tracts.
Plan the irrigated circle and position the pivot so that it can be moved to drier soil at the location from and in the path in which it is to be towed.
Types of Drive Systems
 In electric drive pivots, individual electric motors  power the two wheels at each tower.
Typically, the outermost tower moves to its next position and stops; then each succeeding tower moves into alignment.
Thus, at any time a tower can be in motion.
The rotation speed  of the pivot depends on the speed of the outermost tower and determines the amount of water that is applied.
The operator selects the tower speed using the central power control panel, normally located at the pivot point.
At the 100 percent setting, the end tower moves
 Figure 1a.
Electric drive.
continuously.
At the 50 percent setting, the outer tower moves 30 seconds and stops 30 seconds each minute, etc.
The speed options on most central power control panels range from approximately 2 to 100 percent.
With oil hydraulic drive systems, all towers remain in continuous motion.
The outermost tower speed is the greatest, and each succeeding tower moves continuously at proportionally reduced speeds.
As with electric drive machines, the center pivot travel speed is selected at a central control.
It is a master control valve that increases or decreases oil flow to the hydraulic motor/s on the last tower.
Two motors per tower are used with the planetary drive, one for each wheel.
One motor per tower powers the
 Figure 2.
Hydraulic move.
Figure 1b.
Electric drive.
optional worm drive assembly.
The required hydraulic oil pressure  is maintained by a central pump usually located near the pivot pad.
The central pump may be powered by natural gas, diesel or electricity.
The number of towers and maximum travel speed determine the hydraulic oil flow and the central pump power requirement, which usually ranges from 7.5 to 25 horsepower for quartermile systems.
Additional site specific travel speed options are available.
Theoretically, continuous move systems provide greater irrigation uniformity.
However, other factors influence uniformity, including travel speed , system design, type of water applicator, and operator management, in combination with the amount of water  the machine is nozzled to deliver.
In field tests, both electric and hydraulic drive systems work well.
The choice is often guided by available power sources, personal preference in servicing and maintaining the system, the service history of local dealers, what is being sold in the local market and why, purchase price, and dependability.
Wheel and Drive Options
 The travel speed is determined by the wheel size in combination with the power drive mechanism, and is set at the central control panel.
The speed of the pivot determines the amount of water applied as specified on the corresponding system design precipitation chart.
(See the following discussions on the system design precipitation chart and system management as related to travel speed.
Gear drives should be checked
 for proper oil levels and any water in the gear boxes removed at least once each year.)
 Electric power drive has two gear reductions.
One gear reduction is in the drive shafts connecting the electric motor to a gear box located at each of the two tower wheels.
The second gear reduction is the gear box driving each wheel.
The maximum center pivot travel speed depends on the:
 electric motor speed or rotation in revolutions per minute ;
 speed reduction ratios in both the center drive shafts and gear boxes; and
 Table 1 gives examples of electric center drive and gear box reductions, wheel circumference, travel distance for each revolution, and representative maximum travel speed in feet per hour.
Hydraulic drive pivots have one gear reduction.
Two configurations are used-a hydraulic motor in each wheel hub, or a single motor located at one wheel coupled to a right angle gear drive with a connecting drive shaft that also powers the second wheel.
A hydraulic valve meters oil flow to each set of drives at each tower to maintain system alignment.
Total oil flow is determined by the travel speed, number of drive units , gear reduction, and tire size.
Table 1 lists typical hydraulic drive center pivot oil pump horsepower, tire size, and end tower travel speed.
The design computer printout provides required information about the center pivot and how it will perform on a particular tract of land.
A portion of a typical design printout is shown in Figure 3.
It includes:
 the pivot design flow rate  in GPM;
 irrigated acreage under the pivot;
 elevation changes in the field as measured from the pivot point;
 operating pressure and mainline friction losses;
 the pressure regulator rating in psi ;
 the type of water applicator, spacing and position from the mainline;
 nozzle size for each applicator;
 water applicator nozzle pressure;
 maximum travel speed; and
 A sample precipitation chart is shown in Figure 4.
It identifies irrigation amounts  for optional travel speed settings, gear reduction ratios and tire size.
It corresponds with Figure 3.
Table 1.
Typical gear reduction, wheel drive RPM and maximum end tower travel speed.
Center	Gear	Wheel diam.-inch	End tower
 Motor	drive	box	Rim & tire	Last wheel	feet
 Drive	RPM	ratio	ratio	Rim	Rim & tire	circum.
ft.
drive RPM	per hour
 Electric	1740	58:1	52:1	24	40	10.47	.5769	362
 Electric	1740	40:1	50:1	24	40	10.47	.8700	546
 Electric	3450	40:1	52:1	38	54	14.13	1.6586	1406
 No.
Hydraulic pump	Tire size	Rim & tire	Last wheel	End tower
 towers	drive HP	circum.
ft.
drive RPM	feet per hour
 Hydraulic	8	10	16.9 X 24	10.47	.5730	360
 Hydraulic	8	15	14.9 X 24	10.47	.9312	585
 Hydraulic	8	25	11.2 X 38	14.13	1.5723	1333
 Hydraulic	18	25	11.2 38	14.13	.6286	533
 J J Farms & Section 130 625.00 GPM 4.00 PSI 13.67 PSI identification Pivot location Pivot flow Design rate end the Design Pressure at pivot Pressure at
 ft 1309.00 ft 12.50 ft 12.00 ft ft, +7.0 -8.0 0 length Overall length tube Drop mainline) (from position Regulator elevation of Design end tower End GPM gun
 ACRES	1.84	5.53	9.23	12.92	16.61	20.30	23.99	27.68	5.41	123.51
 6	6	6	6	6	6	6	6	6
 DROP 1st	POSITION		36.60	3.335	3.335	3.335	3.335	3.335	3.335	3.335	3.335
 DROP	DIAMETER		0.75	0.75	0.75	0.75	0.75	0.75	0.75	0.75	0.75
 DROP	SPACING		6.67	6.67	6.67	6.67	6.67	6.67	6.67	6.67	6.67
 19	24	24	24	24	24	24	24	5	192
 MAINLINE	DIAMETER		6.38	6.38	6.38	6.38	6.38	6.38	6.38	6.38	5.78
 SPAN	LENGTH		160	160	160	160	160	160	160	160	29	1309
 SPAN	NO.
1	2	3	4	5	6	7	8	9	Total
 Brand size and/or and applicator of  flow capacity LF often (low expressed as	if is Plug plugged outlet number, 11.
from furro Distance 12.
applicator, in to arm	LENGTH
 (when should nozzle the the the regulators 7.
Pressure used, nozzle at at pressure pressure are	DROP
 12	150	156	156	162	144
 size by applicator's applicator based delivered GPM and the nozzle Actual the 5.
operating on pressure	Applicator mainline number position 9.
on or	flow), flow), (high HF etc.
11	PLUG	NO.
1
 than of be rating) the less the regulator's psi no	by inches) either in number actual size or	10	REG	SIZE	6LF	6LF	6LF	6LF	6LF
 9	SPRK	NO.
1	2	3	4	19
 mainline 6.
the the in in psi Pressure outlet at	LABEL SPRINKLER	SIZE NOZZLE &
 8	4.0	4.0	4.0	4.0	6.5
 based by needed applicator GPM the the covered 4.
area on
 7	NOZZLE	PSI	6.66	6.66	6.66	6.66	6.66
 between feet 2.
length between Distances outlets in towers span or	from feet pivot Distance 3.
in point outlet tower to or
 6	PIPE	PSI	13.27	13.20	13.13	13.05	11.86
 5	GPM	DEL.
0.29	0.29	0.29	0.29	0.76
 4	GPM	NEED	0.18	0.21	0.24	0.27	0.76
 Mainline pivot point from number 1.
outlet
 3	DISTANCE	PIVOT TO	6.08	36.60	43.27	49.94	56.61	156.66
 2	LAST	OUTLET	36.60	6.67	6.67	6.67	6.67
 1	1	2	3	4	5	20
 144	144	150	150	156	144	144	144
 6LF	6LF	6LF	6LF	6LF	6LF	6LF	6LF
 20	21	22	23	24	43	44	45
 6.5	7.0	7.0	7.0	7.0	9.5	9.5	9.5
 6.66	6.66	6.66	6.66	6.66	6.66	6.66	6.66
 11.79	11.72	11.65	11.58	11.50	10.20	10.03	9.96
 0.76	0.88	0.88	0.88	0.88	1.61	1.61	1.61
 0.79	0.82	0.85	0.89	0.92	1.53	1.56	1.59
 160.00	163.33	170.00	176.67	183.84	190.01	316.67	320.00	323.33	330.00
 160.00	6.67	6.67	6.67	6.67	6.67	6.67	160.00	6.67	6.67
 1 Tower	21	22	23	24	25	44	2 Tower	45	46
 Sample Figure chart.
4.
precipitation
 XXXXX IRRIGATOR 1 SIZE  MOTOR = 1745 RPM LOADED MOTOR = 58T01 GEAR RATIO BOX CENTER =
 50T01 RATIO GEAR WHEEL BOX = 11.2 24.0 SIZE TIRE X = 5.90 SPEED MAX.
LAST TOWER =
 water of 1.
applied Total amount this inches speed in setting at
  setting the control on indicated of usually percentage as a speed the maximum
 hours Time complete in make 3.
to a this circle speed setting at
 22.70	28.38	32.44	37.84	45.41	56.76	75.68	90.82	113.53	126.14	151.37	189.22	227.06
 % SETTING TIMER -
 80	70	60	50	40	30	25	20	18	15	12	10
 0.25	0.32	0.36	0.42	0.51	0.64	0.85	1.02	1.27	1.42	1.70	2.12	2.55
 It is essential that correct information about available water supply  and changes in field elevation are used in designing the pivot so that accurate irrigation amounts, operating pressure requirements, and the need for pressure regulators can be determined.
Give this information to your dealer, and then inspect the resulting computer design printout before placing your order to ensure that the system is designed to accommodate your site conditions and will perform as expected.
Always look at the design mainline operating pressure at the pad to determine if it is what you want.
If not, inquire about ways to lower it.
System irrigation capacity is determined by the gallons per minute  and the number of acres irrigated.
System capacity is expressed in terms of either the total flow rate in GPM or the application rate in GPM per acre.
Knowing the capacity in GPM per acre helps in irrigation water management.
Table 2 shows the relationship between GPM per acre and irrigation amounts.
These irrigation amounts apply for all irrigation systems with the same capacity in GPM per acre.
The amounts do not include application losses, and are for systems operating 24 hours a day.
To determine your system's capacity, select the desired irrigation amounts in inches and multiply the corresponding GPM per acre by the number of acres you are irrigating.
For example, if you irrigate 120 acres with 4 GPM per acre, 480 GPM  are required to apply 0.21 inches per day, 1.50 inches per week, and 6.40 inches in 30 days.
Mainline pipe size influences the total operating cost.
Smaller pipe sizes, while less expensive to purchase, may have higher water flow friction pressure loss, resulting in higher energy costs.
Plan new center pivots to operate at minimum operating pressure to
 Table 2.
Daily and seasonal irrigation capacity.
minimize pumping cost.
For a pivot nozzled at 1,000 GPM, rules of thumb are as follows.
Each additional 10 psi pivot pressure requires approximately 10 horsepower.
Each additional 10 psi pivot pressure increases fuel costs about $0.35 per hour  at natural gas costs of $3.00 per MCF.
At $0.07 per KWH for electricity, the cost is $0.60 per hour  for each additional 10 psi pressure.
It costs $0.48 per hour  for each additional 10 psi pressure for diesel priced at $0.80 per gallon.
GPM/	Inches in irrigation days
 acre	Inch/day	Inch/week	30	45	60	80	100
 1.5	.08	.55	2.4	3.8	4.8	6.4	8.0
 2.0	.11	.75	3.2	4.8	6.4	8.5	10.6
 3.0	.16	1.10	4.8	7.2	9.5	12.7	15.9
 4.0	.21	1.50	6.4	9.5	12.7	17.0	21.2
 5.0	.27	1.85	8.0	11.9	15.9	21.2	26.5
 6.0	.32	2.25	9.5	14.3	19.1	25.4	31.8
 7.0	.37	2.60	11.1	16.7	22.6	29.7	37.1
 8.0	.42	2.97	12.7	19.1	25.4	33.9	42.4
 
 Table 3 lists friction pressure losses for different mainline sizes and flow rates.
Total friction pressure in the pivot mainline for quarter-mile systems  on flat to moderately sloping fields should not exceed 10 psi.
Therefore:
 For flows up to approximately 750 GPM, 6 5/8-inch diameter mainline can be used.
Friction pressure loss exceeds 10 psi when more than 575 GPM is distributed through 6-inch mainlines.
Some 8-inch spans should be used when 800 GPM or more are delivered by a quarter-mile system.
For center pivots 1,500 feet long , 6 5/8-inch mainline can be used for 700 GPM while keeping friction pressure loss under 10 psi.
Some dealers may undersize the mainline in order to reduce their bids, especially when pushed to give the best price.
Check the proposed design printout.
If operating pressure appears high, ask the dealer to provide another design using proportional lengths, usually in spans, of larger pipe, or to telescope pipe  to reduce operating pressure.
Table 3, section C shows how friction and operating pressure for half-mile systems can be reduced with size 8and 10-inch mainline pipe.
Saving money on the initial purchase price often means paying more in energy costs over the life of the system.
Telescoping involves using larger mainline pipe at the beginning and then
 Table 3.
Approximate friction loss  in center pivot mainlines.
Mainline pipe diameter, inches
 6	6 5/8	8	10
 Flow rate, GPM	Mainline pressure loss, psi
 800	18	11	4
 900	23	14	5
 1000	28	17	7
 1100	33	20	8
 1200	39	24	9
 600	13	8	3
 700	16	10	4
 800	21	13	5
 900	26	16	6
 1600	134	83	31	10
 2000	125	48	15
 smaller sizes as the water flow rate  decreases away from the pivot point.
Typical mainline sizes are 10, 8 1/2, 8, 6 5/8 and 6 inches.
Mainline pipe size governs options in span length.
Span length options are usually:
 100 to 130 feet for 10-inch;
 130 to 160 feet for 8 1/2and 8-inch; and
 160 to 200 feet for 6 5/gand 6-inch.
Telescoping mainline pipe size is a method of planning a center pivot for minimum water flow friction loss and low operating pressure, and thus, lower pumping costs.
Telescoping uses a combination of pipe sizes based on the amount of water  flowing through.
Telescoping is usually accomplished in whole span lengths.
Its importance increases with both higher flow rates  and longer center pivot lengths.
Dealers use computer telescoping programs to select mainline pipe size for lowest purchase price and operating costs.
If your dealer does not offer this technology, request it.
Table 4 shows examples of telescoping mainline size to manage friction pressure loss.
Example 1 shows that for a center pivot 1,316 feet long, fric-
 Table 4.
Telescoping to reduce mainline friction pressure with outlets spaced at 60 inches.
Feet of mainline size
 GPM	10-inch	8 1/2-inch	8-inch	6 5/8-inch	Total feet	Friction pressure PSI
 1100	0	0	0	1316	1316	19
 1100	0	0	640	676	1316	10
 2500	0	0	1697	927	2624	73
 2500	0	897	800	927	2624	63
 2500	897	o	800	927	2624	48
 2500	1057	640	540	387	2624	32
 2500	1697	0	540	387	2624	25
 tion pressure loss is reduced from 19 to10 psi by using 640 feet of 8-inch mainline rather than all 6 5/8-inch to deliver 1,100 GPM.
Example 2 lists friction pressure losses for various lengths and combinations of mainline pipe size for the delivery of 2,500 GPM by a 2,624-foot system irrigating 496 acres.
Friction pressure loss is reduced from 73 to 25 psi by using more 10and 8and less 6 5/8-inch mainline pipe.
When designing your system, compare the higher cost of larger mainline pipe to the increased pumping costs associated with smaller pipe.
Pressure regulators are "pressure killers." They reduce pressure at the water delivery nozzle so that the appropriate amount of water is applied by each applicator.
Selection of nozzle size is based on the rated delivery psi of the pressure regulators.
Nozzles used with 10 psi regulators are smaller than those used with 6 psi regulators when the same amount of water is applied.
Low rated  pressure regulators, if used, allow center pivot design to be appropriate at minimum operating pressure.
Pressure regulators require energy to function properly.
Water pressure losses within the regulator can be 3 psi or more.
So, entrance  water pressure should be 3 psi more than the regulator rating.
Six-psi regulators should have 9 psi at the inlet; 10-psi regulators, 13 psi; 15-psi regulators, 18 psi; and 20-psi regulators, 23 psi.
Regulators do not function properly when operating pressure is less than their rating plus 3 psi.
Pressure regulator operating inlet pressure should be monitored with a gauge installed upstream adjacent to the regulator in the last drop at the outer end, and should be checked when the machine is upslope.
Another gauge located in the first drop in span Elevation change one will monitor operating pressure Feet when the center pivot is located on 2.3 downslope terrain.
Pressure regulator psi rating influences system design, appropriate operating pressure, the total energy requirements, and the costs of pivot irrigation.
As with other spray and sprinkler systems, pressure regulators are not necessarily needed for all sites.
Table 5
 shows how variations in terrain elevations influence mainline operating pressure.
Elevation changes in the field have the largest impact with lower design pressures.
From the first to last drop on a pivot, the operating pressure at the nozzle should not vary more than 20 percent from the design operating pressure.
Without regulators, operating pressure and pumping cost usually will not increase significantly if the elevation does not change more than 5 feet from the pad to the end of the pivot.
Where elevation changes are greater than 5 feet, the choice is to increase operating pressure  or to use pressure regulators.
This decision is site specific and should be made by comparing the extra costs of pressure regulators to the increased pumping costs without them..
Where the water flow rate, and thus the operating pressure, vary significantly during the growing season, perhaps from seasonal variations in groundwater pumping levels, the design flow rate  and the use of pressure regulators should be evaluated carefully.
If water pressure drops below that required to operate the regulators, then poor water application and uniformity will result.
In contrast, if the design operating pressure is high, pumping costs will be unnecessarily high.
When operating pressure decreases to less than required, the solution is to renozzle for the reduced gallons per minute.
The amount of water flow in the mainline decreases or increases operating pressure for the nozzles installed.
Table 5.
Percent variation in system operating pressure created
 by changes in land elevation for a quarter-mile pivot.
Maintain
 less than 20 percent variation.
System design pressure *
 6	10	20	30	40
 1	16.5	10.0	5.0	3.3	2.5
 4.6	2	33.0	20.0	10.0	6.6	5.0
 6.9	3	50.0	30.0	15.0	10.0	7.5
 9.2	4	40.0	20.0	13.3	10.0
 11.5	5	50.0	25.0	16.6	12.5
 13.9	6	30.0	20.0	15.0
 16.2	7	23.3	17.5
 18.5	8	26.6	20.0
 *pressure at the nozzle
 There are various types of spray applicators available, each with pad options.
Low-pressure spray applicators can be used with flat, concave or convex pads that direct the water spray pattern horizontally, upwards and downwards at minimum angles.
Spray applicator pads also vary in the number and depth of grooves they have, and, thus, in the size of water droplets they produce.
Fine droplets may reduce erosion and runoff, but are less efficient because of their susceptibility to evaporation and wind drift.
Some growers prefer to use coarse pads that produce large droplets, and control runoff and erosion with agronomic and management practices.
There is little published data on the performance of various pad arrangements.
In the absence of personal experience and local information, following the manufacturer's recommendations is likely the best strategy in choosing pad configuration.
Pads are very inexpensive.
Some growers purchase several groove configurations and experiment to determine which works best in their operation.
High-pressure impact sprinklers mounted on the center pivot mainline were prevalent in the 1960s when energy prices were low and water conservation did not seem so important.
Now, high-pressure impacts are recommended only for special situations, such as the land application of wastewater, where large nozzles and high evaporation can be beneficial.
Impact sprinklers are usually installed directly on the mainline and release water upward at 15 to 27 degrees.
Undistorted water pattern diameters normally range from 50 to more than 100 feet.
Water application losses average 25 to 35 percent or more.
Lowangle, 7-degree sprinklers reduce water loss and pattern diameter somewhat, but do not significantly decrease operating pressure.
End guns are not recommended because they are higher volume  impact sprinklers with lower application and distribution efficiencies and high energy requirements.
Very few center pivots in Texas are now equipped with impact sprinklers.
There are improved applicators and design technology for more responsible irrigation water management.
These new applicators operate with low water pressure and work well with current center pivot designs.
Low-pressure applicators require less energy and, when appropriately positioned, ensure that most of the water pumped gets to the crop.
The choice is which low-pressure applicator to use and how close to ground level the nozzles can be.
Generally, the lower the operating pressure requirements the better.
When applicators are spaced 60 to 80 inches apart, nozzle operating pressure can be as low as 6 psi, but more applicators are required than with wider spacings.
Water application is most efficient when applicators are positioned 16 to 18 inches above ground level, so that water is applied within the crop canopy.
Spray, bubble or direct soil discharge modes can be used.
Field testing has shown that when there is no wind, low-pressure applicators positioned 5 to 7 feet above ground can apply water with up to 90 percent efficiency.
However, as the wind speed increases, the amount of water lost to evaporation increases rapidly.
In one study, wind speeds of 15 and 20 miles per hour created evaporative losses of 17 and 30+ percent, respectively.
In another study on the southern High Plains of Texas, water loss from a linear-move system was as high as 94 percent when wind speed averaged 22 miles per hour with gusts of 34 miles per hour.
Evaporation loss is significantly influenced by wind speed, relative humidity and temperature.
The following sections describe three types of lowpressure application systems that can significantly reduce operating pressure and deliver most of the water pumped for crop production.
With Mid-Elevation Spray Application , water applicators are located approximately midway between the main-
 on tall crops such
 as corn and sugar
 extend down to the
 should be used in
 on the type of
 Figure 5.
Drop arrangement.
ment selected.
While some applicators require 20 to 30 psi operating pressure, improved designs require only 6 to10 psi for conventional 8 1/2to 10-foot mainline outlet and drop spacing.
Operating pressures can be lowered to 6 psi or less when spray applicators are positioned 60 to 80 inches apart.
With wider spacings, such as for wobbler and rotator applicators, manufacturers' recommended nozzle operating pressure is greater.
Research has shown that in corn production, 10 to 12 percent of the water applied by above-canopy irrigation is lost by wetting the foliage.
More is lost to evaporation.
Field comparisons indicate that there is 20 to 25 percent more water loss from MESA abovecrop-canopy irrigation than from LESA and LEPA within-crop-canopy center pivot systems.
Low Elevation Spray Application  applicators are positioned 12 to 18 inches above ground level, or high enough to allow space for wheel tracking.
Less crop foliage is wet, especially when planted in a circle, and less water is lost to evaporation.
LESA applicators are usually spaced 60 to 80 inches apart, corresponding to two crop rows.
The usual arrangement is illustrated in Figure 6.
Each applicator is attached to a flexible drop hose, which is connected to a gooseneck or furrow arm on the mainline.
Weights help stabilize the applicator in wind and allow it to work through plants in straight crop rows.
Nozzle pressure as low as 6 psi is best with the correct choice of water applicator.
Water application efficiency usually averages 85 to 90 percent, but may be less in more open, lower profile crops such as cotton.
LESA center pivots can be converted easily to LEPA with an applicator adapter that includes a connection to attach a drag sock or hose.
Figure 6.
Drops with LESA applicators.
Figure 7.
LESA applicator.
The optimal spacing for LESA drops is no wider than 80 inches.
With appropriate installation and management, LESA drops spaced on earlier, conventional 8 1/2to 10-foot spacing can be successful.
Corn should be planted in circle rows and water sprayed underneath the
 primary foliage.
Some growers have been successful using LESA irrigation in straight corn rows at conventional outlet spacing when using a flat, coarse pad that sprays water horizontally.
Grain sorghum and soybeans also can be planted in straight rows.
In wheat, when plant foliage causes significantly uneven water distribution, swing the applicator over the truss rod to raise it.
Low Energy Precision Application  irrigation discharges water between alternate crop rows planted in a circle.
Water is applied with:
 applicators located 12 to 18 inches above ground level, which apply water in a "bubble" pattern; or
 drag socks or hoses that release water on the ground.
Socks help reduce furrow erosion; double-ended socks are designed to protect and maintain furrow dikes.
Drag sock and hose adapters can be removed from the applicator and a spray or chemigation pad attached in its place when needed.
Another product, the LEPA "quad" applicator, delivers a bubble water pattern  that can be reset to optional spray for germination, chemigation and other in-field adjustments.
LEPA applicators typically are placed 60 to 80 inches apart, corresponding to twice the row spacing.
Thus, one row middle is wet and one is dry.
Dry middles allow more rainfall to be stored.
Applicators are arranged to maintain a dry row for the pivot wheels when the crop is planted in a circle.
Research and field tests show that crop production is the same whether water is applied in every furrow or in alternate furrows.
Applicator nozzle operating pressure is typically 6 psi.
Field tests show that with LEPA, 95 to 98 percent of the irrigation water pumped gets to the crop.
Water application is precise and concentrated, which requires a higher degree of planning and management, especially with clay soil.
Center pivots equipped with LEPA applicators provide maximum water application efficiency at minimum operating pressure.
LEPA can be used successfully in circles or in straight rows.
It is especially beneficial for low profile crops such as cotton and peanuts, and even more beneficial where water is limited.
Converting Existing Pivots to LEPA
 Water outlets on older center pivot mainlines are typically spaced 8 1/2 to 10 feet apart.
Because LEPA drops are placed between every other crop row, additional outlets are needed.
For example, for row spac-
 Figure 8.
Double-ended sock.
Figure 9.
LEPA bubble pattern.
ings of 30 inches, drops are needed every 60 inches.
Likewise, for 36-inch row spacings, drops are placed every 72 inches.
Two methods can be used to install additional drops and applicators: 1) converting the existing outlets with tees, pipe and clamps; or 2) adding additional mainline outlets.
Installation is quicker if a platform is placed underneath the pivot mainline.
The platform can be planks placed across the truss rods or the side boards of a truck.
A tractor equipped with a front end loader provides an even better platform.
Using Existing Outlets.
First, the existing gooseneck is removed and crosses, tees or elbows are connected to the mainline outlets as needed.
Galvanized or plastic pipe is cut to extend from the outlet point to the drop location.
A galvanized elbow is used to connect the drop to the extension pipe.
This elbow should be clamped to the mainline to maintain the drop position.
Figure 10.
Multi-functional LEPA head.
Figure 11.
Adding drops.
Adding Outlets.
It is less costly to convert to LEPA by adding outlets than to purchase the tees, plumbing, clamps and labor required to convert existing outlets.
New mainline outlets can be installed quickly using a swedge coupler made of metal alloy.
An appropriate size hole is drilled into the pivot mainline at the correct spacing.
The swedge coupler is then inserted into the hole.
The manufacturer recommends that a small amount of sealant be used with the coupler to ensure a leak-proof connection.
A standard hydraulic press  is attached to the coupler with a special fitting that screws into the coupler.
The press is used to compress the coupler against the inside of the mainline pipe to make a water-tight seal.
The swedge coupler compresses quite easily; be careful not to over-compress the coupler.
Regular goosenecks or furrow arms are then screwed into the coupler.
Figure 12.
Drilling for swedge coupler.
Figure 13.
Installing swedge coupler.
Figure 14.
Swedge coupler installed.
Outlets also can be added by welding threaded 3/4inch female couplings into the existing mainline.
Since welding destroys the galvanized coating, welded couplings should be used only on ungalvanized main lines.
As with the swedge coupler, goosenecks and drops can be used with the welded couplings.
Other Conversion Tips.
When water is pumped into a center pivot, it fills the mainline and drops.
The weight of the water causes the pivot to "squat." With 160-foot spans, the pivot mainline will be lowered approximately 5 inches at the center of the span.
Likewise, a 185-foot span will be about 7 inches lower at the center when filled with water.
The length of the hose drops should be cut to account for this change so that all LEPA heads are about the same height above the ground when the system is running.
Center pivot manufacturers can provide appropriate drop hose cut lengths.
Goosenecks or furrow arms and drops are installed alternately on each side of the mainline to help equalize stresses on the pivot structure for high profile crops.
Also, when crops are not planted in a circle, having drops on both sides of the mainline helps prevent all the water from being dumped into the same furrows when the system parallels crop rows.
A permanently installed, continuously functioning flow meter measures the actual amount of irrigation water applied, and is highly recommended.
It is used in conjunction with the design printout for irrigation water management.
In addition, properly located pressure gauges monitor system performance and, in combination with the flow meter, provide immediate warning of water deficiency and other system failures.
Two pressure gauges are needed on the center pivot, one at the end of the system, usually in the last drop upstream from the applicator or regulator, and one at the pivot point.
A third one in the first drop of span one will monitor operating pressure when the machine is downslope in relation to the pivot point.
On older equipment, conventional mainline outlet spacings were 8 1/2 to 10 feet.
New center pivots should have 60or 80-inch mainline outlet spacings, even if this reduced spacing is not required by the water applicator initially selected.
Manufacturers continue to develop more efficient applicators designed to be spaced closer together to achieve maximum irrigation efficiency and pumping economy.
Ordering your pivot with a closer mainline outlet spacing will ensure that it can be quickly and inexpensively equipped with a new applicator design in the future.
Retrofitting mainline outlet spacing typically costs $5,000 to $7,000 more than when the spacing is specified with the initial purchase.
As with any other crop production investment, a center pivot should be purchased only after careful analysis.
Compare past crop production per acre-inch of irrigation applied to the projected production with center pivot ; also consider how much water is available.
Then answer the question: Will a center pivot cost or make money in my operation?
Remember, personal preference is one of the most important considerations.
Pivot management is centered around knowing how much water is applied in inches.
The system design printout includes a precipitation chart that lists total inches applied for various speed settings on the central control panel.
If a precipitation chart is not provided , contact the dealer who first sold the pivot to obtain a copy.
Dealers usually keep copies of the computer design printout indefinitely.
When a precipitation chart is not available, use Table 6 to identify the irrigation amount based on flow rate and time required to complete a circle.
For other sizes of pivots or travel speeds, irrigation inches can be calculated using the first equation below.
Keep in mind that the equations assume 100 percent water application efficiency.
Reduce the amounts by 2 to 5 percent for LEPA, 5 to 10 percent for LESA, 20 percent for MESA, and 35 to 40 percent for impact sprinklers.
Calculations for other length pivots can be made using the formulas below.
1.
Inches applied = Pivot GPM X hours to complete circle 450 X acres in circle
 2.
Acres per hour =
 Acres in circle Hours to complete circle
 3.
End tower speed in feet per hour = Distance from pivot to end tower in feet X 2 X 3.14 Hours to make circle
 4.
Number of feet the end of machine must move per acre = 87,120
 Distance  from pivot to outside wetting pattern
 Runoff from center pivot irrigation can be controlled by changing the optional speed control setting to match water application to soil infiltration.
Agronomic methods of runoff control include furrow diking , farming in a circular pattern, deep chiseling of clay sub-soils, main-
 Table 6.
Inches of water applied by a 1,290-foot center pivot*
 with 100 percent water application efficiency.
Pivot	Hours to complete 120-acre circle
 GPM	12	24	48	72	96	120
 400	0.09	0.18	0.36	0.53	0.71	0.89
 500	0.11	0.22	0.44	0.67	0.89	1.11
 600	0.13	0.27	0.53	0.80	1.06	1.33
 700	0.16	0.31	0.62	0.93	1.24	1.55
 800	0.18	0.36	0.71	1.07	1.42	1.78
 900	0.20	0.40	0.80	1.20	1.60
 1000	0.22	0.44	0.89	1.33	1.78
 1100	0.24	0.49	0.98	1.47	1.95
 feet/hour	667	334	167	111	83
 Acres/hour	10	5	2.5	1.7	1.3
 *1,275 feet from pivot to end tower + 15-foot end section
 taining crop residue, adding organic matter, and using tillage practices that leave the soil "open."
 Farming in the round is one of the best methods of controlling runoff and improving water distribution.
When crops are planted in a circle, the pivot never dumps all the water in a few furrows as it can when it parallels straight rows.
Circle farming begins by marking the circular path of the pivot wheels as they make a revolution without water.
The tower tire tracks are then a guide for laying out rows and planting.
If the mainline span length  does not accommodate an even number of crop rows, adjust the guide marker so that the tower wheels travel between crop rows.
Furrow diking is a mechanical tillage operation that places mounds of soil at selected intervals across the furrow between crop rows to form small water storage basins.
Rainfall or irrigation water is trapped and stored in the basins until it soaks into the soil, rather than running off.
Furrow diking reduces runoff and increases yields in both dryland and irrigated crops.
A similar practice for permanent pastures, called chain diking, involves dragging a chain-like implement that leaves depressions to collect water.
Maximum crop production and quality are achieved when crops are irrigated frequently with amounts that match their water use or ET.
Irrigating twice weekly with center pivots is common.
Texas has three PET 
 weather station and crop water use reporting networks, located at Amarillo, College Station and Lubbock.
They report daily crop water use based on research.
One strategy used by growers is to sum the daily crop water use  reported during the previous 3 to 4 days and then set the pivot central control panel to apply that amount of water.
2.00 The daily crop water use reported by the PET networks is for full irriga2.22 tion.
Most center pivots operating on 2.44 the Texas South and High Plains are planned and designed for insufficient capacity  to supply full daily 67 crop water use.
Growers with insuffi1 cient capacity should use a high water management strategy that ensures that the soil root zone is filled with water, by either rainfall, pre-watering or early-season irrigation, before daily crop water use exceeds the irrigation capacity.
Most soils, such as Pullman, Sherm, Olton and Acuff series soils, can store approximately 2 inches of available water per foot of topsoil.
Sandy loam soils typically store 1 inch or more of available water per foot of topsoil.
Sandy soils store less.
The County Soil Survey available from the Natural Resources Conservation Service contains the available water storage capacity for most soils.
Be sure to use the value for the soil at the actual center pivot site.
Soil moisture monitoring is highly recommended and complements ET-based scheduling, particularly when there is rainfall during the irrigation season.
Soil moisture monitoring devices such as tensiometers and watermark and gypsum block sensors can identify existing soil moisture, monitor moisture changes, locate the depth of water penetration, and indicate crop rooting depths.
These three types of sensors absorb and lose moisture similar to the surrounding soil.
Gypsum block and watermark sensors are read with resistance-type meters.
Tensiometers have gauges that indicate soil moisture by measuring soil moisture pressures in units of centibars.
Tensiometers are very accurate, but are most useful in lighter soils that are irrigated frequently.
Watermark sensors respond more quickly and are more accurate than gypsum blocks, but cost more.
Readings may be taken weekly during the early growing season.
During the crop's primary water use
 periods, readings should be taken two or three times each week for more timely management.
Plotting sensor readings on a computer spreadsheet or graph paper is the best method of tracking and interpreting sensor readings and managing irrigation.
An example is shown in Figure 15.
It describes soil moisture measured with gypsum blocks in wheat production.
A single block or tensiometer installed at a depth of 12 to 18 inches will measure moisture in the upper root zone; another installed at 36 inches will measure deep moisture.
Sensors usually are installed at three depths-12, 24 and 36 inches-and at a representative location in the field where the soil is uniform.
They should not be placed on extreme slopes or in low areas where water may pond.
Select a location within
 Figure 15a.
Soil moisture measurements in a wheat field.
Soil moisture should not fall below a reading of 40 to 60 for most soil types.
Figure 15b.
Cumulative ET and total water supplied to the wheat field in Figure 15a.
the next to the last center pivot span but away from the wheel tracks.
Locate sensors in the crop row so they do not interfere with tractor equipment.
Follow manufacturers' recommendations on preparing sensors.
It is essential to have the sensing tip in firm contact with undisturbed soil to obtain accurate readings.
The soil auger used to install sensors must be no more than 1/8 inch larger than the sensing unit.
Chemigation is the application of an approved chemical  with irrigation water through the center pivot.
Chemigation is an improved, advanced concept.
Pesticide and other chemical labels must state whether the product is approved for application in this way.
If so, application instructions are provided on the label.
EPA regulations require the use of specific safety control equipment and devices designed to prevent accidental spills and contamination of water supplies.
Using proper chemigation safety equipment and procedures also aids the grower by providing consistent, precise and continuous chemical injection, thus reducing the amounts  of chemicals applied.
As in Texas, state regulatory agencies may have their own requirements in addition to those of the EPA.
For more information contact your county Extension office or state Department of Agriculture.
Uniformity of application.
With a properly designed irrigation system, both water and chemicals can be applied uniformly, resulting in excellent distribution of the water-chemical mixture.
Precise application.
Chemicals can be applied where they are needed and in the correct concentrations.
Economics.
Chemigation is usually less expensive than other application methods, and often requires a smaller amount of chemical.
Timeliness.
Chemigation can be carried out when other methods of application might be prevented by wet soil, excessive wind, lack of equipment, and other factors.
Reduced soil compaction and crop damage.
Because conventional in-field spray equipment may not be needed, there could be less tractor wheel soil compaction and crop damage.
Operator safety.
The operator is not in the field continuously during applications, so there is less human contact with chemical drift, and less exposure during frequent tank fillings and other tasks.
Skill and knowledge required.
Chemicals must always be applied correctly and safely.
Chemigation requires skill in calibration, knowledge of the irrigation and chemigation equipment, and an understanding of the chemical and irrigation scheduling concepts.
Additional equipment.
Proper injection and safety devices are essential and the grower must be in compliance with these legal requirements.
The application of fertilizers with irrigation water, or fertigation, is often referred to as "spoon-feeding" the crop.
Fertigation is very common and has many benefits.
Most fertigation uses soluble or liquid formulations of nitrogen, phosphorus, potassium, magnesium, calcium, sulfur and boron.
Nitrogen is most commonly applied because crops need large amounts of it.
Keep in mind that nitrogen is highly soluble and has the potential to leach; it needs to be carefully managed.
There are several nitrogen formulations that can be used for fertigation, as shown in Table 7.
Be sure a solid formulation is completely dissolved in water before it is metered into the irrigation system.
This may require agitating the mixture for several hours.
Continue agitating throughout the injection process.
Nutrients can be applied any time during the growing season based on crop need.
Mobile nutrients such as nitrogen can be carefully regulated in the soil profile by the amount of water applied so that they are available for rapid use by the crop.
Nutrients can be applied uniformly over the field if the irrigation system distributes water uniformly.
Some tillage operations may be eliminated, especially if fertilization coincides with the application of herbicides or insecticides.
However, do not inject two chemicals simultaneously without knowing that they are compatible with each other and with the irrigation water.
Groundwater contamination is less likely with fertigation because less fertilizer is applied at any given time.
Application can correspond to maximum crop needs.
There is minimal crop damage during fertilizer application.
Table 7.
Amount of fertilizers needed to apply specific amounts
 Pounds of N per acre
 Kind of fertilizer	20	40	60	80	100
 Pounds per acre of fertilizer needed
 for rate of N listed above
 	60	120	180	240	300
 	98	196	294	392	488
 	44	89	133	177	222
 Gallons per acre of fertilizer needed
 for rate of N listed above
 	6.7	13.4	20	26.8	33.4
 	5.7	11.4	17	22.8	28.5
 	8.9	17.8	26.7	35.6	44.5
 Table 8.
Relative corrosion of various metals after 4 days of immersion in solutions of commercial fertilizers.*
 Fertilizer	PH of	Kind of metal
 solution	Galvanized	Sheet	Stainless	Bronze	Yellow
 iron	aluminum	steel	brass
 Calcium nitrate	5.6	Moderate	None	None	Slight	Slight
 Sodium nitrate	8.6	Slight	Moderate	None	None	None
 Ammonium nitrate	5.9	Severe	Slight	None	High	High
 Ammonium sulfate	5.0	High	Slight	None	High	Moderate
 Urea	7.6	Slight	None	None	None	None
 Phosphoric acid	0.4	Severe	Moderate	Slight	Moderate	Moderate
 Di-ammonium phosphate	8.0	Slight	Moderate	None	Severe	Severe
 Complete fertilizer 17-17-10	7.3	Moderate	Slight	None	Severe	Severe
 *Solutions of 100 pounds of material in 100 gallons of water.
Fertilizer distribution is only as uniform as the irrigation water distribution.
Use pressure gauges to ensure that the center pivot is properly pressured.
Lower cost fertilizer materials such as anhydrous ammonia often cannot be used.
Fertilizer placement cannot be localized, as in banding.
Ammonia solutions are not recommended for fertigation because ammonia is volatile and too much will be lost.
Also, ammonia solutions tend to precipitate lime and magnesium salts, which are common in irrigation water.
Such precipitates can form on the inside of irrigation pipelines and clog nozzles.
The quality of irrigation water should be evaluated before using fertilizers that may create precipitates.
Besides ammonia, various polyphosphates  and iron carriers can react with soluble calcium, magnesium and sulfate salts to form precipitates.
Many fertilizer solutions are corrosive.
Chemigation injection pumps and fittings constructed of cast iron, aluminum, stainless steel and some forms of plastic are less subject to corrosion and failure.
Brass, copper and bronze are easily corroded.
Know the materials of all pump, mixing and injector components that are in direct contact with concentrated fertilizer solutions.
Table 8 describes the corrosion potential of various metals when in direct contact with common commercial fertilizer solutions.
B-1670, "Soil Moisture Management."
 L-2422, "Chemigation Equipment and Safety."
 L-2218, "Pumping Plant Efficiency and Irrigation Costs"
 Actual lowest and highest field elevation irrigated in relation to the pivot point was used in the computer design printout.
Actual measured or reduced flow rate and pressure available by pump or water source was used in the computer design printout.
Friction loss in pivot mainline for quarter-mile-long systems is no greater than 10 psi.
Mainline size is telescoped to achieve selected operating pressure.
Mainline outlets are spaced a maximum of 60 to 80 inches or, alternately, two times the crop row spacing.
Gauges are included at the pad and last drop to monitor operating pressure.
For non-leveled fields, less than 20 percent variation in system design operating pressure is maintained when pivot is positioned at the highest and lowest points in the field.
Pressure regulators were evaluated for fields with more than 5 feet of elevation change from pad to the highest and the lowest point in the field.
Tower wheels and motor sizes were selected based on desired travel speed, soil type and slope, following manufacturer's recommendations
 Operation control provides expected performance.
The dealer provided a copy of the pivot design printout.
Educational programs of the Texas Agricultural Extension Service are open to all people without regard to race, color, sex, disability, religion, age or national origin.
Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 30, 1914, in cooperation with the United States Department of Agriculture.
Chester P.
Fehlis, Deputy Director, Texas Agricultural Extension Service, The Texas A&M University System.
Limited Irrigation Management: Principles and Practices
 Fact Sheet No.
4.720
 Water availability in the western United States is limited and declining.
Declining water supplies, drought, compact compliance, water needs for environmental restoration, and water transferred from agriculture to municipality uses have reduced the water available to irrigated agriculture.
As a result, irrigation management for limited water supplies is increasingly important.
What is limited irrigation?
When water supplies are restricted, SO that full evapotranspiration demands cannot be met, limited irrigation results.
Limited irrigation management are practices that incorporate crop rotations, water management during the vegetative growth stages and farming practices to minimize water stress during the critical crop growth stages.
Reasons for limited water supplies include:
 1) Limited capacity of the irrigation well In regions with limited saturated depth of the aquifer, well yields can be marginal and not sufficient to meet the needs of the crop.
2) Restricted allocation upon pumping In some regions that have experienced declining groundwater levels, restrictions have been implemented to decrease the amount of pumping by producers.
In some instances, the allocations are less than what is required to fully irrigate the crops grown.
3) Reduced surface water supplies or storage In regions that rely on surface water to supply irrigation needs, droughts and water transfers can have a major impact upon the amount of water that is available to producers for irrigation.
When producers cannot apply water to meet the ET of the crop, they must realize that with typical management practices, yields and returns from the irrigated crop
 will be reduced as compared to a fully irrigated crop.
To properly manage the water for the greatest return, producers must have an understanding of how crops respond to water, how crop rotations can enhance irrigation management, and how changes in agronomic practices can influence water needs.
There are several important "pieces to the puzzle" that help to facilitate limited irrigation strategies.
Many of these principles come from dryland water conservation management.
They include: the relationship between grain yield and water use , understanding how water stress impacts crops during several growth stages, crop residue management for water conservation, plant population management, crop rotations to balance water use, and irrigation timing.
These factors will be discussed separately and then combined in actual demonstration/case studies of limited irrigation.
Crop Response to Water
 Evapotranspiration  is the amount of water that is used by the crop and is the driving force behind crop yields.
ET is the sum of evaporation of water from the soil or crop surface and transpiration by the crop.
Potential crop yields typically increase linearly with the amount of water that is used by the crop.
Water stress during critical time periods can result in lower than potential yields.
Crops, such as corn, respond with more yield for every inch of water that the crop consumes as compared to winter wheat or soybeans.
However, crops such as corn require more water for development or maintenance before any yield is produced as indicated by where the yieldET line intersects the X-axis.
Corn requires approximately 10 inches of ET to produce the first increment of yield as compared to 4.5 and 7.5 inches of ET for wheat and soybeans
 Limited irrigation occurs when water supplies are restricted and full evapotranspiration  demands cannot be met.
Changes in agronomic and irrigation management practices can improve net returns.
Crop rotation can extend the irrigation season and allow for longer operation of irrigation systems with proper irrigation management.
No-till can increase the capture and utilization of precipitation and reduce irrigation water needs.
Adding lower-water requirement crops that have different critical times for water, can also reduce irrigation.
*Colorado State University Extension Golden Plains Area regional specialist; Colorado State University research scientist and water quality specialist, and associate professor, soil and crop sciences.
1/2009
 Figure 1: Grain yield vs ET relationship for corn, soybeans and winter wheat from North Platte, NE.
Figure 2: Grain yield vs Irrigation relationship for corn from Elsie, NE.
.
These crops also require less ET for maximum production.
Irrigation is important to increasing ET and grain yields.
Irrigation is used to supplement rainfall in periods when ET is greater than precipitation.
However, not all of the water applied by irrigation is used for ET.
Inefficiencies in applications by the system result in losses.
As ET is maximized, more losses occur since the soil is nearer to field capacity and more prone to losses such as deep percolation.
Impact of Water Stress
 Crops respond to water stress differently at several growth stages.
Many grain crops have little yield response to water stress during the vegetative growth stage and during late reproductive or grain fill growth stages.
However, crops are sensitive to water stress during the reproductive growth stages and yields will be impacted during this time period.
When producers have limited water supplies, but have control over when they can irrigate, limiting water during the growth stages that are least sensitive to water stress while saving water for the critical growth stages can be a valuable strategy to maximize yield return from water.
Figure 3 shows the yield susceptibility of corn through the growing season.
Early water stress has less impact on grain yield as compared to the tassel to silk period.
Water stress reduces transpiration as compared to a non-stressed crop.
Stressing a crop during the time periods when water use is lower limits the total impact of water use reductions as compared to water stress
 during growth stages that have higher potential transpiration rates.
Agronomic Practices Residue Management
 The goal when working with limited water is to capture, store, and preserve every possible source of water in the production system.
These sources include rainfall, snowfall and irrigation water.
Residue management can have a significant impact on increasing the availability of water.
Producers in the Central Plains have long advocated no-till for dryland production.
No-till increases the amount of water stored in the soil due to reduced evaporation from tillage operations, improved infiltration and reduced runoff, and increased snow catch during winter snowstorms.
Changes in tillage management have allowed producers to change rotations from the conventional wheat-fallow rotation to more intensive rotations such as wheat-corn-fallow.
The changes in tillage management can be successfully used in irrigated production for moisture conservation.
After harvest, leaving the residue standing can have a major impact on snow catch.
Nielsen  found that standing sunflower residue increased the amount of snow captured in years with strong drifting storms.
In most years, standing residue accounted for nearly 2 inches in increased soil moisture over flat residue.
In one year, standing residue accounted for nearly 4 more inches of stored soil moisture.
Surface residue during the growing season can also impact water conservation.
Todd et al.
found that wheat residue reduced the amount of evaporation from the soil by nearly 2.5 inches during the growing season for irrigated corn as compared to bare soil.
Most of the savings occurred before the corn crop reached full canopy.
Water savings from corn residue would be expected to be less since it does not cover the soil completely.
Runoff from precipitation is also reduced when surface residue is present.
Residue reduces the impact of rainfall and irrigation on surface sealing, which increases infiltration rates.
As droplets impact the soil surface, they destroy the surface structure which will seal the soil surface and reduce infiltration rates.
Residue protects the soil surface from the impact of these droplets.
Residue also acts as small dams that slow water movement and allow for more time for the water to infiltrate into the soil.
Recommended plant populations for dryland production are less than that for irrigated production.
Populations are lowered to reduce ET by the crop to better match precipitation and stored soil moisture.
However, when considering populations reductions for irrigated corn, populations must be reduced to less than 18,000 plants/acre to reduce ET.
Lamm and Trooien  found that corn grain yields generally increased as plant populations increased from 22,000 plants/acre to 34,000 plants/acre for varying irrigation capacities.
The yield penalty at higher plant populations was small compared to lower
 populations when minimal irrigation was applied.
However, during years with aboveaverage precipitation, higher populations have a greater yield potential.
Crop rotations can have a major impact upon the total water needs by irrigation.
Crop rotations that have lower water use crops such as soybean or winter wheat can reduce irrigation needs.
Schneekloth et al.
found that when limited to 6 inches of irrigation, corn following wheat yielded 13 bu/acre  more than continuous corn.
The increased grain yield following wheat was due to increased stored soil moisture during the non-growing season that was available for ET during the growing season.
Crop rotations also spread the irrigation season over a greater time period as compared to a single crop.
When planting multiple crops such as corn and winter wheat under irrigation, the irrigation season is extended from May to early October as compared to continuous corn, which is predominantly irrigated from June to early September.
Crops such as corn, soybean and wheat have different timings for peak water use.
With low capacity wells, planting the acreage with multiple crops with different peak water need periods allows for water to be applied at amounts and times when each crop needs the water.
The net effect of irrigating fewer acres at any one point in time is that ET demand of that crop can be better met.
Irrigation management can be as needed, rather than in anticipation of crop ET.
With low capacity systems, producers generally begin to irrigate early
 to keep the soil moisture as close to field capacity as possible in anticipation that their system cannot meet crop water needs later during peak water needs.
In regions with allocation systems, irrigation management is critical to maximizing water inputs.
As was discussed earlier, crops respond in a linear relationship to ET.
However, each inch of irrigation does not return the same amount of grain yield as the previous inch of irrigation.
This reduction in response is due to greater losses such as leaching and more water left in the soil as applications approach full ET.
Crops have critical time periods when water is more critical to the grain yield.
Typically, that critical time period is during the reproductive growth stages of those crops.
When water allocation cannot meet full crop ET, water should be saved for the reproductive stages where it will have the most impact.
Grain yields are increased when water is properly timed and applied during the reproductive growth stages.
Although there may be years that preirrigation is needed to refill the soil profile to field capacity, the efficiency of preirrigations is low.
Lamm and Rogers  found that the storage efficiency of nongrowing season precipitation was reduced as the fall available soil water content was closer to field capacity.
Although preirrigation may be needed in years with low precipitation, irrigation decisions are
 better made in the spring to take advantage of non-growing season precipitation.
As was indicated by Nielsen , the use of standing stubble increased the storage efficiency of off-season precipitation.
Lamm and Rogers study involved clean tillage; therefore, storage efficiencies were less than what may be expected with undisturbed fields.
Irrigation capacity on a per-irrigated acre basis is important when considering how many acres to irrigate.
In western Kansas, Lamm  found that net returns to land and management are reduced when all acres are irrigated with less than adequate capacities as compared to reducing irrigated acres and maintaining an adequate capacity.
Potential corn yields are reduced as irrigation capacity is reduced as compared to maintaining an adequate capacity with fewer acres.
Some systems can never meet peak crop ET, even with normal precipitation.
O'Brien et al.
found that when irrigation system capacity was increased from 0.1 inches/day to 0.2 inches per day, corn yields increased by 28 percent.
To achieve this change in capacity per irrigated acre, a producer would have to reduce irrigated acres by 50 percent.
Profitability of increasing the irrigation capacity by reducing irrigated acres increased net returns per irrigated acre by nearly four times.
Even though only half of the acres are irrigated, profits would be more than twice that of when irrigating the entire acreage.
Figure 3: Yield susceptibility to water stress for corn.
Figure 4: Example of daily ET during the growing season.
When irrigation capacities are less than adequate, producer strategies to try to compensate for reduced capacity include pre-irrigation, beginning irrigation earlier in the growing season and not shutting off the system during wet time periods.
Many times, this management results in more irrigation water being applied than what would be required with adequate capacity and less grain yields.
These strategies are used to keep soil moisture at or near field capacity as long as possible into the growing season before ET becomes greater than the irrigation capacity and potential average precipitation.
Economics of Limited Irrigation
 Full irrigation management has the greatest return per acre when water  is not limiting.
However, when system capacities or allocations are limiting, reducing irrigated acres and full irrigation management of a single crop is generally not the optimum choice.
A producer must determine what the difference in economic returns when increasing irrigated acres of a low water use crop at lower than optimum water levels as compared to reducing irrigated acres of a high water use crop such as corn.
Crops such as soybean and wheat have greater net returns at lower amounts of irrigation as compared to corn.
Schneekloth et al.
found that net returns were greater when a threeyear rotation of corn-soybean-wheat was irrigated with a 6 acre-inch/acre/year allocation as compared to a continuous corn rotation.
This was due to the increase in corn grain yields following wheat and the inclusion of lower water use crops such as soybean and wheat which had yields that were closer to fully-irrigated grain yields as compared to corn.
They also found that the variability in net returns was also reduced with a three-year rotation as compared to continuous corn.
This was partly due to less variability in grain yields with the three-year rotation as compared to continuous corn.
As the allocations are reduced, the choice becomes, "Do I further reduce the amount of irrigation on corn and further reduce yields, or do I add a lower water use crop with less water applied in return for applying more water on corn?"
 Table 1.
Average Four-Year Net Returns1 by Management Strategy and Site.
FARM	BMP	LATE	ALLOC
 Site	Net Return 
 Arapahoe	$186.69	$191.70	$212.69	$200.86
 Elsie	$193.55	$193.92	$184.68	$153.86
 Dickens2	$196.30	$198.09	$163.08	$161.57
 Benkelman	$193.52	$209.61	$194.15	$199.15
 All Sites	$191.95	$195.53	$191.66	$173.73
 Schneekloth et al.
found that cropping rotations switched to include lower water use crops such as soybean or wheat as the amount of water that could be pumped was reduced.
As the amount of allocation is reduced, irrigation of corn is reduced to slightly less than that of optimum with little reduction in grain yield and net return.
Schneekloth  found that irrigated acres of lower water use crops do increase in favor of applying more water on fewer acres of corn to maximize the net return.
As the amount of water is reduced further, irrigated corn generally is eliminated from the rotation.
When allocations were reduced to 4 inches per acre, corn was no longer as profitable as irrigating soybean or wheat.
Beginning in 1996, Schneekloth and Norton  initiated an irrigation demonstration project on farmer's fields throughout southwestern Nebraska on varying soil types and production systems.
The purpose of this demonstration project was to educate producers on best management practices  and limited irrigation management techniques that were developed for irrigated corn.
Management practices that were demonstrated included current farmer management with full irrigation , BMP, beginning irrigation during the reproductive growth stage  and a strict allocation of 6 to 10 acre-inches/ acre.
Although yields were generally less for late than compared to Farm or BMP, the net return was only slightly reduced and in some instances greater.
The greatest differences in net returns were on soils with lower water holding capacities such as at Elsie and Dickens.
The
 water applied for LATE management was approximately 30 percent less than current farmer management.
General comments by the cooperators were that they would be able to live with less water and that yields with less water managed properly were more than expected.
Fully-irrigated crop production has greater returns per acre as compared to limited irrigation management.
However, when limited by the amount of irrigation water that can be applied, changes in agronomic and irrigation management practices can improve net returns.
Changes in agronomic practices such as no-till can increase the capture and utilization of precipitation and reduce irrigation water needs.
Other changes may include adding lower water requirement crops that also have different critical times for water.
Use of crop rotations can extend the irrigation season and allow for longer operation of irrigation systems with proper irrigation management.
This allows for producers with low capacity systems to effectively manage the irrigation.
Since fewer acres are irrigated at any one point in time, the ability of that system to meet ET needs of each crop improve.
These management changes can improve yields and stretch limited water supplies.
Water Savings from Crop Residue in Irrigated Corn
 During the past 10-15 years, there has been a great deal of emphasis in sprinkler applications to move closer to the target.
The thinking has been to decrease the exposure to potential evaporation in the air.
At the same time sprinkler manufacturers have produced heads with lower operating pressures producing fewer fine spray particles leaving far fewer particles subject to evaporation.
The result is that application efficiencies have improved.
What remains are the same wet soil surfaces beneath the crop canopies.
We need to spread the water to gain infiltration, but then evaporation from the soil surface takes over after irrigation stops.
It has been assumed that evaporation from the soil surface in irrigated crop canopies is relatively small.
The objective of this paper is to report on some of the research in the area of evaporation from soil surfaces.
Transpiration, or the process of water evaporating near the leaf and stem surfaces, is a necessary function for plant life.
It is literally the final driving force for water flow through the plant.
It provides plant cooling.
Transpiration relates directly to grain yield in the crops we produce.
Transpiration rates are driven by atmospheric conditions and by the crop's growth stage.
As a crop grows it requires more water until it matures and generally reaches a plateau.
Daily weather demands cause fluctuations in transpiration as a result.
Soil water begins to limit transpiration when the soil dries below a threshold generally half way between field capacity and wilting point.
Irrigation management usually calls for scheduling to avoid water stress.
Evaporation from the soil surface may have some effect on transpiration in the influence of humidity in the crop canopy.
However, the mechanisms controlling evaporation from soil are independent of transpiration.
The combined processes of evaporation from soil  and transpiration  are measured together as
 evapotranspiration  for convenience.
Independent measurements of E and T are difficult.
Independent measurements are becoming more important as we strive to tighten management of sprinkler irrigation to achieve more efficient water use.
Field research has shown that in sprinkler irrigated corn as much as 30% of total evapotranspiration is consumed as evaporation from the soil surface.
These results were from bare soil conditions for sandy soils with sprinkler irrigation.
For a corn crop with total ET of 30 inches, 9 inches would be going to soil evaporation and 21 inches to transpiration.
This indicates a window of opportunity if the unproductive soil evaporation component of ET can be reduced without reducing transpiration.
Evaporation from Soil Trends
 Evaporation from the soil surface after irrigation or rainfall is controlled first by the atmospheric conditions and by the shading of a crop canopy if applicable.
Water near the surface readily evaporates and does so at a rate that is only limited by the energy available.
This so called energy limited evaporation lasts as long as a certain amount of water that evaporates, 0.47 in  for sandy soils and 0.4 in  for silt loam soils.
The time it takes to reach the energy limited evaporation depends on the energy available from the environment.
Bare soil with no crop canopy on a sunny hot day with wind receives much more energy than a mulched soil under a crop canopy on a cloudy cool day with no wind.
After the threshold between energy limited and then soil limited evaporation is reached, evaporation is controlled by how fast water and water vapor can move through the soil to the soil surface.
The relationships that have been developed to describe soil limited evaporation are shown in Fig 1 for a silt loam soil.
There is a diminishing rate of evaporation with time as the soil surface dries.
The soil surface insulates itself from drying as it takes longer for water or vapor to move through the soil to the surface.
The challenge for sprinkler irrigation is the high frequency that the soil surface is put into energy limited evaporation.
With twice-weekly irrigation events it is likely that the soil surface will be in the higher rates of energy limited evaporation during the entire growing season.
Only during the early growing season with infrequent irrigations and little canopy development would there be a possibility for lower rates of soil limited evaporation.
Fig.1.
Soil limited evaporation after day 2 as described by E = C*t^-1/2.
Evaporation and Crop Residues
 For many years, crop residues in dryland cropping systems have been credited for suppressing evaporation from soil surfaces.
Evaporation research dates back into the 1930's when Russel reported on work with small canister type lysimeters.
Stubble mulch tillage and Ecofallow have followed in the progression of innovations with tillage equipment, planting equipment, and herbicides to allow for crop residues to be left on the ground surface.
These crop residue management practices along with crop rotations have increased grain production in the Central Plains.
Water savings from soil evaporation suppression has been an essential element.
In dryland management saving 2 inches of water during the fallow period from wheat harvest until planting corn the next spring was important because in meant an increase of 20-25 bushels in the corn crop.
This difference came from the presence of standing wheat stubble during the fallow period versus bare ground.
The question is to what extent water savings could be realized from crop residue management in sprinkler irrigation.
A research project was conducted during the mid 1980's to begin to address this question.
Four canister type lysimeters were placed across the inter-row of sprinkler irrigated corn.
The lysimeters were 6 inches in diameter and 8 inches deep and were filled by pressing the outer wall
 into the soil.
The bottoms were sealed and the lysimeters were weighed daily to obtain daily evaporation from changes in daily weights.
Increases in soil water over time due to elimination of root extraction in the lysimeters were compensated with a procedure of switching a duplicate set of lysimeters immediately after each irrigation or significant rainfall.
When a set of lysimeters was not in field use it was dried and brought to field soil water content immediately before replacement in the field.
Half of the lysimeter treatments were bare and half were covered with flat wheat straw at the rate of 6000 pounds/acre or the equivalent to the straw produced from a 60 bu/acre wheat crop.
The other variable was irrigation frequency.
One treatment was dryland, receiving no irrigation.
The next treatment was limited irrigation, receiving three irrigation events, one during vegetative growth, one during flowering, and one during grain filling.
The last irrigation treatment was full irrigation with nine irrigation events.
The first seven irrigations were delivered at week intervals and the last two and approximately two week intervals.
The sprinkler irrigation system was a solid set equipped with low angle impact heads on a grid spacing of 40 ft X 40 ft.
The corn population varied with the irrigation variable and was appropriate with the expected water application and yield goal for that treatment.
The resulting leaf area, shading, and biomass followed accordingly.
The results of the field study conducted near North Platte Nebraska are in Figures 2 and 3.
The soil for the study was a silt loam.
The first striking result was in the dryland treatment.
The unshaded bare and straw covered lysimeters nearly tracked each other for daily evaporation.
There were only six rainfall events that measured over 0.4 in  of precipitation.
The pattern of cumulative evaporation for the bare dryland treatment indicates brief periods of energy limited evaporation.
This indication is more subtle for the straw covered treatment.
Even more interesting is that the straw mulched treatment has the same evaporation as the bare treatment for dryland management under the crop canopy.
The straw mulch did not play an additional role in reducing the energy limited evaporation beyond the roll of the crop canopy.
For limited irrigation, three irrigation events were added, 2.0, 2.0, and 1.75 in.
depths.
The cumulative evaporation for bare soil, unshaded treatment showed the classic patterns of energy limited-soil limited evaporation.
These patterns were suppressed in the other treatments indicating that the canopy and residue
 Fig.
2.
Cumulative evaporation for dryland.
limited irrigation, and full irrigation management.
prolonged the transition from energy limiting to soil limiting evaporation.
During the last 40 days of the season the mulched unshaded treatment and bare treatment under the canopy closely tracked one another and ended with similar cumulative evaporation.
The singular contribution of the straw mulch and crop canopy, each acting alone, were the same.
However, in limited irrigation straw mulch added a benefit to the canopy effect that was not evident in dryland management.
Full irrigation included nine irrigation events, seven of which were at weekly intervals and two were at two-week intervals.
The pattern of cumulative
 evaporation from the unshaded bare soil treatment indicated periods of both energy and soil limited evaporation.
These patterns are more subtle early in the bare soil treatment under the crop canopy.
The magnitude of unshaded bare soil
 Fig.
3.
Mean daily evaporation for dryland, limited irrigation, and full irrigation management.
evaporation is far greater in the fully irrigated treatment, but the unshaded mulched and bare soil evaporation under the canopy is similar to the limited values.
These latter two treatments also track each other closely as they did in they limited management.
The mulching effect was even greater in the fully irrigated management than the limited and dryland management.
This effect started early and carried on throughout the growing season.
Table 1.
Full growing season evaporation including irrigation and rainfall days.
Year	Bare	Straw	Bare	Straw
 1986	7.6	7.6	4.7	5.2
 1987	8.0	7.1	6.1	5.7
 1986	10.4	8.5	7.6	5.2
 1987	11.3	9.4	8.5	5.7
 1986	15.1	8.5	7.6	3.8
 1987	14.6	9.4	8.5	4.7
 2.
Water	Savings	From	Straw	Cover.
Cumulative evaporation results in figure 2 do not include days with occurrences of irrigation or rainfall.
Measurements were not taken on these days.
Data were collected from June 10 to September 13 in 1986 with 78, 75, and 75 days of collection from dryland, limited irrigation, and full irrigation, respectively.
In 1987, data were collected from May 28 to August 20 with 65, 64, and 59 days of collection, for dryland, limited irrigation, and full irrigation, respectively.
To understand the possible full season implications of this study, the average daily evaporation rates were applied to the missing days of data.
The results are shown in Table 1.
These evaporation values may still be conservative since evaporation rates are highest immediately after wetting.
The potential full season reduction in evaporation by the wheat straw cover is then shown in table 2.
A similar study was conducted in Garden City, Kansas during 2003 in soybean canopy.
Two twelve inch diameter PVC cylinders that held 6-inch deep soil cores were placed between adjacent soybean rows.
The soybean rows were spaced 30 inches apart.
The lysimeters were either bare or covered with corn stover or standing wheat stubble, which were cored into natural field settings.
The treatments were replicated four times and the plots were irrigated twice weekly.
The results are in Table 3.
The field measurements were taken from July 18 until September 6.
A projection of evaporation from July 17 to planting was made to estimate full growing season savings from crop residue covers.
Future research will be carried out to confirm these projections.
However, these results give the same possibilities for reductions in evaporation as the results from the previous Nebraska corn study.
Also, the role of corn stover is shown.
The corn stover in the lysimeters covered 87% of the soil surface, which equivalent t very good notill residue cover.
These results reflect the maximum capability of the residue for evaporation suppression.
Table.
3.
Total evaporation and savings by crop residues in soybean.
Data Period	Pre Data Period	Season
 Surface	Total	Savings	Total	Savings	Savings
 Cover	in	In	in	in	in
 Bare Soil	3.1	4.1* *
 Corn Stover	1.8	1.3	2.4*	1.7*	3*
 Wheat Straw	1.5	1.6	2.1*	2*	3.5*
 No matter how efficient sprinkler irrigation applications become, the soil is left wet and subject to evaporation.
Frequent irrigations and shading by the crop leave the soil surface in the state of energy limited evaporation for a large part of the growing season.
Research has demonstrated that evaporation from the soil surface is a substantial portion of total consumptive use.
These measurements have been 30% of ET for E during the irrigation season for corn on sandy soil.
It has also been demonstrated that crop residues can reduce in half the evaporation from soil even beneath an irrigated crop canopy.
The goal is to reduce the energy reaching the evaporating surface.
We may be talking about seemingly small increments of water savings in the case of crop residues.
The data presented here suggests the potential for a 2.53.5 inch savings in water due to the wheat straw during the growing season.
Dryland research would suggest that stubble is worth at least 2 inches in water savings in the non growing season.
In water short areas or areas where water allocations are below full irrigation, 5 inches of water translates into at least 60 bushels of corn.
During 2003, many irrigators in the Central Plains could have used an extra 5 inches of water.
Irrigation of Safflower in Northern Utah
 L.
Niel Allen, Extension Irrigation Specialist J.
Earl Creech, Extension Agronomist Michael G.
Pace, Agriculture/Horticulture Agent Clark E.
Israelsen, Agriculture Agent
 Most safflower in Northern Utah and Southern Idaho is grown under dryland conditions; however, irrigated safflower can provide higher yields and increase net returns.
Two perceived concerns with irrigated safflower are an increase the severity of Alternaria leaf spot disease and delayed maturity in the fall.
The objectives of the studies were to determine impact of irrigation on safflower yield and Alternaria leaf spot disease.
The study was conducted at the Utah State University Greenville Farm in North Logan, Utah,  in 2013 and 2014.
Research included four irrigation treatments and two fungicide treatments.
Irrigation Treatments :
 1.
No irrigation as a control
 2.
Irrigation at elongation 
 3.
Irrigation at elongation and branching 
 4.
Irrigation at elongation, branching, and early flowering 
 1.
No fungicide application
 2.
One fungicide application
 The experimental design was a randomized complete block split-plot with irrigation as the whole plot factor and fungicide as the sub-plot factor.
Treatments were replicated six times.
The whole plots were 210 feet by 50 feet in
 size and were irrigated by sprinklers spaced 30 feet by 50 feet.
Half of each plot  was treated with a fungicide application during flowering.
Safflower was harvested with a small plot combine after the seed reached 8 percent moisture.
Table 1 is a summary of the monthly activities and crop growth stages.
In both years the first irrigation was midJune and the second and third irrigations were in July.
The fungicide application was in early August.
The results of 2013 and 2014 are presented separately because of the difference in soil moisture conditions, precipitation, weather, and previous years cropping.
Figure 1 shows the 2013 yields for the four irrigation levels.
Safflower yields increased with the amount of irrigation water applied.
A single, early irrigation, increased yields over no irrigation and two irrigations were better than one.
However, little difference existed between two and three irrigations.
This suggests that adequate water availability through flowering is more important to yield than after flowering.
Along with the irrigation data in 2013, soil moisture measurements were taken to a depth of 5 feet at six locations at 2 week intervals to estimate crop evapotranspiration and for irrigation scheduling.
This data, coupled with the irrigation and precipitation, show that crop water use ranged from 8.7 to 19.0 inches with respective yields ranging from 1,705 to 3,920 lbs./acre.
The total water use may be slightly higher, because past research by others indicate that safflower may extract water deeper than 5 feet.
Table 1.
Summary of safflower production management.
April	Fertilized 70 lbs./acre N	Fertilized 70 lbs./acre N
 22nd Herbicide Sonalan at 2 pints/acre	11th Herbicide Sonalan at 2 pints/acre
 25th Planted Variety S-208 at 20 lbs.
per	14th Planted Variety S-208 at 20 lbs.
per acre.
acre.
0.19 inch of rain	2.16 inches of rain
 May	1.77 inches of rain	1.3 inches of rain
 June	11th-14th First Irrigation, elongation	11th-14th First Irrigation, elongation
 Only trace of rain	0.96 inch of rain
 July	2nd Second Irrigation, branching	2nd Second Irrigation, branching
 19th Third Irrigation, flowering	17th Third Irrigation, flowering
 0.25 inch of rain	0.97 inch of rain
 August	9th Fungicide application of Quadris Flowable at	5th Fungicide application Quadris Flowable at 12
 12 OZ.
per acre	OZ.
per acre
 No rain	2.38 inches of rain
 September	0.44 inch of rain	2.16 inches of rain
 October	9th and 21st Harvest	9-th 10th Harvest
 Rain totals for April through September 2.67 inches in 2013 and 9.93 inches in 2014.
Figure 1.
Safflower yields for irrigation levels in 2013.
Photos 1 and 2 show the difference in safflower growth in 2013 due to irrigation.
In Photo 1, the greenest plot in the foreground that is just beginning to flower had two irrigations while the safflower in bloom had no irrigation.
Photo 2 shows differences in growth stages and the number of flower heads resulting from the various irrigation levels.
In 2014, the yields were not as strongly correlated with irrigation due to large differences in the beginning soil moisture between the plots.
The differences in beginning soil moisture correlate with the crop and irrigation practices the previous year.
Soil moisture data were obtained for eight sites in 2014.
At the beginning of the season, total soil moisture ranged from 14.4 to 21.3 inches, with soil moisture depletions up to 7.5 inches from the top 5 feet of soil.
Photo 1.
Safflower development prior to third irrigation.
Safflower in bloom had no and one irrigation, while safflower with two irrigation had very few flowers.
Photo was taken July 18, 2013.
There was a strong correlation between beginning soil moisture and yield; the highest yields were obtained where the soil water was at field capacity at the beginning of the growing season.
In 2014, the soil moisture, coupled with irrigation and precipitation data, indicate that about 19 to 20 inches of water is required for a yield of 4,000 lbs./acre.
The 2014 yields were influenced by previously grown crops described as follows:
 2013 Winter Wheat The yields where the winter wheat was grown the previous year were high regardless of the irrigation level due to full soil moisture profile at planting.
The soil moisture was maintained at optimal levels in 2013 for small grain variety trials.
The crop rotation for that field was fallow -winter grains safflower.
Photo 2.
Safflower development for no irrigation, one irrigation, and two irrigations.
Photo taken July 15, 2013.
Figure 2.
Safflower yields for irrigation levels in 2014.
The legend shows the crop grown the previous year.
2013 Safflower The field where safflower was grown the year before had much lower yield due to depletion of water and nutrients by safflower.
The crop rotation for that field was spring grains  safflower  safflower.
In these plots, yield increased with irrigation except there was no significant yield difference between two and three irrigations.
Spring Grain 2013 The field that was planted to spring grains in 2013 had an average yield that was less than the field planted to winter wheat in 2013, but higher than the field planted to safflower in 2013.
The crop rotation for that field was safflower  spring grains  safflower.
Observations on Management Practices
 Cropping Pattern Safflower is a good crop to follow irrigated crops with shallow root zones.
Safflower develops a deep root zone
 during the year.
We monitored soil moisture to a depth of 5 feet and found that safflower had extracted water from all depths.
Other research indicates that safflower can have a rooting depth much more than 5 feet [1, 2].
In addition to water, the safflower could also access nutrients not available to shallow rooted crops.
In our 2014 research, back-to-back safflower yielded poorly, achieving an average of only 59 percent of the yields of plots following small grain.
Weed Control Weed control is important to irrigated safflower.
The application of the herbicide Sonalan at 2 pints/acre pre-planting effectively controlled most weeds  in 2013.
It is important to incorporate Sonalan into the soil prior to planting.
The weed control was a little less effective in 2014 with kochia weed being a problem.
There are few post applied herbicide labeled for safflower SO it is important to start with weed-free fields.
Planting Plant early to ensure that maturity is reached before fall freezes impact seed maturity.
Our planting occurred in mid-April each year with emergence in later April or early May.
In both years the maturity and moisture content of the seed would allow harvesting in mid-September, although we were unable to harvest until October due to equipment scheduling.
Irrigation Yields of 4,000 lbs.
per acre require about 19 to 20 inches of ET.
This water can come from stored soil moisture, rain, and/or irrigation.
Two irrigations of about 3 inches occurring in in mid-June and the first week of July provided the most benefit to yield.
The irrigation that occurred in mid-July did not significantly increase yield in 2013 or 2014.
Based on observation, soil moisture measurements and yields, providing adequate water during the vegetative growth stages  determines the yield potential of safflower.
Beginning soil moisture was a good indicator of yield in 2014.
Soil water availability during elongation, branching, and flowering is also important.
Other studies indicate that late irrigations after flowering can delay maturity and promote Alternaria in seed heads [2].
Fungicide Application While a single fungicide application reduces Alternaria leaf spot disease symptoms, it had little to no effect on yield  and seed quality.
Each plotted point represents the two yields taken from a single plot.
The cost of fungicide application was $51 per acre.
Figure 3.
Yield of split plots showing yield with and without fungicide treatment.
2013 Results In 2013, the average seed color score for the plots treated with fungicide was 1.53 and the average score for the non-treated plots was 1.6.
The number of irrigations and yield made the most difference in color scores.
In 2013, the average color scores were 1.04, 1.47, 1.72, and 2.0 for zero, one, two and three irrigations, respectively.
Photo 3 shows the coloration difference between fungicide treated and non-treated areas.
2014 Results In 2014, there was no significant yield difference between plots treated with fungicide and nontreated plots.
Due to the wet fall in 2014, all plots had a significant amount of Alternaria by harvest.
The average color score was 5.6, with fungicide treated plots averaging 5.8 and non-treated plots 5.4.
There was a range in color scores in 2014 with scores ranging from 1 to 9.
The low scores are associated with low yields and high scores associated with high yields.
Photo 3.
Coloration differences between non-treated  and fungicide treated safflower in the front.
Taken September 19, 2013.
Different climate and soil conditions in 2013 and 2014 provided an opportunity to study safflower response to irrigation under a wide range of conditions.
In 2013, the highest yields occurred with three irrigations of about 3 inches of water each irrigation; however there was no significant difference in yields between two and three irrigations.
In 2014, the safflower yields were highest in plots where the beginning soil moisture was high, regardless of in-season irrigation management.
In 2014, there was adequate rainfall during the growing season to supplement the soil moisture in plots that had full soil moisture at the beginning of the season to produce high yields.
The soil moisture, irrigation, and yield data indicate that adequate soil moisture during vegetative growth and flowering stage  is important to produce high irrigated safflower yields.
Safflower is a crop that has deep roots and effectively utilizes water from the 5 feet of root zone of the soil and was verified in this research project.
The application of a fungicide did not significantly impact yield and provided only minor improvements in seed quality.
This is because Alternaria leaf spot disease did not became a problem until plant maturity had determined yield.
Water sensors with cellular system eliminate tail water drainage in alfalfa irrigation
 by Rajat Saha, Narendra S.
Raghuwanshi, Shrinivasa K.
Upadhyaya, Wesley W.
Wallender and David C.
Slaughter
 Alfalfa is the largest consumer of water among all crops in California.
It is generally flood-irrigated, so any system that decreases runoff can improve irrigation efficiency and conserve water.
To more accurately manage the water flow at the tail  end of the field in surfaceirrigated alfalfa crops, we developed a system that consists of wetting-front sensors, a cellular communication system and a water advance model.
This system detects the wetting front, determines its advance rate and generates a cell-phone alert to the irrigator when the water supply needs to be cut off, so that tail water drainage is minimized.
To test its feasibility, we conducted field tests during the 2008 and 2009 alfalfa growing seasons.
The field experiments successfully validated the methodology, producing zero tail water drainage.
A lfalfa is a major crop in the western United States, cultivated on 1.1 million acres in California, and it is the largest water user of all the state's crops.
It accounts for nearly 20% to 27% of California's irrigation water use.
Alfalfa  is predominantly flood irrigated , with or without cutting off or "checking" the flow before water reaches the bottom of a row.
In these systems, the alfalfa field is divided into bays, which are separated by parallel ridges or borders.
Water flows down the field's slope as a sheet guided by the ridges.
On steeply sloping lands, the ridges are more closely spaced and may be curved to follow the land's contours.
The check technique is often inefficient in terms of water use and management, because water often runs off at the end of
 To irrigate alfalfa, water is pumped in at the top of rows and flows down to the end.
If the flow is not turned off before it reaches the bottom, substantial runoff can result.
A system utilizing water sensors and cellular communications can help irrigators to minimize such runoff.
the row.
Efficiency can be improved if the water is cut off at the right time, before it reaches the bottom end of the field.
The wetting front  then advances to the end of the field, but runoff is minimized, conserving water and improving application efficiency.
Under current practice, the alfalfa irrigator makes several trips to the field to determine when the wetting front has reached a certain distance from the tail  end of the check before turning off the irrigation.
Even making several trips, the irrigator may miss the wettingfront advance, which results in excessive tail water drainage.
Our research sought to develop an efficient alternative irrigation method.
We investigated a wetting-front advance sensor with a cellular communication system, to detect the arrival of the water at a predetermined location and eliminate the need for several trips to the field.
However, reducing tail water drainage and improving efficiency would still depend on the irrigator's judgment of the cutoff distance.
Cutoff distance and time can be precisely determined using a volume
 balance model..
With this model, irrigation system characteristics  and soil infiltration must be known.
In general, irrigation system characteristics are known or can be obtained easily, but infiltration characteristics are not known without taking field measurements.
As a result, available surface irrigation models, which do not consider local soil infiltration characteristics, cannot be used to determine accurate cutoff times for managing check irrigation.
The alternative we considered was to evaluate infiltration parameters using real-time information on the wetting front's advance provided by sensors in the field.
Upadhyaya and Raghuwanshi  characterized furrow infiltration by the Horton infiltration function and
 represented the trajectory of the wetting front's advance by an empirical exponential function.
A decade later, Saha et al.
published details of a modified Horton infiltration equation that could accurately model the field-observed wetting-front advance in a check-irrigated system.
It seemed possible then to accurately determine irrigation cutoff times by combining a wetting-front sensing system with the water advance model.
Our research tested the feasibility of this approach in alfalfa field trials during the 2008 and 2009 growing seasons.
Our objectives were  to develop and evaluate wetting-front sensors that incorporate a cellular communication system and  to develop a water advance model for managing cutoff irrigation in check-irrigated alfalfa.
and low  when the units were filled with water.
plates.
The diameter of the plates is about 3 inches, and the gap between the two terminals is about 1 inch.
To facilitate drainage, the unit was surrounded by gravel and sand and placed in a plastic container with a hole at the bottom.
The jacket of gravel and sand also helped to avoid clogging the sensor with finetextured soil.
The wire leads were about 6 inches long and extended beyond the sensor jacket, making it easy to connect the sensor to a data acquisition system.
Suitable circuitry was designed to interface the sensors to the data logger.
The data logger was programmed to record sensor responses and the time in Julian day, hour, minute and seconds.
Cellular communication system.
Several components supported the cellular communication system.
The data logger monitored the wetting-front sensors at regular time intervals.
When the resistance between terminals of a particular sensor dropped from high to low, the data logger generated an alert message consisting of the check number, sensor number and water arrival time.
To be sure of the sensor's responsiveness, we performed laboratory tests and recorded the change in resistance under dry and wet conditions.
These tests revealed that the sensor resistance was high  when there was no water inside the sensor units
 Designing a sensing system
 Fig.
1.
The water-arrival, or wetting-front, sensor.
Water sensor.
The task was to develop a sensor that recognized the presence of water within a check.
Our idea was to use two separated metal electrode terminals, between which an electrical circuit would close when water arrived; sudden changes in resistance or voltage at the terminals would then be transmitted to a data logger.
When we talked to local growers, we were advised to develop a sensor that would not interfere with cultural operations such as harvesting, SO we designed one that would be buried less than 2 inches below the soil surface.
We investigated several designs.
The most reliable sensor consisted of two conductive terminals with a fine wire mesh surrounding them, enclosed by plastic
 The wetting-front sensor consists of a plastic container surrounded by a gravel and sand jacket.
Fig.
2.
The cellular communication system contains:  wetting-front sensors,  central module/ data logger,  digital cellular modem,  cellular antenna and  cell phone.
15304009929 09/11/2008 12:08 pm Text: Check 1 Alert!!
Water has reached Water Sensor: WS at time: 09/11/2008 12:08:40.01 Reply More
 Text: Check 2 Alert!!
Water
 has reached Water Sensor:
 WS at time: 09/11/2008
 Text: Check 2 Alert!!
Water
 has reached Water Sensor:
 WS at time: 09/11/2008
 Cellular text alert messages were received as a wetting front reached different sensors during an irrigation on Sept.
11, 2008.
To transmit this message to the irrigator, the data logger was interfaced with a GPRS  or EDGE (Enhanced Data rates for GSM
 Evolution) digital cellular modem.
The modem, a full-duplex Airlink product compatible with AT&T digital cellular networks,
 Saha  showed that the wetting-front advance can be modeled by the following relationship, based on the modified Horton infiltration function:  A = Amax 
 where A is the wetted area  of the alfalfa check; Amax is the maximum area  that can be irrigated with a steady inflow rate, q ; if is the final infiltration rate ; t is the ; elapsed time  since the beginning of irrigation; C is given by I is the magnitude of initial infiltration ; and ho is the average depth of wa-
 ter  above the soil surface during an irrigation event.
Note that ho could be found by multiplying the depth of water at the inlet  by a surface shape factor , such that ho = hi 00.
While the values of 60 range from 0.77 to 0.80 for surface irrigation hydraulics, a value of 0.80 is commonly used for level surfaces.
In surface irrigation, particularly of Yolo silt loam or clayey soils, infiltration is often characterized using the Kostiakov equation, which does not include the steady state infiltration term if.
Therefore, in the present study, if we neglect if , the velocity  becomes constant and can be shown to be :
 Field tests conducted during our investigations have indicated that this assumption of if = 0 is reasonable.
The error introduced due to this assumption in water-arrival time at the field end was always less than 15 minutes.
Equation 2 can be solved for the magnitude of initial infiltration I once the wetting-front velocity is known from sensor recordings, since inflow rate , check width  and average depth of water  are known or measured values.
This value of I can be substituted in equation 3 to obtain irrigation water cutoff time :
 to = 2wyidlithi 
 where to is the time  at which water is to be turned off following its arrival at the sensor, Y-L is the distance  to the tail end of the check from the sensor location and hL is the height of water  when the wetting front arrives at the tail end.
Note that the irrigator selects a value of hL based on an acceptable amount of drainage.
transmitted the alert to the local cellular tower with an 800 MHz 1 dBd Omni cellular antenna, using either the GPRS or EDGE network.
The data string was then sent from the tower to the designated cellular phones of the irrigators in the form of text alerts.
To test the wetting-front sensing system and related water advance model that we developed , we conducted experiments in a conventional floodirrigated alfalfa field of Yolo silt loam soil on the UC Davis campus.
The field contained 48 alfalfa checks, out of which four checks  were selected.
Each check was approximately 720 feet  long and 50 feet  wide, with a slope of 0.01%.
Checks on the field edges were excluded to avoid edge effects.
The two checks adjacent to our test checks were separated by slightly raised.
Apart from the sensors, six flags were also placed in each check , to allow manual monitoring of the water advance rate during irrigation and comparison with the sensor results.
These monitoring locations help in capturing the shape  of the wetting front as well as determine its velocity.
In the control checks, which received conventional flood irrigation, water was allowed to reach the end of the check before the source valve was turned off; in these four cutoff trial checks, water was cut off at a distance predicted by the water advance model, assuming a tail water height of 2 inches.
Seven sets of irrigation were performed during the 2008 growing season between May and October (May 23-24, June 5-6,
 June 26, Aug.
4-5, Aug.
19-20, Sept.
11-12 and Sept.
25-26).
Since one inflow valve irrigated two side-by-side checks  during an irrigation , only one of the two was monitored for ease of operation.
For example, on May 28, 2008, checks A and B were both irrigated, but only check A was monitored.
During each irrigation set, the check to be monitored was selected randomly.
Similarly, two sets of irrigations were performed during the 2009 season ; in the Sept.
12, 2009, irrigation, both the side-by-side checks were monitored.
velocity flow meter.
The time of water arrival at each designated location was recorded either manually  or with a CR 3000 data logger.
In this setup, a CR 3000 data logger can monitor up to six buried sensors two checks simultaneously.
The cellular communication system, designed to generate text alerts when the wetting front reaches individual sensors, worked well.
The communication lag time was less than 5 seconds for all irrigations.
During all of them, inflow was monitored with a portable Doppler flow meter , and drainage was recorded with an area
 between two consecutive monitoring locations along the flow was determined by dividing the distance between them by the time difference in water arrival at these locations.
We plotted the observed versus sensor-predicted wetting-front velocity for all the tests.
The very high R2 value  of about 0.94 between the observed  and sensor-predicted  velocities suggests accurate prediction by the wetting-front sensors when they were placed 25 feet  apart.
The wetting-front arrival time was monitored manually for all nine locations  in each check.
The velocity of the wetting front
 The experimental data was analyzed using the water advance model to obtain initial infiltration  based on the measured values of wetting-front advance
 The wireless system can easily be moved from one location to another, reducing the initial investment necessary to implement the system.
Fig.
3.
Layout of experimental plots, including placement of wetting-front sensors  and flags used to verify sensor-measured velocities.
The horizontal lines divide the fields  into quarters.
The sensors were placed at the three-quarter point, where the water front's velocity is steady.
Fig.
4.
Comparison between  observed and sensor-predicted wettingfront advance velocities and  observed and model-predicted times for the wetting front to reach the cutoff.
velocity obtained from the sensors, inflow rate and average water depth.
This information was used to estimate the cutoff time and the location of the wetting front at the cutoff time.
We compared the observed and modelpredicted times for the wetting front to reach the cutoff point for all 2008 and 2009 irrigations.
The very high R2 0.97) and a slope that is close to 1.0  between the observed and predicted times reconfirms that the cutoff irrigation system developed in this study is reliable.
Furthermore, the conventional flood irrigation resulted in a substantial volume of drainage water loss, between about 5,800 and 10,000 liters per irrigation, whereas our cutoff irrigation system resulted in zero tail water drainage for all irrigations.
After successful testing of the system , local growers were asked for their impressions.
They indicated a strong preference for a wireless system, since rodents often chew wires in the field and installing the
 sensors requires additional field operations.
In response, we developed a completely wireless system.
The single sensor communicates with a central module wirelessly when it senses the wetting front.
The central module can monitor up to 99 wireless wettingfront sensing devices within a 2-mile radius and generate a cell-phone message to the irrigator when water arrives in a specific check at the desired location.
The text message is generated in the same way as in the earlier system, and the wireless system works reliably.
TABLE 1.
Observed and sensor-predicted velocities, predicted wetting-front arrival times and drainage from checks in irrigated alfalfa fields, 2008 and 2009
 Date	May 23	May 24	June 5	June 6	June 26	Aug 4	Aug 5	Aug 19	Aug 20	Sept 11	Sept 12	Sept 25	Sept 26
 Check monitored	A	C	D	B	B	A	C	D	B	B	D	C	A
 Irrigation type	Conventional	Conventional	Conventional	Conventional	Cutoff	Cutoff	Cutoff	Cutoff	Cutoff	Cutoff	Cutoff	Cutoff	Cutoff
 Irrigation start time	7:11	7:04	7:17	7:00	7:20	7:55	7:03	7:07	7:03	7:20	7:14	7:15	7:12
 Average inflow (liters	927	846	952	980	851	866	860	903	898	937	923	840	815
 Sensor-predicted	1.43	1.43	1.19	0.88	0.83	1.45	1.29	1.21	1.11	0.85	1.20	1.96	0.78
 Observed velocity (feet	1.08	1.10	1.07	0.98	0.94	1.45	1.28	1.20	1.17	0.91	1.26	1.77	0.77
 Time water reaches last	13:14	12:28	11:58	12:06	13:43	12:30	12:59	12:40	11:56	13:36	12:36	11:06	14:04
 Distance still to travel	NA	NA	NA	NA	101	50	25	26	17	132	80	41	113
 Predicted time for	NA	NA	NA	NA	15:31	13:04	13:20	13:02	12:11	16:01	13:39	11:29	16:30
 water to reach cutoff
 Observed time for	NA	NA	NA	NA	15:45	13:10	13:22	13:06	12:08	16:15	13:32	11:31	16:37
 water to reach cutoff
 Irrigation end time	16:05	14:57	14:37	14:13	15:45	13:10	13:22	13:06	12:08	16:15	13:32	11:31	16:37
 Observed time of	16:05	14:57	14:37	14:13	16:46	14:37	15:28	15:08	14:05	16:37	14:37	12:35	17:42
 Total drainage 	7,252.0	9,975.5	6,709.1	5,842.1	0	0	0	0	0	0	0	0	0
 Date	Sept 12	Sept 12	Sept 13	Sept 28	Sept 29
 Check monitored	C	D	A	A	C
 Irrigation type	Cutoff	Conventional	Cutoff	Cutoff	Cutoff
 Irrigation start time	7:15	7:15	7:35	7:30	7:27
 Average inflow 	1,392	1,389	975	1,032	1,300
 Sensor-predicted velocity 	0.82	0.84	0.84	1.56	1.74
 Time water reaches last set of sensors	13:15	13:16	13:56	12:33	11:46
 Distance still to travel before reaching cutoff 	85	NA	100	112	54
 Predicted time for water to reach cutoff	14:38	NA	14:59	13:00	12:17
 Observed time for water to reach cutoff	14:21	NA	15:09	13:01	12:17
 Irrigation end time	14:39	14:38	15:09	13:01	12:17
 Observed time of reaching check end	16:23	14:38	16:23	15:11	12:50
 Total drainage 	0	6,520	0	0	0
 The model-based cutoff irrigation system developed in this study can minimize drainage water loss from surface-irrigated alfalfa fields and substantially improve water management.
It was successfully demonstrated to dozens of farmers at the Alfalfa Field Day sponsored by UC Cooperative Extension on May 19, 2010, at the UC Davis Agronomy Field Headquarters.
Our sensor and cellular communication-based cutoff irrigation system is still under development and is not currently being used in California alfalfa fields; it may be commercially available by early 2012.
The wetting-front sensors are inexpensive, about $25 per unit.
The central module costs about $500 and the modem about $200, for a total of between $800 and $1,000.
Moreover, the wireless system can easily be moved from one location to another, reducing the initial investment necessary to implement the system.
With the typical five irrigations per alfalfa sea-
 son, water savings could be about 35,000 to 60,000 liters per acre.
Although the experimental system described eliminates guesswork and minimizes tail water drainage, a simpler system, with one sensor per check, may be attractive to some growers as a starting point.
This system would alert the irrigator when the wetting front arrives at the single sensor.
However, the efficacy of the system in minimizing tail water runoff would entirely depend on the irrigator's judgment on placement of the sensor within the check.
R.
Saha is Assistant Engineer, MBK Engineers, Sacramento; N.S.
Raghuwanshi is Professor, Department of Agricultural and Food Engineering, Indian Institute of Technology, Kharagpur, India; S.K.
Upadhyaya is Professor, Department of Biological and Agricultural Engineering, UC Davis; W.W.
Wallender is Professor, Department of Land, Air and Water Resources, UC Davis; and D.C.
Slaughter is Professor, Department of Biological and Agricultural Engineering, UC Davis.
Using the Water Quality Index for Runoff from Agricultural Fields 
 James Burke Program Associate Crop, Soil, and Environmental Science
 Lawrence Berry Program Technician Crop, Soil, and Environmental Science
 Mike Daniels Professor Crop, Soil, and Environmental Science
 Pearl Webb Program Associate Crop, Soil, and Environmental Science
 Andrew Sharpley Professor Crop, Soil, and Environmental Science
 Bill Robertson Professor Crop, Soil, and Environmental Science
 Karl VanDevender Professor Biological and Agricultural Engineering
 Arkansas Is Our Campus
 Understanding and being able to estimate the fate and transport of nutrients in surface runoff from fields is a key component of agricultural and environmental sustainability.
Runoff water containing residual fertilizers, as well as legacy nutrients in soil can enter adjacent waters and pose significant hazards to the health of aquatic ecosystems.
To mitigate these environmental risks, producers may implement conservation practices, such as planting cover crops, installing grassed waterways, and creating riparian buffers.
The U.S.
Department of Agriculture's National Resource Conservation Service  has created a web-based tool with which farmers and farm advisors can estimate the impacts of various land management strategies on water quality.
How to use WQlag
 The WQIag uses a numerical and unit-less rating system based on a scale of one to 10, with one being associated with the lowest water quality and 10 the highest.
The rating system includes several site specific factors that influence nutrient runoff such as physiochemical soil properties, fertility management, tillage regime, and irrigation strategy.
Figure 1.
The WQlag rating value in relation to overall water quality.
This section requires basic farm information such as state, county, and field acreage for the area analyzed.
The hydrologic unit code can be accessed via county extension and state agricultural agencies.
USDA	United States Department of Agriculture
 Natural Resources Conservation Service
 About	Help	Contact Us
 Runoff Water Quality Index	Version: 1.0.15 Date: 07/03/2013
 State:		County:	HUC:
 Field #:	Field name:	Acres:
 Project date:	5/11/2017	15	Description:
 FACTORS	DESCRIPTION	WQI	RANKING FACTOR	WEIGHTING	WEIGHT
 Field Physical Sensitivity Factors
 Slope 	Get Slope Interaction	
 HS group 	0.00	0.00	0.00
 K-factor 	0.00	0.00	0.00
 OM content 	0.00	0.00	0.00
 Rainfall/Veg Get Rain / Vegetation Interaction	0.00	0.00	0.00
 Duration By Year	By Month	By Season	Year: January December	0.00	0.00
 Application rate		0.00	0.00	0.00
 timing		0.00	0.00	0.00
 timing		0.00	0.00	0.00
 application	Soil condition	/		0.00	0.00	0.00
 STIR	Description /		0.00	0.00	0.00
 Description 	0.00	0.00	0.00
 Irrigation / Tile Drain Management
 Irrigation No irrigation 
 Tile Drain No Tile Drain 
 Runoff Water Quality Index 	0.00
 Get Conservation Practice	Selected	0
 Runoff Water Quality Index  with additional Conservation Practices	0.00
 Project file: 	Open	Report
 Figure 2.
The WQlag rating worksheet.
Nutrient management factors address the impact of fertilizer nitrogen  and phosphorus  application rate and soil condition during fertilizer application.
For "application rate," a farmer can simply state they are following the Land Grant University  recommendations.
High WQIag rankings  are given for zero to lower-than-LGU rates; split applications of N fertilizers during the growing season, along with having slow release technologies; split applications of P fertilizers during the growing season to no P applied; and dry/well-drained soil conditions with fertilizers injected or incorporated in to the soil.
Advanced Integrated Pest Management  is generally considered the most appropriate ranking option, or approach, for this set of factors.
This is defined in WQIag as "primarily pest prevention/avoidance without suppression." However, the method that most farmers use and is recommended by the University of Arkansas is "Basic IPM," which is described as "threshold-based suppression with additional site-specific risk mitigation."
 Highest WQIag rankings for irrigation management are given when the impact of runoff water leaving the field is significantly limited.
These options include using no irrigation water; irrigation with a
 trickle/drip system; irrigation using a level basin with a blocked end; and center pivot irrigation with polyacrylamide.
The "Tile Drain Management" factor is based on the type of tile drain system used and weighted for "Nutrient Management Factors," "Tillage Management Factors" and "Pest Management Factors".
A particular tile drain selection could have an impact on the overall effect of the NTP.
These impacts are expressed as percent increase or decrease of NTP and are factored into the ranking.
The highest WQIag rankings are given when no tile drain is used along with standard density  and high density  tile drains, both having drainage water management included.
As there is currently little tile drainage in production-agriculture systems in Arkansas, this factor is zero for State WQIag assessments.
The sum of all weighted inputs represents the final WQIag rating, which can be saved as a "project file" by WQIag or converted to other output-file formats, such as a PDF, Adobe's Portable Document file.
Benefits of using WQlag
 One of the main benefits of using WQIag is that it provides an opportunity to comparing the risk outcomes different management strategies or scenarios.
Another benefit is the ease of use via the user-friendly interface, where certain information can be accessed using Internet resources such as Web Soil Survey and NRCS's STIR rating system.
These tools can be instructive and beneficial to farmers and producers, as well as enhancing their record keeping skills, as the STIR value requires preceding years of farm management data.
The rainfall/vegetation interaction selection is useful through the locating and processing of data from nearby monitoring stations or customizing precipitation data according to an actual location.
Advanced Integrated Pest Management  is generally considered the most appropriate ranking option, or approach, for this set of factors.
If farmers are confident that their applications are not above or below LGU recommendation, then this selection could serve as a valid point of reference.
In addition, the "Soil Condition/Application" tab, along with the categories "Irrigation/Tile Drain Management" and "Con-
 servation Practices," offer options for various situations that farmers may encounter or techniques they may choose to apply.
Future development of WQIag, linking yield or profit projections with nutrient loss risk, could inform management decisions and conservation/environmental protection versus production/profit tradeoffs.
Current limitations of using WQlag
 A noteworthy limitation concerns the "Field Physical Sensitivity Factors" portion of WQIag.
The percent slope, HS group, K-factor, and OM content values are ideal for mostly level soil surfaces and uniform soil composition as primarily observed in row crop agriculture.
However, fields that have drastic fluctuations in slope and soil types, such as mountainous and hilly topography, will be subjected to selecting the most dominant map unit of that AOI and therefore, use of those values.
This can overlook significant portions of a field that may have drastic impacts on soil and water runoff.
Another limitation of the current WQIag is that it was developed for national use and is still a general framework that will be further refined by individual States to better represent management practices.
For example, some practices unique to Arkansas with respect to cotton and rice production or for irrigation techniques are not included at this time.
Currently, the Division of Agriculture is working with Arkansas NRCS to enhance WQIag to better represent locally important agricultural systems.
A further limitation at the moment, occurs with "Application Rate," where there is an option of "20% more than LGU recommendations." However, if a farmer applied more than 20 percent of the LGU recommendation, this would not be factored in the final WQIag ranking.
Over-fertilizing and its potential water quality impact would not be accounted for.
A final limitation deals with "Pest Management Factors." Although all four pest management options are ideal for row crop settings, they are not appropriate for forage and livestock systems, where intensive
 and even basic pest management practices are rarely employed.
The "Basic Pest Control" option results in the lowest WQI rating for this category and is the only one suitable for forage and livestock production.
Penalizing farmers for choosing this selection seems inappropriate when pest control strategies are not typically a significant part of their operation management.
The WQIag tool concisely combines information from multiple water quality factors into a single, easy to interpret value.
Most of the data can be found by accessing web-based services.
In its current form, the tool is primarily geared for use in row crop settings, where soil characteristics and land magement strategies are generally uniform across fields.
Soil characteristics in forage and livestock operations in mountainous or steeply sloped terrain, tend to lack uniformity, and accurate field information has a greater possibility of being omitted or skewed.
Field Evaluation of Container Nursery Irrigation Systems: Measuring Uniformity of Water Application of Microirrigation Systems1
 Dorota Z.
Haman and Thomas H.
Yeager2
 Performance of microirrigation systems can be evaluated by measuring operating pressures, application rates, and uniformity of water application under nursery conditions.
We will present a simple test to determine the uniformity of water application.
There is an easy test to evaluate water application uniformity.
Measurements of the time required to fill the same container must be performed at a minimum of 18 locations throughout the irrigation zone.
The statistical uniformity nomograph  is based on statistical coefficient of variation and can be used to determine the overall application uniformity.
If the uniformity is low, more than 18 measurements of time  may be necessary to increase the confidence level of the uniformity measurement.
To perform the test you need a small container, such as an empty bottle, and a device that denotes seconds SO you can record the time to fill bottle at each location.
The following steps are required.
Determine how many measurements represent one-sixth of the total locations in the zone.
For example, if a total of 18 measurements is performed, this number is 3.
Figure 1.
Microirrigation Uniformity Nomograph
 1.
Add the lowest three measurements of time  and mark the sum on the x-axis of the nomograph.
2.
Add the highest three measurements of time  and mark the sum on the y-axis of the nomograph.
3.
If the sums do not fit on the scale or if the value is very small SO that it is difficult to read, the sums can be multiplied or divided by a common factor.
2.
Dorota Z.
Haman, professor emeritus, Department of Agricultural and Biological Engineering; and Thomas H.
Yeager, professor, Environmental Horticulture Department; UF/IFAS Extension Gainesville, FL 32611.
4.
Read the water application uniformity at the intersection of the two lines passing through these points.
Assume that water was collected randomly from 18 emitters throughout an irrigation zone.
The time to fill the same bottle was recorded in Table 1.
1.
one-sixth of 18 data points = 3
 2.
102+105+110 = 317 seconds.
Mark this value on horizontal  axis of the nomograph and draw a vertical line through this point.
3.
130+145+150 = 425 seconds.
Mark this value on the vertical  axis of the nomograph and draw a horizontal line through this point.
4.
Read the uniformity of application.
The point of intersection of these lines falls in the section of 80% to 90% that indicates "very good" uniformity of the system.
The uniformity of water application by microirrigation emitters should be at least in the category "very good" , especially if fertilizers are injected into the system.
Low uniformities in microirrigation systems can be due to factors, such as:
 Improper pipe diameters 
 Too high or too low operation pressure
 Emitters not appropriate for system design
 Changes or wear on system components
 Changes in pump output and pressure
Chapter: 50 Calibrating Yield Monitors
 To create a yield map, the location, ground speed, swath width, and rate that the grain is collected must be known.
This paper discusses strategies to improve yield monitor data.
Yield monitor data are used for many purposes, some of these are provided in Table 50.1.
Most current yield monitors use an impact plate to estimate the flow rate of grain at the point where the clean grain elevator discharges grain.
The grain mass is thrown from the top of the clean grain elevator toward the base of the fountain auger.
The impact plate is mounted in this space and intercepts the grain.
A strain gage bridge, which measures weight much like an electric bathroom scale, measures the force of the grain on this plate.
More grain mass means more force on the sensor plate.
While the concept is simple, the actual device is not SO simple.
Anything that changes the impact force will be detected as a change in grain flow rate.
While combining uphill, gravity can force the grain harder against the sensor plate to indicate more flow.
While combining downhill, gravity can reduce the indicated flow because the grain is being thrown upward.
Vibrations will also affect the sensor's signal level, and a combine has lots of vibrations.
The heightened sensitivity of this type of system is one reason it requires careful and regular calibration.
The mass flow rate of the grain in pounds/second is determined using the sensor's calibration equation.
To convert the force on the plate into bushel/acre, precise ground speed, swath width, location, temperature, speed of clean grain elevator, and crop moisture content are needed.
Table 50.1 The importance of yield monitors:
 1.
Comparing corn hybrids.
2.
Developing tile-drainage maps.
4.
Developing production plans.
5.
Conducting on-farm research.
6.
Developing management zones.
7.
Developing profitability maps.
8.
Documenting the impacts of adverse climatic conditions on yield.
Figure 50.1 An impact-style flow-rate sensor using a curved plate and strain gage load cell to measure impact force of grain.
The sensor is installed at the base of the fountain auger where grain leaving the clean grain elevator impacts.
A moisture sensor located on the clean grain elevator or fountain auger is used to measure grain moisture , whereas the differentially corrected global positioning systems  can be used to determine the location of the GPS receiver.
The location is determined by calculating the distance between the satellites and the GPS receiver.
The intersection of these distances is the location of the GPS receiver.
These satellites can be located almost anywhere, and the accuracy of the GPS location is dependent on their distribution.
The highest accuracy occurs when they are distributed across the sky.
Ground speed and swath width multiply together to determine the area being harvested.
Preparing a Yield Monitor
 While the flow rate sensor is the most important component of the yield monitoring system, it is actually the last part of the system that should be calibrated.
Other sensors that should be routinely checked include the vibration, temperature, ground speed, and crop moisture sensors.
To calibrate these sensors follow the manufacturer recommendation.
Some yield monitor systems perform vibration calibration without user intervention, whereas others require this calibration.
This calibration provides a baseline signal for the moisture and mass flow sensor.
The calibration is conducted with an empty grain hopper prior to harvesting grain.
Calibration is conducted by: 1) throttling up the combine; 2) engaging the thresher; and 3) lowering the header.
Repairs or upgrades, such as replacing a drive chain, removing a drive chain link, or replacing an auger and flighting, may change the vibration in the system.
Temperature information is needed to accurately calculate grain mass flow and moisture content.
Temperature calibration should be done prior to starting the combine.
The calibration might require the operator to enter the known outdoor temperature.
The temperature output should be checked periodically during the season.
Some systems do this automatically.
Figure 50.2 Moisture sensor sampling system on the side of the clean grain elevator.
The small auger periodically empties the chamber, which refills from the clean grain elevator to take another sample.
Ground Speed Sensor Calibration
 Ground speed can be determined using the GPS or the combine speedometer.
Systems using DGPS as the speed sensor typically don't require calibration, whereas wheel-rotation based sensors  may require calibration.
Speedometers may not be accurate for many different factors, including if there is a change in the wheel configuration.
Ground speed can be checked when the sensor is operating by determining the amount of time that is required to drive a known distance.
Calibration is conducted by entering the actual distance traveled into the yield monitor display.
The known distance should be measured with a tape measure from the beginning location of a nondriven wheel to its final position.
Crop Moisture Sensor Calibration
 Crop moisture sensors provide information needed to measure the yield at 15.5% moisture, or determine whether additional drying is required.
To calibrate the moisture sensor, 4 to 6 samples of grain are collected from the hopper.
This can be done when calibrating the flow sensor, as described below.
The moisture content samples can be added together into a container such a five-quart pail, or large coffee can.
The moisture content of these samples should be determined using a calibrated sensor, such as the
 moisture sensor at a grain terminal or elevator.
Enter the average of this moisture content value into the yield monitor display prior to entering the load weight for the calibration load, below.
Mass Flow Sensor Calibration
 Mass flow sensor calibration is the last step in the overall yield monitor system calibration and is the most critical.
To avoid harvesting delays, mass flow sensor calibration should be conducted during harvest preparation.
Different crops require different mass flow calibrations and the predicted yields are only as good as the calibration.
For this process select a relatively uniform and level area of the field.
Calibration loads should be collected sequentially in the most uniform portion of a field.
Each load should be loaded into a weigh-wagon or instrumented grain cart, with the true weight of the load entered into the yield monitor mass flow calibration screen.
The rule of thumb for a good calibration is to control what you can control while maintaining as much uniformity in the noncontrollable variables as is possible.
The ground speed, header width utilization, and load size are the three variables that are easiest for the operator to control, while the instantaneous yield and field slope are out of the operator's control.
To maintain the desired uniformity, it is best to collect calibration loads in flat areas with relative uniform high yield.
Each load should contain at least 3,000 pounds of grain.
In 150 bu/acre corn, this requires about 800 feet of travel with an 8-row head, or 520 feet with a 12-row head.
There are a variety of methods that could be used to collect calibration loads that span the full range, including loads collected from high-yield areas and low-yield areas.
This method is less desirable than varying speeds in constant-yield areas and should be avoided.
The recommended number of calibration loads varies by manufacturer, but more calibration loads are generally better if they span the range of yields.
The loads should be collected during the same day and with weather conditions as uniform as possible.
Avoid splitting calibration load collections between two separate days, as the crop conditions might change.
In corn, varieties with higher or lower test weight require new calibration curves.
Collect samples where the combine is traveling at 110%, 100%, 75%, and 50% of the expected harvest speed.
For example, if the typical harvest speed in a high-yield area is 4 mph, speeds of 2, 3, 4, and 4.5 mph could be used to span the range of expected grain flow rates.
For each of the harvest speeds, the amount of grain harvested should be weighed.
If one load were collected at each of these four speeds with full header utilization, the resulting calibration would have four points.
While this is fewer than would be optimal, it will produce a calibration that spans expected flows.
To generate further calibration points, it is possible to collect calibration loads at the same 3 to 4 ground speeds while utilizing only a fraction of the header.
If 4 speeds were used with two possible header utilization settings, the resulting calibration would have eight points.
The harvested grain for measurement should be weighed.
Importance of Multiple Point Mass Flow Calibration
 Imagine that a series of 12 different loads of grain were harvested in a perfectly uniform field.
Each load was collected by selecting a swath width and combine speed that were held constant for that whole load.
Each of those loads would have been acquired with a different, but constant flow rate of grain impacting the flow sensor.
Each flow rate and an associated sensor signal are depicted in Figure 50.3.
Note that they do not form a straight line.
Most combine grain flow sensors are nonlinear.
With lots of calibration points, it is easy to calculate an accurate mathematical model.
If only three points were collected, the model could overestimate or underestimate the yields in high-yield areas of the field.
Figure 50.3 A set of calibration loads that represented a wide variety of flows impacting the combine flow sensor.
Most sensors have a curved relationship between flow and signal voltage.
The chart on the left has three loads and the resulting model provides poor estimates at high flow rates.
PLANT SELECTION FOR WATER CONSERVATION
 Plant selection is one of the most important factors in designing a successful drought-tolerant landscape.
Along with concern about plant size, texture, color and so on, we must be concerned about how a plant will perform from an ecological and horticultural standpoint.
Gardens that thrive for many years are those that are horticulturally sound.
By choosing native plants or plants native to similar climatic zones, you ensure that plants will be adapted to the climate in general.
Next look at specific sites.
Choose moisture-loving plants for wet, poorly drained sites and drought-tolerant plants for hotter or sunnier areas.
Because shade trees require 25 to 30 years to mature, homeowners should plant them before any other vegetation.
A shade tree planted to intercept the hot afternoon southwest sun will provide cooling in the summer and reduce the water needs of understory plants.
The following trees are the most drought-tolerant:
 Acer buergeranum, Trident Maple, 20 to 25 feet; full sun.
Assets: Rounded outline, glossy dark green leaves in summer turning to yellow, orange and red in fall.
ID: Three-lobed leaves are three nerved at base.
Triangular lobes are irregularly serrate.
Use: Very handsome small patio, lawn or street tree: might work well in planter boxes.
Carya ovata, Shagbark Hickory, 60 to 80 feet; full sun.
Assets: Straight, cylindrical trunk with an oblong crown or ascending and descending branches.
Bark has a shaggy character.
ID: Pinnately compound, yellow-green leaves.
Use: Trees for large areas.
This tree has a remarkably deep taproot.
Celtis occidentalis, Common Hackberry, 40 to 60 feet; full sun.
Assets: Ascending-arching branches, often with drooping branchlets.
ID: Dull green leaves with serrate margins and oblique base.
Use: Good for park and large area use.
Susceptible to several disease and insect problems.
Fraxinus pennsylvanica, Green Ash, 50 to 60 feet; full sun.
Assets: Shiny medium to dark green leaves turning yellow in fall.
ID: Pinnately compound, 5 to 9 lanceolate leaflets, pubescent beneath.
Use: Used for street, lawn, golf course and park trees; possibly overused.
Ginkgo biloba, Maidenhair Tree, 50 to 80 feet; full sun.
Assets: Interesting, fan-shaped leaves with brilliant yellow fall color.
ID: Bright green fan-shaped, dichotomously veined leaves.
Use: Excellent city tree.
Plant only males, as females produce malodorous fruit after approximately 20 years.
One of the most primitive trees growing on earth.
Gleditsia tricanthos var.
inermis, Thornless Honeylocust, 30 to 70 feet; full sun.
Assets: Delicate and sophisticated  silhouette casting a light shade.
ID: Pinnately or bipinnately compound leaves with the petiole base swollen around a bud.
Use: Excellent lawn tree for filtered shade but overused.
Gymnocladus dioicus, Kentucky Coffeetree, 60 to 70 feet; full sun.
Assets: Bold winter habit, unique and interesting bark pattern.
ID: Bipinnately compound leaves with ovate, dark green leaflets.
Use: A choice tree for parks, golf courses and other large areas.
Quercus coccinea, Scarlet Oak, 70 to 75 feet; full sun.
Assets: Glossy, dark green foliage changing to scarlet in fall.
ID: Large leaves with "C"-shaped lobes.
Tufts of hair in vein axils.
Use: Lawn, park and golf course tree.
Sophora japonica, Japanese Pagodatree, 50 to 75 feet.
Assets: Broadly rounded crown with compound leaves that cast a light shade.
Covered with creamy white flowers in July through mid-August.
ID: Pinnately compound, lustrous green leaves.
Flowers are 6 to 12 inch terminal clusters.
Use: Last of the large ornamental trees to flower in the summer.
Zelkova serrata, Japanese Zelkova, 50 to 80 feet.
Assets: Vase-shaped tree with dark green leaves and interesting bark.
ID: Sharply serrate, ovate leaves.
Bark is reddish-brown and heavily lenticelled; in old age, often exfoliates.
Use: Very handsome tree, well-suited to lawns, streets, parks and large areas.
Many small trees are understory trees that provide an excellent transition planting between natural and more refined areas of a property.
Small trees used as specimen trees should have many seasons of beauty, such as flower display, foliage effects, fall color, fruit and bark or habit interest.
Acer ginnala, Amur Maple, 15 to 18 feet; full sun to light shade.
Assets: Small tree of rounded outline with lustrous, dark green leaves.
ID: Leaves are doubly-serrate and 3-lobed with the middle lobe much longer than the lateral lobes.
Use: Small specimen, patio, screen, grouping and massing tree.
Crataegus phaenopyrum, Washington Hawthorn, 25 to 30 feet.
Assets: A broadly oval tree with reddish-purple new foliage that changes to lustrous dark green, orange to scarlet fall foliage, white flower clusters and glossy red fruit.
ID: Small, sharply serrate, 3 to 5-lobed leaves.
Use: Excellent single specimen tree or screen.
Syringa reticulata, Japanese Tree Lilac, 20 to 30 feet; full sun and requires well-limed soil.
Assets: White, fragrant flowers in large terminal clusters are extremely showy.
Dark green leaves and cherry-like, reddish-brown bark with horizontal lenticels.
Use: Excellent trouble-free lilac makes a good specimen or street tree.
Viburnum prunifolium, Blackhaw Viburnum, 12 to 15 feet; sun or shade.
Assets: Round-headed small tree with creamy, flat-topped flowers and bluish-black fruit.
ID: Dark green leaves with a stiffly branched growth habit.
Use: Interesting as a small specimen tree or in groups.
Evergreens improve our environment by filtering out air pollutants and road dust.
In addition, they retard water runoff, screen out unsightly views and serve as windbreaks.
Evergreen trees must be placed in locations appropriate for their size and form.
Abies concolor, White Fir, 30 to 50 feet; full sun but tolerates light shade.
Assets: Conical tree, branched to the base with bluish or greyish-green needles.
ID: Flattened needles curve outwards and upwards.
Use: Specimen tree with a softer effect than spruce.
This tolerant tree holds needles longer than any other fir.
Juniperus virginiana, Eastern Red Cedar, 40 to 50 feet; full sun.
Assets: The habit is pyramidal when young and slightly pendulous in old age.
Handsome, reddish-brown exfoliating bark.
Many cultivars are available with interesting habits and foliage colors.
ID: Scale-like leaves overlap and bruised needles smell like a cedar chest.
Use: Cultivars can be used as specimens, windbreaks, shelter belts and hedges.
Picea pungens, Colorado Spruce, 30 to 60 feet; full sun.
Assets: The tree forms a regular, narrow pyramid with stiff horizontal branches.
Cultivars have blue foliage.
ID: Stiff, very prickly needles surround the stem.
Use: Popular as a specimen but it is difficult to combine well with other plants.
Dwarf cultivars are available.
Pinus nigra, Austrian Pine, 50 to 60 feet.
Assets: Lustrous, dark green needles and attractive bark with grey or grey-brown mottled ridges.
ID: Densely pyramidal habit in youth, with two stiff needles in a bundle.
Use: A very hardy tree that makes a good specimen, screen, windbreak or mass planting.
Pinus strobus, White Pine, 50 to 80 feet; tolerates some shade.
Assets: A graceful tree with a soft pyramidal habit and bluish needles.
ID: Slender needles in bunches of fives.
Use: A handsome and ornamental specimen, valuable for parks, estates and small properties.
Also makes a beautiful hedge.
Pinus sylvestris, Scotch Pine, 30 to 60 feet; full sun.
Assets: A picturesque habit develops with age.
Bark on the upper trunk is orangish or orangish-brown.
ID: Needles are in pairs, stiff and twisted with a blue-green color.
Use: Useful as a distorted specimen or in masses.
Shrubs are used in the landscape to provide transition between tall vertical trees and the horizontal plane of the ground.
Shrubs are chosen for habit, foliage, flower or fruit attributes.
The most useful shrubs have more than one season of interest.
If bright blossoms are the only attribute, the plant should be tucked away so it doesn't detract from the landscape once the flowers are gone.
Many of the traditional spring-blooming flowering shrubs such as forsythia, spirea, lilac and weigelia are somewhat drought-tolerant.
One flowering shrub that is not drought-tolerant, doublefile viburnum , can be a very useful indicator plant, for it wilts badly under drought stress.
When this plant begins to wilt, it is time to water your sensitive plants.
The following shrubs are considered drought-tolerant.
Aronia arbutifolia, Red Chokeberry, 6 to 10 feet; full sun or half shade.
Assets: Bright red fruits are born in great abundance along the stems.
ID: Upright multistemmed shrub with even, black-tipped teeth along the leaf margins.
Use: Best in masses.
Chaenomeles speciosa, Common Floweringquince, 6 to 10 feet; full sun or partial shade.
Assets: Flowers which range in color from orange through scarlet to white.
ID: Leaves have large conspicuous stipules at the petiole base.
Use: Effective as a hedge or in a shrub border but has a very short period of interest.
Cornus racemosa, Grey Dogwood, 10 to 15 feet; full shade or sun.
Assets: Multistemmed shrub that forms a thicket.
Grey older wood and light, reddish-brown younger stems compliment each other well.
Pinkish-red inflorescences are effective into December.
ID: Leaves with typical dogwood venation and a dull grey-green color.
Use: Best naturalized in masses and used for its winter character.
Elaeagnus pungens, Thorny Elaeagnus, 10 to 15 feet, sun or shade.
Assets: Fragrant, small white flowers and somewhat evergreen leaves flecked with silver.
ID: Leaves have ruffled margins and the undersides are covered with silver scales.
Use: Good for banks, hedges, screens and natural barriers.
Must be pruned to attain a desirable habit.
Myrica pensylanica, Northern Bayberry, 5 to 12 feet; full sun to half shade.
Assets: Semi-evergreen leaves are aromatic when bruised.
Greyish-white berries cover the stems of female plants from September to the following April.
ID: Obovate leaves have a leathery texture.
Use: Excellent in masses or as part of a border; good salt tolerance.
Pinus mugo var.
mugo, Mugo Pine, less than 8 feet tall; sun or partial shade.
Assets: Prostrate evergreen shrub with medium green needles.
ID: Rigid needles in bundles of two.
Use: A low evergreen shrub for foundations, masses or groupings.
Potentilla fruiticosa, Bush Cinquefoil, 1 to 4 feet; full sun to partial shade.
Assets: Dainty clean foliage and yellow flowers that bloom from June through frost.
ID: Pinnately compound leaves are dark green and somewhat silky.
Use: Good plant for the shrub border, massing, edging or as a facer plant in a foundation.
Adds color to the landscape and many cultivars are available.
Pyracantha coccinea, Scarlet Firethorn, 6 to 18 feet; full sun to partial shade.
Assets: Semi-evergreen shrub with flowers that shroud the plant in white.
Orange-red fruit can be spectacular.
ID: Pyracantha have stiff thorny branches with spines along the stems.
Use: Makes a good informal hedge, barrier plant or espalier.
Rhus typhina, Staghorn Sumac, 15 to 25 feet, half to three-quarters shade or full sun.
Assets: Nice leaf texture and spectacular yellow, orange and scarlet fall color.
ID: Pinnately compound leaves have 13 to 27 leaflets.
Stems are densely covered with velvety hair.
Use: Naturalize or use in masses.
Can be invasive as it suckers freely from the roots.
Viburnum lentago, Nannyberry Viburnum, 15 to 18 feet; sun or shade.
Assets: Creamy yellow flowers and a bluish-black fruit are borne on this large shrub with slender arching branches.
ID: Dark green, finely toothed leaves have winged petioles.
Use: Ideal shrub for naturalizing; works well as a background or screen plant.
Vitex agnus-castus, Chastetree, 8 to 10 feet; full sun.
Assets: Flowers are lilac, fragrant and occur from June through September.
ID: Palmate leaves are greyish-green.
Use: Interesting foliage texture and late-season flowers make a good addition to the shrub border.
Yucca filamentosa, Adam's-needle Yucca, foliage 2 to 3 feet, flowers 3 to 6 feet; full sun.
Assets: Dramatic foliage and showy white flower stalks.
ID: Sword-like leaves have thread-like filaments that curl from the margins.
Use: Best used in a mass for dramatic effect.
The use of any groundcover will help to stabilize the soil, reduce weeds and conserve water.
Most groundcovers are less water demanding than turf.
The following are groundcovers that are particularly drought-tolerant.
Aegopodium podagraria "Variegatum", Bishop's Goutweed, 8 to 10 inches; sun or shade.
Assets: Light green leaves with white margins.
ID: A herbaceous plant with compound leaflets that are divided into threes.
Use: This spreading groundcover can become invasive when used with other plants.
Arctostaphylos uva-ursi, Bearberry, 6 to 12 inches; full sun to part shade.
Assets: Low-growing, glossy leaved, evergreen groundcover with leaves that turn reddish in the fall.
Small, white, urn-shaped flowers appear in late April to May.
Bright red fruit is effective from late July through August.
ID: Small obovate leaves.
Use: One of the prettiest, sturdiest and most reliable groundcovers.
Cerastium tomentosum, Snow-in-Summer, 6 inches; full sun.
Assets: White flowers cover the silver leaves in May and June.
ID: Small linear leaves of this mat-forming herbaceous perennial are covered with white woolly hair.
Use: Groundcover or edging plant.
Cotoneaster dammeri, Bearberry Cotoneaster, 1 to 1 1/2 feet.
Assets: Dark green foliage is semi-evergreen.
Red berries are sparsely produced.
ID: Low, prostrate shrub with small leaves.
Use: Excellent groundcover for banks, gentle slopes, masses, shrub borders or foundations.
Hemerocallis cultivars Daylily, 1 1/2 to 4 feet; full sun or partial shade.
Assets: Trumpet-shaped flowers can be found in almost any color of the rainbow.
ID: Long linear leaves appear in clumps and tall flowering stems extend from the center.
Use: When used in masses, daylilies make a good herbaceous groundcover.
Hypericum calycinum, Aaronsbeard St.
Johnswort, 1 to 1 1/2 feet; full sun to partial shade.
Assets: Bight yellow flowers bloom from June through September.
ID: This semi-evergreen shrub has ascending stems with dark green leaves.
Use: Hypericum makes a good groundcover because it grows quickly and effectively covers an area in a short amount of time.
Mow to the ground to induce new growth each spring.
Juniperus horizontalis, Creeping Juniper, 1 to 2 feet; full sun.
Assets: Low-growing shrub that forms a large mat.
Foliage may be steel-blue turning plum purple in winter.
ID: Most of the leaves are scale-like.
Use: This extremely tolerant groundcover has many cultivars with varying habits and foliage colors.
Sedum sp., Stonecrop, 2 inches to 2 feet; full sun.
Assets: Succulent green leaves and small yellow, white or pink flowers that are borne in showy flower clusters.
ID: Fleshy leaves with shapes that vary between species.
Use: Most sedums are mat-forming groundcovers.
A number of different species are available.
Santolina chamaecyparissus, Lavender Cotton, 1 1/2 to 2 feet; full sun.
Assets: This broad spreading herbaceous perennial has silver-grey, fine-textured foliage and button-like yellow flowers.
ID: The pubescent leaves are pinnately divided into very small segments.
Use: Santolina can be used in the rock garden, as a low hedge or as a groundcover.
Thymus serpyllum, Creeping Thyme, 3 to 6 inches tall; full sun.
Assets: This mat-forming herbaceous perennial has greyish-green leaves and small, fragrant, purple flowers.
ID: The small leaves have a strong mint-like odor.
Use: Thyme makes an excellent groundcover around walks where the aroma is released when it is inadvertently crushed.
Oregon Crop Water Use and Irrigation Requirements
 Water Resources Engineering Team, Department of Bioresource Engineering, Agricultural Experiment Station, and OSU Extension Service, Oregon State University; Diputacin General de Aragn, Servicio de Investigacin Agraria, Zaragoza, Espaa ; U.S.
Department of Agriculture, Office of International Cooperation and Development; and Water Resources Department, State of Oregon
 OREGON CROP WATER USE AND IRRIGATION REQUIREMENTS
 PROJECT LEADER: Richard H.
Cuenca
 PROJECT MANAGER: Jeffery L.
Nuss
 LEAD PROGRAMMER: Antonio Martinez-Cob
 ASSISTANT PROGRAMMER: Gabriel G.
Katul
 Department of Bloresource Engineering Oregon State University Corvallis, Oregon United States
 CO-PRINCIPAL INVESTIGATOR: Jos Ms Facl Gonzlez
 Diputacin General de Aragn Servicio de Investigacin Agraria Unidad de Suelos y Riegos  Zaragoza, Espaa 
 1.2 NET IRRIGATION REQUIREMENTS
 3.1 ETcrop and NET IRRIGATION TABLES
 3.2 ETref CONTOUR MAPS
 4.1 APPLICATION TO SYSTEM DESIGN
 4.2 APPLICATION TO IRRIGATION SCHEDULING
 APPENDIX A.Conversion between English and Systme International  units for quantities applicable to irrigation system design and management.
The Office of International Cooperation and Development of the United States Department of Agriculture and the Oregon State University  Agricultural Experiment Station provided major support for this work through a cooperative project.
This project brought together principal investigators from Oregon State University and the Diputacin General de Aragn in northeast Spain to study crop water requirement estimating methods.
As a result, we decided to revise the irrigation recommendations for Oregon and Aragn province in Spain.
This report is the result of that study.
Valuable assistance was provided by Kelly Redmond, former Oregon State Climatologist and Clint Jensen of the U.S.
Weather Service in Portland, Oregon.
The Oregon State Water Resources Department made a significant contribution to publication costs.
Numerous individuals assisted this project through review of draft report material at various stages of development.
The project team is especially grateful for the cooperation of Hugh Hansen, former Extension specialist and WRAES Editor, Marvin Shearer, former Extension irrigation specialist, Walter Trimmer, current Extension irrigation specialist, all of Oregon State University, and Michael Mattik and Randy Sellig, Oregon State Water Resources Department.
Invaluable secretarial assistance was provided by Joanne Wenstrom, department of Bioresource Engineering at OSU.
Nonpoint Source Pollution in the Illinois River Watershed
 The Arkansas portion of the Illinois River watershed is located in northwest Arkansas and includes part of communities in Benton, Crawford and Washington counties.
The watershed crosses state lines into Oklahoma.
A "watershed" is an area of land where all of the water that drains from it goes to the same place, SO rainwater or snowmelt in this watershed eventually drain to a common location.
The Arkansas side of this watershed encompasses 754 square miles.
An estimated 172,428 people lived in the watershed as of 2010, and the rapid growth in the major urban centers from Fayetteville up to Bentonville is expected to continue.
The population of Benton and Washington counties grew 44.3 percent and 28.8 percent, respectively, from 2000-2010.1 While development often occurs in one city center, the Illinois River Watershed is unique in that it includes multiple cities that have
 Water pollution that comes from multiple sources spread over an area, such as runoff from parking lots, agricultural fields, residential lawns, home gardens, construction, mining and logging, is known as nonpoint source pollution.
As runoff moves across the landscape, it carries natural and manmade substances that can accumulate in waterways and make them uninhabitable for aquatic species or unusable by people.
Potential pollutants include bacteria, nutrients, sediment, hazardous substances and trash.
2 Given the number of potential sources and variation in their potential contributions, these pollutants are not easily traced back to their source.
Illinois River Watershed Data source: GeoStor.
Map created March 2011.
Major streams: Ballard Creek, Baron Fork, Cincinnati Creek, Clear Creek, Evansville Creek, Flint Creek, Illinois River, Moores Creek, Muddy Fork, Sager Creek, Osage Creek.
experienced large population increases and building booms.
Despite the urbanization of this watershed, 50 percent of the land remained grassland and 36 percent forestland as of 2006.3
 This fact sheet is intended to provide a better understanding of the Illinois River Watershed and its place on the state's priority list of 10 watersheds impacted by nonpoint source pollution.
Illinois River Watershed Water Quality Issues
 The primary water quality issues in this watershed represent a complex mix of municipal wastewater discharge, nutrient surpluses and rapid urbanization.
4 Agricultural practices and streambank erosion continue to be a water quality concern in this area, but urban development and road construction have joined the list of water quality concerns in recent years.
The region's historical use of animal manure as a fertilizer has contributed to the state designating the region including this watershed as a "nutrient surplus area." There are regulations on applying poultry litter or commercial fertilizer products to land in the area.
5
 Nitrogen and phosphorus are essential nutrients that support the growth of algae and plants.
Nutrients can threaten water quality when people do not follow best management practices, such as applying the right amount of phosphorus as a fertilizer or using grassy buffers to prevent it from entering runoff water or nearby waterways.
Phosphorus can also enter waterways as part of discharge from water treatment plants, which are regulated by the state and have permits that allow specific amounts of nutrients to be discharged.
There are wastewater treatment plants that discharge in this watershed.
However, phosphorous levels in the Illinois River and Sager Creek have decreased significantly in recent years.
In this watershed, the majority of
 Arkansas' Priority Watershed List for Nonpoint Source Pollution
 Arkansas has used a watershed-based approach to nonpoint source pollution management, allowing the public to guide planning to address water quality concerns.
The Arkansas Natural Resources Commission, or ANRC, administers the Nonpoint Source Pollution Management Program.
The program exists to reduce water pollution through the funding of watershed planning and restoration activities, adoption of voluntary best management practices and the development of technologies that assist in water pollution reduction in Arkansas.
Based on public input and the use of a qualitative risk assessment matrix, ANRC has designated 10 priority watersheds as needing the greatest attention.
The current risk matrix6 identifies the following priority watersheds for 2011-2016: Bayou Bartholomew, Beaver Reservoir, Cache River, Upper Illinois River, L'Anguille River, Lake Conway-Point Remove, Lower Ouachita-Smackover, Poteau River, Strawberry River and Upper Saline.
phosphorus entering waterways comes from nonpoint sources, including runoff from farms and urban developments.
The rapid increase in population growth and increase in construction in the watershed over the past two decades could contribute to the concern for nonpoint source pollution.
7
 These concerns and its border state status led to the Illinois River Watershed being designated as a priority by the Arkansas Natural Resources Commission in the state's 2011-2016 Nonpoint Source Pollution Management Plan.
8
 To encourage continued public input, the University of Arkansas Division of Agriculture's Public Policy Center facilitated a water quality stakeholder forum for the Illinois River Watershed in August 2015.
Unlike many of Arkansas' watersheds, the Illinois River Watershed has a history of active groups working to restore waterways or prevent further pollution.
A watershed management plan was created for this watershed in 2012.
Forum participants expressed continued concern that urban development was the greatest risk to water quality and could set back recent water quality improvement efforts.
They referred to this risk as "urban disturbance," which is their term to describe the pollution associated with increased runoff as a result of urban growth and land use changes.
People who live, work or recreate in this watershed are encouraged to consider community priorities and watershed management plan when addressing water pollution.
The public is also welcome to attend an annual stakeholder meeting where priority watersheds and nonpoint source pollution are discussed.
For more information about nonpoint source pollution and its impact on the Upper Illinois River watershed, contact the Cooperative Extension Service, Arkansas Natural Resources Commission or the Arkansas Department of Environmental Quality.
The Arkansas Watershed Steward Handbook is also a good source of information about basic water quality concerns and how the public can get engaged in addressing water pollution.
9
 This fact sheet is one in a series of 10 fact sheets on nonpoint source pollution in priority watersheds.
The University of Arkansas Division of Agriculture's Public Policy Center provides timely, credible, unbiased research, analyses and education on current and emerging public issues.
Printed by University of Arkansas Cooperative Extension Service Printing Services.
Irrigation of Sunflowers in Northwestern Kansas
 Robert M.
Aiken, Research Crop Scientist,
 Abdrabbo A.
Aboukheira, Water Resources Engineer
 National Water Research Center, WMRI, Delta Barrage, Kaliobiya Egypt.
Abstract.
Sunflower was grown in a three year  at the KSU Northwest Research-Extension Center at Colby, Kansas under a lateral move sprinkler irrigation system.
Irrigation capacities were limited to not more than 1 inch every 4, 8 or 12 days but were scheduled only as needed as determined with a weather-based water budget.
Achene  yields and oil yield generally plateaued at the medium irrigation level.
Dormant season irrigation generally had no appreciable effect on achene yield or other yield components.
The optimum harvest plant population for sunflower in this study in terms of achene yield and oil yield was approximately 19,000 to 20,000 plants/acre.
Sunflower and corn have similar peak ET and irrigation rate requirements for full irrigation, but sunflower requires about 2.3 inches less irrigation and its peak needs began at about the time corn needs are starting to decline.
Average full irrigation of sunflowers is approximately 12 inches, but often producers will apply between 8 and 10 inches of irrigation because the amount of yield decline is slight.
Keywords.
Irrigation scheduling, water budget, sunflower.
Sunflower is a crop of interest in the Ogallala Aquifer region because of its shorter growing season and thus lower overall irrigation needs.
Sunflowers are thought to better withstand short periods of crop water stress than corn and soybeans and the timing of critical sunflower water needs is also displaced from those of corn and soybeans.
Thus, sunflowers might be a good choice for marginal sprinkler systems and for situations where the crop types are split within the center pivot sprinkler land area.
Center pivot sprinkler irrigation , the predominant irrigation method in the Ogallala region, presents unique challenges when used for deficit irrigation.
Center pivot sprinkler irrigation cannot be effectively used to apply large amounts of water timed to a critical growth stage as can be done with surface irrigation methods.
The CP systems also cannot efficiently use small frequent events to alleviate water stress as is the case with subsurface drip irrigation.
Thus with CP systems, it is important that available soil water in storage be correctly managed temporally in terms of additions and withdrawals so that best crop production can be achieved both economically and water-wise.
The study was conducted from 2009 through 2012 at the KSU Northwest Research-Extension Center at Colby, Kansas under a lateral move sprinkler irrigation system.
However, data from 2011 is excluded due to a devastating hail storm that destroyed the crop.
Key agronomic characteristics of the annual tests are shown in Table 1.
Table 1.
Agronomic characteristics of an irrigated sunflower study conducted at the KSU
 Northwest Research-Extension Center, Colby, Kansas, 2009-2012.
Data from
 2011 are excluded due to devastating hail storm.
Characteristic	2009	2010	2012
 Hybrid	Triumph S671 1	Triumph S671	Triumph S671
 Planting date	June 18	June 16	June 13
 Emergence date	June 25	June 24	June 26
 Harvest date	October 16	October 13	October 8
 Rainfall, emergence to maturity 	9.89	7.32	5.25
 Preseason irrigation 	5	5	9.2
 First seasonal irrigation	July 27	July 25	July 25
 Last seasonal irrigation	September 15	September 15	September 23
 Whole plot treatments were sprinkler irrigation capacities of 1 inch every 4, 8 or 12 days as limited by ET-based water budget irrigation scheduling.
An additional whole plot irrigation factor was the addition or no addition of dormant preseason irrigation resulting in a total of 6 different irrigation treatments.
The target preseason irrigation amount for those plots receiving it was 5 inches, but in 2012 a total of 9.2 inches of preseason irrigation was applied due to an application error.
Three targeted plant populations 18,000, 23,000, or 28,000 plants/acre were superimposed on the whole plots for a grand total of 108 subplots.
Irrigation amounts were 1 inch applied as needed, but limited by the imposed capacity and the water budget irrigation schedule.
The whole plots  were in a randomized complete block  design.
Soil water was measured periodically in each plot each crop season with a neutron probe to a depth of 8 feet in one foot increments.
Crop water use was calculated as the sum of changes in soil water between emergence and physiological maturity, precipitation and irrigation amount.
Crop water productivity  was calculated as the achene yield in lbs/acre divided by the total crop water use in inches.
Sunflower heads were hand harvested from a representative sample area and threshed for yield and yield component determinations.
The crop year 2009 was very cool and wet and irrigation needs were low.
In-season irrigation amounts for the 1 inch every 4 and 8 days treatments were 7.68, 6.72 and 4.80 inches, respectively.
During the period April through October every month had above normal precipitation and between crop emergence and crop maturity the total precipitation was 9.89 inches.
The early portion of the crop year 2010 was wet and irrigation needs were lower than normal.
However, later in season, it was extremely dry with only 1.08 inches of precipitation occurring between August 4 and crop maturity on October 11.
Precipitation during the sunflower growing period totaled 7.32 inches.
In-season irrigation amounts were 11.52, 6.72 and 4.8 inches for the irrigation capacities limited to 1 inch/4 days, 1 inch/8 days and 1 inch/12 days, respectively.
The 2010 sunflower irrigation amounts appear to be approximately 1 inch less than normal as estimated from long term  irrigation scheduling simulations conducted at Colby, Kansas.
Extreme drought conditions existed for all of 2012 and only 5.25 inches of precipitation occurred during the sunflower growing period.
Additionally, temperatures of 100F or greater occurred on 20 days between June 26 and August 15.
Crop establishment may have been negatively affected by excessively hot temperatures  that occurred for the entire period between planting and emergence even though small amounts of irrigation kept sufficient amounts of water in the seed zone.
Sunflower plant populations at harvest in 2012 averaged approximately 75% of levels that occurred in 2009 and 2010.
In-season irrigation amounts were 13.94, 8.18 and 6.26 inches for the irrigation capacities limited to 1 inch/4 days, 1 inch/8 days and 1 inch/12 days, respectively.
Summarizing the weather conditions, the crop year 2009 was cooler and wetter than normal, the crop year 2010 was approximately normal though a severe drought began in early August, and the crop year 2012 was extremely hot and dry.
Crop Yields and Yield Components
 The addition of dormant preseason irrigation did not significantly increase yields in any of the three years.
Preseason irrigation did significantly increase heads/plant in 2009 and harvest plant population in 2010, but these differences were only about 3% greater.
There were no significant differences in yield attributable to irrigation capacity in 2009 and 2012, but increased irrigation capacity did increase achene yield in 2010.
There were no plant population effects on achene yield in 2009, but increased plant population decreased achene yield in 2010 and increased achene yield in 2012.
The difference between 2010 and 2012 responses is probably related to the differences in harvest plant populations between the two years.
As indicated in earlier section, crop establishment was poor in 2012.
Harvest plant populations in 2010 averaged 19,263, 23,426 and 26,257 plants/acre for the three respective targets as compared to the much lower 2012 values of 14,452, 17,530 and 19,781 plants/acre.
Increasing plant population significantly decreased achenes/head in both 2009 and 2010 but had no consistent effect in 2012, once again probably because harvest plant populations were so low.
Increasing plant population significantly decreased achene mass and significantly increased achene oil content  in all three years.
Within a given year average differences in oil content ranged from 1 to 2% as affected by plant population.
Harvest plant populations above 19,000 to 20,000 plants/acre resulted in reduced achene yields and oil yields.
Crop Water Use and Water Productivity
 In-season crop water use was significantly increased by increased irrigation in all three years.
However, crop water productivity  was significantly reduced by increased irrigation in all three years.
Irrigation amounts ranged from 4.80 to 7.68 inches in 2009, 4.80 to 11.52 inches in 2010 and 6.26 to 13.94 inches in 2012.
Achene yield and oil yield
 both increased with irrigation in all years up through the 1 inch/8 day irrigation capacity but tended to have less or no response above that level.
Achene yields were lower in 2010 than in 2009 and 2012, but still were towards the upper range of yields for the region.
Figure 1.
Achene yield and oil yield as related to harvest plant population in a sprinkler irrigated sunflower study, KSU Northwest Research-Extension Center, Colby, Kansas, 20092012.
Table 2.
Summary of sunflower yield components and water use parameters for a sprinkler irrigated study, 2009, KSU Northwest Research-Extension Center, Colby Kansas.
Irrigation	capacity	Preseason	irrigation	population		Targeted	plant		Yield	population	Harvest	plant		/plant	Heads	Achenes	/head	Achene	Mass		Achene	Oil%	Water use		Productivity		Water
 18	3266	16262	0.94	2114	46.6	45.6	21.94	149
 23	3324	20183	0.92	2043	40.2	46.2	22.49	148
 28	3109	23813	0.93	1720	37.2	46.6	22.10	141
 1 in/4 d	Mean	3233	20086	0.93	1959	41.3	46.2	22.18	146
 	18	3229	16553	0.94	2155	44.3	45.7	22.06	146
 23	3326	20328	0.93	1919	42.0	46.3	22.24	150
 28	3246	22942	0.99	1728	39.3	46.8	22.96	141
 Mean	3267	19941	0.95	1934	41.9	46.2	22.42	146
 Mean 1 inch/4 days	3250	20013	0.94	1947	41.6	46.2	22.30 C	146 b
 18	3376	16698	0.95	2259	43.4	45.7	21.08	161
 23	3189	20183	0.95	1893	40.4	46.0	21.29	150
 28	3081	22506	0.96	1790	37.5	46.5	21.89	141
 1 in/8 d	Mean	3215	19796	0.95	1981	40.4	46.1	21.42	151
 	18	3427	16553	0.99	2214	42.8	45.0	21.56	159
 23	3208	19312	0.96	1934	40.6	46.1	21.21	151
 28	3332	22506	1.01	1766	38.4	46.6	22.01	152
 Mean	3322	19457	0.99	1971	40.6	45.9	21.60	154
 Mean 1 inch/8 days	3269	19626	0.97	1976	40.5	46.0	21.51 b	152 a
 18	3158	16408	0.93	2198	42.8	45.7	20.38	155
 23	3186	19457	0.96	1923	40.3	45.9	20.75	154
 28	3168	24103	0.91	1728	38.3	46.5	20.75	153
 1 in/12 d	Mean	3171	19989	0.93	1950	40.5	46.0	20.63	154
 	18	3100	16117	0.97	2127	42.3	46.1	20.36	152
 23	3345	19166	0.96	1985	41.9	45.6	20.41	164
 28	3279	23522	0.94	1758	38.4	46.2	20.68	159
 Mean	3241	19602	0.96	1957	40.8	45.9	20.48	158
 Mean 1 inch/12 days	3206	19796	0.95	1953	40.7	46.0	20.56 a	156 a
 Study-Wide Mean	3242	19812	0.95	1959	40.9	46.0	21.45	151
 Preseason	None	3206	19957	0.94 a	1963	40.7	46.1	21.41	150
 Irrigation	5 inches	3277	19667	0.97 b	1954	41.1	46.0	21.50	153
 18	3260	16432 a	0.95	2178 a	43.7 a	45.6 C	21.23 a	154 a
 population 	23	3263	19771 b	0.95	1950 b	40.9 b	46.0 b	21.40 a	153 a
 28	3203	23232 C	0.96	1748 C	38.2 C	46.5 a	21.73 b	148 b
 Shaded items within a column are significantly different at P<0.05 when followed by a different lower-cased letter.
Table 3.
Summary of sunflower yield components and water use parameters for a sprinkler irrigated study, 2010, KSU Northwest Research-Extension Center, Colby Kansas.
Irrigation	capacity	Preseason	irrigation	population		Targeted	plant		Yield	population	Harvest	plant		/plant	Heads	Achenes	/head	Achene	Mass		Achene	Oil%	Water use		Productivity		Water
 18	3172	20038	0.94	1916	40.4	44.2	22.69	141
 23	2919	23668	0.89	1631	38.6	44.7	22.74	128
 28	2946	27007	0.85	1570	37.4	45.0	23.32	127
 1 in/4 d	Mean	3012	23571	0.90	1706	38.8	44.6	22.92	132
 	18	3000	19166	0.93	1845	42.3	43.8	20.99	143
 23	3062	23958	0.95	1646	37.3	44.7	21.15	146
 28	2987	25265	0.95	1597	36.1	45.3	20.72	145
 Mean	3172	20038	0.94	1916	40.4	44.2	22.69	141
 Mean 1 inch/4 days	3014 a	23184	0.92	1701	38.7	44.6 a	21.93 a	138 C
 18	3043	19602	0.92	1893	41.0	44.5	19.63	157
 23	2989	23377	0.98	1668	36.1	44.6	20.01	150
 28	3004	25700	0.97	1563	35.7	45.3	19.36	156
 1 in/8 d	Mean	3012	22893	0.96	1708	37.6	44.8	19.66	154
 	18	3091	18440	0.98	1912	40.6	44.3	19.01	164
 23	2892	23087	0.93	1647	37.2	44.7	19.31	151
 28	2951	25410	0.98	1506	36.3	45.3	19.58	152
 Mean	3043	19602	0.92	1893	41.0	44.5	19.63	157
 Mean 1 inch/8 days	2995 a	22603	0.96	1698	37.8	44.8 a	19.48 b	155 b
 18	2983	19312	0.96	1868	39.4	43.2	17.25	175
 23	2886	23522	0.96	1715	34.4	43.6	16.85	175
 28	2705	27588	0.88	1480	34.4	44.0	17.10	159
 1 in/12 d	Mean	2858	23474	0.93	1688	36.1	43.6	17.07	170
 	18	3059	19021	0.95	1983	39.0	43.7	18.12	170
 23	2831	22942	0.94	1613	37.0	43.6	17.99	158
 28	2833	26572	0.91	1511	35.5	44.1	17.67	162
 Mean	2908	22845	0.93	1702	37.2	43.8	17.93	163
 Mean 1 inch/12 days	2883 b	23159	0.93	1695	36.6	43.7 b	17.50 C	167 a
 Study-Wide Mean	2964	22982	0.94	1698	37.7	44.4	19.64	153
 Preseason	None	2961	23313 a	0.93	1700	37.5	44.3	19.88	152
 Irrigation	5 inches	2967	22651 b	0.95	1695	37.9	44.4	19.39	155
 Target plant	18	3058 a	19263 C	0.94	1903 a	40.5 a	43.9 C	19.61	158 a
 population	23	2930 b	23426 b	0.94	1653 b	36.8 b	44.3 b	19.67	151 b
 	28	2904 b	26257 a	0.92	1538 C	35.9 b	44.8 a	19.62	150 b
 Shaded items within a column are significantly different at P<0.05 when followed by a different lower-cased letter.
Table 4.
Summary of sunflower yield components and water use parameters for a sprinkler irrigated study, 2012, KSU Northwest Research-Extension Center, Colby Kansas.
Irrigation	capacity	Preseason	irrigation	population		Targeted	plant		Yield	population	Harvest	plant		/plant	Heads Achenes	/head	Achene	Mass		Achene	Oil%	Water use		Productivity		Water
 18	3145	14956	1.00	1555	61.6	39.4	24.82	126
 23	3265	16988	0.99	1497	59.6	39.8	25.89	126
 28	3315	21635	0.87	1750	52.9	41.6	24.86	133
 1 in/4 d	Mean	3242	17860	0.95	1601	58.0	40.3	25.19	129
 	18	3183	14985	1.00	1666	58.1	39.1	25.33	126
 23	3448	17424	0.99	1572	58.2	40.3	25.64	134
 28	3662	19689	0.99	1599	53.7	40.3	26.79	137
 Mean	3431	17366	0.99	1612	56.6	39.9	25.92	132
 Mean 1 inch/4 days	3328	17635	0.97	1606	57.4	40.1	25.52 a	130 C
 18	3191	13939	1.00	1717	62.6	38.9	20.45	157
 23	3160	16698	0.99	1494	58.8	39.6	20.23	156
 28	3423	19747	1.00	1439	55.3	40.8	20.80	165
 1 in/8 d	Mean	3258	16795	1.00	1550	58.9	39.7	20.49	159
 	18	3148	14375	1.00	1544	65.2	39.2	18.61	172
 23	3310	17569	0.98	1495	59.4	40.1	18.37	181
 28	3480	19747	1.00	1414	58.0	41.5	18.75	187
 Mean	3313	17230	0.99	1484	60.9	40.3	18.58	180
 Mean 1 inch/8 days	3286	17013	0.99	1517	59.9	40.0	19.54 b	169 b
 18	3237	14462	1.00	1610	63.8	39.1	17.41	188
 23	3126	17772	0.98	1280	64.9	39.9	17.18	183
 28	3121	18121	1.00	1490	54.5	40.0	17.43	180
 1 in/12 d	Mean	3161	16785	0.99	1460	61.0	39.7	17.34	183
 	18	3074	14084	1.00	1440	70.1	38.4	18.52	168
 23	3487	18992	0.99	1478	57.5	39.8	18.47	191
 28	3417	19457	0.97	1410	59.3	40.5	18.47	186
 Mean	3316	17424	0.99	1440	62.6	39.5	18.49	181
 Mean 1 inch/12 days	3244	17125	0.99	1450	61.9	39.6	17.95 C	182 a
 Study-Wide Mean	3286	17251	0.99	1525	59.7	39.9	20.99	161
 Preseason	None	3224	17168	0.98	1541	59.2	39.9	21.22	156
 Irrigation	9.2 inches	3350	17337	0.99	1508	60.2	39.9	20.75	166
 Target plant	18	3160 b	14452 C	1.00	1586	63.7 a	39.0 C	20.83	156
 population	23	3294 ab	17530 b	0.99	1472	59.7 b	39.9 b	21.01	161
 28	3404 a	19781 a	0.97	1515	55.7 C	40.8 a	21.13	165
 Shaded items within a column are significantly different at P<0.05 when followed by a different lower-cased letter.
Irrigation and Crop Water Use 
 Figure 2.
Achene yield and oil yield as related to irrigation amount and total crop water use in a sprinkler irrigated sunflower study, KSU Northwest Research-Extension Center, Colby, Kansas, 2009-2012.
Note: Irrigation responses in blue unbroken lines and crop water use responses in green dashed lines.
Yield Water Use Production Function
 Irrigation studies with sunflower have been conducted periodically at the KSU Northwest Research-Extension Center since 1986.
The irrigation treatments in these studies varied with some studies applying various percentages of well-water crop water use , some studies applying water at specific sunflower growth stages, and some studies using water budget irrigation scheduling under various irrigation system capacities.
Yield response varied some from year to year and some between studies as might be anticipated, but on the average 157 lbs of sunflower seed was obtained for each acre-inch of water use above a yield threshold of approximately 3 inches.
It can be noted that the results of the current study  continue to fit the linear response of the earlier studies.
Figure 3.
Sunflower yield response to total seasonal crop water use for selected studies conducted at the KSU Northwest Research-Extension Center, Colby Kansas, 19862007.
The PD data from 2000 and 2001 was from dryland studies.
The IT data from 2000 and 2001 was from studies scheduled by stage of growth.
The data from the PI studies had irrigation applied at various growth periods throughout the summer.
All other studies presented here were scheduled according to various percentages of crop water use or were managed according to various upper limits of irrigation capacity.
Results from Simulation Modeling
 Thirty-nine years  of weather data was used to create simulated irrigation schedules for sunflower and also corn for a comparison crop.
These irrigation schedules were also coupled with a crop yield model to estimate crop yield at various irrigation capacities  and under dryland production.
Although corn has greater crop water use  and requires more irrigation  than sunflower, their peak water use rates and peak irrigation rates are very similar.
Under full irrigation , corn uses approximately 4.3 inches more water than sunflower during the season but only requires approximately 2.3 inches of additional irrigation because of its growth period encompasses some months of greater rainfall.
Although peak ET and peak irrigation needs are similar between the two crops, sunflower's needs are for a much shorter duration and occur at a time when corn's needs are about to start declining.
Figure 4.
Simulated average cumulative crop water use , rainfall and gross irrigation requirement for sunflower and corn for the 39 year period 1972 through 2010 at Colby, Kansas.
Irrigation scheduling simulations were performed for sprinkler irrigation amounts of 1 inch at an application efficiency of 95%.
The shorter duration of peak ET and irrigation needs for sunflower and their occurrence at a time when peak needs for corn are about to decline open up some opportunities to shift irrigation allocations between crops.
Additionally, the yield decline with just slightly deficit irrigation is usually very small with sunflowers compared to corn.
Under the right economics, sunflower can be a good candidate for deficit irrigation.
Figure 5.
Simulated average daily crop water use  and gross irrigation requirements for sunflower and corn for the 39-year period 1972 through 2010 at Colby, Kansas.
Irrigation scheduling simulations were performed for sprinkler irrigation amounts of 1 inch at an application efficiency of 95%.
The data are presented as a 4 day moving average.
Figure 6.
Simulated average relative crop yield of sunflower and corn as affected by irrigation capacity at Colby, Kansas for the 39-year period 1972-2010.
Irrigation capacity data points left to right are dryland, 1 inch every 10, 8, 6, 5, 4 or 3 days, respectively.
A capacity of 1 inch/4 days is equivalent to an irrigation capacity of 589 gpm/125 acre center pivot irrigation system.
Figure 7.
Average monthly distribution of irrigation needs of sunflower and corn at Colby, Kansas for the 39-year period 1972-2010 as determine from simulated irrigation schedules.
Sunflower was grown under sprinkler irrigation in Colby, Kansas for three very different crop years.
Irrigation capacities were limited to not more than 1 inch every 4, 8 or 12 days but irrigation events were scheduled only as needed as determined with a weather-based water budget.
Achene yield was only statistically increased by irrigation in 2010, but tended to increase numerically up through the medium irrigation level  in all three years.
Similarly, oil yield plateued at the medium irrigation level.
Dormant season irrigation generally had no appreciable effect on achene yield or yield components.
The optimum harvest plant population for sunflower in this study in terms of achene yield and oil yield was approximately 19,000 to 20,000 plants/acre.
The yield water use production function for sunflowers in this region is approximately 157 lb/acre for each inch of water use above a yield threshold of 2.7 inches.
Declines in sunflower yield with deficit irrigation are less drastic than with corn, so producers may wish to consider sunflower when irrigation system capacities are marginal.
Sunflower and corn have similar peak ET and irrigation rate requirements for full irrigation, but sunflower requires about 2.3 inches less irrigation and its peak needs began at about the time corn needs are starting to decline.
Average full irrigation of sunflowers would be approximately 12 inches, but often producers will apply between 8 and 10 inches of irrigation because the amount of yield decline is only a few percentage points.
A Guide for Reducing Risk and Improving Production
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 A Guide for Reducing Risk and Improving Production
 Whitney Yeary Extension Assistant, Plant Sciences Amy Fulcher Assistant Professor, Plant Sciences Brian Leib Associate Professor, Biosystems Engineering and Soil Science
 UNIVERSITY OF TENNESSEE PB 1836
 This manual was prepared by Whitney Yeary, Amy Fulcher and Brian Leib, University of Tennessee, with contributions from Quinn Cypher, University of Tennessee, and Adam Blalock, Tennessee State University.
We are indebted to reviewers Quinn Cypher, Jeb Fields, Jim Owen, Tyson Raper and Sarah White.
Their thoughtful review added clarity and greatly improved the content of this publication.
Any errors that remain are those of the authors.
We would also like to express our gratitude to the nursery growers and Extension and research faculty who graciously shared their success stories with us.
They will encourage and inspire readers far beyond what the concepts alone could.
Much appreciation is expressed to the Southern Risk Management Education Center in partnership with the National Institute of Food and Agriculture for financial support that made this project possible.
This guide would not be informative without illustrative images.
We are very grateful to those who provided images.
Unless otherwise indicated, images used in this guide are those of Quinn Cypher and Amy Fulcher.
Current Tennessee Water Regulations Water Quality Trading, Future Water Regulations
 Success Story: The Switch to Drip Saved Water and Fertilizer
Nebraska Extensions Pesticide Education Office is excited to continue offering online training options in 2023.
Online training options are available for new and recertifying private pesticide applicators, new and recertifying commercial/noncommercial pesticide applicators, and new and recertifying chemigators.
A video tutorial is available to help walk users through the process of getting registered for online training.
A written PDF version of this tutorial is also available.
CONSERVE WATER OUTDOORS AND SAVE MONEY
 Follow the Easy 4-Step Checklist to Get Started
 Water levels in Sarasota County are tied closely to the climate, which changes drastically throughout the course of the year.
Those changing conditions can put stress on resources.
You can help, and foster a growing water conservation ethic, by cutting your water use outdoors.
Watering the lawn accounts for 59 percent of water use in an average single-family home, but you can keep your lawn green and still cut water use.
Follow this 4-step approach to begin your year-round savings:
 1.
Check when you water
 Set your sprinkler system clock to run at the right time and day.
Water lawns one day per week, in the early morning hours.
Watering during the day wastes water to evaporation.
Late morning watering can extend natural wetting time from dew, increasing the risk of disease.
2.
Check where and how you water.
Test your sprinkler spray patterns by watching the system run in each zone for about 5 minutes.
Look for odd spray patterns or watering of established landscaping or paved surfaces, and then adjust or cap sprinkler heads accordingly.
A common problem with sprinklers is overgrown grass or vegetation interfering with the spray pattern.
Sprinkler donuts help prevent this.
Established landscape beds typically thrive on normal rainfall, so cap sprinklers or use micro-irrigation in these areas.
Average Water Use in Residential Areas
 Typical irrigation system clock, with "Rain Sensor" setting.
Photo courtesy of Wilma Holley.
Wet driveways and sidewalks are signs of wasted water.
Heads can be adjusted to spray lawn only.
Sprinklers spraying established plants should be moved to the grass or capped.
3.
Check for leaks.
Inspect for leaks by looking for bubbling and/or excessive water coming out of the ground near sprinklers.
Scan around sprinklers for dollarweed, a water-loving plant that might indicate a leak.
The presence of dollarweed is also a sign of overwatering.
Fix leaks immediately: Leaks cost you money and waste water.
A buried sprinkler head wastes water.
Photo courtesy of Wilma Holley.
Leak in a sprinkler due to a worn seal.
Photo courtesy of Ernesto Clark.
4.
Check your rain sensor.
Place your rain sensor away from roof overhangs, trees, or other obstructions.
Make sure to activate the rain sensor setting on your sprinkler system clock.
Test your sensor by spraying it with a hose.
The shut-off device will activate and turn off sprinklers.
Sensor cups need to be cleaned periodically.
More ways to cut outdoor water use:
 1.
Have one of our experts evaluate your irrigation.
Call 941-861-9900 to arrange.
2.
Add a rain barrel to capture water for your garden or potted plants.
Call 941-861-5000.
Rain sensor obstructed by roof line  should be repositioned.
Photos courtesy of Wilma Holley.
Check to make sure that any rotating parts  are actually rotating Look to see if any runoff is occurring, which is most likely to be a problem on the last span and/or on a hillslope.
If available, utilizing a drone or UAS opens up new ways to do this walk-by quickly and may allow you to more easily check system operation in parts of the field that are not easily accessible.
Subsurface drip irrigation  technologies have been a part of irrigated agriculture since the 1960s, but have advanced at a more rapid pace during the last 20 years.
In the summer of 1988, K-State Research and Extension issued an in-house request for proposals for new directions in research activity.
A proposal entitled Sustaining Irrigated Agriculture in Kansas with Drip Irrigation was submitted by irrigation engineers Freddie Lamm, Harry Manges and Dan Rogers and agricultural economist Mark Nelson.
This project led by principal investigator Freddie Lamm, KSU Northwest Research-Extension Center , Colby, was funded for the total sum of $89,260.
This project financed the initial development of the NWREC SDI system that was expressly designed for research.
In March of 1989, the first driplines were installed on a 3 acre study site which has 23 separately controlled plots.
This site has been in continuous use in SDI corn production since that time, being initially used for a 3year study of SDI water requirements for corn.
In addition, it is considered to be a benchmark area that is also being monitored annually for system performance to determine SDI longevity.
In the summer of 1989, an additional 3 acres was developed to determine the optimum dripline spacing for corn production.
A small dripline spacing study site was also developed at the KSU Southwest Research-Extension Center  at Garden City in the spring of 1989.
In the summer of 1989, further funding was obtained through a special grant from the US Department of Agriculture.
This funding led to expansion of the NWREC SDI research site to a total of 13 acres and 121 different research plots.
This same funding provided for a 10 acre SDI research site at Holcomb, Kansas administered by the SWREC.
By June of 1990, K-State Research and Extension had established 25 acres of SDI research facilities and nearly 220 separately controlled plot areas.
Over the course of the past 17 years, additional significant funding has been obtained to conduct SDI research from the USDA, the Kansas Water Resources Research Institute, special funding from the Kansas legislature, the Kansas Corn Commission, Pioneer Hi-Bred Inc., and the Mazzei Injector Corporation.
Funding provided by the Kansas legislature through the Western Kansas Irrigation Research Project  allowed for the expansion of the NWREC site by an
 additional 5.5 acres and 46 additional research plots in 1999.
An additional 22 plots were added in 2000 to examine swine wastewater use through SDI and 12 plots were added in 2005 to examine emitter spacing.
Two research block areas originally used in a 1989 dripline spacing study have been refurbished with new 5 ft spaced driplines to examine alfalfa production and emitter flowrate effects on soil water redistribution.
The NWREC SDI research site comprising 19.5 acres and 201 different research plots is the largest facility devoted expressly to smallplot row crop research in the Great Plains and is probably one of the largest such facilities in the world.
Since its beginning in 1989, K-State SDI research has had three purposes: 1) to enhance water conservation; 2) to protect water quality, and 3) to develop appropriate SDI technologies for Great Plains conditions.
The vast majority of the research studies have been conducted with field corn because it is the primary irrigated crop in the Central Great Plains.
Although field corn has a relatively high water use efficiency, it generally requires a large amount of irrigation because of its long growing season and its sensitivity to water stress over a great portion of the growing period.
Of the typical commodity-type field crops grown in the Central Great Plains, only alfalfa and similar forages would require more irrigation than field corn.
Any significant effort to reduce the overdraft of the Ogallala aquifer, the primary water source in the Central Great Plains, must address the issue of irrigation water use by field corn.
This report summarizes several studies conducted at the KSU Northwest and Southwest Research-Extension Centers at Colby and Garden City, Kansas, respectively.
A complete discussion of all the employed procedures lies beyond the scope of this paper.
For further information about the procedures for a particular study the reader is referred to the accompanying reference papers when so listed.
These procedures apply to all studies unless otherwise stated.
The two study sites were located on deep, well-drained, loessial silt loam soils.
These medium-textured soils, typical of many western Kansas soils, hold approximately 18.9 inches of plant available soil water in the 8 ft profile at field capacity.
Study areas were nearly level with land slope less than 0.5% at Colby and 0.15% at Garden City.
The climate is semi-arid, with an average annual precipitation of 18 inches.
Daily climatic data used in the studies were obtained from weather stations operated at each of the Centers.
Most of the studies have utilized SDI systems installed in 1989-90.
The systems have dual-chamber drip tape installed at a depth of approximately 16-18 inches with a 5-ft spacing between dripline laterals.
Emitter spacing was 12 inches and the dripline flowrate was 0.25 gpm/100 ft.
The corn was planted so each dripline lateral is centered between two corn rows.
Figure 1.
rows.
Physical arrangement of the subsurface dripline in relation to the corn
 grown with perpendicular to the driplines in the dripline spacing corn rows were tillage and match bed spacing to dripline spacing with spacing studies, was not practical conducted to at both locations.
In these dripline dripline planted harvesting equipment.
Additionally at Garden City, the available A inches modified apart, ridge-till system was used in corn production with 30 confined conventional furrows.
production practices for each location, study.
Wheel All corn traffic was was spacing studies grown on a 5-ft wide bed.
Flat planting was used two for corn the rows, it to the
NORTHERN WATER EFFORTS TO IMPROVE IRRIGATION SCHEDULING PRACTICES
 Northern Water formally established an IMS  in 1981 to promote improved on-farm water management.
A principal IMS effort has been the advancement of irrigation scheduling practices through field-by-field demonstrations of improved practices.
This was supported by establishment of a district-wide weather station network along with promotion of accurate on-farm water measurement.
The field-by-field demonstrations of improved irrigation scheduling utilized the root zone water balance method, or checkbook method, coupled with soil moisture sensors.
These efforts proved effective and received good acceptance by local growers.
Water measurement is a key to improved irrigation management.
Needed measurements include flow deliveries to the field, crop water use , available water stored in the crop root-zone, local rainfall, tail water runoff, etc.
Such measurements allow calculation of on-farm irrigation efficiency.
This is a major step beyond just scheduling irrigations.
It allows for an estimation of the volume of water used beneficially.
The full benefits of improved irrigation scheduling are directly tied to the flexibility in water available for deliveries to the farm turnout or field.
However, improved delivery flexibility comes at a cost.
An appropriate balance must be achieved.
Northern Water's IMS programs have experienced considerable success.
However, institutional and economic barriers continue to curtail needed improvements in some areas.
Northern Water is comprised of 1.6 million acres in eight counties on the East Slope of the Rocky Mountains.
Irrigated land totals approximately 693,000 acres.
Northern Water has aggressively promoted improved on-farm water management for more than 26 years.
From its inception in 1981, IMS has been
 focused on education, training, and demonstration.
It shares information regarding new technologies, increases public awareness, and enables producers to implement practical improvements with confidence.
It does not focus on policies or politics.
To date cooperators have not paid any fees to participate in the program.
With a foundation based on information and technology, it has avoided the controversy and resistance often associated with political mandates and regulatory enforcement.
Northern Water operates a network of remote, solar powered, automated weather stations throughout its service area for disseminating crop water use information.
The Weather Station Network is currently composed of 22 stations.
Station sites are carefully selected to ensure readings representative of cropped field conditions, always well within a surface-irrigated field of alfalfa hay or over large areas of well-irrigated urban turf grass.
Stations are approximately 25 to 30 miles apart to provide the best practical coverage and are operated year-round.
In recent years, station density has increased near metropolitan areas.
Each station collects air temperature, relative humidity, wind speed and solar radiation data.
These data are used to calculate ETR  on a daily basis using the ASCE standardized Penman-Montieth combination equation for alfalfa.
Precipitation, wind direction, and soil temperature are also collected.
The weather station data is automatically transmitted hourly to Northern Water headquarters via cdma modem.
Each sensor at each weather station is checked and calibrated annually to ensure data accuracy and to maintain high network reliability.
Station performance is monitored regularly and any problems detected are promptly corrected.
Accurate and reliable crop ET information supports efficient irrigation scheduling, thereby allowing producers to determine how much water to apply given their specific crop and irrigation practices.
Crop ET information is widely accepted and its use continues to grow.
Northern Water began promoting low-cost electronic flow monitoring in 2000 under grant funding from the U.S.
Bureau of Reclamation.
These flow measurements allow calculation of on-farm irrigation efficiency.
This is a major step beyond just scheduling irrigations.
It allows estimation of the volume of
 water used beneficially.
It provides needed tools and information that increase the effectiveness of efforts to improve irrigation scheduling practices.
Local interest in on-farm electronic flow monitoring has increased in recent years.
Lower purchase costs for equipment, coupled with increased confidence in irrigation decisions, are key factors.
Additionally, increased urbanization of the Northern Water service area has increased the operational challenges and constraints facing local ditch companies.
As productive agricultural lands are sold for development and the associated water rights transferred to cities, irrigation and ditch companies are faced with reduced flow rates, decreased exchange opportunities, and shorter delivery seasons.
On-farm efficiency is largely affected by the flexibility in water deliveries available to the farm turnout or field.
Improved flow measurement, remote monitoring, and gate automation are increasingly required for successful water delivery operations.
FIELD-BY-FIELD IRRIGATION SCHEDULING DEMONSTRATIONS
 Since 1981, Northern Water has provided field-by-field demonstrations of irrigation scheduling practices to growers within its boundaries.
These demonstrations have aided irrigation decision-making and supported efficient use of available water.
They provided irrigators with a better understanding of soil moisture management throughout the growing season.
They often gave the grower needed confidence to lengthen the time between irrigations.
The field-by-field irrigation scheduling demonstrations consistently utilized the root zone water balance method, or checkbook method, coupled with soil moisture sensors.
Soil moisture holding capacity and an allowable depletion percentage were estimated.
Readings from the soil moisture sensors were used to calculate remaining available moisture.
Changes in soil moisture readings were compared to the calculated crop ET from Northern Water's weather station network to validate the accuracy of both data.
To estimate the number of days before the next irrigation was needed, the remaining soil moisture in the crop root zone was divided by the predicted daily crop water use from the nearest weather station.
The success of these field-by-field irrigation scheduling demonstrations was directly dependent upon the quality of the crop water use information obtained from the weather station network.
These efforts targeted assistance to 50 area producers annually, with one to two fields per cooperator each season.
Cooperators generally participated in the program for two to three seasons, after which new cooperators replaced past participants.
Regular status reports were either e-mailed or hand delivered to cooperators.
Through 2003, tensiometers were the primary soil moisture device utilized by the program.
Instruments were manually read and serviced during a weekly site visit.
However since 2004, efforts expanded to include automated electronic soil moisture sensors.
Automation allowed continuous monitoring and recording of soil moisture at multiple levels within the crop root zone.
Several manufacturers now market lower cost electronic soil moisture sensors, data loggers, and telemetry equipment.
Cooperator support for automated soil moisture monitoring was dramatic.
Utilization of the root zone water balance method, or checkbook method, coupled with soil moisture sensors proved both effective and reliable for field-by-field irrigation scheduling.
The success of these efforts was directly reliant upon the availability of accurate crop water use information, obtained from the District-wide weather station network.
Additionally, proper measurement of water delivered to the farm turn-out or field was similarly important.
Soil moisture monitoring significantly improved with the transition from manual instruments to electronic sensors coupled to a data logger with cellular telemetry.
Reduced costs and increased reliability of automated instruments has assisted in the adoption of these improved methods.
The full benefits of irrigation scheduling efforts are directly tied to the delivery flexibility of available water to cropped fields.
If deliveries are restricted in available frequency, flow rate, or duration irrigators are often unable to implement improved irrigation scheduling practices.
The consequence is reduced on-farm irrigation efficiency.
Reduced delivery flexibility may result from ditch or canal operations, lack of capacity in irrigation equipment , water right administration, drought conditions, etc.
Delivery flexibility may be increased through more senior water rights, use of groundwater wells, on-farm storage ponds, canal automation, etc.
Irrigation delivery constraints can prevent an irrigator from providing the proper amount of water at the right time to minimize crop water stress.
Minimal restrictions may be overcome by maximizing soil moisture storage in the crop root zone as a buffer against time periods when water availability is limited or restricted.
Northern Water continues to maintain a strong commitment to assisting local irrigators to implement improved irrigation scheduling practices and realize increased on-farm water use efficiency.
Chapter: 42 Herbicide Injury to Corn
 Herbicides can cause predictable symptoms to plants.
Injury symptoms may be due to improper application, unintentional crop exposure , or may develop if adverse environmental conditions  occur after application.
The purpose of this section is to show injury symptoms and discuss the mode of action of commonly used herbicides that occur in South Dakota corn production.
Photographs and information are provided to assist in identification of herbicide injury symptoms, although symptoms may be due to other causes such as disease, or abiotic stress such as drought, cold, or hail damage.
Herbicide injury to corn can occur for many reasons including:
 Carryover from previous year's application.
Carryover from early spring burn-down applications.
Drift from nearby applications.
Improper application of labeled chemicals.
Applying the chemical when corn is under environmental stress.
Tank or boom contamination with chemicals left over from previous applications.
Double or incorrect overlap application.
Herbicide injury is often difficult to diagnose.
At times, chemical carryover problems may not be seen until an application of a similar mode-of-action chemical is applied in the current season.
In addition, the symptoms expressed in corn may not be due to herbicide injury.
Environmental factors such as drought, high temperature, wind scouring, frost, or waterlogged conditions may be responsible.
Root pruning from insects, purpling, yellowing, or dead tissue may occur due to nutrient deficiencies or toxicity levels, or mechanical damage could also result in injury that, at first, appears to be due to herbicides.
When diagnosing problems in the field, there are several things to observe.
Look for patterns in the field associated with soil type, low or high spots, overspray in border rows, or overlap patterns from application equipment.
Operator error  may be the cause.
But interactions with temperature, crop vigor, and soil type may combine to cause injury even if the chemical has been properly applied.
If injury is not severe, most times corn will recover when growing conditions become favorable for growth.
Herbicides control plants in different ways.
Herbicides that target the same specific biochemical or biophysical process in a plant to disrupt plant development are grouped into families.
The Weed Science Society of America has designated a code for the primary site of action  that herbicide manufacturers often list on an herbicide label.
This designation: 1) helps the user understand the way that the herbicide works and 2) should be consulted to help rotate sites of action in order to minimize the outbreak of herbicide-resistant weeds.
The herbicides in each of the families listed below are just examples of herbicide chemistries.
Many herbicides have the same chemical but are listed by various trade names because of marketing.
Premix herbicides may contain two or more of the families listed.
Premix combinations or the addition of spray adjuvants or additives may result in heightened plant injury if applied during periods of stress, or at incorrect timings or rates.
As with any herbicide application, always read and follow label instructions.
Unfortunately, problems can occur, and the information provided may be used as a first reference.
If crop injury is more than cosmetic, more detailed information will be needed to confirm the true cause of the problem.
Acetyl-CoA Carboxylase  Inhibitors 
 WSSA Group 1 herbicides block the ACCase enzyme that is the first step in fatty acid synthesis.
There are two major herbicide chemistries in this group, aryloxphenoypropionate and cyclohexanediones type.
These herbicides are not labeled on corn and are often used to control volunteer corn in broadleaf crops such as soybean.
Examples: quizalofop ; sethoxydim 
 Site and Mechanism of Action: Stops Acetyl-CoA carboxylase  enzyme in the plant and inhibits the formation of lipids used for the formation of cell and intercellular membranes.
Appearance of Symptoms: Corn is sensitive to these grass herbicides.
Symptoms may first appear 2 to 4 days after treatment with wilting plants.
If applied to corn before emergence, corn may not emerge.
Severe symptoms take 1 to 3 weeks to develop after treatment.
Leaf chlorosis  begins followed by death of young leaves, with older leaves looking untouched.
To determine whether this injury has occurred, pull the whorl from the corn plant and the base will be brown and mushy.
Yellowing or reddening of new leaves
 Death of tissue and browning
 Growing point dies, becomes brown and mushy
 Typical Causes of Injury
 Drift from adjacent fields
 Figure 42.1 ACCase inhibitor symptoms, yellowing and bleaching , necrotic leaves.
Figure 42.2 Puma  applied at 10% tank contamination.
Acetolactate Synthase  Inhibitor 
 There are five chemical subgroups of ALS inhibitor chemistries: sulfonylureas ; imidazolinone ; pyrimidinylthiobenzoates; triazolopyrimidines; and sulfonyaminocarbonyl-triazolinones These compounds are found alone or in many premix combinations and, depending on the chemical, will control grasses, broadleaf weeds, or both.
There are many of these herbicides registered for use in corn.
However, the application of the wrong chemical can result in injury.
Sulfonylureas: There are many herbicides in this family and many premix herbicide combinations that contain this herbicide family.
Examples of a few of the herbicides registered for corn include: thifensulfuron ; halosulfuron ; indosulfuron methyl-sodium ; nicosulfuron ; and rimsulfuron.
Imidazolinone: Herbicides of this subgroup include imazaquin ; imazethapyr ; and imazamox.
These herbicides are typically used in broadleaf crops, however, imazethapyr is labeled for use on CLEARFIELD corn varieties.
Pyrimidinylthiobenzoates: An example of an herbicide in this subgroup is pyrithiobac-sodium , which is used for broadleaf weeds and some grasses in cotton.
Triazolopyrimidines: An example of an herbicide in this subgroup is flumetsulam , which is labeled for soil and postemergent application in corn and soybean to control a wide array of broadleaf weeds.
Figure 42.3 Corn in the foreground shorter than plants in the background indicating stunted plants and stunted internode elongation, early signs of injury caused by ALS herbicides.
Figure 42.4 Bottle-brush roots due to ALS herbicides.
application.
Figure 42.5 Shortened internodes due to post-ALS herbicide Figure 42.6 ALS herbicide applied at V8.
Note the pinched
 cobs on each corn ear.
Sulfonyaminocarbonyl-triazolinones: Examples of herbicides in this subgroup include flucarbonzone  and propoxycarbozone.
Both of these chemistries are used to control grass weeds in wheat.
Site and Mechanism of Action: These herbicides block the acetolactate synthase enzyme and stop the formation of branched chain amino acids.
Appearance of Symptoms: Two to 4 days after treatment the growing point becomes yellow and plant death is seen within 7 to 10 days after treatment.
Plants may have red or purple leaf veins.
Shortened internodes may be observed.
Yellow "flash" with chlorosis and yellowing in the whorl and crinkled leaf edge may be observed.
Corn ears may have pinched appearance.
Stunted plants, stunted internodes 
 Death of growing point
 Bottle-brush roots 
 Corn ears may have pinched appearance 
 Typical Causes of Injury
 Carryover from previous application
 Inhibitors of Microtubule Assembly 
 These herbicides bind to tubulin and inhibit polymerization of microtubules in the cell, which leads to loss of structure and function.
This stops the spindle apparatus during cell division and chromosomes cannot separate and form new cells.
Swelling of root tips is often observed as well as shoot malformation.
There are four main chemistry groups in the grouping, benzamides, dinitroanilines, phosphoamidates, and pyridines.
Examples: Pendimethalin ; trifluralin 
 Site and Mechanism of Action: These herbicides bind to tubulin and inhibit polymerization of microtubules in the cell, which leads to loss of structure and function of the microtubule.
This stops the spindle apparatus from forming during cell division and chromosomes cannot separate and form new cells.
Figure 42.7.
Prowl injury to corn root clubbing  compared with uninjured corn .
Appearance of Symptoms: Short, thickened roots.
Swelling of root tips is often observed as well as shoot malformation.
Shoot may leaf out below ground or if above ground, shoot may show purpling.
Root clubbing 
 Shoots may be purple
 Typical Causes of Injury
 Applied at the wrong time
 Shallow planting of crop with exposure to herbicide during germination
 Auxin Mimic Herbicides 
 There are many subfamilies of chemistries that act as synthetic auxin.
The families include benzoic acid, phenoxycarboxylic acids, pyridine carboxylic acids, and quinolone carboxylic acids.
There are many herbicides in this group and many premix herbicide combinations that contain these herbicide families.
Examples: Auxin mimic herbicides include: 2,4-D; dicamba ; clopyralid , fluroxypyr.
Premix combinations such as clopyralid + fluroxypyr  may contain one or more of these herbicide types.
Site and Mechanism of Action: The specific site of binding for these herbicides has not been identified.
These herbicides all act similar to auxin, a growth regulator naturally produced inside the plant.
The addition of synthetic auxin disrupts nucleic acid metabolism and protein synthesis, which ultimately leads to plant death.
These herbicides often accelerate shoot growth and inhibit root growth.
Phenoxycarboxylic Acid Subgroup Example: 2,4-D
 Appearance of Symptoms: Symptoms appear within hours of application on sensitive species.
Corn symptoms may first be observed as wilt.
Later, leaves may be tightly rolled in the whorl  , stalk may be brittle, and brace roots may proliferate.
Some corn hybrids are more sensitive than others.
The amine formulation of 2,4-D is less volatile and less likely to drift compared with ester formulations, especially at warmer temperatures.
If corn is growing quickly, symptoms may be more severe.
High winds may cause treated plants to undergo green snap of corn stems or lodging due to root injury.
If the herbicide is applied too late in the season, grain fill may be poor.
Figure 42.8 Onion leaf and shortened roots due to 2,4-D application.
Figure 42.9 Reduced grain fill due to too late an application of 2,4-D.
Figure 42.10 Dicamba brace root and root injury.
Sarah Berger, Univ.
Florida IFAS Extension and  University of Wisconsin Extension)
 Stalk bending and brittleness
 Missing kernels on ear 
 Examples: dicamba 
 Appearance of Symptoms: First appearance of symptoms can be within hours after application on sensitive species.
Injury may occur if used as a pre-emergence application and corn is planted shallow, planted in an open seed furrow, or if the soil is coarse and sandy.
If applied early post-emergence, onion leafing or brace root abnormalities may be noted if heavy rains occur soon after application.
Corn plants may lodge or have green snap in windstorms.
Grain fill may be compromised, if applied too late in the season.
Inhibitors of Photosynthesis 
 These groups contain many diverse herbicide families, and the classification by group is done by how each family interacts specifically with the Photosystem II binding sites.
If the herbicide binds at Photosystem II site A, then the herbicide is placed in Group 5; if binding occurs at Photosystem II site B, then the herbicide is considered in Group 6; and if at Photosystem II site A but has a different binding mechanism than herbicides in Group 5, then the herbicides are placed in Group 7.
While the site of action differs for these different groups, the herbicide symptoms are similar.
WSSA Group 5: Atrazine  and metribuzin .
WSSA Group 6: Bromoxynil  and bentazon  
 WSSA Group 7: Amides and Ureas
 Typical Causes of Injury
 Site and Mechanism of Action: All inhibit photosynthesis but bind or interact at different sites in Photosystem II.
When photosynthesis stops, electron flow, CO2 fixation, 2 ATP and NADPH, 2 formation are all inhibited.
In addition, the electrons are now free to form free radicles with other compounds and result in cell membrane disruption.
Applied to rapidly growing corn
 Figure 42.11 Atrazine injury to corn from preemergence application when corn was growing under cooler than normal conditions.
Figure 42.12 Buctril  injury to corn.
Note that the leaves that were present are most injured, newest leaves coming out of the whorl have little or no injury.
Figure 42.13 Basagran  injury to corn.
Basagran is not translocated in the plant so injury is seen where droplets hit the leaf.
The premix herbicide Laddok  may also result in this type of injury.
Appearance of Symptoms: Typically first symptoms are seen a few days after application.
Water-soaked appearance of leaves, yellowing, and browning .
Older leaves most affected
 Typical Causes of Injury
 Cool, wet conditions slowing corn growth
 Crop oil synergy if applied postemergence
 Inhibitors of Lipid Synthesis  
 The herbicides in this category inhibit plant processes that include fatty acid and lipid biosynthesis but have a different site of action than those of WSSA Group 1.
There is poor epicuticular wax formation on leaves, which leads to greater abiotic  and/or biotic stresses  for the plant.
Thiocarbamate and phosphorodithioates  are two herbicide chemistries in this grouping.
Examples of Thiocarbamate Herbicides: EPTC + safener ; butylate + safener 
 Site and Mechanism of Action: The specific site of action for these herbicides has not been identified.
The mechanism of action is to inhibit the growth of roots or shoots of seedlings.
These herbicides stop fatty acid biosynthesis and other lipids, reducing the epicuticular wax formation on leaves.
Appearance of Symptoms: Symptoms appear during or soon after plant emergence.
Plant may leaf out underground or if the plant emerges, will be stunted and have malformed leaves, and reduced or stunted root growth.
Amino Acid Derivative Herbicide 
 The active ingredient glyphosate is the common name for all trade-name herbicides in this family.
Glyphosate is also found in premix herbicide combinations.
Only corn hybrids with the glyphosate-resistant trait should be treated by postemergence applications of glyphosate, although this herbicide can be applied in burn-down treatments before corn emergence.
Example: glyphosate 
 Site and Mechanism of Action: This herbicide binds to the 5-enolpyruvyl-shikimate-3-phosphate synthase  enzyme, which stops synthesis of aromatic amino acids.
Figure 42.14 EPTC or butylate injury to corn seedling.
This may occur if herbicide without safener is applied or if emergence is delayed due to cool, wet soils.
Figure 42.15 Glyphosate drift to nonglyphosateresistant corn.
Figure 42.16 Glyphosate drift injury to nonglyphosate-resistant corn.
The depletion of these aromatic amino acids leads to problems in protein synthesis and other growth pathways.
Appearance of Symptoms: Symptoms are slow to develop.
Wilted plants may be seen in as little as 3 to as long as 10 days after exposure.
Symptoms become more severe with time after treatment.
Extreme heat, cold, or drought will slow and reduce the effects of glyphosate.
Yellow, then brown foliage
 Purpling of midveins may be present on older leaves
 Typical Causes of Injury
 Misapplied to nonglyphosate-resistant corn
 Phosphoric Acid Type Herbicide 
 The active ingredient glufosinate is the common name for all trade-name herbicides in this family.
Only corn hybrids with glufosinate-resistant trait  should be treated by postemergence applications of glufosinate, although this herbicide can be applied in burn-down treatments before corn emergence.
Example: glufosinate 
 Site and Mechanism of Action: This herbicide stops the activity of glutamine synthase an enzyme needed
 Figure 42.18 Glufosinate injury to non-LibertyLink corn.
Figure 42.19 Glufosinate  damage to nonLibertyLink corn.
to convert ammonia into other nitrogen compounds.
Consequently, ammonia accumulates to toxic levels in leaves causing cell destruction and inhibiting photosynthesis.
In addition, glutamine, a needed amino acid in plant growth, is depleted.
Appearance of Symptoms: Only apply this herbicide to GMO corn hybrids that have the LibertyLink trait.
Symptoms on LibertyLink corn may appear if applied when corn is stressed  or if applied too late in the season.
Drift on non-LibertyLink hybrids will result in symptoms 3 to 5 days after treatment.
Pale, yellow, or purple leaves
 Applied too late in the season
 Misapplied to non-LibertyLink corn
 Typical Causes of Injury
 Pigment Inhibitors 
 These two groups of herbicides block the formation of pigments, the compounds that provide color to the plant leaves, through two different mechanisms.
Plants affected by herbicides in either of these groups have bleached white leaves because chlorophyll and other pigment compounds are not formed.
Clomazone  is a WSSA Group 13 herbicide that inhibits the 1-deoxy-D-xylose 5-phostage synthatase , which stops plastid isoprenoid synthesis.
Herbicides in Group 27 inhibit the 4-hydroxyhenyl-pyruvatedioxygenasis  enzyme, which stops plastoquinone biosynthesis, inhibiting caretonoid and chlorophyll synthesis.
Example: Group 13 herbicide clomazone 
 Site and Mechanism of Action: This herbicide inhibits the 1-deoxy-D-xylose 5-phostage synthatase  enzyme found in the carotenoid and chlorophyll pigment pathway in plants.
The lack of compounds in the leaf that give the leaf color is the reason why the plant appears bleached white.
Appearance of Symptoms: Plant leaves are white.
Example: Group 27 herbicides include isoxaflutole ; mesotrione ; tembotrione ; topramezone 
 Site and Mechanism of Action: These herbicides bind at 4-hydroxyhenyl-pyruvate dioxygenase , which stops caretonoid biosynthesis and results in bleached  plants
 Appearance of Symptoms: Appearance of bleached  tissue on leaves within a few days after exposure.
Typical Causes of Injury
 Note: Some herbicides are now formulated with safeners to protect the crop plant from injury.
For example, Balance Flexx 2SC*  contains isoxaflutole plus a safener.
Safeners can protect the plant by increasing the herbicide metabolism  in the plant but not the weed.
Figure 42.20 Injury of isoxaflutole + atrazine WITHOUT crop safener.
This type of injury will be similar for both the DOXP and HPPD inhibitors.
Protoporphyrinogen Oxidase Inhibitors 
 The WSSA Group 14 herbicides inhibit protoporphyrinogen oxidase.
This stops chlorophyll and heme biosynthesis, which results a series of events that lead to singlet oxygen and radical formation.
The free radicals then begin a chain reaction of lipid perioxidation.
WSSA Group 14 contains many different types of herbicide chemistries including diphenylethers, oxadiazoles, phenpyrazoles, and pyrimidindiones.
Examples: fomesafen ; carfentrazone ; flumioxazin ; saflufenacil 
 Site and Mechanism of Action: Herbicides in this group inhibit the protoporphyrinogen oxidase  enzyme resulting in cell membrane destruction.
Appearance of Symptoms: Appearance of necrotic  speckling on leaves within a few days after exposure.
Brown tissue in areas that were water-soaked
 Typical Causes of Injury
 Applying under high temperature and humidity increases the potential for crop injury
 Figure 42.21 Symptoms of HPPD injury.
Corn plants have chlorotic  to white veins  and the lower leaves may droop.
and Illinois Extension.)
 Figure 42.22 Corn with fomesafen injury.
Figure 42.23 Saflufenacil injury to corn.
The herbicide was applied postemergence to corn when it is labeled only for pre-emergence.
Note that the symptoms look like symptoms shown for WSSA Group 15.
Inhibitors of Synthesis of Very Long-Chain Fatty Acids 
 Acetamide, chloroacetamide, and oxyacetamide herbicides inhibit very long-chain fatty acid synthesis.
This inhibition, in turn, reduces the formation of cell membranes which then inhibits plant growth.
Examples: metolachlor ; pryroxasulfone ; alachlor ; acetochlor ; dimethenamid-p 
 Site and Mechanism of Action: These herbicides inhibit the formation of very long-chain fatty acids.
The exact site of attachment is unknown.
Plants do not emerge or growth of seedling roots or shoots is poor.
Figure 42.24 S-metolachlor  injury to corn.
Appearance of Symptoms: If plants emerge, shoots often have buggy-whipped appearance .
These symptoms will be observed during or soon after plant emergence.
Leaf out before emergence
 Buggy whipping 
 Typical Causes of Injury
 Delayed corn emergence due to cold or waterlogged soil
 Applied during corn emergence  which is too late
 Application to sandy soils
 Auxin Transport Inhibitor 
 Example: Diflufenzopyr is in this group and is found only in herbicides premixed with other herbicides.
Premix combinations include + Dicamba, Group 4; Distinct has 50% dicamba + 20% difluenzopyr; Status has 44% dicamba + 17% diflufenzopyr + safener; Celebrity Plus has nicosulfuron  + dicamba + diflufenzopyr.
Site and Mechanism of Action: The exact site is unknown.
This auxin transport inhibitor blocks natural auxin transport to roots and stems; there is a safener in Status that reduces the potential for corn injury.
Appearance of Symptoms: Symptoms on susceptible plants are often observed within hours.
Cell Membrane Disruptor, Photosystem I Electron Diverters 
 This herbicide group includes paraquat and diquat.
These postemergence herbicides will injure all crops.
The herbicide accepts electrons from Photosystem I and becomes a radical, which then reduces molecular oxygen to superoxide radicals and form hydrogen peroxide that continue to break down components of the cell.
Example: paraquat 
 Site and Mechanism of Action: The site of action is in Photosystem I.
These herbicides accept electrons from the photosystem, causing free radicals to be formed, followed by production of hydrogen peroxide that leads to destruction of cell membranes and other components of the cell.
Appearance of Symptoms: The free radicals destroy the integrity of cell membranes, which rapidly leads to leaf wilting and desiccation.
Localized symptoms are often observed within hours of application.
The first symptom is water-soaked lesions in spots on the plant.
Because the herbicide is
 contact type, the spots will form only where the herbicide was applied.
Young leaves that had not emerged from the whorl will not show injury.
Plants may outgrow the symptoms and may not suffer yield loss.
Dead tissues but only as spots
 Typical Causes of Injury
 Sprayed after corn emergence
 Figure 42.26 Paraquat injury to older plants.
Note absence of injury to young leaves in the whorl.
Avoid common causes of herbicide injury.
Make sure that there is no residual herbicide left in the tank from another application, and clean the tank using label instructions to avoid contamination.
Avoid overspray  and drift.
Overspray may cause residual herbicide carryover for future crops.
Establish buffer zones with a safe distance to open water and wells.
Be conscious of wind speed and direction to avoid drift to sensitive crops and noncrop areas.
Before application, make sure the sprayer is calibrated.
This should also involve checking all nozzles to make sure that the amount discharged and spray pattern is correct.
Read all label instructions prior to herbicide mixing and make sure the crop is at the correct stage of growth for treatment.
Recheck your calculations about how much herbicide and other adjuvants need to be added to the tank.
Add the herbicide and adjuvants in the same order listed on the label to avoid mixing problems.
If unsure about the compatibility of products, do the quart jar test  prior to adding large amounts to the tank.
If you suspect herbicide injury:
 Document crop injury symptoms , field patterns , and timing of what symptoms were seen, when symptoms were seen, and the progression of symptoms.
Check weather information to determine whether the injury may be due to frost, hail, sheer winds, or other weather-related problems.
Contact the applicator or chemical representative.
Photograph and document injury symptoms.
Check growing points to determine whether plant can recover.
Determine the extent of the injury.
Map areas of the field that are damaged.
Keep records of crop yields from undamaged and damaged areas.
Table 1.
Percent of fields that had a lower soil water content on Sept.
15 than in August:
 In 2018, 42% of fields experienced their 15-25 inch soil zone get drier.
In 2018, 42% of fields experienced their 25-36 inch soil zone get drier.
When yucca covers too much land to spray, the only cost-effective way to reduce its impact is to winter graze.
During winter, yucca often is the only green plant around.
Sometimes cows actually will get down on their knees, lay their head sideways on the ground and chew through the base of the plant to get to the moist, tender parts.
It has been observed, though, that it can take some time for animals to learn to graze yucca and there may be some animals in the herd that will not graze it while others can be quite proficient.
After several consecutive winters of grazing, yucca stands can be reduced so grass again thrives during summer.
Support for People Wanting to Improve Their Irrigation Management
 For those who have not collected data in the past or would like to hone their scheduling skills, take some time now to figure out what will work best for your operation.
Many resources are available to help.
A great five-part video series on this topic can be found on the CropWatch YouTube channel at: How to Schedule Irrigations with Soil Water Data.
Factors in Cotton Irrigation
 quality of cotton fiber not materially affected by different irrigation treatments in experiments on three types of soil
 J.
R.
Stockton and L.
D.
Doneen
 Studies on the relationship between irrigation frequency and cotton yield have included various irrigation practices on a wide variety of soil types.
Investigations at the United States Cotton Field Station at Shafter were on a Hesperia sandy loam soil, and concerned a number of different irrigation treatments.
Under Treatment A-four irrigations -the cotton plants were allowed to definitely wilt prior to each irrigation.
Plants given Treatment B-12 irrigations were irrigated frequently throughout the season.
The Treatment C-six irrigationsplot was irrigated with the first indication the plants were suffering from a lack of soil moisture.
The first sign of stress was a color change in the foliage often accompanied by transient wilting visibly apparent the afternoon prior to the irrigation.
Those three treatments have constituted the basic irrigation schedule for the work at the Cotton Station.
Treatment C-where the number of irrigations was cut from 12 to six-resulted in a significant decrease in vegetative growth, but no significant difference in lint yield.
Similar results have been obtained for several years, and point up the possibility of using the plant as an over-all indicator for soil moisture deficit without reducing yields.
In this case the plant integrates many soil moisture variables-nematodes, clay pans, hardpans, poor water penetration, and others-which are difficult to evaluate.
The color change in foliage is due primarily to the lack of new terminal growth
 Moisture Characteristics for Soils Used in Irrigation Tests
 Location	Soil	moisture	inches
 Shafter	Hesperia	8.8	4.4	0.7
 Button-	Merced	33.6	19.2	2.3
 Corcoran	Tulare	40.8	23.0	2.6
 *ME = Moisture equivalent, and represents the maximum amount of moisture a well drained soil will hold-often referred to as "field capacity.' *PWP = Permanent wilting percentage, and is the lower limit of readily available soil moisture, where plants wilt or a cessation in growth occurs.
Varying the number of irrigations on the plant height in inches.
Cotton Station, Shafter.
and appears to be a better indication of moisture stress on the light sandy soils than on the heavy soils.
Yield in Bales and Plant Height for Three Irrigation Treatments, Shafter
 Treatment	B	C	A
 No.
irrigations	12	6	4
 Yield, bales per acre	2.79	2.67	2.09
 Plant height, inches	42	37	31
 The influence of these soil moisture regimes on insect activity appears to be significant.
Lygus bugs are a serious insect pest of cotton in the San Joaquin Valley.
To determine the abundance of this pest in the irrigation plots, sweep counts were made in treatments A and B, the extreme treatments in irrigation frequency.
The number of lygus bugs caught in an insect net from 50 sweeps down a cotton row is commonly used as an index for determining control measures.
If 10 or more bugs are counted, control measures are indicated.
The average number of lygus bugs found in the four replications of the dry Treatment A was 4.8, and 10.9 in the more frequently irrigated Treatment B.
Early irrigations were made by varying the number of irrigations prior to the initiation of flowering on June 28 and then irrigating frequently for the rest of the season.
In this study two additional treatments were included and compared with Treatment B which is the one usually practiced for the test area.
The additional treatments were:
 Treatment J-14 irrigations-irrigated excessively prior to June 28-the initiation of flowering-after that date irrigation was the same as Treatment B.
The plot receiving Treatment L-10 irrigations-was not irrigated prior to the initiation of flowering.
On June 28 the plants were severely stressed and received their first irrigation.
After that date irrigation was the same as Treatment B.
The vegetative growth, as measured by height of plant, for these treatments throughout the season is shown in the graph on this page.
On June 28 the plant heights for treatments J, B and L were 19", 15" and 12", or a maximum difference of 7", whereas on September 1 the difference between irrigation treatments was less than 3".
Early Irrigations on Yield and Plant Disease, Shafter
 No.
irrig.
prior to 6/28.
4	2	0
 Yield, bales per acre	2.53	2.79	2.49
 % plants infected with
 vert.
wilt	18	6	2
 The number of irrigations prior to June 28, lint yields and per cent plants infected with verticillium wilt are given in the following table.
After June 28 all treatments received 10 irrigations and followed the irrigation schedule for Treatment B.
A complicating factor is the incidence of verticillium wilt as influenced by irrigation frequency early in the season.
This was evaluated by determining the per cent plants exhibiting visual symptoms of the disease.
The severity of the symptoms was more intense for Treatment J than for the other two treatments and may have been responsible for the yield being lower in this treatment.
The yield reduction for Treatment L was probably due to the extremely small plants at flowering as these plants were suffering from a lack of soil moisture for more than three weeks.
Consequently, with frequent irrigations after June 28, rapid vegetative growth occurred, and the boll set was late, followed by a delayed maturity of the crop.
The experiment was essentially repeated-with the exception that Treatment C was substituted for after June 28 all treatments received five irrigations on the same schedule as Treatment C.
These additional treatments are as follows: Treatment K-nine irrigations-irrigated with excessive frequency prior to June 28, after which it was irrigated the same as Treatment C.
Treatment M-five irrigations-was not irrigated prior to the initiation of flowering.
On June 28 the plants were severely stressed and received their first irrigation.
After that date irrigation was as for Treatment C.
These treatments were primarily concerned with the number of irrigations prior to June 28 and then irrigating for the balance of the season at the first signs of soil moisture deficit.
The results of this experiment are given in the following table.
Varying the Early Irrigation and Irrigating by Color Change, Shafter
 Treatments	K	C	M
 No.
irrig.
prior to 6/25	4	1	0
 Plant height, in.
6/25	20	16	11
 Plant height, inches 36	37	35
 Yield, bales per acre	2.61	2.67	2.51
 % plants infected with
 vert.
wilt	15	8	1
 Again, early irrigations have resulted in more plants infected with verticillium wilt.
The plant height on June 25 showed wide differences between treatments, but by September 1 the differences were obliterated.
Although vegetative growth and plant diseases are markedly influenced by early irrigations, the subsequent irrigations timed by color change of the plant, or Treatment C, had a tendency to reduce these variations by harvest.
Other irrigation trials were conducted
 on a Merced clay soil near Buttonwillow and on a Tulare clay soil near Corcoran, in the Tulare Lake Basin.
The irrigation treatments tested in these studies were:
 Treatment A-dry-where the plants were allowed to wilt severely prior to each irrigation;
 Treatment B wet-irrigated frequently all season;
 Treatment C-intermediate-irrigated at a frequency intermediate between treatments A and B.
Treatment D-dry then wet-was severely stressed for moisture prior to the first irrigation and was then irrigated frequently.
At Buttonwillow the first irrigation was applied on July 9 and at Corcoran on July 26.
The results for the various irrigation treatments at Buttonwillow on Merced clay soil are given in the following table.
Results of Irrigation Trials at Buttonwillow on Merced Clay Loam
 Treatment	A	C	B	D
 No.
irrigations	3	4	7	5
 Date, first irrig	7/9	6/25	6/15	7/9
 Yield, bales/acre 2.16	2.11	1.74	2.16
 with vert.
wilt 48	35	71	38
 Only Treatment B received two irrigations in June and consequently had a high soil moisture condition for the early vegetative growth.
The severity of verticillium wilt appears to be directly related to this early June irrigation.
However, general level of infection is much higher than on the sandy soils at Shafter.
Apparently this disease is responsible for the 29% reduction in yield for the B treatment.
Otherwise there are little differences in yield for the various soil moisture conditions as maintained by the different irrigation schedules.
The vegetative growth shows differences, especially for Treatment A, which changed color or wilted before each irrigation
 and for Treatment D for a part of the season.
The experiments at Buttonwillow and at Shafter indicate that high soil moisture or frequent irrigations early in the season will increase the verticillium wilt in plants with a corresponding decrease in yield.
This would be especially significant for seasons favorable for a high incidence of the disease.
The yields and the number of irrigations for the Tulare Lake Basin plots are given in this table.
At the Tulare Lake Basin location verticillium wilt was not a problem, which may be due, in part, to the lateness in June for the first irrigation on Treatment B.
Results of Irrigation Trials at Tulare Lake Basin on Tulare Clay
 Treatment	A	c	B	D
 No.
irrigations	2	3	6	4
 Date, first irrig.
7/26	7/15	6/23	7/26
 Yield, bales/acre	1.15	1.95	2.07	1.72
 This soil is extremely heavy and soil moisture extraction by the cotton roots was limited to the surface 18"-24" of soil.
Because of the poor soil structure, root development in the second foot of soil is variable and sparse.
The yield, to some extent, reflects frequency of irrigation, but not to the degree that is indicated by the vegetative growth.
On July 29 the height of the plant for treatments A and D was 13" as compared to 18" for C and 27" for Treatment B.
The moisture stress early in the season was so severe for treatments A and D that a reduction in both yield and vegetative growth occurred even though Treatment D was irrigated frequently after July 26.
Treatment C received half
 Concluded on page 25
 Frequency of irrigation in relation to vegetative growth as measured by height in inches.
Buttonwillow experiment.
Frequency of irrigation on vegetative growth as measured by height in inches.
Corcoran experiment.
Costs of Irrigation Water
 distance of transport, height of lift and timing of pumping operations influence costs of irrigation water to farmers
 L.
J.
Booher and M.
R.
Huberty
 The price farmers pay for irrigation water depends to a large extent on the cost of constructing and operating the engineering works needed to deliver the water to their farms.
The cost of irrigation water varies from a few cents to more than $50 for each acre-foot of water used.
The higher costs are where the water must be transported long distances or must be lifted against high heads.
The waters within the state-surface waters and ground waters-are presumed to be the property of the people of the state.
However, farmers have spent considerable sums for legal actions relevant to establishing or protecting their rights to the use of water, and these sums are part of the development costs of an irrigation project.
Most of the early irrigation projects were situated in areas where surface waters could be easily diverted, or where shallow ground waters were available for pumping.
The present cost of water delivered by these old established projects is, in many cases, the lowest to be found in the state.
Some projects deliver water to farmers for less than $1.00 an acre-foot.
The cost of water on other projects may range from $2.00 to more than $3.00 an acre-foot.
Water costs on more recently developed projects and for projects that are being proposed reflect the higher costs of constructing irrigation works needed to carry water great distances.
Water from areas of excess supply is often carried several hundred miles to water deficient areas.
Under the Central Valley Project, costs of Class 1 water delivered at canalside vary from $2.75 to $3.50 an acre-foot.
In addition, the farmers pay for the cost of
 the distribution works needed to deliver water to their farms.
Water costs under the Feather River Project will depend on the distance the water must be carried and the lift required.
Where surface waters are not available for irrigation, ground waters may be obtained by pumping from wells.
There are some 75,000 such wells used in California, varying from less than 50' deep and costing less than $1,000 to wells several thousand feet deep and costing $25,000 or more.
Costs for pumping water from wells include annual fixed charges for interest, taxes, depreciation and maintenance on wells and pumping equipment, and charges for energy needed to operate the power unit.
The energy required to pump an acrefoot of water depends on the efficiency of the pumping equipment and on the height of the lift-whether a few feet or several hundred feet.
The cost of power is related not only to the amount of energy used but to the number of hours that the pump is operated each year.
Because of the power rate structure in common use by utility companies in California, power costs will be less for a small pump operating long hours than for a large pump operating a few hours, even though both pumps use the same amount of energy and deliver the same amount of water with the same lift.
Overnight storage reservoirs are used on many farms, to permit continuous operation of pumps tailored to the water requirments of the area to be irrigated.
The reservoirs permit irrigating during daylight hours
 while taking advantage of reduced power costs.
Joint use of a single pump by several farmers is another practice used to reduce pumping costs.
There are wide limits between the costs of pumping water in California.
An average cost for power might be 2 an acrefoot per foot of lift plus a similar amount for fixed charges, making a total of 4c.
To lift water 100'-in this case-would cost $4.00 for each acre-foot pumped.
In many ground-water basins the amount of water being pumped is greater than the normal recharge to those basins.
This has resulted in a lowering of the water table and increased pumping lifts with increased costs.
Many farmers have found it necessary to lower the pumps in their wells as the water table recedes.
During the past several decades, improvements in pump operating efficiencies and reductions in power rates partly compensated for the increased lifting costs, but the trend has been reversed during the last several years.
There has been some increase in power costs and a considerable increase in the cost of pumping equipment.
With some high income crops, water costs may be only a minor part of the total production costs.
In such cases a considerable increase in water costs may not greatly affect the farmer's operations.
On the other hand, with many low income crops, the cost of water is an important item, and any increase in the price a farmer pays for irrigation water may make his operations nonprofitable or place him at a disadvantage in competing with areas where water costs are less.
L.
J.
Booher is Extension Irrigationist, University of California, Davis.
M.
R.
Huberty is Professor of Irrigation and Engineering, University of California, Los Angeles.
Continued from page 17
 the number of irrigations as compared to Treatment B, yet the reduction in yield was only 6% whereas a 29% reduction occurred in vegetative growth.
This is an excellent example of where a soil condition limits root development and the relationship between irrigation frequency on yield and vegetative growth
 when compared with results obtained on the Buttonwillow plots where root development was better.
In all three locations and extremes in irrigation treatments the quality of the fiber was not materially affected.
Lint from Shafter and Tulare basin showed no differences in either grade or staple length even for the extremely dry treatments where the yields were severely reduced.
After the lint was spun into yarn
 there were no outstanding differences.
However, the less frequently irrigated treatments did show a tendency to have slightly stronger yarn with a better appearance index which is probably a reflection of less trash in the seed cotton and fewer nappy thin walled fibers.
J.
R.
Stockton is Assistant Specialist in Irrigation, University of California, Davis.
L.
D.
Doneen is Professor of Irrigation, University of California, Davis.
TEXAS A&M AGRILIFE EXTENSION
 Economics of Irrigation Systems
 Steve Amosson Regents Fellow, Professor and Extension Economist Texas AgriLife Extension Service
 Lal Almas Associate Professor, Department of Agricultural Sciences West Texas A&M University
 Jnaneshwar R.
Girase Research Associate Texas AgriLife Research
 Nicholas Kenny Program Specialist-Agricultural Engineering Texas AgriLife Extension Service
 Bridget Guerrero Program Specialist-Agricultural Economics Texas AgriLife Extension Service
 Kumar Vimlesh Former Graduate Assistant, Department of Agricultural Sciences West Texas A&M University
 Thomas Marek Senior Research Engineer and Superintendent Texas AgriLife Research
 All of The Texas A&M System
 Leon New, Professor Emeritus and Agricultural Engineer with the Texas AgriLife Extension Service, contributed significantly to the earlier work on which this publication is based.
This research was supported in part by the Ogallala Aquifer Program, a consortium of the USDA Agricultural Research Service, Kansas State University, Texas AgriLife Research, Texas AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
Mid-elevation spray application  center pivot
 Low elevation spray application  center pivot
 Low energy precision application  center pivot
 Subsurface drip irrigation 
 Investment cost of irrigation systems
 Estimated Annual Operating Expenses
 Assumptions and crop scenarios
 Savings from field operations and total annual irrigation
 Impact of fuel prices on pumping cost
 Effect of lift on pumping cost
 Correlation between amount of water pumped and fixed pumping costs
 Effect of wage rate on pumping costs
 Effects of efficiency in natural gas engines.
Conversion to an electric-powered irrigation system
 Irrigation can improve crop production, reduce yield variability, and increase profits.
But choosing and buying an irrigation system are both expensive and complex.
When considering investing in an irrigation system, farmers must keep in mind several major factors: financing, crop mix, energy prices, energy sources, commodity prices, labor availability, economies of scale, the availability of water, savings in field operations, the system's application efficiency, the operating pressure of the design, and the depth from which the water must be pumped, or pumping lift.
To assist producers making decisions about irrigation systems, Texas A&M System researchers studied the costs and benefits of five types of irrigation systems commonly used in Texas: furrow  irrigation; mid-elevation spray application  center pivot; low elevation spray application  center pivot; low energy precision application  center pivot; and subsurface drip irrigation.
The study focused on:
 The approximate costs, both gross and net, of buying and operating each system
 Each system's potential benefits for improving water application efficiency and reducing field operations
 The effect of economies of size on center pivots
 The impact of other major factors such as fuel prices, pumping lift, and labor costs
 Economics of improving natural gas engine efficiency
 Natural gas versus electric powered irrigation
 The costs of buying and operating an irrigation system may vary among farms because of differences in individual farming/ranching operations.
Before changing management strategies, producers should compare their operations closely to those in the study.
For the study, it was assumed that each irrigation system was installed on a "square" quarter section of land  or in the case of a half-mile pivot a square section.
It was assumed that the terrain and soil type did not affect the feasibility of the irrigation system.
Not all of the water irrigated is used by the crop.
The percentage of irrigation water used by a crop is called the system application efficiency.
To determine the amount of water required to irrigate crops using the different systems, farmers must know and be able to compare the application efficiency of each system.
Application efficiency can vary among systems because of:
 Differences in design, maintenance, and management of the systems
 Environmental factors such as soil type, stage of crop development, time of year, and climatic conditions
 The availability of water and its potential value for other uses
 Economic factors such as commodity and fuel prices
 For the five systems studied, the application efficiency ranged from 60 to 97 percent.
Those with the highest application efficiencies tended to have the lowest pumping costs.
Of the five irrigation systems, the least efficient was the furrow system; the most efficient was the subsurface drip irrigation system.
An efficiency index was calculated to show the amount of water  that each system would have to additionally apply to be as effective as the LESA system.
Table 1.
Basic assumptions for five irrigation distribution systems
 Irrigation system	Operating	Application	Efficiency	Acres
 pressure	efficiency	index	irrigated
 Furrow	10	60	1.47	160
 Mid-elevation	25	78	1.13	125
 Low elevation	15	88	1.00	125
 Low energy	15	95	0.93	125
 Subsurface drip	15	97	0.91	160
 1psi = pounds of pressure per square inch of water
 The calculations were made using the LESA center pivot system as a base.
It was assumed that applying the same amount of "effective" water would produce the same crop yield.
Therefore, according to the index, a subsurface drip system would need only 91 percent of the water used by the LESA system to be just as effective.
The furrow system would require 47 percent more water than the LESA system to be equally effective.
When evaluating the additional costs of the more efficient systems, farmers can consider the reduced irrigation that will be needed for each system.
A system's operating pressure affects the cost of pumping water.
Higher pressure makes irrigation more expensive.
Of the five systems studied:
 Furrow system usually had an operating pressure of 10 pounds per square inch.
LESA, LEPA, and SDI had an intermediate operating pressure of 15 psi, depending on the flow rate.
MESA center pivot systems required a higher pressure of 25 psi.
Table 1 lists the operating pressures that were used to compare the pumping cost for each system.
To function properly, each irrigation system must maintain adequate and consistent operating pressure.
Water flow  dictates the operating pressure that must be maintained for a system's design.
As GPM drops, growers must close furrow gates, renozzle center pivots, and reduce the number of emitter lines to make the system work properly.
The five irrigation systems studied had varying designs, costs, management requirements, advantages, and disadvantages.
Producers should evaluate these systems in light of the characteristics and requirements specific to their farming/ranching operations.
Furrow irrigation delivers water from an irrigation well via an underground supply pipeline, to which gated pipe is connected.
This configuration is prevalent throughout the Texas High Plains.
The water flows by gravity on the surface through the furrows between crop rows.
The gated pipe must be moved manually from one irrigation set to the next one that accommodates the well GPM, usually every 12 hours.
In the Figure 1.
Furrow irrigation on cotton.
study, two irrigation sets of gated pipe were used to allow the water flow to be changed without interruption.
Polypipe can be used instead of aluminum or PVC gated pipe.
Normally, polypipe is not moved.
Appropriate lengths are cut, plugged, and connected to underground
 .
The limita-
 tion of polypipe is
 that it is much less
 durable and is usually
 replaced every 1 to 2
 Figure 2.
Furrow polypipe on cotton.
With good planning, land preparation, and management, furrow irrigation can achieve 60 percent water application efficiency.
That is, 60 percent of the water irrigated is used by the crop.
The rest is generally lost to deep percolation below the crop root zone.
Furrow systems are best used in fine-textured soils that have low infiltration rates.
For highest crop production, water should be supplied simultaneously and uniformly to all plants in the field.
To make the application more uniform, farmers can consider laser-leveling fields, adjusting gates, and modifying the shape, spacing, or length of the furrow.
Disadvantages of furrow irrigation include:
 It usually requires additional tillage preparation and labor, especially if the terrain varies in elevation.
It can cause some environmental problems, such as soil erosion, sediment transport, loss of crop nutrients, deep percolation of water, and movement of dissolved chemicals into groundwater.
Terrain variations can cause the water to be distributed unevenly, reducing crop growth and lowering overall crop yield.
Furrow irrigation usually applies water at higher increments than do center pivot or subsurface drip systems.
To address these problems, farmers can take remedial measures such as laser leveling, planting filter strips, mechanical straw mulching, reducing tillage, changing furrow design, and installing sediment ponds with tail water pump-back features.
Mid-elevation spray application  center pivot
 Mid-elevation spray application center pivots have water sprayer heads positioned about midway between the mainline and ground surface.
The quarter-mile system considered in this study consisted of 145 drops spaced 10 feet apart.
Polydrops  were attached to the mainline gooseneck or furrow arm and extended down to the water applicator.
In MESA systems, water is applied above the primary crop canopy, even on tall crops such as corn and sugarcane.
Weights and flexible drop hoses should be used to
 Figure 3.
MESA center pivot, half-mile system.
reduce water losses and improve distribution, particularly in windy areas such as the Texas High Plains.
The nozzle pressure for MESA varies according to the type of water applicator and the pad arrangement selected.
Although some applicators require an operating pressure of 20 to 30 psi, improved designs require only 6 to 10 psi for conventional 8to 10-foot mainline outlet and drop spacing.
These applicators are now common and perform well.
The operating pressure can be lowered to 6 psi or less if the sprayer heads are positioned 60 to 80 inches apart.
A disadvantage of mid-elevation spray application is that it is subject to water losses via the air and through evaporation from the crop canopy and soil surface.
Research has shown that when using above-canopy irrigation for corn production, 10 to 12 percent of the water applied is lost from evaporation from the foliage.
Field comparisons showed a total water loss  of 20 to 25 percent from MESA center pivot irrigation systems where applicators were set above the crop canopy.
The research study found that the water application efficiency averaged 78 percent for MESA center pivot systems.
Low elevation spray application  center pivot
 In low elevation spray application center pivot sysitems, water applicators are positioned 12 to 18 inches above ground level or high enough to allow space for wheel tracking.
Each applicator is attached to a flexible drop hose, which is connected to a gooseneck or furrow arm on the mainline.
Weights are positioned immediately Figure 4.
LESA center pivot on cotton.
upstream from the pressure regulator and/or the applicator.
They help stabilize the applicator in wind and allow it to work through plants in straight crop rows.
It is best to maintain nozzle pressure as low as 6 psi with the correct water applicator.
The optimal spacing for LESA drops should be no wider than 80 inches.
If installed and managed properly, LESA drops can be spaced on conventional 8to 10-foot MESA spacing.
Corn crops should be planted in circular rows; the water should be applied beneath the primary foliage.
Some growers have used LESA successfully in straight corn rows at conventional outlet spacing by using a flat, coarse, grooved pad that allows the water to spray horizontally.
The coarser  pads generally result in the
 least evaporation loss because of the larger droplet sizes, but they can cause in soil dispersion with some soils.
Grain sorghum and soybean crops can also be planted in straight rows.
With wheat, the foliage may cause the water distribution to be significantly uneven if the nozzles are within the crop's dense canopy.
To improve water distribution, growers may need to temporarily swing the drop hose and thus the applicator over the truss rod, effectively raising the nozzle above or near the top of the canopy-
 LESA center pivots generally wet less foliage, especially for a crop planted in a circle.
Less water is lost to evaporation.
The water application efficiency for LESA usually averages 85 to 90 percent , but it may be lower in open, lower profile crops such as cotton and peanuts, or in broadcast crops such as wheat or alfalfa.
When the drops are spaced no more than 80 inches apart, LESA center pivots can easily be converted to LEPA with an applicator adapter that includes a connection for attaching a drag sock or hose.
Low energy precision application  center pivot
 Low energy precision application center pivot systems discharge water between alternate crop rows planted in a circle.
Water is applied either with a bubble applicator 12 to 18 inches above ground level or with drag socks or hoses that release water on the ground.
Drag socks help reduce furrow erosion; double-ended socks are designed to protect and maintain the furrow dikes.
When needed, drag socks and hose adapters can be easily removed from the applicator and replaced with a spray nozzle.
Figure 5.
LEPA center pivot with a drag sock.
the LEPA "quad" appli-
 cator, delivers a bubble
 water pattern (Fig.
6
 that can be reset to an
 for germination and other in-field adjustments needed.
LEPA applicators are usually placed 60 to 80 inches apart, corresponding to twice the row spacing.
Thus, one row is wet and one row is dry.
Dry middles allow more rainfall to be stored.
When the crop is planted in a circle,
 Figure 6.
LEPA center pivot with a bubble applicator on corn.
the applicators are arranged to maintain a dry row for the pivot wheels.
Research and field tests show that crop production is the same whether water is applied in every furrow or only in alternate furrows.
The field trials indicated that crops use 95 percent of the irrigation water pumped through a LEPA system.
The water application is precise and concentrated.
LEPA can be used in circles or in straight rows.
It is especially beneficial for low-profile crops such as cotton and peanuts.
This irrigation system is more common in areas with limited water supplies.
A disadvantage of LEPA is that it requires more planning and management, especially for crops in clay soils that infiltrate water more slowly.
Subsurface drip irrigation 
 In subsurface drip irrigation, drip tubes are placed from 6 to 12 inches below the soil surface, the depth depending on the crop, soil type, and tillage practices.
Drip tubes typically include built-in emitters at optional spacings.
The spacing and flow rate of the emit-
 ters depend on the
 required by the crop.
be installed no more
 than two row widths
 Figures 7a and b.
Subsurface drip irrigation.
Considered the most water-efficient system available, SDI has an application efficiency of 97 percent.
The advantages of a subsurface drip system include:
 The amount of water available dictates the system's design, control, and management.
Like the LEPA center pivot, SDI is a lowpressure, low-volume irrigation system.
It is a convenient and efficient way to supply water directly in the soil along individual crop rows and surrounding individual plant roots.
It saves money by using water and labor efficiently.
It can effectively deliver very small amounts of water daily, which can save energy, increase yields, and minimize leaching of soluble chemicals.
Subsurface drip systems have these disadvantages:
 They require intensive management.
During dry springs, an SDI system may be unable to deliver enough water to germinate the crop, and more water than needed must be applied for the crop, resulting in deep-percolation losses.
The system must be designed and installed accurately.
If the system is not managed properly, much water can be lost to deep percolation.
Evaluating the feasibility of investing in a new irrigation system can be very complicated because many factors are involved.
However, once all the factors are taken into consideration, the methodology in making the decision is relatively simple.
Growers should first estimate the gross investment cost, which is the amount of money required to buy the system.
Next, estimate the "true" economic cost, or the net investment.
Net investment takes into account tax savings, future salvage value, and the opportunity cost  of the investment.
Each irrigation system has a combination of annual benefits that reduce costs and/or improve efficiency.
The benefits may include decreased pumping, labor, and field operations.
These benefits may offset the cost of adopting the system.
Because a dollar today is worth more than a dollar 5 years from now, all annual costs and benefits must be discounted to today's dollars.
This will allow you to directly compare the costs and benefits of irrigation systems both initially and across multiple years.
Investment cost of irrigation systems
 The investment costs for the irrigation systems studied are listed in Table 2.
The costs for the well, pump, and engines were assumed to be the same for each irrigation system and were not included in the investment cost.
The gross investment for each quarter-section system  ranged from $208.56 per acre for furrow to $1,200.00 for subsurface drip irrigation with emitter lines
 Table 2.
Investment costs of alternative irrigation systems
 Distribution system			
 Furrow	208.56	183.62	161.99
 Center pivot, quarter mile	556.00	467.57	413.28
 Center pivot, half mile	338.00	284.24	251.24
 Subsurface drip irrigation	1,200.00	1,009.13	891.97
 1Assumes a marginal tax rate of 15 percent and discount rate of 6 percent Assumes a marginal tax rate of 28 percent and discount rate of 6 percent Salvage values and useful system life are in the Appendix, Table A2.
spaced 5 feet apart.
The gross investment for quarter-mile center pivot system is $556.00 per acre.
The total investment costs for each irrigation system, including well, pump, and engine for five pumping lifts, are provided in the Appendix, Table A1.
There are definite economies of scale LEPA associated with center pivot systems.
You SDI can substantially reduce the investment cost of a center pivot irrigation system by increasing the length of the pivot.
Using a half-mile center pivot rather than four quarter-mile systems reduces the gross investment by 40 percent, or $218.00 per acre , as shown in Table 2.
In addition, the corners become more functional for farming increasing from 8 to 40 acres.
To calculate the net investment, subtract the discounted salvage value and the tax savings associated with a new system from the purchase price of the distribution system.
By accounting for discounted tax savings and salvage value, producers can get a true comparison of what they would pay for each system.
The net investments for the different systems vary significantly less than the gross investments.
For example, the difference in net investment between a quarter-mile center pivot and furrow is $283.95 per acre , given a 15 percent tax and 6 percent discount rate.
The net investment for a subsurface drip irrigation system, $1,009.13 per acre, is substantially less than the gross investment of $1,200.00 per acre.
The economic feasibility of a new irrigation system can be affected by the marginal tax rate.
For example, if a producer's marginal tax rate is 28 percent instead of 15 percent, the net investment in subsurface drip is reduced by $117.16  per acre; the net investment in furrow is reduced by $21.63  per acre.
Therefore, all systems become more feasible at the higher tax rate.
The most expensive system is affected the most by the marginal tax rate; the least expensive system is affected the least.
Estimated annual operating expenses
 In the study, annual operating expenses-including both fixed and variable costs-were estimated for each system per acre-inch of water pumped.
These expenses per acre were based on the application efficiency of each system to apply the equivalent amount of water to achieve the same crop yield.
Table 3.
Water pumped for three crop scenarios and five irrigation systems in Texas
 Application	Application	High	Intermediate	Low
 Irrigation	efficiency	efficiency	water use	water use	water use
 system		index			
 Furrow	60	1.47	29.33	20.53	11.73
 MESA	78	1.13	22.56	15.79	9.03
 LESA	88	1.00	20.00	14.00	8.00
 95	0.93	18.53	12.97	7.41
 97	0.91	18.14	12.70	7.26
 The annual pumping costs per acre were calculated by multiplying the total operating estimates per acre-inch by the number of acre-inches of water required for each system:
 Total	Number of acre-inches	Annual
 operating	of water required	=	pumping
 cost per	for the irrigation	costs per
 Assumptions and crop scenarios
 To calculate operating costs, researchers assumed three crop scenarios: high water use , intermediate water use , and low water use.
For each crop scenario, the amount of water needed to be pumped was estimated by multiplying the water required by the LESA center pivot times the application efficiency index for each irrigation system.
Therefore, the effective amount of water pumped would remain constant for all systems.
Water required by the LESA center pivot
 Application efficiency index for the irrigation system
 Amount of water required for the irrigation system
 The application efficiency index for each system was calculated by dividing the LESA application efficiency  by the application efficiency of that system.
For example, the application efficiency index for furrow is 1.47  and 0.93 for LEPA.
Therefore, if 14 inches per acre are pumped through the LESA center pivot system, a furrow system would require 20.53 inches per acre of water X 1.47) to apply the same effective amount of water to the crop at the intermediate water use level.
The fixed cost for operating each system includes the annual depreciation, taxes, insurance, and interest charges associated with an investment.
The straight-line method was used to calculate depreciation.
Taxes were calculated at 1 percent of the assessed value using a tax assessment ratio of 0.20.
Insurance was calculated as 0.60 percent of the purchase value.
Interest
 was assumed to be 6 percent per year.
The operational life of each irrigation system was assumed to be 25 years.
Table 4 lists the fixed costs in dollars per acre-inch of water pumped for the intermediate water-use crop scenario and 350-foot pumping lift for each system.
This cost ranged from $1.10 for furrow to $6.05 for subsurface drip.
The fixed cost per acre-inch for LESA center pivot is estimated to be $2.54, including $1.27 for depreciation, $0.08 taxes, $0.24 insurance, and $0.95 interest.
The assumptions used in the fixed-cost calculations are presented in the Appendix, Table A3.
Variable costs include fuel, lubrication, maintenance, repairs, and labor.
Fuel costs are based on natural gas priced at $6.00 per thousand cubic feet.
Lubrication, maintenance, and repairs are assumed to be 65 percent of the fuel cost.
The labor cost to operate the well, pump, engine, and irrigation system was assessed at $10.30 per hour.
The variable pumping costs in dollars per acre-inch of water pumped for the five irrigation systems at a 350foot pumping lift are shown in Table 4 for each system.
Variable cost estimates by system and lift are given in the Appendix, Tables A4 through A6.
Table 4.
Fixed and variable pumping costs per acre-inch for the intermediate water-use scenario  at a 350foot pumping lift for five irrigation systems
 Cost component/system	Furrow	MESA	LESA	LEPA	SDI
 Depreciation	0.41	1.13	1.27	1.37	3.02
 Taxes	0.02	0.07	0.08	0.09	0.19
 Insurance	0.06	0.21	0.24	0.26	0.57
 Interest charges	0.61	0.85	0.95	1.03	2.27
 Total fixed costs	1.10	2.26	2.54	2.75	6.05
 Fuel costs	6.04	6.55	6.22	6.22	6.22
 LMR charges	3.93	4.26	4.04	4.04	4.04
 Labor costs	1.19	0.91	0.80	0.75	0.73
 Total variable costs	11.16	11.72	11.06	11.01	10.99
 Total fixed and variable
 cost 	12.26	13.98	13.60	13.76	17.04
 Lubrication, maintenance and repairs
 The estimated total cost per acre-inch varied considerably among the systems evaluated.
Furrow had the lowest total cost at $12.26 per acre-inch; subsurface drip had the highest cost at $17.04 per acre-inch.
LESA, LEPA, and MESA center pivot systems ranged from $13.60 to $13.98 per acre-inch.
To calculate the annual pumping cost in dollars per acre in each crop scenario, the total operating costs per
 acre-inch were multiplied by the number of acre-inches of water pumped.
For the intermediate water use scenario, LEPA center pivot had the lowest annual pumping cost, $178.45 , because of its high application efficiency.
Conversely, furrow irrigation, which had the lowest pumping cost per acre-inch , had the highest total annual pumping cost $251.79.
This is because of its relatively low application efficiency, resulting in more water having to be pumped to apply the same effective amount.
Table 5.
Total pumping cost per acre using natural gas fuel at a 350-foot pumping lift for three crop scenarios and five irrigation systems
 System/water use	water use	water use	water use
 Furrow	339.03	251.79	163.89
 MESA	293.86	220.81	147.48
 LESA	252.20	190.40	128.88
 LEPA	235.31	178.45	121.31
 SDI	272.35	216.41	160.51
 Savings from field operations and total annual irrigation
 Center pivot and subsurface drip irrigation systems require fewer field operations than does furrow irrigation.
For example, the field operations commonly used to produce corn under furrow irrigation include shredding, offset disking, chiseling, tandem disking, bedding, rod weeding, planting, and two cultivations.
For center pivot or subsurface drip irrigation, the number of field operations is generally reduced to shredding, offset disking, chiseling, planting, and one cultivation.
This represents a reduction of four field operations.
Assuming a cost of $11 per operation, the estimated savings are $33 per acre under conventional tillage.
The number of field operations performed or saved varies considerably, depending on the crop planted, cropping system, and growing conditions for a particular year.
Corn
 Table 6.
Savings in pumping cost and field operations using natural gas fuel at a 350-foot pumping lift for the intermediate water-use scenario when shifting from furrow to more efficient irrigation systems per acre
 in pumping	from field	irrigation
 System	cost	operations	savings
 MESA	30.97	33.00	63.97
 LESA	61.39	33.00	94.39
 LEPA	73.34	33.00	106.34
 SDI	35.38	33.00	68.38
 producers have estimated that from three to five field operations may be saved under center pivot or subsurface drip irrigation, amounting to $33 to $55 per acre.
Typically, three field operations are eliminated for sorghum, soybeans, and cotton production, saving $33 per acre.
Table 7 lists the net investment cost and benefits of adopting efficient irrigation technology at a 350-foot pumping lifts for high, intermediate, and low water-use crop scenarios.
The benefits include the estimated savings from reduced pumping costs and field operations from the five more efficient systems compared to the least efficient system.
The series of benefits accumulated over the life of irrigation equipment  is discounted at the rate of 6 percent to present value.
It is considered economically feasible to adopt an irrigation system technology when the change in expected benefits exceeds the net investment cost.
Comparing the purchase of furrow system to a LEPA center pivot system reveals that LEPA requires an additional net investment of $283.95  per acre; however, the reduction in field operations and pumping costs would save $1,747.71 per acre under the assumption of high water use.
Even under low water use, adoption of LEPA is favorable, with expected gain in benefits of $966.22 per acre compared to the $283.95 per acre of additional investment.
Evaluating the conversion or replacement of an existing system from the data presented in Table 7 is more difficult.
The expected benefits for each system as given in Table 7 will remain the same.
However, a producer will need to estimate the cost of conversion, or the net investment of the "new" system adjusted for the salvage value of the present system, in order to evaluate its feasibility.
Several conclusions can be made from the results in Table 7:
 It appears that the water and/or field operation savings justify converting furrow to center pivots whenever physically possible.
The lack of difference between the costs of center pivot suggests that producers should buy the system with the highest water application efficiency that works for their operation.
Converting furrow to drip irrigation is not feasible under a low water-use scenario based on water and field operation savings.
The study did not address the potential yield increase of applying water to the crop more often or the ability to irrigate more acreage with the same amount of water because of the improved application effectiveness.
These factors could affect drip irrigation feasibility, especially for high-value crops.
The major factors that influence pumping cost for irrigated crops are price of fuel, pumping lift, inches of water pumped, and labor wage rate.
These factors affect the economic feasibility of alternative irrigation systems.
Below are analyses of the effects of varying fuel price, pumping lift, water pumped, and wage rate on irrigation costs for each irrigation system.
Impact of fuel prices on pumping cost
 The effect of fuel price on the grower's fuel costs was calculated for each of the five irrigation systems.
The fuel costs were estimated using natural gas prices ranging from $4.00 to $14.00 per MCF in increments of $2.00.
It was assumed that corn irrigated by a LESA center pivot requires 20 acre-inches of water annually.
For the other five irrigation systems, the amount of water pumped was adjusted by comparing the relative application efficiency of each system to that of the LESA center pivot.
When the price of natural gas price increases from $4.00 to $14.00 per MCF, the total irrigation cost per acreinch for each system more than doubles.
As natural gas prices rise, so do the savings on pumping costs for the irrigation systems that have higher application efficiencies.
Table 7.
Comparison of net investment cost and benefits of irrigation technology adoption at three water-use scenarios
 Net investment	Change in net	High	Intermediate	Low
 System	cost	investment	water use	water use	water use
 MESA	467.57	283.95	999.17	817.60	631.70
 LESA	467.57	283.95	1,531.75	1,206.25	869.44
 LEPA	467.57	283.95	1,747.71	1,359.04	966.22
 SDI	1,009.13	825.51	1,274.21	873.88	465.17
 Change in net investment cost from furrow
 For example, at $4.00 per MCF, a producer would save $43.22 per acre  by using LEPA center pivot instead of furrow.
At $14.00 per MCF, the savings would increase to $151.30  per acre.
This is the result of fuel costs increasing by $293.34  per acre for furrow, while LEPA increases by
 Table 8.
Annual estimated fuel costs for effective irrigation water applied to 1 acre of irrigated corn at alternative gas prices for five irrigation systems at a 350-foot lift
 Gas price 	4	6	8	10	12	14
 system		Fuel costs 
 Furrow	29.33	117.33	176.00	234.67	293.33	352.00	410.67
 MESA	22.56	90.26	135.38	180.51	225.64	270.77	315.90
 LESA	20.00	80.00	120.00	160.00	200.00	240.00	280.00
 LEPA	18.53	74.11	111.16	148.21	185.26	222.32	259.37
 SDI	18.14	72.58	108.87	145.15	181.44	217.73	254.02
 only $185.26  per acre.
The more efficient the system, the more insulated a producer is from fuel price changes.
Effect of lift on pumping cost
 Fuel costs are affected by the depth from which the irrigation water must be pumped.
In this study, the fuel costs for irrigating corn were estimated for the different irrigation systems at pumping lifts ranging from 150 feet to 550 feet in 100-foot increments to determine the impact of pumping lift (Table The relative efficiency of each system was factored into these calculations.
Table 9.
Annual estimated fuel costs for pumping water to irrigate corn for five pumping lifts and five irrigation systems 
 Pumping lift	150 ft	250 ft	350 ft	450 ft	550 ft
 Furrow	29.33	130.83	182.75	224.99	242.88	268.40
 MESA	22.56	120.94	158.40	187.51	203.75	219.32
 LESA	20.00	95.40	129.80	157.80	169.60	187.00
 LEPA	18.53	88.37	120.24	146.17	157.10	173.22
 SDI	18.14	86.55	117.76	143.16	153.86	169.65
 1Natural gas price of $6.00 per MCF was assumed.
The study found that the less efficient the irrigation system, the greater the effect of the price of fuel and pumping lift on the cost to produce an irrigated crop.
The fuel cost for a LEPA center pivot at a 250-foot pumping lift was $120.24; at 550 feet, the cost was $173.22, an increase of $52.98 per acre of irrigated corn.
For that system, fuel cost increased by 44 percent as pumping lift increased from 250 feet to 550 feet.
For furrow, the pumping cost was $182.75 at 250 feet and $268.40 at 550 feet.
This was an increase of $85.65 per acre, which was $32.67 more than LEPA center pivot.
The fuel costs for each irrigated acre of corn were $224.99 and $146.17 at a 350-foot pumping lift using furrow and LEPA center pivot, respectively.
At 350-foot pumping lift, producers will be able to save about $78.82 in fuel costs for each irrigated acre
 by changing to more-efficient irrigation systems and improved technologies.
The savings in fuel cost by shifting from furrow to LEPA increases to $95.18 for every irrigated acre of corn at the 550-foot pumping lift.
This finding indicates that the farther water must be pumped from the ground, the more savings that growers will realize by adopting a more efficient irrigation system.
Correlation between amount of water pumped and fixed pumping costs
 To analyze the effect of the amount of water pumped on fixed cost per acre-inch, researchers calculated the fixed costs for all irrigation systems at a 350-foot pumping lift.
The amounts of water analyzed ranged from 10 to 30 acre-inches per acre.
It is obvious that fixed cost per acre-inch has an inverse relationship to the amount of water pumped (Fig.
That is, the less water pumped, the higher the fixed cost per acre-inch.
At 10 acre-inches of water, the fixed cost per acre-inch of water pumped using subsurface drip was $7.69; for furrow, the fixed cost was $2.23.
However, as the amount of water pumped increased to 30 acre-inches, the fixed cost dropped to $2.56 for subsurface drip and to $0.74 for furrow.
Therefore, the difference in fixed cost of the systems narrowed significantly, from $5.46 per acre-inch  to $1.82 per acre-inch  as use increased from 10 to 30 acre-inches per year.
Figure 8.
Changes in fixed cost as affected by the amount of water pumped in three types of irrigation systems.
For center pivots, the fixed cost per acre-inch ranged from $3.58 to $1.19 for 10 acre-inches to 30 acre-inches applied, respectively.
It may be deduced that producers tend to pump more water to reduce fixed cost per acre-inch.
The large investments involved in adopting more efficient irrigation technology also encourage investors to increase water pumping to recover their investments as soon as possible.
Effect of wage rate on pumping costs
 The availability and cost of labor greatly affect the selection of an irrigation system.
To evaluate labor charges accurately, growers must identify all costs.
For example, be sure to factor in the costs of transportation, meals, lodging, insurance, and/or taxes if you provide or pay them.
If you do not identify all labor costs, your estimate of the value of a particular irrigation system may be inaccurate.
The labor costs for irrigated corn were calculated at five wage rates for the five irrigation systems.
Labor costs at $12 per hour using furrow and LEPA center pivot were $28.35 and $11.29 per acre, respectively.
By switching to more an efficient irrigation system, growers can reduce labor costs by $17.06 for each acre irrigated annually.
Table 10.
Labor costs for irrigated corn at five wage rates for five irrigation systems
 Wage rate 	10	12	14	16	18
 system	acre-inches	Labor cost $/ac
 Furrow	29.33	23.63	28.35	33.08	37.80	42.53
 MESA	22.56	13.90	16.68	19.46	22.24	25.02
 LESA	20.00	10.88	13.05	15.23	17.40	19.58
 LEPA	18.53	9.41	11.29	13.18	15.06	16.94
 SDI	18.14	9.01	10.82	12.62	14.42	16.22
 The savings in labor cost by shifting from furrow to LEPA center pivot increase to $22.74 for every irrigated acre of corn at the labor wage rate of $16 per hour.
The comparison indicates that as wage rates rise, it becomes more cost effective to adopt a more efficient irrigation system.
Effects of efficiency in natural gas engines
 Natural gas is a preferred irrigation fuel where it is available because it typically costs the least per unit of energy, usually by a significant amount.
However, natural gas power plants are not always the most cost-effective means for pumping irrigation water because of the relatively low thermal efficiency of spark ignition, internal combustion engines.
This is especially true if engine efficiency has declined after multiple years of service.
The standard expected efficiency for a new natural gas engine in a pumping plant setting is about 25 percent, meaning that about one quarter of the fuel that is consumed
 by the engine will be converted to usable power.
When combined with standard efficiencies of the pump  and right-angle gearhead , the standard overall efficiency of a natural gas pumping plant is about 16 percent.
Field studies conducted throughout the Texas High Plains over the past 30 years have indicated that many pumping plants operate with engine efficiencies as low as 15 percent and overall efficiencies as low as 10 percent.
At a natural gas pumping plant, the engine is typically the least efficient component and is, therefore, the component most sensitive to replacement based on efficiency.
Tables 11 and 12 list the first-year energy-cost savings for multiple natural gas prices for 75and 125-horsepower pumping plants.
Seasonal energy savings are found by subtracting the seasonal energy savings of an existing natural gas engine from those of a more efficient, newer natural gas engine.
For example, at a 75-horsepower pumping plant with $8.00 per MCF natural gas, replacing an 18-percentefficient engine with a 24-percent-efficient engine would produce a direct annual energy cost savings of $4,200.
Seasonal energy savings are expected to occur over the life of the engine; however, the benefits in future years must be discounted to account for the time value of money.
Total discounted energy savings prices for 75and 125-horsepower pumping plants at various natural gas prices are estimated assuming an engine life of 5 years and a discount rate of 6 percent.
These values can be used to identify the amount a producer can pay to upgrade engine efficiency.
Again, looking at the same 75-horsepower pumping plant with $8.00 per MCF natural gas, replacing an 18-percent-efficient engine with a 24-percent-efficient engine would produce a discounted energy cost savings of $19,000  over a 5-year period.
This analysis suggests that a producer would be better off financially by choosing the higher efficiency engine if it could be bought for less than $19,000 more, given the useful life and natural gas price assumptions.
This approach makes a compelling argument for replacing inefficient engines with more efficient models, especially considering that engine efficiency decreases with time.
Because of the inefficiency of internal combustion engines and the cost structure of natural gas, researchers have been working to develop highly efficient natural gas engines.
Prototype engines have shown over 40 percent thermal efficiency in controlled environments and up to 30 percent thermal efficiency in field tests, up to 125 horsepower.
Much of the work on improved efficiencies has also helped with emissions compliance, because reduced fuel consumption is an effective way to reduce emissions.
The
 Table 11.
Seasonal and total discounted energy cost reduction from replacing a natural gas engine, based on 75-horsepower pumping requirements: 400 gallons per minute, 300-foot lift, and 20 pounds per square inch 
 Seasonal energy cost reduction	Total discounted energy cost reduction
 Engine efficiency	Natural gas price 
 	4	8	12	4	8	12
 -	-	-	-	-	-
 16	$ 600	$ 1,300	$ 1,900	$ 2,800	$ 5,700	$ 8,500
 18	$ 1,700	$ 3,400	$ 5,100	$ 7,600	$ 15,100	$ 22,700
 20	$ 2,500	$ 5,100	$ 7,600	$ 11,400	$ 22,700	$ 34,100
 22	$ 3,200	$ 6,500	$ 9,700	$ 14,500	$ 28,900	$ 43,400
 24	$ 3,800	$ 7,600	$ 11,500	$ 17,000	$ 34,100	$ 51,100
 26	$ 4,300	$ 8,600	$ 12,900	$ 19,200	$ 38,500	$ 57,700
 28	$ 4,700	$ 9,500	$ 14,200	$ 21,100	$ 42,200	$ 63,300
 30	$ 5,100	$ 10,200	$ 15,300	$ 22,700	$ 45,400	$ 68,200
 16% discount rate, 5 years
 Table 12.
Seasonal and total discounted energy cost reduction from replacing a natural gas engine, based on 125-horsepower pumping requirements: 750 gallons per minute, 400-foot lift, and 20 pounds per square inch 
 Seasonal energy cost reduction	Total discounted energy cost reduction
 Engine efficiency	Natural gas price 
 	4	8	12	4	8	12
 -	-	-	-	-	-
 16	$ 1,100	$ 2,100	$ 3,200	$ 4,700	$ 9,500	$ 14,200
 18	$ 2,800	$ 5,700	$ 8,500	$ 12,600	$ 25,200	$ 37,900
 20	$ 4,200	$ 8,500	$ 12,700	$ 18,900	$ 37,900	$ 56,800
 22	$ 5,400	$ 10,800	$ 16,200	$ 24,100	$ 48,200	$ 72,300
 24	$ 6,400	$ 12,700	$ 19,100	$ 28,400	$ 56,800	$ 85,200
 26	$ 7,200	$ 14,400	$ 21,500	$ 32,000	$ 64,100	$ 96,100
 28	$ 7,900	$ 15,800	$ 23,600	$ 35,200	$ 70,300	$ 105,500
 30	$ 8,500	$ 17,000	$ 25,400	$ 37,900	$ 75,700	$ 113,600
 16% discount rate, 5 years
 current method for meeting emissions compliance is to retrofit existing engine platforms with catalytic convertors and oxygen sensors.
Although catalytic convertors do reduce point source emissions, they also reduce engine efficiency and increase maintenance costs.
At the time of publication, no highly efficient, noncatalyst natural gas irrigation engine is production ready.
Conversion to an electric-powered irrigation system
 Volatile natural gas prices have caused many producers to convert or consider converting their irrigation systems to use alternative energy sources.
Most irrigation systems in Texas are powered by either natural gas or electricity.
To make an informed decision before any actual conversion, producers should compare the costs of their existing natural gas powered system to the cost of converting and operating an electric-powered system.
Following is a comparison between irrigation systems powered by natural gas and those powered by electricity.
The costs associated each system were evaluated over
 a 20-year period using two pumping lifts , three crops , natural gas prices ranging from $2.00 per MCF to $16.00 per MCF, and a flow capacity of 600 gallons per minute for a quarter-mile center pivot.
Table 13 shows the expenses related to investment and maintenance of a natural gas engine and electric motor.
It was assumed that producers had a natural gas powered irrigation system in place.
The investment costs for natural gas engines of about $11,000 at 200 feet and $36,000 at 500 feet were used as the replacement costs of the engine over the 20-year period.
Investment costs for the electric motor were about $4,800 at 200 feet and $8,800 at 500 feet.
Also, the cost to convert from a natural gas system to electric ranged from about $7,500 at 200 feet to $15,400 at 500 feet and included the fuse, control panel, pump conversion, and labor and installation.
The total costs associated with each system over the 20-year period were estimated on a per-acre basis in 2011 dollars and included conversion expenses, irrigation fuel, repairs, and any necessary replacement costs to the
 Table 13.
Fixed and variable costs for a natural gas irrigation engine and an electric motor
 Engine/motor costs-	Useful life	Salvage value	LMR
 Lift 	Investment 	Conversion 	$/ac-yr	Years	Investment	Annual 	$/ac-yr
 Natural gas irrigation engine
 200	10,997	-	7.64	12	10%	1,084	9.03
 500	35,940	-	24.96	12	10%	1,480	12.33
 200	4,812	7,530	6.86	15	10%	420	3.50
 500	8,835	15,440	13.49	15	10%	722	6.02
 1 LMR=Lubrication, maintenance, and repairs
 systems.
Each cost stream was evaluated for the different levels of natural gas prices and pumping lifts.
Conversion to an electric-powered system becomes feasible at the price where the cost lines cross.
For example, the cost lines for each system  for an intermediate water use crop at a pumping lift of 200 feet are presented in Figure 9.
C1 represents the cost of natural gas powered irrigation, which is assumed to be the system currently in use, and C2 represents the cost for converting to electric and associated costs for operating that system over a 20-year time horizon.
The two cost lines intersect at $4.00 per MCF or $0.07 per kWh, indicating that conversion from natural gas to electric is plausible at this point.
The breakeven prices for all pumping lifts and crops are given in Table 14.
The type of crop grown does not significantly affect breakeven prices.
Overall, it is beneficial to convert lower pumping lifts first at natural gas prices above $3.84 per MCF and higher pumping lifts at natural gas prices above $4.38 per MCF.
Table 14.
Breakeven prices for converting an irrigation system from natural-gas powered to electric powered
 Lift 	Water use	BE price	BE price
 200	Intermediate	4.02	0.0701
 500	Intermediate	4.78	0.0730
 Before making a decision, producers should consider other factors:
 Proximity to a three-phase electric line
 Cost of repairs and labor
 Figure 9.
Natural gas and electric irrigation costs for an intermediate water use crop at a 200-foot lift.
Possibly the most important consideration is the proxlimity to a three-phase electric line.
Line extensions were not included in the comparison, and the cost can be high if the well is far from power lines.
The electric company may also assess initial connection fees or peak factor charges.
On the other hand, some electric companies may offer incentives to irrigated agricultural producers to encourage conversion and offset some of the expense.
In addition, electric systems tend to have a longer life with fewer repair and labor expenses.
Finally, electric prices fluctuate somewhat with natural gas prices, but they tend to be more stable overall than natural gas prices, which would be an advantage for producers.
Researchers evaluated the predominant irrigation systems in Texas and analyzed the major factors that affect their economic feasibility.
The discussion of some items was omitted or limited because of study and space limitations.
One limitation in the analysis was that yields were held constant even when the amount of water applied by the distribution system was modified by its application efficiency.
Although this approach is sound, it does not account for potential yield gains from more frequent irrigations that can result through center pivots and especially SDI as compared to furrow.
Investing in a new irrigation system is expensive and complex, with many factors needing to be evaluated, including water availability, pumping lift, labor cost, fuel cost, tax rate, soil type, and field topography.
Overlaying these factors are the differences in the costs and water application efficiencies of the various irrigation systems.
These factors make it difficult to make a wise investment decision.
To help farmers weigh these factors and make these decisions, researchers studied the costs and associated benefits of five commonly used irrigation systems in Texas: furrow, mid-elevation spray application center pivot, low elevation spray application center pivot, low energy precision application center pivot, and subsurface drip.
The study found that:
 Furrow irrigation systems require less capital investment but have lower water application efficiency and are more labor intensive than the other irrigation systems.
Compared to furrow irrigation, center pivot systems offer more than enough benefits in application efficiency and reduction in field operations to offset the additional costs.
Where it is feasible to use, half-mile center pivot offers substantial savings compared to quarter-mile length systems.
Among the three center pivot alternatives, LEPA center pivot systems generate the highest benefits at low, intermediate, and high water-requirement scenarios.
Advanced irrigation technologies are best suited to crops with high water needs, particularly in areas with deep pumping lifts.
Producers using advanced systems will have not only lower pumping costs, but also potential savings from the need for fewer field operations.
Compared to LEPA center pivot systems, subsurface drip irrigation  is not economically feasible for any crop water-use scenario because of its relatively high investment and small gain in application efficiency.
For most crops, adoption of SDI may be limited to land where pivots cannot physically be installed.
However, producers should closely evaluate using SDI systems for high-value crops.
Research suggests that SDI systems may improve the application efficiency and the timing of frequent applications.
These improvements may increase acreage and yields enough to justify the additional investment costs of subsurface drip systems.
Researchers also studied the effect on pumping cost of variations in fuel prices, pumping lift, amount of water pumped, and labor wage rate.
Results indicated that:
 The less efficient the irrigation system, the more effect that fuel price, pumping lift, and wage rate have on the cost of producing an irrigated crop.
Therefore, when there is inflation or volatility of these cost factors, it is more feasible to adopt more efficient irrigation systems and technology.
As more water is pumped, the fixed cost per acreinch drops.
Therefore, pumping more water encourages farmers to recapture their irrigation system investment more quickly.
It is beneficial to replace inefficient engines with more efficient models.
Conversion from natural-gas-powered irrigation to electric-powered irrigation is economically feasible for lower pumping lifts at natural gas prices above $3.84 per MCF and higher pumping lifts at natural gas prices above $4.38 per MCF.
Table A1.
Estimated gross investment costs  for alternative irrigation systems at five pumping lifts in Texas
 	Well	Pump	Engine	system	Total
 150	27,500	26,500	6,000	33,370	96,800
 250	36,500	36,000	6,500	33,370	115,800
 350	45,500	46,000	9,000	33,370	137,300
 450	54,500	56,000	9,000	33,370	156,300
 550	64,000	66,500	35,000	33,370	202,300
 150	27,500	26,500	6,000	69,500	129,500
 250	36,500	36,000	6,500	69,500	148,500
 350	45,500	46,000	9,000	69,500	170,000
 450	54,500	56,000	9,000	69,500	189,000
 550	64,000	66,500	35,000	69,500	235,000
 150	27,500	26,500	6,000	69,500	129,500
 250	36,500	36,000	6,500	69,500	148,500
 350	45,500	46,000	9,000	69,500	170,000
 450	54,500	56,000	9,000	69,500	189,000
 550	64,000	66,500	35,000	69,500	235,000
 150	27,500	26,500	6,000	69,500	129,500
 250	36,500	36,000	6,500	69,500	148,500
 350	45,500	46,000	9,000	69,500	170,000
 450	54,500	56,000	9,000	69,500	189,000
 550	64,000	66,500	35,000	69,500	235,000
 150	27,500	26,500	6,000	192,000	252,000
 250	36,500	36,000	6,500	192,000	271,000
 350	45,500	46,000	9,000	192,000	292,500
 450	54,500	56,000	9,000	192,000	311,500
 550	64,000	66,500	35,000	192,000	357,500
 Table A2.
Useful life and salvage value assumptions used to calculate depreciation of five irrigation systems
 Item/component	life 	value 
 Center pivot	25	20
 Subsurface drip	25	20
 Table A3.
Fixed cost for irrigating at three levels of water use under five irrigation systems
 water use	Depreciation	Taxes	Insurance	Interest	Total
 High	0.28	0.01	0.04	0.43	0.76
 Intermediate	0.41	0.02	0.06	0.61	1.10
 Low	0.71	0.04	0.11	1.07	1.93
 High	0.79	0.05	0.15	0.59	1.58
 Intermediate	1.13	0.07	0.21	0.85	2.26
 Low	1.97	0.12	0.37	1.48	3.94
 High	0.89	0.06	0.17	0.67	1.79
 Intermediate	1.27	0.08	0.24	0.95	2.54
 Low	2.22	0.14	0.42	1.67	4.45
 High	0.96	0.06	0.18	0.72	1.92
 Intermediate	1.37	0.09	0.26	1.03	2.75
 Low	2.40	0.15	0.45	1.80	4.80
 High	2.12	0.13	0.40	1.59	4.24
 Intermediate	3.02	0.19	0.57	2.27	6.05
 Low	5.29	0.33	0.99	3.97	10.58
 Table A4.
Variable costs  for a high wateruse crop  for five irrigation systems at five lifts
 System/lift 	Fuel	LMR	Labor	Total
 150	3.52	2.29	0.83	6.64
 250	4.91	3.19	0.83	8.94
 350	6.04	3.93	0.83	10.80
 450	6.53	4.24	0.83	11.60
 550	7.22	4.69	0.83	12.74
 150	4.23	2.75	0.63	7.61
 250	5.54	3.60	0.63	9.77
 350	6.55	4.26	0.63	11.44
 450	7.12	4.63	0.63	12.38
 550	7.66	4.98	0.63	13.27
 150	3.76	2.45	0.56	6.77
 250	5.11	3.32	0.56	9.00
 350	6.22	4.04	0.56	10.83
 450	6.69	4.35	0.56	11.59
 550	7.37	4.79	0.56	12.72
 150	3.76	2.45	0.52	6.73
 250	5.11	3.32	0.52	8.96
 350	6.22	4.04	0.52	10.79
 450	6.69	4.35	0.52	11.55
 550	7.37	4.79	0.52	12.69
 150	3.76	2.45	0.51	6.72
 250	5.11	3.32	0.51	8.95
 350	6.22	4.04	0.51	10.78
 450	6.69	4.35	0.51	11.54
 550	7.37	4.79	0.51	12.68
 1 Natural gas price of $6.00 per MCF was assumed.
Table A5.
Variable costs  for an intermediate water-use crop  for five irrigation systems at five lifts
 System/lift 	Fuel	LMR	Labor	Total
 150	3.52	2.29	1.19	6.99
 250	4.91	3.19	1.19	9.29
 350	6.04	3.93	1.19	11.16
 450	6.53	4.24	1.19	11.96
 550	7.22	4.69	1.19	13.09
 150	4.23	2.75	0.91	7.88
 250	5.54	3.60	0.91	10.04
 350	6.55	4.26	0.91	11.71
 450	7.12	4.63	0.91	12.66
 550	7.66	4.98	0.91	13.55
 150	3.76	2.45	0.80	7.01
 250	5.11	3.32	0.80	9.24
 350	6.22	4.04	0.80	11.07
 450	6.69	4.35	0.80	11.83
 550	7.37	4.79	0.80	12.96
 150	3.76	2.45	0.75	6.96
 250	5.11	3.32	0.75	9.19
 350	6.22	4.04	0.75	11.01
 450	6.69	4.35	0.75	11.78
 550	7.37	4.79	0.75	12.91
 150	3.76	2.45	0.73	6.94
 250	5.11	3.32	0.73	9.17
 350	6.22	4.04	0.73	11.00
 450	6.69	4.35	0.73	11.76
 550	7.37	4.79	0.73	12.90
 1 Natural gas price of $6.00 per MCF was assumed
 Table A6.
Variable costs  for a low water use crop  for five irrigation systems at five lifts
 System/lift 	Fuel	LMR	Labor	Total
 150	3.52	2.29	2.07	7.88
 250	4.91	3.19	2.07	10.18
 350	6.04	3.93	2.07	12.05
 450	6.53	4.24	2.07	12.85
 550	7.22	4.69	2.07	13.98
 150	4.23	2.75	1.59	8.56
 250	5.54	3.60	1.59	10.72
 350	6.55	4.26	1.59	12.39
 450	7.12	4.63	1.59	13.33
 550	7.66	4.98	1.59	14.22
 150	3.76	2.45	1.40	7.61
 250	5.11	3.32	1.40	9.84
 350	6.22	4.04	1.40	11.67
 450	6.69	4.35	1.40	12.43
 550	7.37	4.79	1.40	13.56
 150	3.76	2.45	1.31	7.52
 250	5.11	3.32	1.31	9.75
 350	6.22	4.04	1.31	11.57
 450	6.69	4.35	1.31	12.34
 550	7.37	4.79	1.31	13.47
 150	3.76	2.45	1.28	7.49
 250	5.11	3.32	1.28	9.72
 350	6.22	4.04	1.28	11.54
 450	6.69	4.35	1.28	12.31
 550	7.37	4.79	1.28	13.44
 1 Natural gas price of $6.00 per MCF was assumed.
Chapter: 27 Sulfur can Increase South Dakota Corn Yields
 Corn sulfur  deficiency symptoms include leaf yellowing and/or striping or interveinal chlorosis of new leaves.
Corn yield responses to S addition were more likely in sandy no-tillage fields where the surface 2 feet of soil contains < 40 lbs of SO S/acre.
4 Sulfur deficiency can be minimized by applying sulfurcontaining fertilizers or manure.
This chapter provides information needed to make informed decisions concerning sulfur fertilizer applications.
Sulfur  is an essential nutrient for crop production that in the past was largely supplied through atmospheric deposition.
However, improvements in air quality have reduced S depositions.
For example, from 1972 to 1980, SO emissions decreased in the United States from 32 million to 26 million tons, which was further 2 reduced to 6.5 million tons in 2011.
Decreasing sulfate depositions have been accompanied by increased applications of sulfurcontaining fertilizers.
In South Dakota from 2002 to 2010, the use of sulfur-containing fertilizers increased from 18,318 tons to 51,592 tons.
Figure 27.1 Corn sulfur deficiency symptoms.
Sulfur in the Soil
 Soil contains between 200 and 1000 lbs of S/acre, which can exist as inorganic SO , gypsum , and organic-S.
Plant requirements for S can be obtained from the mineralization of organic matter, the oxidation of sulfide, the solubilization of gypsum, and/or from atmospheric depositions.
Sulfate , which is then oxidized to sulfate.
Processes that influence microbial activity, such as tillage, will impact sulfur mineralization.
Due to relatively slow mobilization from older leaves to younger leaves, S deficiency generally includes
 yellowing as well as leaf striping of younger leaves.
Nitrogen  has similar symptoms in corn.
However, yellowing is most observed in older leaves.
Sulfur deficiency symptoms are most observed in loworganic-matter, no-till corn.
Research conducted at 130 locations in South Dakota between 1990 and 2014 indicates that corn responds to S if: 1) the amount of sulfate in the surface 2 feet is < 40 lbs SO S/acre, 2) 4 no-tillage is used at the site; and 3) the soil texture is relatively course.
The S source used in these studies was ammonium sulfate and grain yields were adjusted to 15% grain moisture.
Causes of S deficiency may include reduced mineralization resulting from low organic matter contents, cool temperatures, the adoption of reducedtillage systems where soil organic matter is sequestered, and/or the loss of sulfate with leaching water.
Figure 27.2 The influence of tillage  and SO-S amounts in the surface 2 feet on the relative yields in SD studies conducted between 1990 and 2014.
Relative yield values < 100 indicate that sulfur fertilizer increased yield.
Collecting and Analyzing Soil Samples
 Sulfate-S.
Because the sulfate test is not always accurate, soil sulfate analysis should be used as a starting point for determining a sulfur recommendation.
Consider the soil organic matter, soil texture, SO -S, and tillage practices when making a recommendation.
4
 There are a number of fertilizers that can be used to reduce S deficiencies including manure.
For example, ammonium thiosulfate  can be mixed with UAN or ammonium sulfate  can be mixed with urea.
However, the S contained in Elemental S  is not readily available because it requires oxidation prior to plant uptake.
Manure from animals that used distillers grains in their rations may contain relatively high concentrations of S.
Because both N and S are needed to produce plant proteins, the ratio between these nutrients can range from 8:1 to 10:1.
Typically, if crop requirements for nitrogen are 100 lbs N/acre, then the sulfur requirements will be 7 to 13 lbs S/acre.
Approximately 25 lbs of S are harvested in a 15-ton silage crop , and cereal grain crops have the highest S requirements while soybeans have the lowest.
Table 27.1 The sulfur recommendations for South Dakota.
Soil Test	Soil Level	TilledA	Strip or	TilledA	Strip or
 lbs/a 	lbs S/a recommendation
 0-9	Very Low	25	25	25	25
 10-1-	Low	25	25	15	25
 20-29	Medium	15	25	0	15
 30-39	High	15	15	0	15
 >=40	Very High	0	0	0	0
Determine the average rainfall per week for the remaining weeks of crop growth and add it into the prediction of how much water may be needed from irrigation.
This number should be recalculated each week until the crop is mature.
Use Figures 2 and 3 to determine the average rainfall per week in August and in September for central Buffalo County.
The chart shows that, on average, central Buffalo County gets 0.60 inch of rain per week in August and 0.55 inch per week in September.
The crop is expected to continue growing for three weeks in August and two weeks in September.
Remaining available water at maturity is 5.25 inches.
The you subtract the average august rain for three weeks which is 1.80 inches.
Then you subtract the average September rain for 2 weeks which is 1.10 inches.
This gives us that the water we need after accounting for average rain is 2.35 inches.
The chart predicts that if average rainfall is received over the next five weeks, only 2.35 inches of irrigation would be needed to mature the crop.
IRRIGATION MANAGEMENT S E R E S
 Soil, Water, and Plant Relationships
 Danny H.
Rogers Professor, Extension Irrigation Engineer, Biological and Agricultural Engineering
 Jonathan Aguilar Assistant Professor, Water Resources Engineer, Southwest Research Extension Center
 Isaya Kisekka Assistant Professor, Irrigation Research Engineer, Southwest Research Extension Center
 Philip L.
Barnes Associate Professor, Water Quality, Biological and Agricultural Engineering
 Freddie R.
Lamm Professor, Irrigation Research Engineer, Northwest Research and Extension Center
 Plant growth depends on two important natural resources soil and water.
Soil provides the mechanical support and nutrient reservoir necessary for plant growth.
Water is essential for plant life processes.
Effective management of these resources for crop production requires the producer to understand relationships between soil, water, and plants.
Knowledge about available soil water and soil texture can influence the decision-making process, such as determining what crops to plant and when to irrigate.
This publication provides general information on the physical characteristics of soil, soil and water interactions, and how plants use water, particularly as these topics relate to irrigated agriculture.
However, the information is pertinent to rain-fed agricultural production as well.
More in-depth information on other related topics is available in other K-State Research and Extension publications, including MF2389 What is ET?; L935 Important Agricultural Soil Properties; and L934 Agricultural Crop Water Use.
There are many factors that determine the physical characteristics of soil.
These include soil texture, soil structure, bulk density, and soil porosity.
They all affect the interaction between soil, water, and air.
The basic soil, water, and plant relationships are important to agricultural producers, but especially to irrigation users that desire to use best management practices such as irrigation scheduling.
Irrigation scheduling determines when and how much water needs to be added to a crop's root zone to promote optimum yields.
One climaticor evapotranspiration -based irrigation scheduling option is the KanSched program.
Soil Composition.
A unit of soil is a combination of solid material, composed of mineral and organic matter, and open space, called pores.
By volume, most soils are roughly 50 percent solids and 50 percent pore space.
The mineral matter makes up about 45 to 47 percent of the total soil volume.
This mineral matter consists of small particles of either sand, silt, or clay.
Organic matter is made up of decaying plant and animal substances and is distributed in and among the mineral particles.
Organic matter can account for up to about 5 percent of the overall soil makeup by volume, but many agricultural soils have less than 1 percent organic matter.
The pores, spaces that occur between the mineral particles, are important because they store air and water in the soil.
Figure 1 shows the approximate relationship between the substances in the soil composition, with the pore space shown split between air
 Figure 1.
Typical soil composition by volume.
and water.
The amount of water and air present in the pore spaces varies over time in an inverse relationship.
This means that for more water to be contained in the soil, there has to be less air.
The amount of water in soil pore space is essential to crop production and will be further discussed in the section on soil water content.
Soil Texture.
The size of the particles that make up the soil determine soil texture.
The traditional method of determining soil particle size consists of separating the particles into three convenient size ranges.
These soil fractions or separates are sand, silt, and clay.
Generally, only particles smaller than 2 mm  in size are categorized as soil particles.
Particles larger than this are categorized as gravel, stones, cobbles, or boulders.
Sand particles range in size from 2 mm to 0.05 mm.
There are subcategories assigned to this range that include coarse, medium, and fine sand.
Silt particles range in size from 0.05 mm down to 0.002 mm.
The physical appearance of silt is much like sand, but the characteristics are more like clay.
Clay particles are less than 0.002 mm in size.
Clay is an important soil fraction because it has the most influence on soil behavior such as water-holding capacity.
Clay and silt particles cannot be seen with the naked eye.
Soil texture is determined by the mass ratios, or the percent by weight, of the three soil fractions.
The soil textural triangle, Figure 2, shows the different textural classes and the percentage by weight of each soil fraction.
For example, a soil containing 30 percent sand, 30
 percent clay, and 40 percent silt by weight is classified as a clay loam.
Soil Structure.
Soil structure is the shape and arrangement of soil particles into aggregates.
Soil structure is an important characteristic used to classify soils and heavily influences agricultural productivity and other uses, such as load-bearing capacity for structures.
The principal forms of soil structure are platy, prismatic, columnar, blocky, and granular.
These soil structure descriptions indicate how the particles arrange themselves into aggregates.
Aggregated soil types are generally the most desirable for plant growth.
Soil structure terms also are used in conjunction with descriptive words to indicate the class and grade of soil.
Class refers to the size of the aggregates, while grade describes how strongly the aggregates hold
 together.
Structureless soils can be either single-grained  or massive  Soil structure is unstable and can change with weather conditions, biological activity, and soil management practices.
Soil Bulk Density and Porosity.
Soil bulk density expresses the ratio of the mass weight of dry soil to its total volume.
The total volume includes both the solids and the pore spaces.
Soil bulk density is important because it is an indicator of the soil's porosity.
The porosity of a soil is defined as the volume of pores in a soil.
A compacted soil has low porosity and thus a greater bulk density.
A loose soil has a greater porosity and a lower bulk density.
Like soil structure, a soil's bulk
 Figure 2.
A soil textural classification triangle, showing a clay loam soil composed of 30 percent sand, 30 percent clay, and 40 percent silt.
Table 1.
Average water-holding capacity for Kansas soils, depths greater than 12 inches.
Percentage by Mass	Fraction by Volume
 Soil	Bulk	Field	Wilting	Water	Field	Wilting	Water
 Texture	Density	Capacity	Point	Capacity	Capacity	Point	Capacity
 Sand	1.70	7.0	3.0	4.0	0.12	0.05	0.07
 Loamy Sand	1.70	10.0	4.2	5.8	0.17	0.07	0.10
 Sandy Loam	1.65	13.4	5.6	7.8	0.22	0.09	0.13
 Fine Sandy Loam	1.60	18.2	8.0	10.2	0.29	0.13	0.16
 Loam	1.55	22.6	10.3	12.3	0.35	0.16	0.19
 Silt Loam	1.50	26.8	12.9	13.9	0.40	0.19	0.21
 Silty Clay Loam	1.45	27.6	14.5	13.1	0.40	0.21	0.19
 Sandy Clay Loam	1.50	26.0	14.8	11.2	0.39	0.22	0.17
 Clay Loam	1.50	26.3	16.3	10.0	0.39	0.24	0.15
 Silty Clay	1.40	27.9	18.8	9.1	0.39	0.26	0.13
 Clay	1.35	28.8	20.8	8.0	0.39	0.28	0.11
 density and porosity can be affected by weather-related factors, biological activities, and soil management practices.
Table 1 lists typical bulk densities for Kansas soils.
Soil and Water Interactions
 Soil acts like a reservoir that holds water and nutrients plants need to grow.
Some soils are large reservoirs with more holding capacity that release water and nutrients easily to plants, while other soils have limited reservoirs.
The following discussion focuses on soil water as it relates to plant availability and applying irrigation water.
Soil Water Content.
Soil water content is the amount of water stored in the soil at a given time.
The most commonly defined soil water content values are saturation, field capacity, wilting point, and oven dried.
At saturation, which usually occurs immediately after a heavy rainfall or an irrigation application, all pore spaces in the soil are filled with water.
When the soil is at or near saturation, some of
 the water is free to drain or percolate due to the force of gravity.
This excess water is referred to as gravitational water.
Since this percolation takes time, some of this extra water could be used by plants or lost to evaporation.
Field capacity is defined as the amount of water remaining in the soil after rapid percolation has occurred.
This is not a definite soil water point; therefore, field capacity often is defined as approximately one-third atmosphere tension.
Tension is defined in a following section.
Wilting point is defined as the soil water content at which the potential or ability of the plant root to absorb water is balanced by the water potential of the soil.
Most crops show significant signs of stress, such as wilting to the extent of dying, if soil water reaches the wilting point, especially for extended periods of time.
Wilting point is usually approximated by a value of 0.15 atmospheres.
Soil that has been oven dried is used as a reference point for determining soil water content.
When the soil is oven dried, all soil water has been removed from the soil.
The amount of water at any soil-water content varies by soil type.
Specific water-holding capacities can be obtained from various sources; however, NRCS County Soil Surveys are probably the most extensive and readily accessible.
Figure 3 illustrates typical amounts of water held at the defined soil water content for sand, loam, and silty clay loam soils.
The reasons for the differences between soil types is explained in the next sections.
Water content can be expressed as inches of available water or as a percentage.
Typical values of both expressions are shown in Table 1 for soils at depths greater than 12 inches.
Typically the top soil layer has slightly higher available water-holding capacity.
How Soil Holds Water.
Soil holds water in two ways:  as a thin film on individual soil particles and  as water stored in the pores of the soil.
Water stored as a thin
 film on individual soil particles is held in place by adsorption forces.
Adsorption involves complex chemical and physical reactions but in simple terms, a thin film of water adheres to the outside layers of soil particle molecules.
Water stored in the pores of the soil is stored by capillary forces.
An example of the capillary force phenomenon would be to place one end of a glass capillary tube in a pan of water.
Water in the tube will rise to a certain height, which depends on the diameter of the capillary tube.
This phenomenon can act in any direction and is the key to water being stored in soil pores, as illustrated in Figure 5.
Soil Water Tension.
The ease by which water can be extracted from the soil depends on the soil water tension, also known as the soil water potential.
These are equivalent values, except for the sign , which might be thought of as either a push or a pull on the water.
Water being held in pores by the capillary storage is held in the soil at a certain tension.
The same is true for water held with the adsorption phenomenon.
As the soil dries, these tensions become larger.
It is easier for a plant to extract water being held at lower tensions.
The tensions that correspond to the soil-water equilibrium points discussed above is a good example of water tensions affecting plant water use.
At saturation, the soil water tension is approximately 0.001 bar.
One bar tension is equivalent to 1 atmosphere of pressure.
Thus, from the above discussion, it would be easy for a plant to extract water from a saturated soil.
Saturation only
 Figure 3.
Typical soil water content within three soil textures.
lasts a short time, SO plants extract only a small portion of the water above field capacity.
Field capacity is defined to be at approximately one-third atmosphere pressure or approximately 0.3 bar.
At this content, it is still easy for the plant to extract water from the soil.
The wilting point occurs when the potential of the plant root is balanced by the soil water potential; thus, plants are unable to absorb water beyond this tension.
As soil water approaches the wilting point, plants will exhibit increasing symptoms of water stress, such as wilting and leaf senescence.
Prolonged exposure will result in plant death.
As a reference, the soil water tension in an ovendried soil sample is approximately 10,000 bars.
A soil water retention or soil water characteristic curve illustrates the tension relationship.
These curves are slightly different for different types of soils due to different soil textures and structures.
Water between the field
 Figure 4.
Capillary forces illustrated by how far water rises in tubes of various sizes.
Figure 5.
How soil holds water.
capacity and the wilting point is water available to the plant.
Best plant growth and yield for most field crops occur when the soil water content remains in the upper half of the plant available soil water range, which is sometimes referred to as readily available soil water.
Figure 6.
The relationship between soil water content and soil water tension for a loam soil type.
The dividing point between available soil water content and readily available soil water content is named the maximum allowable depletion, or MAD soil water content.
For most field crops, the MAD level is usually defined as about 50 percent available water.
In some water-sensitive crops, such as vegetables and flowers, the MAD level may be less, such as 30 percent available water.
The relationship between the soil water content value, percent available soil water, and soil tension for a silty clay loam soil is illustrated in Figure 7.
Soil water potential is a measure of the energy status of the soil water.
Water flows from a greater potential area to an area of less potential.
The units of measurement are normally either bars or atmospheres.
What can be confusing is that soil water potentials are negative pressures that are also expressed as tension or suction.
In this case, water flows from greater  potential to a lesser  potential.
Plants develop the tension, or potential, to move water from the soil into
 Figure 7.
Illustration of the relationship of soil water content terms, values, percent available soil water, and soil tension for a silty clay loam soil type.
the roots and distribute the water through the plant by adjusting the water potential, or tension, within their plant cells.
Water potential is made up of several components, but one of particular importance is the osmotic or solute potential.
Solute potential is due to the presence of dissolved solutes, such as sugars and amino acids, in the plant cell.
For water to move from soil, into roots, into stems, into leaves, and finally into air, the water potential must always be decreasing.
This is illustrated in Figure 8, moving from the greater water potential soil  to the lower water potential air.
The water potential in air is always low as compared to plants, SO water movement is toward the air through the plants.
However, plants are limited in the amount of adjustment they can make.
Use of Water by Plants
 A plant's root system must provide a negative tension  to extract water from the ground.
This tension must be equivalent to the tension that holds the water in the soil.
For example,
 Figure 8.
Illustration of decreasing water potential to move water from the soil to the atmosphere through a plant.
Water movement is from higher water potential  to lower water potential.
Air is usually at lower water potential than a plant.
if the water in the soil is at 0.3 bars , the plant must provide at least 0.3 bars of negative tension to pull the water from the ground.
At the wilting point, the maximum negative tension that a plant can provide is
 balanced by the soil water tension.
At this point, the plant can no longer extract water from the soil and will be under severe stress to the point of death.
There are several factors that determine when and where a plant uses water, and how much water a plant will use.
These factors include daily plant water need as influenced by climatic conditions and stage of growth, plant root depth, and soil and water quality.
Plant Water Need.
A plant has different water needs at different stages of growth.
While a plant is young, it requires less water than when it is in the reproductive stage.
As a plant approaches maturity, its water needs drops.
Curves have been developed that show the daily water needs for most types of crops.
Figure 9 shows a typical crop water curve.
Perennial crops, such as alfalfa, have crop water-use curves similar to those in Figure 9, except that the crop water use is altered when the crop is cut or harvested.
The water use would drop dramatically at cutting and recover with regrowth, making the water-use curve appear in a sawtooth-shaped pattern.
Plant Root Depth.
A plant's root depth determines the depth to which soil water can be extracted.
A young plant with only shallow roots will not have access to soil water deeper than its rooting depth.
Plants typically extract about 40 percent of their water needs from the top quarter of their root zone, then 30 percent from the next quarter, 20 percent from the third quarter, and taking only 10 percent from the deepest quarter, as illustrated in Figure 10.
Therefore, plants will extract about 70 percent of their water from the top half
 Figure 9.
Typical plant water-use curve by stage of growth.
Figure 10.
Generalized crop water extraction by depth of root zone for a non-layered and unrestricted soil profile.
of their total root penetration.
Table 2 shows the depth of root penetration and 70 percent water extraction for several common field crops.
Deeper portions of the root zone can supply a higher percentage of the crop's water needs if the upper portion is largely depleted.
However, reliance on use of deeper
 water reduces optimum plant growth.
For irrigation scheduling purposes, the total potential plant root zone is not used.
Instead a managed root zone depth of no more than 4 feet is recommended.
Applying water to deeper depths subjects the irrigation to higher potential for deep percolation
 Table 2.
Depth of root penetration and 70 percent of their water extraction for several common field crops.
Crop	Depth of Root	70% of their Water
 Penetration 	Extraction 
 Corn	4 6	2-3
 Grain Sorghum	4.
5 6	2 3
 Alfalfa	6 10	3 4
 Soybeans	5 6	2-3
 Wheat	4 6	3
 Sugar Beets	5 6	3
 losses.
The managed root depth may be much less than 4 feet if soils have restrictive layers that prevent root penetration.
Some sands also result in restricted root penetration.
Soil and Water Quality.
Another factor on the amount of soil water available to the plant is the soil and water quality.
For good plant growth, a soil must have adequate room for water and air movement, and for root growth.
A soil's structure can be altered by certain soil management practices.
For example, excessive tillage can break apart aggregated soil and excessive traffic can cause compaction.
Both of these practices reduce the amount of pore space in the soil, reducing the availability of water and air, and reducing the room for root development.
The quality of the water is also important to plant development.
Irrigation water with a high content of soluble salt is not as available to the plant, SO greater soil water content must be maintained in order to have water available to the plant.
Increasing salt content of the water reduces the potential to move water from the soil into the roots.
Some additional water would also be needed to leach the salt below the crop root zone to prevent salt build-up in the soil.
Poor quality water can affect soil structure.
Most Kansas crops are considered intermediate in terms of their salt tolerance.
Basic knowledge of soil-plantwater relationships makes it possible to better manage and conserve irrigation water.
Some of the important factors to remember include:
 1.
Soil water-holding capacity varies with soil texture.
It is high for mediumand fine-textured soils but low for sandy soils.
2.
Plant roots can use only available soil water, the stored water between field capacity and permanent wilting point.
However, as a general rule, plant growth and yields can be reduced if soil water in the root zone remains below 50 percent of the water holding capacity for a long period of time, especially during critical stages of growth.
3.
Although plant roots may grow to deep depths, most of the water and nutrients are taken from the upper half of the root zone.
Plant stress and yield loss can occur even with adequate water in the lower half of the root zone.
4.
Poor irrigation water quality can reduce the plant's ability to take up water and can affect soil structure.
Therefore, one of the key things to look for in an irrigation system evaluation is the pressure.
After you turn the pivot on, be sure to let it run for a while  until the pressure becomes steady.
It is ideal to check the pressure at multiple locations along the pivot lateral.
If this is not feasible, the next best option is the check the pressure at the location where it is likely to be the lowest.
This is typically at the end of the pivot lateral  and at a relatively high elevation in the field.
Twenty-One Years of SDI Research in Kansas
 This paper will summarize research efforts with subsurface drip irrigation in Kansas that has occurred during the period 1989 through 2009.
Special emphasis will be made on brief summaries of the different types of research that have been conducted including water and nutrient management for the principal crops of the region, SDI design parameters and system longevity and economics.
Annual system performance evaluations have shown that dripline flowrates are within 5% of their original values.
Economic analysis shows that systems with such longevity can be cost competitive even for the lower-valued commodity crops grown in the region.
Introduction and Brief History
 Subsurface drip irrigation  technologies have been a part of irrigated agriculture since the 1960s, but have advanced at a more rapid pace during the last 20 years.
In the summer of 1988, K-State Research and Extension issued an in-house request for proposals for new directions in research activity.
A proposal entitled Sustaining Irrigated Agriculture in Kansas with Drip Irrigation was submitted by irrigation engineers Freddie Lamm, Harry Manges and Dan Rogers and agricultural economist Mark Nelson.
This project led by principal investigator Freddie Lamm, KSU Northwest Research-Extension Center , Colby, was funded for the total sum of
 $89,260.
This project financed the initial development of the NWREC SDI system that was expressly designed for research.
In March of 1989, the first driplines were installed on a 3 acre study site which has 23 separately controlled plots.
This site has been in continuous use in SDI corn production since that time, being initially used for a 3-year study of SDI water requirements for corn.
In addition, it is considered to be a benchmark area that is also being monitored annually for system performance to determine SDI longevity.
In the summer of 1989, an additional 3 acres was developed to determine the optimum dripline spacing for corn production.
A small dripline spacing study site was also developed at the KSU Southwest Research-Extension Center  at Garden City in the spring of 1989.
In the summer of 1989, further funding was obtained through a special grant from the US Department of Agriculture.
This funding led to expansion of the NWREC SDI research site to a total of 13 acres and 121 different research plots.
This same funding provided for a 10 acre SDI research site at Holcomb, Kansas administered by the SWREC.
By June of 1990, K-State Research and Extension had established 10 ha of SDI research facilities and nearly 220 separately controlled plot areas.
Over the course of the past 21 years, additional significant funding has been obtained to conduct SDI research from the USDA, the Kansas Water Resources Research Institute, special funding from the Kansas legislature, the Kansas Corn Commission, Pioneer HiBred Inc., the Mazzei Injector Corporation and Syngenta.
Funding provided by the Kansas legislature through the Western Kansas Irrigation Research Project  allowed for the expansion of the NWREC site by an additional 1 acres and 46 additional research plots in 1999.
An additional 22 plots were added in 2000 to examine swine wastewater use through SDI and 12 plots were added in 2005 to examine emitter spacing.
Three research block areas originally used in a 1989 dripline spacing study have been refurbished with new 5 ft spaced driplines to examine alfalfa production and emitter flowrate effects on soil water redistribution.
The NWREC SDI research site comprising 19 acres and 201 different research plots is the largest facility devoted expressly to small-plot row crop research in the Great Plains and is probably one of the largest such facilities in the world.
Since its beginning in 1989, K-State SDI research has had three purposes: 1) to enhance water conservation; 2) to protect water quality, and 3) to develop appropriate SDI technologies for Great Plains conditions.
The vast majority of the research studies have been conducted with field corn because it is the primary irrigated crop in the Central Great Plains.
Although field corn has a relatively high water productivity , it generally requires a large amount of irrigation because of its long growing season and its sensitivity to water stress over a great portion of the growing period.
Of the typical commodity-type field crops grown in the Central Great Plains, only alfalfa and similar forages would require more irrigation than field corn.
Any significant effort to reduce the overdraft of the Ogallala aquifer, the primary water source in the Central Great Plains, must address the issue of irrigation water use by field corn.
Additional crops that have been studied at the NWREC SDI site are soybean, sunflower, grain sorghum, alfalfa and demonstration trials of melons and vegetables.
This report summarizes several studies conducted at the KSU Northwest and Southwest Research-Extension Centers at Colby and Garden City, Kansas, respectively.
A complete discussion of all the employed procedures lies beyond the scope of this paper.
For further information about the procedures for a particular study the reader is referred to the accompanying reference papers when so listed.
These procedures apply to all studies unless otherwise stated.
The two study sites were located on deep, well-drained, loessial silt loam soils.
These medium-textured soils, typical of many western Kansas soils, hold approximately 18.9 inches of plant available soil water in the 8 ft profile at field capacity.
Study areas were nearly level with land slope less than 0.5% at Colby and 0.15% at Garden City.
The climate is semi-arid, with an average annual precipitation of 18 inches.
Daily climatic data used in the studies were obtained from weather stations operated at each of the Centers.
Most of the studies have utilized SDI systems installed in 1989-90.
The systems have dual-chamber drip tape installed at a depth of approximately 16 to 18 inches with a 60-inch spacing between dripline laterals.
Emitter spacing was 12 inches and the dripline flowrate was 0.25 gpm/100 ft.
The corn was planted so each dripline lateral is centered between two corn rows.
Figure 1.
Physical arrangement of the subsurface dripline in relation to the corn rows.
A modified ridge-till system was used in corn production with two corn rows, 30 inches apart, grown on a 60 inch wide bed.
Flat planting was used for the dripline spacing studies conducted at both locations.
In these dripline spacing studies, it was not practical to match bed spacing to dripline spacing with the available tillage and harvesting equipment.
Additionally at Garden City, corn rows were planted perpendicular to the driplines in the dripline spacing study.
All corn was grown with
 conventional production practices for each location.
Wheel traffic was confined to the furrows.
During the winter of 2020-21, metal sheeting was installed over the ribs to decrease water turbulence and increase flow through these tunnels.
The tunnels are now flowing at 1,400 cfs, which is 97% of their previous maximum capacity of 1,450 cfs.
Current Drought Conditions and Scenarios for this Winter
 Allen Dutcher State Climatologist Nebraska
 Drought conditions continue to plague much of the western United States.
As of January 22, 2004, severe to exceptional drought conditions were reported over 90 percent of the Rocky Mountain States according to the National Drought Monitor.
In addition, much of the western half of Nebraska and Kansas reported severe drought conditions, with a pocket of extreme conditions reported across the western 1/3 of Nebraska, northwestern 1/4 of Kansas, and eastern 1/4 of Colorado.
The lack of strong snow storm activity during the last 4 years has led to significant problems within the Republican and Platte river valleys.
Without significant snowfall this winter, projections for these regions continue to point to below normal to record low flows during the spring runoff season.
Even with normal precipitation during the next 5 months, many reservoirs within this region will not have enough stored water to deliver full irrigation needs during the 2004 production season.
The latest Climate Prediction Center  outlook for the upcoming 18 months  calls for above normal temperatures across most of the southern half of the Rocky Mountain states through the remainder of the winter season.
There are equal chances for above normal, normal, or below normal temperatures across the central Plains region through February.
The models project a tendency toward below normal temperatures during the March June period for a small pocket of the central Plains that includes Nebraska, northern Kansas, along with eastern Colorado and Wyoming.
There is a weak chance for above normal temperatures across the southwestern 1/3 of the United States during the July through October period, which includes Colorado, Kansas, and the southern half of Nebraska.
There are no significant precipitation trends in the outlooks for the central Plains until the September through December period, where a weak tendency for above normal precipitation is indicated.
During last winter, a weak El Nino event led to above normal precipitation across much of the southern United States in a region from eastern Oklahoma and Texas through the southeastern United States.
This area generally has a positive response to above normal precipitation during El Nino events.
However, the typical response to above normal precipitation in the desert southwest failed to materialize.
This in part allowed the semi-permanent high pressure system that
 occurs during the summer in the middle layers of the atmosphere to strengthen and expand toward the northeast.
The resulting pattern during the second half of last summer was a large pocket of drier than normal conditions from New Mexico northeastward into the upper Great Lakes region.
This region of high pressure weakened during the late fall and early winter period.
Strong low pressure systems were to enter the Pacific northwest and carve out occasional upper air troughs across the central and northern Rocky mountains.
Several strong storms developed across the central and northern High Plains region, but precipitation coverage was disappointing.
In many locations where rain and snow did fall, precipitation totals in excess of two inches per storm event were not uncommon.
However, most locations of western Nebraska and Kansas, as well as eastern Colorado and Wyoming missed out on major moisture during the critical fall soil moisture recharge period.
In fact, many of these areas have received less than one inch of liquid equivalent moisture since October 1, which is less than 25 percent of normal.
Snow pack accumulations in the Rocky Mountains have been above normal during the first half of the winter.
As of January 1, 2004, snow packs across most major river basins were above long term normals and 20-40 percent higher than January 1, 2003.
Unfortunately, the Platte river basins failed to receive as much moisture with average basin snow pack percentages between 70 and 90 percent of normal.
A dry pattern developed during the last 3 weeks of January and the cumulative snow pack dropped an average of 14 percent compared to long term normals.
The snow hasn't disappeared, but has lost ground since snow should be accumulating depth until the middle of April.
For each week that there is no precipitation in Colorado and Wyoming, the cumulative snow pack is declining an average of five percent.
There was a strong low pressure system that developed out of the southwestern United States during the January 24-29 period.
It was able to merge with a clipper system moving out of south-central Canada and drop a significant swath of snow, ice, and rain from eastern Nebraska through the mid-Atlantic region.
This may be a one-shot deal or a sign that snow activity may be taking on a more positive trend.
Under normal conditions, we would expect these upper air lows to get stronger as they develop across the central and southern Rocky mountains.
The clash of early spring warmth across Texas, coupled with arctic air over the northern Plains states is the perfect ingredient for major snow storm activity.
If this trend continues for the remainder of the winter, there is a fairly good chance that much of the central High Plains will experience several major precipitation events.
However, if the high pressure dominates the central Rockies for the remainder of
 the winter, then expectations would be for below normal precipitation through the remainder of the winter.
Snowpack impacts on Drought:
 As we move into this spring, a crucial component that I concentrate on in reference to drought susceptibility is the mountain snow pack.
It is essentially critical that an above normal snow pack is maintained from New Mexico northward through Wyoming.
Above normal snowpack in northern Colorado through central Wyoming increases the likelihood of some recovery in the depleted reservoir system within the Platte watershed.
Below normal snowpack in this region would mean that most of the reservoirs in Wyoming and Nebraska will set or be near record low pools by the end of the 2004 production season.
In some locations, significant water delivery restrictions will materialize.
Above normal snowpack across the southern half of the Rockies would serve three significant purposes.
First, melting snow would provide above normal streamflow rates for reservoir recharge.
Second, the longer the snowpack remains during the summer, the less likely that the southwestern high pressure will strengthen and expand northeastward.
Third, the evaporative effects of the melting snow provides moisture and cold air aloft for thunderstorm development along the front range of the Rockies.
It is these thunderstorms during the growing season that provide a substantial portion of the moisture required to complement irrigation deliveries in the semi-arid cropping environment of the western High Plains region.
Without normal thunderstorm activity, most regions of the central Plains would be hard pressed to meet crop demands solely by irrigation.
El Nino and La Nina Impacts:
 At present, slightly warmer than normal sea surface temperatures are being reported in the western Pacific Ocean along the equator.
Although temperatures are above normal, no major El Nino event is projected to materialize during the remainder of the winter.
Typically, La Nina or El Nino events begin to materialize during the late summer and reach there statistical peak around December 25th.
However, their peak strength can vary between December 1 and January 31.
La Nina events are the opposite of El Nino and occur when sea surface temperatures remain colder than normal along the Equatorial Pacific region.
Depending on the strength of the event, impacts can be felt in the United States through the late spring months.
El Nino and La Nina events occur on a frequent basis, with a general return period of 2-5 years.
It is useful to understand their implications on weather patterns over the central United States.
El Nino events do show a slightly positive influence on precipitation across the region during the October-March period.
The best responses come from the strongest events.
During this period, temperatures
 are typically on the warmer than normal side.
During an unusually strong event, above normal precipitation tendencies do occur in the April-June period across southwestern Kansas.
La Nina events generally result in below normal temperatures during the October-December period for areas north of the Kansas-Nebraska border, with above normal temperatures likely during the January-March period across the entire central High Plains region.
During strong events, there is a tendency for below normal temperatures to materialize across southeastern Nebraska and eastern Kansas.
Precipitation patterns during La Nina events are less dramatic across the central High Plains.
There are weak tendencies for above normal precipitation across northeast Colorado, eastern Wyoming, and the Nebraska Panhandle during the October-December period.
Only northeastern Colorado shows an above normal precipitation response during the January-March period.
For strong La Nina events, above normal precipitation tendencies occur across southeastern Nebraska and eastern Kansas during the April-June period.
Outside of the defined response areas stated above for the La Nina and El Nino cases, there is an equal distribution of temperatures and precipitation.
This means that there are equal chances of receiving above normal, normal, or below normal precipitation and/or temperatures during the October-December, JanuaryMarch, or April-June periods.
Carmen T.
Agouridis, Sarah J.
Wightman, Jonathan A.
Villines, and Joe D.
Luck, Biosystems and Agricultural Engineering
 tormwater is excess water from rainfall and snowmelts that flows over the ground and does not infiltrate the soil.
Human disturbances increase the volume of stormwater generated through the addition of impervious surfaces such as parking lots, rooftops, and paved streets.
For example, a typical paved driveway 15 by 50 feet can generate over 230 gallons of stormwater runoff during a half inch rainfall.
This volume of stormwater is enough to fill a 60-gallon bathtub almost four times!
Stormwater is a concern not just in urban areas  but in suburban and agricultural locations as well.
As stormwater runoff flows over the land or impervious surfaces, it picks up and transports trash and debris as well as pollutants such as pathogens, nutrients, sediments, heavy metals, and chemicals.
Stormwater runoff either flows directly into streams, rivers, and lakes or is directed to storm drains, often by curbs, where it enters the storm sewer system.
The storm sewer system is a network of underground pipes that quickly transports stormwater to local surface waters.
Due to its large volume, stormwater typically bypasses water treatment plants and is instead guided to local streams, rivers, and lakes.
Pollutants that accumulate in stormwater flowing over land and impervious surfaces are introduced to these water bodies, which can adversely impact water quality.
Table 1.
Common sources of pollutants in stormwater.
Figure 1.
Flooding of streets is a concern in urban areas.
SUMMARY OF EVALUATIONS OF CENTER PIVOT UNIFORMITY
 Kansas State Research and Extension
 Center pivot irrigation systems are the most common system type in Kansas for a variety of factors one of which is the ability to deliver a uniform depth of water application for a variety of crops and field conditions.
Uniform applications are dependent on properly designed, installed and operated sprinkler nozzle packages.
Uniformity evaluations were conducted as part of the Mobile Irrigation Lab  project to promote adoption of improved irrigation management practices with an emphasis on ET based irrigation scheduling.
Since efficient and uniform water applications are critical to successful irrigation scheduling; MIL included evaluation of sprinkler package performance using a single line catch can test.
Catch data was used to calculate the coefficient of uniformity and average application depth.
The information was used in extension programs to illustrate the effect of various correctible sprinkler package deficiencies on performance and to encourage irrigation farmers to examine their nozzle packages and operating conditions.
A summary of the evaluation results will be presented.
This discussion is an expansion of the data was originally presented by Rogers and Aguilar, 2018.
Center pivot irrigation systems are the dominant irrigation system type in use within Kansas.
This is also true for the CPIA states as nearly 85 percent of the irrigated area in Colorado, Kansas and Nebraska are watered using center pivot sprinkler irrigation systems.
Irrigation is also the dominant use of water supplies for Kansas, but in many areas of the state, water supplies are diminishing.
However, irrigated agriculture makes significant contributions to the economy so improving irrigation water utility and conservation has long term benefits.
Since center pivot irrigation systems serve the bulk of the irrigation acres in the region, it is important that these systems be properly designed, installed and managed to accomplish high irrigation efficiency and crop water productivity and these topics have been a reoccurring discussion in CPIC programs.
For example, Terry Howell, retired director of the USDA-ARS Research Lab in Bushland, TX noted in a 1991 CPIC presentation that "Sprinkler irrigation methods can be efficient even in harsh environments, such as the Texas High Plains",.
The late Dale Heermann and former director of the USDA-ARS
 Research Lab in Fort Collins, CO began his 1992 sprinkler irrigation presentation at CPIc with these cautionary words, "We often assume that if a system is working for someone else, it will work for us too.
Unless all the conditions are identical this myth may cause you troubles".
Encouraging adoption of improved irrigation management practices is a major goal of the Kansas State Research and Extension , including the irrigation scheduling.
In the late 1980's and early 1990's, the development of information networks, communication systems and increasing availability of personal computers combined to make ET-based irrigation scheduling an option for irrigation managers to use but lack of familiarity of ET-based irrigation scheduling as well as lack of user friendly scheduling software and limited farmer skills with the operation of PC's remained as barriers to adoption.
In the early 1990's, on-farm demonstration projects were established in south central and western Kansas to promote ET-based irrigation scheduling using KSU's KanSched scheduling tool.
These projects were the forerunners to the Mobile Irrigation Lab  project which was expanded to include performance evaluate center pivot nozzle packages for uniformity.
One rationale for conducting center pivot nozzle package evaluations was that adoption of improved irrigation management techniques, such as ET-based irrigation scheduling, required a uniform application depth to assure all the crop had equal access to the available water and no areas of the field were either overor underwatered which would reduce irrigation water productivity.
The majority of the tests were conducted using a single line of catch cans of 4 -inch diameter, called Irrigages , spaced at no more than 80 percent of the sprinkler nozzle spacing.
Catch can evaluations require sufficient clearance of the nozzle above the top of the collector.
In a center pivot survey , most systems in south central Kansas could be tested using the irrigage catch can evaluation, since over 92 percent have nozzle heights of greater than 4 foot above ground surface.
However, in western Kansas, almost 60 per cent of the nozzle packages are mounted at 4 foot or less above the ground surface which is insufficient clearance for an irrigage collector, especially since the top of the irrigage is about 16 inches above ground when installed.
The catch can generally used was a 4-inch irrigage which was constructed with a storage bottle attached to the bottom of the collection barrel to which the water drained after capture in the collection barrel.
Once in the bottle, evaporation losses were minimal.
This allowed data collection without concern for accuracy losses due to evaporation, improved time convenience for collection of data and minimized the on-site labor need for data collection.
The majority of the tests were conducted using a single line of catch cans, spaced at no more than 80 percent of the sprinkler nozzle spacing.
The collector spacing was selected so a catch sample would be collected within each nozzle spacing interval but with gradual change in the collection location relative to the nozzle outlet.
Although the overall coefficient of uniformity  value could be calculated, another goal was to document the effect of various operational deficiencies on the performance of the sprinkler package.
Many of performance issues could have been identified with a visual inspection of the nozzles and/or a comparison of the nozzle package as installed to the sprinkler design package.
The center pivot systems initially evaluated were a part of a demonstration project.
Part of the selection criteria for the project field sites included the drive-by visibility of project signage and ease of access for education tours or programs.
These systems also thought to be systems with well-maintained and operated at design specifications.
Other systems evaluated were at the request of individuals, therefore, the evaluated systems were not randomly selected.
The intent was to evaluate as many as systems as possible each year while the MIL program was funded.
However many constraints limited the number of evaluations possible such as winter evaluations were often precluded, spring cultural operations , scheduling limitations of the operators , crop canopy height limitations, and even water right limitations.
Fifty-three center pivot irrigation sprinkler package evaluations were conducted Kansas during the period of 1998 through 2011 using catch cans.
These evaluations were conducted on unique systems, except for tests FI 01A 99.
In this instance, the system was tested in the two modes of operation; with the end gun on and with the end gun off.
Both values are included.
These results are shown in Table 1 which includes the general classification of the sprinkler type, collector spacing, the CU and slope of the average application depth, pressure regulation, collector diameter, and the measures region of the system.
The sprinkler types were classified as fixed plate, impact, and moving plate sprinklers.
Fixed plate sprinklers are primarily spray nozzles with a splash plate that does not move when impacted by the water stream; while a moving plate sprinkler would have a splash plate that spins, oscillates or otherwise moves when impacted by the water stream.
The number of each sprinkler type tested and the average CU of the systems are shown in Table 2.
The averages of CU for the three sprinkler types were similar.
Only four impact sprinkler packages were tested and all were operated by one producer.
In the center pivot survey , only about 2 per cent of the survey observations were impact sprinklers.
In some instances, tested systems may have had either wider nozzle spacing on the first span and/or a different sprinkler type on the first span but the sprinkler type and
 later the sprinkler spacing reported reflects the package used on the bulk of the system.
The measured range of the center pivots are included in Table 1 with the majority of the systems being quarter mile systems of approximately 1300 foot in length, although several are longer including one of one half mile in length and one with a corner system.
Note that some systems were tested only in the outer spans verses nearly to the pivot point.
This range was reflection of whether the test was conducted with the evaluators staying on-site or being able to leave the site to return later for data collection.
Graphs of the applied depths of systems often show higher application depths in inner span but including or excluding these values from the CU calculation, since the values are area weighted, have little impact on the overall CU value.
Early tests were conducted using 17-inch diameter pans before the development of the irrigages.
The pans nested for easy transportation and storage and they were easy to install since they only needed to be placed on the ground surface.
However, they also needed to be read quickly after an irrigation event to minimize pan evaporation losses.
The weight of water collected was used as the measurement method.
The pans had to be carried to a weigh station which was labor intensive and tedious.
While the average CU value of the pan catches was higher than the irrigage catches, the difference was more likely do to the systems selected to tested by the pans rather than the collector size itself.
Early systems were demonstration project fields thought to be well maintained and/or relatively new and selected to promote irrigation scheduling; verses later fields that were tested at the request of producers which were field that they suspected may have an issue.
Table 2 also includes the average CU values for pressure regulated  and nonpressure regulated systems.
In the Kansas center survey  about half of the center pivots in SC Kansas were pressure regulated and about 80 percent in western Kansas.
In western Kansas, many of the spray systems are close to the ground and therefore not able to be tested with a catch can procedure.
The CU values for the various collector spacings are also summarized in Table 2.
Initially, the tests were conducted at about 80 % of the nozzle spacing rounded to the nearest foot.
Over time, the tests migrated to being conducted at either 4 foot or 8 foot spacing as a way to streamline the test procedure.
There is a tendency for the closely spaced collectors to have higher CU but the data set, especially at wider spacing, is limited.
Figures 1a and 1b are the graph of the same system  tested with the end gun on and end gun off, respectively.
Figure 1a shows an area of good uniformity until the high catch at radius 945 feet.
This high catch was due to a leaky tower boot.
The next area of catch shows a gradual decrease in catch until radius 1241 when application depth increases dramatically.
The area with gradually decreasing application was due to a reversal of the outer two spans nozzles, while the sudden increase was caused by over spray from the end gun onto a portion of the main lateral as the end gun was not ratcheting properly.
The area of decreasing application depth due to improper nozzle installation is more visible in figure 1b.
The application depth distribution graph for test PR 5-27-99 is shown in figure 2.
The CU value for this system is 84.3.
The major problem associated with this system was at the outer edge where the application depth dropped to approximately half.
This effect was due to an un-installed nozzle and under sizing of the orifices of the next two adjacent nozzles in both directions from the uninstalled nozzle location as compared to the design specifications.
This under-watered area covered approximately 9.2 acres.
So if the average water application was 12 inches, so this area received around 6 inches of irrigation.
A conservative estimate of yield response would be 10 bu/in, resulting in an estimated annual field loss of over 500 bushels which could easily be repaired at minimal cost.
Figure 3 shows the graph for center pivot test SN 7-18-02 which had the lowest CU value of the systems tested.
The issue associated with this nozzle package was incrustation build-up within the system and on the fixed plate nozzles as shown in figure 4.
A regular maintenance requirement for this system included unclogging nozzles at the start of irrigations and the removal of nozzles in the off-season for cleaning of incrustation.
Incrustation on the splash plate would interfere with the development of the spokes of water typical for this type of nozzle and prevent proper overlap of the water streams.
However, for this very level field, farmed with high residue practices, the applied water was adequately re-distributed on the ground surface as evidenced by the crop appearance.
The ASABE standard  describing the test procedure determining the uniformity of water distribution by center pivots has a maximum can spacing of 3 meters  for spray devices and 5 meters  for impact sprinklers.
The MIL tests were conducted using a single line of cans verses two rows for the ASABE test.
Never-the-less, the impact of can spacing on CU was examined by calculating the CU values for the base can spacing, then every other can  and every third can.
The results are shown in Table 3, arranged by from lowest can spacing to largest spacing.
The first three systems  used a collector spacing of 4 ft.
with CU values ranging from 84.3 to 89.9).
Recalculating CU values for 2x or 3x spacing values resulted in less than 1.0 change in CU as compared to the base CU.
The regression lines through the applied depth of catches were very flat and changed little with the increased spacing.
In this case, the 2x catches would have been at a 8 ft.
spacing which is still within the ASABE spacing recommendation but results varied little when going to a 12 ft.
spacing, which slightly exceeds the ASABE recommendation.
The next two systems  had CU values of 91.9 and 84 measured at 5 ft can spacing with a flat regression line for the applied depth of application for the first system, and a positive slope for the second, meaning increasingly more water was being applied with distance from the pivot point.
The slope of the regression line was not greatly impacted by can spacing and also little impact on the average applied application depth.
The CU for RC-TZ-1998 had a maximum CU change of 1.5 for both 2x and 3x spacing.
The 2x spacing is 10 ft.
or approximately the maximum recommended ASABE spacing, while 3x spacing would exceed the ASABE recommendation.
The change in CU value for ED 6-02-99
 was only 0.2 at 2x spacing but 5.1 for the 3x spacing.
System SN 7-18-02, which was discussed previously and shown in figure 3), had large change in CU calculation estimates with increased spacing, however with the base can spacing at 6 ft, both 2x and 3x catches would exceed the ASABE spacing recommendation.
The estimate of applied application depth and the slope of the applied application depth regression line was also impacted by change in spacing.
The next four systems were tested at 8 ft.
spacing and the last system at 10 ft., which would be within or near ASABE guidelines.
Two systems  showed spacing had little impact on the CU value.
The latter system had a strong slope to the application depth.
This was thought to be from improper input operating conditions.
The maximum change in CU value for the other systems ranged from 7.6 to 8.6 with the largest CU change for the 2x spacing.
A series of center pivot uniformity evaluations were conducted over multiple years providing a snapshot of the performance of these systems at the time of the test.
A single line test with a catch can spacing of less than the sprinkler spacing was used.
The systems tested were not randomly selected.
The average CU value of the tested systems was 78.65 with a range of from 91.9 to 53.2.
Early tests tended to be on producer fields in a demonstration project and tended to have higher CU values, which indicates that high CU values are achievable.
Latter tests, conducted at the request of producers, tended to be systems suspected of having an issue.
Many of the sprinkler package deficiencies could have been identified and corrected with a visual inspection and/or a comparison to the sprinkler package design specifications.
However, the catch test then documents the impact of a sprinkler package deficiency on the performance.
Information from these tests have been used in meetings and publications to encourage irrigation managers that high CU performance is possible with good package designs and proper operating conditions but also regular sprinkler package maintenance.
This project was supported in part by The Mobile Irrigation Lab Project GECG 601490, funded by the Kansas Water Plan Fund administered by the Kansas Water Office, USDA Project GEGC 601448, the Ogallala Aquifer Project GEGC 600468 and the Center Pivot Technology Transfer Project.
ASABE S436.1..
Test procedure for determining the uniformity of water distribution of center pivot and lateral move irrigation machines equipped with spray or sprinkler nozzles.
St.
Joseph, Mich.: ASABE.
USDA National Agricultural Statistical Service.
2012.
Census of Agriculture.
2013 Farm and Ranch Irrigation Survey, Vol.
3, Special Studies.
Part1.
Table 1: Coefficient of Uniformity  and slope of linear regression line of catch depth and selected test information for various center pivot sprinkler packages of fixed plate, moving plate and impact sprinklers.
Can	CU	Pressure	Can	Test
 Type of	Space	Regression	Regulated	Dia.
Area
 Test ID	Nozzle	Line	Ft.
from
 Ft.
%	Slope	No or PSI	Ins.
pivot point
 ED 6-01-99	Fixed	4	86.6	-0.000006	No	17	628 1298
 FI 01A -99 EG On	Fixed	4	74.8	0.00001	No	17	473 1365
 FI 01A 99 Off	Fixed	4	78.2	0.00002	No	17	473 1313
 SV 5-27-99	Fixed	4	73.2	0.0001	No	17	1250 2598
 FI 5-26-05	Fixed	4	72.8	-0.00005	6	4	266 1306
 FI 4-17-06 a	Fixed	4	77.6	0.0004	6	4	12 1294
 HS 8-05-09	Fixed	4	81.7	-0.0004	15	4	20 1324
 BT 6-28-10	Fixed	4	76.3	-0.00003	No	4	295 1470
 FI 8 12 11 a	Fixed	4	89.5	0.00002	10	4	8 1328
 ED 6-02-99	Fixed	5	84.0	0.0001	No	17	660-1352
 SN 7-18-02	Fixed	6	53.2	0.0001	No	4	750 1290
 SV 5-12-05	Fixed	6	79.6	-0.00002	NR*	4	300 1296
 FI 5-27-05	Fixed	6	87.0	-0.0001	10	4	532 1300
 FI 7-02-08	Fixed	6	86.6	0.0002	10	4	24 1302
 FI 7-17-08	Fixed	6	91.1	0.00009	10	4	168 1302
 FI 3-28-08a	Fixed	6	92.1	0.00006	10	4	184 1296
 FI 4-16-02	Fixed	8	81.9	0.00003	No	4	16 1288
 FO 5-16-02	Fixed	8	58.2	-0.0005	No	4	210 1322
 SN 6-02-02	Fixed	8	86.8	0.0002	10	4	537 1249
 FI 7-19-05	Fixed	8	75.5	0.000001	No	4	50 1298
 LN 4-21-03	Fixed	8	71.0	-0.00008	No	4	250 1282
 RNU01	Fixed	8	68.6	0.0002	No	4	360-1528
 FI 6-14-06a	Fixed	8	71.9	0.0003	10	4	24 1304
 FO 5-27-09	Fixed	8	86.7	-7E-07	10	4	120 1392
 FI 7-25-05 b	Fixed	8	71.8	-0.0005	10	4	134 1286
 KI 6-09-99	Fixed	4	89.9	0.00001	No	17	526 1326
 FO 3-13-06	Impact	8	82.4	-0.0001	No	4	264 1352
 FO 3-09-06	Impact	8	72.1	-0.00008	No	4	48 1336
 FO 4-04-07a	Impact	8	82.4	-0.0002	No	4	268 1352
 FO 3-30-07a	Impact	8	73.5	-0.0003	No	4	270 -1344
 PR 5-27-99	Moving	4	84.3	-0.00008	30	4	588 1300
 RN 5-06-11a	Moving	4	90.9	-0.0002	20	4	8 847
 MP GS-1998	Moving	5	91.8	-0.0002	No	17	770 1290
 RC-TZ1998	Moving	5	91.9	-0.00003	NR	17	733 1213
 SG 5-22-02	Moving	6	83.8	-0.0002	No	4	132 1212
 SD 6-15-05	Moving	6	74.1	0.0002	Yes	4	480 1212
 FI 7-15-09	Moving	6	90.9	-0.0002	12	4	30 1140
 GY 4 -01-08 b	Moving	6	73.8	0.0003	10	4	102 1338
 BT 3-27-02	Moving	8	81.7	0.0003	10	4	326 1254
 KI 7-8-02	Moving	8	76.4	-0.0003	Yes	4	340 1308
 MP 8-21-02	Moving	8	76.0	-0.0002	No	4	365 1277
 MP1 8-21-02	Moving	8	67.0	-0.0003	No	4	486 1430
 PN 4-01-03	Moving	8	83.1	-0.00007	10	4	350-1278
 SW 5-15-03	Moving	8	76.3	-0.0007	10	4	350 1278
 HV 10-05-11	Moving	8	79.1	-0.0001	20	4	176 1253
 SG 3-14-03	Moving	8	65.9	0.0002	No	4	148 1284
 FI 7-25-05	Moving	8	72.2	-0.0003	10	4	62 -1422
 RN 6-05-00	Moving	10	74.5	0.0002	NR	4	630 1260
 RN 7-01-00	Moving	10	88.8	0.0003	No	4	845 1335
 RC 7-06-00	Moving	10	72.8	-0.0002	No	4	540 1230
 SF 6-06-00	Moving	10	88	-0.0003	NR	4	624 1244
 HV 4-10-03	Moving	10	62.6	-0.0002	No	4	383 1353
 RN 6-08-02	Moving	12	65.3	-0.00005	NR	4	343 1311
 * *NR = not recorded
 Table 2: Average CU values for center pivot performance evaluations
 Test Summary of CU	CU	Number of Observations
 Overall Average	78.65	53
 Fixed Plate Average	78.72	26
 Impact Sprinkler Average	77.60	4
 Moving Plate Average	78.75	23
 Size of Catch Can
 4 inch Catch Can Average	77.73	45
 17 inch Catch Can Average	83.80	8
 Pressure Regulated	81.67	23
 Non-pressure Regulated	75.62	25
 Not Recorded	79.86	5
 Average 4 ft	81.32	12
 Average 5 ft	89.23	3
 Average 6 ft	81.22	10
 Average 8 ft	75.48	22
 Average 10 ft	77.34	5
 Average 12 ft	65.30	1
 Table 3: Influence of can spacing on CU
 Test ID	Type of	Collector	CU %	Applied	Applied
 Nozzle	Spacing 	Depth	Depth
 PR 5-27-99	Moving	4	84.3	-0.00008	0.3
 Odd	83.8	-0.00009	0.3
 Even	84.7	-0.00007	0.3
 3.1	83.3	-0.00007	0.3
 3.2	84.4	-0.00007	0.3
 3.3	85.2	-0.0001	0.3
 KI 6-09-99	Fixed	4	89.9	0.00001	0.32
 Odd	89.7	0.00002	0.33
 Even	89.9	0.000008	0.32
 3.1	90.8	0.000004	0.32
 3.2	89.4	0.00002	0.32
 3.3	89.2	0.00001	0.32
 ED 6-01-99	Fixed	4	86.6	-0.000006	0.54
 Odd	87.2	0.000008	0.54
 Even	86	-0.00002	0.54
 3.1	86.1	-0.00006	0.55
 3.2	86.4	0.00008	0.55
 3.3	87.4	-0.00004	0.53
 RC-TZ1998	Moving	5	91.9	-0.00003	0.81
 Odd	91.2	0.00005	0.82
 Even	92.7	-0.0001	0.81
 3.1	91	0.0001	0.81
 3.2	92.5	-0.00007	0.83
 3.3	92.2	-0.0001	0.8
 ED 6-02-99	Fixed	5	84	0.0001	0.44
 Odd	83.9	0.00009	0.45
 Even	84.1	0.0001	0.44
 3.1	87.2	0.0001	0.44
 3.2	82.1	0.00008	0.44
 3.3	83.1	0.0001	0.46
 SN 7-18-02	Fixed	6	53.2	0.0001	0.67
 Odd	44.6	-0.0004	0.68
 Even	55.5	-0.0003	0.66
 3.1	44.7	-0.0005	0.62
 3.2	56.2	-0.0001	0.75
 3.3	50.7	-0.0004	0.64
 PN 4-01-03	Moving	8	83.1	-0.00007	0.73
 Odd	77.9	0.0002	0.73
 Even	86.5	-0.0002	0.7
 3.1	81.3	0.000008	0.72
 3.2	79.2	-0.000003	0.74
 3.3	85.4	-0.00001	0.68
 LN 4-21-03	Fixed	8	71	-0.00008	0.56
 Odd	70.6	0.00008	0.57
 Even	71.5	0.00008	0.56
 3.1	71.8	0.000006	0.52
 3.2	70	0.0002	0.61
 3.3	71.5	-0.000009	0.56
 MP 8-21-02	Moving	8	76	-0.0002	0.69
 Odd	78.4	-0.0002	0.67
 Even	74.1	-0.0002	0.72
 3.1	80.5	0.00007	0.66
 3.2	72.2	-0.0003	0.71
 3.3	75.7	-0.0003	0.71
 BT 3-27-02	Moving	8	81.7	0.0003	0.63
 Odd	82.6	0.0003	0.62
 Even	81	0.0003	0.65
 3.1	82	0.0003	0.61
 3.2	81.9	0.0003	0.63
 3.3	81.4	0.0004	0.64
 RC 7-06-00	Moving	10	72.8	-0.0002	0.88
 Odd	72.4	-0.0001	0.89
 Even	73.1	-0.0003	0.88
 3.1	70.9	0.0001	0.85
 3.2	70.2	-0.0005	0.96
 3.3	77.8	-0.0003	0.84
 Figure 1a.
Catch can uniformity analysis for Center Pivot FI 01A End Gun On
 Figure 1b.
Catch can uniformity analysis for Center Pivot FI 01A End Gun Off
 Figure 2: Catch can uniformity analysis for center pivot PR 5-27-99.
Figure 3: Catch can uniformity analysis for center pivot SN 7-18-02.
Figure 4: Nozzles incrustation for center pivot SN 7-18-02.
Figure 5: Crop appearance for center pivot SN 7-18-02.
Timing of fertilizer-N application can be critical to crop yield, N use efficiency, economic returns, and N losses to the environment.
Since fall and winter precipitation cannot be predicted, there is high potential for N loss with heavy precipitation during the fall, winter, or early spring.
Therefore, spring soil sampling combined with N application split between pre-plant and in-season is a good strategy for synchronizing N supply with N uptake and minimizing N loss.
Regulations in Nebraska: In addition, irrigation water must be sampled prior to manure application through the system and at least every 5 years thereafter to verify that manure has not been accidentally drawn into the well.
If the pressure is higher than usual, there may be  plugged sprinklers or the system is set up improperly, which can increase energy costs.
One quick and low cost method to correct low pressure is to change the sprinkler orifices.
All that needs to be done is to have your dealer run a new sprinkler chart with a lower flow rate, buy a few smaller orifices to put in by the pivot point and move the rest of the orifices out a few sprinklers on the machine.
If the pressure is too high, do the opposite.
The categories are as follows:
 Good  At least one sensor out of the three depths drier than 70 cb early and one sensor drier than 70 cb on 9/15.
Fair  At least one sensor drier than 70 cb early and one sensor drier than 30 cb on 9/15.
Wet Late  At least one sensor drier than 70 cb early but no sensor drier than 30 cb on 9/15.
Wet Early  No sensor drier than 70 cb early, but one sensor drier than 30 cb on 9/15.
Wet All Season  Both sensors measuring the second and third foot not drier than 70 cb all year, but one sensor between 30 to 70 cb on Sept.
15.
Very Wet All Season  Both sensors measuring second and third foot not drier than 70 cb all year and no sensor drier than 30 cb on Sept.
15.
Using the Watershed Approach to Maintain and Enhance Water Quality
 John Pennington Instructor, Water Quality Educator
 Michael Daniels Professor/Associate Department Head Extension
 Andrew Sharpley Professor, Crop, Soil and Environmental Sciences
 Arkansas Is Our Campus
 The state motto of Arkansas is "The Natural State." All Arkansans can help keep Arkansas "The Natural State" by being part of a team effort to protect our water resources.
In Arkansas, as well as many other states, watershed management plans are developed locally by many individuals and groups who are interested in maintaining and improving water quality at the watershed level.
These management plans are driven by and give power to a diversity of watershed stakeholders.
A stakeholder-developed management plan gives decision-making power to the local groups most closely connected to a specific watershed.
This approach of utilizing an inclusive and diverse membership of interested stakeholders to form a watershed management plan is known as the watershed approach.
The watershed approach is endorsed by the Environmental Protection Agency  as well as many other conservation professionals and practicioners.
The EPA backs this approach to maintaining and improving water quality because its use has been successful in obtaining results in an effective and voluntary manner.
What Is a Watershed?
A watershed is the land area where all surface and groundwaters drain into a common body of water.
Each watershed has boundaries that divide one drainage area from another, and larger watersheds can be divided into smaller sub-watersheds.
Watershed boundaries often cross political boundaries such as county or state
 lines.
There are no two watersheds exactly alike, due to many inherent differences such as topography, geology, climate, land use, etc.
This means that a watershed approach will be unique for any given watershed.
In general, watersheds include forests, cities, pastures and residential areas.
All activities in a watershed affect the water quality within the watershed.
So, wherever you live, work or play, you, the stakeholder, can have an impact on the quantity and quality of water in that watershed.
Watersheds in Arkansas are identified by their name and by a grouping of numbers.
The grouping of numbers is called the Hydrologic Unit Code or HUC.
In Arkansas, the HUC can range from two to eight digits long.
The more digits there are in a code, the smaller the watershed that is represented.
Who Is a Stakeholder?
The people who live in, work in and have an interest in the watershed are called stakeholders.
Examples of stakeholders are landowners, homeowners and residents of a watershed.
Businesses, industries and representatives from city, county, state and federal governments and agencies also have an impact within a watershed, and they are also considered stakeholders.
Realizing
 we all are stakeholders and we all impact the watersheds we live, work and play in, we must take steps to reduce the potential negative impacts we all can leave behind.
Without inclusive stakeholder involvement, the solutions to natural resource problems are much more difficult to accomplish.
Besides providing a sizable workforce, inclusive stakeholder involvement or partnerships promote a team atmosphere.
This team atmosphere is essential for all parties involved to better understand the problems, identify priorities and buy into the methods used to improve water quality.
What Is the Watershed Approach?
The watershed approach is a decision-making process that reflects a common strategy for information collection, analysis and understanding of the roles, priorities and responsibilities of all stakeholders within a watershed.
The watershed approach is based on the concept that many water quality problems are best addressed at the watershed level by all stakeholders.
In addition, a watershed focus helps identify the most cost-effective pollution control strategies to meet or maintain clean water goals.
There are many different elements involved with a watershed approach, but there are three main components of the watershed approach that will not change:
 Partnerships Ensure a diverse membership working towards a common goal that is understood and accepted by all stakeholders.
Partnerships increase the viability of the watershed approach effort and provide increased avenues for participation, awareness and success.
Partnerships that promote the active participation of all concerned parties from all levels of government and a wide cross-section of public and private entities are essential to the watershed approach.
Geographic Focus The entire watershed or just part of a watershed can be the area in which watershed management activities are targeted.
The size of the watershed area addressed will often influence the parties involved in the watershed effort.
For example, the White River Watershed encompasses multiple counties in both Arkansas and
 Missouri.
Within the White River Watershed, there are several groups that focus on smaller subwatersheds such as the Beaver Reservoir Kings River and Buffalo River watersheds.
These sub-watersheds have different parties involved with the watershed effort as compared to the entire Upper White River Watershed in Arkansas.
Management Management techniques allow for organization of watershed efforts including assessment of the targeted watershed area, identification of potential problems and goals, development of management options and plans, implementation of appropriate actions, procurement of resources and measurement of success.
Who Can Help Identify a Watershed Group in Which I Can Participate?
Not all watersheds have established stakeholder organizations.
To determine if your watershed has such an organization or if you are interested in beginning one check in with your local county extension office or conservation district.
The watershed approach has proven to be an effective means of voluntarily protecting our water resources.
Stakeholder-led watershed organizations can play a vital, non-threatening role in protecting our water resources by empowering a diverse group of stakeholders through partnerships to find common goals and joint solutions.
Midwinter irrigation can reduce deep bark canker of walnuts
 Beth L.
Teviotdale G.
Steven Sibbett
 D.
eep bark canker , a bacterial disease of walnut, occurs in all walnutgrowing regions of the state.
The disease causes deep longitudinal cracks in the bark of trunk, scaffolds, and larger branches.
A dark reddish brown exudate flows copiously from these cracks during late spring through fall.
Internally, streaks of black necrotic tissue develop in inner bark near the cambium and small black pits in outer wood.
Infected limbs usually have less foliage, have yellow leaves, and are weaker than other unaffected sections of the tree.
The pathogen, Erwinia rubrifaciens, attacks English walnut, Juglans regia L., but not black walnut, J.
hindsii Jepson, or Para-
 dox hybrid, J.
regia X J.
hindsii.
Although all commercial cultivars are susceptible, Hartley is most seriously affected.
The bacteria enter through bark injuries.
Mechanical harvesters can spread deep bark canker when shaker pads infested with bacteria injure healthy trees.
Trees not mechanically shaken also contract the disease, implicating other tree-injuring agents, such as sapsuckers, which may directly transmit the bacteria or create entry points.
Surgical techniques to remove existing cankers and sterilization of harvest equipment to prevent spread have not provided control or adequate protection.
Topical applications of protectant chemicals or injec-
 tions of antibiotics are not effective.
Bark canker disease causes deep cracks in trunk, scaffolds, and larger branches of walnut trees.
Weakened trees are the most likely to be infected.
Orchard mapping has associated walnut tree vigor with incidence and severity of DBC.
Trees weakened or stressed by marginal soils, poor water management, nutrition, or pest and disease problems more commonly are infected than those growing vigorously.
Remission of DBC symptoms has occurred where stress conditions are alleviated.
Poor tree vigor in walnut often results from inadequate, or excessive, moisture in the root zone.
In much of the San Joaquin Valley, normal winter rainfall does not replenish deep soil moisture, and orchards irrigated only during the growing season become water-deficient by mid-August.
The study reported here compared the effects of two irrigation regimes on incidence and remission of DBC: standard practice  and standard practice supplemented with winter irrigation sufficient to wet the soil profile to 8 feet.
The experiment began in 1977 in an 11-year-old Tulare County Hartley walnut orchard with initially 51.6 percent of its trees showing DBC symptoms.
The orchard was divided into 5by 5-tree treatment blocks, treatments paired and replicated 10 times.
There was no significant difference in disease incidence between areas destined to be winter-irrigated and those to receive the standard practice.
The peripheral 16 trees in each block served as guard rows; data were collected from the central 9 trees.
Soil moisture content was monitored with tensiometers placed at depths of 18, 36, 60, and 96 inches.
Tensiometer stations were in two blocks of each treatment.
The orchard was irrigated with hosepull sprinklers, and winter irrigations were begun in January and repeated until soil moisture reached 96 inches.
Spring irrigations in both treatments began in March, the final irrigation taking place in mid-October after harvest.
Incidence of deep bark canker was determined by presence or absence of exudate from bark cracks in November and December of each year.
Trees having no DBC cracks were scored healthy, those having one or
 Dark, reddish brown exudate oozes from cracks from late spring through fall and is a sign of active disease.
Effect of supplemental winter irrigation on severity of
 deep bark canker of walnut, Tulare County, cultivar Hartley
 Year	Irrigation regime	Healthy	active	inactive
 1977	Winter plus standard	51.7	48.3
 1978	Winter plus standard	48.8	36.7	14.3
 Standard	36.3	45.3	18.1
 1979	Winter plus standard	44.3	34.1	21.6
 Standard	34.8	52.3	11.6
 1980	Winter plus standard	43.2	28.4	28.4
 Standard	33.0	56.8	8.0
 tData collected from central nine trees in each treatment block.
Figures are mean percent; arcsine transformation.
Data analyzed using t-test; n.s.
is not significant; is significant, P = 0.05, P = 0.01.
more cracks with exudate were scored actively diseased, and those with cracks but no ooze scored diseased but inactive.
The inactive designation was not included until 1978.
Three years of added winter irrigation significantly decreased the percentage of trees with active disease symptoms and correspondingly increased the percentage of trees with inactive cankers.
Tensiometer readings showed more frequent periods of dry soil and lack of available water, particularly from January through July, in the
 standard-practice areas than where winter irrigation was included.
Results of this study support the observation that cultural practices can have a dramatic effect on incidence of deep bark canker disease.
In this case, sufficient soil moisture was maintained by supplementing low rainfall with midwinter irrigations.
Inadequate supply of water is a common problem in walnut culture, but programs aimed at improving tree vigor to combat deep bark canker need to include all aspects of tree
 culture.
Procedures required to enhance recovery will vary with each orchard.
Where increased soil moisture is indicated, the very serious problem of Phytophthora root and crown rot must be considered when designing an irrigation schedule.
Beth L.
Teviotdale is Plant Pathologist, Cooperative Extension, San Joaquin Valley Agricultural Research and Extension Center, Parlier; and G.
Steven Sibbett is Farm Advisor, Tulare County.
The authors thank Marion S.
Bailey for his assistance in this work.
Cabbage aphid control on Brussels sprouts and broccoli
 Cabbage aphids feeding in growing point of broccoli.
C abbage aphids in Brussels sprouts and broccoli heads at harvest are cause for rejection of the crop by processors and fresh market buyers.
To achieve acceptable control, growers apply systemic insecticide sprays at the onset of head formation and additionally as needed to protect the heads from infestation.
Meta Systox-R and Phosdrin are the standard insecticides used in California's Salinas Valley.
The purpose of this investigation was to evaluate candidate insecticides against the cabbage aphid, Brevicoryne brassicae , on Brussels sprouts and broccoli.
Brussels sprouts 'Jade E' were transplanted June 16, 1976, in the first experiment at a test site at Hartnell Community College, Salinas.
Plots 25 feet long by one bed  were replicated four times in a randomized complete block design.
Insecticides were applied
The whitepaper also includes numerous diagrams and pictures to illustrate the complex relationship between soil health and water quality and includes a table outlining soil health properties and their relative impact on water quality  an easy-to-use reference guide and resource for educators.
Included in the whitepaper are two newly designed graphics visually depicting the water cycle and the nitrogen cycle.
CORN YIELD AND WATER USE CHARACTERISTICS AS AFFECTED BY TILLAGE, PLANT DENSITY, AND IRRIGATION
 ABSTRACT.
Corn  was grown on a deep, well drained silt loam soil  at Colby, Kansas, from 2004 to 2007 using three plant densities  under conventional, strip, or no tillage systems for irrigation capacities that were limited to 25 mm every 4, 6, or 8 days.
Corn yield increased approximately 10%  from the minimum to maximum irrigation capacity in these four years of varying precipitation and crop evapotranspiration.
Although strip tillage and no tillage had numerically greater grain yields than conventional tillage in all four years [approx.
8.1% and 6.4% , respectively, for the four-year average], strip tillage was significantly greater in only two years and no tillage in only one year.
Seasonal water use of the crop tended to be greater for the strip tillage and no tillage treatments as compared to conventional tillage and was significantly greater for strip tillage in two years and for no tillage in one year.
The small increases in total seasonal water use  for strip tillage and no tillage correspond with greater grain yields for these tillage systems.
Water productivity  also tended to be numerically greater  for the strip tillage and no tillage treatments as compared to conventional tillage because of increased yields for the reduced tillage schemes.
Increasing plant density from 66, 300 to 82,300 plants/ha generally increased grain yield and water productivity.
Results suggest that strip tillage obtains the residue benefits of no tillage in reducing evaporation losses without the yield penalty that sometimes occurs with large amounts of residue.
Both strip tillage and no tillage should be considered as improved alternatives to conventional tillage, particularly when irrigation capacity is limited.
Keywords.
Corn production, Irrigation management, No tillage, Strip tillage, Water productivity, Yield components.
D eclining groundwater supplies and reduced well capacities are forcing irrigators in the Central Great Plains to look for ways to conserve and get the best utilization from their water.
Residue management can conserve soil water, decrease evaporation and runoff, and increase rainfall infiltration.
Residue management techniques such as no tillage or conservation tillage have long been accepted to be very effective tools for dryland water conservation in the Great Plains.
However, adoption of these techniques is lagging for continuous irrigated corn.
There are many reasons given for this lack of adoption, but some of the major reasons expressed are: difficulty handling the increased level of residue from irrigated production; cooler and wetter seedbeds in the early spring, which may lead to delayed emergence; poor
 Submitted for review in September 2008 as manuscript number SW 7699; approved for publication by the Soil & Water Division of ASABE in December 2008.
Presented at the 2007 ASABE Annual Meeting as Paper No.
072283.
Mention of tradenames is solely for informational purposes and does not constitute endorsement of this product by the authors or Kansas State University.
Contribution No.
09-095-J from the Kansas Agricultural Experiment Station, Manhattan, Kansas.
or slower development of the crop ; and ultimately a corn grain yield penalty as compared to conventional tillage systems.
This can be particularly true in northern climates and at increased elevations such as the western Great Plains, where soils are slower to warm in the spring.
In Ontario, seed zone soil temperature was greater for conventional tillage than no tillage, and the time required for corn to reach the V6 growth stage was 5 to 7 days longer for no tillage relative to conventional tillage in a two-year study.
Karlen and Sojka , in the coastal plain of South Carolina, found more rapid and uniform plant emergence and early season growth with conventional tillage than with conservation tillage.
Water was conserved in conservation tillage, but a yield increase was observed only for the non-irrigated treatments in one of four years.
Under high-yielding production systems, even a reduction of a few percentage points in corn yield can have a significant economic impact with today's crop prices.
Strip tillage might be a good compromise between conventional tillage and no tillage, possibly achieving most of the benefits in water conservation and soil quality management of no tillage, while providing a method of handling the increased residue and increased early growth similar to conventional tillage.
The many terms and definitions related to strip tillage are discussed in detail by Morrison , such as strip-till, zone-till, row-till, and band tilling.
A common feature of these conservation tillage systems is that tillage is restricted to narrow strips or zones of soil  where the individual rows will be planted for
 the next crop.
The actual methodologies and implementation of the strip tillage system depend upon the characteristics of the soil, climate, crop, and other desired cultural practices, such as in association with irrigation or fertilization.
Strip tillage systems allow for more cultural management options than a strict no-tillage regimen and also greater yields than conventional tillage in the drier years.
Strip tillage can retain surface residues and thus suppress soil evaporation and also provide subsurface tillage to help alleviate effects of restrictive soil layers on root growth and function.
Strip tillage for cotton production into terminated wheat stubble in the Texas High Plains resulted in more evapotranspiration being partitioned into transpiration than into soil water evaporation and thus increased lint yield by 35%.
From modeling research, Lascano et al.
estimated that the transpiration to soil water evaporation ratio for conventional tillage would be 0.5, while it would be improved to 0.69 for strip tillage production of cotton into wheat stubble.
Chisel tillage and no-tillage systems resulted in greater near-surface  rooting and total profile root lengths than disked treatments on a silty clay loam soil in Nebraska.
Both dryland and deficit irrigation treatments were also associated with improved root proliferation in this study.
The researchers concluded that better corn rooting under conservation tillage might allow irrigators to increase water productivity.
Strip tillage had greater emergence than conventional tillage and no tillage in a study in Iowa , but the resulting crop yield and water productivity were similar between tillage systems.
Kaspar et al.
studied the effect of removing residue cover from 8, 16, and 32 cm wide row zones for corn production on four soil types near Ames, Iowa.
They found that the removal of some residue from the seed row reduced the time required for both plant emergence and anthesis, increased plant height, and increased yield.
Corn yields were only reduced 3% from bare soil conditions when a 16 cm band of residue was removed from the row location.
The effects of conservation tillage practices on the root environment of corn may differ under deficit irrigation.
Corn roots tend to explore the lower soil profile to a greater extent under water stress conditions.
This phenomenon, in conjunction with soil water conservation by no-tillage methods, may allow irrigators to increase water productivity by better use of stored soil water.
Chaudhary and Prihar  found that conventional tillage encouraged earlier and deeper penetration of corn roots into the soil profile than no tillage, but notillage corn had more roots in the top 0.20 m of soil during early growth stages.
It is clear that tillage systems alter the soil environment, thus providing a potential for affecting corn root distribution within the soil.
Under dryland and deficit-irrigated production in southwest Kansas, a no-tillage system increased corn yield by 0.56 Mg/ha and water productivity by 0.00096 Mg/ha-mm as compared to conventional tillage.
Norwood  concluded that a combination of deficit irrigation and appropriate plant density and soil fertility could be a viable economic alternative to dryland production in an area of declining groundwater.
Optimizing cultural management practices will be a key factor in managing deficit-irrigated corn production, SO a study was initiated in 2004 to examine the effect of three tillage systems for corn production under three different irrigation capaci-
 ties.
Plant density was an additional factor examined because corn grain yield increases in recent years have been closely related to increased plant density.
The study was conducted under a center-pivot sprinkler at the KSU Northwest Research-Extension Center at Colby, Kansas, during the years 2004 to 2007.
Corn  was also grown on the field site in 2003 to establish baseline residue levels for the three tillage treatments.
The study area had conventional tillage in 2003.
The medium textured, deep, well drained, loessial Keith silt loam soil  can supply about 445 mm of available soil water for a 2.4 m soil profile.
The soil is typical of many High Plains soils and is described in more detail by Bidwell et al..
The region has an average annual precipitation of 481 mm with a summer pattern, resulting in an average corn cropping season precipitation of 299 mm.
The average seasonal total crop evapotranspiration  for corn is 586 mm.
The latitude is 39.39 north and the longitude is 101.07 west, with an elevation of 963 m above sea level.
A corn hybrid of approximately 110-day relative maturity  was planted in 76 mm spaced circular rows on 8 May 2004, 27 April 2005, 20 April 2006, and 8 May 2007, respectively.
The two hybrids differ only slightly, with the latter hybrid having an additional genetic modification of corn rootworm control.
Three target seeding rates  were superimposed onto each tillage treatment in a complete randomized block design.
Irrigation was scheduled with a weather-based water budget but was limited to the three treatment capacities of 25 mm every 4, 6, or 8 days.
This results in typical seasonal irrigation amounts of 300-500, 275-375, and 200-300 mm, respectively.
The weather-based water budget was constructed using data collected from an NOAA weather station located approximately 600 m northeast of the study site.
The reference evapotranspiration  was calculated using a modified Penman combination equation similar to the procedures outlined by Kincaid and Heermann.
The specifics of the ETr calculations used in this study are fully described by Lamm et al..
A twoyear  comparison using weather data from Colby, Kansas, of this estimation method to the ASCE standardized reference evapotranspiration equation, which is based on FAO-56 , indicates that the modified-Penman values are approximately 1.5% to 2.8% lower.
This is well within the accuracy of the resultant scheduling and irrigation application procedures.
Basal crop coefficients  were generated with equations developed by Kincaid and Heermann  based on work by Jensen  and Jensen et al..
The basal crop coefficients were calculated for the area by assuming 70 days from emergence to full canopy for corn with physiological maturity at 130 days.
This method of calculating ETc as the product of Kcb and ETr has been acceptable in past studies at Colby.
In constructing the irrigation schedules, no attempt was made to modify ETc with respect to soil evaporation losses or soil water availability, as outlined by Kincaid and Heermann.
Alfalfa-based
 Figure 1.
Physical arrangement of the irrigation capacity  for the nine different pie-shaped sectors and tillage treatments  randomized within the outer sprinkler span.
ETr is considered to give better estimates than short-grass ETo in this region.
Each of the irrigation capacities  was replicated three times in pie-shaped sectors  of the centerpivot sprinkler.
Plot length varied from to 27 to 53 m,
 depending on the radius of the subplot from the center pivot point.
Irrigation application rates  at the outside edge of this research center pivot were similar to application rates near the end of full-size systems in the region.
A small amount of preseason irrigation was conducted to bring the soil water profile  to approximately 50% of field capacity in the fall and as necessary in the spring to bring the soil water profile to approximately 75% in the top m prior to planting.
The preseason irrigation was generally between 50 to 75 mm total for the years but was not kept constant between years.
It should be noted that preseason irrigation is not a recommended practice for fully irrigated corn production, but it allowed the three irrigation capacities to start the season with somewhat similar amounts of water in the profile.
The three tillage treatments [conventional tillage , strip tillage , and no tillage ] were replicated in a Latin-square type arrangement in 18 m widths at three different radii  from the center pivot point.
The various operations and their time period for the three tillage treatments are summarized in table 1.
Planting was in the approximate same row location each year for the conventional tillage treatment to the extent that good farming practices allowed.
The strip tillage and no tillage
 Table 1.
Tillage treatments, herbicide, and nutrient application by period.
Summer	Conventional Tillage	Strip Tillage	No Tillage
 Fall	1.
One-pass chisel/disk plow at 0.20 to 0.25	1.
Strip till + fertilizer  at 0.20 to 0.25
 2003	m with broadcast N 	m depth 
 Spring	2.
Plant + banded starter N and P (8 May	2.
Plant + banded starter N and P (8 May	1.
Broadcast N + plant + banded starter N
 2004	2004)	2004)	and P 
 3.
Pre-emergent herbicide application (9	3.
Pre-emergent herbicide application (9	2.
Pre-emergent herbicide application (9
 May 2004)	May 2004)	May 2004)
 2004	4.
Roundup herbicide application near lay-	4.
Roundup herbicide application near	3.
Roundup herbicide application near
 by 	lay-by 	lay-by 
 5.
Fertigate  	5.
Fertigate  	4.
Fertigate  
 Fall	1.
One-pass chisel/disk plow at 0.20 to 0.25	
 2004	m with broadcast N 
 Spring	2.
Plant + banded starter N and P  at 0.20 to 0.25	1.
Broadcast N + plant + banded starter N
 2005	2005)	m depth 	and P 
 3.
Pre-emergent herbicide application (8	2.
Plant + banded starter N and P (27	2.
Pre-emergent herbicide application (8
 May 2005)	April 2005)	May 2005)
 3.
Pre-emergent herbicide application (8
 Summer	4.
Roundup herbicide application near lay-	4.
Roundup herbicide application near	3.
Roundup herbicide application near
 2005	by 	lay-by 	lay-by 
 5.
Fertigate  	5.
Fertigate  	4.
Fertigate  
 Fall	1.
One-pass chisel/disk plow at 0.20 to 0.25	1.
Strip till + fertilizer  at 0.20 to 0.25
 2005	m with broadcast N 	m depth 
 Spring	2.
Plant + banded starter N and P (20 April	2.
Plant + banded starter N and P (20	1.
Broadcast N + plant + banded starter N
 2006	2006)	April 2006)	and P 
 3.
Pre-emergent herbicide application (22	3.
Pre-emergent herbicide application (22	2.
Pre-emergent herbicide application (22
 April 2006)	April 2006)	April 2006)
 Summer	4.
Roundup herbicide application near lay-	4.
Roundup herbicide application near	3.
Roundup herbicide application near
 2006	by 	lay-by 	lay-by 
 5.
Fertigate  	5.
Fertigate  	4.
Fertigate  
 Fall	1.
One-pass chisel/disk plow at 0.20 to 0.25	1.
Strip till + fertilizer  at 0.20 to 0.25
 2006	m with broadcast N 	m depth 
 Spring	2.
Plant + banded starter N and P (8 May	2.
Plant + banded starter N and P (8 May	1.
Broadcast N + plant + banded starter N
 2007	2007)	2007)	and P 
 3.
Pre-emergent herbicide application (8	3.
Pre-emergent herbicide application (8	2.
Pre-emergent herbicide application (8
 May 2007)	May 2007)	May 2007)
 Summer	4.
Roundup herbicide application near lay-	4.
Roundup herbicide application near	3.
Roundup herbicide application near
 2007	by 	lay-by 	lay-by 
 5.
Fertigate  	5.
Fertigate  	4.
Fertigate  
 treatments were planted between corn rows from the previous year.
Fertilizer N for all three treatments was applied at a rate of 225 kg/ha in split applications with approximately 95 kg/ ha applied in the fall or spring application, approximately 35 kg/ha in the starter application at planting, and approximately 95 kg/ha in a fertigation event near corn lay-by.
Phosphorus was applied with the starter fertilizer at planting at the rate of 50 kg/ha P2O5.
Urea-ammonium-nitrate  and ammonium superphosphate  were utilized as the fertilizer sources in the study.
Fertilizer was incorporated in the fall concurrently with the conventional tillage operation and applied with a mole knife during the strip tillage treatment.
Conversely, N application was broadcast with the no tillage treatment prior to planting.
A post-plant, pre-emergent herbicide program of metolachlor, atrazine, and glyphosate was applied.
Glyphosate was also applied post-emergence prior to lay-by for all treatments, but was particularly beneficial for the strip tillage and no tillage treatments.
Insecticides were applied as required during the growing season for root worm and spider mite control.
Weekly to bi-weekly soil water measurements were made in 0.3 m increments to 2.4 m depth with a neutron probe.
All measured data was taken near the center of each plot.
Crop residue cover of the soil surface was determined in April 2007 prior to planting by the point-intercept method , modified by two sets of 50 knots at 0.3 m increments.
Surface residue biomass was determined from the mean of three stratified samples of selected plots, representing minimum, median, and maximum residue cover within the plot.
Residue collected from 0.76 X 0.76 m sampling area was washed in burlap bags, dried to constant weight, and weighed.
Sampled units represented three replicates of the maximum plant population treatment within minimum and maximum irrigation capacities.
Corn yield was measured in each of the 81 subplots at the end of the season by hand-harvesting the ears from a 6 m section of one corn row near the center of each plot.
Corn grain yield was adjusted to 15.5% wet basis.
Water use and water productivity  were calculated for each subplot using the soil water data, precipitation, applied irrigation, and crop yield.
WEATHER CONDITIONS AND IRRIGATION NEEDS In general, conventional tillage treatments were observed to emerge earlier and have improved growth during May and
 Figure 2.
Calculated well-watered corn evapotranspiration and summer seasonal rainfall for the 120-day period 15 May through 11 September, KSU Northwest Research-Extension Center, Colby Kansas.
June as compared to the strip tillage and no tillage treatments, probably because of warmer soil temperatures.
However, by about mid-summer in most of the years, the conventional tillage treatments began to show greater water stress, particularly for the reduced irrigation capacities, as evidenced by some observed mid-day wilting.
The conventional tillage plots also tended to senesce earlier in most years, with the exception of 2004.
Summer seasonal precipitation was approximately 50 mm below normal in 2004, near normal in 2005, nearly 75 mm below normal in 2006, and approximately 65 mm below normal in 2007 at 253, 304, 228, and 238 mm, respectively, for the 120-day period from 15 May through 11 September.
In 2004, the last month of the season was very dry, but the remainder of the growing season had reasonably timely rainfall and approximately normal calculated well-watered crop evapotranspiration.
In 2005, precipitation was above normal until about the middle of July, and then there was a period with very little precipita-
 Figure 3.
Cumulative irrigation by day of year for the three irrigation capacities during all four years of the tillage and irrigation capacity study of corn, KSU Northwest Research-Extension Center, Colby, Kansas.
Table 2.
Corn grain yield and harvest plant density in a tillage and irrigation capacity study, KSU Northwest Research-Extension Center, Colby, Kansas, 2004-2007.[a]
 Irrigation	Capacity	Tillage	Target Plant	Density	Grain Yield 	Harvest Plant Density 
 Limited to	System		2004	2005	2006	2007	Mean	2004	2005	2006	2007	Mean
 66.3	14.4	13.7	15.0	15.4	14.6	68888	58841	72475	68888	67273
 CT	74.5	14.8	14.9	13.3	17.2	15.0	72475	68170	76781	79651	74269
 82.3	14.7	16.3	13.3	16.1	15.1	79651	74628	86827	86109	81804
 66.3	15.4	14.9	14.6	15.9	15.2	68170	60277	72475	69605	67632
 25 mm/4 d	ST	74.5	14.6	15.7	14.8	16.9	15.5	75346	68888	77498	76781	74628
 82.3	14.9	15.9	16.3	17.5	16.1	81804	76781	81804	88980	82342
 66.3	13.7	14.3	13.2	15.4	14.2	63864	61712	70323	66017	65479
 NT	74.5	14.2	15.9	16.5	16.6	15.8	72475	66017	77498	78216	73552
 82.3	15.7	16.5	15.6	16.0	15.9	83239	77498	85392	86109	83060
 66.3	14.2	12.7	10.1	15.3	13.1	62429	60994	71758	68888	66017
 CT	74.5	13.9	13.8	13.0	15.2	14.0	73193	68170	78934	81086	75346
 82.3	15.3	13.1	10.6	14.8	13.4	80369	76781	83957	86109	81804
 66.3	14.7	14.2	13.0	15.3	14.3	67452	60277	71758	65300	66197
 25 mm/6 d	ST	74.5	14.1	13.0	13.5	15.2	13.9	71040	69605	77498	79651	74449
 82.3	14.9	15.6	13.6	15.7	14.9	82522	78934	84674	87545	83418
 66.3	14.1	12.9	14.4	14.4	13.9	65300	60994	72475	68170	66735
 NT	74.5	13.9	14.1	13.7	16.1	14.4	71758	71758	74628	78934	74269
 82.3	14.3	14.7	14.0	15.5	14.6	79651	78216	81086	88980	81983
 66.3	12.4	11.7	10.8	13.8	12.2	60994	60277	69605	68888	64941
 CT	74.5	13.3	13.7	12.0	15.6	13.6	72475	67452	78216	81086	74808
 82.3	13.6	13.1	12.0	15.6	13.6	78216	78216	83957	84674	81266
 66.3	14.3	13.3	13.4	15.2	14.1	63864	58841	72475	68170	65838
 25 mm/8 d	ST	74.5	14.4	13.5	13.8	16.0	14.4	73911	68170	78934	76781	74449
 82.3	14.7	15.0	14.5	16.8	15.2	81086	77498	85392	88980	83239
 66.3	13.8	13.1	12.8	14.1	13.4	66735	59559	71040	68170	66376
 NT	74.5	14.1	13.2	13.8	15.6	14.2	73193	68170	77498	79651	74628
 82.3	13.8	13.6	13.5	14.7	13.9	81086	76781	83957	86109	81983
 Mean for 25 mm/4 d	14.7	15.3	14.7 a	16.3 a	15.3	73990	68090 a	77897	77817	74449
 Mean for 25 mm/6 d	14.4	13.8	12.9 b	15.3 b	14.1	72635	69525 b	77419	78296	74469
 Mean for 25 mm/8 d	13.8	13.4	13.0 b	15.3 b	13.9	72396	68329 a	77897	78057	74170
 Mean for CT	14.1	13.7 a	12.2 a	15.4	13.8	72077	68170	78057	78376	74170
 Mean for ST	14.6	14.6 b	14.2 b	16.1	14.9	73911	68808	78057	77977	74688
 Mean for NT	14.2	14.2 ab	14.2 b	15.4	14.5	73034	68967	77100	77817	74229
 Mean for 66,300 p/ha	14.1	13.4 a	13.0	15.0 a	13.9	65300 a	60197 a	71598 a	68010 a	66276
 Mean for 74,500 p/ha	14.1	14.2 b	13.8	16.0 b	14.5	72874 b	68489 b	77498 b	79093 b	74489
 Mean for 82,300 p/ha	14.6	14.8 b	13.7	15.9 b	14.8	80847c	77259 c	84116 c	87066 c	82322
 [a] Main effect treatment means followed by different lowercase letters are significantly different at P = 0.05.
tion until the middle of August.
This dry period in 2005 also coincided with a week of greater temperatures and elevated crop evapotranspiration near the reproductive period of the corn.
In 2006, precipitation lagged behind the long-term average for the entire season.
Fortunately, the calculated well-watered seasonal evapotranspiration was near normal, as was the case for 2004 and 2005.
Although precipitation was much less than normal in 2007, crop evapotranspiration was also much less than normal at 507 mm, which resulted in reduced irrigation needs.
Irrigation requirements were least in 2004, with the 25 mm/4 day treatment receiving 305 mm, the 25 mm/6 day treatment receiving 279 mm, and the 25 mm/8 day treatment receiving 229 mm.
The irrigation amounts in 2005 were 381, 330, and 254 mm for the three respective treatments.
The irrigation amounts were greatest in 2006, at 394, 343, and 292 mm for the three respective treatments.
Irrigation amounts in 2007 were 318, 292, and 267 mm for the three
 respective treatments, which were just slightly greater than the minimum irrigation values of 2004.
Although seasonal precipitation was considerably less in 2007 compared to 2004, there was very little difference in irrigation requirements.
This was because calculated evapotranspiration was considerably less than normal in 2007 due to light winds and moderate temperatures during much of the summer.
CROP YIELD, HARVEST PLANT DENSITY, AND RESIDUE
 Corn yield ranged from 10.1 to 17.5 Mg/ha.
Greater irrigation capacity generally increased grain yield in all four years, but yield was only significantly greater for the larger 25 mm/4 d capacity in 2006 and 2007.
When averaged over all irrigation capacities and plant densities, strip tillage produced significantly greater yields than conventional tillage in both 2005 and 2006 and numerically greater yields in all four years of the study.
No tillage had significantly greater yields than conventional tillage in 2006 and numerically greater yields in all four years of the study.
There
 Figure 4.
Corn grain yield as affected by irrigation amount and tillage, 2004-2007, KSU Northwest Research-Extension Center, Colby, Kansas.
Irrigation amounts from left to right represent the three irrigation capacities with applications limited to 25 mm every 8, 6, or 4 days, respectively.
The results are averaged across the three plant densities.
were no significant differences in yields between the strip tillage and no tillage treatments.
Strip tillage tended to have the greatest grain yields for all three tillage systems, and the benefit of this tillage treatment was numerically greatest at the minimum irrigation capacity in all four years of the study.
The grain yield benefits of the reduced tillage systems were greatest in 2005 and 2006 , the years with greater irrigation requirements.
There is the possibility that nitrogen fertilizer placement differences between the tillage systems may have affected yield results, but that is indeterminable in this study.
In this study, fertilizer application and placement was based on typical practices for each tillage system.
Strip tillage and no tillage also tended to have greater stability or less variation in grain yields than conventional tillage across the range of irrigation capacities, as evidenced by the flatter slopes in figure 4, with the exception of 2007 when all tillage treatments had somewhat similar stability in this year of less irrigation water requirements.
Greater yield stability suggests that these reduced tillage treatments would be excellent choices when irrigation is deficit during the season.
Figure 5.
Corn grain yield as affected by irrigation amount and plant density, 2004-2007, KSU Northwest Research-Extension Center, Colby, Kansas.
Irrigation amounts from left to right represent the three irrigation capacities with applications limited to 25 mm every 8, 6, or 4 days, respectively.
The results are averaged across the three tillage treatments.
There were no significant differences in the harvest plant density as affected by irrigation capacity or tillage system.
Increasing plant density had a significant effect in increasing corn grain yields  in both 2005 and 2007, and generally resulted in numerically greater corn yields in all four years.
The greatest response to increased plant density was in 2007, the year with the greatest grain yields.
This emphasizes that increased plant density allows producers to greatly increase gross economic returns when excellent corn production conditions exist.
When averaged across tillage systems and all four years, increasing the plant density from 62,300 to 82,300 plants/ha increased corn
 Corn grain yield had an interesting three-way statistical interaction of irrigation capacity, tillage system, and plant density in 2006.
Yields of the intermediate and maximum plant densities resulted in greater corn grain yields for the strip tillage and no tillage systems, while maximum yield under conventional tillage occurred for the minimum plant density for the maximum irrigation capacity.
Yields were relatively similar across plant densities for the reduced tillage systems at reduced irrigation capacities.
This effect may be the result of increased plant water stress and observed earlier plant senescence for the conventional tillage treatment when plant density was too great for the available plant water supply.
Earlier plant senescence will curtail the amount of intercepted photosynthetically active radiation  and thus
 net photosynthesis during the important grain filling stage of the corn.
Rochette et al.
found that intercepted photosynthetically active radiation  accounted for 90% of the variation observed in net photosynthesis of corn, in the absence of water stress and with nutrient sufficiency.
An interaction of irrigation management and corn plant density also occurred on a coastal plain loamy sand soil in South Carolina  where increased plant density increased corn grain yields under irrigation but decreased corn yields under non-irrigated conditions in two of three years.
Mixed results for increased plant density were also found for sandy loam soils in Georgia.
Under irrigated conditions, grain yield increased with plant density for both wide  row spacings, but under non-irrigated conditions plant densities greater than 50,000 plants/ha resulted in decreased yields for the narrow row spacings.
The results from all of these studies suggest that grain yield response to plant density is influenced by site conditions and that this issue will affect recommendations for a given locale.
Crop residue amounts and the percentage of residue cover in April 2007 were similar for no tillage  and strip tillage  but much less for conventional tillage.
These results suggest that strip tillage can obtain the residue benefits of no tillage in reducing irrigation and rainfall runoff and evaporation losses without the yield penalty sometimes associated with the increased residue levels in irrigated no-tillage management.
CORN WATER USE, PLANT-AVAILABLE SOIL WATER, AND WATER PRODUCTIVITY
 Total seasonal water use in this study was calculated as the sum of irrigation, precipitation, and the change in available soil water over the course of the season.
As a result, seasonal water use can include non-beneficial water losses such as soil evaporation, deep percolation, and runoff.
There were significant differences in seasonal water use as affected by irrigation capacity in three of the four years, with increased water use tending to occur for the maximum irrigation capacity.
There were significant differences in post-anthesis water use attributable to irrigation capacity in all four years  but not in pre-anthesis water use.
This would be the anticipated result because, as the season progresses and evapotranspiration needs increase due to hotter and drier weather conditions and a more extensive plant canopy, greater irrigation capacities would allow for greater water use.
Although the average seasonal irrigation amount for the maximum irrigation capacity was 89 mm greater than the minimum irrigation capacity, there was only an average of 62 mm difference in water use.
The small difference can probably be attributed to reduced non-beneficial water losses and also better root water uptake for the minimum capacity as compared to the maximum irrigation capacity.
Intuitively, one might anticipate that good residue management with strip tillage and no tillage would result in less water use than conventional tillage because of reduction in non-beneficial water losses.
However, in this study, strip tillage and no tillage generally had slightly greater water use.
The small increases in total seasonal water use  for strip tillage and no tillage compared to conventional tillage corresponds with the greater grain yields for these tillage systems (approx.
0.9 mg/
 Figure 6.
Pre-anthesis, post-anthesis, and total seasonal water use  as affected by irrigation capacity for conventional , strip , and no tillage  systems, 2004-2007, KSU Northwest Research-Extension Center, Colby, Kansas.
The results are averaged across the three plant densities.
ha) and may result from the earlier canopy senescence observed under conventional tillage.
There was a significant interaction of tillage and irrigation capacity on post-anthesis water use in 2006, with less water use for conventional tillage for the intermediate and minimum irrigation capacities in contrast to no tillage differences in post-anthesis water use at the maximum irrigation capacity.
This difference can probably be explained by the observed earlier senescence for conventional tillage when water stress existed.
This postanthesis water use difference in 2006 may have further led to an interaction of tillage and irrigation capacity on total seasonal water use, with more crop water use for strip tillage and no tillage at the smallest irrigation capacity in contrast to no differences in water use between tillage treatments at the maximum irrigation capacity.
No tillage had significantly less pre-anthesis water use than conventional tillage in two of the four years  and significantly greater post-anthesis water use than conventional tillage in two of the four years.
Similarly, strip tillage had significantly greater post-anthesis water use than conventional tillage in two years.
The shifting of water use to the post-anthesis period as tillage was reduced may be responsible for the generally improved grain yields for these treatments.
There were no significant differences in total seasonal water use attributable to changes in plant densities alone.
However, there was a significant interaction of plant density and irrigation capacity in 2005, when for some unknown reason total seasonal water use was less for the maximum plant density at the intermediate irrigation capacity in contrast to similar water use values among plant densities for the minimum and maximum irrigation capacities.
One possible reason may be unexplained differences in pre-anthesis water use in that
 Table 3.
Corn water use and water productivity in a tillage and irrigation capacity study, KSU Northwest Research-Extension Center, Colby, Kansas, 2004-2007.[a]
 Irrigation	Capacity	Tillage	Target Plant	Density	Seasonal Water Use 	Water Productivity 
 Limited to	System		2004	2005	2006	2007	Mean	2004	2005	2006	2007	Mean
 66.3	610	718	690	627	661	0.0235	0.0190	0.0217	0.0246	0.0222
 CT	74.5	601	727	679	661	667	0.0246	0.0205	0.0197	0.0260	0.0227
 82.3	584	693	686	619	646	0.0254	0.0236	0.0195	0.0260	0.0236
 66.3	623	718	706	626	668	0.0248	0.0208	0.0206	0.0255	0.0229
 25 mm/4 d	ST	74.5	646	675	698	653	668	0.0226	0.0233	0.0212	0.0260	0.0233
 82.3	643	740	700	626	677	0.0232	0.0215	0.0234	0.0280	0.0240
 66.3	584	713	670	573	635	0.0236	0.0202	0.0198	0.0270	0.0226
 NT	74.5	624	703	700	619	662	0.0229	0.0227	0.0236	0.0268	0.0240
 82.3	615	724	688	607	658	0.0255	0.0228	0.0227	0.0263	0.0243
 66.3	585	671	633	627	629	0.0244	0.0190	0.0159	0.0244	0.0209
 CT	74.5	599	656	627	622	626	0.0233	0.0211	0.0208	0.0243	0.0224
 82.3	606	643	638	610	625	0.0252	0.0202	0.0166	0.0242	0.0215
 66.3	592	679	664	610	636	0.0249	0.0208	0.0196	0.0252	0.0226
 25 mm/6 d	ST	74.5	619	689	660	625	648	0.0227	0.0187	0.0204	0.0242	0.0215
 82.3	619	666	675	615	644	0.0240	0.0233	0.0201	0.0257	0.0233
 66.3	622	679	659	628	647	0.0227	0.0190	0.0219	0.0230	0.0216
 NT	74.5	635	691	653	583	641	0.0219	0.0204	0.0210	0.0276	0.0227
 82.3	595	653	651	624	631	0.0242	0.0225	0.0215	0.0248	0.0233
 66.3	563	579	600	612	588	0.0221	0.0204	0.0180	0.0226	0.0208
 CT	74.5	570	572	561	607	578	0.0233	0.0240	0.0213	0.0260	0.0236
 82.3	559	629	576	620	596	0.0244	0.0207	0.0209	0.0253	0.0228
 66.3	604	605	626	603	609	0.0238	0.0221	0.0216	0.0253	0.0232
 25 mm/8 d	ST	74.5	554	611	628	583	594	0.0260	0.0221	0.0220	0.0274	0.0244
 82.3	589	621	618	590	605	0.0249	0.0242	0.0234	0.0285	0.0252
 66.3	571	625	621	606	606	0.0241	0.0209	0.0206	0.0233	0.0222
 NT	74.5	589	582	627	609	602	0.0240	0.0229	0.0220	0.0256	0.0236
 82.3	574	627	635	591	607	0.0241	0.0217	0.0214	0.0249	0.0230
 Mean for 25 mm/4 d	615 a	712 a	691 a	624	660	0.0240	0.0216	0.0213 a	0.0262	0.0233
 Mean for 25 mm/6 d	608 a	670 b	651 ab	616	636	0.0237	0.0206	0.0197 b	0.0248	0.0222
 Mean for 25 mm/8 d	575 b	606 c	610 b	602	598	0.0241	0.0221	0.0212 a	0.0254	0.0232
 Mean for CT	586 a	654	632 a	623	624	0.0240	0.0209	0.0194 a	0.0248	0.0223
 Mean for ST	613 b	667	663 b	617	640	0.0241	0.0219	0.0213 b	0.0262	0.0234
 Mean for NT	598 ab	656	644 b	611	627	0.0237	0.0214	0.0216 b	0.0255	0.0230
 Mean for 66,300 p/ha	595	665	652	612	631	0.0238	0.0202	a	0.0200 a	0.0245	a	0.0221
 Mean for 74,500 p/ha	604	656	648	618	632	0.0235	0.0217 b 0.0213 b 0.0260 b	0.0231
 Mean for 82,300 p/ha	598	666	652	611	632	0.0245	0.0223 b 0.0210 ab 0.0260	b	0.0234
 [a] Main effect treatment means followed by different lowercase letters are significantly different at P = 0.05.
year.
The intermediate and maximum plant densities had the least and greatest pre-anthesis crop water use for the minimum irrigation capacity in contrast to similar pre-anthesis water use for the greater irrigation capacities.
There were also no significant differences in water use attributable to the single factor of plant density in either the pre-anthesis or postanthesis period of the corn.
Apparently at these corn plant densities in this climatic region, the corn reaches a threshold leaf area index  quickly enough that water use differences were not detectable.
At a threshold LAI of 2.7, corn transpiration is approximately 90% of the maximum value.
LAI of corn at anthesis ranged from approximately 3 to 5 during the four years of the study.
There were no significant differences in available soil water for the 2.4 m soil profile at crop emergence in May, corn anthesis in July, or physiological maturity in September attributable to irrigation capacity or plant density in any of the four years.
When averaged across irrigation capacity and
 plant density treatments, available soil water amounts in the 2.4 m soil profile for no tillage treatments were significantly greater than conventional tillage in all four years at crop emergence in May, for three of the four years at anthesis in July, and for two of the four years at physiological maturity in September.
Differences in available soil water for strip tillage and no tillage were much less, and where there were differences soil water was generally greater under no tillage.
Increased plant-available soil water in the period leading up to corn anthesis for mulched treatments has been also reported by Tolk et al.
, and this led to a subsequently greater LAI after anthesis.
Retaining a greater and non-senesced LAI after anthesis can lead to better grain filling and greater grain yields and biomass amounts.
The water productivity of corn silage was 38% greater for no tillage as compared to conventional tillage in a study on a clay loam soil in North Carolina.
In September 2004, there was a significant interaction between irrigation capacity and tillage treatment, with strip tillage having
 Table 4.
Plant-available soil water at selected times of the corn growing season in a tillage and irrigation capacity study, KSU Northwest Research-Extension Center, Colby, Kansas, 2004-2007.
Available Soil Water [a
 Time of Season	Treatment	2004	2005	2006	2007	Mean
 Conventional	236 a	274 a	266 a	359 a	284
 Plant emergence	in May	Strip tillage	274 b	313 b	321 b	384 ab	323
 No tillage	260 ab	321 b	346 b	386 b	328
 Conventional	273	305 a	256 a	317 a	288
 in July	Strip tillage	305	349 b	313 b	341 ab	327
 No tillage	291	362 b	357 c	353 b	341
 Conventional	206	249	202 a	265 a	230
 Physiological maturity	in September	Strip tillage	221	275	225 ab	298 ab	255
 No tillage	216	284	258 b	310 b	267
 [a] Values followed by different lowercase letters are significantly different at P = 0.05.
Figure 7.
Water productivity for corn as affected by irrigation amount and tillage, 2004-2007, KSU Northwest Research-Extension Center, Colby, Kansas.
Irrigation amounts from left to right represent the three irrigation capacities with applications limited to 25 mm every 8, 6, or 4 days, respectively.
The results are averaged across the three plant densities.
the least available soil water in the 2.4 m soil profile at the maximum irrigation capacity  but having the greatest available soil water at the reduced irrigation capacities  as compared to the other tillage treatments.
These differences may be related to greater soil water extraction and crop production for strip tillage at the maximum irrigation capacity in 2004.
Water productivity as affected by irrigation capacity was significantly different only in 2006, when it was reduced for the intermediate irrigation capacity because of unexplained lower grain yields but similar for the minimum and maximum irrigation capacity.
The general result of no significant effect of irrigation capacity on water productivity suggests that the irrigation scheduling procedures and these irrigation capacities do not grossly overor under-apply irrigation.
Over-application of irrigation will decrease water productivity by increasing the denominator through increased non-beneficial losses of water.
Severe under--
 Figure 8.
Water productivity of corn as affected by irrigation amount and plant density, 2004-2007, KSU Northwest Research-Extension Center, Colby, Kansas.
Irrigation amounts from left to right represent the three irrigation capacities with applications limited to 25 mm every 8, 6, or 4 days, respectively.
The results are averaged across the three tillage treatments.
application of irrigation may result in all or some corn plants not reaching the yield threshold , thus reducing the numerator of the water productivity equation.
An irrigation capacity of 25 mm/4 d when scheduled with an in-season water budget will closely approximate a full irrigation regime in northwest Kansas.
Water productivity as affected by tillage scheme was significantly greater for strip tillage and no tillage in 2006 as compared to conventional tillage and was numerically greater in three of the four years.
The reason for greater water productivity for the reduced tillage systems was primarily that grain yield was increased rather than less water use.
It should also be noted that the reduced tillage treatments had a greater effect on increasing water productivity in 2006 , the year with the greatest difference in seasonal precipitation and evapotranspiration.
This emphasizes that good residue management under irrigation is more beneficial under more water-stressful conditions.
There was a statistically significant effect of plant density on water productivity in 2005, 2006, and 2007, with the intermediate and maximum plant densities generally having greater water productivity than the minimum plant density.
This effect was caused by greater yield for the greater plant densities, because there were no significant differences in water use.
These results contrast with those obtained on a sandy loam soil in northeast Colorado by Al-Kaisi and Yin , who recommended that water productivity  would be maximized at plant densities of 57,000 and 69,000 plants/ha as compared to their maximum value of 81,000 plants/ha.
Their results may differ from those obtained in this Kansas study because of reduced yield potential at the Colorado location, where the maximum reported yield for their full irrigation regime was less than the yield obtained for the minimum irrigation capacity in this study.
Increasing plant density generally increased water productivity of subsurface drip irrigated corn in a four-year study in Kansas with the exception of 1999, a wet year when mixed results occurred.
These different results indicate that plant density is an important factor in maximizing water productivity and that plant density needs to be optimized with respect to grain yield optimization for that locale.
Greater irrigation capacity generally increased grain yield in a four-year study  with varying seasonal precipitation and crop evapotranspiration.
Strip tillage and no tillage, the reduced tillage treatments, generally resulted in greater yields than conventional tillage, and significantly SO in some years.
These reduced tillage systems tended to have slightly greater crop water use but effectively used that water to generate greater yields.
There were also trends in the patterns of water use, with conventional tillage tending to use more water before anthesis and the reduced tillage treatments having more crop water use after anthesis.
These differences in patterns may be related to an observed earlier senescence of the conventional tillage due to greater water stress and also by the reduced tillage treatments retaining more soil water for the post-anthesis period when grain filling occurs.
Water productivity tended to be greater for the reduced tillage treatments and was significantly SO in one year.
The grain yield and water productivity benefits of these reduced tillage systems were greatest in the years when irrigation requirements were greatest.
These reduced tillage systems proved viable at this location for corn production and should be considered as improved alternatives to conventional tillage, especially when irrigation capacity is limited because of the tendency for greater grain yield stability.
Increasing the plant density from 66,300 to 82,300 plants/ ha numerically increased grain yields at all three irrigation capacities in all four years of the study and significantly SO in two years.
Increased plant density did not significantly increase seasonal water use in any of the four years but did increase water productivity in three of the four years.
The increased plant density is easily justified with today's seed costs and crop prices and is recommended as a method to improve overall economic and water productivity.
Measuring Depth to Groundwater in Irrigation Wells November 2017
 R.
Scott Frazier Associate Professor and Extension Specialist Energy Management
 Saleh Taghvaeian Assistant Professor and Extension Specialist, Water Resources
 Groundwater is one of the most valuable of all natural resources and the major source of water in many parts of the world.
Ninety-eight percent of the Earth's available fresh water is groundwater.
In the U.S., groundwater is a key source of drinking water and irrigation.
Nearly half of the total population and 90 percent of the rural population is dependent upon groundwater for their drinking water supplies.
However, agricultural irrigation is the largest user, consuming more than 50 billion gallons of groundwater per day.
A groundwater basin is defined as an underground reserve of water, which may take the form of a single aquifer or a group of linked aquifers.
In Oklahoma, groundwater is found in 21 major basins and 150 smaller basins.
Oklahoma's aquifers store approximately 386 million acre-feet of groundwater.
Groundwater accounts for 73 percent of the total irrigation water use in Oklahoma.
Western Oklahoma's groundwater is found in several formations, including the Arbuckle Group, Dog Creek Shale and Blaine Gypsum, Rush Spring Sandstone, Elk City Sandstone and Ogallala Formation, as well as in alluvium and terrace deposits.
For more information about groundwater physical properties and state laws, please see the Oklahoma Cooperative Extension Fact Sheet WREC-104: Introduction to Groundwater Hydrology and Management.
General groundwater information can be obtained from various national and state level sources.
Some of the sources are mentioned in Table 1.
Specific location details must be measured, however.
Over the years, excessive groundwater pumping has led to a decline in the water table levels at many locations.
For example, the water level in the Ogallala aquifer, which is a major source of irrigation water in the northwest and Panhandle regions, has declined an overall average of 19 feet from 2001-2017.
Similarly, the water level in the Rush Springs location dropped by 10 feet during 2001-2017.
A large portion of this total decline occurred during the drought of 2011-2015.
Some localized areas in the Oklahoma panhandle have experienced drops of over 130 feet in the last 60 years of monitoring.
California black rails depend on irrigation-fed wetlands in the Sierra Nevada foothills
 by Orien M.W.
Richmond, Stephanie K.
Chen, Benjamin B.
Risk, Jerry Tecklin and Steven R.
Beissinger
 After California black rails were discovered at the UC Sierra Foothill Research and Extension Center in 1994, an extensive population of this rare, secretive marsh bird was found inhabiting palustrine emergent persistent  wetlands throughout the northern Sierra Nevada foothills.
We inventoried a variety of PEM1 wetlands to determine which habitats would likely support black rails.
Black rails were positively associated with larger PEM1 wetlands that had flowing water, dense vegetation and irrigation water as a primary source; they were negatively associated with fringe wetlands and seasonal water regimes.
Recommendations for managing black rail habitat in the northern Sierra foothills include prioritizing the conservation of PEM1 wetlands with permanently or semipermanently flooded water regimes and shallow water zones , especially those that are greater than 0.25 acres in size; avoiding wetland vegetation removal or overgrazing, especially during the black rail breeding season ; maintaining and improving wetland connectivity; ensuring that impacts to black rails are considered in the environmental review process for development projects; and integrating management guidelines for black rails into existing wetland conservation programs.
Over the past decade, the threatened, secretive California black rail has been found at more than 160 wetlands in the Sierra Nevada foothills.
T he rare, secretive California black rail depends on emergent wetland habitats for all stages of its life cycle.
It is the smallest rail in North America and has a patchy and poorly understood distribution.
In western North America, it is found in saltwater, brackish and freshwater marshes along the Pacific coast from Bodega Bay to northwest Baja California, in the the San Francisco Bay-Delta Estuary , inland in small numbers in the Salton Trough and along the lower Colorado River, and in the northern Sierra foothills of Butte, Nevada, Placer and Yuba counties, where it was recently discovered.
After California black rails  were discovered at the UC Sierra Foothill Research and Extension Center  in 1994 , an extensive search for this species which is on California's list of threatened species  was carried out
 throughout the Sacramento Valley and Sierra foothills.
While information on the foothill population's distribution has been published , a detailed description of the habitats occupied by black rails in the foothills is lacking.
Study area and data collection
 Little information is available for the state's small , inland, palustrine emergent persistent  wetlands.
Also known as marshes or fens, PEM1 wetlands are nontidal and dominated by perennial, erect, rooted, herbaceous hydrophytes  that normally remain standing from the end of one growing season until the beginning of the next.
We surveyed a network of 228 PEM1 wetlands spanning approximately 400 square miles  in Butte, Nevada and Yuba counties in the
 Fig 1.
Distribution of surveyed palustrine emergent  wetlands and irrigation canals in the northern Sierra Nevada foothills.
northern Sierra foothills, from 2002 to 2008.
The region's Mediterranean climate is characterized by hot, dry summers and cool, wet winters with an average annual precipitation of approximately 30 inches , with approximately 90% falling between October and March.
We identified candidate PEM1 wetlands in the foothills using U.S.
Geological Survey  topographic quad maps, aerial photographs and U.S.
Fish and Wildlife Service National Wetland Inventory maps; we also encountered many sites during field surveys.
We focused on wetlands from 50 to 3,000 feet in elevation with water regimes  consistent with previous descriptions of rail habitat, including those that appeared to be permanently, semipermanently and seasonally flooded, intermittently exposed, and saturated.
We also surveyed wetlands with water regimes that were less likely to support black rails, including ones that were
 temporarily and intermittently flooded.
Habitat assessment.
We conducted habitat assessments between June 1 and Aug.
31 from 2002 to 2008 and
 recorded water source, geomorphic setting, evidence of a seasonal water regime, and hydrological conditions at each wetland.
We visually determined the primary water source at each wetland as irrigation canal, rainfall, spring or stream.
In some cases, flows or downslope seepage from irrigation canals augmented natural stream or spring flows.
We considered a wetland to be primarily stream-fed if it was situated along a stream channel, and primarily spring-fed if it received most of its water from subsurface sources.
Hydrology.
We assigned each wetland to one of four geomorphic setting categories:  slope wetlands formed by the discharge of water to the surface on sloping land,  depressional wetlands situated in local depressions with closed elevation contours,  fluvial wetlands situated along stream channels and  fringe wetlands bordering water bodies such as ponds, lakes or rice fields.
We recorded whether sites exhibited evidence of a seasonal water regime indicating that they might become dry for at least a part of the year by noting dried portions of sites, dead or stressed hydrophytic vegetation, encroachment of upland vegetation, or reduced water levels that exposed bare mud.
We assessed the presence of flowing water, standing water, saturated mud and firm mud.
A "wettest hydrology rating" was determined for each wetland according to the following sequence: flowing water, standing water, saturated mud, firm mud and dry.
For example, a wetland that had standing water, saturated mud and firm mud present would have a wettest hydrology rating of standing water.
Plant species.
We collected data on plant species diversity in 2007 at a subset of 20 PEM1 wetlands ranging in size from 0.7 to 3.2 acres.
Within each wetland we surveyed four randomly placed 10.9-yard  transects and identified all plants to
 genus or species that touched a vertical pole held at ten 3.3-foot  intervals along each transect.
We collected additional hydrological and vegetative data at randomly sampled points at a subset of 184 PEM1 wetlands in 2008.
We generated 10 random points within wetland boundaries for sites greater than 0.62 acre , eight points for sites from 0.25 to 0.62 acre  and five points for sites less than 0.25 acre.
At each point, we recorded the hydrology/substrate , water depth and dominant vegetation using nine broad vegetation groups: cattails , cutgrass , forbs, hardstem bulrush , Himalayan blackberry , other grasses , other sedges , rushes  and willows.
At each point we also measured vegetation density  in six height strata by recording whether or not any vegetation touched a vertically held 3.9-foot  pole.
We estimated vegetation heights using the midpoint of the tallest height strata with vegetation present at each point.
mixed vegetation communities  and land uses.
Wetlands were distributed along the western edge of the northern Sierra Nevada foothills  and ranged from 79 to 2,582 feet  above sea level, with a mean elevation of 545 + 30 feet.
PEM1 wetlands averaged 2.62 + 0.25 acres  in size, with a positive skew.
Most
  PEM1 wetlands were located less than or equal to 547 yards  from irrigation canals.
Most  PEM1 wetlands were on private lands, while 37% were on public lands including Beale Air Force Base, Daugherty Hill Wildlife Area, SFREC and Spenceville Wildlife Area.
Distribution of PEM1 wetlands
 Irrigation water was the most common water source for the PEM1 wetlands that were surveyed, with 68% of wetlands primarily fed by irrigation
 PEM1 wetlands in the northern Sierra foothills were generally small , patchy ecosystems surrounded by a matrix of
 Call-playback surveys.
Concurrent with the habitat assessments, we conducted call-playback surveys between June 1 and Aug.
31 from 2002 to 2008, to determine black rail occupancy.
We played recorded rail vocalizations at stations spaced 44 to 55 yards  apart at each wetland.
Sites were visited up to five times in 2002 and up to three times from 2003 to 2008 using a removal design: in each year, we did not revisit a site after we detected black rails.
The average probability of detecting occupancy at a site after multiple visits  was extremely high  from 2002 to 2006.
All statistical analyses were performed using Program R.
Unless otherwise noted, we report means + S.E.
The nine most-common plant species found in 20 PEM1 wetlands in the northern Sierra foothills were   common rush,  water smartweed,  sand spikerush,  rice cutgrass,  Baltic rush,  dallis grass,  common spikerush,  cattail and  willowherb.
TABLE 1.
PEM1 wetlands with wettest hydrology ratings averaged across wetlands and years, for wetlands fed primarily by irrigation water vs.
nonirrigation sources* during wetter and drier rainfall years
 Wetter years: 2002-20061	Drier years: 2007-2008
 Irrigated	Not irrigated	Irrigated	Not irrigated
 Wettest hydrology rating				
 Flowing water	72	56	73	46
 Standing water	15	35	18	41
 Saturated mud	9	5	3	2
 Firm mud	1	0	3	3
 Dry wetland	4	3	3	7
 Spring, stream or rainfall.
t	In wetter years  total September through August rainfall averaged 31.2 + 2.4 inches.
# In drier years  total September through August rainfall averaged 16.5 + 1.9 inches.
canals, 22% by springs, 6% by streams and 4% by rainfall.
Irrigation water is collected from the Sierra snowpack, stored in reservoirs, transported through a network of canals and delivered to customers who use it mainly for flood irrigation of pastures for livestock grazing.
Of the wetlands primarily fed by irrigation canals, we calculated that 84% were fed by deliberate irrigation and 16% by unintentional canal leaks.
The most common geomorphological setting for PEM1 wetlands was slope , followed by depressional , fluvial  and fringe.
Fringe wetlands were typically located at lower elevations closer to the valley floor averaging 413 feet  above sea level, while the other wetland types were found at higher elevations and averaged 564 feet  above sea level.
Hydrological conditions in PEM1 wetlands differed significantly by water source.
Most PEM1 wetlands  had a wettest hydrology rating of flowing water, 23% standing water, 6% saturated mud, 1% firm mud and 4% dry, averaged over the 2002 to 2008 study period.
The percentage of wetlands with flowing water was higher at irrigated sites versus nonirrigated sites .
Surprisingly, the percentage of wetlands with flowing water did not differ significantly between wetter and drier years at both irrigated  and nonirrigated  sites.
Based on the random-
 point data collected in 2008, the percent surface area covered by the substrate/ hydrology classes in PEM1 wetlands averaged 5% flowing surface water, 13% standing water, 16% firm mud, 20% saturated mud and 46% dry substrate.
PEM1 wetlands were generally shallow, averaging 1.00 + 0.14 inches  in water depth, with a positive skew.
About 24% of PEM1 wetlands exhibited some evidence of a seasonal water regime between June and August 2008, which was a relatively dry year.
Of these wetlands, about half had springs, streams and rainfall as primary water sources, and half had irrigation water as the primary source.
These seasonal wetlands created a shifting patchwork of habitats that varied both spatially and temporally.
The PEM1 wetlands were floristically diverse, both between and within sites.
We identified a total of 46 plant species across 20 sites in 2007.
The average number of plant species identified at each wetland was 10.1 + 0.8.
The most frequent species were common rush  and cattails , which occurred at 38% and 35% of the points sampled, respectively.
Four species, including dallis grass , common spikerush
 Since black rails are listed as threatened by the California Department of Fish and Game, it is important to characterize their precise habitat requirements in this newly discovered part of their range.
, willowherb  and rice cutgrass  each occurred at between 5% and 10% of the points sampled, while all other species occurred at less than 5% of the points sampled.
All species identified in the Poaceae family were nonnative and invasive, except for rice cutgrass.
This does not come as a surprise, given that California's grasslands are dominated by nonnative, invasive species.
A few unexpected species were present, such as large periwinkle , an invasive garden species, and wild grape.
Himalayan blackberry is a nonnative invasive plant and was observed to overgrow wetlands in some settings.
The percentage of obligate wetland plants ranged from 40% to 95%, facultative wetlands or plants from 0% to 60%, and facultative obligate upland plants from 0% to 37% across all sites .
Based on the random-point data collected from 184 PEM1 wetlands in 2008, the percent COVerage by broad vegetation classes was, on average, 26% grasses , 24% rushes, 12% cattails, 12% sedges , 7% Himalayan blackberry, 6% forbs, 5% hardstem bulrush, 3% willows and 1% rice cutgrass.
Black rail use of PEM1 wetlands
 Black rails typically occur in the shallowest zones of wetland edges where water depths are generally less than 1.2 inches .
In the northern Sierra foothills, they are resident and occupy PEM1 wetlands year-round.
They construct well-concealed nests in dense vegetation over moist soil or very shallow water.
The breeding season in the foothills is unknown but extends from approximately March through July in other California locations.
The black rail's preferred wetland habitats have undergone severe historical declines in California due to habitat destruction for agriculture, salt production and urbanization.
Since black rails are listed as threatened by the California Department of Fish and Game, it is important to characterize their precise habitat requirements in this
 newly discovered part of their range.
We found black rails at 158 PEM1 wetland sites during our surveys from 2002 to 2008 in the Sierra foothills.
Black rails had strong positive associations with larger PEM1 wetlands fed by irrigation water.
PEM1 wetlands that had at least one black rail detection (mean area 3.2 + 0.2 acres [1.3 + 0.1
 hectares]; n = 158) were significantly larger  than wetlands without black rails  from 2002 to 2008.
The median size of wetlands with black rails was 1.63 acres  compared to 0.43 acre  for wetlands without black rails.
* N = native; I = introduced.
No significant differences were detected in elevation between wetlands with and without rails.
The occurrence of black rails in PEM1 wetlands was significantly related to water source   and geomorphic setting .
These patterns were driven by the high occurrence of
 TABLE 2.
Plant species and occurance in 20 PEM1 wetlands of the northern Sierra foothills in 2007, and
 U.S.
Fish and Wildlife Service  wetland indicator category
 Family	Common name*	Species	Occurrence	Indicator category+
 Juncaceae	Common rush 	Juncus effusus	18.62	OBL
 Typhaceae	Common cattail , narrowleaf	Typha latifolia, T.
angusti-	16.48	OBL
 cattail  or southern cattail 	folia or T.
domingensis
 Poaceae	Dallis grass 	Paspalum dilatatum	7.92	FAC
 Cyperaceae	Common spikerush 	Eleocharis macrostachya	5.84	OBL
 Onagraceae	Willowherb 	Epilobium ciliatum	5.78	FACW
 Poaceae	Rice cutgrass 	Leersia oryzoides	5.06	OBL
 Polygonaceae	Water smartweed 	Polygonum punctatum	4.54	OBL
 Cyperaceae	Sand spikerush 	Eleocharis montevidensis	4.15	FACW
 Juncaceae	Baltic rush 	Juncus balticus	3.83	OBL
 Cyperaceae	Black cyperus 	Cyperus niger	3.57	FACW
 Poaceae	Velvetgrass 	Holcus lanatus	2.40	FAC
 Polygonaceae	Swamp smartweed 	Polygonum hydropiperoides	2.40	OBL
 Brassicaceae	Watercress 	Rorippa nasturtium-aquaticum	2.34	OBL
 Rosaceae	Himalayan blackberry 	Rubus discolor	2.08	FACW
 Cyperaceae	Woolly sedge 	Carex lanuginosa	1,62	OBL
 Cyperaceae	Tall flatsedge 	Cyperus eragrostis	1,62	FACW
 Cyperaceae	False nutsedge 	Cyperus strigosus	1.17	FACW
 Cyperaceae	Hardstem bulrush 	Scirpus acutus	0.91	OBL
 Verbenaceae	Purple top vervain 	Verbena bonariensis	0.78	FACW
 Aristolochiaceae	California pipevine 	Aristolochia californica	0.65	UPL
 Portulacaceae	Miner's lettuce 	Claytonia perfoliata	0.65	FAC
 Lamiaceae	Pennyroyal 	Mentha pulegium	0.58	OBL
 Poaceae	Rabbitfoot grass 	Polypogon monspeliensis	0.58	FACW
 Asteraceae	Sneezeweed 	Helenium puberulum	0.52	FACW
 Lamiaceae	Sonoma hedgenettle 	Stachys stricta	0.52	FACW
 Vitaceae	California wild grape 	Vitis californica	0.52	FACW
 Cyperaceae	Valley sedge 	Carex barbarae	0.45	FACW
 Polygonaceae	Curly dock 	Rumex crispus	0.45	FACW
 Gentianaceae	Muhlenberg's centaury 	Centaurium muehlenbergii	0.39	FAC
 Lamiaceae	American water horehound 	Lycopus americanus	0.32	OBL
 Asteraceae	Bull thistle 	Cirsium vulgare	0,26	FACU
 Clusiaceae	Klamath weed 	Hypericum perforatum	0.26	FAC
 Lythraceae	Common loosestrife 	Lythrum californicum	0.26	OBL
 Apocynaceae	Large periwinkle 	Vinca major	0.26	UPL
 Cyperaceae	Field sedge 	Carex praegracilis	0.19	FACW
 Cyperaceae	Yellow flatsedge 	Cyperus flavescens	0.19	OBL
 Clusiaceae	Creeping St.
John's wort 	Hypericum anagalloides	0.19	OBL
 Asclepiadaceae	Narrow leaf milkweed 	Asclepias fascicularis	0.13	FAC
 Juncaceae	Taper tip rush 	Juncus acuminatus	0.13	OBL
 Cyperaceae	Black sand spikerush 	Eleocharis pachycarpa	0,06	OBL
 Onagraceae	Dense flowered boisduvalia 	Epilobium densiflorum	0.06	OBL
 Onagraceae	Largeflower spike primrose 	Epilobium pallidum	0.06	FACW
 Poaceae	Italian rye grass 	Lolium multiflorum	0.06	FAC
 Plantaginaceae	Ribgrass 	Plantago lanceolata	0.06	FAC
 Poaceae	Medusahead 	Taeniatherum caput-medusae	0.06	UPL
 t OBL = obligate wetland, plant occurs almost always  under natural conditions in wetlands; FACW = facultative wetland, usually occurs in wetlands , but occasionally found in nonwetlands; FAC = facultative, equally likely to occur in wetlands or nonwetlands ; FACU = facultative upland, usually occurs in nonwetlands , but occasionally found in wetlands ; UPL = obligate upland, occurs in wetlands in another region, but occurs almost always  under natural conditions in nonwetlands in the regions specified.
Fig.
2.
Differences in area and elevation for wetlands in northern Sierra foothills that had at least one black rail present from 2002 to 2008 vs.
wetlands without black rails in 2008, and differences in vegetation height for wetlands with black rails vs.
wetlands without black rails.
Boxes depict lower and upper quartiles, bold lines depict medians, whiskers extend to the most extreme data point, which is no more than 1.5 times the interquartile range, and outliers are shown as open circles.
* Significant difference, t-test, P < 0.01; ** significant difference, t-test, P < 0.001.
atively associated with drier PEM1 wetlands and wetlands with evidence of a seasonal water regime.
The occurrence of black rails in PEM1 wetlands was significantly related to the wettest hydrology rating .
This pattern was primarily driven by the high use of wetlands with flowing water, the low use of wetlands with standing water as the wettest hydrology rating, and the low use of dry wetlands.
Black rail occupancy was significantly negatively associated with wetlands that showed evidence of a seasonal water regime.
While the presence of flowing water was positively associated with black rail occupancy, the average surface area covered by flowing water at wetlands with black rails was only 7%, while standing water covered 16%, saturated mud 27%, firm mud 15% and dry substrate 34%, based on the random -point data collected in 2008.
Water depth at PEM1 wetlands with black rails averaged 0.83 + 0.15 inch.
significantly lower percentage of sample points composed of grasses, excluding rice cutgrass , compared to sites without black rails   and a significantly higher percentage of sample points composed of rushes  compared to sites without black rails  in 2008.
Used and unused sites did not differ significantly for the other seven vegetation classes.
Black rails occupied wetlands dominated by a variety of vegetation types and were positively associated with dense cover.
Sites with black rails had a
 Vegetation cover was significantly higher at PEM1 wetlands with black rails than at wetlands without black rails for stem hits in the following height strata: 8 to 12 inches, 12 to 20 inches, and 20 to 39 inches.
Sites with black rails did not have greater vegetation density near the ground in the 0 to 4 inches and 4 to 8 inches height strata.
However, our methodology may have lacked the resolution to capture finer-scale differences, as we only recorded whether at least one stem touched the pole in a given height category.
Vegetation height at wetlands with black rails  averaged
 Black rails were strongly, positively associated with flowing water and neg-
 black rails in wetlands fed primarily by irrigation water and by the low occurrence of rails in wetlands fed primarily by rainfall and in fringe wetlands.
Black rails rarely used livestock watering ponds  with narrow fringes of emergent vegetation and mostly deep  water; however, seepage zones below bermed ponds often provided suitable shallowwater conditions.
PEM1 wetlands obtain water from a variety of sources in the northern Sierra foothills including:  irrigation canals,  natural springs,  wetlands fed only by rainfall and  streams; irrigation canals are the most common source.
Fig.
3.
Differences in vegetation cover, measured as the average percentage of random sample points with vegetation present, at six different height strata in wetlands of the northern Sierra foothills with and without black rails in 2008.
Error bars represent standard errors.
* Significant difference, permutation test, P < 0.05.
TABLE 3.
PEM1 wetlands with each primary water source and geomorphic setting category, with at least one black rail detected from 2002-2008, and without black rails detected
 black rails	black rails
 Habitat characteristics		
 Irrigation canal	78	47
 TABLE 4.
PEM1 wetlands with each wettest hydrology rating category and average percentage of sample points within a wetland for each vegetation group, with and without black rails detected in 2008
 Habitat	black rails	black rails
 characteristics		
 Flowing water	86	60
 Standing water	13	25
 Saturated mud	1	2
 Firm mud	0	4
 Dry wetland	0	9
 Hardstem bulrush	5	5
 Himalayan blackberry	7	7
 Other grasses	20	30
 Other sedges	11	13
 PEM1 wetlands were situated in four geomorphological settings in the northern Sierra foothills:  slope,  depressional,  fringe and  fluvial.
3.1 inches  taller than at wetlands with no black rails  in 2008 .
Habitat loss and degradation are the primary threats to black rails , SO a comprehensive black rail management strategy should focus on both site-level and landscape-level factors related to habitat.
Notable site-level factors affecting occupancy by black rails include water regime, water depth, vegetation density and wetland size.
Water regime.
Water regime is a critical habitat factor; black rails were most often found in wetlands with perennial standing or flowing water , although they were occasionally found in drier wetlands with seasonally flooded, intermittently exposed or saturated water regimes.
Previous studies have highlighted the importance of stable water levels for inland populations.
In the Sierra foothills, irrigation water and perennial springs and streams provide consistent permanent or semipermanent water sources during the driest part of the year, from mid-April until mid-October.
Wetlands that are fed primarily by rainfall or seasonal springs or streams are more likely to dry out as the summer progresses.
Non-irrigation-fed wetlands had a lower proportion of flowing water present in both wetter and drier summers than irrigation-fed wetlands.
The presence of flowing water in the summer is associated with black rail occupancy  and may be viewed as an indicator of wetland permanence.
We recommend that PEM1 wetlands with permanently or semipermanently flooded water regimes be prioritized for conservation.
Black rails use wetland zones with shallower water than other North American rails , generally less than 1.2 inches .
Wetlands in the Sacramento Valley that are managed for waterfowl or rice typically lack sufficient shallow water zones, and previous surveys indicated that black rails were uncommon in these habitats.
Persistent shallow water conditions can be more easily maintained on gentle slopes rather than in depressions, since continual downslope drainage prevents water from pooling too deeply.
The combination of abundant semipermanent water sources  and the gently sloped
 landscape of the northern Sierra foothills creates an ideal setting for such shallow wetlands to form.
A management strategy that maintains wetland complexes with variable water levels, including shallow  water zones, is recommended.
The creation of more extensive shallow water zones at the margins of managed wetlands on the Sacramento Valley floor should be explored.
Vegetation.
Black rails depend on dense vegetative cover, SO disturbances to wetland vegetation arising from deliberate clearing, burning or overgrazing by wildlife or livestock are potential threats.
Previous research in Arizona found that plant species composition was not as important for black rail habitat selection as appropriate vegetation structure  and substrate characteristics.
The manual removal or burning of emergent vegetation for improved pond access or to facilitate recreation activities  could render a wetland unsuitable for black rails.
While light-to-moderate grazing appears to be compatible with occupancy by black rails and can benefit wetlands by stimulating increased herbaceous plant productivity and improving water quality , our anecdotal observations suggest that black rail occupancy declines when overgrazing substantially reduces wetland vegetation cover.
We recommend that landowners control livestock access to ponds and wetlands and avoid wetland vegetation removal or overgrazing, especially during the black rail breeding season.
Fortunately, wetland vegetation appears to rebound quickly, and a cleared or heavily grazed site can regain dense vegetation within a single growing season.
Additional research is needed to determine the minimum vegetation cover that black rails require for successful breeding.
Wetland area.
A critical question is the minimum wetland area required to support a breeding pair.
We found that wetlands with at least one black rail detection were significantly larger than wetlands with no detections , and 97% of wetlands with at least one
 An artificial wetland created using irrigation water provides habitat for black rails at Spenceville Wildlife Area.
black rail detection were 0.25 acre or larger.
However, we detected black rails occupying wetlands as small as 0.040 acre , although only temporarily.
Since local rail population size should increase with wetland area, conservation priority should increase with wetland size.
Nevertheless, very small wetlands  may also act as "stepping stones" that could facilitate dispersal across the landscape , even if they may be too small to support breeding pairs.
Based on current knowledge, we recommend that existing PEM1 wetlands with suitable water regimes and shallow water zones, especially those 0.25 acre or larger, be prioritized for conservation.
Landscape factors.
Maintaining and improving site-level habitat quality is necessary for black rail management, but a comprehensive strategy must also take into consideration landscape-level factors such as isolation, canal mainte-
 nance and land-use change.
Given the sparse and patchy distribution of PEM1 wetland habitats across the foothills, isolation of habitat patches is a potential concern.
The loss of wetlands can affect metapopulation dynamics by reducing the number or density of dispersing individuals, while simultaneously increasing dispersal distances between wetlands.
Little is known about black rail dispersal aside from a radiotelemetry study in Arizona where three black rails were recorded moving an average of 0.89 + 0.06 mile [1.43 + 0.09 kilometers], range = 0.75 to 1.00 mile between breeding seasons.
We have noted black rails colonizing newly created wetland sites in the foothills within one year.
However, we have also found evidence that the rate of patch colonization decreases and the rate of local patch extinction increases as sites become more isolated.
A regional management
 Slicks Canyon, location of the first northern Sierra foothills black rail detection, is in the UC Sierra Foothill Research and Extension Center.
strategy for black rails should prevent the isolation of wetlands and promote the creation of new habitat to improve connectivity.
In general, sites that are currently well connected should be prioritized for protection and new sites, if created, should be located close  to other occupied sites to maximize potential dispersal opportunities.
Wildlife managers have successfully created several artificial wetlands now used by black rails by maintaining semipermanent flows of irrigation water on sloped land at Spenceville and Daugherty Hill wildlife areas.
The speed with which suitable habitat can be created and then colonized by rails suggests that mitigation for wetland habitat loss from, for example, canal lining projects, may be effective.
The lining of irrigation canals to improve water efficiency can adversely affect black rail habitat ; a balanced approach to such projects should simultaneously address water efficiency and wildlife habitat needs, perhaps through a rotating short-term water-leasing program.
The ongoing replacement of ranching with residential land uses in the Sierra foothills  is probably the greatest long-term threat to black rails because most of their habitat is maintained by irrigation water used for cattle ranching.
PEM1 wetlands not only provide habitat for black rails, but also support wildlife species by improving tailwater quality from irrigated pastures thereby reducing loads of total suspended sediments, nitrate and Escherichia coli.
Long-term protection of wetlands can be achieved through conservation easements and voluntary programs such as the Wetlands Reserve Program and Conservation Reserve Program run by the U.S.
Department of Agriculture's Natural Resources Conservation Service, which provide landowners with opportunities to protect, restore and enhance wetlands in exchange for technical and financial support.
The Central Valley Joint Venture is another important organization that brings together conservation organizations, public agencies and private landowners to conserve bird habitat in California's Central Valley.
We recommend that detailed
Soil Moisture Measurement and Sensors for Irrigation Management
 Water is a limited resource in Utah's semi-arid climate.
The demand on Utah's water supply continues to rise with a rapidly expanding urban population.
Crop irrigation is the largest water use in Utah, accounting for about 80 percent of annual diversions.
Proper irrigation management has a positive effect on water use, plant health, and crop yields.
The use of soil moisture sensors helps growers with irrigation scheduling by providing information about when and how much to water.
This provides for efficient use of water; enough to meet crop needs without applying excess or too little water.
Excessive irrigation increases the cost of production from additional pumping costs and fertilizer lost to runoff and leaching.
It can also decrease yields from waterlogging and leaching of soil nutrients.
Excessive runoff can sometimes be harmful to the environment if fertilizers and pesticides moved to sensitive environments.
Under-watering results in plant stress which can reduce yield and crop quality.
This fact sheet introduces several soil water monitoring options that, when used correctly, can help growers avoid over and under watering.
The use of soil moisture sensors requires an understanding of soil moisture depletion, available soil water, and irrigation application.
Understanding some basic terms, definitions and concepts will help you make irrigation management choices.
Below are some general soil moisture definitions:
 Saturation: At saturation all pore space in the soil is filled with water, no air.
Most agriculture soils have between 40 and 50 percent  voids  that are filled with water and/or air.
Field Capacity: Soil water content after water has drained by gravity.
Field capacity of most agriculture soils ranges between 20 and 45 percent by volume.
Permanent Wilting Point: Soil water content when plants or crops cannot obtain water from the soil.
Permanent wilting point ranges between 7  and 24  percent by volume  for most agriculture soils.
Available  Water: The soil water content between field capacity and permanent wilting point.
Although plants can utilize the water, plant stress occurs as soil water content approaches permanent wilting point.
Allowable Depletion: The soil water content available to crops without causing stress that impacts yield or crop quality.
The allowable depletion is dependent on crop type, crop growth stage, and climate.
Allowable depletion can range between 25 percent of available water for crops very sensitive to small changes in soil moisture to over 50 percent of available water for crops that are less sensitive to water stress.
Dry Bulk Density: The oven-dried weight of soil in a known volume of field-extracted sample.
Soil Porosity: The pore volume of soil divided by the total volume of a soil sample.
The total amount of water a soil can hold  is affected by soil type, soil structure, and organic matter.
There are three basic soil particles: sand , silt  and clay.
Many soils have a mixture of these particle types.
Loam soils have a mixture of all soil particles, and may have a high percentage of a particular soil particle size (e.g., sandy loam, clay loam, silt loam,
 etc.) Sandy soils generally have lower porosity and larger particles , resulting in fairly rapid drainage and low water holding capacity.
Sandy soils need to be watered more frequently than finertextured soils.
Silt soils have a medium drainage rate and infiltration rate.
Clay soils drain slowly, have a low infiltration rate, and higher field capacity as a result of smaller pores and larger porosity.
Clays and silts have similar available water-holding capacity.
Good soil structure  helps improve infiltration rate, drainage, and available water holding capacity.
Depending on soil type, some soil moisture monitoring devices are more effective than others and this should be considered when choosing a sensor.
There are several ways to monitor soil water, with varying costs and accuracy.
Although it is common for growers to estimate soil moisture by feel, appearance, or time between irrigation events, soil moisture can be more accurately and effectively monitored using a variety of commercially available soil moisture monitoring systems.
The effectiveness of the monitoring system is dependent upon proper placement and installation.
The sensors or sampling should be in locations that represent the overall field, garden, or landscape.
Avoid placing sensors where there are variations due to shade, nearby structures, or at the top of a hill or bottom of a depression.
Since there is significant variation across fields, it is recommended that several sensor locations be used for large fields.
Consider soil type, plant distribution, and irrigation when placing the sensors or sampling.
Sensors need to be properly installed and have good contact with the soil.
After installing the sensor, firmly pack the soil around it, avoiding excessive compaction.
When placing sensors or access tubes in a growing crop, care should be taken not to injure plants at the installation site.
If the crop is grown on plastic mulch, place the sensor under the plastic for readings that reflect what the plant roots are experiencing.
Bury sensors in the root zone of the crop.
For row crops, sensors should be installed 2 to 3 inches away from the plant row.
The six common soil monitoring systems are: gravimetric, porous blocks, neutron probes, dielectric sensors, tensiometers, and heat dissipation.
The systems provide indirect measurements  of soil water except for the gravimetric method.
Porous blocks, dielectric sensors and tensiometers can be set to record automatically and even trigger irrigation.
Each of these monitoring systems is briefly discussed below.
Gravimetric: The gravimetric method is a direct measure of soil moisture and does not require expensive sensors.
It involves collecting soil samples and accurately weighing them before  and after  oven drying.
The gravimetric method also requires knowing the dry bulk density of the soil to convert gravimetric water content to volumetric, i.e., weight-based to depth-based.
The inches water per inch of soil is found by the weight-based water content times the dry bulk density of soil).
While it is accurate and fairly simple, the laboratory equipment required is a limitation for many growers.
Additionally, readings are not instantaneous since you must wait for soil to dry completely.
Gravimetric or volumetric soil moisture describes the total soil water but an understanding of allowable depletion is needed to understand what is actually available to plants.
Photo 1.
5-foot soil probe than is incrementally hammered into ground to extract soil samples.
Porous blocks: This common method uses some sort of porous block .
The blocks are buried in the soil at rooting depth and water moves in or out until equilibrium is reached with water in the soil.
Electrodes in the block record the electrical conductivity of the block, which is assume to be equal to that of the soil.
This reading is used to estimate
 volumetric soil moisture.
They are simple to install, cost $30 to $50, and are easy to maintain.
However, they are temperature sensitive, sometimes do not re-wet after drying out, and have a slow reaction time to what is actually happening.
They do not work well in sandy soils, where the water drains too quickly for the block to reach equilibrium.
Also, the electrical conductivity of the soil is increased by salts, SO fertilizers added to the field may result in incorrect readings.
Gypsum blocks provide a buffer against soil salinity changes, helping to get a more accurate reading, but the block dissolves over time.
Most gypsum blocks are good for 3 to 5 years.
Photo 2.
Installation of porous blocks and data logger using electrical conductivity of the block in equilibrium with the soil.
Figure 1 shows data from a porous block soil moisture measurement device in a safflower field.
The data shows irrigation events on June 12, July 1, and July 16 , the drier the soil).
August and September had rain events to keep the soil moisture at an adequate level for full crop production.
The deeper soil layers were being depleted in August and September.
Figure 1.
Soil Moisture Reading  for an irrigated safflower field.
Neutron Probes: A neutron probe involves lowering a radioactive source and receiver into monitoring holes  installed throughout the field.
Neutrons are emitted and slow down when they collide with hydrogen in the soil water.
The slowed neutrons are measured and correlated to water content.
Neutron probes are accurate when properly calibrated, are not influenced by salts, have a large radius of measure, and can take measurements at many depths.
However, they are expensive , pose a radiation hazard , and can be difficult to calibrate and install.
Measurements close to the soil surface are not as accurate because neutrons escape to the atmosphere and are not reflected back to the instrument.
Dielectric Methods: These probes sense dielectric properties of soil and water to monitor soil moisture.
They typically consist of two or more electrodes inserted into the soil.
Most are not affected by salts and temperature and are fairly easy to install.
They may not give accurate readings in clay and organic soils where soil-specific calibration is needed.
The sensors send an electromagnetic signal into the soil and measure properties of the signal.
Good contact with the soil is crucial for gaining an accurate reading.
There are several measurement approaches relying upon the dielectric properties of the soil, including Time Domain Reflectometry  and Frequency Domain  sensors.
Some capacitance probes are portable and can be insert in access tubes to get many readings from one sensor.
Photo 3.
Probe in an access tube using dielectric properties of soil.
Photos 4.
Example of sensor relying on dielectric properties of soil 
 Tensiometers: A tensiometer is a water-filled tube designed to simulate a plant root.
A porous cup is buried in the soil with a negative pressure  gauge is at the other end.
As the soil dries, water is pulled out of the tensiometer making the pressure reading more negative, which indicates decreasing soil moisture.
The more negative the reading, the less water there is in the soil.
Once irrigated, soil water re-enters the cup and the pressure becomes less negative.
They are easy to read and cost about $80 to $100.
Tensiometers are sensitive to
 conditions in a relatively large soil volume and are easy to install and maintain.
Continuous recording of data is possible using a pressure transducer but gauge-based instruments are well suited for periodic manual readings.
The range of measurement is somewhat limited to wet conditions common in irrigated agriculture and good soil contact is critical for accurate readings.
Tensiometers also require frequent maintenance and can have a slow response time.
Tensiometers are not suited to heavytextured clay soils that swell nor to very coarse sandy soils.
For irrigation management, the tensiometer reading needs to be correlated to the soil moisture content to know how much water has been extracted and needs to be replaced by irrigation.
Photo 5.
Tensiometer being installed in soil with the porous cup on the installation end of the tensiometer.
Heat Dissipation: The basic principle behind using heat transfer to estimate soil moisture is that dry soil transfers heat faster than wet soil.
During heat input to the sensor matrix in contact with the soil a temperature sensor monitors the heat dissipation.
Soil moisture is calibrated to differences in soil temperature measurements over a given period.
Heat dissipation is usually accomplished using a block sensor similar to a porous conductivity block.
The blocks require similar maintenance to conductivity blocks and low power heaters are used that utilize direct current batteries for power.
There is a wide range of methods available to monitor soil moisture.
When selecting a sensor, consider the advantages and disadvantages as well as what will work with your soil.
Maintenance, skill level, and cost should
 also factor into your decision.
If you live in an area that has low water availability or if water is expensive, investing in a monitoring system can lower water use and reduce costs and improve yields.
Table 1 is a summary of the methods.
While porous blocks have been commonly used in farmer's fields, prices of multi-function sensors such as the Time Domain Reflectometry instruments are now priced in the same range as porous blocks and have
 many advantages.
The multi-function instruments can provide accurate estimates of soil moisture by volume, and measure soil temperature and soil water salinity , additionally they are less sensitive to salinity and temperature.
Table 1.
Summary of soil water measurement methods used for irrigation scheduling.
Method	Measurement	Installation	Quality of Measurement	Costs
 None, but require soil
 Based on experience of
 Feel Method	Visual and sensory	sampling for each	individual	Labor
 None, but require soil	Accurate measurement can
 Gravimetric	Direct measurement	sampling for each	be used for calibration of	Labor, drying oven, and scales
 Requires calibration to soil
 Tensiometer	potential	Soil water matrix	beginning of cropping	higher maintenance than	water content.
Generally	$80/unit.
Electrical	Sensor installed at	Requires calibration to soil	Data logger/reader $500 to
 Porous Block	porous block in	Resistance of a	beginning of cropping	season.
1,000, then $40 per sensor (2
 contact with the soil	for perennial crops)	salinity.
Neutron Probe	Neutron	content	function of water	thermalization as a	beginning of cropping	years for perennial	Access tube at	season , plus	keeping	dosimetry analysis and record	$15 per access tube.
Regular
 Electromagnetic	Sensors installed or	Is accurate after calibration	Data logger or reader $500 to
 Frequency	soil capacitance as a	access tubes	to soil water content.
Is	$3,000, then $280+ per sensor
 Domain Probe	function of water	.
Access tube
 content	perennial crops)	water salinity levels.
installation kit $2,600.
Time Domain	Reflectometry	Probe	soil capacitance as a	content	function of water	portable probe or	years for perennial	access tube (multiple	insensitive to normal soil	Is accurate and relatively	water salinity levels.
Data logger/reader $1,000 to	3,000, then $100 per sensor.
Uses heat buffering	Sensors installed at	Requires calibration to soil
 Dissipation	Heat	thermal	conductivity of soil	capacity of soil and	beginning of cropping	for perennial crops)	season.
1) Gravimetric  is considered direct measurements of soil water.
All others are indirect, measuring a property of the soil water.
2) Gravimetric and the feel method require sampling, all other methods are in-situ with buried sensors or an access tubes.
Irrigation Scheduling Of Field Corn Under Institutional Constraints
 Two pre-anthesis an two post anthesis  deficit sprinkler irrigation strategies for four corn hybrids where total irrigation was constrained to 11.5 inches against a fully irrigated control were compared in terms of grain yield and yield components, water use, and crop water productivity.
This study was in response to a voluntary agreement of producers in a region of northwest Kansas  where they agreed to reduce irrigation water application to 55 inches over a 5 year period.
This study attempted to determine the best irrigation strategy for these limited applications.
Results indicated full irrigation was still relatively efficient but used 30 to 36% more water.
When corn prices are greater, managing at the full irrigation level and reducing irrigated land area may be more profitable.
Pre-anthesis water stress was more detrimental to grain yield than similar levels of post anthesis stress because of reductions in kernels/ear.
When water is greatly restricted, a 50% reduction in irrigation post-anthesis might fare reasonably well by relying on stored soil water and precipitation for grain filling.
These results might not repeat on less productive soils or under harsher environmental conditions.
In the semi-arid Central Great Plains and particularly northwest Kansas, soils are generally productive deep silt loam soils but precipitation is limited and sporadic with mean annual precipitation ranging from 16 to 20 inches across the region, which is only 60-80% of the seasonal water use for corn.
Irrigation is often used to mitigate these water stress effects but at the expense of the continued decline of the Ogallala Aquifer.
In 2012, the Kansas legislature passed new water laws that allowed creation of a new water management structure known as a Locally Enhanced Management Area.
It allows stakeholder groups of various sizes to locally come together and design a management strategy to reduce overdraft of the Ogallala Aquifer in their area subject to approval by the Kansas Division of Water Resources.
The first LEMA to be approved known as Sheridan High Priority Area 6 became a reality within Sheridan and Thomas Counties in northwest Kansas in 2013.
The stakeholders in a 100 square mile area voluntary agreed to reduce their average water right to 11 inches/year for the next 5 year period.
This area is centered approximately 30 miles east of the KSU Northwest Research-Extension Center at Colby, Kansas.
In Kansas, annual rainfall decreases approximately 1 inch for every 18 miles moving east to west and greatest annual rainfall in western Kansas is in the months of May, June, and July, so a similar appropriate restriction at Colby to the Sheridan HPA #6 LEMA might be approximately 12 inches instead of
 11 inches.
Corn is the major irrigated crop in the region and producers in this LEMA would prefer to continue growing corn due to the availability of good local markets that include two large cattle feeding operations as well as a nearby dairy.
The LEMA reduction of water right to 11 inches represents about a 27% reduction in water from the 80% chance Net Irrigation Requirement for Sheridan County.
The producers within the LEMA have the flexibility to apply their 5-year allocation of water as they so determine, but could benefit from research that determines when water can be restricted without large corn yield penalty.
ET-based irrigation scheduling has been promoted in the Central Great Plains for many years.
As producers move to deficit irrigation strategies this method of scheduling can still be useful in alerting the producer to soil water conditions and can help the producer decide when to allocate their limited supply.
Management Allowable Depletion  values have been established as a means of helping producers know when to irrigate, but these established values have been questioned as too harsh for modern corn production.
Sprinkler irrigation does not allow for large amounts of water to be timed to a specific growth stage without incurring runoff, so strategies must be employed that can slowly restrict or slowly increase water available to the crop and to soil water storage for later usage.
Preliminary computer simulation indicated that on average, approximately 40% of the seasonal irrigation amount is required prior to anthesis , so an imposed reduction of 50% during the preanthesis period might be acceptable most years, yet not be excessive in the drier years.
However, this does not fully reflect the ability of the soil profile to be a "bank", so examining a higher irrigation regime is also warranted.
Figure 1.
Seasonal gross irrigation requirements for field corn at Colby, Kansas.
A 4-year field study was conducted to examine restriction of irrigation to approximately to 50 or 75% of the ET-Rain value for either the pre-anthesis period or during the post-anthesis period.
Since grain filling  is important, intuitively, one might surmise that those strategies restricting water during the pre-anthesis stages would always be preferable, but the pre-anthesis period is also when the number of kernels/acre is being potentially set and also the soil water storage allows for "banked" water to be used later by a deep rooted crop such as corn.
These deficit strategies were compared to a fully-irrigated control treatment.
Four different commercial corn hybrids  were compared under five different irrigation regimes in a three year  field study at the KSU Northwest Research-Extension Center at Colby, Kansas.
For brevity only the average datas from the four hybrids will be discussed here.
The irrigation regimes were: 1) Full irrigation  with no restriction on total irrigation; 2) Irrigation restricted pre-anthesis to 50% of ET, 100% of ET thereafter with 11.5 inches total restriction; 3) Irrigation restricted pre-anthesis to 75% of ET, 100% of ET thereafter with 11.5 inches total restriction; 4) Irrigation restricted post-anthesis to 50% of ET with 11.5 inches total restriction; and 5) Irrigation restricted postanthesis to 75% of ET with 11.5 inches total restriction.
Irrigation amounts of 1 inch/event were scheduled according to water budget weather-based irrigation scheduling procedures only as needed subject to the specific treatment limitations.
As an example, during the pre-anthesis stage Irrigation Trt 3 would only receive 75% ET, but after anthesis would receive irrigation at 100% until such time that the total irrigation is 11.5 inches.
Soil water was monitored periodically  to a depth of 8 ft.
in 1 ft.
increments with neutron moderation techniques.
This data was used to assess MAD values as well as to determine total water use throughout the season.
Corn yield and yield components were determined through hand harvesting a representative sample at physiological maturity.
Crop water productivity was calculated as grain yield/crop water use.
The 5 irrigation treatments  were in a RCB design with irrigation applied using a lateral move sprinkler and the 4 corn hybrid treatments superimposed as split plots.
The data were analyzed using standard PC-SAS procedures.
Weather Conditions and Irrigation Requirements
 Figure 2.
Cumulative calculated crop ET and precipitation during the growing season for Colby, Kansas, 2013 to 2015.
Overall weather conditions for the three years were favorable for excellent corn production during the study.
Calculated crop ET for 2013 through 2015 was slightly lower than long term values and seasonal precipitation was 2 to 3 inches greater than normal in 2014 and 2015 and 2 inches less than normal in 2013.
Full irrigation amounts varied from 12.48 inches in 2014 to 15.36 inches in 2013.
The treatments with pre-anthesis water restrictions  reached their water limitation  in two of the three years  as did the post anthesis deficit irrigated treatment that was irrigated with 75% of ET during the post anthesis period.
The irrigation treatment using the least amount of water during the three years of the study was the treatment where irrigation was restricted to 50% of ET during post-anthesis period.
Figure 3.
Irrigation amounts for the five irrigated corn treatments during the three years of the study.
Crop Yield and Water Use Parameters
 Corn grain yield was greatest in 2014 and was lowest in 2013, the year with the greatest irrigation need.
Fully irrigated corn grain yields ranged annually from 241 to 251 bushels/acre with the deficit-irrigated lowest yields ranging from 215 to 237 bushels/acre.
Corn yield was greatest for unrestricted irrigation  but required 30 to 36% more irrigation, but was still very efficient with only a 2 to 4% reduction in water productivity .
Lower yields occurred for pre-anthesis water restrictions  than for similar post-anthesis restrictions.
These results suggests that obtaining sufficient kernel set was more important than saving irrigation for grain filling in this study.
When irrigation is greatly restricted, a 50% reduction post-anthesis appears as a promising alternative, relying more heavily on stored soil water and precipitation for grain filling.
Figure 4.
Corn yields for the five irrigation treatments during the three years of the study.
Figure 5.
Water productivity for the five irrigation treatments during the three years of the study.
Table 1.
Corn yield, yield component, and water use parameters in an irrigated corn study at Colby, Kansas, 2013-2015.
Irr Trt.
Amount	Irr.
Yield, bu/a	Plant density,	p/a	plant	Ears/	Kernels/	ear	Kernel mass,	mg	Water use,	inches	WP, lbs/acre-in
 1.
100% ET	15.36	241	A	32452	A	1.00	A	542	A	349	A	23.0	A	587	B
 2.
50/100% ET	11.52	215	C	32779	A	0.99	A	483	C	349	A	20.5	C	590	B
 3.
75/100% ET	11.52	230	B	32634	A	0.99	A	522	B	347	A	21.6	B	598	AB
 4.
100/50 % ET	10.56	228	B	32561	A	0.99	A	524	B	344	A	21.7	B	593	B
 5.
100/75% ET	11.52	234	B	32561	A	1.00	A	527	AB	349	A	21.4	B	616	A
 Prob > F	<0.0001	0.8328	0.3872	<0.0001	0.3976	0.0001	<0.0001
 1.
100% ET	12.48	251	A	33215	A	1.00	A	566	A	339	A	28.76	A	490	C
 2.
50/100% ET	9.60	237	B	33360	A	1.00	A	539	B	336	A	26.34	D	504	B
 3.
75/100% ET	10.56	248	A	33251	A	1.01	A	557	A	337	A	26.89	C	516	B
 4.
100/50 % ET	7.68	246	A	33069	A	1.00	A	558	A	338	A	25.82	E	535	A
 5.
100/75% ET	10.56	250	A	33215	A	1.00	A	566	A	338	A	27.22	B	516	B
 Prob > F	0.0010	0.6060	0.1034	0.0059	0.9002	<0.0001	<0.0001
 1.
100% ET	14.40	241	A	32380	A	1.00	A	575	A	330	A	31.50	A	429	A
 2.
50/100% ET	11.52	233	A	32525	A	1.00	A	563	A	323	A	28.98	A	450	B
 3.
75/100% ET	11.52	238	A	32597	A	1.00	A	574	A	324	A	29.65	A	450	B
 4.
100/50 % % ET	9.60	232	A	32452	A	0.99	A	574	A	320	A	28.59	A	456	C
 5.
100/75% ET	11.52	234	A	32670	A	0.99	A	573	A	322	A	29.78	A	441	B
 Prob > F	0.0786	0.6613	0.0900	0.8987	0.6180	0.5629	<0.0001
 1.
100% ET	14.08	244	A	32682	A	1.00	A	561	A	339	A	27.75	A	502	C
 2.
50/100% ET	10.88	228	C	32888	A	1.00	A	529	B	336	A	25.26	D	515	C
 3.
75/100% ET	11.20	239	B	32827	A	1.00	A	551	A	336	A	26.05	C	522	B
 4.
100/50 % ET	9.28	236	B	32694	A	1.00	A	552	A	334	A	25.36	E	528	A
 5.
100/75% ET	11.20	240	B	32815	A	1.00	A	556	A	336	A	26.14	B	524	A
 Prob > F	<0.0001	0.5298	0.3079	<0.0001	0.4560	<0.0001	<0.0001
 Examination of Yield Components
 Yield can be calculated as:
 Yield = Plants Ears X Kernels X Mass Eq.
1.
Plant Ear Kernel
 The first two terms are typically determined by the cropping practices and generally are not affected by irrigation practices later in the season.
Water stresses during the mid-vegetative period through about 2 weeks after anthesis can greatly reduce kernels/ear.
Kernel mass, through greater grain filling, can partially compensate when insufficient kernels/ear are set, but may be limited by late season water stress or hastened senescence caused by weather conditions.
In this study, the yield component most strongly affected  by irrigation practices was kernels/ear and was significantly affected  in two years and also for the average of all years.
Full irrigation  had the greatest number of kernels/ear while the 50% ET pre-anthesis treatment  consistently had the smallest value.
These results suggest that pre-anthesis water stresses must be limited so that sufficient kernels/ear  can be set for modern corn hybrids.
Because all the yields 4 components combine directly through multiplication to 3 Average Annual Data calculate yield, their effect on from 2013 through 2015 yield can be easily compared 2 in Figure 6.
The numbers on 1 Plants/Area the lines refer to the 5 1 Ears/Plant irrigation trts and the lines just 0 --2 Kernels/Ear connect similar data.
A variation of 1% -2 in any yield component would -3 affect yield by the same 1%.
It Numbers on lines refer can be observed that there is -4 2 to irrigation treatments much greater horizontal dispersion for kernels/ear than -4 -3 -2 -1 0 1 2 for all the other yield Yield Component Variation from Mean  components which vary less than approximately 1%.
Thus, Figure 6.
Yield variation as affected by variation in the yield components irrigation treatment had a much for the 5 different irrigation treatments.
greater effect on kernels/ear and the fully irrigated 100%ET, Trt 1 and the pre-anthesis 50% ET, Trt 2 were affected the greatest.
Although Trt 4  averaged using 1.6 inches less irrigation than Trt 2 , its average corn yield was 8 bushels/acre greater.
Treatment 4 also had the greatest water productivity of all five treatments although all water productivities were respectable.
It can be seen in Figure 6 that the major difference between Trt 4 and 2 is that Trt 4 was able to set a kernels/ear value much closer to the mean value than Trt 2.
CLOSING THOUGHTS AND CONCLUSIONS
 Full irrigation was still relatively efficient but used 30 to 36% more water.
When irrigation is not severely restricted, corn prices are greater, and/or irrigation costs are lower, managing irrigation at this level and reducing irrigated land area may be more profitable.
Pre-anthesis water stress was more detrimental to grain yield than similar levels of post-anthesis water stress because of reductions in kernels/ear.
This result is somewhat counter to typical older guidelines which indicated that moderate stress during the vegetative stage for corn may not be detrimental.
This may be indicating that kernel set on modern hybrids is a greater factor in determining final yields.
When water is greatly restricted, a 50% reduction post-anthesis might fare reasonably well by relying on stored soil water and precipitation for grain filling.
The rationale behind this comment is that it is important to establish a sufficient number of kernels/ear  that potentially can be filled if soil water and weather conditions permit.
These results might not repeat on less productive soils or under harsher environmental conditions.
On coarser soils , stored soil water and sporadic precipitation might not be sufficient to "carry" the crop through the post-anthesis period as well as in this study.
However, it can be noted that the 50% ET post anthesis treatment  still performed better than the 50% pre-anthesis treatment  in 2013, the year with the greatest irrigation need.
This research was supported in part by the Ogallala Aquifer Program, a consortium between USDA Agricultural Research Service, Kansas State University, Texas AgriLife Research, Texas AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
So how do sensors actually measure soil water content?
You would think that sensors measure water content directly, but that isnt the case.
Instead they measure soil water content indirectly by looking at other properties in the soil.
By measuring a property and using a calibration, sensors estimate water content.
USING THE K-STATE CENTER PIVOT SPRINKLER AND SDI ECONOMIC COMPARISON SPREADSHEET 2008
 In much of the Great Plains, the rate of new irrigation development is slow or zero.
Although the Kansas irrigated area, as reported by producers through annual irrigation water use reports, has been approximately 3 million acres since 1990, there has been a dramatic shift in the methods of irrigation.
During the period since 1990, the number of acres irrigated by center pivot irrigation systems increased from about 50 per cent of the total irrigated acreage base to about 90 percent of the base area.
In 1989, subsurface drip irrigation  research plots were established at Kansas State University Research Stations to investigate SDI as a possible additional irrigation system option.
Early industry and producers surveys have indicated a small but steady increase in adoption.
In 2004, irrigation water use reports were compiled to obtain a more accurate estimate of SDI acres.
2005 data indicates 9200 acres of fields were exclusively irrigated by SDI systems with another 7600 acres have SDI in combination with another system type.
Although Kansas SDI systems represent less than 1 percent of the irrigated area, producer interest still remains high because SDI can potentially have higher irrigation efficiency and irrigation uniformity.
As the farming populace and irrigation systems age, there will likely be a continued momentum for conversion to modern pressurized irrigation systems.
Both center pivot sprinkler irrigation  and subsurface drip irrigation  are options available to the producer for much of the Great Plains landscape.
Pressurized irrigation systems in general are a costly investment and this is particularly the case with SDI.
Producers need to carefully determine their best investment options.
In the spring of 2002, a free Microsoft Excel 1 spreadsheet template was introduced by K-State Research and Extension for making economic comparisons of CP and SDI.
Since that time, the spreadsheet has been periodically updated to reflect changes in input data, particularly system and corn production costs.
The spreadsheet also provides sensitivity analyses for key factors.
This paper will discuss how to use the spreadsheet and the key factors that most strongly affect the comparisons.
The template has five worksheets , the Main, CF, Field size & SDI life, SDI cost & life, Yield & price tabs.
Most of the calculations and the result are shown on the Main tab.
Figure 1.
Main worksheet  of the economic comparison spreadsheet template indicating the 18 required variables  and their suggested values when further information is lacking or uncertain.
ANALYSES METHODS AND ECONOMIC ASSUMPTIONS
 There are 18 required input variables required to use the spreadsheet template, but if the user does not know a particular value there are suggested values for each of them.
The user is responsible for entering and checking the values in the unprotected input cells.
All other cells are protected on the Main worksheet.
Some error checking exists on overall field size and some items  are highlighted differently when different results are indicated.
Details and rationales behind the input variables are given in the following sections.
Field & irrigation system assumptions and estimates
 Many of the early analyses assumed that an existing furrow-irrigated field with a working well and pumping plant was being converted to either CP or SDI and this still may be the base condition for some producers.
However, the template can also be used to consider options for a currently center pivot irrigated field that needs to be replaced.
The major change in the analysis for the replacement CP is that the cost for the new center pivot probably would not have to include buried underground pipe and electrical service in the initial investment cost.
The analysis also assumes the pumping plant is located at the center of one of the field edges and is at a suitable location for the initial SDI distribution point.
Any necessary pump modifications  for the CP or SDI systems are assumed to be of equal cost and thus are not considered in the analysis.
However, they can easily be handled as an increased system cost for either or both of the system types.
Land costs are assumed to be equal across systems for the overall field size with no differential values in real estate taxes or in any government farm payments.
Thus, these factors "fall out" or do not economically affect the analyses.
An overall field size of 160 acres  was assumed for the base analysis.
This overall field size will accommodate either a 125 acre CP system or a 155 acre SDI system.
It was assumed that there would be 5 noncropped acres consumed by field roads and access areas.
The remaining 30 acres under the CP system are available for dryland cropping systems.
Irrigation system costs are highly variable at this point in time due to rapid fluctuations in material and energy costs.
Cost estimates for the 125 acre CP system and the 155 acre SDI system are provided on the current version of the spreadsheet template, but since this is the overall basis of the comparison, it is recommended that the user apply his own estimates for his conditions.
In the base analyses, the life for the two systems is assumed to be 25 and 15 years for the CP and SDI systems, respectively.
No salvage value was assumed for either system.
This assumption of no salvage value may be inaccurate, as both systems might have a few components that may be reusable or available for resale at the end of the system life.
However, with relatively long depreciation periods of 15 and 25 years and typical financial interest rates, the zero salvage value is a very minor issue in the analysis.
System life is an important factor in the overall analyses.
However, the life of the SDI system is of much greater economic importance in analysis than a similar life for the CP system because of the much higher system costs for SDI.
Increasing the system life from 15 to 20 years for SDI would have a much greater economic effect than increasing the CP life from 20 to 25 years.
When the overall field size decreases, thus decreasing system size, there are large changes in cost per irrigated acre between systems.
SDI costs are nearly proportional to field size, while CP costs are not proportional to field size (Figure
 2).
Quadratic equations were developed to calculate system costs when less than full size 160 acre fields were used in the analysis :
 CPcost% = 44.4 +  	
 SDIcost% = 2.9 +  	
 where CPcost% and CPsize%, and SDIcost% and SDIsize% are the respective cost and size % in relation to the full costs and sizes of irrigation systems fitting within a square 160 acre block.
Figure 2.
CP and SDI system costs as related to field size.
The annual interest rate can be entered as a variable, but is currently assumed to be 8.5%.
The total interest costs over the life of the two systems were converted to an average annual interest cost for this analysis.
Annual insurance costs were assumed to be 0.25% of each total system cost, but can be changed if better information is available.
It is unclear whether insurance can be obtained for SDI systems and if SDI insurance rates would be lower or higher than CP systems.
Many of the SDI components are not subject to the climatic conditions that are typically insured hazards for CP systems.
However, system failure risk is probably higher with SDI systems which might influence any obtainable insurance rate.
Production cost assumptions and estimates
 The economic analysis expresses the results as an advantage or disadvantage of CP systems over SDI in net returns to land and management.
Thus, many fixed costs do not affect the analysis and can be ignored.
Additionally, the analysis does not indicate if either system is ultimately profitable for corn production under the assumed current economic conditions.
Production costs were adapted from KSU estimates.
A listing of the current costs is available on the CF worksheet   and the user can enter new values to recalculate variable costs that more closely match their conditions.
The sum of these costs would become the new suggested Total Variable Costs on the Main worksheet , but the user must manually change the input value on the Main worksheet  for the economic comparison to take effect.
The user may find it easier to just change the differential production costs between the systems on the Main tab rather than changing the baseline assumptions on the CF tab.
This will help maintain integrity of the baseline production cost assumptions.
Figure 3.
CF worksheet  of the economic comparison spreadsheet template and the current production cost variables.
Note that the sums at the bottom of the CF worksheet are the suggested values for total variable costs on the Main worksheet.
The reduction in variable costs for SDI is attributable to an assumed 25% net water savings that is consistent with research findings by Lamm et al..
This translates into a 17 and 13 inch gross application amount for CP and SDI, respectively.
The current estimated production costs are somewhat high reflecting increased energy and other related input costs, but fortunately crop revenues have also increased due to high demand for corn for ethanol production.
This fact is pointed out because a lowering of overall variable costs favors SDI, since more irrigated cropped acres are involved, while higher overall variable costs favors CP production.
The variable costs for both irrigation systems represent typical practices for western Kansas.
Yield and revenue stream estimates
 Changes in the economic assumptions can drastically affect which system is most profitable and by how much.
Previous analyses have shown that the system comparisons are very sensitive to assumptions about
 Size of CP irrigation system
 Shape of field 
 Life of SDI system
 with advantages favoring larger CP systems and cheaper, longer life SDI systems.
The results are very sensitive to
 any additional production cost savings with SDI.
The results are moderately sensitive to
 and very sensitive to
 higher potential yields with SDI
 with advantages favoring SDI as corn yields and price increase.
The economic comparison spreadsheet also includes three worksheet  that display tabular and graphical sensitivity analyses for field size and SDI system
 life, SDI system cost and life, and corn yield and selling price.
These sensitivity analysis worksheets automatically update when different assumptions are made on the Main worksheet.
Figure 4.
The Field size & SDI life worksheet  sensitivity analysis.
Note this is one of three worksheets  providing tabular and graphical sensitivity analyses.
These worksheets automatically update to reflect changing assumptions on the Main worksheet.
SOME KEY OBSERVATIONS FROM PREVIOUS ANALYSES
 Users are encouraged to "experiment" with the input values on the Main worksheet  to observe how small changes in economic assumptions can vary the bottom line economic comparison of the two irrigation systems.
The following discussion will give the user "hints" about how the comparisons might be affected.
Smaller CP systems and systems which only complete part of the circle are less competitive with SDI than full size 125 acre CP systems This is primarily because the CP investment costs  increase dramatically as field size decreases  or when the CP system cannot complete a full circle.
Increased longevity for SDI systems is probably the most important factor for SDI to gain economic competitiveness with CP systems.
A research SDI system at the KSU Northwest Research-Extension Center in Colby, Kansas has been operated for 18 years with very little performance degradation, so long system life is possible.
There are a few SDI systems in the United States that have been operated for over 25 years without replacement.
However, a short SDI system life that might be caused by early failure due to clogging, indicates a huge economic disadvantage that would preclude nearly all adoption of SDI systems.
Although SDI cost is an important factor, long SDI system life can help reduce the overall economic effect.
The CP advantage for SDI system lives between 15 and 20 years is greatly diminished as compared to the difference between 10 and 15 year SDI system life.
The sensitivity of CP system life and cost is much less because of the much lower initial CP cost and the much longer assumed life.
In areas where CP life might be much less than 25 years due to corrosive waters, a sensitivity analysis with shorter CP life is warranted.
Figure 5.
The SDI cost and life worksheet  sensitivity analysis.
Note this is one of three worksheets  providing tabular and graphical sensitivity analyses.
These worksheets automatically update to reflect changing assumptions on the Main worksheet.
The present baseline analysis already assumes a 25% water savings with SDI.
There are potentially some other production cost savings for SDI such as fertilizer and herbicides that have been reported for some crops and some locales.
Small changes in the assumptions can make a sizable difference.
It has already been stated that higher corn yields and higher corn prices favor the SDI economics.
These results can be seen on the Yield and Price sensitivity worksheet  on the Excel template.
This result occurs because of the increased irrigated area for SDI in the given 160 acre field.
The significance of yield and price can be illustrated by taking one step further in the economic analysis, that being the case where there is a yield difference between irrigation systems.
Combining a higher overall corn yield potential with an additional small yield advantage for SDI on the Main tab can allow SDI to be very competitive with CP systems.
Figure 6.
The Yield and Price worksheet  sensitivity analysis.
Note this is one of three worksheets  providing tabular and graphical sensitivity analyses.
These worksheets automatically update to reflect changing assumptions on the Main worksheet.
AVAILABILITY OF FREE SOFTWARE
 1 Mention of tradenames is for informational purposes and does not constitute endorsement by Kansas State University.
This paper was first presented at the 19th annual Central Plains Irrigation Conference, February 19-20, 2007, Greeley, Colorado.
Contribution No.
08-245-A from the Kansas Agricultural Experiment Station.
The correct citation is
 center pivot sprinkler and SDI economic comparison spreadsheet 2008.
In: Proc.
Central Plains Irrigation Conference, Greeley, CO., Feb.
19-20, 2008.
Available from
 CPIA, 760 N.Thompson, Colby, KS.
pp.
61-70.
Decreed rights are water rights determined by court decree.
An example is the North Platte River Decree between Colorado, Nebraska and Wyoming.
One element of the North Platte River Decree is equitable apportionment, in which the U.S.
Supreme Court essentially applied prior appropriation across state lines to determine water rights.
Enterprise Budgets Alfalfa Hay Production, Flood Irrigated, Southern Arizona Blase Evancho, Paco Ollerton, Trent Teegerstrom and Clark Seavert
 This enterprise budget estimates the typical economic costs and returns to grow alfalfa hay using flood irrigation in southern Arizona.
It should be used as a guide to estimate actual costs and returns and is not representative of any farm.
The assumptions used in constructing this budget are discussed below.
Assistance provided by area producers and agribusinesses is much appreciated.
As of the date of this publication, the price for labor, fuel, fertilizer, and chemicals is increasing dramatically, which makes developing a long-term budget difficult.
Therefore, a sensitivity analysis shows the net returns per acre as these inputs increase by 10 and 20 percent.
This budget is based on a 1,500-tillable acre farm.
As Arizona is experiencing irrigation water shortages, approximately 40 percent  of the total farm tillable acres are fallowed.
This fallowed land will allow adequate water to irrigate the following crops: 271 acres in cotton, 45 acres in silage corn, 90 acres in spring barley, 181 acres in durum wheat, and 316 acres of alfalfa hay.
The costs to fallow land are allocated to each crop based on its water use.
All crops are grown using flood irrigation.
Tractor driver labor cost is $17.89 per hour and general labor $14.55 per hour; both rates include social security, workers' compensation, unemployment insurance, and other labor overhead expenses.
For this study, owner labor is valued at the same rate as tractor driver rates, and all labor is assumed to be a cash cost.
Tractor labor hours are calculated based on machinery hours, plus ten percent.
Interest on operating capital for harvest and production inputs  is treated as a cash expense, borrowed for 6-months.
An interest rate of six percent is charged as an opportunity to the owner for machinery ownership.
The machinery and equipment used in this budget are sufficient for a 1,500-acre farm with 1,000 acre in crops.
The machinery and equipment hours reflect producing cotton, silage corn, spring barley, durum wheat, and alfalfa hay.
A detailed breakdown of machinery values is shown in Table 2.
Estimated labor, variable, and fixed costs for machinery are shown in Table 3, based on an hour and per acre basis.
The machinery costs are calculated based on the total farm use of the machinery.
Off-road diesel is $4.00 per gallon.
The cultural operations are listed approximately in the order in which they are performed.
A 175-hp tractor is used to pull the v-ripper, heavy offset disk, moldboard plow, landplane, lister, and planter.
A 125-hp tractor is used to pull the shredder/root puller, drill, cultivator, fertilizer spreader, and boom sprayer.
A charge for miscellaneous and other expenses is five percent of production costs, including additional labor, machinery repairs and maintenance, supplies and materials, tax preparation, memberships in professional organizations, and educational workshops not included in field operations.
In both the establishment and full production budgets the price of alfalfa hay is $250 per ton, with an average
 yield of 8.5 tons per acre, resulting in a gross income of $2,125.
The variable costs in the establishment year are $1,630 per acre and fixed cash costs of $343 per acre, giving a net return above variable cash costs of $152 per acre.
Total fixed costs are $74 per acre and total costs of $2,047 per acre, when all variable and fixed costs are considered.
The gross income minus total costs in the establishment year results in a $78 per acre return.
The variable costs for the three full production years are $1,568 per acre and fixed cash costs of $343 per acre, giving a net return above variable cash costs of $214 per acre.
Total fixed costs are $10 per acre and total costs of $1,922 per acre, when all variable and fixed costs are considered.
The gross income minus total costs results in a $203 per
 acre return.
A breakeven price of $225 per ton would be required to cover variable and fixed cash costs and $226 per ton to cover total costs.
Tables 4 and 5 show the baseline net returns per acre for cash and total costs at various yields and prices for the full production years.
Tables 6, 7, 8, and 9 show a sensitivity analysis of returns per acre as the price for labor, fuel, fertilizer, and chemicals are increased an additional 10 and 20 percent.
NOTE: Not included in these budgets are family living withdrawals for unpaid labor, returns to management, depreciation and opportunity costs for vehicles, buildings and improvements, inflation, property and crop insurance, and local, state, and federal income and property taxes.
Table 1a.
Economic and Cash Costs and Returns of Establishing Alfalfa Hay, $/acre.
Returns	Unit	$/Unit	Quantity	Value
 Alfalfa Hay Establishment	ton	$250.00	8.50	$2,125.00
 Variable Cash Costs	Price	Quantity	Unit	Labor	Machinery	Materials	Total
 Land Preparation and Maintenance
 V-Ripper	1.00	acre	$13.53	$34.60	$0.00	$48.13
 Offset Disk	2.00	acre	9.43	23.76	0.00	33.19
 Moldboard Plow	1	acre	7.73	24.50	0.00	32.23
 Landplane	1.00	acre	3.87	9.31	0.00	13.18
 Drill	1.00	acre	5.41	10.13	140.00	155.54
 Seed	$140.00	1.00	acre
 Ferlilizer Spreader	1.00	acre	1.88	3.73	68.00	73.61
 Ferilizer Program	$68.00	1.00	acre
 Boom Sprayer	2.00	acre	2.38	3.64	90.00	96.02
 Herbicides	$50.00	1.00	acre
 Insecticides	$40.00	1.00	acre
 Irrigation	87.30	0.00	330.00	417.30
 Irrigation Water, Flood	$55.00	6.00	ac ft
 Irrigation Labor, Flood	$14.55	6.00	hours
 Harvest, Custom	$75.00	8.50	tons	0.00	0.00	637.50	637.50
 Other Expenses	5.0%	0.00	0.00	75.34	75.34
 Interest on Operting Capital	6.0%	0.00	0.00	47.46	47.46
 Total Variable Cash Costs	$131.53	$109.69	$1,388.30	$1,629.51
 Fixed Cash Costs	Unit	$/Unit	Value
 Fallow Costs	acre	$173.32	173.32
 Annual Cash Rent Payment	acre	170.00	170.00
 Total Fixed Cash Costs	$343.32
 Total Returns minus Total Varialbe and Fixed Cash Costs	$152.17
 Fixed Non-Cash Costs	Unit	$/Unit	Value
 Power Units, Machinery & Equipment, depreciation & interst	acre	$73.76	$73.76
 Total Fixed Non-Cash Costs	$73.76
 Total Annual Costs	$2,046.59
 Returns minus Total Annual Costs	$78.41
 Table 1a.
Economic and Cash Costs and Returns of Producing Alfalfa Hay, $/acre.
Returns	Unit	$/Unit	Quantity	Value
 Alfalfa Hay Establishment	ton	$250.00	8.50	$2,125.00
 Variable Cash Costs	Price	Quantity	Unit	Labor Machinery	Materials	Total
 Ferlilizer Spreader	2.00	acre	$3.76	$7.47	$297.50	$308.72
 Ferilizer Program	$297.50	1.00	acre
 Boom Sprayer	2.00	acre	2.38	3.64	150.00	156.02
 Herbicides	$90.00	1.00	acre
 Insecticides	$60.00	1.00	acre
 Irrigation	72.75	0.00	275.00	347.75
 Irrigation Water, Flood	$55.00	5.00	ac ft
 Irrigation Labor, Flood	$14.55	5.00	hours	68.00	73.61
 Harvest, Custom	$75.00	8.50	tons	0.00	0.00	637.50	637.50
 Other Expenses	5.0%	0.00	0.00	72.50	72.50
 Interest on Operting Capital	6.0%	0.00	0.00	45.67	45.67
 Total Variable Cash Costs	$78.89	$11.11	$1,478.17	$1,568.17
 Fixed Cash Costs	Unit	$/Unit	Value
 Fallow Costs	acre	$173.32	173.32
 Annual Cash Rent Payment	acre	170.00	170.00
 Total Fixed Cash Costs	$343.32
 Total Returns minus Total Varialbe and Fixed Cash Costs	$213.51
 Fixed Non-Cash Costs	Unit	$/Unit	Value
 Power Units, Machinery & Equipment, depreciation & interst	acre	$10.25	$10.25
 Total Fixed Non-Cash Costs	$10.25
 Total Annual Costs	$,1921.749
 Returns minus Total Annual Costs	$203.26
 Table 2.
Whole Farm Machinery Cost Assumptions.
Width	Market	Annua	Life
 Machine		Value	Use	
 175 HP Tractor	N/A	$180,000	1,365	10
 125 HP Tractor	N/A	80,000	495	15
 V-Ripper	8.0	22,000	459	10
 Offset Disk	18.0	30,000	517	15
 Moldboard Plow	9.3	35,000	138	15
 Landplane	16.0	18,000	78	15
 Lister	10.0	6,500	99	15
 Cotton Shredder/Root Puller	20.0	12,000	41	15
 Row Planter	24.0	40,000	72	15
 Row Cultivator	24.0	22,000	103	10
 Drill	20.0	25,000	97	15
 Fertilizer Spreader	40.0	18,000	109	20
 Boom Sprayer	60.0	9,500	145	20
 Table 3.
Machinery Cost Calculations, on a per hour and per acre basis.
-Variable Costs-	Fixed Cost
 Fuel &	Repairs &	Deprec.
Total Cost
 Machie	Lube	Maint.
& Interest
 175 HP Tractor	$36.80	$7.37	$17.20	$61.37
 125 HP Tractor	23.00	1.78	18.31	43.09
 V-Ripper	0.00	6.16	6.19	12.35
 Offset Disk	0.00	5.40	6.48	11.88
 Moldboard Plow	0.00	18.20	28.29	46.50
 Landplane	0.00	3.24	25.80	29.04
 Lister	0.00	1.78	7.32	9.10
 Cotton Shredder/Root Puller	0.00	2.76	32,57	35.33
 Row Planter	0.00	14.02	64.48	78.50
 Row Cultivator	0.00	3.90	27.10	30.99
 Drill	0.00	12.06	30.14	42.20
 Fertilizer Spreader	0.00	14.31	19.02	33.34
 Boom Sprayer	0.00	5.36	7.51	12.87
 Acre/	Operator	Variable	Fixed	Total
 Field Operation	Hour	Labor	Costs	Costs	Costs
 175 HP Tractor & V-Ripper	1.45	$13.53	$34.60	$16.08	$64.21
 175 HP Tractor & Offset Disk	4.17	4.72	11.88	5.68	22.27
 175 HP Tractor & Moldboard Plow	2.55	7.73	24.50	17.87	50.11
 175 HP Tractor & Landplane	5.09	3.87	9.31	8.45	21.62
 175 HP Tractor & Lister	3.18	6.18	14.44	7.71	28.33
 175 HP Tractor & Shredder	6.64	2.97	4.15	7.67	14.78
 175 HP Tractor & Planter	4.36	4.51	13.34	18.72	36.56
 175 HP Tractor & Cultivator	6.55	3.01	4.38	6.94	14.32
 175 HP Tractor & Drillr	3.64	5.41	10.13	13.32	28.87
 175 HP Tractor & Fertilizer Spreader	10.47	1.88	3.73	3.56	9.18
 175 HP Tractor & Boom Sprayer	16.55	1.19	1.82	1.56	4.57
 Table 4.
Estimated Per Acre Returns Over Cash Cost at Varying Yields and Prices at Full Production.
Price/Ton	5.5	6.5	7.5	8.5	9.5	10.5	11.5
 $220.00					179	399	619
 $230.00				44	274	504	734
 $240.00				129	369	609	849
 $250.00				214	464	714	964
 $260.00			39	299	559	819	1,079
 $270.00			114	384	654	924	1,194
 $280.00			189	469	749	1,029	1,309
 Table 5.
Estimated Per Acre Returns Over Total Cost at Varying Yields and Prices at Full Production.
Price/Ton	5.5	6.5	7.5	8.5	9.5	10.5	11.5
 $220.00					168	388	608
 $230.00				33	263	493	723
 $240.00				118	358	598	838
 $250.00				203	453	703	953
 $260.00			28	288	548	808	1,068
 $270.00			103	373	643	913	1,183
 $280.00			178	458	738	1,018	1,298
 Table 6.
Estimated Per Acre Returns Over Cash Cost at Varying Yields and Prices at Full Production with a 10 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Price/Ton	5.5	6.5	7.5	8.5	9.5	10.5	11.5
 $248.50					168	388	608
 $249.00				33	263	493	723
 $249.50				118	358	598	838
 $250.00				203	453	703	953
 $250.50			28	288	548	808	1,068
 $251.00			103	373	643	913	1,183
 $251.50			178	458	738	1,018	1,298
 Table 7.
Estimated Per Acre Returns Over Total Cost at Varying Yields and Prices at Full Production with a 10 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Price/Ton	5.5	6.5	7.5	8.5	9.5	10.5	11.5
 $248.50					158	378	598
 $249.00				23	253	483	713
 $249.50				108	348	588	828
 $250.00				193	443	693	943
 $250.50			18	278	538	798	1,058
 $251.00			93	363	633	903	1,173
 $251.50			168	448	728	1,008	1,288
 Table 8.
Estimated Per Acre Returns Over Cash Cost at Varying Yields and Prices at Full Production with a 20 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Price/Ton	5.5	6.5	7.5	8.5	9.5	10.5	11.5
 $248.50					157	377	597
 $249.00				22	252	482	712
 $249.50				107	347	587	827
 $250.00				192	442	692	942
 $250.50			17	277	537	797	1,057
 $251.00			92	362	632	902	1,172
 $251.50			167	447	727	1,007	1,287
 Table 9.
Estimated Per Acre Returns Over Total Cost at Varying Yields and Prices at Full Production with a 20 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Price/Ton	5.5	6.5	7.5	8.5	9.5	10.5	11.5
 $248.50					147	367	587
 $249.00				12	242	472	702
 $249.50				97	337	577	817
 $250.00				182	432	682	932
 $250.50			7	267	527	787	1,047
 $251.00			82	352	622	892	1,162
 $251.50			157	437	717	997	1,277
 BLASE EVANCHO Area Agent, Arizona Cooperative Extension, University of Arizona
 Paco OLLERTON Producer in Pinal County
 TRENT TEEGERSTROM Ag Econ Extension Specialist, Department of Agriculture and Resource Economics, University of Arizona
 CLARK SEAVERT Agricultural Economist, Department of Applied Economics, Oregon State University
 Any products, services or organizations that are mentioned, shown or indirectly implied in this publication do not imply endorsement by The University of Arizona.
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Edward C.
Martin, Interim Director, Extension, Division of Agriculture, Life and Veterinary Sciences, and Cooperative Extension, The University of Arizona.
The University of Arizona is an equal opportunity, affirmative action institution.
The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, sexual orientation, gender identity, or genetic information in its programs and activities.
Tillage and Irrigation Capacity Effects on Corn Production
 Freddie R.
Lamm, Professor and Research Irrigation Engineer
 Robert M.
Aiken, Associate Professor and Crop Scientist
 Written for presentation at the 2007 ASABE Annual International Meeting Sponsored by ASABE Minneapolis Convention Center Minneapolis, Minnesota 17 20 June 2007
 Abstract.
Corn production was compared from 2004 to 2006 for three plant populations  under conventional, strip and no tillage systems for irrigation capacities limited to 25 mm every 4, 6 or 8 days.
Corn yield increased approximately 12% from the lowest to highest irrigation capacity in these three years of varying precipitation and near normal crop evapotranspiration.
Strip tillage and no tillage had 8.8% and 7% higher grain yields than conventional tillage, respectively.
Results suggest that strip tillage obtains the residue benefits of no tillage in reducing evaporation losses without the yield penalty sometimes occurring with high residue.
The small increases in total seasonal water use  for strip tillage and no-tillage compared to conventional tillage can probably be explained by the higher grain yields for these tillage systems.
Keywords.
Tillage management, conservation tillage, irrigation management, water use efficiency, corn production
 Declining water supplies and reduced well capacities are forcing irrigators to look for ways to conserve and get the best utilization from their water.
Residue management techniques such as no tillage or conservation tillage have been proven to be very effective tools for dryland water conservation in the Great Plains.
However, adoption of these techniques is lagging for continuous irrigated corn.
There are many reasons given for this lack of adoption, but some of the major reasons expressed are difficulty handling the increased level of residue from irrigated production, cooler and wetter seedbeds in the early spring which may lead to poor or slower development of the crop, and ultimately a corn grain yield penalty as compared to conventional tillage systems.
Under very high production systems, even a reduction of a few percentage points in corn yield can have a significant economic impact.
Strip tillage might be a good compromise between conventional tillage and no tillage, possibly achieving most of the benefits in water conservation and soil quality management of no tillage, while providing a method of handling the increased residue and increased early growth similar to conventional tillage.
Strip tillage can retain surface residues and thus suppress soil evaporation and also provide subsurface tillage to help alleviate effects of restrictive soil layers on root growth and function.
A study was initiated in 2004 to examine the effect of three tillage systems for corn production under three different irrigation capacities.
Plant population was also factor examined because corn yield increases in recent years have been closely related to increased plant populations.
The study was conducted under a center pivot sprinkler at the KSU Northwest ResearchExtension Center at Colby, Kansas during the years 2004 to 2006.
Corn was also grown on the field site in 2003 to establish residue levels for the three tillage treatments.
The deep Keith silt loam soil can supply about 445 mm of available soil water for a 2.4 m soil profile.
The semiarid, summer pattern climate has an annual rainfall of approximately 485 mm.
Average precipitation is approximately 310 mm during the 120-day corn growing season.
A corn hybrid of approximately 110 day relative maturity  was planted in circular rows on May 8, 2004, April 27, 2005 and April 20, 2006, respectively.
Three seeding rates  were superimposed onto each tillage treatment in a complete randomized block design.
Irrigation was scheduled with a weather-based water budget, but was limited to the 3 treatment capacities of 25 mm every 4, 6, or 8 days.
This translates into typical seasonal irrigation amounts of 375-500, 275-375, 200-300 mm, respectively.
Each of the irrigation capacities  were replicated three times in pie-shaped sectors  of the center pivot sprinkler.
Plot length varied from to 27 to 53 m, depending on the radius of the subplot from the center pivot point.
Irrigation application rates  at the outside edge of this research center pivot were similar to application rates near the end of full size systems.
A small amount of preseason irrigation was conducted to bring the soil water profile  to approximately 50% of field capacity in the fall and as necessary in the spring to bring the soil water profile to approximately 75% in the top 1 m prior to planting.
It should be recognized that preseason irrigation is not a recommended practice for fully irrigated corn production, but did allow the three irrigation capacities to start the season with somewhat similar amounts of water in the profile.
The three tillage treatments  were replicated in a Latin-Square type arrangement in 18.3 m ft widths at three different radii (Centered at 73, 91
 and 110 m.) from the center pivot point.
The various operations and their time period for the three tillage treatments are summarized in Table 1.
Planting was in the same row location each year for the Conventional Tillage treatment to the extent that good farming practices allowed.
The Strip Tillage and No-Tillage treatments were planted between corn rows from the previous year.
Tillage and Sprinkler Irrigation Capacity Study
 Figure 1.
Physical arrangement of the irrigation capacity and tillage treatments.
Fertilizer N for all 3 treatments was applied at a rate of 224 kg/ha in split applications with approximately 95 kg/ha applied in the fall or spring application, approximately 34 kg/ha in the starter application at planting and approximately 95 kg/ha in a fertigation event near corn lay-by.
Phosphorus was applied with the starter fertilizer at planting at the rate of 51 kg/ha P2O5.
UreaAmmonium-Nitrate  and Ammonium Superphosphate  were utilized as the fertilizer sources in the study.
Fertilizer was incorporated in the fall concurrently with the Conventional Tillage operation and applied with a mole knife during the Strip Tillage treatment.
Conversely, N application was broadcast with the No Tillage treatment prior to planting.
A post-plant, pre-emergent herbicide program of Bicep II Magnum and Roundup Ultra was applied.
Roundup was also applied post-emergence prior to lay-by for all treatments, but was particularly beneficial for the strip and no tillage treatments.
Insecticides were applied as required during the growing season.
Weekly to bi-weekly soil water measurements were made in 0.3 m increments to 2.4 m depth with a neutron probe.
All measured data was taken near the center of each plot.
These data were utilized to examine treatment differences in soil water conditions both spatially  and temporally.
Table 1.
Tillage treatments, herbicide and nutrient application by period.
Period	Conventional tillage	Strip Tillage	No Tillage
 1) One-pass chisel/disk plow	1) Strip Till + Fertilizer  at
 Fall	at 20-25 mm with	20-25 mm depth,
 2003	broadcast N, November 13,	November 13, 2003.
2) Plant + Banded starter N &	2) Plant + Banded starter N	1) Broadcast N + Plant +
 P, May 8, 2004.
& P, May 8, 2004	Banded starter N & P,
 Spring	May 8, 2004
 2004	3) Pre-emergent herbicide	3) Pre-emergent herbicide	2) Pre-emergent
 application, May 9, 2004.
application, May 9, 2004.
herbicide application,
 4) Roundup herbicide	4) Roundup herbicide	3) Roundup herbicide
 Summer	application near lay-by,	application near lay-by,	application near lay-
 June 9, 2004	June 9, 2004	by, June 9, 2004
 5) Fertigate , June 10,	5) Fertigate , June10,	4) Fertigate , June 10,
 1) One-pass chisel/disk plow	Too wet, no tillage
 Fall	at 20-25 mm with	operations
 2004	broadcast N, November 05,
 1) Strip Till + Fertilizer  at
 20-25 mm depth, March
 Spring	2) Plant + Banded starter N &	2) Plant + Banded starter N	1) Broadcast N + Plant +
 2005	P, April 27, 2005.
& P, April 27, 2005	Banded starter N & P,
 3) Pre-emergent herbicide	3) Pre-emergent herbicide	2) Pre-emergent
 application, May 8, 2005.
application, May 8, 2005.
herbicide application,
 4) Roundup herbicide	4) Roundup herbicide	3) Roundup herbicide
 Summer	application near lay-by,	application near lay-by,	application near lay-
 June 9, 2005	June 9, 2005	by, June 9, 2005
 5) Fertigate , June 17,	5) Fertigate , June 17,	4) Fertigate , June 17,
 1) One-pass chisel/disk plow	1) Strip Till + Fertilizer  at
 Fall 2005	at 20-25 mm with	20-25 mm depth,
 broadcast N, November 10,	November 10, 2005.
2) Plant + Banded starter N &	2) Plant + Banded starter N	1) Broadcast N + Plant +
 P, April 20, 2006.
& P, April 20, 2006	Banded starter N & P,
 Spring	April 20, 2006
 2006	3) Pre-emergent herbicide	3) Pre-emergent herbicide	2) Pre-emergent
 application, April 22, 2006.
application, April 22,	herbicide application,
 2006.
April 22, 2006.
4) Roundup herbicide	4) Roundup herbicide	3) Roundup herbicide
 Summer	application near lay-by,	application near lay-by,	application near lay-
 2006	June 6, 2006	June 6, 2006	by, June6, 2006
 5) Fertigate , June 13,	5) Fertigate , June 13,	4) Fertigate , June 13,
 Similarly, corn yield was measured in each of the 81 subplots at the end of the season.
In addition, yield components  were determined to help explain the treatment differences.
Water use and water use efficiency were calculated for each subplot using the soil water data, precipitation, applied irrigation and crop yield.
Summer seasonal precipitation was approximately 50 mm below normal in 2004, near normal in 2005, and nearly 75 mm below normal in 2006 at 254, 304, and 228 mm, respectively for the 120 day period from May 15 through September 11.
In 2004, the last month of the season was very dry but the remainder of the season had reasonably timely rainfall and about normal crop evapotranspiration.
In 2005, precipitation was above normal until about the middle of July and then there was a period with very little precipitation until the middle of August.
This dry period in 2005 also coincided with a week of higher temperatures and high crop evapotranspiration near the reproductive period of the corn.
In 2006, precipitation lagged behind the long term average for the entire season.
Fortunately, seasonal evapotranspiration was near normal as it also was for the other two years.
Figure 2.
Calculated corn evapotranspiration and summer seasonal rainfall for the 120 day period, May 15 through September 11, KSU Northwest Research-Extension Center, Colby Kansas.
Irrigation requirements were lowest in 2004 with the 25 mm/4 day treatment receiving 305 mm, the 25 mm/ 6 day treatment receiving 279 mm and the 25 mm/8 day treatment receiving 229 mm.
The irrigation amounts in 2005 were 381, 330, and 254 mm for the three respective treatments.
The irrigation amounts were highest in 2006 at 394, 343, and 292 mm for the three respective treatments.
Figure 3.
Seasonal irrigation for the 120 day period, May 15 through September 11 for the three irrigation treatments in an irrigation capacity and tillage study, KSU Northwest Research-Extension Center, Colby Kansas, 2004-2006.
Crop Yield and Selected Yield Components
 Corn yield was relatively high for all three years ranging from 10.1 to 16.4 Mg/ha Table 2 through 4, and Figure 4).
Higher irrigation capacity generally increased grain yield, particularly in 2005 and 2006.
Strip tillage and no tillage had higher grain yields at the lowest irrigation capacity in 2004 and at all irrigation capacities in 2005 and 2006.
Strip tillage tended to have the highest grain yields for all tillage systems and the effect of tillage treatment was greatest at the lowest irrigation capacity.
These results suggest that strip tillage obtains the residue benefits of no tillage in reducing evaporation losses without the yield penalty sometimes associated with the higher residue levels in irrigated no tillage management.
Table 2.
Selected corn yield component data for 2004 from an irrigation capacity and tillage study, KSU Northwest Research-Extension Center, Colby, Kansas.
Irrigation	Tillage	Plant	Grain	Plant	Kernels	Kernels	Kernel
 Capacity	System	Population	Yield	Population	/Ear	106/ha	Weight
 	g/100)
 25 mm/4 d Conventional	64	14.4	68888	550	39.0	37.1
 	74	14.8	72475	557	40.8	36.2
 84	14.7	79651	529	42.5	34.6
 Strip Tillage	64	15.4	68170	537	39.8	38.9
 74	14.6	75346	519	39.5	37.0
 84	14.9	81804	514	42.1	35.5
 No Tillage	64	13.7	63864	548	36.6	37.7
 74	14.2	72475	539	38.8	36.8
 84	15.7	83239	553	46.4	33.8
 25 mm/6 d Conventional	64	14.2	62429	557	36.4	39.0
 	74	13.9	73193	522	39.7	34.9
 84	15.3	80369	522	42.4	36.0
 Strip Tillage	64	14.7	67452	558	40.1	36.9
 74	14.1	71040	556	40.3	35.0
 84	14.9	82522	487	42.0	35.6
 No Tillage	64	14.1	65300	537	37.4	37.8
 74	13.9	71758	556	40.3	34.6
 84	14.3	79651	545	43.8	32.8
 25 mm/8 d	Conventional	64	12.4	60994	509	33.2	37.5
 	74	13.3	72475	531	38.5	34.5
 84	13.6	78216	494	39.7	34.9
 Strip Tillage	64	14.3	63864	644	42.1	34.2
 74	14.4	73911	518	40.5	35.6
 84	14.7	81086	507	41.8	35.1
 No Tillage	64	13.8	66735	541	37.6	36.6
 74	14.1	73193	528	40.9	34.5
 84	13.8	81086	506	42.9	32.2
 Table 3.
Selected corn yield component data for 2005 from an irrigation capacity and tillage study, KSU Northwest Research-Extension Center, Colby, Kansas.
Capacity	Irrigation	System	Tillage		Population	Plant	Mg/ha	Grain	Yield	Population		Plant	Kernels	/Ear	Kernels	106/ha	Kernel	Weight	g/100
 25 mm/4 d	Conventional	64	13.7	58841	644	36.0	37.9
 	74	14.9	68170	594	40.1	37.3
 84	16.3	74628	579	44.0	37.1
 Strip Tillage	64	14.9	60277	620	37.8	39.6
 74	15.7	68888	590	41.1	38.3
 84	15.9	76781	567	43.1	36.8
 No Tillage	64	14.3	61712	628	37.4	38.3
 74	15.9	66017	660	42.6	37.4
 84	16.5	77498	606	46.1	35.8
 25 mm/6 d Conventional	64	12.7	60994	546	33.7	37.7
 	74	13.8	68170	544	36.7	37.5
 84	13.1	76781	472	35.9	36.2
 Strip Tillage	64	14.2	60277	604	36.4	38.9
 74	13.0	69605	487	33.5	38.4
 84	15.6	78934	560	43.4	36.0
 No Tillage	64	12.9	60994	565	33.6	38.2
 74	14.1	71758	547	38.5	36.6
 84	14.7	78216	512	39.7	37.1
 25 mm/8 d Conventional	64	11.7	60277	523	31.1	37.5
 	74	13.7	67452	536	36.6	37.5
 84	13.1	78216	452	35.0	37.3
 Strip Tillage	64	13.3	58841	648	38.6	34.9
 74	13.5	68170	579	37.8	35.8
 84	15.0	77498	537	41.6	36.1
 No Tillage	64	13.1	59559	608	34.9	37.4
 74	13.2	68170	537	36.6	36.2
 84	13.6	76781	502	37.4	36.4
 The number of kernels/ear was lower in 2004 and 2006 compared to 2005.
The potential number of kernels/ear is set at about the ninth leaf stage  and the actual number of kernels/ear is finalized by approximately 2 weeks after pollination.
Greater early season precipitation in 2005  than 2004 and 2006 may have established a higher potential for kernels/ear and then later in the 2005 season greater irrigation capacity or better residue management may have allowed for more kernels to escape abortion.
The time the actual kernels/ear was being set in 2005 was a period of high evapotranspiration  and also coincided with multiple irrigation events for the 25 mm /4 days irrigation capacity.
An intermediate yield component combines plant population, ears/plant and kernels/ear.
There is less variation in kernels/ha for the various plant population treatments than for kernels/ear.
This is further evidence that a key to increased
 yields and profitability is through appropriate plant population increases.
The kernels/ha still tends to be lower for the conventional tillage treatments.
Table 4.
Selected corn yield component data for 2006 from an irrigation capacity and tillage study, KSU Northwest Research-Extension Center, Colby, Kansas.
Capacity	Irrigation	System	Tillage		Population	Plant	Mg/ha	Grain	Yield	Population		Plant	Kernels	/Ear	Kernels	106/ha	Weight	Kernel	g/100
 25 mm/4 d Conventional	64	15.0	72475	542	39.3	38.1
 	74	13.3	76781	476	36.6	36.4
 84	13.3	86827	434	37.1	36.1
 Strip Tillage	64	14.6	72475	514	37.2	39.1
 74	14.8	77498	483	38.8	38.2
 84	16.3	81804	522	42.3	38.6
 No Tillage	64	13.2	70323	497	35.0	37.9
 74	16.5	77498	535	41.1	40.3
 84	15.6	85392	516	43.7	35.7
 25 mm/6 d	Conventional	64	10.1	71758	422	29.4	34.1
 	74	13.0	78934	446	35.2	37.1
 84	10.6	83957	374	30.1	35.0
 Strip Tillage	64	13.0	71758	492	35.7	36.6
 74	13.5	77498	484	36.8	36.7
 84	13.6	84674	476	39.2	34.7
 No Tillage	64	14.4	72475	541	39.2	36.8
 74	13.7	74628	516	38.2	35.9
 84	14.0	81086	484	38.2	36.7
 25 mm/8 d Conventional	64	10.8	69605	417	28.7	37.8
 	74	12.0	78216	411	31.8	37.7
 84	12.0	83957	385	32.3	37.2
 Strip Tillage	64	13.4	72475	565	40.9	32.7
 74	13.8	78934	510	40.2	34.4
 84	14.5	85392	479	40.5	35.7
 No Tillage	64	12.8	71040	501	34.9	36.9
 74	13.8	77498	497	38.5	35.8
 84	13.5	83957	458	38.1	35.6
 Final kernel weight is affected by plant growing conditions during the grain filling stage  and by plant population and kernels/ear.
Deficit irrigation capacities often will begin to mine soil water reserves during the latter portion of the cropping season, so it is not surprising that kernel weight was increased with increased irrigation capacity.
Figure 4.
Corn grain yield as affected by irrigation capacity and tillage, 2004 to 2006, KSU Northwest Research-Extension Center, Colby Kansas.
Figure 5.
Corn grain yield as affected by irrigation capacity and plant population, 2004-2006, KSU Northwest Research-Extension Center, Colby Kansas.
Figure 6.
Kernels/ear as affected by irrigation capacity and plant population, 2004-2006, KSU Northwest Research-Extension Center, Colby Kansas.
Figure 7.
Kernel weight as affected by irrigation capacity and plant population, 2004-2006, KSU Northwest Research-Extension Center, Colby Kansas.
Tillage system also affected kernel weight, but it is thought by the authors that the effect was caused by different factors at the different irrigation capacities.
At the lowest irrigation capacity, final kernel weight was highest for conventional tillage because of the lower number of kernels/ear.
However, this higher kernel weight did not compensate for the decreased kernels/ear, and thus, grain yields were lower for conventional tillage.
Strip tillage generally had higher kernel weights at higher irrigation capacity than the conventional and no tillage treatments for some unknown reason.
The changing patterns in grain yield, kernels/ear, and kernel weight that occurs between years and as affected by irrigation capacity and tillage system may be suggesting that additional factors besides differences in plant water status or evaporative losses is affecting the corn production.
There might be differences in rooting, aerial or soil microclimate, nutrient status or uptake to name a few possible physical and biological reasons.
Total seasonal water use in this study was calculated as the sum of irrigation, precipitation and the change in available soil water over the course of the season.
As a result, seasonal water use can include non-beneficial water losses such as soil evaporation, deep percolation, and runoff.
Intuitively, one might anticipate that good residue management with strip tillage and notillage would result in lower water use than conventional tillage because of lower non-beneficial water losses.
However, in this study, strip tillage and no-tillage generally had higher water use.
The small increases in total seasonal water use  for strip tillage and no-tillage compared to conventional tillage can probably be explained by the higher grain yields for these tillage systems.
Another possibility is that there were increased deep percolation losses in 2005 because of the higher early season precipitation.
Water use in 2004 was similar for the 25 mm/4 days and 25 mm/6 days irrigation treatment and only slightly higher for the 25 mm/8 days treatment, probably reflecting the timely and near normal rainfall pattern throughout the summer.
There was only 72 mm difference in irrigation from highest to lowest amounts.
Water use efficiency was not affected by tillage in 2004 but was higher for strip and no tillage treatments in 2005 and 2006, probably reflecting the greater yields for these two tillage treatments.
Water use efficiency was only slightly increased when irrigation was decreased indicating that non-beneficial water use and losses were relatively low.
Higher water use efficiency was obtained by the higher plant populations because of increased yields.
These increased yields at the higher plant populations occurred with little or no increase in total water use.
Producers often ask about decreasing irrigation requirements with lower plant population.
The data from this study indicate that much sharper reductions in plant population would be required than those examined here and with those reductions there likely would be additional yield reductions.
Although not a part of the study, the efficiency of nutrient use was high in this study.
Total applied nitrogen would be 225 kg/ha of commercial fertilizer and 8 to 12 additional kg/ha in the in irrigation water.
Approximately 61 kg of grain was produced for each kg of N.
An older guideline for corn production in the region is approximately 45 kg grain for each kg of N.
Table 5.
Total seasonal water use and available soil water on selected dates for 2004 from an irrigation capacity and tillage study, KSU Northwest Research-Extension Center, Colby, Kansas.
Irrigation	Tillage	Water	Water use	ASW to	ASW to	ASW to	ASW to
 Capacity	System	Use	efficiency	0.6 m on	0.6 m on	2.4 m on	2.4 m on
 	mg/ha-mm	5-21-04	6-25-04	7-15-04	9-25-04
 25 mm/4 d	Conventional	584	0.02459	100	106	307	259
 	575	0.02565	91	103	299	245
 559	0.02626	97	106	297	243
 Strip Tillage	598	0.02574	98	106	302	229
 620	0.02349	102	107	303	231
 618	0.02411	100	106	301	223
 No Tillage	559	0.02455	102	109	335	287
 599	0.02373	95	102	289	249
 589	0.02669	96	104	341	281
 25 mm/6 d	Conventional	585	0.02425	98	107	261	206
 	599	0.02328	95	103	267	208
 606	0.02515	95	100	250	182
 Strip Tillage	592	0.02489	87	101	306	242
 619	0.02275	96	102	289	126
 619	0.02402	89	97	302	214
 No Tillage	622	0.02268	93	101	254	177
 635	0.02193	92	98	238	147
 595	0.02413	96	102	244	194
 25 mm/8 d	Conventional	563	0.02209	98	107	269	172
 	570	0.02328	102	111	270	177
 559	0.02427	102	105	238	164
 Strip Tillage	604	0.02364	104	111	320	209
 554	0.02594	93	110	316	215
 589	0.02492	100	105	303	209
 No Tillage	571	0.02414	108	114	306	210
 589	0.02395	104	111	303	183
 574	0.02402	103	110	307	212
 Plant available soil water  in the top 0.6 m was similar across tillage treatments in all years except 2006 which had slightly lower amounts for the conventional tillage treatments.
These slight differences in 2006 continued during the next month and possibly may have reduced the potential kernels/ear for the conventional tillage.
However, the differences are not very large.
Table 6.
Total seasonal water use and available soil water on selected dates for 2005 from an irrigation capacity and tillage study, KSU Northwest Research-Extension Center, Colby, Kansas.
Irrigation	Tillage	Water	Water use	ASW to	ASW to	ASW to	ASW to
 Capacity	System	Use	efficiency	0.6 m on	0.6 m on	2.4 m on	2.4 m on
 	mg/ha-mm	5-24-05	6-22-05	7-14-05	9-19-05
 25 mm/4 d	Conventional	718	0.01903	96	105	346	285
 	727	0.02051	104	109	322	266
 693	0.02356	96	98	338	294
 Strip Tillage	718	0.02078	100	106	339	265
 675	0.02329	101	107	381	354
 740	0.02143	95	103	342	265
 No Tillage	713	0.02011	102	111	387	329
 703	0.02264	97	103	383	348
 724	0.02275	103	106	387	334
 25 mm/6 d Conventional	671	0.01899	98	102	284	222
 	656	0.02111	98	101	302	265
 643	0.02030	99	101	299	264
 Strip Tillage	679	0.02084	89	99	354	293
 689	0.01881	98	96	330	257
 666	0.02337	84	88	328	278
 No Tillage	679	0.01896	93	101	322	236
 691	0.02037	95	99	321	235
 653	0.02249	95	103	348	276
 25 mm/8 d Conventional	579	0.02022	98	101	265	206
 	572	0.02387	99	107	309	246
 629	0.02075	100	103	282	189
 Strip Tillage	605	0.02202	105	106	353	255
 611	0.02214	104	113	366	260
 621	0.02422	101	110	348	246
 No Tillage	625	0.02092	108	109	374	254
 582	0.02270	102	109	381	281
 627	0.02165	105	112	359	264
 Plant available water at anthesis in the total 2.4 m soil profile was more consistently higher for strip and no tillage treatments averaging 51 mm over the three years of the study with greatest differences in 2006.
These continuing differences may have resulted in the decreased kernels/ear for the conventional tillage treatments.
Table 7.
Total seasonal water use and available soil water on selected dates for 2006 from an irrigation capacity and tillage study, KSU Northwest Research-Extension Center, Colby, Kansas.
Irrigation	Tillage	Water	Water use	ASW to	ASW to	ASW to	ASW to
 Capacity	System	Use	efficiency	0.6 m on	0.6 m on	2.4 m on	2.4 m on
 	mg/ha-mm	5-19-06	6-21-06	7-14-06	9-19-06
 25 mm/4 d Conventional	687	0.02178	94	97	275	213
 	676	0.01973	91	91	303	244
 684	0.01949	95	96	286	218
 Strip Tillage	703	0.02072	100	108	327	229
 696	0.02125	100	106	326	246
 698	0.02341	99	103	289	211
 No Tillage	667	0.01981	105	112	382	310
 697	0.02365	102	109	368	291
 686	0.02273	102	109	388	305
 25 mm/6 d	Conventional	631	0.01601	91	97	233	177
 	624	0.02089	83	80	247	213
 636	0.01672	95	97	237	186
 Strip Tillage	662	0.01965	98	102	324	248
 657	0.02049	94	99	329	255
 673	0.02014	88	99	310	230
 No Tillage	657	0.02195	104	110	339	240
 651	0.02099	97	109	349	251
 649	0.02159	101	110	342	244
 25 mm/8 d Conventional	597	0.01811	92	92	222	158
 	559	0.02141	100	110	268	225
 574	0.02091	97	105	238	185
 Strip Tillage	624	0.02153	105	109	296	192
 626	0.02208	105	112	316	210
 616	0.02346	101	105	299	208
 No Tillage	619	0.02070	109	115	357	243
 625	0.02212	108	113	337	222
 632	0.02139	104	111	349	221
 Plant available water at physiological maturity in the total 2.4 m soil profile was more consistently higher for strip and no tillage treatments averaging 26 mm over the three years of the study with greatest differences in 2006.
These continuing differences may have resulted in the decreased yields for the conventional tillage treatments.
Figure 10.
Total seasonal water use  as affected by irrigation capacity and plant population, 20042006, KSU Northwest Research-Extension Center, Colby Kansas.
Corn grain yields were high all three years  with varying seasonal precipitation and near normal crop evapotranspiration.
Strip tillage and no tillage generally performed better than conventional tillage.
Yield components of kernels/ear and kernel weight were affected by both tillage and irrigation levels.
Increasing the plant population from 64000 to 84000 plants/ha was beneficial at all three irrigation capacities.
The study is being continued in 2007 to determine if the production trends will remain as residue levels continue to increase.
This is Contribution No.
07-233-A from the Kansas Agricultural Experiment Station, Manhattan, Kansas.
ENERGY SAVINGS USING VARIABLE FREQUENCY DRIVES ON CENTRIFUGAL PUMPING APPLICATIONS
 Modern Electric Motor Starting Means
 There are three primary methods used to start and operate induction AC motors: Full voltage direct across the line starters, reduced voltage soft starts, and Variable frequency drives.
The three methods all have distinctly different effects on both the mechanical system but also the power distribution networks.
Both the full voltage and reduced voltage starting means are only capable of running AC motors at the motor's synchronous speed of 60Hz.
Full voltage cross the line starters allows the utility's full wave form to start the motor.
This method will see a 600% to 800% of full load current in-rush during the starting of the motor.
Many utility providers have begun to limit this starting means to only smaller motor loads due to the effects of the high in-rush current required to start the motor.
Reduced Voltage soft starts will allow for more control of starting ramp rates of the system, but will have a typical in-rush current during starting of 350% to 450% of the motor's full load current and not allow for speed control.
Both of these starting means do not allow for power factor correction within an induction AC motor system.
However, a variable frequency drive allows an induction AC motor to have virtually no in-rush current and is capable of reduced operating speeds of the motor.
As a mode of operation, a variable frequency drive rectifies the incoming AC power to a DC bus first.
It then switches the DC bus power to create a modified AC waveform to the motor.
This technology allows for smoother starts, infinite control of a pump's flow, and significant avoidance of water hammer.
A variable speed drive is also capable bringing an oversized system closer to unity power factor as well.
Affinity's Law Effects on Power consumption
 Affinity's law is the phenomena that a centrifugal pump typically follows as the system's speed is reduced to control flow rather than throttling.
A cubed root relationship allows for significant reductions in energy consumption as the system's speed is lowers.
Typically a reduction in speed by 10% can net an energy saving of 27%.
These savings often justifies the additional cost of the more sophisticated variable frequency drives.
Comparing the Cost to Traditional Engines
 The three popular power sources for irrigation today are Natural Gas fired internal combustion engines, Diesel cycle engines, and Electric AC induction motors.
The more traditional methods of power are far less energy efficient than an AC motor.
These typically run at 50% or less efficient.
Their efficiency will dramatically decrease as their operating speeds are reduced which can negate the benefit of running a system at slower speeds.
However, an AC motor with an applied variable frequency drive system is capable of reducing its energy consumption at slower speeds while maintaining the system's efficiency in excess of 90%.
During this session we will cover the basic calculations for power consumption, speed's effects on a centrifugal pumping system, and a look at the total cost of ownership comparing traditional power means versus AC motors applying variable frequency technology.
Understanding Your Fish Pond Water Analysis Report
 Nathan M.
Stone Extension Fisheries Specialist
 Hugh K.
Thomforde Extension Aquaculture Specialist
 Some sportfish and aquaculture pond owners choose to submit water samples to the University of Arkansas Cooperative Extension Service for analysis.
The water samples are mailed to the Water Quality Laboratory, Arkansas Water Resources Center, University of Arkansas at Fayetteville.
The laboratory tests the water and sends the results back.
Below are some guidelines for interpreting those results.
These guidelines describe how to interpret results for both surface waters and ground waters.
Surface waters are those exposed to the air and sunlight, such as streams, ponds, reservoirs and lakes.
Ground waters are waters from wells or springs tapping underground aquifers and are often devoid of dissolved oxygen.
These waters may also contain high levels of dissolved gasses or iron.
It is important to know the source of the water sample  in order to interpret the results correctly.
Figure 1 is an example of a pond water analysis.
An explanation of each parameter listed in the report follows.
While most of these parameters are important in fish culture, others are measured incidentally in the process of water analysis and are ordinarily of little concern.
Desirable Range	Acceptable Range
 The pH of water is a measure of how acid or basic it is, on a scale of 0
 Figure 1 Water Analysis Report: Fish
 pH -7.24 Electrical Conductivity -205 uSiemens/cm Alkalinity, Total 100.00 mg/l as CaCO Hardness, Total 103.80 mg/l as CaCO CO3  0.09 mg/l as CaCO HCO  99.90 mg/l as CaCO Fe  -0.05 mg/l Mn  -0.01 mg/l F  -0.15 mg/l CI  -3.13 mg/l SO4  3.21 mg/l NO3  0.04 mg/l NO3-N  0.01 mg/l NH3-N  0.11 mg/l NO2-N  0.00 mg/l PO4  0.06 mg/l
 to 14 with 7 being neutral.
In fish ponds, the time of day that a sample is taken often will influence the pH because of variations in the carbon dioxide  concentration.
As plants in the water remove carbon dioxide for photosynthesis, the pH will increase.
At night, the pH will decrease as carbon dioxide accumulates.
Increasing the total alkalinity concentration in water helps buffer against pH changes.
Most fish species do well within the pH range of 6.5 to 9.5.
Chronic pH levels below 6.5 may reduce fish reproduction and are associated with fish die-offs that sometimes occur in the late winter.
Newly hatched fish  are often sensitive to pH levels above 9.0 t o 9.5.
The pH of water sent to the testing laboratory will change during shipment, especially for waters that have significant amounts of organic matter  or elevated carbon dioxide concentrations Nevertheless, pH testing is useful to detect possible mineral acidity.
A pH reading below 4.5 indicates that there is strong mineral acidity, which is harmful to fish and difficult  to neutralize.
Low pH between 4.5 and 6.5 can often be corrected by the addition of crushed limestone.
Desirable Range	Acceptable Range
 100-2,000 uSiemens/cm	30-5,000 uSiemens/cm
 Electrical conductivity  is a measure of how well a solution conducts electricity and is correlated with salt content.
Conductivity is typically reported in units of uSiemens/cm.
Freshwater fish generally thrive over a wide range of electrical conductivity.
Some minimum salt content is desirable to help fish maintain their osmotic balance.
The upper range varies with fish species.
Channel catfish, for example, can withstand salinities up to 1/2-strength seawater.
Seawater has a conductivity of around 50,000 to 60,000 uSiemens/cm.
Electrical conductivity  also can be used to give a rough estimate of the total amount of dissolved solids  in water.
Typically, the TDS value in mg/l is about half of the EC.
Conductivity should change little during shipment to the laboratory.
Desirable Range	Acceptable Range
 50-150 mg/l as CaCO	Above 20 mg/l and less than
 400 mg/l for ponds
 Above 10 mg/l for hatchery
 water 
 Total alkalinity  is a measure of the concentration of bases  in the water that provide buffering capacity.
The units are milligrams per liter  as calcium carbonate.
TA below 20 mg/l limits primary productivity in water, and ponds with such water benefit from lime.
See our publication MP360, Farm Pond Management for Recreational Fishing, for information on liming ponds.
Application rates of copper sulfate for algae control are based on the TA of the water, and copper sulfate should not be used at all in waters with fish if the TA is less than 50 mg/l.
The total alkalinity of a surface water sample sent to the testing laboratory usually will not change significantly over the 2to 3-day shipping period.
Desirable Range	Acceptable Range
 50-150 mg/l as CaCO	Above 10 mg/l as CaCO
 Total hardness is a measure of the calcium and magnesium concentrations in water.
Other divalent ions  contribute to total hardness but are usually present in insignificant amounts.
The amount of calcium hardness is important in pond fertilization because higher rates of phosphorus fertilizer are required at higher calcium hardness concentrations.
At least 5 mg/l of calcium hardness is needed in fish hatchery water supplies.
Like total alkalinity, total hardness will not change very much during shipment.
CO3  and HCO 
The CPC national temperature forecast indicates above-normal temperature are likely across the northern Great Basin, northern Rockies and the High Plains region from North Dakota southward through Oklahoma.
There is a slight to moderate risk of above-normal temperatures for the western two-thirds of the United States surrounding the highest risk areas.
Touch the calculate button and total water available and total water depleted will both be calculated.
These readings can then be saved to your device to be viewed later.
The app also has the ability to graph the data to view trends throughout the growing season.
Water Hammer In Irrigation Systems
 G.A.
Clark and D.
Z.
Haman2
 Irrigation system design includes pump sizing and selection, valve sizing and selection, and pipe sizing as well as the proper selection and placement of many other components.
Good design involves selecting and sizing components to perform their intended tasks within the constraints of the system, to ensure an efficient, cost effective, and durable irrigation system.
Cost effectiveness will result when oversizing is avoided.
Undersizing of components will cut initial costs but often results in poor irrigation distribution uniformity or the complete or partial failure of the system through ruptured pipes, damaged valves, or pump damage.
Like any other moving fluid, flowing water has momentum.
When subjected to a sudden change in flow, shock waves propagate through the system.
This occurrence is referred to as "water hammer." Flow changes can occur due to operation of valves, starting and stopping of pumps, or directional changes caused by pipe fittings.
The intensity of water hammer effects will depend upon the rate of change in the velocity or momentum.
This publication discusses the causes of water hammer and the importance of proper system design and management to ensure a cost effective, long-lasting irrigation system.
Causes of Water Hammer
 Water is slightly compressible.
Because of this characteristic, shock waves can occur and propagate through confined
 water systems.
Shock waves in pipe systems can result from sudden changes in flow such as:
 rapid opening of closing of control valves;
 starting and stopping of pumps;
 the recombination of water after water column separation; or
 the rapid exhaustion of all air from the system
 When sudden changes in flow occur, the energy associated with the flowing water is suddenly transformed into pressure at that location.
This excess pressure is known as surge pressure and is greater with large changes in velocity.
Characteristics of the pipe such as the materials used in construction, the wall thickness, and the temperature of the pipe all affect the elastic properties of the pipe and how it will respond to surge pressures.
The ratio of the diameter of the pipe to the wall thickness  is referred to as the dimension ratio.
All polyvinyl chloride  and some polyethylene  pipe use the outside diameter  of the pipe in this ratio.
Some pipe sizing is based on inside diameter  and uses that diameter in the DR computation.
Certain DR values have been designated to be standards and are referred to as Standard Dimension Ratios.
The DR relationship can be determined when pipe thickness  and either outside diameter  or inside diameter  are known.
For outside diameter based pipe , the DR is calculated as
 DR OD ID + 2 Figure 1.
Dimension ratio for ouside diameter based pipe.
For inside diameter based pipe, the DR is calculated as Sometimes pipe is referred to as Class X pipe where X represents the pressure rating of the pipe in pounds per square inch.
For example, Class 160 PVC pipe is pressure rated for 160 psi.
Table 1 shows the pressure ratings associated with certain SDR values for nonthreaded PVC  and PE 3408 pipe at a water temperature of 73.4F.
ID DR Figure 2.
Dimension ratio for inside diameter based pipe.
Temperature Effects On Plastic Pipe Properties
 Water and environmental temperatures will affect the properties of the pipe material.
As temperatures increase the pipe material will become more ductile.
Therefore the pressure ratings shown in Table 1 must be derated  with a service factor for higher temperature conditions to provide for safe operation.
Table 2 shows the service factors for PVC and PE pipes for temperatures higher than 73.4F.
The pressure rating of the pipe from Table 1 should be multiplied by the appropriate service factor from Table 2 to obtain the temperature compensated pressure rating of the pipe.
For example SDR 26.0 PVC pipe has a 160 psi pressure rating at 73.4F.
When the water temperature is increased to 80F , the pressure rating decreases to [ = ] 128 psi.
Most groundwater sources in Florida will have temperatures of 73.4F or lower.
However, surface water sources  can have higher temperatures.
Also, water traveling through long laterals will be heated by solar radiation.
Therefore, pipe temperatures should be estimated and designs should consider the higher temperatures that will be encountered.
Surge pressures associated with changes in flow or velocity can be calculated.
The change in velocity must be known as well as properties of the conduit or piping system.
The equation for calculating surge pressure is discussed in detail in the Appendix and can be applied to many types of pipes.
Because PVC pipe is perhaps the most common construction material used in irrigation systems, it will be discussed in more detail in this bulletin.
Table 3 shows the maximum or critical surge pressures associated with a sudden change in velocity for 400,000 psi modulus of elasticity   and 100,000 psi modulus of elasticity  pipe material.
Figure 3 displays the surge pressures associated with an abrupt valve closure  for two of the PVC pipe classes shown in Table 3.
These pressure levels represent the additional pressure imposed on the system above the normal operating pressure of the system.
For example, consider an irrigation system which has a normal operating pressure of 75 psi, and has a water velocity of 7 feet per second in a Class 160  PVC conduit.
Figure 1 shows that a surge pressure of about 100 psi can result from a sudden valve closure with an initial velocity of 7 feet per second.
This would bring the total pressure in the system to about 175 psi, exceeding the 160 psi pressure rating of the pipe.
Figure 3.
Surge pressure levels associated with a valve closure for different levels of pipeline water velocity..
Velocity  in a pipeline depends on the volume flow rate of water through the pipeline  and the cross-sectional area of flow.
This basic relationship can be expressed as: Equations, 3a, 3b and 3c all use flow in gallons per minute , but equation 3a uses area in square feet, 3b uses area in square inches, and 3c uses inside pipe diameter in inches.
The inside diameter of the pipe should always be used to determine the area of flow.
Table 4 presents inside diameters and cross-sectional areas of PE pipe.
Table 5 presents the outside diameters of PVC pipes and inside cross-sectional areas which correspond to pipes of different SDR values.
Flow   449 Area  Flow 
  V 3.1 Area  Flow 
  V 2.45 * ID 2 
 Figure 4.
The basic relationship between velocity and flow rate.
The cross-sectional areas from either Table 4 or Table 5 can be used with the pipe flow rate in gpm with equation 2b to determine the average flow velocity in the pipe.
The flow velocity can then be used with Table 3 or Figure 1 to determine the surge pressure associated with a sudden valve closure or other flow restricting action.
Design and Management Considerations
 This section discusses design and management criteria to be followed to minimize the effects of water hammer or surge pressures on the irrigation system.
In the design process, pipe should be selected with a pressure rating equal to or greater than the combination of operating plus surge pressures.
Be certain to consider temperature effects on the pressure rating of the pipe.
If the surge pressures are not known, Table 6 provides recommendations for maximum working pressures for nonthreaded PVC  and PE 3408 pipe.
Table 6 should be used with caution, and only when other data are not available.
It is always better to calculate surge pressures for the specific conditions of the site.
To help minimize surge pressures the maximum velocity of water in the pipeline should be limited.
General
 recommendations are to limit maximum operating velocities to 5 per sec.
In no case should the velocity exceed 10 per sec.
Entrapped air in a pipeline can cause problems.
Air is very compressible and can compress and expand in the pipeline, resulting in varying velocity conditions, and, thus, significant pressure variations.
Water-column separation can also produce significant surge pressures due to the high velocities encountered when the column rejoins.
Problems associated with air entrapment can be minimized by preventing air from accumulating in the system.
This can be accomplished by using air-relief valves positioned at the high points of the piping system.
In areas of relatively flat terrain these should also be used in the vicinity of the pump discharge, near the middle of the line, and at the downstream end of the line.
Additional design considerations include:
 surge arrestors  or automatic pressure reducing valves at flow regulators and at the pump discharge;
 flow controllers used to minimize the rate of filling and to reduce start-up surge in filled lines;
 in cycling systems, design pipelines, if possible, to keep out all air, and then to restart with a filled system.
Water hammer cannot be completely eliminated in an economical design, but, by taking precautions during management and operation, the effects can be minimized.
Start-up is critical, especially when pipe lines are empty.
Empty lines should be filled as slowly as possible to allow entrapped air to escape.
In addition the following cautions should be observed:
 Never completely close the gate valve on the discharge side of a deep-well turbine.
This prevents excessive shut-off head from developing.
Open all manual valves leading to the zones to be irrigated except at the pump discharge.
The pump discharge valve should be opened slowly to allow slow filling of the pipe line.
Caution should be observed when filling is interrupted and restarted because a quick surge may develop during the restart which could slam into a stationary or slow moving body of water.
This situation could result in damaging water hammer pressures, especially if air becomes entrapped between the water
 fronts.
Therefore, follow the same precautions on restart as during initial starting of the system.
Make sure that all air has been discharged from the system before operating the system at full throttle.
Close all manual valves slowly.
No valve should ever be closed in less than 10 seconds; 30 seconds or more is preferable.
Use the same precautions in stopping the irrigation system as used in start-up and general operation.
This publication discussed the causes and effects of water hammer in irrigation systems.
Surge pressures experienced from velocity changes were discussed and presented for PVC and PE pipe materials.
Guidelines for safe design include selection of the proper size and class of pipe to maintain safe velocities and to have a material which can withstand both operating and surge pressures expected from the system.
Components such as air relief and surge arrestors can be positioned at strategic positions in the pipeline to minimize the resultant effects of water hammer in the irrigation system.
Additional discussion focused on management considerations to help ensure safe operation.
HDR Engineering gave an update on the progress of replacing Tunnels 1 and 2 in Wyoming on the Goshen/Gering-Ft Laramie Irrigation Districts mainline canal.
Tunnel 2 collapsed in 2019, causing a canal to breach.
Irrigation water was curtailed for 44 days and affected 107,000 acres of cropland in the North Platte River Valley.
Plans are still proceeding with permitting, design and other logistical requirements.
If all goes well, construction/replacement of the tunnels will commence in the fall of 2024 after the irrigation season, scheduled to conclude by the 2025 spring irrigation season.
WATER POLICIES THAT STOOD THE TEST OF TIME: A MATTER OF PERSPECTIVE
 This paper examines the effectiveness of several water policies in Kansas: 1) limiting appropriation of water to safe yield quantities ; 2) monitoring water use through metering points of diversion and requiring annual water use reporting; and 3) providing the opportunity to manage groundwater through Intensive Groundwater Use Control Areas, in which corrective controls can be tailored to address specific problems.
These policies were selected on the basis of their profound effects on water resource management; their adoption more than 10 years ago, which provides a suitable period of record to judge their performance; and the ability to assess their performance in quantifiable ways.
The policies were evaluated and deemed to have continued relevancy, a record of accomplishing their objectives, and public acceptance.
The importance of water for all human endeavors and the natural world cannot be overstated.
Since there are competing demands for finite water supplies, government policies are necessary to ensure fair allocation and protection of water resources.
Three principal water policies of the state of Kansas are examined in this paper, with the objective being to determine if the policies have "stood the test of time", that is, if they have achieved their purposes and continue to be useful.
The following sections describe the methodology, analysis, and conclusions of this evaluation.
Disclaimer: The opinions and statements expressed in this paper are the personal opinions and statements of the author.
Although informed by the author's work for the Kansas Department of Agriculture's Division of Water
 Resources, the opinions and statements expressed herein do not necessarily reflect the agency's official policy or position on these issues.
Merriam-Webster's Online Dictionary contains several definitions for the word "policy"; the meanings that appear to be most relevant to this discussion are:
 2 a: a definite course or method of action selected from among alternatives and in light of given conditions to guide and determine present and future decisions;
 b: a high-level overall plan embracing the general goals and acceptable procedures especially of a governmental body
 These definitions reflect the purposeful nature of policies.
Water policies, then, are deliberate courses of action adopted by entities to achieve objectives involving water.
Entities establishing water policies range from the United Nations to sovereign nations, states, local governments, corporations, other organizations, and individuals.
An example of federal water policy is EPA drinking water standards.
An example of individual water policy is the decision to install low-flow fixtures in one's home.
Water is a very broad subject.
There are many different facets to consider, including supply and demands, quality, ecosystems, infrastructure, various uses, and so on.
Due to the author's particular role in state government, this paper focuses on Kansas' water resources policies, that is, policies guiding the management of surface water and groundwater.
There is some debate over what constitutes an official policy, or when a policy must be followed.
For example, some argue that policies set by an appointed body such as the Kansas Water Authority  do not have the same weight as statutes passed by the state Legislature, and as such are not mandatory.
Others point to the makeup of KWA which consists of voting members appointed by the Governor and Legislative leadership and that its recommendations may effectively become law if/when the Legislature approves the State Water Plan budget, which is designed to implement KWA's policies.
This paper does not attempt to settle the aforementioned debate.
Instead, it will focus on water policies implemented through state statutes, regulations, or
 agency decisions under the statutes and regulations.
Most people seem to accept these as enforceable water resources policy.
2
 Several criteria were used to select water resources policies for an examination as to whether they have "stood the test of time":
 First, the policies must have significant implications.
It would not be worthwhile to spend time on trivial considerations.
Second, the policies must have been in place for at least 10 years.
Ten years may be the minimum span of time necessary to assess a water resource policy given the multi-year time frame ordinarily required for implementation and some noticeable response, and considering the normal variability in precipitation.
Third, the policies must be measureable in some objective manner.
Although it is beyond the scope of this paper to comprehensively quantify the effects of water policies, it is the author's intent to examine policies that have quantifiable effects.
The Kansas Water Appropriation Act  and the Groundwater Management District Act  would seem to present the best opportunities to identify policies for this examination since as state laws governing water resources they unquestionably represent state water policy.
Some of the policies established in these statutes  are listed below:
 2 Article X in the Bill of Rights effectively grants states authority over management of water resources.
According to the Tenth Amendment, since the U.S.
Constitution does not ascribe that power to the federal government nor specifically withhold it from the states, it is delegated to the states.
"The powers not delegated to the United States by the Constitution, nor prohibited by it to the states, are reserved to the states respectively, or to the people".
Intensive Groundwater Use Control Areas 
 Some policies established in other state laws, which seem to have objectives related to the above-listed policies, include the following:
 Grants for irrigation efficiency improvements
 Incentive payments for water right retirements
 These lists are not intended to be exhaustive, and are just a selection of some of the more obvious choices for policies to examine.
Of the policies listed above, three were selected for further examination in this paper, for the reasons noted below:
 1.
Safe yield This is a fundamental principle mentioned once in the Kansas Water Appropriation Act and nearly 50 times in the associated rules and regulations.
4 "Safe yield' means the long-term sustainable yield of the source of supply, including hydraulically connected surface water or groundwater.
,5 For example, safe yield of an aquifer is typically regarded as the annual average recharge of the aquifer by the portion of precipitation that percolates into the ground and replenishes the aquifer.
It has been a standard criterion in the issuance or dismissal of water appropriation applications since 1993, with some exceptions.
6 Some "Administrative Policies" which preceded the regulations required the application of safe yield principles in certain watersheds as early as 1983.
7 The policy of limiting appropriations to safe yield obviously has had profound effects on water resources in Kansas.
One can estimate the quantitative and qualitative effects of this policy through analysis of water appropriation trends before and after the policy was adopted.
One can also judge the effects of this policy by considering locations where a safe yield policy was not adopted in as timely a manner.
2.
Metering/water use reporting Measuring the amount of water used and reporting the amount of water used are closely related, and are therefore considered together in this paper.
Both requirements are addressed in the
 3 K.S.A.
82a-711: "In ascertaining whether a proposed use will prejudicially and unreasonably affect the public interest, the chief engineer shall take into consideration  the area, safe yield and recharge rate of the appropriate water supply." 4 K.A.R.
5-1-1 et seq.
5 K.A.R.
5-1-1.
6 Exceptions to safe yield include appropriations approved prior to adoption of safe yield policy; appropriations in some Groundwater Management Districts which use an allowable depletion approach; as well as domestic use, some temporary permits, and some term permits.
7 Policies and Procedures of the Chief Engineer, Kansas Department of Agriculture, Division of Water Resources.
Kansas Water Appropriation Act8 and the associated rules and regulations.
These requirements date from 1957  and 1988 , respectively.
Without these tools, it would be much more difficult to effectively regulate and manage Kansas' water resources.
As a result of its metering and water use reporting policy, Kansas is widely regarded as having very good water use data on which to base regulatory decisions.
One can estimate the quantitative and qualitative outcomes of this policy by considering the impacts on water use when meters are installed, as well as the amount of water involved in enforcement activities that rely on data obtained through metering and water use reporting.
One can also judge the effects of this policy by considering other states that do not have equivalent policies.
3.
IGUCAs In recent years, the chief engineer's authority to establish Intensive Groundwater Use Control Areas has come under increased scrutiny by stakeholders, agencies, and the state legislature.
This apparently resulted from dissatisfaction with the Pawnee Valley IGUCA proceedings of 2007, although it may stem from a more general opposition to increased regulation of groundwater.
In any case, the IGUCA authorities9.
which were added to the Groundwater Management Act in 1978, significantly increased the options for managing groundwater resources in Kansas.
IGUCAs provide flexibility and the ability to tailor solutions to a wide variety of groundwater resource problems.
One can estimate the quantitative and qualitative outcomes of this policy by considering the number of water rights curtailed by IGUCAs as compared with the number that would have been curtailed to achieve the same objectives  if first in time, first in right administration under the Kansas Water Appropriation Act had been the only option.
One can also judge the effects of this policy by considering other states that do not have equivalent policies.
Several criteria were used to evaluate whether the selected water resources policies have "stood the test of time":
 First, is the policy still relevant and still applied?
It would not be worthwhile to examine antiquated laws which are no longer enforced.
Second, does the policy accomplish its objectives?
This presupposes a clear intent which, if not explicitly stated, should be readily apparent.
9 K.S.A.
82a-1036 through 1040.
Third, do a majority of people agree with the policy?
This may be difficult to assess quantitatively without the benefit of a proper survey, but one can at least gauge public opinion based on comments from stakeholders and legislators.
An evaluation of the three selected policies is provided in the next section of this paper.
The following analysis of the three selected policies applies the metrics noted above under "Basis for Selection" and the criteria listed above under "Basis for Evaluation":
 1.
Safe yield As illustrated in Figure 1 below, the number of water rights and the cumulative authorized quantity of water rights in Kansas grew exponentially from the mid-1940s through about 1980.
From about 1980 through present the growth was linear, at a significantly slower rate.
There are several main reasons for the shape of the graph in Figure 1.
Water rights that were developed prior to 1945, when the Kansas Water Appropriation Act was enacted, became "vested rights" with a priority date of June 28, 1945.
The increasing use of irrigation systems during the 1950s-1970s fueled much of the growth in water use, as did population growth and industry to lesser extents.
In 1978, the Kansas Water Appropriation Act was amended making it mandatory for individuals to apply for water appropriation permits, whereas previously it had been optional.
And in the early 1980s, the chief engineer began closing some areas of the state to new appropriation and establishing safe yield requirements for areas still open to appropriation.
Since the decelerated growth of the volume of appropriated water in the 1980s was due both to closing areas to new appropriations and limiting appropriations to safe yield quantities, it is difficult to quantify the amount of deceleration attributable to safe yield at least, based solely on the information in Figure 1.
Based on the fact that most "closed" areas were locations where the majority of water right development and water use occurred , it may be that closing areas to new appropriations had the greater effect on reducing the rate of water appropriation.
However, in a way the closing of these areas was akin to implementing a safe-yield policy, since either approach is grounded in the recognition of a finite resource and would have the effect of eliminating most additional appropriations of water in fully developed areas.
From Figure 1, it
 appears that the cumulative total authorized quantity of water rights would have been at least double its present value if the growth rate of the mid-tolate 1970s were linearly extrapolated, that is, if the safe yield/closure policy had not been applied when it was.
Figure 1: Historical Development of Water Rights in Kansas
 
 Obviously, there is a finite amount of renewable water supply in Kansas.
If safe yield  had not been implemented, and had water appropriation continued to grow at 1970s rates, it is probable that groundwater declines and streamflow depletions would have accelerated and the adverse impacts on vested/senior water rights and the public interest would be substantially greater than they are today.
A striking example of what could have happened in Kansas is the growth of wells in Nebraska's Republican River Basin long after Kansas and Colorado closed areas to new appropriation and established safe yield requirements.
As shown in Figure 2 below, approximately 4,000 additional wells  were installed in Nebraska's portion of the basin after 1980, whereas the number of wells leveled out in the other states' portions of the basin.
A consequence of this continued development of the water resource is that Nebraska has been unable or
 unwilling to comply with the Republican River Compact, which may end up costing the state tens of millions of dollars in litigation, restitution and penalties as well as significant challenges in curtailing groundwater use to achieve compact compliance in the future.
Figure 2: Historical Development of Wells in the Republican River Basin
 
 Clearly, Kansas' safe yield policy and its closely-related closure of overappropriated areas have had profound effects on the management of water resources.
This policy is still relevant and applied today.
The intent of the policy, based on the statutory and regulatory language, is presumed to be preventing over-appropriation of water resources.
Stated another way, in the classical mass balance equation inflows minus outflows equals change in storage; the intent of the safe yield policy is to have long-term average inflows equal outflows  so that the long-term average change in storage is negligible.
Based on streamflow records and groundwater measurements exhibiting stable water supplies, it appears that the safe-yield policy has been successful in accomplishing this objective in areas of the state where it was applied before over-appropriation occurred.
In other areas that were closed to new appropriation of water, the policy has not reversed the trend of groundwater declines or streamflow depletions but has apparently kept
 the rate of declines from accelerating further and in some cases has led to decreasing rates of decline.
Figure 3 below shows an example of this.
Rates of groundwater decline accelerated dramatically during the period of heavy development during the late 1960s and 1970s, and then became more gradual in the 1980s and subsequent decades.
The well hydrograph illustrated in Figure 3 is in a high-decline area of Sheridan County.
Figure 3: Groundwater Level Changes in a High Plains Aquifer Well 
 
 It should be noted that while this well exhibits the expected trends as previously described, hydrographs from other wells in the same area show different trends over time from a uniform rate of decline over the period of record to increasing rates of decline through present or in some cases increasing water levels.
This underscores an important fact that the Ogallala-High Plains aquifer is not homogeneous local conditions can vary considerably.
The data presented above suggest that the safe yield/closure policy has been effective in accomplishing its objectives of balancing supply and demand, or avoiding increases in imbalances that may have prefigured the policy in some areas of the state.
Based on anecdotal evidence many stakeholders, organizations, officials and legislators agree with the safe yield/closure policy as evidenced in comments at meetings and hearings and the lack of any noticeable effort to repeal the policy.
It is generally considered a fair and prudent policy for stewardship of the resource and protection of existing water rights.
However, there are examples of some discontent with the policy.
For instance, Big Bend Groundwater Management District No.
5 has indicated that it wants to review whether some areas of the district could be opened to new appropriations.
A hydrologic model is being developed that will help answer this question.
This may not reflect disagreement with the safe yield policy per se, so much as a desire to revisit previous decisions applying the policy using more comprehensive data and analytical tools available today.
Another example involves water appropriation applications filed before certain townships in Southwest Kansas Groundwater Management District No.
3 were closed to new appropriation.
In a number of cases the chief engineer has ruled that the applications cannot be approved on the basis of allowable appropriation specified in the regulations at the time of filing, or that the additional appropriations would impair existing water rights.
These considerations are corollaries to safe yield.
Some of the applicants appealed these rulings, signifying that at some level they disagree with the safe yield policy although ostensibly the appeal may be based on questioning the specific facts and analyses.
2.
Metering/water use reporting Studies have confirmed an intuitive outcome the accuracy of water use reporting increases when meters are installed.
This came about because the requirement to report water use in many cases pre-dated the requirement to install meters, although the authority to require meters pre-dated the requirement for water use reporting.
Typically, meter requirements have been imposed for various areas through orders of the chief engineer or through permit conditions.
In fact, this process is still ongoing today.
Most of the water rights in the western half of Kansas are fully metered, and meter requirements for the eastern half continue to be issued.
Since the majority of water use in Kansas  is for irrigation, and the majority of irrigation occurs in the western half of Kansas, most water use in Kansas is already metered.
In addition, most of the large municipal and industrial uses in eastern Kansas are already metered for other reasons even if the chief engineer has not ordered it.
The most common method for estimating water use without a meter is to track the hours of pumping and multiply it by the pumping rate.
However,
 the hours and rate method was shown to significantly underestimate or overestimate the actual amount of water pumped for irrigation, in some cases by as much as 30%.
10
 Meters and water use reports are essential for accurate enforcement of water rights, management of the state's water resources, interstate compact compliance, and other purposes.
In 2008, the Kansas Department of Agriculture performed thousands of compliance inspections for a number of reasons including to determine if authorized points of diversion were acceptably metered and to ascertain whether water use was within the authorized quantities.
A total of 65 civil penalty orders were issued for over-pumping and meter violations.
As part of the civil penalties, these water rights were assessed reductions in their 2009 authorized use totaling nearly 2,000 acre-feet.
These penalties will be enforceable in part because of the meters installed on these points of diversion.
A 2008 preliminary analysis indicated that it would cost approximately $376,000 per year to monitor consumptive use of water on irrigated farmland in Kansas using Landsat thermal imagery.
11 Based on a 2005 cost estimate, the Kansas Department of Agriculture's water use monitoring program which relies on meters or estimation methods, annual water use reports, compliance inspections and enforcement costs the state about $170,000 per year, less than half the cost of the alternative method.
Not only is Kansas' water metering/water use reporting policy cost effective, it is widely recognized as a model for other states.
Time and again Kansas water resources officials have heard from their counterparts in other states about their desire to have a water use monitoring program as efficient and effective as Kansas'.
The author has heard similar statements from U.S.
Geological Survey staff, which compiles water use data from all 50 states in a national report.
12 They have to estimate water use in states that do not collect this data as Kansas does, and even in states that collect water use data it is often not as comprehensive and useful as Kansas'.
In 2007, the Western States Water Council asked member states  to complete a survey of
 their water supplies and demands.
Several states were unable to provide meaningful responses because they do not collect this type of information.
Kansas was able to provide detailed information in response to the survey.
Figure 4 below illustrates the type of data available to the state for water resource management as a result of metering and water use reporting.
Figure 4: Reported Water Use by County and Type of Use, 2006
 
 Attached in Appendix A is Kansas' response to a 2008 survey from the Western States Water Council on methods and costs to monitor water use from irrigation wells.
This provides additional details on Kansas' water use monitoring program and puts in perspective the magnitude and importance of the data collected.
Also, the data provided in the survey response may be of interest to attendees at this conference.
Besides the benefits to state and federal agencies charged with managing water resources, the Kansas policy on monitoring water use also directly benefits water users by enabling them to actively manage their own water use and avoid violations.
In some cases, irrigators and other users have installed sophisticated equipment to remotely monitor their use and make adjustments in real-time from their office computers in response to
 changing weather conditions, changing demands, and coordination of multiple irrigation systems and water rights.
Kansas' water use monitoring policy remains a viable and necessary practice that accomplishes the state's objectives including water right compliance and enforcement, water resource management, interstate compact compliance, and other purposes.
While some individual water right holders or groups might object to the costs of metering and water use reporting, by and large there is round support for this policy due to the recognition that without this data the state's efforts to manage our precious water resources, including administration of the Kansas Water Appropriation Act, would be severely impeded.
3.
IGUCAs Eight intensive groundwater use control areas  have been established in Kansas and are still in effect.
These are shown on Figure 5 below.
Figure 5: Intensive Groundwater Use Control Areas in Kansas
 
 These IGUCAs were established for a number of reasons including groundwater declines, deteriorating groundwater quality, and other public interest issues.
IGUCAs are designed to address a variety of groundwater problems with customized solutions.
An example of a specific solution is the City of Hays IGUCA which requires city residents with domestic water wells to comply with the city's summer lawn watering ordinance in order to avoid waste of water.
Two examples vividly illustrate the benefits of IGUCAs: the Walnut Creek IGUCA in Kansas, and by contrast a case in Colorado, which lacks
 IGUCA-type authority and flexibility, where the curtailment of irrigation under priority administration of water rights over a large area had devastating effects.
One of the main impetuses for initiation of the Walnut Creek IGUCA was the possibility of a call for administration of water rights by the Kansas Department of Wildlife and Parks in the event their early water right for Cheyenne Bottoms would become impaired.
Figure 6 below illustrates this scenario.
In concept, 78 groundwater rights  senior to the Cheyenne Bottoms surface water right would not be curtailed; conversely, 389 groundwater rights  could be curtailed in this scenario with presumably disastrous effects on the local economy and livelihood of the agricultural community.
Among the principle findings in the Walnut Creek IGUCA hearing was quantification of the long-term sustainable yield of the basin as 22,700 acre-feet of groundwater.
Rights developed before the date when 22,700 acre-feet of water was appropriated in the basin were considered "senior rights" while those that were developed after that date were defined to be "junior rights".
The corrective controls apportioned 22,700 acre-feet among the existing groundwater rights: vested rights were allotted their full authorized quantities; senior rights were allotted reasonable use ; and junior rights were allotted 44% of the senior right allocations.
Five year allocations were developed so that junior irrigators could meet reasonable needs at least two or three out of five years.
While this approach resulted in partial curtailment of many water rights in the basin, remarkably it allowed all water rights to continue operating.
Figure 7 below illustrates this scenario.
Figure 6: Active Water Rights Under Hypothetical Water Right Administration by Priority
 
 Figure 7: Active Water Rights Under IGUCA Corrective Control Provisions
 
 Over the years since the Walnut Creek IGUCA was established, groundwater levels have risen with an overall trend of about one foot per three years.
This represents a return to a hydrologic system with a reasonable balance between recharge and withdrawals.
Water users can rely on the long-term sustainability of the aquifer because rising groundwater levels in wetter years will offset declining water levels in drier years.
Surface water users dependent upon discharge from the aquifer to the stream again have a relatively reliable source from which to exercise their rights.
Figure 8 below contrasts the Walnut Creek basin with two neighboring basins that continue to exhibit long-term declining groundwater trends.
Figure 8: Groundwater Trends in Three Basins
 
 A recent situation in Colorado underscores the value of IGUCAs.
In May 2006, Colorado ordered more than 400 irrigation wells shut down to protect senior water rights on the South Platte River.
This affected 200 farms that had already planted crops.
Farmers estimated their potential losses in the hundreds of thousands of dollars.
Also shut down were two drinking water wells for a trailer park with about 300 residents.
13 A
 newspaper article included in Appendix B of this paper provides more details about this curtailment of water rights and its adverse effects.
In 2008, the Kansas Department of Agriculture conducted an informal survey of western states to determine which ones have authorities for groundwater management tools similar to IGUCAs.
Of the 18 western states , 10 have authorities for groundwater management options similar to IGUCAs in varying degrees.
Colorado is one of the 10 states that have authority for special management of groundwater areas, called Designated Ground Water Basins.
However, it appears that Colorado's rules for Designated Ground Water Basins focus on aspects such as allowable appropriation, metering and operating plans, and apparently do not provide the flexibility for creative solutions such as IGUCAs in Kansas.
14 Hence, Colorado seems to have no other option than administration  of junior water rights in times of shortage.
Kansas' IGUCA policy continues to serve as a viable tool for implementing groundwater management strategies tailored to address specific problems.
As described above for one of the eight existing IGUCAs, this policy has been exceptionally effective, particularly when contrasted with the severe water use curtailment in states such as Colorado which do not have the IGUCA alternative.
IGUCAs remain timely because they can be modified over time as necessary to adjust for changing conditions or better data.
In fact, five of the eight IGUCAs have been amended at least once.
The Walnut Creek IGUCA has been amended three times since it was initially established in 1992.
The most recent IGUCA proceeding was in 2007, related to possible expansion of the Pawnee Valley IGUCA.
During the hearing, several parties expressed opposition to expanding the IGUCA.
Some organizations and legislators also expressed opposition to the IGUCA expansion, for various reasons.
However, during the 2007 IGUCA proceedings and in the legislative hearings and stakeholder meetings that followed it, there has been widespread support by virtually all groups and individuals involved that the IGUCA policy is fundamentally sound and must be preserved so that creative solutions can be applied in areas where strict administration of
 water rights by priority would have more severe adverse impacts on the community and economy.
The above analysis indicates a positive finding that the three policies in question have indeed stood the test of time based on their continued effectiveness and public acceptance.
This naturally leads to the follow-up question: Are there examples of water policies which have not stood the test of time?
The answer is yes.
Several examples are noted below for consideration:
 Not limiting appropriations, etc: This is the opposite of the safe yield policy including closure of fully-appropriated or over-appropriated areas.
Since evidence presented in this paper  suggests that the safe-yield/closure policy is a prudent action for stewardship of resources and protection of water rights, it stands to reason that the opposite policy is antiquated and ineffective.
The same rationale would suggest that policies to not monitor water use or not provide appropriate groundwater management alternatives would be counter-productive.
On the other hand, there are always exceptions to the rule.
There may be instances when it makes sense not to limit appropriations, monitor water use, or have alternatives to first-in-time/first-in-right administration.
Irrigation efficiency improvements as a means to reduce water use: Until a couple of years ago, the state of Kansas had a cost-share program to promote irrigation efficiency improvements.
A main purpose of the program was to reduce water use in areas with declining water resources.
However, over time it became apparent that improving the efficiency of irrigation did not appreciably conserve water, but rather improved crop yields.
While efficiency is important and to be encouraged, the state 15 decided to discontinue this type of cost-share program since it was not achieving a reduction in water use.
Non-conjunctive management of water resources: Kansas has recognized the interconnected, interdependent nature of groundwater and surface water since at least 1945 when the Kansas Water Appropriation Act was passed, regulating both sources in a coordinated manner.
However, to this day there are still states that do not routinely manage groundwater
 15 Effects of Irrigation Practices on Water Use in the Groundwater Management Districts Within the Kansas High Plains, 1991-2003; Scientific Investigations Report 2006-5069; U.S.
Geological Survey.
"The best estimator of irrigation water use incorporated total acres irrigated and annual average or March-October regional precipitation.
A conclusion that can be drawn from the trend analyses described in this report is that, although irrigation water use for all GMDs showed no statistically significant trend, an apparent increased efficiency of center pivots irrigation systems with drop nozzles has allowed more water-intensive crops to be grown on more irrigated acres." 
 and surface water conjunctively, that is, together.
Nebraska is a notable example of non-conjunctive management the state of Nebraska is responsible for management of surface water resources while Natural Resource Districts are supposed to manage groundwater.
In practice, it appears that the two have largely operated independently.
One of the most dramatic outcomes of this disconnect is Nebraska's current noncompliance with the Republican River Compact.
Their violations stem from overuse of groundwater which in turn led to streamflow depletions.
The outcome of this has not been determined, but the matter is in nonbinding arbitration and if that fails to resolve the violations could return to the U.S.
Supreme Court.
The consequences of Nebraska's dichotomous regulation of groundwater and surface water could be severe sanctions such as monetary reparations and shutting down hundreds or thousands of wells.
The objective of this exercise was to evaluate whether some of the more prominent water resource policies in Kansas have "stood the test of time" as signified by their continued relevance, effectiveness, and public acceptance.
By these measures, based on the analyses herein, the author concludes that the three policies listed below have indeed met this standard:
 Limiting appropriation of water to safe yield quantities, and closure of fullyappropriated or over-appropriated areas
 Monitoring water use through metering and water use reporting
 Establishing intensive groundwater use control areas where necessary to implement creative solutions to groundwater problems
 By observation, some of the key attributes of these time-tested water policies include:
 Consistent with basic laws of nature, e.g., conservation of mass
 Reasonable, in the public interest
 Provides essential data for resource management
 Provides flexibility rather than a one-size-fits-all approach
 A well-known saying is, "Laws are like sausages it is better not to see them being made", referring to the often messy process.
Nevertheless, public policy makers usually try to make sure that laws are designed for long-term applicability and effectiveness.
Reflecting on laws that have achieved time-tested status is one way to identify characteristics and principles which can be applied in crafting new policies for achieving present and future objectives.
Kansas' Response to a 2008 Survey on Irrigation
 Western States Water Council
 Survey on the Methods and Costs to Monitor Pumping from Irrigation Wells
 2.
Do you agree with the numbers in table 1, below, for your state?
No.
Based on information from annual water use reports compiled in the Water Rights Information System  maintained by the Kansas Department of Agriculture's Division of Water Resources, as of March 20, 2008 the requested quantities are as follows:
 1995 Total water use : 3,946 1995 Irrigation water use : 3,364 1995 Irrigation as percent of total water use: 85 2003 Number of irrigation wells: 27,770 2003 Total irrigated acreage: 3,151,754 
 3.
Is there a program in your state to monitor pumpage from irrigation wells?
Yes
 i.
How many irrigators participate in the program?
6,511 
 ii.
How much does the average irrigator spend on the program?
Cost of a postage stamp per year
 iii.
How much does the state spend on the program?
$170,000 per year 
 iv.
How many wells are monitored by flow meters?
21,054 
 1.
what is the average cost of a flow meter?
$1,000
 2.
what is the average lifespan of a flow meter?
8 years 
 3.
what is the cost to install a flow meter?
$300 to $2,000 
 4.
what is the cost to calibrate a flow meter?
$400 average
 V.
How many wells are monitored by power consumption?
Data not available; anecdotally relatively few use this method
 vi.
How many wells are monitored by some other method?
5,887 
 vii.
How long does it take before a year's data are analyzed?
1 to 2 years
 viii.
How does the state use the pumpage data?
A partial list follows:
 Safe yield analyses in processing water appropriation applications
 Certification of water rights
 Compliance & enforcement of water rights
 Administration of water right flex accounts and water banking
 National water use reporting
 ix.
What are the three things you would most like to change about the way pumpage data are gathered, reported, and processed, without regard to the cost or practicality of making the changes?
Statewide metering of all non-domestic points of diversion by 2015 
 Online water use reporting ; eventually real-time reporting through data loggers and telemetry 
 Electronic reporting in the future is anticipated to reduce dependence on
 manual data entry and allow improved qualitycontrol
 b.
If no, would such a program be useful?
4.
Can you provide a paragraph or two summarizing the program?
Installation of a water flowmeter or other suitable water measuring device
 Water flowmeter installation specifications
 The Kansas Department of Agriculture's Division of Water Resources and several groundwater management districts share responsibility for compliance & enforcement of these requirements.
Meters are inspected following installation, tested for accuracy, and readings are checked for water right compliance and other reasons.
Total Water	Irrigation	Irrigation	Number	Total
 Use	Water Use	as Percent	of	Irrigated
 State	(million	million	of	Irrigation	Acreage
 gal/day)	1995	gal/day	19952	Total Water	Use	20032	Wells	2003	3
 Alaska	25	0.3	1	57	2,252
 Arizona	3,830	3,180	83	5,149	836,587
 California	25,200	23,500	93	67,637	8,471,936
 Colorado	5,230	4,910	94	11,793	2,562,329
 Idaho	4,340	4,310	99	6,924	3,126,857
 Kansas	3,620	3,220	89	19,526	2,543,950
 Montana	1,960	1,820	93	1,810	2,131,955
 Nebraska	7,020	6,740	96	71,506	7,516,171
 Nevada	1,340	1,060	79	1,986	639,310
 New Mexico	1,980	1,680	85	8,430	769,787
 Dakota	105	181	58	1,734	207,772
 Oklahoma	716	401	56	4,540	508,842
 Oregon	3,210	3,070	96	7,855	1,731,660
 Dakota	249	175	70	1,872	390,406
 Texas	10,500	8,140	77	63,602	4,947,745
 Utah	2,200	1,930	88	2,632	1,082,213
 Washington	3,080	2,800	91	5,626	1,806,782
 Wyoming	2,800	2,660	95	985	1,415,037
 TOTAL	77,405	69,777.03	283,664	40,691,591
 Table 1.
Comparison of total water use and irrigation water use for the 18 member states of the Western States Water Council in 1995 and the number of irrigation wells in 2003.
Both dates are the most recent available.
Article about Colorado Curtailing Water Use
 Farmers sweat lack of water
 Growers mop brows after state edict to shut down wells
 Jerd Smith, Rocky Mountain News Published May 10, 2006 at midnight
 The state ordered more than 400 powerful irrigation wells shut down this week to protect the South Platte River, triggering a crisis for about 200 farms from Brighton to Fort Morgan.
"It's the toughest decision I've ever had to make," said State Engineer Hal Simpson, Colorado's top water regulator.
Farmers who've already planted this year say they stand to lose hundreds of thousands of dollars as a result of Simpson's ruling.
The decree may mean bankruptcy for some.
But others, such as La Salle potato grower Harry Strohauer, are gearing up for battle.
"I'm going to fight like crazy," Strohauer said.
Strohauer is losing the use of 14 wells that normally irrigate 1,100 acres of potatoes and onions.
He's invested $700,000 in seed and fertilizer so far this spring.
"To get hit with this ruling after we've all planted is ludicrous," Strohauer said.
A spokesman for Gov.
Bill Owens said the state may declare an emergency in the counties affected by the shutdown.
But the shutdown was precipitated by a new state law that requires farmers who use deep irrigation wells which draw down the aquifer that also nourishes the river to replace that water.
The law is meant to stabilize the river by reducing the impact of deep wells.
The law was passed after the 2002 drought, when farmers who relied solely on the river's surface water for irrigation saw their fields burn up, while well-dependent farmers continued irrigating.
Surface-water farmers and some cities successfully sued the state for allowing the deep wells to harm the river.
Under the new law, well-dependent farmers were given several years to find additional water supplies, either by securing water leases or with permanent purchases of water.
In 2002, roughly 5,000 irrigation wells were operated in the South Platte basin.
Under the new law, more than 1,500 have already been shut down, while the users of several hundred others have developed new water plans that allow them to legally operate their wells.
But Simpson's ruling signals that time is up for farmers who have been unable to line up sufficient new water supplies.
"This is a wreck," said Tom Cech, manager of the Central Water Conservancy District.
The district has been working frantically since 2003, raising property taxes to lease and buy water and to build small reservoirs to aid this last group of farms.
All told, the district has raised $21 million to help comply with the new law, Cech said, but the lingering drought and competition for water between fast-growing Front Range cities and farmers has made water scarce and expensive.
Cech said the district had projected it would have enough water this year to operate the wells at 15 percent of their capacity.
But the state engineer's decision, prompted by a dry spring and the district's loss of several key water leases, doomed the farmers' efforts just as the new growing season got under way.
The law also stipulates that farmers must show they have enough incoming water to cover future water debts to the river.
Because of the lingering dry spell, the state required that they use a worst-case drought scenario to calculate future needs, which meant finding more water.
"It's a brutal standard," Cech said.
Bob Sakata is a veteran vegetable grower in Brighton and an elder statesman on the South Platte River.
Sakata already has spent $264,000 planting 300 acres in onions, broccoli, sweet corn and carrots.
The three wells he planned to use on that land won't operate this year, and the crops in the ground probably won't survive.
Sakata is a large grower, with 19 other wells and the rights to river water.
Still, he said he was caught off guard by the ruling.
Farmers had expected to be able to use their wells at least for a short period of time this summer.
But to be shut down completely was a surprise.
"There has to be a better solution than this," Sakata said.
"I've put out calls to the governor, to the commissioner  and director of natural resources.
There's just got to be a way."
 North of Brighton, two wells that supply drinking water to Page's Trailer Park will also be shut down as a result of the ruling.
Bernie Pagel, who has owned the park since 1969, said about 70 families live there and depend on the wells for 90 percent of their water.
"I'm just wondering what we're supposed to do," Pagel said.
He's talking to other nearby water providers to see if he can purchase water.
"We're also wondering if there's any emergency exemption," he added, noting that more than 300 residents will be without water if the wells are shut off.
Glen Kobobel is a corn grower outside Wiggins.
He, too, had expected to have at least a small amount of well water to use on his crops this summer.
Tuesday afternoon, he had yet to finish calculating how much money he will lose as those crops dry out.
"Our family will be able to survive this shutdown," Kobobel said.
"I don't know about next year, though.
And I just can't figure out why the state is doing this to us.
I think we're so few in number, our voices mean nothing."
 Simpson, the state engineer, had a different take.
"There just wasn't enough water in their plan," he said of the farmers' efforts to comply with the new law.
"We're very sorry it came to this."
 How trouble got started
 The crisis in the South Platte River basin took root more than 70 years ago, when hundreds of farm families from Brighton to Fort Morgan started digging wells in a shallow aquifer that also supplies the river.
Water engineering was in its infancy, and state agriculture and water officials encouraged the drilling, hopeful that the wells would drought-proof the lush, irrigated high plains region.
No one understood back then that the wells were pulling water from the same aquifer that helped supply the river.
By 1969, the science was clear.
The wells were depleting the river.
The state began requiring farmers to put back into the river some of what their wells had drawn down.
Under the new law, farmers must put about 80 percent of the total water they pump from the ground back into the river.
Previously, their obligation had been as low as 5 percent in some years.
Optimal Corn Management with Diminished Well Capacities
 Alan J.
Schlegel Kansas State University, Tribune, KS
 Loyd R.
Stone Kansas State University, Manhattan, KS
 Troy J.
Dumler Kansas State University, Garden City, KS
 Freddie R.
Lamm Kansas State University, Colby, KS
 Written for presentation at the 5th National Decennial Irrigation Conference Sponsored jointly by ASABE and the Irrigation Association Phoenix Convention Center Phoenix, Arizona December 5 8, 2010
 Abstract.
Many of the irrigation systems today in the Central Great Plains no longer have the capacity to apply peak irrigation needs during the summer and must rely on soil water reserves to buffer the crop from water stress.
Considerable research was conducted on preseason irrigation in the US Great Plains region during the 1980s and 1990s.
In general, the conclusions were that in-season irrigation was more beneficial than preseason irrigation and that often preseason irrigation was not warranted.
The objective of this study was to determine whether preseason irrigation would be profitable with today's lower capacity wells.
A field study was conducted at the KSU-SWREC near Tribune, KS, from 2006 to 2009.
The study was a factorial design of preplant irrigation , well capacities , and plant population.
Preseason irrigation increased grain yields an average of 1.0 Mg ha-1.
Grain yields were 29% greater when well capacity was increased from 2.5 to 5.0 mm day1.
Water use efficiency was not significantly affected by well capacity or preseason irrigation.
Preseason irrigation was profitable at all well capacities.
At well capacities of 2.5 and 3.8 mm day1, a seeding rate of 68,000 seeds ha-Superscript was generally more profitable than lower or higher seeding rates.
A higher seeding rate  increased profitability when well capacity was increased to 5 mm day1.
Keywords.
Preseason irrigation, well capacity, corn, irrigation management
 Irrigated crop production is a mainstay of agriculture in western Kansas.
However, with declining water levels in the Ogallala aquifer and increasing energy costs, optimal utilization of limited irrigation water is required.
The most common crop grown under irrigation in western Kansas is corn.
Almost all of the groundwater pumped from the High Plains  Aquifer is used for irrigation.
In 1995, of 3 billion m of water pumped for irrigation in western Kansas, 1.41 million acre-ft  were applied to corn.
This amount of water withdrawal from the aquifer has reduced saturated thickness  and well capacities.
Considerable research was conducted on preseason irrigation in the US Great Plains region during the 1980s and 1990s.
In general, the conclusions were that inseason irrigation was more beneficial than preseason irrigation and that often preseason irrigation was not warranted because overwinter precipitation could replenish a significant portion of the soil water profile.
Much of this research was conducted during a generally wetter climatic period in the Great Plains and also under circumstances of ample in-season irrigation capacity.
The Great Plains drought that occurred during the early part of the last decade  renewed producer interest and has brought new questions about preseason irrigation.
In a more recent study Stone et al.
used simulation modeling to examine the effectiveness of preseason irrigation.
They found the differences in storage efficiency between spring and fall irrigation peaked at approximately 37 percentage points  when the maximum soil water during the preseason period was at approximately 77% of available soil water.
Many of the irrigation systems today in the Central Great Plains no longer have the capacity to apply peak irrigation needs during the summer and must rely on soil water reserves to buffer the crop from water stress.
Therefore, this study was conducted to evaluate whether preseason irrigation would be profitable when well capacity is limited and insufficient to fully meet crop requirements.
A field study was conducted at the KSU-SWREC near Tribune, KS from 2006 to 2009.
Growing season precipitation  was 188, 328, 266, and 461 mm in 2006, 2007, 2008, and 2009, respectively.
Normal precipitation for the growing season is 319 mm and normal annual precipitation is 443 mm.
The study was a factorial design of preseason irrigation , well capacities , and plant population.
The irrigation treatments were whole plots and the plant populations were subplots.
Each treatment combination was replicated four times and applied to the same plot each year.
The irrigation treatments were applied with a lateral-move sprinkler with amounts limited to the assumed well capacities.
The preseason irrigations were applied in early April and in-season irrigations were applied from about mid-June to early September.
The in-season irrigations were generally applied weekly except when precipitation was sufficient to meet crop needs.
Corn was planted in late April or early May each year.
The center two rows of each plot were machine harvested with grain yields adjusted to 0.155 g moisture.
Plant and ear populations were determined by counting plants and ears in the center two rows prior to harvest.
Seed weights  were determined on 100-count samples from each plot.
Kernels per ear were calculated from seed weight, ear population, and
 grain yield.
Soil water measurements  were taken throughout the growing season using neutron attenuation.
All water inputs, precipitation and irrigation, were measured.
Crop water use was calculated by summing soil water depletion  plus in-season irrigation and precipitation.
In-season irrigations were 243, 320, and 483 mm in 2006; 183, 257, and 397 mm in 2007; 209, 278, and 375 mm in 2008; and 225, 299, and 453 mm in 2009 for the 2.5, 3.8, and 5.0 mm day 1 well capacity treatments, respectively.
In-season precipitation was 176 mm in 2006, 205 mm in 2007, 238 mm in 2008; and 364 mm in 2009.
Non-growing season soil water accumulation was the increase in soil water from harvest to the amount at planting the following year.
Non-growing season precipitation was 381 mm in 2007, 107 mm in 2008, and 217 mm in 2009 with an average of 235 mm.
Precipitation storage efficiency  was calculated as nongrowing season soil water accumulation divided by non-growing season precipitation.
Water use efficiency was calculated by dividing grain yield.
Local corn prices , crop input costs, and custom rates were used to perform an economic analysis to determine net return to land, management, and irrigation equipment for each treatment.
Preseason irrigation increased grain yields an average of 1.0 Mg ha.
Although not significant, the effect was greater at lower well capacities.
For example, with 68,000 plants ha-1, preseason irrigation  increased grain yield by 1.3 Mg ha with a well capacity of 2.5 mm day-1 while only 0.4 Mg ha-Superscript with a well capacity of 5 mm day1.
As expected, grain yields increased with increased well capacity.
Grain yields  were 29% greater when well capacity was increased from 2.5 to 5.0 mm day1.
Preseason irrigation and increased well capacity increased the number of seeds ear` 1 but had little impact on seed weight.
The optimum plant population varied with irrigation level.
With the two lowest well capacities and without preseason irrigation, a plant population of 55,000 plants ha-Superscript was generally adequate.
However, if preseason irrigation was applied, then a higher plant population  increased yields.
With a well capacity of 5 mm day-1 a plant population of 80,000 plants ha-Superscript provided greater yields with or without preseason irrigation.
Water use efficiency was not significantly affected by well capacity or preseason irrigation , although the trend was for greater WUE with increased water supply.
Similar to grain yields, the effect of plant population varied with irrigation level.
With lower irrigation levels, a plant population of 68,000 plants ha-Superscript tended to optimize water use efficiency.
It was only at the highest well capacity that higher plant populations improved water use efficiency.
Crop water use increased with well capacity and preseason irrigation.
Soil water at harvest increased with increased well capacity, but this caused less soil water to accumulate during the winter.
Non-growing season soil water accumulation averaged 69 mm.
Average non-growing season precipitation was 235 mm giving an average non-growing season precipitation storage efficiency of 29%.
Preseason irrigation  increased available soil water at planting by 58 mm.
Seeding rate had minimal effect on soil water at planting or crop water use but increased seeding rate tended to decrease soil water at harvest and increase over-winter water accumulation.
Preseason irrigation was found to be profitable at all irrigation capacities.
At the two lower well capacities, a seeding rate of 68, 000 seeds ha was generally the most profitable.
However, the highest irrigation capacity benefited from a seeding rate of 80,000 seeds ha-1.
Corn grain yields responded positively to preseason irrigation and increases in well capacity.
This yield increase generally resulted from increases in kernels ear1 Preseason irrigation was profitable at all well capacities.
Seeding rate should be adjusted for the amount of irrigation water available from both well capacity and preseason irrigation.
At well capacities of 2.5 and 3.8 mm day1, a seeding rate of 68,000 seeds ha-1 was generally more profitable than lower or higher seeding rates.
A higher seeding rate  increased profitability when well capacity was increased to 5 mm day1
Fate of Precipitation Falling on Oklahoma Cropland
 Jason G.
Warren Assistant Professor
 Tyson E.
Ochsner Assistant Professor
 Chad B.
Godsey Assistant Professor
 Precipitation falling to the land surface can be classified into three primary categories: blue water, green water, and white water.
As illustrated in Figure 1, blue water flow is that portion of precipitation which runs off or drains through surface soils.
Blue water recharges aquifers and rivers and sustains human and ecological water needs.
Green and white water flows are consumptive water uses that return to the atmosphere and
 are lost from the watershed unless re-precipitated.
Green water flow is the productive portion of this consumptive use which drives plant growth.
White water flow is non-productive evaporation from the land surface.
Oklahoma receives on average 34 inches of rainfall annually, with a strong gradient of increasing precipitation from the northwest to the southeast.
Totaled across our 45 million
 Figure 1: Precipitation is the renewable water resource.
It is partially consumed by plant transpiration  and by land surface evaporation.
The surplus goes to recharge aquifers and surface water systems.
Adapted from Falkenmark and Lannerstad.
acres this rainfall provides 127 million acre-feet of renewable water annually.
This is the state's annual water 'income' and the foundation of the state's water budget.
Some of this rainfall is diverted into our surface waters, either through direct runoff or via discharge from shallow groundwater.
This blue water flow supplies important beneficial uses including: maintenance of aquatic and riparian ecosysitems; household industrial water supply; recreation; power generation; irrigation; transportation of commodities.
With the exception of irrigation, these uses are not consumptive.
Using annual mean discharge of the Arkansas and Red rivers near the Oklahoma-Arkansas border, and correcting for river inflows at the Kansas and Texas borders, it is estimated that on average, 7.7 inches of Oklahoma's annual precipitation is directed into blue water flow.
This represents 23 percent of the Oklahoma's annual water budget.
Nearly all the remaining 77 percent of Oklahoma's annual rainfall returns to the atmosphere through evapotranspiration, which is the sum of green and white water flows.
Across Oklahoma's diverse landscape, this consumptive water use accounts for on average 26.3 inches annually.
Green water flow  is inseparable from plant growth and produces valuable economic and ecological benefits including: crop production and livestock gain; timber production; wildlife habitat; recreation; and soil conservation.
The same cannot be said for white water flow  where no benefit is realized.
The distribution of precipitation falling onto Oklahoma's cropland into the blue, green and white water flows can have significant impacts on its productivity.
The remainder of this fact sheet will focus on how crop management practices influence this distribution.
Understanding the interaction between crop management and the movement of water within cropland systems is vital to improving water use efficiency and overall productivity of Oklahoma cropland.
As mentioned, blue water is generally a small component of the water budget in Oklahoma, accounting for approximately 23 percent of the average rainfall.
Blue water flow from cropland is likely larger as a percent of total rainfall in the eastern part of the state, becoming a smaller component farther west.
Blue water flow from cropland can be partitioned into surface runoff and subsurface drainage.
Some management strategies aimed at reducing runoff may in turn increase subsurface drainage.
Although we perceive a reduction in blue water flow from our cropland, we have simply redirected flow of water from the surface to the subsurface.
Structural alterations such as terraces aimed at reducing water erosion can divert surface runoff to subsurface drainage.
Alterations in tillage such as the conversion from conventional tillage to reduced tillage or no-till can result in the diversion of surface runoff to subsurface drainage.
Reduced tillage or no-till allows for more crop residue on the soil surface.
Crop residue protects the soil surface from raindrops.
This prevents surface crusting which can limit water infiltration in conventional tillage systems.
Green and White Water Flow
 Green and white water that is transferred to the atmosphere through transpiration or evaporation is a much larger
 pool of water accounting for 77 percent of the total average rainfall.
However, a simple analysis of the water use of crops commonly grown in Oklahoma shows that in general only a small portion of this water is utilized for crop production with the remaining lost as evaporation.
To understand the magnitude of the evaporative losses from Oklahoma cropland, we must consider the water use efficiency of the crops grown.
Water use efficiency  is defined in various ways depending on the context.
For the sake of this discussion, we define WUE as the harvestable yield of a crop produced per unit of water transpired.
Table 1 shows the 10-year average yields for crops commonly grown in Oklahoma and their estimated WUE.
Among the grains, corn and sorghum are most efficient at converting water to crop yield, wheat and rye have intermediate WUE's, and soybean has the lowest WUE.
The WUE for a forage like alfalfa cannot be directly compared to the WUE of a grain crop, because less than half of the biomass is harvested in the grain crop.
Although, alfalfa has the highest transpiration, the fact that most of the above ground biomass is harvested gives it an intermediate water use efficiency value.
In, contrast, the harvested biomass from a cotton plant is relatively low and therefore it has a low water use efficiency.
Using the average yields and the WUE, the amount of water transpired by these various crops was calculated by dividing the crop yield  by the WUE.
This shows that crops commonly grown in Oklahoma use 3.6 to 14.0 inches of water or 11 to 41 percent of the average Oklahoma rainfall.
An average wheat crop of 33 bushel per acre transpires 6.2 inches of water or 18 percent of the average rainfall.
Recall that on average approximately 23 percent of rainfall is lost from cropland as blue water.
Therefore, roughly 59 percent of the precipitation falling on cropland utilized for continuous winter wheat in Oklahoma is lost as unproductive evaporation.
This evaporative water loss represents inefficient utilization of rainfall in our crop production systems.
Of course much of this water loss cannot be avoided because of the nature of Oklahoma's climate.
The hot, dry and generally windy summer months of Oklahoma provide ideal conditions for evaporative water loss.
However the magnitude of this loss does suggest that controlling evaporative water loss from Oklahoma cropland may provide the greatest opportunity to improve rainfall utilization in crop production systems.
Table 1.
Oklahoma 10-year  average yields, water use efficiencies , and annual transpiration estimates for crops representing more than 1 percent of total cropland area.
yield	yield	WUE	Transpiration
 lbs acre-1	lbs acre1inch	inches
 Winter wheat	33 bu	1980	317	6.2
 Alfalfa	3.3 tons	6600	473	14.0
 Corn	90 bu	5040	580	8.7
 Sorghum	45 bu	2520	435	5.8
 Soybean	23 bu	1380	240	5.8
 Cotton	0.75 bale	360	100	3.6
 Rye	20 bu	1120	310	3.6
 Controlling White Water Losses
 Maintaining crop or residue cover on the soil surface minimizes evaporative water loss from soil.
Residues effectively insulate the soil surface and protect it from solar radiation that drives water evaporation.
Residue also reduces the wind speed at the soil surface, providing a more humid environment above the soil surface.
This humidity at the soil surface also limits water evaporation from the soil surface.
This influence of crop residue on evaporative water losses allows for surface soil moisture in no-till soils to be higher than the moisture content of conventional tillage soils.
Figure 2 shows that the soil water storage to 4-foot depth under no-till wheat at Lahoma, OK was consistently 18 percent higher than in conventionally tilled wheat.
This greater water storage under no-till results from improved water infiltration and a reduction in evaporative water loss.
In cultivated systems, maintenance of crop residue through reduced tillage practices will also reduce evaporative water loss.
However each tillage pass will stimulate evaporative water losses by exposing moist soils to the surface.
Tillage
 Figure 2: Profile soil water content of No-till and conventionally tilled wheat at Lahoma OK during the 1984-85 growing season.
practices such as delayed tillage will allow for a greater level of subsurface soil water recharge.
Of course, if delayed tillage is followed by intensive tillage for seed bed preparation, the surface soils can be dried significantly prior to planting, and rainfall will be required for crop emergence.
Maintenance of crop residue on the soil surface is only effective in minimizing white water losses.
In order to convert this water to productive green water, crop yields must be increased.
In a continuous winter wheat production system this can be done by providing optimum soil fertility and minimizing yield reductions due to disease and pest damage.
However, a 20 percent increase in the average Oklahoma wheat yield from 33 to 39 bushels will still only require 7.4 inches of transpiration, which will allow for 18.8 inches or 55 percent of the average annual rainfall to be lost as white water.
Another option to increase transfer of white water flow to the productive green water flow is intensification of the cropping system.
This can take on many forms and the success of various crop intensification strategies will depend on site specific weather conditions and soil characteristics.
Crop rotations that include three crops in two years have a great deal of potential for central and eastern Oklahoma.
However, moving westward producers must be more cautions and may want to utilize less intensive rotations such as four crops in three years.
Oklahoma's climate is ideal for white water losses  from cropland, especially during summer fallow periods.
White water loss is the single greatest loss of water from Oklahoma cropland and therefore even small reductions in this loss may significantly increase the productivity of our cropland.
Maintenance of crop residue will minimize the base evaporative water loss; however, crop productivity must at the same time be increased.
This can be done through management practices to improve crop yields or through intensification of the cropping system.
IRRIGATION CAPACITIES IMPACT UPON LIMITED IRRIGATION MANAGEMENT AND CROPPING SYSTEMS
 Irrigation capacity is an important issue for irrigation management.
Having enough capacity to supplement precipitation and stored soil moisture to meet crop water needs during the growing season to maximize grain yield is important.
However, declines in the Ogallala Aquifer have resulted in decreases in well outputs to the point where systems on the fringe of the aquifer can no longer meet crop water needs during average growing seasons and especially during drought years.
Changing cropping practices can impact the irrigation management by irrigating crops that have different water timing needs so that fewer acres are irrigated at any one point during the growing season and concentrating the irrigation capacity on fewer acres while still irrigating the majority or all acres during the year.
Many producers have not changed cropping practices with marginal capacity systems due to management increases and the potential for an above average year.
However, the risk of producing lower yields increases.
Crop insurance has been used to offset those lower yields.
However, the frequency of insurance claims has increased to the point where practices need to be changed on these systems.
System capacities are a function of soil type, crop water use and precipitation.
The soil type acts as a bank where moisture reserves can be utilized during times when the irrigation system is not watering between cycles and during time periods when the system capacity is inadequate to meet crop water needs.
Soils such as silt loams have a greater water holding capacity compared to sands which decreases the need for larger system capacities.
Crop water use determines the total water utilized daily.
Greater demand by the crop increases the amount of water needed for the crop over any time period.
Precipitation is an important factor in irrigation capacity.
A region with a greater probability of
 precipitation during the growing season will require less capacity to supplement crop growth.
Heermann determined the net design capacity for Eastern Colorado along with probabilities of meeting the crop water needs for the growing season for full water needs.
As capacities decline the probability of meeting crop water needs declines.
A 50% probability means that on average, you will meet crop water needs one out of two years and you will not meet crop water needs the other year.
The result will be less than desired yields.
Lamm  found that irrigation capacities of 50% of needed to meet crop water requirements resulted in approximately 40 bu/acre less corn yields.
In above average precipitation years, the yield difference is less and in drier than average years, the yield difference is greater.
The economics of reducing irrigated acres until the irrigation capacity was equivalent to full irrigation capacities showed that irrigating those fewer acres was economically equal or greater than irrigating all of the acres for a single crop.
Lower capacity systems generally are inadequate for meeting crop water needs during the peak water use growth stages.
This also coincides with the
 reproductive growth stages and less average annual precipitation during that time period of a summer crop.
Water stress during that time period has more impact upon yield than during the vegetative and late grain fill growth stages.
Having water stress earlier or later is more desirable than during the reproductive growth stages of tassel, silking and pollination.
Figure 2.
Yield susceptibility to water stress for corn.
Management of low capacity systems generally entails by many producers running the system at times when it is not necessarily advantageous for water management but for the factor of "never wanting to fall behind and hope for the best".
This type of management generally applies more water than necessary during low water use time periods, can leach nitrogen and may not alleviate water stress during periods of little or no precipitation during the high water use growth stages.
Two locations in Colorado were chosen for simulation of multiple irrigation system capacities.
Wiggins in 2007 had below average precipitation and Burlington in 2005 had above average precipitation.
Precipitation in Burlington may have been above average but was concentrated in the early growing season for corn.
A water balance model was used to determine crop water use and soil moisture depletion using weather data from each location and predicted irrigation maintaining soil moisture depletion between 0 and 50% if possible.
Irrigation was scheduled to minimize leaching during the growing season.
Beginning soil moisture was assumed to be at field capacity either from off-season precipitation
 or pre-irrigation.
Both sites have similar water holding capacities of 1.8 to 2.0 inches per foot.
Simulated irrigation capacities include: 1 inch every 4 days , 1 inch every 6 days , and 1 inch every 8 days.
These capacities relate to a 600 gpm to a 300 gpm well for a 125 acre field.
These are a typical range of well capacities within eastern Colorado.
Precipitation at Wiggins was below average for May and June and near average for July and August.
The majority of the precipitation in July and August was during the last 7 days of July and first 10 days of August.
Average annual crop water use for corn is approximately 24 inches.
Table 1.
Monthly and average precipitation for Wiggin, Co for 2007 and Burlington, CO for 2005.
Precipitation	Average	Precipitation	Average
 Month				
 May	1.65	2.41	4.03	2.88
 June	0.31	1.98	5.08	2.50
 July	2.29	1.93	2.36	2.77
 August	2.49	1.58	3.15	2.28
 September	0.52	1.21	0.80	1.04
 Irrigation capacities had an impact upon soil moisture depletions.
A capacity of 1 inch every 4 days was adequate for full irrigation.
Soil moisture depletions did not approach 50% until the end of the growing season after the irrigation system was shut off.
A system capacity of 1 inch every 6 days or less was inadequate with soil depletions greater than 50% occurring in late July.
Soil moisture depletions were critical in late July for the 1 inch in 6 and 8 days.
Corn would have been in the critical growth stage of tassel and pollination during this time period.
This is the time period of 60 to 80 days after emergence when Sudar determined that the greatest yield reduction would occur.
This would limit yields dramatically compared to an adequate capacity that would maintain soil moisture less than 50% depletion.
Precipitation of 3.5 inches during late July and early August allowed soil depletions for both the 1 inch in 6 and 8 days to be less than 50%.
However only the 1 inch in 6 days remained less than 50% depletion during the remainder of the growing season.
The soil moisture depletion for the 1 inch in 8 days capacity was greater than 50% after mid-August during the grain fill time period.
This water stress has less impact than during the tassel and pollination time period but still will reduce grain yields.
With an irrigation capacity of 1 in 4 inches per day, the system was rarely turned off.
Only during the time period of above average precipitation of late July and early August could the system been turn off.
If irrigated acreage for corn were reduced to this capacity per acre, the only irrigation option for the remainder of the acres would be an early spring crop with the need for irrigation done by early June.
Precipitation at Burlington in 2005 was above average for May and June and near average for July and August.
Precipitation in May and June totaled more than 9 inches which is 3.5 inches greater than average.
During July, there was a 21 day period where little precipitation occurred.
Less than 1 inch of precipitation occurred during the first 21 days of August.
Average water use for corn is approximately 27 inches at Burlington.
Although precipitation was above average at Burlington, irrigation capacities had a significant impact upon soil moisture depletion.
An irrigation capacity of 1 inch in 4 days was adequate to maintain soil moisture depletions of less than 50% during the growing season.
However, soil moisture depletions during late July and early August were greater than 40%.
System capacities of 1 inch in 6
 days or less were inadequate with soil moisture depletions greater than 50% in late July and to late August.
Soil moisture depletions were critical in late July for the 1 inch in 6 and 8 days.
Corn would have been in the critical growth stage of tassel and pollination during this time period.
This is the time period of 60 to 80 days after emergence when Sudar determined that the greatest yield reduction would occur.
This would limit yields dramatically compared to an adequate capacity that would maintain soil moisture less than 50% depletion.
Soil moisture depletions for system capacities of 1 inch in 6 days or less were greater than 50% during the entire reproductive growth stage.
During a majority of this time period, soil moisture depletions were greater than 60% and approached 80% for the 1 inch in 8 days capacity.
Soil moisture depletions were less than 50% in late August only after two precipitation events totaling more than 2 inches occurred.
Although total precipitation for the entire growing season was above average by almost 4 inches, timing of that precipitation was critical.
Precipitation during July and August was near average showing the importance of adequate system capacities during the time period when crop water use was almost 14 inches.
Figure 4.
Soil moisture depletions for 3 irrigation capacities at Burlington, Colorado for 2005.
Although an irrigation capacity of 1 inch in 4 days was adequate for irrigating corn during the growing season.
The options for irrigating another summer crop are limited since the system rarely was off for long periods of time during July and August.
The only practical option would be to irrigate an early spring crop on those acres.
A second scenario was simulated including the capacity of 1 inch in 3 days and the potential to divert irrigation to the remainder of potentially irrigatable acres.
Crops such as sunflower respond well to limited amounts of irrigation during critical time periods.
Schneekloth found that irrigating oil sunflowers during the early flower to pedal drop yielded similarly to fully irrigated sunflowers.
This time period is a two to three week period that occurs in early August when sunflowers are planted in late May.
Simulating a 1 inch in 3 days system capacity, irrigation to a summer crop such as corn could be reduced during the first 3 weeks of August and with the majority of irrigation being diverted to a crop such as sunflowers.
Soil moisture depletions increased during that time period but were still less than 50% before primary irrigation of the corn resumed.
Figure 5.
Soil moisture depletions for an irrigation capacity that would allow diverting irrigation to a secondary summer crop compared to an adequate capacity for full irrigation at Burlington, Colorado for 2005.
This strategy would allow for more total acres to be irrigated with more diversity but fewer acres of any one single crop.
Although both Wiggins and Burlington had dramatically different weather conditions, the minimum acceptable system capacity was similar at 1 inch in 4 days.
However, this capacity may require diverting water from acres to achieve this capacity for a limited number of acres.
However, spreading water over more acres with lower capacities generally will have water stress at the critical growth stages that will impact yield potential the greatest.
When dealing with system capacities that are not adequate for full irrigation management of the system, the potential for less than optimum yields increases, as does the risk involved.
Alternative cropping practices must be included that diversify crops and reduce the irrigated acreage of any one crop.
However, the critical time periods should not overlap unless alternative water capacity strategies are investigated.
Irrigating all of the acres with a marginal system capacity increases the reliance upon crop insurance to minimize the risk when precipitation is either below average or the distribution is not uniform.
However, crop insurance in the future may limit this due to their increase exposure for risk.
Dean E.
Eisenhauer Derrel L.
Martin Derek M.
Heeren, General Editor Glenn J.
Hoffman
 Dean E.
Eisenhauer Derrel L.
Martin Derek M.
Heeren, General Editor Glenn J.
Hoffman
 Copy editing and layout by Peg McCann Cover design by Melissa Miller Cover photos: Drip lateral, photo courtesy of Toro Lake McConaughy, photo courtesy of Steve Melvin, Nebraska Extension Weather station, canal, furrow irrigation in corn, and center pivot photos by the authors
 This work is licensed with a Creative Commons Attribution 4.0 International License
 The American Society of Agricultural and Biological Engineers is not responsible for statements and opinions advanced in its meetings or printed in its publications.
They represent the views of the individual to whom they are credited and are not binding on the Society as a whole.
This book is dedicated to our wives and children for their love and support:
 Maria, Emily, and April
 JoAnn, Jennifer, and Kimberly
 Amber, David, Elizabeth, Nathan, and Joshua DMH
 Maria, Kimberly, Karen, and Sheryl GJH
Sodicity and Remediation of Sodic Soils in North Dakota
 Dave Franzen, Soil Science Specialist, NDSU Extension Naeem Kalwar, NDSU Extension Soil Health Specialist, Langdon Research Extension Center Abbey Wick, Soil Health Specialist, NDSU Extension Tom DeSutter, Professor, NDSU Soil Science Department
 Sodicity, according to Natural Resources Conservation Service , is the degree to which a soil is affected by sodium , expressed as the sodium adsorption ratio  of sodium ions  to the total of calcium ions  and magnesium ions  from a saturation extract.
The formula is /V/2), where units of each cation are millimoles per liter.
A value for SAR also can be closely estimated through using the percent of the Na value within the soil base exchange capacity.
The effect of sodicity on crop production and soil condition is very different than the effect of soluble salts.
Although sodium enters the soil solution as a salt, sodium is attracted to negative charges of organic matter and particularly soil clays, and becomes a part of the cation exchange capacity.
Figure 1.
Illustration of the flocculation in a calcium-dominated soil, compared with swelling and dispersion in a sodium-dominated soil.
In a calcium-dominated soil, clay particles group together in an orderly fashion, resulting in avenues between the particle groups  through which water can flow and roots can grow.
In a sodium-dominated soil, the clay particles become randomly distributed or dispersed, leading to swelling when wet and sealing when dry, with few avenues for water to penetrate and roots to grow.
The application of soluble calcium amendments may be used to improve soil physical properties due to 1) an increase in electrolyte concentration   and 2) displacement of that displacement Na+ by Ca+ on the cation exchange sites.
The displacement of Na+ by Ca+2 is important; however, the salt concentration  of the soil water is the most crucial factor affecting the stability of soil structure.
Figure 2.
Relationship between sodium adsorption ratio  and soil water ionic strength.
The negative effects of sodium on soil properties  may be reduced with greater EC.
Flocculation, swelling and dispersion happen due to the chemical properties of sodium and calcium.
Sodium ions are satisfied when they have a full array of water surrounding each of them.
The charge configuration of calcium results in binding together clay particles , whereas the hydration property of sodium leads to clay dispersion when sodium reaches a critical concentration.
Figure 3.
Illustration of fully hydrated sodium ion  and coordinated calcium ion.
Figure 4.
Chemical depiction of the effect of Ca  and Na  and wetting on soil swelling and dispersion.
The video shows a cube of sodic soil in water  and a cube of calcium-dominated soil  and the dispersion that takes place through time.
Click the video to see the results.
en dry, sodic soils become quite hard and difficult to seed y wet readily and the soil swells.
When wet, the soil has and farm implements can become stuck easily when the S surrounding them are traveled.
) exists between the swelling properties of sodic soils R and soluble salt concentration.
In a study using a sodic soil with SAR of 14, an EC value less than 1 resulted capacity water content of about 32%.
The field r content at an EC of 4 was about 25%.
spersion and swelling are possible when the SAR is 5 and EC is less than 1.5 millimhos per centimeter.
Maintaining an EC that will prevent dispersion and I sodium is, therefore, part of the management plan for p productivity in sodic soils.
As the SAR increases with ; the water content of the soil at field capacity increases
 Wyndmere CIG Field Soil SARe or Na% = 14
 Figure 6.
Water content at field capacity as affected by soil EC.
Figure 7.
Water content at field capacity as affected by soil SAR.
Restrictions to Crop Productivity
 Soils with excess sodium can develop a natric horizon.
The natric horizon is nearly always within 12 inches of the soil surface, which greatly restricts rooting depth.
A few roots can follow the outside of each natric column, but sometimes the columns are wider than those in Figure 8, and little nutrition or water is taken up from depths under the natric horizon.
When wet, the soil swells and seals the soil from water movement through the columns, and when dry, the soil is very hard, making root growth difficult.
Rooting depth of crops growing in sodic soils will be very shallow.
Figure 8.
Soil with a natric horizon in North Dakota.
Natric soil A soil with an argillic horizon, but with excess sodium with an SAR greater than 15 and/or pH greater than 8.2, possessing a natric horizon of distinct columns
 Glossic soil A soil in which the natric horizon has degraded through time
 Leptic soil A sodic soil with gypsum crystals present within 16 centimeters  of the surface
 Typic soil A sodic soil with properties between Glossic and Leptic
 Although the definition of a natric soil above will be used by NRCS for the foreseeable future, research in North Dakota and in several other parts of the world indicate that dispersion and soil swelling become problems with an SAR greater than 5.
For this reason for management purposes, sodic soils in North Dakota are defined as having an SAR greater than 5.
The higher soil EC may serve to reduce the negative impact of high SAR.
Source of Sodium in North Dakota Soils
 The major source of sodium in North Dakota soils is the shale bedrock that is present in the state.
When glaciers moved across the state, some of the shale was ground up and incorporated in the ice.
When the glaciers melted, the shale sediments remained as part of the glacial till material that makes up the sediments in soils north and east of the Missouri River.
South and west of the Missouri River, the glacial till from the previous glacial period  are mostly eroded away, exposing sodium-rich sediments from bedrock at least 65 million years old.
The main exception to this sodium source is the area west of Grand Forks, where an artesian system brings up sodium chloride imbedded in an ancient seabed hundreds of feet below the valley surface.
In this area, the salts are chloride-based, whereas in most of North Dakota, salts are sulfate-based.
Distribution of Sodic Soils in the Region
 Figure 9 shows the relative distribution of sodic soils in North Dakota and the region.
Sodic soils may be found nearly everywhere in the state, but in some areas, the sodic soils are small and may or may not be marked as "inclusions" in NRCS soil maps.
The major regions in the state with large areas of sodic soil are Burke and Divide counties in the northwest; the Bottineau and Langdon areas where the soil is shallow to shale bedrock; west-river, particularly in Slope, Bowman, Stark and Billings counties; Sioux County; and areas in Dickey and LaMoure counties near the James River.
Figure 9.
Relative distribution of sodic soils in North Dakota.
Remediation of Sodic Soils
 The essential requirements for remediating sodic soils are:
 A soluble calcium source
 Water in excess of crop requirements
 The absence of any of the three essential requirements for remediation will result in the persistent presence of the sodic condition.
Steps in Preparation for Sodic Soil Remediation
 Soil Sampling and Analysis
 The soil sample should be taken to the depth of the intended tile drainage and the core divided into 1-foot increments.
There may or may not be SAR differences to depth and only deeper soil sampling will provide the important information.
Variability of soil properties in sodic soils can be great , but understanding variability is important for proper management and expectations.
Each depth should be analyzed for SAR, EC, pH, base exchange capacity, real cation exchange capacity  and calcium carbonate equivalence.
As earlier stated, using the Na percent of the total base exchange capacity is a very good proxy for the more expensive SAR analysis.
The following images may help explain the limitations of the most common CEC analysis.
The most common method of determining cation exchange capacity  in North Dakota is by the "summation" method.
In this method, a solution of 1-molar ammonium acetate to provide excess ammonium to the anticipated base ions  on the soil clay/organic matter surfaces is added.
The ions associated with the clay/organic matter CEC sites are replaced by the ammonium ions, and the ions in the extracted solution are analyzed and quantified.
The summation method is a reasonable method for determining CEC in soil without measurable EC and free lime, but when soluble salts and/or free lime is present, the ions in the soluble salts are included in the extracted solution, along with those on the CEC sites, and some free lime is dissolved.
The result is that when EC and/or free lime is present, the CEC is overestimated.
Therefore, if EC is measurable and/or soil pH is greater than 7, particularly if the CCE is greater than zero, then the "real" CEC method illustrated in Figure 13 should be used.
Figure 11.
Changes in SAR with depth in a sodic Exline soil.
Each sample was taken within a 10-acre patch of soil in the same field.
Air-dry soil: cations  and anions predominantly in the crystal form.
A sulfatedominated system is used for simplicity.
Cations adsorbed to the soil's exchange sites  in green.
Exchanger phase cations  and solution phase cations  are moved to solution using ammonium acetate.
Cations in red and green are then quantified.
Ammonium adsorbed to the soil's exchange sites.
Figure 12.
Soil with soluble salts  before ammonium acetate laboratory extraction and after.
The CEC by summation method overestimates real CEC in soils with free lime and/or soluble salts.
Figure 13.
A method for "real" CEC determination.
Ammonium acetate is added as extractant to the soil as in Figure 12; however, the extraction solution then is discarded.
A potassium solution then is used to saturate the soil, resulting in removal of the ammonium ions from step B, then the ammonium is analyzed to provide the real CEC.
This method provides real CEC but cannot be used to determine base saturation.
Figure 14.
Illustration of the use of calcium amendments, primarily gypsum, to remediate sodic soils through tile drainage.
Tile drainage is important, or the soil should be sufficiently permeable and have high enough topography  that water can move through the soil and away from the field.
A landmark study from Illinois  showed that gypsum is most effective if tilled to the depth of tile  and tiled.
Mixing the soil without tile actually resulted in soil degradation and further loss of productivity, while a gypsum amendment, tile and mixing to the depth of tile resulted in corn yield increases and improved productivity.
No Ca amendments	With Ca amendments
 Na	Na	Na	Na	Na	Na	Na	Ca	Ca	Na	Ca	Ca
 Na	Na	Na	Ca	Na	Na
 Ca	Na	Na	Na	Ca	Ca	Ca	Ca
 Na	Na	Na	Na	Ca	Ca	Ca	Na
 Na	Ca	Ca	Na	Na
Basic Concepts in Environmental Computer Control of Agricultural Systems1
 Computer control technologies make use of computer systems and other hardware to monitor physical conditions of an environment, make decisions about actions required to modify the environment, and act on devices that will result in changes to the environment.
For example, in a greenhouse, a computer can be used to monitor temperature, and turn heaters on and off at appropriate intervals to maintain a constant temperature.
Computer controls are particularly useful in systems in which 1) many variables are controlled, 2) there is an large number of devices that must be controlled, 3) frequent or constant attention is required, and 4) labor costs are high.
The State of a System
 Environmental systems, such as the biological systems dealt with in agricultural production, are extremely complex in nature.
In fact, their complexity is SO great that describing and predicting their behavior in physical and mathematical terms may not be possible.
In order to manage such a system we must simplify it and describe it in terms of a set of measurable values that are known to have the most important effects on production.
Following the greenhouse example, we find that, the quality and quantity of production will depend on solar radiation, humidity, temperature, gas composition of the air, age of the plant, irrigation water quality, nutrition programs, and many other factors.
Because it is expensive, sometimes impractical, and sometimes impossible to attempt to control all of these variables, the set of controlled variables is generally restricted to a smaller
 set, such as, temperature, humidity, and CO2 2 concentration.
Thus, the state of the system at any given time is defined by the magnitudes of a set of important measurable variables.
Table 1 lists some variables that are often used to define the state of different agricultural productions systems from a control viewpoint.
A control system consists of a combination of hardware and software that acts as a supervisor with the purpose of managing the controlled system.
This is done by the use of a control loop.
A control loop consists of 1) monitoring the state variables, 2) comparing the state variables with their desired or target state, 3) deciding what actions are necessary to change the state of the system, and 4) carrying out the necessary actions.
Performing these functions requires a combination of hardware and software that must be implemented for each specific application.
For the control loop shown in Figure 1, each of the hardware elements is described below.
A sensor is a device placed in the system that produces an electrical signal directly related to the parameter that is to be measured.
In general, there are two types of sensors, continuous and discrete.
Figure 1.
Control loop
 Figure 2.
A tensiomter is used to measure water potential in soils.
This illustrates how it can be used as a descrete or continuous sensor.
1.
Continuous.
Continuous sensors produce a continuous electrical signal, such as a voltage, current, conductivity, capacitance, or any other measurable electrical property.
For example, sensors of different kinds can be used to measure temperature, such as thermistors and thermocouples.
A thermocouple will produce a voltage difference that increases as the temperature increases.
Continuous sensors are used where values taken by a state variable are required, for example, to estimate the material that is transferred using a conveyor belt, the speed of the conveyor belt may be required.
2.
Discrete.
Discrete sensors are basically switches, mechanical or electronic, that indicate whether an on or off condition exists.
Discrete sensors are useful for indicating thresholds, such as the opening and closure of devices.
They can also be used to determine if a threshold of an important state variable has been reached.
Some examples of discrete sensors are, a float switch to detect if the level in a storage tank is below a minimum desirable level, a switching tensiometer to detect if soil moisture is above a desired threshold, and
 a thermostat to indicate if a certain temperature has been reached.
When combined with time, pulses from switches can be used to measure rates.
For example, to the volume of fuel, water or chemical solution passing through a totalizing flow meter with a magnetically activated switch, or the speed of a rotating flywheel.
Because they provide the basic data that drive an automatic control system, sensors are an extremely important component of the control loop.
Understanding the operating principle of a sensor is very important.
Sensors many times do not react directly to the variable being measured.
For example, when a mercury thermometer is used to measure temperature, temperature is not being measured, rather, a change in volume due to a change in temperature is measured.
Because there is a unique relationship between the volume and the temperature the instrument can be directly calibrated to provide temperature readings.
The ideal sensor responds only to the "sensed" variable, without responding to any other change in the environment.
It is important to understand that sensors always have a degree of inaccuracy associated with them and they may be affected by other parameters besides the "sensed" variable.
The classical example is that of soil moisture measurement using electrical conductivity probes.
The electrical signal produced by this sensor is closely related to soil moisture, but is greatly affected by temperature and dissolved salts  in the soil.
Another important factor related to the sensor is its time response.
A sensor must deliver a signal that reflects the state of the system within the frame of time required by the application.
Using the soil moisture measurement example, the sensor must be able to "keep up" with the changes in soil moisture that are caused by evapotranspiration.
Thus, proper selection of the sensors and understanding the principle of operation is critical to the success of a control system.
Since computer systems work internally with numbers , the electrical signals resulting from the sensors must be converted to digital data.
This is done through specialized hardware referred to as the Analogto-Digital  interface.
Discrete signals resulting from switch closures and threshold measurements are converted to 0 and 1.
Continuous electrical  signals produced by the sensors signals are converted to a number related to the level of the sensed variable.
The accuracy of the conversion is affected by the resolution of the conversion equipment.
In general, the higher the resolution the better the accuracy.
For, example if a pressure sensor produces a voltage signal ranging from 0 to 5 volts for a range of
 pressure of 10 atmospheres, an 8 bit resolution A/D board will be able to detect a change in voltage of about 5/255 volts which will results in measurable increments of 50/255 atmospheres.
If the resolution of the A/D board was 12 bit, the board would be able to detect a change in voltage of about 5/4095 volts or a measurable increment of 50/4095.
Figure 3.
A/D Interface
 The A/D conversion hardware is directly connected to the computer system.
Given the current state of technology, the computer system may be a PC , a minicomputer, or a specially designed machine that is solely dedicated to the control task.
The type of machine depends on the type of application, and is greatly affected by factors such as environmental characteristics, complexity of the controlled system, and the speed with which conversions need to take place.
Many agricultural applications can be economically carried out using PCs, as is evident by the increasing number of system integrators and equipment manufactures that are marketing PC-based control systems.
Also, many manufacturers of control equipment have designed and manufactured specialized computer control systems.
Using control software, decisions may be made to modify the controlled system.
The actual changes are achieved by having devices within the system that will affect the controlled variables.
These devices are controlled through actuators that respond to signals from the control interface.
The devices may be of the nearly continuous or discrete types.
For example, the extension of a robot arm of a citrus harvesting robot requires the use of a continuous signal from the computer, while a fan requires only an on/off  signal from the computer.
In general, any device that can be powered electrically can be controlled by a computer.
The software is used to implement procedures as they apply to the controlled system.
These procedures are usually very elaborate, but in a well-engineered piece of software, they are transparent to the user.
Because the user is more concerned with ease of use and performance of the system, good quality software has an interface that allows easy definition of the characteristics of the system to be controlled and simplifies the assignment of hardware resources.
Performance is measured by how well the computer control system maintains the desired state.
Figure 4 compares a thermostatically controlled water boiler and a computer controlled one.
It is clear that the computer control systems better maintains the desired state of the system.
Selecting an Environmental Control System
 Assuming that computer control is being contemplated as an aid in managing an environmental system, four general steps can be followed to appropriately select a computer control system.
Step 1: Identify measurable variables important to production.
It is very important to correctly identify the parameters that are going to be measured by the computer's data acquisition interface, and how they are to be measured.
An example set of variables typically used in greenhouse control is shown in Table 2.
A similar table can be developed for any other application.
The variables to be measured in a control system are limited to those that can be measured in a practical way.
In other words, an electronic sensor that
 can be interfaced with a computer must be readily available, accurate, reliable and low in cost.
If a sensor is not available, the variable cannot be incorporated into the control system, even if it is very important.
Many times variables that cannot be directly or continuously measured can be controlled in a limited way by the system.
For example, fertility levels in nutrient solutions for greenhouse production are difficult to measure continuously, yet the computer can be used to apply a predetermined quantity of nutrient at prespecified intervals.
Here the computer is functioning as an elaborate timer, and not as a feedback control system.
Step 2: Identify variables that are to be controlled.
Measurable variables that directly affect production can be selected as control or target state variables if they can be affected by some controllable action.
These variables are sometimes referred to as set points.
For example, the temperature inside a greenhouse can be affected by controlling heaters, fans, or window openings.
On the other hand, thermal loads due to solar radiation in animal housing operations cannot be controlled, since they depend on weather alone, and there is usually no mechanism  that allows control of this variable.
Those variables that cannot be controlled but affect the state of the system are referred to as disturbances.
Those variables that are not set points but may be useful in making control decisions are referred to as intermediate variables.
Step 3: Investigate control strategies.
An important element in considering a control system is the control strategy that is to be followed.
The simplest strategy is to use threshold sensors that directly affect actuators to devices.
An example is a simple thermostat connected to a furnace.
A second control level is a multistage system based on threshold sensors.
For example the cooling fans for a broiler production house can be divided into four banks.
As the temperature increases one bank may be turned on.
With a further increase in temperature a second bank would be powered, and SO on.
A third control level would include some logic decisions based on other conditions.
For example, if it is desired to decrease the moisture content of grain in a bin, air circulation should not be started if the moisture content of the outside air would result in a relative humidity of the air inside the bin that would not produce drying.
More complex control strategies are those based not only on the current values of the controlled variables, but also on the previous history of the system, including the rates at which the system variables are changing, and a knowledge
 of how energy and mass transfers occur in the system.
For example, the fan banks in an animal housing unit could be turned on or off based on the current temperature, how fast the temperature is changing with time, the external radiation and how it is changing, knowledge of how radiation is converted into heat, and how heat is gained or lost through the structure's walls and the ventilation system.
Systems that base the control strategy on an understanding of the physics of the system and respond to the unsteady nature of the system are usually referred to as dynamic control systems.
Even more advanced, are those strategies that, in addition to the above, implement practical knowledge gathered through experience with the production system and simulations of the effects of the environment on the product.
The implementation of many of these strategies requires sound engineering and, in many cases, they are still at a research stage.
Step 4: Identify the software and the hardware to be used.
It is very important that control system functions are specified before deciding what software and hardware system to purchase.
The main differences between a conventional feedback control system and computer based control systems are the power and flexibility that the computer provides.
From the users viewpoint these include the ability to: 1) Expand the number of measured variables  and controlled devices  SO that growth and changing needs of the production operation can be satisfied in the future, 2) provide a flexible and easy to use interface that allows the user to assign input and output devices, and 3) allow the user to specify important details of the control algorithms that are implemented by the software.
Notice that these three points are primarily software related.
Hardware must always follow the selection of software, with the hardware required being supported by the software selected.
In addition to functional capabilities, the selection of the control hardware should include factors such as reliability, support, previous experiences with the equipment , and cost.
Computer control systems should not be confused with elaborate timers or dedicated feedback control systems.
Computer control systems are usually identifiable because they rely on some type of computer system and the flexibility and power associated with it.
When control systems are very elaborate it is best to seek professional advice in selecting a system.
Several computer control systems are available commercially for a variety of agricultural applications.
It is usually beneficial to study commercially available systems
 when selecting a computer control system.
However, care must be exercised to make sure that the functions served by the system are those that are required by the control application.
Studying where the system has been used before and the differences between the environments in which it has been used, and the environment in which it is to be used, usually provides many insights on the commercial system.
When using commercially available systems it is often necessary to purchase equipment with a higher capacity than required, however, the advantages of available support and access to the experience of other users far outweighs the extra cost.
Figure 5 shows the architecture of a system for computer controlled animal housing.
Figure 5.
The architecture of a system for computer controlled animal housing.
For many control applications it is possible to develop control systems from off-the-shelf components.
This, however, is usually limited to systems that do not require elaborate control algorithms.
For example, home computers with powerline modulators have been used successfully for many years in propagation houses for ornamental production and turf management.
The basic components of a do-it-yourself system are shown in Figure 6.
Figure 6.
Sensor in soil determines if moisture threshold has been reached.
Digital input board aquires data, computer makes decision , and orders receiver module to turn irrigation on.
As a result of the increase in power and decrease in cost of personal computers during the late seventies, and the explosion in tools for application development during the eighties, these past 15 years have seen a rapid increase in computer systems that improve design and management capabilities in agriculture related operations.
This section looks at some new technologies that are closely related to computer control.
These technologies were researched and tested during the last decade, and are likely to find themselves in production agriculture in the future.
These areas are that of 1) real-time expert systems, 2) modelling and 3) robotics.
Expert systems are the most celebrated result of artificial intelligence technology.
An expert system is a computer program that mimics a human expert in finding a solution to a difficult problem.
Expert systems can be applied only to well defined problems for which a human expert has a solution.
Through a process called knowledge engineering, the expert's knowledge of the problem is expressed as a set of rules.
These rules are then used to build the computer program that will emulate the expert.
The computer program consists of two parts, the knowledge base and the inference engine.
The knowledge base is the set of rules obtained from the human expert by the knowledge engineer and a collection of facts that represent the state of the system.
The inference engine applies the rules and user-provided data to reach a diagnostic.
Most conventional expert systems query the user for data until they are able to reach one of several possible diagnostics.
Unlike conventional expert systems, which as a goal try to reach a diagnostic, real-time expert systems operate with dynamic data and time critical responses.
In a real-time expert system most of the input comes from sensors and most of the output goes to effectors.
Because of this, real-time expert systems are said to be data driven.
Although many conventional expert systems have been developed for agricultural applications, few have been used widely in production agriculture.
An example of a real time expert system application in agriculture is RTES.
RTES operates an irrigation system based on soil-moisture sensor input and a set of rules obtained from the system manager and irrigation specialists.
The use of computer models to simulate complex environmental systems such as those found in production
 agriculture have improved by orders of magnitude since the initial attempts 20 years ago.
Modelers have been successful in applying models for improving not only agricultural system management, but also for strategic and tactical planning.
The number of models that have been developed to date are too numerous to mention here.
Collectively, these models include virtually every facet of agricultural production systems.
For various reasons, most models have not achieved broad application in production agriculture.
They have been used mostly by scientists who are studying agricultural production systems.
During the second half of the last decade concerns on usability and transportability in the use of models have resulted in major efforts that address these issues.
An example of these efforts is the International Benchmark Sites Network for Agrotechnology Transfer.
The IBSNAT project consists of 29 sites worldwide that are adapting and implementing models for the integration of new or alternative crops, cultivars, products, and practices into existing farming systems to render them more productive, stable and sustainable.
IBSNAT integrates the use of modeling, expert systems, and information management technologies.
It is clear that these technologies will be used effectively during this decade.
Although the construction of a machine that simulates a human being in its physical and mental attributes is far from being achieved, robotics technology has produced intelligent machines that are able to receive sensory input from the surrounding environment, and manipulate it to achieve prespecified results.
Robotics is an area that incorporates the use of real-time expert systems, and control technologies.
Agricultural robots have been used mostly under experimental conditions.
However, it is clear that given current technology these complex machines can be built.
Table 3 shows some examples of agricultural robots that were built during the recent years.
A Look into the Future
 Given the state of current technology, it is not difficult to envision a closed agricultural production system in which many of the agricultural operations are automated.
All of the elements required to build an "agricultural production machine" exist today.
Such a machine could have some of the following capabilities:
 The aerial environment is controlled.
Temperature, relative humidity, solar radiation, and gas composition are adjusted according to the crop's stage of growth to
 insure the product will be of the required quality at a given market window, for example greenhouse production of Easter.
Nutrition is controlled.
Nutrition and root environment are controlled by means of a hydroponic solution, for example, hydroponically grown lettuce.
Pollination  is controlled.
By maintaining an insect free environment, desired levels of pollination are achieved using mechanical shakers, for example, greenhouse grown winter tomatoes.
Disease and pest control.
Using visual symptom based identification of diseases and pests, control chemicals can be applied.
An example is the identification of molds on oranges and aerial application of pesticides using application towers.
Harvesting and post-harvest.
Using visual identification and mobile robots to select, pick, and transport fruit to a machine where grading and packaging take place.
A robotics citrus picker, for example, displays this capability.
In addition, all of the actions above could be supported in a knowledge based decision system that incorporates the expert rules in several fields that may include for example 1) basic knowledge of the system, such as, population dynamics, soil-plant-air-water relations, market economics, 2) rules of thumb developed from observation, 3) collection of data on the past behavior of the system, and 4) analysis of long term effects of the actions taken on the system using models, that include not only crop growth and yield estimations but also effects of different market conditions and their effect on profits.
Although the above scenarios may seem far in the future, it is clear that all of the technological components are available, and that they have been independently used, or at least tested at a prototype level.
Also, integration of all of these technologies will no doubt encounter problems that will be difficult to overcome.
However, it is clear that the technology is evolving in this direction.
Given the declining cost of powerful computer systems and associated electronic devices, as well as the present trend towards increasingly powerful and easy to use software, it is clear that computer controlled systems will replace many of the manual and static control systems in use today.
Although computer control systems are not without problems, such as the requirement of a high quality electrical source and maintenance, they provide a flexible and precise form of maintaining an environment.
In addition, they allow
 control of complex systems where strong interactions in the controlled variables occur and systems in which traditional control and manual procedures cannot be used.
Overall, computer control coupled with sound knowledge about a production system, provides a tool for better management of resources that results in an improved quality and quantity of production.
The introduction of computer control technology in agriculture is likely to rapidly advance in the immediate future.
The continuously decreasing costs of hardware and software, the wider acceptance of computer systems in agriculture, and an emerging agricultural control system industry in several areas of agricultural production, will result in reliable control systems that address several aspects of production.
Further improvements will be made as less expensive and more reliable sensors are developed for use in agricultural production.
The elements of this technology are in use today.
Table 1.
Examples of Systems and Related State Variables.
Greenhouse	Temperature, relative humidity, and light intensity
 Irrigation	Soil moisture, salinity, and pH of irrigation water
 Grain Dryer	Grain feed rate, temperature, and moisture content of grain
 Table 2.
Examples os Measurable Variables in Greenhouse Control, Sensors that may be Used, and the Importance of the Measured Variables to Production.
Inside temperature	Shielded thermocouple	Affects all plant metabolic functions
 Outside temperature	Shielded thermocouple	Affects inside temperature through ventilation and
 Inside relative humidity	Thermocouple psychrometer	Affects transpiration rate and the plant's thermal control
 Outside relative humidity	Thermocouple psychrometer	Affects inside relative humidity through ventilation.
Solar radiation	Pyramometer	Affects photosynthetic rate, responsible for most thermal
 load during warm periods.
Air velocity	Anemometer	Maintains air-leaf water potential difference, mixed air is
 more uniform in properties.
Table 3.
Examples of Agricultural Robots.
Robot	Main Function	Features
 Magali	Automated apple picker.
Machine vision to locate ripe apples.
Robotic arm with mechanism to
 AID	Chemical application and frost	Weather data acquisition, frost-protection windmill operation, aerial
 protection.
chemical applications under near optimal conditions.
ISETI	Driverless combine.
Automatic steering, header height, and ground speed control.
Robotic Orange Picker	Automated orange picker.
Machine vision to locate ripe oranges.
Robotic arm with mechanism to
Regulations in Nebraska: In the state of Nebraska, manure irrigation regulations are the mostly the same as other methods of manure application to cropland, including recordkeeping, inspections and setbacks.
In addition, irrigation systems that are connected to a water source must have devices installed  to prevent manure from flowing back into the well.
Corn Production in Clump Planting Patterns Simple Observations from Colby, Kansas, 2006
 Planting crops in hills or clumps has received renewed interest for crop production under extremely limited water availability.
The technique is to plant 3 or 4 seeds together in one "clump" rather than intersperse them evenly down the crop row.
This simple observation trial from 2006 at Colby, Kansas for corn is intended to just provide supplementary information to more comprehensive studies being conducted by West Texas A&M University and USDA-ARS Conservation Production Research Laboratory.
Trial Methods and Procedures
 The corn  was planted into a deep silt loam soil on April 27, 2006.
The normally row planted corn was seeded at a resultant plant population of 19,166 plants/acre in 30-inch spaced corn rows with a standard corn planter.
The clumps were hand planted in 4 ft increments along the 30-inch spaced corn rows with the clumping beginning point in each row offset 2 ft from the adjacent row.
This planting arrangement for the clumps resulted in a plant population of 16,880 plants/acre, considering that 31 of 32 planted plants emerged.
Additional clumps were planted as buffers around the plants that were sampled at harvest.
Because the observational clumps were inserted into another research study already in progress, it was not possible to exactly match plant populations for the two planting arrangements.
Emergence was on May 18 and physiological maturity was reached on September 11.
The plot area received extremely limited subsurface drip irrigation  with 1 inch being applied on June 13  and 2 inches on July 14.
Precipitation during the period May 18 through September 11 totaled 8.88 inches which is approximately 3.5 inches below normal.
Fully irrigated corn evapotranspiration during the period was calculated as 21.91 inches which is about 1.2 inches below normal.
Soil water depletion was not measured in the clumping observation, but was measured in the normally planted corn as approximately 5.8 inches.
Total observed water use  was approximately 17.57 inches.
The normally planted corn was hand harvested as a bulk 20 ft of row within the plot with no references being recorded to individual ear location.
Each ear was individually hand shelled for determination of grain weight and number of kernels.
Ear girth or the number of kernel rows around the circumference was determined from 5 consecutive ears down the row.
The number of rows down the length of the ear was determined from algebra by dividing the ear kernel number by the ear girth.
Kernel weight adjusted to the standard 15.5% wet basis was determined from total grain weight divided by kernel number.
Grain yield was also adjusted to 15.5% wet basis.
Eight individual corn clumps were harvested with all clumps except one containing 4 plants.
Ear grain weight, girth and kernel numbers was measured for each ear from each clump.
The number of rows down the length of the ear was determined from algebra by dividing the ear kernel number by the ear girth.
Both grain yield and kernel weight were adjusted to 15.5% wet basis.
Although hot  and dry  conditions existed during the pollination period  there were relatively light wind conditions averaging 3.7 mph at the two ft anemometer height.
As a result the corn pollinated well with the exception of a few ears on plants that apparently germinated late.
These late plants tend to get shaded or crowded to the point where they are very unproductive.
There were two of the 22 normally planted plants that had ear grain weight less than 100 g with one plant missing an ear.
Table 1.
Results for normally planted corn.
Ear Grain, 15.5%	Kernels	Kernel	Kernel Wt.
Yield	Yield
 Ear	wb, grams/ear	/Ear	Rows/Ear	g/100 krnl	bu/a	Mg/ha
 1	146.6	385	28	38.1	111	6.94
 2	113.4	316	23	35.9	86	5.37
 3	179.6	470	34	38.2	136	8.51
 4	130.0	376	27	34.6	98	6.16
 5	179.4	464	33	38.7	135	8.50
 6	204.4	454	32	45.0	154	9.68
 7	158.4	421	30	37.6	120	7.50
 8	159.1	406	29	39.2	120	7.53
 9	210.9	501	36	42.1	159	9.99
 10	186.4	527	38	35.4	141	8.83
 11	178.6	443	32	40.3	135	8.46
 12	157.5	436	31	36.1	119	7.46
 13	103.4	309	22	33.5	78	4.90
 14	110.6	346	25	32.0	83	5.24
 15	159.4	432	31	36.9	120	7.55
 16	61.8	169	12	36.6	47	2.93
 17	150.9	423	30	35.7	114	7.14
 18	140.7	406	29	34.7	106	6.66
 19	99.3	306	22	32.5	75	4.70
 20	100.7	310	22	32.5	76	4.77
 21	124.5	358	26	34.8	94	5.90
 Avg.
145.5	393	28	36.7	110	6.89
 There were 6 plants for the 8 clumps  that had less than 100 g of grain/ear.
One clump only had 3 plants that germinated.
It is very possible the small ears in the clumping observation were late germinating plants caused by the irregular hand
 planting used for the clumps.
One clump had the grain ear within the corn tassel, a phenomenon that tends to express itself under limited water availability and very low plant population.
Ear expression at the tassel is generally poor production because of desiccation of the kernels.
There was no large differences in grain yield, kernels ear, or kernel weight for the two planting arrangements.
The measured grain yield was slightly higher for the normally planted corn, but that planting arrangement had approximately 2290 more plants/acre.
Yield was decreased considerably for the few clumps that had some individually poor ears, once again probably due to late germination.
Kernel number and kernel weight appeared to be quite good and quite good for the clumps that did not have the late germinating plant.
Greatest individual ear grain and kernel weights occurred for the clumped plants.
This may reflect better pollination and grain filling provided by the plant protection provided in the clump, but also could be a result caused by the different plant populations for the two planting arrangements.
The results should be viewed as simple observations but do indicate that this may be a viable planting arrangement under extremely limited water availability.
Corn in clump planting arrangement at Colby, Kansas on September 11, 2006.
Table 2.
Results from the clumped planted corn.
Ear Grain	Kernels	Ear	Kernel	Kernel Wt.
Yield	Yield
 Clump	Ear grams/ear	/Ear	Girth	Rows/Ear	g/100 krnl	bu/a	Mg/ha
 1	1	201.8	510	14	36	39.6	134	8.42
 2	186.8	542	16	34	34.5	114	7.79
 3	171.3	404	14	29	42.4	114	7.14
 4	251.3	590	14	42	42.6	167	10.48
 Avg.
202.8	512	15	35	39.8	132	8.46
 2	1	172.2	435	14	31	39.6	114	7.18
 2	192.9	523	14	37	36.9	128	8.04
 3	136.5	387	14	28	35.3	91	5.69
 4	197.8	565	14	40	35.0	131	8.25
 Avg.
174.9	478	14	34	36.7	116	7.29
 3	1	176.3	450	14	32	39.2	117	7.35
 2	150.2	428	12	36	35.1	100	6.26
 3	241.2	629	16	39	38.3	160	10.06
 4	81.4	242	14	17	33.6	54	3.40
 Avg.
162.3	437	14	31	36.6	108	6.77
 4	1	196.8	473	12	39	41.6	131	8.21
 2	199.6	524	14	37	38.1	133	8.32
 3	168.4	418	14	30	40.3	112	7.02
 4	151.4	433	14	31	35.0	101	6.31
 Avg.
179.0	462	14	34	38.7	119	7.47
 5	1	172.0	456	14	33	37.7	114	7.17
 2	1.2	4	8	1	30.5	1	0.05
 3	203.7	554	16	35	36.8	135	8.49
 4	155.3	417	16	26	37.2	103	6.48
 Avg.
133.0	358	14	23	35.5	88	5.55
 6	1	35.7	128	12	11	27.9	24	1.49
 2	3.3	16	8	2	20.6	2	0.14
 3	250.5	559	14	40	44.8	166	10.45
 4	170.3	500	14	36	34.1	113	7.10
 Avg.
115.0	301	12	22	31.8	76	4.79
 7	1	206.2	495	14	35	41.7	137	8.60
 2	161.5	427	14	31	37.8	107	6.74
 3	218.2	578	14	41	37.7	145	9.10
 4	17.2	73	12	6	23.6	11	0.72
 Avg.
150.8	393	14	28	35.2	100	6.29
 8	1	0.0	0	8	0	0.0	0	0.00
 2	210.0	549	14	39	38.3	140	8.76
 3	52.6	179	12	15	29.4	35	2.20
 -	-	-	-	-	-
 Avg.
87.6	243	11	18	22.6	44	2.74
 Mean all Clumps	150.7	398	13	28	34.6	98	6.17
SPRINKLER IRRIGATION MANAGEMENT OF MODERN CORN HYBRIDS UNDER INSTITUTIONAL CONSTRAINTS
 Two pre-anthesis  and two post-anthesis  deficit sprinkler irrigation strategies for four corn hybrids where total irrigation was constrained to 11.5 inches against a fully irrigated control were compared in terms of grain yield and yield components, water use, and crop water productivity.
This study was in response to a voluntary agreement of producers in a region of northwest Kansas  where they agreed to reduce irrigation water application to 55 inches over a 5-year period.
This study attempted to determine the best irrigation strategy for these limited applications.
Results indicated full irrigation was still relatively efficient but used 30 to 36% more water.
When corn prices are greater, managing at the full irrigation level and reducing irrigated land area may be more profitable.
Pre-anthesis water stress was more detrimental to grain yield than similar levels of post-anthesis stress because of reductions in kernels/ear.
When water is greatly restricted, a 50% reduction in irrigation post-anthesis might fare reasonably well by relying on stored soil water and precipitation for grain filling.
Hybrids responded to irrigation regime similarly with kernels/ear being most affected by irrigation, but the hybrids attained their own maximum yield in different manners.
The greatest yielding hybrid had the greatest kernel mass and the smallest kernels/ear while the lowest yielding hybrid had the greatest kernel number but lowest kernel mass.
These overall results might not repeat on less productive soils or under harsher environmental conditions.
In the semi-arid Central Great Plains and particularly northwest Kansas, soils are generally productive deep silt loam soils but precipitation is limited and sporadic with mean annual precipitation ranging from 16 to 20 inches across the region, which is only 60-80% of the seasonal water use for corn.
Irrigation is often used to mitigate these water stress effects but at the expense of the continued decline of the Ogallala Aquifer.
In 2012, the Kansas legislature passed new water laws that allowed creation of a new water management structure known as a Locally Enhanced Management Area.
It allows stakeholder groups of various sizes to locally come together and design a management strategy to reduce overdraft of the Ogallala Aquifer in their area subject to approval by the Kansas Division of Water Resources.
The first LEMA to be approved known as Sheridan High Priority Area 6 became a reality within Sheridan and Thomas Counties in northwest Kansas in 2013.
The stakeholders in a 100 square mile area voluntarily agreed to reduce their average water right to 11 inches/year for
 the next 5-year period.
This area is centered approximately 30 miles east of the KSU Northwest Research-Extension Center at Colby, Kansas.
In Kansas, annual rainfall decreases approximately 1 inch for every 18 miles moving east to west and greatest annual rainfall in western Kansas is in the months of May, June, and July, so a similar appropriate restriction at Colby to the Sheridan HPA #6 LEMA might be approximately 12 inches instead of 11 inches.
Corn is the major irrigated crop in the region and producers in this LEMA would prefer to continue growing corn due to the availability of good local markets that include two large cattle feeding operations as well as a nearby dairy.
The LEMA reduction of water right to 11 inches represents about a 27% reduction in water from the 80% chance Net Irrigation Requirement for Sheridan County.
The producers within the LEMA have the flexibility to apply their 5-year allocation of water as they so determine, but could benefit from research that determines when water can be restricted without a large corn yield penalty.
ET-based irrigation scheduling has been promoted in the Central Great Plains for many years.
As producers move to deficit irrigation strategies, this method of scheduling can still be useful in alerting the producer to soil water conditions and can help the producer decide when to allocate their limited water supply.
Management Allowable Depletion  values have been established as a means of helping producers know when to irrigate, but these established values recently have been questioned as too harsh for modern corn production.
16
 Sprinkler irrigation does not allow 14 Colby, Kansas, 1972-2010 for large amounts of water to be 12 39.39 North, 101.07 West timed to a specific growth stage Anthesis, July 20  10 without incurring runoff, so strategies must be employed that 8 PostAnthesis, 8.69 inches can slowly restrict or slowly 6 increase water available to the 4 PreAnthesis, 5.85 inches crop and to soil water storage for 2 later usage.
Preliminary computer 0 simulation indicated that on average, approximately 40% of the 0 20 40 60 80 100 120 seasonal irrigation amount is Days Post Emergence  required prior to anthesis , so an imposed reduction of 50% during the pre-anthesis period might be acceptable most years, yet not be excessive in the drier years.
However, this does not fully reflect the ability of the soil profile to be a "bank," so examining a higher irrigation regime is also warranted.
Figure 1.
Seasonal gross irrigation requirements for field corn at Colby, Kansas.
A three-year field study was conducted to examine restriction of irrigation to approximately 50 or 75% of the ET-Rain value for either the pre-anthesis period or during the post-anthesis period.
Since grain filling  is important, intuitively, one might surmise that those strategies restricting water during the pre-anthesis stages would always be preferable, but the pre-anthesis period is also when the number of kernels/acre is being potentially set and also the soil water storage allows for "banked" water to be used later by a deep rooted crop such as corn.
These deficit strategies were compared to a fully irrigated control treatment.
Four different commercial corn hybrids  were compared under five different irrigation regimes in a three-year  field study on a deep silt loam at the KSU Northwest Research-Extension Center at Colby, Kansas.
The irrigation regimes were: 1) Full irrigation  with no restriction on total irrigation; 2) Irrigation restricted pre-anthesis to 50% of ET, 100% of ET thereafter with 11.5 inches total restriction; 3) Irrigation restricted pre-anthesis to 75% of ET, 100% of ET thereafter with 11.5 inches total restriction; 4) Irrigation restricted post-anthesis to 50% of ET with 11.5 inches total restriction; and 5) Irrigation restricted post-anthesis to 75% of ET with 11.5 inches total restriction.
Irrigation amounts of 1 inch/event were scheduled according to water budget weather-based irrigation scheduling procedures only as needed subject to the specific treatment limitations.
As an example, during the pre-anthesis stage Irrigation Trt 3 would only receive 75% ET, but after anthesis would receive irrigation at 100% until such time that the total irrigation is 11.5 inches.
The four corn hybrids were Pioneer brand 35F48, P0876CHR, P1151YXR, and P1498AM1 with the latter two hybrids being marketed as drought tolerant Aquamax hybrids.
Soil water was monitored periodically  to a depth of 8 ft.
in 1-ft.
increments with neutron moderation techniques.
This data was used to assess MAD values as well as to determine total water use throughout the season.
Corn yield and yield components were determined through hand harvesting a representative sample at physiological maturity.
Crop water productivity was calculated as grain yield/crop water use.
The 5 irrigation treatments  were in a RCB design with irrigation applied using a lateral move sprinkler and the 4 corn hybrid treatments superimposed as split plots.
The data were analyzed using standard PC-SAS procedures.
Weather Conditions and Irrigation Requirements
 Overall weather conditions for the three years were favorable for excellent corn production during the study.
Calculated crop ET for 2013 through 2015 was slightly lower than long term values and seasonal precipitation was 2 to 3 inches greater than normal in 2014 and 2015 and 2 inches less than normal in 2013.
Full irrigation amounts varied from 12.48 inches in 2014 to 15.36 inches in 2013.
The irrigation treatments with pre-anthesis water restrictions  reached their water limitation  in two of the three years  as did the post-anthesis deficit irrigated treatment that was irrigated with 75% of ET during the post-anthesis period.
The irrigation treatment using the least amount of water during the three years of the study was the treatment where irrigation was restricted to 50% of ET during post-anthesis period.
Figure 2.
Cumulative calculated crop ET and precipitation during the growing season for Colby, Kansas, 2013 to 2015.
Figure 3.
Irrigation amounts for the five irrigated corn treatments during the three years of the study.
Crop Yield and Water Use Parameters
 Corn grain yield was greatest in 2014 and was lowest in 2013, the year with the greatest irrigation need.
Fully irrigated corn grain yields ranged annually from 241 to 251 bushels/acre with the deficit-irrigated lowest yields ranging from 215 to 237 bushels/acre.
Corn yield was greatest for unrestricted irrigation  but required 30 to 36% more irrigation, but was still very efficient with only a 2 to 4% reduction in water productivity .
Lower yields occurred for pre-anthesis water restrictions  than for similar postanthesis restrictions.
These results suggest that obtaining sufficient kernel set was more important than saving irrigation for grain filling in this study.
When irrigation is greatly restricted, a 50% reduction post-anthesis appears as a promising alternative, relying more heavily on stored soil water and precipitation for grain filling.
In a general sense, all of the irrigation treatments  were relatively efficient with excellent overall average yields  with total seasonal water use  and residual fall soil water  which were both in a fairly narrow range of values, respectively.
Figure 4.
Corn yields for the five irrigation treatments during the three years of the study.
Figure 5.
Water productivity for the five irrigation treatments during the three years of the study.
Figure 6.
Fall available soil water  at harvest and seasonal water use as affected by irrigation regime , KSU Northwest Research-Extension Center, Colby Kansas.
Note: Irrigation Trts 3 and 5 coincidentally resulted in similar values.
Overall, large differences in irrigation  had minimal effect on residual ASW  and total water use , suggesting that all the treatments were relatively efficient.
Table 1.
Corn yield, yield component, and water use parameters as affected by irrigation at Colby, Kansas, 2013-2015.
Irr Trt.
Amount	Irr.
Yield, bu/a	Plant density,	p/a	Ears/	plant	Kernels/	ear	Kernel mass,	mg	Water use,	inches	WP, lbs/acre-in
 1.
100% ET	15.36	241	A	32452	A	1.00	A	542	A	349	A	23.0	A	587	A
 2.
50/100% ET	11.52	215	C	32779	A	0.99	A	483	B	349	A	20.5	B	590	A
 3.
75/100% ET	11.52	230	AB	32634	A	0.99	A	522	A	347	A	21.6	B	598	A
 4.
100/50 % ET	10.56	228	B	32561	A	0.99	A	524	A	344	A	21.7	AB	593	A
 5.
100/75% ET	11.52	234	AB	32561	A	1.00	A	527	A	349	A	21.4	B	616	A
 Prob > F	0.0015	NS	NS	0.0029	NS	0.0161	NS
 1.
100% ET	12.48	251	A	33215	A	1.00	A	566	A	339	A	28.8	A	490	C
 2.
50/100% ET	9.60	237	B	33360	A	1.00	A	539	B	336	A	26.3	C	504	BC
 3.
75/100% ET	10.56	248	A	33251	A	1.01	A	557	A	337	A	26.9	B	516	AB
 4.
100/50 % ET	7.68	246	A	33069	A	1.00	A	558	A	338	A	25.8	D	535	A
 5.
100/75% ET	10.56	250	A	33215	A	1.00	A	566	A	338	A	27.2	B	516	AB
 Prob > F	0.0090	NS	NS	0.0140	NS	<0.0001	0.0053
 1.
100% ET	14.40	241	A	32380	A	1.00	A	575	A	330	A	31.5	A	429	A
 2.
50/100% ET	11.52	233	A	32525	A	1.00	A	563	A	323	A	29.0	CD	450	A
 3.
75/100% ET	11.52	238	A	32597	A	1.00	A	574	A	324	A	29.7	BC	450	A
 4.
100/50 % ET	9.60	232	A	32452	A	0.99	A	574	A	320	A	28.6	D	456	A
 5.
100/75% ET	11.52	234	A	32670	A	0.99	A	573	A	322	A	29.8	B	441	A
 Prob > F	NS	NS	NS	NS	NS	<0.0001	NS
 1.
100% ET	14.08	244	A	32682	A	1.00	A	561	A	339	A	27.8	A	502	A
 2.
50/100% ET	10.88	228	C	32888	A	1.00	A	529	B	336	A	25.3	C	515	A
 3.
75/100% ET	11.20	239	B	32827	A	1.00	A	551	A	336	A	26.1	B	522	A
 4.
100/50 % ET	9.28	236	B	32694	A	1.00	A	552	A	334	A	25.4	C	528	A
 5.
100/75% ET	11.20	240	AB	32815	A	1.00	A	556	A	336	A	26.1	B	524	A
 Prob > F	0.0001	NS	NS	0.0001	NS	<0.0001	NS
 Corn grain yield was significantly greater for hybrid P1151YXR  with average  yield increases ranging from 4 to 9 bu/a over the other three hybrids.
There were significant differences in the yield components with the highest yielding hybrid, P1151YXR 2014, having the smallest number of kernels/ear  but having much greater kernel mass.
Water use though statistically different for the four hybrids actually varied on average less than 0.4 inches.
Water productivity was approximately 3% greater for the highest yielding hybrid, P1151YXR, and was attributable to the greater yield of this hybrid.
In comparing the lowest yielding hybrid, 35F48, to the highest yielding hybrid, P1151YXR , it can be seen that although the lowest yielding hybrid had the greatest number of kernels/ear , it had the lowest kernel mass  and thus grain filling limited its yield.
Combining the hybrid results with the irrigation results suggests that it is important to select a high yielding hybrid and then to make sure that it establishes an appropriate number of kernels/ear for its inherent characteristics.
In the following section, the yield components will be examined more closely to further bolster this conclusion.
Examination of Yield Components
 Yield can be calculated as: Yield = Planes Ears Kernels Mass Eq.
1.
Plant Ear Kernel
 The first two terms are typically determined by the cropping practices and generally are not affected by irrigation practices later in the season.
Water stresses during the mid-vegetative period through about 2 weeks after anthesis can greatly reduce kernels/ear.
Kernel mass, through greater grain filling, can partially compensate when insufficient kernels/ear are set, but may be limited by late season water stress or hastened senescence caused by weather conditions.
In this study, the yield component most strongly affected  by irrigation practices was kernels/ear and was significantly affected  in two years and also for the average of all years.
Full irrigation  had the greatest number of kernels/ear while the 50% ET pre-anthesis treatment  consistently had the smallest value.
These results suggest that pre-anthesis water stresses must be limited so that sufficient kernels/ear  can be set for modern corn hybrids.
Because all the yields components combine directly through multiplication to calculate yield, their effect on yield can be easily compared in Figure 7.
The numbers on the lines refer to the 5 irrigation trts and the lines just connect similar data.
A variation of 1% in any yield component would affect yield by the same 1%.
It can be observed that there is much greater horizontal dispersion for kernels/ear than for all the other yield components which vary less than approximately 1%.
Thus, irrigation treatment had a much greater effect on kernels/ear and the fully irrigated 100% ET, Irr 1 and the pre-anthesis 50% ET, Irr 2 were affected the greatest.
Although Irr 4  averaged using 1.6 inches less irrigation than Irr 2 , its average corn yield was 8 bu/a greater.
Irrigation treatment 4 also had the greatest water productivity of all five treatments although all water productivities were
 respectable.
It can be seen in Figure 6 that the major difference between Irr 4 and 2 is that Irr 4 was able to set a kernels/ear value much closer to the mean value than Irr 2.
As indicated earlier there were appreciable differences in how the hybrids attained their grain yields through combination of their yield components.
The graph indicates that the highest yielding hybrid, P1151YXR, had the least number of kernels/ear while the lowest yielding hybrid, 35F48, had the greatest kernels/ear.
This ranking reversed for kernel mass with P1151YXR having the greatest kernel mass and 35F48 having the least.
The other two hybrids  had near average values of kernels/ear and kernel mass.
It can be noted that hybrid P1151YXR and P1498AM1 are both marketed as drought tolerant.
The effect of irrigation treatment on individual hybrid performance is shown in Figure 9.
Kernels/ear was the yield component most affected by irrigation treatment for all four hybrids, with the adequate pre-anthesis irrigation  being necessary to enhance kernels/ear.
Although as previously discussed, kernel mass was very different for hybrids 35F48 and P1151YXR , both hybrids individually had stable values that were relatively unaffected by irrigation treatment.
The other two hybrids P0876CHR and P1498AM1 had slightly greater ability to flex kernel mass  with differences between Irr 1 and 2 having the greatest effect on kernel mass and subsequently yield.
It can also be seen in Figure 9 when comparing Irr 2 and 4 for all four hybrids that Irr 4  had relatively minor effect on the yield components and thus had little effect on grain yield while Irr 2  negatively affected kernels/ear and severely reduced grain yield.
These differences in how the hybrids attained grain yield clearly indicate the combined importance of good irrigation management and hybrid selection.
Table 2.
Corn yield, yield component, and water use parameters as affected by hybrid at Colby, Kansas, 2013-2015.
Hybrid	Yield, bu/a	Plant density,	p/a	plant	Ears/	Kernels/	ear	Kernel mass,	mg	Water use,	inches	WP, lbs/acre-in
 1.
35F48	219	C	32263	B	0.99	A	549	A	31.53	D	21.31	C	577	B
 2.
P0876CHR	230	B	32902	A	1.00	A	527	B	33.86	C	21.77	AB	595	B
 3.
P1151YXR	243	A	32902	A	1.00	A	493	D	38.31	A	21.93	AB	624	A
 4.
P1498AM1	226	B	32322	B	0.99	A	509	C	35.27	B	21.52	BC	592	B
 Prob > F	<0.0001	0.0117	NS	<0.0001	<0.0001	0.0133	<0.0001
 1.
35F48	241	B	33164	B	1.01	A	571	AB	322	C	26.96	A	502	C
 2.
P0876CHR	249	A	32989	B	1.00	A	581	AB	329	B	26.96	A	519	AB
 3.
P1151YXR	251	A	33599	A	1.00	A	513	C	369	A	26.90	A	523	A
 4.
P1498AM1	244	AB	33135	B	1.00	A	564	B	331	B	27.20	A	504	BC
 Prob > F	0.0183	0.0016	NS	<0.0001	<0.0001	NS	0.0140
 1.
35F48	240	A	32641	A	1.00	A	578	A	325	A	29.4	B	457	A
 2.
P0876CHR	233	A	32583	A	0.99	A	563	A	326	A	29.6	B	442	A
 3.
P1151YXR	234	A	32583	A	1.00	A	564	A	324	A	29.4	B	445	A
 4.
P1498AM1	236	A	32292	A	1.00	A	582	A	320	A	30.3	A	437	A
 Prob > F	NS	NS	NS	NS	NS	<0.0001	NS
 1.
35F48	233	C	32689	BC	1.00	A	566	A	321	C	25.9	C	512	B
 2.
P0876CHR	238	B	32825	AB	1.00	A	557	AB	331	B	26.1	AB	519	B
 3.
P1151YXR	242	A	33028	A	1.00	A	524	C	358	A	26.1	BC	531	A
 4.
P1498AM1	236	BC	32583	C	1.00	A	552	B	335	B	26.3	A	511	B
 Prob > F	<0.0001	0.0031	NS	<0.0001	<0.0001	0.0027	<0.0001
 Figure 7.
Yield variation as affected by variation in the yield components for the five different irrigation treatments, KSU Northwest Research-Extension Center, Colby, Kansas.
Note: Upward sloping lines to the right, such as Kernel/Ear indicate that irrigation treatment heavily affected the yield component and subsequently affected the grain yield, while vertical lines with little yield component variation from zero indicate little irrigation effect.
Figure 8.
Yield variation as affected by variation in the yield components for the four corn hybrids, KSU Northwest Research-Extension Center, Colby, Kansas.
Note: Sloping lines, such as the Kernels/Ear and Kernel Mass indicate that the corn hybrid appreciably affected that yield component and subsequently affected the grain yield, while vertical lines of with little yield component variation from zero indicate little effect of corn hybrid.
Figure 9.
Yield variation for the four different hybrids as affected by variation in the yield components for the five different irrigation treatments, KSU Northwest ResearchExtension Center, Colby, Kansas.
Note: Upward sloping lines to the right, such as Kernel/Ear indicate that irrigation treatment heavily affected the yield component and subsequently affected the grain yield, while vertical lines with little yield component variation from zero indicate little irrigation effect.
Note: Each of the four panels relate to an individual hybrid and all plotted data refers to only that hybrid (i.e., Mean values are calculated across all irrigation treatments only for that hybrid.
CLOSING THOUGHTS AND CONCLUSIONS
 Full irrigation was still relatively efficient but used 30 to 36% more water.
When irrigation is not severely restricted, corn prices are greater, and/or irrigation costs are lower, managing irrigation at this level and reducing irrigated land area may be more profitable.
Pre-anthesis water stress was more detrimental to grain yield than similar levels of post-anthesis water stress because of reductions in kernels/ear.
Reductions in kernels/ear occurred for all four hybrids for when subjected to pre-anthesis irrigation reductions.
This result is somewhat counter to typical older guidelines which indicated that moderate stress during the vegetative stage for corn may not be detrimental.
This may be indicating that kernel set on modern hybrids is a greater factor in determining final yields.
When water is greatly restricted, a 50% reduction post-anthesis might fare reasonably well by relying on stored soil water and precipitation for grain filling.
The rationale behind this comment is that it is important to establish a sufficient number of kernels/ear  that potentially can be filled if soil water and weather conditions permit.
Hybrid selection remains very important and modern corn hybrids exhibited different schemes of attaining yields.
As an example, the highest yielding hybrid attained greater kernel mass which was relatively stable across irrigation regimes while the lowest yielding hybrid attained the largest number of kernels/ear and had a relatively stable but much smaller kernel mass.
These results might not repeat on less productive soils or under harsher environmental conditions.
On coarser soils , stored soil water and sporadic precipitation might not be sufficient to "carry" the crop through the post-anthesis period as well as in this study.
However, it can be noted that the 50% ET post-anthesis treatment  still performed better than the 50% pre-anthesis treatment  in 2013, the year with the greatest irrigation need.
This research was supported in part by the Ogallala Aquifer Program, a consortium between USDA Agricultural Research Service, Kansas State University, Texas AgriLife Research, Texas AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
Users receive those predictions, in numerical values, from their computers or mobile devices without going to the field.
The app also helps producers schedule their work more efficiently by showing the fields that need attention for irrigation.
Using Irrigation Water Legally
 Under Oregon law, the public owns most of the water in the state.
That means that landowners with water flowing past, through, or under their property do not automatically have the right to use it; they need a permit  from the Oregon Water Resources Department.
While there are some exceptions, generally speaking, anyone who wants to use the public's water needs a water right, regardless of whether the water is surface water  or groundwater.
A water right gives a person permission to irrigate a specific piece of land with a specific amount of water during a specific period of time.
Oregon keeps detailed records of which lands can be irrigated and how much water is allowed.
A water right is typically attached to the land described in the right; if the land is sold, the water right stays with the land and the new owner.
Water users are legally obligated to use water beneficially, which means they cannot waste it or use it for a purpose that is inconsistent with Oregon law and the best interest of the public.
For example, tailwater  could be considered wasteful and, thus, unlawful.
To keep a water right, a water right holder has to beneficially use the water at least once every five years.
If not, the holder might lose the water right.
Water right holders should document their usage by taking photos and dating them in the event their water right is contested.
Each water right has a priority date.
The water right priority date determines who gets water in a time of shortage.
The older  the water right, the longer water is available to that water right holder in a time of shortage.
This means that the first person to obtain a water right on a stream is the last to have the water shut off in times of low streamflows.
When water supplies are limited, the water right holders with the oldest priority date  can request the water to which they are entitled, regardless of the needs of those with more recent priority dates.
OWRD's Watermasters regulate and distribute water among the holders of surface water rights to ensure they are receiving and using their legal amount.
Water rights generally have two components: rate and duty.
Rate is the maximum instantaneous flow of water delivered in cubic feet per second or gallons per minute.
Duty is the maximum volume allowed per acre per irrigation season.
For example, 2 acre-feet is the equivalent of receiving enough water to flood each acre with 2 feet of water.
Figure 1.
In this example, water flowing from the hose is the rate and once the bucket is full, the duty has been met.
Water rights can be issued for beneficial uses, such as land irrigation, watering livestock, improving fish habitat and water quality, and municipal and commercial/ industrial needs.
Certain water uses on properties with a well  do not need a water right.
These include: single or group domestic
 use of up to 15,000 gallons per day; water for livestock; irrigating up to 1/2 acre of lawn or noncommercial garden; and commercial use of up to 5,000 gallons per day.
Commercial use does not include irrigation of a for-profit crop but can include the processing of a commercial crop.
Some uses of surface water do not require a water right, but those are less common on small-acreage properties.
Obtaining a Water Right
 In most areas of Oregon, there is not enough surface water available in the summer for new water rights.
Groundwater is also limited in some areas during the summer months.
New water rights are allocated carefully to keep from harming existing water rights for cities, farms, factories, fish habitat, and other uses.
Water rights are not automatically granted; OWRD provides opportunities to protest the granting of a permit.
Other water users can assert that a new permit may cause injury to their water use, and the public can claim that a new permit may harm the public interest.
This process protects both existing water users and public resources.
Figure 2.
Irrigation districts often use a weir  to measure water flow and divert water to patrons.
Irrigation districts distribute water to their patrons based on their water rights of record.
They also make sure their patrons use water according to the terms and conditions of those rights.
Landowners in an irrigation district may not actually own the water rights; irrigation districts often hold them in trust for their patrons.
Property owners within an irrigation district may or may not have a water right.
The title company should provide this information when property is purchased; however, it is always a good idea to check with your local Watermaster if questions arise.
Some irrigation districts are quasigovernmental entities while others are organized as private corporations.
In most cases, they will have a board of directors consisting of district landowners who typically are elected by other district patrons.
Oregon landowners with an irrigation district water right do not have the authority to move that water to other places on their property, use it in excess of their water right, sell the water right to someone else, or build on top of an irrigation district easement.
Wate-right regulations may vary between states.
The irrigation district, and in some cases OWRD, must be consulted on all matters involving changes to the water right or the activity on its easements.
Irrigation districts can stop encroachments that interfere with their easements.
When in doubt, call your local irrigation district, describe your situation, and ask for their help.
For more information on using irrigation water legally, contact your local Extension agent, Natural Resources Conservation Service, or Soil and Water Conservation District.
Technical and financial assistance is available for landowners wishing to address resource concerns on their property.
The phrase "Living on The Land" is used with permission from Living on The Land Stewardship for Small Acreage,  2008, UNCE/WSARE.
Ellen Hammond, Water Quality Specialist, Oregon Department of Agriculture
 Brian Tuck, Extension Regional Administrator, Oregon State University
 Robert Wood District 3 Watermaster The Dalles, Oregon
 Shilah Olson, Conservation Planner, Wasco County Soil & Water Conservation District, Oregon
 Susan Kerr, Extension Regional Livestock and Dairy Specialist, Washington State University
 Listen to our Living on The Land podcasts at iTunes U.
Economic Viability of Grain Sorghum and Corn as a Function of Irrigation Capacity
 Jason Warren Associate Professor
 Art Stoecker Associate Professor, International Agricultural Development
 Rodney Jones Associate Professor, Endowed Professor, Oklahoma Farm Credit
 Karthik Ramaswamy Graduate Student, Agricultural Economics Area Extension Agronomy Specialist
 Grain sorghum is often hailed as a crop with high water use efficiency and low input costs.
For example, NRCS irrigation guide  suggests that at Goodwell, Okla., optimum production of corn requires 20 inches of irrigation water, while grain sorghum only requires 15.5 inches.
This suggests that as water availability in the Panhandle region declines, grain sorghum may become a more viable crop for irrigation.
In addition, it is very well adapted to the southern plains and has a feed value that is comparable to corn.
In fact, the energy content is approximately 90 to 95 percent of that for corn and the crude protein is 20 to 30 percent higher than corn.
The 10-year average price for grain sorghum received by producers in the U.S.
is $4.17 per bushel, compared to $4.39 per bushel for corn.
Despite the higher water use efficiency of grain sorghum, its production in the southern high plains under irrigation is still dwarfed by irrigated corn production.
Specifically, in the three Oklahoma Panhandle counties of Beaver, Texas and Cimarron, there has been an average of 107,935 acres of irrigated corn in the past 10 years, compared to only 37,561 acres of grain sorghum.
This suggests a potential for the expansion of irrigated grain sorghum in the future as water availability declines.
This disparity between cornand grain sorghum-irrigated acres along with declining irrigation capacity in the region prompted the effort to conduct an economic analysis to determine the short-term and long-term profitability of corn and grain sorghum at irrigation capacities ranging from 6.4 to 0.8 gallons per miniute per acre.
This analysis was conducted using simulated crop yields and irrigation estimates produced by the EPIC crop model.
The model was calibrated using variety performance data collected from the OSU corn and sorghum variety performance trials conducted in the Oklahoma panhandle.
It was also validated with data collected at the Oklahoma Panhandle Research and Extension Center.
Crop Yield as a Function of Irrigation Capacity
 The yield and irrigation water applied presented in Tables 1 and 2 are the result of model simulations in which irrigation was applied at 1.4 inches per application event at a frequency constrained by irrigation capacity and/or a soil moisture depletion.
Specifically, the data presented shows the outcome of irrigation triggered when the soil moisture is depleted to 50, 70 or 90 percent of the plant available water capacity.
As expected, this analysis shows that grain yields for both crops are maximized when soil moisture is maintained at 90 percent of plant available water-holding capacity with 6.4 gallons per miniute per acre irrigation capacity.
In this scenario, the sorghum and corn crops received 15.6 and 22.5 inches of irrigation water, respectively.
This is comparable to the NRCS estimates for average crop requirement.
In every scenario presented, the irrigation use efficiency is higher for grain sorghum than corn, as is expected.
These yields may be compared to average yields reported by NASS in Texas County between 2000 and 2008.
Based on this comparison, average corn yields from NASS are on average 20 percent below expected yields with 6.4 gallons per minute per acre irrigation capacity.
In contrast, average grain sorghum yields from NASS are on average 50 percent of the simulated yields at 6.4 gallons per minute per acre.
The 10-year average corn and sorghum yields from performance trials conducted in Texas County of 200 bushels per acre and 141 bushels per acre, respectively, produced with an average of 21 and 8 inches of water , respectively, suggests that the model may underestimate the efficiency of grain sorghum, while it provides outcomes that are consistent with trial data for corn.
Furthermore, the variety performance data also demonstrate
 Table 1.
Results from EPIC Simulation of Irrigated Sorghum Yields and Irrigation rates and irrigation use efficiency using Center Pivot System when irrigation was triggered when soil moisture is depleted to 50, 70 or 90 percent of plantavailable water capacity.
Irrigation Applied	Irrigation Use Efficiency
 Irrigation	Yield 		
 Capacity	Soil Moisture Trigger	Soil Moisture Trigger	Soil Moisture Trigger
 GPM/acre	50%	70%	90%	50%	70%	90%	50%	70%	90%
 6.4	129	149	163	9.2	12.6	15.6	14	12	10
 5.6	129	145	156	9.1	11.8	14.1	14	12	11
 4.8	129	140	148	9	10.7	12.6	14	13	12
 4	126	134	141	8.8	9.8	11.3	14	14	12
 3.2	122	129	134	8.3	9.4	10.4	15	14	13
 2.4	109	112	117	7.1	7.6	8.3	15	15	14
 1.6	90	91	92	3.2	3.4	4.1	28	27	22
 0.8	88	88	89	2.4	2.5	2.8	37	35	32
 Table 2.
Results from EPIC Simulation of Irrigated Corn Yields, Irrigation rates and irrigation use efficiency using Center Pivot System when irrigation was triggered when soil moisture is depleted to 50, 70 or 90 percent of plant available water capacity.
Irrigation Applied	Irrigation Use Efficiency
 Irrigation	Yield 		
 Capacity	Soil Moisture Trigger	Soil Moisture Trigger	Soil Moisture Trigger
 GPM/acre	50%	70%	90%	50%	70%	90%	50%	70%	90%
 6.4	167	194	213	16.2	21.5	22.5	10	9	9
 5.6	165	186	199	16.1	20.4	23.1	10	9	9
 4.8	163	177	187	15.9	19	21.6	10	9	9
 4	158	168	175	15.3	17.4	19.5	10	10	9
 3.2	152	158	164	14.4	15.9	17.6	11	10	9
 2.4	137	139	143	11.8	12.8	13.9	12	11	10
 1.6	119	120	122	9.1	9.7	10.3	13	12	12
 0.8	98	98	99	5.7	5.9	6.1	17	17	16
 Table 3.
Average corn and sorghum yields, and irrigation water applied to hybrid performance trials located in Texas County.
Average	Irrigation	Average	Irrigation
 bu/ac	inches	bu/ac	inches
 2005	196	17	149	10
 2006	183	20	143	5
 2007	178	20	92	4
 2008	246	21	115	6
 2009	226	21	148	9
 2010	179	18	145	8
 2011	85	21	166	10
 2012	240	26	152	11
 2013	236	26	145	10
 2014	228	18	159	9
 Average	200	21	141	8
 t Corn average yields were measured at Joe Webb's farm.
tt Sorghum average yields were measured at OPREC.
that on average, the county corn yields are 14 percent below those achieved in the performance trial and the county grain sorghum yields are 41 percent below what is achieved in the performance trial.
Economic analysis based on Model Simulated Yields
 Tables 4 and 5 contain the production budgets and estimated net revenue for corn and sorghum, respectively, when irrigated to maintain soil moisture at 90 percent of plant available water.
This soil moisture threshold was selected because the lower yields resulting from lower soil moisture thresholds did not increase short term profit.
However, utilization of drier thresholds did show promise in maximizing the long-term net present value of irrigation water.
As expected, corn generates greater profit when irrigation capacity is equal to or greater than 5.0 gallons per minute per acre.
Furthermore, it maximizes net revenue at all irrigation capacities because of the greater yield that can be achieved.
However, this greater yield comes at a higher variable cost of production.
This analysis suggests that although highyielding corn may be an economically superior option when
 Table 4.
Estimated net revenue over variable cost for grain sorghum irrigated by central pivot when irrigation occurs at the 90 percent soil moisture trigger by well capacity for a 120-acre pivot.
Well Capacity	GPM/acre	6.7	5.8	5	4.2	3.3	2.5	1.7	0.8
 Yield	bu/ac	163	156	148	141	134	117	92	89
 Nitrogen	lbs/ac	181.6	173.6	165.5	157.3	149.2	130.7	102.5	98.7
 Phosphorous	lbs/ac	29.4	28.1	26.8	25.4	24.1	21.1	16.6	16.0
 Irrigation	acre-inch	15.6	14.1	12.6	11.3	10.4	8.3	4.1	2.8
 Fertilizer-Nitrogen	$	99.9	95.5	91.0	86.5	82.0	71.9	56.4	54.3
 Fertilizer-Phosphorous	$	15.3	14.6	13.9	13.2	12.5	11.0	8.6	8.3
 Seed Cost	$	16.1	16.1	16.1	16.1	16.1	16.1	16.1	16.1
 Herbicide Cost	$	52.4	52.4	52.4	52.4	52.4	52.4	52.4	52.4
 Insecticide Cost	$	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
 Crop Consulting	$	6.3	6.3	6.3	6.3	6.3	6.3	6.3	6.3
 Drying	$	21.2	20.2	19.3	18.3	17.4	15.2	12.0	11.5
 Miscelleneous	$	10.0	10.0	10.0	10.0	10.0	10.0	10.0	10.0
 Custom Hire	$	132.5	129.4	126.2	122,9	119.7	112.5	101.3	99.8
 Non Machinery Labor	$	18.0	18.0	18.0	18.0	18.0	18.0	18.0	18.0
 Interest	$	15.7	15.1	14.4	13.8	13.1	11.7	9.5	9.2
 Irrigation Cost	$	90.4	79.8	70.3	62.6	56.8	44.9	21.9	14.8
 Sub Total	$	477.7	457.3	437.9	420.1	404.4	369.9	312.5	300.7
 Crop Insurance	$	22.9	22.0	21.0	20.2	19.4	17.8	15.0	14.4
 Total Variable Cost	$	500.6	479.3	458.9	440.3	423.8	387.7	327.5	315.1
 Net Revenue-Var Cost	$	176.8	168.4	158.4	146.5	132.7	100.0	55.1	53.1
 t Irrigation is the depth of water applied with a center pivot irrigation system assuming that only 85% of water is delivered to root zone.
Irrigation depth also reflects depth of water to be applied under intensive irrigation scheduling management.
Table 5.
Estimated net revenue over variable cost for corn irrigated by central pivot when irrigation occurs at the 90 percent soil moisture trigger by well capacity for a 120-acre pivot.
Well Capacity	GPM/acre	6.7	5.8	5	4.2	3.3	2.5	1.7	0.8
 Yield	bu/ac	213	199	187	175	164	143	122	99
 Nitrogen	lbs/ac	196.8	183.0	171.9	160.9	151.0	130.9	112.1	90.9
 Phosphorous	lbs/ac	28.5	26.5	25.0	23.4	21.9	19.0	16.3	13.2
 Irrigation	acre-inch	22.5	23.1	21.6	19.5	17.6	13.9	10.3	6.1
 Fertilizer-Nitrogen	$	108.2	100.7	94.6	88.5	83.0	72.0	61.7	50.0
 Fertilizer-Phosphorous	$	14.8	13.8	13.0	12.1	11.4	9.9	8.5	6.9
 Seed Cost	$	112.6	112.6	112.6	112.6	112.6	112.6	112.6	112.6
 Herbicide Cost	$	61.0	61.0	61.0	61.0	61.0	61.0	61.0	61.0
 Insecticide Cost	$	16.0	15.7	15.5	15.2	15.0	14.6	14.1	13.6
 Crop Consulting	$	6.5	6.5	6.5	6.5	6.5	6.5	6.5	6.5
 Drying	$	27.7	25.9	24.3	22.7	21.4	18.5	15.9	12.9
 Miscelleneous	$	10.0	10.0	10.0	10.0	10.0	10.0	10.0	10.0
 Custom Hire	$	161.5	155.1	149.9	144.7	140.0	130.5	121.5	111.4
 Non Machinery Labor	$	18.0	18.0	18.0	18.0	18.0	18.0	18.0	18.0
 Interest	$	20.0	19.0	18.1	17.3	16.5	14.9	13.4	11.8
 Irrigation Cost	$	130.0	130.5	120.4	107.4	96.1	75.3	55.5	32.7
 Sub Total	$	686.5	668.8	643.9	616.0	591.6	543.8	498.8	447.4
 Crop Insurance	$	33.0	32.1	30.9	29.6	28.4	26.1	23.9	21.5
 Total Varible Cost	$	719.4	700.9	674.8	645.6	620.0	569.9	522.7	468.8
 Net Revenue-Var Cost	$	236.6	190.0	162.5	138,4	116.4	69.1	24.9	-25.0
 t Irrigation is the depth of water applied with a center pivot irrigation system assuming that only 85% of water is delivered to root zone.
Irrigation depth also reflects depth of water to be applied under intensive irrigation scheduling management.
ample water is available, the production of lower-cost crops with greater water use efficiency characteristics should be considered in situations with limited irrigation water.
Limitations to Irrigated Grain Sorghum Production
 There are certainly practical limitations to the extensive production of irrigated grain sorghum in the Oklahoma panhandle.
For example, grain sorghum does not currently contain the crop protection genetics contained in corn, making it more challenging to manage pests such as weeds and insects.
As such, grain sorghum will need to be incorporated as a component of a crop rotation system to succeed.
Work conducted at the Oklahoma Panhandle Research and Extension Center has shown that both corn and grain sorghum production can be improved when they are produced in rotation.
The sugarcane aphid also presents a new uncertainty as to its long-term im-
 pact on grain sorghum production costs.
As such, producers should adjust the production budgets presented to include their costs associated with managing the new pest.
It is unlikely that grain sorghum will gain production acres in excess of the corn acres.
However, this research adds to the body of evidence suggesting that both economic and agronomic benefits could be realized if at least a portion of the 107,935 acres of corn were planted to grain sorghum in situations where irrigation capacities are below 5 gallons per minute per acre.
Use: overlapping pivots , VRI type: zone, prescription type: static, management intensity: low.
Private applicators can certify for a license or recertify an existing one by completing the online private self-study program.
This program allows applicators to complete their certification training on their own time and at their own pace.
The Pesticide Education Office continues to make enhancements to this program each year.
New for 2023, as part of a pilot project, certain county extension offices have agreed to host computer kiosks that private applicators can use to complete the program.
Please contact your county office to inquire.
Pivots operating below or above the designed water pressure can create uniformity issues across fields and/or increase operating expenses.
Insufficient pressure can impact application uniformity by preventing adequate water from reaching the far end of the pivot; whereas, excessive pressure may provide good uniformity but inflates energy costs.
Need to Check Soil Moisture
 Irrigation scheduling is deciding when and how much to irrigate.
A variety of procedures are available, but all involve monitoring of some indicator to determine irrigation need.
Checking soil moisture content is one of the most common procedures.
This can range from kicking clods, turning it with a shovel, pulling cores with a soil probe, using the 'appearance and feel method' to estimate soil water content, or using sensors to measure soil moisture.
Crop water use or ET methods of irrigation scheduling also require periodic checks of soil moisture.
These are commonly referred to as the water budget or 'checkbook method' of irrigation scheduling.
However, it is important to validate the 'checkbook balance' at least every one or two weeks by comparing it to fieldmeasured soil moisture.
If there is a discrepancy, reconcile the 'checkbook balance' by using the measured soil moisture content going forward.
Types of Soil Moisture Readings
 Soil moisture measurements can be obtained many ways, some more readily than others.
However, effective use of soil moisture readings requires experience and judgment and, in many cases, just good old common sense.
They are another tool, another source of information.
They should be duly evaluated and considered before relying upon them for critical decisions.
Some measurements are semi-qualitative while others provide greater quantitative accuracy.
Several of the more common and well known are included below.
Appearance and Feel	Easy, simple, accuracy	Lower accuracy, labor
 improves with experience.
intensive.
Gravimetric	High accuracy with increased	Very labor intensive,
 	sampling, direct measure.
delays to obtain data.
Tensiometers	Instantaneous, approximates	High maintenance,
 	soil moisture content.
tension breaks, freezing
 Electrical Resistance	Instantaneous, increased	Slower response, less
 	range, approximates soil	sensitive at low
 moisture content.
moisture, affected by
 Capacitance and FDR	High accuracy, volumetric	Highly influenced by
 	water content and salinity.
adjacent moisture/voids.
TDR and TDT	High accuracy, volumetric	Highly influenced by
 	water content and salinity,	adjacent moisture/voids.
Water Budget or	Estimates the soil moisture	Needs calibration and
 Checkbook	balance.
periodic adjustments.
Neutron Probe	High accuracy, relative ease	High cost, regulatory
 of deep readings, repeatable.
requirements.
Regardless of the method utilized to measure soil moisture, it is critical the irrigator understand that one measurement is almost never representative of the entire field.
A single soil moisture measurement is for one point at a given time.
It cannot reasonably be assumed to represent the entire field.
It is essential to obtain additional measurements.
However, this does not mean that purchasing more hardware is always required.
The 'checkbook method' is inherently an average for the field, but it does need the periodic 'reality check" to make sure it is representative of soil moisture levels in the field.
This can be accomplished by hand probing and use of the 'appearance and feel method'.
It could also utilize an automated soil moisture monitoring station sited in a representative area of the field.
Significant improvements in soil moisture sensors have occurred in recent years, making them more accurate, reliable, and economical.
Placement of soil moisture sensors is very important.
For representative readings the sensor must typically be installed in the principle soil type, within the active crop root zone, and avoiding high spots, slope changes, or depressions where runoff may collect.
If the sensor requires periodic visits for service or to obtain readings, it is also important for it to be reasonably accessible.
Insertion or Slurry Bedding of Sensors
 It is not okay to simply dig a hole and backfill around a soil moisture sensor.
Destruction of roots and soil structure must be minimized.
Water settling is also taboo.
For soil moisture sensors to provide accurate readings, they must be in full direct contact with undisturbed soil whenever possible.
Air voids, large roots, rocks, etc.
must be avoided.
Direct, clean insertion of sensors into naturally consolidated soil is typically preferred.
It provides for near immediate availability of representative moisture readings.
However, sometimes the soil is too dry, hard, or gravelly to safely allow installation by insertion, even with a pilot slot or hole.
The soil would then be screened, mixed into a slurry  and the sensor installed undamaged with full soil contact, howbeit not natural and undisturbed.
However, it may be some time before this excess moisture is depleted, especially at greater depths and in heavier soils.
Several weeks may pass before the sensor will provide readings representative of field conditions.
The deeper the sensor is to be installed, generally the greater the difficulty with proper installation.
Avoiding the potential for preferential flow of surface water to the sensor is very important.
Small surface mounding of soil around the sensor to avoid surface puddling, good compaction and sealing around wires, etc.
will help prevent extra water from reaching the sensor and falsely elevating the readings.
Unnecessary replacement of hardware should be avoided.
Besides the expense of purchasing and re-installing replacement equipment, the desired soil moisture information is also lost for some period of time.
'Losing' the location of sensors installed in tall corn because of poor flagging and mapping is expensive , especially when eventually 'found' by
 the silage cutter.
Inexpensive hand-held GPS units are a great tool for preventing such mishaps.
Tensiometers are liquid filled and will freeze and break if installed too early in the spring or left in the field too late in the fall.
Always use distilled water and the antibacterial dye provided by the manufacturer to prevent plugging of the ceramic tip.
Rodents  love to chew on exposed sensor wires, etc.
Placing them inside PVC conduit or braided stainless steel sheathing has proven effective.
Rodents have been known to tunnel adjacent to sensors installed at shallow depths and wreak havoc in multiple ways.
If a field is grazed after harvest and sensors are left over-winter, the sensors must be protected from damage.
This is not unusual in alfalfa hay fields.
Be sure the "protection" does not alter the soil moisture conditions from being representative of the rest of the field.
A sensor station fenced off will often become drier because of taller vegetation and increased crop water use during the shoulder seasons.
Automated Soil Moisture Stations
 Installation of an automated soil moisture station can provide continuous measurement of soil moisture levels.
When the data is processed graphically, the changes in soil moisture due to extraction by the crop and replenishment by rainfall and irrigation are readily grasped and understood.
With sensors at multiple depths, the slow drying of the deeper soil levels typical under many center-pivot sprinklers becomes evident.
The benefits of utilizing sensors that provide accurate volumetric measurement of soil moisture is readily realized with automated stations.
The calculated soil moisture balance directly reflects the depth of effective rainfall, the net depth of applied irrigation by a center pivot sprinkler, etc.
This direct correlation to known events helps strengthen grower confidence in the equipment and procedures.
When coupled with radio telemetry, this information can be available to the irrigator 24/7.
When he needs to make an irrigation decision, the real-time status of soil moisture levels is at his fingertips.
This is a great advantage, but one that comes at some cost.
Not all irrigators are equally motivated to adopt these improved practices, even when subsidized, whole or in part.
THE NORTHERN WATER EXPERIENCE
 Beginning in 1982, Northern Water provided a limited irrigation scheduling service for area producers.
The program was intended to be educational and assist producers for only one to two years in a couple of their fields.
These demonstrations used the 'checkbook method' coupled with soil moisture readings obtained from tensiometers.
The program proved popular but was limited to the number of fields a single technician could service each week to manually obtain the soil moisture readings.
The program evolved to include automated soil moisture monitoring stations.
Sensors were installed in each of the four top feet of root zone and connected to a small data logger with battery and solar panel.
Data was downloaded as frequently as once per day via cellular phone telemetry.
Graphical summary reports were routinely provided to growers via email.
Although the computer programs utilized the 'checkbook' method of maintaining a soil water balance, that balance was 'reconciled' at the end of each day with the soil water content measured by the soil moisture sensors.
The procedure was heavily weighted to follow the sensor readings.
However, the crop water use information obtained from local weather stations did fill-in periods when soil moisture data was not available, such as early in the spring or late in the fall.
It also provided estimates or predictions of future crop water use for trending, etc.
Unfortunately, the staff position at Northern Water necessary to continue this irrigation scheduling service was eliminated in 2007.
Local soil conservation districts have expressed interest in continuing similar services for their producers.
Historically, advanced irrigation scheduling has not been for everyone.
Many times, simpler methods seemed wholly satisfactory.
However, increasing pressures are directed towards irrigated agriculture to produce more, with reduced inputs, and without cost increases to consumers.
It is highly unlikely this can be attempted without utilizing the best available tools, including advanced methods of irrigation scheduling.
Fortunately, improved methods and better equipment are available today than was available just a few years ago.
Watermeal and Duckweed Control in Arkansas Ponds
 George Selden Extension Aquaculture Specialist II
 It is estimated that there are more than 300,000 private ponds and lakes in Arkansas.
Because of the interactions of sunlight, water and nutrients, these waterbodies have the potential to develop problems with nuisance aquatic plants.
For small ponds with little to no water flow, duckweed and watermeal can frequently become problem plants.
Duckweed  and watermeal  are free-floating aquatic plants.
They are commonly found together.
Often, mosquito fern  will also be found with these two plants, but its population is usually too low to be a nuisance.
The potential problems caused by duckweed and watermeal fall into two categories.
On calm, still days the plants will spread over the entire surface of the pond, giving it an even, green appearance.
This can be aesthetically unpleasant, a recreational or production nuisance, and even has the potential to be unsafe by fooling the unaware individual into thinking there is no pond present.
Pond covered with watermeal and duckweed
 Mix of duckweed watermeal and mosquito fern
 The plants can also kill fish in these conditions.
By blocking sunlight penetration, little to no oxygen is produced by phytoplankton.
Since plankton, fish and bacteria continue to use oxygen dissolved in the water, the pond can quickly become depleted of dissolved oxygen.
The result is the suffocation of fish.
If the pond has a productive
 fishery, removal or control of these two plants becomes essential.
Watermeal is the smallest and simplest of the flowering plants.
It is rootless and tiny, usually less than 1 mm, and appears as little green pin heads floating on the surface.
To the touch, it can feel somewhat like dry grits.
Duckweed is a little bigger, but still very small, usually 1/8 to 1/4 of an inch across.
The fronds tend to be elliptical, and a small root is present on the lower surface of each frond.
The growth of these plants is linked to high nutrient levels, particularly nitrogen and/or phosphorus, which is why they are common in residential, park and cattle ponds.
Both of these plants tend to grow in dense colonies in quiet waters.
Individual plants stick readily to birds, animals and equipment, often resulting in their spread from one pond to another.
Once in a new pond, growth can be explosive under optimal conditions.
Both species can reproduce by budding, and in some cases double their population every 24 hours.
Both watermeal and duckweed tend to "disappear" from the pond surface in the late fall.
During the summer, the plants have buoyancy due to trapped oxygen
 from photosynthesis.
In the fall, photosynthesis slows down, leading to less oxygen in the plant, and the accumulated starch from a season of growth makes the plant heavier, so it sinks to the sediments.
In the spring, the plants start photosynthesizing, accumulate oxygen and float to the surface again.
On occasion, the plants will not reappear the following spring, though this should not be relied upon as a control strategy.
Both plants are linked to high nutrient loads in the pond.
Eliminating, capturing or diverting nutrient inputs will reduce, but not eliminate, the chance of watermeal or duckweed problems.
This includes growing vegetative buffer strips around the pond, using a fertilizer application setback, excluding livestock, and possibly using materials that can bind up phosphorous, rendering it unavailable for plant grow.
Draining, drying and deepening a pond to eliminate accumulated nutrients may be necessary, but this will be a waste of time if the pond is allowed to become nutrient loaded again.
Removing or inactivating nutrients will not remove or kill plants, or correct an existing problem.
It can potentially lead to lower populations, or reduce the chance of problems occurring in the first place, by reducing nutrients critical for growth.
Both watermeal and duckweed prefer stagnant or slow-moving water.
By adding aeration, it might be possible to eliminate the growth of both plants, or limit it to only the pond edges.
Aeration will also reduce the chances of a fish kill due to low dissolved oxygen.
Azolla or "mosquito fern"
 Raking or seining with a small mesh seine or window screen can reduce coverage.
While laborious, this can be effective for small ponds.
Due to rapid reproduction, repeated removal will likely be required.
If the owner is willing and physically able to manually remove duckweed/watermeal this can be a cost-effective strategy.
Remember to dispose of harvested plant material away from the pond.
This prevents it from washing back into the pond in the event of rain.
A biological control agent is a living organism used to control a particular pest.
The most commonly used biocontrol for aquatic plants are grass carp.
While grass carp will consume both duckweed and watermeal, at their normal stocking rates they will typically not consume the plants at a rate fast enough to keep up with plant reproduction and growth.
The typical stocking rates for grass carp are five to 10 per acre.
If largemouth bass are present, fish at least 8-10 inches long must be used to reduce predation.
Higher stocking rates may lead to the control of these plants, but this has not been proven.
Also, once grass carp get to be three or four years of age and weigh more than 10 pounds, their effectiveness as an aquatic vegetation biocontrol is substantially diminished.
Tilapia will consume, and under the right circumstances, control both plants.
Unfortunately, tilapia are cold intolerant and do not survive water temperatures below 55 degrees F.
As a result, they need to be stocked yearly.
Recommended stocking rates are 15-20 pounds per acre of mixed sex adults.
Again, largemouth bass predation can prevent the tilapia from effectively controlling problem plant populations.
Tilapia is a non-native species that are on the Arkansas Game and Fish Commission  approved species list.
This means that they are legal to stock in private ponds, but the AGFC does not recommend their stocking in any lake or pond that has a watershed or spillway that could allow the fish to escape during a flood event.
The pond owner is liable for any escapes.
In closed-system lakes north of I-40, where the AGFC has stocked tilapia, they have observed no carryover fish surviving the winter.
Tilapia should never be stocked in ponds that connect to other ponds, lakes or streams.
Tilapia can be an effective biocontrol agent under the right circumstances, if the pond owner is willing to accept their inherent drawbacks.
Another potential biological control option for watermeal, but not duckweed, might be goldfish.
The results of this approach have been mixed.
They have been stocked into small ponds at a rate of 35-40 pounds per acre and have sometimes brought watermeal under control.
But this is not universal.
Predation from largemouth bass is suspected as a possible explanation for cases where goldfish failed to control watermeal.
While success is not guaranteed, stocking goldfish is fairly inexpensive and is unlikely to cause harm.
Bispyribac Sodium	E	E
 Diquat 
 Diquat is a contact herbicide that causes rapid plant death.
Results are noticeable within a couple of days.
Diquat will kill duckweed, but not have much effect upon watermeal.
As a result, its use may selectively eliminate the duckweed leading to a pond with only watermeal present.
There are many diquat formulations labeled for aquatic use in Arkansas, but most list 1-2 gallons per acre as the recommended rate.
Consult the label for the rate of the selected formulation.
If the duckweed has been pushed to one side of the pond by wind, the diquat might only affect the top layers.
Repeated application of this product seven to 10 days apart will probably be necessary.
Diquat can be used as a spot treatment.
Use of a non-ionic surfactant is recommended to increase effectiveness.
Product rates vary with formulation.
Diquat has various use restrictions for drinking water, dairy cattle and other livestock and crop irrigation.
Please consult the label.
Diquat requires at least 30 minutes of contact time and is rain-fast in one to two hours.
Copper Complexes  have been shown to increase the effectiveness of Diquat.
Used alone, it will not kill duckweed or watermeal.
The general recommendation is one part chelated copper to two parts diquat.
If adding a copper product other than one of the copper complexes, the alkalinity of the water should be tested to ensure safety of the fish.
Fluridone 
 Fluridone comes in both liquid and granular formulations and can provide excellent control of both plants.
It can be applied to the water surface or subsurface.
Fluridone is a systemic herbicide, is absorbed slowly and can require up to 45 days of contact time to reach maximum effectiveness.
Between 30-90 days may be needed before control is achieved.
This herbicide is not recommended if the pond has any outflow.
Due to the length of contact time, a "bump" application where a partial dose is added, may be needed to maintain an effective concentration in the water.
Label rates are between 45-90 parts per billion , though it is legal to use less, and control may be achieved.
Adding fluridone to the water early in the spring, the moment watermeal or duckweed is spotted, will lead to better results.
Fluridone has a seven to 30 day withdrawal period for crop irrigation and can not be applied within 1/4 mile of a water intake at rates above 20 ppb.
Imazapyr 
 Imazapyr is a systemic herbicide that can be effective against duckweed, but probably not watermeal.
There are currently seven herbicides containing imazapyr that are labeled for aquatic use in Arkansas.
Not all of them list duckweed on the label.
Those that do recommend a 1-1.5 pints per acre  as the rate, with 100 percent coverage of the actively growing foliage.
Imazapyr typically is absorbed by the foliage within 24 hours.
Effects may not be noticeable for one to two weeks.
This herbicide will not work in the water, so it should not be applied subsurface.
It should also be noted that imazapyr has a 120 day withdrawal period if the water body is used for crop irrigation.
This is a contact herbicide and is reported to be effective on both duckweed and watermeal.
Use rates are 6.7-13.5 ounces per acre for duckweed and 13.5 ounces per acre for watermeal as a foliar treatment.
Use of a nonionic surfactant is also recommended to increase effectiveness.
Depending on the percentage of pond surface treated, the label has variable water use restrictions for drinking, livestock and irrigation, so consult the label.
This product is rainfast within one hour and results might be visible within several hours.
This product is also sensitive to the pH of the tank water.
At pH 7, its half-life is 8.6 days while at pH 9 its halflife is 3.6 hours, so tank water pH should be measured prior to filling and buffered accordingly.
A single application will not control plants with high regeneration rates, so it is likely that multiple treatments will be required.
Tank mixing with another herbicide may lead to only a single application being needed.
Penoxsulam is a selective herbicide that has a use patterns similar to fluridone.
While comparatively little product is required, it requires a long contact time, so it shouldn't be used in ponds with rapid water turnover.
It can take several weeks for maximum effectiveness and may require 60-120 days for complete plant death.
The label information lists duckweed as a plant controlled by this herbicide and is said to partially control watermeal.
The recommended rates are 25-75 ppb and should never exceed 150 ppb.
For Galleon SC, this translates to 4.4-13.1 ounces of product per acrefoot.
There are restrictions for using treated water for crop irrigation, which vary by crop being irrigated, SO consult the label for details.
Flumioxazin 
 This is a contact herbicide similar to carfentrazone.
Typical use rates are 6-12 ounces of product per surface acre for foliar applications, or 0.53-2.1 pounds of product per acre-foot  for subsurface application.
Higher rates may be needed if the plants are mature.
The decision to treat the plants on the surface or subsurface will depend upon available equipment and other local factors specific to application site.
This active ingredient is very sensitive to water pH.
At pH 9, the half-life of this product is measured in minutes.
The spray solution should be buffered to pH 7 or less.
Reports by professional applicators indicate that duckweed and watermeal are susceptible regardless of pond water pH, if applied to tops of plants, not into the water.
The label suggests that no more than half of the pond be treated at one time and then wait 10-14 days before treating the remaining area.
Do not retreat the same section within 28 days.
For subsurface application, application in early morning might enhance effectiveness, due to rapid break down of product in water with pH 8.5 or greater.
Flumioxazin may be tank mixed with other approved herbicides for increased effectiveness.
Foliar contact can cause rapid desiccation and necrosis of exposed plant tissue.
This is a systemic herbicide.
It can be applied either sub-surface or foliar, but for watermeal and duckweed, application to the floating foliage is recommended.
Labeled use rates are 1-2 ounces per acre.
For dense or mature vegetation, repeat treatments may be needed, but should not occur prior to 30 days after initial treatment.
No more than 8 ounces per acre per year should be applied.
As a systemic herbicide, the effects of bispyribac sodium on the target plant may take several weeks to become apparent.
The label has variable use restrictions if the water is to be used for irrigation, so consult the label.
In addition to reading herbicide labels for use rates, they should also be consulted for other information.
Most of the herbicides recommend the addition of an adjuvant to increase their efficacy.
This is usually, but not always, a non-ionic surfactant.
When using any adjuvant or second herbicide as a tank mix partner, it is always a good idea to perform a jar test to determine compatibility.
This is accomplished by placing small amounts of both herbicides in a jar with some water.
The jar is sealed and then shaken vigorously.
Incompatible herbicides will form an emulsion, often a mayonnaise-like substance, that is very difficult to clean out of spray equipment.
If the materials are physically compatible, the jar will be cool to the touch and there will be no separation of materials or forming of clumps or emulsions.
Aquatic herbicides tend to be more expensive than their terrestrial counterparts.
The reasons for this are numerous.
Aquatic herbicides also tend to be much more expensive on a per ounce basis if ordered in smaller volume packaging when compared to larger volume packaging.
For example, at an on-line retailer, Sonar AS was $18.75 per ounce when purchased in a quart container and $12.50 per ounce when purchased in a gallon container.
Since prices change fairly regularly, approximate prices used at the time of writing this publication should not be considered as current.
The pond owner should search the prices for each of the herbicides and make a comparison based on the price per acre or acre-feet it would cost to apply.
Herbicide	Approximate Cost 
 Diquat	$99-198/acre 
  With early application, it may be possible to use a rate lower than the labeled rate, reducing cost.
If a pond is small, nutrient rich and generally has little water movement, duckweed and watermeal can be expected to become a nuisance vegetation at some point.
Plants in the duckweed and watermeal family can be very difficult to control under optimal growth conditions.
Dense infestations can often require repeated treatments to achieve an acceptable level of control.
To reduce control costs, treatments should be initiated when the size of the infestation is at a minimum.
If these plants have been a nuisance in the past, they can be expected to be present in the future.
With planning, early treatment and taking steps to minimize nutrient loading, control costs and effort can be minimized.
The University of Arkansas at Pine Bluff is fully accredited by The Higher Learning Commission, 230 South LaSalle Street, Suite 7-500, Chicago, IL 60604, 1-800-621-7440/FAX: 312-263-7462.
Printed by University of Arkansas Cooperative Extension Service Printing Services.
GEORGE SELDEN is an Extension aquaculture specialist located at the Aquaculture/Fisheries Center, University of Arkansas at Pine Bluff.
Issued in furtherance of Extension work, Act of September 29, 1977, in cooperation with the U.S.
Department of Agriculture, Dr.
Doze Y.
Butler, dean/director, 1890 Research and Extension Programs, Cooperative Extension Program, University of Arkansas at Pine Bluff.
The University of Arkansas at Pine Bluff offers all its Extension and Research programs and services without regard to race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
Grower's Guide to Surge Flow Irrigation
 by Guy Fipps Extension Agricultural Engineer
 Surge flow is not magic, and it is difficult to predict whether it will work for a particular situation.
However, where it does work, there are significant benefits.
This paper provides a brief overview of surge flow irrigation, and highlights important considerations if you are planning on experimenting with surge flow.
What is Surge Flow Irrigation?
Surge flow irrigation was first developed in the late 1970's and has the potential to increase surface irrigation efficiencies to levels usually associated with sprinkler or drip irrigation systems.
Another advantage of surge flow is that it makes automation of furrow irrigation possible.
Twice the area can be irrigated with the same amount of water at the same time with an automatic surge valve.
Figure 1 shows a typical surge flow set-up.
In surge, water is applied in a series of on-off cycles or watering periods which, on most soils:
 1) increases the rate of water advance down the furrow,
 2) reduces deep percolation losses,
 3) produces an even wetting front along the furrow, and
 4) produces a more even depth of water penetration into the soil.
Thus, higher irrigation efficiencies result which reduces the total amount of water applied.
In many situations, surge gives you the ability to apply more precise levels of water.
Thus, instead of applying 4-6 inches, for example as in conventional furrow irrigation, you can put out as little as 1-2 inches.
However, surge does not work on all soils and situations.
Adequate furrow stream  is also necessary to see benefits.
Single butterfly type valve
 Figure 1.
Surge flow valve operation.
How Does Surge Work?
Why does alternating on-off cycles of water increase furrow irrigation efficiencies?
The prevailing view is that there are two factors involved: surface sealing and intake rate.
Once wetted, in many soils as they dry out, a surface seal forms.
Soil intake rate or infiltration rate is not constant but decreases as over time during irrigation as the soil moisture level increases.
Soil roughness is also a factor, as the largest benefits of surge are seen during the first few irrigations when the soil is still rough.
Common terminology used related to surge flow is listed below.
The advance phase of surge irrigation is getting the water to the end of the furrow.
The fill  phase are the cycles used to fill the root zone with the targeted amount of water.
Phases of Furrow Irrigation
 Advance Phase The phase in which the dry furrow is wetted.
Out Time The time required for water to reach the end of the furrow.
Soaking Phase The phase in which the required application depth is infiltrated.
Soaking Time The time it takes the required application depth to infiltrate.
Recession Phase The phase that starts when application of water to the furrow is stopped, and ends when water disappears from the soil's surface.
Opportunity time The total time that water is present at each point in the furrow.
Diagram of a split-set gated pipe system used for surge flow irrigation.
Flow is alternated from side to side.
Figure 2.
Typical surge flow set up.
On-Time The time water is applied to one side of the surge valve before it is switched to the other side.
Off-Time The time water is not applied to one side of the surge valve.
Cycle-Time The time required to complete one on/off cycle  Cycle-Ratio The ratio between the on-time and the cycle time..
The United States has two major manufacturers of automatic surge flow valves.
These are actually very simple devices consisting of a programmable controller, a valve, a battery and solar cell recharging panel.
Surge valves come in several sizes as shown in Table 1.
Beware, however, that larger valves can be quite heavy.
Thus, size your surge valve according to the flow that you have available.
Table 1.
Surge Valve Sizes, Capacity and Weight for Two US Manufactured Surge Valves.
Valve Pipe Size	Capacity	Weight
 6 "	625 700	31 37
 8"	1100 1200	44 46
 10"	1700 2000	50 54
 12"	2500 3000	67 90
 * only one US manufacturer makes a 4 inch valve
 Figure 3.
Two automatic surge flow valves manufactured in the United States.
Gated Pipe and Polypipe
 Surge is used with either gated aluminum pipe or polypipe.
If using polypipe, it is important that the holes be punched precisely to achieve the targeted furrow stream size.
Polypipe manufacturers have on-line guides and special hole punchers that will allow you to do this.
Another alternative when using polypipe are insertion gates which pop into the punch holes which can be adjusted like aluminum gated pipe.
Plastic adjustable gate used with polypipe.
Polypipe insertion gate shown with sleeve to reduce erosion at the head of the furrow.
Figure 4.
Recommended insertion gates and sleeve when using polypipe for furrow irrigation.
For most soil types, surge has been found to be very effective in reducing the volume of water during the first irrigation following tillage.
It's effectiveness on subsequent irrigation has varied.
Typically surge has improved efficiencies from 8 to 30%.
General management guidelines are as follows:
 1.
Advance phase should be completed in 4-6 surges.
2.
The next to the last advance phase should stop just short of the end of the field.
3.
Cycle times should be such that individual surges do not overlap or coalesce.
4.
Furrow stream  should be near the maximum non-erosive value.
There are two basic approaches used in surge irrigation as discussed below.
Automatic valves allow you to experiment with both approaches.
In addition, automatic valves allow you to update the current programing based on the time or distance that the advance reaches certain points along the furrow, and will automatically calculate variable cycle times based on such factors as soil type, length of furrow and slope.
The USDA Natural Resources Conservation Service  uses two basic approaches for management of surge irrigation.
As with continuous furrow irrigation, they recommend use of the maximum non-erosive furrow stream size with the following two approaches:
 I.
The variable-distance, constant-time method.
An on-time is selected, usually the time required for the first surge to reach about 25% of the total furrow length.
This on-time is repeated until the advance is complete.
Upon completion of the advance, they recommend reducing the on-time for the post-advance surges SO the wetted advance reaches 75-80% of the furrow length by cutoff, thus allowing the advance to "roll-on" to the tail.
This minimizes tailwater losses during the post-advance phase.
II.
The constant-distance, variable-time method.
The on-time during the advance phase is set SO that the advance progresses a set distance during every surge.
The post-advance phase is dealt with as in  above.
Once the water has reached the end of the furrow, the soaking phase normally will require less time than the advance time.
As a starting point, this soaking phase on-time is set at about 75% of the advance time.
The objective is to minimize the amount of tailwater while still allowing enough soaking to occur at the lower end of the furrow.
Soaking on-times that are too long will result in excessive runoff, and on-times that are too short will result in excessive water on the upper end of the furrow while the lower end of the furrow does not receive enough.
Once the best soaking phase on-time has been achieved, the surges should continue until the desired application depth is achieved.
A soil probe is useful in determining when the application depth has been reached.
As with conventional furrow irrigation, the largest furrow stream  without causing serious erosion provides the best results.
Generally, the best results are obtained with a minimum of at least 15-25 gpm per furrow.
In situations where water is supplied from irrigation canals, be aware that a constant flow rate is needed.
Poor results occur in situations where flow is not constant such as when water levels fluctuate in the irrigation supply canal.
The term "head of water" is not a good guide for determining how much flow you have.
You should have your flow rate measured.
Some irrigation districts and NRCS offices have potable propeller test meters.
To be successful with surge, measure don't guess you flow rate.
Figure 5.
Portable flow test meter with a quick connector for easy insertion into existing pipelines or alfalfa valves.
These potable test meters can be ordered with handles, straightening veins to improve accuracy, and a pressure gauge.
Usually, a smaller pipe-size than the existing pipeline is used to ensure a full pipe in the test meter.
Cycle times with surge irrigation vary, depending upon soil texture, slope and furrow length.
Fine-textured soils respond less to surge irrigation than course soils which have higher intake rates.
Surge works better on leveled fields and furrows with small slopes than on steep slopes.
On soils with low intake rates such as heavy clays or soils with compacted layers, surge is likely to be ineffective in reducing irrigation advance times below those of continuous flow.
However, surge may provide a more uniform application of water.
Surge has shown the largest benefits in the first few irrigations following tillage.
Later in the season, there tends to be less difference between surge and continuous flow when the furrows are smooth.
Will Surge Work For You?
One simple test is to run two furrows of continuous flow alongside two furrows in which flow is interrupted and reapplied.
If the rate of advance is greater with the interrupted streams, surge would work on your soils.
A more effective field test would be to irrigate two blocks of land using surge and another block with continuous flow.
Measure the depth of water penetration in the surge/continuous blocks with a soil probe or soil moisture sensors.
If the depths of water penetration at the lower and upper sections of the furrows are more uniform with surge, then surge would work for you.
Percent of fields that became wetter moving from August to Sept.
15.
The dry years 2020, 21 and 22 fields are much drier than the other years in the fall.
In the weighted average normal to wet years, 2017, 2018, 2019, 65% of fields with soil in the 15-25 in zone became wetter from August to Sept.
15, 66% of fields with soil in the 25-36 in zone became wetter from August to Sept.
15, and 37% of fields with soil in both zones became wetter moving from August to Sept.
15.
CornSoyWater  is an online app for corn and soybean that predicts whether irrigation is needed using precipitation data and the seven-day forecast.
The recommendation is based on predictions of the amount of crop-available water currently in the soil, crop stage and stage-based irrigation threshold, and the possibility of crop water stress at present and in the near future.
That's a pretty significant rise, Young said.
In many areas of the state, it doesn't completely offset, but it helps to offset, some of the declines we had from the drought in 2012 that are still lingering in many areas.
Young said there are some areas of the state that likely will not fully recover from the 2012 drought for an extended period of time, but one of the counties hit hardest by it had some of the biggest gains in groundwater last year.
CROP WATER USE IN LIMITED-IRRIGATION ENVIRONMENTS
 The goal in High Plains agriculture is to use water most effectively in production systems to generate crop yield.
To achieve this goal, we must use effective means to capture and store precipitation in the soil profile during noncrop periods, to capture and efficiently use precipitation received during the growing season, and to apply irrigation water in amounts and at times that are most efficient.
The selection of appropriate crops ones that match the expected water supply conditions of the production system is also a requirement.
This paper discusses options and practices that can lead to more effective use of water.
These discussion points have application to both dryland and irrigated production systems.
YIELD vs.
WATER RELATIONSHIPS
 Crop yield VS.
water relationships provide information that can be used in making decisions on the appropriateness of crops in production systems, through a consideration of the expected water supply conditions.
Figure 1 illustrates the general relationships between seed yield and water amount.
ET refers to evapotranspiration while water use refers to ET plus losses by runoff and internal drainage from the soil profile.
Seed yield VS.
ET is a linear relationship, although variability can and does exist.
Seed yield VS.
water use  is typically a curvilinear relationship, with losses from runoff and drainage increasing with increasing water supply in the system.
The seed yield VS.
ET relationship is more transferable among geographic locations than is the seed yield VS.
water use relationship that is more influenced by soil and landform characteristics that influence runoff and drainage.
Table 1 lists values of "Threshold ET", "Maximum ET for a typical full-season variety", "Slope of seed yield vs.
ET", and "Slope of long-term seed yield vs.
ET" for five crops from research in western Kansas.
"Threshold ET" is the ET necessary to move into the seed producing segment of the yield VS.
ET relationship: at the "Threshold ET" value and below, seed yield is zero.
"Maximum ET" is seasonal ET measured from emergence to physiological
 Fig.
1.
General relationships between seed yield and water amount.
maturity and gives the upper value of ET expected for full-season varieties with good water conditions.
The "Slope of yield VS.
ET" gives the seed yield increase per inch of ET in the seed producing segment of yield VS.
ET.
This is the expected yield increase due to water  in a year with no out-of-theordinary yield reducing factor such as hail or frost damage.
Because out-of-theordinary yield reducing events do occur, the "Slope of long-term yield VS.
ET" is less than the yield vs.
ET slope for an individual good year.
Table 1.
Yield vs.
ET relationship for crops of the central High Plains.
Max.
ET for	Slope of
 full-season	Threshold	Slope of yield	long-term
 Crop	variety	ET	VS.
ET	yield VS.
ET *
 Corn	25 in.
10.9 in.
16.9 bu/ac./in.
13.3 bu/ac./in.
Grain sorghum	21 in.
6.9 in.
12.2 bu/ac./in.
9.4 bu/ac./in.
Sunflower	22 in.
5.4 in.
218 lb/ac./in.
150 lb/ac./in.
Winter wheat	24 in.
10.0 in.
6.0 bu/ac./in.
4.6 bu/ac./in.
Soybean	24 in.
7.8 in.
4.6 bu/ac./in.
3.8 bu/ac./in.
* Long-term  slope is less than full slope due to yield reducing factors such as hail, freeze damage, insects, diseases, etc.
The "Threshold ET" value is of critical importance in assessing if seed yield will likely be obtained in drier crop environments.
Within the four summer row crops of Table 1, "Threshold ET" is 5.4 inches for sunflower, 6.9 inches for sorghum, 7.8 inches for soybean, and 10.9 inches for corn.
If water supply available for crops is limited, the "Threshold ET" values illustrate why sunflower or sorghum would be preferred over corn.
Also, the water stress sensitivity of growth stages of various cops is important in assessing their suitability for drier environments.
The "Slope of yield VS.
ET" is important in assessing the response of crops to irrigation that is converted into ET.
Within the four summer row crops of Table 1, yield response per inch of ET is 218 lb/acre/inch for sunflower, 276 lb/acre/inch for soybean, 683 lb/acre/inch for sorghum, and 946 lb/acre/inch for corn.
These values illustrate the greater yield responsiveness of corn to irrigation.
The relationships of Table 1 were developed from multiple data sources  and represent conditions consistent with fullseason cropping in the central High Plains.
The values of Table 1 can be altered by specific conditions of crops and growing seasons.
Growing season ET of a specific year will be greater, or less, than the "Maximum ET" values of Table 1 if the year has greater, or less, potential ET than the average year.
With waterstress conditions, if water application is beneficially timed, yield can be obtained even when actual ET is less than "Threshold ET." And, if water application is poorly timed and water-stress conditions exist, yield may not be obtained even though actual ET is greater than "Threshold ET." With water-stress conditions, if water application is beneficially timed, the yield benefit will be greater than the "Slope of yield VS.
ET" of Table 1.
And, if water application is poorly timed and water-stress conditions exist, the yield benefit will be less than the "Slope of yield VS.
ET" of Table 1.
YIELD RESPONSE TO WATER STRESS
 sensitivity to water stress in corn being greatest during flowering, daily ET is greatest during flowering through the milky-fluid growth stage.
These two factors working together produce the critical need for water in corn during flowering.
Table 2.
Relative yield response per unit of ET  to water deficit during selected growth periods.
Crop	Vegetative	Flowering	Yield formation	Ripening
 Corn	0.14	0.53	0.19	0.14
 Grain sorghum	0.21	0.42	0.21	0.16
 Sunflower	0.25	0.42	0.27	0.06
 Winter wheat	0.19	0.51	0.25	0.05
 Soybean	0.10	0.40	0.50
 The relative weighting of water stress sensitivity within a crop is illustrated in Table 2.
Relative weightings of water sensitivity give insight into the growth periods of most critical water need for those five crops.
Rainfall during the most sensitive growth periods will give the greatest yield benefit.
Also, limited irrigation should be timed to avoid water stress at the most sensitive growth stages.
That timing strategy will give the greatest yield benefit from a limited water resource.
The timing of limited irrigation to give maximum seed yield benefit is given in Table 3.
Table 3.
Timing of limited irrigation for maximum seed yield benefit.
Initiation of limited	To avoid  water
 Crop	irrigation	stress particularly during
 Corn	Near  or at tasseling	Silking
 Grain sorghum	Head extension	Flowering
 Sunflower	Head development	Disk flowering
 Winter wheat	Head extension	Flowering
 Soybean	Mid to late pod set	Early to mid bean fill
 Of the five crops of Tables 1, 2, and 3, corn and soybean are the two most affected by water-critical growth periods.
Corn yield is most negatively impacted by water stress from near-tasseling through silking, typically mid through late July.
Soybean yield is most negatively impacted by water stress during bean fill, typically mid August to mid September.
Therefore, if in a limited-irrigation production system and the water supply can not be depended on to avoid  water stress in the critical times for corn and soybean, these two crops become much less attractive as crop choices.
The suitability of crops for rainfedonly production systems in drier environments is influenced by "Threshold ET"  and water stress sensitivity.
Crops with greater "Threshold ET", and with greater water stress sensitivity, are less appropriate for rainfed-only systems than crops with lower "Threshold ET" and lower water stress sensitivity.
The suitability of crops for limited-irrigation production systems in drier environments is influenced by "Threshold ET", water stress sensitivity, crop response to added water , and dependability of the irrigation water supply.
Preplant irrigation is often an inefficient use of water in production systems where in-season irrigations are applied.
In Texas, Musick et al.
found that preplant irrigation did not increase grain sorghum yields appreciably when all treatments received the same two or three in-season irrigations.
With irrigated corn in west-central Kansas, Stone et al.
found no significant grain yield increase from preplant irrigation when there were multiple in-season irrigations.
After an analysis of available soil water  data from corn fields receiving inseason irrigation in northwest Kansas, Rogers and Lamm  stated "preseason irrigation of corn should not be a recommended practice for the region."
 As producers attempt to stretch limited water supplies and the times of application to maintain systems that use limited-capacity wells, questions arise on the advisability of using preplant irrigation.
In a review of preplant irrigation in the High Plains, Musick and Lamm  concluded that "benefits of preplant irrigation are likely to be greatest when the soil profile is dry before planting" and "benefits are likely to be low when soil profiles are moderately wet at time of irrigation." The retention and storage of preplant irrigation in our deep silt loam soils are heavily dependent on water content of the soil profile during and after irrigation.
As soil water content increases, water losses from evaporation, profile drainage, and surface runoff increase.
A need exists for guidelines and illustrations of preplant irrigation efficiencies that will aid producers as they consider the practice to stretch limited well capacities and water supplies.
From work in irrigated areas of the Canadian prairies, Hobbs and Krogman  concluded that preseason irrigation was advisable  when soil water was below 50% of maximum ASW.
Dormant-season irrigation research in west-central Kansas found that water loss from the soil profile occurs at
 increasing levels as water content of the soil profile rises above 60% of maximum ASW.
Rogers and Lamm  stated that additional irrigation above the amount required to bring the profile to 50% of maximum ASW has a high probability of being lost or wasted.
To illustrate water loss from preplant irrigation in spring, we used the KS Water Budget software  to project soil water levels and corn grain yields.
Projections were for conventionally-tilled corn  with annual precipitation of 17.5 inches.
As a point of reference, Goodland, KS has long-term annual precipitation of 17.7 inches.
We assumed four levels of ASW in the 6-foot soil profile on 15 March : 10, 30, 50, and 70% of maximum ASW, which are 1.4, 4.2, 7.1, and 9.9 inches of water in the profile, respectively.
We then projected ASW on 15 May and corn grain yield for the four initial levels of ASW with no irrigation, and 17.5 inches of precipitation.
Column 3 shows results where 1.0 inch of water was added to profile water on 15 April, and then no later irrigations.
In each of columns 4, 5, and 6, an additional 1.0 inch of water was added to profile ASW on the indicated date.
We did not estimate irrigation application efficiencies, but were estimating the retention efficiency of water added to stored soil water on the expressed dates.
Where ASW was at 10% of maximum on 15 March, about 0.9 inches of each 1.0 inch added to storage in April was in storage on 15 May, and yield increase was 15 to 17 bu/acre per 1.0 inch of water added to storage in April.
Where ASW was at 30% of maximum on 15 March, there was again about 0.9 inches of each 1.0 inch added to storage in April in storage on 15 May.
Yield increase was 12 to 17 bu/acre per 1.0 inch of water added to storage in April, with the yield increase decreasing with increasing irrigation amount.
Where ASW was at 50% of maximum on 15 March, the first 2 inches showed an increase in storage on 15 May of 0.9 inches per 1.0 inch added to storage.
The fourth 1.0 inch of added water showed a gain on 15 May of only 0.6 inch.
Grain yield showed a similar trend, with the first 2 inches showing yield increase of 13 and 11 bu/acre.
The fourth 1.0 inch added to storage showed a yield increase of 5 bu/acre.
Where ASW was at 70% of maximum on 15 March, water gains and yield benefits resulting from water additions were dropping rapidly.
The third 1.0 inch addition to storage showed an improvement of only 0.4 inch of water and 2 bu/acre of yield.
The fourth 1.0 inch addition showed improvements of only 0.2 inch of water and 1 bu/acre of yield.
The projections in Table 4 illustrate the precipitous decrease in benefits from spring preplant irrigation as ASW increases above about 60% of maximum.
Rainfall conditions for a given year would influence the projected values and efficiencies of Table 4.
Also, these projections do not consider the application efficiencies of preplant irrigation.
The use of spring preplant irrigation on the deep silt loam soils does appear to be a relatively efficient use of water if the ASW level plus added water does not exceed 60% of maximum ASW, and if the water can be added to the soil profile with acceptable water application efficiencies.
Table 4.
Illustration matrix for preplant irrigation 1
 Soil water	Net irrigation during spring  3
 on 15 March2	0.0	1.0	2.0	3.0	4.0
 10%	2.7 in.
4	3.6 in.
4.5 in.
5.4 in.
6.3 in.
1.4 in.
0 bu/ac5	13 bu/ac	30 bu/ac	46 bu/ac	61 bu/ac
 30%	5.1 in.
6.1 in.
7.0 in.
7.9 in.
8.8 in.
4.2 in.
40 bu/ac	57 bu/ac	73 bu/ac	87 bu/ac	99 bu/ac
 50%	7.7 in.
8.6 in.
9.5 in.
10.3 in.
10.9 in.
7.1 in.
83 bu/ac	96 bu/ac	107 bu/ac	115 bu/ac	120 bu/ac
 70%	10.0 in.
10.7 in.
11.2 in.
11.6 in.
11.8 in.
9.9 in.
112 bu/ac	118 bu/ac	122 bu/ac	124 bu/ac	125 bu/ac
 1 Annual precipitation of 17.5 inches.
Conventionally-tilled corn.
Four levels of available soil water  are assumed for 15 March.
2 Available soil water as percentage of maximum, and in inches, for the 6-ft profile on 15 March.
3 If applied, 1st 1.0 in.
of irrigation on 15 April, 2nd 1.0 in.
on 8 April, 3rd 1.0 in.
on 1 April, and 4th 1.0 in.
on 25 March.
4 Inches of available soil water in the 6-ft profile on 15 May.
5 Corn grain yield in bushels per acre.
PRECIPITATION STORAGE DURING NONCROP TIMES
 The improved ability of no-till systems, compared with conventional, stubblemulch  tillage, to capture and retain precipitation during fallow and to have more water stored in the soil profile for the next crop has been quantified in a number of dryland studies in the High Plains.
Key factors that lead to improved capture and storage of precipitation in noncrop periods are reduced levels of tillage, increased amounts of residue, and keeping the residue as upright as possible.
Water loss from evaporation resulting from a single tillage event can be about 1/2 inch.
The water loss amount is influenced by depth of tillage, extent of disturbance, crop residue remaining on the surface after tillage, soil water amount at the time of tillage, and weather conditions after tillage.
The gain in stored soil water during fallow is increased by increasing the amount of residue .
Storage of precipitation during fallow is also increased by having the residue in an upright position.
During winter, standing residue can trap blowing snow and keep this water source on the field.
Standing residue also benefits precipitation storage by decreasing evaporation losses, as compared with flat residue.
Of the atmospheric conditions of air temperature, vapor pressure deficit, solar radiation, and wind speed, "Soil water losses were best correlated with wind movement".
Standing residue decreases wind speed at the soil surface, thereby reducing the evaporation of water.
The decreasing of wind speeds at the soil surface by standing residue is also why standing residue is so effective at reducing soil erosion by wind.
Table 5.
Additional water gain during fallow with no-till compared with conventional-till of various rotations and locations in the High Plains.
Additional stored water in soil profile with no-till compared with conventional-till at planting of:+
 Wheat Wheat Wheat Sorghum
Considering Fall Salt Remediation
 Salts are a natural component of soils, including our soluble plant nutrients.
Excessive levels of any salt can be detrimental to both plant health and soil quality.
On the Delmarva Peninsula, excessive salts can come through several sources, which include fertilizers, irrigation water, and salt water intrusion.
Fertilizer burn due to sidedress N applications.
Issues with fertilizers are related to seed germination and growth, where in-furrow recommendations of starter N+K fertilizers are limited to 10 lb/acre total due to salt effects.
During sidedress applications, fertilizer burn  can damage leaf tissue, particularly UAN greater than 50lb/acre.
As long as corn plants are younger, minimal tissue damage doesnt affect yield.
Considering the above recommendations, salt damage due to fertilizers should be easy to manage.
Many of the nutrients that leach from our soils, particularly anions like NO3 and SO4, will end up in groundwater.
Therefore, most irrigation water will contain some level of salts, which in drier, western climates will build up in the soil.
On the Delmarva, we receive enough rainfall to help wash excess salts from the root zone.
However, in some cases, irrigation water near coastlines  may add appreciable levels of salts.
A similar issue extends from coastal flooding, where ground and surface waters may become inundated with salts at levels difficult to leach through rainwater alone.
The type of salt added makes a difference in soil and plant responses.
Sodium is not considered an essential plant nutrient and can be considered toxic at higher concentrations.
Calcium and magnesium are essential plant nutrients, but at high concentrations, they can prevent the plant from absorbing moisture from the soil.
Both Ca and Mg are cations, but these soils will also contain their anion equivalent in the form of Cl or SO4.
This is why typical literature on remediating salts differentiate between saline  and sodic soils.
Knowing the difference is important in determining remediation.
Low lying coastal lands may experience salt water intrusion, to the detriment of any plant growth in some parts of the soil.
Any well drained soil that received excess Na can easily be remediated using gypsum  in addition to precipitation or irrigation.
Sodium may cause crusting of the soil surface, preventing water percolation, however levels in DE are often not that high.
Excessive salts that include Ca and Mg are not easily remedied with gypsum, which simply adds more Ca to the soil.
These soils will require rainfall or irrigation that contains lower salt levels than the soil itself.
This problem can be compounded in low lying areas, where high water tables prevent soil drainage.
If you suspect salts are an issue in your soils, a soil test can help determine the best method for remediation.
However, the standard definitions of saline and sodic soils are based on a paste extraction compared to the Mehlich3 used at most of our regional labs.
To perform calculations such as the sodium absorption ratio , we would need to correlate those values to regional testing.
The exchangeable sodium percentage , like the amount of Na on the CEC, is considered sodic above 15%, but is also not correlated to regional soil tests.
It may be better to consider typical Na values across our soils, which are often in the 1-3% range on the CEC.
Fields that creep above this level should be watched for salt toxicity, and if saline waste or irrigation water is being added, consider fall gypsum treatments to remediate.
Crop and Wetland Consumptive Use and Open Water Surface Evaporation for Utah
 Utah Department of Natural Resources Division of Water Resources and Division of Water Rights
 Utah Agricultural Experiment Station Project No.
789 Utah State University Control No.
07-0833
 State of Utah Contract No.
09-0265
 Professor and Extension Irrigation Specialist, Graduate and Undergraduate Student Assistants Civil and Environmental Engineering Utah State University Logan, Utah 84322-4110
 Mention of a trademark name or proprietary product does not constitute endorsement by USU and does not imply its approval to the exclusion of other products that may also be suitable
 UTAH AGRICULTURAL EXPERIMENT STATION RESEARCH REPORT # 213
Lawn and Landscape Weed Control for Homeowners
 Gregory Breeden, Extension Specialist Jim Brosnan, Professor and Director Tom Samples, Professor Natalie Bumgarner, Associate Professor Department of Plant Sciences
 Weeds found throughout lawns and landscapes can be challenging to control.
For example, stolons  from a bermudagrass  lawn can encroach into a plant bed, making bermudagrass a weed in one spot but not the other.
There can also be a wide array of plant materials in lawns and landscapes including desirable turfgrass, flowers and shrubs, as well as weeds.
This diversity can make herbicide selection difficult as some products used to control weeds in lawns may be injurious to flowering plants in landscape beds, and vice-versa.
Often, selection of plant materials for the landscape is dictated by aesthetic attributes to showcase a property  while maintenance of weeds  after installation is not considered.
This publication is intended to guide homeowners with decisions pertaining to weed control in lawn and landscape areas and provide suggestions for balancing the management of these areas within residential spaces.
Image 1: Plant selection can enhance residential landscapes.
Photo credit: J.
Brosnan.
Cultural Practices for Lawns
 Lawns across Tennessee can be established using cool-season  or warm-season  turfgrasses.
The most common cool-season turfgrass used to establish lawns in Tennessee is tall fescue  while the most common warm-season turfgrass is bermudagrass.
Whether it's coolor warm-season, the best defense against any weed infestation is maintaining a dense, vigorous stand of turfgrass.
Mowing Height.
Bermudagrass, zoysiagrass , and several other turfgrass species are classified as sod-forming grasses due to their ability to grow laterally by way of stolons and/or rhizomes.
Generally, these sod forming species can be maintained at a slightly lower mowing height than turfgrasses such as chewings, hard and tall fescues which have a bunch-type growth habit.
Mowing height affects root growth with lawns maintained at higher mowing heights producing deeper roots than those mowed lower.
Optimum mowing height ranges vary among turfgrass species and according to weather conditions.
For example, when it is cool , improved, turf-type tall fescues usually perform well at a mowing height from 2 inches to 3 inches.
However, it is advisable to increase the mowing height of this cool-season species in advance of hot, dry weather.
Warm-season turfgrasses can be mowed a bit lower during favorable growing conditions than during cold and dry weather.
For example, hybrid bermudagrass  varieties  usually perform well at a mowing height from 0.75 to 1.5 inches when air temperatures are warm  and the soil is moist.
Increasing the mowing height of hybrid bermudagrass by one-half inch or more in early fall may help plants survive extremely cold and dry periods during winter dormancy.
Table 1.
Optimum Mowing Height  of Several Turfgrasses in Residential Landscapes.
Species	Cool, Humid	Hot, Dry
 Chewings	1-2	11/2 3
 Creeping Red	1-2	11/2 3
 Hard	1-2	11/2 3
 Tall	2-3	21/2 31/2
 Kentucky Bluegrass	11/2 2 1/4	2 1/4 3
 Perennial Ryegrass	11/2 2	2 3
 Species	Warm, Moist	Cold, Dry
 Common Types	1-2	13/4 3
 Hybrid	3/4 11/2	11/4 2
 Centipedegrass	2	11/2 3
 St.
Augustinegrass	23	3 4
 Zoysiagrass	3/4 11/2	11/4 2
 Image 2: Wheel adjustments on rotary mowers can raise or lower mowing height.
Photo credit: J.
Brosnan.
Mowing Frequency.
To reduce mowing damage and prevent large amounts of clippings from being returned to the surface, no more than one-third of each leaf should be removed as the lawn is mowed.
If turfgrass plants are routinely "scalped," stored carbohydrates in roots are mobilized to support leaf growth and recovery, and may not be replenished, resulting in a shallow and very sparse root system.
Mowing frequency will likely vary throughout the season.
For example, a tall fescue lawn might require mowing once a week in April compared to only once per month in July.
Mower Maintenance.
Routine mowing dulls the cutting edges of mower blades, reels and bedknives.
It is possible to reduce leaf damage and the potential for disease by sharpening blades and bedknives when its apparent cut quality has diminished as indicated by a ragged appearance on cut ends of grass blades.
Additionally, thoroughly rinsing mowers  free of debris after use can prevent movement of unwanted weed seeds throughout the landscape.
Mowing Direction.
Changing direction from one mowing to the next will limit soil compaction caused by mower wheels while encouraging turfgrass plants to grow upright.
Clippings.
Turfgrass leaves contain nitrogen , phosphorus  and potassium  along with 11 more essential mineral nutrients.
Research suggests that nitrogen fertilizer application rates can be reduced by as much as 50 percent when clippings are returned to the lawn as it is mowed.
When mowing lawns that contain numerous weeds that are flowering and producing seed, consider collecting clippings to prevent weed seed from being deposited back into the soil profile.
Image 3: Ragged leaf blades after being mowed with dull mower blades.
Photo credit: J.
Brosnan.
Image 4: Changing mowing direction is recommended.
Photo credit: J.
Brosnan.
Soil pH.
Of the nutrients essential for turfgrass growth and survival, three  are not minerals, and are supplied by water or carbon dioxide.
The remaining nutrients are minerals supplied by the soil.
These essential mineral nutrients are available for uptake by turfgrasses when the soil is slightly acidic.
Table 2.
General Nutrient Availability Across Soil pH.
* N , P , Ca , Mg , S , K , Fe , Mn , Zn , Cu , B  and Mo 
 Soil Testing.
A basic soil nutrient test is recommended to determine the soil pH.
Based on the soil test results, limestone can be applied to raise the soil pH, and sulfur can be applied if the soil pH needs to be lowered.
In addition to information regarding the soil's pH, a nutrient test conducted in the UT Extension Soil Testing Laboratory in Nashville includes an estimate of the levels of plant-available phosphorus, potassium, calcium, magnesium, zinc, manganese, iron, sodium and boron.
Cool-season Turfgrasses.
Cool-season turfgrasses grow best when air temperatures range from 60 F to 75 F.
As a result, their nutritional need rises in both spring and fall.
The fertilization schedule for cool-season turfgrasses depends on the level of maintenance provided annually.
Example nitrogen  fertilization schedules are presented in Table 3.
Warm-season Turfgrasses.
Since they grow best at air temperatures from 80 F to 95 F, warm-season turfgrasses require more nutrition in late spring, summer and early fall than during other times of the year.
The fertilization schedule for warm-season turfgrasses, like that of the cool-season turfgrasses, depends on the intensity level at which the lawn is being maintained.
Greater inputs of nitrogen will result in the need for more intensive maintenance, particularly greater mowing and irrigation requirements.
Example fertilization schedules for bermudagrass lawns are presented in Table 3.
Since zoysiagrass requires less N than bermudagrass, zoysiagrass lawns most often perform well when 0.75 pounds of N per 1,000 square feet rather than 1 pound of N per 1,000 square feet is applied as scheduled for bermudagrass below.
Table 3.
Example nitrogen fertilization schedule for cooland warm-season turfgrass lawns in Tennessee maintained at differing levels of intensity.
Turfgrass	Intensity of Maintenance*	Nitrogen Rate (per 1000 ft2	Application Dates
 Cool-season	Low	0.5 lb N	March + September
 Medium	0.5 lb N	March + September + October
 High	0.5 1.0 lb N	March + April + September +
 Warm-season	Low	1 lb N	April + July
 Medium	1 lb N	April + July + September
 High	1 lb N	April + June + July + September
 *High intensity maintenance assumes that the lawn is irrigated
 Turf Fertilizers.
Nitrogen , phosphorus  and potassium  are each classified as a primary nutrient due to the amount required by turfgrasses.
Although the recommended annual application rate of N is based on the turfgrass plant needs and level of lawn maintenance, the recommended annual amount of both P and K is dependent on turfgrass plant need, and soil test value.
In general, turfgrass nutrient needs are ranked in the following order: N>K>P.As a result, granular fertilizers marketed for use in lawns often contain more N than either phosphate  or potash , and more potash than phosphate.
An actively growing turfgrass plant usually contains more than 70 percent water.
Depending on the species, variety, and growing conditions, turfgrasses may use from one-tenth to three-tenths inch of water or more per day.
Irrigation is an essential practice for maintaining a healthy lawn.
However, when irrigating, it is critically important to conserve water which will limit costs associated with irrigation and reduce the potential for disease and weeds to invade the lawn.
Irrigation recommendations include:
 Moisten the soil beneath the lawn without applying too much water.
Runoff of irrigation water or surface ponding are indicators of excessive watering.
Conserve water by irrigating in the morning, but do not increase the potential for spreading disease by irrigating while dew is present.
For example, activate the irrigation system from 3:00 a.m.
to 6:00 a.m.
and 10:00 a.m.
to no later than 1:00 p.m.
Do not irrigate at sunset; turfgrass leaves that remain moist overnight are susceptible to disease.
Have a rain sensor installed if there is none.
In addition to primary cultural practices , several supplemental practices can be used to promote optimal growth and stand density of warmor cool-season turfgrass lawns, which helps to prevent weed encroachment.
Dethatching.
Thatch is an intermingled layer of dead and living leaves, stems and roots located between the aerial shoots and the soil surface that forms as turfgrasses grow.
When organic matter is produced faster than it is decomposed, a thatch layer develops.
Thatch helps insulate crowns and growing points of the turfgrass plant against rapid changes in temperature.
It is also resilient, providing a shock-absorbing cushion from foot and maintenance equipment traffic.
However, too much thatch can restrict the movement of air, water and fertilizer into the turfgrass root zone.
Excessive thatch often accumulates in lawns that are over-fertilized and/or over-irrigated; that production is also typically greater in warm-season lawns compared to those composed of cool-season turfgrass.
Turfgrass plants rooted in thatch are prone to drought stress and disease.
The depth of the thatch layer can be measured with a ruler.
Lawns with more than one-half inch of thatch usually benefit from dethatching.
Dethatch while plants are actively growing so that the soil below the slicing blades does not remain exposed for a long period of time, thereby allowing weed seeds to germinate.
As a general rule, warm-season grasses like bermudagrass can be dethatched more aggressively than cool-season grasses like tall fescue.
Image 6: A thatch layer forms on the soil surface as turfgrasses grow.
Photo credit: T.
Samples.
Image 7: Mechanical dethatchers are engineered to slice into the lawn and lift thatch.
Photo credit: T.
Samples.
Core Aerification.
Soils in which turfgrasses grow often compress, or compact, as the lawn receives foot and maintenance equipment traffic each year.
The amount of pore space in a soil is reduced as it is compacted.
A lack of oxygen and moisture in compacted soil near the surface of the turfgrass root zone leads to very poor root growth.
Walk-behind, rotary-motion core aerifiers can be used to selectively cultivate a lawn and relieve soil compaction.
Topdressing with high-quality compost immediately after aerification can improve the quality and performance of the lawn.
Image 8: Walk-behind core aerifiers equipped with hollow coring tines pull out small plugs, and deposit them on the surface as the lawn is aerated.
Photo credit: T.
Samples.
Cultural Practices for Landscape Beds
 Site Preparation.
Landscape beds can provide aesthetic, environmental and economic benefits to residences when installed and maintained properly.
Weed control in landscape beds actually begins with proper planning and cultural practices even before plants are installed.
First, areas selected for landscape beds should be well prepared.
Site preparation can and should include a focus on amending soil if needed to increase organic matter as well as controlling existing weeds.
Whether via mechanical or manual cultivation and/or herbicides, proper control of weeds in landscape beds prior to planting is critical.
Plant Selection.
Focusing on species and cultivars that are well suited to the site can support weed control through the growth of healthy landscape plants.
Optimize light and moisture conditions within a landscape bed so that selected plants can grow and thrive.
Plant placement that provides as much ground coverage as possible  can reduce weeds in landscape beds by blocking light that induces germination of many annual weed species.
Many ground cover species can also be effective in suppressing weed growth, but care should be taken to not install groundcovers with invasive tendencies.
Additionally, some landscape plants can also reseed and naturalize over time to expand coverage in the landscape bed.
Mulching.
Providing good soil cover through mulching is the foundation for effective weed control in landscape beds.
Mulching functions to support plants through soil stabilization, water holding, and temperature moderation, in addition to suppressing weeds.
Mulch serves to block light required for weed seed germination in addition to providing a physical barrier against weed growth.
Research has shown that for organic mulches, a depth of at least 2 to 3 inches is required for weed suppression.
In general, organic mulches made of coarser materials provide better weed suppression as they dry out faster and do not provide a site for weed germination.
Too much mulch can have a negative effect on desirable landscape plants by blocking water and air movement.
This contributes to plant decline  and potentially provides habitat for damaging wildlife, such as voles.
On the other hand, too little mulch will not provide a lasting barrier against weeds, so proper depth is critical.
The addition of a preemergence  herbicide to the mulch barrier can aid with weed control in landscape beds.
Image 9: Improper  mulching of trees.
Photo credit: L.
Rumble.
Inorganic mulches are also commonly used in residential landscapes, but homeowners should be cautious because landscape fabrics or geotextiles have variable and even negative impacts.
Impermeable materials are not recommended due to their potential negative effects on water, air and nutrients in the soil.
Permeable landscape fabrics can sometimes be an asset in weed control but are not recommended in Tennessee landscapes.
While permeable landscape fabrics can provide short-term suppression of annual weeds, these materials often fail over time when subjected to pressure from perennial weeds.
Additionally, these landscape fabrics  do not degrade or provide benefits to the soil via addition of organic matter.
Because of the valuable role organic mulches play in supporting both soil quality and plant growth when properly used, they are an excellent and sustainable material to support long-term health and performance in landscape beds.
Mechanical Weed Control Methods.
Hand weeding is an effective cultural control in landscape beds.
It can be less damaging to existing plants and soil structure than mechanical tillage, which is most appropriate for initial bed preparation.
Placing irrigation sources in proximity to root systems, such as through individual drippers, instead of spreading broadly over the bed can also reduce weed growth of some species.
These cultural practices implemented both before and after landscape bed planting are essential for plant success as well as effective weed control.
Because many landscape beds contain a range of plant material, herbicide options are often limited in established planting beds.
So, the proper use of preventative cultural practices is critical whether used alone or in combination with chemical control options.
Chemical Weed Control for Lawns and Landscapes
 Many hardware and landscape supply stores offer an array of herbicides to control weeds in lawns and landscape beds.
It is important to understand the attributes of different herbicides in order to select the best option for use in a lawn or landscape area.
An overview of how herbicides are broadly categorized is presented in Image 11.
Selectivity Selective herbicides are used to remove unwanted plants  from those species that are desirable.
These herbicides "select" for a target weed amongst the other desirable species that exist within the lawn or landscape.
Examples of selective herbicides include 2,4-D, MCPP, dicamba and quinclorac.
It is important to note that selectivity is predicated on the herbicide being applied in accordance with label directions.
On the contrary, non-selective herbicides will affect all plant species to which they are applied including both weeds and those that are desired.
Examples of non-selective herbicides include glyphosate, glufosinate and diquat.
Many herbicides marketed as "natural products" contain high concentrations of vinegar, fatty acids or oils that are non-selective and will therefore injure both weeds and desirable species.
Systemic VS.
Contact Systemic herbicides are absorbed into plant tissue and move to growing points  to work properly.
Many selective herbicides are classified as systemic.
Contact herbicides do not move throughout plant tissue and are used for rapid foliar burndown.
Several non-selective herbicides are classified as contact, particularly natural products containing vinegar, fatty acids or oils
 PRE VS POST Preemergence herbicides are applied before weeds are visible aboveground.
These herbicides are selective and typically target annual weeds germinating from seed.
Preemergence herbicides have activity in soil for several weeks after application and must be watered in after application to be effective.
Postemergence  herbicides are applied after weeds are visible aboveground.
They are optimally applied to young plants that are actively growing.
Environmental conditions can affect efficacy of POST herbicides.
For example, rainfall or irrigation immediately following an application of POST herbicide could prevent proper absorption into leaf tissue.
Image 10: Many stores offer an array of different herbicides to chemically control weeds in lawns and landscapes.
Photo credit: J.
Brosnan.
Image 11: Classification of different herbicides used for weed control.
Photo credit: J.
Brosnan.
What are the most common weed species in the Tennessee lawns and landscapes?
There are three types of weeds commonly found in Tennessee lawns and landscapes: grasses, broadleaves, and sedges.
Grasses are referred to as monocots in that they produce one leaf  when germinating from seed.
Grass leaves are linear in shape and often have parallel veins spanning the length of the leaf.
Broadleaves are referred to as dicots in that they produce two leaves  when germinating from seed.
Broadleaf weeds can produce leaves with an array of different shapes from oval to oblong with veins that are often webbed in appearance.
Sedges look similar to grasses in that they are monocots; however, leaves lack characteristics found on most grasses.
Moreover, sedge weeds often have triangular stems  and produce leaves in groups of three.
Some sedge weeds grow from underground tubers making them very difficult to eradicate.
Understanding the life cycle of the weed species requiring control will dictate the best control strategy in lawns and landscapes across Tennessee.
Image 12: Monocotyledon  weed germinating from seed.
Photo credit: J.
Brosnan.
Image 14: Triangular stem of yellow nutsedge.
Photo credit: J.
Brosnan.
Image 13: Dicotyledon  weed germinating from seed.
Photo credit: J.
Vargas.
Many common weeds found in Tennessee landscapes are considered annuals, plants that germinate and produce seeds within a year.
Common annual species include grass and broadleaf weeds such as crabgrass , annual bluegrass , prostrate spurge , yellow woodsorrel , henbit , purple deadnettle  and hairy bittercress.
Summer annuals germinate in the spring, grow throughout the summer, and often die following the first frost in autumn.
Summer annual species will flower and produce seed during summer that facilitates their return the following season.
Common summer annual weeds found in lawns and landscape beds include crabgrass, goosegrass , yellow woodsorrel and prostrate spurge.
Winter annuals germinate in late summer and grow during winter and early spring.
These weeds produce flowers and seed in spring before dying in early summer when temperatures increase.
Common winter annual weeds found in lawns and landscape beds include annual bluegrass, common chickweed , henbit and purple deadnettle.
Image 15: Smooth crabgrass.
Photo credit: J.
Brosnan.
Image 16: Annual bluegrass.
Photo credit: J.
Brosnan.
Image 18: Yellow woodsorrel.
Photo credit: J.
Brosnan.
Image 19: Henbit.
Photo credit: J.
Brosnan.
Image 21: Hairy bittercress.
Photo credit: J.
Brosnan.
Image 22: Goosegrass.
Photo credit: J Brosnan.
Image 17: Prostrate spurge.
Photo credit: J.
Brosnan.
Image 20: Purple deadnettle.
Photo credit: J.
Brosnan.
Image 23: Common chickweed.
Photo credit: J.
Brosnan.
Annual weeds are best managed via a properly timed PRE herbicide application.
These herbicides are designed to control seedling plants before they have emerged from soil.
It is critically important to apply PRE herbicides before weed seed has germinated; if plants are visible  the application is too late and control will be compromised.
Many hardware and landscape supply stores offer PRE herbicides on granular carriers that can be spread easily across lawn and landscape sites.
Always be sure to follow all label directions before application.
To be effective, PRE herbicides must be watered into the soil  within 24 to 48 hours after application.
Labels provide guidance on how much water to apply for maximum effectiveness.
Most PRE herbicides interfere with the establishment and root growth of recently planted or soon-to-be planted desirable species.
Always read and follow label instructions as they relate to application timing both before and after planting desirable species, particularly in landscape beds or when attempting to overseed a lawn.
Generally, PRE herbicides will provide weed control for 12-16 weeks after application depending on the product selected and application rate.
However, the level of control provided will dissipate over time.
Using a split application strategy where an herbicide is applied twice at a lower rate can extend the length of residual control provided by a preemergence herbicide.
For example, when targeting summer annual weeds in lawns, split applications of PRE herbicides are recommended.
Initial applications are made in spring when  soil temperatures average 55 F  for several consecutive days.
These initial treatments are typically and followed by another application eight weeks later.
Perennial weeds live for multiple seasons and are often more difficult to control than annual species.
Preemergence herbicides will not control established perennial weeds, as these species form underground structures, such as rhizomes and tubers, that allow them to overwinter in Tennessee.
Ground ivy  and wild violet  are difficult-to-control perennial broadleaf weed species in many lawns across Tennessee.
Sedges and bermudagrass are also perennial weeds that can be troublesome both in lawns and landscape beds.
Given their perennial nature, there are no PRE herbicides that can be used to control established stands of perennial broadleaf weeds like ground ivy or wild violets in lawns.
These species are difficult to control and often require sequential applications of POST herbicides such as 2,4-D, MCPP or dicamba.
Applications should be made according to label directions when desirable turfgrass is actively growing.
For example, use of POST herbicides to control ground ivy when a tall fescue lawn is subjected to summer stress would not be recommended.
University of Tennessee Extension has several publications on broadleaf weed control in lawns including:
 Image 24: Ground ivy  in a lawn.
Photo credit: J.
Brosnan.
Image 25: Wild violet.
Photo credit: J.
Brosnan.
Image 26: Yellow nutsedge  leaf tip.
Photo credit: M.
Elmore.
Perennial Sedge and Kyllinga
 Yellow nutsedge , purple nutsedge , green kyllinga  and false-green kyllinga  are common sedge weeds found across Tennessee lawns and landscapes.
These perennial species are considered indicators of excessive irrigation and/or poor drainage, as they commonly invade sites that have been excessively moist for an extended period of time.
Sedges emerge in late spring and grow throughout the summer months in Tennessee until the first killing frost in fall.
Yellow nutsedge leaves are lighter green than those of purple nutsedge and end in a direct point.
Seedheads can also help with nutsedge identification given that yellow and purple nutsedge produce distinctive yellow and purple seedheads, respectively.
Kyllinga species have more diminutive leaves than sedges and grow prostrate, forming patches in lawn and landscape areas.
Unlike sedges, kyllinga species persist under very low mowing heights  and produce flowers even under regular mowing.
The two kyllinga species most common in Tennessee lawns and landscapes can be differentiated by flowering time; green kyllinga flowers during all summer months, while false-green kyllinga flowers only during late summer and early fall.
Yellow and purple nutsedge persist from underground tubers referred to as "nutlets" whereas greenand false-green kyllinga persist via rhizomes.
In lawns, yellow and purple nutsedge exhibit more upright growth than greenor false-green kyllinga that form dense mats across the surface.
Sedge species are primarily controlled via postemergence herbicides.
Glyphosate is often used for spot applications in plant beds; however, it's only marginally effective on sedge and kyllinga species.
Image 27: Comparison of yellow nutsedge  and purple nutsedge  flowers.
Photo credit: J.
Vargas.
Image 28: False-green kyllinga  flower.
Photo credit: G.
Breeden.
Image 29: Rhizome of false-green kyllinga.
Photo credit: J.
Vargas.
Bermudagrass is a common turfgrass species used across Tennessee in that it offers aggressive growth and tolerances to heat, drought and traffic stress.
It persists via an extensive network of below and aboveground  vegetative structures.
These characteristics render bermudagrass an extremely difficult-to-control perennial weed in areas it is unwanted.
In many instances, bermudagrass can appear completely dead only to regenerate from rhizomes over time.
Additionally, aggressive aboveground growth from stolons allows bermudagrass to repeatedly advance from lawns into landscape beds, sidewalks and other areas throughout the summer.
Controlling bermudagrass is difficult in any situation.
In lawns and landscape beds where undesirable bermudagrass covers a large percentage of the site, complete renovation should be considered over selective removal.
Option 1 Selective Removal: Selective removal of undesirable bermudagrass is often the best choice for eradication within an established tall fescue lawn.
Selective herbicides target a weed  without inducing injury to a desirable species.
Selective herbicides chosen to control bermudagrass include active ingredients such as fenoxaprop or fluazifop.
Keep in mind that multiple applications will be needed  for complete eradication.
Coupling herbicide applications with interseeding of new turfgrass can improve performance.
Selective herbicides can also be used to control bermudagrass in landscape beds, principally clethodim, sethoxydim and fluazifop.
These are selective herbicides that target bermudagrass within ornamental shrubs and flowering plants.
It is recommended that these products be applied directly to bermudagrass  rather than over-the-top of established ornamental plantings.
Option 2 Nonselective Removal: Non-selective herbicides such as glyphosate  or glufosinate  can be used to control bermudagrass in both lawns and landscape beds.
These are typically applied as spot treatments directly to the undesirable bermudagrass.
Precision is required as these nonselective herbicides will injure any plant material to which they are applied.
Be careful to avoid walking through areas sprayed with these materials before they have dried as they can be tracked into non-treated areas on shoes, with damage presenting as footprints.
In lawns, bare areas present after application will need to be established with new turfgrass to prevent future weed infestations and improve the overall aesthetic quality.
Regardless of product selected, it is best to rotate among the herbicides listed in Table 4 to prevent the onset of weed populations evolving resistance to different herbicide chemistries.
There are numerous cases of annual weed species that reproduce from seed evolving resistance to a particular herbicide when the same application is made over multiple years without rotation or implementation of any other weed management measure.
Image 30: Tall fescue lawn treated with selective herbicide to control an infestation of bermudagrass.
Photo credit: J.
Brosnan.
Image 31: Spot treatments of non-selective herbicide to control bermudagrass  in a lawn.
Photo credit: J.
Benelli.
Table 4.
Example Herbicide Options for Homeowners to Control Weeds in Lawn and Landscape Beds.
Active Ingredients	Example Trade Name	Labeled	Labeled
 for Lawns	for Beds
 2,4-D + MCPP + Dicamba + Dithiopyr	Spectracide Weed Stop for Lawns Plus Crabgrass Preventer	Y	N
 Corn Gluten	Preen Vegetable Garden Natural Weed Preventer	N	Y
 Trifluralin	Preen Garden Weed Preventer	N	Y
 Trifluralin + Isoxaben	Preen Garden Extended Control	N	Y
 Pendimethalin	Scott's Turf Builder with Halts	Y	N
 2,4-D + Quinclorac + Dicamba	BioAdvanced All in One	Y	N
 2,4-D + MCPP + Isoxaben + Dicamba	BioAdvanced Season Long Weed Control	Y	N
 2,4-D + Qinclorac + Dicamba +	Spectracide Weed Stop for Lawns Plus Crabgrass Killer	Y	N
 2,4-D + Dicamba + Quinclorac	Ortho Weed Clear	Y	N
 MCPA + Quinclorac + Dicamba +	Roundup For Lawns	Y	N
 MCPA + Quinclorac + Dicamba +	Roundup For Lawns	Y	N
 Sulfentrazone	Ortho Nutsedge	Y	N
 Imazaquin	Image Kills Nutsedge	Y	Y
 2,4-D + Qinclorac + Dicamba +	Spectracide Weed Stop for Lawns Plus Crabgrass Killer	Y	N
 2,4-D + MCPP + Isoxaben + Dicamba	BioAdvanced Season Long Weed Control	Y	N
 2,4-D + MCPP + Dicamba	Ortho Weed B Gon Weed Killer for Lawns	Y	N
 2,4-D + Dicamba + Quinclorac	Ortho Weed Clear	Y	N
 2,4-D + MCPP + Dicamba + Dithiopyr	Spectracide Weed Stop for Lawns Plus Crabgrass Preventer	Y	N
 2,4-D + Qinclorac + Dicamba +	Spectracide Weed Stop for Lawns Plus Crabgrass Killer	Y	N
 2,4-D + MCPP + DCP	Scotts Liquid Turf Builder with Plus 2 Weed Control	Y	N
 MCPA + Quinclorac + Dicamba +	Roundup For Lawns	Y	N
 Triclopyr	Ortho Weed B Gon	Y	N
 Fluazifop	Ortho Grass B Gon	N	Y
 Fenoxaprop	BioAdvanced Bermuda Control for Lawns	Y	N
 Glyphosate	Roundup	Y	Y
 Glyphosate + Diquat	Roundup Plus Concentrate	Y	Y
 Ammonium Nonanoate	Ortho Groundclear Weed & Grass Killer	N	Y
 Vinegar	Harris 20% Vinegar Weed Killer	N	Y
 Ammoniated Soap of Fatty Acids	Natria	N	Y
 This publication contains pesticide recommendations that are subject to change at any time.
The recommendations in this publication are provided only as a guide.
It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used.
The label always takes precedence over the recommendations found in this publication.
Use of trade or brand names in this publication is for clarity and information; it does not imply approval of the product to the exclusion of others that may be of similar, suitable composition, nor does it guarantee or warrant the standard of the product.
The author, the University of Tennessee Institute of Agriculture and University of Tennessee Extension assume no liability resulting from the use of these recommendations.
UTIA.TENNESSEE.EDU Real.
Life.
Solutions.
TM
Nonpoint Source Pollution in the Bayou Bartholomew Watershed
 The Arkansas portion of the Bayou Bartholomew Watershed is located in southeast Arkansas and encompasses parts of Ashley, Chicot, Cleveland, Desha, Drew, Jefferson and Lincoln counties.
The watershed contains a variety of landscape from rolling hills in the western portion to relatively flat farmland among most of the eastern section before crossing into Louisiana.
A "watershed" is an area of land where all of the water that drains from it goes to the same place, SO rainwater or snowmelt in this watershed eventually drain to a common location.
The Bayou Bartholomew Watershed includes 1,481 square miles.
Half of the land is forested, and 21 percent is used for row crop farming.
1 In recent years, the watershed has lost population.
As of 2011, an estimated 48,000 people lived in the watershed, which includes the city of Pine Bluff.
2
 Water pollution that comes from multiple sources spread over an area, such as runoff from parking lots, agricultural fields, residential lawns, home gardens, construction, mining and logging, is known as nonpoint source pollution.
As runoff moves across the landscape, it carries natural and manmade substances that can accumulate in waterways and make them uninhabitable for aquatic species or unusable by people.
Potential pollutants include bacteria, nutrients, sediment, hazardous substances and trash.
Given the number of potential sources and variation in their potential contributions, these pollutants are not easily traced back to their source.
Bayou Bartholomew Watershed Data source: GeoStor.
Map created March 2011.
Major streams: Bayou Bartholomew, Deep Bayou, Ables Creek, Cutoff Creek, Bearhouse Creek, Overflow Creek and Chemin-A-Haut Creek.
This fact sheet is intended to provide a better understanding of the Bayou Bartholomew Watershed and its place on the state's priority list of 10 watersheds impacted by nonpoint source pollution.
Bayou Bartholomew Watershed Water Quality Issues
 Through water quality monitoring, environmental officials in Arkansas have determined the water quality here has been affected by row crop agriculture and runoff from urban areas.
4 The most prevalent concerns are turbidity, silt and phosphorus.
5
 2BAEG, 2011.
County-Wise Population Data.
Biological and Agricultural Engineering Department.
University of Arkansas: Fayetteville, Arkansas.
See the Nonpoint Source Pollution Management Plan.
4To learn more about the Arkansas Department of Environmental Quality 305 report, see the 2011-2016 Nonpoint Source Pollution Management Plan.
Turbidity is a measure of the clarity of water and is often the result of excess silt or sediment entering a stream.
High turbidity levels mean the water is murky from a variety of materials, such as soil particles, algae, microbes and other substances.
Turbidity can affect aquatic life in waterways.
In 2002, environmental officials determined the maximum amount of turbidity the Bayou Bartholomew River can receive and still meet water quality standards.
This determination is a calculation called Total Maximum Daily Load, or TMDL.
There are also TMDLs established for mercury in fish tissue, pathogens, chloride, sulfate and total dissolved solids.
6,7
 There is also evidence of some fecal coliform bacteria contamination, which has caused some streams to be deemed unsuitable for swimming.
Nutrient
 Arkansas' Priority Watershed List for Nonpoint Source Pollution
 Arkansas has used a watershed-based approach to nonpoint source pollution management, allowing the public to guide planning to address water quality concerns.
The Arkansas Natural Resources Commission, or ANRC, administers the Nonpoint Source Pollution Management Program.
The program exists to reduce water pollution through the funding of watershed planning and restoration activities, adoption of voluntary best management practices and the development of technologies that assist in water pollution reduction in Arkansas.
Based on public input and the use of a qualitative risk assessment matrix, ANRC has designated 10 priority watersheds as needing the greatest attention.
The current risk matrix8 identifies the following priority watersheds for 2011-2016: Bayou Bartholomew, Beaver Reservoir, Cache River, Illinois River, L'Anguille River, Lake Conway-Point Remove, Lower OuachitaSmackover, Poteau River, Strawberry River, and Upper Saline.
enrichment of the water bodies in this watershed has been a concern too, but detecting the source has been a challenge.
These concerns and its border state status led to the Bayou Bartholomew Watershed being designated as a priority by the Arkansas Natural Resource Commission in the state's 2011-2016 Nonpoint Source Pollution Management Plan.
9
 To encourage continued public input, the University of Arkansas Division of Agriculture's Public Policy Center facilitated a water quality stakeholder forum for the Bayou Bartholomew watershed in March 2015.
Participants identified sediment related to agriculture, water flow and nutrient runoff as local priorities that need addressing.
The Bayou Bartholomew Alliance has long worked in this watershed to address nonpoint source pollution issues and completed a watershed plan in 2002 that reflected community priorities.
In recent years, however, the watershed group has not been as active.
People who live, work or recreate in this watershed are encouraged to consider community priorities and the watershed plan when addressing water pollution.
The public is also welcome to attend an annual stakeholder meeting where priority watersheds and nonpoint source pollution are discussed.
For more information about nonpoint source pollution and its impact on the Bayou Bartholomew Watershed, contact the Cooperative Extension Service, Arkansas Natural Resources Commission or the Arkansas Department of Environmental Quality.
The Arkansas Watershed Steward Handbook is also a good source of information about basic water quality concerns and how the public can get engaged in addressing water pollution.
10
 10 See the Arkansas Watershed Steward Handbook.
This fact sheet is one in a series of 10 fact sheets on nonpoint source pollution in priority watersheds.
The University of Arkansas Division of Agriculture's Public Policy Center provides timely, credible, unbiased research, analyses and education on current and emerging public issues.
WATER MANAGEMENT FOR SUGARBEET AND DRY BEAN
 The past several years of sustained drought and expectations for below average snowpack and summer rains have many in agriculture searching for ways to stretch limited supplies of water.
Not only has stream flow decreased, but ground water levels have declined and in many areas pumping restrictions have been imposed.
At the same time, competition for water outside of agriculture further increases the demand for limited resources.
The combination of drought and the increased demand for water will impose even more challenges for irrigated agriculture.
It will require changing current irrigation practices and incorporation of new ideas to better utilize available water supplies as efficiently as possible.
This means not only using irrigation water efficiently, but also using precipitation and stored soil water for crop production.
Understanding the water needs of a crop will be a key to effective water management.
The amount of water needed for irrigation varies by the crop being grown and the climatic conditions from year to year.
Given in Table 1 are estimated water use rates for regionally grown crops.
Alfalfa	Corn	Drybean	Spring	Soybean	Sunflower	Sugarbeet	Winter
 31-33	23-26	15-16	18-20	18-20	18-26	23-25	18-22
 Table 1.
Seasonal crop water use  for regionally grown crops.
The depth from which sugarbeets get most of their water is generally considered to be from the top 3 to 4 ft of the soil profile.
Sugarbeets use approximately 24 inches of water during the growing season and are often considered a crop that uses a large amount of water.
Yet as we look closer, some of the crops we thought used less water, for example sunflowers and winter wheat, we find can use as much water as sugarbeets.
However in the case of sunflowers and winter wheat, these crops can extract more water from the profile than most crops without adversely impacting yield potential.
Sunflowers also have the ability to effectively extract water to depths of up to eight feet.
In this case sunflowers may be viewed as a "drought tolerant" crop when in fact the crop has actually extracted more water from the soil and extracted water from deeper in the soil
 profile.
Anyone growing sunflowers knows that following this crop the soil can be left in a very dry condition the following spring.
Dry beans use approximately 16 inches of water during the growing season, which is approximately 8 inches less than what corn needs.
This makes dry beans a good crop to grow if irrigation water is limited or if used as part of a crop rotation system to reduce overall irrigation needs.
Dry beans are a shallow rooted crop with the majority of roots found in the top 18 in.
of the soil profile.
Roots can grow deeper into the soil profile to get water but this usually occurs late in the growing season as the plants begin to mature.
The question of when is the best time to apply water to a crop often comes up when water supplies are limited.
Some producers feel that stressing dry beans early in the growing season has little impact on yield and may even improve yield by forcing the roots to grow deeper into the soil profile.
A similar question asked at the end of the season is whether stopping irrigation late in the season reduces yield?
For dry beans, early and late season water stress experiments have been conducted at the Panhandle Research and Extension Center in Scottsbluff, NE.
The results of those experiments are given below.
Figure 1a.
Effect of early season water stress on dry bean yield using sprinkler irrigation.
Figure 2a.
Effect of late season water stress on dry bean yield using sprinkler irrigation.
Figure 1b.
Effect of early season water stress on dry bean yield using furrow irrigation.
Figure 2b.
Effect of late season water stress on dry bean yield using furrow irrigation
 Figures 1a and 1b, show the results of dry bean yield when water is limited during early season growth for sprinkler and furrow irrigation systems, respectively.
The no stress treatment had irrigation starting approximately the last week in June to the first week in July.
For the limited and high stress treatments, the initial irrigation was delayed for one week and two weeks, respectively.
When sprinkler irrigation was used, yield tended to decline more as water stress increased compared to the furrow irrigation system.
This is especially true for the high stress treatment under sprinkler.
Yield loss was greater when water was withheld for two weeks because of the inability of the sprinkler system to replace soil water and meet the future water demand of the crop.
A furrow irrigation system tends to refill the soil profile and is thus able to provide adequate water for future water use.
In figures 2a and 2b, the results of shutting off water late in the season are also shown for both sprinkler and furrow irrigation systems.
The no stress treatment had irrigations throughout the growing season.
Starting August 10, the limited stress treatment received every other irrigation that was scheduled for the no stress treatment while the high stress treatment received no further irrigations.
Similar to the early season water stress results, dry beans irrigated with a sprinkler system showed a slightly steeper decline in yield as water stressed increased.
The decline in yield is again likely related to the inability of the sprinkler irrigation system to supply water in excess to the requirements of the crop.
Once irrigation was reduced or stopped less water was available in the soil profile to meet crop demands.
When comparing the early and late season experiments, there is a steeper decline in dry bean yield when water stress occurs at the beginning of the season as compared to water stress late in the season.
These results are probably not uncommon and could be expected for most crops.
Early in the season plant root development is limited and therefore water stress can occur rapidly.
The lack of water during initial stages of plant growth likely impacts the majority of the root system.
Late in the growing season, roots are more developed and reach further into the soil profile.
Therefore water stress late in the season will first impact roots high in the soil profile while those deep in the profile may continue to extract some water to meet the needs of the crop.
Finally, because the plant is nearing maturity, the need for water is declining on a daily basis and the root system can more easily keep up with the needs of the plant as water in the profile slowly moves to replace the water used by the crop.
For sugarbeets, the most critical time period when irrigation can affect final yield is during germination and early plant development.
Inadequate soil water for germination and emergence results in reduced plant populations which in turn reduce final yield.
Water stress after plants have emerged can result in seedling desiccation.
At the early growth stages when root development is minimal, water stress can result in plant death with only a few days of warm dry winds.
Often times if soil water is not adequate and stress begins, it is difficult to replenish the
 soil water in a timely fashion.
Even with center pivot irrigation, adequate water must be applied otherwise a light application merely meets the days evaporation demand.
It is important to have an adequate supply of water in the soil below the seedling which allows soil water to migrate upwards and meet demands of the young seedling.
As the season progresses, adequate water should be available to allow the sugarbeet to develop a good root system for extracting water from the soil.
The impact of late season water stress on sugarbeets was also studied at the Panhandle Research and Extension Center for both sprinkler and furrow irrigation systems.
In these experiments, irrigation was either limited or stopped starting in mid-August.
The results are given in figures 3a and 3b and show a yield decline as water stress increased for sprinkler and furrow systems, respectively.
The decline however, was not as great as what might be expected.
If the sugarbeet is allowed to develop a extensive roots system and water is available in the soil profile, it is capable of retrieving water from depths greater than 3 to 4 ft.
In a current experiment irrigation water is being withheld from sugarbeets from July 15 to August 15.
Preliminary results indicate very little difference in yield between full irrigation and no irrigation during the treatment period.
The results indicate that like wheat and sunflowers, sugarbeets can effectively extract water from depths much greater than 3.0 ft and perhaps sustain periods of water stress without adversely impacting yield.
Based on the results of the dry bean and sugarbeet experiments, if water is limited and the irrigator has the ability to choose when water supplies can be used, the choice should be to use water early in the season.
Reducing irrigation late in the season has a smaller impact on yield than reducing irrigation early in the season and risking more of a yield reduction.
DRY SPRING AND SMALL GRAIN IRRIGATION
 Available soil moisture is becoming a critical issue in small grain fields across the entire state.
For producers fortunate enough to have the means to irrigate small grain fields, now is the time to replenish the top and subsoil moisture supply, especially for winter wheat.
Barley is much further along developmentally  and matures earlier in the year than does winter wheat.
Although I might hesitate to spend the money to irrigate barley that is already past flowering, I would not hesitate to irrigate wheat, which, for the most part, has not reached the heading stage as yet.
In some irrigation work we did on wheat a number of years ago, we found that irrigation after head emergence tended to decrease yield potential, although only by a small amount and this decrease may have been related to disease pressure encouraged by higher humidity conditions created when irrigating.
My preference for small grain irrigation is to apply enough water before heading to build the topsoil and subsoil moisture levels back to near field capacity.
This should provide the water the crop needs to mature since wheat and barley are excellent at using available soil moisture.
As a side benefit, irrigation can help with emergence in the crop following the small grain crop.
Without adequate early irrigation, it can prove difficult to rewet the soil, and especially recharge the deeper layers of soil, with enough moisture to adequately support the second crop if the dry weather continues.
Percent of fields that became wetter moving from August to Sept.
15.
The dry years 2020, 21 and 22 fields are much drier than the other years in the fall.
In 2017, 72% of fields with soil in the 15-25 in zone became wetter from August to Sept.
15, 75% of fields with soil in the 25-36 in zone became wetter from August to Sept.
15, and 66% of fields with soil in both zones became wetter moving from August to Sept.
15.
Ogallala Aquifer Program Center Pivot Irrigation Technology Transfer Effort
 The year 2018 will mark the 40th anniversary of research and development with Low Energy Precision Application  for use with center pivot sprinkler irrigation systems.
Since that time, researchers and extension specialists in the Ogallala region have continued development of multiple types of technologies that are suitable for mobile lateral irrigation platforms.
A two-year technology transfer effort with funding from the USDA-ARS Ogallala Aquifer Program  was initiated in January 2017 to promote adoption of advanced and efficient irrigation technologies and to highlight recommended practices for these mobile irrigation platforms [center pivots  and lateral move systems ].
This paper will report on pertinent mobile irrigation history and the progress and future plans of the project with a particular focus on the current status of the technology and research and educational needs.
The Kansas and Texas High Plains / Southern Ogallala Aquifer Region are noted for limited and declining groundwater resources  and relatively high rate of adoption of efficient advanced irrigation technologies.
One of the earliest advanced mobile sprinkler irrigation technologies, Low Energy Precision Application , was first researched in the OAP region near Halfway, Texas by William Lyle and James Bordovsky beginning in 1978.
Low pressure center pivot irrigation, including , Low Elevation Spray Application , Mid-Elevation Spray Application , and other variations have become the most widely practiced irrigation methods in the region.
This is due in large part to the suitability of the technologies to the crop production systems in the region; relevant applied research programs; collaborations among research and extension programs and with industry; effectiveness of cost-share programs, and the willingness of agricultural producers in the region to adopt technologies and BMPs to adapt to limited water conditions.
From the early work on development on LEPA that began in 1978 and later Low Elevation Spray Application  irrigation and MidElevation Spray Application  to the newer integrated sensor/control systems mounted on CP and LMS systems, OAP affiliated programs have made important contributions to the advancement of irrigation using mobile platforms.
While low pressure center pivot irrigation is widely practiced in the region, applied research continues to refine recommendations, so this technology transfer effort is providing opportunities for end-users to hear up-to-date recommendations to aid in their irrigation decisions.
There is much less understanding
 by "non-practitioner audiences  about the most appropriate uses of these technologies, so this effort will help to improve their understanding of the state of the art, considerations for irrigation management, and appreciation for the advances in agricultural irrigation technology, management and efficiency.
The technology transfer effort will also provide a good opportunity for the engineers and scientists to collaborate and synthesize "what we know" into more accessible publications and media as well as to provide a venue to brainstorm additional improvements to systems and technologies.
A BIT OF HISTORY OF LOW PRESSURE CENTER PIVOT IRRIGATION
 Although by no means do the OAP project participants plan to limit their technology transfer effort to low pressure center pivot irrigation, some historical discussion is warranted to illustrate how the science and conceptualization of LEPA and its prodigies  can lead and has led to improved irrigation management in the OAP region and beyond.
Original development of the LEPA system coincided with a period of relatively high energy costs and concerns about energy availability in the late 1970s, thus low energy usage was a key objective in its development.
In Texas where LEPA was originally developed under semi-arid conditions, air and canopy evaporative losses from sprinkler irrigation can be appreciable, reducing crop yields in water-limited operations with low capacity irrigation systems, so reduction or elimination in these losses were assets to the LEPA system.
Original design issues were development of an application system adaptable to flowrates from 100-1000 gpm with operating pressures between 5 and 20 psi.
The system was to be adaptable to all soil types, and since there are great differences in water infiltration rates across soil types, runoff was to be controlled by using micro-basin tillage techniques.
Early development of LEPA was on land slopes of less than 1 percent and physical geometry limitations of the micro-basins imposes some limitation on their effectiveness on greater slopes.
For example, runoff from LEPA sprinklers was negligible on 1% sloping silt loam soils in eastern Colorado but exceeded 30% when slopes increased to 3%.
Scientifically, LEPA has always been considered to be a system of technologies with both center pivot hardware and adoption of specific farming practices.
Application efficiencies in Texas for LEPA and conventional sprinkler irrigation were measured at 99 and 84%, respectively, when micro-basin tillage was practiced as compared to 88 and 81% when conventional tillage was used.
The worldwide annual benefit of LEPA has been estimated to be $US 1.1 billion with a $US 0.477 billion benefit to consumers in the United States.
Failure to adopt the underlying LEPA system principles will usually result in unsuccessful application of the technology.
Producers' reluctance to adopt some of the guiding principles or land considerations have led to alternate in-canopy or near-canopy application systems such as LESA and MESA, which are spray applications at low and mid elevations, respectively.
These systems with a larger wetting pattern reduce the chance of excessive runoff, particularly when used in conjunction with conservation tillage.
The adoption of LESA and MESA systems as compared to LEPA is more prevalent moving northward in the southern and central Great Plains, particularly on tighter soils, greater land slopes and with greater capacity groundwater wells.
Briefly summarizing the history, the science and conceptualization of low pressure center pivot irrigation technologies led to multiple adaptations of the overall technology that have been adopted on a relatively wide scale.
When the implementation knowledge was ignored or discarded much of the potential water and energy saving benefits were not realized.
CENTER PIVOT BRAINSTORMING AND BRAIN STRETCHING RETREAT
 In the spring of 2017, an invitation was sent out to a broad range of irrigation engineers, scientists, USDA NRCS specialists, and industry representatives associated with center pivot technologies to participate in a brainstorming retreat sponsored by the OAP CP Technology Transfer Project to be held in Amarillo, Texas on March 28-29.
A total of 39 individuals from 16 U.S.
states  were able to participate in the retreat.
There were several goals of the retreat including networking opportunities for both more experienced and less experienced individuals, electronic distribution of large bodies of CP-related publications from the Central Plains Irrigation Conference and the USDA-ARS Conservation and Production Research Laboratory, discussion of past and current research, identification of research, extension and educational needs, and discussion of industry status and information gaps.
Although it is impossible to fully capture the richness and value of this two day event in this brief report, an attempt to tabulate the key topics, their status and the important knowledge gaps was concluded by these two authors.
No attempt to prioritize any of the key topics was intended through this tabulation , nor should it be considered inclusive of all topics discussed during this two-day event.
OTHER PLANS FOR THE TECHNOLOGY TRANSFER EFFORT
 Technical Sessions at Conferences
 The Irrigation Association  technical session for which this paper is a part was developed and coordinated through the USDA-ARS OAP Center Pivot Technology Transfer Effort.
Through coordinating of this session, the project brings together engineers, scientists, agency staff, and industry and the general public for networking and further technology transfer about CP technologies.
Further technical sessions are being planned and coordinated for regional conferences such as the High Plains Conference in Amarillo, Texas on February 7, 2018 and at the Central Plains Irrigation Conference in Colby, Kansas on February 20-21, 2018.
These sessions are geared toward producers, consultants, irrigation professionals and agency staff and they leverage annual educational events and ongoing programs.
Additional technical sessions at national professional conferences are being proposed for IA in Long Beach, California in December 2018, the American Society of Agricultural and Biological Engineers  in Detroit, Michigan in July 2018 and the Agronomy, Crop Science  meeting in Baltimore, Maryland in November 2018.
These meetings are geared more toward scientist to scientist/industry interchanges.
Review or Summary Papers
 Participants in the technology transfer effort have agreed to prepare literature reviews or summary papers during the coming year.
Topics that have been agreed upon thus far are a summary paper on history and development of LEPA, a conceptual discussion of all in-canopy and near-canopy sprinkler irrigation and a summary paper on irrigation decision support systems.
Other possibilities include a state of the art discussion on remote sensing, UAVs and their role in CP management, a review or summary paper on sprinkler chemigation, a summary paper on VRI and a summary paper on future needs for CP.
There are opportunities for non-project participants to lead or collaborate on some of these efforts.
Tours and Field Days
 Specific CP technology transfer field days are being planned for the summer of 2018 in both Texas and Kansas.
Dates and locations have not been finalized as of this time.
Additionally portions of other tours
 and regular university field days will likely encompass some of our presentations.
It is anticipated that the center pivot technology industry will be approached for support of these activities.
If you are interested in supporting this project, feel free to contact either of the authors who are the project's principal investigators.
Website and Activity Listing
 This technology transfer effort is supported by the Ogallala Aquifer Program, a consortium between USDA Agricultural Research Service, Kansas State University, Texas A&M AgriLife Research, Texas A&M AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
Watch for our project logo.
Table 1.
Key topics, comments and information status and key knowledge and/or implementation gaps identified at a center pivot irrigation brainstorming retreat in Amarillo, Texas, March 28-29, 2017.
The order or extent of the listing does not indicate any priority, nor should it be considered inclusive of all ideas discussed during this two day event.
This tabular listing is meant only to portray the wide range of topics and some key gaps that were identified.
Key Topic	Comments and Information Status	Key Knowledge and/or Implementation Gaps
 Hardware development has outpaced development of
 Emerging technology, still uncertainty about extent of future needs
 Variable Rate	Three types identified (Sector Control, Speed Control, VRI Zone or	Although many teams working on dynamic prescriptions,
 continued work is needed to remove this impediment.
Irrigation.
Uncertainty about producer expectations.
Site Specific	Many current  CP systems have more	Abandonment can be high in absence of appropriate
 Irrigation 	capabilities than recognized by system owner.
support to producers from industry, universities,
 VRI not needed by all and some producers will not recoup costs of
 Continued need for research and education.
Maturing technology, many different types of packages are
 provided by industry to meet needs of producers.
Although maturing technology, still many implementation
 Selection should consider crop, soil, water source/quality and	mistakes.
energy.
"One size fits all" mentality ignores the knowledge we
 Sprinkler Packages	LEPA, LESA and MESA have specific requirements that need	have.
consideration.
Runoff must be controlled first for any realistic success
 Greater interest and adoption of in-canopy and near-canopy	with in-canopy and near-canopy sprinkler application.
application when evaporative losses are higher, irrigation capacity	Educational needs of producers still remain.
is lower and land slope is lower.
Hydraulics can be modeled, but catch can results are still instructive
 and can point out hardware and implementation problems.
Uncertainty of continued status of some modeling efforts.
Sprinkler	Catch can tests are still time and labor intensive.
CPED is now available from USDA-NRCS in a MS-Excel
 Mismatch of nozzle package and operating pressure is	format.
Uniformity	commonplace.
Producers still need to monitor and respond to the basic
 Need to remember that crop can integrate some minor uniformity	information of system flowrate and pressure.
Scope of appropriate applicability of the technology (e.g.
soil type, slope, crops) is still unknown.
Mobile Drip	Emerging technology with just a few research studies to date.
Rodents can be a problem.
Irrigation	Can reduce wheel track problems.
Forces applied on CP systems may be concern.
Maintenance issues, filtration needs and other concerns.
Wheel tracks,	Primarily anecdotal or industry-held information.
Need for generic  publication or
 rutting and getting	Actually may negatively affect irrigation management, such as early	guidance on span selection and wheel/flotation system
 stuck.
end-of season irrigation termination.
selection.
Maturing technology, but perhaps not as much recent research	Sprinkler packages and sprinkler spacings.
Chemigation	efforts by Universities.
VRI interactions with chemigation.
Uncertainty of audience (i.e., end-users, regulators or chemical	Safety and standards needs; associated educational
 industry) may result in inertia	needs.
Microbursts	No known resources identified.
What direction to park CP?
/Tornadoes and CPs	Student project or modeling effort??
Loaded with water for downforce or not?
Maturing knowledge base	Producers and installers still need education.
Center Pivot Safety	USDA-NRCS has some materials and trains their own staff about	Need for lay-oriented publications.
approaching CP systems.
Who has expertise/presentations?
Emerging area with large amount of interest
 Lots of approaches are necessary for research but make
 Can interface with VRI research needs but standalone research area
 selection of approach difficult for producer.
Remote Sensing	UAVs are of considerable interest to producers now.
Hardware offerings may presently outpace development
 Remote sensing could encompass weather, soil, or plant
 Continued need for research and education.
information and combinations of the three types.
Technology is maturing and interest is growing due to more usage
 Some evaluations have been done in region but more are
 of electricity as sole energy source for CPs.
Still not economical for many cases.
Drives 	Economic feasibility will depend on field slopes and other changes	More modeling is needed.
VRI will further complicate the need for VFDs
 in pressures, time of operation, and price of energy.
Mature, yet continuing evolving topic area.
How well are we targeting audiences?
Fewer attendees at traditional university-led workshops, tours, and	Do we adjust to the audience (i.e., professional,
 field days.
producers, regulators, industry, legislators, urban
 Not just agricultural problem with attendance, landscape having	audiences, genders and age).
Publications and	similar issues.
Could public/private partnerships be used to greater
 Grower panels can be useful when remaining sufficiently unbiased	advantage?
and scientifically sound.
Individual companies may have material that could be
 Younger generation audiences are definitely more open to	packaged better for broader industry-wide educational
 Fewer, but better, regional conferences may be an option for	Technology farms or large plots research may be better at
 "sounding" the knowledge but may still have attendance issues.
information delivery.
Small and decreasing number of agricultural irrigation programs in	Industry needs well-educated staff that are willing to live
 University Degree	USA and attracting fewer US-born students.
in agricultural regions.
Programs and	Importance of agriculture is not always reflected at universities.
Universities need well-trained faculty and funding to
 Certificate	Community colleges may be able to fill some staffing needs.
retain good faculty.
Programs	USDA-NIFA may need to provide irrigation fellowships to help build	Universities need to develop students to find food and
 capacity.
fiber solutions for 9.6 billion people by 2050.
Average percent of fields by year fitting into the six categories.
The dry years 2020, 21 and 22 are different than the other years.
In 2019, out of 15 reports, 20% were ranked good, 7% were fair, 40% were wet late, 7% were wet early, 0% were wet all season, and 27% were very wet all season.
Lock out and secure system: We dont want the system to be turned on during the offseason without the growers knowledge.
Ice buildup could take the system down.
Internal combustion engines need quite a bit more attention.
Change engine oil and all filters.
Check engine hours and refer to the manufactures service interval on valve adjustments and other service that may be needed.
It would also be a good idea to run the Nebraska Extension App IrrigatePump to see where your well stacks up against the Nebraska Pumping Plant Criteria.
This will give you an idea on the efficiency of the power unit and pump.
In the current economic climate we want to be as efficient as possible.
The sorghum competition, now in its sixth year, will change location, moving to the Henry J.
Stumpf International Wheat Center near Grant, Nebraska.
Participants will still be responsible for managing dryland and irrigated plots in this competition.
Grant is an area more suited to growing sorghum, so we think it is a better fit for the plots and participants, Burr said.
The Chadron aquifer is the sole source of water to more than 160 wells in the Nebraska panhandle and supplies some of the water to at least 50 additional wells, most of which are near the Perkins-Chase county line.
Glossary of Water Terminology
 Fact Sheet No.
4.717
 by R.
Waskom and M.
Neibauer*
 Water is basic to our lives and all of us are affected by how it is used and managed.
In Colorado, the complexity of our water laws and our water management structure is often bewildering.
It seems that water managers in Colorado have their own special language.
This fact sheet offers non-technical definitions of many of the commonly used water terms to help citizens better understand the principles that govern the use of water in Colorado.
Absolute water right: A water right, with a specified priority date, that has been placed to a beneficial use.
Acre foot: The volume of water required to cover one acre of land to a depth of one foot.
Adjudication: The judicial process through which the existence of a water right is confirmed by court decree.
Adverse use: Using decreed water owned by another appropriator.
Alluvial groundwater: Ground water that is hydrologically connected to a surface stream that is present in permeable geologic material, usually small rock and gravel.
Appropriation Doctrine: The system of water law primarily used in the western United States under which: 1.
The right to water is acquired by diverting water and applying to a beneficial use; and 2.
A right to water use is superior to a right developed later in time.
Appropriator: The person or persons who put water to beneficial use.
Aquifer: Underground deposits of sand, gravel, or rock saturated with water.
The two major types of aquifers are confined and unconfined.
Artesian well: A well in which water under natural pressure rises to the surface without being pumped.
Augmentation plan: A court-approved plan that allows a junior water user to divert water out of priority SO long as adequate replacement is made to affected stream system preventing injury to the water rights of senior users.
Base flow: The amount of water in a stream that results from ground water discharge.
Basin: The area of land that drains to a particular river.
Basin rank: The relative seniority of a water right as determined by its date of adjudication and the date of appropriation.
Beneficial use: The application of water necessary to accomplish the purpose of the appropriation, without waste.
Some common types of beneficial use are agriculture, municipal, wildlife, recreation, and mining.
Best Management Practices : Practices that are technically and economically feasible and for which significant water conservation or water quality benefits can be achieved.
California Doctrine: A legal doctrine retaining aspects of both riparian rights and the principles of prior appropriation.
Call: The request by an appropriator for water which the person is entitled to under his decree; such a call will force those users with junior decrees to cease or diminish their diversions and pass the requested amount of water to the downstream senior making the call.
Change of water right: Any change in a way a water right is used.
Can be changed in type, place, time of use, point of diversion, adding points of diversion, etc.
Changes of
 Water in Colorado is administered under the doctrine of prior appropriation or "first in time, first in right doctrine".
The state constitution declares that "the right to divert the unappropriated waters of any natural stream to beneficial uses shall never be denied."
 The concept of beneficial use has changed with changing public values, but includes a notion of wise use, without waste.
Water rights in Colorado are adjudicated or recognized through the court system.
water rights must be approved by the water court to assure that no injury occurs to other water rights.
Colorado Doctrine: The doctrine regulating water usage by priority of appropriation as opposed to riparian rights.
See appropriation doctrine.
Compact: An agreement between states apportioning the water of a river basin to each of the signatory states.
Compact call: The requirement that an upstream state cease or curtail water diversions from the river system that is the subject of the compact SO that downstream states' compact entitlements may be met.
Conditional water right: The legal preservation of a priority date that provides a water user time to develop his or her water right, but reserves a more senior date.
A conditional right becomes an absolute right when water is actually put to beneficial use.
Conservancy district: A special taxing district, created by a vote of the district's electors, that has authority to plan, develop, and operate water supply and/or potable water projects.
Conservation district: A geographical area designated by the State Legislature for water management purposes with a board appointed by county commissioners.
Consumptive use: 1.
Any use of water that permanently removes water from the natural stream system.
2.
Water that has been evaporated, transpired, incorporated into products, plant tissue, or animal tissue and is not available for immediate reuse.
Cubic feet per second : A rate of water flow at a given point, amounting to a volume of one cubic foot for each second of time.
Equal to 7.48 gallons per second, 448.8 gallons per minute, or 1.984 acre feet per day.
Decree: An official document issued by the court defining the priority, amount, use, and location of the water right.
Decreed water right: A court decision placed on a water right that is then administered by Colorado's Water Resources Department.
Depletion: The loss of water from surface water reservoirs or groundwater aquifers at a rate greater than that of recharge.
the geographic boundaries of a designated ground water basin.
Designated ground water: Ground water which, in its natural course, is not available to or required for the fulfillment of decreed surface rights, and which is within
 Designated ground water basins: Those areas of the state established by the Ground Water Commission located in the Front Range and Eastern Colorado.
Developed water: Water that is produced or brought into a water system through the efforts of people, where it would not have entered the water system on its own accord.
Diligence: Action taken towards the perfection of a conditional water right.
Direct flow right: Water diverted from a river or stream for use without interruption between diversion and use except for incidental purposes, such as settling or filtration.
Diversion: Removal of water from its natural course or location by canal, pipe, or other conduit.
Division engineer: The state engineer's principal water official in each of the seven water divisions.
Drainage basin: All the land that serves as a drainage for a specific stream or river.
Drought: An extended period with below average precipitation.
Effluent: Water discharged after use.
Effluent exchange: The practice of exchanging wastewater effluent for other water sources without causing injury to other water rights as a replacement source of water for diversion of water farther upstream that would otherwise have been out of priority.
Endangered Species Act: Federal law that governs how animal and plant species whose populations are dangerously in decline or close to extinction will be protected and recovered.
Erosion: Natural process in which soil and land surface is worn down or washed away by the action of water, wind, ice, or landslides.
Eutrophication: The process of surface water nutrient enrichment causing a water body to fill with aquatic plants and algae.
Evaporation: The process of changing a liquid to a gas ; for example, when water turns into steam or water vapor.
Evapotranspiration : Process by which water is evaporated from soil surface and water is transpired by plants growing on that surface.
diverted out of priority at one point by replacing it with a like amount of water at another point.
Exchange: A process by which water, under certain conditions, may be
 Exempt uses: Any recognized uses that are not subject to administration under the priority system.
Exempt well: A well allowed to be pumped out of priority.
Federal reserved rights: An implied water right that occurs when the federal government withdraws its land from the public domain and reserves it for a federal purpose, the government, by implication reserves appurtenant water then unappropriated to the extent needed to accomplish the purpose of the reservation.
Firm annual yield: The yearly amount of water that can be dependably supplied from the raw water sources of a given water supply system.
Floodplain: A low area of land adjacent to a stream or other water course which is subject to flooding and holds the overflow of water during a flood.
Often delineated on the basis of the 100 year storm event.
Fresh water: Low salt content water.
Futile call: A situation in which a junior priority will be permitted to continue to divert in spite of demands by a senior appropriator in the same watershed, because to curtail the junior from diversion would not be effective to produce water for beneficial use for the senior.
Ground water: Ground water, as opposed to surface water, is water that does not run off, and is not taken up by plants, but soaks down into an aquifer; a supply of fresh water under the earth's surface which forms a natural reservoir.
Ground Water Commission: A twelve member body created by the legislature, nine of which are appointed by the Governor to carry out and enforce the state statutes, rules, regulations, decisions, orders, and policies of the Commission dealing with designated ground water.
Ground water management district: Any district organized for the purpose of consulting with the ground water commission on all designated ground water matters within a particular district.
Head gate: A control structure or gate upstream of a lock or canal; A floodgate that controls the flow of water, as in a ditch.
Hydraulics: Study of practical applications of liquid in motion.
Hydrologic cycle: The cycle of water movement from the atmosphere to earth and back again through evaporation, transpiration, condensation, precipitation, percolation, runoff, and storage.
See water cycle.
Hydrology: The science dealing with the waters of Earth their distribution and movement on the surface and underground; and the cycle involving evaporation and precipitation.
Infiltration: Water moving into the ground from a surface supply such as precipitation or irrigation.
In-stream flow: Non-consumptive water requirements that do not reduce the water supply, such as water required for maintaining flowing streams for fish or for recreational boating.
Irrigation district: A legal entity created by statute in order to develop large irrigation projects.
Irrigation year: The irrigation year for the purposes of recording annual diversions of water for irrigation in Colorado begins November 1 and ends on October 31 of each year.
Junior rights: Water rights that are more recent than older or more senior rights.
Leaching: The process where material in the soil  are washed into lower layers of soil by the downward movement of water.
Minimum streamflow requirement: Water right decreed to the Colorado Water Conservation Board requiring that a set amount of water be maintained in a water course for the purpose of reasonably maintaining the environment.
Municipal water system: A network of pipes, pumps, and storage and treatment facilities designed to deliver potable water to homes, schools, businesses, and other users in a city or town and to remove and treat waste materials.
National Environmental Policy Act : Federal law enacted to ensure the integration of natural and social sciences and environmental design in planning and decision-making for federal projects or projects on federal lands.
National Pollution Discharge Elimination System  Permit: A permit required under Section 401 of the Clean Water Act regulating discharge of pollutants into the nation's waterways.
Native waters: Surface and underground waters naturally occurring in a watershed.
Non-consumptive use: Water drawn for use that is not consumed.
For example, water withdrawn for purposes such as hydropower generation.
It also includes uses such as boating or fishing where the water is still available for other uses at the same site.
Non-exempt uses: Any recognized beneficial uses of water that are administered under the priority system.
Non-exempt well: A well allowed to be used for non-exempt uses such as irrigation.
Non-native waters: Water imported or not originally hydrologically connected to a watershed or drainage basin physically or by statute; non-tributary groundwater and transmountain water are non-native.
Non-tributary ground water: Underground water in an aquifer which is situated so that it neither draws from nor contributes to a natural surface stream in any measurable degree.
Nonpoint source pollution: Pollution coming from a wide, non-specific source such as runoff from cities, farms, or forest land.
Not non-tributary ground water: Statutorily defined as ground water located within those portions of the Dawson, Denver, Arapahoe, and Laramie-Fox hills aquifers that are outside of any designated ground water basin in existence on January 1, 1985.
Over-appropriated: A water rights term used to describe a surface water drainage system that has more decreed water rights claims on the system than can be satisfied by the physical supply of water available.
Percolation: The downward movement of water in soil; the infiltration of water into the ground.
Point of diversion: A specifically named place where water is removed from a body of water.
Point source pollution: Pollution coming from a single identifiable source such as discharge pipes from industry or sewer plants or other means of conveyance including ditches, channels, sewers, and containers.
Potable: Water that is considered safe for domestic human consumption; drinkable water.
Priority: 1.
The right of an earlier appropriator to divert from a natural stream in preference to a later appropriator.
2.
Seniority date of a water right or conditional water right to determine their relative seniority to other water rights and conditional water rights deriving water from a common source.
Priority is a function of both the appropriation date and the relevant adjudication date of the right.
Priority date: The date of establishment of a water right.
The rights established by application have the application date as the date of priority.
Raw water: Untreated water.
Recharge: Ground water supplies are replenished, or recharged, when rain or snowmelt enters the saturation zone.
Recharge area: Reservoirs and ditches that are designed to replenish ground water depletions, due to out of priority diversions, by artificially introducing water into the ground water aquifer.
Reclaimed water: Effluent usable for irrigation or ready for release into lakes and rivers.
Reservoir: A natural or artificial place to store water; water storage created by building a dam; a pond, lake, or basin used for the storage, regulation, and control of water.
Resume: A monthly publication by the water court of a summary of water rights applications filed in the water court that month.
Return flow: The amount of water that reaches a surface or ground water source after it has been released from the point of use and thus becomes available for further reuse.
Reuse: To use again; to intercept for subsequent beneficial use, either directly or by exchange.
Water that would otherwise return to the steam system.
Reverse osmosis: A water treatment method used to remove dissolved inorganic chemicals and suspended particulate matter from a water supply.
Water, under pressure, is forced through a semi-permeable membrane that removes molecules larger than the pores of the membrane.
Riparian Doctrine: A legal concept in which owners of lands along the banks of a stream or body of water have the right to reasonable use of the water and a correlative right protecting against unreasonable use by others that substantially diminishes the quantity or quality of water.
The right is appurtenant to the land and does not depend on prior use.
Riparian rights are not recognized in Colorado.
Riparian water right: The legal right held by an owner of land contiguous to or bordering on a natural stream or lake, to take water from the source for use on the contiguous land.
River basin: The land area surrounding one river from its headwaters to its mouth; the area drained by a river and its tributaries.
River call: Usually a written document filed with the division engineer stating that as of a certain date and time, a water right holder is not receiving all of the water they are entitled to by decree, and are requesting that the Division Engineer shut down or curtail all upstream water rights junior to them until their senior right is satisfied.
Safe Drinking Water Act : Federal legislation that regulates the treatment of water for human consumption.
Requires testing for and elimination of contaminants for the protection of human health.
Senior rights: Water rights that have been established first and are older than junior rights.
Source water protection spring: Plan for maintaining quality of a drinking water supply.
The point at which the water table meets earth's surface, causing water to flow from the ground.
State engineer: The chief executive office in the executive department of the state government who administers the adjudication decrees of court, defining water rights.
Storage water rights: Colorado law provides for "appropriation by storage" of water that will captured in reservoirs and subsequently be put to beneficial use in priority.
Storage water applications are submitted to water court for adjudication and decree similar to other water rights.
Structure: Any apparatus constructed to divert water, such as a head gate, pipe, or well.
Sublimation: The transition of water from the solid phase  directly to the vapor phase without melting.
Surface water: Water on the surface of the ground ; precipitation which does not soak into the ground or return to the atmosphere by evaporation or transpiration.
Surge irrigation: A method of irrigation using computerized valves to turn the water supply on and off to move water more uniformly down the field.
Transbasin diversion: The conveyance of water from its natural drainage basin into another basin for beneficial use.
Transmountain diversion: The conveyance of water from one drainage basin to another across the Continental Divide.
Transpiration: The process by which water absorbed by plants  is evaporated into the atmosphere from the plant surface.
Treated water: Water that has been filtered and/or disinfected; sometimes used interchangeably with "potable" water.
Tributary: A tributary is generally regarded as a surface water drainage system which is interconnected with a river system.
Under Colorado law, all surface and groundwater, the withdrawal of which would affect the rate or direction of flow of a surface stream within 100 years, is considered to be tributary to a natural stream.
Tributary ground water: Water present below the earth's surface that is hydrologically connected to a natural surface stream.
Unappropriated water: Water which has not been appropriated, and in which no other person has or claims superior rights and interests.
User supplied data: Data or records of water uses provided by an owner/ user which has not been verified by state officials.
Wastewater: Water that has been used and contains unwanted materials from homes, businesses, and industries; a mixture of water and dissolved or suspended substances.
Wastewater treatment: Any of the mechanical or chemical processes used to modify the quality of wastewater in order to make it more compatible or acceptable to humans and the environment.
Water and sanitation districts: A special taxing district formed by the residents of the district for the combined purpose of providing potable water and sanitary wastewater services.
Water commissioner: State water officials, appointed by the state engineer and working under the direction of the division engineers, who perform the day-to-day administration of surface and ground water in each water district.
Water conservation: The wise use of water with methods ranging from more efficient practices in farm, home and industry to capturing water for use through water storage or conservation projects.
Water court: A special division of a District Court with a District Judge designated as and called the Water Judge to deal with certain specific water matters principally having to do with adjudication and change of point of diversion.
There are seven water courts in Colorado.
Water cycle: Transition and movement of water involving evaporation, transpiration, condensation, precipitation, percolation, runoff, and storage.
Water development: The process of building diversion, storage, pumping, and/ or conveyance facilities.
Water districts: Eighty geographical divisions of the state that originally were used for the granting of water rights.
The districts are now largely used for administrative purposes.
Water diversion: Changing the natural flow of water to another location by using dams, canals, or pipelines.
Water divisions: The seven geographical areas of the State of Colorado corresponding to the major natural surface water drainages.
Water quality standard: Recommended or enforceable maximum contaminant levels of chemicals or substances in water.
These levels are established for water used by municipalities, industries, agriculture, and recreation.
Standards may also be narrative.
Water right: A right to use, in accordance with its priority, a certain amount of water.
Water storage: The locations in which water is stored.
They can be above ground in lakes, rivers, and other waterways or below ground as ground water.
Water table: The upper level of ground water; the level below which soil and rock are saturated with water.
Watershed: The region draining into a river, river system or body of water; the total land area, regardless of size, above a given point on a waterway that contributes runoff water to the flow at that point; all the land that serves as a drainage for a specific stream or river.
Well: Any structure or device used for the purpose or with the effect of obtaining ground water for beneficial use from an aquifer.
A shaft or hole into the Earth to tap an underground supply of water.
Wellhead Protection Program: An amendment to the federal Safe Drinking Water Act in 1986.
Initiated to minimize the potential for contamination of public ground water supplies.
Wetland: An area of land that is regularly wet or flooded, such as a marsh or swamp.
Other common names for wetlands are sloughs, ponds, and marshes.
Xeriscape: The use of plant materials and practices that minimizes landscaping water use; usually native plants; environmentally friendly form of landscaping.
The term "xeriscape" was copyrighted by Denver Water in 1981.
Note: These definitions are offered to assist the public in understanding some of Colorado's most often used water terms.
If you desire a legal definition, please contact a water attorney.
Nebraska Extension has educators and specialist across the state that would be happy to help you develop a plan as well.
Feel free to send an email to Steve Melvin if you would like to set up a time to talk.
The shape of water: When ag water management pays off
 Years of drought have parched Californias vast agricultural lands, prompting farmers to drill deeper and deeper into aquifers to irrigate their fields.
But this often means higher water costs for everyone  and inefficient use of a precious resource.
When a farmer draws water from a well, it depletes the aquifer for all the other farmers who rely on it; they have to dig deeper, making the water more costly.
But farmers dont take into account the added cost extraction is creating for their neighbors.
That leads them to pump yet more water.
Meanwhile, a crazy quilt of overlapping and sometimes contradictory regulations often encourage too much extraction and lead to more expensive water.
Cornell researchers have a solution: Coordinate water use, taking into account all the farms drawing water from a particular aquifer.
The approach offers the farms a significant payoff when crop prices are high, according to the study.
"Spatial groundwater management: A dynamic game framework and application to California appeared in a special issue of Water Economics and Policy on game theory and water resource management.
If a planner is involved, theyre thinking, If we extract this amount of water at this point of land, itll draw down the water stock at that point and make it more expensive in the future.
Is that advantageous for the total farming thats going on in this area?
said lead author Louis Sears, a doctoral candidate in the field of applied economics and management.
When designing groundwater management policies, its important to account for spatial considerations that may lead users to behave uncooperatively.
His co-authors are David Lim, a postgraduate research assistant at Cornells Think-tank for Resources, Energy, and the Environment: Science and Policy-related Economic Analysis and Research , and C.-Y.
Cynthia Lin Lawell, associate professor of applied economics and management and the Robert Dyson Sesquicentennial Chair in Environmental, Energy and Resource Economics.
Using a dynamic framework based on game theory, the researchers created two competing scenarios  one coordinating water use, the other with no coordination.
They calculated the value of the economic efficiency lost or gained, depending on the scenario, on two 50-acre plots of land in California.
Using data on alfalfa grown in the San Joaquin Valleys Tulare Basin, they calculated the coordinated approach led to an overall efficiency gain of $93,000 for the two farmers when the groundwater supply was moderate and rainfall was normal.
The value of the efficiencies jumped even higher in situations when farmers would normally use water inefficiently.
Coordination would save $125,000 in scenarios with a moderate groundwater supply and high rainfall, or a high groundwater supply during a drought.
To capture the regional diversity of Californias crops, hydrological conditions and climate, the researchers also created scenarios with a variety of crops requiring different growing conditions.
These included strawberries grown in the Central Coast, walnuts grown in the North Coast and olives grown in the Sacramento Valley.
Coordinated management resulted in a value of as much as $812,226 for strawberries  a high-value crop.
But it resulted in no efficiencies for several perennial crops such as walnuts, avocados and oranges.
This shows that the issue can vary in importance with the types of crops grown, Sears said.
He also noted the savings only reflect the gains made on the two 50-acre plots.
The benefits from coordinated management for all the farmers in the entire Tulare Basin or all of California would be orders of magnitude higher, he said.
The research has particular relevance as California reforms its groundwater regulations, Sears said, and as climate change shifts the amount of precipitation regions receive.
The researchers recommend policymakers understand the full extent of an areas hydrology and how many different farmers are impacting each other, he said.
If you have little pockets of different regulations governing one aquifer, that can be really problematic and can create big gulfs in incentives between the different types of farmers, he said.
For example, giving a farmer a more precise irrigation system might encourage them to plant more crops, or more expensive crops, Sears said, which can actually exacerbate the problem.
The research was funded in part by the Giannini Foundation of Agricultural Economics and the Bacon Public Lectureship and White Paper Competition.
Practicum dates are associated with the TAPS Awards Banquet, Central Plains Irrigation Association Conference, TAPS June Field Event, and West Central Water and Crops Field Day, all of which are optional but highly relevant and recommended for practicum participants to attend.
EM 8782 Revised March 2013
 Drip Irrigation: An Introduction
 Drip irrigation tubing used to irrigate wine grapes.
Drip irrigation provides slow, even application of low-pressure water to soil and plants using plastic tubing placed in or near the plants' root zone.
It is an alternative to sprinkler or furrow methods of irrigating crops.
Drip irrigation can be used for crops with high or low water demands.
Why consider drip irrigation?
Drip irrigation can help you use water efficiently.
A well-designed drip irrigation system loses practically no water to runoff, evaporation, or deep percolation in silty soils.
Drip irrigation reduces water contact with crop leaves, stems, and fruit.
Thus, conditions may be less favorable for disease development.
Irrigation scheduling can be managed precisely to meet crop demands, holding the promise of increased yield and quality.
Growers and irrigation professionals often refer to "subsurface drip irrigation," or SDI.
When a drip tape or tube is buried below the soil surface, it is less vulnerable to damage due to UV radiation, cultivation, or weeding.
With SDI, water use efficiency is maximized because there is even less evaporation or runoff.
Agricultural chemicals can be applied more efficiently through drip irrigation.
Since only the crop root zone is irrigated, nitrogen already in the soil is less subject to leaching losses, and applied fertilizer can be used more efficiently.
In the case of insecticides, less product might be needed.
Make sure the insecticide is labeled for application through drip irrigation, and follow the label instructions.
Additional advantages of drip irrigation include the following.
Drip systems are adaptable to oddly shaped fields or those with uneven topography or soil texture; these specific factors must be considered when designing the drip system.
Drip systems also can work well where other irrigation systems are inefficient because parts of the field have excessive infiltration, water puddling, or runoff.
Drip irrigation can be helpful if water is scarce or expensive.
Because evaporation, runoff, and deep percolation are reduced, and irrigation uniformity is improved, it is not necessary to "overwater" parts of a field to adequately irrigate the more difficult parts.
Precise application of nutrients is possible using drip irrigation.
Fertilizer costs and nitrate losses can be reduced.
Nutrient applications can be better timed to meet plants' needs.
Drip irrigation systems can be designed and managed SO that the wheel traffic rows are dry enough to allow tractor operations at any time.
Timely application of herbicides, insecticides, and fungicides is possible.
Proven yield and quality responses are possible through careful irrigation scheduling made possible with drip irrigation.
Yield and quality benefits have been observed in onion, hops, broccoli, cauliflower, lettuce, melon, tomato, cotton, and other crops.
A drip irrigation system can be automated.
For an example of automated drip irrigation, see Shock, et al., 2011.
There are some disadvantages to drip irrigation.
For example:
 Drip irrigation systems typically have initial costs of $1,200 to $1,700 per acre.
This cost range does not include the equipment to install or retrieve the drip tape or hose in nonpermanent systems.
A drip system for use on an annual vegetable crop such as onion will cost about $1,200 per acre, with approximately $900 in capital costs for pumps, filtration, and water distribution, and $300 in recurring annual costs for drip tape.
A drip system using drip tubing with in-line emitters is more often used for grapes, hops, orchards, etc.
It will cost about $1,700 to $2,100 per acre and can last 12 to 15 years.
Part of the large variability in the per-acre cost of drip tubing is related to the distance between
 plant rows.
For example, grapes are planted in rows closer than hops, SO more tubing is used per acre, leading to greater cost.
Hard hose with plug-in emitters is most frequently used for landscape and nursery applications.
The cost per acre of these systems varies widely, depending on their complexity.
Systems can be more elaborate and costly than necessary.
Growers new to drip irrigation might want to start with a simple system on a small acreage.
Drip tape or tubing must be managed to avoid leaking or plugging.
Drip emitters are easily plugged by silt or other particles not filtered out of the irrigation water.
Emitter plugging also can be caused by algae growing in the tape or by chemical deposits at the emitter.
Filtration, acid injection, and chlorine injection remedies to these problems are addressed in "System management and maintenance," page 5, and "Standard maintenance," page 6.
Also see the website Maintenance of microirrigation systems.
You might need to redesign your weed control program.
Drip irrigation might be unsatisfactory if herbicides need rainfall or sprinkler irrigation for activation.
However, drip irrigation can reduce weed populations or reduce weed problems in arid climates by keeping much of the soil surface dry.
Tape depth must be chosen carefully to accommodate crop rotations and for compatibility with operations such as cultivation and weeding.
Except in permanent installations, drip tape causes extra cleanup costs after harvest.
You'll need to plan for drip tape disposal, recycling, or reuse.
Despite all of drip irrigation's potential benefits, converting to drip irrigation can increase production costs, especially where an irrigation system already is in place.
Ultimately, there must be an economic advantage to drip irrigation to make it worthwhile.
Table 1.
Types of drip irrigation systems.
Internal	Wall	Emitter	Emitter
 diameter	thickness	spacing	flow rate
 System type				
 Drip tape	0.375-1.375	4-35	2-36	0.07-0.84
 Tubing (drip	0.410-0.800	23-47	12-60	0.40-1.80
 Hard hose with	0.125-1.5*	29-125	custom	0.50-4.0*
 *Larger diameter hose and higher rate microsprinkler emitters are available for hard hose systems.
A wide range of components and system design options is available.
The Digital Drip Directory  lists equipment and suppliers.
Drip tapes, tubes, and emitters vary greatly in their specifications, depending on the manufacturer and product use.
The distribution system, valves, and pumps must match the supply requirements of the tape.
Tape, depth of tape placement, distance between tapes, emitter spacing and flow, and irrigation management all must be chosen carefully based on crop water requirements and the soil's properties.
Drip tubing, rather than drip tape, usually is used for perennial crops such as grapes or poplar trees.
The wetting pattern of water in the soil from the drip irrigation tape or tube must reach plant roots.
Selection of emitter spacing and tape depth depends on the crop root system and soil properties.
Seedling plants such as onions have relatively small root systems, especially early in the season.
Drip irrigation system design requires careful engineering.
Design must take into account the effect of the land's topography  on pressure and flow requirements.
Plan for water distribution uniformity by carefully considering the tape, irrigation lengths, topography, and the need for periodic flushing of the tape.
Design vacuum relief valves into the system as needed.
When designing a drip system, first identify fairly similar irrigation zones.
Irrigation zones are based on factors such as topography, field length, soil texture, optimal tape run length, and filter capacity.
Irrigation system designers use computer programs to analyze these factors to design efficient drip systems.
Once the drip system is designed and installed, it is possible to schedule irrigations to meet the unique needs of the crop in each zone.
Consider power and water source limitations.
Have your water analyzed by a laboratory that is qualified to evaluate emitter plugging hazards.
Water quality might create limitations and increase system costs.
Filters must be able to handle worst-case scenarios.
For excellent resources on water quality assessment and filter maintenance, see Filtration and Maintenance Considerations for Subsurface Drip Irrigation  Systems.
Finally, be sure to include both injectors for chemigation and flow meters to confirm system performance.
Every trickle counts when you are battling a water shortage.
An ineffective or improperly managed filter station can waste a lot of water and threaten a drip system's fitness and accuracy.
In the western U.S., sand media filters have been used extensively for microirrigation
 Figure 1.
Drip irrigation system with a prefilter, pump station with backflow prevention, and chemical injection site.
A pressure control valve is recommended to adjust the water pressure as desired before it enters the drip lines.
A water meter can be placed after the pressure control or between a solenoid valve and each zone.
An air vent provides vacuum relief.
Vacuum relief is necessary between the solenoid valve and the drip tapes to avoid suction of soil into the emitters when the system is shut off.
systems.
Screen filters and disk filters are common as alternatives or for use in combination with sand media filters.
Sand media filters provide filtration to 200 mesh, which is necessary to clean surface water and water from open canals for drip irrigation.
These water sources pick up a lot of fine grit and organic material, which must be removed before the water passes through the drip tape emitters.
Sand media filters are designed to be selfcleaning through a "back-flush" mechanism.
This mechanism detects the drop in pressure due to the accumulation of filtered particles.
It then flushes water back through the sand to dispose of clay, silt, and organic particles.
Sand used for filters should be between sizes 16 and 20 to prevent excess back flushing.
Because clean water from one filter is needed to back flush another filter, at least two sand media filters are generally used.
In addition to a sand media filter, a screen filter can be used as a prefilter to remove larger organic debris before it reaches the sand media filter, or as a secondary filter before the irrigation water enters the drip tube.
For best results, filters should remove particles four times smaller than the emitter opening, as particles may clump together and clog emitters.
Screen filters can act as a safeguard if the main filters fail, or may act as the main filter if a sufficiently clear underground water source is used.
System management and maintenance
 If a drip hose system is used on the soil surface for perennial crops over a number of years, the drip hose should be lifted periodically SO that leaves, soil, and debris do not cover the hose.
If the drip hose is not lifted, roots can grow over the hose, anchor it to the ground, and eventually pinch off the flow of water.
Place a water flow meter between the solenoid valve and each zone and record its gauge daily.
This provides a clear indication of how much water was applied to each zone.
Records of water flow can be used to detect deviations from the standard flow of the system, which may be caused by leaks or clogged lines.
The actual amount of water applied recorded on the meter can be compared with the estimated crop water use  to help assure efficient water management.
Leaks can occur unexpectedly as a result of damage by insects, animals, or farming tools.
Systematically monitor the lines for physical damage.
Leaks in buried hose or tape are generally difficult to detect.
Ponding on the surface often indicates a leak.
Also, pressure drop and/or flow increase can indicate leaks.
It is important to fix holes as soon as possible to prevent uneven irrigation.
Chlorine clears clogged emitters
 If the rate of water flow progressively declines during the season, the tubes or tape may be slowly plugging, resulting in severe damage to the crop.
In addition to maintaining the filtering stations, regular flushing of the drip tube and application of chlorine through the drip tube will help minimize clogs.
Once a month, flush the drip lines by opening the far ends of a portion of the tubes at a time and allowing the higher velocity water to flush out the sediment.
Because algae growth and biological activity in the tube or tape are especially high during
 warmer months, chlorine usually is applied at 2-week intervals during these months.
If drip lines become plugged in spite of maintenance, many cleaning products are available through irrigation systems suppliers.
Choose a product appropriate for the specific source of contamination.
Manage irrigation and fertilization together to optimize efficiency.
Chemigation through drip systems efficiently delivers chemicals in the root zone of the receiving plants.
Because of the precision of application, chemigation can be safer and use less material.
Several commercial fertilizers and pesticides are labeled for delivery by drip irrigation.
Make sure injected products are compatible with water to prevent chemical precipitation and subsequent plugging of emitters.
Injection pumps with backflow prevention devices are necessary to deliver the product through the drip lines.
These pumps allow for suitable delivery rate control, while backflow prevention protects both equipment and the water supply from contamination.
Remember that in Oregon water belongs to the public, not to the landowner.
Other safety equipment may be required; contact a drip irrigation system supplier for details.
Soil microorganisms convert nitrogen  fertilizers to nitrate.
Nitrate is water soluble, available to plants, and subject to leaching loss.
One of the benefits of drip irrigation is reduction or prevention of nitrate loss.
Typically, when irrigation is monitored closely, less N fertilizer is needed with drip irrigation systems than with furrow irrigation systems because the fertilizer is spoon-fed to the root system and little is lost due to leaching.
For example, if a field is converted from furrow irrigation to drip irrigation and the amount of N fertilizer is not reduced, the crop may become excessively leafy, which can inhibit curing and
 increase harvest costs as well as losses.
Plant tissue analysis performed by a qualified analytical lab can help you determine crop nutrition needs during the season and tailor N fertilizer applications to actual crop needs.
Fertilizer can be injected through the drip system.
Fertilizers containing sulfate, phosphate, calcium, or anhydrous or aqua ammonium can lead to solid chemical precipitation inside the drip lines, which can block emitters.
Obtain chemical analysis of your irrigation water and seek competent technical advice before injecting chemical fertilizers into drip systems.
Plan for seed emergence.
The drip tape must be close enough to the surface to germinate the seed if necessary, or a portable sprinkler system should be available.
A tape tube 4 to 5 inches deep has successfully germinated onion seeds in silt loam soil.
Tape at 12 inches failed to uniformly germinate onions.
Tape placement is often deeper in other row crops.
The total irrigation water requirement for crops grown with a drip system is greatly reduced compared to a surface flood system because water can be applied much more efficiently with drip irrigation.
For example, with furrow irrigation, typically at least 4 acre-feet/acre/year of water are applied to onion fields in the Treasure Valley of eastern Oregon and southwestern Idaho.
Depending on the year, summer rainfall, and the soil, 20 to 32 acre-inches/acre of water have been needed to raise onions under drip irrigation in the Treasure Valley.
Applying more water than plants need will negate most of drip irrigation's benefits.
The soil will be excessively wet, promoting disease, weed growth, and nitrate leaching.
To determine application rates, use measurements of soil water and estimates of crop water use.
For shallow-rooted crops, irrigate only to replace the
 soil moisture deficit in the top 12 inches of soil.
It usually is not necessary to exceed ET.
Local daily crop evapotranspiration estimates are available for some U.S.
Pacific Northwest locations on the AgriMet website.
For measuring soil water, see Instrumentation for soil moisture monitoring  and Irrigation Monitoring Using Soil Water Tension.
For planning irrigation scheduling, see Irrigation Scheduling..
Add chlorine or other chemicals to the drip line periodically to kill bacteria and algae.
Acid might also be needed to dissolve calcium carbonates.
Be sure to follow chemical labels for safe handling instructions.
Acids and chlorine can be very hazardous.
Filters must be managed and sand changed as needed.
Even with filtration, drip tape must be flushed regularly.
The frequency of flushing depends on the amount and kinds of sedimentation in the tape.
Root intrusion must be controlled for some crops.
Rodents must be controlled, especially where drip tape is buried.
OSU Extension Service publications
 Funding to help prepare this publication was provided in part by an Oregon Watershed Enhancement Board grant.
Shown here is a side-by-side comparison of well irrigated corn  and water stressed corn.
Water stress caused by deficit irrigation results in shorter plants with less leaf area and curled leaves.
If water is reapplied as these stressed plants tassel and form ears, about 50 percent of the yield can be salvaged.
A griculture must substantially increase productivity over the next 40 years to feed the growing world population.
Farmers are also being called on to contribute renewable resources for energy production.
Production increases in the past have been partially met by expanding use of irrigation.
Irrigated agriculture contributes about 40 percent of the U.S.
and global crop value on about 15 percent of the cropped land.
In the process, irrigated agriculture uses over 80 percent of the water consumed in many arid and semi-arid areas.
However, irrigation expansion has ceased in many areas of the western United States.
There isn't any more water to divert from rivers, and water is being pumped from groundwater aquifers faster than the natural recharge rates.
In fact, in many areas, including the southwest and west coast states and the southern High Plains, which stretch from Texas through western Kansas to eastern Colorado and western Nebraska, the irrigated area is declining.
is the quest of a group of water management researchers in the High Plains of northern Texas, eastern Colorado, western Kansas, and Nebraska.
This area requires irrigation for good crop yields.
The snowmelt from the Rockies is not enough in most years, and the massive High Plains Aquifer  is being depleted, especially in the south and central portions.
Although each region of the High Plains has its own particular problems and oppor-
 Declining irrigation is also the result of increased competition for our finite freshwater supplies.
Semi-arid irrigated areas like California, Arizona, Nevada, and the front range of Colorado and Utah are desirable places to live, and the new residents expect dependable water supplies.
The residents also want to sustain and improve the green river valleys that meander through these regions and that provide recreational opportunities and critical habitat for plants and animals.
Increased water use to sustain cities and natural environments will reduce water available to grow crops.
If we are to meet future food needs
 we must sustain irrigated agriculture and squeeze as much productivity as possible from every drop of water.
This
 Sunflowers grow in mini-lysimeters at the ARS facility at Bushland, Texas.
Several deficit irrigation treatments can be tested in a variety of soils in this lysimeter complex.
Center-pivot fields dot the high plains of Texas.
Note that some of the fields have not been planted, possibly due to lack of adequate groundwater.
Scientists at the USDA-ARS Conservation and Production Research Laboratory  in the Texas High Plains near Amarillo have been working on maximizing irrigation water productivity for many years.
The CPRL is near the southern end of the High Plains Aquifer, where water levels have been declining for many years and deep pumping depths make water expensive to extract.
ASABE member Terry Howell and his colleagues at the CPRL Soil and Water Management Research Unit use large weighing lysimeters, essentially large square containers filled with soil and sitting in the ground on large scales, to precisely determine crop water requirements.
Lysimeters are the standard for measuring water use on a daily and even hourly basis.
With these large tools, the researchers can precisely measure water use and validate other, alternative ways to measure water use, such as instrumentation that measures the atmospheric energy balance at the surface.
They recently invited researchers from across the United States to come to their fields and compare their own favorite water use measurement methods with each other and with the on-site lysimeters.
The techniques included instrumentation placed just above the crop canopies and satellite remote sensing imagery.
As researchers gain more knowledge and confidence in their ability to measure evapotranspiration, their ability to measure and describe the effects of climatic conditions, water stress, and deficit irrigation also increases.
One of the ways that crops respond to water stress is to close their stomates, which results in reduced water evaporation  and increased temperature of the crop canopy.
ASABE member Steve Evett and his colleagues
 are building infrared thermometers that can measure canopy temperatures and indicate the level of water stress.
Canopy temperature measurements can be used as a trigger to tell the grower, or the irrigation system directly, when irrigation should be started.
Recognizing the importance of sustaining the High Plains Aquifer as long as possible, the USDA-ARS began the Ogallala Initiative in 2003 with the mission to sustain rural economies through water management technologies.
Through this program, the USDA-ARS funds water management projects in Texas and Kansas in a consortium with Kansas State University , Texas A&M University, Texas Tech University, and West Texas A&M University.
ASABE member Freddie Lamm, an agricultural engineer at the KSU Colby Research Station and the ARS Central Great Plains Research Station, has been researching the use of subsurface drip irrigation in the High Plains for 23 years.
He has shown that the systems can last that long if they are well maintained, and that they are a viable water-saving option for several of the crops grown in the region.
With subsurface drip irrigation, the water is precisely placed in the soil root zone and uniformly distributed across the field to help maximize its productivity.
Surface evaporation losses are minimized since the crop and soil surface are not wetted.
Although the initial cost of drip systems is high, the resulting water conservation, high yields, and long life can combine to make drip systems a good economic choice.
One of the main irrigation limitations in many areas of the central High Plains is that the High Plains Aquifer is not very thick, and growers have already drawn down the water table, SO the capacity of their wells has decreased.
Centerpivot sprinkler systems that were installed with an adequate water supply 30 years ago may now pump only 50 percent as much water during the peak water-needs period.
ASABE
 Subsurface drip irrigation tubing is installed at Kansas State University, Colby, Kan.
"Most of the ag and bio engineers named in this article are near retirement, and I wonder how we will replace them, yet
 member Norm Klocke, an agricultural engineer at the KSU Research and Extension Center in Garden City, Kansas, and Allen Schlegel, an agronomist at the KSU Southwest Research and Extension Center in Tribune, Kansas, along with Joel Schneekloth, a regional water resource specialist at Colorado State University , are developing management strategies that will allow growers to maintain productivity with the reduced pumping capacity.
Practices include planting two different crops that have varying water needs and schedules under the same center-pivot system.
For example, an early-season crop like wheat reaches maturity and has reduced water needs by the time a later-season crop like sunflowers reaches full demand.
Through good crop rotations and tillage practices that maximize conservation of both rain and irrigation water, growers can get additional productive years from their wells.
One of the constraints to adoption of deficit irrigation practices is that most farmers depend on federal crop insurance to insure their crops against unplanned catastrophes such as hail or extreme drought.
However, the USDA Risk Management Agency , which manages the Federal Crop Insurance Program, does not know how to establish the potential yield of a crop that is deficit irrigated, SO the agency currently insures deficit-irrigated crops at the same rates as lower-yielding dryland crops.
ASABE members Norm Klocke and Derrel Martin, ag engineers in Kansas and Nebraska, have been working with the RMA to establish the likely crop yields under different planned deficit-irrigation practices.
When farmers know that they can get their crop insured for its intended yield, they will be more willing to try deficit irrigation.
Growing populations, energy development, and overuse of water are resulting in declining water supplies for irrigation in eastern Colorado.
Cities have been buying irrigated land to acquire the rights to use the water-a tactic called "buy and dry." Senior water rights holders in the "first in time, first in right" prior appropriation system have been requesting that the upstream well pumpers stop pumping.
At the same time, oil and gas exploration companies are leasing any available water for future use in hydraulic fracturing.
CSU and the USDA-ARS are partnering with water districts and private companies to devise ways to sustain the rural agricultural economy in the region.
CSU soil scientist Neil Hansen and his colleagues at KSU and the Central Great Plains Research Station at Akron, Colo., have been developing conservation practices for dryland  agriculture and are applying these practices to limited-irrigation production systems.
Reduced tillage and maintenance of surface residues helps collect rainfall, snowfall, and sprinkler water and reduces evaporation losses.
Hansen and his colleagues are
 The irrigation control center for deficit irrigation trials at the ARS Limited Irrigation Research Farm near Greeley, Colorado.
Irrigations are controlled through a data logger and measured with flowmeters.
developing cropping rotations appropriate for ranges of water supplies from dryland to full irrigation.
They have shown that an alfalfa grower with inadequate water can use the limited supply in the spring and fall and let the crop go dormant in the heat of summer and still maintain a viable crop.
The USDA-ARS Water Management Research Unit  in Fort Collins, Colo., is conducting a detailed study of plant responses to deficit irrigation and how to maximize the "crop per drop," or more specifically, the dollars per drop.
The WMRU researchers are developing water production functions based on crop evapotranspiration to quantify the value of water with different amounts of irrigation.
Colorado water law accounts for water in terms of water consumed by the crop rather than irrigation water applied, since water that is not consumed is generally available for others to
 ARS engineer Jordan Varble measures soil water content down to 2 m depth in wheat with a neutron moisture meter.
I have enthusiastic hope that students and young professionals reading this might be inspired to carry on this important work!" TT
 use downstream.
In Colorado, which has interstate compacts with all its neighboring states on both sides of the Rockies, leaving some water for downstream users is critical.
ASABE member Walter Bausch is using remote sensing from both the ground and the air to estimate crop stress and determine how much water is actually used by a stressed crop.
He is finding that canopy size and temperature are good parameters to help estimate water use.
One of Bausch's findings is that many crops are very efficient in using the water they receive, SO getting more crop per drop with deficit irrigation will require better understanding of how crops respond to water stress.
Plant physiologists Dale Shaner and Louise Comas are studying water-stressed plants in detail to see if there are particular irrigation schedules that will help a plant maintain productivity with less water use, and if there are plant characteristics that can be measured to indicate degrees of stress.
designed to sustain productive and economic irrigated agriculture while meeting the water needs of others.
Realizing that research from a given field will not apply to all situations, the WMRU is working closely with the USDA-ARS Agricultural Systems Research Unit in Fort Collins to collect field measurements that will validate and improve crop models, such as the Root Zone Water Quality Model, SO that these models can predict crop yields under water stress for a wide range of conditions.
This is especially important as we face future climate change.
ARS engineer Garrett Banks measures soil water content in wheat with a portable TDR device.
The WMRU is also working closely with a Cooperative Research and Development  partner, the Regenesis Management Group, on the Sustainable Water and Innovative Irrigation Management system.
Regenesis will incorporate the water productivity research results into decision support systems that will help farmers value their water as a commodity.
Water can be used both to produce high value on the farm and for potential income from a city in need of water in times of shortage.
The goal is to keep farmers in control of their water supplies.
A critical part of the effort is to document water savings to the satisfaction of downstream water users, who are always wary of changes upstream that might affect their water supply.
CSU agricultural economist James Prichett is furthering these efforts by surveying farmers to learn how much they feel their water is worth and what types of lease arrangements they might be willing to agree to.
All these efforts are
 With recent declines in irrigated area in California and Texas, Nebraska is now the state with the greatest irrigated area.
Sitting at the north end of the High Plains Aquifer and on the Platte River drainage, Nebraska, the home of many center-pivot manufacturers, is relatively well supplied with water.
However, in the western part of the state, water shortages are critical.
In Nebraska, regional Natural Resources Districts monitor and regulate irrigation water use.
Declining water levels in the High Plains Aquifer have led to restrictions on pumping, but recognizing that these effects are long term, the Natural Resources Districts often restrict the amount a farmer can pump over a multi-year period.
Thus, farmers must decide the value of the water this year for a particular crop mix and precipitation pattern compared to next year-a very complex decision.
Derrel Martin, working at the University of Nebraska, and his colleagues have developed the Water Optimizer to help farmers weigh the many options involved in water management decisions.
Farmers can input information on their water supply, preferred crops, and production costs, and the Optimizer will help them allocate their limited water supply to gain the best overall returns.
Investigating the options is the future
 Although the challenges facing irrigated agriculture in the High Plains and in the rest of the western United States are daunting-farmers must produce more with less-failure is not an option if we are to meet the food and fiber needs of the next 40 years.
Through many researchers from many institutions working together, our understanding of the options is increasing.
Technological breakthroughs, such as new crop varieties that resist water stress, may play a critical role in meeting food needs with limited water resources, but past experience shows that good water and crop management will always be an important part of the solution.
ASABE member Tom Trout, research leader, USDA-ARS Water Management Research Unit, Fort Collins, Colo., USA; thomas.trout@ars.usda.gov.
The project, funded by the Irrigation Innovation Consortium, the Daugherty Water for Food Global Institute, and Valmont Industries, compared various sensor-based irrigation scheduling methods to a common practice treatment.
Each of these irrigation methods were applied at different irrigation levels: 0% , 50% , 100% , and 150%.
Colorado State University xtension
 The Colorado Agricultural Meteorological Network  and Crop ET Reports
 Fact Sheet No.
4.723
 Summaries and Raw Data
 Weather data from CoAgMet can be viewed in several formats.
For those interested in daily values for a specific month and station, 'Monthly Summaries' provide users the option of selecting a year and a month for a specific station, plus setting options for calculating growing degree
 About CoAgMet A brief history of how CoAgMet came to be.
CoAgMet Crop Water Use  Access Page for obtaining crop and turf water use information.
Evapotranspiration Reports ETRs are daily reports for selected stations by region.
Station Description A description of a typical CoAgMet station.
Station Index Metadata on all of the stations on the CoAgMet network.
Monthly Summaries Interactive access to the daily data set for a particular station and selected months.
Daily Summaries  Daily summary files are formatted to display selected parameters for all stations.
Hourly Data Access Interactive access to the hourly data set for a particular station and selected days.
Hourly Data Plots Plots of temperature, humidity and wind for all CoAgMet stations.
Raw Data Access Direct access to the raw data.
Select hourly or daily data from our archives.
Map of CoAgMet Stations A Google Maps based map showing CoAgMet station locations.
Access current data, metadata and images.
Miscellaneous Tools Miscellaneous tools and analyses.
Other Climatic Data The Colorado Climate Center maintains a database of historical climatic data for many weather stations throughout Colorado.
E-mail questions, comments, or concerns about the CoAgMet page to the webmaster
 Figure 1: The CoAgMet home page with links to different information.
days.
Accumulated GDDs from a starting date  can be used to estimate where a crop is in terms of its development.
Different crops require different amounts of GDDs to reach specific developmental stages and maturity.
Those interested in seeing weather data on a specific date for all stations can click on 'Daily Summaries '.
Often times, it is easier to understand data if they are presented in graphs.
The link for 'Hourly Data Plots' allows users to plot temperature, relative humidity, wind speed, wind direction, soil temperature, and solar radiation for a single day or up to an entire year at a selected station.
CoAgMet is a network of automatic weather stations that provides Internet access to weather and crop water use data.
CoAgMet provides weather data in different formats, including daily or monthly summaries, hourly data, and graphs.
Crop water use information from CoAgMet can be used in irrigation scheduling.
Advanced users who require hourly data can click on the 'Hourly Data Access' link.
This link provides hourly data for a selected station on a single date.
Therefore, it will give 24 values for each weather variable.
Users interested in getting hourly or daily weather data that cover extended periods of time can click on 'Raw Data Access'.
This link provides the greatest control in downloading data.
However, the data is given in comma-separated format, which is less user-friendly.
A link to 'Raw Data Documentation' is provided at the bottom of the 'Raw Data Access' page to help users understand the data format.
The link for 'Miscellaneous Tools' provides daily data access linked to a Google map of the stations, daily statistics, and a user interface with more options for obtaining daily data for a specific station.
Clicking on 'Other Climatic Data' takes the user to the homepage of the Colorado Climate Center, which provides links to a wider array of climate information.
Crop Water Use  Access
 CoAgMet provides daily crop water use or evapotranspiration  reports for Colorado locations.
ET reports from CoAgMet can be used to improve irrigation management and conserve limited water resources by fine-tuning irrigation timing and amount.
Because ET is affected by our ever changing weather conditions, it can fluctuate daily and impact the demand for water by crops and landscapes.
For example, mid-season corn water use can be as high as 0.40 inches per day when temperatures are in the mid-nineties, moderate wind, and low humidity, but will drop to half of that on cooler , more humid days.
These changing weather conditions are measured by CoAgMet weather stations.
The weather data is used to calculate and produce ET reports for several common crops.
The CoAgMet website allows users to choose up to eight crops, one or more weather stations, and adjust their planting dates for customizing their reports.
Daily as well as multi-day ET reports are available.
Precipitation from the
 CoAgMet provides daily crop water use or evapotranspiration  reports for Colorado locations.
weather station is also included in the crop ET reports.
This allows users to quickly determine a water balance for an area.
The concept of 'reference crop ET' was developed in the 1970's to represent the potential amount of ET from a standardized unstressed crop, given adequate water and actual weather conditions at a particular location.
The most common reference crops are cool-season grass  and alfalfa  fully covering the ground.
Historically, alfalfa has been used as the reference crop in Colorado.
The ET of other crops can then be estimated by multiplying reference crop ET by a crop coefficient.
At any given point in the growing season, the Kc for a crop is simply the ratio of its ET over reference crop ET.
The Kc can be thought of as the fraction of the reference crop ET that is used by the actual crop.
Values of Kc typically range from 0.2 for young seedlings to 1.0 for crops at peak vegetative stage with canopies fully covering the ground.
CoAgMet users can choose the method used to calculate reference ET.
There are several published equations that calculate ETr from weather data.
Historically, CoAgMet has used the 1982 Kimberly Penman  equation.
However, the American Society of Civil Engineers Standardized PenmanMonteith  equation is also offered as a user option.
This newer equation has broad support in the literature as the standard equation.
However, the 'Crop ET Access' page still defaults to the KP equation, because the crop coefficients used by CoAgMet were originally developed for this equation.
Both of these equations are combination methods, meaning that they consider both the energy supply and the movement of water vapor at the crop surface to calculate ETr.
The ETr values provided are for a tall  reference crop.
The ET values for other crops are calculated automatically by multiplying ETr values with appropriate Kc values obtained from past experiments done in Colorado.
Finally, CoAgMet users will notice that weather stations have been categorized as dryland, partially irrigated or fully irrigated.
These designations describe the predominant land use in the immediate vicinity of the weather station and/or the vegetation growing around the site.
The best conditions for determining ETr include station location over mowed, preferably irrigated, grass and surrounded by irrigated crops.
These conditions often
 are difficult to find and maintain in many remote areas.
Additionally, some CoAgMet stations are purposely located in areas that are predominantly non-irrigated  as these stations were not intended for determining ETr.
ET values from these sites will typically be higher than values from sites in fully irrigated areas.
Weather stations were categorized using site characteristics as well as detailed analyses of historical weather data from each site.
Generating a Crop Water Use Report
 If you clicked on the 'use as end' option, the selected date will be the last day in the report that goes back in time by the specified number of days in the '# to do' column.
For example, selecting June 30, 2009 as the end date and specifying '30' in the '# to do' column will generate a report that covers the period June 1 to June 30, 2009.
On the other hand, clicking on the 'start date' option will give data starting on the selected date and going forward in time by the specified number of days in the '# to do' column.
ET rates are based upon
 weather data that logs from 12:00 midnight to 12:00 midnight.
Therefore, ET rates and other weather data are not available for the current date until the following day.
Next, select the weather station that will be used for the ET report.
In most cases the nearest weather station  is the best choice unless you have specific knowledge that another station is more representative of your area.
If your location for ET rate is between two stations, consider using an average of both.
To select multiple stations, hold down the control key and click on the stations you are interested in and CoAgMet will return data from all selected stations.
Finally, click on the desired crop for ET rates.
Select the planting date for the particular crop of interest.
Be aware that if crop emergence was delayed due to cool weather or other reasons, you may need to adjust the planting date back accordingly.
For alfalfa, change the green-up date with
 each new cutting.
Bookmark your ET output to avoid having to re-enter your preferred crop, station and planting dates.
Then go directly to your bookmark to obtain your customized ET report.
An irrigation manager wants to know the total ET in the past seven  days for Yuma, Colorado.
The current date is June 30, 2009.
The crops of interest are corn planted on April 25, 2009 and dry beans planted on May 31, 2009.
Given below are steps the manager should take to generate the appropriate ET report.
2.
Click on the 'CoAgMet Crop Water Use  Access' link.
3.
Select June 29, 2009 for the date.
Use this as the 'end date' and select '07' for '# to do.
4.
Select 'yum02 Yuma' as the station.
5.
Click 'none' under the "Select crops section to unselect all the crops.
Then click on the 'Corn' and 'Dry beans' boxes.
6.
Select m = 04 and d = 25 as the planting date for corn; and select m = 05 and d = 31 as the planting date for dry beans.
Chapter: 32 The Management and Identification of Saline and Sodic Soils in the Northern Great Plains
 Salt-affected soil is a serious problem in the northern Great Plains.
If high salt concentrations exist, then the problem's type and magnitude must be accurately diagnosed.
The objective of this chapter is to discuss diagnosis and remediation of South Dakota's saline and saline/sodic soils.
Key terms used in this chapter are provided at the end of the chapter.
Clay dispersion can occur when the soil electrical conductivity  is less than 2 dS/m and % sodium on the exchange sites is greater than 4%.
Due to increased rainfall, changing land uses, and that many of South Dakota's soils were developed over marine sediments, the amount of land impacted by high salt concentrations has been increasing.
High salt concentrations have a staggering impact on crop yields.
For example, the NRCS reported that in Beadle, Brown, and Spink counties, high soil salt concentrations have resulted in an annual economic loss of over $26 million.
South Dakota soils affected by saline and sodium  are separated into three groups: saline , saline/sodic , and sodic.
The classification of a salt-affected soil into one of these groups is based on the soil electrical conductivity  and the amount of Na+ on the cation exchange sites.
The soil cation exchange capacity  is the capacity of the soil to retain positively charged cations.
Common cations include Ca2+ Mg2+, NH1 K1+, Fe3+, and Na+1.
The CEC helps the soil retain these nutrients from one year to the next.
Because anions , such as nitrate , chloride  or sulfate  are repelled 3 by the soil's negative charges, anions are more rapidly lost with water percolating through the soil than cations.
Sodic soils have high Na+ concentrations, which can result in soil dispersion, decreased water infiltration, and increased erosion.
Saline/sodic soils have high EC and high Na+ concentrations.
Yields in these soils are reduced by the combined impact of high salt and Na+ concentrations.
In South Dakota, soil clay dispersion  can occur when drainage is placed under soils with an EC value < 2 dS/m and when the percentage of Na on the cation exchange sites is greater than 4.
Figure 32.1 A northern Great Plains dispersed soil.
Diagnosis of Saline Soils
 Climatic records indicate that spring temperatures and rainfall have increased in the northern Great Plains , and these land use changes have resulted in higher water tables and the subsequent transport of subsurface salts to the soil surface.
Soils with salt problems can result from the natural weathering of soil and geologic parent materials, management, or a combination of both.
Throughout South Dakota there are landscapes and geographic locations with naturally occurring high soil salinity levels.
Within a field, salts have the potential to accumulate in some areas and not others.
Generally, poorly drained footslope areas have higher salt contents than well-drained areas.
Problems often occur when the water table rises.
In many South Dakota fields, salt accumulation is not a problem if irrigation water is not applied or if the water table is at least 6 feet below the soil surface.
Figure 32.2 A schematic showing the relationship between water-table depth, increasing rainfall , and salt accumulation.
In the aerial image the salt-affected soils appear white.
To interpret the reported values from a soil testing laboratory, the test results and remediation techniques must be based on a standard analysis method.
Many soil testing laboratories report EC values based on a 1:1 soil-to-water solution ratio, whereas the historical remediation techniques were based on the EC value measured using a saturated paste technique.
Unfortunately, EC values from the two techniques are NOT equivalent, with the 1:1 method having a much lower value than the saturated paste method, thus underestimating the problem.
Therefore, EC values from a 1:1 technique need to be converted to the saturated paste equivalent value, with the 1:1 values multiplied by 2.14, the relationship shown in Figure 32.3.
Figure 32.3 Relationship between EC values of a saturated paste and 1:1  solution.
This South Dakota research data shows the relationship between EC used for remediation  and that reported by the commercial soil testing laboratories.
Figure 32.4 The relationhips between the EC values measured multiple ways and relative yield.
The conversion of EC 1:1 to EC saturate paste was based on Figure 32.3.
Note: The values of dS/m are identical to mmhos/cm.
Max.
EC	% loss above crit.
Max.
EC	% loss above crit.
without loss	value	without loss	value
 Sensitive plants	1:1	paste	Sat.
1:1	Sat.
paste	Moderate Sen.
Plants	1:1	paste	Sat.
1:1	Sat.
paste
 dS/m	dS/m	%loss/	dS/m	%loss/	dS/m	dS/m	%loss/	dS/m	%loss/	dS/m
 Beans	0.47	1	38.5	19	Turnip	0.42	0.9	19.3	9
 Carrot	0.47	1	30.0	14	Radish	0.56	1.2	27.8	13
 Strawberry	0.67	1	70.6	33	Lettuce	0.61	1.3	27.8	13
 Onion	0.56	1.2	34.2	16	Clover	0.70	1.5	25.7	12
 Rice	1.4	3	25.7	12	Foxtail	0.70	1.5	20.5	9.6
 Corn 	0.79	1.7	27.8	13	Orchard grass	0.70	1.5	13.3	6.2
 Timothy	0.93	2	36.4	17	Corn 	0.79	1.7	25.7	12
 Flax	0.79	1.7	25.7	12
 Potato	0.79	1.7	25.7	12
 Alfalfa	0.93	2	15.6	7.3
 Cucumber	1.17	2.5	27.8	13
 Tomato	1.17	2.5	21.2	9.9
 Mod Tol.
Plants	dS/m	dS/m	Oat	1.12	2.4	18.0	7.4
 Wild rye	1.26	2.7	12.8	6	Sorghum	3.18	6.8	34.2	16
 Sudan grass	1.31	2.8	9.2	4.3	Tolerant Plants	dS/m	dS/m
 Crested wheatgrass	1.64	3.5	8.6	4	Tall wheatgrass	3.50	7.5	14.8	6.9
 Fescue, tall	1.82	3.9	11.3	5.3	Barley	3.74	8	10.7	5
 Soybean	2.34	5	42.8	20	Canola or rapeseed	5.14	11	27.8	13
 Birds foot trefoil	2.34	5	31.4	10	Cotton	3.59	7.7	11.1	5.2
 Perennial ryegrass	2.62	5.6	16.3	7.6	Durum wheat	2.76	5.9	8.1	3.8
 Durum wheat	2.66	5.7	11.6	5.4	Forage rye	3.55	7.6	10.4	4.9
 Forage barley	2.80	6	15.2	7.1	Sugar beet	3.27	7	12.6	5.9
 Wheat	2.80	6	15.2	7.1	Crested wheat grass	3.50	7.5	14.6	6.9
 Asparagus	1.92	4.1	4.3	2
 High salt areas can be identified by conducting a visual survey of the area, conducting an apparent electrical conductivity  survey using a Geonics EM 38  or the Veris Soil EC Mapping System manufactured by Veris technologies , tracking changes in yield over multiple years, and collecting and analyzing soil samples for electrical conductivity.
Remediation of Saline Soils
 In saline soils, the high concentrations of soluble cations  and anions  reduce seed germination and plant growth.
One of the first steps in remediating a salt problem is seeding salt-tolerant  plants in the saline and adjacent areas.
For example, alfalfa grown in adjacent areas may help lower the water table, which helps prevent the expansion of the affected soil.
If the saturated paste soil EC1:1 is less than 0.5 dS/m, corn can be seeded.
Table 32.2 Do's and Don'ts when managing saline soils:
 1.
Identify the problem and map its extent.
High salinity is often a symptom of a high water table, and soil layers with low water permeability.
2.
Drainage reduces salinity risks.
On average, the soil EC value will decrease 0.5 dS/m for every 6 inches of water that percolates through the soil.
Drainage details are in Chapter 30.
3.
Prevent expansion of the problem.
Expansion can be slowed by establishing deep-rooted, salt-tolerant  vegetation within the saline area.
If the area is poorly drained, dormant seeding tall wheatgrass into frozen soil can be used to establish a crop in the a.
area.
b.
Alfalfa directly adjacent and above the salt-affected area can intercept water moving into the saline area.
Cover crops seeded in the fall may reduce water flow into the affected area.
Lowering the water table reduces C.
capillary rise and provides the opportunity to leach salts deeper in the profile.
d.
Techniques that reduce surface-soil evaporation, such as no-till and minimum till may be useful.
Things not to do
 1.
Deep tillage, ripping, and spring tillage should be used with caution because tillage can bring salts back to the soil surface.
No-till seeding has been used to overcome this risk.
2.
For sodic or saline/sodic soil , tile drainage can worsen the problem.
Over winter, salts can be transported out of the surface soil with percolating water.
Tillage will bring these salts back to the soil surface, and in many situations dormant seeding is effective because the lowest EC values are observed in the spring following snowmelt.
A partial list of techniques to reduce salt problems is provided in Table 32.2.
Once a high salt area is identified, an interceptor or tile drainage can be used to lower the water table.
See Chapter 30 for details.
Sodium and Saline/Sodic Soils
 Diagnosis of Saline/Sodic soils
 The common Na-containing salts with South Dakota's soils are sodium sulfate.
Managing for Na is important because the sodium cation disperses soil aggregates, slows water infiltration, and increases erosion.
High Na can also result in high soil pH, which can reduce the availability of some nutrients.
If tile drainage is installed the EC can decrease gradually until the tipping point is reached and the soil disperses.
As demonstrated in Figure 32.5, a flocculated soil may have > 4% of the bases extracted being Na if the EC is high.
However, as the EC decreases the risk of soil dispersion increases.
In northern Great Plains dryland agriculture, tile drainage of soils with % Na extracted with ammonium acetate greater than 4 can result in problems.
Diagnosis involves collecting and analyzing soil samples from the problem areas.
The sampling depth depends on the magnitude of the problem.
If the goal is to install tile drainage, the soil sample should be collected from the soil surface for a salt
 Figure 32.5 The influence of drainage on the relative amount Na extracted with ammonium acetate.
Drainage results in a decrease in the soil EC and the concentrations of calcium, magnesium, and sodium.
However, the percentage of Na as a function of all cations increases, which results in soil dispersion.
Table 32.3 Example of soil test laboratory report from a submitted sample.
% Na extracted with
 Sample	Id		pH	salts	sol.
Nitrate	P	Ammonium acetate	cations	Sum	% Bases
 mmhos/	lbs/acre	ppm	K	Ca	Mg	Na	me/100 g	K	Ca	Mg	Na
 cm	ppm	ppm	ppm	ppm
 2275	7.5	0.57	45	22	1037	2273	236	20	16.1	17	70	12	1
 assessment and from the surface 3 feet for a drainage assessment.
Each sample should contain at least 3 pounds of moist soil collected with a soil probe from at least 10 areas within the problem area.
These soil samples should be sent to a laboratory to determine the EC and percent Na extracted by ammonium acetate.
Examples for determining sodium risks are provided in Examples 32.1 and 32.2.
In soil testing reports, the sodium risk is the ratio between amount of Na in the soil and the sum of the cations extracted by the ammonium acetate solution.
[It is important to note that some laboratories refer to the sum of the cations as the cation exchange capacity ].
The percent sodium extracted with ammonium acetate is 100 times the ratio between Na and the sum of the cations.
If the soil has a Na risk, the long-term goal should be to prevent further degradation.
In South Dakota, installing drainage systems in saline/sodic soils can result in serious problems within a few years.
Example 32.1 Sample calculations for determining the percent of Na extracted with ammonium acetate.
A soil sample is sent off for laboratory analysis.
In this analysis, ammonium acetate is used to extract Na, Ca, Mg, and K.
The sample contains 2136 ppm Na+, 2181 ppm Mg2+, 3198 ppm Ca2+, and 200 ppm K1+.
Calculate the % Na extracted by ammonium acetate.
In this calculation 1ppm = 1 mg/kg.
Note: When doing this calculation it is important to know that Na has a valance of +1, Ca has a valance of +2, and Mg has a valance of +2.
In addition, the molecular weight of each cation is needed.
Na = 23 mg/mmol; Mg = 24.3 mg/mmol; Ca = 40 mg/mmol; and K = 39 mg/mmol.
The valances and molecular weights are used to convert mmol to mmolc.
Step 1.
Convert ppm for each cation to mmolc/kg.
For this conversion 1ppm = 1mg/L 2136 mg Na mmol Na cmol 1cmolNa 9.29cmolNa kg 23 mg Na 10 mmol 1cmol 2181 mg Mg mmol Mg cmol Mg kg 24.3 mg Mg 10 mmol 1cmol Mg 3198 mg Ca mmol Ca cmol kg 40 mg Ca 10 mmol 200 mg K mmol K cmol kg 39 mg K
 The sum of cations  is  = 43.8 cmol/kg.
Based on this analysis, the soil contains a high relative amount of Na compared to the total cations in the soil.
Therefore, tile drainage of this soil would NOT be recommended, as tiling may result in soil aggregate dispersion and an associated loss of productivity.
Example 32.2 Estimating % sodium extracted by ammonium acetate.
The sum of bases or cations can be calculated using the following steps.
First, use ammonium acetate to extract the soil cations.
Determine the concentrations of Na+, Ca2+, Mg2+, and K+1 in the soil and the sum of the cations.
In this example, the sum of the cations is 26 cmolc/kg or 26 meq/100 g and Na is 692 ppm.
Note: The sum of cations and the Na value are given in different units.
Therefore, the common unit of cmol_ /kg  must be determined for the Na value to determine the % Na in the soil.
For this calculation 1 ppm = 1 mg/kg.
On the soil testing laboratory reports, Na+ is listed as ammonium acetate extractable and the units are ppm.
For these calculations ppm must be converted to meq/100 g or cmol/kg.
Convert Na in ppm to cmol/kg.
692 mg Na	mmol Na	1	cmol	Na
 kg	23 Na	10 mmol Na = kg soil
 The sum of the bases  is 26 cmol
 3 cmol kg soil % Na 26 cmol 100% = 11.5% kg soil
 This analysis indicates that 11.5% of the ammonium acetate extractable bases are Na This soil has a very high Na concentration.
Caution should be used in this soil's management.
A relatively inexpensive approach to improve the soil structure is to apply low Na-containing manure or apply crop residues to problem areas.
The organic matter in these materials can help stabilize and improve soil structure.
It must be pointed out that not all manures have low Na concentrations.
Manure from animals that have high concentrations of NaCl in their rations to meet animal nutritional requirements may not be desirable for soil applications.
Reseeding to Perennial Plants
 Returning saline and sodic soils to deep-rooted, salt-tolerant perennial plants and grasses appears to reduce salt problems.
These perennial plants can lower the water table and provide the roots needed to stabilize the soil aggregates.
Another Na remediation approach is to replace the sodium on the soil exchange sites with calcium.
In most situations, the least expensive amendments are either gypsum or elemental sulfur.
The oxidation of sulfur reduces soil pH and, if free lime is present, Ca can be released.
If the soil contains high sulfate or gypsum concentrations, then the addition of gypsum may not be effective.
In soils containing high sulfate or gypsum, elemental S may be more effective than gypsum.
However, for elemental S to work, the soil must contain free lime.
To increase the effectiveness of elemental S, the appropriate amount should be mixed into the soil.
Theoretically, 1 ton of gypsum is replaced by 380 lbs of elemental S.
Mitigating Sodium Risks with Tile Drainage
 If % sodium extracted by ammonium acetate is greater than 4 , installing tile drainage can result in soil dispersion and the loss of productivity if the water percolating through the soil is rainwater.
This dispersion is the direct result of a gradual decrease in the soil EC.
Chemical remediation can be used to reduce this risk.
The amount of chemical to apply depends on the
 Example 32.3 Determine how much gypsum is needed.
In this calculation, remember that 1 mmol /100 = 1 cmol /kg.
In this soil, the soil sum of bases  is 20 cmol/kg soil or 20 mmolc/100 grams, and the % Na+ extracted by ammonium acetate was 15%.
The goal is to reduce the surface 6 inches % Na extracted to 5%.
In this calculation assume that the weight of the soil in the surface 6 inches is 1,850,000 lbs.
1.
Calculate the amount of Na that must be exchanged to reduce from 15% to 5%.
Na 15% = 100 X CEC
 in this example CEC is estimated to be 20 mmol /100 grams.
2.
Determine the amount of gypsum to apply.
This calculation assumes that 1 mole of gypsum will replace 2 moles of Na.
Gypsum is used in this calculation because it contains Ca2+ which replaces Na + on the exchange sites.
This assumption is based on Ca having a 2+ valance and Na having a 1+ valance and gypsum having a molecular weight of 172.2 g.
1,850,000 lbs soil 2 mole 1 mole CaSO4 2HO X acre mmol moles Na 172.2 g tons of gypsum 1 mole gypsum 2000 lbs
 0.15 X mmol =
 at 5% Na, the amount of Na on the exchange sites is 1 mmol /100 g 
 To reduce Na from 3 to 1 mmol /100g, then 2 mmol /100g of Na must be replaced with Ca2+.
Based on this calculation 1.59 tons of gypsum are needed if the surface 6 inches/acre weighs 1.85 million pounds.
If the soil weighs 2 million pounds, then 1.72 tons of gypsum are needed [e.g.
X 1.59 tons].
Example 32.4 The soil test reports that the sample contains 2273 ppm Na+, 1037 ppm K1+, 236 ppm Mg2+ and 2273 ppm Ca2+.
Convert these ppm values to meq/100 g soil.
Note: When doing this calculation, it is important to know that K has a valance of 1+, Na has a valance of 1+, Ca has a valance of 2+, and Mg has a valance of 2+.
Note: In these calculations, the answer has the units meg/100 g.
The 100 g in the denominator by dividing by 10 g not 1000 g.
2273 mg Na	mmol	Na
 1037 mg K	mmol	K	1
 236 mg Mg	mmol	Mg	2	Mg
 kg soil	24.3	Mg	1	Mg
 2.
Determine the sum of cations
 =  meq/ = 25.85 meq/100 g soil
 3.
Determine the % Na extracted with ammonium acetate
 Based on this value 38% of the total cations extracted were Na.
incorporation of the selected chemical.
For example, if no-tillage is used in the field, then treating the top 2 inches may be necessary, whereas if the soil is plowed then an 8-inch profile should be treated.
Tables 32.4, 32.5, 32.6, and 32.7 can be used to simplify these calculations.
Mixing Chemical Treatments with Soil
 When applying an amendment, incorporate the amendment with a tillage operation.
Chemical treatments are most effective when they are incorporated into the soil.
If the subsoil contains gypsum, tillage can be used to transport subsurface gypsum to the surface.
The costs of different chemical treatments are provided in Table 32.7.
Before selecting a product, check with a local provider about availability and cost.
In the northern Great Plains saline and sodic soils are serious problems.
The management of salt-affected soils includes diagnosis, prevention, and remediation.
Diagnosis involves collecting a soil sample from the problem area, which must be correctly interpreted.
Many soil testing laboratories use different methods to determine the soil EC and sodium risk.
For example, Midwest Laboratories Inc.
and Ward Laboratories Inc.
report the EC of 1:1 solution to soil ratios, whereas the historical technique was to determine the EC using a saturated paste.
The EC value of a 1:1 is converted to EC of a saturated paste by multiplying the value by 2.14.
Even though many soil testing laboratories report sodium and cation exchange capacity  values, they may not be labeled as such.
For example, in the Ward Laboratories report and Table 32.2, CEC is listed as Sum of Cations, while on the Midwest Laboratories report, CEC is listed as CEC.
AgLab Express, located in Sioux Falls, SD, reports CEC and ESP, while Agvise reports CEC and % base saturation.
A more complete listing of soils laboratories is available in Chapter 21.
In this document, these values are reported as % Na extracted by ammonium acetate.
Prevention and remediation involve planting something at the site.
In sodic soils, a common remediation approach is to add Ca [elemental S; solubilizes CaCO 3 to release Ca; gypsum, and CaSO].
Gypsum additions may not be effective if the soil contains high concentrations of gypsum or SO-S.
Under these conditions, elemental sulfur may be useful.
Table 32.4 The approximate amount of gypsum in tons/acre required to convert the soil surface 6 inches with a specified % Na extracted with ammonium acetate to a soil with a % Na of 5.
The soil's cation exchange capacities are shown on the y-axis.
This calculation assumes that the surface soil weighs 2 million pounds/acre.
However, many soils weigh slightly less than this value.
The weight of soil for 1 acre that is 6 inches deep is approximately 1.7 X 106 if it has a bulk density of 1.25 g/cm.
If the bulk density is 1.45 g/cm, then the weight is approximately 2 million pounds.
To convert from 2 million to 1.7 million pound multiply the gypsum needed by 0.85.
Sum of bases	10	15	20	25	30	35
 10	0.5	1.0	1.5	2.0	2.5	3.0
 15	0.75	1.5	2.25	3.0	3.75	4.5
 20	1	2.0	3	4.0	5.0	6.0
 25	1.25	2.5	3.75	5.0	6.25	7.5
 30	1.5	3.0	4.5	6.0	7.5	9.0
 35	1.75	3.5	5.25	7.0	8.75	10.5
 Table 32.5 The relationship between tons of gypsum and lbs of elemental sulfur required for the surface 6 inches as influenced by desired change in Na This calculation assumes that the surface soil weighs 2 million pounds/acre.
If less than the 6 inches is treated, use the appropriate ratio.
For example, if only 2 inches are treated divide the tons of gypsum by 3.
Desired change in	Tons gypsum	Lbs of elemental S
 %Na meq/100g	6 inches	6 inches
 Table 32.6 The relationship between different chemical treatments and amount of gypsum needed.
1 ton of gypsum
 Gypsum	CaSO4.2H2O	1.0
 Elemental S	S	0.19
 Sulfuric acid	H2SO4	0.57
 Calcium Chloride	CaCl, 2H2O	0.86
 Table 32.7 2015 estimated costs for Na-affected soil remediation with chemical additives:
 Cost of the chemical additives Elemental S at $720/ton Calcium chloride  at $740/ton Gypsum  at $240/ton
 To reclaim a soil needing 1 ton equivalent gypsum Gypsum: 1 ton X $240/ton = $240 CaCl,: 0.86 ton X $740/ton = $636 Elemental S: 0.19 ton X $720/ton = $137
 Table 32.8 Key terms used in this chapter.
Key terms	Definition	Units
 CEC	Cation exchange capacity, number of exchangeable cations that the soil is	meg/100 g = cmol_/kg
 EC	Electrical conductivity, used to measure salts.
dS/m = mmol/cm
 Sum of bases	Value reported on soil test results CEC, may be identical to sum of cations.
meq/100 g = cmol/kg
 Sum of cations	Value reported on soil test results~ CEC, may be identical to sum of bases.
meq/100 g = cmol /kg
 mmhos/cm	units used to measure salts.
identical to dS/m
 dS/m	units used to measure salts.
identical to mmhos/cm
 ESP	Exchangeable sodium percent.
% Na/CEC
 SAR	Sodium adsorption ratio.
=Na1+ 5 x0.5
 Saline soil	Soil containing high salt concentration, based on EC.
Historically EC 4 dS/m
 Sodic soil	Soil containing high sodium concentrations,
 Based %Na/CEC.
Track when ESP > 4
 ppm	The number of parts per million
 meq/100 g	The millequivalents per 100 grams of soil	meq/100g cmol_/kg
 cmol/kg	The centamole of charge of an ion per kg of soil
Garlic in clay loam soil thrives on little irrigation
 Blaine R.
Hanson Don May Ronald Voss Marita Cantwell Robert Rice
 We conducted 4 years of irrigation experiments in garlic on the West Side of the San Joaquin Valley to determine appropriate irrigation frequency and cutoff dates as well as the effect of irrigation on yields for crops grown in sandy and clay loam soil.
In sandy soil with the moisture content at field capacity prior to the rapid growth stage, yield was strongly dependent on applied water, and weekly irrigation was needed for maximum yield.
In clay loam, yield did not depend on applied water because the garlic plants were able to extract sufficient soil moisture to offset deficit irrigation.
Irrigation cutoff in both soils should occur by mid-May.
C alifornia supplies about 80% of the U.S.
commercial garlic used for fresh-market, seed and dehydrated products.
Within California, Fresno County in the San Joaquin Valley produces about 82% of the state's garlic crop, while the rest is grown primarily in Kern  and Monterey  counties.
Few studies have been published on water use and water management of garlic.
One literature review of garlic concluded that  garlic has a rather sparse and shallow root system with roots limited to the top 2 feet of the soil;  best yields occur when the soil moisture content is maintained near field capacity; and  irrigation should cease 3 weeks before harvest to prevent rotting, discoloration of the
 bulb skins and exposure of outer cloves.
Furrow irrigation is the most common in California garlic production, although sprinkler irrigation is sometimes used.
Irrigation practices by California garlic producers vary considerably, reflecting a lack of information regarding garlic's response to timing and the necessary amounts of irrigation.
Our study investigated the effect of different approaches to irrigation on garlic in the San Joaquin Valley.
A look at water
 We conducted 4 years of experiments at the UC Westside Research and Extension Center located in western Fresno County, with the California Early garlic variety, which is used for processing rather than sold fresh.
All experimental plots were planted in mid-October and harvested in July.
We used sprinkler irrigation to establish the stands.
Irrigation timing, 1997.
In 1997, we investigated irrigation timing on garlic yield using a completely randomized-block split-plot design.
The experimental design consisted of four furrow irrigation treatments on silt loam replicated six times as the main plots.
Each 40-foot main plot contained four nitrogen fertilizer subplots, each with four 40-inch beds.
Nitrogen applications were 100, 200, 300 and 400 pounds per acre.
The irrigation treatments, which began in early March, were as follows: once a week with the last irrigation on May 9 ; once a week with the last irrigation on May 16 ; once every 1.5 weeks with the last irrigation on May 9 ; and once every 2 weeks with the last irrigation on May 16.
For each plot, applied water and yield were measured.
We measured soil moisture in three replications of each irrigation/ fertilizer treatment using a neutron moisture meter calibrated for the soil type.
(This device uses a probe con-
 California supplies about 80% of the U.S.
commercial garlic market, but little research has been conducted on appropriate water use and irrigation management for this important crop.
taining a radioactive source that is lowered into the soil using an access tube.
The radiation emitted by the source is sensitive to soil moisture.) Measurements were made at 0.5-footdepth intervals between 0.5 foot and 6 feet.
Irrigation cutoff dates, 1998.
The 1998 experiment initially involved different water applications, using a randomized-block experimental design with six replicates on clay loam soil.
But because of spring rainfall, irrigation did not occur until late April.
As a result, the experiment was changed to investigate different irrigation cutoff times with subplots of nitrogen applications of 100, 175, 250, 325 and 400 pounds per acre.
with sprinklers  spaced every 12 feet.
Areas close to the line received more water than those farther away.
We measured yield and amount of water applied, with distance from the sprinkler line.
The main treatments were irrigation cutoff dates of May 12, May 19, May 25 and June 1.
Each subplot contained three beds with 40-inch spacing.
The main plot length was 45 feet.
Two beds were harvested for crop yield and quality.
software, in order to describe the rate of crop growth.
Canopy coverage is defined as the percentage of soil area shaded by the canopy at midday.
The same fertilizer applications as in 1998 were applied to subplots  installed in a randomizedblock design along both sides of the sprinkler line.
We statistically analyzed the fertilizer effects using the method proposed by Hanks, Sisson et al..
Soil texture at this site was clay loam between the soil surface and a depth of 5 feet with loam below.
Three transects of catch cans , were installed in 12 beds on each side of the sprinkler line to measure applied water.
These beds were harvested for yield.
The sprinklers ran during the early morning hours when wind speed was minimal.
Sprinkler line source, 1999.
In the 1999 experiment, we used a sprinkler line source to determine garlic's response to applied water.
This system uses a single line with sprinklers spaced close together for good water distribution.
The sprinkler line was 295 feet long
 Two transects, each with six neutron-moisture-meter access tubes, were installed in every other bed on each side of the sprinkler line.
Moisture contents were measured down to 3.5 feet at 0.5-foot-deep intervals, which according to 1997 results was deeper than any root growth.
Canopy coverage was determined at each access tube location using a Dycam infrared digital camera and its
 TABLE 1.
Results of 1997 garlic irrigation treatments*
 Sprinkler line source, 2000.
The sprinkler-line-source experiment was repeated in 2000 on a coarse-texture soil.
Soil texture was loam for the top 1 foot with sandy loam below.
This source experiment was divided into four blocks, each containing three nitrogen fertilizer treatments.
The plot was 23 feet long.
In addition to the yield data, soluble solids  were measured for selected plots.
The data collected for 2000 were the same as in 1999.
Irrigation and garlic crops
 Irrigation	Cutoff	Applied water	Yield	Soluble
 Treatment	interval	date			solids 
 T1	1 week	May 9	14.0	9.5 b
 T2	1 week	May 16	17.2	10.2 a	42.0 a
 T3	1.5 weeks	May 9	11.8	8.6 C	41.5 a
 T4	2 weeks	May 16	14.3	8.6
 1997 results.
In 1997, T2 gave the highest yield, which was statistically different from yields of the other treatments.
The yields of T3 and T4, significantly different from yields of T1 and T2, were the lowest.
Less water was applied for T1 compared with T2 due to the earlier cutoff date, which affected yield.
Yield differences due to nitrogen treatments were not statistically significant in 1998, 1999 and 2000.
In 1997, the yields of the highest nitrogen treatments were statistically significant from those of the two smaller treatments.
However, these results may not be meaningful in light of results from the later 3 years, when no interactions occurred between nitrogen and irrigation.
Yields were averaged across all fertilizer treatments.
Values with the same letter are statistically similar at a level of significance of 0.05.
Changes in soil moisture content between irrigation applications in 1997 occurred down to 2.5 feet, with little or no change below 2.5 feet (data not
 Infrared photos show canopy coverage on garlic plants 5 feet, left, and 38 feet, right, from a sprinkler line, demonstrating the effect of decreasing applied water.
shown), suggesting little or no root activity below that depth.
A decline in moisture content occurred for depths less than 2.5 feet during the measurement period.
1998 results.
The 1998 results showed decreasing total yield with later cutoff date: The differences between the May 12 and May 19 yields and the May 25 and June 4 yields were statistically significant.
No irrigation treatment effects on the percent of soluble solids were found.
Lower yields occurred in 1998 compared with 1997 because of late rainfall and garlic rust, a fungal disease.
In 1998, rainfall between early March and early June was nearly 4.4 inches.
applied water.
The linear regression was not significant at a level of significance of 5%.
The coefficient of determination was 0.014, indicating that little of the yield variability is explained by the variability in applied water.
1999 results.
In 1999, yields and applied water were averaged across all nitrogen plots for each measurement distance from the sprinkler line.
Garlic yield showed little or no response to
 Applied water decreased with distance from the sprinkler line on both sides in a fairly linear manner.
Average water amounts ranged from 12.8 inches to 13.2 inches next to the sprinkler line, and from 3.2 inches to 3.4 inches at the farthest distance.
Unit bulb weight increased linearly with more applied water.
The minimum average unit weight was 0.07 pound per bulb and the maximum was 0.12 pound per bulb.
The coefficient of determination was 0.51, and the linear regression was significant.
The canopy coverage increased with time at all distances.
In the 160 days after planting, little dif-
 Fig.
1.
Yield versus applied water for 1999 and 2000 sprinkler-line-source experiments.
Equations describe the relationship between garlic yield and applied water.
ference in canopy coverage was found at each distance.
After 160 days, the canopy coverage continued to increase, but only slightly at 38.1 feet.
Average maximum canopy coverage, which occurred 200 days after planting, ranged from 73% to 78%, but was only 57% at 38.1 feet from the sprinkler line.
Changes in soil moisture were determined between early March, when moisture content was at field capacity, and early June.
Maximum soil moisture content occurred in early March due to rainfall, while complete senescence occurred by early June.
At 5 feet from the sprinkler line, a slight trend of decreasing soil moisture content OCcurred over time, for all depths except at 3.5 feet.
Little change in soil moisture occurred at that depth.
At 38 feet, soil moisture content decreased considerably over time at all depths.
A response to irrigation occurred only at a 0.5-foot depth.
The decrease in soil moisture content at 3.5 feet, from 50% to 35%, suggests that soil moisture extraction was occurring at greater depths.
At this distance, the average change in soil moisture content during the measurement period was 2.3 inches per foot.
2000 results.
In 2000, garlic yield decreased with less applied water.
The regression and coefficients of the linear regression equation were highly significant at a level of significance of 5%.
The coefficient of determination was 0.91, indicating that almost all yield variability is explained by the variability in applied water.
Bulb weight increased linearly with increasing applied water, with a maximum average weight of 0.11 pound per bulb and a minimum of 0.06 pound per bulb.
The coefficient of determination was 0.75; linear regression coefficients were statistically significant.
No significant trend was found between soluble solids and yield, or between soluble solids and nitrogen
 application.
The average soluble solids content of 46 samples analyzed by a commercial processor's laboratory was 44.1%, with a standard deviation of 1.2%.
In addition, no significant trends were found between dry weight and applied water, or between dry weight and nitrogen application.
Up to 16 feet from the sprinkler line, changes in applied water with distance were small, ranging from between 10.8 inches and 12.5 inches.
Beyond about 16 feet, average applied water decreased fairly linearly with distance from the sprinkler line; the average water amounts of 1.2 inches and 1.4 inches were at the farthest distance.
Little difference in canopy coverage occurred with distance from the sprinkler line, up to 137 days after planting.
Thereafter, at distances of 18 feet or less, few differences between distances occurred over time, with maximum values ranging from 72% to 76%.
Beyond 18 feet, maximum canopy coverage values were less and occurred earlier.
At the farthest distance, a maximum value of 57% occurred 171 days after planting.
Soil moisture content decreased over time at all distances  and at all depths.
The trend was less for depths greater than 3.5 feet.
Little or no response due to irrigation occurred at depths greater than 2.5 feet.
The average change in soil moisture content at the farthest distance was about 0.9 inch per foot.
Crop water use.
The crop wateruse values in these experiments do not include effective rainfall.
Cumulative rainfall after early March was 0.6 inch in 1997 and 2000 and 0.9 inch in 1999.
However, much uncertainty exists in estimating effective rainfall, which depends on factors such as amount, soil moisture depletion at time of rainfall, frequency of rainfall and absence or
 Fig.
2.
Distribution of seasonal applied water for 1999 and 2000 sprinkler-line-source experiments.
Fig.
3.
Canopy coverage versus days after planting for  1999 and  2000 sprinklerline-source experiments.
Fig.
4.
Total water, applied water and change in soil moisture content for  1999 and  2000 sprinkler-line-source experiments.
presence of a crop.
Effective rainfall was assumed to be negligible in these analyses because of the small amounts and the uncertainty.
The lack of a yield response to applied water at the clay loam site  indicates that the garlic was able to substitute soil moisture for applied water where there was deficit irrigation.
Although applied water decreased with distance, total water decreased only slightly for distances less than about 26 feet.
However, the change in soil moisture increased with distance.
These data suggest that the garlic extracted moisture from depths greater than 4 feet.
Beyond 26 feet, the total amount of water decreased considerably with distance.
Except for the farthest distance, this decrease probably reflects the lack of soil moisture measurements below 3.5 feet.
At the farthest distance, total water use probably was less because of smaller canopy size.
Maximum total water use during the measurement period was about 17.7 inches.
The canopy coverage behavior indicates similar crop water use with distance, except at 38.1 feet, 160 days after planting.
Canopy size determines the amount of radiation energy intercepted by the plant, and, in turn, the crop water use.
After 160 days, crop water use at 38.1 feet would be less compared with the other distances because of the smaller canopy size.
Nevertheless, this potential reduction in water use had no effect on garlic yield.
Total water use in 2000 decreased with distance.
The change in soil moisture content also decreased with distance.
Soil moisture was insufficient in the sandy soil to offset the decreasing applied water with distance, and thus both canopy coverage and crop yield decreased with distance.
As stated earlier, the average change in soil moisture content at the farthest distance was about 2.3 inches per foot for the clay loam and about 0.9 inch per foot for the sandy loam.
Maximum total water use in 2000 was about 17 inches.
The yield responses to applied water suggest that different irrigation water management strategies should be employed based on soil type.
For both line-source experiments , the soil moisture content was at field capacity at the start of the rapid growth stage.
Sprinkler irrigation  and rainfall should replenish the soil moisture by late February.
Irrigation should start in March.
For clay loam soil, the yield response to applied water indicates that irrigation amounts, and possibly timing, are not critical, assuming a full soil profile at the end of February.
For this type of soil, yield will not be reduced when irrigation amounts are less than the potential crop water use.
This approach may improve irrigation efficiency, stretch limited water supplies during a drought and reduce subsurface drainage.
Sandy loam soil requires weekly irrigation in amounts sufficient to replenish soil moisture between irrigations and prevent yield loss.
The last irrigation should occur by midMay for California Early variety.
The amount used by the crop starting in early March should be about 17 inches to 18 inches plus that needed for irrigation system inefficiencies.
Based on the 2000 results, reduced water applications should not adversely affect the soluble solids or dry weight of garlic crops.
B.R.
Hanson is Extension Irrigation and Drainage Specialist, Department of Land, Air and Water Resources, UC Davis; D.
May is Farm Advisor , UC Cooperative Extension, Fresno; R.
Voss is Extension Vegetable Crops Specialist, and M.
Cantwell is Extension Postharvest Specialist, Department of Vegetable Crops, UC Davis; and R.
Rice is Agronomist , Rogers Foods, Modesto.
COMPARISON OF SPRAY, LEPA, AND SDI FOR COTTON AND GRAIN SORGHUM IN THE TEXAS PANHANDLE 1
 Paul D.
Colaizzi, Steven R.
Evett, and Terry A.
Howell 2 USDA-Agricultural Research Service P.O.
Drawer 10 Bushland, Texas 79012-0010
 Crop responses to MESA , LESA , LEPA, , and SDI  were compared for full and deficit irrigation rates in the Texas Panhandle.
Crops included three seasons of grain sorghum and one season of cotton; crop responses consisted of economic yield, seasonal water use, and water use efficiency.
Irrigation rates were lo, l25, 150, l75, and 100.
Yield and WUE was greatest for SDI and least for spray at the l25 and 50 rates, and greatest for spray at the 100 rate.
Yield and WUE trends were not consistent at the l75 rate.
Seasonal water use was not significantly different in most cases between irrigation methods within a given irrigation rate.
For cotton, the irrigation method did not influence boll maturity rates, but SDI resulted in higher fiber quality at the l25, 150, and 100 rates.
The Southern High Plains region, which includes the Texas Panhandle, is a major producer of corn, grain sorghum, and cotton.
The area centered around Lubbock is one of the largest cotton producing areas in the country, and the area from Amarillo northward has traditionally produced corn, with some of the highest yields in the nation possible with irrigation.
Grain sorghum is often rotated with cotton; sorghum does not require as many heat units as cotton or as much water as corn.
Greater cotton yields have been reported when rotated with grain sorghum, although gross returns were greater for continuous cotton.
Producers in corn producing areas are considering cotton as an alternative crop because cotton
 has a similar revenue potential as corn for about one-half the water requirement, and there has been a net increase in recent years of cotton harvested in the Northern Texas Panhandle, Northern Oklahoma, and Southwestern Kansas.
High crop yields are possible with irrigation, with increases greater than 150% over dryland to be expected.
Nearly all irrigation in the Great Plains is dependent on the Ogallala aquifer, a finite water resource that is declining because withdrawals have exceeded natural recharge.
The rate of decline has been reduced in recent years because irrigated land area has been reduced , and also from conversion from gravity to more efficient center pivot sprinkler systems.
The earliest sprinkler configurations were high-pressure impact, but these have been replaced by low-pressure spray and LEPA   since the 1980s.
Subsurface drip irrigation  also started being adopted by cotton producers in the Trans Pecos and South Plains regions of Texas in the mid 1980s.
Numerous studies have been conduced to document and compare the performance of various sprinkler application packages for a variety of crops and tillage configurations.
These usually consisted of spray and LEPA.
Relatively few studies also included SDI; most comparisons involving SDI were made with gravity  irrigation systems.
A few studies did compare relative performance of spray, LEPA, and SDI for grain sorghum  and cotton , and reported that SDI outperformed other irrigation methods in terms of crop yield and water use efficiency at deficit irrigation rates.
Nonetheless, Segarra et al.
analyzed four years of cotton data at Halfway, Texas and concluded that SDI may not always provide economic returns as high as those from LEPA.
But, this largely depended on system life, installation costs, pumping lift requirements, and hail damage that commonly occurs in West Texas.
Some cotton producers perceive that SDI also enhances seedling emergence and plant maturity due to reduced evaporative cooling compared to LEPA or spray, which is a critical consideration in a thermally limited environment and is seldom considered in economic analyses.
There is, however, limited data in direct support of this view.
Soil water depletion in the root zone appears most responsible for inducing cotton earliness, regardless of the type of irrigation system used.
The purpose of this paper is to summarize recent research findings where crop responses to spray, LEPA, and SDI were compared directly for grain sorghum  and cotton.
The research was
 conducted in the Texas Panhandle, where grain sorghum can be produced reliably, but the climate is marginal for cotton production.
The experiment was conducted at the USDA Conservation and Production Research Laboratory near Bushland, Texas.
Crops included grain sorghum in 2000, 2001, and 2002 and cotton in 2003 and 2004.
The 2004 data have not yet been analyzed so only the results of the 2003 cotton season will be reported.
We plan to continue this experiment for several more seasons of cotton.
The climate is semi-arid with a high evaporative demand of about 2,600 mm per year  and low precipitation averaging 470 mm per year.
Most of the evaporative demand and precipitation occur during the growing season  and average 1,550 mm and 320 mm, respectively.
The climate is also characterized by strong regional advection from the South and Southwest, where average daily wind runs at 2 m height can exceed 460 km especially during the early part of the growing season.
The soil is a Pullman clay loam , with slow permeability due to a dense B21t layer that is 0.15 to 0.40 m below the surface and a calcic horizon that begins about 1.2 to 1.5 m below the surface.
Agronomic practices were similar to those practiced for high yield of grain sorghum and cotton in the Texas Panhandle.
Grain sorghum  Moench, CV.
Pioneer 3 84G62) was planted in the 2000, 2001, and 2002 growing seasons.
In 2001, two plantings  of this variety failed to emerge, so a shorter season variety  was planted on 22 June and emerged by 2 July.
It is thought that the first two plantings in 2001 failed to emerge because of excessive herbicide residual from the previous year.
So in 2002, a different herbicide that was successful in earlier studies  was used.
Cotton  was planted on 21 May 2003, and disked and replanted on 10 June 2003  at 17 plants m-2 All crops were planted in east-west oriented raised beds spaced 0.76 m.
Furrow dikes were installed after crop establishment to control runoff.
The experimental design consisted of four irrigation methods, including MESA , LESA , LEPA , and SDI , and five irrigation rates.
The 100 rate was sufficient to prevent yield-limiting soil water deficits from developing, based on crop
 3 The mention of trade or manufacturer names is made for information only and does not imply an endorsement, recommendation, or exclusion by USDA-Agricultural Research Service.
evapotranspiration  estimates from the North Plains ET Network.
The different irrigation rates were used to estimate production functions, and to simulate the range of irrigation capacities typically found in the region.
The lo rate received irrigation for emergence only and to settle and firm the furrow dikes and represents dryland production.
The MESA, LESA, and LEPA irrigations were applied with a hose-fed Valmont  Model 6000 lateral move irrigation system.
Drop hoses were located over every other furrow at 1.52 m spacing.
Technical details of applicators are given in table 2.
The SDI consisted of Netafim  Typhoon dripline that was shank injected in 1999 under alternate furrows at 0.3-m depth below the surface.
Irrigation treatment rates were controlled by varying the speed of the lateral-move system for the spray and LEPA methods, and by different emitter flow and spacing for the SDI method.
All treatments were irrigated uniformly with MESA at the 100 rate until furrow dikes were installed to ensure crop establishment.
Soil water was measured gravimetrically near the center of each plot prior to planting and just after harvest in the 1.8-m profile in 0.3-m increments, oven dried, and converted to volumetric contents using known soil bulk densities by profile layer.
During the season, soil water was measured volumetrically near the center of each plot on a weekly basis by neutron attenuation in the 2.4-m profile in 0.2-m increments according to procedures described in Evett and Steiner  and Evett et al..
The gravimetric samples were used to compute seasonal water use , and the neutron measurements were to verify that irrigation was sufficient so that no water deficits developed in the 100 treatment.
In 2000, 2001, and 2002, grain yields were measured by harvesting the full length of each plot  using a Hege  combine with a 1.52 m wide  header.
Each plot sample was weighed and three subsamples were dried to determine moisture content.
Grain yields reported here were converted to 14% moisture content by weight.
In 2003, hand samples of bolls were collected from each plot on 19 Nov from a 10 m area that was sequestered from other activity during the season.
Samples were weighed, ginned, and analyzed for micronaire, strength, color grade, and uniformity at the International Textile Center, Lubbock, Texas.
Grain or lint yield, seasonal water use, and water use efficiency  were tested for differences for each irrigation method using the SAS mixed model.
Differences of fixed effects were tested using least square means  within each irrigation rate.
The WUE is defined as the ratio of economic yield  to seasonal water use : WUE = LY WU-1.
Further details of experimental design, procedures, and equipment can be found in Colaizzi et al.
for grain sorghum and Colaizzi et al.
for cotton.
Rainfall was much less than the approximately 350-mm average during the 2000, 2001, and 2003 growing seasons, but slightly less than average during the 2002 growing season.
A large portion of the 2002 rainfall did not occur until the grain sorghum was in its reproductive growth stages , after most of the irrigations were complete, and continued into the winter.
This resulted in the 2002 irrigation totals being the same as those in 2000, despite much less rainfall in 2000.
The 2001 irrigation totals were less than 2000 or 2002 because a shorter season grain sorghum variety was used.
Although cotton and grain sorghum have similar water requirements, the 2003 irrigation totals  were much less than other years  because more water was stored in the soil profile beginning in the 2003 season from the greater rainfall in 2002, and possibly because the shortened cotton season  required less water.
The cotton crop reached full maturity with only 1076 C-days.
This was considerably less than the 1450 C-days thought to be required for full maturity cotton in the Southern High Plains , but only slightly less than that reported by Howell et al.
for the 2000 and 2001 cotton seasons at our location, and was at the minimal range of growing degree days reported by Wanjura et al.
for 12 years of data at Lubbock, TX.
No differences in maturity rates  were noted for any irrigation method.
Differences in maturity rates appeared to vary primarily with the irrigation rate.
Dryland  had the greatest soil water depletion and matured earliest, and maturity proceeded through each subsequent rate, with 100 maturing last.
This was in agreement with Guinn et al.
, Mateos et al.
, and Orgaz et al..
Yields had greater variability by irrigation rate than by irrigation method, and increased with irrigation rate in all years except 2002.
In some cases the increase in grain sorghum yield from lo  to 25 was nearly ten times for both relatively dry  and wet  years.
Yield of both grain sorghum  and cotton  tended to be greatest under SDI at low irrigation rates, but greatest under spray at high irrigation rates.
Yield of grain sorghum under SDI was significantly greater than MESA, LESA, or LEPA at the l25 irrigation rate, and either numerically or significantly  greater than the other irrigation methods at the 150 rate in all three years.
At the 25 and 50 rates, yield with LEPA was usually greater than spray but less than SDI.
Cotton lint yield showed a similar trend at the 25 and 50 rates.
At the 100 rate, yields of both grain sorghum and cotton were either significantly or numerically greatest under spray.
At the 75 rate, this was also true for grain sorghum ; however, lint yield of cotton under LEPA was numerically greater than SDI, and SDI was numerically greater than spray.
We speculate that under low irrigation rates , more water is partitioned to transpiration and less is lost to evaporation under SDI and to a lesser extent LEPA compared to spray.
With larger irrigation rates , the yield depression observed for SDI and sometimes LEPA may have been linked to poor aeration or the leaching of nutrients below the root zone.
We did observe increases in volumetric soil water from about 1.8 m to 2.4 m; we conjecture that this indicates deep percolation.
Also, the enhanced yields under spray may have been due to enhanced plant respiration while reducing transpiration during and after an irrigation event.
In 2002, rainfall during the reproductive stages masked differences in grain sorghum yield among the 150, l75, and 100 rates ; the greatest grain yield of all three years occurred under l75 MESA at 12.2 Mg ha-1.
Grain yield for LESA in 2002 at the l25, 50, and l75 rates was less than the other methods.
We are uncertain why this occurred as we observed no malfunction in irrigation or chemical application equipment.
We did, however, observe a rapid and unexplained decrease in available soil water early in the season, which may have resulted in less water being available during reproductive stages later in the season.
This was not observed again in 2003 for cotton lint yield.
Seasonal water use also had greater variability by irrigation rate than by irrigation method.
In most cases, there were no significant differences between irrigation methods within an irrigation rate, with the following exceptions.
In 2000 at the 75 and 100 rates, and in 2001 at the l75 rate, water use under SDI was significantly less than under spray.
In 2002, water use under SDI was significantly more than under MESA and LEPA at the l25 rate, and LESA and LEPA at the 100 rate.
In 2003, SDI used significantly more water than MESA at the l25 rate, and LESA at the 50 rate.
The greater seasonal water use under SDI was often linked to greater grain or lint yield.
Since irrigation amounts at a given rate were the same for each irrigation method, differences in seasonal water use resulted in different amounts of soil water depletion.
Water use efficiency  generally had greater variability at smaller irrigation rates than at larger rates.
Overall trends paralleled those of crop yield, where SDI yield was greatest at small irrigation rates and spray yield was greatest at large irrigation rates.
At the l25 rate, yield under SDI was significantly greater than that under spray and LEPA for grain sorghum and spray for cotton.
At the 50 rate, yield under SDI was significantly greater than spray in 2000 and 2003, and MESA only in 2001.
At the l75 rate, yield trends were not consistent, but at the 100 rate, yield under MESA was numerically greater than under all other methods in all years.
Note that irrigation had a similar effect on WUE as it did on crop yield, where WUE was increased two to eight times from the lo  to the 25 rate.
Finally, cotton premium as determined by fiber quality parameters  were significantly greater under SDI and LEPA at the 25 and 50 rates, and numerically greater under SDI at the 100 rate.
Further
 details on fiber quality and resulting premiums are given in Colaizzi et al..
Yield and WUE at the 25 and 50 irrigation rates under SDI were greater than for the other irrigation methods, and yield under LEPA was usually greater than that under spray irrigation but less than that under SDI.
These trends were reversed at the 100 rate, where yield and WUE under spray irrigation were greater than that under LEPA or SDI.
Yield and WUE trends at the l75 rate were less consistent.
Seasonal water use had greater variability by irrigation rate than by irrigation method; in most cases, there were no significant differences between irrigation methods within an irrigation rate.
We speculate that under low irrigation capacities, SDI and to a lesser extent LEPA resulted in more water being partitioned to transpiration and less to evaporation.
Under greater irrigation rates, SDI may have resulted in poorer soil aeration and greater nutrient leaching, while the evaporative cooling effect of spray may have enhanced plant respiration and reduced transpiration.
No differences in cotton maturity were observed between irrigation methods; however, fiber quality was slightly enhanced under SDI.
The lack of differences in cotton maturity may have been related to applying spray irrigation  to all plots to ensure uniform establishment.
This experiment has therefore been redesigned beginning with the 2005 season to make better use of SDI to germinate the crop, which may avoid early-season evaporative cooling associated with using MESA in SDI plots.
We thank Don McRoberts, Brice Ruthardt, and Keith Brock, biological technicians, and Nathan Clements, Bryan Clements, and Justin Molitor, student workers for their work in farm operations, data logger programming, data collection, and data processing.
Resources: Challenges and Opportunities, Conference Proceedings, Texas Tech Water Resources Center, Lubbock, TX.
Table 1: Agronomic and irrigation data for three grain sorghum seasons and one cotton season.
Variable	2000	2001	2002	2003
 Crop	Grain sorghum	Grain sorghum	Grain sorghum	Upland cotton
 Fertilizer applied	kg ha -1 preplant N	179 kg ha -1 preplant N	160 kg ha -1 preplant N	31 kg ha -1 preplant N
 76 kg ha -1 preplant P	57 kg ha) -1 preplant P	107 kg ha) -1 preplant P
 45 kg ha irr N  [a]	18 kg ha-Superscript irr N  [a]	48 kg ha -1 irr N  [a]
 Herbicide applied	4.7 L ha -1 Bicep	4.7 L ha Bicep	1.6 kg ha 1 Atrizine	2.3 L ha) Treflan
 Insecticide applied	0.58 L ha -1 Lorsban	none	none	none
 Gravimetric soil	19-May	21-May	3-Jun	20-May
 water samples	11-Oct	30-Oct	18-Nov	24-Nov
 Plant variety	Pioneer 84G62	Pioneer 8966	Pioneer 84G62	Paymaster 2280 BG, RR
 Plant density	30 plants m-2	23 plants m-2	22 plants mi -2	17 plants mi -2
 Planting date	26-May	22-Jun 	31-May	10-Jun	[c]
 Harvest date	21-Sep	29-Oct	14-Nov	21-Nov
 Last irrigation	28-Aug	11-Sep	8-Sep	20-Aug
 lo total irrigation	62 mm	112 mm	62 mm	25 mm
 25 total irrigation	169 mm	194 mm	169 mm	71 mm
 150 total irrigation	275 mm	275 mm	275 mm	118 mm
 75 total irrigation	381 mm	356 mm	381 mm	164 mm
 100 total irrigation	488 mm	438 mm	488 mm	210 mm
 In-season	139 mm	124 mm	317 mm	167 mm
 [a] Liquid urea 32-0-0 injected into irrigation water; deficit irrigation treatments received proportionately less.
[b] Two previous plantings on 22 May 2001 and 5 Jun 2001 failed to emerge.
[c] The first planting on 21 May 2003 sustained severe hail damage on 3 June 2003.
Table 2.
Sprinkler irrigation application device information.
[a]
 Applicator	Model b	Options	furrow surface 
 LEPA	Super Spray head	Double ended	0
 LESA	Quad IV	Flat, medium grooved	0.3
 MESA	Low Drift Nozzle 	Single, convex, medium	1.5
 spray head	grooved spray pad
 [a] All sprinkler components manufactured by Senninger  except where noted.
[b] All devices equipped with 69 kPa pressure regulators and #17  plastic spray nozzles, giving a flow rate of 0.412 L s 1.
[c] A.E.
Quest and Sons, Lubbock, TX.
Table 3.
Subsurface drip irrigation  dripline information.
[a]
 Irrigation Rate	Emitter Flow Rate 	(mm hr 1
 lo	Smooth tubing no emitters
 25	0.68	0.91	0.49
 50	0.87	0.61	0.97
 75	0.87	0.41	1.45
 100	0.87	0.3	1.93
 [a] All SDI dripline manufactured by Netafim.
a) 2000, grain sorghum
 b) 2001, grain sorghum
 c) 2002, grain sorghum Figure 1: Economic yield for grain sorghum and cotton.
Irrigation methods followed by the same letter are not significantly different  within an irrigation rate.
a) 2000, grain sorghum
 b) 2001, grain sorghum
 Figure 2: Seasonal water use for grain sorghum and cotton.
Irrigation methods followed by the same letter are not significantly different  within an irrigation rate.
a) 2000, grain sorghum
 b) 2001, grain sorghum
 Figure 3: Water use efficiency  for grain sorghum and cotton.
Irrigation methods followed by the same letter are not significantly different  within an irrigation rate.
INFLUENCE OF NOZZLE PLACEMENT ON CORN GRAIN YIELD, SOIL MOISTURE AND RUNOFF UNDER CENTER PIVOT IRRIGATION
 Maximizing irrigation efficiency is of enormous importance for irrigators in the Central Great Plains to conserve water and reduce pumping costs.
High temperatures, frequently strong winds and low humidity increase the evaporation potential of water applied through sprinkler irrigation.
Thus, many newer sprinkler packages have been developed to minimize water losses by evaporation and drift.
These systems have the potential to reduce evaporation losses as found by Schneider and Howell.
Schneider and Howell found that evaporation losses could be reduced by 2-3% as compared to above canopy irrigation.
Many producers and irrigation companies have promoted placing sprinklers within the canopy to conserve water by reducing the exposure of the irrigation water to wind.
However, runoff losses can increase due to the reduced wetted diameter which increases the application rate greater than soil infiltrate capacity.
Schneider and Howell  found that furrow dikes were necessary to prevent runoff with in-canopy irrigation.
In 2003 and 2004, a study was conducted comparing sprinkler nozzle placement near Burlington, Colorado in cooperation with a local producer.
The objective of this study was to determine the impact of placing the sprinkler devices within the canopy upon soil moisture, runoff and crop yield.
A secondary objective was to determine the usefulness of in-season tillage on water intake and preventing runoff.
For this study, the current configuration of a center pivot irrigation system owned by our cooperating farmer was utilized.
This configuration included drops with spray heads at approximately 1.5 feet  above the ground surface.
The sprinkler heads on the seventh and outside span of the center pivot were raised to approximately 7 feet above ground level.
This nozzle height allowed for an undisturbed spray pattern for a majority of the growing season.
The sprinkler heads on the sixth span of the center pivot remained at the original height.
In 2003, the nozzles were raised by attaching the
 flexible drop hose using truss rod slings.
Because the farmer decided not to irrigate this field in 2004, the study was moved to an adjacent pivot in 2004.
The pivot nozzles were raised by replacing the drop hoses and 'j-tubes' on this system.
In 2004 the nozzle heights in the outside span were left at 1.5 feet above ground level and the next span into the field were raised to 7 feet.
Spacing was 5-feet between nozzles for both site-years.
For the 2003 growing season, three in-season tillage treatments were replicated three times under each of the sprinkler heights.
The three tillage treatments were cultivation, inter-row rip and basin tillage.
The cooperating farmer implemented the tillage treatments when the corn was at the V6 growth stage.
The tillage treatments were implemented in strips running the length of the field.
The field was planting perpendicular to the sprinkler direction.
In 2004, the cooperating farmer chose to use grow the corn crop using no-till and planted in a circular pattern.
In-season tillage was was to be implemented, inter-row rip and basin tillage operations, it was prevented by wet weather in June..
Thus, the only tillage in 2004 was no-till.
The cooperating farmer conducted all field operations  during 2003 and 2004.
Runoff was measured on cultivation and basin tillage for 2 replications and both sprinkler heights in 2003.
Four-inch, V-notch furrow weirs installed at the bottom of the 8-row plots.
The runoff for two 30-inch rows for the entire length of the pivot span  was directed into the weir by the tillage treatment and soil berms where needed.
The water level height in the stilling-wells of the weirs was recorded using auto-logging pressure transducers.
Because the cooperating farmer chose no-till for the 2004 season, two 10-foot by 38-foot runoff plots using landscape edging were installed.
Furrow weirs were installed on the lower end of the plots to measure runoff.
The soil type at both sites was Kuma Silt Loam.
The slope was approximately 1 to 1.5 percent and was fairly uniform across treatments.
We measured soil moisture from mid-June through early September using a Troxler neutron probe at one-foot increments to five feet of soil depth.
A neutron access tube was installed in each tillage and nozzle height treatment in 2003 and six access tubes were installed in each nozzle height treatment in 2004.
The study was repeated in 2005 but the results are not published.
Problems associated with the bowls created surging and resulted in sections of sprinklers not outputting water.
These sprinklers were generally the above canopy sprinklers.
Grain yields in 2003 were not significantly different for in-canopy and above canopy irrigation.
Statistically significant difference between tillage treatments were not found.
However the yields for above canopy irrigation
 were consistently 4 bushels per acre greater than in-canopy irrigation within each tillage treatment.
This would indicate that moisture stress did not occur under either above canopy or in-canopy irrigation.
Grain yields for above canopy sprinkler placement were not statistically greater than in-canopy placement in 2003 as well.
However, grain yields averaged across tillage treatments over the two-year period suggest that a potential trend where above canopy placement of sprinklers has greater yields than that of in-canopy placement.
We plan to continue measuring grain yield and soil moisture at this site in 2005 to determine if this potential yield trend continues.
Soil moisture was measured for both above canopy and in-canopy sprinklers during the 2003 growing season.
When comparing above canopy to in-canopy irrigation, changes in soil moisture were greater for in-canopy irrigation than above canopy.
The depletion of soil moisture was significantly higher for the in-canopy sprinkler placement than with above canopy sprinklers.
With similar yields, this would indicate that greater runoff losses occurred with incanopy irrigation since soil moisture usage offset reduced infiltration.
The greatest difference in change in soil moisture between above and in canopy irrigation occurred during early August when the difference was greater than 3 inches of soil moisture between the two sprinkler placements.
Differences in soil moisture usage at physiological maturity were 1.7 inches greater for in-canopy irrigation than above canopy irrigation.
Changes in soil moisture between tillage treatments in 2003 were not significantly different from each other within a sprinkler height during the growing season.
This would indicate that sprinkler height was the dominant factor in soil moisture content.
Contrary to 2003, soil moisture initially increased early in the 2004 growing season, declining after drier weather and higher ET rates began in July.
Soil moisture content initially showed a greater increase for in-canopy placement as compared to above canopy placement.
Much of this was due to the incanopy placement being drier at the beginning of the season and above canopy placement reaching field capacity in mid-July.
Most likely, deep percolation occurred in the above canopy placement while stored soil moisture increased for the in-canopy placement.
Changes in soil moisture for both in-canopy and above canopy placement were similar after July 27.
This was after the above canopy and in-canopy placement reached maximum stored soil moisture during the growing season.
Due to inconsistent and unreliable readings from one replication of the data loggers installed on the weirs recording runoff, only one replication of the 2003
 measurements was used for this paper.
Runoff was greater with in-canopy irrigation than above canopy for the conventional cultivation and basin tillage treatments.
Changes in soil moisture between sprinkler placement treatments agree with runoff results collected for each placement.
Greater amounts of runoff between sprinkler packages were offset by greater soil moisture loss.
Runoff amounts were less for basin tillage as compared to cultivation.
The reduction in runoff was due to the increase in surface storage created by the implanted basins.
Although not measured, no or little runoff or signs of runoff was observed in the inter-row ripping tillage plots.
Only two significant runoff events due to irrigation, 1.1 and 0.89 inches of runoff, were recorded in 2004.
This was due to management changes made by the producer.
Irrigation depths in 2003 were 1.5 to 2 inches per application.
In 2004, application amounts were reduced to 0.7 inches per application.
This reduction in application depth reduced runoff in all but two irrigations where the producer applied higher amounts  per application.
Results from this study suggest that above canopy irrigation was more efficient at increasing stored soil moisture and reducing runoff as compared to in-canopy irrigation.
Less runoff from above canopy irrigation in 2003 resulted in more stored soil moisture and similar to slightly more grain yield than in-canopy irrigation.
In-season tillage such as basin tillage decreased runoff as compared to conventional cultivation.
Yields between tillage treatments were not significantly different, but a trend of yield increases was observed when soil intake rates were modified by tillage.
No statistically significant yield differences were observed when irrigation sprinkler nozzles were placed above the canopy and soil moisture differences between above canopy and in-canopy placement reflected the differences in runoff.
The results of this project suggest that sprinkler placement above a corn canopy would be preferable to placing sprinklers in-canopy unless significant changes in irrigation management practices occur.
As plants approach the end of the cropping season, the days are getting shorter and cooler and their leaves begin to lose the ability to transpire water, which opens an opportunity to let the soil dry to a lower water content without affecting yield.
The UNL recommendation is to lower the soil water content to 40% of plant available water to a four-foot depth after the dough stage in corn and R4-end of pod elongation in soybean.
Irrigation Water Flow Measurement
 Saleh Taghvaeian Extension Irrigation Specialist
 Irrigation water management begins with knowing how much water is available for irrigation.
Fact Sheet 1501, discusses water measurement units and useful factors for converting from one measurement unit to another.
The purpose of this fact sheet is to discuss a few basic methods of water flow measurement.
Methods of measuring irrigation flow rate can be grouped into three basic categories-direct velocity-area, and constricted flow.
Choice of method to use will be determined by the volume of water to be measured, the degree of accuracy desired, whether the installation is permanent or temporary, and the financial investment required.
Direct Measurement Methods 
 Measuring the period of time required to fill a container of a known volume can be used to measure small rates of flow such as from individual siphon tubes, sprinkler nozzles, or from individual outlets in gated pipe.
Ordinarily one gallon or five gallon containers will be adequate.
Small wells can be measured by using a 55 gallon barrel as the container.
It is recommended that the measurement be repeated at least three and preferably five times to arrive at a reliable rate of flow per unit of time.
Commercial flow meters are available for measuring the total volume of water flowing through a pipe.
These flow meters
 are relatively expensive; however, they have a good degree of accuracy if properly installed and maintained.
The most common type of flow meter is the propeller meter.
Depending on its type, these meters may give the flow rate or the total volume or both.
Several points should be considered in propeller meter installation and management:
 The readings are accurate only if the pipe is flowing full.
The flow may not be full at cerain parts of the pipe, such as before discharge points.
Meters should be installed at a point where turbulance is minimum.
This usually occurs after an extended length of straight pipe.
Meters should be calibrated on a regular basis.
Debris, weeds and moss in irrigation water reduces the accuracy by impacting the propeller's rotation.
The float method can be used to obtain an approximate measure of the rate of flow occurring in an open ditch.
It is especially useful where more expensive installations are not justified or high degree accuracy is not required.
Select a straight section of ditch from 50 to 100 feet long with fairly uniform cross-sections.
Make several measurements of the width and depth of the test cross-section so as to arrive at an average cross-sectional area.
Using a tape, measure
 the length of the test section of the ditch.
Place a small floating object in the ditch a few feet above the starting point of the test section and time the number of seconds for this object to travel the length of the test section.
This time measurement should be made several times to arrive at a reliable average value.
By dividing the length of the test section  by the average time required , one can estimate velocity in feet per second.
Since the velocity of water at the surface is greater than the average velocity of the stream, multiply the estimated surface velocity by a correction factor  to obtain the average stream velocity.
To obtain the rate of flow, multiply the average cross-sectional area of the ditch  times the average stream velocity  and the answer is the rate of flow in cubic feet per second.
The trajectory method of water measurement is a form of velocity area calculations that can be used for obtaining a rapid and rough estimate of flow rate discharging from a horizontal pipe flowing full.
Two measurements of the discharging jet are required to calculate the rate of flow of the water.
The first measurement is the horizontal distance, "X",  required for the jet to drop a vertical distance "Y" which is the second measurement.
By using "Y" equal to either 6 or 12 inches, the rate of flow for full pipes can be calculated by multiplying the horizontal distance "X"  times the appropriate factor for the nominal pipe diameter.
The following table contains water
 discharge factor where "Y" is measured from the outside of the pipe to the top of the water jet as indicated in Figure 4.
Nominal	Factor When	Factor When
 Pipe Diameter	Y=6	Y=12
 EXAMPLE: A farmer has a well discharging a full 8" pipe.
The horizontal distance  is 19" while the jet surface drops 12".
What is the well yield?
Step 1: Enter the water discharge factor table at 8" nominal pipe diameter.
Moving to the right and under the column headed Y = 12" we find the factor to be 52.9.
Step 2: Multiplying this factor 52.9, times the horizontal distance, 19" calculate the well yield to be 1,005 gpm.
Constriction Flow Methods 
 Methods employing a constriction of pre-determined dimensions are frequently used for measuring flow in irrigation canals and ditches.
Constricting type measuring devices can generally be placed in one of three categories-weirs, flumes, and orifices.
8 Orifice Plate-Open Pump Discharge
 Generally, only one or two measurements are required where the dimensions of the constriction are known.
Using these measurements, rate of flow is determined from either a table, a graph, or by calculation.
Due to the wide variety of types and sizes of constricting devices, flow tables are not included in this publication.
The local County Extension Director or local USDA office can obtain such tables or graphs.
the flow from the orifice discharges entirely into air or "fully submerged" where the downstream water surface is above the top of the orifice and the flow discharges into water.
Avoid orifices that do not flow free or are not completely submerged.
Basically, a weir measures flow by causing the water to flow over a notch of pre-determined shape and dimensions.
They are quite accurate when properly constructed, installed, and maintained.
Weirs do have some limitations.
First, they require considerable drop  between the upstream and downstream water surfaces which is often either not available in flat grade ditches or is undesirable.
Second, it is frequently necessary to construct a pool or stilling area above the weir so the water loses its velocity.
Unless the water appears practically still, discharge readings will be inaccurate.
Weir installations in earthen ditches can be particularly troublesome.
The stilling area in the ditch above the weir frequently tends to "silt in" while excessive erosion may occur immediately downstream from the weir.
Orifice plates properly installed on open pump discharges can provide a relatively inexpensive and reasonably accurate means of measuring well discharge.
It is very important that the opening in the orifice plate be accurately machined to dimension.
Slight variation from specified dimensions can cause wide variation from calculated rate of flow.
The equation for calculating flow through an orifice is: Q = KVH Where Q = flow in gallons per minute.
K = a constant dependent upon a combination of pipe size, orifice size and orifice shape, and discharge conditions.
H = Head in inches.
Aflume measures flow by causing the water to flow through a channel of pre-determined dimensions.
Flumes usually can operate with less difference in elevation between upstream and downstream water surfaces than can weirs.
Like weirs, when properly installed and maintained, flumes are quite accurate means of measuring water flow.
An orifice measures water flowing through an opening of pre-determined shape and size.
For a given amount of head  a specific quantity of water will flow through the opening.
Orifices can be classified as "free flowing" where
 The following table gives values of K for various combinations of orifice sizes and pipe sizes discharging into air.
These values of K should be used only for orifice plates machined to the dimensions shown in Illustration 9.
Pipe Size	Orifice Size in Inches
 Inches	3	4	5	6	7	8
 6	33.3	63.3	123.0
 8	59.0	97.3	155.0
 10	141.0	208.0	311.0
 9 Orifice Plate Construction
 The following graph can be used for determining the "square root" of the head  in inches.
Having measured the head H using the glass tube and a scale, enter the graph at the left side.
Move horizontally to intercept the curve and move downward to determine the square root of H 
 The following is an example of how to calculate flow using an orifice plate on a pump discharge.
A farmer has a 6" orifice plate installed on an 8" pump discharge.
The orifice plate is machined to the dimension and shape shown in the sketch.
He or she determines the head "H" to be 27".
Consulting the table, he or she determines the constant "K" for a 6" orifice in an 8" pipe to be 155.
Using the graph he or she estimates the square root of 27 to be about 5.2.
Substituting the values in the equation Q = KVH, Q is calculated to be 806.0.
The final selection of the type of water flow measurement device will depend on the volume of water to be measured,
 the degree of accuracy desired, the desired permanence of installation, and the grade or fall of the ditch or stream.
The degree of accuracy afforded by the various measurement methods of course depends upon the skill of the operator as well as the proper and careful installation of the device.
The generally accepted degree of accuracy using the trajectory method is +10 percent, while orifices, flumes, and weirs can provide + 3 percent to 5 percent, accuracy.
Commercial flow meters usually fall in the range of + 2 percent to 4 percent.
The importance of proper installation and operation as well as exercising due caution when making measurements or taking readings cannot be over emphasized.
Your local County Extension Director or local USDA office can provide detailed information relative to water measurement devices.
ACKNOWLEDGEMENT: The author wishes to thank James E.
Garton, Delbert Schwab and A.
D.
Barefoot of the OSU Agricultural Engincering Department for their assistance and helpful suggestions in preparing this publication.
A RETURN LOOK AT DORMANT SEASON IRRIGATION STRATEGIES
 Many of the irrigation systems today in the Central Great Plains no longer have the capacity to apply peak irrigation needs during the summer and must rely on soil water reserves to buffer the crop from water stress.
Considerable research was conducted on preseason irrigation in the US Great Plains region during the 1980s and 1990s.
In general, the conclusions were that in-season irrigation was more beneficial than preseason irrigation and that often preseason irrigation was not warranted.
The objective of this study was to determine whether preseason irrigation would be profitable with today's lower capacity wells.
A field study was conducted at the KSU-SWREC near Tribune, Kansas, from 2006 to 2009.
The study was a factorial design of preplant irrigation , well capacities , and seeding rate.
Preseason irrigation increased grain yields an average of 16 bu a-1.
Grain yields were 29% greater when well capacity was increased from 0.10 to 0.20 in day1 Crop water productivity  was not significantly affected by well capacity or preseason irrigation.
Preseason irrigation was profitable at all well capacities.
At well capacities of 0.10 and 0.15 in day-1 a seeding rate of 27,500 seeds a-1 was generally more profitable than lower or higher seeding rates.
A higher seeding rate  increased profitability when well capacity was increased to 0.2 in day-1.
Irrigated crop production is a mainstay of agriculture in western Kansas.
However, with declining water levels in the Ogallala aquifer and increasing
 energy costs, optimal utilization of limited irrigation water is required.
The most common crop grown under irrigation in western Kansas is corn.
Almost all of the groundwater pumped from the High Plains  Aquifer is used for irrigation.
In 1995, of 3 billion m 3 of water pumped for irrigation in western Kansas, 1.41 million acre-ft  were applied to corn.
This amount of water withdrawal from the aquifer has reduced saturated thickness  and well capacities.
Considerable research was conducted on preseason irrigation in the US Great Plains region during the 1980s and 1990s.
In general, the conclusions were that in-season irrigation was more beneficial than preseason irrigation and that often preseason irrigation was not warranted because overwinter precipitation could replenish a significant portion of the soil water profile.
Lamm and Rogers  developed a relationship between fall ASW and over-winter precipitation on spring ASW.
In a review of preplant irrigation, Musick and Lamm  concluded that benefits of preplant irrigation are likely to be greatest when the soil profile is dry and growing season irrigation is reduced.
With recent dry conditions in certain areas and diminished well capacities, this creates a situation where preplant irrigation may be beneficial.
In a more recent study Stone et al.
used simulation modeling to examine the effectiveness of preseason irrigation.
They found the differences in storage efficiency between spring and fall irrigation peaked at approximately 37 percentage points  when the maximum soil water during the preseason period was at approximately 77% of available soil water.
Figure 1.
Available soil water in the 5 ft soil profile in the spring  as affected by available soil water in the fall  and overwinter precipitation.
Results calculated using an equation from Lamm and Rogers, 1985.
Many of the irrigation systems today in the Central Great Plains no longer have the capacity to apply peak irrigation needs during the summer and must rely on soil water reserves to buffer the crop from water stress.
Therefore, this study was conducted to evaluate whether preseason irrigation would be profitable when well capacity is limited and insufficient to fully meet crop requirements.
A field study was conducted at the KSU-SWREC near Tribune, Kansas from 2006 to 2009.
Normal precipitation for the growing season  is 13.2 in and normal annual precipitation is 17.4 in.
The study was a factorial design of preseason irrigation , well capacities , and seeding rate.
The irrigation treatments were whole plots and the plant populations were subplots.
Each treatment combination was replicated four times and applied to the same plot each year.
The irrigation treatments were applied with a lateralmove sprinkler with amounts limited to the specified well capacities.
Preseason irrigation was applied in early April and in-season irrigations were applied from about mid-June through early September.
The in-season irrigations were generally applied weekly except when precipitation was sufficient to meet crop needs.
Corn was planted in late April or early May each year.
The center two rows of each plot were machine harvested with grain yields adjusted to 15.5% moisture.
Plant and ear populations were determined by counting plants and ears in the center two rows prior to harvest.
Seed weights  were determined on 100-count samples from each plot.
Kernels per ear were calculated from seed weight, ear population, and grain yield.
Soil water measurements  were taken throughout the growing season using neutron attenuation.
All water inputs, precipitation and irrigation, were measured.
Crop water use was calculated by summing soil water depletion  plus in-season irrigation and precipitation.
Inseason irrigations were 9.6, 12.6, and 19.0 inches in 2006; 7.2, 10.1, 15.6 inches in 2007; 8.2, 11.0, 14.8 inches in 2008; and 8.8, 11.8, 17.9 inches in 2009 for the 0.10, 0.15, and 0.20 in day well capacity treatments, respectively.
In-season precipitation was 6.9 inches in 2006, 8.1 inches in 2007, 9.4 inches in 2008; and 14.4 inches in 2009.
Non-growing season soil water accumulation was the increase in soil water from harvest to the amount at planting the following year.
Non-growing season precipitation was 15.0 inches in 2007, 4.2 inches in 2008, and 8.6 inches in 2009 with an average of 9.3 in.
Precipitation storage efficiency  was calculated as non-growing season soil water accumulation divided by non-growing season precipitation.
Crop water productivity  was calculated by dividing grain yield  by crop water use.
Local corn prices , crop input costs, and custom rates were used to perform an economic analysis to determine net return to land, management, and irrigation equipment for each treatment.
Preseason irrigation increased grain yields an average of 16 bu a-1.
Although not significant, the effect was greater at lower well capacities.
For example, with a seeding rate of 27,500 seeds a-1, preseason irrigation  increased grain yield by 21 bu a with a well capacity of 0.10 in day while only 7 bu a  with a well capacity of 0.20 in day-1.
As expected, grain yields increased with increased well capacity.
Grain yields  were 29% greater when well capacity was increased from 0.1 to 0.2 in day-1.
Preseason irrigation and increased well capacity increased the number of seeds ear1 but had little impact on seed weight.
The optimum seeding rate varied with irrigation level.
With the two lowest well capacities and without preseason irrigation, a seeding rate of 22,500 seeds a-1 was generally adequate.
However, if preseason irrigation was applied, then a higher seeding rate  increased yields.
With a well capacity of 0.2 in day1, a seeding rate of 32,500 seeds a  provided greater yields with or without preseason irrigation.
Crop water productivity was not significantly affected by well capacity or preseason irrigation , although the trend was for greater CWP with increased water supply.
Similar to grain yields, the effect of seeding rate varied with irrigation level.
With lower irrigation levels, a seeding rate of 27,500 seeds a -Superscript tended to optimize CWP.
It was only at the highest well capacity that a higher seeding rate improved CWP.
Crop water use increased with well capacity and preseason irrigation.
Soil water at harvest increased with increased well capacity, but this caused less soil water to accumulate during the winter.
Non-growing season soil water accumulation averaged 2.7 in.
Average nongrowing season precipitation was 9.3 in giving an average non-growing season precipitation storage efficiency of 29%.
Preseason irrigation  increased available soil water at planting by 1.7 in.
Seeding rate had minimal effect on soil water at planting or crop water use but increased seeding rate tended to decrease soil water at harvest and increase over-winter water accumulation.
Preseason irrigation was found to be profitable at all irrigation capacities.
At the two lower well capacities, a seeding rate of 27,500 seeds a -1 was generally the most profitable.
However, the highest irrigation capacity benefited from a seeding rate of 32,500 seeds a-1.
Corn grain yields responded positively to preseason irrigation and increases in well capacity.
This yield increase generally resulted from increases in kernels ear1 Preseason irrigation was profitable at all well capacities.
Seeding rate
 should be adjusted for the amount of irrigation water available from both well capacity and preseason irrigation.
At well capacities of 0.10 and 0.15 in day1, a seeding rate of 27,500 seeds a-1 was generally more profitable than lower or higher seeding rates.
A higher seeding rate  increased profitability when well capacity was increased to 0.20 in day1.
This research was supported in part by the Ogallala Aquifer Program, a consortium between USDA Agricultural Research Service, Kansas State University, Texas AgriLife Research, Texas AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
Contribution no.
12-315-A from the Kansas Agricultural Experiment Station.
This paper was originally presented at 5th National Decennial Irrigation Conference, Phoenix, Arizona, 5 Dec.
2010.
Table 1.
Crop parameters of corn as affected by well capacity, preseason irrigation, and seeding rate, Tribune, Kansas, 2006 2009.
capacity	Well	irrigation	season	Pre-	Seed	rate	Grain	yield	water	prod.
Crop	Plant	pop.
pop.
Ear	seed	1000	Kernel
 in day 1	bu a 1	lb ac-in-1	103 acre-	-	OZ	# head-1
 0.10	no	22.5	153	386	22.4	21.5	13.20	476
 27.5	158	397	26.7	24.7	12.75	442
 32.5	155	389	31.2	28.8	12.46	379
 yes	22.5	171	403	21.9	21.5	13.43	531
 27.5	179	416	26.7	25.3	13.15	478
 32.5	183	419	31.5	29.6	12.80	427
 0.15	no	22.5	172	389	22.2	21.2	13.24	543
 27.5	173	395	27.0	25.9	12.93	465
 32.5	171	383	31.1	29.2	12.84	406
 yes	22.5	185	405	22.4	21.9	13.36	563
 27.5	197	431	27.0	26.2	13.08	512
 32.5	201	433	31.4	30.2	12.80	466
 0.20	no	22.5	200	404	22.3	22.0	13.29	615
 27.5	211	414	27.0	26.8	13.02	544
 32.5	223	440	31.8	31.3	12.74	503
 yes	22.5	204	396	22.1	21.9	13.59	617
 27.5	218	414	27.0	26.8	13.27	551
 32.5	229	436	31.9	31.2	12.74	517
 Well Capacity 	0.001	0.411	0.086	0.001	0.687	0.001
 Pre-Season	0.002	0.099	0.659	0.107	0.160	0.001
 WC*Pre-Season	0.222	0.297	0.452	0.401	0.752	0.138
 Seed Rate	0.001	0.001	0.001	0.001	0.001	0.001
 Seed Rate*WC	0.001	0.018	0.012	0.001	0.212	0.176
 Seed Rate*Pre-Season	0.018	0.126	0.089	0.345	0.186	0.263
 Seed Rate*W*Pre-Season	0.402	0.626	0.427	0.373	0.518	0.295
 MEANS	Well	0.10	167	402	26.8	25.2	12.97	456
 cap.
0.15	183	406	26.9	25.8	13.04	493
 0.20	214	417	27.0	26.6	13.11	558
 LSD0.05	11	25	0.2	0.5	0.35	21
 Pre-	no	180	400	26.9	25.7	12.94	486
 season	yes	196	417	26.9	26.1	13.14	518
 LSD0.05	9	21	0.2	0.4	0.28	17
 Seed	22,500	181	397	22.2	21.7	13.35	558
 rate	27,500	189	411	26.9	25.9	13.03	499
 32,500	194	417	31.5	30.1	12.73	450
 LSD0.05	3	8	0.2	0.3	0.09	10
 Table 2.
Available soil water in 8 ft profile, crop water use, and non-growing season water accumulation for corn as affected by well capacity, preseason irrigation, and seeding rate, Tribune, Kansas, 2006 2009.
Available soil water	Non-growing
 capacity	Well	Pre-season	irrigation	Seed	rate	Planting	Harvest	Water	use	accumulation.
season
 in day 1	103 a-1	-	in 8 ft.
profile -1	in	in 8 ft.
profile
 0.10	no	22.5	8.36	5.21	21.28	2.79
 27.5	8.24	4.83	21.55	2.73
 32.5	8.02	4.63	21.52	2.78
 yes	22.5	10.66	5.43	23.36	5.02
 27.5	10.52	4.88	23.78	5.30
 32.5	10.83	4.96	24.00	5.33
 0.15	no	22.5	8.78	5.47	24.35	2.71
 27.5	9.17	6.08	24.13	2.56
 32.5	9.06	5.68	24.42	2.98
 yes	22.5	10.51	6.19	25.36	4.05
 27.5	10.46	6.15	25.35	4.77
 32.5	10.71	5.98	25.76	5.05
 0.20	no	22.5	10.51	9.07	27.94	2.14
 27.5	9.95	7.86	28.59	3.02
 32.5	10.56	8.53	28.53	2.82
 yes	22.5	13.44	10.82	29.11	3.15
 27.5	13.22	10.13	29.58	3.68
 32.5	12.90	9.85	29.55	3.55
 Well capacity 	0.010	0.001	0.001	0.001
 Pre-season	0.001	0.266	0.001	0.001
 WC*Pre-season	0.647	0.587	0.010	0.001
 Seed rate	0.779	0.076	0.001	0.002
 Seed rate*WC	0.692	0.173	0.059	0.156
 Seed rate*Pre-season	0.985	0.820	0.546	0.424
 Seed rate*WC*Pre-season	0.389	0.625	0.749	0.303
 MEANS	Well	0.10	9.44	4.99	22.58	3.99
 capacity	0.15	9.78	5.92	24.89	3.69
 0.20	11.76	9.37	28.88	3.06
 LSD0.05	1.49	1.77	0.39	0.38
 Preseason	no	9.18	6.37	24.70	2.73
 yes	11.47	7.15	26.21	4.43
 LSD0.05	1.22	1.44	0.32	0.31
 Seed rate	22.5	10.38	7.03	25.23	3.31
 27.5	10.26	6.65	25.50	3.68
 32.5	10.35	6.61	25.63	3.75
 LSD	0.05	0.34	0.40	0.18	0.24
 Table 3.
Net return to land, irrigation equipment, and management from preseason irrigation  at three irrigation well capacities and three seeding rates at Tribune, Kansas 2006-2009.
Well	Preseason	Seeding rate (10 3 a-1 1
 capacity	Irrigation	22.5	27.5	32.5
 in day	Net return, $ a-1 yr
 0.10	No	231	238	214
 Yes	285	300	297
 0.15	No	290	283	261
 Yes	321	352	357
 0.20	No	415	449	485
 Yes	417	458	492
 Corn research plots being irrigated with a lateral move sprinkler irrigation system at Kansas State University.
Keep in mind that the plants next to the probes are an integral part of the sensor and must be protected so they can represent all the other plants in the field.
Do not install sensors when the soil is too wet and make as few footprints as possible to prevent soil compaction.
SUMMER CROP PRODUCTION AS RELATED TO IRRIGATION CAPACITY
 In arid regions, it has been a design philosophy that irrigation system capacity be sufficient to meet the peak evapotranspiration needs of the crop to be grown.
This philosophy has been modified for areas having deep silt loam soils in the semi-arid US Central Great Plains to allow peak evapotranspiration needs to be met by a combination of irrigation, precipitation and stored soil water reserves.
The major irrigated summer crops in the region are corn, grain sorghum, soybean and sunflower.
Corn is very responsive to irrigation, both positively when sufficient and negatively when insufficient.
The other crops are less responsive to irrigation and are sometimes grown on more marginal capacity irrigation systems.
This paper will discuss the nature of crop evapotranspiration rates and the effect of irrigation system capacity on summer crop production.
Additional information will be provided on the effect of irrigation application efficiency on irrigation savings and corn yields.
Although the results presented here are based on simulated irrigation schedules for 33 years of weather data from Colby, Kansas  for deep silt loam soils, the concepts have broader application to other areas in showing the importance of irrigation capacity for summer crop production.
SUMMER CROP EVAPOTRANSPIRATION RATES
 Crop evapotranspiration  rates vary throughout the summer reaching peak values during the months of July and August in the Central Great Plains.
Long term  July and August corn ET rates at the KSU Northwest Research Extension Center, Colby, Kansas have been calculated with a modified Penman equation  to be 0.267 and 0.249 inches/day, respectively.
However, it is not uncommon to observe short-term peak corn ET values in the 0.35 0.40 inches/day range.
Occasionally, calculated peak corn ET rates may approach 0.5 inches/day in the Central Great Plains, but it remains a point of discussion whether the corn actually uses that much water on those
 extreme days or whether corn growth processes essentially shut down further water losses.
Individual years are different and daily rates vary widely from the long term average corn ET rates.
Corn ET rates for July and August of 2004 were 0.245 and 0.229 inches/day, respectively, representing an approximately 8% reduction from the long-term average rates.
In contrast, the corn ET rates for July and August of 2003 were 15% greater than the long term average rates.
Irrigation systems must supplement precipitation and soil water reserves to attempt matching average corn ET rates and also provide some level of design flexibility to attempt covering year-to-year variations in corn ET rates and precipitation.
Figure 1.
Long term corn evapotranspiration  daily rates and ET rates for 2004 at the KSU Northwest Research-Extension Center, Colby Kansas.
ET rates calculated using a modified Penman approach.
Simulation of irrigation schedules for Colby, Kansas
John Buchanan, Associate Professor and Extension Specialist, Department of Biosystems Engineering and Soil Science, University of Tennessee Travis Chapin, Former State Specialized Extension Agent, Food Safety, University of Florida IFAS Faith Critzer, Associate Professor and Extension Specialist, School of Food Science, Washington State University Michelle Danyluk, Professor and Extension Specialist, Food Science and Human Nutrition, University of Florida IFAS Chris Gunter, Professor and Extension Specialist, Horticultural Science, North Carolina State University Laura Strawn, Associate Professor and Extension Specialist, Food Science and Technology, Virginia Tech Annette Wszelaki, Professor and Extension Specialist, Department of Plant Sciences, University of Tennessee
 Bridging the GAPs: Approaches for Treating Irrigation Water On-Farm
 The goal of this series of modules on water treatment is to equip growers with the knowledge to successfully implement water treatment systems on their farms.
Fruit and vegetable growers are continually assessing their operations to determine where they can limit risk and increase productivity.
As a result, many have expressed interest in learning more about how on-farm preharvest water treatment systems work and how they may fit within their current setup.
These four modules help growers to: 1) understand the background for water treatment; 2) learn about different approaches to treating water on-farm; 3) how to implement these systems to meet requirements of the Produce Safety Rule; and 4) how to verify that the system is operating as intended.
W 920-A, Agricultural Water Treatment and FSMA W 920-B, Agricultural Water Treatment Tools W 920-C, Developing On-farm Agricultural Water Treatment Programs W 920-D, Implementing Agricultural Water Treatments on the Farm
 A special thank you to the Produce Safety Alliance who allowed us to use portions of their curriculum for this module.
1.
Describe the purpose of water treatment within the context of on-farm irrigation and agricultural water as defined by the Produce Safety Rule 
 2.
Communicate scenarios for which a treatment system would help mitigate on-farm food safety risks posed by agriculture water
 3.
Explain the connectivity between implementing a water treatment system and reducing risk on the farm
 4.
Describe the regulatory context of water treatment technologies
 FDA Water Compliance Date Extension
 In March 2019, FDA published a rule called Standards for the Growing, Harvesting, Packing, and Holding of Produce for Human Consumption; Extension of Compliance Dates for Subpart E.
Extends ALL provisions of Subpart E  other than sprouts including the safe and sanitary quality, annual inspection, and postharvest water monitoring requirements.
FDA has stated that the reason for this extension is to allow time "to address questions about the practical implementation of compliance with certain provisions and to consider how we might further reduce the regulatory burden or increase flexibility while continuing to protect public health."
 Until the process of consideration is finished, the water requirements are those currently stated in the Rule
 Water Compliance Date Extension
 Farm Size	Compliance Dates
 Very Small Farms	2024
 Large farms>$500,000 in 2011 dollars, refer to inflation chart to determine actual value for the year you are training Small= $250,000-499,999 Very Small Farms= $249,999-25,000
 *Must have begun testing during while actively growing by January of the compliance year.
For example, if I'm a tomato grower on a large farm and my season starts in May and ends in October.
I would need to begin testing during that 2021 growing season in order to meet the January 2022 compliance date.' *
 Production Agricultural Water 
 Water used in contact with the harvestable portion of covered produce during the growing season
 Define Agricultural Water in the context of the Produce Rule water that comes into contact with the harvestable portion of the crop before harvest.
Then discuss the different types of water this could include listed on the right.
Make relevant for your audience and the types of commodities that they are using.
All agricultural water must be safe and of adequate sanitary quality for its intended use
 Many factors impact the quality of water
 Many sources and uses of water on the farm
 Human pathogens can be introduced into water and contaminate produce during growing activities
 A general requirement of subpart E of the FSMA Produce Safety Rule is that all agricultural water must be safe and of adequate sanitary quality for its intended use.
This requirement applies to agricultural water that is intended or likely to contact covered produce or food contact surfaces and includes agricultural water used during growing activities for covered produce using a direct water application method , and water used for certain activities during and after harvest  and for sprout irrigation.
Evaluating Water Quality: Use of Microbial Water Quality Profiles
 Testing is the only way to quantitatively evaluate the microbial quality of the water
 The microbial water quality profile  can help you:
 Understand the long-term quality of your water source
 Understand appropriate uses for each source
 Determine when corrective measures are needed, if the microbial water quality profile exceeds numerical criteria in the FSMA Produce Safety Rule
 Requirements related to the microbial water quality profile, corrective measures, and numerical GM and STV criteria are discussed in the upcoming slides.
The geometric mean  is a log-scale average, the "typical" value.
The statistical threshold value  is a measure of variability, the estimated "high range" value.
Both of these are discussed in the slide Geometric Means and Statistical Threshold Values.
The microbial water quality profile  is a long-term management strategy, and for production water, it is not meant to be used for day-to-day management and decision making about whether the water is suitable for a use at that particular time.
112.46 requires that growers subject to the rule must establish an initial microbial water quality profile for untreated water sources  that are applied using a direct water application method during growing.
It is important to understand that surface water quality can change quickly over time and throughout the season.
Water testing only provides an indication of the water quality at the time of sampling and may provide information on long-term sources of fecal contamination that impact the water source.
Criteria for Water Used During Growing Activities
 Each source of production water must be tested to evaluate whether its water quality profile meets the following criteria:
 126 or less colony forming units  generic E.
coli per 100 mL water geometric mean 
 410 or less CFU generic E.
coli per 100 mL water statistical threshold value 
  112.44 specifies criteria for untreated agricultural water  that is applied with a direct water application method to covered produce during growing activities.
The numerical GM and STV criteria are used to evaluate the microbial water quality profile.
These criteria capture two different pieces of information about the distribution of generic E.
coli levels in a water source.
The geometric mean  is essentially the average amount of generic E.
coli in a water source.
The STV reflects the amount of variation in the E.
coli levels.
Collectively, both pieces of information provide a more complete description of your water quality than either one alone.
Some terms, as defined in  112.3, are critical to understanding the scope of what is covered under these criteria.
Agricultural water means water used in covered activities on covered produce where water is intended to, or is likely to, contact covered produce or food contact surfaces.
Direct water application method means using agricultural water in a manner whereby the water is intended to, or is likely to, contact covered produce or food contact surfaces during use of the water.
Covered produce means produce that is subject to the FSMA Produce Safety Rule.
The term "covered produce" refers to the harvestable or harvested part of the crop.
Production water that does not meet the definition of agricultural water  is not covered by the GM and STV criteria in the FSMA Produce Safety Rule.
For example, water used for drip or furrow irrigation in apple orchards would not be considered agricultural water as long as the water does not contact the apples.
That same water would be considered agricultural water if it were used to mix protective sprays that were then applied directly to the apples.
For information about how the numerical GM and STV water quality criteria were developed
 For a historical context of water quality standards:
Many irrigators already use soil water monitoring equipment or ET data to make good data-driven decisions.
The only thing they need to do is continue what is working and hone their analysis skills.
Vegetable Irrigation: Leafy Greens
 Dan Drost and Tiffany Maughan
 Proper irrigation is critical for leafy green production.
Optimal irrigation management leads to healthy plants and maximum, high-quality yields.
Under-irrigation results in a reduction of yield.
Irrigation can be used to combat the negative effect of high temperatures on leafy greens but over-irrigation increases disease susceptibility, nutrient leaching, and water use inefficiency.
A consistent moisture supply throughout all growth stages, but particularly during rapid growth is important for reducing tip-burn in leafy greens.
Tip burn is characterized by brown spots or tissue breakdown along the margins of young leaves and is caused by localized calcium deficiency in the tissue.
This occurs even when calcium levels in the soil are high.
It is commonly due to water stress and low evapotranspiration.
Different irrigation methods are commonly used to irrigate leafy greens, each with different management considerations.
Furrow irrigation is quite common but many growers are converting to use drip irrigation to save water, improve plant growth, and optimize productivity.
Regardless of the irrigation system used, there are some basic principles to understand that will help ensure proper irrigation.
This fact sheet will discuss these basic principles.
Properly managing irrigation is analogous to managing money.
In addition to knowing your current bank balance , it is important to track both expenses  and income.
Bank Balance 
 How big is my bank account?
Water holding capacity First, some terminology:
 Field Capacity is the amount of water that can be held in the soil after excess water has percolated out due to gravity.
Permanent Wilting Point is the point at which the water remaining in the soil is not available for uptake by plant roots.
When the soil water content reaches this point, plants die.
Available Water is the amount of water held in the soil between field capacity and permanent wilting point.
Allowable Depletion  is the point where plants begin to experience drought stress.
Depending on soil type, the amount of allowable depletion leafy greens is about 25% of the total available water in the soil.
Figure 1.
Soil water content from saturated to dry.
Optimal soil moisture levels for plant growth are between field capacity and allowable depletion.
Figure 2.
The amount of allowable depletion, or the readily available water, represents about 25% of the total available water.
The goal of a well-managed irrigation program is to maintain soil moisture between field capacity and the point of allowable depletion, or in other words, to make sure that there is always readily available water and that plants do not experience water stress.
The amount of readily available water is related to the effective rooting depth of the plant, and the water holding capacity of the soil.
The majority of leafy greens are very shallow rooted.
About 95% of spinach and 90% lettuce roots are in the top foot of soil.
The water holding capacity within that rooting depth is related to soil texture, with coarser soils  holding less water than fine textured soils such as silts and clays.
A deep sandy loam soil at field capacity, i.e., would contain 0.6 to 0.75 inch of readily available water in an effective rooting depth of 1 foot.
What's in the bank?
Measuring Soil Moisture
 In order to assess soil water content, monitor soil moisture at two depths: 6 inches deep and near the bottom of the effective rooting depth.
One of the more cost effective and reliable methods for measuring soil moisture is by electrical resistance block, such as the Watermark TM sensor.
These blocks are permanently installed in the soil, and wires from the sensors are attached to a handheld unit that measures electrical resistance.
Resistance measurements are then related to soil water potential, which is an indicator of how hard the plant roots have to "pull" to obtain water from the soil.
The handheld unit reports soil moisture content in centibars, where values close to zero indicate a wet soil and high values represent dry soil.
The relationship between soil water potential and available water differs by soil type.
The range of the sensor is calibrated to 0 to 200 centibars , which covers the range of allowable depletion in most soils.
The sensors are less effective in coarse sandy soils, and will overestimate soil water potential in saline soils.
Remember that allowable depletion is approximately 25% of available water, which roughly corresponds to soil water potentials of 20 centibars for a loamy sand soil, and 30 centibars for a loam.
Allowable depletion varies slightly by crop.
For example, allowable depletion for spinach is 20% of available water whereas lettuce is 30%.
Table 1.
Available water holding capacity for different soil textures, in inches of water per foot of soil.
Total available water is the amount of water in the soil between field capacity and permanent wilting point.
Allowable depletion  is the amount of water the plant can use from the total available before experiencing drought stress.
Allowable depletion for leafy greens is approximately 25% of total available.
Total Available	Allowable Depletion inches
 Soil Texture	Water	
 inch/foot	In top1	In top 1.5'
 Sands and fine sands	0.5 0.75	0.13 0.19	0.19 0.29
 Loamy sand	0.8 1.0	0.2 0.25	0.30 0.38
 Sandy loam	1.2 1.5	0.3 0.38	0.45 0.57
 Loam	1.9 2.0	0.48 0.5	0.72 0.75
 Silt loam, silt	2.0 2.1	0.5 0.53	0.75 0.79
 Silty clay loam	1.9 2.0	0.48 0.5	0.72 0.75
 Sandy clay loam, clay loam	1.7 2.0	0.43 0.5	0.65 0.75
 Table 2.
Recommended WatermarkTM sensor values at which to irrigate.
Soil Type	Irrigation Needed
 Loamy sand	20 25
 Sandy loam	22 27
 Silt loam, silt	28 32
 Clay loam or clay	30 35
 TMWatermark is a registered trademark of Irrometer, Co., Riverside, CA.
Water is lost from the field through surface runoff, deep percolation , evaporation from the soil surface, and transpiration through the leaves of the plant.
Of these, the biggest losses are typically due to evaporation and transpiration, collectively known as "evapotranspiration" or ET.
Deep percolation from excess irrigation can be another large loss.
Estimates of ET are based on weather data, including air temperature, relative humidity and wind speed.
Table 3 lists average daily reference ET values
 Table 3.
Daily total alfalfa reference evapotranspiration  for nine Utah cities expressed in  inches per day,  gallons per acre per day, and  drip-irrigated gallons per 100 feet of bed length per day.
Brigham	Salt Lake	Spanish	Cedar	St.
Month	Logan	City	Ogden	Farmington	City	Fork	Richfield	City	George
  Inches per day
 Mar	0.09	0.10	0.10	0.12	0.11	0.12	0.14	0.13	0.15
 Apr	0.15	0.16	0.17	0.19	0.17	0.16	0.20	0.18	0.22
 May	0.20	0.22	0.22	0.25	0.22	0.21	0.23	0.24	0.28
 Jun	0.24	0.27	0.28	0.30	0.28	0.26	0.30	0.31	0.32
 Jul	0.29	0.32	0.32	0.27	0.30	0.28	0.29	0.29	0.31
 Aug	0.26	0.28	0.29	0.23	0.27	0.25	0.27	0.27	0.28
 Sep	0.18	0.20	0.20	0.19	0.19	0.18	0.20	0.21	0.21
 Oct	0.09	0.12	0.12	0.12	0.11	0.10	0.13	0.14	0.14
  Gallons per acre per day.
Irrigation amounts need to be adjusted by Crop Coefficient and Irrigation
 Mar	2444	2716	2716	3259	2987	3259	3670	3451	4073
 Apr	4073	4345	4617	5160	4617	4345	5386	5006	5974
 May	5431	5974	5974	6789	5974	5703	6360	6412	7604
 Jun	6517	7332	7604	8147	7604	7061	8102	8500	8690
 Jul	7875	8690	8690	7332	8147	7604	7937	7788	8418
 Aug	7061	7604	7875	6246	7332	6789	7385	7306	7604
 Sep	4888	5431	5431	5160	5160	4888	5522	5739	5703
 Oct	2444	3259	3259	3259	2987	2716	3609	3741	3802
  Drip-irrigated gallons per 100 feet of bed length per day based on 3-foot bed spacing.
Irrigation amounts
 need to be adjusted by Crop Coefficient and Irrigation Efficiency.2
 Mar	16.8	18.7	18.7	22.4	20.6	22.4	25.3	23.8	28.1
 Apr	28.1	29.9	31.8	35.5	31.8	29.9	37.1	34.5	41.1
 May	37.4	41.1	41.1	46.8	41.1	39.3	43.8	44.2	52.4
 Jun	44.9	50.5	52.4	56.1	52.4	48.6	55.8	58.5	59.8
 Jul	54.2	59.8	59.8	50.5	56.1	52.4	54.7	53.6	58.0
 Aug	48.6	52.4	54.2	43.0	50.5	46.8	50.9	50.3	52.4
 Sep	33.7	37.4	37.4	35.5	35.5	33.7	38.0	39.5	39.3
 Oct	16.8	22.4	22.4	22.4	20.6	18.7	24.9	25.8	26.2
 Conversion to gallons per acre per day  =  X 7.481 * 43560 2Calculation for drip-irrigation:  =  X 3 ft.
/ 435.6.
If different bed spacing is used, adjust calculation accordingly.
Calculated from long-term monthly evapotranspiration values from Hill, 2011.
Some weather stations in Utah are programmed to calculate and report the ET estimates for alfalfa as a reference crop  that is specific to your crop and its stage of development.
ETcrop =ET, x Ketop
 The Kcrop for several common leafy greens are shown in Table 4.
The Kcrop varies as the plant grows, represented in Table 4 as percent ground cover.
Ground cover is
 determined by evaluating a representative section of a planting bed and either estimating or measuring how much bare soil is exposed when looking directly down at the section.
If 60% of the soil is exposed, use the 40% ground cover value.
In general, water use increases gradually as the crop develops until the full canopy is established.
Leafy greens are typically cool season crops.
In Utah, many greens are primarily grown in the spring and fall to avoid summer heat.
Some differences between spring and fall production should be considered for irrigation scheduling.
For example, spring production time for a lettuce crop takes approximately 70 to 80 days.
In the fall this production window shortens to 50 to 60 days.
Table 4.
Description of percent ground cover and crop coefficient estimates for several leafy green crops.
Crop	20	40	60	80	100
 Beets/Chard1	Kcrop	0.26	0.35	0.55	0.77	1
 Broccoli/Mustard2	Kcrop	0.24	0.5	0.79	1.02	1.08
 Cabbage	Kcrop	0.35	0.45	0.65	0.84	0.95
 Lettuce 2	Kcrop	0.24	0.38	0.58	0.77	0.9
 Lettuce 	Kcrop	0.4	0.55	0.85	1.01	1.02
 Spinach	Kcrop	0.25	0.4	0.6	0.75	0.9
 1 From AgriMet Cooperative Agricultural Weather Network with alfalfa as the reference crop.
2 From California Agriculture  with grass as the reference crop.
Income Irrigation and Rainfall
 In Utah's high elevation desert climate, rainfall only contributes a small fraction of the in-season water requirements of the crop.
Therefore, regular irrigation is needed to supply plant water needs.
This irrigation water can be supplied by furrow, sprinkler, or drip lines.
Whichever irrigation system you utilize, it is important to calibrate your system SO that you know precisely how much water is being applied.
When trying to determine application uniformity, it is best to measure output at both ends of your irrigation system.
Also, if your planting is on a slope, you should measure output at the highest and lowest points of your field.
Elevation differences and the distance the water travels through the irrigation lines both affect water pressure, and consequently the flow rate at the nozzle.
Drip irrigation tape comes with recommended operating pressures, a variety of emitter spacing, and various flow rates.
Most drip tapes operate at 10 psi.
Emitters may be
 spaced from 4 to 36 inches apart and come in a variety of flow rates.
Leafy greens do well with 4 to 12 inch emitter spacing.
Flow rates are commonly reported in gallons per100 feet of tape per hour  or gallons/emitter/hr.
For a tape with a 12-inch emitter spacing, 24 gallons/100ft/hr 24/100 = 0.24 gallons/emitter/hr.
Pressure compensating emitters  provide the best uniformity.
Flow rate from each emitter and emitter spacing can be used to calculate rate per area.
Drip irrigation systems are usually operated every day or every few days to maintain optimal soil moisture.
The efficiency of your system is a measure of how much you have to over-water the wettest spots in the field to get adequate water to the dry spots.
Efficiency is related to the uniformity of application and to the amount of evaporation that occurs before the water can move into the soil.
A well-designed drip system can be 70 to 90% efficient.
Overhead sprinkler systems are typically 60 to 75% efficient, while flood and furrow irrigation is
 typically 30 to 50% efficient.
If your water supply is limited, a more efficient system can make a large difference in water savings and crop productivity.
Following is an example of how to calculate water needs for a head lettuce crop in Farmington, Utah, with a full canopy  in June.
The soil is a deep sandy loam with drip irrigated beds every 3 feet.
Water use  o
 ETr values are 0.30 inch/day.
Crop coefficient is 0.90.
ETcrop = ET X Kcrop
 ETcrop = 0.30 inch/day * 0.90 = 0.27 inches/day
 Soil storage capacity 
 The total storage capacity for readily available water over the 1.5 foot effective rooting depth is 1.5 inches.
1.5 inches / 0.27 inch per day = 5.55  days between irrigations.
In 5 days replace 1.5 inches.
Restated, the soil moisture in the rootzone will go from field capacity to plant stress levels in 5.55 days.
Good irrigation management requires:
 1.
An understanding of the soil-plant-water relationship
 2.
A properly designed and maintained irrigation system, and a knowledge of the efficiency of the system
 3.
Proper timing based on
 a.
Soil water holding capacity
 b.
Weather and its effects on crop demand
 c.
Stage of crop growth.
Each of these components requires a commitment to proper management.
Proper management will lead to the
 maximum yields per applied irrigation water, and will optimize the long term health and productivity of your crop.
Surface Irrigation  Inches/hour = cubic feet per second  / acres Example: 4 cfs / 5 acres = 0.8 inches/hour
 Drip Irrigation  Inches/hour = 1.6 * gallons per hour /emitter spacing  Example: 1.6 * 0.5 gph /  = 0.18 inches/hour
 Irrigation Set Times Set time  = Gross Irrigation Need  / application rate  Example: 3 inches / 0.28 inches/hour = 10.7 hours
 Conversions 1 cfs = 448.8 gpm 1 gpm = 60 gph 1 acre = 43,560 feet^2
 This project is funded in part by USDA-Risk Management Agency under a cooperative agreement.
The information reflects the views of the author and not USDA-RMA.
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This publication is issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Kenneth L.
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Corn at the beginning dent stage needs five inches of water to reach maturity.
Using the silt loam soil from above, the example field would have enough water to reach maturity and have an estimated 0.3 inches to spare if the corn is beginning to dent now.
The loamy sand, at field capacity, would have 2.6 inches available above the 40%  level.
This field would need an additional 2.4 inches of water to reach maturity.
With this in mind, we can set up some trigger dates to assess moisture levels and pasture conditions, informing the implementation of a drought management plan.
July 15: Precipitation after this date will have limited benefit to warm-season tallgrass production but can still result in some forage growth from shortgrass warm-season species such as buffalograss and blue grama.
For sugarbeets in the 10-30% Cover crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.17 inches and the estimated water use during the week of June 19-25, 2023 is 1.20 inches.
For sugarbeets in the 30-50% Cover crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.25 inches.
For sugarbeets in the 50-70% Cover crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.40 inches.
Chapter: 28 Common Fertilizers Used in Corn Production
 Many South Dakota farmers spend $170/acre per year on fertilizers.
Reducing these costs requires an understanding of the available products.
Fertilizer can be solid, liquid, and gas, each with unique strengths and weaknesses.
This chapter discusses the different commercially available fertilizers and provides examples on how to determine the cost of nutrients contained within the fertilizer.
Nitrogen can be lost through three major mechanisms: leaching, volatilization, and denitrification.
Different inhibitors are needed for each mechanism.
Nitrification inhibitors can be used to reduce leaching and nitrification losses, whereas urea hydrolysis inhibitors can be used to reduce ammonia volatilization losses.
Nitrification inhibitors slow the conversion of ammonium to nitrate.
Nitrate, which is a negatively charged ion can be leached  through negatively charged soil.
Denitrification is the conversion of nitrate to N gas.
In corn production, leaching and denitrification losses are highest when soil water content is high.
A commercially available nitrification inhibitor, Nitrapyrin, can be purchased as N-Serve or InstinctTM, whereas Docyandiamide  can be purchased in SuperU.
Nitrification inhibitors generally are not recommended when the fertilizer is applied as a sidedressed application.
Urea hydrolysis inhibitors slow the conversion of urea to ammonium, which in turn slow volatilization losses.
Urea inhibitors include NBPT and Agrotain.
Slow-release fertilizers release only a portion of the fertilizer immediately.
Commercially available products include ureaform , which is a combination of urea with formaldehyde; sulfur-coated urea ; isobutylidene diurea ; and polymer-coated urea.
The higher cost of these materials may warrant their use for high-value crops such as vegetables, fruits,
 and ornamentals.
Slow-release N fertilizers are used: 1) to improve fertilizer efficiencies where N losses  are high, 2) to overcome the need for multiple application dates, or 3) in crops where delayed nutrient release is desirable.
Additional information on slowand controlled-release fertilizer is provided by Lui et al..
This product may have limited availability, and it is the only commonly used solid fertilizer that contains N in the NO 3 form.
The chemical formula for ammonium nitrate  is NHNO33' Ammonium nitrate is a hazardous material because it can become combustible if it comes in contact with petroleum, diesel fuel, herbicides, pesticides, elemental S, or powdered metals.
Because ammonium nitrate absorbs water from the air, it should be stored carefully.
Products such as urea ammonium nitrate  contain AN but are considered safe for widespread use.
Ammonium sulfate has a lower risk of volatilization than urea and is a good product in high pH soil.
Ammonium sulfate will lower the soil pH faster than urea and it can be used to provide S in sulfurdeficient soils.
The primary disadvantage is that it requires more lime to neutralize the acidity produced during nitrification than other N fertilizers.
Its cost per unit of N is generally higher than urea.
The main benefit of AMS is using it to supply the crop's sulfur requirements while receiving a nitrogen credit.
These are liquid fertilizers with grades that range from 28-0-0 to 32-0-0.
These solutions are mixtures of urea and ammonium nitrate.
Because the risk of precipitation decreases with increasing temperature, UAN solutions are made more dilute in regions with cold winter temperatures.
These solutions do not have a vapor pressure and can be sprayed or dribbled onto the soil surface.
The UAN solution, 28-0-0, is nonflammable, nontoxic, and therefore is relatively safe and easy to handle, ship, and store.
However, these fertilizes can be corrosive to some metals.
UAN is well-suited for in-season N application, and the density is used to convert gallons to pounds.
A rule of thumb for UAN  is that one gallon of fertilizer contains 3 lbs of N.
Example: 0.8 lbs/gal*.28=3.024 lbs N/gal).
When applied to the soil, volatilization losses are highest when applied to warm, high pH soils.
When applied to soils with high residue, some of the N will likely be immobilized by the residue.
To reduce this risk, broadcast applications are not recommended in high-residue soils.
Immobilization can be reduced in high-residue soils by surface or subsurface banding
 In the manufacturing of N fertilizers, atmospheric N is combined with H+ to form anhydrous ammonia.
NH3 is a colorless gas with a grade of 82-0-0.
Anhydrous ammonia  is typically the most
 inexpensive, commercially available N fertilizer.
To assure stability in the soil, injection is required for this N source.
When applied to soil, it is rapidly converted to NH +1 In addition to its use as a fertilizer, it is a key ingredient in the illegal production of methamphetamine.
When using this material, always follow safety protocols.
The production of most commercial phosphate fertilizers begins with the conversion of rock phosphates to phosphoric acid.
Ammonia is then added to superphosphoric acid to create the liquid, 10-34-0.
Liquid ammonium phosphate , can be mixed with a finely ground potash , water, and UAN solution  to form many different grades of fertilizer.
The addition of ammonia with phosphoric acid produces a slurry that is solidified to produce monoammonium phosphate  or diammonium phosphate.
It is important to consider that P fertilizers are produced from rock phosphate, which is mined.
These resources, like oil, are limited.
Table 28.3 presents guidance for the use the P fertilizers.
The United States is one of the leading producers of apatite.
Plant-available P consists of water and citrate-soluble P.
Water-soluble P is the P solubilized in water, while citrate-soluble P is the amount of nonwater-solubilized P that is solubilized when placed in citrate.
Fertilizer can also contain polyphosphate and orthophosphate forms.
Polyphosphate  is produced by heating orthophosphate  to remove the water.
This process converts 40% to 60% of the ortho-P to poly-P.
MAP fertilizer grades range from 11% to 13% N and 48% to 55% for P2O5 If pure, MAP [H,PO4] would have a fertilizer grade of 12.2-61.7-0.
MAP contains less ammonia than DAP, making it a preferred pop-up fertilizer.
Depending on the manufacturing process, it may contain some sulfur.
MAP is watersoluble and when added to soil, NH + and H2PO4 ions are formed.
The acidity of this product reduces the risk of ammonia volatilization.
Map is a good fertilizer to use as a pop-up.
It should not be mixed with calcium  and magnesium  fertilizer when applied with irrigation water.
Clumping and caking can be reduced by using chemical conditioners.
Purified products may be used as a feed additive, and it may be found in dry chemical fire extinguishers.
The fertilizer grade of DAP can range from 18% to 21% N and 46% to 53% P2O5 If pure, DAP [HHO would have a grade of 21.2% N and 53.8% P2O5 2 Depending on the manufacturing process, it may also contain some sulfur.
DAP is water-soluble and when added to soil, the NH4 + and H2PO4 ions are formed.
The area surrounding the dissolving fertilizer granule is slightly alkaline.
The impact of DAP on seed germination is greater in basic than acid soils.
Ammonia volatilization risk with this product is minimal.
This material is produced by reacting phosphate rock with nitric acid.
The products are phosphoric acid and calcium nitrate.
Depending on the requirement, a range of products is available.
These products attract moisture, SO they should be stored carefully to prevent caking.
Polyphosphates contain orthophosphate and polyphosphate.
Two common ammonium polyphosphate fertilizers have an N-P2O-K2O composition of 10-34-0 or 11-37-0.
This is a liquid fertilizer that does not require special handling and storage.
However, it can be corrosive, SO storage and handling equipment should be made of resistant materials.
With time, polyphosphate splits apart.
A general guideline is to minimize storage time and avoid storage over summer.
Aqua or Anhydrous Ammonia is not compatible with 10-34-0.
Polyphosphates  can be sprayed on to the soil surface and incorporated into the
 soil.
The salting-out temperatures, where precipitation can occur, for 10-34-0 and 11-37-0 are 0F and 32F, respectively.
Rules of thumb for P fertilizers include that:
 1.
MAP and DAP are soluble in water.
2.
Manure can add a significant amount of P to the soil.
Generally, P from organic sources is slightly less available when compared with dry or liquid fertilizers.
In the year following manure applications, 60% to 80% of the P is typically available to the plant.
3.
Orthophosphate or polyphosphate fertilizers are produced by removing the water from phosphoric acid.
a.
The resulting products contain approximately 40% to 60% orthophosphate with the remaining portion in the polyphosphate form.
b.
Examples of fertilizers containing orthophosphates  are MAP and DAP.
C.
Polyphosphates have the chemical formula HPPO 10' and fertilizer grade of approximately 10-34-0.
d.
The P in orthophosphates and polyphosphates is generally considered plant available.
Potassium chloride  is often referred to as potash.
The color of potash can vary from pink or red to white.
White potash is often higher in K analysis.
One of the advantages of potash is that it often provides chlorine, which may provide disease resistance.
Potassium chloride is approximately 47% chloride.
Other fertilizers providing Cl-1 are ammonium chloride , calcium chloride , magnesium chloride , and sodium chloride.
This material should be stored in a dry location.
Heat or cold will have little effect on this fertilizer, and KCl can be blended with a variety of N and P fertilizers to make grades such as 10-30-10, 8-24-24, or 1313-13.
KCl is readily soluble in water and can be applied as a liquid fertilizer.
A range of different S products are available.
The most concentrated fertilizer is elemental sulfur.
To make it available to the plant, it must be oxidized:
 S + 1.5O2+H2O 2H+ + SO + energy
 Elemental S is often used in sodic  soil remediation.
Other solid S sources are gypsum , ammonium sulfate , and potassium sulfate.
Two liquid S fertilizer products are ammonium polysulfide and ammonium thiosulfate.
Ammonium polysulfide is a dark-red solution that contains about 20% N and 40% S.
Ammonium polysulfide has a density of 9.4 lbs/gal and can be mixed with ammonia solutions.
Ammonium thiosulfate  has a density of 11.1 lbs/gal and is compatible with aqua ammonia and UAN.
This fertilizer should not be placed in contact with a seed or mixed with anhydrous ammonia or phosphoric acid.
When this fertilizer is mixed with UAN, the rate that the urea is hydrolyzed (urea-N NH may be slowed, which in turn can reduce N losses.
Chlorine can be applied with potassium chloride , which is 47% chloride, ammonium chloride , calcium chloride , and magnesium chloride.
In many situations, compound fertilizers are applied to soils.
These fertilizers can provide macronutrients and micronutrients.
Many custom blends of N-P2O-K2O are available.
Common dry blends are 20-10-10, 10-20-20, 8-32-16, and 6-24-24.
With dry-blended fertilizers, segregation can occur when these materials are transferred from a bin to a truck or a truck to a bin.
A compound fertilizer is typically a solid product that contains multiple nutrients within each granule.
These fertilizers differ from blends, where the fertilizers were mixed together.
Compound fertilizers are often more expensive than blended fertilizers.
Manure is an excellent source of nutrients in agricultural systems.
Different livestock handling systems are more efficient than others at returning nutrients to the soil.
Average amounts of N and P2O5 contained in different manures are shown in Table 28.3.
Manure can be used to provide the plant nutrient requirements in organic agriculture.
Manure has the added benefit of adding organic matter to soil, which should improve soil heath and water-holding capacity.
Manure should be incorporated into the soil to minimize nutrient losses.
Determining the Lowest Cost Fertilizer Mixture
 There are many different fertilizer formulations commercially available.
The question is, which is least expensive?
Example 1.
Urea co $450/ton, what is the price per pound of N.
$450 pound 2000 lbs 0.46 lbs N
 Example 2.
Ammonium sulfate  costs $375/ton.
Solution a.
Assume the S does not have a value.
$375 1 pound 2000 X 0.21 lbs N
 Solution b.
Assume each lb S has a value of $0.25.
Calculate the value of the S
 0.21 lb S $0.25 2000 lbs fertilizer 1 pound X 1 lb S =105
 Subtract value of S from the cost of the fertilizer and calculate cost of N
 $270 lb pound 2000 lbs X 0.21 lbs N
 Additional examples of calculations for determining the lowest-cost material are available in Clay et al..
When investing in new irrigation technologies , it is important to understand what the benefits are for both the producer and the watershed.
The various components of the water cycle help explain how changes at the field scale impact water resources at the watershed scale.
Consumptive use of water is a particularly important topic for making this connection; however, consumptive use tends to be a difficult concept to grasp.
The CPC national precipitation forecast indicates a moderate risk for below-normal temperatures for an area from eastern North Dakota southward through the eastern half of Texas on the western periphery and from Michigan southward through the western half of Alabama on the eastern periphery.
On a positive note, Colorado is directly underneath a predicted area of above-normal precipitation, which includes the headwater region of the Platte River system that has been drawn down the past three years due to ongoing drought issues and high irrigation demand.
MANAGEMENT FOR REDUCED IRRIGATION DIVERSIONS
 Irrigation scheduling should be the first tool selected and used when reducing irrigation diversions.
Irrigation micromanagement decisions about season initiation and termination are important ways to reduce irrigation diversions.
Cultural practices can affect the success of reduced irrigation diversions.
Irrigation diversions vary widely between years.
Common conditions within the Central Great Plains affect the ability to reduce irrigation diversions.
Irrigation water is diverted to augment natural precipitation and soil water reserves for the provision of crop water needs.
In the Central Great Plains region, these diversions are coming into increased scrutiny as both ground and surface water supplies are becoming increasingly stressed.
These stresses can be entirely hydrologic in nature , institutional  or a combination of the two.
Often the appropriate management strategy to deal with the reduction in irrigation diversions will be affected by what is causing the stresses on the water resources.
There is a myriad of scenarios that can be considered for management for reduced irrigation diversions, many more than can be considered in the scope of this paper.
For that reason, this paper will limit discussion to common conditions in the Central Great Plains region.
The discussion will focus on irrigated corn production on the deep silt loam soils with a semi-arid climate with a summer-dominant precipitation pattern.
The discussion will also focus primarily on corn production under center pivot sprinkler irrigation, although subsurface drip irrigation may be used to emphasize some specific concepts.
The title connotes that the discussion will also be centered on scenarios where irrigation is being reduced, possibly subjecting the corn crop to deficit irrigation.
All these limitations to the discussion are necessary to keep a reasonable scope to the paper, but they do not always match the conditions for an individual producer.
A broader listing of management tools for deficit irrigation of grain and oil seed crops was provided by Lamm et al., 2014, but that publication chose to limit the discussion more-or-less to the listing of tools.
In this paper, a more thorough discussion on the use of some of those tools will be provided, particularly those appropriate for the aforementioned common conditions.
THE NEED FOR IRRIGATION SCHEDULING
 The most common definition of irrigation scheduling is simply the determination of when and how much water to apply.
Modern scientific irrigation scheduling uses a single approach or combination of weather-, soilor plantbased approaches.
Science-based irrigation scheduling has existed for approximately 65 years with one of the earlier discussions of the topic made by van Bavel  of using evapotranspiration to estimate soil water conditions and for timing of irrigation.
Modern scientific irrigation scheduling uses a single approach or combination of weather-, soilor plant-based approaches.
All of these approaches are acceptable and greatly enhance the ability of the irrigator to manage reduced irrigation diversions.
In fact, few if any of the following management approaches discussed in this paper will have much merit when attempted without using scientifically-based, season-long, dayto-day irrigation scheduling.
The rationale for the previous statement will be discussed in the following paragraphs condensed from Lamm and Rogers, 2015.
Although there is a wide body of literature on irrigation scheduling in reference books, journal articles, symposium proceedings, and extension publications, effective methods have not been well adopted by irrigators.
When the accuracy of irrigation scheduling is perceived to be an issue, there is a great impediment to adoption since the economic penalty of over-applying water is usually many times less than that of under-applying water.
Lack of confidence by the irrigator can be the result of changes in cultural practices that affect the field water budget or introduction of new drought resistant varieties or hybrids that seem to indicate a change in the water use of the crop.
An example is drought resistance corn, which is often misinterpreted by irrigators as a corn that needs less water, while actually it may just mean the hybrid may tolerate water stress better.
Figure 1.
Effect of irrigation inaccuracy on crop production points.
Adapted from discussion and graph in Lamm  and provided here after Lamm and Rogers.
Additionally, irrigators, economists, and water planners often want to simplify the question of "How much irrigation water do I need?" to a single annual value when in reality there is no single answer.
Furthermore, as indicated in Fig.
2, averaging several years of data will result in a smooth yield/water response curve that has very little basis for obtaining good yields in a given year.
Fortunately, with science-based irrigation scheduling, irrigators do not need to use average values.
The Kansas USDA-NRCS officially adopted KanSched, developed at Kansas State University, as an approved ET-based irrigation scheduling program and has offered cost share incentives to encourage irrigator adoption of based scheduling and have required adoption as an eligibility requirement for other irrigation improvement cost-share programs.
Figure 2.
Corn yield response to subsurface drip irrigation  amount in seven different years, KSU Northwest Research-Extension Center, Colby, Kansas.
The boldface curve is the average of all seven years emphasizing that average values are insufficient for irrigation management in an individual season.
All years were scheduled according to daily ET-based water budget with individual data points representing differences in available irrigation capacity.
After Lamm and Rogers.
Many irrigators have been unwilling to set aside much time to manage water.
They often feel that if their irrigation capacity is appreciably less than crop water needs, they need to operate their irrigation systems continuously during the growing season.
Although, there are a large number of marginal capacity irrigation systems in the region, there remains opportunities to delay unnecessary irrigations by using ET-based irrigation scheduling.
Simulation modeling has indicated adoption of ET-based irrigation scheduling with an initial soil water condition of 85% of field capacity and 95% application efficiency potentially could save
 on average 8.34 inches water for a 1 inch/4 days irrigation capacity  and 2.80 inches for a severely deficit 1 inch/8 day irrigation capacity.
Irrigators with marginal capacity systems should adopt science-based irrigation scheduling to make best use of their limited irrigation and should not discount their opportunity to save irrigation water even when their system restrictions are severe.
A greater portion of the potential irrigation savings occurs during the early part of the irrigation season and after that period, irrigation water savings are incrementally increased as the season progresses, increasing during cooler, more humid periods and decreasing during warmer and drier periods with a saw-tooth pattern as irrigation events occur.
This emphasizes the need to use season long, day-to-day irrigation scheduling.
Figure 3.
Average savings of irrigation that could be obtained with ET-based irrigation scheduling as compared to maximum seasonal applications possible with various irrigation capacities for an application efficiency of 95% and an initial soil water condition of 85% of field capacity as determined in simulation modeling for 43 years of weather data , Colby, Kansas.
After Lamm and Rogers.
IRRIGATION MACROMANAGEMENT ASPECTS OF SEASON INITIATION AND SEASON TERMINATION
 There are larger irrigation management decisions [i.e., irrigation macromanagement ] that can be considered separately from the step-by-step, periodic scheduling procedures.
Two important macromanagement decisions occur at the seasonal boundaries, the initiation and termination of the irrigation season.
Irrigators sometimes make these seasonal boundary determinations based on a traditional time-of-year rather than with sound rationale or sciencebased procedures.
However, a single, inappropriate, macromanagement decision can easily have a larger effect on total irrigation water use and/or crop production than the cumulative errors that might occur due to small, systematic errors in science-based, day-to-day irrigation scheduling procedures.
INITIATION OF THE IRRIGATION SEASON
 The corn vegetative stage is often considered the least-sensitive stage to water stress and could provide the opportunity to limit irrigation water applications without severe yield reductions.
The vegetative stage begins at crop emergence and ends at tasseling, which immediately precedes the beginning of the reproductive period when the silks start to emerge.
Important yield components such as the ears/plant and the potential number of kernels/ear are established during this period.
Stresses during the 10 to 14 days after silking will reduce the potential kernels/ear to the final or actual number of kernels/ear.
Therefore, in research studies designed to examine water stresses during the first one-half of the corn crop season, both ears/plant and kernels/ear are critical factors.
Additionally, there could be permanent damaging effects from the vegetative and earlyreproductive period water stress that may affect grain filling.
Often, irrigators in the Central Great Plains, start their corn irrigation season after early season cultural practices are completed.
Crop evapotranspiration is beginning to increase rapidly and drier weather periods are approaching, so often there is soil water storage that can be replenished by timely irrigation during this period for use later in the summer.
However, this does not always mean that the corn crop required the irrigation at that point-in-time.
Numerous years of research has indicated that when considering early season crop water stress, the number of kernels/area  is a good surrogate for correlation with the final grain yield.
In other words, the number of kernels per unit area has to be maximized to ensure that grain yield can be maximized.
Maximizing the relative kernels/area was found to be related to the minimum plant available soil water  occurring in the month of July at Colby, Kansas in long term studies.
Figure 4.
Relative kernels/area as affected by July minimum available soil water in the top 4 ft of soil in an early-season corn water stress study, KSU-NWREC, Colby, Kansas, 1999-2007.
The upper  and lower  lines are manually drawn to illustrate years with larger and smaller July evaporative demand.
After Lamm and Aboukheira.
In some years, ASW in the top 4 feet could be depleted as much as perhaps 60% without an effect on relative kernels/area , while in other years reductions began to occur at 30 to 40% reduction in ASW.
When crop evapotranspiration  was greater, a higher level of
 soil water  was required.
These results would match known theories of water stress and water flow through plants.
These results once again emphasize the need for science-based, season long, day-to day irrigation scheduling so that the producer has information about whether crop water stress might be affecting the kernels/area.
It should be noted the data in Figure 4 are from subsurface drip irrigation studies where the water stress after silking was alleviated with daily irrigation amounts of 0.4 inches/day until such time that the ASW was restored to near field capacity.
Alleviating the water stress in this manner is not practical with other types of irrigation systems as irrigation runoff from heavy, frequent irrigation will result in excessive runoff.
The deep silt loam soil profiles of the Central Great Plains region will store considerable amounts of ASW for later usage.
Using ET-Based irrigation scheduling and /or soil water measurements for scheduling, the producer can manage this soil water "bank", sometimes banking water in the vegetative period before the critical reproductive  period.
This runs a bit counter to the earlier statements in this section and that are widely held in older publications about the vegetative period being an opportunity to cut back on water.
However, the criticality of establishing the maximum kernels/area expressed in Figure 4, the common presence of deep silt loam soil profiles, and the discussion in the following paragraphs strongly challenge those older assumptions.
Sprinkler irrigation does not 16 allow for large amounts of 14 Colby, Kansas, 1972-2010 water to be timed to a specific growth stage 12 39.39 North, 101.07 West Anthesis, July 20  without incurring runoff, so 10 strategies must be employed that can slowly 8 PostAnthesis, 8.69 inches restrict or slowly increase 6 water available to the crop 4 PreAnthesis, 5.85 inches and to soil water storage for 2 later usage.
Preliminary computer simulation 0 indicated that on average, approximately 40% of the 0 20 40 60 80 100 120 seasonal irrigation amount is Days Post Emergence  required prior to silking , so a study was conducted to at Colby, Kansas for the preand post anthesis determine if an imposed  periods.
After Lamm.
reduction of 50% during the presilking period might be acceptable most years, yet not be excessive in the drier years.
However, this does not fully reflect the ability of the soil profile to be a "bank," so examining a higher irrigation regime was also warranted.
Corn production was compared under five different irrigation regimes in a three-year  field study on a deep silt loam at the KSU Northwest Research-Extension Center at Colby, Kansas.
The irrigation regimes were:
 1) Full irrigation  with no restriction on total irrigation
 2) Irrigation restricted pre-silking to 50% of ET, 100% of ET thereafter with 11.5 inches total restriction
 3) Irrigation restricted pre-silking to 75% of ET, 100% of ET thereafter with 11.5 inches total restriction
 4) Irrigation restricted post-silking to 50% of ET with 11.5 inches total restriction
 5) Irrigation restricted post-silking to 75% of ET with 11.5 inches total restriction
 Irrigation amounts of 1 inch/event were scheduled according to water budget weather-based irrigation scheduling procedures only as needed subject to the specific treatment limitations.
As an example, during the pre-silking stage Irrigation Trt 3 would only receive 75% ET, but after silking would receive irrigation at 100% until such time that the total irrigation is 11.5 inches.
Full irrigation amounts varied from 12.48 inches in 2014 to 15.36 inches in 2013.
The irrigation treatments with pre-silking water restrictions  reached their water limitation  in two of the three years  as did the post-silking deficit irrigated treatment that was irrigated with 75% of ET during the postsilking period.
The irrigation treatment using the least amount of water during the three years of the study was the treatment where irrigation was restricted to 50% of ET during post-silking period.
Fully irrigated corn grain yields ranged annually from 241 to 251 bushels/acre with the deficitirrigated lowest yields ranging from 215 to 237 bushels/acre.
Corn yield was greatest for unrestricted irrigation  but required 30 to 36% more irrigation, but was still very efficient with only a 2 to 4% reduction in crop water productivity.
Lower yields occurred for pre-silking water restrictions  than for similar post-silking restrictions.
These results suggest that obtaining sufficient kernel set  was more important than saving irrigation for grain filling  in this study.
When irrigation is greatly restricted, a 50% reduction post-silking appears as a promising alternative, relying more heavily on stored soil water and precipitation for grain filling.
Summarizing this study , it appears that if water is limited, there are better opportunities to save water during the post-silking period by relying on stored soil water , occasional precipitation, while moderately reducing the irrigation during this period.
This conclusion relies heavily on the common conditions typically occurring in the Central Great Plains that were expressed in the Introduction.
TERMINATION OF THE IRRIGATION SEASON
 Similarly to the initiation of the irrigation season, the termination of the irrigation season is considered to present opportunities to reduce irrigation diversions.
Plant water stress can cause kernel abortion if it occurs early enough in the post-silking period but is more often associated with poor grain filling and thus reduced kernel mass.
Grain kernel mass is termed as a very loosely restricted yield component , meaning that it can be manipulated by a number of factors.
The final value is also set quite late, essentially only a few days before physiological maturity.
The rate of grain filling is linear for a relatively long period of time from around blister kernel to near physiological maturity.
Yield increases of over 4 bushels/acre for each day are possible during this period, so a premature termination of the irrigation season can be quite costly.
Providing good management during the period can help to provide a high grain filling rate and, in some cases, may extend the grain filling period a few days thereby increasing yields.
Availability of water for crop growth and health is the largest single controllable factor during this period.
However, the rate of grain filling remains remarkably linear unless severe crop stress occurs.
This is attributed to remobilization of photosynthate from other plant parts when conditions are unfavorable for making new photosynthate.
Four separate studies were conducted at the KSU Northwest Research-Extension Center at Colby, Kansas over the years 1993 through 2008 to examine the effects of post-silking water stress on corn.
Prior to silking, all treatments in each of the studies were fully irrigated according to their need.
Results from the studies indicate that silking for corn in Northwest Kansas varies from July 12 to July 24 with an average date of July 19.
Physiological maturity ranged from September 14 through October 10 with an average date of September 27.
The average length of the post-silking period was approximately 70 days.
Using the corn grain yield results from the studies and the individual treatment irrigation termination dates responsible for those yields, Table 1 was created to indicate the problems with using inflexible dates for determining the irrigation season termination date.
Additionally, the corn grain yield results and the treatment irrigation dates were used to estimate the date when a specified percentage of maximum grain yield would occur.
Because there was not an unlimited number of irrigation treatment dates, there are years when the date required for a specified percentage of maximum grain yield was the same as the date for the next higher percentage.
The average estimated termination date to achieve 80, 90, and 100% of maximum corn grain yield was August 2, 13, and 28, respectively, but the earliest dates were July 17, July 17 and August 12, respectively, while the latest dates were September 14, 21, and 21, respectively.
Irrigators that use average or fixed dates to terminate the corn irrigation season are not realistically considering the irrigation needs of the corn that may be greater or smaller in a particular year, and thus, often will neither optimize corn production, nor minimize water pumping costs.
These results once again emphasize the need for science-based, season long, day-to day irrigation scheduling so that the producer has information about when he can safely end the irrigation season.
Table 1.
Anthesis and physiological maturity dates and estimated irrigation season termination dates* to achieve specified percentage of maximum corn grain yield from studies examining post-anthesis corn water stress, KSU Northwest Research-Extension Center, Colby, Kansas, 1993-2008.
Note: This table was created to show the fallacy of using a specific date to terminate the irrigation season.
Note: Because there was not an unlimited number of irrigation treatment dates, there are years when the date required for a specified percentage of maximum grain yield was the same as the date for the next higher percentage.
Adapted from Lamm and Aboukheira.
Date of	Date of	Irrigation Season Termination Date For
 Anthesis	Maturity	80% Max Yield	90% Max Yield	MaxYield
 Average	19-Jul	27-Sep	2-Aug	13-Aug	28-Aug
 Standard Dev.
3 days	6 days	13 days	19 days	13 days
 Earliest	12-Jul	14-Sep	17-Jul	17-Jul	12-Aug
 Latest	24-Jul	10-Oct	14-Sep	21-Sep	21-Sep
 Estimated dates are based on the individual irrigation treatment dates from each of
 the different studies when the specified percentage of yield was exceeded.
When termination of the irrigation season allowed the minimum soil water  fraction to fall below approximately 65% of field capacity, there was a tendency for decreased yields.
Mininum Post-Anthesis Available Soil Water
 Figure 8.
Relative corn grain yield as affected by the minimum value of available soil water  within the 8 ft soil profile occurring during the post-anthesis  period.
Data are from various studies examining the effect of post-silking corn water stress, KSU Northwest Research-Extension Center, Colby, Kansas, 1993-2008.
After Lamm and Aboukheira.
Producers in the Central Great Plains should plan for post-silking water use needs of approximately 17 inches and that water use during the last 30 and 15 days of the season might average nearly 5 and 2 inches, respectively.
This water use would need to come from the sum of available soil water reserves, precipitation, and irrigation.
When irrigation losses are minimized, a percentage decrease in post-silking water use will result in nearly a one-to-one percentage decrease in corn grain yield.
Producers growing corn on deep silt loam soils in the Central Great Plains should attempt to limit management allowable depletion  of available soil water in the top 8 ft of the soil profile to approximately 35%.
CORN RESPONSE TO TILLAGE, PLANT DENSITY AND IRRIGATION REQUIREMENTS AND IRRIGATION CAPACITY
 Tillage management strategies that leave greater amounts of residue on the soil surface are beneficial in sprinkler-irrigated corn production in terms of improving infiltration of both irrigation and rainfall, and in reduction of soil evaporative losses early in the growing season.
Additionally, sometimes early season crop growth is delayed under higher residue conditions and this can result in the shifting of crop evapotranspiration to later in the season for higher residue treatments.
Irrigation requirements and corn water use are typically not affected by plant density  changes in the range of typical economical corn production in the Central Great Plains region.
A four-year study was conducted at KSU Northwest Research-Extension Center, Colby, Kansas to evaluate corn production as affected by tillage management , plant density  and irrigation capacity.
For brevity data in Figure 9 and 10 are averaged across the experimental factors.
The reader is referred to Lamm et al.
for a more detailed examination of the study results.
Reduced or no-tillage increased corn grain yields over conventional tillage and increased plant density was also beneficial.
As anticipated there was some yield reduction with decreased irrigation capacity.
Figure 9.
Corn grain yield as affected by irrigation capacity, tillage treatment and target plant density in a sprinkler-irrigated research study, KSU Northwest Research-Extension Center, Colby, Kansas, 2004-2007.
After Lamm.
Crop water use was greater with strip tillage and no-tillage probably because their plants did not senesce as early in the season as the conventional treatment.
Plant density did not affect corn water use as would be anticipated at these plant densities.
Plant density would likely need to be decreased to 20,000 to 24,000 plants/acre or less before crop water use would decrease.
However, lower plant densities can sometimes help under extreme drought conditions to ensure pollination, though crop water use is unaffected.
Crop water use was affected by irrigation capacity as would be anticipated.
Figure 10 Corn water use as affected by irrigation capacity, tillage treatment and target plant density in a sprinkler-irrigated research study, KSU Northwest Research-Extension Center, Colby, Kansas, 2004-2007.
After Lamm.
IRRIGATION REQUIREMENTS AND IRRIGATION CAPACITY
 Corn grain yields are obviously sensitive to reductions in irrigation below a criticial threshold.
It is common for the slope of the water production function for corn under deficit irrigation to be 12 to 15 bushels/inch and values of nearly 20 bushels/inch have been reported, so it is imperative that deficit irrigation not be too severe to remain in profitable production.
Corn yields were simulated for 42 years  of weather data from Colby, Kansas.
Well-watered corn ETc ranged from 17.6 to 27.1 inches with average of 23.1 inches for these 42 years of record.
In-season precipitation ranged from 3.1 to 21.2 inches with average of 11.8 inches.
Full irrigation ranged from 6 to 22 inches with average of 15.7 inches.
The marginal WP  was 17 bu/acre-in, which might result in an economic benefit of 65 to $85/acre-in.
The yield threshold was 10.9 inches of ETc.
Yields were simulated for irrigation capacities of full irrigation, 1 inch every 4, 6, 8, or 10 days and also for dryland conditions.
As irrigation capacity decreases , corn yields decrease from the fully irrigated yields for some years and the variability in yields also increases.
Typically, crop yields increase with increasing ETc, although this response in not a direct cause and effect.
Rather in many cases, increased ETc is also reflecting better growing conditions.
As irrigation capacity decreases, the positive aspects of greater ETc on yield begins to disappear and the slope is relatively flat for an irrigation capacity of 1 inch/10 days.
Under dryland conditions, corn yields typically decreased over the entire range of increasing ETc experienced at Colby, Kansas during this 42-year period.
Well-watered corn ETc 
 Figure 11.
Simulated corn yields as a function of the calculated well-watered corn evapotranspiration for the 42-year period, 1972-2013, Colby, Kansas as affected by irrigation capacity.
Table 2.
Effect of irrigation capacity on simulated corn yields for the 42-year period, 1972-2013, Colby, Kansas.
Yield variation from full irrigation
 Irrigation	Maximum	Mean	Minimum	for maximum yield at maximum
 capacity	yield	Yield	Yield	well-watered ETc
 Full	273	204	112
 1 inch/4 day	261	202	112	-4.4%
 1 inch/6 day	226	181	112	-17.2%
 1 inch/8 day	216	162	103	-20.9%
 1 inch/10 day	202	148	94	-26.0%
 Dryland	138	77	23	-49.5%
 When irrigation is carefully managed with efficient irrigation systems, such as subsurface drip irrigation , corn grain yield and crop water productivity both often begin to plateau with irrigation levels  in the range of 80% of full irrigation.
The aspect of maximum water productivity with irrigation levels of 80% was also reported by Howell.
Figure 12.
Relative corn grain yield for a given SDI research study and year as related to the fraction of full irrigation, KSU Northwest Research-Extension Center, Colby, Kansas.
After Lamm.
Figure 13.
Relative water productivity  of corn for a given SDI research study and year as related to the fraction of full irrigation, Colby, Kansas.
After Lamm.
This suggests that both waterand economically-efficient production potentially can be obtained with irrigation levels of approximately 80% of full irrigation across a wide range of weather conditions in many years on the soils in this region.
The weather conditions in the individual years can have a large effect on corn grain yield as affected by irrigation system type and irrigation capacity.
Figure 4.
Corn yields for SDI and mid elevation spray application  sprinkler irrigation in wet years and dry years at Colby, Kansas.
Note: Results are from different but similar studies, so these are not statistical differences.
Science-based, season long, day-to-day irrigation scheduling is a prerequisite to obtaining appropriate reductions in irrigation diversions.
Irrigation scheduling and the data associated with its implementation inform many of the other techniques to potentially reduce irrigation diversions.
Irrigation micromanagement decisions about irrigation season initiation and termination present large opportunities to reduce irrigation diversions, but they must be carefully determined using science-based information.
Cultural practices such as tillage management and selection of appropriate plant density can affect crop yield and water productivity under reduced irrigation diversions.
Irrigation requirements and the necessary irrigation capacity are quite variable between years.
Common conditions or characteristics of the Central Great Plains affect selection of water saving techniques.
This paper was first presented at the Central Plains Irrigation Conference, Feb.
18-19, 2019, Burlington, Colorado.
Rhoads F.
M.
and J.
M.
Bennett.
1990.
Corn.
Chapter 19 in Irrigation of Agricultural Crops.
pp.
569-596.
ASA-CSSA-SSSA, Mono No.
30, B.
A.
Stewart and D.R.
Nielsen.
1218 pp.
LEPA CONVERSION AND MANAGEMENT
 Leon New and Guy Fipps*
 Center pivot irrigation is used widely in Texas, largely because of the low labor requirements, improved water distribution, and relatively low capital costs on a per irrigated acre basis.
There are approximately 9,500 pivots in operation, irrigating 1.75 million acres.
Center pivot technology has developed greatly since it was patented in 1952.
Escalating energy costs in the 70s and 80s contributed to the development of more efficient pivot technology.
In certain areas of Texas, concern for the decline in underground aquifers and the long-term availability of water for irrigation has continued to foster the development and adoption of water conserving nozzles and pivot systems.
The LEPA concept grew out of efforts by agricultural engineers at Texas A&M University to develop a system that would reduce energy requirements of mechanical-move systems, while maximizing the use of both rainfall and applied irrigation water.
Since the concept was first introduced in 1981, LEPA has been transformed into various commercial products that are now installed on more than 400 pivots in the state.
LEPA is a highly efficient method of delivering water to crops from center pivot and linear move irrigation machines.
LEPA, which stands for Low Energy Precision Application, reduces water losses from wind drift and evaporation, improves yields and lowers energy costs for pumping.
In many situations, these benefits warrant the conversion of existing equipment to LEPA.
The extra cost of LEPA on a new center pivot is even more justified and should be carefully considered by prospective buyers.
LEPA discharges water through accurately designed and often pressure-regulated nozzles located from 8 to 18 inches above the furrow.
This low discharge point greatly reduces spray and drift losses caused by wind, low relative
 humidity and high temperature.
Water losses are only 2 to 3 percent, compared to at least 20 to 25 percent from typical impact sprinklers and low pressure drop nozzles.
For a center pivot operating at 800 gpm , this difference means that from 160 to 200 gpm more water will reach the ground and crop.
LEPA's lower operating pressure normally will significantly reduce pumping costs.
Twelve to 15 psi pivot pressure at ground level can be used for many quarter-mile systems on flat land.
Half-mile center pivots that carry 2,000 to 3,000 gpm can be designed for 20 to 30 psi pivot pressure.
Fuel consumption and costs have been found to average 15 to 20 percent less than for a center pivot equipped with low pressure spray heads, which is often 50 to 75 cents per hour less for quarter-mile units.
Table 1.
LEPA systems advantages and disadvantages compared to conventionally equipped center pivot systems.
1.
High Irrigation application efficiency 
 low wind drift losses
 at least 20 percent more water will reach ground/crop
 potential elimination of dry and wet areas
 ideal system for chemigation
 3.
Reduced wetting of foliage
 potential reduction in certain disease problems
 4.
Potential reduction in energy costs for pumping due to
 high irrigation application efficiency
 5.
Three modes of operation allows the placement of water/chemicals exactly where needed.
6.
Pivot tower wheel tracks remain dry when planting in a circle.
1.
Higher material and installation costs.
2.
Wetter soil conditions and runoff may occur without proper management; furrow diking and planting in a circle are recommended.
3.
Pressure regulators are generally required for proper nozzie flow.
*Extension agricultural engineers, The Texas A&M University System.
LEPA technology developed from efforts to find methods of reducing water and energy use in irrigated agriculture.
One aspect involved the elimination of the high spray evaporation losses common in Texas.
For instance, Clark and Finley  found that at a wind speed of 15 miles per hour  evaporative losses were 17 percent, and at speeds of 20 miles per hour losses were over 30 percent.
In the Southern High Plains, losses on a linear-move sprinkler system have been measured as high as 94 percent when wind speed averaged 22 miles per hour with gusts of 34 miles per hour.
Another aspect involved designing a system to be used in conjunction with micro-basin land preparation or furrow diking, which prevents runoff and maximizes the use of rainfall and applied irrigation water.
A double-ended sock  was developed to accomplish both goals.
No wind losses result since water is discharged directly into the furrow.
Also, the open ends help preserve the dikes.
However, this method can be used only for irrigation.
Figure 1.
Low pressure, double-ended sock designed to be used in conjunction with furrow dikes.
The sock prevents wind losses and helps preserve the dikes but can only be used for Irrigation.
Lyle and Bordovsky  of the Texas Agricultural Experiment Station in Lubbock conducted the first experimental work on LEP/ using a linear-move system.
In order
 to reduce erosion of the furrow dikes, the researchers developed prototype orifice controlled nozzles which operated in the 1 to 5 psi  range and discharged water at low velocities in a bubble pattern.
The orifices were attached to drops and located at a height of 2 to 4 inches above the furrows.
Water losses with this system were found to be only 2 to 5 percent, compared to 25 to 30 percent for the conventional sprinkler system.
On the experimental unit, a LEPA head was located in each furrow and furrow diking was used to increase surface storage to retain rainfall and applied irrigation water without runoff.
In 1983, Leon New of the Texas Agricultural Extension Service  began working with LEPA with the goal of exposing growers to the experimental concept, developing a commercialized LEPA system which would be economical and suitable for use on both existing and new center pivots, and determining the design and management restraints of the concept.
The most challenging aspects of this effort were developing and testing a commercial LEPA nozzle and head, reducing the costs of materials for LEPA and determining operation and management practices to make the most effective use of the developing technology in production agriculture.
Having drops in every furrow would have made LEPA too costly for most applications.
Thus, a number of field trails were conducted during the 1983 and 1984 growing seasons on the Texas High Plains to determine whether LEPA heads could be placed in alternate furrows of crops planted in straight rows and in a circle.
In these trials, individual spans on existing center pivot systems were converted to LEPA.
One span or a portion of a span had LEPA drops in every furrow and one had LEPA drops in alternate furrows.
All spans received appropriate inputs and the crops were harvested individually under each span.
Yield data were obtained and are given in Table 2.
These results demonstrated that LEPA heads could be placed in every other furrow without any yield reduction.
Table 2.
Yields under spans converted to LEPA with drops in
 every row and in alternate rows on the same center pivot for
 crops planted in a circle.
ID	CROP	YIELDS 	percent difference of
 every row alternate rows	alternate rows
 83C	corn	13,293	13,372	+ 0.6
 84CA	corn	11,982	11,948	0.3
 84CB	corn	11,859	11,758	-0.8
 83GS	grain sorghum	7,555	7,530	-0.3
 83SF	sugar beets	48,540	49,600	+ 2.1
 In the development of commercial LEPA heads and nozzles, TAEX worked with growers, manufacturers and distributors to develop a product that could be used in three modes of operation as illustrated in Figure 2.
In this manner, the same product could be used for pre-irrigation and germination, irrigation in the highly efficient bubble mode during most of the growing season, and for chemigation of both low and high profile crops.
The pressure regulator, when used,
 Figure 2.
The three modes of operation for a modern LEPA sprinkler head: the bubble mode; the horizontal spray mode; and the chemigation  mode.
was lowered and combined with the nozzle and other components to form the LEPA head.
This lowered the required operating pressure by 4 to 5 psi and was a key development in lowering pumping costs for center pivot irrigation.
This also necessitated the development and testing of higher pressure, flexible LEPA drop hose.
Experimental work and field tests also showed that the optimum height for the LEPA head for growers was 8 to 18 inches above the ground.
The development and design of LEPA heads continues to evolve.
In cooperation with manufacturers, field evaluations are still
 being conducted to improve designs, performance and convenience, and to increase application of the LEPA concept.
Two commercial applications of LEPA currently on the market are illustrated in Figure 3.
On one product , the three modes of operation are accomplished by changing the pad and hood positions.
Veins are necessary in pressure regulators for pivots operating at high pressures  to reduce vibrations and turbulent flow which can cause damage.
On another product , pads are interchanged for each mode of operation and the position of the hood is changed and held with a clamp.
LEPA heads are connected to drops which, in turn, are connected to the center pivot main pipeline by a gooseneck or furrow arm.
Drops are usually located in every other furrow.
However, this arrangement is adjusted near the towers to keep a drop out of the wheel tracks so that they will remain dry.
On some vegetable crops, drops are used in every furrow.
The two multi-functional LEPA heads illustrated in Figure 3 usually are equipped with 6 psi pressure regulators.
A pressure of 9 psi at the inlet of these regulators is required for them to operate properly.
By placing a pressure
 Figure 3.
Two commercial, multi-functional LEPA heads currently available.
gauge in the lost drop , pressure can be easily monitored to ensure proper, economical operation.
One manufacturer also uses a 10 psi regulator for nozzle sizes up to 10.5  in order to provide a good upward spray pattern in the chemigation mode.
the design pressure.
Generally, systems can be designed without regulators when the maximum elevation change is 5 feet or less from the pad to the end of the pivot  without significantly increasing operation pressure and pumping costs.
Where elevation changes are greater than 5 feet, the increased cost of regulators often can be recovered due to lower design pressures and the resulting lower pumping costs.
Table 3.
Percent variation in system operating pressure created by changes in land elevation.
Maintain less than 20 percent variation.
Elevation	System design pressure 
 change	6.0	10.0	20.0	30.0	40.0
 2.3	1	16.5	10.0	5.0	3.3	2.5
 4.6	2	33.0	20.0	10.0	6.6	5.0
 6.9	3	50.0	30.0	15.0	10.0	7.5
 9.2	4	40.0	20.0	13.3	10.0
 11.5	5	50.0	25.0	16.6	12.5
 13.9	6	30.0	20.0	15.0
 16.2	7	23.3	17.5
 18.5	8	26.6	20.0
 Figure 4.
Typical drop arrangement for LEPA irigation.
As with other sprinkler systems, pressure regulators are not necessarily needed for all sites.
Pressure variations created by differences in land elevation can be controlled either by design pressure or with pressure regulators.
Pressure at the LEPA nozzle should not vary more than 20 percent from
 Of special concern are locations where flow rate or pressure varies significantly during the growing season because of increases in pumping lift such as those caused by seasonal variations in water tables.
In such cases, the design flow rate  and the use of pressure regulators should be evaluated carefully.
If operating pressure drops below 9 psi and regulators are used, poor water application and uniformity will result.
In contrast, if the design operating pressure is high, pumping costs will be unnecessarily high.
The pumping capacity of the well should be measured under anticipated system pressure to improve LEPA nozzling accuracy.
A number of the field trials have been conducted to obtain yield comparisons between LEPA and conventionally equipped center pivots using partially-converted systems.
Typical partial conversions used in these comparisons are shown in Figure 5.
Usually the next to last full span is converted to LEPA.
Yield from the next interior unconverted span is obtained for comparison and is given in Table 4.
Yields are consistently greater from the LEPA span than from the unconverted span since more irrigation water reaches the soil and crop.
Table 4.
Yields under LEPA with and without furrow diking.
ID	CROP	YIELD 	INCREASE WITH DIKES
 diked	undiked		$/ac
 84SF1	corn	10,580	10,170	410	22
 89CT	peanuts	5,357	4,821	536	168
 84SF	sugar beets 2	8,260	7,189	1,080	178
 1	gross value of price received
 2	yields expressed in pounds of sugar produced per acre
 Figure 5.
Arrangement used in field trials to compare LEPA to conventional sprinklers on partially converted systems.
Water outlets on existing center pivot mainlines are typically spaced 8 1/2 to 10 feet.
Since LEPA drops are placed between every other crop row, additional plumbing is needed.
For example, for row spacings of 30 inches, drops are needed every 60 inches.
Likewise, for 36-inch row spacings.
drops are spaced each 72 inches.
Two methods can be used to install extra drops: 1) using the existing outlets and tees, hose and clamps; or 2) adding additional outlets.
Figure 6 illustrates specially designed clamps attached to the center pivot mainline.
Clamps are sized exactly for individual mainline diameters and are located to position LEPA heads in every other furrow.
A rigid plastic drop is inserted through u-bolts in the clamp.
Water is supplied from the existing mainline outlets to the drops with flexible 1/2inch polyethylene drip tubing.
Tees are installed at the outlets as needed.
Flexible plastic hose is used to connect the drop to the LEPA head.
Total material costs for conversions varies depending on the supplier and location, but is often about $22 per drop.
Cost to convert quarter-mile center pivots for 40-inch crop rows is approximately $4,500, and about $5,500 for 30-inch rows.
Conversion of a quarter-mile pivot can usually be completed in 100 to 120 man-hours.
Installation time can be reduced by providing a platform underneath the pivot mainline, such as planks placed across the truss rods or the side boards of a truck.
New mainline outlets can be quickly installed using a swedge coupler made of metal alloy.
An appropriate size hole is drilled into the pivot mainline at the correct spacing.
The swedge coupler is then inserted into the hole.
The manufacturer recommends that a small amount of sealant be used with the coupler to ensure a leak-proof connection.
A standard hydraulic press  is attached to the coupler with a special fitting that screws into the coupler.
The press is used to compress the coupler against the inside of the mainline pipe to make a water-tight seal.
The swedge coupler compresses quite easily; care is needed to prevent over-compressing the coupler.
Regular goosenecks or furrow arms are then screwed into the coupler.
Conversion costs are about $500 less per span due to the elimination of tees, plumbing, clamps and labor.
Conversion to LEPA also can be accomplished by welding threaded 3/4-inch female couplings to the existing main line.
Since welding destroys the galvanized coating, welded couplings are most applicable for ungalvanized main lines.
As with the swedge coupler, existing goosenecks and drops can be used with the welded couplings.
To accommodate LEPA, most center pivot manufacturers offer outlets spaced either 60 or 80 inches apart on the mainline as an option.
Either spacing fits conveniently into 160-foot span lengths.
This length and spacing also makes farming in a circle easier.
A regular gooseneck (or furrow
 Figure 6.
Mainline clamps for conversion of an existing pivot to LEPA by the addition of tees and plumbing.
arm) connects into the mainline outlet.
LEPA heads are attached to a flexible hose that connects either to standard rigid drops or directly to the gooseneck.
Both the 60and 80inch outlet spacing are suitable for 36-inch row spacing  and most other row spacings by using appropriate length furrow arms.
New quarter-mile center pivots can be equipped with LEPA components for $3,000 to $4,000 more than the cost of a new system equipped with conventional spray nozzles, depending on row spacing and the number of drops.
When water is pumped into a center pivot, it fills the mainline and drops.
Weight of the water causes the pivot to "squat." For 160-foot spans, the pivot mainline will be lowered approximately 4 inches at the center of the span.
Likewise, a 185-foot span will be about 6 inches lower at the center when filled with water.
Length of the hose drops should be cut to account for this change so that all LEPA heads will be at the same height above the ground when the system is running.
Goosenecks and drops are installed alternately on each side of the mainline.
This arrangement is recommended to
 help equalize stresses on the pivot structure for high profile crops.
Also, when crops are not planted in a circle, having drops on both sides of the mainline prevents all the water from being dumped into the same furrows when the system parallels crop rows.
IRRIGATION WATER AND SYSTEM MANAGEMENT WITH LEPA
 At least 20 percent more water will reach the ground with LEPA than with conventionally equipped center pivots.
Operation and management practices must be adjusted to compensate for the additional water.
Also, water is discharged directly into the furrow on a smaller soil area.
Runoff will likely occur, especially on clay soils with slopes greater than one-half percent, unless furrow diking or other tillage is used to contain the water until it can move into the soil.
Cultural practices such as furrow ripping, deep chiseling or other tillage and crop residue practices may be needed to improve the infiltration rate of the soil.
Often the pivot must run at a greater travel speed to compensate for the additional water that reaches the ground.
On most soils, individual applications of 2/3 to 1 inch can be made without runoff.
Water can run up to 100 feet, but significant amounts should be prevented from leaving where it is needed by using appropriate tillage and management practices.
Planting in a Circle
 Farming in the round is one of the best methods of reducing runoff and improving water distribution for both LEPA and conventionally equipped pivot systems.
When crops are planted in a circle, the pivot never dumps all the water in a few furrows as it can when it parallels straight planted rows.
Along with circular planting, ripping or other tillage practices are highly recommended with LEPA.
Plan tillage operations so that LEPA heads always discharge water into the "soft" furrow and never into tractor wheel tracks.
Circle farming begins by marking the circular path the center pivot will follow.
This is done by making a revolution without water.
The tower tire tracks are then used as a guide.
Next, calculate the number of rows that will fit into the span length of a pivot.
For example, 48 40-inch rows  will fit into a 160-foot-long span.
Likewise, 74 30-inch rows will match up with 185-foot spans.
In some cases, row spacing will not match up exactly with the span length.
For example, there are 71.6 30-inch rows in a 179-foot span.
In order to produce an even number of rows , 12 inches less is needed.
To lose 12 inches, set the tillage marker for the guide rows to proportionally lose 12 inches in the number of planter passes between and/or beyond towers.
Put a furrow at the tower wheel tracks.
Some growers prefer to list towards the center from the tower track and make up any differences at the center by adjusting the drop position.
Longer furrow arms may be required to achieve the necessary adjustment.
Exactness is not essential since LEPA drop hoses are flexible.
The hose and head can temporarily ride over the crop, then cross over
 into another furrow if needed.
Each attempt at planting in a circle will be more successful.
Planting in a circle is essential to achieve the full benefits of insectigation of corn and similar high profile crops.
Furrow Diking and Other Tillage Practices
 Furrow diking is very effective at reducing runoff from LEPA irrigation, and was used in conjunction with the initial research.
Furrow diking is a mechanical tillage operation that places mounds of soil at selected intervals across the furrow between beds to form small storage basins.
Rainfall or irrigation water is trapped and stored in the basins so that it soaks into the soil rather than running off.
Furrow diking has been found to reduce runoff and to increase yields in both dryland and irrigated crops.
A complete discussion of furrow diking is given by Gerard.
A number of field trials with furrow diking have been conducted under LEPA center rivots.
In these trials, portions of the rows were diked with the remainder left open.
Yields were taken separately from the rows with and without dikes.
The results given in Table 5 show consistently higher yields with furrow diking.
Similar results have been obtained by individual growers using ripping and other tillage practices, after the crop is up, in conjunction with LEPA.
Where crops are planted in a circle, rip the furrow where water will be applied.
Table 5.
Yield comparisons under LEPA converted spans and conventionally equipped spans on the same pivot.
ID	CROP	YIELD		INCREASE WITH LEPA
 LEPA conventional 	$/ac
 86DM	corn 	56,000	51,400	4,600	41
 89LFA	corn 	1,909	1,763	146	54
 89TH	cotton	797	705	92	64
 89 DK	cotton	562	483	79	73
 89LFB	peas 	1,267	1,055	262	42
 85JHFA	peanuts 	4,765	4,445	320	52
 85JHFB	peanuts 	4,235	3,725	510	115
 86JHF	peanuts 	4,310	3,210	1,100	203
 89GTA	peanuts 	6,462	6,050	412	53
 89GTB	peanuts 	6,534	5,978	556	120
 89LF	peanuts 	3,689	3,267	422	177
 83SF	sugar beets2	8,260	7,360	900	151
 1 gross value of price received
 yields expressed in pounds of sugar produced per acre
 The best furrow dikes are put in with moderate soil moisture.
Do not attempt combined diking and ripping when soil is wet.
The soil will not seal adequately underneath the dike and water will undermine the dike.
In wet soils, use one or the other.
Ripping or chiseling before planting is recommended where runoff is anticipated or has been a problem, and where it can be done in conjunction with land preparation.
Rainfall can prevent timely tillage after the crop is up.
LEPA irrigations should be scheduled using soil moisture monitoring devices.
Soil moisture sensors can identify existing soil moisture, monitor moisture changes, locate the depth of water penetration and describe crop rooting.
Gypsum blocks absorb and lose moisture from the surrounding soil; thus the moisture levels of the blocks is similar to that of the soil.
Blocks are read with a resistance-type meter which indicates 10  to 0 , although some newer digital meters read from 100 to 0.
Tensiometer gauges indicate soil moisture by measuring soil moisture pressures in units of centibars, ranging from 0  to 70 or 80.
Blocks can sense lower soil moisture and perform better than tensiometers in clay soils or in situations where the crops are irrigated infrequently.
Readings may be taken at weekly intervals during most of the growing season.
During peak water use periods, readings should be taken two or three times a week depending on rainfall and irrigations.
Plotting readings on graph paper is the best method of tracking and interpreting sensor readings and determining when to irrigate.
Table 6 shows soil moisture content for different sensor readings.
Table 6.
Guides of soil moisture content.
Instrument	Excellent	Good	Fair	Low
 Gypsum blocks1	9.5 10.00	7 8	5-6	3 4
 Tensiometer	20 or less	30 40	50 60	70 80
 Based on readings taken with Delmhorst type
 Centibars of suction 
 A single block or tensiometer installed at a depth of 12 to 18 inches will measure moisture in the upper root zone; another installed at 36 inches will measure deep moisture.
Generally, sensors are installed at three depths--12, 24 and 36 inches--and at a representative location in the field where the soil is uniform.
Avoid slopes and low areas where water may stand.
Select a location within the next to the last span but away from the wheel tracks.
Locate sensors in the crop row so they do not interfere with tractor equipment.
Follow manufacturers' recommendations on preparing sensors.
Gypsum blocks are usually soaked in clean water for 15 minutes and then allowed to dry two times before installation.
Tensiometers are usually charged 36 to 48 hours before installation.
Keep the porous tips submerged in a pail of water until installation.
Install the sensors in a tight fit hole made with an auger or driver the same diameter as the gypsum block or porous tip.
Pour a half cup of water in the hole before inserting the sensor.
It is essential to have the sensing tip in firm contact with undisturbed soil to obtain accurate readings.
Pressure Gauges and Monitoring
 As discussed previously, LEPA systems installed with pressure regulators require at least 9 psi to operate properly.
To ensure adequate pressure, install a pressure gauge in the last drop at the end of the pivot.
Maintaining a pressure of 9 psi at this point will ensure proper operation.
When the pressure gauge is installed directly on the end of the mainline, a reading of 4 psi is needed to ensure proper operation.
Nine psi at the regulator is achieved by adding the 5 psi gain resulting from the 11 to 12-foot distance from the mainline
 to the pressure regulator.
A pressure gauge at the pivot point will give little indication whether proper pressure is being maintained.
However, pressure gauges at the pivot point and at the well are effective for monitoring overall system performance.
Operating pressures are low with LEPA which makes the system more sensitive to pressure changes.
Chemigation with center pivots is proving to be a costeffective method of applying chemicals in a safe and timely manner.
The high application efficiency and uniformity of the multi-functional LEPA heads make LEPA an ideal system for chemigation and a more valuable investment.
Preliminary research has indicated that in some situations the amounts of chemicals applied can be reduced, resulting in lower costs and reduced environmental hazard.
Federal regulation requires the use of specific chemigation injection and safety equipment.
These regulations were a part of EPA's Label Improvement Program  which became effective in April 1988.
In addition to the regulations on equipment, the LIP requires that pesticide labels state whether the product may be applied through the irrigation system.
If so, then application instructions are provided on the label.
These requirements also aid the grower by providing for consistent, precise and continuous chemical injection, thus reducing the amounts  of chemicals applied.
Table 7.
Summary of chemigation equipment requirements.
a.
Check valve between well and injection points.*
 b.
Vacuum relief valve between check valve and well.
C.
Low pressure cut off.
d.
Low pressure drain.
a.
Anti-back flow injection valve 10 psi.
b.
Normally closed solenoid valve between injection pump and chemical tank.*
 C.
A metering type injection pump.*
 a.
Interlock injection pump and water pump power.
b.
Interlock normally closed solenoid valve and injection pump power.
Alternative safety equipment may be substituted according to regulations approved by the EPA in March 1989.
See TAEX Publication B-1652, "Chemigation Workbook."
 Chemigation of Corn Pests with LEPA
 Research at the Texas Agricultural Experiment Station in Lubbock  has demonstrated that miticides can be effectively applied to the undersides of lower corn leaves  with LEPA in the upward chemigation mode.
LEPA nozzles designed for insectigation became commercially available in 1987 and were evaluated for control of corn pests under actual field conditions in 1987 and 1988.
No difference in effective control was observed with start/stop electric-drive and continuous-move center pivots.
More information is included in B-1652, "Chemigation Workbook," available from the Texas Agricultural Extension Service.
The insecticide formulations best suited for chemigation are those which are soluble in oil but insoluble in water.
However, since most insecticide formulations contain emulsifiers, the addition of a nonemulsified oil may be necessary to counter the effect of the emulsifiers.
Nonemulsified vegetable and petroleum based oils have been used for chemigation with equal success.
Typically, oils are mixed 1:1 with the insecticide.
For vegetable oils such as cottonseed and soybean oil, use only "once refined" grade, as emulsifiers are sometimes added during later refinement.
Some insecticides such as pyrethroids and Lorsban have low water solubility, so an oil carrier is not always needed.
Other insecticides such as Azodrin and methomyl are water soluble but not oil soluble, and perform poorly when chemigated since their high water solubility cannot be overcome by mixing with an oil.
For additional recommendations see B-1652.
This publication was funded by the State Agricultural Soil and Water Conservation Fund.
Educational programs conducted by the Texas Agricultural Extension Service serve people of all ages regardless of socioeconomic level, race, color, sex, religion handicap or national origin.
Dairy Production and Center-Pivot Irrigation Systems
 Center pivots are historically known for their role in row-crop production but have more recently been considered for their application in livestock operations.
Dairy producers in New Zealand have started using center-pivot irrigation systems to reduce heat stress as well as increase their forage yields.
Because of their success in New Zealand, these practices are now being adopted and researched in the United States.
Mississippi State University's Bearden Dairy Research Center has used a center-pivot system with its grazing herd since 2015.
The pivot system has reduced drought risk on the associated pastures.
During the drought of 2016, the MSU grazing herd was able to start grazing ryegrass in the beginning of October 2016 and continued to graze irrigated pastures until the end of May 2017.
Producers without irrigation are sometimes forced to delay or prolong grazing, depending on environmental conditions in their area.
Irrigation lessens these impacts and allows for a more controlled grazing season.
This publication will review some of the reasons for production loss in Mississippi dairies and evaluate the costs and benefits of a center-pivot irrigation system on a dairy operation.
Common reasons for production loss within the dairy industry include:
 Restrictions to feed and water can cause decreases in milk production.
A shortage or insufficient amounts of water can cause drastic drops in milk yield.
Feed imbalances can reduce milk fat and protein percentages.
Research has shown that a shorter calving interval can increase milk production and profitability.
Twelve months is ideal.
Chop size and length of cut
 When the chop size or length of cut is too small, cows will chew less.
Less chewing lowers their rumen pH, causing them to produce lower amounts of fatty acids that aid in milk production.
Longer chop length will increase effective fiber in their diet and help keep them chewing.
When a cow's environment gets above 68 THI , production levels can decrease by as much as 25 percent.
When cows are heat-stressed, fertility rates decrease; elevated body temperature influences ovarian function, reduces oocyte health, and reduces embryonic development.
Potential Benefits of Center-Pivot Systems
 Some possible benefits that could result from installing a center-pivot irrigation system are:
 Consistent and timely irrigation allows forages to respond quicker to harvest events than just relying on rain.
Reduction in forage yield variability
 A reduced risk of drought could cause less variability in the dry matter yield of forage being produced.
With the ability to irrigate pastures in addition to rainfall, forage crops can reach optimal grazing heights sooner and recover faster.
Reduction of the 10-25 percent production loss during summer months
 With cows being cooled under the sprayers of the center pivot, heat stress will be less likely to affect production.
Installing a center-pivot irrigation system depends on the specifics of each operation.
Some of the main differences will be:
 Certain soils are not favorable for irrigation because of drainage and runoff.
Soil characteristics should be determined before installation.
It might be necessary to level or form land to make the center pivot able to move with ease.
The need to install an irrigation well can be up to 25 percent of total installation costs.
Cost of establishing electricity
 The estimated costs for establishing a center-pivot irrigation system for a 42-acre field are displayed in Table 1.
These costs do not represent any specific operation but are representative of the average costs for a typical operation.
Costs will vary depending on each farm's specific characteristics.
This information can be used as a guide for anyone considering installing a center-pivot system.
Fixed costs could be reduced if some installation materials are already available or if a well is already established.
We assume that center pivots have a 20-year useful life expectancy and an interest rate of 4 percent per year.
Further, we assume for this example that the center pivot will have zero salvage value at the end of the 20-year period.
If the center pivot is used for the full 20 years, the annual fixed cost per acre would be $129.21.
Note that the fixed costs per acre shown in Table 1 are very sensitive to changes in the size of the irrigated area.
Fixed costs per acre will likely drop substantially as irrigated area increases because the investment in the well, pump, motor, and electrical components is not likely to
 Table 1.
Average installation costs and annual fixed
 cost per acre for a 42-acre field and a 20-year useful
 Center pivot 	$40,000
 Pump, motor, and electrical	$17,500
 Average years of life	20
 Annual fixed cost per acre	$129.21
 increase significantly for an irrigated area up to 128 acres.
While the center-pivot investment will increase as the size of the irrigated area increases, that increase will not negate the economies of size generated by the other components.
Therefore, it is important to budget for your specific size of operation.
Table 2 shows the operating costs of a typical centerpivot irrigation system per year for a 42-acre grazing pasture.
Water cost and use is an important factor in center-pivot operating costs.
The estimates below assume that water is freely available and that increasing use only affects the cost of electricity.
During drought years, more water will be used to keep the fields optimally irrigated and, therefore, more electricity will be used.
These costs can also change with increased maintenance requirements or increased electrical usage.
The annual operating cost is estimated to be $83.24.
Table 2.
Operating costs and total annual costs per
 acre for a 42-acre field.
Repair and maintenance	$996
 Total operating costs per year	$3,496
 Annual operating costs per acre	$83.24
 Annual fixed and operating costs per acre	$212.44
 Combining the $129.21 annual fixed cost with the $83.24 annual operating cost brings the total annual cost to $212.44 per acre.
This is the cost that must be offset by either gains in revenue or a reduction in other costs of production.
It is important to note that additional costs associated with forage production are not included here.
It is possible that producers will spend more on forage management practices, but, for this scenario, we assume that the addition of the irrigation system is the only change.
There are multiple scenarios in which installing and maintaining a center-pivot irrigation system could be a profitable investment.
Experimental data is not currently available to estimate the anticipated benefits for a dairy operation in Mississippi.
The ability to monitor and reduce water deficits can lead to improved forage production, causing a reduction in costs associated with other feeding programs.
The ability to reduce feed costs will be directly related to the current forage and feeding systems.
The
 level that forage programs can improve with more control over water application also depends on the type of forages grown, soil characteristics, and other management practices.
Because we do not have experimental data to estimate expected benefits, we will consider the benefits that would be required to make the center pivot profitable.
Scenario 1 examines the amount that milk production would have to increase as a result of heat-stress abatement.
We also discuss the reduction of feed costs that would be needed to offset the increased cost of irrigation.
If either of the scenarios or a combination of the two can be obtained, then a center pivot could be a profitable investment.
Scenario 1.
Increased Milk Production
 This scenario evaluates a 4 percent increase in milk production per cow due to a reduction of heat stress.
During the summer months, producers can commonly see up to a 25 percent decrease in milk production.
Cows can be heat stressed for up to 6 months out of the year in the South.
If the production loss in the summer months were to be lowered to 10 percent, annual production could be increased by as much as 7.5 percent.
To offset the cost of the center-pivot system, a 4 percent increase in milk production would be required.
Using the assumptions in Table 3, this would raise the total annual benefit per cow to $5.98.
Milk-quality bonuses and extra costs for increased forage were not considered in these assumptions.
Table 3.
Hypothetical production and revenue impact.
Production per cow 	16,500
 Price per cwt	$17
 Revenue per cow	$2,805
 Production per cow with a 4%
 annual increase 	17,160
 Revenue per cow	$2,917.20
 Total annual benefit	$112.20
 Scenario 2.
Reduced Feed Costs
 Increased forage production could result in a $106.22 reduction in annual feed costs per cow.
For dairy producers in Mississippi, feed costs are around $12.50 per cwt of milk produced.
With a center-pivot installation, there would be a reduction in the amounts of hay, supplemental forage, and TMR feeding needed.
Forage grown under a pivot can be a more consistent, higher-quality feedstuff.
This, in turn, can reduce supplemental feedings and extend grazing periods.
A primary advantage of a center-pivot system is the potential alternative uses.
This gives dairy producers more flexibility to switch to other production systems as practices and market forces change.
Center-pivot irrigation systems have uses in other livestock-, hay-, and cropproduction systems, among others.
When compared to a freestall barn, a center-pivot system is less specific to only dairy production.
If desired, you could disassemble and sell the system; on the other hand, freestall barns have limited alternative uses without significant alteration.
This publication explores factors that cause milk production levels to decrease and discusses how a center-pivot irrigation system could be advantageous to dairy producers.
For approximately half of the year, Mississippi's dairy cattle are under heat-stress conditions.
When dairy cattle are heat-stressed, their production levels tend to drop.
The center-pivot irrigation system is an alternative to help increase production.
The average installation cost for a center-pivot system can be offset by either an increase in milk production or a decrease in feed costs.
While experimental data is not yet available, it appears that a combination of these two benefits could make an investment in a center-pivot system profitable.
Water Use Efficiency in Agricultural Trickle Irrigation Systems
 Water availability is a key factor in achieving top crop yields.
Since water supply for irrigation in drought situations is often limited, achieving the most efficient way to irrigate is critical to agricultural success.
Trickle irrigation was first introduced in the 1960's and 1970's with the development of tubing and header lines which made the system function.
A trickle irrigation system is most suited for high value produce crops and the trickle tube is usually buried in the root zone at planting time.
Sometimes if the weather turns dry after planting the trickle tubes could be placed on the surface.
The tubing is made with evenly spaced emitters where the water slowly drips out leading to the nickname "dripping irrigation".
It reduces water use approximately 50% compared to overhead sprinklers.
The system starts with distribution main lines which deliver water to the fields which are above ground and could be aluminum or polyvinyl chloride.
Then the water flows through submains which are often layflat lines that collapse into a flat shape when empty.
Connectors or couplings connect the layflat to the trickle tubes.
A number of different types of tubing are available with different emitter spacings, range of operating pressure, and wall thickness.
A key part of successful trickle irrigation systems is filtration to remove any contaminants from the water supply.
This is especially critical if the water supply is surface water from a pond or stream.
Water that is not filtered could result in clogged emitters and cause failure of the system.
In order to get maximum efficiency from the trickle system, one needs to manage the water application.
Part of that is understanding the water holding capacity of your soil which is influenced by both the soil type and soil depth.
Knowing your water holding capacity is an important part of scheduling the irrigation.
An appropriate strategy is to irrigate when the soil drops to 50% capacity.
One tool to assist in scheduling irrigation is a tensiometer.
Water is held by the soil particles and as the soil dries and the water remaining in the soil is less, the soil particles hold the water with ever greater tension.
Tensiometers are a tube filled with water which has a porous ceramic tip and a pressure gauge on the top.
As the soil dries out the tension between soil particles and water increases.
This tension also starts to draw water through the porous tip on the tensiometer and the tension created is measured by the gauge on the tensiometer.
Thus the tensiometer is one way to measure water depletion in the soil by reading the pressure gauge on the top of the tensiometer.
While this is a useful tool, tensiometers require maintenance so some farmers go with their judgment based on their experience to schedule irrigation.
Trickle irrigation systems require regular maintenance for successful operation.
This includes regular cleaning of the filters and water treatment to control bacteria, algae, and slime growth in the system.
For more information see the Penn State Extension article on drip irrigation for vegetable production.
WHERE DID ALL THE IRRIGATORS GO?
TRENDS IN IRRIGATION AND DEMOGRAPHICS IN KANSAS
 The 2000 United States Census indicated that Kansas had grown by 8.51 percent in population since 1990, compared to the national average growth rate of 13.15 percent.
Only nine  of 105 counties in Kansas experienced growth equal to or greater than the national average growth rate.
From 2000-2004 only 8 counties grew at or above the national average growth rate.
In 1990, Kansans were 1.00 percent of the U.S.
population, in 2004 only 0.94% of the population.
The 2004 population estimates had 56 of 105 counties in Kansas declining in population since 2000.
Of the 54 counties overlying the High Plains aquifer, only three  counties had equal or greater growth than the national average.
In addition the census also indicated a cultural transition as many counties experienced domestic out-migration and foreign immigration.
Agricultural Census data document a 5.26 percent decrease in the total market value of agricultural products from 1997 to 2002, while the total number of farms increased 4.58 percent in Kansas during the same period.
The number of Irrigated farms decreased by 3.58 percent with total irrigated acres declining by only 1.07 percent to 2.678 million acres over the same five year period.
Total acreage in crop production declined 1.59 percent, while the market value of crops sold decreasing 24.9% from $3.22 billion in 1997 to $2.42 billion in 2002.
Since 1990, irrigation technology has dramatically changed to more efficient low pressure pivot and SDI  systems.
With more efficient water use, irrigators have been able to grow significantly more corn and other water intensive crops.
Given the 3.5 percent decrease in the number of irrigated farms since 1997, the resulting 1.08 percent decline in irrigated acres indicates increased acreage efficiency by remaining irrigators.
This presentation intends to demonstrate spatial and temporal trends in irrigation and demographics for Kansas, with focus on the 54 counties overlying the High Plains Aquifer.
Population Change in Kansas Contrasted with the US
 In the 20th century, the population of Kansas increased from 1.5 to about 2.7 million people, growing approximately 8 percent per decade.
In the latest decade , the US Census indicated Kansas growth at 8.51 percent, compared to the national average of 13.15 percent.
Historically, when comparing two decennial census, Kansas has experienced 5-10 percent less growth than the nation.
During the last decade, 9 of 105 Kansas counties  experienced growth equal to or greater than the national average growth rate as illustrated in the Population Ratio 1990:2000 map.
Figure 1.
Kansas Population Ratio 1990-2000
 Comparing the latest population estimate  with 2000, only 8 counties grew at or above the national average growth rate.
In 1990, Kansans totaled 1.00 percent of the U.S.
population, in 2004 only 0.94% of the population.
The 2004 population estimates had 56 of 105 counties in Kansas declining in population since 2000.
Of the 54 counties overlying the High Plains aquifer, only three  counties had equal or greater growth than the national average.
In the last century  census data indicate that county population peaked in 1939 on average across the state as illustrated in Figure 2 and Table 1.
Figure 2.
Kansas Counties Year of Population Peak
 Figures 1 and 2 indicate growth of counties having larger communities or metropolitan areas.
Both US, and Kansas population growth has been mainly concentrated in metropolitan areas throughout the last hundred years as illustrated in the following maps comparing the population distribution by county in 1900 and 2004.
In Figure 3 note that in 1900 a more even statewide distribution of population existed than 2004.
KS Counties: Year of Population Peak
 Table 1.
Kansas Counties Year of Population Peak
 2640	5241	9234	11325	14442	16384	19420	18248	21963	24355	20376	22369	1507 9
 3341	4112	3819	5173	7960	11844	14647	1807 1	15833	18470	17117	17533	40940
 1178	1962	2441	2722	8626	8489	9686	21816	10744	12813	53727	25096	18104
 493	1197	1096	1563	4535	6134	13784	2507
 14745	21421	20676	8246	16643	13938	16689
 1426	1107	3469	2032	9629	17591
 3682	29027	16196	10022	19507	24712
 327	422	457	5497	2365	7085	10663	44037	15621	19254	38809
 304	620	822	1581	1701	1619	6594	10310	25631	30156	11804	29039	27387	42694
 Kansas Population 1900 KS_CNTY POP1900 as Percent of Total 0.02 0.5% 0.50 1.00% 1.00 1.50% 1.50 2.00% 2.00 2.50% 2.50 3.00% 3.00 3.50% 3.50 4.00% 400 4.50% 4.50 5.00%
 Figure 3.
Kansas County Population 1900 and 2004 as a Percent of State Population
 Figure 4.
Kansas County Population 1900 and 2004 Extruded by Population
 The three-dimensional maps of Kansas emphasize a drastic change in population distribution from 1900-2004, as well as the trend toward metropolitan growth which parallels the US.
Kansas counties near the metropolitan areas of Kansas City and Wichita, and along the Interstate 70 and 35 corridors from Kansas City to Topeka and Wichita experienced the greatest growth.
In contrast, there were counties in Western Kansas that lost more than 10 percent of their population between 1990 and 2000-Graham, Ness, Greeley and Comanche.
Population projections by US Census Bureau and the Kansas Water Office indicate a steady and similar trend for Kansas as seen in the past century.
Between 2000 and 2030 the population of Kansas is projected to increase approximately 9 percent, again well below the projected 29 percent increase in the US.
The projected growth disparity between Kansas and the US creates both economic and political challenges.
More challenging however, is the compositional aspect of the population change.
Of the predicted increase between 2000 and 2030, approximately 237,000 of 252,000 people, will be in the 65+ age category.
As illustrated in Figure 5 for Sheridan County, which is representative of many counties in western Kansas, there is an erosion of the base population age cohort of 0-4, and drastic thinning of the 20-34 age cohorts which normally replace the base age cohort.
Figure 5.
Sheridan County Kansas Population Pyramids for 1980 and 2000
 Therefore the bulk of the predicted population increase will be the transition of the baby boomers into higher age cohorts above 60.
Since Kansas does not have significant retirement migration destinations, the population will be aging in place, further perpetuating economic and social challenges for particular communities, especially those in Western Kansas.
Aging will not be the only compositional change in Kansas.
Southwestern counties experienced a rapid influx of international migrants in recent history.
This corresponds with the dominant economic activities in animal and meat production, a pattern that likely will not change.
The spread of the Hispanic population across the rural Midwest is a relatively new phenomenon facing policy makers and community professionals.
The Hispanic population in 1990 comprised 4 percent of the total population of Kansas, and in 2000 increased to 7% of the state population.
In High Plains Aquifer Counties, Hispanics in 2000 accounted for 9 percent of the population and the total White percentage fell to 76%, while Kansas as a whole went from 86% to 80% in the same period.
Figure 6.
Kansas Population Composition 1990-2000
 Agricultural Changes in Kansas
 Kansas Agricultural Census data for 1997 and 2002 document a 5.26 percent decrease in the total market value of agricultural products, while the total number of farms increased 4.58 percent in Kansas during the same period.
The number of Irrigated farms decreased by 3.58 percent with total irrigated acres declining by 1.07 percent to 2.678 million acres over the same five year period.
Total acreage in crop production declined 1.59 percent, while the market value of crops sold decreasing 24.9% from $3.22 billion in 1997 to $2.42 billion in 2002.
Table 2.
Kansas Agricultural Census Comparison 1997-2002
 Comparing the 1997 and 2002 Agricultural Census data for Kansas by county reveals that 31 of 105 counties lost total numbers of farms with six counties losing 10% or more farms.
See Figure 7.
The Average size of farms decreased in 54 of the 105 counties with the greatest decrease in average size per farm being 37%, and the greatest increase being 36% in Marshall County.
Nine counties experienced a 10% or greater increase in average farm size.
See Figure 8.
Total crop acres decreased in 67 counties and increased in the remaining 38, with the greatest increase in crop acres being 16% in Barber County.
See Figure 9.
Average Farm Sales declined in 83 of the 105 counties.
Of the 22 counties that had increased average farm sales between 1997 and 2002, Decatur and Sheridan counties experienced the largest increases at 80.6% and 95.3% respectively.
On average Kansas counties Average Farm Sales were 89.95% of the 1997 values.
See Figure 10.
Figure 7.
Kansas County Farms  Ratio 1997-2002
 Figure 8.
Kansas County Farms Average Size Ratio 1997-2002
 Figure 9.
Kansas County Crop Acres Ratio 1997-2002
 Figure 10.
Kansas County Average Farm Sales Ratio 1997-2002
 Since 1990, irrigation technology has dramatically changed to more efficient low pressure pivot and SDI  systems.
With more efficient water use, irrigators have been able to grow significantly more corn and other water intensive crops.
Given the 3.5 percent decrease in the number of irrigated farms since 1997, the resulting 1.08 percent decline in irrigated acres indicates increased acreage efficiency by remaining irrigators.
Figure 11 illustrates changes in irrigated acres, sprinkler and SDI acreage in Kansas.
Figure 11.
Kansas Irrigated Acres, Sprinkler, and SDI Acreage Trends 
 Figure 12.
Kansas County Irrigated Acres 2002.
Kansas County irrigated acres in 2002  indicate only one county outside the extent of the High Plains Aquifer with greater than 20,000 irrigated acres.
Total irrigated acres in 2002 for the 54 counties overlying the High Plains Aquifer were 2,452,734.
The Kansas Geological Survey estimated lifetime of High Plains Aquifer water resources indicates a dire situation for counties that have not grown in the past decade and a bleak outlook for parts of most counties that had experience growth since 1990.
Figure 13.
Estimated Useable Lifetime 
 Research questions regarding the drivers of socio-economic, agriculture and irrigation change are just beginning to be formulated and researched, however one apparent connection between population growth and irrigation has been identified in this study.
When Population Ratio 1990-2000 colors are placed on 3D County Irrigated Acres, counties in the southwest corner of the state that irrigate the largest number of acres are also those that have shown growth in the last decade.
Given the KGS estimated useable lifetime of the aquifer, the same southwestern counties are likely the only counties in the western half of the state with potential to grow into the future based on the continuation of existing agricultural practices and estimated useable lifetime of the aquifer.
Many important questions remain, however one very large issue for southwestern counties will be the age cohort projections and potential impact on agriculture production due to workforce aging.
Figure 14.
Kansas County Population Ration 1990-2000 and Irrigated Acres Extruded
THE TEXAS HIGH PLAINS EVAPOTRANSPIRATION  NETWORK
 Development, adoption and use of an evapotranspiration  network system designed for irrigation scheduling entail the integration of several factors that include a simplified data acquisition approach, user understanding, multiple dissemination venues, user clientele education, resource support plus operational commitment by network personnel to maintain accurate meteorological and ET data.
The Texas High Plains Evapotranspiration  network was developed with these factors in mind and continues to gain adoption by irrigated users to date.
The TXHPET system, its development, use, output and operations are discussed.
As irrigation continues to be the majority user of water  in Texas  and other states, increases in other water use sectors are typically dependent on transfers from the agricultural sector.
Thus, agriculture is likely to continue to have to produce more with less water and depend more on conservation measures, technological advances and irrigation scheduling to optimize irrigation management.
Conservation districts and other water governing agencies are increasingly embracing network based evapotranspiration  requirements as the maximum allowable pumping for crops.
Appropriate  meteorological data are necessary for application of widely accepted standard ET models and calculations.
Numerous meteorological networks have been developed and are in existence today in the U.S.
Most of these systems have differing primary objectives and targeted users.
The purpose and scope of these networks vary in size and intent along with differing interrogation intervals.
Some are large-scale climate based and can be used for varying purposes.
Others are specific in nature and the data are controlled and restricted to the designated application or agency.
Agriculturally based ET networks generally have the defined purpose of estimating crop ET within a particular region.
Networks such as "school net" sites are basically teaching tools for students and for illustration of the variability of localized rainfall events and typically are not suitable for agricultural applications because of city and urban  based parameter influences.
Agricultural meteorological stations need to be representative of the environment they are located in with sensors conforming to standardized accuracy and placement.
Data interrogation, processing, and transfers  must be consistent and timely for producer adoption and use.
Sensor maintenance should be a priority issue of the network and adhered to for accurate, continuous quality assured and quality controlled data streams.
Most importantly, ET computations should be scientifically based and documented adequately for comparison with the latest standardized ET equations.
Placement of ET weather stations should be a key component in the establishment of a successful and useful network station grid.
Stations should be located in areas where irrigated agriculture is practiced.
Additional considerations for placement involve known or anticipated topographical differences such as elevation.
Station placement should be adequately "free" from biasing influences such paved roads, tree rows, valleys, large depression areas, potential water holding areas such as playas, lakes, large water holes, unpaved roads with dust potential, feedyard or other confined animal feeding operations, grain elevators, or other influences that may alter representative agriculturally based acquisition of meteorological parameters.
The number of stations within an ET network is not as important as their representation.
The TXHPET network currently has 18 stations over an area representing more than 1.5 million irrigated acres.
In the TXHPET network, representation in the Texas High Plains intensively irrigated areas typically ranges from to 900 to 1500 square miles per station.
This figure can vary depending on the surrounding topography and prevailing upwind influences.
Redundancy or overlap of weather stations is a good design consideration as data from adjacent units can be more easily estimated with redundant units.
In many cases, redundancy cannot be determined until adequate data are acquired to indicate that it exists.
Development of a regionally based ET network should involve a multi-disciplinary scientific based team as well as industry and commodity representatives.
Additionally, large operation, progressive growers and crop consultants should be invited to provide valuable input in to the design and format of the output materials.
Others that may be included are area agricultural agency representatives and governing water agency personnel.
Early input is necessary as the crop consultants and large producers are the ones who will most likely use the outputs and they sometimes will have strong opinions as to how they want the data formatted for integration into their operations.
Most producers and even many consultants do not want to spend time calculating values from equations each day.
Most want a single value of daily ET to use in a straightforward, easy to understand irrigation scheduling checkbook type method or equivalent irrigation scheduling program.
These desires have been learned by the development team of the Texas High Plains ET  network in the early 1990's.
In addition, the following should be strongly considered:
 1) Data must be accurate and scientifically based and supported.
2) Data must be timely.
3) Data must maintain integrity.
4) Data must be comparative, calibrated and verified.
5) Data must be sustainable.
6) Data should conform to agriculturally based and scientific standards.
Initially, the TXHPET development team brought a group of producers to listen to their needs and they decided jointly that they wanted a single "fax sheet" of the ET data delivered on a daily basis whereby they could read a single crop value of ET for yesterday's conditions.
After the initial design draft, the consultant and producer members rearranged much of the sheet to their liking to fit their needs.
This involvement by the users virtually ensured that the data output format was what they wanted and not just what the science based members dictated.
The single page fax file format is still in use today and contains data for cereal grain crop daily, 3-day, and 7-day ET's plus growing degree day heat units and average growth stage for short and long season crops with four dates of planting.
Figure 1 illustrates the information in the TXHPET fax file format.
Another file that is created daily and that has hourly formatted information for researchers and other related agricultural industry users is designated as an hourly file.
A copy of this file in illustrated in Figure 2.
Date	ETo	Air	Soil Min	Prec.
Growing	Degrees	Days	
 in.
Max	Min	2in.
6in.
in.
Crn	Srg	Pnt	Cot	Soy	Wht
 07/16/08	.22	89	63	71	75	0.00	25	26	0	16	29	0
 07/17/08	.27	91	62	70	74	0.00	24	27	0	17	28	0
 07/18/08	.25	90	66	73	76	0.01	26	28	0	18	30	0
 10-day avg min soil temp	68	72	Wind	6.3	mph	from	226	deg.
CORN	Short Season Var.
Water	Use	Long	Season	Var.
Water	Use
 Seed	Acc	Growth	Day 3day 7day	Seas.
Growth	Day	3day	7day	Seas.
Date	GDD Stage	in/d	in.
Stage	in/d	in.
04/01	1860 Milk	.32	.32	.29	22.8	Blister	.32	.32	.29	22.5
 04/15	1761 Milk	.32	.32	.29	20.4	Silk,	.32	.32	.29	20.2
 05/01	1550 Blister	.32	.32	.29	16.1	14-leaf	.31	.31	.28	15.9
 05/15	1379 Silk,	.32	.32	.29	12.7	14-leaf	.31	.31	.28	12.6
 SORGHUM	Short	Season	Var.
Water	Use	Long	Season	Var.
Water	Use
 Seed	Acc	Growth	Day 3day 7day	Seas.
Growth	Day	3day	7day	Seas.
Date	GDD	Stage	in/o	in.
Stage	in/d	in.
05/01	1693 Flag	.23	.23	.21	13.8	Flag	.23	.23	.21	12.7
 05/15	1521 Flag	.23	.23	.21	11.2	Flag	.23	.21	.18	10.3
 06/01	1206 GPD	.20	.20	.18	7.7	5-leaf	.17	.17	.16	7.2
 06/15	853 5-leaf	.17	.17	.16	4.2	4-leaf	.15	.15	.13	4.1
 COTTON	North Plains Area Water	Use	South	Plains	Area	Water	Use
 Seed	Acc	Growth	Day 3day 7day	Seas.
Growth	Day 3day 7day	Seas.
Date	GDD	Stage	in/d	in.
Stage	in/d	in.
05/01	894	1st Sqr	.24	.24	.22	10.4	1st Sqr	.24	.24	.22	10.0
 05/15	868	1st Sqr	.24	.24	.22	9.6	1st Sqr	.24	.24	.22	9.3
 06/01	727 1st Sqr	.24	.24	.22	6.6	1st Sqr	.24	.24	.18	6.3
 06/15	513 Emerged	.12	.12	.11	3.5	Emerged	.12	.12	.11	3.5
 SOYBEANS	Late	Group	4-Var.
Water	Use
 Seed	Acc	Growth	Day 3day 7day	Seas.
Date	GDD	Stage	in/d	in.
05/15	1629	R 3	.26	.26	.23	12.8
 06/01	1271	V-6	.20	.20	.18	8.3
 06/15	917	V-4	.17	.17	.15	4.8
 07/01	489 Emerged	.14	.14	.12	2.0
 Fescue/Bluegrass lawn water use 0.24 inch Bermuda grass lawn water use 0.18 inch Buffalo grass lawn water use 0.12 inch
 Figure 1.
Fax output format from the TXHPET network illustrating daily crop ET values for multiple crops and planting dates.
Time	Rs	Ts2	Ts6	Tair	TDew	RH	AVP	VPD	WSpd	Wdir	SDD	PREC	BP	EToG	EtoA
 CST	W/m^2	C	C	C	C	%	kPa	kPa	m/s	deg	deg	mm	kPa	mm	mm
 100	0.0	25.0	26.6	23.2	16.3	65	1.85	1.00	2.2	202	15	0.00	-99.9	0.04	0.07
 200	0.0	24.6	26.3	22.0	16.7	72	1.90	0.74	1.3	213	26	0.00	-99.9	0.02	0.03
 300	0.0	24.1	26.0	20.5	17.0	81	1.94	0.46	0.7	311	9	0.00	-99.9	0.00	0.00
 400	0.0	23.7	25.7	20.3	17.2	83	1.97	0.41	0.9	272	31	0.00	-99.9	0.00	0.01
 500	0.0	23.3	25.3	20.4	17.2	82	1.97	0.43	1.5	208	15	0.00	-99.9	0.01	0.02
 600	3.5	23.0	25.1	20.1	17.3	84	1.98	0.37	1.4	238	26	0.00	-99.9	0.01	0.02
 700	36.8	22.8	24.8	20.3	17.4	83	1.99	0.40	1.7	214	13	0.00	-99.9	0.03	0.05
 800	103.7	22.8	24.6	21.0	17.1	78	1.95	0.54	2.5	242	16	0.00	-99.9	0.10	0.13
 900	220.4	23.1	24.4	22.1	17.2	74	1.96	0.70	2.9	258	13	0.00	-99.9	0.18	0.23
 1000	443.6	24.0	24.3	24.2	17.1	65	1.95	1.07	3.5	256	13	0.00	-99.9	0.35	0.44
 1100	727.5	25.9	24.4	27.2	16.6	52	1.89	1.72	2.9	250	16	0.00	-99.9	0.57	0.68
 1200	883.6	28.7	24.8	29.1	16.8	48	1.92	2.12	2.8	234	21	0.00	-99.9	0.70	0.84
 1300	992.2	31.0	25.5	29.9	16.9	46	1.93	2.29	3.8	202	20	0.00	-99.9	0.80	0.98
 1400	996.1	33.2	26.4	31.0	16.2	41	1.84	2.64	3.9	192	20	0.00	-99.9	0.83	1.03
 1500	905.7	34.5	27.4	31.3	14.5	36	1.66	2.90	3.7	207	23	0.00	-99.9	0.78	0.98
 1600	760.0	35.2	28.3	31.7	14.0	34	1.61	3.08	4.2	203	19	0.00	-99.9	0.71	0.92
 1700	388.6	34.8	29.0	30.9	13.4	34	1.54	2.93	3.7	213	19	0.00	-99.9	0.45	0.63
 1800	147.6	33.1	29.5	27.7	15.7	49	1.80	1.94	4.4	184	27	0.00	-99.9	0.27	0.42
 1900	71.8	31.2	29.5	25.2	17.3	61	1.98	1.24	4.4	175	12	0.00	-99.9	0.17	0.27
 2000	14.7	29.7	29.2	24.9	16.7	61	1.91	1.24	3.4	176	11	0.00	-99.9	0.11	0.19
 2100	0.0	28.5	28.8	24.0	16.7	64	1.90	1.08	3.6	188	40	0.00	-99.9	0.06	0.10
 2200	0.0	27.5	28.4	22.7	17.1	71	1.95	0.80	2.8	310	21	0.00	-99.9	0.04	0.07
 2300	0.0	26.7	27.9	20.6	17.4	82	1.99	0.44	3.3	295	17	0.00	-99.9	0.03	0.04
 2400	0.0	25.9	27.5	19.6	17.8	90	2.04	0.23	2.8	248	18	0.25	-99.9	0.01	0.02
 Sum	24.1 MJ	0.25	6.28	8.16
 Avg	27.6	26.7	24.6	16.6	64	1.89	1.28	2.8	226	43	-99.9
 Max	1320.4	35.2	29.6	32.2	18.8	93	2.16	3.33	8.6	-99.9
 Time	1158	1531	1748	1523	1216	2345	1216	1458	1724	9999
 Min	22.7	24.3	19.1	11.8	30	1.39	0.16	-99.9
 Time	655	949	2358	1450	1457	1450	2345	9999
 Precipitation by 15 minute periods 2345 0.25
 Figure 2.
Hourly file output format of the TXHPET network containing hourly meteorological data and ETo values plus daily values.
While these file formats are simple for the producers and other agricultural users, researchers generally desire more options and advanced type outputs.
Both can be programmed into the system but the main focus should be on the producer utilization; otherwise, it becomes cumbersome and more of research effort than a user product.
The research parts of the system may be "hidden" from the general user as necessary to prevent confusion.
Rainfall at the respective network sites is possibly the least relevant ET parameter of the data set although it is one of the most monitored by users.
Users should use site specific field rainfall in their irrigation scheduling method.
The values recorded by the TXHPET network are frequently in question from both producers and researchers alike and large differences often result from highly variable precipitation events or even from common rain gauge problems, including plugged funnels and ports.
Development with an ET network is typically not complete but rather an ongoing process.
Advances in the hardware and software change over time and most of this activity should be transparent to the user.
Over time new interrogation instrumentation and data modules plus computational methods have replaced the initial and earlier methods of acquisition.
Much of the original instrumentation and sensors are no longer available so upgrades are seemingly always forthcoming.
Additionally, researchers are progressing to evaluate ET values on smaller  time scales for new future irrigation application systems with data interrogation times becoming shorter.
Data and Calculated Values
 The TXHPET network has kept statistics of use and downloads since its inception and has in recent years averaged about 300,000 pages of disseminated information per year.
This past summer season, an additional 180,000 plus pages of crop ET downloads were noted indicating that as energy based pumping costs increased in 2008, users wanted more exacting ET
 Figure 3.
TXHPET network web page containing weather data selection.
data to assess and refine irrigation management practices.
This also coincided with an enhanced extension education effort by the limited staff associated with the TXHPET network in the Texas High Plains.
While the majority of users have been irrigated producers and crop consultants, others include farm managers, production consultants, seed production agronomists, agricultural engineers, researchers, extension specialists, water district managers and technicians, water planners and consultants, state agency regulators, design engineers and city water and parks superintendents.
The highest priority network users are the
 producers as they are the ones who have the opportunity to conserve the greatest amount of water in the region.
Also, most state water agencies appreciate the use of the network as it provides a sound basis for regional water planning efforts and documentable and consistent inputs into the groundwater availability model  used for future supply and demand planning.
The single most difficult challenge of operating an ET network, which has been experienced by others throughout the western U.S.
is that of securing sustained funding for operations and maintenance.
Development and upgrade dollars can be acquired but sustained funds for personnel are hard to secure.
Operational attempts to sustain operations from sales of the data have proved unsuccessful for almost all ET based networks and only account for approximately 5% of the needed revenue annually.
A well developed and maintained ET network is essential for implementation of irrigation scheduling within an intensively irrigated region.
The development of such a system should be an on-going effort whereby the interested parties, particularly the irrigated producers should provide input into future needs for integrated use of their operations.
The network can also provide data for a variety of other interests that use the data for wise and efficient use of water resources.
ASABE Standards.
2004.
EP505: Measurement and reporting practices for automatic agricultural weather stations.
St.
Joseph, Mich.: ASABE.
Texas Water Facts, 2008.
Texas Water Resources Institute, College Station, Texas.
However, the winter and spring of 2022-23 has been an exception for most of Nebraska, with off-season precipitation well below normal.
This has highlighted the only downside to leaving the soil dry at the end of the irrigation season: In years when we have a very dry off-season, we will need to pump some water in June to refill the profile before the high water demand days of July arrive.
The data showed that some fields were at field capacity at the end of the irrigation season in 2022, but many of the silt loam soil fields would require four to five inches of water to refill the profile.
The problem is, without soil water monitoring equipment, one will not know if their field is already refilled to field capacity or not.
Other lighter soil texture fields will take less water to refill them.
FLOW MEASUREMENT SERIES: FLOW METER CALCULATOR
 Water flow meters have become an increasingly common component of agricultural irrigation systems in Mississippi.
Besides indicating instantaneous flow rate, many flow meters also include a totalizer.
Totalizers keep a running tally of the water amount that has flowed through and been measured by the flow meter.
If you know how much irrigation water has been applied, you can more accurately assess the performance of an irrigation system.
Here are some examples:
 How does the water amount applied by this irrigation system compare with the water amounts associated with precipitation, evaporation, soil moisture, surface water supplies, groundwater recharge, etc.?
Should changes in system hardware and/or in management behavior be explored?
What is the cost of each application by this irrigation system?
Would the extra expenses from the next application exceed the extra revenue from the expected increase in crop yield?
How efficient is this irrigation system at using fuel or electricity to lift and pressurize water?
Would improvements in the pumping plant be attainable and justified?
Depending on product design, you might see totalizer readings in a mechanical set of rolling digits on the dial face of the flow meter or from an electronic display.
The units of the totalizer readings tend to be marked nearby.
See Figure 1.
Figure 1.
Correct inputs to the NCAAR Flow Meter Calculator for the example scenario.
Figure 2.
Corresponding outputs from the NCAAR Flow Meter Calculator for the example scenario.
Beginning Totalizer Reading: Enter the nonnegative number equal to the totalizer reading from which you wish to start calculating irrigation water volume.
Ending Totalizer Reading: Enter the nonnegative number equal to the totalizer reading at which you wish to stop calculating irrigation water volume.
Totalizer Units: Among the options within the dropdown menu, select the one that matches exactly the units of the totalizer readings.
Table 1 explains what each of the units signify.
Acres Irrigated: Enter the nonnegative number equal to the land area in acres that received the irrigation water volume being calculated.
If zero is entered instead, the Flow Meter Calculator will calculate gross water volume but not gross water depth.
Table 1.
Five options for the units of the totalizer readings in the NCAAR Flow Meter Calculator.
Totalizer units	Whenever the rightmost digit of the totalizer increases by 1,
 the flow meter has measured an additional
 "acre-feet X 0.001"	0.001 acre-feet = 0.012 acre-inches = 326 gallons
 "acre-feet X 0.01"	0.01 acre-feet = 0.12 acre-inches = 3259 gallons
 "acre-inches X 0.01"	0.00083 acre-feet = 0.01 acre-inches = 272 gallons
 "gallons X 100"	0.00031 acre-feet = 0.0037 acre-inches = 100 gallons
 "gallons X 1000"	0.0031 acre-feet = 0.037 acre-inches = 1000 gallons
 Gross Water Volume: Calculated as the difference between the beginning and ending totalizer readings, this quantity represents the total amount of irrigation water applied between the two reading times.
The Flow Meter Calculator reports the equivalent of this quantity in acre-feet, in acre-inches, and in gallons, respectively.
See Figure 2.
Gross Water Depth: Calculated as the ratio of the gross water volume over the irrigated area, this quantity represents the per-unit-area amount of irrigation water applied between the two reading times.
The Flow Meter Calculator reports this quantity in inches just like rain: the increase in depth if the irrigation water were added evenly across a pond the size of the irrigated area.
Converting water volumes to water depths enables comparisons among irrigation systems with different irrigated areas.
Before the first irrigation and after the last irrigation of a growing season, a farmer recorded the totalizer of a flow meter that measures all irrigation water for 160 acres.
Figure 3 shows the appearance of this mechanical totalizer at the two times when it was recorded.
Figures 1 and 2 give the correct inputs to and the corresponding outputs from the Flow Meter Calculator for this scenario.
Figure 3.
Illustration of a flow meter totalizer before the first irrigation  and after the last irrigation  of a growing season for the example scenario.
This publication is a contribution of the National Center for Alluvial Aquifer Research , the Mississippi State University Extension Service, and the Row-Crop Irrigation Science Extension and Research  initiative.
NCAAR is supported by the Agricultural Research Service, United States Department of Agriculture, under Cooperative Agreement number 58-6066-2-023.
RISER is supported jointly by the Mississippi Soybean Promotion Board, Mississippi Corn Promotion Board, Mississippi Rice Promotion Board, Cotton Incorporated, and Mississippi Peanut Promotion Board.
In addition to reducing pumping costs, when properly used to manage irrigation, sensors may also improve crop growth and yield by helping to avoid the detrimental effects of over watering on soil conditions and nutrient leaching.
As shown in NebGuide G1904 Plant Growth and Yield as Affected by Wet Soil Conditions Due to Flooding or Over-Irrigation, over irrigation of a Hastings silt-loam soil at the South Central Agricultural Laboratory near Clay Center reduced yields from 8 to 15 bushels per acre.
IRRIGATION RESEARCH WITH SUNFLOWERS IN KANSAS
 Sunflower is a crop of interest in the Ogallala Aquifer region because of its shorter growing season and thus lower overall irrigation needs.
Sunflowers are thought to better withstand short periods of crop water stress than corn and soybeans and the timing of critical sunflower water needs is also displaced from those of corn and soybeans.
Thus, sunflowers might be a good choice for marginal sprinkler systems and for situations where the crop types are split within the center pivot sprinkler land area.
CURRENT IRRIGATED SUNFLOWER STUDY AT KSU-NWREC
 A study was conducted in 2009 and 2010 at the KSU Northwest ResearchExtension Center in Colby, Kansas to examine the effect of three in-season irrigation capacities  with and without a preseason irrigation application  on sunflower yield and water use parameters.
All in-season irrigation events were scheduled using a weather-based water budget, so the irrigation capacities represent limits on irrigation not the actual applied amounts.
Volumetric soil water content was measured in each subplot to a depth of 8 ft in one-foot increments on a weekly to biweekly basis throughout the crop production seasons.
Additionally, the irrigation treatments were superimposed with three target seeding rates of plant populations.
A short stature hybrid  was planted on June 18, 2009 and June 16, 2010 and the crop emerged on June 25, 2009 and June 24, 2010, respectively.
Sunflower yield and yield components  seed oil quality, irrigation, total crop water use and crop water productivity  were determined for each subplot.
The data was analyzed using statistical procedures from PC-SAS.
The crop year 2009 was very cool and wet and irrigation needs were very low.
In 2009, wet weather resulted in no irrigation being required before July 27, 2009.
Irrigation amounts for the 1 inch every 4 and 8 days treatments were identical in 2009 at 2.88 inches  because the climatic water budget did not require the 1 inch every 4 days frequency to be used at maximum capacity.
The 1 inch every 12 days had two irrigation events for a total of 1.92 inches over the course of the season.
During the period April through October every month had above normal precipitation and between crop emergence and crop maturity the total precipitation was 10.18 inches.
There was a significant interaction of in-season irrigation capacity and plant population in 2009.
The general trend was for greatest yields at the lowest and intermediate plant population  when in-season irrigation capacity was at intermediate or the greatest levels.
At the lowest irrigation level, the trend was for the greatest yields at the intermediate and greatest plant population.
There were no other significant irrigation treatment effects on any yield component or water use parameter in 2009.
In 2009, plant population significantly affected all of the water use parameters and all of the sunflower yield components except seed yield and heads/plant.
The number of seeds/head and seed mass compensated for differences in plant population to achieve similar yield levels.
The early portion of the crop year 2010 was wet and irrigation needs were lower than normal.
However, later in season, it was extremely dry with only 1.08 inches of precipitation occurring between August 4 and crop maturity on October 11.
Wet weather resulted in no irrigation being required before July 25, 2010.
Inseason irrigation amounts were 11.52, 6.72, and 4.8 inches for the irrigation capacities limited to 1 inch/4 days, 1 inch/8 days and 1 inch/12 days,
 respectively.
The 2010 sunflower irrigation amounts appear to be approximately 1 inch less than normal as estimated from long term  irrigation scheduling simulations conducted at Colby, Kansas.
Figure 1.
Sunflower yield, seed mass and oil content as related to total crop water use and the targeted plant population at KSU Northwest Research-Extension Center, Colby, Kansas in 2010.
The three clusters of data points from left to right represent irrigation capacities of 1 inch/12 days , 1 inch/8 days  and 1 inch/4 days , respectively.
Table 1.
Summary of sunflower yield components and water use parameters for a sprinkler irrigated study, 2009, KSU Northwest Research-Extension Center, Colby Kansas.
capacity	Irrigation	Preseason	irrigation		Targeted	plant pop	Yield		plant pop	Harvest		Heads	/plant	Seeds	/head	mass	Seed		Seed	Oil%	Water	use		productivity		Water
 18	3266	16262	0.94	2114	46.6	45.6	17.14	191
 23	3324	20183	0.92	2043	40.2	46.2	17.69	189
 28	3109	23813	0.93	1720	37.2	46.6	17.30	180
 1 in/4 d	Mean	3233	20086	0.93	1959	41.3	46.2	17.38	186
 	18	3229	16553	0.94	2155	44.3	45.7	17.26	187
 23	3326	20328	0.93	1919	42.0	46.3	17.44	191
 28	3246	22942	0.99	1728	39.3	46.8	18.16	179
 Mean	3267	19941	0.95	1934	41.9	46.2	17.62	186
 Mean 1 inch/4 days	3250	20013	0.94	1947	41.6	46.2	17.50	186
 18	3376	16698	0.95	2259	43.4	45.7	17.24	197
 23	3189	20183	0.95	1893	40.4	46.0	17.45	183
 28	3081	22506	0.96	1790	37.5	46.5	18.05	171
 1 in/8d	Mean	3215	19796	0.95	1981	40.4	46.1	17.58	184
 	18	3427	16553	0.99	2214	42.8	45.0	17.72	193
 23	3208	19312	0.96	1934	40.6	46.1	17.37	185
 28	3332	22506	1.01	1766	38.4	46.6	18.17	184
 Mean	3322	19457	0.99	1971	40.6	45.9	17.76	188
 Mean 1 inch/8 days	3269	19626	0.97	1976	40.5	46.0	17.67	186
 18	3158	16408	0.93	2198	42.8	45.7	17.50	181
 23	3186	19457	0.96	1923	40.3	45.9	17.87	178
 28	3168	24103	0.91	1728	38.3	46.5	17.87	178
 1 in/12d	Mean	3171	19989	0.93	1950	40.5	46.0	17.75	179
 	18	3100	16117	0.97	2127	42.3	46.1	17.48	177
 23	3345	19166	0.96	1985	41.9	45.6	17.53	191
 28	3279	23522	0.94	1758	38.4	46.2	17.80	184
 Mean	3241	19602	0.96	1957	40.8	45.9	17.60	184
 Mean 1 inch/12 days	3206	19796	0.95	1953	40.7	46.0	17.68	182
 Study-Wide Mean	3242	19812	0.95	1959	40.9	46.0	17.61	184
 Preseason	None	3206	19957	0.94	1963	40.7	46.1	17.57	183
 Irrigation	5 inches	3277	19667	0.97	1954	41.1	46.0	17.66	186
 Target plant	18	3260	16432 C	0.95	2178 a	43.7 a	45.6 C	17.39 b	188 a
 population	23	3263	19771 b	0.95	1950 b	40.9 b	46.0 b	17.56b	186 a
 28	3203	23232 a	0.96	1748 C	38.2	46.5a	17.89 a	179 b
 Values within the same shaded column are significantly different at P<0.05 when followed by a different lower-cased letter.
Table 2.
Summary of sunflower yield components and water use parameters for a sprinkler irrigated study, 2010, KSU Northwest Research-Extension Center, Colby Kansas.
capacity	Irrigation	Preseason	irrigation		Targeted	plant pop	Yield		plant pop	Harvest		Heads	/plant	Seeds	/head	mass	Seed		Seed	Oil%	Water	use		productivity		Water
 18	3172	20038	0.94	1916	40.4	44.2	22.69	141
 23	2919	23668	0.89	1631	38.6	44.7	22.74	128
 28	2946	27007	0.85	1570	37.4	45.0	23.32	127
 1 in/4 d	Mean	3012	23571	0.90	1706	38.8	44.6	22.92	132
 	18	3000	19166	0.93	1845	42.3	43.8	20.99	143
 23	3062	23958	0.95	1646	37.3	44.7	21.15	146
 28	2987	25265	0.95	1597	36.1	45.3	20.72	145
 Mean	3172	20038	0.94	1916	40.4	44.2	22.69	141
 Mean 1 inch/4 days	3014 a	23184	0.92	1701	38.7	44.6 a	21.93 a	138 C
 18	3043	19602	0.92	1893	41.0	44.5	19.63	157
 23	2989	23377	0.98	1668	36.1	44.6	20.01	150
 28	3004	25700	0.97	1563	35.7	45.3	19.36	156
 1 in/8d	Mean	3012	22893	0.96	1708	37.6	44.8	19.66	154
 	18	3091	18440	0.98	1912	40.6	44.3	19.01	164
 23	2892	23087	0.93	1647	37.2	44.7	19.31	151
 28	2951	25410	0.98	1506	36.3	45.3	19.58	152
 Mean	3043	19602	0.92	1893	41.0	44.5	19.63	157
 Mean 1 inch/8 days	2995 a	22603	0.96	1698	37.8	44.8 a	19.48 b	155 b
 18	2983	19312	0.96	1868	39.4	43.2	17.25	175
 23	2886	23522	0.96	1715	34.4	43.6	16.85	175
 28	2705	27588	0.88	1480	34.4	44.0	17.10	159
 1 in/12d	Mean	2858	23474	0.93	1688	36.1	43.6	17.07	170
 	18	3059	19021	0.95	1983	39.0	43.7	18.12	170
 23	2831	22942	0.94	1613	37.0	43.6	17.99	158
 28	2833	26572	0.91	1511	35.5	44.1	17.67	162
 Mean	2908	22845	0.93	1702	37.2	43.8	17.93	163
 Mean 1 inch/12 days	2883 b	23159	0.93	1695	36.6	43.7 b	17.50 C	167 a
 Study-Wide Mean	2964	22982	0.94	1698	37.7	44.4	19.64	153
 Preseason	None	2961	23313 a	0.93	1700	37.5	44.3	19.88	152
 Irrigation	5 inches	2967	22651 b	0.95	1695	37.9	44.4	19.39	155
 Target plant	18	3058 a	19263 C	0.94	1903 a	40.5a	43.9 C	19.61	158 a
 population	23	2930 b	23426 b	0.94	1653 b	36.81	44.3 b	19.67	151 b
 28	2904 b	26257 a	0.92	1538 C	35.9 b	44.8a	19.62	150 b
 Values within the same shaded column are significantly different at P<0.05 when followed by a different lower-cased letter.
Summary of Current Field Study
 The crop year 2009 was too wet to gain much information on response of sunflower to irrigation, but there was the general trend of greater yields for lower or intermediate plant populations  under intermediate or higher irrigation capacities.
In contrast, sunflower yield increased with greater plant population at the lowest irrigation level.
In 2010, a year that was wet in the early portion of the season, but very dry after August 4, sunflower seed yield increased with in-season irrigation capacity up until a capacity of 1 inch/8 days.
The lowest plant population  gave the greatest yield  and also had significantly greater seeds/head and seed mass.
Crop water use was slightly, but significantly greater  for the highest plant population in 2009 but was not affected in 2010.
Crop water productivity was not affected by irrigation in 2009 but increased with decreased levels of irrigation in 2010.
Increased plant population tended to decrease crop water productively primarily because of seed yield reduction.
The field study will be continued in 2011 because of the wetter than normal conditions experienced in 2009 and 2010.
RESULTS FROM EARLIER STUDIES AT KSU-NWREC
 Irrigation studies with sunflower have been conducted periodically at the KSU Northwest Research-Extension Center since 1986.
These irrigation treatments in these studies varied with some studies applying various percentages of wellwater crop water use , some studies applying water at specific sunflower growth stages, and some studies using water budget irrigation scheduling under various irrigation system capacities.
Yield response varied some from year to year and some between studies as might be anticipated, but on the average 154 lbs of sunflower seed was obtained for each acre-inch of water use above a yield threshold of approximately 3 inches.
Figure 2.
Sunflower yield response to total seasonal crop water use for selected studies conducted at the KSU Northwest Research-Extension Center, Colby Kansas, 1986-2007.
The PD data from 2000 and 2001 was from dryland studies.
The IT data from 2000 and 2001 was from studies scheduled by stage of growth.
The data from the PI studies had irrigation applied at various growth periods throughout the summer.
All other studies presented here were scheduled according to various percentages of crop water use.
RESULTS FROM SIMULATION MODELING
 Thirty-nine years  of weather data was used to create simulated irrigation schedules for sunflower and also corn for a comparison crop.
These irrigation schedules were also coupled with a crop yield model to estimate crop yield at various irrigation capacities  and under dryland production.
Although corn has greater crop water use  and requires more irrigation  than sunflower, their peak water use rates and peak irrigation rates are very similar.
Under full irrigation , corn uses approximately 4.3 inches more water than sunflower during the season but only requires approximately 2.3 inches of additional irrigation because of its growth period encompasses some months of greater rainfall.
Although peak ET and peak irrigation needs are similar between the two crops, sunflower's needs are for a much shorter duration and occur at a time when corn's needs are about to start declining.
Figure 3.
Simulated average cumulative crop water use , rainfall and gross irrigation requirement for sunflower and corn for the 39 year period 1972 through 2010 at Colby, Kansas.
Irrigation scheduling simulations were performed for sprinkler irrigation amounts of 1 inch at an application efficiency of 95%.
Figure 4.
Simulated average daily crop water use  and gross irrigation requirements for sunflower and corn for the 39-year period 1972 through 2010 at Colby, Kansas.
Irrigation scheduling simulations were performed for sprinkler irrigation amounts of 1 inch at an application efficiency of 95%.
The data are presented as a 4 day moving average.
The shorter duration of peak ET and irrigation needs for sunflower and their occurrence at a time when peak needs for corn are about to decline open up some opportunities to shift irrigation allocations between crops.
Additionally, the yield decline with just slightly deficit irrigation is usually very small with sunflowers compared to corn.
Under the right economics, sunflower can be a good candidate for deficit irrigation.
Figure 5.
Simulated average relative crop yield of sunflower and corn as affected by irrigation capacity at Colby, Kansas for the 39-year period 19722010.
Irrigation capacity data points left to right are dryland, 1 inch every 10, 8, 6, 5, 4 or 3 days, respectively.
A capacity of 1 inch/4 days is equivalent to an irrigation capacity of 589 gpm/125 acre center pivot irrigation system.
Figure 6.
Average monthly distribution of irrigation needs of sunflower and corn at Colby, Kansas for the 39-year period 1972-2010 as determine from simulated irrigation schedules.
Research continues with developing irrigation strategies with sunflower in western Kansas.
Declines in sunflower yield with deficit irrigation are less drastic than with corn, so producers may wish to consider sunflower when irrigation system capacities are marginal.
Sunflower and corn have similar peak ET and irrigation rate requirements for full irrigation, but sunflower requires about 2.3 inches less irrigation and its peak needs began at about the time corn needs are starting to decline.
Average full irrigation of sunflowers would be approximately 12 inches, but often producers will apply between 8 and 10 inches of irrigation because the amount of yield decline is only a few percentage points.
This paper was first presented at the Central Plains Irrigation Conference, February 22-23, 2011, Burlington, Colorado.
It can be cited as
Chapter: 25 Liming South Dakota Soils
 Corn production can be limited by too low or too high soil pH values.
The soil pH is a measure of the concentration of the H+ ion in the soil solution and it is reported on the logarithmic scale.
It can range from 0 to 14 and a neutral solution has a pH value of 7.
A pH change in one pH unit represents a 10-fold increase or decrease in acidity or alkalinity.
Soil pH is highly variable and in many fields it can range from 6.0 in well-drained upper landscape positions to 8.0 in poorly drained lower landscape positions.
Soil pH influences many soil properties, including nutrient availability and toxicities, plant growth, nutrient transformation, and herbicide effectiveness.
The purpose of this chapter is to discuss liming requirements and the implications of soil pH on the soil chemical and biological properties.
Why Soil pH is Important
 Figure 25.1 Landscape variability resulting in soil pH variability.
Soil pH influences crop productivity and it is a measure of soil acidity  and alkalinity.
Soil pH requirements vary for different crops.
For example, legumes typically require a higher soil pH than grasses or cereals.
Herbicide effectiveness can also be influenced by soil pH.
For example, Hitbold and Buchanan  reported that atrazine persistence increases with pH, whereas imazaquin , imazethapyr , and atrazine effectiveness are decreased with decreasing soil pH.
Soil phosphorus is generally most available at pH values between 6.5 and 7.0.
At low soil pH values  the microbial process that converts ammonium  to nitrate  can be slowed.
Soils have varying abilities to moderate pH changes resulting from the addition of acids and bases.
This ability to moderate pH is called buffering capacity.
As a rule of thumb, soils with high clay and organic matter contents have higher buffering capacities than low organic matter, sandy soils.
One of the primary factors contributing to reductions in the soil pH  is the transformation of ammonium  based fertilizers ,
 Table 25.1 The impact of fertilizer source on the amount of calcium carbonate  lime required to neutralize the acidity produced during the nitrification of the ammonia contained within the fertilizer.
Fertilizer source	Chemical	% N	Lbs lime/	Lbs lime/
 composition	lb fertilizer	lb of N
 Anhydrous ammonia	NH3	82	1.48	1.80
 Urea	CO2	46	0.84	1.83
 Ammonium sulfate	(NH	21	1.12	5.33
 anhydrous ammonia) to nitrate .
This transformation process acidifies soil by producing hydrogen ions when the ammonium ion is nitrified to nitrate.
In South Dakota fields with low soil pH values, yields can be increased by applying lime.
Research conducted between 1999 and 2013 showed that corn yields were reduced 10% to 20% when the soil pH value was less than 5.8 , and that applying lime minimized these yield reductions.
The amount of lime required is dependent on both the soil pH and soil buffering capacity.
Low pH soils are most often observed in the eastern side of South Dakota.
South Dakota Lime Recommendation
 South Dakota lime  recommendations are based on the buffer pH  index method.
In this method, a soil extractant is used to measures the reserve alkalinity.
Lime requirements may be different for different problems  and the rates should be adjusted based on the lime composition, purity, and fineness.
In the past, lime has not been widely used in South Dakota, and available liming materials may include agricultural lime, pelleted agricultural lime, or municipal water-treatment lime.
South Dakota research showed that: 1) pelletized lime and municipal water-treatment lime have similar impacts on soil pH ; 2) there are differences between conventional and no-tillage systems ; and 3) the lime effectiveness was higher when tilled into the soil because lime is not mobile in the soil.
Figure 25.2 Relationship between pH and relative corn yields in South Dakota conventional-tillage and no-tillage plots.
The dashed line represents the 95% confidence interval, and the research was conducted between 1999 and 2013.
Table 25.2.
Influence of N rate management on surface soil pH  at the South Dakota Southeast Research Farm.
The recommended N rates were based on the yield goal, rotation, and the amount of nitrate-N contained in the surface 2 feet.
In this experiment, urea fertilizer was applied at rates of 0, 200, and 400 lbs N/ acre from 1988 to 2006.
Nitrogen treatment	N Rate	pH 
 Check no nitrogen	0	6.3
 Spring recommended N rate	110	6.0
 Split recommended N rate	110	5.7
 Fall recommended N rate	110	6.0
 Spring 200	200	5.5
 Spring 400	400	5.0
 Table 25.3 The influence of South Dakota NASS region [northeast, NE; southeast, SE; north-central, NC; southcentral SC; and western regions, WR ] on the pH value of soil samples submitted to the SDSU Soil Testing Laboratory.
South Dakota	pH range
 RegionB	<6.1	6.1-6.5	6.6-7.0	7.1-7.5	>7.5
 -log[H+]	% of samples
 NE	6.61	21	27	27	17	8
 SE	6.37	32	30	23	11	4
 NC	6.49	26	30	25	14	5
 SC	6.78	6	24	43	22	4
 WR	6.98	8	25	20	19	29
 Overall	6.54	24	28	26	15	7
 A samples analyzed by the SDSU Soil Testing Laboratory B NE=northeast, SE=southeast, NC=north-central, SC=south-central, WR=west river
 Table 25.4 The amount of lime in South Dakota needed to raise the soil pH to 6.0.
Lime rates were based on the CaCO equivalent of 90% and total effectiveness of 70%.
One ton of pure 3 CaCO 3 is equivalent to 1.6 tons of material.
Buffer Index	Lime required for 0-6 inch soil depth
 Table 25.5 The influence of the dry weight of different liming products and tillage on soil pH.
Lime sludge was applied in 2005 and it was obtained from the Brookings Municipal Water Treatment Plant, while the Super Cal was obtained from Calcium Products Inc., located in Gilmore City, IA.
Within a column, pH values with different letters are significantly different.
The LSD is the least significant difference between treatment means, NS means not significantly different.
Source	Rate	0-2"	2-4"	4-6"	0-6"	0-2"	2-4"	4-6"	0-6"
 Check	0	5.3 b	5.5 b	5.6 b	5.4 b	5.2 b	5.4 b	5.5	5.3 b
 Lime sludge annually applied 1998-2005	1	7.6 a	7.4 a	6.3 a	7.1 a	7.3 a	6.4 a	5.9	6.5 a
 Super Cal annually applied 1998-2005	1	7.4 a	7.2 a	6.2 a	7.0 a	7.3 a	6.5 a	5.9	6.6 a
 Super Cal applied in 1998 and 2002	4	7.5 a	7.5 a	6.3 a	7.1 a	7.4 a	6.5 a	6.4	6.8 a
 LSD	0.3	0.4	0.5	0.4	0.2	0.4	NS	0.3
 Field research suggests that corn yields can be increased by lime in soils with pH values <5.8.
Relatively low pH values are attributed to acidity produced during nitrification of applied N.
Lime effectiveness is determined by CaCO content and fineness of the material.
Pelletized and water-treatment lime appear to be equally effective in changing soil pH.
Soil pH changes from lime application was less effective at subsurface depths with no-till compared with conventional-tillage, however, grain yields were comparable.
Corn grain yield improvement can be expected from lime applications if buffer pH is <6.4 and when the soil pH is <5.8.
Examples for determining lime requirements are available in Clay et al.
and US USDA-NRCS.
Chemigation pumps: Drain and clean pump and hoses.
Also, keep in mind the corn roots grow about an inch each day into soil that is at field capacity, providing much of the water the plants need for that day.
Generally, irrigation needs to be delayed until the soil begins to dry down.
Furthermore, research conducted in the North Platte area has shown that irrigation could be reduced by one to four inches, compared to a fully irrigated crop, during the vegetative period without a significant yield reduction and can stimulate deeper root growth.
For more information, go to "Vegetative Growth Stage Irrigation, Is It Needed This Year?"
UNIFORMITY OF IN-CANOPY CENTER PIVOT SPRINKLER IRRIGATION
 Freddie R.
Lamm Research Agricultural Engineer KSU Northwest Research-Extension Center 105 Experiment Farm Road, Colby, Kansas 67701 USA
 Written for Presentation at the 1998 ASAE Annual International Meeting Sponsored by ASAE
 Disney's Coronado Springs Resort Orlando, Florida July 12-16, 1998
 Portions previously presented at the Irrigation Association's 14th Annual International Irrigation Exposition and Technical Conference, San Diego, California, November , 1993.
Using center pivot sprinkler nozzles below the top of the corn crop canopy presents unique design and management considerations.
Distortion of the sprinkler pattern can be large and the resultant corn yield can be reduced.
Concepts are presented to help explain the different design and management considerations.
Keywords: Sprinkler irrigation, LEPA, Spray nozzles, Irrigation management
 UNIFORMITY OF IN-CANOPY CENTER PIVOT SPRINKLER IRRIGATION
 Using center pivot sprinkler nozzles below the top of the corn crop canopy presents unique design and management considerations.
Distortion of the sprinkler pattern can be large and the resultant corn yield can be reduced.
Concepts are presented to help explain the different design and management considerations.
There is much interest in LEPA and in-canopy center pivot sprinkler irrigation.
However, there are additional management and system design considerations whenever the sprinkler application pattern no longer results in a relatively uniform broadcast application.
This paper will primarily discuss from a conceptual approach, ideas such as symmetry of sprinkler application within the crop, spatial orientation of sprinklers with respect to crop canopy, and crop canopy sprinkler pattern distortions with respect to time-of-season.
Symmetry of sprinkler application is when each plant or crop row has approximately equal opportunities for the irrigation water.
An example of the concept of spatial orientation of sprinklers with respect to crop canopy might be the crop row orientation in relation to the direction of center pivot sprinkler travel.
The importance of the time-of-season pattern distortion depends on whether the distortion occurs for the full season or whether it only occurs for a short period.
SYMMETRY OF SPRINKLER APPLICATION
 Traditionally, sprinkler irrigation systems have been designed to uniformly apply water to the soil at a rate less than the soil intake rate to prevent runoff from occurring.
These design guidelines need to be either followed or intentionally circumvented with appropriate design criteria when designing and managing a center pivot irrigation system using LEPA and other in-canopy sprinklers.
The importance of uniformity of water application and/or infiltration has been documented by numerous workers.
Seginer  reported that an increase in uniformity can increase yields and decrease percolation.
Duke et al.
reported on several scenarios where improving the uniformity of center pivot sprinkler irrigation systems would be highly desirable from both an economic and environmental standpoint.
Their results show irrigation non-uniformity such as overirrigation resulting in nutrient leaching or underirrigation resulting in water stress can cause significant economic reductions.
In some cases where irrigation is limited, a lower value of uniformity can be acceptable.
For example, if the maximum water application amount still falls upon the upward sloping line of the yield production function, a crop area deficient of water will be compensated for by an area receiving a larger amount of water.
The example of nonuniform deficit irrigation has the same average application amount as the uniform irrigation amount.
Overall production under the two systems would be identical because the production function is linear over the range of water applications.
Figure 1.
Hypothetical relationship of relative crop yield and relative water needs for non uniform deficit irrigation  and for uniform deficit irrigation.
Average relative water need is the same for both irrigation schemes and consequently the average relative yield would also be the same.
The use of LEPA and other in-canopy sprinklers does not necessarily result in nonuniform application.
In explaining the concept of the LEPA system, Lyle  points out that one of the seven defining principles is that each plant should have an equal opportunity for water.
Using the LEPA nozzle in the furrow between adjacent pairs of crop rows obeys this principle.
Using a 1.5 m nozzle spacing with 0.75 m spaced crop rows planted circularly results in plants being approximately 0.38 m from the nearest sprinkler.
Figure 2.
LEPA concept of equal opportunity for plants to applied water.
LEPA nozzles are centered between adjacent pairs of corn rows.
Some irrigators are experimenting with wider in-canopy sprinkler spacings to reduce investment costs.
In the Central Great Plains, some irrigators are trying 2.3, 3.0 and even 4.6 m in-canopy sprinkler spacings.
Spray nozzles which perform adequately at these spacings above bare ground have a severely distorted pattern when operated within the canopy.
Hart  concluded from computer simulations that differences in irrigation water distribution occurring over a distance of approximately 1 m were probably of little consequence and would be evened out through soil water redistribution.
Seginer  noted that the overall effect on production of irrigation nonuniformity is related to the horizontal root zone of the crop.
Figure 3 shows large differences in uniformity of irrigation application.
These differences may or may not always translate into yield differences, but they should be considered in design.
is too wide for in-canopy application.
Nozzles are located at right and left edge of each graphed line.
Figure 3.
Differences in application amounts and application patterns that can occur when nozzle spacing
 Distortion of the pattern will usually result in overwatering some areas which leads to runoff or deep percolation and underwatering in other areas which leads to crop yield reductions.
Some irrigators in the Central Great Plains have tried to counter this argument by stating that their low capacity systems on nearly level fields restrict runoff to the general area of application.
If this is so, using the concepts expressed by von Bernuth , this non uniformity is probably acceptable.
However, nearly every field has small changes in land slope and field depressions which do cause runoff if the irrigation application rate exceeds the soil infiltration rate.
Another requirement of true LEPA point.
In many cases this will require tillage management such as a system is that there should be no runoff from the application furrow dams.
The directionof travel of the center pivot sprinkler lateral with respect to crop row direction has added importance when in-canopy application is used.
Generally, it has been recommended that irrigators plant rows circularly so that the rows are perpendicular to the sprinkler lateral.
This satisfies two of the principles of LEPA irrigation noted by Lyle : 1) be capable of conveying and discharging water into a single crop furrow; and 2) each plant has equal opportunity for irrigation water.
In the Central Great Plains farmers have been reluctant to plant row crops such as corn in circular rows.
Much of this reluctance is related to the concern about narrow or wide "guess" rows which cause cultivation and harvesting problems.
However, using in-canopy sprinklers in non-circular planted rows can pose two problems.
If the sprinkler lateral is perpendicular to the crop rows and the sprinkler spacing exceeds twice the crop row spacing, there will be nonuniform water distribution because of pattern distortion.
If the sprinkler lateral is parallel to the crop rows there may be excessive runoff due to the large amount of water being applied in one or a few crop furrows.
Differences in application amounts and patterns can be very large between the two crop row orientations.
Figure 4.
Two problematic orientations for in-canopy sprinklers in non-circular rows.
Figure 5.
Differences in application patterns and amounts for in-canopy sprinklers in circular and noncircular rows.
PATTERN DISTORTION AND TIME OF SEASON
 The duration and the time of season that sprinkler pattern distortion occurs significantly affect the performance of in-canopy irrigation.
It has been a common practice for several years in northwest Kansas to operate drop spray nozzles just below the center pivot truss rods.
This results in the sprinkler pattern being distorted after corn tasseling.
This has had relatively little negative effects on crop yields.
The reasons are that there is a fair amount of pattern penetration around the tassels and because the distortion only occurs during the last 30-40 days of growth.
In essence the irrigation season ends before severe deficits occur.
Compare this situation with in-canopy sprinklers at a height of 0.45-0.60 m that may experience pattern distortion for more than 60 days of the irrigation season.
If one assumes that a 50% pattern distortion might occur after tasseling, some corn rows would experience a 76 mm irrigation deficit.
Assuming a 50%
 distortion for the 0.45-0.60 m sprinklers beginning 30 days earlier would result in irrigation for some rows being 43% less than the needed amount.
Yield reductions would be expected for the latter case because of the extended duration and severity.
When the pattern is distorted and the nozzle spacing is wide enough to prevent some corn rows from getting equal opportunity to water, yields can be reduced  Even though the average yield for both rows was high, there is a 3 Mg/ha yield difference between the row 38 cm from the nozzle and the corn row 114 cm from the nozzle for the 0.6 m nozzle height and 3 m nozzle spacing.
There was slightly less row to row difference as the nozzle height is increased in 1997, as would be expected since pattern distortion was for a shorter period of time for the higher nozzle heights.
Figure 6.
Hypothetical cumulative effect of 50% irrigation reductions for some corn crop rows as caused by in-canopy pattern distortions as related to time of occurrence, 30 or 60 days into the crop season at Colby Kansas.
Figure 7.
Row-to-row variations in corn yields as affected by sprinkler height for 3.0 m spaced in-canopy sprinklers.
Data averaged across 4 irrigation levels.
Data from 1997 sprinkler height study at Colby, Kansas.
Most, if notall, of the concepts expressed in this paper are not new and many are intuitively obvious.
However, there are still poorly designed and poorly managed in-canopy irrigation systems.lt is the responsibility of irrigation professionals to remind irrigators that efficientand effective irrigation delivery starts with sound hardware design and ends with good management.
1 The mention of trade names or commercial products does not constitute their endorsement or recommendation by the authors or by the Kansas Agricultural Experiment Station.
YEAR TO YEAR VARIATIONS IN CROP WATER USE FUNCTIONS
 As well capacities continue to decline, many producers cannot meet full crop evapotranspiration  if they decide to irrigate all their acres.
To optimize net returns they have to allocate limited water resources to a mix of crops.
In addition, they have to efficiently manage the water during the season in order to maximize crop water use efficiency.
Crop water use functions also known as production functions have been widely used by agronomists, engineers and economists to quantify crop yield response to water.
Although production functions have proved to be robust and useful for long term planning, they are not well suited for predicting crop yield response to water on short time scales  because they exhibit substantial year to year variation and they are site specific.
Several studies have reported the year to year variation in crop water use curves.
Vaux and Pruitt  reviewed literature on crop production functions from several studies and noted that there was a great deal of variability in both the estimated coefficients and functional forms of the productions functions from year to year and from site to site.
INTER-ANNUAL VARIATION IN CROP YIELD VERSUS IRRIGATION FUNCTIONS
 Corn Yield Response to Water at Garden City Kansas
 More recently work by Klocke et al.
based on a long term limited irrigation cropping systems study at Garden City Kansas showed that crop water use functions varied substantially from year to year as shown in Figure 1.
The study consisted of 6 frequency based irrigation treatments ranging from dry land to full irrigation.
Irrigation frequencies included irrigating every 5, 7, 8, 12, 16 and 22 days.
Figure 1.
Corn response curves to irrigation from 2005 to 2013; the numbers in parentheses are annual rainfall recorded at Garden City Kansas.
The substantial year to year variability shown by the different curves in Figure 1 indicates that production functions are not well suited for making short term or seasonal water management decisions.
The observed variability can be attributed to several factors including: 1) seasonal changes in rainfall amounts and patterns, 2) changes in evaporative demand, 3) cultural practices , 4) salinity, 5) differences in crop cultivars and their response to water use, 6) effect of water deficit at different growth stages and inter-dependency of growth stage water stress effects and 7) other miscellaneous factors such as hail or freeze damage.
Howell  gives a review of how some of the above factors influence major crop production processes such as CO2 assimilation, transpiration and dry matter production.
It can be seen in Figure 1 that during wet years without hail, the yield versus irrigation function are curvilinear while for the two drought years of 2011 and 2012 the response functions were linear mimicking the yield versus evapotranspiration relationship which is typically linear.
This probably indicates that during drought years crop water use efficiency was high with little losses to percolation and runoff thus the yield versus irrigation curve approximated a straight line.
Hail damage occurred in 2005, 2006 and 2008 which also contributed to the increased inter-annual variations in crop yield response to irrigation water applied.
In order to minimize the effect of inter-annual variations in weather, relative corn yield was plotted against irrigation as shown in.
It can be seen in Figure 2 that during drought years  18 inches of irrigation water was needed to attain maximum yield while during wet years like 2009 only 8 inches of irrigation water was required to attain maximum yield.
This large variability makes it impractical to use the average crop water use function in Figure 2 for seasonal prediction of crop yield response to water applied.
However it can be seen from Figure 3 that uncertainty in crop yield response to water decreased as the amount of irrigation increased, probably due to the reduced effect of variable weather conditions.
Irrigation Water Applied 
 Figure 2.
Corn relative yield response to irrigation from 2005 to 2013 at Garden City Kansas.
Figure 3.
Corn yield response to irrigation from 2005 to 2013 at Garden City Kansas.
Weather Conditions during the Study Period
 Figure 4 shows seasonal variation in both amount and distribution of rainfall at Garden City Kansas from 2005 to 2013.
In addition, to rainfall other factors that influence production of dry matter and eventually yield include evaporative demand, solar radiation and atmospheric CO2 concentration.
Evaporative demand expressed in the form of vapor pressure deficit  shown in Figure 4 has a direct effect on the partitioning between soil evaporation and transpiration which depends on soil surface wetness  and the amount of crop
 development  and thus has a direct effect on transpiration efficiency.
In Figure4 it can be seen that VPD was highest during the drought years of 2011 and 2012 and the year following the drought in 2013.
This variation in VPD could probably explain the observations in Figure 2 where you needed much more water  to attain maximum yield.
For example you needed 8 inches of irrigation to attain maximum yield in 2009 which was a wet year with lower VPD compared to 19 inches in 2011 which was a dry year with high VPD.
The rate of dry matter production is also governed by the amount of photosysthetically active radiation  that is intercepted by the plant canopy.
PAR is directly influenced by the amount of solar radiation.
From Figure 4 it can be seen that solar radiation varied during the study period from 2005 to 2013.
Although this variation does not appear to have limited yields  with lower solar radiation but with high rainfall producer higher yields compared to 2012 with slightly higher solar radiation but low rainfall.
Temperature which mainly influences crop phenology/development did not exhibit substantial inter-annual variations during the study period.
Given the dynamic nature of environmental factors and their influence on key crop production processes such as assimilation, transpiration and dry matter production, some investigators have recommended use of dynamic process-based crop growth models as an alternative to static production functions when predicting crop yield response to water on short time scales.
Howell  recommended using crop growth models coupled with monitoring as expert systems for making real time irrigation management decisions.
Others have recommended use of crop growth models that account for the biophysical processes controlling the soil-plant-atmosphere system.
Figure 4.
Weather variation during the limited irrigation cropping study at Garden City Kansas from 2005 to 2013.
Dynamic Crop Growth Models for Predicting Crop Yield Response to Water
 Crop growth models can be used for both strategic and tactical irrigation water management.
For example in a strategic mode they could be used for evaluating alternative irrigation management strategies  to determine the one that will optimize net returns during the season.
In a tactical mode, dynamic crop growth models could be executed several times in-season with actual data such as measured or forecasted weather data, leaf area index, canopy cover and soil water with the goal being to refine prior irrigation management options selected at the beginning of the season.
There are various types of process-based crop growth models that incorporate various levels of complexity.
Despite their potential usefulness, simulations from crop growth models should be considered as aids and not absolute recommendations.
This is because models are only simplifications of the complex biophysical system e.g., most models do not account for weed and insect pressure or even freeze or hail damage.
Crop yield response to water functions exhibit large year to year variations and therefore should only be used for long term planning and not seasonal prediction of crop yield response to water.
Environmental and management factors that influence key processes that determine yield such as assimilation, transpiration and dry matter production need to be considered when predicting crop yield response to water on a daily or seasonal basis.
Dynamic crop growth models coupled with monitoring offer promise for improved on-farm seasonal water management.
Contribution no.
15-284-A from the Kansas Agricultural Experiment Station.
OPTIMIZING CROPPING SYSTEMS UNDER LIMITED IRRIGATION CONDITIONS
 Research was initiated in 2001 and conducted through 2010 under sprinkler irrigation at Tribune, Kansas to evaluate limited irrigation in several no-till crop rotations on grain yield, water use, and profitability.
Crop rotations were 1) continuous corn, 2) corn-winter wheat, 3) corn-wheat-grain sorghum, and 4) corn-wheat-grain sorghum-soybean.
Irrigation was limited to 10 inches annually with 5 inches applied to wheat, 15 inches to corn , and 10 inches to grain sorghum, soybean, and continuous corn.
Crop water productivity and yield of corn was greater when grown in rotation than with continuous corn.
The length of the rotation did not affect grain yield or crop water productivity of grain sorghum or winter wheat.
Continuous corn was generally the most profitable cropping system.
However, changes in prices or yields could result in multi-crop rotations being more profitable, indicating the potential for alternative crop rotations to reduce risk under limited irrigation.
Irrigated crop production is an important component of agriculture in western Kansas.
However, with declining water levels in the Ogallala Aquifer and high energy costs, optimal utilization of limited irrigation water is required.
Precipitation is limited and sporadic in the region with annual precipitation supplying about 60-90% of the seasonal water requirement for grain sorghum and only 50-75% for corn.
While crop rotations have been used extensively in many dryland systems, the most common crop grown under irrigation in western Kansas is corn (about 50% of the irrigated
 acres), often in a continuous corn system.
While corn responds well to irrigation, it also requires substantial amounts of water to maximize production.
Almost all of the groundwater pumped from the High Plains  Aquifer is used for irrigation  with 57% applied to corn.
This amount of water withdrawal from the aquifer has reduced saturated thickness by as much as 150 ft.
Although crops other than corn are grown under irrigation, they have not been grown as extensively because of relatively inexpensive water and a ready market for corn to the livestock feeding industry in the area.
The trend in western Kansas during the 1990s has been towards increasing acreage of irrigated corn  with corresponding reductions in grain sorghum  and winter wheat .
Although corn is expected to remain the dominant irrigated grain crop , the need exists to develop strategies to more effectively utilize limited irrigation water for corn.
While there have been increases in irrigated soybean acreage , there has been limited research on its water use characteristics in western Kansas.
Alternative crop management practices are needed to reduce the amount of irrigation water required while striving to maintain economic returns sufficient for producer sustainability.
To prepare for less water available for irrigation in the future, whether from physical constraints  or from regulatory limitations, information on crop productivity and profitability with less irrigation water will be beneficial for agricultural sustainability.
A field study was conducted at the Kansas State University Southwest ResearchExtension Center near Tribune, Kansas from 2001 to 2010 on a deep silt loam soil.
Only data collected beginning in 2003 are presented to allow time for establishment of the crop rotations.
The region is semi arid with a summer precipitation pattern and an average annual precipitation of 17.3 inches.
The study consisted of four crop rotations; continuous corn , corn-winter wheat , corn-winter wheat-grain sorghum , and corn-winter wheat-grainsorghum-soybean.
Each phase of each rotation was present each year and replicated four times.
The plots were approximately 60 ft wide and 120 ft long.
Irrigations were scheduled to supply water at the most critical stress periods  for the specific crop and were limited to 1.5 inches per week.
If precipitation was sufficient within a week, then irrigation was postponed.
In some years, the maximum amount of irrigation was not applied because of above normal precipitation.
The average first irrigation was 14 June for corn in rotation,
 23 June for continuous corn, and 4 July for sorghum and soybean.
The final irrigation averaged 28 August for corn in rotation, 15 August for continuous corn, and 22 August for sorghum and soybean.
If needed to aid emergence of wheat, irrigation was initiated in the fall  otherwise irrigation was reserved for spring application with average final irrigation on 6 June.
Average plantings dates were 3 May for corn, 20 May for soybean, and 27 May for grain sorghum.
Winter wheat was planted after corn harvest.
Cultural practices  typical for the region were used in all years of the study.
The center portion of all plots was machine harvested with grain yields adjusted to 15.5% moisture  for corn, 13% for soybean, and 12.5% for sorghum and wheat.
Plant densities were determined along with the other yield components.
The plots were irrigated with a linear move sprinkler irrigation system which had been modified to allow for water application from different span sections as needed to accomplish the randomization of plots.
Soil water measurements  were taken throughout the growing season using neutron attenuation.
Available soil water was calculated by subtracting unavailable water from measured soil water.
All water inputs, precipitation and irrigation, were measured.
Crop water use was calculated by summing soil water depletion  plus in-season irrigation and precipitation.
Non-growing season soil water accumulation was the increase in soil water from harvest to the amount at emergence the following year.
Precipitation storage efficiency was calculated as non-growing season soil water accumulation divided by non-growing season precipitation.
Crop water productivity  was calculated as grain yield  divided by crop water use.
Statistical analyses were performed using the GLM procedure from SAS version 9.1.
Local crop prices and input costs were used to perform an economic analysis to determine net return to land, management, and irrigation equipment for each treatment.
Custom rates were used for all machine operations.
Harvest prices and input costs were kept uniform for all years based on 2010 prices.
The objectives of this research were to determine the effect of limited irrigation on crop yield, water use, and profitability in several crop rotations.
All rotations were limited to an average of 10 inches of irrigation annually; however, corn following wheat received 15 inches because the wheat received only 5 inches.
This extra 5 inches of irrigation water increased the level of irrigation to nearly full and increased corn yields about 40 bu/acre compared to continuous corn.
Thus, limited irrigated corn yielded about 80% of full
 irrigation.
These results are similar to those reported by Klocke et al.
that found limited irrigation  corn yields were 80 to 90% of fully irrigated yields at a location in Nebraska with average annual precipitation of 20 inches.
In a simulation study using weather data from Northwest, Kansas, Lamm et al.
found a 38% reduction in applied irrigation from nearly ful irrigation  only reduced yields about 21 %.
Corn grain yields averaged across different tillage treatments and plant densities were only reduced 9%  for a 25 % reduction in applied irrigation amount  in a field study at Colby, Kansas.
Corn yields in the multi-crop rotations were similar regardless of length of rotation.
Wheat and grain sorghum yields were similar in all rotations.
Table 1.
Average grain yields of four crops as affected by crop rotation, KSU Southwest Research-Extension Center, Tribune, Kansas, 2003-2010.
Crop	CC	CW	CWS	CWSB
 Corn	163 b	203 a	202 a	203 a
 Wheat	-	35 a	36 a	37 a
 Sorghum	134 a	138 a
 t CC = continuous corn; CW = corn-wheat; CWS = corn-wheat-grain sorghum; CWSB = corn-wheat-grain sorghum-soybean.
I Means within a row with different letters are significantly different.
Statistical analysis was not completed for column means.
Crop water productivity was ranked in the order of corn > sorghum > wheat = soybean.
Crop water productivity of corn was increased when irrigation was increased to 15 inches and grown in rotation with other crops.
Grain sorghum grown in 4-yr rotations had slightly greater crop water productivity than grown in 3-yr rotations.
The length of rotation had no effect on crop water productivity of wheat.
Table 2.
Average crop water productivity of four crops as affected by crop rotation, KSU Southwest Research-Extension Center, Tribune, Kansas, 2003-2010.
Crop	CC	CW	CWGS	CWSB
 Corn	377 b+	411 a	398 a	410 a
 Wheat	-	115 a	125 a	122 a
 Sorghum	-	-	314 b	326 a
 t CC = continuous corn; CW = corn-wheat; CWS = corn-wheat-grain sorghum; CWSB = corn-wheat-grain sorghum-soybean.
I Means within a row with different letters are significantly different.
Statistical analysis was not completed for column means.
An economic analysis  found that the most profitable crop was corn in rotation with other crops.
Profitability was similar for grain sorghum and soybean in the 3and 4-yr rotations.
The least profitable crop was wheat, primarily because of reduced yields caused by hail and spring freeze injury in about 50% of the years.
However, the most profitable crop rotation was continuous corn.
All multicrop rotations had net returns of $57-69 acre-1 less than CC.
Lower returns in the multi-crop rotations were due to low returns from wheat.
Table 3.
Net return to land, irrigation equipment, and management from four crop rotations, KSU Southwest Research-Extension Center, Tribune, Kansas, 2003-2010.
Crop	CC	CW	CWS	CWSB
 Corn	237	332	326	321
 Wheat	-	4	1	5
 Net for rotation	237	168	172	180
 t CC = continuous corn; CW = corn-wheat; CWS = corn-wheat-grain sorghum; CWSB = corn-wheat-grain sorghum-soybean.
With limited irrigation , continuous corn has been more profitable than multi-crop rotations including wheat, sorghum, and soybean primarily because of spring freeze and hail damage to wheat in the multi-crop rotations.
In multi-crop rotations, relatively poor results with one crop  can reduce profitability compared with a monoculture, especially when the monoculture crop does well.
However, the multi-crop rotation can reduce economic risk when the monoculture crop does not perform as well.
All multi-crop rotations had net returns $57-69 acre-1 less than continuous corn.
However, changes in prices or yields could result in any of the rotations being more profitable than continuous corn, indicating the potential for alternative crop rotations under limited irrigation.
This research was supported in part by the Ogallala Aquifer Program, a consortium between USDA Agricultural Research Service, Kansas State University, Texas AgriLife Research, Texas AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
Contribution no.
12-314-A from the Kansas Agricultural Experiment Station.
This paper was originally presented at Innovations in Irrigation Conference, San Diego, CA, 6 Nov.
2011.
Kansas Department of Agriculture.
1997.
Kansas reported water use summary, calendar year 1995.
State of Kansas, Topeka, Kansas.
Kansas Farm Facts.
1991 and 2001.
Kansas Agricultural Statistics.
Kansas Dept.
of Agriculture and U.S.
Dept.
of Agriculture, Topeka, Kansas.
Kansas Water Office.
1997.
1995 Kansas irrigation water use.
State of Kansas, Topeka, Kansas.
ENVIRONMENTAL QUALITY INCENTIVE PROGRAM AND PRACTICING IRRIGATION WATER MANAGEMENT
 Allen Gehring Nebraska State Water Management Engineer Natural Resources Conservation Service Grand Island, Nebraska Voice: 308-395-8586 Fax: 308-382-3688 Email: Allen.Gehring@ne.usda.gov
 All conservation water management practices done in cooperation with the Natural Resources Conservation Service  Environmental Quality Incentive Program  Ground and Surface Water Management  involve some level of irrigation water management.
The EQIP project does not end with the installation of an irrigation practice, it is only the beginning.
Once the NRCS and an EQIP Participant have entered into a contract it is the goal of NRCS to be involved "in the field" by demonstrating and showing the irrigator how to utilize the available water management tools.
Although the irrigator is in control of when and how much to irrigate; NRCS teaches that irrigation water management is a balance of science and forecasts predictions to determine when and how much to irrigate.
NRCS hopes to improve upon the current water management techniques while preserving and sustaining our natural resources.
The level and techniques of irrigation water management are a function of how the irrigator wishes to manage the irrigation system.
NRCS traditionally teaches and demonstrates conventional techniques such as: using soil moisture probes for soil sampling, using the appearance-feel method for available soil moisture content, and using locally published crop Evapotranspiration  data to forecast crop water use.
These measurement techniques, or versions there-of, can be a very effective means of practicing irrigation water management.
NRCS also recognizes the technological advances in the arena of automated irrigation water management.
These automated techniques can use data logging and/or telemetry type equipment with soil moisture sensing equipment to provide continuously recorded real time soil moisture readings.
This information can then be readily available to the system operator in order to adjust and schedule the irrigation system for real time field conditions.
Once the technique of irrigation water management has been established record keeping and documentation become a vital means of implementing the irrigation water management part of the EQIP Contract.
Every EQIP Ground and Surface Water Contract contains a clause in which the irrigator agrees to practice and document his or her particular irrigation water management program for a specified time.
Typically this is for two to three irrigation seasons after the practice has been installed on the field.
Subsequent records are provided to the NRCS for the items agreed to within the EQIP Contract.
The primary documentation tool that NRCS has offered to irrigators for use in documenting their irrigation water management program is the attached NE-ENG-80 Form.
Instructions on how to complete and use this form are also attached.
Assistance in completing this form can also be provided through your local NRCS Office.
Populating and utilizing this form regularly can aid in the process of deciding when and how much to irrigate.
It will also allow the irrigator to know exactly how much water has been pumped per irrigation and how much has been pumped over the course of an irrigation season.
An irrigator can use a different version of this form if they so chose, as long as the form is equivalent in content.
The irrigation water management tools, techniques, documentation forms and one-on-one NRCS Technical Assistance all work toward sustaining and preserving our natural resources.
It is also the hope that after EQIP contractual requirements have been met the irrigator will continue to utilize these tools to fine tune their irrigation water management techniques.
IRRIGATION WATER MANAGEMENT RECORD SHEET
 Length of Run  
 Average Furrow Grade or Slope
 Well/Water Source Output 
 Available Water at Field Capacity in Root Zone 
 Maximum Allowed Depletion 
 Soil Moisture Def 
  Rate2 2 
 Inches Appl.
3 
 Meter Read Start 
 Meter Read Stop 
 No.
Gates Open 
 Out Time4 4 
 Set or Rev.
Time 
 Soil Moisture Deficit in inches beginning of day in root zone.
2
 The ET rate used for scheduling the current irrigation.
3
 Gallons pumped /27,154/acres = inches applied.
4
 Average time for water to reach the end of 50% of the rows.
Seasonal Water Application 
 INSTRUCTIONS FOR IRRIGATION WATER MANAGEMENT RECORD SHEET
  Name of producer.
Field number in which IWM is being applied.
ASCS tract number.
Number of acres in field.
Length of furrows if gravity irrigated.
Average furrow grade if gravity irrigated or slope of field if sprinkler irrigated.
The well or water source output in gallons per minute.
The date that the water source output was last checked or measured.
Location, phone number, radio station, of evapotranspiration  data for the nearest weather station.
Available water at field capacity in the crops root zone for the soil listed.
The maximum allowed depletion of the available water before irrigation should be scheduled.
The date each irrigation is started.
The soil moisture deficit on the day that irrigation is started, this is the amount in inches that the soil will hold, without runoff or deep percolation.
The evapotranspiration  rate, or the average daily crop water use rate on the day the irrigation is started.
Inches applied, this is the gross amount of water pumped or delivered to the field or to the set, whichever applies.
The sum of this line equals the gross amount delivered to the field for the season.
This is to record the meter reading, clock time or hour meter reading at the beginning of each irrigation.
Meter reading at the end of each irrigation.
The number of furrows being irrigated for this set or irrigation.
The average gallons per minute flowing down the furrows may be substituted when furrow length varies or set size is not constant.
This is the average time it takes for one half of the furrows in any given set to reach the end of the field, and the data can be used to evaluate the irrigation to make adjustment to achieve higher efficiency, more uniform distribution, or decrease deep perk.
This line is used to record the time water is allowed to run on the set being evaluated.
In cases where this record is being pushed on Center Pivot irrigation, record the hours for one revolution of the pivot.
Record the dates of rainfall during the growing season.
Record the rainfall amounts for the field.
Keep factors that need explanation in the notes.
Total irrigation water application for the season.
Total rainfall for the growing season, at a minimum rainfall from May through September must be kept.
Note: The use of this form is intended to satisfy requirements to record irrigation information for various water quantity or quality programs in Nebraska.
It is not intended for this form to be considered a water management plan or complete scheduling tool.
The information included on this form will be used to evaluate the irrigation system to determine the effectiveness of the system.
In this scenario, the tenant typically pays for and owns removable, above ground equipment: power unit, pivot, etc.
Personal property taxes will be increased for the tenant, with the ownership of a new or additional pivot.
Another consideration is insurance of the pivot.
If the pivot is owned by the tenant, it should be insured by the tenant.
The primary source of low uniformity is faulty sprinkler nozzles as well as pressure differences along the system.
Faulty sprinklers can be comprised of missing, clogged, and worn nozzles, stuck sprinklers, and out of sequence nozzle packages.
Joel P.
Schneekloth Reg.
Water Resource Spec.
Colorado State Univ.
Akron, Colorado Voice:  345-0508 Fax:  345-2088 Email: Joel.Schneekloth@Colostate.Edu
 Dennis A.
Kaan Reg.
Ag.
Economist Colorado State Univ.
Akron, Colorado  345-2287  345-2288 Dennis.Kaan@Colostate.Edu
 James Pritchett Extension Specialist Colorado State Univ.
Fort Collins, Colorado Voice:  491-5496 Fax:  491-2067 Email: James.Pritchett@Colostate.Edu
 Full irrigation is the amount needed to achieve maximum yield.
However, when water supplies for irrigation are insufficient to meet the full evapotranspiration  demand of a crop, limited irrigation management strategies will need to be implemented.
The goal of these strategies is to manage the limited water to achieve the highest possible economic return.
Restrictions on water supply are the primary reasons for using limited irrigation management.
These restrictions may come in the form of mandated water allocations, from both ground water and surface water supplies, low yielding wells, and/or drought conditions which decrease available surface water supplies.
KEY MANAGEMENT STRATEGIES FOR DEALING WITH LIMITED IRRIGATION
 The key management choices for dealing with insufficient irrigation supplies are as follows:
 Reduce irrigated acreage and maintain the irrigation water applied
 Reduce amount of irrigation water applied to the whole field
 Rotate high water-requirement crops with those needing less water
 Delay irrigation until critical water requirement stages of the crop
 Manage the soil water reservoir to capture precipitation
 Reducing irrigated acreage is one response to limited water supplies.
When the irrigated area is reduced the amount of irrigation per acre more closely matches full irrigation requirements and it's corresponding per acre yield.
Ideally, the land that reverts to dryland production should still produce some level of profitable returns.
Another strategy may be to reduce the amount of irrigation per acre that is applied to the entire field.
This would create the possibility for near normal crop yields if above normal precipitation occurred.
In normal to below normal rainfall years, grain yields per acre would be less than those achieved with full irrigation.
Rotating high water-requirement crops, such as corn, with crops needing less water would also be a possibility.
Soybean, edible bean, winter wheat, and sunflower are the major crops with lower water requirements.
Splitting fields between corn and one of these crops would reduce total water requirements for the field and distribute the water requirements across a longer portion of the growing season.
For example, peak water demands for wheat are during May and June, while corn uses the most water during July and soybean water needs peak in August.
Splitting the field into multiple crops allows producers with low-capacity wells to more completely meet the peak requirements of all crops.
Delaying irrigation until critical times is also a possible alternative if the volume of water is limited but well capacity is normal.
Water availability during reproductive and grain filling growth stages is the most important for grain production.
During vegetative growth some water stress can be tolerated without affecting grain yield and root development can be encouraged so that the crop can utilize deeper soil water.
This period also typically coincides with the highest monthly rainfall amounts in the central plains.
Field research from the West Central Research and Extension Center  near North Platte has shown that corn can utilize water from deep in the soil profile when necessary.
However, the irrigation system must be capable of keeping up with water demands during the reproductive growth stage of the crop if irrigation is delayed.
Delayed irrigation is more feasible with center pivots than with furrow irrigation.
In furrow irrigation, dry and cracked furrows do not convey water very well, especially during the first irrigation.
A combination of furrow packing during the ridging operation, surge irrigation, and increased stream size may overcome some of the effects of late initiation of furrow irrigation.
An important management strategy under all limited irrigation situations is to capture and retain as much precipitation as possible.
Crop residues on the soil surface intercept rainfall and snow, enhance infiltration, and reduce soil evaporation.
Again, residue management is much easier with center pivot irrigation than furrow irrigation.
Advancing water down a furrow may be more difficult with high residue levels.
Ridge-till management along with furrow packing and surge irrigation may overcome some of these problems.
Leaving room in the soil to store precipitation during the non-growing season enhances the possibility for capturing rainfall for the next growing season.
Leaving room in
 the soil to store rainfall during the growing season may ensure more water availability during grain filling under limited water conditions.
It is very important to know the soil water status during the entire season.
Limited irrigation management causes the irrigator to operate with more risk of crop water stress and grain yield reductions.
Knowledge of soil water can help anticipate how severe the stress might be and help avoid disaster.
HOW CROPS RESPOND TO WATER
 Crops respond to evapotranspiration  in a linear relationship.
For each inch of water that crop consumptively uses, a specific number of bushels is the resulting output.
This relationship holds true unless excessive crop water stress occurs during the early reproductive growth stages.
Where the response function intercepts the X-axis is the development and maintenance amount for each crop.
The more drought tolerant crops  typically have lower development requirements than do high response crops.
Not all of the water that is applied to a crop through rainfall or irrigation is used by the crop.
Losses such as runoff or leaching occur and are not useable for ET.
Irrigation is applied to supplement rainfall when periods of ET are greater than available moisture.
However, not all of the water applied by irrigation can be used for ET.
Inefficiencies in applications by the system result in losses.
As ET is maximized, more losses occur since the soil is nearer to field capacity and more prone to losses such as deep percolation.
When producers are limited on the amount of water that they can apply by either allocations or low capacity wells, wise use of water is important for maximizing the return from water.
The yield increase of crops to water decreases as input levels approach maximum yield levels.
In simple terms, as the amount of input and yield increases, the return from each unit is less than the previous unit.
The yield increase from adding water from amount A to amount B is more than when increasing from amount B to C.
A producer must use this type of input to make informed decisions.
The decision that must be made is irrigating at amount C with fewer acres or at amount B with more acres.
The same question must be asked when comparing irrigation amount B to A.
Developing a realistic yield vs irrigation production function is critical to managing limited water supplies.
Producers must know what the yield increase from adding additional units of irrigation water to that crop is to determine the optimal amount of water to apply to that crop.
The trade off that must be evaluated is the potential return per acre with each scenario.
ALLOCATING LIMITED WATER SUPPLIES
 When water is unlimited, the management strategy is to add inputs such as water until the return from that input is equal in value to the added crop production.
However, when water is limited, the management strategy should look at maximum return from each unit of input of water.
When producers are limited in the amount of water they can either pump or are allocated and that amount of water is less than what is needed for maximum economic production, producers must look at management options that will provide the greatest possible returns to the operation.
A Single Irrigated Crop and a Dryland Crop
 The easiest production option would be to look at a single irrigated crop with the remainder of production in either a dryland crop or fallow.
When the amount of water is less than adequate for maximum production, producers must ask themselves whether the yield increase from increasing the amount of irrigation to each acre will offset the reduction in irrigated acres and increased dryland production.
Increasing the amount of irrigation to a crop reduces the total number of irrigated acres.
An example of this would be if you have 10 inches per acre available for irrigation.
One option is to irrigate all acres at 10 inches.
A second option would be to irrigate 2/3 of the acres at 15 inches and have the remainder at dryland production.
The question to answer is "Does the yield increase offset the reduction in irrigated acres and having 1/3 of the potential irrigated acres in dryland production?" With a 130 acre irrigation system, a change in strategy such as this would reduce the irrigated acres from 130 to 87 acres and increase the dryland acres from 0 to 43 acres.
If corn is the primary irrigated crop, several crops could be used as dryland crops in this scenario including winter wheat, soybeans or sunflowers.
Two or More Irrigated Crops
 The use of two or more irrigated crops in a rotation may increase the number of irrigated acres as compared to a single irrigated crop and a dryland crop.
The philosophy of this strategy is to use a high water use and response crop such as corn and a low water use and response crop such as winter wheat, soybean, dry edible beans or sunflowers.
This strategy uses the yield vs irrigation to its maximum advantage.
The first amounts of irrigation that are applied are used efficiently resulting in a yield response similar to that of the yield vs ET response shown in Figure 2.
The strategy to find the most economical split of water and acres is similar to that of the one irrigated crop strategy.
Producers must look at the yield increase of adding water to one crop and the effect upon the irrigated acres and yield of the other irrigated crop.
The potential options become more numerous because now producers need to look at increasing the irrigation amount for one crop versus
 reducing the irrigation amount to the other crop or increasing the number of irrigated acres for the other crop to compensate for the additional water to that crop.
An example of this would be if you again had a water supply of 10 inches per acre available and are irrigating two crops such as corn and winter wheat.
If a producer were irrigating corn at 15 inches per acre and wheat at 5 inches per acre, the irrigated acres would be even at 65 acres per crop to match your water supply.
If this producer decides to irrigate wheat at 6 inches per acre, a first option would be irrigating corn at 14 inches per acre to keep the irrigated acres of each crop similar.
A second option to keep corn at the 15 inch per acre of applied water would be to reduce the irrigated acres of corn and increase the irrigated acres of wheat.
Using the second option, the final acres would be irrigating 58 acres of corn and 72 acres of wheat.
When using three potentially irrigated crops, the options become even more numerous.
It is important to look at the short-term rotation aspects with multiple crops being grown.
One of the more important aspects is can a crop be grown after itself.
There are several crops that do not perform well when planted after the same crop.
The typical problem associated with this is the build up of diseases and weeds in the system.
Crops such as winter wheat, soybeans or sunflowers should not be grown immediately after itself so this must be a consideration in how many acres of each crop can be grown or whether to grow more than two irrigated crops to increase the options in the rotation.
When working with low capacity systems, irrigation management strategies are limited due to the systems ability to meet the ET of the crop during the critical and high ET time periods.
Irrigators must start their systems before the soil moisture reaches typical management criteria with best management practices.
This must be done since the system can not replace the used soil moisture and crop ET so the soil must be managed so that it is closer to field capacity in anticipation of the greater crop ET demand later in the season.
The use of more than one irrigated crop decreases the amount of irrigated acres at any one point in time so the system can apply water closer to or in excess of the demand by the crop.
Another important consideration with more than one irrigated crop is to choose crops that do not have critical water timing needs.
Crops such as winter wheat and corn fit together well in a system such as this since wheat uses water in May and early June while corn requires water during July and early August.
Planting two crops that have similar water timing needs together is not advantageous since both crops would be irrigated at the same time.
CALCULATING CROP ENTERPRISE COST OF PRODUCTION
 Calculating cost of production and enterprise net returns is accomplished with enterprise budgeting techniques.
In basic terms, an enterprise budget is a listing of income generated and expenses incurred to produce that income.
In this setting, the enterprise is the production of corn, winter wheat, soybean, dry edible bean or sunflower, whichever crop is used in the rotation.
The income section of the budget lists all the income generated per acre from production of the crop.
This would also include any secondary income such as aftermath grazing or roughage sales.
For planning purposes, it would be more efficient not to include government programs in this analysis, but recognize net income will be lower as a result.
The price received for each commodity can be based on national crop loan rates as a minimum.
A realistic expectation of price received will produce realistic results in the analysis.
The expense section of the enterprise budget lists all the expenses associated with production of the commodity.
The expenses can be broken down by variable and fixed costs.
Variable costs of production are those costs that change with the level of production.
For instance, fertilizer cost increase as more fertilizer is applied to increase crop yield.
Other variable costs include seed, chemical inputs, fuel and labor among others.
In the absence of accurate machinery operating costs, custom rate estimates can be substituted in the enterprise budget.
A breakdown of all expenses included in the custom rate will be required to avoid double counting of fixed or variable expenses.
Fixed costs of production are those costs that need to be covered regardless of whether production occurs or not.
These include machinery replacement, land and machinery debt payments, lease payments and other overhead costs such as insurance, taxes and interest payments.
The net income section of the budget calculates the difference between estimated cost and returns.
A positive difference  indicates there is a positive return to the factors of production whereas a negative return would indicate the income generated is not sufficient to cover the factors of production.
Once net return per acre is calculated for each enterprise, then net return for the chosen mix of crops to be produced under a limited irrigation situation can be
 determined.
Working through this process on paper will identify the best option for producing the greatest net returns given resource limitations.
A spreadsheet is under development to help producers determine the optimum crop mix is under development.
This tool will allow producers to input cost of production, yield vs irrigation production functions and water allotments.
The spreadsheet will then give producers a starting point in helping them determine the optimum crop mix and water allocation for several management options.
This spreadsheet should be available in March or April.
It is important for producers to consider management and cropping practice changes when faced with limited water availability.
Management strategies for limited water generally favor introduction of low water use crops to supplement high response crops.
Full irrigation management strategies favor high water usehigh response crops.
An economic analysis will help producers with decisions on what irrigated crops are to be grown and how much water will be applied to each crop.
It is important to for producers to have accurate information relating to yield response of crops to irrigation in making these decisions.
During the peak of summer heat and plant growth, alfalfa may use over one half inch of water per day.
This compares to cooler spring days water usage of less than  inch of water per day.
Hunting Waterfowl and Doves on Agricultural Lands in Arkansas
 A Summary of Migratory Bird Baiting Regulations for Landowners and Hunters
 Rebecca McPeake Professor Wildlife
 Arkansas Is Our Campus
 Arkansas has a wealth of ducks and doves, thanks to public support for maintaining and improving wildlife habitat and hunters who abide by hunting rules and regulations.
Setting out bait for waterfowl or doves, or even hunting over a baited agricultural field, is not only unsportsmanlike and unethical, it is illegal.
Determining what is "baiting" can be a problem if hunters and landowners do not understand federal regulations about baiting migratory game birds.
Waterfowl and doves are treated differently under these regulations.
Hunting migratory game birds, which includes doves, ducks, geese, coots and cranes, in baited areas is illegal.
The U.S.
Fish and Wildlife Service and the Arkansas Game and Fish Commission are the agencies empowered to enforce regulations about baiting migratory birds.
Baiting migratory game birds either by placing bait or directing the placement of bait is a criminal offense with fines up to $100,000 for an individual or $200,000 for an organization and up to a one-year prison term.
Hunting over a baited area can result in a fine up to $15,000 and imprisonment for six months.
Both hunters and landowners are responsible for understanding regulations about baiting.
A baited area is where "salt, grain or other feed has been placed, exposed, deposited, distributed or scattered" in such a way as to lure or attract waterfowl or doves where hunters are attempting to take them.
This includes luring birds "to, on or over areas" where
 hunting occurs.
Current regulations make it unlawful to take or hunt any migratory game bird by the aid of baiting if the person "knows" or "reasonably should know" an area is baited.
Even after the bait has been removed, a hunter could be convicted if it is proven that he or she knew or reasonably should have known the area was baited within 10 days prior to the hunt.
Landowners who established the baited area for hunters can be prosecuted as well.
The presence of any grain or feed, particularly grain or feed that is scattered or piled, should alert a hunter or landowner that the area may be baited.
Figure 1.
Agricultural lands provide habitat for waterfowl and doves.
Photo by Tim McCabe, Natural Resources Conservation Service.
Discarded grains, such as corn affected by aflatoxin or other plant diseases, should be buried or spread and incorporated into the soil.
Hunters cannot hunt migratory game birds over discarded grain from storage bins or livestock feeders where grain is piled.
Such baits must be removed from the hunting area at least 10 days prior to the hunt.
Even after bait removal, an area is considered baited for up to 10 days because waterfowl and doves may continue to return after the bait has been removed.
Agricultural and Soil Conservation Practices
 Some agricultural practices attract wildlife although the producer may not have intended to attract waterfowl or doves for hunting.
Practices conducted in a normal agricultural operation include planting, harvesting and post-harvest manipulation for the purpose of producing and gathering a crop or preparing for next season's crop.
Manipulation means the alteration of natural vegetation or agricultural crops and residue by activities that include mowing, shredding, discing, rolling, chopping, trampling, flattening, burning or herbicide treatments.
Hunters are allowed to hunt waterfowl and doves in harvested fields if part of a normal agricultural harvest.
This includes rice field crop residue that has been flooded, rolled or mowed.
What if a field hasn't been harvested?
The rules for waterfowl are more strict than for doves.
It is legal to hunt ducks and geese if the unharvested cropland has not been mowed, rolled or otherwise manipulated.
Dove hunting regulations are more liberal.
Dove hunting is considered legal when unharvested fields have been mowed, rolled or manipulated.
Doves can also be hunted over pasturelands that are planted to improve grazing conditions for livestock.
Figure 2.
Unlike the past, baiting and harvesting large numbers of waterfowl is illegal.
Photo courtesy of the U.S.
Fish and Wildlife Service.
Other farm management activities, such as soil stabilization practices, may attract waterfowl or doves to an area.
A normal soil stabilization practice means planting for controlling soil erosion for agricultural purposes or post-mining land reclamation.
Hunters may legally hunt over areas that are planted as part of a normal soil stabilization practice for agricultural purposes.
Factors determining whether a soil stabilization practice is "normal" are slope, aspect and other existing conditions at the site.
Use of native plant species is encouraged for stabilizing creek sides and road construction.
An added benefit is that hunting over natural vegetation is not considered baiting.
Many normal agricultural operations and soil stabilization practices are not considered baiting.
However, any additional effort made to attract waterfowl or doves could be a problem.
This includes overseeding a field, piling or shoveling grain in a plowed field or other actions that are unreasonable or economically unsound as a farming practice.
What Is a "Normal Agricultural Operation"?
Federal regulations identify state Cooperative Extension Service specialists as experts for determining what constitutes a normal agricultural operation or soil stabilization practice.
Whether an agricultural operation is considered "normal" is a very difficult and complex assessment based on many variables, such as type of grain, seeding or planting date, seeding rate, method of planting or harvest, single or multiple applications, preand post-harvest manipulations, seasonal weather conditions and geographic location, to name a few.
It may also involve an economic analysis of the cost of harvest versus market prices for the crop to determine whether a particular agricultural operation would be profitable.
University of Arkansas Cooperative Extension Service specialists have provided recommendations  to the Arkansas Game and Fish Commission and the U.S.
Fish and Wildlife Service for distinguishing a normal agricultural operation from baiting migratory game birds.
These recommendations will help hunters, farmers, landowners, natural resource professionals and the general public distinguish a normal agricultural planting from baiting for several common commodity crops.
The U.S.
Fish and Wildlife Service makes the final determinations about whether recommendations were followed.
These recommendations  are intended to provide a general understanding of what constitutes a normal agricultural operation in a typical year.
A wide margin has been built into these guidelines for differences which may occur in any given year or geographic
 location in Arkansas; however, even these margins may not reflect accurately a normal agricultural operation in extreme or uncommon situations.
Any planting date or seeding rate that falls outside these parameters could be considered baiting, unless particular conditions or circumstances indicate otherwise.
Farmers who practice sustainable agriculture may plant wildlife food plots as part of their integrated management system.
Hunting leases for deer, turkey, quail and other wildlife can provide supplemental income for farmers.
Confusion arises when food plots planted for a particular wildlife species also attract doves or waterfowl.
The legality of hunting doves over top-sown, freshly-planted food plots  is debatable and could be construed as baiting.
To avoid any questions, planting of wildlife food plots should occur early enough to allow time for the seeds to germinate at least 10 days before dove or waterfowl season.
The recommendations for distinguishing
 baiting from a normal agricultural operation  apply to planting wildlife food plots.
Wildlife food plots may be planted at other times or have heavier seeding rates applied, but it is advisable that hunters do not hunt doves in these areas, since these areas could be considered baited.
Agricultural and Hunting Practices for Doves
 What options do landowners have for developing good habitat for a dove hunt?
Natural vegetation and crops, such as millet, sunflower, corn and other grains, can be grown and manipulated to improve dove hunting.
After the grain is ripe and just before the hunt, standing crops can be mowed, dragged down, disced or burned to attract doves.
The manipulation of crops or natural feeds is an effective technique to improve dove hunting.
Manipulation provides a good chance for attracting many doves during the
 Table 1: Recommendations for Identifying Planting Dates and Seeding Rates as Part of a Normal Agricultural Operation
 Earliest Planting Date	Latest Planting Date	Rate Per Season
 Barley	August 15	April 1	288 lbs/ac
 Corn	February 15	July 1	25 lbs/ac
 Millets	April 1	August 31	40 lbs/ac
 Browntop	132 seed/sq ft
 Japanese	142 seed/sq ft
 Pearl	78 seed/sq ft
 Proso	74 seed/sq ft
 Oats	August 15	April 15	256 lbs/ac
 Rice	March 1	July 1	180 lbs/ac
 Rye 	August 15	April 1	224 lbs/ac
 Sorghum 	March 1	July 1	15 lbs/ac
 Sorghum 	April 1	August 15	60 lbs/ac
 Soybeans 	March 15	August 1	120 lbs/ac
 Sunflower	March 1	July 15	15 lbs/ac
 Triticale 	August 15	April 1	240 lbs/ac
 Wheatb	August 15	April 1	240 lbs/ac
 Winter annual	August 15	April 1	60 lbs/ac
 forage legumes	29 seed/sq ft
 Unmanipulated, second-year growth reclassifies millet as natural vegetation.
PRecommendations are that wheat can be replanted once within two weeks of its initial planting if germination does not occur.
A maximum of 80 seeds/square foot total is allowable to be considered a normal agricultural practice.
hunting season.
Also, many other species of wildlife may benefit from food that is scattered because of a normal agricultural planting or harvest.
However, it is illegal to deliberately scatter grain on a field after a crop has been harvested.
The grain grown in the field may not be redistributed onto the field after it has been collected, harvested or gathered.
Grain found in piles or in other large concentrations is not a normal agricultural planting, thus hunting over piles of grain is considered baiting.
Specifically, it is legal to hunt doves:
 where unharvested crops have been manipulated, including a crop or portion of a crop that has not been harvested due to equipment failure, weather, insect infestation, disease or any reason;
 where seeds or grains have been scattered  as a result of a normal agricultural operation or agricultural soil stabilization practice, including top-sown or aerial seeding;
 where grain grown on the land is scattered solely as the result of the manipulation  of an agricultural crop;
 over standing or manipulated natural vegetation;
 over "hogged down" fields where livestock have fed on standing crops;
 from a blind camouflaged with natural vegetation;
 from a blind camouflaged with vegetation from agricultural crops, provided that grains or other feed from the crops are not exposed or scattered, thus creating a baited area.
Figure 3.
Dove hunting marks the beginning of the fall season for many hunters.
Photo courtesy of the Missouri Department of Conservation.
Agricultural and Hunting Practices for Waterfowl
 Regulations governing baiting are more restrictive for waterfowl than for doves.
Hunting ducks and geese is permitted in areas where there has been a normal agricultural planting, harvesting or postharvest manipulation or soil stabilization practice.
However, unlike doves, waterfowl hunting is not permitted when unharvested crops are manipulated  to attract waterfowl, especially if such practices occur near a duck blind.
Producers may sometimes leave portions of a field unharvested because the grain is of poor quality, diseased or
 otherwise uneconomical to harvest.
It is legal to hunt over these unharvested portions of the field if no manipulation has occurred.
Flooding of unharvested agricultural crops is legal as long as the crop has not been manipulated.
Hunters should avoid hunting in any field where a portion of the crop is unharvested and the stalks knocked down to attract waterfowl.
Specifically, it is legal to hunt waterfowl:
 over standing crops or flooded standing crops, including aquatic plants;
 over standing, flooded or manipulated natural vegetation;
 in flooded fields after crops are harvested;
 where grains or top-sown seeds have been scattered solely as the result of a normal agricultural harvest or post-harvest manipulation;
 from a blind camouflaged with natural vegetation;
 from a blind camouflaged with vegetation from agricultural crops, provided that grains or other feed from the crops are not exposed or scattered, thus creating a baited area;
 where grain from standing or flooded standing agricultural crops is inadvertently scattered by hunters entering or leaving an area, placing decoys or retrieving downed birds.
It is illegal to hunt waterfowl:
 where unharvested crops have been manipulated, including a crop or portion of a crop that has not been harvested due to equipment failure, weather, insect infestation, disease or any reason;
 anywhere seed or grain is present, unless the seed or grain was scattered solely for the purpose of planting or harvest to produce and gather a crop, or normally would have remained after manipulating and removing a harvested crop;
 over harvested grains arranged in rows or piles;
 where grain is fed to livestock;
 where seeds remain on the surface of ground from planting for erosion control on a construction site.
Using Natural Vegetation to Attract Migratory Game Birds
 To avoid problems with interpreting regulations about baiting, landowners and hunters can attract migratory game birds using natural vegetation.
Natural vegetation that is manipulated for improving hunting conditions is not considered baiting.
Federal
 regulations specifically allow mowing, shredding, discing, rolling, chopping, trampling, flattening, burning and herbicide treatments of natural vegetation in a hunting area.
However, landowners and hunters need to be certain that the vegetation being manipulated is classified as "natural." Natural vegetation means any nonagricultural, native or naturalized plant species.
Landowners who want to manage their land for waterfowl are encouraged to plant native or natural vegetation.
The following are some examples of what is considered natural vegetation for doves and waterfowl in Arkansas:
 American sweetgum	Annual sedge
 Croton	Chufa 
 Common pokeberry	Fall panicum
 Loblolly pine	Pennsylvania smartweed
 Prairie sunflower	Redroot flatsedge
 Amaranth 
 amaranth, pigweed)	Rice cutgrass
 White pricklypoppy	Water smartweed
 Note that this list contains conservation plantings that occur naturally in Arkansas and that some can be seeded to attract wildlife.
An exception is "planted" millet, which is not classified as natural vegetation and, therefore, cannot be mowed or otherwise manipulated for attracting waterfowl.
However, planted millet that regrows in subsequent years without human intervention is considered natural vegetation.
Hybridized species of rice and other commodity crops are not considered natural vegetation.
Responsibility of the Hunter
 It is the responsibility of the hunter to determine whether or not a field is baited.
Being unaware of the baited area is a difficult defense.
There is a regulation that provides some legal relief for hunters who have
 no possible way of knowing an area is baited.
The strict liability interpretation of the former regulation has been removed.
The regulatory agency must prove that the hunter knows or reasonably should know that the area was baited.
However, it is still a violation of the law to hunt over a baited area.
What can a hunter do to fulfill this responsibility?
A hunter should inspect the area before bringing a gun to the field.
Always look for grain or other feed on a field.
Determine if the grain on the field is there because of a normal agricultural planting or harvest.
Check for signs of baiting; for example, the presence of grain that was not grown on the field or grain that is not evenly distributed on the field.
A hunter should inspect the field carefully if there is an unusually heavy concentration of doves or waterfowl in a field.
When dove hunting on a freshly plowed field, a hunter should look closely on the surface and under the soil for grain.
If grain or feed is found and you are uncertain of the reason, leave the area.
A hunter should ask if the field is legal.
Ask if any grain or feed has been on the area the previous 10 days.
If you have questions about regulations regarding baiting in Arkansas, contact these agencies:
 Arkansas Game and Fish Commission #2 Natural Resources Drive Little Rock, AR 72205-1572 501-223-6300
 U.S.
Fish and Wildlife Service 1500 Museum Road, Suite 105 Conway, AR 72032-4761 501-513-4474
 U.S.
Fish and Wildlife Service 700 West Capital Avenue, Suite 3020 Little Rock, AR 72201-3238 501-324-5643
 University of Arkansas Cooperative Extension Service 2301 South University Avenue Little Rock, AR 72204-4940 501-671-2000
 Programs Supporting Wetland Habitat Management in Arkansas
 Many agencies and organizations offer technical and financial support to landowners who implement wildlife management practices.
Following is a brief description of these programs and contact information.
Arkansas Partners Project a cooperative effort among several agencies which offers free technical assistance, water control structures and reforestation equipment/cost-sharing to private landowners for restoring and enhancing selected wetlands and agricultural fields for waterfowl during winter.
Contacts: Arkansas Game and Fish Commission , Ducks Unlimited, Inc.
, Natural Resources Conservation Service , U.S.
Fish and Wildlife Service.
Conservation Reserve Program and Continuous Conservation Reserve Program large-scale land retirement programs in which farmers are paid a rental fee per acre for conserving and enhancing soil, water, wetlands and wildlife habitat.
Requires farmers cease production of agricultural commodities on enrolled land and establish grasses, trees or shallow water.
Can receive up to 90 percent cost-share for wildlife habitat improvement.
Contact: Farm Service Agency.
Conservation Stewardship Program provides payments to producers who historically practiced good stewardship on their lands and incentives for those who want to do more.
Payments for initial treatment, management and maintenance of conservation practices.
Contact: Natural Resources Conservation Service.
Environmental Quality Incentives Program provides educational, technical and financial assistance to farmers for implementing conservation practices on priority lands, which include wetlands and waterfowl habitat.
Only farmers currently engaged in agricultural
 production are eligible.
Contacts: Natural Resources Conservation Service  or Farm Service Agency.
Farm Loan Program Conservation taxpayer-subsidized lender for farmers who cannot get credit in the private sector.
"Debt-for-nature" swap allows borrowers to enter a conservation contract in exchange for reducing the loan.
Contact: Farm Service Agency.
Private Lands Assistance private lands biologists assist landowners with developing wildlife management plans and habitat enhancements; provide information including application process for federal and state incentive programs, such as Wetlands Reserve Program, Conservation Reserve Program, Continuous Conservation Reserve Program, Environmental Quality Incentive Program, Arkansas Partners Project and Riparian and Wetland Restoration Tax Credit.
Contact: Arkansas Game and Fish Commission  and ask for the private lands biologist nearest your county.
Riparian and Wetland Restoration Tax Credit landowners receive state tax credit  for restoring existing or creating new wetlands or riparian zones maintained for a minimum of ten years.
Applications must be reviewed and approved before tax credit is issued.
Contact: Arkansas Natural Resources Commission.
Wetlands Reserve Program land-retirement program for former or degraded wetlands that are restorable.
Offers three options: permanent leasements, 30-year easements and restoration cost-share easements.
Landowner retains control of access to land and hunting/fishing rights.
Contacts: Natural Resources Conservation Service  or Farm Service Agency.
Wildlife Habitat Incentives Program land management program that helps landowners plan and pay for wildlife habitat improvements.
Provides technical and cost-share assistance for lands not currently enrolled in other federal conservation programs.
Contacts: Natural Resources Conservation Service  or Farm Service Agency.
Printed by University of Arkansas Cooperative Extension Service Printing Services.
Optimal Performance from Center Pivot Sprinkler Systems
 Bradley A.
King and Dennis C.
Kincaid
 A good supply of groundwater and the commercial development of center pivot irrigation systems significantly increased sprinkler-irrigated acreage in southern Idaho during the late 1960s and early 1970s.
Today, center pivot systems, with their automation, large areal coverage, reliability, high application uniformity, and ability to operate on relatively rough topography, are replacing surface, handline, and wheelline systems.
The irrigated area under a center pivot system expands substantially with increasing system length.
To accommodate the increased area, the application rate increases linearly along the center pivot lateral through one of two methods: increased flow rates through equally spaced sprinklers or gradually decreased spacing of equal-flow sprinklers along the center pivot lateral.
The most common approach is to have equally spaced sprinklers with increasing flow rates  along the center pivot lateral.
In the 1960s, center pivot irrigation systems had standard high-pressure  impact sprinklers.
These sprinkler packages provided good application uniformity when the system nozzles were properly sized and pressure variation along the lateral was within recommended limits.
However, losses from wind drift and evaporation under the dry, windy conditions often encountered in arid and semi-arid environments were excessive.
The sprinkler irrigation industry addressed this problem by developing low angle and low pressure  impact sprinklers.
These effectively reduced wind drift and evaporation losses, but flow rate variation caused by undulating topography continued to be a significant problem.
In the mid 1970s, flow control sprinkler nozzles and fixedpressure regulators were developed.
They reduce the flow rate variation due to topography to within tolerable limits.
As a result, reduced-pressure impact sprinklers could be used on center pivots.
In the mid 1970s, escalating energy costs made the high energy requirement of impact sprinklers a major concern among producers.
The sprinkler irrigation industry responded by developing low-pressure spray sprinklers  for center pivots.
These have a fixed-head and a part or fullcircle application pattern.
A deflection plate creates spray by deflecting the water jet exiting the nozzle.
The deflection plate can be smooth or grooved with a concave, convex, or flat shape.
Water leaves the smooth plates as a mist-like spray and leaves grooved plates as tiny streamlets.
The sprinklers are either mounted upright on the top of the lateral or mounted upsidedown on drop tubes or booms that extend below the lateral.
On undulating topography, pressure regulators are required to minimize flow rate variations and are commonly used to minimize the influence of pressure loss along the lateral.
Spray sprinklers have a smaller wetted area than impact sprinklers and require closer sprinkler spacing.
The smaller wetted area greatly increases application rates along the center pivot system.
This can intensify runoff problems, particularly on loam and silt-loam soils.
Various types of sprinkler booms have been developed to reduce application rates by increasing the wetted area under the center pivot lateral.
Today, the most popular type is an offset boom with a horizontal length of 10 to 20 feet perpendicular to the center pivot lateral.
These offset booms are commonly used on the outer one-half to one-third of a center pivot lateral.
Recently developed moving-plate spray sprinklers also decrease application rates by increasing wetted area.
These sprinklers, such as Rotators, Spinners, and Wobblers, reduce the number of water streamlets which increasing drop size and water throw distance.
At the same time, they maintain good application uniformity.
Moving-plate spray sprinklers combined with offset booms along the outer spans of the center pivot provide efficient irrigation.
In the early 1980s, a low pressure application package for center pivot systems known as LEPA  was developed for the southern plains states.
A LEPA package has very-low-pressure  bubblers or furrow drag socks suspended on drop tubes at a height of 1 to 3 feet above the soil surface.
Crop rows are planted to follow the circular path of the center pivot system, and alternate furrows are wetted.
LEPA systems have characteristically high application rates that usually exceed the water infiltration rate.
Basin tillage is required to provide soil-surface storage until the water infiltrates.
Some LEPA applicators can be converted to spray heads having wetted areas on the order of 10 to 25 feet in diameter.
These have good sprinkler pattern overlap and apply water uniformly.
When used in the crop canopy, the heads are usually spaced to match alternate crop rows.
Irrigation application efficiencies of 90 to 95 percent have been measured using LEPA sprinkler packages.
This efficiency is the result of reduced evaporation.
By locating the applicators within the crop canopy and near the soil surface, the amount of wetted soil and wetted plant surface area is minimized.
Wind drift and spray evaporation are also eliminated.
However, their high application rates and their limited clearance of the applicators make the LEPA packages unsuitable for slopes.
They can not be transferred directly to the agricultural production systems of Idaho where undulating topography is common.
One study in idaho on a silt loam soil with 1 percent slope that compared a LEPA sprinkler package against low-pressure sprinklers mounted on offset booms found no significant difference in crop yield.
The increase in application efficiency of the LEPA system was offset by increased runoff 
 The main disadvantage of center pivot irrigation systems is the high water application rates under their outer spans.
Since sprinkler flow rate increases linearly along the system lateral, application rates at the outer end also increase with the length of the system.
Application rates under the outer spans of the standard quartermile-long low-pressure center pivot normally exceed infiltration rate and result in runoff.
Runoff, the lateral redistribution of applied water, causes areas of excessive and deficient soil water content in the field, reducing crop yield and quality in these regions.
The potential for localized chemical leaching from the crop root zone also increases in places where runoff collects.
Soil-surface water storage in small, natural depressions decreases the actual volume of runoff.
Surface storage can be enhanced by tillage practices, such as basin or reservoir tillage.
Infiltration rate, which determines the potential for runoff, is dynamic.
Infiltration rate decreases during irrigation.
The initial soil water content also affects the infiltration rate; an increase in the initial soil water content decreases the infiltration rate.
In addition, infiltration rates normally decrease over the season due to soil-surface sealing from sprinkler droplet impact.
As a result, in row crops such as potatoes, runoff may increase throughout the season.
Decreasing infiltration rates combined with high water application rates make runoff a near certainty for standard quarter-mile-long center pivots on all but sandy soils.
Optimal center pivot system performance requires the use of both proper sprinkler packages to minimize water application rates and basin or reservoir tillage to minimize runoff.
Figure 1.
Graphical representation of how water application rates under a center pivot exceed infiltration rate.
Potential runoff is represented by the shaded area.
Typical relative water application rate patterns for various center pivot sprinkler packages are shown in figure 2.
High-pressure impact sprinklers have the lowest application rates followed by lowpressure impact sprinklers.
Low-pressure spray sprinkler packages, listed from lowest application rate to highest, are offset booms with rotators, offset booms with sprays, drop tubes with rotators, drop tubes with sprays, and in-canopy sprays.
The peak application rate along the outer spans of a standard quarter-mile-long center pivot system for all the sprinkler packages exceeds the infiltration rate of most soils.
Booms are an effective means for increasing sprinkler wetted area while decreasing water application rate.
Since application rates are lower nearer the center pivot point, booms are usually only used on the outer one-half to one-third of a quarter-mile-long center pivot system.
Figure 2.
Comparison of relative application rates under various center plvot sprinkler packages.
For a low-pressure center pivot sprinkler package, the shape of the application rate pattern is defined by pressure, nozzle size, plate configuration, sprinkler height, and wind speed.
Sprinkler application rate pattern and spacing determine application uniformity.
Pressure and nozzle size
 Pressure and nozzle size control the drop size distribution from a sprinkler and drop size influences the application rate pattern.
Higher pressure creates smaller drops while bigger nozzles produce larger drops.
Drop size also influences the trajectory of a given sprinkler droplet.
When initial velocities are equal, large droplets will travel farther from the sprinkler than small droplets.
Consequently, high pressure or small nozzle sizes, which tend to produce smaller droplets, increase application rates near the sprinkler while low pressure or large nozzle sizes, which tend to produce larger droplets, increase application rates farther from the sprinkler.
Obtaining suitable application rate patterns is dependent on following the manufacturer's nozzle size and pressure range recommendations.
However, donut application rate patterns may be accentuated at the lowest recommended pressure, reducing application uniformity.
At the highest pressure recommendation, droplet size is smaller and wind drift losses will increase.
The best results are often found near the middle of the manufacturer's recommended pressure range.
Sprinkler deflection plate configuration has a large effect on the sprinkler application rate pattern.
In general, smooth deflection plates produce small drop sizes, which are highly susceptible to wind drift losses, except at lower pressures.
Serrated deflection plates have many small grooves and are used with fixed-plate sprinklers.
Grooved deflection plates have four to six large grooves and are used on moving-plate sprinklers.
Moving-plate sprinklers are the most common type in Idaho.
They maximize wetted sprinkler area while minimizing operating pressure.
The application rate pattern depends on the number of grooves, trajectory angle, and speed of motion.
The number of grooves in the plates affects the drop size distribution.
Fewer grooves produce larger streamlets and larger drop sizes, which travel farther from the sprinkler and maximize wetted area.
Within limits, greater trajectory angles produce more uniform application rate patterns.
The primary disadvantage of higher trajectory angles is a greater susceptibility to wind drift.
Lowering the sprinkler elevation will reduce wind drift.
The effect of plate configuration and motion on sprinkler application rate pattern is shown in figures 3 through 7.
Figure 3.
Application rate pattern from a 4-groove rotating-plate spray sprinkler with an 8 trajectory angle.
A 4-groove plate with an 8 degree trajectory  produces a concentrated application of water near the outer spans of the wetted pattern, creating a donut-shaped application rate pattern.
The application rate pattern for the same sprinkler with a 6-groove plate and a 12 degree trajectory angle  creates smaller droplet sizes and increases water application near the sprinkler.
The smaller droplet sizes combined with the higher trajectory angle reduce the wetted area slightly.
The donut-shaped application rate pattern remains but to a lesser degree because a larger percentage of the water is applied near the sprinkler,
 Figure 4.
Application rate pattern for a 6-groove rotating-plate spray sprinkler with a 12 trajectory angle.
Figure 5.
Application rate pattern from a 6-groove spinning-plate sprinkler with a 12 trajectory angle.
The application rate pattern for a fast rotating-plate  with 6 grooves and 12 degree trajectory angle is shown in figure 5.
The faster rotation of the plate provides a more uniform application rate pattern of elliptical shape with the highest application rate near the sprinkler.
The application rate pattern for the same sprinkler with a 20 degree trajectory angle is shown in figure 6.
The greater trajectory angle slightly increases the wetted area of the sprinkler, reducing the application rate near the sprinkler.
Figure 6.
Application rate pattern from a 6groove spinning-plate spray sprinkler with a 20 trajectory angle.
Figure 7.
Application rate pattern from a 9-groove wobbling plate spray sprinkler with a 15 trajectory angle.
The application rate pattern from a wobbling-plate type sprinkler having 9 grooves and a 15-degree trajectory angle is shown in figure 7.
This application rate pattern resembles a truncated cone with an additional elliptical shaped peak near the sprinkler.
The application rate pattern is very uniform except near the sprinkler.
For donut-shaped application rate patterns, such as those illustrated in figures 3 and 4, the cumulative application rate pattern produced by multiple sprinkler overlap is reasonably uniform.
This, combined with the effect of averaging the cumulative application rate pattern as a center pivot passes over a point on the soil surface, provides excellent application uniformity.
Application rate patterns that are more uniform in shape, such as those in figures 6 and 7, provide excellent application uniformity with less sprinkler overlap.
However, the individual sprinkler wetted areas are usually smaller so the required sprinkler spacing is about the same as that of sprinklers with larger donut-shaped application rate patterns.
Sprinkler height influences the size of the sprinkler wetted area and wind drift losses.
Increasing sprinkler height increases sprinkler wetted area slightly with no significant effect over the practical heights of 6 to 10 feet.
Sprinkler heights greater than 6 feet on short crops  do not significantly increase application uniformity.
However, sprinkler heights less than 6 feet significantly decrease application uniformity, particularly for sprinklers having deflection plates with low trajectory angles.
With taller crops, the optimal sprinkler height is the maximum canopy height.
Sprinkler heights greater than 6 feet significantly increase spray losses due to wind drift and evaporation.
Spray losses average about 3 and 5 percent for sprinkler heights of 3 and 6 feet, respectively.
Spray losses increase to 10 percent for sprinklers  mounted on the top of the center pivot at heights of 12 to 15 feet.
Spray losses can double as wind speed increases from 0 to 5 miles per hour to 5 to 10 miles per hour.
For short crops; sprinkler heights near 6 feet provide good application uniformity while maintaining reasonable spray losses.
Wind distorts the application rate pattern from spray sprinklers and affects application uniformity.
The effects of wind on the application rate patterns for a Spinner and a Wobbler type spray sprinkler are depicted in figures 8 and 9, respectively.
Comparing these patterns with those of figures 6 and 7 for the same sprinklers under lower wind speeds reveals that the application rate patterns are largely shifted downwind.
Distortion of the application rate pattern is most pronounced near the sprinkler where the smallest droplets occur.
Computer simulation of composite wind-affected application rate patterns under a center pivot indicates that application uniformity is not significantly reduced for wind speeds up to 10 miles per hour.
This favorable result is largely due to the multiple sprinkler.
overlap.required to obtain good uniformity with low-pressure sprinklers and to limiting sprinkler height to about 6 feet.
Figure 8.
Wind-affected application rate pattern from a 6-groove spinning-plate spray sprinkler with a 20 trajectory angle.
Figure 9.
Wind-affected application rate pattern from a 9-groove wobbling-plate spray sprinkler with a 15 trajectory angle.
Sprinkler Droplet Kinetic Energy
 Many soils, particularly those containing significant silt fractions, are susceptible to soil-surface sealing from sprinkler droplet impact.
The force of the droplets hitting the ground breaks down the surface soil structure, forming a thin compacted layer that greatly reduces infiltration rate.
The application rate and the kinetic energy of sprinkler droplets at impact are the major factors affecting soilsurface seal formation.
The infiltration rate reduction is a function of the particular soil and the energy flux density.
Energy flux density combines the effects of sprinkler, droplet kinetic energy and water application rate into a single parameter that is expressed as power per unit area.
It correlates very well with infiltration rate.
Energy flux density 
 The relationship between energy flux density and depth of infiltration prior to runoff is illustrated in figure 10 for two different soils under dry, bare conditions.
The silt loam soil is very susceptible to soil-surface sealing.
The infiltration depth prior to ponding decreases very rapidly with a minimal increase in energy flux density.
The loam soil is less susceptible to soil-surface sealing, but the depth of infiltration prior to runoff still decreases significantly as energy flux density increases.
The effect of sprinkler droplet impact on the infiltra-
 Inflitration rate reduction by energy density flux of sprinkler droplets for two solls.
Adapted from Thompson and James  and Mohammed and Kohl.
tion rate of a particular, soil must be measured to develop a quantitative relationship similar to that of figure 10.
This is difficult because the results depend on soil surface conditions, soil structure, and soil water content.
However, the general trend shown in figure 10 is applicable to any soil and useful in the selection of sprinklers for a center pivot irrigation system.
Studies of runoff under center pivot irrigation systems indicate that soil-surface sealing continues to develop with each additional irrigation.
The only way to recover from soil-surface seal formation is to physically destroy it with a tillage operation.
The best approach for limiting soil-surface seal formation is to protect the soil surface through residue management and to exclude water application from bare soil conditions.
When water applications must be made on bare soils, the energy flux density should be reduced to delay formation of the soilsurface seal.
This can be accomplished by either using sprinklers with reduced droplet kinetic energy, reducing application rate, or both.
Reducing the application rate is easiest and can be done by renozzling the center pivot system to reduce flow rate.
The application rate under a center pivot is independent of system speed, so adjusting the system speed does not affect formation of a soilsurface seal.
The kinetic energy of a sprinkler droplet depends on droplet size  and velocity at impact with the soil surface.
Droplet velocity is also a function of drop size.
Drop size distribution is determined by sprinkler nozzle size, pressure; and deflection plate configuration.
Figure 11 shows the kinetic energy per unit volume of water applied  versus the dimensionless ratio  of nozzle size to pressure head for several types of sprinklers.
Droplet kinetic energy is highest for sprinklers producing the largest drop sizes, such as standard impact sprinklers and rotator type sprinklers having deflection plates with few grooves.
Droplet kinetic energy is the lowest for sprinklers producing small drop sizes such as those using fixed sprays with flat or serrated plates.
There is little difference in droplet kinetic energy between the various spray sprinklers, except for the 4-groove rotating-plate sprinkler.
Overall, droplet kinetic energy varies only by a factor of three across all sprinkler types.
Despite this limited range in droplet kinetic energy, a 0 study of sugar beet emergence 0.0 0.2 0,4 comparing sprinklers with 105 ft-lb/ft3 and 315 ft-lb/ft3 of droplet kinetic energy found a 13 percent increase in sugar beet emergence under the sprinkler with two thirds less droplet kinetic energy 
 Sprinkler selection does influence soil-surface seal formation.
This not only affects infiltration rate, but has other agronomic implications such as soil erosion, water application efficiency, and nutrient distribution in the soil profile.
Sprinkler droplet kinetic energy for various sprinkler types as a function of the dimensionless ratio of sprinkler nozzle diameter to sprinkler pressure head.
Adapted from Kincaid.
Optimal Sprinkler Package Selection and Installation
 Sprinkler selection and installation have a significant effect on the performance of a center pivot irrigation system.
Both application rate relative to infiltration rate and the susceptibility of the soil to surface sealing need to be considered in the system design.
The application rate of low-pressure spray sprinklers can be reduced by using offset booms on alternate sides of the center pivot lateral, On soils with extremely low infiltration rates or with a high susceptibility to soil-surface sealing, offset booms on both sides of the center pivot lateral can be used at each sprinkler outlet to further reduce application rate.
The effectiveness of offset booms for reducing application rate is shown in figures 12, 13, and 14.
The composite application rate for 6-groove rotating-plate sprinklers on drop tubes is shown in figure 12.
Figure 13 shows the composite application rate under the same sprinkler conditions with offset booms on alternate sides of the center pivot lateral.
The average application rate is reduced about 30 percent by offset booms.
The composite application rate with two offset booms at each sprinkler location and each sprinkler nozzle providing one-half the flow rate is shown in figure 14.
The application rate is reduced 5 percent compared to the single offset boom.
The major advantage of the double offset boom is that it uses smaller nozzles, which reduces the kinetic energy of the droplets.
Table 1 lists the average and highest 10 percent application
 Figure 12.
Composite application rate pattern under a center pivot from 6-groove rotating-plate sprinklers on drop tubes with 10-foot sprinkler spacing and 10 gallons-perminute flow rate.
Application rates and application rate reduction provided by offset booms of various lengths with a 10-foot sprinkler spacing and flow rate of 10 gallons per minute.
Offset	Application rate	reduction	Application
 Sprinkler	distance	Average High 10%	Average High 10%	uniformity
 type						
 Fixed-plate	0	2.13	4.35	-	-	98
 serrated	10	1.52	3.51	71	81	98
 15	1.32	2.87	62	66	98
 20	1.15	2.75	54	63	98
 Rotator	0	1.54	2.47	-	-	97
 6-groove	10	1,17	2.27	76	92	97
 15	1.04	2.12	67	86	97
 20	0.94	1.65	61	67	97
 Wobbler	0	1.42	2.41	-	-	100
 low angle	10	1.11	2.27	79	94	100
 15	1.00	1.94	70	80	100
 20	0.90	1.41	64	58	100
 The highes Ten percentrapplically rateus of life welled sceeds.in) value It provides better.measu for companing application.ra than the absolute Highest Tar
 Table 1 lists the average and highest 10 percent application rates for various types of spray sprinklers on offset booms installed on alternate sides of a center pivot lateral.
The same information for two offset booms is listed in table 2.
The exact application rates will change with sprinkler flow rate, but the relative reductions will remain nearly the same.
Offset booms are relatively inexpensive and very effective in reducing the application rate, Since the application rate under low-pressure spray sprinklers can be minimized by using offset booms, sprinkler selection should be based on drop size distribution.
Small drop sizes have the least droplet kinetic energy but are the most susceptible to wind drift losses.
Large drop sizes have the highest droplet kinetic energy but are the least susceptible to wind drift losses.
Sprinklers that provide a compromise between these two extremes are best.
Most movingplate sprinklers have medium drop sizes and maximum wetted area.
Because they all have about the same droplet kinetic energy, the final selection of the brand rests on personal preference.
The significant differences in the application rate patterns of the various moving-plate sprinklers influence the spacing of the sprinkler heads.
Fixed-plate spray sprinklers with their smaller wetted area require closer spacing than the moving plate spray sprinklers.
Wobbler type sprinklers with their more uniform application rate pattern allow for larger spacing.
Application rates and reduction provided by double offset booms of various lengths with a 10-foot sprinkler spacing and flow rate of 5 gallons per minute.
Offset	Application rate	Reduction	Application
 Sprinkler	distance	Average High 10%	Average High 10%	uniformity
 type						
 smoott	1942	276	Gi
 Fixed-plate	0	2.24	3,93	-	-	99
 serrated	10	1.52	3.23	68	82	99
 15	1.33	1.96	59	50	99
 20	1.15	1.96	51	50	99
 Rotator	0	1.90	3.37	-	-	97
 6-groove	10	1.35	2.65	71	79	97
 15	1.19	1.80	62	54	96
 20	1.05	1.69	55	50	97
 6 grooy	2.82	m	as
 Wobbler	0	1.55	2.58	-	-	98
 low angle	10	1.17	2.19	75	85	98
 15	1.02	1.80	66	70	98
 20	0.94	1.33	61	52	98
 Pressure also has a significant effect on the required spacing.
Higher pressure allows wider spacing because of the resulting smoother application rate pattern and slight increase in the wetted area.
With most spray sprinklers, low pressure produces a donutshaped application rate pattern.
As a result, closer spacing is needed in order to maintain application uniformity.
Due to the high flow rates required on the outer portion of center pivots, large spacings require large nozzle sizes, which may result in excessively large drops, particularly at low pressures.
Center pivot sprinkler outlets are normally spaced about 8 to 10 feet apart.
This spacing is adequate for all but fixed-plate spray sprinklers and rotators at 10 pounds per square inch.
Since every sprinkler outlet is normally used along the outer half of a standard quarter-mile-long center pivot, all the moving-plate type spray sprinklers provide good application uniformity.
The difference between sprinklers occurs when spacing exceeds 10 feet, such as along the inner portion of the center pivot where alternate sprinkler outlets are commonly used and flow rates are small.
There may be a slight increase in application uniformity with sprinklers that allow larger spacings.
The actual application uniformity under field conditions will likely be less than 95 percent due to wind effects and actual sprinkler height.
In general, all moving-plate type sprinklers provide good application uniformity with spacings normally encountered on center pivots.
Recommended maximum sprinkler spacings for low pressure spray sprinkler, at a 6-foot height.
type	10	15	20	30
 Fixed-plate	6	8	8	10
 Rotator 4-groove	8	10	12	14
 Rotator 6-groove	8	10	12	14
 Spiriner 16-groove	8	10	12	14
 Wobbler low angle	12	14	14	16
 Wobble high angle	14	16	16	18
 Advantages and disadvantages of spray sprinkler deflection plate features and sprinkler mounting.
Fixed-plate, smooth	Minimum droplet kinetic energy	High application rate, high wind
 drift loss, close sprinkler spacing
 required for high application
 Fixed-plate, serrated	Low droplet kinetic energy	High application rate, high wind
 drift loss; clse sprinkler spacing
 required for high application
 Moving-plate, 4 groove	Lowest average application rate,	Highest droplet kinetic energy
 low wind drift loss, larger sprinkler
 Moving-plate, 6-groove &	Low average application rate, low Moderate droplet kinetic energy
 9-groove	wind drift loss, larger sprinklr
 Less than 15 degrees	Reduced wind drift loss	Donut application rate pattern
 requiring closer sprinkler spacing to
 maintain high application uniformity
 More than 15 degrees	More uniform application rate	Increased wind drift loss
 pattern allowing larger sprinkler
 Overhead	Low cost, higher uniformity with	High wind drift loss
 Drops	Reduced wind drift loss	Increased cost, slightly increased
 application rate, spacing more
 critical for high application
 Offsets	Reduced application rate	High cost
 Center pivot sprinkler packages have changed significantly since they were first introduced.
The original high-pressure impact sprinklers have been largely replaced by low-pressure spray sprinklers.
The current moving-plate spray sprinklers, the result of years of development by the sprinkler industry, minimize operating pressure while increasing application uniformity.
When properly selected and installed, these sprinklers provide an efficient center pivot irrigation system.
In general, there is very little difference in application uniformity and irrigation efficiency between the common low-pressure movingplate spray sprinklers available today.
The primary advantages and disadvantages of the various low-pressure spray sprinkler features are listed in table 4.
Offset booms are usually required on the outer spans of a center pivot to reduce application rates to acceptable levels to minimize runoff potential, especially on silt loam soils.
Soils susceptible to soil-surface sealing can be protected by reducing application rates and droplet kinetic energy via the use of two offset booms at each sprinkler outlet, temporarily renozzling the sprinkler package to reduce the system flow rate, and managing residue through conservation tillage practices.
Even with the use of offset booms, application rates from low pressure spray sprinklers exceed the infiltration rate of most soils.
Basin or reservoir tillage can increase surface storage and significantly reduce actual runoff.
Low pressure spray sprinklers should be installed at a height of about 6 feet for low growing crops.
This height maintains good application uniformity, limits wind drift; and reduces droplet evaporation losses to acceptable levels.
LEPA packages should only be used on near level topography.
The increase in application efficiency of LEPA systems from reduced evaporative and wind drift losses is easily overcome by increased runoff on silt loam soils.
The increased cost of LEPA sprinkler packages relative to low pressure sprinkler packages and the additional effort needed to plant crop rows to follow the circular travel of the center pivot system are not justified by the marginal increase in application efficiency.
The two different speeds can be achieved by a simple setup in the computer pivot panel.
The degree of rotation at which the end gun turns on, the program simply slows the speed down and then returns it to the faster speed at the time the end gun turns off.
The idea is that we want the pivot to cover a constant number of acres per hour.
The key is to know how to calculate the slower speed.
Building Rain Barrels to Harvest Rainwater
 Brad Hufhines County Extension Agent, Urban Stormwater
 Katie Teague County Extension Agent, Staff Chair
 John Pennington Instructor Water Quality Educator
 Mike Daniels Professor CSES Associate Department Head Extension
 Jane Maginot County Extension Agent, Urban Stormwater
 Arkansas Is Our Campus
 Arkansas can be prone to temporary drought during summer months.
As demand for potable  water increases, so do controls of water use by municipalities during peak demand in times of drought.
To address this challenge, there is new interest in the age-old practice of harvesting and storing rainwater for nonpotable uses.
The most common harvesting method is capturing stormwater from rooftops into rain barrels and cisterns.
A one-inch storm on a 1,000 ft2 roof generates over 600 gallons of free, soft, nonchlorinated rainwater.
Capturing even a fraction of this volume in rain barrels can serve as a cost-effective alternative to using tap water for watering landscapes and gardens.
Harvesting stormwater with rain barrels can offer many benefits including:
 Saving money on municipal water bills.
Reducing use of treated water for home irrigation.
Lowering peak demands on public water systems.
Reducing stormwater run-off volume.
Reducing stormwater run-off velocity.
Rain barrel with soaker hose attachment leading to a flower bed.
How to Build a Rain Barrel
 Jig saw or reciprocating saw
 hole bit to match bulkhead tank fitting and spigot
 Scissors or utility knife
 Parts List 
 Food-grade plastic, 55-gallon barrel
 3/4" hose bibb  
 3/4" bulkhead tank fitting
 3/4" X 3/4" pipe-togarden hose connector
 Bricks or cement blocks
 Garden hose to pipe connecter.
If you are reusing a 55-gallon barrel, make sure it is food grade and wash it out thoroughly.
Spigot stem wrapped in plumber tape.
Barrels can be purchased new or used from several locations.
The cheapest place to buy barrels is directly from food or juice processing plants.
Other companies, such as container supply businesses, may be a good, consistent source of used foodgrade barrels.
Industrial strength trash containers may be used if barrels are hard to track down.
Step 1: Preparation.
Mark all cuts and holes to be drilled on your clean 55-gallon barrel.
The overflow hole can be located on either side of the barrel and should be at least 2 inches from the top edge of the barrel.
The spigot hole should also be 2 to 3 inches from the bottom edge of the barrel.
Rain barrels are available commercially and vary in design and price.
However, rain barrels are relatively easy and inexpensive to construct and maintain and are applicable to residential, commercial and industrial sites.
This fact sheet provides guidelines for constructing your own collection system using rain barrels.
Step 2: Cutting and drilling.
Drill a 1" pilot hole in the top of the barrel to start your saw blade and cut the top out of the barrel using a jig saw or reciprocating saw.
Make sure to leave at least a 1" rim to secure the fiberglass screen later.
Next, drill the overflow hole at the top of your barrel with a 1" drill bit.
Then drill the spigot hole using a 1 1/2" hole bit.
Use a utility knife to smooth out the plastic burrs around all holes and cuts.
Finally, clean the inside of the barrel to remove plastic shavings.
Step 3: Inserting fixtures and fittings.
Insert the bolt-shaped end of the bulkhead tank fitting into the barrel from the inside, keeping the rubber gasket between the "bolt" and the inside of the barrel.
The plastic washer fits between the outside of the barrel and the nut of the tank fitting.
These fittings have left-handed threads, SO tightening seems backwards.
Wrap the spigot stem in plumbers tape and insert it into the bulkhead
 Barrel with top cut out.
tank fitting.
For the overflow, the hose-to-hose connector will screw directly into the plastic barrel in the 1" overflow hole.
If desired, you can use a 1" internal diameter metal washer between the barrel and the overflow adaptor to give more support to the fitting.
Step 4: Screening the top of your barrel.
Cut your fiberglass screen large enough to cover the entire top of your barrel to prevent mosquito breeding.
Staple one edge of the screen to the rim of the barrel , stretch the screen smoothly across and staple the screen on the opposite side.
Staple the screen at 3 and 9 o'clock, then fill in with additional staples around the rim of the barrel, keeping the screen tight as you staple.
Trim off the excess screening material with a utility knife or scissors to give it a clean appearance.
If stapling the screen is not an option, the the barrel.
screen can be wrapped over the edges of the barrel and fastened down with bungee cords or straps.
Ensure a tight fit to prohibit insects from entering
 Spigot attached to a bulkhead tank fitting.
Screen stapled to top.
Screen fastened to top.
to cut the downspout.
Disconnect the elbow at the bottom of your downspout.
Hold the disconnected elbow up to the downspout to mark where to cut the downspout to provide at least 2 inches between the elbow and the rain barrel SO the barrel can be easily removed for future maintenance.
Cut the down spout at the line and reconnect the elbow to the downspout.
Painted rain barrel on stand with flexaspout attachment.
Step 5: Installing your rain barrel.
Your rain barrel needs to be raised above the ground to allow access to the spigot and provide enough head pressure to water your plants through gravity flow.
Cinder blocks or landscape blocks work well as a stable means of raising rain barrels off the ground.
If you are connecting one barrel to another to increase storage capacity, be sure to make the connection in the appropriate  place to ensure hydraulic connection between barrels.
Once you know the height of the barrel, it is time
 Making the gutter cut for new elbow placement.
Rain barrel placed without a stand will have reduced water pressure.
Outfitting rain barrel to house.
Maintaining Your Rain Barrel
 Rain barrels can be an inexpensive way of collecting rainwater for use in home landscaping and gardens, but they also provide environmental and societal benefits by reducing stormwater runoff and by reducing peak demands on potable water.
For more information on using or constructing rain barrels, contact your local Cooperative Extension Service office.
To keep your rain barrel functioning well, you will need to clean it periodically to remove algae and grit.
Take off or pull back a portion of the window screen to wash out the interior with a scrub brush.
During winter, either empty and store your barrel or maintain a low water level SO repeated freezing and thawing of water in your rain barrel does not split the screen or cause cracks in the plastic.
Over time, the window screen may also need to be replaced.
Thanks and recognition to Berni Kurz, Mark Brown, and Trish Ouei for their contributions to the publication.
Printed by University of Arkansas Cooperative Extension Service Printing Services.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Director, Cooperative Extension Service, University of Arkansas.
The University of Arkansas System Division of Agriculture offers all its Extension and Research programs and services without regard to race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
Electrical resistance sensors, also known as granular matrix sensors, estimate soil water tension by measuring the change in resistance between two electrodes.
Turfgrass Consumptive Use: Flagstaff, Arizona
 Turf Irrigation Management Series
 Irrigation of turfgrass is an issue of growing concern in northern Arizona cities and towns as population growth places increasing demands on limited water supplies.
Understanding the water requirements of turfgrass is essential if we are to improve irrigation management and better plan for future urban growth.
Consumptive use  tables and curves that provide average rates of turfgrass water use  supply this much needed information.
The original bulletin on turfgrass consumptive use for the Flagstaff area  was developed in conjunction with the University of Arizona TRIF1 Water Sustainability Program that also funded the installation and operation of an automated weather station to improve future estimates of turfgrass CU.
This bulletin provides revised estimates of turfgrass CU developed from data sets collected by this weather station.
Turfgrass CU values  were estimated by applying crop coefficients  appropriate for acceptable  and high quality  turf to daily values of standardized reference evapotranspiration :
THE ROLE OF WIND ENERGY IN AGRICULTURE A COOPERATIVE'S POINT OF VIEW
 We are not-for-profit entities
 Electric rates are based on cost of service, not on a return on investment
 Member consumers are the cooperative's owners
 Consumers elect a governing board of directors from their members
 The mission is long-term low-cost reliable service
 SUNFLOWER  MEMBERS SERVE RURAL WESTERN KANSAS
 Sunflower Electric Power Corporation
 Mid-Kansas Electric Company, LLC
 Lane-Scott Electric Cooperative, Inc., Dighton
 Pioneer Electric Cooperative, Inc., Ulysses
 Prairie Land Electric Cooperative, Inc., Norton
 Western Cooperative Electric Association, Inc., WaKeeney
 Wheatland Electric Cooperative, Inc., Scott City
 Victory Electric Cooperative Association, Inc., Dodge City
 ELECTRIC DEMAND IS STEADILY RISING
 2% TO 3% per year for the past 15 to 20 years
 Recently load growth for irrigation has far exceeded the average
 Growth from other agriculture based industries such as ethanol plants
 SERVING LOAD REQUIRES DIVERSE CAPACITY RESOURCES
 Seasonal variations in load change the energy supply and cost
 Base-load, coal and hydro
 Peaking-load, natural gas and diesel
 Holcomb Station, 360 MW, Coal
 Garden City Station, 225 MW, Natural Gas
 Smoky Hills 1 Wind Farm, 50 MW, Wind
 Great Bend Station, 98 MW, Natural Gas
 Fort Dodge Station, 145 MW, Natural Gas
 Jeffrey Energy Center, 177 MW PPA, Natural Gas
 Clifton Station, 73 MW, Natural Gas
 Cimarron River Station, 76 MW, Natural Gas
 Smoky Hills 2 Wind Farm, 24 MW, Wind
 Gray County Wind Farm, 50 MW, Wind
 WIND ENERGY IS NEGATIVE LOAD TO A UTILITY
 Intermittent capability to generate energy
 Does not provide Capacity or base load energy
 Compares favorably with intermediate and peaking variable costs
 Increases system volatility and costs
 CUSTOMER-OWNED GRID-CONNECTED RENEWABLE GENERATION
 Parallel Generation, a buy/sell arrangement
 FOUR COMPONENTS TO A TYPICAL RETAIL ENERGY CHARGE
 Distribution Costs: 2 to 6 cents/kWh
 Transmission Costs:.5 to 1.5 cents/kWh
 Generation Fixed Costs: 2.5 to 3.5 cents/kWh
 Generation Variable Costs: 1.5 to 8 cents per kWh 
 KANSAS' EXISTING PARALLEL GENERATION STATUTE
 A buy/sell arrangement that allows for "behind the meter" connection of renewable generation by a customer-generator
 No changes to existing retail rate schedule are required
 Compensation for energy sold back to utility is 150% of avoided cost
 Avoided cost is energy component of generation only
 25 kW limit for residential
 200 kW limit for commercial
 Must be appropriately sized for customers load
 Not more than 10 irrigation pumps per customer under this statute
 Must meet all utility safety and reliability standards
 Retail wheeling is not allowed
 Most value is to offset existing load
 Standard procedures in place to accommodate the PGS statute
 Provisions for some latitude in generator sizing
 Renewable generators can be very expensive and payback can be long or non-existent
 Net metering is a concept where a customer can use the utility system as a "bank" or "battery" to store and withdraw energy 
 Often described as a system where the meter can run backwards when customer generates more energy than needed
 The problem is that the product taken out costs the utility much more than the benefit of the product put in
 Net metering is not currently available in Kansas but is currently being discussed
 Coops opposition to net metering is an issue of fairness
 Why should the utility be forced to pay retail cost  to receive only wholesale energy?
Why should some customers be advantaged at the cost of other customers on the system?
Would probably not advantage a commercial customer with a demand/energy rate structure
 Could benefit cost recovery for residential customer-generators
 Actively support customer-owned renewable generation
 Are pursuing a 25x25 renewable energy goal
 However, intermittent renewable energy does not, and cannot, cure the shortage of economical base-load generation
Much like the TAPS program, coordinators hope to uplift the peer-to-peer connections and exchange of ideas among the participants, instructors and facilitators.
Presenters are being lined up and will include University of Nebraska specialists, as well as others from throughout the Ogallala Aquifer region.
Industry professionals will also be invited for different portions of the practicum.
Contestants make production and management decisions for individual plots including, irrigation scheduling, nitrogen management, hybrid selection, plant population, grain marketing and risk management.
Come and learn from some of the best corn and sorghum growers in Nebraska.
B.C.
SPRINKLER IRRIGATION MANUAL
 Prepared and Web Published by
 BRITISH COLUMBIA Ministry of Agriculture
 LIMITATION OF LIABILITY AND USER'S RESPONSIBILITY
 The primary purpose of this manual is to provide irrigation professionals and consultants with a methodology to properly design an agricultural irrigation system.
This manual is also used as the reference material for the Irrigation Industry Association's agriculture sprinkler irrigation certification program.
While every effort has been made to ensure the accuracy and completeness of these materials, additional materials may be required to complete more advanced design for some systems.
Advice of appropriate professionals and experts may assist in completing designs that are not adequately convered in this manual.
All information in this publication and related materials are provided entirely "as is" and no representations, warranties or conditions, either expressed or implied, are made in connection with your use of, or reliance upon, this information.
This information is provided to you as the user entirely at your risk.
The British Columbia Ministry of Agriculture and the Irrigation Industry Association of British Columbia, their Directors, agents, employees, or contractors will not be liable for any claims, damages or losses of any kind whatsoever arising out of the use of or reliance upon this information.
In irrigation, the term gun is used to describe high volume sprinklers with discharge rates exceeding 50 US gpm.
This chapter will discuss both stationary and travelling guns.
Flow rates for guns can vary from 50 to 1,000 US gpm.
Gun operating pressures may range from 40 to 120 psi, depending on the gun and type of nozzle selected.
For travelling guns, the pressure required at the cart will include the nozzle pressure and friction losses through the hose delivering water from the machine to the gun.
Water is usually supplied to the gun by above ground aluminum pipes or buried PVC pipe with hydrants spaced to meet the designed gun spacing.
Figure 6.1 shows an example of a travelling gun system.
Figure 6.1 Travelling Gun System
 Guns come in a variety of sizes, trajectory angles, and available nozzles.
The trajectory angle is important in determining maximum spray height and distance of throw.
Gun systems can utilize three types of nozzles: taper bore, taper ring, and ring nozzles.
Taper bore nozzles provide better stream integrity and create maximum distance of throw with less distortion due to wind.
See Tables 6.8 6.12.
Due to the large discharge rates of gun systems, higher operating pressures than sprinkler system are required to ensure good stream break up.
An increase in pressure at the gun nozzle increases stream velocity which breaks the water into finer droplets.
A fast stream velocity also provides a larger wetted diameter which helps to reduce the instantaneous application rate of the gun system.
Proper selection of a gun operating pressure must take into account the nozzle type, soil and crop conditions.
In most instances, large droplets are to be avoided as they cause soil compaction and may also cause crop damage.
Gun systems are available in various trajectory angles.
The higher trajectories maximize the wetted radius and allow for a near zero horizontal droplet velocity before reaching the crop.
Lower trajectories operate more efficiently in windy conditions but do not have desirable droplet conditions.
Lower trajectory guns need even higher operating pressures to ensure proper stream dispersal before contacting the crop.
Table 6.1 indicates recommended minimum operating pressures for various gun sizes based on flow rate.
Table 6.1 Recommended Minimum Operating Pressures for Gun Systems
 Flow Range [US gpm]	Minimum Pressure [psi]
 Special nozzle configurations have been developed to allow some gun systems to operate at pressures as low as 40 to 50 psi.
Designers should check manufacturer's recommendations when using these low pressure gun systems.
Warning Gun System Design
 When operating gun systems near electrical transmission lines the operator must be very careful that the gun stream does not contact the power line.
High voltage power lines can arc over to an irrigation stream if sufficient stream break up has not occurred.
See Section 6.7 regarding minimum clearances between the jet stream and high voltage power lines.
Selecting a gun spacing, flow rate, nozzle size and operating pressure can be simplified using Tables 6.9, 6.10, 6.11 and 6.12.
The designer must be conversant with application rates, spacing selection, crop and soil parameters and gun operation before using these tables.
Both instantaneous and overlap application rates should be calculated.
Gun systems are spaced on the same design parameters as sprinkler irrigation systems, as explained in Section 3.2.
However, extra caution should be taken with guns as they are subject to very poor distribution uniformities during windy conditions, due to the large wetted radius and height of throw.
Instantaneous application rates also increase substantially when guns are operated during windy conditions.
It is strongly recommended that gun systems not be operated during windy conditions.
Table 6.2 provides a guide to gun spacing.
Since gun systems are susceptible to wind drift, the maximum sprinkler spacing should not exceed 50% of the wetted diameter and the lateral spacing should not exceed 65% of the wetted diameter.
Travelling guns can be spaced up to 65% of the wetted diameter in appropriate conditions.
Table 6.2 Gun Spacing Recommendations
 Gun Type	Spacing as a Percentage of Wetted Diameter
 Maximum sprinkler spacing = 50%
 Maximum lateral spacing = 65%
 Travelling Gun	Maximum lane spacing = 65%
 Gun systems should be operated differently from conventional sprinkler systems due to the inherent high application rates that are produced.
Irrigation set times are therefore much shorter to apply the amount of water required by a crop.
To reduce the rate at which water is applied to the soil, two guns should never be operated simultaneously side by side.
Even so, it is difficult to design stationary gun systems SO that the maximum application rate does not exceed the values stated in Table 4.4.
Exceeding these values slightly may be acceptable if the set time is less than four hours.
However, moving a gun system every three hours may not be practical.
To match the gun operation with soil conditions the instantaneous application rate and the overlap application rate should both be calculated as described in the next sections 6.5 and 6.6.
Stationary guns are usually used in smaller odd-shaped fields, or to irrigate corners or areas not covered by the primary irrigation system such as a centre pivot or a wheelmove.
They provide advantages in tall crop situations but the difficulty of moving them is also a limiting factor.
Stationary guns have the lowest application efficiency  of all sprinkler system due to their inherent poor uniformity; however, they are still used because of their low capital cost and flexibility in irrigating odd-shaped areas.
Stationary guns should not be used if the goal is improved irrigation performance and efficiency.
Typical Application Efficiencies of Sprinkler Irrigation Systems, Table 3.1
 Since two guns are not operating side by side at one time, the application rate formula that needs to be matched to the soil infiltration rate is different than it is for a sprinkler system.
The instantaneous application rate is the actual rate that water is applied to the soil surface by the stationary gun while it is operating.
It takes into account the wetted diameter of the gun and the amount of water discharged by the gun.
The instantaneous application rate is the value that is checked against the maximum soil infiltration rate values shown in Table 4.4 to minimize runoff from the soil surface.
For a stationary gun the Instantaneous Application Rate  can be calculated using equation 6.1:
 Equation 6.1 Instantaneous Application Rate
 IAR = Qx96.3 2 R
 IAR = Instantaneous Application Rate [in/hr]
 Q = Gun Flow Rate [US gpm]
 II = 3.14 
 R = Wetted Radius of the Gun [ft]
 The instantaneous application rate may be increased significantly in windy conditions.
The formula used above calculates the instantaneous application rate for perfect operating conditions.
Helpful Tips Stationary Gun Operation
 The maximum soil infiltration rates shown in Table 4.4 are based on irrigation system operation times exceeding 4 hours.
The infiltration capacity of a soil will be higher than the values shown for application times less than 4 hours.
To reduce runoff consider the following:
 1.
Monitor the soil while the gun is running to determine the maximum run time that can be achieved before signs of puddling and runoff occur.
2.
Determine the MSWD of the crop and soil to ensure the gun application rate and run time does not exceed the soil storage capacity.
Stationary gun sets should be spaced according to the recommendations in Table 6.2 to give sufficient overlap for proper uniformity.
Insufficient overlap will result in parts of the field being under-irrigated.
The aerial photo in Figure 6.2 illustrates a poor overlap.
No circles should be shown in the photo if the gun system had been set up with a spacing that provided a proper overlap.
Sprinkler Layout, Figure 5.1
 For a stationary gun, the overlap application rate  is used to determine the total amount of water applied to the soil after all of the irrigation sets have been completed.
It will be used to determine the maximum irrigation interval.
The overlap application rate is calculated using the gun spacing and flow rate as shown in Equation 6.2:
 Equation 6.2 Overlap Application Rate
 where OAR = Overlap Application Rate [in/hr]
 Q = Gun Flow Rate [US gpm] S1 = Gun Spacing along Lateral [ft] S2 = Lateral Spacing [ft]
 Figure 6.2 Poor Overlap in Stationary Gun Operation
 Stationary gun systems are less efficient than sprinkler systems due to higher operating pressures, susceptibility to wind drift and high application rates.
The set times for gun systems are usually shorter than sprinkler systems to avoid over application and runoff.
For design purposes, if guns are spaced at no more than 50% of the wetted diameter, application efficiencies of 58% to 60% are the best that can be achieved for these kinds of systems.
Typical Application Efficiencies of Sprinkler Irrigation Systems, Table 3.1
 Helpful Tips Stationary Gun System Design
 Stationary guns are often used in pastures where soils are compacted and the grass grown has a very shallow rooting depth.
Take care to ensure that the MSWD is not exceeded.
Most stationary gun systems should not run for more than four hours at one location.
Automatic shutoffs should be incorporated where the system cannot be shutdown manually within this time frame.
Example 6.1 Stationary Gun in Merritt
 A farmer in Merritt intends to use a stationary gun to grow grass in a series of four pastures.
The soil is a deep loam.
The pasture area is made up of four 5 acre parcels that are 660 ft X 330 ft each.
Total pasture area is 1320 ft X 660 ft.
What nozzle, spacing, pressure should be selected and what is the set time and irrigation interval?
Farm location	Merritt	1
 Crop type	Pasture	2
 Soil texture	Loam	3
 Rooting depth 	1.5	4	ft
 Available water soil capacity 	2.0	5	in/ft
 Availability coefficient 	0.50	6
 Maximum application rate 	0.35	7	in/hr
 Peak Evapotranspiration 	0.28	8	in/day
 Estimated peak flow rate 	7.0	9	US gpm
 Irrigated acreage	20	10	acres
 Application efficiency 	0.58	11
 Step 1.
Determine the maximum soil water deficit , maximum irrigation interval , and system peak flow rate.
Step 2.
Select a gun nozzle, and determine gun set spacing.
Gun flow rate 	136	15	US gpm
 Wetted diameter 	283	16	ft
 Nozzle type 	Taper bore	17
 Nozzle size 	0.75	18	in
 Operating pressure 	70	19	psi
 50% of wetted diameter
 50% of wetted diameter
 65% of wetted diameter
 Step 3.
Determine the set time.
US gpm X 96.3
 in/hr must be less than Max AR of
 The system needs to be designed to match up with MSWD; therefore, NWR=MSWD.
This example shows the problems that are inherent with Stationary Guns.
The poor efficiency, difficulty in matching gun spacing to fit the areas to be irrigated, and inability to move the system as often as required usually mean that the area is not irrigated as well as it should be.
In this case, the irrigation interval is exceeded even if the system could be moved every five hours  which is not practical and not likely.
Since travelling guns move during application, the application uniformity is much better than a stationary gun system.
The efficiency of application may also be slightly higher as the potential for runoff is reduced.
The maximum application efficiency for a travelling gun as shown in Table 3.1 is 65% for most B.C.
conditions.
As indicated in Figure 6.3, travelling guns use a hose to drag the gun cart across the field.
Hose and machine friction losses must therefore be taken into account when selecting machine connection pressure, ensuring that the
 nozzle operates above the minimum pressures required as shown in Table 6.1.
Travelling gun systems are susceptible to striking electrical transmission lines.
The design standards shown in Section 6.7 should be followed when designing a system in the vicinity of high voltage power lines.
Travelling gun systems overcome the problem of the short set time generally required with stationary gun designs.
The travelling gun system can irrigate larger parcels of land during one irrigation set.
Flow rates generally range from a minimum of 50 US gpm up to 700 US gpm.
For agricultural irrigation purposes in B.C., travelling gun systems in the 100 to 350 US gpm range are often used.
Figure 6.3 shows how a travelling gun is operated to irrigate a field.
Figure 6.3 Hard Hose Reel Machine Layout
 The travel speed of a travelling gun can be adjusted to vary the amount of water applied.
Adjustments to the travel speed can also be used to help reduce or eliminate puddling and runoff.
Set times can be selected to suit the farm operation, however it is important that the irrigation system design and operation allows the machine to operate at least 23 hours per day to maximize efficiency of use.
If total operating times are less than 23 hours per day then a peak flow rate per acre exceeding the values estimated in Table 4.6 may result.
The 23 hour set time is selected to allow time for moving the gun to the next set.
The travel speed required is determined from Equation 6.3.
Equation 6.3 Travel Speed 
 T Field length Set Time
 T = gun cart travel speed [ft/hr] Field length = length of field [ft] Set time = time to irrigate one set [hr]
 Amount Applied per Irrigation
 The amount applied by a travelling gun system is dependent upon the travel speed of the gun cart, the gun flow rate and gun spacing.
The amount applied by the machine can be calculated by using Equation 6.4.
Equation 6.4 Gross Water Applied 
 GWA = gross water applied during an irrigation interval [in]
 Q = gun flow rate [US gpm]
 S = lane spacing between sets [ft]
 T = gun cart travel speed [ft/hr]
 As a quick guide, Table 6.3 provides information on the GWA by a travelling gun for various flow rates, lane spacings and travel speeds.
The net water applied  is calculated by applying the application efficiency of the gun to the gross water applied.
See Equation 6.5.
Equation 6.5 Net Water Applied 
 NWA = GWAx AE
 NWA = net water applied during an irrigation interval [in]
 GWA = gross water applied during an irrigation interval [in]
 AE = application efficiency [% in decimal form]
 Table 6.3 Depth of Water Applied by Travelling Guns 
 Flow per	Lane	Travel Speed [ft/hr]
 [US gpm]	[ft]	20	30	40	60	80	100	120	150	180
 100	120	4.01	2.68	2.00	1.33	1.00	0.80	0.67	0.54	0.43
 135	3.56	2.38	1.78	1.18	0.89	0.71	0.59	0.48	0.39
 150	3.21	2.14	1.60	1.07	0.80	0.64	0.54	0.43	0.36
 150	135	5.35	3.57	2.68	1.78	1.34	1.07	0.89	0.71	0.59
 150	4.82	3.21	2.41	1.61	1.20	0.96	0.80	0.64	0.54
 165	4.37	2.92	2.19	1.46	1.09	0.88	0.73	0.58	0.49
 180	4.01	2.68	2.00	1.34	1.00	0.80	0.67	0.54	0.45
 200	150	-	4.28	3.21	2.14	1.61	1.28	1.07	0.86	0.71
 165	5.83	3.89	2.92	1.95	1.46	1.17	0.97	0.78	0.65
 180	5.35	3.56	2.68	1.78	1.34	1.07	0.89	0.71	0.59
 200	4.81	3.21	2.40	1.60	1.20	0.96	0.80	0.64	0.54
 250	160	-	5.01	3.76	2.50	1.38	1.50	1.25	1.00	0.84
 180	-	4.46	3.34	2.23	1.67	1.34	1.11	0.89	0.74
 200	-	4.00	3.00	2.00	1.50	1.20	1.00	0.80	0.67
 220	5.47	3.65	2.74	1.82	1.34	1.09	0.91	0.73	0.61
 300	180	-	5.35	4.01	2.68	2.00	1.60	1.34	1.07	0.89
 200	-	4.81	3.61	2.40	1.81	1.44	1.20	0.96	0.80
 220	-	4.37	3.28	2.19	1.64	1.31	1.09	0.88	0.73
 240	-	4.00	3.00	2.00	1.50	1.20	1.00	0.80	0.67
 350	180	-	-	4.68	3.12	2.34	1.87	1.56	1.25	1.04
 200	-	5.61	4.21	2.81	2.11	1.68	1.40	1.12	0.94
 220	-	5.11	3.83	2.55	1.92	1.53	1.28	1.02	0.85
 240	-	4.68	3.51	2.34	1.76	1.40	1.17	0.94	0.78
 400	200	-	-	4.81	3.21	2.41	1.92	1.60	1.28	1.07
 220	-	5.84	4.37	2.92	2.19	1.75	1.46	1.17	0.97
 240	-	5.35	4.01	2.68	2.00	1.60	1.34	1.07	0.89
 260	-	4.94	3.70	2.47	1.85	1.48	1.23	0.99	0.82
 450	200	5.42	4.33	3.61	2.71	2.17	1.81	1.55	1.35	1.20
 220	4.92	3.94	3.28	2.46	1.97	1.64	1.41	1.23	1.09
 240	4.51	3.61	3.00	2.26	1.81	1.50	1.29	1.13	1.00
 260	4.17	3.33	2.78	2.08	1.67	1.39	1.19	1.04	0.93
 500	220	5.47	4.38	3.64	2.74	2.18	1.82	1.56	1.37	1.22
 240	5.01	4.01	3.34	2.51	2.00	1.67	1.43	1.25	1.11
 260	4.62	3.70	3.09	2.31	1.85	1.54	1.32	1.16	1.03
 280	4.30	3.44	2.87	2.15	1.71	1.43	1.23	1.07	0.95
 550	220	6.01	4.81	4.01	3.00	2.40	2.00	1.71	1.50	1.34
 240	5.51	4.41	3.67	2.76	2.20	1.84	1.58	1.38	1.23
 260	5.09	4.07	3.40	2.55	2.04	1.70	1.46	1.27	1.13
 280	4.73	3.78	3.15	2.36	1.89	1.58	1.35	1.18	1.05
 600	240	6.02	4.82	4.01	3.00	2.40	2.00	1.72	1.50	1.34
 260	5.55	4.44	3.70	2.78	2.22	1.85	1.59	1.39	1.23
 280	5.15	4.13	3.44	2.58	2.06	1.72	1.47	1.29	1.15
 300	4.81	3.85	3.21	2.41	1.92	1.60	1.38	1.20	1.07
 650	240	-	5.21	4.35	3.26	2.60	2.17	1.86	1.63	1.45
 260	6.02	4.82	4.01	3.00	2.40	2.00	1.72	1.50	1.34
 280	5.59	4.47	3.73	2.79	2.24	1.86	1.60	1.40	1.24
 300	5.22	4.17	3.48	2.61	2.09	1.74	1.49	1.30	1.16
 700	260	-	5.19	4.32	3.24	2.59	2.16	1.85	1.62	1.44
 280	6.02	4.82	4.01	3.00	2.40	2.00	1.72	1.50	1.34
 300	5.62	4.49	3.75	2.81	2.24	1.87	1.61	1.40	1.25
 320	5.27	4.21	3.51	2.63	2.10	1.75	1.50	1.32	1.17
 Note: The blanks indicate depths of application exceeding 6 inches, which will exceed the MSWD for most plant and soil
 combinations; therefore, are not recommended.
Part circle guns are used on travelling gun systems to ensure that the cart is pulled along dry ground, ahead of the area being irrigated.
This also ensures that the gun does not irrigate beyond the field boundary when the gun cart approaches the machine.
The instantaneous application rate  of the gun will be affected by the part circle.
For a proper design, the IAR must not exceed the maximum application rate for the type of soil texture and field type.
The part circle of the gun should be maximized while still allow the cart to be dragged through the non-irrigated area.
Equation 6.6 illustrates how to determine the instantaneous application rate for part circle guns.
Equation 6.6 Instantaneous Application Rate 
 IAR = Qx96.3 C
 IAR = Instantaneous application rate [in/hr]
 Q = gun flow rate [US gpm]
 R = wetted radius of the gun [ft]
 C = percentage of full circle covered by gun [% in decimal form]
 Table 6.4 can be used as a guide to determine the instantaneous application rate of a travelling gun.
The application rates shown are theoretical values that can be obtained in perfect operating conditions.
Windy conditions may substantially affect the application rates shown.
The gun radius values indicated are average values taken from manufacturer's specifications.
Helpful Tips Travelling Gun System Design
 Travelling gun machines are often designed to swivel the machine 180 SO that the gun cart can be pulled out in both directions without having to move the machine.
If the field is large enough then consider putting the mainline down the middle to utilize this option.
It will reduce moving set up time.
The travel speed selected should ensure that the soil and crop MSWD is not exceeded.
Note that in Table 6.4 the IAR of the gun is reduced as the arc of the gun is increased.
Designers should consider increasing the arc if possible where the IAR of the gun is exceeding the maximum soil infiltration rate.
Table 6.4 Instantaneous Application Rates for Part Circle Guns
 Instantaneous Application Rate [in/hr]
 Gun Flow Rate	Gun Radius
 [US gpm]	[ft]	180 arc	240 arc
 	
 100	130	0.36	0.27
 150	150	0.41	0.31
 200	160	0.48	0.36
 250	175	0.50	0.37
 300	185	0.54	0.40
 350	190	0.59	0.44
 400	200	0.61	0.46
 450	210	0.63	0.47
 500	215	0.66	0.49
 550	220	0.70	0.52
 600	225	0.73	0.54
 650	230	0.75	0.56
 700	235	0.78	0.58
 Helpful Tips Travelling Gun System Design Example 6.2
 In example 6.2, note that the MSWD for the crop and soil is 3.0 inches and the maximum irrigation interval is 14 days if the soil is filled up entirely to the MSWD.
However, for the travelling gun system, since the net amount of water applied is 1 inch, the actual irrigation interval during peak conditions is 5.5 days.
This indicates that slower travel speeds could be used to increase the amount of water applied and lengthening the actual irrigation interval.
No more than 3.0 inches could be applied at one time however or the MSWD would be exceeded.
Helpful Tips Irrigation Design Parameters
 The travelling gun irrigation design plan shown here is also provided in Appendix C with the corresponding design parameters shown on the adjacent page.
The design parameter summary is useful for evaluating the irrigation system design and performance characteristics.
This information should be included with every irrigation system plan.
Example 6.2 Travelling Gun in Armstrong
 The farmer in Armstrong  wants to use a travelling gun to irrigate three 40-acre  alfalfa fields consisting of deep sandy loam soil.
What nozzle, pressure and lane spacing will be required per travelling gun?
What would will be the net water applied per irrigation?
Farm location	Armstrong	1
 Crop type	Alfalfa	2
 Soil texture	SL	3
 Maximum soil water deficit 	3.0	4	in
 Maximum irrigation interval 	14	5	days
 Maximum application rate 	0.45	6	in/hr
 Peak Evapotranspiration 	0.21	7	in/day
 Estimated peak flow rate 	5.25	8	US gpm
 Irrigated area per field	40	9	acres
 Field length	1,320	10	ft
 Application efficiency 	0.65	11
 The set time for a travelling gun is generally 23.5 hours with 0.5 hour for moving the gun
 to the next set.
Set time	23.5	12	hr
 Step 1.
Determine the system peak flow rate.
Estimated Peak Flow Rate Requirement per Acre X Irrigated Area
 =	5.25	8	US gpm X	40	9	acres
 =	210	13	US gpm
 Step 2.
Select a gun nozzle, and determine gun set spacing.
Gun flow rate 	210	14	US gpm
 Wetted diameter 	335	15	ft
 Nozzle type 	Taper bore	16
 Nozzle size 	0.9	17	in
 Nozzle pressure 	80	18	psi
 C value	0.67	19
 Wetted Radius 	=	50% of wetted diameter
 =	50% X	335	14	ft
 =	168	20	ft
 Maximum Lane Spacing	=	60% of wetted diameter
 =	60% X	335	14	ft
 =	201	21	ft
 A round number will be easier to work with in the field.
For convenience, set
 Lane Spacing	=	200	22	ft
 Step 3.
Check the Instantaneous Application Rate.
From Table 6.4, IAR = 0.48 in/hr for a 180 arc, and IAR = 0.36 in/hr for a 240 arc.
The maximum application rate cannot be exceeded.
Therefore, the gun should be operated with at least a 240 arc in this case.
US gpm X 96.3
 in/hr which must be less than Max AR of
 Step 4.
Determine the travel speed , gross water applied , and net water applied.
Note: With a spacing of 200 feet the unit will take 6.5 days to cover the field.
In hot weather the crop water demand may be greater than the irrigation systems ability to supply water.
If the travelling gun application rate exceeds the soil capability, even at arcs approaching full circle, the gun travel speed should be increased to shorten the duration of application as much as possible.
6.7 System Design Consideration near Electrical Transmission Lines
 Striking electrical transmission lines with an irrigation water jet can cause current transfers that may be dangerous to an operator touching the machine.
Current transfers can occur in the following conditions:
 Direct contact of the irrigation system with the transmission line.
Leakage current the result of an alternative path being provided for the conduction of electrical current.
This situation can arise when concentrated jets of water from the irrigation system come into contact with transmission line conductors..
Flashovers occur when the insulating qualities of the air are not great enough to overcome the potential difference between a conductor and objects at another potential.
Flashovers can occur between conductor to tower, phase to phase and conductor to ground due to a water jet interacting with the power line.
An irrigation water jet striking a transmission line is also a nuisance to the power utility because:
 The force exerted on the lines by the water jet can be many times the weight load or expected wind loading.
Swaying of the conductors can result.
A flashover can create power outages which may interrupt service to thousands of customers.
To ensure safe operation of irrigation equipment near transmission lines, minimum separation distances are required from the gun to the transmission lines.
The clearance required between the water jet and the live conductors is a function of the voltage of the conductor.
The values shown in Table 6.5 are the minimum acceptable clearances provided by BC Hydro for various line voltages.
The total water spray height includes the working height of the nozzle plus the maximum stream height above the nozzle.
Two irrigation system types that have working heights which interact with power lines are centre pivots and gun systems.
Working heights of centre pivot systems range from 12 to 25 feet ; however, most pivots are less than 14 feet  in height.
The working height of a travelling gun ranges from 6 to 11 feet.
These heights are required to permit these systems to operate over crops such as corn, providing good uniformity without damaging the crop.
Table 6.5 Irrigation Water Jet to Power Line Clearance Standards
 Line Voltage [kV]	Phase Spacing  [ft]	Min.
Mid-Span Height	 [ft]	Conductor-to-Water	Clearance  [ft]	Spray Height  [ft]	Allowable Stream
 69	5.0	18.0	2.0	16.0
 138	14.0	22.6	3.0	19.6
 230	18.0	24.3	5.0	19.3
 387	22.0	25.6	6.2	19.4
 345	34.8	28.5	7.5	21.0
 500	45.0	32.8	10.5	22.3
 Calculating Maximum Stream Height
 While the working height of a nozzle can be measured easily, the maximum stream height is more difficult.
The maximum stream height is a function of the type of sprinkler, angle of trajectory, nozzle size and operating pressure.
Manufacturers indicate maximum stream heights for various impact sprinklers but not for giant guns
 Nelson Irrigation Corporation has developed a formula for determining the maximum stream height and location of maximum stream height for gun systems based on the wetted diameter and pressure.
Equation 6.7 Stream Height
 X = Horizontal distance from the nozzle at which maximum stream height occurs 
 Z = Maximum stream height above sprinkler nozzle 
 D = Wetted diameter 
 C = Dimensionless factor dependent on barrel trajectory
 K = Dimensionless factor dependent on barrel trajectory and operating pressure
 Figure 6.4 shows the various parameters used in Equation 6.7.
The dimensionless factors "C" and "K" can be determined from Table 6.6 and Table 6.7.
Figure 6.5 Schematic Indicating Gun Spray Trajectories
 Table 6.6 C Values
 Trajectory	15	18	21	24	27
 C Value	0.067	0.081	0.096	0.111	0.127
 Source: Nelson Irrigation Corporation
 Table 6.7 K Values
 PSI	15	18	21	24	27
 40	0.181 X 10-3	0.187 X 10-3	0.194 X 103	0.203 X 10-3	0.213 X 10-3
 68	0.121 X 10-3	0.125 X 10-3	0.129 X 10-3	0.135 X 10-3	0.142 X 10-3
 80	0.091 X 10-3	0.093 X 10-3	0.097 X 10-3	0.101 X 10-3	0.107 X 10-3
 100	0.072 X 10-3	0.075 X 10-3	0.078 X 101 3	0.081 X 10-3	0.085 X 10-3
 Source: Nelson Irrigation Corporation
 Helpful Tips Distance from Electrical Transmission Line
 The maximum stream height and the distance this height occurs from the nozzle are useful when designing systems that are close to transmission lines.
However as demonstrated in Example 6.3, the distance the gun cart must be kept from a transmission line is difficult to determine as there is no calculation for determining how fast the stream height diminishes after the maximum height is reached.
Field observation should also be used in addition to the calculations.
The transmission line height will be the lowest on the hottest day of the year.
The minimum setback distance will be the required clearance distance plus the distance from the cart that the maximum stream height occurs.
Actual distance should probably be further at a point where good stream breakup has occurred.
The field should be staked at the point where the gun should be towed to.
Example 6.3 Maximum Stream Height
 Question: What is the maximum stream height of the gun system selected in example 6.2 if the cart height is 7 ft?
The nozzle selected was a 0.9-inch taper bore nozzle operating at 80 psi with a 24 trajectory.
The flow rate is 210 US gpm with a wetted diameter of 335 ft.
What is the distance that the gun cart should be kept from a 500 kV transmission line?
Flow rate	210	1	US gpm
 Wetted diameter 	335	2	ft
 C value 	0.111	3
 Cart height	7	4	ft
 Select a K value for the pressure that is closest to 80 psi:
 K value 
 A maximum stream height of 25.9 ft occurs 100 ft from the gun operating a 0.9 inch taper bore nozzle at 80 psi with a 24 trajectory.
Adding the cart height of 7 ft means the total height is 32.9 ft.
From Table 6.5, the mid-span height  of a 500kV transmission line is 32.8 ft, approximately the same height of the gun stream.
The conductor to water clearance  is a minimum of 10.5 ft.
Visual observation will be required to determine where a safe distance for the gun cart to start irrigating will be.
The minimum distance will be 110.5 ft away from the transmission line..
Table 6.8 provides close approximations for stream heights and the distance the height occurs from the nozzle for various nozzles, pressures, flow rates and nozzle trajectories.
Equations 6.7  and 6.7  were used to determine these values.
The nozzle height from the ground must be added to these values to get the overall height.
Comparing values in Table 6.8 with clearance requirements in Table 6.5, only the smaller nozzles with lower trajectories have stream heights that may go under the larger transmission lines.
Table 6.8 Stream Trajectory Data for Giant Guns with Taper Bore Nozzles
 Nozzle	Pressure	Flow Rate	Nozzle	Wetted	Radial Distance to	Maximum Stream
 [psi]	[US gpm]	Trajectory	[]	Diameter 	Maximum Stream	Height 	Height 
 0.6"	60	81	18	229	69	12.0
 21	233	70	15.4
 24	240	72	18.9
 80	94	18	251	75	14.5
 21	253	76	18.1
 24	260	78	22.0
 0.7"	60	110	18	252	76	12.5
 21	257	77	16.1
 24	265	80	19.9
 80	128	18	278	83	15.3
 21	281	84	19.3
 24	290	87	23.7
 0.8"	60	143	18	272	82	12.8
 21	276	83	16.7
 24	285	86	20.7
 80	165	18	302	91	16.0
 21	304	91	20.2
 24	310	93	24.7
 0.9"	60	182	18	287	86	13.0
 21	296	89	17.1
 24	305	92	21.3
 80	210	18	323	97	16.5
 21	328	98	21.0
 24	335	101	25.9
 1.0"	60	225	21	315	95	17.4
 24	325	98	21.8
 80	260	21	344	103	21.5
 24	355	107	26.7
 100	290	21	364	109	24.6
 24	375	113	30.2
 1.1"	80	330	21	375	113	22.4
 24	387	116	27.8
 27	395	119	33.5
 100	370	21	400	120	25.9
 24	412	124	32.0
 27	420	126	38.3
 1.3"	80	445	21	409	123	23.0
 24	421	126	28.8
 27	430	129	34.8
 100	500	21	437	131	27.1
 24	451	135	33.6
 27	460	138	40.4
 1.6"	80	675	21	470	141	23,7
 24	475	143	29.9
 27	485	146	36.4
 100	755	21	494	148	28.4
 24	510	153	35.5
 27	520	156	43.1
 Values are approximations only.
Table 6.9 Gun Nozzle Performance Series 75 Guns 24 Trajectory
 0.5"	0.55"	0.6"	0.65"	0.7"	0.75"	0.8"
 PSI	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA
 35	40	164'	49	172'	59	178'	69	191'	81	196'	93	202'
 40	43	171'	52	180'	63	190'	74	198'	87	204'	98	213'	112	221'
 45	46	180'	56	189'	67	198'	79	206'	91	214'	104	223'	118	230'
 50	48	186'	59	195'	70	203'	83	212'	95	220'	109	230'	123	237'
 55	50	193'	62	203'	74	213'	87	221'	100	230'	115	239'	130	247'
 60	53	198'	64	208'	77	220'	91	228'	104	237'	120	245'	136	254'
 65	55	205'	67	216'	80	227'	95	237'	109	247'	125	254'	142	263'
 70	57	210'	69	221'	83	232'	98	243'	113	254'	129	260'	147	270'
 75	59	217'	72	228'	86	239'	101	250'	117	261'	134	268'	153	277'
 80	61	222'	74	234'	89	244'	105	256'	121	266'	138	274'	158	283'
 The diameter of flow is approximately 3% less for the 21 trajectory angle, and 6% less for 18.
Source: Nelson Irrigation Corporation
 Table 6.10 Gun Nozzle Performance Series 100 Guns 24 Trajectory
 0.50"	0.55"	0.60"	0.65"	0.70"	0.75"	0.80"	0.85"	0.90"	1.0"
 PSI	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA
 40	47	191'	57	202'	66	213'	78	222'	91	230'	103	240'	118	250'	134	256'	152	262'
 50	50	205'	64	215'	74	225'	87	235'	100	245'	115	256'	130	265'	150	273'	165	280'	204	300'
 60	55	215'	69	227'	81	240'	96	250'	110	260'	126	270'	143	280'	164	288'	182	295'	224	316'
 70	60	225'	75	238'	88	250'	103	263'	120	275'	136	283'	155	295'	177	302'	197	310'	243	338'
 80	64	235'	79	248'	94	260'	110	273'	128	285'	146	295'	165	305'	189	314'	210	325'	258	354'
 90	68	245'	83	258'	100	270'	117	283'	135	295'	155	306'	175	315'	201	326'	223	335'	274	362'
 100	72	255'	87	268'	106	280'	123	293'	143	305'	163	316'	185	325'	212	336'	235	345'	289	372'
 110	76	265'	92	278'	111	290'	129	303'	150	315'	171	324'	195	335'	222	344'	247	355'	304	380'
 0.64"	0.68"	0.72"	0.76"	0.80"	0.84"	0.88"	0.92"	0.96"
 PSI	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA
 40	67	212'	76	219'	86	225'	98	233'	110	242'	125	250'	136	254'	151	259'	166	275'
 50	75	224'	85	231'	97	240'	110	250'	123	258'	139	266'	152	271'	169	279'	185	288'
 60	83	239'	94	246'	106	254'	120	264'	135	273'	153	281'	167	286'	186	294'	203	303'
 70	89	249'	101	259'	114	268'	130	277'	146	286'	165	295'	180	300'	200	309'	219	320'
 80	95	259'	108	269'	122	278'	139	288'	156	297'	176	306'	193	313'	214	324'	235	336'
 90	101	268'	115	278'	130	289'	147	299'	166	308'	187	317'	204	324'	227	334'	249	345'
 100	107	278'	121	288'	137	298'	155	308'	175	318'	197	327'	216	334'	240	344'	262	355'
 110	112	288'	127	298'	143	308'	163	317'	183	326'	207	336'	226	342'	251	353'	275	364'
 0.71"	0.77"	0.81"	0.86"	0.89"	0.93"	0.96"
 PSI	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA
 40	66	208'	78	212'	91	215'	103	224'	118	235'	134	238'	152	242'
 50	74	220'	88	225'	100	230'	115	240'	129	250'	150	255'	167	260'
 60	81	235'	96	240'	110	245'	125	260'	141	270'	164	275'	183	280'
 70	88	245'	104	250'	118	260'	135	275'	152	290'	177	295'	198	300'
 80	94	255'	111	265'	127	275'	145	285'	163	300'	189	305'	211	315'
 90	99	265'	117	275'	134	285'	154	295'	173	310'	201	315'	224	325'
 100	105	270'	124	280'	142	295'	162	305'	182	320'	212	325'	236	335'
 110	110	275'	130	290'	149	305'	170	315'	191	325'	222	335'	248	345'
 The diameter of flow is approximately 3% less for the 21 trajectory angle, and 6% less for 18.
Source: Nelson Irrigation Corporation
 Table 6.11 Gun Nozzle Performance Series 150 Guns 24 Trajectory
 TAPER BORE NOZZLES	Flow Path
 0.70"	0.80"	0.90"	1.0"	1.1"	1.2"	1.3"	1.4"
 PSI	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA
 50	100	250'	130	270'	165	290'	205	310'	255	330'	300	345'	350	360'	408	373'
 60	110	265'	143	285'	182	305'	225	325'	275	345'	330	365'	385	380'	446	396'
 70	120	280'	155	300'	197	320'	245	340'	295	360'	355	380'	415	395'	483	412'
 80	128	290'	165	310'	210	335'	260	355'	315	375'	380	395'	445	410'	516	427'
 90	135	300'	175	320'	223	345'	275	365'	335	390'	405	410'	475	425'	547	442'
 100	143	310'	185	330'	235	355'	290	375'	355	400'	425	420'	500	440'	577	458'
 110	150	320'	195	340'	247	365'	305	385'	370	410'	445	430'	525	450'	605	471'
 120	157	330'	204	350'	258	375'	320	395'	385	420'	465	440'	545	460'	632	481'
 TAPER RING NOZZLES	Flow Path
 0.88"	0.96"	1.04"	1.12"	1.2"	1.28"	1.36"
 PSI	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA
 50	135	270'	164	286'	196	302'	233	318'	274	333'	319	347'	369	358'
 60	148	284'	179	301'	214	317'	255	334'	301	351'	350	367'	405	378'
 70	159	299'	194	315'	231	331'	276	349'	325	366'	378	382'	437	393'
 80	170	310'	207	330'	247	346'	295	364'	347	381'	404	397'	467	409'
 90	181	320'	220	340'	262	357'	313	377'	368	396'	429	411'	495	424'
 100	191	329'	231	350'	277	366'	330	386'	388	405'	452	423'	522	436'
 110	200	339'	243	359'	290	376'	346	397'	407	416'	474	433'	548	446'
 120	209	349'	253	369'	303	386'	361	407'	425	426'	495	443'	572	457'
 RING NOZZLES	Flow Path
 0.86"	0.97"	1.08"	1.18"	1.26"	1.34"	1.41"	1.47"
 PSI	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA
 50	100	245'	130	265'	165	285'	205	300'	255	320'	300	335'	350	350'	385	353'
 60	110	260'	143	280'	182	300'	225	315'	275	335'	330	350'	385	365'	423	368'
 70	120	270'	155	290'	197	310'	245	330'	295	350'	355	365'	415	380'	458	383'
 80	128	280'	165	300'	210	320'	260	340'	315	360'	380	380'	445	395'	490	399'
 90	135	290'	175	310'	223	330'	275	350'	335	370'	405	390'	475	405'	522	409'
 100	143	300'	185	320'	235	340'	290	360'	355	380'	425	400'	500	415'	550	419'
 110	150	310'	195	330'	247	350'	305	370'	370	390'	445	410'	525	425'	577	429'
 120	157	315'	204	335'	258	360'	320	380'	385	400'	465	420'	545	435'	603	439'
 The diameter of throw is approximately 3% less for the 21 trajectory angle.
Source: Nelson Irrigation Corporation
 Table 6.12 Gun Nozzle Performance Series 200 Guns 27 Trajectory
 TAPER BORE NOZZLES	Flow Path
 1.05"	1.1"	1.2"	1.3"	1.4"	1.5"	1.6"	1.75"	1.9"
 PSI	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA
 60	250	345'	285	355'	330	375'	385	390'	445	410'	515	430'	585	445'	695	470'	825	495'
 70	270	360'	310	380'	355	395'	415	410'	480	430'	555	450'	630	465'	755	495'	890	515'
 80	290	375'	330	395'	380	410'	445	430'	515	450'	590	470'	675	485'	805	515'	950	535'
 90	310	390'	350	410'	405	425'	475	445'	545	465'	625	485'	715	505'	855	535'	1005	555'
 100	325	400'	370	420'	425	440'	500	460'	575	480'	660	500'	755	520'	900	550'	1060	575'
 110	340	410'	390	430'	445	450'	525	470'	605	495'	695	515'	790	535'	945	565'	1110	590'
 120	355	420'	405	440'	465	460'	545	480'	630	505'	725	530'	825	550'	985	580'	1160	605'
 130	370	425'	425	445'	485	465'	565	485'	655	515'	755	540'	860	560'	1025	590'	1210	620'
 1.29"	1.46"	1.56"	1.66"	1.74"	1.83"	1.93"
 PSI	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA	GPM	DIA
 50	230	325'	300	355'	350	370'	410	390'	470	405'	535	420'	640	435'
 60	250	340'	330	370'	385	390'	445	410'	515	425'	585	440'	695	455'
 70	270	355'	355	385'	415	405'	480	425'	555	440'	630	455'	755	475'
 80	290	370'	380	400'	445	420'	515	440'	590	455'	675	470'	805	490'
 90	310	380'	405	415'	475	435'	545	455'	625	470'	715	485'	855	505'
 100	325	390'	425	425'	500	445'	575	465'	660	480'	755	500'	900	520'
 110	340	400'	445	435'	525	455'	605	475'	695	490'	790	510'	945	535'
 120	355	410'	465	445'	545	465'	630	485'	725	500'	825	520'	985	545'
 130	370	415'	485	450'	565	470'	655	490'	755	505'	860	525'	1025	550'
 The diameter of flow is approximately 2% less for the 24 trajectory angle, and 5% less for 21.
Source: Nelson Irrigation Corporation
For corn in R4 Dough stage of growth, there are approximately 34 days to maturity and 7.5 water use to maturity.
For corn in R4.7 Beginning Dent stage of growth, there are approximately 24 days to maturity and 5.0 water use to maturity.
For corn in R5 1/4 milk line stage of growth, there are approximately 19 days to maturity and 3.75 water use to maturity.
For corn in R5 1/2 milk line stage of growth, there are approximately 13 days to maturity and 2.25 water use to maturity.
For corn in R5 3/4 milk line stage of growth, there are approximately 7 days to maturity and 1.0 water use to maturity.
For corn in R6 physiological maturity stage of growth, there are approximately 0 days to maturity and 0.0 water use to maturity.
Irrigation Scheduling Made Easy: Using the Look and Feel method
 Accurate irrigation scheduling maximizes the benefits of irrigation while minimizing potential negative impacts of overirrigation or underirrigation.
Overirrigation 
 Drowns roots, thus stressing plants
 Cools soil, thus reducing root growth
 Leaches nutrients and pesticides from the root zone to groundwater
 Underirrigation 
 Reduces crop quality 
 Many people schedule irrigation by the calendar rather than by plant need.
Calendar-based scheduling can be very inaccurate since plant water needs and the amount of soil water available to plants are affected by factors such as climate, plant size, soil type and rooting depth.
The goal of accurate irrigation scheduling is to replace soil water lost by evaporation and plant use as precisely as possible.
To accomplish this goal, you need to accurately assess soil moisture content.
Then you can determine the need for irrigation and how much water to deliver.
Irrigation scheduling can seem complicated.
It doesnt have to be.
Anyone can use a simple, effective method known as the look and feel method to determine when to irrigate.
How does it work?
This method is based on three simple ideas:
 Soil is at field capacity when it is holding as much water as possible after the excess has drained away.
Similarly, a wet sponge is at field capacity when it holds all the water it can without any dripping away.
It is best to irrigate when half of the water is depleted
 Your goal when irrigating is to return the water to field capacity.
So all you need to know to schedule irrigation is:
 What is the effective root zone of your crop, pasture or orchard?
What does the soil look like when half of that water is gone?
How much water should be applied to return to field capacity?
1.
Effective root zone depth.
Determine the rooting depth of the trees or plants to be irrigated based on site-specific considerations.
Be mindful of intrusive clay or plow layers that may prohibit water movement.
If you have questions please consult a crop production guide or your LSU Extension agent.
2.
Evaluate soil moisture.
Use a probe, auger or shovel to take a soil sample from the rooting depth.
Squeeze each sample until it forms a ball.
Usually, gentle pressure is sufficient.
Look carefully at the soil ball:
 Are there loose sand grains or small clumps of soil?
Are there clay stains on your fingers?
A little?
A lot?
Does the ball hold together when bounced gently in your hand?
Using Table 2, estimate the soil texture and determine how much water is left in the soil.
If soil moisture is 50 percent depleted, its time to irrigate.
3.
Apply the correct amount of irrigation water.
Multiply the recommended irrigation depth  by the depth of the effective root zone to find out how much irrigation water you need to apply to return the soil to field capacity.
Example: Suppose your irrigation field is a sandy loam soil with a 15-inch root zone.
You feel the soil and observe that it forms a weak ball, which falls apart.
Based on the guidelines given in Table 1, you can irrigate 0.3 to 0.4 inch of water per foot of root zone depth.
For a 15-inch  root zone depth, the permissible irrigation amount is:
 0.3 inches/foot of root zone x 1.25 feet = 0.38 inches
 0.4 inches/foot of root zone x 1.25 feet = 0.50 inches
 The recommended irrigation amount is between 0.38 and 0.50 inches.
Apply only the amount of water needed to return the soil to field capacity.
Consider the efficiency of your irrigation system when calculating how much water to apply.
Check with your parish LSU Extension agent or irrigation supplier for irrigation system efficiency estimates.
You may want to know What is the field capacity of my soil?
Determine the soil water-holding capacity of the different soil horizons within this rooting depth.
This can found online at the Web Soil Survey.
This map-based tool for use by the general public provides interpretations, data and soil maps for parishes all over Louisiana.
Soil water-holding capacities are found in the Soils Data Explorer, Soil Reports, Soil Physical Properties, Physical Soil Properties.
To determine how much water is in the rooting zone when the soil is at field capacity, multiply the rooting depth times the water-holding capacity.
Example: If the rooting depth of a soil is 10 inches and the water-holding capacity is 0.2 inch of water per inch of soil, then the rooting zone holds 2 inches of water at field capacity.
Applying nitrogen fertilizer or crop protection products through a center pivot is an efficient and effective method.
In fact, it is a well-documented best management practice to apply nitrogen fertilizer as close to the time the corn will use it to get the most efficient use of the fertilizer.
Most of the products are injected into the pivot with a fixed rate injection pump.
So, how does one figure the pumping rate to set the pump at, and what about the change the end gun causes when it's turned on and off?
We will discuss both challenges in this article.
COMPARISON OF GRAIN SORGHUM, SOYBEAN, AND COTTON PRODUCTION UNDER SPRAY, LEPA, AND SDI
 Paul D.
Colaizzi Agricultural Engineer Phone: 806-356-5763 paul.colaizzi@ars.usda.gov
 Steven R.
Evett Research Soil Scientist Phone: 806-356-5775 steve.evett@ars.usda.gov
 Terry A.
Howell Research Leader  Phone: 806-356-5746 terry.howell@ars.usda.gov
 R.
Louis Baumhardt Research Soil Scientist Phone: 806-356-5766 r.louis.baumhardt@ars.usda.gov
 USDA-ARS P.O.
Drawer 10 Bushland, Texas 79012-0010 FAX: 806-356-5750
 Crop production was compared under subsurface drip irrigation , low energy precision applicators , low elevation spray applicators , and mid elevation spray applicators  at the USDA-Agricultural Research Service Conservation and Production Research Laboratory, Bushland, Tex., USA.
Each irrigation method was compared at irrigation rates meeting 25, 50, 75, and 100% of full crop evapotranspiration.
Crops included three seasons of grain sorghum, one season of soybean , and four seasons of upland cotton.
For grain sorghum, SDI followed by LEPA, MESA, and LESA resulted in greater grain yield, water use efficiency, and irrigation water use efficiency at the 25and 50% irrigation rates, whereas MESA followed by LESA outperformed LEPA and SDI at the 75and 100% irrigation rates.
For soybean, the same trend was observed at the 25and 50% irrigation rates, whereas SDI followed by MESA, LEPA, and LESA resulted in the best crop response at the 75% irrigation rate, and MESA followed by SDI, LESA, and LEPA resulted in the best crop response at the 100% irrigation rate.
Cotton response was consistently best for SDI, followed by LEPA, and either MESA or LESA at all irrigation rates.
Within each irrigation rate, few significant differences were observed among irrigation methods in total seasonal water use for all crops.
Irrigation is practiced on approximately 4 million of the 8.5 million cultivated acres in the semiarid Texas High Plains.
Irrigation results in substantially greater crop productivity and water use efficiency compared with dryland production where precipitation is limited or sporadic.
The Ogallala Aquifer is the primary water resource for irrigated agriculture in the U.S.
Great Plains, including the Texas High Plains, and is one of the largest freshwater resources in the world.
However, the Ogallala Aquifer has been declining in many areas because withdrawals  have greatly exceeded recharge.
The Ogallala is the major part of the High Plains aquifer, which underlies 175,000 square miles across eight Great Plains states, representing 27 percent of U.S.
irrigated land.
The practice of efficient irrigation is therefore imperative to simultaneously prolong the life of the Ogallala and High Plains aquifers, conserve energy used for pumping, and sustain rural economies.
Center pivot irrigation systems equipped with low-pressure application packages and subsurface drip irrigation  can be highly efficient in terms of uniformity, application efficiency, and crop water productivity compared with gravity irrigation.
In the Texas High Plains, about 75 percent of the irrigated area is by center pivot, with gravity and SDI comprising about 20 and 5 percent, respectively.
Center pivot application packages initially included impact sprinklers, but these have been supplanted by packages that operate at lower pressure and hence reduce energy consumption, including mid elevation spray applicators , low elevation spray applicators , and low energy precision applicators .
Surface and subsurface drip irrigation were first adopted in Texas during the mid-1980s for cotton production ; SDI has greatly expanded in the Trans Pecos and Southern High Plains cotton producing regions.
There is anecdotal evidence that SDI results in greater crop yield, greater water use efficiency, and earlier cotton maturity relative to center pivot systems equipped with spray or LEPA packages.
Cotton earliness under SDI is thought to be related to reduced evaporative cooling from the soil surface and plant canopy relative to that under center pivot systems.
Reduced evaporation could result in warmer soil temperatures and encourage more vigorous early-season plant development.
However, this may be countered somewhat by the greater cooling effect on the soil from the more frequent irrigation inherent with SDI.
In any case, warmer soil temperatures would be a critical advantage for cotton production in thermally-limited climates where corn is traditionally produced, such as the northern Texas Panhandle and southwestern Kansas.
In addition, SDI has been shown to be technically feasible and economically advantageous over center pivot under certain circumstances for corn production in western Kansas.
Despite these apparent
 advantages, the initial capital expense, greater maintenance and management requirements, and difficulty with crop germination in dry soil , have been persistent barriers to greater adoption of SDI.
The objective of this paper was to compare crop production under MESA, LESA, LEPA, and SDI in a multi-year experiment at Bushland, Tex., USA.
Crops included grain sorghum, soybean, and cotton.
Production parameters measured included crop yield, seasonal water use , water use efficiency , and irrigation water use efficiency.
WUE was defined as the ratio of economic yield  to seasonal water use, or WUE = Y .
IWUE was defined as the increase in irrigated yield  over dryland yield  due to irrigation , or IWUE =  IR.
Loan value and gross returns were also reported for cotton.
This research was conducted at the USDA Agricultural Research Service Conservation and Production Research Laboratory at Bushland, Texas.
The soil is a Pullman clay loam  with slow permeability due to a dense B21t horizon that is 6to 20-in.
below the surface.
A calcic horizon begins at approximately 4 ft below the surface.
The relative performance of mid elevation spray applicators , low elevation spray applicators , low energy precision applicator , and subsurface drip irrigation  were compared for irrigation rates ranging from near dryland to meeting full crop evapotranspiration  in a strip-split block design.
The irrigation rates were designated lo, 25, 50, l75, and 100, where the subscripts were the percentage of irrigation applied relative to meeting full ET.
The lo plots were similar to dryland production, in that they received only enough irrigation around planting to ensure crop establishment, except irrigated fertility and seeding rates were used.
The MESA, LESA, and LEPA methods  were applied with a hose-fed, three-span Valmont lateral-move irrigation system, where each span contained a complete block.
Irrigation rates were imposed by varying the speed of the lateral.
The SDI method consisted of laterals chiseled beneath alternate furrows at the 12-in.
depth, where irrigation rates were imposed by varying emitter flow rates and spacing.
Cropping seasons included grain sorghum , soybean , and cotton.
Soybean was planted after the 2005 cotton crop was destroyed by hail.
All crops
 1 The mention of trade names of commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S.
Department of Agriculture.
were planted in east-west oriented raised beds on 30-in.
centers.
Dikes were installed in all furrows after crops had developed true leaves to control run on and runoff of irrigation water and rain.
Crop varieties and cultural practices were similar to those practiced in the region for high crop yields.
Table 1.
Sprinkler irrigation application device information [a]
 Applicator	Model [b]	Options	
 LEPA	Super Spray head	Double-ended drag	0
 LESA	Quad IV	Flat, medium-	1.0
 MESA	Low-drift nozzle	Single, convex,	5.0
  spray head	medium-grooved
 [a] All sprinkler components manufactured by Senninger Irrigation, Inc., Orlando, Fla., except where noted.
[b] All devices equipped with 10 psi pressure regulators and No.
17  plastic spray nozzles, giving a flow rate of 6.5 gpm.
[c] Manufactured by A.
E.
Quest and Sons, Lubbock, Tex.
Table 2.
Subsurface drip irrigation  dripline information [a]
 Irrigation	Emitter Flow	Emitter	Application
 rate	Rate 	Spacing 	Rate 
 l25	2.6	36	0.019
 150	3.3	24	0.038
 75	3.3	16	0.057
 100	3.3	12	0.076
 [a] All SDI dripline manufactured by Netafim USA, Fresno, Calif.
[b] Smooth tubing, no emitters
 Volumetric soil water was measured by gravimetric samples to the 6 ft depth in 1ft increments at planting and harvest.
Soil water was also measured during the crop season by neutron scattering to the 7.5-ft depth in 8-in.
increments  using a depth control stand.
Neutron moisture meters were field-calibrated and achieved accuracies better than 0.005 m mi -3 (or 0.06 in.
ft1 Near-surface soil water and temperatures were also measured with time-domain reflectometry and copper-constantan thermocouples,
 respectively  during the soybean and last two cotton seasons.
Irrigations for grain sorghum were scheduled using the Texas High Plains Evapotranspiration Network.
Irrigations for soybean and cotton were scheduled when measured soil water deficit  averaged 1 in.
in the 100 plots.
The 100 plots received sufficient irrigation to bring the soil profile to field capacity; the l75, 150, and l25 plots received proportionately less.
In some years, all plots received a uniform 1-in.
spray application to ensure germination.
Table 3.
Agronomic data for grain sorghum  and soybean.
Year	2000	2001	2002	2005
 Crop	Grain	Grain	Grain	Soybean [c]
 Variety	Pioneer	Pioneer	Pioneer	Pioneer
 84G62	8966	84G62	94M90
 Plant density	121,000	93,000	89,000	182,000
 Planting date	26-May	22 June 	31-May	20-Jun
 Harvest date	21-Sep	29-Oct	14-Nov	26-Oct
 Precipitation 	5.5	4.9	12.5	5.5
 Fertilizer	68 lb ac-	51 lb ac-	102 lb ac-
 applied	preplant P	preplant P	preplant P
 52 2bla	160 lb ac-1	143 lb ac-	158 lb ac-1
 preplant N	preplant N	preplant N	preplant N [c]
 40 lb ac-	16 lb ac-
 irr.
N  [a]	irr.
N  [a]
 Herbicide	2.0 qt ac-1	2.0 qt ac-1	1.4 lb ac-1	1.0 qt ac-1
 applied	Bicep	Bicep	Atrazine	Treflan
 Insecticide	0.25 qt ac-1	None	None	None
 [a] Liquid urea 32-0-0 injected into irrigation water; deficit irrigation treatments received proportionately less.
[b] Two previous plantings on 22 May and 5 June failed to emerge.
[c] Replaced cotton that was destroyed by hail.
Table 4.
Agronomic data for cotton.
Year	2003	2004	2006	2007
 Crop	Cotton	Cotton	Cotton	Cotton
 Variety	Paymaster	Paymaster	Paymaster	Paymaster
 2280 BG,	2280 BG,	2280 BG,	2280 BG,
 RR	RR	RR	RR
 Plant density	70,000	80,000	80,000	60,000
 Planting date	10-Jun [a]	20-May	17-May	29-May
 Harvest date	21-Nov	14-Dec	13-Dec	5-Nov
 Total heat units	1940	1560	2280	1980
 Precipitation 	6.6	19.5	14.3	8.0
 Fertilizer applied	95 lb ac-1	102 lb ac-	74 lb ac-	78 lb ac
 preplant P	preplant P	preplant P	preplant P
 28 lb ac-1	30 lb ac-1	16 lb ac-1	17 lb ac-1
 preplant N	preplant N	preplant N	preplant N
 43 lb ac-1	45 lb ac-	70 lb ac-	120 lb ac-
 irr N  [b]	irr N  [b]	irr N 	irr N  [b]
 Herbicide applied	1.0 qt ac-	1.0 qt ac-	1.0 qt ac-	1.0 qt ac-
 Treflan	Treflan	Treflan	Treflan
 Insecticide	NONE	NONE	0.5 qt ac-1	0.5 qt ac-1
 Growth regulator	NONE	NONE	NONE	NONE
 Defoliant applied	NONE	NONE	NONE	0.5 qt ac-
 Boll opener	NONE	NONE	NONE	0.5 qt ac-1
 [a] The first planting on 21-May sustained severe hail damage on 3-Jun.
[b] Liquid urea 32-0-0 injected into irrigation water; deficit irrigation treatments received proportionately less.
Crop yield , seasonal water use, water use efficiency , and irrigation water use efficiency  were compared using the SAS PROC MIXED procedure.
Loan value and gross return were also compared for cotton.
Any differences in these parameters were tested using least squared differences , and means were separated by letter groupings using a macro by Saxton.
The relative performance of the irrigation methods changed with the irrigation rate for grain sorghum.
For the lower irrigation rates , grain yield was greatest for SDI, followed by LEPA, MESA, and LESA.
For the higher irrigation rates , grain yield was greatest for MESA, followed by LESA.
The only significant difference  occurred at l25, where grain yield under SDI was significantly greater than for the other irrigation methods.
The other differences were only numerical, although some additional significant differences did occur within individual seasons.
Grain yield was significantly different for each irrigation rate average , and was positively correlated with the irrigation rate as expected.
For irrigation method averages, grain yield was greatest for SDI, followed by MESA, LEPA, and LESA, where the only significant difference was observed between SDI and LESA.
For seasonal water use, the only significant differences observed were between irrigation rate averages.
WUE and IWUE followed the same trends observed for grain yield among irrigation rates and for irrigation method averages.
For irrigation rate averages, however, WUE was greatest at l75, followed by 150, 100, 25, and lo, and IWUE was greatest at 150, followed by l25, l75, and 100.
The least WUE occurred at 10, which was only about 38 percent of WUE at 50, and shows the impact of irrigation on WUE.
It appears that diminishing crop response to water was reached around l75, as yield was not much greater at 100 and maximum WUE occurred at 77.
We speculate that different factors, depending on irrigation rate, may have influenced the relative performance of the irrigation methods that were observed for grain sorghum.
One rationale of SDI and LEPA is that evaporative losses from the plant canopy and air above the canopy and losses to wind drift are virtually eliminated, and that evaporative looses from the soil are greatly reduced  compared with spray applicators.
This would allow a greater proportion of irrigation water to be available for plant transpiration  and hence increase crop productivity.
This hypothesis was supported by the greater grain yield observed for SDI compared with the other methods at the 25 and 50 irrigation rates.
Grain yield with LEPA was only slightly greater than MESA, suggesting both had similar total evaporative losses.
However, MESA
 loss pathways may have also included evaporation from the canopy and overlying air and wind drift , but less loss pathways by soil water evaporation compared with LEPA.
Grain yield was greater for MESA compared with LESA at all irrigation rates, but more so at l25 and 150.
This may have been caused by greater erosion of furrow dikes and runoff away from the center of the plot  under LESA.
The spray applicator height of LESA was 1 ft, whereas it was 5 ft for MESA.
Therefore, the plant canopy would be expected to intercept more irrigation water with MESA, whereas greater risk of furrow dike erosion may result with the low applicator height of LESA, which does not divert water away from furrow dikes like the double-ended drag sock used with LEPA.
At the l75 and 100 irrigation rates, the lack of soil aeration and nutrient leaching by deep percolation may have reduced grain sorghum yield for SDI  compared with MESA and LESA.
Colaizzi et al.
observed increases in volumetric soil water between the 6and 10-ft depths over successive measurements with neutron scattering for SDI at l75 and 100, LEPA at 100, but not for MESA or LESA.
This was attributed to deep percolation rather than upward capillary movement, since the depth to saturated thickness of the Ogallala Aquifer was approximately 250 ft.
Lamm et al.
reported that corn yield with SDI was lower at 125% of full ET compared with 100% ET in two out of three years in a study at Colby, Kan., and also attributed this to poor soil aeration and leaching of nutrients by deep percolation.
In that study, Darusman et al.
deduced deep percolation using tensiometer measurements for the 100% and 125% irrigation rates.
In the grain sorghum study at Bushland, Tex., the presence of deep percolation suggests that irrigation rates exceeded 100% in some cases for LEPA and SDI.
The irrigations were scheduled using the Texas High Plains Evapotranspiration  Network , which used crop coefficients derived from large weighing lysimeters  for several crops including grain sorghum.
The crop coefficients reflect crops irrigated with MESA, and probably have larger values  compared with crop coefficients that might have resulted had the coefficients been determined using LEPA or SDI.
Consequently, the subsequent studies with soybean and cotton used neutron scattering as the basis for irrigation scheduling.
Table 5.
Grain sorghum response, average of 2000, 2001, and 2002 seasons; Colaizzi et al., 2004.
Irrigation	Irrigation	yield	[b]	water use	WUE	IWUE
 Rate [a]	method			(bu ac in.
25	MESA	60.8	b c	18.1 a	3.80	b	8.57	b
 	LESA	49.7	b	18.5	a	3.07	b	6.37	b
 LEPA	65.3	b	18.5	a	3.97	b	9.49	b
 SDI	99.5	a	18.9 a	5.96	a	16.32	a
 50	MESA	123.3	a	22.1	a	6.12	ab	11.77	a
 	LESA	109.3	a	22.5	a	5.36	b	10.36	a
 LEPA	127.0	a	22.2 a	6.24	ab	12.23	a
 SDI	140.7	a	22.3 a	7.02	a	13.74 a
 75	MESA	152.3	a	25.0 a	6.71	a	10.48 a
 	LESA	144.5	a	25.7	a	6.12	a	9.92 a
 LEPA	141.5	a	25.3	a	6.09	a	9.63 a
 SDI	142.1	a	24.8 a	6.33	a	9.55 a
 100	MESA	162.7	a	28.6 a	6.14 a	8.69 a
 	LESA	155.9	a	28.5 a	5.90 a	8.26 a
 LEPA	146.6 a	28.0 a	5.67 a	7.69 a
 SDI	144.8	a	28.6 a	5.47 a	7.47 a
 lo 	18.1	d	14.9	e	1.59	C
 l25 	68.8	C	18.5	d	4.20	b	10.19	ab
 50 	125.1	b	22.3	C	6.19	a	12.03	a
 75 	145.1	a	25.2	b	6.31 a	9.90	bc
 100 	152.5	a	28.4 a	5.80 a	8.03	C
 MESA	124.8	ab	[e]	23.4 a	5.69	ab	9.88	ab
 LESA	114.9	b	23.8 a	5.11	b	8.73 b
 LEPA	120.1	ab	23.5 a	5.49	b	9.76	b
 SDI	131.8	a	23.6 a	6.20 a	11.77	a
 [a] Numbers in parenthesis are average seasonal irrigation totals for each irrigation rate.
[b] Yields were converted from dry mass to 14% moisture content by mass; 1 bu = 55 lb.
[c] Numbers followed by the same letter are not significantly different  within an irrigation rate.
[d] Numbers followed by the same letter are not significantly different  between irrigation rate averages.
[e] Numbers followed by the same letter are not significantly different  between irrigation method averages.
Soybean response was generally more favorable under SDI compared with other irrigation methods at the l25, 150, and l75 irrigation rates.
At l25, SDI resulted in significantly greater crop yield, WUE, and IWUE compared with MESA and LESA; at 150, these parameters were all significantly greater for SDI compared with MESA, LESA, and LEPA.
Seasonal water use was not significantly different among irrigation methods at l25; however, seasonal water use was significantly greater for MESA compared with LESA at 50 due to an outlying value in a MESA plot, the cause of which could not be determined.
At l75, SDI also resulted in the largest yield, WUE, and IWUE values, followed by MESA, LEPA, and LESA, whereas the ranks of greatest seasonal water use were in opposite order.
At 100, however, MESA resulted in the largest yield and IWUE, followed by SDI, LESA, and LEPA.
SDI did result in the largest WUE at 100, followed by MESA, LESA, and LEPA.
As expected, yield and seasonal water use increased significantly as irrigation rate increased, but maximum WUE and IWUE both occurred at 150, and the smallest WUE occurred at 10.
For irrigation method averages, SDI resulted in significantly greater yield, WUE, and IWUE compared with other methods.
Here, no significant differences were observed for seasonal water use; however, SDI resulted in numerically less seasonal water use compared with other methods.
Soybean yield, WUE, and IWUE followed the same trends as those observed for grain sorghum at 25, 50, and irrigation method averages.
At all irrigation rates, MESA outperformed LESA, a result also observed for grain sorghum.
These results suggest that similar loss pathways occurred for soybeans as did for grain sorghum, except that poor soil aeration and nutrient leaching may not have been as prevalent at the l75 and 100 irrigation rates, since irrigations were scheduled using direct measurements of the soil water profile, and no increases in volumetric soil water were observed below the root zone.
In addition, soil temperatures were greater with SDI compared with other methods during early development stages.
This may have promoted pod development, and further suggests that SDI results in less evaporative loss  from the soil, a result that was predicted by Evett et al.
for corn.
Table 6.
Soybean response, 2005 season; Colaizzi et al., 2006a.
Irrigation	Irrigation	Yield	water use	WUE	IWUE
 Rate [a]	method			(bu ac-1 in.1	(bu ac-1 in.1
 25	MESA	31.4 b	14.7 a	2.15	b	2.41	bc
 	LESA	29.9	b	15.5	a	1.93	b	1.87	C
 LEPA	33.1	ab	15.1	a	2.19	b	3.00	b
 SDI	36.9	a	14.7	a	2.52	a	4.34 a
 50	MESA	42.1	b	19.2	a	2.20	b	3.11	b
 	LESA	38.2	b	17.6	b	2.18	b	2.42	b
 LEPA	42.3	b	17.9	ab	2.36	b	3.14 b
 SDI	49.8	a	18.0	ab	2.77 a	4.47 a
 75	MESA	51.2	ab	21.4	ab	2.39 ab	3.14 a
 	LESA	46.6	b	22.5	a	2.09 C	2.60 a
 LEPA	48.4	ab	22.1	ab	2.18 bc	2.80 a
 SDI	52.7	a	20.9	b	2.53 a	3.32 a
 100	MESA	58.6	a	24.7	a	2.37 ab	3.01 a
 	LESA	55.2	ab	24.3 a	2.27 ab	2.71 a
 LEPA	51.5	b	24.4 a	2.11 b	2.38 a
 SDI	57.6 a	23.8 a	2.43 a	2.92 a
 lo 	24.6	e	[d]	12.4 e	1.98	b
 l25 	32.8	d	15.0	d	2.21	b	2.91	a
 50 	43.1	C	18.2	C	2.38 a	3.28 a
 75 	49.7	b	21.7	b	2.30 ab	2.96 a
 100 	55.7	a	24.3 a	2.30	ab	2.76 a
 MESA	45.8	[e]	20.0	a	2.28	b	2.92 b
 LESA	42.5	b	19.9	a	2.14	b	2.40 b
 LEPA	43.8	b	19.9 a	2.21 b	2.83 b
 SDI	49.3 a	19.3 a	2.56 a	3.76 a
 [a] Numbers in parenthesis are average seasonal irrigation totals for each irrigation rate.
[b] Yields were converted from dry mass to 13% moisture content by mass; 1 bu = 60 lb.
[c] Numbers followed by the same letter are not significantly different  within an irrigation rate.
[d] Numbers followed by the same letter are not significantly different 0.05) between irrigation rate averages.
[e] Numbers followed by the same letter are not significantly different  between irrigation method averages.
Cotton response was most favorable with SDI, followed by LEPA for all irrigation rates and irrigation method averages.
SDI resulted in the largest lint yield, WUE, and IWUE values compared with all other irrigation methods for all irrigation rates, followed by LEPA, LESA, and MESA.
In many cases these differences were significant, with SDI usually being significantly greater than MESA and/or LESA.
Seasonal water use, however, was not significantly different among irrigation methods, although SDI resulted in slightly greater numerical values.
Preliminary soil temperature data during the 2006 season indicated that SDI maintained warmer soil temperatures early in the season compared with LEPA, LESA, or MESA, which was probably due to reduced evaporative cooling, and supported the hypothesis that SDI may enhance early cotton establishment and growth compared with other irrigation methods.
Lint yield, seasonal water use, WUE, and IWUE were all significantly greater with increasing irrigation rate, with the largest values observed at 100.
This result for WUE and IWUE differed from those for soybean and grain sorghum, where maximum WUE and IWUE occurred below 100.
The fiber quality of cotton has become increasingly important as textiles have adopted high spin technology that requires longer and stronger fibers.
Fiber quality is comprised of several parameters , and cotton producers receive a premium or discount, called loan value, based on overall fiber quality.
The irrigation method generally did not result in significant differences in loan value ; for irrigation amount only 100 was significantly greater than l25.
This would result in gross returns being mostly correlated to lint yield rather than loan value, and SDI resulted in the largest gross returns for all irrigation rates, followed by LEPA.
Both SDI and LEPA resulted in significantly greater gross returns compared with MESA and LESA when irrigation methods were averaged.
The relative performance of SDI, LEPA, and spray for cotton were consistent with results of studies at Halfway, Tex..
Halfway is approximately 75 miles south of Bushland with lower elevation , and typically has greater heat units during the cotton season, resulting in greater lint yield and loan value compared with Bushland.
Lint yield and loan values herein were similar to those reported by Marek and Bordovsky , who evaluated several cotton varieties  at Etter, Tex., which is approximately 60 miles north of Bushland but has similar heat units available for cotton production.
Table 7.
Cotton response, average of 2003, 2004, 2006, and 2007 seasons; Colaizzi et al., 2005; Colaizzi et al., 2006b.
Irrigation	Irrigation	yield	water use	WUE [b]	IWUE [b]
 Rate [a]	method			(lb ac in.
25	MESA	413 a [c]	16.4 a	14.5 b	26.7 b
 	LESA	441	a	16.8 a	18.6	b	27.6	b
 LEPA	492	a	16.8 a	25.6	ab	29.9 ab
 SDI	572	a	16.9 a	37.1 a	34.8 a
 l50	MESA	497	b	18.8 a	14.2	b	27.1	b
 	LESA	500	b	18.7 a	13.8 b	27.0	b
 LEPA	660	ab	19.4 a	36.7 a	34.4 a
 SDI	715	a	19.5 a	40.8 a	36.4 a
 75	MESA	697	b	21.2 a	32.5 b	32.6 bc
 	LESA	674	b	21.2 a	29.5 b	31.3 C
 LEPA	777	ab	20.7 a	42.9 ab	37.3 ab
 SDI	911	a	21.5 a	59.6 a	42.8 a
 100	MESA	778	b	23.2 a	37.2 b	33.3 b
 	LESA	791	ab	23.2 a	37.9 b	33.9 b
 LEPA	885	ab	23.3 a	45.3 ab	37.2 ab
 SDI	951 a	22.8 a	57.3 a	42.1 a
 lo 	354	e	[d]	14.5 e	25.6 C
 l25 	479	d	16.7	d	29.8	bc	23.9	b
 50 	593	C	19.1	C	31.2 b	26.4	b
 l75 	765	b	21.1	b	36.0 a	41.1 a
 100 	851	a	23.1 a	36.6 a	44.4 a
 MESA	596	b [e]	19.9 a	29.9 C	24.6 C
 LESA	601	b	19.9 a	30.0	C	24.9 C
 LEPA	703	a	20.1 a	34.7	b	37.6	b
 SDI	787 a	20.2 a	39.0 a	48.7 a
 [a] Numbers in parenthesis are average seasonal irrigation totals for each irrigation rate.
[b] WUE and IWUE were computed based on lint yield.
[c] Numbers followed by the same letter are not significantly different  within an irrigation rate.
[d] Numbers followed by the same letter are not significantly different  between irrigation rate averages.
[e] Numbers followed by the same letter are not significantly different  between irrigation method averages.
Table 8.
Cotton loan value and gross return, average of 2003, 2004, 2006, and 2007 seasons.
Irrigation	Irrigation	Value [b]	return
 Rate [a]	method		
 25	MESA	46.39	a	[c]	$192 a
 	LESA	46.96	a	$209 a
 LEPA	48.59	a	$240 a
 SDI	49.23	a	$284 a
 50	MESA	48.13	ab	$240	bc
 	LESA	45.77	b	$228	C
 LEPA	49.53	a	$334	ab
 SDI	49.29	ab	$354	a
 75	MESA	49.20	a	$347	b
 	LESA	49.41	a	$336	b
 LEPA	49.40	a	$390	ab
 SDI	49.45	a	$453	a
 100	MESA	48.94	a	$388	a
 	LESA	49.29	a	$395	a
 LEPA	50.05 a	$452 a
 SDI	50.35	a	$481 a
 lo 	48.11	ab	[d]	$173	d
 l25 	47.79	b	$231	d
 50 	48.18	ab	$289	C
 l75 	49.37	ab	$382	b
 100 	49.65	a	$429	a
 MESA	48.16	a	[e]	$292	b
 LESA	47.86	a	$292	b
 LEPA	49.39	a	$354 a
 SDI	49.58	a	$393 a
 [a] Numbers in parenthesis are average seasonal irrigation totals for each irrigation rate.
[b] Base loan value was 51.60 cents lb for all years, from International Textile Center, Lubbock, Texas
 [c] Numbers followed by the same letter are not significantly different  within an irrigation rate.
[d] Numbers followed by the same letter are not significantly different  between irrigation rate averages.
[e] Numbers followed by the same letter are not significantly different  between irrigation method averages.
Crop production was compared under four irrigation methods and four irrigation rates in the Southern High Plains, Tex., USA.
Crops included three seasons of grain sorghum, one season of soybean , and four seasons of upland cotton.
Irrigation methods included subsurface drip irrigation , low energy precision applicators , low elevation spray applicators , and mid elevation spray applicators.
For each irrigation method, irrigation was applied at rates of 25, 50, 75, and 100% of meeting the full crop water requirement , and an additional near-dryland rate  was included to compute irrigation water use efficiency.
Grain sorghum and soybean response to irrigation method changed with irrigation rate, with SDI and LEPA generally outperforming MESA and LESA at low irrigation rates, and vice-versa at high irrigation rates.
For grain sorghum at high irrigation rates, deep percolation was observed for SDI and to a lesser extent LEPA.
The yield depressions at high irrigation rates may have resulted from nutrient leaching and lack of soil aeration.
Cotton response was consistently best for SDI, followed by LEPA, and either MESA or LESA at all irrigation rates.
Preliminary soil temperature data for soybean and cotton indicated that SDI maintained warmer soil temperatures compared with the other irrigation methods early in the season.
Warmer soil temperatures may have been the result of less soil water evaporation.
Thus, SDI may have partitioned more soil water to plant transpiration, which enhanced crop yields, especially at low irrigation rates.
Warmer soil temperatures would make SDI advantageous for cotton production in thermally-limited climates.
LEPA may also result in greater partitioning to plant transpiration compared with MESA or LESA, as crop response to LEPA was generally almost as favorable as SDI.
Despite possible differences in evaporation pathways, there were few significant differences in total seasonal water use among irrigation methods within an irrigation rate for all crops.
This, along with the potential for deep percolation and other losses , underscores the need for proper irrigation management if the full benefits of advanced irrigation technology are to be realized.
Beginning in the 2009 season, this experiment will continue with corn, which is also a major crop in the Southern Great Plains.
The cost and return of crop production under each irrigation method will be assessed to determine the longterm economics of SDI, LEPA, LESA, and MESA with various irrigation rates.
It is hoped that these results will assist producers in selecting the irrigation technology that will result in the greatest profit potential while prolonging the life of the Ogallala Aquifer.
This research was supported by the Ogallala Aquifer Program and USDA-ARS National Program 211, Water Availability and Watershed Management.
We thank the numerous biological technicians and student workers for their meticulous and dedicated efforts in executing experiments and obtaining and processing data.
Thanks also to Dr.
Arland Schneider, USDA-ARS, Ret., for initiating the grain sorghum study, and to Drs.
Sara Duke and Kathy Yeater, USDA-ARS, Statisticians, for their assistance with the statistical analysis.
SENTEK DRILL & DROP SERIES: DATA INTERPRETATION
 This publication series provides information and recommendations pertaining to the Sentek Drill & Drop, a multisensor capacitance probe commonly used in Mississippi for scheduling irrigation.
Other publications discuss other types of soil moisture sensors.
Users should choose tools that best fit their needs.
Soil moisture measurements by the Drill & Drop probe are often reported in terms of volumetric water content.
Expressed as a percentage or as a decimal fraction, VWC identifies how much of the soil volume is occupied by water.
Suppose a soil sample of 10 cubic inches contained 3 cubic inches of water.
The VWC of this sample would be 30%, 0.3 in/in , or 0.3 inch/inch.
The VWC of a soil increases with wetting and decreases with drying.
Figure 1 shows the VWC at twelve depths as reported by Drill & Drop probes in a Sharkey soil near Stoneville, Mississippi.
The soil started wet and dried gradually over 5 weeks with minimal rain and no irrigation while the soybean crop progressed from early R3 to late R5 growth stage.
A 0.3-inch rain on July 25 moistened the topsoil slightly, but the root zone was not refilled until 3.4 inches of rain fell on August 13.
This example dataset will be used to illustrate four methods of interpreting the depth-by-depth Drill & Drop data for scheduling irrigation.
Profile Volumetric Water Content
 The profile VWC can be calculated by averaging the VWC across multiple depths.
The range of depths to include in this average might be specified by independent knowledge of root water uptake or be determined by sensor detection of which depths are/had been experiencing root water uptake.
In Figure 1, the maximum depth of root water uptake appeared to increase from 26 inches to beyond 46 inches.
Profile VWC increases with wetting and decreases with drying.
Figure 2 shows the profile VWC across the top 40 inches for the example dataset.
One way to schedule irrigation is to wait until profile VWC becomes lower than the selected trigger.
Depletion is the difference between the current VWC and the full  VWC level.
In Figure 1, the full VWC level was around 59%.
The profile depletion can be calculated by averaging the depletion across multiple depths.
The range of depths to include in this average should be chosen based on root water uptake, just like for profile VWC as explained in the previous section.
Profile depletion decreases with wetting and increases with drying.
Figure 3 shows the profile depletion across the top 40 inches for the example dataset.
One way to schedule irrigation is to wait until profile depletion becomes higher than the selected trigger.
Rate of Profile Depletion
 The rate of profile depletion is the increase in profile depletion during a day with no rain and no irrigation.
Over a period with steady weather and crop canopy conditions, a reduced rate of profile depletion would suggest that the crop is not getting enough water from the soil.
To normalize the effect of significant changes in weather or canopy, the sensorobserved rate of profile depletion on each day can be divided by a model-expected rate of profile depletion on the same day.
Figure 4 shows the  rate of profile depletion across the top 40 inches for the example dataset.
The rate of profile depletion reached its peak on July 12  and then hovered around a plateau before dropping sharply from July 16  onwards.
One way to schedule irrigation is to wait until the rate of profile depletion descends from its plateau and becomes lower than the selected trigger.
Median Depth of Daily Depletion
 The median depth of daily depletion represents the center depth of root water uptake.
Half of the daily increase in depletion occurs above the median depth of daily depletion, while the other half occurs below it.
Even after the crop completes the development of its root system, the median depth of daily depletion is not constant but
 instead fluctuates in response to soil moisture distribution.
When soil moisture is abundant throughout the root zone, root water uptake tends to be concentrated at shallow depths.
Thus, the median depth of daily depletion would be relatively shallow.
When easily extractable water has been exhausted at shallower depths but remains available at deeper depths, root water uptake tends to migrate downward.
Thus, the median depth of daily depletion would be relatively deep.
Both trends can be seen in Figure 1.
Figure 5 shows the median depth of daily depletion for the example dataset.
The median depth of daily depletion reached its minimum on July 12  and then increased with further drying.
One way to schedule irrigation is to wait until the median depth of daily depletion rises from its minimum and becomes larger than the selected trigger.
Although multiple methods exist for interpreting Drill & Drop data, the methods differ in reliability to indicate optimal irrigation timing across diverse scenarios on Mississippi row-crop farms.
Research is being conducted to assess the reliability of various methods and to establish appropriate triggers for the most reliable method.
The resultant findings will be presented in future publications.
This publication is a contribution of the National Center for Alluvial Aquifer Research , the Mississippi State University Extension Service, and the Row-Crop Irrigation Science Extension and Research  initiative.
NCAAR is supported by the Agricultural Research Service, United States Department of Agriculture, under Cooperative Agreement number 58-6066-2-023.
RISER is supported jointly by the Mississippi Soybean Promotion Board, Mississippi Corn Promotion Board, Mississippi Rice Promotion Board, Cotton Incorporated, and Mississippi Peanut Promotion Board.
Dr.
Brent Black, USU Extension Fruit Specialist, Dr.
Robert Hill, USU Extension Irrigation Specialist, and Dr.
Grant Cardon, USU Extension Soils Specialist
 Proper irrigation is essential to maintaining a healthy and productive cherry orchard.
Over irrigation slows root growth, increases iron chlorosis in alkaline soils, and leaches nitrogen, sulfur and boron out of the root zone leading to nutrient deficiencies.
Over irrigation can also induce excessive vegetative vigor.
Excessive soil moisture also provides an environment ideal for crown and collar rots.
Applying too little irrigation water results in drought stress.
One of the most critical stages in fruit development is from the end of pit hardening to harvest, and typically occurs concurrently with the highest temperatures of the season.
During this period rapid fruit growth takes place through cell expansion that is dependent upon available water, and the tree is initiating flower buds for the following season's crop.
Properly managing irrigation is analogous to managing money.
In addition to knowing your current bank balance , it is important to track both expenses  and income.
Bank Balance 
 How big is my bank account?
Water holding capacity First, some terminology:
 Field Capacity is the amount of water that can be held in the soil after excess water has percolated out due to gravity.
Permanent Wilting Point is the point at which the water remaining in the soil is not available for uptake by plant roots.
When the soil water content reaches this point, plants die.
Available Water is the amount of water held in the soil between field capacity and permanent wilting point.
Allowable Depletion  is the point where plants begin to experience drought stress.
For cherries, the amount of allowable
 depletion, or the readily available water represents about 50% of the total available water in the soil.
The goal of a well-managed irrigation program is to maintain soil moisture between field capacity and the point of allowable depletion, or in other words, to make sure that there is always readily available water.
Figure 1.
Soil water content from saturated to dry.
Optimal levels for plant growth are between field capacity and allowable depletion.
The amount of readily available water is related to the effective rooting depth of the plant, and the water holding capacity of the soil.
The effective rooting depth for cherries in Utah's climate and soils is typically between 2.5 and 3.5 feet.
The water holding capacity within that rooting depth is related to soil texture, with coarser soils  holding less water than fine textured soils such as silts and clays.
A deep sandy loam soil at field capacity, for example, would contain 1.8 to 2.25 inches of readily available water in an effective rooting depth of 3 feet.
Table 1.
Available water holding capacity for different soil textures, in inches of water per foot of soil.
Available water is the amount of water in the soil between field capacity and permanent wilting point.
Readily available water is approximately 50% of available.
Soil Texture	Available	Readily available 
 	2 ft root depth	3 ft root depth
 Sands and fine sands	0.5 0.75	0.5 0.75	0.75 1.13
 Loamy sand	0.8 1.0	0.8 1.0	1.2 1.5
 Sandy loam	1.2 1.5	1.2 1.5	1.8 2.25
 Loam	1.9 2.0	1.9 2.0	2.85 3.0
 Silt loam, silt	2.0	2.0	3.0
 Silty clay loam	1.9 2.0	1.9 2.0	2.85 3.0
 Sandy clay loam, clay loam	1.7 2.0	1.7 2.0	2.6 3.0
 Figure 2.
The amount of allowable depletion, or the readily available water, represents about 50 percent of the total available water.
What's in the bank?
-Measuring Soil Moisture
 In order to assess soil water content, one needs to monitor soil moisture at several depths, from just below the sod layer or cultivation depth , to about 70 percent of effective rooting depth.
One of the more cost effective and reliable methods for measuring soil moisture is by electrical resistance block, such as the Watermark sensors.
These blocks are permanently installed in the soil, and wires from the sensors are attached to a handheld unit that measures electrical resistance.
Resistance measurements are then related to soil water potential, which is an indicator of how hard the plant roots have to "pull" to obtain water from the soil.
The handheld unit reports soil moisture content in centibars, where values close to zero indicate a wet soil and high values represent dry soil.
The relationship between soil water potential and available water differs by soil type.
The maximum range of the sensor is 200 centibars, which which covers the range of allowable depletion in most soils.
The sensors are less effective in coarse sandy soils, and will overestimate soil water potential in saline
 soils.
Remember that allowable depletion is 50% of available water, which roughly corresponds to soil water potentials of 50 centibars for a loamy sand soil, and 70 centibars for a loam.
Table 2.
Recommended WatermarkTM sensor values at which to irrigate.
Soil Type	Irrigation Needed
 Loamy sand	40 50
 Sandy loam	50 70
 Silt loam, silt	70 90
 Clay loam or clay	90 120
 TM Watermark is a registered trademark of Irrometer, Co., Riverside, CA.
Water is lost from the orchard through surface runoff, deep percolation , evaporation from the soil surface, and transpiration through the leaves of the plant.
Of these, the biggest losses are typically due to evaporation and transpiration, collectively known as "evapotranspiration" or ET.
Deep percolation from excess irrigation can be another large loss.
Estimates of ET are based on weather data, including air temperature, relative humidity and wind speed.
Some weather stations in Utah are programmed to calculate and report the ET estimates for alfalfa as a reference crop  that is specific to your crop and its stage of development.
The Kcrop for sweet cherry is shown in Figure 3 and differs depending on whether or not the alleys have grass or are clean cultivated.
At bud break , a cherry orchard with grass between rows is using about 40% of the amount of water used by the alfalfa reference crop, compared to 20% under clean cultivation.
Water use increases until full bloom and fruit set  when water use is 105% of a reference alfalfa crop with grass cover and 80% without.
By leaf senescence in the fall , water use has decreased to 40% of the reference crop.
Table 3.
Typical weekly alfalfa reference evapotranspiration  values for Utah locations.
Location	May	June	July	August
 Logan	1.38	1.83	1.94	1.68
 Ogden	1.48	1.98	2.10	1.80
 Spanish Fork	1.48	1.94	2.08	1.74
 Santaquin	1.47	1.92	2.03	1.67
 Moab	1.63	2.08	2.19	1.87
 Cedar City	1.57	1.95	2.04	1.74
 St.
George	1.95	2.40	2.53	2.02
 Income Irrigation and Rainfall
 In Utah's high elevation desert climate, rainfall contributes a small fraction of the in-season water requirements of the crop.
Therefore, regular irrigation is needed to supply orchard water needs.
This irrigation water can be supplied by flood, furrow, impact sprinklers, drip lines or microsprinklers.
Whichever irrigation system you utilize, it is important to calibrate your system SO that you know precisely how much water is being applied.
With sprinklers and microsprinklers, the simplest way to do this is to place catch cans in multiple locations in your orchard and collect water for a set period of time.
The amount of water collected over time will give you an application rate , and differences in water collected among the catch cans will tell you how uniform the application is within your planting.
When trying to determine application uniformity, it is best to measure output at both ends of your irrigation system.
Also, if your orchard is on a slope, you should measure output at the highest and lowest points of your
 field.
Elevation differences and the distance the water travels through the irrigation lines both affect water pressure, and consequently the flow rate at the nozzle.
If you have trickle irrigation, you can place catch cans under the emitters and determine flow rate for each emitter.
Flow rate from each emitter and emitter spacing can be used to calculate rate per area.
The efficiency of your system is a measure of how much you have to over water the wettest spots of the orchard to get adequate water to the dry spots.
Efficiency is related to the uniformity of application and to the amount of evaporation that occurs before the water can move into the soil.
A well-designed microsprinkler or drip system can be 70 to 90% efficient.
Overhead sprinkler systems are typically 60 to 75% efficient, while flood and furrow irrigation is typically 30 to 50% efficient.
Following is an example of how to calculate water needs for a mature cherry orchard just prior to harvest (Growth
 Stage = 120).
The orchard is on a deep sandy loam soil with row middles planted to grass cover.
ETr values are 2.10 inches per week.
Crop coefficient is 1.05.
ETcrop = ET, X Kcrop
 ETcrop = 2.10 inches/week * 1.05 = 2.205 inches/week
 Soil storage capacity 
 The total storage capacity for readily available water over the effective rooting depth is between 1.8 and 2.25 inches.
1.8 to 2.25 inches / 2.205 inches per week = 0.8 to 1.0 weeks or 6 to 7 days between irrigations
 Restated, the soil moisture in the rootzone will go from field capacity to plant stress levels in 6 days.
To recharge the soil profile, you will need to add 1.8 inches of water.
Assuming a microsprinkler irrigation system with an efficiency of 90%, 2.0 acre inches of water application will be required per acre for each watering.
Good irrigation management requires:
 1.
An understanding of the soil-plant-water relationship
 2.
A properly designed and maintained irrigation system, and a knowledge of the efficiency of the system
 3.
Proper timing based on
 a.
Soil water holding capacity
 b.
Weather and its effects on crop demand
 C.
Stage of crop growth.
Each of these components requires a commitment to proper management.
Proper management will lead to the maximum per available water and will optimize the long term health and productivity of your orchard.
Utah State University is committed to providing an environment free from harassment and other forms of illegal discrimination based on race, color, religion, sex, national origin, age , disability, and veteran's status.
USU's policy also prohibits discrimination on the basis of sexual orientation in employment and academic related practices and decisions.
Utah State University employees and students cannot, because of race, color, religion, sex, national origin, age, disability, or veteran's status, refuse to hire; discharge; promote; demote; terminate; discriminate in compensation; or discriminate regarding terms, privileges, or conditions of employment, against any person otherwise qualified.
Employees and students also cannot discriminate in the classroom, residence halls, or in on/off campus, USU-sponsored events and activities.
This publication is issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Noelle E.
Cockett, Vice President for Extension and Agriculture, Utah State University.
Steps in the Irrigation Series
 1.
Understanding Irrigation Efficiency
 2.
Pumping Plant Performance
 3.
Energy Source Selection
 4.
System Performance and Efficiency
 5.
Irrigation Application Uniformity
 7.
Incentives and Technical Assistance
Now is a good time to do a quick evaluation of the pumping plant, well, and center pivot to ensure they are in good working order before we have to rely on them during the heat of the summer.
Here are a few quick checks you can do to hopefully ensure a successful irrigation season.
We all live in a watershed
 What watershed do you live in?
Watersheds and water quality
 Protecting our watersheds and waterbodies
 Understanding and Protecting Kentucky's Watersheds
 Ashley Osborne, Environmental and Natural Resource Issues; Jenny Cocanougher, 4-H and Youth Development; and Amanda Gumbert, Water Quality
 We all live in a watershed
 Regardless of where you are, you are always in a watershed.
A watershed is any area of land that drains water to a single water body such as a stream or lake.
Watersheds can be as small as just a few acres draining into a small stream or as large as several rivers draining into the ocean.
Watersheds do not follow county, state, or national boundaries.
The land in a watershed affects how the water flows.
If a watershed has numerous hills and mountains, precipitation runs off quickly.
This runoff will reach the stream or body of water soon after a rain or snow event.
If the land in the watershed is mostly flat, precipitation will run off more slowly and will not reach the stream or body of water as quickly.
The rain or snowmelt may soak into the soil and become groundwater.
What watershed do you live in?
Watersheds and water quality
 As humans, we impact the health of our watersheds.
We use the land in watersheds for many purposes such as houses, shopping centers, parks, golf courses, factories, farms, and roads.
These uses affect how water flows.
They also affect the quality of the water.
Precipitation washes pollutants from the land into our streams, lakes, and other waterbodies.
Everyone who lives in a watershed impacts water quality.
Take a moment to think about the path precipitation follows.
When it
 reaches the ground, it will either soak into the soil or run along the surface.
Precipitation that lands on a parking lot can pick up motor oil and other types of pollutants.
Precipitation that lands on a lawn or farm field may carry fertilizer or loose soil with it as it travels.
Precipitation that lands on a bare hillside can wash part of the soil away as it moves.
All of these are examples of nonpoint source pollution.
Nonpoint source pollution, also referred to as runoff pollution, cannot be traced back to a single starting place.
The pollutants are carried in water as it runs off the land.
Nonpoint source pollution is the largest water quality problem in the United States today.
Runoff can travel directly to rivers, lakes, and streams, or it may travel through storm drains.
Stormwater is runoff water from rain and snowmelt.
In cities and towns, a system of drains and pipes is often used to carry stormwater.
These systems usually empty into a nearby body of water.
They most often do not take water to a treatment plant.
The most common pollutants carried in runoff are sediment and nutrients.
Sediment is soil that is carried in water.
The soil can come from farm fields, construction sites, logging sites, or any bare land.
As the water moves across the land, it picks up soil particles.
This soil travels with the water until it reaches a stream, lake, or river.
Nutrients are found in waste from animals and humans and in fertilizer.
Pasture fields and animal feeding lots can be sources of nutrients.
Pet waste can be carried in runoff water from lawns.
Farm fields, golf courses, and lawns may use fertilizers.
If not applied properly the fertilizers can wash away in runoff.
Runoff water can also carry other pollutants.
Pathogens can enter runoff water from animal wastes or failing sewer systems.
Oil and automotive fluids can wash off streets, roads, parking lots and driveways.
Vehicle emissions contain nitrogen oxides and sulfur dioxides that create acid rain when when released into the air.
Pesticides may be found in runoff from farm fields, lawns and gardens.
Toxic chemicals such as paint and household cleaning products are sometimes washed away when spilled on the ground.
Even if you are not in agriculture, construction or logging, you can help prevent nonpoint source pollution with actions you take at your own home.
Protecting our watersheds and waterbodies
 We all can help prevent nonpoint source pollution.
Farmers and developers use best management practices  to help prevent water pollution.
Best management practices are techniques or management strategies that help prevent water pollution.
These practices can help stop soil erosion and keep nutrients out of water.
BMPs can also be used to keep soil from running off construction sites and logging sites.
Even if you are not in agriculture, construction, or logging, you can help prevent nonpoint source pollution with actions you take at your own home.
Make a difference in your watershed by:
 Choosing hardy plants in landscaping that require little to no watering, fertilizers, or pesticides
 Covering bare soil with straw or mulch to prevent soil erosion
 Using permeable surfaces, such as wood, brick, or gravel for decks, patios, and walkways
 Picking up after your pet and disposing of their waste in the toilet or trash
 Keeping your septic system in good working condition
 Walking, biking, or carpooling
 On average, Kentuckians use 70 gallons of water per day per person.
Approximately 70 percent of our water use is indoors, most of it used in the bathroom.
By making a few simple changes in your daily routine, such as turning the water off while brushing your teeth, taking a shorter shower, and fixing any leaky faucets or toilets, you can do your part.
Disposing of hazardous waste properly
Shortand Long-term Consequences of Corn Stover Harvesting
 Over the past 20 years the amount of corn residue produced has increased with grain yields.
High yields require that these materials be carefully managed.
In some situations, corn-residue harvesting can increase the yield of the following corn crop.
However, yield gains as a result of stover harvesting maybe short-lived.
Stover harvesting reduces soil residue cover, which increases the risk of wind and water erosion, and, in the long term, may reduce organic matter, and soil health.
In addition, a failure to account for harvesting costs and nutrient removal can further decrease shortand long-term monetary gains.
This chapter discusses the shortand long-term consequences of corn stover harvesting.
Stover Harvesting Ethanol and Livestock Feed
 In the United States, there is an increased use of corn stover to provide livestock feed and bedding and to produce cellulosic ethanol.
The use of corn stover for bedding is definitely not new.
The use of corn stover as a feed, which is protein deficient  , was not practical without the availability of an inexpensive high-protein source  from the ethanol industry.
Details on creating distillers grain-enhanced diets are provided in Garcia and Kalscheur.
and Carlson et al..
They suggested that stover harvesting, when combined with the application of livestock manure to the residue-harvested land, has many benefits.
Table 24.1 Nutrient content of various feed components.
In this table, CP is crude protein, ADF is acid detergent fiber, NDF is neutral detergent fiber, TDN is total digestible nutrients, Ca is calcium, P is phosphorus, and S is sulfur.
Feed component	CP	ADF	NDF	Fat	TDN	Ca	P	S
 Distillers grain	29.7	19.7	38.8	10	78.5	0.22	0.83	0.44
 Soy hulls	13.9	44.6	60.3	2.7	67.3	0.63	0.17	0.12
 Beet pulp	10	23.1	45.8	1.1	69.1	0.91	0.09	0.3
 Corn silage	8.8	28.1	45	3.2	68.8	0.28	0.26	0.14
 Corn stalks	5.4	46.5	77	1.1	54.1	0.35	1.16	0.1
 Oat straw	4.4	47	70	2.2	50	0.24	0.06	0.23
 Wheat straw	4.8	49.4	73	1.6	47.5	0.31	0.1	0.11
 Maintaining Soil Organic Matter
 The harvesting of cornstalks for off-farm sale reduces the amount of plant material available to maintain soil organic matter.
The amount of corn stover that can be sustainably removed is dependent on many factors, including rotations, the amount of organic matter in the soil, the amount of crop residue returned to the soil, slope, climate, and tillage.
Tillage generally increases soil organic C mineralization and the associated soil organic C maintenance requirement.
Research suggests that: 1) in a rotation that includes both corn and soybean, removing corn stover most likely will contribute to a gradual decrease in soil organic matter; 2) soil carbon loss is linked to the tillage intensity; and 3) from 1985 to 2010, South Dakota soil carbon contents in the surface 6 inches increased 24%.
The increase in soil organic carbon was attributed to increasing corn yields, reduced tillage intensity, and improved corn genetics.
Clay  reported that 22%, 63%, and 36% of the yield increases in corn, soybean, and wheat, respectively, from 1974 to 2012 could be linked to improved soil health, providing a $1.1 billion impact on the South Dakota economy in 2012.
Fertilizer Recommendations and Residue Harvesting
 South Dakota fertilizer recommendations do not account for corn-residue harvesting.
A 200 bu/acre corn crop produces about 4.75 tons of stover per acre.
The amount of N, P2O5' and K2O contained in the grain of a 200 bu/acre corn crop is approximately 180, 76, and 54 lbs, respectively.
In contrast, N and P2O5 in residue is 16 and 5.8 lbs/ton, whereas, K2O in residue is about 40 lbs/ton.
This suggests that about 190 lbs of K20 could be removed annually, if all corn residue is harvested.
Over time, this removal can lead to K deficiencies.
Stover Harvesting and Corn Pathogens
 Although several corn pathogens are residue borne, it is not recommended in South Dakota to harvest corn stover specifically for disease management.
In South Dakota, rotations, tillage, hybrid selection, scouting, and foliar fungicides applied at V6 or tasseling, if warranted, are the recommended practices for disease management in corn.
Table 24.2 The amount of nutrients  contained in the grain and straw of plants routinely grown in South Dakota.
The nitrogen , phosphorus , potassium , magnesium , and sulfur  removal rates for corn residue were based on a 0.5 harvest index ) and dry corn weighing 47.32 lbs/bu.
Plant	N	P2O	K2O	Mg	S
 Alfalfa	51	12	49	5.4	5.4
 Barley straw	13	5.1	39	3	3
 Corn residue	16	5.8	40	5	3
 Oat straw	12	6.3	37	4	4.5
 Soybean residue	40	8.8	37	8.1	6.2
 Wheat straw	14	3.3	2.4	2	2.8
 Barley grain	0.99	0.04	0.32	0.06	0.09
 Corn grain	0.9	0.38	0.27	0.09	0.08
 oat grain	0.77	0.28	0.19	0.04	0.07
 soybean grain	3.8	0.84	1.3	0.21	0.18
 wheat grain	1.5	0.6	0.34	0.15	0.1
 lbs/acre 
 Corn grain	180	76	54	18	16
 corn residue	76	27	189	24	14
 6-Year Budget with Residue Harvesting
 When harvesting stover in a continuous corn rotation, there are at least two extreme scenarios that can be envisioned.
The first strategy is where stover is used as livestock bedding or feed and the manure is returned to the field.
This management system represents a "closed loop," with at least some nutrients and organic matter returned via manure application.
The closed-loop question is considered in Carlson et al..
The second system is where the stover is sold and leaves the farm with no returning nutrients or residue.
This chapter addresses the second scenario.
Table 24.3 The impact on corn yields of removing 60% of corn residue annually.
This experiment was conducted at Aurora, SD, from 2008-2012.
Tillage used at the site was chisel plow and 150 lbs N/acre was broadcast-applied in the spring following seeding.
Each treatment had eight replicates.
A p-value < 0.05 means that the two values are significantly different.
Residue	Yr 1	Yr 2	Yr 3	Yr 4	Yr 5
 removed	2008	2009	2010	2011	2012
 60%	207	200	176	175	164
 0%	196	183	172	183	172
 p	ns	0.05	ns	0.05	ns
 Table 24.4 The value of a ton of stover based on current  or future  fertilizer cost and upon the amount of N, P2O, and K2O removed in 1 ton of harvested stover.
The table also shows how different values of the N contained in the stover would impact the estimated value.
Retail Price	Estimated	Value/ ton
 N	0.48	16	7.68
 PO	0.42	5.8	2.44
 K2O	0.40	40	16
 Table 24.5 A net budget of residue harvesting on the economic returns over a 6-year period.
Investments	Years 1-5	Total	Year 6	Harvest	Total
 Nutrient	Harvest	$/acre	Nutrient	$/acre	$/acre
 310.18	208.53	518.71	62.04	41.71	103.75
 Yield	Selling	Yield	Selling
 84	532.85	616.85	-28	106.57	78.57
 Net change	98.14	-25.1795
 Annual profit	19.63	-25.1795
EQUATIONS FOR DRAINAGE COMPONENT OF THE FIELD WATER BALANCE
 ABSTRACT.
Accurate estimates of the drainage component of the field water balance are needed to achieve improved management of drainage in irrigated crop production systems and obtain improved estimates of evapotranspiration  from soil water measurements.
Estimating drainage for numerous soil and field conditions necessitates the use of simple, yet accurate, drainage equations containing easily measured parameters.
The Wilcox drainage model is a relatively simple mathematical equation with a high degree of accuracy and applicability to field conditions.
Our objectives were to develop Wilcox-type drainage rate equations for three coarse-textured soils of the west-central Great Plains and assemble previously determined, but fragmented, Wilcox-type drainage equations and supporting information for three medium-textured soils of the region.
Drainage plots for collection of data for development of Wilcox-type drainage equations were established on two coarse-textured soil profiles in 2008 near Garden City, Kansas.
Total water content of the soil profiles was measured over time during ~48-day drainage events.
Total water was plotted against drainage time on log-log scales, and the linear regression equation relating the two variables was determined.
These linear equations of profile water  vs.
drainage time  were used to develop Wilcox-type drainage equations in which drainage rate  is expressed as a function of soil profile water content.
Drainage rate equations in this article can be used to estimate the drainage component of the field water balance for improved irrigation water management and more accurate estimates of ET from soil water measurements.
Keywords.
Field water balance, Profile drainage, Wilcox-type drainage equation, Soil water storage, Water management.
T he primary objective of irrigation water management is to provide water to achieve maximum attainable crop production while minimizing deep percolation .
Despite its importance in water management, internal drainage from the root zone is a component of the field water balance that is seldom measured adequately.
This is not surprising considering that drainage is the component of the field water balance that is most difficult to measure or calculate.
In both dryland and irrigated environments, estimation of the rate and quantity of drainage is essential for accurate application of the field water balance.
The inability to distinguish between profile water loss by evapotranspiration  and drainage is a major problem when using soil water measurements to obtain estimates of ET.
Submitted for review in May 2010 as manuscript number SW 8579; approved for publication by the Soil & Water Division of ASABE in February 2011.
Internal drainage  is continual and shows no sharp changes or static levels, and in the absence of a water table, the drainage process continues indefinitely, albeit at a decreasing rate.
Profile drainage rates of a few millimeters per day have been observed in deep dryland soils with matric potential as low as -0.06 MPa.
Profile drainage of a Ulysses silt loam  was shown to be a measurable water loss component with profile water content at 60% of available water capacity  and greater, with drainage increasing as water increased above 60% of AWC.
Agreement between Baver et al.
and Stone et al.
is shown by the fact that at -0.06-MPa matric potential the Ulysses soil had water content at ~65% of AWC.
Research by Nielsen and Vigil  and several studies cited by Peterson and Westfall  showed decreased efficiency of water storage in the later portion of the fallow phase of dryland crop rotations, with efficiency likely being decreased by increased drainage from the wetter soil profiles of the later portion of fallow.
The association between extensive use of fallow and formation of saline seeps in the northern Great Plains is indicative of water drainage from soil profiles during later stages of long fallow phases.
Accurate estimates of the drainage component of the field soil water balance are needed to achieve improved management of drainage in irrigated crop production systems and obtain improved estimates of crop water use from soil water measurements.
Estimating drainage for numerous soil types and field conditions necessitates the use of simple, yet accurate, drainage equations that contain easily measured parameters.
The Wilcox drainage model
 , as discussed by Sisson et al.
, is a relatively simple mathematical equation with a high degree of accuracy and applicability to field conditions.
Our objectives in this study were:  develop Wilcox-type drainage rate equations for three coarse-textured soils of the west-central Great Plains and  assemble previously determined, but fragmented, Wilcox-type drainage rate equations and supporting information for three medium-textured soils of the region.
BACKGROUND OF DRAINAGE RATE EQUATIONS
 Richards et al.
measured soil water content over time during 59 days of drainage following deep irrigation of a fine sandy loam profile free of plants and with evaporation.
When plotted on log-log scales, the relationship between total water and drainage time was linear and could be expressed by the equation: W = aTb  where W is the equivalent depth of water in a soil profile, T is drainage time, a is water amount  at T = 1, and b is the slope of W VS.
T plotted in log-log scales.
Differentiating equation 1 with respect to T yields: dW/dT = abT 
 where a and b are constants for a given soil profile, and drainage rate  is expressed as a function of time .
In a continuation of the work by Richards et al.
, Ogata and Richards  measured water content during drainage following deep irrigation with the soil surface sealed from evaporation.
Ogata and Richards  found that profile water amount and drainage time were linearly related when plotted on log-log scales, confirming the findings of Richards et al..
Wilcox  measured soil water content and drainage time during 12 drainage tests with bare soils that had been irrigated to fill the soil profile and covered to prevent evaporation.
Relationships between profile water content and drainage time were linear when plotted on log-log scales , supporting the findings of Richards et al.
and Ogata and Richards.
Some drainage time is required following complete profile wetting  before the water amount VS.
time data will fit a linear log-log plot.
Wilcox  proposed that drainage rate be expressed as a function of profile water content instead of relating drainage rate to drainage time as in equation 2.
Rearranging equation 1 per Wilcox  yields:
 T = 1/b  Substituting equation 3 into equation 2 yields: dW/dT = ab/b 
 where drainage rate  is expressed as a function of profile water content  as suggested by Wilcox.
Estimating drainage rate with equation 4 was useful in estimating drainage from soil profiles and was referred to as the Wilcox method by Miller and Aarstad.
In
 Australia, Aston and Dunin  found that agreement between computed  and measured soil water drainage over 5 years was good and concluded the Wilcox method was appropriate for describing drainage from soil under field conditions.
Sisson et al.
discussed the Wilcox  modification of the original Richards et al.
equation by expressing drainage rate at a specific depth as a function of total water above that depth.
They concluded from their examination of models for estimating drainage from field plots that the resulting expression (eq.
4 was useful in accurately estimating drainage from soil profiles.
DRAINAGE PLOT DATA COLLECTION
 Field plots for determination of Wilcox drainage equations were established in 2008 on two coarse-textured soil profiles located 245 m apart on a near north-south line on the slope  immediately south of the Arkansas River near Garden City, Kansas.
The two soil surfaces were at elevations 18 m above  and 22 m above  the riverbed.
Soils of the immediate study area are coarse-textured, deep, and excessively drained, having formed in sandy eolian sediments that overlie terrace gravels in a broad band along the south side of the river valley.
The soils previously were mapped  as Tivoli fine sands , but are now classified  as Valent fine sands.
Drainage plots were level, vegetation-free areas of m.
Vertical boards 0.30 m tall were installed around the perimeter of each plot to retain water ponded on the soil surface.
Four aluminum access tubes  were installed in each of the two drainage plots; one tube was placed at each of the four corners of the center 0.92X 0.92-m plot area.
Three tensiometers were installed 1.9 m deep in the center 0.30.3-m area of each drainage plot.
Drainage plots were ponded with water to achieve thorough wetting of the 2.44-m soil profile prior to drainage measurements.
Steady-state infiltration rates during ponding were 13 cm/h  and 19 cm/h.
Tensiometers, read only during ponding, were used to gauge profile wetting.
Ponding was maintained for 2 h after tensiometers at the 1.9-m depth had reached equilibrium at matric potential of near zero.
The supply of water was then stopped and water remaining on the surface was allowed to infiltrate.
As soon as standing water disappeared from the surface, plots were covered with black polyethylene sheeting to prevent evaporation during the drainage period.
The sheeting was pierced SO tensiometers and neutron probe access tubes could protrude.
The time when standing water left the soil surface was designated as zero drainage time and soil water was measured during ~48 days of drainage.
Soil water data collected 1 h after zero drainage time by neutron probe confirmed that thorough wetting through the 2.44-m profile depth had been achieved.
Coated vinyl tarps  were maintained over the drainage plots to deflect rain from plots.
Volumetric water content in the drainage plots was monitored with a neutron probe.
The neutron probe was
 Y = -0.0200 + 0.1709X 
 where sample size  = 72, coefficient of simple determination  = 0.849, and root mean square error  = 0.014 m/m.
Neutron probe readings were taken periodically over time during the 48 days of drainage, more frequently at earlier and less frequently at later drainage times, at soil depths of 0.15 m through 2.29 m in 0.305-m depth increments.
Total water of the 1.52-, 1.83-, and 2.44-m soil profiles was calculated as 305 mm times volumetric water content measured at individual depths and summed over the respective total profile depth.
Particle size distribution and water content at -1.5-MPa matric potential were determined with composited soil samples collected from the eight profile depths during gravimetric water content determination.
Particle size
 distribution was determined by hydrometer and sieving.
Sample mass was 80 g, sodium hexametaphosphate was the dispersing chemical, and corrected hydrometer readings at the 8-h settling time represented clay content.
Sediment and suspension were poured through sieves with openings of 2.0 and 0.053 mm, and the oven-dry mass of material retained represented sand  and gravel.
Silt content was calculated as oven-dry sample mass minus the mass of clay plus sand plus gravel.
Water content at -1.5-MPa matric potential was determined with a cellulose acetate membrane system.
Particle size distribution was determined on three subsamples , and water content at -1.5 MPa was determined on five subsamples ; means from the multiple runs are reported.
Soil physical properties of the two Garden City drainage plots are presented in table 1.
The north plot  had 13% by mass of gravel below the 1.5-m soil profile depth.
The south plot  had gravel content of <2% by mass at all soil depths.
Both plots had clay content of >3% to <5% by mass in the upper 1.2 m of the soil profile.
Below the 1.5-m profile depth, clay content was >7% by mass in the south plot  and <2% by mass in the north plot.
Dry bulk density by depth ranged from 1.60 to 1.73 g/cm in the north plot  and from 1.48 to 1.63 g/cm in the south plot.
Water adsorbed and held at -1.5-MPa matric potential is positively correlated with specific surface of soil material.
Therefore, water content at -1.5 MPa was greater at soil depths having greater clay concentration.
Below the 1.5-m soil profile depth, water held at -1.5 MPa was <0.01 g/g in the north plot  with clay content <2% by mass; in the south plot , water held at -1.5 MPa was slightly >0.03 g/g.
Table 1.
Descriptive physical properties  at eight centering depths within two Valent fine sand soil profiles near Garden City, Kans.
Gravel,	Sand,	Silt,	Clay,	Dry Bulk	Water Content
 Soil Depth	>2.0 mm	0.053 to 2.0 mm	0.002 to 0.053 mm	<0.002 mm	Density	at -1.5 MPa
 						
  Valent fine sand  
 0.15	7	904	53	36	1.62	0.0238
 0.46	10	889	57	44	1.60	0.0238
 0.76	25	883	44	48	1.63	0.0215
 1.07	57	878	29	36	1.67	0.0131
 1.37	71	891	18	20	1.65	0.0097
 1.68	135	825	23	17	1.73	0.0076
 1.98	220	738	26	16	1.73	0.0078
 2.29	148	812	25	15	1.73	0.0078
  Valent fine sand 
 0.15	1	942	17	40	1.56	0.0211
 0.46	0	955	10	35	1.54	0.0168
 0.76	0	959	5	36	1.48	0.0167
 1.07	1	956	9	34	1.58	0.0167
 1.37	11	924	19	46	1.63	0.0202
 1.68	5	881	43	71	1.57	0.0342
 1.98	5	840	84	71	1.58	0.0325
 2.29	2	843	85	70	1.52	0.0312
 Total water content of the two 1.83-m Valent fine sand profiles was measured over time during the ~7-week drainage events and is shown in figure 1.
Watts  graphically presented total water and available water VS.
time during drainage as well as soil water content at -1.5 MPa matric potential for a 1.5-m profile of Valentine loamy sand  and these data were used in a soil-water-nitrogen model for irrigated corn .
From the graphed data of Watts , total water was determined for the 1.5-m soil profile and then extrapolated to a profile depth of 1.83 m by assuming a continuation of similar soil properties with depth and by multiplying total water for 1.5 m by 1.22.
Total water of the 1.83-m Valentine soil profile was graphed versus time for an ~3-week drainage event and is shown in figure 2.
Stone et al.
plotted total water of 1.83-m profiles of Keith , Richfield , and Ulysses silt loam soils against time during long-term drainage events.
Because total water over time during drainage was graphed for the Keith, Richfield, and Ulysses
 Figure 1.
Total water VS.
drainage time of 1.83-m profiles of  Valent fine sand  and  Valent fine sand located near Garden City, Kans.
Figure 2.
Total water VS.
drainage time of Valentine loamy sand  located near North Platte, Nebr.
Data are from Watts.
soils by Stone et al.
, those plots are not repeated in this article.
Depending on objectives and conditions of soil water balance research activities, different profile depths are appropriate for use in estimating the water drainage component.
For example, the 1.52-m soil profile depth version of the Wilcox-type drainage equation for Keith silt loam was used by O'Brien et al.
and Lamm et al.
, the 1.83-m profile depth version for Ulysses silt loam was used by Stone et al.
, and 2.44-m profile depth versions were used by Caldwell et al.
and Lamm et al.
.
Therefore, we developed total water VS.
drainage time similar to that shown for the 1.83-m profile depth in figures 1 and 2 also for the 1.52and 2.44-m soil profile depths.
From the linear equations involving log-log plots of profile water in millimeters and drainage time in days,
 Figure 3.
Total water  VS.
drainage time  of 1.83-m profiles of  Valent fine sand  and  Valent fine sand located near Garden City, Kans.
Results shown are from linear regression analyses.
Figure 4.
Total water  vs.
drainage time  of Valentine loamy sand  located near North Platte, Nebr.
Results shown are from linear regression analysis.
Data are from Watts.
Wilcox-type drainage rate equations were developed by using equation 4, with dW/dT being drainage rate in millimeters/day.
The variable W in equation 4 is total water content of the soil profile in millimeters, and constants a and b are total water at 1 day and slope of water content VS.
time from the linear equation of log-log data, respectively.
The drainage rate equations for soil profiles of 1.52-, 1.83-, and 2.44-m depth, along with the profile total water contents at the drained upper limit and at -1.5 MPa matric potential, are presented in table 2.
Total profile water at -1.5 MPa shown in table 2 was calculated from data of table 1 for the two Valent soils, graphical data of Watts  for the Valentine soil, tabular data of Stone et al.
for the Ulysses soil, and tabular data of Darusman  for the Keith and
 Richfield soils.
Water content at -1.5 MPa establishes an estimate of the lower limit of soil water availability.
There are reported instances where field-measured profile water was less than that held at -1.5 MPa.
For example, the 1.83-m profile of Ulysses silt loam in table 2 contains 332 mm total water at -1.5 MPa, whereas profile water measured at harvest after dry seasons was 290 mm.
Drained upper limit water content values were estimated as the location of primary slope change in the graphed data of figure 1  and figure 2  and from similar graphs for the three silt loam soils of Stone et al..
The drained upper limit water contents of 660, 642, 650, 282, 190, and 178 mm  were reached after 5.8, 6.1, 7.1, 2.0, 1.2, and 1.2 days of drainage for the 1.83-m profiles of Keith, Richfield, Ulysses, Valentine, Valent, and Valent  soils, respectively.
These lengths of drainage time for reaching field-determined drained upper limit water capacity values were not unexpected.
Working with 61 field soil profiles from 15 states of the United States, Ratliff et al.
found that 2 to 12 days of drainage usually were required for soils to reach the drained upper limit water content, and some fine-textured soils with restrictive layers required up to 20 days of drainage.
We developed Wilcox-type drainage rate equations for two coarse-textured soils  of the west-central Great Plains and assembled information from various sources on the Wilcox-type drainage equations for three medium-textured soils  of the region.
The drainage rate equations can be used
 Table 2.
The developed Wilcox drainage equations and upper  and lower  bounds of available water capacity for three profile depths of six soils of the west-central Great Plains.
Water at DUL[b]	Water at -1.5 MPa
 Soil	Location	Wilcox Drainage Equation[a]		
  1.52-m deep soil profiles
  1.83-m deep soil profiles
  2.44-m deep soil profiles
 [a] dW/dT is drainage rate in millimeters per day and W is profile water content in millimeters.
[b] DUL = drained upper limit.
[c] Soil textures represented as sil , fs , and Is.
to simulate drainage conditions of irrigated cropping systems and partition soil water measurements into ET and drainage components.
The equations can be used to extend to multiple locations and soils the simulation of drainage for the field water balance that is used in developing yield versus water supply relationships of the principal crops of the west-central Great Plains, as used by Stone et al..
The yield versus water supply results could then be used to expand the application and usefulness of software developed to provide for improved water management and conservation, such as the water allocation software developed by Klocke et al..
The Klocke et al.
software involves a database of one soil and one weather data file , but the drainage rate equations of this report will allow software expansion to include multiple soils and locations.
This work was supported in part by funds from the USDA-CSREES under Award no.
2008-34296-19114 and the Ogallala Aquifer Project of the USDA-ARS under Agreement no.
58-6209-6-031.
Contribution 10-276-J from the Kansas Agricultural Experiment Station.
Darusman.
1994.
Drainage evaluation under subsurface drip irrigated corn.
PhD.
diss.
Diss.
Abstr.
94-26232.
Manhattan, Kans.: Kansas State University.
Happy World Water Day!
Annually on this day, we bring special attention to the importance of groundwater & freshwater around the world.
This year's theme focuses on "Groundwater: Making the invisible visible" to bring attention to this hidden water resource, that all too often goes unrecognized when sustainable policies are developed.
LONG TERM WATER STRATEGY PLANNING USING CROP WATER ALLOCATOR 
 The CWA allows program operators to customize the inputs to their specific conditions but loads with default values that represent typical costs, yields, etc.
The opening input page is shown in Figure 1.
The program operator can customize the model by clicking on each input box and either selecting an input option from the dropdown menu or entering the desired value.
Boxes with a question mark provide additional background information on the input as a help to the user.
Crops of interest to a producer would be checked by clicking on the crop box next to the name.
The land split selection determines how the acreage can be divided between crops or irrigation amount.
A 50-50 selection means one half of the field can be of one crop that receives a certain irrigation amount and the one-half of another crop or amount.
The same crop could be selected but with
 different irrigation amounts.
The total amount of irrigation application however cannot exceed the annual gross irrigation amount specified, although one split could receive the total amount and the other split, a reduced amount or none.
For each crop selected for consideration, the user should select current or projected crop price and the maximum yield that might be expected for each crop if grown under well watered conditions.
Embedded into CWA are yield-water relationship curves for each crop.
These curves are specific to the annual rainfall which is also an input.
Crop specific production costs can also be changed, if desired, by clicking on the "Costs/Returns" box.
Total Acres:	130	?
Annual Rainfall	15	Land Split:	?
Soil:	Silt Loam	?
Annual Gross Irrigation	9	?
100	33 33 33
 Irrigation	Costs and	Enter Irrigation	Information	?
Calculated Gross	1,170	?
50 50	50 25 25
 Irrigation Efficiency %	90	?
75 25	25 25 25 25
 Select the Crops to Evaluate:
 Price per unit:	?
Maximum Yield / Acre:	Input Costs & Returns
 Alfalfa	150	$/ton	10	tons	Costs/Returns
 Corn	4.5	$/bu.
240	bushels	Costs/Returns
 Grain Sorghum	4.3	$/bu.
170	bushels	Costs/Returns
 Soybeans	10.
$/bu.
60	bushels	Costs/Returns	Default	Values
 Sunflower	0.20	$/lb.
3500	pounds	Costs/Returns
 Wheat	6.5	$/bu.
70	bushels	Costs/Returns
 *Enable Batch Processing by Selecting Enable Batch Processing from the Tools menu
 Figure 1: Main input page of the CWA.
CWA begins evaluating the possible combination when the "Generate Output" button is clicked.
The results are then shown as options as shown in Figure 2.
Option 1 would be the combination of crops and irrigation amount that resulted in the largest net return.
Option 2, the next largest combination and so forth.
Sensitivity changes could be made by altering an input and generating new output.
It is best to change only one input at a time.
Land Split	Irrigation  Total Operating
 	Crop	Yield	Gross / Net	Costs**	Total Returns	*Net Return
 65.0	Grain Sorghum	70.4 bu./ac	3.6" / 3.2"	$218 /acre	$303 /acre	$85 /acre	(Details
 65.0	Corn	201.2 bu./ac	14.4" /13.0"	$519 /acre	$905 /acre	$386 /acre	Details
 <<	Option 1	>>	*Net Return
 *Net returns to land, management, and irrigation equipment
 Figure 2: Example of evaluation results from CWA.
Option 1 is the combination of crops and irrigation amount that resulted in the largest net return.
The result of an analysis for a 130 acre field of silt loam soil and a 50-50 split option with an irrigation pumping cost of $1.96 per acre-inch and the crops, crop prices and yield levels as shown in Table 1 for a rainfall year of 18 inches and 11 inches of water availability for the field.
The annual rainfall is approximately average for Colby, Kansas and the 11 inch average application depth is the amount of depth allowed by the Sheridan 6 Local Enhanced Management Area  in GMD4 of northwest Kansas.
The actual water depth allowed by the LEMA is 55 inches in 5 years, but CWA looks at annual values.
The top option in Table 1 is corn on both splits with the same water level of 11 inches.
In this case, the net return for each half of the field is the same, so the field average net return also is $375/acre.
The next option selected is also corn on both halves but with one with an irrigation application depth of 13.2 and the other with 8.8.
Notice the predicted yield levels also changed for the more deficit irrigated corn and the higher water side had yields higher than the 11 inch application of option 1.
However, the average return for the field decreased to $358 as compared to $375.
Wheat, soybean and fallow do not appear in the first 10 options as shown in Table 1 but were considered in the ranking process.
Corn was selected in each of the ten options shown and received average or above average irrigation depth.
Table 1.
CWA results for the selection of crops, crop prices, yield levels for annual rainfall of 18 inches and irrigation of 11 inches.
Option	Crop Split	Yield	Gross Irr.
Cost	Returns	NET Return
 Ranking	Selected	*		 +		**
 Corn	193	11	493	868	375
 1	Corn	193	11	493	868	375
 Corn	158	8.8	432	709	277
 2	Corn	215	13.2	526	966	439
 Sorghum	137	8.8	323	589	267
 3	Corn	215	13.2	526	966	439
 Sorghum	120	6.6	291	516	225
 4	Corn	229	15.4	559	1032	473
 Sunflower	2772	8.8	229	554	256
 5	Corn	215	13.2	526	966	439
 Corn	133	6.6	387	600	213
 6	Corn	229	15.4	559	1032	473
 Sunflower	2429	6.6	279	486	207
 7	Corn	229	15.4	559	559	473
 Sorghum	151	11	350	648	298
 8	Corn	193	11	493	868	375
 Sorghum	100	4.4	259	430	170
 9	Corn	237	17.6	582	1066	483
 Sunflower	2100	4.4	262	420	158
 10	Corn	237	17.6	582	1066	483
 *Yield for sunflower is pounds per acre.
+Includes irrigation costs ** Net returns to land, management and irrigation equipment
 Table 2.
CWA results for the selection of crops, crop prices, yield levels for annual rainfall of 18 inches and irrigation of 11 and 9 inches.
11 inches of irrigation	9 inches of irrigation
 Option	Crop Split	Yield 	NET Return	Crop Split	 *	NET Return
 Ranking	Selected	 * 	**	Selected		**
 Corn	193 	375	Sorghum	109 	195
 1	Corn	193 	375	Corn	208 	420
 Field Net	375	Field Net	308
 Corn	158 	277	Sorghum	93 	150
 2	Corn	215 	439	Corn	223 	454
 Field Net	358	Field Net	302
 Sorghum	137 	267	Sorghum	125 	234
 3	Corn	215 	439	Corn	190 	368
 Field Net	353	Field Net	301
 Sorghum	120 	225	Corn	141 	229
 4	Corn	229 	473	Corn	190 	368
 Field Net	349	Field Net	298
 Sunflower	2772 	256	Sunflower	2100 	156
 5	Corn	215 	439	Corn	208 	420
 Field Net	347	Field Net	288
 Corn	133 	213	Sorghum	73 	97
 6	Corn	229 	473	Corn	232 	479
 Field Net	343	Field Net	288
 Sunflower	2429 	207	Sunflower	2450 	206
 7	Corn	229 	473	Corn	190 	368
 Field Net	340	Field Net	287
 Sorghum	151 	298	Corn	161 	286
 8	Corn	193 	375	Corn	161 	286
 Field Net	337	Field Net	286
 Sorghum	100 	170	Sunflower	1834 	116
 9	Corn	237 	483	Corn	223 )	454
 Field Net	327	Field Net	285
 Sunflower	2100 	158	Corn	113 	150
 10	Corn	237 	483	Corn	208 	420
 Field Net	320	Field Net	285
 *Yield for sunflower is pounds per acre.
** Net returns to land, management and irrigation equipment
 Table 3.
CWA results for the selection of crops, crop prices, yield levels for annual rainfall of 18 inches and irrigation of 7 and 5 inches.
7 inches of irrigation	5 inches of irrigation
 Option	Crop Split	Yield 	NET Return	Crop Split	 *	NET Return
 Ranking	Selected	 * 	**	Selected		**
 Sorghum	84 	128	Sorghum	51 	40
 1	Corn	195 	382	Corn	180 	336
 Field Net	255	Field Net	188
 Sorghum	68 	83	Sorghum	105 	185
 2	Corn	208 	420	Sorghum	105 	185
 Field Net	251	Field Net	185
 Sorghum	98 	165	Sorghum	96 	160
 3	Corn	176 	333	Sorghum	115 	210
 Field Net	249	Field Net	235
 Sorghum	51 	40	Sorghum	87 	134
 4	Corn	220 	447	Sorghum	123 	230
 Field Net	244	Field Net	182
 Sunflower	1750 	103	Sorghum	76 	103
 5	Corn	195 	382	Corn	151 	257
 Field Net	243	Field Net	180
 Sunflower	1491 	64	Sorghum	63 	69
 6	Corn	208 	420	Corn	161 	286
 Field Net	242	Field Net	178
 Sunflower	2023 	145	Sorghum	87 	134
 7	Corn	176 	333	Corn	138 	221
 Field Net	239	Field Net	177
 Sorghum	111 	200	Sorghum	76 	103
 8	Corn	154 	267	Corn	131 	250
 Field Net	234	Field Net	177
 Sorghum	123 	230	Sunflower	1680 	94
 9	Sorghum	123 	230	Corn	151 	257
 Field Net	230	Field Net	175
 Sorghum	111 	200	Sunflower	1960 	135
 10	Sorghum	134 	258	Sorghum	115 	210
 Field Net	229	Field Net	173
 *Yield for sunflower is pounds per acre.
** Net returns to land, management and irrigation equipment
 Tables 4, 5 and 6 show the results of the 9 inch irrigation for 18, 21, and 15 inches of annual rainfall respectively.
This would show what effect rainfall might have on the selection of the best option.
The effect of annual rainfall is also illustrated in Table 7 on the top option of the three years.
A crop mix of sorghum/corn was selected for the 18 and 15 inch rainfall years and corn/corn for the 21 inch ranfall year.
The sorghum/corn split was the top option for the average and dry year.
In the wet year, the sorghum/corn mix appeared as option 4 with a net return of $368.
In the wet year, the corn/corn split's net return estimate was $393, which gave it an advantage of $25 over the sorghum/corn mix.
The comparison seems to suggest the sorghum/corn slection may be the more robust selection for the range of rainfall conditions used.
This example illustrates how CWA might be used as a tool for long term term comparison of crop options for a given amount of irrigation under varying rainfall conditions.
It can be used to compare production options for any of the production inputs, such as yield, irrigation amount, and crop prices.
Table 4.
CWA results for the selection of crops, crop prices, yield levels for annual rainfall of 18 inches and irrigation of 9 inches.
Option	Crop Split	Yield	Gross Irr.
Cost	Returns	NET Return
 Ranking	Selected	*		 +		**
 Sorghum	109	5.4	274	469	195
 1	Corn	208	12.6	517	936	420
 Sorghum	93	3.6	248	389	150
 2	Corn	223	14.4	549	1003	454
 Sorghum	125	7.2	303	537	234
 3	Corn	190	10.8	489	857	368
 Corn	141	7.2	407	636	229
 4	Corn	190	10.8	489	857	368
 Sunflower	2100	5.4	264	420	156
 5	Corn	208	12.6	517	936	420
 Sorghum	73	1.8	218	314	97
 6	Corn	232	16.2	564	1043	479
 Sunflower	2450	7.2	284	490	206
 7	Corn	190	10.8	489	857	368
 Corn	161	9	437	723	286
 8	Corn	161	9	437	723	286
 Sunflower	1834	3.6	251	367	116
 9	Corn	223	14.4	549	1003	454
 Corn	113	5.4	356	506	150
 10	Corn	208	12.6	517	939	420
 *Yield for sunflower is pounds per acre.
+Includes irrigation costs ** Net returns to land, management and irrigation equipment
 Table 5.
CWA results for the selection of crops, crop prices, yield levels for annual rainfall of 21 inches and irrigation of 9 inches.
Option	Crop Split	Yield	Gross Irr.
Cost	Returns	NET Return
 Ranking	Selected	*		 +		**
 Corn	176	7.2	454	793	338
 1	Corn	216	10.8	523	971	447
 Corn	194	9	481	872	390
 2	Corn	194	9	481	872	390
 Corn	149	5.4	405	670	265
 3	Corn	227	12.6	542	1023	480
 Sorghum	130	5.4	302	558	256
 4	Corn	227	12.6	542	1023	480
 Sorghum	144	7.2	328	617	289
 5	Corn	216	10.8	523	971	447
 Sunflower	2800	7.2	297	560	263
 6	Corn	216	10.8	523	971	447
 Sorghum	115	3.6	278	493	205
 7	Corn	236	14.4	565	1058	493
 Sorghum	154	9	345	660	315
 8	Corn	194	9	481	872	390
 Sunflower	2450	5.4	227	490	213
 9	Corn	227	12.6	542	1023	480
 Soybeans	41	5.4	210	412	202
 10	Corn	227	12.6	542	1023	480
 *Yield for sunflower is pounds per acre.
+Includes irrigation costs ** Net returns to land, management and irrigation equipment
 Table 6.
CWA results for the selection of crops, crop prices, yield levels for annual rainfall of 15 inches and irrigation of 9 inches.
Option	Crop Split	Yield	Gross Irr.
Cost	Returns	NET Return
 Ranking	Selected	*		 +		**
 Sorghum	70	3.6	218	303	85
 1	Corn	201	14.4	519	905	386
 303	Field Net	236
 Sorghum	88	5.4	246	380	135
 2	Corn	178	12.6	476	800	324
 Sorghum	48	1.8	183	206	23
 3	Corn	217	16.2	544	975	432
 Sunflower	1484	3.6	238	297	58
 4	Corn	201	14.4	519	905	386
 Sorghum	104	7.2	275	449	174
 5	Corn	157	10.8	444	705	262
 Sorghum	118	9	298	509	211
 6	Sorghum	118	9	298	509	211
 Sunflower	1750	5.4	252	350	98
 7	Corn	178	12.6	476	800	324
 Sorghum	104	7.2	275	449	174
 8	Sorghum	137	10.8	326	575	248
 Fallow	0	0	38	0	-38
 9	Corn	230	18	573	1030	458
 Sorghum	24	0	142	102	-40
 10	Corn	229	18	573	1030	458
 *Yield for sunflower is pounds per acre.
+Includes irrigation costs ** Net returns to land, management and irrigation equipment
 Table 7.
Top option of CWA results for 18, 21 and 15 inch rainfall years and that crop mix in the ranking for the other rainfall years with 9 inches of irrigation.
and	Crop Split	Yield	Gross Irr.
Cost	Returns	NET Return
 	Selected	*		 +		**
 Sorghum	109	5.4	274	469	195
 Corn	208	12.6	517	936	420
 1 	Field Net	308
 Corn	176	7.2	454	793	338
 Corn	216	10.8	523	971	447
 1 	Field Net	393
 Sorghum	70	3.6	218	303	85
 Corn	201	14.4	519	905	386
 1 	Field Net	236
 Corn	141	7.2	407	636	229
 Corn	190	10.8	489	857	368
 4 	Field Net	298
 Sorghum	130	5.4	302	558	256
 Corn	227	12.6	542	1023	480
 4 	Field Net	368
 Corn	105	7.2	359	474	115
 Corn	157	10.8	444	705	262
 31 ++ 	Field Net	188
 *Yield for sunflower is pounds per acre.
+ Includes irrigation costs
 Net returns to land, management and irrigation equipment
 ++ The corn/corn selection option ranked 31st of all possible crop and irrigation water combinations.
Producers need to make decisions on how to use their available land and irrigation water resources that result in the optimal economic returns.
Many factors influence the outcome.
The Crop Water Allocator program may be a tool to help them determine the best crop acreage mix for the increasingly limited water resources avialable to them.
Contribution no.
15-288-A from the Kansas Agricultural Experiment Station.
A chemigation applicator certification card will be issued to successful applicants by the NDEE.
The certification expires on January 1, 4 years after it is issued.
For example, certifications issued in 2011 will expire on January 1, 2015.
Young said there are some areas of the state that likely will not fully recover from the 2012 drought for an extended period of time, but one of the counties hit hardest by it had some of the biggest gains in groundwater last year.
Regulated deficit irrigation reduces water use of almonds without affecting yield
 by William L.
Stewart, Allan E.
Fulton, William H.
Krueger, Bruce D.
Lampinen and Ken A.
Shackel
 A plant-based regulated deficit irrigation  experiment in the northern Sacramento Valley determined that crop consumptive water use and irrigation could be reduced without significant detrimental effects on almond production.
Tree stress was measured by recording midday stem water potential, a direct measure of tree water stress.
With a water stress level of -14 to -18 bars during the hull-split period, average annual water savings were about 5 inches.
Over 5 years, no significant yield reductions were observed, although average kernel weight was slightly lower.
The results suggest that water savings can be achieved without affecting yield, even in soils with low water-holding capacity.
A lmonds are California's top agricultural export 80% of those consumed worldwide are grown here.
As water resources become increasingly scarce due to population growth, environmental needs and periodic drought, it will become more difficult both monetarily and politically to obtain sufficient water for crop irrigation.
Drought tolerance in almonds has been documented in previous studies, but substantial irrigation is still required to maintain current production levels.
Over the last 14 years there has been a steady increase in both bearing acres and yields about 70 pounds per acre in almond yield improvement annnually , indicating a steady improvement in cultural practices, among them, irrigation.
There is a pressing need to reliably maintain current almond production with less water.
Surface-water
 Microsprinklers are used in most almond orchards, allowing very precise measurements of how much water is being used by the trees.
Above, Allan Fulton augured holes to install neutron-probe access tubes for monitoring stored soil moisture.
allotments for irrigation during drought are often significantly reduced because precedence is given to other uses.
Water reserves in California were low following the droughts of 2007, 2008 and 2009.
In fact, spring 2008 was the driest on record.
The current basis for estimating the irrigation need of a crop is to combine the water lost from the soil  with the water lost through leaves , into an overall loss, the crop evapotranspiration  ET is calculated by multiplying a weatherbased reference crop ET , by a crop coefficient , to give the final estimate (ETc = ET.
Research in the late 1980s and 1990s estimated the average seasonal ET for almonds at 40 to 42 inches , with estimated seasonal irrigation requirements of 36 to
 38 inches  under typical soil and rainfall conditions of the southern San Joaquin Valley.
But later field research suggested that almond ETc may average from 48 to 54 inches .
Reasons for the higher recent estimates probably reflect the many changes that have occurred in almond culture over the past two decades.
Almond orchards are now intensively managed with pressurized  rather than surface  irrigation systems, and crop water status can also be monitored directly using midday stem water potential.
SWP is measured directly on leaves sampled in the orchard using a pressure chamber, and it indicates the level of physiological water stress that is being experienced by the trees at the time of sampling, much as blood pressure or temperature can be a measure of any physiological stress in humans
 .
Furthermore, nitrogen fertility management is more intensive than it was when the earlier research was conducted, and pruning practices have changed to manage canopy light differently, both producing more foliage and potentially higher ETc.
In fact, a higher ET rate and higher yields may both be responses to moreintensive almond management.
The ET method of irrigation scheduling aims to maintain the crop in a nonstressed condition by supplying enough water to satisfy ETc.
Alternative methods have been proposed that attempt to reduce unnecessary vegetative growth in orchard and vine crops in order to make water use more efficient; they include deficit irrigation, partial root-zone drying and regulated deficit irrigation .
of the way into each row.
Orland in the northern Sacramento Valley, which was planted with 'Nonpareil' and 'Carmel' trees spaced at 12 feet by 24 feet.
The orchard was divided into five approximately equal blocks; two were planted in 1993 and three in 1999.
From the first year of the experiment , the canopy shaded area in midsummer  at noon was greater than 50% in all blocks, SO all blocks were considered to exhibit fully developed  crop water requirements.
The five blocks were each subdivided into two sections to match the existing irrigation system design, with control and regulated deficit irrigation treatments assigned to the sections on alternating sides.
SWP values were initially taken on weekly field visits using a pressure chamber, and were collected biweekly during the hull-split period.
Leaves, still on the tree, were covered with an aluminized Mylar bag for a minimum of 10 minutes prior to measurements.
Meters were installed on a single lateral line in each irrigation section to measure water applications.
Two rows of 'Nonpareil' almond trees in the center of each section were designated as the experimental plots, with two trees from each block used as the monitoring trees for SWP measurements.
The rows averaged approximately 69 trees per block, and monitoring trees were positioned approximately one-third and two-thirds
 In 2004 and 2005, block-specific recommendations for regulated deficit irrigation were communicated to the grower, who was responsible for dayto-day irrigation management.
In 2005, the orchard exhibited defoliation due to Alternaria leaf spot, and the grower was reluctant to withhold water from the large regulated deficit irrigation plots.
The objective of regulated deficit irrigation is typically to irrigate SO that trees experience mild-to-moderate levels of water stress, in order to achieve an optimal horticultural balance between vegetative growth, which is very sensitive to stress, and fruit production, which is less sensitive.
Previous studies in almonds and other crops have shown the beneficial effects of regulated deficit irrigation, including control of excessive vegetative growth, reduced hull rot and improved hull split in almonds , increased fruit density in prunes and pears  and reduced vegetative growth in peaches.
Our study took place in a microsprinkler-irrigated, 270-acre  almond orchard near
 Previous studies of regulated deficit irrigation have created stress by applying a fraction of ET but for this 5-year study we used a plant-based indicator of stress  and set a target level of mild-to-moderate stress during the hull-split period.
We undertook this study to determine whether meaningful reductions in consumptive water use  could be achieved with minimal impacts on orchard productivity.
Grids of neutron-probe access tubes allowed the researchers to take soil moisture readings at different depths.
They found a shallow water table that receded throughout the growing season, especially during two drought years.
According to the U.S.
Drought Monitor, 98% of Nebraska is currently in drought.
Extreme and exception drought covers a combined 32%, primarily in the northeast and southwest.
In these areas, precipitation over the past three years is half to 70% of normal with 36-month deficits in the 1620 inch range.
Soil moisture reserves here are low and without appreciable precipitation over the winter and spring, the next growing season will begin quite dry.
A PLACE FOR GRAIN SORGHUM IN DEFICIT IRRIGATION PRODUCTION SYSTEMS?
Crop selection and management, under deficit irrigation, will likely shape water requirements and yield potential.
Deficit irrigation indicates the available water supply and/or distribution system cannot meet the requirements of a fully irrigated crop.
One strategic decision can guide water allocation within a deficit irrigation production system: shall limited irrigation capacity be spread throughout the field?
Or shall limited irrigation capacity be concentrated on a portion of the field, which can be fully irrigated.
Grain sorghum provides management opportunities for deficit irrigation production system, whether water is spread throughout the field, for a deficit-irrigated crop or concentrated on a portion of the field, for a fully irrigated crop.
Crop Water Production Functions
 Crop water productivity, also known as water use efficiency, is the ratio of grain yield and crop water use.
Crop water production functions also relate expected yield to crop water use.
A production function for grain sorghum, derived from the Kansas Water Budget  is shown in Figure 1.
This production function indicates that a yield threshold of 5.3" of crop water use; more than 5.3" of water use is required for expected grain production.
Further, the production function indicates that 529 Ib/A  grain production is expected for each additional inch of water use, beyond the yield threshold.
The symbols shown in Figure 1 correspond to grain sorghum yields and crop water use observed in a long-term dryland tillage study conducted at Colby, Kansas.
The dashed line, fit by regression to these data, also relates expected grain yield to crop water use.
This regression indicates a yield threshold of 7.0", with yield response of 489 Ib/A  for each additional inch of water use.
The small yield threshold for grain sorghum  and positive yield response , along with heat tolerance, indicate advantages for grain sorghum relative to deficit irrigation.
The yield threshold and response to water use, derived from KSWB are not statistically different from the regression relationship derived from the long-term tillage study.
Figure 1.
Grain sorghum yield is shown in relation to crop water use.
The solid line is a crop water production function derived from the Kansas Water Budget.
Symbols correspond to tillage treatments  on a long-term dryland tillage study.
The dashed line was derived by regression from the tillage study.
Yields and water use from 2009 and 2011 were excluded due to effects of an early freeze  and hail damage.
Deficit Irrigation Crop Sequence
 One strategy for spreading limited irrigation water is to maximize the utility of precipitation through improved capture, storage and use which helps prevent crop failure.
As an example, splitting a pivot in half could support a two-year, three-crop sequence such as winter wheat and double-crop soybean on one half, with grain sorghum on the other half.
This deficit irrigation crop sequence was included in a limited irrigation study conducted at Colby in 2004 2007.
Irrigation amounts of 2.25" were applied at once using flood irrigation to wheat at boot; to soybean at V8, R1 and R6; and to grain sorghum at V10, boot, post bloom and soft dough stages.
Both the winter wheat/soybean phase and the grain sorghum phase of the crop sequence received 9" irrigation during the growing season.
Crop water use  and grain production, averaged over the four growing seasons, are shown in Table 1.
This illustrates the use of grain sorghum in a deficit irrigation system which is more reliant on precipitation than a fully irrigated crop.
Table1.
Water use and grain productivity of winter wheat/soybean grain sorghum crop sequence under deficit irrigation; conducted at Colby, Kansas, 2004 2007.
Crop	Water Use 	Yield 2
 Winter wheat	12.8	29
 Grain Sorghum	20.1	136
 Spreading versus Concentrating Water, considering Grain Sorghum
 Declining pumping capacities and frequent droughts confront a growing number of western Kansas growers.
These constraints on irrigation provide new challenges for water allocation.
Howell et al.
framed the problem in terms of 'spreading' or "concentrating' water.
The decision to apply water over many acres under deficit irrigation is referred to as 'spreading' the water; the decision to irrigate only a portion of a field and meet full crop ET is referred to as 'concentrating' the water.
A related question is which crop mix would optimize net returns?
Grain sorghum being a drought tolerant crop might be suitable for limited irrigation.
We applied a limited irrigation decision support tool called Crop Water Allocator  to assess the effect of concentrating the water or spreading the water on net returns and also to determine under what scenarios grain sorghum would be most suitable.
Howell et al.
provides a good review on the topic of spreading versus concentrating water, for this paper we will focus on demonstrating how CWA could be used in aiding decision making in relation to crop and water allocation.
CWA was developed to aid producers in making such decisions.
This tool uses Yield-Crop water use relationships  derived from an empirical water balance model called the Kansas Water Budget coupled with experimental data.
To execute CWA, the user needs to provide values of input and operating costs, crop price, total area, soil type, gross irrigation, annual rainfall, irrigation efficiency, and land split.
Default values are available for western Kansas if information is not available.
Rogers et al.
provides more details how to run CWA and use CWA.
Since production functions are site specific, before applying CWA we validated it against simulations from Kansas Water Budget for grain sorghum and adjusted the
 maximum yield to 161 bu/ac  in order to improve the fit between KSWB and CWA as shown in Fig.
2.
Figure 2.
Grain sorghum production function of yields versus crop water use generated from Kansas Water Budget and Crop Water Allocator models, assuming grain sorghum maximum yield of 161 bu/A, corresponding to yield and water use reported in Table 1.
is required for benefits such as weed control and soil water conservation, a corn-wheat-grain sorghum crop mix might be selected, though expected net returns would be reduced due to wheat crop failure.
Crop mixes with strategic allocation of deficit irrigation provided greater net returns than spring water over sole crops of corn, sorghum or wheat.
Grain sorghum was included in the crop mixes with greater net returns, under the drought conditions simulated with 12" annual precipitation, indicating a strong role for grain sorghum in deficit irrigation during drought.
Weighted Average Net Returns=341 $/ac
 Weighted Average Net Returns=340 $/ac
 Crop: Grain Sorghum Area:37.5 Net returns=145 $/ac Gross Irrigation: 4.4 inches Av Annual Rainfall: 18 inches
 Weighted Average Net Returns=189 $/ac
 Weighted Average Net Returns=200 $/ac
 Fallow Area=32.5 acres Net returns=-38 $/ac Gross Irrigation: 0 inches Av Annual Rainfall: 12 inches
 Garin Sorghum Area=32.5 acres Net returns=114 $/ac Gross Irrigation: 8.8 inches Av Annual Rainfall: 12 inches
 Crop: Grain Sorghum Area: 37.5 acres Net returns=243 $/ac Gross Irrigation: 13.2 inches Av Annual Rainfall: 12 inches
 Figure 3.
Showing weighted net returns  for different land, water, and crop allocation under a typical 130 acre center pivot.
Weighted Average Net Returns=174 $/ac
 Crop: Wheat Area:32.5 acres Net returns=-33 $/ac Gross Irrigation: 0 inches Annual Rainfall: 12 inches
 Weighted Average Net Returns=171 $/ac
 Crop: Grain Sorghum Area:32.5 acres Net returns=116 $/ac Gross Irrigation: 8.8 inches Annual Rainfall: 12 inches
 Crop: Wheat Area:32.5 acres Net returns=-107 $/ac Gross Irrigation: 0 inches Annual Rainfall: 12 inches
 Figure 4.
Showing weighted net returns for a Corn-Wheat-Grain Sorghum crop mixes and land allocation.
Table 2.
Best land and water allocations options which maximize net returns for corn, grain sorghum and wheat for annual precipitation of 18 inches and well capacity of 300 gpm supplying a typical 130 acre center pivot.
Land	Crop	Yield	Gross	Operating	Total	Net	Net
 Split		Irrigation	Cost	Returns	Returns	returns
 				
 130	Corn	169.6	11	497	838	341	341
 97.5	Corn	178.0	11.7	510	879	369	341
 37.5	140.6	8.8	439	695	695
 97.5	Corn	189.5	13.2	530	936	405	340
 37.5	G.
Sorghum	92.5	4.4	266	411	145
 97.5	Corn	189.4	13.2	530	936	405	337
 37.5	Wheat	46.6	4.4	187	317	130
 130	G.
Sorghum	140.2	11	360	622	262	262
 130	Wheat	69.0	11	260	428	168	168
 Table 3.
Best land and water allocations options which maximize net returns for corn, grain sorghum and wheat for annual precipitation of 12 inches and well capacity of 300 gpm supplying a typical 130 acre center pivot.
Land	Crop	Yield	Gross	Operating	Total	Net	Net
 Split		Irrigation	Cost	Returns	Returns	returns
 				
 97.5	G.
Sorghum	74.5	10.3	243	428	185	200
 32.5	G.
Sorghum	90.1	13.2	275	518	243
 32.5	Fallow	0.0	0.0	38	0.0	-38
 32.5	G.
Sorghum	88.4	8.8	279	393	114	189
 65.0	Corn	177.8	17.6	538	878	340
 65.0	Corn	207.7	22.0	614	1026	412	187
 65.0	Fallow	0.0	0.0	38	0	-38
 65.0	G.
Sorghum	48.6	4.4	207	216	9	174
 65.0	177.8	17.6	538	878	340
 97.5	G.
Sorghum	90.1	13.2	275	518	243	174
 32.5	Wheat	19.6	4.4	155	122	-33
 65	Corn	177.8	17.6	540	878	338
 32.5	Wheat	0.0	0.0	107	0	-107	171
 32.5	G.
Sorghum	88.4	8.8	278	393	116
 130	G.
Sorghum	105.9	11	312	470	156	158
 130	Corn	108.0	11	488	534	122	122
 130	Wheat	47.6	11	225	295	70	70
 Field data support a grain sorghum production function showing 8.7 9.4 bu/A-in yield response to water use, exceeding a corresponding yield threshold of 7.0" or 5.3" water use.
Annual precipitation affects the productivity risk of split-pivot water allocation alternatives.
Under normal conditions, spreading deficit irrigation over corn maximized net returns.
Under drought conditions, spreading deficit irrigation over sorghum maximized net returns.
Crop mixes with strategic allocation of water provided alternatives, where multiple management objectives are involved.
This research was supported in part by the Ogallala Aquifer Program, a consortium between USDA Agricultural Research Service, Kansas State University, Texas AgriLife Research, Texas AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
Contribution no.
15-282-A from the Kansas Agricultural Experiment Station.
CENTER PIVOT EVALUATION AND DESIGN
 The Center Pivot Evaluation and Design Program  is a simulation model.
It is based on the first model presented by Heermann and Hein  which was verified with field data.
Their simulation model required input of the sprinkler location, discharge, pattern radius and an assumed stationary pattern shape of either triangular or elliptical.
The application depth versus distance along a radial line from the pivot was determined and application rates at a specified distance from the pivot were determined.
The hours per revolution were input and each tower was assumed to move at a constant speed for the complete circle.
Kincaid, Heermann and Kruse  used the model to calculate potential runoff for different system capacities and infiltration rates.
Kincaid and Heermann  added the calculation of the flow resistance and verified with measured pressure distribution along the center pivot lateral.
Chu and Moe  studied the hydraulics of a center pivot system and developed a quick approximation for determining the pressure loss from the pivot to the outer end of the lateral as a constant  times the loss that would occur if the entire discharge flowed the total length of the lateral.
The model was adapted by Beccard and Heermann  to include the effect of topographic differences in the resulting application depths along radii of the center pivot in non level fields.
The model included the pump and well characteristics and calculated the hydraulic equilibrium point as the system moved to different positions on a rough terrain.
The model was exercised to determine the uniformity changes when converting from high pressure to low pressure on rough terrain.
Edling , and James  also used simulation models to study the performance of center pivot systems on variable topography and with different pressures.
The current simulation model has been expanded to include donut shaped stationary patterns that can be used to represent many of the low pressure spray heads.
The start-stop of the electric motors and the speed variation in hydraulic drives can also effect the uniformity in the direction of travel.
The input of the start-stop sequence for each tower replaces the assumption of a constant speed and the variability of application depths in the direction of travel has been simulated.
EXAMPLES OF SIMULATION EVALUATION
 The uniformity of application depths can be calculated by inventorying the sprinkler head models, nozzles sizes and distance from the pivot.
The pump curve and drawdown, or pivot pressure, or discharge is also needed.
Figure 1 illustrates a simulation as designed and the distribution if the sprinkler heads were reversed between 2 towers made at the time of installation.
The application rate and potential runoff are illustrated in Figure 2.
Figure 1.
Typical center pivot as designed  and with 10 sprinkler heads incorrectly installed shown as a dashed line.
Figure 2 Example application rate curve versus 0.5 and 1.0 SCS intake curve.
The selection or development of an evaluation standard and procedures should focus on the need for the evaluation.
The USDA, Environmental Quality Incentive Program  administered by the Natural Resource Conservation Service  currently can provide cost sharing on the installation and upgrading of irrigation systems for improving water quality or conservation under irrigation.
Center pivots are frequently the system of choice.
There is a need to assure that installed systems will provide the desired improvement in irrigation performance.
A similar need exists for any user of center pivot systems to assure that an installed or modified system will perform as designed.
It must be recognized that the scheduling of irrigations is most important for the beneficial use of water.
Efficient scheduling of irrigation systems requires knowing the amount of water applied per irrigation.
The CPED program has been streamlined and simplified for use in evaluating center pivot systems for cost sharing on new and upgraded systems.
The CPEDLite program is similar to the one being used in this workshop.
The primary difference is the simulations are for 1 foot intervals beginning and ending at fixed distances.
This assures that any simulation will provide the same results.
The uniformity is output in 5% bands.
The following pages will present the various windows that are presented to the user for controlling the input and operation of the program.
The program illustrated is the full version of CPED.
The CPEDLite program has the same look at the window level but requires less input with some of the options being fixed so that similar results will be obtained independent of the operator.
The program is available on request but the user is cautioned that there is always the possibility of program errors when different systems present conditions that have not been experienced prior to this time.
The program is therefore limited in its release to minimize the problems of users that are not familiar with center pivot operation and terminology.
The options available are to select or create a new system file, view output from previous simulations, and quit the program.
Once a system file is selected or created, the options to run, edit, or delete the system file are enabled.
In all cases throughout the program "click" means click the left mouse button.
A system file can be Selected by clicking one of the systems listed in the list box labeled System File List.
The name of the selected system file will be displayed in the label box labeled Name of Selected System File.
The New button allows the user to create a new system file.
There are two ways to create a new system.
The first way is to enter a name and click the OK button.
You are then transferred into the Edit window that is discussed below.
The second option is to create a system from an existing file.
You then select the existing file; name the new system; click the OK button and you will be in the Edit window where only changes need to be entered.
The Delete button will delete the selected system file from the user's hard drive.
The user will be asked for confirmation before deleting a system file.
The View button allows examining previous simulation results.
The View previous output button will bring up the data files that have been saved from previous simulations.
Selecting one of these files will plot to the screen the simulated depth versus distance data.
The Analyze catch can data button allows you to enter catch can data for uniformity evaluation.
A simulation output data set can be input to the catch can data file and allow the uniformity analysis for different distances along the lateral.
The procedure to save simulation data is presented latter with running the program.
The Edit button allows editing of the selected system file.
More detail is below.
The Run button moves to the screen for entering the parameters to run the simulation.
More detail is given below.
The Quit button exits the program.
Pressing CTRL +Q anytime during the simulation will have the same effect.
EDIT SYSTEM FILE WINDOW
 The different information groups of data can be entered or edited by moving the mouse pointer over the image of the sprinkler system.
The labels Pump Information, Tower Information, Sprinkler Information, Span Information, and System Information can be selected by clicking on the text to open its edit window.
The Add/Edit Sprinkler Model button opens a window for adding or editing sprinkler models.
This is password protected and normally is not needed by the user.
Those supporting the program will do this editing.
The Previous Window button saves the changes and returns to the main program window.
KOMET202	Sprinkler Patterns: 1 Triangle
 Sprinkler	Sprinkler Model	Sprinkler	Sprinkler	Range Nozzle	Spread Nozzle	Pressure Control	Starting Part	Stoppin
 Number	Name	Distance 	Pattern	diameter 		Circle Angle 	Circle A
 1	SNIWOBS6	32,4	3	7	14.01
 2	SNIWOBS6	50.42	3	7	14.01
 3	SNIWOBS6	68.42	3	7	14.00
 4	SNIWOBS6	86.42	3	7	14.00
 5	SNIWOBS6	104.36	3	8	13.99
 6	SNIWOBS6	122.36	3	8.5	13.98
 7	SNIWOBS6	140.3	3	9	13.96
 8	SNIWOBS6	158,3	3	9.5	13.95
 9	SNIWOBS6	176.3	3	10	13.94
 10	SNIWOBS6	194.6	3	10.5	13.92
 11	SNIWOBS6	212.6	3	11	13.90
 12	SNIWOBS6	230,6	3	11.5	13.89
 13	SNIWOBS6	248.6	3	12	13.87
 14	SNIWOBS6	266.6	3	12.5	13.85
 15	SNIWOBS6	284.5	3	13	13.83
 16	SNIWOBS6	302.5	3	13.5	13,81
 17	SNIWOBS6	320.5	3	13.5	13.78
 18	SNIWOBS6	338.5	3	14	13.76
 19	SNIWOBS6	356.5	3	12.5	13.85
 20	SNIWOBS6	365.8	3	10.5	13.93
 21	SNIWOBS6	374.8	3	10.5	13.93
 Add Sprinkler	Delete Sprinkler	Reorder Sprinklers	Previous Screen
 A new sprinkler can be added by clicking the Add Sprinkler button.
If no sprinklers are present by pressing the Add Sprinkler button a sprinkler with zero distance will default and you can begin by entering the other information for the first sprinkler.
The sprinkler model is selected by clicking on the model listed in the box labeled Sprinkler Model List.
Sprinklers can be added in any order.
If one sprinkler is missed you can merely add it at any time.
By clicking the Reorder Sprinklers button the sprinklers will be ordered from the pivot to the outer end based on their individual distances from the pivot.
You do not enter the sprinkler number as this is done automatically.
If sprinklers are present the information from the previous record will be used and the distance will automatically be incremented.
Edit the information for the newly added sprinkler.
Many systems will have the same sprinkler models and these will need no editing.
If the sprinkler spacing is uniform this will also require minimal editing.
Even the nozzle sizes may be the same for several sprinklers minimizing the editing required.
The start and stop angles are viewed from the pivot toward a part circle sprinkler.
Check if the sprinkler starts on the right or left.
Then using the pipe as the zero reference point, measure the angle back toward the pivot.
Use the same technique for the stop angle.
All angles are positive and between 0 and 180 degrees.
Figure 3.
Part circle sprinklers angles.
Angles are between 0 -180 degrees with an L or R prefix.
Alternatively you can move to the bottom row marked with an I*I and enter the new sprinkler information manually.
A sprinkler can be deleted by selecting any column in the row for the sprinkler and click the Delete button.
The Reorder button will sort and number the sprinklers by sprinkler distance from the pivot.
The Previous Screen button returns to the Edit system file window.
Tower	Distance From Pivot	Ground Elevation -	For linear systems the carl is assumed to be the pivo
 Number	ft.
ft.
point and should be entered as tower 1 with a
 1	180.92	187	distance of 0.
Add Tower	Delete Tower	Reorder Towers	Previous Screen
 Towers are added by clicking on the Add Tower button and editing the distance from the pivot and its elevation.
It is often assumed that the pivot and all towers are at an elevation of 100 feet if no field information is available.
For the linear system, the first cart is assumed to be the pivot with a distance of 0.
As the Add Tower button is clicked, the towers are added with the spacing of the previous two towers and the same elevation as the previous tower.
The Reorder Towers will sort the towers by distance from the pivot if there happen to be entered in the wrong sequence.
Select a tower and click the Delete Tower button if a tower needs to be deleted.
The Previous Screen returns to the Edit system file window.
Clicking the Add Span button inserts a starting distance of 0 and the Pipe I.D.
and the Darcy-Weisbach resistance coefficient must be entered.
A typical value of the D-W coefficient is 0.xxx to 0.xxx for center pivots.
Multiple pipe sizes can be added by clicking the Add Span button and entering the starting distance from the pivot and its resistance coefficient.
The spans are assumed to go from the starting distance to the next span or end of the pivot for the last span.
Spans can be deleted  and reordered  by clicking the appropriate button.
Never delete the span with starting distance of 0.
The Previous Screen button returns to the Edit system file window.
The piping to the pivot, pump curve, and pivot elevation are entered in this window.
If the pump curve information is not available, either a constant discharge or constant pressure can be selected.
Number of Pump Stages	1
 Pump Intercept GPM	800
 Pump Curve Slope on Linear Term	60.6
 Pump Curve Slope on Quadratic Term	9999
 Total Dynamic Lift Ft.
90
 Pad Elevation Ft.
200
 Sprinkler Height Ft.
8.5
 Pump to Riser Pipe Length Ft.
200
 I.D.
Pump to Riser Pipe In.
7.84
 D-W Resistance Coefficient	0.015
 I.D.
Riser Pipe In.
6.407
 Normal	Constant Discharge	Constant Head
 Selecting the Normal option requires the quadratic equation for the pump curve.
The curve of the total head vs discharge for the pump is needed to develop the regression equation that describes the pump.
This relationship can be determined externally from this program or there is an option that will fit the pump curve equation with points from a pump curve or field measured data.
At least 4 points that span the operating range are needed, however 8-10 will give a better fit.
Problems have occurred where the operating point is beyond the pump curve data.
Use caution.
The form of the equation for the pump curve is:
 Q = B, + B,H + B2H2
 Q discharge gpm H head/stage psi B intercept B linear slope coefficient on head B quadratic slope coefficient on head
 The number of stages for the pump must be entered when the manufacturers pump curve is for a single stage.
However, if the pump curve comes from field measurements, set the number of stages equal to one.
The Calculate Pump Curve button can be selected for calculating the coefficients when data are available from
 either the manufacturers pump curve or field measured data.
The paired data of discharge in gpm and head in feet can be entered and the three coefficients calculated.
The total dynamic lift in feet must also be entered.
It is the elevation difference  between the center pivot pad elevation and the depth to the water table including the drawdown while pumping.
The pad elevation is the elevation for the center pivot at from an assumed or measured datum elevation.
The sprinkler height is the distance above the pad height for the sprinklers as if they were on a level field.
The inside diameter  of the pipe size and length of pipe from the pump to the pivot and the I.D.
of the riser pipe must be entered.
Include the Darcy-Weisbach coefficient for both pipes.
The Constant Head option is where the pivot pressure  is specified.
This is the most stable option where the pump curve is not known.
Estimate the discharge in gpm and set the number of stages equal to one.
The estimate discharge is only to shorten the calculation time and the actual value is not critical.
The Constant Discharge in gpm can also be specified.
The potential problem with constant discharge is when all sprinklers are regulated.
If the discharge does not match the calculated discharge with the regulated pressure an error will occur when attempting to have the calculated discharge on the system match that specified.
Again set the number of stages equal to one.
The constant head and constant discharge does not require pump to riser pipe and riser pipe sizes or resistance coefficient since the pressure or discharge is assumed to be at the pivot and no head loss is calculated for these sections.
The Previous Screen button returns to the Edit system file window.
Three options for the Type of Pressure Control can be select from the drop down box.
They are none, pressure regulated, or constant orifice.
Systems with booster pumps for the big gun at the end of a center pivot system are simply estimated with a pressure increase in psi just prior to the big gun or guns.
The number of sprinklers beyond the booster pump is specified.
The actual pressure is dependent on the center pivot system and the inlet pressure, discharge or pump curve.
The Previous Screen button returns the Edit system file window.
All parameters below must be filled in for the simulation to run correctly.
Optional: Information From Catch Can File Can be Included in the Simulation Print Out.
Adjust output graph to starting distance.
This is the screen that you will enter when you click RUN and all of the system files with the necessary data have been entered.
Minimal input is required on this screen before the simulation is run.
The Default button will restore the default values that were used on the previous simulation run for this system.
The hours/revolution are entered to obtain the depth for this condition.
Normally the sprinkler number is set to "all" for including all the sprinklers to be simulated.
However, you can select one sprinkler by entering its number to see the contribution to the depths from the specified sprinkler.
The start, stop distances and distance increment specifies the location for simulation depths.
For example you can start at 10 feet and go to 500 feet with 5 foot increments.
The minimum depth specifies that only locations with depths greater than that will be included in the uniformity calculations.
This is often desirable when not including the small depths at the outer boundary where there is not sufficient overlap with other sprinklers.
The CPEDLite program fixes these four parameters and only the speed in hours/revolution can be changed.
Clicking the RUN button will start the simulation.
You will automatically be moved to another window that will plot the simulated depth versus distance data on the monitor.
Prior to pressing RUN you can select a catch can data set or data saved from a previous run to be displayed on the monitor after the simulation is completed.
This provides a visual comparison of the current simulation with other data.
The data for comparison can be selected from the files listed in the Catch Can File Window.
The Previous Screen button will return to the Main Window.
You will note a possible selection to Adjust output graph to starting distance.
This is normally not needed when simulating the entire system.
Clicking this selection is beneficial if you are not simulating from near the pivot and want the plot to begin at the starting distance instead of 0.
The output window plots the simulated depth versus distance from the pivot for the parameters set in the run window.
The Coefficient of Uniformity, the Distribution Uniformity, and mean application depth are printed.
The Q-Depths, gpm, is the discharge calculated from all simulated depths while the Effective Q-Depths, gpm, is calculated from the depths that are above the specified minimum depth used in the Uniformity and mean depth calculations.
The effective area is the simulated area for those areas receiving more than the minimum depth between the starting and stop distances.
The window below is an example of plotting catch can data from a previous simulation run.
Additional data can be printed either to the printer or to a file.
The Return to Main Menu button will return to the main menu screen.
The Print to File button will ask for the file name for storing the information.
You will then be prompted for saving the individual
 sprinkler and tower data followed for a prompt to save the simulated depth data and the name for its file.
The saved simulated depth data are then available for comparison with future simulations for the same center pivot system.
The following information can be printed to the printer after the simulation run.
1.
The head per stage of the pump gpm
 2.
The pivot pressure psi
 3.
The system discharge based on the pump curve gpm
 4.
The system discharge based on all the integrated depths gpm
 5.
The system discharge based on all depths above the minimum depth gpm
 6.
The effective irrigated area, which is the area receiving water above the minimum depth acres
 7.
The mean depth in.
8.
Christiansen's uniformity coefficient 
 9.
Mean low quarter uniformity 
 10.
Plot of depth vs distance
 The information that is available for each sprinkler is the line pressure psi, the nozzle pressure psi, the discharge gpm, and the pattern radius ft.
The application depths are the final piece of information provided.
They are listed by distance.
The Previous Window button saves the changes to the system file and returns to the main program window.
The Previous Window button saves the changes to the system file and returns to the main program window.
Bacterial transport through the air: In a study done by USDA-ARS in Wisconsin on dairy manure and shared through the Livestock and Poultry Environmental Learning Center Webinar Considerations for the use of Manure Irrigation Practices, it was found that distance from the application was the most significant factor when considering risk of infection from manure-borne pathogens being transported through air.
Application of liquid manure to growing crops is often a convenient and agronomically acceptable means of land application.
Center pivots have been adapted to apply a broad range of fertilizers and pesticides.
Development of large animal production facilities has added manure application to the list of materials that can be applied via center pivots if appropriate equipment is selected for pumping and distributing the liquid and solids contained in storage facilities.
Al-Kaisi, et al.
reported on the impact of using a center pivot to apply dilute swine lagoon water to cropland in Colorado.
However, some producers have learned the hard way that more concentrated manure contains some good and some bad materials.
Crop damage can occur as a result of application of concentrated manure presumably because of high salt concentrations.
Sprinkler application of animal manure to growing crops is a different issue than most of the salinity research that has been conducted across the country.
Soluble salt levels in liquid manures are often greater than in the saline water used for irrigation in the western U.S.
When irrigating with saline irrigation water the major problem is buildup of salt over time due to removal of the water by the crop leaving the salts behind.
However, application of manure occurs at relatively low rates per acre and the annual rainfall or irrigation tends to leach the undesirable salts from the profile between applications.
An additional concern with center pivot application of concentrated swine manure is the potential for plant damage  due to high ammonia levels.
Electrical conductivity  level is an indication of the salt concentration in the manure sample.
Crop damage due to sprinkler application of liquid manure with high  levels occurs because of the direct contact of the salt with plant leaves and potentially the roots.
Early research reporting the salinity thresholds for induced foliar injury concluded that since damage was caused by salt absorption into plant tissues, foliar application should be avoided in hot, dry, windy conditions that produce high potential evapotranspiration.
It was noted that species varied in the rate of foliar absorption of salts, such as: sorghum < cotton = sunflower < alfalfa = sugar beet < barley < potato.
However, the susceptibility to injury was not related to salt absorption, as injury varied as: sugar beet < cotton < barley = sorghum < alfalfa < potato.
They found that leaf absorption of salts may be affected by leaf age, with generally less permeability in older leaves, and by angle and position of the leaf, which may affect the time and amount of leaf salt exposure.
However, in other research, Mass et al.,  found that corn yield was not affected at soil water EC levels less than 5.5 dS m -1 for conditions in California.
Producers need to know what the safe salinity levels are and the effect of timing of application on potential plant damage for corn and soybeans.
The goal of the project was to establish the safe level of liquid manure salt levels that could be applied to corn and soybean at different stages of growth.
To accomplish this goal, a range of swine manure concentrations was applied to a growing crop in a manner that simulated application via a center pivot.
Salt and ammonia concentration data from over 2700 manure samples were obtained from a private laboratory to determine the range in concentrations that should be evaluated in the field research.
Figure 1 is a summary of the samples analyzed where the median EC level was 6.7 dS m  with a range from 0.1 to 70 dS m .
The median ammonia concentration was 497 ppm NH4-N with a range from 0.03 to 12,646 ppm NH4-N.
Work with several swine production facilities indicated that lagoon style facilities could have EC's around 12 and below ground pits could have EC's around 20-25.
The field research was conducted at the Haskell Agricultural Laboratory of the University of Nebraska located near Concord, Nebraska.
The soil was a Kennebec silt loam with a pH of 7.3, and 3.5% soil organic matter.
Corn  was planted on 16 May 2003 at 27,000 seeds per acre.
Soybean  was planted on 28 May 2003 at 189,000 seeds per acre.
Field plots were 8-30 inch rows wide and 35 feet long randomly arranged with three replications.
The experimental area was irrigated with a lateral-move
 sprinkler irrigation system equipped with low-pressure spray nozzles mounted on top of the pipeline.
The EC of the irrigation water was 0.6 dS m  Irrigation was applied as needed to maintain greater than 50% available water in the rootzone.
Irrigation supplied 8 inches of irrigation water to both crops, and precipitation supplied 14.4 inches between 1 May and the end of the season.
Figure 1.
Cumulative distribution of electrical conductivity of liquid manure submitted for analysis to a commercial laboratory in Nebraska.
The concentrations used in this study are also presented.
Swine manure from a commercial confined feeding operation was pumped from an under-building storage pit through a 2 mm screen to remove large solids.
The liquid manure was passed through a 0.4 mm screen and then pumped to transfer tanks equipped to continuously agitate the liquid.
Multiple screening was necessary to prevent the applicator nozzles from plugging during application.
The EC of the solutions was determined using a conductivity meter  calibrated with either a 1 or 10 dS m solution.
Liquid manure samples for both applications were collected from -1 the supply tank outlet between the tank and the applicator and sent to Ward Laboratories to determine EC and nutrient concentration.
The screened manure was diluted with fresh water to create four levels of EC in the liquid manure.
The original manure had an EC level of 20.3 dS m  Fresh water was added to dilute the manure down to 6.4 and 11.7 dS m  Fresh water with an EC of 0.6 dS mi -1 was used as a control treatment.
A portable applicator was developed and attached to the boom of a Hi-Boy sprayer.
The applicator consisted of 21 nozzles arranged in a 3-nozzle wide by 7-nozzle long
 grid with a spacing of 3 feet between nozzles in each direction.
The liquid manure application treatments consisted of a single application of four soluble salt concentrations applied at one of two selected growth stages of corn and soybean.
The first application was applied on July 2when corn was at the V7 growth stage and soybean was in the V3 stage.
Air temperatures during application were in the upper 80's.
The second application was applied on July 24 when corn was at the V14 stage and soybean was at the R1 stage.
Air temperatures during application were again in the upper 80's.
Approximately 0.5 inches of liquid manure was applied over a 10-minute period to corn and soybeans at each EC level.
Table 1.
Chemical analysis of liquid manure applied to corn and soybean at Concord, Nebraska, in 2003.
EC Level (dS m 1  1
 0.6	6.4	11.7	20.3
 Mean	SD	Mean	SD	Mean	SD	Mean	SD
 Organic N	0.04	0.04	23.8	3.1	63.6	22.0	179.2	41.0
 Ammonium N	0.5	0.1	78.6	9.6	170.4	6.0	365.7	15.9
 P as P2O5	0.6	0.4	33.7	4.6	112.8	61.3	301.0	72.9
 K as K2O	0.9	0.1	60.7	5.6	130.6	8.8	281.5	26.3
 S	3.5	0.5	12.2	1.8	25.5	4.5	53.4	7.1
 Ca	8.9	1.0	19.4	1.6	57.9	36.2	131.6	33.0
 Mg	2.0	0.1	8.9	0.9	23.2	10.6	57.9	13.4
 Na	2.5	0.1	13.8	1.2	27.7	1.2	59.7	3.6
 Soluble salts	37.0	1.3	412.4	43.6	753.5	24.2	1303.1	65.0
 EC (dS m 1	0.60	0.00	6.4	0.67	11.7	0.38	20.3	1.01
 pH	7.87	0.72	6.9	0.12	6.6	0.06	6.2	0.12
 Dry matter 	0.05	0.01	0.5	0.05	1.8	0.97	4.2	0.86
 Mean EC levels for the fresh water used as a control treatment and liquid manure dilutions applied to corn and soybean.
Figure 2.
Applicator used to apply liquid swine manure to corn and soybean.
Each of the production indices was decreased by the 20.3 dS m -1 liquid manure for both application times.
Soybean plant population at harvest was less with the V3 application of 20.3 dS m  liquid manure than with the 0.6, 6.4, or 11.7 dS m 1 treatments, but the R1 application did not affect plant population.
Leaf area was damaged by the V3 application but the plants recovered due to less inter-plant competition from a reduced plant population.
Thus, the final plant LAI was not significantly different between application dates except for the 20 dS mi -1 application.
Table 2.
Effects of EC level of liquid manure and application time on soybean plant populations, leaf area, dry matter production, and grain yield for the 2003 growing season.
EC Level 
 0.6	6.4	11.7	20.3	Time	EC Level	T x R2
 V33	93800	102700	92000	24300	0.001*	0.003*	0.26
 R1 	100900	106200	102700	104400
 P > F	0.67	0.82	0.55	<0.0001*
 V3	4.6	4.5	2.2	0.3	0.85	0.0001	0.03*
 R1 	3.5	4.1	2.5	1.5
 P > F	0.06	0.46	0.48	0.03*
 Whole-plant dry matter at maturity 
 V3	7447	7893	7395	1071	0.52	< 0.0001	0.07
 R1 	6760	7400	7044	3909
 P > F	0.50	0.63	0.73	0.01 *
 V3	43	39	40	5	0.12	< 0.0001	0.02*
 R1 	42	41	38	23
 P > F	0.57	0.40	0.32	<0.0001* *
 1 Statistical significance of ANOVA main effects are given by the probability of the F-test ; significant differences are indicated by *.
2 T X R is the timing X rate interaction.
3 V3 and V7 are leaf stage at the time of application.
R1 is the stage of growth, but V7 indicates that seven trifoliates were on the plant at the time of application.
When averaged over both application timings, grain yields were the same for the 0.6, 6.4, and 11.7 dS m 1 manure applications, averaging 41 bu/ac, as compared the 20.3 dS m -1 application.
Soybean with the 20.3 dS m  to 14 bu/ac for -1 application at R1 had much higher grain yield  than with the 20.3 dS m 1 application at V3.
Thus, swine manure applied at EC levels less than 11.7 dS m  -1 have little impact on final yield despite causing plant damage at lower concentrations early in the growing season.
Figure 3.
Plant damage to soybean caused by a single application of liquid swine manure with a EC of 20.3 at the R1 growth stage.
Corn growth was less affected than soybean, and damage was detected only with the V8 application at the 20.3 dS m -1 concentration.
The V14 application caused even less damage, likely due to salt tolerance of the fully developed cuticle on the corn leaves.
The V8 application of 20.3 dS m -1 concentration caused some stunting of plants but no plant death.
Overall, the manure increased the corn yields when applied at V14  compared to V8.
Figure 4.
Plant damage to corn at the V8 stage following application of liquid swine manure with an EC of 20.3 in 2003.
Table 3.
Effects of EC level of liquid manure and application time on corn plant populations, leaf area, dry matter production and grain yield for the 2003 growing season.
EC Level 
 0.6	6.4	11.7	20.3	Time	EC Level	T X R2
 Mature plant population 
 23522	24103	22216	24684	0.12	0.11	0.04*	*
 V14	22506	25410	25555	24394
 P> F	0.33	0.22	0.005*	0.78
 Leaf area (cm2 2 plant 
 V8	5161	5211	5149	4428	0.09	0.41	0.17
 V14	4899	5667	5326	5543
 P > F	0.53	0.29	0.67	0.02*
 Whole plant dry matter at maturity 
 V8	6987	7800	6883	5784	0.15	0.04*	0.35
 V14	6894	7654	7944	6874
 P>F	0.89	0.82	0.11	0.11
 Grain yield (Mg ha
 V8	175	181	154	149	0.02*	0.08	0.02*
 V14	164	186	179	185
 P> F	0.28	0.65	0.02*	0.003*
 1 Statistical significance of ANOVA main effects are given by the probability of the F-test ; Significant differences are indicated by *.
2 T X R is the Timing X Rate statistical interaction.
3 V8 and V14 are leaf stages at the time of application.
Weather conditions following liquid manure application may be important to crop tolerance.
Crop damage is expected to be more severe under dry, hot, and windy conditions  with more foliar absorption of salts at higher temperatures.
Although this study was conducted during one growing season, the weather conditions were within the range of most likely conditions for the time of application.
The liquid manure applications in this study were greater than typically applied by farmers in order to induce measurable damage.
Application through a center pivot may keep the foliage wet and the salts soluble longer than the approximate 10 min in our study, especially near the center of the pivot circle.
Our application rate was 0.5 ac-inches, but some pivots can apply as little as 0.2 ac-in), reducing the total amount of soluble salts applied and the potential for leaf damage.
Producers can use inexpensive EC meters to estimate the potential for damage with liquid manure application.
Application of liquid manure to corn and soybean through a sprinkler system is feasible with proper management and equipment selection.
These results support the hypothesis that growth stage and liquid manure soluble salt concentration  influence plant damage.
Based on the conditions of this study, liquid manure with EC levels greater than 6.4 dS m-1 should not be applied to soybean during early vegetative growth.
Liquid manure with EC levels less than 11.7 dS m can be applied to corn and to soybean after flowering.
If the soybean plants are not defoliated as a result of liquid manure application, yield is not likely to be reduced.
Crop tolerance to soluble salt application is greater during the reproductive growth stages of the season than during the early vegetative stages.
Applications of liquid manures to other crops and earlier in the growing season should be conducted to make sure phytotoxicity is not greater earlier in the season or for other commonly irrigated crops such as wheat and alfalfa.
PERFORMANCE OF CENTER PIVOT IRRIGATION SYSTEMS
 Sprinkler irrigation systems are the largest irrigation system type in the US with about 63 per cent of the irrigated acres served; center pivot irrigation systems cover over one-half of the irrigated land in the US.
Center pivot irrigation has increased to an even greater extent in some area of the country, for example, in Kansas in 2012 about 93 per cent of all irrigation was sprinkler irrigation which was mostly center pivot irrigation systems.
Irrigation accounts for about one-third of all water withdrawals in the US.
In Kansas, irrigation water withdrawals are greater and account for about 85 per cent of freshwater withdrawals.
Since irrigation represents a large water use and center pivot irrigation is a dominant irrigation system type, it is important that these systems be properly designed, installed and managed to accomplish high irrigation efficiency and crop water productivity.
Terry Howell, recently retired director of a USDA-ARS Research Lab in Bushland, TX noted at the 1991 CPIA short course that "Sprinkler irrigation methods can be efficient even in harsh environments, such as the Texas High Plains",.
The late Dale Heermann and former director of a USDA-ARS Research Lab in Fort Collins, CO began his 1992 sprinkler irrigation presentation at CPIA with these cautionary words, "We often assume that if a system is working for someone else, it will work for us too.
Unless all the conditions are identical this myth may cause you troubles".
These two comments are still appropriate today, center pivot sprinkler packages, including a number of "non-sprinkler" options, can efficiently irrigate crops but only if applied and managed appropriately for the condition of use.
DESIGN CONSIDERATIONS FOR NOZZLE PACKAGES
 Center pivot sprinkler irrigation systems are used on many fields with various soil and topographical conditions in many climatic zones for a wide variety of crops and cultural practice and can be equipped with many different types of nozzle types or other water distribution outlet devices that have preferred flow and pressure ranges and mounting specifications; essentially meaning there is no universally ideal sprinkler nozzle package.
Nozzle package design and select is now generally handled by the irrigation dealer using information provided by the producer.
Important field information includes soils and topography and water supply availability, especially the flow rate of a well but crop, cultural practices and producer preferences are factors also.
These and other factors affect the selection of the nozzle type, configuration etc.
for which many sources information are available Kranz et al., 2012 from CPIA and Extension bulletins such as Rogers et al., 2008 and Kranz et al., 2005.
The process of designing the sprinkler nozzle package is essentially a selection process involving a series of compromises.
Most producers who irrigate would like to prevent yield limiting water stress as part of
 their irrigation goal.
The uniformity of the water application and the irrigation efficiency of the system were often secondary goals, especially in situations of abundant water supply and low pumping costs.
When center pivot systems were first being adopted in Kansas and other central plains area, many wells had discharge rates that would have been sufficient to select nozzle packages that could exceed the peak water use rate of the crop.
However, irrigation capacity  effects the application rate for a given nozzle type and placement  with higher application rate having higher irrigation capacity.
The application rate should be less than the soil intake rate and the ability of the soil surface to hold applied water in place until the water is infiltrated.
The ability to store water on the surface is related to soil type, slope and surface residue.
Runoff from the field and/or water redistribution within the field is an irrigation efficiency loss.
Run off loss and other irrigation loss components are illustrated in figure 1.
Run off and/or water redistribution for a field should be prevented since it can represent the largest single loss of efficiency if it is occurring.
Figure 1: Illustration of where irrigation water losses can occur from KSU Extension Bulletin MF-2243, "Efficiencies and Water Losses of Irrigation Systems"
 As wells yields in many areas of the Central Plains and other parts of the world decrease due to declining aquifers levels, deficit irrigation strategies become important to the design process, including trying to minimize irrigation efficiency losses due to air losses and canopy losses.
Minimization of these losses can be accomplished by using a nozzle that has a small wetted diameter and lowering the mounting height.
These two actions will increase the application rate which could lead to run off.
Reducing the application rate can also be accomplished by reducing the irrigation capacity which results in less ability to meet the crops needs.
Run off may also be reduced for a given condition by speeding up the system but for a given seasonal irrigation amount, this increases the total number of irrigation applications and results in increased air, canopy and surface losses.
Thus, large application depths can be more efficient than small application depths but only if no run off occurs and the soil has the storage capacity to hold the water in plant available root zone.
The nozzle package selection is also affected by other management considerations such as whether the producer wants to use chemigation or apply irrigation in the non-growing season or during cold weather.
Once a suitable nozzle package design is completed and installed to the specification of the sprinkler package chart, the irrigation operator begins the process of managing system to maintain the integrity of the design specifications.
A major specification is the input pressure and flow specifications at the pivot point but if the nozzle selection was also based on certain soil surface treatments and/or residue levels or other operational conditions, these also must be maintained in order for efficient and uniform irrigation to occur.
MANAGEMENT CONSIDERATIONS FOR NOZZLE PACKAGES
 Just as routine and emergency maintenance on the pumping plant and center pivot system are essential to longevity and functionality of the equipment, so should maintenance of the nozzle package.
While a missing nozzle or completely clogged nozzle can be visually detected, other flow variations between nozzles may not be as obvious.
After the system is installed and correct nozzle placement is verified, the design operating pressure and flow must be supplied to the package for it to perform properly.
If properly designed and operated, the water application depth should be delivered with high uniformity across the field.
Perfect uniformity is not possible since at each outlet a specific flow rate is required but only a fixed number of nozzle sizes are available.
For example, Table 1 shows a portion of a sprinkler package design chart.
Notice at each location, the chart shows the required flow rate and the delivered flow rate for each position.
The delivered flow rate is sometimes higher or lower than required since manufacturers make nozzle diameters in fixed intervals.
The spacing between the nozzle outlets are also sometimes disrupted by the tower structure of the center pivot.
This is illustrated by outlet 100 of table 1 when the spacing differs from the previously used value.
Table 1: A Portion of Sprinkler package design printout 
 Outlet	Sprinkler	Flow Rate,	Pressure
 No.
Loc.
No.
Sep.
Model	Nozzle	Req.
Del.
PSI
 86	836.5	39	19	5006H2	RN-#14 X #14	12.4	12.4	61.5
 88	855.5	40	19	5006H2	RN-#14 X #14	12.6	12.3	61.4
 90	874.5	41	19	5006H2	RN-#15 X #14	13.1	13.1	61.3
 92	893.5	42	19	5006H2	RN-#15 X #14	13.2	13.1	61.3
 94	912.5	43	19	5006H2	RN-#15 X #15	13.5	13.9	61.2
 96	931.5	44	19	5006H2	RN-#15 X #14	13.3	13.1	61.1
 98	950.5	45	19	5006H2	RN-#17 X #16	15.7	16.0	61.0
 100	973.5	46	23	5006H2	RN-#16x#16	15.5	15.2	60.9
 As noted, visually inspecting for flow variations on an operating system is difficult but best accomplished when sunlight angles are low.
The patterns between nozzles should appear similar and if a variation is detected, that area should be inspected more closely.
Closer inspection can involve comparing the installed nozzle diameter to the design nozzle diameter to make certain the correct diameter is in place.
If water distribution patterns seen dissimilar at a number of locations, the nozzles may be worn and could be checked by inserting a drill bit of the same diameter
 size as the design diameter.
It should be a snug fit.
This could be an issue with water supplies containing sand.
The deflection pads can also be affected by sand and other water quality issues, especially certain salts or minerals that can become encrusted on the pads and cause the deflection pattern to be drastically altered.
To a lesser degree, the producer also needs to be aware that certain chemicals and/or chemical combinations could impact the nozzle.
Another component of many nozzles packages are pressure regulators.
These also must be operating correctly in order for the nozzle to deliver the correct flow.
A study of pressure regulators collected from Kansas fields for older systems indicated good longevity for the sites sampled at the outlet positions sampled on the systems.
However, one complete system package was tested and many of the pressure regulators for the first two spans were not functioning properly.
Since most clogging problems occur due to the small diameter nozzles at this location on the system, it was thought freeze damage to the regulators might have occurred over time.
The combined flow of the individual nozzles is dependent on the proper operating pressure and flow rate at the pivot point.
These should be monitored with a pressure gauge and flow meter.
The input pressure and flow rate should match the design specification.
The sprinkler package cannot operate properly and provide uniform water application if these values are not correct.
The uniformity of application for many sprinkler packages can be evaluated using a catch can test.
To be a viable test, certain test conditions must be met, one of which is that there should be at least three feet of clearance between the top of the catch container and the nozzle.
In Kansas, many systems have low to the ground drop nozzles  and therefore cannot be tested with catch cans.
However as part of the Mobile Irrigation Lab program , a streamlined testing procedure was developed and used to evaluate a number of systems to document center pivot uniformity performance.
Figure 2 shows the results of an evaluation with different sections of the evaluation designated with letters.
Section A designates the portion of the evaluation which had a coefficient of uniformity of about 90 per cent which is acceptable.
Section B represents the area that was catching water from a leaky boot connection between two spans.
Section C represents the outer area two spans of the system.
Notice a gradual decline in application depth in this section, which was due to improper nozzle installation.
The nozzles from the two spans were switched during installation.
Section D represents the effect of an improperly operating end gun.
In this case the end gun operation angle was incorrect and the end gun was over spraying about one-third of the last span and the overhang section of the pivot system.
These three problem areas could have been identified with a comparison of the installed nozzle sequence to the design package specification and visual inspection during operation.
Figure 2.
Uniformity test results for a Mobile Irrigation Lab uniformity evaluation 
 Figure 3 shows the results of another uniformity evaluation conducted in Kansas.
The coefficient of uniformity for this system was 84, largely due to the low catch values at the end of the last span and overhang in the area marked with the dashed lines.
The producer had noticed low production around the edge of the field but was attributing this to edge effects.
The issue was improper installation which included a missing drop nozzle  and under sized nozzles on either side of the missing nozzle location.
Since this location was near the end of the system, the area affected represented approximately 9.2 acres.
The application depth in this area was about one-half of the target depth, so over the course of the season, this area might have received 6 inches less water.
Assuming only a marginal yield response to water by corn of 10 bushels per inch, the yield loss would be estimated to be at least 60 bushels per acre or over 550 bushels for the affected area.
This nozzle package repair would be a minimal expense as compared to the loss of annual crop production.
This nozzle package deficiency could have been detected with a comparison of installed nozzles to the design nozzle package.
MANAGEMENT CONSIDERATIONS IRRIGATION SCHEDULING
 The overall irrigation requirement for a field is effected by more than just the irrigation efficiency of the irrigation system.
Other factors are the effect of the tillage or cultural practice on off season capture and storage of precipitation and soil water losses to evaporation within the growing season
 Figure 3.
Unformity test results for a Mobile Irrigation Lav uniformity evaluation.
and deep percolation of water below the root zone.
These factors would not be directly associated with the sprinkler package but are important to managing the overall water budget of an irrigated field.
The effects on the water budget of these factors have been discussed in previous meetings and will be discussed in other sessions at this meeting.
However, irrigation scheduling is at least indirectly linked to irrigation efficiency as a single irrigation event that is in excess to the crop needs can offset the entire gain of improving the irrigation efficiency of a system with a sprinkler package up grade.
For example, if the gross irrigation application to a field was 10 inches and it was applied at 85 % efficiency, the net irrigation applied is 8.5 inches.
If the system efficiency could be improved to 90 %, then the net irrigation application is 9.0 inches, a net gain of 0.5 inches that could either be saved  or applied to gain crop productivity if the system was deficit irrigation mode.
However if the crop needs were being met and a single extra irrigation event occurred, assuming a 1.0 inch application amount, the extra irrigation event was greater than all the potential savings from increasing irrigation efficiency.
Irrigation scheduling is a tool to help prevent over application of irrigation water.
Although no scheduling method will be perfect in light of unpredictable rainfall events for the central plains region and other areas of the world, it is an important tool to help effectively utilize the high uniformity and application efficiency potential of the nozzle packages.
Irrigation scheduling can be accomplished using climatic or crop evapotranspiration based scheduling tools, soil water content based scheduling tools, or a complimentary combination of these type of methods and plant health based methods that are being developed and discussed at this conference.
The nozzle package of a center pivot irrigation system can apply water in a uniform and efficient manner but only if it is properly matched to the conditions of the field and crop, installed to the design specifications, and operated at the design specifications which include proper pressure and water flow
 and could include other field conditions, such as a certain level of crop residue to prevent soil surface water movement.
Proper maintainance of sprinkler packages include checking of the nozzles to ensure the proper size is at the proper location and that all nozzles are operating without obstuction and distrubing the water in a similar water distribution pattern for the individual nozzles.
The package needs to be operated at the design pressure and flow rate specifications which can be monitored with pivot point pressure gauges and water meters.
KDA.
2012.
Kansas Irrigation Water Use.
Annual report from the KS Department of Agriculture, Division of Water Resources and U.S.
Geological Survey.
USDA and NASS Census of Agriculture.
2012.
Farm and Ranch Irrigation Survey.
Volume 3, Special Studies, Part 1.
ECONOMICS OF IRRIGATION ENDING DATE FOR CORN: USING FIELD DEMONSTRATION RESULTS
 Troy J.
Dumler, Danny H.
Rogers, and Kent Shaw Extension Agricultural Economist, SW Research-Extension Center, Garden City, KS; Professor, Kansas State University, Manhattan, KS; and Mobile Irrigation Lab Program coordinator, SWREC, Garden City, KS, respectively.
The results from a field study indicate that corn growers of western Kansas may cut back last one or two irrigation events of the season without appreciable loss in production.
This will improve the economic return by reducing input cost from water.
Recent increase in energy cost for pumping water has necessitated this study to compare the benefits of continuing irrigation until black layer formation.
With the decline of Ogallala aquifer groundwater level and rising fuel cost, any reduction of pumping makes economic sense.
The first irrigation ending date around August 10-15, corresponding to denting and starch layer formation of 1/4 to 1/2 towards the germ layer resulted in an yield reduction of 17 bushels averaging for four years of data for a silty loam soil as compared to second ending date around August 21-22, which corresponded to starch layer at 1/2 to 3/4 towards the germ layer.
However, continuing irrigation until September 1, corresponding to the start of black layer formation, improved yield by only 2.5 bushels per acre.
Economic sensitivity tests show that irrigating until the formation of starch layer at 1/2 to 3/4 towards germ layer is feasible with a corn price of $2 per bushel and $8 per inch pumping costs.
However, irrigating past this stage of grain development is not feasible even with $2.75 / bushel of corn and pumping costs as low as $4 / inch.
Crop production in western Kansas is dependent on irrigation.
The irrigation water source is groundwater from the Ogallala aquifer.
The water level of the Ogallala aquifer is declining causing the depth of pumping to increase.
The additional fuel consumption required for greater pumping depths and higher energy costs have resulted in higher pumping costs in recent years.
Because of declining water levels and higher pumping costs, it is necessary to conserve water by adopting efficient water management practices.
Irrigation scheduling is an important management tool.
Farmers are interested in information on optimum timing for ending the irrigation season.
There are some misconceptions regarding the optimum irrigation ending dates.
Some farmers believe that the corn crop must continue to have water to avoid eardrop.
Over application at the end of season based on this thought cause waste of water, increases cost of production, and may even cause degradation of quality of the grain due to high humidity or disease.
Most of all, the excess use of water may reduce the useful life of the Ogallala aquifer which is a confined aquifer with little or no recharge.
Depletion of the Ogallala aquifer will impact
 irrigated agriculture and the present economy of the area.
The objective of the study was to determine the affect that irrigation ending date had on corn yield and economic return.
A producer's center pivot sprinkler irrigated field was selected for the study.
A silty loam soil of Ulysses series was selected and the study was conducted for four years.
Two sets of six nozzles were shut progressively after the formation of starch layer in the corn grain.
The first closure was done when the starch layer was 1/4 to 1/2 to the germ.
This corresponded to August 10th to 15th, depending on growing degree units.
The second closure was done when the starch layer was 1/2 to 3/4 to the corn germ.
This corresponded to August 21 to 24.
The third closure occurred when the producer ended irrigation for the year.
This happened during the first week of September.
Four random plots of 30 ft.
by 30 ft.
were identified within the center pivot sprinkler circle over which the selected nozzles would pass during an irrigation event.
Ridges were built around the plots to prevent entry of water from the adjacent areas.
Gypsum block soil water sensors were buried in the plots at three different depths  below the soil surface.
The soil of the test field is Ulysses silt loam series.
It is relatively dark with a deep profile and good water holding capacity.
The soil surface, however, cracks when dry.
Corn ears were hand harvested.
Four contiguous rows measuring ten feet each were harvested at the middle of each plot to remove any border effect.
Grain yields were adjusted to 15.5% moisture content.
In 2005, the study was moved to a field with loamy fine sand soil  to evaluate irrigation ending date for a light textured soil with lower water holding capacity.
The hypothesis is that the sandy soil may require continuation of irrigation and irrigation ending date may be delayed compared to a silty loam soil with higher water holding capacity.
The procedure followed was similar to the earlier study where two sets of six nozzles were closed progressively as the grain formed starch layer.
Continuation of irrigation from the first ending date in early August  to the second ending date in the beginning of the fourth week  gave an increase of average 19.5 bushels of grain per acre.
The additional irrigation application amounted to 2.1 inches.
The yield difference from the August 22 ending date to the first week of September ending date, as normally practiced, was only 2.5 bushels per acre on average for four years.
The additional irrigation quantity for the period from the first ending to last irrigation date amounted to 4.6 inches  as an average for four years.
The yearly yields are shown in figure 1.
Figure 1: Yield of corn grain as affected by irrigation ending date at different growth stage on a silty loam soil, Stevens County, Kansas, 2000 -2003.
The tool used to determine the optimum irrigation ending date was the marginal value VS.
marginal cost analysis.
In this analysis corn price ranged from $2.00 to $2.75 per bushel, while pumping cost ranged from $3.00 to $8.00 per inch.
Positive returns indicate that the marginal benefit of continuing irrigation was greater than the cost of applying water.
Figure 2 shows that under nearly all scenarios, irrigation remains profitable until the second ending date.
However, irrigation past this growth stage may not be profitable.
Return becomes negative at pumping cost of $4.00 per inch for corn even at $2.75.
Figure 2: Returns at different levels of input cost and price of corn for difference between 1st and 2nd ending dates
 Figure 3: Returns at different levels of input cost and price of corn for difference between 2nd and 3rd ending dates
 Kansas State University water management bulletin No.
MF-2174 presents a table showing normal water requirements for corn between stages of growth and maturity.
Corn grain, at full dent, will use 2.5 inches of water for the remaining 13 days before reaching physiological maturity.
The available water holding capacity of the soil in the study field is estimated to be approximately six inches or more per 3 feet of root zone.
It is expected that at a 50 percent management allowable depletion level this soil will provide about 3 inches of water.
This may be the reason that there was no appreciable benefit from continuing irrigation past August 21 or after the starch layer has moved past 1/2 to 3/4 towards germ layer.
The soil water sensors indicated that the soil water condition was adequate to carry the crop to full maturity.
Soil water status monitored by gypsum block sensors is presented in Figure 4-6.
Figure 4: Soil water status for 1st irrigation ending date.
Figure 4 shows that the soil water at first and third feet depths were falling below Management Allowable Depletion  level for the first ending date that caused reduction in yield.
Figure 5 shows that soil water in first foot started to go down in the plots of second ending date, but there was enough in second and third foot to carry the crop to maturity.
It is also seen that at this site for some reason the moisture level at 1-2' feet were at MAD level in the very beginning of the season.
However, this changed as irrigation started.
Figure 5: Soil water status for 2nd irrigation ending date.
Figure 6: Soil water status on 3rd irrigation ending date.
Figure 6 shows soil water readings taken until September 11 at the area where irrigation continued until September 1 under producers practices, indicate that soil water was almost at Field Capacity, except for the first foot of the profile.
The crop was already mature and there was no more water use.
The profile was left with high water content over the winter.
Most of the irrigated cornfields in western Kansas reflect this situation and have little room to store winter and early spring precipitation.
This causes double loss from not taking advantage of natural precipitation and leaching of nutrient with the deep percolation of excess water.
A three-year study by Rogers and Lamm  also indicated that the irrigation practices of corn producers of western Kansas leave approximately 1.4 inches of available soil water per foot of soil profile.
Irrigated agricultural producers are continuously being educated on irrigation scheduling.
Kansas State University Biological and Agricultural Engineering developed computer software called KanSched to provide the producers with an easy to use tool for irrigation scheduling.
The irrigation events, rainfall, and crop water use  data were entered to track soil water depletion pattern, which is presented in Figure 8.
Tracking of crop water use and irrigation application show that the soil profile was pretty full at the end of the season when irrigation was continued until September 1.
Figure 7: Chart showing water balance between soil water storage at field capacity and permanent wilting point.
The dashed line in the middle represents management allowable depletion.
It would be worthwhile to mention that there was no appreciable eardrop observed in the field within the circular area with the first irrigation ending.
However, the plants were dryer as compared to the rest of the field at the time of harvest.
Results of 2005 trial on Vona loamy fine sand needs to be continued to establish a trend.
However, the first year results do indicate that the return remains in the positive at pumping cost of $5.00 per inch although the rate of return has been greatly reduced, Figure 9-10.
Figure 8: Returns at different levels of input cost and price of corn for difference between 1st and 2nd ending dates.
Figure 9: Returns at different levels of input cost and price of corn for difference between 2nd and 3rd ending dates
 A four-year field study indicates that the present practice of irrigating until the formation of black layer in corn grain may not be economical.
An earlier ending date for irrigation corresponding to the starch layer at 1/2 to 3/4 of the grain may help improve the economic return and best utilize the soil profile water in a silt loam soil.
Using KanSched or Soil water monitoring by other means may help in the decision process.
However, this may require more cautious evaluation in a sandy soil for its low water holding capacity.
Selecting a Sprinkler Irrigation System
 The four basic methods of irrigation are: subsurface irrigation , surface or gravity irrigation, trickle irrigation  and sprinkler irrigation.
Of the acres currently irrigated in North Dakota, more than 80 percent use some type of sprinkler system.
Statewide, the center pivot is the most popular sprinkler system.
If the sprinkler system is for a new installation, two important tasks must be performed prior to purchasing the system.
First, you must check the county soil survey maps to make sure the soils in the field can be irrigated.
Second, you must have a readily available source of water near the field and a water permit issued by the State Water Commission for that water.
The water source must be of sufficient quantity and quality for successful irrigation.
Extension publication AE-92, "Planning to Irrigate A Checklist," provides more information on what is required to begin irrigating.
A sprinkler "throws" water through the air to simulate rainfall, whereas the other three irrigation methods apply water directly to the soil, either on or below the surface.
A sprinkler system can be composed of one sprinkler or many.
When many sprinklers are used, they are attached to a pipeline at a predetermined spacing to achieve a uniform application amount.
When selecting a sprinkler system, the most important physical parameters to consider are:
 1.
The shape and size  of the field.
2.
The topography of the field.
Does the field have many hills with steep slopes?
3.
The amount of time and labor required to operate the system.
How much time and labor do you have available?
The center pivot system is very adaptable but doesn't fit very well on irregularly shaped fields; long, narrow fields; and fields that contain some type of obstruction.
In these situations, other sprinkler systems may be used more effectively.
The sprinkler system capacity is the flow rate needed to irrigate an area adequately and is expressed in gallons per minute per acre.
The system capacity is dependent on the:
 1.
Peak crop water requirements during the growing season
 2.
Effective crop rooting depth
 3.
Texture and infiltration rate of the soil
 4.
The available water-holding capacity of the soil
 5.
If the water source is a one or more wells, the well or wells' pumping capacity
 6.
The State Water Commission permitted pumping rate
 Table 1 shows the system capacity needed for the most commonly irrigated crops in North Dakota and various soil textures.
To use this table, you must determine the dominant soil texture in the field and what type of crops will be grown , then determine the appropriate system capacity.
For example, if you plan a rotation of potatoes, corn and alfalfa on loamy sand, you can determine from Table 1 that potatoes require 7 gpm/acre, corn 5.9 gpm/acre and alfalfa 5.6 gpm/acre.
You would select a design system capacity for the crop requiring the largest amount, in this case the potatoes at 7 gpm/acre.
If you install a center pivot system covering 130 acres, you would need about 910 gpm for proper design.
However, what you need for proper design and what a well will produce is frequently different.
As a general rule, under full-season irrigation, you need a minimum flow rate of 6 gpm/acre 
 Table 1.
System capacity in gallons per minute per acre  for different soil textures needed to supply sufficient water for each crop in nine out of 10 years.
An application efficiency of 80 percent and a 50 percent depletion of available soil water were used for the calculations.
Zone	Sand	Fine	and
 Depth	and	Loamy	Sandy	Sandy	Silt
 Crop		Gravel	Sand	Sand	Loam	Loam	Loam
 Potatoes"	2.0	8.2	7.5	7.0	6.4	6.1	5.7
 Dry Beans	2.0	7.9	7.1	6.4	6.1	5.7	5.4
 Soybeans	2.0	7.9	7.1	6.4	6.1	5.7	5.4
 Corn	3.0	7.3	6.6	5.9	5.5	5.3	4.9
 Sugarbeets	3.0	7.3	6.6	5.9	5.5	5.3	4.9
 Small Grains	3.0	7.3	6.6	5.9	5.5	5.3	4.9
 Alfalfa	4.0	6.8	5.9	5.6	5.1	5.0	4.5
 NDSU Extension Service North Dakota State University Fargo, North Dakota 58105 JANUARY 2010
 "Adjusted for 40 percent depletion of available water.
What It Looks Like
 This self-propelled sprinkler system rotates around the pivot point and has the lowest labor requirements of the systems considered.
It is constructed using a span of pipe connected to moveable towers.
It will irrigate approximately 132 acres out of a square quarter section.
Center pivot systems are either electric or oil-drive and can handle slopes up to 15 percent.
Sprinkler packages are available for low to high operating pressures.
Sprinklers can be mounted on top of the spans or on drop-tubes, which put them closer to the crop.
The water application amount is controlled by the speed of rotation.
Center pivots are adaptable for any height crop and are particularly suited to lighter soils.
They are generally not recommended for heavy soils with low infiltration rates.
Deep wheel tracks can be a problem on some soils; however, a number of management methods are available to control this problem.
Electric-drive pivots are the most popular due to flexibility of operation.
Computerized control panels allow the operator to specify speed changes at any place in the field, reverse the pivot, turn on auxiliary pumps at a specified time and use many other features.
Center Pivot With Corner Attachment
 Corner attachment systems that allow irrigation of most of the corner areas missed by a conventional center pivot system are available.
Depending on the method of corner irrigation, pivot systems with corner attachments will irrigate 145 to 154 acres out of a 160-acre quarter section.
The most common method of corner irrigation has an additional span, complete with a tower attached to the end of the center pivot system main line, which swings out in the corners.
As it swings out, sprinklers are turned on to irrigate the corners.
A buried wire, global positioning system unit or mechanical switch controls the movement of the corner span.
Another type of corner system uses several end-guns mounted on the end of the center pivot system main line.
The end-guns are activated in sequence from smallest to largest and back again as the machine moves past the corners.
A corner span generally costs about half as much as the rest of the pivot, thereby increasing the capital cost per acre on a square 160 acres.
However, if the field is rectangular, the corner span can be extended on one or both ends, thereby increasing the amount of irrigated acreage from 170 to 185 acres.
High-value crops and/or high land value, as well as scarcity of irrigable land, are necessary to justify additional costs for more than a "plain" center pivot.
Sample 160 Acre Layout
 The linear move  irrigation system is built the same way as a center pivot; that is, with moving towers and spans of pipe connecting the towers.
The main difference is that all the towers move at the same speed and in the same direction.
Water is pumped into one of the ends or into the center.
Water can be supplied to the linear move either through a canal or by dragging a supply hose that is connected to a main line or by connecting and disconnecting from hydrants as the linear moves down the field.
To gain acreage and make the transition from one side of the field to the other, some linear move systems pivot at the end of the field.
Due to the lateral movement, powering a linear with electricity is difficult.
Usually, a diesel motor with a generator is mounted on the main drive tower and supplies the power needed to operate the irrigation system.
The primary advantage of the linear move is that it can irrigate rectangular fields up to a mile in length and a half mile wide.
Due to the high capital investment, linear moves are used on high-value crops such as potatoes, vegetables and turf.
The traveling big gun system uses a large-capacity nozzle  and high pressure  to throw water out over the crop  as it is pulled through an alley in the field.
Traveling big guns come in two main configurations: hard-hose or flexible-hose feed.
With the hard-hose system, a hard polyethylene hose is wrapped on a reel mounted on a trailer.
The trailer is anchored at the end or center of the field.
The gun is connected to the end of the hose and is pulled to the trailer.
The gun is pulled across the field by the hose wrapping up on the reel.
With the flexible-hose system, the gun is mounted on a four-wheel cart.
Water is supplied to the gun by a flexible hose from the main line.
A winch cable on the cart pulls the cart through the field.
The cable is anchored at the end of the field.
Most traveling big gun systems have their own power unit and cable winch mounted directly on the machine.
The power unit may be an internal combustion engine or a water drive.
at this point the linear would be moved to this side of the field and irrigation would begin in the opposite direction
 Particularly adaptable to various crop heights, variable travel speeds, odd-shaped fields and rough terrain, the big gun requires a moderate initial investment, more labor and higher operating pressures than center pivots and linear moves.
One 1,320-foot-long  set usually covers eight to 10 acres, but many variations using different water quantities and operating pressures are available.
Irrigated cropland is sacrificed because the alley is generally two rows wide.
Most big gun systems are used on a maximum of 80 to 100 acres per gun.
The side roll  system, as shown, consists of a lateral, usually a quarter mile long, mounted on 4to 10-foot-diameter wheels with the pipe acting as an axle.
Common pipe diameters are 4 and 5 inches.
The side roll irrigates an area from 60 to 90 feet wide.
When the desired amount of water has been applied to this set area, a gasoline engine at the center is used to move the side roll to the next set.
The sprinklers generally are mounted on weighted, swiveling connectors so that no matter where the side roll is stopped, the sprinklers always will be right side up.
This type of system is not recommended for slopes greater than 5 percent and should be used mainly on flat ground.
When not being used, side rolls are subject to damage from high winds.
Side roll systems also are adapted only to lowgrowing crops; have medium labor requirements, moderate initial investment, medium operating pressure  and generally rectangular field requirements; and each lateral is capable of irrigating a maximum of 40 acres.
The side roll is better adapted to heavier soils than a continuous moving system.
Special wheels must be purchased for moving this system from field to field without disassembly.
One variation of the side roll system has trail lines with up to three additional sprinklers on 60-foot spacing.
This reduces the number of sets required to irrigate a particular field.
because most of the soils irrigated in North Dakota are loamy sands or sandy loams.
A lesser flow rate can be used but more intensive water management will be required.
A sprinkler system must be designed to apply water uniformly without runoff or erosion.
The application rate of the sprinkler system must be matched to the intake rate of the most restrictive soil in the field.
If the application rate exceeds the soil intake rate, the water will run off the field or relocate within the field, resulting in underwatered areas.
Using tillage that improves surface storage, such as
 deep cultivation or making basins, will help control runoff.
The intake rate of the soils in your field can be found in the county soil survey available at your local Natural Resources Conservation Service or Extension office.
Selecting the Most Appropriate Sprinkler System
 Five of the most common sprinkler systems in use in North Dakota are compared in this publication using the following criteria:
 1.
A square 160-acre field
 2.
A 100-foot-deep well near the center of the field
 3.
An adequate water supply for any sprinkler system
 4.
Suitable soils for the system application rate
 Table 2 shows the costs of irrigation development using the criteria stated above.
The costs shown are averages; actual costs for most farms will vary depending on the distance from the water source to the field, whether the sprinkler system is new or used, options selected and the type of financing package.
Take care to ensure that the cash flow generated is sufficient to cover payments on the irrigation investment.
Table 2.
Comparative cost of new sprinkler irrigation systems.
Assumes three-phase electric power lines run along the edge of the field.
Center Pivot Pivot w/Corner1 Linear Move2	Big Gun	Side Roll
 Number of Systems Required	1	1	1	2	4
 Acres Irrigated 	128	152	158	158	158
 Required Flow Rate 	768	912	948	948	948
 Irrigation System Cost	$65,000.00	$95,000.00	$114,000.00	$63,000.00	$64,000.00
 Well, Pump, Motor	$27,000.00	$30,000.00	$30,000.00	$35,000.00	$32,000.00
 Pipe, Meter, Valves	$4,500.00	$4,500.00	$11,000.00	$20,000.00	$23,000.00
 Electric Panel and 1,400 ft of Wire	$10,000.00	$10,000.00	$10,000.00	$10,000.00	$10,000.00
 TOTAL CAPITAL COST	$106,500.00	$139,500.00	$165,000.00	$128,000.00	$129,000.00
 CAPITAL COST PER ACRE	$832.03	$917.76	$1,044.30	$810.13	$816.46
 ANNUAL OWNERSHIP COST 
 Depreciation on System (25 year life,	$20.31	$25.00	$28.86	$15.95	$16.20
 Depreciation on Well, Pump, Motor	$12.97	$11.71	$12.91	$16.46	$16.46
 and Pipe 
 Interest on Investment (6% rate averaged	$24.96	$27.53	$31.33	$24.30	$24.49
 TOTAL ANNUAL OWNERSHIP COST	$62.40	$68.83	$78.32	$60.76	$61.23
 OPERATING COSTS 
 Power 	$18.90	$19.02	$19.84	$29.34	$20.94
 Maintenance 	$12.48	$13.77	$15.66	$12.15	$12.25
 TOTAL ANNUAL OPERATING COST	$41.38	$42.79	$50.51	$71.49	$68.19
 OPERATING AND OWNERSHIP COST	$103.78	$111.62	$128.83	$132.25	$129.42
 Annual Cash Cost of Ownership	$70.50	$74.91	$87.06	$99.85	$96.77
 Kilowatts Hours  of Energy	33.69	42.44	46.95	74.74	50.17
 (pumping energy plus tower motor energy
 on pivot and linear)
 Pressure at Well 	40	40	45	100	60
 1 Buried wire guidance.
For GPS guidance system, add $12,000 Guidance uses a furrow-sensing wheel.
For GPS guidance system, add $20,000 2 3 Based on an off-peak electric rate of 6 cents per kilowatt-hour ; annual meter charge of $600 and 900 hours of pump operation per growing season
Western Oregon Irrigation Guides
 Why should I use these guides?
Limitations of these guides
 Important data for irrigation scheduling
 Background on evapotranspiration calculation
Strategies for Early Season Irrigation
 Last years irrigation will have left the soil fairly wet compared to dryland fields.
On a typical year, a silt loam soil that was reasonably well irrigated the previously year  may only hold two to four inches of water from precipitation in the non-growing season.
Sandy soils will hold even less.
This means most years, irrigated fields will be at or above field capacity in May, particularly in the eastern two-thirds of Nebraska.
Instalando sistemas subsuperficiales de riego por goteo para cultivos en lnea
 El xito de un sistema subsuperficial de riego por goteo  para cultivos en lnea depende de su diseo, instalacin, operacin, manejo y mantenimiento.
Todas las fases son igualmente importantes.
Esta publicacin describe los componentes e instalacin de un sistema SDI.
Los pasos en el proceso de instalacin son:
 instalacin de las lneas principales, instalacin de lneas distribuidoras  y lneas de lavado
 conexin de la cinta con las lneas distribuidoras y las lneas de lavado;
 relleno de las zanjas; e
 instalacin del equipo de filtrado.
Componentes del sistema de irrigacin
 Los componentes principales del sistema de irrigacin son los filtros, las lneas principales, las lneas distribuidoras , los bloques de campo o secciones de riego, las lneas de lavado, las lneas de goteo  y los accesorios.
Todas las lneas de goteo  conectadas a la misma subprincipal componen un bloque de campo o seccin de riego.
Varios bloques de campo pueden ser agrupados juntos formando una estacin o zona de riego, y pueden operar simultneamente.
El agua se suministra a las lneas de goteo de los bloques de campo por medio de la lnea distribuidora .
En algunos sistemas permanentes, las lneas de goteo estn tambin conectadas a una lnea de lavado, para que el sedimento que se ha acumulado pueda ser lavado de las lneas
 Figura 1.
Trazo tpico de un sistema de riego por goteo.
de goteo utilizando una sla vlvula.
La lnea de lavado es tambin llamada lnea de coleccin.
En algunos bloques de campo, particularmente aquellos con lneas laterales ms largas , la lnea de lavado puede estar conectada tambin a la lnea principal por una vlvula y lnea distribuidora separada, para poder suministrar agua por ambos extremos de la lnea de goteo.
Esto previene la prdida de presin excesiva en las lneas de goteo ms largas.
La lnea de lavado siempre debe tener una vlvula de descarga, aunque sea utilizada tambin como una lnea de abastecimiento.
Los sistemas de riego temporales no usan lneas de lavado; sus cintas solamente duran una o dos temporadas de riego antes que necesiten ser reemplazadas.
Las lneas de goteo pueden estar conectadas a la lnea distribuidora de diferentes maneras como lo muestra la Figura 2.
La lnea distribuidora puede ser colocada en la superficie del suelo, o estar enterrada.
Figura 2.
Conexiones tpicas de la tubera distribuidora a las cintas de goteo En este caso la tubera de suministro est conectada a las cintas de goteo con alambres de acero inoxidable.
Figura 3.
Implementos con inyectores de cinta de goteo.
Inyeccin de cintas de riego
 El inyector consiste en un rollo que detiene la cinta y un cincel que abre el suelo para enterrar la cinta.
A medida que el cincel abre el suelo, la cinta es guiada dentro del suelo, usualmente a travs de un tubo curvo montado atrs del cincel.
El cincel debe ser lo suficientemente durable para resistir el impacto de las piedras u otras obstrucciones presentes en el suelo.
El tubo que est montado atrs del cincel debe de ser liso y curvo para no romper la cinta.
Ejemplos de la inyeccin de la lnea de goteo se muestran en las Figuras 4 y 5.
Los pasos para inyectar la cinta son:
 1.
Marque los lugares donde sern instaladas las lneas distribuidoras y las lneas de lavado utilizando banderas o trazando lneas con cal en el campo.
2.
Si la cinta se instala a ms de 8 pulgadas de profundidad o en suelo pedregoso, pase el cincel sin instalar la cinta.
El pasar el cincel previamente hace que la profundidad y el espaci-
 Figura 4.
Instalando la cinta de goteo.
Figura 5.
Cambiando el rollo de cinta a la mitad del terreno.
Figura 6.
Unin de dos cintas de riego.
amiento entre las cintas sea ms uniformes y ayuda a remover piedras del camino que pudieran daar la cinta.
Esta operacin no es necesaria en campos que se pueden arar fcilmente.
3.
Sea extremadamente cuidadoso para no cortar la cinta cuando desempaque el plstico que cubre el rollo..
El manejo descuidado o tosco de la cinta puede resultar en fugas mayores despus de la instalacin.
4.
Coloque la cinta en el suelo con el lado de los emisores hacia arriba para evitar taponamientos condicin que se presenta cuando el riego termina y las particulas se sedimentan.
Los rollos traen indicadores que muestran la direccin de los emisores.
5.
Poco antes de bajar el cincel, fije la cinta temporalmente a mano o con una estaca para que pueda ser jalada al suelo.
Las estacas pueden ser hechas de varillas de soldar o de alambre rgido.
6.
La profundidad de la cinta depender del cultiVO.
La cinta normalmente se ha instalado a una profundidad de 12 a 14 pulgadas en sistemas de riego por goteo permanentes en cultivos tales como algodn y alfalfa en las reas de St.
Lawrence, Trans-Pecos y Lubbock.
En la parte
 baja del Valle de Ro Grande, la cinta se ha colocado de 2 a 6 pulgadas de profundidad en cultivos tales como cebollas y melones.
Revise que la cinta est a la profundidad adecuada y ajuste la profundidad si es necesario.
7.
Si la cinta se termina en medio del campo durante su instalacin un pedazo de manguera de PVC flexible de 364 pulgadas puede ser utilizado para unir la cinta del rollo nuevo con la que ya se instal, asegurando la cinta en cada extremo de la manguera con dos alambres de acero inoxidable o con conexiones especiales.
El zanjeo puede ser necesario para instalar las lneas principales, las lneas distribuidoras y las lneas de lavado.
Las lneas distribuidoras y las lneas de lavado pueden ser instaladas en algunas ocasiones sobre la superficie del suelo, requirindose solamente una zanja para la lnea principal.
El zanjeo puede ser hecho con un abre zanjas rotativo o retro-excavadora.
Se recomienda el abre zanjas rotativo.
Los pasos son los siguientes:
 1.
1.
Antes de abrir las zanjas, pase el tractor por en medio de la cinta, pasando una llanta en cada extremo de la cinta.
(Fig.
2.
Las zanjas deben de ser de 2 pies de ancho o del tamao del cucharn de la retroexcavadora.
Las zanjas para las lneas subprincipales deben de tener una profundidad de al menos 16 pulgadas por debajo de la cinta de riego, y un pie bajo la cinta en la lnea de lavado.
3.
Exponga la cinta de la zanja formando un tringulo.
Deje Figura 8.
Conexin de la cinta de goteo a la tubera suficiente espacio para distribuidora.
trabajar con sus manos y asegurar la cinta con el tubo de PVC.
4.
Nivele y compacte la tierra en el fondo de la zanja con la tierra que caiga al exponer la cinta.
Esta tierra puede servir de cama para la tubera subprincipal de PVC.
Figura 7.
Compactando el suelo con la llanta del tractor a cada lado de la cinta.
5.
Coloque banderas donde termine cada estacin.
6.
Conecte las tuberas de PVC de los subprincipales.
Figura 9.
Perforando el tubo distribuidor de PVC , metiendo el insertor con manguera de PVC al empaque de plstico que est sobre el tubo de PVC  conectando la manguera de PVC a la cinta utilizando un alambre de acero.
Conectando las lneas de goteo a las lneas distribuidoras y lneas de lavado
 Si las lneas distribuidoras y las lneas de lavado estn bajo la superficie del suelo:
 Hay varias formas de hacer las conexiones.
El siguiente ejemplo utiliza anillos o empaques de plstico y conectores.
1.
Abra un hoyo con una broca en la parte superior de la lnea distribuidora o la lnea de lavado justo donde ser conectada a la cinta..
Use una broca de 13/16-pulgadas para anillos #700.
Use una broca de 9/16-pulgadas para anillos #400.
2.
Limpie el hoyo con un cuchillo para eliminar el residuo de plstico.
Este plstico podra producir fugas ms adelante.
3.
Inserte el empaque en el hoyo.
4.
Conecte previamente el insertor de plstico a la manguera de PVC utilizando pegamento.
5.
Humedezca el insertor con agua con jabn para que pase fcilmente en el empaque.
6.
Inserte la manguera de PVC en la cinta, teniendo cuidado de no doblar la manguera.
7.
Amarre la cinta a la manguera con un alambre de acero inoxidable.
Si las lneas subprincipales y las lneas de lavado estn arriba de la superficie del suelo:
 Figura 10.
Conectando la cinta a la tubera de distribucin sobre la superficie del suelo con microtubos A) y con conexiones de plstico B)
 El mtodo de conexin ms comn es insertar un tubin de PE de dimetro pequeo  dentro del PVC, PE o manguera plana "lay flat" como lo muestra la Figura 10a.
Despus, se abre un hoyo en la cinta y el tubin es insertado en la cinta.
El tubin se sujeta a la cinta con un pedazo de cinta doblado.
Otro mtodo es usar conexiones como se muestra en la figura 10b.
Relleno de las zanjas
 Oper cada estacin por 4 horas y revise si hay fugas.
Si hay una fuga en medio del campo, se requerir hacer un hoyo y unir la cinta con un pedaZO de manguera de PVC.
Si hay una fuga en la tubera subprincipal, la conexin entre la cinta y la tubera necesitar hacerse de nuevo (en algunas ocasiones los simples remanentes del plstico al hacer el hoyo en la tubera pueden causar que el empaque no
 Figura 11.
Trazo tpico de una estacin de bombeo en el que se muestra el equipo de filtracin.
selle bien y que haya fugas en la tubera).
Si no hay fugas, SUAVEMENTE coloque tierra suelta en la zanja.
Luego agregue agua a la zanja para que la tierra alrededor del tubo se asiente para sostenerlo y prevenir que se mueva.
No mueva mucha tierra a la vez sobre la tubera, esto puede daar las conexiones.
Comprima la tierra, luego agregue ms agua hasta tapar la zanja completamente.
Instalando el equipo de filtracin
 Los filtros deben ser instalados sobre superficies slidas, preferentemente bases de concreto.
Una instalacin tpica del equipo de filtracin y sus componentes se muestra en las Figuras 11 y 12.
Los filtros remueven la materia Proceso de filtracin Proceso de retrolavado slida suspendida en el agua y evitan que los emisores de goteo se tapen.
El tamao ms comn de filtro para riego Entrada Valvola de Entrada superficial por goteo es de 200 mesh retrolavado , que representa una apertura de 0.003 pulgadas.
Los tipos de filtros ms Salida Salida comunes son los centrfugos, los filtros
 de arena y los filtros de malla, los cuales con frecuencia se utilizan en combinacin.
Por ejemplo, si el agua proviene de un acufero, un filtro centrfugo se puede usar para atrapar arena, en combinacin con un filtro de discos o de arena.
Cuando el agua proviene de un canal, es comn usar un filtro de arena y uno de mallas.
Los filtros de arena son los que ms necesitan ajustes durante su instalacin.
Estos filtros consisten en varios tanques que filtran el agua, y cada tanque necesita ser retrolavado.
Esto se logra pasando agua limpia a travs de un tanque en direccin contraria; el agua limpia viene de otro tanque que no ha sido
 Figura 12.
Proceso de filtracin y retrolavado.
retrolavado.
Los tanques deben ser retrolavados cuando estn sucios, una condicin que se indica con un aumento de presin de 10 psi.
Los filtros de arena experimentan prdida de presin debido a la friccin dentro del filtro, siendo aproximadamente de 3 a 5 psi.
La instalacin incorrecta puede aumentar la prdida hasta aproximadamente 10 a 25 psi.
Siga estos pasos para instalar un filtro de arena:
 1.
Ordene solamente grava prelavada.
2.
Instale la grava y la arena a la profundidad recomendada por el fabricante.
3.
Cierre todas las vlvulas que se encuntran despus de los tanques de filtrado.
4.
Abra la vlvula principal , procurando no excederse del rango total del flujo del sistema.
Un rango alto puede destruir la integridad de las capas de arena/grava en el tanque.
5.
Abra completamente la vlvula de retrolavado de uno de los tanques.
Luego abra la vlvula de ajuste del flujo de retrolavado lentamente.
Recuerde que la vlvula de ajuste del flujo de retrolavado debe ser calibrada una sola vez.
El rango de flujo del retrolavado debe ser determinado visualmente.
El rango de flujo de retrolavado debe ser suficiente para expandir la cama de arena y separar la arena en partculas individuales.
Las partculas pequeas y aquellas que floten deben ser sacadas del tanque.
El rango de flujo de retrolavado no debe exceder el lmite de la cantidad de arena que se saca del tanque.
La primera vez que el tanque es retrolavado, es normal que salga un poco de arena.
Use una malla 100  en la descarga para atrapar la arena que se ha acumulado.
6.
Repita el proceso, abriendo vlvula de ajuste del flujo de retrolavado de cada tanque.
7.
Ajuste la frecuencia y el tiempo de la operacin de retrolavado.
Es importante retrolavar por lo menos una vez al da y controlar la descarga automticamente encendindolo con un interruptor de presin diferencial.
Este interruptor se programa para que empiece cuando la presin diferencial aumenta de 5 a 8 psi.
Figura 13.
Equipo de filtracin.
Texas Water Resources Institute make every drop count
 Este material est basado sobre trabajo apoyado por la Iniciativa de la Baha del Rio Grande de del Servicio Cooperativo Estatal de Investigacin y Extensin, Departamento de Agricultura de EE.
UU.
bajo el acuerdo No.
2001-45049-01149.
La informacin proporcionada en este folleto tiene fines educativos nicamente.
Las referencias a productos o nombres comerciales se hacen bajo el entendimiento de que no existe intencin de discriminar y no implican su aprobacin por parte del Texas A&M AgriLife Extension Service.
Texas A&M AgriLife Extension Service
 Los programas educativos de Texas A&M AgriLife Extension Service estn disponibles para todas las personas, sin distincin de raza, color, sexo, discapacidad, religin, edad u origen nacional.
El Sistema Universitario Texas A&M, el Departamento de Agricultura de EE.UU.
y las Cortes de Comisionados de Condado de Texas en Cooperacin.
Water flowing into and out of the state can be expressed as a generalized water budget.
Per the Groundwater Atlas of Nebraska  and the USGS National Water Survey Summary , the generalized calculated numbers are: Streams in, 0.4 inches per year; precipitation, 22.6 inches; runoff, 0.9 inches; evapotranspiration , 19.9; recharge, 1.9; and streams out, 2.2.
Note that precipitation is the largest in component and evapotranspiration is the largest out component; and that streams flowing into the state carry less water than streams flowing out of the state.
Turf Irrigation Water Quality: A Concise Guide
 Justin Quetone Moss, PhD Turfgrass Water and Environment Research and Extension Specialist
 Michael Kress Turfgrass Water Quality Laboratory Manager
 This Fact Sheet helps turf managers assess their irrigation water by using four key water properties that are listed on water reports and four key soil properties listed on soil salinity and texture reports.
The second half of this Fact Sheet provides six illustrative case-studies for bermudagrass lawns to model site-specific irrigation strategies.
Four Key Irrigation Water Properties
 Total salts is typically reported in units of milligrams per liter  as TDS  or TSS ; for all practical purposes, TDS and TSS are interchangeable terms.
However, TDS and TSS are often indirectly measured as EC  multiplied by 0.64.
While EC is the historical method of classifying irrigation water, total salts makes more intuitive sense; either can be used.
The SAR  is used for determining the ratio of sodium to calcium and magnesium in soils.
This relationship is important because sodium strips calcium from soil particles and prevents soil aggregates from forming and creating flow paths in the soil.
Although SAR is typically a soil parameter, it can also be used to classify irrigation water  because that water will eventually determine the salt chemistry of the soil.
The SAR is unitless because it is a ratio.
The Adj SAR  is another parameter typically used for soils.
It adjusts for lost calcium in the form of calcium carbonate deposits.
This calcium loss essentially increases the SAR of irrigation water
 Table 2.
Classification of irrigation water based on SAR.
1-2	Good	Little concern; add pelletized
 2-4	Fair	Aerify soil, sand topdress, apply
 pelletized gypsum, monitor soils
 4-8	Poor	Aerify soil, sand topdress, apply
 pelletized gypsum, monitor soils
 8-15	Very Poor	Requires special attention; consult
 > 15	Unacceptable Do not use
 and decreases the soil's ability to form soil aggregates.
Use Adj SAR when it exceeds the unadjusted ratio.
The regular classification system for SAR  is still used after the adjustment.
The SAR and total salts together help predict water infiltration rates.
Infiltration rates are improved by high total salts, but high salts may damage turfgrass.
Therefore, water with high salts can be helpful  and harmful  simultaneously.
Boron is a nutrient, but in high concentrations is toxic to plants.
In addition, boron is difficult to leach from the soil.
It requires about three times the water to leach boron from the soil as it does salts.
Water containing less than 1.0 mg/L boron should be of no concern for most plant materials, while water with more than 2.0 mg/L boron is unsuitable for irrigation use.
Table 1.
Classification of irrigation water based on total salts  and EC.
Total Salts	EC	Classification	Management
 < 320	< 500	Excellent	None
 320-960	500-1,500	Good	Little concern, especially with periodic rainfall
 960-1,920	1,500-3,000	Fair	Leach salts from soil as needed
 1,920-3,200	3,000-5,000	Poor	Routinely leach; monitor soils
 3,200-3,840	5,000-6,000	Very Poor	Requires special attention; consult water specialist
 > 3,840	> 6,000	Unacceptable	Do not use
 Figure 1.
Total salts and SAR are used together to predict the effect of irrigation water on infiltration hazard..
Table 3.
Classification of soil extracts based on TSS  and EC.
TSS	EC	Classification	Management
 < 2,560	< 4,000	Normal	None
 2,560-5,120	4,000-8,000	Above Normal	Little concern, especially with periodic leaching
 > 5,120	> 8,000	Saline	Leach regularly with best available water
 Four Key Soil Properties
 The TSS  in soil is similar to that in water; the difference is that the classification limits are higher.
ESP  is the percent of soil exchange sites occupied by sodium.
Few laboratories actually measure this relationship; instead, they calculate ESP from SAR.
Since the relationship between calculated ESP and SAR are proportional, either parameter can be used to classify sodium in soil.
Boron in soil can be toxic to plants, depending on boron concentrations and plant sensitivity.
Ornamental trees and shrubs are sensitive at levels above 0.5 mg/L boron.
At boron levels above 2.0 mg/L, Kentucky bluegrass is sensitive.
Most other turfgrass are not sensitive until the levels are above 6.0 mg/L.
Soil texture is the percent sand, silt, and clay in the soil.
Soils with high clay content have very low permeability rates.
The permeability rates for sandy soils are very high.
Texture analysis can be performed by turf professionals using textureby-feel or by soil laboratories.
Table 4.
Classification of irrigation water based on ESP and SAR.
SAR	ESP	Classification	Management
 < 12	< 15	Normal	None
 12	15	Sodic	Aerify soil, sand topdress,
 leach regularly with best
 Six Illustrative Case Studies for Bermudagrass Lawns
 Water with high total salts makes for a saline soil.
Water report	Soil salinity report	Texture report
 Total Salts I 2,700 mg/L, Poor	TSS I 6,000 mg/L, Saline	35% Sand
 SAR I 1.5, Good	SAR I 2.2, Normal	30% Silt
 HCO I 0.0 mg/L; No Adj SAR	Boron I 0.03 mg/L, No Concern	35% Clay
 Boron I 0.05 mg/L, No Concern
 This irrigation water is classified as Poor because of the high total salts.
This soil is classified as Saline because of the high TSS.
This soil is classified as a Clay Loam with low permeability.
Plant symptoms.
Brown areas, similar to drought stress.
Management strategy.
Regularly use excess irrigation water to leach salts from the soil.
Use best available water.
Water with high sodium makes for a sodic soil.
Water report	Soil salinity report	Texture report
 Total Salts I 1,320 mg/L, Fair	TSS I 2,000 mg/L, Normal	35% Sand
 SAR I 7.0, Poor	SAR I 16, Sodic	20% Silt
 HCO2 3 I 0.0 mg/L; No Adj SAR	Boron I 0.45 mg/L, No Concern	45% Clay
 Boron I 0.12 mg/L, No Concern
 This irrigation water is classified as Poor because of the high SAR.
This soil is classified as Sodic because of the high SAR.
This soil is classified as a Clay with very low permeability.
Plant symptoms.
Brown areas, similar to drought stress; soil water fails to drain.
Management strategy.
Aerify soil and sand topdress; apply 10 pounds pelletized gypsum/1,000 sq.
ft.
and repeat in 30 days.
Utilize a maintenance program of 5 pounds pelletized gypsum/1,000 sq.
ft.
per month during growing season.
Leach regularly with best available water.
Water with both high total salts and high sodium makes for a saline-sodic soil.
Water report	Soil salinity report	Texture report
 Total Salts I 2,120 mg/L, Poor	TSS I 5,400 mg/L, Saline	40% Sand
 SAR I 6.6, Poor	SAR | 14, Sodic	40% Silt
 HCO, I 0.0 mg/L; No Adj SAR	3	Boron I 0.95 mg/L, Concern for	20% Clay
 Boron | 0.55 mg/L, No Concern	Sensitive Ornamentals
 This irrigation water is classified as Poor because of high total salts and high SAR.
This soil is classified as Saline-Sodic because of the high TSS and the high SAR.
This soil is classified as a Loam with moderate permeability.
Plant symptoms.
Brown areas, similar but not identical to drought stress.
Management strategy.
Aerify soil and sand topdress; apply 10 pounds pelletized gypsum/1,000 sq.
ft.
and repeat in 30 days; utilize a maintenance program of 5 pounds pelletized gypsum/1,000 sq.
ft.
per month during growing season.
Leach regularly with best available water.
Use different water supply for ornamental trees.
Water with high bicarbonate makes for a sodic soil.
Water report	Soil salinity report	Texture report
 Total Salts I 416 mg/L, Good	TSS I 1530 mg/L, Normal	22% Sand
 SAR I 3.2, Fair	SAR I 13, Sodic	40% Silt
 HCO I 305 mg/L; Adj SAR 4.2, Poor	Boron I 0.15 mg/L, No Concern	38% Clay
 Boron I 0.06 mg/L, No Concern
 This irrigation water is classified as Poor because of the high Adj SAR of 4.2; this Adj SAR poses a potential, long-term soil problem where calcium is removed from the soil.
This soil is classified as Sodic with an SAR of 13 because of the high Adj SAR in the water.
This soil is classified as a Clay Loam with low permeability.
Plant symptoms.
Brown areas, similar to drought stress; soil water fails to drain.
Management strategy.
Aerify soil and sand topdress; apply 10 pounds pelletized gypsum/1,000 sq.
ft.
and repeat in 30 days.
Leach regularly with best available water.
Investigate the possibility of acidifying this water because of the bicarbonates, but consult with a water quality specialist.
Water with high boron makes for a soil with high boron.
Water report	Soil salinity report	Texture report
 Total Salts I 756 mg/L, Good	TSS I 1,260 mg/L, Normal	40% Sand
 SAR I 0.7, Excellent	SAR I 0.9, Normal	40% Silt
 HCO, I 0.0 mg/L; No Adj SAR	Boron | 3.50 mg/L, Concern	20% Clay
 Boron I 1.93 mg/L, Concern	for Sensitive Plant
 This irrigation water is classified as Good because of the low total salts, but the high boron makes it potentially harmful to sensitive plants such as Kentucky bluegrass and ornamentals.
This soil is classified as Normal because of the TSS and SAR, but boron in this soil can be a problem; most turf can tolerate relatively high concentrations of boron, but ornamentals such as trees cannot.
This soil is classified as a Loam with moderate permeability.
Plant symptoms.
Burnt leaf tips; however, frequent mowing removes the problem.
Management strategy.
Do not use this water on ornamental trees and cool season grasses; consult a water quality specialist if necessary.
Water from very heavy rainfall makes for unexpected results.
Water report	Soil salinity report	Texture report
 Total Salts I 0 mg/L, Excellent	TSS I 95 mg/L, Normal	93% Sand
 SAR I 0.0, Excellent	SAR I 0.1, Normal	4% Silt
 HCO 3 I 0.0 mg/L; No Adj SAR	Boron I 0.00 mg/L, No Concern	3% Clay
 Boron I 0.00 mg/L, No Concern
 This rainfall water is classified as Excellent because of the very low total salts and the very low SAR, but the very low salts may be too much of a good thing in sandy soils.
This soil is classified as Normal, but very heavy rainfall leaches minerals and nutrients.
This soil is classified as a Sand with very high permeability.
Plant symptoms.
Yellowing from nutrient deficiencies.
Management strategy.
Test soil for nutrient deficiencies; apply 1 lb N/1,000 sq.
ft.
per month during the growing season; monitor turf.
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Director of Oklahoma Cooperative Extension Service, Oklahoma State University, Stillwater, Oklahoma.
This publication is printed and issued by Oklahoma State University as authorized by the Vice President, Dean, and Director of the Division of Agricultural Sciences and Natural Resources and has been prepared and distributed at a cost of 20 cents per copy.
0216 GH
Reasons for choosing irrigation over other application methods vary, including timing of application, labor needed, or cost of transport, but for many farmers, irrigation is a great option for application of effluent to cropland.
Risk of infection from manure-borne pathogens decreases as distance from the application area increases and as levels of pathogens are decreased in the manure.
While theres always a small chance that someone could get sick from a pathogen that they pick up following exposure to a manure application, that risk is very low in most cases.
Use; Irrigate lighter soils when needed while crop uses the water in the heavier soils, VRI type: both, prescription type: static, management intensity: medium.
The highest totals were reported in south-central Nebraska and portions of the northeast with more than two inches for the month.
wth and Yield of Cotton
 only one year's study of one soil type and nds in research development toward imtion to yield and quality of cotton.
# irrigation treatments in studies on nd yield.
treatments used in termine the effects gation and varying ture on plant revality of the cotton
 A-the driest treatwas irrigated opseks after the first $ which resulted in to each irrigation.
high soil moisture, #ly as once a week #, which is considby some growers nfested with nema-
 first sign of stress indicated by a disand sometimes by the late afternoon.
any color change, sie in frequency of reatments B and C.
treatment to mainrel of soil moisture all times.
This treat.
ed approximately xing July and Au-
 B irrigated once a and to August 10, irrigation for the
 treatment with the the season on Au-
 irrigated once a 1st, and September, tion for the season
 Detailed growth measurements of cotton-under the various irrigation treatments in the experimentsindicate the extent to which the plant can be manipulated by varying the time and amount of water available.
Plant height measurements were made weekly during the season, and flowering and fruiting measurements were made daily, as shown in the graph on page 8.
Flowers were tagged beginning with the first on June 21 and continuing to August 19.
Flowers in this period accounted for 99% of the total yield and gave precise information as to occurrence of flowering and fruiting.
Vegetative growth is a factor in limiting the fruiting of most plants; however, excess foliage-plant height-to the amounts of fruit is usual for cotton.
In Treatment A where moisture was a limiting factor in growth, the plants were 28.7" tall and produced 573 bolls on 40 row feet.
The different levels of growth are shown in the two-column table on page 11.
Increasing the soil moisture-Treatment C-increased the plant height 23% and yield 18% over A.
High moisture levels by frequent irrigations Treatments B and C-gave increases in plant height up to
 fruiting, defoliation, lodging, boll opening related to available moisture
 V.
T.
Walhood and B.
Counts
 41% greater than Treatment A, while yields were not increased above those ob.
tained in Treatment C, as shown in the table in column 1, page 10.
Flowering was correlated with the number of irrigations up to 12; further irrigations did not increase the number of flowers produced during the season.
This correlation is plotted in the graph at the lower right of this page.
While the plots receiving less frequent irrigations produced a smaller number of total flowers, the tendency was toward earlier blooms, The flowering rate in Treatment A was limited by plant size.
Treatment C produced more flowers the first 30 days than B, and more than E for 35 days.
There was no difference in number of bolls set in Treatments B, C, and E, which outyielded A, as illustrated in the graph in column 2 on this page.
Above seven irrigations boll set was not increased in number.
Boll in Treatment A was limited by low flower production and plant growth.
Although boll production was equal in B, C, and E, Treatment C produced 80% of the boll crop approximately six days ahead of Treatments B and E.
This may be a reflection of its earlier flower production.
Within an environment extending over the summer season, cotton plants have been found to be very uniform in flower retention percentages.
Only by extremes in cultural practices do percentages vary
 Accumulated number of bolls set on 40 row feet of cotton from different Irrigation treatments at Shafter, 1954.
over 10%.
Luxurious amounts of nutrients and water tend to reduce, and water stresses tend to increase, retention percentages.
In this study less frequent irrigations resulted in more efficient flower retention; the moisture stress in Treatment A resulted in 42% flower retention, and Treatment C retained 34%, B 29%, and E 31%.
The increased retention of flowers in A was not sufficient to make up for the low number of blooms in that treatment; in C, however, the increase in retention was sufficient to maintain maximum boll set even though it had 11-15% fewer flowers than Treatments B and E.
The largest bolls were produced by Treatment B, followed closely by C and E, while bolls from Treatment A were six to 11% smaller than other treatments.
The cotton plant grown under the prevailing cultural practices in the San Joaquin Valley of California is high yielding and luxuriant in growth.
It has a tendency toward prolonged foliage retention, and lodging occurs.
Chemical defolia.
tion, hand and mechanical harvesting are difficult under such conditions.
Characteristic fruiting phenomena for Concluded on page 11
 Number of flowers opening daily and number of flowers retained to become bolls on 40 row feet of cotton from different Irrigation treatments at Shafter, 1954.
Irrigation dates indicated by arrows.
Cotton plants Ave weeks after emergence, without Irrigation, dry plot Treatment A.
Background wet Treatment a.
is also dependent upon certain other fiber characteristics that enable the closely twisted fibers to resist slippage.
Nep counts are based on the number per 100 square inches of card web.
These are small tangled knots of fibers that show up as specks in cotton yarn and cloth.
The chief cause of neps is considered to be a high proportion of thin wall fibers.
Relative freedom from this condition is highly desirable since neppy yarns absorb dyes unevenly and detract from yarn appearance.
The yarn appearance index is based on the relative smoothness of the yarn
 Effect of the Timing of the Last Irrigation on Fiber and Yarn Properties
 Date last irrigation	/10	8/31	9 27
 Fiber grade	M*	M*	M*
 Staple length, Inches	1 1/8	1 1/8	1 1/8
 Yorn strength, lbs.
122	124	125
 Nep count	23	24	20
 Yorn appearance index	95	95	95
 and freedom from neps and other foreign materials.
The effect of various irrigation frequencies on these fiber and yarn properties is presented in the two-column table on page 10.
Not until the extremes in irrigation frequency are considered does any appreciable effect on these propertics become noticeable.
Treatment E, the most frequently irrigated treatment, had the longest fiber and the weakest yarn.
Treatment A, the least frequently irrigated treatment, had the shortest fiber, the highest grade, lowest nep count, and the best-appearance index.
The short fiber and low nep count are due to severe stress for water, but the increase in grade and appearance index is probably due to the absence of very small trash particles that were not readily separated in cleaning the fiber.
The low nep count for Treatment A probably was partly responsible for the increased yarn appearance index.
The effect of the intermediate irrigation frequencies on these yarn and fiber properties is insignificant, and it would appear that if extremes in the frequency
 of irrigation are avoided, the grower will not materially affect fiber quality.
The timing of the last irrigation as affecting fiber and yarn properties is apparently insignificant when the crop as a whole is considered.
Lint samples for these tests were taken from machinepicked cotton.
However, damage to many late bolls was quite evident where the water was cut off on the earliest date, and the results of fiber tests made on lint from these late bolls did show some reduction in fiber length.
These pinched bolls constituted such a small fraction of the total crop that they did not measurably affect these fiber and yarn properties.
J.
R.
Stockton is Assistant Specialist in Irrigation, University of California, Davis.
L.
D.
Doneen is Professor of Irrigation, University of California, Davis.
The above progress report is based on Research Project No.
918,
 Continued from page 9
 the Shafter region are: 1.
Flowering beginning in late June and reaching a high rate, with usually 90% of the total flowers produced by early August in approximately 50 days.
After that time, flowering is reduced to a slow rate or ceases altogether by early September.
2.
Boll setting proceeds rapidly early in the season but is reduced to a slow rate after 45 days.
The rapid decrease in boll set is called the cutout, and when it occurs, the vegetative and fruiting buds do not develop.
However, the large number of bolls retained preceding the cutout continue to grow.
Basic causes of cutout and the physiological shedding throughout the season are not fully understood, except that they are related to the fruiting-vegetative status of the plant.
Growth resumes when the bolls mature.
This study was made on the three treatments G, B2, and I.
A number of measurements were made on the cotton plant to evaluate the timing of the last irrigation.
The treatments were timed to correspond to varying degrees of cutout.
Treatment G-last irrigation August 10 -was timed for the early part of the cutout, with the last irrigation August 31; and Treatment irrigation September 27-when complete cutout occurred.
The last irrigation at beginning of cutout.
Treatment G-August 10-reduced
 Effect of Time of Last Irrigation on Natural Defoliation, Boll Opening, and Lodging at Shatter, 1955.
treatment	irrigation	Final	Aug.
10	Sept.
10	Sept.
20	Sept.
30	Oct.
13
 Aug.
0	60	80	80
 Aug.
31	0	0	20	20
 Sept.
27	0	0	0	0
 Aug.
10	65	87	93	98
 Aug.
31	60	78	83	89
 Sept.
27	31	50	66	84
 Aug.
10	none	none	none	none	none
 Aug.
31	none	some	some	some	some
 Sept.
27	none some much much much
 yields 15% below Treatments B2 and I, and the continuation of irrigation to September 27 did not increase yield.
As far as fruit production is concerned, cutout occurred toward the end of August.
Natural defoliation of 80% had occurred by September 20 in Treatment G: 20% in B2 and negligible in Treatment / when plants were still being irrigated on September 20.
Moisture stresses occurred sooner following the last irrigation August 10 than for the other two treatments, due to higher temperatures in August than in September.
The Effect of Different Levels of Growth, Flower Production, Boll Retention, and Boll-Leaf Ratios in Cotton at Shafter, 1955.
Plant	Number	Number	Per cent	Number	Bolls
 Treatment	height,	of	of	reten-	leaves	per
 inches	flowers	bolls	tion	per boll	lb.
A-3 irrig	28.7	1364	573	42.0	4.9	68
 C-7 irrig	35.0	1876	639	34.1	4.8	63
 B-12 irrig	37.4	2211	639	28.9	5.1	61
 E-21 irrig	40.6	2124	651	30.6	64
Understanding Center Pivot Application Rate
 Brian Leib, Associate Professor, Irrigation Systems and Management Tim Grant, Research/Extension Assistant, Soil and Water Resources Department of Biosystems Engineering and Soil Science
 Financial support from the Tennessee Soybean Promotion Board, Cotton Incorporated and USDA NRCS Conservation Innovation Grant
 Many irrigation systems are designed with a known flow rate but an unknown application rate , such that we don't automatically know how long to operate a system to apply, for example, 1 inch of water.
Center pivots rely on a percent timer to adjust the speed of the last tower from 100 percent to 1 percent.
With a faster speed, less water is applied, and with a slower speed, more water is applied per revolution.
Table 1 shows the application amount per revolution time for a standard design flow of 6 gallons per minute/acre.
Adjusting the percent timer to apply a desired amount of water can be different for every center pivot depending on the design flow, length of the pivot, and the motor chosen to operate the last tower.
Older center pivots required a printed chart showing the relationship between percent on-time to application depth that is placed in each individual control panel box.
Thankfully, modern control panels perform these calculations internally and automatically set the percent timer to deliver a desired application amount.
These panels can also be programed to change the application depth and speed of the center pivot in different pie-shaped zones as it irrigates.
Setting a single application depth and operating a center pivot are very easy with modern control panels, whereas programing the pivot to water differently in pie-shaped zones will require greater effort.
An understanding of how center pivot application amount and rate is calculated can be helpful for managing irrigation even though it is calculated by the control panel.
One way to better conceptualize the conversion of flow rate to application depth is with the simple equation, AD = QT.
This relationship can be visualized as a constant flow  from a faucet running into a container that has a constant area.
If the faucet is turned on for a specified time , the result will be a known depth of water  in the container.
The same is true of irrigation systems that apply water at a known rate into a known area.
If the above units of measure are used, there is no need for a conversion constant in the AD = QT equation.
However, center pivot flows  are usually in gpm, requiring a conversion constant in the AD = QT equation.
Typically, it is easier to calculate application rate  from the AD = QT equation  in inches per hour.
Table 2 shows two types of center pivot AR: one based on applying water to the entire circle  and the other directly under the pivot span.
As an example of calculating AR a 130-acre center pivot with a well and sprinklers designed to deliver 780 gpm applies water at 0.0133 in/hr, which
 means 0.4 inches would be applied in a 30-hour revolution, as shown in the example in Table 2.
You can use the average application rate to make sure the panel is programed correctly by either entering your pivot's design flow rate or a measured flow rate into the AR equation along with the acres under 5 the pivot.
Also, 4 the application amount per revolution can be measured with a rain gauge.
Note that only 85 percent to 95 percent of the water applied by the pivot will end up in the rain gauge because sprinklers do not apply water in an entirely vertical direction.
Also, multiple rain gauge readings are more representative of application rate due to some disunity of sprinkler application.
AR, shows how intensely irrigation hits the ground surface.
As you move out from the center point, each sprinkler needs to apply more water to cover the increased acreage in each segment added to the circle.
Therefore, when using a pivot designed at 6 gpm/ac and spray sprinklers with a 25-foot diameter of throw, the instantaneous AR, is 1.7 in/ hr at 500 feet from the pivot point and 4.2 in/hr at 1,250 feet, as shown in the table below.
Even though the AR, increases along the pivot, the same total amount of water is applied to the entire area; the outer sprinklers move much faster so they need to apply water faster.
The AR, can be reduced by sprinklers that have a greater radius of throw, but these sprinklers require more pressure and produce larger droplets that can impact the soil surface, reducing infiltration.
In a Tennessee test on a 4 percent slope, no significant difference in runoff was noted between spray sprinklers and drop
 spinners with a larger radius of throw.
Still, it seems logical to consider using drop-rotating sprinklers to reduce the potential for runoff on sloping ground with silt loam soil that occurs in Tennessee as compared to spray sprinklers that concentrate water in a smaller area.
Most center pivots are designed to be capable of applying 0.3 inches over 24 hours at 6 gpm/ac, meaning you could potentially apply just over 2 inches in a week.
Two inches per week or 9 inches in a month is more than enough water to meet a crop's water use requirements in the humid East.
Often, the problem with center pivot irrigation is not the supply rate, but the ability to infiltrate water into the soil due to the high AR, as noted above.
The portion of irrigation that runs off is not available for use by the crop.
Also, runoff into wheel tracks can increase rutting to the point where a center pivot cannot move Pivot run off across the field as often as desired.
Due to these center pivot application characteristics, there are some base recommendations on how much water to apply per revolution.
In flat river bottom grounds, where runoff is not a big concern, application amounts of 0.5 to 0.8 inches per revolution can be utilized.
However, on sloping fields or fields where infiltration is an issue, 0.3 to 0.5 inches per revolution leads to a more effective irrigation application.
If your goal is to apply 1 inch of water in a week, you could accomplish this by one heavy irrigation, two 0.5-inch irrigations, or three 0.33-inch irrigations.
All options result in the same amount of water over the same amount of time if the pivot is running continuously, but the multiple smaller irrigations may have greater evaporation
 loss due to wetting the canopy and ground surface more often, whereas the single large irrigation may have significant runoff.
Therefore, we recommend setting pivot application amounts as high as possible per revolution without creating significant runoff.
In summary, an understanding of average application rate can help you verify that your center pivot is performing as expected, while instantaneous application rate provides insight into how to avoid excess runoff.
Table 1: Center Pivot Application Amount by Revolution Time
 Design Flow Rate:	6.0 gpm/ac
 Average Application Rate:	0.0133 in/hr
 Revolution	10	20	30	40	50	60	70	80	90	100
 Amount	0.13	0.27	0.40	0,53	0.66	0.80	0.93	1.06	1.19	1.33
 Table 2: Calculating Application Rates for Center Pivot Irrigation
 Average AR for water applied to the entire field	Instantaneous AR for water being applied under the span
 ARA = average application rate in inches/hour,	AR, = instantaneous application rate in inches/hour,
 Qc = flow for entire system or per acre in gpm	Dpp = distance from the pivot point in feet
 Ac = area for entire system in acres or one acre	QAC = design flow rate in gpm per acre
 Sp = Sprinkler diameter of throw in feet
 Example ARA Calculation	Example AR, Calculation
 Qc=780gpm =	Dpp = 500 feet and 1250 feet
 Ac = 130 acres	QAC  = 6 gpm/acre
 Sp = 25 feet for a spray sprinkler
 ARA / = 0.0133 in/hr
 Depth = 0.0133 in/hr X 30 hrs per rev = 0.40 inches	AR1500 =  /  = 1.7 in/hr
 AR11250 =  /  = 4.2 in/hr
 AG.TENNESSEE.EDU Real.
Life.
Solutions.
Piper Farms Saves Big with a Center Pivot
 Piper Farms is a dairy operation located alongside the Kennebec River in Embden, Maine.
The farm is operated as a partnership created by Matt and Marsha Hamilton with Lowell and Karen Piper.
Putting a waste product to use
 The farm milks 525 cows three times daily, with about 4,000 gallons of water used per day to flush the milk room.
Unlike other farms which might combine manure solids with the milk room wastewater or gray water, Piper Farm diverts the wastewater to its own holding pool below the milk room.
Beyond the pool expands 60 acres of flat, sandy cropland adjacent to the river.
Matt recalled a time about five years ago when the fields were dry and the farmers were pumping irrigation water from the river to feed into their center pivot irrigation system.
Why cant we do gray water instead?
Matt asked.
Since then, the farm has been running gray water through their center pivot to irrigate the 60-acre parcel that is in no-till corn.
Running gray water through the center pivot
 The gray water is filtered through a screened suction line that floats in the center of the 8-foot-deep holding pool.
A generator pumps the gray water into a pipe feeding into the center pivot.
The computer-programmed center pivot sprays 350 gallons per minute and spreads 0.3 inches of water per acre.
It takes approximately 7-10 days to empty the holding pool down to a layer of solids.
In terms of challenges, Matt said the screens on the suction line can clog with manure and sand and lose suction.
However, Matt recognizes that the benefits of using the center pivot outweigh the cons in terms of soil heath benefits and costs.
Soil health side effects
 The alternative to the center pivot is to truck and spread the gray water directly on the fields or to another storage pond.
Matt estimates this would take a month of hauling or about 400 trips over the fields.
While the center pivot saves on trucking fuel and labor it also reduces the threat of soil compaction.
Soil compaction causes a general deterioration of the soil structure.
Compaction decreases porosity which reduces water infiltration, air and gas exchangeability, and root penetration.
Matt hasnt measured soil compaction directly but has anecdotally noted the soil feels more cushiony underfoot since starting.
Down the road, Piper Farms looks forward to monitoring how this practice in combination with cover cropping and no-till impacts their corn yields.
The program also will show an up-to-date summary of: Amount of available water in soil root zone.
Available water in soil root zone at planting.
Total rainfall since planting.
Total irrigation amount.
Total crop water use.
Total water losses 
How to Prepare, Test & Install Watermark TM Sensors
 Chris Henry Ph.D., Associate Professor and Water Management Engineer Rice Research and Extension Center
 P.B.
Francis Ph.D., Professor University of Arkansas at Monticello
 L.
Espinoza Ph.D., Soil Scientist Crop, Soil and Environmental Science
 Arkansas Is Our Campus
 This is the first in a series of three fact sheets on using Watermark Soil Moisture Sensors to aid in irrigation management.
This fact sheet provides guidance on the proper construction and preparation of sensors for field installation.
The second fact sheet discusses "How to Use Watermark Soil Moisture Sensors," and the third fact sheet provides guidelines for "Timing the Final Irrigation Using Watermark Soil Moisture Sensors."
 This publication shows how to construct Watermark Sensors using polyvinyl chloride  water pipe for use in monitoring soil moisture in row crops.
Watermark sensors are manufactured by the Irrometer Company in Riverside, California.
PVC pipe 1/2 inch 
 Blue PVC cement 
 PVC cleaner and primer 
 1/2 inch PVC cap
 Rubber washer 
 Saw or PVC cutter
 7/8 inch X 33 inch soil sampling probe, part number 400.96.
Other tools can be used.
Side hammer, Part Number M401.01, 
 Figure 1.
The sensor is attached to a length of PVC pipe which facilitates installation to the desired depth in soil.
The 1/2-inch SCH 20 PVC pipe  is the right size to provide a snug fit with the Watermark sensor collar.
Do not use ordinary 1/2-inch PVC pipe.
1.
Cut the PVC tubing in lengths approximately 4 inches longer than the desired depth for sensor installation.
For example, to prepare a sensor to measure soil moisture at a 6-inch depth, a 10-inch length of PVC pipe is needed.
Sensor Install Depth	Minimum Recommended
 	PVC pipe length 
 Figure 2.
Use PVC pipe cutter to get the desired lengths.
2.
Cut a 1-inch notch or drill a hole at the top of the pipe for the sensor wire so that when the PVC cap is placed on the top of the installation tube, the wire is not pinched.
3.
Drill a small 1/8-inch hole about 1/4 inch from the end of the pipe.
This is a drain hole.
4.
Extend the wire through the pipe from the sensor.
5.
Apply PVC primer and glue to the sensor collar and pipe.
The slot on the sensor and hole should align so that water can drain.
Wipe off excess glue so the surface is smooth.
Do not allow excess glue to build up around the seam.
6.
Measure from the end of the sensor and mark PVC pipe using a permanent marker at the desired sensor install depth.
You can also label the tube cap.
7.
Place rubber washer on PVC pipe to ensure sensor is installed to correct depth.
8.
Tape cap with electrical tape.
al reader.
This reading should be greater than 150 cb.
Submerge the sensor in water and the meter reading should be less than 5 cb.
Let the sensor air dry for 30 to 48 hours.
For a dry sensor, the reading should be 150-199 cb.
Put the sensor back in water, and within 2 minutes, the meter reading should return to less than 5 cb.
For manual read sensors, put the excess wire in the pipe by looping it inside before routing the wire out of the PVC.
Leave 2-4 inches of wire outside for the leads, just enough to connect a manual reader less is better.
Figure 3.
Soak sensors preferably in the irrigation water that will be applied to the field or fresh rainwater; however, tap water also can be used.
Suggested Color Bar Code for Watermark Sensor Depths
 10.
Soak sensors overnight before installation, and keep sensors in water until installation.
11.
Make a sensor access hole in the row or between plants at desired depth using a slide hammer.
For twin row systems, install between the twin rows.
Always install the sensor in the top of the bed.
Install a wet sensor in a dry hole.
Push the sensor down the hole until it bottoms out.
Gently tap sensor with the handle of the slide hammer so that it is solid in the bottom of the hole.
Sensors will need at least 2 days to acclimate.
Install sensors at least 3 plants apart from each other in the row, preferably in order of depth.
Sensors to be used with collection units: these require 15 ft or longer leads for connection to telemetry units or data loggers.
Excess wire can be wrapped around the completed sensor.
Figure 3.
Sensors should be installed early in the season when plants are small so that the installation does not damage roots.
Plants with roots that are damaged by sensor installations may not use water the same as undamaged plants.
9.
Prior to field installation, new Watermark sensors should be conditioned through two wetting and drying cycles.
Soak sensors overnight  and then allow them to dry during the day.
Test with a manu-
 12.
Push rubber washer into place so that it contacts the soil.
Remove soil from slide hammer probe and place on top of washer and gently pack down.
Use enough soil so that washer is no longer visible.
13.
Locating the sensors for troubleshooting, or for removal prior to harvest, will be easier if flags are placed at the installation site and at the end of rows where sensors are positioned.
Sensors are easier to extract when the soil is moist.
Printed by University of Arkansas Cooperative Extension Service Printing Services.
DR.
CHRIS HENRY, is an associate professor and Water Management Engineer with the Rice Research and Extension Center in Stuttgart.
P.B.
FRANCIS, is a professor with the University of Arkansas at Monticello.
L.
ESPINOZA, is a soil scientist with the department of Crop, Soil and Environmental Science.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Director, Cooperative Extension Service, University of Arkansas.
The University of Arkansas System Division of Agriculture offers all its Extension and Research programs and services without regard to race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
Sinkhole Management for Agricultural Producers
 Sarah Wightman and Steve Higgins, Biosystems and Agricultural Engineering, and Rob Blair, Kentucky Division of Water
 M ore than 50% of the state of Kentucky has moderate or high potential for karst landscape development, and nearly 25% of the state has intense karst development in areas such as the Inner Bluegrass and Western Pennyroyal regions.
A karst landscape develops when the limestone or dolostone bedrock underneath the soil dissolves and/or collapses due to weathering.
A karst system can be recognized by surface features such as depressions, sinkholes, sinking streams, and caves.
In karst systems, surface water and groundwater are interconnected: surface water runoff flows into sinkholes and sinking streams and recharges the groundwater; likewise, springs maintain stream flow in the dry season.
The swallow hole in Figure 3 is an example of a karst feature that connects surface water and groundwater.
Once water in the stream reaches the swallow hole, it goes directly into the karst system with little or no filtration through the soil.
Kentuckians living in karst areas need to be acutely aware that any pollutants that reach either surface water or any karst feature can pollute the entire groundwater system.
In addition, the cave system that accompanies a karst aquifer can allow pollutants to contaminate miles of water resources in just a few hours.
In a rural landscape, karst features can occur anywhere, but they are a concern in crop fields, pastures, and near production areas.
It is important for agricultural producers to understand the risks associated with farming near karst features, which include water pollution and injuries and losses due to sinkhole collapse.
This publication is designed to explain to agricultural producers the types of best management practices  that should be implemented in a karst landscape to reduce these risks.
Figure 1.
Potential for karst development in Kentucky based on bedrock type.
The best way to protect a sinkhole is to buffer the area that drains into the sinkhole with vegetation.
This practice is similar to creating riparian zones or buffer strips along streams.
This BMP is especially important for sinkholes near animal feeding operations, crop fields, or any other intensely used or developed land.
Buffering a sinkhole allows vegetation to filter out contaminants
 in stormwater runoff before it reaches the bottom of the sinkhole.
Plant roots also help stabilize the rim of a sinkhole and slow erosion.
Buffering a sinkhole's entire drainage area may be impractical if it is multiple acres, but any amount of buffering around a sinkhole provides water quality and stability benefits.
At a minimum, the area immediately around a sinkhole should be buffered with grass, bushes, and trees.
In some cases, sinkholes have traditionally been left out of
 Figure 2.
Features associated with karst landscapes.
Figure 3.
This swallow hole connects the surface stream to the underground water system and does not filter out contaminants, which allows them to enter the system rapidly.
the production area and may already have some vegetation growing around them, but this traditional vegetative buffer can often be expanded or more intensely planted.
If it becomes necessary to remove invasive species or toxic plants near sinkholes, use mechanical means or spot applications of herbicides that are considered safe around water sources.
Sinkhole buffers in crop areas may require the use of herbicide-ready plants or species that can tolerate the herbicides used on the crops.
Sinkhole formation occurs as a result of soil erosion from both the surface and subsurface.
Surface runoff-especially fast-moving water-erodes soil from the sinkhole surface and carries it underground.
As that runoff moves through the sinkhole and into bedrock fractures, it also carries soil away from the bedrock, resulting in erosion of both the surface and subsurface.
These erosive forces of surface runoff can weaken the overlying soil to the point that a sinkhole will begin to collapse.
When this weakening occurs, it is very important
 to stabilize the sinkhole without sealing it off.
Various methods can be used to stabilize sinkholes safely and effectively.
The following is a general description of one recommended stabilization method.
In general, the use of standpipes or the drilling of dry wells is discouraged, as they can cause flooding problems and
 allow contaminated runoff and debris to enter the karst system.
Additionally, pouring cement or concrete into a sinkhole in an attempt to seal it is strongly discouraged and will cause more problems and expense in the long run.
Disturbances such as soil or water movement near sinkholes can cause them to become unstable, which can result in the sinkhole deepening or widening and in some cases sudden surface collapse.
Also, as more water enters a sinkhole, the potential for water resource contamination greatly increases.
Landowners should attempt to reduce and/or slow down the water flowing into sinkholes by creating grassed waterways or placing riprap in ditches and gullies leading to sinkholes.
In cases where water flows by sheet action, it is best to create a large vegetative buffer.
As a last resort, landowners may want to install diversion ditches or grassed waterways that direct water away from the sinkhole, which slows the growth of the sinkhole and lessens the potential for water pollution.
However, when diverting water, producers must consider where the runoff will be diverted to ensure that it doesn't cause additional erosion or water quality problems.
Figure 4.
Water was channeled into this sinkhole, causing it to grow deeper and wider.
Figure 5.
Manure dumped in this sinkhole can contaminate ground and surface water with both pathogens and nutrients.
Figure 6.
Dumping trash in a sinkhole can pollute ground and surface water.
Traditionally, sinkholes have not been used in agricultural operations; however, since space often becomes limited as operations grow, some producers have converted sinkholes and other karst features into dumps for muck, household and shop wastes, fencing material, and any other inconvenient waste.
Placing contaminants in a sinkhole can contaminate groundwater often used for irrigation, livestock water sources, and drinking water for rural communities.
This means that a depression or sinkhole should never be used as an open dump.
Any waste, including dead animals, household trash, and construction debris, should not be placed in a sinkhole or even buried within 100 feet of a sinkhole, as these materials can release pollutants underground that could then easily be transmitted to water resources through the karst system.
Additionally, grey water, septic system waste, or surface drainage should never be diverted to a sinkhole.
Only sand, soil, rock, gravel, or untreated wood should be deposited in a sinkhole; anything else should be removed immediately and disposed of properly.
Finally, never plug a sinkhole.
Sinkholes in pastures are common in Kentucky.
Livestock should be excluded from sinkholes and other karst features by fencing off the sinkhole's drainage area.
Many Central Kentucky horse farmers already fence off sinkholes to protect animals from injury, but excluding livestock also protects water quality by preventing manure, sediment, and other pollutants from entering the sinkhole.
Sinkholes should be fenced at least 25 feet out from the top rim of the depression, since it may be impractical to fence off the entire drainage area.
In cropped areas, sinkholes should be protected with a vegetative buffer.
This buffer should be marked to prevent it from being sprayed before nearby row crop or forage planting.
Although this practice enhances water quality by reducing herbicide and fertilizer  applications, it can also save money and prevent equipment damage that frequently occurs near sinkholes and other karst features.
New pesticide and fertilizer storage facilities should be located at least 100 feet from sinkholes, other karst features, and surface water bodies, and chemicals should never be mixed near a sinkhole.
Figure 7.
Livestock are excluded from these sinkholes, which protects animals and water quality.
Underground and Aboveground Storage Tanks
 An underground storage tank is any tank that has at least 10% of its volume underground.
An aboveground tank is located entirely aboveground.
These tanks can contain a variety of substances, but among the most common on agricultural operations are petroleum products.
To minimize the impact of potential leaks, these tanks should be located as far as possible from sinkholes.
Underground tanks should be equipped with secondary containment or leak detection devices as a safeguard in the event of a release from the primary tank.
Aboveground tanks should have secondary containment, such as a poured concrete floor and containment berms, placed under and around them to ensure that leaks and spills are contained.
Sinkhole treatment or closing any kind of karst opening is allowed by law but should be accomplished using technical assistance from the Natural Resources Conservation Service.
For more information see the NRCS Conservation Practice Standard Sinkhole and Sinkhole Area Treatment Code 527 or contact your local NRCS office.
See the following publications from the Kentucky Cooperative Extension Service: Assessingand Reducingthe Risk of Groundwater Contamination from Petroleum Product Storage  BMP #4: Sinkholes  Household Waste Management: Hazardous Waste  Household Waste Management: Recycle  On-Farm Composting of AnimalMortalities  On-Farm Disposal of Animal Mortalities  Vegetative Filter Strips for Livestock Facilities 
Field Evaluation of Container Nursery Irrigation Systems: Measuring Uniformity of Water Application of Sprinkler Systems1
 Dorota Z.
Haman and Thomas H.
Yeager
 One may ask: Why should I be concerned with the uniformity of my irrigation system?
Why is it important to maintain high uniformity?
This is important because high uniformity signifies that all the plants in the irrigated zone will receive almost the same amount of water in a given time.
For sprinkler irrigation, it means that the depth of water application throughout the entire irrigated area is about the same.
Consequently, uniform water application is necessary to maximize the efficiency of water use in the nursery and save water.
Low uniformity in sprinkler systems can be due to numerous factors, such as:
 Inadequate selection of delivery pipe diameters.
Too high or too low operation pressure.
Inadequate selection of sprinkler heads and nozzles.
Wind effects on water distribution.
Changes in system components with time, such as changes in pump efficiency, pressure regulation, or nozzle size.
There is a simple method to evaluate the uniformity of irrigation and the test should be performed at least once a year.
The uniformity may change with time, and often simple repairs or changes can improve system performance.
Nursery Evaluation of Sprinkler Irrigation Uniformity
 Uniformity of water application with sprinkler irrigation systems is often reported as Distribution Uniformity.
It is an indicator of how equal  the application rates are in the nursery.
A low DU  indicates that application rates are very different, while a high DU  indicates that application rates over the area are similar in value and the water is distributed evenly to all the plants.
Distribution Uniformity is based on the low quarter of the irrigated area.
The calculation of DU requires that the catch-can test be performed in the irrigation zone.
The following is an example of the catch-can test.
In Figure 1, 16 straight-sided catch cans have been placed in the irrigation zone.
The depth of water collected in these cans after running the system for one hour is presented below each can.
The average application rate in this zone is
 2.
Dorota Z.
Haman, professor emeritus, Department of Agricultural and Biological Engineering; and Thomas H.
Yeager, professor, Environmental Horticulture Department; UF/IFAS Extension, Gainesville, FL 32611.
the average depth collected in the cans and is equal to 0.8 in/hr.
/ 16 = 0.8 in/hr
 0	0	0	0
 0.7	0.8	0.9	0.6
 O	O	0	O
 0.8	0.7	0.9	0.7
 O	O	O	O
 1.0	0.8	0.8	0.9
 O	O	O	O
 1.0	0.8	0.9	1.0
 Figure 1.
Straight-sided catch cans are spaced in a square grid pattern between four sprinklers.
The number below each circle represents the depth of water caught in one hour at that location.
Now, to calculate Distribution Uniformity, the lowest onefourth or quarter of the measurements from our example are selected.
The other value we must know is the average depth of application during the test which was calculated above.
DU =  X 100%
 For the application rates presented in Figure 1.
Average low quarter depth =  / 4 = 0.7 in/hr
 DU = 0.7 / 0.8 X 100% = 87.5%
 For high value crops, such as container-grown nursery plants, it is recommended that the DU be greater than 80%.
When DU falls below the acceptable value, system repairs and adjustments should be performed as soon as possible.
Two Soil Health Nexus members, Francisco Arriaga, Associate Professor and Extension Specialist at the University of Wisconsin-Madison, and Anna Cates, Assistant Professor and State Soil Health Specialist at the University of Minnesota, recently published a long-awaited whitepaper exploring the connection between soil health and water quality.
Variable rate irrigation or VRI is the ability to spatially vary water application depths across a field to address specific soil, crop, and/or other conditions.
This technology has many potential uses that might enhance farm profitability, irrigation water productivity , and water quality.
Scheduling Tips For Drip Irrigation of Vegetables
 Florida's sandy soils are well known for their inability to hold water.
Very little water is stored in the root zone, and excessive water applications result in the loss of mobile nutrients such as nitrogen, due to deep percolation.
These soil properties require precise irrigation scheduling to avoid unnecessary loss of water and nutrients while providing a sufficient amount of water for optimum plant growth and production.
The available water in typical Florida sandy soils is approximately 6%.
For shallow-rooted vegetable plants  and 24 inches wetted along the drip line, the 6% moisture content translates to the number of gallons presented in the second column of Table 1.
A general rule for vegetable irrigation, is to provide irrigation before 50% of this water is used in order to avoid plant stress.
Drip irrigation offers the possibility of frequent water application.
Frequent, low-volume application allows the soil moisture content in the root zone to be maintained near the optimal levels.
If possible, 33% depletion should be used for scheduling drip irrigation.
This requires frequent , short water applications.
The amounts of water to be applied and the times to run the irrigation system at 33% and 50% depletion levels are shown in Table 1.
These calculations were done for a drip tape discharging 0.5 gallons per minute  per 100 feet of row length.
For example, to irrigate a 1-ft root depth at a 33% depletion level requires 30 gal/100 ft per application, and the irrigation duration is 1 hour.
If the tape discharge rate is not 0.5 gpm/100 ft, the irrigation duration can be calculated as follows:
 Multiply the tape discharge rate by 2.
Divide the duration of irrigation time in Table 1 by this value.
For example, if a drip tape with a discharge rate of 0.3 gpm/100 ft is used, for previous example, then divide the 1 hour irrigation duration read from Table 1 by 0.6.
The result is 1.67 hours or 1 hour and 40 minutes.
Remember, frequent, short irrigations  are always better than infrequent and long irrigation cycles.
Tensiometers should be used to monitor soil moisture and avoid water stress to the plants.
They are relatively inexpensive and have been proven to be very reliable in Florida's sandy soils.
However, they must be serviced regularly and placed in the active root zone of the plants to function properly.
For most vegetables, it is recommended that irrigations be scheduled when the tensiometer reading reaches 10 cbars for a tensiometer placed at the 6-inch depth.
For typical Florida sandy soils, this corresponds to 50% water depletion.
A reading of 7-8 cbars is approximately a 33% depletion.
Image 3.
The collapse site above Tunnel No.
2 on the Goshen/Gering-Fort Laramie supply canal, as it appears in the summer of 2021, two years after the collapse.
Subsequent repairs allow the tunnel to carry 97% of the previous maximum capacity.
CORN YIELDS AND PROFITABILITY FOR Low-CAPACITY IRRIGATION SYSTEMS
 ABSTRACT.
In many areas of the central U.S.
Great Plains irrigation well capacities are decreasing due to declines in the Ogallala aquifer.
Many producers using furrow surface irrigation are faced with a decision on whether they should convert to a higher efficiency center pivot sprinkler irrigation system.
An irrigation scheduling model using 27 years of climatic data for western Kansas was combined with a corn yield production function and economic model to simulate crop yields and economics under four combinations of irrigation system and application efficiency for six different irrigation capacities.
Center pivot sprinkler irrigation systems were found to give higher corn yields and greater profitability than furrow surface irrigation, particularly when system flow rates were less than 40 L/s.
Sprinkler irrigation systems with application efficiencies of 100, 95, and 85% and a furrow surface irrigation system with 70% application efficiency produced simulated crop yields of 12.3, 12.2, 12.1, and 11.3 Mg/ha, respectively, when irrigation capacity was 6.35 mm/day.
Reducing the irrigation capacity to 2.54 mm/day reduced yields to 9.4, 9.2, 8.9, and 8.3 Mg/ha for the respective irrigation systems.
Net annual returns for a 65 ha field were increased by US$1000 to $4000 with center pivot sprinkler irrigation compared to furrow surface irrigation for system flow rates between approximately 20 and 40 L/s.
Labor savings with sprinkler irrigation are a significant factor in profitability, but increased crop yields are also very important, particularly at lower system flow rates of approximately 20-30 L/s.
Keywords.
Irrigation scheduling, Irrigation economics, Crop production functions.
T he profitability of converting from furrow surface irrigation to a center pivot sprinkler irrigation system in the U.S.
Great Plains depends upon a number of engineering, agronomic, and economic factors.
The most commonly considered elements in this decision are purchase and installation costs of the new sprinkler system, expenses of potential renovations on the existing pumping plant, changes in irrigated crop area, and potential labor savings.
However, other elements often are overlooked in this investment decision due to lack of reliable information.
The most important overlooked element is the yield differential between the furrow surface and the center pivot sprinkler irrigation system.
Crop yield potential for the alternative systems is heavily dependent on the net system irrigation capacity, which is determined by the system flow rate, application efficiency, and irrigated area.
Other
 Article was submitted for review in June 2000; approved for publication by the Soil & Water Division of ASAE in January 2001.
Contribution No.
00-454-J from the Kansas Agricultural Experiment Station.
overlooked elements include long-run expectations of crop prices, irrigated production cost differences for the two systems, and tax deductions for related depreciation and interest expenses for the investment in the center pivot sprinkler irrigation system.
Previous studies have indicated that a strong trend exists among irrigated crop producers in the Great Plains region to convert to more efficient irrigation systems and to adopt more water-efficient cropping systems in response to declining groundwater supplies , 1996; Council for Agricultural Science and Technology , 1996; Lee et al., 1985).
However, results vary in the Great Plains and other regions regarding which type of irrigation system is most profitable to use.
Letey et al.
found under California growing conditions that surface gravity flow systems were more profitable than pressurized irrigation systems when there was no constraint on the amount of drainage water generated or cost for its disposal.
Conversely, when irrigation drainage water constraints and water disposal costs were accounted for, pressurized irrigation systems became more profitable.
Wichelns et al.
examined the economic viability of alternatives to siphon tube irrigation systems in California's San Joaquin Valley.
They found that savings in water use from gated pipe and manually moved sprinkler systems was outweighed by the added energy and labor costs those systems entailed.
In a comparison of low energy precision application , drip, sprinkler, and furrow irrigation systems under Texas conditions, Hall et al.
found that LEPA sprinkler irrigation systems were the most profitable.
However, Lee et al.
found that converting from furrow
 surface to LEPA center pivot sprinkler irrigation systems was less profitable than improving the application efficiency of existing furrow surface systems.
The study focused on cost of production and investment impacts of alternative irrigation systems and application efficiencies, but did not account for potential effects upon irrigated crop yields.
Dhuyvetter  indicated that conversion from furrow surface to low-pressure center pivot sprinkler systems was profitable assuming cost and production factors common in Kansas.
Some important assumptions in that analysis were that corn yields were equal under irrigation for both systems, but 51 ha of irrigated corn was produced with a full-sized center pivot sprinkler system whereas only 32 ha of irrigated corn were produced under furrow surface irrigation when the flow rate for both systems was 38 L/s.
Williams et al.
concluded that surge and furrow surface irrigation systems were more profitable than LEPA sprinkler or low-pressure center pivot sprinkler systems for 50-L/s capacity.
Full 65-ha irrigation-cropping systems were used for surface irrigation as opposed to 51 ha for center pivot sprinkler irrigation with the corners of the 65-ha field in dryland cropping systems.
Yields of irrigated corn and grain sorghum were calculated with a crop yield model.
Improved furrow irrigation system application efficiencies were estimated to range from 65% for conventional furrow surface to 75% for surge furrow surface irrigation.
In comparison, water application efficiencies of unimproved and less well-managed furrow irrigation systems often fall as low as 50 to 60% in the Great Plains region.
An 85% application efficiency was used for the low-pressure center pivot sprinkler irrigation system.
The LEPA center pivot sprinkler irrigation systems were assumed to have 95% application efficiency.
Such systems typically use suspended low drift spray or bubbler nozzles to apply water in-canopy at heights of 0.3 to 0.6 m above the ground.
Delano et al.
also found that it was not profitable to convert from furrow surface to low in-canopy center pivot sprinkler systems with either 35or 60-L/s well pumping capacities.
The sensitivity analysis indicated that for conversion to low in-canopy center pivot sprinkler systems to be profitable, existing furrow surface systems had to either have very low application efficiency, sprinkler-irrigated corn yields had to be substantially higher than those for furrow surface irrigation, sprinkler investment costs had to be reduced, or deficit irrigation was not a desired option.
The study also showed that when producer's options were furrow irrigating 63 ha or sprinkler irrigating 51 ha with 35-L/s pumping capacity wells, switching to center pivot sprinkler irrigation was profitable.
Strickland and Williams  analyzed optimal irrigated area and crop mixes for a low in-canopy center pivot sprinkler system with a 25-L/s capacity.
They found that growing irrigated corn or grain sorghum on a full-sized 51-ha center pivot sprinkler system was more profitable than reducing the irrigated area to allow increased water application.
In summary, earlier studies produced mixed results regarding the profitability of shifting from furrow surface to center pivot sprinkler irrigation systems.
Those studies that found the transition to be unprofitable were affected by the high initial investment costs for the center pivot sprinkler irrigation systems and/or moderate-to-high irrigation
 pumping capacities that resulted in approximately equal crop yields for the two systems.
This study was conducted to analyze the profitability of converting from furrow surface to center pivot sprinkler irrigation systems as affected by system flow rate  for typical square 65-ha fields.
The expected irrigated corn yields at various system flow rates were determined.
This analysis assumed that a crop producer with a typical, square, furrow surface-irrigated 65 ha of farmland was determining whether or not to convert to a center pivot sprinkler irrigation system.
The existing furrow surface irrigation system covers 65 ha of irrigated corn and is assumed to have an improved application efficiency of 70%.
The center pivot sprinkler irrigation system covers 51 ha of irrigated corn.
The remaining 14 ha in the corners of the 65-ha field will no longer be irrigated, but instead are placed in a dryland wheat-corn-fallow rotation.
Alternative application efficiencies of 85, 95, and 100% for the center pivot sprinkler irrigation system were examined.
The 100% application efficiency is impossible to achieve but serves as a theoretical upper boundary for the purposes of this economic analysis.
Irrigation water budget schedules were simulated for the 1972-1998 period using climatic data from the Kansas State University  Northwest Research-Extension Center in Colby, Kansas.
The continental climate can be described as semi-arid with an average annual precipitation of 474 mm and approximate annual lake evaporation of 1400 mm.
The alfalfa-based reference evapotranspiration  was calculated using a modified Penman combination equation similar to the procedures outlined by Kincaid and Heermann.
The specifics of the ET1 calculations used in this study were described fully by Lamm et al..
Basal crop coefficients  were generated with equations developed by Kincaid and Heermann  based on work by Jensen  and Jensen et al..
The basal crop coefficients were calculated for the region by assuming 70 days from emergence to full canopy for corn and physiological maturity at 130 days.
This method of calculating actual crop evapotranspiration  as the product of Kcb and ETr has been acceptable in past studies at Colby.
In constructing the irrigation schedules, no attempt was made to modify ET with respect to soil evaporation losses or soil water availability as outlined by Kincaid and Heermann.
Irrigation was scheduled as needed by the crop, but was limited to the frequencies for the furrow surface and the center pivot irrigation systems.
The initial soil water at the beginning of each season was assumed to be at 85% of the maximum plant-available soil water  in the 1.52-m soil profile.
Bidwell et al.
describes in more detail the medium-textured, deep, well-drained, loessial, Keith silt loam , typical of many High Plains soils.
The 1.52-m soil profile will hold approximately 370 mm of PAW at field capacity.
The irrigation season was limited to the 90-day period between 5 June and 2 September.
The first furrow surface
 Table 1.
Equivalent irrigation frequencies and flow rates for center pivot sprinkler and furrow surface irrigation systems.
Gross	Center Pivot Sprinkler	Furrow Surface
 Irrigation	Flow Rate	Flow Rate
 Capacity	Frequency and	(L/s for	Frequency and	(L/s for
 	Application	51 ha)	Application	65 ha)
 6.35	25 mm in 4 days	37	76 mm in 12 days	48
 5.08	25 mm in 5 days	30	76 mm in 15 days	38
 4.24	25 mm in 6 days	25	76 mm in 18 days	32
 3.18	25 mm in 8 days	19	76 mm in 24 days	24
 2.54	25 mm in 10 days	15	76 mm in 30 days	19
 irrigation event in each year was on 15 June, reflecting a typical date of the first irrigation following the final furrowing process.
After that, furrow irrigation events were scheduled as the irrigation system capacity limitation allowed and if the calculated soil water deficit exceeded 76 mm.
Center pivot sprinkler irrigation events were scheduled as the system capacity limitation allowed and if the calculated soil water deficit exceeded 25 mm.
The root zone management depth was held constant over the entire season.
The daily water budget included effective precipitation  and irrigation  as deposits and ET and drainage  as withdrawals.
Effective rainfall for corn grown in this region was assumed to be 88% of the rainfall amount as used by Stone et al..
An overall limit on daily effective rainfall was set at a maximum of 57 mm to handle the occasional extreme events that occurred over the 27-year period.
Amounts in excess of this maximum amount were discarded from the analysis as runoff.
Daily drainage  from the soil was calculated as a function of profile water content using a drainage equation developed for the 1.52-m soil profile of the Keith silt loam soil at Colby, Kansas:
 D = -24.5 25.39 
 where total soil water  including plant available and unavailable soil water was expressed in mm, and D was expressed in mm/day.
The procedure to characterize drainage rates from the soil using equations of this type was discussed thoroughly by Miller and Aarstad.
Irrigated corn yields for the various alternative irrigation systems and irrigation capacities were simulated for the same 27-year period using the cumulative seasonal ET estimates from the irrigation schedules and a yield production function developed by Stone et al..
For the yield functions, the daily ETc values were modified to reflect any water stress imposed by lower soil water availability.
This soil water availability coefficient  as outlined by Hanks  was calculated conditionally using locally derived factors as:
 If PAW > 70% maximum PAW then K = 1 
 If PAW < 70% maximum PAW then K = PAW /  
 Many functional forms for K have been proposed  and many researchers have used a lower limit of PAW of 0.5 before allowing K to change when using this functional form.
However, data from Lamm et al.
suggests that the traditional 0.5 cutoff is too low for these soils.
Allowing a deep-rooted corn crop to extract
 water to 50% for a deep profile  does not occur without reducing the maximum potential ETc
 An additional potential weighting factor  was used to reflect the effect of water stress on corn yields during particular growth stages.
WFp was 0.36, 0.33, 0.25, and 0.06 for the vegetative , flowering , seed formation , and ripening  growth stages, respectively.
The actual weighting factor  for a particular growth stage was determined by multiplying WFp by the average of all daily K during the period.
Wfai values for all four periods were then added together to reflect the fraction of maximum yield.
The overall yield production model was
 Y = X 
 with yield  expressed in Mg/ha and cumulative seasonal ETc in mm.
Stone et al.
discussed in detail the weighting factors and their application to the model.
Cost projections from Kansas State University and irrigation industry were used to estimate the purchase cost of a sprinkler irrigation system.
The total cost of the full-sized 51-ha center pivot sprinkler system was projected to be US$45,209, including the standard seven towers with low in-canopy nozzles on drops, underground pipe from the field edge to the center pivot point, electrical wiring and connectors, and an electric generator.
The total system and pump modification costs were US$49,709.
The Modified Accelerated Cost Recovery System  150% Declining Balance method  of the U.S.
Internal Revenue Service was used to calculate tax depreciation on the purchased center pivot sprinkler irrigation system and pump modification costs.
Both principal and interest payments were calculated for a 5-year amortized note at 9% interest, with
 Table 2.
Capital requirements for a center pivot sprinkler irrigation system.
Item			
 Standard 7 tower center pivot
 System base price	402	28,000
 Low pressure spray heads	2,400
 20 cm underground pipe	402	8.26	3,326
 Electrical wiring	402	6.23	2,508
 Total cost of center pivot system	45,209
 Pump modification cost	4,500
 Total system & pump cost	49,709
 the total payment for each of the 5 years equaling US$12,780.
The combined federal , state , and self employment  tax rate used here was 36.30%.
This same combined total tax rate was used in the final after-tax profitability calculations.
assumed to be unchanged by the switch to a center pivot sprinkler irrigation system.
The time period for this analysis was 15 years, which is a conservative approximation of the expected life span of a newly purchased center pivot sprinkler system.
No inflation or deflation in crop prices or input costs was assumed during the 15-year period for the baseline analysis.
The yield results are presented as the average of the 27 years of simulation.
The net returns are presented using a cash flow analysis.
All computations were made in spreadsheet templates.
Simulated irrigation schedules and the corn yield model were used to generate estimates of the irrigation application requirement and corn yields for the various irrigation systems and capacities for each year during the 1972 through 1998 period.
Center pivot sprinkler irrigation systems with application efficiencies of 95 and 100%  and a capacity of 25 mm/4 days applied nearly the full irrigation requirement  in most years.
As a result, average corn yields were approximately equal  for this capacity and fully irrigated conditions.
Similar maximum and minimum yield ranges were also obtained for these two capacities.
Average corn yields dropped slightly  for the sprinkler system at 85% application efficiency  with a capacity of 25 rmm/4 days.
A larger yield reduction occurred for the 70% efficient furrow surface irrigation system  at an equivalent irrigation capacity , resulting in an average yield of 11.3 Mg/ha.
Average irrigation requirements for FS70 were 518 and 429 mm, respectively, for full irrigation and the 76-mm/12-day irrigation capacity.
Table 3.
Irrigation application amounts and irrigated corn yields at the indicated gross irrigation capacity.[a]
 6.35 mm/day	5.08 mm/day	4.24 mm/day	3.18 mm/day	2.54 mm/day	Full Irrigation
 Depth	Yield	Depth	Yield	Depth	Yield	Depth	Yield	Depth	Yield	Depth	Yield
 											
 Center Pivot Sprinkler System at 100% application efficiency on 51 ha 
 Average	338	12.3	305	11.9	272	11.2	218	10.2	183	9.4	353	12.4
 Std deviation	99	2.7	79	2.3	61	1.9	43	1.5	30	1.4	107	2.8
 Maximum	508	16.4	432	16.1	356	14.7	279	12.0	229	11.2	533	16.8
 Minimum	127	7.0	127	7.0	127	7.0	102	6.7	102	6.0	127	7.0
 Average	351	12.2	312	11.8	277	11.1	221	10.0	183	9.2	371	12.4
 Center Pivot Sprinkler System at 95% application efficiency on 51 ha 
 Std deviation	102	2.6	79	2.2	61	1.8	43	1.4	30	1.4	114	2.8
 Maximum	508	16.4	432	15.8	356	14.2	279	11.9	229	11.2	559	16.8
 Minimum	127	7.0	127	7.0	127	7.0	102	6.5	102	6.0	127	7.0
 Center Pivot Sprinkler System at 85% application efficiency on 51 ha 
 Average	371	12.1	328	11.4	290	10.7	229	9.6	188	8.9	419	12.4
 Std deviation	99	2.4	74	1.9	53	1.6	41	1.4	30	1.4	130	2.8
 Maximum	508	16.3	432	15.0	356	13.2	279	11.8	229	11.2	635	16.8
 Minimum	152	7.0	152	7.0	152	6.9	127	6.2	102	5.8	152	7.0
 Furrow Surface Irrigation System at 70% application efficiency on 65 ha 
 Average	429	11.3	378	10.5	338	9.9	277	9.0	221	8.3	518	12.4
 Std deviation	97	1.9	79	1.6	61	1.4	43	1.4	25	1.4	157	2.8
 Maximum	533	14.9	457	13.2	381	11.9	305	10.8	229	10.5	762	16.8
 Minimum	152	7.0	152	16.8	152	6.5	152	5.9	152	5.6	152	7.0
 [a] Based on 1972-1998 climatic conditions at the Northwest Research Extension Center in Colby, Kansas, and on the Stone et al.
corn yield prediction model.
As gross irrigation system capacities declined further, the projected yields for each of the four irrigation systems also declined.
However, the higher application efficiencies for CP95 and CP100 resulted in higher yields and less total water pumped for a given irrigation capacity.
As irrigation capacity becomes more and more limited, there is less chance for natural rainfall and soil water reserves to buffer the crop through the stressful period.
In addition, the 30-day frequency for the lowest examined irrigation capacity for FS70 leaves the crop vulnerable to water stress for a long period of time as compared to the sprinkler irrigation systems.
As irrigation capacity decreased, the range  in crop yields was generally less across the 27-year period.
This reduction in yield variation was because less opportunity existed for lower irrigation capacity systems to compensate for higher irrigation needs in crop years that might otherwise be considered favorable to good yields.
Corn yields also were simulated for full irrigation.
Adequate irrigation water was supplied to meet the crop's evapotranspiration needs without potential timing delays caused by inadequate irrigation system capacity.
The analysis showed that if full irrigation were possible for all three systems, equal corn yields of 12.4 Mg/ha would be obtained.
The average full irrigation requirement would be 353, 371, 419, and 518 mm for the CP100, CP95, CP85, and FS70 systems, respectively.
Quadratic relationships between corn yields and pumping capacity were generated for each alternative irrigation system-application efficiency scenario.
Linear effects in these corn yield equations were all positive and statistically significant at the 0.01 probability level.
In addition, the quadratic effects were all negative and statistically significant at the 0.01 level.
Taken together, these results indicate that corn yields increased at a decreasing rate in response to increases in irrigation pumping capacity.
Notable differences existed among irrigation systems across the range of irrigation capacities.
Corn yields were 1.3-1.9 Mg/ha less for FS70 than for the center pivot sprinkler irrigation systems.
These equations can be used by producers to project long-term yields for a given irrigation capacity and to allocate area for irrigated and dryland cropping.
The equations also can be used as guides to yield potential in allocation decisions related to input resources such as seed and fertilizer.
The quadratic relationships between annual, average, after-tax, net returns to land and management and irrigation
 Table 4.
Regression equations and statistics for irrigated corn yields  as related to irrigation system type and flow rate.
Efficiency	Regression Equation[a]	R2	
 sprinkler 	Y = 0.005677 0.4298 F + 4.2 0.999	0.04
 sprinkler 	Y 0.005298 F2 + 0.4149 F + 4.1 0.999	0.06
 sprinkler 	Y 0.004068 F2 + 0.3582 F + 4.4 0.999	0.05
 	Y = 0.001545 F2 0.2069 F + 4.9 0.999	0.04
 [a] Yield  in Mg/ha and flow rate  in L/s.
Figure 1.
Irrigated corn yields as affected by irrigation system type, capacity, and application efficiency.
capacity also were estimated for each of the four irrigation systems.
Similar to the grain yield models, the signs of all of the linear effects in these net revenue equations were positive, and each linear effect was statistically significant.
In addition, the quadratic effects of these net returns models were all negative and statistically significant at the 0.01 level.
Together, these results indicate that annual, average, after-tax, net returns increased at a decreasing rate in response to increases in irrigation pumping capacity.
The results indicate that across this range of low irrigation capacities, it was profitable to convert from FS70 to center pivot sprinkler irrigation systems with 85% or greater application efficiencies.
For example, at 19 L/s pumping capacity for the full 65 ha area, annual net returns to land and management with the FS70% system were US$1,953, US$3,409, and US$3,929 lower than those for the CP85%, CP95%, and CP100% systems, respectively.
For wells with 38 L/s pumping capacity, net returns for the FS70% system were US$1,029, US$1,809, and US$2,059 lower than those for the CP85%, CP95%, and CP100% systems, respectively, for the full 65-ha area.
These results indicate that the advantage for converting to center pivot sprinkler systems was greater at lower capacities, and declined as well pumping capacity increased.
The curvilinear nature of the equations indicates that converting from furrow
 Table 5.
Regression equations and statistics for annual net returns  from a 65-ha field as related to irrigation system type and flow rate.
Efficiency	Regression Equation	R2 
 Center pivot	NR = 14.434 F2 + 1065.60 F
 sprinkler 	9012	0.999	101
 Center pivot	NR = 13.322 F2 + 1016.62 F
 sprinkler 	9003	0.999	127
 sprinkler 	NR = 9.969 F2 + 854.76 F 8378 0.999	109
 	NR = 4.347 F2 + 591.61 F 7584 0.999	103
 [a] Annual net returns  in US$ for a 65 ha field and flow rate  in L/s.
Figure 2.
Annual after-tax net returns  for a 65-ha field as affected by irrigation system type, capacity, and application efficiency.
surface to center pivot sprinkler irrigation systems may become unprofitable at irrigation system capacities of approximately 45 L/s or more.
The finding that converting from furrow surface to center pivot sprinkler systems was profitable is consistent with conclusions of Dhuyvetter , but contradicts the general conclusions of Letey et al.
, Williams et al.
, and Delano et al..
However, Delano et al.
also found that such conversions were profitable when producers were forced to cover either 63 ha with furrow surface or 51 ha with low in-canopy center pivot sprinkler systems at 35-L/s flow rates.
In this study, labor expenses were reduced and profits were increased by switching from furrow surface to center pivot sprinkler irrigation systems.
Labor costs for center pivot sprinkler-irrigated cropping systems were projected to be lower  than those for furrow surface irrigation  for the full 65 ha.
Including labor costs in this analysis resulted in lower net returns for furrow surface irrigation relative to center pivot sprinkler system returns.
Williams et al.
, Delano et al.
, and Wichelns et al.
each included labor costs in their analyses.
The latter two studies discussed how constraints on labor availability could be determining factors in the decision to convert from furrow surface to center pivot sprinkler irrigation systems.
However, this study shows that reduction in crop yields for the furrow surface irrigation system with lower application efficiency is also a contributing factor.
As irrigation capacity decreases, reduction in crop yields becomes an increasingly dominant factor in the relative profitability of center pivot sprinkler systems.
This study showed that as irrigation system capacity declines below moderate levels, it becomes more profitable to convert to center pivot sprinkler irrigation than to continue to use furrow surface systems.
These findings are dependent upon assumptions about irrigation system investment costs, irrigated corn yields, crop production costs, and crop prices.
The results hold true in spite of irrigators having to pay principal and interest costs for the debt associated with the purchase of the center pivot sprinkler irrigation system and pump modification costs and having to revert 14-irrigated ha to an intensive dryland cropping system.
Decreased irrigation capacity has negative effects upon both the production and the profitability of an irrigated corn enterprise.
Average yield estimates for irrigated corn under furrow surface irrigation with 70% application efficiency were reduced appreciably  as irrigation well capacity declined from 44 to 19 L/s for a 65-ha field.
Average yield estimates for irrigated corn decreased from 12.2 to 9.2 Mg/ha as irrigation capacity declined from 38 to 13 L/s for a 51-ha center pivot sprinkler-irrigated field with 95% application efficiency.
In response to declining irrigation capacity, crop producers typically reduce the irrigated area to the level for which they can still provide adequate water for crop growth.
Further analysis might determine how irrigated corn yields and cropping system profitability respond to decreases in irrigated area as irrigation capacity declines, given the climate of the region.
The associated economic analysis would be driven primarily by changes in irrigated corn yields and declines in irrigated area as producers seek to find the most productive and profitable irrigated area given their limited water pumping capacities.
These findings support the claims of irrigators that labor savings at least partially motivate the decision to convert from furrow surface irrigation to center pivot sprinkler irrigation systems.
However, this analysis suggests that actual corn production levels attained with furrow surface irrigation are also very important, particularly for low system flow rates that cannot adequately supply corn water needs.
Additionally, at very low system flow rates, the infrequency of furrow surface irrigation events may increase crop vulnerability to water stress.
.
1999b.
Flood irrigated corn cost-return budget.
KSU Farm Management Guide.
MF-578.
K-State Research and Extension, Kansas State Univ., Manhattan, Kans.
1985.
Corn yield response to different irrigation regimes.
ASAE Paper No.
MCR85-131.
St.
Joseph, Mich.: ASAE.
Irrigated Pastures in Arizona
 Michael Ottman and Ashley Diane Wright
 Salt and Mineral Supplements
 Animal Disorders Caused by Forages
 APPENDIX I Plant Species Descriptions
 APPENDIX II Rotational Stocking Calculations
 A pasture is a parcel of land sown to low growing plants suitable for grazing by animals.
The plants could be grasses and/or legumes.
Pastures may be intended for only a single cropping season or, more typically, are more permanent in nature and based on perennial plant species although annual plant species may be over-seeded into a permanent pasture.
The animals that graze pastures may include cattle, horses, sheep, and goats.
Irrigated pastures are used as a convenient way to feed livestock without the labor, expense, and equipment required to harvest forage particularly for small farms.
Most pastures in Arizona are not productive without irrigation and tend to be intentionally seeded with particular plant species, which will be the focus of this publication.
Before establishing a pasture, the goals and feasibility of the project should be seriously considered.
For example, is the goal of the pasture to provide all or just some of the feed requirement for livestock, a holding area, an exercise lot, or a safe place during breeding and while giving birth.
All these goals can be achievable, but it is difficult for pastures to provide all the feed requirement of livestock due to the seasonal nature of pasture plant growth.
For the number of animals a pasture can support  see the "Carrying Capacity" section in this publication.
The feasibility of establishing and maintaining a pasture depends on the site characteristics, available equipment and resources, and the ability to commit the time required.
Successful pastures are planted on deep well-drained soil with adequate water-holding capacity.
The area is usually fenced and divided into smaller sections for the purposes of moving animals, or at the very least, an area needs to be provided for the animals when the soil is too wet to tolerate animal traffic.
The most important resource is the availability of irrigation water of sufficient quality for growing plants, and a method for applying the water through surface or sprinkler irrigation.
Necessary equipment includes a tractor capable of pulling tillage equipment, a fertilizer spreader or a way to inject the fertilizer into irrigation water, a mower to knock down weeds and non-palatable forage, a harrow to distribute manure, a sprayer for weeds, and possibly a swather and baler to make hay in cases where the animals are not able to graze all the available forage.
Well-managed pastures are preferably inspected daily and at a minimum, a few days a week.
The number of animals and their specific feed requirements must be determined.
For an excellent discussion of pasture resources, goals, and planning see Williams and Baker.
Figure 1.
Horses grazing bermudagrass pasture in Tucson, AZ.
The typical soil contains the following components by volume: minerals , water , air , and organic components.
The organic components include humus, roots, and organisms.
Humus is a partially decomposed plant and animal matter.
The organic component of soils is primarily in the surface soil to a depth of approximately 6 inches.
The subsoil is beneath the surface soil, has lower organic matter content than the surface soil, and the thickness of this layer may vary tremendously.
Beneath the subsoil is the weathered bedrock.
Various soil characteristics pertinent to pastures are discussed below.
Soil Texture is defined as the relative composition of soil particle sizes classified as sand , silt , and clay.
Coarse-textured soils have a higher percentage of large particles  than fine-textured soils which have less sand and more fine particles.
There are 12 major soil texture classes with varying percentages of sand, silt, and clay and are as follows listed from most to least amount of sand: sand, loamy sand, sandy loam, sandy clay loam, loam, clay loam, silt loam, clay, silt, silty clay loam, and silty clay.
A loam contains mostly sand and silt with a smaller percentage of clay.
Water-holding Capacity Irrigated pastures require a deep soil with adequate water holding capacity.
A deep soil is one that has at least 3 feet of soil below which is weathered bedrock that cannot sustain plant growth.
Soils with adequate water holding capacity are those that can provide plants with enough water to prevent water stress before the next irrigation which is generally 10 to 14 days with flood irrigation and about half that time with sprinkler irrigation.
Infiltration Rate Irrigated pastures require a well-drained soil.
A well-drained soil is one that allows water to infiltrate in at least 24 hours after an irrigation or rain event.
Infiltration rate is affected by soil texture.
Coarse-textured soils have a faster infiltration rate than fine-textured soils assuming the texture is uniform and there are no obstructive layers in the soil.
Abrupt changes in soil texture in the soil profile will slow water infiltration.
Soil texture changes with depth are common with soils in Arizona which are alluvial in nature, meaning the soil was deposited by water from numerous flooding events.
Obstructive layers in the soil can also be found, and most commonly these layers are caliche , a cement-like mixture of calcium carbonate  and clay.
pH, Sodium, and Salt Soil pH is a measure of the acidity of the soil.
Soils may be classified as acidic  or alkaline.
Most Arizona soils are alkaline and do not require pH adjustment but there are exceptions.
Soils
 with pH>8  may have reduced availability of phosphorus and micronutrients , but acidifying these soils is usually not cost effective especially for pastures.
However, soils with a pH above 8.5  definitely need amending because a preponderance of sodium compared to other salts causes the soil to disperse and seal leading to poor water infiltration.
Many Arizona soils are salty  but contain a balance of salts other than sodium such as calcium, magnesium, and potassium that prevents the soil from dispersing as in sodic soils.
Nevertheless, saline soils inhibit plant growth and are amended by leaching of the salts with irrigation water.
Nutrient Content Most Arizona soils contain enough nutrients for plant growth except for nitrogen , phosphorus , and potassium.
Fertilizers can be applied as dry granules or as liquid solutions in the irrigation water.
When applying fertilizer in the irrigation water, be aware that the distribution uniformity of the fertilizer will only be as good as that of the irrigation water.
Also, nitrogen in particular is subject to leaching below the root zone which is more likely on coarse-textured compared to fine-textured soils.
Because nitrogen is subject to leaching it is called a "mobile" nutrient whereas phosphorus and potassium are not subject to leaching and are called "immobile" nutrients.
The organic matter in the soil  are good sources of plant nutrients but especially of phosphorus.
The ability of the soil to provide the nutrients necessary for plant growth can be determined with a soil analysis  by a soil testing lab.
After the previous crop is removed and crop residue incorporated into the soil, land leveling is usually the first step in the seedbed preparation for irrigated pasture to be flood irrigated.
However, land leveling may not be required if sprinkler irrigation is to be used.
After land leveling, the soil should be tilled with a disk, harrow, or other implements.
The goal is to prepare a firm seedbed that can be depressed by your foot by no more than 1/2 inch and is not overworked to a powder.
When earthen dykes  are used along the edges of areas to be flood irrigated, they should be constructed SO that SO that the entire border ridge can be seeded.
Border ridges should be large enough to withstand livestock walking over them.
On sandy soils, earthen dykes may need to be rerun periodically.
Pasture plant species for Arizona are described in Table 1 and Appendix I.
Climate and Elevation The best-adapted pasture plant species for a particular location is influenced by climate, which is determined in Arizona by elevation, primarily.
In this publication, elevation is used as an indicator of plant species adaptation.
Plant Species Classification Pasture plant species can be classified as either grasses or legumes, annual or perennial, and cool season or warm season.
Grasses are resistant to trampling by animals, suppress weeds, and are generally more productive whereas legumes are lower in fiber, higher in protein, and do not need the addition of nitrogen fertilizer.
Pastures are often based on some sort of perennial species for longevity, but annual pastures can be very productive although they do require reseeding each year.
Cool-season species are often recommended for higher elevations over warm-season species.
Pasture Mixes Pasture mixes, when used, should be kept simple, usually consisting of one grass and one legume.
The exception is mixtures of similar species such as found in winter grass pasture mixes.
A mixture of tall fescue and alfalfa is an example of a common and viable pasture mix.
Complex mixtures of grasses and legumes, consisting of 4 or more dissimilar species are not recommended since they are more difficult to manage because species may not mature at similar times.
The type of grazing schedule used determines the plant species and should influence your species choice.
For example, frequent grazing favors grasses over legumes.
Nevertheless, the addition of a legume to a grass will help maintain the animals' nutritional needs through the summer period when nutritional quality of grasses is low.
Dairy cattle have high nutritional requirements to support lactation and are most productive when a fairly high percentage of the pasture mixture consists of legumes.
However, they will still likely require a supplemental concentrate feed  to meet all of their nutritional requirements.
Beef cattle, sheep, and goats have much lower energy requirements and generally do well even when most plants in the mixture are grasses.
A pasture that is mostly alfalfa may be too rich for sheep and some horses.
Horses can do well with an all-legume pasture if they are heavily worked, growing, or lactating, however a grass-legume mix may be more appropriate for overweight or lightly used recreational horses.
Seeding Best results are usually obtained when seeds are planted in pre-irrigated soil with borders in place.
The rate of seeding varies with the method of seeding, and more seeds are required with broadcast methods than when a drill or cultipacker type seeder is used.
One should use the correct amount of seed sown at the appropriate depth.
The goal is to plant seeds about four times as deep as their greatest length.
After planting use light irrigations to keep the surface soil moist to increase germination rates and seedling emergence.
As seedling plants become established, the irrigation interval may be lengthened.
Planting Date The optimum planting date depends on the elevation and whether planting a warm or cool-season species.
For cool-season species, the optimum planting date is August , September , and October.
For warm-season species, the optimum planting date is April  May , and June (>4000
 Lightweight, chaffy seeds may be mixed with rice hulls, or other inert material and drilled to obtain a more uniform distribution.
Some fertilizer spreaders are equipped to plant seeds in this manner.
Grain drills are often equipped with agitators specifically designed for fluffy seed.
Inoculation of Legume Seed Legumes form associations with bacteria in the soil which convert atmospheric nitrogen into a form useable to the plant.
The most effective bacterial strains are specific to the plant species.
Most agricultural areas with a history of alfalfa production contain Sinorhizobium meliloti, a strain specific to alfalfa.
This may not be the case for legume species other than alfalfa, and the seed may be pre-inoculated with the appropriate bacterial strain by the seed company or added as fresh bacteria by the farmer at the time of planting.
If using pre-inoculated seed, be sure the inoculation date is not expired and the seed has not been exposed to high temperatures during storage.
Bacteria that will be used to inoculate seed or self-inoculated seed should be stored at cool temperatures specified on the container and out of direct sunlight.
Plant self-inoculated seed within 24 hours after treatment.
Sprigging Bermudagrass Coastal bermudagrass and other non-seed producing varieties are established by sprigging.
Sprigging should be done as soon as possible after plant parts have been harvested.
Sprigging may be done May through August, but best results are obtained when sprigs are planted in May, after the soil is warm, but before hot weather.
Machine planters may be used to place sprigs in rows 2040 inches apart, with 12-18 inches between sprigs in the row.
Usually, 10-20 bushels of sprigs are used per acre.
For best results, sprigs should be placed with about one inch of the tip remaining above the moist soil surface.
Sprigs may also be spread over the surface of the soil and disked in.
Growth is most rapid when the soil is firmed around the sprigs after the planting operation.
Soil should be maintained in a moist condition until plants are well established.
Herbicides may be used to control weeds after bermudagrass has become established.
Table 1.
Pasture plant species for Arizona and botanical name, adapted elevation, palatability, seeding rate, and seeding depth.
Common name	Botanical name	elevation	Adapted	Palatability	Seeding rate*		Seeding depth	
 Annual  ryegrass	Lolium multiflorum	All	Excellent	30	1/4-1/2
 Barley	Hordeum vulgare	All	Excellent	100	1-1 1/2
 Oats	Avena sativa	All	Excellent	80	1-1 1/2
 Triticale	xTriticosecale	All	Excellent	120	1-1 1/2
 Wheat	Triticum aestivum	All	Excellent	120	1-1 1/2
 Pearl millet	Cenchrus americanus	All	Good	20	1/2-1
 Sorghum**	Sorghum bicolor	All	Good	10	1-1 1/2
 Sorghum X sudan hybrid**	Sorghum bicolor X S.
bicolon var.
sudanese	All	Good	10	1-1 1/2
 Sudangrass**	Sorghum sudanense	All	Good	20	1/2-1
 Meadow bromegrass	Bromus biebersteinii	>3000	Excellent	10	1/4-1/2
 Orchardgrass	Dactylis glomerata	>3000	Excellent	10	1/4-1/2
 Tall fescue	Lolium arundinaceum	>2000	Fair	15	1/4-1/2
 Tall wheatgrass	Thinopyrum ponticum	>2000	Poor	15	1/4-1/2
 Bermudagrass	Cynodon dactylon	<4000	Good	5	1/8 1 1/4
 Blue panicgrass	Panicum antidotale	<4000	Poor	10	1/4-1/2
 Kleingrass	Panicum coloratum	<4000	Good	2-4	1/8 1/4
 Rhodesgrass	Chloris gayana	<4000	Good	10	1/8 1/4
 Alfalfa	Medicago sativa	All	Excellent	20	1/4-1/2
 Birdsfoot trefoil, narrowleaf	Lotus tenuis	>2000	Excellent	5	1/81/4
 Red clover	Trifolium pratense	>2000	Good	10	1/4-1/2
 Strawberry clover	Trifolium fragiferum	>2000	Good	2-4	1/8 1/4
 White  clover	Trifolium repens var.
giganteum	>2000	Excellent	2-4	1/8 1/4
 Crimson clover	Trifolium incarnatum	All	Excellent	20	1/4
 Berseem clover	Trifolium alexandrinum	All	Excellent	15-20	1/4-1/2
 Hairy vetch	Vicia villosa	All	Poor	20-25	1
 Cowpea	Vigna unguiculata	All	Excellent	30	1-2
 Lablab	Lablab purpureus	All	Excellent	15-20	1
 Tepary bean	Phaseolus acutifolius	All	Excellent	60	1
 Seeding rate Double seeding rate if broadcasting seed and half seed rate if species in a mixture.
Sorghum, sorghum X sudangrass hybrids, and sudangrass should not be fed to horses due to possibility of causing cystitis ataxia syndrome.
Kleingrass should not be fed to horses, sheep, or goats due to photosensitization and possible liver damage from saponins in the forage.
Pastures are maintained longer when they are properly managed.
When a seed mixture is used, try to maintain each species in its original proportion.
The management program should plan to use pasture forage when it is high in protein, low in fiber, and prolong the life of the stand.
In practice, the grower usually utilizes plants somewhat later than their point of maximum nutritive value.
This is done to maintain strong plants.
Plants require 17 elements for crop growth.
Three of these elements plants receive from air and water.
The remaining 14 elements are minerals that are provided by soil.
Mineral nutrients are classified by the relative amount in the plant.
Macronutrients are those mineral elements taken up in largest quantities by plants and most commonly deficient in soils for plant growth.
Macronutrients include nitrogen, phosphorus, and potassium and will be discussed below.
Secondary nutrients  are taken up in a moderate amount and micronutrients  are taken up in a small amount.
Secondary and micronutrients are rarely deficient and will not be discussed below.
Pastures often require less fertilization than most crops.
The reason is that grazing animals return as much as 85 to 95% of the plant nutrients they consume in the forage back to the pasture in the form of dung and urine.
The problem is that the dung and urine are not evenly distributed and tend to be concentrated near water sources and shade.
Dung and urine distribution may be more uniform in rotational vs continuous grazing systems which will be discussed in the grazing section below.
Because of the non-uniformity of the nutrient distribution in animal waste, most pastures will require fertilizer application and a soil analysis can help with this decision.
Soil testing labs are listed in Schalau.
Nitrogen Nitrogen is the nutrient element most commonly needed by pasture plants, except for legumes which obtain their nitrogen from the air through a symbiotic relationship with nitrogen-fixing bacteria.
Legumes do not benefit from nitrogen fertilizer but grasses in mixtures with legume will benefit.
Therefore, nitrogen fertilization of pure stands of legumes is not necessary, but the grass component of seed mixtures of legumes and grasses will respond to nitrogen fertilization.
Nitrogen fertilizer is usually applied after animals are removed from the pasture and incorporated with an irrigation in order to stimulate growth for the next grazing cycle.
The
 fertilizer may be applied as a liquid in the irrigation water or broadcast as granules.
When fertilizing with granules, it is important to irrigate as soon as possible after fertilization to prevent fertilizer nitrogen loss from volatilization and foliage burn.
The amount of fertilizer to be applied depends on the anticipated amount of dry matter forage to be removed during a grazing cycle.
Generally, about 30 to 50 pounds of nitrogen is required per are per ton of dry matter forage growth  and 1 ton per acre of forage is equivalent to approximately 10 inches of growth.
Small applications of nitrogen  at planting time is usually necessary to establish the plant before any appreciable growth is evident.
The largest portion of the total annual nitrogen application should be made when the most vigorous growth occurs, usually during the spring and early summer.
For cool season grasses, apply nitrogen again in the early fall to prepare the pasture for growth in the coming cool season.
Vigorous, dark green plants associated with livestock manure or urine spots suggest plants in adjacent areas may be deficient in nitrogen ; however, excessive rates of nitrogen fertilization may result in pasture forage containing toxic amounts of nitrate.
Do not use pastures for at least 2-3 weeks after heavy fertilization with nitrogen because of risks associated with nitrate poisoning.
See "Nitrate Toxicity" section below for more details about this syndrome.
Phosphorus Phosphorus is the second most commonly deficient nutrient.
On phosphorus deficient soils, the yield of legumes and grasses may be increased by phosphate fertilizer application.
The phosphate requirement for several years can be worked into the soil during seedbed preparation.
Phosphate may also be applied on an annual basis after stand establishment.
For these applications, broadcast the fertilizer on the surface of the soil when this operation will not interfere with the pasture management program.
Soil phosphorus tests provide information that is useful in determining optimum levels of phosphate fertilization.
Fertilizer application can influence the makeup of the stand when a mixture of grass and a legume has been planted.
Phosphorus favors legume and nitrogen favors grasses.
Careful attention to fertilizer application practice helps to keep the desired ratio of legume to grass plants.
Potassium Generally, potassium applications have failed to increase the yields of field crops in Arizona.
Soils in Arizona contain clays with high levels of potassium and the ability to provide this potassium to the plant.
It is possible, however, that there are specific locations where applications of potassium may increase dry-matter yield and the potassium content of forage, especially on sandy soils.
Fig.
2.
Vigorous growth spots in a bermudagrass pasture from urine or manure indicating probable soil nitrogen deficiency.
Water may be applied by surface methods or by sprinklers.
For surface irrigation, make certain the soil has been properly leveled before planting, because high spots receive insufficient water and ponding in low spots scalds plants and encourages weeds.
There are many advantages to planting in pre-irrigated, moist seedbed.
Tillage operations during seedbed preparation that follow pre-irrigation help to destroy weeds and allow water to be stored deep in the profile for later use.
Many growers prefer to plant in dry soil and irrigate afterwards.
After the pasture has been seeded, apply several light irrigations to prevent crusting and to keep the soil surface moist during germination.
The frequency of irrigation will be determined by soil type, solar radiation, temperature and other factors, such as humidity and wind velocity.
Avoid erosion, which washes seeds out or covers them too deeply, by adjusting rate of water flow into the field or placing concrete blocks or other obstacles to disperse the water as it enters the field.
Growers often prefer using sprinklers because cost of land preparation is greatly reduced; however, the expense of sprinkler irrigation equipment must be considered.
Sprinkler irrigation is especially effective during stand establishment since frequent, small irrigations can be applied keeping the surface soil wet and avoiding formation of a crust as often occurs with flood irrigation.
Two or three irrigations are usually needed between grazing cycles during the period of active growth.
Less frequent irrigations are required in late fall, winter and early spring when the grasses are dormant.
The irrigation interval for sands or sandy loam soils is much shorter than it is for fine-textured soils due to differences in water-holding capacity.
Irrigation should be scheduled SO the soil will be firm enough to support livestock without injury to plants when the grazing cycle begins.
This helps to avoid soil compaction.
Compacted soils take water slowly, are poorly aerated, and produce less forage.
There is currently no proven method to correct compacted soils in an existing pasture.
A pasture with compacted soil can only be managed to avoid further compaction by making sure the soil is firm before allowing livestock to graze.
Provide readily available water in the soil to the full depth of the root zone to maximize production.
Drought causes severe plant stress, depletes food reserves in the root, and reduces forage production.
To check soil moisture, observe plants carefully and use a soil probe.
Grazing animals complicate irrigation scheduling.
Animals should not be introduced into a pasture if the soil is still too wet and soft from irrigation because soil compaction may result.
Once the animals are allowed to graze, they should be removed before the plants are stressed for water and irrigation
 is required.
In a pasture with paddocks and a rotational grazing system, grazing should be allowed for about 7 days, the animals removed, then the pastured paddock should be fertilized and irrigated.
A second irrigation is applied about 10 days later if plant appearance suggests moisture stress and if moisture depletion is verified by examination of the soil with a probe.
A third irrigation may be needed during the summer, before the next grazing cycle.
All paddocks should be managed the same.
Ideally each paddock is grazed 1 week of each of the 5 weeks if the pasture is divided into five parts.
Modification of a management plan can be done to fit an individual pasture situation.
Temperature, texture of the soil, species of plant, availability of water, month of the year, and other factors will determine the most effective and efficient pasturing and irrigation schedule.
Weeds are rarely a problem in properly managed pastures, but can become an issue if weed sources are not eliminated.
Pastures are vulnerable to weed encroachment due to poor irrigation, fertilization, or grazing practices.
Weeds are undesirable since because they are often innutritious, unpalatable, spiny, or poisonous.
Strategies to manage weeds include:
 1.
Eliminate sources of weed seed
 a.
A reservoir of seed may have built up in the soil.
Before seeding a new pasture, pre-irrigate to germinate any weeds then till the ground to destroy the germinating seedling.
b.
Manure is a source of weed seed.
Do not apply manure to pastures that is not composted.
Do not allow animals into a pasture that have fed on forage that contain weeds.
C.
Plant certified seed which is virtually free of weed seed.
d.
Never allow weeds in a pasture to produce seed.
If necessary, clip pastures after grazing at a blade setting high enough to cut off the developing seed head of the weeds.
e.
Control weeds in adjacent fields and pastures since they can be a source of contamination.
f.
Keep irrigation ditch banks free of weeds to eliminate the chance that seed will fall into the irrigation ditch and be transported via the water into the pasture.
g.
Clean equipment before entering a pasture.
Hay harvesting equipment in particular may be contaminated with weed seed.
2.
Maintain a vigorous stand
 a.
Irrigate to meet the water use demands of the pasture.
Underor over-irrigating can lead to stand loss in dry or wet spots where opportunistic weeds may encroach.
b.
Apply enough fertilizer for optimal growth of the pasture.
C.
Do not overgraze the pasture since doing SO will weaken the stand.
Continuous grazing, where animals are left on a specific paddock for an extended period of time, can lead to weed problems due to preferential grazing of the forage and not weeds.
Rotational grazing is preferred from a weed management perspective.
d.
Do not allow animals to graze a pasture if the soil is still wet from an irrigation or heavy rainfall.
This will lead to soil compaction and a weakening of the stand.
3.
Mechanical control of weeds
 a.
Mowing pastures periodically may be necessary to reduce competition from weeds not grazed by animals and invigorate the pasture by removing old growth near the base of the plant.
Mowing is most effective against broadleaf weeds, does not control prostrate weeds, and may be ineffective against perennial weeds with an established root system.
b.
Weeds may be removed with a shovel if sparsely scattered on small acreages.
C.
Certain woody species such as mesquite can become a problem in pastures, and it is important to remove these species early before they become difficult to control.
4.
Chemical control of weeds
 a.
Chemical control of weeds may be the only option in certain situations.
However, herbicide choices for pastures are limited compared to conventional crops.
Many herbicides that are effective against weeds commonly found in pastures are not registered for use in pastures.
b.
An appropriate herbicide may not be available 1) for controlling weeds in pasture mixtures of legumes and grasses or 2) for controlling grass weeds in a grass pasture.
These problems may be overcome in some cases by applying herbicides in the dormant season of the pasture species if the weeds are actively growing or by applying the herbicide to the weeds only if possible.
Herbicide may be sprayed over the entire field, spot C.
sprayed where infestations are low, or applied with a rope wick to the weeds only.
This method is useful if the weeds are taller than the pasture plants and the herbicide applied is non-selective or will damage the pasture.
d.
When using herbicides, always follow the directions on the label, and be aware of the "waiting period" after the chemical is applied before animals are permitted back on the pasture.
The waiting period may be different for different animal species, horses VS beef or lactating cattle, for example.
For current recommendations concerning the use of herbicides for the control of weeds, contact your Cooperative Extension County Agent.
Several excellent references are available for weeds  and poisonous plants.
Grazing animals can physically damage pasture plants; therefore, the stand should be well-sodded before they are introduced.
Horses in particular can damage pastures rapidly because of their active behavior, larger size, and their ability to graze pasture plants more closely than other classes of livestock.
They also tend to spot graze resulting in an uneven pasture growth.
Grazing animals often leave mature, unpalatable clumps of grass.
Remove these clumps and uneven growth by clipping or with a flail type chopper SO that these areas will not be avoided next grazing cycle.
Do this before weed seed has developed and cut high enough to avoid damage to pasture plants.
Clippings may be raked and placed along fences or on the tops of border ridges.
Livestock may eat these dried plants during the next pasture cycle.
Plants near manure spots may not be eaten by animals.
As these plants become mature, they are still avoided.
Spread manure with a harrow or other suitable implement once or twice each year after animals are removed from the pasture and before irrigation.
After spreading droppings it may be desirable to mow, fertilize and irrigate.
This practice helps reduce parasite loads in pastures.
Worms are spread through fecal contamination of feedstuffs, but are very susceptible to hot, dry conditions.
By spreading manure, parasites are exposed to the sun and manure piles dry out quickly, reducing worm loads on the pasture.
Additionally, moving animals before pastures become short and overgrazed can prevent excessive parasite loads.
Work with your veterinarian to ensure you have a parasite control program.
This may include proper pasture management, multi-species grazing, and use of anthelmintics  at strategic times.
Forage production can exceed what is used by livestock.
The excess may be mowed and left on the soil without windrowing, or a portion of the forage may be used for hay.
Cut when grass seed heads have emerged or when most legume stems have flowers.
Do not leave large quantities of dry forage in the field in windrows for livestock.
The windrows shade plants beneath them and the animals trample plant crowns growing near the windrows.
Remove the forage from the field, fertilize, irrigate, and allow sufficient time for regrowth before pasturing again or making hay.
Plant species composition of the pasture can be affected by grazing frequency.
Most legumes do not tolerate frequent
 grazing.
For example, alfalfa needs a rest period of about 1 month between grazing cycles.
More frequent grazing in a grass/legume mixture will favor grasses which will become more predominant in the mixture.
In addition, bunch grasses are less tolerant of frequent grazing than sod-forming grasses.
Animal Management Pasturing Systems
 There are several options available for managing animals on an irrigated pasture.
The traditional and perhaps most common method is continuous grazing.
Another method which has grown in favor is rotational grazing where a pasture is divided into several smaller paddocks which are grazed intensively in sequence allowing a rest period for each paddock.
Tactical grazing is a combination of continuous and rotational grazing which is a flexible approach that allows the needs of the animals and pastures to be met.
Continuous grazing is the simplest pasturing system and has advantages and disadvantages.
Animals are left on a single pasture for an extended period of time, usually as long as the growing season itself.
This system has modest fencing costs, low management requirements, and produces acceptable results if the stocking rate is correct.
The disadvantages of continuous grazing are that the forage utilization may be uneven, supplemental feed is required if pasture productivity is low, weeds are more likely to become a problem and some forages may not withstand the grazing pressure from this system.
Forage plant species not desired by the animals may go to seed and spread in the pasture while desirable species will be overgrazed and reduced in number leading to a lower quality pasture.
Additionally, a continuously grazed pasture will not support as many animal units as the same pasture divided and grazed rotationally.
Rotational grazing allows pastures or portions of pasture time to recuperate after grazing.
During the recuperation period, the plants are able to increase their leaf area, and some of the sugars produced by the leaves in photosynthesis are transferred to the lower stem, crowns and roots which may be used for plant growth in the next regrowth cycle.
Rotational grazing can be simple or intensive, the difference being the frequency of the movement of animals.
Animals are allowed into a paddock when the plants have achieved a certain amount of growth and removed at a certain stubble height specific to each plant species.
Animals are not allowed back into a paddock until a certain amount of plant regrowth has occurred.
An example rotational grazing system that has worked well in Arizona is to divide a pasture into five paddocks and graze each paddock for a week allowing a recovery period of 4 weeks.
The number of animals supported in this system will depend on the size of each of the smaller paddocks.
The advantage of this system is the forage is consistently newer, high-
 Table 2.
The target plant height to begin and end grazing and the usual rest period between grazing cycles for pasture plant species in Arizona.
Each inch of plant height is roughly equivalent to 200 lb/acre of forage on a dry matter basis, but the actual amount of forage can be half or twice this number depending on growing conditions.
Adapted from Ball et al..
Common name	Begin grazing plant height  End grazing plant height 	Rest between grazing 
 Annual  ryegrass	6 to 12	3	7 to 15
 Barley	8 to 12	4	7 to 15
 Oats	8 to 12	4	7 to 15
 Triticale	8 to 12	4	7 to 15
 Wheat	8 to 12	4	7 to 15
 Pearl millet	20 to 24	8 to 12	10 to 20
 Sorghum	20 to 24	8 to 12	10 to 20
 Sorghum X sudan hybrid	20 to 24	8 to 12	10 to 20
 Sudangrass	16 to 20	6 to 8	10 to 20
 Meadow bromegrass	8 to 12	3 to 4	20 to 30
 Orchardgrass	8 to 12	3 to 6	15 to 30
 Tall fescue	4 to 8	2 to 3	15 to 30
 Tall wheatgrass	8 to 10	3 to 6	20 to 30
 Bermudagrass	4 to 8	1 to 2	7 to 15
 Blue panicgrass	18 to 24	8 to 10	25 to 35
 Kleingrass	12 to 16	4 to 6	20 to 24
 Rhodesgrass	16 to 20	6 to 8	25 to 30
 Alfalfa	10 to 16	3 to 4	20 to 30
 Birdsfoot trefoil, narrowleaf	8 to 10	3 to 5	10 to 20
 Red clover	8 to 10	3 to 5	10 to 20
 Strawberry clover	8 to 10	3 to 5	10 to 20
 White  clover	6 to 8	1 to 3	10 to 20
 Crimson clover	8 to 10	3 to 5	10 to 20
 Berseem clover	8 to 10	3 to 5	10 to 20
 Hairy vetch	8 to 10	3 to 5	10 to 20
 Cowpea	24	6	28 to 56
 Lablab	24	6	28 to 56
 Tepary bean	24	6	28 to 56
 quality growth.
If the pasture productivity is higher, the grazing season may be extended, allowing the producer to rely less on stored feed.
Rotational systems allow for manure to be distributed more evenly and less forage is wasted.
Disadvantages of rotational grazing are more fence needs to be constructed, extra management is required to move the animals, and water and nutrient supplements need to be moved along with the animals or provided in the paddocks where animals are grazing.
Tactical grazing is a flexible system that uses a combination of continuous and rotational grazing.
This system allows the producer to meet specific needs of the pasture and animal during the year.
Continuous grazing may be best during reproductive times of the animal or for finishing livestock for market, or when there is more than enough forage to meet the needs of the animal.
Rotational grazing may be used to increase pasture utilization and growth, control animal intake, or improve the persistence of perennial grasses.
Regardless of the system being used, having a sacrificial "dry lot" area can be of use when environmental conditions  interrupt the planned grazing rotation.
This area is set aside to house all of the animals when grazing would be detrimental to the longevity of the pasture.
Animals are instead provided with supplemental feed , allowing the pasture to rest and recover before grazing is reintroduced.
This "dry lot" area is likely just large enough to comfortably house the animals and will probably not grow forage, nor should it be expected to.
The purpose of this area is to preserve your cultivated pastures when conditions require it, which could occur seasonally or only in extreme circumstances.
Actual carrying capacity during the period of grazing is dependent on many factors.
A well-managed pasture will provide sufficient forage for 1 animal unit equivalent  per acre during its growing season.
An AUE is a 1,000 pound animal or an appropriate combination of animals.
For example, looking at Table 3 we see that a sheep is 0.2 animal units, SO five sheep would be approximately equal to one cow, or one AUE.
In a rotational grazing system, the pertinent acreage is the entire pasture, not the individual paddock being grazed at a particular time.
Pasture growth will vary depending on the species and time of year.
Cool-season species are most productive in early spring where most of the annual growth may occur, production stops in the summer and growth resumes in the fall.
Warm-season species are most productive in the summer but may begin growing in mid-spring or into the fall depending on elevation and temperatures.
Little to no growth of any plant species should be expected in the winter.
Supplemental feed may be required during the dormant
 season when a pasture is not actively growing.
The carrying capacity depends on the type of animal, the amount of forage produced by the pasture, and pasture growth utilization.
Most animals on pasture consume 2 to 3% of their body weight per day in forage dry matter.
This is influenced by the production status of the animal.
For example, nonworking horses and dry beef COWS will consume about 2% of their body weight per day while growing steers and lactating dairy COWS may consume closer to 3% of their body weight per day.
Each inch of height of a pasture plant is roughly equivalent to 200 acre of forage on a dry matter basis , but the actual amount of forage can be half or twice this number depending on growing conditions.
It is important to remember pasture forage is not 100% dry matter but can vary between 20 and 30% dry matter.
Additionally, animals can only utilize 40 to 70% of the pasture growth due to trampling and spoilage from manure and urine.
Utilization tends to decrease with lower stocking rates and longer grazing times.
In rotational grazing systems, it is important to know the usual resting period for a pasture species  and the optimum grazing period in order to calculate the number of paddocks needed.
Lower growing species such as bermudagrass often have a shorter rest period than taller species such as alfalfa.
The range in values for the usual rest period is due to seasonal variation in growth.
In contrast to the resting period, the grazing period is somewhat fixed.
A grazing period of 3 days is considered optimum to prevent grazing of plant regrowth, and a grazing period of 1 day may be even better to optimize forage yield and quality.
However, a 7-day rotational period is often used to reduce the amount of labor required to move animals or fences.
This period is also convenient for producers with another job and may only have the weekend to manage grazing animals.
Calculations for rotational grazing systems can be found in APPENDIXI
 The time of first harvest of a newly established stand or the first harvest of the season, should be delayed until most grass seed heads have emerged or until most legume stems have flowered.
This permits storage of carbohydrates and nutrients in the roots and stems which the plants will rely on during the dormant season.
After the initial harvest, forage should be grazed at or before seed head emergence in grasses and flowering in legumes.
Pasture forage quality decreases as the plants grow and progress through various growth stages.
Early growth is the most palatable and nutritious since it is comprised primarily of leaves.
As plants continue to grow, the proportion of stem to leaves increases and quality decreases because stems are less digestible than leaves.
Once heading or flowering occurs, quality continues to decline to such an extent that the
 nutritional content of the forage becomes unacceptable and may be unpalatable to animals.
Grazing should be terminated in the fall soon enough to permit plants to grow to full bloom, just before their period of inactive growth or dormancy.
Forage may be removed after the plants have become dormant by pasturing or by cutting for hay.
Salt and Mineral Supplements
 Livestock on well fertilized and managed pastures always need salt supplement.
Granular salt is preferred but block salt is often used out of convenience.
If the pasture is grazed after the growing season is finished, one should use a source of phosphorus with the salt since phosphorus concentration is low in mature plants.
This could be 50% salt plus 50% steamed bone meal, or 60% salt and 40% dicalcium phosphate.
A loose mineral supplement may also be necessary, depending on the nutritional quality of your pasture and the production status of your animals.
It is preferable to provide one supplement that meets all of your production needs rather than multiple products to ensure animals are not over or under-consuming.
This is often the more economical approach as well.
Production records can provide data and feedback on animal performance and the success of a grazing and supplement program.
Body condition score, BCS, for cattle , horses , and sheep  can give an indication of production status and general animal health, but sub-clinical mineral deficiencies more often show up as reduced reproductive performance , as well as reduced immune response to vaccinations and increased susceptibility to disease.
Deficiencies can be confirmed through liver biopsies  or blood serum  performed by a veterinarian.
If you provide a loose mineral supplement, be sure it meets the needs of your livestock.
Arizona soils are deficient in selenium and copper, therefore a supplement with added selenium is recommended.
Many "nationally" marketed supplements do not include added selenium because some parts of the country  contend with selenium toxicity from excessive selenium in the soil.
Sheep are susceptible to copper toxicity and should only be supplemented with products specifically labeled for sheep.
Mineral supplement consumption can be altered by adding salt to the mixture or adding a palatable feedstuff such as molasses.
Animal Disorders Caused by Forages
 Bloat Bloat is a condition in ruminants where excessive amounts of gas accumulate in the rumen due to an interruption of normal gas elimination by belching and can lead to death by asphyxiation.
Any plant with highly digestible new growth can cause bloat.
However, bloat is most common with immature growth of legumes, like alfalfa, and when animals are first introduced into a new pasture grazing system.
The higher the percentage of legume species a pasture contains, the greater the chance of bloat.
Maintaining levels of grass other than legume above 50% helps to reduce bloat incidence but does not prevent it.
Bloat can occur in any type of ruminant including cattle, sheep, and goats.
The primary sign of bloat is distension on the left, upper flank of the animal.
Other symptoms of bloat are bellowing and frequent urination and defecation.
There are two types of bloat, frothy bloat and free-gas bloat.
The treatment for frothy bloat is anti-foaming agents and the treatment for free-gas bloat is placing a stomach tube into the esophagus.
Horses may develop gas colic when placed onto new, lush pastures.
Similar to bloat, excess fermentation gases from digesting lush, growing grasses build up in the intestines of the animal and cause colic symptoms.
Colic is a general term for gastrointestinal pain in the horse, caused by several potential factors.
Gas colic is generally mild and treatable, with interventions ranging from simply treating the pain and allowing the gas to dissipate naturally, to nasogastric tubing and antispasmodic drugs.
Veterinary treatment is advised if you think your horse is colicking.
To reduce the risk of bloat with legumes, provide animals dry forage before turning them into pastures and provide dry roughage for them while they are on pasture.
This may be done by mowing strips in the pasture.
Dry forage helps to increase the total consumption of dry matter and reduces the incidence of bloat.
When heavy rains and wind cause legume plants to fall over, crowns are exposed to sunlight and shoot growth is stimulated.
Pasturing this undergrowth has been observed to be especially hazardous from the bloat standpoint.
Nitrate Toxicity toxicity is a condition where nitrates  are converted to toxic nitrites  in the rumen.
These nitrites are absorbed into the bloodstream where they bind hemoglobin , turning it into methemoglobin.
As a result, cattle are unable to receive adequate oxygen to their tissues or organs and suffocate.
Common signs of nitrate toxicity include blue-tinged membranes, excessive salivation, urination, difficulty breathing, and chocolate colored blood.
As poisoning progresses, cattle become
 Table 3: Animal unit equivalents  of common domestic species.
Cow 	1.0
 Table 4.
Guidelines for interpretation of nitrate content of forages and water for livestock consumption.
Form of nitrate measured
 Potassium nitrate 	Nitrate Nitrogen 	Nitrate 	Recommendations for use in livestock
 ppm	%	ppm	%	ppm	%
 0-7,220	0-0.72	0-1,000	0-0.10	0-4,430	0-0.44	Generally considered to be safe for livestock
 Safe for non-pregnant animals; limit to 50% of
 7,220-10,830	0.72-1.08	1,000-1,500	0.10-0.15	4,430-6,645	0.44-0.66
 dry matter for pregnant animals
 10,830-14,440	1.08-1.44	1,500-2,000	0.15-0.20	6,645-8,860	0.66-0.88	Limit to 50% of ration dry matter for all animals
 Limit to 30 to 35% of ration dry matter; do not
 14,440-25,270	1.44-2.52	2,000-3,500	0.20-0.35	8,860-15,505	0.88-1.55
 feed to pregnant animals
 Limit to 25% of ration dry matter; do not feed
 25,270-28,880	2.52-2.88	3,500-4,000	0.35-0.40	15,505-17,720	1.55-1.77
 >28,880	>2.88	>4,000	>0.40	>17,720	>1.77	Danger; do not feed
 Water 
 0-720	0-0.072	0-100	0-0.01	0-443	0-0.04	Generally considered to be safe for livestock
 Caution: possible problems; consider additive
 720-2,166	0.072-0.21	100-300	0.01-0.03	443-1,329	0.04-0.13
 effect with nitrate in feed
 Danger: could cause typical signs of nitrate
 >2,166	>0.21	>300	>0.03	>1,30	>0.13
 weak.
Moving cattle around may exacerbate symptoms or cause death because movement of muscle requires oxygen.
Pregnant cattle may abort even at low, non-lethal doses of nitrate.
Poisoning from nitrate can happen very quickly, often cattle are unexpectedly found dead.
Horses, as hind gut fermenters rather than ruminants, are less susceptible than cattle to nitrate toxicity.
If cattle are found early, they may be treated with methylene blue.
Post-mortem diagnosis can be made through testing the ocular fluid in the eye of a deceased animal.
Any plant can accumulate toxic nitrate levels, although it is most common with annual grasses.
Nitrates can accumulate in certain weeds such as curly dock, johnsongrass, kochia, lambsquarter, nightshade, pigweed, Russian thistle, pale smartweed, and wild sunflower.
Excess nitrates can also be found in hay even if wellcured.
Nitrate concentration in plants may increase to toxic levels from high inputs of nitrogen from manure, nitrogencontaining fertilizer or environmental conditions where plant growth is slowed such as cold temperature, cloudy weather, and drought.
In the case of drought, the highest level of nitrate may occur 3 to 7 days after the drought condition is alleviated by rainfall or irrigation.
Despite the severity of nitrate toxicity, it is relatively rare for grazing animals whose rate of feed intake is slow.
Nevertheless, caution is advisable when animals are grazing on forage that has been subjected to environmental stress.
After an environmental stress, it may be warranted to delay grazing by 1 week.
In grasses, the lower part of the stem  and 6 inches in warm-season grasses ) contain the most nitrate, SO reducing grazing intensity to not exceed a certain stubble height may be justified in cases where toxic levels of nitrate are suspected.
If you suspect a pasture has excessive nitrogen levels, you can sample your pasture for testing at a lab.
Be sure to check how the lab reports the results, they may be reported as Potassium Nitrate , Nitrate Nitrogen , or Nitrate.
Use the appropriate table values to determine if your pasture is safe to graze at that time (Table Remember, nitrogen levels may fluctuate based on environmental factors after sampling.
Prussic Acid Poisoning Prussic acid, also known as cyanide or hydrocyanic acid , is similar to nitrate poisoning in that it is usually preceded by some sort of plant stressor, such as a frost or drought, and affects the cattle's ability to utilize oxygen.
Ruminants are more susceptible to prussic acid poisoning because enzymes in the rumen microbes release prussic acid from plant tissue.
Rather than preventing hemoglobin from binding oxygen , HCN acts to prevent the cattle's tissues from utilizing oxygen.
Cattle often have difficulty breathing, foam
 at the mouth, become progressively weakened, or found dead.
Instead of the chocolate-colored blood characteristic of nitrate toxicity, the blood of affected cattle is a bright cherry red color.
Treatment is possible with methylene blue or sodium nitrate, however a veterinarian should be consulted to ensure a differential diagnosis from nitrate toxicity.
Sorghum and related species such as sudangrass and sorghum-sudangrass hybrids can cause prussic acid poisoning.
The compounds that lead to prussic acid formation are found in the leafy portion of new growth.
Prussic acid may accumulate in leaves after frost damage.
New growth following any environmental stress such as drought or grazing can be particularly high in prussic acid.
Pastures grown with high levels of nitrogen and low levels of phosphorus and potassium are at high risk to develop prussic acid.
The risk of prussic acid poisoning can be reduced by not grazing sorghum and related species until the plants are 18 to 24 inches in height, delaying grazing by at least 7 days after frost damage, feeding ground cereal grains before turning the animals out to pasture, and using heavy stocking rates.
Grass Tetany While not a widespread problem in Arizona, there are a few regions around the state that regularly experience bouts of grass tetany in the spring.
Grass tetany, also called grass staggers, develops from an imbalance of magnesium and potassium and is most common in ruminants although horses are susceptible as well.
Animals grazing cool-season grasses in the spring are subject to grass tetany.
Contributing causes to grass tetany are nitrogen and potassium fertilizer use on the pasture, and vigorous pasture growth, high moisture content of the forage, cool and cloudy days associated with wet weather in the spring, low energy and/or roughage intake, stress to the animal from transport or other factors, and low intake of phosphorus or salt.
If the balance of potassium to magnesium becomes too great , and animals are unable to mobilize magnesium stores from their skeletal system they may develop grass tetany.
In many cases, animals are simply found dead with signs of convulsions.
Less severely affected animals may become ill over 2 to 3 days, exhibiting decreased milk, and appearing uncomfortable and nervous.
They may stop grazing, stagger, and develop twitches in the face, ears, and flank.
Animals may act more flighty than normal and get up and down frequently.
If startled or stimulated, they act erratically, and run with an altered  gait.
Eventually, these animals will collapse and suffer convulsions, facial twitching, foreleg paddling, and chewing that increase if the animal is handled.
Death from this point usually occurs in a few hours.
Older animals, especially those in early lactation, are most susceptible although any animal
 can be affected.
If caught early, animals can be treated with an injection of calcium and magnesium.
There is a risk of causing heart failure if this treatment is administered incorrectly, it is best performed by a veterinarian.
The best preventative measure against grass tetany is to not graze cool-season grasses until at least 4 to 6 inches tall and supplementing animals with extra magnesium during potential danger periods.
This is most often accomplished through a providing high magnesium lick or switching temporarily to a high magnesium mineral supplement.
Magnesium boluses are available, although they are more labor intensive.
Magnesium in some forms is somewhat bitter and unpalatable, SO make sure that the form you are using is being consumed by the animal.
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 Estimating Soll Maisture Feel-and Appearance
 Intrication Water Management  is applying water according to crop needs in an amount that can be stored in the plant root zone of the soil.
4.
Observing soil texture, ability to ribbon, firmness and surface roughness of ball, water glistening, loose soil particles, soil/water staining on fingers, and soil color.
[Note: A very weak ball will disintegrate with one bounce of the hand.
A weak ball disintegrates with two to three bounces.]
 5.
Comparing observations with photographs and/ or charts to estimate percent water available and the inches depleted below field capacity.
The "feel and appearance method" is one of several irrigation scheduling methods used in IWM.
It is a way of monitoring soil moisture to determine when to irrigate and how much water to apply.
Applying too much water causes excessive runoff and/or deep percolation.
As a result, valuable water is lost along with nutrients and chemicals, which may leach into the ground water.
The feel and appearance of soil vary with texture and moisture content.
Soil moisture conditions can be estimated, with experience, to an accuracy of about 5 percent.
Soil moisture is typically sampled in 1-foot increments to the root depth of the crop at three or more sites per field.
It is best to vary the number of sample sites and depths according to crop, field size, soil texture, and soil stratification.
For each sample the "feel and appearance method" involves:
 2.
Squeezing the soil sample firmly in your hand several times to form an irregularly shaped "ball".
3.
Squeezing the soil sample out of your hand between thumb and forefinger to form a ribbon.
1.
Obtaining a soil sample at the selected depth using a probe, auger, or shovel.
Result: A 3.1" net irrigation will refill the root zone.
*Available Water Capacity **Determined by "feel and appearance method"
 Available Water Capacity  is the portion of water in a soil that can be readily absorbed by plant roots of most crops.
Sample	USDA	AWC* for	Soil Moisture	Percent
 Depth	Zone	Texture	Zone	Depletion	Depletion
 6"	0-12"	sandy loam	1.4"	1.0"	70
 18"	12-24"	sandy loam	1.4"	.8"	55
 30"	24-36"	loam	2.0"	.8"	40
 42"	36-48"	loam	2.0"	.5"	25
 Soil Moisture Deficit  or Depletion is the amount of water required to raise the soil-water content of the crop root zone to field capacity.
Appearance of fine sand and loamy fine sand soils at various soil moisture conditions.
Available Water Capacity 0.6-1.2 inches/foot
 Percent Available: Currently available soil moisture as a percent of available water capacity.
In./ft.
Depleted: Inches of water currently needed to refill a foot of soil to field capacity.
0-25 percent available 1.2-0.5 in./ft.
depleted
 Dry, loose, will hold together if not disturbed, loose sand grains on fingers with applied pressure.
25-50 percent available 0.9-0.3 in./ft.
depleted
 Slightly moist, forms a very weak ball with welldefined finger marks, light coating of loose and aggregated sand grains remains on fingers.
50-75 percent available 0.6-0.2 in./ft.
depleted
 Moist, forms a weak ball with loose and aggregated sand grains on fingers, darkened color, moderate water staining on fingers, will not ribbon.
75-100 percent available 0.3-0.0 in./ft.
depleted
 Wet, forms a weak ball, loose and aggregated sand grains remain on fingers, darkened color, heavy water staining on fingers, will not ribbon.
100 percent available 0.0 in./ft.
depleted 
 Wet, forms a weak ball, moderate to heavy soil/water coating on fingers, wet outline of soft ball remains on hand.
Appearance of sandy loam and fine sandy loam soils at 1various soil moisture conditions.
Available Water Capacity 1.3-1.7 inches/foot
 Percent Available: Currently available soil moisture as a percent of available water capacity.
In./ft.
Depleted: Inches of water currently needed to refill a foot of soil to field capacity.
0-25 percent available 1.7-1.0 in./ft.
depleted
 Dry, forms a very weak ball, aggregated soil grains break away easily from ball.
25-50 percent available 1.3-0.7 in./ft.
depleted
 Slightly moist, forms a weak ball with defined finger marks, darkened color, no water staining on fingers, grains break away.
50-75 percent available 0.9-0.3 in./ft.
depleted
 Moist, forms a ball with defined finger marks, very light soil/water staining on fingers, darkened color, will not slick.
75-100 percent available 0.4-0.0 in./ft.
depleted
 Wet, forms a ball with wet outline left on hand, light to medium staining on fingers, makes a weak ribbon between the thumb and forefinger.
100 percent available 0.0 in./ft.
depleted 
 Wet, forms a soft ball, free water appears briefly on soil surface after squeezing or shaking, medium to heavy soil/water coating on fingers.
Appearance of sandy clay loam, loam, and silt loam soils at various soil moisture conditions.
Available Water Capacity 1.5-2.1 inches/foot
 Percent Available: Currently available soil moisture as a percent of available water capacity.
In./ft.
Depleted: Inches of water needed to refill a foot of soil to field capacity.
0-25 percent available 2.1-1.1 in./ft.
depleted
 Dry, soil aggregations break away easily, no staining on fingers, clods crumble with applied pressure.
25-50 percent available 1.6-0.8 in./ft.
depleted
 Slightly moist, forms a weak ball with rough surfaces, no water staining on fingers, few aggregated soil grains break away.
50-75 percent available 1.1-0.4 in./ft.
depleted
 Moist, forms a ball, very light staining on fingers, darkened color, pliable, forms a weak ribbon between the thumb and forefinger.
75-100 percent available 0.5-0.0 in./ft.
depleted
 Wet, forms a ball with well-defined finger marks, light to heavy soil/water coating on fingers, ribbons between thumb and forefinger.
100 percent available 0.0 in./ft.
depleted 
 Wet, forms a soft ball, free water appears briefly on soil surface after squeezing or shaking, medium to heavy soil/water coating on fingers.
Appearance of clay, clay loam, and silty clay loam soils at various soil moisture conditions.
Available Water Capacity 1.6-2.4 inches/foot
 Percent Available: Currently available soil moisture as a percent of available water capacity.
In./ft.
Depleted: Inches of water needed to refill a foot of soil to field capacity.
0-25 percent available 2.4-1.2 in./ft.
depleted
 Dry, soil aggregations separate easily, clods are hard to crumble with applied pressure.
25-50 percent available 1.8-0.8 in./ft.
depleted
 Slightly moist, forms a weak ball, very few soil aggregations break away, no water stains, clods flatten with applied pressure.
50-75 percent available 1.2-0.4 in./ft.
depleted
 Moist, forms a smooth ball with defined finger marks, light soil/water staining on fingers, ribbons between thumb and forefinger.
75-100 percent available 0.6-0.0 in./ft.
depleted
 Wet, forms a ball, uneven medium to heavy soil/water coating on fingers, ribbons easily between thumb and forefinger.
100 percent available 0.0 in./ft.
depleted 
 Wet, forms a soft ball, free water appears on soil surface after squeezing or shaking, thick soil/water coating on fingers, slick and sticky.
GUIDE FOR ESTIMATING SOIL MOISTURE CONDITIONS
 Coarse Texture-	Moderately Coarse Texture-	Medium Texture-Sandy Clay Loam,	Fine Texture-Clay, Clay Loam, or
 Fine Sand and Loamy Fine Sand	Sandy Loam and Fine Sandy Loam	Loam, and Silt Loam	Silty Clay Loam
 Available Water Capacity 
 0.6-1.2	1.3-1.7	1.5-2.1	1.6-2.4
 Soil Moisture	Soil Moisture Deficit  in inches per foot when the feel and appearance of the soil are as described.
Dry, loose, will hold together if	Dry, forms a very weak ball, ag-	Dry, soil aggregations break	Dry, soil aggregations eas-
 not disturbed, loose sand grains	gregated soil grains break away	away easily, no moisture stain-	ily separate, clods are hard to
 0-25	on fingers with applied pressure.
easily from ball.
ing on fingers, clods crumble	crumble with applied pressure.
SMD 1.2 0.5	SMD 1.7 1.0	SMD 2.1 1.1	SMD 2.4 1.2
 Slightly moist, forms a very	Slightly moist, forms a weak	Slightly moist, forms a weak ball	Slightly moist, forms a weak
 weak ball with well-defined	ball with defined finger marks,	with rough surfaces, no water	ball, very few soil aggrega-
 finger marks, light coating of	darkened color, no water staining	staining on fingers, few aggre-	tions break away, no water
 25-50	loose and aggregated sand grains	on fingers, grains break away.
gated soil grains break away.
stains, clods flatten with applied
 remain on fingers.
pressure.
SMD 0.9 0.3	SMD 1.3 0.7	SMD 1.8 0.8
 Moist, forms a weak ball with	Moist, forms a ball with defined	Moist, forms a ball, very light	Moist, forms a smooth ball
 loose and aggregated sand grains	finger marks, very light soil/water	water staining on fingers,	with defined finger marks, light
 50-75	on fingers, darkened color,	moderate water staining on	color, will not slick.
staining on fingers, darkened	darkened color, pliable, forms a	weak ribbon between thumb and	ribbons between thumb and	soil/water staining on fingers,
 fingers, will not ribbon.2	forefinger.
forefinger.
SMD 0.6 0.2	SMD 0.9 0.3	SMD 1.10.4	SMD 1.2 0.4
 Wet, forms a weak ball, loose and	Wet, forms a ball with wet out-	Wet, forms a ball with well	Wet, forms a ball, uneven me-
 aggregated sand grains remain	line left on hand, light to medium	defined finger marks, light to	dium to heavy soil/water coating
 75-100	not ribbon.
on fingers, darkened color, heavy	water staining on fingers, will	a weak ribbon between thumb	water staining on fingers, makes	heavy soil/water coating on	fingers, ribbons between thumb	between thumb and forefinger.
on fingers, ribbons easily
 and forefinger.
and forefinger.
SMD 0.3 0.0	SMD 0.4 0.0	SMD 0.5 0.0	SMD 0.6 0.0
 Wet, forms a weak ball, moderate	Wet, forms a soft ball, free	Wet, forms a soft ball, free water	Wet, forms a soft ball, free
 Field Capacity	to heavy soil/water coating on	fingers, wet outline of soft ball	water appears briefly on soil	surface after squeezing or	appears briefly on soil surface	after squeezing or shaking, me-	after squeezing or shaking, thick	water appears on soil surface
 	remains on hand.
shaking, medium to heavy	dium to heavy soil/water coating	soil/water coating on fingers,
 soil/water coating on fingers.
on fingers.
slick and sticky.
SMD 0.0	SMD 0.0	SMD 0.0	SMD 0.0
 1 Ball is formed by squeezing a hand full of soil very firmly with one hand.
Ribbon is formed when soil is squeezed out of hand between thumb and forefinger.
2
 SOIL TEXTURE BY FEEL FLOW CHART
 1 Sand paricle size should be estimated  for these textures.
Individual grains of very fine sand are not visible without magnification and there is a gritty feeling to a very small sample ground between teeth.
Some find sand particles may be just visible.
Medium sand particles are easily visible.
Examples of sand size descriptions where one size is predominate are: very fine sand, fine sandy loam, and loamy coarse sand.
Field Evaluation of Container Nursery Irrigation Systems: Part 2: Measuring Application Rates1
 Dorota Z.
Haman and Thomas H.
Yeager2
 Performance of sprinkler and microirrigation systems can be evaluated by measuring operating pressures, application rates, and uniformity of water application under nursery conditions.
We discuss the measurement of application rates for overhead sprinkler systems.
The application rate is defined as the average depth of water applied per unit time of system operation.
For a sprinkler system, application rate is usually expressed in inches per hour.
The measurement of application rates in the nursery will verify the design of the system.
It is also important to ensure periodically that application rates of the system have not changed with time.
For this reason, the application rate test should be performed at least once a year.
Also, it is important to realize that to time the irrigation events, it is necessary to know the depth of water applied in a given  unit of time.
Basically, there are three techniques to determine the water application rate of a system:
 The water flow into the irrigation zone can be measured using a flow meter, and the application rate can be calculated based on the area of the zone.
The application rate can be calculated from the average flow rate of a sprinkler in the zone and the area covered by this sprinkler.
The application rate can be directly measured with catch cans or rain gauges placed in the irrigated zone.
To use the first method, it is necessary to install a flow meter at the entrance to the irrigation zone.
Flow meters are strongly recommended as management tools because it is difficult to manage the system efficiently without knowing how much water is applied during an irrigation event.
In addition, flow meters help to detect changes in water application with time or due to malfunctioning of some components.
For example, clogged pipe or nozzles will decrease the flow rate, whereas a break in a water delivery line will increase it.
However, flow meters are an additional cost, and in many nurseries they are not installed at each irrigation zone.
To use the second method, sprinkler discharge can be determined by directly measuring the volume of water discharged by the sprinkler in a unit of time and dividing it by the area where the water is applied.
A flexible hose, which can be slipped over the sprinkler, can be used to direct the water into a container of known volume.
For recently installed nozzles, the manufacturer's specification tables can be used after measuring the pressure at the nozzle with a pitot tube.
It is important to realize that the discharge may change with time, especially if the water contains abrasive particles such as sand.
The nozzle size should be periodically checked for wear using a drill bit with a diameter specified for the nozzle.
2.
Dorota Z.
Haman, professor emeritus, Department of Agricultural and Biological Engineering; and Thomas H.
Yeager, professor, Environmental Horticulture Department; UF/IFAS Extension, Gainesville, FL 32611.
In the third method, the application rate is measured directly by placing a grid of catch cans or rain gauges between four sprinklers  in the field.
It is recommended that a minimum of 16 cans be used in the test.
Catch cans should be of the same size and shape, and they should be located in a regular grid clear of obstruction by vegetation.
It is good to perform this test before the containers are placed in the zone on a windless day.
If the test must be performed with the plants in place, the cans should be elevated above the canopy to avoid interception.
A few drops of lightweight oil can be placed in the cans before the test to reduce the evaporation.
If the cans have vertical walls, the depth of water in the can will represent the depth of application.
However, if the walls are tapered, the depth of application will be the volume of collected water divided by the surfacearea of the can opening.
The test should be performed in several representative places in the irrigation zone.
Following are three examples representing the methods discussed.
The flow rate into a 1/3-acre zone is 100 gpm as measured by a flow meter.
One acre-inch  is 27,154 gallons.
To calculate the application rate: 100 x 60 min/1 gallons/min hr = 0.67 in/hr 0.33 acre X 27, 154 gallac-in Example 1.
Calculate the application rate for sprinklers with a discharge of 3 gpm and a square spacing of 20 ft X 20 ft.
Application = where 96.3 is a conversion constant.
Example 2.
Figure 1 presents a layout of 16 cans in the irrigation zone.
The depth of water collected in these vertical cans after running the system for one hour is presented below each can.
The average application rate in this zone is the average depth collected in the cans and is equal to 0.8 in/hr.
/ 16 = 0.8 in/hr Example 3.
O	O	O	O
 0.7	0.8	0.9	0.6
 O	O	O	O
 0.8	0.7	0.9	0.7
 O	O	O	O
 1.0	0.8	0.8	0.9
 O	O	O	O
 1.0	0.8	0.9	1.0
The conference, situated in the middle of a living laboratory and atop the vast Great Plains Aquifer, will provide a platform to explore win-win scenarios to support improved water use in agriculture and increase productivity at a variety of scales  from smallholders, collectives and coops to commercial farm operations  while preserving water resources for other human and environmental needs.
Additional topic-focused side events, meetings and site tours will round out the conference.
Table 1.
Crop water use for the remainder of the growing season for corn and soybean.
For soybeans in the R4 End of pod elongation stage of growth, it needs approximately 37 days to maturity and 9.0 water use to maturity.
For soybeans in the R5 Beginning seed enlargement stage of growth, it needs approximately 29 days to maturity and 6.5 water use to maturity.
For soybeans in the R6 End of seed enlargement stage of growth, it needs approximately 18 days to maturity and 3.5 water use to maturity.
For soybeans in the R6.5 leaves begin to yellow stage of growth, it needs approximately 10 days to maturity and 1.9 water use to maturity.
For soybeans in the R7 beginning maturity stage of growth, it needs approximately 0 days to maturity and 0 water use to maturity.
A WORD OR TWO ABOUT GARDENING
 Conserving water in a Miami-Dade vegetable garden.
After June's near record rainfall, evaluating how best to conserve water is probably not near the top of your gardening 'must do' list.
You are doubtless more concerned about potential storm damage, and belatedly realizing that you should have already attended to pruning those black olives at the front of the house!
So why devote this article to the topic of water use in the garden?
The unfortunate fact is that like a hurricane, restrictions on water use are more a case of when rather than if.
We shouldn't need the threat of enforced restrictions before evaluating how to use water economically and conserve soil moisture.
This should have been fully integrated into the way we plant and manage our landscape.
Last month's article in this column dealt with raised beds, including the many advantages for those planning a home vegetable garden.
At this time as you decide how best to construct your raised bed, consider which of the irrigation methods discussed below could also be incorporated into your plans.
For those new to gardening in Miami-Dade, a little perspective as to local climate conditions will probably be helpful.
Late fall through early spring, which corresponds to our vegetable growing season, is dry season.
Annual rainfall for Homestead is about 60", but 40-50" of this total falls between mid May to October.
In contrast from mid December to mid May the average rainfall is about 8", and for the past 6 years this has ranged from 4"  to almost 11 1/2" , when a moderate El-Nio event influenced our weather.
As these figures demonstrate a reliable means of watering is fundamental to a successful winter vegetable garden.
As a rule of thumb the Miami-Dade vegetable garden should receive 1-2" of water  per week in two applications the upper level more likely for a raised bed.
Distribute several rain gages to measure rainfall.
For 100 sq ft of garden 65 gallons will provide 1" of water.
The best time to water is early morning, though this is not so important if a drip or capillary irrigation system is being used.
If you aren't sure when and how much it has rained or when you last watered, inspect the top 1" of soil.
If this has dried out it is time to water.
While there is clearly a need for a reliable means of watering the winter vegetable garden, it is more than just simply turning on an outdoor faucet.
Oh, and before turning on the faucet remember it is a Miami-Dade code requirement that any outdoor water outlet must be fitted with an anti-siphon device.
Now that our faucet is up to code, how do we deliver water to the vegetable garden?
Obviously the simplest method is to hand water, but even here we can save water.
Rather than a pistol type nozzle use a wand type extension fitted with a water breaker.
Water can then be gently directed to the soil around the base of the plant where it is needed.
This also avoids wetting foliage and splashing soil onto the stem/lower leaves
 thereby lessening the risk of disease.
For a very small garden you don't even need a hose; use a long neck watering can fitted with a fine rose spray.
If you don't have time to water by hand, a variety of simple irrigation systems are available.
The most basic rely on gravity feed from a container of water, which is attached to a plastic probe that allows water to slowly seep into the surrounding soil.
These are worth considering if you have a small raised bed, don't have room to store a hose pipe or for a small vegetable garden  that lacks piped water.
One simple system uses old soda bottles with the bottoms cut out as water reservoirs.
A special plastic cone screws onto each bottle to regulate water flow.
The bottle is inverted and the cone inserted into the soil at the base of the plant.
Another slightly more expensive device utilizes an upturned plastic bottle supported by a screw-on plastic spike  with attached tubing.
The tubing feeds water to an adjustable metering device that is pushed into the soil between each plant.
Several settings are available depending on the type of soil and the water needs of the crop.
Gravity is but one of two principal forces that influence the movement of water in soil the other is capillary action.
Once the pull of gravity on bulk water is lost, capillary action exerts an influence on the movement of water that remains in between soil particles.
Capillary water is the most significant source of water for plant roots.
Capillary action is the result of both adhesive and cohesive molecular forces.
Adhesive forces act to tightly bind a film of water to individual soil particles this water is unavailable to plant roots.
Cohesive forces attract water molecules to one another, including those held by adhesive forces to soil particles.
As the soil surface dries, these forces act to cause water to be drawn up into the now open pores between soil particles.
Soil particle size determines pore size: water will move more rapidly through larger pores, but further through a narrow size pore.
Once soil becomes saturated, through rainfall or irrigation, gravity becomes the dominant force, moving water downward.
A simple example of irrigation by capillary action is a potted plant placed in a saucer of water.
Much more sophisticated are underground irrigation systems that rely on capillary action to draw water to plant roots.
One such method of irrigation, only recently available in N.
America, has been in use in Europe for more than twenty years, where it has found applications from watering planters and raised beds to shrubs and even trees.
The method uses special plastic reservoirs which are positioned below the root ball prior to planting and covering with soil/backfill.
A fill tube incorporating a water level indicator extends from the reservoir to above the soil surface.
Like the gravity feed devices just described, this approach should prove especially useful where piped water is unavailable  or a hose inconvenient.
Although more expensive, water need not be replenished as frequently as is the case with gravity feed.
Water reservoirs come in a range of capacities from 1qt to 21/2 gallons and more, and should require refilling no more than once a week.
For a raised bed, allow about 4" between the reservoir and the root ball of whatever is to be planted.
Placement depends on the type of soil, especially particle size and its influence on the capillary action of the soil the coarser the soil the closer the reservoir should to be placed to the root ball.
Irrigation systems requiring piped water are available from relatively inexpensive kits for a small garden to elaborate custom designed installations requiring the services of an irrigation specialist.
Lawn sprinklers are designed to distribute water over a wide area and are inappropriate for the vegetable garden.
Used for this purpose they are wasteful of water and wet the foliage, increasing the risk of disease.
In addition use of such sprinklers is severely limited when Phase II water restrictions are in force during water shortages.
Two alternatives, soaker hoses and drip emitters are ideal for vegetable gardens and bedding plants and are not subject to water use restrictions.
Porous rubber soaker hoses 'sweat' water along their length and are a popular and relatively inexpensive system.
The soaker hose is connected to a regular garden hose and either lies on top of or is buried just below the soil surface.
If laid on the soil surface the hose should be covered by mulch organic or plastic.
Bend heavy gage wire into U shaped fasteners to hold the soaker hose in place.
Connect a 200 mesh filter, to remove particulates, followed by a regulator to maintain water pressure at no more than 10 lbs psi.
If a supply hose is used attach the filter and regulator between this and the soaker hose.
Soaker hoses can be purchased as a kit which will include all required fittings, though the pressure regulator and the filter are not usually included.
With water containing high levels of dissolved calcium, soaker hoses are more likely to become clogged.
This is a potential problem in Miami-Dade, especially if well water is used.
Consider installing a special filter that uses sodium hexametaphosphate to inhibit calcium deposits, but be wary of magnetic devices that claim to reduce calcium deposits.
Most of the evidence of their efficacy is anecdotal, the limited research available rendering their household use questionable.
Don't use water from conventional water softeners.
This can cause a build up of salt in the soil resulting in plant injury.
Frequent back flushing will help to remove mineral deposits.
Once the vegetable season is over or the bedding plants finished short lengths of soaker hose can be removed and immersed in soapy water containing a descaling chemical.
The hose should then be flushed with clean water.
No more than 100' lengths of hose should be used for a single run.
This can be snaked down a 4' wide vegetable bed with 3' wide loops, leaving 1' between each loop.
Laid in this fashion a 100' length of hose could water a 25 X 4' bed.
At a pressure of 10 psi and flow rate of 1 gallon/min/100' length of hose it would take about 65 minutes to provide 1" of water.
The flow rate can differ depending on which brand of soaker hose you purchase consult the manufacturer's specifications.
Soaker hoses are ideal for intensive systems , being far easier to install compared to drip emitters.
By adding a timer to the system it can be set to automatically deliver the requisite amount of water.
Alternatively, there are metering devices that will turn off after a pre-set volume of water has been applied.
You can estimate the volume in cubic inches by multiplying the area to be irrigated by the depth of water to be applied, dividing this by 231 to convert to gallons.
Alternatively use a soil moisture meter to estimate how much water is required to penetrate the top 10" of soil.
More expensive but less liable to clog  drip emitters deliver a slow trickle of water to the root zone of a single plant or group of small plants.
The least expensive have emitters built into the tubing, their spacing dependent on the intended use.
For small raised beds, there are low pressure systems that operate using gravity feed from a bucket of water placed 2-3' above the soil surface.
More widely used for growing vegetables are flat drip tapes.
These require a regulator to provide a water pressure of 25 lbs psi, a 200 mesh filter and must be laid perfectly straight without kinks.
More costly are systems that use lengths of polypropylene tubing with drip emitters inserted using a punch tool.
This allows greater flexibility over the type of emitter chosen and their spacing.
For a vegetable garden choose those delivering 0.5 to 1 gallon per hour, spaced every 12 -16".
Spacing depends upon soil type the coarser the soil particles, the less distance between emitters.
Capillary action will be more pronounced where soil particles are smaller and result in greater lateral spread of applied water.
As a guide place the dripper line about 45" from a row of tomatoes, and for a double row  in the center of the row.
Various types of drip emitters are available but use only one type of emitter per irrigation line.
Where clogging is liable to be a problem choose button drippers or those that can be disassembled and cleaned.
The total flow rate of the installed system should not exceed 75% of the flow rate of the main water supply.
If in excess, divide the garden into sections that fall within the 75% limit and water each individually.
Where sequential irrigation is necessary timers can be programmed to deliver the correct amount of water to each section of the garden.
It is possible to introduce plant nutrients into the irrigation water using special injectors.
This is most often used to deliver nitrogen, but other nutrients can be included, though some  can come out of solution where water has a high pH.
Routinely back flush and check the lines for breaks and leaking/blocked emitters.
No matter how much you invest in an irrigation system, long term benefits will only be realized if it is properly maintained.
As well as considering an efficient means of delivering water, do not overlook the need to conserve soil moisture, thereby reducing the frequency of irrigation.
Mulch not only conserves water, it reduces weed problems and moderates fluctuations in soil temperature.
In addition mulch can lessen the risk of problems from parasitic soil nematodes as well as disease from soil borne pathogens splashed onto plant surfaces.
While there are advantages to using plastic mulch , there are disadvantages.
First is cost the 1.5 mil black plastic that is used for winter vegetables is not cheap followed by the problem of disposal at the end of the growing season.
In addition plastic mulch is impervious to water.
For rainfall or above ground irrigation  to be effective moisture needs to move laterally  from soil at the edge of the mulch that receives water.
A partial solution is to punch small holes in the plastic.
This is not very reliable and wasteful of water.
Plastic mulch should always used in conjunction with an installed irrigation system.
At least one kit is available consisting of plastic mulch with a soaker hose already woven is available.
Before laying plastic mulch, a slow release fertilizer should be incorporated into the soil.
Lay the mulch flush with the soil surface which should be smooth and level with a slight slope toward both edges to prevent pooling of water around the planting hole.
The edges of the mulch should be secured beneath soil.
If the plastic does not already have planting holes, these can be cut using a bulb planter.
Inverted T slits can be made in the plastic adjacent to the crop row to permit later side dressing with fertilizer.
For reasons of space organic mulches will have to be left for a future article, but they are a viable alternative for a home garden.
However remember, if using a wood based product as opposed to shredded bark incorporate some extra fertilizer nitrogen into the mulch before use.
Finally I cannot close without thanking Dr Kati White, irrigation specialist at UF Tropical Research and Education Center for the benefit of her expertise.
Chapter: 18 Corn Silage Production and Utilization
 Silage is a high moisture fermented fodder used as a feed for livestock.
It is produced by allowing chopped green vegetation to ferment under air-tight conditions.
During the ensiling process watersoluble carbohydrates are converted to acids, which lowers the pH and protects the silage from further deterioration.
To optimize silage production, management practices specifically designed for this purpose should be followed.
This chapter focuses on the production of the corn crop used to produce silage and provides examples on how to assess its quality.
When growing corn for silage, it is important to consider animal performance in addition to yield.
Selecting a Corn Hybrid
 Selecting the same corn hybrids and management practices to produce silage and grain may reduce silage feed quality.
Good corn silage hybrids have high yields, high energy, high digestibility, and good animal performance.
Critical to maximize silage yields is the selection of the right variety.
With lower corn silage yields, there is a greater need for livestock supplementation, which increases feed costs.
However, because grain provides needed starch, it is unlikely that corn grain will be completely removed from the ration.
Since starch is deposited in the kernels, the amount of grain in the ration is associated with the energy content of the silage.
In the past, the rule of thumb for the corn silage grain-to-forage ratio was 50:50.
The improved grain yield per unit area of modern corn hybrids is because of the increased optimum plant population rather than the improved grain yield per plant.
For example, hybrid 1 produces 150 bu/acre or 20 tons/acre of corn silage at 65% moisture.
This hybrid has a grain equivalent per ton of corn silage of 7.5 bushels, and the proportion of grain per ton of dry silage as percent of the whole plant is 420 lbs  divided by 700  or 60% grain per ton of dry matter.
Hybrid 2, produces 200 bu/acre or 29 tons per acre at 65% moisture.
This corn hybrid has a grain equivalent per ton of corn silage of 6.8 bushels, and the proportion of grain per ton of dry silage as percent of the whole plant is 380 lbs  divided again by 700  or 54% grain per ton of dry matter.
By difference, one can infer that the forage fraction of 150-bushel corn yielding 20 tons of silage per acre is 40% , whereas the forage fraction of the 200-bushel corn is 46%.
If we estimate, 0.7 megacalories  of net energy for gain  per pound of corn grain the 150-bushel produces:
 0.7x56x150 = 5,880 MCal NEg per acre, whereas the 200-bushel corn produces: 0.7x56x200 = 7,840 MCal NEg per acre or 33% more energy.
These calculations show trade-off often seen between hybrids.
Desirable hybrid characteristics for grain production, such as hard and fast-drying kernels, are exactly the opposite of what are needed in corn silage.
Corn hybrids for silage need to have both high yields and increased starch and fiber  digestibility.
Corn Silage Planting Date, Population, Fertilizer, and Insect Control
 Where possible, select corn silage hybrids that have a slightly higher maturity rating that grain hybrids, and cultivate early at rates 2,000 to 3,000 plants/acre higher than for grain producation.
Row spacing should be approprate for the agricultural system, and harvesting corn for silage removes more N, P, and K than harvesting corn for grain.
If the field is routinely harvested for silage, consider increasing the amount of fertilizer or manure applied to the field.
Climatic conditions can impact silage quality.
Dry conditions during stalk development generally increase digestibility, but drought conditions can result in silage with very high nitrate concentrations.
However, because much of the nitrate is contained in the lower portions of the stalk, high nitrate concentrations can be minimized by raising the chopper cutter blade.
The concentration of nitrate that causes toxicity in ruminants depends on total intake , the acclimation of the animal to the nitrate, and its overall nutritional and health status.
As a rule of thumb, forage with less than 5,000 ppm nitrate  or 1130 ppm NO-N is considered safe.
Forage containing 5,000 to 10,000 ppm NO  is considered potentially toxic when it is the only source in the diet.
If the forage has more than 10,000 ppm NO 3  it can be fed to nonpregnant, healthy ruminants provided it's diluted with other safe, nitrate-free forages.
Generally, pest control practices are similar in corn grown for silage and grain.
However, if pesticides are applied to the field, it is important to follow labeled rates for silage.
Improving the Nutritive Value
 The energy value of corn silage is highly dependent on the content and digestibility of starch and fiber components.
The digestibility of Prolamin percent of starch classification both fractions in ruminants differs.
Fiber is mostly fermented in the 10 reticulo-rumen and the products of this fermentation are utilized 9 Very high by rumen microorganisms.
There are corn silage varieties that have 8 higher starch digestibility.
In general, corn silage hybrids with softer 7 High and slower drying kernels, preserve better in the silo and have 6 higher total starch digestibility.
Starch is mostly fermented in the rumen.
However, some may escape and potentially be digested and 5 Moderate its end products absorbed in the lower digestive tract.
Its high water4 resistance allows some starch to escape rumen fermentation before 3 Low bacteria can degrade it.
This "protection" from degradability can 2 also reduce accessibility to starch-degrading enzimes in the small Very low intestine.
With corn silage starch of lower digestibility , a portion can end up in the manure, particularly with higher rates of passage typical of animals with high feed intakes.
Thus, it is important to understand the consititutional factors influencing grain digestion.
Table 18.1 The relationship between prolamin percent and starch classification.
In a University of Wisconsin study, Hoffman and Shaver  showed that starch digestibility decreased 0.86 percentage units per percentage unit increase in prolamin content when expressed as percent of the starch.
This negative relationship was attributed to the prolamins interfering with starch digestion.
Corn hybrids with a more diffuse protein matrix allow for greater water penetration and improved starch accessibility.
During the fermentation process, prolamin protection of starch is reduced.
Source: AgriAnalysis Inc.
2010
 Corn silage nutritive value is affected by its content of grain, stalks, cobs, leaves, and ash.
Relative proportions of these plant components in corn silage will determine the amount of fiber , starch, and protein content.
Corn silage is low in protein and provides fermentable starch, energy, and relative amounts of effective fiber.
Fiber has a greater negative impact on nutritive value because of its lower digestibility compared with starch.
When confronted with high corn prices, livestock producers need to decide whether the corn should be harvested for silage or sold as a cash crop.
To address this question one important consideration is forage digestibility.
More tonnage means more grain but also more plants and, consequently more fiber-rich stems that dilute energy concentration.
To make the most out of corn silage, it is very important to select varieties not only with more grain, but also with increased fiber digestibility.
This is particularly important in diets for milking COWS where forage fiber represents the largest nutrient fraction.
In ruminant diets, the fiber fraction is reported as neutral detergent fiber  and acid detergent fiber.
The residue in the NDF is negatively correlated with feed intake and thus with energy uptake.
Analyzing samples for NDF digestibility  provides an estimation of the amount of energy the ruminant is able to obtain from that forage.
For example, an increase of 1 percentage unit in NDFD can result in 0.37 lb increase in forage dry matter  intake per day.
Jung et al.
reported that dairy COWS ate 0.26 lb/day more feed DM when in vitro NDFD of corn silage increased by one unit.
Cows fed corn silage with greater NDFD are able to eat more and obtain more total energy.
This is the result of a faster emptying of the rumen, which reduces distension and allows for additional feed to be consumed.
As a result, energy requirements can be fulfilled with less grain.
Brown midrib  is a natural mutation that occurs in corn and other crops.
Brown midrib varieties have lower lignin concentrations and greater NDFD.
Research has shown that NDFD of BMR corn silage varieties ranges from 64.4% to 72.8%, whereas NDFD in normal corn silages ranges from 44% to 63.8%.
One other concern of BMR varieties is that they can have approximately 10% to 20% lower DM yields than normal varieties.
Recent results  reported by the University of Vermont showed that 22 tons of corn silage at 35% DM per acre  were achieved with one BMR corn silage variety.
Research has shown that although BMR varieties have slightly less starch than forage-quality hybrid counterparts, they can be up to 30% more digestible.
This is the reason, livestock producers should evaluate corn silage hybrids not only by tonnage and yield, but more importantly by animal performance.
In dairy cows, a milk-per-acre index can aid in this evaluation.
The University of Wisconsin has the milkper-acre selection index that combines yield and quality into a single term allowing an easier ranking of forages and hybrid selection.
Using this information, the milk-per-ton of corn silage is estimated, and then multiplied by the silage yield to calculate the amount of milk produced per acre of corn silage.
Research conducted by Penn State University together with the W.H.
Miner Agricultural Research Institute  suggest that improved plant digestibility can compensate for reductions in DM yields of BMR varieties.
Researchers from the latter institution reported that NDF ratio is lower in the BMR hybrid, whereas starch content is higher.
These findings suggest that the quality of the BMR hybrid is better than that of the conventional corn hybrid.
This is true, however, only when COWS respond with production.
Several studies have shown that milk production can be increased by BMR corn.
Based on forage quality, BMR corn should be targeted to fresh and peak lactation cow groups to maintain intake and reduce rumen fill, leading to greater production and feed efficiency.
This underscores the economic importance of assigning the right forage to the right animal group regardless of corn silage hybrid.
Harvesting corn silage at the black layer stage maximizes starch content in the kernels.
Research has shown that digestibility decreases with increasing maturity.
Bal et al.
reported that corn silage moisture content decreased from 69.9% to 58% and NDF of the silages decreased from 52% to 41.3% as corn matured from early dent to black layer.
Milk production was maximized at the 2/3 milk line stage, when the silage was 64.9% moisture.
A second trial by the same research group evaluated silages at early dent , half milk line , and black layer.
In this trial, milk production was highest at the early dent stage.
The researchers found that starch and fiber digestibility decreased at the black layer stage.
Based on these results, there is limited benefit in harvesting after the half milk line stage.
The authors concluded that a target of 65% moisture seemed best, but that producers should begin harvesting at 70% moisture to avoid silage drying down excessively.
Roth  reported that corn silage moisture contents have increased from 58% to 63% from 2000 to 2010.
To harvest corn silage at higher maturities and maintain animal performance, the protein matrix that encapsulates the starch needs to be disrupted.
This has sparked the interest in feeding processed  corn silage.
Processing is a harvesting method where corn silage harvesters are equipped with postcutting processing rolls.
These rolls consist of two opposing, groove-ridged cylinders that roll to crush and physically damage grain and forage outer layers, which improves digestibility.
For the system to work properly, the separation between roll surfaces is critical.
It needs to be close enough to allow for proper "damage" of the plant material, yet not SO close as to create excessive friction that wears the rolls.
Selfpropelled forage choppers are now available in the market.
In an early trial, Bal et al.
compared corn silage harvested at half milk line, 67% moisture, and chopped at 3/8" theoretical length of cut  using a pull-type chopper and no rollers with other silages that were rolled.
The other corn silages were harvested at 3/8", 9/16", and 3/4" TLC and were rolled using the same pull-type chopper but fitted with a crop processor.
On the unrolled silages, whole and half cobs were retained in the upper sieve of the Penn State particle separator, which could result in feed sorting in the feedbunk.
Cows fed the rolled silages ate 1.5 lbs more dry matter per day compared with those fed unrolled silage.
Cows fed the rolled silage also produced 2.5 lbs more milk and 3.5 more fat-corrected milk  daily.
Milk fat was also 0.10% units higher on these cows, which could possibly be explained because of less sorting of the cobs in the bunk.
The authors recommended a 3/4" TLC with 1-mm roller clearance, except on wetter silages where the clearance could be expanded to 2 to 3 mm.
Longer chop lengths are not recommended because of the potential for equipment wear and less packing in the silo.
On a posterior trial, the same authors found that processing corn silage harvested later  did not improve the digestibility of the fiber in the corn silage, which was reduced.
From these results it does not appear that harvesting should be delayed.
New silage processors handle grain better than previous ones, allow for greater flexibility at harvest, and reduce feed sorting by the cows.
In 2010 a new method of harvesting corn silage was developed in South Dakota.
The system, named "Shredlage"  consists of cross-grooved crop-processing rolls mounted on a conventional corn silage harvester.
According to the developer, Shredlage silage has a number of benefits compared with traditional kernel processing silage as follows:
 1.
Longer chopped particles , which reduce other forage fiber sources in the total mixed ration.
2.
Longer plant stems, which increase the disrupted surface area.
This enhances rumen microbial accessibility to cell contents, improves total tract digestion, and results in an overall enhanced rumen fermentation.
3.
Stalks ripped lengthwise into planks and strings allowing for better packing.
4.
Prolonged window for silage harvesting since it allows processing at greater maturities without losing too much digestibility.
In general, Shredlage manufacturer guidelines show  the higher the forage moisture, the longer the cut and wider the roll gap, whereas at lower moistures, the cut will be shorter and the roll gap narrower.
Brown midrib  corn silage has spongier stalks and as a result may require a narrower roll setting than the current recommendations for conventional corn.
The use of Shredlage as part of the total mixed ration for dairy COWS was tested recently.
In one trial, Shredlage and conventionally processed corn silage were harvested using self-propelled forage harvesters.
The Shredlage processing rolls were set for a 30-mm length of cut .
The processor gap spacing was set at 2.5 mm, whereas the conventional silage was set for a 19-mm LOC, with conventional processing rolls with 3-mm separation.
The percentage starch passing through a 4.75-mm screen was greater for Shredlage than conventional  silage.
The proportion of coarse particles retained on the Penn State top sieve was greater for the shredded silage.
Packing density in the silo bags was similar and averaged 272 kg of DM/m3.
Feed sorting was minimal and not different between silage processing methods.
Cows fed TMR with Shredlage tended to consume more feed but there was no difference in average milk yield.
Milk component concentrations and yields were not affected by the type of silage.
Cows fed Shredlage, however, tended to have greater yields of 3.5% fatand energy-corrected milk.
Starch digestibility in the rumen was greater in COWS fed Shredlage.
Table 18.2 Length of cut and roller gap suggestions for different corn silage moistures.
Forage Moisture	Length of Cut	Roller gap 
 Figure 18.1 Corn silage harvested with Shredlage technology.
Ferrareto and Shaver  suggested that feeding Shredlage may be a potential tool for dairy producers and their nutritionists desiring to feed higher corn silage diets without compromising kernel breakage for corn silage chopped at a greater LOC.
The research also suggests that shredded silage maintained an adequate packing density of 17.5 lbs of DM per cubic feet compared with 17.2 of the conventional kernelprocessed corn silage.
The proportion of coarse particles retained on the 19-mm screen of the Penn State Particle Separator at feed-out was 31.5% VS.
5.6% for the Shredlage and kernel processed corn silage, respectively.
Once the shredded and kernel-processed corn silages were fed, milk yield tended to be greater  in COWS fed shredded VS.
those fed kernel processed corn silage.
The key to successful application of this technology would be to determine whether feeding shredded corn silage results in less risk of acidosis in high-producing cows.
In addition, it will be necessary to ensure that Shredlage allows for adequate processing of the corn kernel to ensure maximum starch utilization by the COW.
Being able to maximize the inclusion of corn silage in the diets of high-producing dairy COWS will allow for the reduction of highly priced corn grain.
There are some critical aspects to the production and utilization of corn silage as a livestock feed.
In very broad terms, they can be classified as plant, procedure, and feeding.
Adapting animal and plant genetics to the environment  makes more sense environmentally and economically than attempting to modify the environment to fit the genetics.
Harvesting the hybrid at the optimum time is determined by a compromise between yield and livestock performance.
It makes little economical sense to sacrifice silage yield and maximize quality, if the livestock producer will have to add wheat straw to the TMR to increase effective fiber and make it a safer diet.
Corn silage is chopped to improve silo preservation and enhance animal performance.
From this perspective a one-size-fits-all chopping strategy is not available.
More mature, drier corn silages  may have more starch stored in their kernels, however this starch is not as accessible as in those harvested earlier.
If too dry it will not pack and ferment well, and thus heating and molding are possible.
Drier, mature silages may benefit from post-chopping kernel processors or Shredlage, described previously.
On the other hand, corn silage with moisture levels higher than 70 percent, may lead to butyric acid fermentation.
If the odor of the silage changes because of butyric fermentation, it may result in reduced palatability and total feed intake, as well as feed sorting at the feed bunk.
This may result not only in reduced milk production or weight gains, but also in increased incidence of other disorders, such as acidosis and displaced abomasum as a result of feed sorting.
Extremely wet silages also have more seepage with high nutrient loss, and they make it more difficult to remove silage for feeding during the cold winter months because of freezing.
In addition seepage from fermented silage has a very high biochemical oxygen demand.
The BOD is the oxygen required for bacteria to convert biologically available nutrients into energy and new cells.
To avoid problems from too wet or too dry corn, it should be periodically tested for moisture content.
If it is too wet, chopping should be delayed several days.
The low protein concentration in corn grain and corn silage could be considered a disadvantage from a nutritional standpoint.
However, this feature turns out to work in favor of the nutritionist.
One of the constraints with feeding corn and its associated feedstuffs is that its protein is deficient in the amino acid lysine.
As a result, there is oftentimes a need for higher-quality forages  and other feedstuffs that will supply additional lysine in the diet.
This is particularly true when feeding high-performance animals such as the dairy cow in early lactation.
If low-protein corn grain and silage did not dilute the protein supplied by alfalfa and other high-protein feeds, the protein requirements of the ruminant would be exceeded and the excess nitrogen excreted in the urine and feces.
Corn and corn silage can thus be considered "ideal" feedstuffs particularly in the Midwest.
When corn prices increase sharply, livestock producers consider replacing corn grain in livestock diets with other forages.
In this scenario, corn silage may become the primary forage in the ration.
Corn silages with greater percentage of leaves usually have greater digestibility as the higher lignified stalks represent a smaller portion of the total silage mass.
This is the reason that leafy corn hybrids are more digestible.
Researchers conducted two trials evaluating hybrid differences.
In the first trial they compared a conventional hybrid with a leafy hybrid.
Hybrids were evaluated at two plant populations-24,000 plants per acre or 32,000 plants per acre.
These were chopped at 3/4" TLC without a processor and fed in a ration that consisted of 2/3 of the forage from corn silage and 1/3 from alfalfa.
They observed lower ADF digestibility and higher starch digestibility with the leafy hybrid.
The higher starch digestibility was presumably due to the softer kernel texture of the leafy hybrid.
They found no milk production difference among hybrids or population treatments.
Silages varied in these trials by 2 units in NDF and 2.8 units in digestibility, yet no milk response was noted.
These results are similar to another trial recently conducted by the University of Minnesota.
Based on these results, the authors suggested that hybrid selection for leafy and normal hybrids could be based on yield per acre and agronomic performance.
Digestibility of corn silage can be increased by adjusting corn silage height to prioritize ears and leaves over stems.
Cutting corn plants at 8 inches  compared with 24 inches  and chopped at 0.4 inches reduced total silage dry-matter yield by 8.3%, increased grain content by 11.6% and decreased stalks by 38.5%.
With the high-cut silage, the concentration of dry matter, protein and starch increased 9.1%, 4.8% and 22.3%, respectively, while the fiber fractions and lignin were reduced.
Feed intake was similar between the normal and high-cut corn-silage diets.
However, the high-cut silage diet increased production and 3.5% fat-corrected milk.
Feed efficiency  increased with the high-cut treatment.
Cutting corn silage higher, although reducing total forage yield by 8%, resulted in increased total milk and fat-corrected milk production, and improved efficiency of feed utilization.
Leaving 16 additional inches of cornstalks in the field can also be an advantage when high nitrate concentrations might pose a problem.
Frost-damaged or Immature Corn Silage
 Harvesting frost-damaged and  immature corn as silage is similar to producing silage from more mature corn.
However, it is difficult to estimate the moisture content of damaged corn because it appears drier than it actually is.
Leaves that have been damaged by frost will brown and dry rapidly; however, the stalk, ears, and undamaged leaves are still wet.
Milk line alone should not be used as an indicator of moisture content in frost-damaged, immature corn.
When determining the appropriate time to harvest silage, it is important to ponder the moisture content of the whole plant against the potential reduction in dry matter because of leaf loss.
If extensive leaf loss has already occurred, the nutritive value and amount of dry matter remaining should be carefully evaluated to determine whether it is economically feasible to harvest the crop as silage.
The nutritive value of corn silage from immature plants depends on plant growth stage.
Drought-stressed corn or corn that has not been pollinated will produce little or no grain crop for the crop farmer to sell, but producers can use the nonpollinated corn for silage.
On a dry-matter basis, the drought-stressed corn may be nearly equal in feeding value to normal corn silage.
The best way to determine the feeding value of drought-stressed silage is to test the forage.
Forage analysis is useful for buying, selling, or using the silage for ration balancing.
Buyers of drought-stressed silage high in crude protein and slightly lower total digestible nutrients values may be willing to pay a price similar to that of well-eared silage of equal dry matter content.
Silage from corn that has had some ear and kernel development can have similar energy content as that produced under normal conditions.
According to the University of Minnesota, corn in the blister stage can be as high as 80% moisture.
To ensure proper fermentation in a horizontal silo, the moisture content should be between 63% and 68%.
For upright silos, moisture should be between 60% and 65%.
Silage that is too wet, may have excessive seepage and off odor.
The effluent  contains high nutrient concentration, which reduces the nutritive value of the forage and could potentially contaminate the environment.
In terms of N, P and K, the nutrient concentration of silage effluent is similar to typical liquid dairy manure.
The effluent has an approximate pH of 4.0, as it contains organic acids that are necessary for proper ensiling and preservation.
This acidity is another potential pollution issue that can be observed as characteristic burnt/dead plants surrounding ensiled material.
Silage effluent ranks among the highest sources from a contamination standpoint because of its high biological oxygen demand.
The oxygen demand of silage seepage is approximately 50,000 mg of oxygen per L of effluent, 100 times more than raw domestic sewage.
From a biological impact standpoint, a gallon of silage effluent can deplete the amount of oxygen needed for fish to survive in 10,000 gallons of freshwater.
Finally, the fermentation that occurs at higher moisture concentrations can result in the production of butyric acid, which gives silage a sour smell that can reduce palatability and potential feed intake.
In contrast to immature corn, mature corn will dry very rapidly after a killing frost.
It is suggested to consider cutting the silage as soon as possible after the frost, setting the equipment to chop the silage as
 fine as possible.
Harvesting silage that is too dry can create packing problems that can lead to heating and mold development.
Silos that contain silage of questionable moisture content should be monitored closely and care should be taken when opening the silo for feeding.
Both pH and dry-matter content are used as criteria for measuring silage quality.
In silages with more than 35% dry matter, low pH becomes less critical from the point of view of preservation, as limited availability of water will inhibit proliferation of undesirable bacteria.
Silages that undergo limited fermentation, as measured by pH and acid content, tend to show heat damage more frequently.
This is also true for high dry-matter silages, which tend to be higher in pH and "brown" more frequently.
As dry-matter loss increases, there is an increase in the pH as a result of losses of sugars that are not available for lactic acid production.
It has been demonstrated that low pH by itself is not enough to prevent aerobic deterioration, as there are yeasts that can grow under acid conditions.
Silage that has undergone heating can be a safety concern.
When opening a heated silo, there is potential for spontaneous combustion that could result in personal injury or property damage.
Corn silage test results are of little value unless they are understood and used appropriately.
Results can be used to balance rations and to improve future crop management.
Results of analysis are expressed on an "as received" and on a "100% dry matter " basis.
As-received is sometimes referred to "as-fed" or "fresh." The as-received basis includes the water or moisture contained in the feed.
Nutrients expressed on this basis represent the nutrient content of the feed when it was received at the lab.
Dry matter basis means all moisture has been removed.
The nutrient concentration is that which is contained in the dry-matter portion of the feed.
Values reported on a dry-matter basis are always larger than the as-received values.
To convert from an as received to a dry-matter basis, use the following formula:
 Nutrient  X 100 = Nutrient  % DM
 For example, if a sample of corn silage  contains 2.7% crude protein  on an as-received basis, it contains 9.0%  on a dry-matter basis: 2.7% CP X 100 = 9% CP 30% DM
 Moisture content is the amount of water in the feed.
Percent moisture = 100 % DM.
Dry matter is the percentage of feed that is not water.
Percent DM = 100 % moisture.
A sample of corn silage with 30% dry matter contains 70% water.
Knowing moisture content of corn silage is critical to balancing rations properly.
Lower moisture contents are usually associated with more mature plants, which can alter its digestibility and energy content.
Adequate fermentation is also highly dependent on adequate moisture content, which for corn silage should be between 60% and 70%.
If ensiled in an upright silo, 60-65% moisture is desirable to minimize seepage.
Knowing the moisture content of forages is essential for making and preserving high-quality hay and silage.
Using a microwave oven can be a fast and reliable method to determining moisture content.
Changing weather conditions can oftentimes make adequate predictions of moisture in corn plants to be ensiled difficult.
Testing the plants for the right moisture content is critical to determine the ideal conditions for an adequate fermentation.
Oetzel et al.
evaluated on-farm methods to determine the drymatter content of ensiled feeds.
In this study, the authors looked at ease of use, time required to conduct the determination, repeatability, and accuracy relative to a standard drying method.
The methods evaluated were: sequential drying in a microwave oven, Koster tester method, and the electronic moisture tester method.
All methods produced repeatable results.
Although the microwave-oven method was more accurate than the standard method, it also required the most time.
The Koster tester tended to leave some moisture on the feeds and was not as repeatable as the microwave.
The procedure for measuring crop moisture content using a microwave oven was described by Tidwell et al..
Regardless of the method used, it is critical to obtain a representative sample of the silage.
About 2 gallons of silage should be collected from random locations of the exposed surface, avoiding areas close to the top, bottom, and sidewalls.
The measuring procedure requires a paper plate, a glass of water, a small scale, and a microwave oven.
Follow these simple directions:
 1.
Dry the paper plate on high power for 1 1/2 to 2 minutes and weigh it.
2.
Weigh  about 100 grams  of forage sample and spread it evenly on the plate.
3.
Place a glass of water in the back corner of the microwave oven to protect the oven magnetron when sample moisture is low.
4.
For corn silage or chopped corn plant samples, dry for 5 minutes at 50 percent power.
5.
Repeat this step as needed, shortening the drying period to 2 minutes once the sample dries substantially.
6.
Continue until weight change between dryings is less than 2 grams.
7.
If the sample is charred, discard and repeat the test.
8.
Calculate % moisture content with the equation.
% moist = 100 X [-weight of dry paper plate]
 The rest of the nutrient fractions analysis should be performed in a reputable forage testing laboratory.
These laboratories can use wet chemistry or near infrared reflectance spectroscopy  to determine quality.
In wet chemistry, a feed sample is chemically analyzed to determine the nutrient fractions.
In the NIRS analysis, a dried ground feed sample is subjected to infrared light and the divergence of this light is measured and used to calculate the feed composition.
The chemical analysis is more time-consuming and expensive than the NIRS analysis.
Crude protein is an estimation of total protein based on nitrogen in the feed.
Crude protein includes true protein and nonprotein nitrogen  such as urea nitrogen and ammonia nitrogen.
The crude protein value provides no information about amino acid composition, intestinal digestibility of that protein, or the rumen degradability of that protein.
Acid Detergent Fiber 
 ADF consists primarily of cellulose, lignin, and acid detergent fiber crude protein.
It is closely related to indigestibility of forages and is the major factor in calculating energy content of feeds.
The greater the ADF, the less digestible the feed and the less energy it will contain.
Neutral Detergent Fiber 
 The total fiber content of a forage is contained in the NDF or cell walls.
This fraction contains cellulose, hemicellulose, and lignin.
NDF gives the best estimate of the total fiber content of a feed and is closely related to feed intake.
As NDF values increase, total feed intake will decrease.
Grasses will contain more NDF than legumes at a comparable stage of maturity.
Digestible NDF 48 
 The importance of measuring dNDF 48 has been recently recognized.
Fiber digestibility differs between legumes and grasses harvested at a similar stage of maturity, and even for the same species when grown under different weather conditions.
By digesting NDF more rapidly, ruminants can move feed through their rumen faster, thus allowing for enhanced animal performance.
Decreases in dNDF 48 are usually a reflection of higher lignin content in the NDF fraction.
DNDF 48 is measured from an in vitro NDF digestion for 48 hours.
Lignin is a polymer component of the plant cell walls that provides rigidity and structural support to plants.
It cannot be digested by animal enzymes.
It increases as plants mature and is higher for a same plant species grown under warm weather conditions.
The higher the lignin content of a forage, the lower the dNDF.
Also known as ether extract.
This term comprises all substances that are soluble in ether (thus the
 term ether extract).
Although it will mainly contain lipids, it will also include other fat-soluble substances such as chlorophyll and fat-soluble vitamins, and it is high in energy when the fraction represents primarily lipids.
Neutral Detergent Fiber Digestibility 
 NDFD is dNDF expressed as a percent of NDF.
Therefore, NDFD = dNDF/NDF X 100.
Ash is the remaining residue after all organic matter present in a sample is completely incinerated, thus 100 ASH = organic matter.
It comprises all inorganic matter  in the feed, as well as inorganic contaminants, such as soil or sand.
Calcium , phosphorus , magnesium , and potassium  values are expressed as a percentage of each in the feed.
Total Digestible Nutrients 
 TDN represents the sum of digestible crude protein, digestible carbohydrates, and digestible fat.
Since feeds are utilized differently by different species, percent TDN in a feed is different for each species, and it is highly correlated with the energy content in feeds.
TDN is estimated in many different ways.
TDN in SDSU lab reports is estimated from the NEL value, which in turn is calculated from the ADF content of the silage.
The equation for calculating TDN is: TDN = 31.4 + 
 Net Energy for Lactation 
 Net energy for lactation is the term used by the NRC  for assessing the energy requirements and feed values for lactating cows.
It is expressed as megacalories per pound  or megacalories per kilogram.
Corn silage NEl is calculated from ADF with the following equation: NEI = 1.044 (0.0124
 Net Energy for Maintenance  and Net Energy for Gain 
 The net energy system used by NRC for beef cattle assigns both energy values to each feedstuff and similarly subdivides animal requirements for energy.
Feed energy is used less efficiently for depositing new body tissue than for maintaining existing body tissue.
NEm is the net energy value of feeds for maintenance.
NEg is the net energy value of feeds for the deposition of body tissue, growth, or gain.
Both NEm and NEg are needed to express the total energy needs of growing cattle.
They are usually expressed as megacalories per pound  on SDSU lab reports and can also be expressed as megacalories per kilogram.
NEm = -0.508 +   +  NEg = -0.7484 +   + (0.0593 x ME3
 Where ME  = 0.01642 TDN.
ADVANTAGES AND LIMITATIONS OF ET-BASED IRRIGATION SCHEDULING
 A key ingredient for improving irrigation water management to help conserve water resources is utilizing crop water use information, often referred to as evapotranspiration.
This information can be used by growers and their advisers to understand daily crop water use for scheduling irrigations and to determine the amount of water to apply to replenish soil water depletion.
Many resources have been used to develop, promote, and make available ET information for irrigating farmers in Eastern Colorado.
Recent survey results suggest that this effort has had some success, but ET-based scheduling has not gained wide acceptance as a primary method for timing irrigations.
Rather, a greater number of producers in Eastern reported they use weather station ET as a secondary method of scheduling irrigations, supplemental to
 Figure 1.
Irrigation scheduling methods chosen by Colorado irrigators in a 2002 mailed survey.
Responses are an average of all Colorado regions by primary water source.
other information or methods.
Likewise, only a minority of growers  reported knowing the crop water use of their 2001 irrigated crop in the same survey.
This suggests that tracking ET through the growing season and scheduling irrigations accordingly is not a frequently used practice.
As shown in Figure 1, experience, crop appearance, and ditch or a fixed-day schedule are the most frequently used irrigation scheduling methods used by Colorado irrigators.
However, water source  had a large impact on which methods producers use.
These survey results suggest that growers may find ET-based scheduling unattractive and perhaps more work should be done to make ET information more convenient and understandable.
Table 1.
Use of ET-related irrigation scheduling methods as found by 2002 Colorado irrigation survey.
Platte	Plains	Valley	Colorado
 Percent of Respondents Using
 Crop Consultant	6	34	8	7
 Weather Station ET	2	2	3	3
 Atmometer	1	0	0	< 1
 Computer Program	0	0	0	0
 Crop Consultant	5	11	6	4
 Weather Station ET	16	19	7	12
 Atmometer	2	0	1	1
 Computer Program	2	0	0	1
 *State average includes other regions of the state not shown.
Table 2.
Colorado irrigation survey respondents reporting knowledge of crop water use, application amounts and irrigation records.
Platte	Plains	Valley	Colorado
 Percent  of Respondents
 Know Crop Water Used 	7	9	7	7
 Know Amount of Water Applied	48	63	39	41
 Keep Records of Water Applied	21	25	25	23
 *State average includes other regions of the state not shown.
Understanding the processes that impact crop ET should help growers and consultants make better use of ET information.
Daily ET rates for a given crop depend upon the local weather conditions and the cropping system for which
 estimates are needed.
Local weather conditions are important because ET is driven by weather factors that determine the drying power of the air.
Solar radiation and air temperature provide the energy required to vaporize water.
Water vapor loss from the soil or plant is determined by the difference between the water vapor pressure  at the evaporating surface and the surrounding atmosphere.
As ET proceeds, the air surrounding the leaf or soil surface becomes gradually saturated and the process will slow down.
The ET process might stop if the wet air is not transferred to the atmosphere.
The replacement of saturated air close to the plant or soil surface, with drier air from above, explains why wind speed also impacts ET.
Fig.
1.
Relationship between winter wheat grain yield and available soil water at wheat planting at Akron, CO.
FACTORS AFFECTING WATER STORAGE
 Time of Year/Soil Water Content The amount of precipitation that finally is stored in the soil is determined by the precipitation storage efficiency.
PSE can vary with time of year and the
 water content of the soil surface.
During the summer months air temperature is very warm, with evaporation of precipitation occurring quickly before the water can move below the soil surface.
Farahani et al.
showed that precipitation storage efficiency during the 2 1/2 months  following wheat harvest averaged 9%, and increased to 66% over the fall, winter, and spring period .
The higher PSE during the fall, winter, and spring is due to cooler temperatures, shorter days, and snow catch by crop residue.
From May 1 to Sept 15, the second summerfallow period, precipitation storage efficiency averaged -13% as water that had been previously stored was actually lost from the soil.
The soil surface is wetter during the second summerfallow period, slowing infiltration rate, and increasing the potential for water loss by evaporation.
Fig.
2.
Precipitation Storage Efficiency  variability with time of year.
Residue Mass and Orientation
 Studies conducted in Sidney, MT, Akron, CO, and North Platte, NE  demonstrated the effect of increasing amount of wheat residue on the precipitation storage efficiency over the 14-month fallow period between wheat crops.
Fig.
3.
Precipitation Storage Efficiency  as influenced by wheat residue on the soil surface.
As wheat residue on the soil surface increased from 0 to 9000 lb/a, precipitation storage efficiency increased from 15% to 35%.
Crop residues reduce soil water evaporation by shading the soil surface and reducing convective exchange of water vapor at the soil-atmosphere interface.
Additionally, reducing tillage and
 maintaining surface residues reduce precipitation runoff, increase infiltration, and minimize the number of times moist soil is brought to the surface, thereby increasing precipitation storage efficiency.
Fig.
4.
Precipitation Storage Efficiency  as influenced by tillage method in the 14-month fallow period in a winter wheat-fallow production system.
Snowfall is an important fraction of the total precipitation falling in the central Great Plains, and residue needs to be managed in order to harvest this valuable resource.
Snowfall amounts range from about 16 inches per season in southwest Kansas to 42 inches per season in the Nebraska panhandle.
Akron, CO averages 12 snow events per season, with three of those being blizzards.
Those 12 snow storms deposit 32 inches of snow with an average water content of 12%, amounting to 3.8 inches of water.
Snowfall in this area is extremely efficient at recharging the soil water profile due in large part to the fact that 73% of the water received as snow falls during non-frozen soil conditions.
Standing crop residues increase snow deposition during the overwinter period.
Reduction in wind speed within the standing crop residue allows snow to drop out of the moving air stream.
The greater silhouette area index  through which the wind must pass, the greater the snow deposition.
Data from sunflower plots at Akron, CO showed a linear increase in soil water from snow as SAI increased in years with average or above average snowfall and number of blizzards.
Typical values of SAI for sunflower stalks  result in an overwinter soil water increase of about 4 to 5 inches.
Fig.
5.
Influence of sunflower silhouette area index on over-winter soil water change at Akron, CO.
Silhouette Area Index 
 Because crop residues differ in orientation and amount, causing differences in evaporation suppression and snow catch, we see differences in the amount of soil water recharge that occurs.
The 5-year average soil water recharge occurring over the fall, winter, and spring period in a crop rotation experiment at Akron, CO shows 4.6 inches of recharge in no-till wheat residue, and only 2.5 inches of recharge in conventionally tilled wheat residue.
Corn residue is nearly as effective as no-till wheat residue in recharging soil water, while millet residue gives results similar to conventionally tilled wheat residue.
Fig.
6.
Change in soil water content due to crop residue type at Akron, CO.
Good residue management through no-till or reduced-till systems will result in increased soil water availability at planting.
This additional available water will increase yield in both dryland and limited irrigation systems by reducing level of water stress a plant experiences as it enters the critical reproductive growth stage.
Agronomic Guidelines for Pima Cotton Production in Arizona
 American Pima  cotton production has historically been a very important feature of Arizona cotton production.
The first commercial crop of extra-long staple cotton in Arizona was produced in 1912.
A total of 11 extra-long staple varieties have been developed and released for production in Arizona and the desert Southwest.
Pima S-1 was released in 1951 after development of a selection from a series of crosses involving Sea Island, Pima, Tanguis, and a variety of Stoneville Upland  cotton.
These crosses provided a broad germplasm base for the development of improved fiber and yield characteristics for further Pima selections.
Subsequently, five additional Pima varieties have been released: Pima S-2, 1960; Pima S-3 and S-4, 1966; Pima S-5, 1975; and Pima S-6, 1983.
Improvements in each successive release have provided higher yield potentials through increasing heat tolerance and earliness.
Improved heat tolerance and earliness have been beneficial to lower elevation areas , and improved earliness has been a benefit to higher elevation areas.
Continued improvements in yield potential through increasing heat tolerance and earliness, while maintaining or improving fiber properties, is an ongoing goal within the Pima breeding program for the development of future variety releases.
With the interest and activity in Pima cotton production in Arizona, perhaps an outline of some of the major points concerning some of the agronomic factors involved in the production of Pima cotton in Arizona would be in order.
Newcomers and veterans to the Pima production process recognize that differences do exist between Upland and Pima in terms of growth habits and management.
Even with the release of Pima S-6 in 1983, Pima remains to be more inde-terminate than its Upland relatives, a factor which figures very predominantly in several aspects of its management.
Planting Date and Rate
 A series of experiments have been conducted in the past several years, where Pima S-6 was included as a variety planted at four locations, with four to five planting dates at each.
Locations included Yuma, Maricopa, Marana, and Safford.
Dates of planting ranged from late February to early April at Yuma, late March to early June at Maricopa, and very early April to early June dates at both Marana and Safford.
The planting dates were separated by about 14 days in each case.
The results are fairly consistent among these tests with regard to the yield response of Pima S-6 to date of planting.
Even though Pima seeds are generally regarded as being more cold tolerant, they emerged and became an established stand best when planted in suitable warm soil conditions.
Such conditions could be generally described as 60-65F in the zone of seed placement for several days prior to and after planting, with a well-prepared seedbed.
We also found from these experiments that Pima S-6 tended to perform best when planted early, and realized rather consistent declines in yield with delayed plantings as used in these experiments.
The point to be taken is that planting of Pima S-6 is probably best for as early a date as conditions will allow.
This is to say generally that late March to April plantings are best for most areas,
 THE UNIVERSITY OF ARIZONA COLLEGE OF AGRICULTURE AND LIFE SCIENCES TUCSON, ARIZONA 85721
 J.C.
Silvertooth Extension Agronomist Cotton
 and that delays past that time may be quite costly in terms of yield potentials.
For Yuma, this possibly could be extended to say that Pima plantings should optimally occur from late February to the first of April.
Another way of describing optimum planting dates is by the use of heat units  using 86 and 55F upper and lower limits.
A range of about 300 to 900 HU accumulated since January 1 at any given Arizona location, can best describe the time frame for Pima  plantings that provide an optimum for yield potential.
This range of accumulated HU may vary by calendar date from year to year, and by location; but can provide a better measure of seasonal patterns.
By the time 300 HU have been accumulated, adequate soil temperatures likely will have been reached.
This does not eliminate the need for monitoring soil temperatures and weather forecasts, but serves as a guideline for planting.
Other things learned from these experiments included the fact that as Pima was planted later  plants grew taller, more vegetative, and less productive.
This is seen as a plant response to greater amounts of heat  being accumulated in shorter periods of time, which causes greater internode length, larger leaves, and a lesser tendency to begin fruiting.
So a delayed planting of Pima will tend to bring about taller, more vegetative plants, with lower yield potential, after causing a grower a degree of concern and difficulty in management.
In fact, as HU accumulations since January 1 exceed 700, yield potentials from subsequent Pima plantings become increasingly marginal as vegetative tendencies under warm weather conditions become more likely.
Acceptable plant populations for Pima cotton range from approximately 20,000 plants per acre  to 50,000 ppa.
Optimum populations range from about 25,000 ppa to 40,000 ppa.
Pima plants typically have long fruiting branches, with as many as eight fruiting sites per branch.
Therefore, Pima plants have a very flexible nature in terms of compensating for varying plant populations, and maintaining high yield potentials.
High plant populations  can lead to plants that are tall, vegetative, and generally poor in total fruit  retention per plant.
Therefore, high populations contribute to plants that are difficult to manage for high fruit retention, and delay maturity.
Pima cotton typically has been grown on a 40 inch row spacing, which is generally accommodating to the wide branching nature of the plants.
At present, insufficient data are available to determine the advantages or disadvantages associated with the use of 30-inch-row spacings.
Further research with more determinate Pima selections may prove to be of benefit under narrow  row systems in an effort to improve earliness with this type of cotton.
Probably one of the most difficult decisions to make in a Pima production season is the time to initiate the first irrigation.
Plant water stress itself is a tool that many veteran Pima growers have found useful with pre-S-6 varieties, and also sometimes with S-6, to control vegetative growth.
However, most successful Pima S-6 growers currently do not intentionally water stress a Pima crop at any time except during very early periods in the season.
This is usually just prior to the first irrigation.
Just how much to stress a Pima crop at this time is a very good question and a delicate one.
It does not appear that anyone has established some easily measured point at which enough stress has been incurred and irrigation is needed before serious harm is done.
This still remains a somewhat "artistic" act that Pima cotton producers must carry out.
Most Pima growers and researchers agree that an imposed water stress should be avoided up to the time one is preparing the crop for termination.
Substantial data on consumptive use patterns of Pima versus Upland cotton are not available.
However, on a daily basis, Pima cotton requires essentially the same amount of water as its Upland counterparts do.
Any differences in total water used on a Pima crop probably occurs later in the season when an additional one  irrigation may be provided to mature later-set bolls.
In terms of water management throughout the course of the season, Pima S-6 is usually managed very much like full-season Upland varieties.
With the abundance of HU that Arizona cotton crops commonly accumulate, the two main controls an Arizona cotton grower has are water and nitrogen  fertilizer.
Keeping the plant in good condition with regard to water relations through the season is an obvious objective.
Since the control of the vegetative/ reproductive balance is particularly critical in Pima, one must also consider the N fertilization of Pima in a unique light.
Many producers and researchers agree that Pima is sensitive to excessive N levels, and can convert extra growth to pure vegetation without any trouble.
In fact, many Pima growers purposely avoid fields where a high level of residual available N  will be present.
This should be a point of consideration for growers placing Pima in a field after vegetable or alfalfa crops.
Guidelines have been developed for managing N fertility in Pima by use of petiole sampling in-season.
The Arizona Cooperative Extension publication 8373: The Cotton Petiole: A Nitrogen Fertilization Guide  outlines procedures and ranges in petiole nitrate -N  levels for management through the growing season.
In
 comparison to Upland levels of petiole nitrates, Pima levels should be somewhat lower throughout the season.
Caution should particularly be taken to avoid excessive levels of NO -N in the Pima petioles early in the season, to avoid excessive vegetative growth before fruit set begins.
Further details describing N management for Upland and Pima cotton are provided in Arizona Cooperative Extension publication 9024: Nitrogen Management in Arizona Cotton Production.
In terms of insects, weeds, and diseases; the general cases that pertain to Upland cotton can be transferred to Pima.
However there are a few points of difference.
Pima bolls seem to be more susceptible to pink bollworm ) damage than Upland.
This is primarily due to Pima bolls maintaining a higher moisture content and softer boll walls that are prone to pink bollworm damage over a longer period of time.
Pima bolls are not sufficiently hardened until 35 to 40 days after bloom.
The sweet potato whitefly ) is becoming a pest of concern in both Upland and Pima cotton production.
Concern is particularly associated with the diminished quality that results from the sooty mold and the stickiness of the lint that may be caused by the honeydew secreted by whiteflies.
Pima cotton has appeared to some to be more attractive to whitefly populations.
Regardless of the degree and cause of attractiveness, we know that whiteflies and Pima are not good companions.
Pima is an indeterminate plant, often grown in a long, fullseason setting.
When whitefly populations characteristically grow at nearly exponential rates late in the season, very little remedy appears to be available at present.
Termination, defoliation, and quick removal of the crop has proven to be a good alternative to growers faced with this problem.
This is one point causing interest in evaluating the length of season a Pima cotton crop requires for optimum economic return, and the option of early termination.
Particularly considering the strong emphasis that quality has in Pima production systems.
In terms of disease control, Pima cotton has demonstrated several differences to Upland.
Pima cotton is often thought of as being more susceptible to Texas Root Rot than Upland cotton.
Probably due to a deeper rooting tendency, and due to the fact that Pima plants often don't accomplish a significant fruit set until later in the season.
Many growers avoid fields known to have substantial Texas Root Rot kill patterns.
Pima also has been cited as being more prone to developing Alternaria Leaf Spot, a fungal pathogen which attacks the leaves of the plant.
This however, has not yet developed into a problem of any broad extent in Arizona.
In order to obtain the highest possible returns on a Pima crop, one must maintain the highest quality lint as possible.
The quality of harvested lint is often a result of the preparation and picking process at the end of the season.
Accordingly, the late season management of the crop, and the defoliation of the crop affect the timeliness in which the cotton is harvested from the field.
The choice and timing of defoliant chemicals that are applied certainly are important in achieving satisfactory defoliation.
But other factors such as the late season plant-water status, the N fertility status, and the boll load that the crop plants are carrying have a definite impact on the way a cotton crop defoliates.
This is true of both Upland and Pima due to their perennial nature, but particularly Pima with its robust and indeterminate growth pattern.
By using chemical defoliants, one is attempting to enhance the natural physiological process of plant senescence and leaf abscission.
Defoliation requires a degree of natural senescence which can be brought along to some extent by the development of water stress late in the season.
Plants carrying a good boll load also naturally senesce a little more rapidly.
A certain degree of physiological activity is needed to realize the effects of chemical defoliants, and also to have a sufficient green leaf weight to actually drop the leaf from the plant once an abscission layer is developed.
Otherwise, leaves may be burnt but not dropped, leading to a possible trash problem.
Recent research conducted in an effort to develop better guidelines for Pima cotton would reinforce these points.
Exceedingly dry Pima plants are difficult to defoliate , while fresh, lush growth also is very difficult to slow down and defoliate, and has strong regrowth tendencies.
Developing a slight water stress following termination encourages senescence, but too much will hinder defoliation efforts.
Allowing three to four weeks  after the final irrigation before defoliant applications, generally provides adequate plant senescence to accommodate defoliation.
Late season N levels that are high also can cause the plant to maintain strong vegetative growth.
Based upon the guidelines mentioned previously, petiole NO -N levels should be drawn down below 3,000 ppm prior to defoliation.
This will not cause a yieldlimiting decline in N fertility, while allowing for a stronger trend in plant senescence.
Not every aspect of Pima cotton production has been addressed in this bulletin.
However, a discussion of the points in Pima production where principal differences exist in comparison to Upland cotton
 production has been attempted.
Basic agronomics are essential for producing both the quantity and the quality required for successful Pima production in Arizona.
WATER WITHDRAWAL REGULATION IN SOUTH CAROLINA
 Published: Apr 27, 2022 |  Printable Version  | Peer Reviewed
 Heather B.
Nix and Mani Rouhi Rad
 Water use and reporting regulations in South Carolina have gone through substantial changes over time.
Current regulations contain permitting, registration, and reporting requirements for significant water withdrawals throughout the state.
The relevant regulations vary across sectors and different sources of water.
Understanding how water use is regulated and reported will contribute to the sustainable management of water supplies into the future.
This article describes the main regulations and reporting requirements for water withdrawals, including a brief overview of historical and additional discussion regarding current requirements of water use sectors for surface or groundwater sources.
Historical Water Withdrawal Regulation and Reporting
 Significant changes to water use regulations and reporting requirements in South Carolina include
 1967: The passage of the SC Water Resources Planning and Coordination Act laid the groundwork for the creation of the SC Water Resources Commission in 1969 to advise and assist in developing a comprehensive water resources policy.1
 1969: The passage of the SC Groundwater Use Act initiated reporting requirements for groundwater withdrawals greater than or equal to 100,000 gallons on any day that were located within a Capacity Use Area.2
 1982: The SC Water Use Reporting and Coordination Act was passed and gave authority to the SC Water Resources Commission to require reporting by anyone using greater than or equal to 100,000 gallons of surface or groundwater in any one day.3 However, reporting remained voluntary, and not all water users provided withdrawal information.2
 1985: The SC Drought Response Act formalized the need for a drought response plan and formed a statewide Drought Response Committee.4
 1993: Revisions to the SC Water Resources Planning and Coordination Act dissolved the SC Water Resources Commission and divided its responsibilities between the SC Department of Health and Environmental Control , which implements water regulations, and the SC Department of Natural Resources, which leads water planning.1 The SC Drought Response Act was revised.5
 2000: Previous legislation was renamed and revised to implement a mandatory reporting threshold of more than three million gallons  in any one month.2 Water users below the 3MG in any month threshold may continue to voluntarily report their water withdrawals to SCDHEC; therefore, comprehensive data for smaller water users has not been collected since this legislative revision.
The SC Drought Response Act was revised to update options for response to drought.5
 2010: Passage of the SC Surface Water Withdrawal, Permitting Use, and Reporting Act effectively converted South Carolinas water law from riparian water rights to a regulated riparianism system.6 The Act  applies to any entity that withdraws more than 3MG of surface water in any month.
Exemptions include the following water uses: instream dredging or sand mining, emergency withdrawals, naturally occurring evaporation from impoundments, hydropower generation, withdrawals for wildlife habitat management, agricultural withdrawals from a private source that meets the definition of farm pond, and specific withdrawals from a pond supplied only by groundwater or surface water entirely situated on a privately owned property.7 Annual reporting requirements were maintained for water uses that exceed 3MG in any month.8
 Current Water Withdrawal Regulation and Reporting
 Currently, in South Carolina, a permit or registration is required for a surface or groundwater withdrawal in excess of 3MG in any month unless specifically exempted.
However, surface water and groundwater withdrawals are managed under separate regulations and planning processes.
Surface water withdrawal regulations apply statewide, with permits and registrations required depending on the use of the water withdrawn.7,8 Groundwater withdrawals require a permit if located within a Capacity Use Area , generally to the south and east of the Fall Line, and a registration if located outside of a CUA.9 Both surface and groundwater permits are issued for the total amount of water that a user can withdraw from a specific source.
Surface water registrations include a withdrawal limit, but users may withdraw beyond their registered volume without modifying their surface water registration, as long as withdrawals are not substantially greater than the registered amount.8 Groundwater registrations require reporting and do not contain specific limits on withdrawal volume.
Per the SC Surface Water Withdrawal, Permitting, Use, and Reporting Act, if withdrawing more than 3MG in any one month, a water user must secure either a registration or a permit from SCDHEC.7 Surface water withdrawal requires registration for agricultural use or a permit for all other uses, unless otherwise exempted.7 The largest reported water usage, hydroelectric power generation, is exempted from permitting as this water is passed through turbines but is not technically removed from the river; however, reporting requirements do apply.
Table 1 summarizes requirements by water use sector.
Violations of these regulations are subject to a civil penalty of up to $10,000 per day.8
 Permit durations range from twenty to fifty years.8 Water users initiating withdrawals after January 1, 2011  should be issued a permit for a minimum duration of twenty years; while water users prior to January 1, 2011  should have been issued a permit for a minimum duration of thirty years.7 Municipalities or other governmental agencies may receive a permit duration of up to fifty years.8 Agricultural registrations for surface water withdrawal do not expire and cannot be transferred.
Fees and additional requirements vary depending on water use sector and timing of initial withdrawal.
For example, application fees are higher for new users  than for existing users , while the same annual operating fees  are required for all permittees.
Additional permit fees include $2,000 for processing a permit modification and $1,000 for permit renewal with modifications.8 No fees are charged to surface water withdrawal registrations.8
 Decisions to approve a water withdrawal are based on different factors depending on if the application is for a permit or registration and if the applicant is considered new or existing.
For non-agricultural withdrawals that existed pre-2011, permits were issued based on the largest volume as determined by previously documented use, current treatment capacity, or designed capacity of the intake structure.10 For new or expanded existing non-agricultural users, permits are issued based on reasonableness, availability of water at point of withdrawal based on Safe Yield calculations, and are subject to minimum instream flows.10 Permits for new users also require public notice, including a mandatory public hearing for proposed new interbasin transfers.10 For agricultural users, existing registrations were based on the highest previous water usage, and new registrations are based on the amount of water requested by the proposed withdrawer and availability of water at the point of withdrawal based on Safe Yield calculations.10 Reported surface water withdrawals are typically significantly less than permitted amounts.
Actions taken according to the SC Drought Response Act  supersede surface water withdrawal permits.7 An Operations and Contingency Plan  is required of some permittees to address providing an adequate water supply during low flow periods.8 For new permittees, or expanded withdrawals by existing permittees, the Contingency Plan is an enforceable part of the permit and controls withdrawal volumes when the flow volume in the surface water source is less than the minimum instream flow.8 The Contingency Plan may require the use of a supplemental water source  in response to low-flows to protect minimum stream flows as well as downstream permitted and registered withdrawals.
Existing withdrawals must only address appropriate industry standards for water conservation.8 A Contingency Plan is not required for permittees withdrawing from a federally licensed impoundment or for any registered  withdrawal.8
 During low-flow conditions, existing permittees must implement industry-appropriate water conservation measures.8 Registered  water withdrawals are not required to have Contingency Plans nor to meet Minimum Instream Flow standards.
To summarize, reductions in surface water withdrawals may be required for permittees based on low flow conditions; however, reductions in registration withdrawals may only be triggered if substantially more surface water than the registered amount is withdrawn and if it results in detrimental impacts.8
 Table 1.
Overview of SC surface water withdrawal permit and registration requirements, applicable if more than three million gallons are withdrawn in any month.
Groundwater is not uniformly distributed across the state.
Most of the groundwater and all the major aquifers are located to the east of the Fall Line.2 Capacity Use Areas  have been created to improve the effectiveness of monitoring and managing the use of the states aquifers.
Establishment of CUAs has occurred over time: Lowcountry , Waccamaw , Trident , Western , and Santee Lynches.2,11
 A map of South Carolina showing designation of counties outside of or within each Capacity Use Area.
Figure 1.
Map of Capacity Use Areas in South Carolina.
Image Credit: SCDHEC.
Note that the Santee-Lynches Capacity Use Area was approved by the SCDHEC Board on July 15, 2021.11
 Regardless of water use sector, each groundwater user capable of withdrawing more than 3MG in any month requires registration if located outside of a Capacity Use Area  or a permit if the withdrawal is located within a Capacity Use Area, with some exemptions.12 Exemptions from the regulation include groundwater withdrawals for emergency use, non-consumptive use, wildlife habitat management, and noncommercial household use.13 Exemptions from permitting and public notice include dewatering operations, Type I wells in crystalline bedrock within a CUA, and replacement wells of equivalent capacity.13
 Groundwater withdrawal permits must be in accordance with the approved groundwater management plan for the appropriate CUA, and permit limits may be reduced based on demonstrated need  or adverse impacts to the aquifer or other water users.10 Permits for all water use sectors are issued for up to five years in duration.13 Groundwater permit applications must include a Best Management Plan that identifies water conservation measures to protect water quality and should include conservation techniques, alternate sources of water, justification that water use is necessary, and a statement specifying the beneficial use of the withdrawn water.13 A public notice is required if the groundwater permit application requests a new or increased withdrawal or if there is sufficient public interest.13 A permit may be revoked for failure to provide a groundwater use report.13 No fees apply to groundwater withdrawal applications.10
 Table 2.
General guidelines, by water sector, for reasonable use determination in SC groundwater withdrawal applications.
Anyone withdrawing more than 3MG in any month must report the quantity of water withdrawn on an annual basis; qualifying groundwater withdrawers must report before January 30,13 and surface water withdrawals must be reported before February 1 of the following year.8 Water quantity may be measured with a meter or may be determined using a variety of other methods, including the capacity of the pump , the capacity of cooling systems, United States Geological Survey standard methods, or other reliable methods approved by SCDHEC.8 Even still, obtaining accurate and complete data on water withdrawals in South Carolina has been recognized as a challenge for many years.
In fact, a Water Resources Commission established in 1969 to study water policy noted the difficulty of the task without having transparent data on actual water usage.14
 Understanding both how much water is available and how water is regulated are critical to evaluating the potential sustainability of future supplies.
Changes in regulations, including reporting requirements, impact the amount of data available and the period of record that can be evaluated.
This article discussed a brief history of water regulations in the state and permitting, registration, and reporting requirements.
Future work can further consider the water withdrawal and consumption as well as the spatial and temporal distribution of water use in the state.
SOIL MANAGEMENT AND SOIL TESTING FOR IRRIGATED COTTON PRODUCTION
 Whenever we are studying an important crop plant such as cotton, it is a natural tendency to focus on the above ground portions of the plant, because that's where the bolls are.
However, an equally important part of the plant is the root system, which is hidden from view and totally immersed in the soil.
The soil provides all of the mineral nutrition, water, and mechanical support to the plant through the root system, and therefore, is a vital link to the health and productivity of any cotton plant.
The soil is a focal point of any farming operation.
At the beginning of each season, growers use various tillage operations to incorporate residues from previous crops and to prepare an adequate seedbed for the subsequent crop.
As a result, most farmers are very familiar with their fields in terms of surface soils, where and how the textures change  and what is required to till them properly.
Most of us working in the field also notice that despite the excellent soil maps and surveys available to us, which provide general descriptions of soils we encounter in a given field, the most detailed mapping of the soils in that field will be performed by the  plants.
For example, areas of a field with better soils will produce better plants, and vice versa.
An excellent time to make note of this is during harvest.
When you are riding a picker through the field you have an excellent vantage point from which to map the soils in the field, from strong to weak.
In dryland areas this may be from a hilltop to a side-slope to the bottom of a swale in a field.
Or in the irrigated west it may be from areas which were cut or filled in the process of land leveling, or from the presence of coarse soils which are remnants of old washes that passed through the area before cultivation.
In this article we will discuss various aspects of soil evaluation including physical examination, soil sampling and analysis, and soil test interpretation.
We will also discuss how these approaches to soil evaluation can be incorporated into both shortand long-term management plans.
Therefore, this time of the year it is good to make note of patterns associated with your fields and to even make an effort to map them out, particularly if there are definite production problems associated with certain parts of any field.
One might ask, however, "so what are you going to do about it even if you know where the problem spots are?" The first step would be to review plant conditions found in 1995 and previous years, and the evaluate the extent to which problem areas exist, and if they are getting better, worse, or staying about the same.
The second step would be to actually go out into the areas in question, and compare what you might describe as a "problem area" versus a "good area".
The next step, and commonly where someone's curiosity begins to wane, involves taking a shovel, soil probe, or a soil auger into the field to excavate and evaluate the soil conditions throughout the rooting depth.
Soil Evaluation Physical Conditions
 In a general sense, we can describe soil management practices and evaluations as being either physical or chemical.
The main thing one would be looking for in a field evaluation would be the physical condition of the soil through the profile.
Problem areas may show evidence of a clay layer, a hardpan , abrupt changes in soil texture from one horizon to another, a gravel layer, or even a water table.
All of these factors can vary tremendously within a given field and can affect crop growth and productivity.
Physical conditions in the soil, for the most part, are not easily altered , but they can impact the way in which we manage these areas in terms of tillage, cultivation, irrigation practices.
The presence of a hardpan or plowpan can be dealt with to some extent by the use of deep tillage.
High water tables may require the use of some drainage techniques.
The depth at which gravel, compaction, or free water layers occur can
 indicate to us the general depth to which roots will grow.
For example, as shown if Figure 1A, if a coarse gravel or compacted layer were detected about 18 inches below the surface, this would be a good indication that our effective rooting zone would be limited to this depth as well.
So instead of having a full soil profile of four feet available for rooting , as shown in Figure 1B, we would only be working with about 18 inches.
The bottom line in this respect is "if you don't know what your soils look like below the surface, it may be worthwhile to go find out".
This could be useful in addressing some of the problems common to fields or parts of fields.
Soil Evaluation Chemical Conditions
 The other aspect of soil evaluation that is important is that of the chemical condition.
Soils are very active chemically and they can differ a great deal in terms of chemical conditions present.
The soil chemical environment is very important in that it determines the composition of the soil solution within which the roots live and function, which directly impacts plant nutrition.
Physiologically, plant nutrition is clearly recognized as a fundamental aspect of a healthy, vigorous, and productive cotton plant.
Accordingly, soil testing has become an integral part of modern agriculture and certainly for cotton production.
In developing an assessment of soil chemical conditions or a soil fertility evaluation, it is probably worthwhile to review some basic aspects of making a soil fertility program functional and profitable.
This would be true if we were dealing only with problem areas or entire fields.
As an example, soil pH conditions alone  can have a strong impact on nutrient availability, root growth, and overall plant health.
In some portions of the cotton belt , acid subsoils can reduce or prevent root growth, which can limit the depth of the soil profile utilized by the plant and have a similar end result as the gravel layer described in Figure 1A.
This condition may not be detected by augering through the soil and visually inspecting it, but it would be readily apparent if soil samples were collected at regular depth intervals and subjected to a simple pH analysis.
Soil Sampling Collecting the Sample
 Again, the only way to conduct this type of soil evaluation is to get out into the field with your favorite soil probe, auger, or a shovel and collect a good set of samples.
Commonly, a recommended frequency for sampling a given field is once every three to four years, assuming no nutritional or production problems develop.
This type of soil sampling frequency is usually considered as a minimum for developing a soil fertility maintenance program.
Usually, it is recommended that a single soil sample should be collected for any given field or management unit.
However, a single soil sample should consist of at least 25 individual cores collected from representative areas of the field or management unit, which are then mixed together into
 a common "composite" soil sample.
How much of this sample to send into the soil testing lab will depend on the analyses to be performed and the specific lab, but usually about 20-30 ounces  are required.
Therefore, of the 25 or more soil cores which are collected from a field, management unit or problem area, only the amount needed to fill an appropriate soil sample container is actually collected from the composite sample and sent into the lab.
Depth of sampling is usually at least six inches, but may extend to 12 inches or more, depending on the situation.
Sampling technique  may also depend on whether the field is irrigated, bedded or flat, and also on what is needed from the analysis such as nitrate-nitrogen , sulfate-sulfur  phosphate-phosphorus , sodium  or total salt concentration, etc..
In reference to sample frequency, depth, amounts of soil needed, and tests to run; this will all depend to some extent on the nature and intent of the sampling process as to whether it involves routine management or diagnosis of problem areas in a field.
The identification of a field or management unit for soil sampling relates to the evaluation of field conditions at the end of the recent cotton production season.
Individual fields are usually the largest unit that is recommended for an individual soil sample.
However, if there are parts of a given field which are obviously unique and may require specific management, they should be sampled independently.
For example, a relatively uniform field , can be easily managed in a consistent manner, and therefore could be sampled by collecting at least 25 soil cores from representative areas.
Figure 2B on the other hand, could represent a field that has three distinct areas , each of which should be sampled independently.
How one delineates between these areas in the field should depend first of all on plant growth and performance, which could relate to our end of season evaluations discussed earlier.
The results you get back from the lab will only be as representative as the sample you collect.
Soil tests and analyses are of course performed after a soil sample is collected, but it is probably a good idea to consult with some labs and select one before you actually collect the sample.
You should discuss your situation with the consultants or managers of the soil testing lab you chose to use regarding the sample collection process to insure that you provide adequate materials to the lab for analysis.
They can also help you determine what you want the samples to be analyzed or tested for.
This will depend to some extent on your location, the problems you have encountered , and past fertilization history.
The 13 essential mineral nutrients for cotton include the macronutrients: nitrogen , phosphorus , and potassium ; the secondary nutrients: magnesium , calcium , and sulfur ; and the micronutrients: boron , copper , chlorine , iron , molybdenum , manganese , and zinc.
Some sources now may also include sodium , cobalt , vanadium , and silicon  among the list
 of essential plant nutrients.
Because a nutrient is considered as being essential for cotton growth and development, does not necessarily mean that you will need to test for or fertilize with each and every one of these.
This too will depend upon location, plant symptoms, and fertilization history.
The nutrients to test for in a standard soil analysis will normally include N, P, K, and pH.
In some cases it will also be necessary to include Zn, Fe, and B.
In the western portions of the cotton belt it will always be important to evaluate soil salinity by measuring the electrical conductivity of the soil extract  and the Na levels, commonly expressed as an exchangeable sodium percentage  or the sodium adsorption ratio.
Salinity levels can impact crop vigor and yield potential, particularly in the early stages of development.
Sodium represents an aspect of the soil system that is evaluated chemically, but it's primary impact is physical in that high Na concentrations cause a dispersal of soil particles which in turn results in a breakdown in soil structure, reducing water penetration and infiltration, aeration, and increasing crusting problems.
Salinity and Na levels represent good examples of where it can be important to consider sample collection for a specific analysis.
Instead of collecting a soil sample to a depth of six to 12 inches, it may be necessary to sample only the upper few inches of the soil surface when determining salt or Na levels.
Relatively high concentrations of salt or Na in the upper few inches of the soil can have a severe impact on early seedling vigor  or create soil crusting problems.
Interpretation of Soil Test Results
 The purpose in subjecting a soil sample to analysis for a given nutrient is not to determine the total amounts of the nutrient in question in the soil.
In fact, the total amount of a given nutrient in a soil seldom has much relationship to what amount is available to a cotton crop.
A key challenge in conducting a soil analysis is to use an extraction procedure that removes a portion of the nutrient from the soil that relates to the plantavailable form and amount.
For example, if one is analyzing a soil for P levels relative to cotton needs, a chemical extract is commonly used that measures a portion of the total soil P which is available to the cotton plant.
The soil tests and extracting procedures can vary a great deal across the cotton belt due to differences in soils, climates, and production conditions.
One may also find a considerable amount of variation among soil testing labs within a given state concerning soil testing methods, due to differences in philosophy, experience, and technique.
The differences in soil testing methods, and the assertions and allegations that can go along with them, can be confusing and tiring to even the best and most patient of experts.
It is no wonder that farmers can sometimes become disillusioned with the value in investing in a soil testing program.
The fundamental key to look for in the abilities of any lab to analyze your soils and to make reliable recommendations for fertilizing a cotton crop is that of having a satisfactory database relating the following factors: 1) soil test results, 2) fertilization rates, and 3) crop yields.
Unfortunately, some labs do not make a successful connection among these three points.
Some labs analyze a lot of soils and make a lot of recommendations for fertilization, which are often followed diligently, but they are not able to follow through with connecting the resultant crop yields to the soil test levels or the fertilization rates.
Collecting and developing a database inclusive of each of these factors for a large number of fields and seasons is referred to as soil test calibration and correlation, and is critical to the development of a reliable and successful soil test system.
Essentially, this means it is important for a lab to be able to show that for a given soil test value and corresponding amount of fertilizer recommended , a corresponding yield can be produced.
This represents a time consuming and expensive process, but it is absolutely critical to developing a truly functional soil test.
It is not absolutely necessary for every lab to develop this type of a soil test calibration system, but it is important that labs use soil test procedures that have been calibrated and correlated sufficiently to crop yields.
This is why different soil test procedures can be used in a given region with satisfactory results, providing that the soil tests in question were properly developed  to crop response for that region.
Therefore, it would be advisable for one to inquire into the background and support a given lab has for their soil tests and the fertilizer and soil management recommendations they offer from the soil test results.
Generally, the farther away a lab is, the less likely they are to use locally applicable soil test procedures and interpretations that are appropriate.
Developing a Soil Management Plan
 Protecting our soil resources is an important responsibility of those involved in crop production and land management.
Our soils serve as the basic foundation upon which the entire cotton production system is developed.
As we push every acre of land for higher yields, we squeeze a little bit more and more out of it.
As national and global populations continue to increase, the demands being placed on the agricultural lands, including cotton fields and their soils in the U.S., will increase as well.
Future generations will need a fully functional soil resource if they are to successfully supply society's need for food and fiber.
It is up to us to pass on such a soil resource, hopefully in better condition than we found it.
Our understanding and capabilities have improved a great deal in recent decades, our expectations have increased, and SO have our incentives for sound land stewardship.
The development of a soil management plan can have both shortlong-term implications.
In the short-term, the incentive is to be sure to provide both the best physical and chemical soil conditions possible for next year's crop of cotton plants.
Reviewing field conditions from this past year can help identify potential problem fields or parts of fields in need of attention in the offseason.
Making good use of a soil auger to check soil profile conditions concerning the presence of absence of any compacted or restrictive layers, and the general organization of soil textures throughout the crop rooting depth  can be done in the off-season.
Tillage
 operations and their timing can be very important in improving or maintaining soil tilth and physical conditions.
Tillage operations should be avoided whenever soils are too wet, particularly in finer textured soils, that can lead to compaction and loss of soil structure, which is severely damaging to soil physical conditions.
Preparing fields to provide soil fertility levels sufficient to meet high yield and quality demands is the primary incentive for addressing a soil and fertilizer management plan each season.
In a long-term sense, we don't want to deplete a soil's basic productive potential due to neglect and a gradual decline in the soil fertility level.
The key objective agronomically, economically, and environmentally is to provide adequate, but not excessive levels of any plant nutrient.
The most reasonable and effective way to get this done is to avoid the guesswork and embark on a soil testing program.
As was mentioned before, soils should probably be sampled at least once every few years, unless specific problems are noticed.
A good lab, with a well developed soil testing, interpretation, and recommendation program should be employed once the samples are collected.
Most labs can provide advise and recommendations for many combinations of soil types and cropping systems, one year at a time and for a long term approach as well.
Certain areas or regions in the cotton belt have specific needs to be addressed in soil management.
For example, in irrigated areas of the western cotton states, soil salinity and Na problems are important to address.
Both of which can effect crop water use, irrigation efficiencies, crop vigor, and management.
These also represent factors that may not pose a problem one year, but due to subtle yet increasing amounts of salt and or Na, they may become limiting to the productivity of a cotton crop in a gradual yet devastating fashion.
It is also important to consider the quality of the irrigation water that is being applied to the soil and the crop.
The irrigation water not only is the lifeblood of the crop in these regions, but it can also be the source of both salt and sodium which can accumulate over time, if not
 recognized and managed properly.
The best approach is to monitor the system with both soil and water samples on a regular basis and to be capable of responding appropriately.
In some parts of the country a new approach to soil fertility management is being implemented as a part of precision agriculture with site-specific soil management.
This involves a detailed soil sampling scheme in which samples are collected in a systematic fashion in relation to specific field coordinates.
Field maps are then developed from the soil test results and the variability encountered in any given field is then accounted for and fertilizers are applied with equipment capable of adjusting rates in the field for specific spots.
So instead of treating an entire field in a uniform fashion to address the average case, the soil needs are addressed in a site-specific fashion.
This technology provides the opportunity to improve upon fertilization and soil management efficiency, accomplishing agronomic, economic, and environmental objectives simultaneously in the field.
Some labs and fertilizer application facilities currently have this technology and it may soon become commonplace across the cottonbelt.
The future holds many potential opportunities and challenges for those of us involved in cotton production.
To realize our potentials, we need to take care of our soil resources upon which we and our cotton plants depend.
We can have the finest varieties in the world, make use of all the plant-oriented technologies that are available, but it won't do us any good if our plants do not have a proper nutritional or soil foundation to grow upon.
We can take our soils for granted, use them and abuse them, but that can catch up with us when we least expect it.
It is a good time in the offseason to take a look at your soil management program, get out the soil probes, and spend a little time working with your lab to develop the program that is best your farm and fields.
The benefits can be found with your crop this next year and in your grandchildren's crops on the same fields in the years to come.
Figure 1.
A soil profile with a sandy loam surface underlain by a course gravel layer at approximately 18 inches, and  an open soil profile with a slight gradient in textures to a depth of four feet.
Figure 2.
Soil sampling pattern within a relatively uniform field, and  soil sampling pattern within three distinct zones of a field, each having unique characteristics warranting a separate sample.
COLLEGE OF AGRICULTURE & LIFE SCIENCES Cooperative Extension
 THE UNIVERSITY OF ARIZONA COLLEGE OF AGRICULTURE AND LIFE SCIENCES TUCSON, ARIZONA 85721
 J.C.
SILVERTOOTH Extension Agronomist Cotton Associate Dean and Director, Extension & Economic Development Associate Director, Arizona Experiment Station 
For potatoes in the early emergence crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.12 inches and the estimated water use during the week of June 19-25, 2023 is 0.85 inches.
For potatoes in the vegetative crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.15 inches.
Estimating Financial Costs and Benefits of Supplemental Irrigation with the Irrigation Financial Estimator Tool 
 J.
Mitchell Paoletti, Research Assistant, Virginia Tech Department of Biological Systems Engineering Julie Shortridge, Assistant Professor and Extension Specialist, Virginia Tech Department of Biological Systems Engineering
 Virginia agriculture has historically relied mostly on rainfall to water crops.
For instance, a recent census taken by the U.S.
Department of Agriculture  shows that only a small portion of Virginia's farmland, about 70,000 acres, is irrigated.
However, in recent years, farmers in humid regions like Virginia have shown increased interest in irrigation.
In fact, crop irrigation has increased in almost every state east of the Mississippi River over the past 10 years.
Studies show that irrigating crops can potentially double their yield  and save an agricultural producer's harvest in times of drought.
Still, farmers must also consider the additional costs before deciding to purchase an irrigation system.
Irrigation systems have a high initial investment cost and additional annual operating expenses.
One irrigation professional was recently quoted as saying "the cost of power is usually the biggest shock to a new irrigator".
Determining whether the potential additional income earned from higher yields is worth the cost of installing an irrigation system is difficult to do, particularly in places like Virginia where, in many years, rainfall alone may be sufficient for crop water needs.
The purpose of this publication is to describe the Irrigation Financial Estimator Tool.
IFET is a Microsoft Excel spreadsheet tool to help Virginia's row crop producers determine if it is financially advantageous to install an irrigation system on their farm.
The tool is available for download from the Virginia Cooperative Extension website.
Users input information about their farm, including location, size,
 crops grown, and soil type, as well as information about the desired irrigation system.
The tool then calculates and provides a summary of financial returns that could result from installing an irrigation system on the farm with the specified characteristics.
The report includes system purchase and installation costs, and annual operating expenses associated with fuel, labor, and maintenance.
The tool also calculates the added revenue from increased crop yields a producer might expect to obtain with irrigation.
Precise financial returns will always be uncertain due to variability in rainfall, crop response to water deficits in a specific location, and prices for crops, fuel, and the irrigation system itself.
The tool accounts for this uncertainty and presents a range of values for system costs and benefits.
This information can be used to estimate typical irrigation costs, compare different types of systems and irrigation scheduling methods, and determine if it is economically advantageous to install an irrigation system.
Irrigation Financial Estimator Tool Calculations
 IFET works by combining user-provided information on farm characteristics with data on irrigation costs, historic weather and crop price data, and crop/ water response information.
These figures are used to calculate a range of values for installation costs, operating costs, and additional revenues.
IFET estimates installation costs for irrigation system type and size specified by the user, assuming all acres specified by the user are under irrigation.
It then calculates how much irrigation water is needed and the yield improvements that would result from this
 Produced by Virginia Cooperative Extension, Virginia Tech, 2018
 Figure 1: Overview of how the tool calculates costs and revenues.
additional water.
The tool then uses this information to estimate the operating costs and additional revenue earned by applying that volume of water.
An overview of this process is provided in figure 1, and additional details are described below.
To estimate irrigation cost and benefit information, IFET requires users to input information about their farm operation along with financial information associated with the purchase of an irrigation system.
Users specify where their farm is located, how many acres of each crop are grown, and the predominant type of soil.
This data specifies which yield equation and weather data to use when calculating rain-fed and irrigated crop yield.
IFET requires users to select which type of irrigation system they want the tool to analyze, along with some information about how the system will be financed.
IFET uses this information to output cost information based on the selected system and information entered in the previous sections.
Figure 2 shows the user input section of the tool and the information that users are required to enter.
After all information has been entered, IFET calculates the annual costs of purchasing and operating the chosen irrigation system.
Operating expenses are calculated based on the volume of irrigation water applied.
Applied irrigation water is calculated by one of two user-selected options: "Rainfall Deficit" or
 "Scheduled." If users select "Rainfall Deficit," the tool assumes that the irrigation water applied is the minimum amount of water necessary to cover the deficit from rainfall and achieve maximum yield as determined by the crop modeling software AquaCrop version 6.1.
This method would be appropriate if a grower planned on using soil moisture sensors or weather-based scheduling apps to apply water.
If a user selects "Scheduled," then the tool assumes that the same amount of irrigation water is applied each week.
For instance, if a grower applied one inch of water per week throughout the growing season, this would be "scheduled." If the "Rainfall Deficit" method is selected, then no information about the amount of water applied per week is necessary.
IFET uses crop price data along with information on how crop yields respond to water deficits to calculate additional revenues from irrigating.
IFET selects a random historic year within its dataset and uses stored weather information and equations to calculate rain-fed and irrigated yields that would be expected based on weather conditions for that year.
IFET takes this estimated yield and uses historic crop prices to determine the estimated income for that year.
The difference between income earned from the maximum irrigated yield and rain-fed yield is the additional estimated income that could result from using irrigation.
5	Farm Information	User Inputs	Units
 7	County	Culpeper County
 8	Primary Crop	Corn	.
9	Secondary Crop	Notrimary Crop
 Please select the primary
 10	Acres of Primary Crop	I	cop grown	Acres
 11	Acres of Secondary Crop	entry must out	This	Acres
 12	Soil Type	Lo	before
 14	Irrigation System Information	User Inputs	Units
 16	System	Center Pivot
 18	Water Source	Surface Water
 19	Irrigation Schedulling Method	Rainfall Deficit
 20	Irrigation Water Applied per Week	0	Inches
 22	Financial Information	User Inputs	Units
 24	Labor Cost	$10.00	S/hour
 25	Repayment Period	15	Years
 26	Useful Life of System	25	Years
 27	Interest	5	%
 28	Down Payment	$20,000	$
 32	Irrigation System	Suggested Useful Life	Units
 34	Center Pivot	20-25	Years
 35	Drip	10-15	Years
 36	Hose Pull	15-20	Years
 37	Linear Move	15-20	Years
 Figure 2: The user-input section of the tool.
When users click on a box to enter information, a guidance box  will appear that provides more detail about the information required.
At the bottom, the suggested useful life for different types of systems is included for reference; users do not have to enter any information in this section.
After users have entered all information, they click the "Calculate" button to see results.
Many uncertain factors ultimately influence the costs and revenues associated with irrigating.
For instance, no one can predict exactly how much rain will occur during the next 10 years or even if they will be wetter or dryer than average.
No one can know for certain what crop or energy prices will be in coming years.
In addition, certain conditions at an individual farm may make irrigation more or less expensive than it is on average.
All of these issues mean there is uncertainty in any cost estimate, and it is important to account for such uncertainty.
This is accomplished in IFET by repeating the above process thousands of times using different years of climate and cost data stored within the tool.
By repeating the same process but with different data, the tool can account for the range of financial outcomes that could occur.
From the calculated results, the tool presents the average, lower estimate, and upper estimate of costs and benefits.
This way of displaying data provides information on the
 potential range of financial outcomes that might result from irrigating.
How to Interpret Tool Outputs
 This section describes what results users can expect to see within the tool.
Within IFET, the "Results Summary" allows users to see the estimated costs and benefits expected from purchasing an irrigation system.
On this tab, users will see a table and a pie chart as shown in figure 3.
The table on this tab shows the breakdown of installation costs and operating expenses.
At the bottom of the table, users will see a section about anticipated increased revenues.
This section presents information about the potential additional income a producer could earn if their farm were irrigated.
"Average annual additional income with irrigation" is the difference between income earned with irrigation and without irrigation.
"Average Annual Net Revenue " is that same additional income minus the operating costs and loan repayment expenses.
"Average Annual Net Revenue"  is the additional income minus operating costs, without including the annual loan repayment.
This represents additional revenue with irrigation after the loan has been repaid.
The pie chart on this tab graphically shows users the distribution of annual expenses.
For example, figure 3 shows users that the largest annual irrigation-related expenses that they should expect are fuel and loan repayment.
The tab labeled "Detailed Cost Results" presents more information about the costs of purchasing and operating an irrigation system.
Similar to the results summary tab, this tab contains a table and pie charts.
The table gives users a range of expected annual expenses that accounts for uncertainty stemming from system operation requirements, water requirements, and fuel costs.
The two pie charts are similar to the one on the "Results Summary" tab, but show the full range of cost estimates.
For instance, in figure 4, users can see that average annual fuel costs for irrigation are likely to range from $6,200 to $11,300.
The final tab in the tool is the "Detailed Benefits Results" tab.
This tab shows users a range of additional revenue they can expect from additional yield under irrigation.
This tab contains a table and several different graphs.
The table  shows
 Total Investment Cost	$76,100
 Annual Loan Repayment	$7,300
 Average Annual Fuel Cost	$8,700
 Average Annual Labor Cost	$800
 Average Annual Maintenance Cost	$1,300
 Total Annual Operating Costs	$10,800
 Total Annual Costs	$18,100
 Average Annual Additional Income with
 Average Annual Net Revenue (including loan
 Average Annual Net Revenue (not including
 Figure 3: Results summary tab.
This tab presents a table with a summary of different costs and expected additional revenue, as well as a pie chart showing the breakdown of annual costs.
Results shown here are for a center pivot system growing 100 acres of corn in Culpeper County on loamy soil.
Low Estimate	Average Estimate	High Estimate
 Fuel	$6,200	$8,700	$11,300
 Labor	$600	$800	$1,000
 Maintenance	$1,000	$1,300	$1,600
 Total	$7,800	$10,800	$13,900
 Low Estimate	Average Estimate	High Estimate
 Total Investment	$68,300	$76,100	$84,100
 Annual Loan Payment	$6,600	$7,300	$8,100
 Low Estimate	Average Estimate	High Estimate
 Total Annual Cost	$14,400	$18,100	$22,000
 Annual Operating Cost 
 Annual Operating Cost 
 Figure 4: Lower, average, and upper cost estimates for a center pivot system in Culpeper County for growing 100 acres of corn on loamy soil.
ResultsReturn on Investment Information
 Value of Investment	Low Estimate	Average Estimate	High Estimate
 Average Annual Additional Income with Irrigation	$14,100	$19,700	$25,700
 Average Annual Net Revenue 	$4,600	$8,900	$13,800
 Average Annual Net Revenue 	-$2,600	$1,600	$10,300
 Figure 5: Lower, average, and upper estimates of average annual additional revenue from irrigating.
the range of benefits that users can expect including average additional annual income, additional revenue after operating expenses, and additional revenue after operating expenses and loan repayment.
These values all represent long-term averages over the expected life of the irrigation system.
Of course, the system will not result in the same amount of increased revenue each year.
Added revenues will be highest in years with little rainfall and high crop prices.
In years with heavy rainfall, operating the irrigation system may not result in any increased revenue at all.
The graphs on this tab are designed to also help users see the factors that influence these year-to-year changes.
Figure 6 shows two graphs that display projected income for 25 possible sample years.
The top graph compares the income a producer would earn with and without irrigation, year-by-year.
The bottom graph shows the additional income generated from irrigating (in other words, the difference between the
 irrigated and non-irrigated revenues shown in the top graph).
It shows that in most years, using an irrigation system results in higher net revenue.
However, there are years when operating costs and loan repayment expenses are greater than the additional income from irrigated yields.
This situation is likely due to years of higher rainfall when irrigation makes less of an impact on yield.
It is important to realize that this is not a prediction of how much additional income users will earn in a particular year, since no one can predict exactly how much rainfall will occur.
However, it is a random selection of years that shows, on average, how often the grower can expect to earn additional revenue.
The detailed benefits tab also shows how revenues from irrigation are impacted by the amount of growing season rainfall and crop commodity prices.
The top graph shows how additional revenue is possible with any amount of rainfall below about 23 inches.
However, even in dry years, revenue can
 Figure 6: Twenty-five year projection of possible revenues with and without irrigation.
Net Revenue from Irrigating
 Figure 7: Graphs showing how additional income from irrigating varies based on rainfall during the growing season  and crop prices.
vary significantly based on crop prices.
Collectively, these graphs demonstrate how both rainfall and crop prices contribute to the amount of additional revenue possible with irrigation.
Limitations, Assumptions, and Future Improvements
 IFET was designed to be widely applicable to multiple irrigation system types, locations, farm sizes, crops, and soil types across the state.
However, to make a tool that would apply in many different contexts, some simplifications and assumptions were made that limit the precision of the tool's estimates.
One simplification is that estimated rain-fed crop yields are based only on growing season rainfall and whether prolonged dry periods occurred.
The tool does not account for the timing of when rainfall and dry periods
 occur during the growing season, and the different impacts that these can have on crop growth.
Also, the tool assumes that no other factors, such as nutrient shortages or pest damage, reduce estimated yields.
Another assumption is that the cost per acre of each irrigation system is constant.
Costs for each system are stored as cost per acre, and multiplied by the acres of a user's farm to give the total installation cost.
In reality, installation costs per acre will likely be higher for small farms than they are for large farms.
For example, center pivot irrigation systems have a high initial cost and certain equipment that is required regardless of the farm size , but have a low cost to scale up to larger farms since this may only require additional spans and flow capacity.
Thus, users installing a center pivot
 on a large parcel may find that their installation costs are towards the lower end of the range provided.
The opposite is true of subsurface drip irrigation systems.
They have a much lower initial installation cost on smaller plots of land compared to a center pivot but their installation cost is higher with larger plots of land.
IFET includes many, but not all, of the costs associated with installing and operating an irrigation system.
For instance, IFET does not consider the costs of taxes and insurance since that information can differ substantially depending on the farm location and operational details, and the available studies used to estimate tax costs were not based in Virginia.
For similar reasons, IFET does not include depreciation and the salvage value of equipment, assuming instead that users will keep the irrigation system until the end of its useful life.
Finally, the tool does not include costs associated with obtaining a water withdrawal permit, which may be required to pump groundwater in Eastern regions of Virginia.
For more information associated with obtaining a groundwater withdrawal permit, please see Virginia Cooperative Extension Publication BSE-215P, "Using Groundwater for Agricultural Irrigation in Virginia."
 This first edition of IFET can provide initial information for planning purposes.
Future versions will include improvements in terms of accuracy, scope, and areas of coverage.
A current limitation within the tool is that it is only applicable to Virginia farmers, but in future research we hope to expand the tool's coverage to other regions in the Southeast and MidAtlantic with similar climate and cropping conditions.
Additionally, the tool's current form requires that users have the ability to download and run Microsoft Excel on their computer.
In future work, we hope to host the tool online, allowing easier access.
The tool currently only allows users to pick from four crops and four irrigation system types.
Future versions could also allow users to have more options of irrigation systems and types of crops.
Future upgrades will allow users to select more than two different types of crops and account for crop rotations within fields.
These versions will allow users to see a side-by-side comparison of cost-benefit information for different irrigation systems paired with different crops or crop rotations.
All updates to the tool will be maintained on the Virginia Cooperative Extension website SO that users can have access to the newest improvements.
Effective, well-managed irrigation can improve crop yields and farm revenues.
However, installing an irrigation system is expensive, both in the initial expense and operating costs.
Deciding whether or not to install an irrigation system requires producers to determine if these costs will lead to sufficient financial returns.
The Irrigation Financial Estimator Tool provides estimated cost/benefit projections based on user-supplied information unique to an individual farm.
While precisely predicting the costs and revenue associated with irrigation in a specific operation is impossible, IFET allows users to see a range of possible financial outcomes.
By reviewing this information, growers can be better informed about the financial impacts of using irrigation.
Irrigation Scheduling with Tensiometers
 Craig A.
Storlie, Ph.D., Extension Specialist in Agricultural Engineering
 Irrigation scheduling is a management practice used to determine how often to irrigate and how much water to apply with each application.
Soil moisture monitoring is an important procedure used in many irrigation scheduling schemes.
Proper irrigation timing can be determined from soil moisture content measurements.
Proper irrigation depth can be determined from known plant and soil characteristics.
Soil Water-Holding Capacity and Available Water
 Soil in the plant root zone acts as a reservoir for water.
Soil texture is the primary factor influencing the amount of water that the soil reservoir can store.
Available water is defined as amount of water that plants are able to withdraw
 from the soil and use.
Fine textured soils, such as clays, silt loams, or loams, are able to hold much more available water than sandy, coarse-textured soils.
Soil water-holding capacity is an important factor to consider in determining the proper depth of irrigation water to apply.
The water storage capacity of soils is also influenced by soil depth.
Nearly all vegetables and agronomic crops grown under irrigated conditions extract water from the top 2 feet of the soil profile, even though the roots of some crops can extend much deeper.
In fact, in most crops, 75%-95% of the roots are in the top 12 inches of the soil profile.
For this reason, manage irrigation events with the top 12 inches of the root zone in mind.
Water which seeps beyond this depth may
 TABLE 1.
Influence of Soil Texture on Available Water-Holding Capacity
 
 Loamy sand	0.75 1.50
 Sandy loam	1.25 1.75
 Loam and Silt loam	2.00 2.75
 Clay loam	1.75 2.50
 not be used by the crop.
Together, soil waterholding capacity and plant rooting depth can be used to determine the appropriate irrigation depth.
The appropriate irrigation frequency is influenced by soil water-holding capacity and by the rate at which plants use water, and can be determined by monitoring soil moisture.
Tensiometers are simple and inexpensive devices which can be used to monitor soil moisture.
Tensiometers measure soil tension.
This is also often referred to as soil suction or vacuum.
Soil tension is a measure of how tightly water is held in the soil, and is measured in pressure units of centibars  or kilopascals.
These are equivalent units.
One-hundred centibars are approximately equal to 15 psi.
Soil tension increases as moisture in the soil is depleted.
This force also draws water out of the tensiometer through its porous tip, creating a vacuum inside the tensiometer.
This negative pressure, or tension, is registered on the tensiometer vacuum gauge.
The soil tension measured with tensiometers is an indirect indication of soil moisture content and can be used as an indicator of irrigation need.
Shown in Table 2 are guidelines for using soil tension data to schedule irrigation events.
Field capacity is the moisture content at which a soil is holding the maximum amount of water it can against the force of gravity.
This moisture content is reached 24-72 hours after a saturating rain or irrigation.
Field capacity corresponds to soil tension levels ranging from 5-10 cb in coarsetextured soils and as high as 40 cb in fine-textured soils.
The soil tension range corresponding to the time when irrigation should begin is also influenced by soil texture.
In coarse-textured soils, irrigation should begin at soil tensions of 20-40 cb.
In extremely coarse-textured soils, irrigation may be necessary at even lower tensions.
Mediumand fine-textured soils do not need to be irrigated until soil tensions reach higher values, as shown in Table 2.
In all soils, irrigate when 50% of available water has been depleted.
The utility of tensiometers in fine-textured soils is limited because of the upper limit of tension that can be measured with tensiometers.
When soil dries beyond the 80 cb tension level, the column of water in the tensiometer "breaks," allowing air to enter the device.
After breaking tension, the device ceases to operate correctly until it is serviced.
Thus, tensiometers are more
 TABLE 2.
Irrigation Guidelines for Using Tensiometers
 Soil Moisture and	Status	Irrigation	Soil Texture	Soil	Tension	
 Sand, loamy sand	5 10
 Soil at Field Capacity	No
 Sandy loam, loam, silt loam	10 20
 Clay loam, clay	20 40
 Sand, loamy sand	20 40
 50% of Available Water Depleted
 Sandy loam, loam, silt loam	40 60
 Clay loam, clay	50 100
 practical in coarse-textured soils where appropriate soil tension levels are well below the point of breaking tension.
Tensiometers-Preparation, Placement and Service
 A new tensiometer is prepared for use by filling the tensiometer with clean water and placing it upright in a container of water deep enough to cover the tensiometer tip.
The tensiometer cap is removed during this procedure.
Water will drain through the tip over the next few hours.
This procedure should be repeated two or three times.
Next, an indicating solution  is prepared and used to fill the tensiometer.
This solution can easily be seen through the transparent tensiometer and allows the user to visually assure that the tensiometer contains fluid.
Air can be extracted from the fluid in the tensiometer using a hand-operated vacuum pump.
This step is not absolutely necessary but may increase meter sensitivity.
More importantly, the vacuum pump may also contain a pressure gauge which can be used to assure that the tensiometer vacuum gauge is operating properly.
Finally, the tensiometer is capped shut and transported to the field with the tensiometer tip remaining submerged in water.
Field installation is relatively simple.
Using a pipe, rod or soil probe which is the same diameter as the tensiometer, a hole is made to the depth to which the tensiometer will be installed.
Next, a small amount of water is poured down the hole and the tensiometer is inserted, making sure it is well seated in the hole without using excessive force.
Rough treatment may break the fragile tensiometer tip.
It is important to use more than one tensiometer in a single management zone because of soil texture variability.
Four tensiometers per management zone are suggested, with at least one in the droughtiest portion of the zone.
This area will need water sooner than other parts of the field.
Tensiometer placement location influences measured soil tension levels.
Tensiometers should be placed where plant roots are actively growing.
Therefore, it is appropriate to monitor soil tension 6-12 inches below the soil surface and within 6-12 inches from the plant base.
If using trickle irrigation, place the tensiometer close to the trickle tape or hose.
This will insure that tensiometer readings decrease when an irrigation occurs.
Placement near the trickle tape is even more important when using raised, mulched beds and on coarse-textured soils.
In these situations, the bed shoulders often remain dry.
Placing tensiometers in the bed shoulders will not give an accurate measure of soil tension in the active crop root zone.
Tensiometers can also be used in other ways.
Placing tensiometers at various soil depths at the same location is useful for determining whether or not an irrigation or rainfall has reached a certain depth.
Placing tensiometers at various depths is also useful for determining the depth from which plants draw the most water.
Service of tensiometers after they are placed in the field is simple but very important.
Very little service is required unless a tensiometer breaks tension.
This occurs when soils are allowed to dry to tensions greater than 80 cb.
When the tensiometer breaks tension, the gauge reading will either remain at 70-80 cb or it will drop to a deceptively low value.
In either case, the tension reading is meaningless and the tensiometer must be serviced before readings can again be made.
The only reliable method for judging when a tensiometer has broken tension is to observe the water column near the vacuum gauge.
If a break in the water column can be seen, the gauge has broken tension.
After breaking tension, some of the water is lost from the tensiometer.
To service the meter, the device must be refilled with water by uncapping the tensiometer and assuring that water from the reservoir fills the tensiometer body.
Gently slapping the open reservoir with a cupped hand may be necessary to coax water from the reservoir into the tensiometer column.
After being refilled and capped shut, the tensiometer is ready to use.
It is not necessary to remove the tensiometer from the soil when servicing.
At season's end, tensiometers must be removed from the field to prevent freezing and splitting.
Tensiometers should be emptied and cleaned before being stored for the season.
As with any tool, expect to spend extra time at first to learn how the tensiometer reacts to soil moisture and to learn how to base irrigation decisions on tensiometer readings.
Begin by reading the tensiometer every day, noticing how it climbs quicker on bright, hot, windy days than it does on cool, cloudy days when plants use less water.
Observe how young, small plants use less water than older, larger plants by noting how the tensiometer climbs slower early in the season.
Use Table 2 to guide your first irrigation decisions.
Adjust your practices as required to meet plant water demands.
With time, you will begin to place faith in basing irrigation decisions on tensiometer readings.
As an example of how to schedule irrigations
 using tensiometers, assume tomatoes are being grown on soils of fine sand texture, and that the plants have a 1-foot root zone depth.
Use Table 1 to determine that these soils have an available water-holding capacity of 1 inch per foot of soil depth.
After using the tensiometers and Table 2 to decide that irrigation is required, determine the appropriate irrigation depth by multiplying the root zone depth by the available water-holding capacity of the soil and by the percent available water depletion.
In this case:
 Irrigation depth = 1 in.
available water 1-ft root zone depth X X 50% = 1/2 inch foot of soil
 Tensiometers are one of many tools available for irrigation management.
With practice, tensiometers can provide you with the information required to make proper irrigation decisions.
Improving irrigation management practices will allow you to maximize yields and profits by more efficiently using water and nutrients.
2004 by Rutgers Cooperative Research & Extension, NJAES, Rutgers, The State University of New Jersey.
Desktop publishing by Rutgers-Cook College Resource Center
For Scenario 2 an end gun was installed at the end of the center pivot pipeline.
Adding the end gun improved the economics somewhat because the end gun does not operate for the full rotation of the center pivot.
Most designs have the end gun turned on for 40 degrees in each corner, which means they would operate for 160 degrees out of a 360-degree revolution or 44% of the time.
Use of a VFD could reduce pumping costs by about $0.70 per hour.
Still, this scenario was not economical for most center pivot installations.
Management-intensive Grazing  on Irrigated Pasture
 By Casey Shawver, Joe Brummer, Jim Ippolito, Jason Ahola, and Ryan Rhoades* 
 Management-intensive Grazing , a concept credited to grazing specialist Jim Gerrish, is often defined as "a flexible approach to rotational grazing management whereby animal nutrient demand through the grazing season is balanced with forage supply and available forage is allocated based on animal requirements".
This type of system requires manipulating the length of time animals graze and space allotted based on available forage resources to achieve desired objectives.
It also requires an understanding of how plant, animal, soil, and environmental components work together to make management decisions.
MiG is often characterized by relatively frequent movements of animals, typically every 14 days.
This method ranks MiG as more "management-intensive" than planned rotational grazing , but less so than mob grazing.
Figure 1: Daily cattle move in the irrigated MiG system at Colorado State University's research facility.
More intensive, irrigated systems are being considered as an option by many ranchers due to pressure to reduce grazing on public lands and the declining land available for pasture.
Within intensive, irrigated pasture systems, MiG can result in more homogenous utilization of available forage, increased forage yield and quality, less severe soil compaction, improved soil health, and more evenly distributed manure and urine over an area leading to reduced production costs by providing increased animal output and greater land use efficiency.
At Colorado State University , an irrigated, full-scale MiG project was established in 2016.
Experiences and lessons learned from this project are included within this document to provide further insight.
Although some of the principles discussed in this document apply to management of native rangeland, keep in mind that there are also many differences, especially with respect to the potential for forage regrowth to occur under irrigated conditions compared to dry, native rangeland in the western US.
Core components of MiG can be summarized by the FIO principle: minimizing frequency of plant defoliation , controlling intensity of plant defoliation , and allowing
 MiG emphasizes "intensive management" and not "intensive pasture use" by controlling grazing time and space to balance available forage with animal demand.
Balancing grazing frequency and intensity with the opportunity for forage regrowth are core MiG principles.
Determining pasture size incorporates estimates of forage supply and animal demand.
Shortand long-term monitoring is integral for making management decisions to achieve goals and objectives more effectively.
*Casey Shawver, Former Graduate Student, Joe Brummer, Associate Professor-Forage Extension Specialist, and Jim Ippolito, Associate Professor-Soil Fertility and Environmental Soil Quality, Department of Soil and Crop Sciences; Jason Ahola, Professor-Beef Production Systems, and Ryan Rhoades, Associate Professor-Beef Extension Specialist, Department of Animal Sciences.
9/20.
Grazing Systems by How Often Animals Are Being Moved
 Figure 2: Diagram illustrating frequency of animal movements based on grazing strategy.
opportunity for plant growth/regrowth.
These factors are all focused on maximizing productivity and utilization while protecting plant health to ensure long-term pasture productivity.
MiG involves frequent movements that result in infrequent defoliation of individual plants.
In contrast, allowing animals to spend time in an area for an extended period can lead to multiple defoliations of individual plants during a grazing event.
Multiple defoliations of individual plants impact the energy balance between roots and shoots.
This leads to weakening of plants, which ultimately results in reduced productivity and eventual thinning of the stand.
Bare soil in a pasture is an open invitation for invasion by unwanted weeds.
Figure 3.
Illustration of forage utilization and its impact on root growth.
Intensity of defoliation has direct impacts on rate of forage regrowth as well as overall root growth.
When
 forage utilization exceeds 50%, regrowth and productivity slow due to reduced leaf area, which limits photosynthesis.
In addition, root growth slows and will eventually cease at utilization levels greater than 50%.
Continued utilization above 50% will weaken plants, eventually leading to plant death and invasion by weeds.
In addition, it is important to note that sufficient leaf area needs to be maintained to enable initiation of plant regrowth.
The residual height at which sufficient leaf area is maintained varies depending on the grass species, however, most cool-season irrigated pasture grasses should not be grazed below 4 inches.
Grazers often refer to these 4 inches as "belonging to the plant" to ensure energy is maintained for quick regrowth and overall plant health.
As a general guideline, a minimum of 8 inches of forage should be available before grazing to assist in maintaining both the 4-inch residue height and 50% utilization objectives that will ultimately ensure adequate plant recovery.
Although 50% use is generally the desired target, there are circumstances in which lower or higher levels of utilization are warranted.
Examples of when you might want to graze more intensively  would be to remove more of the grass canopy to allow light to penetrate and stimulate growth of legumes like white clover or increase establishment success of interseeded forages.
An example of when you might want to graze less intensively  would be during spring growth when cool-season species grow rapidly and forage can begin to mature faster than it can be grazed.
On the CSU grazing project, we found
 that it was important to move animals quickly through the first rotation early in the season, generally only utilizing 20-30% of available forage in an effort to remove growing points from some of the grass and keep it from jointing and becoming over-mature.
In other words, since forage was growing rapidly in the spring, we moved livestock more quickly between units in response to conditions, whereas livestock spent longer time periods in each unit later in the year.
This example illustrates the adaptive nature of MiG where we were monitoring plant growth rates and utilization levels in order to make decisions on when to move our livestock.
The emphasis of MiG is on "intensive management" and not "intensive pasture use" which is why fixed grazing periods do not work well to maintain plant health and vigor.
The period of rest following a grazing event is vital for regrowth.
In general, over-utilization results in decreased animal performance and the need for longer rest periods.
Shorter grazing periods and proper utilization, as discussed above, can help mitigate the need for prolonged rest periods.
In a cool-season, irrigated pasture system, the optimum rest period is not only dependent on grazing management practices, but also temperature, which is related to the point in time during the growing season.
Cool-season grasses experience a period of slower growth during the hottest period of the growing season, also known as "summer slump." During this period, length of the rest period should be longer to compensate for slowed growth.
Figure 4.
Optimum rest period  for fast and slow plant growth periods to maintain plants in the most rapid growth stage.
In the spring, cool-season species grow rapidly, requiring cattle to be moved quickly to keep up with growth as well as remove growing points before grass begins heading.
The ultimate goal of determining a rest period is to maintain plants in their most rapid rate of growth.
This gives enough time for plants to recover and produce adequate forage before another grazing event, but not so long that plants become mature and quality and rate of growth begins to decline.
The recommendations in Figure 4 are approximate and actual values are site dependent and can change based on environmental factors, primarily temperature and moisture.
The rest period on the CSU grazing project was not fixed and averaged around 30 days over the 6-month grazing season.
The amount of regrowth is what we keyed on to determine if a paddock was ready to be grazed again.
As mentioned above, a minimum of 8 inches of regrowth and a full  canopy is what was targeted.
Rest periods ranged from 18 to 24 days early in the season during rapid growth, to 35 to 40 days during the summer slow growth period, to 28 to 32 days later in the season when temperatures cooled and the rate of regrowth increased again.
There are many cool-season species that perform well under irrigated MiG.
However, based on experiences from the grazing project at CSU, there are pros and cons associated with some of these species that need to be considered when choosing what species to include in a mixture and if altered management strategies are required for establishment and grazing.
Orchardgrass is commonly included in irrigated pasture mixes.
It is a very palatable species that is high in quality and productive in an irrigated pasture setting.
If including orchardgrass in a mixture with grasses such as meadow brome that have increased seedling vigor, include a higher percentage of orchardgrass seed in the mix.
This will help mitigate competition between orchardgrass seedlings and more vigorous species such as meadow brome.
Meadow brome is also included in many irrigated pasture mixes and is very productive, nearly to a fault during early season growth.
During early growth, meadow brome tends to joint  before most other cool-season grasses.
If the growing points are not removed early with grazing, then meadow brome plants will set seed, which reduces palatability and utilization.
Rapid rotation in con-junction with a high stock density  is critical during the first 4 to 6 weeks of the growing season if meadow brome is included in the grass mixture.
This is not as much of an issue with most other coolseason grasses.
Another issue with meadow brome is related to the morphology of its leaves which are soft and lax.
During rapid spring growth, leaves become long  and tend to lodge or lay on the ground.
When cattle enter a paddock to graze, the leaves are easily trampled.
This was observed on the grazing project at CSU which resulted in the accumulation of dense layers of litter on the soil surface that slowed regrowth.
Slowed regrowth can be a disadvantage in a MiG system resulting in paddocks where grazing needs to be delayed or skipped on the following rotation.
Although a common, productive irrigated pasture species, tall fescue is not very palatable to cattle if they have a choice within a pasture mix, especially when using the older, tough-leafed cultivars.
This was observed clearly within our paddocks at CSU when cattle overgrazed other species and mostly avoided tall fescue in the mixture that contained one of the older cultivars.
However, another species mixture on the project had a newer, soft-leafed cultivar of tall fescue that was not avoided by cattle.
It was evident that the tough-leafed tall fescue deterred cattle and utilizing a soft-leaved cultivar can alleviate this issue.
Older varieties of tall fescue are better utilized in monocultures or as stockpiled forage for fall/winter grazing to reduce selectivity.
Creeping meadow foxtail is a complementary addition to a cool-season pasture mix due to its rhizomatous growth habit.
Many of the cool-season species used in irrigated pastures are bunchgrass types, which have generally less resilience to grazing.
Grasses such as creeping meadow foxtail will fill in gaps between bunchgrasses over time to create thicker ground cover.
Ground cover in a pasture is vital to maximizing productivity because bare ground is a missed opportunity for photo-synthesis and plant growth.
Another quality that this species has is that it thrives in wet environments where other species cannot.
If there are wet, low lying areas in your pasture, this species should be con-sidered for inclusion in the mix.
One caveat is that creeping meadow foxtail can become dominant in areas such as high mountain meadows due to the wild flood irrigation method which creates saturated soil conditions conducive to growth of this species.
Smooth brome is rhizomatous and is often included in irrigated pasture mixes to help fill in bare areas between bunchgrasses to maintain thick stands.
Smooth brome is very palatable and produces an abundance of forage during initial spring growth.
However, it regrows slowly during the hot part of the summer which can limit forage availability, leading to the need to reduce stocking rates during that time.
It can also lead to sod-bound conditions if it makes up too much of the stand, which results in reduced productivity.
The key to including smooth brome in mixtures is to keep the percentage low, no more than 5 to 10% of the total mix.
Even when seeded at low rates, smooth brome will often come to dominate a stand over time due to its aggressive spread through rhizomes.
However, this can be minimized with proper grazing management that maintains the health and vigor of the bunchgrasses in the mix.
Worldwide, perennial ryegrass is one of the most common grasses planted for improved pasture.
However, most varieties do not persist well under Colorado's fluctuating environmental conditions and will often winterkill.
Because it establishes quickly and
 easily, it is often included in irrigated pasture mixes but stands will tend to thin within 1 to 3 years.
If you look at the tag on a typical seed mixture, perennial ryegrass will often make up 25% or more of the mix, which can result in significant declines in productivity as it disappears from the stand.
Several seed companies are working on cultivars adapted to Colorado's continental climate, so be sure to ask where the cultivar in the mix was developed.
Otherwise, be wary and keep the percentage in the mix to a minimum.
Estimating how much forage is available is an integral step prior to determining paddock size.
One of the simplest, most affordable, and quickest methods is measuring average sward height with a pasture/grazing or yard stick.
To utilize this method, choose a pattern that you will take measurements along  to eliminate bias of certain areas of the pasture.
When taking your first measure-ment, place the measuring stick into the grass and record the height below which 90% of forage mass is found.
You do not want to measure the tall, wispy leaves or pull the grass leaves up to the stick.
If this method is practiced enough, you can calibrate yourself to visually estimate available forage in our pastures.
While walking, take measure-ments at regular intervals so that you collect 20-30 values.
Take an average of the measurements to determine sward height.
Generally, in a cool-season irrigated pasture with 75-90% ground cover, 250-350 pounds of forage dry matter  per acre are available per
 Figure 5.
Demonstrating sward height measurement with a pasture/grazing stick.
inch of sward height.
Multiply the average sward height by the pounds of DM per acre inch to estimate yield in pounds per acre.
It is a judgement call as to what yield per inch of height to use.
If the ground cover is a little sparse , then use 250 lbs/acre/inch but if it is a nice dense stand , then use 350 lbs/acre/inch.
Remem-ber that this is just a ballpark estimate, so using the midpoint of 300 lbs/acre/inch will provide an acceptable estimate in most situations.
Other methods such as the rising and falling plate meters are also reliable options for estimating forage yield.
More information on these methods can be found in Pasture and Grazing Management in the Northwest by Shewmaker and Bohle.
Note that these methods work best in areas of relatively uniform vegetation, like irrigated pasture, but do not translate well to estimating available forage on dryland pastures or rangelands with sparse plant cover.
Common pasture infrastructure in an irrigated, MiG system includes barbed wire or high-tensile electrified perimeter fence, electrified polywire and step-in posts used to establish cross fences, waterers, and gates.
Infrastructure design and day-to-day setup varies by ranch; however, the common concept is utilizing moveable fence and posts to create paddocks based on forage availability and animal demand.
Moveable, temporary fence makes this system extremely flexible depending on how quickly forage is growing or how many animals are being grazed at a point in time.
Animal demand and forage supply are in a constant state of flux and it is important that the infrastructure can adapt to account for that variability.
In the system installed at CSU, three concentric, permanent, electrified high-tensile fences create the foundation within a 200-acre pivot, while electric polywire is connected from outer to inner circles to create temporary paddocks of varying sizes based on number of animals being grazed and current forage supply.
This is an effective fence design for a pivot system of this size, particularly when managing multiple herds.
The three-ring fence design allows flexibility to graze up to 3 herds simultaneously within a given quarter of the pivot while having access to separate watering points and allowing for irrigation on the other 3 quarters.
Figure 6.
MiG system design on a 200-acre pivot including hightensile concentric fences , moveable polywire paddock fencing , and watering locations at Colorado State University.
Polywire locations represent areas associated with given water points and are often further subdivided into 2 or 3 smaller paddocks depending on animal numbers and current forage supply.
Determining Paddock Size and Stocking Rate
 The paddock size needed to balance forage supply with animal demand can be determined through two simple equations.
For the first equation, forage supply is determined by multiplying estimated available forage  by the utilization goal.
Animal demand is then determined by multiplying estimated daily intake as a percent of body weight  by the number of days planned to graze.
The percent of body weight value changes based on cattle characteristics (e.g.
sex, reproductive
 state, and age).
Steers and heifers will generally consume between 3 and 3.5% of bodyweight.
Then, forage supply is divided by animal demand to get pounds of liveweight per acre.
In the second equation, total pounds of liveweight  is divided by the pounds of liveweight per acre  to get the size of paddock in acres.
Once the area is determined, the paddock can be constructed using poly-wire and step-in posts.
However, knowing where to set the fence to achieve the desired area can be difficult.
There are numerous free phone apps that use GPS and can measure land area while in the field.
Paid apps, such as PastureMap, are designed specifically for grazing systems and offer the paddock building tool as well as recordkeeping, grazing reports, and many other options.
This is the tool we used and found it very useful.
An example of the map you can create of your pasture layout can be found in Figure 6.
If you are not into technology, you can always just pace off, count fence posts, etc.
to estimate the area to fence off for a paddock and then evaluate your level of use the next time you go out and adjust the size of the next paddock accordingly.
Regardless if you do or do not use technology, visual estimation of utilization should be part of your daily monitoring followed by subsequent adjustment of paddock size or time in a paddock.
Although it is important to accurately estimate paddock size, please keep in mind that you also need to estimate and set a realistic stocking rate based on what the pasture will produce over the growing season.
Changing paddock size and speed of the rotation will not make up for a deficit in forage production if you have too many animals.
The first equation in Figure 7 can be used to estimate stocking rate for your pasture in lbs of
 Available forage estimation  X.50  lbs of liveweight acre Estimated daily intake  X Duration of grazing 
 Total lbs of liveweight for entire herd = Size of paddock in acres lbs of liveweight acre
 Figure 7.
Equations to calculate paddock size based on animal and forage information.
liveweight per acre.
Instead of the amount of forage available at a point in time when determining paddock size, you need to use what you think the pasture will produce over the growing season.
At lower elevations , it is generally safe to assume that most well managed irrigated pastures in Colorado will produce at least 4 tons or 8,000 lbs per acre.
As you move up in elevation, production will decline due to the shorter growing season down to 1.5 to 2 tons per acre at around 8,000 ft.
For utilization, you can conservatively assume about 70% of what is produced over the growing season will be utilized by the livestock.
At any point in time, you do not want to use more than about 50%, but when you add up utilization from all grazing periods over the season, it will generally total 70% or more of what was produced.
Use the average intake over the season for the type of animals you will be grazing and how many days they will graze.
In our system at CSU, the approximate stocking rate was 1,000 lbs of liveweight per acre.
To arrive at this value, we assumed 8,000 lbs/ac, 70% utilization, 3% bodyweight intake , and 180 days of grazing which equates to 1,037 lbs of liveweight per acre.
This estimate proved to be very close for our situation.
Table 1.
Pounds of dry matter intake  by a mature cow at varying weights and reproductive stages.
Body Weight		PostPartum	Lactating &	Pregnant	Gestating	Calving	Pre-
 DMI 
 1100	2.62	2.51	2.13	2.27
 1200	2.76	2.65	2.28	2.44
 1300	2.91	2.80	2.43	2.58
 1400	3.04	2.94	2.56	2.73
 Pasture assessment over the shortand long-term is important for making management decisions to achieve goals.
Examples of goals that we had for the CSU grazing project included:
 maintaining an average residue height of 4 inches following grazing to ensure adequate leaf area for photosynthesis and rapid regrowth
 utilization of 50% or less of the vegetation in a paddock during a grazing period
 rest periods no shorter than 18 days  with an average over the grazing season of about 30 days
 COWS that maintained or increased in body condition over the grazing season
 calves that weaned as heavy or heavier than average
 minimal animal health issues
 Table 2 outlines some of the factors to consider monitoring, what those factors tell you, how often to monitor, and monitoring methods.
Short-term assessments can be done visually when animals leave a pasture to determine if residue height/utilization goals are being met and assess livestock health.
Moving animals more often allows managers to have a more intimate knowledge of weight gain/body condition status or illness within the herd.
This information can be used to make more responsive improvements to the system.
Pasture productivity can be assessed less frequently, approximately twice per month.
This monitoring provides an idea of what forage production looks like moving forward in the grazing rotation and how forage is regrowing from previous grazing events.
Longer term monitoring, which can be done once to a few times a season, focuses more broadly on overall pasture health.
Observations in this type of monitoring could include plant diversity, basal cover, residue, fertility, soil characteristics, and others.
There are several score sheets that can be used to record pasture observations and aid in determining overall pasture health.
The Pasture Condition Scoresheet published by the NRCS is one good example to check out.
When grazing cool-season irrigated pastures, one of the biggest challenges is balancing livestock forage demand with available forage throughout the season as both are always changing.
As hard as one might try, it is difficult to rotate fast enough in the spring to keep up with rapid forage growth.
Grass in some paddocks will end up transitioning to the reproductive phase and palatability and forage quality will decline.
There are several options to address this issue.
One is to have a flexible herd size with more animals available for grazing in the spring.
If you are primarily grazing cow/calf pairs, you could also run some additional stocker steers for a couple of months.
If you are running stocker steers, you could have a larger number in the
 Table 2.
List of monitoring indicators, what they tell you, suggested frequency of effort, and method to accomplish.
Monitoring Indicator	What It Tells You	Frequency of Effort	Method
 Dry Matter Yield	Amount of forage present	2x per month	See above Assessing
 to inform paddock size	Forage Availability
 Residue Height	Intensity of utilization -	At every move	Pasture/grazing stick
 does enough leaf area	measurement combined
 remain for photosynthesis	with visual assessment
 and rapid regrowth, does	to determine if the
 paddock size need to be	minimum 4-inch residue
 adjusted	height was achieved
 Body Condition	Weight gain/loss	Beginning and end	Body condition score or
 of grazing season	actual weight
 Animal Health	Need to treat an animal or	At every move	Visual assessment of
 remove it from the herd	such things as droopy
 slow to move to new
 Trend Monitoring	General ecological trend to	Once per season at	See Pasture Condition
 determine if changes in	about the same time	Scoresheet by NRCS
 management are required	every year
 of the plant community,
 soil, and water resources
 spring and either sell the larger ones after a couple of months or move part of the herd to other forage re-sources such as native rangeland.
A second option is to stock the pasture for when forage supply will be at its lowest point, which will be during the summer slump in July and August, and plan on haying some of the paddocks.
The third option is to allow the forage in some paddocks to stockpile during June which will provide a reserve to help make it through the summer slump in July and August.
We found that although palatability of standing, stockpiled forage declines significantly, if you mow the stand just prior to turning cattle into a stockpiled paddock that animals will do a good job of cleaning up the mowed forage.
It has that nice smell of freshly cut, curing hay which draws animals to it.
They will eat much of the cut forage along with grazing some of the leaves down in the canopy.
We found that mowing between 6 and 10 inches  with a rotary mower was ideal and led to quick regrowth of the forage which was nice and leafy by the next rotation through the mowed paddock.
A final consideration to keep in mind is that, although cool-season forages will regrow in the late summer/early fall, the amount and rate of regrowth will drop off quickly in late September into early October in Colorado.
This means that the grazing season will generally be over by the end of October unless you have set aside paddocks earlier in the
 season  for stockpiling of forage.
If grazing later into the fall is an objective, then having about a quarter of the area in monoculture tall fescue is a good option since it grows later into the fall, stands up well under a snow load, and stockpiles well.
When grazing late in the growing season, you want to leave at least 4 inches of stubble for the plants to have enough stored carbohydrates to ensure survival and vigorous spring growth.
Grazing too close  in the fall will lead to weakened stands the following year that green up later in the spring and are not as productive.
Just like earlier in the growing season, you must "leave some grass in the fall to grow some grass the next spring".
More information on MiG can be found at:
 1.
Management-intensive Grazing: The Grassroots of Grass Farming by Jim Gerrish
After some prehistoric irrigation in the Great Plains, irrigation development began in the late 1800s, starting with projects diverting water from rivers to fields.
Eventually, irrigation projects also included reservoirs for storing water along with complex systems of canals to deliver water to fields up to 100 miles away.
Percent of fields that became wetter moving from August to Sept.
15.
The dry years 2020, 21 and 22 fields are much drier than the other years in the fall.
In 2018, 58% of fields with soil in the 15-25 in zone became wetter from August to Sept.
15, 58% of fields with soil in the 25-36 in zone became wetter from August to Sept.
15, and 47% of fields with soil in both zones became wetter moving from August to Sept.
15.
LIMITED IRRIGATION RESEARCH AND DEMONSTRATION IN COLORADO
 The combination of climate variability, drought, groundwater depletion, and increasing urban competition for water has created water shortages for irrigated agriculture in Colorado and is driving the need to increase water use efficiency.
A statewide water supply survey predicts that 428,000 irrigated farm acres will be converted to dryland cropping or pasture within the next 15 years, mostly due to transfer of water from agricultural uses to meet the water needs associated with population growth.
A shift from irrigated to dryland cropping would significantly impact the economic viability of agricultural producers and have far reaching indirect effects on businesses and communities that support irrigated agriculture.
Water conservation options other than complete land fallowing are desirable because of the potential economic and environmental concerns associated with conversion to dryland.
One approach to reducing consumptive use of irrigation water is adoption of limited irrigation cropping systems.
With limited irrigation, less water is applied than is required to meet the full evapotranspiration demand of the crop.
Crops managed with limited irrigation experience water stress and have reduced yields compared to full irrigation, but management is employed to maximize the efficient use of the limited irrigation water applied.
These systems are a hybrid of full irrigation and dryland cropping systems and are currently of great interest to Colorado farmers.
Successful limited irrigation systems are based on the concepts of: 1) managing crop water stress, 2) timing irrigation to correspond to critical growth stages for specific crops, 3) maximizing water use efficiency by improving precipitation capture and irrigation efficiency, and 4) matching crop rotations with local patterns of precipitation and evaporative demand.
Research in the Great Plains illustrates that limited irrigation cropping systems are significantly more profitable alternatives than dryland.
Two demonstration sites were developed in 2006.
Site 1 is located near LaSalle, Colorado on a sandy loam soil.
This field is furrow irrigated and the crop rotation is continuous corn.
Irrigation management strategies include full irrigation
 management and limited irrigation management.
Limited irrigation management tries to limit water during the vegetative growth stage and irrigate during the reproductive growth stage.
Cultural practices such as populations were also studied at this site.
Impacts on reducing plant populations with limited and full irrigation management were observed.
A second site was located near Burlington, Colorado on a silt loam soil.
This field is center pivot irrigated.
Alternative water management strategies were studied at this site within a 4-year crop rotation of corn-sunflower-soybean and winter wheat.
This study looked at full irrigation management, an average allocation of 10 inches per year and an intermediate irrigation management strategy that limits water applied between that of full irrigation and allocation management.
Reduced irrigation compared to full irrigation reduced corn yields for limited irrigation.
Full irrigation grain yields were 182 and 190 bu/acre for 2006 and 2007 respectively.
Reducing irrigation during the vegetative growth stage reduced grain yields to 155 and 151 bu/acre for 2006 and 2007 respectively.
This was an average yield reduction of 18% for limited irrigation compared to full irrigation.
Irrigation was reduced from an average of 28 inches for full irrigation to 15.5 inches for limited irrigation.
The irrigation for limited irrigation was 55% of full irrigation.
Precipitation for both 2006 and 2007 was below average.
Average growing season precipitation is approximately 7 inches.
Reducing plant populations may be a strategy to reduce input costs and limit crop evapotranspiration during the growing season.
Plant populations did impact grain yield for each of the irrigation strategies.
For full irrigation management, 34,000 plants per acre resulted in slightly greater yields as compared to 26,000.
Reducing the population to 20,000 plants per acre reduced grain yield by 15 bu/acre.
However, with limited water, reducing plant population from 34,000 to 26,000 did not impact grain yield on average.
Reducing the plant population to 20,000 plants per acre reduced the grain yield for limited water by 14 bu/acre, which was similar to that of full irrigation.
Reducing plant populations below 26,000 plants per acre is not regarded as an economical practice for limited irrigation.
If a water savings and increase in yield was to be obtained, 2006 and 2007 should have been optimal years due to the limited amounts of precipitation during the growing season.
Grain yield components such as kernels per ear, ear length and kernel weight were taken.
At the optimum plant population for each of the irrigation strategies, the number of kernels per ears was not significantly greater for full irrigation as
 compared to limited irrigation.
Ear length was slightly greater for limited irrigation compared to full irrigation, but was offset by a reduction in the number of kernels around the ear.
Kernel weight was less for limited irrigation than full irrigation by almost 20%.
This reduction is similar to the reduction in grain yield for limited irrigation compared to full irrigation.
Average grain yields for corn and soybeans were reduced when irrigation was limited as compared to full irrigation.
However, in 2006, corn grain yields for all irrigation strategies were similar.
Precipitation during 2006 was above average for the growing season by 1.0 inches.
Timing of irrigation for the reproductive growth stage did increase early season utilization of stored soil moisture.
Approximately 1.4 inches of stored soil moisture was utilized for allocation irrigation as compared to full irrigation.
Irrigation requirements for allocation management were 8 inches while full irrigation required 12 inches.
This is less than what is estimated for full irrigation management in a normal year.
However, there is a potential savings of 4 inches of applied irrigation when limiting water during the vegetative growth stage.
Grain yields in 2007 were less than in 2006.
Approximately two weeks prior to tassel, a severe infestation of corn rootworm was noted in the entire field with 6 larvae per plant being observed.
The allocated and intermediate corn was more severely impacted as compared to full irrigation.
An insecticide was applied at planting but apparently failed due to insect pressure.
After visual observations of damage were taken, it was noted by entomologist that the reduction in grain yield by damage to the roots was approximately 20% for full irrigation.
This would have increased yields too approximately 200 bu/acre which was observed in adjacent fields with this variety.
The yield reduction for the allocation irrigation was adjusted at approximately 40%.
Soybean grain yields  were greater for full irrigation than either intermediate or allocation irrigation by 7 to 10 bu/acre.
Grain yields in 2006 were substantially less than would be expected due to herbicide damage.
Residual dicamba was in the farmers' sprayer and damage was done when the soybeans were sprayed with glyphosate.
Evidence of herbicide damage was evident by leaf cupping on the top of the soybean plants.
Soybean yields of a test plot near this region had soybean yields for this variety average near 70 bu/acre.
In 2007, soybeans were drilled.
Grain yields for full irrigation were 56 bu/acre with intermediate and allocation management yields of 50 and 45 bu/acre.
Although yields were greater than 2006, harvest loss was significant.
A fixed 30 foot wheat header was used for harvest.
The ability to adjust the location of the head in the field was difficult and losses for the entire field averaged 28 plus bu/acre.
The potential yield of the soybean was 70 to 80 plus bu/acre.
These yields were also verified by crop adjuster estimates.
After further discussion with
 the producer, harvesting of the soybeans will be changed to include a flexheader.
This harvesting equipment floats along the soil surface and automatically adjusts to terrain differences.
Irrigation requirements for full irrigation soybeans in 2007 were 13 inches with 9 inches applied to allocation management.
Sunflowers respond well to limited amounts of irrigation.
Sunflower grain yields in 2006 averaged 2500 to 2600 lbs per acre for allocation and intermediate irrigation management.
Full irrigation yields were 2400 lbs per acre.
These yields were 400 to 500 lbs per acre less than hand harvested yield.
Harvest losses were greater than expected due to increased lodging from insect pressure.
Oil content for the allocation and intermediate management averaged 47% while full irrigation management oil content was 42%.
This yield response is similar to previous research which has shown in average precipitation years, sunflowers do not respond to irrigation during the vegetative growth stage.
Irrigation requirements for full irrigation management were 8 inches while the allocation management had 4 inches of applied irrigation.
In 2007, grain yields for sunflower were less than 2006.
Full irrigation management averaged 2050 lbs per acre while allocation and intermediate irrigation management averaged 1700 and 1550 lbs per acre respectively.
Harvest losses were again a significant impact on grain yields.
Hand harvested yields were approximately 2500 lbs per acre for each of the three management strategies.
The full irrigation management sunflowers were planted approximately 1 week later than the intermediate and allocation management sunflowers due to rainfall.
The full irrigation management sunflowers did stand better than the earlier planted sunflowers which may have increased harvested yield of the full irrigation compared to allocation management.
Limited irrigation management of crops is management intensive and is potentially more risky than full irrigation management.
However, research and demonstration projects in Colorado have successfully shown that irrigation water can be reduced and economical yields obtained.
Alternative crops such as sunflower and soybeans can reduce the amount of irrigation needed as compared to corn.
Education and marketing will play an important factor in the acceptance of these crops for irrigation conservation.
However, under current water law and regulations, water management such as limited water is not practical in years other than water short years in ditch and reservoir systems.
In groundwater management areas, declining water resources and compact litigation may force limited irrigation changes with less water in the future.
Figure 1.
Grain yield for irrigation strategies and plant population at LaSalle, Colorado.
Figure 2.
Soil moisture for irrigated corn on July 6, 2006.
Table 1.
Irrigation and precipitation for LaSalle, Colorado.
Year	Full	Limited	Precip.
2006	34.5	18.1	3.0
 2007	21	13.1	4.0
 Average	27.75	15.6	3.5
 Table 2.
Grain yields for corn, soybean and sunflower at Burlington, Colorado.
Irrigation	Corn, bu/acre	Soybean, bu/acre	Sunflower, lbs/acre
 Strategy	2006	2007	Avg	2006	2007	Avg	2006	2007	Avg
 Allocation	193	127	160	40	45	42.5	2490	1710	2100
 Interm.
203	145	174	37	50	43.5	2580	1560	2070
 Full	198	160	179	47	56	51.5	2390	2050	2220
Strategies for Reducing Consumptive Use of Alfalfa
 There is increasing competition for a limited water supply throughout much of the western U.S.
Urban and municipal water users, declining groundwater levels, and drought are factors that are leading to reduced irrigation water quantities for large areas of agricultural land.
As an example, Colorado's population is expected to grow about sixty-five percent in the next twenty-five years.
Most of this growth will occur in the corridor from Fort Collins to Colorado Springs, CO.
As Colorado's population grows, water is expected to shift from agriculture to municipal and industrial uses.
Estimates are as high as 400,000 acres of irrigated farmland that will dry up to meet changes in water supply and demand.
Changes in water allocation have important implications for the economic and environmental sustainability of agriculturally based economies.
There is growing interested in the potential of limited irrigation in cropping systems as a means of addressing changing water supply and demand issues while maintaining profitable irrigated agricultural systems.
Limited irrigation consists of applying water at rates lower than full ET demand by the crop.
Such a practice requires managing crop water stress and depends on the ability to irrigate during critical crop growth stages.
This paper outlines strategies for reducing consumptive water use of alfalfa through limited irrigation practices.
There has been much work done in the past to determine the relationship between consumptive water use and alfalfa yield .
Studies of alfalfa water use conducted across a range of climates and geographic areas in the U.S.
illustrate a linear relationship of yield to ET with the slope of this line indicating alfalfa yield per unit of consumed water.
The slope of this relationship is 0.18 tons/ac/in can also be interpreted that it requires an average of 5.6 in of ET per ton of alfalfa hay produced.
This result corresponds well with a rule of thumb among Colorado irrigators that it takes 6" of water to produce a ton of hay.
The data in Figure 1 illustrates that there is a lot of variability in the yield and ET relationship, resulting from the many factors that can affect alfalfa
 water use efficiency.
One study  compared the yield and ET relationships for individual hay cuttings across a growing season and found that the relationship changes depending on the cutting.
In that study, the first and fourth cuttings had higher WUE than the middle two cutting.
This makes sense because alfalfa is a C3 plant that is adapted to the cooler temperatures in the spring and fall cuttings, while loosing efficiency during the hotter summer cuttings.
Thus, we hypothesized in our study that we would get the highest water use efficiency by focusing irrigation water to the early or late season growth.
Alfalfa is a good candidate crop for limited irrigation for several reasons.
First, under full irrigation, alfalfa consumes large quantities of water during the growing season, leaving a large potential for water savings under limited irrigation practices.
Second, alfalfa has drought tolerance mechanisms that make it biologically suited to deficit irrigation.
Alfalfa is a deep rooted perennial crop with the ability to go into dormancy during drought.
During dormancy, alfalfa limits above ground growth while storing energy for rapid growth from buds when water becomes available.
This characteristic gives the irrigation manager flexibility to apply water during times when it is available and withhold water when it is in short supply.
A third reason that alfalfa is suited for limited irrigation is the potential for managing irrigation in a way that promotes higher quality hay, partially offsetting yield reductions with potentially higher price for quality hay.
The study objectives were to:
 1.
Quantify alfalfa growth responses and consumed water  under full and limited irrigation regimes.
2.
Evaluate alfalfa forage and stand quality under full and limited irrigation regimes.
The study was located at the Northern Colorado Water Conservancy District  headquarters in Berthoud, CO.
Average rainfall at this site is 13-15 inches and the soil type is a clay loam.
The elevation is about 5,000 feet above sea level.
The water table is located about 20 ft.
which was monitored using onsite observation wells.
The study area is about 2.5 acres divided into twelve plots each measuring 290 ft.
long by 51 ft.
wide with a 15 ft.
buffer separating each replicate.
There were three replicates of four irrigation treatments and the treatments were randomized within each replicate.
The plots were irrigated with a state-of-the-art linear sprinkler that had drop valves with solenoids controlled by GPS to automatically turn on and shut off sections of the sprinkler as it passed over the different plots.
The irrigation water was ditch water supplied from a holding pond on the site.
Dairyland Magna Graze alfalfa from AgLand was planted in August of 2004 and overseeded in 2005 to improve stand density.
Irrigation treatments began in 2006.
The four irrigation treatments applied to the alfalfa crop were as follows:
 Full Irrigation  No water stress.
Crop was irrigated to fully meet crop ET demands.
Stop Irrigation After 2nd Cutting  Crop was irrigated to meet ET demands through the 2nd cutting then received no irrigation for the rest of the season.
Spring and Fall Irrigation  Crop was irrigated to meet ET demands through the 1st cutting, was terminated, and was resumed after 3rd cutting to meet ET demands during the 4th cutting.
Stop Irrigation After 1st Cutting  Crop was irrigated to meet ET demands through the 1st cutting then received no more irrigation for the rest of the season.
Yields samples were collected by weighing a 20 ft.
section of windrow.
Subsamples from the large sample were taken to determine percent dry matter as well as for forage quality analysis.
Dry matter was determined by drying the sample to 0% moisture in an oven at 105C until no weight change was detected.
Once dry matter was determined, that percentage was applied to the total fresh weight and then extrapolated to a full acre.
Forage subsamples were ground and analyzed for protein content and fiber digestibility by standard methods and quality analysis was used to compute relative feed value.
ET was determined using a water balance method.
This method balances all of the water inputs and losses according to the following formula:
 is the change in soil moisture during a period of time.
I is the amount of irrigation applied.
is an irrigation efficiency factor.
P is the amount of precipitation.
R is run-off  D is the deep percolation 
 The value was determined at greenup and after each harvest period by taking soil samples down to 8 feet in 1 foot increments.
The samples were weighed wet, then oven-dried at 105C until no weight change was detected, then weighed dry to determine the moisture in each foot.
The moistures for each foot were summed to get an 8 foot profile total.
Run-off was assumed to be zero
 because the irrigations were small  and the plots were fairly flat.
Deep percolation was also assumed to be zero because of the small irrigations, the heavy soil type being able to hold large amounts of moisture, and the deep root system of alfalfa.
Stand density was assessed in April 2007 by counting the crowns/ft2 by randomly sampling in each plot four times to get and average stand density.
Alfalfa yields were responsive to irrigation level, decreasing with reductions in irrigation amount.
The average total season yields for 2006 were 8.2, 6.4, 5.9, and 3.6 tons ac-1 for the FI, S2, SF, and S1 irrigation treatments, respectively.
It should be noted that the individual average fourth cutting yields for the FI and SF treatments were almost the same even after two months of water stress in the SF treatment indicating the ability of alfalfa to recover after severe water stress within the growing season.
The average total season yields for 2007 were 8.5, 7.9, 7.7, and 6.9 tons ac-1 for the FI, S2, SF, and S1 treatments, respectively.
It should be noted that the average first cutting yields for 2007 were virtually the same for all four treatments, even after one growing season of water stress for the limited irrigation treatments illustrating again the ability of alfalfa to recover from severe water stress across growing seasons.
Also, the average fourth cutting yields for the FI and SF treatments were again similar.
Individual cutting yields can also be compared for both years in Figures 3 and 4.
Over the two years of the study, with 2006 being a dry year and 2007 being a more average year in terms of precipitation, the average yields were 8.4, 7.2, 6.8, and 5.3 tons ac for the FI, S2, SF, and S1 treatments respectively.
The average total season ET values for 2006 were 26.6, 15.6, 15.1, and 10.0 inches for the FI, S2, SF, and S1 treatments, respectively  with only 3.7 inches coming from precipitation.
Irrigation amounts were 24.0, 12.0, 11.5, and 3.6 inches for the FI, S2, SF, and S1 treatments, respectively.
Also, on average, 1.1 inches of soil moisture was stored in the profile in the FI treatment, 0.1 inches were stored in both the S2 and SF treatments, and 2.7 inches of moisture were extracted from the soil profile in the S1 treatment.
These results illustrate that alfalfa will utilize moisture from the soil profile to a greater degree under limited irrigation.
This moisture depletion has been accounted for in the ET reported in this study.
In 2007 the average total season ET values were 34.4, 23.4, 24.7, and 17.9 inches for the FI, S2, SF, and S1 treatments, respectively  with 11.9 inches contributed by precipitation.
Irrigation amounts were 21.3, 9.5, 10.4, and 2.7 inches for the FI, S2, SF, and S1 treatments, respectively.
On average, 1.2 , 2.0 , 2.4 , and 3.3  inches of soil moisture were extracted from the soil profile.
The average ET values for both years were 30.5, 19.5, 19.9, and 14.0 inches for the FI, S2, SF, and S1 treatments, respectively.
When looking at the change in soil moisture it seems strange that during 2006, the drier year, that moisture was actually stored in some treatments.
This may be caused by the alfalfa going into dormancy longer in 2006 than in 2007 and
 using less water in general and therefore storing some in the soil.
The exception is the S1 treatment in 2006 where soil moisture was still used.
This may have happened because the alfalfa was in dormancy so long and so little water was applied through irrigation and precipitation that it eventually had to use some from the soil.
In contrast, soil moisture was used from profile across all treatments in 2007, perhaps because the alfalfa was more actively growing and was supported by timely precipitation keeping it from going completely dormant.
Water use efficiency  is reported here as a measure of the amount of hay produced per unit of water consumed.
The WUE values for 2006 were 0.31 , 0.41 , 0.39 , and 0.39  tons ac- in-Superscript This data shows that alfalfa under the limited irrigation system uses water more efficiently than under furrow irrigation.
A similar trend was observed in 2007, where WUE was 0.26 , 0.33 , 0.31 , and 0.39  tons ac-1 in -1.
While these WUE values for individual treatment seem high compared to the literature, when all yield and ET data on a seasonal basis are regressed, the slope of that relationship is 0.234 and 0.116 tons ac in for 2006 and 2007 with an average slope of 0.185 tons ac-1 in-Superscript for both years, which matches very well with the average relationship found in the literature.
The stand density assessment yielded some interesting and, at first, counterintuitive results.
Random sampling found that there were a higher number of crowns per square foot in the S1 and S2 treatments than in the FI and SF treatments.
One of the main factors that reduces alfalfa plant density is disease.
Perhaps, because the limited irrigation treatments have a drier microclimate in the canopy there is less disease pressure acting on the plants and therefore, preserving the stand.
The late season irrigation applications must also have an effect to decrease the crown density in the SF treatment, but it is not understood yet.
The findings of this study have potentially important implications for alfalfa producers with limited irrigation water supply.
Over the two years of the study, an average 11.0, 10.6 and 16.5 ac-in of ET water were saved in the S2, SF, and S1 treatments, respectively, relative to fully irrigated alfalfa.
These ET reductions resulted in yield reductions of 1.2, 1.6, 3.1 tons ac in the S2, SF, and S1 treatments, respectively.
However, as ET declined, WUE increased, indicating more efficient use of water by the crop.
For alfalfa producers faced with decreasing irrigation water supplies, this is encouraging.
Economically speaking, as production decreases, so should most input costs resulting in only a slightly reduced return per acre.
On the other hand, if irrigation water is not limiting but limited irrigation strategies are still employed to conserve water for lease to municipalities to supplement farm income, the enterprise would increase in profitability depending on the market price of water.
Currently, water rights
 cannot be partially leased but there is current debate in the state of Colorado that could lead to allowing such transactions in the future.
Poor water distribution can result in overand under-irrigated areas.
Insufficient irrigation can reduce total biomass, grain yield, and grain quality; whereas, excessive irrigation can cause runoff, soil erosion, deep percolation of water and nutrients, and anaerobic soil conditions.
Consequently, poor water distribution can have a negative effect on a farms net return as well as lead to potential environmental concerns.
Routine maintenance to improve and maintain high system uniformity and application efficiency is desired
Meeting the growing demands for fuel in the United States will require a variety of alternative energy strategies and technologies.
One of the emerging sources of alternative energy is biofuels, and one of those biofuels is biodiesel.
Biodiesel can be produced from oil extracted from a number of oilseed crops, including canola , mustard , camelina , sunflower , safflower , and soybean.
This paper discusses basic agronomic differences between these crops, their responses to varying water supply, and expected dryland and irrigated yields for northeastern Colorado.
Canola, mustard, and camelina are Brassica crops, among the oldest cultivated plants known to humans.
The term "canola" is a registered trademark of the Canadian Canola Association and refers to cultivars of oilseed rape that produce edible seed oils with less than 2% erucic acid  and meals with less than 30 mmol of aliphatic glucosinolates per gram.
In northeastern Colorado all three are generally planted in the early April and harvested in late July.
Seed oil contents for these species generally run between 37 and 45%.
Sunflower and safflower are both deep-rooted species.
Sunflower is native to the Americas while safflower is believed to have originated in southern Asia.
Oil content generally runs from 40 to 47% for both species.
Sunflower is generally planted in late May and matures by the end of September, while safflower is planted at the beginning of May and harvested at the end of August.
Soybean is a legume native to east Asia.
It is generally planted in mid-May and harvested at the end of September.
Oil content generally runs 18 to 20%.
There is wide variation in the 400000 seed size of the six oilseed crops.
The figure shows that the number of seeds 300000 per pound ranges from 3250 seeds per pound for soybean to 371,800 seeds 200000 per pound for camelina.
The small seed size for canola, 100000 mustard, and camelina generally requires that a good seed bed be formed to ensure good 0 Sunflower Canola Camelina germination.
That usually requires some Soybean Safflower Mustard tillage operations and a rolling operation to pack and firm the seed bed.
Accurate depth control on the seeding drill is also essential for proper placement of these small seeds.
On the other hand, the larger seeds of sunflower and soybean, while easier to plant, require more water for imbibition and germination to occur.
0 In the figure at the right the open -15 circles are soil water content at -30 planting, and the filled squares are -45 water content at harvest.
The space between the two lines is an -60 Canola Camelina indication of the amount of soil -15 water extracted.
Canola, mustard, -30 and camelina extract soil water Planting mostly from the top four feet of the -45 Harvest soil profile.
More water is -60 Mustard Safflower extracted by safflower  in the fifth Volumetric Water  Volumetric Water  foot.
Safflower and sunflower can extract soil water to lower water contents  than canola, mustard, and camelina.
Other data  indicates that safflower and sunflower can extract soil water to less than 10% water content in the sixth foot as well.
This more aggressive soil water extraction by safflower and sunflower compared with the other oilseed species means that subsequent crop yields will be adversely affected by safflower and sunflower as the previous crops in a cropping system, and that dryland farmers will likely need to incorporate a year of fallow into the system before another crop is planted.
Irrigated producers will need to perform some off-season irrigations to restore soil water contents to near field capacity in the lower half of the soil profile prior to planting the next crop.
The seed yield response of five of the six oilseed crops to water use is shown in the figure to the right and the regression equations for the production functions
 are given in Table 1.
The
 
 range from 110.5 lb/a per
 inch of water use for
 camelina to 175.2 lb/a per
 inch of water use for canola.
Soybean shows the highest
 seed yield for any given
 amount of water use.
The
 safflower, and sunflower will
 water use in the 15 to 20
 Yield Response to Water
 all yield about the same for
 inch range.
Table 1.
Linear regression production functions for five oilseed crops grown at Akron, Colorado.
Crop	
 Canola	lb/acre = 175.2* 
 Camelina	lb/acre = 110.5* 
 Soybean	lb/acre = 148.1*
 Safflower	lb/acre = 121.4*
 Sunflower	lb/acre = 150.6* 
 ESTIMATING YIELDS UNDER A RANGE OF WATER AVAILABILITY
 Table 2 shows seed yields predicted using the production functions given in Table 1  at three Great Plains locations.
The production functions indicate that soybean would produce the largest yields at all of the locations under all of the water availability conditions.
However, soybean yields would likely be lower than shown due to seed loss from not being able to effectively harvest the lowest node of pods  and seed shatter as pods spontaneously open due to very low afternoon humidity and high winds at harvest time in the Great Plains.
Also it should be remembered that the oil content of soybean seed is lower than that of the other oilseed crops.
For the
 other four crops grown at Briggsdale, camelina would yield highest under rainfed conditions and with three inches of irrigation, but canola would yield highest with six inches of irrigation.
At all three locations and all three water availability conditions sunflower yields the least of all of the oilseed crops.
Table 2.
Estimated seed yields of sunflower, safflower, camelina, canola, and soybean at three Great Plains locations assuming six inches of soil water use and average precipitation, average precipitation plus three inches of irrigation, and average precipitation plus six inches of irrigation.
Location	Crop	Rainfed	3" Irrigation	6" Irrigation
 Briggsdale, CO	Sunflower	863	1315	1767
 Safflower	1306	1670	2034
 Camelina	1350	1681	2013
 Canola	1042	1568	2093
 Soybean	2087	2531	2975
 Wray, CO	Sunflower	1056	1508	1959
 Safflower	1570	1935	2299
 Camelina	1604	1935	2267
 Canola	1445	1971	2496
 Soybean	2365	2809	3254
 McCook, NE	Sunflower	1285	1737	2188
 Safflower	1802	2166	2531
 Camelina	1805	2136	2468
 Canola	1764	2290	2815
 Soybean	2636	3080	3525
One of the easiest ways to check sprinklers is to get back a little ways from the pivot and get at an angle where you can see the sun light gleaming off the water.
From this vantage point closely look at each sprinkler, as well as the overall pattern looking for any inconsistencies or leaks, you can use binoculars if it is helpful.
The overall pattern should show less water closer to the pivot point and gradually increasing toward the out end of the pivot.
Visually look for leaks or any nozzles that are plugged.
A simulation was performed to predict the effect of low pressure on the uniformity of irrigation application depth along the pivot lateral.
For this example, the design pressure at the pivot point was 41 psi.
When the inlet pressure at the pivot point was reduced to 36 psi, 26% of the length of the pivot lateral  had an irrigation application depth less than the intended application depth.
When the pressure was reduced to 29 psi, 65% of the length of the pivot lateral  had an irrigation application depth less than the intended application depth.
GETTING THE MOST OUT OF YOUR RAISED BED OR POTTING MIX TEST REPORT
 Natalie Bumgarner, Assistant Professor and UT Extension Specialist, Department of Plant Sciences
 Robert Florence, Director, UT Soil, Plant and Pest Center
 Soil or potting mix testing and fertilizer application are an important part of any productive vegetable garden, whether in ground, raised beds or containers.
However, these test reports often include terminology and concepts that may not be familiar to gardeners.
This publication provides supplementary information that will enable gardeners to get the most out of their potting mix test report and recommendations.
Understanding Media Tests and Fertilizer Recommendations
 Media and Fertilizer FAQs
 Are soil and potting mix different?
Yes, they are.
Soil is a mixture of minerals  and organic matter.
It functions to supply water and nutrients to plants and physically support them.
Most potting mixes are composed of primarily organic matter , and are often called soilless mixes or growing substrate.
These soilless mixes fill the same roles as soil, but they are better for containers and raised beds because they drain better and are less likely to become compact over time.
They also are lightweight and can be prepared largely free of plant pathogens.
Rapid drainage in soilless substrates can require more frequent irrigation and fertilization as water and some nutrients move more quickly through the profile.
Soilless substrates also require closer management because there are limited volumes of substrate from which the plants can take up water and nutrients.
However, these mixes often warm up faster in the spring due to their drainage and darker color.
Why are soil and potting mix tests different?
Fertilizer recommendations are based on tests that extract nutrients from the mixture to determine what nutrients are available for plant use and what the estimated nutrients needs will be for specific crops.
Because of the physical and chemical differences in soil and soilless substrates, different extraction methods are used.
The methods used for soil tests will not provide accurate results for soilless mixes, and vice versa.
So, selecting the appropriate test is quite important.
As a rule of thumb, if there is 25 percent or more organic material , then a potting mix test should be selected instead of a soil test.
Why does pH matter?
Soil or substrate pH affects the availability of nutrients because pH that is too low or too high can result in plants being able to access too little or too much of the nutrients in the substrate.
The pH affects the chemical form of nutrients,
 and high or low pH can result in nutrients being present in a form that is not ideal for plant uptake.
Different growing substrates can affect the pH range required.
For instance, organic soils or substrates do not have clay minerals that can release aluminum and cause toxicity at low pH.
Because of the this, media pHs mays be lower than mineral soil pH with a lower probability of aluminum toxicity.
What are soluble salts  and why are they important?
Soluble salts describes the total amount of ions in the substrate, and they are usually measured by electrical conductivity, or EC.
EC includes nutrients and non-nutrient ions, such as sodium.
While SS can give an overall view of possible nutrients available, it is best to also measure specific plant nutrients.
Soluble salt measurements are important in making sure that the mixture does not contain so many dissolved ions that it could impede water and nutrient uptake or lead to salt stress.
Salt stress can also be caused by using water that has gone through your water softener.
These systems generally add sodium to replace other ions, so always water your garden from a separate faucet installed before the softener.
Why are two values for nitrogen provided?
Nitrogen  can be taken up by the plant in more than one form, including nitrate  and ammonium , microbial communities are less commonly found than in soil, so N forms mostly reflect what forms were present in added fertilizers.
Use caution in providing all ammonium to crops.
It can lead to lower fruit quality or even root issues because of the way it is taken up by and utilized in the plant.
A fertilizer that has both N forms is often best.
Can I use compost alone to provide needed nutrients for my garden?
Compost is an excellent source of organic matter and is often added to garden soil or used to make growing mixes.
However, the typical available nutrient content of finished composts make them difficult to use as the sole source of fertilizer.
For instance, common composts are often listed as a 1-1-1 fertilizer, which means 10 times the amount of compost would be needed to provide nitrogen as a 10-10-10 fertilizer.
That can be especially challenging when growing in containers or raised beds where the volume is limited.
Additionally, some nutrients found in compost are in forms not immediately available to the plant, so biological breakdown may be needed, which takes time and appropriate environmental conditions.
Because of space and time, it is best to use compost as an amendment and other fertilizers to provide the majority of needed plant nutrients.
If some fertilizer is good, more is better, right?
No, applying more fertilizer than recommended will not support additional plant growth because recommendations are based on plant needs.
Exceeding recommendations can even lead to nutrient deficiencies because excesses of some nutrients can lead to poor uptake of others.
Excess nutrients in soilless mixes can also lead to an accumulation of salts that can reduce plant growth and health.
Additionally, excess nutrients can leach from containers and raised beds into soil and streams that lead to accumulation in other larger bodies of water.
Fertilizer Terms and Methods of Application
 Granular Fertilizer Applying granular fertilizers prior to planting is the most common type of early season fertilization.
For a pre-plant application, the material is spread evenly over the surface of the substrate prior to planting according to recommendations.
Then the substrate can be turned or mixed in place to evenly distribute the fertilizer.
Alternatively, fertilizer can be surface applied and the watered in to undisturbed areas, rather than mixing the substrate and fertilizer.
Pre-Plant Fertilizer Recommendations for Raised Bed/Container Vegetable Crops
 Recommended rates per	10-10-10 fertilizer rates for common raised bed sizes
 1,000 sq.
ft.
1 ounce is approximately 2 tablespoons of 10-10-10)
 N	10-10-10	10 gallon container	4 feet X 4 feet X 12	4 feet X 8 feet X 12	4 feet X 10 feet X
 fertilizer	inches deep bed	inches deep bed	12 inches deep
 1 lb.
10 lbs.
0.2 ounces	2.5 ounces	5 ounces	6.4 ounces
 1.5 lbs.
15 lbs.
0.3 ounces	3.8 ounces	7.5 ounces	9.6 ounces
 2 lbs.
20 lbs.
0.4 ounces	5 ounces	10 ounces	12.8 ounces
 2.5 lbs.
25 lbs.
0.5 ounces	6.3 ounces	12.5 ounces	16 ounces
 3 lbs.
30 lbs.
0.6 ounces	7.5 ounces	15 ounces	19.2 ounces
 Water Soluble Fertilizer These fertilizers are formulated to completely dissolve in water and do not contain the insoluble materials found in many granular fertilizers.
Their solubility makes them rapidly available for plant uptake.
It also makes them more likely to leach away from plant roots as water moves through the substrate, so soluble fertilizers are often applied at more frequent intervals.
Soluble fertilizers are simple to use.
Although more costly than some other formulations, soluble fertilizers are useful for small spaces and containers.
They are also used in irrigation systems because there are no materials that will clog nozzles or drippers.
Fertilization and Irrigation Connections
 Proper moisture is essential for plants to access nutrients dissolved in water in the substrate.
So, lack of water in your garden can cause poor nutrient uptake.
However, excessive irrigation can leach nutrients away from plant roots.
These relationships are especially important in soilless mixes because they do not hold as much water as soil.
In these systems, it is common to provide regular fertilization with irrigation to be able to provide water and nutrients consistently for plants.
A possible downside of applying water and fertilizer together would be when high rainfall provides adequate water for plants, but leaches nutrients.
So, being able to provide either fertilizer alone or fertilizer with irrigation can be helpful.
It is also possible to cause salt damage from connecting fertilizer and irrigation.
This occurs when fertilizer added to irrigation water creates a high salt water.
Allowing rain water or irrigation water alone to flush the salts periodically, may be beneficial.
In-Season Soluble Fertilizer Recommendations for Raised Bed/Container Vegetable Crops*
 Vegetable garden crops	Timing	Soluble Fertilizer Weekly Application Rate for 100 sq.
ft.
dissolved in at least 3 gallons of water
 (1 ounce is approximately 3 tablespoons of water
 All purpose 	Balanced or fruiting
 formula	
 Tomatoes	Weekly 0 to 6 weeks	3/4 ounce
 Weekly 7 weeks or more	1.5 ounces
 Peppers, eggplant, okra	Weekly	----	1 ounce
 Vine crops (cucumbers,	Weekly	1 ounce
 Broccoli, cabbage, cauliflower,	Weekly starting 2 to 3 weeks	1.3 ounces
 Brussels sprouts	after transplanting
 Turnip greens, kale, collards,	Weekly starting 3 to 4 weeks	1.5 ounces	----
 lettuce, spinach, mustard	after seeding
 * Adapted from Southern Vegetable Crops Production Guide
 AG.TENNESSEE.EDU Real.
Life.
Solutions."
 W 804-B 2/19 19-0144
indicating the possibility that the major causative agents may differ between the two counties.
Tissue or fecal samples for microbiologic study were not collected during the survey, but such a study should probably be made.
One of the most important factors related to diarrhea in calves in these counties appeared to be the site of calving.
Farms on which calving usually occurred in a corral seemed to have higher losses than farms on which cattle dropped their calves in pastures or calving occurred in maternity stalls.
The high risk of loss when calving occurs in a corral may reflect unsanitary conditions in the corral, such as dust in summer, mud in winter, concentration of cattle resulting in concentration of feces and urine in the corral, close proximity of other  animals, and contamination of soils by possibly infected birth fluids and waste.
A number of difficulties were encountered in conducting this small survey.
A relatively poor response was obtained in Tulare County, at 11 randomly selected farms it was impossible to complete interviews.
As in any retrospective study, the ability of the interviewee to recall events that occurred as long as a year ago is highly questionable.
However, in this pilot study, in which we sought clues to additional factors which may be related to calf scours, we accepted the risk of memory errors.
A prospective, follow-up study would have been more desirable, but was far too expensive to be considered seriously.
The data collected have been subjected to factor analysis, however, and the results are being reported separately.
Elva Lopez-Nieto is Ancillar Professor, Programa Academico de Medicina Veterinaria, Lima, Peru.
George Crenshaw is Extension Veterinarian; Charles E.
Franti is Associate Professor of Biostatistics, and Alvin D.
Wiggins is Assistant Professor of Biostatistics, Department of Epidemiology and Preventive Medicine, School of Veterinary Medicine, University of California, Davis,
 Effects of Irrigation and Fertilizer on INIA 66 WHEAT
 yields, protein, and bushel weights
 H.
YAMADA J.
ST.
ANDRE R.
M.
HOOVER
 Application of phosphorus and properly timed irrigation appreciably increased yields of late planted wheat.
However, phosphorus applications reduced the bushel weights.
Higher protein content was obtained by increasing nitrogen rates and by timely irrigation.
T HE SOUTHERN SAN JOAQUIN valley has traditionally been a barley region.
With the introduction of Mexican wheat varieties in the past few years, additional cultural information was needed so the full yield potential of these varieties and their competitive status could be determined.
Fertilizers and irrigation variables appropriate to conditions in Fresno County's west side were selected to test a single promising variety which represented these genotypes.
Variety INIA 66 was planted on January 21, 1971 at a seed rate of 135 lbs per acre on a Panoche clay loam soil that had been preirrigated with 21 inches of water.
Soil moisture samples indicated that moisture was available to the 6 ft depth.
Fertilizer treatments were :  200N, 160P, 130K, 1.3Zn, 1.3Fe, 0.88Mg, and 0.08Mn;  200N, 160P, and 130K;  200N and 160P;  200N and 130K; and  100N.
The stage of growth and the amount of water for plots at the time of irrigation was:  secondary root stage-5.4 inches;  secondary root-5.4 inches and late boot stages-5.9 inches;  early boot 6.9 inches and heading stages-5.1 inches;  secondary root-5.4 inches early boot-5.1 inches late boot-4.2 inches and milk stage-7.9 inches.
Fertilizer and irrigation treatments were combined factorially for a 20-treatment total.
TABLE 1.
INIA 66 WHEAT YIELD IN LBS.
PER ACRE UNDER VARIOUS IRRIGATION AND FERTILIZER TREATMENTS
 Irrigation	Fertilizer treatments	Irrigation	DMR*
 treatments	F1	F2	F3	F4	F5	means	1%
 1	2841	2776	2936	2057	2013	2525	a
 2	3172	3132	3175	2592	2316	2877	b
 3	4029	3925	3894	2980	2798	3525	C
 4	4035	3998	4037	3162	2961	3639	di
 Fert.
mean	3458	3511	2698	2522
 DMR 1%	C	c	C	b	a
 *Duncan Multiple Range Test.
Coefficient of variation  3.9%
 The experiment was conducted in a randomized complete block unit with four replicates.
Individual plots  were harvested June 29, 1972.
The yield, bushel weight, and protein data were determined.
Application of phosphorus resulted in pronounced yield increases for all irrigation management systems.
The addition of potassium and minor elements did not influence yields.
Yield responses to fertilizer treatments were essentially constant at all irrigation levels.
The mean yield  for treatments containing phosphorus  was 3,496 lbs per acre, whereas, mean yield for treatments without
 phosphorus  was only 2,610 lbs per acre; a difference of nearly 900 lbs per acre.
Yield differences significant at the 1% probability level were noted between all irrigation means.
Although I-2 and I-3 plots received essentially the same amount of water, a difference of 648 lbs per acre was observed.
The I-2 irrigation treatment was irrigated during the early stages of growth when the water requirements of plants was low.
Irrigation water applied during the early stage of growth percolated beyond the depth of rooting and became unavailable to plants.
Prior to application of the I-3 treatment, which was applied during the later
 stages of growth, some soil moisture had been utilized and subsequent crop irrigations replenished the soil moisture rather than percolating beyond the depth of rooting.
It would appear from the data that an early crop irrigation is not required following adequate pre-irrigation.
Fertilizer treatments containing higher rates of nitrogen were significantly higher in protein while phosphorus and potassium had no influence on protein levels.
The greatest difference in protein (2.10% was between fertilizer treatment F-3 and F-5; whereas, the extreme in the irrigation treatments, I1 and I-2, resulted in protein content difference of only 0.79% Protein concentration of grain was influenced primarily by nitrogen addition, but, timely irrigation was of some benefit.
The bushel weight was significantly increased by the I-4 wet treatment.
The other irrigation treatments were the same.
Fertilizer treatments containing phosphorus  suppressed bushel weights appreciably.
Nitrogen had less affect on the bushel weight than phosphorus.
Treatments containing potassium and minor elements did not materially influence the bushel weight.
The bushel weights were all above the normal range for wheat and none of the treatments resulted in an inferior grain.
TABLE 2.
INIA 66 PROTEIN PERCENTAGE BY WEIGHT 
 Irrigation	Fertilizer treatments	Irrigation	DMR
 treatments	F1	F2	F3	F4	F5	means	1%
 1	14.32	14.98	15.14	15.09	12.93	14.49	a
 2	14.88	15.84	16.42	15.43	13.81	15.28	b
 3	14.63	15.57	15.79	15.45	13.30	14.95	b	a
 4	14.41	14.93	14.59	15.33	13.48	14.55	a
 Fert.
mean	14.56	15.33	15.48	15.33	13.38
 DMR 1%	b	C	c	c	a
 TABLE 3.
INIA 66 WHEAT BUSHEL WEIGHT
 Irrigation	Fertilizer treatments	Irrigation	DMR
 treatments	F1	F2	F3	F4	F5	means	1%
 1	62.0	61.5	62.0	62.9	63.0	62.3	a
 2	61.8	62.4	61.6	62.6	62.8	62.2	a
 3	62.0	61.5	61.3	62.4	62.8	62.0	a
 4	62.3	62.4	61.9	63.8	63.5	62.8	b
 Fert.
mean	62.0	61.9	61.7	62.9	63.1
 DMR 1%	a	a	a	b	b
Technology Transfer: Promoting Irrigation Progress and Best Management Practices
 Dana O.
Porter, Ph.D., P.E.
Terry Howell, Ph.D., P.E.
Written for presentation at the 5th National Decennial Irrigation Conference Sponsored jointly by ASABE and The Irrigation Association Phoenix Convention Center Phoenix, Arizona December 5-8, 2010
 Abstract.
Educational efforts promoting irrigation best management practices are designed to increase adoption of these practices and increase public understanding of the importance of irrigation.
They increase visibility and impact of the Ogallala Aquifer Program and promote affiliated research and extension programs to agricultural producers, consultants and water resources managers.
Building upon existing programs and collaborations, successful programs are being expanded to accommodate additional audiences and applications.
Improved quality, effectiveness and efficiency of educational programs are made possible through improved communication and complementary expertise of the collaborators.
A variety of methods and media  are being used to reach an expanding and diverse audience.
Evaluation surveys and levels of participation in education events indicate that audience response has been very positive.
Keywords.
irrigation, educational methods, best management practices, Ogallala Aquifer, irrigation management, water conservation
 Efficient advanced irrigation technologies and best management practices  have been developed, evaluated and made widely available through the combined efforts of research, extension, the irrigation industry and end-users.
Successful application of these technologies and management strategies has proven cost-effective, technically feasible and effective in achieving water savings and/or increased water use efficiency.
However, adoption of irrigation BMPs, as well as proficiency and appropriateness of applications, have been highly variable.
This implies that BMPs are not well understood, and that additional educational efforts are warranted to promote proper adoption and implementation.
Technology transfer efforts supported in part through the USDA-ARS Ogallala Aquifer Program   were initiated to increase public awareness of program-related research and improve accessibility and application of associated research products and information resources.
Objectives of this ongoing work include 1) promoting adoption of efficient irrigation technologies and management practices through easily accessible, audienceappropriate educational materials; 2) increasing public awareness of irrigation research activities, innovations, and technology contributions of participants in the OAP and research/extension programs of associated universities and agencies; 3) promoting use of information resources, including evapotranspiration networks and related tools, for improved irrigation scheduling and management; and 4) increasing value of the OAP research and technology transfer products.
These efforts should promote a positive public perception of the OAP by providing a range of practical, accessible information and educational resources and opportunities.
This paper describes how the OAP and related technology transfer efforts are reaching the diverse needs of target audiences through a variety of educational methods, and how audience feedback is used to assess and improve effectiveness of the technology transfer program.
The primary target audiences for these technology transfer efforts are agricultural producers, crop consultants, technical service providers, irrigation professionals and similarly interested professionals working with irrigated agriculture.
Most of these audiences are college educated and familiar to some degree with crop production systems, irrigation technologies and irrigation water resources.
They have access to a variety of information sources, including trade journals, Internet, and conferences/workshops sponsored by industry, trade/irrigation associations, and agencies.
They are increasingly technologically sophisticated; many are rapid adopters of new technology.
They are generally the primary decision makers  regarding irrigation technology selection and irrigation management.
A second, yet still very key group of audiences include agribusiness professionals, bankers, offsite landowners , research scientists, policy makers and others who are interested in agricultural irrigation  or in agriculture and/or water issues in general.
These audiences generally are college educated and interested in the subject matter, but they may be less familiar with specific irrigation technologies, methods and management.
While not generally involved in field level irrigation scheduling and management, they can have strong influence in some irrigation decisions.
Youth and general public audiences are becoming increasingly important target audiences.
Goals for these audiences include increasing water awareness and literacy, support for water conservation programs, and understanding of the economic significance of irrigated agriculture on local, regional and national scales.
It is reasonable to conclude that there is overlap among the audiences, their needs and expectations, and that individuals do not necessarily fit readily into categories.
There also is a growing need for irrigation outreach for small scale landowners.
Many small scale landowners are highly educated professionals, but lack experience in rural and agricultural settings.
Many are seeking information related to agricultural irrigation  on a smaller scale.
A high percentage of this group prefers electronic, web-based information access.
While this group does not consume the largest amount of resources, they are nonetheless a very important voting constituency and can be key supporters of water conservation programs.
As the audience base becomes increasingly broad, more highly educated, and technologically sophisticated, their information needs and information delivery mechanism expectations continue to expand.
Traditional on-farm demonstrations, as well as workshops, conferences, classes, crop tours, and other "face to face" formats continue to be important and effective for many, particularly for the traditional primary target audiences.
While venue, agenda topics and presentation quality are very important in successful technology transfer, these occasions also seem to derive much of their value as social networking events and general information sharing opportunities.
Given that the number of extension personnel is decreasing on a national scale, resources to support effective in-person program delivery likely will become more limited.
Evaluation instruments are being used to monitor and improve effectiveness of these delivery formats and events.
On-farm demonstrations are a traditional Extension technology transfer format wherein technologies and BMPs are "proven" locally effective and applicable in commercial farm settings.
Often with participating local grower/cooperators, these short-term or multi-season demonstrations afford opportunities for on-farm training for individuals, as well as for local educational events.
Experts from universities, agencies and industry interact with producers in settings that are comfortable to the audiences and afford opportunities for hands-on learning.
Examples of such programs include on-farm center pivot studies to verify and promote the KanSched tools  and other irrigation management tools and strategies; on-farm subsurface drip irrigation  system evaluations; center pivot uniformity evaluations ; and center pivot in-canopy nozzle package performance evaluations, such as those conducted by the Kansas State University Irrigation Research and Extension Mobile Irrigation Lab.
Targeted meetings and workshops often attract producers, crop consultants and irrigation professionals by offering Continuing Education Units necessary for maintenance of licenses and certifications.
They can be stand-alone events, or they may be held in conjunction with farm shows or larger conferences.
They may even be developed as coordinated series.
Examples of such events and results of evaluation surveys are summarized in the results section.
Secondary audiences  often prefer alternative technology transfer mechanisms, including Internet-based delivery that allows them to access information any time, anonymously and on-demand.
They often prefer concise "sound bite"
 answers over more comprehensive educational packages, and they expect higher level webbased packaging of resources.
Development of these packages requires additional web programming skills, hardware and software maintenance, and visual design expertise.
Yet the overall delivery and potential to reach an expansive audience base makes electronic delivery very efficient.
Meteorological data made available through evapotranspiration networks are essential to application of various irrigation scheduling tools  Application of these tools has been further promoted through expansion of information delivery and improved data management by existing ET networks.
Related outreach efforts include development  of the user interface and data query pull-down menus for the database driven TXHPET Network website.
Terminology and query tools have been improved to be more intuitive for a wider range of end users.
User manuals, special bulletins, newsletter features and invited papers are available in hardcopy and electronic  formats.
The resources have been featured in Extension and other public meetings; technical, professional, and similarly targeted meetings; Extension curricula and workshop series; strategic planning documentation and other venues.
General public and youth audiences often have no specific goal in learning about irrigation technology and management.
Yet, the need for better public understanding of water issues and of the value of efficient agricultural irrigation warrants effective outreach to these audiences.
A variety of media and formats designed to engage them in context of other events can be more effective than traditional meetings or classes.
An off-shoot of the KSU Mobile Irrigation Lab is a mobile exhibit used at county fairs and youth water festivals.
Computer based interactive games and quizzes engage audiences and invite them to become more involved in water issues and more familiar with available educational resources.
Internet websites; presentations at public meetings, fairs and festivals; articles in newspapers; and features on local news television and radio broadcasts expand the opportunities for public access to bulletins, fact sheets, videos and other educational resources.
Evaluation of effectiveness of educational programs is increasingly emphasized, as agencies are required to document program outcomes.
Evaluation survey instruments have been developed to document program effectiveness, and seek feedback from audiences to further improve program quality and relevance.
Survey results, such as those summarized in Table 1, provide agency leaders a quick assessment of program venue, content, audience and outcomes.
Detailed item-by-item results from the surveys provide useful information to event coordinators and speakers.
They answer critical questions.
Was the agenda appropriate for the audience?
Which speakers were well received, and which speakers were less well received, and why?
Which topics needed more time on the program?
Which topics should have been deemphasized or omitted?
What omitted or overlooked topics would the audience like to see on future programs?
Did the program answer the questions or meet the needs of the target audience?
If not, why not?
By incorporating audience feedback into program development, educators can better serve the clientele with relevant and quality information.
Linking survey instruments through common terminology and core knowledge goals allows for easier documentation of program effectiveness on local, regional and statewide scales.
Internet site counters recording the number of requests for information provide a valuable mechanism to measure relative usage of online resources.
Increase in inquiries and usage of the websites, with expected cropping  seasonal fluctuations, indicates increased interest and application of the resources.
Positive feedback on the resources and requests for additional utilities for application with the data indicate that while the current tools are appreciated, additional utilities are desired, and are expected to further increase adoption and application.
Table 1.
Summary of example educational events and evaluation survey results.
Adoption or Intent to
 Event	Audience	(% indicating increase in	Adopt
 Making the	agricultural	crop water	100%	Low pressure center	87%
 Most of	producers, crop	requirements	pivot or SDI
 Workshop	Irrigation	professionals,	consultants,	irrigation	soil moisture	management	100%	maintenance	Equipment	86%
 Lubbock, TX	educators	irrigation efficiency and	100%	BMPs irrigation
 02/01/2008		economics	scheduling	85%
 Irrigation	agricultural	crop water	76%	Low pressure center
 Training	producers, crop	requirements	pivot or SDI	73%
 Program	consultants,	soil moisture
 Series	irrigation	management	68%
 extension	center pivot irrigation	56%	Equipment
 TX	Chillicothe,	educators	irrigation	subsurface drip	84%	maintenance	program	86%
 08/19/2008		irrigation scheduling	64%	BMPs irrigation	86%
 Subsurface	Drip	agricultural	producers, crop	system components,	layout, planning	40%*	Apply knowledge	gained to irrigation	89%
 Irrigation	consultants,	SDI system	decisions
 Field Days	irrigation	professionals,	maintenance and	40%
 Colby, KS	educators	applicability,	Change practices as	50%
 08/04/2009	(100 attending	advantages and	49%	a result of BMPs
 &	Colby event;	disadvantages of SDI	presented
 Halfway, TX	118 attending	BMPs to improve	46%
 08/25/2009	Halfway event)	efficiency
 * Note: Many participants in this event were experienced irrigation professionals who indicated a
 high initial level of knowledge and experience with the technologies and BMPs presented.
Technology transfer to promote adoption and appropriate application of efficient irrigation technologies and best management practices is essential to maximizing their benefits.
Traditional and emerging audiences present opportunities to deliver information and educational resources in a variety of formats and venues, and over a range of technical levels.
Evaluation of educational program effectiveness provides important feedback for ongoing improvement of programs to ensure relevance and quality.
These efforts will increase awareness of irrigation research and technology transfer programs and products, and ultimately will improve irrigation management.
We found that the pivot-mounted sensors had high correlations and low mean errors when compared to the stationary sensors mounted on posts in the field.
The pivot-mounted multispectral sensors were able to detect differences in crop development between rainfed and irrigated crop when the crops were approaching maturity.
It Pays to Water Wisely
 People waste water; plants don't.
Water is wasted when it is applied too rapidly and runs off rather than soaking in or is applied to bare soil surfaces and evaporates.
Make the most of your water
 Choose the best irrigation system
 Trees, shrubs, flowerbeds, and vegetable gardens are best irrigated with drip or trickle systems.
Large trees and shrubs may need a hose trickling water for several hours.
Microspray emitters or a pop-up-type irrigation system are good for plants in sandy soils.
Water infrequently and deeply Irrigate plants to a depth of 8 to 10 inches to encourage deep roots.
Water at night or in early morning Less water evaporates when it's cool, humid and calm.
High: New plants require at least 1 inch of water per week from June through September and during other dry periods.
Medium: Established landscapes can be strategically watered; important areas can be watered regularly and less-prominent areas to be left dormant.
Low: Forego annual bedding plants with high water requirements.
High: Mature trees need to be watered deeply every 2 weeks.
Medium: Healthy shrubs are a lower priority than trees.
Remove overgrown, unhealthy, or improperly placed bushes.
Low: Perennial plants.
Mulch the bed to reduce evaporation.
FIGURE 1.
Simple garden drip system.
The Basics of Micro Irrigation
 Scott Sanford and John Panuska
 A micro irrigation system consists of valves, pipes, tubing, and emitters that slowly dispense water near the plant root zone.
There are several types of micro irrigation.
Drip irrigation, also called trickle irrigation, delivers one water droplet at a time or a very small stream of water to plants.
Micro spray irrigation delivers small amounts of water in a fine mist, in a stream of water, or by means of a micro sprinkler.
Micro spray irrigation systems are often used in orchards to distribute water over a larger area of a tree's root zone than would a drip emitter.
Micro irrigation can be used in greenhouses, orchards, vineyards, fields, lawns, and gardens.
Micro irrigation has many advantages over sprinkler irrigation:
 Water use can be reduced by 25 to 50%  because water is distributed to only the root zone of the target plants and not the area between rows, reducing losses by percolation and evaporation from wet soil.
The plant foliage is not wetted, thus reducing the potential for foliar diseases.
Since the area between rows isn't irrigated, fewer weeds grow, which can reduce herbicide use.
Water is distributed more uniformly, with typically 90% or greater uniformity.
Growers see reduced energy costs, because the system operates at lower pressure and less water is used.
Water can be distributed on the soil surface  or through lines buried in the plant root zone , which will reduce damage to irrigation components by machinery.
The drip irrigation system can be used to distribute water-soluble fertilizers.
Fertigation allows fertilizer to be applied to the crop as needed during the growing season, reducing nutrient losses and leaching.
Due to low water application rates, drip irrigation can be used on sloping ground without causing erosion or runoff.
There are also some drawbacks to drip irrigation:
 The initial cost of the system can be high  relative to other types of irrigation systems, and there can be recurring costs if tubing is replaced annually.
Emitter openings are very small, so all water must be filtered to prevent plugging.
Depending on the source water quality, chlorination or acid rinsing the system may be necessary to prevent emitters from plugging.
THE BASICS OF MICRO RIGATION
 A higher level of management is necessary to operate a drip system, because growers find it more difficult to judge the amount of water applied, which can result in underor overwatering.
Though drip irrigation reduces leaching, it can lead to high soil salinity or alkalinity over time because excess salts are not leached from the root zone.
This can occur in soils that have a high clay content, high compaction, very high sodium content, or high water tables.
Drip systems are also more prone to damage from machinery and wildlife, and at the end of the growing cycle there are cleanup costs to remove, recycle, or dispose of surface drip tape.
In crops that could be damaged by frost during bloom, such as strawberries, a sprinkler irrigation system or floating row crop covers will be needed for frost control.
A basic drip irrigation system consists of a water supply, backflow prevention valve, fertilizer injector , water filtration system, pressure regulator, a main line to transport water to the field, submains to distribute water within a field, laterals or poly tubes to distribute water down a row, and emitters to meter water to the plants.
There may also be valves for zone control; various pipeline appurtenances such as vacuum relief valves, air relief valves, and pressure relief valves; flushing valves; pressure gauges; and system controllers.
For garden applications, this may be a very simple system, with a main line along the edge of the garden and laterals running down the rows all in one zone  with manual water shutoff valves for individual rows.
A large field may require multiple filtration systems, multiple zones, and a controller to automate irrigation of the zones sequentially.
Figure 2 shows a water supply, a filtration system, and one zone of a multiple-zone, larger-scale drip irrigation system.
When designing a new micro irrigation system, whether drip or micro spray, it is important to work from the field to the water source, or from the emitter or sprinkler to the water supply.
FIGURE 2.
Components of a field-scale drip irrigation system.
Three types of piping are used in drip irrigation systems:
 Main line pipe routes the water from the source to the edge of the field.
Submain pipe distributes the water to zones in a field.
Lateral pipe distributes the water to the plants.
In a small system, the main and submain pipes may be the same.
Main lines are typically made of aluminum, polyvinyl chloride , polyethylene , or lay-flat tubing,.
They can be laid on top of the ground for seasonal use or buried for more permanent installations.
The type of pipe will determine whether it can be buried.
Some types of pipe, such as lay-flat tubing and thin-walled polyethylene, cannot be buried because they will collapse.
The pipe should be sized to minimize friction loss at the maximum expected flow rate and have a maximum flow velocity of less than 5 feet per second.
For long runs, a larger pipe may be needed to reduce friction losses.
The friction losses per hundred feet for different pipe materials and pipe sizes can be found in tables, such as the one published by the Irrigation Association in 2008.
Pipe fittings  also need to be considered when
 TABLE 1.
Example of friction loss calculation.
Pipe size/type	Length of pipe	/100 feet	Total friction loss
 4-inch PVC pipe	200 feet	0.22	0.44 psi
 3-inch PVC pipe	300 feet	0.74	2.22 psi
 Fitting allowance	na	25% of total pipe	X 0.25 = 0.67
 calculating friction losses.
A rule of thumb is to add 20% to the friction losses of your straight pipes to account for fittings.
Example: A system will require 750 feet of 2-inch PVC pipe, which has a friction loss of 1.37 pounds per square inch  per 100 feet at a flow rate of 50 gallons per minute.
The total friction loss is 10.3 psi for the pipe.
The fittings are estimated to add an additional 20% in losses, or 2.0 psi.
The estimated total friction losses for fittings and piping will therefore be 12.3 psi.
If the main or submain size is reduced along the pipe run , then the percentage to account for fittings is increased to 25%.
If the pressure drop information for fittings is available from the manufacturer, it should be used instead of estimating.
Example: A system has 200 feet of 4-inch PVC pipe followed by 300 feet of 3-inch PVC pipe to the farthest field from the well at a flow rate of 100 gpm.
Look up
 the friction loss on the friction loss chart.
Calculate the pressure drop for each section of pipe .
Calculate the allowance for fittings.
Add the pipe and fitting losses to estimate the total friction loss.
Pipes will need to be purged of water for the winter to prevent pipe breaks.
For permanent installations, pipe slope and drain locations need to be considered during installation.
Temporary or seasonally installed piping or permanent piping above ground needs to be protected from damage by vehicle traffic and field operations.
Submains are used to route water from the main line to zones in the field.
The lateral tubing with emitters is connected to the submains and delivers water to individual plants.
Submain piping can be PVC, PE, or lay-flat tubing.
The laterals are connected to PE  or lay-flat
 FIGURE 3.
From left, aluminum, PVC, and lay-flat pipe materials.
FIGURE 4.
Polyethylene tubing.
FIGURE 5.
Drip tape barbed connector with and without valve.
FIGURE 6.
Lay-flat tubing with adaptor for lateral.
tubing with barbed end connectors , while PVC requires a gasket , glue connector, or transfer tube.
Fittings installed into PVC piping should be considered permanent.
Ultraviolet  light from the sun degrades PVC.
This causes PVC piping to become discolored and more brittle over time.
If PVC piping is used above ground, it can be painted with a white water-based latex paint, wrapped with an opaque material, or purchased with UV protection.
The UV-resistant PVC pipe is termed PVC UVR.
It still degrades over time but at a slower rate than it would without the protection.
Most suppliers recommend painting the PVC pipe or using a thicker pipe rather than using PVC UVR pipe.
Drip tape, a thin-walled tubing with emitters incorporated at preset intervals, is the most common type of lateral used for row crops.
Drip tape comes in different wall thicknesses  to meet various durability and pressure requirements.
A thin-walled drip tape  would be most economical for an annual crop.
For a crop such as strawberries that will be grown for 3 to 4 years, a medium wall thickness  will provide durability to last the crop cycle.
If drip tape will be reused or moved for multiple seasons, a wall thickness of 10 mil is recommended.
For permaculture , or where there is more field traffic or where rodent damage is more likely, a heavy-walled tubing  is available.
The drip tape can remain in or on the ground over winter as the water will drain, so freezing will not damage it; however, it still can be damaged by rodents or equipment.
would be used for sandy soils, while a wider spacing could be used for soils with higher clay content due to the difference in lateral water movement within the soil.
Crops with large in-row spacing, such as tomatoes or pumpkins, can have emitter spacing that matches the plant spacing.
Closer spacing in row crops reduces the variation in water distribution between emitters.
Typically, a 12-inch spacing works well for most soils.
An emitter is a device that meters water out along a lateral.
Typical flow rates for a drip emitter range from 0.4 to 2.0 gallons per hour.
The emitter opening can be a single point or a slit.
Figure 9 shows the external view of the emitter and a cut-away of the internal part of the emitter that is bonded to the inside of the plastic tubing.
Emitter spacing can range from 4 to 24 inches; 8 to 16 inches is common for vegetable crops.
A closer spacing
 Another type of emitter is a point source emitter.
This type can be used in greenhouses or nurseries for potted plants and in orchards or vineyards.
For orchards and vineyards, multiple emitters may be required per tree or vine.
One advantage of point source emitters in orchards and vineyards is that you can insert them at any spacing needed-just punch a hole and insert the barbed end.
They are available in pressure-compensating or non-compensating types.
Pressurecompensating emitters  are designed to maintain uniform water flow over a range of pressures.
Typically they have a diaphragm to regulate the pressure.
They help to maintain uniform water flow when there are elevation differences in a system or long pipe runs.
Spray emitters, misters, and micro sprinklers  are other types of emitters and are typically used in orchards, landscape applications, or greenhouses.
FIGURE 11.
Micro sprinklers on stakes or risers.
FIGURE 12.
Heavy-walled drip tubing for surface or sub-surface applications.
They can distribute water across a large area of the root zone of a plant or tree.
These emitters can cover areas from about 5 to 30 feet in diameter depending on orifice size, distribution pattern, and water pressure.
The water flow rates range from 5 to 20 gph.
The micro sprinklers are typically attached to a to 3-foot-long stake with spaghetti tubing  connecting the sprinkler to the lateral.
These are typically used in orchards with full-size or semi-dwarf trees.
Micro sprinklers or misters may also be useful for frost control for strawberries and other early-flowering crops.
These types of sprinklers have the disadvantage of higher evaporative losses and may increase canopy humidity levels, increasing conditions favorable for fungal diseases.
Traditionally, drip tape is placed on top of the soil surface or under plastic mulch, which can expose the drip tape to damage.
When tape is placed on top of the soil, some evaporation will occur due to the wet soil surface.
For subsurface drip irrigation , the emitter is
 FIGURE 13.
Drip tubing supported on wire in vineyard about 1 foot above the ground.
TABLE 2.
Recommended subsurface drip tubing spacing and depth.
Crop	Depth 	Drip line spacing
 Fruit trees and grapes	16	Same as rows
 Blueberries, raspberries	>8	Same as rows
 Row crops-corn, asparagus	> 12	Maximum of 60 inches
 Raised beds-single row	2-4	One drip line offset 4 to 6
 	inches from center of bed
 Raised beds-double row	One drip line in center
 	of bed
 Raised beds-double row	Two drip lines spaced half
 	the bed width apart
 Adapted from Van der Gulik, 1999.
placed in the root zone.
This reduces the exposure of wetted soil to evaporation.
For deep-rooted crops the SSDI lines are installed permanently below the tillage zone, but for shallow-rooted crops the tubing may be removed after the crop rotation.
Subsurface installation can reduce the cost over the long run but has a higher initial cost because installation is more complex, requiring a thick-walled emitter line and trenching equipment.
Subsurface drip tubing can be knifed in, but submain piping must be trenched in at the ends of the field or zone.
Typically, tubing has an 8 to 15 mil wall thickness, but piping is available up to 60 mil.
Thickerwalled tubing is used with higher system pressures and in rough  terrain.
Very thin-walled tubing  should not be used for permanent subsurface drip irrigation applications because it will collapse.
Drip tubing should be pressurized shortly after burying to prevent crushing of the tubing as the ground settles.
Subsurface drip irrigation installed permanently in a field or orchard typically will have a longer life if thicker-walled tubing is used, and it can last 20 years or more if properly installed and maintained.
The biggest disadvantage of subsurface irrigation is the difficulty of monitoring the water applied and being aware of problems such as plugged emitters or damaged tubing.
Using water meters on each zone and on each field can help identify problems by making it possible to compare current flow rates with those observed at installation.
The use of soil moisture monitoring sensors can help determine when water is needed.
Subsurface drip irrigation won't wet the soil near the surface so other means of applying water may be needed during germination if the weather is dry; however, this is typically not a problem in Wisconsin.
Drip line spacing and depth
 The spacing and depth of subsurface irrigation piping varies greatly with the type of plant.
The installation depth for fruit trees and grapes will be the deepest, while the installation depth for crops like strawberries and tomatoes will be shallow.
Raised beds may require multiple drip lines, depending on the bed width.
Table 2 provides guidance on the depth and spacing to use for various crops.
THE BASICS OF MICRO RRIGATION
 The number and type of emitters varies with the crop type and spacing.
See table 3 for guidelines.
Drip tape should be placed as close to the crop row as possible with consideration given to avoiding damage during field operations.
If drip tape is placed under plastic, the location is important so that the drip line is not damaged during planting.
For grapes and berries, the drip line can be buried  or suspended from a trellis wire.
A suspended line should be high enough not to impede mowing or tillage operations.
When suspended, the drip line will sag, causing water to drip from the lowest point.
Increasing support of the drip line will help to direct water to the intended location.
If using point source emitters, install them on the underside of the pipe to drop water directly to the ground where desired.
As water is emitted, it enters the soil and may spread horizontally beneath the soil surface, depending on the soil texture.
This will affect the wetted volume of soil, width of the wetted root zone, and possibly the number and spacing of laterals needed.
Table 4 provides a rough estimate of the lateral movement of the water away from the drip emitter in different soil textures.
Growers will need to dig holes, take soil core samples, or use a soil moisture sensor to determine the extent of lateral movement in their soils.
TABLE 3.
Guide for number of emitters per plant.
Crop type	Minimum number of emitters
 Drip tape-orifice spacing not greater than 1.5 times
 Drip tape-orifice spacing not to exceed plant
 Grapes	Point source or drip line-2 emitters per plant
 Strawberries	Drip tape-12-inch spacing recommended
 Point source-spaced every other plant
 Drip line-1 emitter per plant
 Blueberries	Point source-1 per plant, match plant spacing
 Fruit trees	Point source-halfway between trees
 	Drip line-2 emitters per tree
 Point source or drip line-2 per tree spaced 2 feet
 	Spray or micro sprinkler-spaced halfway between
 trees with 360 head or 2 spray emitters at tree base
 with 180 or 270 heads
 Point source or drip line-2 per tree spaced 2.5 feet
 from tree trunk, spacing greater than 15 feet use 3 or
 more emitters per tree
 
 Spray emitters-2 at tree base with 180 heads
 discharging away from tree
 Spray or point source-2 emitters per pot to ensure
 Container plants	plants get water should one orifice plug; large pots
 can benefit from spray to distribute water
 Adapted from Van der Gulik, 1999.
FIGURE 14.
Wetted root zone pattern by soil type.
TABLE 4.
Lateral water movement from point emitter.
UNIVERSITY OF WISCONSIN EXTENSION
 FIGURE 15.
Split slope lateral layout.
The layout of the laterals or drip tape needs to minimize the effects of elevation changes to maintain high water distribution uniformity.
Whenever possible the laterals should lie along the contour of slopes in order to minimize elevation pressure losses or gains.
If that is not possible you may compensate by regulating the pressure at the lateral manifold or submain, by using pressurecompensating emitters, or by splitting the field so that the lateral going up the slope is shorter than that going down the slope.
The split is to balance the elevation effect so that pressures at the emitters are more uniform.
A variety of nominal sizes of lateral pipe and drip tape are available.
Most manufacturers offer drip tapes from 1/2 to 13/8 inches in diameter.
The 5/s-inch tubing is sufficient for most fields, costs less, and is available in a wide range of emitter spacings and flow rates.
The larger 7/8-inch tubing can be used in longer runs and will still maintain high uniformity.
It will also possibly require fewer submains, which could reduce the number of obstacles you will need to maneuver around during field operations.
Although 7/8-inch tubing and fittings cost more than 5/8-inch tubing, the possibility of needing fewer submains may reduce the overall system cost.
Drip tape sizes of 1 1/8 and 13/8 inches in diameter permit higher flow rates and longer runs, but are not commonly used.
The maximum drip tape length will depend on the distribution uniformity required, the slope of the field, the flow rate, the inlet pressure, and the diameter of the drip tape.
On a flat field, the lateral length can be 1,000 feet or more, but an uphill slope can reduce the maximum length by 15 to 60% depending on inlet pressure and slope.
Drip tape manufacturers publish tables or charts indicating the maximum length of run based on operating pressure, flow rate per 100 feet, percent slope, emitter spacing, and uniformity.
Drip irrigation can be controlled manually, with a timer, or by using a sophisticated controller that interacts with sensors that determine soil moisture levels and turn on the irrigation when the moisture level reaches a predetermined value.
In larger systems controllers can be used to sequence zones by activating multiple valves.
Figure 16 shows a valve bank with an automated controller in a vineyard.
Water sources for drip irrigation can be surface water, groundwater, or a public water utility.
A groundwater or public water source is usually best because it typically provides cleaner water.
If a surface water source is used, additional filtration will be required to remove biological materials  to prevent emitter plugging.
When considering a drip irrigation system, remember it is important to have an adequate water supply for the irrigated area during a drought period.
If the water source cannot supply enough water for the system to function efficiently during a drought period, then installing an irrigation system may not result in sufficient additional yield or crop quality to pay for the investment.
In Wisconsin the peak growing season evapotranspiration, or plant water use, is about 0.30 inches per day.
FIGURE 16.
Valve bank with an automated controller in a vineyard.
FIGURE 17.
Backflow preventer for hose.
FIGURE 18.
Anti-siphon vacuum breaker.
FIGURE 19.
Inline screen filter.
The recommended maximum water application time is 12 hours per day , which means a minimum water flow rate of 6 gallons per minute per irrigated acre.
Converting the plant water use into gallons of water per acre results in a requirement of 8,146 gallons per acre per day before irrigation system losses are considered.
Drip irrigation typically reduces the total water volume needed by reducing deep percolation and surface evaporation, and by only watering the crop root zone and not the aisle between the rows.
It can also reduce weed growth due to the dry soil surface.
The total amount of water the plants use will remain the same but there should be less unused water if the system is managed effectively.
Water quality is an important consideration when using drip irrigation.
The amount and size of suspended solids in the water is important in selecting the type of filtration system to use to prevent emitters from plugging.
Measures of water quality include Total Dissolved Solids , which is a measure of the concentration of soluble salts, and Sodium Absorption Ratio , which is a ratio of sodium to calcium and magnesium.
If total dissolved solids are high, they can become a problem if they precipitate out of the water and plug the very small openings of the emitters.
Sometimes water treatment is needed to control TDS.
A backflow prevention valve is required to prevent contaminated water from being drawn back into a well or public water system.
It is basically a check valve and a vacuum relief valve in one unit that will allow the water to flow in only one direction, but will also allow air into the pipeline to replace the water draining from the system.
For a small system it consists of a small valve that attaches to a garden hose.
A large system will use a vacuum breaker that is permanently installed in the water supply line.
Drip irrigation emitters have very small openings that can plug from biological particulates  or chemical particulates.
It is imperative that the water be free of any debris in order to reduce emitter clogging and to maintain uniform distribution.
Most systems will need a 120to 150-mesh filtration screen, but some will require 200-mesh filtration to keep emitters from plugging.
Manufacturers of drip tape and emitters will provide a specification sheet with recommended filtration levels measured in microns or mesh.
There are four types of filtration systems: screens, disks, media , and separators.
Often more than one type of filter will be used in series in a system.
A simple drip irrigation system for a small area such as a garden may include a screen or disk filter; a system serving a larger area will often include a media filter for primary filtration in combination with a screen or disk filter.
Screen filters have a fine screen to remove debris from the water.
They are used in small systems that have clean water supplies or as secondary filters after a media filter.
Regular maintenance is required to remove any debris on the screen.
If the screen is allowed to become clogged, the water force can push debris through the screen or rupture it.
Screens can be cleaned by reversing the water flow to dislodge debris either manually or by using a flushing valve.
The screen should be cleaned after the pressure drop across the filter reaches 4 to 5 psi.
UNIVERSITY OF WISCONSIN EXTENSION
 TABLE 5.
Media type and filtration range.
Sand media type	Mesh range	Mean effective
 and designation	size 
 #8 crushed granite	100-140	1.50
 #12 silica sand	130-140	1.20
 #11 crushed granite*	140-180	0.78
 #16 silica sand	150-200	0.70
 #20 silica sand*+	200-250	0.47
 * Widely used media types.
t Use a base layer of garnet media  in bottom of tank.
Fill to 6 inches above underdrain.
FIGURE 20.
Media filter.
Source: Van der Gulik, 1999; Burt and Styles, 2011.
Media filters , similar to swimming pool filters, are effective for removal of suspended particulate matter in the water supply.
They use sand or crushed rock as a media and are capable of trapping large quantities of suspended solids while still maintaining rated flow rates.
The media type selected will affect the filtration mesh range.
Table 5 lists different types of media and the effective mesh range.
Media filters can be easily cleaned by backflushing to remove the trapped particles.
During backflushing water is routed backwards through the media to dislodge trapped particles and discharge them to a waste drain.
With proper controls, backflushing can be programmed to occur automatically at a fixed time interval or based on the pressure difference between the incoming and outgoing flow.
To provide continuous water flow for irrigation, at least two filters are needed so that at least
 one is filtering while the second filter is being backflushed.
Three-filter systems are often used so two are filtering while one is backflushing.
The filter should be backflushed for 3 to 5 minutes or until the drain water runs clear.
The frequency of backflushing will depend on the amount of particulates in the source water.
The recommendation is to backflush every 2 to 4 hours of operation or, if differential pressure is used, when pressure loss across the filter  is 5 to 7 psi.
FIGURE 21.
Backwashing of a media filter:  both vessels in filtration mode;  one vessel in backwash mode and one vessel in filtration mode.
FIGURE 22.
Separator/cyclone filter.
FIGURE 24.
Disk filter.
FIGURE 23.
Separator flows.
FIGURE 25.
Disk filter element assembly.
Separator filters make use of centrifugal force to separate particles from the water.
They work well for removal of sand and particles that are heavier than water.
They are not effective for removing organic matter and particles that are less dense than water.
The water flow enters the top of the cone-shaped separation vessel tangential to the vessel wall.
As the water flows circularly, the heavier particles move towards the vessel wall and settle to the bottom while the water flows out the top center of the cone.
The accumulated particles are removed as required, either manually or automatically.
This type of filter has the advantage of low pressure drop because the debris is separated out without obstructing the flow path.
Disk filters use a stack of thin doughnutshaped filter material.
These are often used to remove organic matter and small particles after the water goes through a media or separator filter, but they can also be used on small systems to avoid the expense of a media filter.
Multiple disk filters can be used in parallel in large systems to provide greater volume.
They have greater capacity than screen filters of similar size and are easy to clean without scrubbing.
Mesh sizes range from 40 to 200 microns and they can be cleaned by backflushing or reversing water flow to remove debris.
This can be done either automatically with a controller and valves or manually.
Backflushing scheduling can be based on time or on inflow/outflow pressure differential.
A screen or disk filter should be installed after a media or separator filter to remove any particles that were not removed by the initial device.
UNIVERSITY OF WISCONSIN EXTENSION
 Drip irrigation systems operate at pressures from 6 to 60 psi at the field lateral.
A field lateral is piping that supplies water to the drip tape or piping that contains the emitters.
The pressure needed will depend on the elevation change along the pipe length, length of the pipe, water flow rate, distribution uniformity required, and type of emitter system used.
Most drip tape has an operating pressure range of 6 to 15 psi with a general recommended range of 8 to 10 psi.
The recommended operating pressure for micro sprinklers or misters will vary depending on the type and can range from 20 to 60 psi.
Higher pressures result in larger wetted diameters and fewer emitters per lateral.
When selecting a pressure regulator, the desired pressure and flow rate need to be matched to the device.
Pressure regulators can have a fixed pressure setting  or can be adjustable.
Since a drip irrigation system can operate at lower pressure than other types of irrigation systems, it can utilize gravitypressurized flow, given that the pressure provided by gravity is sufficient to operate the system.
The lower recommended operating pressure range for most drip tape is 4 psi.
A filter should be used in the system and this may cause a pressure drop
 of 2 psi, depending on the water flow rate and the number of emitters being supplied at one time.
Assuming negligible pressure drop between the reservoir and the drip line, the total pressure required would be 6 psi.
It requires 2.31 feet of elevation to produce 1 psi of pressure, so to achieve the 6 psi would require the water supply to be elevated about 14 feet above the field.
A system might be operated on less pressure, but the length of run may need to be reduced or the water distribution uniformity may be lower.
See manufacturer's data for recommended pressures and length of runs.
Drip irrigation systems need to be flushed periodically to remove sediment, precipitated minerals, and particles that could plug the emitters.
Even when the filtration system is well designed and well managed, flushing is essential.
Systems should always be flushed before the first use after installation and at the beginning and end of each growing season.
Where water quality issues exist, flushing may also be needed during the growing season.
Flushing involves opening the terminated ends of the submains and laterals and allowing water to freely flow for a period of time.
The flow rate needs to be sufficient to maintain a velocity of at least 1 foot per second in the pipes to suspend particles
 for removal.
This will require higher pressure and water flow rates, so zoning the system is important in order to be able to flush portions of the system one at a time to achieve enough water velocity.
If the irrigation water contains high amounts of dissolved solids, algae, or bacteria, it may require frequent chlorination or the addition of algaecides or acid to remove these materials and keep them from plugging the emitters.
Refer to the B.C.
Trickle Irrigation Manual or Drip and Micro Irrigation Design and Management for Trees, Vines and Field Crops in the reference section for more information on source water treatment options.
FIGURE 26.
Pressure regulator for small system with fixed pressure setting.
FIGURE 27.
Adjustable pressure regulator.
THE BASICS OF MICRO RRIGATION
 The drip irrigation system can be used to apply water-soluble fertilizers and systemic pesticides.
This is done using an injector or dosing system to meter the chemical into the irrigation water.
A drip irrigation system that has high distribution uniformity for irrigation water will also have high distribution uniformity for fertilizers and pesticides if managed correctly.
The injector should be installed before the filtration unit.
A backflow preventer must be installed between the injector and a well or public water source.
There are several different types of injection units: venturi , proportional injector, or injector pump .
For small systems
 a venturi or proportional injector are the least expensive methods but may require that the chemical or fertilizer be diluted with water so the proper concentration will be distributed across the field.
Refer to the B.C.
Trickle Irrigation Manual or Fertigation in the reference section for more information on equipment and process for fertilization through a drip irrigation system.
The amount of water to apply to a crop will depend on the stage of growth, daily evapotranspiration , soil moisture, water volume, and area to be irrigated.
The first step is to estimate the wetted root zone volume using table 4 to consider lateral water movement, the emitter
 FIGURE 28.
Venturi injector.
spacing, and the managed root zone depth.
Refer to UW-Extension bulletins Irrigation Management in Wisconsin  and Methods to Monitor Soil Moisture  for suggested root zone depth for different crops.
Overlap between emitters must be taken into account when estimating the wetted root zone volume.
The following example demonstrates how to determine the amount of irrigation water to apply and the interval between irrigation events.
FIGURE 29.
Water-powered fertilizer injector.
Example calculation of water requirements
 Plants are 1 foot apart in rows 4 feet apart with row lengths of 200 feet.
The root depth is assumed to be 1 foot ).
Irrigation system: 5/8-inch drip tubing with 12-inch emitter spacing and a flow rate of 0.22 gallons per minute /100 feet at 8 psi.
Soil type: Silt loam with 2.5 inches of available water per foot ) and 3 feet of lateral movement.
Is Irrigation Real or Am I Imagining It?*
 Terry A.
Howell / and Freddie R.
Lamm
 Irrigation is an ancient practice of applying water to crops and/or plants to sustain their life SO they can be productive for their intended purpose.
Through the years and into today's literature there are many terms such as "artificial irrigation" and "supplemental irrigation." We know irrigation is real not artificial!
We know ALL irrigation supplements either precipitation  resources, ground water uptake by crops, or existing soil water resources.
Other terms such as "limited irrigation" and "deficit irrigation" emerged in the 1960s to 1970s, while more recently newer terms like "partial root zone drying " and "regulated deficit irrigation " have emerged.
We propose that "artificial" not be used to describe irrigation.
We recommend that "deficit irrigation" should be the preferred term rather than "limited irrigation." We describe "regulated deficit irrigation" and illustrated clearly its difference from "deficit irrigation." We describe "partial root zone drying" as an irrigation management strategy, but we believe PRZD will be effective mainly in improving crop quality of tree or vine crops.
It is important that irrigation literature utilize "correct" terminology to describe current technologies.
Keywords: terminology, deficits, water potential, irrigation scheduling
 Irrigation is an ancient practice mentioned in the Bible, early Egyptian writings, and likely predates the birth of Christ as practiced in Mexico and Central America.
Several terms are ingrained into irrigation literature that are ambiguous or unnecessary while other newer terms are often misused or misunderstood.
This brief article discusses several of these terms in the current irrigation technology context.
Proceedings of the Irrigation Association 28th Annual Irrigation Show 9-11 December 2007, San Diego, California
 The term "artificial irrigation" permeates irrigation literature.
For anyone that has donned irrigation boots, worked a shovel, set siphon tubes, moved pipelines, etc., there is little about irrigation, especially the labor, that is "artificial." Yet, the term remains in relatively wide use today.
It likely implies that sprinkler irrigation is like "artificial rain" instead of the term artificial irrigation used in most cases today.
Nevertheless, it is a term that is unclear and confusing.
"Artificial" irrigation is in the language of the U.S.
Statutes  that formed the basis for westward expansion of the U.S.
to populate the land in 65 ha  parcels in the western U.S.
territories  and thus rendered the land more productive and habitable.
Even more recently, the U.S.
EPA  used the language "Extensive Garden: Extensive gardens have thinner soil depths and require less management and less structural support than intensive gardens.
They do not require artificial irrigation {emphasis added}.
Plants chosen for these gardens are low-maintenance, hardy species that do not have demanding habitat requirements.
The goal of an extensive planting design is to have a self-sustaining plant community." It was used before the U.S.
Supreme Court  in Lee et al.
V.
Nash "That said land of plaintiff above described is arid land and will not produce without artificial irrigation {emphasis added}, but that, with artificial irrigation, the same will produce abundantly of grain, vegetables, fruits, and hay."
 A Google  search of the term "artificial irrigation" produced 38,000 hits.
Clearly, "artificial irrigation" is simply irrigation.
The Webster's New Collegiate Dictionary  defines "artificial" as "1, humanly contrived often on a natural model: man-made; 2, having existence in legal, economic, or political theory; 3, artful, cunning; 4a, feigned, assumed; 4b, lacking in natural quality; 4c, limitation, sham; 5, based on differential morphological characters not necessarily indicative of natural relationships." One could argue that 1, 2, and 5 might fit appropriately as irrigation is designed, constructed, and operated by humans, at least the hardware/software; but irrigation is certainly genuine and not an imitation in terms of 3 or 4, although in some eyes irrigation is certainly artful!
We argue that the adjective, "artificial", adds marginally in describing irrigation.
In fact, it likely detracts from the term "irrigation."
 Equally permeating irrigation literature is the term "supplemental irrigation." A Google  search on this term reported 117,000 hits.
The very nature of irrigation is to "supplement" the crop/plant water supply to achieve economic production.
Clearly, in arid regions, little growing season rainfall occurs SO irrigation supplies almost all crops water requirement with some additional water sources coming from ground water or harvested runoff  or residual soil water.
In more semi-arid regions, Oweis  proposed adding small, but varying amounts of irrigation to traditionally dryland crops growing mainly on winter or pre-season stored soil water to improve crop yields and water productivity.
Although the concept certainly
 Proceedings of the Irrigation Association 28th Annual Irrigation Show 9-11 December 2007, San Diego, California
 has merit, we question its economic feasibility in regions to "spread" relatively small amounts of water.
In addition, the on-farm or infrastructure costs must be recaptured, leading one to favor a more fully irrigated system that might be more sustainable.
It is widely known that supplying even rather small irrigation amounts  at critical crop growth stages can dramatically improve crop yields and thus water productivity, yet the logistical protocols to perform this task may be impractical.
Hence, we offer that all irrigation is "supplemental" in its basic sense although there are wide variations in the need, amount, and timing for the "supplemental" irrigation.
We prefer to simply describe all irrigation as just "irrigation" without the adjective "supplemental".
Limited and Deficit Irrigation
 The term "limited irrigation" is widely used but ambiguous.
We don't know its exact origin.
We both attribute it largely to the pioneering research on irrigation by the late Jack Musick at the USDA-ARS Bushland, Texas laboratory.
He used it to imply a single or perhaps two seasonal irrigations timed at critical crop development growth stages using predominately furrow irrigation.
Basically, it was aimed at ground water irrigation where the producer knew that a farm or field had inadequate water to meet the crop demand.
The literature on "limited irrigation" is quite jumbled from constraints on irrigation amount  to constraints on irrigation capacity.
Although not specifically intended to augment dryland water availability , "limited irrigation" assumes an irrigation infrastructure and water availability, albeit inadequate, and aims to pinpoint applications at the crop development stage known to be the most sensitive to soil water deficits.
A Google  search on the term "limited irrigation" returned 50,500 hits.
The term "limited irrigation" was basically analogous to the term "deficit irrigation" that Miller  used in the Pacific Northwestern United States.
Deficit irrigation as characterized by English et al.
has the fundamental goal to increase water use efficiency.
English and Nakamura  and English  further discussed the term deficit irrigation.
They stated that the fundamental goal of "deficit irrigation" was to increase water use efficiency, either by reducing irrigation adequacy {i.e., not fully meeting the crop water requirement evenly} or by eliminating the least productive irrigations." Fereres and Soriano  recently reviewed deficit irrigation and concluded that the level of irrigation supply should be 60-100% of full evapotranspiration  needs in most cases to improve water productivity.
They indicated "regulated deficit irrigation"  was successful in several cases, especially with fruit trees and vines, to not only increase water productivity but also farm profit.
We conclude for many reasons that the term "deficit irrigation" should be preferred over the term "limited irrigation" in future literature.
In using "deficit irrigation", it is important to distinguish irrigation amount  from irrigation capacity  or both.
These constraints might be physical  or regulatory (e.g., a water right for
 Proceedings of the Irrigation Association 28th Annual Irrigation Show 9-11 December 2007, San Diego, California
 the former).
One inherent characteristic with "deficit irrigation" is that dependence on precipitation and/or soil water reserves to meet a significant proportion of the crop requirement.
During the course of the irrigation season, soil water reserves may become nearly depleted.
Thus, deficit irrigation usually has less applicability in arid regions where there is little precipitation for replenishment of soil water reserves.
Additionally, rainfall is difficult to predict, non-uniform, and perhaps occurs at a rate that exceeds the soil infiltration, and can occurs at a non-critical crop development growth stage.
Hence, the need for irrigation is enhanced to reduce risk, increase yield, stabilize profits, and improve water productivity.
The term "water use efficiency"  is likely one of the most widely used irrigation terms, but it also is largely misused as often, too.
A Google  search on this term returned 795,000 hits.
The term was popularized by Viets , but it is the inverse of the early transpiration ratio used in the late 19th and early 20th century.
One problem with WUE is that it encompasses scales from cellular, leaf, plant to field and time scales from instantaneous to a season.
Typically, WUE is the yield per unit evapotranspiration , and as such it really isn't an "efficiency" at all.
A better term for WUE gaining popularity is water productivity.
"Water productivity" is basically the same definition as WUE and has the same spatial-, time-scale shortcomings but without the confusing "efficiency" terminology for basically a bio-physical term.
Water productivity places the emphasis properly on the productivity from a unit of water without implying an incorrect efficiency concept.
"Regulated deficit irrigation"  has been successful in tree and vine crops to enhance yield and, especially, crop quality.
Jim Hardie  defined RDI as "the practice of using irrigation to maintain plant water status within prescribed limits of deficit with respect to maximum water potential for a prescribed part or parts of the seasonal cycle of plant development.
The aim in doing this is to control reproductive growth and development, vegetative growth and/or improve water use efficiency {water productivity}." RDI is similar to deficit irrigation, but RDI varies the deficit level by crop development growth stage to either enhance yield or quality.
Implicit with RDI is an irrigation capacity sufficient to increase irrigation rate or volume, if required, to reduce the soil water deficit  at a specific crop development growth stage.
With RDI the re-wetting frequency should be determined by detection or prediction of a decrease in plant water potential  below a prescribed set-point.
This set-point should be measured in terms of plant water potential but in practice, for convenience and cost saving, this could be inferred from soil water depletion or estimates of evapotranspiration based on weather conditions or direct measurement of stem/sap flow.
For convenience and cost saving, this set-point could be
 inferred from soil water depletion or estimates of evapotranspiration based on weather conditions or direct measurement of stem/sap flow.
Often RDI is utilized with "partial root zone drying".
Jim Hardie  defined RRZD as "the practice of using irrigation to alternately wet and dry  two spatially prescribed parts of the plant root system to simultaneously maintain plant water status at maximum water potential and control vegetative growth for specific crop development growth stages." These alternating wetting zones have controlled vegetative growth or improved water productivity or both while maintaining reproductive growth and development.
The rewetting frequency under PRZD should be based on the measurement or prediction of soil water uptake from the drying side.
In practice, this can be accomplished by soil water measurements or estimates of evapotranspiration based on weather data or direct measurement of stem/sap flow.
PRZD is impractical for center pivot sprinklers, unless LEPA  drops are in every furrow and alternated.
PRZD might be accomplished by alternating furrows in surface irrigation, but PRZD seems more practical with microirrigation.
But even with microirrigation, PRZD would require almost double the lateral line installations.
Both RDI and PRZD depend on measurement of actual plant water potential compared with a known or controlled site having a full-irrigation regime.
In practice, PRZD success should not be based on whether or not reproductive growth, berry or fruit size or mass has been decreased because this seems unlikely if maximum plant turgor has been maintained.
PRZD will result in a plant/crop deficit  ; however, because the irrigation applications to maintain maximum plant water potential throughout the wetting cycle as follows:
 Insufficient size of the wetted zone relative to canopy size and evaporative demand
 Several issues that impact PRZD applications are:
 Determination of the allowable or desirable set-point in plant water potential  for any departure from the fully irrigated site?
Determination of the consequences of regional/site differences in vapor pressure deficit or evaporative demand, crop rooting characteristics, or soil water redistribution as they impact the daily range of plant water potential of plants under PRZD regimes?
summarized that "relation to water deficit strategies in general, a barrier to implementation, apart from lack of convenient plant based measures
 Proceedings of the Irrigation Association 28th Annual Irrigation Show 9-11 December 2007, San Diego, California
 of water potential, appears to be the lack of broad recognition that plant stress is a quantifiable continuum and that any attempt to regulate the deficit to achieve plant responses must involve defining, measuring and controlling the stress within prescribed limits.
Satisfactory implementation of deficit strategies in warm areas i.e.
high vapor pressure deficit, generally requires responsive watering systems and soils with high infiltration rates." In general, in the United States., few experiments have verified the success of PRZD, but RDI has had success in tree and vine crops to improve yield and especially quality while enhancing water productivity.
We reviewed widely used historical irrigation terms like "artificial irrigation," supplemental irrigation," and "limited irrigation.
We suggest the first two are not descriptive and add little to just "irrigation." The third term has been largely replaced by the more descriptive term, "deficit irrigation;" however, it requires some clarification to the constraints.
We believe the term "water use efficiency"  although still widely used should be replaced by the term "water productivity" as it doesn't perpetuate the incorrect use of an "efficiency" name and emphasizes the positive aspects of crop yield per unit water.
Newer terms like "regulated deficit irrigation"  and "partial root zone drying"  were discussed, and they each require a measure of direct plant/crop water potential.
PRZD requires knowing or estimating the state of a "fully irrigated" crop, as well.
In our opinion, RDI is a specialized case of "deficit irrigation" with a crop development stage set point for irrigation management.
Panel boxes: Check for loose or damaged connections.
Seal up openings to avoid rodent damage.
The Nebraska Extension NebGuide G888, Flow Control Devices for Center Pivot Irrigation Systems, describes the working principles of pressure regulators and provides guidelines for selecting a regulator.
When regulators stop functioning properly, due to a worn out diaphragm and/or spring, they no longer provide the desired constant outlet pressure, and consequently flow rate.
Putting Recycled Water to Work in Maryland Agriculture A Public-Private Partnership for Agricultural Water Reuse
 "It's just good, clean water." -Franklin Dill, Piccadilly Farm
 Though farming practices are constantly advancing, crop production in many places is still largely reliant on weather, particularly rain.
Given the unpredictable nature of rainfall, some farmers install irrigation systems to have more control over how much water goes on their fields.
One possible water source for farm irrigation systems is recycled water highly treated municipal wastewater.
Twenty-nine percent of recycled water in the United States is already used for agricultural irrigation, including in Maryland.
Municipal wastewater treatment plants often discharge or send the treated water back into nearby bodies of water like streams, rivers, and oceans.
Wastewater treatment plants are interested in reusing recycled water to meet regulations on how and where their effluent is discharged.
Wastewater managers in Kent County, Maryland realized that recycled water offers a reliable, cost-effective, and highly regulated water source for farmers.
Sending recycled water to a
 reuse site has many benefits for both wastewater treatment plants and farmers.
The Kent County wastewater managers began searching for a farmer interested in spraying effluent water onto crop fields.
However, finding a farmer to partner with was difficult.
Farmers were concerned about using treated wastewater, particularly over whether it was safe enough for their crops.
Franklin Dill and his family had been operating their farm, Piccadilly Farm, since the 1970's.
Dill had lived through lean years where yields were low because of drought and had been looking for ways to increase the amount of water on his farm.
On-farm creeks were not able to supply enough water, and he knew that "water is the key to growing crops".
After learning more about the advanced water treatment processes at the wastewater treatment plant, including visits to the plant and
 Figure 1.
A field on Piccadilly Farm that is irrigated with recycled water.
reviewing water quality information, Dill was convinced the water was suitable for his corn and soybean operation.
After working through the permitting process and construction of pipes and irrigation infrastructure, the effluent was delivered to Dill's fields, providing his crops with muchneeded water.
This report details how an innovative partnership led to the creation of a dynamic, mutually beneficial water reuse system, with important implications for the environment and the future of food production.
Wastewater Treatment Plant Must Secure a Permit from Maryland Department of Environment to Discharge Effluent Water to Farms
 Greg Swartz acting division chief of the Kent County Department of Water and Wastewater, likes to say that his work in wastewater management has the ultimate job security; as long as people flush toilets, he'll have work to do.
Maryland Department of Environment  encouraged the county to look into discharging effluent onto a farm field during
 construction of a new wastewater treatment plant, as it would reduce the amount of water going to local waterways.
The Worton-Butlertown plant is an advanced wastewater treatment plant that uses membrane filtration and ultraviolet light to treat wastewater to a high degree.
After finding a willing partner in Dill, the wastewater treatment plant obtained a spray irrigation discharge permit, issued by MDE.
The permit:
 requires detailed analyses, including soil and water testing, nutrient monitoring, and ensuring the fields would be able to absorb or uptake all the water and nutrients.
requires detailed ongoing reports about how much effluent is discharged to the fields, when, and to which parts of the field the effluent is being sent.
states exactly what the water quality must be, such as levels of turbidity, pH, and total nitrogen.
The treatment plant is responsible for monitoring the water quality.
Figure 2.
The effluent at Worton-Butlertown Wastewater Plant is highly treated.
When the treatment process is complete, the water  looks the same as tap water , but it is not drinkable.
Once the permit was approved, construction on the piping and irrigation system began.
In order to send out the water, the treatment plant needed to own and operate the receiving spray irrigation system.
Building the irrigation system cost approximately $3 million, on top of the $19 million upgrade to the plant.
The funds came from a combination of county, state, and grant funding.
Once the system was fully built and running, the wastewater treatment plant was able to send its effluent to the fields.
Using Effluent Water for Irrigation Requires Partnership and Cooperation
 The wastewater treatment plant is responsible for controlling the effluent, which means a certified operator needs to know when to send it through the system.
Cory Boynton, the lead operator of the Worton-Butlertown Wastewater Treatment Plant, stays in constant communication with Dill to know when to send the water.
When deciding to have the effluent on his field, Dill noted that it was important to him to have control.
"I don't have to take the water when I don't need it.
I wouldn't do it if I didn't have control over it.".
As Boynton jokes, though he controls and maintains the irrigation system, monitors the water quality, and ultimately sends the water through the system, he at least has not yet been tasked with planting the crops.
According to Boynton, Dill "saw the future" when he partnered with the treatment plant.
Due to the importance of getting water to a crop at certain phases of its growth, working with the treatment plant gives Dill more security than relying on rainfall alone.
Both Boynton and Dill emphasized the importance of open communication in the success of this process.
"You have to have a two-way partnership, and I am lucky to have Cory who does an excellent job.".
For Boynton, this innovative system also has a personal impact.
Growing up on a farm in Utah, Boynton recalls water being a problem for his family farm.
As a result, he has "a compassion for [Dill]" that shapes their relationship and "makes it work for both parties".
Benefits for the Farmer Include Higher Yields
 Figure 3.
These ears of corn were grown in two different fields in the same season.
During a dry period, the ear on the left did not develop fully due to the lack of rain.
The ear on the right was irrigated with recycled water so it grew despite the lack of rain.
Dill has seen increased yields since having the effluent irrigation system.
During a dry year, Dill recalled using 18 million gallons of water from the plant, which was most of the effluent they produced.
Dill said, "I'd like to see them put some more in because we've got another farm up the road we could use it on!".
Dill noted that in years with average precipitation, the additional irrigation on the cornfields yields approximately 30 additional bushels more per acre.
In dry years, Dill estimates that the irrigation leads to 100 bushels or more of corn per acre than without the irrigation system.
On double-cropped soybeans in dry years, using the irrigation system leads to 11-12 additional bushels
 In addition to higher yields, another benefit to the farm operation is having a reliable, highquality water source that is monitored by the wastewater treatment plant.
With the new federal agriculture water standards of the Food Safety Modernization Act, documented water testing is becoming more important for all farmers.
For Dill, there is assurance that the water coming from the WortonButlertown wastewater treatment plant has to meet strict standards for nitrogen, salinity, pathogens, and other parameters for water quality.
As Precipitation and Water Resources Become More Variable, Future of Maryland Agriculture Depends on Finding Forward-thinking, New Solutions
 The Piccadilly Farm and Worton-Butlertown Wastewater Treatment Plant partnership is an example of a new way to think about water management in Maryland.
Bringing private and public partners together has helped create a new source of water for agriculture in Kent County.
This partnership has been successful because of the strong working relationship between Dill and the plant operators, especially Boynton.
The relationship is mutually beneficial to the plant and the farm and provides important environmental and economic benefits to the community.
Lastly, for the flagship sprinkler corn competition, competitors will have a new aspect with the addition of cover crops.
Although this may not change the management decisions that corn participants have made in the competition the last six years, it may change the way participants manage those decisions.
The six decisions sprinkler corn competitors have to determine for their plots include: crop insurance, hybrid, seeding rate, nitrogen and irrigation timing and amounts, and grain marketing.
China, and Japan, maintained their import demand for California's agricultural products.
Overall, the major export commodities such as cotton, almonds, wine, beef and oranges did not suffer a significant reduction in demand due to the Asian crisis.
Those commodities that did suffer a decline in demand are a relatively small share of California's overall agricultural export value, with table grapes a possible exception.
Our conclusion is that California exports dropped little as a consequence of the crisis.
Within Asia, currency devaluations improved agricultural export competitiveness, and at the same time, increased the domestic prices  of agricultural products.
So many local Asian farmers actually benefited from the financial crisis.
While we cannot make the same claim for California farmers, at least they were not unduly harmed.
Pumping energy costs, frost protection and irrigation blocks are major factors to consider
 C.A.
Carter is Professor of Agricultural and Resource Economics, Davis.
M.
Quinn is a student in Agricultural Economics at the University of Sydney, Australia, and was an exchange student at Davis when this paper was written.
The authors thank John Dyck, George Goldman, JooHo Song, and two anonymous reviewers for helpful comments.
In 1972, Nebraska transitioned from a system of Soil and Water Conservation Districts to a system of Natural Resource Districts , maintaining local control through a locally elected board, which led to pumping and usage policies that contributed to the reduction in the rate of decline of groundwater levels.
Many of these NRDs have imposed an allocation-based system in which producers are allowed to use a specified amount of water in a particular time interval.
Approximately 68% of pivots below the required pressure  were in low topography.
Approximately 45% of pivots below the required pressure  were in moderate topography.
Approximately 50% of pivots below the required pressure  were in high topography.
Water Temperature in Irrigation
 cold water damage to rice can be controlled by use of small unshaded warming basins before water is applied to fields
 Franklin C.
Raney, Robert M.
Hagan, and Dwight C.
Finfrock
 Rice yields have been reduced during recent years in northern California, because of cold water damage near field intake boxes.
Since the construction of Shasta Dam, water temperature in the Sacramento River approximately 13 river miles below the dam has dropped an average of 16F, to approximately 51F and at the city of Sacramento, 260 river miles south, reduced by 5F, to about 66F.
As more dams are built to maintain high summer flow rates for irrigation in other areas of central and southern California, water temperatures may be expected to fall still farther.
Construction of Oroville Dam can be expected to cause the Feather River-from which much rice is irrigated-as well as the Sacramento River to become colder during the growing season.
rice has seriously affected about 5% of the planted area.
Even this apparently small percentage represents a direct loss to growers who must bear the cost of land preparation, seeding and irrigation on the unproductive acreage.
Plants are delayed in heading, heads do not fill, or maturity is not reached by the end of the normal growing season.
Cold water in the large rivers or canals warms up some, it is true, but only about 10F during the growing season at any one place and about 1F per 10 miles moved by the water.
At the grower's headgate in northern California, water temperatures in the high fifties or low sixties are common during the season.
After water enters the rice field it spreads out and warms up as it runs through successive checks.
The mean water temperature may increase at least 7F in going from the intake to the end of the
 third check.
It continues to warm going down the field.
Even during the last half of the summer-when the water is shaded by the maturing rice plantssome warming occurs as it passes across the rice field.
Such water warming in the field is reflected in higher rice yields.
As intake water is warmed yields increase and after the first few checks they reach field average.
In this way the first checks are serving as water warming basins, although inefficiently.
Field studies during the last three years have shown that small weed-free water warming basins can successfully raise the mean water temperature to 70F or higher throughout the growing season.
A temperature of 70F is about the lowest that the present varieties endure without showing damage or seriContinued on next page
 In past years cold water damage to
 Rice field in Glenn County in October 1953, showing water circulation-white arrows-and plant immaturity in checks near intake.
Damaged areas are dark colored in the photograph and enclosed by a dotted line.
Note stagnant area with mature rice in first check.
Continued from preceding page
 ously delayed maturity.
Approximately square basins, equal to about 2% of the planted area and 24" deep raised the mean water temperature about 5F; basins 12" deep, about 7F; 6" deep, about 9F above intake temperature.
The yield of rice was related to the degree of shading and depth of water in the warming basin serving the rice plot.
If the warming basin were kept weedfree, even the checks near the intake produced a nearly normal yield.
On the other hand, plots served from warming ponds shaded by weeds-or immature rice-consistently produced the lowest yields.
In two years out of three, yields in plots served from unshaded ponds 12" and 24" deep were lower than those from unshaded ponds 6" deep.
During the third year, however, yields below the 6" weed-free ponds were lower than those below the deeper ponds, presumably be-
 Warming of water in passing through a rice field during the latter half of the season when the water is shaded by rice plants.
Checks are numbered successively downfield from the intake check.
cause of a different combination of meteorological factors.
The relationships involved are receiving further study.
Studies were made at Davis in outdoor plots during the last two years to determine water temperature requirements of Caloro rice grown under continuous flooding with water 6" deep.
Ten water temperature treatments with four replications were used.
In Treatments 1-4, water temperature-day and night, from sowing until the water was drained prior to harvest-was constant at 65F, 70F, 80F, and 90F.
In Treatment 5, water temperature cycled with days at 80F and nights at 70F.
In Treatment 6, days were 70F and nights 80F.
In Treatments 7-10, water tem-
 perature was constant at 70F day and night, except that the temperature was held at 90F during one of the four growth stages and then returned to 70F until water was drained prior to harvest.
The four growth stages during which the temperature was elevated were: germination to emergence in Treatment 7; emer-
 Rice yields in successive checks downfield from intake in the same field.
gence to tillering in Treatment 8; tillering to heading in Treatment 9; and, in Treatment 10, from heading to maturity.
The higher the constant water temperature the earlier was the maturity date.
The two cyclic treatments-5 and 6-matured on the same date.
Of the plants held at 70F, application of 90F water from tillering to heading resulted in earliest maturity.
In the constant temperature treatments, grain yields diminished in the following order: 80F, 90F, 70F and 65F.
Both day-night cyclic treatments outyielded all other treatments.
Elevating the temperature to 90F from emergence to tillering resulted in a higher yield than by the same elevation of temperature during other growth stages.
Thus, it appears that the commercial rice variety Caloro shows two effects from water temperature: it matures only when water temperatures average above a minimum threshold of about 70F, and yield is increased by applying warmed water at certain growth stages.
The possibilities of minimizing rice yield losses from cold water by use of warming ponds point to the importance of finding ways to increase the warming efficiency of the ponds.
During most days of the growing season about 40% of the incoming solar energy is lost from a water basin through evaporation.
This loss can be much greater on windy days.
A combination of membranes or films which sharply curtail evaporation could result in higher water temperatures.
The required area of warming basins might be considerably reduced.
Recent trials were made at the Rice Experiment Station at Biggs with polyethylene floating membranes 2-4 milsthousandths of an inch-thick.
A transparent membrane permitted light to pass and at first produced higher water temperatures.
However, weeds flourished beneath and tended to lift the membrane.
Algae and diatoms coated the under side of the membrane while dust deposits on the top increased the reflectivity of the surface.
As a consequence the water temperature gains later fell sharply.
A floating black, opaque membrane completely eliminated weeds.
However, even with baffled, turbulent flow in the basin, the energy saved by reducing evaporation was approximately offset by the energy lost because of the opacity of
 Effect of water depth and shading in warming ponds on rice yield in basins directly served from ponds.
1953-1956.
the film.
Accordingly water temperature gains were small.
A proposed combination of membranes may be more successful.
A black, opaque membrane covering the basin floor would eliminate weeds.
Baffles placed to minimize thermal stratification would ballast the bottom membrane.
Use of a flexible surface film of a long chain carbon compound would permit dust to fall through, reduce evaporation, permit free light passage, and result in large water temperature gains.
Installation and maintenance costs appear reasonable.
The design of an efficient water warm-
 Concluded on page 37
 Continued from page 24
 phere suction value-about 75% of the available water has been removed from the Fallbrook soil and approximately 60% from the Holtville soil.
Further studies of moisture extraction from soils are being made under controlled conditions without using plants.
Soil columns are positioned horizontally and brought to equilibrium with water at approximately 30 millibars.
This is often a value read on tensiometers following an irrigation in the field.
A constant suction is then applied at one end of a soil column, by applying a controlled vacuum to one side of a porous ceramic disc the other side of which is in direct contact with the soil.
The lower left graph on page 24 shows the accumulated water extracted from soil columns when the suction of 900 millibars was maintained constant.
The extracted water was measured in surface inches in relation to the area of the soil column.
In the same length of time, 80% more water was extracted from a column of soil 14" long compared with the same column when it was cut down to 7" in length.
This would indicate that, for this Fallbrook sandy loam, root-free portions of the soil 7" away from roots can make substantial contributions to water extracted by roots.
Soils vary greatly in their ability to conduct water.
A comparison of three types shows that under the same controlled laboratory conditions the water extracted from a Ramona sandy loam soil was approximately twice as much as from a Fallbrook sandy loam and threefold that from a Yolo loam.
The curves comparing various soils were all obtained using 14" soil columns.
For these studies of soil moisture movement, fragmented soil samples were screened and compacted in the columns.
Further studies will be made on undisturbed cores.
If only moisture flow rates are measured-to compare the ability of various soils to conduct water-the size and shape of the soil sample and suction equipment would need to be standardized.
However, when continuous records of the moisture suction values are obtained at various locations along the soil column, as well as moisture extraction rates, computations can be made expressing the conductivity values of a soil as a function of the moisture suction.
These values are characteristic of the soil and independent of the methods of measurement.
They can be used to characterize different soils or study the effects of soil management practices on the same soil.
Also, when suction values in the field are measured by tensiometers, flow rates can be estimated.
Studies of moisture movement in soils in the liquid phase are made under constant temperature conditions.
Thermal gradients within the soil column, which result in water vapor diffusion, can cause significant disturbances to the measured liquid flow.
S.
J.
Richards is Associate Irrigation Engineer, University of California, Riverside.
Weeks is Senior Laboratory Technician, University of California, Riverside.
The above progress report is based on Research Project No.
1546
 Continued from page 29
 In most cases not enough water can be stored in the soil to last throughout the season.
Where water penetration is slow, more water can be applied by irrigating more frequently or by increasing the time the water is on the land surface at each irrigation.
Both approaches have advantages and limitations.
More frequent irrigation may be accomplished without any other change in the system or in practice, but has the disadvantage of higher labor costs.
It may be an inadequate measure for the more difficult problems.
Prolonged irrigation may require substantial changes such as converting from furrows to basins in which water can be ponded for long periods or using small furrows to insure better coverage of border strips with small streams.
Irrigation of crops susceptible to injury or disease under prolonged irrigation can not be managed in this way, and the practice may encourage growth of waterloving weeds.
However, such methods may be the only means of increasing the productivity of soils with very slow water penetration even though changes in cropping pattern or farming operations are required.
D.
W.
Henderson is Assistant Professor of Irrigation, University of California, Davis.
J.
A.
Vomocil is Assistant Professor of Soil Physics, University of California, Davis.
Continued from page 20
 ing facility must provide for maximum energy capture, discharge water at a temperature giving maximum rice yields, occupy a minimum land area, with reasonable installation and maintenance costs.
From experience in rice irrigation, water temperature may be expected to influence the growth of other crops.
However, it is difficult to predict the influence of water temperature on yields because of its numerous direct and indirect effects on the plant.
In addition to the cold water damage reported here, crop injury is sometimes associated with warm water.
As more is learned about its effects on
 irrigated crops, water temperature may become a factor of considerable importance in the selection of crops and their management for maximum yield and minimum unit cost.
Franklin C.
Raney is Principal Laboratory Technician in Irrigation, University of California, Davis.
Robert M.
Hagan is Associate Professor of Irrigation, University of California, Davis.
Dwight C.
Finfrock is Associate Specialist in Agronomy and Superintendent of the Biggs Rice Experiment Station, University of California, Davis.
Bruce ylie, Glenn County rice grower; the Glenn-Colusa Irrigation District, and Milton D.
Miller, Extension Agronomist, University of California, Davis, participated in the studies reported in the above article.
Continued from page 22
 grove was on a two week irrigation schedule.
The irrigation water applied July 19 and August 3 reached the 12" soil depth but did not wet the soil at the 18" depth to field capacity.
The time and place to use either tensiometers or blocks depends to a large extent on climatic conditions and soil types and to a lesser extent on the nature of the crop.
In inland areas of southern California where high water losses may cause stress conditions in plants, timing of irrigations becomes very important.
Tensiometers have proved to be valuable tools for timing irrigations in citrus and avocado groves.
However, in the more humid areas where irrigations are intermittent, along with rainfall, resistance blocks are used with satisfactory results.
Resistance blocks made of gypsum rather than fiberglass or nylon are generally preferred in agricultural soils.
The neutron method is still a research tool although it might be valuable on large agricultural acreages.
L.
H.
Stolzy is Assistant Irrigation Engineer, University of California, Riverside.
G.
A.
Cahoon is Assistant Horticulturist, University of California, Riverside.
E.
Szuszkiewicz is Senior Laboratory Technician, University of California, Riverside.
The above progress report is based on Research Project No.
1612.
Continued from page 31
 in the Imperial Valley.
Here Colorado River water is used for irrigation and contains large quantities of sulfate, which produces this toxic symptom.
L.
D.
Doneen is Professor of Irrigation, University of California, Davis.
D.
W.
Henderson is Assistant Professor of Irrigation, University of California, Davis.
The above progress report is based on Research Project No.
1529.
Benefits from Using Sensors: One of the main benefits of using sensors to better manage irrigation is the reduced costs of pumping.
When surveyed, users of sensors from the Nebraska Ag Water Management Network and industry have indicated water savings of 2 inches per acre.
The cost of applying an additional 2 inches of water is going to vary depending on your depth to water, system pressure, and equipment costs, but could easily run from $10 to $30 per acre.
For Scenario 1 the center pivot system did not have an end gun.
Despite the rolling terrain in some of the counties, use of VFDs resulted in less than $0.25 per hour savings in energy cost.
For the systems evaluated, a VFD would not pay for itself over a 15-year life.
Each time the user logs in and selects a field, the program will make a prediction regarding the need for irrigation , using up-to-date weather data for that field and other crop and soil information the user provided at field registration.
When the user irrigates a field, the irrigation date and amount must be entered into the program so the next prediction will reflect the irrigation.
Corn growers who irrigate in the Great Plains face restrictions in water, either from lower well capacities or from water allocations, and/or rising energy costs.
They need water management practices to maximize grain production.
When there is not enough water available to produce full yields, the goal for water management is to maximize transpiration and minimize non-essential water losses.
One avenue for reducing non-essential water use is to minimize soil water evaporation.
Evapotranspiration is the combination of a two processes, transpiration and soil water evaporation.
Transpiration, water consumed by the crop, is essential for the plants and correlates directly with grain production.
Non-productive soil water evaporation has little utility.
Soil water evaporation rates from bare soil are controlled by two factors.
When the soil surface is wet, atmospheric energy that reaches the ground drives evaporation rates.
As the surface dries, evaporation rates are limited by the movement of water in the soil to the surface.
In sprinkler irrigation during the growing season, most of the evaporation results from the energy limited process because of frequent soil wetting.
Crop residues insulate the surface from energy limited evaporation.
Crop residues which are left in the field have value for soil and water conservation during the following non-growing season and the growing season of the next crop.
Crop residues that are removed from the field after harvest are gaining value for livestock rations, livestock bedding, and as a source of cellulous for ethanol production.
The water conservation value of crop residues needs to be quantified so that crop producers can evaluate whether or not to sell the residues or keep them on their fields.
Reducing soil water evaporation in sprinkler management is one of the values of crop residues.
This project was designed to measure soil water evaporation with and without a growing corn crop.
1.
Determine the water savings value of crop residues in irrigated corn.
2.
Measure soil water evaporation beneath crop canopy of fully and limited irrigated corn.
a.
From bare soil.
b.
From soil covered with no-till corn residue.
C.
From soil covered with standing wheat residue.
3.
Calculate the contribution of evaporation to evapotranspiration.
4.
Quantify soil water evaporation from partially covered soil with no crop canopy.
5.
Predict potential economic savings from reducing evaporation with residues.
Soil water evaporation was measured beneath a growing corn crop during the summers of 2004, 2005, and 2006 at Kansas State University's Research and Extension Center near Garden City, Kansas.
The soil at the research site was a Ulysses silt loam.
Mini-lysimeters were used for the primary evaporation measurement tool.
They contained undisturbed soil cores 12 inches in diameter and 5.5 inches deep.
The soil cores were extracted by pressing PVC tubing into the soil with a custom designed steel bit.
The PVC tubing became the sidewalls for the mini-lysimeters.
The bottom of the cores were sealed with galvanized discs and caulking.
Therefore, water could only escape from the soil by surface evaporation, which could be derived from daily weight changes of the minilysimeters.
Weighing precision produced evaporation measurements with a resolution of 0.002 in/day.
Volumetric soil water content was measured bi-weekly in the field plots to a depth of 8 ft in 1 ft increments with neutron attenuation techniques.
The change in soil water, form the start to the end of the sampling period, plus measurements of rainfall and net irrigation were the components of a water balance to estimate crop evapotranspiration.
Measurements of crop residue coverage on the soil surface were adapted from line transect techniques.
A coarse screen was laid over a mini-lysimeter.
Observations of the presence or absence of residue were recorded for each intersection of screen material.
The fraction of the presence of residue and total observations was converted into a percentage of coverage.
Two mini-lysimeters with the same surface cover treatment were placed in a diagonal pattern between adjacent 30-inch rows under the crop canopy.
Comparison of evaporation data  indicated no statistical difference between the two locations.
Four replications of bare, corn stover, or wheat stubble surface treatments were placed in high and low frequency irrigation treatments.
High frequency irrigation was managed to meet atmospheric demand for full crop evapotranspiration.
The low frequency irrigation treatment received approximately half this amount in half the irrigation events.
An additional experiment was conducted to find the soil water evaporation rates from soil surfaces that were partially covered with crop residues.
A controlled area was established for the experiment where the mini-lysimeters were buried in PVC sleeves at ground level, arranged adjacent to one another in a geometric pattern.
Movable shelters were available to cover the mini-lysimeters during rain events but were open during other times.
There was no crop canopy over the mini-lysimeters, which were surrounded by mowed, irrigated grass.
The minilysimeters were weighed daily.
Two irrigation treatments, that approximated the companion field study, were watered with 1 or 2 per hand irrigations per week.
Partial surface cover treatments had 25%, 50%, and 75% of the surface covered with corn stover which was placed on the mini-lysimeters.
Mini-lysimeters with 100% coverage from corn stover and 85% coverage with standing wheat stubble were the same configuration as the field experiment.
Evaporation results were normalized with reference ET  which was calculated with on-site weather factors and an alfalfa referenced ETr model.
Within Canopy Field Results
 Soil surface cover on the mini-lysimeters was measured at the start of the growing season.
Corn stover and standing wheat stubble completely covered the minilysimeters in 2004.
Corn stover continued to completely cover the minilysimeters in 2005 and 2006, but the wheat stubble coverage was 91-92% in those years.
The 2004 and 2005 wheat crops were shorter in stature due to less fall growth.
This led to less wheat stubble coverage of the mini-lysimeters during the following year.
All of the surface cover and irrigation frequency treatment data were averaged so that only year-to-year differences could be evaluated.
Annual differences in average daily soil water evaporation , average daily crop evapotranspiration , average daily reference ET , and the ratios of Avg E with both ETc and ETr were calculated.
The climatic conditions in 2004 were cooler and wetter than normal which produced 230 bu/ac of corn with full irrigation.
Hail storms during July 2005 and July 2006 caused leaf loss, as indicated by the peak leaf area index measurements, and produced grain yields of 165 bu/ac in 2005 and 185 bu/ac in 2006.
The combination of more E and less ETc and ETr in 2004 than in the other two years caused the E/ETc and E/Etr ratios to be more in 2004.
The most ETc occurred in 2005 with the least peak LAI; however, more atmospheric demand for water, as indicated by more ETr, may have masked some of the effects of less leaf area.
Table 1.
Crop residue percentage cover at the end of the growing season for minilysimeters in corn field plots during 2004-2006 near Garden City, Kansas.
*Percentage of soil surface covered by residue, determined by the modified line transect method.
Table 2.
Average soil water evaporation  and evaporation as a ratio of crop evapotranspiration  and reference ET  for all mini-lysimeter treatments under a corn crop canopy during 2004-2006 in Garden City, KS.
Irrigation	Avg E	ETc	E/ETc	ETr	E/ETr	Peak
 Frequency*	in/day	in/day	In/day	LAI*
 2004	0.046a	0.21c	0.25a	0.26	0.18a	4.4
 2005	0.043b	0.27a	0.16c	0.36	0.12b	3.4
 2006	0.042b	0.22b	0.21b	0.30	0.14a	3.7
 LSD.05	0.002	0.01	0.02	0.005
 Means with same letters in the same columns are not significantly different for alpha=.05.
When data from all years and water frequency treatments were combined, the effects of surface treatments could be isolated.
Average soil water evaporation  from the bare surface treatment was significantly more than Avg E from the two residue covered treatments.
Wheat stubble surface coverage was than corn stover coverage in 2005 and 2006, resulting in more E with wheat stubble.
Daily average ETc and ETr data were the same over all mini-lysimeters since the annual data was averaged over all irrigation treatments.
Bare soil E for the Ulysses silt loam was 30% of ETc, which was the same result as a study with Valentine fine sandy soils in west-central Nebraska.
E as a ratio of ETc or ETr showed that crop residues reduced E by 50% compared with bare soil.
A similar study with silt loam soils in west-central Nebraska showed that bare soil E under a corn canopy during the growing season could be reduced from
 0.07 inches/day to 0.03 inches/day by adding a mulch of wheat stubble lying flat on the surface with 100% surface coverage.
Differences in E between bare soil and residue treatments, which were 0.02-0.03 inch per day, may seem small; however, if these daily differences were extrapolated over a 110 day growing season, total differences in E would be 2.23.3 inches.
Similarly, E as a fraction of ETc was 0.30 for bare soil and 0.15-0.16 for the residue cover treatments.
Growing season ETc values for corn can be 2426 inches in western Kansas.
Using the values of E as a fraction of ETc , potential water savings could be 3.7-4.0 inches with full soil surface coverage.
Table 3.
Average soil water evaporation and evaporation as a ratio of crop evapotranspiration  and reference ET  for all bare soil and crop residue covered treatments under a corn crop canopy during 2004-2006 in Garden City, KS.
Surface	Avg E	ETc	E/ETc*	ETr	E/ETr
 Cover	in/day	in/day	in/day
 Bare	0.06a	0.23	0.30a	0.27	0.22a
 Corn Stover	0.03c	0.23	0.15c	0.27	0.11c
 Wheat Straw	0.04b	0.23	0.16b	0.27	0.12b
 LSD.05	0.003	0.02	0.05
 Means with same letters in the same columns are not significantly different for alpha=.05.
The influence of crop canopy shading canopy on soil water evaporation rates was observed by averaging data over years, surface cover treatments, and irrigation frequency treatments.
Evaporation decreased as crop canopy and ground shading increased.
The trend reversed as the crop matured and shading decreased.
Concurrently, crop ET and reference ET increased from planting through mid-season and then decreased through the rest of the growing season.
The ratio of Avg E to ETc and ETr declined during the growing season when the two factors were combined.
Table 4.
Soil water evaporation  and evaporation as a ratio of crop ET  and reference ET  during the growth stages of corn for all minilysimeter treatments during the 2004-2006 growing seasons at Garden City, KS.
Stage	In Growth Stage	Avg E	ETc	E/ETc	ETr	E/ETr
 in/day	in/day	in/day	in/day
 Vegetative	28	0.06a	0.22b	0.27a	0.35	0.17a
 Pollination	18	0.05b	0.27a	0.20b	0.33	0.15b
 Seed Fill	30	0.03c	0.20c	0.15c	0.25	0.12c
 LSD.05	0.002	0.02	0.02	0.05
 Means with same letters in the same columns for the same year are not significantly different for alpha = 0.05.
More frequent irrigations led to slightly more soil water evaporation and ETc.
The small differences were probably because on average there were two to three more wetting events in the high versus low frequency treatments.
More ETc in the high frequency treatment led to slightly smaller ratio of Avg E with ETc.
Table 5.
Soil water evaporation  and evaporation as a ratio of crop ET  and reference ET  for low and high frequency irrigation for all minilysimeter treatments in during the 2004-2006 growing seasons.
Irrigation	Wetting	Avg E	ETc	E/ETc	ETr	E/ETr
 Frequency	Events	in/day	in/day	in/day
 Low	3	0.043b	0.21b	0.21a	0.30	0.14b
 High	5	0.044a	0.25a	0.20b	0.30	0.15a
 LSD.05	0.0013	0.009	0.02	0.004
 Means with same letters in the same columns are not significantly different.
Partial Cover Results from Control Area
 Even though average daily evaporation rates among the bare and 25%, 50%, and 75% residue covered treatments could be measured and were significantly different from one another, the magnitudes of these differences were small.
The 100% covered treatment with corn stover and the standing wheat stubble with 85% cover produced significantly less E than the other treatments.
Lateral heat flow from the bare portion of the partially covered surface could have caused increased surface temperatures under the corn stover.
Similarly, soil water could move from under partially covered surface to the bare portion of the surface, increasing E.
Based on averages of surface cover treatments, twice per week irrigation frequency over a six week period produced 23% more evaporation than the once per week frequency.
Summary and Significance of Results
 Corn stover and wheat stubble residues that cover 85-100 % of the soil surface have the potential to reduce soil water evaporation.
During the growing seasons of 2004 2006 in Garden City, Kansas, average E measured under a growing corn crop was reduced from 0.06 inch per day for bare soil to 0.03 to 0.04 inch per day for complete surface coverage with corn stover or wheat stubble.
The difference in E between bare soil and residue covered surfaces over a 110 day growing season could be 2.2 to 3.3 inches.
E as a fraction of crop evapotranspiration  was 0.30 for bare soil and 0.15 to 0.16 for complete soil surface coverage.
The total growing season ETc for corn grown in west-central Kansas is 24-26 inches.
Based on the reduction of E as a fraction of ETc, growing season water savings could be 3.4 to 3.9 inches.
Table 6.
Soil water evaporation during Spring and Fall 2005 and Fall 2006 for full and partial crop residue surface covers at Garden City, Kansas.
a.
Surface Cover	--in/day--
 Bare 0%	0.08a	0.26a
 Corn 25%**	0.07b	0.25b
 Corn 50%	0.07c	0.24c
 Corn 75%	0.07a	0.26a
 Corn 100%	0.04e	0.14e
 Wheat 85%	0.05d	0.18d
 LSD.05	0.002	0.005
 LSD.05	0.0009	0.003
The UNL Cropwater App is an excellent tool for a producer who utilizes Watermark soil moisture sensors in their field to aid in irrigation scheduling.
Here is a brief overview of how to use this app in your operation.
Drought symptoms in soybean: Soybean respond to drought stress by flipping their leaves over so the underside of the soybean leaf is turned up.
A less obvious sign of drought stress in soybean is diminished vegetative growth which normally occurs prior to leaf flipping.
In severe drought conditions, the leaf trifoliates will close or clamp together with the center leaflet being sandwiched between the outside leaflets.
The team also observed that the rusty pivots occurred in patches.
Although the researchers are not sure of what is responsible for the nitrate-rust link, they do have a hypothesis.
This hypothesis involves the microorganisms, especially the bacteria, living in soil and groundwater.
This information can potentially be used to help screen for areas for the potential absence of nitrate and, in an ideal world, could indicate areas at higheror lower-risk for nitrate contamination before it becomes a problem.
However, the proposed screening method is only applicable in areas that feature a fair amount of iron, typically areas adjacent to streams or rivers.
The Basics of Cotton Irrigation in Tennessee
 Brian Leib, Associate Professor, Irrigation Systems and Management Tim Grant, Extension Assistant, Soil and Water Resources Department of Biosystems Engineering and Soil Science
 Tyson Raper, Assistant Professor, Cotton and Small Grains Department of Plant Sciences
 Financial support from the Cotton Incorporated and USDA NRCS Conservation Innovation Grant
 1.
The four essential factors for making effective irrigation decisions in cotton are growth stage, water-use rate, soil type and rainfall pattern.
2.
In most years, cotton grown in deep silt loam soils has yielded best when irrigation was delayed until after first bloom.
3.
In a majority of years, cotton in sandy soils yielded best when irrigation was initiated at square.
4.
For a majority of years in silt loam soil and for a couple of years in sandy soil, yield reduction has been observed when high rates of irrigation were applied during square.
5.
Since variable rainfall can create soil conditions too wet or too dry for optimal cotton yield, a managed depletion irrigation  approach is recommended.
MDI prescribes a significant withdrawal of soil water before initiating irrigation to create storage capacity for capturing rainfall that alleviates crop stress from water logging and inhibits excess vegetative growth while maintaining a buffer of easily available soil water to prevent drought stress.
6.
Once the MDI level is reached, water should be applied at a rate equal to crop-water use from rainfall and supplemental irrigation.
7.
Center pivot application amounts should be set as high as possible without creating significant run-off: 0.3 to 0.5 inches per revolution on sloping fields and 0.5 to 0.8 inches per revolution on flatter river bottoms.
8.
Cotton irrigation should be terminated at cracked boll if there is sufficient soil water and/or rainfall to finish filling viable bolls.
In sandier soils, cotton yield can benefit from added irrigation just prior to cracked boll.
9.
MDI can be implemented by a water balance method that keeps track of both the water added to the soil by rainfall and irrigation as well the amount used and removed by the crop.
10.
MDI also can be implemented by soil sensor methods that are a direct measurement of soil water status at specific locations and depths.
Cotton irrigation recommendations for Tennessee are based on more than 10 years of AgResearch and Education Center trials and farm demonstration sites.
A more detailed understanding of these recommendations is provided in the remainder of the publication.
Water Use, Soil Type, Rainfall and Irrigation Approach 1
 Figure 1: Historic average weekly crop-water use of cotton shown as a solid red line.
Crop-water use of any given time period can vary from this line by up to 15 percent, as the weather conditions vary from normal.
Cotton water use varies by growth stage and weather conditions.
The rate of water use is an important factor for deciding when and how much to irrigate.
As shown in Figure 1, water use is less than 0.5 inches per week after establishment and increases to just above 1.0 inch per week by square.
From square to bloom, water use increases rapidly from 1.0 to 1.7 inches per week.
Thereafter, water use averages about 1.6 inches per week until after cracked boll.
Note that these are historic averages, and a sunny, hot week could require up to 15 percent more water while a cloudy, cool week could require up to 15 percent less water.
2
 Soil type is also an important consideration when making irrigation decisions.
A soil profile that is
 deep silt loam could contain 4 inches of readily available water in a cotton root zone when it is at field capacity.
However, a soil profile that is sandy throughout may only contain around 1.5 inches of readily available water when it is at field capacity.
If a deep silt loam and a sandy soil are refilled to field capacity by a large rain event in early bloom, how long would it be before we would need to irrigate each soil?
Since water use is averaging over 1.6 inches per week at this point, we can expect the sandy soil to need water in less than a week.
On the other hand, the deep silt loam soil can provide enough readily available water to supply that crop for almost three weeks before the crop starts losing yield potential.
The differing abilities of soils to hold water can have implications on irrigation management across fields and even within the same field.
3
 Adjusting to rainfall in combination with cropgrowth stage and soil type is the key to good irrigation management in cotton.
Yet, this can be complex since rain is extremely variable in a humid region
 like Tennessee.
To illustrate the impact of highly variable rainfall patterns, consider this question that is faced by Tennessee irrigators: What is coming next a four-week drought, a 4-inch rain, or something in between?
If we knew a four-week drought was coming, we would irrigate frequently to keep soil moisture close to field capacity to avoid stress and ensure high yield.
If we knew a 4-inch rain was coming, we would let the soil dry out in order to utilize that rainfall and avoid overly wet conditions that could harm yield.
Since we do not know what weather is on the horizon with a high degree of accuracy, we need to allow soil moisture to deplete to a reasonable level that will facilitate the capture and use of rainfall yet not lose yield potential.
Since center pivots are usually designed to "keepup" with crop-water use during peak demand periods with no rain, and cannot "catch-up" and return the profile to field capacity once significant
 depletion has occurred, these systems are best managed by maintaining a desired level of soil water depletion.
A guiding principle of our irrigation approach is to allow a significant but safe soil water depletion to develop according to soil type and crop-growth stage, and then use center pivot irrigation to maintain a "managed depletion" of soil water that facilitates rainfall capture while preserving some readily available water to prevent crop stress.
We are calling this approach managed depletion irrigation or MDI.
Tennessee-based research has consistently shown that cotton grown on differing soil types ought to begin receiving irrigation at different growth stages.
In most years, cotton grown in deep silt loam soils has yielded best when irrigation was delayed until after first bloom.
The exception to this was in
 2012 when an extended dry period occurred in June requiring irrigation during square.
Even in the severe drought of 2007, cotton yield in silt loam soils was optimized by waiting to irrigate until two weeks after first bloom and then supplying a high rate of irrigation.
However, in four out of 11 years, cotton has not needed irrigation to maximize yield in silt loam soils because rainfall was sufficient 
 In contrast, soils with much higher sand content and lower water-holding capacity required irrigation in every year tested; however, determining when irrigation should begin has varied year-to-year.
Soils with higher sand content are found primarily in the major river bottoms, especially in the Mississippi River Delta.
While some wet years have allowed cotton on sandy soils to do well without early irrigation, in a majority of years, cotton in sandy soils yielded best when irrigation was initiated at square.
4
 The simplest solution may be to "start irrigation at square," thereby taking care of both sandy and silt loam soils in case of early dry periods.
However, yield reduction has been observed when high rates of irrigation were applied during square for a majority of years in silt loam soil and for a couple of years in sandy soil.
Saturation and poor drainage are known to cause yield loss in most crops but did not appear to be the cause for this yield loss in cotton because the sites tested were well drained with soil water depletions managed below field capacity.
This yield loss is thought to be related to promoting vegetative instead of reproductive growth through early irrigation in a crop that would be a perennial if not terminated at harvest.
4
 Irrigation with "managed depletion" of soil water can be beneficial to cotton yield while reducing irrigation inputs.
On average, a yield increase of 900 lbs/ac of lint in sandy soil, 500 lbs/ac in silt over sand, and 200lb/ac in deep silt loam was obtained with 7.0, 4.0 and 2.0 inches of irrigation for each soil, respectively.
The irrigated yield in all soil types was fairly equal approaching 1,500 lbs/ac of lint.
Remember that these are average amounts of water applied and individual years will require more or less irrigation based on rainfall.
4
 We have discussed the impact of soil textural differences on irrigation initiation, but much of our cotton is grown on rolling loess hills where the texture is consistently silt loam.
In this case, we expect topography to be the primary driver of irrigation decisions with side slopes requiring earlier irrigation than hilltops and low-lying areas due to soil erosion limiting the rooting depth on the side slopes.
However, from 2013 to 2017 in several fields across West Tennessee, this pattern did not appear, and in fact the opposite has most often been true with higher soil moisture measured on the sloping ground due to the fragipan impeding drainage of water in wetter years.
Yield maps tell us that in a dry year, sloping grounds can certainly become water-limited, and in those years the sloping ground could benefit from either earlier irrigation or more irrigation.
In wet years, however, there does not appear to be much merit to irrigating sloping grounds differently than level ground on the loess hills of Tennessee.
5
 Another important part of irrigation decisions is how much water to apply and rates of 1.5, 1.0 and 0.5 inches per week were tested as a combination of rain plus irrigation.
In silt loam soils, the best yields occurred at various supplemental irrigation rates depending on the year.
In wetter than average years when there was more soil water in the profile at bloom or more rain after first bloom, lower irrigation rates optimized yield including no irrigation at all.
In drier than average years, the silt loam soils required 1.5 inches per week as a combination of rainfall and irrigation.
In contrast, sandy soils, once irrigation was initiated, always required a water input of 1.5 inches per week, between rainfall and irrigation.
Because sandy soils cannot provide nearly as much available soil water carryover, it is necessary to supply water to match crop-water demand.
Once soil moisture is at the desired "managed depletion" level, you should strive to provide water input equal to crop-water use through rainfall and supplemental irrigation in order to maintain soil moisture near the "managed depletion" target level.
There are also some practical considerations concerning the amount of water applied per irrigation.
Most center pivots are designed to be capable of applying 0.3 inches over 24 hours, meaning you potentially could apply just over 2 inches in a week.
In flat river bottom ground, where many of our sandy soils are found, it is appropriate to apply higher amounts like 0.5 to 0.8 inches per revolution where runoff is not a substantial concern.
However, on sloping fields or fields where infiltration is an issue, limiting irrigation to 0.3 to 0.5 inches per revolution will lead to a more effective irrigation application.
We recommend setting pivot application amounts as high as possible without creating significant runoff 6
 In an effort to limit water applied to open bolls which can degrade cotton quality, typically irrigation is stopped once the crop reaches cracked boll.
While water is still needed to finish maturing the crop, soils with good water-holding capacity will usually have sufficient available water to supply the remaining crop-water needs.
An exception to this rule occurred in 2007 when irrigating a week past cracked boll helped obtain nearly four-bale yields in deep silt loam soil.
In low water-holding capacity soils, there is more potential benefit to irrigating past the first cracked boll.
In two years of cotton irrigation termination studies, sandy soils yielded higher with irrigation either continuing past cracked boll or with a heavy application of irrigation leading up to cracked boll.
Because these results have not been as consistent as desired, it is recommended that irrigation in sandy soil also be ended at cracked boll to avoid unnecessary water on open bolls.
When possible, though, a high rate of water application leading up to cracked boll on sandy soils could increase yield, especially when dry conditions are likely.
4
 Variation in soils and unpredictable rainfall make real-time irrigation decisions for cotton challenging.
Soil moisture sensors, a water balance or both methods together can be utilized to manage cotton
 Irrigation Scheduling by Water Balance
 WATER IN Rainfall Irrigation High Water Table
 WATER OUT Crop Water Use Soil Evaporation Run-off & Drainage
 WATER STORED IN SOIL Managed Depletion of Soil Water
 irrigation.
The water balance method keeps track of both the water added to the soil by rainfall and irrigation as well the amount used and removed by the crop.
Table 1 presents MDI  target values depending on soil type and growth stage for a water balance.
Also shown is the Maximum Allowable Depletion  of 65 percent, beyond which point yield loss is likely.
These values are percentages of plant available water that has been removed from the soil profile such that field capacity is o percent depletion and permanent wilting is 100 percent.
Maintaining soil moisture around the MDI value creates storage space in the soil to capture rainfall while keeping a buffer of easily available soil water to prevent yield loss.
Water balance tools like the MOIST  spreadsheet can help you maintain soil-water in a reasonable depletion range, thus increasing the potential of obtaining optimum yield with minimum irrigation.
7
 A water balance approach can be very inexpensive  while soil moisture sensors require the purchase and installation of sensor equipment.
Soil moisture sensors are a direct measurement of soil water status at a specific location.
Matric potential sensors  measure how difficult it will be for a plant to extract moisture from the soil while volumetric sensors  measure the percentage of water in bulk soil.
More detailed articles are available to describe the differences between sensor types and how to best use each sensor type.
UT's recommendations are built around matric potential sensors because their readings are more transferable across soils than volumetric sensors, which require very different trigger points based on soil type compounded by the fact that not all types of volumetric sensors are calibrated the same.
Soil moisture sensors should be installed at more than one depth because the soil profile does not dry or rewet uniformly.
This means there will be multiple values to consider when making irrigation decisions.
A shallow sensor or sensors are needed to detect rainfall and irrigation events while deeper sensors reveal whether water is being used throughout the entire root zone.
While cotton needs adequate soil moisture somewhere in the root zone, it does not necessarily need easily available water throughout the soil profile.
Soil at some sensor depths should be allowed to dry significantly in an MDI approach as long as water is easily available to the crop at other points in the root zone.
Table 2 presents the MDI target values for matric potential sensors.
The MPS-6/Terros-21 values have been incorporated into the MOIST+ APP.
9
 Maximum Allowable Depletion of 65%
 MDI Target 
 Squaring to 2 wks past First Bloom	45	55
 2 weeks past First Bloom to Open Boll	30	45
 Table 1: Maximum allowable depletion and managed depletion irrigation  Levels.
The MDI Target Value is not the only soil water depletion target level that can result in optimum yield.
It is recommended as a means to balance the effect of unpredictable rainfall patterns by leaving enough water in the soil to prevent drying below the maximum allowable depletion  and over wetting the soil from excess rainfall; both conditions can lead to yield loss.
Watermark   Easily Available Soil Water Range
 Squaring to 2 weeks past First Bloom	8 to 60	8 to 120
 2 weeks past First Bloom to Open Boll	8 to 45	8 to 80
 MPS-6/TEROS-21   Easily Available Soil Water Range
 Squaring to 2 weeks past First Bloom	11 to 80	11 to 200
 2 weeks past First Bloom to Open Boll	11 to 45	11 to 100
 Table 2: Guideline matric potential values for Watermark and MPS-2 sensors in cotton to maintain a managed depletion irrigation  strategy by growth stage and soil type.
1.
Saturated conditions occur at values less than the range minimums.
2.
Easily available water is not required or recommended in the entire soil profile.
Only one sensor needs to be within the recommended range.
3.
Yield loss may occur if all parts of the crop root zone are greater than the range maximums.
Extension provides several resources to assist producers in implementing cotton irrigation scheduling.
Additionally, several crop consultants in Tennessee are offering irrigation management as part of their services.
10
 1.
Irrigation Water Management A Simple Analogy.
2.
How Much Water Is Your Crop Using?
3.
How Soils Hold Water, a Home Experiment.
4.
Summary of Cotton Irrigation Studies in Tennessee.
5.
Determining Irrigation Management Zones for Center Pivots.
6.
What Is Your Center Pivots Application Rate?
7.
Using a Water Balance to Make Irrigation Decisions: MOIST spreadsheet.
8.
Using Soil Moisture Sensors for Irrigation Management in Tennessee.
9.
Automating and Combining Water Balance and Sensor Based Irrigation Scheduling: MOIST+ APP.
10.
List of Irrigation Consultants in Tennessee.
At right, Torpedos are dragged in nonwheel furrows at the UC Davis test site.
Below,Blaine Hanson inspects concrete-filled torpedoes used in the San Joaquin Valley.
Furrow torpedoes improve irrigation water advance
 Lawrence J.
Schwankl Blaine R.
Hanson Anthanasios Panoras
 To increase irrigation uniformity and to reduce drainage volumes, some San Joaquin Valley growers drag weighted steel cylinders  in furrows before irrigation to speed the advance of water across the field.
The effectiveness of this practice and the reasons it works have been investigated.
In much of the San Joaquin Valley, where there is no outlet for irrigation drainage water, growers have two choices:  adopting disposal methods that include establishing evaporation basins, employing agroforestry , and reusing the drainwater and/or  improving furrow/border irrigation and irrigation scheduling or converting to pressurized sprinkler or drip irrigation systems.
Irrigating with improved furrow/border irrigation techniques or with pressurized irrigation systems decreases drainage volumes because irrigation water is applied more uniformly, resulting in less water being used to adequately irrigate all parts of a field.
A major cause of nonuniformity in furrow irrigation is the time it takes to ad-
 vance water across the field.
The advance time is the additional time water is infiltating at the head of the field versus the tail of the field.
Frequently, the head of the field is overirrigated SO that the tail of the field can be adequately irrigated.
In turn, nonuniform water application leads to deep percolation.
An objective, therefore, of furrow irrigation is to minimize the infiltration time difference between the head and tail of the field by using one of several techniques, including reducing the length of the field and increasing the rate at which water advances across the field.
The rate water is advanced can be speeded by compacting and smoothing the furrow.
This is evident in furrows that have had a tractor wheel run in them  versus those with none.
Water advance is significantly faster in wheel furrows.
Because running a tractor wheel down every furrow in a field is impractical, some growers in the San Joaquin Valley drag "torpedoes"  in the furrows to smooth, compact, and change the shape of the furrows; thus, the advance rate of water across the field is increased.
This study was undertaken to determine the effects of using torpedoes on advancing irrigation water, water infiltration, furrow shape, and furrow roughness.
Three sites were chosen to investigate torpedo effects: a site in Fresno County  with Panoche fine sandy loam soil and furrows 2,600 feet  long; a site in Fresno County  with a Westhaven clay loam soil and furrows 1,150 feet  long, and a site at the UC Davis Campbell Tract with a silt loam soil and furrows 1,000 feet  long.
Each site was divided into portions of the field where torpedoes were dragged in the furrows and portions where furrows were not torpedoed.
This allowed side-byside comparisons.
At each site, measurements of pre-irrigation furrow cross-sectional shape and roughness were taken at 82-foot  intervals over selected sections of both torpedoed and nontorpedoed furrows.
These sites were measured again following irrigation.
Each site was irrigated, with a detailed evaluation performed on both selected torpedoed and nontorpedoed sections.
Evaluation measurements included monitoring furrow inflow rates, measuring steady-state intake rates by monitoring inflow and outflow with flumes placed in individual furrows until the furrow outflow rate became constant, and measuring advance times of water at specified distances down the furrow.
Furrow cross section.
Analysis of furrow cross-sectional shape measurements revealed that the furrow cross-sectional area available for shallow-depth water flow, which occurs as water advances down the furrow, is increased by dragging torpedoes in the furrow.
This was evident at all three sites investigated.
Use of
 Fig.
1.
The pre-irrigation cross-sectional area at the 2-cm  flow depth for torpedoed and nontorpedoed furrows at three sites are compared.
the torpedoes creates a semicircular channel in the bottom of the furrow.
Hydraulically, the circular-shaped channel carries water more efficiently than the original, Vshaped furrow 
 Furrow cross-sectional shape measurements, taken after irrigation, indicated no difference in the final furrow area between torpedoed and nontorpedoed furrows.
Water flowing in the furrow eroded both torpedoed and nontorpedoed furrows, resulting finally in similar furrow shapes.
For equal flow depths, the furrow crosssectional flow area for both torpedoed and nontorpedoed furrows was substantially larger in post-irrigation furrows than in pre-irrigation furrows.
Fig.
3.
The pre-irrigation furrow roughnesses of torpedoed and nontorpedoed furrows at three sites is compared.
Furrow roughness.
The impact of using torpedoes on furrows is most evident when evaluating the furrow's roughness.
The roughness of a channel is a measure of the frictional resistance to water flow.
The rougher the furrow is, the slower and more deeply water moves along it.
Thus, water advance along a rough furrow is slower than in a smoother furrow.
At all three sites evaluated, the pre-irrigation roughness of the nontorpedoed furrows was substantially greater than in the torpedoed furrows.
The torpedo effect was most evident at the two Fresno County sites which had heavier-textured soils.
Heavier soils tend to have more clods and are rougher following furrow
 Fig.
2.
Channel shapes for pre-irrigation torpedoed and nontorpedoed furrows are compared.
preparation than are lighter-textured soils.
Dragging torpedoes in furrows breaks up the clods, resulting in a substantially smoother furrow.
Following irrigation, the roughness of both torpedoed and nontorpedoed furrows was statistically equivalent at both Fresno County sites.
These irrigations were long 24 hours at Fresno County No.
1 and 18 hours at Fresno County No.
2.
The UC Davis site showed evidence that the post-irrigation torpedoed furrows were statistically smoother than the postirrigation nontorpedoed furrows.
At UC Davis, irrigation time was 8 hours, substantially less than at the other sites.
It is likely that irrigation water in the nontorpedoed furrows had less time for smoothing and reshaping at UC Davis, compared with the Fresno County sites, and that the residual effects of the torpedoes were evident at UC Davis due to the lesser irrigation time.
Advance.
Evaluation at UC Davis allowed us the greatest control over furrow inflow, and therefore provided the best comparison between torpedoed and nontorpedoed furrows.
At UC Davis, torpedoes were dragged in nonwheel furrows but not in wheel furrows a common practice of growers using torpedoes in the San Joaquin Valley.
Torpedoing decreased advance times in the nonwheel furrows  by an average of 30%.
Water advance in wheel furrows  was similar to that in torpedoed furrows, indicating that the impact of using torpedoes in furrows was similar to that of wheel traffic.
In practice, torpedoing furrows would be advantageous since advancing irrigation water in wheel furrows tends to reach the end of the field before the water in nonwheel furrows and contributes significantly to tailwater runoff.
For many growers, managing tailwater runoff is difficult and undesirable.
TABLE 1.
Comparison of irrigation advance times  to 200 meters at UC Davis and two
 Site	Avg.
CV*	Avg.
CV
 UC Davis	164	0.146	230	0.091
 Fresno Co.
No.
1	249	0.474	294	0.347
 Fresno Co.
No.
2	560	0.116	715	0.210
 *CV = coefficient of variation.
TABLE 2.
Steady-state water intake rates in gallons per minute per 100 feet of furrow length for UC Davis and Fresno County test sites
 UC Davis	1.10	1.20
 Fresno Co.
No.
1	1.40	1.22
 Fresno Co.
No.
2	0.10	0.67
 At the Fresno County sites, there was no statistically significant difference between furrow inflow rates to torpedoed and nontorpedoed sections.
Soil cracking, evident at both Fresno County sites, particularly at Fresno County No.
2, complicated isolating the impact of torpedo use.
At Fresno County No.
2, there was a statistically significant  difference in irrigation advance rates between torpedoed and nontorpedoed furrows.
This was not true at Fresno County No.
1, where there was no statistically significant difference in irrigation advance rates between torpedoed and nontorpedoed furrows.
The differences in advance rates shown in table 1 are the result of furrow torpedoing and not simply a result of differences in furrow inflow rates, an indication that use of furrow torpedoes effectively increased the advance rate of irrigation water.
Furrow infiltration.
During irrigation, the water infiltration rate begins high and decreases with time until a final, constant, steady-state infiltration rate is achieved.
The time required for the steady-state infiltration rate to be reached varies with soil type.
At the three sites evaluated, flumes placed at the head and near the tail of the furrows allowed determination of the timing and value of the steady-state intake rate.
Table 2 shows the steady-state water intake rates for the three sites.
Differences in the steady-state intake rate between torpedoed and nontorpedoed furrows were small at Fresno County No.
1 and UC Davis, and data analysis showed that these differences were not statistically significant.
This suggests that the torpedoes had little effect on the steady-state intake rate of the furrow.
For Fresno County No.
2, however, differences in intake rate were substantial and were statistically significant, indicating that torpedoes reduced the furrow's final intake rate.
The infiltration measurements taken did not allow determination of furrow torpedoing impacts on the water intake rate before infiltration reached the steady-state rate.
Infiltration characteristics during this period merit attention because a decrease in the furrow
 intake rate can result in faster water advancement along the field.
The torpedo effect on the soil infiltration rate may depend on the surface soil moisture content at the time of torpedoing.
At the Fresno County No.
1 and UC Davis sites, observations at the time of torpedoing indicated that the soil was probably air-dry.
Thus, while use of the torpedo smoothed the soil surface, soil compaction was apparently minimal.
We hypothesize, however, that because of rainfall shortly before torpedoing, the soil surface at Fresno County No.
2 may have been wetter at the time of torpedoing, resulting in greater soil compaction and a lower intake rate.
Although not measured in this study, it has been the authors' observation that soil moisture content at the time the field is torpedoed has an impact on both furrow cross-sectional shape and furrow roughness.
If torpedoes are dragged when the soil is slightly moist, the result is a more definite, semicircular channel with sides that do not slough back into the furrow bottom.
The resulting furrow is also smoother with the furrow bottom being almost slick in appearance.
It is speculation, backed by field observations, that using torpedoes when the soil surface is moist may also cause a "slicking" of the soil surface, resulting in a reduced water intake rate in the furrow.
Therefore, dragging torpedoes when the soil surface is moist tends to accentuate the impact of torpedoes.
Torpedoing a dry furrow tends to break up clods, reducing furrow roughness, but it does not leave as definite a semicircular channel.
Torpedo shape and weight also appear to play a role in their effectiveness.
In practice, growers use torpedoes that vary in diameter and weight.
The authors have seen in use torpedoes ranging in diameter from 6 to 12 inches, in length from 18 inches to 4 feet, and in weight from hollow torpedoes to those filled completely with concrete.
Westlands Water District recommends for use as a torpedo a 3.5-foot-long,
 10-inch-diameter steel pipe, domed at the front end and filled with concrete.
This heavier torpedo more effectively smoothes furrows and "tracks" better when being towed, but its additional weight makes handling more difficult.
Currently, some growers make a separate equipment pass through the field to torpedo the furrows.
It is suggested, where possible, that furrow torpedoing be done in conjunction with other furrow preparation operations.
Use of furrow torpedoes effectively smoothes and changes furrow shape before irrigation.
The resulting cross-sectional shape change and reduced furrow surface roughness increases the water advance rate during irrigation a positive result because the uniform water application is thereby improved.
Improved irrigation uniformity allows the water manager to more closely match the crop's water demands and to minimize water losses due to deep percolation.
At one site, torpedoing reduced the furrow's steady-state water infiltration rate.
A similar phenomenon was not observed at the other two sites investigated.
An increase in the irrigation advance rate of torpedoed furrows, ranging from 15 to 30%, was noted at each site evaluated.
Torpedoed, nonwheel furrows had water advance characteristics similar to wheel furrows.
Torpedoing nonwheel furrows therefore resulted in more equal water advance rates among furrows.
L.
J.
Schwankl and B.
R.
Hanson are Extension Specialists, Department of Land, Air and Water Resources, UC Davis, and A.
Panoras is Irrigation Specialist, Land Reclamation Institute, Greece.
Federal Voluntary Conservation Programs
 The federal government has developed voluntary conservation programs to encourage the adoption of pollution prevention practices.
A variety of programs have been implemented with specific conservation goals, such as restoring wetlands, improving water quality, protecting watersheds and preserving wildlife habitat.
Taking land out of agricultural production can be costly for a property owner.
Additionally, most of the programs have eligibility requirements and impose restrictions on land use.
The federal incentive programs are designed to offset the costs of carrying out conservation practices and to stimulate interest in reducing off-site impacts on water quality.
How Conservation Programs Protect Water
 Conservation programs incorporate practices that reduce soil erosion and improve water quality.
Vegetative covers such as trees and grasses are often planted on marginal croplands.
The vegetation reduces the speed of water runoff and intercepts sediment before it can enter surface water.
Conservation buffers are strips of land where permanent vegetation is established in and around row crops.
The buffers are designed to block sediment and agricultural chemicals before they can pollute surface water.
Buffers also help enhance water quality by preventing banks from falling into waterbodies.
The programs are administered by either the United States Department of Agriculture's  Farm Service Agency  or Natural Resources Conservation Service  in cooperation with the states.
The Conservation Reserve Program , enacted in 1985, is the federal government's largest private land retirement program.
It provides payments to farmers to take highly erodible or environmentally sensitive cropland out of production for 10 years or more to conserve soil and water resources.
The program is administered by FSA with technical assistance provided by NRCS.
CRP has several subprograms:
 Conservation Reserve Enhancement Program  and
 Farmable Wetlands Program.
To be eligible for any CRP, a landowner must have owned or operated the land for at least 12 months prior to close of the CRP sign-up period, unless it was inherited or it can be shown that it was not acquired for the purpose of enrolling it in the program.
All CRP programs require landowners to sign a contract agreeing to follow specified conservation practices for 10 to 15 years.
In return, landowners receive technical and financial benefits including annual rental payments, cost share for conservation practices and additional incentive payments.
However, the amount of funding available to individual landowners is oftentimes not enough to justify participation in federal conservation programs.
General and Continuous CRPs
 There are two types of sign-ups for enrolling land in CRP: General and Continuous.
General sign-ups have specified enrollment periods during which landowners compete nationally to enroll their land in CRP.
Applicants must meet certain eligibility criteria, evaluate their land according to FSA's Environmental Benefits Index and submit bids to FSA for enrollment.
FSA accepts applications that demonstrate the highest environmental benefits.
Eligibility criteria include but are not limited to:
 Cropland that has been planted or considered planted to an agricultural commodity four of the six crop years between 1996 and 2001
 Cropland that is physically and legally capable of being planted in a normal manner as an agricultural commodity
 Land that is located in national or state CRP priority area or
 Land that is eligible for continuous sign-up.
In addition, cropland must have a weighted average erodibility index of eight or greater.
An erodibility index is a formula that considers such factors as slope, land cover, soil type and amount of annual rainfall.
Environmentally desirable land devoted to certain conservation practices may be enrolled at any time under Continuous CRP.
Certain eligibility requirements still apply, but offers are not subject to competitive bidding.
CCRP accepts eligible land on which property owners are willing to incorporate such practices as riparian buffers and wetland restoration.
To be eligible under CCRP, land must first meet the general sign-up CRP eligibility requirements.
Nearly 88.5% of CRP acreage 30.7 million is enrolled through general sign-up.
There are 2.7 million acres enrolled under continuous sign-ups.
Approximately 1.1 million acres are enrolled in CREP.
There are 179,448 acres enrolled in FWP.
Source: Congressional Research Service, Conservation Reserve Program: Status and Current Issues, April 11, 2008.
Land must be determined by NRCS to be eligible and suitable for any of the following practices:
 Riparian buffers plantings of trees, shrubs and grasses that catch pollutants in both surface runoff and groundwater before those pollutants reach a waterbody, such as a stream or lake.
Riparian buffers also improve fish and wildlife habitat.
Filter strips strips of grass used to trap sediment, fertilizers, pesticides and other pollutants before they reach streams and lakes.
Grassed waterways strips of grass seeded within cropland where water tends to concentrate or flow off a field.
While they are primarily used to prevent gully erosion, grassed waterways can be combined with filter strips or riparian buffers to trap sediment and other pollutants.
Shelter belts a row or rows of trees or shrubs used to reduce wind erosion, protect young crops and control blowing snow.
These practices also provide protection for wildlife, livestock, houses and farm buildings.
Field windbreaks similar to shelter belts but are located along field borders or within the field.
In some areas field windbreaks may be called hedgerow planting.
Living snow fences similar to field windbreaks and shelter belts, living snow fences help manage snow deposits by protecting buildings, roads and other property.
They can also be designed and placed to provide cover for livestock or wildlife and to collect snow to increase soil moisture and nearby water supplies.
Conservation Reserve Enhancement Program
 CREP is a land retirement program that helps agricultural producers protect environmentally sensitive land, decrease soil erosion, restore wildlife habitat and safeguard surface and groundwater.
The program is a partnership among landowners, tribal, state and federal governments, and, in some cases, private groups.
For example, in 2001, The Nature Conservancy helped fund Arkansas' Bayou Meto CREP.
They are also partnering with the state to support the 2008 Cache River/Bayou DeView CREP.
As with CRP and CCRP, property owners must own land for at least one year before they can enroll it in CREP.
Cropland must also have been planted or considered planted to an agricultural commodity four of the six crop years
 between 1996 and 2001, and it must be physically and legally capable of being planted in a normal manner as an agricultural commodity.
Enrollment is on a continuous basis, allowing landowners to join the program at any time rather than waiting for specific sign-up periods.
Cropland that is on highly erodible soil  within 1,000 feet of a perennial or intermittent stream, wetland or other qualifying waterbody, and is suitable for planting grasses, shrubs and/or trees
 Cropland or marginal pasture that is adjacent to a perennial or intermittent stream, wetland or other qualifying waterbody, and is suitable for establishing buffer practices 
 Cropland that is suitable for restoration of wetlands or the creation of shallow water habitats
 Cropland that is suitable for habitat restoration to benefit declining species of plants or animals.
Farmable wetlands those wetlands that have been partially drained, or are naturally dry enough to allow crop production in some years, but otherwise meet the definition of a wetland may be enrolled in CRP on a continuous basis.
Eligible land includes farmed and previously converted wetlands that have been impacted by farming activities.
The maximum acreage for enrollment of wetlands and buffers is 40 acres per tract.
A landowner may enroll multiple wetlands and associated buffers on a tract as long as the total acreage does not exceed 40 acres.
FWP eligibility requirements include:
 Cropland that has been planted to an agricultural commodity three of the 10 most recent crop years and is physically and legally capable of being planted in a normal manner to an agricultural commodity
 A wetland of 10 acres or less 
 A buffer that does not exceed the greater of three times the size of the wetland or an average of 150 feet on either side of the wetland and
 Agreements from participants to restore the hydrology of the wetland to the maximum extent possible.
Violating a CRP Contract
 There are severe penalties when landowners do not comply with CRP rules or intentionally break the contract.
A landowner who terminates a contract early faces a penalty fee plus repayment, with interest, of all the funds already paid to the landowner.
This includes any cost-share payments.
Penalties would apply to any contract holder who re-enrolls or extends acreage and then decides to terminate the contract.
An expiring contract that is extended and then later terminated would have penalties based on the original contract, not just the period since contract extension.
Expiring acreage that is re-enrolled is under a new contract and would incur penalties only on the period covered by the new contract.
If a landowner sells land currently enrolled in CRP, the new owner must become the successor to the CRP contract.
If the new owner does not become the successor, then the CRP contract is terminated and the former landowner is liable and may be required to refund all previous payments, plus interest received.
Environmental Quality Incentives Program
 The Environmental Quality Incentives Program  was established in 1996.
EQIP funds conservation practices on working agricultural land to achieve the following national priorities:
 Reduction of nonpoint source pollution such as nutrient and pesticide runoff
 Protection and conservation of groundwater resources
 Reduction of air pollutants
 Reduction of soil erosion and
 Promotion of habitat conservation for species whose populations are declining.
The program aims to limit nonpoint source pollution.
Eligible recipients must be directly involved with agricultural production.
Cost-sharing is not available for confinement operations with more than 1,000 animal units.
NRCS state conservationists, with the approval of the NRCS Chief, can modify the national standard.
Assistance consists of payments up to $10,000 per person, per year, for up to three years.
The total of the contract payments cannot exceed $50,000.
The Wetlands Reserve Program  is a voluntary incentive program administered by NRCS in agreement with FSA.
WRP provides technical and financial assistance to eligible landowners to address wetland, wildlife habitat, soil, water and related natural resource concerns on private land in an environmentally beneficial and cost-effective manner.
The program provides an opportunity for landowners to receive financial incentives to enhance wetlands in exchange for retiring marginal land from agriculture.
To be eligible for WRP, an applicant must show:
 Evidence of ownership of the land for 12 months before submitting an application
 Clear title to the land as well as consent or subordination agreements from each holder of a security interest in the land and
 A recorded right of way that provides access to the easement area from a public road.
NRCS enrolls a mixture of small and large restoration projects ranging in size from two acres to several thousand acres.
Wildlife Habitat Incentives Program
 The Wildlife Habitat Incentives Program  is a voluntary program that encourages the creation of high-quality wildlife habitats that support wildlife populations of national, state, tribal and local significance.
Through WHIP, NRCS provides technical and financial assistance to landowners and others to develop upland, wetland, riparian and aquatic habitat areas on their property.
Fact Sheet 109  Glossary of WaterRelated Terms contains a comprehensive list of terms used in the Arkansas Water Primer Fact Sheet Series.
The University of Arkansas Division of Agriculture's Public Policy Center provides timely, credible, unbiased research, analyses and education on current and emerging public issues.
The Arkansas Water Primer Fact Sheet Series was funded by a grant from the U.S.
Department of Agriculture with additional financial assistance from the University of Arkansas Division of Agriculture.
Original research for the Series was provided by Janie Hipp, LL.M., and adapted by Tom Riley, associate professor and director of the University of Arkansas Division of Agriculture's Public Policy Center, and Lorrie Barr, program associate, University of Arkansas Division of Agriculture's Public Policy Center.
It also summarizes up-to-date water inputs , crop water uses and losses, and overall water balance.
Users get those up-to-date predictions without going to the fields.
With this in mind, we can set up some trigger dates to assess moisture levels and pasture conditions, informing the implementation of a drought management plan.
June 15 to June 30: Approximately 75% to 90% of grass growth on cool-season dominated range sites and 50% of grass growth on warm-season dominated range sites will have happened.
Rainfall after late June results in limited benefit to cool-season grass production.
Irrigation method does not affect WIII pee pommators of hybrid sunflower
 by Hillary Sardias, Collette Yee and Claire Kremen
 Irrigation method has the potential to directly or indirectly influence populations of wild bee crop pollinators nesting and foraging in irrigated crop fields.
The majority of wild bee species nest in the ground, and their nests may be susceptible to flooding.
In addition, their pollination of crops can be influenced by nectar quality and quantity, which are related to water availability.
To determine whether different irrigation methods affect crop pollinators, we compared the number of ground-nesting bees nesting and foraging in drip-and furrow-irrigated hybrid sunflower fields in the Sacramento Valley.
We found that irrigation method did not impact wild bee nesting rates or foraging bee abundance or bee species richness.
These findings suggest that changing from furrow irrigation to drip irrigation to conserve water likely will not alter hybrid sunflower crop pollination.
factors that determine crop success, such as pollination.
Wild bees are the most effective and abundant crop pollinators.
The majority of wild bees excavate nests beneath the soil.
Irrigation has the potential to saturate nests, possibly drowning bee larvae and adults.
It could also indirectly impact crop pollinators by affecting their foraging choices.
Bee foraging decisions are often related to floral reward, namely nectar quantity and quality.
Nectar production is related to water availability; increased water leads to higher nectar volume expressed.
Thus, an irrigation method that delivers more water, such as furrow, could make fields more attractive to wild bee pollinators, thereby increasing potential yields.
We compared the number of bees nesting and foraging in conventionally managed hybrid sunflower  fields that were either furrow or drip
 I irrigation practices and water use efficiency are increasingly scrutinized by growers.
Irrigated agriculture accounts for 80% of human-related water use in California.
In periods of drought, growers adopt water-saving irrigation practices at higher rates.
Drip irrigation, introduced to California in
 1969, delivers water directly to the plant root zone, thus improving water efficiency; it is now used in approximately 40% of all irrigated fields.
Increases in irrigation efficiency can improve yield , which is another reason growers may consider switching to drip irrigation.
However, changes in irrigation practices may negatively impact other
 irrigated.
We predicted that drip-irrigated fields would support higher numbers of nesting bees, but that more bees would forage in furrow-irrigated fields, due to indirect effects.
We also examined whether irrigation had the same effect on different bee groups.
Sunflower is visited by both specialist and generalist ground-nesting native bee pollinators that nest within
 crop fields.
Generalist bees visit a variety of plant species, whereas specialists collect only sunflower pollen to provision their nests.
While both of these types of pollinators could be susceptible to irrigation methods, sunflower specialists are more tied to the crop and could experience potential negative effects of irrigation more strongly.
We sampled five drip-and five furrowirrigated sites in 2013 during the summer months at peak sunflower bloom.
Site types were paired by bloom time, sunflower variety and landscape context  to reduce extraneous factors that could contribute to differences in
 The stages of furrow irrigation, also known as flood irrigation: during irrigation , following saturation  and after water applied to the field has dried.
Drip-irrigated fields lack the cracking found in furrows of flood-irrigated fields; the soil surface appears dry, even during irrigation events.
nesting and foraging patterns observed.
All fields were located in Yolo County, California.
We used 1.96-square-foot emergence traps  to sample nesting bees.
The traps have open bottoms to allow nesting bees to leave their nest.
However, when they emerge, they are funneled to the top of the trap and into a kill jar.
We placed the traps at dusk, after bees had returned to their nests, and weighted down the edges with soil to prevent bees from entering or exiting the trap.
There were 20 traps in each field along two parallel 328-foot transects that ran into each field.
Traps were 32.8 feet apart.
Approximately 20 hours later, we removed all bees from apical kill jars.
The day following emergence trap sampling, we netted foraging bees visiting sunflowers for 30 minutes along each of the two transects.
We set emergence traps only if weather conditions the following day were predicted to be ideal for netting: temperature > 64F, wind speed < 5.5 mph and low cloud cover.
All bees were pinned, then identified by Dr.
Robbin Thorp, professor emeritus, UC Davis Department
 Nest entrances of the ground-nesting sunflower specialist bee, Diadasia enavata.
Sunflower is visited by both specialist and generalist pollinators, including the generalist Halictus ligatus  and the specialist Diadasia enavata.
of Entomology.
They are currently housed in UC Berkeley's Essig Museum of Invertebrate Zoology.
To determine whether vegetative factors influenced bee abundance or species richness, we estimated percentage sunflower bloom, stem density , weed density  and weed bloom.
Sunflower bloom and stem density were correlated, as were weed density and weed bloom, which allowed us to use only one metric for each category in our analyses.
We examined the effect of irrigation method on the abundance of nesting bees captured in emergence traps and foraging bees netted at blooms using a generalized linear model with a Poisson distribution in the R package lme4.
Independent variables were irrigation type, stem density and weed density.
Site was a random effect.
We repeated this analysis for species richness, which was calculated using the R package vegan.
We included only female bees in our analyses of nesting rates, as male bees do not excavate nests.
Fig.
1.
Emergence traps  were used to collect bees nesting in sunflower fields and were placed along two parallel transects  running 328 feet into the fields.
Transects were located 164 feet from field edges and 328 feet apart.
Ten traps , 32.8 feet apart, were placed along each transect.
Bee nesting and foraging counts
 We collected 42 bees from six species nesting within fields and 735 bees from 14 species foraging on sunflower blooms.
All of the species we collected nesting were also found foraging.
The two most abundant species nesting in
 sunflower fields were the sunflower specialist Melissodes agilis and the generalist sweat bee Lasioglossum incompletum.
These bees were among the most abundant bee species found foraging.
One other species of sweat bee  and three other sunflower specialist bees  foraged in high
 TABLE 1.
Species collected nesting in sunflower fields and foraging on sunflowers
 Species	Specialization	Nesting	Foraging
 Bombus vosnesenskii	Generalist	0	1
 Diadasia enavata	Specialist	0	53
 Halictus ligatus	Generalist	1	51
 Halictus tripartitus	Generalist	1	20
 Lasioglossum  spp.
Generalist	6	1
 Lasioglossum incompletum	Generalist	16	43
 Megachile parallela	Specialist	0	1
 Melissodes agilis	Specialist	17	393
 Melissodes lupina	Specialist	0	8
 Melissodes robustion	Specialist	0	63
 Peoponapis prunoisa	Specialist*	0	1
 Svastra obliqua expurgata	Specialist	0	88
 Triepeolis concavus	Parasite	0	3
 Triepeolis subnitens	Parasite	1	9
 Total no.
of bees	42	735
 Total no.
of species	6	14
 * Specialist of squash, not sunflower.
Fig.
2.
Irrigation method did not affect the abundance or species richness of nesting bees  or foraging bees  in sunflower fields.
Boxes are upper and lower quartiles, dark bar is the mean, whiskers show the maximum and minimum values, and points are outliers.
numbers, yet were not detected nesting within fields.
Bee response to irrigation method
 We did not find a difference in the abundance of bees nesting in dripversus furrow-irrigated fields.
Similarly, the species richness of nesting bees did not vary with irrigation type.
Sunflower stem density  and weed density  did not impact nesting rates , which is not surprising given that we attempted to control for variability in bloom by sampling at peak bloom in all fields.
As with nesting rates, the abundance  and species richness  of native bees actively foraging on sunflower was unaffected by irrigation type.
Sites that were sampled at the same time appeared to contain similar numbers of foraging bees  except for sites D3 and F3, where the drip-irrigated site contained almost twice as many foraging bees.
However, we were unable to assess the effect of sampling date in our analyses as each site was sampled only once.
This study was conducted during a single year; therefore, the results reflect nesting and foraging during this one sampling season.
Our sample size may not have been large enough to detect small differences in nesting rates.
While the strength of the nesting results indicates that sunflower bee nesting is likely not linked to irrigation method, additional evidence from future studies could help confirm this conclusion.
We collected numbers and species of bees in our netted sample that were similar to those in other studies in sunflower in our study region ; this similarity suggests our findings on the relationship of foraging bees to irrigation type may be robust to the effects of small study size.
Soil moisture has been shown to positively affect nesting (Julier and Roulston
 Fig.
3.
Foraging bee abundance in site pairs , which were drip and furrow irrigated sunflower fields that had the same variety and bloom time.
2009; Xie et al.
2013); therefore, irrigation may help make fields attractive nest site locations for crop pollinators.
Soil moisture, however, may be correlated to a number of other conditions, including soil compaction.
In the sunflower study system, generalist wild bees have been found to nest both within crop fields as well as along un-irrigated field edges.
Soil moisture may not exert as strong of effects as other characteristics that affect nest site
 selection and nesting success of generalists, while sunflower specialists may be better adapted to the within field conditions where sunflowers are grown.
Bees' adaptation to inundation
 The most abundant foraging and nesting sunflower specialist species, M.
agilis, has been recorded nesting between irrigation furrows in crop fields since the early
 1980s.
The cells in their nests are lined with wax, which may have some hydrophobic properties.
Water-resistant wax linings have been recorded in the nests of other bee species.
Species whose nests are not regularly exposed to wet conditions may be able to withstand extreme conditions, such as flooding from a hurricane , although some species may have local nesting aggregations wiped out by similar events if the soil structure is compromised, for example by mud slides.
The ability to withstand irrigation or natural saturation events has not been recorded for most of the bees in this study; however, the bees' presence in regularly irrigated fields indicates that irrigation may not be a factor that significantly limits or disrupts their nesting activity.
Which irrigation method is best?
Although drip irrigation is often considerably more expensive than furrow irrigation, there are numerous benefits other than water use efficiency associated with drip irrigation, including disease management and the ability to irrigate oddly shaped or uneven fields.
Drip irrigation, especially subsurface drip, can reduce the total amount of acre-feet applied because it reduces evaporation
 .
Over 85% of processing tomato fields in California have been converted to drip irrigation systems, which has increased yields without compromising crop quality.
Sunflower is often rotated into fields that contained tomato the year prior because
 .
The current drought is driving up the cost of water and limiting water access, leading growers to increase well drilling to obtain groundwater.
Wells were expected to account for 53% of all irriga-
 Drip irrigation is a viable method to combat the drought without compromising crop pollination from wild bees.
the two crops have similar row spacing.
Growers leave the drip tape down , maximizing their investment through reuse of the drip tape.
Water efficiency is especially important in California's Central Valley, where climate change is expected to increase temperatures 2F to 3.6F by 2050 and the frequency, intensity and duration of summer heat waves are expected to increase
 tion water in 2015; however, increased rates of pumping caused by the prolonged drought has caused the water level to drop below the depth of many wells ; this excess pumping is also leading to land subsidence.
Although this study was conducted in hybrid sunflower fields, the irrigation methods applied are typical of those used in row crops throughout the Central Valley.
The generalist sweat bees that nest
 and forage on sunflower are among the most common crop pollinators in the region, and pollinate a variety of crops from watermelon to tomato.
We would therefore expect our findings to apply to a number of different annual crop types.
The combined efficiency benefits and lack of negative effects on native bee crop pollinators indicate that drip irrigation is a viable method to combat the drought without compromising crop pollination from bees nesting within crop fields.
H.
Sardias is Pacific Coast Pollinator Specialist at the Xerces Society for Invertebrate Conservation, Berkeley; C.
Yee participated in this research as part of her undergraduate thesis at UC Berkeley; and C.
Kremen is Professor in the Department of Environmental Science, Policy and Management at UC Berkeley.
Enterprise Budgets Spring Barley, Following Cotton, Flood Irrigated, Southern Arizona Blase Evancho, Paco Ollerton Trent Teegerstrom and Clark Seavert
 This enterprise budget estimates the typical economic costs and returns to grow spring barley after a cotton crop using flood irrigation in southern Arizona.
It should be used as a guide to estimate actual costs and returns and is not representative of any farm.
The assumptions used in constructing this budget are discussed below.
Assistance provided by area producers and agribusinesses is much appreciated.
As of the date of this publication, the price for labor, fuel, fertilizer, and chemicals is increasing dramatically, which makes developing a long-term budget difficult.
Therefore, a sensitivity analysis shows the net returns per acre as these inputs increase by 10 and 20 percent.
This budget is based on a 1,500-tillable acre farm.
As Arizona is experiencing irrigation water shortages, approximately 40 percent  of the total farm tillable acres are fallowed.
This fallowed land will allow adequate water to irrigate the following crops: 271 acres in cotton, 45 acres in silage corn, 90 acres in spring barley, 181 acres in durum wheat, and 316 acres of alfalfa hay.
The costs to fallow land are allocated to each crop based on its water use.
All crops are grown using flood irrigation.
Tractor driver labor cost is $17.89 per hour and general labor $14.55 per hour; both rates include social security, workers' compensation, unemployment insurance, and other labor overhead expenses.
For this study, owner labor is valued at the same rate as tractor driver rates, and all labor is assumed to be a cash cost.
Tractor labor hours are calculated based on machinery hours, plus ten percent.
Interest on operating capital for harvest and production inputs  is treated as a cash expense, borrowed for 6-months.
An interest rate of six percent is charged as an opportunity to the owner for machinery ownership.
The machinery and equipment used in this budget are sufficient for a 1,500-acre farm with 1,000 acres in crops.
The machinery and equipment hours reflect producing cotton, silage corn, spring barley, durum wheat, and alfalfa hay.
A detailed breakdown of machinery values is shown in Table 2.
Estimated labor, variable, and fixed costs for machinery are shown in Table 3, based on an hour and per acre basis.
The machinery costs are calculated based on the total farm use of the machinery.
Off-road diesel is $4.00 per gallon.
The cultural operations are listed approximately in the order in which they are performed.
A 175-hp tractor is used to pull the v-ripper, heavy offset disk, moldboard plow, landplane, lister, and planter.
A 125-hp tractor is used to pull the shredder/root puller, drill, cultivator, fertilizer spreader, and boom sprayer.
A charge for miscellaneous and other expenses is five percent of production costs, including additional labor, machinery repairs and maintenance, supplies and materials, tax preparation, memberships in professional organizations, and educational workshops not included in field operations.
In this budget the price of spring barley is $15 per cwt, with an average yield of 60 cwt, resulting in a gross
 income of $900 per acre.
Variable costs are $642 per acre and fixed cash costs of $252 per acre, giving a net return above variable cash costs of $5 per acre.
Total fixed costs are $46 per acre and total costs of $941 per acre, when all variable and fixed costs are considered.
The gross income minus total costs results in a -$41 per acre return.
A breakeven price of $14.90 per cwt would be required to cover variable and fixed cash costs and $16.73 per cwt to cover total costs.
Tables 4 and 5 show the baseline net returns per acre for cash and total costs at various yields and prices as in this study.
Tables 6, 7, 8, and 9 show a sensitivity analysis of returns per acre as the price for labor, fuel, fertilizer, and chemicals are increased an additional 10 and 20 percent.
NOTE: Not included in these budgets are family living withdrawals for unpaid labor, returns to management, depreciation and opportunity costs for vehicles, buildings and improvements, inflation, property and crop insurance, and local, state, and federal income and property taxes.
Table 1.
Economic and Cash Costs and Returns of Producing Spring Barley Following Cotton, $/acre.
Returns	Unit	$/Unit	Quantity	Value
 Spring Barley	ton	$0.08	22,000.00	$1,760.000
 Variable Cash Costs	Price	Quantity	Unit	Labor	Machinery	Materials	Total
 Land Preparation and Maintenance
 V-Ripper	1.00	acre	$13.53	$34.60	$0.00	$48.13
 Offset Disk	1.00	acre	9.43	23.76	0.00	33.19
 Drill	1.00	acre	5.4	10.13	58.50	74.04
 Seed	$0.39	150.00	pounds
 Ferlilizer Program	1.00	acre	1.88	3.73	182.91	188.52
 Nitrogen	$182.91	1.00	acre
 Boom Sprayer	1.00	acre	1.19	1.82	32.00	35.01
 Herbicides	$17.00	1.00	acre
 Insecticides	$15.00	1.00	acre
 Irrigation	36.38	0.00	137.50	173.88
 Irrigation Water, Flood	$55.00	2.50	ac ft
 Irrigation Labor, Flood	$14.55	2.50	hous
 Harvest custom 	$25.00	1.65	ton	0.00	0.00	41.25	41.25
 Other Expenses	5.0%	0.00	0.00	29.70	29.70
 Interest on Operting Capital	6.0%	0.00	0.00	18.71	18.71
 Total Variable Cash Costs	$126.11	$74.05	$500.578	$642.44
 Fixed Cash Costs	Unit	$/Unit	Value
 Fallow Costs	acre	$82.42	$82.42
 Annual Cash Rent Payment	acre	170.00	170.00
 Total Fixed Cash Costs	$252.42
 Total minus Total Variable and Fixed Cash Costs
 Fixed Non-Cash Costs	Unit	$/Unit	Value
 Power Units, Machinery & Equipment, depreciation & interst	acre	$45.88	$45.88
 Total Fixed Non-Cash Costs	$45.88
 Total Annual Costs	$940.75
 Returns minus Total Annual Costs	-$40.74
 1 Cost includes cutting and hauling wheat from field to a market within a round trip of 20 miles.
Table 2.
Whole Farm Machinery Cost Assumptions.
Width	Market	Annua	Life
 Machine		Value	Use	
 175 HP Tractor	N/A	$180,000	1,365	10
 125 HP Tractor	N/A	80,000	495	15
 V-Ripper	8.0	22,000	459	10
 Offset Disk	18.0	30,000	517	15
 Moldboard Plow	9.3	35,000	138	15
 Landplane	16.0	18,000	78	15
 Lister	10.0	6,500	99	15
 Cotton Shredder/Root Puller	20.0	12,000	41	15
 Row Planter	24.0	40,000	72	15
 Row Cultivator	24.0	22,000	103	10
 Drill	20.0	25,000	97	15
 Fertilizer Spreader	40.0	18,000	109	20
 Boom Sprayer	60.0	9,500	145	20
 Table 3.
Machinery Cost Calculations, on a per hour and per acre basis.
-Variable Costs-	Fixed Cost
 Fuel &	Repairs &	Deprec.
Total Cost
 Machie	Lube	Maint.
& Interest
 175 HP Tractor	$36.80	$7.37	$17.20	$61.37
 125 HP Tractor	23.00	1.78	18.31	43.09
 V-Ripper	0.00	6.16	6.19	12.35
 Offset Disk	0.00	5.40	6.48	11.88
 Moldboard Plow	0.00	18.20	28.29	46.50
 Landplane	0.00	3.24	25.80	29.04
 Lister	0.00	1.78	7.32	9.10
 Cotton Shredder/Root Puller	0.00	2.76	32.57	35.33
 Row Planter	0.00	14.02	64.48	78.50
 Row Cultivator	0.00	3.90	27.10	30.99
 Drill	0.00	12.06	30.14	42.20
 Fertilizer Spreader	0.00	14.31	19.02	33.34
 Boom Sprayer	0.00	5.36	7.51	12.87
 Acre/	Operator	Variable	Fixed	Total
 Field Operation	Hour	Labor	Costs	Costs	Costs
 175 HP Tractor & V-Ripper	1.45	$13.53	$34.60	$16.08	$64.21
 175 HP Tractor & Offset Disk	4.17	4.72	11.88	5.68	22.27
 175 HP Tractor & Moldboard Plow	2.55	7.73	24.50	17.87	50.11
 175 HP Tractor & Landplane	5.09	3.87	9.31	8.45	21.62
 175 HP Tractor & Lister	3.18	6.18	14.44	7.71	28.33
 175 HP Tractor & Shredder	6.64	2.97	4.15	7.67	14.78
 175 HP Tractor & Planter	4.36	4.51	13.34	18.72	36.56
 175 HP Tractor & Cultivator	6.55	3.01	4.38	6.94	14.32
 175 HP Tractor & Drillr	3.64	5.41	10.13	13.32	28.87
 175 HP Tractor & Fertilizer Spreader	10.47	1.88	3.73	3.56	9.18
 175 HP Tractor & Boom Sprayer	16.55	1.19	1.82	1.56	4.57
 Table 4.
Estimated Per Acre Returns Over Cash Cost at Varying Yields and Prices.
Price/CWT	54.0	56.0	58	60.0	62.0	64.0	66.0
 $13.50							
 $14.00						1	29
 $14.50					4	33	62
 $15.00				5	35	65	95
 $15.50			4	35	66	97	128
 $16.00		1	33	65	97	129	161
 $16.50		29	62	95	128	161	194
 Table 5.
Estimated Per Acre Returns Over Total Cost at Varying Yields and Prices.
Price/CWT	54.0	56.0	58	62.0	64.0	66.0
 $13.50						
 $14.00						
 $14.50						16
 $15.50				20	51	82
 $16.00				51	83	115
 $16.50			16	82	115	148
 Table 6.
Estimated Per Acre Returns Over Cash Cost at Varying Yields and Prices with a 10 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Price/CWT	54.0	56.0	58	62.0	64.0	66.0
 $13.50						
 $14.00						
 $14.50						3
 $15.50				7	38	69
 $16.00				38	70	102
 $16.50			3	69	102	135
 Table 7.
Estimated Per Acre Returns Over Total Cost at Varying Yields and Prices with a 10 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Price/CWT	54.0	56.0	58	60.0	62.0	64.0	66.0
 $13.50							
 $14.00							
 $14.50							
 $15.00							
 $15.50							24
 $16.00						25	57
 $16.50					24	57	90
 Table 8.
Estimated Per Acre Returns Over Cash Cost at Varying Yields and Prices with a 20 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Price/CWT	54.0	56.0	58	62.0	64.0	66.0
 $13.50						
 $14.00						
 $14.50						
 $15.50						7
 $16.00					8	40
 $16.50				7	40	73
 Table 9.
Estimated Per Acre Returns Over Total Cost at Varying Yields and Prices with a 20 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Price/CWT	54.0	56.0	58	62.0	64.0	66.0
 $13.50						
 $14.00						
 $14.50						
 $15.50						
 $16.00						
 $16.50						27
 THE UNIVERSITY OF ARIZONA Cooperative Extension
 BLASE EVANCHO Area Agent, Arizona Cooperative Extension, University of Arizona
 Paco OLLERTON Producer in Pinal County
 TRENT TEEGERSTROM Ag Econ Extension Specialist, Department of Agriculture and Resource Economics, University of Arizona
 CLARK SEAVERT Agricultural Economist, Department of Applied Economics, Oregon State University
How is Kentucky doing?
Conserving water at home and in the landscape
 Saving Water at Home
 Ashley R.
Osborne, Agriculture and Natural Resources, and Joe Taraba, Biosystems and Agricultural Engineering
 Many may consider Kentucky a "water-rich" state with over 90,000 miles of streams and rivers, thousands of ponds, lakes, reservoirs, and wetlands, and 40 to 50 inches of precipitation per year.
So, it's not surprising that water, one of our most valuable natural resources, is often taken for granted.
For many Kentuckians, fresh water is no more than a turn of the faucet, the push of a button, or the twist of a cap away.
Yet with increased water consumption, managing the supply and availability of water is a major issue in the U.S.
and the world.
Over the past fifty years, water consumption has tripled.
In the last five years, almost every region in the U.S.
has dealt with water shortages.
At least 36 states are predicting local, regional, or statewide water shortages by the year 2013, even under nondrought conditions.
The water we use today is the same water our ancestors used thousands of years ago and will be the same water future generations will use in years to come.
There is no new water.
Water travels from the air through condensation to the earth as precipitation and back to the atmosphere by evaporation.
Only about one-third of the precipitation that falls on the landscape flows in our rivers, streams, and lakes.
Evaporation and plant transpiration of water back to the atmosphere accounts for the other two-thirds.
Water conservation is not about saving water but about having sufficient clean water at any given time and place to meet our needs.
Condensation: A part of the water cycle during which water vapor turns into a liquid.
Evaporation: A part of the water cycle during which liquid water turns into water vapor.
Transpiration: The process by which water vapor is released to the atmosphere by living plants.
Letting your faucet run for 5 minutes uses about as much energy as letting a 60-watt light bulb run for 14 hours.
-WaterSense
 How is Kentucky doing?
In 2005, approximately 4,330 million gallons of water were withdrawn per day  in Kentucky.
Table 1 lists the total water withdrawn in 2005 in Kentucky by water use.
Public supply water is used for domestic, commercial, and industrial purposes, public services  and system losses.
Domestic use includes indoor
 residence use  and outdoor residence use .
Of the 558 Mgal/d of water withdrawn for public supply, 243 Mgal/d was withdrawn for domestic use.
Thus, in 2005, total water withdrawn for domestic use in Kentucky was approximately 278 Mgal/d or 67 gallons per person per day.
Table 1.
Water withdrawn in Kentucky by water use, 2005
 * Mgal/d=Million gallons per day
 Public supply is water withdrawn by public and private water suppliers that distribute water to a minimum of 25 people or that have no less than 15 connections.
Figure 2.
Water use in the United States
 Using less water can better prepare us for water shortages and drought situations.
The Kentucky Energy and Environmental Cabinet has developed a drought notification system.
The cabinet will announce a water shortage watch for a geographical area when conditions could lead to a water shortage, and they will issue a water shortage warning when one or more water supply systems in an area is currently in a water shortage emergency.
Conserving water conserves energy.
Obtaining water from streams, rivers, aquifers, and other water bodies and transporting it to water treatment facilities requires large amounts of energy.
At water treatment facilities, energy is needed to pump and process water and to distribute water to consumers.
Further energy is used by consumers to treat water with softeners and filters, circulate and pressurize water with pumps and irrigation systems, and heat and cool water.
Then the spent water or wastewater consumes more energy as it is pumped to treatment plants, where it is aerated and filtered.
By conserving water, we decrease our demand for energy-intensive systems that obtain, treat, and distribute water.
Simply put, by conserving water we save energy.
Conserving water saves money.
Each year the average household spends as much as $500 on water and sewer bills.
With more efficient water use, around $170 per year could be saved.
Conserving water at home and in the landscape
 The following are simple steps to save water at home and in the landscape during day-to-day activities and in emergencies situations.
Turn the water off when brushing your teeth, washing your hands or face, or shaving.
When shaving, fill the basin with water and dip your razor in the basin as needed.
Flush the toilet only when necessary.
Do not use the toilet as a wastebasket.
Throw tissues, insects, and other trash in the garbage not the toilet.
When taking a bath, plug the drain before turning on the faucet.
As the tub fills, adjust the temperature.
Use less than 5 inches of water when taking a bath.
Install low-flow showerheads and aerators to restrict the flow of water.
While waiting for water to get warm when taking a shower, catch the water in a pitcher or bucket, and use to water plants.
Save the water you use when bathing or showering to flush the toilet or water non-edible landscape plants.
Limit showers to 3 to 4 minutes.
Check your toilet and faucet for leaks.
Reuse bath towels at home or in hotels.
Replace old toilets  with new WaterSense labeled toilets.
When possible, purchase products, such as toilets, faucets, and faucet accessories, that have the WaterSense label.
Aerating vs.
Non-aerating Showerheads
 An aerating low-flow showerhead mixes air into the water stream maintaining a steady pressure and providing an even, full shower spray.
However, the temperature of the water may cool down slightly towards the floor of the shower since air is mixed with the water.
A non-aerating low-flow showerhead does not mix air into the water stream; rather the water flow pulses, providing a strong, massaging type spray that maintains temperature.
Take "navy showers." Turn the water on to get wet.
Turn the water off.
Lather with soap and shampoo.
Turn the water on to rinse.
Use a pan of water and a sponge or cloth to clean up in place of a bath or shower.
Dispose of fruit and vegetable scraps in a compost pile instead of a kitchen garbage disposal.
Garbage disposals use a lot of water and can create septic problems.
Thaw meat and other frozen foods in the refrigerator or use the defrost setting on your microwave instead of using running water.
Scrape, rather than rinse, dishes before putting into the dishwasher.
Set your dishwasher to the water saving or short cycle.
Only run the dishwasher with a full load.
Keep a pitcher of water in the refrigerator for drinking instead of running water and waiting for it to get cold.
Forgo bottled water.
While waiting for the water to get warm, catch the water in the sink or a pitcher and use for cleaning vegetables, washing or rinsing dishes, watering plants, or cleaning.
Don't wash or rinse dishes under a running faucet.
Instead use a pan or sink of water.
Cook food in as little water as possible to save water and prevent nutrient loss.
Use disposable plates, cups, and utensils to reduce the need to wash dishes.
Save the gray water from rinsing dishes to use when flushing the toilet or to water non-edible landscape plants.
Wash full loads of clothes.
If you must wash smaller loads, adjust the water-level control to the appropriate setting.
Use cold water whenever possible to wash clothes.
Read the manufacturer's instructions for your washer.
Some cycles, such as the permanent press cycle, may use more water.
Re-wear clothes when possible.
Check your washer's hoses for cracks and leaks regularly.
Use good laundering techniques.
To avoid rewashing or re-rinsing, pretreat stains, sort clothes, and follow product recommendations.
Gray water is household waste water from baths, showers, and sinks.
It can be reused for toilet flushing or to water non-edible landscape plants.
Gray water is of lesser quality than tap water and can contain bacteria and other pathogens; do not keep it for longer than 24 hours.
Gray water that contains detergents or bleach, including dishwater and water used for laundry purposes, should not be used on landscape plants because chemicals in the products can adversely affect soil chemistry and root growth.
Rinse water collected from washing dishes or clothes may be used only if the amount of detergent or bleach present is minimal.
Bath water is generally acceptable for irrigation purposes because soaps are typically less of a problem than detergents.
Alternating the use of gray water with clean water will decrease the risk of any long-term effects of the use of gray water.
Save the water you use when rinsing clothes to flush the toilet.
Equipment and Appliances Everyday Tips
 Read the manufacturer's instructions for your appliances.
Washing machines and dishwashers often have cycles that use less water.
Insulate your water heater tank and hot water pipes.
Lower the temperature on your water heater.
A savings of 3 to 5 percent in energy costs can be seen for each 10F reduction in water temperature.
If you plan to be traveling for 3 or more days, adjust the thermostat on your water heater to the lowest setting or turn off the water heater.
Consider purchasing a water alarm system for sump pumps, dishwashers, and washing machines to alert you if a major water leak should occur.
Landscape and Garden Everyday Tips
 To avoid water loss to evaporation, water your plants early in the morning.
Weed your garden regularly to eliminate competition for water.
Mulch plants, shrubs, and trees to retain moisture.
Leaves and lawn clippings can be used as an alternative to purchasing mulch.
In your garden, group together vegetables that need more water.
This will allow for more efficient watering.
Replace high-water-use plants with native or drought-tolerant plants.
Native plants have adapted to local conditions and can survive seasonal temperature extremes, such as periods of drought.
When purchasing an irrigation system, investigate which system is best for you and your lawn and garden needs.
Micro-irrigation sysitems for gardens, trees, and shrubs irrigate slowly and decrease evaporation, runoff, and overspray.
When planning to irrigate, take into account soil type, sun or shade exposure, the type of sprinkler, and time of day.
W later treatment devices improve the smell, taste, color, or quality of drinking water.
Reverse osmosis  is a water treatment device used to remove dissolved and suspended impurities from water.
A major disadvantage of RO is that it uses large amounts of water, generally recovering only 5 to 15 percent of the water entering the system.
A RO device dispensing 5 gallons of treated water per day may use anywhere between 20 to 100 gallons of water per day, which is discharged to the home's septic or sewer system.
This amount is dependent upon the model.
The RO discharge can be collected and used as a source of gray water.
When purchasing a water treatment device compare and contrast the primary use and advantages and disadvantages of the device.
Use condensation from air conditioning  units and dehumidifiers as a source of gray water.
A window AC unit can collect 1 to 2 gallons of condensate water per day, whereas a central AC unit for an entire home can collect 5 to 20 gallons of condensate water per day.
The condensate produced can range from 3 to 10 gallons of water per day for every 1,000 square feet of air-conditioned space and may vary depending on the local climate.
Dehumidifiers in basements may produce up to 8 gallons of condensate per day.
Depending on the location of the AC units, this water may be easily captured, stored, and used as a source of gray water.
Conserving water saves money.
Each year the average household spends as much as $500 on water and sewer bills.
With more efficient water use, $170 could be saved each year.
Inspect irrigation equipment once a month for leaks, broken or clogged heads, or other problems.
Reduce overwatering by decreasing each irrigation cycle by 2 minutes and eliminating one entire irrigation cycle per week.
Adjust sprinklers to eliminate overspray on sidewalks, driveways, and other impervious surfaces.
Invest in a rain shutoff switch to turn off your irrigation system in wet weather.
Raise the mowing height of your lawn mower.
This promotes root growth, decreases heat stress, and helps your lawn stay more hydrated.
Water young trees and shrubs first, as they need the most water and are more expensive to replace.
Water non-edible landscape plants with gray water.
Other Outdoor Uses Everyday Tips
 When giving your pet fresh water, use the old water for non-edible plants.
For outdoor play, use a small pool instead of a hose or sprinkler.
Check hoses and spigots for leaks regularly.
Clean sidewalks, patios, and driveways with a broom instead of a hose.
Install a rain barrel to collect rainwater to use on your lawn or garden.
Instead of hand washing vehicles, use a commercial carwash that recycles water.
Repair leaks around pool or spa pumps.
Install a pool or spa cover to reduce evaporation.
When using a water hose, use a
 nozzle to turn off the water when you are not using it.
Disconnect outdoor water hoses in winter.
Ashley Osborne, Extension Associate for Environmental and Natural Resource Issues Task Force, Plant and Soil Science Department
 Joe Taraba, Biosystems and Agrigultural Engineering
We are excited to incorporate cover crops within the sprinkler irrigated corn competition, Daran Rudnick, irrigation management associate professor and TAPS team member, commented.There has been growing interest of how to incorporate cover crops and, more importantly, how do we think about managing our water and nitrogen when cover crops are integrated into our corn and soybean rotation, so this competition will let us dive into what practices are leading to efficient and profitable crop production.
If you, or someone you know, might want to participate in the TAPS program in 2023, please visit the TAPS website to register.
Of course, spots are limited, due to the field sizes, so make sure to register soon if you want to participate in 2023.
Developing a Strategy to Achieve 300 Bushel Corn per Acre or Incrementally Increasing Current Yields
 Clues on how to maximize corn yields can be gleaned from corn contest winners.
Most winning corn growers agree that achieving higher yields requires: 1) paying attention to management details, 2) building soil organic matter, 3) using innovative technologies combined with appropriate variety selection that can minimize pest stress, 4) timely planting, fertilizing, and scouting for pests, and 5) conducting on-farm testing.
This chapter provides an eight-step plan to optimize corn yield.
Table 1.1 An eight-step plan to optimize corn yield and profit for South Dakota producers includes:
 1.
Be a lifelong learner and conduct your own on-farm product testing.
2.
Identify site-specific yield limiting factors.
3.
Use archived field records to: a) identify successful, as well as unsuccessful management strategies, b) design crop rotations that build soil health, and c) select hybrids and plant populations.
4.
Actively manage crop residues.
5.
Proactively manage field water.
This may involve installing tile drainage in poorly drained soils.
However, prior to installing tile drainage, check the soils for suitability with NRCS personnel to determine legal requirements.
6.
Improve the soil nutrient program.
a.
Conduct N and P assessments.
b.
Optimize fertilizer rates, timing, and sources.
7.
Proactively manage weeds, insects, and diseases.
a.
Select hybrids that optimize yield and minimize pest stress.
b.
Monitor weather conditions, scout fields regularly, track and map pest infestations.
C.
Use pre-emergence and post-emergence herbicides, apply insecticides and fungicides when needed, and rotate pesticide chemistries to avoid pest resistance.
8.
Prepare and calibrate field equipment.
a.
Calibrate and prepare your planter for seeding.
b.
Clean, repair, and calibrate fertilizer and pesticide applicators.
C.
Prepare the combine for harvest.
1.
Be a Lifelong Learner
 Over the past 160 years, researchers and growers have learned that corn responds to multiple stresses simultaneously , and for this reason, the strategy to increase corn yields involves examining many factors simultaneously.
Companies are constantly introducing new products, all touted to help relieve plant stress, and enhance yield.
However, not all products can be tested through unbiased research.
Growers need to take responsibility
 to gain information about the appropriate use of these technologies.
On-farm research will help provide information for deciding whether a product or technology is a good fit for your operation.
Some of the products that are tested may fail, but this information is also valuable, and in the long run, will help in deciding what, if any, changes should be made.
2.
Identify Site-specific Yield-limiting Factors
 Most land parcels are not uniform, exhibiting variability in soil types and topography.
This variability often means that cropping problems are not uniform and that a one-size-fits-all solution may not work.
Therefore, fields should be scouted to determine WHAT and WHERE the problems are occurring.
Scouting can be a complex process, but the ultimate goal is to identify yield-limiting factors by area and rectify the problem in a timely manner.
Scouting intensity should be increased during high-risk periods.
However, scouting is labor intensive and its efficiency may be improved through the use of a drone, aerial, or satellite imagery , if combined with groundtruth information.
Figure 1.1 Aerial images from a South Dakota production field.
Within the field different problems were confirmed by ground scouting.
It is important to understand that solutions to problems may require multiple years of intervention.
A specific example, crop lodging, is outlined below.
Following scouting, the local agronomists determined that 40% of the field's higher elevation areas was lodged.
Solving this problem will take multiple years.
At harvest, the farmer should consider harvesting the field against the direction of lodging.
In following years, lodged areas should be scouted to determine the amount of volunteer corn.
These volunteer plants may harbor diseases and insects or be a highly competitive weed for the planted crop.
To solve the problem, the core problem must be identified.
Lodging can result from many causes, including extremes in soil moisture, poor root development, high-wind events, poor plant nutrition , excessive population, disease incidence , and/or insect damage , alone or in combination.
Possible solutions may include:
 1.
Decreasing the corn seeding rate.
2.
Seeding corn hybrids with quick dry-down time, shorter maturity rating, and improved stalk rot and insects resistance.
3.
Increasing the amount of K added to the field.
K deficiency symptoms often include yellowing and necrosis of lower leaves and can contribute to weak stalks and increased incidence of stalk rot.
The deficiency may be exacerbated by crop residue harvesting, adverse climatic conditions, and organic or sandy soils.
3.
Use Archived Field Records
 Archived field records can be used to assess the effectiveness of the soil fertility program and pest strategies.
For example, if the soil test P values have increased from 20 to 30 ppm over the past 10 years, consider reducing the P application rate.
Archived field records will also provide critical information needed to select an appropriate hybrid and plant population and areas where specific pests have, in the past, been problematic.
Selecting a Corn Hybrid
 Selecting the most appropriate hybrid is complicated by the release of new products with different traits or trait combinations.
This means that varieties seeded last year may not be available or the best choice
 for next year.
Corn hybrids are often classified as "racehorses," "workhorses," and "defensive." Racehorse hybrids produce relatively high yields under good and excellent conditions but low yields under poor conditions.
Workhorse hybrids produce good yields under highand low-yielding conditions.
However, the maximum yield for these hybrids in the best conditions is often below the yield potential of the racehorse hybrid.
Defensive hybrids produce relatively high yields under poor conditions but lower yields than racehorse or workhorse hybrids under good conditions.
Variable-hybrid seeders provide the opportunity to replace workhorse hybrids that are typically uniformly sown across a field with defensive hybrids sown into low-yielding areas and racehorse hybrids sown into high-yielding areas.
Determining the Plant Population Rate
 Corn grows taller and produces a larger ear and thicker stalk when grown at low populations and has the opposite response at high population.
This observation suggests that lodging can be partially solved by decreasing the seed rate.
However, the population must be matched with water availability because if water is limiting, especially during the early reproductive stages, portions of the ear or whole ears may be barren.
Too high of a population can result in poor root development that will increase the chance of lodging.
Examples for calculating site-specific corn seeding rates are provided in Chapter 8.
Corn's growth in high populations also provides an opportunity to increase yields by reducing 30-inch row spacing to narrower rows, such as 20-inch spacing.
The 30-inch row spacing was developed to: 1) allow for traffic of field equipment during in-season management of nutrients and pests, 2) reduce disease problems, and 3) match rows to harvest equipment.
The advantages of narrow row systems include rapid closure of the canopy, reduced weed pressure, improved light interception, reduced evaporation, and less in-row crowding.
The primary disadvantages of narrow rows are increased risk of compaction, reduced opportunity for field cultivation, and difficulty in making in-crop applications of fertilizers and pesticides.
4.
Manage Plant Residues
 Managing residue is critical for optimizing seed germination.
Over the past 30 years, residue-management problems have increased because corn yield, and consequently, corn residue have doubled.
When returned to the soil, corn residue has helped South Dakota farmers increase soil organic matter  content of most fields.
Soil OM in cornfields of eastern South Dakota increased an average of 24% from 1985 to 2010.
However, the higher amounts of crop residues have complicated seedbed preparation, slowed soil warming, and contributed to a corn "yield drag" .
Techniques to reduce residue problems include:
 1.
Chopping the corn residue with a stalk chopper or chopping combine header.
Combine corn headers often are integrated with stalk choppers that have enhanced capacity to chop residue.
Chopping residue helps improve stand uniformity and yields.
2.
Adopting tillage techniques that minimize contact between the seed and the surface residue,.
3.
Harvesting and baling residue after grain harvest.
This technique has been widely adopted in the recent past.
However, problems with soil erosion, soil organic matter reduction, and nutrient deficiencies should be considered when deciding whether to harvest residue or how much to harvest.
Baling residue may also have the benefit of helping the soil warm up.
5.
Proactively Manage Water
 Over the past 40 years, corn yield increases in eastern South Dakota have been linked to improvements in water-use efficiency.
For example, corn WUE was 6 bushels per acre-inch of rain in the 1950s, whereas in 2012 the water-use efficiency was over 9 bushels of grain per acre-inch of water.
New hybrids are being developed that are expected to further improve WUE.
The location and magnitude of water problems are predictable in each field.
Upper landscape positions  are often limited by too little water, whereas lower landscape positions  are frequently limited by too much water.
In addition, rainfall generally decreases from the east to west in South Dakota.
If yields are limited by too little water, reducing the tillage intensity, installing
 irrigation, and/or planting drought-tolerant hybrids may increase yields.
Irrigation is costly and in many areas high-quality water suitable for irrigation is not available.
Additional information on irrigation is available in Chapter 33.
If water is available, proper permits from the South Dakota Department of Water and Natural Resources must be obtained.
In addition, an economic assessment should be conducted prior to installing a system.
A general rule of thumb is that to pay for the irrigation costs, the irrigation water must produce a 50 to 70 bu/acre annual increase in corn grain yield.
Glaciation on the eastern side of the state has produced rolling topographies, and many fields contain troughs between the hill slopes.
Drainage and grass waterways have been used to reduce ponding and erosion in these areas.
Additional information on drainage is available in Chapter 30.
In areas where too much water limits crop growth , the installation of drain tile can increase yields from near zero to match a field's highest yielding areas.
Fundamental differences between drainage in South Dakota and surrounding states include:
 1.
Most South Dakota fields do not have a designated drainage ditch, therefore discharging drainage water can be legally challenging.
2.
South Dakota has many sodium-affected soils where tile drainage can contribute to the conversion of productive soil to nonproductive soil.
Historically, tillage was conducted to prepare a seedbed and help manage excess water.
Tillage reduces plant available water 2 to 3 inches annually.
To save water, tillage should be minimized and the amount of crop residue on the soil surface increased.
6.
Improve the Soil Nutrient Program
 Each nutrient has unique chemical reactions that impact its availability.
Some negatively charged nutrients.
Soil testing has been used to assess the relative amount of nutrients available to the plant.
In a general sense, soil test results provide an indication of the probability of a response to added fertilizer.
If the soil test value is low, then the likelihood of a positive yield response is high.
When considering soil test P levels, it is important to remember that soil nutrient levels are highly variable across a field and that even if the average soil test value for a composite sample is very high, there may be large portions of the field that would be considered deficient.
For example, if 10 soil cores are composited across a field and 2 cores  have a soil test P level less than 10 ppm, the average could still be 20 ppm P or greater if the other 8 cores have medium, high, or very high values.
These low soil test areas would benefit from P application, whereas the high and very high testing areas would not.
Many farmers use precision grid sampling to help define this variability and areas where nutrient application would or
 Nutrient	Dominant	species	in soil	Leaching	potential	erosion	Loss	with	Gaseous	losses	Transport	to root	Reactions	within	plant	Deficiency	symptom	as capital	Consider	expense
 N	NO3	high	moderate	low	mass flow	mobile	yellowing	no
 N	NH4+	low	high	high	diffusion	mobile	yellowing	no
 P	H2PO4	low	high	none	diffusion	mobile	dark green/purple	yes
 K	K+	low	high	none	diffusion	mobile	dark green with necrosis	yes
 Mg	Mg+2	low	high	none	diffusion	mobile	green-yellow with	yes
 S	SO	moderate	low	low	mass flow	moderate	uniform pale yellow	no
 would not be profitable.
Scouting, tissue sampling with laboratory analysis, or remote sensing, through aerial, satellite or drone technologies, may be used to better assess the effectiveness of the nutrient program.
The effectiveness of the transport process is dependent on the mobility of the nutrient.
For mobile nutrients, deficiency symptoms are first observed in older vegetation, whereas for immobile nutrients, the deficiency symptoms are first observed in younger vegetation.
The mobile nutrients are N, P, K+, and Mg, whereas B and Ca are considered immobile.
Nutrients that are moderate mobility include Cu, Fe, Mn, Mo, S, and Zn.
During a plant's reproductive growth stages, the nutrients contained in the grain increase from zero at tasseling to accounting for over 50% of the N and P contained in the plant at black layer .
Figure 1.2 Relative corn response to increasing soil K and P levels.
Theoretically, long-term nutrient sustainability requires that nutrient removal be balanced with nutrient supply or resupply.
A 300 bu/acre corn crop contains approximately 404 lbs N , which is supplied by the soil and supplemental fertilizer applications.
When nitrogen fertilizer is applied, there is a potential that a portion can be lost through volatilization or leaching.
Using products that slow urea hydrolysis or nitrification can reduce N losses under some conditions.
Table 1.3 Nutrients removed in corn, soybeans, and wheat.
Crop	unit	N	P2O5	K2O	Mg	S
 lbs/unit	lbs/unit	lbs/unit	lbs/unit	lbs/unit
 Corn grain	bu	0.90	0.38	0.27	0.08	0.08
 Corn stover	ton	16	5.8	40	5	3
 Corn silage	ton	9.7	3.1	7.3	2	1.1
 Soybean grain	bu	3.8	0.84	1.3	0.21	0.18
 Soybean stover	ton	40	8.8	37	8.1	6.2
 Wheat grain	bu	1.5	0.6	0.34	0.15	0.1
 Wheat straw	ton	14	3.3	24	2	2.8
 To grow 300 bu/acre corn, most agronomists believe that soil phosphorous and potassium levels should be in the very high soil test category.
In South Dakota, very high soil test levels of P and K are > 16 ppm and > 161 ppm, respectively.
Sampling date and soil drying can impact soil test P and K values based on laboratory analysis.
Generally, nutrient concentrations are lower in the fall following harvest than in the spring following a period of recharge.
In addition, drying and grinding a soil sample can increase the amount of extractable K.
When considering raising the soil test results, on average  approximately, 20 lbs of P2 2 acre are needed to increase the soil test P value by 1 ppm, whereas 12 lbs of
 K2O/acre are needed to increase the soil test K value by 1 ppm.
In most fields, P leaching through the soil to groundwater is not a problem.
However, if the soil P levels are extremely high or the soil has a sandy texture, leaching can occur.
Environmental impacts can generally be eliminated by band injecting the P fertilizer into the soil or incorporating surface applied P into the soil.
However, in South Dakota, it is not recommended to apply P, either as fertilizer or manure, if the Olsen soil test value is > 100 ppm.
During grain harvest , secondary  and micronutrients  are also removed from the field.
Mass balance dictates that for long-term sustainability, these nutrients must be returned.
Even though South Dakota research has not consistently documented the need for these nutrients, many farmers routinely supply micronutrients.
Recent research suggests that drought stress can result in the down expression of many genes associated with nutrient uptake.
These findings suggest that if nutrient levels are low, plants may respond to micronutrient fertilizers in water-stressed areas  due to greater availability.
Summit/shoulder areas also may have experienced high soil erosion rates, which would reduce the topsoil depth, water-holding capacity, and nutrient-supplying ability of the soil.
The plant population and nutrient applications need to be well-managed to optimize yield.
7.
Use Proactive Management for Weeds, Insects, and Diseases
 Scouting and mapping pest infestations provides valuable information for improved management.
Preventative measures, such as cleaning equipment, should not be skipped in the interest of time as new infestations often can be traced to poor sanitation.
To prevent the development of pests that are resistant to chemical control mechanisms, rotate the control approaches.
Weeds present during the critical weed-free period of corn growth  can irreversibly reduce corn yields.
These yield reductions are not necessarily caused by plant competition for water, nutrients, and light but rather by a reduction in the plant's photosynthetic capacity.
To minimize these losses, pre-emergence compounds should be applied to minimize early weed development and supplemental post-emergence herbicides should be applied if further control is needed.
Since early planting is often recommended to maximize yield, fungicide and insecticide seed treatments are also recommended.
Combining appropriate genomic traits and good agronomic practices with pesticide solutions for weeds, insects, and disease control is also encouraged.
8.
Prepare and Calibrate Field Equipment
 Many agronomists believe that the most important machine on the farm is the planter and that it must be in perfect condition to obtain top yields.
Assessing seed population and spacing between adjacent seeds within a row can help determine planter efficiency.
The desired and measured population should be similar, and in a general sense, decreasing seed spacing variability improves yield.
Over the past several years, planter improvements in seed singulation, seed delivery, depth of placement, and opener technology have improved planter efficiency.
It is recommended that planters be tested and calibrated annually by a knowledgeable planter mechanic.
Fertilizer and pesticide applicators also need to be calibrated.
Maladjusted sprayers can apply either too little or too much in different portions of the field.
If the rates are too low, the chemical treatment may not work, whereas if the rates are too high, yields may be reduced.
Combines that are not properly adjusted can result in grain that is left on the field.
A rule of thumb is that 2 kernels of corn/ft2 or 5 soybean seeds/ft2 on the ground behind a combine amounts to a 1 bu/acre harvest loss.
Techniques to minimize grain losses include: 1) driving at an appropriate speed, 2) measuring yield losses and making appropriate adjustments, 3) using a reel speed  that is 10% to 25% faster than the combine speed, and 4) harvesting the crop at an appropriate moisture content.
Guidelines and Additional Resources
 Tips for ensuring that your pivot is operating in an ideal pressure range :
 Obtain a sprinkler package for your pivot and ensure its proper installation
 Ensure the pump and pivot are properly matched and ensure that engine and pump speeds are correct for the required voltage and pressure
 Operate the system when crops are small and inspect for broken or plugged sprinklers and regulators, as well as leaks
 Buy a good pressure gauge and operate the pivot at design pressure
 Install an additional pressure gauge at the distal end of the pivot, periodically checking the gauge at the highest elevation.
The pressure should be at least the required regulator inlet pressure, which is 5 PSI above the pressure regulator rating.
I personally measure about 125 wells out of about 5,000, Young said.
Last year, there were six that I attempted to measure where, as you were driving up to it, you could look down the road and it was just water.
You couldn't even see the wells sticking out of the ground.
The flooded areas may have been underrepresented in this year's report.
This year, several hundred wells that we normally measure, particularly in Kearney County, around Fremont and some other hard-hit areas, didn't get measured.
Watershed Prioritization for Managing Nonpoint Source Pollution in Arkansas
 The Arkansas Natural Resources Commission  administers programs aimed at protecting water resources on behalf of the state.
These efforts include programs that address soil and water conservation, nutrient management, water rights, dam safety and water resources planning and development.
When establishing policies and regulations, it is often necessary to identify priority areas where much of ANRC's focus will be directed.
For the state's Nonpoint Source  Pollution Management Program, the agency identifies priority watersheds with the input of engaged stakeholders and federal guidance.
NPS pollution is caused by rainfall or snowmelt moving over and through the ground.
As the runoff moves, it picks up and carries away natural and human-made pollutants, finally depositing them into lakes, rivers, streams, wetlands and even underground sources of drinking water.
ANRC receives federal assistance each year from the Environmental Protection Agency  to fund projects associated with the abatement, reduction or control of NPS pollutants.
Using the NPS Management Program Plan and federal guidelines as a guide, the NPS management plan currently targets eight-digit watersheds for project spending.
The agency's prioritization process and recent efforts to administer the program are explained in this fact sheet.
What are eight-digit watersheds?
The EPA defines a watershed as "the area of land where all of the water that is under it or drains off it goes into the same place."
 Watersheds are classified based on their drainage area using the Hydrologic Unit Code  system developed by the United States Geologic Service.
The HUC system classifies watersheds in four levels using two to 12 digits to identify a unique area of the watershed.
The greater the number of digits there are, the smaller the watershed area being described.
For example, the eight-digit HUC "11010012" refers to the Strawberry Creek watershed , while the 12-digit HUC "110100120201" refers to the Greasy Creek subwatershed  within the Strawberry Creek watershed.
1
 Figure 1.
Eight-digit hydrologic unit code  boundaries in Arkansas
 Why use a watershed prioritization approach in developing management plans?
Several watersheds in Arkansas are considered impaired because of nonpoint pollution and are unable to support their designated uses.2 Financial or staff constraints typically limit the ability of agencies to fully rehabilitate these impaired watersheds.
Sometimes, political considerations also influence the choice project selections.
Different states use a variety of methods for prioritizing watersheds.
In Arkansas, a science-based process with meaningful stakeholder involvement was developed to help identify critical watersheds for NPS program planning purposes.
This process is meant to ensure proper resource utilization and minimize political influence in project selection.
Why use a watershed-based approach in addressing nonpoint source pollution?
Implementing nonpoint source pollution programs at the watershed level has been a goal of the nation's NPS pollution management plan from its inception.
Section 319 of the Clean Water Act states: "A state shall, to the maximum extent practicable, develop and implement a management program
 under this subsection on a watershed-by-watershed basis within such state." 
 In 1997, the EPA increased its commitment to watershed implementation with the publication of Picking Up the Pace.
The strategic plan included policies on "targeting risk" or tasks that would help prevent or address nonpoint source pollution.
The guide called for enhancing the total maximum daily load  program by creating tools and establishing best practices, helping states identify water quality standards and improving identification of water impaired by nonpoint sources.
Supplemental guidance for the program published that year said that states are to use "a balanced approach that emphasizes both statewide nonpoint source programs and on-the-ground management of individual watersheds where waters are impaired or threatened".
In the years since, the EPA has strengthened its stance on the use of the incremental funds for restoration of impaired waters.
In 2003, supplemental grant guidance issued for section 319 grants indicated that the spending priority would be on nonpoint source programs implemented expeditiously to achieve the goals of the Clean Water Act.
Programs included the restoration and maintenance of the chemical, physical and biological integrity of waterways.
To achieve this objective, the guide places top priority on implementing on-the-ground measures and practices that will reduce pollutant loads and contribute to the restoration of impaired waters.
How are Arkansas' watersheds prioritized?
ANRC follows an established process to allocate its incremental Section 319 funds for the development and implementation of watershed-based plans designed to restore impaired waters identified under Section 303 of the Clean Water Act.
In 2004, the Ecological Engineering unit of the University of Arkansas Department of Biological and Agricultural Engineering initiated the development of a qualitative risk assessment-based prioritization approach for Arkansas watersheds.
On behalf of ANRC, an NPS Task Force was established with representatives from state and federal agencies, commodity and industry trade groups, environmental organizations, soil and water conservation districts and other interested individuals.
Through a series of meetings and facilitated discussions, the task force identified 11 risk categories and subcategories that should be statewide priorities of a NPS program.
The risk categories were based on either readily available data or derived from available datasets.
The importance or weight of each category/subcategory was determined through discussions with the task force.
The available data for each selected category/subcategory was compiled in a geodatabase, a database designed to store and query geographic information.
Finally, a risk matrix was developed that tied together weights for all the categories on an eight-digit HUC watershed basis.
Subsequently, watersheds were divided into quintiles according to the values assigned by the matrix.
ANRC's executive director then selected eight watersheds from the top quintiles as the agency's priorities.
Data in categories one through four are updated on a two-year cycle using biennial water quality inventory data published or compiled by the Arkansas Department of Environmental Quality.
This is the most frequently updated data in the risk matrix.
The other data in the matrix is updated when new information becomes available.
The watershed prioritization risk matrix used for the draft 2011-2016 NPS Pollution Management Plan was based on the 2010 biennial water quality inventory published by ADEQ.
As a result of these deliberations, the current risk matrix consists of 12 categories/subcategories, compared to 11 that were used for ANRC's previous plan for years 2005-2011 [Figure 2].
1.
Water body impairment
 2.
Designated use impact
 9.
Livestock and pasture
 12.
Priority of neighboring states
 Figure 2.
Schematic of the geodatabase used to prioritize eight-digit watersheds in Arkansas
 Figure 3 shows the categories and their assigned weights for the watershed prioritization risk matrix used in developing Arkansas' 2011-2016 NPS Pollution Management Plan.
How is the priority for a watershed calculated within the matrix?
For the purposes of Arkansas' 2011-2016 NPS Pollution Management Plan, the state's 58 eight-digit watersheds have been scored using 12 different categories and subcategories, with each watershed receiving a score between 0 and 10.
While some categories receive scores on a scale of 0 to 10 , scoring for other categories is arrived at using a formula based on watershed-specific information.
The source and link to data layers used for each category is provided in Table 1.
The continuous categories are first assigned a percentile score between 0 and 1, which is then multiplied by 10 to provide a score between 0 and 10.
Weights for each category are discussed annually during a NPS stakeholder meeting to arrive at a consensus.
The formula used for calculating the priority rankings for eight-digit watersheds is as follows:
 = Value of category 1 * Sum of the weights for categories 2 through 12
 What is the ARWAP tool and why was it developed?
The Arkansas Watershed Prioritization  tool was developed to improve understanding of Arkansas' eight-digit watershed prioritization process, to increase collaboration and to make watershed prioritization more accessible to stakeholders [Figure 4].
This desktop-based computer tool uses a spatial database and user-defined weighting to identify watersheds that are at greater risk for nonpoint source pollution.
Various watershed data layers in Arkansas on the eight-digit hydrologic unit code
  scale are built into the spatial database, based on the 2008 iteration of the Arkansas watershed prioritization approach [Figure 2 and Table 1].
Users are allowed to interactively adjust weighting for these layers to instantaneously visualize priority watersheds.
ARWAP seeks to educate current and new users and to create transparency in the process of designating and allocating greater resources to a few watersheds in Arkansas.
How can the public obtain and use the ARWAP tool?
The ARWAP tool can be obtained by contacting Tony Ramick, Nonpoint Source Program manager at the Arkansas Natural Resources Commission.
He can be contacted by calling 501-682-3914 or by e-mailing tony.ramick@arkansas.gov
 The tool comes with a user's manual containing step-by-step instructions for installing the program on the desktop.
Once installation is complete, the tool allows the user to adjust the weight each category/subcategory holds and evaluate possible "what if" scenarios [Figure 5].
For example, Figure 3 shows the default weight for subcategory le  as 5, while the default weight for 1d  is 2.
What if the user feels 1d is of more priority than le?
The user can simply adjust the base weights of 1d and le, recalculate the risk matrix with the new weights and reprioritize the watersheds.
Figure 4 shows a screen capture of the ARWAP tool showing Category 1.
The user can select any of the six tabs on this tool titled Category 1, Category 2, Category 3, Category 4, Category 5-8 and Category 9-12 to adjust the weights.
Finally, using the Display tab, the user has the option of visualizing and printing a customized map of the priority watersheds.
Figure Arkansas' prioritize assigned of weights used and chart Flow categories watersheds 3.
to
 prioritization of location in used Source Arkansas layers watershed data Table and 1.
Source Data	ADEQ*	ANRC	ADEQ	ADEQ	ADEQ	ADEQ	Various	U.S.
Census	Bureau	CAST	CAST	AOGC	ADEQ	USDA	CAST	USDA	AHTD	Various	ANRC
 Description	body Water	impairments	Nutrient sensitive	watersheds	Water use	impairments	Environmentally	sensitive waters	Extraordinary	waters resource	Biotic impacts	Human exposure	Urban/suburban	population	surface Impervious	Change in economic	activity	development Shale	Other economic	activity	Cropland	Pasture	Livestock	Unpaved roads	Forestry	Neighboring state's	priority
 f a-d,	e	f a-c,	d	e	a-e	a-d	a	b	C	a	b	a-C	a-b
 1	2	3	4	5	6	7	8	9	10	11	12
 of Commission; Resources Transportation Highway Environmental and Arkansas Quality; State Arkansas *ADEQ Arkansas Natural Department Department; AHTD ANRC = = = for Spatial Technologies; Oil Commission; Advanced Arkansas of CAST Agriculture.
Gas and AOGC Center Department U.S.
USDA = = =
 12 categories across 6 tabs
 Figure 4.
Arkansas Watershed Prioritization  tool user interface
 Figure 5.
ARWAP tool's procedure to test a "what if" scenario
 The University of Arkansas Division of Agriculture's Public Policy Center provides timely, credible, unbiased research, analyses and education on current and emerging public issues.
Printed by University of Arkansas Cooperative Extension Service Printing Services
For soybean at R6, days until maturity is 18 and water use to maturity is 3.5 inches.
If today was 08/26, the date that soybean is at maturity would be 09/13.
If the soybean experiences weekly rainfall in August in Hitchcock county, it would have a 0.5 inches expected rainfall.
If the soybean experiences average daily rainfall in August in Hitchcock county, it would have a 0.071 inches expected rainfall.
It would have an expected number of 6 days of rainfall in August.
The rainfall in august would be 0.43 inches.
The weekly rainfall in September would be 0.4 inches.
The average daily rainfall in September is 0.057.
The number of days in September that there is rainfall is 13.
The rainfall in September is 0.74 inches.
Rainfall to maturity would be 1.17.
In a scenario with soybean at R6 in silty loam soil, the holding capacity at the top 4 feet of soil is 8.0 inches.
The maximum allowed soil water depletion based on 60% is 4.8 inches.
The crop water to maturity is 3.5 inches.
The total rainfall to maturity is 1.17 and the final soil water available is 2.47 inches.
INFLUENCE OF NOZZLE PLACEMENT ON CORN GRAIN YIELD, SOIL MOISTURE, AND RUNOFF UNDER CENTER PIVOT IRRIGATION
 Maximizing irrigation efficiency is of enormous importance for irrigators in the Central Great Plains to conserve water and reduce pumping costs.
High temperatures, frequently strong winds and low humidity increase the evaporation potential of water applied through sprinkler irrigation.
Thus, many newer sprinkler packages have been developed to minimize water losses by evaporation and drift.
These systems have the potential to reduce evaporation losses as found by Schneider and Howell.
Schneider and Howell found that evaporation losses could be reduced by 2-3% as compared to above canopy irrigation.
Many producers and irrigation companies have promoted placing sprinklers within the canopy to conserve water by reducing the exposure of the irrigation water to wind.
However, runoff losses can increase as the application rate exceeds the soil infiltration capacity with a reduced wetted diameter of the spray pattern within the canopy.
Schneider and Howell  found that furrow dikes were necessary to prevent runoff with in-canopy irrigation.
In 2003 and 2004, a study was conducted comparing sprinkler nozzle placement near Burlington, Colorado in cooperation with a local producer.
The objective of this study was to determine the impact of placing the sprinkler devices within the canopy upon soil moisture, runoff and crop yield.
A secondary objective was to determine the usefulness of in-season tillage on water intake and preventing runoff.
For this study, we utilized the current configuration of a center pivot irrigation system owned by our cooperating farmer.
This configuration included drop nozzles with spray heads at approximately 1.5 feet  above the ground surface.
The sprinkler heads on the seventh and outside span of the center pivot were raised to approximately 7 feet above ground level.
This nozzle height allowed for an undisturbed spray pattern for a majority of the growing season.
The sprinkler heads on the sixth span of the center pivot remained at the original height.
In 2003, the nozzles were raised by
 attaching the flexible drop hose to the center pivot using truss rod slings.
Because the farmer decided not to irrigate this field in 2003, we moved to an adjacent pivot in 2004.
We raised the pivot nozzles by replacing the drop hoses and 'j-tubes' on this system.
In 2004 the nozzle heights in the outside span were left at 1.5 feet above ground level and the next span into the field were raised to 7 feet.
Spacing was 5-feet between nozzles for both site-years.
For the 2003 growing season, three in-season tillage treatments were replicated three times under each of the sprinkler heights.
The three tillage treatments were cultivation, inter-row rip and basin tillage.
The cooperating farmer implemented the tillage treatments when the corn was at the V6 growth stage.
The tillage treatments were implemented in strips running the length of the field.
The field was planted perpendicular to the sprinkler direction.
In 2004, the cooperating farmer chose to use grow the corn crop using no-till and planted in a circular pattern.
Although we intended to implement the inter-row rip and basin tillage operations, it was prevented by wet weather in June.
Thus, the only tillage in 2004 was no-till.
The cooperating farmer conducted all field operations  during 2003 and 2004.
Runoff was measured on cultivation and basin tillage for 2 replications and both sprinkler heights in 2003.
Four-inch, V-notch furrow weirs were installed at the bottom of the 8-row plots.
The runoff for two 30-inch rows for the entire length of the pivot span  was directed into the weir by furrows created during the tillage treatments and by soil berms where needed.
The water level height in the stilling-wells of the weirs was recorded using auto-logging pressure transducers.
Because the cooperating farmer chose no-till for the 2004 season, we installed two 10-foot by 32-foot runoff plots using landscape edging.
Furrow weirs were installed on the lower end of the plots to measure runoff.
The soil type at both site-years was Kuma Silt Loam.
The slope was approximately 1 to 1.5 percent and was fairly uniform across treatments.
We measured soil moisture from mid-June through early September using a Troxler neutron probe at one-foot increments to five feet of soil depth.
A neutron access tube was installed in each tillage and nozzle height treatment in 2003 and six access tubes were installed in each nozzle height treatment in 2004.
Grain yields in 2003 were not significantly different for in-canopy and above canopy irrigation.
Statistically significant differences between tillage treatments were also not found.
However the yields for above canopy irrigation were consistently 4 bushels per acre greater than in-canopy irrigation within each tillage treatment.
This would indicate that moisture stress did not
 occur under either above canopy or in-canopy irrigation.
Grain yields for above canopy sprinkler placement were not statistically greater than in-canopy placement in 2003 as well.
However, grain yields averaged across tillage treatments over the two year period suggest that a potential trend of yield advantage for above canopy placement of sprinklers over in-canopy placement.
We plan to continue measuring grain yield and soil moisture at this site in 2005 to determine if this potential yield trend continues.
We measured declining soil moisture for both above canopy and in-canopy sprinklers during the 2003 growing season.
When comparing above canopy to in-canopy irrigation, changes in soil moisture were greater for in-canopy irrigation than above canopy.
The depletion of soil moisture was significantly higher for the in-canopy sprinkler placement than with above canopy sprinklers.
With similar yields, this would indicate that greater runoff losses occurred with incanopy irrigation since soil moisture usage offset reduced infiltration.
The greatest difference in change in soil moisture between above and in canopy irrigation occurred during early August when the difference was greater than 3 inches of soil moisture between the two sprinkler placements.
Differences in soil moisture usage at physiological maturity were 1.7 inches greater for in-canopy irrigation than above canopy irrigation.
Changes in soil moisture between tillage treatments in 2003 were not significantly different from each other within a sprinkler height during the growing season.
This would indicate that sprinkler height was the dominant factor in soil moisture content.
Contrary to 2003, soil moisture initially increased early in the 2004 growing season, declining after drier weather and higher ET rates began in July.
Soil moisture content initially showed a greater increase for in-canopy placement as compared to above canopy placement.
Much of this was due to the incanopy placement being drier at the beginning of the season and above canopy placement reaching field capacity in mid-July.
Most likely, deep percolation occurred in the above canopy placement while stored soil moisture increased for the in-canopy placement.
Changes in soil moisture for both in-canopy and above canopy placement were similar after July 27.
This was after the above canopy and in-canopy placement reached maximum stored soil moisture during the growing season.
Season long runoff under center pivot irrigation proved challenging to measure with the equipment available.
Due to inconsistent and unreliable readings from one replication of the data loggers installed on the weirs recording runoff, only one replication of the 2003 measurements was used for this paper.
Thus, runoff
 values provided in Table 3 should be considered estimates of the differences between the treatments.
Both sprinkler heights produced runoff in 2003 as the cooperating farmer often applied irrigation at a rate greater than the soil intake capacity.
Runoff was greater with in-canopy irrigation than above canopy for the conventional cultivation and basin tillage treatments.
Changes in soil moisture between sprinkler placement treatments closely agreed with runoff results collected for each placement.
Greater amounts of runoff between sprinkler packages were offset by greater soil moisture loss.
Runoff amounts were less for basin tillage as compared to cultivation.
The reduction in runoff was due to the increase in surface storage created by the implanted basins.
Although not measured, no or little runoff or signs of runoff was observed in the inter-row ripping tillage plots.
Only two significant runoff events due to irrigation, 1.1 and 0.89 inches of runoff, were recorded in 2004.
This was due to management changes made by the producer.
Irrigation depths in 2003 were 1.5 to 2 inches per application.
In 2004, application amounts were reduced to 0.7 inches per application.
This reduction in application depth reduced runoff in all but two irrigations where the producer applied higher amounts  per application.
Results from this study suggest that above canopy irrigation was more effective at increasing soil moisture and reducing runoff as compared to in-canopy irrigation.
Less runoff from above canopy irrigation in 2003 resulted in more stored soil moisture and similar grain yield than in-canopy irrigation.
In-season tillage such as basin tillage decreased runoff as compared to conventional cultivation.
Yields between tillage treatments were not significantly different, but a trend of yield increases was observed when soil intake rates were modified by tillage.
No statistically significant yield differences were observed when irrigation sprinkler nozzles were placed above the canopy and soil moisture differences between above canopy and in-canopy placement reflected the differences in runoff.
The results of this project suggest that sprinkler placement above a corn canopy would be preferable to placing sprinklers in-canopy unless significant changes in irrigation management practices occur.
Irrigated crop producers in the U.S.
Central Plains have come under pressure in recent years as groundwater levels have declined and energy prices have risen.
With the limitations on the amount of water available to irrigate, and the additional cost of pumping that water, many producers are trying to determine if they should change their irrigation practices, or perhaps stop irrigating altogether.
Making decisions such as these involves many variables and is therefore often complex.
However, there are some economic principles that can guide producers in making complicated decisions regarding irrigated crop production decisions.
The issues of declining water and rising energy costs undoubtedly are related in terms of decisions facing irrigators.
Certainly, both irrigators with maximum irrigation capacity, and those with diminished irrigation capacity face the issue of rising energy costs.
However, the impact of rising energy costs may be more acute with limited irrigation capacity as lower capacity wells require more energy to apply an inch of water than higher capacity wells.
In addition, the options producers with limited irrigation capacity have in terms of cropping options may be limited as well.
For example, low capacity irrigation wells may not be able to supply sufficient water during critical stages of crop production for certain crops.
Consequently, high water use crop may not be an option for some producers.
To address the issue of limited well capacity, two studies were started at the KState Southwest Research Center in Tribune, KS.
The first study is a limitedirrigation study that compares four crops  at three irrigation levels.
Average yields from 2001-2005 are shown in table 1.
Corn, which increased in yield from 114 bu/a with 5 inches of irrigation to 173 bu/a and 191 bu/a with 10 and 15 inches of irrigation, respectively, had the highest response to water.
The other three crops experienced yield increases from 21% to 28%  as
 irrigation increased from 5 to 10 inches.
On a percentage basis, all crops except sunflower had similar yield increases as irrigation was increased from 10 to 15 inches.
Sunflower actually had a small reduction in yield.
Table 1.
Average Yield at Three Irrigation Levels in Tribune, KS.
Crop	5 in	10 in	15 in
 Corn 	114	173	191
 Grain sorghum 	93	114	125
 Soybean 	30	39	42
 Sunflower 	1,547	1,872	1,821
 Table 2 shows the corresponding returns for each crop at each irrigation level.
The values in the table represent returns to land, irrigation equipment, and management based on average production practices, costs, and prices during the study.
At five inches of water, soybean had the highest average return at $35/a.
Corn, grain sorghum, and sunflower followed next at $31/a, $16/a, and $-9/a, respectively.
At 10 and 15 inches of irrigation, returns for corn more than double soybean, the next most profitable crop.
Table 2.
Average Returns  at Three Irrigation Levels in Tribune, KS.
Crop	5 in	10 in	15 in
 Corn	31	134	151
 Grain sorghum	16	31	31
 Soybean	35	61	57
 Sunflower	-9	0	-23
 The second study initiated at the Southwest Research Center in Tribune in 2003 is a limited-irrigation crop rotation study.
In this study, four rotations involving four different crops were limited to 10 inches of irrigation per rotation.
The rotations include continuous corn, corn-wheat, corn-wheat-grain sorghum, and cornwheat-grain sorghum-soybean.
Since corn has a higher response to water than wheat, in all the rotations that included wheat, the wheat crop was limited to 5 inches of irrigation water, while the corn crop in that rotation received 15 inches.
Continuous corn, and other crops in the rotation with corn and wheat received 10 inches of irrigation.
Average yields from the limited-irrigation rotation study are shown in table 3.
Continuous corn averaged 170 bu/a, while corn  in the other rotations averaged between 211 and 213 bu/a.
Wheat yields averaged
 from 32 to 34 bu/a across all rotations.
These yields were lower than expected, but were largely due to late spring freezes in 2004 and 2005 and stripe rust in 2005.
Yields for grain sorghum  and soybean  were similar to yields observed in the limited-irrigation study.
Table 4 shows the average returns for each rotation.
Continuous corn had the highest average return to land, irrigation equipment, and management at $111/a.
The other three rotations earned returns in the range of $66 to $73/a.
Table 3.
Average Yields in Limited Irrigation Rotations in Tribune, KS.
Crop	Corn-	Corn-	Corn-Wheat-	Corn-Wheat-
 Corn	Wheat	Sorghum	Sorghum-
 Corn	170	213	211	213
 Wheat	--	33	32	34
 Grain Sorghum	--	--	125	129
 * Each rotation is limited to average total of 10 inches of irrigation.
In the rotations containing wheat, the wheat crop receives 5 inches of irrigation, while the corn crop receives 15 inches, for an average of 10 inches across the rotation.
Table 4.
Average Returns  in Limited Irrigation Rotations in Tribune, KS.
Crop	Corn-	Corn-	Corn-Wheat-	Corn-Wheat-
 Corn	Wheat	Sorghum	Sorghum-
 Corn	118	185	204	208
 Wheat	--	-23	-27	-22
 Grain Sorghum	--	--	39	45
 Rotation	118	81	72	80
 Each rotation is limited to average total of 10 inches of irrigation.
In the * rotations containing wheat, the wheat crop receives 5 inches of irrigation, while the corn crop receives 15 inches, for an average of 10 inches across the rotation.
When water levels decline and energy prices increase, one of the first questions many producers ask is whether they should continue growing irrigated corn.
According to the two studies from Tribune, the answer to that question appears to be "Yes".
This is still the case with assumed irrigation pumping costs being 72% higher in 2005 than 2004.
However, every producer needs to run his own numbers as everyone's situation may be different.
For example, because of differences in well depths, or inefficient pumping or delivery systems, one producer's pumping cost per acre-inch may be significantly higher than another's.
Likewise, one producer's yield response to irrigation may vary from his neighbor's.
Therefore, it is critically important that producers understand the relationship between irrigation water and yield and other yield increasing inputs.
Only then can accurate economic comparisons of crops be conducted.
Arguably the biggest concern of crop producers in the Central Plains region is the issue of high energy prices.
This issue, of course, affects all crop growers, but impacts irrigators to a greater extent.
Consequently, all irrigators are asking questions that perhaps only producers with limited irrigation well capacities were asking in the past.
In addition to considering other crop options, producers are also considering planting high input crops, but cutting back on inputs such as seed, fertilizer, and irrigation water.
Historically, such practices have not always maximized profits.
Following is a discussion of the economic principles governing optimal use of fertilizer and irrigation water.
The economic principle guiding the use of yield increasing inputs such as fertilizer and irrigation water is the marginal cost equal marginal revenue  principle.
In other words profit will be maximized at the point where the cost of an additional unit of an input  equals the revenue associated from the use of the additional unit of that input.
In crop production, this principle would dictate that fertilizer and irrigation water should continue to be added as long as the benefit  is greater than the cost of adding another pound of fertilizer or acre-inch of irrigation water.
The greatest difficulty in determining the input level where MR just covers MC is knowing the relationship between crop yield and that input.
These yield response functions to fertilizer and irrigation water are necessary to calculate the economic optimum amount of those inputs to apply.
Fortunately, research has been conducted in Kansas to develop yield response functions for the major crops in Kansas.
This research has been used to generate adjustments to the KSU nitrogen recommendations to reflect current high nitrogen  prices.
It has also been incorporated into a spreadsheet that is designed to help producers determine which crop is most profitable for their operation.
In addition, KSU-Crop Budgets 2006.xl will help producers determine the economic optimum amount of nitrogen fertilizer and irrigation water to apply given their yield goals, expected fertilizer and irrigation costs, and forecasted crop prices.
The KSU-Crop Budgets 2006.xls spreadsheet and paper describing how the
 Table 5.
Economic Optimum Nitrogen Fertilizer and Irrigation Rates Based on Historical Energy Prices.
Wheat	Corn	Sorghum	Soybean	Sunflower
 Yield Goal	75	225	125	65	2,800
 Soil Test N, lbs/a	20	20	20	20	20
 Organic matter, %	2.0	2.0	2.0	2.0	2.0
 N price, $/lb	0.21	0.21	0.21	0.21	0.21
 cost, $/in	3.10	3.10	3.10	3.10	3.10
 lb/a	112	278	114	0	125
 irrigation, inches	12.6	17.1	12.8	16.6	15.0
 optimum	71.1	221.0	119.5	58.5	2,706
 Clearly, the historically high energy prices have an impact on crop production decisions.
Both optimal fertilizer N and irrigation rates decline as energy prices rise above historical averages.
However, the magnitude of the decline will depend on each producer's situation, so it is again important that every producer run his own numbers to determine the economic optimum N and irrigation rates for a given farm.
Table 6.
Economic Optimum Nitrogen Fertilizer and Irrigation Rates Based on Current Energy Prices.
Wheat	Corn	Sorghum	Soybean	Sunflower
 Yield Goal	75	225	125	65	2,800
 Soil Test N, lbs/a	20	20	20	20	20
 Organic matter, %	2.0	2.0	2.0	2.0	2.0
 N price, $/lb	0.40	0.40	0.40	0.40	0.40
 cost, $/in	6.50	6.50	6.50	6.50	6.50
 lb/a	67	225	67	0	83
 irrigation, inches	7.6	14.2	8.3	15.2	10.6
 optimum	59	209	103	59	2,420
 Current energy prices also have the possibility of impacting crop land lease arrangements.
How much a crop lease agreement will be affected will depend on the type of agreement, the terms of the agreement, and the magnitude of the cost increase.
While crop share leases are most common in Kansas, other types of rental arrangements have been increasing in use in recent years.
The most popular type of these leases include cash rental arrangements, and "net share" leases, which are basically crop share arrangements in which the tenant provides all crop inputs, but would receive a higher percentage of the crop than they would in a typical crop share arrangement.
Equitable crop share arrangements should follow five principles: 1) Yield increasing inputs  should be shared, 2) lease terms should be reviewed and technology changes, 3) crop returns should be shared in the same percentage as resources contributed, 4) tenants should be compensated for any unused long-term investments at lease termination, and 5) effective tenant-landlord communications.
In terms of managing rising input costs, principles 1 and 3 are particularly relevant.
If a crop share lease is equitable , then sharing the yield increasing input guarantees that it will be applied at the economic optimum.
In addition, sharing the yield increasing input guarantees that the lease will remain equitable regardless of the price of that input.
Table 7.
Effect of High Energy Prices on Equitable Crop Share Percentages.
Lease Scenario	Equitable Share % 
 Crop share not sharing irrigation with high
 Diminishing groundwater levels and rising energy costs have had a negative impact on irrigated crop production.
Producers have many decisions to make regarding crop selection and crop input use.
Research has been conducted to evaluate crop response to irrigation levels and alternative limited-irrigation rotations.
Results indicate that corn has a higher response to irrigation to produce
 higher yields and therefore higher returns in most situations.
Higher energy costs may impact optimal application rates for nitrogen fertilizer and irrigation.
Depending on the crop, yield goal, and soil test nitrogen, economic optimum fertilizer rates may decline by 10 to 30%.
When irrigation pumping costs are considered simultaneously, economic optimum fertilizer and irrigation rates may fall even more.
Crop share lease arrangement that share fertilizer and irrigation pumping costs will not be impacted by the higher energy costs.
Crop share leases that do not share fertilizer and irrigation pumping costs may need to be evaluated to determine whether any changes need to be made to the lease.
Likewise, cash rents may need to be evaluated to determine whether any adjustments need to be made.
With any of these issues, producers need to evaluate their situations individually, as what may be optimal for one situation may not be optimal for another.
KanSched An ET-Based Irrigation Scheduling Tool for Kansas Summer Annual Crops
 Gary A.
Clark, Professor Danny H.
Rogers, Extension Engineer, Irrigation Steven Briggeman, Extension Assistant Biological and Agricultural Engineering K-State Research and Extension Manhattan, KS 66506
 KanSched is a computer software program that is designed to help monitor the root zone soil profile water balance and schedule irrigation events on a field using evapotranspiration  data.
The program can also be used to monitor the soil profile water content of non-irrigated fields.
ET-based irrigation scheduling is a tool that can help you determine when and how much irrigation water to apply.
The basic process involves using data on crop water use , rainfall, and soil water storage to assess when an irrigation event is needed and how much water could be applied.
KanSched was developed to be user friendly with minimal training requirements and operational inputs.
This program was developed as part of the Mobile Irrigation Lab, which is supported by a partnership between K-State Research and Extension, the Kansas Water Office with State Water Plan Funds, Kansas Water Resources Research Institute, and the Kansas Corn Commission.
Irrigation scheduling that uses ET information is much like checkbook accounting procedures where the valued commodities are tracked.
In this case, soil water, rather than money, is the valued commodity and the debit is crop water use while credits are rainfall and irrigation.
One notable difference is that the water balance can be too high as well as deficient.
ETc, short for crop evapotranspiration, is the amount of water that a crop withdraws from the soil water reserve.
Deposits to the soil water reserve are rainfall and applied irrigation.
The major goal of the accounting procedure is to help the irrigation manager keep the amount of water in reserve above a minimum soil water balance level to prevent water stress to the growing crop.
The upper limit to the account is the amount of water that can be physically stored in the root zone area of the soil profile.
Deposits of water, once the upper limit is exceeded, result in the water being lost as either deep percolation or surface runoff.
Irrigation scheduling can help minimize deep percolation losses, although even the most rigorously followed schedule cannot prevent all losses since large rainfall events can exceed soil water storage capacity by themselves.
The benefits of irrigation scheduling generally translate into increased net returns
 through several possible avenues.
Irrigation scheduling may also reduce irrigation labor and equipment operation pumping cost, and may also result in improved yields due to less water stress or less loss of fertilizer due to leaching.
One of the major obstacles to adoption of on-farm irrigation scheduling has been the time management problem of gathering, processing, and implementing scheduling on a daily irrigation cycle period.
Computer technology presents the opportunity for information gathering, transferring, and processing to be done much more easily, efficiently, and sometimes automatically.
Scheduling software, communication, and control technology exists that can provide management recommendations which could then be remotely implemented.
This text will describe the basics of KanSched and illustrate some of the input windows and help screens.
Each time KanSched is started the screen in Figure 1 appears and the operator has several options to choose from depending on how the program is to be used.
Figure 1 The start screen of KanSched
 To initialize a new field, click the green button labeled "Start a new field".
A new window will appear displaying the input boxes for the initial field information and soil information.
The input screen will be discussed in detail later.
Figure 2 The input data screen of KanSched
 KanSched can be set up to allow quick entry of daily reference ET data for a group of fields that are in the same region with the use of the "Quick ET Update".
When an ET group is selected, the fields within the group can all be updated with ET values at one time.
Entering Information Into KanSched
 Before KanSched can begin tracking the field's soil water content and crop water usage, information about the soil type, growing season, and crop for each field are needed as follows.
The Input Screen
 The Input screen (Figure requires some information that characterizes the soil type, growing season, and crop type for a field.
All of the inputs on this screen must be entered before KanSched can track your field's soil water content and crop water
 usage.
If some of these values are unknown, simply click the question mark button in the lower right corner of the screen to obtain a help screen.
Help is available in any of the sections that become highlighted, and accessed by clicking on the question mark button associated with a section.
Help screens are available for soil characteristics, crop growth characteristics, and crop coefficients.
Soil Available Water Holding Capacity and Soil Permanent Wilting Point:
 The soil available water  holding capacity value is a measure of the maximum amount of water a soil can hold that is usable to the crop.
The soil permanent wilting point  value is the water content of the soil when the crop cannot pull the water from the soil, causing the plant to wilt.
Both of these values are measured in inches of water per inch of soil.
If these values are not known, simply click the help button in the lower right hand corner of the input screen to enable the help options, then select the help button in the soil characteristics section.
The help screen for the soil section is
 shown in Figure 3.
The soil's water holding characteristic value can be selected based on the soil texture from the drop-down list at the top of the screen.
The default values on this help page are from the NRCS soil characteristic database.
Figure 3 The Soil Help Screen
 KanSched needs to know the emergence date of the crop in order to start tracking water usage.
The emergence date is simply the date your crop emerges from the ground after planting.
Date to Start the Water Budget:
 The water budget start date is the date that KanSched will actually start tracking the soil water content.
This date must be after the emergence date.
Root Depth on the Start Date:
 KanSched tracks root growth throughout the season.
In order to do this, it must know the root depth on the date it starts the water budget.
This can be determined by going out to the field on the start day and dig around the crop to measure the root depth.
The root depth can also be set to the desired management depth at this time as well.
Maximum Managed Root Zone:
 Entering a maximum managed root zone lets KanSched calculate the maximum depth of the soil profile that your crop can draw water from.
While the actual root depth may be deeper, this value is the managed depth for the crop's roots.
Normally, managed root zone depth is 3 to 4 feet unless the root-depth is limited by restrictive soils.
Date the Crop Canopy Cover Exceeds 10% of the field area, Date the Crop Canopy Cover Exceeds 70-80% of the field area, Date when the Crop is at Initial Maturation, and Date of the End of the Growing Season :
 Figure 4 The Crop Date Help Screen
 The above dates are required by KanSched in order to monitor the growth stages of the crop and to create a crop coefficient curve.
Assistance with calculating these values is available using the help option in this section, shown in Figure 4.
Select the crop type, enter the season length and emergence date and press the Calculate Values button.
The calculated values are displayed at the bottom of the screen.
Click the "Use these values on the input page" button to automatically enter these values on the input screen; however, they can be adjusted later if needed.
Figure 5 The Crop Coefficient Help Screen
 The Initial Crop Coefficient, The Maximum Crop Coefficient, and The Final Crop Coefficient:
 To determine how much water the crop is using, KanSched uses crop coefficients.
The crop coefficient changes over the season; starting very small, increasing as the crop grows, peaking at the beginning of reproduction, then declining as the plant's water usage stops with maturation.
To gain assistance with calculating these values, enable the help options and click the associated question mark button.
The Crop Coefficient Help screen is shown in Figure 5.
Select the crop type and the reference ET system.
Management Allowed Deficit :
 The Management Allowed Deficit is the guideline on the percentage of the available water in the soil that will be removed by the crop before crop water stress is likely.
The MAD value will vary across different crops and according to how risk adverse a producer is a MAD of 50 percent is recommended for most row crops.
Initial Soil Water Availability:
 Before KanSched starts tracking your soil water content, it must have an initial value to start with.
The initial soil water availability is the percentage of available water to the crop on the budget start date entered earlier.
A value of zero  is associated with the permanent wilting point water content while a value of 100% represents a full profile at the field capacity level.
KanSched defaults to 100%, but this value usually needs to be changed to reflect the initial soil water value.
The Budget screen  consists of rows of input for each day.
These inputs include reference ET, rainfall, and gross irrigation.
When these inputs are entered into
 File Options ET Field Groups About
 KanSched	Monday, August 26, 2002
 Demo Field Budget Sheet	Current Field:
 Irrigation System Efficiency:	100	%
 Previous Day Values	Measured	Calculated	Soil Water
 Input	Ref ET	Crop ET	Rain	Irrigation	Gross	Availability	Soil Water	Availability	Soil Water	Above PWP	Content	Root Zone	Water	Effective
 Day 							Deficit 	Rain 
 6/25	0.22	0.16	55.3%	1.32	1.06
 Budget	6/26	0.15	0.12	1.00	92.7%	2.28	0.18	1.00
 6/27	0.23	0.18	85.6%	2.17	0.36
 6/28	0.24	0.20	78.3%	2.04	0.57
 Summary	6/29	0.25	0.22	70.8%	1.90	0.78
 6/30	0.23	0.21	64.0%	1.76	0.99
 7/1	0.05	0.05	63.3%	1.79	1.04
 Soil Water	7/2	0.08	0.08	0.50	78.8%	2.29	0.62	0.50
 Chart	7/3	0.17	0.17	73.5%	2.19	0.79
 7/4	0.23	0.24	66.3%	2.03	1.03
 7/5	0.22	0.24	1.00	91.5%	2.87	0.27
 Quick ET	7/6	0.24	0.27	83.3%	2.67	0.54
 Update	7/7	0.24	0.28	0.10	78.3%	2.57	0.71	0.10
 7/8	0.25	0.29	70.3%	2.36	1.00
 Figure 6 The Budget Sheet
 KanSched, it can track the soil water that is available to the crop.
The following sections describe the individual inputs needed and the program's output.
Using this information for a center pivot that is set to apply one inch of water per irrigation, the suggested recommendation would be that the system should be off for the next few days to use some of the remaining water.
The next inch of water should be applied within the next seven days.
Then, the next irrigation should be recalculated using updated soil water readings.
The best way to use the remaining water is to delay the start of the last few irrigations a few days each time and react to any rain that might occur during the period.
Slowly using the water in the lower portion of the root zone starting in early to mid-August is much better than keeping the profile full until the very end and expecting the crop to use the water all at once.
Average percent of fields by year fitting into the six categories.
The dry years 2020, 21 and 22 are different than the other years.
In 2022, out of 60 reports, 70% were ranked good, 8% were fair, 3% were wet late, 15% were wet early, 2% were wet all season, and 2% were very wet all season.
Effect of Irrigation Amount and Preharvest Irrigation Cutoff Date on Vine Water Status and Productivity of Danlas Grapevines
 Abdelaziz Ezzahouani1 and Larry E.
Williams2*
 Abstract: An irrigation study was conducted in a Vitis vinifera L.
table-grape vineyard in Morocco with vines receiving no applied water  or one of two applied water amounts with subplots composed of three irrigation cutoff dates: early cutoff  at berry set, late cutoff  at veraison, and no cutoff.
Midday leaf water potential , canopy temperature , and soil water content were measured in several of the treatments.
Midday was significantly correlated with soil water content , ambient temperature , and vapor pressure deficit.
The highest yield and berry weights were measured in TI vines followed by LC vines.
NI vines had the lowest soluble solids at harvest.
No significant differences were observed for fruit pH and titratable acidity among treatments.
A comparison of NI and TI treatments indicated that yields increased as T  and increased.
Under the conditions of this study, an average TC TA -2.5C or a , of MPa would be sufficient to maintain yield and fruit quality, while a value of -1.2 MPa would indicate water stress.
Estimated vineyard evapotranspiration was much greater than the amount of water normally applied to vines in this region, and values of , and temperature differentials indicated such.
However, since grapes produced in this region are destined for the early table-grape market, results indicate that vines could be deficit irrigated or water applications could be terminated at veraison without a significant yield loss.
Key words: grapevines, irrigation, leaf water potential, canopy temperature, water status, growth, yield
 Most studies conducted on grapevines have indicated that water deficits affect vegetative growth to a greater degree than fruit growth.
Therefore, it is important not to stress grapevines during canopy development to protect the berries from sunburn, particularly in hot grapegrowing regions.
Vegetative growth of grapevines is much more affected by water deficits than is photosynthesis.
After the canopy has developed sufficient leaf area, moderate water deficits can be imposed such that leaves remain functional while the rate of shoot growth is much reduced.
The degree to which berry growth is affected by water deficits depends upon the time when the water stress is imposed and the severity of stress.
Withholding water between budbreak and veraison resulted in a 60% reduction in the maximum berry weight compared with berries from nonstressed vines (Smart et al.
1974).
Berry growth is most susceptible to water stress during stage I of berry growth .
During this time cell division takes place in the berry , and the smaller size of berries is due to a reduced number of cells per berry.
Differences in vine water status before veraison has been shown to have no effect on the onset of veraison, while withholding water after veraison can delay the accumulation of soluble solids under severe water deficits.
An objective irrigation management strategy requires information on yield loss associated with quantified field water deficits and the ability to assess the adequacy of irrigation amount and frequency during the growing season.
Seasonal  water requirements  of a mature Thompson Seedless vineyard in the San Joaquin Valley of California varied from 700 to ~800 mm , depending on canopy size and how grapevines are farmed, such as for table-grape production.
Rainfall during the dormant portion of the growing season may provide 75 to 150 mm of the water requirement in semiarid grapegrowing regions depending on the timing of the rainfall, water-holding capacity of the soil, and rooting depth.
It is important to detect onset of vine water stress and subsequent decrease in turgor to a level that interferes with normal plant functioning in commercial vineyards.
There are various means of determining
 the water status of grapevines, such as the measurement of predawn leaf and midday leaf and stem water potentials; these methods are highly correlated with one another and with measures of soil water availability and leaf physiology.
It has also been shown that seasonal mean midday measurements of leaf water potential  and stomatal conductance  are highly correlated with yield of Thompson Seedless grapevines.
Numerous studies have used canopy temperature to detect water stress in crops, including grapevines.
Investigators have standardized this procedure by determining the difference in canopy temperature  with that of ambient temperature .
Throughout the greater portion of the daylight period, T TA was a linear function of vapor pressure deficit  for plants transpiring at their potential rate, irrespective of other environmental parameters except cloud cover and wind.
This linear relationship was defined as a nonstressed baseline.
As soil water was depleted from the root zone or as the evaporative demand increased, a point would occur where the crop could no longer transpire at its potential rate, and T TA versus VPD would be located above the non-water-stressed baseline.
In one study, canopy temperature of grapevines irrigated at various fractions of full ET differed throughout the day.
Vines that were not irrigated or deficit irrigated at 0.2 of ET had canopy temperatures greater than ambient temperature, while those given applied water amounts at full ET or greater had canopy temperatures less than that of ambient on a hot day.
Canopy temperature of vines irrigated at 0.6 of ET was equal to or slightly less than ambient temperature throughout the diurnal period.
It is unknown if similar results would have been obtained on cooler days.
It has been demonstrated that canopy temperature of grapevines was linearly correlated with soil water content.
Lastly, the Crop Water Stress Index , which uses the canopy/ambient temperature differential departure from the nonstress baseline, was linearly related to yield of Thompson Seedless grapevines.
This study was conducted to evaluate the effect of various irrigation treatments, applied water amounts, and strategies  on grapevine productivity in Morocco.
This study also correlated various methods of determining vine water status with climatic conditions to derive objective criteria to be used in a vineyard irrigation management scheme in this table-grape production region.
The study was conducted in a commercial vineyard located in Skhirate , south of Rabat,
 near the Atlantic coast of Morocco.
This region is known for its early production of table grapes.
Vitis vinifera L.
used in this study were 12-year-old Danlas grapevines grafted onto the rootstock 110R.
The vineyard soil was about 1 m in depth and composed of 70% sand, 6% silt, and 24% clay.
Vine and row spacing were 1.5 and 3.0 m, respectively, with a row direction northwest to southeast.
Vines were head-trained and pruned to four canes of 5 to 7 buds each.
The trellis system was a double T.
The lower cross arm was 0.4 m wide, and located 0.8 m aboveground.
The upper cross arm was 0.8 m wide, and located 0.4 m above the lower one.
The fruiting canes were tied to the wires on the lower cross arm and the current season's shoots were positioned over the uppermost wires.
The vines were drip-irrigated using pressure compensating emitters.
Four irrigation stratlegies were used in the study: no irrigation , early irrigation cutoff at berry set , late irrigation cutoff at veraison , and irrigation the entire season.
The TI treatment represented the amount of water the cooperator normally would apply to vines in the vineyard.
Within irrigated treatments, two applied water amounts were obtained by using different emitter sizes  rate, depending upon treatment, to the end of August, amounting to 108  and 120  L vine-1 in 2000 and 2001 for 4 L h emitter treatments and half that for 2 L h-Superscript emitter treatments.
Seasonal irrigation timing and length during an irrigation event was determined by the grower-cooperator.
Reference evapotranspiration  was estimated according to the Hargreaves and Samani  formula using weather data  obtained from an Institut Agronomique et Vtrinaire Hassan II weather station located 20 km from the vineyard.
The crop coefficients  used to calculate ET,.
Vine water status and soil water content were simultaneously measured over two growing seasons in selected treatments.
Soil samples from each block were taken weekly from the wetted zone to gravimetrically determine soil water content to a depth of 0.2 m.
Seasonal midday leaf water potential  was determined weekly with a pressure chamber as previously described.
Two to three leaves per replicate plot were measured on each sample date.
Canopy temperature  was measured with a hand-held infrared thermometer.
The infrared thermometer was held perpendicular to the upper portion of the sunexposed canopy for a distance of 3 to 4 m.
Readings were always taken with the sun behind the operator, care being taken not to include sky, soil, or clusters in the field of view.
Vapor pressure deficit  was calculated from ambient air temperature  and relative humidity determined with a ventilated psy-
 chrometer held 2 m above the soil surface.
The Crop Water Stress Index  was determined by a published empirical procedure.
The CWSI is the ratio of the deviation of the measured T TA from a lower nonstressed baseline to the range between the nonstressed baseline and a zero transpiration baseline at a given VPD.
The nonstress baseline in this study was determined with data collected from vines in the TI treatment  water application rate) early in the growing season both years, as the amount of water supplied by the cooperator to the treatments used in the study later in the season was considerably less than estimated ET During this time frame, the vines were still actively growing and it was assumed they were not stressed for water.
The equation for the nonstressed baseline was T TA = 0.80 3.25*VPD.
Shoot length was measured weekly in 2001 on the same eight shoots in each plot until the shoots were hedged the second week of May.
Cluster number and yield per vine were measured at harvest.
Samples of 100 berries per replicate were randomly collected and analyzed for weight, soluble solids, titratable acidity , and pH.
Pruning weights were measured during the dormant portion of the growing season.
The experimental design was a split-plot replicated four times with irrigation amount as the main plot and irrigation strategy as the subplots.
Each irrigation amount  was randomly established within each block down a
 single row with 24 vines.
Individual plots  consisted of six vines within an irrigation amount treatment row leaving two buffer vines between plots.
Data collected from the middle four vines were analyzed using analysis of variance and linear regression.
Mean separations were determined using the Student-NewmanKeuls test.
Means were averaged across years, as there was only one  significant year-by-treatment interaction.
Anthesis, berry set, and veraison occurred earlier in 2000 than in 2001, with harvest taking place one week earlier in 2000.
The mean March through July high and low temperatures in 2000 were 23.6 and 17.1C in 2000 and were 22.6 and 15.2C in 2001, respectively.
During the period between budbreak and harvest, rainfall amounted to 73 and 21 mm in 2000 and 2001, respectively.
Table 1 Dates of anthesis , berry set, veraison, harvest, and early and late cutoff for Danlas grapevines over a two-year period.
Year	Anthesis	Berry	set	Veraison	Harvest	Early	Late
 2000	Apr 18	May 04	Jun 29	Jul 14	May 04	Jun 29
 2001	Apr 12	Apr 21	Jun 09	Jul 07	Apr 21	Jun 20
Effects on pollinating corn: Drought stress 7-10 days ahead of silking can result in delayed silk development.
When combined with heat stress this delay could result in poor anthesis silking interval.
Water stress during pollination  not only delays silking, but also reduces silk elongation, and if severe, impedes embryo development.
With temperatures greater than 95oF, low humidity, and low soil moisture level, silks will desiccate or become non-receptive to pollen.
Pollen grains may also be damaged from desiccation when they are released for tassel anthers.
When temperatures greater than 100oF , pollen grains are killed.
Drought stress during pollination ultimately results in poor pollination and fewer kernels per ear.
Mobile Drip Irrigation 
 Mobile drip irrigation  drags drip tubing with in-line emitters behind a center pivot.
This paper describes the advantages and disadvantages of MDI and concludes that growers should consider MDI if they have inadequate water for non-stressed crop production and field runoff problems make it difficult for them to use low elevation spray application  or low energy precision application.
Figure 1.
Mobile Drip Irrigation  in an alfalfa field.
What is Mobile Drip Irrigation ?
Mobile Drip Irrigation  combines the high efficiency of surface drip irrigation with the flexibility, lower hardware costs, and convenience of center pivot irrigation.
In this system, the drip tubing is attached to center pivot irrigation systems to apply water directly to the soil surface as the driplines are dragged across the field and to create a uniform wetting pattern across the entire irrigated area.
MDI consists of heavy wall, in-line drip hoses in place of nozzles or sprinkler heads that are spaced at 20 to 40 inches apart.
The sprinklers can also be left in place in addition to the drip line in a dual-purpose setup that allows switching between sprinklers and drip.
This spacing is chosen based on the crop, the soil type, and the rooting depth of the crop.
The length of the dripline that drags behind the center pivot depends on the flow rate needed and the area that is irrigated
 during the movement.
The length of the dripline is increased with distance from the center pivot to apply more water similar to a center-pivot nozzle package.
Netafim, and Dragon-line are some companies that provide commercial MDI components and/or design services.
Netafim refers to their product as precision mobile drip irrigation  while Dragon-line is a tradename used by that company.
Figure 2.
An MDI system that uses rigid drops.
MDI is not a new technology.
Rawlins et al.
was the first to develop and test mobile drip irrigation in California.
MDI was later studied by additional researchers like Phene et al.
, Kanninen , Howell and Phene , and Helweg,.
These researchers found that MDI caused a reduction in foliar wetting, salt damage, and spray evaporation.
In the past 19 years, MDI has been modified and commercialized.
Now MDI is considering to be the most efficient method possible for irrigating with a moving irrigation system like a center pivot, linear move, or boom-cart system.
MDI Design, Installation and Costs
 MDI systems are designed by irrigation professionals with longer drip lines  towards the outer end of the pivot and shorter lines towards the center.
Installing the MDI system onto the center pivot is not complicated and most growers could do it on their own with a short training.
The required spacing between the driplines depends on the soil type and the crop, but usually needs to be between 20 to 40 inches.
Sandier soils and shallow rooted crops require closer drip-line spacing to avoid water stress in between drip lines.
Emitters usually have a 1 or 2 gallon per hour flowrate, and are spaced approximately every 6 inches on the driplines.
The spacing between the drippers can be varied to match the infiltration of the soil.
Soils with low infiltration rates  may need greater distance between the emitters to allow a
 greater amount of time for the water to infiltrate into the soil as the drip tubing is drug over the soil surface.
Shorter spacing between the emitters can be used on sandier soils.
Table 1.
A comparison of the different center pivot water application technologies.
Numbers are approximate and can vary significantly.
Wind Drift	Emitter	Wetted
 and	Height	Sprinkler	Length
 Evaporation	From Soil	or Drop	(Infiltration
 Pivot Configuration	Losses	Surface	Spacing	Time)
 Impact Sprinklers on Top of Pivot	40%	15 ft	20 ft	50 60 ft
 Mid Elevation Spray Application 	20%	5-10 ft	10 ft	30 ft
 Low Elevation Spray Application 	3%	1 2 ft	< 5 ft	15 ft
 Low Energy Precision Application 	0%	0 ft	< 5 ft	1 ft
 Mobile Drip Irrigation 	0%	0 ft	1.5 ft	Up to 65 ft
 There are various ways to connect MDI lines to pivots.
Which method is ideal depends on the types of crops in the rotation, row spacing, and row orientations.
For shorter crops, a manifold that is 3-4 feet from the ground can be used.
The driplines are connected to the manifold that is suspended from, and is fed water from the pivot.
Alternatively, this manifold can be attached to the truss rods  or attached to rigid drops.
These would be more flexible for taller crops.
Sometimes the water is fed through existing sprinkler drops that are left in place and functional to switch back and forth to help with crop germination.
The MDI system needs filtration sufficient for drip irrigation to prevent clogged emitters.
The additional filtration can create significant additional costs compared to the mid elevation spray application  or low elevation spray application.
It is recommended to plant the crop in circles and locate a drip line in between every row if possible to ensure equal water to all plants.
This avoids dragging the drip tubing over the crop rows and potentially damaging the crops.
However, circular planting can add additional cost to MDI management  and planting in straight rows is possible with some crops and MDI attachment configurations.
Figure 3.
The filters can be seen on the feed lines from the pivot pipe above.
Whole system filtration near the pump is recommended if the entire pivot uses MDI.
The ties used to keep the rigid drops vertical can also be seen secured to the truss rods.
The costs of an MDI system have been reported to be between $150-$200 per acre.
If converting from low elevation spray application  to MDI costs have been reported to be $250-$280 per acre.
Figure 4.
MDI installed on a center pivot while retaining the sprinklers for switching between MDI and MESA.
The driplines on the outside spans of the pivot are longer since it covers a larger area in the field.
Although the crop is wheat, the MDI system is set up for taller crops.
Reasons to Consider MDI
 There are several reasons why a grower might be interested in mobile drip irrigation.
These include water savings, reduced runoff, greatly reduced wheel tracking issues, and decreased disease pressure.
MDI is much more efficient than the most common MESA sprinkler configuration on center pivots.
The wind-drift and evaporation losses of MESA vary with the weather but can are average about 20%.
However, since MDI emitters deliver water directly to the soil surface, wind drift and evaporation losses are near zero.
MDI also does not wet the entire soil surface and some areas of the soil remain dry.
This results in a significant decrease in soil surface evaporation losses after the pivot has passed.
Because water is distributed by MDI over a longer time period and the soil has more time to absorb the water compared to MESA, and especially compared with LESA and LEPA, the runoff from MDI is significantly decreased.
MDI can also help eliminate the overwatering under the inside spans of center pivots and this can save up to 10% of total water distributed to the system.
A scientific and peer reviewed research study comparing center-pivot sprinkler irrigation to MDI in Germany found a 10-20% , and 25%  water saving by using MDI.
Another study in Kansas comparing LESA with MDI showed that the soil evaporation component of evapotranspiration from MDI was 35% lower than the in-canopy LESA nozzles.
This is because MDI does not completely wet the entire surface of the soil.
There were some trial reports presented by Jones in 2015 that found a 31% water savings of MDI trials in Colorado in 2014, and another trial that showed 50% more available soil moisture for crops in trials in Kansas in 2013.
In an alfalfa field in Oregon that compared MESA system with MDI, the resulting soil moisture graphs showed that the available moisture at 38 inches under MDI was significantly greater than for MESA.
Energy Savings.
Because MDI is more efficient it uses much less water.
In addition, MDI needs lower pressure than sprinklers to operate properly.
Lower pressure and run times can result in significant power savings.
Depending on the water source, power costs, and pump efficiency, these power savings alone may justify the conversion of a pivot to MDI.
Research studies showed that MDI resulted in energy savings of 20-70% , 40-50% , 70%.
Reduced Runoff.
One drawback to more efficient sprinkler configurations on center pivots such as LESA is that they have a small wetted radius and water is often applied faster than the soil can take the water in resulting in ponding and runoff.
In addition, the kinetic energy of sprinkler droplets as they hit the soil surface can break up the soil surface structure, create surface sealing and further decrease infiltration and lead to additional runoff problems.
MDI applies the water more slowly along the drip tube as it is pulled through the field.
Towards the end of a pivot sprinklers apply more water using larger nozzles and create potential runoff issues especially in those areas.
However, MDI drip tubing towards the end of the pivot is longer to apply more water making the application rate to the soil the same along the entire length of the pivot.
Many growers that have tried MDI have commented on the reduced runoff issues.
Some research studies have expressed the reduction in runoff in the field by using MDI.
Figure 5.
Shows how driplines move through the crop and how less surface area is wetted compared to sprinklers on MESA systems.
Reduced Wheel Track Rutting
 Center pivots are heavy, especially when they are full of water.
These create large pressures under the tires.
Increasingly deep wheel tracks are created as the pivot runs through the same track that is made muddy by the irrigating sprinklers.
However, because MDI tubing both drags behind the pivot to some degree, and because it applies water directly to the soil, it is easy to keep wheel tracks dry.
This greatly reduces frustrating problems with pivots becoming stuck in deep wheel tracks.
In 2017 at Umapine, Oregon one span of a pivot that was fully converted to MDI was left to run as MESA for comparison.
The wheel tracks in the MDI system were dry and shallow  compared to the MESA section.
In all research studies, MDI has resulted in significantly shallower and drier wheel track compared to the MESA, LESA and LEPA ; O'Shaughnessy and Colaizzi, ; Swanson et al., ; Kisekka et al.
; Okera et al.
; Yost et al ).
Figure 6.
As a test, even though MDI was available, the span on the left was left running MESA sprinklers.
Water ponding in the deep wheel tracks is visible.
The wheel tracks in the MDI spans on the right were shallow and dry.
Wet leaves encourage many different diseases including a wide variety of rots, molds, and wilts.
MDI does not get the leaves wet and instead the water is applied directly to the soil.
This can often result in decreased plant disease pressure and salt damage to the foliage.
Figure 7.
Using of MDI on alfalfa in Oregon in 2017.
MDI does not wet a significant part of plant canopy, which makes it easy to walk through and maintain the field as needed.
Common Questions about MDI
 Can the Pivot Pull the Tubing?
The drip tubing is slick and wet and slides easily over the soil and through the crop.
Pivot wheel drives can easily pull the tubing.
Even when the drip tubing is attached to the truss rods of the pivot, there were no apparent problems with tilting or excessive torque on the pivot structure.
However, it may be wise to be aware of times when the drip tubing may have frozen to the soil surface before starting the pivot.
Can MDI Adequately and Uniformly Irrigate?
Yes, if designed properly.
The most important design consideration is probably drip tube spacing, emitter flow rate, and length.
Putting the tubes too far apart can result in uniformity issues.
Okera et al., 2018 reported that MDI has higher distribution uniformity and application efficiency compared to the LESA and MESA.
The result of their studies showed that MDI spacing lower than 60 inches give great irrigation uniformity.
Can MDI increase the crop Yield?
Since MDI has higher uniformity compared to LESA and MESA it has the potential to increase yield.
There was no significant difference in crop yield, aboveground biomass, LAI, or water use efficiency in the research studies compared MDI, LEPA, or LESA ; O'Shaughnessy and Colaizzi ; Swanson et al.
; Kisekka et al.
, Okera et al.
).
In the studies that compared the MDI with the conventional sprinkler on the center pivot like MESA, higher crop yield was observed in the MDI treatments.
Potential Issues and How to Address Them
 Like most things, in addition to the benefits, MDI has several challenges.
Preventing plugging is a huge concern with any type of drip irrigation, including MDI, and needs to be managed.
Once drip tubing emitters are plugged there is little you can do except replacing the tubing.
In some studies, it was highly recommended to use the filtration system to prevent clogging in the drippers.
It is also recommended to open the ends of the drip tubes periodically to flush out sediment that may have gotten past the filters.
Striping or Water In Between the Tubing.
In sandy soils, with shallow rooted crops, or when the drip tubing is spaced too far apart the plants in between where the tubing drags through the soil may have less access to water than those directly underneath the drip tubing.
Figure 8.
The different green color strip in the peas field is because the spacing between the driplines is too great for this soil and crop.
The darker green means the crop is under water stress.
Tangling of the Tubing by the Wind
 The ability to efficiently apply water under windy conditions is a clear advantage of MDI over MESA.
However, the drip tubes can sometimes be blown next to the tower wheels and drive line.
When these wheels are rotating it can tangle the tubes around the wheels.
We recommend a little extra space next to the towers to prevent this and to reduce potential for wheel track rutting issues.
Reversing the pivot direction with MDI can tangle the lines.
Although, growers say that untangling the lines does not take long this can take additional time.
Growers also report that this has been much less of an issue when the drip tubing is full of water  than when the lines are empty and therefore light and less stiff.
Because of this, MDI may not work as well on a partial circle pivot.
Limited Ability to Chemigate the Foliage
 Fertigation  is simple with MDI.
However, there is limited ability to use MDI to apply foliar chemigation products
 because the crop canopy does not get wet.
If a grower needs to chemigate with the pivot, then leaving the existing MESA sprinkler system intact and operational will allow the conversion back to MESA for chemigation operations.
Crop germination of small seeded crops can be a challenge with MDI, especially on sandy soils and with greater drip tube spacing.
If problems with germination are anticipated, we recommend also leaving the existing MESA sprinkler system intact for this important development stage.
Crop Damage by Drip Lines
 Many growers report that even without planting crops in a circle they had no problem sliding MDI driplines through the crops and they were not pulling hard or damaging the crops.
Lines where the drip tubing slid through alfalfa were visible  but these lines did not persist through to the next irrigation event.
However, some growers in Texas mentioned that when the driplines were traveling perpendicular to the rows and being dragged over crop canopies there was limited damage to the leaves and crops , Olson and Rogers  and Kisekka et.
al.
).
It was unclear whether this caused measurable yield loss.
Figure 9.
Drip line trace after irrigation with MDI did not persist to the next irrigation.
Crops Planted in Beds or Hills
 Some crops, especially vegetables like onions or potatoes, are planted on beds or hilled rows.
There is a lack of data for MDI on these crops, but it is reasonable to expect that MDI can create some additional difficulties as the drip line placement relative to these rows and slopes in the row may cause local dry or wet spots.
Additional trials should be done with dripline spacing and placement relative to the rows as well planting straight or circular rows.
Figure 10.
This picture shows part of the field before the irrigation which shows no dripline trace in the crop.
Animal Damage to Tubing
 Some growers were concerned about dripline damage by wild animals.
Some studies in Texas observed animal damage to the tubing in some instances..
Mobile Drip Irrigation is an irrigation method that many growers could be benefitting from that are not.
MDI can get 10-25% more water to the soil per gallon of water pumped than traditional MESA sprinklers.
MDI has been found to use less water than LESA, and a similar amount of water compared with LEPA, and LESA has been shown to use about 18% less water than MESA.
In addition, there was found to be 35% less evaporation from the soil surface compared with LESA after the water was applied.
The primary benefit of MDI is that the water is applied more slowly over time, giving the soil more time to absorb the water.
This means that MDI will have less runoff than LESA or especially LEPA.
Growers should strongly consider MDI if they do not have enough water, and have runoff problems.
If they do not have runoff problems, then growers will likely be more interested in the lower cost methods of LESA or LEPA.
SOIL WATER SURVEY AFTER CORN HARVEST IN NORTHWEST KANSAS
 ABSTRACT.
A survey of available soil water after corn harvest was conducted in Thomas and Sherman counties, Kansas, in 1988, 1989, and 1990.
Soils in the region are deep, well-drained, silt loams in the Keith  or Ulysses  series.
Eighty-two randomly selected fields were sampled to a depth of 1.5 m  in 30-cm  increments at two locations within each field.
Each field was equipped with either a surface-irrigation or sprinklerirrigation system.
Available soil water  contents were found to be generally high, ranging from 31 mm  to 287 mm  for the 1.5-m  profile.
Within-field variation in ASW was higher for the surface-irrigated fields than for the sprinkled fields.
An analysis of data from a previously developed model to predict ASW in the spring based on available fall soil water suggested that preseason irrigation of corn should not be a recommended practice for the region.
Keywords.
Irrigation conservation.
I irrigated agriculture is the largest water user in northwest Kansas and, because of declining groundwater supplies, is under pressure to reduce water consumption.
One option to conserve water is to use management procedures that result in higher irrigation efficiency.
Declining water levels often cause reduced pumping capacity from wells, which some irrigators try to compensate for by using preseason irrigation.
Others use preseason irrigation as insurance against deficient soil water conditions at planting.
However, there is no need for preseason irrigation in corn production if irrigation scheduling procedures used by farmers leave a high level of water in the soil profile at harvest or over-winter precipitation is sufficient to recharge the crop root zone.
Irrigators often extend corn irrigation until late in the growing season, resulting in high residual soil water after harvest.
A limited survey in Thomas County, Kansas, in 1980 and 1981 indicated that soil water after harvest averaged 80% of field capacity.
A three-year study at Colby, Kansas , was conducted to determine the efficiency of water use of preseason irrigation and compared irrigation treatments applied in the fall , spring, and late summer , to a control of no preseason irrigation.
In 1982, the control, , did have lower available soil water  at planting, but
 Article was submitted for publication in March 1993; reviewed and approved for publication by the Soil and Water Div.
of ASAE in June 1993.
Presented as ASAE Paper No.
91-2560.
Contribution No.
93-171-J from the Kansas Agricultural Experiment Station.
ASW was still over 80% of field capacity.
No significant yield differences among treatments were noted.
Other studies in the region with corn  indicated no yield benefit from preseason irrigation, when in-season irrigation was sufficient.
A study by Lamm and Rogers  indicated that the need for preseason irrigation of fully irrigated corn in northwest Kansas is minimal because over-winter precipitation is generally sufficient to recharge the crop root zone to near field capacity.
Water quality has become an issue in many areas.
Low ASW at harvest could help reduce over-winter drainage losses and reduce residual pesticide and fertilizer losses to groundwater.
Soil water content could also have influence on surface water quality because excess soil water movement contributes to stream flow and high soil water content increases the amount of direct runoff.
The focus of this study was to quantify post-harvest ASW in corn fields of northwest Kansas.
An additional objective was to use the model developed by Lamm and Rogers  to demonstrate the need, or lack thereof, for preseason irrigation with various levels of ASW found in irrigated fields.
The study was conducted from 1988 through 1990 in Thomas and Sherman counties of northwest Kansas.
Lists of individuals with irrigation water rights were obtained, and names were selected at random to contact for permission to sample their fields in the fall after harvest.
A new random selection was made each year, since some fields are not in continuous corn.
The nature of the project was discussed with the individual growers and no one refused to cooperate.
Fields were sampled on 7 to 9 November 1988; 20 to 21 November 1989; and 10 to 12 December 1990.
The random selection resulted in
 34 surface-irrigated fields and 48 sprinkler-irrigated fields, which may reflect the distribution of system types in northwest Kansas.
The number of fields sampled were 28, 24, and 30 for 1988, 1989, and 1990, respectively.
All sprinkler systems in this study were center-pivots.
Soil samples were taken at two locations in each field in 30-cm  increments to a depth of 1.5 m  using a soil probe.
Surface-irrigated fields were sampled near the head and near the tail-end of the run.
Sprinkler-irrigated fields were sampled near the center of the outside span and near the center of the middle span, except in 1988, when only the outer sample was collected.
These samples were weighed, oven-dried, and weighed again to determine gravimetric water content.
This value was used to calculate the plant ASW for each sample and then totaled to obtain the profile ASW, based on representative soil information for the area.
The soils in this two-county area are predominately Keith  and Ulysses  silt loams, which are generally deep and well drained.
A 1.5-m  soil profile of these soils will hold approximately 250 mm  of plant-available soil water at field capacity.
The exact holding capacity of these soils will vary between locations and with depth with changes in density.
For the purposes of this survey, a constant bulk density of 1.2 was assumed.
Although this does introduce some uncertainty into the sampling, the objective of determining whether fields are left wet or dry is largely accomplished.
The annual precipitation data in all three years  was 2.5 to 7% below the 97 year mean value of 474 mm.
However, rainfall for 1988 and 1990 May through September corn seasons was near normal , and May precipitation for the same grow season in 1989 was 81 mm , or 25% above normal.
Corn water use requirements calculated at the Northwest Research Extension Center were 687, 575, and 592 mm , for 1988 to 1990, respectively, indicating that irrigation was required in each year to meet water-use demand of corn.
The ASW data for each irrigation system type for all three years are shown in figures 2 and 3.
The average ASW
 Table 1.
Growing season, non-growing season, annual and average precipitation for various years in northwest Kansas, NWREC, Colby, KS
 1988	1989	1990	97 Year Average
 mm 	mm 	mm 	mm
 May-Sept.
336 	403 	309 	323 
 1988 to '89	1989 to '90
 Oct.-April	54 	121		152	
 Annual	442 	463		460		474 
 is represented by the circle, the bar through the circle represents the range of the samples.
High levels of ASW remained in the profile after harvest, particularly in 1989 and 1990.
Available soil water in surface-irrigated fields varied more than in sprinkler-irrigated fields.
Table 2 also includes soil water variations expressed as a percentage.
The mean and standard deviation of variation of surface-irrigated fields are larger than for the sprinkler-irrigated fields.
A standard statistical t test compared ASW at the head and tail-ends of the surface-irrigated fields.
Based on this test, the null hypotheses of equal soil water levels was rejected at a significant level of less than 0.001.
A similar t test compared ASW for the center and outer spans of the sprinkler-irrigated fields.
There was not enough evidence to reject the null hypotheses of equal soil water levels at even a relatively low significance level of 0.35.
However, average values of ASW for surface and sprinkler-irrigated fields were similar regardless of the year.
A standard statistical t test compared the mean ASW for the two irrigation system types.
Based on this test, there was not enough evidence to reject the null hypotheses of equal soil water levels for the two system types at even a low significance level of 0.24.
Averaged across both irrigation system types and years, the ASW was 176 mm/1.5 m  or about 70% of field capacity.
Lamm and Rogers  developed an empirical model to predict spring-available soil water  based on the fall-available soil water  and winter precipitation :
 Figure 1-Monthly and average monthly precipitation for northwest Kansas, NMREC, Colby, KS.
Figure 2-Available soil water content of surface irrigated fields surveyed after corn harvest in northwest Kansas.
Figure 3-Available soil water content of sprinkler-irrigated fields surveyed after corn harvest in northwest Kansas.
SASW FASW +  P) 
 SASW FASW +  P) 
 where all variables are expressed in millimeters for equation 1a and in inches for equation 1b.
As with every empirical model, certain limitations exist.
Although the model should be reasonably valid over a wide range of precipitation amounts, any SASW value in excess of the allowable storage amount should be truncated back to an acceptable storage value for the soil.
At no or very low fall-to-spring precipitation the model would tend to overpredict SAWS, since some evaporation and precipitation losses would likely continue.
The average ASW across both irrigation system types was 186 mm  in 1989 and 197 mm  in 1990.
Using an FASW of 190 mm , a value similar to the soil water data collected in 1989 and 1990, and the mean December-through-May rainfall at Colby of 182 mm , the model predicted an SASW of 253 mm  or field capacity.
For these two years, preseason irrigation appears to be unnecessary.
The driest field in 1989 and 1990 had an FASW of 87 mm , and using this, the model predicted a SASW value of 230 mm , which is about 90% of field capacity, assuming mean over winter precipitation.
Most systems have sufficient irrigation capacity to supply water in excess of corn water use in May and June, which would
 allow at least partial replenishing of a deficient soil-water profile during this period.
Although the 1989 and 1990 data analysis suggested that preseason irrigation should not be recommended, particular fields may have sufficiently low soil water to effectively store some preseason irrigation.
Stone and Gwin  suggested preseason irrigation would be a relatively efficient practice if the fall ASW is less than 50% of field capacity.
Examination of 1989 and 1990 field data, using the 50% or less available soil water [125 mm/1.5 m ] as a critical point, showed that three sprinklerirrigated fields and one surface-irrigated field met this criterion.
The randomly selected fields should reflect the typical distribution of system capacities for the region.
A number of sprinkler systems exist in the region that have capacity of much-less-than-average seasonal evapotranspiration rate and therefore cannot maintain a stable level of ASW during the peak water use period of the growing season.
Thus, the survey might be expected to find some fields with very low ASW.
In the case of sprinkler-irrigated systems, which can add small increments of water during the growing season, extremely low fall ASW suggests the need for spring preseason irrigation to raise ASW to mid-range.
However, additional irrigation above the amount required to bring the profile to 50% of field capacity has a high probability of being lost or wasted.
Surface-irrigated systems, in general, require more labor and management than sprinkler systems, but can obtain relatively high irrigation efficiency if designed and operated properly.
However, the surface-irrigated systems in northwest Kansas tend to be operated at less overall irrigation efficiency than sprinkler systems, which may be partially reflected by the higher within-field variability in soil water.
After corn harvest in 1989, one surface irrigated field  had an average ASW amount of 132 mm , slightly above 50% of field capacity.
However, ASW was extremely variable, with a maximum ASW at the head of the field of 209 mm  compared to the minimum ASW at the tail-end of the field of 55 mm.
To conserve water resources, the farmer might decide to use pre-irrigation on only the lower portion of the field.
In the future, the farmer should consider other in-season management options, such as shorter surface runs or surge application that would improve the overall distribution efficiency of irrigation water.
Table 2.
Summary of results from a soil water survey after corn harvest in Thomas and Sherman counties, Kansas 
 Surface-Irrigated Fields	Sprinkler-Irrigated Fields
 1988	1989	1990	Mean	1988	1989	1990	Mean
 Plant Available Soil Water [mm/1.5 m soil profile ]
 Average	143 	198 	194 	178 	146 	179 	199 	174 
 Standard deviation	48 	34 	39 	40 	59 	50 	55 	55 
 Maximum value	213 	244 	268 	242 	230 	243 	287 	253 
 Minimum value	61 	132 	119 	104 	31 	90 	118 	79 
 Variation in Soil Water  Within Field, %, calculated as 100  / Max ASW)
 Average	40	26	28	31	19	15	17
 Standard deviation	26	26	14	22	-	16	10	14
 Maximum value	91	74	54	73	-	58	32	45
 Minimum value	0	2	13	5	-	5	1	3
 The surface-irrigated fields in 1988 also included several with very poor water distribution characterized by large differences in the maximum and minimum available soil water amounts which generally occurred at the head and tail-ends of the field, respectively.
Three of the fields, in addition to having average ASW amounts less than the 50% of field capacity criteria, had poor water distribution and could be considered for either partial preseason irrigation treatment or some other change in in-season irrigation management to improve overall water distribution, as previously discussed.
Three other surfaceirrigated fields which had average available soil water amounts above the 50% criteria could benefit from alternative in-season irrigation management procedures because of poor water distribution as reflected by the differences in their maximum and minimum available soil water amounts.
The soil water profiles for 1988 were much drier and variable than those for either 1989 or 1990.
In 1988, five surface-irrigated fields and five sprinkler-irrigated fields met the 50% or less soil water criterion for preseason irrigation consideration.
There were two surface-irrigated fields with average available soil water amounts less than 40% of field capacity and could be considered candidates for needing preseason irrigation.
However, the model predicted the fields will be at nearly 90% of field capacity by spring with average December-through-May rainfall.
Because the first surface irrigation application is generally the least efficient, it might be wise to withhold preseason irrigation and use the early part of the season to recharge the soil profile with water, if the seed can be germinated and plant growth established.
This would allow the maximum amount of precipitation to be stored.
Another management option is to reduce the irrigated portion of the field.
One strength of a surface-irrigated system is more flexibility in adjusting the total irrigated area under a given well to match the irrigation system capacity with crop water needs.
A three-year survey of ASW in 82 surface-irrigated and sprinkler-irrigated corn fields, after harvest in northwest Kansas, indicated the fields had an average of 176 mm
  of ASW remaining in the profile.
Using this figure in a model developed by Lamm and Rogers , which predicts ASW in the spring based on fall soil water, would indicate that preseason irrigation is an unnecessary practice.
However, individual irrigators should determine their need for preseason irrigation by evaluating their ASW and applying the model with an estimate of winter precipitation.
Preseason irrigation field preparation and application of water on surface-irrigation often occurs in the fall.
Evaluation of fall ASW to predict spring ASW would help convince irrigators of the lack of need for preseason irrigation, sparing them of field preparation and pumping expenses.
Mean available soil water for the two system types were similar.
However, surface-irrigated fields had larger within-field variations in available soil water than the sprinkler-irrigated fields.
This suggests the need for either more careful in-season management to increase uniformity of water application or a reduction of the irrigated area for surface-irrigated fields to insure all parts of the field have adequate soil water in order to assure high crop yields.
How to Calculate Irrigation Pumping Costs with MITOOL
 Follow These 14 Steps to Calculate Your Irrigation Costs and Break-Even Yield
 Consider this: Hover over or click the question mark icon in the tool to learn more about each parameter.
1.
Select Irrigation Type
 Select the irrigation type.
This aids the calculator in determining the dynamic head.
Furrow Sprinkler Other Non-Pressured
 Enter the acreage of the field where irrigation is being considered.
3.
Enter Flow and Irrigation Depth or Hours per Irrigation
 4.
Select Pump Fuel Type
 Select fuel type and then adjust the energy price depending on current fuel prices.
Gasoline and diesel costs are in dollars per gallon, and electricity price is in dollars per kilowatt-hour.
5.
Determine Pumping Lift
 Use the dropdown menu to select a county to obtain the average depth  to water for that county or enter the depth to water of your well if known.
If surface water is used, enter the elevation change from the water source to the riser.
6.
Adjust Discharge Pressure
 Discharge pressure has been pre-estimated based on irrigation type.
You can also manually enter the numbers yourself.
7.
Enter Pump Efficiency
 This parameter is prepopulated to 65% but can be manually entered if known.
Pump efficiency ranges from 50% to 80%, depending on pump impeller age; older impellers will have more wear and be less efficient.
Write percentages as whole numbers.
8.
Enter Gear Head Efficiency
 This parameter is prepopulated depending on your selected pump type.
Gear head efficiency ranges from 90% to 100% depending on pump drive type.
Fuel-based engines with direct shaft drive are approximately 95%, belt-driven pumps are usually around 90%, and electric pumps are 100%.
Enter manually if known, and write percentages as whole numbers.
Gear Head Efficiency 95 C
 9.
Enter Management Time
 Management time includes coordinating labor to accomplish the irrigating task.
The default is 15 minutes, but time can be manually entered.
10.
Enter Labor Time
 This parameter is prepopulated based on given acreage.
Studies suggest that it takes 1.53 minutes for each acre irrigated.
This tool uses acreage to estimate labor costs but can be manually entered if known.
Consider this: Labor costs regarding irrigation are often underestimated.
Labor time varies depending on type of irrigation, infrastructure, distance to the field, pump maintenance, number of sets per event, progress monitoring, and other factors.
11.
Enter Hourly Wages
 Management and labor hourly wages are default for Mississippi median hourly wage but can be manually entered if known.
Management Hourly Wage	27	C V
 Labor Hourly Wage	13	C V
 12.
Pump Ownership Costs
 Cost of repair, maintenance, and financing of the pumping station are measured in dollars per acre-inch.
The default is $0.40 per acre-inch, but values can be manually entered if known.
Repair, Maintenance and Finance cost	0.40	S
 13.
Enter Crop Values
 Individual market price of corn, cotton, and soybeans can be entered to determine yield needed to break even.
Corn Price in $/bushel	5	C V
 Cotton Price in $/lb of lint	1	CV
 Soybean Price in $/bushel	9	CV
 Click "Calculate." If the calculator does not generate results, check that every field is filled, follow the prompts, and try again.
Understanding MITOOL Calculator Output
 Pumping Cost Pumping costs consider the pump's workload, fuel type, runtime, efficiency ratings, and energy prices.
Labor costs are calculated by time spent and the cost of labor.
Capital Cost This is the cost of repair, maintenance, and financing of the pumping station for the proposed irrigation event.
Total Irrigation Event Cost
 This is the sum of pumping, labor, and capital costs.
Consider this: Costs not estimated in this calculator, such as vehicle mileage, and additional equipment, should also be considered.
This is the needed yield benefit from irrigation to breakeven.
If the expected yield gains from an additional irrigation exceeds the breakeven yield point, applying irrigation water will be profitable.
Consider this: Other factors can affect the need to irrigate.
Consider the precipitation and temperature forecast, current soil moisture conditions, and expected crop water use.
Crops usually require less water during later growth stages.
This publication is a contribution of the National Center for Alluvial Aquifer Research , the Mississippi State University Extension Service, and the Row-Crop Irrigation Science Extension and Research  initiative.
NCAAR is supported by the Agricultural Research Service, United States Department of Agriculture, under Cooperative Agreement number 58-6066-2-023.
RISER is supported jointly by the Mississippi Soybean Promotion Board, Mississippi Corn Promotion Board, Mississippi Rice Promotion Board, Cotton Incorporated, and Mississippi Peanut Promotion Board.
By Carson Roberts, Graduate Research Assistant; Drew Gholson, PhD, Assistant Professor and Coordinator of the National Center for Alluvial Aquifer Research; Nicolas Quintana, PhD, Assistant Research Professor; and Himmy Lo, PhD, Assistant Extension/Research Professor, Delta Research and Extension Center.
Produced by Agricultural Communications.
Mississippi State University is an equal opportunity institution.
Discrimination in university employment, programs, or activities based on race, color, ethnicity, sex, pregnancy, religion, national origin, disability, age, sexual orientation, gender identity, genetic information, status as a U.S.
veteran, or any other status protected by applicable law is prohibited.
Extension Service of Mississippi State University, cooperating with U.S.
Department of Agriculture.
Published in furtherance of Acts of Congress, May 8 and June 30, 1914.
STEVE MARTIN, Interim Director
Field Evaluations of Irrigation Systems: Solid Set or Portable Sprinkler Systems1
 This bulletin describes techniques for measuring operating pressures, water application rates and uniformity during field evaluations of solid set or portable sprinkler irrigation systems.
These irrigation systems typically use groups of impact or gear-driven sprinklers which operate at the same time to sprinkle water onto the soil or crop canopy.
Sprinkler spacings are relatively close SO that overlap between them increases the uniformity of water application.
The techniques presented do not apply to self-propelled irrigation systems such as center pivot, linear move, or traveling gun systems.
Nor do they address single sprinkler systems such as large guns or small individual lawn sprinklers.
The unique geometries of self-propelled and individual sprinkler systems require other procedures to measure application rates and uniformities of water application.
Solid set sprinkler irrigation systems are those in which sprinklers, with their assorted riser, lateral, and
 manifold pipes, are placed in a regular pattern over the entire irrigated area.
All of the sprinklers may be operated at once, or the crop may be irrigated in zones by operating only a portion of the sprinkler laterals at a time.
Solid set sprinkler systems may be permanent, in which case laterals and manifolds are typically constructed of buried PVC plastic pipe.
This is common in many Florida citrus, nursery, strawberry, and ornamental fern production systems and in lawn and landscape irrigation systems.
Alternatively, solid set sprinklers may be set in place only during a crop growing season.
Sprinklers are then typically mounted on risers above portable aluminum pipelines which are placed on the surface.
Laterals may be fed by either portable  manifolds placed on the soil surface or permanent  buried manifolds.
These systems are common for many Florida vegetable, tobacco, and turf crops.
In portable set sprinkler irrigation systems, the sprinklers and associated pipelines are temporarily set up and operated for each irrigated zone.
They are then
 Field Evaluations of Irrigation Systems: Solid Set or Portable Sprinkler Systems
 moved to a new zone for another irrigation.
These systems are used to irrigate several zones; thus, they are designed SO that all zones can be irrigated before the first zone needs to be re-irrigated.
Because these systems are portable, less pipe and fewer sprinklers must be purchased as compared to solid set systems.
However, labor requirements are normally much greater than for solid set systems.
The specific system used normally depends on the relative availability of capital versus labor.
Both the solid and portable set sprinkler systems described here use sprinklers that are regularly spaced, typically in square, rectangular, or triangular patterns.
The individual sprinkler spacings and discharge rates determine the average irrigation application rate.
Many additional factors, including operating pressure, changes in elevation, friction pressure losses, wind, and individual sprinkler characteristics affect the uniformity of water application within an irrigated zone.
The specific objectives of this publication are to present techniques  to measure operating pressures,  to measure application rates, and  to measure the uniformity of water application under field conditions for existing solid set or portable sprinkler irrigation systems.
Knowledge of these three factors and changes in their magnitudes over time is important to determine the causes of deficiencies in application rates or uniformities observed.
This information is also needed to efficiently and effectively manage sprinkler irrigation systems.
Field evaluations should be conducted at least annually to reveal changes which require system maintenance or repair.
Always operate sprinklers within the manufacturer's specified pressure ranges.
Sprinkler effectiveness is reduced by operation at either excessively high or low pressures.
Pressures that are too high produce fogging and irregular turning.
Fogging produces too many small droplets that fall too close to the sprinkler.
Pressures that are too low cause improper jet breakup, producing a doughnut-shaped spray pattern.
Under either condition, water is not uniformly distributed.
Operating pressures should be within the range specified by the irrigation system designer.
Pressure gauges should be permanently installed at the irrigation pump and at entrances to zones.
Test gauges periodically to verify that pressures are being measured accurately.
This can be done by substituting a test gauge for the field gauges.
Replace the field gauges if they are no longer accurate.
Pressures within zones can be measured at the sprinkler nozzles using pitot tube pressure gauges.
Position pitot tubes in the discharge stream about 1/8-inch from the nozzle.
Adjust the pitot tube by moving it slowly within the stream until the highest constant pressure reading is obtained.
Pressures recorded at critical points within the system, including at the pump discharge, at the entrance to zones, at the distant end of laterals, and at extreme high and low elevations, should be near the pressures specified by the system designer.
Extreme deviations from the design pressures should be corrected before proceeding with further system tests.
As examples, low pump discharge pressure may occur because of pump wear, insufficient pump operating speed, insufficient water supply, a broken pipe downstream, too many open valves downstream, or eroded sprinkler nozzles that discharge excessive flow rates.
Conversely, high pump pressures may indicate excessive pump speed, valves that are closed or partially closed downstream, or components that are clogged.
Pump discharge rate measurements and visual inspections will help to determine which problem may have occurred.
Similar flow rate measurements and visual inspections should be used to determine causes of excessively low or high pressures at other points in the system.
Measuring Sprinkler Application Rates
 Sprinkler application rates must be known SO that irrigation durations needed to apply specific depths of water can accurately be determined.
Measure application rates under field conditions  to verify irrigation system designs and  to determine whether changes in application rates have occurred with time.
Measurements to verify irrigation
 Field Evaluations of Irrigation Systems: Solid Set or Portable Sprinkler Systems
 system design should be made soon after installation.
Subsequent measurements should be made at least annually to track changes in system performance and to schedule repairs.
Three techniques can be used to measure application rates:
 1.
Measure the flow rate and area of each irrigated zone.
Measure the flow rate with either a flow meter at the pump or at each zone.
Units are normally gallons per minute.
To convert to acre-inches per hour, divide the measured flow rate by 453.
The average application rate per zone can then be calculated from:
 Rate = Q / Area
 where Rate = application rate in inches per hour ,
 Q = total flow rate per zone in acre-inches per hour, and
 Area = total irrigated zone area in acres.
For example, if the measured flow rate to a 10-acre zone is 906 gpm, this is equivalent to 906/453 = 2.0 acre-inches per hour.
Then, the average application rate is 2.0 acre-inches per hour / 10 acres = 0.20 iph.
2.
Measure the average flow rate and area covered by each sprinkler.
For regularly spaced sprinklers, the application rate is then calculated from:
 Rate = =96.3 g / [ ]
 where Rate = application rate in inches per hour ,
 q = sprinkler discharge rate in gallons per minute ,
 SI = sprinkler spacing along the lateral in feet , and
 Sm = sprinkler spacing along the manifold between laterals in ft
 As examples of the use of Equation , if 5-gpm sprinklers are spaced on a 40 ft X 40 ft square pattern, the application rate would be 0.30 iph.
If 6-gpm sprinklers were spaced on a 40 ft X 60 ft rectangular pattern, the application rate would be 0.24 iph.
If 4-gpm sprinklers are spaced on a 30 ft X 30 ft triangular pattern, the application rate would be 0.43 iph.
Sprinkler flow rate can be determined by either  measuring the volume discharged from typical sprinklers per unit time, or  measuring the sprinkler operating pressure with a pitot tube and using the manufacturer's specifications to determine the flow rate.
Measuring the volume discharged is preferred because nozzle wear can increase the flow rate over manufacturer's specifications.
Sprinkler discharge can be diverted to a graduated cylinder or other volumetric container by slipping a flexible tube over the sprinkler nozzle.
The tube should be large with respect to the nozzle diameter to avoid restricting the flow.
Flow should only be measured while the sprinkler is operating at its design pressure.
A stopwatch can be used to measure the sprinkler discharge collection time.
Figure 1.
Using a pitot tube measure pressure at a sprinkler nozzle.
The pressure at the sprinkler nozzle can be measured by holding a pitot tube connected to an accurate pressure gauge in the discharge stream of the nozzle as shown in Figure 1.
The nozzle size should be checked for wear or distortion with a feeler gauge
 Field Evaluations of Irrigation Systems: Solid Set or Portable Sprinkler Systems
 such as a drill bit having the diameter specified for the nozzle.
If the nozzle is worn or misshapen, it should be replaced with a new one.
The sprinkler flow rate can then be determined by consulting the sprinkler manufacturer's specifications for the measured operating pressure and nozzle size.
If the sprinklers have more than one nozzle, the total sprinkler flow rate can be determined by adding the flow rates of the individual nozzles.
Figure 2.
Typical layout of catch cans for uniformity.
To accurately determine the average sprinkler flow rate in an irrigated zone, measure several sprinklers.
Some of the sprinklers measured should be near the inlet ends of the laterals, some near the center, and some at the distant ends.
If the measured values are highly variable , the number of sprinklers tested should be increase.
If different sizes of sprinklers or nozzles are used in a zone, such as part-circle sprinklers at field boundaries, flow rates must be determined separately for each size.
The total zone flow rate can then be determined by adding the average flow rates for the total number of sprinklers of each size in the zone.
Finally, Equation  can be used to calculate the average application rate for the zone.
3.
Measure the application rate directly with catch cans or rain gauges.
The average application rate is then the average depth of water measured divided by the time during which the data were collected.
Because water is never applied with perfect uniformity under a sprinkler irrigation system, several catch cans must be placed between adjacent sprinklers.
Normally at least 16 to 24 cans should be used.
To simplify later uniformity calculations, use a number of cans that is a multiple of 4.
Also, these tests should be conducted under the same conditions as those during typical applications.
Avoid making tests during high wind conditions because wind distorts sprinkler patterns.
Figure 2 shows a typical layout of catch cans for uniformity measurements between the four sprinklers shown.
The 16 cans are evenly spaced between sprinklers SO that each is centered within and represents equal land areas.
The numbers shown adjacent to the catch cans in Figure 2 are example catch can data which are used in later example problems.
Catch cans should all be of the same size and type, and should be placed upright SO that their tops are level.
Cans should be located on or near the soil surface, but above any vegetation which might obstruct access to the cans.
For annual crops, schedule catch can tests when plants are small SO that they do not interfere with the tests.
For large perennial plants such as citrus or other tree crops, catch can tests may be very difficult to conduct because of the need to elevate the cans above the canopies.
Tests with cans under tree canopies are not appropriate because the canopies will distort the water distribution.
If large unobstructed areas are available between trees, these areas may be used to estimate uniformities.
This might be the case with young citrus trees.
However, as trees grow, the tall canopies will distort water distributions, and the catch cans will need to be elevated to avoid the canopies.
In some citrus groves, sprinklers are located at about the same height or just above the tree canopy.
In these cases, catch can tests may not be appropriate because the cans cannot be elevated sufficiently to clear the canopies and still be positioned sufficiently below the sprinklers to accurately measure water applications.
To avoid evaporation losses during data collection, place a few drops of lightweight oil in the cans.
The oil will disperse over the water surface and
 Field Evaluations of Irrigation Systems: Solid Set or Portable Sprinkler Systems
 restrict evaporation.
This is especially important for tests that require several hours to conduct.
In Figure 2, the depth of water collected in each can is given in inches.
The average of the 16 depths is 0.31 inches.
If the test was conducted for a 1-hr period of operation, then the application rate was 0.31 iph.
Figure 3.
Example distribution of locations of catch can tests in a large irrigated field.
Because application rates may vary throughout a large irrigated field, measurements should be made at several locations as shown in Figure 3.
Test locations should be selected over the entire range of pressures that might be encountered in the irrigation system.
That is, locations should be selected both near and distant from the irrigation pump.
Locations should also be selected at points of both high and low elevation.
Measuring Uniformity of Water Application
 Uniformity of water application is a measure of the variability in depths of water applied at different points throughout an irrigated zone.
Uniformity of water application can be measured using catch cans set on or near the soil surface.
Follow the procedures previously described in this bulletin for application rate measurements.
Uniformities are normally measured under no-wind conditions.
Under no-wind conditions, the maximum possible uniformity is measured for the existing system hydraulic characteristics and sprinkler selection.
Uniformity will be lower when sprinkler systems are operated during windy conditions.
However, that uniformity may be more representative of the long-term average uniformity if the sprinklers are normally operated under windy conditions.
Where prevailing winds are consistently strong, such as along the coasts in Florida, sprinklers must be spaced closer together than under no-wind conditions.
For no-wind conditions, sprinklers are typically spaced at 55% to 60% of their diameters of coverage.
This should be reduced to 50% for low wind speeds  and to 30% for wind speeds above 10 mph.
Uniformity of water application with sprinkler irrigation systems is usually reported as either the distribution uniformity  or Christiansen's Uniformity Coefficient 
 DU is calculated as the ratio of the depth measured in the low quarter of the irrigated area to the overall average depth applied.
DU = 100% 
 where DU is expressed as a percent.
The average low quarter depth is determined by inspecting the data collected and calculating the average of the smallest 1/4 of the measured depths.
The overall average is the arithmetic average of all of the catch can data.
The computations are simplified if the total number of data are a multiple of 4.
DU can be calculated using the data shown in Figure 2.
The low quarter of the 16 data points are the four values: 0.24, 0.25, 0.27, and 0.28 inches, shown underlined in Figure 2.
The average of these four low quarter values is 0.26 inches.
The overall average of all 16 points is 0.31 inches.
Then, from Equation :
 DU = 100%  / 0.31 inches = 83.9%
 Christiansen's Uniformity Coefficient  is another widely-used method of calculating the
 Field Evaluations of Irrigation Systems: Solid Set or Portable Sprinkler Systems
 uniformity of water application from sprinkler irrigation systems:
 UC = 100% [1 ]
 where UC is expressed as a percent.
The average deviation from the average depth of application is calculated by averaging the absolute values of the differences between each of the individual depths and the average depth, and the overall average depth of application is defined as before.
Acceptable values of uniformity coefficients vary with the type of crop being grown and the specific uniformity equation used.
Both equations result in approximately the same values when uniformity is high.
However, DU values are normally much lower than UC values when uniformities are low.
For high cash value crops, especially shallow rooted crops, the uniformities should be high.
For typical field crops, DU values should be greater than 70%.
For deep rooted orchard and forage crops, uniformities may be fairly low if chemicals are not injected.
Uniformity coefficients should be high  whenever fertilizers or other chemicals are injected into the irrigation systems.
If uniformity
 coefficients are lower than these values, system repair, adjustment or modification may be required.
If uniformity coefficients are periodically measured , system repairs or adjustments can be scheduled when coefficients fall below the above values.
Runoff will reduce the amount of water applied to high areas and may increase the amount applied in low areas where the water may collect and infiltrate.
During system tests and during normal sprinkler operation, runoff should not occur.
This is normally not a problem on typical Florida sandy soils, but if runoff occurs, design or management changes should be made to eliminate it.
Shorter, more frequent irrigations may be scheduled to reduce runoff, or it may be necessary to reduce nozzle sizes to reduce application rates.
If the system operation must result in runoff , recovery ponds can be used to collect runoff for future use.
This publication described techniques which can be used to evaluate sprinkler irrigation systems under field conditions.
Techniques were presented  to measure operating pressures,  to measure application rates,  to measure the uniformity of water application, and  to avoid runoff under field conditions for existing solid or portable set sprinkler irrigation systems.
Critical values of uniformity coefficients for various crops and production systems were presented.
Potential disadvantages are the importance of good soil contact which can be challenging in some soil types, and the lag time after installation and after wetting events.
Capacitance probes measure volumetric water content by emitting an electromagnetic field around the sensor to calculate the dielectric properties of soil.
Agriculture and Natural Resources
 Associate Professor and Extension Specialist Vegetables
 Arkansas Is Our Campus
 Light sunny Soil well-drained, sandy Fertility medium pH 6.0 to 7.0 Temperature hot Moisture average
 Planting transplants or direct seed after danger of frost Spacing hills 6 to 8 feet apart Hardiness very tender annual Fertilizer heavy feeder
 Watermelons are indigenous to tropical Africa, where they are found wild on both sides of the equator.
They were developed from a native African vine.
Their cultivation by man dates back 4,000 years to the ancient Egyptians, as proven by artistic records.
Watermelons spread from ancient Egypt to India and Asia and were widely distributed throughout the remainder of the world by Africans and European colonists.
Watermelons are tender, warm-season vegetables.
The fruit of the watermelon is one of the largest vegetables we eat.
Watermelons commonly weigh 18 to 25 pounds, with the world's record melon tipping the scales at 291 pounds.
They can be grown in all parts of Arkansas.
Melons are usually planted in the field
 around April 15 to May 1 in south Arkansas and between May 10 and 15 in north Arkansas.
Watermelons do not transplant well bare-rooted, but they may be started in containers three to four weeks before field planting to promote early development.
Mulching with black plastic film also promotes earliness by conserving moisture and warming the soil.
Plant after the soil is warm  and when all danger of frost is past.
Hot caps and floating row covers may prove useful for earlier production.
Days to	100 Feet	Resistance
 Crop	Cultivar	Maturity	of Row	or Tolerance	Remarks
 Watermelons	Crimson Sweet	85	1/2 OZ	Anthracnose,
 Jubilee II	90	1/2 OZ	Anthracnose,
 Star Brite	90	1/2 OZ	Anthracnose,	Oblong, dark green stripes.
Sweet Favorite	90	1/2 OZ	Anthracnose,
 Shiny Boy	90	1/2 OZ	Anthracnose,
 Yellow Baby	85	1/2 OZ
 Triple Crown	88	1/2 OZ
 Moon and Stars	90	1/2 OZ
 Watermelons grow best on a deep sandy loam soil high in organic matter, well drained and slightly acidic.
Sandy loam soils are preferred for growing watermelons because sandy soils generally warm faster in the spring, are easier to plant and cultivate and allow deep root penetration.
When planted on very heavy soils, the plants develop slowly and fruit size and quality are usually inferior.
Yields on clay soils can be increased significantly by mulching with black plastic film to conserve moisture.
Fine sands produce the highest-quality melons when adequate fertilizer and water are provided.
Wind breaks of wheat or rye are advisable on sandy soils to reduce "sand blast" damage and stunting to young seedlings during spring winds.
To reduce the risk of diseases, do not plant on land where vine crops have grown during the past four years.
Avoid low, damp areas or pockets where cool air may collect.
Soil pH can vary from 5.5 to 8.0.
Don't be concerned with adjusting soil pH unless it is below 5.8.
Spacing and Depth of Planting
 Watermelon vines require a lot of space.
Plant seed 1 inch deep in hills spaced 6 feet apart.
Allow 7 to 10 feet between rows.
After the seedlings are established, thin to the best three plants per hill.
For earliness, start the seed inside about three weeks before they are to be set out in the garden.
Plant two or more seeds in 3-inch deep pots or peat pots, then thin to the best two plants.
Do not start too early; large watermelon plants transplant poorly.
Growing transplants inside at warm temperatures ensures germination of seedless varieties that require temperatures between 80 and 85 degrees F.
Place black plastic over the row before planting.
Use a starter fertilizer solution when transplanting.
If you
 grow seedless melons, you must also plant a row of a standard seeded variety as a pollinator for every three rows of the seedless melons.
The seedless melon varieties do not have the fertile pollen necessary to pollinate and set the fruit.
Watermelons should be kept free from weeds by shallow hoeing and cultivating.
The plants are deep rooted, and watering is rarely necessary unless the weather turns dry for a prolonged period early in the growing season.
Cucumber beetles and squash bugs will attack watermelon plants.
Apply a suggested insecticide for control.
Anthracnose is a major foliar disease of melons in Arkansas.
It is also a common destructive disease of most cucurbits.
Use a fungicide to control.
Gummy stem blight causes stem end rot, leaf spotting and a fruit rot on all cucurbits.
Lesions on leaves, petioles and stems become pale brown or gray.
Those on stems elongate into streaks and produce an amber, gummy exudate.
The leaves may turn yellow and die.
Occasionally, the whole plant wilts and dies.
Use a fungicide to control leaf and stem blights.
Mosaic Viruses Many strains of mosaic viruses infect cucurbits.
In Arkansas and in the southern states, certain watermelon strains of a mosaic virus have caused extensive losses of fruits of zucchini and other summer squash, cucumber and pumpkin because of the occurrence of mosaic-patterned, yellow and green, knobby fruits.
Plants of cucurbits may become infected at any growth stage.
Poor pollination and fruit set can cause low yields.
Watermelon has male and female flowers.
Male flowers produce the pollen, and the female flowers produce the watermelon fruits.
Honeybees and other bees transfer the pollen.
After the plant produces many male flowers, every seventh flower on a plant branch is female.
All male and most female flowers drop off the plant, and fruits set more or less irregularly throughout the season.
The condition of the plant and the number of melons already set determine the number of female flowers that set fruit later.
Therefore, pruning misshapen melons while small is essential to encourage additional fruit set.
Flowers open one to two hours after sunrise.
Female flowers are receptive to pollen throughout the day, although most pollination takes place before noon.
The flowers close in the afternoon never to reopen whether pollinated or not.
Bees must deposit adequate pollen on all three lobes of the female flower's stigma or a misshapen melon develops.
Cold, rainy and windy weather reduces bee activity, which can cause poor melon production due to inadequate pollination.
Even though a melon has normal shape, it will ripen at a smaller size and contain fewer seeds if pollination was marginal.
When flowers are developed on the plants, do not use insecticides, such as carbaryl or Sevin, that are extremely toxic to bees.
Many home gardeners do not know how to determine when watermelons are ripe.
Use a combination of the following indicators: 1) light-green, curly tendrils on the stem near the point of attachment to the melon turn brown and dry when the melon is ripe; 2) the surface color of the fruit turns dull; 3) the skin becomes resistant to penetration by the thumbnail and is rough to the touch; and 4) the bottom of the melon  turns from a light green to a yellowish color.
These indicators for choosing a ripe watermelon are much more reliable than "thumping" the melon with a knuckle.
Many watermelons do not emit the proverbial "dull thud" when ripe.
pests deer, crows and coyotes diseases bacterial wilt , fusarium wilt, anthracnose leaf spot, powdery and downy mildews, alternaria blight, gummy stem blight
 insects cucumber beetles, squash vine borer, pickleworms, squash bug
 cultural poor flavor and lack of sweetness due to poor fertility, low potassium, magnesium or boron; cool temperatures; wet weather; poorly adapted variety; loss of leaves from disease or picking melons unripe.
Blossom end rot on melons grown on acidic soils with a lack of irrigation.
Misshapen melons caused by poor pollination during wet, cool weather
 and lack of bee pollinators.
Planting too close results in excessive vegetative growth.
A heavy rain when melons are ripening may cause some of the fruit to split open.
Fruit in contact with soil may develop rotten spots or be damaged by insects on the bottom.
Place a board or several inches of light mulching material, such as sawdust or straw, beneath each fruit when it is full-sized.
days to maturity 70 to 130
 harvest Become familiar with the variety being grown to determine the best stage for harvesting.
The best indicator is a yellowish color on the underside where the melon touches the ground.
A dead tendril or curl near the point where the fruit is attached to the vine is used by some as an indicator that the fruit is ready for harvest.
You may also thump the fruit, listening for the dull sound of ripe fruit rather than a more metallic sound; however, this technique takes some practice.
If you have just a few fruit, it is probably wise to include all of the above when making your decision.
approximate yields  8 to 40 pounds amount to raise per person 10 to 15 pounds storage medium-cool , moist
  conditions preservation cool, moist storage
 Q.
My watermelons are not very sweet and flavorful.
Is the low sugar content caused by the watermelons crossing with other vine crops in the garden?
A.
No.
Watermelon varieties will cross with one another, but not with muskmelons, squash, pumpkin or cucumbers.
The poor quality of your melons may result from wilting vines, high rainfall, cool weather or late planting.
Q.
What can I do to prevent my watermelons from developing poorly and rotting on the ends?
A.
This condition may be caused by a combination of factors.
It may be caused by an extended period of extremely dry weather when the melons were maturing or by a lack of calcium.
It may be aggravated by continued deep hoeing or close cultivation.
Mulching the plants with black plastic film helps reduce this problem, especially on heavy and droughty soils.
Q.
Do watermelons readily cross with other vine crops resulting in off-flavor and poorquality fruit?
A.
Watermelon varieties readily cross with each other and with the wild citron.
Watermelons will not cross with cantaloupes, cucumbers, pumpkins, squash or cushaws.
Off-flavor or odd-shaped fruit is generally caused by growing conditions and not cross-pollination.
Q.
What determines the sweet flavor of watermelons?
A.
There are differences in sugar content from one variety of watermelon to another.
The sweeter varieties include Crimson Sweet, Dixilee and the old variety Black Diamond.
Excessive moisture caused by late irrigations or rainfall near maturity of the watermelon will result in poor flavor.
Q.
How can you tell when a watermelon is ripe?
A.
Determining ripeness in watermelons is difficult.
The area touching the soil or the belly of the fruit turns from a light grass-green color to a cream color as the fruit ripens.
Thumping is used to check ripeness, but the results will vary.
The dark green fruits, such as Black Diamond, will also develop a dull fruit color compared to an immature melon.
The tail or tendrils located on the vine connecting the fruit to the plant will dry as the melon matures.
If tendrils closest to the fruit are dry and brown, chances are the fruit is mature.
Q.
What causes watermelon plants to fail to set fruit?
A.
Poor fruit set in watermelons is usually a result of poor pollination.
The watermelon plant produces male and female blooms, and bees are necessary to transfer the pollen from the male to female bloom.
Common causes of poor fruit set include lack of bees for pollinating or cool, wet weather that slows bee activity during bloom.
Q.
What causes the end of the watermelon fruit to turn black and rot?
A.
Watermelon fruit is affected by blossom end rot just as tomato fruit.
This condition occurs on watermelon fruit if the plant loses excessive moisture through an unusually dry period.
The inability of the plant's roots to keep up with water loss by the plant results in desiccation and blackening of the blossom end of the fruit.
Prevent blossom end rot by maintaining adequate moisture, especially as the fruit matures.
Q.
Are there really seedless varieties of watermelons?
A.
Yes.
There are several hybrid varieties of watermelons that produce seedless or nearly seedless fruit.
A common variety is Jack of Hearts.
Since the seeds of this variety are relatively weak, start them indoors in a warm area.
When setting the plant out in the garden, also plant a few seed of a standard variety because they provide pollen for fruit set.
Seedless melons were created by crossing melons with two different chromosome numbers.
A diploid  melon is
 crossed with a tetraploid  melon to produce the triploid  seed.
This seed germinates and the fruit are pollinated but do not produce viable seed, hence the name "seedless melons."
 Q.
As my watermelons begin to set fruit, the leaves around the crown of the plant develop necrotic lesions and die rapidly.
A.
A number of foliage diseases attack watermelons causing this condition.
The one most often observed is anthracnose.
Alternaria and downy mildew cause similar lesions.
Control all these by using a fungicide.
Begin applications at the first sign of the disease and continue at 7to 14-day intervals as long as weather conditions are favorable for disease development.
Q.
As my watermelon plants began to grow, the stem near the crown cracked and oozed an amber-colored liquid.
Soon after this the plants died.
A.
This is gummy stem blight caused by a soilborne fungus that attacks watermelons, cantaloupes and cucumbers.
Control with fungicide sprays when the runners begin to form.
Spray the crown of the plant carefully.
Crop rotation will decrease this problem.
Q.
What is a citron and is it edible?
A.
The citron is the wild watermelon, a native vine of Africa.
In the arid interior of Africa, it supplies the people with water from its fruit.
It is also called a preserving melon because the fruit rind is used to make pickles or preserves.
Q.
My watermelon plants grew vigorously.
There was slight twisting at the stem end, and the leaves were distorted.
Fruit was either not formed or was distorted on these plants.
A.
This is watermelon mosaic.
It is transmitted by aphids and can be partially prevented by spraying plants on a regular basis.
Once the plant becomes infected with the virus, there is no control.
Early planting will decrease this problem.
Q.
My watermelons were growing and doing well when, all of a sudden, they began to wilt and died soon after.
I found the stems have a tan ring on the inside.
A.
This is fusarium wilt of watermelon, a soilborne disease.
Plant resistant varieties such as Charleston Gray and Jubilee to reduce this problem.
There are other wilt-resistant varieties, but consult seed catalogs before planting varieties other than the two mentioned.
There is no chemical control for this disease.
Printed by University of Arkansas Cooperative Extension Service Printing Services.
DR.
CRAIG R.
ANDERSEN is associate professor and Extension specialist vegetables, Horticulture Department, University of Arkansas Division of Agriculture, Fayetteville.
ERRATICITY OF SPRINKLER-IRRIGATED CORN UNDER DROUGHT
 Terry A.
Howell Agricultural Engineer USDA Agricultural Research Service Bushland, Texas Voice: 806-356-5746 Fax: 806-356-5750 terry.howell@ars.usda.gov
 erraticity  n.
The quality or state of being erratic, characterized by the lack of consistency, regularity or uniformity.
That's correct, there is no such word, but you sure know it when you see it.
Unfortunately, we saw a lot of it during some extreme droughts in sprinkler irrigated corn.
Figure 1.
Nonuniformity of sprinkler irrigated corn under extreme drought conditions in southwest Kansas in 2011.
These instances of erraticity resulted in low quality, lowor non-yielding corn production.
Crop water stress caused by the extreme drought in portions of the central and southern Great Plains is ultimately responsible for the erraticity.
However, there may be ways to reduce erraticity and its harmful effects by improvements in design and management of center pivot sprinklers for corn production that can minimize water losses.
SPRINKLER PACKAGE EFFECTS ON WATER LOSSES
 Center pivot sprinkler management techniques to avoid water losses begin at the design and installation stages with selection of an appropriate sprinkler package.
Typical sprinkler packages in use to today are medium and high pressure impacts which are located on top of the sprinkler span , low pressure rotating spray nozzles which are typically located on the span or at least above the crop canopy, low pressure fixed spray applicators that are located above and within the crop canopy and LEPA  that are located near the ground surface.
Commercial LEPA applicators often can apply water in multiple modes.
The popular low pressure fixed spray applicators have also been categorized by their location with respect to the canopy with the terms LESA  and MESA .
Application with MESA is typically above the crop canopy for all or most of the crop season depending on the crop.
There are numerous water loss pathways using center pivot sprinklers and each type of sprinkler package has advantages and disadvantages as outlined by Howell  that must be balanced against the water loss hazards.
Table 1.
Water loss components associated with various sprinkler packages.
Adapted from Howell.
Water Loss Component	(Impact sprinklers,
 Canopy evaporation	Yes		
 Impounded water evaporation	No	Yes	
 Wetted soil evaporation	Yes	Yes	
 Surface water redistribution	Yes,	Yes	Yes
 No,		(not major unless
 Runoff		Yes	Yes	surface storage is	not used)
 Percolation	No	No	No	No
 Windy and hot conditions during the growing season affect center pivot sprinkler irrigation uniformity and evaporative losses.
As a result many producers in the southern and central Great Plains have adopted sprinkler packages and methods that apply the water at a lower
 height within or near the crop canopy height, thus avoiding some application nonuniformity caused by wind and also droplet evaporative losses.
In-canopy and near-canopy sprinkler application can reduce evaporative losses by nearly 15% , but introduce a much greater potential for irrigation nonuniformity.
These sprinkler package systems are often adopted without appropriate understanding of the requirements for proper water management, and thus, other problems such as runoff and poor soil water redistribution occur.
Table 2.
Partitioning of sprinkler irrigation evaporation losses with a typical 1 inch application for various sprinkler packages..
Sprinkler package	Air	Canopy	Ground	Total	Application
 loss, %	loss, %	loss, %	loss,%	efficiency, %*
 = 14 ft height	3	12	--	15	85
 = 5 ft height	1	7	--	8	92
 = 1 ft height	--	--	2	2	98
 * Ground runoff and deep percolation are considered negligible in these data.
Traditionally, center pivot sprinkler irrigation systems have been designed to uniformly apply water to the soil at a rate less than the soil intake rate to prevent runoff from occurring.
These design guidelines need to be either followed or intentionally circumvented with appropriate design criteria when designing and managing an irrigation system that applies water within the canopy or near the canopy height where the full sprinkler wetted radius is not developed.
Peak application rates for in-canopy sprinklers such as LESA  and LEPA  might easily be 5 to 30 times greater than above-canopy sprinklers.
Runoff from LEPA sprinklers was negligible on 1% sloping silt loam soils in eastern Colorado but exceeded 30% when slopes increased to 3%.
Runoff from LEPA with basin tillage was approximately 22% of the total applied water and twice as great as MESA  for grain sorghum production on a clay loam in Texas.
Basin tillage created by periodic diking of crop furrow , rather than reservoir tillage created by pitting or digging small depressions , is often more effective at time averaging of LEPA application rates, and thus, preventing runoff.
Figure 2.
Application intensities for LEPA, LESA, MESA, rotating sprays on span and impact sprinklers on the span as related to the typical size of their wetting pattern.
Decreasing the application intensity is the most effective way to prevent irrigation field runoff losses and surface redistribution within the field  When runoff and surface redistribution occurs using in-canopy sprinklers because of a reduced wetting pattern, one solution would be to raise the sprinkler height.
Figure.
3.
Illustration of runoff or surface water redistribution potential for impact and LESA sprinkler application packages for an example soil.
After Howell.
One might assume that the erraticity observed under drought in sprinkler irrigated fields was primarily associated with the evaporative water loss components shown in Table 1, but that is probably not the case.
When using fixed plate applicators near or within the canopy , the magnitude of field runoff and particularly surface redistribution within the field may overwhelm the evaporative loss reductions possible with these packages.
Surveys conducted by Kansas State University have indicated that approximately 90% of the center pivot sprinkler systems in western Kansas use fixed plate applicators and nearly 60% have sprinkler nozzle height less than 4 ft above the soil surface.
The erraticity can be caused by failure to follow appropriate guidelines for irrigation with nearand in-canopy sprinklers.
SOME GUIDING PRINCIPLES FOR IN-CANOPY APPLICATION
 A prototype of the LEPA system was developed as early as 1976 by Bill Lyle with Texas A&M University.
Jim Bordovsky joined the development effort in 1978  and the first scientific publication of their work was in 1981.
Although, originally LEPA was used in every furrow, subsequent research  demonstrated the superiority for alternate furrow LEPA.
The reasons are not always evident, but they may result from the deeper irrigation penetration , possible improved crop rooting and deeper nutrient uptake, and less surface water evaporation.
The seven guiding principles of LEPA were given by Lyle  as:
 1) Use of a moving overhead tower supported pipe system 
 2) Capable of conveying and discharging water into a single crop furrow
 3) Water discharge very near the soil surface to negate evaporation in the air
 4) Operation with lateral end pressure no greater than 10 psi when the end tower is at the highest field elevation
 5) Applicator devices are located so that each plant has equal opportunity to the water with the only acceptable deviation being where nonuniformity is caused by nozzle sizing and topographic changes
 6) Zero runoff from the water application point
 7) Rainfall retention which is demonstratively greater than conventionally tilled and managed systems.
The other types of in-canopy and near-canopy sprinkler irrigation do not necessarily require adherence to all of these seven guidelines.
However, it is unfortunate that there has been a lack of knowledge or lack of understanding of the importance of these principles because many of the problems associated with in-canopy and near-canopy sprinkler irrigation can be traced back to a failure to follow or effectively "work around" one of these principles.
In-canopy and nearcanopy application systems can definitely reduce evaporative losses , but these water savings must be balanced against runoff and within field water redistribution, deep percolation and other soil water nonuniformity problems that can occur when the systems are improperly designed and managed.
PROVIDING PLANTS EQUAL OPPORTUNITY TO SOIL WATER
 The No.
5 LEPA guiding principle listed earlier emphasizes the importance of plants having equal opportunity to root-zone soil water.
Ensuring this equal opportunity requires sufficient uniformity of water application and/or soil water infiltration.
Key issues that must be addressed are irrigation application symmetry, crop row orientation with respect to center pivot sprinkler direction of travel, and the seasonal longevity of the sprinkler pattern distortion caused by crop canopy interference.
SYMMETRY OF SPRINKLER APPLICATION
 Increased sprinkler application uniformity will often result in increased yields, decreased runoff, and decreased percolation.
Their study indicated irrigation nonuniformity can result in nutrient leaching from over-irrigation and water stress from under-irrigation.
Both problems can cause significant economic reductions.
Sprinkler irrigation does not necessarily have to be a uniform broadcast application to result in each plant having equal opportunity to the irrigation water.
Equal opportunity can still be ensured using a LEPA nozzle in the furrow between adjacent pairs of crop rows provided runoff is controlled.
Figure 4.
LEPA concept of equal opportunity of plants to applied water.
LEPA heads are centered between adjacent pairs of corn rows.
Using a 5-ft nozzle spacing with 30inch spaced crop rows planted circularly results in plants being approximately 15 inches from the nearest sprinkler.
After Lamm.
Some sprinkler application nonuniformity can also be tolerated when the crop has an intensive root system.
When the crop has an extensive root system, the effective uniformity experienced by the crop can be high even though the actual resulting irrigation system uniformity within the soil may be quite low.
Additionally, when irrigation is deficit or limited, a lower value of application uniformity can be acceptable in some cases  as long as the crop economic yield threshold is met.
Many irrigators in the U.S.
Great Plains are using wider in-canopy sprinkler spacings  in an attempt to reduce investment costs.
Surveys from western Kansas in 2005 and 2006 indicated only 34% of all sprinkler systems with nozzle
 height of less than 4 ft had consistent nozzle spacing less than 8 ft.
Sprinkler nozzles operating within a fully developed corn canopy experience considerable pattern distortion and the uniformity is severely reduced as nozzle spacing increases.
Figure 5.
Differences in application amounts and application patterns as affected by sprinkler nozzle height and spacing.
Center pivot sprinkler lateral is traversing parallel to the circular corn rows.
Data are from a fully developed corn canopy, July 1996, KSU Northwest ResearchExtension Center, Colby, Kansas.
Data are mirrored about the nozzle centerline for display purposes.
Arrows on X-axis represent location of corn rows and thus the location for higher stemflow amounts.
Although Figure 5 indicates large application nonuniformity, these differences may or may not always result in crop yield differences.
Hart  concluded from computer simulations that differences in irrigation water distribution occurring over a distance of approximately 3 ft were probably of little overall consequence and would be evened out through soil water redistribution.
Some irrigators in the Central Great Plains contend that their low capacity systems on nearly level fields restrict runoff to the general area of application.
However, nearly every field has small changes in land slope and field depressions which do cause field runoff, in-field redistribution or deep percolation in ponded areas when the irrigation application rate exceeds the soil infiltration rate.
In the extreme drought years of 2000 to 2003 that occurred in the U.S.
Central Great Plains, even small amounts of surface water movement affected sprinklerirrigated corn production.
Similarly some of the worst erraticity in sprinkler-irrigated corn observed in the summer of 2011 was for sprinklers with 10 ft spaced in-canopy sprinkler packages.
Figure 6.
Large differences in corn plant height and ear size for in-canopy sprinkler application over a short 10-ft.
distance  as caused by small field microrelief differences and the resulting surface water movement during an extreme drought year, Colby, Kansas, 2002.
The upper stalk and leaves have been removed to emphasize the ear height and size differences.
Figure 7.
Erraticity of sprinkler irrigated corn in southwest Kansas in 2011 under extreme drought conditions thought to be related to a nozzle spacing too wide  for in-canopy application.
CROP ROW ORIENTATION WITH RESPECT TO DIRECTION OF SPRINKLER TRAVEL
 When using in-canopy sprinkler application, it has been recommended that crop rows be planted circularly so that the crop rows are always perpendicular to the center pivot sprinkler lateral.
Matching the direction of sprinkler travel to the row orientation satisfies the important LEPA Principles 2 and 5 noted by Lyle  concerning water delivery to one individual crop furrow and equal opportunity to water by for all plants.
Producers are often reluctant to plant row crops in circular rows because of the cultivation and harvesting difficulties of narrow or wide "guess" rows.
However, using in-canopy application for center pivot sprinkler systems in non-circular crop rows can pose two additional problems.
In cases where the CP
 lateral is perpendicular to the crop rows and the sprinkler spacing exceeds twice the crop row spacing, there will be nonuniform water distribution because of pattern distortion.
When the CP lateral is parallel to the crop rows there may be excessive runoff due to the great amount of water being applied in just one or a few crop furrows.
There can be great differences in incanopy application amounts and patterns between the two crop row orientations.
Sprinkler perpendicular to crop rows
 Sprinkler parallel to crop rows
 Figure 8.
Two problematic orientations for in-canopy sprinklers when crops are not planted in circular rows.
Figure 9.
Differences in application amounts and application patterns as affected by corn row orientation with respect to the center pivot sprinkler lateral travel direction.
Dotted lines indicate location of corn rows and stemflow measurements.
Data are from a fully developed corn canopy, July 23-24, 1998, KSU Northwest Research-Extension Center, Colby, KS.
Data are mirrored about the centerline of the nozzle.
PATTERN DISTORTION AND TIME OF SEASON
 Drop spray nozzles just below the center pivot sprinkler lateral truss rods  have been used for over 30 years in northwest Kansas.
This configuration rarely has had negative effects on corn yields although the irrigation pattern is distorted after corn tasseling.
The reasons are that there is only a small amount of pattern distortion by the smaller upper leaves and tassels and this distortion only occurs during the last 30 to 40 days of the irrigation season.
In essence, the irrigation season ends before a severe soil water deficit occurs.
Compare this situation with spray heads at a height of 1 to 2 ft that may experience pattern distortion for more than 60 days of the irrigation season.
Under dry and elevated evapotranspiration conditions in 1996, row-to-row corn height differences developed rapidly for 10-ft spaced sprinkler nozzles at a 4 ft nozzle height following a single one-inch irrigation event at the KSU Northwest Research-Extension Center, Colby Kansas.
A long term study  at the same location on a deep silt loam soil found that lowering an acceptably spaced  spinner head from 7 ft further into the crop canopy  caused significant row-to-row differences in corn yields.
Figure 10.
Crop height difference that developed rapidly under a widely spaced  in-canopy sprinkler  following a single 1 inch irrigation event at the KSU Northwest ResearchExtension Center, Colby, Kansas.
Photo taken on July 6, 1996.
Figure 11.
Row-to-row variations in corn yields as affected by sprinkler height for 10 ft.
spaced in-canopy sprinklers.
Sprinkler lateral travel direction was parallel to crop rows.
Data was averaged from four irrigation levels for 1996 to 2001, KSU Northwest Research-Extension Center, Colby, Kansas.
COMBINATION OF EFFECTS CAN CAUSE ERRATICITY
 Sometimes poor design, installation or maintenance problems can exist for years before they are visually observed as sprinkler irrigation erraticity.
It may take severe drought conditions for some of these subtle effects to combine to such an extent to be noticeable erraticity.
In addition, smaller row-to-row differences in crop yield cannot be measured with yield monitors on commercial-sized harvesters.
An example of a combination several of these subtle effects was observed during the severe drought of 2002 in northwest Kansas.
The small nozzle height difference on this sprinkler allowed at least three small effects to combine negatively to cause the sprinkler erraticity:
 1.
Since there are no pressure regulators, the small height difference results in unequal flow rates for these low pressure spray nozzles.
2.
There is an incorrect overlap of the sprinkler pattern due to the height difference with one sprinkler within the canopy while the other two nozzles are above the canopy.
3.
Evaporative losses would be greater for the nozzles above the crop canopy.
Figure 12.
Erraticity of sprinkler-irrigated corn near Colby, Kansas during an extreme drought.
The severe droughts of the early 2000s and 2011-2012 in Kansas was devastating to production on many sprinkler irrigated corn fields, but the erraticity did highlight some design and management issues that producer might need to address before the next irrigation season:
 1.
Does the selected sprinkler package strike the correct balance in reducing evaporative losses without increasing irrigation runoff or in-field water redistribution?
2.
Does the sprinkler package and its installation characteristics provide the crop with equal opportunity to applied or infiltrated water?
3.
Are the sprinkler nozzle heights and spacings appropriate for the intended cropping?
4.
Should planting of taller row crops such as corn be in circular patterns if in-canopy sprinklers are used?
5.
Are there subtle irrigation system characteristics  that might combine negatively to reduce crop yields?
These design and management improvements won't change the weather conditions, but they might change how the crop weathers future droughts.
This paper is part of a center pivot irrigation technology transfer effort is supported by the Ogallala Aquifer Program, a consortium between USDA Agricultural Research Service, Kansas State University, Texas A&M AgriLife Research, Texas A&M AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
While crop water use is essential for crop production , some irrigation technologies reduce non-beneficial evapotranspiration , which improves application efficiency.
Reductions in evapotranspiration  while maintaining yields directly improve the CWP and reduces the amount of water pumped.
Water is essential for normal plant growth and makes up to 90 percent or more of the weight of fresh growing plants.
Irrigation is used to maintain proper soil moisture for achieving optimal yields or for maximizing return on investment.
Understanding the basic principles of soil moisture storage and management is necessary for the efficient use of water in irrigated agriculture and to reduce the pollution potential from runoff and deep percolation.
increasing demands on water necessitate efficient irrigation practices to apply correct amount of water at proper time
 Jewel L.
Meyer, Norman W.
Ross, Verne H.
Scott and Clyde E.
Houston
 Economic production of practically all crops in California is dependent on irrigation.
Efficient use of irrigation water requires knowledge of soil characteristics and of water use by the plant-among other factors-to design an irrigation system that can apply the correct amount of water to the proper depth of soil at the required time interval.
Research workers have investigated these factors and developed standards for design under relatively ideal conditions.
The farm operator's problem is to apply those standards to his crop, soil and water conditions.
Procedures used to develop information on consumptive use of water by peaches and irrigation efficiencies possible are exemplified by a study conducted on a one-acre plot in a commercial bearing orchard near Hughson, Stanislaus County.
The trees-Fay Elberta variety-were planted on 20' centers in 1949.
The orchard is clean cultivated and the 1956 yield was 25 tons per acre.
The soil in the study plot is Hanford sandy loam with an apparent specific gravity of 1.55.
It is formed from recent alluvial material of granitic origin, absorbs water readily, and retains it fairly well.
It is an excellent agricultural soil, well adapted to a wide variety of crops, and has a Storie Index of 95%.
The study plot was surrounded by a l' levee and all water applied was retained in the basin.
The first step in an irrigation evaluation study is to measure-as accurately as field conditions will permit the water applied.
In this study, water was delivered through a 24".
monolith concrete
 pipe on a rational-demand schedule, normally in flow rates of 15 cubic feet per second.
The flow was discharged simultaneously through two 24" valves each located in the center of a 5' concrete box.
The box was open on one side, permitting the water to flow into the check after some of the high velocity of water dis-
 Type of weir used in field irrigation study.
charging from the pipe line had been dissipated.
For these conditions a sharp-edged suppressed weir, equipped with an automatic water stage recorder, was used.
It consisted of a steel plate extending across the full width of the concrete box.
A stilling well connected to the face of the weir housed a float which responded to the height of water passing over the weir.
This level was transmitted to the chart of the recorder.
The amount of water applied to the plot was computed from the length of weir and the length of time the average depth of water passed over the weir.
There was practically no rainfall during the irrigation study season.
Soil sampling was done to show extent and control of a continuous supply of moisture.
Soil samples were obtained in l' increments in 9' of soil profile before and after each of the irrigations during the season.
The samples were immedi-
 Concluded on page 38
 Continued from page 6
 The experience of the two water conservation districts in Santa Clara County illustrates the role of the public district in dealing with conflicts of this type.
The Santa Clara Valley Water Conservation District was organized in 1929 after two attempts to use alternative boundaries.
The South Santa Clara Valley Water Conservation District was created in 1938.
This southern district was unable to execute its program until the original area within the district was enlarged in 1951 from 18,000 acres to 34,900 acres.
In both cases difficulties were encountered in reaching agreement on the incidence of benefits.
One of the primary purposes of the district was to encompass within its boundaries the interests which were to be benefited from the collective action so that the costs of executing the action could fall upon these benefited interests.
However, the anticipated benefits from the early water management proposals were not distributed uniformly to all ground-water users.
Santa Clara County contains two distinct ground-water basins, one sloping north toward San Francisco Bay while the other slopes toward the Pajaro River in the south.
The small Coyote Valley connects the larger northern and southern basins.
Water users in Coyote Valley were reluctant to join the district because they feared detention dams and stream flow diversion would lessen the ample volume of influent seepage of water from the stream to their portion of the groundwater reservoir and that the management of the poorly drained areas would become more difficult.
In addition, water spreading at a lower elevation in either district would have been of no benefit.
Consequently, Coyote Valley was omitted from inclusion in the two original districts.
In fact, the Central Santa Clara Valley Water Conservation District was formed to protest a water-right application by the northern district.
With the failure of this action, Coyote Valley was annexed to the Santa Clara Valley Water Conservation District in 1952 and the original plan was adjusted to provide benefit to the area.
The district procedure provided for local interests to register their approval or disapproval with respect to the proposed plan.
In these instances the lack of coincidence of district and basin boundaries was a factor leading to conflict and contributing to delay in the initiation of effective ground-water management.
The method of assessing project costs is one of the terms of organization which is frequently a source of conflict with respect to ground-water management.
These conflicts of interest center around the question of whether the distribution of costs reflects a reasonable relationship to the distribution of benefits.
In the case of the attempt to establish a ground water management organization in Santa Clara County, agreement was not reached concerning the method for raising revenue until four methods had been considered: 1, a tax upon each parcel of land proportionate to the project benefits assessed to it; 2, a tax upon the quantity of water pumped from each well; 3, an assessment upon the value of the land and improvements; and 4, taxing the land-exclusive of improvementswhich was the method that finally won general agreement and was incorporated into enabling legislation of 1929.
The role of the district in these conflicts of interest was to provide the means for reaching a decision in a situation of conflict and to have the authority to collect the required revenue.
The election procedure and informal interest group committee were used to settle these conflicting interests.
The authority of these districts to collect revenues was never seriously questioned although the ability to issue bonds and the size of bond issues did become questions of electoral conflict.
The district form provides a flexible management tool for determining the incidence of project costs or, to put it differently, of pricing the services rendered.
Because of this flexibility, revenue or pricing schemes may be used to fit local ground-water management problems so that there is a coincidence of the incidence of project benefits and costs or that a reasonable relationship exists between them.
The ability of the district to associate costs with benefits should not be confused with the incidence of expenditure.
In fact, the largest expenditures of the water conservation districts in Santa Clara County were made to construct detention dams outside of the district.
This would suggest that, if a particular watershed management practice in the area above the reservoirs were measurably beneficial to the district program, the incidence of expenditure could be made to fall upon the landowners above the dam while the incidence of cost and of benefit would be within the district or could be partially shared by the district.
For example, the district could enter into contractual arrangements with the watershed landowners and pay them to follow agreed-upon practices.
Stephen C.
Smith is Associate Specialist in Agricultural Economics, University of California, Berkeley.
Foregoing article is based on Giannini Foundation Paper No.
152, "Problems in the Use of the Public District for Ground-Water Management" by the same author
 Continued from page 26
 ately brought to the laboratory, weighed and dried for 24 hours at 230F to determine moisture percentage on a dry basis.
About 43" of water were applied to the test plot during the season by seven irrigations with the individual amounts varying from 5"-8" at an average of about 6".
The soil moisture extraction during the period of the seven irrigations in 9' of the soil profile was 36".
The 7" difference between the 36" and the 43" applied can be attributed to deep percolation below the root zone.
The water application efficiency or amount of water retained in the root zone divided by the amount applied was 84%.
This is a high efficiency, as should be expected with an irrigation system wherein large flows of water are contained in relatively small areas.
The total amount of water consumed from the time that leaves appeared on the trees, in the middle of March, until the time they were shed, around the first of November, was nearly 44".
The 8" difference between total water consumed and water furnished by irrigation is attributable to winter rains.
Of the total water consumed 23% was extracted from the top foot of soil; 63% extracted from the top and 87% from the top 7'.
Jewel L.
Meyer is Farm Advisor, Stanislaus County, University of California.
Norman Ross is Farm Advisor, Stanislaus County, University of California.
Verne H.
Scott is Associate Professor of Irrigation, University of California, Davis.
Clyde E.
Houston is Extension Specialist in Irrigation and Drainage, University of California, Davis.
Grower Alfred Wilson, of Hughson, cooper.
ated in the study reported in the above progress report.
Continued from page 5
 Other studies include the development of reconnaissance techniques to evaluate rainfall disposal and possibilities of yield increase, and to investigate watershed paving as a possible means of yield maximization and debris control.
The potentialities of vegetation management as a means of increasing California water supplies are being considered in detail.
Early results indicate that vegetative management may be a new tool to assist in the beneficial utilization of watersheds to produce increased runoff.
R.
H.
Burgy is Assistant Professor of Irrigation, University of California, Davis.
F.
Pillsbury is Professor of Irrigation and Engineering, University of California, Los Angeles.
How does water price affect irrigation technology adoption?
The 815N values at most sites were fairly consistent with depth from the surface to the water table.
There is no evidence from our data that denitrification is a significant process at any of the sites, with the possible exception of the Salinas Valley septic tank site.
Thus, except for one site in the eight main test sites, the results demonstrate that measuring the 815N value immediately below the NO3 source can be an accurate indicator of the fingerprint of that source and that, under the conditions prevailing at these sites, the fingerprint will not change much during NO3 transport to groundwater.
This is a very important conclusion for use of the N isotope technique to indicate sources of NO3 in groundwater.
Nevertheless, users of the 815N approach should be aware of the potential for mixing of 815N from multiple sources and of denitrification under some circumstances.
Careful hydrogeologic characterization as well as sampling of both the unsaturated and saturated zones beneath potential sources are therefore typically required for successful application of the 815N approach.
Gareth Green David Sunding David Zilberman Doug Parker Cliff Trotter Steve Collup
 The use of water price or best management practices have been advocated by some commentators to induce adoption of low-volume irrigation technologies and to encourage water use efficiency.
However, the method of water application is only one of many inputs and constraints in agricultural production.
California's highly diverse topography, soil types and variety of crops influence irrigation technology choices, therefore a policy mandating adoption of modern technologies is likely to have undesirable impacts.
Crop type appears to be a major consideration in technology choice, as some technologies may be incompatible with some types of crops.
Continued urban population growth, heightened public awareness of the environmental benefits of in-stream water flows, and the virtual halt of water supply development in California have increased pressure on state and federal agencies to reallocate water away from agriculture.
Many publicinterest groups and policy makers have suggested that growers could increase their use of low-volume irrigation technologies while maintaining current production levels.
Some interests have even advocated imposing agricultural "best management practices" mandating the adoption of irrigation technologies.
California growers have been criticized for their "irrational" and "inefficient" irrigation technology choices.
It has been suggested that growers could maintain or increase their profitability while using
 fewer resources.
In this article, we assess whether technology choice is consistent with the assumption of profit maximization and, if so, determine which factors most influence technology choice.
This research was supported by the California Water Resources Control Board, Interagency Agreement No.
1-155253-0, Monterey County Water Resources Agency and the U.S.
Environmental Protection Agency Assistance Agreement Nos.
I009564-91-0 and C9009532-90-1.
The contents do not necessarily reflect the views and policies of the U.S.
EPA, Monterey County or the California Water Resources Control Board.
The authors appreciate the assistance of Heike Clausnitzer, Amy Wong, Mike Tolin and Brian Lindsay in laboratory analytical work and of Dr.
Richard Mulvaney at the University of Illinois for 815N analysis.
Some commentators have advocated the use of water price as a policy tool to induce adoption of low-volume irrigation technologies and to encourage increased water-use efficiency.
Specifically, environmentalists and many economists frequently assert that irrigation water should be priced to encourage adoption of modern technologies and reflect the value of water outside agriculture.
However, the effectiveness of water price to achieve these goals may be limited because the method of water application is only one of many crucial inputs and constraints in agricultural production.
Our model demonstrates that large increases in the price of water generally encourage heavier reliance on drip and other low-pressure irrigation systems for certain crops, but may have only modest effects on adoption decisions for other modern irrigation technologies.
Irrigation decisions in Arvin
 We selected the Arvin Edison Water Storage District, located in the southern San Joaquin Valley at the terminus of the Friant-Kern Canal, as our study area.
There is wide variation in the types of irrigation technologies employed in the District: 25% furrow or flood, 49% high-pressure sprinkler and 26% low-pressure drip and microsprinkler.
This variation makes the District ideal for analysis because there is a large amount of variability, yet the area is relatively
 small SO the growers participate in many of the same markets and institutions.
The District was initially formed in 1942 to contract for irrigation water, and in 1965 began percolating water to recharge the local groundwater aquifer.
Because of the regional climate and favorable soils, growers in the District have diverse cropping patterns, as shown in table 1.
Grapes, citrus, deciduous, truck crops, potatoes and cotton make up 89% of the cultivated acres in the District.
We employed a standard multinomial logit statistical model to estimate the probability that a given irrigation technology would be adopted on a given field.
Under this modeling framework, if a particular crop is irrigated almost solely under one irrigation technology, the summary statistics of the adoption probabilities will not be accurate.
In the District, both potatoes and cotton use a high percentage of high-pressure sprinkler irrigation.
In this case it is reasonable to combine potatoes with truck crops because they have similar production characteristics and are irrigated under each of the technologies considered.
However, cotton is not similar to any of the other crop types and only uses gravity and high-pressure irrigation.
Therefore it is necessary to remove cotton from the statistical analysis.
Eliminating cotton and combining potatoes with truck crops does not substantially change the results.
The data on land allocation, irrigation technology, cost of water and water source were collected by the District.
Our study includes truck crops , citrus trees, deciduous trees and grape vineyards, which make up 76% of the planted acreage in the District.
There are 1,493 field-level observations from the 1993 growing year in our data set, which includes all growers in the District who grow the crops listed.
The remaining acreage is planted in cotton, grains, irrigated pasture and dry-land crops.
We consolidated irrigation technologies into three groups, based on the level of pressurization they require: furrow, flood and border, which are considered gravity technologies
 and are used on all types of crops; high-pressure sprinklers, which are used primarily on truck and deciduous crops; and low-pressure systems, including drip, microsprinklers and fan-jet systems, which are also used in each crop group.
The use of highand low-pressure irrigation technologies may reduce water use on fields with coarse soils or steep slope by increasing water application uniformity and reducing deep percolation and runoff.
There are several important points to be raised concerning low-volume technologies and perennial crops in the District.
First, low-volume systems such as drip only wet a small area of soil.
As a result, perennial crops under drip irrigation form a smaller root system than if gravity irrigation were used.
Many growers feel that this makes the crop more susceptible to disease and increases the accumulation of salts, which reduces the attractiveness of these systems.
Second, the cost of switching to low-volume technologies is high.
This implies that the benefits from adopting low-volume technologies must be substantial in order to outweigh the cost of investing in the new technology, and that water savings alone may not justify technology adoption.
Finally, many of the perennial crops in the District were established prior to the introduction of lowvolume systems.
Because different types of root systems develop under the different types of technologies, growers are reluctant to switch technologies on established perennial crops for fear of damaging them.
This is most evident in vine crops, where 61% of the acreage employs gravity irrigation.
However, in response to these criticisms some growers have
 Crop type may influence adoption of lowvolume irrigation technology such as microsprinklers.
stated that use of multiple drip emitters for each tree, and a long transition period using both gravity and lowpressure systems, allows technology switching without damaging crops or making them susceptible to disease.
The District estimates groundwater pumping costs based on pumping depths of groundwater and the energy cost for the size of pump needed to lift water from a given depth.
The variable price for surface water is the use fee that the District charges for each acre-foot that is actually delivered; on average this is $25 less per acre-foot
 TABLE 1.
Irrigation technology and acreage by crop
 Crop	Acreage	Gravity	pressure	pressure
 Citrus	12,065	15	1	84
 Deciduous	11,700	27	33	40
 Grapes	23,665	61	2	37
 Truck crops	12,856	22	73	5
 Potatoes	14,721	1	98	1
 Cotton	17,286	1	99	0
 Total	92,293	25	49	26
 TABLE 2.
Irrigation technology and acreage by variable water price
 Range of variable	High-	Low-
 water price	Acreage	Gravity	pressure	pressure
 Less than $30	20,304	27	49	24
 $31 to $45	19,382	17	48	35
 $46 to $60	34,148	27	49	24
 $61 to $75	13,844	21	33	46
 Greater than $75	4,615	27	59	14
 Fig.
1.
Irrigation technology by slope.
than groundwater pumping costs.
Growers in the District pay a relatively high variable price for water.
In 1993 the price ranged from $12 to $57 per acre-foot for surface water and from $40 to $88 per acre-foot for groundwater.
However, the District adjusts the fixed fee for surface water SO that the total price for ground and surface water are approximately the same, ranging from $50 to $110.
The price of both ground and surface water in the District has increased since 1993.
The wide range of water prices in the District creates an ideal forum for analyzing the effect of price on irrigation technology choices.
Table 2 shows that there is not a clear pattern of technology choice as water price increases from less than $30 to more than $75 per acre-foot.
For example, low-pressure irrigation is used on 24% of the acreage that receives water at less than $30 per acre-foot.
The acreage increases to 35%
 in the next price range, but falls to 14% for those acres that pay more than $75 per acre-foot of water.
However, it is important to note that only 5% of the cultivated acreage in the District faces a water price of more than $75 per acre-foot, SO this has only a small effect on our results.
Soil permeability and field slope are the two dimensions used to define land quality.
These data were collected from the Kern County office of the U.S.
Natural Resource Conservation Service.
The data provide soil type for each quarter section.
District land maps were used to place each field in the corresponding quarter section.
Permeability and slope were given in inches per hour and percent, respectively.
Both permeability and slope were given in ranges; the midpoint was taken and used to construct weighted averages for each quarter section.
Figure 1 shows the distribution of irrigation technology for given slope ranges.
Note that as slope increases the percent of acreage under lowpressure irrigation also increases.
This indicates that the grower's irrigation technology choice is conditioned on land characteristics.
The effect of permeability on technology choice is not as distinct.
These data are used with a statistical model of technology adoption.
The crops, irrigation technology and agronomic diversity of the District are especially well suited to give insight into the constraints that growers face when responding to
 TABLE 3.
Effect of variable on probability of technology adoption
 Field size	-	+	+
 Soil permeability	-	+	+
 Receive surface water	-	-	+
 Citrus	-	-	+
 Deciduous	-	-	+
 Grapes	+	-	+
 "+" indicated an increase and indicates a decrease in the probability that the irrigation technology will be adopted.
The model predicts the probability that a given irrigation technology is adopted as a function of crop, land characteristics, water source and water
 price.
The results in table 3 show whether a specific variable increases , decreases  or does not affect that probability of technology adoption.
The results indicate that the adoption of irrigation technologies is highly dependent on crop type.
After controlling for field-specific factors, highpressure systems are less likely to be adopted on all perennial crop ; low-pressure technologies are more likely to be adopted on all perennial crops.
This finding can be attributed to the physical interaction between highpressure sprinklers and perennial crops.
High-pressure sprinklers disperse water over a large area, saturating the crop, which can cause disease in many perennial crops as well as some annual crops.
Therefore highpressure sprinklers are not used on some perennial crops.
Under gravity irrigation, the results are less pronounced but still evident.
This corresponds with the knowledge that many perennial crops can still be competitively grown with the traditional technology under the right growing conditions.
However, we found that the choice to grow annual crops increases the probability of adopting highpressure irrigation technologies.
The results also show that the adoption of low-pressure technology is highly sensitive to water price.
This finding agrees with standard economic theory that water-saving technologies are adopted as the price of water increases.
However, this does not hold true for high-pressure technology, which has a negative sign.
In the study area, high-pressure irrigation has been in use since the late 1950s.
Currently high-pressure irrigation is near the top of its diffusion curve; that is, it has been adopted on most crops that it can be productively used on.
For example, potatoes are grown almost exclusively under highpressure irrigation.
As a result, the adoption of high-pressure irrigation is not sensitive to changes in water price in the District.
Instead, the results indicate that growers have begun to switch from high-pressure to low-pressure irrigation.
In fact, as the
 price of water has increased over time, growers have begun experimenting with different types of low-pressure irrigation on crops that previously used high-pressure irrigation.
This suggests that the growers' response to water policy depends on where a given technology is on the diffusion curvefactor that varies substantially throughout California.
For a better understanding of the effect of water cost on adoption of irrigation technologies, we calculated and graphed the change in adoption probability as a function of water price.
All other variables were held at their mean values.
We observed that as the price of water increases, growers switch from both gravity and highpressure to low-pressure irrigation technologies.
Although we found that highpressure technologies are not as sensitive to land quality as low-pressure or gravity irrigation technologies, the results show that land characteristics are important to technology choice.
Low-pressure irrigation is highly dependent on land-quality characteristics, especially field slope.
The introduction of low-pressure technologies allowed cultivation of land that previously had been difficult and costly to farm due to its topography.
Variations in soil permeability and slope have a dramatic effect on gravity and lowpressure irrigation adoption.
This also indicates that growers who have relatively flat fields with nonpermeable soils are likely to continue using gravity technologies rather than adopt low-pressure technologies.
Other economists have shown theoretically that modern irrigation technologies are less likely to be adopted on fields with surface water supplies rather than groundwater supplies.
This is because it is easier to provide the additional pressure required for pressurized systems with groundwater pumping.
This holds true for highpressure but not for low-pressure irrigation.
There are two explanations for this.
First, the District supplies pressurized water to many of its growers.
However, the pressure is not consistent throughout the District and is of-
 ten only high enough to run a low-pressure system.
Second, there is an important issue of reliability of water supply that has not been addressed.
The District's water contracts with the U.S.
Bureau of Reclamation guarantee it only a small amount of Class 1 priority surface water supply each year.
Although historically the District has met water demands by pumping groundwater with District-owned wells, surface water is perceived as a less reliable source of water than groundwater because it is under bureaucratic control.
Therefore the adoption of low-pressure irrigation in areas that receive surface water may be intended to minimize the risk of an uncertain water supply to perennial crops.
This is not the case with high-pressure irrigation, which is used primarily on annual crops that can be taken out of production if the water supply is limited.
Our model shows that growers behave in a manner consistent with economic theory.
The adoption of various irrigation technologies can be partially explained by a model based on an assumption of profit maximization.
This observation implies that agricultural water use can be controlled by changing economic incentives such as water price and availability.
However, growers face rigid constraints related to their land and crop experience that condition their response to price incentives.
As a result, policy makers should expect a wide variation in irrigation technology choices among growers in response to water policy.
Fig.
2.
Probability of adoption by water price.
Fig.
3.
Probability of adoption by soil permeability.
Fig.
4.
Probability of adoption by field slope.
We have verified that there are many determinants of irrigation technology choice, including crop choice and soil characteristics, in addition to water price and availability.
Crop choice appears to have a profound effect on technology choice, as some technologies may be incompatible with some types of crops.
Therefore it is important to consider the crops grown in a region when implementing policy.
Field characteristics are also important.
For example, if a field is flat and has low water permeability, a grower is unlikely to switch to a modern irrigation technology.
In such a case, increases in price may simply reduce retained earnings, with little or no effect on irrigation technology adoption.
In particular we found that lowpressure irrigation technologies are
 High-pressure sprinklers disperse water over a large area, which may make them a more desirable choice than a low-volume irrigation system for large fields.
more likely to be adopted as water price increases.
Adoption of lowpressure systems is especially sensitive to water price in the District because there are many crops grown with gravity irrigation that can be grown with low pressure.
In this case an increase in water savings, in addition to other benefits associated with low-pressure irrigation, may make adoption a cost-effective response to higher water prices.
The impact of changing how irrigation water is priced and delivered has
 an important distributional component.
Whether or not a grower adopts irrigation technology in response to price increases depends on crop, topography and soil characteristics.
However, using water price rather than best management practices as a policy tool allows growers flexibility in their response, which minimizes policy impacts.
As a result, technology adoption that stems from changes in water-pricing policy will be gradual.
This will minimize policy impacts because growers will be able to make the
 decision of when to adopt, depending on their own particular circumstances.
Best management practices that dictate agricultural technology choices will have potentially large impacts on California growers.
A policy that mandates when a given technology is to be adopted will probably be inefficient because it does not allow for the diversity among growers.
Our results show that California's highly diverse climate and soil conditions influence irrigation technology choices, and a "one-sizefits-all" policy mandating adoption of modern technologies is likely to be highly inefficient.
CALIFORNIA AGRICULTURE ASSOCIATE EDITORS
 Animal, Avian, Aquaculture and Veterinary Sciences Bennie I.
Osburn
 Economics and Public Policy Harold O.
Carter Alvin Sokolow
 Food and Nutrition Barbara Schneeman Eunice Williamson
 Human and Community Development Linda M.
Manton Karen P.
Varcoe
 Land, Air & Water Sciences Garrison Sposito Henry J.
Vaux, Jr.
Natural Resources Daniel W.
Anderson Richard B.
Standiford
 Pest Management Michael Rust Frank Zalom
 Plant Sciences Calvin O.
Qualset G.
Steven Sibbett
Irrigation Sensor Installation Tips
 Value of Using Sensors to Manage Irrigation and Tips for Proper Installation
 Irrigation Scheduling: Checkbook Method
 Soil Water Sensors for Irrigation Management
 How Much Irrigation is Needed on Corn in the Vegetative Growth Stage?
Each year, the Upper Big Blue NRD requires each farmer to use soil water monitoring equipment in one irrigated field, and to turn the data in to the NRD.
After reviewing the data over the past few years, I found about 1/3 are doing a good job of applying the correct amount of water that will minimize deep percolation while producing top yields.
The other 2/3s could save some money and water without lowering yield.
In fact, about 25% could save a lot!
Understanding Soil Water Content and Thresholds for Irrigation Management
 Sumon Datta Research Assistant
 Saleh Taghvaeian Assistant Professor and Extension Specialist, Water Resources
 Jacob Stivers Research Assistant
 The ever-growing population in the world is expected to reach 9 billion by 2050, and there is an urgent need to produce more food, feed and fiber to meet these increasing demands.
Irrigated agriculture plays a pivotal role in supplying this demand.
In the U.S., only 16 percent of cultivated croplands are irrigated, yet, this small portion produces nearly 50 percent of crop revenues.
Simultaneously, the irrigated croplands use a large amount of water to maintain a maximum yield of crops.
According to a 2013 Farm and Ranch Irrigation Survey  conducted by the National Agricultural Statistics Service of United States Department of Agriculture, Oklahoma had more than 400,000 acres of irrigated land.
About half million acre-feet of water was applied in these fields in the survey year.
The high water requirement of irrigated agriculture necessitates Oklahoma growers to continue improving irrigation management to maximize water and crop productivity.
Without advanced irrigation management, overor underirrigation may occur, leading to several negative environmental and economic impacts.
In the case of over-irrigation, growers can lose money due to higher energy costs of pumping additional water without an economic increase in production.
In addition, if the irrigation pumps are run more often, the wear and tear will decrease the overall lifespan.
Over-irrigation also may increase topsoil erosion and can cause the contamination of downstream resources due to movements of water-soluble chemicals.
But most importantly, over-irrigation depletes water resources, which could consequently increase a region's susceptibility to drought.
On the other hand, under-irrigation results in reduced yield of crops, which in turn, causes loss of revenue for growers and food security issues for the region.
Several methods can be implemented to achieve efficient and improved irrigation management.
Examples include tracking crop water use based on weather data, using crop indicators such as canopy temperature and monitoring soil water status.
It is best to use multiple methods  to more accurately determine when to irrigate and how much water to apply.
This fact sheet will focus on one of the most promising methods in irrigation management: soil water monitoring.
In Oklahoma, only 11 percent of farms used soil water monitoring sensors for irrigation scheduling
 .
Hence, there is a great potential for improving irrigation management by promoting the use of advanced soil water monitoring sensors.
To plan for irrigation scheduling, growers need to know how to interpret the numbers reported by these sensors, which requires understanding of the basic soil water concepts and thresholds.
This fact sheet provides agricultural producers with the basic concepts of soil water and the thresholds utilized for proper interpretation of sensor data for efficient irrigation scheduling.
With efficient irrigation management practices, producers can manage and conserve water, maximize the yield of crops and improve economic benefits.
Reporting Soil Water Content
 The soil water content  or soil moisture is the amount of water present in the soil.
It influences plant growth, soil temperature, transport of chemicals and groundwater recharge.
The two most widely used parameters for quantifying SWC or water availability for plants are i) volumetric water content; and ii) soil matric potential.
Volumetric water content 
 The volumetric water content is the ratio of the volume of water to the unit volume of soil.
Volumetric water content can be expressed as ratio, percentage or depth of water per depth of soil , such as inches of water per foot of soil.
For example, if the volume of water is 20 percent of the unit volume of soil containing it, the VWC can be reported as 20 percent, 0.20  or 2.4 inches per foot of soil.
Soil matric potential 
 Soil matric potential, also called soil suction or soil water tension, represents the forces that bind water molecules to solid particles and to each other in soil pores, thus restricting the movement of water through the soil matrix.
Plants must apply a force greater than SMP to be able to extract water from the soil.
As the water is removed from the soil, the remaining water is held more strongly, making it harder for the plant to extract water from the soil through its roots.
The SMP increases as the water is removed from the root zone of the plant.
The SMP is expressed in two major units: kilopascal  and centibar.
One kPa is equal to one cb.
Since SMP is a negative pressure , the values
 have a negative sign.
However, some sensors and sources do not show the negative sign and report the magnitude of SMP without the proper sign.
Relationship between VWC and SMP
 Some soil water sensors provide SWC data in VWC format, while others report SMP.
In some cases, it may be needed to convert between VWC and SMP.
The relationship between these two parameters is not linear, with most of the VWC changes occurring at SMP values of zero to 300 kPa.
Beyond 300 kPa, the soil is too dry for the roots of most plants to extract water and VWC changes per unit change in SMP are significantly smaller.
A soil water characteristics curve, also known as soil water retention curve, graphically displays the relationship between VWC and SMP for a particular soil type.
This curve can be used for converting VWC values to SMP and vice versa.
However, some error may be introduced during the conversion, especially if generalized curves are used rather than those developed for the specific soil where sensors are installed.
Figure 1 shows the soil water characteristics curves developed by OSU for four soils from central and southwest Oklahoma.
Soil water thresholds are specific values of SWC indicating water availability for plant consumption.
These thresholds are used to determine when and how much irrigation is needed.
Saturation is the threshold at which all the pores  are filled with water.
The VWC at this threshold varies from 30 percent in sandy soils to 60 percent in clay soils.
The SMP at saturation is less dependent on soil texture and is close to zero, indicating that there is minimal restriction to water movement and plant roots can extract water from the soil with minimum energy.
Field capacity  is the threshold at which water in larger pores has been drained away by the force of gravity.
An irrigation application depth that causes SWC to go above FC is not desirable, because the additional water will percolate to deeper layers and will not be available to plant roots.
At FC, the water content of the soil is considered to be ideal for crop growth.
Thus, FC is usually considered as the upper threshold for irrigation management.
Most agricultural soils reach field capacity one to three days after an irrigation or rainfall event.
At this threshold, typical VWC varies from 20 percent in sandy soils to 40 percent in clay soils.
Typical value of SMP at field capacity varies from 10 kPa to 33 kPa.
When salinity is a concern, increasing SWC to levels above FC may be appropriate to leach salts below the root zone.
Permanent wilting point  is the threshold where it becomes impossible for plants to extract water at a rate fast enough to keep up with their water demand.
At PWP, soil particles hold the water so strongly that it becomes difficult for plant roots to extract it.
At this threshold, transpiration  and consequently other processes
 Figure 1.
Soil water characteristics curves of four types of Oklahoma soils.
All pores are filled with water
 Water in larger pores has drained
 Plants can no longer extract water
 Figure 2.
Soil water content at saturation, field capacity and permanent wilting point thresholds.
vital to plant survival come to a near stop.
This causes a significant reduction in crop growth and yield of crops.
If SWC remains below the PWP for an extended period, the plant will eventually die.
Irrigation should be applied well before SWC starts approaching the PWP.
The value of PWP varies with the type of plant, soil and climate, ranging from 7 percent in sandy soils to 24 percent in clay soils  when expressed in VWC.
The soil matric potential at this threshold ranges from 500 to 3,000 kPa.
The value of 1,500 kPa is usually considered as the average SMP at PWP for most agricultural soils.
Total available water  is the total amount of water available to plants, estimated as the difference between soil water content at FC and PWP.
Above FC, water is available to plants only for a short period of time , then lost to drainage.
Below PWP, plants cannot apply enough force to extract the remaining water.
Thus, SWC outside this range is considered not available to plants.
Sandy soils cannot hold a large amount of water and have the lowest amount of TAW, whereas, medium texture soils, such as silt loam and silty clay loam have the largest TAW.
Therefore, sandy soils need to be irrigated more often than loam soils.
Although plants can extract water in the full TAW range, stress occurs before SWC approaches PWP.
Water must be applied at a SWC level above PWP to avoid water stress in plants.
Table 1 shows typical values of FC, PWP and TAW for different types of soils sampled across the U.S., and Table 2 shows these values for agricultural soil samples taken from central and southwest Oklahoma.
A comparison between values presented in these two tables shows differences in soil water thresholds for the same soil types.
This is because numbers in Table 1 represent U.S.
averages and include a large variation due to diversity in soil types.
Except for the loam soil, all other soil samples collected from Oklahoma had a smaller TAW compared to national averages.
This suggests more frequent irrigations and smaller volumes may be required since sampled soils had a smaller capacity for holding water available to plants.
Management allowable depletion  is the portion of the total available water  that can be depleted
 Table 1.
Typical soil water thresholds for different soil textures sampled across the U.S.
Soil texture	FC 	PWP 	TAW 
 Sand	10	4	6
 Loamy sand	16	7	9
 Sandy loam	21	9	12
 Loam	27	12	15
 Silt loam	30	15	15
 Sandy clay loam	36	16	20
 Sandy clay	32	18	14
 Clay loam	29	18	11
 Silty clay loam	28	15	13
 Silty clay	40	20	20
 Clay	40	22	18
 Source: Ratliff et al.
; Hanson et al.
Table 2.
Soil water thresholds for different soil types sampled in central and southwest Oklahoma.
Soil texture	FC 	PWP 	TAW 
 Loam	25	13	12
 Silt loam	23	10	13
 Sandy clay loam	31	20	11
 Clay loam	32	22	10
 before plants experience water stress and potential growth reduction.
Although plants can extract water across the entire range of TAW, the cost is not the same.
If TAW is depleted below the MAD limit, plants begin to face water stress.
The greater the depletion, the greater the water stress until PWP threshold is reached and a plant's vital processes cease.
Unlike previous thresholds that were mainly a function of soil type, the value of MAD is a function of stress tolerance,
 growth stage and water use of the crop.
This value is small for sensitive crops, such as some vegetables and is larger for crops that can tolerate higher water stress without affecting their yield.
For example, a sensitive crop like lettuce has MAD of 0.30, meaning that it will start experiencing stress once 30 percent of the TAW is depleted.
A less sensitive crop, such as cotton has MAD of 0.65, suggesting that stress  will occur at 65 percent removal of TAW.
Table 3 shows typical values of MAD and maximum root zone depth for different types of crops.
The MAD values represent average crop water use condition of 0.20 inch per day.
If the crop water use is higher than 0.20 inch per day, smaller MAD values should be used to avoid stress.
For sensors that report VWC, the MAD values provided in Table 3 are multiplied by TAW and then subtracted from FC to estimate irrigation trigger points.
For sensors that report SMP, the irrigation can be triggered at values presented in Table 4 for different types of crops.
Irrigation must be applied when SMP values, recorded by soil water sensors and averaged over the root depth reach or exceed limits in Table 4, depending on the climate.
The smaller values of SMP are for a dry, warm climate and larger values are for humid, cool climate.
Managing Irrigations Based on Soil Water Content
 An optimum irrigation management primarily aims to control the depth and frequency of applied irrigation water to meet crop water requirements, while preventing losses and conserving water resources.
An effective approach to achieve this is to manage irrigations based on SWC information.
The
 Table 3.
Management allowable depletions  and maximum root zone depths for selected crops.
Type of crop	MAD*	depth **
 Cotton	0.65	3.3 5.6
 Barley and oats	0.55	3.3 4.5
 Maize	0.50 0.55	2.6-6.0
 Sorghum	0.50 0.55	3.3 6.6
 Rice	0.20	1.6 3.3
 Soybeans	0.50	2.0 4.1
 Alfalfa	0.50 0.60	3.3-9.9
 Cool season Turf grass	0.40	1.6-2.2
 Warm season Turf grass	0.50	1.6-2.2
 Walnut orchard	0.50	5.6-8.0
 Cantaloupes/watermelons	0.40 0.45	2.6-5.0
 Sweet peppers	0.30	1.6 3.2
 Cucumbers	0.50	2.0 4.0
 MAD values are for crop water use of 0.20 inch/day * Root depths can vary with soil and other conditions.
Effective root depth is usually shallower.
Source: Allen et al.
Table 4.
Recommended SMP values at MAD for selected crops.
Type of Crop	SMP 
 Sweet corn	50 80
 Source: Hanson et al.
three major types of data required for managing irrigations based on this approach are:
 1.
SWC: The soil layer and actual value of SWC at any given time must be known before any decisions on improving irrigation management can be made.
Different types of soil water sensors are available in the market, with the ability to provide SWC data in either VWC or SMP units.
These sensors are significantly different in cost, accuracy and ease of installation and data retrieval.
A factor to consider when collecting SWC information is root depth, which varies with crop type; growth stage; soil type and physical restrictions such as hard-pans  and shallow water tables.
Crops with shallower rooting depths have reduced access to stored soil water and require more frequent irrigations than crops with deep roots.
When installing soil water sensors, it is important to have sensors at several depths across the effective root zone to obtain a complete picture of soil water dynamics.
This is because water deficiency at one depth does not necessarily mean the crop is undergoing water stress, as the plant roots can extract water from other soil layers.
2.
FC and PWP: These thresholds can be obtained from published tables  using soil texture information at the site of interest.
Soil texture can be identified by sending soil samples to the Soil, Water and Forage Analytical Laboratory at OSU through the local Extension office.
The value of FC can also be determined using the soil water reading a day or two after a large irrigation/rainfall event, if sensors were already installed and if the soil had reached saturation.
Once FC and PWP are identified, TAW can be calculated  and used in conjunction with other information to schedule irrigation events.
However, the value of FC alone can be very useful in the preliminary assessment of irrigation efficiency through determining water losses from the bottom of the root zone.
If the numbers reported
 by soil water sensors after irrigation events indicated that SWC was above the FC limit, water is being lost to drainage.
The amount of water in excess of FC will not remain at the measurement depth to be extracted by plant roots.
Going above the FC limit can be allowed for shallower layers, because the water percolating to lower levels will be still within the root zone.
At deeper layers , any drainage becomes a loss to plant roots, resulting in waste of water, energy that was used to apply that water and many nutrients carried with water.
3.
MAD: The value of this threshold can be obtained from published tables based on the type of crop and its sensitivity to water stress.
It can also be modified with time, based on experience and observing the impact of different MAD values on crop yield.
If the goal is to avoid even small stresses, then irrigation should be applied as soon as SWC reaches the MAD limit and should be stopped before SWC exceeds FC.
In situations where an irrigation decision must be made in advance , the time it will take to reach MAD can be predicted based on SWC fluctuations in previous days and forecasted weather conditions.
In some cases, it is acceptable  to allow soil water to drop below MAD.
Examples include crops, such as grape that require some level of water stress to reach a specific chemical concentration and develop a richer taste.
Another example is during late growing stages, when experiencing some water stress does not affect yield.
provide examples of interpreting SWC data collected from two cotton fields in central and southwest Oklahoma, one based on VWC and the other based on SMP.
Managing irrigations based on VWC data
 Figure 3 shows hourly fluctuations of VWC monitored by soil water sensors at two depths for a period of 45 days during summer 2016.
Irrigation water was applied using a furrow system with cotton planted on the center of the beds.
Arrows represent irrigation dates and dashed lines mark soil water thresholds.
The soil texture at this field was sandy clay loam, with FC of 30 percent and PWP of 18 percent.
The total available water  can be calculated as: TAW =  =  = 12 percent or 1.4 inch per foot.
The MAD for cotton was taken from Table 3 as 0.65.
This is equal to 8 percent when multiplied by the TAW.
In other words, the largest amount of soil water content that can be depleted from the root zone of the crop below field capacity before stress occurs is 8 percent.
Therefore, soil water content should not be allowed to drop below 22 percent  in the effective root zone if the goal is to avoid any stress.
The effective root zone depth is smaller than the maximum root zone and might change, depending on water stress the plant is facing and the crop growth stage.
When the upper portion  of the root zone is dry, the plants have the ability to extract water from deeper layers with larger water content.
Managing irrigations based on the data mentioned above is somewhat different depending on how SWC is reported by soil water sensors.
The following sections
 According to Figure 3, four irrigations were applied during the studied period.
The first irrigation event, around July 22, took place when the volumetric water content at both 8-inch and 20-inch depths was below MAD, suggesting that cotton was under some stress when irrigation was applied.
The irrigation event brought the VWC above FC, meaning that some water percolated below both layers.
However, cotton roots go
 Figure 3.
Hourly VWC fluctuations at 8 and 20 inches below soil surface over a 45-day period.
deeper than 20 inches and the drained water may have not necessarily become unavailable to the crop if it remained at lower layers within the root zone.
Soon after this irrigation SWC started declining, with a rapid phase during the first two days and then at a slower rate after July 24.
On July 26, the 8-inch layer became dryer than then 20-inch layer because it is shallower and prone to larger evaporation and root extraction.
The second irrigation event on July 30 was similar to the first in terms of increase in SWC and the rate of water depletion.
The third event on August 7 was somewhat similar, but the 20-inch depth did not respond in the same way.
This could be likely due to applying a smaller amount of irrigation water not enough to saturate the 20-inch soil depth.
VWC at this depth had a smaller increase that did not even reach the MAD threshold Hence, no water was lost to deep percolation below this layer.
The fourth irrigation event was similar to the first two events in terms of changes in soil water content.
lost to drainage.
In this case, reducing irrigation intervals  would be more effective in minimizing stress.
In general, the SWC data collected at this site indicated irrigation management was fairly efficient, with some deep percolation below 20 inches that may have been retained at lower levels of the root zone.
Some water stress may have occurred in between irrigation events as SWC dropped below MAD and even PWP for short periods.
However, this does not necessarily suggest a decline in crop yield, since stress periods did not last too long.
In addition, the entire root zone should be considered, since plants can take up water from deeper soil, which has a greater water content and compensate for water deficiency at shallower layers.
Adding sensors at deeper layers  can help better evaluate the effectiveness of irrigation applications.
The data suggest that increasing the amount of water applied in each irrigation would not help with avoiding stress since with current amounts SWC exceeded FC and thus any additional water could be
 Managing Irrigations based on SMP data
 Figure 4 demonstrates hourly fluctuations of SMP monitored by soil water sensors at two depths during a period of 45 days in the summer of 2015.
Irrigation water was applied to cotton using a sprinkler  system.
Arrows represent irrigation/precipitation dates and dashed lines mark soil water thresholds.
The soil type at this field was silt loam, with the FC of 25 percent and PWP of 11 percent.
The TAW was 14 percent.
The MAD for cotton is 0.65.
So, the maximum amount of water that can be depleted below FC was 9 percent.
The VWC level for triggering irrigation events is 16 percent.
Since the soil water sensor used in this case provided SWC estimates in SMP, calculated thresholds were converted from VWC to SMP, using the soil water characteristics curve.
The SMP value at FC was 23 kPa and at the MAD was 105 kPa.
The estimated MAD is consistent with the range of 100-120 provided in Table 4 as cotton MAD.
Based on the estimated thresholds, irrigations should have been managed to keep the SMP in between 23 and 105 kPa to avoid water loss and stress.
According to Figure 4, the SMP at 10 inches remained above FC for most of the study period , indicating that water was lost to drainage below 10 inches.
However, the drained water was not necessarily lost to the crop since the 24-inch layer was below FC at most times, except a few days at the beginning of the study period.
As stated before, irrigation events could have been triggered at SMP of about 105 kPa.
However, the SMP at the 10and 24-inch layers never exceeded 68 and 87 kPa, respectively.
The average SMP for these two layers
 Figure 4.
Hourly SMP fluctuations at 10 and 24 inches below the soil surface over a 45-day period.
ranged from zero to 60 kPa.
Hence, irrigation intervals could have been longer without affecting crop yield.
A lower irrigation frequency  would have resulted in smaller energy use for pumping water, as well as smaller evaporation losses from wet soil and crop surfaces.
This material is based upon work supported by the Natural Resources Conservation Service, United States Department of Agriculture, under number 69-3A75-16-013.
Funding was also provided by Cotton Incorporated Oklahoma State Program under project number 15-657OK.
Understanding Motor and Gear Drive Nameplate Information for Irrigation Pump Evaluations
 Divya Handa Graduate Research Assistant
 Saleh Taghvaeian Assistant Professor and Extension Specialist, Water Resources
 R.
Scott Frazier Associate Professor and Extension Specialist, Energy Management
 Electric-powered irrigation pumps are widely used in the U.S.
In 2013, nearly 428,000 irrigation pumps were powered by electric motors in the U.S..
As such, there are significant opportunities for energy savings that can be achieved by improving the performance of irrigation pumping plants.
Conducting energy audit studies helps in assessing the efficiency of these systems.
One of the most important first steps is to accurately identify installed equipment.
Original installation notes or manuals are often lost, leaving it up to the energy auditor to identify the make, model and serial numbers of pumping plant system components.
In the case of electric motors and gear drive units, nameplates often remain intact and attached to the equipment, giving the auditor a wide variety of important information to accurately evaluate system efficiency.
Figure 1 shows a complete listing of the various parameters of interest for a gear drive and a typical three-phase AC induction motor.
This is the most common motor found in irrigation systems and most of industry in general.
Basic knowledge of the terms listed on a nameplate allows the auditor to better understand the performance limits of the motor and gear drive, as well as their combined efficiency.
The purpose of this Fact Sheet is to explain the meaning and purpose of nameplate information and show how to use nameplate and measured motor speed to calculate motor loading.
Nameplate information gives the auditor a snapshot understanding of several important operating limits.
For example, if the motor's nameplate Full Load Amps  is 45 and the auditor measures 50, then excessive Amp-pull or load is highly likely.
Alternatively, if 15 Amps on a 45 FLA motor is measured, the motor is very under-loaded and operating inefficiently.
Significant deviations in measured operating levels from nameplate information identify specific problem areas.
Not all motor manufacturers stamp all information given in Figure 1 on the nameplate.
As federal energy efficiency guidelines for motors has increased , nameplate information has become more complete.
Therefore, older motors may have only basic information; and just because a nameplate is still attached to equipment does not guarantee its legibility.
In irrigation audits, the equipment can be old and weather-beaten due to constant exposure to the elements.
Normally, there are two ways to display information on a nameplate.
The first is stamping a metal plate.
This method normally prevents component information from fading over time.
Sometimes the descriptive name where the
 Figure 1.
Common nameplate information found on gearhead housings and AC motors.
stamped data is located cannot be read, but if one is familiar with the data fields it is easy to guess the category of data.
A second way is the information is painted on a metal or plastic plate riveted to the component.
This becomes problematic with older equipment because painted data fades under sunlight or is wiped off by solvents or abrasion.
In this case, the auditor has little to start with.
Figure 2.
Stamped metal nameplate.
An explanation of motor nameplate abbreviations and terms is given below:
 Model Number and Serial Number
 The model and serial number are usually a sequence of letters and numbers determined by the manufacturer.
Having just the model number can help the auditor track down motor specifications even when all other information is missing.
Motor weight must specify pounds or kilograms.
Larger electric motors  used for irrigation can easily weigh 1,300 pounds.
AMB stands for ambient temperature.
The rating or AMB is the maximum room temperature or air space where the motor is located and time it can safely operate under those conditions.
The common rating of 40C-AMB-CONT means continuous operation at 40 C.
Motor life will be longer if ambient temperatures are less.
FLA, voltage and Hz
 FLA is an abbreviation for the Full Load Amp rating.
Motors are designed to operate at 50 to 100 percent of their rated load.
At FLA, the motor runs at 100 percent of its rated load and the label specifies the current it will draw.
Many electrical components like wiring, circuit breaker and starter are sized based on FLA.
Most electric motors are designed to operate at a specific voltage.
Motors can run safely at +10 percent of the rated voltage.
Exceeding the specified range can cause permanent damage.
Some motors are designed to operate at dual voltages, i.e., 230V and 460V, depending on the selected wiring.
For a dual voltage motor, the nameplate should have wiring information for the desired voltage at the bottom of the nameplate.
The abbreviation Hz is the Hertz or input voltage frequency of the motor.
Motor speed is directly related to the line input voltage frequency.
In the U.S., 60 Hz is the standard frequency while 50 Hz is common elsewhere.
HP, phase and RPM
 Output horsepower, or HP, is the motor output at its rated load.
It is dependent on the kilowatts, or KW, demanded by the motor along with efficiency, power factor and actual load.
In energy audits conducted in central, northwest and Panhandle regions of Oklahoma, the horsepower of electric motor-driven irrigation pumps varied from 14 to 100.
As the depth to water table  increases, higher motor HP is required.
Figure 3.
Nameplate of a dual voltage motor with high and low voltage wiring diagrams.
One can easily determine groundwater depth using a water level meter, then determine required motor horsepower.
For more information on how to measure groundwater depth, please refer to Oklahoma Cooperative Extension Fact Sheet BAE-1538, "Measuring Depth to Groundwater in Irrigation Wells".
Generally, electric motors are either single phase or three phase.
Motors larger than about 30 HP are usually three phase.
Three-phase motors typically can be wired for different voltages and amperages described above.
RPM stands for revolutions per minute and is the shaft speed of the motor at the rated HP load.
Depending upon the number of poles, frequency, design and motor slip , the RPM will vary slightly for each manufacturer.
For a four-pole motor operating at 60 Hz, the  RPM would be 1,800.
Design, frame and type
 Design categorizes the motor's starting torque using letters B, C and D to correspond with normal, high and very high starting torque, respectively.
Induction AC motors experience high starting torques as they go from a standstill to FLA RPM.
This is related to Locked Rotor Amps, or LRA, where the starting current can be four to eight times higher than FLA for a few seconds.
LRA may be separately labeled on the nameplate.
The National Electrical Manufacturer's Association, or NEMA, has defined frame sizes using a combination of numbers and letters.
There are two categories of frame sizes based on whether it is a fractionalor integral-type motor.
Fractional sizes include 42, 48 and 56; whereas, 140, 180 and larger are integral type motors.
If a new motor's frame size differs from the old motor, it might not properly fit.
"Type" refers to the category of motor enclosure protecting the windings, bearings, and other vulnerable parts.
There are many types of enclosures listed by NEMA, but the most common ones are Open Drip Proof, or ODP, and Totally Enclosed Fan Cooled, or TEFC.
ODP motors have an open enclosure, so air can freely enter, but liquids and solids cannot enter the motor from an angle of 0 to 15 degrees.
An ODP enclosure is not waterproof and is better suited for indoor applications.
In contrast, a TEFC motor enclosure is totally enclosed and comes with an external cooling fan.
Proper selection of the motor enclosure is very important because it must provide around-the-clock protection, regardless of the situation.
TEFC motors are typically found on irrigation sites because they are designed to work outdoors.
A TEFC enclosure also is required when explosive vapors are present.
Service factor, or SF, is a number that indicates how much overloading a motor can handle without causing permanent damage.
For example, 1.15 SF means the motor can be loaded 15 percent over its maximum rated load for a short time until its internal temperature becomes excessive.
This means a 100 HP motor with a SF of 1.15 can operate at 115 HP load for some time before overheating.
Continuously operating the motor at its SF will adversely affect its efficiency and reduce useful life.
NEMA nominal efficiency and guaranteed efficiency
 Motor efficiency is the ratio of output mechanical power produced to input electrical power.
NEMA nominal efficiency is the average motor efficiency obtained by testing a representative group of motors.
Minimum or guaranteed motor efficiency allows for losses up to 20 percent more than nominal efficiency.
It accounts for output variation among the motors.
Reduction in efficiency will increase pumping costs.
Over time, federal regulations have required newer motors to be more efficient.
It is safe to assume newer motors are more efficient due to a lack of degradation and lower past efficiency standards.
Economic analysis can help users decide if a newer motor will pay for itself within its useful life.
PF and maximum KVAR
 All inductive devices in an AC circuit have a Power Factor, or PF, rating.
It is the ratio of active or real power to total power  while "kVAR" is the amount of reactive power that produces no practical work.
A PF of one means reactive power  is zero and motor is using all delivered power.
Motor efficiency increases with PF because the motor better utilizes supplied power.
Low PF  can result in a utility company's power factor penalty on the customer's electric bill.
An under-loaded motor can cause the PF to drop lower than the PF listed for nameplate rated load.
Actual motor load can be calculated using the method described under Motor Load Calculation Using Nameplate information.
The label Ct stands for constant torque and Vt stands for variable torque.
The presence of these nameplate abbreviations on a motor nameplate indicates it is rated for a variable speed drive.
This is important for customers wishing to retrofit electronic drives onto existing motors.
Duty, insulation and code
 Duty is the duration of safe motor operation.
Most motors operate continuously without requiring a cooling period.
Others operate intermittently, and require a cooling period between on/ off cycles.
For larger motors, continuous duty is common.
The NEMA insulation class describes the motor's ability to handle maximum allowable operating temperature over time.
Figure 4.
Power Factor triangle.
Gear drives play an important role in agricultural machinery.
Prior to variable speed drives, changing drive-to-driven gear or pulley ratios was the only way to vary delivery shaft speed and torque.
Gear drives are not only used to transmit and vary both, but also to alter power delivery orientation.
For example, a right-angle gear drive transposes power from a horizonally-mounted motor to the vertical driveshaft of a turbine pump.
Gear drives have nameplates that are not as detailed as an electric motor.
Figures 5 and 6 illustrate this fact.
The serial number  of a gear drive is often expressed using a combination of letters and numbers.
These will vary from company to company, depending on the type of the gear drive.
Letters S, SH and SL denote three different types of gear drives: standard hollow shaft drive with standard thrust capacity, standard hollow shaft drive with heavy thrust capacity and standard hollow shaft drive with opposed thrust capacity, respectively.
The listed ratio represents the ratio of the input speed to output speed of the gear drive.
A 1:1 ratio means motor and pump shaft speed are identical.
A 1:1.5 ratio for a motor running at 1,770 rpm means pump drive speed will be: 1,780 rpm  = 1,190 rpm.
Output speed is important when determining suitability of a particular pump for a given set of depth, flow and pressure conditions.
Figure 5.
A gear drive nameplate.
Figure 6.
Gear Drive nameplate for a 1:1  drive ratio.
Oil and lubrication requirements are often specified on the gear drive nameplate.
Only use the recommended oil type and grade.
Oil flow rate recommended by the manufacturer should be followed.
Normally, a drip oiling system supplies needed lubrication.
Following the manufacturer's recommendations will prevent over-oiling that will contaminate groundwater or under-oiling that leads to premature wear and tear.
RPM stands for recommended revolutions per minute of the gear drive.
The rpm of a gear drive unit is proportional to the rpm of the attached motor.
The input rpm of the gear drive should match the output rpm of the motor.
Mismatched motor/ gear drive rpm  could lead to premature failure of the gear drive.
Some of the additional specifications that are unique to the manufacturer and general requirement like oil capacity may often be found on the nameplate.
Motor Load Calculation Using Nameplate Information
 This section gives an example of how to use nameplate information to determine motor loading or slip, also known as Slip Calculation.
One of the easiest ways to determine load is to calculate "slip." Full or design load slip is the difference between full load speed and no-load speed.
Full load speed is motor rpm at its rated voltage at maximum rated load.
No load speed is higher than full load speed because there is minimal resistance to movement.
No-load synchronous speeds of 3,600; 1,800; 1,200 and 900 RPM correspond with 2-, 4-, 6and 8-pole motors, respectively.
No load speed is inversely related to the number of poles of the motor.
A greater number of poles proportionately decreases rpm.
Information about full load rpm and design horsepower can be found on the nameplate.
Sometimes the no-load rpm is not listed.
However, the full load rpm will be close to 1,800 or 3,600 rpm.
Actual load is the ratio of true slip to design slip.
True slip is the difference between synchronous and measured rpm.
A tachometer is used to measure the actual speed.
An example on how to calculate load is below.
Given: Full Load rpm  = 1,770 No Load rpm  = 1,800 Measured rpm = 1,780 Design hp = 60
 Required: Calculate a) design slip, b) true slip, c) percent load and d) true load.
Solution:
 a) Design Slip = NLRPM FLRPM 1,800 1,770 = 30 b) True Slip = NLRPM Measured RPM = 1800 1780 = 20 c) % load = Design Slip 30 or 67% True Slip 20 d) True load = design HP X % load hp X 0.67 = 40 hp
 In this particular case, the motor will operate efficiently as it is loaded above 50 percent.
This material is based on work supported by the Natural Resources Conservation Service , U.S.
Department of Agriculture , under number 69-3A75-16-013.
Funding was also provided by the Agricultural Research Service, USDA, under number 3070-13000-011-47S.
The authors are thankful to Dr.
Don Sternitzke, the Water Management Specialist with NRCS Oklahoma State Office for his valuable comments.
Session topics will be tailored to address participants current issues, aspirations and goals for their own operations.
Topics will be supported by data and insights from the past five years of the TAPS farm management competitions.
GROWING VEGETABLES IN WYOMING
 Home vegetable gardening is a popular activity all across the United States.
Gardening serves many purposes such as providing sources of food, exercise, and maybe even profit for many people.
Wyoming residents can grow excellent vegetable gardens if they are aware of the special problems they may encounter.
In Wyoming, the following environmental characteristics may be problems:
 Growing seasons range from short to very short.
Growing season temperatures are often too low, sometimes too high, and often include untimely frost.
High or steady winds can cause physical damage to plants plus soil erosion and rapid drying.
Low relative humidity levels increase the rate of water loss from plants and soil.
Poor native soils are usually alkaline, low in organic matter, shallow, rocky, and cold.
Water is possibly low in quantity and poor in quality.
Hailstorms can be disastrous to vegetable gardens, as well as other crops
 Smart home gardeners find many ways to tailor the garden environment to favor the growth of vegetables.
One way is to locate the garden on a gentle slope facing south, southeast, or southwest.
By orienting the garden in those directions, the soil will warm up more quickly in the spring and cold air will drain away, provided there is no barrier on the lower side.
Choose a spot in full sun.
Vegetables planted on the south side of a building often mature sooner because of the reflected heat from the building and possible protection from the wind.
A Wyoming garden needs a good windbreak on the side facing prevailing winds.
The windbreak can be a fence, trees, or shrubs and usually will give adequate wind protection for a distance downwind equal to 10 times the height of the windbreak.
Avoid placing a vegetable garden close to trees or shrubs whose roots will compete with the vegetables for water and nutrients.
In Wyoming, the growing season is short and summer temperatures can be cool.
When selecting crops, choose from quickly maturing plants that grow well in cool weather, like radishes, leaf lettuce, and onions.
Other crops to consider are cabbage, cauliflower, head lettuce, spinach, beets, carrots, and peas.
Some vegetables, such as tomatoes, peppers, eggplants, melons, winter squash, pumpkins, and sweet corn, must have hot weather and a long growing season to produce well.
Seed catalogs will list many varieties of each crop, but gardeners should choose varieties recommended for their growing areas.
Varieties that have short maturation times or that have been developed in the northern United States or Canada are usually best for Wyoming's climate.
Many vegetable crops can and should be started indoors to avoid potential damage from frost.
These seedlings can be transplanted outdoors when the weather gets warmer.
A gardener can gain a few days or even weeks of growing time by setting out transplants at the normal time for outdoor seed planting.
Transplanting inevitably causes some slowing of plant growth, but it is temporary.
Most plants recover quickly and resume growing if they are given good care.
Some crops, such as sweet corn, cucumbers, melons, squash, and pumpkins, will not recover well from transplanting if their roots are damaged in the process.
Use care when transplanting these vegetables to the outdoor garden.
Often, individual plants or rows of plants are given frost protection early in the season.
Individual plastic plant covers or circular plastic tubes filled with water can help.
A fabric cover over a row of plants will give some frost protection and also will raise the air and soil temperatures under the cover, speeding plant growth.
Clear plastic tunnels, 14 inches tall and 12 inches wide, placed over wire hoops, can be helpful in boosting growth of warm-season plants such as tomatoes and peppers.
Portable cold frames also can be used to give early season protection to small plants.
Gardeners can refer to UWE bulletin B-1148 Gardening: Extending the Vegetable Growing
 Season as well as bulletin B-1151 Hot Beds and Cold Frames for more information.
Wyoming gardeners should give particular attention to the fertilization of their gardens SO growth will not be slowed by lack of nutrients.
An early season soil test will determine which nutrients and how much fertilizer may be needed in the garden.
Vegetables require adequate and constant nutrient sources, especially as they approach maturity.
Reputable dealers sell many different types of fertilizers, SO options are many, ranging from liquid formulations to slow-release types, organic to synthetic.
Always read and follow label directions and do not over-apply fertilizers.
Over-application does more harm than good.
Organic matter is usually lacking in native Wyoming soils.
Pre-plant incorporation of a high-quality, well-composted organic matter will lighten heavy clay soils, improve soil structure, allow better water penetration, allow air to reach root systems , and provide some essential nutrients.
Organic matter is recommended as an amendment for sandy soils to improve water-holding capacity, as well.
As an added benefit, organic matter aids soil microorganisms, helping to make nutrients more available for plants.
Organic matter is the best amendment for vegetable gardens.
Apply 2 inches evenly across the garden area, then till or spade it to a depth of at least 6 inches.
Never add sand to a clay soil because compaction and density will become problematic.
Irrigation of the vegetable garden will be necessary anywhere in Wyoming.
Use the highest quality water available.
Water containing large amounts of dissolved salts will require occasional leaching of the garden to remove these salts.
Overhead sprinklers and drip irrigation tubes or even hand watering can be used to irrigate.
HOW DO I KNOW HOW MUCH WATER I'VE APPLIED?
To easily determine the amount of water you have applied while irrigating, follow these steps:
 Choose a straight-sided can or jar.
A soup, tuna, or single-serve vegetable can will work well.
Place the can in the area to be irrigated.
Irrigate as you normally would.
Using a ruler, measure the amount of water in the can or jar.
Determine how much more or less you need to water at each irrigation to give your vegetables about 11/2 inches of water weekly.
Keep in mind the soil should be moist to a depth of 6 to 8 inches after each irrigation.
Most vegetables will require at least 1 1/2 inches of water each week as they near maturity.
There are no hard and fast rules for frequency of irrigation because of variations in weather, soil types, and garden micro-climates.
Gardens growing in sandy soils will require more frequent watering than gardens in clay soils.
Trickle systems often use less water than other irrigation methods.
Most plants touted as being "repellent plants" have been selected because they have a strong odor to humans, not because insects react to them the same way we do.
In fact, insects detect chemicals very differently from humans.
They are frequently attracted to plants that give off odors humans find offensive, including mustard gas, which is produced by radishes and cabbage.
The real key to a healthy garden is diversity.
The positive effects of using companion plantings come from the added diversification, not necessarily the introduction of a plant that produces a repellent chemical.
Companion planting is sometimes promoted as a means to deter insect pests from attacking garden vegetables.
There is little evidence to support this notion, which is based upon the human sense of smell.
Overhead sprinkler irrigation is satisfactory, but few gardeners know how much water they are applying with this method.
Sprinkler irrigation also wets leaves, which can lead to foliar disease problems.
Trickle or drip irrigation applies water at a very slow rate through tubes set on the ground next to the row of plants.
Foliage does not get wet, and the slow trickle allows water to penetrate and soak the area around the roots.
Mulching with an organic matter source is an excellent home garden practice that helps maintain uniform moisture and temperature in the soil; reduces erosion, water loss, and weed problems; and adds organic matter when the mulch is turned under.
Organic mulches should be applied only after the soil has warmed up in the late spring or early summer; otherwise, the soil temperature will not warm up enough for proper plant growth.
Materials that can be used as organic mulches include grass clippings , sawdust, straw, peat moss, wood chips, leaves, or good quality compost.
When using organic materials, spread a 2to 3-inch layer around the plants in mid-June.
Keep it in place through the growing season.
Additional fertilizer will probably be needed, especially nitrogen, because using of any of these materials may cause nutrient deficiencies to develop in vegetable plants.
Always fertilize when organic mulches are used.
PLANNING THE VEGETABLE GARDEN
 Perennial vegetables, such as rhubarb and asparagus, should be planted along one side of the garden.
This way they are out of the way of tilling and other preparations.
Tall plants, such as corn and tomatoes, should be planted on the north side of the garden, SO they don't shade the smaller crops.
Try to group plants by the length of their growing period.
Separate quick crops from those requiring a full season to mature.
Early maturing crops can be planted in the same row or between rows of later-maturing crops.
For example, radishes can be planted in the same row with transplanted cabbage, cauliflower, and broccoli.
Lettuce may be grown where tomatoes, peppers, and corn will be planted later.
Make sure plants are spaced according to seed or label recommendations.
Remember to leave space in the garden for maintenance and harvest.
Leave enough room to walk and kneel between rows during the growing season.
Cool-season crops grow from early to late spring.
Usually, light frosts will not injure them.
If planted too late, long hot summer days cause many spring crops to "bolt," that is, to flower and form seeds.
Some plants will develop off-flavors, bitterness, poor texture, and low yields.
Examples of vegetables suitable for spring gardens are beets, carrots, lettuce, onions, peas, radishes, spinach, and turnips.
Many of these can be replanted in late summer or early fall for late harvest.
Warm-season crops grow in early through late summer.
Late spring and early fall frosts will damage these plants.
Examples of warm-season crops include tomatoes, peppers, melons, cucumbers, squash, pumpkins, and sweet corn.
Select a sunny site that is easily accessible.
Stake out the site and clean out debris, brush, and rocks.
Have a soil test done.
Contact the local University of Wyoming Extension office for information on soil testing laboratory options.
Work the garden in the fall if possible.
This allows for decomposition of organic matter during the winter.
Loosen the soil but don't overwork it, to a depth of 6 to 8 inches.
Incorporate organic matter at a depth of 2 inches on top of the soil, then turn it under to at least 6 inches.
Sow fresh, new, high-quality seeds.
Generally, old seeds will have low germination rates and may lack seedling vigor.
Drop seeds into continuous marked rows.
Space them according to package instructions.
Cover the seeds according to package directions, and lightly water them.
When using transplants, purchase high-quality, healthy plants.
Follow label instructions for spacing and planting depth.
Thin seedlings as they emerge.
Thinning may actually be harvesting for some plants such as lettuce, radishes, beets, and turnips.
These seedlings make excellent salad greens.
Keep the soil evenly moist until seedlings have emerged or transplants are established.
Plan on routine care of your vegetable garden during the growing season.
The following are some of the tasks to be done throughout the season.
Early on, make sure to thin plants within rows.
This is especially important for root crops, such as carrots and beets, which may be deformed or small if they are crowded.
This is also important for vegetables that have small seeds as they are very difficult to SOW uniformly.
Weeding is essential.
Weeds can rob your vegetable plants of necessary water, nutrients, and light.
There are several ways to weed: pull them by hand, cultivate them with a hoe or cultivator, or use a mulch to inhibit their growth.
Chemical herbicides are not recommended in vegetable gardens.
Small weeds can be pulled by hand or hoed.
Use shallow hoeing or cultivating in vegetable gardens SO the
 plants, especially root crops, are not damaged.
If weeds are allowed to get too large pulling them may damage maturing vegetables, SO weed early and often.
Scout and monitor vegetables often, at least weekly, for insect and disease pests.
If caught early, simple measures, such as hosing off aphids and spider mites or removing a diseased leaf, will be enough to prevent the problem from worsening.
If the problem persists, make sure it is properly diagnosed, then use an appropriate treatment.
Sometimes an insecticide or fungicide may be warranted, but read and follow label directions carefully.
Some gardeners prefer to use cultural methods  and beneficial organisms  for managing pests.
There are many options available.
Vegetable water requirements will vary during the growing season and with the weather.
As crops develop more leaf area, they will usually require more water.
If a garden is irrigated using an automatic timer, the settings will need to be changed during the growing season.
Fertilization is very important, especially as vegetables start to mature.
There is no one best fertilizer to use and the choice is up to the gardener.
When trying to decide how much to apply, have the soil tested by a reputable
 laboratory.
The local UWE office can help.
There are several types of fertilizers available, including slow release, water-soluble, and organic.
Slow release types are useful for those who do not like to mix and apply fertilizers in a liquid form.
They are usually applied once at the beginning of the growing season.
Water-soluble fertilizers must be applied frequently during the growing season.
Organic fertilizers should be well-cured to minimize chances of root damage from salts.
The gardener should understand that organic fertilizers are usually lower in nutrient levels than other types of fertilizers and may need to be applied frequently.
With any fertilizer, read and follow label instructions carefully.
Harvesting should be done frequently and at the proper stage of vegetable maturity.
It is often the most rewarding part of vegetable gardening.
A common mistake is allowing produce to become over-mature, losing the best flavor or appetizing texture.
Try to harvest produce at the stage found at the grocery store.
Frequent harvesting is important for some crops like asparagus, cucumbers, summer squash, and sweet corn.
The best time of day to harvest is in the early morning.
Use or process fresh produce as soon as possible.
VEGETABLE DESCRIPTIONS AND SUGGESTED VARIETIES
 The following information will be helpful in planning a garden, buying seeds or transplants, and growing and harvesting vegetables.
Days from seeding or transplanting to harvest are given in parentheses for most crops to indicate an approximate growing period.
These days will vary in cooler or warmer parts of the state.
Some varieties will not mature where the growing season is short.
Cucumbers, eggplant, muskmelons, okra, winter squash, peppers, tomatoes, and watermelons are not recommended for elevations above 6,500 feet.
Aphids on young pepper plants
 A perennial vegetable, an asparagus plant can live 10 to 25 years.
Plant asparagus in an area of the garden where it will not be disturbed.
Start from 1or 2-year-old crowns planted in April.
Dig a trench 6 inches wide and 6 to 8 inches deep.
Set the crowns 15 to 18 inches apart in rows 48 inches apart.
Place the crown in the bottom of the trench, spreading the roots out.
Keep the crown itself higher than the roots.
Cover the roots with soil and firm it around the plants.
Harvest asparagus the second year after planting, for a period of 1 to 3 weeks.
The root systems need to develop and store food reserves to produce growth the following spring.
Plants harvested for too long a period while they are young will become weak and spindly.
The third year and thereafter, harvest for 8 to 10 weeks.
The tops of the plants can be removed after they die back either in the fall or, preferably, in the spring.
Asparagus spears should be snapped off when they are 5 to 7 inches tall.
It is best to break them off instead of cutting them, as cutting can injure the crown buds that will produce the next spears.
Suggested varieties: Transplants: Jersey King, Jersey Knight, Mary Washington, Purple Passion.
Beans are available either as bush or pole varieties.
Bush beans are popular because they mature early and require relatively little space.
Many bush bean varieties can be harvested 50 to 60 days after seeding.
Pole beans require staking, a trellis, a fence, or some other kind of support.
They also require several more days to harvest, usually about 65 days from seeding.
Interest in these old-fashioned plants has soared recently, in part because of a back-to-basics movement in home gardening.
Heirloom varieties may be desirable for many reasons, but can be challenging in the garden.
If you choose to use heirloom varieties, keep in mind they probably do not have early maturity or disease resistance genes bred into them.
This means heirlooms typically take longer to reach maturity  and may be prone to more insects and diseases than newer hybrid varieties.
Green beans should be planted after the last killing frost in the spring.
Bean seeds planted in cold soil grow very slowly and are more susceptible to seed and stem rotting.
Staggered plantings, 2 to 3 weeks apart, can be made until July 1.
Plant bush bean seeds in rows 24 to 30 inches apart.
Seeds should be sown 2 inches apart in the row and 1 to 11/2 inches deep.
Pole beans should be planted in rows 40 to 60 inches apart.
Green bean plants have shallow roots, SO be careful during cultivation and hoeing.
They also require consistent soil water availability, especially at bloom and pod set time.
Beans should be picked as they reach eating maturity.
Healthy plants will continue to produce for several weeks if the beans are picked regularly.
Suggested bush type varieties: Bush Blue Lake 274 , Early Contender , Kentucky Wonder , Tenderpick , TopCrop , Mascotte , Derby 
 Suggested pole type varieties: Kentucky Blue , Kentucky Wonder , Scarlet Runner , Seychelles , White Half Runner 
 Beets will tolerate cool temperatures and can be planted about 2 weeks before the average date of the last killing frost.
They grow well in cool weather and during the summer.
Plant beets in rows 18 inches apart.
Space the seeds 2 inches apart and cover them with 1/2 inch of soil.
Each beet seed is actually a dry fruit that contains several seeds.
This tends to produce clumps of plants, which must be thinned early.
Leave a final spacing of about 3 inches between plants for best root growth.
As beets increase in size, the tops may grow out of the ground and should be covered with soil to prevent sunscald.
Young beets harvested early when the roots are small are very tender and are of excellent quality.
Heavier yields are produced by letting the roots grow larger, but these beets often will be woody, fibrous, and undesirable.
Beet tops make excellent salad greens a great use for the small plants removed in thinning.
Suggested varieties: Detroit Dark Red , Red Ace , Ruby Queen , Avalanche 
 Broccoli has long been recognized as a good home garden vegetable for fresh use or for freezing.
Sprouting broccoli has a central green head.
After this is harvested,
 small lateral heads often will develop.
Varieties differ in their compactness and the number of sprouting lateral heads they will produce.
Buy or produce transplants and set them out in the early spring, as early as 4 weeks before the average last frost date.
Set plants 18 inches apart in rows 30 inches apart.
The edible broccoli head is actually composed of flower buds.
The heads must be harvested before the flowers open or show any yellow color.
A good mature head will be 3 to 6 inches across.
Heads that develop later will be smaller.
When harvesting, cut 3 to 4 inches of the stem and the accompanying leaves with the head.
Suggested varieties: Bonanza , Green Comet , Green Goliath , Packman , Artwork 
 Brussels sprouts do best as an early spring, fall, or cool weather crop.
For growing in early spring, start seeds about 8 weeks before May transplanting, allowing for harvest around August 1.
Sprouts produced on the lower leaves of the plant should be harvested when they are about 1 to 11/2 inches in diameter.
Lower leaves should be broken away and the sprouts can then be twisted or cut off close to the stem.
Harvest from the base upward as the sprouts develop.
Suggested varieties: Jade Cross , Long Island Improved , Tasty Nuggets , Hestia 
 Cabbage can grow from early spring until late fall and will withstand spring temperatures as low as 15 to 20 degrees Fahrenheit.
Buy or produce transplants by starting them 4 to 6 weeks before the outside transplanting date.
Since cabbage is relatively hardy, it can
 * Number in parentheses indicates days to maturity.
be transplanted outdoors as early as 4 weeks before the average last frost date.
Plant spacing affects head size.
Crowded plants, less than 12 inches apart in the row, will produce small heads.
Spacing should be about 18 inches apart in rows 30 inches apart.
Large headed or late-maturing varieties may need wider spacing.
Harvest cabbage when the heads are of adequate size and are firm and fully mature.
Mature heads left on the plant may split from the pressure of excessive water entering the head.
Make successive plantings of cabbage to avoid a glut of cabbage needing to be harvested at the same time.
Suggested varieties: Copenhagen Market , Earliana , Golden Cross , Salad Delight , Stonehead , Katarina 
 Carrots are another cold-tolerant crop that can be planted 1 to 2 weeks before the average last frost date.
The seeds germinate slowly and often will not emerge until after the frost has passed.
There are many different varieties of carrots with varying colors, shapes, and sizes.
The shorter, half-long, types are better suited to the heavy soils found in Wyoming.
Carrots should be planted in rows at least 18 inches apart with the distance between seeds in the row 1 to 2 inches.
Cover seeds with 1/4 to 1/2 inch of soil.
Seeds germinate slowly and seedlings are often tiny and weak.
Thin seedlings after emergence if necessary.
For carrots to grow and develop properly, there should be at least 2 inches between plants.
Deep, loose soil is best for carrot root formation.
Rocky, heavy, or shallow soils make it difficult to grow good-quality carrots.
In these situations, carrots can be grown in raised beds of well-prepared soil about 10 to 12 inches deep.
Carrots provide a long period of harvest.
They can be used as soon as they are large enough and they can be left in the soil until late fall.
Fall's cool temperatures help increase sugar content and improve flavor.
Suggested varieties: Danvers Half Long , Little Finger , Short 'n Sweet , Sweet Treat , Thumbelina , Purple Haze 
 These plants need a cool climate to develop a good center head, but cold temperatures also can cause stunting of growth and premature heading.
Cauliflower plants should be started about 4 to 5 weeks before transplanting outdoors.
They can be planted outside as early as 2 weeks before the average last frost date and as late as June 15 for a fall crop.
Set the plants 18 inches apart in rows 30 inches apart.
Exposure to sunlight discolors white cauliflower and produces off flavors.
To prevent this, gather the long leaves below the head and tie them together over the head as soon as the head is visible in the center of the plant.
Some newer varieties of cauliflower, such as purple and green types, do not need to be covered.
Cauliflower heads will be mature about 2 weeks after tying, reaching about 6 inches in diameter.
The heads turn from clear white at the peak of maturity to yellowish-brown when over-mature.
Suggested varieties: Early White , Self-Blanching Snowball 
 There are many varieties of cucumbers from which to choose, including those specifically bred for slicing and those used for pickling.
Pickling cucumbers are short and
 blocky in shape.
They mature and become seedy at a smaller size than slicing cucumbers.
Cucumber vines will spread over a considerable area, SO give them plenty of room.
Rows or hills should be 4 to 6 feet apart.
The vines also can be trained on a trellis or fence along the edge of the garden, taking up less space and keeping the fruit off the soil.
For the flower to develop into a fruit, pollination by bees must take place.
Bees carry pollen from male flowers to female flowers.
Female flowers look like they have a tiny "pickle" at their base.
Male and female flowers may be on the same or different plants.
Poor cucumber set is common during rainy or cool weather when bees are inactive.
Cucumber plants often produce male flowers earlier than female flowers and in much greater numbers.
Newer hybrids will produce only female flowers and, as a result, have a high yield potential if plants with male flowers are located nearby.
Cucumbers may be harvested and used from the time they are 11/4 inches long until they begin to turn yellow.
Cucumber fruits may become bitter if plants are grown under severe stress caused by lack of water, low fertility, disease, or unusually hot weather.
Harvest cucumbers regularly to keep them producing longer.
A mature fruit left on the vine will inhibit further flower formation.
Suggested pickling types: Bush Pickle , County Fair , Homemade Pickles , Pick a Bushel ,
 Suggested slicing types: Bush Crop , Early Spring Burpless , Salad Bush , Sweet Success , Green Light , Saladmore Bush 
 Eggplants require hot weather to grow well, limiting their suitability in many areas of Wyoming.
Buy transplants and move them to the garden when the weather is warm,
 after the last frost, or seed them indoors about 7 weeks prior to planting outside.
Fruits are edible from the time they are one-third grown until they are ripe.
They will remain edible after reaching full color.
Harvest mature fruits SO new ones will develop.
Over-mature eggplants are dull in color and will be soft, spongy, and seedy.
Suggested varieties: Ghostbuster  , Vittoria , Patio Baby , Hansel , Fairy Tale 
 Varieties of kale are available in many sizes, shapes, and colors.
Although not widely grown, kale is a nutritionally valuable crop.
Kale is quite hardy and can be planted in the spring as early as the soil can be prepared.
The plants may be grown indoors and transplanted to the garden after about 3 weeks.
Space the plants in rows 24 to 30 inches apart with plants 10 to 12 inches apart in the row.
Directly seeded plants should be thinned to a 10to 12-inch final spacing.
Suggested varieties: Blue Curled Vates , Dwarf Siberian , Red Russian Heirloom , Prizm 
 Kohlrabi is a member of the cabbage family that produces an edible, enlarged stem.
Seeds can be planted directly in the garden or 4-week-old transplants can be planted outdoors.
The plants should be spaced 6 inches apart in rows 18 inches to 2 feet apart.
The crop is cold-resistant and can be planted as early as cabbage.
It grows best in cool spring and fall weather or in locations where the summer climate is cool.
The quality of kohlrabi is best when growth is rapid and unchecked.
Stems should be harvested when they are about 2 to 3 inches in diameter and still tender.
They become woody and fibrous when they get too large.
Make several plantings 2 to 3 weeks apart to have a continuous supply of tender kohlrabi.
Suggested varieties: Early White Vienna , Grand Duke , Purple Vienna , Sweet Vienna , Konan 
 Lettuce is a cool-season vegetable crop that will withstand light frost.
High sunlight and warm summer temperatures cause seed stalk formation  and bitter flavors, especially in bibb types.
Slow bolting or heat resistant varieties are available.
Lettuce is a good choice to grow in a partially shaded garden area.
There are four types of lettuce: head, bibb, romaine or cos, and leaf.
Head lettuce is the most common for fresh market and grocery store sales.
Bibb lettuce is often grown in forcing structures such as greenhouses.
Romaine or cos lettuce is a very nutritious type that forms an upright head.
Leaf lettuce is the most common for home gardens and will have green or red-tinged leaves.
Sow leaf lettuce varieties in rows 8 to 12 inches apart, with 10 to 20 seeds per foot.
Alternatively, sprinkle the lettuce seed evenly over prepared soil and simply scratch it into the soil.
The three heading types are usually started as transplants and spaced 12 to 18 inches apart in rows 24 to 30 inches apart.
Lettuce can be started or set in the garden 2 weeks before the last average frost date.
Lettuce can be planted on the shady side of tall crops, such as sweet corn, tomatoes, and pole beans, or in other cool areas of the garden.
Leaf lettuce matures quickly and can be interplanted between or in rows of slower growing crops such as tomatoes, broccoli, and brussels sprouts.
Leaf lettuce also makes a good border around flower
 beds.
Make several plantings to have lettuce available over a long period of time.
Leaf lettuce can be harvested, outer leaves first, when plants are 5 to 6 inches tall.
Harvest every other plant, or the very largest plants, in order to thin the crop.
Bibb lettuce is mature when the leaves begin to cup inward and form a loose head.
Romaine is ready to use when the leaves have elongated and overlapped to form a tight head about 4 inches wide at the base and 6 to 8 inches tall.
Head lettuce is mature when the leaves overlap, forming a moderately firm head similar to those found in the grocery store.
Suggested head type varieties: Buttercrunch , Ithaca , Summertime 
 Suggested leaf type varieties: Black Seeded Simpson , Prizeleaf , Red Sails , Royal Oak , Simpson Elite , Sandy 
 Muskmelons are a warm-season crop.
Most varieties require a long growing season of at least 80 days from seed to produce mature fruit, plus a considerable amount of space.
Muskmelons can be produced from transplants or can be sown directly.
Transplanting will gain a few days of growing time.
Rows should be 5 feet apart with hills spaced 2 to 3 feet apart.
Seeds should be sown 1/2 to 3/4 inch deep after the danger of frost has passed.
Grow two or three plants per hill.
Start transplants about 3 weeks before planting outdoors.
As with cucumbers, male and female muskmelon flowers are separated on the same plant.
Bees must carry pollen from flower to flower to ensure fruit set.
Harvest melons when the fruit pulls away from the vine attachment easily and smoothly.
Suggested varieties: Minnesota Midget , Sweet 'n Early 
 Okra is a warm-season vegetable requiring much the same growing conditions as sweet corn.
The edible pods are produced in leaf joints on plants that can reach 6 feet tall.
Plant after the danger of frost has passed.
Seeds should be sown 1 inch apart and thinned later to 5 to 8 inches apart in rows 21/2 to 4 feet apart.
Harvest okra frequently, as plants will stop producing if fruits are not picked regularly.
Suggested varieties: Annie Oakley II , Baby Bubba , Cajun Delight , Clemson Spineless 80 , Candle Fire 
 Onions are available in a wide variety of colors and degrees of pungency.
Yellow, white, and red onions are common, as are green onions  and their cousins, leeks.
Onions can withstand some cold temperatures and can be planted in early spring.
Gardeners can purchase sets, which are simply small onions, or seeds.
Sets should be planted 1 to 2 inches apart and 1 to 2 inches deep in the row.
Later, they can be thinned to 4 inches apart.
Use the thinned plants as green onions.
Avoid sets that are too large, more than 1 inch in diameter, as they may produce seed stalks instead of bulbs.
Seed stalk development is also favored by planting too early in the spring and cold temperatures.
Seeds or sets should be planted in rows at least 18 inches apart and thinned to 2 to 3 inches between plants.
Since onion plants have quite shallow roots, regular irrigation is important to encourage best growth.
Harvest onions when about two-thirds of the tops have fallen over.
Dig the bulbs out carefully to avoid cuts and bruises.
If the onions will not be used right away, they can cure for several days in a dry, airy spot out of the sun.
Remove tops before or after curing, leaving about 3/4 inch on the bulb.
Suggested varieties: Candy , Red Hamburger , White Bunching , Warrior  
 Parsnips require a long growing time, at least 100 days.
Therefore, these vegetables can be grown only in the warmest areas of Wyoming.
They should be planted about 2 weeks before the average last frost date in rows 18 inches apart with seeds 2 to 3 inches apart.
Parsnip seed loses its viability quickly within one year SO make sure to use fresh seed.
The seed is slow to germinate and a good stand may be difficult to produce in heavy soils and with low moisture.
Dig parsnips in late fall or leave them in the ground throughout the winter.
They will tolerate alternate freezing and thawing but will be damaged if frozen after harvest.
Harvest them in the spring, before top growth starts, for tender, sweet roots.
Suggested varieties: All-American , Hollow Crown 
 Garden peas are frost hardy and should be planted in early spring.
They will not yield well if they mature during hot weather.
In some areas, they can be planted from July 1 to 15 for fall maturation.
Peas will produce during the summer in high altitude areas where the summer climate is cool.
Plant seeds 1 inch apart in rows 18 to 24 inches apart.
They will usually produce better if they are later thinned to 3 inches apart in the row.
Pea varieties vary in height from 18 inches to 6 feet.
The taller varieties should be
 grown on a trellis for easier picking and less disease problems.
The trellis can be made of wire fencing, wood, or even string.
Harvest edible pod peas while the pods are still flat, before the seeds inside start to enlarge.
Pick them consistently to prolong the harvest season.
Suggested edible-pod varieties: Dwarf Gray Sugar , Little Sweetie , Oregon Sugar Pod II , Snowbird , Snak Hero 
 Suggested snap varieties: Sugar Ann , Sugar Daddy , Sugar Snap , Super Snappy 
 Suggested garden varieties: Early Alaska , Little Marvel , Maestro , Mr.
Big 
 There are too many types of peppers to name them all.
Both sweet and hot types can be grown in the warmer parts of Wyoming.
Pepper plants require warm temperatures and should not be transplanted to the garden until after the last frost.
Space the plants 2 feet apart in the row with rows 3 feet apart.
Peppers simply will not grow if the temperature falls below about 55 degrees Fahrenheit.
Fruit set on peppers is also temperature sensitive.
The flowers will not form fruits if the night temperature drops below 60 degrees Fahrenheit, or if the day temperature rises much above 90 degrees.
Hot, dry winds can cause the flowers to fall without forming fruits.
Harvest peppers as soon as they reach a usable size by cutting them off the stem close to the fruit.
Green peppers can be left on the plant to mature to their red or yellow color.
The mature fruits are often sweeter than the green ones.
Suggested sweet types: Crispy Bell , Early Crisp , King of the North , Red Beauty , Just Sweet , Orange Blaze , Pretty N Sweet 
 Suggested hot types: Big Chile , Biker Billy , Garden Salsa , Tam Mild Jalapeno , Flaming Flare , Aji Rico 
 Both white-skinned and red-skinned potatoes can be grown as a crop for fresh use in early summer and as a late crop for table use in winter.
Choose an early variety and a medium-to-late maturing variety.
In most parts of Wyoming, plant early potatoes about May 1.
Potatoes yield best with cool spring weather and uniform moisture throughout the growing season.
Purchase certified seed  that has been inspected for diseases that contribute to low yields.
Seed potatoes should be firm with no sprouts.
Wilted or sprouted seed usually has lost vigor from being too warm in storage.
Seed pieces for planting should be cut in about 1 1/2 inch cubes.
A 6-ounce potato will yield about four seed pieces.
Each seed piece must have at least one good bud or "eye." Plant the seed pieces in furrows 3 to 4 inches deep, 10 to 12 inches apart, in rows about 36 inches apart.
Make sure to be careful during cultivation to avoid damaging developing potatoes.
An early crop of potatoes can be dug before the skins are set and while the potatoes are somewhat green.
However, yield will be greater if the crop is harvested after the vines have been dead for about 2 weeks.
At this point, the skins of the potatoes will have toughened and losses from peeling will be minimized.
Dig the late potato crop after the first frost has nipped the vines in the fall.
Suggested varieties: All Blue , Early Ohio , Kennebec , Norland ,
 Red Pontiac , Yukon Gold , Clancy 
 Radishes are a hardy, quick crop.
They can be planted in the early spring in rows 12 to 18 inches apart.
Thin the seedlings to 1 to 2 inches apart in the row soon after they emerge.
Plantings of radish seeds should be made every 10 days or SO for 4 to 6 weeks to give a continuous harvest.
The plants should be grown rapidly with regular watering.
Roots from such plants will be crisp and flavorful.
Suggested varieties: Champion , Cherry Belle , Crimson Giant , Easter Egg , White Icicle , Roxanne , Rivoli 
 Rhubarb is another perennial vegetable, like asparagus, that is grown by planting pieces of crown.
These crown pieces can be purchased commercially or can be cut from older plants.
If you have an old plant, cut down through the crown, between the buds, leaving as large of a piece of storage root as possible with each large bud.
Plant the crown in early spring.
If it is necessary to hold the crown for a week or SO before planting, store it in a cool, dark place.
Crowns may need to be divided and new plantings made when numerous small stalks appear.
These indicate the crowns are crowded.
Seed is not recommended for growing rhubarb because rhubarb seedlings may not be identical to the parent plant.
Crowns are usually planted 3 feet apart in rows 4 to 5 feet apart.
Cover each piece with 2 to 3 inches of soil.
Since rhubarb will stay in the garden for several years, plant it along the edge of the garden or in an area where it will
 not be disturbed.
Deeply dug, well prepared soil will prolong the life and productivity of rhubarb.
Harvest rhubarb for a short period during its second year.
A full harvest period of 8 to 10 weeks should follow in succeeding years.
Pull the stalks with a twisting motion instead of cutting them.
The green leaf blades contain large amounts of soluble oxalates and are poisonous.
Eat only the stalks.
Suggested varieties: Chipman's Canada Red, Crimson Red, Valentine
 Rutabagas are close relatives of turnips but have thickened yellow roots instead of white roots.
They are a late-maturing crop whose flavor is often made sweeter by fall frosts.
Seedlings can tolerate late frosts, SO plant them a few weeks before the last frost date.
Seeds should be planted 1 inch apart, then thin them to 5 to 8 inches apart in rows 12 to 18 inches apart.
Harvest in the fall for best flavor.
Suggested varieties: American Purple Top , Laurentian 
 Spinach, like lettuce, is a quick-maturing, cool-season crop of high nutritional value grown in early spring and in the fall.
Under favorable weather conditions, some varieties will mature as early as 40 days after planting.
Warm temperatures in the summer will cause bolting and seed development.
In early May, SOW seeds in rows 12 to 18 inches apart or start fall planting in late July.
Thin plants to 4 to 6 inches apart.
When the plants reach 4 to 6 inches in diameter,
 cut the whole plant at soil level.
Make several staggered plantings to produce spinach over a longer period of time.
Suggested varieties: Avon , Bloomsdale Long Standing , Teton , Tyee , Melody 
 Summer squash grows on large, bushy plants.
The immature fruits are eaten before the skin hardens and the fruit becomes seedy.
Most varieties of summer squash produce fruit 7 to 8 weeks after planting and will continue to bear for several weeks.
Some types of summer squash include zucchini and yellow varieties.
Plant summer squash after the danger of frost is over in hills 4 feet apart with 2 or 3 seeds in each hill.
All squash are warm-season plants and grow best when soil and air temperatures are above 60 degrees Fahrenheit.
For earlier fruit, plant seeds indoors and transplant them to the garden about 3 weeks later.
Squash plants have male and female flowers on the same plant.
The flowers are pollinated by bees.
Suggested varieties: Black Beauty Zucchini , Bossa Nova Zucchini , Early Golden Summer Crookneck  , Early Prolific Straightneck  , Jackpot Zucchini , Saffron  , Sunny Delight  
 Sweet corn varieties vary tremendously in their quality and time to maturity.
Weather is a big factor in how long it takes a variety to mature.
Corn is a warm-season vegetable.
Plant sweet corn on the average date of the last killing frost.
Plants can be started from seed or you can purchase transplants.
For a longer harvest period, plant early, mid-season, and late-maturing varieties at the same time.
Or, make successive plantings of the same variety every week or two.
Use only the earliest maturing varieties for July plantings.
Sweet corn varieties that mature in the fall will usually be the highest quality because of cool night temperatures.
For early maturing varieties that produce small plants, plant in rows 30 inches apart with plants 8 to 9 inches apart in the row.
For medium to large plant sizes, use a 30 to 36 inch row spacing with plants 12 inches apart in the row.
Plant at least three or four rows of the same variety in a block for good pollination and full ears.
Some early varieties may produce suckers from the base of the plant.
There is no advantage in removing these.
Harvest sweet corn in the morning when it is cool.
Normally, sweet corn is ready for harvest about 20 days after the first silk appears on the ear.
Suggested varieties: Early and Often , Early Xtra-Sweet , Honey and Cream , Northern Seneca Snowshoe , Quickie , Sugar Baby 
 Swiss chard is grown for its green leaf blades and fleshy leaf stalks.
It will withstand both hot weather and frost, from spring until late fall.
Plants may be started indoors and transplanted to the garden 1 or 2 weeks before the last frost, or seed may be sown directly at that time.
Make rows 18 inches apart and SOW seeds 3/4 inch deep.
Thin the seedlings to 8 to 12 inches after emergence.
Many harvests can be made from the same plant throughout the growing season.
Remove outer leaves near ground level with a sharp knife, leaving the smaller central leaves.
Avoid cutting into the growing point or the bud in the center of the plant, as this is where new leaves develop.
Suggested varieties: Bright Lights , Lucullus 
 Tomatoes require relatively little space for the large production they yield.
However, they are warm-season plants and high temperatures and abundant sunshine are important for best growth and development.
Set tomato plants out after the danger of frost is past.
Select healthy, stocky transplants that are 6 to 10 inches tall.
Set the transplants in the soil a little deeper than they were in the container.
If the plants are tall, do not prune them as this will delay harvest and reduce yields.
A better practice is to trench the plant SO the roots and a portion of the stem are covered with soil.
New roots will develop along the buried stem.
Experts highly recommend using tomato cages to support the growing plants and their fruit load.
During the growing season, regular irrigation is important.
Harvest the fruits when they are fully ripe.
Late-season green tomatoes can be ripened indoors if they are picked before the frost.
Suggested determinate  types: Celebrity , Patio Choice Yellow , Fantastico , Terenzo , Italian Gold , Roma , Sub-Arctic Plenty 
 Suggested semi-determinate types: Cold Set 
 Suggested indeterminate  types: Early Girl , Gardener's Delight , Lemon Boy , Super Sweet 100 
 Turnips, a rapidly maturing cool-season crop, can be planted for late-spring or late-fall harvest.
Some varieties are grown only for their leaves or "greens" while others are grown for their fleshy root.
Turnip greens are
 nutritionally rich; white fleshed turnips are recommended for the roots.
Plant the seeds 1/2 inch deep in rows 12 to 15 inches apart for uniform growth.
Two plantings 3 weeks apart will provide a uniform supply.
The plants should be thinned to 3 to 4 inches apart in the row after they are established.
Harvest turnips when they are 2 to 3 inches in diameter.
Large turnips become woody and unappetizing.
Suggested varieties: Purple Top White Globe , Tokyo Cross , Just Right 
 Because of their large vines, watermelons require considerable space.
For early harvest, start seeds indoors 2 to 3 weeks before the outdoor transplanting date.
Then transplant them after the danger of frost has passed.
Watermelons are warm-season plants and require warm soil and air to thrive.
The most common way of planting watermelons is by direct seeding.
Plant 2 to 3 seeds per hill about 1 inch deep after frost is passed.
Hills should be 5 to 6 feet apart in the row with rows 6 feet apart.
The best indicator of harvest time is a yellowish color where the melon lies on the ground, and a dull appearance compared to a slick, shiny appearance prior to maturity.
A dead tendril or curl near the point where the fruit is attached to the vine is used by some as an indication the fruit is ready for harvest.
Thump the fruit and listen for a dull sound.
If the sound is more metallic, the fruit is not yet ripe.
Suggested varieties: Charleston Gray , Crimson Sweet , Sugar Baby , Yellow Doll  , Faerie , Mini Love 
 This squash is typically harvested in the fall when the fruits are ripe and mature.
They are generally used in pies and baking.
Some types include acorn and butternut, as well as pumpkin.
Growing winter squash is similar to summer squash.
The plants, however, will require more room as the fruits are harvested later.
Suggested varieties: Early Acorn , Early Butternut , Sweet Mama , Table Queen Acorn , Waltham Butternut 
 Most root vegetables need storage temperatures between 32 and 40 degrees Fahrenheit.
A cellar under a house, with no heat source, will work.
Alternatively, an extra refrigerator might be a good investment for storage of large quantities of garden produce.
However, there may be considerable temperature variation from one shelf to the next, especially in older refrigerators.
Use a refrigerator thermometer to check temperature; they are available at virtually any store that sells kitchen tools and equipment.
In order to keep vegetables from drying and shriveling, store them in burlap bags or plastic bags with holes punched in them.
Air circulation is important.
Storage containers that allow air to move through them are also satisfactory.
Sort freshly dug potatoes to remove those that are diseased or damaged.
Gently brush off most of the soil, then spread them out to cure for about 10 days in a shady, well-ventilated space, at 50 to 55 degrees Fahrenheit.
Curing helps condition potatoes for long storage times.
After curing, place them in a darkened, unheated room, cellar, or refrigerator that is kept as close to 40 degrees
 Fahrenheit as possible, is fairly humid , and has adequate air circulation.
Keep potatoes away from light as this can cause them to turn green and become unsuitable for eating.
Carrots, turnips, parsnips, rutabagas, beets
 Trim off all but 1/2 inch of the tops of carrots, turnips, parsnips, rutabagas, and beets and brush off excess soil.
Always sort vegetables before storage and discard any that are diseased or damaged.
Keep these vegetables between 32 and 40 degrees Fahrenheit.
Harvest cabbage when the heads are solid and remove roots and outer leaves.
Cabbage will store easily for 1 to 4 months in a cellar or in a refrigerator at 32 to 40 degrees Fahrenheit.
Green, yellow, or red peppers will keep for 2 to 3 weeks in the refrigerator.
Freeze any surplus.
Hot peppers can be dried in the sun or other warm location.
Store them after they dry in a cool, dry, dust-free place at about 45 to 50 degrees Fahrenheit.
Put cured onions in mesh bags, spread them on wire screens, or hang them in bunches in a dry, cool , airy place.
Greens do not store well, but they can be held 1 to 2 weeks in a cool  section of the refrigerator.
Ripe tomatoes will keep about one week in a refrigerator at 45 to 50 degrees Fahrenheit.
Harvest full-size, mature, green tomatoes before frost.
They will keep for 3 to 6 weeks at 55 to 60 degrees Fahrenheit with 80 to 90 percent relative humidity.
Make sure to check for ripeness every few days.
Root cellars are too cold and moist for pumpkins or winter squash.
Cure them first, then store them at 55 to 60 degrees Fahrenheit.
Store them in a single layer to minimize decayed spots.
The following tips will help prevent losses caused by insects and diseases:
 Have a soil analysis done on garden soils.
Contact the local UWE office for available labs.
Follow recommended fertilization practices.
If in doubt, under-fertilize; never over-do it.
Plants crops suited to a specific soil and local climate.
Use fresh seed from reputable seed companies.
Select vegetable varieties with disease resistance.
Seed catalogs and garden centers will have this information.
Select transplants that are sturdy and have a healthy green foliage and a white, well-developed root system.
Rotate the garden plan if possible.
Do not grow the same type of produce in the same spot each year.
Mix crops as opposed to maintaining solid plantings of each type in order to separate disease or insect problems and to reduce potential damage.
Thin young plants to the proper spacing.
Water plants early in the morning.
If overhead watering is used, morning irrigation will allow plant foliage to dry before darkness sets in.
If drip irrigation is used, the timing is not as critical, simply because the foliage will not get wet.
Morning is still best, though, SO the plants can utilize the water during the day.
Keep weeds to a minimum.
They often harbor pests and also compete with vegetable plants for water, light, and nutrients.
Remove all plant debris at the end of the growing season to reduce carry over of disease and insect problems.
When a garden plant is no longer producing, remove it.
If it is healthy, turn it under or use it in compost.
Never compost diseased plant material.
Many naturally occurring, beneficial insects and diseases can be used to help manage insect pests in the vegetable garden.
Many garden centers carry supplies of beneficial organisms, and many can be ordered through catalogs or via online websites.
Be aware, however, that once their food supply is gone, the beneficials will be too.
When
 using biological management methods, the gardener will have to put up with a certain number of pests in order to keep the predators around.
The use of any biological management organism effectively rules out the use of any pesticides in or around the vegetable garden.
Beneficial insects are highly sensitive to many pesticides, SO be careful.
Tachinid flies.
The larvae of these insects will eat soft-bodied insect pests.
Parasitoid wasps.
These wasps lay their eggs in the pupae of insect pests, effectively killing them.
Ladybird beetles.
The larvae of "ladybugs," as they are commonly known, are voracious aphid-eaters.
The larvae will eat many more aphids than adult ladybird beetles will.
Bacillus thuringiensis.
B.t., as it is commonly called, has been around for many years.
It is highly effective against lepidopterous caterpillars that often damage vegetable plants.
B.t.
is a naturally occurring bacteria that is lethal against moth and butterfly larvae.
For this reason, spray it only when necessary because it will harm moths and butterflies that are not plant pests.
The range of chemical pest management products available today is quite large, and ranges from quite safe  to fairly toxic.
It is important to positively identify the cause of the problem.
Identification may take the expertise of a diagnostic laboratory or UWE personnel.
Once the problem has been identified, management tools can be recommended.
Always look for pesticides labeled for the particular problem on the particular type of plant.
Then, read and follow the label instructions carefully.
And remember, applying more than the label says may not only be harmful, it is also illegal.
Karen Panter, Extension Horticulture Specialist, Department of Plant Sciences, University of Wyoming
 Editor: Katie Shockley, University of Wyoming Extension
 Design: Tanya Engel, University of Wyoming Extension
 Originally published January 2002.
Karen Panter, Extension Horticulture Specialist, Department of Plant Sciences, University of Wyoming
 Issued in furtherance of extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture.
Kelly Crane, director, University of Wyoming Extension, University of Wyoming, Laramie, Wyoming 82071.
The University's policy has been, and will continue to be, one of nondiscrimination, offering equal opportunity to all employees and applicants for employment on the basis of their demonstrated ability and competence without regard to such matters as race, sex, gender, color, religion, national origin, disability, age, veteran status, sexual orientation, genetic information, political belief, or other status protected by state and federal statutes or University Regulations.
The Economics of Converting from Surface to Sprinkler Irrigation for Various Pumping Capacities
 Daniel M.
O'Brien Extension Agricultural Economist Northwest Research and Extension Center, Hays, KS
 Freddie R.
Lamm Research Irrigation Engineer Northwest Research and Extension Center, Hays, KS
 Loyd R.
Stone Research and Teaching Soil Scientist Manhattan, KS
 Danny H.
Rogers Extension Agricultural Engineer Manhattan, KS
 Kansas State University Agricultural Experiment Station and Cooperative Extension Service Manhattan, Kansas
 The profitability of converting from furrow surface irrigation to a center pivot sprinkler irrigation system depends upon a number of factors.
These include: a) the pumping capacity of the irrigation well, b) the cost of converting to the sprinkler irrigation system and loan repayment period, c) changes in irrigated acreage, and d) comparative irrigated crop yields for the old and new systems.
Labor savings are also commonly thought to be a major consideration in switching from furrow surface irrigation to center pivot irrigation systems.
Other factors include long run crop prices, production costs, and tax-related depreciation and interest deductions for the pivot system investment.
A number of studies have been performed to analyze the profitability of irrigation system conversion including Dhuyvetter 1996 and Williams, et.al.
1996.
These studies have typically relied on a number of assumptions about the initial furrow irrigated field size and crop yield, irrigation well capacity, irrigation system water application efficiencies, crop yields and net returns, labor use for alternative irrigation systems, sprinkler irrigation system investment, and pump repair costs.
Lamm, et.al.
1997, focused on the impact of sprinkler irrigation capacity on corn yield potential and economics.
Lower irrigation pumping capacities were shown to affect both crop yields and net returns under western Kansas conditions, particularly in high water use years when limited irrigated water applications were unable to fulfill crop needs.
This study focuses on the impact of differing irrigation well pumping capacities and weather conditions on irrigated corn yields and the profitability of converting from furrow surface irrigation to center pivot irrigation systems.
The analysis concentrates on irrigation system capacities of 700 gallons per minute  and less.
The value of labor savings gained by switching from furrow surface
 irrigation to center pivot irrigation systems are also examined.
The results of this analysis are presented on an annual basis over the life of the alternative irrigation systems, accounting for the impact of tax deductions and debt repayment on annual cash flows.
This analysis assumes that a crop producer with a square furrow, surface-irrigated quarter section of farmland is determining whether or not to convert to a center pivot irrigation system.
The existing surface irrigation system produces 160 acres of irrigated corn and is assumed to have an irrigation application efficiency of 70 percent.
The center pivot sprinkler irrigation system will produce 125 acres of irrigated corn.
The remaining 35 acres in the corners of the 160 acre field will no longer be irrigated, but instead are placed in a wheat-corn-fallow rotation.
Alternative center pivot system application efficiencies of 85% and 95% are examined in this study.
Center Pivot Sprinkler Investment Costs & Tax Deductions
 Current budget estimates from KSU Farm Management Guide, MF-836, Irrigation Capital Requirements and Energy Costs, as well as irrigation industry cost projections are used to estimate the purchase cost of a center pivot irrigation system.
An additional $4,500 is budgeted to modify the existing well pump for the higher pressure requirements of sprinkler irrigation.
The total cost of the center pivot system is projected to be $45,209, including a standard 7 tower pivot system with drops, low drift nozzles, underground pipe from the field edge to the pivot point, electrical wiring and connectors and an electric generator.
The total system and pump modification costs are $49,709.
Table 1.
Capital Requirements for a Center Pivot irrigation System.
Item	Feet	Price/ft	Costs
 Standard 7 Tower Center Pivot
 System Base Price	1,320	$28,000
 Drops on 80" Spacing	2,100
 Low Drift Nozzles	2,400
 38" X 11.2 Tires	3,000
 8" Underground Pipe	1,320	$2.52	3,326
 Electrical Wiring	1,320	$1.90	2,508
 12 KVA Generator	2,375
 Total Cost of Center Pivot System	$45,209
 Pump Modification Cost	$4,500
 Total System & Pump Cost	$49,709
 The MACRS 150% Declining Balance method  is used to calculate tax depreciation.
Both principal and interest payments are calculated for a 5 year amortized note at 9% interest, with the total payment for each of the 5 years equaling $12,780 per year.
The combined federal , state  and self employment  tax rate used is 36.30%.
In the final after-tax profitability calculations this same combined total tax rate is used.
Water Application Rates and Well Pumping Capacities
 A key aspect of this analysis involves the comparison of irrigated corn yields and net returns across a range of five different gross irrigation pumping capacities for alternative irrigation systems.
Irrigation schedules  are simulated for the 1972-1998 period using climatic data from the KSU Northwest Area Research and Extension Center, Colby, Kansas.
Irrigation is scheduled as needed according to the climatic conditions, but is limited to the
 frequencies for the two systems as indicated in Table 2.
The irrigation season is the 90-day period between June 5 and September 2.
The first surface irrigation event in each year is on June 15, reflecting a typical date of first irrigation following the final furrowing process.
After that, surface irrigation events are scheduled as the capacity limitation allows and if the calculated irrigation deficit exceeds 3 inches.
Center pivot irrigation events are scheduled during the 90-day period as the capacity limitation allows and if the calculated irrigation deficit exceeds 1 inch.
Table 2.
Equivalent Irrigation Frequencies and Pumping Capacity for Furrow Surface and Center Pivot Sprinkler Irrigation Systems.
Center Pivot	Furrow Surface
 Gross Irrigation	Frequency	Flowrate	Frequency	Flowrate
 Capacity	& Amount	Gpm per	& Amount	Gpm per
 Inches per Day	Applied	125 acres	Applied	160 acres
 0.250"	1" in 4 days	589	3" in 12 days	754
 0.200"	1" in 5 days	471	3" in 15 days	603
 0.167"	1" in 6 days	393	3" in 18 days	503
 0.125"	1" in 8 days	295	3" in 24 days	377
 0.100"	1" in 10 days	236	3" in 30 days	302
 Irrigated corn yields for the various alternative irrigation systems and irrigation capacities are also simulated for the same 27 year period using the evapotranspiration  estimates from the irrigation schedules and using a yield production function developed by Stone et al..
In its simplest form, the model results in the following equation:
 Yield = -184 + 
 with yield expressed in bushels per acre and ET in inches.
Further application of the model reflects weighting factors for specific growth periods.
These additional weighting factors are incorporated into the simulation to better estimate the effects of irrigation timing for the various systems and capacities.
The weighting factors and their application to the model are discussed in detail by Stone et al..
Crop Revenues, Costs, and Net Returns
 No land costs are included in these budgets to avoid the effects of varying land rental or purchase market
 conditions in the High Plains region.
These analyses are performed both with and without K-State labor cost estimates included for the alternative crop enterprises.
By paying special attention to labor costs it may be possible to determine the degree to which claims of labor savings from system conversion are valid or not.
In the following analyses, profitability estimates that represent returns to land, labor and management do not include labor cost estimates.
When labor cost estimates are accounted for, profitability measures represent returns to only land and management.
The time period for this analysis is 15 years.
This time span is a conservative approximation of the expected life span of a newly purchased center pivot system.
No inflation or deflation in crop prices or input costs is assumed during the 15 year period.
Long term average crop selling prices and production costs were taken from KSU Farm Management Guide Budgets.
Specific budgets used
 Table 3.
Average Irrigated Corn Yields and Irrigation Application Amounts for 1972-1998
 Irr.
Corn	Irr.
Corn	Irr.
Corn	Irr.
Corn	Irr.
Corn	Irr.
Corn
 Amount	Yield	Amount	Yield	Amount	Yield	Amount	Yield	Amount	Yield	Amount	Yield
 						(bu/a
 A.
Center Pivot Sprinkler System @ 95% Application	Efficiency on	125	acres	CP95%)
 Frequency	1" in 4 days	1" in 5 days	1" in 6 days	1" in 8 days	1" in 10 days	Full Irrigation
 GPM Rate	589 gpm	471 gpm	393 gpm	295 gpm	236 gpm
 Average	13.8	195	12.3	188	10.9	177	8.7	159	7.2	146	14.6	197
 Std Deviation	4.0	42	3.1	35	2.4	29	1.7	23	1.2	22	4.5	44
 Minimum	5	111	5	111	5	111	4	104	4	96	5	111
 Maximum	20	261	17	251	14	226	11	189	9	179	22	268
 B.
Center Pivot Sprinkler System @ 85% Application Efficiency on 125 acres 
 Frequency	1" in 4 days	1" in 5 days	1" in 6 days	1" in 8 days	1" in 10 days	Full Irrigation
 GPM Rate	589 gpm	471 gpm	393 gpm	295 gpm	236 gpm
 Average	14.6	192	12.9	182	11.4	171	9.0	153	7.2	141	16.5	197
 Std Deviation	3.9	39	2.9	31	2.1	26	1.6	23	1.2	23	5.1	44
 Minimum	6	111	6	111	6	110	5	99	4	92	6	111
 Maximum	20	259	17	239	14	210	11	188	9	178	25	268
 C.
Furrow Surface Irrigation System @ 70% Application Efficiency on 160 acres 
 Frequency	3" in 12 days	3" in 15 days	3" in 18 days	3" in 24 days	3" in 30 days	Full Irrigation
 GPM Rate	754 gpm	603 gpm	503 gpm	377 gpm	302 gpm
 Average	16.9	180	14.9	168	13.3	158	10.9	144	8.7	132	20.4	197
 Std Deviation	3.8	31	3.1	25	2.4	23	1.7	22	1.0	23	6.2	44
 Minimum	6	111	6	109	6	104	6	94	6	89	6	111
 Maximum	21	237	18	211	15	189	12	172	9	167	30	268
 a.
Based on 1972-1998 climatic conditions at the Northwest Research Extension Center in Colby, Kansas, and on the Stone et al.
corn yield prediction model.
included those for: Center Pivot Irrigated Corn In Western Kansas, , Flood Irrigated Corn in Western Kansas, , Wheat in a W-S-F Rotation in Western Kansas, , and No-Till Corn in a W-CF Rotation in Western Kansas,.
Long-term planning prices for western Kansas for corn and wheat were taken from, Prices for Crop and Livestock Cost-Return Budgets,.
Specific information on the seed, fertilizer, herbicide, insecticide, fuel, oil, machinery, crop insurance, operating interest, and other costs used here are found in the KSU Farm Management Guide Budgets, and are available from either the authors or through local county Research and Extension offices in Kansas.
RESULTS Long Term Average Irrigation Requirements and Corn Yields
 The simulated irrigation schedules and corn yield model are used to generate estimates of the irrigation requirement and corn yields for the various irrigation systems and
 capacities for each year.
This data is summarized into averages, standard deviations, and maximum and minimum values of irrigation requirements and corn yields.
Standard deviation is used as a measure of yield variability.
The higher the standard deviation of a particular value, the higher the variability of the estimate and vice versa.
The 1 inch/4 days  gross irrigation capacity generates average yield estimates of 195 and 192 bushels/acre for the 95 percent efficient center pivot system  and the 85 percent efficient center pivot , respectively.
For the 70 percent efficient furrow surface irrigation system  the equivalent application of 3 inches/12 days  leads to an average yield estimate of only 180 bushels/ acre.
Gross average irrigation requirements for the three systems, CP95 percent, CP85 percent and FS70 percent are 13.8, 14.6 and 16.9 inches per acre, respectively.
As gross irrigation system capacity declines further, the projected yields
 for each of the three irrigation systems decline.
However, CP95 percent yields decline slightly less than CP85 percent yields.
Yields for FS70 percent trailed both CP95 percent and CP85 percent, declining from 180 to 132 bushels/per acre.
Yield results for these three irrigation systems percent are nearly equal in variability across the alternative irrigation capacities.
Water application amounts per acre are higher for FS70 percent than for CP85 percent, which in turn are higher than for CP95 percent.
Corn yields are also simulated for full irrigation.
Under the full irrigation scenario, adequate irrigation water is supplied to meet the crop's ET needs without potential timing delays caused by inadequate irrigation system pumping capacity.
In essence, irrigation water is being optimally supplied to the crop at the same rate in which the crop is using it.
The analysis results show that if full irrigation is possible for all three systems , equal corn yields of 197
 Table 4.
After-tax Net Returns for Alternative Irrigation Systems.
Center Pivot	Center Pivot	Furrow Surface
 95% Efficiency	85% Efficiency	70% Efficiency
 Pump Capacity	Total Net	Net Per	Total Net	Net Per	Total Net	Net Per
 	Revenue	Acre	Revenue	Acre	Revenue	Acre
 200	$1,704	$11	$86	$1
 300	5,466	34	4,010	25	$2,057	$13
 400	8,168	51	6,905	43	4,578	29
 500	9,810	61	8,772	55	6,753	42
 600	10,391	65	9,611	60	8,582	54
 Table 5.
Net Present Value  Analysis of Irrigation System Conversion Alternatives 
 Center Pivot	Center Pivot	Furrow Surface
 95% Efficiency	85% Efficiency	70% Efficiency
 Pump Capacity	Total	Ave.
Total	Ave.
Total	Ave.
NPV	NPV	NPV	NPV	NPV	NPV
 300	$65,490	$5,063	$51,911	$4,013	$26,602	$2,057
 400	100,442	7,765	90,009	6,958	59,214	4,578
 500	121,675	9,407	113,339	8,761	87,349	6,753
 600	129,188	9,987	121,188	9,423	111,009	8,582
 bushels/acre would be obtained.
The average irrigation water application for the three systems would be 14.6, 16.5, and 20.4 inches for the CP95 percent, CP85 percent, and FS70 percent systems, respectively.
Regression equations are generated for yields as related to irrigation capacity.
This allows for the calculation of corn yields for specific irrigation well capacities ranging from 200 to 700 gpm for the three alterna-
 tive irrigation systems.
This perspective is important to decision makers in the Central Great Plains of Kansas, who are often dealing with wells that have pumping capacities in this range.
Projected annual average corn yields for CP95 percent ranged from 4 to 9 bushels/acre higher, than for CP85 percent corn yields across the range of well capacities considered here  on 125 acre fields.
However, average corn yields for FS70 percent
 on 160 acre fields are from 21 to 28 bu./acre lower than CP85 percent yields for wells in the 300 to 600 gpm pumping capacity range.
The impact of lower surface-irrigated corn yields on this analysis of conversion profitability depends in part on how profitable the non-irrigated crop on the 35 acres in the center pivot corners is.
No 200 gpm yield outcomes are presented for FS70 percent, and no 700 gpm yield outcomes are presented for CP95 percent and CP85 percent,
 Figure 3.
After-tax Net Present Value of Alternative Irrigation Systems 
 because this would require extrapolation beyond the range of the generated equations.
Annual After-Tax Net Returns
 Regression equations are also generated for annual after-tax net returns to land, labor and management as related to irrigation capacity for the three irrigation systems.
The results are shown in Table 4 and Figure 2.
These findings indicate that it is profitable to convert from furrow surface irrigation to center pivot irrigation systems, given the yield results and cost-return assumptions used in this study.
At 600 gpm well pumping capacities, both the center pivot irrigation systems examined have $6 to $11 per acre annual net returns advantages over the furrow surface irrigation system.
As well pumping capacity declines to 300 gpm, the advantage of center pivot systems over furrow surface irrigation increases to $21 per acre and $12 per acre for 95 percent and 85 percent efficient center pivots, respectively.
The inclusion of labor costs based on K-State Research and Extension budget estimates for these crop enterprises causes furrow surface irrigation net returns to be even lower relative to the center pivot sprinkler system returns.
The addition of labor costs leads to a $15/acre decline in center pivot after-tax annual net returns, and a $22/acre decline in furrow surface irrigation after-tax annual net returns in comparison to the results presented in Table 4 and Figure 2.
After-Tax Net Present Value Analysis
 An analysis is made of the after-tax Net Present Value  of the existing furrow surface irrigation and
 the installed center pivot systems.
NPV is a financial analysis method used to account for the discounted value of future income.
Essentially, income in a future time period is worth less than it is today, because of the opportunity cost of interest.
All present and discounted future income is summed to derive one NPV for a specific investment.
The investment alternative with the highest NPV is the most profitable one to choose according to NPV analysis.
Nominal and real inflation adjusted discount rates of 6.09 percent and 3 percent, respectively, were assumed in this analysis.
These discount rates are further adjusted to reflect after-tax NPVs.
Both the total after-tax NPV findings and the annual average NPV estimates support the earlier conclusions of this paper, conversion from furrow surface irrigation to center pivot sprinkler irrigation is profitable.
In the 300 to 600 gpm range of well capacities, the total after-tax NPV values for the center pivot sprinkler irrigation systems are markedly higher, than for the furrow surface irrigation system, even after the extra investment to establish the center pivot irrigation systems.
This same result is shown in the annual average NPV findings.
This study shows that it is economically profitable to convert from surface irrigation to center pivot irrigation systems.
These findings are dependent upon this study's assumptions about production, costs, and returns of the alternative irrigation systems.
These results hold true in spite of the irrigator having to pay principal and interest costs for the debt associated with the purchase of the center pivot irrigation system, pump modification costs, and having to switch 35 acres of previously irrigated cropland out of irrigated corn production and placing it in an intensive dryland cropping system.
both the production and the profitability of an irrigated corn enterprise.
For a 160 acre field, annual average irrigated corn yield estimates under surface irrigation are dramatically reduced , as irrigation well capacity declines from 700 to 300 gpm.
To deal with this problem, producers typically reduce irrigated acreage to the level that they can still provide adequate water for irrigated crop growth.
A future direction of this analysis may be to provide better information on how many acres of irrigated crop production can be adequately irrigated under these reduced well capacity scenarios, given the climate of the region.
The associated economic analysis would be driven primarily by changes in irrigated corn yield levels and a decline in irrigated acreage, as producers seek to find the most productive and profitable irrigated acreage level given their limited water pumping capacities.
Decreased irrigation well pumping capacity has a negative affect upon
 These findings support the claims of irrigators that labor savings are a factor, encouraging them to convert from surface irrigation to center pivot irrigation systems.
When labor costs were included in this analysis, the relative profitability of surface irrigation systems is made even worse compared to the profitability of investing in a center pivot irrigation system.
While labor is an important consideration, this analysis suggests that actual corn production levels with furrow surface irrigation, versus a center pivot system are more important than labor considerations in the system conversion decision.
Earlier studies typically found that the high initial investment costs for the center pivot irrigation systems typically made them less profitable relative to the existing furrow surface irrigation system.
However, most of these studies were based on the expectation that furrow surfaceirrigated corn yields would be approximately equal to those under center pivot irrigation.
This analysis shows that as pumping capacity declines below moderate levels, furrow irrigation of larger fields becomes less profitable relative to investing in a center pivot system.
Dhuyvetter, Kevin C.
1996.
"Converting from Furrow Irrigation to Center Pivot Irrigation Does It Pay?" Proceedings of the Central Plains Irrigation Short Course and Exposition, pp.
13-22.
This material is based upon work supported by USDA Cooperative State Research, Education and Extension Service under Agreement No.
98-342966342.
Any opinions, findings, conclusions, or recommendations are those of the authors and do not necessarily reflect the views of the USDA.
Brand names appearing in this publication are for product identification purposes only.
No endorsement is intended, nor is criticism implied of similar products not mentioned.
Contents of this publication may be freely reproduced for educational purposes.
All other rights reserved.
In each case credit, Daniel M.
O'Brien, Freddie R.
Lamm, Loyd R.
Stone, and Danny H.
Rogers, The Economics of Converting from Surface to Sprinkler Irrigation for Various Pumping Capacity, Kansas State University, November 2000
 Kansas State University Agricultural Experiment Station and Cooperative Extension Service
 It is the policy of Kansas State University Agricultural Experiment Station and Cooperative Extension Service that all persons shall have equal opportunity and access to its educational programs, services, activities, and materials without regard to race, color, religion, national origin, sex, age or disability.
Kansas State University is an equal opportunity organization.
Issued in furtherance of Cooperative Extension Work, Acts of May 8 and June 30, 1914, as amended.
Kansas State University, County Extension Councils, Extension Districts, and United States Department of Agriculture Cooperating, Marc A.
Johnson, Director.
Different methods can be used to determine how many gallons/hour  the chemigation injection pump should be set to inject.
We are going to talk about two of them today.
The first one is using the speed chart  in the sprinkler chart for the pivot or looking up circle time on the computer panel or the pivot app.
The second one involves calculating the chemical injection rate using a spreadsheet.
This method gives you more details about the system and is still easy to figure.
You will just need to enter the basic information for the pivot.
If you are interested, download the spreadsheet from UNL Water.
CORN ROOTING DEPTH WILL IMPACT IRRIGATION SCHEDULING
 As you should expect, the strange weather pattern of a cool to cold spring followed by excessive moisture in many fields has limited the rooting depth and pattern for corn.
While with a grower the other day checking on the timing for the next irrigation, we dug beside a number of corn plants checking the rooting depth.
Corn roots were abundant in the top half to three quarters of a foot of soil although there were many fewer roots reaching the middle of the corn row than I would have expected.
This also may have been due to the excessive rainfall following the nitrogen  sidedressing application which would have moved the applied N both downward and outward from the center dribble zone.
Of course, fertigation contributed to the limited horizontal spread of corn roots since it provided N over the entire soil surface.
The surprising observation we made was the lack of significant rooting in the 12 to 24 inch soil layer.
Although we could find a few roots going that deep, the number and density of roots seemed far below our expectations.
I believe that the explanation for this lack of deep rooting is a combination of the very slow warm up of the soil and the excessive moisture many fields experienced whereby much of the applied N fertilizer was either denitrified and lost to the crop or was leached far below the rooting zone.
I attended a national agronomy meeting of crop physiologist one year and although I dont remember the exact temperature mentioned the group of scientists pointed out that corn rooting depth follows almost exactly the soil temperature curve as it warms in the late spring.
The point of the meeting was to explain corn rooting under a no-till system versus a conventional tillage system.
It was obvious from their data presentations that corn roots grew downward only as fast as the critical temperature for corn root growth moved down through the soil.
Obviously in a no-till system, the more moist soil warmed more slowly than in the drier conventional soil and therefore the rooting depth for corn at any given stage of development was greater in a conventional system than in the no-till system until that critical temperature was reached at the maximum rooting depth for corn in a given soil type.
Whats this mean for our irrigated corn growers?
To me, the shallower and possibly less dense root system of corn means that growers will need to monitor field soil moisture levels very closely to prevent corn from undergoing some yield limiting drought stress.
Adequate moisture in the top 6 to 8 inches of soil will be critical to keeping the crop from being stressed, since the root system could be restricted mostly to this surface soil layer.
With the scattered heavy downpour thunderstorms that have been moving across Delaware, the really difficult part will be maintaining that surface soil moisture without having more standing water injury to the corn crop.
For many growers, the bottoms or low areas in fields have already drowned out and expectations for yield from these areas is at or near zero so making an error by irrigating too often likely will have less impact than applying too little water.
A last comment about shallow rooting in corn relates to standability following black layer.
Im a bit concerned that the shallow root system will mean that corn this fall will not stand as well as we expect.
If we have warning of tropical storm development with a possible hit in our region, growers should try to harvest those fields hit hardest by the excessive rainfall and cold soil conditions this past spring and early summer.
Growers also should consider beginning harvest as soon as harvest moisture falls into a range that they and the elevators can handle.
Bacterial Water Sample Collection and Submission to a Water Quality Lab for Compliance with the Food Safety Modernization Act's Produce Safety Rule
 Amanda G.
Philyaw Perez Assistant Professor
 Natacha Cureau Postdoctoral Associate
 Julia Fryer Program Associate
 Erin E.
Scott Arkansas Water Resources Center Program Manager
 Brian E.
Haggard Arkansas Water Resources Center Director
 Arkansas Is Our Campus
 Why Should Produce Growers Test Water for Bacteria?
Understanding the quality of water used in every aspect of production is an important step in protecting the safety of fresh fruits and vegetables.
Bacteria responsible for foodborne illnesses can be found in water which can then contaminate produce.
Produce growers may need to test water for bacteria to ensure that water used on farm meets a standard for its intended use and limits microbial contamination to produce during growing, harvesting, holding, or packing activities.
Produce growers should first evaluate if they are subject to the Food Safety Modernization Act  Produce Safety Rule  before determining if they need to follow the water testing requirements.
All farms should understand the safety of water used for growing, harvesting, packing, and holding produce and should, at a minimum, test each well water and surface water source at least annually.
The next section will help growers understand the federal FSMA PSR minimum requirements for agricultural water for farms that must comply with the rule.
Compliance dates to meet the agricultural water requirements have been extended and are determined by farm size.
Farms are required to comply with the agricultural water requirements in Subpart E by the following dates:
 Large farms, greater than $568,125  in annual  gross produce  sales by January 26, 2022;
 Small farms, greater than $284,063 but less than $568,125 in annual  gross produce sales by January 26, 2023; and
 Very small farms, greater than $28,406 but less than $284,063 in annual  gross produce sales by January 26, 2024.
Small farms and very small farms may qualify for an exemption:
 If a farm has less than $568,125 in annual  gross food  sales, and
 a majority of the food  is sold directly to "qualified end-users"
 Qualified end-user as defined by Section 112.3 means:
 the consumer of the food or
 a restaurant or retail food establishment  that is located
 in the same State or the same Indian reservation as the farm that produced the food; or
 not more the 275 miles from such farm
 If you need assistance in determining if you farm is subject to the FSMA PSR, please contact your county extension office.
Inflation adjusted by 2020 values from the Implicit Price Deflators for Gross Domestic Product
  Produce: means any fruit or vegetable  and includes mushrooms, sprouts , peanuts, tree nuts, and herbs.
Food: means food as defined in section 201 of the Federal Food, Drug, and Cosmetic Act and includes seeds and beans used to grow sprouts.
Farms are still responsible for ensuring that the food they produce is not adulterated under the Food, Drug, and Cosmetic Act.
For more information on complying with the water regulations, view our fact sheet Food Safety Modernization Act Produce Safety Rule: Microbial Water Quality Compliance.
To receive an accurate water quality bacterial analysis, the individual conducting the testing needs to know what supplies are necessary, how to properly take a sample, and where to send the sample for analysis.
What Supplies Do You Need to Collect Water Samples?
1.
Sterile bottle -provided by a public or private laboratory, a local county extension office, or a local county health unit
 2.
New and sterile nitrile or latex gloves
 3.
Permanent marker 
 4.
Cooler and ice or ice packs  bacteria may degrade in route to testing; temperature control increases stability of the sample
 Additional supplies needed :
 7.
Extension pole if collecting from the bank of surface water to avoid sediment contamination in your sample
 8.
Additional Collection bottle  if your sterile bottle contains powder or tablet that needs to remain in the sterile bottle.
For more information, refer to note 4 under "Instructions for collecting water" and contact your water testing laboratory.
9.
Water boot waders if collecting in surface water
 How to Collect Your Water Samples
 All water sources fall into one of the following categories: municipal, ground , or surface.
Each source presents a different level of risks for contamination and requires a specific method of collecting your water sample.
Since municipal sources are already treated, they do not need to be tested unless there is some reason to suspect a distribution line concern.
Ground and surface water will need to be tested.
Depending on your water source, the instructions to collect your water sample will slightly vary.
1.
Well Water Sampling Method
 If you use well water directly from your well tap, collect your sample from that location.
If you use well water that goes through your home plumbing, collect your sample from an indoor or outdoor faucet.
If you collect from an indoor or outdoor faucet, you might be interested in the source of the water , or you might be interested in the "standing water" in your pipes and the influence that the pipes have on your water quality.
Sample collection for these two purposes will be almost the same, but the amount of time you allow your water to run before collecting your sample will be different.
If you treat water for certain uses but use untreated water in the field, collect the water sample before it goes through treatment.
If you want to know the quality of the treated water, collect an additional sample after the treatment process.
Instructions for collecting water from a well or faucet:
 1.
Wash your hands thoroughly with soap and water.
2.
Put on nitrile or latex gloves.
3.
With a permanent marker , label the sample container with your name, the type of sample, the location on the farm , the date, and time.
4.
Select the tap you will sample from; if collecting from an indoor tap, avoid swing or swivel faucets if possible.
5.
Prepare the faucet:
 a.
To test the quality of well water, remove any screens, filters, aerators, or splash guards; these items can trap bacteria.
Thoroughly wipe the end of the tap with disinfectant for one or two minutes.
Turn on water and leave running for at least five minutes; this flushes water
 from the well line or household plumbing so the water tested is from fresh well water.
b.
To test the quality of your entire system , do NOT remove faucet components, do NOT disinfect the tap, and do NOT run water before collecting your sample.
6.
Reduce the flow rate to avoid splashing.
7.
Remove the lid of the sterile bottle Do NOT touch the inside of the container or the inside of the lid.
Do NOT lay the lid down.
Do NOT rinse the sterile bottle.
8.
Fill the sterile bottle to the indicated line ; do NOT fill over or under the line.
9.
Replace the lid tightly and put the sterile bottle upright in a cooler with ice coming up to the sample level.
10.
Deliver the sample and submission form or chain of custody form to the water testing lab as soon as possible.
Check the water testing lab delivery time and temperature requirements.
Time between collection and testing is critical to get an accurate test result.
If you want to test your treated  water, the water testing lab will provide you with a specific sterile bottle that contains a sodium thiosulfate tablet or powder used to neutralize chlorine.
In this case, the water sampling methods will vary slightly, and you will need to use an additional collection bottle.
The collection bottle can be any type of new water bottle that has been emptied, but make sure to not contaminate it.
Do NOT drink from the bottle.
Do NOT touch the inside of the lid or bottle.
Do NOT lay the lid down.
You will use this bottle to collect your water sample after rinsing it three times with your water source and then transfer the water sample from the collection bottle to the sterile bottle.
2.
Surface Water Sampling Method
 For produce farmers who use surface water, carefully collect your sample close to your intake area.
If you treat this water before use, and you want to know the quality of the treated water, collect your sample after the treatment process.
Instructions for collecting a sample from a stream, pond, or other surface water source:
 3.
With a permanent marker, label the sample container with your name, the type of sample, the location on the farm , the date, and time.
4.
Position yourself to collect the water sample:
 5.
If you plan to wade into the waterbody:
 a.
Go to the collection site; face upstream or up current.
b.
Wait a moment to allow time for any kicked-up sediment to settle to the bottom; also, be sure to avoid leaves, sticks, or other debris.
C.
Remove the lid of the sterile bottle.
Do NOT touch the inside of the container or lid.
Do NOT lay the lid down.
Do NOT rinse the sterile bottle.
d.
Tilt the opening of the sterile bottle down toward the water; dip straight down into the water until submerged a few inches from the surface.
While submerged, tilt upright to fill to the indicated line of the sterile bottle.
e.
Remove the sterile bottle from the water and replace the lid tightly.
f.
Put the sterile bottle upright in a cooler with ice coming up to the sample level.
6.
If you plan to use an extension pole:
 a.
Stand on the stream bank next to the area where you will collect your water sample.
b.
Fix your sterile bottle to the pole and remove the lid.
Do NOT touch the inside of the container or the inside of the lid.
Do NOT lay the lid down.
C.
Extend the pole and submerge the sterile bottle into the water; rinse 3 times.
d.
Bring the bottle in and replace the lid tightly.
Put the sterile bottle upright in a cooler with ice coming up to the sample level.
7.
Deliver sample and submission form or chain of custody form to the water testing lab as soon as possible.
Check the water testing lab delivery time and temperature requirements.
Time between collection and testing is critical to getting an accurate test result.
If you want to test your treated  water, the water testing lab will provide you with a specific sterile bottle that contains a sodium thiosulfate tablet or powder used to neutralize chlorine.
In this case, the water sampling methods will vary slightly, and you will need to use an additional collection bottle.
The collection bottle can be any type of new water bottle that has been emptied, but make sure to not contaminate it.
Do NOT drink from the
 1.
Wash your hands thoroughly with soap and water.
2.
Put on nitrile or latex gloves.
bottle.
Do NOT touch the inside of the lid or bottle.
Do NOT lay the lid down.
You will use this bottle to collect your water sample after rinsing it three times with your water source and then transfer the water sample from the collection bottle to the sterile bottle.
Avoid sampling from deep or fast-moving surface water and use instead an extension pole.
Where to Send Your Water Sample for Microbial Analysis
 Be sure to send the water sample to a laboratory that uses a detection method that is equivalent to "Method 1603: Escherichia coli  in Water by Membrane Filtration Using Modified membrane-Thermotolerant Escherichia coli Agar " .
Water testing laboratories perform different microbial tests at different cost and might have different instructions to follow for water sampling and sample delivery.
You can find a short list of laboratories that use approved methods and are conveniently located for Arkansas produce growers at the end of this document.
If you treat your water, inform the water testing laboratory before collecting your samples.
They may have slightly different procedures or give you another type of sterile bottle.
Before you send your water samples, make sure you specify to the water testing laboratory:
 What you want to detect: Generic Escherichia coli 
 What type of results you want: Quantitative results.
The numerical values cannot be preceded by the "greater than sign"  because you need to know the specific number of E.
coli present in your water, not an estimation.
You can ask for qualitative results  as well, but ONLY FOR postharvest/harvest water.
Quantitative results are allowed FOR BOTH postharvest/ harvest water and production water, so it is easier to ask for quantitative results to avoid any confusion : Alternative Laboratory Methods).
Most labs will automatically run qualitative detection methods.
Avoid having to send them another sample and paying twice by verifying that they will run the quantitative detection method.
Which equivalent testing methodology for Agricultural Water need to be performed by the lab: list of FDA FSMA PSR equivalent methods.
How to Interpret Your Results
 The acceptable amount of E.
coli in water samples can vary based on the intended use of that water.
For produce farmers who are subject to the PSR, additional information to assist you in interpreting the results of the agricultural water samples can be found in our fact sheet Food Safety Modernization Act Produce Safety Rule: Microbial Water Quality Compliance and in our Microbial Water Quality Profile : How-to Guide document.
Once you have your water results, use the number of E.
coli to calculate the geometric mean  and statistical threshold value.
For more information on these calculations, see our fact sheet Food Safety Modernization Act Produce Safety Rule: Microbial Water Quality Compliance.
For help building and maintaining your MWQP see the Arizona State University's free Ag Water tool or the Western Center for Food Safety's free Excel tool.
To know the number of water samples required to build your initial MWQP  and the threshold criteria that must be met for your water samples to be considered safe, see our Microbial Water Quality Profile : How to Guide document.
Table 1.
E.
coli limits for various intended uses of a water resource.
Water Use	E.
coli Limit	Information Source
 U.S.
EPA Primary Drinking
 Human consumption	zero	Water Standards
 Preharvest activities	GM 6 CFU/100mL,	See FSA9901
 for covered produce	STV <410 CFU/100mL
 Postharvest activities	See FSA9901
 Covered produce refers to the harvestable or harvest portion of the crop subject to the requirements of the FSMA PSR.
Appendix Table 1: List of Water Laboratories Available for Arkansas Produce Growers and Water Sampling Protocols
 Water Lab	Contact Information	availability	Sterile Bottle	Form and	Account	Method requested	and Delivery Day	Holding Time	Cost per	sample
 Standard Methods 9223	samples on the
 B IDEXX Colilert Test Kit	same day.
MICROBIOLOGY	DEPARTMENT	 WATER	OF HEALTH	ARKANSAS	adh.lab@arkansas.gov	OR local county health	Little Rock, AR 72205	201 S.
Monroe St.
501-661-2218	available at your	sterile bottles.
Use only ADH	Sampling kit	local county	submission form	included in the	sampling kit	Fill out the	is not checked, the ADH	with Quanti-Tray/2000.
Check mark "raw water	submission form; if this	with count" on the	Monday through	holidays) from	8 am to noon.
(excluding	Thursday	checks; no	cash	Only	$17
 LABORATORY	units	health unit	lab will only analyze for	local health unit	Contact your
 4 hrs, < 6C
 ANALYTICAL, INC.
ARKANSAS	Little Rock, AR 72209	117011-30, Bldg.
1,	501-455-3233	Suite 115	available at the	Sterile bottle	lab	create an account	Chain of custody	lab and need to	available at the	Standard Methods 9223	B IDEXX Colilert Test Kit	with Quanti-Tray/2000	Friday, Saturday,	the day before a	or Sunday or	accepted on	Samples not	credit card	method by	Preferred	payment	$25
 Hach Method 10029 for
 TESTING LABS	ARKANSAS	204 E.
Lincoln Ave.
Searcy, AR 72143	501-268-6431	available at the	Sterile bottle	lab	available at the	and additional	instructions	coli, using m-ColiBlue 24	Broth PourRite Ampules	Coliforms Total and E.
< 8 hrs on ice	$36
 1371 W.
Altheimer Dr.
Hach Method 10029 for
 CHEM LAB	4302 Wheeler Avenue	Fort Smith, AR 72901	479-646-1585	available at the	Sterile bottle	lab	Chain of custody	available at the	lab	coli, using m-ColiBlue 24	Broth PourRite Ampules	Coliforms Total and E.
6 hrs on ice at	4C	processing	sample	+ $35
  Information retrieved in October 2020.
Please contact water laboratories to make sure the information is still up-to-date.
If you treat your water, inform the water testing laboratory before to collect your samples.
They might have slightly different procedures or give you another type of sterile bottle.
Appendix Table 1: List of Water Laboratories Available for Arkansas Produce Growers and Water Sampling Protocols 7
 Water Lab	Contact Information	availability	Sterile Bottle	Submission	Form and	Account	Method requested	and Delivery Day	Holding Time	sample	Cost	per
 Hach Method 10029 for
 TESTING, INC	DATA	3434 Country Club Ave.
Fort Smith, AR 72903	479-649-8378	available at the	Sterile bottle	lab	Chain of custody	available at the	lab	coli, using m-ColiBlue 24	Broth PourRite Ampules	Coliforms Total and E.
< 8 hrs on ice	$20
 Hach Method 10029 for
 to Friday 8 am to	5 pm or shipped	Register on the	website and fill	coli, using m-ColiBlue 24	Broth PourRite Ampules
 if requesting the	all the supplies needed
 Memphis, TN 38133	150mL plastic	Standard Methods 9223
  Information retrieved in October 2020.
Please contact water laboratories to make sure the information is still up-to-date.
you treat your water, inform the water testing laboratory before to collect your samples.
They might have slightly different procedures or give you another type of sterile bottle.
Printed by University of Arkansas Cooperative Extension Service Printing Services.
AMANDA PHILYAW PEREZ is Assistant Professor, University of Arkansas System, Division of Agriculture Cooperative Extension Service.
NATACHA CUREAU is Postdoctoral Associate, University of Arkansas System, Division of Agriculture Cooperative Extension Service.
JULIA FRYER is Program Associate, University of Arkansas System, Division of Agriculture Cooperative Extension Service.
ERIN E.
SCOTT is Program Manager, Arkansas Water Resources Center, University of Arkansas System, Division of Agriculture.
BRIAN E.
HAGGARD is Director, Arkansas Water Resources Center, University of Arkansas System, Division of Agriculture.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Director, Cooperative Extension Service, University of Arkansas.
The Arkansas Cooperative Extension Service offers its programs to all eligible persons regardless of race, color, national origin, religion, gender, age, disability, marital or veteran status, or any other legally protected status, and is an Affirmative Action/ Equal Opportunity Employer.
VISUAL GUIDE TO CORN GROWTH STAGES
 Published: Jun 16, 2023 |  Printable Version  | Peer Reviewed
 Michael Plumblee, Bennett Harrelson and Sarah Holladay
 Identifying corn growth stages is essential for successful crop management of pests, irrigation, and fertility.
This guide will help growers, consultants, Extension, and research personnel properly identify corn growth stages in field corn hybrids.
Generally, corn growth and development can be divided into vegetative  and reproductive  growth stages.
The beginning of each stage starts when at least 50% of plants in the area are at that stage.1,2,3 The vegetative growth stage begins with corn emergence and is completed by tasseling.
The reproductive growth stages start with silking and end when a black layer forms, indicating physiological maturity.
Vegetative  Growth Stages
 Vegetative growth stages of corn progress through leaf stages, which are designated V1, V2, V3, etc., through V, where  represents the last vegetative stage prior to initiation of reproductive growth stages.
Pictures of each stage and a description of that stage are presented below.
Vegetative growth stages in corn begin with seedling emergence .
Prior to germination, the corn seed absorbs water equal to approximately 50% of its weight.2,3 Once germination begins, the mesocotyl, which connects the developing root with the developing shoot, pushes the coleoptile, or developing shoot, to the soil surface.
During this time, the developing root, known as the primary root, begins to grow downward in the opposite direction and develops lateral roots making up the seminal root system.2,3,4 This seminal root system absorbs water and nutrients until the V3 growth stage.3
 Corn plant emerging from soil.
VE growth stage.
Figure 1.
VE  depends on soil temperature and moisture.
Image credit: Michael Plumblee, Clemson University.
Description of a corn plant during early development.
Figure 2.
Description of corn plant during early development.
Image credit: Steven Ritchie, Iowa State University.
Following emergence, the coleoptile and mesocotyl elongation stop.
The growth continues from the growing point , located just above the mesocotyl and below the soil surface until the V5V6 growth stage.
The rapidly developing embryonic leaves grow through the coleoptile tip.2,3
 V1, V2, V3 to V Stages
 Stages between VE and VT are designated numerically as V1, V2, through V.
The  represents the stage with the top leaf fully expanded before the VT stage.
A leaf is considered fully expanded if a leaf collar  is visible.2,3
 Corn leaf fully expanded.
Figure 3.
V1 growth stage occurs when the first true leaf is fully expanded and a leaf collar has formed, denoted by the 1 in the picture.
Image credit: Michael Plumblee, Clemson University.
Corn plant with three leaves and leaf collars.
Figure 4.
V3 growth stage occurs when three leaves are fully expanded and have visible leaf collars, denoted by the numbers in the picture.
Image credit: Eric Larson, Mississippi State University.
Vegetative growth stages in corn cease with the production of a tassel, VT.
This stage occurs when a tassel is fully extended  prior to the production of silks.
Tassels will be visible for approximately two to three days before the formation of silks.2,3 This growth stage indicates the total vegetative growth that will occur on the plant, with all the leaves present.
Corn plant at tassel growth stage, VT.
Figure 5.
VT growth stage occurs when a fully extended tassel has formed prior to silk emergence.
Image credit: Lori Abendroth, Iowa State University.
Development of a corn tassel.
Figure 6.
Tassel growth and development from the V9 growth stage until pollen shed.
Image credit: Seven Ritchie, Iowa State University.
Reproductive  Growth Stages
 The reproductive stages of corn progress through six growth stages before reaching physiological maturity.
Pictures of each stage and a description of that stage are presented below.
R1 and R2 Stages
 Corn plant at R1 growth stage, when silks are present.
Figure 7.
R1 occurs when silks are first visible outside the husks.
Image credit: Michael Plumblee, Clemson University.
At the R1 growth stage, or silking , silks are first visible outside the husks.
Silks emerge at the base growing towards the tip of the developing ear in two to five days and remain receptive to pollen for up to two weeks.2,5 Pollination occurs when falling pollen grains from the tassel are caught by the silks.
For successful pollination, it is important that silks emerge and pollinate simultaneously.
Moisture stress during this stage causes poor pollination and reduced seed set, reducing yield.
R2, or blister stage , occurs when the kernels begin to expand, dare white on the outside, and have a blistered appearance.
This growth stage typically occurs ten to fourteen days after R1, with silks beginning to dry down and turn brown.
Corn plant at R2 growth stage when kernels have blistered appearance.
Figure 8.
R2 occurs when kernels are developing and have a white blistered appearance.
Image credit: Eric Larson, Mississippi State University.
Close-up of a developing kernels with a blistered appearance.
Figure 9.
Close-up of developing kernels at the R2 or blister growth stage.
Image credit: Bob Nielsen, Purdue University.
R3 and R4 Stages
 In the R3, or milk growth stage , the kernel is pale yellow outside and filled with a milk-colored fluid which is mainly starch.
Kernels at this stage have 80% moisture.
This growth stage typically occurs eighteen to twenty-two days after R1.
In the R4, or dough stage , starch continues to accumulate and thickens to a pasty consistency.
As the kernels develop through the R4 stage, they begin to expand and turn darker yellow.
This growth stage typically occurs twenty-four to twenty-eight days after R1.
Corn plant at R3 growth stage, or milk stage.
Figure 10.
R3 occurs when kernels are pale yellow and filled with milk-colored fluid.
Image credit: Eric Larson, Mississippi State University.
Corn at R4 growth stage, or dough stage.
Figure 11.
R4 occurs when kernels are darker yellow and filled with starch that is thick and pasty in consistency.
Image credit: Eric Larson, Mississippi State University.
R5 and R6 Stages
 In the R5, or dent stage , most kernels are dented.
The kernels at the R5 stage are drying down, beginning at the top, where a small hard white layer of starch forms.
The line indicating the hard starch layer will advance toward the base of the kernel.
This growth stage occurs approximately thirty-five to forty-two days after R1.
R6, or the black layer , occurs when the hard starch layer has advanced completely to the cob and formed a brown or black abscission layer  right above the kernel tip.
The black layer is an indication of physiological maturity, and kernels are at their maximum dry matter weight.
Kernels at the R6 stage have 30% to 35% moisture content.
This growth stage occurs approximately fifty-five to sixty-five days after R1.
Corn at R5 growth stage, or dent.
Figure 12.
R5 occurs when most kernels are dented.
Corn at R6 or black layer.
Corn has reached physiological maturity.
Figure 13.
R6 occurs when kernels have reached their maximum dry matter weight and a black abscission has formed.
Image credit: Michael Plumblee, Clemson University.
The water requirement of a crop must be satisfied to achieve potential yields.
The crop water requirement is also called crop evapotranspiration and is usually represented as ETc.
Evapotranspiration is a combination of two processes evaporation of water from the ground surface or wet surfaces of plants; and transpiration of water through the stomata of leaves.
The water requirement can be supplied by stored soil water, precipitation, and irrigation.
Irrigation is required when ETc  exceeds the supply of water from soil water and precipitation.
As ETc varies with plant development stage and weather conditions, both the amount and timing of irrigation are important.
Estimates of ETc can be included in a simple water balance  method of irrigation scheduling to estimate the required amount and timing of irrigation for crops.
This method can be used if initial soil water content in the root zone, ETc, precipitation, and the available water capacity of the soil are known.
SIMPLE WATER BALANCE FOR IRRIGATION SCHEDULING
 As the crop grows and extracts water from the soil to satisfy its ETc requirement, the stored soil water is gradually depleted.
In general, the net irrigation
 requirement is the amount of water required to refill the root zone soil water content back up to field capacity.
This amount, which is the difference between field capacity and current soil water level, corresponds to the soil water deficit.
The irrigation manager can keep track of D, which gives the net amount of irrigation water to apply.
On a daily basis, D can be estimated using the following accounting equation for the soil root zone:
 where Dc is the soil water deficit  in the root zone on the current day, Dp is the soil water deficit on the previous day, ETc is the crop evapotranspiration rate for the current day, P is the gross precipitation for the current day, Irr is the net irrigation amount infiltrated into the soil for the current day, U is upflux of shallow ground water into the root zone, SRO is surface runoff, and DP is deep percolation or drainage.
The last three variables in equation 1  are difficult to estimate in the field.
In many situations, the water table is significantly deeper than the root zone and U is zero.
Also, SRO and DP can be accounted for in a simple way by setting Dc to zero whenever water additions  to the root zone are greater than Dp + ETc.
Using these assumptions, equation 1 can be simplified to:
 De = Dp + ETc P Im  [2]
 Take note that Do is set equal to zero if its value becomes negative.
This will occur if precipitation and/or irrigation exceed  and means that water added to the root zone already exceeds field capacity within the plant root zone.
Any excess water in the root zone is assumed to be lost through SRO or DP.
The amounts of water used in the equations are typically expressed in depths of water per unit area.
Equation 2 is a simplified version of the soil water balance with several underlying assumptions.
First, any water additions  are assumed to readily infiltrate into the soil surface and the rates of P or Irr are assumed to be less than the long term steady state infiltration rate of the soil.
Actually, some water is lost to surface runoff if precipitation or irrigation rates exceed the soil infiltration rate.
Thus, equation 2 will under-estimate the soil water deficit or the net irrigation requirement if P or Irr rates are higher than the soil infiltration rate.
Knowledge of effective precipitation , irrigation, and soil infiltration rates  are required to obtain more accurate estimates of Dc.
Secondly, water added to the root zone from a shallow water table  is not considered.
Groundwater contributions to soil water in the root zone must be subtracted from the right hand side of the equation in case of a shallow water table.
Equation 2 will overestimate Dc if any actual soil water additions from groundwater are neglected.
It is a good practice to occasionally check  if Dc from equation 2 is the same as the actual deficit in the field.
Remember that Dc is the difference between field capacity and current soil water content.
Therefore, the actual deficit in the field can be determined by subtracting the current soil water content from the field capacity of the root zone.
If Do from equation 2 is very different from the observed deficit, then use the observed deficit as the Dc value for the next day.
These corrections are necessary to compensate for uncertainties in the water balance variables.
Field measurements of current soil water content can be performed using the gravimetric method  or using soil water sensors like gypsum blocks.
In irrigation practice, only a percentage of AWC is allowed to be depleted because plants start to experience water stress even before soil water is depleted down to PWP.
Therefore, a management allowed depletion  of the AWC must be specified.
Values of MAD can range from 0.20 for crops highly sensitive to water stress to 0.65 for crops with high tolerance to water stress.
Also, MAD is lower for more sensitive growth phases of the crop.
The rooting depth and MAD for a crop will change with developmental stage.
The MAD can be expressed in terms of depth of water  using the following equation.
dMAD =  * AWC * Drz
 where MAD is management allowed depletion , AWC is available water capacity of the root zone , and Drz is depth of root zone.
The value of dMAD can be used as a guide for deciding when to irrigate.
Typically, irrigation water should be applied when the soil water deficit  approaches dMAD, or when Dc dMAD.
To minimize water stress on the crop, Dc should be kept less than dMAD.
If the irrigation system has enough capacity, then the irrigator can wait until Dc approaches dMAD before starting to irrigate.
The net irrigation amount equal to Dc can be applied to bring the soil water deficit to zero.
Otherwise, if the irrigation system has limited capacity , then the irrigator should not wait for Dc to approach dMAD, but should irrigate more frequently to ensure that Dc does not exceed dMAD.
However, keep in mind that more frequent irrigations increase evaporation of water from the soil surface, which is considered a loss.
In addition, when rainfall is in the forecast, the irrigator might want to leave the root zone below field capacity to allow for storage of forecasted precipitation.
Crop evapotranspiration , in inches per day, is estimated as:
 where ET, is the evapotranspiration rate  from a reference crop , Ko is a crop coefficient that varies by crop development stage , and Ks is a water stress coefficient.
A Ks of 1 means that the crop is not experiencing water stress, so a value of 1 can be assumed for fully irrigated conditions.
At any given point in the growing season, the Kc for a crop is simply the ratio of its ET over the reference crop ET.
The Ko can be thought of as the fraction of the reference crop ET that is used by the actual crop.
Values of Ko typically range from 0.2 for young seedlings to 1.0 for crops at peak vegetative stage with canopies fully covering the ground.
In some instances, peak Kc might reach 1.05-1.10, for crops showing similar biomass characteristics as alfalfa, when the soil and canopies are wet.
An example crop coefficient curve  is shown in Figure 1.
Crop coefficient values for commonly grown crops are provided by Allen et al..
Figure 1.
Example crop coefficient curve that shows K values that change with crop development.
The water-holding capacity of a soil varies with its texture and needs to be considered when determining how much soil water is available.
For example, a loamy sand will hold about 1.1 inches of water per foot or 4.4 inches in top 4 feet while a silt loam soil can hold 2.2 inches per foot or 8.8 inches in the top 4 feet.
If the silt loam is at field capacity and we draw down the available soil water to 40% , we would have about 5.3 inches of useable water in the top four feet of soil.
However, the data shows that in the dry years, 2020, 21 and 22, 15-20% of the irrigators let their fields get dry late in the season, maybe even dry enough to have resulted in small yield losses.
So, in dry years, data driven decisions could lead some irrigators to apply more water.
i PORQUE NECESITAMOS AGUA?
MEJOREI agua se compone entre el 50 y el 75por ciento de nuestro cuerpo.Es un nutriente esencial y nuestro cuerpo no puede hacer todo lo que necesitamos.
Si bien el agua es el nico nutriente ms importante para mantener una buena salud, inos olvidamos de beberla!
Beber 48 a 64 onzas de agua diariamente es una buena idea, pero la cantidad de agua que la persona necesita se ve afectada por muchas cosas.
Nuestros cuerpos pueden sobrevivir solo unos das sin agua.El agua transporta nutrientes por todo el cuerpo y mantiene los alimentos en movimiento a travs de los intestinos.
Ayuda a elimina los productos de desecho y previene el estreimiento.
El agua tambin amortigua las articulaciones que se mueven suavemente y regulan la temperatura corporal a travs de la sudoracin.
Si experiment sequedad en la boca, orina oscura y mareos o aturdimiento, es posible que deba consumir ms agua.
La Divisin de Agricultura del Sistema de la Universidad de Arkansas ofrece todos sus programas de Extensin elnvestigacin a todas las personas elegibles sin distincin de raza, color, sexo ,identidad de gnero, orientacin sexual, origen nacional, religin, edad, discapacidad, estado civil o de veterano, informacin gentica, o cualquier otro estatus protegido legalmente, y es una accion afirmativa/ ofrecelgualdad de Oportunidades de Empleador /.
Este material fue financiado por elPrograma de Asistencia Nutricional Suplementaria del USDA.
CONTENIDO DE AGUA EN LOS ALIMENTOS
 Lo crea o no,el agua se encuentra en casi todos los alimentos.
Como puede ver, frutas y verduras tpicamente contiene la mayora por onza.
Lechuga 95% Sanda 92% Brocoli 91% Fresas 91% Zanahoria.
87% Bananas 75% Yogur 75% Pasta 66% Pollo 65% Pan 38%
 Si tiene la tentacin de reemplazar su producto con jugo, tenga en cuenta que no todos los jugos son iguales.
Algunos estn empacados con nutrientes, mientras que otros son simplemente agua con azcar.
Lea la etiqueta y solo compre jugos que contengan jugo de fruta 100%.
Algunas bebidas de frutas pueden costar menos del 100% de jugos de frutas, pero debido a que brindan pocos nutrientes, jrealmente no son mejores para comprar!
AGREGUE AGUA A SU DA
 Aqu hay 5 consejos para beber ms agua a lo largo del da:
 1.
Tome pausas para tomar agua, no caf.
2.
Tome agua con sus comidas y / o refrigerios.
3.
Congele una botella de agua y llvela al trabajo todos los das para un suministro de hielo y fro.
4.Nunca deje pasar la opourtunidad de una fuente de agua.
5.
Beber agua antes, durante y despus del ejercicio.
Escriba a continuacin cmo le gustara aadir agua a su da:
For sugarbeets in the emergence crop growth stage the estimated water use during the previous week of May 29 June 4, 2023 is 0.12 inches and the estimated water use during the week of June 5-11, 2023 is 0.90 inches.
For sugarbeets in the cover 10-30% crop growth stage the estimated water use during the previous week of May 29 June 4, 2023 is 0.17 inches.
Irrigation Scheduling For Corn: Macromanagement
 Freddie R.
Lamm Danny H.
Rogers Gary A.
Clark
 Corn irrigation scheduling issues such as initiation and termination of the irrigation season, determining the need for dormant season irrigation, and non-crop water decisions are defined as macromanagement in this discussion.
Macromanagement can have a significant effect on water conservation and production.
The water conservation and crop production advantages of efficient step-by-step irrigation scheduling using the crop water balance can be greatly reduced by inappropriate macromanagement.
Irrigators should use sound rationale for macromanagement.
In some cases, researchers need to develop, re-evaluate or update macromanagement procedures.
Keywords: Irrigation strategies, Irrigation management, Water conservation, Zea mays L., Maximum allowable deficit , management allowed depletion
 Corn  is a major irrigated crop in the Central Great Plains.
Any realistic attempt to reduce irrigation withdrawals from the Ogallala Aquifer must address this fact.
A number of excellent irrigation scheduling methods for corn can be used to schedule irrigation on a real time, daily, or short-term basis throughout the season.
These methods of irrigation scheduling achieve water conservation by delaying any unnecessary irrigation event with the prospect that the irrigation season might end before the next irrigation event is required.
However, larger irrigation management issues can have a greater impact on water conservation than the step-by-step, periodic scheduling procedures.
These include strategies for initiation and termination of the irrigation season, determining the need for dormant-season irrigation, and noncrop water issues.
Macromanagement strategies can provide the potential for increased water conservation when used in conjunction with the step-by-step periodic scheduling procedures.
This paper will discuss macromanagement using research-based rationale for corn irrigated with groundwater in the semi-arid Central Great Plains, but has implications for other regions and other crops.
An implicit assumption of the concepts is that efficient irrigation scheduling based on the crop water balance is used throughout the irrigation season.
INITIATION OF IRRIGATION SEASON
 The date for the first irrigation can usually be effectively determined by comparing the daily calculated rootzone soil water balance to a preset maximum allowed deficit  also termed as management allowed depletion.
The MAD is often assumed to be 50% of the available soil water in the active crop rootzone, but soil and climate conditions and irrigator judgment may dictate other criteria.
The soil water balance is initialized with a measured or assumed initial soil water condition.
The initial measurements or assumptions must be appropriate for the given year.
For example, excessive temperatures can limit early season root growth and thus limit the rootzone available to the corn crop.
Similarly, if irrigation with discrete application has been used, such as furrow or line-source drip irrigation, measurements or assumptions need to be based on the active rootzone, not the wetted portion of the soil.
In some cases, additional irrigation may be required to satisfy this early-season rootzone distribution.
This event can have a low application efficiency due to increased percolation and due to applications to nonrootzone areas.
Furrow irrigators may initiate the first irrigation following the last cultivation or furrowing process to eliminate water stress associated with root pruning and to help seal soft furrows, rather than an irrigation need dictated by the crop water balance.
Irrigators should carefully evaluate the need for these additional or early irrigations which are not dictated by the soil water balance if water conservation is important.
This is particularly true in areas with a continental climate where there is a high probability of precipitation exceeding the early season corn evapotranspiration.
Simulations of sprinkler irrigation schedules for corn  at Colby, Kansas indicate the first 25 mm irrigation event occurs between June 5 and July 5, with most years between June 10 and June 15.
Some irrigators with low capacity irrigation systems start irrigation sooner than normal.
The simulations indicate that usually there is no need to start irrigating in northwest Kansas before June 10 unless the soil profile is extremely dry from the previous crop or from a dry overwinter period.
Crop water stress problems associated with decreased irrigation capacity in July and August is not alleviated by the excess system capacity in June, when the soil profile is already relatively full of water.
An overall point of the simulations that should not be missed is the variability in initial irrigation dates.
An objective of step-bystep irrigation scheduling is to delay irrigation until necessary in hopes of replenishment by natural precipitation.
Proper determination of the first irrigation date is an important step in water conservation.
Irrigators should use crop water balances and/or soil water measurements to establish the first irrigation date and not rely on traditional calendar dates.
TERMINATION OF IRRIGATION SEASON
 Conceptually, the irrigation season is terminated when the marginal cost of additional irrigation equals the marginal benefits of the harvested economic yield of the crop.
Two noteworthy points of wording in the previous statement should be made.
First, in many cases, the cost of deep percolation caused by additional late-season irrigation has not been assessed.
If groundwater contamination due to excessive percolation is a concern, then the marginal cost of irrigation must reflect that fact.
The second point is that the marginal costs must be balanced against the harvested economic yield.
For example, if the termination decision  affects harvesting,  then the actual economic yield could be reduced in a way not traditionally considered.
From a practical standpoint, termination of the irrigation season is most effectively determined by comparing the anticipated soil water balance at physiological maturity to the MAD.
It should be noted that the MAD for the end of the season may not be the same as at other growth stages during the season.
Doorenbos and Kassam  indicate the MAD may approach 80% near physiological maturity for corn.
The MAD point should be established according to crop sensitivity and the maximum daily ET during the period in question.
They list MAD values of 0.8, 0.6 and 0.5 for maximum corn ET values of 3, 5 and 7 mm/day, respectively.
Extension publications from the Central Great Plains often suggest limiting the MAD at the end of the season to 0.6 in the top 1-1.2 m.
These values may need to be re-evaluated and perhaps adjusted downward.
Lamm et al.
found subsurface, drip-irrigated corn yields in northwest Kansas to begin to decrease rapidly when available soil water in the top 2.4 m was lower than 56-60% of field capacity for extended periods in July and August.
Lamm et al.,  permitted small daily deficits to accumulate on surface-irrigated corn after tasseling, and subsequent analysis of those data showed declining yields when available soil water levels approached 60% of field capacity for a 1.5-m soil profile at physiological maturity.
Current high corn yield levels may require greater available soil water levels than were used in earlier studies.
The anticipated soil water balance at physiological maturity is projected from historical ET and precipitation data.
Irrigators should time the last irrigation to ensure a reasonable probability of remaining above the chosen MAD level at physiological maturity.
In the absence of good historical estimates of ET, extension publications are available that give crop water use values for the latter part of the season.
Figure 1.
Corn yields as related to available soil water  in a 1.5-m soil profile at harvest in an irrigation-scheduling study where slight deficits were allowed to occur after tasseling.
Data analyzed from Lamm et al.,.
The advantages of preseason irrigation  are to 1) provide water for seed germination; 2) delay the initiation of seasonal irrigation; 3) improve tillage and cultural practices associated with crop establishment; and 4) more fully utilize marginal irrigation systems on additional land area.
The disadvantages are that it may 1) increase production costs; 2) increase irrigation requirements; 3) lower overall irrigation efficiencies; and 4) lower soil temperatures.
Preseason irrigation for crops such as corn has been advocated for the semi-arid Great Plains for most of the 20th century, and the practice has been debated for nearly as long.
Knorr  found that at Scottsbluff, Nebraska, fall irrigation normally increased corn yields.
Farrell and Aune  found opposite results at Belle Fourche, South Dakota.
Knapp  recommended winter irrigation for most of western Kansas with the exception of sandy soils.
Off-season labor utilization was seen as an important factor, along with avoiding conflicts with busy summer schedules.
Power et al.
in a North Dakota study found that when fall irrigation was practiced, nearly all the winter precipitation was lost.
On dryland plots, significant amounts of soil water were stored during the winter.
Adding fall irrigation to normal seasonal irrigation did not significantly affect yields of barley or of corn silage.
Hobbs and Krogman , finding that storage efficiency of winter precipitation decreased as fall irrigation increased, concluded that fall irrigation to bring soil water in the profile to 50% of field capacity would be advisable.
Stone et al.
, at Tribune, Kansas, reported that the net benefit of additional irrigation decreased linearly with increases in soil-water content in the fall.
There were no significant differences in corn yields  between fields irrigated in the fall and those not irrigated in the fall.
They concluded that fall irrigation to bring soil water in the profile to approximately 50% of field capacity was an efficient practice.
Willis et al.
observed that fall irrigation subsequently increased runoff during natural precipitation, thus contributing to inefficient water storage.
Stone et al.
concluded irrigation water should be reserved for inseason application unless needed for stand establishment.
Despite considerable controversy over preseason irrigation for corn, it remains a common practice in parts of the Great Plains.
Greb  advocated it as an efficient practice in much of the Central Great Plains, and Hay and Pope  reported that preseason irrigation should always be considered as a management tool in corn production in western Kansas.
Elimination of unnecessary preseason irrigation could result in the largest single water savings an irrigator might obtain in a season.
Musick and Lamm  indicated that for surface irrigation systems the preseason irrigation is normally the largest event and may be as much as 25% of the total irrigation applied for corn.
Lamm and Rogers  developed an empirical model to aid in decisions concerning fall preseason irrigation for corn production in western Kansas.
Available soil water at spring planting was functionally related to overwinter precipitation and initial available soil water in the fall.
An extension of this simple model by incorporating
 precipitation probabilities is presented in Fig.
2.
Using probability and the model, the irrigator can determine the need for preseason irrigation and the irrigation amount necessary to reach a desired soil-water content at planting.
Procedures used to develop this model could be used in other regions, even though the coefficients are likely to be site specific.
In most years, fall preseason irrigation for corn is not needed to recharge the soil profile in northwest Kansas, unless residual soil water remaining after corn harvest is excessively low.
Rogers and Lamm  found in a post-corn harvest survey of 82 randomly selected fields in northwest Kansas that the available soil water in the 1.5-m soil profile averaged 70% of field capacity.
Available soil water was similar for center pivot sprinklerand surface-irrigated fields, but within-field variation was higher for surface-irrigated fields.
A number of low-capacity sprinkler irrigation systems exist in the Great Plains region, and many irrigators assume they must compensate with dormant-season irrigation.
However, even though an irrigation system may have insufficient capacity during a critical period, an irrigator may try to catch up with irrigation later in the season, which builds soil-water reserves but may not affect yield.
The survey results indicate irrigators should evaluate their conditions prior to initiating preseason irrigation.
DORMANT-SEASON SOIL WATER MANAGEMENT
 Drier soil profiles at harvest result in greater opportunity for capturing winter precipitation and also reduce the potential for overwinter drainage losses and leaching of chemicals to groundwater.
Research in Kansas by Rice  found nitrate leaching during the growing season was minimal, and the overwinter period was of greater concern because evapotranspiration is usually lower than the precipitation.
One method of obtaining drier soil profiles and conserving water is to mine the plant-available soil water gradually during the irrigation season in anticipation of recharge from precipitation during the off season.
This concept of irrigation scheduling with planned soil water depletion was developed by Woodruff et al.
under semi-humid conditions in Missouri.
Further experimental testing of the concept  found it could be used successfully on deep soil profiles with high water holding capacity, provided irrigation frequency was sufficient to maintain adequate soil water in the most active zone of water and nutrient uptake.
Martin et al.
reported that mining of 50% of the soil water may be acceptable if off-season precipitation is sufficient to fully recharge the crop rootzone.
Figure 2.
Probability of reaching specified percentage of field capacity by June 1 with a specified value of fall  available soil water  in the 1.5-m soil profile on a Keith silt loam soil at Colby, KS.
After Lamm and Rogers.
Lamm et al.
found in a surface-irrigated study that irrigation scheduling with planned soil water depletion for corn was not justified for water conservation.
Reductions in soil water at harvest were accompanied by reductions in corn yields.
Water use efficiencies were similar across treatments.
Mining plant-available soil water to a low level would be acceptable, and even desirable, if corn yields could be maintained.
However, deficit irrigation of corn is difficult to implement successfully without incurring yield reductions.
After reviewing numerous studies, Rhodes and Bennett  reported that water stress imposed at any growth stage on corn will generally lower the efficiency of the water used in transpiration.
Lamm et al.
found irrigation needed to be reduced about 4 units for each unit reduction in available soil water at harvest.
They concluded that irrigation scheduling with planned soil water depletion was not justified for use with surface irrigation , but might be successful with surge, sprinkler or drip irrigation.
Stegman et al.,  reported that an irrigation interval of seven days or less should be used when scheduling irrigation with planned soil water depletion.
Figure 3.
Available soil water  at maturity in the 1.5-m soil profile as related to seasonal irrigation on a Keith silt loam soil at Colby, KS.
After Lamm et al.,.
Traditional step-by-step, periodic irrigation scheduling using the crop water balance has been used successfully for many years.
Conceptually, these methods attempt to minimize the number of irrigations and the total seasonal irrigation amount by providing irrigation "just-in-time." Macromanagement for irrigation scheduling attempts to provide the seasonal boundaries and governing parameters that provide the framework for conducting the step-by-step irrigation scheduling.
The seasonal boundaries are the initiation and termination of the irrigation season.
Irrigators sometimes make these seasonal boundary determinations based on a traditional timeof-year rather than with sound rationale or procedures.
In some cases, researchers need to develop, evaluate, or update the procedures used in these determinations.
Dormant-season irrigation and dormant season water quality management are governing parameters instituted by the irrigator, but will affect in-season, step-by-step irrigation scheduling.
Inattention to irrigation scheduling macromanagement or practice of traditional macromanagement without adjustment for the conditions  can lead to inefficient use of irrigation water and/or decreased corn yields.
A single, inappropriate macromanagement decision can easily have a larger effect on total irrigation water use and/or crop production than the cumulative errors in step-by-step irrigation scheduling that might occur due to small systematic errors in the crop water balance.
This does not discount step-by-step irrigation
 scheduling.
To the contrary, the use of it has been an implicit assumption of this entire discussion.
Using rational macromanagement strategies and step-by-step irrigation scheduling closely together offers the best opportunities to conserve irrigation and maintain high production levels.
This paper was first presented at the Evapotranspiration and Irrigation Scheduling Conference, San Antonio, TX, Nov.
3-6, 1996.
WHEN CAN ONE STOP IRRIGATING!
CROP "ET" SLOWLY REDUCES AS MATURITY NEARS
 Keeping track of daily crop water usage  for the past 2 to 5 days can greatly assist an irrigation manager in deciding when to startup the next irrigation and when one can start to think about stopping for the season.
Daily water usage for most crops slowly starts reducing in mid August as they work themselves towards maturity.
However, daily ET can still reach rates of.25 or higher at any time through mid September if air temperature spikes into the upper 80s to low 90s and the sky is cloud free.
Under normal temperature conditions however a corn crop generally will need only 2 to 2.5 inches of additional soil water after first dent to come to full maturity.
For a soil holding at least 3.5 inches of available water at first dent there should be no additional irrigation needed if temperatures remain at or below normal.
Lighter soils however may need one or two more irrigations while a heavier soil may tolerate even an earlier cutoff time.
As irrigated corn and soybeans near maturity, the field's soil moisture level generally can be allowed to decrease to greater limits without causing stress to the crop.
For corn starting to dent, research has shown that the soil moisture deficit can be allowed to start increasing to 5065 percent by maturity time without reducing yields under normal late summer temperatures.
The table below lists estimated average crop ET requirements for corn and soybeans under normal September weather conditions within central Minnesota from different growth stages to maturity:
 Stage of	Days to	Inches of ET
 Crop Growth	Maturity	to Maturity
 milk	38 42	4.8 5.3
 dough	30 35	3.2 3.6
 first dent	23 27	2.1 2.4
 full dent	19 21	1.6 1.8
 1/2 milk line	12 14	0.9 1.2
 1/4 milk line	6 8	0.4 0.6
 full flower	48 54	6.8 7.6
 full pod	35 39	4.0 4.8
 begin seed fill	27 31	2.7 3.3
 full seed fill	16 18	1.1 1.4
 begin maturity	9 11	0.4 0.7
 Regular in-field soil moisture checking with a soil probe and keeping track of a crop's daily ET use can go a long ways in helping an operator optimize a crop's growth as well as utilizing the irrigation water most efficiently.
Estimated ET  for 4 August 2013
 Several local daily ET information services also exist for specific Minnesota counties and they are listed below:
 DAILY CROP 'ET" FOR 2013 AVAILABLE
 North Dakota Ag Weather & Crop
EFFECT OF TILLAGE PRACTICES AND DEFICIT IRRIGATION ON CORN
 KSU Northwest Research-Extension Center 105 Experiment Farm Road, Colby, Kansas Voice: 785-462-6281 Fax: 785-462-2315
 Corn production was compared from 2004 to 2007 for three plant populations  under conventional, strip and no tillage systems for irrigation capacities limited to 1 inch every 4, 6 or 8 days.
Corn yield increased approximately 10%  from the lowest to highest irrigation capacity in these four years of varying precipitation and crop evapotranspiration.
Strip tillage and no tillage had approximately 8.1% and 6.4%  greater grain yields than conventional tillage, respectively.
Results suggest that strip tillage obtains the residue benefits of no tillage in reducing evaporation losses without the yield penalty sometimes occurring with high residue.
The small increases in total seasonal water use  for strip tillage and notillage compared to conventional tillage can probably be explained by the greater grain yields for these tillage systems.
Declining water supplies and reduced well capacities are forcing irrigators to look for ways to conserve and get the best utilization from their water.
Residue management techniques such as no tillage or conservation tillage have been proven to be very effective tools for dryland water conservation in the Great Plains.
However, adoption of these techniques is lagging for continuous irrigated corn.
There are many reasons given for this lack of adoption, but some of the major reasons expressed are difficulty handling the increased level of residue from irrigated production, cooler and wetter seedbeds in the early spring which may lead to poor or slower development of the crop, and ultimately a corn grain yield penalty as compared to conventional tillage systems.
Under very high production systems, even a reduction of a few percentage points in corn yield can have a significant economic impact.
Strip tillage might be a good compromise between conventional tillage and no tillage, possibly achieving most of the benefits in water conservation and soil quality management of no tillage, while providing a method of handling the increased residue and increased early growth similar to conventional tillage.
Strip tillage can retain surface residues and thus suppress soil evaporation and also provide subsurface tillage to help
 alleviate effects of restrictive soil layers on root growth and function.
A study was initiated in 2004 to examine the effect of three tillage systems for corn production under three different irrigation capacities.
Plant population was an additional factor examined because corn grain yield increases in recent years have been closely related to increased plant populations.
The study was conducted under a center pivot sprinkler at the KSU Northwest Research-Extension Center at Colby, Kansas during the years 2004 to 2007.
Corn was also grown on the field site in 2003 to establish residue levels for the three tillage treatments.
The deep Keith silt loam soil can supply about 17.5 inches of available soil water for an 8-foot soil profile.
The climate can be described as semi-arid with a summer precipitation pattern with an annual rainfall of approximately 19 inches.
Average precipitation is approximately 12 inches during the 120-day corn growing season.
A corn hybrid of approximately 110 day relative maturity  was planted in circular rows on May 8, 2004, April 27, 2005, April 20, 2006 and May 8, 2007, respectively.
Three target seeding rates  were superimposed onto each tillage treatment in a complete randomized block design.
Irrigation was scheduled with a weather-based water budget, but was limited to the 3 treatment capacities of 1 inch every 4, 6, or 8 days.
This translates into typical seasonal irrigation amounts of 16-20, 12-15, 8-10 inches, respectively.
Each of the irrigation capacities  were replicated three times in pieshaped sectors  of the center pivot sprinkler.
Plot length varied from to 90 to 175 ft, depending on the radius of the subplot from the center pivot point.
Irrigation application rates  at the outside edge of this research center pivot were similar to application rates near the end of full size systems.
A small amount of preseason irrigation was conducted to bring the soil water profile  to approximately 50% of field capacity in the fall and as necessary in the spring to bring the soil water profile to approximately 75% in the top 3 ft prior to planting.
It should be recognized that preseason irrigation is not a recommended practice for fully irrigated corn production, but did allow the three irrigation capacities to start the season with somewhat similar amounts of water in the profile.
The three tillage treatments  were replicated in a Latin-Square type arrangement in 60 ft widths at three different radii  from the center pivot point.
The various operations and their time period for the three tillage treatments are summarized in Table 1.
Planting was in the same row location each year for the Conventional Tillage treatment to the extent that good farming practices allowed.
The Strip Tillage and No-Tillage treatments were planted between corn rows from the previous year.
Each Tillage Trt.
includes 3 plant populations 
 Tillage and Sprinkler Irrigation Capacity Study
 Figure 1.
Physical arrangement of the irrigation capacity and tillage treatments.
Fertilizer N for all 3 treatments was applied at a rate of 200 lb/acre in split applications with approximately 85 lb/ac applied in the fall or spring application, approximately 30 lb/acre in the starter application at planting and approximately 85 lb/acre in a fertigation event near corn lay-by.
Phosphorus was applied with the starter fertilizer at planting at the rate of 45 lb/acre P2O5.
Urea-AmmoniumNitrate  and Ammonium Superphosphate  were utilized as the fertilizer sources in the study.
Fertilizer was incorporated in the fall concurrently with the Conventional Tillage operation and applied with a mole knife during the Strip Tillage treatment.
Conversely, N application was broadcast with the No Tillage treatment prior to planting.
A post-plant, pre-emergent herbicide program of Bicep II Magnum and Roundup Ultra was applied.
Roundup was also applied post-emergence prior to lay-by for all treatments, but was particularly beneficial for the strip and no tillage treatments.
Insecticides were applied as required during the growing season.
Weekly to bi-weekly soil water measurements were made in 1-ft increments to 8ft.
depth with a neutron probe.
All measured data was taken near the center of each plot.
Surface crop residue and surface residue cover was sampled in April 2007 prior to planting.
Table 1.
Tillage treatments, herbicide and nutrient application by period.
Period	Conventional tillage	Strip Tillage	No Tillage
 1) One-pass chisel/disk plow	1) Strip Till + Fertilizer  at
 Fall	at 8-10 inches with	8-10 inch depth,
 2003	broadcast N, November 13,	November 13, 2003.
2) Plant + Banded starter N &	2) Plant + Banded starter N	1) Broadcast N + Plant +
 P, May 8, 2004.
& P, May 8, 2004	Banded starter N & P,
 Spring	May 8, 2004
 2004	3) Pre-emergent herbicide	3) Pre-emergent herbicide	2) Pre-emergent
 application, May 9, 2004.
application, May 9, 2004.
herbicide application,
 4) Roundup herbicide	4) Roundup herbicide	3) Roundup herbicide
 Summer	application near lay-by,	application near lay-by,	application near lay-
 June 9, 2004	June 9, 2004	by, June 9, 2004
 5) Fertigate , June 10,	5) Fertigate , June10,	4) Fertigate , June 10,
 1) One-pass chisel/disk plow	Too wet, no tillage
 Fall	at 8-10 inches with	operations
 2004	broadcast N, November 05,
 1) Strip Till + Fertilizer  at
 8-10 inch depth, March
 Spring	2) Plant + Banded starter N &	2) Plant + Banded starter N	1) Broadcast N + Plant +
 2005	P, April 27, 2005.
& P, April 27, 2005	Banded starter N & P,
 3) Pre-emergent herbicide	3) Pre-emergent herbicide	2) Pre-emergent
 application, May 8, 2005.
application, May 8, 2005.
herbicide application,
 4) Roundup herbicide	4) Roundup herbicide	3) Roundup herbicide
 Summer	application near lay-by,	application near lay-by,	application near lay-
 June 9, 2005	June 9, 2005	by, June 9, 2005
 5) Fertigate , June 17,	5) Fertigate , June 17,	4) Fertigate , June 17,
 1) One-pass chisel/disk plow	1) Strip Till + Fertilizer  at
 Fall 2005	at 8-10 inches with	8-10 inch depth,
 broadcast N, November 10,	November 10, 2005.
2) Plant + Banded starter N &	2) Plant + Banded starter N	1) Broadcast N + Plant +
 P, April 20, 2006.
& P, April 20, 2006	Banded starter N & P,
 Spring	April 20, 2006
 2006	3) Pre-emergent herbicide	3) Pre-emergent herbicide	2) Pre-emergent
 application, April 22, 2006.
application, April 22,	herbicide application,
 2006.
April 22, 2006.
4) Roundup herbicide	4) Roundup herbicide	3) Roundup herbicide
 Summer	application near lay-by,	application near lay-by,	application near lay-
 June 6, 2006	June 6, 2006	by, June6, 2006
 5) Fertigate , June 13,	5) Fertigate , June 13,	4) Fertigate , June 13,
 Period	Conventional tillage	Strip Tillage	No Tillage
 1) One-pass chisel/disk plow	1) Strip Till + Fertilizer  at
 Fall	at 8-10 inches with	8-10 inch depth,
 2006	broadcast N, November 28,	November 28, 2006.
2) Plant + Banded starter N &	2) Plant + Banded starter N	1) Broadcast N + Plant +
 P, May 8, 2007.
& P, May 8, 2007	Banded starter N & P,
 Spring	May 8, 2007
 2007	3) Pre-emergent herbicide	3) Pre-emergent herbicide	2) Pre-emergent
 application, May 8, 2007.
application, May 8, 2007.
herbicide application,
 4) Roundup herbicide	4) Roundup herbicide	3) Roundup herbicide
 Summer	application near lay-by,	application near lay-by,	application near lay-
 June 16, 2007	June 16, 2007	by, June 16, 2007
 5) Fertigate , June 21,	5) Fertigate , June 21,	4) Fertigate , June 21,
 Similarly, corn yield was measured in each of the 81 subplots at the end of the season.
In addition, yield components  were determined to help explain the treatment differences.
Water use and water use efficiency were calculated for each subplot using the soil water data, precipitation, applied irrigation and crop yield.
Weather Conditions and Irrigation Needs
 Summer seasonal precipitation was approximately 2 inches below normal in 2004, near normal in 2005, nearly 3 inches below normal in 2006, and approximately 2.5 inches below normal in 2007 at 9.99, 11.95, 8.99 and 9.37 inches, respectively for the 120 day period from May 15 through September 11.
In 2004, the last month of the season was very dry but the remainder of the season had reasonably timely rainfall and about normal crop evapotranspiration.
In 2005, precipitation was above normal until about the middle of July and then there was a period with very little precipitation until the middle of August.
This dry period in 2005 also coincided with a week of greater temperatures and high crop evapotranspiration near the reproductive period of the corn.
In 2006, precipitation lagged behind the long term average for the entire season.
Fortunately, seasonal evapotranspiration was near normal as it also was for the 2004 and 2005.
Although precipitation was smaller than normal in 2007, crop evapotranspiration was much smaller than normal at 19.96 inches which resulted in less irrigation needs.
Figure 2.
Corn evapotranspiration and summer seasonal rainfall for the 120 day period, May 15 through September 11, KSU Northwest ResearchExtension Center, Colby Kansas.
Irrigation requirements were lowest in 2004 with the 1 inch/4 day treatment receiving 12 inches, the 1 inch/ 6 day treatment receiving 11 inches and the 1 inch/8 day treatment receiving 9 inches.
The irrigation amounts in 2005 were 15, 13, and 10 inches for the three respective treatments.
The irrigation amounts were highest in 2006 at 15.5, 13.5, and 11.50 inches for the three respective treatments.
Irrigation amounts in 2007 were 12.5, 11.5 and 10.5 inches for the three respective treatments which were just slightly greater than the low irrigation values of 2004.
Although seasonal precipitation was considerably smaller in 2007 compared to 2004, there was very little difference in irrigation requirements.
This was because evapotranspiration was considerably smaller than normal in 2007 due to light winds and moderate temperatures during much of the summer.
Figure 3.
Cumulative irrigation by day of year for the three irrigation capacities during all four years of the tillage and irrigation capacity study of corn, KSU Northwest Research-Extension Center, Colby, Kansas.
Crop Yield and Selected Yield Components
 Corn yield was relatively high for all four years ranging from 161 to 279 bu/acre.
Greater irrigation capacity generally increased grain yield, particularly in 2005 and 2006.
Strip tillage and no tillage had greater grain yields at the lowest irrigation capacity in 2004 and at all irrigation capacities in 2005 and 2006.
In 2007, all tillage treatment yields were very high but strip tillage had slightly greater yields at the lowest and highest irrigation capacity.
Strip tillage tended to have the highest grain yields for all tillage systems and the effect of tillage treatment was greatest at the lowest irrigation capacity in the four years of the study.
Crop residue and residue cover were similar for no tillage
  and strip tillage  but much less for conventional tillage.
These results suggest that strip tillage obtains the residue benefits of no tillage in reducing evaporation losses without the yield penalty sometimes associated with the greater residue levels in irrigated no tillage management.
Table 2.
Selected corn yield component and total seasonal water use data for 2004 from an irrigation capacity and tillage study, KSU Northwest Research-Extension Center, Colby, Kansas.
Irrigation	Capacity	System	Tillage	Population		Plant	bu/acre	Grain	Yield	Population	Plant		Kernels	/Ear	Weight	Kernel	g/100		Water	Use
 1 in/4 days Conventional	26	229	27878	550	37.1	23.0
 	30	235	29330	557	36.2	22.6
 34	234	32234	529	34.6	22.0
 Strip Tillage	26	245	27588	537	38.9	23.5
 30	232	30492	519	37.0	24.4
 34	237	33106	514	35.5	24.3
 No Tillage	26	218	25846	548	37.7	22.0
 30	226	29330	539	36.8	23.6
 34	251	33686	553	33.8	23.2
 1 in/6 days Conventional	26	226	25265	557	39.0	23.0
 	30	222	29621	522	34.9	23.6
 34	243	32525	522	36.0	23.9
 Strip Tillage	26	235	27298	558	36.9	23.3
 30	224	28750	556	35.0	24.4
 34	237	33396	487	35.6	24.4
 No Tillage	26	225	26426	537	37.8	24.5
 30	222	29040	556	34.6	25.0
 34	229	32234	545	32.8	23.4
 1 in/8 days Conventional	26	198	24684	509	37.5	22.1
 	30	211	29330	531	34.5	22.4
 34	216	31654	494	34.9	22.0
 Strip Tillage	26	227	25846	644	34.2	23.8
 30	229	29911	518	35.6	21.8
 34	234	32815	507	35.1	23.2
 No Tillage	26	220	27007	541	36.6	22.5
 30	225	29621	528	34.5	23.2
 34	220	32815	506	32.2	22.6
 Table 3.
Selected corn yield component and total seasonal water use data for 2005 from an irrigation capacity and tillage study, KSU Northwest Research-Extension Center, Colby, Kansas.
Irrigation	Tillage	Plant	Grain	Plant	Kernels	Kernel	Water
 Capacity	System	Population		bu/acre	Yield	Population		/Ear	Weight	g/100		Use
 1 in/4 days	Conventional	26	218	23813	644	37.9	28.3
 	30	238	27588	594	37.3	28.6
 34	260	30202	579	37.1	27.3
 Strip Tillage	26	238	24394	620	39.6	28.3
 30	251	27878	590	38.3	26.6
 34	253	31073	567	36.8	29.1
 No Tillage	26	228	24974	628	38.3	28.1
 30	254	26717	660	37.4	27.7
 34	262	31363	606	35.8	28.5
 1 in/6 days Conventional	26	203	24684	546	37.7	26.4
 	30	221	27588	544	37.5	25.8
 34	208	31073	472	36.2	25.3
 Strip Tillage	26	226	24394	604	38.9	26.7
 30	207	28169	487	38.4	27.1
 34	248	31944	560	36.0	26.2
 No Tillage	26	205	24684	565	38.2	26.7
 30	224	29040	547	36.6	27.2
 34	234	31654	512	37.1	25.7
 1 in/8 days Conventional	26	187	24394	523	37.5	22.8
 	30	218	27298	536	37.5	22.5
 34	208	31654	452	37.3	24.8
 Strip Tillage	26	212	23813	648	34.9	23.8
 30	216	27588	579	35.8	24.1
 34	240	31363	537	36.1	24.5
 No Tillage	26	208	24103	608	37.4	24.6
 30	211	27588	537	36.2	22.9
 34	216	31073	502	36.4	24.7
 Table 4.
Selected corn yield component and total seasonal water use data for 2006 from an irrigation capacity and tillage study, KSU Northwest Research-Extension Center, Colby, Kansas.
Irrigation	Tillage	Plant	Grain	Plant	Kernels	Kernel	Water
 Capacity	System	Population		bu/acre	Yield	Population		/Ear	Weight	g/100		Use
 1	in/4 days Conventional	26	239	29330	542	38.1	27.1
 	30	213	31073	476	36.4	26.6
 34	212	35138	434	36.1	26.9
 Strip Tillage	26	232	29330	514	39.1	27.7
 30	236	31363	483	38.2	27.4
 34	260	33106	522	38.6	27.5
 No Tillage	26	211	28459	497	37.9	26.3
 30	263	31363	535	40.3	27.5
 34	248	34558	516	35.7	27.0
 1 in/6 days Conventional	26	161	29040	422	34.1	24.8
 	30	208	31944	446	37.1	24.6
 34	169	33977	374	35.0	25.0
 Strip Tillage	26	207	29040	492	36.6	26.1
 30	215	31363	484	36.7	25.9
 34	216	34267	476	34.7	26.5
 No Tillage	26	230	29330	541	36.8	25.9
 30	218	30202	516	35.9	25.6
 34	223	32815	484	36.7	25.5
 1 in/8 days Conventional	26	172	28169	417	37.8	23.5
 	30	191	31654	411	37.7	22.0
 34	191	33977	385	37.2	22.6
 Strip Tillage	26	214	29330	565	32.7	24.6
 30	220	31944	510	34.4	24.6
 34	230	34558	479	35.7	24.3
 No Tillage	26	204	28750	501	36.9	24.4
 30	220	31363	497	35.8	24.6
 34	216	33977	458	35.6	24.9
 Table 5.
Selected corn yield component and total seasonal water use data for 2007 from an irrigation capacity and tillage study, KSU Northwest Research-Extension Center, Colby, Kansas.
Irrigation	Tillage	Plant	Grain	Plant	Kernels	Kernel	Water
 Capacity	System	Population		bu/acre	Yield	Population		/Ear	Weight	g/100		Use
 1 in/4 days Conventional	26	245	27878	629	34.5	24.7
 	30	274	32234	652	32.8	26.0
 34	256	34848	611	31.9	24.4
 Strip Tillage	26	254	28169	684	33.5	24.6
 30	270	31073	671	33.0	25.7
 34	279	36010	603	32.9	24.6
 No Tillage	26	246	26717	680	33.0	22.6
 30	265	31654	660	32.8	24.4
 34	254	34848	651	28.7	23.9
 1 in/6 days Conventional	26	244	27878	673	33.2	24.7
 	30	242	32815	603	31.3	24.5
 34	235	34848	612	28.2	24.0
 Strip Tillage	26	244	26426	678	33.5	24.0
 30	242	32234	620	30.7	24.6
 34	251	35429	658	27.7	24.2
 No Tillage	26	230	27588	635	33.3	24.7
 30	256	31944	655	30.5	22.9
 34	247	36010	605	29.6	24.6
 1 in/8 days Conventional	26	220	27878	606	32.4	24.1
 	30	248	32815	628	31.0	23.9
 34	249	34267	634	29.3	24.4
 Strip Tillage	26	242	27588	683	32.5	23.7
 30	255	31073	637	32.5	23.0
 34	267	36010	619	30.5	23.2
 No Tillage	26	225	27588	661	31.3	23.9
 30	248	32234	631	30.4	24.0
 34	235	34848	587	29.2	23.3
 Figure 4.
Corn grain yield as affected by irrigation amount and tillage, 2004 to 2007, KSU Northwest Research-Extension Center, Colby Kansas.
reduced kernel weight by 2.0 g/100 kernels.
However, this was compensated by the increase in population increasing the overall number of kernels/acre by 9.2%.
Figure 5.
Corn grain yield as affected by irrigation amount and plant population, 2004-2007, KSU Northwest Research-Extension Center, Colby Kansas.
The number of kernels/ear was reduced in 2004 and 2006 compared to 2005 and 2007.
The potential number of kernels/ear is set at about the ninth leaf stage  and the actual number of kernels/ear is finalized by approximately 2 weeks after pollination.
Greater early season precipitation in 2005  than 2004 and 2006 may have established a greater potential for kernels/acre and then later in the 2005 season greater irrigation capacity or better residue management may have allowed for more kernels to escape abortion.
The number of kernels/ear was even greater in 2007 than 2005.
Winds and temperatures were very moderate for much of 2007 and the resulting reduced evapotranspiration probably allow a greater potential kernel set.
Figure 6.
Kernels/ear as affected by irrigation capacity and plant population, 2004-2007, KSU Northwest Research-Extension Center, Colby Kansas.
The number of kernels/ear was generally greater for the strip and no tillage treatments compared to conventional tillage, particularly in 2005 and 2006.
This response is probably due to better management of soil water reserves with strip and no tillage.
Final kernel weight is affected by plant growing conditions during the grain filling stage  and by plant population and kernels/ear.
Under deficit irrigation capacity, the crop will deplete soil water reserves during the latter portion of the cropping season, so it is not surprising that kernel weight was increased with greater irrigation capacity.
Tillage system also affected kernel weight, but it is thought by the authors that the effect was caused by different factors at the different irrigation capacities.
At the lowest irrigation capacity, final kernel weight was often highest for conventional tillage  because of the reduced number of kernels/ear.
However, this greater kernel weight did not compensate for the decreased kernels/ear, and thus, grain yields were reduced for conventional tillage.
Strip tillage generally had greater kernel weights at greater irrigation capacity than the conventional and no tillage treatments for some unknown reason.
Figure 7.
Kernel weight as affected by irrigation capacity and plant population, 2004-2007, KSU Northwest Research-Extension Center, Colby Kansas.
The changing patterns in grain yield, kernels/ear, and kernel weight that occurs between years and as affected by irrigation capacity and tillage system may indicate that additional factors besides differences in plant water status or evaporative losses affect corn production.
There might be differences in rooting, aerial or soil microclimate, nutrient status or uptake to name a few possible physical and biological reasons.
Total seasonal water use in this study was calculated as the sum of irrigation, precipitation and the change in available soil water over the course of the season.
As a result, seasonal water use can include non-beneficial water losses such as soil evaporation, deep percolation, and runoff.
Intuitively, one might anticipate that good residue management with strip tillage and no-tillage would result in reduced water use than conventional tillage because of reduced nonbeneficial water losses.
However, in this study, strip tillage and no-tillage generally had greater water use.
Figure 8.
Total seasonal water use  as affected by irrigation capacity and plant population, 2004-2007, KSU Northwest Research-Extension Center, Colby Kansas.
The small increases in total seasonal water use  for strip tillage and no-tillage compared to conventional tillage can probably be explained by the greater grain yields for these tillage systems  as well as earlier canopy senescence under conventional tillage.
Corn grain yields were high all four years  with varying seasonal precipitation and crop evapotranspiration.
Strip tillage and no tillage generally performed better than conventional tillage.
Increasing the plant population from 26,800 to 33,300 plants/acre was beneficial at all three irrigation capacities.
This paper was first presented at the 19th annual Central Plains Irrigation Conference, February 19-20,2007, Greeley, Colorado.
Contribution No.
08-246-A from the Kansas Agricultural Experiment Station.
Applying strip tillage treatments in the fall of 2005 in preparation for 2006 cropping season, KSU Northwest Research-Extension Center, Colby, Kansas.
Use: reduce application rate to reduce soil surface sealing in early season.
VRI type: zone, prescription type: static, management intensity: low.
LIMITED IRRIGATION CROPPING SYSTEMS FOR CONSERVING WATER RESOURCES IN THE PUMPKIN CREEK WATERSHED
 Declining ground water is not a new dilemma in Nebraska, however, the drought across the high plains and inter-mountain west the last eight years has magnified the problem.
In Nebraska law, surface water is regulated by the Department of Natural Resources  and ground water is regulated by the 23 Natural Resources Districts.
In 2002, the North Platte NRD  requested a DNR study to examine the interaction of hydrologically connected ground and surface water in the Pumpkin Creek Watershed.
The report was completed in early 2004.
Figure 1.
Major soil series and GPS referenced irrigation wells  in the
 The Pumpkin Creek Watershed  is located in the southern tablelands of the NPNRD.
Pumpkin Creek flows into the North Platte River near Bridgeport, NE and on average delivered 20,000 acre feet of water per year until levels began to decline in the 1970's due to ground water development.
Pumpkin Creek was closed to new surface water development over 20 years ago due to low stream flow.
In 2001 the NPNRD established the Pumpkin Creek ground water management area and ceased new well drilling.
Existing wells were metered in 2003 and pumping has been reported since 2004.
The NPNRD approved a14 inch allocation in 2004 which has remained in effect.
Reservoir construction in the Rocky Mountains plus diversions of surface flow created irrigation districts in Nebraska beginning in the 1920's.
Irrigation from ground water developed slowly in major river valleys through the 1940's until the 1970's, but expanded rapidly in the 1970's due to introduction of center pivots and continued into the 1980's.
Research on limited irrigation in Nebraska began in the 1970's at the former UNL Sandhills Ag Lab where Gilley et al.,  used line-source sprinkler irrigation to study the effects of water-stressing corn.
They found no significant yield reduction when the crop was moderately stressed during the vegetative stage, but significant yield reductions were noted when stress occurred during pollination and grain fill.
Under limited irrigation, less water is applied than is required to meet full evapotranspiration demand.
As a result, the crop will be stressed.
The goal is to manage cultural practices and irrigation timing such that the resulting water stress has less of a negative impact on grain yield.
The concepts of moisture conservation from dryland no-till ecofallow  and the timing of limited irrigation  were combined in a project initiated in 1982 at North Platte, NE.
Over a 10-year period, this cropping systems approach for stretching limited irrigation  on a silt loam soil showed winter wheat yields were 99% of full irrigation, corn yields were 86% and soybeans were 88% of fully irrigated yields.
This area has annual precipitation near 20 inches per year.
These concepts have also been successfully tested on producers fields.
This study showed the obvious--less water means less income, but the good news is that proper management showed that 25-50% reductions in water application only reduced income by 10-20%.
In the Nebraska Panhandle limited irrigation of sugar beet and dry bean showed that late season water stress reduced yield only 7 percent.
In a different study , delaying the first irrigation of the season for a one week period, reduced dry bean yield by 5 percent.
There had been no major research on no-till limited irrigation cropping systems in the NE Panhandle until
 2005, although dryland no-till research had been conduced since the 1960's.
The overall goal of this project was to initiate a demonstration project to educate growers about the advantages of using no-till cropping systems to stretch limited irrigation supplies in the Pumpkin Creek Watershed.
This project was funded by a USDA NRCS Conservation Innovation Grant with matching support from the NPNRD and the University of Nebraska.
The idea was to transfer information from the North Platte research to an area that receives only 15 to 17 inches of annual precipitation.
Individual project objectives were: 1.
to demonstrate limited irrigation no-tillage cropping systems that make the best use of natural precipitation and limited ground water supplies 2.
to educate area farmers, natural resource groups, local and state government agencies and agricultural businesses about the effect of different management scenarios on production, cultural practices, economics and natural resource impacts, and 3.
to develop economic scenario case studies for limited irrigation.
The project built on previous Nebraska limited irrigation research.
However, part of the innovation and unknown of this project was adapting those concepts to the sandier soils, a different cropping mix  and lower rainfall in western NE compared to North Platte.
PROJECT DESCRIPTION AND RESULTS
 A Steering Committee of University specialists, NPNRD and NRCS personnel met to discuss goals and procedure and to help select demonstration sites and cooperators.
Cooperators need to currently be practicing no-till and be willing to put up with the extra time required to be a part of a demo project.
We also wanted to select representative operations according to size.
Cooperators also needed to be willing to host field days and discuss their operations at other educational meetings.
Demonstration sites were located to provide easy access during future field days.
Three producers were selected: one in the western part , one in the middle  and one in the eastern portion  of the watershed.
The operations also varied in size.
Current crops grown by the producers were used.
We selected one or two halves of a center pivot for the demonstration.
Although there is a 14-inch irrigation allocation within the Pumpkin Creek watershed, western portions of the watershed  can only supply 4 to 6 inches of irrigation before water is depleted in early August.
Irrigation levels of 10 to 11 inches are
 available in the center  whereas the eastern part of the watershed has the deepest aquifer  and no water limitations.
An Extension Educator was hired as the Project Manager.
Table 1.
Cooperators, crops and operation description.
Cooperator	#	Dry	Crops*	Cows	Range	Feedlot
 	Pivots	land	land	head
 Alton Lerwick	2	2,400	WH, SF,	7,500	0
 	Cn, MI, Fr	300
 Kirk Laux	9	--	C, WH,	4,000	3,500
 	DB, Fr	300
 Lane Darnall	15	4,000	C, WH,	500	8,000	20,000
 *C=corn; WH=winter wheat; SF=sunflower; Cn-spring canola; MI-millet; Fr=forage
 Alton Lerwick's site represents a medium size no-till farm and livestock operation and a small irrigated operation located in the western part of the watershed.
Alton uses a continuous cropping system with no fallow to maximize crop residue to conserve soil and moisture.
Alton Lerwick applies less than 6-inches water per acre to produce various 'conventional' and 'alternative' crops, which require less moisture.
These include corn, winter wheat, sunflowers, canola, forage sorghum and millet.
Alton's yields were 1,650 lb/ac spring canola in 2005, 60 bu/ac winter wheat  in 2006 and 1650 lb/ac sunflowers in 2007.
Lane and Gary Darnall's site represents a large no-till farm and livestock operation with a large feedlot in the central part of the watershed.
Lane Darnall utilizes his water allocation to grow more conventional crops such as corn and alfalfa for his feeding operation and also grow alternative crops such as winter wheat, irrigated pasture and canola which require less moisture.
Lane's yields were 1,100 lb/ac spring canola  in 2005, 1,200 lb/ac winter canola  in 2006 and 52 bu/ac winter wheat in 2007.
Kirk Laux's site represents a medium size no-till farm and livestock operation with a medium feedlot in the eastern part of the watershed.
Kirk utilizes a similar water allocation plan as Lane, but with a different cropping system.
He uses water from irrigated acres he has 'retired' back to dryland to gain additional water for use on his crops.
Kirk grows corn, alfalfa, winter wheat, dry beans and forage turnips for fall / winter grazing for his livestock.
Kirk's yields were 48 bu/ac dry beans plus approximately 3.8 tons/ac forage turnips for grazing in 2005 and 40 bu/acre dry beans in 2006; applying approximately 10-inches water each year.
Kirk is also trying something new to the Panhandle no-till dry beans.
He has planted no-till dry beans into corn stalk residue, in 15-inch and 30-inch row spacing's along with drilling.
To maintain a no-till system , he has tried swathing and direct harvest methods.
Currently, Kirk has also gone to planting 20-inch row corn and dry beans.
The narrow row spacing provides quicker canopy cover to help compete with weeds and help shade the soil surface sooner for moisture conservation.
Kirk is also developing a method to direct harvest his dry beans with a Shelbourne Reynolds stripper-header, to maximize crop residue left on the soil surface for soil and moisture conservation.
The project has demonstrated that no-tillage can be adapted for the sandy soils in the Pumpkin Creek basin.
The three cooperators are using no-till for common and alternative crops and making it work.
There is still much work to do to match crops and cropping systems due to the wide range of water availability.
Producers practicing limited irrigation must think like a dry land producer who has some irrigation water for only part of the season.
There are also many agronomic and production factors we must 'perfect' before making no-till and limited irrigation production systems common practice.
There is also the need for additional research information for a wide range of cropping systems to look at conventional and alternative crops that fit the Panhandle plus economics before more producers adopt this system.
Work also needs to be done to 'fine' tune irrigation systems for improved pumping efficiency.
Field days and tours have demonstrated to neighbors what can be done with less water.
Additional field days and / or meetings need to be held to inform more growers and the agricultural community  to promote the benefits and potential problems with these systems so they can understand them better and work through them.
Using limited irrigation cropping and no-till systems can be successfully accomplished if the producer is willing to be patient when switching to these practices.
Cropping practices / systems need to be determined and refined by the individual producer for their operation as they become more flexible in their management and marketing practices.
Because there were no existing no-till plots at PHREC, complimentary research was started in 2005.
A crop rotation including winter wheat-corn-dry bean-spring canola is being used.
Irrigation levels are 4, 8 and 12 inches per cropping season except corn which receives 5, 10 and 15 inches.
Treatments are replicated four times with each crop present each year in a one-acre block under a linear move system at the Panhanlde R & E Center at Scottsbluff.
The soils is a Tripp fine sandy loam  with a pH of 8.4, 1.2% OM and1.3-1.6 inches of plant available water per foot.
Rooting depth is usually 4 to 5 feet for a total available root zone water holding capacity of 6 to 8 inches.
Three years of research have been conducted and confirm that the principles applied in the earlier limited irrigation work fit the NE panhandle.
The 3 years of the project represented a year with above average precipitation  and tow with below  and much below normal  precipitation.
The information will provide the basis to do detailed water balance calculations plus provide information for economic analysis for crops that fit the high plains region and hopefully will be presented next year at this conference.
2005 Relative Grain Yields
Chapter: 34 Estimating Corn Seedling Emergence and Variability
 The ability to nurture the planted seed to a mature plant depends on many factors, including the seed germination rate and seedling emergence.
Both of these factors depend the effectiveness of the seeding process.
Seedling emergence is used to calculate the seeding rate and to assess the effectiveness of the planting system.
These calculations require that the row spacing and plants per row be estimated.
The purpose of this chapter is to discuss guidelines for determining the seeding rate and measuring seed emergence.
Calculating the Corn Seeding Rate
 An important consideration in achieving the yield goal requires that the appropriate number of seeds be planted in the soil.
A very coarse rule of thumb is to seed 10% more seeds than your target population.
However, this rate can be fine-tuned by considering the seed germination rate and the number of germinated seeds that survive to harvest.
Information on germination is provided by the seed dealer and found on the seed bag or box label.
Expected survival, which is impacted by diseases, insects, weather events, and seedbed characteristics, is harder to estimate.
The survival of germinated seeds to harvest can be calculated by measuring seed emergence and the harvested plant population.
The seeding rate is calculated with the equations:
 Desired population at harvest  Seedling rage  = % emergence of planted seeds 100
 In this equation, the % emergence of planted seeds can be estimated based on seed germination rate and prior records.
Common estimated values for % emergence of planted seeds range from 90% to 95%, and it can be calculated using the equation:
 The % germinated seeds can be estimated using the germination rate provided by the seed seller and the % of germinated seeds that emerged from the soil.
Unfortunately, the % of germinated seeds that emerged from the soil is not known and therefore it must be estimated.
This value is important because it can reveal planter problems.
Sample calculations for these values are provided in Examples 34.1, 34.2, and 34.3.
Calculating the % seed emergence requires a measurement of the plant population.
The percent seed emergence is influenced by many factors, including seedbed preparation, crusting, and diseases, and it is calculated with the equation:
 Plant population after emergence % Seed emergence = 100% Seeding rate
 The plant population in a cornfield is determining by counting the number of plants in 1/1000 of an acre.
Based on data in Table 34.1, for a 30-inch row, the length of the row for 1/1000 of an acre is 17 feet and 5.1 inches.
Table 34.1 The distance along a row representing 1/1000 of an acre.
On the row, the number of plants should be counted.
The plant population is 1000 times the number of plants in 1/1000 of an acre.
6	7	8	10	14	15	20	21	28	30
 Feet	87	74	65	52	37	34	26	24	18	17
 Inches	1.4	7.1	4.1	3.3	4	10.2	1.6	10.7	8	5.1
 Corn plants that are too close can act as a weed to the adjacent plant.
The newest of planters, if accurately calibrated, have the capacity to reduce this variability to near zero.
Stand uniformity can be determined by calculating the standard deviation of the distances between adjacent corn plants.
The field variability can be determined by placing a 20-foot tape measure next to a row of corn plants, as shown in Figure 34.2.
Record the location of each plant within the row in inches.
Use a tape measure that documents inches rather than feet and inches.
Repeat the process at 4 or 5 separate locations within the field.
Type these numbers into a spreadsheet and use the spreadsheet to calculate the distance, the average distance, and standard deviation of the distances.
Optimum yields are obtained by minimizing the spacing variability.
The standard deviation provides an index of the ability of the seeder to plant a uniform stand.
Most agronomists believe that yield is optimized by a standard spacing distance  between the plants.
Research suggests
 Figure 34.2 The number of corn plants along a transect within a single row.
In this example, corn plants are located at 2, 5, 19, 25, 37, 42, 46, 55, and 57 inches.
Example 34.1 Determine the emergence of germinated seeds.
If the seed container label germination rate is 90%, the seeding rate is 35,000 seeds/acre, and the post-emergence counted plant population is 30,000 plants per acre, what is the % emergence of germinated seeds?
%seed emergence 30,000 plts/acre 100 %EGS 100
 This calculation suggests that 95.2% of the germinated seeds emerged from the soil.
Example 34.3.
If the % germination is 96%, the expected survival of germinated seed to harvest is 92.2%, and the target plant population is 34,000 seed/acre what is the seeding rate?
Target population at harvest Seeding rate = %seed germination rate 30,000 plts/acre 100 35,000 plts/acre
 Example 34.2 If the seedling plant population is 32,000 plants/acre and the plant population at harvest is 31,000 plants/acre what is the survival of seedlings to harvest
 Example 34.4 Determine the seed emergence rate if the seeding rate is 38,000 plants/acre.
Measure the row width, and if your row width is 30 inches, count the number of plants in a row that is 17 feet and 5.1 inches long.
If 35 corn plants are contained in the row, then your plant population is 35,000 plants/acre.
Seed emergence=100% = 35,000
 In a second example, you plant corn in 15-inch rows, what is the length of row to produce 1/1000th of an acre?
Based on data in Table 34.1, count the number of plants in a row that is 34 feet and 10.2 inches long.
Table 34.2 Sample spreadsheet showing how to calculate plants/acre and yield losses due to variable seeding.
The tables below show the locations on a tape measure.
In the table on the right, the equations behind the values in column B are shown.
The value in column C is the row spacing.
Measured location	Spacing distance between
 of each corn plant	each pair of plants
 13	Standard deviation	5.12
 14	Bu/acre in estimated yield loss	12.5
 that a standard deviation of 2 inches is excellent.
There is about a 4 bu/acre yield loss per inch for standard deviations greater than 2 inches.
Table 34.3 Definition of terms used in this chapter.
Seed germination	The germination rate of the seed.
Specified by the seller.
Seedling emergence	The emergence of the seedlings from the soil.
Seeding rate	The number of seeds/acre planted in the soil.
Plant population	The plant population following emergence.
% emergence of germinated seeds	Difficult to measure, can be estimated based on the seed germination rate.
Standard deviation of the stand uniformity	The standard deviations  in the distances between adjacent corn plants.
Table I.
Normal water requirements for corn, grain sorghum, soybeans, and dry beans between various stages of growth and maturity in Nebraska.
For Corn R2 crop stage, the stage of growth is known as blister, the approximate days to maturity is 45, and the water use to maturity is 10.5 inches.
For Corn R4 crop stage, the stage of growth is known as dough, the approximate days to maturity is 34, and the water use to maturity is 7.5 inches.
For Corn R4.7 crop stage, the stage of growth is known as beginning dent, the approximate days to maturity is 24, and the water use to maturity is 5.0 inches.
For Corn R5 crop stage, the stage of growth is known as 1/4 milk line, the approximate days to maturity is 19, and the water use to maturity is 3.75 inches.
For Corn R5 crop stage, the stage of growth is known as 1/2 milk line full dent, the approximate days to maturity is 13, and the water use to maturity is 2.25 inches.
For Corn R5 crop stage, the stage of growth is known as 13/4 milk line, the approximate days to maturity is 7, and the water use to maturity is 1.0 inches.
For Corn R6 crop stage, the stage of growth is known as physiological maturity, the approximate days to maturity is 0, and the water use to maturity is 0.0 inches.
Small Acreage Irrigation Guide
 Boyd Byelich Jennifer Cook Chayla Rowley
 Water Rights and Irrigation Management
 Boyd Byelich District Conservationist, USDA-NRCS, Longmont, CO
 Jennifer Cook Small Acreage Management Coordinator, NRCS/CSU Extension, Brighton, CO
 Chayla Rowley Civil/Environmental Engineer, USDA-NRCS, Steamboat Springs, CO
 Allan Andales, Assistant Professor in Soil and Crop Science, CSU Jos Chavez, Assistant Professor in Civil and Environmental Engineering, CSU Sean Cronin, Executive Director, St.
Vrain and Left Hand Water Conservancy District Bill Haselbush, agricultural producer, Longmont Ray Jones, alfalfa Farmer, Adams County Brady McElroy, State Water Management Engineer, USDA-NRCS Glen Murrey, wheat and hay farmer, Adams County Jason Peel, Irrigation Water Management Specialist, USDA-NRCS Rick Romano, District Conservationist, USDA-NRCS Joel Schneekloth, Research Scientist, CSU Extension Mike Stonehaker, President of West Adams Conservation District
 Considerations For Water Users Frequently asked  questions:
 Improving an Irrigation System
 Table 1: Irrigation Conveyance Efficiencies
 Table 2: Irrigation System Comparisons
 Table 3: Estimated Consumptive Use or ET 
 Table 4: Estimated Average Weekly Water Consumption
 Table 5: Irrigation Depths Based on Crop Root Zone Depths
 Table 6: Soil Water Holding Capacity
 Table 7: Pumping Across Horizontal Distances 
 Table 8: Sprinkler System Selection Matrix
 Table 9: Manufacturers Contact List
 This guide provides information about water rights and irrigation for small acreage landowners.
While the content is largely directed towards those engaged or interested in some form of agricultural production, it may also be useful for those simply interested in maintaining their yard and garden plot.
This guide addresses many important questions about water rights and water use for landowners and for those thinking of purchasing land.
Questions include: do I have water, can I get it, how much can I get, how do I determine how much to order, when can I get it, how do I get it, what will it cost, and what factors affect how much water ultimately ends up where I need it?
Crop water requirements and irrigation scheduling are discussed, and examples are provided to help the user with common calculations necessary for irrigation scheduling and ordering the necessary amount of water to meet crop needs.
In addition, information is provided on irrigation systems that are appropriate for 5 acres or less, including pumps, pipelines, and water application options.
In short, this guide is intended to help the water user get started with irrigation, and to help all landowners better understand water rights and the legal use of water.
CONSIDERATIONS FOR WATER USERS FREQUENTLY ASKED  QUESTIONS:
 1.
What is a 'water right'?
It is a property right in the form of a legal decree that allows for the beneficial use of a measurable amount of water and is subject to the historical date it was first recorded.
In fact, some of the earliest recorded water rights in Colorado date to the 1860s.
A water right is usually limited to a specific volume of water described in terms of acre-feet , acre-inches , or cubic feet-per-second , and limited to a specific beneficial use, such as agriculture or domestic uses.
2.
Who owns the 'water right'?
A person does not 'own' the water.
Rather, they have a legal 'right' to use a specified volume of water for a predetermined beneficial use.
In some cases, individuals own this decreed right.
However, it is more likely that individuals have a pro-rata interest  in a right that is managed by a mutual ditch company.
While the ditch company manages the water supply and delivery, the shareholders own the water rights held by the ditch company.
Therefore, the landowner would have 'shares' of water through their mutual ditch company.
3.
What is a ditch company?
Ditch companies as a group are typically referred to as a mutual ditch company and are similar to other corporations , but organized to provide water to their shareholders on a pro-rata basis.
Ownership in a mutual ditch company is evidenced by a stock certificate.
4.
What is a lateral ditch company?
Lateral ditch companies differ from mutual ditch companies in that they do not own water rights.
They tend to be smaller ditches that branch off from the larger ditches owned by mutual ditch companies.
Their functions are to deliver water to the users along that lateral ditch and to maintain that ditch.
They are separate legal entities from the mutual ditch company.
It is very important to note that if your property is along a lateral ditch, then you need to be a shareholder in the mutual ditch company that delivers water to that lateral; otherwise you have no shares of water.
Conversely, if you acquire shares of water in a mutual ditch company, but your property is along a lateral ditch, then you will also need to have shares in the lateral company in order to receive your water.
5.
What is a stock certificate in a ditch company?
It specifies a predetermined amount of water  and is different for every ditch company.
Within a ditch company, the amount of water allotted to a stock can vary by year, depending on the total available water supply that particular year.
So, in a year of drought, the allocation of water for a particular ditch company may be less than it is during a year of average or abundant water supply.
6.
How is my water measured?
Water is usually measured at the headgate of the ditch that delivers water to your property.
Shareholders on the ditch, or a ditch rider, open the headgate an incremental amount that allows the desired flow for the intended use on your property.
The amount of water you may get is determined by the need of the crop at that point in time or your pro-rata interest in the ditch company, whichever is less.
It is accurately measured by the size of the opening of the headgate or by using a device, such as a measuring weir or flume.
7.
What is a ditch rider?
A ditch rider is hired by the ditch company to maintain the ditch and open headgates as appropriate to divert water for water deliveries to shareholders in the ditch system.
The ditch rider also calculates water volumes and oversees ditch operations.
The ditch rider stays in close communication with the water commissioner  during the irrigation season to coordinate water
 diversions and 'calls' on the river.
Some of the smaller mutual ditch companies use a rotating ditch captain to coordinate ditch operation and maintenance activities.
8.
What is a 'call'?
If a decreed water user has an insufficient water supply, they can make a request to the district water commissioner that all upstream, 'junior' users curtail their use.
This is known as placing a 'call'.
For a 'call' to be valid, the shorted user must have a genuine need for water for purposes permitted by their decree, and there must be no downstream 'call' senior to their own.
If the 'call' is valid, the commissioner will communicate the date of the 'call'  to water users upstream of the party making the 'call'.
All upstream users that are junior to that priority date are then required to curtail water use until the calling user's water need is satisfied.
9.
Can I apply water anywhere I want on my land?
In most parts of Colorado, you can apply irrigation water only to land that has a documented irrigation history.
Applying water to land that has not been historically irrigated is considered an 'expansion of use' and is prohibited by many ditch companies.
There may be localized exceptions, so check with your ditch company or local District of the Colorado Division of Water Resources office to determine if this provision of Colorado water law applies to your land.
10.
How does one water right compare to another?
In other words, who gets their water first?
The state of Colorado operates using an appropriation system.
In times of water shortage , those holding the earliest historically recorded water right have priority over those with a more recently recorded water right.
For example, if you hold or have interest in a water right that was originally filed in 1869, you would get water before a neighbor that has a water right that was filed in 1902, regardless of location.
Using this same example, the 1869 right is known as a 'senior' right, while the 1902 right is referred to as a 'junior' right.
11.
How is water delivered to my land?
Some individuals are located near a perennial stream or lake/reservoir and are permitted to draw water directly from that source.
However, the vast majority of irrigators receive
 water from a ditch that connects to a stream or reservoir, often many miles from their property.
12.
What if an irrigation ditch crosses my land?
Can I use the water?
If you buy or own a parcel of property with a ditch either along or through the property, you are not automatically a shareholder in a ditch company or an owner of a water right.
This means that you can't remove water from that ditch that runs through or along your property unless you either have a legal decree for a portion of that water, or are a shareholder in a ditch company that provides that water.
13.
How long will a mutual ditch or lateral run water?
Each ditch or lateral has a unique time frame of water flow that is dependent upon the water supply.
Some run for 6 months, some for only 6 weeks.
It is imperative to know the period of time that your ditch runs water when it starts and when it goes dry each year.
This will determine the kinds and amounts of crops that you can produce.
14.
Can I pump water into a storage tank or some other type of reservoir?
A water user in Colorado typically has 72 hours to apply any irrigation water that they order, unless they have a storage right.
This applies to each time you irrigate.
15.
How do I order water?
Contact your ditch rider or ditch company and put in your order for water.
Your ditch rider will fill your water order by opening and closing headgates to allow the permitted water to flow.
Keep in mind that if water is limited, the more senior water rights will get their water before you, even if you put in your order first.
16.
When should I order water?
The typical recommendation is to order water 48 hours before you want to apply it on your crop.
It is best to talk to your ditch rider to find out how much lead time is needed when ordering water at your location.
17.
How much water should I order?
If your target crop needs an inch of water for one irrigation, you might think that you only need to order an inch.
However, you must take into account how far you are from the
 headgate, the type of delivery system , and the condition of that delivery system.
As water flows towards your property, some will seep or soak away.
If the ditch is not well maintained, and the water moves slower due to debris or vegetation, even more will seep or soak away before it reaches your property.
Furthermore, some irrigation water applied to your crop  is lost to surface runoff and some to deep percolation  and is not available to the plant.
So, you have to order more water than you actually need to account for the seep, soak, and surface runoff.
The total amount ordered counts against your total water right allocation, even though you don't receive all that you order.
Examples follow in the guide that will help you calculate how much water to order.
Additional information regarding irrigation efficiency can be found in Bauder, et al.
2011 and Howell, 2003.
18.
What is the minimum amount of water that I can order?
It depends on the ditch company but it is usually 1 cfs for 24 hours, which equals 2 acrefeet.
This amount is usually more than one small acreage landowner can effectively use at one time for their crop, so it can be important to collaborate with other small acreage neighbors.
You share your water for this irrigation event, and then they share their water with you next time.
Each of you ends up with 2 irrigations for your crop instead of one, thus stretching out the water supply for both of you.
Often, several neighbors can partner in this fashion.
19.
What if my water right is not sufficient to meet my needs?
Do I have other options?
You do.
You can lease water from other users who have more water in their right than they need, or you can lease water from ditch companies that have excess water.
You can also take advantage of 'free' water, which is excess water available in the ditch system or river when all other user demands are being met.
This usually occurs in the spring when snowmelt and runoff are at their highest, and available water at that time exceeds the combined water rights for that system.
When choosing an irrigation system, consider the needs of the target crops , the water availability , how the water gets to your land
 , and the soil type.
Irrigation conveyance refers to the type of system that delivers your water from the source to the point of use.
The length, slope, substrate , and presence of vegetation and other debris all affect how much and how quickly your water gets to your application system.
The further you are from the source, combined with the presence of unmaintained vegetation or debris, and the type of ditch  means that you will lose more water to seep and soak before it gets to your property.
Each type of conveyance system has an associated efficiency that needs to be accounted for in your irrigation planning.
Once you have water at your property or field, there are three basic irrigation systems flood, sprinkler, and trickle  that are applicable for use.
Table 1: Irrigation Conveyance Efficiencies
 Conveyance Method	Efficiency 
 Earthen Ditch	70 80
 Concrete-lined Ditch	90 95
 Source: USDA-NRCS NEH Part 23, Chapter 2, Irrigation water requirements.
Surface irrigation options include wild flood ; furrow ; border ; and corrugation.
Corrugated field for surface irrigation
 One of the most common water application methods is to place a plastic or canvas dam in the head ditch  to back up the water, and then cut a notch in the ditch to let the water out.
Each time the dam is moved and reset, it is called a set.
A typical length of a set is 12-24 hours.
Other variations include head gates , siphon tubes , and gated pipes (series of pipes fastened together with uniformly spaced openings covered with
 adjustable gates that can be opened to let the desired amount of water out into the field).
Surface irrigation methods are more suitable to relatively flat land.
It is difficult to obtain uniform water distribution on fields that are long, have an irregular surface, or have coarse soils.
Surface irrigation methods require very little energy  compared to sprinkler or drip, but labor is more intensive.
Sprinkler irrigation options include a mini gun ; portable hand line ; and solid set.
Sprinklers are more expensive than flood, but if designed, installed, and managed properly, can apply water more efficiently and uniformly.
There is a potential to decrease the amount of water applied while maintaining or increasing crop yields.
Mini gun sprinkler system
 Drip irrigation systems can be surface or subsurface.
Individual emitters are used to frequently apply water to the soil surface at a low flow rate and pressure.
A continuous supply of water  is needed for this system during operation.
Water must be filtered or screened to protect emitters from clogging.
An additional issue with drip irrigation is bacteria and other water quality issues that may require chemical injection to prolong the life of the system.
Poor water quality can potentially plug emitters.
Although the initial cost is high, it is a great option if the amount of water is limited or if the cost of water is high.
An above ground, spray-type trickle system is less likely to clog than drip and sub-surface drip systems.
In spray irrigation, small sprinkler-like devices  spray water as a mist  over the land surface.
Micro-sprinklers can be spaced to cover the entire land surface as with conventional sprinkler systems or a portion of the land surface like other trickle systems.
Discharge rates are usually less than 0.5 gpm.
Table 2: Irrigation System Comparisons
 Irrigation System	Application	Cost' (irrigation	labor not	Advantages	Disadvantages
 Wild Flood	15 40%	$0 $20 (home	Low input cost	Low efficiency
 made plastic or	Low	Increased
 canvas dam)	maintenance	labor
 Furrow	40 80%	Control of	High labor
 Gated pipe	40 55%	$2 $3/foot	delivery time	Low efficiency
 Corrugation	50 80%	and space
 Sprinkler	High efficiency	Higher cost
 Mini gun	55 75%	$2,500 $8,000	Low labor	Higher
 (depends on	Suitable for	operation &
 hose size)	most crops	maintenance
 Portable	60 85%	Good choice	Needs
 hand lines	for fields with	continuous
 Solid set	60 85%	varied soil &	supply of
 Pod	60 85%	$3,000 -	topography	water
 $6,000/ac ( $250	Requires
 $350 per pod	pressurized
 plus supply line)	water source
 Surface Drip	70 95%	$1,000 -	Higher	High initial
 Less time and	Higher
 pumping costs	supply of
 Source: Barta, et.
al, 2004 Application Efficiency refers to the percent of water delivered that ends up in the root zone of the * crop.
Efficiencies can be much lower due to poor design and management.
Based on 2018 cost estimates
 How much water does my crop need?
Water requirements for grass and other crops are determined by weather conditions and soil moisture available for plant uptake.
Irrigation scheduling is the decision of when and how much water to apply to a field.
Water requirements are typically described by the term evapotranspiration or ET, which is the combined water loss from the processes of evaporation and transpiration.
The cumulative amount of ET for a crop over an entire growing season is roughly equivalent to that crop's seasonal water requirement.
ET losses in a given area can be accurately predicted from measurements of four local weather variables: air temperature, incoming shortwave solar radiation, air relative humidity, and horizontal wind speed.
These weather variables differ significantly in Colorado due to latitude and elevation, which results in varying amounts of potential ET by grass and other crops.
Table 3: Estimated Consumptive Use or ET 
 Greeley	Lamar	Monte Vista	Fruita
 Fruit trees	N/A	N/A	N/A	25.71
 Alfalfa	31.58	39.06	23.58	36.22
 Grass Hay/Pasture	26.63	34.16	19.85	31.44
 Small Vegetables	17.70	18.85	6.79	18.06
 Precipitation	12.20	15.33	7.25	8.30
 Precipitation	7.32	11.00	3.93	3.98
 Source: Colorado Irrigation Guide, 1988, USDA-NRCS.
Net irrigation requirement is the difference between crop consumptive use and effective precipitation.
Effective precipitation is the amount of rainfall that actually infiltrates the soil and is available within the crop root zone.
The gross irrigation requirement is the net irrigation requirement divided by irrigation system application efficiency.
System efficiency makes a big difference.
Example 1: How much water do I need for a particular crop?
Sarah lives in Greeley and has a 1-acre grass pasture irrigated by a portable sprinkler system.
The average ET or consumptive use of grass pasture in Greeley is 26.63 inches/season.
How many inches per season does Sarah need to water her pasture?
1.
Subtract the average effective precipitation from the ET to determine the net irrigation.
26.63 inches/season/acre 7.32 inches/season/acre = 19.31 inches/season/acre
 2.
The irrigation system efficiency must also be considered.
To find the gross irrigation, divide the net irrigation by the irrigation application efficiency.
19.31 inches/season/acre / 0.70  = 27.59 inches/season/acre
 3.
To convert inches/acre to acre feet, divide by 12.
Therefore, Sarah needs 27.59 inches/season/acre or 2.29 acre feet per season for the portable sprinkler system to water 1 acre of grass pasture in Greeley.
Once you have calculated an estimated gross irrigation water requirement, in order to find out if you have enough seasonal water for your crop, you must determine the flow rate of the water you will be receiving and the amount of time it will be available to you.
Crops such as vegetables need water on a regular basis throughout their growing stages.
So, if you have the right to "X" number of water shares that equal "X" amount of water, you can determine if you have adequate water for the target crop.
You can rent additional water or sell excess water.
Table 4: Estimated Average Weekly Water Consumption
 Crop	Water Use *
 Fruit trees	1 4
 How do I know when to irrigate?
Irrigation scheduling is the decision of when and how much water to apply to a field.
Table 4 contains estimates of average weekly water demand for select crops, but irrigation timing and amounts are best determined by root zone soil moisture.
This irrigation management root depth can be estimated by crop type.
Soil moisture content can be assessed using several methods, such as the Feel Method, tensiometers, and other sensors.
Typically, irrigation should occur before the soil reaches 50% available water holding capacity.
Plant appearance is NOT an accurate method of determining soil moisture content.
In all soils other than sands, a rough check on soil moisture can be done using the Soil Ball Method.
Dig a hole and remove a handful of soil from 6 to 12 inches deep.
Squeeze the soil into a ball.
Then 'bounce' the ball in the palm of your hand.
If it remains in a stable shape, the soil has more than 50 percent of its available water.
If it crumbles, it needs irrigation.
How long should I irrigate?
Water within the crop root zone is the source of water for crop evapotranspiration.
An irrigator can estimate the amount of water applied at a desired depth by knowing the soil water holding capacity.
Soil water holding capacity is determined by the soil texture, which can range from clay  to sand.
Example of estimating soil moisture by feel and appearance
 Example 2: How much water do I need to order?
Beth gets irrigation water from an earthen ditch.
She irrigates her 2-acre grass pasture with wild flood.
Her pasture requires about 1 inch of effective water per week.
But Beth needs more than 1 inch of water because the delivery system  and application system , are only about 70% and 40% efficient, respectively.
If she wants to apply the effective water required for the week  over the course of one day, how much water will she need to order?
1.
1 inch/ = 3.6 inches total water needed per acre
 2.
We know 1 inch = 1 acre-inch/acre, so 3.6 in = 3.6 ac-in/ac.
Then convert to volume: 3.6 ac-in/ac X  X 2 acres = 0,6 acre-feet of water needed.
3.
Most ditch water is ordered by cfs.
We know that 1 cfs = 23.76 ac-in/day, or 1.98 ac-ft/day, so
 Therefore, to meet her grass pasture's weekly needs using wild flood, Beth needs to order a constant 0.303 cfs for a full day or 0.6 acre-foot  over the course of one day.
Table 5: Irrigation Depths Based on Crop Root Zone Depths
 Turfgrass	1 or less
 Because plants take up water faster from upper roots, irrigation water management typically targets * upper 60 to 80% of actual rooting depths.
Source: Midwest Plan Service, Sprinkler Irrigation Systems, Table 2-2 
 Table 6: Soil Water Holding Capacity
 Water Available For Use
 Soil Texture	Between Irrigations *
 Sand	0.5 inch/foot	1 3
 Loam	1 inch/foot	0.3 0.8
 Clay	1 inch/foot	0.01 0.2
 *Intake rate can vary greatly with soil structure and stability.
Source: Fundamentals of Irrigation, USU Extension
 Example 3: How long should I irrigate a specific crop?
John wants to grow alfalfa in a loam soil.
He is debating between using a sprinkler system which delivers 0.25 inches/hour and flood irrigation which delivers 0.5 inches/hour.
How long should he irrigate each time if he uses the sprinkler system and if he uses flood irrigation?
1.
First look up important information.
Loam soil absorbs an average of 0.5 inches of water per hour.
Loam soil needs to be irrigated with 1 inch of water/foot.
The irrigation management depth for alfalfa is 4 feet deep.
2.
1 inch of water per foot for loam soil X 4 feet deep = 4 inches of water to be applied.
3.
Next consider the irrigation system.
Sprinkler: If the sprinkler system waters 0.25 inches/hour, it should run for 16 hours to apply 4 inches.
Flood: Since loam soils absorb 0.5 inches per hour, it should flood for 8 hours.
Therefore, if John uses the sprinkler system, he has to run it for 16 hours, but if he uses flood irrigation, he has to irrigate for 8 hours.
When should I consider using a small-scale pump?
Consider using a small-scale pump if you are looking to irrigate a small area of land, such as a front lawn or small garden.
The water source must also be shallow , such as a pond or ditch.
Typically, the desire is to move water for distances of 0 to 200 or so feet, and sometimes up inclines.
Details on how to choose a pump are located in the following section.
How do you choose a pump?
Remember that the power required  is not the only important factor to consider when choosing a pump.
There are four key elements to consider when choosing a pump:
 1.
head against which the flow is delivered,
 2.
required flow rate,
 4.
and power required.
These combined elements help determine the efficiency of the pump.
Every pump is designed for a different purpose, so in some instances high horse-powered pumps have higher efficiencies and in other instances low horse-powered pumps have higher efficiencies.
To choose the most efficient pump for your purposes, you will have to consult the pump manufacturer so they can match a pump to your system using their pump curves and graphs.
Flow rate, pressure, and power required are always indicated by the pump manufacturer.
Remember that your pump needs an energy source.
Most pumps run on electricity or gas, however solar power panels are an option, especially since the system is small.
Remember that the more horsepower your pump requires, the more energy you will have to supply and pay for.
The most appropriate pumps to move water from a shallow water source to a small application area are the centrifugal, jet, and sump pumps.
Before buying a pump, contact the pump manufacturer.
The technicians will be able to tell you if the pump you selected will work for your desired application.
Centrifugal pumps , sometimes called sprinkler or lawn pumps, are best used when you want to move water from a shallow water source to a small system with high volume required.
The shallow water source can be a pond, ditch, reservoir, etc.
that is 25 feet deep or less.
The small system can be a lawn sprinkler system with many sprinkler heads.
Jet pumps  are best used when you want to move water from a shallow water source to a small system with low volume required.
The shallow water source again can be a pond, ditch, reservoir, etc.
that is 25 feet deep or less.
The small system can be a lawn sprinkler system with few sprinkler heads.
Submersible  sump pumps  are best used when you want to take water from a shallow water source to a single outlet with high volume.
The shallow water source, can be a pond, ditch, reservoir, etc.
that is 20 feet deep or less.
The single outlet is typically a garden hose.
The common use for the sump pump would be to water a small garden with a hose.
Table 7: Pumping Across Horizontal Distances 
 Distance	Pump	Pump	Pump
 Pump Type*	Common Use		Pressure	Flow Rate	Power
 Centrifugal/	Move water from one	0 100	30 50	15 45	11.5
 Sprinkler/	source to many sprinkler	100 200	30 50	25 55	1 1.5
 heads along one line (low
 Lawn Pump	pressure, high volume)	200+	30 50	35 60	1.5 2
 Move water from one	0 100	30 60	5 10	0.25 0.5
 source to very few
 	sprinkler heads along one	100 200	30 60	10 20	0.5 0.75
 line (high pressure, low
 volume)	200+	30 65	10 25	0.5 1.5
 Drops into water and
 Submersible	attaches straight to
 Sump Pump	garden hose (low	0 150	30 60	25 80	0.25 1
 * All pumps considered are for shallow depth  water sources.
When dealing with hills, or any other inclines over which you would like to pump water, there are a variety of options.
The main options involve using jet pumps or booster pumps.
1.
Jet pumps can be used if you are using a shallow water source, but want to pump the water up 70 feet or so.
2.
Generally, adding a booster pump  is the easiest way if you have hills greater than 70 feet in elevation.
Adding a booster pump simply allows you to provide the extra pressure you need to get up the incline.
This pump would be in addition to whatever pump you chose given your needs.
Operation & Maintenance of Pumps
 Be sure to consult the pump manufacturer about the proper operation and maintenance of your pump.
A few general guidelines are:
 1.
Do not let trash get into your pump!
You should make sure the intake pipe to your pump has a screen that does not allow trash through it, or it will reach the pump and the pump will die.
2.
Check valves eliminate the need for priming.
If you do not wish to prime your pump for every use, it is a good idea to have a check valve or foot valve installed.
They are inexpensive.
3.
Pressure relief valves protect your pump.
If you do not purchase a pump that automatically shuts off when a maximum pressure is reached, buy a pressure relief valve to release the buildup pressure thereby protecting your pump.
The valves are inexpensive.
4.
Flush out your system!
Flush out your system with debris-free water every so often.
5.
Install a pressure gauge.
You might want to install a pressure gauge to periodically check the pressure within your system.
This is highly recommended if you opt out of buying a pressure relief valve.
The gauges are also inexpensive.
6.
Know that it is normal for pump performance to decrease over time.
Pay attention to the water pressure: after some years it will get to the place where the pressure is too low for your purposes.
If you can catch it early, it is more likely you will just have to buy a part for it, rather than running the pump until it dies, forcing you to buy a whole new pump.
There are a few things which typically affect pump price:
 1.
Horsepower: Generally, as you increase in horsepower, the price of the pump increases, and the energy needed to run the pump increases.
2.
Electronic features: The more electronic features you desire, the more expensive the pump gets.
3.
Material: Stainless steel is more expensive than cast iron or plastic.
How do I choose a small acreage sprinkler system?
There are a few key factors to consider when choosing a sprinkler system:
 1.
Flow rate the amount of water  that goes through the system and is delivered to the application area.
2.
Pressure the pounds per square inch your system needs to move water through it.
You need to make sure your system can withstand the amount of pressure coming through it.
As a reference, most garden hoses run at 35 to 65 psi.
3.
Mobility the ease with which you can move your system from place to place.
4.
Application area the area you want to irrigate.
Mini gun sprinkler systems  are best used when you want to irrigate a small area by moving a portable sprinkler with a wide application area.
Mini gun systems come with a sprinkler attached to a water reel.
The reel is connected to a hose which supplies it water.
Because the reel is set on wheels, it is very easy to move.
Once you have placed the reel, you pull out the sprinkler and then the reel pulls it back in automatically, irrigating as it goes.
The reels are grazing animal friendly.
Solid set sprinkler systems come in two basic forms, portable and permanent.
These systems may have a variety of sprinkler heads attached to them, depending on your needs.
The solid set system is made up of sprinkler risers  spaced evenly along the length of a horizontal pipe running on the ground.
This system can be permanent or portable.
These systems are labor intensive.
Portable solid set sprinkler system pipes can be removed from the field, eliminating the need to farm around sprinkler risers.
Because the pipe is not permanently fixed in one location, these systems can be moved to different fields to follow the grazing or crop rotation.
Permanent solid set sprinkler system pipes, valves, and sprinklers are permanently installed in the field , so it is easy to automate these systems compared to the portable ones.
This means there is less irrigation labor required.
Permanent solid set systems are not very common.
The risers can be difficult to mow around and the permanent above-ground risers do not allow for flexibility in crops grown.
The sprinkler risers need to be protected from grazing animals, so it is suggested that they be encased in PVC pipe.
K-Line 5 Pod 2 Acre Kit
 K-Line sprinkler systems  are highly mobile.
If you are interested in irrigating more than a couple of acres, it is easy to expand by simply buying more of the K-Line sprinkler kits.
The kits include the sprinklers, the tubing, and the rest of the system.
The sprinkler sits in a black pod which looks like a tire.
The pods are connected along a line of hose, generally 5 pods to a hose.
They are very easy to move and are grazing animal friendly.
They perform well on flat or hilly ground.
For less than 5 acres, the most appropriate irrigation systems are the mini gun and K-Line sprinkler systems.
Be sure to consult the sprinkler manufacturer about the proper operation and maintenance of your sprinkler system.
Table 8: Sprinkler System Selection Matrix
 Sprinkler System Type	Features	Area 	Pressure	Rate
 Mini Gun	Can be used on irregularly	0.2 2*	45 150*	4 80*
 Easily automated.
More	1 8
 Solid Set	As desired	25 65
 required.
Expandable to	sprinkler
 more acres if more kits are
 K-Line 	friendly.
Can be used on	2	40 50	12 24
 flat and hilly ground, as
 well as irregularly shaped
 * *Depends on the mini gun model.
Table 9: Manufacturers Contact List
 Manufacturer	Phone No.*	Website*	Products
 *Website and telephone information last updated Dec.
2018.
IMPROVING AN IRRIGATION SYSTEM
 1.
Improve your irrigation management by understanding plant water requirements and soil properties that influence irrigation amount and timing.
2.
Improve irrigation uniformity.
Look for signs that water is not being distributed uniformly patches of stressed plants, water runoff from the field, and areas of ponding.
Remedies for flood irrigation uniformity include corrugation and land leveling.
Sprinkler irrigation uniformity can be corrected by adjusting sprinkler locations or nozzle type.
3.
Improve irrigation system efficiency.
a.
Many earthen delivery ditches are extremely permeable to water.
Installation of plastic, concrete, steel ditch linings, or some type of delivery pipe can help conserve water.
C.
Irrigation system efficiency can be measured with devices such as headgate flumes, weirs, and flow meters.
d.
Improve your irrigation management.
Many times water is over or under applied to meet crop water needs.
Improving your scheduling can improve your water use efficiency and potentially increase yields or improve quality.
The U.S.
Department of Agriculture  prohibits discrimination in all of its programs and activities on the basis of race, color, national origin, age, disability, and where applicable, sex , marital status, familial status, parental status, religion, sexual orientation, political beliefs, genetic information, reprisal, or because all or part of an individual's income is derived from any public assistance program.
The largest development for 2023 is the expansion of TAPS into Colorado, where a new competition will take place this year at Colorado State University.
The inaugural sprinkler corn competition will be hosted at CSUs Agricultural Research, Development and Education Center  applied farm research facility located near Fort Collins, Colorado.
Several former UNL-TAPS participants from Nebraska and Colorado have signed on to support this new programs development and launch, including intent to compete.
Before-and-after tests on emitters show
 Organic fertilizers can be injected through low-volume irrigation systems
 The practice of injecting organic fertilizers into low-volume irrigation systems is not widespread, partly because of concerns that the materials will clog emitters.
This study looks at two spray-dried organic fertilizers  that were injected through various low-volume irrigation systems, and finds only minimal clogging and even distribution of fertilizer throughout the irrigated area.
Low-volume  irrigation is gaining popularity because it has the potential to conserve water and energy, it is easy to manage and operate, and it has a positive impact on crop yield and quality.
Another benefit is its capacity to carry injected fertilizers in the irrigation water, known as "fertigation." When applying fertilizers through the irrigation system, growers can expect more efficient fertilizer use and improved plant response because the plants'
 nutritional demands are more closely matched throughout the growing season.
Organic growers using low-volume irrigation systems have expressed interest in finding an organic fertilizer that can safely be injected through their irrigation systems.
Available organic fertilizers such as fish emulsion frequently clog emitters when used for this purpose.
Chilean nitrate , an available and affordable nitrogen  source, is used by some organic growers, but it has a disadvantage: it adds sodium to the soil.
Formulations of sodium nitrate frequently contain as much as 26% sodium.
High sodium levels in the soil can result in a dispersed soil that exhibits poor infiltration.
It was suggested to the authors that animal and plant proteins rendered by a process known as "spray-drying" may be suitable for injection.
In this process, plant or animal tissues are hydrolized with enzymes, concentrated into a slurry under warm temperatures in a vacuum column, and then sprayed though a rotary nozzle spinning at 11,000 revolutions per minute in the center of a cyclone tank with winds of 140 miles per hour.
The resulting products are very fine, uniform in size, and
 Organic fertilizers were mixed in the black tank , and then injected by pump into the drip system.
Control valves and pressure gauges  were used to monitor and control emitter performance.
The systems tested five different types of drip emitter; one is shown below.
have high N analysis  for organic fertilizers.
Fish protein, blood protein, poultry protein, and brewers yeast all are available as spray-dried materials.
During the summers of 1989 and 1990, the authors investigated the potential usefulness of such spray-dried fertilizers as injected materials in low-volume irrigation systems.
We sought answers to these questions:
 1.
Can spray-dried organic fertilizers be applied by injection without clogging low-volume irrigation systems using drip emitters, drip tape, or microsprinklers?
2.
Are there any differences between the clogging potential of the various lowvolume irrigation products when organic fertilizers are injected?
3.
How uniformly can organic fertilizers be delivered throughout a low-volume irrigation system?
In June 1989, an irrigation system was assembled at the Hopland Field Station in Mendocino County to assess the potential for various low-volume emission devices to clog as a result of organic fertilizer injection.
Injection was accomplished with a positive-displacement, water-powered
 pump.
The drip system consisted of seven brands of drip emitters: Irredelco Flapper 2-gph dripper, Hardie Turbo-key 1-gph dripper, Netafim pressure-compensating 1-gph dripper, Bowsmith S-series 1-gph dripper, Bowsmith Truflow Gripper 1-gph dripper, Netafim 1/2-gph button dripper, and Netafim 1-gph button dripper.
Each was replicated 20 times for a total of 140 experimental units.
Emitters were installed 2 feet apart on four 70-foot-long 1/2-inch polyethylene lines, with water pressure set at 7 pounds per square inch.
Six different microsprinkler types with a range of sprinkler patterns and orifices were used: Bowsmith Red Fanjet, Bowsmith Green Fanjet, Bowsmith Blue Fanjet, Olsen Blue Minisprinkler, Olsen Green Mini-sprinkler, and Hardie Black Fan-Spray.
The microsprinklers were installed in a system similar to the drip-emitter system, with line pressure set at 20 psi.
The sprinklers were installed 2 feet apart on five 3/4-inch black polyethylene lines 80 feet long.
Two products blood protein and fish protein were evaluated during the 1989 Hopland screening test.
Test results indicated that both the blood protein and the fish protein could be injected with minimal clogging through low-volume emitters.
It was also found that portions of both products went into suspension rather than solution and would tend to settle out.
This was true of the blood protein where higher concentrations of fertilizer  were emitted near the inlet end of the drip lines.
The fish protein product was more easily held in suspension, resulting in a more even distribution of fertilizer along the entire length of drip line.
The 1989 screening test indicated that injection of the fish protein product merited further more detailed and more extensive investigation under irrigation system conditions typical of grower installations.
Irrigation equipment.
In summer of 1990, a low-volume irrigation system was designed and installed at the Campbell tract of the University of California at Davis.
Tested were a microsprinkler, five drip emitters, and two drip-tape materials to examine their susceptibility to clogging.
The microsprinkler model was a Bowsmith Blue Fanjet, and these were placed at 15-foot intervals along 3/4-inch polyethylene tubing.
Four 300-foot-long microsprinkler laterals were installed.
The Bowsmith Blue Fanjet was chosen as a result of information gathered from the 1989 Hopland screening.
It has a relatively small orifice size, and would therefore be more likely to clog.
If injected fertilizer materials failed to clog the Bowsmith Blue
 Fanjet, we felt that microsprinklers with larger orifice sizes would suffer even less clogging.
Five drip emitters were investigated: Bowsmith Truflow Gripper drippers, Netafim pressure-compensating 1-gph drippers, Netafim 1/2-gph button drippers, Bowsmith S-series drippers, and Netafim 1-gph Button drippers.
Four lateral lines , each one 300 feet long and with emitters at 5-foot intervals, were laid out for each type of emitter.
Finally, two drip tapes Netafim Typhoon tubing with 0.45-gph emitters at 18-inch spacings, and T-Tape Low Flow with 12-inch outlet spacings were installed.
Again, four 300-foot lengths of each drip-tape material were laid out.
The 32 lateral lines were connected to four 1-inch solenoid valves SO that the flow to each station was approximately equal.
The valves were connected to a control clock SO that the irrigation system could be operated automatically.
Pressure to the system was controlled by a Hardie Irrigation adjustable pressure regulating valve, which could sense downstream water pressure and compensate to maintain the desired system-operating pressure.
Irrigation was performed daily to simulate actual grower operations.
The water source was the UC Davis water supply system.
After an initial "break-in" period of approximately 1 week, a baseline set of emitter flow-rate measurements for the entire system was taken on July 26, 1990.
For the drip emitters and microsprinklers, emitters were selected at 50-foot intervals along each lateral line and the flow rate from each selected emitter during a 1minute interval was collected.
For the drip-tape materials, the flow rates of 5-foot sections of drip tape at 50-foot intervals were monitored for 1 minute using a PVC trough laid under the drip tape.
All monitored locations were marked and became the sampling sites for all future flow measurements.
Fig.
1.
Distribution of total nitrogen concentration along the length of drip line when fish protein fertilizer was injected into the system.
Fertilizer injection.
The spray-dried fish protein fertilizer was evaluated first.
For injection, the fish protein was added to a tank of water at a concentration of 160 grams of fertilizer per gallon of water and thoroughly mixed using a mechanical stirring device known as a drum beater.
The fish protein mixed easily into solution; once mixed, it stayed well in suspension.
The fertilizer solution was injected into the irrigation system using an adjustable electrically driven diaphragm pump.
An injection rate was chosen to attain a nitrogen concentration of approximately 75 ppm in the irrigation water.
During fertilizer injection, one of the four lateral lines for each of the tested emission devices was shut off with a ball valve.
These selected control lines never had fertilizer-injected water run through them.
Fertilizer was injected in the middle of the irrigation cycle to allow a period of "clean" water to follow the injection.
This practice worked well, is easily done, and is recommended for anyone injecting the organic fertilizers we tested.
Without a flushing period, residual fertilizer is left in the line, with the result that fertilizer settles out before the next irrigation.
Although we have no data to indicate this would increase the potential for clogging, there is no reason to take unnecessary risks.
Following the first fish protein injection , emitter flow rates were again monitored at the same sites as had been selected and monitored before.
No emitter clogging was evident as a result of the fertilizer injection.
Subsequently, the irrigation system was operated daily, with fish protein injection occurring weekly until seven fertilizer injections were completed.
A final set of emitter flow-rate measurements was taken October 9, 1990.
During the second fish protein injection , water samples were collected at 50-foot intervals along the lateral lines to determine whether the fish protein was being discharged uniformly along the entire lateral length.
The samples were later analyzed by a diagnostic laboratory for total nitrogen levels.
Following the fish protein injections, a spray-dried poultry protein product was also evaluated in a manner identical to that used for the fish protein fertilizer.
We made six injections of the poultry protein, and collected final flow measurements December 6, 1990.
The two drip tapes had been damaged by rabbits and ground squirrels, so they were not evaluated during the poultry protein experiment.
Injection of the poultry protein was easily managed, although it was slightly more difficult to mix into solution than was the fish protein.
Once mixed, however, the poultry protein stayed in suspension very well.
tapes were analyzed similarly, with similar results.
control emission devices  on an emitter device basis again revealed that no clogging could be attributed to the poultry protein injection.
Statistical analysis of the flow-rate information gathered during the fish protein injection indicated that for four of the lowvolume products Bowsmith Fanjets, Bowsmith Truflow Grippers, T-Tape drip tape, and Netafim Typhoon drip tape the average flow rates before and after the fish protein injections were not equal.
The statistical analysis used a two-sample analysis that computed a confidence interval for the difference between sample means and a hypothesis test for the difference between sample means, which computed a T-statistic.
A 95% confidence interval and an alpha of 0.05, respectively, were used for the tests.
After completion of the fish protein injection on October 9, 1991, we evaluated the spray-dried poultry protein.
We followed the experimental procedure previously described for the fish protein evaluation to evaluate the suitability of the poultry protein for injection.
Daily irrigations and six weekly fertilizer injections were performed.
Final low-volume emitter flow measurements were taken on December 6, 1990.
The uniformity of the injected poultry protein emission along the lateral line was measured by collecting water samples in a manner similar to that described for the fish protein product.
As with the fish protein, the injected fertilizer was uniformly discharged along the entire 300-foot-long lateral.
Table 1 lists the percentage change in drip-emitter average flow rates across the poultry protein injection period.
Little change occurred in emitter discharge rates across the injection period.
Statistical analysis indicated no significant change in emitter discharge rates except for the Bowsmith S-series dripper, which showed an increase in average discharge rate  during the injection period.
A comparison between the average flow rates of the treated versus the
 TABLE 1.
Percentage change in discharge rates
 across the injection period for various drip emit-
 ters when fish or poultry protein fertilizers were
 injected into irrigation water
 Emitter	% change	% change
 Bowsmith Blue Fanjet	-3.0	1.7
 Gripper dripper	-4.7	0
 Netafim, 1 gph pressure-
 compensating dripper	1.7	1.1
 button dripper	1.1	0.9
 Bowsmith S-series dripper	0.3	3.8
 Netafim 1-gph button dripper	-0.4	0
 	-3.1	NT*
 TABLE 2.
Average changes in discharge rates with fertilizer injection, relative to changes in discharge rates for uninjected controls, for two organic fertilizers and various drip emitters
 Table 1 summarizes the percentage change in average flow rates from lowvolume emitters across the period of fish protein injection.
It is evident that changes in the flow rate across the injection period of the various emitters were minimal, with a 6% decrease being the greatest change.
Emitter	% change	% change
 Bowsmith Blue Fanjet	-2.1	0.9
 Gripper dripper	-8.3	0.8
 Netafim, 1 gph pressure-
 compensating dripper	1.5	-0.3
 button dripper	0.3	1.9
 Bowsmith S-series dripper	-1.8	0.8
 Netafim 1-gph button dripper	-0.2	2.5
 	-2.0	NT*
 18" spacing)	-7.1	NT*
 A statistical comparison of the post-injection, average flow rates of the treated versus the control , on an emitter device basis, revealed that no clogging could be attributed to the fish protein injection.
For example, the average flow rate of the T-Tape sections that had fish protein injected through them and those that experienced no injection  were statistically equal.
Table 2 illustrates this for each irrigation product tested.
There were some small-but statistically significant average flow-rate changes across the fish protein injection period, because  prepost-injection measurements were taken at slightly different operating pressures or  clogging resulted from other sources.
Although the water quality made clogging by chemical precipitates unlikely, organic growth was noticed in the system because of the entire irrigation system's exposure to sunlight.
Chlorine was injected periodically into the system to control organic growth, but the minimal flow-rate changes experienced might be attributable to clogging with organic matter.
The uniformity of fertilizer distribution along the lateral line was measured during injection by collecting water discharged from the selected emission devices at 50foot intervals along the lateral.
The water was analyzed by the diagnostic laboratory for total nitrogen chosen as an indicator of the fertilizer content in the irrigation water.
The source water, UC Davis domestic water, had less than a 1-ppm background nitrate level.
Figure 1 illustrates the nitrogen distribution along a lateral containing Netafim 1-gph button drippers.
Clearly, uniformity of fertilizer emission was very good.
Microsprinklers and drip
 Both the fish protein and poultry protein products are sold dry and finely ground.
In this form, they are easy to handle and to store.
It is recommended that once mixed with water, the entire batch be injected and the fertilizer tank rinsed.
Both products tend to take on offensive odors if allowed to sit for more than a few days.
Frequently, nitrogen fertilizer applications are calculated in terms of pounds of applied nitrogen.
One acre-foot of water with a 75-ppm nitrogen concentration of injected fish or poultry protein products  contains approximately 200 pounds of nitrogen.
The fish protein and poultry protein products contain 14% nitrogen, 0.5% phosphorus, and 0.7% potassium.
Both fish and poultry protein products cost approximately $1.60 per pound of material, depending on quantity purchased, resulting in a final cost of approximately $12 per pound of nitrogen.
As a comparison, sodium nitrate costs approximately $1.50 to $2 per pound of nitrogen.
Both organic nitrogen sources are substantially more expensive than nonorganic nitrogen sources, such as UN-32 , which are commonly injected into low-volume irrigation systems.
The two organic fertilizer products tested spray-dried fish protein and spraydried poultry protein were both shown to be injectable through microsprinkler, drip, and drip-tape irrigation systems with minimal clogging.
Both fertilizer products were also shown to be emitted uniformly along the 300-foot lateral lines tested.
J.
Schwankl is Extension Specialist, Department of Land, Air, and Water Resources, UC Davis, and G.
McGourty is Farm Advisor, Mendocino County.
Types of On-Farm Demonstrations
 Jason Warren Soil and Water Conservation Extension Specialist
 Randy Taylor Extension Machinery Specialist
 Jeff Edwards Small Grains Extension Specialist
 On-farm demonstrations are a valuable tool in the teaching of new management practices or technologies.
Demonstrations allow producers, educators and agency personnel alike to learn how an alternative management option will perform on actual farms at field scale.
In addition, unlike research and demonstration projects located on university farms, onfarm demonstrations can be located anywhere a cooperating producer/landowner is willing to host the demonstration.
This allows for greater geographic distribution of demonstrations compared to the use of university research farms.
It allows demonstrations to be targeted toward a community of producers that are particularly interested in the technology or management alternative, but need validation in a production environment that represents their farm.
Types of On-Farm Demonstrations
 There are three general types of demonstrations: proof of concept, strip trials and replicated field trials.
Each can be valuable in demonstrating alternative management or technologies, but there are benefits and challenges for each type that should be considered along with the intended goals to be achieved by the demonstration.
Proof of concept is the simplest form of on-farm demonstration and can be a useful educational tool.
A proof-ofconcept demonstration applies an alternative management practice on a field or group of fields, it is discussed during field days to provide an understanding of how it was done and the outcome.
This is often combined with a discussion of how the new or alternative practice compared to a neighboring field, where the standard management practice was used.
Thus, a proof of concept approach is useful in demonstrating how to implement an alternative practice or how it will perform in a production environment.
Proof-of-concept demonstrations have limitations and are not useful tools for quantifying the impacts of an alternative practice relative to the standard practice.
This is because the outcomes experienced on the different fields could be impacted
 by management unrelated to the alternative practice being demonstrated.
For example, planting date, fertilization date, herbicide application date as well as a host of other possible management differences could impact outcomes observed in both the alternative and standard practices.
In addition, there could easily be inherent differences in soil type or even rainfall received between the different fields compared.
These limitations of the proof-of-concept demonstration are important, if the goal of the demonstration is to quantify the effects of the alternative practice on soil health, soil fertility, crop growth or crop yield.
However, they are less important if the goal is to simply provide proof of the concept or to demonstrate how the alternative practice can be implemented locally.
The second form of on-farm demonstration is the strip trial, in which alternative management practices are imposed in strips within the same field.
These provide useful side-by-side comparisons of different practices, hybrids or varieties, which can provide more information and stronger comparisons than comparing one field to another.
However, as farmers know, each field has areas that are more fertile than others, and spatial variability within the field must be considered when comparing outcomes from one practice to another.
The simplest form of strip trial is one in which two alternative practices are imposed on two halves of a field and can serve as an example of how spatial variability can influence results.
Figure 1 shows a yield map for soybean grown in 2012 in Noble County, OK.
Notice the west side of the field contains yields in excess of 50 bu/acre, whereas maximum yields on the east were 36 bu/acre to 50 bu/acre.
In fact, the average yield for the west half of this field was 30 bu/acre and the average for the least was 25 bu/acre.
This difference was observed without imposing different management strategies on the two sides of the field.
In this instance, if two different management practices were imposed , which actually had no impact on yield, we would erroneously conclude that the management practice imposed on the west side increased yield.
Split field comparisons such as this illustrate the problem with using strip trials to compare the outcome of alternative management practices.
However, strip trials do provide more valid comparisons than proof-of-concept demonstrations because the impact of variations in rainfall is reduced.
Strip trials can also provide a better comparison than field-to-field
 Figure 1.
Soybean field from Noble County, Oklahoma.
The average yield on the west side of this field was 30 bu/acre  and the yield on the East side was 25 bu/acre.
Figure 2.
Map of Soybean yields collected in Noble County.
Replicated strips are randomly located within this figure.
The average yield for strips outlined in black is 29 bu/acre and for those outlined in dotted lines the average yield is 27 bu/acre.
comparisons in proof of concept demonstrations because there is a greater chance that all of the strips received similar management such as planting date, fertilization and herbicide application.
Crop hybrid or variety demonstrations are often conducted using strip trials.
While this type of demonstration decreases the spatial variability between treatments, it still has the same limitations for comparison between treatments.
Consider a soybean variety strip trial in Figure 1 with rows planted north to south and each plot width being two passes of a planter.
The soybean varieties planted on the west side of the field would have a clear advantage, but unlike the split field comparison, plots would not be wide enough to include lower-yielding areas to offset the high production on the west edge of the field.
This flaw can be overcome by replication, which will be discussed in the next section.
The value of strip trials can be increased if there are multiple fields with the same management practices imposed in strips.
This decreases the likelihood that spatial variably within the field erroneously impacts the performance of the practices.
In fact, this creates a replicated study as will be discussed in the following section where each field is a replicate.
Another option is to only assess the impact of the management practices in adjacent strips where they are truly side-by-side.
This will minimize the spatial variability of the entire field, but the design still provides only one observation for comparison of a practice.
Replicated field trials are most commonly used by University Extension Specialists because they allow for statistical analysis to determine the probability that the alternative management practices will result in a different outcome compared to the standard practice.
Replicated field trials are very powerful because they allow for the determination of whether or not an alternative practice is really  better than the standard practice through statistical analysis.
Like proof-of-concept demonstrations, replicated field trials can be used to demonstrate a practice is viable at a particular location.
However, replicated field trials also allow us to determine the likelihood that a new practice will result in a better outcome compared to the standard practice.
Replicated field trials require each management alternative be imposed in multiple locations within a field.
Figure 2 shows the layout for a replicated demonstration, comparing two practices, imposed on the previously mentioned soybean
 field.
Notice that each management practice is replicated four times and placed in random positions in the field.
This reduces the impact of the spatial difference in soil type on the measured outcomes.
For example, the average yield for the areas outlined in black in Figure 2 is 29 bu/acre and in areas outlined in dotted lines, the average yield is 27 bu/ acre.
By using multiple replications randomly placed in the field, the influence of yield variability unrelated to the management practices imposed is decreased as compared to the split-field example provide in Figure 1.
Remember, the yield differences are the result of variability in the field, without the application of different treatments.
The introduction of GPSguided equipment has made this type of design much easier to implement, as the drill or sprayer can easily be set to apply a skip  every other pass.
Replicated field trials are very powerful tools, especially when one of the goals of the demonstration is to compare the alternative practice to a standard practice.
If this type of design is used, statistical analysis can be used to determine if the differences among treatments, hybrids or varieties are likely to occur on a consistent basis or, conversely, if they simply occurred due to luck of the draw.
The details of performing this type of statistical analysis is beyond the scope of this fact sheet, but will be covered in another factsheet provide as part of this series about on-farm demonstrations.
Replication is also critical if the information is intended to affect policy.
On-farm demonstrations are probably the most powerful tool available to educate landowners, producers and other agricultural professionals about new management practices and technologies.
When determining which of the three types of demonstration to choose, it is important to have a clearly defined goal.
If your goal is to simply show people how to implement a practice or technology in a specific location, then the proof-of-concept demonstration is appropriate.
However, if your goal is to demonstrate that a new practice is likely to result in a better outcome than a standard practice, strip demonstrations or replicated field trials are required.
Replicated field trials are preferred unless strip demonstrations are implemented in multiple fields to reduce the erroneous interpretation of outcomes that can be caused by inherent variability within a field.
The Oklahoma Cooperative Extension Service Bringing the University to You!
The Cooperative Extension Service is the largest, most successful informal educational organization in the world.
It is a nationwide system funded and guided by a partnership of federal, state, and local governments that delivers information to help people help themselves through the land-grant university system.
Extension carries out programs in the broad categories of agriculture, natural resources and environment; family and consumer sciences; 4-H and other youth; and community resource development.
Extension staff members live and work among the people they serve to help stimulate and educate Americans to plan ahead and cope with their problems.
Some characteristics of the Cooperative Extension system are:
 The federal, state, and local governments cooperatively share in its financial support and program direction.
It is administered by the land-grant university as designated by the state legislature through an Extension director.
Extension programs are nonpolitical, objective, and research-based information.
It provides practical, problem-oriented education
 for people of all ages.
It is designated to take the knowledge of the university to those persons who do not or cannot participate in the formal classroom instruction of the university.
It utilizes research from university, government, and other sources to help people make their own decisions.
More than a million volunteers help multiply the impact of the Extension professional staff.
It dispenses no funds to the public.
It is not a regulatory agency, but it does inform people of regulations and of their options in meeting them.
Local programs are developed and carried out in full recognition of national problems and goals.
The Extension staff educates people through personal contacts, meetings, demonstrations, and the mass media.
Extension has the built-in flexibility to adjust its programs and subject matter to meet new needs.
Activities shift from year to year as citizen groups and Extension workers close to the problems advise changes.
Understanding and Installing Drainage Systems
 Juan Enciso, Xavier Pris, Lus A.
Ribera , and Dean Santistevan4
 Farmers can increase yields and net returns by installing artificial drainage systems on soils that have poor natural drainage.
Artificial drainage systems can also increase land value, improve crop insurance coverage, and reclaim saline land.
When planning a drainage system, farmers should consider factors such as the types and functions of such systems, methods to detect drainage problems, design options, and the environmental effects of drainage installation.
Why artificial drainage is needed
 Good drainage is essential for the success of irrigated agriculture: It ensures that the crop's root system has a good mixture of water and air and that the salt balance in the soil is favorable for plant growth.
Poor drainage causes several problems for agricultural production:
 Because the soil has little or no permeability, excess water accumulates on and below the surface after rainfall or irrigation.
Water tables that remain high for 48 hours or longer can saturate the soil and leave too little oxygen in the soil pores for the root system, damaging the plant.
Agricultural machinery is difficult to move on wet ground for soil preparation.
Bacteria that provide nitrogen to the crops cannot grow.
Nutrient processes and transformations are impeded, such as the prevention of usable forms of nitrogen and sulfur.
The soil temperatures are 7 to 14 degrees F lower than that of similar soil with good drainage.
This impedes germination and slows crop growth, making the plants more susceptible to diseases.
Figure 1.
Typical field with poor natural percolation.
Water ponds for several days after a heavy rainfall storm or heavy irrigation.
Poor drainage can occur in arid and humid areas and can be caused by natural or human reasons, including:
 The presence of semi-permeable or impermeable layers of soil
 Proximity to reservoirs or coastal areas
 When the rate of water input is greater than the natural drainage capacity, the water table rises.
Coastal areaswhere the altitude ranges from 10 to 100 feet above sea level-generally need regional collective drainage systems.
An on-farm drainage system may also be required where the water table is high, depending on the area's topography, soil type, and soil conditions.
Most agricultural soils are alluvial soils formed by materials carried by water and deposited on the lower parts of a valley.
These soils may have layers of coarse and fine materials such as sand, clay, silt, and gravel.
Some alluvial soils have poor natural drainage, and artificial drainage may be needed to remove excess water from an irrigated field.
Artificial drainage systems can lower high water tables, keep salts from building up, increase crop yields, and make irrigation successful.
In general, farmers have noticed big increases in yield after the installation of a drainage system.
To optimize production potential, the water table should be below 3 feet deep for field crops and below 4 feet for citrus.
A shallower water table may require artificial drainage.
In the Rio Grande Valley, a water table in any soil within 30 inches of the soil surface is a definite problem.
As the water table rises, salts can move upward and accumulate closer to the surface, mainly because more water evaporates from the soil and transpires from plants than
 is gained through rainfall.
A drainage system allows salts to leach downward with rainfall or irrigation.
The benefits of removing salts include improved germination, enhanced crop yield, and an improved growth environment for crops that are less salt tolerant.
Growers may need to add soil amendments where the soil has too much sodium and/or a lack of calcium.
Poor drainage is also connected with high levels of calcium carbonates.
Once a drainage system has been installed, the collective drainage systems must be maintained properly.
Types of drainage systems
 The main types of drains are surface and subsurface.
Surface drains  are typically ditches from which low-gravity conditions remove excess surface water from agricultural land.
When deep enough, the ditches can also provide relief to adjacent areas.
Surface drainage also can be used as an outlet for collection and disposal of water from subsurface drainage systems.
Surface drainage can be achieved by building ditches, improving natural channels, or shaping the land.
Open ditches have a low initial cost and are easy to inspect.
Disadvantages to these systems include that they reduce the cropping area, require a right-of-way, and have high maintenance costs.
Subsurface drains  are installed underground to remove excess groundwater below the ground surface.
These systems are often called tile drains.
In the past, perforated clay tile and concrete pipe sections  were used to help drain agricultural land.
Today, perforated corrugated polyethylene pipe is used instead of tiles.
To keep silt and sand from clogging the system and to increase water flow through the pipe, the laterals are surrounded by a nylon envelope or "sock".
A subsurface drainage system should be complemented by an open drainage system.
Function of the drains
 Both types of drainage systems can be divided into two classes: relief drainage and interception drainage.
Relief drains are used when the water table is close to the ground surface and the area is static and flat.
Interception drains prevent or reduce water flowing to the problem area.
In planning a subsurface drainage system, the designer must evaluate the site conditions and decide which type of drainage system to install.
Figure 2.
The perforated lateral  can be covered by a "sock".
Relief drains for subsurface drainage use a system of polyethylene pipe laterals to lower a high water table.
The laterals drain the field by gravity.
At the lower part of the field, the laterals are connected to a collector drain.
Figure 3.
Typical design layout of a subsurface drain system that shows the spacing, size, and grade of laterals and the collector and the outlet of ground waters.
The collector drain receives the flow from all of the laterals and generally discharges into an open drainage ditch.
If the outlet point is at lower elevation than the water level in the drainage ditch, a sump well must be installed to temporarily hold the ground water and pump it to the drainage ditch.
The intention is to maintain the ground water at a level below that of the root zone for a given crop.
The Natural Resource Conservation Service requires that the installation be at least 5 feet deep.
The most common relief drain system in the Lower Rio Grande Valley consists of parallel lateral drains located perpendicular to the main drain.
The drain's arrangement can vary according to the site location.
The arrangement can be random, consist of two parallel sysitems, or have the laterals connected to the collector at an angle.
The laterals in the main system are spaced at any interval according to the site conditions, permeability, and soil type.
Most relief drainage parallel systems are composed of laterals that are spaced between 100 and 150 feet apart, depending on the soil texture.
The laterals are installed at a grade of between 0.025 foot per 100 feet to 0.1 foot per 100 feet as shown in the example of Figure 3 and Table 1.
The overall effectiveness of artificial drainage can be improved by the use of relief drainage systems in conjunction with other best management practices, such as land leveling.
Locate	Ground	Proposed	Depth
 elevation 	elevation 	
 A	99.70	93.34	6.36
 B	99.05	94.05	5.00
 C	98.60	93.08	5.52
 D	99.30	93.78	5.52
 Table.
1.
Existing ground elevations, proposed elevations of subsurface lines, and depth of cover for field locations shown in Figure 3.
Figure 4.
Typical sump well schematic showing the transfer of ground water into a drainage ditch.
Interception drains are placed perpendicular to subsurface flows to capture water and reduce the creation of excessively wet areas.
On agricultural land, interceptor drain lines are often installed along earthen irrigation canals that have high seepage potential.
In this situation, an open drain can be used to intercept excess water from the leaky canal.
When the conduct drains are closed, the depth of the interceptor line will vary with that of the water table.
Well drainage systems pump water from deep wells to lower and maintain the water table at a level suitable for proper crop growth.
The pumped water can sometimes be used for irrigation if it is of good quality and has low salinity.
When designing a well drainage system, several test wells must be installed to determine the drawdown and the spacing of the wells.
This method of drainage is expensive, and its application is limited to lands that produce a high return value per acre.
Before any subsurface drain system is installed, the water tables must be monitored to determine whether drainage is needed or to evaluate the performance of the drainage system.
An observation well can help the designer study the fluctuation of water tables and monitor salinity in the water during the growing season.
Observation wells consist of open auger holes drilled at various locations in which a perforated PVC pipe (of
 about 1 to 2 inches in diameter) is pushed into the soil profile.
The PVC pipe is commonly referred as piezometer.
Several piezometers must be installed to determine the direction of the groundwater flow and fluctuations of the water table during the year.
Topographic maps and soil surveys are also useful when monitoring water tables.
The field topography can indicate seep areas or low areas in the soil.
Figure 5.
Installing a piezometer  up to 9 feet deep with a 2-inch auger to monitor fluctuations of the water table level.
A drainage system should be designed to remove excess gravitational water and lower the water table far enough from the ground surface SO it does not interfere with plant growth.
The system designer must determine:
 The desired depth to which the water table should be lowered 
 The amount of rainfall received and the amount of irrigation to be applied
 The proper depth and spacing of the relief and collector lines
 The maximum length of laterals
 The material and diameter of the pipe
 The slope grade at which the lines should be installed
 The design should take into consideration critical soil properties  that will determine the drainage water relief outflow rate, the drain depth, and spacing.
Permeability and hydraulic conductivity
 Permeability is the capacity of the soil to transmit water.
Soil can have low, moderate or high permeability.
The hydraulic conductivity is a numerical value of a soil's permeability.
It represents the speed that water seeps through the soil; this speed is determined by several properties such as pore size, structure of the soil, and soil chemistry.
Sandy soils have higher permeability and higher hydraulic conductivities than do clay soils.
A designer needs to know the soil texture and conductivity to determine the size of the drains.
Drainage coefficient or water relief outflow rate
 The drainage coefficient is the rate of water removal needed to obtain the desired protection of the crop from excess water.
It is based on local field experience and is generally expressed in flow rate per unit of area.
Most drainage systems are designed to remove 0.005 to 0.01 inch of water per hour.
The designer determines the drainage coefficient according the deep percolation expected, rainfall received, and irrigation depths applied.
The designer then uses the drainage coefficients and the amount of area to be drained to determine the diameter of the lateral and collector drains needed.
Drain depth and spacing
 The spacing between drain lines may vary from 50 to 175 feet, depending on the soil type, the drain depth, and the crop grown.
In soils with moderate permeability, the drains can be spaced between 100 and 150 feet apart.
They must be spaced more closely in soils with low permeability.
A closer spacing reduces the amount of time to drain a certain volume of water but increases the cost of the system.
The spacing will also be influenced by the pipe diameter of the interceptor lines.
The depth of installation of the laterals is affected by the drain spacing, the crop and soil texture, and the desired drop of the water table.
The drains are usually placed at a minimum depth of 6.5 feet  in arid areas and at 5 feet in humid areas.
Soil type	Soil	Drain spacing  and drainage efficiency for	Drain depth
 permeability	various hydraulic conductivities	
 Raymond-Rio Clay Loam	Olmito-Runn Silty Clay	Very low to low	Fair drainage 	66-100	5.0-6.0
 Hidalgo Sandy Clay Loam	Moderately low	Good drainage 	5.0-6.0
 Laredo Silty Clay Loam	to moderate	79-150
 Willacy-Pharr-McAllen	Fine Sandy Loam	Moderately high	Excellent drainage 	97-175	5.0-6.0
 Table 2.
Examples of drain lateral spacing and depth usually adopted in the Lower Rio Grande Valley, Texas, for different soils.
Fig.
6.
Comparison of water table level in drained and undrained conditions with root and plant development and water flux exchanges.
Installing a relief drainage system: a step-by-step process
 To install a drainage system, follow these steps:
 1.
Analyze the economic feasibility of installing a drainage system to ensure that the predicted net return will offset the initial cost.
2.
Review regulations and assess the environmental impact of building the drainage system.
Consider ways to avoid any harm to the environment, and adopt best management practices to protect the water quality of the area.
3.
Conduct field studies to determine the characteristics of the soil profile, such as soil texture and structure, stratification of the soil layers, field topography, soil variability on the farm, hydraulic conductivity of the soil.
Determine the hydraulic conductivity in several parts of the field.
Know the variables of irrigation management, such as maximum rainfall and irrigation depths.
4.
Design the drainage system.
During the design process, determine the depth of installation of the relief laterals, the maximum length and diameter of the laterals and collector lines, and the grade of the drainage pipes.
5.
Install the drainage system:
 a.
The trencher machine is moved to the desired starting position.
b.
A back hoe digs a hole where the trencher will install the first drainage lateral.
C.
The trencher machines starts trenching 
 d.
The trencher lays the pipe at the desired depth  at the bottom of the trench as shown in Fig.
11.
e.
The trencher machine injects the drainage pipe as it uncoils from its roll.
f.
The grade of the trencher is determined by a global position system or laser system such as the one shown in Fig.
13.
g.
The laterals are tied to the collector using tees.
Figure 7.
Moving the trencher to install the subsurface drain pipe.
Figure 8.
Digging a hole to start installing the subsurface drain.
Figure 9.
Installing an interceptor drain tile.
Figure 10.
A trenching machine is used to install an interceptor drain lateral.
The two disks help backfill the trench.
Figure 11.
The interceptor drain lateral is placed at the bottom of the trench.
Figure 12.
The machine unrolls the polyethylene pipe as it is laid into the soil by the trencher.
Figure 13.
A dual grade laser gives the grade to the trencher.
Figure 14.
Collector drain tee.
Figure 15.
The interceptor drain is connected to the collector drain.
Economics of installing drainage systems
 To be cost effective and generate a return on the investment, the artificial drainage system must be designed properly.
In the Lower Rio Grande Valley, the cost of an on-farm drainage system can range from $400 to $600 per acre.
The cost of a drainage system depends on several factors, including the drain spacing, the length and diameter of the collectors, the number of outlets, and the elevation and proximity of the open drains.
The elevation of the drain ditch will determine whether the system will require a sump pump and electricity.
The period needed to obtain a return on investment for the installment of the drainage system depends on factors such as actual and potential crop yield gains after the installation of the system, compared to the losses of crop value from salinity and water table conditions before drainage.
Crop		Ib/acre	Yield	Price	Yield	loss	Value of	loss	investment	Returns of	per acre*	investment*	Years to	recover
 Grain sorghum	6,000	$ 9.80	/cwt	10%	$ 58.80	15.9
 Sugarcane 	10,000	$ 0.12	/lb	10%	$ 120.00	$ 	7.8
 Grain sorghum	6,000	$ 9.80	/cwt	20%	$ 117.60	8.0
 Sugarcane 	10,000	$ 0.12	/lb	20%	$ 240.00	$ 85.31	3.9
 Grain sorghum	6,000	$ 9.80	/cwt	30%	$ 176.40	5.3
 Sugarcane 	10,000	$ 0.12	/lb	30%	$ 360.00	$ 174.71	2.6
 Grain sorghum	6,000	$ 9.80	/cwt	40%	$ 235.20	4.0
 Sugarcane 	10,000	$ 0.12	/lb	40%	$ 480.00	$ 264.11	1.9
 Grain sorghum	6,000	$ 9.80	/cwt	50%	$ 294.00	3.2
 Sugarcane 	10,000	$ 0.12	/lb	50%	$ 600.00	$ 353.51	1.6
 *Figures are based on a $600 per acre cost of drainage, a $334.92 per acre interest cost for a 10-year loan at 9.0% rate and depreciated over a 10-year period.
Table 3.
Example of a projected return on investment for the installment of subsurface drainage on land where salinity substantially reduced yield
 the investment on the drainage system for grain sorghum alone and 7.8 years for sugarcane alone.
Similarly, a 20 percent yield loss represents a gross returns loss of $117.60 and $240.00 per acre for grain sorghum and sugarcane, respectively.
The return of investment is $85.31 per acre on a 50-50 percent mix of grain and cane, and it will take 8.0 and 3.9 years to recover the initial investment on the drainage system for sorghum and cane, respectively.
Farmers' experiences with the performance of subsurface drainage
 Farmers in the Lower Rio Grande Valley of Texas have reported two main reasons for installing drainage sysitems:
 To alleviate high water tables and salinity problems, which has caused poor germination and yield loss
 To improve poor water infiltration, which has impeded field operations
 The farmers attributed these problems to several causes: the natural soil texture of the region characterized by poor hydraulic conductivity; long-term overirrigation,
 especially for crops such as sugarcane; and seepage from irrigation canals.
The growers mentioned that irrigation districts in the late 1960s greatly reduced the seepage problems by replacing canals with pipelines, which enabled these soils to recover completely.
Unfortunately, after Hurricane Beulah swept through in 1967, some farmers noticed that the water table rose drastically.
The storm saturated the soil profile for a long period, and salt accumulated in some fields.
Some farmers installed drainage systems to counteract the use of saline runoff water on good, nonsaline soils over several years.
Saline had built up in the soils, precipitating the need for drainage systems to reclaim the fields.
Some farmers also noted that their fields were located on low topographical places and in some instances their soils presented clay barriers in the lower profile, resulting in stagnant water and salt buildup especially after a big rainfall or irrigation event.
Relief drainage has been extensively used to lower water table and leach the salts accumulated over the years on the soil surface.
Some growers have working systems made of either clay tiles that were installed in the 1940s,
 surrounded by a gravel layer and a tarpaper on the outside to limit clogging.
Other systems made of concrete tiles with fiberglass joints were installed in the 1960s.
Several farmers have installed drainage systems over several seasons according to their available budgets.
Some farmers installed drains at 200-foot spacing even if they were recommended for 100-foot spacing.
Most of them later added additional drain lines between those lines.
However, some growers installed subsurface drainage little by little-such as one lateral line at a time-whenever they felt it was needed, without any design.
Recently, several government programs have offered cost-sharing for the installation of the systems under the supervision and design of a field engineer.
These programs, such as the Environmental Quality Incentives Program under the Natural Resource Conservation Service, have resulted in the most efficient systems, which have benefited the farmers.
The farmer, in exchange, needs to adopt the best irrigation management practices to reduce environmental impacts.
In some clay soils, water from upper irrigated lands resulted in stagnant water downhill.
Interception drainage was installed in those soils to capture that water.
It has been also installed to capture seeping water coming from irrigation canals.
In some cases, these interceptors have been enough to improve and restore soil and salt conditions and avoid the cost of a large-scale drainage relief system.
However, each field was previously laser-leveled and separated by a few feet of elevation against the next one.
Farmers also mentioned that in some cases, the installation of a subsurface drainage system did not improve their conditions, especially in Olmito clay soils.
Water that drains from a property may have been polluted by sediment, nutrients, and pesticides.
Runofffrom agricultural lands and irrigation sometimes causes natural streams to have low levels of dissolved oxygen.
These levels may be too low to meet the requirements for aquatic life designated by the State of Texas and described in the Texas Water Quality Standards.
An indication of low quality could be the increase of fish kills in natural streams.
Because water is a precious resource, drainage water may be reused or managed to avoid harming the environment.
To reduce the runoff of nutrients, residues, and sediment from agricultural lands:
 Avoid over-fertilization, and control the placement and timing of fertilizer applications.
Manage pests responsibly by monitoring thresholds and taking into account beneficial and harmful pests.
Rotate crops and manage residue to avoid transporting sediment in which nutrients and pesticides can attach.
Apply leaching irrigation depths but avoid overirrigation and waste by scheduling irrigation.
Where necessary, consider the following additional practices also to reduce erosion and runoff: leveling irrigation land, installing grade stabilization structures, reducing tillage, and installing filter strips between the drainage ditches and irrigated field.
Filter strips are areas of herbaceous vegetation situated between cropland, grazing land, or disturbed land  and environmentally sensitive areas.
The use of artificial drainage practices on lands that are or have a potential to be wetlands is strictly prohibited.
Soils with poor natural drainage can reduce yields and profits for farmers.
Those problems can be solved by installing a properly designed an artificial drainage system.
In addition to the agricultural factors, farmers need to consider the environmental effects of installing an onfarm drainage system.
Valuable suggestions and recommendations were made for this manuscript by Boyd Davis, who owns a company  that installs drains, and John Whitfield, who has installed several drain systems on his farm.
Lou Garza and Bob Wiedenfeld also made suggestions to improve this manuscript.
Texas A&M AgriLife Extension Service
CRITERIA FOR SUCCESSFUL ADOPTION OF SDI SYSTEMS
 Subsurface drip irrigation  systems are currently being used on about 15,000 acres in Kansas.
Research studies at the NW Kansas Research and Extension Center of Kansas State University begin in 1989 and have indicated that SDI can be adapted for efficient, long-term irrigated corn production in western Kansas.
This adaptability has been demonstrated on other deep-rooted irrigated crops grown in the region by demonstration plots and producer experience.
Many producers have had successful experiences with SDI systems; however most experienced at least some minor technical difficulties during the adoption process.
However, a few systems have been abandoned or failed after a short use period due to problems associated with inadequate design, inadequate management, or a combination of both.
Both research studies and on-farm producers experience indicate SDI systems can result in high yielding crop and water-conserving production practices, but only if the systems are properly designed, installed, operated and maintained.
SDI systems in the High Plains must also have long life to be economically viable when used to produce the relatively low value field crops common to the region.
Design and management are closely linked in a successful SDI system.
A system that is not properly designed and installed will be difficult to operate and maintain and most likely will not achieve high irrigation water application uniformity and efficiency goals.
However, proper design and installation does not ensure high SDI efficiency and long system life.
An SDI system must be operated at design specifications and utilize good irrigation water management procedures to achieve high uniformity and efficiency.
An SDI is also destined for early failure without proper maintenance.
This paper will review important criteria for successful adoption of SDI for Kansas irrigated agriculture.
MINIMUM SDI SYSTEM COMPONENTS FOR WATER DISTRIBUTION AND EFFICIENT SYSTEM OPERATION
 Design considerations must account for field and soil characteristics, water quality, well capabilities, desired crops, production systems, and producer goals.
It is difficult to separate design and management considerations into distinct issues as the system design should consider management restraints and goals.
However, there are certain basic features that should be a part of all SDI systems, as shown in Figure 1.
Omission of any of these minimum components by a designer should raise a red flag to the producer and will likely seriously undermine the ability of the producer to operate and maintain the system in an efficient manner for a long period of time.
Minimum SDI system components should not be sacrificed as a design and installation cost cutting measure.
If minimum SDI components cannot be included as part of the system, serious consideration should be given to an alternative type of irrigation system or remaining as a dryland production system.
Figure 1.
Minimum components of an SDI system.
K-State Research and Extension Bulletin MF-2576, Subsurface Drip Irrigation  Component: Minimum Requirements.
The water distribution components of an SDI system are the pumping station, the main, submains and dripline laterals.
The size requirements for the mains and submains would be similar to the needs for underground service pipe to center pivots or main pipelines for surface flood systems.
Size is determined by the flow rate and acceptable friction loss within the pipe.
In general, the flow rate and acceptable friction loss determines the dripline size  for a given dripline
 lateral length.
Another factor is the land slope.
An SDI system consisting of only the distribution components would have no method to monitor system performance and the system would not have any protection from clogging or any methods to conduct system maintenance.
Clogging of dripline emitters is the primary reason for SDI system failure.
The actual characteristics and field layout of an SDI system will vary from site to site, but often irrigators will want to add additional capabilities to their system.
For example, the SDI system in Figure 2 shows additional valves that allow the irrigation zone to be split into two flushing zones.
The ability to flush SDI systems is essential.
Filter systems are generally sized to remove particles that are approximately 1/10 the diameter of the smallest emitter passageway.
However, this still means small particles pass through the filter and into the driplines.
Overtime, they can clump together and/or other biological or chemical processes can produce materials that need removal to prevent emitter clogging.
The opening of the flushline valves and allowing water to pass rapidly through carrying away any accumulated particles flushes the driplines.
A good design should allow flushing of all pipeline and system components.
If the well or pump does not have the capacity to provide additional flow and pressure to meet the flushing requirements for the irrigation zone, splitting of the zone into two parts may be an important design feature.
The frequency of flushing is largely determined by the quality of the irrigation water and to a degree, the level of filtration.
A good measure of the need to flush is to evaluate the amount of debris caught in a mesh cloth during a flush event.
If little debris is found, the flushing interval might be increased but heavy accumulations might mean more frequent flushing is needed.
The remaining components, in addition to the water distribution components of Figure 1, are primarily components that allow the producers to monitor the SDI system performance, to protect or maintain performance by injection of chemical treatments, and to allow flushing.
The injection equipment can also be used to provide additional nutrients or chemicals for crop production.
The backflow preventive device is a requirement to protect the source water from accidental contamination should a backflow condition occur.
The flow meter and pressure gauges are essentially the operational feedback cues to the manager.
In SDI systems, all water application is underground.
In most properly installed and operated systems, no surface wetting occurs during irrigation, so no visual cues are available to the manager concerning the system operating characteristics.
The pressure gauges at the control valve of each zone allow the measurement of the inlet pressure to driplines.
Decreasing flow and/or increasing pressure can indicate clogging is occurring.
Increasing flow with decreasing pressure can indicate a major line leak.
The pressure gauges at the distal ends of the dripline laterals are especially important in establishing the baseline performance characteristics of the SDI system.
Flowrate and pressure measurement records can be used as a diagnostic tool to discover operational problems and determine appropriate remediation techniques.
Figure 2.
An example layout for a well designed SDI system.
Anomaly A: The irrigator observes an abrupt flowrate increase with a small pressure reduction at the Zone inlet and a large pressure reduction at the Flushline outlet.
The irrigator checks and finds rodent damage and repairs the dripline.
Anomaly B: The irrigator observes an abrupt flowrate reduction with small pressure increases at both the Zone inlet and the Flushline outlet.
The irrigator checks and finds an abrupt bacterial flare-up in the driplines.
He immediately chlorinates and acidifies the system to remediate the problem.
Anomaly C: The irrigator observes an abrupt flowrate decrease from the last irrigation event with large pressure reductions at both the Zone inlet and Flushline outlet.
A quick inspection reveals a large filtration system pressure drop indicating the need for cleaning.
Normal flowrate and pressures resume after cleaning the filter.
Anomaly D: The irrigator observes a gradual flowrate decrease during the last four irrigation events with pressure increases at both the Zone inlet and Flushline outlet.
The irrigator checks and find that the driplines are slowly clogging.
He immediately chemically treats the system to remediate the problem.
Figure 3.
Hypothetical example of how pressure and flowrate measurement records could be used to discover and remediate operational problems.
The heart of the protection system for the driplines is the filtration system.
The type of filtration system needed will depend on the quality characteristics of the irrigation water.
Clogging hazards are classified as physical, biological or chemical.
The illustration in Figure 1 depicts a pair of screen filters, while Figure 2 shows a series of sand media filters.
In some cases, the filtration system may be a combination of components.
For example, a well that produces a lot of sand in the pumped water may require a cyclonic sand separator in advance of the main filter.
Sand particles in the water would represent a physical clogging hazard.
Another common type of filtration system is the disc filter.
Biological hazards are living organisms or life by-products that can clog emitters.
Surface water supplies may require settling basins and/or several layers of bar screen barriers at the intake site to remove large debris and organic matter.
Sand media filtration systems, which consist of a bank of two or more large tanks with specially graded filtration sand, are considered to be well suited for surface water sources.
Water sources that have a high iron content, can also be vulnerable to biological clogging hazards, such as when iron bacteria flare-up in a well.
Control of bacterial growths generally requires water treatment in addition to filtration.
Chemical clogging hazards are associated with the chemical composition or quality of the irrigation water.
As water is pulled from a well and introduced to the distribution system, chemical reactions can occur due to changes in temperature, pressure, air exposure, or also by the introduction of other materials into the water stream.
If precipitants form, they can clog the emitters.
The chemical injection system is often considered to be a part of the filtration system but it can also be used to inject nutrients or chemicals to enhance plant growth or yield.
There are a variety of types of injectors that can be used; the choice of unit depends on the desired accuracy of injection of a material, the rate of injection, and the agrochemical being injected.
There are also state and federal laws that govern the type of injectors, required safety equipment , appropriate agrochemicals and application amounts that can be used in SDI systems.
Always follow all applicable laws and labels when applying agrochemicals.
Many different agrochemicals can be injected, including chlorine, acid, dripline cleaners, fertilizers, and some pesticides.
Producers should never inject any agrochemical into their SDI system without knowledge of the agrochemical compatibility with the irrigation water.
For example, many phosphorus fertilizers are incompatible with many water sources and can only be injected using additional precautions and management techniques.
If a wide variety of chemicals are likely to be injected, then the system may require more than one type of injection system.
The injection systems in Figures 1 and 2 are depicted as a single injection point, located upstream of the main filter.
Some agrochemicals might require an injection point downstream from the filter location to prevent damage to the filter system.
However, this should only be done by experienced irrigators or with an expert consultant, since the injection bypasses the protection of the filter system.
Positive Displacement Pump Injection System
 Figure 4.
Typical layout for an injection system showing many of the safety interlocks and backflow prevention devices required to prevent contamination of the environment..
Chlorine is commonly injected to disinfect the system and to minimize the risk of clogging associated with biological organisms.
Acid injection can also lower the pH chemical characteristic of the irrigation water.
For example, high pH water may have a high clogging hazard due to a mineral dropping out of solution in the dripline after the filter.
The addition of a small amount of acid to lower the pH to slightly acidify the water might prevent this hazard from occurring.
Water quality can have a significant effect on SDI system performance and longevity.
In some instances, poor water quality, such as high salinity, could cause soil quality and crop growth problems.
However, with proper treatment and management, water with high mineral loading, water with nutrient enrichment or water with high salinity can be used successfully in SDI systems.
However, no system should be designed and installed without first assessing the quality of the proposed irrigation water supply.
WATER QUALITY ANALYSIS RECOMMENDATIONS
 Prevention of clogging is the key to SDI system longevity and prevention requires understanding of the potential problems associated with a particular water source.
Information on water quality should be obtained  and made available to the designer and irrigation manager in the early stages of the planning process so that suitable system components, especially the filtration system, and management and maintenance plans can be selected.
Table 1.
Recommended water quality tests
 1.
Electrical Conductivity  measured in ds/m or mmho/cm a measure of total salinity or total dissolved solids;
 2.
pH a measure of acidity where 1 is very acid, 14 is very alkali, and 7 is neutral;
 3.
Cations measured in meq/L, , includes; Calcium , Magnesium , and Sodium ;
 4.
Anions measured in meq/L, includes: Chloride , Sulfate , Carbonate , and Bicarbonate ;
 5.
Sodium Absorption Ratio  a measure of the potential for sodium in the water to develop sodium sodicity, deterioration in soil permeability and toxicity to crops.
SAR is sometimes reported as Adjusted  SAR.
The Adj.
SAR value better accounts for the effect on the HCO concentration and salinity in the water and the subsequent potential damage by sodium to the soil.
6.
Nitrate nitrogen  measured in mg/L;
 7.
Iron , Manganese , and Hydrogen Sulfide  measured in mg/L;
 8.
Total suspended solids a measure of particles in suspension in mg/L;
 9 Bacterial population a measure or count of bacterial presence in # / ml, ;
 10.
Boron* measured in mg/L;
 11.
Presence of oil**
 * The boron test would be for crop toxicity concern.
** Oil in water would be concern for excessive filter clogging.
It may not be a test option at some labs, and could be considered an optional analysis.
Results for Tests 1 through 7 are likely to be provided in a standard irrigation water quality test package.
Tests 8 through 11 are generally offered by water labs as individual tests.
The test for presence of oil may be a test to consider in oil producing areas of the state or if the well to be used for SDI has experienced surging, which may have mixed existing drip oil in the water column into the pumped water.
The fee schedule for Tests 1 through 11 will vary from lab to lab and the total cost for all recommended tests may be a few hundred dollars.
This is still a minor investment in comparison to the value offered by the test in helping to determine proper design and operation of the SDI system.
As with most investments, the decision lies with the investor.
Good judgments generally require a good understanding of the fundamentals of the particular opportunity and/or the recommendations from a trusted and proven expert.
While the microirrigation  industry dates back over 40 years now and its application in Kansas as SDI has been researched since 1989, a network of industry support is still in the early development phase in the High Plains region.
Individuals considering SDI should spend time to determine if SDI is a viable systems option for their situation.
They might ask themselves:
 What things should / consider before / purchase a SDI system?
1.
Educate yourself before contacting a service provider or salesperson by
 C.
Visit other producer sites that have installed and used SDI.
Most current producers are willing to show them to others.
2.
Interview at least two companies.
a.
Ask them for references, credentials  and sites  of other completed systems.
b.
Ask questions about design and operation details.
Pay particular attention if the minimum SDI system components are not met.
If not, ask why?
System longevity is a critical factor for economical use of SDI.
C.
Ask companies to clearly define their role and responsibility in designing, installing and servicing the system.
Determine what guarantees are provided.
3.
Obtain an independent review of the design by an individual that is not associated with sales.
This adds cost but should be minor compared to the total cost of a large SDI system.
Subsurface drip irrigation offers a number of agronomic production and water conservation advantages but these advantages can only be achieved with proper design, operation, and maintenance, so that the SDI system can have an efficient, effective, and long life.
One management change from current irrigation systems is the need to understand the SDI system sensitivity to clogging by physical, biological and/or chemical agents.
Before designing or installing an SDI system, be certain a comprehensive water quality test is conducted on the source water supply.
Once this assessment is complete, the system designer can alert the manager of any potential problems that might be caused by the water supply.
The old adage "an ounce of prevention is worth a pound of cure" is very appropriate for SDI systems.
Early recognition of developing problems and appropriate action can prevent larger problems.
While this may seem daunting at first, as with most new technology, most managers quickly will become familiar with the system and its operational needs.
The SDI operator/manager also needs to understand the function and need for the various components of an SDI system.
There are many accessory options available for SDI systems that can be included during the initial design and installation phases, and even added at a later time, but more importantly, there are minimum design and equipment features that must be included in the basic system.
SDI can be a viable irrigation system option, but should be carefully considered by producers before any financial investment is made.
The SDI operator/manager should monitor and record zone flowrates and pressures during ever irrigation event so that through observation of short and long term performance trends, operational problems can be discovered and remediated immediately.
The above discussion is a very brief summary from materials available through K-State.
The SDI related bulletins and irrigation-related websites are listed below:
 This paper was first presented at the 18th annual Central Plains Irrigation Conference, February 21-22, 2006, Colby, Kansas.
Contribution No.
06-197-A from the Kansas Agricultural Experiment Station.
Variable Frequency Drives for Irrigation Pumps
 Dr.
Matt Yost1, Tom Young2, Dr.
Niel Allen1, Dustin Larson3, and Jonathan Holt1 Utah State University Extension, 2Precision Automation Systems, and Wish-Northwest Irrigation Distributor 1
 What is a VFD?
Many irrigation systems have variable flow and pressure needs.
Variable frequency drives  are electric controllers that vary the speed of the pump motor, allowing the pump to respond smoothly and efficiently to fluctuations in flow and/or pressure demand.
They are also sometimes referred to as variable speed drives.
When installed correctly in the right applications, they can effectively reduce energy costs, decrease electrical system stress, and extend the life of a pump.
Due to their effectiveness, many energy companies and governments cost-share or incentivize their use.
This can sometimes lead to VFDs installed on pumps where costs outweigh benefits.
This guide will help irrigators and irrigation dealers understand when and where VFDs make sense.
When Does a VFD Make Sense?
A VFD can make sense in a variety of irrigation applications.
Here are 6 of the major applications where one might consider a VFD :
 1.
The load  varies on a single pump.
Some examples include multiple sprinkler systems  or zones with random start times.
2.
The load  varies on multiple pumps on the same main line.
A single VFD can help trim the total load when multiple pumps are on the system.
3.
The system needs to "soft-start" AND the load varies.
If you just need soft start, a VFD is usually not warranted.
4.
A smaller pump is needed and it is less expensive to use a VFD than to pull/rebowl the existing pump.
5.
When phase conversion  is needed.
6.
When an old pumping system needs major overhaul or replacement resulting from pumping system age and condition, or changes in the irrigation system that require different flows and/or pressures.
What Factors Should I Consider When Purchasing a VFD?
If you determine that a VFD might make sense for your application based on the six scenarios  above, the next step is to select the right product for your application.
Many VFD options from multiple companies exist.
It is wise to resist the temptation to skip immediately to cost when considering which VFD is right for you.
While cost is certainly important, many other factors will contribute to the performance and maintenance of your VFD for its useful life.
Seven considerations for purchasing VFDs are discussed in detail below.
Figure 1.
Automated pressure and flow control canal pumping station  including VFD  for pressurized irrigation systems in Fairview, Idaho.
Photo credit: Niel Allen.
1.
Warranty, Service, and Technical Support
 One of the first factors to consider for VFD purchases is the warranty, service, and technical support.
The importance of this step cannot be overstated.
Extended downtime for VFD or pump maintenance can get expensive extremely fast for most irrigation systems.
For warranties (both
 factory and manufacturer), consider these four questions:
 What is the duration ?
What does it cover ?
How quickly are warranty claims processed?
Are repair parts stocked near where the VFD will be used?
For service and tech support , consider asking these or similar questions:
 How long has the dealer, installing electrician, control panel manufacturer, and VFD manufacturer been in business?
Do they offer 24/7 support all year?
How far away is the nearest factory service center?
Who is responsible to service warranty claims?
Where is the nearest technician located?
Which certifications and qualifications do the technicians have?
What is available for phone technical support?
In addition to these questions, it may also be important to ask the supplier for references, tour the manufacturing facility, and if purchasing from an irrigation dealer, ask about the dealer's history and relationship with the VFD supplier.
The life cycle of a VFD is how many years the manufacturer intends to produce and support their product.
Drives go through four phases in their lives: Active, Classic, Limited and Obsolete.
The Active phase is the sales and manufacturing phase, following which the product moves into the Classic phase.
Complete life cycle support is guaranteed throughout these two phases.
In the Limited phase, product support is ramped down, ending in the Obsolete phase where product support is no longer available.
Be wary of VFDs that are near the limited and obsolete phases if parts and service are important for the long-term operation of your VFD.
3.
Cooling and Cleanliness
 The standard life expectancy of most VFDs is 10-15 years, yet many factors can influence this.
Some of these factors include initial quality, maintenance, environmental exposure, cooling, cleanliness, and protections.
Two of the factors to consider during the purchasing process are cooling and cleanliness.
There are three main types of VFD cooling methods.
In order from least to most expensive,
 these include air-to-air , airto-water , and air conditioner.
The cooling method influences cleanliness of the VFD, which also should be considered as it affects life expectancy.
Table 1 summarizes some of the advantages and disadvantages of these three types of cooling/cleanliness.
Most VFDs are designed for full operating loads between 32-104 F.
Consider extra cooling and heating devices if your possible environmental temperatures are outside of that range.
Table 1.
Advantages and disadvantages of cooling methods for variable frequency drives.
Least expensive initial cost	Best overall value	Works everywhere
 Simple to maintain	Below ambient temperatures	Below ambient temperatures
 Easily repaired or replaced	Simple to maintain	No plumbing needed
 Closed-loop cooling	Closed-loop cooling
 Cabinet stays clean	Cabinet stays clean
 Uses ambient air temperature	Relies on water temperatures	Uses electricity
 Allows dirt and dust	MUST be winterized	Can be costly to repair
 Clogs up easily and fast	Requires some maintenance	Requires some maintenance
 Cabinet runs warmest	Requires initial plumbing	Requires A/C technician
 Uses electricity	Cannot be field repaired
 Most VFDs have a fully integrated control panel where all the needed components are in a single cabinet with single source accountability.
One reason for this is that it saves VFD manufacturers and installers time and money.
Because a single control panel is used, a VFD sits inside a steel cabinet confined in the generated heat.
That is why cooling  is SO important.
In addition to cooling, other protections for your VFD investment are important to consider during the purchasing process.
These include protection from i) dirt/dust buildup on circuit boards and fans; ii) environmental contaminants such as moisture, chemicals, smoke, bugs, rodents, or snakes; and iii) power quality problems such as line surges, phase loss phase reversal, low voltage, high voltage, and lightning.
Remember that most VFDs have built-in internal protection from power fluctuations, but none are capable of absorbing or
 protecting from moderate-to-major high voltage events.
The appropriate protections usually help reduce downtime and maintenance costs, and improve life expectancy.
Several other low-cost additional protection devices should be considered:
 Voltage monitors with interrupt relays
 Lightning and surge arrestors
 Harmonic filters 
 These low dollar add-ons will greatly increase your VFDs chances of surviving a harmful line disturbance and also increase your chance of meeting the VFD manufacturer's warranty requirements.
Figure 2.
Schematic of major components of an integrated VFD control panel.
When trying to decide which power input protections are necessary, in regard to power output, it is also wise to consult with the motor manufacturer prior to installing a VFD.
Every motor manufacturer may have a different insulation class and National Electrical Manufacturers Association  rating standard; therefore, every type of motor has a different protection requirement.
Most newly manufactured motors are built with "inverter duty" windings SO that they are more compatible with VFD operation.
Older motors may not have inverter duty rated windings, but can still be successfully operated long term with a VFD.
There are several available options to help protect motors, and they are typically low-cost additions well worth including.
5.
Sizing and De-Rating
 Selecting the correct VFD size is crucial for optimal performance and proper return on investment.
VFDs are marketed by horsepower rating and sized by amperage.
Three major things to ask about when sizing a VFD include:
 1.
What is the incoming voltage and phase to the pump?
2.
What is the full load amps  and service factor amps  of the pump?
Is the pump underor over-loaded?
VFDs are often sold
 undersized.
Be aware of the horsepower needs and size accordingly.
Most irrigation pump motors run in an overloaded condition and run higher amperages than other types of motors.
3.
What condition is the pump motor in and has it been rewound?
This is important because the old motor could damage the new VFD.
Always run a megohm test of the motor windings.
VFDs may also need to be de-rated for the following:
 Heavy-duty or overloaded motor
 Low input voltage or long motor cables
 Outdoor locations in the hot sun
 Single-phase or open-delta power
 A basic definition of harmonics is the amount of disruption that a VFD causes a power source due to its load.
Harmonics are important because electrical grids are governed by power quality standards.
The IEEE-519 Power Quality Standard  is the set of limits of electrical properties that allow electrical systems to function in their intended manner without significant loss of performance or reduced lifespan.
Problems can arise if VFDs interfere with the electrical grid beyond the allowable amount.
Some of the common problems that harmonics can cause include:
 1.
Increased utility current requirement
 3.
Nuisance circuit breaker tripping and fuses blowing causing lost productivity
 4.
Irrigation equipment malfunction
 5.
Noise transfer to other loads 
 6.
Nearby motor failures due to counter rotational harmonics
 7.
Incorrect meter readings, control relays malfunctioning
 8.
Communication or telephone interference problems
 9.
Excitation of power system resonance's creating over-voltages
 Calculations for harmonics are complex.
Work with your supplier to consider and calculate harmonics.
Correct calculations need to include these six factors:
 1.
Size of transformers in kva
 2.
Impedance rating of transformers in "Z" percentage
 3.
Isc value short circuit current rating
 4.
IL value total linear and total non-linear demand load current
 5.
Load in amps
 6.
Point-of-common coupling 
 Depending on the harmonic calculation results, a variety of additions such as a choke, reactor filters, or active front-end may need to be integrated into the VFD cabinet or installed separately in their own cabinets.
If you have determined that a VFD is economical for your irrigation systems, follow these tips to ensure your VFD is functional for its productive life:
 A simple, inexpensive sunshade will extend the life expectancy of your VFD.
Keep the air intakes on your cooling system clean and free flowing with no obstructions to air flows; a slight obstruction or build-up of dirt can heat up your panel.
Clean, maintain, and replace filters as recommended.
Install the pressure sensor for the VFD near the last span of the pivot or at the critical location using a telemetry system, if needed, to optimize performance.
In the correct applications, VFDs can be a great way to save energy and protect and extend the life of irrigation pumps and motors.
VFD economics will be highly dependent on the conditions on each field or set of fields.
Considering the complete costs of ownership should ensure that VFDs are purchased and installed where they will be economical.
When is the Best Time to Stop Irrigating?
Duane R.
Berglund  231-8135 NDSU Extension Agronomist
 The last watering of the season can be as important as the first.
To ensure optimum yields, adequate soil moisture must be available to crops until they are physiologically mature.
Applying excessive irrigation water to the root zone beyond maturity can result in reduced profits.
For management decisions on final irrigation, you will need to know the current moisture condition of your soil and the amount available for crop use.
Both soil texture and effective root zone will determine the amount of water that can be stored for crop utilization.
Stage of crop maturity and weather conditions will affect the period when the crop continues to use water prior to maturity.
Know the signs and symptoms of physiological maturity in crops you are irrigating.
Both the extra savings of irrigation and peace of mind that the crop is safe from frost are worth knowing.
Some crops, such as corn, can endure an increased soil water deficit as the crop nears maturity, while others, such as potato or alfalfa, should continue to be irrigated until harvest, maturity or frost.
Corn should be irrigated until sufficient soil moisture is available to ensure that the milk layer of the kernel moves down to the tip of the kernel or black layer formation.
If the milk layer is a third to halfway down the kernel no additional water application is needed.
Physiological maturity is reached about 55 days after 75 percent of the plants have visible silks.
The grain moisture may range from 32 to 40 percent at the time depending on the hybrid.
Yellow dent corn is usually well dented at physiological maturity.
Once corn is physiologically mature, the drydown rate is approximately 0.5 percent moisture loss per day.
Dry edible bean: The last irrigation should occur when the first pods are filling, or irrigation stopped when 50 percent of the leaves are yellowing on the plants.
When over watered, indeterminate varieties  may continue to vine and set flower with delayed maturity.
For navy bean, physiological maturity is reached when at least 80 percent of the pods show yellowing and most are ripe, with 40 percent of the leaves still green.
Pinto beans are physiologically mature when 80 percent of the pods show yellowing and mostly ripe and only 30 percent of the leaves are still green.
Beans within pods should not show evidence of any green.
If the beans have begun to dry, irrigation will not be needed because the beans no longer are removing much water from the soil profile.
Soybean should be irrigated until sufficient moisture is available to allow full bean development and pod fill.
This stage is when leaves are yellowing  and all pods filled with lower pods just starting to turn brown.
At physiological maturity, pods are all yellow and over 65 percent of the lower pods have turned brown.
Beans within pods should have little evidence of green color and should be shrinking.
Studies do show that yellow pods sprinkled with brown are the best clue of physiological maturity.
Usually if one or two pods show this symptom on the upper two or nodes of the plant the plant has reached P.M.
The soybeans also should be tolerant of a killing frost at this time also.
Sunflower should be irrigated until sufficient moisture is available for the sunflower achenes  to fill.
This is when the back of the head turns from a lime green to yellow-green color and ray petals are completely dried.
Potato will utilize soil moisture until harvest.
Maturation stage begins with canopy senescence as older leaves gradually turn brown and die.
Research has shown final irrigation can be used to reduce bruising during the harvesting process.
On sandy soils, soil moisture content between 60 to 80 percent of field capacity  provides conditions for a desirable soil load into the harvester with optimum separation of potatoes and soil.
This soil moisture level also minimizes physical tuber damage.
If soil is dry before harvest, a final irrigation should be applied at least one week prior to harvest to raise the soil moisture level and raise the tuber hydration level.
Alfalfa should be irrigated to maintain active growth until growth is stopped by hard frost.
Alfalfa going into the winter with adequate soil moisture has a much better chance of little or no winterkill.
Small grains should be irrigated until adequate soil moisture is available to bring the crop to the hard dough stage.
Sugarbeet will utilize moisture until harvest time.
Irrigation is usually terminated seven to 14 days before harvest to allow the soil to dry.
Evaporation Loss During Sprinkler Irrigation
 Both agricultural crops and landscapes are extensively irrigated in Florida, and sprinkler irrigation is widely used for both types of plants.
In 1992, approximately 625,000 acres of commercial agricultural crops in Florida were irrigated with sprinklers.
This figure represents almost 31 percent of Florida's 2,033,000 irrigated crop acres.
In addition, sprinklers are used to irrigate approximately 1 million acres of turf and landscape, including golf courses, commercial landscapes, and home lawns.
Method of Water Distribution
 When irrigation is applied by the sprinkler method, water is distributed over the irrigated area by spraying it through the air.
Nozzles may be rotated to cover circular or partcircle land areas, or they may be fixed and equipped with deflectors that break up the water stream and deflect it onto the area to be irrigated.
High uniformity of water application is achieved by overlapping the spray patterns from adjacent sprinklers.
During sprinkler operation, a stream of water is discharged into the air at high velocity.
Friction between the air and the water stream causes the stream to break apart into water droplets that fall to the surface, similar to rainfall.
When there is no wind, the sizes of droplets and their distribution patterns primarily depend on the nozzle design and any associated stream breakup mechanisms, the sprinkler's operating pressure, and the height of the sprinkler above the ground surface.
Under windy conditions, wind speed
 and direction also affect droplet sizes and distribution patterns.
During sprinkler operation, water evaporates from droplets sprayed through the air.
The amount of evaporation depends on three factors:  the climate demand;  the time available for evaporation to occur; and  the surface area of the water droplets.
The climate demand is a measure of the energy available for evaporation and the capacity of the air to store and transmit water vapor.
The evaporation process requires 580 calories of energy to convert 1 gram of water from the liquid to the vapor form.
This energy must be available from the environment surrounding the sprinkler.
Energy is readily available during summer months, as indicated by high air temperatures and high levels of solar radiation.
Conversely, low temperatures and low levels of solar radiation during winter months provide less energy for evaporation.
Air humidity is often expressed as relative humidity, which ranges from near 0 to 100 percent, with low values indicating dry air and high values indicating moist air.
Since dry air has a greater capacity for moisture, evaporation will occur more rapidly when the air is dry than when it is moist.
When the relative humidity is 100 percent, the air is saturated at its current temperature and cannot hold more water; thus, no further evaporation occurs.
This condition exists after dewfall at night, during foggy conditions, and
 during rainfall.
Also, since humidity levels are normally high during early morning and early evening hours in humid areas such as Florida, evaporation rates are low during these times on most days.
Wind increases evaporation rates by transporting water vapor away from the evaporating surface.
Wind also increases evaporation by transporting warmer or drier air from surrounding areas to displace the moist, cool air above an irrigated surface.
Time Available for Evaporation to Occur
 The time available for evaporation to occur is the relatively short time beginning when a water droplet leaves the nozzle and ending when it falls on the ground or vegetated surface.
When water is sprayed at greater heights and over greater distances, this opportunity time for evaporation is increased.
Thus, more evaporation would be expected to occur from a sprinkler installed on a tall riser than from the same sprinkler  installed on a short riser.
Wind speeds are faster at greater heights above the ground surface, where there are few obstacles to air movement.
Thus, evaporation loss from sprinklers mounted on tall risers is also increased because of these higher wind speeds.
Surface Area of Water Droplets
 Because evaporation occurs from the surface of the water droplets, the total surface area of the water droplets greatly affects the amount of evaporation loss.
For a unit volume of water, the surface area doubles as the droplet diameter decreases by half.
For this reason, evaporation rate increases as droplet size decreases if other factors remain constant, and the factors that cause droplet size to decrease will cause evaporation loss to increase.
Wind drift loss occurs when wind carries water droplets away from the irrigated area.
Droplets may either evaporate while they are being transported or may fall outside the irrigated area.
In either case, the water is lost because it is not available to the plants being irrigated.
Wind drift loss increases as wind speeds increase and as droplet sizes decrease.
At higher wind speeds, larger droplets can be transported by the wind, and droplets can be transported greater distances.
Estimating Sprinkler Evaporation Loss
 Many studies of evaporation loss during sprinkler irrigation have been conducted, and some are listed as references to this publication.
The most extensive early work was done by Frost and Schwalen  in Arizona.
In their 1960 article, Frost and Schwalen summarized the results of 700 field tests conducted under a variety of climate conditions.
They developed a nomograph that enables the user to estimate the percentage of evaporation loss during sprinkler irrigation as a function of sprinkler characteristics, operating pressure, and climate factors.
They concluded that evaporation loss could be accurately estimated using three climate factors: air temperature, relative humidity, and wind speed.
The Frost and Schwalen nomograph has been widely used to estimate sprinkler evaporation loss.
It has been published in several irrigation textbooks.
Seginer  found strong correlations between sprinkler evaporation loss in Israel and both solar radiation and air temperature.
He found weaker correlations with relative humidity and wind speed.
He concluded that evaporation loss due to wind drift was negligible for the 3 to 4 mph wind speed conditions of his study.
Myers et al.
conducted wind tunnel tests of sprinkler evaporation loss for typical Florida climate conditions.
They stated it is unlikely that evaporation from water droplets in transit from the sprinkler to the ground or plant surface could represent more than 5 percent of the water applied by typical sprinkler irrigation systems under Florida climate conditions.
The Frost and Schwalen  nomograph can be used to estimate evaporation loss for specific climate and operating conditions.
This nomograph allows the user to estimate the amount of evaporation loss for different times of day or for daytime and nighttime irrigation.
The Frost and Schwalen nomograph is shown in Figure 1.
It consists of vertical columns numbered 1 through 9.
Data must be entered in columns 1, 2, 5, 7, and 9.
The nomograph is used by drawing straight lines that connect the input data to calculate intermediate factors in columns 3, 4, and 8.
Finally, a straight line is drawn between columns 4 and 8 to provide an estimate of the percentage of
 evaporation loss in column 6.
The use of the nomograph is illustrated by the following example: Estimate the percentage of evaporation loss from a sprinkler with a 3/16-inch nozzle diameter operated at 40 pounds per square inch  when wind speed is 5 miles per hour , temperature is 90F, and relative humidity is 10 percent.
The sprinkler discharge rate in this example is 6.3 gallons per minute.
Figure 1.
Sprinkler evaporation nomograph.
This example represents very extreme climate conditions for a humid area such as Florida.
In most cases, the relative humidity would be much higher than 10 percent.
Therefore, the normal amount of sprinkler evaporation loss in Florida would be expected to be much smaller than that calculated in this example.
The solution is illustrated by the broken lines in Figure 1.
The calculations are done in the following steps:
 1.
Draw a straight line from the point representing 10 percent relative humidity in column 1 through the mark for 90F temperature in column.
Extend this line to indicate a vapor-pressure deficit of 0.63 psi in column 3.
2.
Draw a straight line from the point representing 0.63 psi vapor-pressure deficit in column 3 to the mark that indicates 3/16-inch  nozzle diameter in column 5.
Locate point A where this line intersects the pivot line in column 4.
Point A will be used in step 4 below.
3.
Draw a straight line from the mark for 40 psi nozzle pressure in column 7 to the point representing 5 mph wind speed in column 9.
Locate point B where this line intersects the pivot line in column 8.
Point B will be used in step 4 below.
4.
Draw a straight line from point A on the pivot line in column 4 to point B on the pivot line in column 8.
Read the percentage of evaporation loss where this line intersects column 6.
For this example, evaporation loss is 8.5 percent.
Thus, 8.5 percent of the water discharged from an irrigation system using 3/16-inch nozzle diameters and operating at 40 psi would evaporate under these extreme climate conditions.
Under typical Florida climate conditions, evaporation loss would not be expected to exceed this value.
For the 6.3 gpm sprinkler discharge rate, 8.5 percent, or 0.54 gpm, would be expected to evaporate, while the remaining 5.76 gpm would be expected to reach the soil surface or plant canopy.
Sprinkler Evaporation Loss in Florida
 Despite typical high temperatures, there is relatively little sprinkler evaporation loss in Florida because of high humidity levels and low wind speeds.
As an example, long-term average climate data for Gainesville, Florida are listed in Table 1.
Long-term daily maximum, average, and minimum daily temperatures are shown for each month and as annual averages.
Daily average temperatures range from 56F in winter to 81F in summer.
Daily maximum temperatures range from 68F in winter to 92F in summer.
Table 1 also lists long-term minimum and average daily relative humidity values for each month.
Maximum values  are near 100 percent for each month.
Relative humidity values do not change greatly throughout the year.
Minimum relative humidity values range from 40 percent in April to 53 percent in August.
Average relativehumidity values range from 70 percent in April to 77 percent in August.
Long-term daily and daytime average wind speeds also are listed in Table 1.
Daytime averages are shown because most evaporation takes place during daylight hours, when wind speeds and temperatures are highest and relative humidity values are lowest.
Daytime wind speeds were estimated as being 1.3 times the daily  average values.
In Gainesville, wind speeds are highest  during February and March and lowest  in August.
The combined effects of temperature and relative humidity determine the vapor pressure deficit.
The vapor pressure deficit is a measure of the dryness of the air; thus, it is an index of the evaporation rate.
Figure 2 shows the general relationships among air temperature, relative humidity, and vapor pressure deficit from the Frost and Schwalen  nomograph.
This figure illustrates that the vapor pressure deficit  will be highest when temperatures are high and the relative humidity is low.
Notice that when temperatures are low, the vapor pressure deficit will be low, despite the humidity level.
Also, when
 the relative humidity is high, the vapor pressure deficit will be low, despite the temperature.
Figure 2.
Air vapor pressure deficit as a function of temperature and relative humidity.
Because high humidity levels are typical in Florida, the vapor pressure deficit is typically low despite the high temperatures.
Figure 3 shows monthly vapor pressure deficits for Gainesville.
These were calculated from the temperature and relative humidity data in Table 1 using the Frost and Schwalen nomograph.
Both maximum and average monthly values were calculated.
The maximum values were calculated from the maximum temperature and minimum relative humidity data.
These values would be expected to represent peak vapor pressure deficits occurring during the early afternoon, when temperatures are highest and humidities are lowest.
The average values were calculated from average temperatures and average relative humidity readings.
These values would be expected to represent average daily vapor pressure deficits, the average of both daytime and nighttime conditions.
Figure 3.
Long-term maximum and average monthly vapor pressures at Gainesville, FL.
In Gainesville, average daily vapor pressure deficits are low, ranging from 0.06 psi in January to 0.14 psi in July and August.
Maximum daily vapor pressure deficits are larger and more variable, ranging from 0.2 psi in January to 0.4 psi in July.
Monthly evaporation percentages for Gainesville were calculated using the vapor pressure deficit data from Figure 3 and the wind speed data from Table 1.
A mid-range sprinkler nozzle diameter  and a mid-range pressure  were assumed.
Figure 4 shows the monthly distribution of average and maximum daily evaporation percentages.
The average daily values were low and uniform at about 1.5 percent throughout the year.
The maximum  values were more variable, ranging from 2.1 percent in January and December to 3.1 percent in July.
Figure 4.
Maximum and average evaporation percentages for a 5/16inch sprinkler nozzle diameter and operating pressure of 45 psi at Gainesville, FL.
Reducing Evaporation Loss from Sprinklers
 Evaporation loss from a sprinkler irrigation system can be reduced by changing the sprinkler operating conditions to increase the sizes of water droplets or by irrigating when climate demands are low.
Evaporation loss will be reduced by changing either or both of the following operating conditions:  increasing the nozzle diameter, or  decreasing the operating pressure.
Both of these changes will increase the proportion of large droplets, thus decreasing the surface area from which evaporation can occur.
However, sprinkler users must follow the manufacturer's recommendations when selecting nozzle diameters and operating pressures.
Otherwise, poor distribution patterns will occur, reducing the uniformity of water application.
The effect of changing the nozzle diameter is illustrated in Figure 5.
Calculations for this example were made using Gainesville climate data for June and sprinklers operated at 45 psi.
As shown in Figure 5, the evaporation percentage is large when small nozzles are used.
It is small when large nozzles are used and other factors remain constant.
Notice that the evaporation percentage is not linearly related to the nozzle diameter.
It increases rapidly when nozzle sizes are decreased below 5/16-inch but decreases slowly when nozzle sizes are increased.
Figure 5.
Sensitivity of evaporation percentage to changes in sprinkler nozzle diameter for an operating pressure of 45 psi and June climate data at Gainesville, FL.
The effect of changing the operating pressure is shown in Figure 6.
Calculations for this example were made using Gainesville climate data for June and 5/16-inch nozzle diameters.
As Figure 6 illustrates, the evaporation percentage is small when small pressures are used; it is large when large pressures are used and other factors remain constant.
Also, the relationship between evaporation percentage and pressure is approximately linear.
It increased from 1.4 percent at 20 psi to 5 percent at 80 psi.
Figure 6.
Sensitivity of evaporation percentage to changes in sprinkler operating pressure for a 5/16-inch nozzle diameter and June climate data at Gainesville, FL.
The use of excessively large nozzles or excessively small pressures must be avoided.
Excessively large nozzles will increase sprinkler and distribution pipeline flow rates, making the system cost too high.
Also, soil infiltration rates may be exceeded, causing runoff.
Thus, allowable increases in nozzle sizes will be limited by economic considerations and production system characteristics.
Excessively low pressures will reduce the uniformity of water application and waste water because of low application efficiencies.
Sprinkler mechanisms will not operate properly at pressures that are too low.
Excessively low pressures also will produce droplet sizes that are too large, creating the potential for crop damage or soil erosion from the impact of the droplets.
Thus, allowable reductions in pressures will be limited by sprinkler operating characteristics and the requirement for uniform water applications.
Evaporation loss can be reduced by operating sprinklers only when climate demand is low.
This means operating sprinklers when relative humidity is high and air temperature and wind speed are low.
In Florida, the relative humidity is very high during nighttime, early morning, and late evening hours on most days.
At those times, air temperatures are also low and wind speeds are normally reduced, minimizing sprinkler evaporation loss.
Figure 7 illustrates the effects of wind speed on evaporation loss, using Gainesville climate data for June, sprinklers with 5/16-inch nozzle diameters, and operating pressures of 45 psi.
For this example, the relationship between evaporation percentage and wind speed ranging from 0 to 15 mph was approximately linear.
Evaporation loss increased from 2.1 percent to 8.0 percent as wind speed increased from 0 to 15 mph.
Figure 7.
Sensitivity of evaporation percentage to changes in wind speed for a 5/16-inch nozzle diameter, 45 psi, and June climate data at Gainesville, FL.
Reducing Wind Drift Loss
 Wind drift loss occurs when small water droplets are transported from the irrigated area by wind.
This occurs when droplets are small and wind speed is high.
If the wind is blowing when irrigation occurs, some wind drift loss is unavoidable.
To avoid excessive wind drift loss, irrigation systems should not be operated when wind speeds are high.
Also, a sprinkler should be operated only within the operating pressure range for which it was designed.
If operating pressures are too high, too many small droplets will be created and wind drift loss will increase.
Most sprinkler companies manufacture nozzles specifically designed to reduce the number of small droplets and minimize wind drift loss.
Increasing Evaporation Loss from Sprinklers
 Under some conditions, it may be desirable to increase the amount of evaporation loss from sprinklers.
Such increases would be desirable when sprinklers are being used for crop cooling, as is the case during the establishment of transplants, or when water disposal is the objective -for example, in the design of sprayfields for land applications of wastewater.
Evaporation from sprinklers cools plant and ground surfaces and the surrounding air.
Thus, sprinkler irrigation is used to prevent excessive water stress while plant roots  are developing.
It is often required to establish such fruits and vegetables as strawberries and cabbage, and many ornamental plants.
In the design of sprayfields for wastewater disposal, the size of the required sprayfield can be reduced if evaporation loss is increased.
Such reductions are possible because some of the water discharged from sprinklers evaporates before it reaches the ground or plant surface.
To increase evaporation loss, small nozzles should be used and sprinklers operated at high pressures and when climate demand is greatest.
Climate demand will normally be greatest during the early afternoon, when relative humidity is lowest and air temperature and wind speed are highest.
Excessively high operating pressures should be avoided because both diameter of coverage and water application uniformity will be reduced if the pressure is too high.
Also,
 sprinkler mechanisms may not operate properly at excessively high pressures.
Under windy conditions, the distribution of the very small water droplets created by excessive pressures will be easily distorted by wind.
These small droplets may be transported to surrounding areas by wind drift.
Under calm conditions, these small droplets will fall nearer the sprinkler, reducing the effective diameter of coverage and possibly reducing the uniformity of water application.
Thus, the maximum operating pressure should be limited based on the sprinkler manufacturer's recommendations SO that acceptable diameters of coverage and uniformity of water application may be achieved.
During sprinkler operation, some evaporation occurs from water droplets as they are sprayed through the air.
The amount of evaporation depends on  the climate demand;  the time available for evaporation to occur; and  the surface area of the droplets.
A nomograph for estimating evaporation loss from sprinklers was presented.
For climate conditions typical of Gainesville, Florida, the average daily evaporation loss would be expected to be about 1.5 percent.
The average loss would be expected to be about 3 percent for sprinkler operation during early afternoon hours on typical summer days.
The amount of loss would be very small for operation during nighttime, early morning, and early evening hours.
Sprinkler evaporation loss can be reduced by changing sprinkler operating conditions to increase water droplet size or by operating the system under conditions of low climate demand.
Climate demand is low at night and during early morning and early evening hours.
Evaporation loss can be increased by using small nozzles and operating sprinklers at high pressures to produce small water droplets, and by operating systems when climate demand is greatest.
Climate demand will normally be greatest during the early afternoon, when relative humidity is lowest and air temperature and wind speed are highest.
Sprinklers should not be operated outside the manufacturer's recommended pressure range because they may perform poorly under such conditions.
The Hybrid-Maize model predicted generally less rainfed corn yield in 2020 compared to 2019 across nine locations in Nebraska.
Across these nine locations, West  and South Central  sites have more than 50% rainfed corn yield decrease compared to 2019, and eastern sites  have almost the same the yield as 2019, while the rest of the locations have yield decrease of 25% , 30% , and 45% .
Average percent of fields by year fitting into the six categories.
The dry years 2020, 21 and 22 are different than the other years.
In 2021, out of 53 reports, 57% were ranked good, 6% were fair, 6% were wet late, 25% were wet early, 4% were wet all season, and 4% were very wet all season.
MAINTENANCE OF WHEELMOVE IRRIGATION SYSTEMS
 F.
Richard Beard, Agricultural Equipment, Structures and Electricity Robert W.
Hill, Biological & Irrigation Engineering Boyd Kitchen, Uintah County Extension Agricultural Agent
 A wheelmove irrigation system, also known as wheel line, side roll, or lateral roll system, constitutes a major investment on the part of a farming operation.
Regular maintenance of wheelmove equipment will reduce repair costs, help the system last longer, and keep irrigation efficiency at design levels.
This bulletin describes regular maintenance activities including pre-operational procedures, a schedule of regular maintenance, and guidelines for winter storage, that will maximize the life of wheelmove systems.
Each wheelmove manufacturer provides guidelines and manuals for equipment operation and maintenance.
Such information is the preferred source and should be referenced when performing irrigation equipment repair and maintenance.
The wheelmove is a mechanical irrigation system that can be moved intact, from one location in a field to another, by means of an internal combustion engine.
A wheelmove system consists of a power mover, lateral pipe with wheels, sprinklers, couplers, connectors, and flexible supply line.
The power mover is mounted in the center of the wheelmove system and provides the power to move or drive the irrigation system.
The joints of pipe that make up the lateral pipeline serve as the axle for the wheelmove system and are supported above the ground by wheels mounted midway along their length.
Sprinklers are located at the connections and ends of the lateral pipe, positioning a sprinkler head midway between each wheel and at the ends of the lateral pipeline.
Normally, a wheelmove system has impact sprinkler heads with levelers to keep the sprinklers in an upright position.
Located adjacent to each sprinkler is a drain that automatically empties the lateral pipeline when water pressure drops off.
The couplers between the pipe joints provide a watertight connection and also transmit torque, produced by the power mover, to the entire length of the system.
One end of the lateral line is connected via a flexible hose to a pressurized mainline pipe with risers at suitable intervals.
SPRING MAINTENANCE OF THE WHEELMOVE SYSTEM
 A wheelmove system should be tested and any necessary repairs completed prior to the start of irrigation season.
All irrigation systems should receive special attention at the end and prior to the beginning of each irrigation season.
If a wheelmove system has been properly prepared for winter storage, spring maintenance is much easier.
The following maintenance should be completed during the spring pre-operational inspection of the wheelmove unit.
1.
If the engine and/or transmission components were removed for repair or storage during the winter, they should be reinstalled and all gears and chains should be replaced according to manufacturer's specifications.
2.
The chain and gears of the drive mechanism should have dirt or debris removed and the teeth and chains should be lubricated.
If necessary the drive chains should be realigned.
Follow manufacturer's recommendations for lubricant selection and application.
3.
Check the oil level in the engine crankcase and fill it as needed, taking special care not to overfill.
If the engine oil is dirty or it was
 not changed last year, this would be a good time to drain and replace the engine oil.
4.
Clean the air filter or replace it, depending on what the manufacturer recommends.
Normally, the air filters in smaller engines may be cleaned and reused several times before they must be replaced.
A clean air filter is critical for prolonged engine life.
5.
Remove dirt, oil, and debris from the exterior engine surfaces, paying special attention to the cooling fins, the surfaces near the air intake, and the carburetor linkages.
6.
Check the fluid reservoir of the hydraulic transmission.
If needed, fill it to the proper level.
If the fluid appears dirty it may require changing.
If there is an inline filter in the pickup line of the transmission, this should be serviced also.
7.
Make sure the fuel tank is free of debris and fill the tank with clean fuel.
If the fuel tank was not emptied at the end of last season, drain the tank and fill it with new fuel.
Try not to use gasoline left over from the previous season.
8.
Inspect the entire length of the wheelmove unit, inspecting the wheels and power mover for loose bolts, equipment wear, and winter damage.
Repair as necessary.
9.
Grease wheel axles and main drive hub bearings with water resistant, multipurpose grease.
If available, follow manufacturer's recommendations concerning lubrication selection and application.
This bulletin provides generic information for the type and frequency of lubrication.
10.
To test the nozzles and connections, water must be pumped through the wheelmove system.
The cover on the power mover should be closed before turning the irrigation water on.
The wheelmove cover should be closed whenever the power mover is not being worked on.
Check all nozzles and
 impact sprinklers for plugging, mismatched sizes, breakage, corrosion or other damage caused by wear or winter weather.
Check couplers and connections for leaks, and do repairs/ replacements early.
It is a good practice to identify problem components at the end of the irrigation season and to have the replacement parts on hand for spring installation.
11.
Before testing the power mover, the stakes and/or tie-downs that anchored the irrigation system during winter should be removed.
It is a good ideal to complete the majority of maintenance activities before attempting to relocate the wheelmove unit.
12.
Special attention should be directed at the carburetor of gasoline engines.
If fuel is left in the carburetor through the winter, fuel passages may have become clogged by sediment, residue, or additives, which remain after the fuel evaporates and/or ages.
If gas is not entering the engine cylinder from the carburetor , the carburetor may require adjustment or cleaning before the engine will start and operate properly.
13.
If the engine on the power mover has not operated since last fall, the following activities are good practices to follow.
Make sure the drive mechanism of the wheelmove unit is disengaged before attempting to start the engine.
Remove the sparkplug to clean and set the spark gap of the electrode.
If the sparkplug is damaged or the electrode shows excessive heat erosion it should be replaced.
Pour a tablespoon of clean engine oil into the sparkplug hole to lubricate the piston and rings.
With the sparkplug removed and the sparkplug wire positioned away from the cylinder head, rotate the engine crankshaft to lubricate the cylinder and rings.
Reinstall the sparkplug, attach the ignition coil wire, and prime the carburetor.
Some engines do not have a manual method of priming the engine and must rely on the engine choke to prime the engine.
When cold starting  a small engine, completely filling the fuel tank often improves the starting characteristics.
Set the carburetor linkage in the start position and pull the starting rope.
If in good repair, the engine should start without difficulty.
Once the engine starts, blue smoke will exit the exhaust system for a few moments as the oil burns from the piston chamber and rings.
If the engine will not start there are three things that should be checked.
These are the ignition spark, fuel delivery, and cylinder compression.
If any of these items are not working properly, the engine will not provide the necessary power and often the engine will not start.
14.
To check the operation of the power mover, engage the transmission and slowly power the wheelmove unit forward or backward to make sure all wheels, chains, and gears are working properly.
When attempting to operate the power mover, make sure the wheelmove unit is straight or the ends are slightly lagging behind the power mover's direction of travel.
Also, wheelmove units should not be moved with water in the pipeline.
During spring maintenance activities, the engine and transmission of the wheelmove unit should receive special attention.
If they fail to operate during the growing season, the irrigation equipment will not readily advance across the field and, in addition to frustration, the producer risks yield losses.
Careful attention to these components will contribute to an irrigation season with fewer problems.
MAINTENANCE OF THE WHEELMOVE SYSTEM DURING IRRIGATION SEASON
 Regular maintenance of the wheelmove system during the irrigation season will prevent many of the problems that can occur during a busy irrigation season.
An operator will obtain far better service and performance from the wheelmove unit when it is regularly maintained throughout the irrigation season.
The daily maintenance procedures that wheelmove operators should perform are listed below.
1.
The wheelmove unit must be moved with the irrigation pipe  straight or with the ends lagging slightly behind the mover.
If the pipeline becomes crooked, or an end gets ahead of the center mover, the operator should manually pull the pipeline into proper position.
This should be done when the wheelmove system first begins to advance.
Do not attempt to operate the wheelmove unit with the ends ahead of the power mover.
If the ends are in front of the power mover, they will tend to roll toward the center, which can buckle the pipeline line.
2.
Do not move the wheelmove unit with water in the pipeline.
When the irrigation water is turned off the pressure release valves should drain the pipeline.
Allow the water to drain before relocating the irrigation unit.
A wheelmove system specifically the pipe couplers are not designed to carry the additional weight of water when being moved.
3.
Lubricate the wheel chains every two weeks with SAE 30 oil.
Adjust chain linkage to correct for chain stretch, and sprocket wear.
Realign chain sprockets when improper tracking occurs.
4.
Lubricate the wheel axle, main drive hub, and jack shaft bearings every two weeks with water-resistance, multipurpose grease.
5.
If water leaks occur at joints or drain plugs during irrigation, check the gaskets and pipeline
 connections for wear or cracks and replace them as needed.
Check and tighten the couplers and connectors as required.
6.
Check and replace worn nozzles and impact sprinklers.
This will keep the irrigation pattern and application rate at design specifications.
7.
Inspect and tighten bolts and nuts on the wheels, power mover, and engine mounts.
The power mover is mounted in the center of the wheelmove system and includes the engine, transmission, and drive wheels.
Maintaining the engine and transmission during the irrigation season is vital to irrigation scheduling.
The following are daily maintenance operations for the wheelmove engine.
1.
Check the engine oil once each week or every five operating hours.
Change the engine oil after every 25 hours of engine operation.
Engine oil should be changed more often if the air cleaner shows evidence of extremely dusty or dirty operating conditions.
When adding or changing engine oil, fill the crankcase to the proper level.
Under or over filling the crankcase can damage the engine.
2.
Inspect the air filter every time the oil is checked.
Clean the air filter or replace it after every 25 hours of engine operation.
More frequent cleaning or replacement is required under extremely dusty or dirty operating conditions.
The air filters in smaller engines may be cleaned and reused several times before they must be replaced.
Follow the manufacturer's guidelines for air filter cleaning and replacement.
A clear air filter is critical for prolonged engine life.
3.
Periodically remove the sparkplug to clean and set the spark gap of the electrode.
If the sparkplug is damaged or the electrode shows excessive heat erosion it should be replaced.
4.
Remove dirt, oil, and debris from the exterior engine surfaces, paying special attention to the cooling fins, those surfaces near the air intake, and the carburetor linkages.
5.
Check the fluid reservoir of the hydraulic transmission after every 25 operating hours.
If needed, fill it to the proper level.
If the fluid appears dirty it may require changing.
If there is an in-line filter in the pickup line of the transmission, this should be serviced also.
PREPARING THE WHEELMOVE SYSTEM FOR WINTER
 1.
After the last irrigation in the fall, relocate the wheelmove unit to the edge of the field next to a fence or to an area where it will be out of the way during the winter.
Each wheelmove manufacturer provides guidelines for equipment operation and maintenance.
Such information is the preferred source when performing wheelmove repair and
 maintenance.
The following guidelines are the general steps for winterizing a wheelmove irrigation system.
2.
Remove the end plug and empty any remaining water, debris or sediment that may have accumulated in the ends of the pipe, then replace the end plugs to keep birds and other animals out of the pipeline.
This will reduce the effects of corrosion.
3.
Leave the pipe joints coupled together and anchor the entire wheelmove system SO the wind cannot roll it.
Tie the unit to a fence or secure it with posts or anchors in the ground.
Secure the wheelmove unit every 200 to 400 feet depending on wind conditions in the area.
If the field is used for winter pasture, secure the irrigation system every 100 to 150 feet to prevent livestock from moving or damaging the wheelmove system
 4.
Water sediment is abrasive and can damage sprinklers and nozzles.
During the late fall, with the wheelmove unit operating, evaluate the system components and look for problems.
Mark for repair, worn impact sprinklers, nozzles, leaky pipes, gaskets and drain gaskets.
Note these problems during the fall irrigation season and purchase replacement equipment for installation during the spring maintenance activities.
5.
Lubricate all chains or remove and store them in a dry place to prevent rust and corrosion.
6.
Grease wheel axles and main drive hub bearings with water resistant, multipurpose grease.
7.
Secure the fiberglass cover over the engine for the winter months.
This cover should be latched or tied in place to keep wind from blowing it open and exposing it to winter weather.
PREPARING THE ENGINE AND TRANSMISSION FOR WINTER
 After each season's final irrigation, position the wheelmove at the edge of the field or out of the way for the winter.
All irrigation equipment should receive special attention at the end and prior to the beginning of each irrigation season.
If a wheelmove system is properly prepared for winter storage, placing the system in operation during the spring is much easier.
The following guidelines are the general steps for winterizing the engine and transmission of a wheelmove unit.
1.
If the engine is to be removed during the winter months, the engine maintenance can be completed after the engine is removed.
2.
Start the engine and after it has run for a few minutes, turn off the fuel tank and let the engine  run out of fuel.
Drain/siphon all of the fuel from the tank and flush any debris from the tank.
If some cases it may be necessary to start the engine, stop the engine, drain the tank, and restart the engine, for the fuel to be
 removed from the carburetor.
Storing the engine without fuel in the carburetor will improve the chances of trouble free starting in the spring.
3.
Check the engine oil and change it if needed, filling the crankcase to the proper level.
4.
Clean or replace the air filter as necessary.
5.
Remove the sparkplug and pour a tablespoon of clean motor oil into the sparkplug hole.
Position the sparkplug wire away from the cylinder opening and rotate the crankshaft by hand to lubricate the piston and the rings.
Replace the sparkplug.
6.
The engine should remain covered to protect it from the winter weather.
Exposure to moisture is the major problem that must be controlled.
7.
If appropriate, check the fluid reservoir of the hydraulic transmission.
If needed, fill it to the proper level.
If the fluid appears dirty it may require changing.
If there is an inline filter in the pickup line of the transmission, this should be serviced also.
The information included in this bulletin is provided to increase the life and operating effectiveness of your wheelmove system.
More detailed information concerning wheelmove systems may also be obtained from manufacturers and dealers of irrigation equipment.
Please contact a wheelmove manufacturer or local dealer for replacement parts and complete operating guidelines.
WHERE ELSE CAN YOU GET HELP?
Some information in this bulletin was adapted from The Colorado River Salinity Control Program, Information Bulletins 5, 6, and 7 by Ron B.
Sorensen and Robert W.
Hill.
According to rainfall gauges located near the TAPS fields, 8.92 inches of rainfall was collected from May 1 to Sept.
30, 2022.
In 2021, that amount totaled 14.45 inches, with 2020 being almost identical with 8.95 inches, following the wettest year in recent history in 2019 when 21.2 inches was collected.
Whereas 2018 was very similar to 2021 with 14.9 inches.
The 2022 TAPS irrigation season began earlier than last year with participants having the opportunity to irrigate starting June 6 and concluding Sept.
15.
An ETgage costs about $250 and can be placed on the outer edge of a field attached to a post.
It is filled with distilled water and should be read once a week.
It has a ceramic plate on it that allows water to evaporate from the unit.
In addition there is a canvas cover simulating the crop characteristics, typically for alfalfa.
As you can see from the photo it has a sight gage on the side that allows you to read how much water evaporated during the week.
ALTERNATIVE ENERGY SOURCES FOR IRRIGATION POWER UNITS
 Evaluation of Biofuel Driven Irrigation Pumps and/or Electric Generators for Use during Peak Electricity Demand
 The goal of this research is to support the development of a biofuel power unit industry in Nebraska to increase the use of agricultural resources, crops and the resulting biofuels that are produced in the region.
Nebraska companies have developed systems to utilize denatured ethanol and other biofuels in industrial power-units.
The successful validation and demonstration of these systems will support their adaptation in water pumping and electrical generation plant applications.
It also will document exhaust emissions and compare operating costs with traditional engines and fuels.
These systems could reduce peak load electrical energy demand resulting from electrical powered irrigation pumping stations, improve emissions compared to petroleum power irrigation pumping stations or peak load electrical generating stations, and may reduce production costs for irrigated farming operations.
Pumping Plant Efficiency and Irrigation Costs
 Inefficient pumps and power units are major contributors to excessively high irrigation costs.
To minimize fuel consumption and pumping cost, pumping equipment must be carefully selected, properly maintained and replaced when necessary to maintain high efficiency.
Efficient pumping plants with their lower pumping cost combined with efficient application of carefully timed irrigations can make the difference between profit and loss in irrigated crop production.
Factors which affect the amount of fuel required to pump a given quantity of water  are:  the pumping lift or vertical distance from the water surface to the point of discharge,  the pressure required at the pump discharge to operate the irrigation system and  the efficiency of each component  of the pumping plant.
Fuel requirements are lower when pumping lift is lower, discharge pressure is lower and pumping unit efficiency is higher.
Pumping unit components in good condition and carefully selected to match requirements of a specific pumping situation can operate at efficiencies as high as those shown in Table 1.
However, many pumping units on farms operate at efficiencies far below those shown.
Table 1.
Irrigation pumping equipment efficiency.
Pumps 	75-82
 Right angle pump drive 	95
 Reasons for low efficiency include wear, improper adjustment or failure to select equipment to match the specific pumping conditions.
An engine operating at 8 percent efficiency will use three times as much fuel to do the same amount of work (pump the same amount
 of water at the same total head) as one operating at 24.
percent efficiency.
A pump that is 25 percent efficient requires three times as much power  to do the same amount of work as a pump that is 75 percent efficient.
From the standpoint of pumping cost, a very serious condition exists when both the engine and the pump operate at low efficiency.
For example, if the engine operates at 8 percent efficiency and the pump at 25 percent efficiency, the pumping plant would use nine times as much fuel to pump the same amount of water as one with an engine efficiency of 24 percent and a pump efficiency of 75 percent.
An irrigation pumping plant has three major components: a power unit, a pump drive or gear head and a pump.
The pump lineshaft and the motor shaft of electric-powered pumping plants are usually directconnected which makes a pump drive or gear head unnecessary.
Pump.
A pump properly selected to match specific conditions of pumping rate, pumping lift and discharge pressure can operate at 80 percent efficiency, or more.
However, many pumps operate at much lower efficiency because of failure to select the pump to match pumping conditions, changes in pumping lift or discharge pressure, improper adjustment and wear.
Pump wear occurs rapidly and efficiency declines when the water contains sand or other abrasives.
The effect of pump efficiency on annual fuel cost is illustrated in Table 2.
Irrigation pumps should be selected to match specific well characteristics of well yield and pumping lift.
Add any required discharge pressure  to pumping lift to obtain total pumping head.
If the water source is a lake, pond or stream, substitute desired pumping rate for well yield.
Use pump manufacturer's performance ratings and the well pumping test results to obtain the best match for high pump efficiency.
Pump performance ratings or curves are available from the dealer or manufacturer, Figure 1.
The pump described would operate at 77 percent efficiency, or higher for any pumping situation between 600 gallons per minute with
 Table 2.
Influence of pump efficiency on annual fuel cost for pumping rate of 100 gallons per minute and 2,400 hours of annual operation.
For other pumping rates, multiply costs in the table by the appropriate number.
For example, for a pumping rate of 600 GPM, multiply costs by 6.
Pump	Pumping Lift in Feet
 	100	200	300
 Natural gas	75	$364	$728	$1,092
 $4.00 per Mcf	50	546	1,092	1,638
 25	1,092	2,184	3,276
 Electricity	75	$549	$1,097	$1,646
 $0.08 per KWH	50	823	1,646	2,469
 25	1,646	3,292	4,938
 Diesel	75	$555	$1,110	$1,664
 $1.00 per gallon	50	832	1,664	2,497
 25	1,664	3,329	4,993
 Propane	75	$529	$1,057	$1,586
 $0.60 per gallon	50	793	1,586	2,379
 25	1,586	3,171	4,757
 64 feet total pumping head and 800 GPM at 57 feet total head.
Peak efficiency of 82 percent occurs when pumping 800 GPM at 57 feet total head.
Performance information is available for every pump.
Use it to achieve maximum efficiency.
A thorough pumping test on new wells to determine the optimum well yield and pumping lift is essential for accurate pump selection.
Measurement of pumping rate and pumping lift on old wells at least once each year is a useful management tool.
A record of these measurements will help identify and diagnose pump or well problems and provide a basis for selection of a replacement pump, if that becomes necessary.
The measurements can be especially helpful in the event of sudden pump failure.
Power unit.
Power unit efficiency is also important to pumping plant performance.
Efficiency of electric motors up to 10 horsepower usually ranges between 75 and 85 percent.
Motors of 100 horsepower or larger
 Figure 1.
Typical pump performance curves.
Curves describe performance for one stage of a vertical turbine pump.
Stages would be added as necessary to obtain required total head.
usually attain efficiencies of 90 to 92 percent while motors in the 15 to 75 horsepower range may have efficiencies of 85 to 90 percent.
Regular maintenance to ensure proper bearing lubrication and unobstructed air passages will maintain high motor efficiency.
Efficiency of internal combustion engines is inherently low.
The top efficiency for automotive engines is 23 to 26 percent.
Heavy industrial engines may achieve efficiencies of 24 to 37 percent while light industrial engines have efficiencies of 25 to 26 percent.
Achievement of these efficiencies is possible only with engines in excellent condition, properly tuned, running at optimum speed and properly loaded.
Primary reasons for lower efficiency and higher fuel consumption are: wear, improper tuning and partial loading.
Partial loading may be difficult to overcome, especially in situations requiring relatively small engines.
Since every percentage point improvement in engine performance means reduced fuel consumption, checking engine suppliers and shops for the best engine for a specific job can pay good dividends.
Some shops offer engine modifications that improve performance.
Modifications have improved automotive engine efficiency 3 to 5 percent in some cases.
Each percentage increase in engine efficiency reduces fuel consumption about 5 percent.
An engine that operates at 19 percent efficiency will use 26 percent more fuel doing the same work than one operating at 24 percent efficiency.
Figure 2 illustrates the relationship between engine efficiency and fuel consumption using 24 percent as the "standard" basis for comparision.
Pump drive.
The pump drive transmits power from the power unit to the pump.
The lineshaft of electricdriven pumps is normally connected directly to the
 Figure 2.
Influence of engine efficiency on fuel consumption.
Based on 24 percent as "standard" engine efficiency.
motor shaft, eliminating the necessity for a pump drive.
When the pump is driven by an internal combustion engine, the pump drive changes the horizontal direction of the engine shaft to the vertical direction of the pump lineshaft.
The most common pump drive is a right-angle gear drive, or "gear head." It must be selected in the correct horsepower size and with an appropriate gear ratio to allow the engine and the pump to operate at optimum speeds.
Efficiency of right-angle gear drives is about 95 percent.
Belt drives may vary in efficiency from about 85 to 95 percent.
Efficiency of combined belt and gear head drives is about 80 percent.
Field Measurements to Determine Efficiency
 Determination of overall pumping plant efficiency requires measurement of pumping rate, pumping lift, fuel use and discharge pressure, if any.
Assuming that fuel use rate is determined from the installed utility meter or by measuring liquid fuel in the fuel tank, the only special equipment needed is an electric well sounder or an air line in the well to measure pumping lift, a flow meter to measure pumping rate and pressure gauge in the pump discharge pipe to measure discharge pressure.
The procedure for determining overall pumping plant performance and comparing it to a standard for irrigation pumping plants is described in Texas Agricultural Extension Service publication L-1718, "Evaluating Irrigation Pumping Plant Performance."
 Unfortunately, determination of overall pumping plant performance only shows whether overall performance is good or bad, it does not identify pump and power unit efficiency separately.
Efficiency of electric motors can be reasonably assumed and pump efficiency calculated, but pumping plants with internal combustion engines require a more comprehensive testing procedure to determine both engine and pump efficiency.
In addition to the measurements listed above, a complete pumping plant efficiency test requires measurement of the actual power output of the engine when the power unit is an internal combustion engine.
The drive shaft between the engine and gear head is replaced temporarily with a special drive shaft including a torque cell to measure engine power output.
Efficiency of the engine and the pump can then be determined during the test.
If the efficiency of either unit is very low, the test provides the basis for a decision about major repair or replacement.
Measurements to determine overall pumping plant efficiency can be made by most producers.
Determining overall pumping plant efficiency each year and maintaining a record of the measurements is a management practice that can pay excellent dividends.
If overall efficiency is found to be low, assistance of a pump company, consulting firm, service agency or organization can be obtained to perform a complete pumping plant evaluation to identify the problem.
Demonstration Program Results and Recommendations
 More than 500 pumping plant efficiency tests have been performed in a Texas Agricultural Extension Service demonstration program conducted since 1975.
Pump efficiencies range from less than 20 percent to more than 80 percent with an average of 55 percent.
The average overall natural gas-powered pumping plant efficiency is 11.6 percent with an average natural gas engine efficiency of 20 percent.
For comparison, the standard for natural gas-powered deep-well turbine pumping plants is 75 percent pump efficiency, 24 percent engine efficiency and 17 percent overall efficiency.
The demonstration tests show that average fuel use is 32 percent more than required by a pumping plant operating at the performance standard.
A summary of pumping plant performance data from the Extension efficiency testing demonstrations is shown in Table 3.
Table 3.
Average power unit and pump efficiencies, fuel consumption, and specific fuel cost for natural gas, electric and diesel pumping plants.
Extension pumping plant efficiency demonstration tests, 1975-85.
Natural Gas	VHS	Submersible	Diesel
 1.
Number of tests	455	91	38	35
 a.
Horsepower, HP	87	81	20	108
 b.
Fuel per HP,	12.3	-	-	.062
 C.
Efficiency, %	20	90	79	30
 a.
Flow rate, GPM	574	594	136	688
 b.
Pumping lift, ft.
300	267	248	289
 C.
Discharge head, psi	14	20	12	40
 d.
Efficiency, %	58	58	51	66
 4.
Overall efficiency, %	11.6	52	40.0	19.3
 5.
Specific fuel consumption	272	17.3	22.9	1.16
 a.
$ Per acre-inch	3.45	4.28	4.98	4.15
 b.
Specific water cost,	1.08	1.45	1.83	1.10
 *Natural gas-cubic feet @ $4.00 MCF Electricity-KWH @ $.08 KWH Diesel-gallon @ $.95 gallon
 There is no exact efficiency at which major repair costs are automatically justified.
Factors which influence the monetary effect of low pumping unit efficiency are pumping rate, pumping lift, fuel price and the number of hours the pumping unit is operated each year.
Projected savings, considering the combined influence of all these factors compared with the cost of pumping unit repairs, are the best basis for a decision about repairs.
Repair costs can often be recovered in 1 to 2 years when pumping level is 300 feet or more, pumping rate is 600 gallons per minute or more and pump efficiency is less than 50 percent.
Five to 6 years may be required to recover pump repair costs when pump efficiency is 60 percent, or more.
Higher fuel prices, increased pumping head and more annual operating time shorten the period required to recover major repair costs, even when pump efficiency is 60 percent, or higher.
The efficiency of engines in poor mechanical condition or improperly tuned or adjusted may be very low.
For example, fuel use does not change if one or more cylinders misfire but power output decreases drastically.
Lower engine efficiency caused by partial loading alone does not justify engine replacement.
Consider rotation of engines to other wells to improve loading.
Choose a smaller engine when normal replacement is needed.
Use of alternative fuels is often considered as a means of reducing pumping cost.
The cost of the amount of each fuel needed to produce the same amount of work must be considered.
The performance standard for irrigation pumping plants provides a basis for comparing the amount of fuel needed if all components of the pumping unit perform at the standard level.
On this basis, the following quantities of fuel would be needed to do the same work as 1 MCF of natural gas: 6.1 gallons of diesel, 9.7 gallons of propane or 75.4
 KWH electricity.
Use fuel bills to identify current fuel use.
Determine the quantity of an alternative fuel needed and apply the appropriate price.
However, to determine whether changing to a different fuel would be advisable, all costs of owning  and operating  the power unit must be considered.
High pumping efficiency is likely to be even more important in the future.
Although energy prices may moderate at times, the long term trend for increased price is not likely to change.
Identification of pumping rate, pumping lift and fuel use per hour for individual wells or pumping plants is recommended.
A record of these data determined regularly, perhaps annually, provides a basis for comparison of current and past performance and may prevent unwarranted repairs or allow timely scheduling of repairs to prevent costly down-time during the irrigation season.
Published by the Texas Agricultural Extension Service  and the Texas Agricultural Experiment Station  in cooperation with the Texas Water Resources Institute.
Educational programs conducted by the Texas Agricultural Extension Service serve people of all ages regardless of socioeconomic level, race, color, sex, religion, handicap or national origin.
David W.
Sams, Professor Plant and Soil Science
 Raised bed gardening offers gardeners the opportunity to increase production while decreasing garden area.
Raised beds are especially helpful to gardeners with limited gardening space and those who have difficulty with fine-textured, clayey soils which do not dry early.
Efforts to improve undesirable soils can be concentrated on growing areas only.
Raised beds drain and warm up earlier in the spring, which allows planting of cool season vegetables at recommended planting dates.
Raised bed gardens can be entered soon after rains or irrigation without compacting soils.
Water will penetrate better during heavy rains and there will be less danger of erosion.
Once they are built, raised beds are easy to prepare for planting and to care for throughout the growing season.
Root crops grow longer and straighter in mediumto coarse-textured soils.
Raised beds are well suited to a wide range of intensive gardening techniques such as row covers, trickle irrigation, intercropping, successive plantings, use of plant supports, compact varieties and mixtures of food and ornamental plantings.
Their orderliness usually produces an extremely attractive and appealing appearance.
Raised beds also have a few disadvantages.
They make it difficult or impossible to use large, mechanical equipment.
Their edges break down unless they are supported.
They require time, labor and perhaps money to develop.
They are not well suited to sprawling vegetables such as pumpkins and winter squash.
The close spacings used in raised beds can promote plant diseases by reducing air circulation and allowing plants to remain moist longer.
The most severe problem associated with raised beds, however, is drainage.
Rapid drainage is an advantage when a gardener is trying to plant early spring vegetables.
It is a disadvantage during the summer when drought stress can quickly lead to reduced yield and quality and increased physiological disease such as blossom-end-rot.
Sandy soils and very high beds are particularly susceptible to drying out.
Use low beds and add organic matter to them to help retain moisture.
Apply mulches to the surface of the beds.
Supplemental irrigation should also be considered essential when gardening on raised beds.
The simplest raised beds are temporary.
They may be formed by raking or plowing freshly worked soil into ridges and away from aisles where one walks.
Fouror 5-foot wide beds with 1 or 2 feet between beds are appropriate.
Be sure that you can reach half way across each bed from one side to plant, weed and harvest.
Make raised beds 4 to 8 inches high and any convenient length.
Raised beds should never be walked on once they are formed.
The absence of soil compaction in raised beds is one of their strongest advantages.
Compost worked into the soil annually reduces soil crusting and enhances seedling emergence.
A combination of soil from the aisles, top soil, compost, sand, shredded leaves and other material may be added to fill the raised bed to the desired height.
Some gardeners form permanently raised beds using a system known as double digging.
Double digging  is a lot more work than the above system but assures that the raised bed will contain soft, enriched soil to a depth of nearly 2 feet.
Flatten the top of temporary raised beds with a rake and they are ready to plant.
Fertilizer, lime and organic matter are applied to the entire garden area before temporary raised beds are formed.
These beds break down over the gardening season and must be reformed each year.
Gardening with temporary raised beds is really not very different from traditional gardening.
Formation of temporary raised beds is illustrated in figure 1.
Permanently raised beds make much better use of the advantages of raised beds.
Begin to form permanently raised beds by marking off the desired area with stakes and twine.
Fertilize, lime and cover the enclosed area with compost, shredded leaves or other organic material as desired.
Work this material into the soil as deeply as possible using a spading fork or rototiller.
Next, edge the beds.
Raised beds may be edged with old lumber, landscape timbers, railroad ties, concrete blocks or whatever is convenient.
Begin the double digging process by marking off the boundaries of the raised bed as described before.
Use a spading fork to work the bed.
Dig a trench 1 or 2 feet wide and one fork length deep across the end of the bed.
Remove this soil to the far end of the bed.
Apply fertilizer, lime and organic material to the trench.
Using the
 spading fork, loosen the soil in the bottom of the trench to the depth of the fork tines and work in the fertilizer, lime and organic material.
Now step back and dig another trench, placing the loosened soil on top of your previous trench.
Again add what you wish, loosen the soil in the bottom of this trench and mix in the materials you have added.
Continue to the end of the bed.
Fill in the last trench with soil removed from the first trench.
Edge the bed with the desired materials.
The loosened soil will be several inches higher than the adjoining aisles.
This double digging process is illustrated in figure 2.
Never step in a raised bed after it has been double dug.
The soil will settle gradually and beds will not need to be redug for one or even several years.
Raised beds will have maximum efficiency if plants are spaced equidistant from each other rather than in rows.
Plants should ideally just touch, forming a canopy over the soil when they are mature.
One way to accomplish this spacing is to set plants a little farther apart than suggested spacings in the row and use the same distance between rows.
It may be more practical to plant two or three rows of vegetables such as bush beans
 parallel to the bed length without worrying about equidistant spacings.
Small vegetables that tend to mature all at once or that are used only in small amounts may be planted in short rows across the bed.
Several plantings two or three weeks apart will maintain uniform production over many weeks.
Vegetables such as tomatoes and cucumbers do well in raised beds if they are supported and allowed to grow up rather than to sprawl.
Corn is not well adapted to raised beds as it needs to be well anchored.
Large sprawling vegetables such as watermelons and pumpkins are also better suited to traditional gardening systems than raised beds.
Small vegetables such as radish and lettuce may also be interplanted between tomatoes and other large vegetables.
They will mature and can be removed before the tomatoes need the space.
Reversing this procedure, peppers can be interplanted between lettuce plants in the same way.
To use raised beds efficiently, they should be well fertilized, watered and kept filled with growing plants.
When a spring vegetable is harvested, plant a summer vegetable in its place.
Follow summer vegetables with fall vegetables.
Recommended spacings for common vegetables in raised beds are given in Table 1.
Table 1: Recommended Spacings Between Plant Centers For Raised Beds*
 Vegetable	Inches Between Plant Centers
 * Gardeners new to raised bed gardening should use the wider spacings.
More experienced raised bed gardeners can use the closer spacings.
Domestic Water Quality Criteria
 Fact Sheet No.
0.513
 The appearance, taste or odor of water from a well or other source offers some information on obvious contamination, but chemical analysis is needed to detect most contamination in water.
Obvious contaminates include silt  and hydrogen sulfide, which can be detected by smell.
As a rule, the senses will not detect impurities that cause hard water, corrode pipe and stain sinks.
Two types of tests bacteriological and chemical are used to assess water quality.
The two tests are separate and distinct and normally are not made in the same laboratory at the same time.
The Colorado State University Soil, Water and Plant Testing Laboratory is equipped to analyze chemical tests.
The analysis determines chemical constituents of water as they relate to drinking or irrigation purposes.
Direct questions about testing water for bacterial or microbial contamination, including Giardia, to the local health department.
Bacteriological tests are used to determine if water is bacteriologically safe for human consumption.
There are tests based on detection of coliform bacteria, a group of microorganisms that are recognized as indicators of pollution from human or animal wastes.
Coliform bacteria are found in the intestinal tracts and fecal discharges of humans and all warm-blooded animals.
Anyone who wants a bacteriological test performed on their drinking water should contact the local county health department to obtain the specially prepared bottles and instructions for taking a water sample.
It is important to note that special techniques are required to collect samples because the samples can be contaminated if procedures are improper.
If the county does not offer a bacteriological test for water, contact
 the Colorado Department of Public and Environmental Health, 4300 Cherry Creek Drive South, Denver, CO 80246-1530,  692-3500.
Chemical tests identify impurities and other dissolved substances that affect water used for domestic purposes.
Water begins to decrease in palatability when the amount of minerals, i.e., dissolved salts, exceeds 500 to 1,000 ppm, but this depends on the nature of the minerals.
Note that sea water contains 30,000 ppm of dissolved salt.
Beyond these limits, the water becomes increasingly unpalatable.
Table 1 lists the constituents and parameters that are routinely determined on a water sample by the Colorado State Soil, Water and Plant Testing Laboratory.
Table 2 lists additional constituents in water that can be determined on request by the Colorado State Soil, Water and Plant Testing Laboratory.
Laboratory Reports What Do The Numbers Mean?
Most testing laboratories report quantities of chemical substances by weight in volumetric units such as milligrams per liter.
For all practical purposes, 1 ppm = 1 mg/L.
The factors reported on a water analysis report are discussed below and represent the parameters that are considered in the evaluation of domestic water quality.
The pH value is a measure of intensity of alkali or acid contained in the water.
Absolutely pure water has a pH value of 7.0.
In Colorado, the pH of well water normally is between 6.5 and 8.5.
Water with pH lower than 5 may cause problems due to corrosion because many metals become more soluble in low-pH waters.
A pH value higher than 8.5 indicates that a significant amount of sodium bicarbonate may be present in the water.
Two types of tests bacteriological and chemical are used to assess domestic water quality.
The Colorado State University Soil, Water and Plant Testing Laboratory is equipped to determine the chemical constituents of water.
Local county health departments or the Colorado Department of Health will perform bacteriological tests.
Chemical tests are needed to detect water contaminants such as nitrates, sodium, chlorides and the hardness capacity of water.
Table 1.
The parameters determined for the routine domestic water analysis test
 pH 	6.5-8.5
 Total Alkalinity as CaCO	400
 Total Dissolved Solids	500
 a Limits recommended for good quality domestic water.
Limits suggested by U.S.
Environmental
 Protection Agency; Drinking Water Regulations and Health Advisories, EPA 822-R-94-001, May
 b	Mandatory upper limit for nitrate.
*	Limits not established.
Table 2.
Additional tests that can be determined in water on request
 Nitrate 	10
 Nitrite 	1.0
 Secondary maximum contaminant level
 Table 3.
Hardness expressed as mg/L of CaCO2
 mg/L or ppm	Water Hardness
 Over 300	Very Hard
 aWWen expressed as grains of hardness, 1 grain = 17.1 mg/L.
Calcium and magnesium cause water hardness and result from limestone-type materials in underground soil layers.
Separate values are of minor concern but they are combined for calculating hardness.
Hardness is the soap-consuming capacity of water; that is, the more soap required to produce lather, the harder the water.
Hard water also causes greasy rings on bathtubs, film on dishes or hair after washing, and poor laundry results.
Problems caused by hard water in bathing or washing can be overcome by the use of synthetic detergents or packaged softening compounds.
The hardness of water may be removed by a water softening unit containing exchange resins.
This will result in the exchange of calcium and magnesium  by sodium SO it may be a concern to people on a low-sodium diet for medical reasons.
Do not use softened water for gardens, lawns or plants.
Hardness is reported as calcium carbonate in milligrams per liter.
A commonly used classification for hardness is given in Table 3.
Sodium may be of health significance to people on a low-sodium diet.
Sodium can be reduced or removed by expensive treatment systems, but when Ca and Mg are removed from water by passing through a water softener, sodium replaces it.
Potassium is an essential nutritional element, but its concentration in most drinking water is trivial and quantities seldom reach 10 mg/L.
Carbonates and bicarbonates are the major contributors to the "total alkalinity" that may be determined in a routine water test.
The alkalinity of a water sample is a measure of its ability to neutralize acids.
Naturally occurring levels of total alkalinity up to 400 mg/L as CaCO, 3 are not a health hazard.
Low alkalinity is associated with low pH values and may indicate potential for problems due to corrosion of metal in plumbing systems.
Chloride concentrations in drinking water may be important to people on low-salt diets.
Most people will detect a salty taste in water containing more than 250 mg/l of chloride.
Expensive treatment methods are needed to remove chloride from water.
Sulfate content in excess of 250 to 500 ppm  may give water a bitter taste and have a laxative effect on people not adapted to the water.
Expensive treatment methods are necessary to remove or reduce sulfate in a private water system.
Nitrate in excess of 45 mg/L  is of health significance to pregnant women and infants under six months.
Do not use high nitrate-water in infant formulas or other infant foods.
Considerably higher nitrate content apparently is tolerated by most adults.
Nitrate can be removed from private water supplies, but the equipment is expensive and not commonly used.
Total dissolved solids, also called "total mineral content" or "total residue," is the total amount of material remaining after evaporation of the water.
Values of less than 500 ppm  are satisfactory and up to 1,000 ppm  can be tolerated with little effect.
Fluoride is important in the development of teeth in infants and youth.
The optimum fluoride content to assist in the control of tooth decay is 0.9 to 1.5 ppm.
Excessive amounts are rarely found in Colorado waters, but a concentration over 3.0 ppm  may cause darkening of the tooth enamel and other undesirable effects.
Iron and manganese are nuisance chemicals that cause troublesome stains and deposits on light-colored clothes and plumbing fixtures.
Iron causes yellow, red or reddish-brown stains and deposits,
 while manganese stains and deposits are gray or black.
Excessive amounts also may cause dark discoloration in some food and beverages and cause an unpleasant taste.
Iron and manganese can be removed or reduced in a softener equipped with special resins or by small treatment systems involving aeration, filtration and chlorination.
Copper and zinc will cause an undesirable taste if concentrations are above the recommended limits.
A water softening system should significantly lower the levels of these elements.
Arsenic, selenium, barium, cadmium, lead and mercury are potentially toxic elements.
Fortunately, these elements rarely exceed the mandatory limits in most Colorado well water.
If high concentrations are found, it is necessary to remove these elements using expensive treatment methods, such as distillation or reverseosmosis.
Lead contamination in drinking water can come from lead pipes and leadbased solder pipe joints.
Aluminum, ammonium, phosphorus, nickel and molybdenum are additional constituents that can be determined by the laboratory.
Although no limits are established for these parameters, pollution of some sort is indicated if significant concentrations are detected in a water sample.
Taste and odor problems are difficult to solve.
Some inorganic compounds may impart detectable tastes without odor.
Hydrogen sulfide , when present, will impart an undesirable odor and taste.
Generally, undesirable tastes may be caused by any of numerous organic compounds.
These may be present naturally in the water or due to sewage or other surface contamination sources.
They can impart disagreeable taste and odor in minute concentrations (a few parts per billion or a few milligrams per
 kiloliter) and specialized chemical tests are needed to detect such small levels.
Turbidity in drinking water is caused by suspended sediments from erosion and runoff discharges.
The maximum contaminant level in drinking is one to five turbidity units.
Some water constituents can be removed or reduced by ion-exchange resins, distillation, reverse osmosis or a combination of these methods.
Other treatment processes might involve aeration or chemical oxidation followed by filtration.
Organics can be removed by filtration through charcoal, but this may not be an effective method for removing inorganic contaminants.
Treatment methods are specific to the type of chemical problems and generally are quite costly.
For additional information on water quality or treatment systems, refer to the fact sheets listed below or call the EPA Safe Drinking Water Hotline,  426-4791.
Design and Construction of Screened Wells for Agricultural Irrigation Systems
 Brian Boman, Sanjay Shukla, and J.D.
Hardin
 Irrigation wells must be capable of producing adequate water during peak seasonal use and under drought conditions.
Without a reliable, efficient, and economical supply of water, the entire irrigation system, regardless of the most sophisticated well head equipment design, becomes nearly useless.
The well is the "heart" of irrigation systems with groundwater supplies; it must be properly designed and compatible with the pump and distribution system to ensure long life, efficiency, and economic operation.
Water well construction  in the state of Florida is regulated by statute and various agency rules enforced by the Florida Department of Environmental Protection , principally through delegation to the five water management districts.
The potential ground water sources of irrigation water in Florida include the surficial, intermediate, and Floridan Aquifer systems.
The choice of aquifer is often dictated by location.
It also depends on the quantity and quality of water desired.
The cavernous nature of Florida's limestone formations produces abundant quantities of water from open bore holes  constructed into the limestone.
In some areas of Florida, especially near the coast, the depth of bore holes may be limited due to increases of salinity with depth.
If well
 yield is too low, additional properly spaced wells may be required.
Back-plugging of some irrigation wells has been successful as a remedy against upcoming deep saline waters.
Figure 1.
Typical well construction with hollow stem rotary drilling rig.
Credits: B.
Boman 
 2.
Brian Boman, professor, UF/IFAS Indian River Research and Education Center; Sanjay Shukla, professor, Department of Agricultural and Biological Engineering; and J.D.
Hardin, research coordinator, UF/IFAS Southwest Florida REC, Department of Agricultural and Biological Engineering; UF/IFAS Extension, Gainesville, FL 32611.
The Floridan Aquifer is the primary groundwater source for agriculture throughout the state.
Exceptions occur in coastal and extreme South Florida locations, where the Floridan Aquifer has poor water quality for irrigation.
In these areas, surficial and intermediate  aquifers are used along with surface water.
Surficial aquifer wells usually do not produce adequate quantities of water for large operations.
However, they may be suitable for small systems.
In areas where the Floridan Aquifer has poor water quality or is fully allocated and where the surficial and intermediate aquifers are suitable sources for agricultural irrigation use, screened wells may be required to withdraw the needed water in the most efficient manner.
A well consists of many or all of the following key parts: casing, grout, screen, open bore hole, and a well head configuration.
The standards enforced by the WMDs address each of these parts with alternatives given to account for variation in geology in various areas.
The local water management district should be contacted to obtain a consumptive use permit and information on well specifications.
In most cases, the district will be able to provide sufficient geologic data to help growers select the best well design with regards to water supply and construction cost.
The well drilling contractor should be licensed and have experience in the construction of screened irrigation wells.
The depth by which the water level is lowered below the static level in a well when pumping is in progress is called drawdown.
Drawdown is the difference, measured in feet of water, between the static water level and the water level during pumping.
This term represents the hydraulic head, in feet of water, that is needed to cause water to flow through the aquifer toward and into the well at the rate that water is being removed from the well.
Gravel-packed wells have a bore hole through the waterbearing formation that is larger in diameter than the well screen.
The zone immediately surrounding the well screen is made more permeable than the aquifer by filling the space between the face of the bore hole and well screen with graded sand or gravel that is coarser than the formation.
A well in which the well screen is placed directly in contact with the water-bearing sand and gravel is a naturally developed well.
The width of the openings in the screen is selected SO that fine sand in the aquifer immediately surrounding the screen can be removed by pumping during development to create a highly permeable zone consisting of the coarser formation particles.
The yield of the well per unit of drawdown, usually expressed as gallons per minute  per foot of drawdown, is called specific capacity.
It is obtained by dividing the pumping rate by the drawdown for a specific pumping period.
For example, if the pumping rate is 1500 gpm and the drawdown is 20 feet, the specific capacity of the well is 75 gpm per foot of drawdown.
Well Capacity or Yield
 The volume of water per unit of time discharged from a well is its capacity.
Well capacity is usually measured as the pumping rate in gallons per minute  or cubic feet per second.
This is the level at which water stands in a well when no water is being removed from the well either by pumping or natural flow.
It is generally expressed as the distance from the ground surface  to the water level in the well.
The level to which the water level rises in a well that taps an artesian aquifer is also referred to as the piezometric level.
An imaginary surface representing the artesian pressure or hydraulic head throughout all or part of an artesian aquifer is called the piezometric surface.
The piezometric surface is the real water surface, or the water table, in a water table aquifer.
The artesian aquifer is different from the water table aquifer in that the saturated zone is confined by the confining layers or aquicludes.
Well development is the process of using a variety of mechanical and chemical methods to correct damage to the formation which occurs during the drilling operation, and to remove the finer material adjacent to the screen or gravel pack.
The process cleans the openings or enlarges passages in the water-bearing sand and gravel SO that water can enter the well freely.
The ratio of the actual specific capacity of a well at the design yield to the maximum specific capacity possible calculated from formation hydraulic characteristics and well geometry is the well efficiency.
This is the same as the ratio of the theoretical drawdown to obtain design yield from a 100% efficient well to the actual drawdown measured in the well when producing at the design yield.
Efficiency is usually expressed as a percent.
The difference  between the theoretical drawdown and actual drawdown represents the head loss required to force water through the well screen.
This head loss should be a minimum.
Well efficiency should not be confused with pump efficiency.
Pump efficiency is a characteristic of the pump only and is completely independent of well efficiency.
For example, the pump efficiency may be 75% while the well efficiency of a poorly designed and constructed well may be only 45%.
Well Design and Construction Preliminary Investigation
 The preliminary investigation is the foundation upon which a well design depends.
An examination of records from existing wells in the area should be made to determine yield, depth, and characteristics of the aquifers presently being used.
Consultation should be made with the United States Geological Survey  or any other agency that may have geologic information about the area in question.
Reputable local well drillers are also an important source of useful information.
If sufficient records are unavailable, test holes should be drilled to allow selection of the site with the best water production potential and to help formulate the production well design for the selected site.
The information gained from test holes usually justifies the investment.
In drilling test holes, samples of the aquifer should be collected SO that sieve analyses and permeability tests can be made.
From the completed test holes, the well designer should determine aquifer thickness, aquifer depth, and static water level of the aquifer and estimate the yield and specific capacity of a full-sized production well.
A water sample should be collected and analyzed to determine the corrosion and/or incrustation characteristics of the water.
After the preliminary investigation and site selection, a well design can be selected which best utilizes the hydrogeological conditions present at the site.
The cased portion of the well should be designed first, and then the intake portion of
 the well.
The cased portion of the well consists of the well casing that serves as both a housing for the pump and as a vertical conduit through which water flows upward from the intake portion of the well to the level where it enters the pump.
The casing  is a very critical element in well construction.
Casing may be metallic  or nonmetallic  or ABS plastic).
It must be adequately seated in a consolidated formation  or attached to a screen suitably designed and situated in unconsolidated materials.
The purpose of casing is to seal off materials that may enter the pumping system from strata other than the aquifer selected and prevent mixing between aquifers.
To prevent contamination from surface flow into the well, the casing must be extended above surface flood water levels, and the top portion must be grouted with cement or an approved alternative material.
Figure 2.
Components of gravel-packed well.
Credits: B.
Boman 
 Casings are sealed in place with grout which protects against contamination by pollutants from the surface and acts as a seal for the casing seated into a consolidated formation.
In areas where the beds of consolidated material that the casing is seated into are friable , the grout also helps to prevent deterioration of the casing seat  due to turbulence developed during pumping.
Poor grouting may create problems later as pump impellers and other mechanical parts are scoured by small particles moving into the well around the casing shoe.
Poor grouting may also create voids where eventual corrosion of the casing wall allows unconsolidated matter to enter the well.
The casing must be large enough to accommodate the pump.
In selecting the size of the casing, the controlling factor is usually the size of pump that is required for the design yield.
Table 1 shows recommended casing sizes for various ranges of well yields.
The well should be of sufficient diameter to allow the ascending water to move at a velocity of 5.0 feet per second or less up the well casing.
Data from the preliminary investigation and chemical analyses of water samples should be reviewed to determine if the water is corrosive or encrusting.
When necessary, extra heavy steel casing should be installed.
In cases of severe corrosive water, stainless steel, PVC, or fiberglass casing should be used.
The capacity of individual wells is highly variable from location to location.
Average estimates of expected capacities for various size wells are given in Table 1.
Although Table 1 can serve as a general guideline, the specific capacity depends on the yield characteristics of the water-bearing formation and the design of the well.
The overall installation must be carefully evaluated.
For instance, although 1,000 gpm may be obtained from a 10-inch pump with reasonably good efficiency, the life cycle cost of a 12-inch pump installation may be less, even including the higher cost of the larger well.
Commercially manufactured quality well screen should be used for the wells.
The well screen should have an efficient design.
A well screen is considered adequate when it allows ample sand-free water to flow into the well with minimum hydraulic head loss.
A properly designed well screen should have close spacing of slot openings to provide uniform open area distribution, maximum open area per foot of length, V-shaped slot openings that widen inwardly, corrosion resistance, and ample strength to resist external forces to which the screen may be subjected during and after installation.
Screens with tapered slots provide hydraulic efficiency and offer self-cleaning properties.
Sand grains smaller than the screen opening are easily brought into the well in the development process, while large grains are retained outside.
Screen length is an important design consideration.
A screen that is too short seriously affects the efficiency of the well, whereas a well screen that is too long causes problems such as cascading water, entrained air, and accelerated corrosion and/or incrustation.
The optimum length of well screen is chosen with relation to the thickness of
 the aquifer, available drawdown, and stratification of the aquifer.
In an artesian aquifer, the lower 70% to 80% of the thickness of the water-bearing sand should be screened, assuming the pumping level is not expected to be below the top of the aquifer.
It is generally not necessary to screen the entire thickness of artesian aquifers.
About 90% of the maximum specific capacity can be obtained by screening only 75% of an artesian aquifer.
An exception to this rule should be made when the aquifer is highly stratified and interbedded with low permeability layers.
In this case, all of the aquifer may need to be screened.
Optimum design practice dictates that the maximum available drawdown in an artesian well should be the distance from the static water level to the top of the aquifer.
If it is necessary to lower the pumping level below the top of the aquifer to obtain greater yield, the screen length should be shortened and the screen should be set at the bottom of the aquifer.
Attempts should be made to design and construct the well SO that the pumping level stays above the top of the uppermost well screen.
For water table wells, selection of screen length is something of a compromise between two factors.
While high specific capacity is obtained by using as long a screen as possible, short screens provide more available drawdown.
These two conflicting aims are satisfied, in part, by using an efficient well screen.
Available drawdown in a water table well is the distance between the static water level and the top of the screen.
Screening the bottom 1/3 to 2/3 of the aquifer normally provides the optimum design.
Gravel-packed wells are particularly well suited to some geologic environments, but gravel packing is not a cure-all for every sand condition.
Gravel pack construction is recommended:
 in aquifers consisting of fine sand,
 in loosely cemented sandstone formations,
 in extensively stratified formations consisting of alternating layers of fine and coarse sediments or thin silt and clay layers.
Gravel packing makes the zone immediately surrounding the well screen more permeable by removing the formation materials and replacing them with artificially graded coarser materials (Figure 3 The size of this artificially graded gravel should be chosen SO that it retains essentially
 all of the formation particles.
The well screen slot opening size is then selected to retain the gravel pack.
Figure 3.
Differences in gravel pack for naturally developed well  and artificial gravel pack.
Credits: B.
Boman 
 Gravel pack design includes specification of gradation, thickness, and quality of the gravel pack material.
Part of the aquifer thickness to be screened should be evaluated by examining the samples collected during the test hole drilling.
Plain casing should be set in intervals with unfavorable strata  of the aquifer.
It may be necessary to place plain  casing between screen sections that are positioned in the best strata of the aquifer.
One advantage of placing plain casing against strata composed of the finest sands and low permeability intervals is that a coarser gravel pack can be utilized.
The coarser pack will allow the coarser strata of the water-bearing formation to yield maximum water.
Little potential yield will be lost by setting plain casing opposite the finest sands and other low permeability strata because these layers produce little water.
A sieve analysis should be prepared for the strata comprising the portion of the aquifer where the screen will be set.
Results of sieve analysis for the finest stratum should be used to design the gravel pack grading.
It is best to design as uniform a pack as possible.
A uniform gravel pack has significantly greater permeability and is easier to install without segregation.
The gravel pack material should consist of clean and well-rounded grains that are smooth.
These characteristics increase the permeability and porosity of the gravel pack.
In addition, the particles should consist of siliceous  rather than calcareous material.
The calcareous material should be limited to less than 5 percent.
To ensure that an envelope of gravel will surround the entire screen, a thickness of 3 to 8 inches is recommended.
This thickness will successfully retain formation particles regardless of how high the water velocity tends to carry the particles through the gravel pack.
When more than 8 inches of gravel pack is provided, development of the aquifer is hampered.
A thicker envelope does not significantly increase the yield of the well and does little to control sand pumping because the controlling factor is the ratio of the grain size of the pack material to the formation material.
To ensure that the envelope of gravel completely surrounds the
 entire screen, centering guides should be used to center the screen in the borehole.
The pack material should be placed continuously, but slowly, to avoid bridging and sorting of the particles.
If the screen is not centered in the bore hole and is in direct contact with the formation material , sand pumping will result.
The gravel pack retains the water-bearing formation, while the well screen retains the gravel pack particles.
In a gravel-packed well, the size of the screen slot is selected to retain 90% or more of the gravel pack material.
For the sand sieve analysis in Figure 3, the proper size screen in a gravel-packed well would have a slot opening of 0.015 inch to retain 90% of the material in the water-bearing strata.
For naturally developed wells, the size of well screen slot openings will depend on the gradation of the sand, and slot openings are selected using the results of sieve analyses of water-bearing formation samples.
A sieve analysis curve, such as shown in Figure 4, is plotted for each sand sample.
The size of the screen opening is selected SO that the screen will retain 40-50% of the sand.
The remaining 50-60% of the sand particles will pass through the openings during development.
If the formation is heterogeneous, it may be necessary to select various sizes of slot openings for different sections of the well screen.
The use of a multiple-slot screen to custom fit the gradation of each stratum will assist in attaining the highest specific capacity possible, and will greatly reduce the possibility of pumping sand with the water.
The screen opening size that retains 40% of the particles is usually chosen when the groundwater is not particularly corrosive and when there is little doubt as to the quality of the formation samples.
For example, a slot size of 0.050 inch would provide 40% retention of the materials in the water-bearing strata.
The screen opening size that retains 50% of the sand is chosen if the water is corrosive or if the reliability of the sample is in question.
If the water is corrosive, enlargement of the openings of only a few thousandths of an inch due to corrosion could cause the well to pump sand.
If the water is encrusting, a size that retains 30% of particles may be selected.
When this larger slot opening is selected, longer well life can be expected before plugging reduces the well yield.
Large slot size also makes it possible to develop a larger area of the formation surrounding the screen.
This generally increases the specific capacity of the well by increasing the well efficiency.
Figure 4.
Example sieve analysis for materials from water-bearing strata.
Credits: B.
Boman 
 One important consideration that must be kept in mind when selecting the screen diameter is that the diameter can be varied without greatly affecting the well yield.
Doubling the diameter of the well screen can be expected to increase the well yield by only about 10%.
Screen diameter can be varied after the length of the screen and size of the screen openings have been selected.
Screen diameter is selected to provide enough total area of screen openings so that the average entrance velocity of the water through the slot openings does not exceed the design standard of 0.1 feet per second.
A quality well screen with maximum open area offers a decided cost advantage when different types of screening devices are compared at this entrance velocity.
The entrance velocity  is calculated by dividing the expected or desired yield  of the well by the total area  of openings in the screen.
If the velocity is greater than 0.1 foot per second, the diameter should be increased.
If the calculated entrance velocity is less than 0.1 foot per second, the screen diameter may be reduced.
However, the screen diameter should not be reduced to the point that the velocity of vertical water flow to the pump exceeds 5.0 feet per second.
Laboratory tests and field experience show that if the screen entrance velocity is equal to or less than 0.1 foot per second, the friction loss through the screen openings is negligible, resulting in a higher well efficiency.
The percentage of open area of the screen should be equal to or greater than the porosity of the sand and gravel in the water-bearing formation and artificial gravel pack supported by the screen.
Where the irrigation well screening device provides only 2% to 5% open area, as in perforated pipe, flow restrictions are unavoidable.
This is one of the most common reasons for low efficiencies of irrigation wells.
Suppose that the water-bearing sand has 30% porosity  and the screening device installed has only 5% open area.
With such a small open area, there will be constriction of flow.
As a result, there will be additional drawdown caused by increased head loss as water moves toward and into the well.
Depending on the results of preliminary investigation, the well screen should be fabricated of materials that are as corrosion resistant as necessary.
If the screen corrodes, sand and/or gravel will enter the well, which may eventually require either replacement of screen or drilling a new well.
Corrosion of screens can occur from bimetallic corrosion if two different metals have been used in the fabrication; therefore, bimetallic screen should always be avoided.
Water with high total dissolved solids accelerates this type of corrosion because the water is a more effective electrolyte.
Corrosion can also occur from dissolved gases in the water such as oxygen, carbon dioxide, and hydrogen sulfide.
Well plugging by the deposits of incrustation is a common problem.
Such deposits plug the screen openings and the
 formation and/or gravel pack immediately surrounding the well screen.
When incrustation is a problem, acid treatments can be used.
Therefore, corrosion-resistant material should always be used to resist the attack of strong acids introduced into the well screen during treatment.
Corrosion and incrustation can occur simultaneously in some groundwater environments.
The products of corrosion can relocate themselves on the screen and form incrustations that plug the screen openings much like waters which are naturally incrusting.
Removal of these deposits often requires strong acids.
The choice of the well screen material is sometimes based on strength requirements regarding column load and collapse pressure.
When a long screen supports a considerable weight of pipe, it functions as a slender column.
The pressure of the formation and materials caving into the well pipe can squeeze the screen.
Therefore, the well material should be able to withstand the pressure.
It is impossible to accurately determine or calculate earth pressures with depth but generally greater strength is needed at greater depths.
Well screens can be constructed of materials which are especially adapted to resist the corrosive attack of aggressive waters and acids.
Stainless steel offers the maximum in corrosion resistance for most fresh groundwater environments and it also provides good strength.
Galvanized steel is suitable for many irrigation wells where the water environment is not corrosive.
It provides strength comparable to stainless steel.
PVC well screens are resistant to corrosion and are often used in shallow wells.
However, only limited open area can be provided and still maintain strength requirements.
Therefore, nonmetallic well screens are not usually adequate for deep irrigation wells.
Well development includes those steps in completion of a well that aim to clean, open, and enlarge passages in the formation near the bore hole SO that water can enter the well more freely.
Three benefits of development are to:
 correct damage or clogging of the water-bearing formation which occurred as a result of the drilling operation;
 increase the porosity and permeability of the natural formation in the vicinity of the well; and
 stabilize the sand formation around the screen or artificial gravel pack SO that the well will yield sand-free water.
All of these benefits can be obtained for wells in unconsolidated aquifers if the wells are properly screened and development procedures are properly applied.
The key to successful development is to cause vigorous reversals of water flow through the screen openings that will rearrange the formation particles.
Provided that adequate energy is applied to the formation, this action breaks down bridging of the gravel pack by clumps of fine particles.
Better results can be obtained if development begins slowly and increases in vigor with time and when the well is pumped during the development procedure.
When the development method makes simultaneous pumping impractical, the well should at least be pumped occasionally.
At times, it may be wise to incorporate chemical development with the mechanical methods.
This is particularly true when silt and clay are suspected of plugging of the formation.
No one particular development procedure is the best method for all geologic formations or types of well construction.
Some methods are more adaptable to the particular type of drilling equipment used to construct the well, but other factors such as availability of water, air compressor, or pump may also dictate which development procedure is the most practical to use.
The selection of the best method should be made on evaluation of the hydrogeologic conditions at the well site and past experience with irrigation wells in the same geologic formation.
Once a method has been selected, the designer should specify the details of the procedure.
Well development methods are always needed and are generally economical regardless of the type of drilling methods used to construct the well.
Proper development will improve almost any well.
Surging with compressed air conveniently allows pumping from the well while development is in progress.
Mechanical surging by operating a plunger in the casing, like a piston in a cylinder, is particularly adaptable when cable tool drilling equipment is used.
Mechanical surging with the use of a bailer is adaptable to both cable tool and rotary drilling.
Starting and stopping of a pump to produce a back lashing action is often called "rawhiding" the well.
This is the simplest method of development, but it is usually the least effective since the surging effect that is created is usually not vigorous enough to obtain maximum results.
High-velocity horizontal jetting with water is the most effective method of well development in most cases and is especially useful for development of gravel-packed wells.
Following completion of development, the well should be test pumped.
The well should be pumped for at least 12 hours at a constant pumping rate, during which time drawdown measurements are taken within the pumped well and any nearby observation wells.
The primary objectives of the test pumping are to obtain information about the performance and efficiency of the well and to collect data which are used to select the permanent pumping equipment to ensure maximum pump efficiency.
The information is used to evaluate the success of the design and development procedures and provides the basis to make other performance judgements and evaluations.
In some cases, this information indicates that further development is necessary.
Well testing will also allow collection of data from which the hydraulic characteristics of the aquifer can be evaluated.
Measurements of water table recovery at the end of a pumping test  can be beneficial in evaluating performance of irrigation wells.
This data can also be used to make calculations of the aquifer hydraulic characteristics.
Drawdown is the distance that the water level in a well drops after pumping begins.
Drawdown will always occur because the water in the well is not replaced instantly when it is removed by the pump.
Also, drawdown creates the gradient in water levels that causes flow to the well.
Figure 5.
Drawdown characteristics for a well in an unconfined aquifer.
Credits: B.
Boman 
 The amount of drawdown depends on well size and efficiency, aquifer properties, and pumping.
For the same well size and pumping rate, drawdown is greater in a sand or
 gravel aquifer as compared to the Florida limestone aquifer.
Typical well drawdowns for the Floridan Aquifer are in the range of 10 to 20 feet, although drawdown can be significantly greater in specific wells.
Accurate measurements of drawdown are important SO that the pump can be properly positioned in a well.
Well Problems Sand Pumping
 Sand pumping causes excessive abrasion of the pump bowls and impellers, distribution pipe, emitters, and other irrigation system components.
It reduces the useful life of the entire system and significantly increases maintenance costs.
In addition, unnecessary costs result when sand must be periodically cleaned from the laterals, pipelines, and in some cases even from the well and pump.
Sand pumping can create large underground cavities which collapse and cause land subsidence in the vicinity of the well bore.
This eventually can cause total collapse of the well casing and the screen.
It is best to control sand at the well screen or gravel pack.
A 2,000-gpm irrigation well operated 800 hours per year with 20 ppm sand in water will remove about 7 tons  of fine sand from the water-bearing strata.
In many cases, proper well design and development can prevent sand from being pumped.
In naturally developed wells, sand pumping is most often caused by using openings in the screen device that are too large to retain the finer materials of the water-bearing formation.
An improper relationship between the grain size of the gravel pack material and the size of the aquifer sand grains is the major cause of sand pumping from gravelpacked wells.
Often, the slot opening size in the well screens for gravel-packed wells is chosen first.
A gravel pack size is then selected that will not pass through the openings in the screening device.
This method gives no consideration to the size of the sand and gravel particles of the water-bearing formation.
As a result, the gravel pack is often too large to properly retain the water-bearing sand, and the well pumps sand.
A sieve analysis of formation samples is necessary for proper gravel pack and slot opening selection.
The design procedure should proceed from the aquifer to the screening device rather than from the screening device to the formation.
In most cases, sand control cannot be achieved by merely installing a thick gravel pack.
A thick gravel envelope does not significantly increase the yield of the well.
Thick gravel packs don't reduce the possibility of sand pumping because
 the controlling factor is the ratio of the grain size of the gravel pack material to the aquifer material.
Wells with poor efficiency result in high pumping costs due to excessive drawdown.
Irrigation well efficiency should be at least 80%.
Often the added operating cost in one pumping season can offset the slightly greater initial cost required for the design and construction of an efficient irrigation well.
The cost resulting from inefficient operation for electric motors can be calculated by:
 Q = Pumping rate 
 H = Additional head required as a result of increased drawdown 
 C P = Cost per kWh 
 E = Pump and drive efficiency  p
 E = Motor efficiency  m
 Assume a well with 90% efficiency when producing 2000 gpm with 20 ft drawdown.
Calculate the cost savings for 90% efficient well compared to a 45% efficient well for 800 hours per year of operation.
The motor efficiency is 90%, the pump efficiency is 85%, and the power cost averages 10 cents per kWh.
Specific capacity for 90% efficiency = 2000 gpm/20ft = 100 gpm/ft of drawdown
 Specific capacity for 45% efficiency = 100/ =50gpm/ ft
 Drawdown for 45% efficient system to produced 2000 gpm = production/specific capacity = 2000/50
 Additional head required  40 ft 20 ft = 20 ft
 Q = 2000 gpm
 C1 p = $0.10 per kWh
 Poor well development upon completion of drilling is another factor causing well inefficiency.
Without proper development, wells will not achieve maximum efficiency, and this results in increased pumping costs throughout the life of the system.
Although it is important to first properly design and construct the well with quality materials, it is equally as important to follow through with thorough well development.
Additional cost per year = $1.10 per hour x 800 hour = $880 per year
 Many times, well inefficiency is related to the improper selection of both the gravel pack particle size and the size of slot openings in the well screen.
If the ratio of the gravel pack particle size to the formation particle size is too large, it allows migration of formation particles into the gravel pack.
As this migration proceeds for a period of time, successively smaller and smaller particles become lodged in the gravel pack.
Eventually, its permeability is drastically reduced.
As a result, the movement of water to the well is impeded.
Low efficiency is also related to skimping on construction costs with cheap, makeshift screens including various types of perforated, punched, sawed, or cut casing or pipe.
These types of screens generally have limitations such as low open area percentage, poor distribution of slot openings, and slots that are inaccurate and vary in size.
Usually these lower cost screens do not have openings small enough to control fine sand or retain finely graded gravel packs.
Hand-perforated or torch-slotted casing normally provides less than 3% open areas.
In addition, the shape of the openings in punched or slotted pipe is such that the openings lend themselves to rapid plugging by sand particles.
Slotted pipe screens typically have less than 5% of the total surface area as openings or passageways for water to enter the well.
With these types of screens, the flow of water from the aquifer is restricted, since porosity of the formation is generally greater than the amount of open area provided by the well screen.
Therefore, additional drawdown is required to force the water into the well, which makes the well inefficient.
A properly designed well screen allows both radial and horizontal flow to the entire well screen.
Perforated pipe contains only a small number of holes, resulting in only a small percentage of the water approaching the well having direct access.
As a result, there is excessive convergence of flow near the individual slot openings, which is a common cause of excessive drawdown and lower well efficiency.
Irrigation wells should be constructed for an expected useful life of at least 25 years.
The cost of drilling two or three replacement wells that would be necessary to replace the service of one properly designed and constructed well is much greater than the one-time construction cost of a good well capable of 25 years of service.
In addition, maintenance costs are higher for poorly designed and poorly constructed wells.
Early failure of irrigation wells is often related to the improper selection of gravel pack and size of slot openings.
Complete collapse of a well can occur due to excessive sand pumping.
However, more well failures occur as a result of installing low-quality screening devices such as perforated or slotted pipe.
These devices provide little open area and poor distribution of open area, which causes water to enter the well at excessively high velocities.
As the velocity of water moving into a well increases, the rate of corrosion or incrustation is accelerated at the screen and within the formation or gravel pack near the bore hole.
Incrustation can cause premature decrease of yield, while corrosion can cause early structural failure of the well.
Placement of the screen at elevations too near the static water level may result in premature well failure.
If drawdown lowers the pumping level below the top of perforated section, water entering the well above the pumping level will free-fall  to the pumping water surface.
Cascading water reduces the life of an irrigation well because it accelerates corrosion and incrustation.
In addition, cascading water causes air entrainment which results in pumping of air, reduction in well yield, and erosion of pump components.
Center pivot manufacturers have developed options to place the pressure sensor somewhere on the center pivot.
Part of Brars thesis research evaluated where the pressure sensor should be located to achieve maximum energy conservation.
Knowing when to pull the trigger on drought plans is not an easy decision, but it can mean the difference between managing with conditions or scrambling to catch up.
This year, use trigger dates for your operation to successfully implement drought mitigation strategies.
Arkansas Water Primer Series: Total Maximum Daily Loads 
 The Arkansas Department of Environmental Quality's  Water Quality Planning Branch is responsible for monitoring water quality, developing water quality standards and allocating groundwater and wasteloads.
The agency's oversight also includes ensuring Section 303 the Total Maximum Daily Load  program of the Clean Water Act  is enforced.
Section 303 of the Clean Water Act
 Total Maximum Daily Load  is a term used to describe the amount of a pollutant that a stream or lake can receive and still meet water quality standards.
TMDLs play a role in helping the state meet federal clean water standards.
The development of TMDLs is a critical issue for environmental compliance because it has the potential to create increased standards for existing facilities and can lead to new regulatory requirements for nonpoint sources that have not previously been regulated.
They differ from other pollution management efforts in that TMDLs require loads from all pollution sources within an impaired watershed be allocated among the users.
Other efforts focus on loads from a few identifiable sources.
TMDLs identify sources of pollution and potential reductions needed to attain standards.
Point sources, such as municipal or industrial discharges, and nonpoint sources, such as runoff from urban or agricultural lands, are considered in calculating TMDLs.
In addition, TMDLs must account for seasonal variation and include a margin of safety.
Arkansas' Impaired Waterbody List
 An impaired waterbody is any water that is not meeting the water quality standards that have been established for that water after technologybased discharge limits on point sources are implemented.
Section 303 requires each state to maintain a list of impaired waterbodies and revise the list in even numbered years.
EPA suggests placing impaired waterbodies within one of five categories when compiling a 303 List.
Category 5 is defined as a waterbody that is "truly impaired." Such waterbodies must have a TMDL developed or other corrective action must be taken.
Between 2004 and 2006, the number of 5 stream segments in Arkansas decreased from 60 to 35.
In essence, a TMDL is a planning document.
The "allowable budget" is determined by scientific
 study of a stream to determine the amount of pollutants that can be assimilated without causing the stream to exceed water quality standards set to protect its designated uses.
Once the capacity is determined, sources of the pollutants are considered.
All sources, both point and nonpoint, are accounted for, and the pollutants are allocated or budgeted among the sources in a manner which will describe the total limit that can be discharged into the waterbody without causing the stream standard or budget to be exceeded.
ADEQ is responsible for conducting TMDL studies that examine the source and the extent of the water quality impairment and providing the appropriate information necessary for achieving surface water quality standards.
The next steps in the TMDL process are developing an action plan outlining affordable, efficient and effective alternatives to restore water quality, and implementing the plan.
During all phases of TMDL planning and implementation ADEQ involves stakeholders by coordinating public meetings and encouraging comments and input.
Load allocations are determined through the review of monitoring data and watershed modeling.
A watershed is the area of land that drains or seeps into a marsh, stream, river, lake or groundwater.
The starting point of a river, the landscapes it flows through and the point where the river ultimately ends all make up a watershed.
Watersheds are complex systems whose features are constantly changing.
Climate, geology, topography, hydrology, soils, land use and other factors influence watersheds and the streams that flow through them.
Each TMDL Arkansas submits to EPA must contain the following components:
 Problem Statement describes the pollutant causing the impairment and the designated uses that are impaired
 Desired Future Condition defines measurements that will ensure recovery of the impaired waterbody and how the objectives will be met
 Source Analysis identifies the amount, timing and point of origin of pollutants
 Load Allocations identifies the parties responsible for taking specified actions to alleviate the impairments
 Implementation Plan describes the actions that will be undertaken to alleviate the impairments
 Linkage Analysis describes how the actions to be taken will result in achievement of the relevant standards
 Monitoring/Re-Evaluation describes the monitoring strategy that will be used to develop more refined information for performance evaluation and consideration of TMDL revisions for phased TMDLs and
 Margin of Safety describes how the required margin of safety was incorporated into the TMDL.
EPA either approves a state's actions or intervenes if a state is not following the TMDL process.
States have latitude to determine their own priorities for developing and implementing TMDLs.
That flexibility provides states an opportunity for incorporating rotating basin or other watershed approaches into the TMDL process.
Benefits of TMDL Monitoring
 Water that is assigned a TMDL is monitored often.
Monitoring helps reveal the actual amounts of pollution from point sources and nonpoint sources that enter the water.
The information helps environmental and regulatory agencies supply money for voluntary pollution prevention.
Monitoring also reveals the effectiveness of the voluntary efforts, which can lead to increased funding or mandatory regulation, as necessary.
Incentives for Meeting Allocation Goals
 Once a TMDL is determined, the following programs help industrial, agricultural and municipal participants meet their output goals:
 Cost-share programs for reducing or removing fertilizers
 Low-cost loans for activities that prevent pollution
 Grants for storm water activities
 Grants for restoration activities
 Programs for improving mines
 Updated limits for National Pollutant Discharge Elimination System  permits
 Best Management Practices and
 Technical and educational assistance.
Although the TMDL program has been part of CWA since 1972, very few TMDL programs have been implemented in any of the nation's states, including Arkansas.
The development of TMDLs is resource intensive.
Most states have lacked the funds and manpower to do TMDL analyses, which involve complex assessments of point and nonpoint sources of pollution to quantify the environmental effects for particular discharge sources.
If states do not submit impaired waterbody lists or TMDLs, or if submissions are deemed inadequate by EPA, the federal agency is required to establish lists and TMDLs in lieu of the states.
However, EPA has been reluctant to intervene and has also lacked resources to establish lists and TMDLs for the states.
Beginning in the 1980s, citizens and environmental groups around the country began suing EPA for not enforcing the TMDL program.
These groups view the implementation of Section 303 as important to achieving the overall goals and objectives of CWA.
The groups also view litigation as the only vehicle for pressuring EPA and states to address nonpoint and other sources of pollution, which, they believe, are responsible for many of the existing water quality impairments nationwide.
Environmental groups have filed lawsuits in 38 states, including Arkansas, in the last few years.
Of the suits tried or settled, 22 have resulted in court orders and consent decrees mandating EPA to establish TMDLs.
In 1999, five Arkansas environmental groups the Sierra Club, Federation of Fly Fishers, Crooked Creek Coalition, Arkansas Fly Fishers and Save Our Streams filed a lawsuit in Federal Court against EPA.
In Sierra Club, et al.
V.
Browner,
 et al., the plaintiffs alleged, among other claims, that EPA failed to establish Arkansas' TMDLs in a timely manner.
Under the terms of a settlement decree EPA agreed to fund a number of TMDL studies in the state.
ADEQ was given responsibility for conducting studies.
ADEQ data indicates that 135 TMDLs have been completed on Arkansas' impaired waterbodies as of October 2007.
The state has until 2010 to complete TMDLs on the rest of Arkansas' impaired waterbodies.
TMDL litigation falls into five general categories, according to EPA:
 Situations in which a state has failed to perform any Section 303 activities
 Situations in which a state has engaged in some but insufficient activities to implement Section 303
 Challenges to EPA's listing of impaired waters, TMDL approval decisions or EPA's promulgation of TMDLs
 Situations in which plaintiffs are using TMDL requirements to achieve other CWA objectives, such as forcing improved water quality monitoring programs and
 Challenges to the substance or content of TMDLs.
Fact Sheet 109  Glossary of WaterRelated Terms contains a comprehensive list of terms used in the Arkansas Water Primer Fact Sheet Series.
The University of Arkansas Division of Agriculture's Public Policy Center provides timely, credible, unbiased research, analyses and education on current and emerging public issues.
The Arkansas Water Primer Fact Sheet Series was funded by a grant from the U.S.
Department of Agriculture with additional financial assistance from the University of Arkansas Division of Agriculture.
Original research for the Series was provided by Janie Hipp, LL.M., and adapted by Tom Riley, associate professor and director of the University of Arkansas Division of Agriculture's Public Policy Center, and Lorrie Barr, program associate, University of Arkansas Division of Agriculture's Public Policy Center.
In the accompanying map, the extent of the High Plains Aquifer in Nebraska is shown in blue; black dots represent wells completed in secondary aquifers.
These secondary aquifers are the sole water supply for more than 4,000 active wells spread across 30 counties in eastern and western Nebraska.
Irrigation Management in High Tunnels
 Dan Drost, Brent Black, and Melanie Stock, Extension Specialists
 High tunnels provide season extension for various high-value horticulture crops in a diverse range of climates.
These large, plastic-covered structures modify the environmental conditions of the covered area.
Temperature management is commonly the focus when growing in high tunnels as this may be the key factor limiting plant growth during much of the year.
While high tunnel temperature management is important, growers also need to address water management to ensure plants are not waterstressed.
Common mistakes are underestimating water needs, which stresses plants or creates conditions favoring plant diseases and nutrient leaching from overwatering.
The key to good tunnel management is to understand how tunnel temperature impacts water use and how the water requirements of the crop respond to tunnel conditions.
With a consistent moisture supply throughout all plant growth stages, growth improves, and fewer negative effects on productivity occur.
Knowing when to irrigate and how much water to apply will ensure the high tunnel is properly managed for high productivity.
This fact sheet discusses how to best manage irrigation for a range of seasonal growing conditions.
Water and Plant Growth
 Figure 1 illustrates how soil water content changes from wet to dry conditions.
When water is added to soils from irrigation or precipitation, the soil exceeds field capacity.
After 1-2 days of draining due to gravity, the soil reaches field capacity.
If no additional water is added to the soil, the soil eventually reaches the permanent wilting point, where the amount of available water is less than a plant can extract.
Plant available water is
 the amount of water in the soil between field capacity and permanent wilting point.
While plant available water is useful to know, it is more important to know and understand the amount of allowable depletion SO plants do not become water-stressed.
Depending on soil type, the allowable depletion  is the point where plants begin to experience some stress as the roots find it harder to extract water from the soil.
Plants vary in how they respond to soil water depletion and where the point of stress begins.
The primary goal of soil water management is to maintain soil moisture between field capacity and the crop's allowable depletion level.
By doing this, water is readily available, and plants do not experience water stress.
The amount of readily available water is related to the effective rooting depth of the plant and the water holding capacity of the soil.
Figure 1.
Typical Relationship of Soil Water Content for Any Soil Type: Saturated, Field Capacity, Plant Available Water, Allowable Depletion, and Permanent Wilting Point
 Flower, fruit, and vegetable crops grown in high tunnels vary greatly in their rooting depth.
Often, growers want to mix crops in high tunnels.
Just like plants have different temperature optimums, they also respond differently to water stress.
If the crops grown have very different levels of allowable depletion, it is harder to manage irrigation.
For some
 crops, you may be keeping the soil too wet or letting it get too dry, particularly if they are on the same irrigation system or watering schedule.
In addition to knowing the allowable depletion, high tunnel growers need to identify the soil texture in the structure.
Soils with a coarser texture, like sands and loamy sands, have less water-holding capacity than finer textured soils, like silt loams and clays.
A deep sandy soil at field capacity may contain 0.5-0.8 inches of available water in the top 1 foot of soil while a clay loam may have 1.7-2.0 inches in the same depth of soil.
Table 1.
Typical Rooting Depth for a Variety of High Tunnel Crops and Recommended Allowable Depletion
 Crop	Minimum	Average	Maximum	% Root Location in Soil Profile	Allowable
 			0-12"	12-24"	24-36"	Depletion 
 Blackberry	6	24	45	70	25	<5	50
 Raspberry	6	24	45	70	25	<5	50
 Strawberry	6	12	18	80	20	<5	30
 Beans	6	12	18	70	25	<5	25-35
 Cucumber	6	12	18	80	15	<5	30-40
 Lettuce	6	12	24	60	30	<5	25-35
 Pepper	6	15	36	50	30	<15	30-40
 Spinach	6	18	36	70	20	<5	25-35
 Summer squash	12	30	48	60	30	<10	40
 Tomato	6	18	30	50	30	<15	40
 Dahlia	8	12	16	80	20	<5	25-30
 Lisianthus	3	4	6	90	10	<5	25-30
 Peony	6	12	24	80	20	<5	30-40
 Ranunculus	4	6	8	90	10	<5	25-30
 Snapdragon	4	6	12	90	10	<5	25-30
 Stock	8	10	12	80	20	<5	25-30
 Sunflower	6	18	36	60	30	<10	40-50
 Sweet pea	6	18	30	60	30	<10	30-40
 Zinnia	8	12	16	80	20	<5	30-40
 Table 2.
Available Water-Holding Capacity for Different Soil Types
 Allowable Depletion 
 25% of total	35% of total	45% of total	55% of total
 Sands and fine sands	0.5-0.8	0.13-0.19	0.18-0.28	0.23-0.36	0.28-0.44
 Loamy sand	0.8-1.0	0.20-0.25	0.28-0.35	0.36-0.45	0.44-0.55
 Sandy loam	1.2-1.5	0.30-0.38	0.42-0.53	0.54-0.68	0.66-0.83
 Loam	1.9-2.0	0.48-0.50	0.67-0.70	0.86-0.90	1.05-1.10
 Silt loam and silts	2.0-2.1	0.50-0.53	0.74-0.90	0.90-0.95	1.10-1.16
 Silty clay loam	1.9-2.0	0.48-0.50	0.70-0.86	0.86-0.90	1.05-1.10
 Sandy clay loam and clay loam	1.7-2.0	0.43-0.50	0.70-0.77	0.77-0.90	0.94-1.10
 Note.
Total available water is the amount of water in the soil between field capacity and the permanent wilting point.
Allowable depletion  is the amount of water a plant can use before experiencing some water stress.
Values are ranges typically reported and may vary slightly.
Figure 2.
Automated Soil Moisture Recording Device for WatermarkTM Sensors.
Water use by plants in a high tunnel is often different from that of plants grown in the field.
Thus, plant water use and irrigation inputs are quite different.
Most high tunnel growers understand that sunlight warms the plants and soil that then warms the air within the tunnel.
Temperatures change rapidly on
 sunny days, even when outside air temperatures are relatively cold.
It is common to ventilate tunnels on sunny days in early spring or even in the late fall to prevent temperatures inside the tunnel from exceeding the crop's temperature optimum.
Just as the temperature is carefully monitored, SO too, the soil moisture content in the tunnel needs to be tracked to maintain optimum plant growth conditions.
Simple Steps to Save Water Indoors
 Simple Ways to Save Water Outdors
 Saving Water Saves Energy Tips for Conserving Water at Home
 Ashley Osborne, Environmental and Natural Resource Issues
 Obtaining water from streams, rivers, aquifers, and other water bodies, and transporting it to water treatment facilities requires large amounts of energy.
Once at water treatment facilities, energy is needed to pump and process water, and to distribute water to consumers.
Further energy is used by consumers to treat water with softeners and filters, circulate and pressurize water with pumps and irrigation systems, and heat and cool water.
Then the spent water or wastewater consumes more energy as it is pumped to treatment plants, where it is aerated and filtered.
By conserving water, we decrease our demand for energy-intensive systems that obtain, treat, and distribute water.
Simply put, by conserving water we save energy.
Figure 1.
Energy used during the transport, treatment, distribution, and use of water and wastewater.
Aerating VS.
non-aerating showerheads: An aerating low-flow showerhead mixes air into the water stream maintaining a steady pressure and providing an even, full shower spray.
However, the temperature of the water may cool down slightly toward the floor of the shower since air is mixed with the water.
A nonaerating low-flow showerhead does not mix air into the water stream; rather the water flow pulses, providing a strong, massaging type spray that maintains temperature.
On average, Kentuckians use 100 to 150 gallons of water per day per person.
Approximately 70 percent of our water use is indoors, most of it used in the bathroom.
Simple Tips to Save Water Indoors
 Do not allow water to run when brushing your teeth, washing your hands or face, or shaving.
When shaving, fill the basin with water and dip your razor in the basin as needed.
Check your toilet and faucet for leaks.
Replace old  toilets with new WaterSense-labeled toilets.
Flush the toilet only when necessary.
Do not use the toilet as a wastebasket.
Throw tissues, insects, and other trash in the garbage, not the toilet.
When taking a bath, plug the drain before turning on the faucet.
As the tub fills, adjust the temperature.
Use less than 5 inches of water when taking a bath.
Install low-flow showerheads and aerators to restrict the flow of water.
While waiting for water to get warm when taking a shower, catch water in a pitcher or bucket, and use to water plants.
Limit showers to 3 to 4 minutes.
Dispose of fruit and vegetable scraps in a compost pile instead of a kitchen garbage disposal.
Garbage disposals use a lot of water and can create septic problems.
Thaw meat and other frozen foods in the refrigerator or use the defrost setting on your microwave instead of using running water.
Scrape, rather than rinse, dishes before putting into the dishwasher.
Set your dishwasher to the water saving or short cycle.
Only run the dishwasher with a full load.
Keep a pitcher of water in the refrigerator for drinking instead of running the faucet for the water to get cold.
Cook food in as little water as possible to save water and prevent nutrient loss.
While waiting for the water to get warm, catch the water in the sink or a pitcher and use for cleaning vegetables, washing or rinsing dishes, watering plants, or cleaning.
Don't wash or rinse dishes under a running faucet.
Instead use a pan or sink of water.
Wash full loads of clothes.
However, if you must wash smaller loads, adjust the water-level control to the appropriate setting.
Some ENERGY STAR models adjust water needs automatically.
Use cold water whenever possible to wash clothes.
Read the manufacturer's instructions for your washer.
Some cycles, such as the permanent press cycle, may use more water.
Wear clothes more than once when possible.
Check your washer's hoses for cracks and leaks regularly.
Replace rubber hoses with reinforced stainless steel or at least reinforced rubber hoses to reduce the risk of leaks and water damage.
Use good laundering techniques.
Pre-treat stains, sort clothes, and follow product  recommendations to avoid rewashing or re-rinsing.
Read the manufacturer's instructions for your appliances.
Washing machines and dishwashers often have cycles that use less water.
Insulate your water heater tank and hot water pipes.
Lower the temperature on your water heater.
A savings of 3 to 5 percent in energy costs can be seen for each 10F reduction in water temperature.
If you plan to be traveling for three or more days, adjust the thermostat on your water heater to the lowest setting or turn off the water heater.
Letting your faucet run for 5 minutes uses about as much energy as letting a 60-watt lightbulb run for 14 hours.
-WaterSense
 If you can stick a screwdriver into your lawn easily, your grass does not need to be watered.
Simple Ways to Save Water Outdoors
 To avoid water loss to evaporation, water your plants early in the morning.
Weed your garden regularly to eliminate competition for water.
Mulch plants, shrubs, and trees to retain moisture.
Leaves and lawn clippings can be used as an alternative to purchasing mulch.
In your garden, group vegetables that need more water together.
This will allow for more efficient watering.
Landscape with native plants.
Replace high water-use plants with native or drought-tolerant plants.
When purchasing an irrigation system, investigate which system is best for you and your lawn and garden needs.
Micro-irrigation sysitems for gardens, trees, and shrubs irrigate slowly and decrease evaporation, runoff, and overspray.
Only irrigate the areas of the lawn that need watering.
Take into account soil type, sun or shade exposure, and the type of sprinkler when planning to irrigate.
Inspect irrigation equipment once a month for leaks, broken or clogged heads, or other problems.
Reduce overwatering by decreasing each irrigation cycle by 2 minutes and eliminating one entire irrigation cycle per week.
Adjust sprinklers to eliminate overspray on sidewalks, driveways, and other impervious surfaces.
Invest in a rain shutoff switch which turns off your irrigation system in wet weather.
Raise the mowing height of your lawn mower.
This promotes root growth, decreases heat stress, and helps your lawn stay more hydrated.
When giving your pet fresh water, use the old water for plants.
For outdoor play, use a small pool instead of a hose or sprinkler.
Check hoses and spigots for leaks regularly.
Clean sidewalks, patios, and driveways with a broom instead of a hose.
Install a rain barrel to collect rainwater to use on your lawn or garden.
Instead of hand washing vehicles, use a commercial carwash that recycles water.
Repair leaks around pool or spa pumps.
Install a pool or spa cover to reduce evaporation.
When using a water hose, use a hose nozzle to turn off the water when you are not using it.
About the author Ashley Osborne, Extension Associate for Environmental and Natural Resource Issues Task Force, Plant and Soil Science Department
CornSoyWater is current being evaluated using data from irrigators field and research plots.
Irrigators and crop consultants are encouraged to try it out and send their comments and feedbacks to the developers.
Potentially, this software could be implanted into irrigation control modules for automated irrigation control, variable rate irrigation, and other irrigation decision supports packages.
May and June are particularly vulnerable times for nitrate leaching in our irrigated fields because of several factors.
First, the fields are left fairly wet from last season's irrigation, precipitation from October through May usually puts more water into the soil than it can hold, the crop is still small and not using much water, and most  if not all  the nitrogen for the corn crop has been applied.
One thing to note is that the time needed for corn to mature is dependent on growing degree days.
If corn needs 5 inches of water to reach maturity and we receive some hot, dry windy days in early September the corn will still use 5 inches, it will just finish up a few days quicker.
Thirty-one center pivots equipped with pressure regulators across Nebraska were analyzed.
Data were collected by AgSense Field Commander units mounted at the end of the pivots.
For this analysis, the ideal range of pressure at the end of the pivots was considered to be 0 to 10 psi above the required regulator inlet pressure; equivalent to 5 to 15 psi above the pressure regulator rating.
Approximately 55% of the center pivots evaluated had a pressure below the required regulator inlet pressure for at least 5% of the time.
Percent of fields that became wetter moving from August to Sept.
15.
The dry years 2020, 21 and 22 fields are much drier than the other years in the fall.
In 2019, 54% of fields with soil in the 15-25 in zone became wetter from August to Sept.
15, 54% of fields with soil in the 25-36 in zone became wetter from August to Sept.
15, and 38% of fields with soil in both zones became wetter moving from August to Sept.
15.
Knowing approximately, how much plant available water is remaining in the active root zone is critical for calculating the last few irrigations and will be referred to as the "remaining available water." The best method for determining the amount of remaining soil water is to use a soil water monitoring system.
COLLECTING SAMPLES FOR AGRICULTURAL IRRIGATION WATER QUALITY TESTING
 Published: Aug 11, 2020 |  Printable Version  | Peer Reviewed
 Dara Park, Sarah A.
White, Daniel R.
Hitchcock and Grayson Younts
 Irrigation water contains organic and inorganic compounds that influence plant health, soil health and structure, and irrigation system longevity.
This article will primarily help agricultural irrigation users  understand how to collect a representative water sample based on the source and prepare it for transport to a laboratory for analyses.
It is important to regularly test the quality of your irrigation source water.
The frequency of testing depends upon use.
The analysis should be conducted in the same laboratory over time to create a record of changes in water quality.
Keep the reports to create a baseline of stability or seasonal changes in water quality to compare to future reports.
Information contained in each report can help you understand how your irrigation water supply may influence plant health, soil health, and irrigation system longevity.
Direct Impacts on Plant Health
 Certain chemical compounds in water can directly influence the health and productivity of plants.
For example, water sources can contain macronutrients and micronutrients.
If these nutrients are not present in high enough concentrations, then the agricultural manager may need to apply fertilizers as supplemental nutrient sources.
Some compounds are toxic to plants if present at threshold concentrations.
Ions such as chloride and sodium can cause direct ion toxicity in roots and leaves, while other ions  become toxic as they accumulate in plant tissue after passive uptake from water.1
 Soil Impacts and Subsequent Plant Health Impacts
 Water can also impact soil physical, chemical, and biological properties, eventually affecting plant health.
For example, source water that contains minimal to no additional elements , as well as water that is high in sodium, can cause soils to disperse.
Dispersed soil particles settle close to each other, which can result in a loss in soil permeability and porosity; dispersed soils are more susceptible to becoming compacted.1, 2 Clogging and sealing can also reduce gas exchange and water holding capacity, reducing the activity of microorganisms.
The roots of some plants also have difficulty penetrating the compacted soil.3
 Impacts on Irrigation System Performance
 Water quality can also reduce the efficiency of irrigation systems.
Lead-based pipes in older irrigation systems may corrode due to iron present in the water.
Low pH  water may accelerate the corrosion of critical irrigation systems components.
Limescale may accumulate in an irrigation system if the source contains moderate to high concentrations of bicarbonates.
Bicarbonates bind with magnesium and calcium and settle out of the water forming the limescale.
Limescale can build up on inner walls of pipes and clog sprayer nozzles.1
 Where to Collect Water Samples
 The following information relates to how to collect water samples based on the source of irrigation water.
Collecting your sample from the correct location is essential, as it influences the accuracy and usefulness of the water quality test results.
Groundwater varies in water quality.
Factors include the depth of the well  and proximity to the coast.
For well water testing, collect the sample from the pump housing so that results are not influenced by contaminants within the irrigation lines.
Collect one sample from each well.
If a contaminant is thought to originate within the irrigation lines or sprinkler configuration, collect an additional water sample at a spray head or quick-connect shortly after turning on the pump after it comes to operating pressure and flow.
This task will allow the collection of a representative sample of water that has been sitting in the system since the last irrigation cycle.
Next, collect a separate sample after the stagnant water has been flushed through the system.
The time this takes will vary with the type and size of the irrigation system.
If wells are used to fill an irrigation reservoir , sample the wells as outlined above, then follow surface water collection directions outlined below to obtain a separate sample from the reservoir.
Table 1.
Typical water quality constituents tested and whether they potentially pose a risk to plants , soils, or irrigation systems.
The quality of surface water depends primarily on land uses within the contributing watershed, the frequency, intensity and duration of rainfall, and exchange with other connected surface and groundwater resources.
If irrigation water is applied via an overhead sprinkler, a pivot system, or spray stakes, collect the sample directly from a sprinkler head or quick connect.
If water is not applied overhead and there is a pump station, follow the directions outlined above for obtaining samples at the pump housing.
Municipalities are required by law to test drinking water provided to the public.
In many cases, this water is used for irrigation purposes.
Some water quality constituents are tested more frequently than others.4 The results of the water quality tests  are publicly available by request from the relevant public water utility.
Access the SC Department of Health and Environmental Control Testing your Drinking Water website for specific municipality information and regulations.5
 Some municipalities also offer clients access to treated wastewater  as a potential irrigation source.
Specific guidelines regulate what types of reclaimed water can be used for different irrigation purposes.
Consult the EPAs Guidelines for Water Reuse for identifying specific uses.6 In certain instances, reclaimed water can be a better water source than well water for agriculture.
For example, a golf course in Bluffton, South Carolina was using well water high in bicarbonates and sodium for irrigation.
The course also had access to reclaimed water.
Water quality analyses for both sources were compared.
The reclaimed water contained less bicarbonates and sodium than the well water and provided additional phosphorus and potassium needed to support the health of turf and ornamental plants.1 The golf course switched to the reclaimed water as an irrigation source and saw a significant improvement in plant health.
Registration is open for the 2023 Water for Food Global Conference, organized by the Daugherty Water for Food Global Institute at the University of Nebraska.
Dr.
Brent Black, USU Extension Fruit Specialist, Dr.
Robert Hill, USU Extension Irrigation Specialist, and Dr.
Grant Cardon, USU Extension Soils Specialist
 Proper irrigation of strawberries is essential to maintaining a healthy and productive planting.
Over irrigation slows root growth, increases iron chlorosis on alkaline soils, and leaches nitrogen, sulfur and boron out of the root zone leading to nutrient deficiencies.
Excessive soil moisture also promotes root rot, particularly on heavy soils.
Applying insufficient irrigation water results in drought stress.
Drought stress during fruit development results in reduced fruit size and yield, and poorer fruit quality.
In the matted row strawberry production system, drought stress also reduces runnering and prevents proper establishment of daughter plants, which negatively affects the following season's crop and allows for more weed growth.
Properly managing irrigation is analogous to managing a bank account.
In addition to knowing the current bank balance , it is important to track both expenses  and income.
Bank Balance 
 How big is my bank account?
Water holding capacity
 Field Capacity is the maximum amount of water that can be held in the soil after excess water has percolated out due to gravity.
Permanent Wilting Point is the point at which the water remaining in the soil is not available for uptake by plant roots.
When the soil water content reaches this point, plants die.
Available Water is the amount of water held in the soil between field capacity and permanent wilting point.
Allowable Depletion is the point where plants begin to experience drought stress.
For straw-
 berries, the amount of allowable depletion, or the readily available water represents about 50% of the total available water in the soil.
The goal of a well-managed irrigation program is to maintain soil moisture between field capacity and the point of allowable depletion, or in other words, to make sure that there is always readily available water.
The amount of readily available water is related to the effective rooting depth of the plant, and the water holding capacity of the soil.
The effective rooting depth for strawberries in Utah's climate and soils is typically between 8 and 18 inches.
The water holding capacity across that rooting depth is related to soil texture, with coarser soils  holding less water than fine textured soils such as silts and clays.
A deep sandy loam soil at field capacity, for example, would contain 0.6 to 0.75 inches of readily available water in an effective rooting depth of 1 foot.
Figure 1.
Soil water content from saturated to dry.
Optimal levels for plant growth are between field capacity and allowable depletion.
Table 1.
Available water holding capacity for different soil textures, in inches of water per foot of soil.
Available water is the amount of water in the soil between field capacity and permanent wilting point.
Readily available water is approximately 50 percent of available.
Soil Texture	Available	Readily available 
 Sands and fine sands	0.5 0.75	0.25 0.38	0.4 0.6
 Loamy sand	0.8 1.0	0.4 0.5	0.6 0.75
 Sandy loam	1.2 1.5	0.6 0.75	0.9 1.1
 Loam	1.9 2.0	0.9 1.0	1.4 1.5
 Silt loam, silt	2.0	1.0	1.5
 Silty clay loam	1.9 2.0	0.9 1.0	1.4 1.5
 Sandy clay loam, clay loam	1.7 2.0	0.85 1.0	1.3 1.5
 Figure 2.
The amount of allowable depletion, or the readily available water, represents about 50 percent of the total available water.
What's in the bank?
-Measuring Soil Moisture
 In order to assess soil water content, one needs to monitor soil moisture where the concentration of strawberry roots exist.
One of the more cost effective and reliable methods for measuring soil moisture is by electrical resistance block, such as the Watermark sensors.
These blocks are permanently installed in the soil, and wires from the sensors are attached to a handheld unit that measures electrical resistance.
Resistance measurements are related to soil water potential, which is an indicator of how hard the plant roots have to "pull" to obtain water from the soil.
The handheld unit reports soil moisture content in centibars, where values close to zero indicate a wet soil and high values represent dry soil.
The relationship between soil water potential and available water differs by soil type.
The maximum range of the sensor is 200 centibars, which covers the range of allowable depletion in most soils.
The sensors are less effective in coarse sandy soils, and will overestimate soil water potential in saline soils.
Remember that allowable depletion is 50% of available water, which roughly corresponds to soil water potentials of 25 centibars for a
 loamy sand soil, and 70 centibars for a loam.
Table 2.
Recommended Watermark TM sensor values at which to irrigate.
Silt loam, silt	70
 Clay loam or clay	90
 Watermark is a registered trademark of Irrometer, TM Co., Riverside, CA.
Plant available moisture is lost through surface runoff, deep percolation , evaporation from the soil surface, and transpiration through the leaves of the plant.
Of these, the biggest losses are typically due to evaporation and transpiration, collectively known as "evapotranspiration" or ET.
Estimates of ET are based on weather data, including air temperature, relative humidity and wind speed.
Some weather stations in Utah are programmed to calculate and report the ET estimates for alfalfa as a reference crop  that is specific to your crop and its stage of development.
ETcrop =ET, x Kerop
 The Kcrop for matted row strawberries are shown in Figure 3.
At leaf emergence in the spring , strawberries are using about 16% of the amount of water used by the alfalfa reference crop.
Water use increases until first bloom  when water use is 95% of a reference alfalfa crop.
Water use
 stays relatively high through fruiting and summer runnering, declining in the fall until a killing frost stops leaf activity.
Typical weekly ET, values are shown in Table 3.
Calculated ET, for your location can be determined by accessing weather data from a nearby weather station at the following Web sites,
 Table 3.
Typical weekly alfalfa reference evapotranspiration  values for Utah locations.
Location	May	June	July	August
 Laketown	1.35	1.74	1.91	1.68
 Logan	1.38	1.83	1.94	1.68
 Ogden	1.48	1.98	2.10	1.80
 Spanish	1.48	1.94	2.08	1.74
 Fork	1.57	1.95	2.04	1.74
 Cedar City	1.95	2.40	2.53	2.02
 Income Irrigation and Rainfall
 In Utah's high elevation desert climate, rainfall contributes a small fraction of the in-season water requirements of the crop.
Therefore, regular irrigation is needed to supply strawberry water needs.
Irrigation water can be supplied by overhead sprinklers, drip lines or microsprinklers.
Flood and furrow irrigation are not typically recommended for strawberries, due to sensitivity to water-borne pathogens that cause root rot.
Overhead sprinklers should also be used with care during fruiting, as excessive wetting can lead to fruit rot.
When using overhead irrigation, watering cycles should be completed early enough in the day to allow for adequate drying of the leaves and fruit.
During hot summer weather however, overhead irrigation can give some evaporative cooling of the leaves and fruit.
Whichever irrigation system you utilize, it is important to calibrate your system SO that you know precisely how much water is being applied.
With sprinklers and microsprinklers, the simplest way to do this is to place catch cans in multiple locations in your planting and collect water for a set period of time.
The amount of water collected over time will give you an application rate , and differences in water collected among the catch cans will tell you how uniform the application is within your planting.
When trying to determine application uniformity, it is best to measure output at both ends of your irrigation system.
Also, if your planting is on a slope, you should measure output at the highest and lowest points of your field.
Elevation differences and the distance the water travels through the irrigation lines both affect water pressure, and consequently the flow rate at the nozzle.
If you have trickle irrigation, you can place catch cans under the emitters and determine flow rate for each emitter.
Flow rate from each emitter and emitter spacing can be used to calculate rate per area.
The efficiency of your system is a measure of how much you have to over water the wettest spots of the planting to get adequate water to the dry spots.
Efficiency is related to the uniformity of application and to the amount of evaporation that occurs before the water can move into the soil.
A well-designed microsprinkler or drip system can be 70 to 90% efficient.
Overhead sprinkler systems are typically 60 to 75% efficient, while flood and furrow irrigation is typically 30 to 50% efficient.
Following is an example of how to calculate water needs for a mature matted row strawberry planting on a sandy loam soil, during harvest.
ETr values are 2.10 inches per week.
Crop coefficient is 0.95.
ETcrop=ET, x = Kcrop
 ET crop = 2.10 inches/week * 0.95 = 2.00 inches/week
 Soil storage capacity 
 The total storage capacity for readily available water over the effective rooting depth is 0.6 inches.
0.6 inches / 2.00 inches per week = 0.3 weeks or 2.1 days between irrigations
 The soil moisture in the rootzone will go from field capacity to plant stress levels in 2.1 days.
To recharge the soil profile, you will need to apply 0.6 inches of water.
Assuming a microsprinkler irrigation system with an efficiency of 90%, 0.7 acre inches of water will be required per acre for each watering.
Good irrigation management requires:
 1.
An understanding of the soil-plant-water relationship
 2.
Properly designed and maintained irrigation system, and a knowledge of the efficiency of the system
 3.
Proper timing based on
 a.
Soil water holding capacity
 b.
Weather and its effects on crop demand
 C.
Stage of crop growth.
Each of these components requires a commitment to proper management.
Proper management will lead to the maximum yields per available water and will optimize the long term health and productivity of your planting.
Utah State University is committed to providing an environment free from harassment and other forms of illegal discrimination based on race, color, religion, sex, national origin, age , disability, and veteran's status.
USU's policy also prohibits discrimination on the basis of sexual orientation in employment and academic related practices and decisions.
Utah State University employees and students cannot, because of race, color, religion, sex, national origin, age, disability, or veteran's status, refuse to hire; discharge; promote; demote; terminate; discriminate in compensation; or discriminate regarding terms, privileges, or conditions of employment, against any person otherwise qualified.
Employees and students also cannot discriminate in the classroom, residence halls, or in on/off campus, USU-sponsored events and activities.
This publication is issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Noelle E.
Cockett, Vice President for Extension and Agriculture, Utah State University.
Enterprise Budgets Cotton, Flood Irrigated, Southern Arizona Blase Evancho, Paco Ollerton, Trent Teegerstrom and Clark Seavert
 This enterprise budget estimates the typical economic costs and returns to grow cotton using flood irrigation in southern Arizona.
It should be used as a guide to estimate actual costs and returns and is not representative of any farm.
The assumptions used in constructing this budget are discussed below.
Assistance provided by area producers and agribusinesses is much appreciated.
As of the date of this publication, the price for labor, fuel, fertilizer, and chemicals is increasing dramatically, which makes developing a long-term budget difficult.
Therefore, a sensitivity analysis shows the net returns per acre as these inputs increase by 10 and 20 percent.
This budget is based on a 1,500-tillable acre farm.
As Arizona is experiencing irrigation water shortages, approximately 40 percent  of the total farm tillable acres are fallowed.
This fallowed land will allow adequate water to irrigate the following crops: 271 acres in cotton, 45 acres in silage corn, 90 acres in spring barley, 181 acres in durum wheat, and 316 acres of alfalfa hay.
The costs to fallow land are allocated to each crop based on its water use.
All crops are grown using flood irrigation.
Tractor driver labor cost is $17.89 per hour and general labor $14.55 per hour; both rates include social security, workers' compensation, unemployment insurance, and other labor overhead expenses.
For this study, owner labor is valued at the same rate as tractor driver rates, and all labor is assumed to be a cash cost.
Tractor labor hours are calculated based on machinery hours, plus ten percent.
Interest on operating capital for harvest and production inputs  is treated as a cash expense, borrowed for 6-months.
An interest rate of six percent is charged as an opportunity to the owner for machinery ownership.
The machinery and equipment used in this budget are sufficient for a 1,500-acre farm with 1,000 acres in crops.
The machinery and equipment hours reflect producing cotton, silage corn, spring barley, durum wheat, and alfalfa hay.
A detailed breakdown of machinery values is shown in Table 2.
Estimated labor, variable, and fixed costs for machinery are shown in Table 3, based on an hour and per acre basis.
The machinery costs are calculated based on the total farm use of the machinery.
Off-road diesel is $4.00 per gallon.
The cultural operations are listed approximately in the order in which they are performed.
A 175-hp tractor is used to pull the v-ripper, heavy offset disk, moldboard plow, landplane, lister, and planter.
A 125-hp tractor is used to pull the shredder/root puller, drill, cultivator, fertilizer spreader, and boom sprayer.
A charge for miscellaneous and other expenses is five percent of production costs, including additional labor, machinery repairs and maintenance, supplies and materials, tax preparation, memberships in professional organizations, and educational workshops not included in field operations.
There are two products sold in this budget, cotton lint and seed.
The price of lint is $1.00 and $0.15 per pound for seed; the average yield for lint is 1,500 and seed 2,250 pounds, for a 1.50 ratio of lint to seed production.
The gross income for lint is $1,500 and $338 per acre for seed.
The total gross income is $1,838 per acre.
Variable costs are $1,206 per acre and fixed cash costs of $335 per acre, giving a net return above variable cash costs of $297 per acre.
Total fixed costs are $116 per acre, with a total cost of production of $1,656 per acre when all variable and fixed costs are considered.
The gross income minus total costs results in a $181 per acre return.
Tables 4 and 5 show the baseline net returns per acre for cash and total costs at various yields and prices as in this study.
Tables 6, 7, 8, and 9 show a sensitivity analysis of returns per acre as the price for labor, fuel, fertilizer, and chemicals are increased an additional 10 and 20 percent.
NOTE: Not included in these budgets are family living withdrawals for unpaid labor, returns to management, depreciation and opportunity costs for vehicles, buildings and improvements, inflation, property and crop insurance, and local, state, and federal income and property taxes.
Table 1a.
Economic and Cash Costs and Returns of Producing Cotton, $/acre.
Returns	Unit	$/Unit	Quantity	Value
 Cotton Lint	pound	$1.00	1,500	$1,500.00
 Cotton Seed	pound	0.15	2,250	337.50
 Variable Cash Costs	Price	Quantity	Unit	Labor	Machinery	Materials	Total
 Land Preparation and Maintenance
 V-Ripper	1.00	acre	$13.53	$34.60	$0.00	$48.13
 Offset Disk	3.00	acre	14.15	35.64	0.00	49.79
 Moldboard Plow	1.00	acre	7.73	24.50	0.00	32.23
 Landplane	1.00	acre	3.87	9.31	0.00	13.18
 Lister	1.00	acre	6.18	14.44	0.00	20.63
 Cotton Shredder/Root Puller	1.00	acre	2.97	4.15	0.00	7.12
 Row Planter	$110.00	1.00	acre	4.51	13.34	110.00	127.85
 Ferlilizer Spreader	1.00	acre	1.88	3.73	175.50	181.11
 Nitrogen	$175.50	1.00	acre
 Boom Sprayer	3.00	acre	3.57	5.47	74.00	83.03
 Herbicides	$24.00	1.00	acre
 Insecticides	$50.00	1.00	acre
 Row Cultivator	2.00	acre	6.01	8.76	0.00	14.78
 Irrigation	72.75	0.00	275.00	347.75
 Irrigation Water, Flood	$55.00	5.00	ac ft
 Irrigation Labor, Flood	$14.55	5.00	hours
 Harvest, Custom	$160.00	1.00	acre	0.00	0.00	160.00	160.00
 Research and Protection Assessment	$3.00	3.00	bales	0.00	0.00	9.00	9.00
 National Cotton Council	$0.45	3.00	bales	0.00	0.00	1.35	135
 Arizona Cotton Growers Association	$0.65	3.00	bales	0.00	0.00	1.95	1.95
 Cotton Board Assessment	$1.00	3.00	bales	0.00	0.00	3.08	3.08
 0.005%	gross lint sales
 Classing Fee	$2.30	3.00	bales	0.00	0.00	6.90	6.90
 Other Expenses	5.0%	0.00	0.00	55.75	55.75
 Interest on Operting Capital	6.0%	0.00	0.00	35.12	35.12
 Total Variable Cash Costs	$140.11	$158.10	$907.65	$1,205.86
 Fixed Cash Costs	Unit	$/Unit	Value
 Fallow Costs	acre	$164.84	$164.84
 Annual Cash Rent Payment	acre	170.00	170.00
 Total Fixed Cash Costs	$334.84
 Total Returns minus Total Varialbe and Fixed Cash Costs	$296.80
 Fixed Non-Cash Costs	Unit	$/Unit	Value
 Power Units, Machinery & Equipment, depreciation & interst	acre	$115.64	$115.64
 Total Fixed Non-Cash Costs	$115.64
 Total Annual Costs	$1,656.34
 Returns minus Total Annual Costs	$181.16
 1 The cost to shred cotton stocks are not included in this budget, however, when cotton follows a cotton crop include the shredding costs listed in Table 3.
Width	Market	Annua	Life
 Machine		Value	Use	
 175 HP Tractor	N/A	$180,000	1,365	10
 125 HP Tractor	N/A	80,000	495	15
 V-Ripper	8.0	22,000	459	10
 Offset Disk	18.0	30,000	517	15
 Moldboard Plow	9.3	35,000	138	15
 Landplane	16.0	18,000	78	15
 Lister	10.0	6,500	99	15
 Cotton Shredder/Root Puller	20.0	12,000	41	15
 Row Planter	24.0	40,000	72	15
 Row Cultivator	24.0	22,000	103	10
 Drill	20.0	25,000	97	15
 Fertilizer Spreader	40.0	18,000	109	20
 Boom Sprayer	60.0	9,500	145	20
 Table 3.
Machinery Cost Calculations, on a per hour and per acre basis.
-Variable Costs-	Fixed Cost
 Fuel &	Repairs &	Deprec.
Total Cost
 Machie	Lube	Maint.
& Interest
 175 HP Tractor	$36.80	$7.37	$17.20	$61.37
 125 HP Tractor	23.00	1.78	18.31	43.09
 V-Ripper	0.00	6.16	6.19	12.35
 Offset Disk	0.00	5.40	6.48	11.88
 Moldboard Plow	0.00	18.20	28.29	46.50
 Landplane	0.00	3.24	25.80	29.04
 Lister	0.00	1.78	7.32	9.10
 Cotton Shredder/Root Puller	0.00	2.76	32.57	35.33
 Row Planter	0.00	14.02	64.48	78.50
 Row Cultivator	0.00	3.90	27.10	30.99
 Drill	0.00	12.06	30.14	42.20
 Fertilizer Spreader	0.00	14.31	19.02	33.34
 Boom Sprayer	0.00	5.36	7.51	12.87
 Acre/	Operator	Variable	Fixed	Total
 Field Operation	Hour	Labor	Costs	Costs	Costs
 175 HP Tractor & V-Ripper	1.45	$13.53	$34.60	$16.08	$64.21
 175 HP Tractor & Offset Disk	4.17	4.72	11.88	5.68	22.27
 175 HP Tractor & Moldboard Plow	2.55	7.73	24.50	17.87	50.11
 175 HP Tractor & Landplane	5.09	3.87	9.31	8.45	21.62
 175 HP Tractor & Lister	3.18	6.18	14.44	7.71	28.33
 175 HP Tractor & Shredder	6.64	2.97	4.15	7.67	14.78
 175 HP Tractor & Planter	4.36	4.51	13.34	18.72	36.56
 175 HP Tractor & Cultivator	6.55	3.01	4.38	6.94	14.32
 175 HP Tractor & Drillr	3.64	5.41	10.13	13.32	28.87
 175 HP Tractor & Fertilizer Spreader	10.47	1.88	3.73	3.56	9.18
 175 HP Tractor & Boom Sprayer	16.55	1.19	1.82	1.56	4.57
 Table 4.
Estimated Per Acre Returns Over Cash Cost at Varying Yields and Prices at Full Production.
Change in Prices/Lb	1,200	1,300	1,400	1,500	1,600	1,700	1,800
 $0.85				$72	$179	$287	$394
 $0.90			34	147	259	372	484
 $095			104	222	339	457	574
 $1.00		52	174	297	419	542	664
 $1.05		117	244	372	499	627	754
 $1.10	49	183	314	447	579	712	844
 $1.15	109	247	384	522	659	797	934
 Table 5.
Estimated Per Acre Returns Over Total Cost at Varying Yields and Prices at Full Production.
Change in Prices/Lb	1,200	1,300	1,400	1,500	1,600	1,700	1,800
 $0.85					$64	$171	$279
 $0.90				317	144	256	369
 $095				106	224	341	459
 $1.00			59	181	304	426	549
 $1.05		1	129	256	384	511	639
 $1.10		66	199	331	464	596	729
 $1.15		131	269	406	544	681	819
 Table 6.
Estimated Per Acre Returns Over Cash Cost at Varying Yields and Prices at Full Production with a 10 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Change in Prices/Lb	1,200	1,300	1,400	1,500	1,600	1,700	1,800
 $0.85				$16	$124	$231	$339
 $0.90				91	204	316	429
 $095			49	166	284	401	519
 $1.00			119	241	364	486	609
 $1.05		61	189	316	444	571	699
 $1.10		126	259	391	524	656	789
 $1.15	54	191	329	466	604	741	879
 Table 7.
Estimated Per Acre Returns Over Total Cost at Varying Yields and Prices at Full Production with a 10 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Change in Prices/Lb	1,200	1,300	1,400	1,500	1,600	1,700	1,800
 $0.85					$8	$116	$223
 $0.90					88	200	313
 $095				50	168	285	403
 $1.00			3	125	248	370	493
 $1.05			73	200	328	455	583
 $1.10		10	143	275	408	540	673
 $1.15		75	213	350	488	625	763
 Table 8.
Estimated Per Acre Returns Over Cash Cost at Varying Yields and Prices at Full Production with a 20 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Change in Prices/Lb	1,200	1,300	1,400	1,600	1,700	1,800
 $0.85				$68	$175	$283
 $0.90				148	260	373
 $095				228	345	463
 $1.05		5	133	388	515	643
 $1.10		70	203	468	600	733
 $1.15		135	273	548	685	823
 Table 9.
Estimated Per Acre Returns Over Total Cost at Varying Yields and Prices at Full Production with a 20 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Change in Prices/Lb	1,200	1,300	1,400	1,500	1,600	1,700	1,800
 $0.85						$60	$167
 $0.90					32	145	257
 $095					112	230	347
 $1.00				70	192	315	437
 $1.05			17	145	272	400	527
 $1.10			87	220	352	485	617
 $1.15		20	157	295	432	570	707
 THE UNIVERSITY OF ARIZONA Cooperative Extension
 BLASE EVANCHO Area Agent, Arizona Cooperative Extension, University of Arizona
 Paco OLLERTON Producer in Pinal County
 TRENT TEEGERSTROM Ag Econ Extension Specialist, Department of Agriculture and Resource Economics, University of Arizona
 CLARK SEAVERT Agricultural Economist, Department of Applied Economics, Oregon State University
When flash grazing mixed cooland warm-season grass pastures, we do want to be a little more cautious as to not overgraze any desirable cool-season grasses.
In areas where cheatgrass or downy brome is a problem, grazing at strategic windows  such as during the cheatgrass elongation phase right before seed set  appears to be the best time to apply grazing.
Grazing at this time matches diet preference by grazing animals with the cheatgrass growth period and limits over use on perennial cool-season grasses growing at the same time.
Targeted grazing is a long-term management option that can utilize cheatgrass as a forage resource and limit the potential seed proliferation within a system.
The data given in Table 1 shows how much water corn and soybean will need until they reach maturity based on each growth stage.
This is the baseline information needed when it comes to deciding the last irrigation of the season.
Figures for grain sorghum and dry beans can be found in NebGuide G1871, "Predicting the Last Irrigation of the Season".
MEASURING WATER FLOW IN SURFACE IRRIGATION DITCHES AND GATED PIPE
 Arizona Water Series No.31
 Measuring water in surface irrigation systems is critical for peak efficiency management.
Without knowing the amount of water being applied, it is difficult to make decisions on when to stop irrigating or when to irrigate next.
A good irrigation manager should know the flow rate of the irrigation water, the total time of the irrigation event and the acreage irrigated.
From this, the total amount of water applied can be determined, which will help determine whether the irrigation was adequate and when the next irrigation should be.
Irrigation management decisions should be made based on the amount of water applied and how this relates to the consumptive use demands of the plants and the soil water holding capacity.
Units of Measuring Water
 There are many ways to express water volume and flow.
The volume of water applied is usually expressed in acre-inches or acre-feet for row crops or gallons per tree in orchards.
Flow rate terminology is even more varied.
Flow rate is expressed as cfs , gpm  and in some areas, miner's-inches.
Below is a description of each.
Acre-inch : An acre-inch is the volume of water required to cover an acre of land with one inch of water.
One acre-inch equals about 3,630 cubic feet or 27,154 gallons.
Acre-foot : An acre-foot is the volume of water required to cover an acre of land with 1 foot of water.
One acre-foot equals about 43,560 cubic feet, 325,848 gallons or 12 acre-inches.
Cubic feet per second : One cubic foot per second is equivalent to a stream of water in a ditch 1foot wide and 1-foot deep flowing at a velocity of 1 foot per second.
It is also equal to 450 gallons per minute, or 40 miner's-inches.
Gallons per minute : Gallons per minute is a measurement of the amount of water being pumped, or flowing within a ditch or coming out of a pipeline in one minute.
Miner's inches: Miner's-inches was a term founded in the old mining days.
It is just another way of expressing flow.
Some areas in the West still use this measurement unit.
Caution needs to be taken because there are Arizona miner'sinches, California miner's-inches and probably some that are locally used.
Approximately 40 Arizona miner'sinches equals 1 cfs or 450 gpm.
Pressure or Head : People often use the phrase "head of water." A foot of head usually implies that the water level is one foot above some measuring point.
However, head can also mean pressure.
For example, as the level of water rises in a barrel, the pressure at the bottom of the barrel increases.
One foot of water exerts 0.43 pounds per square inch  at the bottom of the barrel.
Approximately 2.31 feet of water equals 1 psi.
Thus, if a tank of water were to be raised 23.1 feet  in the air with a hose connected to it, the pressure in the hose at the ground would be about 10 psi.
Area: The cross sectional area of a ditch is often required to calculate flow.
Some ditches are trapezoids and others or more like ellipses.
To find the area of a trapezoid , measure the width of the bottom  and the width of the ditch at the water surface  and add them together.
Divide that number by 2 and then multiply by the height  of the water.
If the ditch is more elliptical in shape , take the depth of the water , multiply it by the width of the ditch at the surface , divide by 4 and then multiply by PI.
To calculate the cross-sectional area of a pipe, the formula is PI r2, where PI is 3.14 and "r" is the radius of the pipe.
NOTE: All measurements should be in feet.
Figure 1.
Cross-sectional dimensions for trapezoidal  and elliptical  ditches.
Table 1.
Coefficients to correct surface float velocities to mean channel velocities..
Average Depth 	Coefficient
 Measuring Water Flow in Ditches
 The Float Method: This method is useful to get a rough estimate of flow.
First, choose a 100-foot section of ditch that is fairly uniform in depth and width.
Mark the zero point and the 100 ft point with a flag or stick.
The 100 ft mark should be downstream from the zero point.
For most people, one good, long stride equals three feet.
If there is no tape measure available, step off about 33 paces.
Next, calculate the ditch cross sectional area.
Use an average of several measurements along the ditch.
Now, take a float  and place it a few feet up stream from the zero point, in the center of ditch.
Once the float hits the zero point, mark the time.
Then, mark the time the float passes the 100 ft mark.
Record the time.
Do this several times.
Try to place the float in the center of the ditch flow SO that it won't bounce off the sides or get caught up in any weeds.
After 5-10 tries, average the recorded times.
The flow rate is determined by calculating the velocity of the water and multiplying it by the cross sectional area of the ditch.
First, take the length of the ditch  and divide it by the time.
This will give the surface velocity  in feet per second.
However, water at the surface flows faster than water in the center of the flow and it is the average flow or center flow that is needed.
Therefore, a conversion factor must be used to determine the mean channel velocity.
The factor by which the surface velocity should be multiplied by is a function of the depth of the water in the ditch.
Table 1 gives the coefficients to be used.
Find the depth measured on the left and the corresponding coefficient on the right.
Then multiply the surface float velocity by the coefficient to obtain the mean channel velocity.
Finally, take the cross sectional area of the ditch  and multiply it by the corrected velocity  and this will compute the flow rate in cubic feet per second.
To convert to gallons per minute, multiply the cfs by 450.
Tracer Method: This method is very similar to the float method but with one exception, a colored dye or salt is used instead of a float.
Estimates of the ditch area are still required.
Pour the dye upstream of the zero point, and record how long it takes the dye to travel from the zero point to the 100 ft mark.
Then the calculations are exactly the same as the float method.
This method often works well if the float keeps getting caught on the sides of the ditch.
However, in many cases the dye is difficult to see because of the color of the water itself.
Test the dye first to make sure it can be seen.
The correction factors used with the float method (Table are not required for the tracer method.
Velocity Head Rod: The velocity head rod is used to measure the velocity of water in a ditch and is relatively inexpensive and fairly accurate.
The rod is in actuality a ruler used to measure the depth of the water.
The water height is first measured with the sharp edge of the ruler parallel with the flow and the again with the ruler turned 90 degrees.
The difference in the height of water is the head differential and using Table 2, an estimate of the velocity  can be made.
From there, follow the same formula as with the float or tracer method, i.e., multiply the velocity by the cross sectional area of the ditch to get cubic feet per second.
The velocity head rod method works only for velocities greater than 1.5 and less than about 10 ft/sec.
Place the rod with the sharp edge upstream.
Record the depth of the water.
Place the rod sideways.
This will cause some turbulence and the water level will "jump" causing the water level to rise.
Record the level again.
Subtract the normal depth from the turbulent depth and this will be the jump height.
Find the corresponding velocity from Table 2.
Multiply the velocity by the cross sectional area of the ditch to get the flow rate.
Weirs: There are several different types of weirs that can be constructed and used to determine the flow rate in a ditch or stream.
The three most common weirs are:  V-Notch or Triangular  Rectangular and  Cipolletti.
The simplest design is to make the weir out of a sheet of plywood or sheet metal.
Cut the wood or metal to fit ditch with the particular shape notch cut out of the top.
Make sure
 Table 2.
Conversion chart for velocity head rod measurements from inches to ft/sec.
Jump 	1/2	1	2	3	4	5	6	7	8	9	10	11	12	15	18
 Velocity 	1.6	2.3	3.3	4.0	4.6	5.2	5.7	6.1	6.5	6.9	7.3	7.7	8.0	9.0	9.8
 Figure 2.
Using a velocity Rod..
the weir is sturdy enough to hold up against the flow of the water.
Figure 3 shows an example of the three different types.
The top two are rectangular weirs.
The first is a rectangular contracted weir and is one of the most commonly used.
The second is another rectangular weir but since the sides of the weir are actually the sides of the ditch, it is called a suppressed rectangular weir.
The third type shown in Figure 3 is the Cipolletti weir.
This type of weir has a trapezoidal shaped notch.
The last type shown is a triangular or V-notched type.
With proper installation, all of these weirs can be accurate.
Contracted Triangular or V-Notch
 Figure 3.
Diagrams of various types of weirs used to measure flow rate in an open ditch..
Figure 4.
Diagram of a rectangular weir where L = width of weir opening , H = head of weir  and a = at least 3*H.
The dimensions for a contracted rectangular weir are given in Figure 4.
An estimate of the actual flow rate must be made before construction of the weir in order to make sure the notch size is correct.
For the V-notch, the dimension requirements are the same and for the Cipolletti, the requirements are also the same but with a 25% slope rising outward at the sides of the notch.
To measure the head or height of the water for these weirs, pound in a stake about 6 feet upstream SO that the top of the stake is even with the bottom of the notch in the weir.
Once in place, the water will rise behind the weir.
Measure the depth of water above the stake.
Then, use charts like the ones in Tables 3-5 to estimate the flow rate.
The length  refers to the width of the opening at the base of the weir notch.
CAUTION: Installing a weir in a ditch will cause the water behind the weir to rise.
Make sure there is enough freeboard or the water in the ditch will overflow.
Other Methods: There are several other methods available and many devices that can be purchased "off the shelf." One is a current meter, which is a propeller meter that is lowered into the stream of water and records velocity.
The flow rate  is calculated by multiplying the velocity  by the area.
There are flumes, submerged orifices and even acoustic ultrasonic meters that use ultrasonic pulses to measure the velocity of the flow stream.
All of these methods have limits to their use.
For more information, refer to the Arizona Cooperative Extension publication "Measuring Water Flow and Rate on the Farm", publication AZ1130, Arizona Water Series No.
24.
Counting Tubes: If siphon tubes are used to irrigate out of an open ditch, an estimate of the flow rate can be obtained by counting the number of tubes.
The size of the siphon tube and the distance from the water level in the ditch to the water level in the field  is needed to estimate the flow rate.
Figure 5 shows two possible conditions.
In Condition I  the drop is the distance from the water level in the ditch to the end of the tube on the field side.
In Condition II , the drop is the distance from the water level in the ditch to the water level in the field.
The larger the tube size or the greater the drop, the higher the flow rate.
Table 6 shows some typical sizes and drops used for irrigation.
Table 3.
Approximate flow over rectangular weirs..
Head	Crest length 
 	: 1 foot	: 2 feet	: 3 feet	: 2 feet
 	gpm	ac-in/hr	gpm	ac-in/hr	gpm	ac-in/hr	gpm	ac-in/hr
 2	98	0.22	198	0.44	298	0.66	398	0.88
 3	181	0.40	366	0.81	552	1.22	738	1.63
 4	278	0.62	560	1.24	852	1.88	1140	2.52
 5	772	1.70	1164	2.58	1560	3.54
 6	1010	2.22	1535	3.40	2055	4.54
 7	1270	2.80	1980	4.27	2590	5.75
 8	1540	3.40	2330	5.18	3120	6.90
 Table 4.
Approximate flow over 90-degree triangular weirs..
in inches	per minute	per hour
 Table 5.
Approximate flow over trapezoidal weirs.
The length "L" refers to the length of the bottom of the trapezoid..
Head	Crest length 
 	: 1 foot	: 2 feet	: 3 feet	: 2 feet
 	gpm	ac-in/hr	gpm	ac-in/hr	gpm	ac-in/hr	gpm	ac-in/hr
 2	101	0.22	202	0.45	302	0.67	404	0.89
 3	190	0.42	376	0.83	560	1.24	750	1.66
 4	296	0.65	580	1.28	864	1.91	1160	2.56
 5	802	1.77	1196	2.66	1500	3.52
 6	1062	2.34	1530	3.50	2100	4.64
 7	1350	2.98	2000	4.42	2660	5.88
 8	1638	3.62	2430	5.38	3220	7.14
 Figure 5.
Diagrams where to measure the drop distance for siphon tubes..
Table 6.
Approximate flow rate in gallons per minutes for siphon tubes.
Flow Rate 
 Drop 	4"	6"	8"	10"
 3/4"	3.6	4.4	5.0	5.6
 1"	6.4	7.9	9.0	10.0
 1 1/4"	10.4	12.7	14.6	16.2
 1 1/2"	14.3	17.5	20.2	22.5
 2"	25.6	31.8	35.9	40.0
 3"	57.2	70.0	80.8	90.0
 Figure 6.
Three photos demonstrating how to measure the "drop" in a surface system.
The drop is the distance from the level of the water in the ditch to the water level in the field.
Use the hose to siphon water out of the ditch;  Raise the hose up until water stops flowing out of the hose end;  Measure the distance between the end of the hose and the water level in the field.
It is often difficult to measure the difference in water levels between the ditch and the field.
One easy way is to do this is to get a piece of hose and a tape measure.
Put the hose in the ditch and use it to siphon water into the field.
Next, slowly raise the hose in the field until the water stops coming out.
Now, use your measuring tape to measure the distance between the end of the hose and the water level in the field or the outlet of an irrigation siphon tube.
Make sure to keep the end up just at the level where the water stops coming out.
This distance is your drop!
Measuring Flow in Gated Pipe
 Measuring water flow in gated pipe can be accomplished many different ways.
Probably the most commonly used method is the propeller meter.
These meters are normally installed inside a section of pipe at the distributor's shop.
The buyer then simply buys a meter section for whatever diameter pipe used.
There are some other methods that can be used but for convenience and lease of measurement, the propeller is a simple and accurate method.
Table 7.
Typical range of flows for different size propeller meters.
Meter size	Minimum flow	Maximun flow
 Figure 7.
A Mc Propeller from McCrometer, Inc.
This propeller meter is installed inside a pipe section.
Figure 8.
Two photos showing how to measure the head  in a gated pipe system.
The head is the distance between the water level in the tube and the center of the pipe.
These are Rite-Flow gates and there is about 3 ft of head.
According to Table 8, the flow is approximately 39 gpm per gate.
Table 8.
Approximate flow capacities in gallons per minute  for some commercially available gates.
Gates are wide open..
Head 	Rite-Flow	Epp TM Snap-Top	Epp	Tex-Flow
 Boot Gate	Fly Gate	Yellow Top
 0.25 	11	12	15	22
 0.50 	16	17	21	32
 1.00	22	24	30	46
 2.00	32	35	42	67
 3.00	39	42	52	82
 Propeller meters are permanent pipeline devices that measure and record the volume and flow of water moving through a pipe.
The pipe must be running at full flow for the meters to operate properly.
Also, there must be a straight length of pipe upstream from the meter at least 10 times the diameter of the pipe.
This is to reduce the turbulence in the water as it enters the meter section.
Thus, a 6-inch pipe would require 60 inches of straight pipe upstream from the meter.
Table 7 gives the range of flows for various size meters and Fig.
7 shows a cross-sectional view of a typical meter.
The meters are usually placed inside a length of aluminum pipe that is inserted into the gated pipe system.
If poly-type plastic pipe is being used, there are connectors that will allow a meter section to be put in place.
If you don't want to pay the expense for the meter, you can use a piece of tubing, similar to the tube method for ditches.
Find a piece of tubing  that either fits tight inside a gate or even better, can be attached tightly to the outside of the gate.
Raise the tubing into the air until the water stops flowing out.
Measure the distance from the water level in the tubing to the center of the gated pipe.
If clear tubing is used, then you can raise the tube well above the point when the water stops coming out and it makes for an easier measurement.
Table 8 gives some estimate of flow rates for various manufacturers gates.
Most manufacturers should be able to supply this information.
There are many methods that can be used to measure flow rate and only the most common have been covered in this paper.
In addition, there are meters that use ultrasound waves to measure flow in pipes, flumes, gates and even a Doppler-type acoustic meter.
Although these are relatively expensive, the price has come down in recent years and the technology is being applied throughout the agricultural sector.
Measuring flow is the first step in determining how much water is being applied to a field.
With the flow rate, the area irrigated and the time of irrigation, you can calculate the amount of water applied.
For information on calculating how much water was applied, read the University Arizona Cooperative Extension publication Determining the Amount of Water Applied to a Field, Pub.
No.
AZ1157, Arizona Water Series No.
29.
Chapter: 43 Identification and Control of Herbicide-resistant Weeds
 Since the 1960s, when the first triazine-resistant weed was reported, there has been a steady increase of herbicide-resistant biotypes, with over 250 incidents of herbicide resistance reported in the U.S.
in 2015.
The frequent use of single site-of-action herbicides across multiple crops and years has been reported to accelerate herbicide-resistance selection in weed populations.
Using application rates below the label recommended rates may also reduce herbicide effectiveness and promote herbicide resistance.
Often the problem is first observed as a few scattered plants that survive herbicide applications.
However, due to the ability of these weeds to produce thousands  of seeds per plant, the survival of even a few plants allows the biotype to quickly become a widespread infestation.
Herbicide resistance is a inheritable trait, passed from one generation to the next.
This means that once the trait is in the population, other methods of control are needed to control the remaining plants.
In addition, some herbicide-resistant biotypes show resistance to different herbicides that have different sites of action.
To reduce selection for herbicide-resistant biotypes, it is necessary to diversify weed-management programs, crop rotations, and the types of herbicide chemistries and sites of action that are used.
The best time to take action against pesticide resistance is BEFORE the resistance is in your field or area.
Unfortunately, most action is taken as a REACTION to the problem when it occurs, rather than before it is seen.
Programs for herbicide-resistance management should include cultural, mechanical, sanitation, herbicide mode-of-action rotations, and crop rotations.
Herbicide-resistant Biotypes in South Dakota
 Kochia biotypes resistant to ALS herbicides   were first reported in South Dakota in 1998.
The problem was noted in northeastern SD after only three consecutive seasons of ALS herbicide use.
In 2007, a common ragweed biotype was the first glyphosate-resistant 
 Weed Species	State	Resistance Sites of Action and WSSA Group Number
 Kochia	SD, MN, ND	ALS inhibitors 
 	IA, ND, NE	Photosystem II inhibitors 
 ND, NE	Synthetic auxins 
 SD, NE, ND	EPSPS inhibitors 
 ND	Multiple resistance : Photosynthesis inhibitors
 
 Common sunflower	SD, IA	ALS inhibitors 
 Common ragweed	SD, ND, MN, NE	EPSPS inhibitors 
 	MN	ALS inhibitors 
 MN	Multiple resistance : ALS ;
 EPSPS inhibitors 
 Giant ragweed	NE, MN, IA	EPSP inhibitors 
 	IA	ALS inhibitors 
 MN	Multiple resistance : ALS inhibitor (WSSA
 Group 2); EPSPS inhibitors 
 Wild oat	SD, MN, ND	ACCase inhibitors 
 	SD, ND	ALS inhibitor 
 SD	Multiple Resistance : ACCase inhibitors
 ; ALS inhibitors 
 Tall  Waterhemp	SD, NE, MN, IA, ND	EPSPS inhibitors 
 	IA, MN	ALS inhibitors 
 IA, NE	Photosystem II inhibitor 
 IA	PPO inhibitor 
 NE	Synthetic auxins 
 NE	HPPD 
 MN	Multiple Resistance : ALS inhibitors (WSSA
 Group 2); EPSPS inhibitors 
 IA	Multiple Resistance : ALS inhibitors ; HPPD
 ; Photosystem II inhibitor 
 IA	Multiple Resistance : ALS inhibitors (WSSA
 Group 2); HPPD ; Photosystem II inhibitor
 ; EPSP synthase inhibitor 
 Redroot pigweed	MN	Photosystem II inhibitor 
 	ND	ALS inhibitor 
 Palmer amaranth	NE	Photosystem II inhibitor 
 	NE	HPPD 
 Horseweed	SD, NE, IA	EPSPS inhibitors 
 Common lambsquarters	MN, IA	Photosystem II inhibitor 
 Velvetleaf	MN	Photosystem II inhibitor 
 Common cocklebur	IA, MN	ALS inhibitors 
 Weed Species	State	Resistance Sites of Action and WSSA Group Number
 Marshelder	ND	ALS inhibitors 
 Shattercane	NE, IA	ALS inhibitors 
 Wild mustard	ND	ALS inhibitors 
 Eastern black nightshade	ND	ALS inhibitors 
 Pennsylvania smartweed	IA	Photosystem II inhibitor 
 Giant foxtail	IA	Photosystem II inhibitor 
 	IA	ACCase inhibitors 
 MN	ALS inhibitors 
 Yellow foxtail	MN	ALS inhibitors 
 Giant green foxtail	MN	ALS inhibitors 
 	MN	ACCase inhibitor 
 WSSA group	Site of action	Examples
 1	ACCase inhibitor	Clethodim, quizalofop
 2	ALS inhibitor	Imazethapyr, cloransulam
 3	Microtubule inhibitor	Pendimethalin, trifluralin
 4	Growth regulator 	2,4-D, clopyralid, dicamba
 5	Photosynthesis inhibitor  	Atrazine, Metribuzin
 6	Photosynthesis inhibitor 	Bentazon
 9	EPSPS inhibitor	Glyphosate
 10	Glutamine synthetase inhibitor	Glufosinate
 13	HPPD inhibitor or "Bleacher"	Clomazone
 14	Cell membrane disrupter 	Carfentrazone, lactofen
 15	Seedling shoot inhibitor  	Acetochlor, metolachlor
 22	Cell membrane disrupter  1 inhibitor)	Paraquat
 weed identified in South Dakota.
Since then, glyphosateresistant biotypes of waterhemp, kochia, and horseweed have been confirmed and grass weeds, particularly wild oat, have been reported to be resistant to ALS  and ACCase  herbicides.
Among all the resistant biotypes reported, kochia and waterhemp appear to be the most widespread and problematic.
Figure 43.1 shows where glyphosateresistant biotypes of several weed species have been confirmed, but unconfirmed populations maybe much more extensive.
How and Why do Herbicide-resistant Weeds Develop?
Weeds become resistant to an herbicide when offspring from a once-controlled weed develops a characteristic that makes it less susceptible to an herbicide.
Resistance may occur from a biochemical change, such as enhanced production of a sensitive enzyme, or a physical change  that reduces herbicide uptake or reduces movement of an herbicide within a plant.
Glyphosate-resistant biotypes have been reported to have seven different and distinct mechanisms of resistance, including hypersensitivity  that does not allow the herbicide to translocate; changed site of action caused by one or two amino acid changes in the sensitive region of the enzyme; and multiple  copies of the gene targeted by the herbicide.
These mechanisms of resistance can cause the biotype to have 3 to 100 times less sensitivity to glyphosate than the wild, sensitive types.
Repeated use of herbicides with the same mode-of-action allows any offspring that possesses these new characteristics to survive, produce seed, and develop increased densities after a few years.
Confirmed glyphosate resistant weeds in South Dakota
 Figure 43.1 Approximate locations of confirmed glyphosate-resistant weed species in South Dakota.
Management to Prevent Resistance
 Preventing herbicide resistance requires a diversified and integrated weed-control program.
Fieldscale changes in weed species composition occur slowly.
Utilize a diverse management system that conscientiously and proactively selects methods to minimize the chances of resistant weeds becoming a problem.
This management tactic is more practical than responding after resistance has occurred.
By the time the problem has been noticed, populations often have become widespread across one or multiple fields and weed seed banks have increased.
It should be noted that using ANY single method of management continuously can produce problems.
For example, tillage at the same time every year reduces the weeds that emerge at that time but may favor early emerging species that are now too large to control, or encourage late-emerging species that are missed by the tillage implement.
Diversified weed-management programs should include biological, mechanical, cultural, sanitation, and herbicide options.
Such management programs should:
 Rotate crops that do not require the use of the same herbicides year after year.
Use mechanical weed-control options when appropriate.
Practice good sanitation for equipment , seeds, manure spreading, and areas around fields.
Crop Rotation: Crop rotations may include different crop species, such as wheat, soybean, or crops that
 require different herbicide programs, such as conventional or LibertyLink varieties.
Rotating crops with different life cycles, such as winter annuals , annuals , or short-season annuals , also can disrupt weed life cycles and enable different control options.
Note that to minimize problems of not matching herbicides with crop characteristics or rotating to crops where carryover may be a problem, excellent field records are required.
In addition, always follow labeled instructions including rate, herbicide compatibility, surfactant addition, application timing, use frequency, and maximum allowable rate in a season.
Scout Fields: Always scout the field to understand what weeds are present prior to an herbicide application and choose the chemical solutions with the best efficacy for the weed spectrum present.
Scouting after application and recording weed escapes is vital information for future planning.
Poor herbicide efficacy could be caused by a number of issues, including faulty equipment, skips, incorrect mixing, and climate issues.
These problems must be ruled out before claiming that herbicide resistance was the cause.
Use Pre-emergence Herbicides: Pre-emergence herbicide application is recommended to ensure consistent weed control.
Pre-emergence and postemergence herbicides should be chosen with different sites of action to avoid selecting for resistance to another herbicide site of action.
In addition, it is also important to avoid using herbicides with similar sites of action during two consecutive years.
If Herbicide-resistant Biotypes are Present
 When controlling herbicide-resistant biotypes always include herbicides that have a different site of action than the confirmed  resistance.
In no-till fields, added challenges associated with managing herbicideresistant biotypes have caused some people to abandon no-till practices.
However, tilling fields may prolong the persistence of herbicide-resistant weed seed banks.
South Dakota State University research has demonstrated that common ragweed seed left on the soil surface in a no-tillage field may cause greater weed densities the following year, but if emerged plants are controlled, the seed bank becomes depleted in just a few years, compared with densities in tilled fields where seeds may be dormant and persist for a longer period of time.
As herbicide-resistant biotypes become more common, it will become increasingly important to minimize weed seed movement among fields.
It is always important to clean equipment before entering different fields to prevent the spread of weed species.
It is commonly believed that new infestations of glyphosate-resistant weeds are most often caused by independent selection within that field rather than movement of seeds between fields.
However, some weeds may be adapted particularly well to movement into different fields.
"Tumbleweed" species, such as kochia, may roll to adjacent fields, while spreading weed seeds.
Other weed species may be SO problematic that preventing new infestations may justify the time required to clean equipment.
Palmer amaranth  is an annual weed that looks similar to waterhemp, but may have a slightly faster growth rate and may adapt to herbicides more quickly (see
 Figure 43.3 Kochia shoots can be trapped by a roadside vegetation 
 Chapter 38).
In the Southern U.S., Palmer amaranth has proven to be a very challenging weed to control in fields.
Some biotypes have developed resistant to formulations that contain single, as well as multiple modes-of-action, including glyphosate , ALS  and PPO  herbicides.
There is concern that Palmer amaranth has moved to South Dakota and other Northern states as a contaminant of cotton seed used as livestock feed, with livestock manure, or through unclean harvesting equipment.
This has already occurred in Michigan and Nebraska.
As of 2015, there are confirmed patches of Palmer amaranth in Sully, Douglas, and Bennett counties of SD.
In one case, manure from animals fed in the Southern states was spread, along with Palmer amaranth.
Avoiding Selection for Additional Herbicide-resistant Weed Biotypes
 Diversifying weed-management programs to control a particular resistant-biotype in a field does not mean that another species will not be selected in the future.
Most herbicides are effective only on a limited number of weed species.
There are many weeds that are not resistant to glyphosate but are difficult to control because they are less sensitive to glyphosate.
If not carefully managed, these weeds could produce glyphosate-resistant biotypes.
It is important to consider other challenging weed species when developing a management plan to control herbicide-resistant species.
For example, adding fomesafen with glyphosate may effectively control glyphosate-resistant biotypes of waterhemp but would provide only limited control of common lambsquarters or velvetleaf.
Therefore, it will be important to monitor populations of these other difficult species, make management adjustments when necessary, and be sure to use effective management programs for these species in rotational crops.
South Dakota Glyphosate-resistant Weeds
 Herbicide-resistant kochia  is a challenging weed in corn.
ALSresistant kochia was first seen in the mid-1990s in wheat and soybean fields of northeastern SD  after just 3 years of ALS inhibitor herbicide applications.
In some fields, over 1000 seedlings per ft2 were present early in the season.
Glyphosate-resistant kochia was confirmed near Gettysburg, SD in 2009.
Since then, scouting reports suggest that infestations have been expanding.
Kochia is a very prolific seed producer as plants may produce approximately 500 seeds/g shoot biomass , which is nearly three times as much as common lambsquarters and five times as much as giant foxtail.
Seed spreads very rapidly to form new infestations because of the plant's tumbleweed tendencies when it becomes mature, which scatters plants across fields and in mats along fence lines.
Pre-emergence herbicides such as atrazine may be very effective in controlling kochia infestations, but care must be taken as triazine-resistant kochia has been reported in neighboring states.
There are several broadleaf herbicides available for kochia control in corn.
However, consecutive use of the same site of action and even mixtures with herbicides having multiple sites of action may contribute to resistance.
In no-till fields, kochia may be one of the first weeds to emerge in the spring.
Therefore, an effective
 burn-down herbicide program prior to corn planting may eliminate much of the kochia infestation.
However, effective burn-down herbicide options are not well-known as glyphosate has previously been the standard herbicide.
2,4-D is a common burn-down herbicide but will not likely be effective on many kochia populations.
Indeed, some auxin-resistant biotypes have been reported in North Dakota, SO care must be taken to rotate out of this herbicide family as well.
Potentially effective options could be paraquat , glufosinate , or lactofen.
Since kochia emerges very early in spring, a late-fall application of a soil residual herbicide may provide suppression or control in early spring.
LibertyLin corn may be an alternative option.
Since Liberty acts like a contact herbicide with limited mobility in plants, the first application must be applied to small weeds  with few growing points.
Like contact herbicides, glufosinate requires the use of more water per acre  than glyphosate, but this will be necessary for any postemergence herbicide for glyphosate-resistant kochia.
The lack of kochia seed dormancy may be a characteristic that could be exploited to minimize densities in soybeans.
Recent research at SDSU and elsewhere indicates that less than 10% of kochia seed may survive in soil for longer than a year.
Therefore, it may be possible to reduce kochia densities by aggressively managing it in corn or wheat.
However, the prolific seed production potential of kochia will require nearly complete control in order to deplete the seed bank.
In addition, since the kochia shoot acts as a tumbleweed, fencerows can have extremely high densities of seedlings that could result in over 10 mature plants/ft2 by the end of the growing season.
Treating these areas with a selective herbicide may reduce one potential source of future kochia infestations.
A glyphosate-resistant biotype of the annual weed waterhemp  was confirmed in 2010 in South Dakota.
Since then, field surveys suggest that glyphosate-resistant waterhemp is common.
Table 43.1 indicates that in surrounding states, waterhemp biotypes have been found that are resistant to five other site-of-action chemistries, with some biotypes having multiple resistances.
In most cases, effective management requires both pre-emergence and postemergence herbicide applications to ensure consistent waterhemp control.
To avoid selecting for additional herbicide-resistant weed biotypes, herbicides with different sites of action should be used when possible.
Most of the waterhemp in SD is also resistant to WSSA Group 2 herbicides , SO those herbicides will not control the ALS-resistant waterhemp.
It has not been shown that waterhemp resistant to both chemicals is present in South Dakota fields.
However, no matter which herbicide program is followed, best control of waterhemp results when the application is applied to small  plants and uses enough water per acre to ensure thorough herbicide coverage of the weeds.
Auxin herbicides  in corn may give excellent control, but care must to taken to apply at these herbicides at the correct corn growth stage to avoid green snap or brace root problems.
Waterhemp can produce upwards of 100,000 seeds per plant, if the plant emerges early.
Later emerging waterhemp may produce only 100 seeds.
This emphasizes the importance of
 early season control.
Waterhemp seed may survive in the soil for 4 to 5 years , SO seed bank depletion may require aggressive control for several years.
Aggressive control would require pre-emergence and postemergence herbicides, at labeled use rates, in corn and rotational crops, such as soybean.
In addition, field edges may be treated with selective herbicides  to control waterhemp plants that may be a seed source for future infestations.
Horseweed  
 Glyphosate-resistant horseweed  has become relatively common in eastern South Dakota no-till fields.
Horseweed is generally a winter annual species that emerges in the fall and continues growth in the spring, but some plants may emerge in the spring after burn-down applications.
Consequently, fall herbicide applications may reduce horseweed densities the following year.
Spring burndown herbicide programs may require herbicides that have foliar and soil residual activity.
Herbicides with foliar activity include 2,4-D, or saflufenacil.
Soil residual herbicides include saflufenacil, atrazine, or flumetsulam.
Postemergence herbicide options are limited and should be applied while horseweed is small.
However, the goal should always be to control horseweed prior to corn emergence.
Common Ragweed 
 Glyphosate-resistant common ragweed  was first confirmed in 2007 and was the first confirmed glyphosate-resistant weed in South Dakota.
However, occurrences of resistance seem to be expanding much more slowly than kochia and waterhemp.
There are a number of pre-emergence and postemergence herbicides that can provide good to excellent control of common ragweed in corn.
Figure 43.7 Horseweed seedlings in the fall may be very small and difficult to see.
Although volunteer crops are often not considered typical weeds, they do reduce yields.
In addition they may be herbicide resistant.
Volunteer corn in hybrid corn and volunteer soybean in corn can be
 problematic.
Low densities (1 plant/ft2 of volunteer corn can reduce hybrid corn yield by about 3% with higher densities reducing yield up to 30%.
Grain from volunteer corn can be harvested, but it may be of lower quality, be at an incorrect moisture content, or be a bridge to insect and disease problems.
Even partial control of volunteer corn can increase corn yields.
Hybrid selection is crucial to successfully control corn from past corn crops.
For example, if the recent past hybrid corn was glyphosateresistant, conventional hybrids, of ALS-resistant or glufosinate-resistant hybrid corn may be selected.
In most instances, volunteer soybean has not been thought of as a weedy species.
However, Alms et al.
reported that volunteer glyphosate-resistant soybean at low densities (1-5 plants/ft can reduce corn yield 10%.
This corn yield reduction is similar to reductions that can be observed with similar densities of velvetleaf or redroot pigweed.
At high densities, volunteer soybean can reduce corn yield by 50% or more.
Volunteer soybean, at present, can be managed using common corn herbicides, however, as new herbicide-tolerant varieties are introduced, control may become more difficult.
North Carolina Cooperative Extension Service North Carolina State University
 Irrigated Acreage Determination Procedures for Wastewater Application Equipment
 Irrigation continues to be the most practical and cost effective method of applying wastewater to fields so that the nutrients contained in the wastewater can be used by growing crops.
However, irrigation systems have inherent application limitations that make field calibration, irrigation scheduling, and determination of irrigated acreage critical for proper use of the nutrients contained in the applied wastewater.
Irrigation systems are normally designed to satisfy equipment specifications provided in manufacturers' charts.
Information presented in manufacturers' charts are based on average operating conditions for relatively new equipment.
Discharge rates and precipitation rates change over time as equipment ages and components wear.
Poor designs and/or improper operation can also cause poor performance.
As a result, equipment should be field calibrated regularly to ensure that application rates and uniformity are consistent with values used during the system design and given in manufacturers' specifications.
Field calibration is a simple procedure that involves collecting and measuring the material being applied at several locations.
Step-by-step guidelines for field calibration of stationary sprinkler irrigation systems are given in Extension publication AG-553-1, Field Calibration Procedures for Animal Wastewater Application Equipment: Stationary Sprinkler Irrigation System.
Irrigation must be scheduled when fields are dry enough to retain all of the applied liquid within the root zone.
If soils are too wet during irrigation, some of the applied wastewater may run off the field or leach below the root zone and become unavailable to the crop.
These unused nutrients could contaminate surface or ground water supplies.
Determining when and how much wastewater to apply for the prevailing conditions is referred to as irrigation scheduling.
Irrigation scheduling techniques and procedures are outlined in Extension publication AG-452-4 Irrigation Scheduling to Improve Waterand Energy-Use Efficiencies.
Sprinkler irrigation systems do not uniformly apply water throughout their entire wetted area.
Application depths tend to be higher near the sprinkler and decrease gradually within the first 60 to 70 percent of the wetted radius.
Beyond this point, the application depth declines quickly to zero at the outer edge.
Irrigation design guidelines take equipment limitations into account in establishing recommended overlap ranges to optimize uniformity of coverage.
Determining the uniformly irrigated area for stationary sprinklers can be difficult for sprinklers located along the perimeter of the field, for nonuniform sprinkler spacings, or for sprinkler systems with improper overlap.
This publication contains step-by-step guidelines for determining irrigated acreage of stationary sprinkler irrigation systems.
Sprinkler spacing and design guidelines have been developed primarily for freshwater irrigation with the primary goal of ensuring that those areas of the field receiving the least amount of water receive an adequate amount to sustain the crop and achieve yield goals.
To achieve minimum desired application depths within the "lighter application zones," sprinkler spacings of 50 to 65 percent of the wetted sprinkler diameter have been determined to be "optimum" to compensate for the declining application along the perimeter.
Narrower spacings are typically justified for smaller sprinklers and higher value crops.
However, narrower spacings may also result in some zones receiving more water than necessary, and certainly more than the average.
A good irrigation design considers these factors and uses a sprinkler spacing that achieves a balance between the relative proportion of "under" and "over" irrigated areas in order to achieve the most uniform application possible.
The application uniformity can be quantified using one of several uniformity indices.
The uniformity index recommended for wastewater application is the Christiansen Uniformity Coefficient, U Step-by-step computational procedures are outlined in Extension publication AG-553-1, referenced in the previous section.
An application uniformity index of 50 is the minimum acceptable for wastewater application using stationary sprinklers.
Irrigation systems should be field calibrated regularly to ensure that application uniformity is within the acceptable range.
Field calibration can also be used to determine the area within a field receiving an acceptable uniform application.
In an effort to answer technical specialists' questions and to provide uniform interpretations of the state's animal waste management rules, the North Carolina General Assembly formed an interagency committee in 1996.
The SB 1217 Interagency Committee is composed of two representatives of each of the five agencies with responsibilities for the development and/or enforcement of animal waste management rules.
The committee recently adopted guidelines and procedures for determining the irrigated acreage that can count toward the acreage needed to
 satisfy the land application requirements in the Certified Animal Waste Management Plan.
The committee considered many factors including recommendations from irrigation engineers, certified irrigation designers, and industry representatives before arriving at these guidelines.
The irrigated acreage determined by these procedures is intended to "reasonably and practically" account for physical limitations of the application equipment.
The "irrigated acreage" computed by the procedures presented below must equal or exceed the acreage requirement specified in the CAWMP for proper nutrient use.
The irrigated area determination includes two broad categories: existing irrigation systemsthose systems installed before the guidelines were finalized-and new or expanded irrigation systems installed after the SB 1217 committee released the third revision of the Sixth Guidance Document.
Future updates and revisions may occur, SO you should refer to the most recent Guidance Document for the latest interpretation and effective dates.
For the purpose of computing the irrigated acreage available to satisfy the CAWMP, the SB 1217 Interagency Committee adopted the term "CAWMP wettable acre" to be applied to existing systems.
The irrigated acreage for new or expanded systems should be based on standard irrigation design guidelines, which are based on the effective design area.
The term expanded irrigation system applies to new irrigation components that wet an area of a field that was not wetted before adoption of the new guidelines.
These terms are defined below.
Existing irrigation systems-For stationary sprinkler systems designed and installed in accordance with standard overlap recommendations  and laid out with multiple overlapping laterals, the irrigated area allowance is the entire "net wetted area" in the field.
The net wetted area is the part of the field that gets "wetted" by one or more sprinklers when operated during normal conditions, i.e., wind speed under 5 mph.
The "wetted area" for a single sprinkler operated without overlap is the area inscribed within its wetted diameter as shown in Figure 1.
For multiple sprinklers such as shown in Figure 2, the entire shaded area gets wetted; however, in this case, the wetted area is
 STATIONARY SPRINKLER IRRIGATION SYSTEM
 Figure 1.
Wetted area of a stationary sprinkler operated without overlap.
referred to as "net wetted area." Due to overlap, some areas are wetted by multiple sprinklers.
Obviously these overlap areas cannot be counted twice, hence the term "net" is used.
The sprinkler spacing is represented by the inscribed rectangle.
For a stationary sprinkler system, there are two sprinkler designations within the field that affect determination of irrigated acreage.
An interior sprinkler is any sprinkler that receives overlap on all sides.
For a rectangular spacing within the recommended spacing range , an interior sprinkler receives overlap from eight adjacent sprinklers as shown in Figure 3, although only four sprinklers contribute significant overlap.
An interior sprinkler is a sprinkler that receives overlap from the four adjacent sprinklers along perpendicular transects
 Figure 2.
Net wetted area for multiple sprinklers in a square sprinkler pattern.
Figure 3.
Relative position of interior and exterior sprinklers.
drawn through the sprinkler in question.
For the sprinkler pattern shown in Figure 3, only the three center sprinklers are interior sprinklers, and the net wetted area for one interior sprinkler is represented by the center shaded rectangle.
The other 12 sprinklers are exterior, and the net wetted area of one exterior sprinkler is represented by the top shaded area.
Note that the two shaded areas are not the same size.
For stationary sprinkler systems arranged in a single lateral pattern, the net wetted area should be computed based on 90 percent of the wetted diameter as shown in Figure 4.
The outer portion that does not overlap with an adjacent sprinkler is not included for reasons explained in the next section.
For any system in which the lateral spacing exceeds 70 percent of the wetted diameter, each lateral should be treated as a "single lateral" case.
If sprinkler spacing along the lateral also exceeds 70 percent of wetted diameter, each sprinkler should be treated as a single sprinkler case.
Figure 4.
Net wetted area of stationary sprinklers arranged along a single lateral.
The system layout, including determination of lateral and sprinkler spacing, lateral configuration, and number of interior and exterior sprinklers, must be determined in order to compute the CAWMP wettable acres.
New or Expanded Irrigation Systems-
 New or expanded irrigation systems should follow recommended design standards, which base the allowable irrigated area on the effectively irrigated area, referred to as the "design area."
 The effective irrigated area is the wetted area that receives at least 50 percent of the target application amount.
Recent field calibration measurements have determined this to be the area that falls within 78 percent of the wetted radius as shown in Figure 5.
Note that application depths remain within 90 percent of the target amount out to 60 percent of the wetted radius.
Between 60 and 70 percent of the wetted radius, application amounts still remain within 80 percent of the target application amount.
But beyond 70 percent of the wetted radius, application amounts drop off quickly, declining to 50 percent by 78 percent of the wetted radius.
Beyond 90 percent of the wetted radius,
 Figure 5.
Application depth as a function of distance from gun sprinklers as determined from field calibration measurements.
Figure 6.
Sprinkler spacing as a percent of wetted diameter where the 50 percent application from adjacent sprinkler overlaps.
the application depth drops below 20 percent.
Traditional design spacing guidelines established by the North Carolina Cooperative Extension Service for stationary sprinklers have been 50 to 65 percent of manufacturers' published wetted diameter.
When sprinklers are arranged in a square pattern, the point of intersection of the 50 percent application amount  occurs at a sprinkler spacing of 68 percent of the wetted diameter.
This is shown graphically in Figure 6.
At wider spacings, there is inadequate overlap resulting in "dry zones." The relative proportion of dry zone  increases as the spacing increases.
A conservative rule of thumb for sprinkler spacing has been not to exceed 65 percent of the manufacturer's published wetted diameter.
Recent measurements on more than 50 systems determined that field-measured wetted diameters averaged 10 percent less than values published by manufacturers.
A spacing based on 70 percent of field-measured diameter is roughly the same as a spacing based on 65 percent of manufacturers' values.
The data presented in Figure 5 confirm irrigation design specifications previously recommended by the North Carolina Cooperative Extension Service and should continue to
 STATIONARY SPRINKLER IRRIGATION SYSTEM
 be applied to new or expanded systems.
Spacings greater than 70 percent of the verified wetted diameter or 65 percent of the wetted diameter published in manufacturers' literature are considered excessive and result in unacceptable uniformity.
The irrigated area allowance of a single or excessively spaced sprinkler is the area inscribed within 78 percent of the wetted radius as shown in Figure 7.
This is regardless of when the system was installed.
You should treat a stand-alone sprinkler or any sprinklers located on laterals in which the lateral spacing and the sprinkler spacing along the lateral exceed 70 percent as a single sprinkler.
For example, in Figure 7, the spacing along the lateral is 90 percent of the wetted diameter, SO the area of each sprinkler is computed as a single sprinkler rather than as a single lateral as was shown in Figure 4.
In Figure 4, the shaded areas overlap, therefore computations are based on a "single lateral." In Figure 7, the shaded areas do not overlap, therefore the computations are based on each sprinkler individually.
To accurately calculate the irrigated area, determine the wetted diameter or radius of the sprinkler system.
There are two methods for determining the wetted diameter, and both require operating the system:
 Directly measure the wetted diameter , which is the preferred method
 Estimate wetted diameter from field-measured sprinkler pressure and values published in manufacturers' charts for the observed pressure.
Footprint measurement-Footprint measurement involves observing, marking, and measuring the farthest distances from the sprinkler that get wetted.
Field data should be collected on at least two sprinklers located on two different lateral lines farthest from the pump.
In both cases, the sprinklers should be located at least 1/4 of the way down the lateral line.
Measurements should be made during very light wind.
The wetted distance from each sprinkler should be determined at four points along the perimeter as indicated in Figure 8.
The system should be operated long enough for all air to be purged from the system before starting to make measurements.
With the system operating at normal pressure:
 1.
Standing just outside the wetted perimeter, observe and flag the farthest point getting wetted for each of three consecutive passes of the sprinkler.
2.
Select one flag to mark the average distance of the three observations.
Remove the other two flags.
3.
Move 90 degrees around the wetted perimeter and repeat steps 1 and 2.
Continue until the wetted perimeter has been flagged on four sides of the sprinkler as shown in Figure 8.
4.
Move to sprinkler #2 and repeat steps 1 through 3.
5.
Measure and record the distances from the sprinkler to each flag.
6.
Determine the average of the four measurements for each sprinkler.
7.
Compare the two sprinklers, and if the measurements are within 10 percent, compute the average of the two and this will be the wetted radius.
If the difference between the measurements is more than 10 percent, repeat steps 1 through 6 for a third sprinkler.
8.
Compare the measurements for all three sprinklers and identify the two that are closest.
If their difference is less than 10 percent, compute the average of the two, and this value is the wetted radius.
If the difference is more than 10 percent, repeat steps 1 through 6 until you identify two sprinklers that fall within 10 percent of each other.
Pressure measurement-The wetted diameter can also be estimated from pressure measurements if the pressure is measured at the sprinkler.
Pump pressure is NOT an acceptable substitute.
Collect field data for at least two sprinklers located on two different lateral lines farthest from the pump.
In both cases, the sprinklers should be located at least 1/4 of the way down the lateral line.
The system should be operated long enough for all air to be purged from the system before measuring the pressure.
If you are using portable quick-connect risers, it is suggested that you configure one riser with a pressure gauge SO that you can easily move the entire assembly
 Figure 7.
Effective irrigated area of a single sprinkler when sprinkler spacing exceeds 70 percent of wetted diameter.
to several laterals.
This riser-pressure gauge assembly should be an "extra" riser and used only when pressure measurements are needed.
If it is used routinely, the gauge will soon foul and give erroneous measurements.
For permanent risers, you should install a tee with a threaded reducing port in two riser pipes.
You should temporarily install a pressure gauge in the threaded port to make pressure measurements.
Once the measurement has been made, it is recommended that you remove the gauge and plug the port.
The same gauge can be used at all locations.
An alternative approach is to install a shut-off valve between the riser pipe and pressure gauge and leave the gauge permanently mounted.
It is also necessary to determine the exact size of the nozzle opening.
Most manufacturers stamp the nozzle size on the end of the nozzle.
If this is not readable, a drill index can be used to determine the size of small nozzles.
Simply insert the shank end of a drill bit into the nozzle opening until a bit providing a snug fit is found.
Read and record the size of the drill bit.
Once you have measured the operating pressure and nozzle opening, you can estimate the wetted diameter from manufacturers' literature.
When using Tables 1 through 5 to determine irrigated acreage, reduce the value taken from manufacturers' charts by 10 percent.
Once you have collected the necessary field data and determined the wetted radius or diameter, you can compute the CAWMP wettable acres.
Figure 8.
Field determination of sprinkler wetted radius.
Computations are not difficult; but they can become cumbersome for non-uniform sprinkler spacings, sprinkler systems with improper overlap, and sprinklers located along the perimeter of the field.
To simplify the determination of irrigated acreage, computations have been tabulated in Tables 1 through 5 for typical spacings and patterns.
Use of these tables requires precise determination of wetted diameter, system layout, and the number of interior and exterior sprinklers as defined earlier.
A flowchart for using the tables is shown in Figure 12.
Irrigated acreage based on net wetted area for existing systems is shown in columns , , and  in Tables 1 through 5.
Irrigated acreage based on design area for new or expanded systems is shown in columns , , and.
You should follow these general guidelines in using these tabulated values.
Decisions are to be made on a field-by-field basis as referenced in the CAWMP.
1.
Determine the number of interior and exterior sprinklers for each field.
2.
Determine whether the system in each field satisfies the existing or new designation.
3.
From the Field Data Worksheet, determine the lateral spacing and sprinkler spacing along the lateral.
4.
Determine whether the system satisfies the multiple lateral or single lateral pattern.
If the lateral spacing exceeds 70 percent of the
 wetted diameter but the sprinkler spacing along the lateral is less than 70 percent, you should treat the systems as a single lateral system and base the irrigated acreage read from column F  on sprinkler spacing along the lateral.
If both the lateral and sprinkler spacing exceeds 70 percent, the irrigated area should be read from Table 6.
5.
Read the irrigated area per sprinkler for the given wetted diameter from the appropriate column based on pattern, spacing, and sprinkler type.
If the lateral or sprinkler spacing falls between the tabulated values, interpolate or round down and use the table for the next lowest value shown.
For example, if the computed spacing is between 60 and 64 percent, use the 60 percent table.
If the pattern is rectangular , for example, lateral spacing is 65 percent but sprinkler spacing along lateral is 55 percent, average these two values and use the appropriate table.
In this case, use Table 3, 60 percent table.
As before, if the averaged value falls between the tabulated values, interpolate between the appropriate tables or round down to the next lowest tabulated value.
6.
Multiply the tabulated irrigated acreage value per sprinkler by the number of sprinklers in each category.
Add all of these, and the sum is the total irrigated acreage for the field.
A flowchart summarizing the decision processes for using Tables 1 through 6 is shown in Figure 12.
has eight laterals of varying length laid out in the field.
Figure 9 shows a typical lateral and sprinkler pattern for a stationary sprinkler system.
This existing system
 1.
Determine the number of interior and exterior sprinklers for each field.
Referring to Figure 9, count all sprinklers along the perimeter of the field to determine the number of exterior sprinklers.
Any sprinkler not receiving overlap on four sides should be counted as an exterior sprinkler.
Number of exterior sprinklers = 30 Number of interior sprinklers = 42
 2.
Determine whether the system in each field satisfies the existing or new designation.
System satisfies existing designation.
3.
From the field data, determine the lateral and sprinkler spacing along the lateral and wetted diameter.
The appropriate Field Data Worksheet shows the lateral spacing  is 80 feet and the sprinkler spacing  along the lateral is 80 feet.
The wetted diameter  is 127 feet.
Determining Irrigated Acreage EXAMPLES Case I: Multiple laterals with uniform spacing.
Figure 9.
Layout of multiple lateral stationary sprinkler system.
Sprinkler spacing as a percentage of wetted diameter is: 80 feet / 127 feet = 63 percent
 4.
Determine whether the system satisfies the multiple lateral or single lateral definition.
System satisfies multiple lateral system definition with lateral spacing equal to 63 percent of wetted diameter.
5.
Read the irrigated area per sprinkler for the given wetted diameter from the appropriate column based on pattern, spacing, and sprinkler type.
To use the tables without interpolating, round down the wetted diameter to 125 feet and the lateral spacing to 60 percent of wetted diameter.
Using Table 3, for wetted diameter equal to 125 feet, existing system with multiple laterals, 60 percent lateral spacing, read
 area of interior sprinkler from Column  = 0.129 acres area of exterior sprinkler from Column  = 0.165 acres
 6.
Multiply the tabulated irrigated acreage value per sprinkler by the number of sprinklers in each
 Figure 10.
Layout of single lateral stationary sprinkler system.
category.
Add these.
The sum is the total irrigated acreage for the field.
30 exterior sprinklers X 0.165 acres = 4.95 acres
 42 interior sprinklers X 0.129 acres = 5.42 acres
 Total irrigated area of field 4.95 ac + 5.42 ac = 10.37 acres
 Case II: Single laterals with uniform sprinkler spacing along lateral.
Figure 10 shows a typical lateral and sprinkler pattern for a stationary sprinkler system in narrow fields.
Data and irrigated area must be reported on a field-by-field basis.
In this example, fields are surrounded by drainage ditches spaced 330 feet apart.
This existing system has one lateral per field with model 100 guns.
1.
Determine the number of interior and exterior sprinklers for each field.
Referring to Figure 10, treat each lateral as a single lateral; therefore, you do not have to distinguish between interior and exterior sprinklers.
Number of sprinklers per lateral = 4
 2.
Determine whether the system in each field satisfies the existing or new designation.
System satisfies existing designation.
3.
From the field data, determine the lateral and sprinkler spacing along the lateral and wetted diameter.
The Field Data Worksheet  shows the sprinkler spacing along the lateral is 180 feet.
The wetted diameter  is 275 feet.
Sprinkler spacing as a percentage of wetted diameter is: 180 feet / 275 feet = 65.5 percent
 4.
Determine whether the system satisfies the multiple lateral or single lateral definition.
System satisfies single lateral system definition
 with sprinkler spacing along laterals equal to 65.5 percent of wetted diameter.
5.
Read the irrigated area per sprinkler for the given wetted diameter from the appropriate column based on pattern, spacing, and sprinkler type.
To use the tables without interpolating, round down wetted diameter to 270 feet and sprinkler spacing to 65 percent of wetted diameter.
Using Table 4, wetted diameter equal to 270 feet, existing system with single laterals, 65 percent sprinkler spacing, read area of sprinkler from Column 
 6.
Multiply the tabulated irrigated acreage value per sprinkler by the number of sprinklers per lateral.
This gives the CAWMP Irrigated Acreage for the field.
4 sprinklers X 0.886 acres = 3.54 acres per field
 Case III: Non-uniform sprinkler spacing along lateral.
Figure 11 shows an irregular sprinkler pattern sometimes fitted to an odd-shaped field.
This existing system has seven irregularly spaced model 100 guns.
Figure 11.
Irregularly shaped field with nonuniform sprinkler spacing.
1.
Determine the number of interior and exterior sprinklers for each field.
Referring to Figure 11, treat all sprinklers the same.
Number of sprinklers per field = 7
 2.
Determine whether the system in each field satisfies the existing or new designation.
System satisfies existing designation.
3.
From the field data, determine the lateral and sprinkler spacing along the lateral and wetted diameter.
The Field Data Worksheet  shows the sprinkler spacing along the laterals ranges from 200 to 240 feet.
The wetted diameter  is 275 feet.
Sprinkler spacing as a percentage of wetted diameter varies from:
 200 feet / 275 feet = 72.7 percent 240 feet / 275 feet = 87.3 percent
 4.
Determine whether the system satisfies the multiple lateral or single lateral definition.
With irregular lateral and sprinkler spacings varying from 72 to 87 percent of wetted diameter, the system satisfies neither multiple nor single lateral criteria.
Therefore, treat it as an excessively spaced sprinkler system.
5.
Read the irrigated area per sprinkler for the given wetted diameter from the appropriate column based on pattern and spacing.
Using Table 6, for wetted diameter equal to 275 feet, existing system with sprinkler spacing greater than 70 percent, read
 area of sprinkler from Column G 0.80 for wetted dia.
= 270 feet 0.86 for wetted dia.
= 280 feet Interpolating, area = 0.83 ac for wetted dia.
= 275 feet
 6.
Multiply the tabulated irrigated acreage value per sprinkler by the number of sprinklers.
Add these.
The sum is the total irrigated acreage for the field.
7 sprinklers X 0.83 acres = 5.81 acres per field
 Animal waste management operations that rely on spray irrigation systems may be required to have a wettable acre determination completed to ensure nutrients contained in the wastewater are applied to adequate land at agronomic rates.
All CAWMP will be
 reviewed by state Division of Water Quality or Division of Soil and Water field inspectors to determine whether a wettable acre determination is indeed required.
If so, the Field Data Worksheets and Computational Worksheet that follow will have to be completed for stationary sprinkler or stationary gun systems and added to the CAWMP.
A wettable acre  designated technical specialist must complete and sign the Computational Worksheet to certify that the irrigation system can be operated SO that the wastewater nutrients are applied to appropriate areas.
Step-by-step procedures for completing the CAWMP wettable acres determination have been developed, along with tables from which irrigated acreage can be determined for various irrigation system designs.
Figure 12.
Flowchart showing decision-making process for identifying which tables to use to determine CAWMP wettable acres.
CAWMP Wettable Acre Terms
 CAWMP wettable acre-the irrigated acreage that the SB 1217 Interagency Committee allows to be counted toward the land application area requirement of the Certified Animal Waste Management Plan for existing irrigation systems.
Effective design area-the portion of the wetted area that receives at least 50 percent of the target application amount.
Excessively spaced sprinkler-sprinkler spacing along a lateral that exceeds 70 percent of the verified wetted diameter or 65 percent of the wetted diameter value published in manufacturers' literature.
Existing irrigation system-an irrigation system that was installed before release of the third revision of the Sixth Guidance Document.
Multiple lateral irrigation system-an irrigation system with two or more laterals equally spaced between 50 and 70 percent of the verified wetted diameter.
Net wetted area-the part of the field that gets wetted by two or more sprinklers operated with partially overlapping radii.
New or expanded irrigation system-any component of an irrigation system that wets a portion of a field that was not wetted before the CAWMP wettable acre rules were finalized.
Single lateral irrigation system-an irrigation system with only one lateral per field, or laterals spaced farther apart than 70 percent of the verified wetted diameter.
Verified wetted diameter-field-measured distance from one side of a wetted perimeter to the opposite side of the wetted perimeter.
Wetted area-the area that becomes wetted as a sprinkler rotates.
It is the area within the circle inscribed by the wetted radius.
Wetted diameter-the diagonal distance from one side of a wetted perimeter through the point of sprinkler rotation to the opposite side of the wetted perimeter.
Wetted diameter is twice the wetted radius.
Wetted radius-the distance from a sprinkler to a point along the edge of the wetted perimeter.
Wetted radius is the distance the sprinkler throws water.
STATIONARY SPRINKLER SYSTEM FIELD DATA WORKSHEET *
 Sprinkler make and model number
 [feet] by sprinkler spacing along lateral
 Operating pressure at the sprinkler
 Number of sprinklers operating at one time
 Total number of sprinklers or sprinkler locations in the system
 Sprinkler locations permanently marked:
 [inch].
If there is more than one size, indicate the size and
 approximate length of each.
Can be done on the map.
[inch].
If there is more than one size, indicate the size and
 approximate length of each.
Can be done on the map.
[feet].
Maximum pumping distance.
Pump make and model number
 Engine make and model number
 Electric motor horsepower and rpm
 Note: It is strongly recommended that you field measure the sprinkler wetted diameter.
You should do this on the longest lateral about half-way down the lateral.
Locate each sprinkler or sprinkler location on the map.
Indicate whether it is full circle or part circle.
Show the
 location of the supply line.
Irrigated acres are determined by lateral line, by zone, or by field.
**
 Optional data, furnish where possible
 Signature of owner or facility representative
 Signature of technical specialist
 Printed name of owner or facility representative
 Printed name of technical specialist
 STATIONARY GUN SYSTEM FIELD DATA WORKSHEET *
 Gun make and model number
 [feet] by gun spacing along lateral
 Operating pressure at the gun
 determined from gun chart
 Number of guns operating at one time
 Total number of guns or gun locations in the system
 Gun locations permanently marked:
 [inch].
If there is more than one size, indicate the size and approximate length of
 each.
Can be done on the map.
[inch].
If there is more than one size, indicate the size and approximate length of
 each.
Can be done on the map.
[feet].
Maximum pumping distance.
Pump make and model number
 Engine make and model number
 Electric motor horsepower and rpm
 Note: It is strongly recommended that you field measure the gun wetted diameter.
It should be done on the longest lateral about half-way down the lateral.
Locate each gun or gun location on the map.
Indicate whether it is full circle or part circle.
Show the location of
 the supply line.
Irrigated acres are determined by lateral line, by zone, or by field.
Optional data, furnish where possible
 Signature of owner or facility representative
 Signature of technical specialist
 Printed name of owner or facility representative
 Printed name of technical specialist
 STATIONARY SPRINKLER /GUN SYSTEM WETTABLE ACRE COMPUTATIONAL WORKSHEET
 1.
Farm number  Field number 
 2.
Irrigation system designation Existing irrigation system
 3.
Number of stationary sprinklers # Interior sprinklers # Exterior sprinklers
 4.
Wetted diameter [feet] from Field Data Worksheet
 5.
Spacing Sprinkler spacing along lateral [feet]
 Sprinkler spacing as a percentage of wetted diameter
 6.
Sprinkler pattern Multiple laterals Single lateral
 7.
Read the irrigated area per sprinkler for the given wetted diameter from the appropriate table and column based on pattern, spacing, and sprinkler location.
Acres per interior sprinkler from
 Acres per exterior sprinkler from Table Column
 8.
Multiply the tabulated irrigated acreage value per sprinkler by the number of sprinklers of each category in the field.
Add all of these.
The sum is the total irrigated acreage for the field.
Acres per interior sprinkler X # Sprinklers = Acres
 Total wettable acres for field 
  Acres per exterior sprinkler X # Sprinklers = Acres
 Wettable Acre Computational Worksheet completed by:
 Signature of technical specialist
 Table 1.
Irrigated Area Allowances for Stationary Sprinkler Systems with Square Spacing 
 Existing System with proper	New or Expanded System	Existing	New/Expanded
 overlap and multiple laterals	with multiple laterals	single	single
 net wetted	net wetted	design	design	lateral	lateral
 area of an	area of an	area of an	area of an	net wetted	design
 wetted	interior	exterior	interior	exterior	area of each	area of each
 diameter	sprinkler	sprinkler	sprinkler	sprinkler	sprinkler	sprinkler
 						
 						
 80	0.037	0.053	0.037	0.045	0.063	0.053
 85	0.041	0.060	0.041	0.051	0.071	0.060
 90	0.046	0.068	0.046	0.057	0.079	0.067
 95	0.052	0.075	0.052	0.063	0.088	0.075
 100	0.057	0.084	0.057	0.070	0.098	0.083
 105	0.063	0.092	0.063	0.077	0.108	0.091
 110	0.069	0.101	0.069	0.085	0.118	0.100
 115	0.076	0.111	0.076	0.093	0.129	0.110
 120	0.083	0.120	0.083	0.101	0.141	0.119
 125	0.090	0.131	0.090	0.110	0.153	0.130
 130	0.097	0.141	0.097	0.119	0.165	0.140
 135	0.105	0.152	0.105	0.128	0.178	0.151
 140	0.112	0.164	0.112	0.138	0.192	0.163
 145	0.121	0.176	0.121	0.148	0.206	0.174
 150	0.129	0.188	0.129	0.158	0.220	0.187
 155	0.138	0.201	0.138	0.169	0.235	0.199
 160	0.147	0.214	0.147	0.180	0.250	0.212
 165	0.156	0.228	0.156	0.191	0.266	0.226
 170	0.166	0.242	0.166	0.203	0.283	0.240
 175	0.176	0.256	0.176	0.215	0.299	0.254
 180	0.186	0.271	0.186	0.227	0.317	0.269
 185	0.196	0.286	0.196	0.240	0.335	0.284
 190	0.207	0.302	0.207	0.253	0.353	0.300
 195	0.218	0.318	0.218	0.267	0.372	0.316
 200	0.230	0.334	0.230	0.281	0.391	0.332
 210	0.253	0.369	0.253	0.310	0.431	0.366
 220	0.278	0.404	0.278	0.340	0.473	0.402
 230	0.304	0.442	0.304	0.371	0.517	0.439
 240	0.331	0.481	0.331	0.404	0.563	0.478
 250	0.359	0.522	0.359	0.439	0.611	0.519
 260	0.388	0.565	0.388	0.474	0.661	0.561
 270	0.418	0.609	0.418	0.512	0.713	0.605
 280	0.450	0.655	0.450	0.550	0.766	0.651
 290	0.483	0.703	0.483	0.590	0.822	0.698
 300	0.517	0.752	0.517	0.632	0.880	0.747
 310	0.552	0.803	0.552	0.674	0.939	0.797
 320	0.588	0.856	0.588	0.719	1.001	0.850
 330	0.625	0.910	0.625	0.764	1.065	0.904
 340	0.663	0.966	0.663	0.811	1.130	0.959
 350	0.703	1.024	0.703	0.860	1.198	1.017
 360	0.744	1.083	0.744	0.910	1.267	1.075
 370	0.786	1.144	0.786	0.961	1.338	1.136
 380	0.829	1.207	0.829	1.014	1.412	1.198
 390	0.873	1.271	0.873	1.068	1.487	1.262
 400	0.918	1.337	0.918	1.123	1.564	1.328
 410	0.965	1.405	0.965	1.180	1.643	1.395
 420	1.012	1.474	1.012	1.238	1.724	1.464
 430	1.061	1.545	1.061	1.298	1.808	1.534
 440	1.111	1.618	1.111	1.359	1.893	1.607
 450	1.162	1.692	1.162	1.421	1.980	1.680
 Table 2.
Irrigated Area Allowances for Stationary Sprinkler Systems with Square Spacing 
 Existing System with proper	New or Expanded System	Existing	New/Expanded
 overlap and multiple laterals	with multiple laterals	single	single
 net wetted	net wetted	design	design	lateral	lateral
 area of an	area of an	area of an	area of an	net wetted	design
 wetted	interior	exterior	interior	exterior	area of each	area of each
 diameter	sprinkler	sprinkler	sprinkler	sprinkler	sprinkler	sprinkler
 						
 						
 80	0.044	0.061	0.044	0.051	0.068	0.057
 85	0.050	0.068	0.050	0.057	0.077	0.065
 90	0.056	0.077	0.056	0.064	0.086	0.073
 95	0.063	0.085	0.063	0.072	0.096	0.081
 100	0.069	0.095	0.069	0.080	0.106	0.090
 105	0.077	0.104	0.077	0.088	0.117	0.099
 110	0.084	0.114	0.084	0.096	0.128	0.108
 115	0.092	0.125	0.092	0.105	0.140	0.118
 120	0.100	0.136	0.100	0.115	0.153	0.129
 125	0.109	0.148	0.109	0.124	0.166	0.140
 130	0.117	0.160	0.117	0.134	0.179	0.151
 135	0.127	0.172	0.127	0.145	0.193	0.163
 140	0.136	0.185	0.136	0.156	0.208	0.176
 145	0.146	0.199	0.146	0.167	0.223	0.188
 150	0.156	0.213	0.156	0.179	0.239	0.202
 155	0.167	0.227	0.167	0.191	0.255	0.215
 160	0.178	0.242	0.178	0.204	0.272	0.229
 165	0.189	0.257	0.189	0.216	0.289	0.244
 170	0.201	0.273	0.201	0.230	0.307	0.259
 175	0.213	0.290	0.213	0.244	0.325	0.274
 180	0.225	0.306	0.225	0.258	0.344	0.290
 185	0.238	0.324	0.238	0.272	0.363	0.307
 190	0.251	0.341	0.251	0.287	0.383	0.323
 195	0.264	0.359	0.264	0.302	0.404	0.341
 200	0.278	0.378	0.278	0.318	0.425	0.358
 210	0.306	0.417	0.306	0.351	0.468	0.395
 220	0.336	0.458	0.336	0.385	0.514	0.434
 230	0.367	0.500	0.367	0.421	0.562	0.474
 240	0.400	0.545	0.400	0.458	0.611	0.516
 250	0.434	0.591	0.434	0.497	0.663	0.560
 260	0.469	0.639	0.469	0.538	0.718	0.606
 270	0.506	0.689	0.506	0.580	0.774	0.653
 280	0.544	0.741	0.544	0.623	0.832	0.702
 290	0.584	0.795	0.584	0.669	0.893	0.754
 300	0.625	0.851	0.625	0.716	0.955	0.806
 310	0.667	0.908	0.667	0.764	1.020	0.861
 320	0.711	0.968	0.711	0.814	1.087	0.917
 330	0.756	1.029	0.756	0.866	1.156	0.976
 340	0.803	1.093	0.803	0.919	1.227	1.036
 350	0.851	1.158	0.851	0.974	1.300	1.098
 360	0.900	1.225	0.900	1.031	1.376	1.161
 370	0.951	1.294	0.951	1.089	1.453	1.227
 380	1.003	1.365	1.003	1.148	1.533	1.294
 390	1.056	1.438	1.056	1.210	1.614	1.363
 400	1.111	1.513	1.111	1.272	1.698	1.434
 410	1.167	1.589	1.167	1.337	1.784	1.506
 420	1.225	1.668	1.225	1.403	1.872	1.581
 430	1.284	1.748	1.284	1.470	1.963	1.657
 440	1.344	1.830	1.344	1.540	2.055	1.735
 450	1.406	1.914	1.406	1.610	2.149	1.814
 Table 3.
Irrigated Area Allowances for Stationary Sprinkler Systems with Square Spacing 
 Existing System with proper	New or Expanded System	Existing	New/Expanded
 overlap and multiple laterals	with multiple laterals	single	single
 net wetted	net wetted	design	design	lateral	lateral
 area of an	area of an	area of an	area of an	net wetted	design
 wetted	interior	exterior	interior	exterior	area of each	area of each
 diameter	sprinkler	sprinkler	sprinkler	sprinkler	sprinkler	sprinkler
 						
 						
 80	0.053	0.068	0.053	0.057	0.073	0.061
 85	0.060	0.076	0.060	0.064	0.082	0.069
 90	0.067	0.086	0.067	0.072	0.092	0.077
 95	0.075	0.096	0.075	0.080	0.103	0.086
 100	0.083	0.106	0.083	0.089	0.114	0.096
 105	0.091	0.117	0.091	0.098	0.126	0.105
 110	0.100	0.128	0.100	0.108	0.138	0.116
 115	0.109	0.140	0.109	0.118	0.151	0.126
 120	0.119	0.152	0.119	0.128	0.164	0.138
 125	0.129	0.165	0.129	0.139	0.178	0.149
 130	0.140	0.179	0.140	0.151	0.193	0.162
 135	0.151	0.193	0.151	0.162	0.208	0.174
 140	0.162	0.207	0.162	0.175	0.224	0.187
 145	0.174	0.223	0.174	0.187	0.240	0.201
 150	0.186	0.238	0.186	0.201	0.257	0.215
 155	0.199	0.254	0.199	0.214	0.274	0.230
 160	0.212	0.271	0.212	0.228	0.292	0.245
 165	0.225	0.288	0.225	0.243	0.311	0.260
 170	0.239	0.306	0.239	0.258	0.330	0.276
 175	0.253	0.324	0.253	0.273	0.349	0.293
 180	0.268	0.343	0.268	0.289	0.370	0.310
 185	0.283	0.362	0.283	0.305	0.390	0.327
 190	0.298	0.382	0.298	0.322	0.412	0.345
 195	0.314	0.402	0.314	0.339	0.434	0.364
 200	0.331	0.423	0.331	0.357	0.456	0.383
 210	0.364	0.467	0.364	0.393	0.503	0.422
 220	0.400	0.512	0.400	0.431	0.552	0.463
 230	0.437	0.560	0.437	0.472	0.604	0.506
 240	0.476	0.610	0.476	0.513	0.657	0.551
 250	0.517	0.661	0.517	0.557	0.713	0.598
 260	0.559	0.715	0.559	0.603	0.771	0.647
 270	0.602	0.772	0.602	0.650	0.832	0.697
 280	0.648	0.830	0.648	0.699	0.894	0.750
 290	0.695	0.890	0.695	0.750	0.959	0.804
 300	0.744	0.953	0.744	0.802	1.027	0.861
 310	0.794	1.017	0.794	0.857	1.096	0.919
 320	0.846	1.084	0.846	0.913	1.168	0.979
 330	0.900	1.153	0.900	0.971	1.242	1.042
 340	0.955	1.223	0.955	1.030	1.319	1.106
 350	1.012	1.297	1.012	1.092	1.398	1.172
 360	1.071	1.372	1.071	1.155	1.479	1.240
 370	1.131	1.449	1.131	1.220	1.562	1.309
 380	1.193	1.528	1.193	1.287	1.647	1.381
 390	1.257	1.610	1.257	1.356	1.735	1.455
 400	1.322	1.693	1.322	1.426	1.825	1.530
 410	1.389	1.779	1.389	1.498	1.918	1.608
 420	1.458	1.867	1.458	1.572	2.013	1.687
 430	1.528	1.957	1.528	1.648	2.110	1.768
 440	1.600	2.049	1.600	1.726	2.209	1.852
 450	1.674	2.143	1.674	1.805	2.310	1.937
 Table 4.
Irrigated Area Allowances for Stationary Sprinkler Systems with Square Spacing 
 Existing System with proper	New or Expanded System	Existing	New/Expanded
 overlap and multiple laterals	with multiple laterals	single	single
 net wetted	net wetted	design	design	lateral	lateral
 area of an	area of an	area of an	area of an	net wetted	design
 wetted	interior	exterior	interior	exterior	area of each	area of each
 diameter	sprinkler	sprinkler	sprinkler	sprinkler	sprinkler	sprinkler
 						
 						
 80	0.062	0.075	0.062	0.063	0.078	0.065
 85	0.070	0.085	0.070	0.072	0.088	0.073
 90	0.079	0.095	0.079	0.080	0.098	0.082
 95	0.088	0.106	0.088	0.089	0.110	0.091
 100	0.097	0.117	0.097	0.099	0.122	0.101
 105	0.107	0.129	0.107	0.109	0.134	0.111
 110	0.117	0.142	0.117	0.120	0.147	0.122
 115	0.128	0.155	0.128	0.131	0.161	0.134
 120	0.140	0.169	0.140	0.143	0.175	0.145
 125	0.152	0.183	0.152	0.155	0.190	0.158
 130	0.164	0.198	0.164	0.167	0.205	0.171
 135	0.177	0.214	0.177	0.180	0.221	0.184
 140	0.190	0.230	0.190	0.194	0.238	0.198
 145	0.204	0.247	0.204	0.208	0.255	0.212
 150	0.218	0.264	0.218	0.223	0.273	0.227
 155	0.233	0.282	0.233	0.238	0.292	0.243
 160	0.248	0.301	0.248	0.253	0.311	0.259
 165	0.264	0.320	0.264	0.270	0.331	0.275
 170	0.280	0.339	0.280	0.286	0.351	0.292
 175	0.297	0.360	0.297	0.303	0.372	0.309
 180	0.314	0.380	0.314	0.321	0.394	0.327
 185	0.332	0.402	0.332	0.339	0.416	0.346
 190	0.350	0.424	0.350	0.357	0.439	0.365
 195	0.369	0.446	0.369	0.376	0.462	0.384
 200	0.388	0.470	0.388	0.396	0.486	0.404
 210	0.428	0.518	0.428	0.437	0.536	0.445
 220	0.469	0.568	0.469	0.479	0.588	0.489
 230	0.513	0.621	0.513	0.524	0.643	0.534
 240	0.559	0.676	0.559	0.570	0.700	0.582
 250	0.606	0.734	0.606	0.619	0.759	0.631
 260	0.656	0.794	0.656	0.669	0.821	0.683
 270	0.707	0.856	0.707	0.722	0.886	0.736
 280	0.760	0.921	0.760	0.776	0.953	0.792
 290	0.816	0.987	0.816	0.833	1.022	0.849
 300	0.873	1.057	0.873	0.891	1.094	0.909
 310	0.932	1.128	0.932	0.951	1.168	0.971
 320	0.993	1.202	0.993	1.014	1.244	1.034
 330	1.056	1.279	1.056	1.078	1.323	1.100
 340	1.121	1.357	1.121	1.144	1.405	1.167
 350	1.188	1.438	1.188	1.213	1.489	1.237
 360	1.257	1.522	1.257	1.283	1.575	1.309
 370	1.328	1.607	1.328	1.355	1.664	1.383
 380	1.401	1.696	1.401	1.429	1.755	1.458
 390	1.475	1.786	1.475	1.506	1.848	1.536
 400	1.552	1.879	1.552	1.584	1.944	1.616
 410	1.630	1.974	1.630	1.664	2.043	1.698
 420	1.711	2.071	1.711	1.746	2.144	1.781
 430	1.793	2.171	1.793	1.830	2.247	1.867
 440	1.878	2.273	1.878	1.916	2.353	1.955
 450	1.964	2.378	1.964	2.005	2.461	2.045
 Table 5.
Irrigated Area Allowances for Stationary Sprinkler Systems with Square Spacing 
 Existing System with proper	New or Expanded System	Existing	New/Expanded
 overlap and multiple laterals	with multiple laterals	single	single
 net wetted	net wetted	design	design	lateral	lateral
 area of an	area of an	area of an	area of an	net wetted	design
 wetted	interior	exterior	interior	exterior	area of each	area of each
 diameter	sprinkler	sprinkler	sprinkler	sprinkler	sprinkler	sprinkler
 						
 						
 80	0.072	0.083	*	0.082	*
 85	0.081	0.094	*	0.093	*
 90	0.091	0.105	*	0.104	*
 95	0.102	0.117	*	*	0.116	*
 100	0.112	0.129	*	*	0.128	*
 105	0.124	0.143	*	*	0.142	*
 110	0.136	0.157	*	*	0.155	*
 115	0.149	0.171	*	0.170	*
 120	0.162	0.186	*	*	0.185	*
 125	0.176	0.202	*	*	0.201	*
 130	0.190	0.219	*	*	0.217	*
 135	0.205	0.236	*	*	0.234	*
 140	0.220	0.254	*	*	0.252	*
 145	0.237	0.272	*	*	0.270	*
 150	0.253	0.291	*	*	0.289	*
 155	0.270	0.311	*	*	0.308	*
 160	0.288	0.331	*	*	0.329	*
 165	0.306	0.352	*	*	0.349	*
 170	0.325	0.374	*	*	0.371	*
 175	0.344	0.397	*	*	0.393	*
 180	0.364	0.419	*	*	0.416	*
 185	0.385	0.443	*	*	0.439	*
 190	0.406	0.467	*	*	0.463	*
 195	0.428	0.492	*	0.488	*
 200	0.450	0.518	*	*	0.513	*
 210	0.496	0.571	*	*	0.566	*
 220	0.544	0.627	*	*	0.621	*
 230	0.595	0.685	*	*	0.679	*
 240	0.648	0.746	*	*	0.739	*
 250	0.703	0.809	*	*	0.802	*
 260	0.760	0.875	*	*	0.868	*
 270	0.820	0.944	*	*	0.936	*
 280	0.882	1.015	*	*	1.006	*
 290	0.946	1.089	*	*	1.079	*
 300	1.012	1.165	*	*	1.155	*
 310	1.081	1.244	*	*	1.233	*
 320	1.152	1.326	*	*	1.314	*
 330	1.225	1.410	*	*	1.398	*
 340	1.300	1.497	*	*	1.484	*
 350	1.378	1.586	*	*	1.572	*
 360	1.458	1.678	*	*	1.663	*
 370	1.540	1.773	*	*	1.757	*
 380	1.624	1.870	*	*	1.853	*
 390	1.711	1.969	*	*	1.952	*
 400	1.800	2.072	*	*	2.054	*
 410	1.891	2.176	*	*	2.157	*
 420	1.984	2.284	*	*	2.264	*
 430	2.080	2.394	*	2.373	*
 440	2.178	2.507	2.485	*
 450	2.278	2.622	2.599	*
 Table 6.
Irrigated Area Allowances for Stationary Sprinkler Systems on any Pattern Where Lateral and Sprinkler Spacing Is Greater than 70 percent of Wetted Diameter
 Existing System with	New or Expanded System	Existing	Excessively
 multiple laterals	with multiple laterals	single	spaced
 net wetted	net wetted	design	design	lateral	sprinklers
 area of an	area of an	area of an	area of an	net wetted	design
 wetted	interior	exterior	interior	exterior	area of each	area of each
 diameter	sprinkler	sprinkler	sprinkler	sprinkler	sprinkler	sprinkler
 						
 						
 80	0.070	0.070	*	*	0.070	0.070
 85	0.079	0.079	*	0.079	0.079
 90	0.089	0.089	*	0.089	0.089
 95	0.099	0.099	*	0.099	0.099
 100	0.110	0.110	*	0.110	0.110
 105	0.121	0.121	*	0.121	0.121
 110	0.133	0.133	*	*	0.133	0.133
 115	0.145	0.145	*	0.145	0.145
 120	0.158	0.158	*	*	0.158	0.158
 125	0.171	0.171	*	0.171	0.171
 130	0.185	0.185	*	*	0.185	0.185
 135	0.200	0.200	*	*	0.200	0.200
 140	0.215	0.215	*	*	0.215	0.215
 145	0.231	0.231	*	0.231	0.231
 150	0.247	0.247	*	0.247	0.247
 155	0.264	0.264	*	*	0.264	0.264
 160	0.281	0.281	*	*	0.281	0.281
 165	0.299	0.299	*	*	0.299	0.299
 170	0.317	0.317	*	*	0.317	0.317
 175	0.336	0.336	*	*	0.336	0.336
 180	0.355	0.355	*	*	0.355	0.355
 185	0.375	0.375	*	*	0.375	0.375
 190	0.396	0.396	*	*	0.396	0.396
 195	0.417	0.417	*	*	0.417	0.417
 200	0.439	0.439	*	*	0.439	0.439
 210	0.484	0.484	*	*	0.484	0.484
 220	0.531	0.531	*	*	0.531	0.531
 230	0.580	0.580	*	*	0.580	0.580
 240	0.632	0.632	*	*	0.632	0.632
 250	0.686	0.686	*	0.686	0.686
 260	0.742	0.742	*	*	0.742	0.742
 270	0.800	0.800	*	0.800	0.800
 280	0.860	0.860	*	0.860	0.860
 290	0.923	0.923	*	0.923	0.923
 300	0.987	0.987	*	0.987	0.987
 310	1.054	1.054	*	1.054	1.054
 320	1.123	1.123	*	*	1.123	1.123
 330	1.195	1.195	*	1.195	1.195
 340	1.268	1.268	*	*	1.268	1.268
 350	1.344	1.344	*	*	1.344	1.344
 360	1.422	1.422	*	*	1.422	1.422
 370	1.502	1.502	*	*	1.502	1.502
 380	1.584	1.584	*	*	1.584	1.584
 390	1.669	1.669	*	*	1.669	1.669
 400	1.755	1.755	*	*	1.755	1.755
 410	1.844	1.844	*	*	1.844	1.844
 420	1.935	1.935	*	*	1.935	1.935
 430	2.029	2.029	*	2.029	2.029
 440	2.124	2.124	*	*	2.124	2.124
 450	2.222	2.222	*	*	2.222	2.222
 Prepared by Robert 0.
Evans, PE; Biological and Agricultural Engineering Associate Professor Ronald E.
Sneed, PE, CID; Biological and Agricultural Engineering Professor, Emeritus Ron E.
Sheffield, Biological and Agricultural Engineering Extension Specialist Jonathan T.
Smith, Biological and Agricultural Engineering Extension Assistant
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Elevated Sodium in Irrigation Water and Crop Injury
 Elevated sodium and chloride levels are being observed more frequently in private water supplies in rural areas.
In some cases the water is being derived from large limestone aquifers and in other cases the water is being derived from shale formations which have been the site of historic oil and natural gas drilling.
In other cases, the wellheads are sited in karst areas which are frequently promulgated with sinkholes and caves that can act as conduit for surface contaminants like road salt to contaminate the aquifer.
Most greenhouse operators do not request that their irrigation water be tested for chloride and/or sodium.
One new operator purchased a farm that had four sources of water on the property.
At first the grower ignored the extension agent's recommendation to test the quality of the well water before initiating production.
After observing cropping issues  the grower opted to test his well water for "everything".
The tests revealed that the EC of the well water was 2.37 m/S with chloride levels at 523 mg/l and sodium levels at 226 mg/l.
While the EC level was high and had to be accounted for, the grower had two bigger problems to worry about.
The upper limits for chloride and sodium in irrigation water are both 30 mg/l  and the levels of both were extremely elevated.
Subsequent testing and evaluation of the grower's pond and spring revealed that both of these water supplies also contained elevated levels of chloride and sodium which would render them "unusable" from an irrigation perspective.
The use of a series of cisterns to collect rainwater to dilute the well water was considered impractical and the cost to treat the water through a reverse osmosis system was too high for the volume of water needed.
As a result, the grower opted to connect to the public water supply rather than pump water with variable water quality from his stream which was located almost a half mile away.
In conclusion, please remember to annually evaluate the quality of your irrigation water even if the water source has been used safely for years.
Poor quality water may impact your fertigation programs while reducing crop quality and crop yield.
A Water Quality Toolkit for Greenhouse and Nursery Production
 Water Quality Checklist for Greenhouse Growers
 This article also appears on the eGrow Blog.
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Louise Mabulo, chef, farmer, entrepreneur and founder of The Cacao Project, which cultivates resilient and climate-smart livelihoods, positioning farmers for sustainable success in the Philippines.
Mabulo is a National Geographic Young Explorer, a featured honoree for Forbes Asias list 30 Under 30, a Young Champion of the Earth under United Nations Environment Program, and a member of the UN Women 30 for 2030 Network.
Felicia Marcus, attorney and consultant, Water Policy Group; Landreth Visiting Fellow, Stanfords Water in the West Program; DWFI board member.
Ted Carter, president, University of Nebraska system.
John Berge, state executive director, USDA Farm Service Agency.
Mike Boehm, vice chancellor of agriculture and natural resources, University of NebraskaLincoln.
Mark Svoboda, director and climatologist, National Drought Mitigation Center.
Rachael McDonnell, deputy director general  research for development, International Water Management Institute.
Cracks affect infiltration of furrow crop irrigation
 Cracks can play a major role in water advance and infiltration in a cracking soil.
Water flowing directly into subsurface cracks dominated the cumulative intake for the preirrigation at a site in the San Joaquin Valley.
Differences in furrow inflow rates had little effect on cumulative infiltration for preirrigation.
However, for subsequent irrigations, different furrow inflow rates significantly affected cumulative infiltration.
Crack flow was a significant factor in cumulative infiltration for the crop irrigations.
Uniformity of water advance among furrows was high for the preirrigation but was less for the crop irrigations.
A comparison of surge irrigation and continuousflow furrow irrigation with furrow lengths of about 1/4 mile and 1/2 mile showed little difference in cumulative infiltration.
Furrow irrigation is used on about 70% of the irrigated acreage in California.
The main advantage of furrow irrigation is the low capital cost.
Properly managed, furrow irrigation can be
 The performance of a furrow irrigation system depends on furrow length, furrow inflow rate, slope, surface roughness, infiltration rate and furrow geometry.
Water flowing into cracks in the soil can affect overall infiltration.
efficient if appropriate furrow lengths, furrow inflow rates and irrigation set times are used and the surface runoff is beneficially used.
The performance of a furrow irrigation system depends on furrow length, furrow inflow rate, slope, surface roughness, infiltration rate and furrow geometry.
The rate at which water flows down the furrow reflects an integration of these factors.
By plotting the time water arrives at various distances down the furrow against the distance, an advance curve is developed that describes the rate at which water moves down the furrow length.
Water infiltration plays a major role in the performance of furrow irrigation systems.
Soils with high infiltration rates require short furrow lengths for efficient operation, while long furrow lengths can be used for soils with low infiltration rates.
In noncracking soils, infiltration consists of water flowing directly into the porous matrix of the soil.
Initial infiltration into a cracking soil consists of water flowing into the cracks and the soil matrix, causing a very high initial infiltration rate.
Once the cracks close, the infiltration rate drops to very low values.
During the period of crack flow, water movement can occur as far as 15 to 20 feet beyond the furrow.
Water flow into cracks, and subsequent subbing may affect the performance of a furrow irrigation system.
The objective of this study was to evaluate the performance of a furrow irrigation system in a cracking clay loam soil.
We evaluated a furrow irrigation system in a cracking clay loam soil over a 2-year period.
The site was a cotton field located near Stratford, on the west side of the San Joaquin Valley.
Data on furrow inflow and outflow rates, advance times, depth of flow, slope and furrow geometry were collected on 3 to 6 furrows.
The inflow rates were 37, 43 and 56 gallons per minute for the January preirrigation; 32, 38 and 48 gallons per minute for the June 17 irrigation; and 22, 32 and 45 gallons per minute for the Aug.
4 irrigation.
The lowest inflow rate was the grower's normal flow rate.
Advance times were also measured on 20 to 30 furrows at distances of 590 feet,
 1,180 feet and 2,360 feet, irrigated with the normal inflow rate.
Broadcrested weir flumes were used for the flow rate measurements.
Irrigation set times were 22 to 24 hours.
Siphons were used for the irrigations.
inflow and outflow rates.
Distance between the inflow and outflow flumes was 1,640 feet for the preirrigation and 2,360 feet for the crop irrigations.
For the second year, we changed design and management based on the first year's data.
The pressure chamber was used for irrigation scheduling during the second year.
Furrow length of the preirrigation was reduced from 2,360 feet to 1,260 feet and the irrigation set time was reduced to 10 hours.
For the crop irrigations, we used furrow lengths of 1,260 feet  and 2,360 feet  with a block of 50 furrows per treatment.
Treatments were not replicated due to farm-level restrictions.
Gated pipe was used for the irrigations.
Surge irrigation was also evaluated during the second year.
A furrow length of 1,180 feet was used for the surge preirrigation, and a length of 2,360 was used for all crop irrigations.
During the second year, we measured inflow rate and outflow rate for each block of 50 furrows for each treatment.
Water advance times were recorded for 40 furrows during the February preirrigation, the June 20-21 irrigation and the July 11-12 irrigation.
Soil moisture was measured during the crop irrigations with a neutron moisture meter at 50 locations  along transects installed over the furrow length of 2,360 feet  and the surge irrigation treatment.
Soil type was a clay loam in the upper half of the field , but gradually changed to a loam in the lower half.
Our observations revealed that below the cultivated top soil, cracking of the subsurface soil occurred prior to the preirrigation and the first crop irrigation.
Once cultivation ceased, the cracks extended to the surface.
Cumulative infiltration of the first year was determined by the differences between the cumulative furrow
 process, and that differences in the wetted perimeters of the different inflow rates had little effect on infiltration.
For the preirrigation, cumulative infiltration increased at a decreasing rate with time for all three inflow rates, which would be expected.
Little difference occurred in cumulative infiltration between the three furrow flow rates, even though the highest flow rate was 1.5 times greater than the lowest flow rate.
No trend in increasing slope of the cumulative infiltration curve with increasing inflow rate occurred.
In general, cumulative infiltration expressed as a volume of infiltrated water per unit length of furrow should increase as the furrow inflow rate increases.
Higher inflow rates mean more wetted area of the furrow available for infiltration, and thus higher infiltration rates.
For this irrigation, however, cumulative infiltration was not affected by the furrow inflow rate.
The subsurface cracks caused this behavior.
During the irrigation, the plowed top soil periodically sloughed off into subsurface cracks.
Water in the furrow then drained into the crack, and water advance down the furrow ceased.
This crack flow lasted several minutes.
The behavior of cumulative infiltration with furrow inflow rate indicates that the water flow into the cracks dominated the early infiltration
 Figure 1 shows cumulative infiltration with elapsed time for the 1987 June and August irrigations.
A trend of increasing cumulative infiltration with increasing furrow inflow rate OCcurred during the early stages of the irrigations.
Note that for both irrigations, the slopes of these curves increased with increasing inflow rate for the early stages of infiltration.
The steeper the slope, the higher the infiltration rate.
Differences in cumulative infiltration between the inflow rates were less for the June irrigation than for the August irrigation.
Soil cultivation occurred prior to the June irrigation, SO no surface cracks existed at the time of the irrigation.
Drainage into subsurface cracks was visually observed during this irrigation.
However, this crack flow apparently was less of an influence on the cumulative infiltration compared with the preirrigation because of the trend of increasing infiltration with increasing inflow rate.
No cultivation occurred prior to the August irrigation.
Surface cracks were observed in the furrow and bed.
During the irrigation, interfurrow water flow was observed, caused by water flowing through the bed cracks.
This flow eroded the cracks and created channels in the bed for water flow.
Fig.
1.
Cumulative infiltration with inflow rate for the preirrigation, first crop irrigation and last crop irrigation of the first year.
Fig.
2.
Advance times of the preirrigation, first crop irrigation and last crop irrigation of the first year.
The strong relationship between cumulative infiltration and furrow inflow rate of the August irrigation suggests that water infiltration was strongly affected by the depth of flow in the furrow.
The deeper the depth of the flowing water, the larger the wetted surface available for infiltration, both on the furrow surface and inside the cracks.
The steady-state or basic infiltration rate, determined for the smallest inflow rates, was 0.48 gallons per minute per 100 feet of furrow length for the preirrigation, 0.27 gallons per minute per 100 feet for the June irrigation and 0.07 gallons per minute per 100 feet for the August irrigation.
One implication of this behavior is that the method used for measuring infiltration rates must account for the crack flow.
Methods such as blocked furrows, ring infiltrometers and flowing furrow infiltrometers, which may use several feet of furrow length, might not account for the water flow into cracks, particularly where crack filling accounts for much of the infiltration.
Methods such as inflow and outflow or the volume-balance "2point" approach would be more appropriate for cracking soils because a long length of the furrow is used as the infiltrometer.
Measurements should also be made on a block of adjacent furrows because of the crack flow.
Those furrows with a tendency for faster water advance could have larger infiltration rates because of crack filling, whereas slower furrows could have smaller infiltration rates because the cracks have already been filled.
Uniform advance times among the furrows occurred at 590 feet and 1,180 feet for the 30 furrows of the preirrigation.
Variability among advance times increased with distance down the furrow, with the variability at 2,360 feet nearly three times more than at the other distances.
No correlation was found between advance times and furrow inflow rates.
For the June irrigation, average advance times were similar to those of the preirrigation due to smaller inflow rates.
More variability in advance times occurred for this irrigation compared with the preirrigation.
Again, variability among the advance times increased with distance.
Variability among the advance times of the August irrigation was much higher than those of the previous irrigations.
Large advance times in two furrows contributed to much of the variability caused by water flowing through cracks into adjacent furrows.
However, average advance times of this irrigation were similar to those of the other irrigations, which reflected the smaller furrow inflow rates used for this irrigation compared with the other irrigations.
The relatively uniform advance times of the upper part of the field were caused by crack flow.
Flow into the subsurface cracks of the preirrigation and the June irrigation would slow down the advance in those furrows that tended to have faster advance.
At the same time, water flow
 into the cracks would be small for those furrows that tended to have slow advance because the cracks were already full.
Interfurrow flow occurred for the August irrigation.
Water flowed through the bed cracks from those furrows that tended to have faster advance into adjacent furrows with slower advance rates.
The advance times progressively increased during the irrigation at 1,180 feet for the second year.
The same inflow rates were used for all irrigations, which resulted in the smaller advance times as the irrigation season progressed and the infiltration characteristics of the soil porous matrix changed.
Little variability in advance times occurred among the 40 furrows for the preirrigation for the first 30 furrows.
Much longer times were found for the remaining furrows, believed to be caused by crack flow into an adjacent unirrigated block.
Penetrometer measurements made after the irrigation revealed that subsurface water flowed though cracks for nearly 15 to 20 feet into this adjacent block.
Much more variability occurred for the first crop irrigation  compared with the preirrigation.
These advance times showed relatively short times every 2and 8-furrow spacings.
Reasons for this behavior of 2-furrow spacings are unknown.
The behavior of 8-furrow spacings reflects differences in the advance times between the wheel furrows and nonwheel furrows, because two wheel furrows occurred for every block of eight furrows.
Advance times were less variable for the July 12 irrigation than with the other two irrigations.
No cultivation occurred prior to this irrigation.
A slight trend of decreasing times occurred across the block of furrows.
No periodic behavior was found in these data, indicating that differences between wheel and nonwheel furrows was no longer a factor.
Only slight changes in soil moisture content occurred with time at depths below 2 feet.
The increase in
 soil moisture content at the end of the field was caused by surface runoff from preceding irrigation sets backing up the furrows.
The last 10 measurements were excluded from the statistical analysis because of the effect of surface runoff from earlier sets.
Before each irrigation, a trend OCcurred; soil moisture decreased with increasing distance along the furrow until near the end of the field.
After the irrigation, a slight trend of decreasing soil moisture occurred for the June and August irrigations, similar to that before the irrigations.
The trend, however, was much larger for the July irrigation, particularly along the lower part of the furrow length.
An analysis of the changes in soil moisture content due to an irrigation showed a slight trend of increasing change in soil moisture with increasing distance along the furrow for the June and August irrigations.
For the July irrigation, a trend of increasing change occurred over about the first 1,400 feet, followed by a trend of decreasing change for the remaining distance.
Uniformity of the soil moisture content along the furrow length was quite high.
Distribution uniformities after an irrigation ranged between about 87% and nearly 98%, whereas before the irrigation distribution uniformities were about 84% to 86%.
Distribution uniformities of the change in soil moisture ranged between 83% and 96%.
Similar average respective soil moisture contents occurred before and
 Fig.
3.
Advance times at 1,180 feet for the second year, 1988.
after the irrigation, although differences in the average values after the irrigation were statistically different.
The average change in soil moisture content ranged between 3.2 inches for the June irrigation and 4.6 inches for the July irrigation.
Based on the first year's data, the infiltration rate though the soil per irrigation should decrease with time.
Yet for the same irrigation set times, the average change in soil moisture did not decrease with time during the irrigation season.
This behavior suggests that water flow into cracks played a major role in the infiltration process because this flow would not be affected by any seasonal reductions in the infiltration rate into the soil matrix.
Inflow was measured with a propeller flow meter installed at the irrigation district turnout.
Surface runoff was measured with a WSU flume installed in the tailwater ditch at the end of the field.
The depth of infiltration is
 the difference between inflow and outflow.
Values for the 1/4-mile lengths are for both upper and lower halves of the field.
A slight trend of decreasing infiltration with time of year occurred, although the difference between the preirrigation and the last irrigation was only 1.2 to 1.4 inches.
For the crop irrigations, little difference in inflow, outflow and infiltration was found for the 1/4and 1/2-mile furrow lengths, even though the irrigation set times of the 1/4-mile length were about half those of the 1/2-mile length.
The amount of infiltration under surge irrigation was 0.8 inch more than that of the continuous-flow irrigations for the preirrigation.
Normally the opposite would be expected because many field trials comparing surge irrigation with continuous-flow irrigation revealed less infiltration under surge irrigation.
The amounts of applied water and surface runoff were considerably higher under surge irri-
 TABLE 1.
Statistics of advance times
 Distance	Advance time	Standard deviation	Coefficient of variation
 590	165	9	5.5
 1,180	367	19	5.2
 2,360	1,119	164	14.7
 590	177	28	15.8
 1,180	374	44	11.8
 2,360	962	148	15.3
 590	160	41	25.6
 1,180	436	151	34.6
 Preirrigation	396	41	8.0
 June irrigation	288	80	31.4
 July irrigation	264	11	4.2
 TABLE 2.
Average soil moisture content, standard deviation, coefficient of variation  and
 distribution uniformity  for the second year
 Average	Standard deviation	CV	DU
 Before 4.8	0.5	11.1	86
 After 8.0	0.4	5.3	94
 Change	3.2	0.2	4.9	96
 Before4.2	0.6	14.5	85
 After 8.8	0.7	8.2	87
 Change	4.6	0.3	6.9	90
 Before 4.6	0.7	16.0	84
 After 8.3	0.4	4.5	98
 Change	3.8	0.6	15.7	83
 TABLE 3.
Depth of inflow, outflow, and infiltration of the second-year irrigations
 Irrigation	Inflow	Outflow	Infiltration
 Continuous-flow 	7.7	1.8	5.4
 Surge 	11.7	5.5	6.2
 Continuous-flow 	6.1	0.9	5.2
 Continuous-flow 	5.9	0.9	5.0
 Surge 	5.2	0.3	4.9
 Continuous-flow 	4.9	0.3	4.6
 Continuous-flow 	4.9	0.3	4.6
 Surge 	5.1	0.4	4.7
 Continuous-flow 	5.3	0.5	4.8
 Continuous-flow 	6.3	0.8	5.5
 Surge 	5.0	0.3	4.7
 Continuous-flow 	5.2	1.2	4.0
 Continuous-flow 	5.2	1.0	4.2
 Surge 	4.4	0.4	4.7
 gation than under continuous-flow irrigation.
This was due to a longer irrigation set time used for this surge irrigation compared with the set times of the continuous flow treatments.
For the crop irrigations, little difference in infiltrated amounts occurred between the continuous-flow irrigations and the surge irrigation.
These results show little difference in infiltrated amounts between the three irrigation methods, particularly for the crop irrigations.
This behavior indicates that under a cracking soil, improvements such as reduced furrow lengths, increased furrow inflow rates and surge irrigation may have little effect on infiltration.
Two factors appear responsible for this behavior.
First, for the earlier irrigations, water flow into the subsurface cracks appeared to dominate the infiltration process.
These improvements could not reduce this crack flow compared to that which occurred
 under the unimproved furrow system.
Second, for the later irrigations after cultivation had ceased, water flow into shallow surface cracks coupled with a very low steady-state infiltration rate controlled the infiltration.
Little could be done to reduce infiltration below these amounts under these conditions.
Cumulative infiltration was not affected by furrow inflow rate for the preirrigation because the water flowed into the subsurface cracks.
For the first crop irrigation, cumulative infiltration increased slightly with increasing furrow inflow rate, indicating that infiltration directly into the porous soil matrix from the furrow was more of a factor for this irrigation than for the preirrigation.
Cumulative infiltration increased substantially with increasing furrow inflow rate for the August irrigation of the first year.
The wetted pe-
 Fig.
4.
Soil moisture content of top 2 feet of soil before and after the June 21, July 12 and Aug.
10 irrigations of the second year, 1988.
rimeter thus increased for the larger inflow rates during this late-season irrigation.
Steady-state infiltration rates decreased substantially with time during the year based on the measurements of the first year.
Uniform advance times up to 1,180 feet, caused by crack flow, occurred for the preirrigation and crop irrigations, except for the later irrigation of the first year.
High uniformity of soil moisture occurred with distance along the furrow.
Values of distribution uniformity after the irrigation exceeded about 87% for each irrigation.
Average changes in soil moisture content after the irrigation were similar, even though the steady-state infiltration rate decreased with time.
This behavior reflects the role of the surface cracks in the infiltration process.
For all practical purposes, little difference in infiltrated amounts was found for the two continuous-flow irrigation treatments and the surge irrigation treatment.
This indicates that in cracking soils, measures normally recommended for improving furrow irrigation systems may have little impact on system performance compared with the unimproved system.
Sprinkler irrigation may be necessary to reduce infiltration under these conditions.
B.R.
Hanson is Irrigation and Drainage Specialist; Department of Land, Air, and Water Resources, UC Davis; A.E.
Fulton was Farm Advisor, UC Cooperative Extension, Kings County; and D.A.
Goldhamer is Water Management Specialist, Department of Land, Air, and Water Resources, UC Davis.
We acknowledge the assistance of Hossein Shakouri , Sarkis Joulfayan , Eric Cartwright , Karin Hilding  and Kent Kaita  in collecting the evaluation data of the furrow irrigation system.
We appreciate the cooperation of the Stone Land Company, Stratford.
Irrigation Scheduling to Improve Water and Energy-use Efficiencies
 Robert Evans, Extension Agricultural Engineering Specialist R.
E.
Sneed, Extension Agricultural Engineering Specialist D.
K.
Cassel, Professor of Soil Science
 Published by: North Carolina Cooperative Extension Service
 Publication Number: AG 452-4
 Last Electronic Revision: June 1996 
 Much of the irrigation in the U.S.
is practiced in arid regions where little or no rainfall occurs during the growing season.
Under arid conditions, irrigation water can be applied at fairly routine intervals and in routine amounts.
However, North Carolina is located in a humid region where irrigation must be planned in conjunction with prevailing rainfall conditions.
In humid regions such as ours, applying routine amounts of irrigation water at regular intervals will almost always result in over irrigation and the needless waste of water and energy.
You can make most efficient use of water and energy by applying the right amount of water to cropland at the right time.
Irrigation scheduling is the use of water management strategies to prevent over application of water while minimizing yield loss due to water shortage or drought stress.
Many different crops are irrigated in North Carolina.
These crops are grown under a wide range of soil conditions and production practices.
Therefore, irrigation scheduling is an extremely important management practice for irrigators in North Carolina.
Importance of Irrigation Scheduling
 Some irrigation water is stored in the soil to be removed by crops and some is lost by evaporation, runoff, or seepage.
The amount of water lost through these processes is affected by irrigation system design and irrigation management.
Prudent scheduling minimizes runoff and percolation losses, which in turn usually maximizes irrigation efficiency by reducing energy and water use.
You can save energy by no longer pumping water that was previously being wasted.
When water supplies and irrigation equipment are adequate, irrigators tend to over irrigate, believing that applying more water will increase crop yields.
Instead, over irrigation can reduce yields because the excess soil moisture often results in plant disease, nutrient leaching, and reduced pesticide effectiveness.
In addition, water and energy are wasted.
The quantity of water pumped can often be reduced without reducing yield.
Studies have shown that irrigation scheduling using water balance methods  can save 15 to 35 percent of the water normally pumped without reducing yield.
Maximum yield usually does not equate to maximum profit.
The optimum economic yield is less than the maximum potential yield.
Irrigation scheduling tips presented in popular farm magazines too often aim at achieving maximum yield with too little emphasis on water and energy use efficiencies.
An optimum irrigation schedule maximizes profit and optimizes water and energy use.
Irrigation scheduling requires knowledge of:
 the status of crop stress
 the potential yield reduction if the crop remains in a stressed condition.
In this publication, it is assumed that the reader understands these basic relationships.
Their importance to irrigation scheduling is briefly summarized below.
The terms that are normally used in irrigation scheduling are summarized in the box on the back cover.
For more information on these subjects refer to Extension Publication AG-452-1, Soil Water and Crop Characteristics Important to Irrigation Scheduling.
Relating Soil-Water to Plant Stress
 The amount of water that should be applied with each irrigation depends primarily on the soil and the amount of water it can retain for plant use, referred to as plant-available water.
The amount of water removed from the soil by the plant since the last irrigation or rainfall is referred to as the depletion volume.
Irrigation should begin when the crop comes under water stress severe enough to reduce crop yield or quality.
The level of stress that will cause a reduction in crop yield or quality depends on the kind of crop and its stage of development; the level varies during the growing season as the crop matures.
For example, corn will tolerate more stress without causing a yield reduction when the stress occurs during the vegetative stage as opposed to the pollination stage.
Thus, determining when to irrigate is a scheduling decision that should take into account the crop's sensitivity to stress.
Figure 1.
The relationship between water distribution in the soil and the concept of irrigation scheduling when 50 percent of the PAW has been depleted.
Recently, scheduling techniques have been developed that are based on the moisture status or stress condition of the crop.
For example, to predict crop stress by infrared thermometry, the temperature of the crop's leaves is related to transpiration rate.
Remote sensing of crop stress using infrared satellite imagery is another method being evaluated.
Although these methods hold promise for the future, most of the work on them has been conducted in arid regions.
Guidelines have not been developed for humid regions such as North Carolina.
In humid regions, the most reliable method currently available for estimating when to irrigate is based on allowable depletion of PAW.
The basic assumption is that crop yield or quality will not be reduced if crop water use is less than the allowable depletion level.
In North Carolina, 50 percent depletion of PAW is recommended for most soils.
However, allowable depletion may range from 40 percent or less in some coarse, sandy soils to as high as 60 to 70 percent in some clayey soils.
Droughtsensitive crops  tolerate less depletion than drought-tolerant crops.
In humid regions, the irrigation frequency and the amount of water to apply are strongly influenced by seasonal rainfall.
Efficiently and effectively supplementing rainfall is one of the greatest challenges to irrigation scheduling in North Carolina.
During periods when no rainfall occurs, 1 inch of irrigation water may be required every three to four days.
During a season when rainfall occurs frequently, irrigation may be needed only once or twice a month.
In most years, the need for and frequency of irrigation falls between these extremes.
Figure 2.
Rainfall during the growing season  at the Raleigh-Durham airport from 1956 to 1985.
Consumptive use is the total amount of water extracted by a corn crop during the growing season.
Figure 2 illustrates the annual variation in rainfall at the Raleigh-Durham airport during the corngrowing season for the 30-year period from 1956 to 1985.
Notice that the average rainfall during the growing season was nearly equal to the cumulative consumptive use for a corn crop.
On the average, then, enough rain-water was received to satisfy crop needs, suggesting that irrigation was unnecessary.
But in some years more than enough rainfall was received, whereas in other years rainfall was not adequate and irrigation was needed.
These data illustrate that the timing of rains is more important to irrigation decisions than the total amount of rainfall.
Corn planted between April 10 and 15 consumes the most water and is most susceptible to water deficits from June 5 to July 5.
During that 30-day period, corn requires about 0.25 inches of water per day, or a total of 7.5 inches.
Figure 3 shows that in only three years between 1956 and 1985 was rainfall adequate to satisfy the water needs of corn throughout this critical growth stage.
The average 30-day rainfall was approximately 4 inches, indicating that the average amount of irrigation water required was 3.5 inches during the 30-day period.
But routinely applying that average amount would have been suitable in only 10 out of the 30 years.
In 10 of the years, applying 3.5 inches would have been inadequate, and in the 10 remaining years it would have been excessive.
The annual irrigation requirements ranged from none to 7 inches.
Figure 3.
Yearly rainfall fluctuation at the Raleigh-Durham airport during the 30-day critical moisture period for corn  from 1956 to 1985.
Consumption is the amount of water a corn crop would extract from the soil during the critical 30-day period if soil-water is not limiting.
Most irrigation systems have the capacity to satisfy crop needs in the driest year or at least in 9 out of every 10 years.
In this example, the amount of irrigation water needed to satisfy crop demand during the critical growth phase in 9 out of 10 years was 6.5 inches, or more than 1.5 inches per week.
Yet if this amount were applied every week, over irrigation would result 90 percent of the time.
This example clearly shows that the weekly, monthly, and annual variability in rainfall must be taken into account when making irrigation decisions.
Irrigation scheduling is the process of answering two basic questions:
 Do I need to irrigate?
How much water should I apply?
Determining When to Irrigate
 There are three ways to decide when to irrigate:
 estimate soil-water using an accounting approach 
 Measuring Soil-Water.
There are many different methods or devices for measuring soil water.
These include the feel method, gravitational method, tensiometers, electrical resistance blocks, neutron probe, Phene cell, and time domain reflectometer.
These methods differ in reliability, cost, and labor intensity.
For more information on the operation, reliability, and cost of these methods, refer to Extension Publication AG-452-2, Measuring Soil-Water for Irrigation Scheduling: Monitoring Methods and Devices.
Tensiometers and electrical resistance blocks are the most cost-efficient and reliable devices for measuring soil-water for the irrigation of North Carolina soils.
Tensiometers are best suited for sandy,
 sandy loam, and loamy soil textures, while electrical resistance blocks work best in silty or clayey soils.
You should be aware that the calibration curves and recommendations supplied by the manufacturer for these devices were developed for general conditions and are not adequate for specific soil conditions and fields.
For best results, all soil-water measuring devices should be calibrated for the major soils in each field being irrigated.
Calibration procedures for soil-water measuring devices are outlined in Extension Publication AG-452-3, Calibrating Soil-Water Measuring Devices.
Checkbook Method.
The check-book method is an accounting approach for estimating how much soilwater remains in the effective root zone based on water inputs and outputs.
Irrigation is scheduled when the soil-water content in the effective root zone is near the allowable depletion volume.
Some of the simpler checkbook methods keep track of rainfall, evapotranspiration, and irrigation amounts.
More sophisticated methods require periodic measurements of the soil-water status and moisture-use rates of the crop.
Some methods may even require inputs of daily temperature, wind speed, and solar radiation amounts.
Checkbook methods require detailed daily record keeping, which can become time consuming for the more complex methods.
One of the advantages of the checkbook approach is that it can be programmed on a computer.
Computer programs have been developed to handle the accounting and provide timely and sometimes precise scheduling recommendations.
Some of the more advanced programs can predict the effect of an irrigation or irrigation delay at a given growth stage on crop yield and maturity date.
Computer programs can be very reliable tools for scheduling irrigation; however, it is very important to remember that the computer recommendations are only as good as the data you supply.
Regardless of the method used to estimate or measure soil-water, there will be occasions when the soil will have reached the "turn on" level of dryness, yet your judgment suggests that irrigation should be delayed.
For example, if the crop has not reached the most critical stage and the water supply is in danger of being exhausted before the end of the irrigation season, then irrigation should be delayed.
This delay may cause some reduction in yield or quality, but the reduction would be greater if the water supply became depleted before the crop reaches a more critical stage of growth.
If a high probability of rain-fall has been predicted during the next one or two days, it may be advantageous to wait and see before starting to irrigate.
This decision must also take into account the capacity of the irrigation system.
If the system is already being used to full capacity and water supplies are sufficient, then irrigate on schedule.
If predicted rainfall does not occur, it is impossible to get back on schedule when the irrigation equipment is already being used to full capacity.
A wait-and-see approach is practical only when the irrigation system is not being used at full capacity.
Determining How Much to Irrigate
 Enough irrigation water should be applied to replace the depleted PAW within the root zone and to allow for irrigation inefficiencies.
Root depth and root distribution are important because they determine the depth of the soil reservoir from which the plant can extract available water.
About 70 percent of the root mass is found in the upper half of the maximum root depth.
Under adequate moisture conditions, water uptake by the crop is about the same as its root distribution.
Thus, about 70 percent of the water used by a crop is obtained from the upper half of the root zone.
This zone is referred to as the effective root depth.
This depth should be used to compute the volume of PAW.
Irrigation amounts should be computed to replace only the depleted PAW within the effective root zone.
The depleted volume is referred to as the net amount of water to be replaced.
Additional water must be applied to account for irrigation inefficiencies SO that the desired  amount reaches the root zone.
Inefficiencies might include leakage at couplings, surface runoff, or percolation below the effective root depth.
Irrigation efficiency is typically 70 to 80 percent of the total water applied.
Thus, if the net irrigation amount required to replace the depletion volume is 1 inch and the irrigation efficiency is 75 percent, the total amount of irrigation water needed to apply 1 inch of net water is approximately 1.3 inches.
This amount  is referred to as the gross water application.
For a discussion on strategies to maximize irrigation efficiency, refer to Extension Publication AG-452-5, Irrigation Management Strategies to Improve Water and Energy Efficiencies.
There may be occasions when only part of the depletion volume should be replaced by irrigation.
For example, if irrigation replaces all the depletion volume, there is little or no PAW storage remaining within the effective root zone should a rainfall occur soon after the irrigation.
In this situation, most of an ensuing rainfall amount could be lost through runoff or percolation.
Applying only part of the scheduled amount of irrigation water in anticipation of rainfall will result in more efficient use of water and energy, although this approach may require more frequent irrigation.
Table 1.
Determining When and How Much to Intgate
 Calculating When to Irrigate	Calculating How Much to Irrigate
 Plant-available water	Net irrigation amount 
 PAW = field capacity witting point	H depletion volume times effective
 0.20 In./In.-0.08 in./in.
root depth
 0.12 In./In.
= 0,06 in./in.
x 8 in.
50 percent depletion of PAW	Gross water application
 = 0.12 in./in.
x 0.50	net amount divided by Irrigation
 = 0.06 in./in.
efficiency
 Water content at 50 percent depletion	Net irrigation amount 
 water content  minus	= 0.06 in.
/in.
x 12 in.
allowable depletion	= 0.72 In./Irigation
 I 0.20 in./In.
0.06 in.
(in.
Tension when water content is in./In.
Gross water application
 read from plot  at 0.14 in./in.
0.72 in./0.75
 = 30 cb	= 0,96 in./irrigation
 The above discussion has shown that determining when and how much to irrigate is a complex decisionmaking process.
Critical elements of this process are summarized in Figure 4.
Every irrigator must evaluate these critical elements daily to utilize water and energy efficiently and effectively.
The following examples demonstrate two irrigation scheduling procedures recommended for North Carolina.
Figure 4.
Daily decision process required to schedule irrigation effectively.
Calibrating soil-water measuring equipment and measuring soil-water are the first steps in developing an effective irrigation schedule.
The information obtained allows you to determine when the soil-water content has reached the normal irrigation range.
The calibration data are used to determine the readings of the soil-water measuring device at the allowable depletion volume, usually 50 percent depletion of PAW.
Using a tensiometer for irrigation scheduling is demonstrated in the following example.
A similar procedure is followed if electrical resistance blocks or one of the other soil-water measuring devices is used.
Figure 5.
Calibration curve of water content versus tensiometer reading.
Field capacity is normally interpreted to be the point at which the rate of decrease of water content versus tension flattens out, in this case, about 10 cb.
Irrigation Scheduling Using Tensiometers
 A calibration curve showing soil-water tension  versus water content for a sandy soil is plotted in Figure 5.
From this graph, field capacity is estimated to occur where the steeper portion of the curve begins to flatten out, at about 10 centibars.
Field capacity occurs in a sandy soil about one day after a soaking rain.
The water content at 10 cb is 0.20 in/in.
The PAW of this soil as calculated in Table 1 is 0.12 in/in.; therefore, the allowable depletion  is 0.06 in/in.
The water content of the soil when irrigation should begin is 0.14 in/in.
The corresponding tension at this water content is 30 cb.
Therefore, irrigation water should be applied to this soil when the tensiometer reading reaches 30 cb.
At the time of irrigation, the effective root depth must be known in order to determine the total amount of irrigation water to apply and to install tensiometers or electrical resistance blocks at the appropriate depth.
As discussed earlier, the effective root depth represents the depth of soil from which the plant extracts most of its water.
The effective root depth increases during the growing season as the crop develops.
It begins at zero at planting and increases to its maximum depth by the time the crop reaches its reproductive stage of growth, which occurs about midseason for most crops.
In North Carolina, soil conditions usually limit the maximum effective root depth to about 12 inches.
When irrigation is scheduled during early growth stages before maximum root development, assume that the rate of root elongation increases linearly from planting time up to the maximum effective depth of 12 inches at midseason.
For example, corn reaches its maximum effective root depth of 12 inches at the tasseling growth stage, 60 to 65 days after planting.
Before tasseling, the rate of effective root growth is about 0.2 inches per day.
Thus, at the knee-high growth stage, 40 days after planting, the effective root depth is about 8 inches.
Table 2.
Example of Irrigation Scheduling Using a Simple Checkbook Approach
 PAW in soll at start	Consumptive	Net	PAW In soll end
 Date	of day	use for day	Rainfall 	Irrigation	of day	Comments
 					{Inches)	
 5-31	1.00	1.44	100	Soaking rain, FC assumed
 6-1	1.44	100	0.14	1.30	90
 2	1.30	90	0.15	1.15	80
 3	1.15	80	0.16	0.99	69
 4	0.99	69	0.17	0.68	47
 5	0.82	57	0.18	0.04	0.68	47	Time to irrigate
 6	0.68	47	0.19	0.04	0.72	1.25	87
 7	1.25	87	0.20	0.15	1.20	83
 8	1.20	83	0.21	0.01	1.00	69
 9	1.00	69	0.22	0.88	61
 10	0.88	61	0.22	0.66	46	Time to Irrigate
 11	0.66	46	0.23	0.72	1.15	80
 12	1.15	80	0.23	0.20	1.12	78
 13	1.12	78	0.23	0.89	62
 14	0.89	62	0.24	0.65	45	Time to irrigate
 15	0.65	45	0.24	0.08	0.72	1.21	84
 16	1.21	84	0.24	0.19	1.16	81
 17	1.16	81	0.24	0.92	64
 18	0.92	64	0.25	1.26	1.44	100	0.49 in.
rain above FC
 19	1.44	100	0.25	0.31	1.44	100	0.06 in.
rain above FC
 20	1.44	100	0.25	1.19	83
 21	1.19	83	0.25	0.94	65
 22	0.94	65	0.26	0.68	47	Time to Irrigate
 23	0.68	47	0.26	0.72	1.14	79
 24	1.14	79	0.26	0.88	61
 25	0.88	61	0.26	0.62	43	Time to irrigate
 26	0.62	43	0.25	0.72	1.08	75
 27	1.08	75	0.25	0.83	58	
 28	0.83	58	0.25	0.72	1.30	90	Irrigate sooner than 50%
 29	1.30	90	0.25	0.21	1.26	88
 30	1.26	88	0.24	0.38	1.40	97
 Sandy loam soil of calibration example.
Effective root zone assumed to be 12 Inches.
Total x 12 In.
= 1.44 In.
Irrigate at 50% of PAW.
Inigar lion amount based on 50% depletion of 1.44 Inches, which is a net amount of 0.72 inches, Values shown do not Include Inigation Inefficiency 2Consumptive use for com from Figure 7.
Planting assumed to be April 15, soJune 1 corresponds to 45 days after planting 'Rainfall from Roleigh-Durham airport.
1985.
The amount of water to be added at each irrigation is determined by multiplying the allowable depletion by the effective root depth.
For example, if irrigation is scheduled when corn has reached the knee-high stage and the effective root depth is 8 inches; the irrigation amount is then 0.48 inches, as shown in Table 2.
This represents the net  irrigation amount.
Assuming an irrigation efficiency of 75 percent, the gross water application amount is 0.64 inches.
Once corn reaches the tasseling stage, the effective root depth has increased to 12 inches.
The net irrigation amount at this stage is 0.72 inches and the gross water application is 0.96 inches.
Frequently, irrigation systems in North Carolina have been sized to apply approximately 1 inch of water every three to four days, which is a general rule of thumb to satisfy expected peak-use demands.
This amount would be appropriate in the above example when corn has reached the tasseling stage.
But notice that this amount of water is 50 percent more than should be applied at the knee-high stage.
Few irrigators adjust their application amount during the growing season, which often results in overirrigation early in the season.
Applying the design system capacity of 1 inch at the knee-high stage in the above example would result in applying 0.24 inches per irrigation that would percolate below the effective root zone.
Thus, the irrigation efficiency would be reduced from 75 percent to about 50 percent.
This wastes water and energy.
Locating Soil-Water Measuring Devices
 In general, soil-water should be measured at the center of the effective root zone.
If the effective root depth is 12 inches, the soil-water measuring device should be installed at a depth of about 6 inches.
When an irrigated field contains more than one soil type, at least one device should be installed within each major soil type in the field.
The above calculations should also be made for each different soil.
When stationary sprinklers are used , the system should be managed such that an irrigation zone encompasses only soils with similar soil-water properties.
In this manner, irrigation amounts can be adjusted according to the soil-water retention properties within a particular zone.
To check the computed irrigation amount, a second soil-water measuring device can be used at the bottom of the root zone to indicate when irrigation should stop.
The two soil-water measuring devices are used as an on-off switch, as shown in Figure 6.
One device  is installed in the center of the effective root zone and indicates when irrigation should start.
The second device, installed at the bottom of the root zone, indicates when irrigation should stop.
As soon as the root zone is rewetted to field capacity, water begins to percolate below the effective root zone.
The percolation is indicated by a decrease in soil-water tension of the 'ower tensiometer.
As soon as the tension reading on the deep tensiometer starts to decrease, irrigation should be stopped.
Figure 6.
Use of two tensiometers to schedule irrigation.
The upper tensiometer indicates when irrigation should start and the lower indicates when it should stop.
Scheduling irrigation is more difficult for mechanical-move type irrigation systems  because the irrigator must anticipate the time required for the system to move across the field.
In this situation, irrigation must be started sooner, typically after 30 to 40 percent depletion of
 PAW SO that the last section irrigated will not be drier than 60 to 70 percent depleted.
The situation is further complicated by rainfall events occurring during this period.
The PAW content may be uniform following a rainfall, but depending on the time required for the system to make a complete cycle, PAW may vary across the field by 50 percent following irrigation.
Shallow tensiometers can still be used to determine when to irrigate, but irrigation must be started sooner SO that the last portion to be irrigated does not become too dry.
Deeper tensiometers should be located near the midpoint of the travel cycle.
They should be monitored as the system passes to determine whether the proper amount of water is being applied.
If no change in the tensiometer reading is observed as the system passes, too little water is being applied and the travel speed should be reduced.
Likewise, if the tensiometer reading decreases before the system is 90 percent past the tensiometer, too much water is being applied and the travel speed should be increased.
With mechanical-move systems, soil-water measurements are used in conjunction with the checkbook approach to schedule irrigation properly and account for the additional soil-water depletion that will occur while the system travels across the field.
Irrigation Scheduling Using the Checkbook Approach
 The checkbook approach to irrigation scheduling involves a daily accounting of water withdrawals and additions to the effective root zone.
The additions include rainfall and irrigation amounts and the withdrawals include crop water use, runoff, and percolation.
Figure 7.
Daily water use by corn as influenced by stage of development.
Irrigation scheduling decisions should be adjusted to reflect changes in water consumption by the crop during the growing season.
Rainfall and irrigation can be measured with rain gauges installed above the crop canopy in the irrigated field.
Plant withdrawals can be estimated from crop soil-water use curves or by measuring pan evaporation.
Moisture use curves such as those shown in Figure 7 indicate the amount of water  that a crop would remove from the soil if the atmospheric evaporative demand was high; that is, on a clear, warm day if the amount of water stored in the effective root zone is sufficient.
When these conditions are not present, actual consumptive use will be less than the consumptive use values shown in Figure 7.
For example, on a cool, rainy, or very overcast day, consumptive use may be near zero.
Consumptive use rates should be adjusted to reflect prevailing weather conditions.
Daily pan evaporation measurements reflect the effects of prevailing weather conditions.
Pan evaporation is approximately equal to potential evapotranspiration.
Evapotranspiration is the process by which water is lost from the soil surface by evaporation and by the transpiration process of plants growing on the soil.
Potential evapotranspiratron  is the maximum amount of water that could be lost through this process under a given set of atmospheric conditions, assuming that the crop covers the entire soil surface and that the amount of water present in the soil does not limit the process.
However, when pan evaporation is used to estimate PET, a crop coefficient is required to adjust the pan evaporation value to actual evapotranspiration.
AET is the actual amount of water removed from the soil and can be limited by the crop or by the water content of the soil.
Actual evapotranspiration equals PET  for an actively growing crop that completely shades the soil surface  and is growing in a soil near field capacity.
But a young seedling does not transpire at the same rate as a crop with full canopy.
In fact, during much of the growing season, AET is less than PET because the crop canopy is small or the crop is approaching senescence and not transpiring at its peak rate.
The crop coefficient corrects for the difference between AET  and PET.
Figure 8.
Crop coefficient curve for corn for adjusting pan evaporation to actual evapotranspiration of the crop.
For most crops growing in soils with nonlimiting soil moisture, the coefficient will be 1 during the peak moisture-use period, indicating that AET is equal to evaporation from a screened Class A evaporation pan.
Crop coefficients for many plants have been developed.
An example crop-coefficient curve for corn is shown in Figure 8.
AET can also be limited when the soil becomes too dry to supply water to plant roots SO that the plant can transpire at PET.
The plant undergoes temporary wilting when this occurs.
The checkbook approach includes no corrective measures to account for soil limitations.
It is assumed that the soil does not limit water supply to the crop as long as PAW is not depleted below 50 percent.
The National Weather Service records pan evaporation at several weather stations across the state.
This information can be obtained from the local Extension Service office through the CAROLINE network.
Pan evaporation can also be measured on site with a fairly large pan, such as a washtub.
The pan should be covered with some type of screen or netting  to keep birds and animals from drinking the water.
The most common source of error using the checkbook approach occurs in estimating water losses due to runoff end percolation losses; that is, estimating the effective
 rainfall or irrigation that remains in the effective root zone.
These errors accumulate as the season progresses.
For best results, it is necessary to measure soil-water several times during the growing season  to make periodic corrections of the checkbook balance of soil-water.
To use the checkbook method, you must begin computations when the soil is at a known water content.
Field capacity is the usual starting point and should be assumed to occur soon after a rainfall or irrigation of an amount large enough to wet the effective root zone.
For many of the loamy soil textures found in North Carolina , field capacity can be assumed to occur one day after rainfall or irrigation.
A simple checkbook approach for scheduling irrigation is shown in Table 2.
Irrigation amounts are computed as shown in Table 2.
Notice that many of the adjustments discussed above, which are needed to correct for potential errors, have been omitted.
The checkbook method becomes time consuming and tedious but more reliable when these corrections are included.
When data needed to make corrections are available, the use of a computer program is recommended.
Technical Assistance Is Available
 While simple in concept, irrigation scheduling is rather complex in practice.
As costs of energy and water continue to increase, irrigation scheduling will become increasingly important.
By making more efficient use of both energy and water, irrigation scheduling can save you money.
Your county Cooperative Extension Service and Soil Conservation Service can help with irrigation decisions.
Their staff members know how to apply irrigation scheduling techniques.
Irrigation consulting and scheduling services are also available in some areas.
Soll, Water, and Plant Terms Used in Irrigation Scheduling
 Field Copacity 	The soil-water content after the force of gravity has drained or removed all the
 water It can, usually 1 to 3 days after rainfall.
Permonent Willing Point 	The soll-water content at which healthy plants can no longer extract water from
 the soil at a rate fast enough to recover from witting.
permanent willing point is
 considered the lower limit of plantavailable water.
Plant-Avallable Water 	The amount of water held In the soil that Is available to plants; the difference be
 tween field capacity and the permanent willing point.
Depletion Volume	The amount of plant-available water removed from the soil by plants and
 evaporation from the soll surface.
Allowable Depletion Volume	The amount of plant-available water that can be removed from the soil without
 is seriously affecting plant growth and development
 Effective Root Depth	The upper portion of the root zone where plants get most of their water.
Effective
 root depth Is estimated as one-half the maximum rooting depth.
Topics will include, but not be limited to the following:
 Limited Irrigation for Maximum Profitability
 Scheduling Irrigation Tools and Techniques
 Soil and Plant Sensors
 Satellite, Aerial and Drone Imagery
 N Effects on Water Use
Managing Corn Diseases with Seed Treatments
 Figure 49.1 Treated corn seed with different color coats.
Table 49.1 Tips for using seed treatments:
 1.
Match your seed treatment to your problem.
2.
Use high-quality seed.
3.
Use proper handling techniques and labeled rates.
4.
If treating the seed yourself, calibrate your equipment and use dedicated seed treatment equipment when available.
Grain auger mounted treatment equipment may provide adequate coverage.
5.
Treated seed should not be allowed to contaminate equipment used to transport or store, food or feed grains.
a.
Do Not Use Treated Seed for Food or Feed!!
6.
Use caution when considering planter-applied  seed treatments.
History of Seed Treatments
 Seed treatments were the first form of crop protection in modern agriculture.
Egyptians and Romans treated seeds with sap from onions.
In Europe before the 1800s, manure, chorine salts, copper, and hot water were used as seed treatments.
Today, fungicides, insecticides, nematicides, and fertilizer are used as seed treatments for various agricultural crops and are useful tools in promoting stand establishment and seedling vigor.
Seed treatments may also help preserve yield potential and prevent quality losses in grain by preventing development of seedand soil-borne diseases.
The development of effective seed treatments can be noted as one of the most significant
 advancements in plant disease management.
In general, fungicidal seed treatments are used for three primary reasons:
 To manage soil-borne pathogens that can cause seed rots, seedling blights in many crops, root rots, smuts, or downy mildew.
To manage diseases caused by seed-borne pathogens residing on the seed surface.
To manage diseases caused by seed-borne fungi surviving inside the seed.
Developing Your Seed Treatment Strategy
 Disease management in agricultural crops requires a multifaceted approach as part of an integrated pest management  program.
Weather conditions cannot be precisely predicted at the time of planting, therefore seed treatments can be cheap insurance when conditions are conducive for seed and seedling diseases.
When making a decision about seed treatments, consider:
 1.
Do you expect an economic return?
a.
Estimate the yield response relative to cost.
2.
What is the history of seedling diseases in your field?
For example, if a field is known to have high incidence of damping-off, then fungicide seed treatment is warranted.
Likewise, if a field has a history of corn nematodes, a nematicide seed treatment then would be warranted.
3.
What are the prevailing or expected climatic conditions at the time of planting?
a.
Wet and cool soils are favorable conditions for most seedling pathogens, including Pythium spp.
b.
Cool soil conditions also reduce seedling growth rate, providing a longer interaction time between the pathogen and the seed.
4.
Is the crop for seed production?
a.
Grain for seed attracts higher prices, therefore, it may be beneficial to consider seed treatment in addition to other factors below.
b.
Fungicide seed treatments also can increase the likelihood of the seed being produced and offered for sale as disease-free.
5.
Is corn following corn?
a.
Survival of seedling pathogens is typically higher in nonrotated fields.
6.
Is corn being planted in a till or no-till/minimum-till field?
a.
No-till fields may have an increased risk of seedling diseases.
7.
When will you plant?
Planting early in the spring when the soil temperatures are low may increase the risk of seed/ a.
seedling infection.
8.
What is the disease rating for the cultivar to be planted?
a.
Seed companies provide disease ratings for cultivars.
b.
For hybrids susceptible to seedling diseases, a seed treatment may be beneficial.
9.
What is the germination rate for the seed lot?
For seed with a low germination percentage, seed treatment may protect young seedlings with a.
marginal vigor and improve plant stands compared with nontreated seed.
10.
What is the desired plant population per acre?
With increasing costs of seed, growers may opt for lower plant populations per acre, therefore to a.
avoid further loss of plants; a fungicide seed treatment may be justified.
11.
What is the expected price per bushel?
Higher prices per bushel would indicate that fewer additional bushels are needed to offset seed a.
treatment costs.
12.
Is the seed for replanting?
a.
If replanting because of stand establishment problems  is considered, using fungicide treated seeds may increase chances of survival of replanted seed.
13.
Fungicide seed treatments are not effective against bacterial pathogens or in managing viral diseases.
a.
Most seed treatment products do not control all types of fungal pathogens.
14.
Residue and volunteer plant management for reduction of residue-borne and overwintering diseases.
15.
High quality, disease-free seed to prevent the spread of seed-borne diseases and promote healthy stand establishment.
16.
Proper hybrid selection for host resistance and adaptation to the growing region.
17.
Proper plant health management.
a.
Healthy plants have a higher tolerance to the development of plant diseases.
18.
Judicious use of plant protectant products such as herbicides, insecticides, and fungicides to reduce losses, promote healthy plants, prevent quality losses in seed, and for resistance management.
Determining the Appropriate Chemical Treatment
 Field history is a key component in the decision-making process when selecting appropriate seed treatments.
The cropping sequence and the history of major disease or insect pests within the field can be important factors in seed treatment decisions.
Proper identification of disease agents is also important.
Agronomy or Plant Pathology Extension Field Specialists at the Regional Extension Centers or the Plant Disease Diagnostic Clinic at SDSU can assist producers in identifying plant health problems throughout the growing season.
Other web resources that can help with corn disease identification are outlined in the reference section of this chapter.
Effectiveness of control will vary with seed treatment product, rate, environmental conditions, and pests present.
Seed treatments may provide some level of control for early season diseases as well as control of seedling blights and seedor soil-borne diseases.
They should not be viewed as season-long protection.
Newly opened land, such as CRP being returned to crop production, may present a special consideration  and most certainly will be a situation where seed treatments should be considered.
Diseases such as root rots and seedling blights can often be more severe when crops are planted into these high-residue situations.
Also, insect pressure on newly cultivated lands may differ from a typical cropping situation.
In-furrow Seed Treatment vs.
On-seed Treatments vs.
Biotechnology Traits
 In-furrow fungicide application treats the soil, whereas on-seed treatment targets pathogens on the seed and those in the soil that will come in contact with the seed/root early in the season.
In-furrow treatments usually require high active-ingredient rates compared to on-seed treatments.
Both methods are effective in managing seed and soil-borne diseases.
However, in-furrow fungicide treatments may require high application rates and also nontarget effects may be high with in-furrow treatments.
As of 2015, biotechnology traits for disease management have not been incorporated in commercial corn hybrids.
Disease-resistance genes in corn have been bred using the traditional/conventional approach.
Therefore, plant disease management relies heavily on host resistance, cultural practices, and fungicides.
Classification of Fungicidal Seed Treatments
 Fungicidal seed treatments can be classified based on movement of the seed treatment product in relation to the seed.
Fungicides used as protectants  are effective only on the seed surface, providing protection against seed surface-borne pathogens and providing some level of control of soil-borne pathogens.
These products generally have a relatively short residual.
Protectant fungicides such as captan, maneb, thiram, or fludioxonil help control most types of soil-borne pathogens, with the exception of root-rotting organisms.
Systemic seed treatment fungicides are absorbed into the emerging seedling and inhibit or kill the fungus inside host plant tissues.
Systemic fungicides used for seed treatment include the following: azoxystrobin, carboxin, mefenoxam, metalaxyl, thiabendazole, trifloxystrobin, and various triazole fungicides, including difenoconazole, ipconazole, tebuconazole, and triticonazole.
4.
Manage Plant Residues
 Managing residue is critical for optimizing seed germination.
Over the past 30 years, residue management problems have increased because corn yield, and consequently, corn residue have doubled.
When returned to the soil, corn residue has helped South Dakota farmers increase soil organic matter  content of most fields.
Soil OM in corn fields of eastern SD has increased an average of 24% from 1985 to 2010.
However, the higher amounts of crop residues have complicated seedbed preparation, slowed soil warming, and contributed to a corn "yield drag" .
Techniques to reduce residue problems include:
 Chopping the corn residue with a stalk chopper or chopping combine header.
Combine corn headers a.
often are integrated with stalk choppers that have enhanced capacity to chop residue.
Chopping residue helps improve stand uniformity and yields , and
 b.
Adopting tillage techniques that minimize contact between the seed and the surface residue, ;
 C.
Harvesting and baling residue after grain harvest.
This technique has been widely adopted in the recent past.
However, problems with soil erosion, soil organic matter reduction, and nutrient deficiencies should be considered when deciding if, and how much, residue is harvested.
Bailing residue may also the positive benefit of helping the soil warm up.
Proper Applications and Precautions
 Fungicides and seed treatment products vary in formulation type, packaging, and use requirements.
Products may be dry or liquid and in concentrate or ready-to-use formulations.
While many seed treatments may be applied on-farm, several products are limited to use only by commercial applicators using closed application systems.
Caution should be used when handling or working with seed treatment products.
Fungicide seed treatments can be highly poisonous and many are irritants, therefore proper handling precautions must be taken when handling seed treatment chemicals, and producers or applicators must strictly adhere to all label directions regarding safe handling, mixing, storage, and disposal.
Using personal protection, including an approved chemical respirator, goggles, and pesticideresistant gloves, is recommended even if not specifically required by the fungicide label.
Follow label rates, as overapplication may result in unintentional injury to the seed, and underapplication may reduce the effectiveness of products.
Properly calibrate all application equipment to assure uniform coverage.
Uniform coverage of the seed is critical to optimize effectiveness of the seed treatment.
Several seed treatment methods are available, though not all are appropriate for every situation.
Commercial application or application through dedicated seed treatment equipment will likely provide the most uniform coverage.
Grain auger mounted treatment equipment is available, and may provide adequate coverage in an on-farm situation; however, an auger that has been used to treat seed may be unusable for moving grain intended for food or feed.
Likewise, treated seed should not be allowed to contaminate equipment used to transport or store food or feed grains.
Use caution when considering planter-applied  seed treatments.
Good disease control depends on uniform fungicide coverage of the seed, and this is more difficult to accomplish in planter-applied situations.
Always read and follow label directions.
Understand the product-specific guidelines for proper application: how and when to apply, feeding or grazing restrictions, as well as important safety precautions.
Always dispose of pesticide containers properly.
What a year 2020 has been.
After a year of record flooding over much of the state, we are now in various stages of drought.
With limited rainfall over most of the state this year and fairly extended hot, dry periods, many irrigators may be wondering when is the irrigation season going to end?
With the price of grain, it is also worth considering do I need to apply that last inch or two of water to get that last bushel or two?
Scheduling the last irrigation can reduce your pumping costs, improve harvest conditions, and in allocated groundwater areas, may save some irrigation water for next year.
including those currently in use in the Carneros and MST regions.
Original data listed by Maas and Hoffman  are in relation to maximal Cl concentrations in the soil water, but data were converted to maximal tolerance in the irrigation water by assuming that EC of soil water is twice ECe and that a long-term leaching fraction of 10% is achieved using high-frequency drip irrigation.
These are reasonable yet conservative assumptions.
For sensitive grape cultivars , the maximum Cl concentration of irrigation water to avoid crop injury is about 7.4 meq/L .
Since no tolerance data have been compiled for the predominant grape rootstocks in the Carneros and MST regions , we took a conservative approach and selected 7.4 meq/L  as an upper limit for Cl in our study.
As more research is conducted on these rootstocks, the limit can be adjusted accordingly.
Since the Cl content in NSD water averages 4.3 meq/L , this water will not likely cause Cl toxicity in grapes, assuming good irrigation water management.
If winter leaching is also taken into consideration, the case is even stronger that the recycled water will not pose a problem for vineyard production.
Sodium.
The ability of vines to tolerate Na varies considerably among rootstocks, but tolerance is also dependent upon Ca nutrition.
Much of the early research on Na toxicity was done in the 1940s and '50s before the importance was understood of adequate Ca nutrition for maintaining ion selectivity at the root membrane level.
Since then, a considerable amount of literature has indicated Na can cause indirect effects on crops, rather than toxicity exactly, either through nutritional imbalances   or by disrupting soil physical conditions.
These indirect effects make diagnoses of Na toxicity per se very difficult.
Moreover, Na toxicity is often reduced or completely overcome if sufficient Ca is made available to roots  through the addition of gypsum or by acidifying soils high in residual lime.
Ca addition reduces the ratio of Na to Ca  in the soil water, thereby reducing the SAR and exchangeable sodium
 percentage , resulting in both improved soil conditions and reduced Na toxicity.
Ayers and Westcot  indicate that there are no "restrictions on use"
 provided that the SAR is less than 3.
They provide no concentration limits for Na above which toxicity will result, presumably because of the indirect interactions
 Irrigation of deciduous orchards and vineyards influenced by plant-soil-water relationships in individual situations
 Today this article may seem too simplistic an explanation of basic irrigation concepts field capacity, permanent wilting point, readily available moisture.
But in 1957, much more land in California was still dry-farmed, and the widespread use of irrigation Grapes and Fruits was a new idea to many.
1957 "One of the principal cultural practices in deciduous fruit orchards and vineyards is irrigation and its successful accomplishment frequently determines whether the grower makes a profit.
"The cost of irrigation preparing the land for surface irrigation, the labor of applying the water and the cost of the water may be one of the important items in the production of fruit.
Because experience has shown that much time and labor may be wasted, the selection of a rational program of irrigation is of great importance.
"Whether to irrigate or not, or when to irrigate, are questions that can be answered only from consideration of the moisture properties of the soil, the kind of plant, its depth of rooting, the kind of root system, prevailing climatic conditions, and whether there is a supply of water for irrigation.
"A grower should consider the soil as a reservoir for the storage of water for use by the plants.
Therefore, he needs to know how much readily available water can be stored in the soil "
 Veihmeyer FJ, Hendrickson AH.
1957.
Grapes and deciduous fruits: Irrigation of deciduous orchards and vineyards influenced by plant-soil-water relationships in individual situations.
Calif Agr 11:13-8.
Frank J.
Veihmeyer was already an emeritus professor of irrigation at UC Davis when this article was published in 1957.
He joined the university in 1918 as an assistant professor of irrigation at Davis, then still known as the University Farm.
Veihmeyer was recognized and honored worldwide for his research and writings on irrigation.
The home of the UC Davis Department of Land, Air and Water Resources, Veihmeyer Hall, is named in his honor.
Emeritus pomologist Arthur H.
Hendrickson joined the UC Berkeley faculty in 1913 as assistant in pomology, and in 1924 moved to UC's Agricultural Experiment Station SO he could conduct his research full100 time.
Together, he and longtime research associate Frank Veihmeyer practically invented many of the irrigation science terms defined in this article, words and understanding hydrology on the farm.
ideas that today are considered fundamental to UC Cooperative Extension
Irrigation trial with Morro Bay wastewater
 William E.
Wildman Roy L Branson John M.
Rible Wilfred E.
Cawelti
 T he coastal community of Morro Bay, like many other cities in California, is upgrading its sewage treatment plant.
As elsewhere, these plant improvements are financed to a large extent with federal and state funds, and a string is attached: Consideration must be given to possible reuse of the treated wastewater or effluent.
Morro Bay now disposes of its effluent into the ocean but has the possible alternative of beneficial reuse by piping it inland 1 to 5 miles for irrigation of field and forage crops, under conditions that meet Public Health Department regula-
 A close look at this alternative showed that the quality of the effluent, judged by guidelines used for regular irrigation waters, was satisfactory except for its sodium adsorption ratio , which indicates an irrigation water's sodium hazard.
Irrigating with a high SAR water can lead to accumulation of sodium in the soil, which, in turn, can drastically lower water intake rate.
According to water quality guidelines, this can be expected to occur if the SAR of an irrigation water is above 6.
The Morro Bay effluent SAR is 16.
It should be pointed out, however, that the guideline of 6 is based on experience with regular irrigation waters.
How well it applies to sewage effluents is not known, because researchers have had little experience in evaluating effluent effects on infiltration rate.
At Morro Bay's request, an irrigation trial was carried out in 1976 by Uni-
 versity of California Cooperative Extension to determine what effects the city's effluent would have on sodium accumulation and infiltration rate in two different soilsa fine sandy loam and a clay in the local farming area.
Treatments, replicated three times, included:  effluent,  effluent plus gypsum , and  city water, representing normal irrigation water, because it is from the same underground source as local farmers' well water.
Chemical composition of the two waters is shown in the table.
Measurements of infiltration rate and SAR were made periodically to assess the effects of the treatments.
All plots were prewetted with several inches of city water and planted to an oat-pasture grass mix in February 1976.
Differential treatments started early in March and continued for six months, ending in late September Once
 View of water percolation basins on Diablo clay soll.
Fiberglass septic tank in background served as storage tank for effluent water.
each week a volume of water equivalent to a 42/3-inch irrigation was applied to each plot.
After 5 feet of water had been applied, the application rate was doubled so that, by the end of the project, each plot had received a total of 17 feet of water.
Five sets of soil samples were collected: before treatment; after 70, 103, and 168 inches of water had been applied; and after termination of the treatments.
The SAR values for the 0to 3-inch depths are shown in figures 1 and 2.
Similar relationships were found at lower depths.
City water had a negligible effect on the SAR.
Effluent water raised SAR levels at both sites, but gypsum acted to lessen this effect.
Maximum SAR values of 4.5 to 5.5 were reached after less than
 Chemical Composition of Waters Used for Irrigation
 Item	City water	effluent
 Calcium	58	mg/l	62	mg/l
 Magnesium	96	mg/l	45	mg/l
 Sodium	77	mg/l	269	mg/l
 Potassium	15	mg/l	12	mg/
 Chloride	144	mg/l	321	mg/l
 Sulfate	55	mg/l	81	mg/l
 Bicarbonate	543	mg/1	505	mg/l
 Boron	0.1	ppm	0.6	ppm
 EC x 10	11	2.0
 Fig.
1.
Sodium adsorption ratio  values of saturation extracts of Salinas fine sandy loam to 3-inch depth) versus total depth of water applied.
Fig.
2.
SAR values of saturation extracts of Diablo clay  versus total depth of water applied.
half the total amount of effluent water had been added.
Further applications did not increase the SAR value.
Electrical conductivity of the saturation extract  for the surface foot of soil from effluent-treated plots did not rise above 1.9 mmhos at either site.
Infiltration tests were made at approximately three-week intervals throughout the six months of water application.
Initial rates were high for the Salinas fine sandy loam  and gradually declined to about 7 inches per hour after six months.
There was no significant difference in infiltration rates between city water and effluent water, with or without gypsum on the plots.
Initial rates were moderate for the Diablo clay , and actually increased during the experiment to around 4 inches per hour.
These high rates were attributed to the applied water being conducted downward through vertical cracks in the soil, which never closed up completely.
To compensate for this anomaly, duplicate 6-inch-diameter infiltrometer rings were driven into each plot.
Resulting in-ring infiltration rates were dependent on whether or not the rings intersected cracks.
Those that did gave rates of 1 to 3 inches per hour.
Those that did not gave rates as low as 0.01 inch per hour.
Again, there was no consistent difference between the city and effluent waters.
On the basis of information obtained in this trial, it may be concluded that use of this effluent water on these soil types would not be expected to result in excessive sodium accumulation and serious water penetration problems.
Even though amounts of water equivalent to at least four years of irrigation were applied, soil SAR values leveled off and remained below 6 in the effluent treatments.
At this level, no lowering of infiltration rates would be expected from continued use of effluent water, and none was found.
The trial results also indicate that guidelines used for evaluation of the sodium hazard of irrigation waters may need to be modified to make them applicable to sewage effluents.
Irrigating with wastewater in Sonoma County
 T reated wastewater has been used successfully to irrigate forage crops on 1,100 acres in Sonoma County during the past two years.
The city of Santa Rosa, with the help of federal and state funding, is delivering effluent to local farmers from a treatment plant with a dry-weather flow of approximately 5.5 million gallons per day.
The North Coast Regional Water Quality Control Board, which has jurisdiction over the area being served, has established discharge requirements governing the use of secondary-treated effluent for irrigation of forage crops.
One important problem is wastewater disposal during winter months, when farmers cannot use the water.
The Board also allows secondary-treated effluent from this plant to be discharged into Santa Rosa Creek during the winter months, as long as certain dilution factors are maintained.
Meanwhile, various cities and sanitation districts within Sonoma County are working on plans to irrigate an additional 4,000 acres with treated wastewater.
These agencies are considering crop irrigation with wastewater for a specific purpose to meet their discharge requirements with costs equal to or lower than other methods.
The following comments were made by Brandon J.
Riha, director of public works for Santa Rosa, in discussing plans for a large new regional treatment facility serving the cities of Santa Rosa, Sebastopol, Rohnert Park and Cotati:
 "The decision to go to land irriga-
 Estimated Profit or Loss Based on Operator Owning
 Crop	costs	value	Profit	Loss
 Barley	$162.58	$194.94	$32.36
 Wheat	166.42	205.10	38.68
 Calif.
Red	157.91	165.00	7.09
 Kanota	156.14	142.34	$13.80
 Forage mix	195.08	183.30	11.78
 Piper	211.24	207.45	3.79
 Trudan 6	207.51	211.50	3.99
 Corn	235.55	361.50	125.95
 Note: Rent or interest on land not included
 *Rental charge for pump.
motor.
electrical panel.
main line and laterals was $45.1 per acre.
Invoice price of the rental equipment was $66.36.
Using a 10year depreciation factor and interest charge at 10% on one-half of capital investment.
the cost per acre would be $19.13
 Silage crops at $3.75 per ton for harvest costs
 Fertilizer rate on all crops: Nitrogen 64 lb per acre: phosphorus 80 lb P 0 basis per acre.
Cultural costs Tractor  at $20 per hour: smaller tractor at $12 per hour
Chapter 14: Soil Compaction Impact on Corn Yield
 Soil compaction reduces soil drainage, aeration, yields, root growth, and the ability of plants to recover from disturbance, while simultaneously increasing surface runoff and soil erosion.
Compaction can be severe in wet, clay soil and it is increased by the use of heavy machinery during planting and harvesting, especially in wet soil conditions.
Generally, conventional-tillage  leads to the development of a plow layer or pan near the interface of soil and the bottom of the tillage implement.
This chapter discusses soil compaction and possible remediation strategies to reduce these risks.
Figure 14.1 Compaction created by a tandem disk.
Compaction is caused by a downward pressure that squeezes the soil and increases the soil bulk density.
Compacted zones can be located by scouting the field for reduced crop growth.
Compacted areas are typically associated with areas where tillage was conducted on wet soil and areas with extensive traffic.
Compaction problems can be diagnosed by:
 1.
Driving a metal stake into noncompacted and suspected compacted zones.
2.
Digging a trench across two corn rows in a suspected area or pushing a long screwdriver into soil in the suspected compacted area.
3.
Inspecting root growth  or assessing soil hardness by crushing soil aggregate.
4.
Determining the soil bulk density or penetrometer resistance.
Bulk density of soil is the dry weight of soil in a given volume of soil.
It is measured by using core method, and calculated by the weight of soil mass divided by the volume of the soil core.
Most rocks have a bulk density of > 2.65 g/cm, whereas productive soils have bulk densities between 1.2 and 1.3 g/cm.
3 Sandy soils have higher bulk densities than silt loam soils.
Bulk densities can be used to identify problem areas where root growth is restricted.
Tools needed to measure bulk density include a steel ring of known dimensions, a shovel, plastic bag, balance, microwave, and a knife.
The steps are:
 1.
Push the ring into the soil.
2.
Use the shovel to recover the ring.
3.
Cut the soil, outside of the ring, from the top and bottom.
4.
Place soil into a plastic bag.
5.
Dry using a microwave.
6.
Determine the volume of the ring, vol= r2h
 7.
Calculate the density, dry weight/volume of ring.
Additional details for determining the bulk density are available in Arshal et al..
Soil penetration resistance is the resistance that a root experiences as it tries to expand into a new soil zone.
Penetration resistance is measured with a penetrometer that is pushed into the soil.
Details for this method are provided by Duiker.
Root growth critical resistance values are dependent on plant species.
Duiker  suggested a compaction assessment can be determined by measuring resistance at a number of points across a field.
Duiker reports that if the resistance exceeds 300 PSI, root growth is severely slowed.
The results of these measurements are then compiled and interpreted.
Check Soil Moisture Prior to Field Operations
 Wet soils are more prone to compaction than dry soils.
To minimize compaction, it is recommended that the soil moisture content can be checked prior to field operations.
For medium-textured soils such as silt loams and silty, clay loams, soil from the top 6 inches should be placed between the forefinger and the thumb and squeezed.
If the ribbon breaks within several inches, the soil is most likely appropriate for additional work.
If the soil stretches out for 4 to 5 inches, it is most likely too wet.
Table 14.1 Bulk densities where root growth is restricted in sandy, silty, and clayey soils.
Soil type	Root growth restricted
 Figure 14.2 Measuring the bulk density  and soil resistance  in a field.
Table 14.2 Interpretation of penetrometer results.
This analysis is based on root growth being restricted with PSI values > 300.
% points with	Compaction rating
 values > 300 PSI
 < 30	little to none
 Only conduct tillage that is absolutely necessary.
Primary and secondary tillage  and cultivation break soil aggregates and speeds up the mineralization of soil organic matter.
Tillage problems can be minimized by:
 1.
Carefully balancing the need for timely planting and field operations.
2.
Using equipment that has an appropriate size and weight.
3.
Varying the tillage depth from year to year.
4.
Using tillage equipment that is well-maintained with sharp, soil-engaging leading edges.
5.
Delaying tillage until the soil has an appropriate moisture content.
Strip-tillage, no-tillage, and ridgetillage systems are techniques that can be used to reduce tillage and thus compaction.
Improve Soil Organic Matter
 Adding organic matter increases surface-soil friability, water infiltration, soil structure, and water-holding capacity, and reduces soil erosion.
Generally, tillage breaks the soil clods, which, in turn, accelerates soil organic matter oxidation.
Organic matter can be increased by adding manure, growing perennial crops, planting cover crops, reducing tillage, and not removing crop residues.
The impact of adding organic matter on compaction generally decreases with increasing depth.
Information on rotations and cover crops are available in Chapters 9 and 15.
Grain carts can increase soil compaction and reduce yields.
Grain carts can have axle loads that often exceed the axle load of a combine, large manure tank, or tractor.
To minimize the compaction risk from grain carts, load them in the road or headlands and don't drive across the field to catch the combine.
Table 14.3 Relationship between equipment and weight.
Combine with 250 bu grain	18
 Grain cart with 875 bu grain	23
 Large manure applicator	17
 175 hp 2-wheel-drive tractor	8
 Use of Deep Tillage
 If compaction is between 10 to 20 inches deep in the soil, consider subsoiling.
Subsoiling is a temporary solution and it should be combined with other techniques to minimize deep compaction.
Subsoilers can have: 1) parabolic shanks with or without wings, or 2) straight shanks with or without a coulter.
Subsoilers work by shattering the soil and they can leave the soil very rough.
Secondary tillage is often needed to prepare a seedbed.
Additional information on deep tillage is available in Thomason et al..
Check Air Pressure in Field Equipment
 Field equipment often has tire pressures that are higher than recommended.
Using the lowest recommended tire pressure widens the tire footprint and reduces the down pressure.
Tandem axles will have less surface compaction than single-axle equipment.
Staton  recommended:
 1.
Tires should be inflated to the lowest manufacturer-recommended tire pressure.
2.
Instructions from the manufacturer for your configuration  should be followed.
3.
Correctly ballasting the tractor and determining weight carried per tire.
4.
Tire pressure should be checked frequently with a high-quality gauge.
5.
All tires on the same axle should be set to the same pressure.
6.
That if the tires contain fluid ballast the pressure should be checked with the stems in the same location.
EMERGING TECHNOLOGIES FOR SUSTAINABLE IRRIGATION: SELECTED PAPERS FROM THE 2015 ASABE AND IA IRRIGATION SYMPOSIUM
 A Tribute to the Career of Terry Howell, Sr.
ABSTRACT.
This article is an introduction to the "Emerging Technologies in Sustainable Irrigation: A Tribute to the Career of Terry Howell, Sr.
Special Collection in this issue of Transactions of the ASABE and the next issue of Applied Engineering in Agriculture, consisting of 16 articles selected from 62 papers and presentations at the joint irrigation symposium of ASABE and the Irrigation Association , which was held in November 2015 in Long Beach, California.
The joint cooperation on irrigation symposia between ASABE and IA can be traced back to 1970, and this time period roughly coincides with the career of Dr.
Howell.
The cooperative symposia have offered an important venue for discussion of emerging technologies that can lead to sustainable irrigation.
This most recent symposium is another point on the continuum.
The articles in this Special Collection address three major topic areas: evapotranspiration measurement and determination, irrigation systems and their associated technologies, and irrigation scheduling and water management.
While these 16 articles are not inclusive of all the important advances in irrigation since 1970, they illustrate that continued progress occurs by combining a recognition of the current status with the postulation of new ideas to advance our understanding of irrigation engineering and science.
The global food and water challenges will require continued progress from our portion of the scientific community.
This article serves to introduce and provide a brief summary of the Special Collection.
Keywords.
Center-pivot sprinkler irrigation, Deficit irrigation, Evapotranspiration, Irrigation management, Irrigation scheduling, Microirrigation, Sensors, Sustainability, Turf and landscape irrigation, Variable rate irrigation.
O n November 9 through 11, 2015, in Long Beach, California, ASABE and the Irrigation Association  jointly convened a symposium entitled "Emerging Technologies for Sustainable Irrigation: A Tribute to the Career of Terry Howell, Sr." This
 symposium had some similarities to other joint conferences held by ASABE and IA, such as the decennial national irrigation symposia held in 1990, 2000, and 2010 that were discussed by Dukes et al.
, the 1995 Fifth Microirrigation Congress, and the 1996 Evapotranspiration and Irrigation Scheduling International Conference.
The conference title seemed fitting, as all along the career of Dr.
Howell, which spanned six decades, reliable and robust irrigation technologies  were emerging and helping irrigation, an alteration of the rural and urban environment, to become more sustainable.
The authors believe that these aspects  continue and will need to continue as we strive to provide the global community with food, fiber, greenspace, and forestry products, while providing stewardship of the earth's natural resources.
The irrigated land area has continued to increase slightly in the U.S., but with a migrating geographic location.
While irrigation remains most heavily concentrated in the semi-arid and arid western U.S., Arkansas and Mississippi now have the third and ninth largest irrigated land areas, respectively.
Irrigated land area in the period 1998 through 2012 increased by only 6.4% in the top ten irrigated states while experiencing a
 Figure 1.
Irrigated land area in the U.S., the top ten irrigated states and the remaining 40 states during the period 1998 to 2012.
Data from USDA-ARS Farm and Ranch Irrigation Surveys.
22.0% increase in the remaining 40 states.
From 2008 to 2012, irrigated land area actually decreased by 1.3% in the top ten irrigated states and increased by 5.8% in the remaining states.
These geographic shifts may be occurring for several reasons, such as increasing competition for water resources in the western U.S.
and the increasing desire in the eastern semi-humid and humid regions to mitigate crop production risks due to drought or poor soil water-holding capacities.
As crop yields rise due to increasing use of appropriate crop genetics and cultural technologies, it is only logical that irrigation will be desirable to mitigate crop water constraints.
Additionally, increases in commodity crop prices periodically spur further irrigation development and technology improvements.
These changes in U.S.
irrigation emphasize that emerging technologies will continue to be needed in the waterstressed western areas to optimize water productivity , but also in the areas where irrigation is increasing, and may require further adaptation or even newer approaches to irrigation management.
Sustainability of irrigation will continue to be important, and its necessity will only grow as we address a growing world population and impending climate change.
Dr.
Howell's research career focused on evapotranspiration  determination and measurement to improve water productivity, irrigation systems and their associated technologies, and irrigation scheduling and water management.
As these are core topics for irrigation engineers and scientists, it should not be surprising that nearly all of the 62 papers presented at the 2015 ASABE and IA symposium dealt with these issues.
For the first time within ASABE, the authors of these papers had the option of seeking simultaneous dual publication in the symposium proceedings and through the journal peer-review process.
A total of 16 papers were published in both media, and those selected works are summarized in the following sections along with related key highlights from the career of Dr.
Howell.
EVAPOTRANSPIRATION MEASUREMENT AND DETERMINATION
 Although Dr.
Howell's whole career is closely associated with evapotranspiration  measurement and determination, some of his earlier efforts were natural progressions of his early 1980s exposure to the emerging California Irrigation Management Information System  and to his excitement in waking up each morning to alarm clock radio reports of calculated potential ET.
A desire for better ET measurements for the San Joaquin Valley led to the construction and installation of two large weighing lysimeters in California , which set the path for future development of the extensive lysimeter facilities at the USDA-ARS Conservation and Production Research Laboratory at Bushland, Texas.
The lysimeter facilities at Bushland and the associated research efforts are summarized by Evett et al..
Those research accomplishments include development of crop coefficients for the major crops of the Southern High Plain, improvements in determination of reference ET and associated algorithms; field-scale crop simulation modeling; development, testing, and improvement of both ground-based and remote sensing equipment; and methodologies associated with ET determination.
Accurate partitioning of ET into its two components, evaporation  and transpiration , is important when comparing the effectiveness of different types of irrigation systems and in evaluating strategies aimed at increasing water use efficiency  or crop water productivity.
A two-source energy balance  model, initially developed by Norman et al.
and Kustas and Norman , can be used for direct calculations of E and T, which cannot be done with single-source ET models.
Recent physically based advances of the TSEB model were tested in field studies on cotton and are reviewed by Colaizzi et al..
The advances were tested using independent measurements of E, T, and ET from microlysimeters, sap-flow gauges, and weighing lysimeters, respectively, at Bushland, Texas.
Calculation errors of E and T using the new approach were greatly reduced  compared to previous TSEB model versions.
Rice is a major U.S.
crop, but it currently uses great amounts of freshwater and is considered one of the major crop contributors to greenhouse gas production.
Eddy covariance techniques were used by Reba and Counce  to quantify H2O and CO2 fluxes for rice at the field scale in the largest rice-growing region in the U.S., the lower Mississippi River basin.
The researchers found that the maximum rice crop ET was approximately 6.1 mm d-1 occurring during the later vegetative stages, and that there was a net CO2 influx to the rice plants during the production season.
These findings show that both plant growth stage and management impacted measured H2O and CO2 fluxes.
Turfgrasses are an integral part of landscape ecological systems worldwide, and the U.S.
land area in turfgrasses, estimated to be approximately 16.4 million ha , uses a considerable amount of water resources.
A review of turfgrass evapotranspiration  and crop coef-
 ficients  for both warm-season and cool-season grasses is provided by Romero and Dukes  for different locations across the U.S., as well as a discussion of the methods used to determine or estimate these values.
A great amount of variability in both ET and K between and within turfgrass species was reported, as was substantial changes in both that occur during the growing season.
The authors conclude that although published ETc and Kc values may be helpful in irrigation scheduling of turfgrasses, they should be used with caution and with an understanding of the local conditions under which they were developed.
IRRIGATION SYSTEMS AND ASSOCIATED TECHNOLOGIES
 Although a change in irrigation systems or associated technologies does not automatically result in improvements in water use and sustainability, improved management capabilities inherent in the technology are often associated with such improvements when coupled with greater human engagement and decision making.
In an oral presentation in 2002, Dr.
Howell posited that one of the principal reasons that pressurized irrigation systems, such as center-pivot  systems and subsurface drip irrigation , are considered easier to manage than surface irrigation is because they remove the relatively complex surface water transport phenomena from management considerations.
In the U.S., the majority of irrigated cropland uses CP sprinkler irrigation.
The amount of land irrigated using CP systems has increased by 0.91 million ha while the number of farms using CP systems has increased by 7.5% during the period 2008 through 2012.
Much of this increase has resulted from converting surface and other types of sprinkler systems to mediumand lowpressure CP systems, which can have greater uniformity and application efficiency and thereby increase WUE.
Improved designs and management of these CP systems reduces the potential for water losses and other off-target applications that would negatively affect WUE, runoff, and soil erosion.
The effectiveness of sprinkler irrigation in minimizing water losses requires both selection of appropriate sprinkler hardware and implementation of appropriate management for the crop, soil, landscape, and weather conditions.
Many types of sprinkler nozzles can be selected for CP and lateral-move sprinkler irrigation systems, and their advantages and disadvantages with regard to water losses were discussed by Howell.
Although there is growing interest in lower-pressure sprinkler systems with applications within or near the crop canopy to potentially save energy and reduce evaporative losses, their effectiveness can be greatly affected by their increased runoff potential.
A soil-independent, quantitative runoff-potential index has been developed by King  to facilitate selection of moving spray-plate sprinklers for CP and lateral-move sprinkler irrigation systems.
The methodology was evaluated for a number of commer-
 cially available sprinkler packages.
The results indicated that substantial differences exist, and several packages can have similar runoff potential.
The runoff index provides an effective means for comparing sprinkler choices by identifying sprinklers with large droplets and relatively small wetted diameters.
Management of CP systems through site-specific variable-rate irrigation  offers potential to further improve and refine WUE within a crop field by more closely managing crop evapotranspiration, which can be affected by numerous factors, including crop type, irrigation method, weather, crop condition, cultural practices, and soil properties.
A discussion of recent advances in site-specific VRI platforms for CP and a description of a conceptual framework for such systems is provided by 'Shaughnessy et al..
In this supervisory control and data acquisition  framework, integrated soil and plant sensors within a wireless communication system provide inputs for algorithms to control and manage the VRI system and to improve the spatial WUE.
The authors further discuss three topic areas or applications of site-specific VRI that have already successfully improved spatial WUE: optimizing irrigation application depth within the field, managing crop water stress under deficit irrigation, and adjusting irrigation management spatially in relation to the presence of crop disease and its severity.
Although the use of site-specific VRI systems is growing, there is less understanding of how management of these systems should be optimized for wise use of natural resources and increased farm profitability.
A traditional statistical analysis using analysis of variance was compared to a Bayesian semiparametric model for assessing the spatial variation in corn yields as affected by site-specific VRI.
Although both statistical methods resulted in similar analysis conclusions, the researchers indicated that the Bayesian model, which was more spatially explicit, preserved more accuracy in the estimations of actual recorded yields and should be considered more robust and scientifically acceptable.
Stone and Sadler  conclude that this technique could provide additional insights into the spatial responses of crops to spatially variable irrigation, thus providing irrigation system managers and designers with improved tools for site-specific VRI management.
Dr.
Howell's involvement with microirrigation can be traced back to his graduate school days, with his research using mist irrigation for crop production  and his senior authorship of the microirrigation chapter for ASAE Monograph No.
3.
Although the U.S.
land area in microirrigation is only about 14% of the amount of sprinkler-irrigated land , it continues to grow, and microirrigation still constitutes an emerging technology in some regions.
From 2008 to 2012, drip irrigation increased by nearly 0.46 million ha in the U.S..
Surface drip irrigation  comprises the overwhelming
 microirrigation land area, but subsurface drip irrigation  has increased substantially in the past ten years.
Over 93% of the SDI land area is concentrated in ten states.
In some of these states, SDI is the primary microirrigation method, rather than DI.
This is attributed to those states' greater production of lesser-value commodity crops, for which a deeper, multiple-year SDI system, which can be amortized over several years, is often the only economical microirrigation option for a producer.
Although SDI has been considered the most appropriate microirrigation system for row-crop applications since the 1970s , limitations in SDI materials and in knowledge of SDI initially made any large-scale advances difficult.
In a review of SDI production of four crops , Lamm  reports moderate or larger yield increases over alternative irrigation systems for cotton, processing tomato, and onion, with the latter two crops obtaining differences particularly in marketable yield and quality.
This was not the case for field corn, for which a review of 12 studies averaged little or no differences between SDI and alternative systems.
Design parameters such as dripline spacing and installation depth are also discussed for the four crops, along with combined irrigation and nutrient management.
Microirrigation systems can be used with lower-quality water that may contain biological contaminants.
Shock et al.
evaluated the potential of using water containing moderate levels of E.
coli for both subsurface drip-irrigated and furrow-irrigated onion for fresh market consumption.
They found that the silt loam soil retained most of the E.
coli close to the water entry point into the soil for both irrigation systems.
However, a small fraction of the E.
coli was found in the soil immediately adjacent to the onion bulbs, although no E.
coli uptake was detected within the bulbs.
Although more research may be needed, it may be safe and practical to use the soil as a filter for E.
coli for onion production when using furrow and subsurface drip irrigation.
Traditionally, nutrient fertilization through microirrigation systems is only recommended for systems with a design emission uniformity of 70% or greater, depending on system characteristics.
However, spatial variability in the soil can greatly affect the ultimate nutrient distribution in the soil.
Using simulation, the researchers found that spatial variabilities in saturated hydraulic conductivity, saturated water content, and the initial soil water and soil nitrate contents all resulted in significant differences in nitrate leaching.
Wang et al.
conclude that microirrigation system uniformities as low as 60%, although lower than the current standards, may be acceptable in terms of nitrate leaching, as the soil spatial variability may dampen the uniformity effects of the microirrigation system.
SMART CONTROLLERS FOR LANDSCAPE IRRIGATION
 Although Dr.
Howell's career focused on irrigation of agricultural crops, much of his work with establishment of
 micrometeorological weather stations , evapotranspiration measurement , remote sensing , and irrigation management  is closely related regardless of the type of plant.
Irrigation of home lawns and landscapes can greatly impact municipal potable water supplies.
In most municipalities, it is difficult to separate indoor and outdoor water use.
To get a more accurate estimation of outdoor water use, Romero and Dukes  tested methods for separating indoor and outdoor water use using municipal potable meter data for single-family homes in Florida.
Two methodologies were compared for estimating indoor water use: a method in which the minimum monthly use  was assumed to represent indoor use, and a second method based on a per-capita use of 250 d-Superscript.
While indoor use was overestimated by 140% and underestimated by 34% by the minimum month and per-capita methods, respectively, the corresponding outdoor use  calculated by the per-capita method was underestimated by 5% to 19% for an additional 5% and 15% assumed impervious area, respectively.
The authors conclude that the per-capita method will result in the most reliable estimates of indoor and outdoor water use for central Florida conditions.
Davis and Dukes  evaluated how end-user programming in a particular brand of ET controller might affect residual landscape irrigation amounts and performance.
The controllers they evaluated  did not fully account for rainfall and consequently consistently over-irrigated the landscapes, although there were substantial reductions in over-irrigation with customized programming.
The inaccuracy in rainfall accounting might result in over-irrigation of 50% to 100% greater than the gross irrigation requirement in that region of Florida, SO the authors conclude that better rainfall accounting would be extremely beneficial to overall water conservation and water use efficiency.
With the increasing demands on freshwater resources, the use of reclaimed water for landscape irrigation has gained considerable interest in many parts of the U.S.
Landscape irrigation controllers that incorporate soil moisture sensors  for feedback control can have improved performance, but there has been concern about using SMS with reclaimed water, which can affect the soil dielectric permittivity and thus affect the SMS values.
In a controlled field-plot study, Cardenas and Dukes  compared time-based irrigation control to control incorporating one of four different SMS as affected by both potable and reclaimed water.
Water savings using SMS controllers averaged 63% and 59% for the potable and reclaimed water sources, respectively, compared to irrigation control without SMS.
The authors conclude that the small accuracy reduction in SMS when using reclaimed water would be acceptable.
This study led them to a second study that implemented one of the SMS controllers in residential landscape settings  that used reclaimed water.
In a study involving 64 homes in Palm Harbor, Florida, that was conducted for a 32-month observa-
 tion period, the homes that used SMS-based control had statistically significant water savings, averaging 44%, as compared to the homes that were monitored only for water use.
IRRIGATION SCHEDULING AND WATER MANAGEMENT
 Dr.
Howell is a recognized expert in irrigation scheduling, having written two book chapters on the topic , and he was asked to give a keynote presentation on the topic at the 1996 ASAE and IA joint conference on evapotranspiration and irrigation scheduling.
Although modern sciencebased irrigation scheduling has existed for approximately 60 years, with one of the first reports by Van Bavel , the long-term and consistent adoption of appropriate irrigation scheduling has been dismal.
To facilitate better adoption rates and improved irrigation scheduling, Migliaccio et al.
developed a software application  to provide real-time irrigation schedules for various crops  in the southeastern U.S.
The application can use real-time weather data from both the Florida Automated Weather Network and the Georgia Environmental Monitoring Network to calculate crop ET using a water balance method for scheduling irrigation.
The software inputs vary by crop, but nearly all scenarios require root depth, irrigation rate, and soil type.
Similarly, a variety of output information is available to better serve the needs of irrigators.
Many areas of the U.S.
are experiencing water shortages, and irrigators often cannot meet the full crop water needs using their current irrigation and cropping system scenarios.
As a result, many producers are implementing strategies such as deficit irrigation to address water shortages.
The CERES-Maize crop model was used by Kisekka et al.
to examine several deficit-irrigation strategies for corn production in southwest Kansas.
Their modeling combined experimental results from field studies and longterm weather data to evaluate management-allowable depletion  for corn, the optimum level of plantavailable soil water at planting, and the irrigation season termination criteria.
They found that irrigation scheduling based on a 50% plant-available soil water threshold  maximized net returns compared to initiating irrigation at a greater soil water content, that it was important to have adequate soil water reserves at planting , and that terminating irrigation at 90 to 95 days after planting maximized net economic returns.
Although the simulation results were specific to the region, the authors suggest that the simulation techniques can be applied in other areas with constrained water supplies for irrigation.
Dr.
Howell's contributions to irrigation engineering and
 science encompass three major topic areas: evapotranspiration measurement and determination, irrigation systems and their associated technologies, and irrigation scheduling and water management.
Some of the articles in this Special Collection present a review of past efforts and the current status in these topic areas, while other articles discuss promising opportunities to advance our knowledge in these topic areas.
This scope emphasizes that the status of irrigation engineering and science should be considered a continuum, with emerging technologies building on earlier knowledge and progress, and hopefully leading toward sustainable irrigation that will be necessary to provide food, fiber, greenspace, and forestry products for an increasing world population.
This article introduces the 16 articles in the "Emerging Technologies in Sustainable Irrigation: A Tribute to the Career of Terry Howell, Sr." Special Collection in this issue of Transactions of the ASABE and the next issue of Applied Engineering in Agriculture.
The authors wish to thank the ASABE publications staff, associate editors, and reviewers for their contributions to and timely management of the review process, and the authors and co-authors of the articles in this collection for their contributions to the research literature represented by this collection.
In particular, the authors would like to thank Natural Resources and Environmental Systems  Editor Kyle DouglasMankin for his invaluable assistance in encouraging and shepherding this collection through the submission and review process.
What Is Water Quality?
Mike Daniels Professor Water Quality and Nutrient Management
 Thad Scott Assistant Professor Crop, Soil and Environmental Sciences
 Brian Haggard Director Arkansas Water Resources Center
 Andrew Sharpley Professor Crop, Soil and Environmental Sciences
 Tommy Daniel Professor Crop, Soil and Environmental Sciences
 ARKANSAS WATER RESOURCES CENTER
 Arkansas Is Our Campus
 The term water quality describes a broad spectrum of items related to how we identify water concerns and how we collectively address them.
Thus, the term water quality can be confusing and mean different things to different people.
The most widely used definition of water quality is "the chemical, physical and biological characteristics of water, usually in respect to its suitability for a designated use." As we all know, water has many uses, such as for recreation, drinking, fisheries, agriculture and industry.
Each of these designated uses has different defined chemical, physical and biological standards necessary to support that use.
For example, we expect higher standards for water we drink and swim in compared to that used in agriculture and industry.
Figure 1.
As the area of a watershed in forest increases relative to agricultural and urban land uses, the concentration of nutrients in streams at base flow tends to decrease.
Water quality standards are put in place to protect the various designated uses of a waterbody.
Waterbodies are then monitored by states to ensure that these standards are being met and that a waterbody supports its designated uses.
When water quality assessment reveals that a waterbody does not support its designated uses, then it is considered impaired by the United States Environmental Protection Agency.
Impairments result from two major categories of water pollution: point source or nonpoint source pollution.
Point source pollution originates in effluent that is discharged regularly  from industrial and municipal wastewater treatment plants through permanent conduits such as pipes or ditches.
Nonpoint source pollution originates from diffuse sources scattered across the landscape and is delivered to waterbodies during runoffproducing precipitation events.
It may include pollutants derived from residential, agricultural, forested and urban areas.
Common nonpoint source pollutants include sediment, plant nutrients, pesticides and organic compounds.
Rainfall runoff events transport materials into waters High even in undisturbed natural sites.
Figure 2.
Effect of land use on accelerated eutrophication.
Figure 3.
An example of the variability of nonpoint source pollution.
Areas in red near the stream channel have a greater potential to contribute phosphorus to the stream channel  than fields further from the stream.
Most of the landscape or watershed is at risk for nitrogen loss in leaching to groundwater.
Human activities however, can increase the amount of sediment and nutrients entering waterways and introduce new contaminants such as pesticides.
Nonpoint source pollution is harder to identify than point source pollution because of its diffuse nature.
The amount of runoff volumes as well as physical, chemical and biological constituents in runoff can vary greatly among storm events and specific watershed characteristics.
This makes it harder to determine the impact of nonpoint sources on water quality and thus harder to control.
With the enabling of the Clean Water Act in 1972, EPA began to control point source pollution by
 After 15 years of administering the NPDES program, nationwide water quality monitoring revealed that many waterbodies were still not meeting their water quality standards for a given designated use.
In 1987, Congress reauthorized the Clean Water Act to place increased emphasis on nonpoint source pollution, which focused much more on nonpoint sources including agriculture.
Due to its diffuse nature and delivery during episodic rainfall events, progress towards reducing nonpoint source pollution has been slower in nature than for point sources.
How Are Water Quality Concerns Determined?
In some cases, water quality concerns can arise quickly from public complaints about odor or taste, outbreak of water-borne illnesses or widespread death of aquatic species such as fish kills.
Because many water quality concerns do not have such obvious or dramatic consequences, it may not be readily apparent that there is a problem.
Instead, many important water quality parameters are routinely monitored and compared with water quality standards adopted for these parameters.
Water quality standards are adopted by states to protect various designated uses and are often specific to ecoregions within the state.
Ecoregions are simply areas of the state with topographic and geologic similarities.
Routine monitoring allows states to assess whether or not water quality standards, and ultimately designated uses, are being met for a particular waterbody.
Figure 4.
Examples of water quality monitoring.
The Arkansas Department of Environmental Quality  and the United States Geological Survey  conduct extensive monitoring in Arkansas.
The University of Arkansas Water Resources Center also monitors water quality through the nonpoint source pollution program administered through the Arkansas Natural Resources Commission.
Water samples are often analyzed for constituents such as dissolved oxygen, pH, ion composition, suspended solids, nutrients, pathogens, metals, oils and pesticides.
Additionally, sediment and fish tissue are often collected and analyzed for metals and some organic
 Figure 5.
Location of Ambient Water Quality Monitoring Stations in Arkansas.
pollutants.
Physical measurements of general conditions such as temperature, flow, color, turbidity  and the condition of stream banks and lake shores are also collected.
Biological monitoring is conducted to determine health of aquatic systems.
Biological assessments often include the abundance and diversity of aquatic plant and animal life as well the ability of test organisms to survive in sample water.
Monitoring can be conducted at regular sites on a continuous basis ; at selected sites on an "as needed" basis or to answer specific questions ; on a temporary or seasonal basis ; or on an emergency basis.
Monitoring can be conducted for many purposes, such as:
 1.
Characterize waters and identify changes or trends in water quality over time.
2.
Identify specific existing or emerging water quality problems.
3.
Assess the usefulness or attainability of water quality standards.
4.
Gather information to design specific pollution prevention or remediation programs.
5.
Determine whether program goals, such as compliance with pollution regulations or implementation of effective pollution control actions, are being met.
6.
Response to emergencies, such as spills and floods.
Table 1.
Water quality parameters routinely measured in Arkansas' ambient water monitoring program.
Air Temperature	Water Temperature	Turbidity	Filterable Residue
 Nonfilterable	Dissolved Oxygen	5-Day Biochemical
 Beryllium	Cobalt	Barium	Vanadium
 Nickel	Copper	Lead	Iron
 pH	Total Hardness	Chlorides	Sulfates
 Sodium	Calcium	Magnesium	Manganese
 Ammonia Nitrogen	Total Phosphorus	Potassium
 What Is the "Designated Use" Approach?
Where Can I Find Water Quality Standards in Arkansas?
Water quality standards in Arkansas that are assigned to protect the designated uses of waterbodies are also specified in State Regulation 2.
Standards in Arkansas are dependent on three
 items: 1) water quality criteria as set forth in Section 304 of the Clean Water Act, 2) the designated uses and 3) the ecoregion where the stream or waterbody is located.
The ecoregion concept is important for establishing water quality criteria because aquatic life supported by streams, lakes and
 Figure 6.
The designated stream ecoregions in Arkansas for distinguishing water quality standards.
Table 2.
Designated uses of waterbodies in Arkansas as set forth in State Regulation 2.
Extraordinary Resource Waters	This beneficial use is a combination of the chemical, physical and biological
 characteristics of a waterbody and its watershed which is characterized by scenic
 beauty, aesthetics, scientific values, broad scope recreation potential and intan-
 Ecologically Sensitive Waterbody	This beneficial use identifies segments known to provide habitat within the existing
 range of threatened, endangered or endemic species of aquatic or semi-aquatic
 Natural and Scenic Waterways	This beneficial use identifies segments which have been legislatively adopted into a
 state or federal system.
Primary Contact Recreation	This beneficial use designates waters where full body contact is involved.
Any
 	streams with watersheds of greater than 10 square miles are designated for full
 body contact.
All streams with watersheds less than 10 square miles may be
 designated for primary contact recreation after site verification.
Secondary Contact Recreation	This beneficial use designates waters where secondary activities like boating,
 	fishing or wading are involved.
Fisheries 	This beneficial use provides for the protection and propagation of fish, shellfish and
 other forms of aquatic life.
Domestic Water Supply	This beneficial use designates water which will be protected for use in public and
 private water supplies.
Conditioning or treatment may be necessary prior to use.
Industrial Water Supply	This beneficial use designates water which will be protected for use as process or
 cooling water.
Quality criteria may vary with the specific type of process involved
 and the water supply may require prior treatment or conditioning.
Agricultural Water Supply	This beneficial use designates waters which will be protected for irrigation of crops
 and/or consumption by livestock.
Figure 7.
The Environmental Protection Agency's  ecoregions.
Arkansas' ecoregions are based on this national designation.
Draft Aggregations of Level III Ecoregions for the National Nutrient Strategy
 wetlands can vary greatly depending on climate, topography, hydrology, geology and many other factors.
The ecoregion approach allows standards to reflect natural differences that exist in these parameters throughout our state.
Standards may be reflected as: 1) numerical values, 2) narrative limitations or 3) prohibitions on physical alterations of certain waters.
In Arkansas, most standards are numerical.
However, standards for nitrogen and phosphorus are narrative in nature because nutrient concentrations in streams do not always correlate directly with stream impairments.
Impairment of a waterbody from excess nutrients is dependent on characteristics unique to each natural waterbody such as stream flow, residence
 time, stream gradient, substrate type, canopy, riparian vegetation and season of the year.
How Are Impairments Determined and Reported?
Section 305 of the Clean Water Act requires the states to perform a comprehensive water quality assessment and submit an assessment report to Congress every two years.
Arkansas relies on its water quality monitoring data to compile its assessment report.
In its latest report from 2004
 Table 3.
Selected water quality standards by stream ecoregion in Arkansas for watershed contributing areas of less than 10 square miles.
Ozark	Boston	River	Ouachita	Typical	Altered	Altered
 Water Quality Parameter	Highlands	Mountains	Valley	Mountains	Gulf Coast	Delta	Delta
 Maximum Allowable	84.2	87.8	87.8	86	89.6	86	89.6
 Turbidity 1 Base	10 / 17	10 / 19	21 / 40	10 / 18	21 / 32	45 / 84	75 / 250
 Flow / All Flow2
 Dissolved Oxygen: 	6/2	6/2	5/2	6/2	5/2	5/2	5/2
 Primary Season / Critical
 Total Dissolved Solids	250	95.3	112.3	142	138	411.3	411.3
 1 NTU Nephelometric Turbidity Unit Based on comparison of the intensity of light scattered by a sample of water with the intensity of light scattered by a standard reference suspension.
Turbidity when the stream sample is taken at base flow and when a sample is averaged across all flows including samples 2 taken at storm flows.
3 Primary season refers to the period of year when water temperatures are 71.6F or below.
In Arkansas, this generally ranges from mid-September to mid-May.
Critical season refers to the period of year when water temperatures are 71.6F or above.
In Arkansas, this generally ranges from mid-May to mid-September.
Pressure differences along the system can be attributed to elevation change and pipeline friction losses.
When the sprinkler design flow rate varies by at least 10% for more than 15% of the system due to pressure differences, the use of pressure regulators is encouraged.
How does CornSoyWater work in the background?
CornSoyWater uses crop simulation models  to predict crop growth, development, crop water use, and soil water balance.
Based on the location of the field, the program automatically determines the weather station that is closest to the field in the weather station network, and the soil texture for the field.
In its seventh year, the Testing Ag Performance Solutions  program will make some modifications and see more growth in a number of competitions and locations in 2023.
Carmen T.
Agouridis and Evan T.
Wesley, Biosystems and Agricultural Engineering
 What Do Streams Do?
Streams are all around us.
Most of us drive by or over streams every day.
Some streams are big-such as rivers-and some are small rivulets; some flow year-round while others flow only a few months of the year or only when it rains.
Regardless of their size and flow duration, streams serve a number of important purposes.
The water supply for many people, from cities to small towns, is rivers and streams.
Streams help transport or move the water, sediment, and nutrients generated in our watersheds to downstream reaches.
Streams provide habitat for aquatic organisms such as macroinvertebrates and fish as well as terrestrial ones such as birds, deer, fox, raccoons, and other mammals.
Larger streams and rivers serve as transportation routes helping us move crops, manufactured goods, and natural resources to domestic and international markets.
Streams also provide us with recreational opportunities such as swimming, fishing, and boating.
Perennial, Intermittent and Ephemeral Streams
 One way to classify streams is by the amount of time that flow is present in a stream.
Perennial streams  are those with flow in at least part of the streambed year-round.
Intermittent streams  are seasonal streams that hold water during the wetter parts of the year but cease to flow during drier periods.
Ephemeral streams  flow only in response to precipitation events such as rainfall and snowmelts.
The health of our waters is the principal measure of how we live on the land.
-Luna Leopold
 Aquatic macroinvertebrates are organisms without an internal skeleton; they are visible with the naked eye.
Insects, worms, and mollusks all are examples of aquatic macroinvertebrates that live in streams.
You can typically find these organisms living under rocks and logs or in leaf packs.
Aquatic macroinvertebrates are a vital part of the food web.
They are a food source for higher-order organisms such as birds, fish, and larger insects.
Aquatic macroinvertebrates are also indicators of water quality.
Because aquatic macroinvertebrates live in streams, cannot relocate very quickly, and have different sensitivities to changes in water quality, sampling the number and types of aquatic macroinvertebrates can provide us with insights into the health of a stream.
Mayflies , for example, are sensitive to pollution but pouch snails  are not.
Figure 1.
Healthy streams are physically stable and have good water quality and habitat features.
water temperature increases, dissolved oxygen levels in the water decrease, thus negatively affecting aquatic life.
If the water quality is poor, the types and numbers of fish and macroinvertebrates that can live in the stream will be limited.
What Are the Traits of a Healthy Stream?
Healthy streams have three main components: physical stability, good water quality, and good habitat.
Physical stability does not mean streams are rigid and unmoving.
Streams, by their nature, are dynamic systems.
Their locations and shapes are expected to change over time.
Physical stability means that as streams move, they do SO in a way that allows them to maintain their dimensions  without filling up with sediment  or down-cutting.
Good stream habitat encompasses more than water quality.
Good stream habitat refers to both the quality and quantity of instream and riparian  spaces that are inhabitable by aquatic life.
Aquatic organisms are influenced by a number of habitat features, such as the type of substrate  present, the depth and velocity of flow, the depth and frequency of pools and riffles, and the amount and types of riparian vegetation present.
These features influence factors such as feeding, reproduction, and refuge.
The physical and chemical components of the water in a stream, such as dissolved oxygen, temperature, suspended sediments, and nutrients and metals, reflect its water quality.
In turn, a stream's water quality strongly influences habitat.
For example, as
 Photos: Blake Newton, Entomology,  and Evan Wesley 
 Graphic: Corey Wilson, Landscape Architecture
 Stable and Unstable Streams
 Stable streams are those that maintain their dimension , pattern and profile over time.
Stable streams have good connections to their floodplains SO that flows can frequently overflow the streambanks and spread out onto the floodplain.
Stable streams also have thick, deep rooted riparian vegetation which holds streambank soils tightly in place.
And since streams act as drains, the elevation of the stream bed in perennial streams will largely control the depth of the water table.
Unstable streams are those that show signs of degradation, such as eroded stream beds and banks, or aggradation, such as pools filled in with sediment.
Unstable streams are often incised, meaning flows do not reach the floodplain except for during rare, large storm events.
And because of the incision, the water table is lower.
In addition, riparian vegetation is often lacking or has shallow roots, such as with mown grass.
What Impacts the Health of a Stream?
Streams are ultimately influenced by the land through which they flow.
What occurs in a stream's watershed affects its shape, the water quality, and what lives in it.
When land use changes OCcur, streams are inevitably impacted.
Without proper land management, changes such as urbanization and development, agriculture, mining, and silviculture can negatively impact streams.
With urbanization, for example, development increases the amount of impervious area leading to increased amounts of runoff.
Impervious surfaces such as roads, buildings, and parking lots prevent stormwater from naturally soaking into the ground.
Instead, stormwater travels as runoff across impervious surfaces, where it picks up pollutants before entering the storm sewer system, where it is then quickly routed to streams through stormwater pipes.
Unlike the sanitary sewer system, water in the storm sewer system is not treated.
Streams receive this larger amount of runoff, often of poor quality, quickly.
This rapid influx of stormwater and pollutants into streams often results in eroded streambanks and beds, degraded water quality, and poor quality habitat.
Riparian buffers are areas characterized by high levels of interaction between water, soil, and vegetation.
These vegetation zones link aquatic environments such as streams to terrestrial ones such as upland pastures.
Riparian buffers typically consist of three zones.
Zone 1 is adjacent to the water.
This zone consists of water tolerant trees.
Zone 2 consists of shrubs located next to the trees in Zone 1.
Zone 3 is a zone of grasses and forbs next to the shrubs.
At a minimum, riparian buffers should be 25 feet wide.
Graphic: Corey Wilson, Landscape Architecture
 Figure 2.
Urbanization can cause streams to widen and deepen.
Each stream restoration project has its own unique characteristics, but most share the same main components:
 Reconstruction of the stream's dimension , pattern , and profile 
 Reconnection of the stream to its floodplain
 Stabilization of streambanks using riparian vegetation or other erosion control measures
 Use of instream structures for gradecontrol, streambank protection, habitat creation, and/or water quality improvement
 Establishment of a riparian zone, preferably greater than 25 feet on each side of the stream, using native vegetation
 Establishment of habitat enhancement features, such as vernal pools and wetlands, in the riparian zone
 What is Stream Restoration?
Stream restoration is the re-establishment of the structure  and function  of a degraded stream as closely as possible to pre-disturbance conditions.
Stream restoration projects are often performed to reduce and/or prevent streambank erosion, restore or maintain water quality, restore or maintain aquatic habitat, protect infrastructure  and land, enhance recreational opportunities, and improve aesthetics.
Photo: Matt Barton, Agricultural Communications Services
 Figure 3.
An intermittent stream before  and after  stream restoration.
What Technical Expertise is Needed?
Because restoring a stream is a complex endeavor requiring knowledge from a wide range of areas such as hydrology, hydraulics, geomorphology, ecology, botany, and construction management, it is important to get professional assistance.
Trained engineers, hydrologists, biologists, and other such technical professionals are necessary to properly design and construct a stream restoration project.
Before construction can begin on a stream restoration project, it is important to obtain the necessary permits.
Federal, state, and local agencies administer and distribute permits for stream restoration projects.
At the federal level, consult with the U.S.
Army Corps of Engineers.
The Kentucky Division of Water administers the state-level permits in Kentucky.
Local agencies should also be consulted regarding permit needs for stream restoration projects.
The permitting process can take several months, SO plan accordingly.
Who Funds Stream Restoration Projects?
HENV-206 Understanding and Protecting Kentucky's Watersheds IP-73 Living Along a Kentucky Stream ID-185 Planting a Riparian Buffer HENV-202 Planting Along Your Stream, Pond, or Lake ID-175 Riparian Buffers: A Livestock Best Management Practice for Protecting Water Quality
Chapter: 41 Chemical Sprayer Application and Calibration
 The purpose of this chapter is to discuss chemical application and calibration.
Applying pesticides at labeled rates is the legal obligation of the user.
If too little is applied, you may not control the targeted pest.
If too much is applied, your chemical costs increase, you may be in violation of the law, and there may be negative effects on the crop, humans, livestock, and the environment.
Calibration doesn't need to be complicated but should be done frequently to ensure correct rates and provide optimum efficacy for target pests.
Rate controllers have automated calibration, however, they contain mechanical sensors that can wear or become sticky, SO they also need to be checked to ensure that they function properly.
Figure 41.1 Flow from a spray nozzle.
Sprayer Calibration and Maintenance
 Well-maintained equipment that applies treatments at the prescribed rate optimizes control and reduces application errors.
A small investment of time and money for the replacement of worn-out or faulty parts can be minimal compared to loss of product or crop yield.
Details on equipment calibration is outlined in FS 933 "Calibration of Pesticide Spraying Equipment" available online at Wilson.
In South Dakota, anyone who applies pesticides  to an agricultural commodity that has a value greater than $1,000 is required to be a certified applicator.
There are two categories of certification: private applicators and commercial applicators.
Contact your local Extension educator or the South Dakota Department of Agriculture for more information on certification.
Pesticides are a regulated material and must be stored, handled and applied in compliance with federal and state law.
Some general safety tips for transport, storage and pesticide mixing are presented in Table 41.1.
Questions regarding regulatory compliance should be directed to the SD Department of Agriculture, Office of Agronomy Services  773-4432.
Safety and Worker Protection
 Table 41.1 Safety tips for transport, storage, and mixing of pesticides:
 Place small containers  in water-tight totes.
Do not exceed weight limits of trailers.
Tie down tanks with load straps strong enough to secure the load.
Avoid transportation on vehicles or trailers where the load can cause a rollover.
Store herbicides away from sensitive areas such as wells, populated buildings, animal feed, etc.
Avoid storing herbicides in unheated storage over the winter, freezing may break containers or compromise the integrity of the product.
Avoid storing or transporting near direct heat.
Triple rinse, store in appropriate locations, and dispose of containers as labels direct.
Lock doors to avoid accidental opening or vandalism.
Secure hoses, containers and pumps.
Lock valves to avoid accidental opening or vandalism.
Load and mix herbicides 150 ft from wells, lakes, or wetlands.
Have an anti-back siphon device when filling equipment.
When working with agricultural chemicals, it is important to wear the appropriate protective clothing.
Manufacturers must provide information about the type of personal protective equipment  that must be worn when mixing, loading, handling, and applying pesticides.
This information has to be on the pesticide label.
There are different types of equipment needed  based on the solvents used in the pesticide formulation and the length of time you will be exposed to the chemical.
Read and follow label directions to handle pesticides safely.
Before spraying a field, it is important to check the machine to see whether it is in good order.
Walk around the sprayer to make sure booms are straight, level, and not bent or kinked; braces and springs are intact; shields are in place; and hoses, pumps, and gauges are operational and do not leak.
If something failed at the last job, fix it.
If you need to do welding, rinse off the sprayer prior to the operation.
After repairing or replacing worn and broken parts, clean the strainer, nozzle screens, and nozzles with water mixed with ammonia or tank cleaner, based on label recommendations.
Use a nozzle brush or a toothbrush to clean the nozzles.
Do not use a wire or knife blade because they can damage the screens and nozzles.
Once you determine that the sprayer is in good working order, you are ready to calibrate the sprayer.
Directions for calibrating sprayers are available at Wilson.
How Much Pesticide and Adjuvant per Tank?
If the carrier application rate is 5 gallons/acre and you want to apply 16 fluid ounces of product/acre, then you need to put 16 fluid ounces of product for each 5 gallons of water.
If you have a 100-acre field, then you need 500 gallons of water , and you will need 12.5 gallons of product (16 fluid ounces x100
 acres = 1,600 ounces/128 ounces per gallon = 12.5 gallons).
These values can be scaled up or down as needed.
Carefully read the label to determine whether and what type of adjuvants or surfactants should be included in the spray mix.
Adjuvants may be recommended as an amount in volume/volume of the gallons in a sprayer OR as an amount per acre.
If the amount is given as a volume/volume, then know how much of the herbicide mix is in a tank and then determine the amount to add.
For example, if you have a full 500-gallon tankload and the adjuvant is suggested at 2% v/v, then:
  = 10 gallons of surfactant should be included.
If the 500-gallon tank has only 300 gallons then  = 6 gallons.
If instead, the adjuvant is suggested on an acre basis, then the number of acres that will be treated with the sprayer load needs to be estimated and the amount of adjuvant calculated.
For example, if the adjuvant should be applied at 1 quart/acre, the tank has 500 gallons of pesticide mix, and the output is 10 gal/a, the amount of adjuvant that should be added would be:
 500 gal/ = = 50 a/tank; 1 quart/a 50 a/tank = 50 quarts/tank; 1 gallon = 4 quarts so 50 quarts/tank * 1 gallon/4 quarts 12.5 gallons
 Always double-check calculations, as this is easier and cheaper than making a mixing error.
Read and follow label instructions for minimum carrier application rates.
In some cases, 15 or 20 gallons of carrier per acre is needed to optimize spray coverage, especially for contact-type chemicals.
Also add any recommended surfactants or spray additives at the correct rate.
Label instructions will also provide the correct order for mixing chemicals in the tank.
When applying a tank-mix of chemicals, make sure that the highest minimum rate of carrier is used for the application.
Simple Technique to Calibrate a Sprayer
 1.
Measure the width covered by one nozzle.
This is the center of one nozzle to the center of the next nozzle along the boom.
2.
Measure the amount of time to travel 1/128th of an acre.
3.
Using an ounce-delineated measuring container, with your sprayer loaded, collect spray from one nozzle for the time required to drive 1/128th of an acre.
4.
If your nozzles are 18 inches apart and the sprayer is traveling at 5 mph collect spray for 30.8 seconds.
Each ounce equals 1 gal/acre.
Also, make sure the spray pattern across the boom and from individual nozzles is correct.
If more or less flow is needed across the boom, adjust the pressure  or adjust the rate controller as needed.
Nozzle wear will affect the output and pattern of the nozzle.
The material of the nozzle and type of formulation used will influence the wear.
For example, abrasive materials will cause the nozzle orifice to open, causing greater output and less
 Table 41.2 The relationship between swath width of a spray nozzle, distance, and length of time required to collect the spray.
The number of ounces collected is equal to gal/acre.
width	for 1/128th a	5	10	15	20
 inch	feet	sec	sec	sec	sec
 6	681	92.9	46.4	31	23.2
 8	507	69.1	34.6	23	17.3
 10	408	55.6	27.8	18.5	13.9
 12	340	46.4	23.2	15.5	11.6
 14	292	39.8	19.9	13.3	10
 16	255	34.8	17.4	11.6	8.7
 18	226	30.8	15.4	10.3	7.7
 24	170	23.2	11.6	7.7	5.8
 Example 41.1 A sprayer has a nozzle width of 14 inches and the sprayer is traveling at 15 mph.
How long should spray be collected from one nozzle?
You collect 21 ounces in 13.3 seconds, how many gallons per acre is the sprayer calibrated for?
precise pattern over time.
Stainless-steel and ceramic nozzles are less affected by formulation type.
Plastic nozzles are affected by the solvents in an herbicide formulation and may swell shut, lowering the nozzle output.
If the output pattern of a nozzle is nonuniform, check to make sure that the screen for the nozzle  is not plugged.
If individual nozzle output is 10% higher or lower than the average, then the nozzle should be replaced.
As you are spraying the field, conduct routine checks to make sure the correct amount of solution is being applied.
For example, if you know that each trip around the field is 20 acres and the application rate is 5 gal/acre, then each trip should use 100 gal.
If < 100 gallons are used, you are underapplying and if > 100 gallons are used, you are overapplying.
Recalibrate the sprayer as needed to match the desired and true output.
If the amount is slightly less, the pressure gauges may not be correct or main screen or nozzles may be plugged.
If the amount is more, check the pressure output and the system for leaks.
Once cauliflower emerged, its growth was rapid in both trials.
The only weed species able to achieve greater height growth was London rocket.
After hand hoeing 4 weeks after emergence, few weeds emerged, probably because of the dense canopy development of cauliflower.
Using the normal herbicide rate for cauliflower  or reducing it to 6 or 4 lb ai/ac did not influence yields relative to weed-free conditions.
Four or six pounds per acre of Dacthal provided temporary control of the weeds used in this study, enough time for the cauliflower to emerge and gain a height advantage.
We performed no hand hoeing in combination with herbicides, since weed populations were not significant when Dacthal was used.
Lower herbicide rates seem practical for this crop under these field conditions.
High populations of London rocket, however, could interfere with harvest and necessitate hand hoeing.
Winter weeds used in both cauliflower and lettuce trials grew more slowly than the summer weeds used in the other vegetable trials.
Although weed cover values in untreated plots were similar for the four crops studied, weed density and biomass were lower in the lettuce and cauliflower trial controls.
Once weeds were removed by hand hoeing in these crops, invasion by new weeds was sparse.
The weed-free period necessary to achieve full crop yield depends upon the vegetable crop, the weed species, and the weed density.
Cucumber, by virtue of its rapid growth and vining habit, was able to compete successfully against high weed populations with as few as 2 or 3 weeks' weed-free maintenance.
Bell pepper, a slower-growing vegetable crop, required a much longer weedfree period than cucumber to reach its full yield potential.
Lower weed populations in the lettuce and cauliflower crops meant that yields were not reduced if the crops were weed-free for at least 2 weeks after emergence.
Hand hoeing appeared to harm crop yields once the crop or weeds had grown to a large size, SO late-season hand hoeing should be avoided.
Cucumbers, lettuce, and cauliflower were able to achieve full yield potential with 2 weed-free weeks after crop emergence.
For these crops in combination with the weed species examined in this study, reducing the standard herbicide treatment by half can be combined with timely hand hoeing to equal or better the crop yields resulting from the standard herbicide treatment alone.
W.
Thomas Lanini is Cooperative Extension Weed Ecologist, UC Davis; and Michelle Le Strange is Cooperative Extension Farm Advisor, Tulare and Kings counties.
Irrigation uniformity and cotton yields in the San Joaquin Valley
 Dennis Wichelns J.
D.
Oster
 Cotton yield data collected from 32 fields in the Broadview Water District are negatively correlated with several measures of soil salinity, sodicity, and irrigation uniformity.
Results suggest that farmers may be able to increase cotton yields by improving irrigation uniformity on surface-irrigated fields.
Since 1979, when federal and state agencies began seeking long-term solutions to agricultural drainwater problems in the San Joaquin Valley, many experts have been suggesting that improvements to irrigation management that would reduce drainwater volumes be made at the farm level.
One proposal is to improve irrigation infiltration uniformity within farm fields.
Non-uniform infiltration increases drainwater and may reduce crop yields.
More uniform infiltration, on the other hand, may reduce drainwater volumes while increasing crop yields.
The most common irrigation method in the San Joaquin Valley's drainage problem area is siphon-tube furrow irrigation with 1/2-mile runs.
Irrigators generally run set times of 12 or 24 hours to accommodate labor and water availability.
They can improve infiltration uniformity in furrow irrigation in a number of ways: reducing the length of furrow runs; increasing water inflow rates, and SO reducing set times; using surge irrigation techniques, especially during pre-irrigations; or scheduling water deliveries and irrigations accurately to keep applied water depths in balance with evapotranspiration losses and soil water holding capacity.
Variations characteristics constrain the degree to which irrigators can reduce drainwater volumes through improved water management.
Soil characteristics govern the infiltration rates and uniformity of a surface-irrigated field.
A properly designed and maintained pressurized irrigation system transfers most of the infiltration control to the system.
Sprinkler irrigation, low-energy precision application , and subsurface drip systems may improve infiltration uniformity in a field with considerable variation in soil characteristics.
Farm-level decisions regarding irrigation system improvements must take into ac-
 count the costs and returns involved in installing a new irrigation system or managing an existing system more efficiently.
The annualized capital costs of siphon-tube and gated pipe systems range from $20 to $30 per acre, while those costs for pressurized sprinkler and drip irrigation systems range from $40 to $180 per acre.
Reduced production costs  offset some of the higher capital costs of a pressurized system, but the pressurized system's total annual costs remain the higher of the two, according to the 1988 report of the UC Committee of Consultants on Drainage Water Reduction, Associated Costs of Drainage Water Reduction.
Farmers need to see that there are economic advantages to pressurized irrigation if they are to switch over.
The water savings from more efficient water application and the associated potential increases in yield resources of increased net revenue.
A lower drainwater volume will mean a major cost reduction for farmers who have to dispose of drainwater on their own property.
The profitability of a furrow irrigation system for cotton falls below that of a subsurface drip, LEPA, or linear-move sprinkler system when the cost of drainwater disposal exceeds about $70 per acre-foot, assuming the pressurized system applies water with greater uniformity.
Once farmers see field-level data that describe the potential benefits of improved irrigation uniformity, they will be more likely to implement irrigation management improvements and adopt pressurized systems where appropriate.
We collected data describing the soil characteristics, crop yields, and irrigation depths of 32 cotton fields  in the Broadview Water District during summer, 1987.
Soil salinity and sodicity data came from the soil samples we collected, while irrigation and crop yield data came from district water delivery records and annual crop reports.
One sample was collected from the 0to-3-foot depth interval at each of 20 sites arrayed in a rectangular grid in each field.
Most fields encompassed 160 acres.
Each sample was mixed thoroughly before subsampling.
prepared 8 samples for analysis of sodium adsorption ratio and the electrical conductivity of the saturated extract.
Variations in crop canopy color are visible to the eye in these aerial photographs.
The mean and standard deviation of transmissivity for the more uniform field  were 118.8 and 7.8, respectively.
A second field  appeared lighter and less uniform in color, and had
 a mean transmissivity of 135.4 and a standard deviation of 25.1.
These fields are typical of the large range observed in the mean  and standard deviation  of transmissivity, among the cotton fields.
Electrical conductivity  describes the amount of salt present in a soil, indicating the likelihood that plant growth may be affected by soil salinity.
Cotton is a relatively salt-tolerant crop; an ECe below 7.7 decisiemens per meter  usually will not reduce its yield.
The sodium adsorption ratio  is a measure of the number of sodium ions attached to soil particles, relative to the number of calcium and magnesium ions.
A large number of sodium ions  will degrade soil particles and reduce the number of large pore spaces in the soil.
Such a soil is not very permeable, and it is difficult to leach accumulated salts from such a soil by applying excess water.
Fields where soils have high ECe and high SAR may contain areas of low permeability with accumulated salts.
placed in field turnout structures to record water deliveries.
For each field, we determined applied water depths for pre-irrigation and seasonal irrigations by dividing the total volume of delivered water by the total planted area.
Surface runoff flowed into district drainage ditches, and was not recirculated by individual farmers.
We did not separately measure runoff and deep percolation, SO the applied water depths reported in this study include these amounts.
Aerial photographs of all cotton fields were obtained from an elevation of 4,800 feet on July 29, 1987.
Each color photograph was taken when the plane was directly over the center of the appropriate field.
After processing, we put each color positive on a light table where it was scanned by a video camera attached to a computer running an imageprocessing program.
The software analyzed the positive's ability to transmit light at each dot  in the video image.
High transmissivity values of individual pixels indicated light-colored soils showing through spaces in the crop canopy, while low values indicated densely covered, dark green areas.
Each pixel represented an area of 46 square feet, SO 947 pixels described 1 acre of land.
Software written by the Image Processing Facility in the Electrical Engineering Department at UC Davis calculated the mean and the standard deviation of transmissivity for each field.
The mean transmissivity describes the average light value for the field.
The standard deviation of transmissivity
 describes how much it varied within a field.
A high standard deviation indicates that many individual pixels were lighter and darker than the mean.
Low standard deviations indicate that most individual pixels were very close to the mean.
Like the aerial photographs, our salinity and sodicity data show considerable variation among farm fields.
The field average SARs in saturated soil extracts ranged from 3.95 to 15.83, with an overall mean of 7.77 and a standard deviation of 2.85.
The field average ECe ranged from 1.36 to 8.16 dS/m, with an overall mean of 4.23 dS/m and a standard deviation of 1.99 dS/m.
The within-field variability range of soil salinity and sodicity is described by therange in the standard deviations of site-specific measurements.
The lowest standard deviation of SAR for a single field was 0.49, and the highest was 4.75.
Standard deviation of ECe ranged from a low of 0.11 dS/m to a high of 3.27 dS/m.
Table 1 lists minimum, maximum, and mean values and standard deviations for pre-irrigation depth, seasonal irrigation depth, total applied water, and cotton crop yield per field.
Cotton yields correlate negatively with the mean and standard deviation of the soil salinity and sodicity measures.
The negative correlations are statistically significant , and suggest that fields with low salinity and low sodium
 Five of the eight soil samples analyzed from each field were composites: four contained soil from each of five sites along a single transect, and one contained equal portions of soil from all twenty sites.
The other three samples contained soil from individual sites: two were selected from sites with the highest apparent ECe as determined with a portable salinity meter, and one was from the site with the lowest apparent ECe.
Most of the cotton fields were irrigated from earthen head ditches, using siphon tubes to deliver water to furrows that were 1/2 mile long.
We obtained field-specific irrigation data for 28 of the 32 fields, using irrigation district data from propeller meters
 adsorption ratios also have higher cotton yields.
Higher yields are also associated with fields having little variation in ECe and SAR.
Cotton yields are negatively correlated with the standard deviation of crop canopy color.
That negative correlation is not statistically significant, but it appears to suggest that fields with relatively uniform crop canopy color have higher yields.
Cotton yields correlate positively with pre-irrigation depth, while total applied water correlates positively with the mean and standard deviation of ECe and the standard deviation of SAR.
These results suggest that more irrigation water is applied on fields that are more saline and on fields where the variation in ECe and SAR is high.
Fields receiving larger pre-irrigations had greater cotton yields.
Several of the measures of soil salinity, sodicity, and transmissivity are correlated with each other and with crop yield.
The mean of transmissivity is positively correlated with the mean and standard deviation of ECe and SAR (table suggesting that fields that look lighter from the air are more saline and more sodic than darker fields.
The standard deviation of crop canopy color is positively correlated with the mean ECe and the standard deviation of SAR.
We did not expect to find significantly negative correlations between crop yield and the means and standard deviations of ECe and SAR, given our knowledge of cotton's
 The correlation between yield and the standard deviation of ECe is statistically more significant than the correlation with the mean.
This suggests that some areas in many of the cotton fields are excessively saline.
However, fewer than 15% of sitespecific and transect-average ECe values for the 32 cotton fields exceeded cotton's threshold ECe of 7.7 dS/m.
This low percentage is particularly significant because we had selected two of the eight soil samples based on their having the highest apparent conductivity in the field.
The ECe values describing soil salinity in the first three feet of soil depth may be lower than the average salinity in the root zone for mostfields.
The negative correlation between yield and ECe may result from salinity that exceeds the threshold value in some portions of the root zone.
Salinity often increases with soil depth in irrigated fields.
A more fundamental question arises when we look at the ECe and SAR values: Why are some of the values SO high?
Most of the fields in Broadview have been drained artificially by 6to 9-foot-deep tile drains since the 1960s and 1970s.
Before 1983, all of the collected drainwater was recirculated
 Table 1.
Range and variation of irrigation and yield data collected from 28 cotton fields in the
 Broadview Water District, 1987
 Measurement	Minimum	Maximum	Mean	Std dev
 Pre-irrigation depth 	0.74	1.91	1.19	0.29
 Seasonal irrigation depth 	1.15	3.61	2.06	0.43
 Total applied water 	2.46	4.99	3.24	0.51
 Yield 	2.29	3.80	3.09	0.38
 Table 2.
Correlations between cotton yields, applied water, soil characteristics, and crop canopy color
 in the Broadview Water District, 1987*
 Pre-	Total	Soil	adsorption	color, or
 irrigation	applied	salinity 	ratio #	transmissivity$
 deptht	water+	Mean	Std dev	Mean	Std dev	Mean	Std dev
 Yield	0.33d	-0.02	-0.29d	-0.38e	-0.45e	-0.41e	0.11	-0.28c
 depth 	0.55e	0.24	0.13	-0.24	0.02	0.12	-0.29
 water 	0.33d	0.33d	0.15	0.36d	0.01	-0.16
 Mean	0.77e	0.55e	0.67e	0.34d	0.33d
 Std dev	0.59e	0.76e	0.45e	0.07
 Mean	0.73e	0.37d	0.34d
 Std dev	0.35d	0.23
 Letters in columns indicate significant differences: c = 15% level, d = 10% level, e = 5% level.
t Irrigation data are from 28 fields.
# Soil salinity, sodicity, and transmissivity data are from 32 fields.
The transmissivity measurement is not actually calibrated to any standardized scale or unit.
The numbers are
 meaningful in a relative sense, but do not carry an actual set of units.
and blended with irrigation deliveries.
As soil salinity thus increased in the district, growers shifted to salt-tolerant crops including cotton and grains.
When an outlet was opened for disposal of drainwater in 1983, irrigation water quality improved, soil salinity decreased, and growers became more interested in moderately salt-tolerant crops including tomatoes and melons.
Since 1983, good-quality irrigation water has been used on all fields in Broadview.
The maximum observed means of ECe and SAR in soils of individual fields are respectively 20.4 and 31.7 times greater than the corresponding values for the irrigation water.
ECe and SAR will be low in areas of high infiltration because of substantial leaching with good-quality irrigation water.
In areas with low infiltration rates, ECe and SAR will be higher because they experience less leaching and because evapotranspiration exercises a greater concentrating effect.
The effects of this "evapoconcentration" are enhanced by lateral movement of water and salt within the soil from areas of high infiltration to areas of low infiltration.
In addition, high SARs in the soil can reduce the infiltration of low-salinity irrigation water.
The high ratios of soil ECe and SAR to the corresponding values for irrigation water in Broadview suggest that some fields and areas within fields have low infiltration rates.
The observed negative correlations between the crop yield and the mean and standard deviation of salinity and sodicity probably result from infiltration variability, which causes variability in the amount of water available for plant growth.
This conclusion is consistent with the positive correlations between yield and pre-irrigation depth and between total applied water and soil salinity.
Logically, farmers would apply more water to saline fields and to fields that exhibit poor plant growth in various areas of the field.
Our results suggest that growers can increase cotton yields by improving the infiltration uniformity on surface-irrigated fields.
Estimates of yield increases may give growers part of the economic incentive they need before adopting irrigation methods that improve infiltration uniformity.
Reductions in irrigation water costs and drainwater disposal costs provide even more incentive.
Dennis Wichelns is Assistant Professor, Department of Resource Economics, University of Rhode Island, Kingston; and J.
D.
Oster is Extension Specialist, Department of Soils and Environmental Sciences, University of California, Riverside.
Funding for this research was provided by the San Joaquin Valley Drainage Program and the UC Salinity and Drainage Task Force.
The authors greatly.
appreciate the assistance provided by the Broadview Water District.
MOBILE DRIP IRRIGATION EVALUATION IN CORN
 Kansas State Research and Extension
 Diminishing well capacities coupled with the desire to extend the usable life of the Ogallala aquifer have stimulated the quest for efficient irrigation application technologies in the central High Plains.
Mobile Drip Irrigation , which integrates driplines onto a mechanical irrigation system such as a center pivot, has attracted interest from farmers and other stakeholders as water supplies have become more constrained.
By applying water along crop rows, it is hypothesized that MDI could eliminate water losses due to spray droplet evaporation, water evaporation from wetted canopy, and wind drift.
MDI also may reduce soil evaporation due to limited surface wetting especially before canopy closure.
The idea of replacing center pivot sprinkler nozzles with drip lines is not new.
However, what is new is the advancement in the way the dripline is precisely connected to the center pivots and dripline emitter technology, e.g., pressure compensated emitters.
Such emitters ensure uniform water application over a wide range of pressure variation.
Another advantage of MDI is that in areas where this technology could prove very useful, such as central High Plains, many producers already own center pivots; therefore the transition from sprinklers to MDI would be relatively easy.
However, there are still many issues that need to be understood and resolved before this technology can become widely accepted e.g., precision positioning of the drip under circular planting, effect of on yield and water productivity as well as onfarm operation and maintenance requirements.
To quantify the benefits of MDI, a study was conducted with the following objectives: 1) compare soil water evaporation under MDI and in-canopy spray nozzles in 2015; and 2) compare corn grain yield, water productivity, irrigation water use efficiency, and end of season profile soil water under MDI and LESA  at various irrigation capacities.
The study was conducted at the Kansas State University Southwest Research-Extension Center  near Garden City, Kansas.
The soil at the study site is a deep, well-drained Ulysses silt loam.
The climate of the study area is semi-arid, and average annual rainfall is 18 inches.
Two independent studies were conducted to compare MDI and LESA in 2015.
Study 1 compared the two application technologies at a high irrigation capacity  and Study 2 compared the technologies at low irrigation capacity 2.3 gpm/ac).
The two irrigation capacities were intended to mimic a range of pumping capacities experienced by producers in southwest Kansas.
The experimental design in each study was a randomized complete block with four replications.
The study was repeated during the 2016 corn growing season but the experimental design was modified to add more treatments and to compare the technologies and irrigation capacities under one study instead of two independent studies.
In 2016, the irrigation application technologies compared included drip line of 1 gph, drip line 2 gph, LESA, and bubblers.
Three irrigation capacities were compared 1.2, 2.3, and 4.6 gpm/ac.
The experiment was conducted in a field that was previously under fallow.
The corn hybrid planted in 2015 was DKC 61-89 GENVT2P and in 2016 it was DKC64-89, with relative maturities of 111 and 114 days respectively.
Planting was done on May 18, 2015 and on May 06, 2016 at a seeding rate of 32,000 seeds per acre using a no-till planter, planting depth was 2 inches.
Nitrogen fertilizer was applied preplant at a rate of 300 pounds of N per acre as urea 46-0-0.
Weed control involved application of 3 qt/a of Lumax EZ  and 2 oz/a of Sharpen  as pre-emergence herbicide and 32 oz/a of Mad Dog Plus  and Prowl H2O  as post-emergence herbicides.
Harvesting was done by hand by taking two 40 feet corn rows in the center of each plot at physiological maturity
 Irrigation was applied using a center pivot sprinkler system.
A 130 micron disc filter with a flow rating of 200 gpm was installed at the pump station also equipped with a Variable Frequency Drive  to prevent emitter clogging.
Irrigation treatments for 2015 are listed below:
 1.
MDI 1 gph 4.6 gpm/ac
 2.
LESA 4.6 gpm/ac
 1.
MDI 1 gph 2.3 gpm/ac
 2.
LESA and 2.3 gpm/ac
 Irrigation treatments arranged in a split-plot RCBD for 2016 are listed below:
 1.
MDI 1 gph 4.6 gpm/ac
 2.
MDI 2 gph 4.6 gpm/ac
 3.
LESA 4.6 gpm/ac
 4.
Bubbler 4.6 gpm/ac
 5.
MDI 1 gph 2.3 gpm/ac
 6.
MDI 2 gph 2.3 gpm/ac
 7.
LESA 2.3 gpm/ac
 8.
Bubbler 2.3 gpm/ac
 9.
MDI 1 gph 1.2 gpm/ac
 10.
MDI 2 gph 1.2 gpm/ac
 11.
LESA 1.2 gpm/ac
 12.
Bubbler 1.2 gpm/ac
 Irrigation was triggered based on an ET soil water balance but limited by irrigation capacity.
Soil water measurements were taken weekly using a neutron probe  at 1-foot depth increments from 1 to 8 feet deep to assess adequacy of the irrigation schedule.
Each irrigation event applied 1.0 inch for all treatments scheduled to be irrigated on a given day.
Soil water evaporation was measured using four-inch mini-lysimeter placed within the variably wetted surface by the dripline in the MDI plots, and under LESA plots in 2015.
Lysimeters were installed approximately 24 hours after an irrigation event or after the soil had drained.
Changes in lysimeter weight were recorded every 24 hours and converted to soil water evaporation rates.
Rainfall during the 2015 growing season from May 1 to October 31 exceeded the long-term average in the same period from 1950 to 2013.
The 2015 summer growing season rainfall exceeded the long-term average by 4.2 inches.
Above normal rainfall in May of 2015 ensured sufficient soil water at corn planting.
Also, above normal rainfall at tasselling in July and during grain fill in August contributed substantially to crop water needs.
In 2016, growing season rainfall exceeded long-term average  by 2.8 inches and was equally well distributed during the growing season.
Preliminary results indicate soil water evaporation was significantly lower  under MDI, compared to LESA, on average by 35%.
The differences could be attributed to the reduced surface area wetted by the dripline compared to the sprinklers.
These results indicate there is potential to increase water productivity using MDI by partitioning more water to transpiration and less to soil water evaporation.
Figure 1.
Comparing soil water evaporation under MDI and spray nozzles for three days during the 2015 corn growing season at the Kansas State University Southwest ResearchExtension Center, near Garden City, Kansas.
During the 2016 growing season the effect of irrigation application method on yield was not significant at 5% level  but the effect of irrigation capacity on yield was significant.
At all irrigation capacities MDI produced the highest mean yield of 235 bu/ac, 211 bu/ac and 205 bu/ac for 4.6 gpm/ac, 2.3 gpm/ac, and 1.2 gpm/ac irrigation capacities respectively.
Results for all other irrigation application methods and irrigation capacities are shown in Table 1.
These results suggest that farmers might be able to harness the advantages of drip irrigation such reduction in water evaporation losses using MDI.
Table 1.
Corn grain yield for different irrigation application methods and irrigation capacities at the Kansas State University, Southwest Research-Extension Center near Garden City Kansas.
Irrigation Type	Well Capacity	Yield 	Means with the same letter
 	are not significantly different
 1MDI 1gph	4.6	234	A
 Bubbler	4.6	219	B	A
 MDI 2 gph	2.3	215	B	A
 2LESA	4.6	211	B	A
 MDI 1gph	2.3	210	B	A
 MDI 1gph	1.2	204	B	A
 Bubbler	2.3	204	B	A	C
 MDI 2 gph	1.2	203	B	A	C
 MDI 2 gph	4.6	195	B	C
 LESA	2.3	192	B	C
 Bubbler	1.2	190	B	C
 LESA	1.2	169	C
 1Mobile Drip Irrigation 2Low Elevation Spray Application
 Crop water use during the 2015 corn growing season under Study 1 was 29.8 and 29.0 inches for MDI and LESA respectively.
Study 2 crop water use was 22.6 inches and 23.3 inches for MDI and LESA, respectively.
The differences in seasonal crop water use  could be attributed to differences in irrigation application amounts between the two studies.
Fourteen inches were applied in Study 1 while 8 inches were applied in Study 2.
High irrigation amounts under Study 1 probably increased water losses in form of soil water evaporation and deep drainage.
The effect of application method on water productivity and irrigation water use efficiency was also not significant at high and low irrigation capacities.
In Study 1, average water productivity of MDI and LESA was 8.3 and 8.9 bu/a/in, respectively.
In Study 2, average water productivity of MDI and LESA was 10.7 and 9.5 bu/a/in, respectively.
Irrigation water use efficiency was not significantly different in studies 1 and 2.
However, it can be seen from Figures 2 and 3 that water productivity and IWUE were higher under the low well capacity, implying irrigation water was used more efficiently as the number of irrigation applications was reduced.
Figure 2.
Water productivity of Mobile Drip Irrigation  and Low Elevation Spray Application  for irrigation capacity of 4.6 gpm/ac during the 2015 growing season at the Kansas State University SWREC, near Garden City, Kansas.
Figure 3.
Irrigation water use efficiency of Mobile Drip Irrigation  and Low Elevation Spray Application  for irrigation capacity of 2.3 gpm/ac during the 2015 growing season at the Kansas State University Southwest Research-Extension Center, near Garden City, Kansas.
In 2016, a total of 7, 4 and 3 inches of irrigation were applied corresponding to 1.2, 2.3 and 4.6 gpm/ac irrigation capacity respectively.
Crop water use for the different treatments are summarized in Table 2.
Irrigation capacity and irrigation application method both had a significant effect on water productivity at 5% significant level with p-value< 0.0001, and pvalue= 0.0163 respectively.
The lowest irrigation capacity produced the highest water productivity and irrigation water use efficiency as shown in Tables 3 and 4.
Irrigation water use efficiency increased with decrease in irrigation capacity and was higher for MDI compared to LESA and bubbler as shown in Table 4.
This is due to the fact that as the number of irrigation applications reduced nonproductive water losses due to evaporation or deep drainage were minimized.
Table 2.
Crop water use for the different irrigation application methods and irrigation capacities during the 2016 corn growing season at Kansas State University, Southwest Research-Extension Center near Garden City Kansas
 Irrigation	Irrigation application methods
 Capacity	1MDI2	MDI 1	2 LESA	Bubbler
 4.6	15.7	17.8	17.6	17.3
 2.3	19.7	18.1	20.6	18.4
 1.2	24.0	24.6	24.6	24.1
 SuperscriptMobile Drip Irrigation 2Low Elevation Spray Application
 Table 3.
Water productivity for the different irrigation application methods and irrigation capacities during the 2016 corn growing season at Kansas State University, Southwest Research-Extension Center near Garden City Kansas
 Irrigation	Irrigation application methods
 Capacity	1MDI 2	MDI 1	2 LESA	Bubbler
 4.6	8.2	9.6	8.7	9.2
 2.3	11.1	11.8	9.3	11.1
 1.2	13.0	11.6	9.8	11.0
 1Mobile Drip Irrigation 2Low Elevation Spray Application
 Table 4.
Irrigation water use efficiency for the different irrigation application methods and irrigation capacities during the 2016 corn growing season at Kansas State University, Southwest Research-Extension Center near Garden City Kansas
 Irrigation	Irrigation application methods
 Capacity	1MDI 2	MDI 1	2 LESA	Bubbler
 4.6	68	68	57	63
 2.3	54	53	48	51
 1.2	28	34	31	31
 1 Mobile Drip Irrigation 2Low Elevation Spray Application
 End of Season Soil Water
 End of season soil water measured on October 6 2015, showed that total soil water in the 8 foot profile was significantly higher in MDI compared to LESA in Study 2.
However, in Study 1, end-of-season soil water was not significantly different between MDI and LESA.
Figures 4 and 5 also show that MDI was able to store more water at deeper depth compared to LESA.
In Study 2, plant available water at harvest under MDI was twice that under LESA.
We can conclude that storage efficiency was higher
 under MDI particularly under low irrigation capacity during the 2015 growing season.
It was also observed that plots under MDI did not have deep wheel tracks associated with sprinkler nozzles as shown in Figure 6.
Volumetric soil water conternt
 Figure 4.
End of season soil water under Mobile Drip Irrigation  and Low Elevation Spray Application  for irrigation capacity 2.3 gpm/ac during the 2015 growing season at the Kansas State University Southwest Research-Extension Center, near Garden City, Kansas.
Volumetric soil water conternt
 Figure 5.
End of season soil water under Mobile Drip Irrigation  and Low Elevation Spray Application  for at high irrigation capacity of 4.6 gpm/ac during the 2015 growing season at the Kansas State University Southwest Research-Extension Center, near Garden City, Kansas.
Figure 6.
Difference between wheel tracks in Mobile Drip Irrigation  and Low Elevation Spray Application  at the Kansas State University Southwest Research-Extension Center, near Garden City, Kansas.
Mobile Drip Irrigation was evaluated under 1.2, 2.3 and 4.6 gpm/ac irrigation capacities during the 2015 and 2016 corn growing seasons at the Kansas State University Southwest Research-Extension Center, near Garden City, Kansas.
Soil water evaporation was significantly lower under MDI compared to LESA.
The effect of irrigation application method on yield at high irrigation capacity was not significant  during the 2015 and 2016 corn growing seasons.
However, the effect of irrigation capacity on yield was significant.
Also irrigation application method had a significant effect on water productivity with MDI 1gph producing the highest average water productivity.
Irrigation water use efficiency increased with decrease in irrigation capacity and was higher for MDI compared to LESA and bubbler.
End-of-season soil water measured at harvest showed that total soil water in the 8 foot profile was significantly higher in MDI compared to LESA under low irrigation capacity during the 2015 growing season.
However, at the high well capacity, end of season soil water was not significantly different between MDI and LESA.
It is worth noting that plots under MDI did not have deep wheel tracks associated with sprinkler nozzles.
More research is needed to confirm benefits of MDI.
THE UNIVERSITY OF ARIZONA
 COLLEGE OF AGRICULTURE AND LIFE SCIENCES COOPERATIVE EXTENSION
Basic Tips for Designing Efficient Irrigation Systems 1
 Haimanote K.
Bayabil, Kati W.
Migliaccio, Michael Dukes, and Laura Vasquez2
 Freshwater resources are becoming scarce due to population increase and associated increases in water, food, and energy demands.
The state of Florida alone is projected to add 6 million people by 2030.
Moreover, extreme weather events  are becoming common phenomena.
Therefore, as freshwater resources become increasingly scarce and droughts become more frequent, there is a need for efficient use of water resources.
There have been significant advancements in irrigation technologies  that can allow water savings.
However, the effectiveness of these technologies depends on several factors such as the design of the irrigation system.
Designing efficient irrigation systems and equipment will not only save money but also conserve water.
Factors to Consider When Designing Irrigation Systems
 This document provides a basic overview of the major factors to consider when designing irrigation systems and choosing irrigation equipment.
Figure 1 presents a few of the major factors that affect design of irrigation systems.
Figure 1.
Schematic of major factors involved in designing an irrigation system.
Credits: Haimanote K.
Bayabil, UF/IFAS
 Total freshwater withdrawal in Florida across all uses is 6.4 billion gallons per day.
Almost two-thirds of this is from groundwater, while the rest is from surface water.
Almost 40 percent of freshwater withdrawal is accounted for by agricultural use, while 36 percent is for public supply.
The remaining 24 percent of freshwater withdrawals goes to other uses such as power generation, recreational-landscape irrigation, commercial-industrial mining, and domestic self-supplied uses.
Freshwater withdrawal in Florida follows the population density and the
 2.
Haimanote K.
Bayabil, assistant professor, Department of Agricultural and Biological Engineering, UF/IFAS Tropical Research and Education Center; Kati W.
Migliaccio, chair and professor, Department of Agricultural and Biological Engineering; Michael Dukes, professor, Department of Agricultural and Biological Engineering, and director, UF/IFAS Center for Land Use Efficiency; and Laura Vasquez, supervisor, Florida Yards & Neighborhoods Program, UF/IFAS Extension Miami-Dade County; UF/IFAS Extension, Gainesville, FL 32611.
intensity of irrigated croplands.
Freshwater withdrawal is the highest in Palm Beach county.
Knowing the quality and available quantity of the irrigation water source is critical.
Water sources could be from reclaimed water, surface water, or groundwater.
Depending on the water source used, the amount of water available and the equipment needed to deliver the water will differ.
Water allocations for irrigation could be subject to local ordinance, depending on several factors.
Field characteristics  could affect the choice of the irrigation system, necessary irrigation equipment , and plant types.
Field size  affects the maximum number of plants that can be planted and, as a result, total irrigation requirement.
The maximum area that can be irrigated at any given time should be determined based on the availability of water, the pump's allowable flow rate, and the pressure at the source.
Pressure loss should be considered when designing an irrigation system to minimize pressure drops and variations across the irrigated area.
Terrain slope affects the flow of water and irrigation distribution uniformity.
Water flows from high potential  to low potential.
Depending on the irrigation system layout, fields at lower elevation could receive too much water while higher-elevation locations could receive too little water.
Pumps might be needed to deliver enough water against a slope gradient.
In addition, terrain slope could promote runoff and erosion.
In some cases, leveling of uneven fields could be considered.
by the USDA Natural Resources Conservation Service.
However, accuracy of such information should be verified through field measurements.
Plant type affects irrigation system selection.
Irrigation requirements differ depending on plant growth stage.
In addition, reports show that annual crops have smaller water requirements compared to perennial plants.
In addition, different plants have different planting densities.
If the same irrigation system is used to irrigate different plants, plants should be placed in different zones SO they will be irrigated independently.
Crop coefficients  vary at distinct growth stages for different plants.
Thus, plant-specific Kc values should be used when calculating actual evapotranspiration  and irrigation requirements.
Crop market values affect the feasibility of more expensive irrigation systems.
Higher-value crops may allow for greater investment in an irrigation system; this may not be a viable option for lower-value crops.
The following documents contain additional information about crop coefficients and crop irrigation requirements.
Regarding the drought and the growing season, area meteorologist Don Day said La Nina is finally moving off after three years of drought.
El Nino is moving into the U.S., but the High Plains may not see the full benefits until the spring or summer of 2024.
THE IMPORTANCE OF IRRIGATION SCHEDULING FOR MARGINAL CAPACITY SYSTEMS GROWING CORN
 ABSTRACT.
Many irrigators in the Central Great Plains region do not use science-based irrigation scheduling for a variety of reasons, many of which are not strongly related to the technical feasibility.
Evapotranspiration -based irrigation scheduling has been shown to be an acceptable irrigation scheduling method within the region.
Many irrigators have expressed the rationale that there is no need to implement irrigation scheduling because their marginal capacity irrigation must be ran continually throughout the season to meet corn irrigation needs.
ET-based irrigation schedules were simulated using 43 years  of weather data for Colby, Kansas, to determine irrigation needs as affected by irrigation capacity, center pivot sprinkler system application efficiency and the initial soil water condition at corn emergence.
Adoption of ET-based irrigation scheduling with an initial soil water condition of 85% of field capacity and 95% application efficiency potentially could save on average 212 mm of water for a 25.4 mm/4 days irrigation capacity and 71 mm for a severely deficit 25.4 mm/8 day irrigation capacity.
As application efficiency was decreased from 95% to 80% these savings for similar initial soil water conditions decreased from 176 to 67 mm for the greater and smaller irrigation capacities, respectively.
Potential irrigation savings using an application efficiency of 95% were reduced but still appreciable when the initial soil water condition was 60% of field capacity averaging 154 and 25 mm for the 25.4 mm every 4 or 8 days irrigation capacities, respectively.
Irrigators with marginal capacity systems should adopt science-based irrigation scheduling to make best use of their limited irrigation and should not discount their opportunity to save irrigation water even when their system restrictions are severe.
Keywords.
Corn, Evapotranspiration, Irrigation management, Irrigation scheduling, Water budget.
T he most common definition of irrigation scheduling is simply the determination of when and how much water to apply.
Modern scientific irrigation scheduling uses a single approach or combination of weather-, soilor plant-based approaches.
Science-based irrigation scheduling has existed for approximately 60 years with one of the earlier discussions of the topic made by van Bavel  of using evapotranspiration to estimate soil water conditions and for timing of irrigation.
Although there is a wide body of literature on irrigation scheduling in reference books, journal articles, symposium proceedings, and extension publications, effective methods have not been well adopted by irrigators.
Submitted for review in September 2014 as manuscript number NRES 10966; approved as a Technical Note for publication by the Natural Resources & Environmental Systems Community of ASABE in December 2014.
Lack of adoption was recognized many years ago as a key problem to advancing irrigation scheduling.
Behavior patterns and attitudes of irrigators were identified as more significant barriers to adoption than reliability and accuracy of scheduling methods.
They further concluded it was difficult to get long-term acceptance of irrigation scheduling without continuing technical support from cooperative extension or others.
Although anecdotal, it seems wise to mention some of the experiences the authors have had over the years with irrigators concerning acceptance of science-based irrigation scheduling.
Several irrigators have expressed a concern for accuracy of ET estimates , although often being an irrational concern about accuracy.
The USDA-NRCS has offered cost-sharing for implementation of ET-based scheduling in several of the U.S.
Great Plains states.
On more than one occasion, irrigators have unsuccessfully approached the authors after the irrigation season for ex post facto assistance in creating irrigation schedules to satisfy their USDA-NRCS contract.
When the accuracy of irrigation scheduling is perceived to be an issue, there is a great impediment to adoption since the economic penalty of over-applying water is usually many times less than that of under-applying water.
Lack of confidence by the irrigator can be the result of changes
 Figure 1.
Effect of irrigation inaccuracy on crop production points.
Adapted from discussion and graph in Lamm.
in cultural practices that affect the field water budget or introduction of new drought resistant varieties or hybrids that seem to indicate a change in the water use of the crop.
An example is drought resistant corn, which is often interpreted by irrigators as a corn that needs less water.
These examples suggest that some of the reasons for nonacceptance of irrigation scheduling are cultural and not strongly related to technical feasibility.
Still, when asked in an extensive 1990 survey, the most strongly preferred water saving management practice indicated by High Plains irrigators was irrigation scheduling with over 53% willing to adopt this practice voluntarily.
They also found little to no differences in acceptance in north to south counties within the High Plains.
This survey suggests that irrigators are willing to consider using irrigation scheduling.
Additionally, irrigators, economists, and water planners often want to simplify the question of "How much irrigation water do I need?" to a single annual value when in reality there is no single answer.
Furthermore, as indicated in figure 2, averaging several years of data will result in a smooth yield/irrigation response curve that has very little basis for obtaining good yields in a given year.
Fortunately, with science-based irrigation scheduling, irrigators do not need to use average values.
On the deep silt loam soils of western Kansas, ET-based water budget irrigation scheduling is often an easy and acceptable method.
In demonstration projects in South Central Kansas, ET-based irrigation scheduling calculated from weather data was tested against ET data from atmometers .
The irrigators soon developed confidence in the weather station values that matched the field atmometer readings, and they recognized that weather station values were much easier to obtain than traveling to the field and reading the atmometer.
The Kansas USDA-NRCS officially adopted KanSched, developed at Kansas State University, as an approved ET-based irrigation scheduling program  and has offered cost
 Figure 2.
Corn yield response to subsurface drip irrigation  amount in seven different years, KSU Northwest Research-Extension Center, Colby, Kansas.
The boldface curve is the average of all seven years emphasizing that average values are insufficient for irrigation management in an individual season.
All years were scheduled according to daily ET-based water budget with individual data points representing differences in available irrigation capacity.
share incentives to encourage irrigator adoption of ETbased scheduling and have required adoption as an eligibility requirement for other irrigation improvement cost-share programs.
Since 1997, approximately 730 contracts have been issued in Kansas.
Similar programs exist in other parts of the U.S.
Great Plains.
Many irrigators have been unwilling to set aside much time to manage water.
They often feel that if their irrigation capacity is appreciably less than crop water needs, they need to operate their irrigation systems continuously during the growing season.
Although, there are a large number of marginal capacity irrigation systems in the region, opportunities remain to delay unnecessary irrigations by using ET-based irrigation scheduling.
The possible savings attributable to adoption of ET-based scheduling can be estimated from simulation modeling, SO the goal of this article is to more fully quantify these savings for irrigators.
The study was conducted in northwest Kansas, a semiarid region with summer pattern rainfall and deep silt loam soils.
Argiustolls-Haplustolls soils are typical to the region and are well drained and have good available soil water holding capacities of approximately 180 mm/m of profile.
Annual rainfall at the location averages 481 mm with 374 mm of that occurring during the April through September period.
Weather data from 1972 through 2014  for Colby, Kansas , collected at the Kansas State University Northwest Research-Extension Center, was used to simulate annual ET-based irrigation scheduling water budgets for corn  production.
Briefly, the water budget model schedules a
 25.4 mm irrigation event when two criteria are met.
The first criterion was that there is at least 22% depletion of plant available water in the 1.5 m profile to allow storage of the irrigation event plus retaining some additional room for storage of precipitation.
The 22% depletion is equivalent to approximately 80 mm of soil water storage.
The second criterion is that there was sufficient irrigation capacity to conduct the event on that date.
Irrigation capacities of 25.4 mm for 4, 5, 6, and 8 days were simulated at application efficiencies of 95% and 80% representing a typical range of efficiencies for center pivot sprinklers in the region.
An irrigation capacity of 25.4 mm/4 days will typically approximate full irrigation on the deep silt loams and for the climatic conditions of this region.
The irrigation season was constrained to the 90-day period, 5 June through 2 September in all years which approximates the typical season for most irrigators in the region.
This results in potential maximum seasonal gross irrigation applications of 584, 457, 381, and 305 mm for the irrigation capacities of 25.4 mm for 4, 5, 6, or 8 days, respectively.
The irrigation scheduling water budget used in the simulations can be simplified to the following equation: Sc=Sp+P+I-R-F-ET 
 where Sc and Sp are the plant available soil water amounts in the soil profile on the current and preceding days, ET is daily crop evapotranspiration, R is irrigation runoff, P is effective precipitation, I is the irrigation water applied, and F is flux across the lower boundary of the control volume , all in any consistent unit of length.
Runoff was assumed to be controlled to negligible amounts by surface storage management with the exception of large rainfall events which were capped at a maximum infiltrated amount.
Complete details of the model and the specific parameters used in the simulations are described in Lamm et al..
Additionally, two initial soil water conditions at corn emergence were simulated, a wetter 85% of field capacity for the 1.5 m soil profile and a drier 60% of field capacity.
Irrigators in the region are typically leaving soil profiles at 60% of field capacity or greater after corn harvest even in severe drought years.
Overwinter and spring precipitation would typically increase the soil water reserves before emergence of the corn.
Irrigation savings were calculated daily and accumulated throughout the season as the difference between full applications of the gross irrigation amount possible at a given capacity minus the gross irrigation amount predicted in the ET-based irrigation scheduling water budget for the same capacity.
The probability of needing a given amount of irrigation was computed using a normal distribution for the mean and standard deviation values of the 43 years.
It should be reiterated that the model assumed two criteria must be satisfied before an irrigation event would be scheduled: 1) specified soil water depletion or greater is
 reached; and 2) irrigation capacity is sufficient to cycle the event on that day.
These constraints would describe practical operating procedures for the irrigator, avoiding irrigation when the soil profile is reasonably full and scheduling only events when they could possibly be accomplished.
Therefore, some of the marginal irrigation capacities examined here will not be sufficient during the greater water use periods towards the critical growth periods and crop yields would be reduced.
However, conducting additional irrigation events water earlier in the season onto soil profiles with little or no depletion is inefficient and should be avoided.
Irrigation capacity had a great effect on the amount of irrigation that could be saved as would be anticipated.
On average, the irrigation capacity of 25.4 mm/4 days had the potential of saving approximately 3 to 5 times more irrigation with ET-based irrigation scheduling than with the lowest 25.4 mm/8 day capacity for the range of application efficiencies and initial soil water scenarios evaluated.
A greater portion of these savings for the greater capacities occurred during the early part of the irrigation season, as indicated by the increased slope on this portion of the curves , when irrigation capacity and increased chances for precipitation greatly exceed corn evapotranspiration.
After that period, irrigation water savings are incrementally increased as the season progresses, increasing during cooler, more humid periods and decreasing during warmer and drier periods with a saw-tooth pattern as irrigation events occur.
This emphasizes the need to use season long day-to-day irrigation scheduling.
Greater irrigation system application efficiency  increases the possibility for saving irrigation with ET-based irrigation scheduling.
Potential irrigation savings for the 95% application efficiency compared to 80% at the 85% of field capacity initial soil water condition ranged from 6% for the 25.4 mm/8 day irrigation capacity  to 20% for the 25.4 mm/4 day irrigation
 Figure 3.
Average savings of irrigation that could be obtained with ET-based irrigation scheduling as compared to maximum seasonal applications possible with various irrigation capacities for an application efficiency of 95% and an initial soil water condition of 85% of field capacity as determined in simulation modeling for 43 years of weather data, Colby, Kansas.
Table 1.
Calculated seasonal gross irrigation amounts  using ET-based irrigation scheduling for corn for the 90 day period June 2 September) at various irrigation capacities using 43 years  of actual weather data from KSU Northwest ResearchExtension Center, Colby, Kansas as affected by initial profile soil water conditions and sprinkler application efficiency.
Potential	Actual	Actual	75% Probability of	50% Probability of	25% Probability of
 Irrigation	Maximum	Maximum	Minimum	Needing to Apply	Needing to Apply	Needing to Apply
 Capacity	Application	Application	Application	Less Than	Less Than	Less Than
 Initial Profile Soil Water Condition, 85% of Field Capacity and sprinkler Application Efficiency of 95%
 25.4 mm/4 d	584	508	152	431	372	313
 25.4 mm/5 d	457	432	152	379	333	287
 25.4 mm/6 d	381	356	152	327	294	261
 25.4 mm/8 d	305	279	127	257	234	211
 Initial Profile Soil Water Condition, 85% of Field Capacity and Sprinkler Application Efficiency of 80%
 25.4 mm/4 d	584	533	178	465	408	350
 25.4 mm/5 d	457	457	152	392	350	309
 25.4 mm/6 d	381	381	152	340	307	274
 25.4 mm/8 d	305	305	152	260	238	216
 Initial Profile Soil Water Condition, 60% of Field Capacity and Sprinkler Application Efficiency of 95%
 25.4 mm/4 d	584	584	178	500	430	360
 25.4 mm/5 d	457	457	203	432	385	337
 25.4 mm/6 d	381	381	229	374	345	316
 25.4 mm/8 d	305	305	178	302	280	258
 Initial Profile Soil Water Condition, 60% of Field Capacity and Sprinkler Application Efficiency of 80%
 25.4 mm/4 d	584	584	254	547	487	427
 25.4 mm/5 d	457	457	254	453	416	379
 25.4 mm/6 d	381	381	254	380	356	331
 25.4 mm/8 d	305	305	203	305	286	267
 [a] Sprinkler irrigation events were gross 25.4 mm applications.
[b] The 50% probability amount is equivalent to the actual average application due to the fact that a normal distribution was assumed in calculation of the probability.
capacity  emphasizing the importance of increasing application efficiency whenever it is economically and technically practical to do SO.
The effect of increasing Ea from 80% to 95% for the drier initial soil water condition  was even greater, ranging from 31% to 58% across the range of irrigation capacities evaluated.
This increase occurs because the drier initial soil water condition results in greater irrigation needs during the season.
Greater initial soil water greatly increased the potential savings that could be obtained with adoption of ET-based irrigation scheduling  because of the opportunity to avoid some early season irrigation events
 with the greater soil water reserves at a time when evapotranspiration is reduced and chances for appreciable precipitation are greater.
When the initial soil water condition is only 60% of field capacity and the irrigation capacity is restricted to only 25.4 mm/8 days, then the average potential irrigation savings is essentially just one 25.4 mm event.
However, when considering the range of 43 years examined there was one year where over 102 mm could have been saved even with this severely restricted scenario.
Considering the fact that most of the marginal system capacities are also related to groundwater wells with reduced and declining saturated thicknesses, saving any water in these restricted scenarios may extend the longevity
 Figure 4.
Average savings of irrigation that could be obtained with ET-based irrigation scheduling as compared to maximum seasonal applications possible as affected by sprinkler application efficiency, Ea, for an initial soil water condition of 85% of field capacity for irrigation capacities of 25.4 mm every 4 or 8 days as determined in simulation modeling for 43 years of weather data, Colby, Kansas.
Figure 5.
Average savings of irrigation that could be obtained with ET-based irrigation scheduling as compared to maximum seasonal applications possible with initial soil water conditions of 85% and 60% of field capacity for irrigation capacities of 25.4 mm every 4 or 8 days for an application efficiency of 95% as determined in simulation modeling for 43 years of weather data, Colby, Kansas.
of irrigation for those wells.
Additionally, one nearby area in Kansas has converted their fixed water application water rights to flexible 5-year accounts, where water saved in one year might be utilized in a subsequent more water-stressed year.
Considerable water savings are possible when ET-based irrigation scheduling is adopted for marginal capacity irrigation systems.
Although these potential savings are increased for greater irrigation capacity systems, for systems with greater application efficiencies and for situations where initial soil water conditions are wetter, there are potential savings even under very restricted scenarios.
The importance of science-based irrigation scheduling should not be discounted by irrigators just because they typically are operating in a deficit condition.
Consistent, season-long use of science-based irrigation scheduling, such as the ET-based water budgets used in this study, can point out the opportunities and timing of when irrigation systems can be temporarily shut off.
Contribution no.
15-209-J from the Kansas Agricultural Experiment Station, Kansas State University, Manhattan, Kansas.
LIMITED IRRIGATION OF GRAIN SORGHUM
 Grain sorghum yield under full and limited irrigation was evaluated at three locations in western Kansas.
The top-end yield under full irrigation was about 190 bu/ac measured at Tribune in 2015 and Colby in 2017.
In 2015, there were no significant differences among irrigation treatments at any of the three locations due to the above normal rainfall.
In 2016, the fully irrigated treatment  was not significantly different from deficit irrigated treatments at Tribune and Colby.
However, dryland yields were lower than irrigated grain sorghum yields at Colby and most irrigated treatments at Garden City.
In 2017, there were no significant differences in yields among any treatment at any location.
These results also indicate that there is potential to improve grain sorghum yields and that management that constrains irrigation to replenish only 50% ET prior to boot can enhance water productivity.
There were no substantial differences in yield between irrigation management limited to 6 and 10 inches of water per season in a normal to wet years, which makes grain sorghum a suitable crop choice for limited irrigation.
Grain sorghum is one of the major irrigated crops in Kansas.
Irrigators are faced with the problem of declining well capacities due to water withdrawals from the Ogallala aquifer for irrigation exceeding mean annual recharge.
In addition to limited well capacities, public policy may also impose limits on total amounts of water that can be pumped.
For examples, a Local Enhanced Management Area  policy in a portion of Groundwater Management District  4 with a 20% reduction in pumped water and several Water Conservation Areas  that have been implemented in GMD 3.
The drought tolerance attributes of grain sorghum make it a good choice for limited irrigation.
However, grain sorghum irrigated area lags those of other irrigated crops in Kansas mainly corn and soybean.
One of the major challenges facing irrigated grain sorghum producers in Kansas is how to increase yields under declining well capacities or limited water supplies.
To develop limited irrigation management strategies for grain sorghum, we evaluated yield response under well-watered conditions as well as under very limited water supplies.
The purpose of the study was to 1) determine the top-end grain sorghum yield potential under well-watered conditions  at three locations in western Kansas  and 2) the effect of growth stage based irrigation timing on grain sorghum yields, water productivity and yield components with water supplies limited to 6 or 10 inches total.
The study was conducted at three locations in western Kansas including; 1) the Kansas State University, Southwest Research-Extension Center  near Garden City, 2) SWREC, near Tribune and 3) the Northwest Research-Extension Center , near Colby.
The soil type at Tribune and Garden City is Ulysses silt loam while that at Colby is a Keith silt loam.
The climate at the three locations is semi-arid with mean annual rainfall of 17, 18, and 19 inches for Tribune, Garden City, and Colby respectively.
Cumulative rainfall and reference evapotranspiration during the 2015 2017 growing seasons at each location are shown in Figures 1-3.
The experimental design was a randomized complete block design with four replications at each location.
Factors When Considering an Agricultural Drainage System
 Zachary M.
Easton, Associate Professor and Extension Specialist, Biological Systems Engineering, Virginia Tech Emily Bock, Graduate Research Assistant, Biological Systems Engineering, Virginia Tech Amy S.
Collick, Research Assistant Professor, Agriculture, Food, and Resource Sciences, University of Maryland-Eastern Shore
 Drainage of excess soil water is essential to sustainable agronomic production on many soils in the Mid-Atlantic region.
Drainage can improve crop yields, reduce year-to-year yield variability, and provide trafficable conditions for field operations at critical times of planting or harvest.
Drainage system design and management can impact crop production and have environmental consequences.
This fact sheet presents the benefits and potential consequences of artificially draining agricultural land, the steps to follow when considering a drainage system, and some aspects of proper drainage system operation and management.
Improving drainage of agricultural fields can be achieved by three primary means:  installing subsurface, artificial "tile"  drains at some depth below the soil surface;  surface ditching; and/or  land shaping.
Both the subsurface tile drainage and ditch-type systems function to lower the water table in the soil below the crop's root zone, while land shaping prevents water ponding on soils with very low infiltration capacity by building a crown or convex surface to direct surface flow from the field.
These practices are usually used in combination; tile lines and/or surface-shaped fields need to drain to a ditch.
Selection of a drainage system depends in part on the drainage problem that exists and the particular soil characteristics causing the problem.
Table 1.
Common drainage problems, the soil characteristics associated with the problem, and the potential drainage solution.
Soil frequently	Poorly drained	Ditch or tile
 Low infiltration	Clay or	Land shaping
 rate	compacted soils	with ditches
 Shallow	Layer of low	Ditches or tile
 impeding soil	permeability	with surface
 *Surface inlets are usually standpipes or stone backfill that provides a means to attach a subsurface tile to the soil surface to drain ponded surface water.
Lowering the water table has several crop production benefits:
 1.
Drainage removes excess soil water in the root zone, allowing for improved soil aeration.
Prolonged exposure to saturated conditions and poor soil aeration can stress the crop, reducing yield.
2.
Drainage can improve field trafficability, allowing more reliable field access while reducing compaction.
Drier soils are less susceptible to compaction than wetter soils.
3.
Drainage enables crops to establish deeper root systems in fields without impeding or compacted layers , allowing them greater access to nutrients and soil water.
Figure 1.
Poor aeration and shallow root systems  can be alleviated through drainage , which improves aeration and allows for deeper rooting.
4.
Drainage can reduce the year-to-year variability in yields from poorly drained fields.
Drainage can increase nitrification  in most soils, providing more nitrate for plant uptake.
5.
Removing excess soil water with drainage can help the soil warm up faster in the spring, allowing for earlier planting.
6.
Subsurface drainage can help reduce surface erosion and surface runoff.
Drainage can also have negative consequences:
 1.
Drainage can increase the loss of nitrates, phosphates, and other chemicals that move easily through soil with drainage water.
These soluble constituents can negatively impact downstream water bodies.
For instance, agricultural drainage is associated with increased eutrophication or algal growth caused by nitrate export from drained fields.
This is because drainage increases nitrification and reduces the opportunity for nitrate to be used by crops or soil microorganisms by removing soil water from a field more quickly.
2.
Drainage alters the hydrology of a field.
In undrained systems, the soil acts as a sponge to store water, providing it is not already saturated, and releases it slowly to adjacent streams or water bodies.
Subsurface drainage can also enhance the
 sponge effect by lowering the water table, which allows more water to infiltrate during a storm event.
However, drainage systems are designed to shortcircuit the natural flow paths and lower the water table more quickly, directly transferring the water to adjacent streams or water bodies.
Surface drainage systems can increase the flashiness of the system , causing greater high flows  and smaller low flows.
This increase in peak flows can worsen erosion in receiving streams and pollutant delivery to water bodies, while lower baseflows can harm fish and aquatic organisms that rely on adequate flow to survive.
3.
Drainage systems  have contributed significantly to wetland loss in the United States.
Hydrological modifications do not mean that wetlands are explicitly or purposely drained, but rather that alterations to water tables resulting from drainage can change adjacent wetland hydrology and function.
4.
Surface ditches and land shaping can increase erosion and surface runoff.
Figure 2.
Tile outlet discharge causing water quality problems  in receiving water body.
Drainage System Planning Considerations
 There are many factors to consider when deciding whether or not to install a drainage system.
Several factors that should be considered by anyone thinking about drainage are discussed in this publication.
Local, State, and Federal Regulations
 Because there are many regulations that govern artificial drainage systems, it is critical that landowners  understand all the applicable laws.
The first step of any drainage project should include meetings with the Soil and Water Conservation District, the Natural Resources Conservation Service, and local watershed organizations, as appropriate, to determine what is required.
This should be done well in advance of the intended installation.
Typically, agricultural producers must file Form AD-1026 with their U.S.
Department of Agriculture Farm Service Agency to ensure there will be no loss of USDA program benefits.
This initiates a soils evaluation by NRCS to determine if wetlands could be impacted.
Easements and Rights of Way
 An easement is the right to use the land of one person for a specific purpose to benefit another's interests.
In drainage, this equates to the right  of an upstream landowner to discharge drainage water to a downstream landowner.
Natural drainage from an upstream property is an inherent right; that is, a downstream landowner cannot adversely affect this drainage by blocking or otherwise altering the upstream drainage patterns.
Before the natural drainage patterns are altered by a drainage system, landowners may need to acquire an easement from the downstream landowner to discharge the resulting altered flow.
Drainage associations or drainage districts manage many drainage systems, particularly large ditch and tile networks.
Because these systems encompass large areas, there are generally easements or rights of way required to modify natural channels and to convey the water from the drained area.
Landowners thinking about installing a drainage system should first consult with the appropriate legal or regulatory authorities.
A good place to start planning or to get more information is to contact the local Soil and Water Conservation District or the NRCS.
Detailed information about specific soil properties  must be known to properly design and manage a drainage system.
For example, clay soils generally conduct water much more slowly than
 Figure 3.
Effect of depth to restricting layer on drainage spacing.
A drainage system installed in fields with shallow restricting layers in the soil needs to be spaced more closely together  and/or closer to the soil surface than a drainage system installed in fields with a deep restricting layer in order to achieve the same water table level.
This is because the shallow restricting layer prevents soil water from reaching the tile via deeper flow paths.
This can increase the cost of system installation or reduce the system effectiveness.
sand; thus, to adequately drain water from a clay soil, a surface system could be needed and tile drains will have to be spaced more closely.
This will make installation more expensive.
For sandy soils, which are more permeable, both surface ditches and tile drains can be spaced farther apart.
Soil depth is another important consideration; there must be adequate soil depth 3 to 5 feet is generally recommended to install a tile drainage system.
In shallow soils, surface systems can be used, and tile drains must be installed more closely together or closer to the soil surface to adequately lower the water table.
The shallow restricting layer reduces the amount of water that a drain can intercept because it cuts off the deeper flow paths that water can follow to the drain.
Again, this makes installation more expensive.
Subsurface drains should also be deep enough to provide protection against tillage operations, equipment loading, and frost.
All subsurface drains in mineral soils should have at least 2 feet of soil cover over the drain to protect them against overloading from heavy machinery; organic soils should have at least 2.5 feet.
Another important consideration in system design is the drainage coefficient, which is the design capacity of a drainage system.
The drainage coefficient is also defined as the desired water removal rate to support crop development and growth, and it depends on soil and crop type.
The drainage coefficient is a measure of the amount of water  that needs to be drained from a soil in 24 hours.
In the system design, the drainage coefficient will affect the spacing or the diameter of the tiles in a field.
Table.
2.
Drainage coefficients.
Soil type	Field crops*	Row crops*
 Organic	1/2-3/4	3/4-1 1/2
 *Field crops include crops such as hay or grain; row crops are crops such as corn or soybean.
+Organic soils contain a minimum of 20% organic matter and are called Histosols.
Mineral-based soils have low organic matter content, generally less than 10%, and are composed of primary  or secondary  minerals.
A properly designed drainage system will remove excess water from the root zone 24 to 48 hours after a heavy rain.
NRCS guidelines consider additional factors when determining the desired drainage coefficient for a given drainage system and recommend that the drainage coefficient be increased if any of the following situations are encountered:
 The crop has high value.
Soils have a coarse texture.
Crops cannot tolerate wetness.
The topography is flat.
Crop residue is left on the soil surface.
There is poor surface drainage.
Crop evapotranspiration is low.
Frequent and low-intensity precipitation is common.
Field access times are critical.
Compacted soils or those with high clay content can result in low infiltration rates and water ponding in surface depressions.
In these situations, land shaping or strategic placement of surface inlets could be an appropriate drainage option.
In contrast, some fine, sandy soils and silty soils have insufficient colloidal material to hold the soil particles together.
This can cause excessive movement of soil particles into subsurface drains.
Special precautions, such as gravel filters or synthetic drainage envelopes, are often required to prevent drain clogging.
The location of the drainage system outlet is an important consideration and should be determined before any design begins.
Drains may discharge by gravity into natural streams or water bodies, constructed open ditches, or larger underground drainage mains.
Any of these outlets are suitable if they are deep enough and of sufficient capacity to convey water from the entire drainage system.
Drainage system outlets should generally be located 3 to 5 feet below the soil surface.
Where a gravity outlet is not available, pumping can be
 considered.
Note that installing and maintaining a pump system adds considerable expense to any drainage system.
Additional information on system outlets and outlet design can be found in the chapter on drainage in the NRCS "National Engineering Handbook".
The ultimate goal of a drainage system is to provide uniform drainage across a field, thereby reducing yield variability.
Thus, consideration of the field topography  must be considered in any system design.
Topography influences water movement and drainage within a field.
Steeper field slopes allow excess water to move laterally downslope in the soil, draining more rapidly than flatter fields.
Fields with steep slopes tend to require less drainage  than flatter fields.
Localized wet spots can form where hill slopes converge, presenting unique challenges for drainage system design because these areas will require more drainage than other field areas.
A topographic analysis can help identify potential problem spots.
In more hilly terrain, topography can influence soil depth and soil physical characteristics such as permeability, texture, and water-holding capacity all of which influence drainage system design.
Topography also influences where the outlet can be located.
An outlet should be hydraulically down
 gradient of the system it drains; otherwise pumping will be required.
Finally, topography affects what type of system is most practical.
There are two common ways that subsurface drainage systems are installed.
First, when drainage is consistently restricted across the field, the more complete and beneficial approach is to pattern drain an entire field at regular intervals.
Pattern drain spacing varies by soil type, depth, and topography, but installations of 50 to 150 feet for both ditches and subsurface drains are common in the Mid-Atlantic region.
In pattern drainage systems, it is important that the tile lateral drains and/or field ditches are aligned parallel to the field slope contours.
Tiles or ditches that are aligned across slope contours especially where slopes exceed 5 percent will not intercept much groundwater and will fail to adequately drain a field.
The second approach is placing random tile lines or ditches to drain a specific wet area in a field, also called a targeted approach.
This approach is appropriate when the rest of the field is reasonably well-drained but has local wet spots.
Land shaping might also be appropriate to alleviate specific wet areas in the field when ponding is due to lowinfiltration soils rather than a perched water table.
Another option in fields that have limited surface drainage due to low-infiltration soils is to use a blind or surface inlet.
Figure 4.
Various drainage system layouts.
A, The herringbone system consists of parallel tile laterals that enter the main drain at an angle.
This system is used for long, narrow areas with steeper slopes.
B, The parallel system is similar to the herringbone system except that the laterals enter the main from only one side.
This system is used on flat, uniform, and regularly shaped fields with consistent soil types.
C, The double-main system is used where a landscape feature such as a stream or ditch divides the field.
D, A random system is used where the field contains isolated saturated areas.
The economic benefit of a drainage system depends on several factors, including the crops being grown, the drainage intensity, whether financing is required, and the potential yield improvements from drainage.
As a rough guideline, the cost of a subsurface drainage installation is about $1 per foot of tile, with the actual price determined by the tile spacing, the method of installation, and whether or not difficult excavation conditions are expected.
Intensive tile installation can cost $800 to $1,000 per acre or more.
Subsurface tile systems are generally more expensive to install than surface ditches due to specialized equipment needed for installation , but they can be more economical because a subsurface tile system does not remove land from production like a surface ditch system does.
While land shaping is the least expensive option and also does not remove land from production, this strategy only reduces surface ponding and does not remedy the effects of a perched water table or saturated, poorly drained soil.
Some questions that anyone considering a drainage system should ask include
 What is the potential yield improvement?
What is the NRCS soil-specific optimum yield value?
What is the yield of similarly managed well-drained soils?
What is the yield in an optimum weather year?
What is the benefit of improved trafficability on field operations and yield?
Is drainage truly the yield limiter?
Is drainage a problem on a regular basis?
Across an entire field?
Or will targeted drainage achieve the same response?
Is there a benefit to installing all the drainage at once?
How does drainage cost compare to the cost of other strategies ?
Cropping strategies are important to consider because  they can change the economic payback period of any drainage system; higher yielding or higher value crops will benefit more from drainage than lower yielding, lower value crops.
Cropping strategies also influence factors such as drainage depth or drainage spacing.
Crops that are intolerant of saturated conditions might require greater drainage intensity than crops that can tolerate wet conditions for longer periods.
Deep-rooted crops could require drains to be installed at a greater depth than shallow-rooted crops.
If planting, harvesting, or field management operation timing are critical for specific crops to ensure adequate yield, this needs to be considered in the system design.
Like any system, drainage systems require maintenance to perform correctly.
The maintenance required depends on the drainage system type; tile and ditch systems have different maintenance needs.
Developing a drainage system management plan is a good first step to ensuring that a drainage system continues to function correctly.
Any drainage system management plan should include good documentation maps of the location of ditches, outlets, and buried tile and should begin with periodic inspections of the system.
Ditch systems should be inspected regularly for any obstructions or impedance to flow in the ditch, bed erosion, or bank failures.
Obstructions should be removed as they are encountered, and any bed erosion or bank failures should be repaired and comply with design standards.
Also, any junctions where two or more ditches meet should be inspected for erosion or scour and fixed as appropriate.
Vegetation can grow rapidly in ditches, which reduces the ability of the ditch to convey water.
Mowing the bottoms of ditches is more effective than mowing the sides for water conveyance.
Similarly, ditches can fill in with sediment from surrounding fields or upslope contributing areas, further reducing conveyance capacity.
A ditch management plan should include vegetation and sediment control measures.
Vegetation can be controlled by mowing, pasturing of livestock, burning,
 applying chemicals, or mechanical removal , although pasturing of livestock can cause bank stability problems and using chemicals can increase off-site contamination.
Sediment control usually involves periodic "dip-outs"  of sediments that have accumulated in the ditch.
Grade stabilization of ditch bottoms and sides is important as well.
Over time, the ditch sidewalls, in particular, can change their slope, especially in sandier noncohesive soils, which affects the hydraulic function of the ditch.
Grade stabilization should be employed periodically to ensure the ditch maintains its design capacity.
Tile systems and outlets should be inspected regularly as well.
Given that these systems are underground and more difficult to visually inspect, one of the best times to assess system function is during periods of high drain flow.
Verify that all tile outlets are flowing freely and that the flow is sediment-free.
Sediment in the tile flow could indicate a failure in the tile system in the field.
Any debris encountered at the outlets should be removed; a submerged tile outlet  can cause back pressure in the tile system and lead to blowouts.
Walk the field in which the tiles are installed and make sure there are no blowouts, sinkholes, or animal burrows that could allow sediment or surface contamination to enter the tile system; repair them as necessary.
Wet spots in new locations could be an indication of a clogged or damaged tile, and careful excavation and repair could be required.
Crop growth is also a good indicator of a well-functioning tile system in which the field should dry evenly and produce similar yields.
Changes in yield in different areas of the field could indicate a problem with the system.
While drainage has clear benefits to crop production, there are also several negative environmental consequences of drainage.
Because conventional drainage management emphasizes the export of water rather than the prudent management of local water tables generally resulting in excessive drainage there is the possibility of excessive nutrient export from tile-drained fields.
In addition, routine ditch management practices, including scraping and vegetation management, can minimize the internal
 cycling of nutrients in ditch vegetation and destabilize ditch walls, resulting in erosion and water quality concerns.
Some drainage best management practices to reduce off-site losses of undesirable contaminants into receiving waters begin with implementing good nutrient and pesticide management to reduce nutrient or herbicide losses from the plant root zone, using winter cover crops to sequester nutrients and reduce erosion, and rotating row crops with perennials in the cropping system.
Additional best management practices specific to the drainage system include
 1.
Avoid excessive drainage or store and recycle drainage water.
Drain only what is needed to benefit the crop.
Excessive drainage could remove valuable nutrients that would otherwise be used by crops and can lead to greater nutrient losses to waterways.
Storing and recycling drainage water can be advantageous when droughty conditions occur at other times of the growing season and water is needed for irrigation purposes.
3.
Use water table management or the control of the water table by backing up the water in a tile or ditch system by mechanical means to improve water quality.
By increasing drainage water residence time in a field, more nutrients can be removed and used by crops or adsorbed to soil particles.
Water table management  can also improve crop water use, reducing drought stress and increasing yields.
Care must be
 Drainage control unit in controlled drainage mode
 Figure 5.
Example of how a drainage control unit can be used to adjust the water table in a field.
If the stoplogs are removed from the drainage control unit, the drainage system is free-draining, and the water table falls to the level of the tiles.
When the stoplogs in the drainage control unit are in place, water is backed up into the drainage system, raising the water table in the field to the level of the stoplogs.
Note that the same effects are possible in ditch-drained systems.
Figure 6.
Controlled drainage retrofit on a tile system  and a ditch system.
taken to maintain the water table at a level that does not harm crops.
An optimal use of controlled drainage is to close the drain during the winter months to prevent nutrient loss and then open it prior to planting to drain the soil.
Water table management is often an easy and low-cost retrofit to existing tile or ditch systems.
4.
Provide reliable and effective drainage with a welldesigned and well-engineered drainage system.
Shortcuts in the design can lead to severe erosion in and around the drainage system, excessive loss of productive land, and export of valuable fertile soil to adjacent water bodies where it can be problematic.
5.
Follow the drainage management plan to ensure sound management of the drainage system and productive cropping in drained fields.
Drainage in the Mid-Atlantic region can improve crop yields and reduce year-to-year variability in those yields by removing excess soil water.
Mismanagement of drainage systems or drainage discharge has environmental consequences as well.
Producers should consider the costs, benefits, and consequences of adopting a drainage system before installation.
This publication has provided the steps to follow when considering a drainage system and some management considerations of drainage system operation.
USDA Natural Resources Conservation Service.
Related Virginia Cooperative Extension Publications
in South and South Central Texas
 Charles Stichler and Guy Fipps*
 ATER IS ALL we sell in agriculture." Whether the enterprise is corn, cattle, cauliflower, cotton, or grain sorghum, water is essential for its production and the single most important aspect of production that determines yield.
Grain sorghum is a tropically adapted plant that can survive under drought and adverse conditions.
Because of its ability to survive in unfavorable conditions, sorghum is often relegated to poor soils and poor management.
However, to be profitable, a sorghum crop needs sufficient water at critical points in its development.
Therefore it is vital that growers manage irrigation properly.
If grain sorghum is managed well, it will produce profitable, high yields.
Like other grains, the ultimate purpose of a sorghum plant is to produce seeds.
Seed production is a singular event the plant's root, leaf and stem development are all directed toward this outcome.
Because yield is determined by both the number and weight of seeds, it is vital for growers to understand the plant processes that affect seed development.
One such process is photosynthesis, in which green plant tissues take carbon dioxide from the air, water and nutrients from the soil and energy from sunlight and convert them into sugars or carbohydrates.
The products of photosynthesis are also called photosynthates.
The more active, functioning leaves a plant has, the more photosynthates it will produce, and thus the greater its yield potential.
To increase yield potential, growers need to take management steps that support leaf development, maximize photosynthesis and limit water loss.
A critical component of the photosynthesis process is water.
Water can be said to be part of a plant's circulatory system water moves throughout the plant, carrying with it plant minerals, nutrients and plant chemicals such as enzymes, proteins, sugars and carbohydrates.
Water evaporates from the leaf and is replaced with water from the soil in a process called transpiration.
A sorghum plant gets more than 75 percent of its water and nutrients from the top 3 feet of soil.
Plants can use about 50 percent of the total available water without undergoing stress.
Associate Professor and Extension Agronomist, and Professor and Extension Irrigation Engineer, The Texas A&M University System
 The availability of water is the key factor to consider when deciding on row spacing and plant population.
Moisture dictates yield goals, which in turn dictate seeding rates and spacing.
For irrigated production, growers should aim for between 70,000 and 80,000 established plants per acre; for dryland production, the total should be 50,000 to 60,000
 established plants per acre.
Yields will be reduced if the plants are too crowded.
The more plants that are established, the more water the crop will use.
If too many are planted, much of the soil moisture will be used before the reproductive stage begins, rendering the plants unable to produce seeds.
Research has been conducted at Texas Tech University on the amount of water per acre required by sorghum.
The studies have shown that sorghum at pre-bloom uses 8 to 10 inches of water per acre and that each additional inch will produce 385 to 400 pounds of grain.
For a grain yield of 7,000 pounds per acre, total water use from both soil and plant evaporation is about 28 inches of water per acre.
However, water use varies greatly in sorghum, depending on the final yield, the maturity of the hybrid, planting date and weather conditions.
For this reason, prior to planting, the soil profile should be filled to 24 inches deep if a grower desires a maximum yield.
Water needs at different growth stages
 Water needs for sorghum vary according to the different plant stages different amounts are used in the seedling development phase, the rapid growth and development stage, and the bloom to harvest phase.
Estimated Daily Water Use for Grain Sorghum
 Figure 1.
Water needs for sorghum rise sharply at the rapid growth stage, peak during the boot stage and then drop off afterward.
The seedling development stage begins at germination and ends at about 26 days after planting,
 when the plants have five to six mature  leaves.
This early-growth stage does not directly affect the number of seeds produced, but it does set the direction of development.
Although water management is not critical during the seedling development period, minor stress does affect future growth, plant size and yield potential.
During the seedling stage when the soil is not shaded, more moisture is lost through soil evaporation than by transpiration from leaves.
To minimize moisture losses from the soil, it is important that you adopt water-conserving practices, such as:
 Good weed control, and
 Proper planting date for rapid canopy establishment
 Rapid growth and early reproductive phase
 The need for water is extremely critical during the rapid growth stage and before the reproductive stage.
If the plants are water stressed during the rapid growth stage, it does not matter what steps a grower takes afterward the number of flowers has already been determined and yield will be reduced.
After seedling development, water needs begin to increase as the leaves enlarge and expand.
Because leaves are the part of the plant that collect energy from the sun, growers should adopt production practices  that encourage early leaf development.
About 40 days after planting, the total number of leaves has been determined and one-third of the total leaf area has developed.
During this period, the growing point changes from vegetative to reproductive, and the seed panicle begins to form inside the stalk.
During the next 30 to 35 days, the immature leaves continue to grow and the number of ovules that will develop into seed are formed until the flag leaf  emerges and the plant begins to boot.
The size of the panicle and number of seeds are determined between day 35 and 65 by adequate water, fertility and photosynthate production.
Root formation is completed and the panicle  is
 visible in the bottom of the plant inside the stalk.
The demand for water is extremely critical during this stage because the potential head size has already been determined before head exertion begins.
The goal is to limit moisture stress during the rapid growth phase so that a robust plant structure and full panicle have been produced.
Growers should not wait too long to irrigate, else production will suffer.
Water use will be about 0.2 to 0.3 inch per acre per day.
Up to bloom, sorghum will use about 8 to 10 inches and any moisture stress during this period will reduce the yield potential.
Bloom to harvest 
 In the next stage, the plant develops from bloom to physiological maturity, which is when the seeds are fully developed and no further weight is added.
This phase requires about 45 days to complete.
Sorghum blooms over a 5to 9-day period.
During this time, the proteins and photosynthates that are produced and stored in the leaves are moved into the developing grain.
During the period just before bloom and until early grain fill, sorghum will use about 0.35 inch of water per day, declining to 0.1 inch a day when the grain is dry.
Anything that reduces leaf function such as leaf loss, water or nutrient stress, or disease or insect damage will eventually reduce yield.
Growers should time the final irrigation to carry the crop from the last irrigation to black layer, or physiological maturity.
Any additional irrigation just before and after this point is wasted.
From physiological maturity until harvest, the crop is just drying down.
By harvest, the plant will have absorbed about 35 pounds of nitrogen and 11 pounds of phosphate for each 1,000 pounds of grain and stover produced.
After the initial 8 to 10 inches of water to reach bloom, each additional 1 inch of water will produce 350 to 425 pounds of grain, bringing the total to 28 inches of water for a 7,000pound yield.
Furrow irrigation is best timed according to the plants' stage of growth.
Furrow irrigation is not as exact as is sprinkler irrigation.
If furrow irrigation is managed well, most water applications will be about 3 to 4 inches per irrigation.
A good guide is to apply irrigations at key growth stages if there is no rain and additional soil moisture is needed:
 1.
If the soil profile is full at planting, the stored soil moisture should supply the water requirements until the first irrigation at the reproductive stage.
2.
The onset of the reproductive stage is 30 days after planting.
One 4-inch irrigation will last the 25 days until flag leaf.
3.
At flag leaf or boot stage, two 3-inch irrigations about 2 weeks apart will last until soft dough in the grain fill period.
4.
The last irrigation will maximize yield, but is generally not economical and does not pay for the water.
One 3or 4 inch-irrigation is needed at soft dough to complete grain fill, which takes about 45 days from bloom to reach black layer.
Using this schedule, the appropriate amount of irrigation water will be applied during each growing period if rainfall is not received.
If those amounts are totaled for the entire growing period, the amount need by the crop will approximate the following:
 6 8 inches rainfall or pre-irrigation to fill the soil profile if totally dry
 + 4 inches 30 days after planting
 + 6 inches in two 3-inch irrigations at flag leaf or boot stage
 + 3 inches at soft dough
 = 19 21 inches of total water
 The 19 to 21 inches is the amount of water needed to produce a crop without stress.
The total amount needed will vary somewhat, depending on weather conditions such as heat, low humidity, cloud cover and wind.
How much replacement water is needed?
The amount of water a crop uses is known as evapotranspiration , which is the water lost through a combination of two processes: evaporation, which is the water removed from the soil, and transpiration, which is the water removed from the plant leaves.
The amount  of water used by a crop in a day is called daily ET.
ET varies by weather conditions  and by plant characteristics (such as canopy
 closure).
Because it is related to the leaf surface area, smaller plants transpire less than do larger plants, and ET is lower.
Growers can minimize evaporation from the soil by:
 Spacing the plants equally in narrow rows.
Narrow-row crop production reduces the amount of bare soil, which loses more moisture through evaporation than do shady and mulched soil surfaces.
Leaving crop residues, which can reduce soil evaporation by 1 to 3 inches during the season.
Irrigation scheduling based on potential evapotranspiration
 Researchers have developed a simple way for growers to calculate the water requirements of their crops.
First, the water requirements of a standard plant were developed to use as a reference.
That plant's water requirements are referred to as PET.
Growers can now use PET to calculate the estimated water needs of their crops.
To determine the amount of water being used by their crop, growers multiply the PET by the crop coefficient  for the specific crop being grown and for that crop's growth stage.
For sorghum, the crop coefficients in the North High Plains are listed by stage of growth in Table 1.
Researchers at the Uvalde Research and Extension Center are working to determine the sorghum crop coefficients for South Texas.
Please note that the dates listed are provided only as a general guide, as crop growth rate is affected by many factors, including location, variety, current weather and soil moisture conditions.
How to Use PET
 To calculate the water requirements of your crop, multiply the PET by the crop coefficient using the following equation:
 PET X Kc = Crop water requirements
 PET is the sum of daily PET over the period of interest, such as the 3-day or weekly total.
Table 1.
Sorghum crop coefficients in the North High Plains.
Growth	Crop	Days After
 Stage1	Coefficient 	Planting
 Seeding	0.40	3 4
 Emergence	0.40	5 8
 3-leaf	0.55	19 24
 4-leaf	0.60	28 33
 5-leaf	0.70	32 37
 GPD	0.80	35 40
 Flag	0.95	52 58
 Boot	1.10	57 61
 Heading	1.10	60 65
 Flower	1.00	68 75
 Soft dough	0.95	85 95
 Hard dough	0.90	95 100
 Black layer	0.85	110 120
 Harvest	0.00	125 140
 1 Sorghum will bloom at different times, depending on location, planting date and maturity of the variety.
The days after planting are for a medium-early to medium-late variety.
Kc is the crop coefficient for the current stage of crop growth.
Example 1: The 5-day PET total is 1.32 inches.
Your sorghum is in the "heading" growth stage.
What are the water requirements?
1.32 inches X 1.10 = 1.45 inches
 Thus, to irrigate the sorghum adequately during this period, apply 1.45 inches to replace the water used by the sorghum in the past 5 days.
Adjusting for irrigation system efficiency
 If your irrigation system is inefficient, you may need to compensate for it by increasing the amount of water you irrigate.
See Table 2 for the typical efficiency ranges of on-farm irrigation systems.
To adjust for irrigation system efficiency, use the following equation:
 PET X Kc = Eff = Irrigation water requirements
 Eff is the overall efficiency of the irrigation system.
Example 2: You are irrigating with a low-pressure center pivot.
You estimate that your overall system efficiency is 85 percent.
What are the irrigation water requirements for the sorghum in Example 1?
1.32 inches X 1.10 = 0.85 = 1.71 inches
 You will need to irrigate 1.71 inches to meet the plants' water requirements for that period.
Table 2.
Typical overall on-farm efficiencies for various types of irrigation systems.
Land leveling and water	0.70 0.80
 volume per row meeting
 Surge	0.60 0.90 1
 Center Pivot	0.55 0.902
 1 Surge has been found to increase efficiencies 8 to 28% over non-surge furrow systems.
2 2Higher efficiencies are for low wind conditions.
STrickle systems are typically designed at 80 to 90% efficiency.
Adjusting for rainfall and soil moisture
 Rainfall reduces the amount of irrigation water needed to meet plant requirements.
However, not all rainfall can be used by plants and crops.
Some of the rainfall will be lost to evaporation from the top 2 to 3 inches of soil, runoff and deep percolation , depending on such factors as soil type and slope, soil moisture levels and the duration and intensity of rainfall.
In irrigation scheduling, the term effective rainfall refers to the part of the rainfall that can be used by
 plants the part that infiltrates into and is stored in the root zone.
Growers must estimate the effective rainfall for each field and for each rainfall.
Generally, do not record rainfall of less than 1/4 inch because it evaporates so quickly.
Then subtract the amount of effective rainfall from the irrigation requirement determined with Equation 1 or 2.
You may use soil moisture monitoring devices to determine soil moisture levels and the date to restart irrigations after rains.
For more information on this procedure, see Texas Cooperative Extension publications B-1670, Soil Moisture Management, and B-1610, Soil Moisture Monitoring
 Growers need to avoid these common mistakes affecting water usage:
 Waiting too long to put on the first irrigation.
The head begins to form about 35 days after planting.
If the plant is stressed during this period, the number of seeds per head will be reduced.
Irrigating too late.
Do not irrigate after the hard dough stage.
Also do not irrigate after the plants have reached physiological maturity, which is 45 days after flowering or at black layer.
After that point, the individual seed's "umbilical cord" is sealed off and stops functioning.
It will not gain any more weight after this event, which occurs at about 30 percent moisture.
Over-planting.
For irrigated production, do not exceed 70,000 to 80,000 established plants per acre; dryland production should not exceed 50,000 to 60,000 established plants per acre.
Over-planting reduces head size, increases the chance of charcoal rot and lodging, increases plant competition, and increases water use with little increase in yield.
Proper irrigation management is critical for profitable yields.
If you pay attention to timely and adequate irrigation, you can keep costs to a minimum while maximizing production.
Texas A&M AgriLife Extension Service
Dates, locations and registration information for 2023 face-to-face chemigation training sessions are listed online.
Please note that additional training sessions may be added to this list as time goes forward.
When selecting a training session from the list, be sure to check the rightmost column of the table for pre-registration instructions for each session.
Early general public registration runs through March 13 and is $400.
Regular registration runs to April 28, and is $500.
The 2023 Water for Food Global Conference is a regional event for the 10th World Water Forum, the worlds largest water-related forum organized by the World Water Council.
Early Season Alfalfa Irrigation: Early season irrigation may be delayed if there are limits for yearly irrigation amounts.
However, if soil profiles are currently very dry, spring irrigation should be considered, especially since first cutting alfalfa may be twice as productive as any subsequent cuttings.
For maximum season production, the first alfalfa cutting typically requires six to seven inches of water.
Since established alfalfa is a deep-rooted perennial, the risk of excess water running off fields is low.
Even if rainfall comes after early spring irrigation, the water will likely be stored in the soil profile for use later in the growing season when summer heat increases water demand.
Paved Feeding Areas and the Kentucky Agriculture Water Quality Plan
 Stephen Higgins and Sarah Wightman, Biosystems and Agricultural Engineering
 K entucky's abundant forage makes it well suited for grazing livestock.
Livestock producers can make additional profits by adding a few pounds before marketing calves; however, adding those pounds requires keeping calves during the winter months , when pasture forages are dormant and supplemental feed is required.
The areas used to winter calves need to be conducive to feeding and need to avoid negatively impacting the environment, especially water quality.
Some livestock producers use a paved feeding area to limit mud, ease manure removal, and facilitate feeding and management.
Typically, producers are interested in improving herd health, limiting expenses, and increasing profits, but environmental issues also need to be addressed to prevent degradation of natural resources and limit the possibility of nuisance complaints and notices of violation.
Best management practices  are particular management methods that consider the nutrients in manure; reduce runoff; and trap, filter, and control pollution.
This publication is intended to provide an overview of the impacts associated with paved feeding areas and highlight the Kentucky Agriculture Water Quality Plan  and the BMPs it recommends for livestock producers.
When densely stocked animals are fed concentrated diets and the area on which the animals are standing is impervious , the manure and dirty water that is produced will pollute runoff.
It needs to be managed.
The following sections describe the environmental impacts of paved feeding areas.
Figure 1.
Aerial view of a paved feeding area with soil test phosphorus levels of adjacent land.
First consider a pasture system.
One brood COW and her calf  require 2 acres, or about 5,800 sq ft for every 100 lb of animal.
Conversely, a feeding area has a stocking density of approximately 40 sq ft for every 100 lb of animal, which means that a feeding floor has a stocking density that is approximately 150 times greater than that of a pasture system.
Now consider the manure generated.
If a calf started at 400 lb and was marketed at 1,300 lb, the average animal weight is 850 lb.
An 850-lb animal produces approximately 60 lb of nitrogen and 35 lb of phosphorus, and feedstuffs commonly used for winter feeding such as distiller's grains, gluten meal, and mineral supplements can contain high concentrations of phosphorus, which can increase the amount of phosphorus produced by wintering livestock.
It is estimated that approximately 80% of the
 phosphorus consumed by an animal is excreted in the feces, and the majority of this phosphorus is contained in manure solids.
Assuming no nutrient losses during storage and application, that 850-lb animal produces enough nitrogen to fertilize about 1 acre of pasture and enough phosphorus to fertilize almost 6 acres.
If a producer applies the manure from a paved feeding area to a hayfield based on nitrogen requirements, about six times more phosphorus has been added than the crop needs.
If the producer continues this practice year after year, the phosphorus fertility in the soil will increase exponentially.
Once the soil particles are saturated with phosphorus, the phosphorus is free to move through the soil profile, possibly contaminating surface and groundwater.
Because phosphorus and pathogens can become attached to soil particles, any erosion could also move those pollutants off site and pollute surface waters.
Impervious area refers to concrete or other hardened surfaces on which animals are often fed.
About 95% of the rain that falls on these areas runs off  and carries with it the nutrients and pathogens produced by the animals.
If there is an adjoining barn that is used to provide shelter for the animals, it too can produce polluted runoff if the barn is not properly guttered.
A roof is also impervious and has a runoff coefficient of 95%.
Free-flowing polluted runoff has the ability to move off site and increase soil test phosphorus, as shown in Figure 1, for which soil samples were collected along the side of a production area where runoff occurs.
The soil test phosphorus data show high concentrations of phosphorus immediately adjacent to the production area and lower phosphorus levels farther from the production area.
If this production area was placed near a stream, it would be fairly easy for phosphorus and possibly other pollutants to pollute the stream.
Also consider the barn's roof.
If it was not guttered and downspouts did not redirect clean water away from the production area, more water would pour onto the impervious surface and increase movement of pollutants off site.
The Kentucky Agriculture Water Quality Act
 In order to protect water quality, the Kentucky Agriculture Water Quality Act  was passed in 1994.
It was written as a guide for reducing water quality impacts associated with agriculture and silviculture activities.
The main focus of the act is to protect surface and groundwater resources, primarily through the use of best management practices.
The Kentucky Agriculture Water Quality Plan  is a product of the act and is a statewide guide for developing individual water quality plans for use on individual farms.
All agriculture or silviculture operations on 10 or more contiguous acres of land have been required to have a fully implemented water quality plan since 2001.
Table 1.
Kentucky Agricultural Water Quality Plan paved feeding BMPs and
 Paved Feeding BMP	Number	Resources for Implementation
 Manure Management	Livestock #5
 Systems	The Agronomics of Manure Use for Crop
 Manure Storage Ponds	Livestock #6	Production 
 Manure Storage	Livestock #7	Managing Liquid Dairy Manure 
 Structures: Holding Tanks	Sampling Animal Manure 
 Potential for Livestock and Poultry Manure to
 Sediment or Solids	Livestock #9	Provide the Nutrients Removed by Crops and
 Separation Basins	Forages in Kentucky 
 Manure Storage	Livestock #10	Using Animal Manures as Nutrient Source
 Structures: Stack Pads	
 Nutrient Management	Livestock #11
 Filter Strips	Livestock #13	Vegetative Filter Strips for Livestock Facilities
 Stormwater Diversion	Livestock #18	Stormwater BMPs for Confined Livestock
 KAWQP Best Management Practices
 Because the polluted runoff from paved feeding areas can be SO significant, regulatory agencies require that the runoff be collected and stored until it can be land-applied and used as part of a nutrient management plan or comprehensive nutrient management plan.
Examples of liquid and solid storage structures are described below.
Other BMPs, such as stormwater diversion and filter strips, can help keep clean water clean and reduce the amount of pollution that makes it to surface water resources.
Livestock producers should implement at least one of the BMPs listed in Table 1 where paved feeding areas are used; however, trapping, controlling, and preventing pollution usually requires more than one.
Producers also must consider site-specific conditions when choosing and implementing any BMP.
Each of the BMPs listed in Table 1 can be used individually or in combination to protect the environment.
Livestock BMP #5: Manure Management Systems
 A manure management system is a planned system for managing liquid and solid manure in which all necessary components are installed in a manner that does not degrade soil or water resources.
Such systems are planned to preclude the discharge of pollutants to surface or groundwater and to recycle manure
 through soil and plants to the fullest extent possible.
A system may consist of a single component, such as diversion, or may consist of several components as part of a planned system.
Components of a complete manure management system may include, but are not limited to
 Grassed waterways or outlets
 Pond sealings or linings
 The overall system should include sufficient land for proper use or disposal of manure at locations, times, rates, and volumes that maintain desirable water, soil, plant, and other environmental conditions.
System components should be planned and installed in a sequence that ensures that each will function as intended without being hazardous to others or to the overall system.
Appropriate handling equipment should be available for effective operation of the system, and safety features and devices should be included, as appropriate, to protect animals and humans from drowning, dangerous gases, and other hazards.
Fencing should
 be provided to prevent livestock and others from using the facilities for other purposes.
Livestock BMP #6: Manure Storage Ponds
 A manure storage pond is a reservoir, pit, or pond made by excavation or earth fill for the temporary storage of liquid and/or solid livestock manures, wastewater, and/or other polluted runoff prior to land application.
Construction and proper management of a storage pond for animal manure allows it to be used more effectively for fertilizer and reduces degradation of water resources.
thereby increasing stream water quality and aquatic habitat.
It also concentrates labor requirements and allows spreading to occur during more favorable weather and crop application conditions.
A manure storage pond should be located out of the floodplain area, and soils, rock depth, topography, and underlying geology should be investigated for site suitability.
The pond should also be close to the manure source to reduce excess surface runoff water in the holding pond.
Sufficient land must be available for a disposal area without overloading soils or exceeding crop requirements.
The size of a manure storage pond should accommodate projected liquid and solid manures and surface runoff water  and take into account the planned frequency of pumping the pond.
Depth and shape are not critical as long as the design capacity is achieved.
Also consider future livestock expansion as well as the present number of livestock when determining pond size.
Manage the pond to avoid overflow, and adhere closely to the design and construction plan developed by a government or private engineer.
A permit is required.
Contact the county conservation district for local information.
Livestock BMP #7: Manure Storage Structures-Holding Tanks
 A holding tank is an essentially watertight structure made of concrete, concrete block, steel, fiberglass, or similar materials to temporarily store livestock liquid and slurry manure.
Holding tanks are an effective means of storing animal
 manure on site, reducing its access to streams, and decreasing organic material, thereby improving aquatic habitat and minimizing insect problems and manure odors.
The manure can be hauled and applied in a slurry form when soil conditions permit and it is most needed for crop production.
A holding tank should be located out of the floodplain area, and soils, rock depth, topography, and underlying geology should be investigated for site suitability, especially when the tank is located underground.
The tank should also be close to the manure source to reduce excess surface runoff water in the holding pond.
Sufficient land must be available for a disposal area without overloading soils or exceeding crop requirements.
Estimate tank size according to the kind and number of livestock, the amount of flushing water for dilution, and the planned retention time.
Allow a minimum 6-inch freeboard at the top of the tank and 6 inches at the bottom for accumulated wastes.
Construct according to engineering design by a government or private engineer.
A permit is required.
Contact the county conservation district for local information.
Livestock BMP #9: Sediment or Solids Separation Basins
 A separation basin is a structure that temporarily restrains runoff and permits liquids to drain gradually to a holding pond, lagoon, or infiltration area.
Solids remain in the basin for drying and later removal for field application.
Generally consisting of a shallow basin designed for low velocities and the accumulation of settled materials, a separation basin should be constructed between the manure source and manure storage or treatment facilities.
An infiltration area may be used to further treat effluent.
Locate the basin on soils of slow-to-moderate permeability or on soils that can seal through sedimentation and biological action.
Avoid gravelly soils and shallow soils over fractured or cavernous rock.
If selfsealing is not probable, the basin must be sealed by mechanical treatment or by the use of an impermeable membrane.
Do not construct to an elevation below the seasonal high water table.
The separation basin should also have adequate capacity
 to store settled solids for a reasonable period based on climate, equipment, and method of disposal.
Livestock BMP #10: Manure Storage Structures-Stack Pads
 A stack pad is a stacking facility constructed of durable materials to temporarily store solid livestock manure or other agricultural waste until it can be removed and properly disposed of on land for fertilizer.
Other management components such as manure storage ponds and filter strips may be used effectively with stack pads to reduce nutrient-rich runoff from reaching surface waters.
To minimize potential pollution, locate the stack pad close to the manure source to reduce scraping time and also away from residences, water supplies, and streams.
Also, before locating the site and designing the structure, check soils, depth to rock, water table, and topography, and investigate local and state regulations that relate to site location and design.
The structure's size depends on the type and number of animals, amount of bedding used, and proposed retention time.
Fence as necessary to prevent livestock and people from using the facility for other purposes, and use vegetative screens or other methods as needed to shield structure from public view and/ or improve visual conditions.
Follow a design construction plan prepared by a government or private engineer.
A permit may be required.
Contact the county conservation district for local information.
Livestock BMP #11: Nutrient Management
 Nutrient management involves carefully monitoring all aspects of soil fertility and making necessary adjustments SO that crop needs are met while minimizing the loss of nutrients to surface or groundwater.
It includes management of all plant nutrients associated with animal manure, commercial fertilizer, legume crops, crop residues, and other organic wastes.
Nutrient management provides the crop with the correct amount of nutrients at the optimum time and location SO they are used efficiently.
It limits the amount of plant nutrients lost to leaching, runoff, and volatilization.
Nutrient
 management is one of the most important conservation practices protecting our natural resources.
Tremendous benefits to water quality can be achieved, it is relatively easy to implement, and it can increase profits.
To implement nutrient management, an operation must comply with the USDA Natural Resources Conservation Service  Kentucky Standards and Specification for Nutrient Management Practice Code 590.
Elements included in the practice code include:
 Maintaining an adopted sequence of crop rotations to use nutrients
 Taking soil tests to determine the pH , pH , phosphorus, potassium, zinc, magnesium, and calcium needed to optimize plant production
 Analyzing animal manure for total nitrogen, phosphate, potash, calcium, and magnesium prior to land application to establish nutrient credits and to formulate application rates
 Managinganimal manure in manner that prevents degradation of water, soil, and air and protects public health and safety
 Making sufficient land available for a disposal area without overloading soils or exceeding crop requirements for nutrients
 Minimizing edge-of-field delivery of nutrients where no setbacks are required.
Livestock BMP #13: Filter Strips
 A filter strip is a strip of close growing, dense vegetation that filters sediment, nutrients, and pathogens.
Ideally, filter strips are established down slope of animal production areas to capture and treat runoff before it reaches environmentally sensitive areas.
Potential sites for filter strips include areas directly below manure management systems and adjacent to perennial streams, farm ponds, and lakes.
To establish a filter strip, plant or maintain a dense grass sod in strips to help protect water quality by reducing soil movement.
When there is little or no existing vegetation, follow pasture and hayland planting or forage and biomass best management practices.
Leave existing natural vegetation along streams or
 Figure 2.
A typical paved feeding area with a guttered roof to redirect clean water away from the production area.
lakes if it is effective in removing sediment and manure.
Filter strips can also provide additional forage for hay production when needed if they are properly managed.
Livestock BMP #18: Stormwater Diversion
 Stormwater diversion is the practice of diverting clean water to keep it clean and to reduce the volume of dirty water that must be managed.
Appropriate practices include, but are not limited, to
 Guttered buildings that reduce the volume of water flowing onto open animal confinement areas where animals are held or fed 
 Vegetative filter strips or rock-lined channels that divert headwater away from production facilities, feeding areas, lagoons, and manure storage ponds
 Detention/retention structures that hold large amounts of stormwater generated from impervious areas
 Hardened structures, such as hardened ditches and check dams, that prevent soil erosion associated with high storm flows.
The purpose of these BMPs is to reduce issues associated with the "first flush," a high concentration of pollutants that washes away into surface water once a rainfall begins.
In many cases, diverting clean water also reduces the amount
 of water that requires containment and management, creates a drier environment for the animals, and reduces odors.
BMPs that avoid, trap, or control possible pollution sources associated with a paved feeding area could be implemented for the production facility shown in Figures 1 and 2 by taking the following steps:
 Clean or scrape the open production area often or at least immediately before significant rainfall events to limit the chances of manure, nutrients, and pathogens moving off site in runoff..
Place the manure in a covered shed for storage and hold until it can be land applied..
Land-apply manure solids away from the production area to soils that need phosphorus, such as those planted in grains, silage, or alfalfa.
These cropsremove large qualities of phosphorus per yield unit, which reduces the need for expensive fertilizers and decreases the chance of water pollution..
Create a filter strip in order to use the fertility in the soils.
Use the soil test data adjacent to the production areato determine the best location.
Manage the area by interseeding cool-season grasses into warm-season grasses to trap and use nutrients year round.
the filter strip with temporary electric fencing to allow flash grazing or to allow the area to grow up and be harvested.
The point is to use some sort of adaptive management and a BMP, in this case an enhanced filter strip, to trap and use nutrients before they become a point or non-point source pollution source..
Gutter the area of the roof that drains onto the production area and use downspouts to redirect the water to keep clean water clean..
Bed the barn with an absorbent material such as wood shavings, sawdust, or straw to reduce odors.
Although this BMP is not recommended by the Agricultural Water Quality Plan, it could reduce the generation of gases that often leads to nuisance complaints.
Cost share assistance for the BMPs listed in the KAWQP may be available through the Natural Resources Conservation Service and/or the Kentucky Division of Conservation.
For more information, contact the local offices of the U.S.
Department of Agriculture Farm Service Agency  or the local conservation district.
Food Safety Modernization Act Produce Safety Rule: Microbial Water Quality Compliance
 Erin E.
Scott Program Manager Arkansas Water Resources Center
 Amanda G.
Philyaw Perez Assistant Professor Food Systems and Food Safety
 Julia M.
Fryer Program Associate Food Systems and Food Safety
 Brian E.
Haggard Director Arkansas Water Resources Center
 Arkansas Is Our Campus
 I.
Who is this Fact Sheet For?
This fact sheet is designed for producers who must comply with the federal Food Safety Modernization Act  Produce Safety Rule  and those interested in learning how to meet the agricultural water requirements in Subpart E of the FSMA PSR.
The agricultural water requirements set standards for water quality and require periodic testing to ensure the water is safe and of adequate sanitary quality for its intended use.
This means that your water may need to be tested periodically to ensure it is safe for how you plan to use the water.
II.
Why Should You Test Your Agricultural Water for Fecal Indicator Bacteria?
Do you get your water from a stream, spring, pond or well?
Do you use your water on the farm for your produce operation, drinking water, handwashing or other farm uses?
If the answer is yes, it is important that you test your water.
Just like municipal water suppliers test water quality, so should you.
You are responsible for ensuring the water is safe for its intended agricultural use.
The PSR section Subpart E, which focuses on agricultural water quality, establishes science-based standards for the safe growing, harvesting, packing and holding of fruits and vegetables that are grown for human consumption.
These mandatory standards are designed to reduce the chances of contamination in the food supply and ultimately reduce the number of human illnesses from contaminated produce.
Compliance dates related to the agricultural water provisions have been extended for covered produce.
Covered produce is defined as produce that is subject to the FSMA PSR regulations,
 produce that is in its unprocessed state and that is usually consumed raw.
Sprouts are covered by Subpart M and are required to be in compliance with the agricultural water subpart of the FSMA PSR as the relevant compliance dates have all passed.
The compliance dates related to agricultural water for covered produce  are in the table below.
See 84 FR 9706  for more information.
Size of farm	Compliance date
 Very small	January 26, 2024
 Small	January 26, 2023
 All others	January 26, 2022
 The U.S.
Food and Drug Administration  does not expect growers of covered produce  to implement Subpart E until the new compliance dates.
The FDA encourages farms to use good agricultural practices to maintain and protect the quality of their water sources.
Farms that currently test their water may choose to continue with their testing programs, and farms that do not currently test their water may begin doing SO.
IV.
Requirements for Microbial Testing according to the FSMA PSR
 Agricultural water is defined, in part, as water used in covered activities on covered produce where water is intended to, or is likely to, contact covered produce or food contact surfaces.
A covered activity means growing, harvesting, packing or holding covered produce on a farm.
When determining whether or not you have to test your agricultural water, it is important to identify which category of agricultural water you are evaluating is it production water or post-harvest water?
Also, what is the source of your water is it
 surface water , groundwater or municipal water that you store open to the environment?
There are different testing frequency and evaluation requirements for these different categories and water sources.
You will also need to know how to properly collect your water sample for water testing.
For information about this, see our related fact sheet "Bacterial Water Sample Collection and Submission to the Water Quality Lab."
 A.
Production Water versus Post-Harvest Water
 There are two categories that your agricultural water might fall under: production water or post-harvest water.
1.
Production water is water used during growing activities.
2.
Post-harvest water is water used during and after harvest that presents high risk for contamination to occur.
Depending on the water source being used, both of these types of water must be evaluated for bacterial water quality.
B.
Microbial Water Quality Profile
 As a fruit and vegetable producer, you must establish an initial microbial profile for each untreated water source that you use as agricultural water during growing activities.
In future years, you must maintain your microbial profile by testing your water periodically.
Surface water quality can change quickly throughout the year and with changing seasons.
Groundwater does not tend to change very dramatically or quickly, but there is potential for your groundwater supply to become contaminated.
Water testing only gives you a snapshot in time, but it can provide important information regarding fecal contamination of your water supply.
There are
 countless types of fecal pathogens that can be found in water, including different bacteria, viruses and parasites.
Generic E.
coli is a type of fecal bacteria and is the accepted indicator of fecal contamination because it is logistically not possible to test for all potential types of pathogens.
The water quality profile is designed to provide you with long-term information about the quality of your water for agricultural use.
V.
How You Can Interpret Your Results
 In order to understand what your results mean, here are a few important definitions:
 1.
Geometric mean  is a type of average, or measurement of central tendency, that is calculated from multiple observations or testing results.
2.
Statistical threshold value  is a measure using each of your observations or results to assess how different or variable your water quality is over time.
3.
CFU/100 mL is the unit of measure for E.
coli results specified in the PSR; this stands for "Colony Forming Units per 100 mL of sample water." But, other laboratory methods are acceptable under this rule, and MPN/100 mL may be used; this stands for "Most Probable Number per 100 mL of sample water."
 It is also important to identify which category of agricultural water you are evaluating is it production water or post-harvest water?
Also, what is the source of your water is it surface water or groundwater?
There are different testing frequency and evaluation requirements for these different categories and water sources.
B.
How to Calculate GM and STV
 There are resources available to help you calculate the GM and STV and understand whether your water meets the requirements of the FSMA PSR:
 1.
Online tool developed by the University of Arizona
 b.
Enter sample information and bacteria results
 C.
The tool automatically calculates the GM and STV values and determines if your water meets the criteria for the rule.
2.
Microsoft Excel tool developed by the Western Center for Food Safety at the University of California-Davis.
b.
Enter sample information and bacteria results.
C.
The tool automatically calculates the GM and STV and tells you if your water meets the criteria for the rule.
3.
Explanation of the calculations for GM and STV Cornell University.
C.
Untreated Groundwater for Production Activities
 You must test your groundwater supply as close to harvest as practicable, with the following frequency:
 Year 1: Four times during the growing season
 Year 2, 3, etc: Once a year during the growing season
 The samples collected and tested in the first year develop your initial microbial profile, and testing for subsequent years keeps your profile updated.
Each year you update, you must recalculate the GM and STV using the most recent four years of data.
The following is the evaluation criteria for water used for production activities.
As noted above, results in "MPN/100 mL" is acceptable given the laboratory method being used.
GM must be 126 CFU /100mL or less; AND
 STV must be 410 CFU /100mL or less
 The following outlines the corrective actions you must take if your water sample exceeds the criteria given above:
 Apply a time interval to allow microbial die-off; in other words, wait a specific amount of time to use this water to harvest your produce.
Inspect your water source and entire system for possible causes of contamination.
Implement practices to reduce the risk of contamination.
D.
Untreated Groundwater for Harvest and Post-Harvest Activities
 Harvest and Post-Harvest activities include water used in the field during harvest; water used during packing, holding, cooling activities; water used to clean surfaces that food will contact; water used for making ice; water used for washing hands; etc.
You must test your groundwater supply with the following frequency:
 Year 1: Four times during the growing season 
 Year 2, 3, etc: Once each year during the growing season
 However, if E.
coli are detected in any sample , you must start over as if beginning with year 1.
This means if, for example, in year 3, your result shows that E.
coli is present, you must test your water four more times that year.
If results yield no detectable generic E.
coli in 4 samples, then move to once per year thereafter.
The following is the evaluation criteria for water used for harvest and post-harvest activities:
 NO amount of E.
coli is acceptable; your result must indicate that no detectable generic E.
coli are present per 100 mL of water.
Some labs report "<1" for the lowest reportable value; this is accepted by the federal FSMA PSR to indicate that no detectable E.
coli are present.
The following outlines corrective action you must take if your water sample has detectable levels of generic E.
coli:
 First, immediately stop using that water source
 for all uses listed under post-harvest water activities.
If you want to resume using that water source, you must first do at least one of the following:
 Re-inspect the entire agricultural water system to the extent that it is under your control; identify anything that might lead to contamination of your produce or water source; make any necessary changes and test your water to determine if those changes are effective.
This event resets your microbial water quality profile and will require retest to demonstrate the corrective action was successful.
o Put your water through a treatment process before use; if you treat your water with sanitizers or other treatment actions, you must monitor your water treatment often enough to ensure that the treatment is continually and consistently effective; you will be responsible for keeping documentation on the results of your water treatment monitoring.
E.
Untreated Surface Water for Production Activities
 You must test your surface water supply as close to harvest as practicable, with the following frequency:
 Years 1-4: at least 20 times total
 You must collect and analyze 20 samples in the first, second, third or fourth year.
For example, you could collect 10 samples per year for years 1 and 2, or you could collect 5 samples per year for years 1, 2, 3, and 4.
You cannot collect all 20 samples in the first year; you must collect samples over a period of at least two and less than four years.
Subsequent years: Five times per year
 Five times per year could begin with year 3 if you collected all 20 initial samples in the first two years.
Each year you update, you must recalculate the GM and STV using the most recent four years of data.
You must also confirm that your water continues to be in compliance with the numerical requirements.
The following is the evaluation criteria.
As noted previously, results in "MPN/100 mL" are also acceptable, given the laboratory method used.
GM must be 126 CFU /100mL or less; AND
 STV must be 410 CFU /100mL or less
 The following outlines the corrective actions you must take if your water sample exceeds the criteria given above:
 Apply a time interval to allow microbial die-off; in other words, wait a specific amount of time to use this water to harvest your produce.
Inspect your water source and entire system for possible causes of contamination.
Implement practices to reduce the risk of contamination.
F.
Untreated Surface Water for Post-Harvest Activities
 You CANNOT use untreated surface water for post-harvest activities under any circumstances.
You may use untreated ground water with no detectable generic E.coli.
Municipal water is preferred.
VI.
Avenues for Bacteria Analysis
 Laboratories provide results as numerical values , or as Presence/Absence, depending on the method used.
Production Water: generic E.
coli must be quantified as numeric values.
Harvest and Post-Harvest Water: generic E.
coli can be reported in terms of presence or absence.
A.
The AWRC Water Quality Lab in Fayetteville:
 B.
The Arkansas Department of Health  in Little Rock:
 ADH can also test for generic E.
coli in your water
 sample using a method that is accepted under the PSR.
ADH can analyze for the presence or absence of E.
coli, as well as numeric values.
For analysis of Harvest and Post-Harvest Water, you should be sure to request the method that provides quantitative results , which is required by the FSMA PSR.
To request quantitative results, be sure to check "raw with count"o: the submission form; if this is not checked, the ADH lab will only analyze for presence/ absence, and you will have to submit a new sample to comply with the federal rule.
VII.
About the University of Arkansas System Division of Agriculture
 The Produce Safety Alliance  is a national program offering training, outreach and technical assistance to produce safety educators and producers.
The PSA Grower Training on Agricultural Water and FDA resources on the water regulations can be found below.
Acknowledgments: Stephen Hughes, Kruti Ravaliya and Chelsea Davidson of the FDA Produce Safety Network reviewed this fact sheet.
Kathryn Seely of the Arkansas Department of Health reviewed this fact sheet.
Funding for this publication was made possible, in part, by the Food and Drug Administration through grant PAR-16-137.
The views expressed in written materials or publications do not necessarily reflect the official policies of the Department of Health and Human Services; nor does any mention of trade names, commercial practices, or organization imply endorsement by the United States Government.
Printed by University of Arkansas Cooperative Extension Service Printing Services.
ERIN E.
SCOTT is a program manager Arkansas Water Resources Center, University of Arkansas System Division of Agriculture.
AMANDA G.
PHILYAW PEREZ is an assistant professor, University of Arkansas System Division of Agriculture Cooperative Extension Service.
BRIAN E.
HAGGARD is the director Arkansas Water Resources Center, University of Arkansas System Division of Agriculture.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Director, Cooperative Extension Service, Universi-ty of Arkansas.
The University of Arkansas System Division of Agriculture offers all its Extension and Research programs and services without regard to race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
Weve had above average inflows to the river, and were not anticipating an allocation this year, said Lyle Myler, area manager for the Bureau of Reclamation Wyoming Area office in Mills.
Both 21 and 22 were allocation years, and the irrigators did a good job of conserving water and managing their supplies over those two years.
In 2020, the rainfed crop had significantly lower crop yield as compared with the irrigated treatments.
The deficit irrigation resulted in 5% loss of maize yield as compared to full irrigation in 2020.
Training for Initial and Recertifying Chemigatorsthe online training program covers all of the information presented at the in-person training events and uses the same test.
It consists of a series of modules which contain text, video clips and calculators to provide chemigators with the necessary information to employ chemigation in an effective, efficient and environmentally safe manner while safeguarding farm workers involved in chemigation.
Enterprise Budgets Guayule, Flood Irrigated, Southern Arizona
 Trent Teegerstrom, Clark Seavert, Paul Gutierrez, Hailey Summers, Evan Sproul, Blase Evancho and Paco Ollerton
 This series of enterprise budgets estimate the typical economic costs and returns to establish, grow, and harvest guayule over a six-year period, using flood irrigation in southern Arizona.
It should be used as a guide to estimate actual costs and returns and is not representative of any farm.
The assumptions used in constructing these budgets are discussed below.
Assistance provided by area producers and agribusinesses is much appreciated.
The results of this study are based on our current understanding of guayule production, market, and yields.
As research advances, we expect these assumptions to change.
This budget is based on a 1,500-tillable acre farm.
As Arizona is experiencing irrigation water shortages, approximately 40 percent  of the total farm tillable acres are fallowed.
This fallowed land will allow adequate water to irrigate the following crops: 271 acres in cotton, 45 acres in silage corn, 90 acres in guayule, 181 acres in durum wheat, and 316 acres of alfalfa hay.
The costs to fallow land are allocated to each crop based on its water use.
All crops are grown using flood irrigation.
The six-year sequence for guayule production is to establish the crop in year 1, harvest in years 2, 4, and 6, and grow the crop between harvests in years 3 and 5.
Crop removal occurs in year 6 after harvest.
Tractor driver labor cost is $17.89 per hour and general labor $14.55 per hour; both rates include social security, workers' compensation, unemployment insurance, and other labor overhead expenses.
For this study, owner labor is valued at the same rate as tractor driver rates, and all labor is assumed to be a cash cost.
Tractor labor
 hours are calculated based on machinery hours, plus ten percent.
Interest on operating capital for harvest and production inputs  is treated as a cash expense, borrowed for 6-months.
An interest rate of six percent is charged as an opportunity to the owner for machinery ownership.
The cultural operations are listed approximately in the order in which they are performed.
A 175-hp tractor is used to pull the v-ripper, heavy offset disk, moldboard plow, landplane, lister, and planter.
A 125-hp tractor is used to pull the shredder/root puller, drill, cultivator, fertilizer spreader, and boom sprayer.
A charge for miscellaneous and other expenses is five percent of production costs, including additional labor, machinery repairs and maintenance, supplies and materials, tax preparation, memberships in professional organizations, and educational workshops not included in field operations.
A detailed breakdown of machinery values is shown in Table 7.
Estimated labor, variable, and fixed costs for machinery are shown in Table 8, based on an hour and per acre basis.
The machinery costs are calculated based on the total farm use of the machinery.
Off-road diesel is $4.00 per gallon.
Table 8 shows the machine operations by year during guayule production.
Six-Year Sensitivity Analysis of Net Returns
 Adding together the six years of costs and three years of guayule production results in a break-even price of $0.0347 per pound to cover all variable costs and $0.0624 per pound
 to cover total variable and fixed costs.
Table 1 shows the total net returns over six-years of guayule production at various yields, prices, and a 20 percent increase and decrease in total costs.
The $0.08 cents per pound or midpoint on the sensitivity analysis  was derived from the breakeven cost of production.
This was used as there is no established market for guayule.
Table 2 represents the net cost and returns per year for the six-year production cycle of guayule.
More detailed cost of establishing guayule is $1,189 per acre  and $619 per acre in the growing years between harvests.
The gross income in the harvest years is $1,760 per acre;
 guayule price at $0.08 per pound, with an average yield of 22,000 pounds at 15 percent moisture content.
Variable costs are $282 per acre, giving a net return above variable cash costs of $1,478 per acre.
Total fixed costs are $1,373 per acre, which includes an amortization charge of $809 is included as an opportunity cost to establish and grow guayule in years 1, 3, and 5 during the six-year rotation.
The gross income minus total costs results in a $387 per acre return.
NOTE: Not included in these budgets are family living withdrawals for unpaid labor, returns to management, depreciation and opportunity costs for vehicles, buildings and improvements, inflation, property and crop insurance, and local, state, and federal income and property taxes.
Table 1.
Estimated Total Net Returns from Six Years of Guayule Production at Varying Price, Yields, and Percentage of Production Costs, $/acre.
% Change in	Yield,	Guayule Price per Pound of Biomass
 Total Costs	Lbs/Acre	$0.06	$0.07	$0.08	$0.09	$0.10
 19,000			$442	$1,012	$1,582
 20,000		$82	$682	$1,282	$1,882
 21,000		$292	$922	$1,552	$2,182
 0%	22,000		$502	$1,162	$1,822	$2,482
 23,000	$22	$712	$1,402	$2,092	$2,782
 24,000	$202	$922	$1,642	$2,362	$3,082
 25,000	$382	$1,132	$1,882	$2,632	$3,382
 19,000	$126	$696	$1,266	$1,836	$2,406
 20,000	$306	$906	$1,506	$2,106	$2,706
 21,000	$486	$1,116	$1,746	$2,376	$3,006
 -20%	22,000	$666	$1,326	$1,986	$2,646	$3,306
 23,000	$846	$1,536	$2,226	$2,916	$3,606
 24,000	$1,026	$1,746	$2,466	$3,186	$3,906
 25,000	$1,206	$1,956	$2,706	$3,456	$4,206
 19,000				$188	$758
 20,000				$458	$1,058
 21,000			$98	$728	$1,358
 20%	22,000			$338	$998	$1,658
 23,000			$578	$1,268	$1,958
 24,000		$98	$818	$1,538	$2,258
 25,000		$308	$1,058	$1,808	$2,558
 Table 2.
Annual Net Returns of Income and Expenses to Establish and Produce Guayule, $/acre.
1
 Income	Cash Costs	Fixed Costs	Returns
 Year 1: Establishment	$0	$770	$419	-$1,189
 Year 2: Harvest	1,760	282	282	1,196
 Year 3: Growing	0	336	283	-619
 Year 4: Harvest2	1,760	282	282	1,196
 Year 5: Growing	0	336	283	-619
 Year 6: Harvest2	1,760	282	282	1,196
 Guayule yield is estimated to be 22,000 pounds per acre, with 15% moisture content, at a price of $0.08 per pound.
1 2 Harvest costs are paid by the processor
 Table 3.
Year 1: Guayule Establishment Year, Economic and Cash Costs, $/acre.
Variable Cash Costs	Price	Quantity	Unit	Labor	Machinery	Materials	Total
 Land Preparation and Maintenance
 V-Ripper	1.00	acre	$13.53	$34.33	$0.00	$47.86
 Offset Disk	2.15	acre	10.14	25.34	0.00	35.48
 Landplane	1.00	acre	3.87	9.24	0.00	13.10
 Lister	1.00	acre	6.18	14.35	0.00	20.54
 Bed Shaper	1.00	acre	3.09	6.90	0.00	9.99
 Row Planterl	1.00	acre	4.51	13.42	75.20	93.10
 Seed	$75.20	1.00	acre
 Ferlilizer Spreader	1.00	acre	1.88	3.70	99.60	105.17
 Nitrogen	$0.46	60.00	pounds
 -Phosphorus	$0.36	200.00	pounds
 Boom Sprayer	3.00	acre	3.57	5.45	90.25	99.26
 Prowl	$6.06	9.00	pints
 Aim	$5.94	1.80	ounces
 Fusile	$1.25	20.00	ounces
 Row Cultivator	2.00	acre	6.01	8.80	0.00	14.81
 Irrigation	56.99	0.00	215.42	272.40
 Irrigation Water, Flood	$55.00	3.92	ac ft
 Irrigation Labor, Flood	$14.55	3.92	hour
 Other Expenses	0.05	0.00	0.00	35.59	35.59
 Interest on Operting Capital	0.06	0.00	0.00	22.42	22.42
 Total Variable Cash Costs	$109.77	$121.52	$538.47	$769.76
 Total Returns minus Total Variable Cash Costs	-$769.76
 Fixed Cash Costs	Unit	$/Unit	Value
 Fallow Costs	acre	$110.99	$110.99
 Annual Cash Rent Payment	acre	170.00	170.00
 Total Fixed Cash Costs	$280.99
 Fixed Non-Cash Costs	Unit	$/Unit	Value
 Power Units, Machinery & Equipment, depreciation & interst	acre	$137.79	$137.79
 Total Fixed Non-Cash Costs	$137.79
 Total Annual Costs	$1,188.54
 Returns minus Total Annual Costs	-$1,188.54
 Table 4.
Year 2, 4 and 6: Guayule Harvest Years, Economic and Cash Costs and Returns, $/acre.
Returns	Unit	$/Unit	Quantity	Value
 Guayule Biomass	pound	$0.08	22,000.00	$1,760.000
 Variable Cash Costs	Price	Quantity	Unit	Labor	Machinery	Materials	Total
 Land Preparation and Maintenance
 Offset Disk	0.10	acre	$0.47	$1.180	$0.00	$1.65
 Ferlilizer Program	0.00	0.00	27.60	27.60
 Nitrogen	$0.46	60.00	pounds
 Irrigation	48.50	0.00	183.33	231.83
 Irrigation Water, Flood	$55.00	3.33	ac ft
 Irrigation Labor, Flood	$14.55	3.33	hour
 Harvest expenses paid by the processor	1.00	acre	0.00	0.00	0.00	0.00
 Other Expenses	0.05	0.00	0.00	13.05	13.05
 Interest on Operting Capital	0.06	0.00	0.00	8.22	8.22
 Total Variable Cash Costs	$48.57	$1.18	$232.21	$282.36
 Total Returns minus Total Varialbe Cash Costs	$1,477.64
 Fixed Cash Costs	Unit	$/Unit	Value
 Fallow Costs	acre	$110.99	$110.99
 Annual Cash Rent Payment	acre	170.00	170.00
 Total Fixed Cash Costs	$280.99
 Fixed Non-Cash Costs	Unit	$/Unit	Value
 Amortized Establishment and Maintenance Costs	acre	$808.69	$808.99
 Power Units, Machinery & Equipment, depreciation & interst	acre	0.60	0.60
 Total Fixed Non-Cash Costs
 Total Annual Costs	$1,372.64
 Returns minus Total Annual Costs	$387.36
 Table 5.
Year 3 and 5: Guayule Growing Years, Economic and Cash Costs and Returns, $/acre.
Returns	Unit	$/Unit	Quantity	Value
 Guayule Biomass	pound	$0.08	22,000.00	$1,760.000
 Variable Cash Costs	Price	Quantity	Unit	Labor	Machinery	Materials	Total
 Land Preparation and Maintenance
 Offset Disk	0.05	acre	$0.24	$0.59	$0.00	$0.83
 Ferlilizer Program	0.00	0.00	27.60	27.60
 Nitrogen	$0.46	60.00	pounds
 Boom Sprayer	1.00	acre	1.19	1.82	47.28	50.29
 Prowl	$6.06	2.50	pints
 Aim	$5.94	1.20	ounces
 Fusilade	$1.25	20.00	ounces
 Irrigation	48.50	0.00	183.33	231.83
 Irrigation Water, Flood	$55.00	3.33	ac ft
 Irrigation Labor, Flood	$14.55	3.33	hour
 Harvest expenses paid by the processor1
 Other Expenses	0.05	0.00	0.00	15.535	15.53
 Interest on Operting Capital	0.06	0.00	0.00	9.78	9.782
 Total Variable Cash Costs	$49.93	$2.40	$283.52	$335.85
 Total Returns minus Total Varialbe Cash Costs	-$335.85
 Fixed Cash Costs	Unit	$/Unit	Value
 Fallow Costs	acre	$110.99	$110.99
 Annual Cash Rent Payment	acre	170.00	170.00
 Total Fixed Cash Costs	$280.99
 Fixed Non-Cash Costs	Unit	$/Unit	Value
 Amortized Establishment and Maintenance Costs	acre	$1.93	$1.93
 Power Units, Machinery & Equipment, depreciation & interst	1.93
 Total Fixed Non-Cash Costs
 Total Annual Costs	$618.77
 Returns minus Total Annual Costs	-$618.77
 Table 6.
Whole Farm Machinery Cost Assumptions.
Width	Market	Annual	Life
 Machine		Value	Use	
 175 HP Tractor	N/A	$180,000	1,293	10
 125 HP Tractor	N/A	80,000	467	15
 V-Ripper	8.0	22,000	408	10
 Offset Disk	18.0	30,000	483	15
 Moldboard Plow	9.3	35,000	138	15
 Landplane	16.0	18,000	81	15
 Lister	10.0	6,500	104	15
 Cotton Shredder/Root Puller	20.0	12,000	41	15
 Row Planter	24.0	40,000	76	15
 Row Cultivator	24.0	22,000	108	10
 Drill	20.0	25,000	72	15
 Fertilizer Spreader	40.0	18,000	101	20
 Boom Sprayer	60.0	9,500	144	20
 Table 7.
Machinery Cost Calculations, on a per hour and per acre basis.
-Variable Costs-	Fixed Cost
 Fuel &	Repairs &	Deprec.
Total Cost
 Machie	Lube	Maint.
& Interest
 175 HP Tractor	$36.80	$6.98	$18.16	$61.37
 125 HP Tractor	23.00	1.68	19.42	44.10
 V-Ripper	0.00	6.16	6.98	13.14
 Offset Disk	0.00	5.40	6.94	12.34
 Moldboard Plow	0.00	18.20	28.29	46.50
 Landplane	0.00	3.24	24.85	28.09
 Lister	0.00	1.89	6.99	8.87
 Cotton Shredder/Root Puller	0.00	2.76	32.57	35.33
 Row Planter	0.00	14.76	61.55	76.31
 Row Cultivator	0.00	4.10	25.95	30.05
 Drill	0.00	8.71	40.53	49.24
 Fertilizer Spreader	0.00	14.02	20.37	34.39
 Boom Sprayer	0.00	5.35	7.56	12.91
 Acre/	Operator	Variable	Fixed	Total
 Field Operation	Hour	Labor	Costs	Costs	Costs
 175 HP Tractor & V-Ripper	1.45	$13.53	$34.33	$17.28	$65.15
 175 HP Tractor & Offset Disk	4.17	4.72	11.79	6.02	22.52
 175 HP Tractor & Moldboard Plow	2.55	7.73	24.35	18.25	50.33
 175 HP Tractor & Landplane	5.09	3.87	9.24	8.45	21.55
 175 HP Tractor & Listen	3.18	6.18	14.35	7.90	28.44
 175 HP Tractor & Shredder	6.64	2.97	4.14	7.83	14.93
 175 HP Tractor & Planter	4.36	4.51	13.42	18.27	36.19
 175 HP Tractor & Cultivator	6.55	3.01	4.40	6.93	14.33
 175 HP Tractor & Drillr	3.64	5.41	9.18	16.49	31.08
 175 HP Tractor & Fertilizer Spreader	10.47	1.88	3.70	3.80	9.37
 175 HP Tractor & Boom Sprayer	16.55	1.19	1.82	1.63	4.63
 Table 8.
Machine Operations by Year in Guayule Production
 Machine Operation	X/Acre	X/Acre	X/Acre
 175 HP Tractor & V-Ripper	1.00
 175 HP Tractor & Offset Disk	2.15	0.10	0.05
 175 HP Tractor & Landplane	1.00
 175 HP Tractor & Lister	1.00
 175 HP Tractor & Bed Shaper	1.00
 175 HP Tractor & Planter	1.00
 125 HP Tractor & Cultivator	2.00
 125 HP Tractor & Fertilizer Spreader	1.00
 125 HP Tractor & Boom Sprayer	3.00	1.00
 THE UNIVERSITY OF ARIZONA Cooperative Extension
 TRENT TEEGERSTROM Ag Econ Extension Specialist, Department of Agriculture and Resource Economics, University of Arizona
 CLARK SEAVERT Agricultural Economist, Department of Applied Economics, Oregon State University
 PAUL GUTIERREZ Department of Agricultural Economics & Agricultural Business, New Mexico State University
 HAILEY SUMMERS PhD Students, Department of Mechanical Engineering, Colorado State University
 EVAN SPROUL PhD Students, Department of Mechanical Engineering, Colorado State University
 BLASE EVANCHO Area Agent, Arizona Cooperative Extension, University of Arizona
 Paco OLLERTON Producer in Pinal County
The Relationship between Priority and Value of Irrigation Water Used with Prior Appropriation Water Rights
 ABSTRACT This article examines the relationship between water right priority and value of use for rights defined by prior appropriation, and tests whether this relationship is different for rights that have been transferred from their original locations to new locations, versus those that have not.
We develop an empirical model using data for agricultural irrigation water rights and show that for transferred water rights, more senior  rights are reallocated from lowerto higher-valued agricultural uses.
For water rights that remained unchanged, we find that priority order and potential profitability, as indicated by land characteristics, are not well aligned.
Agricultural irrigation accounts for the majority of water used in the western U.S., where water rights are defined predominantly by the prior appropriation doctrine.
1 A prior appropriation water right defines  the source for the water, with its expected annual yield;
 1 Alaska, Arizona, California, Colorado, Hawaii, Idaho, Kansas, Montana, Nebraska, Nevada, New Mexico, North Dakota, Oklahoma, Oregon, South Dakota, Utah, Washington, and Wyoming follow the prior appropriation doctrine.
Land Economics August 2020 96 : 384-398 ISSN 0023-7639; E-ISSN 1543-8325  2020 by the Board of Regents of the University of Wisconsin System
  the maximum quantity of water that the right-holder may request annually;  the specific location where the water may be used; and  the priority of the claim relative to all other claims to the same source, defined by the date that each water right was initially assigned to its original location.
2 Priorities date back to the mid-1800s when the U.S.
west was originally settled, with seniority referred to by date of establishment; in other words, a particular water right is referred to as an "1865 right" or an "1898 right." Priority determines the order in which claims are filled when available water for a given source is below average annual yield and insufficient to fulfill all claims.
Water is delivered first, in full, to lands with the earliest priority dates, and then to lands with sequentially later priority dates.
The total amount of water available annually thus determines the "cutoff" priority.
Lands with priority rights before the cutoff receive full water claims, while priority rights after the cutoff receive no water, although some may become available through return flows from lands irrigated with more senior rights.
As a result, lands with higher-priority rights are, on average, less likely to be affected by drought conditions, while lands with more junior rights generally face more variable water supply and receive
 Two other rules associated with prior appropriation are "use it or lose it," whereby a water right unused for a period of time is forfeited; and "beneficial use," whereby the governing water authority may alter a water right if deemed beneficial to society.
These rules have evolved SO that the former is rarely used against agricultural water right holders , and the latter includes support of ecosystem services.
on average less water.
In order that water be used in its highest-valued uses during periods of drought, and because water right seniority is not necessarily aligned with expected value for water used in the locations where those rights were initially established, most states permit the transfer of water rights from one location to another, as long as such transfers do not adversely affect third parties or pose significant environmental harm.
Transfers of priority between locations is expected to improve welfare by realigning priority with the value of water used.
This article examines the relationship between water right priority and use value for a surface water source and tests whether this relationship is different for rights that have been transferred from their original locations to new locations, versus those that have not.
There is little previous empirical evidence regarding the effectiveness of permitted transfers of priority to increase social welfare.
We develop an empirical model using data from Carson Valley, Nevada, and show that for transferred water rights, more senior rights are, on average, reallocated from lowerto higher-valued agricultural uses, resulting in welfare improvements.
For water rights that remained unchanged, however, we find that priority order and potential profitability, as indicated by land characteristics, are not well aligned.
Previous empirical studies  quantify benefits of water transfers between different types of use, rather than values of transfers between locations for the same use , and do not consider priority differentials.
Lefebvre, Gangadharan, and Thoyer  use a lab setting to demonstrate that priority-differentiated water rights increase expected profits in water allocation and water rights markets.
The few econometric studies that include priority use it as an independent variable and show that seniority is associated with increased crop revenue , irrigation infrastructure investment , and the overuse effect induced by the "use it or lose it" rule.
Processes to verify no third-party injury can be costly and time-consuming, particularly if others protest a proposed transfer.
While the no-harm rule is intended to prevent external costs, the costs involved to verify no third-party harm may prevent higher-priority water rights from moving from lowerto higher-valued agricultural land uses.
Huffaker, Whittlesey, and Hamilton  note that policies that lower costs of transferring water rights between locations could improve allocation efficiency without the welfare redistributions and losses associated with more extensive institutional changes, as described by Libecap  and Young.
We do not examine the costs of transferring water rights.
Instead, we examine how transfers influence the relationship between priority and value of water use, thereby shedding some light on the potential gains from transfers.
Our result, that priority and value are not well aligned for water rights that have not been transferred, suggests room for future research.
This includes, for example, examining policies intended to facilitate transfers to improve welfare, including efforts to reduce costs of determining third-party effects and negotiations to mitigate such effects, should they arise.
We use data from the Carson Valley, Nevada, where the Carson River is the main source for agricultural water rights, the maximum quantity of water per acre assigned to each water right is more or less constant across all water rights, and transfers are not permitted to increase this amount per acre.
Of the four prior appropriation water right characteristics described above, permitted transfers in the valley affect two: location of use and priority order.
There are only two primary crops in the valley, grass hay and alfalfa, both of which require irrigation.
Data that describe potential yields indicate that individual parcels favor either grass hay or alfalfa, but not both; that is, yields are negatively correlated.
Further, while alfalfa is the higher-valued crop, historical circumstances led to comparatively more junior priority rights being assigned to the best alfalfa land, and the more
 Table 1 Water Rights Transferred from the 496 Original Locations, with Priority Dates
 Number of Water Rights	Number of Water	Percent
 Priority Date Ranges	as Initially Established	Rights Transferred	Transferred
 1852-1860	100	20	20.0
 1861-1870	122	21	17.2
 1871-1880	119	17	14.3
 1881-1890	60	15	25.0
 1891-1900	73	17	23.3
 1901-1916	22	4	18.12
 Total	496	94	19.0
 Source: Data from Alpine Decree , NDWR , and USGS.
Note: Wald test results suggest no differences between priority groups, significant at the 95% confidence level.
senior rights assigned to lands best for grass hay.
These features allow us to identify the relationship between priority and value of use for water rights that have been transferred and those that have not been transferred to new locations.
2.
Study Area, Priority Agricultural Water Rights, and Locations of Use
 Flowing eastward from the Sierra Nevada range, the Carson River is the primary agricultural irrigation water source in Nevada's Carson Valley.
Overall, the water rights regime is representative of prior appropriation doctrine in other western states.
Carson Valley surface water rights were first established in 1852 and were fully appropriated by 1916, with 496 individual water rights claims on parcels of varying acreages located throughout the valley.
3 Table 1 shows that 341 of the 496 original water rights  were claimed before 1880.
Of these, 58 water rights were subsequently moved to new locations.
The map in Figure 1 shows the 2010 locations of agricultural irrigation water rights and priority dates in Carson Valley, with lighter shading indicating more senior rights and darker shading indicating more junior rights.
Variation in Flow Rates and Cutoff Priorities
 The Sierra snowpack is the source of the Carson River.
Annual fluctuations in winter precipitation and spring temperatures produce considerable variation in timing and quantity of Carson River flow rates throughout the spring and summer.
As with other western surface water systems, Carson Valley irrigation district managers endeavor to deliver water according to priority by holding water behind headgates and then releasing it when sufficient flow volume or "head" is attained to move it the desired distance.
Thus, the amount of water received at each location is determined in part by upstream flow rates and priorities, the amount of water available at various times within an irrigation season, and the force of gravity.
Historical stream flow rates, measured regularly throughout each season using gauges throughout the Carson River system, show that between 1936 and 2015, annual stream flows fell below average in 44 out of 79 years, with flows in the lowest 10th percentile for 14 of the 79 years.
As a result, cutoff calls frequently affect the more junior water rights.
4 Morway, Niswonger, and Triana  develop a spatial model that overcomes practical difficulties by calibrating stream flow records for water allocated to each water right.
5 Their
 4E.
James, Director, Carson Water Subconservancy District, personal communication, July 31, 2019.
5 While streamflow rates and cutoff calls are highly correlated, there is substantial variation in flow rates, and thus cutoff calls, within a given year, between years, and in dif-
 Lee, Rollins, and Singletary: Water Right Priority and Value
 Water Right Locations and Priority Dates  Source: Data from NDWR  and USGS.
model simulates the quantity delivered to each water right location in the study area.
Their results approximate the impacts of cutoffs by estimating which water rights would have received no water during a 35-year simulation period based on flows from 1981 to 2015.
Their results indicate that 23% of Carson Valley water rights established after 1890 would have experienced curtailment in 3 or more
 ferent locations across the valley.
Water delivery records for individual water rights and locations exist as handwritten logs, most of which do not explain why the quantity of water delivered to each location was less than its prescribed maximum amount; lower amounts may be the result of a cutoff call for that part of the river, or the producer may have called for less water due to other circumstances.
years out of 35 years.
As explained below, this is also the period in which much of the land best suited for alfalfa production was claimed and water rights on these lands established.
In particular, the simulation showed 23%  of water rights established after 1890  would have experienced curtailment in at least 3 or more out of the 35 years.
Crop Yields, Water Value, Priorities, and Transfers
 The valley's two main crops are grass hay and alfalfa.
6 The maximum allowable amount of irrigation water that can be claimed is limited to a constant number of acre-feet per acre across the valley, and water rights transfers are not permitted to increase this entitlement beyond the set limit.
7 Therefore, total irrigable acreage in the valley is fixed.
Alfalfa was not introduced to Carson Valley until the late nineteenth century, after the majority of water rights had already been claimed.
The more senior water rights were established on lands closest to the river for grass pastures using flood irrigation.
Townley  points out that with livestock as the earliest primary agricultural product, settlers would have favored land with good pasture productivity and river access.
8 Alfalfa, on the other hand, prefers well-drained soils located farther from
 Potential Yields for Alfalfa  and Grass Hay  for Water Rights in the Carson Valley Source: Data from NDWR , USGS , and USDA-NRCS.
the river.
Investments in networks of ditches eventually extended irrigation infrastructure to these lands, where relatively more junior water rights were established for alfalfa cultivation.
Figure 2 illustrates potential yields  for alfalfa and grass hay for lands in the Carson Valley, obtained from USDA-NRCS  crop yield maps for the Carson Valley.
9
 We overlay the GIS layers for crop yields with 2010 water rights boundaries.
For water rights boundaries that span more than one NRCS crop yield prediction, we calculate weighted average potential crop yields for each water right location.
Figure 2 shows that lands with higher potential alfalfa yields are located farther from the river, while lands closer to the river and between the river forks show higher yields for grass hay.
Figure 3 shows average land productivity for alfalfa and grass hay, by water right priority.
have lacked sufficient information to accurately pair the most profitable lands with senior water rights.
9 NRCS uses soils, landscape, climate, and other data for the region to estimate potential crop yields based on ob-
 Lee, Rollins, and Singletary: Water Right Priority and Value
 Average Alfalfa and Grass Hay Potential Yields for Water Right Priority Date Ranges and Number of Water Rights Source: Data from NDWR , USGS , and USDA-NRCS.
Figure 4 Grass Hay versus Alfalfa Potential Yields on All Land Parcels with Water Rights Source: Data from Web Soil Survey.
Figure 4 shows the relative productivity for alfalfa  versus grass hay  for each location to which a water right is attached.
We see that each location is higher yielding in either alfalfa or grass hay, with few locations showing similar yields for both, aside from observations with very low yields.
Together, these data illustrate that more senior water rights were established initially on lands better suited to grass hay, while relatively more junior rights were established on lands better suited to alfalfa.
Alfalfa eventually came to be the major cash crop for Carson Valley, sold today mainly to out-of-state markets, while grass hay remains largely as pasturage for local livestock production.
10 Lands in the valley most suitable for alfalfa yield about twice as many tons per acre of alfalfa relative to grass hay.
The protein content of alfalfa is about twice that of grass hay
 10 Townley  describes late-nineteenth century changes leading to alfalfa surpassing grass hay production.
.
For almost every year between 1972  and 2016, the average alfalfa price per ton was higher than that for grass hay in Nevada.
Introduced later to the valley, alfalfa production was made possible by  switching from grass hay on land that already had water rights but was not as well suited for alfalfa,  through establishment of very junior rights on new locations best suited for alfalfa, or  through the transfer of senior water rights from lower-valued locations in the valley to new locations in the valley.
Because land characteristics that favor highest yields for each crop are strongly negatively correlated, simply switching from grass hay to alfalfa on lands with senior rights may have been less profitable in some locations than incurring the costs to transfer senior rights to lands better suited to alfalfa.
Additionally, the value of moving a senior water right to new land with high alfalfa yield potential may have been greater than the value of establishing a much more junior water right on that same land.
We identify the relationship between priority and potential profitability of the location where water is used for water rights that have and have not been transferred to new locations through a set of features unique to the study area.
These are  a constant water duty per acre for all irrigated lands,  only two crops grown, representing lower and higher potential values, and  negatively correlated yields for each location to where the most senior water rights are initially allocated with lands with a lower-valued crop , with more junior rights allocated to a higher-valued crop.
Our major interest is in the relationship between priority and irrigation water use values, and how this differs for water rights that have been transferred to new locations and those remaining in their original locations.
Each observation represents a water right i, with a dummy variable indicating whether it has been transferred.
We predict priority as a function of the agricultural value of water
 used at each location, proxied by soil and land characteristics.
We hypothesize transfers have aligned water right seniority with potential value, and expect these to be more closely aligned for transferred rights, relative to rights that have not been transferred.
We use a linear regression model, equation [1], where dependent variable Priority is the year the claim was established, from 1852 to 1916.
A negative coefficient on an explanatory variable therefore indicates that a oneunit increase contributes to more senior priority, while a positive coefficient implies more junior priority: Priority + STi Ui.
[1]
 Water rights that have been transferred are indexed by Ti, where Ti = 1 for observation i if the water right was transferred , and Ti = 0 for observations with water rights that have not been transferred.
We interact Ti with other independent variables to capture heterogeneous effects on water right priority.
Noninteracted coefficients capture effects influencing initial establishment.
Z is a vector denoting potential yields for grass hay and alfalfa for each water right location.
Potential yield is used to approximate the profitability differential at that location depending on which crop is grown.
We expect the coefficient of alfalfa productivity for YT to be negative, because with permitted transfers, we expect the more senior rights  to be associated with lands with higher alfalfa yields.
Vector Xi represents factors other than crop yields that influence profitability, described in more detail in the data section below.
The last term, Ui, in equation [1] is unobserved error.
We use three models to address correlations in error terms potentially arising from two types of clusters within subgroups of our data, as described in detail in the last part of the data section below.
The three models are an ordinary least squares  model with cluster robust variance-covariance estimators , a random-effects  model, and a mixed-effects  model.
The latter two methods can be applied to nonrepeated
 Lee, Rollins, and Singletary: Water Right Priority and Value
 Table 2 Description of Variables for 2010 Water Rights 
 Variable	Description	Mean	Std.
Dev.
Min.
Max.
Priority 	Year established	1874	15.80	1852	1914
 Alfalfa 	Average tons/acre alfalfa	1.22	1.52	0	5.55
 Grass 	Average tons/acre grass hay	0.06	0.27	0	2.25
 Dist_River 	Distance to river	1,192	1,090.1	3	6,454
 Sup_Source 	Number of supplemental groundwater permits	0.50	0.93	0	5.00
 WestFork 	West fork of the Carson River = 1	0.32	0.47	0	1.00
 M_Carson 	Main Carson River = 1	0.04	0.20	0	1.00
 LandSize 	Acres associated with water right	81.08	140.4	0.45	1,683
 Transferred 	Permitted transfer to this location = 1	0.14	0.35	0	1.00
 observations clustered by groups, as suggested by Cameron and Miller.
The CRV and RE models address only one cluster level, while the ME model addresses two-level clusters.
We provide further details regarding our empirical methods to address clusters in Appendix Section A.1
 Our data include priority year, location, geophysical characteristics, and potential yields for alfalfa and grass hay at the location to which each water right is attached in 2010.
Table 2 displays the variables used in our analyses.
We determined which water rights had been transferred at least once by comparing GIS data for each right as it was initially established, as documented in the Alpine Decree , with its location and boundaries in 2010.
11 We use 2010 for our "current" water rights locations because the approval process for transferring a water right from one location to another in the Carson Valley can take up to five years.
Our data include a small number of water rights with open transfer permit applications dated 2011 and later that had not yet been certified.
We treat these as remaining at their 2010 locations.
11 The Alpine Decree documents the locations of water rights as they were first established.
While a water right may change its location several times since its establishment, the NDWR  system includes only digital records for the most recent location.
Most of the historical records are handwritten, making it extremely difficult to trace the path of individual water rights and transfers over time.
The third column of Table 1 shows that of the original 496 water rights established between 1852 and 1916, 19% were transferred out of agriculture by 2010, suggesting that a total of 413 remained in agriculture.
Table 1 also illustrates the challenges with identifying precisely which water rights were transferred.
Of the 402 original water rights not transferred out of agriculture, some were subsequently split with land sales.
In these cases, an original parcel with a single water right was subdivided into smaller parcels, and each of the smaller parcels retained the original priority date, with a maximum water amount claimable based on the proportion of land in the subparcel.
Through many iterations of this process over time, by 2010 there were a total of 413 water rights.
Of these, 57 were transferred from their original locations to new locations.
These 57 water right transfers are associated with lands that account for 17.24% of the total land area and 13.8% of observations.
Because most of the historical records are handwritten, making it difficult to trace individual transfers over time, our data do not include the dates of transfers, locations from where water rights were transferred, nor whether multiple transfers occurred for a single water right.
We use yield potentials for alfalfa and grass hay  as proxies for relative differences in land profitability.
As explained above, we generate potential yields for alfalfa and grass hay by overlapping 2010 water right boundaries with USDA-NRCS  Web Soil Survey layers, which pro-
 vide predicted potential yield per acre by crop based on soils and landscape characteristics.
We use satellite land use data  to identify land area that was paved, devoted to buildings, and otherwise clearly no longer used for irrigated agricultural production, which we omitted from the cultivated acreage for each water right location.
Other Factors Affecting Productivity
 We use distance to the river  to represent variation in receivable return flows.
We expect land closer to the river to have greater potential for receiving return flows from irrigated lands at higher elevations.
Since the majority of lands in the valley are flood-irrigated and lands closer to the river are at lower elevations, this implies greater potential for receiving water from return flows from irrigated lands at higher elevations.
We expect a negative sign on this coefficient without transfers, and a positive sign for its interaction term with transfers.
We include Sup_Source, the number of supplemental groundwater well permits associated with each water right location.
While the majority of irrigation water in the Carson Valley is sourced from Carson River surface flows, agricultural water right holders may apply for permits to drill wells to access and use groundwater only when the surface water cutoff priority date precedes the priority date associated with the water right.
Landowners bear the costs of drilling these wells and investment in irrigation technology to utilize supplemental groundwater.
Multiple permits are required for larger parcels.
The mean size of land areas for water rights with supplemental groundwater permits is twice that of water rights without supplemental permits.
We expect a negative sign on Sup_Source, since the larger farms are presumably more reliant on alfalfa income and have the capital to invest in drilling wells.
Recall, supplemental groundwater wells cannot be used to increase claimable water amount, only to provide some water during curtailment.
As illustrated by the maps in Figures 1 and 2, the Carson River separates into two forks, creating three river segments: Main River, East Fork, and West Fork.
Irrigation water delivery
 is managed in three subdistricts according to these subunits.
We create three variables to control for differences in water management by segment.
In our regression models, the East Fork serves as the base, while M_Carson and WestFork identify the other two segments with which a water right is associated.
Acreage associated with each water right varies considerably in the Carson Valley.
Total acreage of each water right parcel in 2010, LandSize;, approximates unobserved owner endowments and/or access to capital.
We expect more senior water rights to be associated with larger owner endowments.
12
 Common Point of Diversion and Owner Clusters
 As is typical for surface water rights to many western rivers, irrigation ditch networks deliver surface water from various points of diversion on the river.
A headgate at each point of diversion on the river controls the timing and amount of surface water delivered to lands through ditch networks.
Shared headgates indicate shared infrastructure to move water to a new location, shared maintenance costs, and potentially cooperative water management practices among water rights holders, causing systematic correlation in our data.
To control for these effects, we include the point of diversion for each water right in our data.
Our data also include several sets of adjacent parcels with different priority dates owned by a single agricultural operation.
The choice for water right priority among these adjacent locations may differ from the nonadjacent parcels and those involving multiple owners.
As the need for more senior rights is relevant only during drought years, single
 12 The data describe acreage of 2010 parcels to which water rights are attached.
As noted by a reviewer, it may not be reasonable to consider acreage as a proxy for endowment during original establishment of water rights in the West.
Relative to land grants in the Midwest, which were restricted to 160 acres , cash purchases of settlement lands west of the 100th meridian carried no acreage restrictions or residency requirements , allowing for the acquisition of land tracts of varied sizes during settlement on which to establish water rights.
Lee, Rollins, and Singletary: Water Right Priority and Value
 Table 3 Regression Results for 2010 Water Rights Transferred to New Locations
 Alfalfa	2.829*** 	2.773*** 	2.442** 
 Grass	-5.139** 	-4.762* 	-4.170* 
 Dist_River	0.007*** 	0.007*** 	0.007* 
 Sup_Source	-1.045+ 	-1.233+ 	-1.023 
 WestFork	-7.443*** 	-7.931 	-9.381 *** 
 M_Carson	-8.438* 	-8.265+ 	-6.983 
 LandSize	-0.014*** 	-0.012*** 	-0.009* 
 Transferred	20.786*** 	20.556*** 	18.773*** 
 Alfalfa_T	-3.534** 	-3.558*** 	-3.414* 
 Grass_T	6.295* 	4.399 	0.932 
 Dist_River_T	-0.006*** 	-0.006* 	-0.005* 
 Sup_Source_T	-11.043*** 	-9.607*** 	-7.931 
 WestFork_T	-19.618*** 	-17.282** 	-12.099* 
 M_Carson_T	-15.796** 	-15.859** 	-15.623 
 LandSize_T	0.041*** 	0.036*** 	0.027 
 Constant	1,867.536*** 	1,867.732*** 	1,868.216	
 Note: Variables interacted with Transferred are indexed with T.
Cluster robust standard errors are reported in parentheses in the OLS column.
Heteroskedasticity robust standard errors are in parentheses in the RE and ME columns.
Cluster is defined by common-owner cluster in the OLS-CRV and RE estimators.
In the ME model, headgate is nested under common-owner groups.
All models are jointly significant at the 0.01% level.
ME, mixed effects; OLS-CRV, ordinary least squares with cluster robust variance-covariance estimators; RE, random effects.
+p<0.15;*p<0.1;**p<0.05;***p<0.01.
owners of multiple parcels might temporarily reallocate water across their own parcels on an as-needed basis, instead of taking on the costs of a permanent permitted transfer.
The optimal choice of water right priority of adjacent parcels thus may generate correlations in the data.
In either case, such circumstances that influence costs of water right transfers between locations within a single point of diversion, or for a single owner, suggest decisions within these groups may be correlated.
For the purpose of this article, we refer to groups of adjacent parcels with a single owner as "common-owner clusters" and groups with a common point of diversion as "headgate clusters," with variables to identify these in our data.
The Appendix contains details concerning the two types of clusters in our data.
Summarizing Appendix Table A.1.
the frequency of water rights sharing a headgate range from a maximum of 66 water rights within a single point of diversion to 33 water rights with points of diversion shared with no other water rights.
After 66, the next largest number of water rights clustered within a single point of
 diversion is 15, followed by 14, 12, 11, and 10.
A total of 33 points of diversion service single water rights, followed by 15 points of diversion in which there are only 2 water rights, and 10 with just 3 water rights.
As for water rights with common-owner clusters, 117 are not in common-owner clusters.
The greatest numbers of water rights within a single-owner cluster is one cluster each with 22, 16, and 13 water rights.
Our results show that priority and value of water use are aligned for water rights that have been transferred to new locations, but not for those that remain in their original locations, suggesting that transfers serve to align higher-value agricultural lands with more senior water rights.
Table 3 reports coefficient estimates from equation [1].
Results using headgate clusters and common owner clusters are SO similar that the we report only the OLSCRV and RE results with common-owner clusters.
For the ME model two-level clusters, the common owners are assumed to be the
 higher-level cluster and point of diversion as the lower-level cluster.3
 Looking at variables without interaction-that is, for water rights that have not been transferred-the negative coefficients for grass hay yields  suggest seniority aligns with grass hay productivity, while the positive coefficients for alfalfa yields  suggest potential misalignment between water use value and seniority.
The positive coefficient on Dist_River indicates, as expected, that for rights that have not transferred, farther distance from the river is associated with more junior rights.
The coefficients on Transferred alone show that, all else equal, lands with transferred water rights have 18.8 to 20.8 years more junior priority, significant at the 99% confidence level, depending on the model used.
That is, all else equal, transferred water rights are relatively more junior than those not transferred, indicating obstacles for transferring senior water rights.
Third parties are more likely to oppose a transfer of the most senior water rights on the basis that such transfers can impact the original order of water deliveries on the river and alter return flows receivable.
Looking at variables interacted with Transferred suggests that transfers have aligned priority with value, as approximated by potential yields and other land characteristics.
Grass hay productivity for locations with transferred water rights, Grass_T, is no longer significant in explaining priority allocation, except for the OLS-CRV model, in which the estimate is slightly above the 90% significance level.
Instead, the coefficients for alfalfa productivity conditional on transfer, Alfalfa_T, are all negative at the 95% confidence level, suggesting that a one-unit increase in potential alfalfa
 13 In the ME effects model, the variance-covariance structure of the unobserved constant intragroup effect is set to be exchangeable SO that correlation between lower-level clusters is allowed with a constant covariance term.
We check for robustness by altering assumptions regarding cluster choice and variance-covariance and residual structures, and find similar results, which are available from the authors upon request.
Additional analyses concerning effective cluster numbers and potential spatial autocorrelation are provided in Appendix Sections A.2 and A.3.
yield per acre on lands receiving transfers contributes to 3.41 to 3.53 years of increase in seniority of water rights transferred.
The negative sign on the coefficient for Dist_River_T suggests that greater distance of the new locations from the river lead to obtaining more senior rights, consistent with expectation of lower return flows.
The small positive coefficient of LandSize_T implies that a one-acre increase in land parcel size is associated only slightly with more junior priority.
One explanation for this result is that a larger operation faces greater challenges in obtaining senior water rights through permitted transfers, because a larger amount of water involved may increase the possibility of negatively impacting other water right holders.
Whether a water right has been transferred or not, one additional permit for supplemental groundwater  contributes to a more senior water right.
These results are consistent with the observation that farms with the capacity to expand production prefer more senior water rights.
We further verify that the transfer effects are robust to the supplemental water source by allowing it to interact with Grass_T and Alfalfa_T.
Appendix Section A.4 describes in detail this triple interaction model and its results.
Overall, our conclusions remain unchanged for observations without supplemental groundwater permits.
We find that with greater alfalfa productivity, a farmer who is permitted to pump supplemental groundwater when surface water flows are insufficient may be indifferent to seeking a more senior water right.
We find also that that one additional supplemental groundwater permit enlarges the permitted surface water transfer effect by associating more senior priority with greater alfalfa productivity.
Potential Gains from Permitted Water Transfers
 Because our data do not track specific water rights as they were transferred between locations over time, we estimate welfare gains from transfers by comparing estimated annual agricultural revenues between two sets of observations:  parcels where water rights were initially established, but no longer have water rights as of 2010, and  parcels with water
 rights in 2010 that were transferred from other locations.
Among the locations where water rights were initially established, a total of 6,366 acres no longer have agricultural water rights as of 2010.
Water rights associated with 592 acres were transferred out of agriculture in the Carson Valley prior to 2010, leaving water for 5,774 acres  bundled in 57 individual water rights remaining in agriculture to have been transferred to new locations in the Carson Valley.
Of the 57 water rights transferred for agricultural use, two are associated with lands having senior water rights that were swapped with lands having junior water rights.
The remaining 5,774 acres to which water rights were transferred did not have rights before 1916; that is, without transfers, these lands could not have been brought into irrigated agricultural production.
We first calculate potential annual yields for the old locations totaling 6,366 acres and the new or transferred locations totaling 5,774 acres, using yield potential data for each parcel from the USDA-NRCS  Web Soil Survey.
Irrigation intensity is irrelevant in this region, because the yields for alfalfa and grass hay in the area are based on similar water use.
For a fair comparison, we use 91% of the yields from the lands where water rights originated, to account for water rights that were transferred out of agricultural use.
We calculate revenues in the old and new locations using 2010 Nevada prices of $126/ton for alfalfa and $116/ton for grass hay.
We assume each producer makes crop decisions based upon whichever of the two crops would yield greater revenues for each parcel.
We thus obtain annual revenues of $1,044,637 if water rights were used in the old locations, and $1,484,681 if used on new  locations, for a 42% increase in revenues.
The 5,774 acres of new lands amount to 17.24% of total irrigated acreage  and 29.44% of the total revenue.
We calculate the total revenue in the same manner for all 2010 lands with water rights, including lands where there were no water rights transfers.
We note that this estimate is likely to be conservative since our calculation does not account for the benefit from transfers that prevent losses in alfalfa production during
 drought years nor for marginal lands that are likely fallowed during drought years.
This ballpark estimate does, however, provide a reference point for economic outcomes that demonstrate the potential benefit from permitted transfers that align priority with land use values.
Limitations and Future Research
 Our analysis to predict seniority of water rights as a function of value of water use for rights that have and have not been transferred is somewhat limited by data constraints.
First, time-series dynamics are not observable in our data.
Therefore, we are not able to estimate the improvements to production by tracking location changes for each water right over time.
Also, the data do not capture water reallocation through temporary transfers of water between locations, and therefore the observed permitted transfer effects represent conservative results.
In addition, we cannot test hypotheses related to increased numbers of transfers OCcurring in more recent years with increasing occurrences of realized annual water supply falling below expected yields.
This would be of interest given that the region has been experiencing warmer annual mean temperatures, less mountain snowpack, earlier peak snowmelt rates, and reduced soil moisture-factors that each contribute to less available surface water for irrigation.
Finally, our data do not include water rights transferred to nonagricultural uses and/or to other basins.
As theory and indirect evidence from water trades generally suggest efficiency improvements from these types of transfers, our results capture only the outcomes of within-basin transfers intended for agricultural use, resulting in a conservative assessment.
This article empirically investigates the relationship between priority and value for water rights defined by the prior appropriation doctrine, where transfers allow for relocation of priority rights.
We use a unique data set that includes water right geographic boundaries
 and priorities as they were established with the settlement of the Carson Valley in northwestern Nevada, and as they are over a century later in 2010, to explore the role of permitted transfers between locations in aligning priority with profitability of water rights.
Our results show for our study area, for agricultural irrigation water rights that have been transferred to new locations, priority and profitability are well aligned; however, such alignment is not the case for water rights that remain in their original locations.
We estimate the welfare gain attributable to the transferred water rights, relative to them staying in their original locations, to show that the transfers increased crop revenue by roughly 42%.
Our findings provide empirical evidence that suggests permitted transfers of water right location and priority can provide flexibility to align and redirect limited and variable irrigation water resources to higher-valued uses.
We find also that for rights that had never been transferred, there was no discernable alignment between priority and value.
This lack of alignment by itself does not necessarily imply that rights not transferred are not currently in their highest-valued uses, but it does not rule out that the costs of transfers and permitting may impede further welfare gains.
Actions to facilitate and/or reduce costs associated with the water transfer application and permitting process may enhance welfare further.
This includes developing more cost-effective methods to estimate how consumptive use and net return flows might change due to proposed transfers, as a measure of third-party injury.
Steps to reduce water rights transfer costs also include facilitation of negotiated outcomes to address potential thirdparty injuries.
Additional steps that could lead to further transfers include investments in river-basin-scale hydrologic studies to identify the extent to which future water transfers may induce third-party injury or environmental damage and means to mitigate such damage.
Libecap  points out that overly vague no-harm standards for transfers can generate additional transaction costs that ultimately limit transfers.
Yet, unexpected third-party impacts from transfers can arise due to previously unknown hydrologic anomalies or as
 a result of a changing climate.
Transfers that inadvertently generate externalities and subsequent conflict due to lack of conjunctively managed surface and groundwater supplies also can lead to presumptions that prior appropriation performs poorly as an allocation institution.
As climate change and population growth continue to stress water supplies across the western United States, the efficiency of prior appropriation water allocation, as compared with alternative water allocation institutions, will continue to be a major discussion point.
However, adopting and transitioning to alternative water allocation institutions that alter entitlements may lead to welfare redistributions that are not well understood and may be socially undesirable.
Our analyses suggest that water allocation efficiency of water rights under the prior appropriation doctrine may be improved by facilitating transfers of water right location of use and priority ordering, while reducing costs associated with proving that such transfers will not cause third-party effects, and negotiated mitigation.
Alternative institutions that transfer water rights without adhering to no-harm criteria cannot guarantee a net improvement in water allocation efficiency.
14 Priority is likely to play a larger role in areas of the West where fluctuations in winter mountain snowpack and increasingly early warming trends for spring temperatures may lead to occurrences of curtailments of agricultural water for water rights with increasingly earlier priority dates.
This may lead to requests for further transfers from lowerto higher-valued locations, as well as increasing third-party effects from such transfers.
This study is supported by a grant from the National Science Foundation  Division of Earth Sciences Water Sustainability and Climate program.
This study is also supported by the Nevada Agricultural Experiment Station.
Acknowledge-
 14 The correlated rights doctrine may be an exception  but can be implemented only for water resources managed as a common pool.
ment to the U.S.
Geological Survey and the Nevada Division of Water Resources.
CROP PRODUCTION AND ECONOMICS IN NORTHWEST KANSAS AS RELATED TO IRRIGATION CAPACITY
 ABSTRACT.
Crop production and economics of corn, grain sorghum, soybean, and sunflower under irrigated and dryland conditions were simulated using 34 years  of weather data in Northwest Kansas.
Irrigation system capacities ranged from 2.5 to 8.5 mm/day.
The simulated long-term annual average net irrigation requirements for corn, grain sorghum, soybean, and sunflower were 375, 272, 367, and 311 mm, respectively.
Assuming a 95% application efficiency , the average long-term crop yield is approximately 12.9, 8.2, 4.4, and 3.2 Mg/ha for corn, grain sorghum, soybean, and sunflower, respectively.
Although corn is currently the predominant irrigated crop in western Kansas, projections for the year 2006 indicate soybean is a more profitable alternative.
Net irrigation requirements for soybean are only about 2% lower than corn, so a shift to soybean will not result in significant water conservation.
If the price of corn increased just 10% relative to stable prices for the other crops, it would become the most profitable irrigated crop.
This indicates that net return projections are very volatile, subject to changes in crop prices and input costs.
Keywords.
Irrigation management, Irrigation economics, Evapotranspiration, Modeling, Corn, Grain sorghum, Soybean, Sunflower, Ogallala aquifer.
I n arid regions, it has been a design philosophy that irrigation system capacity should be sufficient to meet the peak evapotranspiration needs of the crop to be grown.
This philosophy has been modified for areas having deep silt loam soils in the semi-arid U.S.
Central Great Plains to allow peak evapotranspiration needs to be met by a combination of irrigation, precipitation, and stored soil water reserves.
The major irrigated summer crops in the region are corn , grain sorghum , soybean , and sunflower.
Corn yield is very responsive to irrigation with responses of up to 0.05 Mg/ha-mm or higher possible in this region.
Other major crops in the region are less responsive to irrigation and are sometimes grown on more marginal capacity irrigation systems.
Since many of the systems have marginal capacity, it is important to have good information about how the various crops will perform in
 Submitted for review in December 2006 as manuscript number SW 6789; approved for publication by the Soil & Water Division of ASABE in June 2007.
Presented at the 2006 ASABE Annual Meeting as Paper No.062208.
This is Contribution No.
07-141-J from the Kansas Agricultural Experiment Station, Manhattan, Kansas.
This material is based upon work supported by USDA-ARS Specific Cooperative Agreement No 58-6209-5-0026.
Any opinions, findings conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the USDA-ARS or the Kansas Agricultural Experiment Station.
terms of grain yield and profitability as related to irrigation system capacity.
Irrigation water allocation and cropping strategies has been a research topic in numerous studies in the Great Plains region.
Many of these studies focused on various fixed water application amounts and the resulting crop production.
Martin et al.
developed a dynamic programming model to annually allocate a limited water supply over a multi-seasonal period.
This model can also be used to help producers choose the correct mix of crops and balance of irrigated and non-irrigated land.
These allocation procedures are very suitable to water-banking systems that are regularly discussed as possible water management alternatives being instituted under state authority.
Martin and van Brocklin  reported multi-seasonal allocation decisions depend on whether the objective is to maximize net income or to reduce economic risk by maximizing the lowest annual net income during the period.
Maximizing net income will favor using the water earlier in the period.
Reducing the risk of a low net income will favor saving some of the water for a drier than normal year.
Strickland and Williams  analyzed optimal irrigated area and crop mixes for a low in-canopy center pivot sprinkler system with a 25-L/s capacity.
They found that growing irrigated corn or grain sorghum on a full-sized 51-ha center pivot sprinkler system was more profitable than reducing the irrigated area to allow increased water application.
However, they tempered their conclusions with the caution that the production risk would be higher utilizing the larger land area and that annual variation in weather conditions might result in wide variations in cropping profitability.
A comparison of several irrigation strategies on commercial farms in Nebraska has indicated that economic
 A water allocation model for crop planning has been developed for use in the Central Great Plains.
This model simulates crop production and net economic returns with a minimal number of inputs.
This tool has been promoted as a decision aid for annual crop planning and received attention from the USDA Risk Management Agency as a means of reducing production risk.
Crop yield production functions as related to water use were presented for six crops  for the west-central Great Plains by Stone et al..
These relationships can be used to optimize water allocations and maximize profit for crops grown under various precipitation and irrigation scenarios.
This article will discuss the simulated irrigation requirements and the effect of irrigation system capacity on summer crop production and net returns.
Although the results presented here are based on simulated irrigation schedules for 34 years  of weather data from Colby, Kansas  for deep silt loam soils, the concepts have broader application to other areas in showing the importance of irrigation capacity for summer crop production.
Weather data from 1972 through 2005 for Colby, Kansas  collected at the Kansas State University Northwest Research-Extension Center was used to calculate alfalfa-based reference evapotranspiration, ET, using a modified Penman equation.
This ET estimation method is similar to the procedures outlined by Kincaid and Heermann  and has been proven acceptable for this location.
A two-year  comparison for weather data from Colby, Kansas, of this estimation method to the ASCE standardized reference evapotranspiration equation which is based on FAO-56  indicates that the modified-Penman values are approximately 1.5% to 2.8% lower.
This is well within the accuracy of the resultant scheduling procedures.
The ET, was further modified with empirical crop coefficients for the region  to give the crop evapotranspiration, ETc.
The crop coefficients  for the four crops  were developed using procedures outlined in FAO-56  with region-specific adjustments made to the various growth periods.
Additionally the single time-averaged crop coefficients from FAO-56 for the various crops were approximately reduced by 1/K FAO-56 MidPoint to provide better crop water estimates for the alfalfa-based reference ET This generally reduced the FAO-56 crop coefficients tabulated for short crops  by approximately 15% to 20%.
Alfalfa-based
 Figure 1.
Alfalfa-based crop coefficients used in the simulated irrigation schedules and crop yield modeling.
ET1 is considered to give better estimates than short-grass ET in this region.
Irrigation schedules  for the major summer crops  were simulated with a daily time-step for the same 34-year period using precipitation and the calculated ETc.
The water budget included effective precipitation  and irrigation  as deposits and ETc and drainage  as withdrawals.
Typical emergence, physiological maturity, and irrigation season dates for Northwest Kansas were used in the simulation.
The simulations assumed a medium-textured, deep, well-drained, loessial Keith silt loam , typical of many High Plains soils and is described in more detail by Bidwell et al..
The 1.52-m soil profile will hold approximately 370 mm of plant available soil water  at field capacity.
The initial soil water at the beginning of each crop season was assumed to be at 85% of the PAW in the 1.52-m soil profile.
Effective summer rainfall for this region was assumed to be 88% of the rainfall amount as used by Stone et al..
An overall limit on effective rainfall was set at a maximum of 57.2 mm within a 24-h period to handle the occasional extreme events that occurred over the 34-yr period.
Daily drainage from the soil was calculated as a function of time using a drainage equation developed for the 1.52-m soil profile for the Keith silt loam soil at Colby, Kansas :
 D = -24.5  25.39
 where both D and the total soil water  including plant available and unavailable soil water were expressed in mm.
The procedure to characterize drainage rates from the soil using equations of this type was thoroughly discussed by Miller and Aarstad.
The application efficiency, Ea, was initially set to 100% to calculate the simulated full net irrigation requirement, SNIR.
Center pivot sprinkler irrigation events were scheduled if the calculated irrigation deficit exceeded 25.4 mm.
The irrigation-scheduling model was coupled with a crop yield model to calculate crop grain yields as affected by irrigation capacity.
Irrigation levels or capacities such as no irrigation and 25.4 mm every 3, 4, 5, 6, 8, or 10 d were used in these simulations.
Irrigation was scheduled according to climatic needs, but was limited to these capacities.
Table 1.
Parameters and factors used in the simulation of irrigation schedules and crop yield.
Corn	Sorghum	Soybean	Sunflower
 Emergence date	15 May	1 June	25 May	15 June
 Physiological maturity	11 Sept	13 Sept	16 Sept	11 Sept
 Crop season 	120	105	115	100
 End of irrigation season	2 Sept	4 Sept	7 Sept	2 Sept
 Irrigation season 	110	95	105	90
 Factors for crop yield model
 Vegetative period 	66	54	38	53
 Susceptibility factor	36.0	44.0	6.9	43.0
 Flowering period 	9	19	33	17
 Susceptibility factor	33.0	39.0	45.9	33.0
 Seed formation period 	27	22	44	23
 Susceptibility factor	25.0	14.0	47.2	23.0
 Ripening period 	18	10	-	7
 Susceptibility factor	6.0	3.0	-	1.0
 Sv, Slope on yield eq.
0.0416	0.0301	0.0121	0.0096
 Iy, Intercept on yield eq.
-11.55	-5.32	-2.40	-1.33
 [a] Susceptibility factors in this table are the water stress weighting factors, WFai, from equation 5.
Crop yields for the various irrigation capacities were simulated for the 34-yr period  using the irrigation schedules and a yield production function developed by Stone et al..
In its simplest form, the model results in the following equation: Y =  + I y  with yield  expressed in Mg/ha, yield intercept  and slope  as shown in table 1, and ETc in mm.
For the yield functions, the daily ETc values were modified to reflect any water stress imposed by lower soil water availability by using a soil water availability coefficient.
This soil water availability coefficient  as outlined by Hanks  was conditionally calculated using locally derived factors as:
 If PAW > 70% maximum PAW then K = 1  If PAW < 70% maximum PAW then K = PAW / 0.70 PAW 
 The 70% PAW threshold for K reduction is higher than typical values expressed in the literature that are often near 50%, but is supported by experimental studies for this soil type in this region.
The threshold values for K reduction and the functional relationships for the reduction remain widely debated and often reflect crop, climate, and soil differences.
A summary of the many forms and their rationale is presented by Howell et al..
Further application of the yield model reflects crop susceptibility weighting factors for specific growth period
 .
These additional weighting factors were incorporated into the simulation to better estimate the effects of irrigation timing at the various crop stages for the various system capacities.
The weighting factors and their application to the model are discussed in detail by Stone et al..
Soybean weighting factors were developed by using yield response factors of Doorenbos and Kassam.
The actual weighting factor  for a particular growth period was multiplied by the average of all /ETc ratios during the period.
WF values for all four periods were added together to reflect the fraction of maximum yield.
The overall yield production model was:
 where End is the total crop period in days and all other variables are previously defined.
The economic component of this analysis estimates economic returns from crop production over annual variable cash production costs.
The 2006 cost estimates used here  include variable cash crop production costs for seed, herbicides, insecticides, fertilizer, crop consulting, and custom harvest.
Also included are annual irrigation fuel, oil, repair and irrigation labor costs, as well as custom rates-based estimate of machinery expenses.
Crop price, farm program revenue, interest cost, and other crop production enterprise assumptions in this study are consistent with 2006 Farm Management Guide Crop Production Budgets for irrigated and dryland crops developed by K-State Research and Extension.
In this analysis, cost items that do not vary across the alternative crop enterprises were not considered.
These items include land charges, depreciation and interest on irrigation equipment, a $25/ha miscellaneous crop expense charge, and non-machinery labor charges.
Crop insurance was not included in these budgets.
Additionally, since crop prices are relatively volatile in this period of high
 Table 2.
Economic parameters varying by crop.
Corn	Sorghum	Soybean	Sunflower
 Crop price 	$0.1012	$0.0894	$0.2065	$0.2575
 Herbicide 	$75.48	$66.98	$36.74	$46.60
 Insecticide 	$95.63	$0.00	$0.00	$35.40
 Consulting 	$16.06	$15.44	$15.44	$16.06
 Custom rates	$74.67	$66.53	$62.56	$74.15
 Yield threshold	4.77	2.26	1.75	NA
 Extra charge for	$6.06	$5.71	$5.33	NA
 Crop hauling cost	$5.00	$5.59	$5.10	$4.96
 Table 3.
Economic parameters varying by crop and irrigation capacity.
Crop and Item	8.5	6.4	5.1	4.2	3.2	2.5	Dryland
 Corn seeding rate 	84.0	79.1	74.1	69.2	64.2	59.3	44.5
 Corn seed cost 	$125.18	$117.82	$110.45	$103.09	$95.73	$88.36	$66.27
 Corn N fertilizer cost 	$182.73	$179.15	$168.40	$161.23	$143.32	$128.99	$71.66
 Corn P fertilizer cost 	$52.51	$49.42	$46.33	$43.24	$40.15	$37.07	$18.53
 Grain sorghum seeding rate 	7.3	7.3	7.3	7.3	7.3	6.7	3.4
 Grain sorghum seed cost 	$42.88	$42.88	$42.88	$42.88	$42.88	$39.59	$19.79
 Grain sorghum N fertilizer cost 	$75.24	$75.24	$75.24	$71.66	$71.66	$64.49	$43.00
 Grain sorghum P fertilizer cost 	$33.98	$33.98	$33.98	$33.98	$30.89	$27.80	$18.53
 Soybean seeding rate 	371	371	371	358	346	334	297
 Soybean seed cost 	$77.84	$77.84	$77.84	$75.24	$72.65	$70.05	$62.27
 Soybean P fertilizer cost 	$33.98	$33.98	$33.98	$33.98	$30.89	$27.80	$18.53
 Sunflower seeding rate 	43.5	43.5	43.5	43.5	43.5	43.5	39.5
 Sunflower seed cost 	$58.28	$58.28	$58.28	$58.28	$58.28	$58.28	$52.98
 Sunflower N fertilizer cost 	$100.32	$100.32	$96.74	$93.16	$85.99	$82.41	$57.33
 Sunflower P fertilizer cost 	$30.89	$30.89	$29.03	$27.80	$25.95	$24.71	$18.53
 energy costs, a sensitivity analysis was performed by examining each individual crop increasing 10% relative to the base price assumption from 2006 input costs.
The probability of exceeding a given crop yield or net return as affected by irrigation capacity was computed using a normal distribution for the mean and standard deviation of the 34 years.
RESULTS AND DISCUSSION SUMMER CROP EVAPOTRANSPIRATION RATES
 Crop evapotranspiration  rates varied throughout the summer reaching peak values during the months of July and August in the Central Great Plains.
Long term  July and August corn ET rates at the KSU Northwest Research Extension Center  were calculated to be 6.8 and 6.3 mm/d, respectively.
However, it is not uncommon to observe short-term peak corn ET values in the 9to 10-mm/d range.
Occasionally, calculated peak corn ET rates may approach 13 mm/d in the Central Great Plains.
Individual years are different and daily rates vary widely from the long-term average corn ET rates.
Irrigation systems must supplement precipitation and soil water reserves to match average crop ET rates and also provide some level of design flexibility to attempt covering year-to-year variations in crop ET rates and precipitation.
The mean simulated net irrigation requirement  for corn, grain sorghum, soybean, and sunflower for the 34-yr period was 375, 272, 367, and 311 mm, respectively
 Figure 2.
Calculated daily corn evapotranspiration at Colby, Kansas, for the long-term average  as compared to the crop year 2005.
Average daily July and August ET values are shown in the table inset.
.
The maximum SNIR for the crops was in 1976 and 1983 ranging from 432 for grain sorghum to 533 mm for corn and soybean.
The minimum SNIR occurred in 1992, ranging from 76 mm for grain sorghum to 127 mm for corn and soybean.
This emphasizes the tremendous year-to-year variance in irrigation requirements.
Good irrigation management will require the irrigator to use effective and consistent irrigation scheduling.
Simulation results indicated that July and August required the highest amounts of irrigation for all four summer crops with the two months accounting for about 86% of the total seasonal needs.
However, it might be more
 appropriate to look at the SNIR and seasonal distribution in relation to probability, similar to the exceedance probability tables from the USDA-NRCS irrigation guidebooks.
In this sense, SNIR values will not be exceeded in 80% and 50% of the years, respectively.
The minimum gross irrigation capacities  generated using the SNIR values are 6.7, 4.8, 6.1, and 5.4 mm/d  for corn, grain sorghum, soybean, and sunflower, respectively, using center-pivot sprinklers operating at 85% Ea.
It should be noted that this simulation procedure only allows significant soil water depletion at the end of the growing season after the irrigation season has ended and that it would not allow for the total capture of major rainfall amounts  during the irrigation season.
Thus, this procedure is markedly different from the procedure used in the USDA-NRCS-Kansas guidelines.
However, the additional in-season irrigation emphasis does follow the general philosophy expressed by Stone et al.
that concluded in-season irrigation is more efficient than off-season irrigation in corn production.
It also follows the philosophy expressed by Lamm et al.
, that irrigation scheduling with the purpose of planned seasonal soil water depletion is not justified for corn in this region from a water conservation standpoint, because of yield reductions occurring when soil water was significantly depleted.
Nevertheless, it can be a legitimate point of discussion that the procedure used in these simulations would overestimate full net irrigation requirements because of not allowing large rainfall events to be potentially stored in the soil profile.
In simulations where the irrigation capacity is restricted to levels significantly less than full irrigation, any inefficiencies  caused by irrigating at a 25-mm deficit becomes moot, since the deficit often increases well above 25 mm as the season progresses.
SIMULATION OF CROP YIELDS AS AFFECTED BY IRRIGATION CAPACITY
 Although crop grain and oilseed yields are generally linearly related with ET from the point of the yield threshold up to the point of maximum yield, the relationship of crop yield to irrigation capacity is a polynomial.
This difference is because ETc and precipitation vary between years and sometimes not all the given irrigation capacity is required to generate the crop yield.
In essence, the asymptote of
 Table 4.
Simulated net irrigation requirements for four major irrigated summer crops for Colby, Kansas, 1972-2005.
Parameter	Corn	Sorghum	Soybean	Sunflower
 Seasonal cumulative SNIR 
 Maximum from 34 yr	533	432	533	483
 Minimum from 34 yr	127	76	127	102
 Mean	375	272	367	311
 Standard Dev.
110	92	109	100
 Monthly distribution of SNIR 
 June	13.7	6.0	10.0	2.3
 July	42.6	38.9	43.2	25.5
 August	41.9	50.5	40.5	53.2
 September	1.8	4.6	6.4	19.1
 maximum yield in combination with varying ETc and precipitation cause the curvilinear relationship.
When crop yield as related to irrigation capacity is simulated over a number of years, the curve becomes quite smooth.
Using the yield model , the 34 years of irrigation schedules and assuming a 95% Ea, the maximum yield is approximately 12.9, 8.2, 4.4, and 3.2 Mg/ha for corn, grain sorghum, soybean, and sunflower, respectively.
Estimates of crop yields as affected by irrigation capacity at a 95% Ea can be calculated from the polynomial equations in table 6.
Corn has a much steeper slope than the other three crops when the capacity is less than 6.5 mm/d.
In a probabilistic sense, corn and soybean yields are similar in response to irrigation capacity and their chances of
 Figure 3.
Simulated summer crop yields in relation to irrigation system capacity for the 34 years, 1972 to 2005, Colby, Kans.
Table 5.
Simulated net irrigation requirements  of four summer crops not exceeded in 80% and 50% of the 34 years 1972-2005, associated July through August distributions of SNIR, and minimum irrigation capacities to meet the critical July through August irrigation needs.
Corn	G.
Sorghum	Soybean	Sunflower
 Criteria	SNIR	July-August	SNIR	July-August	SNIR	July-August	SNIR	July-August
 SNIR value not exceeded in 80% of the years	483 mm	93.80%	356 mm	100.00%	483 mm	88.90%	381 mm	84.20%
 452 mm	356 mm	429 mm	342 mm
 July August capacity requirement	7.3 mm/d	5.7 mm/d	6.9 mm/d	5.5 mm/d
 Min.
gross capacity at 85% application efficiency	8.6 mm/d	6.7 mm/d	8.1 mm/d	6.5 mm/d
 Min.
gross capacity at 95% application efficiency	7.7 mm/d	6.0 mm/d	7.3 mm/d	5.8 mm/d
 SNIR value not exceeded in 50% of the years	406 mm	87.50%	279 mm	90.90%	381 mm	84.20%	356 mm	80.00%
 355 mm	254 mm	321 mm	285 mm
 July August capacity requirement	5.7 mm/d	4.1 mm/d	5.2 mm/d	4.6 mm/d
 Min.
gross capacity at 85% application efficiency	6.7 mm/d	4.8 mm/d	6.1 mm/d	5.4 mm/d
 Min.
gross capacity at 95% application efficiency	6.0 mm/d	4.3 mm/d	5.4 mm/d	4.8 mm/d
 Table 6.
Relationship of crop yield, Mg/ha, to irrigation capacity for four summer crops at Colby, Kans.
for 34 years  of simulation at a 95% application efficiency.
Crop	Crop Yield Relationship  in Mg/ha to Irrigation Capacity  in mm/d	R2	Standard Error
 Corn	Y = 4.85 + 1.9507 IC 0.0915 IC2 0.0031 IC3	1.000	0.027
 Grain Sorghum	Y = 4.76 + 1.1730 IC 0.1232 IC2 + 0.0038 IC3	0.999	0.041
 Soybean	Y = 1.62 + 0.6173 IC 0.0137 IC2 0.0025 IC3	0.999	0.024
 Sunflower	Y = 1.75 + 0.3973 IC 0.0291 IC2 + 0.0002 IC3	1.000	0.010
 significant yield reductions are greater under deficit irrigation than for grain sorghum and sunflower.
There are little or no differences in exceedance probability of yield reduction for each of the four individual crops when comparing the highest two capacities.
This further emphasizes that the lower 25-mm/day irrigation capacity is sufficient for this soil type in this region, provided center pivot irrigation equipment is in good working condition and that no downtime for repairs is needed and that there is relatively high PAW at crop emergence.
At the 50% exceedance probability level, corn and soybean yields are reduced by 6.2% and 5.5%, respectively, for the 25 mm/6 day irrigation regime while grain sorghum and sunflower yields were reduced only by 1.5% and 3.0%, respectively.
SIMULATION OF ECONOMIC NET RETURNS AS AFFECTED BY IRRIGATION CAPACITY
 The net returns for the four summer crops can be estimated for the different irrigation system capacities.
Although corn is currently the predominant irrigated crop in western Kansas, current 2006 projections indicate soybean is a more profitable alternative.
Production costs which are typically tied to energy costs  are much greater for corn than soybean, SO during these times of rapidly increasing energy costs, corn is less economically competitive.
Net irrigation requirements for soybean are only about 2% lower
 than corn , SO a shift to soybean will not result in significant water conservation.
Sunflower and grain sorghum are better economic alternatives than corn under dryland and extremely deficit irrigation, but with current 2006 yield projections and prices, they are noncompetitive at the higher irrigation capacities.
They do offer the opportunity for stable production at a wider
 Figure 5.
Simulated net returns above direct cash costs for four summer crop yields in relation to irrigation system capacity for the 34 years, 1972 to 2005, Colby, Kans.
The open symbols are for the base assumption 2006 crop price and the closed symbols are for a crop price increase of 10%.
Probability of exceedance, %
 Figure 4.
Probability of exceedance of a given crop yield as affected by irrigation capacity for corn, soybean, grain sorghum, and sunflower assuming a normally distribution, based on simulations for the 34 years, 1972 to 2005, Colby, Kans.
range of irrigation capacity.
This analysis shows that dryland grain sorghum is more profitable than any level of irrigated grain sorghum.
This is reinforced by the fact that irrigated grain sorghum is also not typically chosen by producers in the area.
This may be related to the fact that higher elevations and the resulting cool nights in the region during August and September limit higher grain yields from occurring.
An increase in all crop prices of 10%  indicates that a rise in prices generally has more benefit at the higher irrigation capacities.
If price of one crop rises 10% relative to the others  then in some cases the relative ranking of crops may change.
For instance if corn prices increase by 10% relative to stable prices for the other three commodities, corn becomes the most profitable irrigated crop but not SO under dryland conditions.
This shows the volatility of net return projections and such crop shift scenarios are not that unreasonable.
Ethanol and bioenergy demand is driving up corn price projections for 2007 at a much higher rate than for the other crops.
Similarly, a 10% increase in sunflower prices relative to stable corn indicates that it can be a better and more economically stable crop than corn at all irrigation capacities.
Grain sorghum even with a price increase appears to be a poor irrigated crop choice in this region.
Estimates of the economic net returns above direct cash costs for the base 2006 assumptions as affected by irrigation
 capacity at a 95% Ea can be calculated from the polynomial equations in table 7.
Similar to crop yields, the economic net returns can be shown in a probabilistic sense.
Soybean net returns are more stable for a much broader range of probability than corn particularly at irrigation capacities of 25 mm/6 days or greater.
There is a 75% exceedance probability of net returns exceeding approximately $125/ha for corn for the upper three capacities while net returns for the same exceedance probability for soybean exceeds approximately $275/ha.
Grain sorghum and sunflowers have similar probabilities of net returns and are relatively unaffected by irrigation capacity compared to corn and soybean.
CROP YIELD AND NET RETURN PENALTIES FOR INSUFFICIENT IRRIGATION CAPACITY
 The crop yield and net return penalties for insufficient irrigation capacity at a 95% Ea can be calculated for various irrigation capacities by using the yield and net return relationships in table 6 and 7 and comparing these values to the maximum yield and net returns.
Table 7.
Relationship of net returns above direct costs, $/ha, to irrigation capacity for four summer crops at Colby, Kansas, for 34 years  of simulation at a 95% application efficiency.
Crop	Crop Net Return Relationship  in $/ha to Irrigation Capacity  in mm/d	R2	Standard Error
 Corn	NR = 7.58 + 62.614 3.0145 IC2 0.1552 IC-3	0.999	3.03
 Grain Sorghum	NR = 136.46 2.713 IC + 0.0112 IC2 0.0036 IC3	0.726	4.43
 Soybean	NR = 122.77 + 46.32 IC + 0.1101 IC2 0.3117 IC3	0.996	4.58
 Sunflower	NR = 109.61 + 22.112 IC 2.3911 IC2 + 0.0463 IC3	1.000	0.01
 Probability of exceedance, %
 Figure 6.
Probability of exceedance of a given crop net return as affected by irrigation capacity for corn, soybean, grain sorghum, and sunflower assuming a normally distribution, based on simulations for the 34 years, 1972 to 2005, Colby, Kans.
Table 8.
Penalty to crop yields for center pivot irrigated crop production at 95% application efficiency when irrigation capacity is below 8.5 mm/d.[a]
 Irrigation	Penalty to Crop Yield 	Penalty to Economic Net Returns [b]
 	Corn	Grain Sorghum	Soybean	Sunflower	Corn	Grain Sorghum	Soybean	Sunflower
 8.5	0	0	0	0	$0.00	$0.00	$0.00	$0.00
 6.4	0.19	0.02	0.04	0.01	-$13.70	-$1.72	-$2.00	-$6.34
 5.1	0.9	0.12	0.26	0.1	-$2.88	-$12.82	$11.32	-$14.51
 4.2	1.66	0.35	0.55	0.22	$20.37	-$15.79	$33.20	-$12.78
 3.2	2.9	0.85	1.01	0.44	$59.87	-$10.91	$75.66	-$3.87
 2.5	3.75	1.21	1.31	0.58	$81.86	-$16.72	$100.81	$7.84
 Dryland	8.06	3.43	2.74	1.4	$220.14	-$23.93	$211.29	$44.22
 [a] Results are from simulations of irrigation scheduling and yield for the 34 years, 1972 to 2005, Colby, Kans.
[b] Negative net return penalties indicate a more economically favorable capacity than 8.5 mm/d.
It should be noted that the yield model used in the simulations was published in 1995.
The model may need updating to reflect yield advancements.
However, it is likely that yield improvements would just shift the curves upward in figure 3.
Differences in yield improvements between crops could also affect the relative net returns position of the crops.
WATER USE AND WATER USE EFFICIENCY OF CORN
 Corn is the major irrigated crop in the region, SO additional discussion of this crop is warranted.
The results of the simulations indicate corn yields decrease when irrigation capacity falls below 6.4 mm/d.
The argument is often heard that with today's high yielding corn hybrids it takes less water to produce corn.
So, the argument continues, we can get by with less irrigation capacity.
These two statements are not true.
The actual water use  of a fully irrigated corn crop probably has not decreased in the last 100 years.
Summarizing five studies conducted by different investigators worldwide from 1886 to 1913, Briggs and Shantz  found the average water requirement of corn to be 335 mm.
Further examination of these studies indicates that water requirements varied with crop production, fertilization, and soil texture.
In one of these studies from Logan, Utah , water requirements ranged from 386 to 601 mm depending on soil texture.
Considering the yield potential, fertilization and cropping cultures of that earlier period, the range in corn water use appears comparable to the total calculated ETc for today's corn of about 585 mm in this region.
The more correct statement is more corn grain can be produced for a given amount of water because yields have increased not because water demand is less.
There is some evidence that modern corn hybrids can tolerate or better cope with water stress during pollination.
However, once again this does not reduce total water needs.
It just means more kernels are set on the ear, but they still need sufficient water to ensure grain fill.
Insufficient capacities that may now with corn advancements allow adequate pollination still do not adequately supply the seasonal needs of the corn crop.
OPPORTUNITIES TO INCREASE DEFICIENT IRRIGATION CAPACITIES
 There are many center pivot sprinkler systems in the region that this article would suggest have deficient irrigation capacities.
There are some practical ways irrigators might use to effectively increase irrigation capacities for summer crop production.
These include: 1) plant a portion of the field
 to a winter irrigated crop ; 2) remove end guns or extra overhangs to reduce system irrigated area; 3) clean or chlorinate well screen and gravel pack to see if irrigation capacity has declined due to encrustation or bacterial contamination; 4) determine if the well and pumping plant capacity are appropriate for the irrigation system capacity; 5) check well, pump, and engine/motor efficiencies, and repair or replace if needed.
Corn and soybean have similar net irrigation requirements that are approximately 27% greater than grain sorghum and sunflower.
The minimum recommended gross irrigation capacities  were 6.7, 4.8, 6.1, and 5.4 mm/d  for corn, grain sorghum, soybean, and sunflower, respectively, using center pivot sprinklers operating at 85% Ea.
Using the base economic assumptions from 2006, soybean was a more profitable alternative to irrigated corn.
If corn prices rise at least 10% relative to stable soybean prices due to higher demand that may be driven by ethanol production, corn then becomes the more profitable irrigated crop.
Grain sorghum is a poor crop choice for irrigation in this region and is more profitable under dryland conditions.
Penalties to yield and net returns for corn increase rapidly when irrigation capacity falls below 5.1 mm/d with soybean beginning to decrease rapidly at capacities less than 6.4 mm/d.
Soybeans have a shorter period of irrigation and overall use slightly less irrigation water, but the penalty increases at a faster rate because there is a shorter period to buffer inadequate irrigation capacity with the summer precipitation that does occur.
The question often arises, "What is the minimum irrigation capacity for an irrigated crop?" This is a very difficult question to answer because it greatly depends on the weather, your yield goal, and the economic conditions necessary for profitability.
Corn, grain sorghum, soybean, and sunflower can be grown at very low irrigation capacities and these crops are grown on dryland in this region, but often the grain yields and economics suffer.
Evidence presented in this article would suggest that it may be wise to design and operate center pivot sprinkler irrigation systems in the region with irrigation capacities in the range of 6.4 mm/d for corn and soybean.
In wetter years, lower irrigation capacities can perform adequately, but not SO in drier years.
It should be
 noted that the entire analysis in this article is based on irrigation systems running 7 days a week, 24 hours a day during the typical 90-day irrigation season if the irrigation schedule  demands it.
So, it should be recognized that system maintenance and unexpected repairs will reduce these irrigation capacities further.
Other ideas for a system evaluation that take more time but are good to do occasionally include: 1) check nozzle colors to make sure they match the nozzle chart, 2) do a catch can test on level ground to evaluate the uniformity of the sprinkler package and the irrigation application efficiency, and 3) check the performance of the pumping plant, e.g.
with the Nebraska Pumping Plant Performance Criteria.
When we plug these numbers into the IrrigateCost app, we end up with operating costs of $7.31 per inch of water applied, and ownership costs of $8.76 per inch assuming an average application of 8 inches per year, giving a cost of $16.07 per inch of water applied.
Therefore, the 8 inches of water applied during the year would result in a total annual cost of $128.58 per acre .
The most important rule of thumb is that all equipment will fail.
Job one for the manufacturer, installer, operator, and maintenance personnel is to make sure when electrical devices fail, that it fails in a way that protects human and animal life..
LONG-TERM EFFECTS OF THE DROUGHT ON THE CENTRAL GREAT PLAINS
 Much of the US Central Great Plains is in the midst of a drought that started in 2000 and has persisted through today, 2003.
Although the drought areas shift about and there is sometimes some temporary relief, the persistence and severity of the drought has made successful dryland crop production nearly impossible and even strained many of the irrigated production systems.
Questions have arisen about the long term effects of the drought.
My remarks will be confined to drought effects on crop production and on the Ogallala.
Therefore, my remarks will not specifically address the very real problems of wind erosion hazards and of individual financial strains and bankruptcies.
These indeed can have long term effects.
WHAT EFFECTS ARE BEING OBSERVED?
In my opinion, we are in a historical drought situation.
By that I mean, this extreme drought has not been seen by most of us still actively engaged in farming and ranching and that it will be a story we are likely to refer back to by, "We-II, I remember back in 02, it was so dry " Now, having implied that these are rare conditions, let me point out that with our present situtaion, 2003 could be just as bad or worse.
The drought of 2002 was an Equal Opportunity Drought in that it had broad conditions:
 Widespread across Central Great Plains
 Affected both dryland and irrigated areas
 Affected all irrigation system types
 Affected winter and summer crops
 Affected all crop types
 In mid-summer 2002, all of Colorado was in extreme or exception drought.
Nearly all of Nebraska was in severe to exceptional drought and nearly 2/3 of Kansas was in moderate to exceptional drought.
Dryland crop production even with conservation tillage systems often were a disaster in 2002, particularly for corn  which has less tolerance for extreme drought compared to grain sorghum and sunflowers.
U.S.
Drought Monitor July 30, 2002 Valid 8 a.m.
EDT
 Released Thursday, August 1, 2002 Author: Rich Tinker, CPC N WS/NOAA
 Figure 2.
Failure of the dryland corn leg of the wheat-corn fallow system in 2002, Colby, Kansas.
The severity of the drought in 2002 affected all types of irrigation systems.
Center pivot irrigation systems Problem in 2002: Erratic crop height, pollenation and grain fill.
Furrow  irrigation systems Problem in 2002: Difficulty staying within water right; Water stress between infrequent events.
Subsurface drip irrigation  systems Problem in 2002: Lack of surface soil water for germination
 Since center pivot sprinkler irrigation is the predominate irrigation system in the Central Great Plains, there was obviously a more easily seen and recognized problem with them.
Tremendous differences in crop height, pollination and grain fill were even observed over very short distances.
Many of these differences are attributed to slight amounts of runoff and runon occurring within the field.
Although these differences probably existed for the problem fields in previous years, more average rainfall and lower evapotranspiration would allow these differences to be masked out.
A good way to characterize this problem is to consider a planned irrigation amount of 1 inch.
If only 1/10 inch runoff occurs from a small high spot and then runs into a microdepression, now you have nearby areas receiving 1.1 inches and 0.9 inches, a 22% difference in irrigation.
Compounding this problem over the course of the season by multiple events, resulted in the extremely erratic corn production we experienced under center pivot sprinklers.
The major cause of runoff and runon under sprinklers is too high an irrigation application rate for the soil conditions.
High application rates are a potential problem under many incanopy sprinkler irrigation systems, because the wetted radius of the sprinkler is greatly distorted and reduced by the crop canopy.
We would expect runoff/runon problems to be worse with widely spaced incanopy sprinklers, poorly regulated sprinkler packages, undulating slopes, and conventional tillage.
Examination of many of the problem fields in 2002 showed some of these same design and operational characteristics.
An easy way to determine if runoff/runon occurred was to go to an area in the field where the sprinkler had passed over within the previous day or two.
You could observe wet damp soil in runon depressions by kneeling down and looking at the microrelief.
Another way was to look for a flush of small late season grasses in areas receiving slightly more irrigation.
Some of these characteristics are solvable problems that irrigators could avoid, should 2003 be a twin to 2002.
The economic benefits of correcting a sprinkler package or spacing problems in a year such as 2002, would dwarf the added costs of correcting the problems.
Research conducted at the KSU Northwest Research Extension Center at Colby, Kansas  has shown row-to-row yield differences can be as high as 10-15 bushels/acre for incanopy sprinkler irrigation with 10-foot spaced nozzles.
In 2002, these differences could have been greater.
Figure 3.
Erratic height and ear size differences over very short distances in center pivot sprinkler irrigated corn in 2002, Colby, Kansas.
Figure 4.
Drastic differences in row-to-row ear size for sprinkler irrigated corn in 2002, Colby, Kansas.
Note: Ears from same area depicted in Figure 3.
Often a group of relatively small or unrecognized sprinkler problems combined negatively to add up to a major problem in 2002.
Figure 5 depicts a poor yielding area in a field where three additive sprinkler problems existed.
This combined problem has probably existed for years, but only became strongly recognizable in 2002.
Figure 5.
Poor yielding corn under a sprinkler nozzle in 2002, Colby, Kansas.
The three problems that caused the reduced yield are sprinkler height differences  with no pressure regulators, incorrect overlap due to height differences and the evaporation difference due to the height difference.
Since the system had a relatively low operating pressure  it would be presumed that the lack of pressure regulation on the height difference is the major cause of yield reduction.
Other problems in 2002 involved irrigation wells and pumps experiencing decreased pumping capacity, sucking air and cascading water.
Some irrigators have expressed concern that these problems are long-term.
In general these problems are probably not long term, but will be discussed later in this paper.
Both winter and summer crops were affected in 2002 and this placed additional financial burdens on the producer already experiencing poor economic conditions.
No crop really escaped the wrath of the drought.
In some cases, lack of germination stopped the crop from day one.
WHAT IS THE SEVERITY OF THESE EFFECTS?
While the individual factors of lower precipitation, higher temperatures and higher evapotranspiration were all abnormal values, their combining in such a negative fashion resulted in the extreme situation we experienced.
The annual precipitation for 2002 at the KSU Northwest Research-Extension Center was 12.93 inches, approximately 2/3 of the long term average value, but the spring and early summer precipitation was extremely deficient.
Very similar drought conditions were also present in 2000 and 2001.
Figure 6.
Precipitation patterns at the KSU Northwest Research-Extension Center, Colby, Kansas for 1999-2002.
In addition, elevated temperatures in the early summer  and continuing into July  resulted in larger than normal evaporation and transpiration losses from the soil and crop, respectively.
The evapotranspiration for 2000, 2001 and 2002 were all 3 to 4 inches above the long-term average amount.
Figure 7.
Monthly average maximum daily temperatures for KSU Northwest Research-Extension Center, Colby, Kansas for 1999-2002.
Figure 8.
Cumulative corn evapotranspiration  for 2000-2002 as compared to the 30 year average, KSU Northwest Research-Extension Center, Colby, Kansas.
Many irrigation systems in western Kansas do not have the capacity in the typical 90 day irrigation season to apply the irrigation requirements of 2000, 2001 and 2002 Figure 9.
Thus, many irrigated corn fields failed or had very poor yields.
Figure 9.
Required irrigation amounts in 2000-2002 were 5-7 inches greater than normal based on simulated irrigation schedules for the KSU Northwest Research-Extension Center, Colby, Kansas.
The problem of decreasing inseason well performance and pumping rates resulted in:
 Increased labor and management to renozzle center pivots.
Increased water stress due to less capacity.
Poor uniformity and/or pump damage if not recognized and fixed.
ARE THESE EFFECTS TEMPORARY OR PERMANENT?
Well, it's a good news/bad news situation.
The Good News is good crop yields will return when more average climatic conditions return.
The Bad News is the drought continues and the normal winter period precipitation is low, so soil water reserves may be low next spring.
U.
S.
Seasonal Drought Outlook
 Through April 2003 Released January 16, 2003
 KEY: Drought to persist or intensify Drought ongoing, some improvement Drought likely to improve, impacts ease Drought development likely
 Depicts general, large-scale trends based on subjectively derived probabilities guided by numerous indicators, including short and long-range statistical and dynamical forecasts.
Short-term events-such as individual storms -cannot be accurately forecast more than afew days in advance, so use caution if using this outlook for applications -such as crops -that can be affected by such events "Ongoing" drought areas are schematically approximated from the Drought Monitor.
For weekly drought updates, see the latest Drought Monitor map and text.
The Bad News is increased groundwater use during the drought and for its duration is essentially a permanent loss from the Ogallala.
The Good News is the Ogallala is still a huge resource and the annual effect of the drought on the aquifer is relatively small.
The Bad News is in the future, problems of decreased pumping rates and cascading water will likely increase as groundwater levels further decline.
The Good News is these effects will be seasonal with considerable overwinter recovery.
When the drought ends these effects will lessen somewhat, due to less pumping requirements.
Figure 11.
Long term decline in aquifer water levels and partial overwinter recovery of observation well at KSU Northwest Research-Extension Center, Colby, Kansas.
Note: Seasonal declines are caused by drawdown.
In summary, the effects on crop production and on the Ogallala are to a great extent temporary.
The direct effects on the Ogallala are slow to be realized, so when the drought ends, the scale of these effects is not large.
Hopefully, the greatest effect will be social--the renewed understanding of the value of water and its importance in Central Great Plains.
OK, That is Great, But I Want to Use My End Gun.
The best answer may be to just not use the end gun because of its lower uniformity and the fact that it will lower the nitrogen application rate when it comes on.
However, two methods of solving this problem come to mind.
The first is to purchase a variable rate injection pump and the second is, if the pivot is equipped with a computer panel, keep using the lower cost fixed rate injection pump and simply slow the pivot down when the end gun turns on.
Twenty-Two Years of SDI Research in Kansas
 This paper will summarize research efforts with subsurface drip irrigation in Kansas that has occurred during the period 1989 through 2010.
Special emphasis will be made on brief summaries of the different types of research that have been conducted including water and nutrient management for the principal crops of the region, SDI design parameters and system longevity and economics.
Annual system performance evaluations have shown that dripline flowrates are within 5% of their original values.
Economic analysis shows that systems with such longevity can be cost competitive even for the lower-valued commodity crops grown in the region.
Introduction and Brief History
 Subsurface drip irrigation  technologies have been a part of irrigated agriculture since the 1960s, but have advanced at a more rapid pace during the last 20 years.
In the summer of 1988, K-State Research and Extension issued an in-house request for proposals for new directions in research activity.
A proposal entitled Sustaining Irrigated Agriculture in Kansas with Drip Irrigation was submitted by irrigation engineers Freddie Lamm, Harry Manges and Dan Rogers and agricultural economist Mark Nelson.
This project led by principal investigator Freddie Lamm, KSU Northwest Research-Extension Center , Colby, was funded for the total sum of
 $89,260.
This project financed the initial development of the NWREC SDI system that was expressly designed for research.
In March of 1989, the first driplines were installed on a 3 acre study site which has 23 separately controlled plots.
This site has been in continuous use in SDI corn production since that time, being initially used for a 3-year study of SDI water requirements for corn.
In addition, it is considered to be a benchmark area that is also being monitored annually for system performance to determine SDI longevity.
In the summer of 1989, an additional 3 acres was developed to determine the optimum dripline spacing for corn production.
A small dripline spacing study site was also developed at the KSU Southwest Research-Extension Center  at Garden City in the spring of 1989.
In the summer of 1989, further funding was obtained through a special grant from the US Department of Agriculture.
This funding led to expansion of the NWREC SDI research site to a total of 13 acres and 121 different research plots.
This same funding provided for a 10 acre SDI research site at Holcomb, Kansas administered by the SWREC.
By June of 1990, K-State Research and Extension had established 10 ha of SDI research facilities and nearly 220 separately controlled plot areas.
Over the course of the past 22 years, additional significant funding has been obtained to conduct SDI research from the USDA, the Kansas Water Resources Research Institute, special funding from the Kansas legislature, the Kansas Corn Commission, Pioneer HiBred Inc., the Mazzei Injector Corporation and Syngenta.
Funding provided by the Kansas legislature through the Western Kansas Irrigation Research Project  allowed for the expansion of the NWREC site by an additional 1 acres and 46 additional research plots in 1999.
An additional 22 plots were added in 2000 to examine swine wastewater use through SDI and 12 plots were added in 2005 to examine emitter spacing.
Three research block areas originally used in a 1989 dripline spacing study have been refurbished with new 5 ft spaced driplines to examine alfalfa production and emitter flowrate effects on soil water redistribution.
The NWREC SDI research site comprising 19 acres and 201 different research plots is the largest facility devoted expressly to small-plot row crop research in the Great Plains and is probably one of the largest such facilities in the world.
Since its beginning in 1989, K-State SDI research has had three purposes: 1) to enhance water conservation; 2) to protect water quality, and 3) to develop appropriate SDI technologies for Great Plains conditions.
The vast majority of the research studies have been conducted with field corn because it is the primary irrigated crop in the Central Great Plains.
Although field corn has a relatively high water productivity , it generally requires a large amount of irrigation because of its long growing season and its sensitivity to water stress over a great portion of the growing period.
Of the typical commodity-type field crops grown in the Central Great Plains, only alfalfa and similar forages would require more irrigation than field corn.
Any significant effort to reduce the overdraft of the Ogallala aquifer, the primary water source in the Central Great Plains, must address the issue of irrigation water use by field corn.
Additional crops that have been studied at the NWREC SDI site are soybean, sunflower, grain sorghum, alfalfa and demonstration trials of melons and vegetables.
This report summarizes several studies conducted at the KSU Northwest and Southwest Research-Extension Centers at Colby and Garden City, Kansas, respectively.
A complete discussion of all the employed procedures lies beyond the scope of this paper.
For further information about the procedures for a particular study the reader is referred to the accompanying reference papers when so listed.
These procedures apply to all studies unless otherwise stated.
The two study sites were located on deep, well-drained, loessial silt loam soils.
These medium-textured soils, typical of many western Kansas soils, hold approximately 18.9 inches of plant available soil water in the 8 ft profile at field capacity.
Study areas were nearly level with land slope less than 0.5% at Colby and 0.15% at Garden City.
The climate is semi-arid, with an average annual precipitation of 18 inches.
Daily climatic data used in the studies were obtained from weather stations operated at each of the Centers.
Most of the studies have utilized SDI systems installed in 1989-90.
The systems have dual-chamber drip tape installed at a depth of approximately 16 to 18 inches with a 60-inch spacing between dripline laterals.
Emitter spacing was 12 inches and the dripline flowrate was 0.25 gpm/100 ft.
The corn was planted so each dripline lateral is centered between two corn rows.
Figure 1.
Physical arrangement of the subsurface dripline in relation to the corn rows.
A modified ridge-till system was used in corn production with two corn rows, 30 inches apart, grown on a 60 inch wide bed.
Flat planting was used for the dripline spacing studies conducted at both locations.
In these dripline spacing studies, it was not practical to match bed spacing to dripline spacing with the available tillage and harvesting equipment.
Additionally at Garden City, corn rows were planted perpendicular to the driplines in the dripline spacing study.
All corn was grown with
 conventional production practices for each location.
Wheel traffic was confined to the furrows.
In order to complete your training, you need to study each chapter and complete any activity related to that module.
Each module/activity is "locked" meaning you will not be able to proceed until completing the previous section.
Please Note:  You must complete all video verfications for each Chapter  before the option to take the Chemigation test will appear.
A list of Nebraska certified applicators and the year their certifications will expire can be found on the NDEE website by selecting the 'Focus on Water', then clicking on Chemigation Applicator List.
Water Efficiency Irrigation Program
 Dr.
Ethan Orr ,Robert Masson, and Stephanie Brennan
 Agriculture in the American Southwest provides the nation with high quality food, feed, and fiber.
Blessed with hot summers, mild winters, and dry climates Arizona has become a center for growing specialty crops of unparalleled quality.
In our current climate, one of the most limiting factors to crop production in Arizona is water availability, driving the desire for more conservative use on the farm.
State funding has been allocated to assist commercial growers transitioning to more efficient water use practices.
Reimbursement grants will be awarded up to $1,500 per acre to support infrastructure costs of farms transitioning away from flood irrigation to more efficient technologies, expected to provide a 20% or greater water savings.
The University of Arizona Cooperative Extension group is tasked with administering the reimbursement grants and will assist growers with understanding available options and development of best use practices.
Program Overview and Requirements
 Applicants must have a grower permit issued by the Arizona Department of Agriculture pursuant to A.R.S.
3-363.
Landowners or active leaseback farmers identify current flood irrigated fields that would benefit from irrigation improvement technology.
A grant request form is emailed to the Extension review committee who will assist with designing and reviewing an irrigation efficiency plan for the land.
Up to $1,000,000 in grant funds per farm will be paid directly to approved vendors to install irrigation improvement infrastructure that has previously demonstrated the ability to reduce water use by >20%.
Irrigation water use will be monitored by the review committee for three years after improvement to advise on optimal in-season use and assist with adjustments to salinity management program.
Application process is ongoing, and proposals may be submitted until October 2026
 DR.
ETHAN ORR Associate Director ANR and Economic Development
 STEPHANIE BRENNAN Assistant Agricultural Agent, Arizona Cooperative Extension, University of Arizona
 ROBERT MASSON Administrative Assistant III Water Irrigtion Efficiency Program
Approximately 40 attendees gathered for a tour of the Corteva Agriscience production facility just south of Doniphan, beginning at 4 p.m.
Much was learned about Corteva as a company, their westernmost production facility located in Doniphan, and their processes in the production of seed corn.
The TAPS group was split into two smaller groups and then taken on a detailed tour of the facility, which processes the seed corn from on-the-ear harvest stage to packaging.
Harvest is completed when corn is still at 35% to 37% moisture and delivered to the plant by producers that are mainly within a 45-mile radius of the plant.
The facility can hold about a million bushels onsite, but around 1.5 million bags of seed corn are processed in a year.
Proper irrigation of grapes is essential to maintaining a healthy and productive planting.
Over-irrigation slows root growth, increases iron chlorosis on alkaline soils, and leaches nitrogen, sulfur, and boron out of the root zone leading to nutrient deficiencies.
Excessive soil moisture also promotes root rot, particularly on heavy soils.
Applying insufficient irrigation water results in drought stress.
Excessive drought stress during fruit development results in reduced fruit size and yield, and poor fruit quality.
Properly managing irrigation is analogous to managing a bank account.
In addition to knowing the current bank balance , it is important to track both expenses  and income.
Bank Balance 
 How big is my bank account?
Water holding capacity First, some terminology:
 Field Capacity is the amount of water that can be held in the soil after excess water has percolated out due to gravity.
Permanent Wilting Point is the point at which the water remaining in the soil is not available for uptake by plant roots.
When the soil water content reaches this point, plants die.
Available Water is the amount of water held in the soil between field capacity and permanent wilting point.
Allowable Depletion  is the point where plants begin to experience drought stress.
Depending on soil type, the amount of allowable depletion for grapes is about 60 percent of the total available water in the soil.
However, allowable depletion can also differ during the seasonal development of grapes.
The goal of a well-managed irrigation program is to maintain soil moisture between field capacity and the point of allowable depletion, or in other words, to make sure that there is always readily available water and that plants do not experience water stress.
The amount of readily available water is related to the effective rooting depth of the plant, and the water holding capacity of the soil.
The effective rooting depth depends on soil conditions and variety.
Although some roots grow deeper, the majority of grape roots are found in the top 3 feet of soil.
The water holding capacity within that rooting depth is related to soil texture, with coarser soils  holding less water than fine textured soils such as silts and clays.
For example, a sandy loam soil at field capacity would contain 0.72 to 0.9 inches/foot of readily available water, compared to a clay loam which holds 1.02 to 1.20 inches/foot.
Figure 1.
Soil water content from saturated to dry.
Optimal soil moisture levels for plant growth are between field capacity and allowable depletion.
What's in the bank?
-Measuring Soil Moisture
 In order to assess soil water content, one needs to monitor soil moisture at several depths.
Monitors should be placed in the primary root zone  and near the bottom of where the thickly branched lateral roots grow.
One of the most cost effective and reliable methods for measuring soil moisture is by electrical resistance block, such as the WatermarkTM sensor.
These blocks are permanently installed in the soil, and wires from the sensors are attached to a handheld unit that measures electrical resistance.
Resistance measurements are then related to soil water potential, which is an indicator of how hard the plant roots have to "pull" to obtain water from the soil.
Figure 2.
The amount of allowable depletion, or the readily available water, represents about 50 percent of the total available water.
The handheld unit reports soil moisture content in centibars, where values close to zero indicate a wet soil and higher values represent an increasingly dry soil.
The relationship between soil water potential and available water differs by soil type.
The range of the sensor is
 calibrated to 0 to 200 centibars which covers the range of allowable depletion in most soils.
The sensors are less effective in coarse sandy soils, and will overestimate available soil water in saline soils.
Remember that allowable depletion is about 60% of available water, which roughly corresponds to soil water potentials of 4555 centibars for a loamy sand soil, and 65-95 centibars for a loam.
Some weather stations in Utah are programmed to calculate and report the ET estimates for alfalfa as a reference crop.
The ET of grapes can be determined by multiplying the ET, by a correction factor or crop coefficient  that is specific to grapes and stage of development.
Note: Some publications use ETo which is a grass reference ET, which uses a different set of Kcrop values.
= ETr X Kcrop
 Table 1.
Available water holding capacity for different soil textures, in inches of water per foot of soil.
Total available water is the amount of water in the soil between field capacity and permanent wilting point.
Allowable depletion  is the amount of water the plant can use from the total available before experiencing drought stress.
For grapes, allowable depletion is approximately 60 percent of total available.
Total Available	Allowable Depletion inches
 Soil Texture	Water	
 inch/foot	In top 1'	In top 3'
 Sands and fine sands	0.5 0.75	0.3 0.45	0.9 1.35
 Loamy sand	0.8 1.0	0.48 0.6	1.44 1.8
 Sandy loam	1.2 1.5	0.72 0.9	2.16 2.7
 Loam	1.9 2.0	1.14 1.2	3.42 3.6
 Silt loam, silt	2.0	1.2	3.6
 Silty clay loam	1.9 2.0	1.14 1.2	3.42 3.6
 Sandy clay loam, clay loam	1.7 2.0	1.02 1.2	3.06 3.6
 The Kcrop for table and juice grapes are shown in Figure 3.
At leaf emergence in the spring , both types of grapes use the same amount of water, about 16% of the amount of water used by the alfalfa reference crop.
For table grapes, water use steadily increases until full canopy  when water use is 83% of a reference alfalfa crop.
Crop coefficient remains steady through the end of summer and fall, until a killing frost stops leaf activity.
Supplying full irrigation ensures large berry size, an important characteristic for table grapes.
For wine grapes, water use increases somewhat more quickly than table grapes during the early growth stages until just over half-filled canopy 
 when water use levels off at a much lower 65% of a reference alfalfa crop.
Water use remains steady for the rest of the growing season until a killing frost.
Table 2.
Recommended WatermarkTM sensor values at which to irrigate.
Soil Type	Irrigation Needed
 Loamy sand	45 55
 Sandy loam	55 75
 Silt loam, silt	75 95
 Clay loam or clay	95 125
 TMWatermark is a registered trademark of Irrometer, Co., Riverside, CA.
Table 3.
Daily total alfalfa reference evapotranspiration  for nine Utah cities expressed in  inches per day,  gallons per acre per day, and  drip-irrigated gallons per 100 feet of row length per day.
Month	Logan	Brigham	Ogden	Salt Lake	Spanish	Green	Richfield	Cedar	St.
George
 City	City	Fork	River	City
  Inches per day
 Mar	0.09	0.1	0.1	0.11	0.12	0.15	0.14	0.13	0.15
 Apr	0.15	0.16	0.17	0.17	0.16	0.23	0.2	0.18	0.22
 May	0.2	0.22	0.22	0.22	0.21	0.29	0.23	0.24	0.28
 Jun	0.24	0.27	0.28	0.28	0.26	0.32	0.3	0.31	0.32
 Jul	0.29	0.32	0.32	0.3	0.28	0.32	0.29	0.29	0.31
 Aug	0.26	0.28	0.29	0.27	0.25	0.25	0.27	0.27	0.28
 Sep	0.18	0.2	0.2	0.19	0.18	0.2	0.2	0.21	0.21
 Oct	0.09	0.12	0.12	0.11	0.1	0.12	0.13	0.14	0.14
  Gallons per acre per day.
Irrigation amounts need to be adjusted by Crop Coefficient and Irrigation
 Mar	2444	2716	2716	2987	3259	4073	3670	3451	4073
 Apr	4073	4345	4617	4617	4345	6246	5386	5006	5974
 May	5431	5974	5974	5974	5703	7875	6360	6412	7604
 Jun	6517	7332	7604	7604	7061	8690	8102	8500	8690
 Jul	7875	8690	8690	8147	7604	8690	7937	7788	8418
 Aug	7061	7604	7875	7332	6789	6789	7385	7306	7604
 Sep	4888	5431	5431	5160	4888	5431	5522	5739	5703
 Oct	2444	3259	3259	2987	2716	3259	3609	3741	3802
  Drip-irrigated gallons per 100 feet of row length per day based on 10-foot2 row spacing.
Irrigation
 amounts need to be adjusted by Crop Coefficient and Irrigation Efficiency.
Mar	56	62	62	69	75	94	84	79	94
 Apr	94	100	106	106	100	143	124	115	137
 May	125	137	137	137	131	181	146	147	175
 Jun	150	168	175	175	162	199	186	195	199
 Jul	181	199	199	187	175	199	182	179	193
 Aug	162	175	181	168	156	156	170	168	175
 Sep	112	125	125	118	112	125	127	132	131
 Oct	56	75	75	69	62	75	83	86	87
 SuperscriptConversion to gallons per acre per day  =  X 7.481 * 43560 / 12.
210-foot bed spacing is appropriate for grape.
Adjust calculation according to row spacing.
Calculation for drip-irrigation:  =  X 10 ft.
/ 435.6.
If different row spacing is used, adjust calculation accordingly.
Calculated from long-term monthly evapotranspiration values from Hill, 2011.
Table and Juice Grapes
 Some grape producers will intentionally drought stress their plants at certain stages of crop development by applying less water than the vineyard would typically use under those conditions.
This intentional drought stress is called Regulated Deficit Irrigation.
RDI during the appropriate stage of development will reduce berry size, resulting in increased skin/pulp ratio.
Smaller berries allow for better airflow within the cluster, reducing potential for disease and split berries.
In red grape varieties, RDI often results in improved color.
Vegetative growth is reduced with RDI, which decreases pruning and fruit shading.
However, total yield is also reduced when compared to a planting receiving irrigation for 100% ET replacement.
Growers accept this lower yield because of the increase in wine grape quality.
Although many effects of deficit irrigation are beneficial, some can be harmful depending on timing and severity.
Severe water deficits limit photosynthesis and the production of sugar and cause defoliation and sunburn.
The most important times to avoid water stresses are from flowering to pea-size grapes, softening of grapes to harvest, and then after harvest.
Water use is relatively low from leaf emergence  to flowering and water stress from pea-size to softening  is less critical than other stages.
Avoid water stress from softening to harvest , especially with table and juice grapes, because grape size significantly increases and water use is high due to hotter temperatures and fruit growth.
Avoid water stress after harvest SO plants can build reserves for next season and grow roots.
As fall air temperature decreases, less water is needed by the plants.
Other factors that increase water use are groundcover between rows, grass cover or weedy alleys, and excessive canopy growth.
A very common RDI regime is to apply 60 to 70 percent of ET between fruit set and harvest.
Once harvest is complete, RDI is not recommended.
Instead, increase irrigation to facilitate root growth and to prepare the plant for winter.
Since each vineyard is different  and production goals vary, exact irrigation scheduling must be determined individually.
Knowing what level of water reduction, at what time and for how long takes careful monitoring of soil moisture, shoot length and growth rate, shoot tip condition, and leaf water potential.
See the additional resources section for more information on RDI.
Vineyards with very low vigor should not be subjected to RDI.
Income Irrigation and Rainfall
 In Utah's high elevation desert climate, rainfall only contributes a small fraction of the in-season water requirements of grapes.
Therefore, regular irrigation is needed to supply plant water needs.
Irrigation water can be supplied by furrow, impact sprinklers, microsprinklers, or drip lines.
Flood and furrow irrigation requires the land to be well graded to allow for uniform distribution.
Slope of the field should not exceed 2% to reduce erosion.
Flood irrigation can increase pest problems such as powdery mildew and increased weed pressure from weed seed in unfiltered irrigation water.
Field access after irrigation events is also limited.
Overhead sprinklers can be used on uneven lands and can save on field grading costs.
The irrigation water must be low in salts to reduce the risk of leaf burn.
Excessive wetting can lead to disease problems.
Sprinkler irrigation frequency should allow several days for canopy drying.
During hot summer weather,
 overhead irrigation can give some evaporative cooling of the leaves and fruit, but irrigation must be stopped in the late afternoon to allow leaves and fruit to dry out before night time, to prevent disease incidence.
Microsprinklers and drip irrigation  both have the advantage of being able to be used over uneven topography, like overhead sprinklers, but do not wet the plant canopy, which minimizes disease risks.
Irrigation events must be more frequent than flood and overhead sprinklers.
This may be an issue if timing of your irrigation water is limited.
In a drip system the irrigation water must be filtered to prevent particles in the water from clogging emitters.
Whichever irrigation system you utilize, it is important to calibrate your system SO that you know precisely how much water is being applied.
With sprinklers and microsprinklers, the simplest way to do this is to place catch cans in multiple locations in your planting and collect water for a set period of time.
The amount of water collected over time will give you an application rate , and differences in water collected among the catch cans will tell you how uniform the application is within your planting.
When trying to determine application uniformity, it is best to measure output at both ends of your irrigation system.
Also, if your planting is on a slope, you should measure output at the highest and lowest points of your field.
Elevation differences and the distance the water travels through the irrigation lines both affect water pressure, and consequently the flow rate at the nozzle.
Figure 4.
Grape vineyard with drip irrigation suspended between trellis posts.
Drip irrigation tubing comes with recommended operating pressures, a range of emitter spacings, and flow rates.
Most drip tubes operate at 10-20 psi depending on field topography.
Emitters may be spaced from 4 to 36 inches apart and come in a variety of flow rates.
Flow rates are commonly reported in gallons per 100 feet of tape per hour  or gallons/emitter/hr.
For a tube with a 12-inch emitter spacing, 24 gallons/100ft/hr = 0.24 gallons/emitter/hr.
Pressure compensating emitters  provide the best uniformity.
Flow rate from each emitter and emitter spacing can be used to calculate rate per area.
Drip irrigation systems are usually operated every day or every few days to maintain optimal soil moisture.
The efficiency of your system is a measure of how much you have to over-water the wettest spots in the field to get adequate water to the dry spots.
Efficiency is related to the uniformity of application and to the amount of evaporation that occurs before the water can move into the soil.
A well-designed drip system can be 80 to 90% efficient.
Overhead sprinkler systems are typically 60 to 75% efficient, while flood and furrow irrigation is typically 30 to 50% efficient.
If your water supply is limited, a more efficient system can make a large difference in water savings and crop productivity.
Good irrigation management requires:
 1.
An understanding of the soil-plant-water relationship.
2.
Properly designed and maintained irrigation system, and understanding of system efficiency.
3.
Proper timing based on
 a.
Soil water holding capacity
 b.
Weather and its effects on crop demand
 C.
Stage of growth.
Each of these components requires a commitment to proper management.
Proper management will lead to the maximum yields per available water and will optimize the long-term health and productivity of your planting.
Following is an example of how to calculate water needs for a wine grape vineyard in St.
George, Utah, in July with a full canopy.
The soil is a deep loam with drip irrigated rows every 10 feet.
o Water use 
 ETr values are 0.31 inches per day.
Crop coefficient is 0.65.
ETcrop = ET X Kcrop
 ETcrop = 0.31 inches/day * 0.65 = 0.2 inches/day
 Soil storage capacity.
The total storage capacity for readily available water over the 3-foot effective rooting depth is 3.5 inches (Table However, using a drip system with a single drip line per row results in only about 1/4 of the soil being irrigated.
Therefore, storage capacity is 1/4 of 3.5 inches, or 0.88 inches.
0.88 inches of storage, with 0.2 inches consumed per day = 4 days between
 irrigations.
In 4 days replace 0.88 inches.
Restated, the soil moisture in the root zone will go from field capacity to plant stress levels in 4 days.
Surface Irrigation Flow  Inches of application per hour  = cfs divided by the number of acres  Example: 4 cfs /5 ac = 0.8 in/hr
 Sprinkler Irrigation Flow  per nozzle ) In/hr = 96.4 times gpm/noz divided by nozzle coverage area 
 Note: Nozzle coverage area is calculated as the nozzle spacing times the line spacing, or the width times the length of the coverage area under a single nozzle.
Example: 96.4 X 7 gpm/noz /  = 0.28 in/hr
 Drip Irrigation Flow  In/hr = 1.6 times gph divided by emitter coverage area  Note: Emitter coverage area is calculated as the emitter spacing times the line spacing.
Example: 1.6 0.5 gph/  = 0.32 in/hr
 Irrigation Set Times Set time  = Gross Irrigation Need  divided by the application rate 
 Example: Set Time = 3 in / 0.28 in/hr = 10.7 hrs
 Conversions 1 cfs = 448.8 gpm 1 gpm = 60 gph 1 acre = 43,560 feet2
 This project is funded in part by USDA-Risk Management Agency under a cooperative agreement.
The information reflects the views of the author and not USDA-RMA.
Utah State University is committed to providing an environment free from harassment and other forms of illegal discrimination based on race, color, religion, sex, national origin, age , disability, and veteran's status.
USU's policy also prohibits discrimination on the basis of sexual orientation in employment and academic related practices and decisions.
Utah State University employees and students cannot, because of race, color, religion, sex, national origin, age, disability, or veteran's status, refuse to hire; discharge; promote; demote; terminate; discriminate in compensation; or discriminate regarding terms, privileges, or conditions of employment, against any person otherwise qualified.
Employees and students also cannot discriminate in the classroom, residence halls, or in on/off campus, USU-sponsored events and activities.
This publication is issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Kenneth L.
White, Vice President for Extension and Agriculture, Utah State University.
landowners, state action through the PGMA process, or adding territory to an existing district.
Most districts have been created through the Legislature, where the local senator or representative often introduces and carries the bill on the district.
All GCD creations with authority to levy ad valorem  taxes are subject to a confirmation election by voters within the proposed district.
Voters also elect directors and approve the ad valorem tax rate to finance the district.
Educational programs of the Texas Agricultural Extension Service are open to all people without regard to race, color, sex, disability, religion, age or national origin.
Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 30, 1914, in cooperation with the United States Department of Agriculture.
Chester P.
Fehlis, Deputy Director, Texas Agricultural Extension Service, The Texas A&M University System.
Texas Agricultural Extension Service
 T exas is blessed with extensive groundwater resources.
Most areas of the state are underlain by one or more of nine major aquifers and 20 minor aquifers.
As a result, approximately 57 percent of fresh water use and nearly 80 percent of agricultural water use in Texas come from groundwater supplies.
Proper management and protection of the quality of this groundwater resource are widely recognized as being vital to Texas' economy and growth, human health and well being, and preservation of ecosystems.
To help protect and manage the groundwater resources, the Texas Legislature has established a process for local management through groundwater conservation districts.
Texas law distinguishes between surface water and groundwater.
All surface water, including streams, rivers and lakes, belongs to the state.
The only exception is diffused water, such as storm water runoff, which belongs to the landowner.
Surface waters are "held in trust" by the state and appropriated to users through permits or "water rights."
 In sharp contrast to surface water, groundwater law is based on the English common law doctrine.
This doctrine and its interpretation through case law provide that the landowner may withdraw groundwater without limitations and without being liable to neighboring landowners for any harmful effects resulting from the withdrawal.
This is commonly referred to as the "right of capture." The right of landowners to capture and make "nonwasteful" use of groundwater has been upheld by Texas courts over the years with only a few exceptions.
Texas groundwater law has often been called the "law of the biggest pump"; the deepest, largest well and most powerful pump gets the water.
Texas has established local groundwater conservation districts  to manage groundwater through a number of powers they can invoke.
Landowners outside of conservation districts have little recourse in protecting local groundwater or in limiting groundwater pumping impacts by neighbors.
The Texas Legislature first provided for the voluntary creation of groundwater conservation districts in 1949.
These conservation districts could be
 created over any groundwater reservoir designated by the state.
The Texas Legislature, while continuing to acknowledge the "right of capture" of groundwater by landowners, passed additional legislation in 1985 and 1997 to encourage the establishment of groundwater conservation districts and, in limited cases, to allow for the creation of districts by state initiative.
This legislation confirmed that locally controlled groundwater conservation districts are the state's preferred method of managing groundwater resources.
The legislation also stressed the importance and responsibility of GCDs in developing and implementing comprehensive management plans to conserve and protect groundwater resources.
As of January 1999, 45 groundwater districts exist in Texas.
The rationale supporting the local creation and control of groundwater districts is related to the large diversity of climatic conditions, water use patterns, growth projections and aquifer characteristics across the state.
This diversity would make it difficult to formulate and administer uniform laws and regulations to govern the development and use of groundwater statewide.
Locally controlled ground water conservation districts, with rules, programs and activities specifically addressing the local problems and opportunities, is perceived as the preferred method in Texas.
Priority Groundwater Management Areas
 The 1985 legislation, House Bill 2, contained provisions for the Texas Water Commission  to identify
 groundwater management areas.
PGMAs may be designated by the TNRCC in regions that are experiencing or that are expected to experience, within the next 25 years, critical groundwater problems such as shortages of surface water or groundwater, land subsidence and contamination of groundwater.
A detailed study is conducted before a "study area" is declared a PGMA.
To the extent possible, PGMAs are to coincide with the boundaries of groundwater formations.
To date, 16 PGMA studies have been completed, and four study areas have been designated as PGMAs.
GCD Powers and Responsibilities
 Groundwater conservation districts are charged to manage groundwater by providing for the conservation, preservation, protection, recharging and prevention of waste of the groundwater resources within their jurisdictions.
Groundwater conservation districts have required duties that must be performed, as well as a number of authorized powers that may be invoked.
Some of the required duties of ground-water conservation districts are to:
 Develop and adopt a comprehensive management plan for the most efficient use of groundwater, for controlling and preventing waste of groundwater, and for controlling and preventing land subsidence.
Require permits for drilling, equipping or completing wells that produce more than 25,000 gallons per day or for alterations
 to well size or well pumps.
Regulations also specify requirements on the organization and operation of a groundwater conservation district, such as operating on the basis of a fiscal year, holding regular board meetings, etc.
Adopt rules to conserve, preserve, protect, recharge and prevent waste of groundwater and control land subsidence.
Provide for the spacing of water wells and regulate the production of wells.
Acquire land to erect dams or to drain lakes, draws and depressions; construct dams; and establish sites for groundwater recharge.
Purchase, sell, transport and distribute surface water or groundwater for any purpose.
Carry out research projects and collect information regarding the use of groundwater, water conservation and the practicability of recharging a groundwater reservoir.
Promulgate rules to require permits for transferring groundwater out of the district.
Groundwater conservation districts can be created by one of four procedures: legislative action, petition by
 areas of the state that have critical groundwater problems.
Such problems include aquifer depletion, water quality contamination, land subsidence or shortage of water supply.
Accordingly, beginning in 1986, the TWC and the Texas Water Development Board identified possible critical areas and conducted further studies.
In 1997, the Texas Legislature enacted Senate Bill 1, a major water planning and management bill that, among other provisions, required regional water planning and development of a state plan.
The bill also reconfirmed and strengthened provisions for the creation of groundwater conservation districts by state initiative in priority
* by Dennis Cash, Raymond Ditterline and Robert Dunn
 Alfalfa-the most productive and most widely adapted forage species-is indeed "Queen of the Forages." A grower's initial decision to produce alfalfa and subsequent choice of varieties have long-term consequences.
There are over 200 alfalfa varieties available in the northern USA and Canada, and this number increases by 30 to 40 new varieties each year.
Alfalfa varieties should be chosen on the basis of winter hardiness, yield potential, pest resistance, persistence, forage quality and availability.
Montana has variety performance trials in major irrigated and dryland hay production areas.
Performance summaries are published annually and are available to Extension agents, growers and seed companies.
"Recommended" varieties have been widely tested in Montana for a minimum of three years at four locations.
Obviously, local information should be used by growers to narrow down the list of potential varieties.
The final step is to choose a reputable local seed supplier.
In most cases, the seed companies have a complete lineup of alfalfa varieties, as well as additional performance information and recommendations
 "Extension Crop Specialist, Professor of Forage Genetics and Research Associate in Forages, respectively, Department of Plant & Soil Sciences, Montana State University, Bozeman, MT 59717
 In most areas of the northern US and Canada, winter hardiness is the key factor influencing stand longevity and forage yield.
Alfalfa varieties are classified depending upon how rapidly they become dormant in late summer.
Early fall-dormant varieties are more winter-hardy than nondormant varieties; thus earliness of fall dormancy has historically been used as a measure of winter hardiness.
Very dormant varieties  such as 'Ladak 65' have heavy first cut yields but have very little fall growth.
Very nondormant varieties  produced in the desert southwestern USA continue growth late into the fall and can be harvested nine or ten times per year.
Varieties in fall dormancy classes 1 through 4 are suitable for production in Montana.
On large farms, it is advisable to split acreage between varieties differing in fall dormancy.
Less dormant varieties generally have faster recovery and higher yield potential, but are more susceptible to winter injury.
The more dormant varieties typically mature later, but persist better for long-term stands.
Forage yield is probably the most important factor considered by an alfalfa grower or seed marketer.
In Montana and other regions with
 cold winters, forage yield potential is restricted by both the climate and a variety's level of winter hardiness.
For example, in moderate or hot climates, nondormant varieties can outyield very dormant varieties by 75 to 100 percent.
In contrast, the range in forage production of high VS.
low yielding dormant varieties is typically less than 25 percent in Montana.
Nondormant varieties can outyield dormant varieties in the seeding year in cold environments, but because of winterkill, they are considered to be "annuals." Alfalfa breeders constantly struggle to improve forage yield potential while maintaining adequate winter hardiness.
Extension agents and growers should be acquainted with alfalfa variety trials in their own region.
Data from several replicated trials evaluated for at least three years should be examined.
Actual forage yields are often misleading, but relative differences between varieties are very reliable.
Although most growers are unfamiliar with statistics, they can easily look for the "least significant difference".
This test statistic provides a yardstick for comparing variety performance in a yield trial.
Variety averages that differ by one LSD unit are statistically and significantly different.
Typically, when yields are ranked from highest to lowest, up to a third of the varieties are not statistically different from the best entry.
Obviously varieties that consistently perform well in several replicated trials should be chosen.
Pest resistance is also important when selecting an alfalfa variety.
Over 50 disease, insect or nematode pests affect alfalfa but losses can be prevented by using resistant varieties.
For irrigated alfalfa production in Montana, varieties should have good levels of resistance to bacterial wilt, Verticillium wilt, Fusarium wilt, Phytophthora root rot, and stem nematode.
Alfalfa varieties are cross-pollinated populations with varying degrees of genetic resistance to pests.
Varieties are classified according to the percentage of plants resistant to a particular pest: highly resistant , resistant , moderately resistant , low resistance , and susceptible.
For most pests, it has been determined that about 40 percent resistant plants provides adequate field protection.
Most alfalfa breeding programs breed for multiple pest resis-
 tance.
A variety should have adequate resistance to all major and potential pest problems, rather than high resistance to some pests and susceptibility to others.
Among varieties with proper winter hardiness and good forage yield potential, a grower should choose varieties with the best package of multiple pest resistance.
Aside from known differences in winter hardiness and pest resistance, some varieties differ in persistence.
In short rotations, high-yielding and moderately winter-hardy alfalfa varieties should be chosen.
Growers concerned with stand longevity should examine performance in yield trials evaluated into the third and fourth production years.
Suitable varieties often perform well or average during the first two years but become even more competitive in subsequent years.
There is currently much interest in developing and selecting alfalfa varieties for improved forage quality.
Several companies have released "high quality"  or multifoliolate  varieties, and these reportedly represent improvements in forage quality.
Alfalfa growers supplying hay to dairies or other markets based on hay analysis know that premium hay is very valuable.
High quality alfalfa varieties will not overcome poor management practices or weather; however, under good conditions, these varieties will be profitable.
Within the next five years, it is likely that university trials will publish both forage quality and yield information.
It is also likely that new ML, HQ, or ML-HQ varieties will have significant improvements in forage quality as well as good yield, pest resistance and winter hardiness.
Public vs.
proprietary varieties
 Prior to 1970, most alfalfa acreage was seeded to varieties developed by state or federal agencies.
During the 1970s, private research programs expanded for major crops such as corn, soybean, cotton and alfalfa to release "proprietary" varieties.
Presently there are about 15 companies actively breeding alfalfa or producing seed.
Alfalfa seed is a multimillion dollar industry, and the commercial programs in North America invest heavily in research.
About 95 percent of the alfalfa varieties released since 1980 are proprietary varieties and this trend will likely continue.
The older common or public varieties are still available in the West and remain popular in some areas.
Under certain conditions such as drought or in old pastures, many of the older varieties perform as well as modern varieties.
However, reliable sources of high quality seed of the older varieties are not widely available.
In spite of efforts to maintain genetic purity and certification standards, many older alfalfa varieties are now extinct.
Seed of newer proprietary varieties is generally considered expensive.
However, depending on seeding rate and stand life, seed costs account for less than 5 percent of grower input costs.
An improved, high-yielding alfalfa variety will usually offset any higher initial seed costs during the first production year.
Cost-conscious growers might consider planting a premium variety in their best fields for top production, and less expensive older varieties in poorer fields or pastures.
Many factors should be considered by a grower prior to selecting an alfalfa variety.
Producers who use alfalfa for hay or pasture often face a hay deficit and rely on purchased hay.
Depending on the type of livestock, size of operation, equipment, land value, moisture, etc.
there are many ways alfalfa can improve efficiency.
Grass pastures with adequate rainfall can be renovated, and a winter-hardy, pasture-type alfalfa can be established.
Marginal older hay fields could be rotated out, and replaced with an improved variety.
In some beef operations, cash flow has been improved by producing and selling premium cash hay, then buying back cheaper feeder-grade hay.
Alfalfa producers desiring to sell cash hay should consider joining or forming a hay marketing association.
Several marketing associations in the West sell alfalfa hay throughout North America and overseas.
The commercial hay market is becoming more sophisticated in terms of quality testing, moisture, physical appearance and storage conditions.
Therefore, a grower should anticipate using the best alfalfa varieties and intensive management techniques.
An alfalfa variety should be selected based on its winter hardiness, yield potential, pest resistance, persistence, forage quality and availability.
Although there are over 200 alfalfa varieties available, very few have been widely tested in Montana.
Growers are advised to choose varieties that are recommended each year by the Montana State University Extension Service.
The chemigation injection pump setting can be easily determined using the sprinkler chart.
The method is very simple to use if one has the chart, or at least the speed chart part of it.
The information can also be gained from looking at the readout on a computer-style pivot panel or the pivot control app.
The chemigation certification program is responsible for training Nebraska producers about the Nebraska Chemigation Act and the Rules and Regulations as developed by the NDEE.
Certification applicants are required to attend a training program and pass an exam.
The Act allowed the NDEE to contract with the University of Nebraska to deliver the training program.
North Dakota State University Fargo, North Dakota
 Tom Scherer Agricultural Engineer and Associate Professor
 Need for Field-size Pump Stations
 Locating the Pump Station
 Combination Horizontal and Vertical Storage
 Pump Controlled With a Variable-frequency Motor Drive 
 Two Pumps in a Sump
Sodic Soils Are Occurring More Frequently in Utah.
How Should They Be Managed?
D.
W.
James Extension Soil Specialist
 Sodic soils are soils with excess sodium.
Sodic soils are encountered with increasing frequency in Utah, usually in the lower, flatter areas of our valleys.
Sodic soils probably developed over many years when the water table was high and the soils were too wet for cultivation.
Apparently these wet lands are drying out because farmers are changing their irrigation practices.
Formerly, upland soils were flood and furrow irrigated.
Sprinkling is replacing the older practices to conserve water.
Thus, there is less recharge of the ground water and water tables are dropping in the lower parts of the valleys.
Accordingly, lands that were formerly too wet are becoming susceptible to cultivation and production of more profitable crops.
Sodic soils represent a special management problem for farmers and land managers because of their peculiar nature.
Whereas the pH of Utah soils normally lies in the range of 7.0 to 8.2, the pH of sodic soils will be above 8.5, to as high as 10.0.
In addition, the exchangeable sodium percentage  will be above 15; clays and organic matter will be highly dispersed resulting in very slow water infiltration and percolation through the soil; and the soil will be very hard when dry.
Sodic soils may appear black at the surface because of dissolved organic matter; years ago these soils were referred to as black alkali soils.
The net effect of soil sodicity is extremely poor crop yields.
Reclamation of Sodic Soils
 Sodic soils differ from saline soils, or soils that simply have high concentrations of dissolved salts.
Saline soils have an ESP less that 15% and their structure will be good and water intake and percolation should not be a problem.
Reclamation of both sodic and saline soils requires the application of excess irrigation water after assuring adequate drainage.
The important difference between sodic and saline soil reclamation is that, in addition to good drainage and excess irrigation, the excess sodium must be replaced on the soil cation exchange complex in order to mobilize the sodium and render it susceptible to leaching.
For this purpose calcium is supplied by adding gypsum.
Acid-forming materials such as elemental sulfur and sulfuric acid, which mobilize calcium already present in soil as lime, also serve this purpose.
The amount of gypsum needed to reduce the ESP to less than 15 is referred to as the gypsum requirement.
Whether or not a soil is actually sodic, and the determination of the GR, requires laboratory analysis of the soil.
Instructions for soil sample collection, types
 of analyses needed, and interpretation of results are available upon request from County Extension offices.
The U.S.
Environmental Protection Agency  defines wetlands as "areas where water covers the soil, or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season." A simple definition of a wetland is an area within a watershed where land and water meet.
Once considered of little or no value, today wetlands are recognized as precious resources for nurturing wildlife, purifying waters, checking the destructive power of floods and storms, helping to recharge groundwater supplies and maintaining water tables in adjacent ecosystems.
Federal Wetlands Protection Programs
 Section 404 of the Clean Water Act makes it illegal to discharge dredge or fill materials into the "navigable waters of the United States" without a permit.
Basically, discharge of dredged or fill material is not allowed if  a practicable alternative exists that is less damaging to the aquatic environment or  the nation's waters would be significantly degraded.
Proposed activities are regulated through a permit review process overseen by the U.S.
Army Corps of Engineers.
EPA along with the Corps establishes environmental standards for reviewing permits for discharges that affect wetlands, such as residential development, roads and levees.
The conservation-compliance provisions of the 1985 Farm Bill introduced the concept of "swampbuster." The provisions require all agricultural producers to protect the wetlands on the farms they own or operate if they wish to be eligible for certain USDA farm program benefits.
Producers are not eligible if they have planted an agricultural commodity on a wetland that was converted by drainage, leveling or any other means after December 23, 1985, or if they have converted a wetland for the purpose of agricultural commodity production, or for making such production possible, after November 28, 1990.
The Food, Agriculture, Conservation and Trade Act of 1990 created the Wetland Reserve Program.
It is a voluntary program that provides technical and financial assistance to According to NRCS' eligible landowners to Wetlands Reserve address wetland, wildProgram 2007, Arkansas is second in the nation life habitat, soil, water in WRP with 190,401 and related natural acres enrolled in 2007.
resource concerns on Through NRCS, there private lands.
The are wetland projects in program provides 40 counties in each financial incentives for region of the state.
landowners to restore, protect and enhance wetlands in exchange for retiring marginal lands from agriculture.
Enrollment options include permanent easements, 30-year easements and restoration cost-share agreements.
WRP is administered by the Natural Resources Conservation Service  and funded by the Commodity Credit Corporation.
State Wetlands Protection Programs
 Statewide cooperation on wetland policy issues began in 1993 with the creation of the Water Resources and Wetlands Task Force.
Task Force members include representatives from federal and state agencies, environmental organizations, tourism and agricultural interests, and academic institutions, as well as members of the Arkansas General Assembly.
The Task Force recommended two legislative initiatives that were passed during the 1995 legislative session.
The Arkansas Wetland Conservation Plan  is a comprehensive planning document developed by the Arkansas Multi-Agency Wetlands Planning Team.
It combines wetland inventory information and state strategy recommendations to:
 Address wetland issues and concerns
 Identify priority areas for restoration, protection and enhancement through individual Wetland Planning Area reports
 Evaluate existing state agency resources, responsibilities and wetland programs and
 Provide recommendations for plan implementation in a State Wetland Strategy.
Arkansas Wetlands Mitigation Bank Program
 The Arkansas Wetlands Mitigation Bank Program provides off-site mitigation opportunities to Section 404 permit recipients who are required to provide compensatory wetlands.
Mitigation banking is the restoration, creation, enhancement or preservation of wetlands by a government agency or private business who sell "credits" in bank sites to permittees.
Mitigation banks are able to consolidate many small, scattered compensatory sites into one large site, which may ensure a more successful aquatic ecosystem.
This consolidation also brings together financial resources and scientific expertise that may not be available for small sites.
Often, existing sites are improved through the consolidation of sites and resources.
Permit recipients must get approval from the Corps, and usually must be within the mitigation bank's geographic service area.
The Arkansas Wetlands Mitigation Bank is administered by the Arkansas Natural Resources Commission.
The Director of ANRC, in consultation with the Wetlands Technical Advisory Committee, has the authority to buy or accept donations of mitigation sites and to set prices and sell credits.
ANRC may also acquire banking sites through conservation easements negotiated with interested landowners.
Mitigation sites are chosen based on the land's potential to serve as a wetland, the land's proximity to other public lands, wetlands or other waters, and state wetland strategies.
The Corps determines the number of credits available at a bank site based on the potential for restoring or enhancing the wetland.
The potential for restoring the wetland is assessed by a technique called the Hydrogeomorphic Wetland Assessment Method.
Mitigation sites are evaluated by the Wetlands Technical Advisory Committee based on the following criteria:
 Historical wetland trends, including the estimated rate of wetlands loss
 The Wetlands Technical Advisory Committee is made up of the directors, or their designees, of the:
 Current and potential contributions to wildlife, fisheries and groundwater quality
 Arkansas Game and Fish Commission
 Arkansas Highway and Transportation Department
 Department of Arkansas Heritage
 Arkansas Department of Environmental Quality and
 Two public members appointed by ANRC.
Location of site in relation to permit actions
 Economic impact of establishing the site
 Costs of land acquisition, establishment and maintenance
 Cost effectiveness of site based on percentage of land in prior converted wetlands to be restored and based on existing wetlands, and
 Requirements of permitting agencies.
Riparian Zone Restoration and Wetland Creation Tax Credit
 Arkansas private landowners who are engaged in the development or restoration of wetlands and riparian zones are eligible for a state income tax credit.
The Wetland and Riparian Tax Credit Program was created by the Arkansas Private Wetland Riparian Zone Creation and Restoration Incentive Act of 1995.
The state recognizes that most of its riparian zones and its potential wetlands are privately owned.
By restoring this land, the state hopes to improve water quality, fish and wildlife habitat, recreation, groundwater recharge and flood control.
The program is administered by ANRC in consultation with the Private Lands Restoration Committee.
ANRC has established criteria to indicate what costs are eligible for credit and what environmental standards must be met for riparian zones and for wetland.
Project activities must meet or exceed program standards and comply with applicable federal, state and local laws.
The Private Lands Restoration Committee is made up of the directors, or their designees, of the:
 Arkansas Game and Fish Commission
 Arkansas Department of Finance and Administration
 Department of Arkansas Heritage
 Arkansas Department of Environmental Quality and
 Two public members appointed by ANRC.
An enrollment fee of 3 percent of the total approved tax credit is due at the time of application.
If
 a project is rejected, the fee is refunded.
Prior to enrollment, structural aspects of the project must be reviewed by a professional engineer.
Taxpayers claiming a tax credit under this act may not claim a credit under the Water Resources Conservation and Development Incentives Act of 1985 or any similar act for costs related to the same project.
Any portion of a project that is a required mitigation activity is not eligible for tax credit.
Tax credits issued to partnerships or other corporate entities may pass through to their members, managers, partners, shareholders and/or other beneficiaries, but not to other individuals or entities.
The tax credit amount for a taxable year may not exceed the lesser of 1) the total individual or corporate income tax due, or 2) $5,000 per taxpayer.
Unused credit may be carried over for nine years for a total tax credit of $50,000 per project.
Projects must be completed and functioning within three years, and maintained for a minimum of 10 years past the time of completion.
The taxpayer must maintain records, provide notification of project completion and provide proof of maintenance.
If the project is not completed within the specified time period, any tax credits already received must be repaid.
The project will not be authorized for further tax credits of any kind.
If the project cannot be completed because of conditions beyond the taxpayer's control, the project may be extended for one year.
Noncompliance with ANRC requirements will result in an assessment according to the Tax Procedures Act.
Fact Sheet 109  Glossary of WaterRelated Terms contains a comprehensive list of terms used in the Arkansas Water Primer Fact Sheet Series.
The University of Arkansas Division of Agriculture's Public Policy Center provides timely, credible, unbiased research, analyses and education on current and emerging public issues.
The Arkansas Water Primer Fact Sheet Series was funded by a grant from the U.S.
Department of Agriculture with additional financial assistance from the University of Arkansas Division of Agriculture.
Original research for the Series was provided by Janie Hipp, LL.M., and adapted by Tom Riley, associate professor and director of the University of Arkansas Division of Agriculture's Public Policy Center, and Lorrie Barr, program associate, University of Arkansas Division of Agriculture's Public Policy Center.
Given the broad potential impact of SDI technology on Delaware agriculture, a cooperative project to create a SDI research facility was initiated in 2011.
Project partners include the University of Delaware with USDA-NRCS, Delaware Department of Agriculture, Toro Ag, John Deere Water, Sussex Irrigation and Vincent Farms.
The installation of a 42 zone sub-surface drip irrigation research station on a 20-acre parcel of the University of Delawares Warrington Irrigation Research Farm in Harbeson, DE, began in December 2012.
This facility will enable the University of Delaware to research specific questions regarding the installation, maintenance and management of these systems for 15 to 20 years and generate localized recommendations for Delaware producers.
As is typical with the introduction of a technology new to a region, several questions have arisen regarding the best ways to implement and manage SDI technology for Delaware conditions.
Questions involving installation parameters such as drip tape row spacing, depth of placement and flow rates can be partially addressed utilizing research experience from other regions combined with a site specific soil profile.
However, most of the unanswered questions involve management strategies such as, determining crop water needs, ideal soil moisture sensor placement, planting configuration, pulsed irrigation and crop establishment.
These strategies are more difficult to address and require intensive local field research.
The sole purpose for the creation of this SDI research facility is to develop the management recommendations essential to continue the successful adoption of this technology.
1  450 gallon per minute well with submersible pump controlled by a variable frequency drive to maintain constant pressure over varying flowrates.
42 individual computer controlled irrigation zones.
1  2 zone, tape placement study with tape installed at 10 & 16 depths on 30 and 60 row spacings.
2  20 zone irrigation management study areas; each capable of randomizing four replications of five different irrigation treatments in two different crops.
The tape will be installed at the typical Delaware SDI installation parameters of 16 deep on 60 rows.
Average zone dimensions will be 60 x 300.
Soil moisture monitoring utilizing an extensive Irrometer Watermark 950T and 950R wireless data logger network.
For dry edible beans in the emergence-10% Cover crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.07 inches and the estimated water use during the week of June 19-25, 2023 is 0.50 inches.
For dry edible beans in the 10-50% Cover crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 0.07 inches.
B.C.
SPRINKLER IRRIGATION MANUAL
 Prepared and Web Published by
 BRITISH COLUMBIA Ministry of Agriculture
 LIMITATION OF LIABILITY AND USER'S RESPONSIBILITY
 The primary purpose of this manual is to provide irrigation professionals and consultants with a methodology to properly design an agricultural irrigation system.
This manual is also used as the reference material for the Irrigation Industry Association's agriculture sprinkler irrigation certification program.
While every effort has been made to ensure the accuracy and completeness of these materials, additional materials may be required to complete more advanced design for some systems.
Advice of appropriate professionals and experts may assist in completing designs that are not adequately convered in this manual.
All information in this publication and related materials are provided entirely "as is" and no representations, warranties or conditions, either expressed or implied, are made in connection with your use of, or reliance upon, this information.
This information is provided to you as the user entirely at your risk.
The British Columbia Ministry of Agriculture and the Irrigation Industry Association of British Columbia, their Directors, agents, employees, or contractors will not be liable for any claims, damages or losses of any kind whatsoever arising out of the use of or reliance upon this information.
There are several types of irrigation systems that can be used to apply water to agricultural crops.
Each type of system has its own advantages and disadvantages.
Some may be less expensive but may require more labour to move around and/or have lower system application efficiencies.
The more expensive systems may have higher capital costs but can save money over time by having lower operating costs through reduced labour requirements and/or better operating efficiencies.
Often, system selection is determined by the shape of the field and the type of crop being grown.
Certain types of systems require larger fields to be cost effective.
Others work better on flat fields and will not operate to designed efficiencies on uneven fields.
Table 3.1 shows the typical application efficiencies of all sprinkler irrigation system types.
The five main types of agricultural irrigation systems are Sprinkler Systems, Stationary Gun Systems, Travelling Gun Systems, Centre Pivot Systems and Trickle Systems.
Trickle systems will not be covered in this manual.
A separate manual has been prepared for trickle irrigation design.
B.C.
Trickle Irrigation Manual
 Table 3.1 Typical Application Efficiencies of Sprinkler Irrigation Systems
 Irrigation System Type	Typical Application Efficiency [%]
 Overtree Solid Set	70
 Undertree Solid Set	75
 Centre Pivot	Sprinklers	72
 Drop Tube Rotors	80
 Sprinkler irrigation systems include handmove and wheelmove systems, undertree and overtree solid set systems and micro-sprinkler systems which are usually also solid set.
Figure 3.1 Handmove System
 A handmove system consists of aluminum piping which is moved by uncoupling the lateral lines and manually transferring the pipes to the next set.
Lateral line sizes of 2-inch and 3-inch aluminum are normally used.
Lateral pipe lengths are usually 30 or 40 feet long.
Each lateral pipe usually contains one sprinkler; therefore, sprinkler spacing along the lateral will often be 30 or 40 feet.
Figure 3.1 shows a typical handmove system.
Handmove systems originated in the 1950's and are very labour intensive.
However, this system is still being used today in older orchards and pastures and is often used to irrigate corners of odd-shaped fields that are not covered by a travelling gun or centre pivot.
Sprinkler System Design, Chapter 5
 Figure 3.2 Wheelmove System
 On larger alfalfa and forage fields, many handmove systems have been replaced by wheelmove systems to reduce labour requirements.
A wheelmove system consists of 4-inch or 5-inch aluminium pipe that is attached to wheels.
Figure 3.2 shows an example of a wheelmove system.
Heavier gauged aluminum pipe is used as the lateral pipe must also act as an axle.
Figure 3.3 shows a powered mover which is usually situated in the centre of the lateral and rolls the lateral ahead when the system is shut down.
The lateral remains stationary when the irrigation system is in operation.
It can only be moved after the line has been shutdown and drained.
Drain ports are installed on each pipe to allow the line to drain automatically when water is turned off.
The drain ports close when the shutoff valve is opened and the lateral line is pressurized.
Figure 3.3 Powered Mover
 Sprinklers are usually spaced 40 feet along the wheelline with one sprinkler per pipe section.
Sprinkler spacing can be adjusted as required with spacings ranging from 30 to 60 feet.
Self levellers are recommended, especially on sprinklers located further away from the mover, to ensure that the sprinkler heads remain upright.
Wheelmoves should be no longer than 1,500 feet in length as longer lengths make it difficult to advance the system.
Wheel sizes can vary from 5 to 7 feet, depending on crop growth height.
The circumference of the wheel usually coincides with lateral spacings of 60 feet, that is, an even number of complete revolutions of the wheel will be 60 feet.
Mainline lengths are usually 30 feet which allows the hydrant locations to match the wheelmove spacing.
Sprinkler System Design, Chapter 5
 Sprinkler Solid Set System
 Figure 3.4 Overtree Solid Set System
 Figure 3.5 Undertree Solid Set System
 A solid set system is usually a permanent sprinkler installation, consisting of above or below ground piping.
The sprinklers are located at permanent positions and are not moved.
Unlike handmove and wheelmove systems, which are usually designed in denominations of 30 or 40 feet to accommodate aluminum pipe lengths, solid set spacings can be adjusted to match tree or vine plantings if buried PVC pipes are used.
For a tree spacing of 8 feet, the sprinkler spacing on a lateral may be as wide as 32 feet.
For above ground solid set systems, aluminium pipe is most often used but the sprinkler spacing is then usually 30 or 40 feet.
Solid set systems may be either overtree or undertree depending on the length of risers used.
Solid set systems are common in orchards, vineyards and berry plantings.
Overtree systems generally have larger sprinkler spacings than undertree systems and therefore require larger sprinklers with higher flow rates and operating pressures.
Overtree systems are often used whenever the crop will interfere with an undertree system.
Undertree systems are more common however and have the advantage of keeping the foliage dry when the irrigation system is operating, reducing crop diseases.
Where tree fruits and other horticultural crops have been pulled out, it is not uncommon to see solid set systems on pasture or alfalfa fields because the systems were originally designed for use on horticultural crops.
Figures 3.4 and 3.5 illustrate both types of solid set sprinkler systems.
Sprinkler System Design, Chapter 5
 Figure 3.6 Micro-Sprinkler System
 Micro-sprinklers are another type of solid set system.
A micro-sprinkler system is mostly used in orchards and nurseries.
The micro-sprinklers are often placed between the plants and on every row as the wetted diameter is much less than in sprinkler systems.
The overall number of sprinklers required on a per acre basis is therefore also much higher.
Due to the small droplet size, micro-sprinklers are usually installed undertree.
Wind drift on overtree systems would be too high.
Micro-sprinkler flow rates are higher than spray emitters used in trickle irrigation but are still often less than one gallon per minute.
The lateral pipe used is either buried PVC or aboveground polyethylene.
Micro-sprinkler systems use the same design principles as other sprinkler systems.
Figure 3.6 shows a close-up of a micro-sprinkler.
Sprinkler System Design, Chapter 5
 In agricultural irrigation, the term gun is used to describe high volume sprinklers with discharge rates exceeding 40 US gpm.
Flow rates for a gun can go as high as 1,000 US gpm but normally the larger guns in British Columbia are around 300 US gpm.
There are two types of gun systems: Stationary Gun and Travelling Gun.
Figure 3.7 Stationary Gun System
 Stationary guns are usually operated from a tripod or a stand on wheels.
These systems are moved by hand from one location to another.
Water is usually supplied to the gun by above ground aluminum pipes or buried PVC pipe with hydrants at strategic locations.
Operating pressures may range from 40 to 130 psi depending on the gun and type of nozzle selected.
Figure 3.7 shows an example of a stationary gun system.
Gun nozzles are available in a variety of sizes and trajectory angles.
The trajectory angle is important in determining maximum spray height and distance of throw.
Gun systems can utilize two types of nozzles: taper bore or ring nozzles.
Taper bore nozzles provide better stream integrity and create maximum distance of throw with less distortion due to wind.
Ring nozzles provide better stream break up and offer greater choice in nozzle sizes.
Stationary Gun systems can be purchased in four different series or sizes.
The smallest guns, Series 75 should be operated with nozzle sizes ranging from 0.5 to 0.8 inches at operating pressures from 40 to 80 psi.
Flow rates are then generally between 40 and 150 gpm.
The Series 100 gun can be operated with nozzles ranging from 0.5 to 1.0 inches at operating pressures from 40 to 110 psi.
Flow rates will generally be between 40 and 300 gpm.
The medium range gun size  can utilize nozzles from 0.7 to 1.4 inches at operating pressures from 50 to 120 psi.
Discharge rates are typically from 100 to 500 US gpm.
The largest gun  uses nozzles from 1.0 to 2.0 inches at operating pressures from 60 to 130 psi.
Discharge rates are typically 250 to 1,000 US gpm.
Gun System Design, Chapter 6
 Helpful Tips Stationary Gun Use
 For most cases in B.C., the 75, 100 and 150 series gun sizes are used for agricultural applications.
Stationary gun systems have low efficiencies and high application rates.
It is difficult to operate the system to match the crop and soil type present.
The maximum set time for a stationary gun is usually 4 to 6 hours.
Stationary guns are not recommended where inefficient use of irrigation water is a concern.
Travelling gun systems overcome the problem of the short set time generally required with stationary gun designs.
The travelling gun system also allows for large parcels of land to be irrigated during one irrigation set.
Flow rates generally range from a minimum of 75 US gpm up to 700 US gpm.
For agricultural irrigation purposes in B.C., travelling gun systems in the 150 to 350 US gpm range are most often used.
There are two types of travelling gun machines: the water winch  and the hose reel.
Water Winch or Soft Hose Traveller
 The water winch machine travels by use of a cable anchored at the end of the field.
The hose is dragged behind as the machine is winched in along the cable.
The hose is flexible SO it can be easily rewound onto a hose reel for transport after completing its run.
However, the major drawback is that the soft hose is easily damaged by dragging.
While some of these systems may still be found, they are no longer sold as they have been replaced by the hose reel system.
Hose Reel or Hard Hose Traveller
 Figure 3.8 Travelling Gun System
 Hard hose reel machines have a revolving drum that is rotated by water pressure or an engine.
The machine itself does not actually travel as the revolving reel pulls the hose and gun cart towards the machine.
These systems have high flow rates and high operating pressures.
Figure 3.8 shows a typical hard hose reel machine.
These machines are available in different hose and drum sizes and are capable of high travel speeds.
The drive mechanisms that are available are turbine, piston, bellows, gas engine, gas driven oil hydraulic and turbine driven oil hydraulic.
If a piston or bellows drive is selected, a small sprinkler operating close to the machine is used to discharge waste water from the piston.
The flow rate capacity of a hard hose machine is determined by the hose size and length.
High pressures are required to operate a travelling gun because of the high friction loss in the hose.
If a turbine drive is used, there is also some pressure loss through the driving mechanism.
Total machine hook up pressure should be kept to less than 140 psi to accommodate Class 200 PVC and aluminum mainline pressure ratings.
To keep the hook-up pressures acceptable, the maximum hose lengths recommended are 1,000 to 1,150 feet.
With the gun radius taken into account, the large hard hose reel machines can irrigate 1/4 mile per setting.
Many manufacturers do make longer length machines but due to shipping restrictions, these very large machines are not supplied in Canada.
Figure 3.9 shows a typical layout for a hard hose machine.
Figure 3.9 Hard Hose Reel Machine Layout
 Hard hose machines are also often used for applying manure.
A small engine is then coupled to the drive train to prevent the turbine or piston drive from becoming plugged.
Most machines can also be reeled in using the power take-off  tractor.
Travelling Gun Design, Chapter 6
 3.3 Centre Pivot System
 A center pivot system consists of a single lateral, supported by trusses and towers on wheels, with one end anchored to a fixed pivot structure and the other end free to move in a circle about the pivot point.
The span between drive towers ranges from 120 to 215 ft.
Standard span systems of 125 to 130 ft are usually designed to take the stresses of slopes up to 30%.
Long span systems of 170 to 215 feet between towers can effectively irrigate slopes up to 15%.
Long span systems are less expensive than standard span systems as fewer drive train components and controls are required.
Center pivot laterals can vary in length from 200 to 2,600 feet depending on span lengths and number of towers used.
An end gun shown in Figure 3.10 is usually used on the overhang of the last tower to increase the effective wetted radius of the center pivot.
Figure 3.11 shows the centre pivot components.
Figure 3.10 Pivot End Gun
 Figure 3.11 Centre Pivot Components
 Centre pivot systems can be powered by an electric motor drive, hydraulic oil drive or hydraulic water drive.
The most common type of drive mechanism in the industry is electric.
There are a limited number of older water drive units in B.C.
but the new water drives are for a single tower pivot only.
Electric motor drive units include 1/4, 1/2, 3/4, 1 and 1 1/2 hp motors, selected according to the rotation speed required and the type of gearbox used.
The motor is coupled to a reduction gearbox at the centre of each drive unit with drive shafts extending to reduction final drives at each wheel.
The ratio at which the drive unit and lateral pipe advance about the pivot point is determined by the speed of the outermost drive unit.
Alignment devices detect misalignment of any drive unit and start the motor on that tower.
The tower then drives forward or reverses depending on direction selected.
Since it has less distance to go than the next tower, it catches up and is shut off by the alignment switch.
Therefore, the advancement of the outermost drive unit starts a series of advances by each drive unit, starting with the second unit from the outer end and progressing along the lateral to the pivot point.
If any drive unit becomes too far out of alignment, a safety device shuts down the system to prevent damage to the lateral.
Full circle and part circle centre pivots are installed in British Columbia.
All
 electric pivots will reverse.
The part circle units often have an automatic stop-and-reverse mechanism that is signalled by a tower barricade positioned in the path of the last tower.
Pivot systems are controlled in a number of ways.
The most basic is a percentage timer that controls how long the end tower drives in one minute period.
The most advanced pivots use full computer control.
GPS units can speed up the pivot over heavy soils, connect to weather stations and soil moisture controls.
With most pivots that have a controller a depth to apply can be selected.
Common depths are 1/4, 1/2 and 3/4 inch.
This of course would depend on the ability of the soil to infiltrate the water.
Centre Pivot Design, Chapter 7
 Centre Pivot Sprinkler Selection
 Centre pivot systems can utilize a number of different sprinkler configurations to accommodate crop, soil type and terrain.
Figure 3.12 illustrates the different types of water patterns.
An end gun is generally used with all system types to increase the wetted radius of the pivot.
A booster pump on the end tower is used for the gun if the pressure is not sufficient.
Older centre pivots often use different sized sprinklers that increase in size along the lateral out from the pivot point.
The sprinkler flow rate near the pivot point is much less than sprinklers located near the end tower.
Each successive sprinkler must put out more volume to maintain uniform application along the lateral.
Sprinkler operating pressures may be as high as 70 psi with a wetted diameter of 80 ft or more for the larger sprinklers.
This type of centre pivot is well suited for rough terrain and soils with low infiltration rates.
If operated properly, this type of pivot is also less susceptible to wind drift and evaporation loss.
Figure 3.12 shows a typical centre pivot with larger sprinklers.
For variable spaced sprinklers, approximately the same size sprinklers are used along the entire lateral.
The sprinkler spacing decreases from the pivot point to the end of the lateral.
Therefore, the number of sprinklers per foot of lateral at the end of the pivot is much higher than at the pivot point.
This type of system has a slightly lower operating pressure than the larger sprinkler system and also has smaller droplets which reduce soil compaction.
Two types of variable spaced impact sprinklers are available:
 a.
Single nozzle impact sprinklers with a minimum operating pressure of 45 psi.
b.
Low pressure double nozzle sprinklers with a minimum operating pressure of 35 psi.
Figure 3.12 shows the pattern of a pivot with larger sprinklers.
This type of pivot is more susceptible to wind drift and evaporation loss due to the high operating pressure.
Figure 3.12 Application Pattern of Pivot Sprinklers
 Figure 3.13 Pivot with Spray Nozzles
 In an effort to reduce operating pressures, spray nozzles were introduced to pivot systems as shown in Figure 3.13.
However these systems, while operating at lower pressures, were very susceptible to wind drift and their reduced wetted diameter increased the application rates dramatically.
The increased application rates made it difficult to match soil infiltration rates and spray systems now no longer recommended.
Figure 3.14 Rotator Sprinkler
 Spray nozzles have been replaced by rotator sprinklers.
Unlike a spinner head that can spin freely, a rotator has a breaking mechanism that controls the spin.
Rotators provide an increase wetted diameter over spray heads but still can operate at lower pressures.
In addition different dispersion plates are available that allow for a selection of droplet sizes to match the crop type and soil type that are to be irrigated.
Figure 3.14 shows a picture of a rotator sprinkler.
Rotator heads are usually installed with drop tubes as shown in Figure 3.15.
The configuration is similar to sprinklers in that the size of the rotator increases along the pivot and the spacing of the rotators decrease, increasing the number of rotators per unit length of pivot towards the end of the pivot.
Rotators are also used in the nursery industry.
Rotary nozzle sizes can be found in Chapter 7.
Centre Pivot Design, Chapter 7
 Figure 3.15 Application Pattern of Rotator Sprinklers
 Center pivots are able to operate in various shaped fields by turning the end gun on and off, using a tower that can swing out where necessary or limiting the arc of the pivot itself.
Figure 3.16 shows a pivot that is operating as a 3/4 circle and has the end gun turning on only in the corners.
Precipitation continued the trend of a general lack of moisture during the first month of fall.
Our monthly statewide total came in at 27th driest and makes for the 12th driest three-month  period on record.
At the start of October, nearly all of Nebraska is in a drought category, according to the U.S.
Drought Monitor.
Portions of the northeast and southwest are in exceptional drought.
Temperatures averaged above normal for September and quite a few new daily high temperature records were set, most in the triple digits.
The October outlook doesnt appear to have much relief in sight with a higher-than-average probability of the warmth and dryness to continue.
Given the dryness, fire danger will be high particularly on windy days.
A LTHOUGH ALFALFA HAY is not a high income crop for California ranchers, it has a relatively high water requirement and usually occupies some of the best irrigated soils.
In times of water shortages or high water costs, ranchers are forced to make decisions about irrigating a relatively low-value crop that occupies good soil, knowing however, that the decision may influence more than one year's yields.
The decision usually involves proportioning the available water, and deciding whether to apply water at each cutting or early in the season-or perhaps not to irrigate at all late in the season.
Alfalfa irrigation systems are usually designed to achieve a fairly uniform distribution of water from the upper to the lower end of the field.
Most growers also recognize that certain deviations from uniform water distribution may result in a more economical irrigation system.
The question then is: how much deviation from uniform water distribution will allow the greatest net returns?
An alfalfa irrigation project was initiated at Davis in 1961, on Yolo silty clay loam soil with the objective of determining the yield and quality of alfalfa hay produced under different irrigation systems.
One of the irrigation treatments represented a good, desirable irrigation practice: depths of water applied at each irrigation were designed to replace the soil moisture used since the last irrigation, and to maintain adequate soil moisture at all times.
All other treatments were then irrigated at exactly the same time, but with different depths of water as summarized below:
 B Depth of water applied = 50% of treatment D
 C Depth of water applied = 75% of treatment D
 D Depth of water applied to maintain good soil moisture conditions and to replace soil moisture used since the previous irrigation
 A Depth of water applied = 25% of treatment D
 E Depth of water applied = 150% of treatment D
 F Depth of water applied 200% of treatment D for the first two irrigations, and no water applied after the third cutting at the end of June
 G Depth of water applied = treatment D, but with no winter irrigation
 H Depth of water applied = treatment C, but with no winter irrigation
 Application of additional irrigation water increased hay yields, but water in excess of about 2 feet did not appear to be particularly beneficial, according to recent tests at Davis.
Adding the depth of initial soil moisture storage, and assuming an irrigation efficiency of 70%, the total annual water requirement of alfalfa under these conditions is about 4 1/2 acre-feet.
When water supplies are deficient, a good crop can be maintained with less than 8 inches of water applied, if the soil moisture reservoir is full in the spring.
If about 2 feet of water is available for the hay crop, there appears to be little difference between applying water early or in equal amounts throughout the season.
Water supply and irrigation effects on Alfalfa
 Early in 1961, a good stand of Lahontan alfalfa was established, and all plots were maintained at the same soil moisture level during the year.
The differen-
 J.
R.
DAVIS A.
W.
FRY L.
G.
JONES
 A randomized plot design with six replications of each treatment was selected for the field study.
Each plot was 20 X 50 ft.
and was surrounded by earth levees with a plastic film core.
The plastic film, extending about 2 feet below the soil surface, was to reduce moisture movement from one plot to another.
Before seeding, all plots were leveled to a flat grade, and water was applied at each irrigation by quick flooding through a meter.
tial treatments were started in 1962, after good uniform stands had been obtained.
At all times, cultural practices such as fertilization, insect and rodent control were maintained.
Good winter rainfall during 1961-62 filled the soil moisture profile to a depth of at least 10 feet, so no winter irrigation was necessary in the spring of 1962.
Thus, treatments G and H were equivalent to treatments D and C, respectively.
All 48 plots were harvested on the same morning, using a 12 ft.
wide swather to cut a 12 ft.
X 20 ft.
area in the center of each plot.
All hay was immediately weighed and samples were taken for moisture content and hay quality.
The results of this study are shown on the graph and are also listed below
 Total Hay	Total Water	acre-foot
 Treatments	Yield	Applied*	Applied
 A	9.10	7.87	13.9
 B	9.59	15.75	7.3
 C	&	H	10.19	23.62	5.2
 D & G	10.38	31.51	4.0
 E	10.49	47.28	2.7
 F	10.24	27.44	4.5
 Exclusive of soil moisture storage at the beginning of the season, which would total about 15 to 18 inches
 All yields are based on hay of 12% moisture content.
Although these data were not analyzed statistically, it is apparent that essentially no yield differences existed between treatments C, D, E and F, but that,a total yield difference of at least one ton per acre of hay occurred between treatment A and these four treatments.
Treatment F, which involved only two irrigations  still yielded as high as treatments C or D, which received five irrigations.
Reasons for these results lie primarily in the amount of moisture retained in the soil throughout the season.
As seen on the graph, all yields were about the same through the third cutting on June 29.
The extraction of soil moisture from treatments A and B through June far exceeded the application of water, however, caus-
 ing a yield decline to appear.
This would indicate that in a normal year, the first two cuttings of alfalfa may not be influenced a great deal by irrigation, but that an increasing lack of soil moisture in the top 3 to 4 ft.
depth of soil would soon decrease crop growth.
In the case of treatment F, each of the two irrigations added almost 14 inches of water to the soil profile and yield decreases would not be expected until after the fourth cutting.
Hay quality was affected by irrigation treatment.
Protein and carotene contents tended to be lower as the depth of water applied increased.
For the drier treatments , protein and carotene percentages increased slightly throughout the season, probably because the leaf-tostem ratio increased as plant growth was slowed down.
Based particularly on the protein content, the hay quality was improved by the same soil moisture stresses that reduced yields.
Analyses of fiber content, which would aid in this discussion, were not completed at the time of this writing.
A tentative economic analysis and an evaluation of alternative decisions the rancher could make, if water were deficient or water costs were high, is possible from the data already presented.
The table included to illustrate such an analysis was based on a roadside value of hay at $20 per ton.
Using treatment E, which had the highest yields as a base, the table shows the gains or losses in annual income per acre for various prices of water,
 should the total depth of water applied be decreased from 47.28 inches.
The underlined values in the table are those which would result in the greatest net gain in income.
For example, if the total cost of water application were $1 per acre foot, an annual seasonal application of about 4 feet of water  would be the best; any lesser depth would result in a loss of income.
On the other hand, if the total cost of water were $20 per acre foot, then reducing applications from 4 feet to 8 inches would save almost $38 per acre, per year, even though the yield would decrease.
This table illustrates a demand schedule for water as a function of price or cost of water application, and shows that the magnitude of probable water demands generally decreases as the price of water increases: a twofold increase in cost from $10 to $20 per acre foot would create a threefold decrease in water applied  ; however, a twofold increase from $2.50 to $5.00 per acre foot would have no effect on demand.
Analyses such as these must be available for other locations and additional crop years, however, before good generalizations can be made.
J.
R.
Davis was formerly Specialist, Department of Irrigation, Davis, California, and is now with Stanford Research Institute; A.
W.
Fry was formerly Assistant Engineer, Department of Irrigation, Davis, and is now Superintendent, Kearney Horticultural Field Station; and L.
G.
Jones is Specialist, Department of Agronomy, Agricultural Experiment Station, University of California, Davis.
GAINS  OR LOSSES  OF ALFALFA INCOME PER ACRE ANNUALLY AS A FUNCTION OF WATER APPLIED AND WATER COST
 Changes in Depth	Cost of Applying Water, per Acre Foot*
 of Water Applied	$1.00	$2.50	$5.00	$10.00	$20.00	$30.00
 From E to F	$3.35	$0.87	$ 3.26	$+11.53	$+28.06	$+44.59
 E to D	0.89	+ 1.09	+ 4.37	+10.94	+24.08	+37.22
 E to C	4.03	1.07	.
3.86	+13.72	+33.44	+53.16
 E to B	-15.37	-11.43	4.86	+ 8.28	+34.56	+60.84
 E to A	-24.52	-19.59	-11.38	+ 5.04	+37.88	+70.72
 These costs include capital, labor, power, water and all other irrigation costs.
Underlined values offer greatest net gain in income.
The newest feature that has been incorporated into the app is prediction of the last irrigation.
When this option is selected you can enter the crop, and growth stage and the app will give you the predicted maturity date and water needed to finish out the crop.
This can be stored soil moisture, rainfall, or irrigation.
Irrigation System Descriptions for Tropical and Subtropical Fruit Crops in Florida
 Jonathan Crane, Haimanote Bayabil, Edward A.
Evans, and Fredy Ballen2
 Florida has a diverse and vibrant tropical fruit industry of about 14,562 acres with an estimated economic impact of greater than $300 million to the state's economy.
Commercial subtropical fruit crops include but are not limited to avocado, carambola, dragon fruit , guanabana , guava, jackfruit, longan, lychee, mamey sapote, mango, papaya, passionfruit, sapodilla, and sugar apple.
To meet crop water needs and for freeze protection in certain areas, irrigation is a key cultural input for subtropical and tropical fruit production in Florida.
Irrigation during dry periods prevents drought stress that may result in a delay to full production, nutrient deficiencies, and reduced fruit set, fruit yields, and quality.
Cold protection of tropical and subtropical fruit crops in Florida becomes necessary during freeze events, which occur periodically.
Many types of irrigation systems have been utilized by Florida's tropical fruit industry, and each has advantages and disadvantages with respect to use, infrastructure requirements, management, costs, and potential for freeze protection.
Different types of highan low-volume irrigation systems are commonly used for tropical and subtropical fruit crop production in Florida.
New and prospective tropical fruit producers need information to make an informed choice as to which irrigation system may meet their irrigation and freeze protection needs.
The choice of an irrigation system depends on several factors.
The objective of this publication is to describe and comment on the major types of irrigation systems currently used by the tropical fruit industry of Florida.
High-Volume Overhead Irrigation Systems 
 High-volume overhead irrigation systems are used for irrigation and freeze protection.
High-volume overhead irrigation systems consist of buried mainlines connected to 8-15 ft tall metal pipes generally spaced at 40-60 ft apart throughout the grove and topped with high-impact sprinklers.
These systems are designed to apply 0.2-0.25 inches of water per acre per hour or more.
They are usually powered by a diesel or gas engine and pump, are designed to run at 30-60 psi, have an output of about 91-113 gallons per minute , have a spray radius of up to 30 feet , and are designed for complete land coverage.
Typically in these systems, impact sprinklers spray water on a 360 radius at ~45 trajectory, and depending upon output pressure, spray 5-7 ft above 90.
Typically, these high-volume systems are not automated but managed manually.
Figure 1.
High-volume overhead irrigation pipe  with brass high-impact sprinkler head  in a carambola grove  and a mango grove.
Credits: J.
H.
Crane, UF/IFAS TREC
 1.
High-volume overhead irrigation systems provide irrigation and freeze protection to trees.
Freeze protection potential depends upon pumping capacity, water distribution pattern, and management of the system.
2.
High-volume overhead irrigation systems are designed to cover nearly all the grove land surface area with water in an overlapping pattern.
This is important for the shallowly rooted fruit trees planted in Miami-Dade County, where land consists of well-drained crushed oolitic limestone about 6 to 8 inches deep.
The grove may or may not also be transected in a grid pattern of
 16-to-24-inch-deep by 45-inch-wide trenches.
These systems provide water to most of the lateral tree root system.
1.
Freeze damage may occur if the system is not designed for sufficiently high water output and complete canopy coverage or is not managed properly during a freeze event.
2.
During prolonged freezing weather events, accumulation of ice on tree limbs may cause them to break.
On occasion the trunk splitting may cause further damage.
3.
During advective freezes when winds may be >5 mph, the water distribution pattern may be distorted and result in parts of the tree canopy to experience evaporative cooling and be damaged or killed.
4.
Irrigation application efficiency ranges from 60%-80% with an average of 75%.
Efficiency declines rapidly due to increased evaporation during windy or dry air conditions.
5.
High-volume overhead systems require large pump capacity and engines to operate properly.
Purchase and operational costs are generally higher than low-volume systems.
While effective, these systems have gone out of favor during freeze events due to the potential for branch and trunk breakage when the weight of the ice accumulated along the tree branches and trunk.
In addition, installing these systems  and maintenance for these tall metal pipes with impact sprinklers is expensive.
High Volume Under-Tree Irrigation Systems 
 High-volume under-tree irrigation systems also provide irrigation and freeze protection.
These systems are more common than overhead systems, and some overhead systems have been modified  to under-tree systems.
These systems generally cause much less ice accumulation and therefore less tree damage.
Maintaining these short PVC or metal pipes is easier than overhead systems.
However, due to the increased number of irrigation lines and pipes necessary along with the large pumps and engines, cost may be about the same as for the high-volume overhead systems.
High-volume under-tree irrigation systems consist of buried mainlines connected to 2-5 ft tall metal or hard PVC pipes generally spaced 20-50 ft apart throughout the grove  and topped with high-impact sprinklers.
They are usually spaced SO every other row and every second tree has a sprinkler between trees in-row.
These systems are designed to apply 0.2-0.25 inches of water per acre per hour.
They are powered by either diesel or gas engines and pumps and are designed for an output of 30-50 psi, with an output of about 91-113 gallons per minute , a spray radius of up to 30 feet and complete land coverage.
Impact sprinklers spray water on a ~45 angle and depending upon output pressure, spray 5-7 ft above 90.
Typically, these highvolume under-tree systems are not automated but managed manually.
Figure 2.
High-volume irrigation system with a 2 ft high sprinkler  made of PVC pipe and plastic high-impact sprinkler head in a lychee grove , a system made of 3 ft high metal pipe with brass high-impact sprinkler head in an avocado grove , a close-up of a 2 ft PVC pipe and plastic high-impact sprinkler head , and a 2 ft PVC pipe with high-impact spinner-type head.
Credits: J.
H.
Crane, UF/IFAS TREC
 High-volume systems under tree must be properly designed because an insufficient number of risers or poor waterdistribution pattern  results in uneven water distribution, and some trees or parts of trees may experience freeze damage by evaporative cooling.
Figure 3.
High-volume under tree irrigation impact sprinklers  arrangement in and between trees in the rows  and ground coverage .
1.
This system provides irrigation and freeze protection to trees.
However, because the distribution of water reaches only 5 to 7 ft from the ground into the canopy, the canopy above about 9 ft may be damaged.
This is more of a problem for older/larger trees than younger/smaller trees; however, recovery from the upper-tree freeze damage is usually rapid.
Generally, ice accumulation on the lower trunk and main limbs does not result in limb breakage because these lower limbs are stronger than upper limbs.
These systems are now preferred over high-volume systems over tree for this reason.
2.
Like overhead, these systems are designed to cover a large area of the grove surface area with an overlapping distribution pattern.
Similarly, for groves planted in Miami-Dade County these systems provide water to nearly all the lateral tree root system.
3.
Irrigation application efficiency is potentially better than high-volume overhead systems if there is minimal tree canopy interference, mainly due to less wind distortion and evaporation.
1.
High-volume under-tree systems require large pumping capacity and engines to operate the system properly.
Purchase and operational costs are generally higher than low-volume systems.
2.
There is potential for tree freeze damage if the wetting pattern is obstructed by adjacent or nearby trees.
High-Volume Irrigation Placed inside the Tree Canopy 
 High-volume in-tree irrigation systems also provide irrigation and freeze protection.
These systems are much less common than other high-volume systems.
These systems generally result in much less ice loading and tree damage because of the high volume of water applied per acre.
Maintaining these PVC or metal pipes is generally easier than the overhead systems, but the increased number of irrigation lines and pipes necessary  along with the large pumps and engines needed make this the most expensive high-volume system.
Figure 4.
High-volume irrigation with PVC pipes with spinner-type high-impact sprinklers inside the tree canopy  of lychee trees.
High-volume sprinkler on 18-inch PVC pipe and  high-volume sprinkler on 5-foot-tall PVC pipe.
Credits: J.
H.
Crane, UF/IFAS TREC
 High-volume in-tree irrigation systems consist of buried mainlines and submains connected to 2-9 ft tall hard PVC pipes placed 2-5 ft adjacent to the trunk of each tree.
The pipes are typically placed within the tree dripline and are topped with either a high-impact sprinkler or spinner-type sprinkler.
These systems are designed to apply 0.20-0.40 inches of water per acre per hour.
They are powered by either diesel or gas engines and pumps and are designed for an operating pressure of 30-60 psi, with an output of 91-181 gallons per minute  and a spray radius dependent upon the size of the tree canopy area.
In mature trees the distribution of water is mostly confined to the inside of the tree canopy.
Like the other high-volume systems, most systems are not automated but managed manually.
1.
This system confines irrigation distribution to the canopy dripline around the trunk.
Observations of these systems during freeze events indicate that very little ice accumulates on tree limbs and the trunk due to high volume of water and heat released during freeze events with this system.
2.
This system provides excellent cold protection.
It may be used for irrigation, but because of the high volume of water output and limited lateral water distribution, establishment of an additional low-volume irrigation system  for meeting crop water needs may reduce annual water usage and energy costs.
3.
The in-tree riser may be installed higher by adding a pipe and thereafter adjusting to increasing tree height as trees age.
4.
Irrigation application uniformity is better than highvolume overhead and under-tree systems because of much less wind distortion and evaporation.
1.
The system usually requires a high-capacity pump and engine that have the capability to apply more than 0.25-0.40 inches of water per acre per hour.
2.
High-volume in-tree systems require large pump capacity and engines to operate the system properly.
This is the most expensive irrigation system to purchase and operate.
Drip systems are very efficient at applying water to the soil surface and are commonly placed under plastic or organically mulched beds.
Drip is used primarily for papaya and banana production in Florida.
The output of drip irrigation depends upon the pump pressure, tube sizing, number and size of emitters, and number of tubes per plant bed.
However, they provide no cold protection.
These systems may be powered by 5 hp electric or fuel engines and pumps, may be modified to inject fertilizers, and are generally automated.
The cost of drip systems is less than the high-volume and microsprinkler systems.
Figure 5.
Low-volume drip tubing underneath plastic mulch.
Photo credit:
 Credits: H.
Crane, UF/IFAS TREC
 1.
Properly managed, these systems use low volumes of water and directly apply water to the root zone.
They may be managed to meet crop needs and, if properly operated, minimize leaching of nutrients beyond the root zone.
2.
Fertilizers and other chemicals can be distributed through properly designed and equipped injection systems.
3.
These systems require less pressure to pump water than high-volume systems; therefore, smaller pumps and engines can be used.
Generally, low-volume drip systems are less expensive to install and maintain than high-volume systems.
However, regular maintenance is necessary to prevent or correct clogging of the emitters or drip-tubing.
4.
Irrigation application efficiency is higher than in highvolume systems and ranges from 70%-90%, with an average of 85%.
5.
These systems are ideal for plasticor organic-mulch bedded planting systems where the water is generally confined to the bed soil volume.
6.
Drip systems are generally less costly to install and maintain than high-volume systems.
1.
The lateral spread of water is limited in sandy soils of Florida and the oolitic limestone-based soils in MiamiDade County.
This may not be too important for young woody trees, but for mature woody trees, most of their root system is well beyond the dripline, and therefore drip systems may not be capable of meeting crop water needs.
2.
These systems do not provide freeze protection.
3.
Due to the low pressures used to move water, clogging of the emitters can be a problem.
Clogging can be caused by particulate matter , proliferation of microorganisms, chemical precipitation , and chemical residues.
4.
Tubing on the soil surface is easily damaged by sunlight, rodents, and wildlife, and as a result it requires frequent maintenance and replacement of parts.
Lowand High-Volume Microsprinkler Irrigation Systems
 Lowand high-volume microsprinkler systems are efficient at applying water to much of the tree root system area from the trunk to the canopy dripline when managed properly.
Their use in cold protection depends upon their capacity for water output and management during a freeze event.
Like drip systems, microsprinkler systems may be designed to inject agrochemicals through the system.
These systems may be powered by electric or diesel/gas fuel engines and pumps and are generally automated.
The cost of microsprinkler systems is lower than that of the high-volume overhead, under-tree, and in-tree systems, but higher than for drip systems.
Depending upon system design and components, microsprinkler systems are designed to apply water within a confined radius and/or wetting pattern .
The systems are generally composed of an electric motor and pump, buried main and submain lines, aboveground flexible lateral-line tubing, and hard plastic stakes with an emitter.
There is a huge selection of emitters that influence the spray volume and uniformity of irrigation water distribution.
Depending upon the system design and pumping pressure these systems may be classified as low-volume systems, 5-10 gal per emitter per hour, or high-volume, >15 gal per emitter per hour.
With tropical and subtropical fruit crops, there is very little experience using microsprinkler systems for freeze protection.
For example, young sapodilla trees 1-3 years old were successfully protected from freezing temperatures  by a high-volume microsprinkler irrigation system used in conjunction with fiberglass batting installation of trunk wraps and placement of the emitters about 3 ft high in the tree canopy .
In contrast, there is a wealth of information on microsprinkler freeze protection for citrus.
However,
 for most tropical fruits there is no experience using these systems during a prolonged or very cold freeze event.
Figure 6.
Microsprinkler irrigation in a young lychee grove , avocado grove  and guava grove.
Credits: J.
H.
Crane, UF/IFAS TREC
 For freeze protection of young trees, the ground-based microsprinklers need to be located on the north or northwest side of the tree, 2 to 3 feet away from the tree trunk.
This allows winds during advective freeze  events to blow water toward the tree.
The best emitters for freeze protection are fan-type of either 90 or 180 wetting pattern that concentrate their spray onto the lower portion of the tree canopy and trunk.
Alternatively, microsprinklers with 360 fan-type microsprinklers may be placed on 24-to-36-inch-high stakes in the center of the tree canopy  of young trees.
The emitter tubing needed is much longer than ground-based microsprinklers and should be wrapped around the stake to keep ice formation from pulling down the elevated emitter.
In conjunction with microsprinklers the installation of high-insulating-value tree wraps provides additional freeze protection to young trees.
Tree wraps should have a high insulation R-value, which indicates its resistance to heat flow.
Tree wraps made of fiberglass batting have a relatively high R-value .
Figure 7.
Young sapodilla tree with a fiberglass batting tree trunk wrap and elevated microsprinkler  prior to and  during the December 27-28, 2010 freeze event in Homestead, Florida.
Credits:.H.
Crane, UF/IFAS TREC
 1.A larger area and volume of soil and rhizosphere is irrigated with these systems compared to drip systems.
2.
Properly used, these systems direct the application of water to the root zone area of one tree or two adjacent trees.
3.
Fertilizers and other chemicals may be distributed through properly designed and equipped systems.
4.
Irrigation application efficiency is higher than highvolume overhead, under-tree, and in-tree systems and ranges from 70%-85%, with an average of 80%.
Efficiencies decline in young plantings where sprinklers are more exposed to windy conditions.
5.
These systems require less pump pressure to distribute water than high-volume overhead, under-tree, and in-tree systems, and therefore smaller pumps and engines may be used.
6.
Generally, low-volume microsprinkler systems are less expensive to install and maintain than high-volume systems, but they cost more than drip systems.
1.
The low-volume microirrigation systems provide little to no freeze protection.
This is because the volumes of water applied are too low, and distribution patterns  are generally insufficient to protect tropical and subtropical fruit trees during freezing weather events.
Winds of >5 mph can alter the application pattern, often resulting in uneven water distribution and evaporative cooling of plant surfaces.
2.
Due to the low pressures used to distribute water, clogging of the emitters can be a problem.
Clogging can be caused by particulate matter , microorganisms, and chemical residues.
Highand low-volume irrigation systems are used by Florida's subtropical and tropical fruit industry.
Historically, high-volume systems were installed and used for irrigation and freeze protection.
As the water-use and fuel efficiency of low-volume systems became apparent, some producers installed these systems along with their high-volume systems, limiting the high-volume system use to freeze protection.
During the last decade, many new groves and older established groves have installed microsprinkler irrigation systems.
Many of these may not have the capacity to afford much freeze protection for tropical fruit trees, especially young trees.
Current, new, and potential tropical and subtropical fruit producers should carefully review the water requirements and cold and freeze tolerance needs of their fruit crops and install or upgrade an existing system to meet those needs.
Table 1.
Range in cost to establish and maintain highand low-volume irrigation systems for one acre of tropical fruit production in south Florida.
System type	Cost to establish 	Cost to maintain per year 
 High volume over tree	7,000-8,000	100-200
 High volume under tree	7,300-8,400	100-200
 High volume in-tree	8,000-9,000	100-300
 Drip system with injection capability	1,200-2,000	250-300
 Low-volume microsprinkler with injection capability	2,000-3,000	300-350
 High-volume microsprinkler with injection capability	2,500-3,500	300-350
For corn in the V2 crop growth stage the estimated water use during the previous week of May 29 June 4, 2023 is 0.12 inches and the estimated water use during the week of June 5-11, 2023 is 0.85 inches.
For corn in the V4 crop growth stage the estimated water use during the previous week of May 29 June 4, 2023 is 0.21 inches.
For corn in the V6 crop growth stage the estimated water use during the previous week of May 29 June 4, 2023 is 0.42 inches.
Example of a center pivot with a leak at the end of the pivot lateral.
An inspection of the pivot early in the season provides time to repair leaks or other problems before irrigation is needed.
Saleh Taghvaeian Extension Irrigation Specialist
 Drip or trickle irrigation refers to the frequent application of small quantities of water at low flow rates and pressures.
Rather than irrigating the entire field surface, as with sprinklers, drip irrigation is capable of delivering water precisely at the plant where nearly all of the water can be used for plant growth.
The uniformity of application is not affected by wind because the water is applied at or below the ground surface.
A well designed and maintained drip irrigation system is capable of an application efficiency of 90 percent.
According to the Farm and Ranch Irrigation Survey conducted by USDA, 11,239 acres of agricultural lands in Oklahoma were under drip irrigation in 2007, out of which 81 percent was under SDI.
Drip irrigation systems can be arranged in a number of ways.
The arrangement of components in Figure 1 represents a typical layout.
Variations in pressure within the system due to changes in elevation and pressure loss within the pipes will affect the discharge of individual emitters.
For a system to irrigate satisfactorily the application of water must be uniform.
There should be no more than a 10 percent variation in discharge between the emitters with the lowest and highest output.
To achieve this, pipes and tubing must be sized correctly.
Laterals should run across slope, following contour lines, or run slightly downhill.
Areas of a field at different elevations should operate as separate sub-units with separate pressure regulators.
Drip irrigation laterals can be divided into two categories: line source emitters and point source emitters.
Line source emitters have built-in perforations where the volume of soil irrigated by each perforation overlaps with that of the perforation next to it, resulting in a long, narrow block of irrigated soil that surrounds the roots of the entire row crop.
Line source emitters are used when plants are closely spaced within a row, with the rows separated several feet apart, as with row crops and most vegetable crops.
The typical line source emitter is a twin-wall tubing, with two pipe chambers.
The larger, inner chamber is for water flow along the row length.
The smaller outer chamber has the pressure dissipating emitting device.
The emitting devices are typically spaced from 6 to 36 inches apart.
The dual chamber design reduces the effect of pressure loss in the tubing, permitting a more uniform rate of discharge along the tube length.
Typical operating pressures for drip tubing range from 6 psi to 12 psi.
The maximum length of tubing that can be used satisfactorily depends upon the inlet pressure of the tubing, tubing diameter, emitter discharge rate, emitter spacing, and field slope.
The limitation on length is imposed because of the need to maintain uniformity in water application.
Maximum permissible lengths of run while maintaining a uniformity of 90 percent, and other pertinent operating characteristics for typical drip tubing are listed in Table 1.
The rate of water application from drip tubing depends upon the design discharge rate, emitter spacing, and the operating pressure.
Manufacturers may express drip tubing
 Figure 1.
Typical drip irrigation system layout.
Table 1.
Maximum Length of Drip Tubing Laterals.
Emitter	Emitter	Emission Uniformity
 Spacing	Flow Rate	90%	85%
 		Tubing Diameter	Tubing Diameter
 5/8"	7/8"	5/8"	7/8"
 12-inch	0.22	750 ft	1300 ft	1,000 ft	1,750 ft
 0.45	500 ft	900 ft	650 ft	1,150 ft
 24-inch	0.34	672 ft	1203 ft	850 ft	1,521 ft
 0.50	519 ft	929 ft	657 ft	1,175 ft
 36-inch	0.50	672 ft	1203 ft	850 ft	1,521 ft
 1.00	427 ft	765 ft	541 ft	967 ft
 discharge in terms of gallons per minute per 100 feet of tubing, or in terms of gallons per hour per emitter.
The emitter spacing that should be used depends largely upon the type of soil being irrigated.
On coarse textured soils, water will not spread horizontally a great deal.
It is necessary that the emitters in the drip tubing be relatively closely spaced to ensure a uniform line of water is discharged along the row length to promote even crop growth.
More than one drip tubing may be needed to uniformly irrigate wide planting beds on coarse textured soils because of limited capillary action.
On finer textured soils, the capillary action of the small soil pores will permit greater horizontal movement of the applied water from the point of emission.
Water from each emitter could easily spread to cover three feet or more of row length and width on fine textured soil.
Recent developments in tubing manufacturing techniques now permit the production of drip tubing with turbulent flow properties in the outer chamber at reasonable costs.
These devices are generally conceded to be superior to the original drip tubing with mechanical or laser drilled orifices.
The advantages of turbulent drip tapes include larger openings at the same rate of discharge, which makes them less susceptible to blockages.
They also exhibit improved pressure compensating characteristics, which permits their use on longer rows and irregular slopes.
Another type of line-source laterals that have been used widely is drip tape.
Drip tape has thin walls , usually ranging from 5 to 15 mils, where 1,000 mils is equal to one inch.
Drip tapes with thicker walls last longer and can be used multiple seasons, but they are pricier due to the more plastic used in manufacturing.
The most common inner diameter of drip tape is 5/8 inches, but diameters as large as 14/16 inches are also available in the market.
Drip tape is the preferred type for subsurface drip irrigation  of row crops.
Point source emitters are used when widely spaced point sources of water are needed, as in the case of orchard crops where the trees are spaced several feet apart.
In this type of system one or more emitting devices are attached to a pipeline at or near the base of the plant, irrigating a bulb of soil surrounding the root mass of the plant.
Emitting devices for widely spaced plants are normally attached onto polyethylene  tubing.
Most deliver either 1/2 gallon per hour , 1 gph, 2 gph, or 4 gph at their design operating pressure.
The maximum length of run for a single lateral depends upon the emitter design, emitter discharge
 Table 2.
Maximum Length of Level, Point Source Laterals
 2-gph emitter/5	8 4-gph emitters/tree,
 C,=0.05, x=0.5	70-ft tree spacing,
 Tubing	Lateral Inlet Pressure	Lateral Inlet Pressure
 Diameter	12 psi	15 psi	12 psi	15 psi
 1/2-in	415 ft	475 ft	560 ft	630 ft
 3/4-in	850 ft	980 ft	1,330 ft	1,400 ft
 1-in	1,650 ft	1,800 ft	2,310 ft	2,590 ft
 rate, emitter spacing, tubing diameter, lateral inlet pressure, and field slope.
Maximum permissible length of laterals for two example crop layouts are given in Table 2.
In both cases, the emitters are high quality , non-pressure compensating emitters.
Emitters for trees should be located to provide balanced root development.
While a single, small capacity emitter may be sufficient during the early years of plant development, a higher flow rate will be needed as the tree matures.
This large flow should be divided between several emitters, spaced around the trunk within the canopy dripline.
The dripline is simply the line marking the extent of the tree canopy coverage on the ground surface.
Since drip irrigation systems operate at relatively low pressures, even small variations in pressure can have a significant effect on how uniformly the system applies water to the crop.
For this reason, pressure regulators should be used, especially on fields where the elevation varies considerably.
For every 2.31 feet of elevation fall the pressure on water in a pipe will increase one pound per square inch.
If a field has a variation of 10 feet in elevation from the highest to the lowest point, the emitters at the lowest point will be operating at a pressure more than 4 psi greater than the highest emitter.
In a system which may have a design operating pressure of only 8 psi, that is an extremely large variation.
Variations in pressure due to elevation change can be handled by using pressure regulators, or pressure compensating emitters.
Regulators are devices that maintain an outlet pressure that is virtually constant as long as they are driven by an input pressure higher than their output pressure.
There are two common types of regulators used in drip systems.
There are adjustable regulators where the output pressure is set by the irrigator, and preset regulators that have a fixed output pressure to match the pressure requirements of the emitting devices.
Preset regulators are generally less expensive than adjustable regulators.
Fields with elevation variations must be broken into sections with only slight variations of elevation within each section.
A pressure regulator would be placed at the inlet to each section, and the delivery system pressurized to maintain adequate pressure to the regulator in the section with the highest elevation.
All sections with lower elevations would have their increased pressure reduced by the regulators and a reasonably uniform application of water would result.
Pressure compensating emitters are emitting devices that maintain a virtually constant discharge as long as their operating pressure stays within a certain range.
Most pressure
 compensating emitters maintain an acceptable uniformity of discharge in the operating range of 10 psi to 30 psi.
Pressure compensating emitters require no pressure regulator, but are substantially more expensive to purchase than ordinary emitters.
On undulating fields where it is impossible to create zones of uniform elevation pressure compensating emitters are the only way to design a drip irrigation system with satisfactory uniformity.
Water Quality and Filtration
 Water quality and filtration are probably the most serious concerns when considering drip irrigation.
In order to discharge very low flow rates, the diameter of the emitter orifices must be very small.
This results in the emitters being blocked very easily by even the smallest contaminants in the water supply.
Of particular concern are suspended solids, such as silt and sand, minerals that precipitate out of solution, such as iron or calcium, and algae that may grow in the water.
Virtually every drip irrigation system must include a filtration system adequate to prevent plugging of the emitters.
A system with poor quality water and poor filtration simply will not function reliably enough to warrant the maintenance requirements needed to keep it in operation.
Manufacturers typically rate emitters with regard to the degree of filtration required to prevent plugging by particles.
This can be expressed in terms of a screen mesh number, or as the diameter of the width of the maximum filter opening.
The relationship between the two sizing methods is given in Table 3.
Filters may be constructed of stainless steel or plastic screens that are reusable and require periodic cleaning.
They may also use disposable fiber cartridges.
For water that has a heavy load of large contaminants, a separator, which uses centrifugal force to remove most of the particles, may be used.
Moderately dirty water can be filtered by disk filters.
These units have a large number of thin plastic disks with grooves of precise dimensions cut into them.
They are relatively easy to flush and reuse and are moderately expensive.
Water with large amounts of fine silt and clay in suspension will normally require filtration with a media filter.
Media filters use graded layers of fine sand to remove sediment.
They are effective filters, capable of handling very large flow rates, but are relatively expensive to purchase and maintain.
Suspended solids will normally be less of a problem when ground water is used for irrigation than when surface water is used.
The precipitation of minerals in irrigation water is usually a problem only with groundwater sources.
Dissolved minerals may come out of solution with a change of pH or temperature or when aeration occurs.
If calcium is the problem, injecting acid into the water to lower the pH will prevent precipitates from forming.
Sometimes there is not sufficient calcium to precipitate out of solution, but enough to form a "lime" crust over
 Table 3.
Filter Size Conversions.
Mesh Size	Maximum Opening Width
 the openings of emitters after the system is shut off and the components dry.
If this situation causes frequent blockage of emitters, injection of acid into the system for the final few minutes of operation before shutdown should eliminate the problem.
If iron is the problem, oxidizing the iron by chlorination or aeration and then filtering the water will be necessary.
Injection of chemicals such as fertilizers or pesticides into the water may cause precipitation of minerals.
Consequently, any filtration should take place after chemical injection has been done.
Occasional flushing of the system by opening the ends of the lateral lines to discharge accumulated sediment and precipitates is recommended.
Growth of algae within the irrigation system is seldom a problem, since most algae require sunlight to grow, and virtually all system components are made of opaque materials.
However, if surface water is used to irrigate, algae quite often exist in the water supply.
Pumping unfiltered water from an algae laden source will result in frequent blockage problems, so adequate filtration is important.
Treatment of ponds with algae problems by the addition of copper sulfate will greatly reduce the filtration load if the pond is used for drip irrigation.
A bacterial slime may develop in systems where the water has considerable organic matter.
Routine use of a 2 ppm chlorine rinse at the end of each irrigation set will normally prevent slime development.
If a slime problem does develop, a 30 ppm chlorine treatment will clean the system.
The use of high quality water and an adequate filtration system cannot be over emphasized.
Use of poor quality irrigation water in a drip irrigation system can result in so many maintenance problems related to emitter plugging that any labor savings you would expect relative to other irrigation methods will be eliminated.
Maintaining the filtration system satisfactorily, chemically treating the water if necessary, and frequent flushing of the system will go a long way toward eliminating these problems.
The water in drip irrigation pipes and tubes is contaminated with numerous chemicals, whether from direct injection or from contact with soil water where fertilizers, pesticides and herbicides have been applied.
Thus, it is important to prevent the water in drip systems from flowing back to and contaminating water resources.
This can be accomplished by including a device to break the vacuum and prevent water from flowing back.
Such devices are usually installed between the injection point and the water source.
The hours of operation needed to meet the irrigation requirement will depend upon the flow rate of the emitting device, the irrigation interval, and the rate of consumptive water use by the crop.
In no case should the total system be designed to operate more than 18 hours per day.
This allows time for system maintenance, and excess capacity for catchup in case of breakdowns.
Nor should any zone be irrigated for more than 16 hours continuously, to allow some time for aeration of the crop root zone.
When computing the daily water requirement, the calculations are based only on the area of the field that is actually covered by vegetation.
This is possible because only the vegetated area is irrigated with drip irrigation systems.
For example, if tomatoes are planted in rows that are five feet apart but the vegetation is only three feet wide, 100 feet of row length would have an area of 300 square feet, not 500
 square feet.
It is assumed that the unvegetated strip between rows uses no water and is not irrigated.
If the tomatoes were estimated to require 0.25 inch of water per day, the daily water requirement would be 52.5 gallons per day per 100 feet of row length.
This answer is given by:
 Q = daily water requirement, gallons
 W = row width of vegetation, feet
 L = length of row, feet
 D = depth of water use by crop, inch/day
 0.7 = constant 
 If the tomatoes are to be irrigated every two days by a drip tubing that emits 0.5 gpm per 100 feet of length, the operating time for the system would be 210 minutes  per irrigation.
This is determined from the equation:
 where T = operating time, minutes/irrigation Q = water requirement, gallons/day/100 feet of row | = interval between irrigations, days R = application rate of tubing, gpm/100 feet
 Making the calculations based upon a unit row length of 100 feet makes computations for a larger system simple.
For every 100 feet of row length added in this system, another 0.5 gpm of flow is needed from the water supply.
Once the maximum capacity of the water supply is reached, the system must be divided into sub-units.
Each sub-unit operates independently, in this case requiring 3.5 hours to apply sufficient water for a two day period and is then shut off while another sub-unit is irrigated.
For example, if the tomatoes to be irrigated were in a plot with 24 rows, each 240 feet long, the total row length would be 5,760 feet.
At 0.5 gpm per 100 feet, the total flow rate required from the water supply would be 28.8 gpm.
If your water supply is capable of delivering only 10 gpm, not all of the system can be operated at once.
If the plot is irrigated in three sub-units, each with eight rows, only 9.6 gpm is needed at one time.
After the first sub-unit is irrigated for the required 3.5 hours, it is switched off and the next sub-unit is irrigated for 3.5 hours and so on until all the subunits have been irrigated.
As long as there is sufficient time to cover all of the sub-units in the field before the interval between irrigations  has elapsed, the water supply will be adequate for the entire field.
In this example, the system could irrigate up to 10 sub-units in two days without operating longer than 18 hours per day.
For widely spaced plants, such as orchard trees, water requirements are best determined on a "per plant" basis.
For example, if a peach tree has a canopy that is 12 feet in diameter and uses water at a rate of 0.24 inches per day, drip irrigation must replace 18.8 gallons of water per day.
This figure is computed by the equation:
 Q = 0.544 d2 D
 where Q = water requirement, gal/day d = tree diameter, ft D = water use rate, in/day 0.544 = constant 
 Each tree will require 18.8 gallons of water per day at this stage of development.
While a single 1 gph emitter could provide this amount of water, proper root system development would be better promoted by dividing this flow among three or four emitters.
The emitters should be placed out near the canopy dripline, equally spaced around the tree.
The required operation time per irrigation will be given by:
 where T = Time of operation, hours/day Q = Water requirement, gal/tree-day N = Number of emitters per tree R = Emitter flow rate, gal/hour
 For example, with four emitters of 2 gph flow capacity, the required 18.8 gallons would be applied in 2.4 hours.
If the irrigation interval is longer than one day, the time of operation per irrigation will be multiplied by the number of days that elapse between irrigations.
If the trees in the example above were to be irrigated every seven days, the system would need to operate 16.5 hours per irrigation.
In the case of home gardening irrigation, maximum system capacity is limited by water system flow rate.
A standard outside hydrant has a maximum capacity of about 5 gpm, and can operate a maximum of 1000 feet of drip tubing with 0.30 gph emitters on a 12 inch emitter spacing , or about 300 1-gph point source emitters.
Drip irrigation can stretch a limited water supply to cover up to 25 percent more acreage than a typical sprinkler system.
It can reduce the incidence of many fungal diseases by reducing humidity in the crop canopy and keeping foliage dry.
It allows automation of the irrigation system, reducing labor requirements.
It delays the onset of salinity problems when irrigation water of marginal quality must be used.
Drip irrigation requires careful water treatment to prevent emitter blockage problems.
Frequent inspection of the system is necessary to insure it is functioning properly.
Improper design and component sizing can result in a system with poor uniformity of application and a much lower than expected application efficiency.
A properly designed and installed drip irrigation system will normally be substantially more expensive than a sprinkler irrigation system initially.
However, the lower operating cost and higher efficiency of the drip system can justify the added expense very quickly in many horticultural production systems.
Credit is extended to Mikael Kizer, retired Extension Irrigation Specialist for the original content of this publication.
Oklahoma State University, in compliance with Title VI and VII of the Civil Rights Act of 1964, Executive Order 11246 as amended, Title IX of the Education Amendments of 1972, Americans with Disabilities Act of 1990, and other federal laws and regulations, does not discriminate on the basis of race, color, national origin, gender, age, religion, disability, or status as a veteran in any of its policies, practices, or procedures.
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Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S.
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This publication is printed and issued by Oklahoma State University as authorized by the Vice President, Dean, and Director of the Division of Agricultural Sciences and Natural Resources and has been prepared and distributed at a cost of 20 cents per copy.
Revised 0414 GH.
The main switch in the pivot panel does not turn off all of the power inside the panel.
So if you need to work inside the panel to fix a problem or clean out a nest from a mouse that got in the panel through conduit that was not properly installed, make sure to turn the power off to the panel or call your dealer if you are unsure how to turn it off.
Optimal irrigation management under poor drainage and saline conditions
 Ariel Dinar Keith C.
Knapp
 Decision-making is more demanding than for land free from these problems
 Agricultural production on the west side of California's San Joaquin Valley is jeopardized by rising water tables over a fairly wide area.
The perched water tends to be brackish and may contain significant concentrations of trace metals, particularly selenium.
Viable production under these conditions depends on installation of drainage systems and a means of disposing of the drainage water.
Optimal agricultural management might be considerably different in this area than in locations not subject to high water tables or salinity.
Decisions such as crop selection, water application quantity, type of irrigation system, means of drainage water disposal, and use of brackish waters for irrigation must be based on economic as well as physical-biological considerations.
This report summarizes some recent research on optimum crop management under saline and high water table conditions.
Economic analysis of water management requires information on the relationship between crop yield and the quantity and quality of irrigation water.
It is also necessary to know the relationships between the quantity and quality of irrigation water and the quantity and quality of the water moving beyond the root zone to the water table.
Under poor drainage and saline conditions, there is a trade-off between
 benefits from higher yields and costs of increased drainage water resulting from increased water applications.
One approach to developing crop production functions is to conduct field experiments in which the quantity and quality of irrigation water are experimental variables.
The combination of the two variables, however, leads to a large number of treatments, which are expensive to conduct on a field scale.
Furthermore, the results are limited to the specific crop and physical conditions at the experimental site.
A less time-consuming and expensive approach is to use a model based on scientifically established physical-biological relationships to compute production functions.
We developed such a model by combining three relationships previously established in the scientific literature:  yield and evapotranspiration ,  yield and average root zone salinity, and  average root zone salinity and the fraction of the applied water that moves below the root zone.
The model allows plant growth adjustment and therefore evapotranspiration adjustment to root zone salinity.
The crop water production function can be expressed in relative terms, which is helpful in transferring the relationships among geographical areas of different climates and growing conditions.
Yields are expressed on a relative basis with the
 value of 1.0 representing maximum yield.
The seasonal values of applied water  are scaled by seasonal pan evaporation  to adjust for climatic conditions affecting evaporation.
The model allows not only computation of yield as related to applied water, but also computation of quantity and quality of water percolating below the root zone to the water table.
Results from the production function model are now available for alfalfa , cauliflower, celery, corn, cotton, cowpea, lettuce, oats, sugarbeets, tall fescue, tomato, and wheat.
We checked the validity of the model by using limited available experimental data obtained at different locations in the United States and Israel with quite good agreement between observed and predicted yields.
For a given level of applied water to alfalfa, the yield decreases with increasing salinity of irrigation water.
Increasing water application can contribute to higher yields when using brackish water, but it also results in higher volumes of drainage water.
The amount of deep percolation from a given quantity of applied water increases as the salinity of that water increases, because the reduced plant growth under saline conditions results in less evapotranspiration.
Some deep percolation occurs even with very low water applications if the irrigation water is saline.
The production functions are for cases of uniform irrigation.
Irrigation is never completely uniform and is sometimes highly nonuniform.
Optimum water application on all parts of the field is not possible under such circumstances; some parts of the field are over-irrigated and others under-irrigated.
We expanded the model to compute yield as a function of average amount of applied water on a field basis for assumed irrigation uniformity distributions.
These crop production functions served as the basis for economic evaluation of water management at the field level under various drainage situations typical of the west side of the San Joaquin Valley.
The assumption under one situation was that no perched water table developed, so that no disposal of drainage water was required.
In another situation, we assumed a perched water table requiring a drainage system and three drainage water disposal options: a free off-farm facility for disposal, an on-farm evaporation pond on nonproductive land, and an on-farm evaporation pond constructed on productive land.
Optimum applied water and associated profits, yields, and drainage volumes were computed for corn and cotton, representing crops sensitive to and tolerant of salinity, respectively.
We used
 Fig.
1.
Computed relationship between relative alfalfa yield and applied water  scaled to pan evaporation.
Each curve is for a given electrical conductivity of the irrigation water.
At a particular level of applied water, yield decreases with increasing salinity.
Fig.
2.
Computed values of deep percolation when alfalfa is irrigated with various quantities of applied water at a given dSm.
Increasing application of brackish water increases the volume of drainage water.
a range of hypothetical irrigation uniformities and irrigation water salinities in the analyses.
Results indicate that high yields can be achieved with very little deep percolation under perfectly uniform irrigation with nonsaline water, a condition which rarely, if ever, exists.
Under those circumstances, optimal water management and profits were about the same for all drainage situations.
With nonuniform irrigation, saline water, or both, high yields are achieved by larger water applications, resulting in greater drainage volumes.
The benefits of increased yields are offset by costs of increased drainage volumes.
Optimal irrigation and profits are highly dependent on the costs associated with drainage.
The situation without a perched water table has no drainage costs, so there is an incentive to apply large quantities of water under nonuniform and/or saline conditions; decreases in profit are comparatively low, except when irrigation water prices are very high.
With a perched water table, drainage volumes have definite costs.
These are relatively low if a free off-farm facility is available, so that the optimal management and profits do not differ greatly from the case with no perched water table.
On the other hand, on-farm evaporation ponds are costly, particularly if productive land must be used, so that significantly lower irrigation amounts are optimal and profits decrease accordingly.
Because of the high costs associated with placing evaporation ponds on productive land, growers have an incentive for a cooperative arrangement to transport the drainage waters to nonproductive land.
Since the effect of irrigation uniformity on economically optimal yields and profits is strongly related to the costs associated with drainage volumes, investments to upgrade irrigation are more likely to be profitable when costs associ-
 lated with drainage are high.
In principle, uniformity can be improved by changing irrigation management or systems, or both.
Unfortunately, we do not yet have reliable procedures for characterizing irrigation uniformity in the field in a manner that can be used in crop production analysis.
Such procedures are the missing link for combining all the factors in a complete quantitative economic analysis for a given field or farm.
Breeding for salt tolerance
 We investigated the profitability of breeding more salt-tolerant varieties of crops for the same drainage situations by adjusting parameters in the model as if the plant were more salt tolerant.
Increasing tolerance had relatively little effect on yields and profits when irrigation waters were low in salinity, regardless of drainage conditions.
When high-salinity waters were used, however, greater salt tolerance increased yields and profits.
The effects of increasing tolerance by breeding are more significant for crops that are initially sensitive than for tolerant crops.
Since most surface supplies of irrigation water in the Valley are relatively low in salinity, crop breeding for salt tolerance becomes a factor only when use of saline drainage water for irrigation is considered.
Reuse of drainage water
 Results showed that using a combination of fresh and saline water was not feasible for the more sensitive crops.
Combining fresh and drainage waters became more feasible as the salinity of the drainage water decreased, crop tolerance to salinity increased, or the relative price of drainage to fresh water decreased.
In other words, disposal of brackish drainage water by irrigating crops is feasible only under a limited set of circumstances and cannot be considered a general solution.
Nevertheless, conditions can be specified for profitably using drainage waters for irrigation.
Using the production function model, we determined the optimal combination of fresh surface and saline drainage waters in a crop production system.
Equal yield curves  were calculated from the production function model for different quantities of fresh and saline water.
Information about crop prices, water prices, and other variable costs is required in determining the optimal rate of combining the two water sources.
Optimal water management on farmland plagued by saline conditions and high water tables is considerably different from management on land free from such problems.
With appropriate data, solutions can be computed for water management.
One major limitation is the lack of reliable procedures for characterizing irrigation uniformity in a manner that can be used in the models.
Our analyses assumed no subsurface lateral flows from one farm to the next.
To the extent that considerable subsurface lateral flow is occurring, the analysis would have to be expanded to a regional basis, whereas the present analysis has been restricted to individual farms and in some cases to individual fields.
Also, the analysis does not address the potential hazard of trace elements in some drainage waters.
The research, however, does provide some insights and guidelines to water management under saline and drainage problem conditions.
J.
Letey is Professor of Soil Physics, Ariel Dinar was Postdoctoral Research Agricultural Economist, and Keith C.
Knapp is Assistant Professor of Resource Economics, Department of Soil and Environmental Sciences, University of California, Riverside.
Ariel Dinar is now associated with the Center of Agricultural Economic Research, Hebrew University of Jerusalem, Rehovot, Israel.
This research was supported by the UC Kearney Foundation of Soil Science.
The preliminary October temperature and precipitation outlook issued Sept.
17 indicates that above-normal temperature are expected statewide, while the eastern two-thirds of the state is projected to receive below-normal moisture during the month.
October marks the official start to the offseason soil moisture-building period that last until the end of April.
If the current preliminary forecast verifies, soil moisture reserves would begin the 2023 crop production season below normal.
Chapter: 52 Stored Grain Pests of Corn
 Several species of insects, as well as rodents and other animals, are economically important pests of stored grains.
Unfortunately, this means that integrated pest management  for your corn crop is not finished until the grain has been delivered and accepted by the commercial buyer.
The final stages of an IPM plan for your corn actually start before harvest and continue while the corn is being stored in bin facilities.
During this storage period, the kernels are susceptible to direct damage from feeding unless necessary precautions are taken.
The purpose of this chapter is to discuss storage sanitation considerations, stored grain insect pest management, bin aeration, and common stored grain insect pests of corn.
Direct insect feeding reduces germination, nutrition, weight, and ultimately market value.
Insects and other animals also cause indirect damage, which results in the contamination and deterioration of the grain.
This in turn, leads to reduced quality and lower market value, which can be attributed to the presence of heat damage, intact dead insects, insect parts, odors, or molds.
The current Federal Grain Inspection Service  regulation used to determine whether corn is infested, and also grading based on the maximum limits for broken corn and foreign material  are presented in Table 52.1.
Table 52.1 FGIS infested designation and grade standards for corn.
Crop	Insects per 2.2 pounds of grain to	Maximum limits of broken corn and
 receive FGIS "infested" designation	foreign material,  by grade
 U.S.
No.
1: 2.0
 U.S.
No.
2: 3.0
 U.S.
No.
3: 4.0
 Corn	1 live weevil + 5 other live stored grain pests	U.S.
No.
4: 5.0
 10 other live stored grain pests
 U.S.
No.
5: 7.0
 U.S.
Sample Grade: > 7.0
 1 Foreign material includes all matter that will pass through a 12/64 round-hole sieve.
It is important to remember that the insect pests attacking corn in the field are not the same species as the ones attacking the stored crop.
Because damaged grain results in docked or reduced market prices, it is important to use an IPM plan with preventative tactics and routinely monitor grain bins for pest activity.
These approaches rely heavily on preventative actions including sanitation, pre-binning insecticide
 applications, and early detection of problems post-binning.
This type of IPM plan should be employed until the grain leaves the farm.
To ensure that the quality of stored grain is preserved, it is important to establish and follow an IPM plan.
A leading cause of decreased grain quality is improper storage conditions, especially poor sanitation.
Proper sanitation accounts for approximately 80% of an effective IPM plan for stored grain.
"Good" sanitation includes:
 1.
Determining whether the bin is weatherproof and does not have any leaks.
Any holes or gaps should be caulked/sealed.
After the bin is filled, the door should be caulked/sealed to remove potential entry points for insects and rodents.
2.
Removing any established pests and their food sources prior to filling the grain bin.
Bins should be swept and/or vacuumed, with special attention given to cracks and crevices of the floor.
3.
Cleaning up any grain spills around the outside of the bin.
All grain and dust should be disposed of away from the bin.
4.
Establishing a 10-ft perimeter outside the bin that is devoid of vegetation and garbage.
5.
Cleaning equipment used seasonally for handling or transporting grain.
Following these steps will reduce the chances of stored grain pests accidentally being introduced to the new crop during binning, and also reduce the overall chances of infestation.
Stored Grain Insect Pest Management
 It is recommended that new grain should never be stored on top of old grain.
However, if this situation arises, the old grain must be fumigated prior to the addition of new grain.
Fumigants are extremely hazardous, restricted-use insecticides and require a commercial applicators license with class 14 certification, or a private applicator certification in South Dakota.
Because of the hazards associated with these insecticides, it is recommended to leave the application of fumigants to professionals.
Additionally, fumigants have no residual period and are effective only against insects present in the grain at the time of application.
Grain is susceptible to reinfestation within 72 hours post-application.
For an empty bin, a pre-binning application of a residual insecticide should be applied to all of the interior surfaces and also to the exterior walls and base once the debris has been removed.
Follow the label instructions regarding application rate, personal protective equipment, and re-entry times.
Once the re-entry interval has expired, remove any insects that were killed by the insecticide.
For corn that will be removed from storage in May or June or used as a livestock feed within a year of harvest, protectant insecticides most likely will not be required.
A protectant insecticide should be applied to corn that is expected to be stored for greater than one year, and it should be applied only after high-temperature drying when the corn moisture is approximately 14% to 15%.
These insecticides can be applied at the auger while the bin is being filled, or as a surface treatment that is referred to as either topdressing or capping-off.
Stored corn with a temperature above 55-60F should be inspected each week, and every two weeks when the temperature is below 55F.
When inspecting stored grain, it is important to remember the associated hazards.
If an insect infestation is detected in stored grain, the grain can be: 1) moved to have a protectant insecticide applied; 2) fed to livestock as-is; 3) sold at a reduced market value; or 4) fumigated.
Stored grain insect pest development slows down when grain temperatures decrease to 60F, and essentially stops when the temperature decreases below 55F.
Because of this, it is important to reduce grain temperatures to limit the risks of developing stored grain pest issues.
Stored grain can be cooled once the outdoor temperatures begin to drop in the fall.
For bins that are equipped with fans, run the fan during cooler temperatures.
In addition to reducing potential insect issues, proper grain aeration will help
 Table 52.2 The seven steps to a stored grain integrated pest management  plan:
 Step 1.
Structural maintenance: keep bins clean and repaired.
Keep a 10-ft perimeter around the bin free of vegetation and trash.
Clean up grain spills outside of the bin.
Confirm that bin facilities are weathertight and rodent-proof; seal any holes.
Screen ventilation openings to prevent entry of rodents and birds.
*Do not mix new and old grain; remove all old grain from bin or fumigate old grain.
*Use a broom, shop vacuum, or compressed air to clean the interior bin walls, ceiling, ledges, floors, and sills prior to filling with new grain.
*Use a broom, shop vacuum, or compressed air to clean combines, wagons, grain carts, trailers, augers, and aeration equipment prior to handling new grain.
Dispose of any debris removed from bins or machinery as insects may be present.
Examine the outer bin perimeter to determine whether rodent bait stations are necessary.
Caulk around any doors.
Do not seal roof aeration exhaust of inlet vents except during fumigation.
Step 2.
Residual insecticide sprays.
Pre-binning:
 Spray the interior wall surfaces, ledges, floors, and sills with a residual insecticide.
Spray exterior walls  and exterior base.
For long-term storage  consider fumigating the area beneath the slotted floor.
Step 3.
Condition grain: store clean, dry grain.
Pre-binning:
 For long-term storage, corn moisture should be 15% or less.
Use a grain cleaner to remove cracked kernels and other debris.
Step 4.
Use insecticide protectants.
Treat grain at the auger as it is moved into storage or apply a topdressing.
Step 5.
Proper aeration of grain.
Post-binning:
 Run bin fan and stirator to ensure uniform temperatures and prevent moisture buildup.
This will reduce mold growth.
Cool bin to a temperature below 55F to reduce insect activity and inhibit mold growth.
Step 6.
Regularly inspect the grain.
Post-binning: 
 Monitor the grain regularly for the presence of insects, or insect parts.
For grain above 55-60F inspect weekly.
For grain below 55F inspect every two weeks.
Inspection should continue from binning until the grain is marketed.
Use a grain probe to take samples in a pattern from the surface and from the base of the grain mass.
Take samples from the center to the areas near the wall, with samples being no farther than 20 feet apart.
"Hot spots" felt on the grain surface or unusual odors are indicators of insect activity and should be examined.
During the winter, insects will move to the center of the bin, SO sampling at that location is important.
Step 7.
Treating detected infestations.
Post-binning:
 If an insect infestation is detected:
 1.
Move the grain and re-treat as in Step 4.
It is possible to kill some of the insects if the grain is moved during cold weather.
2.
Feed the grain to livestock.
3.
Sell at a reduced price.
4.
Fumigate.
*These precautionary maintenance steps should be taken 2-3 weeks prior to binning.
Table 52.3 Fumigant insecticides that can be used on stored corn grain.
1
 Active Ingredient	Insecticide*	Restricted Entry Interval 	Comments
 Do not fumigate if temperature is below
 Fumex	Corn must be aerated after fumigation.
40F.
Follow the minimum exposure
 Fumitoxin	Do not enter bin if phosphine or	period guide on the label.
Fumigated
 Aluminum phosphide	Gastoxin	hydrogen phosphide gas levels are above	areas must be placarded according to
 Phostoxin	0.3 ppm unless protected by approved	each product's label.
Some products
 Weevil-cide	respirator.
require grain to be aerated for 48 hours
 prior to offering to end consumer.
Works best with grain bins designed
 for "closed-loop fumigation." Requires
 Carbon dioxide 	Carbon dioxide	When CO, 2 levels are below 5%.
Fumigation with CO2 2 takes 10 or more
 days.
Self-contained breathing apparatus
 must be worn; respirators are not
 Do not fumigate if temperature is below
 Corn must be aerated after fumigation.
40F.
Follow the minimum exposure
 Do not enter bin if phosphine gas level
 Magnesium phosphide	Magtoxin	is above 0.3 ppm unless protected by	period guide on the label.
Fumigated
 areas must be placarded according to
 Corn must be aerated after fumigation.
Do not fumigate if temperature is
 Do not enter the bin if methyl bromide
 below 40F.
Fumigated areas must be
 Methyl bromide	Meth-O-Gas 100	levels are above 5 ppm unless protected	placarded according to each product's
 by a full-face supplied-air respirator or
 All fumigant insecticides are restricted-use products and cannot be purchased or applied without proper certification and permit 1 or licensing.
Follow all label instructions.
Parts per million 
 *This list is not meant to be comprehensive.
Mention of a trade name neither constitutes endorsement of the products mentioned nor criticism of similar ones not used or mentioned.
Table 52.4 Pre-binning corn grain residual and protectant insecticides.
Active Ingredient	Insecticide*	Interval 	Comments
 Protectant insecticide to be applied as a topdressing to the
 Bacillus thuringiensis	DiPel DF	4 hours	top 4 inches of stored corn.
kurstaki	Biobit HP	Will not control weevils or other beetles.
Effective against
 Indian meal moth larvae.
Labeled for organic production.
Do not allow runoff to occur.
Pre-binning residual spray
 Beta-cyfluthrin	Tempo SC Ultra	When spray has dried.
only.
Suspend: Do not allow runoff to occur.
Pre-binning
 Deltamethrin	Centynal	When spray has dried.
Centynal: Do not reapply within 21 days.
May be applied as
 a protectant while grain is being loaded into the bin.
Can
 be used as a pre-binning residual spray.
Treatment normally lasts 4 months.
One 16 gram strip
 strips 	Nuvan Prostrips	N/A	treats 100-200 cubic feet.
Place strips in the headspace of
 the bin.
Wear gloves when applying strips.
May be applied while grain is being loaded into bin or as a
 Pirimiphos-methyl	Actellic 5E	When spray has dried.
topdressing, cannot be used for both.
Do not make more
 than one application per year.
Do not reapply within 30 days.
May be applied as a
 Pyrethrin	Pyronyl	12 hours	protectant while grain is being loaded into the bin.
Can be
 used as a pre-binning residual spray.
Malathion dust: Apply to grain prior to loading bin.
Do not
 apply to grain within 7 days of selling.
Malathion	Grain Dust	12 hours	Malathion 5EC: Pre-binning residual spray only, do not
 spray directly onto grain.
Apply to grain as it is being loaded into bin, or apply as
 -methoprene	Diacon D IGR	30 minutes	a topdressing, but do not flood area.
May be used with
 Can be applied to grain when being loaded into the bin.
Silicon dioxide	Dryacide	Once dust settle	Can also be applied as a pre-binning residual insecticide.
Insecto	Labeled for organic production.
Overapplication of
 products may reduce grade of grain.
Follow the label instructions for all pesticides.
Always wear proper personal protective equipment.
*This list is not meant to be comprehensive.
Mention of a trade name neither constitutes endorsement of the products mentioned nor criticism of similar ones not used or mentioned.
Table 52.5 Bin-sampling safety protocol.
There are many potential hazards associated with sampling inside of a grain bin.
For instance, suffocation can occur in grain bins due to bridged grain.
Bridged grain occurs when grain mats together and forms a false floor.
When the false floor is broken during sampling procedures, cave-ins can occur.
Where possible:
 1.
Always have another person with a cellphone outside the bin in case there is a problem.
2.
Wear a harness that is attached to a properly secured rope when entering a grain bin.
3.
Use a pole to break up crusted grain from a distance.
4.
If the grain begins to flow stay near the outer wall of the bin and continue walking and get to the bin ladder as quickly as possible.
maintain uniform temperatures throughout the bin.
This will eliminate "hot pockets" that are favored by insects and mold.
To ensure optimal airflow, level off the grain once the bin has been filled.
When the grain is not level, areas with peaks can provide optimal conditions for stored grain insect outbreaks and mold growth.
Common Stored Grain Insect Pests of Corn
 There are several species of insects that feed on stored grain in South Dakota.
Both immature  and adult stages of stored grain beetles are capable of causing damage to grain, while only the larval stage of the stored grain moths cause damage.
These insect pests can be grouped based on whether they are internal feeders or external feeders.
Internal feeders feed within the kernels, whereas external feeders consume grain dusts, cracked kernels, and other grain debris.
Below are the common internal and external stored grain pests.
In addition to these, other species including the foreign grain beetle and hairy fungus beetle may be observed in a bin feeding on molds or fungi growing on the grain.
Of the internal feeders, the weevils  are generally given the most attention because they are among the most destructive pests of stored grain.
The larvae of grain weevils develop within the kernels, and this pest can cause nearly complete destruction when infested grain is left undisturbed for long periods of time.
Adult weevils are easily distinguished from other beetles by their elongated snouts.
The lesser grain borer  is a pest of a wide variety of grains including corn.
The larvae and adult bore holes into whole undamaged kernels.
Evidence of feeding may include a sweet musty odor and dust and thin brown shells on grain kernels.
The larvae of the angoumois grain moth  are typically not a pest of shelled corn.
However, the larvae are a pest of ear corn and can infest the corn before it is harvested.
The larvae feed inside kernels, and cause an unpleasant smell.
During a warm fall, several generations of the moth can complete their life cycle, resulting in significant damage.
External feeders consume grain dusts, cracked kernels, or other grain debris when present.
The best management for these insects is prevention that includes proper aeration and corn grain cleaning.
The cadelle beetle , confused flour beetle , flat grain beetle , red flour beetle , and sawtoothed grain beetle  are present in the grain due to the availability of cracked kernels, dust, and other grain debris.
In some instances, these beetles will feed on kernels that were damaged by internal feeders.
The larvae of the Indian meal moth  cause direct damage to the grain by feeding on the seed germ.
The larvae of this pest also reduce the quality of grain by producing waste and constructing silken webs in the grain.
Enterprise Budgets Guayule, Flood Irrigated, Southern Arizona Trent Teegerstrom, Clark Seavert, Hailey Summers, Evan Sproul, and Blase Evancho
 This series of enterprise budgets estimate the typical economic costs and returns to establish, grow, and harvest guayule over a six-year period, using flood irrigation in southern Arizona.
It should be used as a guide to estimate actual costs and returns and is not representative of any particular farm.
The assumptions used in constructing these budgets are discussed below.
Assistance provided by area producers and agribusinesses is much appreciated.
The results of this study are based on our current understanding of guayule production, market and yields.
As research advances, we expect these assumptions to change.
These budgets are based on a 1,500-tillable acre farm with 300 acres of guayule, 225 acres in cotton, 75 acres in corn, sorghum, and barley each, 225 acres in winter wheat, and 525 acres of alfalfa hay production.
All crops are grown using flood irrigation.
Typical guayule yield in this budget is 22,000 pounds per acre at 15 percent moisture content.
The six-year sequence for guayule production is to establish the crop in year 1, harvest in years 2, 4, and 6, and grow the crop between harvests in years 3 and 5.
Crop removal occurs in year 6 after harvest.
Tractor driver labor cost is $14.44 per hour and general labor $13.13 per hour, both rates include social security, workers' compensation, unemployment insurance, and other labor overhead expenses.
For this study, owner labor is valued at the same rate as tractor driver rates, and all labor is assumed to be a cash cost.
Tractor labor hours are calculated based on machinery hours, plus ten percent.
Interest on operating capital for harvest and production inputs  is treated as a cash expense, borrowed for 6-months.
An interest rate of six percent is charged as an opportunity to the owner for machinery ownership.
The machinery and equipment used in this budget are sufficient for a 1,500-acre farm in crops.
The machinery and equipment hours reflect producing guayule, cotton, corn, sorghum, barley, winter wheat, and alfalfa hay.
A detailed breakdown of machinery values is shown in Table 6.
Estimated labor, variable, and fixed costs for machinery are shown in Table 7, based on an hour and per acre basis.
The machinery costs are calculated based on the total farm use of the machinery.
Off-road diesel is $2.70 per gallon.
Table 8 shows the machine operations by year during guayule production.
A 175-hp tractor is used to pull the v-ripper, heavy disk, landplane, 4-row lister, bed shaper, and 8-row planter.
A 125-hp tractor is used to pull the 8-row cultivator, baler, fertilizer spreader, and boom sprayer.
A charge for miscellaneous and other expenses is five percent of production costs, including additional labor, repairs and maintenance, supplies and materials, tax preparation, memberships in professional organizations, and educational workshops not included in field operations.
Six-Year Sensitivity Analysis of Net Returns
 Adding together the six years of costs and three years of guayule production results in a break-even price of $0.045 per pound to cover all variable costs and $0.056 per pound to cover total variable and fixed costs.
Table 1 shows the total net returns over six-years of guayule production at various yields, prices, and a 20 percent increase and decrease in total costs.
The $0.07 cents per pound or mid-point on the sensitivity analysis  was derived from the breakeven cost of production.
This was used as there is no established market for guayule.
Table 2 represents the net cost and returns per year for the six-year production cycle of guayule.
More detailed cost of
 establishing guayule is $604 per acre  and $551 per acre in the growing years between harvests.
The gross income in the harvest years is $1,540 per acre; guayule price at $0.07 per pound, with an average yield of 22,000 pounds.
Variable costs are $505 per acre, giving a net return above variable cash costs of $1,035 per acre.
Total fixed costs are $734 per acre, which includes an amortization charge of $569 is included as an opportunity cost to establish and grow guayule in years 1, 3, and 5 during the six-year rotation.
Total costs are $1,238 per acre, variable costs are 41% of total costs.
Note: Not included in these budgets are family living withdrawals for unpaid labor, returns to management, depreciation and opportunity costs for vehicles, buildings and improvements, inflation, and local, state, and federal income taxes.
Funding provided by the USDA-NIFA, Grant # 201768005-26867.
"Any opinions, findings, conclusions, or recommendations expressed in this publication/ work are those of the author and do not necessarily reflect the view of the U.S.
Department of Agriculture."
 Table 1.
Estimated Total Net Returns from Six Years of Guayule Production at Varying Price, Yields, and Percentage of Production Costs, $/acre.
% Change in	Yield,	Guayule Price per Pound of Biomass
 Total Costs	Lbs/Acre	$0.05	$0.06	$0.07	$0.08	$0.09
 19,000			$275	$845	$1,415
 20,000			$485	$1,085	$1,685
 21,000		$65	$695	$1,325	$1,955
 0%	22,000		$245	$905	$1,565	$2,225
 23,000		$425	$1,115	$1,805	$2,495
 24,000		$605	$1,325	$2,045	$2,765
 25,000	$35	$785	$1,535	$2,285	$3,035
 19,000		$448	$1,018	$1,588	$2,158
 20,000	$28	$628	$1,228	$1,828	$2,428
 21,000	$178	$808	$1,438	$2,068	$2,698
 -20%	22,000	$328	$988	$1,648	$2,308	$2,968
 23,000	$478	$1,168	$1,858	$2,548	$3,238
 24,000	$628	$1,348	$2,068	$2,788	$3,508
 25,000	$778	$1,528	$2,278	$3,028	$3,778
 19,000				$201	$672
 20,000				$342	$942
 21,000				$582	$1,212
 20%	22,000			$162	$822	$1,482
 23,000			$372	$1,062	$1,752
 24,000			$582	$1,302	$2,022
 25,000		$42	$792	$1,542	$2,292
 Table 2.
Annual Net Returns of Icome and Expenses to Establish and Produce Guayule, $/acre.1
 Income	Cash Cost	Fixed Cost	Returns
 Year 1: Establishment	$0	$383	$220	-$604
 Year 2: Harvest2	1,540	505	165	870
 Year 3: Growing	0	387	164	-551
 Year 4: Harvest2	1,540	505	165	870
 Year: 5 Growing	0	387	164	-551
 Year 6: Harvest2	1,540	505	165	870
 Table 3.
Year 1: Guayule Establishment Year, Economic and Cash Costs, $/acre.
Variable Cash Costs	Price	Quantity	Unit	Labor	Machinery	Materials	Total
 Land Preparation and Maintenance
 VRipper	1.00	acre	$6.42	$15.64	$0.00	$22.06
 Offset Disk	2.00	acre	$3.64	$8.69	$0.00	$12.33
 Lister	1.00	acre	$4.10	$8.90	$0.00	$12.99
 Bed Shaper	1.00	acre	$2.20	$4.64	$0.00	$6.84
 Row Cultivator	2.00	acre	$3.67	$11.29	$40.50	$55.46
 Fertilizer Spreader	1.00	acre	$1.56	$2.73	$67.00	$71.29
 Nitrogen	$0.25	100.00	pounds
 Phosphorus	$0.21	200.00	pounds
 Boom Sprayer	1.00	acre	$1.34	$1.83	$90.42	$93.59
 Prowl	$6.50	9.00	pints
 Aim	$5.62	1.80	ounces
 Fusilade	$1.09	20.00	ounces
 Row Planter	1.00	acre	$1.64	$2.25	$0.00	$3.89
 Irrigation, Flood	$9.85	$0.00	$60.00	$69.85
 Water	$60.00	1.00	ac ft
 Labor	$13.13	0.75	hour
 Other Expenses	0.05	$0.00	$0.00	$17.73	$17.73
 Interest on Operating Capital	0.06	$0.00	$0.00	$11.17	$11.17
 Total Variable Cash Costs	$36.34	$60.32	$286.81	$383.47
 Total Returns minus Total Variable Cash Costs	-$383.47
 Fixed Cash Costs	Unit	$/Unit	Value
 Property Insurance	acre	$0.85	$0.85
 Property Taxes	acre	$9.44	$9.44
 Annual Cash Rent Payment	acre	$150.00	$150.00
 Total Fixed Cash Costs	$160.29
 Fixed Non-Cash Costs	Unit	$/Unit	Value
 Power Units, Machinery & Equipment, depreciation & interest	acre	$59.89	$59.89
 Total Fixed Non-Cash Costs	$59.89
 Total Annual Costs	$603.65
 Returns minus Total Annual Costs	-$603.65
 Table 4.
Years 2,4 and 6: Guayule Harvest Years, Economic and Cash Costs and Returns, $/acre.
Returns	Unit	$/Unit	Quantity	Value
 Guayule Biomass	pound	$0.07	22,000.00	$1,540.00
 Variable Cash Costs	Price	Quantity	Unit	Labor	Machinery	Materials	Total
 Land Preparation and Maintenance
 Offset Disk	0.20	acre	$0.36	$0.87	$0.00	$1.23
 Broom Sprayer	1.00	acre	$1.34	$1.83	$90.42	$93.59
 Prowl	$6.50	9.00	pints
 Aim	$5.62	1.80	ounces
 Fusilade	$1.09	20.00	ounces
 Row Cultivator	1.00	acre	$1.83	$5.65	$0.00	$7.48
 Irrigation, Flood	$9.85	$0.00	$247.00	$256.85
 IWater	$60.00	3.00	ac ft
 Labor	$13.13	0.75	hour
 Harvest, Custom	1.00	acre	$0.00	$0.00	$100.00	$100.00
 Other Expenses	0.05	$0.00	$0.00	$23.33	$23.33
 Interest on Operatiing Capital	0.06	$0.00	$0.00	$14.70	$14.70
 Total Variable Cash Costs	$15.22	$14.00	$475.45	$504.66
 Total Returns minus Total Variable Cash Costs	$1,035.34
 Fixed Cash Costs	Unit	$/Unit	Value
 Property Insurance	acre	$0.85	$0.85
 Property Taxes	acre	$9.44	$9.44
 Annual Cash Rent Payment	acre	$150.00	$150.00
 Total Fixed Cash Costs	$160.29
 Fixed Non-Cash Costs	Unit	$/Unit	Value
 Power Units, Machinery & Equipment, depreciation & interest	acre	$4.70	$4.70
 Amortized Establishment and Maintenance Costs	acre	$568.69	$568.69
 Total Fixed Non-Cash Costs	$573.39
 Total Annual Costs	$1,238.35
 Returns minus Total Annual Costs	$301.65
 Table 5.
Years 3 and 5: Guayule Growing Years, Economic and Cash Costs, $/acre.
Variable Cash Costs	Price	Quantity	Unit	Labor	Machinery	Materials	Total
 Land Preparation and Maintenance
 Row Cultivator	1.00	acre	$1.83	$5.65	$0.00	$7.48
 Boom Sprayer	1.00	acre	$1.34	$1.83	$90.42	$93.59
 Prowl	$6.50	9.00	pints
 Aim	$5.62	1.80	ounces
 Fusilade	$1.09	20.00	ounces
 Irrigation, Flood	$9.85	$0.00	$247.00	$256.85
 IWater	$60.00	3.00	ac ft
 Labor	$13.13	0.75	hour
 Other Expenses	0.05	$0.00	$0.00	$17.90	$17.90
 Interest on Operating Capital	0.06	$0.00	$0.00	$11.27	$11.27
 Total Variable Cash Costs	$13.02	$7.48	$366.59	$387.09
 Total Returns minus Total Variable Cash Costs	-$387.09
 Fixed Cash Costs	Unit	$/Unit	Value
 Property Insurance	acre	$0.85	$0.85
 Property Taxes	acre	$9.44	$9.44
 Annual Cash Rent Payment	acre	$150.00	$150.00
 Total Fixed Cash Costs	$160.29
 Fixed Non-Cash Costs	Unit	$/Unit	Value
 Power Units, Machinery & Equipment, depreciation & interest	acre	$3.83	$3.83
 Total Fixed Non-Cash Costs	$3.83
 Total Annual Costs	$551.21
 Returns minus Total Annual Costs	-$551.21
 Machine	Width	Market	Annual	Life
 	Value	Use	
 175 HP Tractor	N/A	$180,000	947	15
 125 HP Tractor	N/A	$80,000	1,502	10
 V-Ripper	8.0	$22,000	152	10
 Offset Disk	18.0	$30.000	195	15
 Landplane	16.0	$18,000	52	15
 Lister	10.0	$6,500	110	15
 Bed Shaper	20.0	$6,500	38	20
 Row Planter	20.0	$40,000	84	15
 Row Cultivator	20.0	$22,000	144	10
 Fertilizer Spreader	20.0	$18,000	56	20
 Boom Sprayer	30.0	$9,500	171	20
 Table 7.
Machinery Cost Calculations, on a per hour and er acre basis.
Variable Costs	Fixed Cost
 Machine	Fuel & Lube	Repair & Maint.
Deprec &	Total Cost
 175 HP Tractor	$24.84	$7.67	$21.05	$53.56
 125 HP Tractor	$12.42	$3.60	$6.86	$22.88
 V-Ripper	$0.00	$6.16	$18.76	$24.92
 Offset Disk	$0.00	$5.40	$17.18	$22.58
 Landplane	$0.00	$3.24	$39.04	$42.28
 Lister	$0.00	$2.01	$6.64	$8.64
 Bed Shaper	$0.00	$0.97	$18.77	$19.73
 Row Planter	$0.00	$16.43	$55.63	$72.26
 Row Cultivator	$0.00	$5.81	$19.42	$25.23
 Fertilizer Spreader	$0.00	$11.76	$36.60	$48.36
 Boom Sprayer	$0.00	$5.64	$6.37	$12.00
 Field Operation	Acres/Hour	Operator Labor	Variable Costs	Fixed Costs	Total Costs
 175 HP Tractor & V-Ripper	2.47	$6.42	$15.64	$16.10	$38.16
 175 HP Tractor & Offset Disk	8.73	$1.82	$4.34	$4.38	$10.54
 175 HP Tractor & Landplane	8.24	$1.93	$4.34	$7.29	$13.56
 175 HP Tractor & Lister	3.88	$4.10	$8.90	$7.14	$20.13
 175 HP Tractor & Bed Shaper	7.21	$2.20	$4.64	$5.52	$12.37
 175 HP Tractor & Planter	8.67	$1.83	$5.65	$8.87	$16.35
 125 HP Tractor & Cultivator	9.70	$1.64	$2.25	$2.71	$6.60
 125 HP Tractor & Fertilizer Spreader	10.18	$1.56	$2.73	$4.27	$8.56
 125 HP Tractor & Boom Sprayer	11.82	$1.34	$1.83	$1.12	$4.30
 Table 8.
Machine Operations by Year in Guayule Production
 Establishment Year	Harvest Years	Growing Years
 Machine Operation	X/Acre	X/Acre	X/Acre
 175 HP Tractor & V-Ripper	1.00
 175 HP Tractor & Offset Disk	2.00	0.20
 175 HP Tractor & Landplane	1.00
 175 HP Tractor & Lister	1.00
 175 HP Tractor & Bed Shaper	1.00
 175 HP Tractor & Planter	1.00
 125 HP Tractor & Cultivator	2.00	1.00	1.00
 125 HP Tractor & Fertilizer Spreader	1.00
 125 HP Tractor & Boom Sprayer	1.00	1.00	1.00
 THE UNIVERSITY OF ARIZONA Cooperative Extension
 TRENT TEEGERSTROM 1Ag Econ Extension Specialist, Department of Agriculture and Resource Economics, University of Arizona
 CLARK SEAVERT Agricultural Economist, Department of Applied Economics, Oregon State University
 PAUL GUTIERREZ Department of Agricultural Economics & Agricultural Business, New Mexico State University
 HAILEY SUMMERS PhD Student, Department of Mechanical Engineering, Colorado State University
 EVAN SPROUL PhD Student, Department of Mechanical Engineering, Colorado State University
 BLASE EVANCHO Area Agent, Arizona Cooperative Extension, University of Arizona
Determining the Quality of Aglime: Using Relative Neutralizing Values
 Monroe Rasnake, Lloyd Murdock, Greg Schwab, and Bill Thom
 Most Kentucky soils need to have lime applied in order to keep the pH in the optimum range for growing crops.
Lime applications should always be based on a good soil test that takes into account the existing pH and the buffering capacity of the soil.
However, even when all this is done and lime is applied as recommended, the desired change in soil pH may not occur.
The problem may be due to the use of low quality lime.
Agricultural limestone in Kentucky is tested by the Department of Agriculture for purity and fineness of grind.
This gives three values  that make it difficult to compare the relative effectiveness of different sources of lime.
This publication discusses the use of Relative Neutralizing Values , which is a method of combining the three values determined by the Department of Agriculture into a single value that can be used to compare the effectiveness of lime from different sources.
One factor affecting the ability of lime to neutralize soil acidity is the amount of calcium and magnesium carbonates it contains.
The test used in Kentucky combines the two and is expressed as calcium carbonate equivalent.
The minimum CCE to qualify as ground agricultural limestone in Kentucky is 80%.
This means that at least 80% of the material could dissolve and neutralize soil acidity.
Some limestone that is very pure and contains significant amounts of magnesium carbonate can have a CCE greater than 100%.
This is because magnesium carbonate can neutralize more acidity than calcium carbonate.
Clay, sand, organic matter, or other minerals present in limestone rock dilute its purity, leading to low CCE lime.
Since limestone rock is slow to dissolve, it must be ground very fine to be effective as a liming material for soil.
In order to effectively neutralize soil acidity, aglime should be fine enough to dissolve within four years after application.
Fineness of aglime is determined by sieving it through screens of known mesh size.
The Kentucky lime law requires that aglime be ground fine enough that 90% will pass through a 10-mesh sieve and 35% through a 50-mesh sieve.
How quickly lime of different particle sizes dissolves in the soil is illustrated in Table 1.
It shows that very little of the particles larger than 8 mesh dissolved in four years, while all of
 Table 1.
Solubility of ground limestone based on particle size.
1
 Size of Particles	Years after Application
 Coarser than 8 mesh	5	15
 8 to 30 mesh	20	45
 30 to 60 mesh	50	100
 Finer than 60 mesh	100	100
 NCSA Aglime Fact Book
 that passing a 60-mesh screen dissolved in one year.
Based on this and other data on lime dissolution rates, the effectiveness of Kentucky aglime over a four-year period was estimated as:
 Larger than 10 mesh	0
 Between 10 and 50 mesh	50
 Less than 50 mesh	100
 Relative Neutralizing Value of Aglime
 The percent of effective material in lime based on particle size can be combined with lime purity values to calculate the overall quality of aglime.
The term used in Kentucky for this calculated lime quality is Relative Neutralizing Value.
RNV is calculated using the lime purity value  and fineness values for percent less than 50 mesh and percent between 10 and 50 mesh.
The equation used is:
 RNV = CCE/100 [% between 10 and 50 mesh + % less than 50 mesh] 2
 Where CCE is % Calcium Carbonate Equivalent.
The amount of particles between 10 and 50 mesh is divided by two because it is only half as effective as those smaller than 50 mesh.
Since the values reported for lime fineness are the percentage passing 50 mesh and the percentage passing 10 mesh, the equation can be modified as:
 RNV = CCE/100 [0.5 ]
 For aglime with a CCE of 90% and with 95% passing a 10mesh sieve and 40% passing a 50-mesh sieve, the RNV would be calculated as follows:
 RNV = 90/100 [0.5] = [0.5] = 60.75
 The RNV of aglime with the minimum requirements of 80% CCE, 90% passing a 10-mesh sieve, and 35% passing a 50-mesh sieve would be:
 RNV = 80/100 [0.5] = 5 50
 Some high quality sources of aglime may have an RNV of 100 or slightly higher.
It would take only half as much of the high quality lime to be as effective as the lime with a 50 RNV.
Therefore, lime rates should be adjusted based on the quality of lime to be used.
Using RNV to Adjust LimeRates
 The current lime recommendations made by the University of Kentucky College of Agriculture are based on using lime with an RNV of 67.
If the source of lime to be used has an RNV substantially different from this, the recommended rates should be adjusted.
For practical purposes, adjustments should be made in 1/2-ton increments.
The equation to be used is:
 Adjusted Rate = 
 A field has a lime recommendation of 3 tons per acre.
The lime to be used has an RNV of 85.
Adjusted Rate =  = 2.36 tons per acre = 2.5 T/ac
 This field also has a lime recommendation of 3 tons per acre.
However, the lime to be used has an RNV of only 55.
Adjusted Rate =  = 3.65 tons per acre = T/ac
 The lime recommendation for a lawn is 150 pounds of lime per 1,000 square feet and the lime to be used has an RNV of 90.
Adjusted Rate =  = 112 pounds/1000 sq.
ft.
UsingRNVs to Compare LimeCosts
 The first two examples shown above can be used to illustrate the differences in cost to lime a field.
The following equation can be used:
 Cost of lime per acre = 
 If we assume the price of lime in Example 1 was $12 per ton and Example 2 was $10 per ton, the cost of each would be:
 Cost of lime =  = $30 per acre
 Example 2.
Cost of lime =  = $35 per acre
 Therefore, the cost per acre of using the lime in Example 2 was $5 more than Example 1 even though the price of lime in Example 1 was $2 more per ton.
This was the result of needing 1 ton more of the lime in Example 2 to get the pH change needed.
County Extension Agents for Agriculture receive reports of aglime quality two times each year.
These reports are prepared from the tests conducted by the Kentucky Department of Agriculture, Division of Regulation and Inspection, each spring and fall.
County Extension agents can assist in adjusting lime rates based on RNV of the sources of lime available in their area.
The calculator can be used to calculate an adjusted lime application rate based on RNV of the lime to be used.
It will calculate cost per ton of effective lime and cost per acre at the adjusted rate.
The most recent lime quality report can be found on the Lime page at this site.
Using Weep Berms to Improve Water Quality
 Richard C.
Warner, Carmen T.
Agouridis, Ross Guffey, Department of Biosystems and Agricultural Engineering
 N Ton-point source pollution  occurs when rainfall and snowmelt flows over the ground, picking up pollutants such as pathogens, sediments, and nutrients on its way to streams, rivers, lakes, and other bodies of water.
More than 50 percent of the nation's rivers and streams and nearly 70 percent of the nation's lakes are impacted by NPS.
Pathogens, sediments, and nutrients are the biggest contributors to impairment of rivers and streams while mercury, nutrients, and PCBs  are the biggest contributors to the impairment of lakes.
One method of managing NPS pollution is through the use of structural best management practices.
Structural BMPs are designed to decrease the volume of runoff that enters water bodies by increasing infiltration rates.
Examples of structural BMPs include rain gardens, stormwater wetlands, and riparian buffers.
A newer structural BMP is a weep berm.
A weep berm is a structural BMP that is used in combination with a grassed or forested riparian buffer to manage runoff volumes and improve water quality.
It is an earthen berm constructed perpendicular to the direction of runoff.
The weep berm is designed to capture and infiltrate frequently occurring small storms.
For larger storms, the weep berm stores runoff, allowing pollutants to settle out of suspension before the water is slowly released, passively, through multiple outlets to a grassed or forested riparian zone.
The rate of water release is quite slow to maximize the treatment effectiveness of the riparian zone.
The term "weep" describes the appearance of the water as it is slowly released through the pipes, earthen berm, and/or is infiltrated.
It is this weeping or gradual
 Figure 1.
Bare soils and livestock manure contribute to non-point source pollution.
Figure 2.
Red arrows point to a contour weep berm installed on a horse farm.
seepage of water out of the berm that makes it such an effective BMP.
The two types of weep berms are contour weep berms and gradient weep berms.
Contour weep berms typically
 are used in agricultural and construction operations.
Gradient weep berms are typically most applicable to surface mining operations.
Contour weep berms are constructed along the contour which represents points of equal elevation.
The ends of the contour weep berm turn up-gradient, perpendicular to the contour, to provide runoff storage.
The shape of the contour weep berm resembles that of a horseshoe.
If properly designed and constructed, contour weep berms blend into the landscape.
For long contour weep berms, earthen dikes can be installed at regular intervals to create runoff storage cells.
The advantage being that if one cell fails, then the entire stored volume of runoff is not discharged and the impact is minimized.
Gradient weep berms are constructed in conjunction with a diversion ditch or a sediment ditch.
Gradient weep berms incorporate the use of check dams along the length of the weep berm for the purpose of providing runoff detention.
During larger storm events, check dams slow runoff flow along the weep berms, thus increasing infiltration and settling rates.
Effectiveness of Weep Berms
 Weep berms offer excellent results for small storms  and good results for large storms.
For design storms greater than the fiveyear 24-hour event, weep berms provide structural stability.
Weep berms are quite effective at reducing the volume of runoff entering streams and rivers with measured reduction rates typically between 60-90 percent.
Weep berms are most effective in reducing sediment and sediment-associated constituents in runoff.
When properly designed and maintained, reductions in sediment concentrations of about 90 percent are possible with a weep berm, with additional treatment occurring through the use of a riparian buffer.
Reductions in fecal coliforms, nitrogen, and phosphorus also have been measured.
Figure 3.
Slow release of water from weep berm outlet to grassed riparian zone.
Figure 4.
Contour weep berm and riparian buffer treatment system.
Figure 5.
Cross-sectional view of a contour weep berm.
Advantages of Weep Berm
 Weep berms offer a number of advantages.
First, weep berms provide linear runoff control, meaning they require less land for construction.
Often times weep berms are constructed along the perimeter of a land disturbance.
Weep berms promote infiltration and sedimentation.
With gradient weep berms, the spaces between the check damsa allow for sediment storage, as do the spaces between the earthen dikes for contour weep berms.
In many instances, weep berms allow for the down-sizing or even elimination of sediment ponds.
Runoff from small storm events is completely captured and infiltrated while a sizeable portion of runoff from large events is stored and infiltrated.
Additionally, weep berms are simple and cost effective to construct.
For small areas , a skid steer, backhoe, or track hoe can be used.
Designing a Weep Berm
 Weep berms are placed down-gradient of disturbed areas.
Linear developments such as haul roads, pipe lines, and transmission lines are ideal.
Other appropriate locations include those downgradient of topsoil/spoil stockpile areas, cut or fill slopes, manure storage and/or composting facilities, high livestock use areas, fields receiving manure applications or injections, and dairy or hog waste lagoons.
For contour weep berms, the slope of the land up-gradient of the weep berm should not exceed 25 percent.
With gradient weep berms, the slope of the diversion channel, which is parallel to the weep berm, should not exceed 10 percent.
No restrictions are on the slope of the land up-gradient of gradient weep berms.
Consideration should also be given to the type of soil on which the weep berm is constructed.
Sandy soils have high infiltration rates while clay soils have low infiltration rates.
The type of soil present will affect the size of the weep berm and dewatering rates.
Larger
 weep berms will be needed for soils with low infiltration rates.
In addition to soil type, consideration should be given to the effect of pollutant loads on infiltration rates.
Runoff high in organic matter, such as with runoff from areas with manure, can result in the formation of a thick biofilm or mat immediately up-gradient of the weep berm.
Over time, infiltration rates will decrease.
To prevent this decrease, the mat should be removed and the underlying soil loosened.
When siting the weep berm, be sure to consider accessibility for cleaning out sediments deposited behind the
 Figure 6.
Gradient weep berm installed at a school construction site in Georgia.
Table 1.
Typical Infiltration Rates for Soil Types.
HSG1	Soil Texture	
 A	Sand, loamy sand,	>0.30
 B	Silt loam, loam	0.15-0.30
 C	Sandy clay loam	0.05-0.15
 D	Clay loam, silty clay	<0.05
 1 Hydrologic soil group  is a grouping of soils based on their minimum infiltration rate after prolonged wetting.
Source: Haan et al.
Table 2.
Curve Numbers1 for Agriculture and Disturbed Lands.
Land Use	Condition2	A	B	D
 Newly graded are as (pervious areas only, no	77	86	91	94
 Pasture or grassland-continuous forage for	Poor	68	79	86	89
 grazing4	Fair	49	69	79	84
 Good	39	61	74	80
 Row crops-straight rows5	Poor	72	81	88	91
 Good	67	78	85	89
 1 Average runoff condition and la=0.2S.
2 Hydrologic condition refers to factors that affect infiltration and runoff such as canopy cover, vegetation density, and surface roughness.
3 Hydrologic soil group  is a grouping of soils based on their minimum infiltration rate after prolonged wetting.
4 Poor: less than 50% ground cover or heavily grazed; fair: 50%-75% ground cover and not heavily grazed; Good: Greater than 75% ground cover and lightly grazed.
5 Poor: factors impair infiltration; good: factors promote average or better infiltration.
Source: National Engineering Handbook Part 630 Hydrology ; lowa Stormwater Management Manual 
 weep berm.
The required frequency of sediment cleanouts will depend on the quality of the incoming runoff and the size of the weep berm.
Typically, weep berms are designed to completely contain the one-year six-hour design storm plus any required sediment storage capacity, meaning the runoff volume is contained below the invert of the outlets.
Captured runoff mainly will infiltrate, though some losses will occur through seepage through the weep berm with minimal occurring as evaporation.
The five-year 24-hour storm normally is used to establish the crest elevation of the weep berm.
Runoff from this storm exits the system in the same manner as the one-year six-hour storm as well as through the outlet structures.
For storms larger than the five-year 24-hour event, the weep berm functions as a long broadcrested weir or emergency spillway.
Water flows over the top of the weep berm as a thin sheet, SO shear stresses along the crest of the weep berm remain low and the water has little erosive power.
methods are used to estimate runoff, a commonly used method is the Natural Resource Conservation Service  Curve Number  method.
With this method, the amount of rainfall that becomes runoff is expressed in the form of a CN.
Higher CNs, up to 100, indicate that more rainfall becomes runoff while lower CN indicate more rainfall is intercepted, stored, and infiltrated.
Table 2 contains typical CNs for agricultural and disturbed lands.
The amount of runoff or runoff volume is based on drainage area, land slope up-gradient of the weep berm, land use, and soil type.
While various
 To calculate runoff depth, a CN is selected for the site based upon land use and soil type or hydrologic soil group.
Based on their minimum infiltration rates after prolonged wetting, the NRCS classified soils into one of four HSGs.
Tables of CN are widely available.
Table 2 contains CN values commonly used in weep berm design.
Once the CN is selected, runoff depth  is computed using equations 1 and 2.
0.2S)2 Runoff depth =   1000 S 10  CN P = precipitation  S = maximum soil water retention parameter  CN = curve number
 Once the runoff depth is known, it is multiplied by the drainage area to determine the runoff volume and then converted to units of acre-foot.
The method for designing a weep berm varies depending on the type of weep berm selected.
Contour weep berms involve fewer design steps than gradient weep berms.
To accommodate the runoff volume from subsequent storm events, both types of weep berms should be designed to allow for 60 percent dewatering within 24 hours and complete dewatering in 72 hours.
While the general methods for designing both types of weep berms will be discussed, a design example will be presented only for the contour weep berm.
The first step in designing a contour weep berm is to determine the height and length of the weep berm such that the appropriate amount of runoff volume is contained.
The length of the weep berm is generally determined based on the extent of the land disturbance.
Longer weep berms are typically shorter in height while short weep berms are typically taller.
For larger areas of land disturbance, multiple weep berms in series may be required.
The weep berm height is set such that the runoff volume from the five-year 24-hour storm event is contained.
For instances when the weep berm is used to control sediment-laden runoff, the weep berm height should also accommodate the necessary sediment storage capacity.
A trade-off exists between sediment storage capacity, meaning a larger weep berm, and frequency of clean out.
The inverts of the outlets are set such that the one-year six-hour storm is contained in addition to any sediment storage capacity requirements.
Sufficient equipment access to the weep berm should be provided to allow for the removal of deposited sediments.
The main design components of a gradient weep berm involve a trapezoidal channel, check dams within the trapezoidal channel, and outlets through the down-gradient side slope of the trapezoidal channel.
The designer must determine the bottom width, side-slopes, and overall slope of the trapezoidal channel.
For the check dams, the top or crest determines amount of runoff that is stored.
The heights of the check dams are set such that the runofffrom the five-year 24-hour storm is contained while considering sediment storage requirements.
The spacing of check dams affects the volume of runoff that is stored.
Typically check dams are spaced such that the crest of the adjacent down-gradient check dam equates to 25-50 percent of the height of the immediate up-gradient check dam.
As with the contour weep berm, the inverts of the outlets are set such that the one-year six-hour storm is contained in addition to any sediment storage capacity requirements.
Though a number of outlet types have been used in the past, such as fixed siphons and perforated risers, only straight pipes and rock lenses are recommended at this time.
While the invert of the outlet is set such that the one-year six-hour storm is contained, over any sediment capacity requirements, the designer must determine the type, size, shape, and spacing of the outlets.
These
 Figure 7.
Outlet options for weep berms include pipes and rock lenses.
characteristics will control the rate of water discharge from the weep berm.
For straight pipe outlets, schedule 40 PVC is often used.
The designer must determine the pipe diameter and the pipe slope.
For rock lenses, the designer must determine the width and height of the outlet along with the size of rock used.
Figure 7 shows commonly used outlet configurations.
A grassed or forested riparian buffer is an important part of the weep berm design.
The required width of the riparian buffer is a function of slope, vegetation type, and soil types.
A riparian buffer with sufficient width can infiltrate all runoff, from a five-year 24-hour storm, discharged from the weep berm.
Such high efficiencies are achieved when runoff is slowly discharged.
If space constraints limit the width of the riparian buffer, then smaller outlets will release water more slowly.
However, the tradeoff is that the weep berm will be bigger to contain the five-year 24-hour storm event.
Constructing a Weep Berm
 Typical on-site construction or farm equipment such as a skid steer, backhoe, or track hoe are generally used to construct weep berms.
The first step is to remove all vegetation from the footprint of the weep berm, taking care to minimize damage to any up-gradient or down-gradient vegetation.
As the rate of infiltration is important to the efficiency of the weep berm, it is important to minimize soil compaction both up-gradient and down-gradient of the weep berm.
If necessary, these soils may require loosening following construction of the weep berm.
It is important to compact the weep berm such that it is structurally stable but not to the point that runoff cannot seep through the earthen berm.
Soils most suitable for constructing weep berms are those with greater than 10 percent clay content, greater than 20 percent silt and clay content, and the remaining percentage sand and gravel.
It is recommended that the weep berm be constructed in 6to 9-inch lifts using the wheels or tracks of the equipment to compact the berm.
It is important to survey the crest of the weep berm to ensure it is level within the allowable design tolerance.
Alternatively, compaction with the bucket of a backhoe or track hoe is often adequate.
construction, an excavator is needed to dig trenches for outlet placement.
Depending on the outlet configuration, backfilling and careful compaction using the bucket on an excavator or similar piece of equipment may be required.
Alternatively, a steel pipe with a conical end can be used to develop a hole for subsequently inserting the PVC pipes.
when selecting the method of mowing.
Riding lawn mowers typically should not be operated on slopes steeper than 15 percent.
Be sure to check all appropriate owner's manuals before operating mowing equipment.
Lastly, erosion control measures are needed.
Seed the weep berm and install an erosion-control blanket.
Use products that are free of plastic netting.
Plastic netting can trap and kill wildlife and is easily entangled in mowers.
It is not a requirement to mow the weep berm, however some landowners prefer a mowed appearance.
If mowing is desired, be sure to consider the steepness of the berm
 Placement of the outlets is done either during berm construction or immediately following berm construction.
If the outlets are placed during berm construction, care must be taken not to crush the outlets when compacting soil, particularly when using PVC pipes.
In such instances, larger soil llifts are recommended.
For outlet placement post-berm
 Weep berms require little maintenance outside of periodic sediment removal and occasional mowing, if desired by the landowner.
Clogging of outlets is rare as the outlets are above the sediment storage layer.
A long piece of rebar is useful for unclogging a pipe.
For rock lenses, any reduction in efficiency is most likely to occur at the lower portion of the lens closest to the sediment storage layer.
Contour Weep Berm Design Example
 Alexa wants to design a contour weep berm to collect sediment-laden runoff from a 4 acre newly graded construction site in Fayette County, Kentucky.
The land slope up-gradient of the planned location of the weep berm is 2 percent.
The linear extent of disturbance is 500 feet.
Soils at the project site are Bluegrass-Maury silt loam, which places them in HSG B.
For sediment storage requirements, she needs 67 cubic yards per acre of disturbed land.
Using the Rainfall Frequency Values for Kentucky, Engineering Memorandum No.
2, Alexa determines that the one-year six-hour rainfall depth is 1.9 inches and the five-year 24-hour rainfall depth is 3.8 inches for Fayette County.
To design the contour weep berm, Alexa must complete the following steps:
 1.
Develop a berm height to storage volume relationship for a 2 percent slope and a 500-foot berm length.
2.
Determine the sediment storage requirements for the weep berm.
3.
Determine the runoff volume associated with the one-year six-hour design storm.
4.
Determine the invert elevation of the outlet by adding the sediment storage requirements.
5.
Determine the runoff volume associated with the five-year 24-hour design storm.
6.
Determine the crest elevation of the weep berm by adding the sediment storage requirements  to the runoff volume of the five-year 24-hour storm event.
7.
Select an outlet type and size.
Step 1: Stage-Storage Relationship
 Assume the deposited sediment will form a triangular wedge, the watershed slope is constant, and the interior weep berm slope is 1.5:1.
Calculate the volume of sediment that could be stored behind a 500 ft long weep berm of varying heights.
Table 3 contains the weep berm height to storage relationship for a 500 ft length of weep berm with the aforementioned characteristics.
Recall 1 ac=43,560
 The given sediment storage requirement is 67 yd3 per acre of disturbed land.
For 4 acres, 268 yd3 or 0.166 ac-ft is required.
Recall 1 yd3=27ft3.
Use Table 3 to determine the associated weep berm height  for a sediment storage volume of 0.166 ac-ft.
Step 2: Sediment Storage Requirements
 Table 3.
Weep Berm Height-to-StorageVolume Relationship.
Weep Berm Height	Storage Volume
 Step 3: Runoff Volume for One-year Sixhour Design Storm
 The CN for a newly graded BluegrassMaury silt loam  is 86.
For a 1.9 inch rainfall depth over 4 acres, the associated runoff volume is 0.258 acft.
Step 4: Outlet Invert Elevation
 Add the sediment storage requirement.
Use Table 3 to determine the elevation of the outlet invert.
This elevation corresponds to the point along the weep berm where the contour elevation is lowest.
Step 5: Runoff Volume for Five-year 24hour Design Storm
 For a 3.8 in.
rainfall depth over 4 acres and a CN of 86, the associated runoff volume is 0.789 ac-ft.
Step 6: Crest Elevation
 Add the sediment storage requirement  and the runoff volume from the five-year 24-hour design storm.
Use Table 3 to determine the elevation of the crest of the weep berm.
This elevation corresponds to the point along the weep berm where the contour elevation is lowest.
Step 7: Outlet Type and Size
 Select both the type and size of the outlets SO that stored runoff is slowly released, preferably to a down-gradient riparian area.
Discharge should be relatively uniform across the weep berm.
For this example, 24 equally spaced 1-in.
PVC pipes are used.
Maintaining Subsurface Drip Irrigation Systems
 Juan Enciso, Dana Porter, Jim Bordovsky and Guy Fipps*
 Subsurface drip irrigation  systems can deliver water at low flow rates very uniformly.
A permanent system, properly designed and maintained, should last more than 20 years.
A maintenance program includes cleaning the filters, flushing the lines, adding chlorine, and injecting acids.
These preventive measures will reduce the need for major repairs and extend the life of the system.
The purpose of preventive maintenance is to keep the emitters from plugging.
Emitters can be plugged by suspended solids, magnesium and calcium precipitation, manganese-iron oxides and sulfides, algae, bacteria and plant roots.
Each SDI system should contain a flow meter and at least two pressure gauges-one gauge before the filters and another after the filters.
Flow meters and pressure gauges, which should be inspected daily, indicate whether the system is working properly.
A low pressure reading on a pressure gauge indicates a leak in the system.
A difference in pressure between the filters may mean that the system is not being backflushed properly and that the filters need to be cleaned.
In larger systems, pressure gauges should be installed in each field block or zone.
Plugging potential of irrigation water
 Chemical property	Low	Moderate	Severe
 PH	< 7.0	7.0 8.0	>8.0
 Iron 	<0.2	0.2 1.5	>1.5
 Sulfides 	<0.2	0.2 2.0	>2.0
 Manganese 	<0.1	0.1 1.5	>1.5
 Water quality determines the relative risk of emitter plugging and other problems; therefore, the properties of the water should be taken into account in the system maintenance program.
Examples of water quality parameters and their effect on emitter plugging potential are summarized in the following table.
Filters are essential components of an SDI system; they remove suspended solids from the water.
There are three main types of filters: cyclonic filters ; screen and disk filters; and media filters.
It is common practice to install a combination of filters to remove particles of various sizes and densities effectively.
These filters need little maintenance, but they require regular flushing.
The amount of sediment in the incoming water, the volume of water used, and the capacity of the collection chamber at the bottom of the filter will determine how often and
 *Assistant Professor and Extension Agricultural Engineer, Assistant Professor and Extension Agricultural Engineer, Agricultural Engineer and Associate Research Scientist, Professor and Extension Agricultural Engineer, The Texas A&M University System.
Figure 1.
Typical layout of the irrigation system.
how long the flushing valve needs to operate.
The sediment can be released manually or automatically.
If it is done manually, the bottom valve of the filter should be opened and closed at regular intervals.
Or, an electronic valve controlled by a timer can automatically open the bottom valve.
Automated operation of the valve should be checked at least every other day during the season.
Screen and disk filters
 Small screen filters use a nylon strainer or bag, which should be removed and checked periodically for small holes.
The flush valve controls the flushing of the screen filter.
This can be operated manually or automatically.
Flush the screen filter when the pressure between the two pressure gauges drops 5 psi.
Automatic filters use a device called a "pressure differential switch" to detect a pressure drop across the filters.
Other systems use a timer, which is usually
 set by the operator.
The flushing can be timed according to the irrigation time and the quality of the water.
The interval between flushing can be adjusted to account for differences in pressures across the filters.
Automated flushing devices should be checked at least every other day on large systems.
With these filters the most important task is to adjust the back-flush adjustment valve.
If the backflow rate is too high, sand filter media will be washed out of the filter container.
If the backflow rate is too low, contaminating particles will not be washed out of the filter.
Bacterial growth and the chemistry of the water can cause the sand media to cement.
Cementing of the media causes channels to form in the sand, which can allow contaminated water to pass unfiltered into the irrigation system.
Chlorination can correct or prevent sand media cementing.
One way to evaluate clogging problems is to place a container under selected emitters as shown in Figure 2.
The emitter flow rate  collected at different locations should be compared against the design flow rate.
The upper picture of Figure 3 shows a field where plants are stressed because emitters are clogged by manganese oxides.
The general condition of a drip system can be easily evaluated by checking system pressures and flow rates often.
If emitters become plugged, system pressures will increase and flows will decrease.
Flushing lines and manifolds
 Figure 3.
Plants in this field are drought-stressed because emitters are clogged.
Acid injection can reduce clogging problems so fields are irrigated uniformly.
Very fine particles pass through the filters and can clog the emitters.
As long as the water velocity is high and the water flow is turbulent, these particles remain suspended.
If the water velocity slows or the water becomes less turbulent, these particles may settle out.
This commonly occurs at the distant ends of the lateral lines.
If they are not flushed, the emitters will plug and the line eventually will be filled with sediment from the downstream end to the upstream end.
Systems must be designed so that mainlines, manifolds  and laterals can all be flushed.
Mainlines and manifolds are flushed with a valve installed at the very end of each line.
Lines can be flushed manually or automatically.
It is important to flush the lines at least every 2 weeks during the growing season.
At a low concentration , chlorine kills bacteria and oxidizes iron.
At a high concentration , it oxidizes  organic matter.
Bacteria produced by iron and manganese
 The most serious problems with bacteria occur in water that contains ferrous or soluble iron or manganese.
Iron and/or manganese concentrations higher than 0.1 ppm can promote bacterial growth and chemical precipitation that clogs emitters.
Iron bacterial growth looks reddish, whereas manganese bacterial growth looks black.
These bacteria oxidize iron and manganese from the irrigation water.
In the western part of Texas, these bacteria often are found in well water.
Be extremely cautious when injecting chlorine into irrigation water containing dissolved manganese, because chlorine can oxidize this element and cause precipitation beyond the filter system.
Figure 4 shows an emitter plugged by manganese oxides.
It is hard to eliminate iron bacteria, but it may be controlled by injecting chlorine into the well once or twice during the season.
It might also be necessary to inject chlorine and acid before  the fil-
 Figure 4.
An emitter clogged by manganese oxides.
ters.
When the water contains a lot of iron, some of the iron will feed the bacteria and some will be oxidized by chlorine to form rust.
The precipitated ferric oxide is filtered out and flushed from the system.
If the iron concentration is high and problems persist, aerating the irrigation water will help to oxidize the iron and settle the sediment.
Aerate the water by pumping it into a reservoir and then repumping it with a booster pump to the irrigation system.
Use a swimming pool test kit to test for free or residual chlorine in the water at the end of the lateral line.
It is worth noting that some of the injected chlorine may be removed from solution  through chemical reactions with other constituents or absorbtion by organic matter in the water.
If chlorine is continuously injected, a level of 1 ppm of free residual chlorine at the ends of the laterals will be enough to kill most bacteria.
With intermittent injection , the chlorine concentration at the ends of the laterals should be maintained at 10 to 20 ppm for 30 to 60 minutes.
If emitters are already partially plugged by organic matter, "superchlorination" treatment is warranted; it involves maintaining a concentration of 200 to 500 ppm chlorine in the system for 24 hours.
Some extra chlorine should be injected to account for the tied up chlorine.
Acids are injected into irrigation water to treat plugging caused by calcium carbonate  and magnesium precipitation.
Water with a pH of 7.5 or higher and a bicarbonate level higher than 100 ppm has a risk of mineral precipitation, depending on the hardness of the water.
Hardness of water, which is determined by the concentrations of calcium and magnesium, is classified as follows: soft ; moderate ; hard ; very hard.
Moderate, hard and very hard water needs acid injection.
Sulfuric, phosphoric, urea-sulfuric, or acetic acid can be used.
The type most commonly used in drip irrigation is 98% sulfuric acid.
Acetic acid, or vinegar, can be used in organic farming, although it is much more expensive.
If the irrigation water has more than 50 ppm of calcium, phosphoric acid should not be injected unless enough is added to lower the pH below 4.
Acid is usually injected after the filter so that it does not corrode the filter.
If the filter is made of polyethylene, which resists corrosion, acid can be injected before the filter.
Injection rate for chlorine
 Calculate the injection rate with these formulas:
 English units calculation IR = 0.006xFxC
 IR = Injection rate, gallons/hr
 F = Flow rate of the system, GPH
 C = Concentration of chlorine wanted, ppm
 P = Percentage of chlorine in the solution*
 Metric units calculation IR = 0.36xFxC
 Where: IR = Injection rate, liters/hour F = Flow rate of the system, LPS C = Concentration of chlorine wanted, ppm P = Percentage of chlorine in the solution*
 *The percentage of chlorine for different compounds is as follows: calcium hypochlorite-65% sodium hypochlorite -5.25% lithium hypochlorite-36%
 A farmer wants to inject chlorine into his system at a concentration of 5 ppm in a system with a flow rate of 100 GPM.
He is injecting household bleach that has a chlorine concentration of 5.25%.
IR = 0.006xFxC 0.006x100x5 0.571 GPH sodium hypochlorite  = 5.25
 The following tables show the necessary injection rate of chlorine in gallons per hour.
Desired	Gallons of chlorine  per hour
 level in	Gallons per minute  of irrigation water
 ppm	100	150	200	250	300	350	400	450	500
 1	0.114	0.171	0.229	0.286	0.343	0.400	0.457	0.514	0.571
 2	0.229	0.343	0.457	0.571	0.686	0.800	0.914	1.029	1.143
 5	0.571	0.857	1.143	1.429	1.714	2.000	2.286	2.571	2.857
 10	1.143	1.714	2.286	2.857	3.429	4.000	4.571	5.143	5.714
 15	1.714	2.571	3.429	4.288	5.143	6.000	6.857	7.714	8.571
 20	2.286	3.429	4.571	5.714	6.857	8.000	9.143	10.286	11.429
 25	2.857	4.286	5.714	7.143	8.571	10.000	11.429	12.857	14.286
 30	3.429	5.143	6.867	8.571	10.286	12.000	13.714	15.429	17.143
 50	5.714	8.571	11.429	14.286	17.143	20.000	22.857	25.714	28.571
 Desired	Gallons of chlorine  per hour
 level in	Gallons per minute  of irrigation water
 ppm	100	150	200	250	300	350	400	450	500
 1	0.060	0.090	0.120	0.150	0.180	0.210	0.240	0.270	0.300
 2	0.120	0.180	0.240	0.300	0.360	0.420	0.480	0.540	0.600
 5	0.300	0.450	0.600	0.750	0.900	1.050	1.200	1.350	1.500
 10	0.600	0.900	1.200	1.500	1.800	2.100	2.400	2.700	3.000
 15	0.900	1.350	1.800	2.250	2.700	3.150	3.600	4.050	4.500
 20	1.200	1.800	2.400	3.000	3.600	4.200	4.800	5.400	6.000
 25	1.500	2.250	3.000	3.750	4.500	5.250	6.000	6.750	7.500
 30	1.800	2.700	3.600	4.500	5.400	6.300	7.200	8.100	9.000
 50	3.000	4.500	6.000	7.500	9.000	10.500	12.000	13.500	15.000
 The amount of acid to use depends on the characteristics of the acid you are using and the chemical characteristics of the irrigation water.
A titration curve of the well water used for drip irrigation can be developed by a laboratory.
It will show the amount of acid needed to reduce the pH to a certain level.
If a titration curve is not available, use a trial-and-error approach until the pH is reduced to 6.5.
Colorimetric kits or portable pH meters can be used to determine the water pH at the ends of lines.
Many farmers inject 1 to 5 gallons of sulfuric acid per hour, depending on the water pH, water quality and well capacity.
Most chemicals used in drip system maintenance are extremely hazardous.
Sulfuric acid is very corrosive and must be handled with proper personal protection equipment.
Store sulfuric acid in polyethylene or stainless steel tanks with extra heavy walls.
Always add acid to water; do not add water to acid.
Never mix acid and chlorine or store them together in the same room; a toxic gas will form.
Besides clearing clogged emitters, acid injected into irrigation water may improve the infiltration characteristics of some soils and release micro-
 nutrients by lowering the soil pH.
To reduce the cost, acid can be injected only during the last third of the irrigation time.
Keep out plant roots
 It is important to keep plant roots from penetrating the drip emitters.
Metam sodium and trifluralin are two compounds that control roots.
In cotton, metam sodium is generally used at defoliation to keep roots out as the soil dries,
 Figure 5.
Roots penetrating a drip emitter.
while trifluralin is used before harvest.
Superchlorination at a dosage of 400 ppm chlorine also will keep roots out.
Fill the tapes with chlorine and leave it overnight.
Back-siphoning is the backflow of water from the soil profile back into the tape at the end of an irrigation cycle.
It is caused by a vacuum that develops as residual water in the tape moves to the lower elevations in the field.
Back-siphoning may pull soil particles and other debris through emitters and into the tape.
Figure 6 shows some live worms that were flushed from SDI lines during normal maintenance.
It is thought that the eggs or cocoons of worms were pulled into the drip lines at the higher elevations in the field when zone valves were closed.
Once in the drip lines, the eggs hatched and the worms started to grow.
Worms and other contaminants were removed during normal flushing cycles.
Figure 6.
Worms flushed from an SDI system.
Flushing twice a week solved the problem.
Texas Water Resources Institute make every drop count
Questions and Answers About Drainage Water Management for the Midwest
 Jane Frankenberger, Eileen Kladivko, Gary Sands, Dan Jaynes, Norm Fausey, Matt Helmers, Richard Cooke, Jeff Strock, Kelly Nelson, Larry Brown
 Purdue University University of Minnesota lowa State University University of Missouri University of Illinois The Ohio State University USDA-Agricultural Research Service
 Subsurface tile drainage is an essential water management practice on many highly productive fields in the Midwest.
However, nitrate carried in drainage water can lead to local water quality problems and contribute to hypoxia in the Gulf of Mexico, SO strategies are needed to reduce the nitrate loads while maintaining adequate drainage for crop production.
Practices that can reduce nitrate loads on tile-drained soils include growing winter forage or cover crops, fine-tuning fertilizer application rates and timing, bioreactors, treatment wetlands, and modifying drainage system design and operation.
Drainage water management is one of these practices and is described in this fact sheet.
Answers given here apply specifically to Midwest corn and soybean cropping systems, and not to perennial or winter annual crops.
1.
What is drainage water management?
Drainage water management is the practice of using a water control structure in a main, submain, or lateral drain to vary the depth of the drainage outlet.
The water table must rise above the outlet depth for drainage to occur, as illustrated at right.
The outlet depth, as determined by the control structure, is:
 Raised after harvest to limit drainage outflow and reduce the delivery of nitrate to ditches and streams during the off-season.
Lowered in early spring and again in the fall SO the drain can flow freely before field operations such as planting or harvest.
Raised again after planting and spring field operations to create a potential to store water for the crop to use in midsummer.
Figure 1.
The outlet is raised after harvest to reduce nitrate delivery.
Figure 2.
The outlet is lowered a few weeks before planting and harvest to allow the field to drain more fully.
Figure 3.
The outlet is raised after planting to potentially store water for crops.
Questions and Answers Drainage Water Management for the Midwest
 2.
Is drainage water management the same as subirrigation?
No.
Drainage water management relies on natural rainfall to raise the water table, and the water table will fluctuate below that depth without sufficient rainfall.
Subirrigation adds water to the subsurface drainage system to raise the water table close to the outlet depth and to maintain it there.
Subirrigation typically requires closer spacing of the tiles than that in a conventional or controlled drainage system.
Subirrigation also requires an adequate water supply to meet crop needs throughout the growing season.
3.
What fields are most suitable for drainage water management?
The practice is only suitable on fields that need drainage, and is most appropriate where a pattern drainage system  is installed or is feasible.
The field should be flat  SO that one control structure can manage the water table within 1 to 2 feet for as many acres as possible.
If drainage laterals are installed on the contour, the practice could be used with greater slopes.
The producer must be able to manage the drainage system without affecting adjacent landowners.
The practice can be used with any drain spacing; however, narrower drain spacing reduces the risk of yield loss due to excess wetness during the growing season.
If a new drainage installation is being planned for a field, drains should be designed for minimum grade , SO each control structure can control the maximum possible area of the field.
In drainage water management, water control structures are used to vary the depth of the drainage outlet.
Flatter fields require fewer structures.
4.
How many acres can I manage with one structure?
It depends on field topography and the desired uniformity of water table management.
Flatter fields require fewer overall structures and allow each structure to manage a larger area.
A field is typically divided into "drainage management zones," each managed by one control structure.
The zones are delineated by the desired feet of elevation change within the zone, which corresponds to the desired uniformity of water table management.
For example, to maintain control of the water table to within 1 foot of the desired depth, a structure must be placed in a drainage management zone with 1 foot or less of elevation change.
One structure can typically control at least 10 or 20 acres, and the larger the area that can be controlled with one structure, the more economical the practice.
5.
How much management is required?
The level of management required depends on whether the water control structures will be used to raise the system outlet during the fallow season, the growing season, or both.
During the fallow season, the only management required is to raise the outlet after harvest and field operations in the fall, and to lower it about two weeks before the start of field operations in the spring.
During the growing season, management may involve temporarily lowering the outlet height to increase the drainage during periods of heavy rain or sustained wet periods.
Automated devices are available to aid in management.
6.
How do I manage the outlet?
Current recommendations are to place the control structure outlet within 6 inches of the field surface for maximum water quality benefits in the winter months.
Researchers have yet to determine the optimum outlet height during the growing season, but they suggest an outlet depth of 2 or more feet below the field surface.
The goal is to provide enough drainage for good aeration and root development but to capture some of the water that would otherwise drain out under conventional systems.
It is important to understand that the drainage outlet setting does not ensure that a water table will be present at the desired depth; sufficient rainfall must occur for the water table to rise to the depth of the outlet setting.
Caution should be exercised during the growing season, because maintaining water table depths shallower than 2 feet may increase the risk of crop excess water stress during pro-
 Management includes raising the outlet after harvest and planting, and lowering the outlet before field operations in the spring and fall.
longed wet periods in spring/summer.
Particular attention should be paid to the management of soybean fields, since soybeans are less tolerant of wet roots.
7.
Do I need a pump for drainage water management?
Not unless you need a pump for your existing drainage system, such as drainage systems that outlet into pumped sumps where gravity flow outlets are difficult or impossible to establish.
8.
When is it possible to retrofit an existing system?
Most drainage systems can be retrofitted with control structures, but sometimes the benefits will not be significant because of the slope and layout of the pipes.
The best candidates for retrofitting are pattern drainage systems where the grade of the laterals is 0.2 percent or less.
9.
Will I need more drain tile ?
No.
This practice is not like subirrigation, which is only economical with narrower spacing.
Drainage water management is more likely to increase yield on fields with pattern drainage, rather than those with random drainage.
Narrower drain spacing may reduce the risk of yield loss during times of heavy rainfall, because water is removed faster.
10.
What yield impact can I expect?
With proper management of the structures and timely rainfall, the potential exists to improve crop yields beyond the typical crop response to drainage.
However, field research on the agronomic benefits of the practice is very limited and inconclusive.
Field studies in North Carolina have found average yield increases of about 5 percent, with greater response in some years.
For Midwest conditions, computer modeling studies show limited long-term crop yield benefits  with controlled drainage, because yield benefits will not accrue in years where rainfall is not sufficient or not at the right time to raise the water table above the tile depth.
Potential crop yield increases will be greater in regions where drains typically
 With proper management of the structure and timely rainfall, drainage water management may improve crop yields in some years.
flow for long periods after planting, because more water is available to be stored in the root zone.
In all regions, increases in crop yields will be much greater in some years than in others.
There may be a risk of excessive moisture in some years, but the risk can be minimized with proper management.
11.
How much less nitrate flows into ditches and streams?
Studies have found reductions in annual nitrate load in drain flow ranging from about 15 percent to 75 percent, depending on location, climate, soil type, and cropping
 Questions and Answers Drainage Water Management for the Midwest
 Drainage water management reduces the nitrate that flows to ditches and streams from tile drains compared to unmanaged drainage.
practice.
Nitrate load is reduced by about the same percentage as drain flow is reduced, since most studies have found that drainage water management does not change the nitrate concentration in the drain flow.
In regions where much of the drainage takes place during the winter , the reduction is likely to be greater than where most of the drainage takes place in April or later, such as in parts of Iowa and Minnesota.
12 Can I use less nitrogen fertilizer?
No.
Reducing the annual drain flow does not imply that all of that unreleased water with its soluble nitrate is still in the field.
Most of this water and nitrate leave the field by some other route.
That flow path is longer and slower, giving more opportunity for denitrification or assimilation of the nitrate into organic nitrogen forms, and any nitrate that remains in the root zone will be lost when water is released before planting.
13.
Where does the rest of the nitrate go?
Nitrate reductions from drainage management systems result from three factors:  reduced volume of drainage water exported from the system,  denitrification within the soil profile, and  deep seepage.
The decrease in drainage water has been measured in several locations and is a major factor in reducing nitrate flow to ditches and streams.
Some of the water that is not drained becomes surface runoff instead, but nitrate concentrations are considerably lower in the surface runoff.
Denitrification converts some of the nitrate to harmless nitrogen gas  as well as a small amount of nitrous oxide , a potent greenhouse gas, but the extent of denitrification is not
 known.
The amount of deep seepage has not been quantified, nor has the extent to which the nitrate will be denitrified as it travels through these pathways.
14.
How does drainage water management affect soil quality?
This question has not been studied under field conditions, SO the answer is based on knowledge from related studies.
A small increase in soil organic matter content is likely with drainage water management, and this would be a positive effect on soil quality.
Drainage water management will cause prolonged wetness during the non-growing season, and this may promote the breakdown of aggregates.
But normal drying of the soil is likely during the growing season, and this process contributes to aggregate formation and stability.
Field operations carried out when the soil is wet add to soil compaction, but proper drainage water management would allow drainage for a sufficient amount of time before field operations SO that soil wetness would be comparable to that in fields with conventional drainage.
15.
Will earthworms be affected?
Maybe.
Worms in general do not like soil that is too wet, but scientists are not sure how wet is "too wet" for earthworms.
The effect of drainage water management is likely to vary for different species of worms.
Some evidence suggests that nightcrawlers may be most sensitive to excessive wetness, although more studies are needed.
Worm populations are also highly variable.
Some fields or portions of fields have high populations, and other areas have low populations.
To understand whether the higher water table has affected worms at specific sites, researchers must count
 Earthworms may be impacted by drainage water management, but more research is needed.
worms before drainage water management is initiated and then again several years later.
These studies are just beginning.
16.
Will the practice cause blowouts?
Not with most commercially available control structures installed on shallow gravity flow drainage systems.
Excessive pressure heads within a drainage pipe cause blowouts.
Most commercial control structures do not close tile outlets, but simply raise the elevation or height of the outlet.
Water is free to flow over the top of the control structure, keeping pressure heads within the field drainage system only marginally greater than that at the top of the control structure.
Some control structure designs use pressure-sensitive valves that, again, will not allow excessive buildup of pressure heads within the drainpipe.
However, if the drains are closed using valves, excessive pressure heads are possible and these need to be monitored carefully.
Finally, if the downstream drainage mains are not sized correctly, the large discharge volumes that can result from lowering the water table in the spring, especially if several fields are lowered at once, could cause blowouts below the farmer's field.
17.
Will drainage water management cause tile plugging?
Probably not.
Raising the water table can cause water to move more slowly or stagnate in the tile drains, allowing any sediment to settle out.
However, the high flow rates that result from setting the control structures to lower the water table in the spring will probably flush any accumulated sediment from the tile system, especially systems that are installed on a self-cleaning grade.
18.
Will tile freeze?
Soils rarely freeze as deep as the tile, and they are less likely to do SO when the water table has been raised with the control structure.
Freezing of the control structure itself could be an issue, as cold air can settle in the structure housing.
A frozen control structure could make it impossible to lower the outlet depth in the spring to lower the water table.
However, there have been no reports of control structures being frozen in the spring at the recommended time for lowering the water table.
19.
Will my neighbors be affected?
Maybe.
Site selection certainly needs to include consideration of potential impacts on neighbors.
Upstream neighbors on the same drainage main could be affected,
 Freezing is unlikely to be a concern, as soils rarely freeze as deep as the tile.
SO managing the outlet of a shared main is not a good idea unless the upstream field is at least 2 to 4 feet higher in elevation than the outlet being managed.
There are no anticipated impacts on downstream neighbors on the same drain system, unless mains are not sized correctly.
Other potential problems include raising the water table near home septic fields.
Septic leach fields need several feet of unsaturated soil below them for adequate treatment.
20.
Will surface runoff, erosion, and the loss of other chemicals be increased?
Maybe.
Wetter soils are likely to have more runoff and erosion.
Since some contaminants such as phosphorus and pesticides are lost through surface runoff and erosion, this is an important consideration.
If there is a pathway for runoff to leave the field, drainage water management may increase runoff and associated contaminants during the time that the water level is raised.
However, most pesticides are applied just before planting, when the water controlled over the winter would have already been released.
Also, land that is most suitable for drainage water management is very flat, and is therefore less likely to be susceptible to water erosion.
A wetter soil profile due to drainage water management could potentially reduce wind erosion on selected soils and landscapes.
21.
Will manure application be affected?
Possibly.
Spring application of manure is generally not compatible with drainage water management, while summer and fall application can be.
When the water table is near the soil surface, as it would be in spring with drainage water management, manure cannot be applied because of trafficability and soil compaction problems.
Lowering the outlet even earlier in the spring to allow for spring application would negate much of the nitrate reduction benefit of drainage water management.
When the soil is dry, however, such as in summer or early fall, raising the subsurface drain outlets can prevent the entry into surface water
 Questions and Answers Drainage Water Management for the Midwest
 of liquid manure that has leaked directly into drainage pipes through macropores caused by roots, earthworms, or cracks.
In fact, raising subsurface drain outlets before liquid manure application is a recommended practice in some states.
In most years in the fall, there is an adequate time window for manure application between when the outlets are raised and sufficient rainfall occurs to raise the water table to near the surface.
Because of an increased potential for surface runoff after the water table has risen, manure should be injected or incorporated into the soil.
22.
How much does drainage water management cost?
Costs include purchase of the water control structure, installation of the structure, and management time.
Structure costs range from $500 to $2,000, depending on height, size of tile, structure design, manufacturer, and whether it is automated.
Some contractors and farmers fabricate their own structures.
Installation costs may be about $200 for a basic structure in a new drainage system installation, but may increase depending on the size of the structure, level of automation of the structure, and for retrofit situations.
Assuming grades are flat enough for one structure to control 20 acres, initial costs would be in the range of $20 to $110 per acre.
A producer should also consider the cost of the time spent on management of the structure.
23.
What is the life of a water control structure?
The practice of drainage water management is still fairly new, SO there is not a large body of experience on which to base estimates of structure life.
Materials used in control structures may include plastics, metal, rubber , and electronic components , each with varying durability and longevity of use.
One manufacturer's structures have been used for water management in wetlands and are still working well after 20 or 25 years.
24.
What crop varieties work best?
No research has considered this question.
The best varieties may vary by location.
High-yield varieties with good early vigor and disease resistance should perform well in a managed drainage system.
25.
How is the application of other conservation practices affected?
Drainage water management should be one of a suite of practices in an overall conservation plan.
Drainage water
 The cost of drainage water management includes installation, as well as purchase and management of the structure.
may need to be managed differently, depending on other practices in a plan.
For example, drainage water management may not work well with cover crops unless the water is not raised as high in the winter and is let out earlier in the spring.
No-till soils tend to be colder and wetter, and water may need to be released earlier to allow for longer warm-up.
Drainage water management can work well in conjunction with riparian buffers to remove nitrate not otherwise treated by the buffer.
26.
Who will help pay for the practice?
The USDA National Resource Conservation Service  has approved conservation practice standards that support drainage water management in some states.
The standards are 554, "Drainage Water Management," and 587, "Structure for Water Control." Farm Bill programs, including the Environmental Quality Incentives Program  and the Conservation Security Program , may provide some of the cost of structure installation and/or a management incentive for a number of years in some states.
The Conservation Reserve Program  and Conservation Reserve Enhancement Program  may provide funding for the installation of structures in riparian buffers in some states.
For more information, talk with your local District Conservationist.
27.
Where can I get more information?
More information about USDA cost-share programs is at www.nrcs.usda.gov/programs/
 The following Extension publications, NRCS standards and handbook chapters, and books provide information on what is known about drainage water management.
NRCS Conservation Practice Standard 554, "Drainage Water Management," and 587, "Structure for Water Control." State and local standards are in Section IV of the Electronic Field Office Technical Guide  at www.nrcs.usda.gov/technical/efotg/.
American Society of Agricultural and Biological Engineers Standard ASAE EP479 "Design, Installation and Operation of Water Table Management Systems for Subirrigation/Controlled Drainage in Humid Regions" March 1990.
Agricultural Drainage, by R.W.
Skaggs and J.
van Schilfgaarde , ASA, CSSA, SSSA: Madison, Wis., 1999.
Chapters 20, 21, and 22 consider controlled drainage.
USDA NRCS National Engineering Handbook Part 624, Chapter 10, "Water Table Control," is a guide for the evaluation of potential sites and the design, installation, and management of water table control in humid areas.
<ftp://ftp.wcc.nrcs.usda.gov/water_mgt/EFH&NEH Drainage_Chapters/neh624_10.pdf>
 Subirrigation and Controlled Drainage.
Edited by H.W.
Belcher and Frank M.
D'Itri.
1995.
Lewis Publishers, an imprint of CRC Press Inc., Boca Raton, Fla.
482 pages.
Drainage water management can work well in conjunction with riparian buffers to remove nitrate not treated by the buffer.
Jane Frankenberger, Agricultural and Biological Engineering, Purdue University Eileen Kladivko, Agronomy, Purdue University Gary Sands, Bioproducts and Biosystems Engineering, University of Minnesota Dan Jaynes, USDA-ARS National Soil Tilth Laboratory, Ames, Iowa Norm Fausey, USDA-ARS Soil Drainage Research Unit, Columbus, Ohio Matt Helmers, Agricultural and Biosystems Engineering, Iowa State University Richard Cooke, Agricultural and Biological Engineering, University of Illinois Jeff Strock, University of Minnesota Southwest Research & Outreach Center Kelly Nelson, Agronomy, University of Missouri Larry C.
Brown, Food, Agricultural and Biological Engineering, The Ohio State University
 The authors thank the following reviewers, whose comments improved the publication.
Patrick Willey, USDA-NRCS West National Technology Support Center, Portland, Ore.
Robert Evans, Biological and Agricultural Engineering, North Carolina State University James Fouss, USDA-ARS Soil and Water Research Unit, Baton Rouge, La.
Larry Geohring, Biological and Environmental Engineering, Cornell University
Check for proper operation by making sure there is not any water squirting from the side of any regulators.
This is a sign that the rubber bladder has failed.
Keep in mind that sprinklers and pressure regulators do have a life span.
If your system is approaching 10 years old you might need to take a closer look at them.
Uniformity of water application can suffer greatly if your sprinkler package is out of date.
These irrigation decisions that participants made will be vital as the 2022 program comes to an end and the winners are determined for this years competitions.
Please watch for more information to come after biomass sampling results are released and as harvest is completed.
The final results and awards will be presented at the annual Awards Banquet, scheduled for Saturday, Jan.
14 in Kearney, Nebraska.
The description of a zone or nozzle control VRI system is that the sprinklers are pulsed on and off and pivot speed may vary and that irrigation management zones may be any shape or size.
Considerations for this VRI system are that has greatest flexibility in application, it is more expensive, and may require additional maintenance and management effort.
Example uses include avoiding application on irregularlyshaped uncropped areas for water surfaces.
It can also vary irrigation on irregularlyshaped management zones as needed to maximize yield and profits.
The state corn, soybean and sorghum crop all reached at least 85% maturity by the end of the month.
Harvest activity was just beginning to ramp up by months end and preliminary dryland yields are below last year and trend adjusted expectations.
This comes as no surprise considering the lack of moisture since the middle of July, coupled with average temperature running 4F to 6F above normal across the western half of the state and 2F to 4F across the eastern half of Nebraska.
MIL EVALUATION OF CENTER PIVOT IRRIGATION SYSTEMS
 IrriGage Nozzle Package Testing
 MIL has an emphasis on field evaluation center pivot sprinkler packages for distribution uniformity.
The initial rational for testing was to make certain that water was distributed so that individual plants within a field had equal access to the water.
This is particularly important when using irrigation scheduling procedures to minimize irrigation water application depth.
If "just in time, just enough" water is applied, then the water must be distributed so that plants have equal access to the water to prevent overor under-water within the field, which would have yield implications.
Center pivot systems are the dominate irrigation system type in Kansas, representing about 80 percent of the irrigated acres.
The sprinkler package design is based on a number of factors with system pressure and flow rate as major considerations.
Center pivot irrigation systems have been largely assumed to be properly operating if the pivot point pressure and flow rate are set at the design operating specifications.
Routine evaluation of the center pivot sprinkler packages are seldom performed after installation.
Testing involves placement of multiple catch containers along the lateral of the system and then measurement of each catch.
The catch containers used had to be measured quickly in order to avoid measurement error that would be introduced by evaporation losses.
Therefore, a number of individuals had to be present at the test site for quick measurement.
Measurement required entry into a very wet field, making for difficult data collection.
Development of a more streamlined testing procedure has been made possible through the use of IrriGages.
IrriGages are a non-evaporating collection device as shown in Figure 1.
A series of IrriGages are placed along the center pivot or linear lateral and are normally spaced at about 80 percent of the nozzle spacing.
The IrriGages are placed so that all water from a complete pass of the center pivot is collected.
The data collected includes the volume of catch and the position radius of the IrriGage relative to the center pivot point or the end of the linear system.
System operating and package characteristics are also recorded.
The catch data is entered into a MIL uniformity evaluation program where the average depth of application and the coefficient of uniformity  value is calculated.
The program also plots the catch data, which helps to visually identify the location of package weakness.
Center pivot package evaluations using IrriGages are limited to sprinkler packages that are at least four feet above ground as three feet of clearance is recommended between the top of the collector and nozzle outlet.
Another restriction is the need for the top of the collector to be above the crop canopy or be placed in a non-vegetated strip of a width of about three times the height differential between the collector top and the nozzle on each side of the catch container.
The height restriction means many in-canopy systems can not be evaluated using IrriGages.
Field test results have found a number of center pivot nozzle packages that were not performing to expectations.
Some non-uniform system results may be related to the original design where possibly the incorrect well yield and pivot pressure was provided to the designer.
Some non-uniformity may be due to incorrect input pressure and flow settings due to well or pump changes or faulty gauge or meter readings.
A number of systems have been found that had the package incorrectly installed, while some had performance problems related to nozzle maintenance issues.
The uniformity evaluation results for three systems using IrriGages are shown in Figures 2 through 4.
Figure 2 is center pivot system equipped with rotators and tested at a CU of 84 percent.
The major spike in application depth in the inner part of this system was due to a leaky tower boot.
This catch data for this system extended nearly to the center pivot point.
The inner spans of many systems often have an application depth that is greater then the system average due to size limitations on nozzle orifices.
There is also a tendency to see some choppiness in the application uniformity, which can also be due to the range of orifice size availability at the lower flow rates but also due to the nozzle spacing configuration.
The results for a new system equipped with I-Wob1 nozzles in Figure 3 showed an increasing depth of application with increase of radius.
Although the CU value is acceptable at 82 percent, the application depth was approximately one-third greater in the outer portion as compared to the inner portion.
The cause of this condition is believed to be due to improper flow and pressure conditions at the pivot point.
However, independent measurements were not taken at the time of the test.
This system was re-tested the following season.
When the pivot point pressure and flow was measured and was verified as correct, the average application depth was constant along the lateral.
This illustrates the importance of making certain design operating conditions are met for proper performance.
Figure 4 shows the results from another system equipped with rotator nozzles.
The CU value of this system was low at 67 percent and there was also decreasing water application depth with increasing distance from the pivot point.
The design inflow rate to the nozzle package was below specifications.
The field also had a considerable elevation increase at the outer edge at the test location.
Some of the major spikes were noted to be several tower boot leaks, goose neck leaks and non-rotating rotators.
Remediation for this system would likely be best achieved with a new package design, including consideration of pressure regulators.
While the systems evaluated to date have found many systems to be performing as designed, the evaluation program has found a number of systems not meeting
 performance expectations.
The industry has developed a large number of nozzle options that can perform very well under a wide range of operating conditions, but only if they are properly designed, installed, and operated.
The Other tests have revealed installation problems, such as missing drop nozzles and reversal of tower nozzle sequences.
Poor performances have also been attributed to changes in operating conditions as compared to original design specifications.
Another possible cause of low uniformity could be internal incrustation similar to the material encrusted on nozzles splash types, which would alter friction loss characteristic of the system resulting in loss of design integrity.
In-canopy Nozzle Package Testing
 Unlike an above canopy nozzle package, where the uniformity of water distribution is dependent on non-interference by the crop canopy, the in-canopy nozzle package almost always has the water streams from the nozzle being intercepted and/or redirected by the crop stocks and leaves.
The primary exception to this would be a LEPA system, utilizing circularly planted rows and bubble mode nozzles or drag tubes.
Few of these types of system are utilized in Kansas.
However, even these types of systems would have non-uniform water distribution if the design flow rate and pressure requirement were not met.
As with above-canopy nozzle packages, in-canopy systems must be properly designed, installed, and operated to perform properly.
The concept of the in-canopy test was to develop a protocol to minimize data collection from a system that would still allow a determination of whether design and operating conditions matched.
The intent was to take a number of pressure and flow readings from nozzles along the center pivot lateral and measure total flow and pivot point pressure and compare this information to the design sheet specifications.
It was thought that eventually only readings of a few nozzles at the beginning and end of the pivot lateral would be sufficient to verify the system performance in terms of water distribution along the center pivot lateral.
Since the nozzles are near the ground and many are mounted on a flexible drop tube, the installation of a pressure shunt is generally accomplished by crimping off the water flow to an individual nozzle and installing the pressure shunt to determine the nozzle pressure.
The flow rate could be determined by volume flow measurement and a stop watch.
However before testing began, several small digital flow meters (F-1000-RB flow rate meters from Blue-White Industries were purchased and configured with the pressure shunt.
This procedure is only effective in determining if the design operating conditions are being met.
It will not reveal installation errors, such as tower reversals or missized nozzles.
However, these types of problems can be much more easily
 1 No criticism or endorsement is intended by the use of commercial name.
The use is only for clarity of the presentation.
detected for an in-canopy system by visual inspection and comparison to the design chart, since the nozzles are low to the ground
 Most irrigation wells are metered in Kansas and flow meter readings were accepted for use in the previous above-canopy evaluations.
However, several of the systems that were evaluated had poor performance ratings for no apparent reason.
One reason might have been improper flow or pressure at the pivot point.
However input flow and pressure readings were not initially independently verified, so this could not be proven.
One of the systems was retested at a later date and the performance rating was good and both input flow and pressure were verified independently.
To allow this to routinely occur, a non-intrusive flow meter was obtained.
The digital flow meters were lab tested and worked well over the specified flow range.
However, during field tests, we have had some difficulty with moisture accumulation in the LED display to the degree that the display can not be read.
Although the instrument specifications indicate they can be used in a wet environment, the instruments would also shut down after several readings presumably due to the moisture condensation within the body of the instrument.
The instrument bodies can be opened to allow drying without apparent effect on accuracy.
Several ideas to prevent condensation have been tried without much success, so this remains an issue for these particular instruments.
The back up method for obtaining flow readings is the bucket and stop watch.
Test results from the first in-canopy pivot analysis are shown in Figures 5 and 6.
Most of the measurements were taken adjacent to a pivot tower.
The test was conducted early in the irrigation season.
The center pivot was 1305 feet long and equipped with LDN 1 nozzles using concave grooved by chemigation pads with 6 and 10 psi pressure regulators.
The design flow rate was 350 gpm with a top of pivot pressure of 14 psi.
Figure 5 shows the field measured pressure distribution and the design pipe pressure.
The field pressures were measured at approximately the nozzle height of 3 feet from the ground.
The design pipe pressure would be at an elevation of approximately 12.5 feet, for about a 4 psi pressure differential.
The measured values appear to be slightly higher than the design values.
However, all nozzles are pressure regulated, so much of the pressure differential would be dampened out through the regulators.
Figure 6 shows measured flow rates and design flow rates.
Measured observations appeared to be slightly higher at the end of the center pivot than design values.
The test was conducted before the start of the general irrigation season, which could mean the well yield was higher than what it might be after long term pumping.
However flow measurements at the beginning of the pivot lateral were matched very closely to the design values.
Overall, it appears this system's performance was satisfactory.
The obvious improvements needed for the in-canopy test procedure are 1) reliable measurement of the pivot point flow rate and pressure, 2) either a different nozzle flow measurement instrument or a method to better seal the existing instrument, and 3) a standardized data collection routine.
The latter comes with multiple testing and analysis.
Items one and two are being addressed.
In addition to moisture condensation or accumulation within the instrument, the instruments also shut down completely after a number of uses.
This was originally thought to be due to the moisture exposure, but an additional suggestion that exposure to cold ground water may be having an effect on the instrument.
This will be tested in the lab.
During the test, the instruments are not exposed to direct spray from other nozzles, but do get wet from handling.
The Mobile Irrigation Lab is supported in part by the Kansas Water Plan Fund administered by the Kansas Water Office, and USDA Project 2005-34296-15666.
The In-canopy Center Pivot Performance Evaluation Study Project is also supported by Ogallala Initiative, Project GEGC 5-27798.
Chapter: 31 Reducing Nitrate Losses from Drained Lands
 Subsurface  drainage removes excess water; improves trafficability; reduces excess water stress, soil compaction, surface runoff, erosion, and phosphorous transport; enhances soil aeration; encourages root development; removes excess salts; and leads to greater and more consistent yields.
In spite of these numerous benefits, tile drainage can also increase the transport of nitrate from the field to nontarget areas.
Nitrate is transported from surface soil to nontarget areas with percolating water because it is not attached to the soil particles.
The goal of this chapter is to discuss in-field and edge-of-field practices that reduce nitrate transport through tile-drained systems.
Nitrate-N concentrations in drainage water are highly Denitrification variable and often exceed the EPA drinking water bioreactors standard of 10 ppm.
Reducing high nitrate concentrations to levels at or below the EPA drinking Edge-of-field or off-field Wetlands practices water standard can be expensive and may require expanding urban and rural water treatment facilities.
Saturated buffers For example, the Des Moines Water Works installed expensive nitrate-removing treatment facilities to clean river water that receives tile-drainage waters from upstream sources.
To recover these costs, it filed a lawsuit against three Iowa counties where tile drainage is prevalent.
In South Dakota, nitrate-N concentration in ground and surface waters is highly variable, ranging from near zero to much higher than 10 ppm.
Generally, however, nitrate-N concentrations in South Dakota rivers are less than 10 ppm.
On a broader scale, nitrate-N derived from drained croplands in the Upper Midwest is a major contributor
 Figure 31.1 Classification diagram of practices for reducing nitrogen loads from drained croplands.
to hypoxia in the Gulf of Mexico.
The hypoxic zone results from nitrogen and phosphorous stimulating microbial growth in the Gulf of Mexico.
The dissolved oxygen in the water decreases when the microbial organisms die and are decomposed, which reduces oxygen availability to desirable species.
Hypoxia has environmental and economic consequences because the amounts of harvestable fish and shellfish from the affected regions are reduced.
To reduce hypoxia, states along the Mississippi River, not including South Dakota, have been tasked with reducing nutrient loading to streams and tributaries that feed the Mississippi River.
The strategy to achieve this goal is the adoption of nutrient Best Management Practices.
The feasibility and potential impacts of nutrient BMPs on nitrate loading in Iowa is available in IDALS  from the Iowa Department of Agriculture and Land Stewardship.
In South Dakota, cost share may be available for implementing BMPs from the USDA NRCS.
As public scrutiny about drainage and water quality increases, the potential exists for increased regulation.
One way for farmers to be proactive about water quality is to voluntarily adopt practices that reduce off-site nitrate deposition.
This chapter describes some of the most promising practices currently available.
In-field Practices Cropping and Management Strategies
 Improved nitrogen management.
Applying N in excess of plant requirements increases the risk of nitrate leaching.
Nitrate-N concentrations in drainage water can be reduced by multiple practices, including adopting N management strategies that improve N-fertilizer efficiency.
These practices include reducing fall N applications, splitting the N application into two or more applications to target plant uptake requirements, and adopting cropping systems that enhance nutrient cycling.
Optimizing nitrogen application rates, timing, and using nitrification inhibitors can limit nitrate losses and improve N efficiency.
Additional information about alternative in-field techniques is available in Chapters 20 and 29.
Cover crops.
Cover crops reduce nitrate losses by utilizing NOthat otherwise would be lost through leaching.
In South Dakota, integrating cover crops into corn and soybean rotations is complicated by the region's short growing season.
Research is being conducted to overcome this limitation.
In Iowa, it was estimated that cover crops have the potential to reduce nitrate loading by 31% , whereas in Minnesota, it was estimated that cover crops have the potential to reduce nitrate loading by 20%.
Similar estimates are not available for South Dakota.
Perennial crops.
Including perennial plants, such as alfalfa or native grasses, in a cropping rotation, has the benefit of reducing N fertilizer additions and nitrate losses while providing habitat for wildlife and insect pollinators.
In Iowa, it was estimated that adopting a crop rotation that consists of two years of alfalfa, followed by three years of annual crops, could reduce nitrate loading Conventional Drainage Controlled Drainage 42%.
Control Structure
 Controlled drainage.
Controlled drainage  uses flow-control structures to manage the timing and amount of drain flow by controlling the outlet elevation.
Many controlled drainage systems raise the outlet elevation during the late fall and winter.
Reducing drain flow by raising the outlet elevation reduces total nitrate transport.
In the spring and perhaps during harvest the outlet
 Figure 31.2 Controlled drainage  uses control structures to raise and lower the outlet elevation.
The outlet is raised at times when drainage is not needed  or after spring field operations to store water in the soil for later availability for the crop.
By reducing drain flow, controlled drainage also reduces nitrate losses from the drainage system.
is lowered and the system operates like a conventional drainage system.
Water for the growing crop is increased by raising the outlet following spring operations.
It is important to note that controlled drainage only manages the outlet elevation and that the actual water-table level is a function of precipitation, evapotranspiration and other water losses.
In drainage systems requiring a lift station, this often is accomplished by turning off the pump.
Controlled drainage is best suited to relatively flat fields.
Typical recommendations are to install a control structure for each 1to 2-foot change in field elevation.
For fields with slopes greater than 1%, more control structures are required, which increases the cost.
Aligning the drainage laterals with the field contours minimizes costs and maximizes the area served by each control structure.
In some situations, traditional drainage systems can be retrofitted with control structures.
However, if this option was not considered during the drainage design process, retrofitting may be impractical on all but the flattest of fields.
Producers can receive technical and financial assistance through the USDA NRCS to help with the installation of a controlled drainage system.
Controlled drainage has little effect on actual nitrate concentrations in the water.
Instead, nitrate load reductions are achieved by reducing the amount of drain flow.
In a review of controlled drainage studies, Skaggs et al.
found that controlled drainage reduced nitrate loading 18% to 79%.
In Iowa, it was estimated that controlled drainage reduced nitrate loading 33%.
The costs of installing controlled drainage can be partially recovered by higher yields.
Shallow drainage.
In shallow drainage systems, the tile lines are installed 2.5to 3-feet deep in the soil as opposed to > 3.5 feet.
Placing the tile lines at shallower depths reduces the total amount of water drained from the soil, which reduces nitrate losses.
However, shallow drainage, when compared with deep drainage, requires more tile lines, which increases cost.
By not lowering the water table as deeply, more water is stored in the soil, which may contribute to higher yields.
Figure 31.3 Shallow drainage is the practice of installing the drain lines at shallower depths  instead of at deeper conventional depths.
By not draining the water table as deeply, shallow drainage reduces nitrate losses from the drainage system.
In order to have the same drainage effectiveness, however, the drain lines must be spaced more closely than for conventional drainage.
Like controlled drainage, shallow drainage reduces nitrate losses by reducing drain flow.
However, unlike controlled drainage, shallow drainage does not have any topographic limitations.
In Iowa, it was estimated that shallow drainage could reduce nitrate loading 32%.
Similar estimates for South Dakota are not available.
Recycling drainage water.
In drainage-water recycling, captured drainage water is stored in a holding pond or reservoir, and used to irrigate the crop in the summer.
The benefits of this approach include increased yields and recycled nutrients.
Although the practice of drainage-water recycling is attractive, it is limited by topographic requirements, the availability of a storage reservoir, unknown economic returns,
 and, if high in other salts, could result in soils with greater salinity problems.
A denitrification bioreactor is a trench filled with a carbon source, typically wood chips.
Drainage water is diverted though the bioreactor by a control structure.
During periods of high flow, a portion of the drainage water is allowed to bypass the bioreactor so that drainage in the field is not affected.
In the drainage water that passes through the bioreactor, a portion of the nitrate is transformed to benign nitrogen gas through the microbial respiration process of denitrification.
The bioreactor is designed to enhance this process by providing food  and minimizing dissolved oxygen in the water.
Since denitrification is a biological process, the nitrate reduction depends on the temperature and the water flow rate.
Water that does not flow through the bioreactor receives no treatment.
Bioreactors can be retrofitted to wide variety of drainage systems, and they can generally fit within the edge-of-field buffer areas.
Bioreactors are best suited for fields < 80 acres and they should function for 10 to 15 years before the woodchips need replacement.
Testing Bioreactors in South Dakota
 Four bioreactors have been installed and monitored for performance in South Dakota.
Findings from these reactors suggest that their efficiency decreases with increasing flow rate.
During periods of high flow, nitrate concentrations can be reduced 30% to 40%, whereas during periods of low flow, nitrate concentrations can be reduced > 90%.
In Iowa, it was estimated that bioreactors reduced nitrate concentrations 43%.
The estimated cost  for installing a bioreactor in South Dakota is approximately $10,000.
Unfortunately, bioreactors provide no real benefit to the farmer; the benefits are all downstream.
Cost-share assistance is available through the USDA NRCS.
Figure 31.4 Drainage-water recycling is the practice of capturing subsurface drainage water, along with surface runoff, in a storage reservoir.
The captured water is then used as an irrigation water supply for the crop during periods of deficit water conditions.
By recycling some or all of the drainage water, the nitrate in that drainage water is also recycled, resulting in reduced losses of nitrate downstream.
Figure 31.5 Schematic diagram of a denitrifying bioreactor.
A control structure is used to divert water from the drainage system through a trench filled with woodchips.
Another control structure is used to regulate the time the water spends in the bioreactor.
Denitrifying bacteria in the woodchips convert nitrate in the drainage water into inert nitrogen gas, reducing the amount of nitrate delivered to the outlet.
Water in excess of the bioreactor is allowed to bypass the system so that drainage in the field is not impeded.
By routing drainage water through a wetland, the nitrate concentration can be reduced, while simultaneously providing habitat for wildlife, pollinators, and a variety of other benefits.
The nutrient reduction results from the combination of plant nutrient uptake, microbial immobilization, and denitrification.
An analysis of Iowa wetlands showed that on average nitrate concentrations were reduced 52%.
Compared to bioreactors, wetlands require a much greater land area, making
 them better suited for the capture of water from multiple fields.
Vegetated buffers between the edge of the field and the surface water are a long-established practice to reduce sediment and nutrient losses from surface runoff.
However, in fields with subsurface drainage, the drainage water has no chance for it to interact with the buffer since it's confined to the pipe.
Saturated buffers work by using a control structure to divert drainage water through the buffer area's soil.
By reconnecting the drainage water with the soil in the buffer, nitrate concentration in the water is reduced.
Saturated buffers are relatively new, so limited information is available about their long-term effectiveness.
However, in an Iowa study, most of the nitrate was removed from water diverted into the buffer.
The major drawback to this practice is that there is generally insufficient buffer area to handle all of the drainage water during high flows, SO a bypass may be required.
The bypass water receives no treatment, SO the nitrate removal efficiency of the saturated buffer is a function of how much water can be diverted through the buffer.
In Iowa, it was estimated that saturated buffers have the potential to reduce nitrate loading 50%.
Subsurface drainage, or tiling, provides a number of economic production benefits to corn producers.
However, impacts of drainage on the environment are mixed.
Drainage can reduce sediment and phosphorous losses but increase nitrate-N losses compared with undrained croplands.
There is Stream or Not to scale.
increasing pressure to reduce nitrogen losses from ditch subsurface drained land because of concerns over the Gulf of Mexico hypoxic zone from excess nutrients and public health concerns over elevated nitrate levels.
A number of practices are emerging to maintain the production benefits of drainage while reducing the nitrate-nitrogen lost from these systems.
A few of these practices offer the potential of added yield benefits to the producer, but many do not.
There are, however, cost-share incentives in place to assist with implementing many of these practices.
Adopting one or more of these practices is a proactive way for agricultural producers to demonstrate a commitment to water quality.
Even if a practice won't be implemented immediately, evaluating and planning for practices that could be implemented within a producers cropping and drainage system will make it much easier for future adoption if financial or regulatory incentives change.
Figure 31.6 Photo of a partially completed bioreactor near Baltic, SD, showing the woodchips, plastic liner, geotextile cover, and soil cap.
Outlet with Saturated Buffer
 Figure 31.7 Saturated buffers use a control structure to divert water laterally in the buffer through perforated distribution pipes that release the water into the soil in the buffer.
The water flows through the soil in the buffer, where it has a chance to interact with the vegetation and bacteria in the buffer for additional nitrate removal, before it discharges into the receiving water.
SUDANGRASS HAY PRODUCTION IN THE IRRIGATED DESERTS OF ARIZONA AND CALIFORNIA
 Tim C.
Knowles and Michael J.
Ottman
 High-Value Sudangrass Hay Exports
 Since 1989, high demand for fine-stemmed sudangrass hay by Pacific Rim countries has created a market opportunity for Arizona and hay producers.
The compressed bale hay is shipped in 40-foot seagoing containers
 Foreign sudangrass hay buyers want dust-free hay with a bleached light green color and a stem diameter less than one quarter of an inch.
Generally, Japanese hay buyers prefer sudangrass hay that resembles their familiar rice straw hay in appearance.
Additionally, they will reject sudangrass hay with a nitrate-nitrogen concentration exceeding 1,000 parts per million.
Hay growers have learned to adapt to these strict Japanese standards by using sudangrass seeding rates in excess of 120 pounds per acre to reduce stem size, by lengthening field curing time to give hay a bleached color, by carefully managing nitrogen and irrigation water to reduce nitrate accumulation, and by growing time-proven standard varieties.
Sudangrass Types and Hybrids
 Common sudangrass has been grown in the United States since 1909.
Varietal improvements have been made over the years for smaller stem diameter , superior leafiness, disease/insect resistance, lower potential for prussic acid and nitrate-nitrogen accumulation, and sweet, juicy stalks.
Sudangrass is distantly related to Johnsongrass , but sudangrass does not develop fleshy roots or rhizomes.
Since sudangrass develops only fibrous roots, sudangrass never becomes a noxious weed.
Many stems develop from a single seed when given plenty of space.
Seed size ranges from 37,000 to 45,000 seeds/pound.
Two types of sudangrass hybrids are currently grown in the United States: true sudangrass hybrids and sorghum-sudan hybrids.
True sudangrass hybrids resemble common sudangrass in growth and quality characteristics, however they tend to be taller, have an intermediate stem diameter , and are higher yielding than common sudangrass.
These hybrids recover rapidly after harvest, and when managed properly are very productive.
Seed size is variable, ranging from 25,000 to 45,000 seeds/pound.
When planting for a given population, larger seeded sudangrass hybrids require a 15 to 30% higher seeding rate by weight compared to common sudangrass.
Sorghum-sudangrass hybrids are taller than sudangrass, have larger stems and coarser leaves, and give higher forage yield when harvested only two or three times per season at the flower stage for green chop or silage.
Since they tiller less and have larger stems  and coarser leaves, they are often used for silage and grazing.
Sorghumsudangrass hybrid stands often thin excessively after the third or fourth cutting, and these hybrids are more likely to accumulate prussic acid.
They are large seeded ranging from 16,000 to 18,000 seeds/pound, thus they require a 30 to 50% higher seeding rate by weight when planting for population, compared to common sudangrass varieties.
Sudangrass Hay Production General
 Sudangrass and related hybrids are annual warm season grasses grown for pasture, green chop, silage, and hay.
Sudangrass forages include common sudangrass , sudangrass hybrids, and sorghum-sudangrass hybrids  Moench X Sorghum sudanense Stapf.) As many as 4 to 5 cuttings can be obtained in a season on a 21 to 30 day cutting cycle.
Sudangrass does well on all types of well drained soils from a heavy clays to light sands, however the yield may be low on sandy soil if the crop is not well fertilized.
It tolerates moderately saline soils with an electrical conductivity of the soil extract up to 4.0  with yield reductions of 10% when soil EC > 5.0 , 25% if > 7.0 , and 50% at soil EC's > 11.0.
Commercial seed guides recommend sudangrass seeding rates ranging from 10 to 30 pounds of seed per acre.
However, sudangrass grown for export is planted at a higher density to decrease stem diameter and increase leafiness of the forage.
When planted at drill seeding rates from 100 to 125 lb acre, common sudangrass has stems about 0.2 inches in diameter and can grow to 3 to 5 feet high.
For hay production, it should be cut at the boot growth stage.
Hay yields ranging from 1.0 to 2.5 ton/acre/cutting can be expected at each of the four harvests.
Sudangrass is often sheeped off at the final  harvest.
Sudangrass is normally planted in late spring when the soil has become warm, or about two weeks after corn planting time.
After mid-March, western Arizona soil temperatures generally
 reach or exceed 65 degrees F, and sudangrass plantings can be safely made.
When soil temperatures at planting are from 50 to 60 degrees F, sudangrass germination drops to 25 to 60%, and plants require 14 to 21 days to emerge.
At soil temperatures above 60 degrees F, sudangrass germination is increased to 90 to 96%, requiring four to six days to emergence.
Typical sudangrass planting dates are from March 15 through May 1 for low elevation desert locations.
Hay production begins following 60 to 70 days after a mid-March planting.
Sorghum sudangrass hybrids and sudangrass are equivalent in their ability to germinate at low temperatures.
Seedbed Preparation and Planting
 Sudangrass produces well on all soil types, however best yields are obtained on well-drained, deep loam soils that have a high capacity to absorb and hold water.
Sandy soils will produce good crops of sudangrass when fertilized and irrigated frequently.
When impermeable soil layers are close to the soil surface, root development is reduced and water movement is restricted.
Compacted soil layers below the plow depth, resulting from tillage and heavy equipment traffic, should be broken by subsoiling prior to seedbed preparation.
Land leveling improves irrigation efficiency and increases production.
High spots in a field may be less productive because they receive less irrigation water and salts tend to accumulate in these areas.
Preliminary cultural operations such as plowing, disking, harrowing, and leveling should be completed before borders are established.
Border widths vary from 50 to 200 feet or more, depending on side slope, size of irrigation head available, and width of machinery to be used.
Due to its tolerance of moderately saline soils and the high amount of residue or organic matter returned to the soil, sudangrass is often grown on fields with historically low cotton lint yields.
Fields should be relatively level and laid out with low, wide borders spaced to fit haying equipment.
The soil should be prepared well with a mellow, firm seedbed similar to that for alfalfa.
A seedbed which gives good contact between seed and soil particles improves germination and early seedling growth.
Pre-irrigation will reveal high and low areas where spot leveling may be necessary prior to planting.
This preirrigation also sprouts weed seeds which can be killed during seedbed preparation at planting time.
Heavy  ground is often bedded prior to planting sudangrass due to its lower water infiltration rate, while sandier soils are normally planted flat in narrow basins with a grain drill.
Use certified seed since poor quality seed may contain Johnsongrass or other varieties of sorghum.
Johnsongrass and sorghum-sudan hybrids can produce more prussic acid than common and hybrid sudangrass.
Suggested planting dates are similar to corn.
Plant as soon as the soil temperature is 60 degrees F at a 1 1/2 inch depth for several consecutive days at 8:00 a.m., along with a favorable five day forecast.
Typical earliest planting dates for elevations below 3,000 feet range from March 15 through April 1, or from April 1 through May 15 at elevations above 3,000 feet.
Cultipack before seeding and use a grain drill with press wheels or other equipment that will accomplish a firm loose seedbed.
Plant from 100 to 120 pounds or 3,700,000 to 4,400,000 common sudangrass seeds per acre up to one inch
 deep in heavy soils or one and one half inch deep in sandier soils.
Plant sudangrass with a sixto eight-inch drill row spacing on flat ground, or with five to seven sixto eight-inch wide rows on raised beds.
Sufficient nitrogen should be applied at planting to ensure establishment of the crop and hasten development.
Typically, 40 to 80 pounds of actual nitrogen per acre are suggested at planting, based on results from a preplant nitrate-nitrogen soil test.
This should be followed by split applications of 60 to 120 pounds actual nitrogen per acre in irrigation water following each cutting.
Sudangrass planted in early spring into cool soil may benefit from an application of phosphorus.
Nitrogen and phosphorus requirements at planting can be determined from a preplant soil test.
Sudangrass has a seasonal nitrogen  requirement of 320 to 400 pounds actual N per acre, split applied at planting and following each cutting.
Overfertilization with nitrogen, especially when combined with stand loss in the later cuttings, can result in unacceptably high levels of nitrate-nitrogen in the forage 1000 ppm).
Nitrogen fertilizer can be water-run in the five to eight 4to 6acre inch flood irrigations that are normally applied during the growing season.
This includes one irrigation at or near planting, one to two irrigations prior to the first hay harvest, then one to two irrigations following each of the first three hay harvests.
Remember, one pound of actual nitrogen per acre is equivalent to approximately 0.24 gallon of anhydrous ammonia, 0.28 gallon of urea ammonium nitrate , or 2.2 pounds of urea.
Pre-irrigation on many soils requires about one acre-foot of water to wet the soil to a depth of six feet.
This practice aids in irrigation control and helps reduce weed problems where the grower is unsure of field conditions.
Another two or three acrefeet of water will be required in four to six irrigations during the growing season with sandy soils requiring a more frequent irrigation interval than heavy soils.
It is important to avoid undue moisture stress of sudangrass since stress can cause accumulation of nitrate-nitrogen and/ production of prussic acid in forages that can be toxic to livestock.
Sudangrass uses from 7 to 11 acre-inches of water per month in May, June, July, and August.
During the hottest periods this means irrigation about every two to three weeks on heavy loam, silt loam, and clay loam soils which hold more water than coarse textured sandy and sandy loam soils, which will require an irrigation interval of from one to two weeks.
Generally, when grown for hay on fine textured soils, sudangrass will require a six to eight inch irrigation each month during April and September, and every 20 to 25 days during May through August in order to meet the water requirements.
Sudangrass grown for hay on coarse textured soils will require from three to five inches of irrigation water applied every 15 to 25 days during April and September, and every 10 to 15 days, May through August.
Common sudangrass crop pests include weeds, and several diseases and insects.
Normally, insecticide applications are not required, but a preplant or postemergence herbicide application may be necessary.
Weeds probably cause the most damage to sudangrass stands as they compete for light, moisture and
 nutrients.
Proper seedbed preparation and planting dates that allow rapid germination and stand establishment will help control weeds.
Periodic cultivation is possible when forage is planted in rows.
Leaf blights which cause elongated straw-colored lesions with reddish margins on leaves and downy mildew which causes yellowish or reddish deformed leaves are the most serious sudangrass diseases.
Insects including the greenbug, corn earworm, armyworms, wireworm, and southwestern corn borer are occasional pests of sudangrass.
Tolerant varieties, crop rotations, early and frequent harvests, and crop destruction following the final harvest are the best controls for most disease and insect pests of sudangrass.
Greenbug aphids are potentially the most damaging insect pest since they inject a toxin into sudangrass plants and vector dwarf mosaic virus.
When plants are infected by this virus early, they are stunted and their leaves are mottled.
The leaves of older infected plants have necrotic areas that appear in streaks and their leaves have a reddish cast.
Although genetically resistant, small sudangrass seedlings may incur enough damage from large greenbug infestations to thin the stand, thus chemical control may be justified.
The greenbug aphid is pale green and approximately inch long, with a characteristic dark green stripe down its back.
Scout for greenbugs from emergence up through the first cutting of sudangrass.
A minimum of 40 randomly selected plants per field should be examined each week during this period.
Greenbugs are seldom evenly distributed across a field, SO examine plants from all parts of the field.
In seedling sudangrass up to six inches tall, greenbugs may be found on any part of the plant including the whorl and occasionally in the soil at the base of the plant.
On larger plants, greenbugs usually colonize on the undersides of lower leaves and move up the plant.
The undersides of lower leaves on larger plants need to be examined carefully.
Plants below six inches tall should be treated when unparasitized greenbugs are present, when there is visible yellowing and reddening of the plant, and when stand loss is probable.
Larger plants can tolerate more greenbugs than seedling sudangrass.
Soil pests of sudangrass are not common, but can include wireworms, white grubs, corn rootworms, and cutworms.
Crop rotation, cultivation practices, and/or the use of herbicides that reduce crop residues and provide weed free fields are important to control soil pests.
Proper seedbed preparation that promotes rapid seedling emergence and stand establishment, and preplant inspection for the presence of soil insects are important in fields with a history of production problems due to these pests.
Wireworms are immature stages of click beetles.
The larvae range in color from yellow to brown, can grow to approximately one long, and are shiny, cylindrical, and hard-bodied with six short legs close together near the head.
White grubs are the larval stages of May or June beetles.
Larvae are typically C-shaped, from 1/2 to one inch long, with a white body and tan to brown head.
Soil samples one square foot by four inches deep should be examined thoroughly for the presence of these soil pests.
If wireworm or white grub numbers exceed two or more per square foot, control measures should be implemented.
Cutworms are the immature stages of night-flying moths.
The larvae are dull brownish smooth skinned caterpillars over one inch long that curl into a C-shape when disturbed.
Insecticidetreated seed or planter box seed treatments have proven effective in controlling wireworms and cutworms, when these insects are present in damaging numbers in the soil.
Fall webworm, armyworm, corn earworm, and Southwestern corn borer moths can deposit eggs on the leaves of sudangrass plants.
Larvae of these moths cause damage by feeding on sudangrass leaves and stems.
They range in color from pale green to almost black, with longitudinal stripes running along the back.
They often feed in the plant whorl, and as leaves emerge from the whorl, ragged "shot hole" damage is evident.
Although this damage may be dramatic, control of worms in sudangrass beyond the seedling stage is seldom economically justified.
Early planting and practices that encourage the development of beneficial insect populations aid in control of armyworms and earworms.
Timely destruction of crop residues and crop rotation are important cultural controls of these sudangrass pests.
Spider mites can also damage young sudangrass plants.
Adult spider mites are tiny, up to 1/20 inch long, with eight legs and an oval body often with a dark blotch on either side.
They are easily seen with a 10X hand lense.
Spider mites live in colonies mostly on the lower surfaces of leaves where they often spin a silken webbing resembling a spider web.
They feed on leaves by piercing cells and removing plant juices.
Yellow or red blotches are found on leaves damaged by spider mites.
Eventually the entire leaf turns brown and dies.
Infestations are often first observed on the lower leaves of plants located in the outside rows of fields, SO edge treatments are possible with early detection.
Mite density and sudangrass plant size will dictate the need for miticide applications.
Spider mites have many natural enemies and frequently become a problem after other insecticides destroy natural enemies.
Grazing and Hay Harvest
 Harvest sudangrass when it is at least 18 to 24 inches tall at the first cutting.
This generally occurs from four to six weeks after planting.
It may be pastured or cut for hay every three to four weeks thereafter.
When sudangass is grazed down quickly it has a longer time for regrowth.
Common and sudangrass hybrids recover more quickly than sorghum-sudangrass hybrids which tend to lose stand following two or three harvests.
Rotation of livestock in strips or sections will facilitate irrigation after quick grazing, promote better regrowth, and avoid uneven grazing which can result in tall, unpalatable plants.
Regrowth from stubble four to six inches tall will recover faster than shorter stubble heights.
Hay generally may be cut three or four times in a season, and sheeped off at the final harvest.
A fifth cutting may be possible in late October or early November before frost, however this cutting is often sheeped off.
Highest hay yields are obtained by cutting at the soft dough stage of growth, but curing is difficult at this stage and quality is unacceptable for export and feeding.
Highest hay quality is obtained when sudangrass is harvested at the boot growth stage prior to heading.
The feed value of good sudangrass hay is about equal to that of millet, timothy, Johnsongrass, and
 other grasses.
Crude protein ranges from nine to twelve percent and TDN ranges from 55 to 60 percent.
Because of the large amount of juice in the stems of sudangrass, the leaves cure first and the hay often appears ready to bale when the stems are not dry.
Use of hay conditioners or crimping to split stems will reduce the drying time and give better quality bright, leafy hay.
Typical curing times range from 10 to 20 days after cutting depending on maturity at harvest, hay conditioning, and weather conditions.
Sudangrass cut for hay is often raked once or twice prior to baling to turn windrows and facilitate drying.
Sudangrass hay is easily baled when moisture content of the forage does not exceed 8 to 10 percent.
Lengthening the field curing time to give the hay a bleached color is preferred if sudangrass hay is destined for the Japanese export market.
Potential Sudangrass Forage-Livestock Disorders
 Nitrates present in hay crops are considered toxic to many classes of livestock.
There is considerable variation among animal species in their susceptibility to nitrate poisoning, with pigs being the most susceptible, followed by cattle, sheep, and horses.
The higher susceptibility of cattle relative to sheep is due either to the ability of cattle to convert nitrate to nitrite in the rumen or to the greater ability of sheep to convert nitrite to ammonia in the stomach.
The lethal dose  of nitratenitrogen for pigs ranges from 19 to 21 mg/kg body weight; for cattle it ranges from 88 to 110 mg/kg body weight; and for sheep it ranges from 40 to 50 mg/kg body weight.
Forages containing more than 2,000 ppm nitrate-nitrogen can cause toxic effects in cattle.
Nitrate poisoning in livestock is often results from the consumption of pasture or feedlot hay containing high levels of nitrate-nitrogen.
Sudangrass takes up nitrogen from the soil primarily in the form of nitrate.
Under normal growth conditions this nitrate is converted to plant protein at about the same rate it is taken up by plant roots.
However, when plant growth is slowed or stopped by stress conditions including low soil moisture, low humidity , cloudy conditions that reduce solar radiation, frost, or herbicide applications, nitrate can accumulate.
Nitrate levels will be highest in the stalks or stems and lowest in the new leaf growth.
Nitrate levels are usually higher in young plants and decrease as plants mature.
Another type of poisoning from nitrate occurs when nitrate is converted to nitrite in the plant or animal.
Conditions may be conducive for nitrate to be reduced to nitrite in forages.
This is especially true for forage produced during wet and hot weather conditions, or if the harvested hay is damp for some time before feeding.
Nitrates can also be reduced to nitrites within the digestive tract of livestock.
Nitrites can then oxidize the iron in blood hemoglobin and prevent adequate oxygen transport.
Animal symptoms are labored breathing, muscle tremors, and a staggering gait after which the animal collapses, gasps for breath and dies quickly.
The membranes of the eyes and mouth will appear bluish indicating a lack of oxygen, and the blood will be chocolate brown, but will turn bright red when exposed to air.
Forages heavily fertilized with nitrogen often will accumulate toxic quantities of nitrate-nitrogen during periods of drought, cloudy weather, or when stands start to thin.
Export hay brokers prefer sudangrass with a nitrate-nitrogen concentration less than 1000 ppm and crude protein levels ranging from 9 to 12%.
If you suspect nitrate accumulation in forage, it is a good idea to have the forage tested.
If there is a good chance that weather or other factors causing nitrate accumulation may improve, it is a good idea to postpone harvesting for a couple of days.
Generally, once the stress is removed, and normal plant growth has resumed, nitrate accumulation disappears quickly.
If it is necessary to harvest forage high in nitrate, it generally is recommended to hay producers that they mow higher than normal, because nitrate accumulation is greater in the lower parts of the plant and in regrowth.
Also, postponing harvest until afternoon will allow sunlight to convert as much of the nitrate to plant protein as possible.
Furthermore, ensiling can reduce nitrate levels by 40% or more compared to haying.
Nitrate is fairly stable in harvested forages or hay.
Damp hay high in nitrate seems to be more toxic when fed to susceptible animals than dry hay.
Forages high in nitrate can be diluted to a safe level with other forages or grains that are low in nitrate.
Hydrocyanic or Prussic Acid Poisoning
 Most cases of hydrocyanic or prussio acid poisoning are caused by the ingestion of plants that contain cyanogenetic glucosides.
Cyanogenetic glucoside itself is non-toxic but hydrocyanic acid  may be liberated from the organic complex by the action of an enzyme which may also be present in the same or other forage plants, or by the activity of rumen microorganisms.
Horses and pigs are much less susceptible to the glycosides because the acidity of the stomach in monogastric animals helps to destroy the enzyme.
Sheep are much more resistant than cattle, apparently because of differences between enzyme systems of the forestomachs of the two animals.
The minimum lethal dose of hydrocyanic acid is about 2 mg/kg body weight for cattle when taken in the form of a glucoside.
Plant material containing more than 200 ppm hydrocyanic acid can cause toxic effects in cattle.
Prussic acid causes death in livestock by interfering with the oxygen transferring ability of the red blood cells, causing animals to suffocate.
Symptoms include excessive salivation, rapid breathing, and muscle spasms.
Symptoms normally occur within 10 to 15 minutes after the animal consumes toxic quantities of prussic acid-containing forage.
Animals may stagger, collapse, and die within 2 to 3 minutes of first showing symptoms.
The greatest danger of poisoning exists when hungry animals gorge themselves on forages containing toxic levels of prussic acid.
Naturally occurring glycosides may form prussic acid which can build up to toxic levels in young plants and leaves of sudangrass.
As with nitrate accumulation, some stress usually triggers HCN production.
Since prussic acid is most likely to build up to dangerous levels immediately after a killing frost, the last sudangrass hay cutting of the season can likely be suspect.
Occasionally, hot, dry winds induce temporary moisture stress on sudangrass plants which also can increase the potential for prussic acid accumulation by sudangrass.
The potential for poisoning
 of livestock by forage is greater with excessive soil nitrogen and young plants.
Toxicity is also more likely when periods of rapid growth are followed by cool, cloudy weather.
Lush regrowth after cutting for hay or frost is particularly dangerous.
Stress resulting from high rates of herbicide that stunt sudangrass growth may temporarily increase prussic acid levels in the plant.
Livestock may be poisoned if they eat large amounts of forage with a prussic acid content above 600 ppm.
Milking cows and stockers may show reduced performance if they eat large amounts of forage with a prussic acid content above 200 ppm.
Danger of poisoning is minimal by the time sudangrass reaches a height of 18 to 22 inches.
Prussic acid levels are normally highest in lush regrowth following a period of stress, and also higher in the leaves compared to the stems.
As with nitrate, most problems with prussic acid can be avoided with proper management of forage and animals.
Since sheep are much more resistant to prussic acid poisoning than are cattle, and because of the low tonnage of the final sudangrass cutting in fall or early winter, this cutting is often sheeped off, rather than harvested for hay.
Glycoside levels increase during the morning, then level off and begin declining in the afternoon and evening.
Postponing harvest till the evening can reduce the potential for prussic acid production in forage.
Sudangrass fertilized heavily with nitrogen and stunted by moisture stress, inclement weather, or an herbicide application can produce toxic levels of prussic acid.
Hay producers can reduce risk of livestock poisoning by using a maximum of 60 to 80 pounds of actual nitrogen per fertilizer application.
Proper field curing before baling or ensiling results in considerable loss of prussic acid.
Test any forage thought to contain high levels of prussic acid or nitrate-nitrogen before animals are grazed or fed.
Grazing or hay cutting should not begin until plants have reached 24 inches in height or more.
Do not harvest sudangrass regrowth following a frost for hay.
Frosted sudangrass may be used for silage, however do not feed new silage for two to three weeks since this delay will allow prussic acid to escape.
Do not pasture or sheep off sudangrass following a killing frost until plants thaw and wilt for a few days.
Average percent of fields by year fitting into the six categories.
The dry years 2020, 21 and 22 are different than the other years.
In 2018, out of 50 reports, 40% were ranked good, 18% were fair, 16% were wet late, 12% were wet early, 10% were wet all season, and 4% were very wet all season.
The description of a dynamic VRI irrigation prescription is that it changes frequently during the season, possible for each irrigation event.
Considerations include that it may be complicated and increase management efforts and that it may provide maximum gross benefit.
Example uses include varying irrigation to each part of the field as needed and adjusting areas as needs change over the season as well as variable rate chemigation.
Irrigation frequencies and soils are the primary factors in the allocation of different crop acreages.
In general, as water quality declines, the number of irrigations increases.
For example, at 900 ppm most 16X irrigations are selected, but from 1,100 ppm on, the other irrigation frequencies become more common until at 1,400 ppm only cantaloupe on the Indio soil is still using a 16X routine.
This indicates that using a high irrigation frequency and maintaining high soil moisture level would minimize the impact of reduced water quality.
The substitutions of the varions production factors become evident from table 2.
For example, cotton is grown on the Imperial Complex  with 16X irrigation frequencies at 900, 1,000, and 1,100 ppm water.
At 1,200 ppm the model shifts cotton to the HoltvilleImperial soil, a better drained soil than the Imperial Complex, substituting a soil type for water quality.
Cotton stays on Holtville-Imperial until 1,400 ppm is reached: then it is shifted back to Imperial Complex, but the irrigation frequencies change from 16X to 22X.
The irrigation routine or water management system is being substituted for a decrease in both soil quality and water quality.
The same general conclusion can be made for sugar beets.
This analysis supports the observation that better drained soils can handle lowquality water without drastically affecting crop yield.
An indication of a soil's economic value is its productivity when compared to other inputs that go into growing a crop.
This study indicates that both Indio and Holtville-Imperial soils increase in relative value  as the water quality becomes poorer.
The Indio soils show the least loss in productivity due to their ability to handle high-salt irrigation water.
Sprinkler irrigation, although commonly used on Imperial Valley farms, especially for germination purposes, did not enter into the optimum irrigation management results until extreme
 water-quality values were reached.
This is partially explained by the higher costs in renting and moving sprinkler systems.
Secondly, it is difficult to quantify some of the secondary benefits of sprinklers on replanting costs and crop quality.
The impact of reduced water quality on farm income is indieated by a 19.5 percent decrease in farm income from 900 ppm to 1,400 ppm water, an average 3.9 percent decrease in income for every 100 ppm increase of total dissolved salts in the irrigation water.
In summary, an economic model defining one of many possible combinations of characteristics of a composite farm firm was developed, representing resources available in the Imperial Valley.
The model was used to project significant shifts in cropping patterns as the salt content of irrigation water increased within the framework of the defined system.
A substitution effect appears between water quality and the quantity of water applied through both higher leaching fractions and more frequent irrigations.
At high irrigation-water salinity levels, lighter, better drained soils maintain their productivity and therefore their value in agriculture as compared to the heavy clay soils.
Finally, decreased yields and higher water use per acre of crops planted are projected to have a negative effect on fann incomes in the Valley as salt content of the Colorado River increases.
Jay Noel is Research Assistant, Department of Agricultural Economies, Davis; Charles V.
Moore is Agricultural Economist, Dept.
of Agriculture, stationed at University of California, Davis; Frank Robinson is Water Scientist, Department of Land, Air, and Water Resources, University of California Imperial Valley Field Station; and J.
H.
Snyder is Director of the University of California Water Resources Center, Davis.
This experiment indicates that a high yield of alfalfa seed can be obtained in the Imperial Valley if water management and insects are properly controlled.
Irrigations guided by tensiometer at the 50centibar level during seed production gave the best yield in 2 years of testing.
Irrigation control was obtained by using surface drip irrigation.
The three main requisites for good alfalfa seed production are irrigation, pollination, and insect control.
The latter two can be accomplished with established management practices.
The strength of the honey bee force required for pollination depends on factors such as plant population.
time of year, and temperature.
Insect control can be accomplished with available, proven insecticides.
Insecticides that repel honey bees should be avoided.
Irrigation is the major alfalfa seed production problem in the Imperial Valley.
Compared with alfalfa plants in other seed-producing areas, those in the Valley have a very shallow root system, normallv 18 inches in depth or less, and the evapotranspiration rate is high.
Alfalfa seed production is much easier to manage when the plants are deep-rooted Deep roots are able to pick up moisture from a greater soil storage volume, which can supply moisture to the plant at a constant slow rate throughout the seed production period.
Shallow-rooted alfalfa requires frequent irrigations.
If too much water is applied, the plant remains vegetative.
To stimulate flower production and pollination, mild plant stress must be created by restricting the soil water supply.
If too
 L.
S.
WILLARDSON A.
W.
MARSH C.
F.
EHLIG
 Field plots used for study on irrigoting alfalfa for seed.
little water is applied, the plant is overly stressed and loses its flowers.
To obtain maximum yield, Imperial Valley alfalfa must be irrigated after the crop's seed has set, sufficient to prevent excessive stress until seed filling is complete.
In most other seed-producing areas, irrigations after seed set are unnecessary.
Application of too much water to an alfalfa field in full bloom causes a decline in the sugar content of the flower nectar.
The nectar's attractiveness to honey bees is reduced, and the bees go elsewhere.
Drier conditions also are more favorable for pollen-collecting honey bees, because they prefer more powdery pollen.
An irrigation trial was conducted in 1972 and 1973 at the Imperial Valley Conservation Research Center near Brawley to develop a better understanding of alfalfa seed soil moisture requirements for the Imperial Valley.
The trial included four irrigation treatments, which were based on soil suction levels at the 9-inch depth measured by tensiometer and/or gypsum block readings.
The levels used to schedule irrigations were, respectively, 10 centibars , 50 cb, 100 cb, and 200 cb, starting at the mid-May bud stage.
These levels were used from the beginning of bloom, about June 1, until the crop was ready for harvest.
During the "hay producing period," all plots were irrigated at 10 cb for maximum hay production.
Drip irrigation was used, because it can be precisely con-
 trolled.
Moapa 69 alfalfa was planted February 14, 1972, on double-row, 40-inch beds  and irrigated with a drip system..
The plot size was 10 feet by 20 feet.
Data were taken only from the center beds.
The trial included 24 plots, with the four soil water treatments replicated six times.
Phosphoric acid was applied through the drip system at the rate of 100 pounds P2O5 per acre after removing the hay crop and immediately before seed production.
Pesticides were applied for lygus bug control, as necessary.
Before seed production started, the hay crop was cut in mid-May in both years.
The seed crops were harvested in July 1972 and August 1973.
Four bee colonies were placed near the plots to aid crop pollination.
The table shows the average alfalfa seed yields.
For both years, a peak seed yield of over 1,200 pounds per acre was obtained when the soil suction was controlled at 50 centibars during the seed production period.
Soil suction of 10 centibars resulted in excess vegetative growth.
Tensions of 100 and 200 cb caused excessive plant stress and reduced seed yields.
These effects are properly reflected in the 1972 data but are masked by an equipment malfunetion in the 1973 trial.
The differences between treatment yield averages were not statistically significant in either year, though
 treatment effects were observably large in 1972.
Because a wind storm destroyed part of the material as it was being harvested, data from only one complete replication were obtained in 1972.
In spite of unfortunate problems in obtaining these data, the advantage of controlling soil suction at 50 eb seems real from these experiments.
AVERAGE ALFAIFA SEED YIELDS WITH CONTROLLED SOIL WATER TENSION AND DRIP IRRIGATION
 Soil water tension 
 Year	10	50	100	200
 1972	718	1,267	870	288
 1973	1,288	1,372	1,010	1,086
 The best seed yields were obtained by irrigating at a soil water tension of 50 centibars during the seed production period.
Lower soil water tension increased vegetative growth and reduced seed set.
Higher soil water tensions resulted in reduced seed yields.
Fortunately, the best yield was obtained at a soil moisture condition easily measured with tensiometers.
SO that any grower can utilize the technique.
Some already have.
A Study of Irrigation Requirements of Southwestern Landscape Trees
 Ursula K.
Schuch and Edward C.
Martin
 Trees are an important component of our landscapes, providing many benefits from shade to cleaning the air.
Large, mature trees provide the greatest benefits in urban landscapes compared to smaller, younger trees and it is therefore important to ensure that trees in our urban forests receive the amount of water they need to develop into healthy, mature specimens.
Trees planted in urban landscapes need regular watering during establishment to develop a healthy root and shoot system.
After establishment, tree species differ in how much supplemental irrigation they need to grow to their mature size and to remain healthy.
Increasing the amount of irrigation water does not always result in more tree growth.
Responses vary by how often and how much water a tree receives, the degree to which the soil dries between irrigations, and the amount of water a plant needs based on weather conditions, primarily solar radiation, temperature and wind.
Recommendations for irrigation amounts and frequencies can be found in several publications  however, these values are generally based on expert agreements or anecdotal evidence and not on scientific experiments.
Following are the results of a study conducted at the University of Arizona Maricopa Agricultural Center in Maricopa, Arizona to determine the irrigation needs of nine species of commonly planted landscape trees.
After planting, trees were well watered for 1.5 years for establishment, allowing approximately 25% soil moisture depletion between irrigations during summer  and 35% depletion during the remainder of the year.
In summer, this required weekly irrigation with 20 gallons of water per tree.
After this establishment period, three irrigation frequency treatments were applied to trees.
This study describes the subsequent four seasons of irrigation regimes after establishment and the irrigation frequency study.
During the last year of the study, trees were grown without supplemental irrigation to simulate what happens when irrigation is suddenly turned off.
Recommendations are given for irrigating the nine species of trees that were studied.
Trees used in this study and their characteristics are listed in Table 1.
Trees were transplanted from # 15 containers in
 Table 1.
List of species used and their characteristics.
Latin Name	Common Name	adapted	Type
 Cupressus arizonica	Arizona cypress	SW native	evergreen conifer
 Chilopsis linearis 'Art's Seedless'	Desert willow	SW native	deciduous
 Ebenopsis ebano	Texas ebony	SW native	semi-deciduous
 Fraxinus velutina 'Rio Grande'	Rio Grande ash	SW native	deciduous
 Parkinsonia thornless hybrid	Palo verde hybrid	desert adapted	semi-deciduous
 Pinus eldarica	Afghan pine	desert adapted	evergreen conifer
 Pistacia X 'Red Push"	Red Push pistache	desert adapted	deciduous
 Prosopis velutina	Velvet mesquite	SW native	deciduous
 Quercus virginiana	Southern live oak	desert adapted	evergreen broadleaf
 January 2007 at a spacing of 20 feet within a row and 45 feet between rows.
Eighteen trees of each species were planted, providing six replicate plants for three irrigation treatments.
Irrigation Treatments and Data Collection
 In September 2008 after establishment of the trees, an irrigation frequency study was initiated and applied for 18 months.
The three treatments applied were to allow the soil moisture in the root zone  to deplete to 70%, 50% or 30% of available soil water and then irrigated to fill the profile.
Water depletion was calculated based on the local reference evapotranspiration from the nearby local weather station.
Once the root zone was depleted to the appropriate amount, all trees in a treatment were irrigated using a bubbler system with one bubbler placed in a circular trench 3 feet from the trunk.
The amount of water applied to each treatment on a yearly basis was the same, but irrigation frequencies varied between treatments.
Growth and plant quality of each species did not differ between the treatments and trees for each species were of similar size when the study was concluded in April 2010.
For the following study, all trees irrigated most often  were moved to the medium treatment, those watered with medium frequency were moved to the wet treatment, and the ones watered least  remained in the dry treatment.
Each treatment is described in detail below.
From May 2010 until March 2014, three different irrigation treatments were applied to determine how tree growth and quality are affected by different irrigation regimes.
Irrigation treatments were applied as a percentage of the reference evapotranspiration  at the site.
Evapotranspiration is the amount of water lost due to the evaporation of water from the soil surface and the loss of water through plant transpiration.
All weather data, including reference ET was obtained from the Arizona Meteorological Network  weather station located about 600 feet from the experimental site.
Irrigation was applied when the available soil moisture in the root zone was depleted by 50%.
The bubbler irrigation system then delivered the wet, medium, and dry treatment consisting of 80%, 60%, or 40% of ET from May until October and 40%, 30%, or 20% of ET from November to April.
Irrigation was cut in half during the cool season to test whether plants can tolerate less supplemental water during the winter months when evapotranspiration demand is low.
Rainfall of more than 0.2 inches was subtracted from the accumulated ET since the most recent irrigation and delayed the next irrigation.
Each irrigation event in this study applied between 48 to 58 gallons per tree.
This was based on wetting an area of a circle about 6 feet in diameter to a depth of 2 feet.
The amount of water applied was calculated based on the soil texture and soil water holding capacity at the study site.
Table 2 shows some of the irrigation events and weather conditions at the site.
In April 2014 the irrigation system was removed to determine how trees respond when they are suddenly left to rely only on natural rainfall.
In January 2015 trees were cut about 5-10 inches above the ground.
Sections of the trunk were prepared for tree ring analysis.
Root systems of trees were excavated in March 2015 with a backhoe and soil in the root system was removed with an air spade.
In spring and fall of each year, plant height, trunk diameter , and two canopy diameters  which were used to calculate canopy area, were measured.
Monthly quality ratings evaluated foliage appearance and density, health problems, and overall appearance.
The rating system for overall quality was 0 = dead, 1 = barely alive or very poor quality, 2 = poor quality and unacceptable appearance, 3 = medium quality, minimum acceptable appearance, 4 = high quality, good appearance, 5 = outstanding quality and appearance.
Tree ring growth of the most recent six years was measured on the trunk sections.
The diameter of the ten largest roots was measured at a constant distance  from the center of the root ball.
Qualitative evaluation of root systems included a rating on the degree of girdling or root bound condition, the percentage of fibrous roots, and vertical and radial root distribution emerging from the original root ball.
Irrigation application times and quantities were recorded continuously.
Irrigation Regimes and Weather
 The experimental site was located in the arid climate of the Sonoran Desert at an elevation of 1180 feet in Arizona where summer temperatures exceed often 100F up to several weeks and freezing temperatures occur in December and January.
ET at the experimental site ranged from 2 inches per month in December to 11 inches per month in June, the month with the highest ET demand.
Rainfall is almost equally divided between the summer rains from July to September and during the winter months.
The frequency of irrigation differed substantially between treatments resulting in about 10 irrigation events for the dry and 21 events for the wet treatments per year.
Irrigation during the summer was applied more than once per week for the wet and only every other week for the dry treatment.
In winter, trees in the wet treatment were irrigated about every three weeks, whereas trees under the dry treatment went without irrigation for over four months.
This was primarily the case when ET was low and rainfall more than 0.5 inches partially filled the soil profile and delayed the next irrigation.
Plant Responses to Irrigation Treatments
 The three irrigation treatments did not cause differences in height, canopy area, and trunk diameter for each species
 Table 2.
Irrigation events and weather conditions during irrigation treatments at the experimental site from May 2010 to March 2014.
Events	Wet	Medium	Dry
 Irrigation events per year 	19-23	14-17	9-11
 Average annual irrigation per tree 	940	644	518
 Longest interval  between irrigations	76-124	132-155	135-189
 Shortest interval  between irrigations	4-6	6-10	10-15
 Annual reference evapotranspiration 	73.1 74.5 inches
 Annual rainfall	3.1 7.4 inches
 Annual highest average monthly maximum temperatures	105 107F
 Annual lowest average monthly minimum temperatures	32 35F
 Table 3.
Plant height, canopy area, and trunk diameter at the beginning of the irrigation experiment in March 2010 and at the conclusion of irrigation treatments in March 2014.
Means are the average of 18 trees grown under three irrigation treatments.
Species	Height 	increase	Height	Canopy area		increase	Canopy	diameter 	Trunk	increase	Trunk
 2010	2014	%	2010	2014	%	2010	2014	%
 Palo verde hybrid	13.2	20.0	52	167	524	214	5.5	9.6	76
 Velvet mesquite	9.6	12.3	28	100	269	170	3.5	5.9	67
 Red Push pistache	11.4	13.6	19	27	119	340	4.1	7.0	70
 Desert willow	9.2	12.6	36	38	103	171	3.1	5.7	80
 Texas ebony	6.6	7.8	18	30	53	76	2.6	3.6	40
 Arizona cypress	9.0	10.3	14	21	48	127	3.2	4.1	27
 Live oak	8.7	9.5	10	14	31	118	2.6	3.6	35
 Afghan pine	9.2	11.8	29	11	31	177	3.9	5.1	32
 Rio Grande ash	9.9	10.3	4	20	30	49	2.7	3.7	35
 over a period of four growing seasons.
Average means of the three irrigation treatments are presented in Table 3.
The one exception was the Southern live oak where the dry treatment had a smaller canopy area than the wet treatment.
Representative trees of each species at the beginning of the irrigation treatments are shown in Figure 1.
By March 2014, all plants had significantly increased in size, particularly in canopy area.
Palo verde grew fastest, followed by mesquite, pistache, and desert willow, while the other trees grew at a slower rate.
Analysis of tree ring growth after four seasons of irrigation treatments and one season without supplemental irrigation
 showed no difference between irrigation treatments for each species.
Figure 2 shows the trunk section samples and tree ring growth demonstrating that irrigation regime had little effect on trunk circumference.
The small diameter of one pine tree growing under the medium treatment may have been related to some factor other than irrigation.
All plants were in good condition in 2010 when the irrigation treatments started.
Their ratings were between 4 and 5  for overall plant quality, indicating that they had foliage, flowers, and fruit as would be expected of a healthy tree, and there was no
 Fig.
1.
Plants in May 2010 at the beginning of the irrigation experiment.
Upper row left to right: live oak, Rio Grande ash, Texas ebony; middle row left to right: Red Push pistache, desert willow, Arizona cypress, Afghan pine; lower row left to right velvet mesquite and palo verde hybrid.
Figure 2.
Trunk samples collected in January 2015 of Red Push pistache  and Afghan pine  prepared for measuring annual growth rings.
Trees under wet, medium, and dry treatment are in the top, middle, and bottom row, respectively.
Figure 3.
Trees that tmaintainedgoodquality when irrigated with1 the wet treatment for four seasons..
Figure 4.
Arizona cypress  under wet and dry irrigation, and Afghan pines  under wet and dry irrigation treatments.
evidence of insect, disease, or abiotic stress.
Quality ratings of palo verde, mesquite, pistache, desert willow, Texas ebony, and live oak  never dropped below 4.0  for any treatment from May 2010 until February 2014.
Although all plants continued to increase in size, overall quality of Afghan pine, Arizona cypress, Rio Grande ash, and live oak under the dry or medium irrigation treatment started to decline in quality.
Afghan pines under the dry treatment slipped to 2.8 in July 2013, below the minimum acceptable rating of 3.0, and remained there until February 2014.
The pines under the wet treatment maintained good quality ratings around 4.4, and those under the medium treatment maintained the minimum acceptable rating.
Arizona cypress ratings for the dry treatment were 3.3 from July 2013 until February 2014.
The lower quality was due to loss of foliage or foliage with marginal leaf burn or dead leaves.
Ash trees under the dry treatment dropped to a 3.0 quality rating in May 2013, down to 2.4 for a couple of months, and recovered to a 3.0 rating by February 2014.
From November 2013 until February 2014, Rio Grande ash under the medium and wet treatments had quality ratings barely above the minimum acceptable rating.
Live oak overall quality under the dry treatment  was consistently lower than the excellent rating of the wet treatment, however their appearance and functionality was still good.
Many of the stressed trees showed some recovery during early spring, but then continued to decline again as temperatures increased and irrigation was suspended.
Plant Responses under Simulated Drought when Irrigation was Discontinued
 Mesquite, pistache, desert willow, live oak and palo verde were not detrimentally affected by lack of irrigation during the 2014 growing season with overall quality rating between 3.4 and 4.8 by January 2015 at the conclusion of the experiment.
Palo verde produced fewer leaves although the plant quality was still good.
Tree quality of several species deteriorated by June, which is not surprising considering that the total reference evapotranspiration  was 28.4 inches during the three months with no precipitation at the site.
Average monthly high temperatures were 97F, 106F, and 109F for the months of April, May, and June, respectively.
During the simulated drought in June 2014, the average overall quality of Arizona cypress was 2.9, Afghan pine 2.6, Texas ebony 2.7 and Rio Grande ash 3.1.
One Arizona cypress previously irrigated with the wet treatment had started to decline in spring and died by June.
Plants from the previous wet treatment which received an overall quality rating indicating unacceptable appearance and poor health included four Texas ebony, one Rio Grande ash, one live oak, and one Afghan pine.
Plants from the previous
 medium treatment with unacceptable appearance included three pines, two Texas ebony, two Rio Grande ash, and one Arizona cypress.
Plants from the previous dry treatment had the fewest ratings of 5.
Only pistache, mesquite, four desert willow and two live oaks received this high rating while most plants received ratings of 3 or 4.
A total of eight trees under the previous dry treatment were rated as unacceptable overall quality: four Afghan pines, two Texas ebony, and two Arizona cypress.
Summer rains starting in July 2014 caused a flush of new foliage in several trees followed by milder decline.
Heavy rains totaling 1.4 inches from September 27 to October 8, 2014, helped many trees recover and cooler temperatures in fall slowed the decline.
Afghan pine, Arizona cypress, and Rio Grande ash trees lost more foliage during the drought.
Some live oak also dropped leaves and had some branch tip dieback.
Texas ebony had been performing well under all three irrigation treatments until the onset of drought.
Trees started to fold their leaves, then lose their leaves and developed branch dieback starting at the terminal end.
One tree from the previous dry treatment died and several others sustained major branch and trunk dieback.
The September rain likely saved several of the trees of this and other species from further decline.
Some Texas ebony were however, damaged beyond complete recovery and likely would have declined further had the experiment continued.
The fact that Texas ebony does not seem to tolerate sudden drought is surprising since it is native to the Southwestern United States, though not the Sonoran Desert where this study was done.
By the end of the year as temperatures were cooling and aided by the fall rains, some plants recovered and grew new foliage.
However, overall quality of most pine, cypress, ash, and some Texas ebony remained unacceptable.
At the conclusion of the study in January 2015, all trees of mesquite, desert willow, pistache, and Southern live oak survived.
and survival of ash, palo verde, and Arizona cypress was between 78% and 89%.
Of the eleven trees that died, four trees each were in the wet and medium, and three trees were in the dry irrigation treatment.
Three palo verde trees were lost due to a microburst in the second year of the study which was unrelated to irrigation treatments.
The Texas ebony and the Afghan pine died after the irrigation was suspended in 2014.
Irrigation treatments followed by one year without supplemental irrigation had no effect on root diameter or qualitative root characteristics when compared for each species.
Root size and morphology differed between species.
The fast growing species palo verde , mesquite, desert willow, and pistache , had similar root diameter for the ten largest roots we measured, between 35 to 39 mm.
Fig.
5.
Trees in June 2014, previously under the dry  and medium  treatment, and without irrigation since the beginning of March 2014.
Fig.
6.
Summer rains resulted in some trees growing new foliage and recovering from the drought by August 2014.
Fig 7.
A healthy and a dead Texas ebony.
By June 2014 several Texas ebony trees showed partial defoliation, branch dieback, and damage to the trunk.
Fig.
8.
Rio Grande ash canopy healthy  and increasing stages of defoliation and leaf burn.
The range of root diameter was between 20 mm and 64 mm for these species.
Roots of live oak  and ash  were on average 20 mm and 17 mm in diameter.
The two conifers had the most fibrous root system with average root diameter of the ten largest roots at 11 mm for the Afghan pine and 12 mm for the Arizona cypress.
The systems were almost exclusively composed of very small diameter roots.
Contrary, the root systems of desert willow, ash, palo verde and mesquite consisted mainly of large diameter primary roots with very few fibrous roots.
Root girdling and deformations leading back to pot bound conditions at the time of transplanting were severe in ash  and may have contributed to their poor growth performance throughout the study.
Arizona cypress, live oak, and Texas ebony also showed some of these defects, but not to the degree observed in the excavated root systems of ash trees.
All excavated root systems had horizontally spreading roots outside of the originally planted root ball.
This indicated that the trees had established well at the beginning
 of the study and we found no evidence that any irrigation treatment affected the horizontal root growth.
Palo verde was the only species where greater numbers of roots grew vertically from the original root ball.
The two conifers had almost no vertical roots growing from the original root ball and the other species had only a few.
Summary and Conclusions of the Irrigation Study
 After 4 years of irrigating trees at half or three quarter of the highest treatment, the following species were not significantly smaller in size with less water: mesquite, palo verde thornless hybrid, 'Red Push" pistache, Desert willow 'Art's Seedless', Texas ebony, and Southern live oak.
All species increased in height, canopy area, and trunk diameter with few significant differences for the same species receiving different irrigation treatments.
Southern live oak under the dry treatment developed a smaller canopy area than under the wet treatment.
Fig.
9.
The coarse root system of palo verde had the largest diameter roots and the greatest number of roots growing straight down into the soil.
Fig.
10.
Desert willow , mesquite , and Red Push pistache  developed large diameter roots that grew primarily horizontally and well beyond the irrigated area.
Desert willow and mesquite had a coarse root system with few fibrous roots, while the pistache root system had more fibrous roots.
Fig.
11.
Live oak  and Texas ebony  root systems had a few larger diameter roots and were intermediate in fibrosity.
Afghan pine  and Arizona cypress  root systems had the smallest diameter roots and the greatest percentage of fibrous roots.
Root systems of live oak, Texas ebony, and Afghan pine were sprayed with white paint to improve the visibility of the roots.
Severe symptoms of deficit irrigation  started to develop on Arizona cypress, Afghan pine, and Rio Grande ash, especially under the dry and sometimes medium treatment even before the onset of drought.
Summary and Conclusions of the Simulated Drought Study
 Mesquite, desert willow 'Art's Seedless', 'Red Push' pistache, palo verde thornless hybrid, and Southern live oak maintained good quality during the simulated drought in the 2014 growing season.
Overall quality of Afghan pine, Arizona cypress, and Rio Grande ash was unacceptable at ratings below 3.0 for most of the trees.
Texas ebony had ratings below 3 during the summer months but recovered in fall.
Texas ebony could not tolerate an abrupt lack of irrigation once accustomed to regular irrigation.
Fig 12.
Roots of Rio Grande ash were severely root bound and girdled.
Table 4.
Overall quality rating of trees in February 2014 after four growing seasons of irrigation treatments and in January 2015 after one season without supplemental irrigation, survival rates in January 2015 and recommended irrigation rates.
Quality rating scale is 1-5 with 1=dead, 3=minimum acceptable, 5 = excellent.
February 2014	January 2015	Recommended
 Species	Dry	Medium	Wet	Dry	Medium	Wet	Survival	irrigation ET	rate*	Comments
 40/20**	60/30	80/40	40/20	60/30	80/40	
 Palo verde hybrid	5.0	4.8	5.0	3.4	3.8	4.0	83	40/20
 Velvet mesquite	4.7	4.5	4.8	4.3	4.2	4.2	100	40/20	After establishment,
 plant may thrive with
 Red Push pistache	5.0	5.0	5.0	4.8	4.3	4.2	100	40/20	less than recommended
 Desert willow	5.0	5.0	5.0	4.5	4.0	4.5	100	40/20
 plant may thrive with
 Texas ebony	4.5	4.8	5.0	4.2	3.8	3.2	94	40/20	less than recommended
 rate but cannot tolerate
 abrupt lack of irrigation.
Plant may benefit from
 higher irrigation rates in
 Live oak	3.8	4.5	5.0	3.5	3.8	4.8	100	60/30	winter than used in this
 Arizona cypress	3.3	4.0	3.2	3.0	3.6	2.0	89	Conifers may benefit
 from more irrigation in
 Afghan pine	2.8	3.0	4.4	1.8	2.2	3.3	94	winter than used in this
 Rio Grande ash	3.0	3.3	3.4	1.8	2.6	2.3	78	60-80/30-40	root system defects
 40/20 refers to 40% ET from May to October and 20% ET from November to April.
* o
 This study was conducted on trees that received ample irrigation for the first three years after transplanting to ensure their root systems were well established.
In this study the wetted soil surface area was not increased over time.
As trees grow and further increase in canopy size, the irrigated area and the amount of water they receive at each irrigation needs to be increased.
Each irrigation event in this study applied between 48 to 58 gallons per tree which filled the soil volume in an area of a 6 feet diameter circle to a depth of 2 feet.
The amount of water applied was calculated based on
 the soil texture and soil water holding capacity at the study site.
The amount of water to be applied at any site will depend on the soil texture and the volume of soil to be irrigated at each cycle.
For species tolerating the low or medium irrigation treatment , irrigation with 40% ET from May to October and 20% ET from November to April, or 10 to 16 irrigation events per year depending on ET o' resulted in healthy trees of similar size compared to trees in the wet treatment.
During the period of highest evapotranspiration in summer, irrigation applied every 8 to 14 days was sufficient for trees tolerating low or medium irrigation treatment.
The evergreen conifers Afghan pine and Arizona cypress likely would benefit from receiving more irrigation in winter compared to the deciduous or semi-deciduous trees in this study.
They should receive
 irrigation based on 60-80% of ET at their location year round to remain functional and healthy.
If irrigation needs to be cut back or eliminated for any reason, providing the conifers  and Texas ebony with some supplemental irrigation will be critical to maintain their long-term health and survival.
Cotton Irrigation in Kansas
 Troy Dumler, Danny H.
Rogers, Tom Roberts, Kent Shaw
 Professor and Extension Specialist Irrigation; Extension Agricultural Economist; Kansas State University Research and Extension, 4500 E.
Mary, Garden City, KS; Professor, Kansas State University, Manhattan, KS; ex-Extension Agent, Stevens County, Kansas; and MIL Coordinator, respectively.
Abstract: Kansas is north of the traditional Cotton Belt and considered to be a thermally limited area for cotton; however cotton is being grown as an alternative to corn to stretch declining water resources.
Cotton is a non-determinate plant that continues to grow with favorable condition.
Irrigation timing is critical to ensure satisfactory crop growth and to achieve boll maturity for favorable lint quality and yield before a killing frost.
Both over irrigation or under irrigation may affect yield and quality.
Declining water resources make it necessary to conserve water but, at the same time, maintain acceptable revenue.
Cotton is a new alternative crop and there is a lack of research based irrigation management information.
One year data from a field research on a grower field indicates that 5 inches of irrigation plus rainfall produced a slightly better yield  compared to an application of 7 inches plus rain.
Although the difference is not significant, yet the trend was same for all replications.
The treatment receiving only 2.4 inches of water plus the rain produced 1.73 bales, which is significant.
Total rainfall during the growing season was 14.31 inches of which 8.81 was considered to be effective rainfall.
It was also noticed that the water extraction by roots were mostly within the first 2 feet of root zone; barely reaching to third foot depth.
It was also observed that the roots were more laterally distributed rather than deep in depth, although there appeared to be no restricting soil layer.
Keywords: alternative crop cotton, heat units for cotton,
 Introduction: Crop production in western Kansas is dependent on irrigation.
The irrigation water source is groundwater from the Ogallala aquifer.
The water level of the Ogallala aquifer is declining, causing the depth of pumping to increase.
The additional fuel consumption required for greater pumping depths and higher energy costs have resulted in increased pumping costs in recent years.
Because of declining water levels and higher pumping costs, the growers are looking for alternative crop that may provide somewhat acceptable revenue at a lower water requirement.
Cotton has made some inroads from south moving northward as an alternative crop.
Acreage grown in 2006 reached to 110 thousand acres, which has gradually come down due to recent commodity price changes.
Most of the crops grown are still in southern counties within Kansas.
Procedures: A producer's field with center-pivot sprinkler irrigation system was selected for the study.
The soil belongs to Richfield series and the texture is silt loam.
Three outer spans were selected to establish three replication of the study.
Three sets
 of eight nozzles in each span were fitted with a closing valve to establish three irrigation treatments.
The nozzles are five feet apart giving a length forty feet in each set of eight nozzles for individual plots.
A width of forty was marked to establish 40 ft by 40 ft individual plots.
The total number plots were nine.
Three irrigation treatments in terms of timing and number were randomly scattered in these nine plots.
Treatment T1 was set for four irrigation of one inch application depth each time during the growing season.
The tentative timing of irrigation was set for July 10, July 20, August 1, and August 10.
However, this was changed to meet the field condition and an application of 1.6" inches were applied as pre-irrigation to make the soil water condition suitable for planting and was followed by an application of 0.8" inches after seeding to secure good germination.
This was done for all the plots in the trial.
Afterwards, T1 received five irrigations starting on June 12 as the first differential treatment.
Total irrigation application amounted to 7" inches for the growing season.
Fig.
1 showing soil water chart for T1 treatment with irrigation and rainfall events.
Treatment T2 was set for two irrigation of same depth of application as T1 each time and the timings were set for July 10 and August 1.
However, as mentioned above for treatment T1, the treatment T2 also received pre and post irrigation amounting to 2.4" inches prior to treatment differential application.
The first differential application was provided on June 12 followed by one application on July 14.
Total irrigation application amounted to 5" inches.
Treatment T3 was set for no irrigation during the growing season except for what was applied to the field as pre-plant and post seeding
 for germination.
Gypsum blocks were placed at one foot depth interval to a depth of four feet to monitor soil water status.
Tom Lehey T2 Water Chart Cotton
 Fig.
2 showing soil water chart for T2 treatment with irrigation and rainfall events
 Paymaster 2141, a stripper cotton variety, was planted on May 19, 2008.
Plants started to emerge by May 26, 2008.
Cotton was harvested on October 28, 2008 by hand to record yield.
This was done after the freeze on October 23, 2008, when all mature bolls were open.
Weather data from Garden City experiment station was used for ET data and to calculate cotton growing degree days.
Alfalfa based reference ET was used in KanSched irrigation scheduling software to obtain crop ET for cotton under different irrigation treatments.
Results and Discussion: One year study results for 2008 indicate that cotton grown in Kansas for a growing period of 140 days used about 16 inches of water as crop ET ; out of this amount 7" inches were provided by irrigation and 8.8 inches were provided by effective rainfall.
Seasonal ET of 14.22" inches for treatment T2 was made up from 5" inches of irrigation, 8.8" inches from effective, and less than one half of an inch from soil water.
T3 received only pre and post seeding watering amounting to 2.4" inches.
Soil water use as shown in figure 3 is based on 100 percent application efficiency of irrigation.
At 85 percent application efficiency of water, which is more likely for a center pivot irrigation system the amount of soil water use will probably be a little higher than shown.
Figure 3 showing seasonal water uses by cotton crop of 2008 in southwest Kansas.
Cotton yield in bales per acre is shown in figure 4.
Cotton yield for all three replications were higher for irrigation treatment of 5" inches at an average yield of 2.52 bales per acre.
An ET difference of less than an inch between the treatments T2 and T3 has made a yield difference of 400 lbs.
per acre.
The timing of irrigation to remove water stress is important for cotton crop.
It is also critical to avoid high soil water condition for cotton quality and yield.
Figure 4 showing cotton yield for different irrigation treatment in 2008.
The harvested samples were sent out to USDA cotton classing office in Abilene, TX, for classification.
The salient results are presented in table 1.
Table 1 showing cotton classing results.
Treatment	Color	Mike	Length	Strength
 T1	24.3	2.80	1.14	27.20
 T2	27.7	2.87	1.13	27.57
 T3	31	2.97	1.10	27.23
 It appears that the color and mike are inversly related to increased irrigation contributing to prolonged growth.
This is probably due to having some late maturing bolls contributing to the production.
The length of staple appears to improve with irrigation, but strength of fiber may be sensitive to balanced water management.
The gypsum block readings showing soil water extraction according to gypsum block readings for T1 and T3 are shown in Figure 5-6.
Fig.
5 shows soil water chart according to readings obtained by gypsum blocks.
The soil water status corresponds to what was observed in soil water charts developed by KanSched irrigation scheduling software.
The soil water increased back to about field capacity , after a rainfall of 2.6" inches that was spread over three days from August 17 to 19, 2008.
Soil water status fell to management allowable depletion level  for T1 treatment by the end of the first week of September.
However, no further irrigation was provided to encourage plants to go for life cycle completion.
Fig.
6 shows soil water chart from readings obtained by gypsum blocks.
In figure 6 it is visible that the soil water status for first two feet of soil profile, where the roots were most active in early season fell below management allowable depletion by first week of August, and stayed that way until 2.6" inches of rain of third week of August.
The results presented are from one year study only.
The crop of 2009 was completely destroyed by hail storm.
The study needs to be repeated for making any conclusive remark.
However, it is evident that in a thermally limited area like Kansas, it is critical to manage water for optimum maturity.
The yield of cotton may also be limited due to limited growing season and cotton GDD  needed for full maturity of a crop.
The cotton GDD from May 26 to October 10 was 1,690 units only and no further increase occurred until freeze on October 23, 2008.
Some states use the commercial navigability test to determine stream bed ownership, whether the state or the adjoining landowners own the bed of the stream.
Some states use the less restrictive recreational navigability test to determine whether the public has a right to recreate on the stream or not.
So, you can have states where the bed of the stream is privately owned  but the public nonetheless has a right to recreate on the stream because you can canoe it.
In Nebraska, the law is unclear.
Promoting Efficient Water Management through Effective Outreach Education in the High Plains and Beyond: Role of the Ogallala Aquifer Program
 Dana O.
Porter1 Danny Rogers, David Brauer4 4 Thomas H.
Marek5, Prasanna H.
Gowda Freddie Lamm, James Bordovsky 1 Terry A.
Howell4
 1 Biological and Agricultural Engineering, Texas A&M University, Lubbock, TX, United States; 2 Kansas State University, Manhattan, KS, United States; SKansas State University, Colby, KS, United States; 4USDA-ARS, Bushland, TX, United States; STexas A&M University, Amarillo, TX, United States
 Written for presentation at the
 Emerging Technologies for Sustainable Irrigation
 A joint ASABE/IA Irrigation Symposium Long Beach, California November 10-12,2015 -
 
 Abstract.
The Ogallala Aquifer Program  is a consortium between the USDA Agricultural Research Service and partnering universities in Texas and Kansas.
The OAP has coordinated and leveraged highly effective irrigation research and extension programs with overarching goals to prolong the life of the Ogallala Aquifer and enhance rural economies in the US Southern High Plains.
The OAP has increased capability of research and extension programs to address local and regional issues more collaboratively and comprehensively, generating national and international recognition.
Stakeholders include agricultural producers; irrigation practitioners; crop and technical advisers; educators; off-farm decision makers; water resource planners/managers, in particular; and the general public.
Stakeholders possess wide ranges of specific interests, technical understanding, and information delivery preferences.
This paper describes how educational events, research and extension publications and products, media outreach, and mentoring are used to meet stakeholder information needs and promote basic and applied research programs in the High Plains.
Keywords.
irrigation scheduling, water management, education, water conservation, communication, agricultural extension
 Limited and declining water resources; increasing regulatory limits on pumping; drought; economic and environmental concerns, and other impacting issues enhance the need for efficient and advanced water management in agriculture.
Physical and regulatory limits on irrigation capacities and program requirements  complicate water management decisions from field to regional levels.
Decision-makers  are better equipped to address these complex issues when they have access to appropriately presented, pertinent, objective information resources.
Ongoing Extension and other technology transfer programs supported through the Ogallala Aquifer Program  provide excellent educational support for traditional audiences  and new audiences.
They also have been expanded to provide greater support for other decision-making stakeholders, including landlords, policy makers, agricultural lenders, educators and similar "off-farm" leaders and decision makers.
Online tools and advanced educational resources are being developed to complement traditional methods to support distance education and CEU programs for these audiences.
Agricultural irrigators in the Ogallala Aquifer region are among the most progressive adopters of efficient irrigation technologies and best management practices.
Still there is a need for sustained and expanded technology transfer to support agricultural irrigators , as well as significant emerging audiences.
Informational materials relevant for agricultural water management decisions are being developed and provided for both technical and non-technical audiences that include educators, practitioners, and a variety of decision-making stakeholders.
Some very useful technical resources have been developed for less technical audiences, emphasizing the "big picture", as well as local considerations, with special consideration of "bottom line" economic analyses.
The scope of subject matter addresses a range of issues from irrigation technologies and best management practices , program requirements , water resources management tools, and strategies for mitigating physical and regulatory limitations to water availability.
Technology transfer and the OAP: The OAP has leveraged, strengthened and connected established applied research programs in irrigation systems and technology; water management; cropping systems; animal agriculture; economics; hydrology and climatology.
Through supporting multi-agency and interdisciplinary research, the OAP fosters comprehensive systems approaches to find answers to critical questions of water resources management and practical solutions to agricultural water users' problems.
Innovative applications of advanced irrigation technologies, crop rotations and tillage systems to sustain production in water limited cropping systems; multi-faceted technical and economic analyses of water management strategies; and local and regional scale groundwater resources modeling provide relevant information and sound management recommendations.
Dr.
Terry Howell and other OAP leaders acknowledged early in the program planning that one key to maximizing the impact of OAP associated research and sustaining the program is an effective technology transfer program to interpret the research for the various audiences, increase visibility of the program, and promote adoption of appropriate tools and strategies.
Like the applied research projects and programs, the OAP technology transfer program has leveraged, connected and strengthened established educational venues.
A measure of success of the OAP effort has been the national recognition and awards associated with the program
 The objectives of the OAP technology transfer program are to 1) enrich OAP capabilities and extend benefits and visibility of OAP efforts; 2) deliver useful, objective information and educational opportunities for stakeholders efficiently; and 3) promote OAP-developed resources to an expanding stakeholder base to improve water management decisions.
The goal of amplifying water conservation and economic benefits of the OAP and associated agricultural research programs is met through reaching diverse audiences in communicating economic impacts of agricultural water use and effects of declining water resources; promoting adoption of appropriate technologies and management practices; and interpreting research results and developments for targeted audiences.
in the San Joaquin Valley
 The distance a pump must lift underground water to the surface is the most important single factor in the per acrefoot cost of irrigation pumping.
Other physical factors in the cost complexpump and well life, maintenance and repairs, changes in the water table and the total amount of water pumped per year -are influenced by the pump lift.
Practically every grower of irrigated
 crops in the San Joaquin Valley between the Merced River and the Tehachapi Mountains relies, at least in part, on pumps and underground water supplies.
The pumping plants range from those with five horsepower motors, lifting less than 100 gallons of water per minute, to 300 horsepower units discharging in excess of 2,000 gallons per minute.
An analysis of a sample of 11,000 pump tests
 conducted over a five-year period by power companies serving the area showed no constant relationship between total lift and horsepower, horsepower and discharge in gallons per minute, or either lift or horsepower and kilowatt hours per acre-foot.
It was evident from the analysis that geography and ground water conditions, as well as pumping lift, affect remaining well characteristics.
The area of the San Joaquin Valley studied was divided into 16 subareas with boundaries drawn on township lines for convenience but oriented to hydrographic areas.
To prepare estimates of irrigation pumping costs, logbook records from drillers of 800 wells put down within the past five years were tabulated by hydrographic areas.
The tabulated material supplied the physical characteristics of
 Concluded on next page
 Investment in Wells and Pumping Plants and Costs of Pumping Water by Hydrographic Area, San Joaquin Valley
 Area	Well	cost	well	Est.
life	Pump	cost	pump	life	Est.
depreci-	annual	ation1	Total	Insurance	interest	and tax	to lower	Cost due	table2	water	mainte-	Repair	nance	and		Service	charge	energy	except	Total	cost	Energy	charge	pumped	Acre	feet	Total cost	per acre	foot
 $	yrs.
$	yrs.
$	$	$	$	$	$	$	$
 A	2,301	20	2,790	20	242.85	204.89	0	55.80	134.60	638.14	439.40	449.7	2.40
 B	1,406	20	1,860	20	140.89	138.80	74.40	37.20	74.60	465.89	135.65	218.1	2.76
 C	2,600	20	2,598	20	217.55	220.92	103.92	51.96	168.25	762.60	495.50	358.2	3.51
 D	7,044	15	2,598	20	583.15	409.78	103.92	51.96	168.25	1,317.06	547.82	361.5	5.16
 E	8,122	20	3,545	20	483.38	495.85	0	70.90	201.90	1,252.03	625.02	495.6	3.79
 F	2,002	20	2,580	20	197.38	194.74	0	51.60	134.60	578.32	393.48	265.5	3.66
 G	2,002	20	2,580	20	197.38	194.74	0	51.60	134.60	578.32	384.66	252.6	3.81
 H	2,002	20	2,887	20	212.73	207.78	0	57.74	134.60	612.85	437.38	217.8	4.82
 I	1,177	20	2,160	20	146.73	141.82	0	43.20	174.60	506.35	130.25	82.2	7.74
 J	2,836	20	2,891	20	246.29	243.40	0	57.82	134.60	682.11	387.51	160.5	6.66
 K	12,980	20	4,422	20	721.55	737.58	309.54	132.66	201.90	2,103.23	686.32	213.0	13.10
 L	9,766	15	4,769	20	864.22	617.74	333.83	143.07	299.50	2,258.36	962.14	306.0	10.52
 M	2,836	20	3,179	20	260.69	255.64	0	95.37	134.60	746.30	377.84	80.4	13.98
 O	15,007	15	16,206	20	1,731.77	1,326.55	1,134.42	486.18	789.00	5,467.92	3,016.78	475.8	17.83
 P	14,000	15	17,700	15	2,013.33	1,347.25	1,239.00	531.00	789.00	5,919.58	3,288.32	406.8	22.63
 1 Salvage value of 40% of motor cost was credited to pump unit.
4% of new pump cost for areas B, C, and D; 7% for areas K, L, O, and P.
2 3 Thirty-six acre inches per acre of summer crops.
This will understate the amount pumped in areas where winter crops are irrigated and will cause the cost per acre foot to be overstated for these same areas.
4 Insufficient information.
areas and competitive areas can switch more easily to other transportation.
The air freight rates applicable to California cut flowers are intended to correct the directional imbalance of in-and-out movement of easterly and northerly traffic.
With the introduction of jet air cargo carriers-around 1962-the imbalance may reappear and directional rates will need readjustment.
Lower jet carrier rates might divert freight from other transportation so the new freight capacity could be utilized fully in both directions.
In such a case, any future freight reduction is apt to be general rather than
 based on directional imbalance.
California producers might benefit by a straight percentage reduction, but the differentials probably would be too small to influence the competitive position significantly.
For example, a 10% reduction on the Los Angeles-New York rate of $19.65 would amount to $1.96, and the Miami-New York rate of $13.80 would be reduced by $1.38.
It is doubtful that the demand for cut flowers or the competitive position of California growers would be improved solely by reduced air freight rates.
Factors leading to the present supply-demand situation probably started when the high profits just after World War II attracted new areas into flower production and
 expanded the production of existing growers.
Improved methods-such as low cost cooling-heating systems in greenhouses-increased production, but also reduced the cost and climatic advantages of California growers.
The California cut flower industry must examine packaging and other cost components to discover the most efficient marketing methods, because lower air frieght rates alone will not provide an answer to the competitive problems in out-of-state markets.
W.
Miklius is Junior Specialist in Agricultural Economics, University of California, Los Angeles.
D.
B.
DeLoach is Professor of Agricultural Economics, University of California, Davis.
Continued from preceding page
 the wells-including casing diameter and thickness, depth of well, depth of casing, extent of gravel packing and casing perforationwere priced at the rates currently charged by well drillers.
Investments in pumps and accessories were determined from current list prices supplied by manufacturers.
Costs of pumping plant equipment have risen rapidly in the past few years.
Therefore, the prices used in this study overstate the cost of pumping plants installed at earlier dates.
The amount of such overstatement is reflected by the wholesale price index for electrical machinery and equipment, which has increased from 96.1 in 1947 to 154.5 in 1959 on the base period of 1947-49 as 100%.
Pump discharge, plant efficiency and electric energy-in kilowatt hours-per acre-foot were adjusted for the seasonal drawdown of the pumping level in the wells.
The total energy bill was determined by assuming one-fourth of the water was pumped in the spring when the water table was high, one-half from a lift midway between the seasonal high and seasonal low, and one-fourth in the late summer and early fall when the water table was low.
The investment and annual per acrefoot costs of pumping water in the 16 hydrographic areas ranged from a low of $2.40 per acre-foot in area A at the northern end of the valley to a high of $22.63 per acre-foot in area P, the west side of Fresno and Kings counties.
How costs were determined is illustrated by area D, where the total pump
 lift is 62.7' with a discharge of 1,084 gallons per minute at the midpoint during the pumping season.
The seasonal drawdown is 20'; in the spring the total lift is 52.7' and late in the season the lift is 72.7'.
That change in head gave a spring discharge of 1,284 gallons per minute and a fall discharge of 885 gallons per minute.
To determine the number of acrefeet pumped it was assumed that the pump had a service area equal to one acre for each nine gallons per minute of discharge at midseason and the area irrigated with 31 acre-inches of water under a farm irrigation efficiency of 86% or 36 acre-inches of water per acre pumped.
The assumption was for the irrigation of summer crops only.
In areas such as the Westside-Fresno and Kings counties-where a large share of the land is in winter barley, the total acre-feet pumped would be as much as one-third greater.
The greater volume would have a marked effect upon the unit cost of pumping water by spreading the heavy fixed charges over more units.
For example, if the acre-feet pumped on the west side were increased by one-third, the cost per acre-foot would drop to $18.38 compared to the $22.63 shown in the table.
Area D experiences ground water overdraft at the rate of about 3' per year.
Therefore, an additional average annual cost equal to 4% of the new pump cost was charged to cover lowering of bowls and other capital improvements associated with the lower water table.
For area D, the well life was estimated at 15 years and the pump life at 20 years.
Total annual depreciation was calculated by summing the two initial costs, less salvage value of the motor, and dividing by the estimated life.
Interest was calculated at 6% of mid-value and insurance and taxes at 2.5% of mid-value.
Repair costs were estimated at 2% of new pump costs for areas with a pump lift of less than 100' and 3% for areas with lifts of more than 100'.
The wide differences in ground water conditions among the subareas in the valley cause sharp variations in the cost per acre-foot of water pumped.
Low water cost areas have a definite economic advantage when other factors, such as yields, climate, and land values, are held constant.
The effect of the seasonal supply and cost of surface water will be explored in detail in further studies.
Charles V.
Moore is Assistant Research Agricultural Economist, University of California, Davis.
Trimble R.
Hedges is Professor of Agricultural Economics, University of California, Davis.
Speakers from academia, nonprofit organizations, government agencies and private industry, as well as growers from around the world, will share best practices and advances in science, technology and policy that are helping to achieve greater food security with less pressure on scarce water resources.
The conference includes collaborative sessions developed with key partners of the Daugherty Water for Food Global Institute, including the International Water Management Institute, The World Bank, the Food and Agriculture Organization of the United Nations, the National Drought Mitigation Center, the United States Department of Agriculture, the International Food Policy Research Institute, the Environmental Defense Fund, the Nature Conservancy and the World Wildlife Fund, among others.
Dr.
Brent Black, USU Extension Fruit Specialist, Dr.
Robert Hill, USU Extension Irrigation Specialist, and Dr.
Grant Cardon, USU Extension Soils Specialist
 Proper irrigation of caneberries  is essential to maintaining a healthy and productive planting.
Over irrigation slows root growth, increases iron chlorosis on alkaline soils, and leaches nitrogen sulfur and boron out of the root zone leading to nutrient deficiencies.
Excessive soil moisture also promotes root rot, particularly in raspberry.
Applying insufficient irrigation water results in drought stress.
Drought stress during fruit development results in reduced fruit size and yield, and poorer fruit quality.
Drought stress also reduces primocane vigor and flower bud development, which then negatively affects the following season's crop.
Properly managing irrigation is analogous to managing a bank account.
In addition to knowing the current bank balance , it is important to track both expenses  and income.
Bank Balance 
 How big is my bank account?
Water holding capacity
 Field Capacity is the maximum amount of water that can be held in the soil after excess water has percolated out due to gravity.
Permanent Wilting Point is the point at which the water remaining in the soil is not available for uptake by plant roots.
When the soil water content reaches this point, plants die.
Available Water is the amount of water held in the soil between field capacity and permanent wilting point.
Allowable Depletion is the point where plants begin to experience drought stress.
For caneberries, the amount of allowable depletion, or the readily available water represents about
 50% of the total available water in the soil.
The goal of a well-managed irrigation program is to maintain soil moisture between field capacity and the point of allowable depletion, or in other words, to make sure that there is always readily available water.
The amount of readily available water is related to the effective rooting depth of the plant, and the water holding capacity of the soil.
The effective rooting depth for raspberries and blackberries in Utah's climate and soils is typically between 1.5 and 2 feet.
The water holding capacity across that rooting depth is related to soil texture, with coarser soils  holding less water than fine textured soils such as silts and clays.
A deep sandy loam soil at field capacity, for example, would contain 1.2 to 1.5 inches of readily available water in an effective rooting depth of 2 feet.
Figure 1.
Soil water content from saturated to dry.
Optimal levels for plant growth are between field capacity and allowable depletion.
Table 1.
Available water holding capacity for different soil textures, in inches of water per foot of soil.
Available water is the amount of water in the soil between field capacity and permanent wilting point.
Readily available water is approximately 50% of available.
Soil Texture	Available	Readily available 
 	l'	1.5'	2'
 Sands and fine sands	0.5 0.75	0.25 0.38	0.4 0.6	0.5 0.75
 Loamy sand	0.8 1.0	0.4 0.5	0.6 0.75	0.8 1.0
 Sandy loam	1.2 1.5	0.6 0.75	0.9 1.1	1.2 1.5
 Loam	1.9 2.0	0.9 1.0	1.4 1.5	1.9 2.0
 Silt loam, silt	2.0	1.0	1.5	2.0
 Silty clay loam	1.9 2.0	0.9 1.0	1.4 1.5	1.9 2.0
 Sandy clay loam, clay loam	1.7 2.0	0.85 1.0	1.3 1.5	1.7 2.0
 Figure 2.
The amount of allowable depletion, or the readily available water, represents about 50 percent of the total available water.
What's in the bank?
-Measuring Soil Moisture
 In order to assess soil water content, one needs to monitor soil moisture at several depths, from just below cultivation depth , to about 70% of effective rooting depth.
One of the more cost effective and reliable methods for measuring soil moisture is by electrical resistance block, such as the Watermark sensors.
TM These blocks are permanently installed in the soil, and wires from the sensors are attached to a handheld unit that measures electrical resistance.
Resistance measurements are then related to soil water potential, which is an indicator of how hard the plant roots have to "pull" to obtain water from the soil.
The handheld unit reports soil moisture content in centibars, where values close to zero indicate a wet soil and high values represent dry soil.
The relationship between soil water potential and available water differs by soil type.
The maximum range of the sensor is 200 centibars, which covers the range of allowable depletion in most soils.
The sensors are less effective in coarse sandy soils, and will overestimate soil water potential in saline soils.
Remember that allowable depletion is 50% of available
 water, which roughly corresponds to soil water potentials of 25 centibars for a loamy sand soil, and 70 centibars for a loam.
Table 2.
Recommended Watermark TM sensor values at which to irrigate.
Loamy sand	40	50
 Sandy loam	50	70
 Silt loam, silt	70	90
 Clay loam or clay	90	120
 Watermark TM is a registered trademark of Irrometer, Co., Riverside, CA.
Water is lost from the planting through surface runoff, deep percolation , evaporation from the soil surface, and transpiration through the leaves of the plant.
Of these, the biggest losses are typically due to evaporation and transpiration, collectively known as "evapotranspiration" or ET.
Estimates of ET are based on weather data, including air temperature, relative humidity and wind speed.
Some weather stations in Utah are programmed to calculate and report the ET estimates for alfalfa as a reference crop.
The ET of your crop can be determined by multiplying the ET, by a correction factor or crop coefficient  that is specific to your crop and its stage of development.
The Kcrop for raspberry and blackberry are shown in Figure 3.
At budbreak , cane berries are using about 15% of the amount of water used by the
 alfalfa reference crop.
Water use increases until full bloom and fruit set  when water use is 101% of a reference alfalfa crop.
By leaf senescence in the fall , water use has decreased to 80% of the reference crop.
Table 3.
Typical weekly alfalfa reference evapotranspiration  values for Utah locations.
Location	May	June	July	August
 Laketown	1.35	1.74	1.91	1.68
 Logan	1.38	1.83	1.94	1.68
 Ogden	1.48	1.98	2.10	1.80
 Spanish Fork	1.48	1.94	2.08	1.74
 Cedar City	1.57	1.95	2.04	1.74
 St.
George	1.95	2.40	2.53	2.02
 Income Irrigation and Rainfall
 In Utah's high elevation desert climate, rainfall contributes a small fraction of the in-season water requirements of the crop.
Therefore, regular irrigation is needed to supply orchard water needs.
Irrigation water can be supplied by overhead sprinklers, drip lines or microsprinklers.
Flood and furrow irrigation are not typically recommended for raspberry, due to sensitivity to water-borne pathogens that cause root rot.
Overhead
 sprinklers should also be used with care during fruiting, as excessive wetting can lead to fruit rot.
When using overhead irrigation, watering cycles should be completed early enough in the day to allow for adequate drying of the leaves and fruit.
During hot summer weather however, overhead irrigation can give some evaporative cooling of the leaves and fruit.
Whichever irrigation system you utilize, it is important to calibrate your system SO that you know precisely how much water is being applied.
With sprinklers and microsprinklers, the simplest way to do this is to place catch cans in multiple locations in your planting and collect water for a set period of time.
The amount of water collected over time will give you an application rate , and differences in water collected among the catch cans will tell you how uniform the application is within your planting.
When trying to determine application uniformity, it is best to measure output at both ends of your irrigation system.
Also, if your planting is on a slope, you should measure output at the highest and lowest points of your field.
Elevation differences and the distance the water travels through the irrigation lines both affect water pressure, and consequently the flow rate at the nozzle.
If you have trickle irrigation, you can place catch cans under the emitters and determine flow rate for each emitter.
Flow rate from each emitter and emitter spacing can be used to calculate rate per area.
The efficiency of your system is a measure of how much you have to over water the wettest spots of the planting to get adequate water to the dry spots.
Efficiency is related to the uniformity of application and to the amount of evaporation that occurs before the water can move into the soil.
A well-designed microsprinkler or drip system can be 70 to 90% efficient.
Overhead sprinkler systems are typically 60 to 75% efficient, while flood and furrow irrigation is typically 30 to 50% efficient.
Following is an example of how to calculate water needs for a mature summer-bearing red raspberry planting on a deep sandy loam soil, just after fruit harvest.
ETr values are 2.10 inches per week.
Crop coefficient is 0.95.
ETcro = ET, X Kcrop
 = 2.10 inches/week * 0.95 = 2.00 inches/week
 Soil storage capacity 
 The total storage capacity for readily available water over the effective rooting depth is 1.2 inches.
o 1.2 inches / 2.00 inches per week = 0.6 weeks or 4.2 days between irrigations
 The soil moisture in the rootzone will go from field capacity to plant stress levels in 4.2 days.
To recharge the soil profile, you will need to apply 1.2 inches of water.
Assuming a microsprinkler irrigation system with an efficiency of 90%, 1.33 acre inches of water will be required per acre for each watering.
Good irrigation management requires:
 1.
An understanding of the soil-plant-water relationship
 2.
Properly designed and maintained irrigation system, and a knowledge of the efficiency of the system
 3.
Proper timing based on
 a.
Soil water holding capacity
 b.
Weather and its effects on crop demand
 C.
Stage of crop growth.
Each of these components requires a commitment to proper management.
Proper management will lead to the maximum yields per available water and will optimize the long term health and productivity of your planting.
Utah State University is committed to providing an environment free from harassment and other forms of illegal discrimination based on race, color, religion, sex, national origin, age , disability, and veteran's status.
USU's policy also prohibits discrimination on the basis of sexual orientation in employment and academic related practices and decisions.
Utah State University employees and students cannot, because of race, color, religion, sex, national origin, age, disability, or veteran's status, refuse to hire; discharge; promote; demote; terminate; discriminate in compensation; or discriminate regarding terms, privileges, or conditions of employment, against any person otherwise qualified.
Employees and students also cannot discriminate in the classroom, residence halls, or in on/off campus, USU-sponsored events and activities.
This publication is issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Noelle Cockett, Vice President for Extension and Agriculture, Utah State University.
Beating the Heat: A Statewide Assessment of Drought and Heat Mitigation Practices  with Oregon Farmers and Ranchers
 Oregon State University Extension Services prepared this report per section 17 of SB 5561.
The results presented here are intended to provide insights to the state legislature on what farmers and ranchers are currently doing to manage drought and heat and how to best support them in mitigating these pressures moving forward.
These results are also intended for farmers and ranchers, in the hopes that they may glean useful insights from other producers actively working to manage drought and heat.
Lead Author: Berit Dinsdale, Ph.D.
Project Supervisors and Co-Contributors: Mara Zamora Re, Ph.D.
and Abigail Tomasek, Ph.D.
In addition to the farmers and ranchers that made this assessment possible, the authors also would like to thank the following individuals and their associated organizations for their time and assistance:
 Ashley Rood, Megan Kemple, and Andrew Collins-Anderson, Oregon Climate and Agriculture Network 
 Brittney Deming, Friends of Family Farmers 
 Lisa Kilders, Clackamas SWCD
 Ellen Hammond, Jefferson SWCD
 Michelle Smith, University of Oregon School of Law
 Kelly Delpit, Sustainable Northwest
 Greg and Malia Kupillas, Pacific Hydro-Geology Inc.
Finally, a big thank you to all of the OSU faculty and staff that contributed to this project for their outreach, insights, and support.
Farmers and ranchers across Oregon are increasingly facing challenges related to extreme drought and heat.
While emergency funds have been made available to producers impacted by these pressures in recent years, their recurrence indicates the need for both pre-emptive and longer-term solutions.
The Oregon State Legislature requested that Oregon State University Extension Services conduct a statewide needs assessment with Oregon farmers and ranchers to pursue this goal.
This report provides an overview of what actions are already being taken by producers to manage drought and heat and what resources and support they need to become more resilient in the face of these challenges.
This project began in the spring of 2022 with an evaluation of drought and heat-related projects already in progress and the identification of prospective collaborators.
The team then worked to recruit and interview 59 farmers and ranchers over the next seven months.
Project participants spanned all regions, commodities, and operation sizes in Oregon.
This process resulted in a generalized assessment of current drought and heatrelated mitigation practices, obstacles, and resource needs.
The results of this assessment are presented here.
IRRIGATION INFRASTRUCTURE AND MANAGEMENT
 Irrigation Systems in Use.
Project participants had mostly already adopted the highest efficiency irrigation systems possible for their operation's needs.
Obstacles to upgrading to higher efficiency systems for those who had not were predominantly related to cost, the need for overhead for frost and heat protection, and a lack of compatibility of higher efficiency systems with certain commodity types.
Water storage was also an essential component of many producers' systems.
Costs to develop storage, permitting obstacles, and a lack of water were all challenges to increasing water storing capacity.
Assistance with upgrading systems, financial support to integrate remote monitoring and automation, and moderated energy rates were suggested as potential pathways to support producers.
Irrigation Management Strategies.
As participants face water curtailments, many have to make difficult decisions about allocating their limited water supply.
For some producers, this has meant allocating water to only the highest-value fields.
In contrast, for others, it has meant spreading more limited water over the entire operation.
Producers also increase water applications in extreme heat events, which poses obvious problems when drought conditions accompany heat.
Participants with groundwater rights are also digging deeper or drilling new wells to access water tables when permitted.
Costs and regulations are the main obstacles to pushing limited groundwater resources further.
Off-Farm Irrigation Infrastructure.
In central, eastern, and southern Oregon, off-farm infrastructure improvements were recommended to manage drought pressures.
However, there was a lack of consensus among producers regarding the relative costs and benefits of decreasing evaporative losses by replacing irrigation ditches with buried pipe.
On-going large-scale reservoir and water storage projects are being discussed in eastern Oregon.
Producers expressed frustration, however, at the speed of the projects' progress and the perceived lack of compromise from government groups.
SOIL, COMMODITY, AND ECOSYSTEM STRATEGIES
 Ecosystem Management.
Silvopasture, riparian restoration, and enhancing ecosystem biodiversity were all approaches used by participants to engender increased on-farm resilience to drought and heat.
Ecosystem management was also seen as a pathway to avoiding wildfire hazards.
Soil Management.
One of the most common approaches to increasing on-farm resilience was soil health management through reduced or no tillage, composting or mulching, soil moisture monitoring, cover cropping, and rotational grazing.
Obstacles to these practices often involved accessing equipment or necessary materials and interpreting soil-related data to inform appropriate actions.
Commodity Management.
Adapting planting and harvest times, transitioning to new varieties, and transitioning to new crops are all strategies being implemented by producers.
Participants also noted utilizing non-irrigation techniques such as shading and intercropping to manage heat pressures.
Other strategies included experimenting with new cultivation strategies , using weather stations to make management decisions, reducing or limiting production size, or leaving or stopping farming.
The main obstacles associated with commodity management included loss of income, cost of shading equipment, and untenable risk to transition to new production systems.
Data Resources and Needs.
Data resources for producers were primarily OSU and OSU Extension Services and farmer-to-farmer information networks.
Data needs focused on translating climate and moisture-related data into actionable items, researching drought and heat-resistant varieties, and context-specific data informed by financed on-farm trials.
Producers also noted a disintegration of farmer-to-farmer networks, which limited community-based information exchanges.
Funding Resources and Needs.
While funding programs were extremely well utilized, producers noted that funding systems could be challenging to navigate, and application processes were often extensive and had slow turnaround times.
Participants also suggested that more grants be made available for those already exhibiting efficient water use rather than only be provided to those seeking to improve efficiency.
It was also recommended that services be expanded to improve application assistance and turnaround times and that cost-share parameters be updated to account for inflation and increased losses due to drought and heat.
ADDITIONAL OBSTACLES AND PATHWAYS FORWARD
 Conflicting Uses.
Project participants suggested conflicting uses with wildlife, recreation, and urban users were an obstacle to on-farm drought and heat resilience.
It was also common, however, for participants to express concern about preserving wildlife habitat and protecting vulnerable species.
Participants suggested more straightforward and transparent communication on the data used to make decisions and ongoing mediated conversations and planning.
Inclusion and Applicability.
Farmers and ranchers appreciated being included in this assessment and suggested the ongoing inclusion of agriculturalists in policy-making and more nuanced and context-specific research and policies.
Potential next steps could include the creation of locally-based teams with farmers/ranchers and experts from various disciplines  to address locally-specific drought and heat-related problems and solutions.
Other Policy-Related Issues and Potential Solutions.
In addition to concrete actions such as increased costsharing and relaxed water-related regulations, participants suggested clear and honest communication, mediated talks and workgroups between stakeholders, and ongoing multi-organization collaborations to achieve on-farm drought and heat resilience.
Chapter 1: Introduction and Project Overview
 How to Read This Report
 Phase I: Project Design, Project Identification, and Inter-Organizational Collaborations
 Phase II: Participant Recruitment and Data Collection
 Phase III: Data Analysis
 Chapter 2: On-Farm Irrigation Systems
There are over 107,000 registered irrigation wells in the state.
Eighty percent of the states public drinking water and private water supplies come from groundwater sources.
But Nebraskas water is not confined to the states borders.
Surface water enters the state as stream flow and precipitation, and the water that isnt used here might flow into other states.
Guayule Cultivation and Irrigation Methods for the Southwestern United States
 As water becomes scarce in Arizona there is a desire by growers to grow crops that use less water.
With hundreds of acres already planted across the state and the plan to scale to 10,000 acres over the course of three years, guayule has become a more water wise crop than traditional desert row crops like silage corn, alfalfa, and cotton.
In this guide, cultivation and irrigation methods will be discussed to increase area under guayule across the state.
Guayule  is a perennial shrub, native to the desert north-central Mexico and southwest Texas., It produces high quality natural rubber that is suitable for use in passenger and commercial-grade tires.
The latex is hypoallergenic, desirable in the medical device market , and resin can be used in a variety of industrial products such as adhesives and coatings.
The primary parts of the guayule plant of economic interest are in the parenchyma tissues of the stems and roots
 where most of the rubber particles accumulate.
However, stems and roots only constitute about 6 and 9% of the total plant dry weight, respectively.
Research has shown the best seeding method is to plant in 40"-rows using a pneumatic small seed planter.
Seeding in dry, raised beds is recommended, 10" wide and 6.0"8.0" high.
After two years of growth, in early trial plots in Arizona  reported that out of 6 cultivars registered to be grown in Arizona, AZ2 and AZ6 had the highest rubber yield.
The AZ2 line is an interspecific hybrid with good seedling vigor and high biomass production.
AZ6 has less biomass than AZ2 but produces higher rubber content..
Flood, solid-set sprinkler, and gravity drip irrigation methods have been used for germination.
Soil surface should be kept wet for about 5-10 days after planting for
 seedling germination, as recommended by Dissanayake et al..
After germination, guayule seedlings should be kept well-watered by irrigating several times during the next seven weeks using level furrow irrigation , a common surface irrigation method used in the Arizona.
Nitrogen, water use, and tolerance to drought
 Guayule can be grown with moderate nitrogen applications ranging from 58 to 89 lb N/ per year.
It can be injected into the water  to guarantee even distribution across the entire field.
Cotton and silage corn for example requires about 200 lb N/ac.
The amount of water required for germination of direct seeded guayule ranges from 6-15 inches , depending on weather and the irrigation method.
An example of the irrigation amounts, and number of events are given in Table 1.
The flood irrigation data is based on a field study conducted by Elshikha et al., 2022.
The table indicates small difference in water use 6.3"-6.8") during germination with sprinkler and gravity drip.
However, germination under flood required more than twice  compared to drip and sprinkler.
Once established, flood irrigation can be used at a rate of 4.0"5.8" per event.
There are two irrigation events per season, in spring, summer and fall of the first year.
In the second year, one of the two irrigations during fall may be skipped.
No irrigation is required during winter as the plants go dormant.
The annual water required under flood and drip irrigation is approximately 2.5-2.9 year with the irrigation schedule in Table 1, which is within the probable annual water allocation depth for many Central Arizona growers.
The flood irrigation in Table 1 represents a deficit treatment in our recent irrigation study, where we skipped every other irrigation.
In this treatment, crop was irrigated approximately every six weeks in summer, which was half the recommended rate for clay soil.
No reduction in rubber production was observed in this treatment.
This implies that cycles of wetting and drying maybe advantageous for rubber production.
The drip irrigation data draws upon a previous study conducted by Elshikha et al.
in 2021, with an adjustment to the irrigation frequency.
The deficit irrigation study showed that guayule fared well with no detrimental effect other than decreased growth during the hottest and driest summer on record with no irrigations between June and September.
With water shortage, and the uncertainty of water supply in some areas, growers may be forced to cut irrigations for several months.
Under such circumstances the guayule crop will be an adequate fit, as they begin to grow when water is applied.
Guayule is a drought tolerant crop and can survive extreme moisture stress in the desert south-west, where it remains in a semi-dormant state, until irrigation is resumed.
Its ability to survive long periods of drought comes from the capability of its roots to extract moisture from the lower depths of the soil profile.
Previous research indicated that even though guayule can withstand long periods of drought, well-watered guayule grown from transplants can have cumulative crop evapotranspiration  of over 59 inches during its first year of growth, and
 Table 1.
Irrigation for guayule grown in Arizona 
 Flood	Drip	Sprinkler	No.
of events
 growth				F	D	S
 Germination	5	0.79	0.85	3	8	8
 Spring	5.1	0.50	2	11	May
 Summer	4.0	0.40	2	22	June-Aug.
Fall	5.5	0.50	2	22	Oct.-Nov.
Spring	5.8	0.55	2	22	Mar.-May
 Summer	5.1	0.50	2	22	June-Aug.
Fall	5.4	0.50	1	11	Oct
 Total 	71.4	60.2
 over 79 inches during its second year.
In these studies, when total water applied either matched or exceeded ETc requirements, gave the highest biomass production.
Guayule growers in the U.S.
Southwest will likely not meet 100% of ETc.
When grown on lighter soils, literature indicates an irrigation deficit of 20-25% from full ETc would not reduce rubber yield significantly.
However, on heavier soils there appears to be a greater opportunity to reduce irrigation.
A field study on a heavier soil type in central Arizona, Elshikha et al., 2022, indicated that exposing direct-seeded guayule to a pre-determined soil water deficit periods, over a 23 monthlong growing season, did not reduce the yield significantly, compared to fully irrigated guayule.
As water efficiency becomes more important to Arizona, growers will resort to produce more with less.
With a severe reduction in water stored in Lake Mead, as inflow rates of Colorado river water slows, growers will mine finite groundwater.
Guayule is a water wise and profitable crop that provides an in-demand domestic source of elastic and rubber goods.
Planting guayule will be one way to avoid the field going fallow during extended drought in the Southwest region of the United States.
NOTE: Information about guayule seeds and planting methods can be obtained from Bridgestone Americas, Inc.
at 4140 West Harmon Rd, Eloy, Arizona 85131.
Matthew C.
Burnette and Carmen T.
Agouridis, Biosystems and Agricultural Engineering
 What is Streambank Erosion?
Streambank erosion refers to the removal of soil and other material, such as rock and vegetation, from the streambank.
Streambank erosion is a naturally occurring process, but the rate at which it occurs is often increased by anthropogenic or human activities such as urbanization and agriculture.
Changes in land use can cause streambanks to erode at rates much faster than those seen in natural, undisturbed systems.
What Causes Streambank Erosion?
Streambank erosion occurs when the driving forces of water  and gravity  are greater than the ability of the streambank to resist them, thus resulting in a failure.
A hydraulic failure occurs when the flowing water from the stream directly hits the streambank.
A geologic failure occurs when an overhanging bank collapses due to gravity.
Activities both at the watershed  as well as the stream or reach scale  can cause streambank erosion to occur.
Urbanization is a large-scale activity that results in an increase in the amount of impervious surfaces such as parking lots, buildings and roads within a watershed.
Impervious surfaces prevent water from infiltrating or soaking into the soil SO more rainfall during storm events becomes runoff, which in turn flows to streams.
Consquently, streams in urbanized watersheds transport a
 Figure 1.
Streambank erosion occurs when soil is removed from the banks.
Photo: David Collett, University of Kentucky, Robinson Center for Appalachian Resource Sustainability Figure 2.
Hydraulic failures occur when flowing water erodes streambanks.
Photo: Matthew Peake, University of Kentucky, Animal Research Center
 Figure 3.
The collapse of overhanging banks is an example of a geologic failure.
much larger volume of stormwater than streams in undeveloped watersheds.
Larger volumes of stream flow mean that the waters in these streams are deeper.
Deeper waters mean increased levels of stress on the bed and banks, which in turn means higher streambank erosion rates.
At the reach scale, streambank erosion is increased largely by activities that impact riparian vegetation, soil stability, and channel sinuosity.
Riparian vegetation with dense roots that extend the full length of the stream bank offers the greatest protection against streambank erosion.
Mowed grasses offer little protection as their roots are typically short.
Livestock and vehicles entering and exiting streams can accelerate streambank erosion , SO stream crossings should
 Figure 4.
Livestock trample streambanks, SO their access to streams should be controlled.
be constructed.
Changes in channel sinuosity or curviness can occur naturally or may be human induced.
For example, the practice of straightening streams increases streambank erosion.
Streams may be straightened to increase the accessibility of lands , but the practice often results in a shorter stream.
Since the same drop in elevation must occur over a shorter distance, the stream becomes steeper, which in turn increases stress on the stream's banks and bed and thus streambank erosion.
Why Is Streambank Erosion Problematic?
Photo: Jim Hanssen, EcoGro
 Streambank erosion is problematic for a number of reasons.
When streambanks erode, valuable land, such as crop or livestock fields, is lost.
Critical infrastructure such as bridges, roads, and underground utilities may be damaged.
Eroding streambanks are often a safety concern for humans, livestock and wildlife.
Overhanging banks can collapse from the weight of a person or animal.
Streambank erosion also negatively impacts water quality largely by increasing the amount of suspended sediment in the stream water.
When suspended sediment levels in streams are high, aquatic life suffers as the amount of suitable habitat is reduced.
Suspended sediments cause the water to become turbid or cloudy making it difficult for aquatic life such as fish to breathe and find food.
When sediments begin to settle out, they can cover and fill in the spaces around rocks, reducing the places aquatic life can live and reproduce.
Studies have shown that streambank erosion accounts for a large portion of the suspended sediment load in streams, in some cases as much as 90 percent.
Figure 5.
Streambank erosion threatens infrastructure.
Photo: Eric Dawalt, Ridgewater, LLC
 Figure 6.
Streambank erosion can pose a safety hazard.
How Are Streambanks Stabilized?
Streambanks are stabilized largely through one or a combination of the following methods: 1) providing floodplain access, 2) establishing a dense cover of deep-rooting riparian vegetation, and/or 3) redirecting stream flows away from the streambanks and towards the center of the channel.
One of the main reasons streambank erosion occurs is a lack of floodplain access.
Streams with low levels of streambank erosion often have good access to their floodplains.
This means that the waters in the channel regularly, typically once per year on average, spill out onto the adjacent lands or floodplain.
Such streams have low bank heights, meaning that water depths and hence stress remains low.
For streams with high banks, floodwaters rarely escape the confines of the channel.
Such streams are considered incised.
Because waters become deep with incised channels, stresses and erosion potential are high.
One way to reduce streambank erosion is to create floodplain access.
For streambank stabilization projects, floodplain access is often created by excavating a small floodplain.
In some instances, large-scale efforts such as stream restoration are needed.
Stream restoration involves the re-establishment of the structure and function of a stream as closely as possible to pre-disturbance conditions.
Figure 7.
Streams with good floodplain access have less potential for erosion.
Figure 8.
Streams with poor floodplain access have a high potential for erosion.
Figure 9.
Excavating a new floodplain is one way to create floodplain access along the stream.
Figure 10.
A stream before  and after  restoration.
Riparian zones or buffers are sections of land that border water bodies such as streams, rivers and ponds.
These zones serve as the transition from the aquatic environment to the uplands or terrestrial environment.
While riparian buffers can consist of one vegetation community, often riparian buffers include a zone of fast-growing and water tolerant trees , a zone of shrubs , and a zone of grasses and forbs.
A common and cost-effective method for reducing streambank erosion is to plant vegetation with deep, thick root systems such as trees in riparian zones, especially along the streambanks.
Some vegetation, such as dogwoods and willows, can be planted using live stakes.
Live stakes are dormant, unrooted plant cuttings that can be driven into the streambank.
Once planted, they will begin to develop roots.
Due to their low cost and ease of implementation, live stakes are an attractive option for landowners seeking to reduce streambank erosion.
Another option is to use containerized plants, though the cost is higher.
Photo: Eric Dawalt, Ridgewater, LLC
 A live stake is a piece of live hardwood material from a woody species of plant.
Live stakes are cut to specific lengths depending on soil and site conditions but should be at least 0.5 in.
in diameter and 18 in.
in length.
When harvested, the plant material is usually in a dormant state.
When selecting live stake species, a quick growth rate and a dense root mat are essential.
Commonly used species include black willow  and silky dogwood.
Live stakes are often planted on the outside of meander bends where shear stress is highest.
Photo: Christopher Barton, University of Kentucky, Department of Forestry
 Streambank soil bioengineering is the practice of using plant material  to stabilize streambanks.
Both engineering practices and ecological principles are used as the plant material provides structural support as well as habitat benefits.
Because of the use of plant material, streambank soil bioengineering is often referred to as "soft" engineering.
The National Engineering Handbook contains detailed information on a variety of streambank soil bioengineering techniques.
For additional information on streambank soil bioengineering, contact your local University of Kentucky Cooperative Extension Service office or Natural Resources Conservation Service  office.
"Hard" engineering, often termed armoring, refers to the practice of stabilizing streambanks using hard structures made of rock, concrete or metal.
Examples of hard engineering techniques include rip-rap and gabion baskets.
Rip-rap is large rock that is placed on the streambanks to prevent bank erosion.
Gabion baskets are wire baskets that are filled with rock.
Because gabion baskets hold the rock in place, they are used when the available rock material is too small to withstand the erosive power of the stream.
Because of the amount of rock, concrete and/or metal required, hard engineering techniques are often costly to install and maintain.
Unlike soft engineering, hard engineer-
 ing techniques offer little in the way of habitat improvement.
Instream structures help reduce streambank erosion by redirecting the flowing water away from the streambanks and toward the center of the channel.
Examples of instream structures include vanes such as crossvanes, single vane arms, and J-hooks.
Such structures are often constructed using large rock, although logs can be used.
The National Engineering Handbook contains detailed information on instream structures.
For additional information on instream structures, contact your local University of Kentucky Cooperative Extension Service office or Natural Resources Conservation Service  office.
What Technical Expertise Is Needed?
Reducing streambank erosion can be a complex process requiring an understanding of engineering, hydrology, hydraulics, soils, vegetation and construction management.
Therefore, landowners should consult their local University of Kentucky Cooperative Extension Service office or Natural Resources Conservation Service  office for assistance.
Prior to grading streambanks or installing instream structures, it is important to determine if any federal, state or local permits are required.
Contact the U.S.
Army Corps of Engineers to inquire about any necessary federal permits.
Contact the Kentucky Division of Water regarding state-level permits in Kentucky.
Consult local agencies such as city and/or county governments regarding local permit requirements.
Note that the permitting process can take several months to complete.
Photo: Jim Hanssen, EcoGro
 Figure 11.
Streambank soil bioengineering uses living and nonliving plant material to stabilize streambanks.
Figure 13.
Gabion baskets are wire mesh baskets filled with rock.
Figure 12.
Rip-rap is a common form of "hard" engineering to reduce streambank erosion.
Figure 14.
Instream structures such as this cross vane help reduce streambank erosion by redirecting flows to the center of the channel.
Further Reading Stream Crossings for Cattle  Restoring Streams  Living Along a Kentucky Stream  Planting a Riparian Buffer  Planting Along Your Stream, Pond, or Lake 
Seasonal Water Needs and Opportunities for Limited Irrigation for Colorado Crops
 Fact Sheet No.
4.718
 by J.
Schneekloth and A.
Andales*
 Crop water use, consumptive use and evapotranspiration , are terms that are used interchangeably to describe the water that is consumed by a crop.
This water is mainly used for cooling purposes; a negligible amount is retained by the crop for growth.
For more information on ET refer to Fact Sheet No.
4.715.
Water requirements of crops depend mainly on environmental conditions.
Plants use water for cooling purposes and the driving force of this process is prevailing weather conditions.
Different crops have different water use requirements, under the same weather conditions.
Crops will transpire water at the maximum rate when the soil water is at field capacity.
When soil moisture decreases crops have to exert greater forces  to extract water from the soil.
Usually, the transpiration rate doesn't decrease significantly until the soil moisture falls below 50% of available water capacity.
Knowing seasonal crop water requirements is crucial for planning your crop planting mixture especially during drought years.
For example, in the Greeley area, the seasonal water use of sugar beets is 27.1 in.
while corn uses only 23.9 in.
of water.
That means, to fully irrigate sugar beets you need to apply 13% more water as compared to corn.
These water requirements are net crop water use, the amount that the crop will use  in an average year, given soil moisture levels didn't fall below critical levels.
Under ideal conditions this net water requirement is reduced by the effective rain, which for the Greeley area is 6.5 inches for the growing season and effective stored soil moisture at
 the beginning of the season.
Beginning soil moisture will also supply some water for ET.
If soils are at field capacity at planting, 50% of that water holding capacity in the effective root zone is useable by the plant.
A sandy loam soil holds approximately 1.4 inches per foot of soil.
Assuming field capacity and a 3 foot effective root zone, a sandy loam soil will supply 2.1 inches of moisture.
If soil moisture is less than field capacity at planting, that moisture must be supplied by irrigation.
Net Crop Water Requirement
 Net crop water requirement is estimated using models, which are based on weather data.
Seasonal crop water requirement can be estimated using these models by averaging weather conditions for many years, creating an average weather year.
Tables 1 and 2 are a summary of net water requirements of different crops and effective precipitation for different locations in
 Knowing seasonal crop water requirements is crucial for planning your crop mixture.
Net crop water requirements are estimated using models, based on weather data.
To irrigate for the greatest return, producers need to understand how crops respond to water, how crop rotation enhances water availability, and how changes in agronomic practices affect water needs.
*J.
Schneekloth, Colorado State University Extension water resource specialist, Central Great Plains Research Station, Akron, Colorado; A.
Andales, Colorado State University assistant professor, soil and crop sciences.
9/2009; revised 2/2017.
Table 1.
Estimated seasonal water requirement  in eastern Colorado.
Burlington	Wells	Penrose	Holly	Greeley	Lamar	Ft.
Lupton	Ford	Walsh	lliff	Trinidad	Wray
 Alfalfa	44.1	51.6	46.2	46.3	37.1	49.7	43.5	45.7	59.0	39.2	46.4	36.2
 Grass hay/pasture	29.9	35.2	31.4	31.5	25.7	33.8	29.8	31.0	39.9	26.9	31.5	25.0
 Dry beans	15.7	21.8	19.7	19.3	15.7	20.8	17.7	18.4	24.6	16.9	18.4	16.6
 Corn, grain	26.2	28.2	26.6	26.3	23.9	27.4	25.9	26.5	29.3	24.5	26.7	24.5
 Corn, silage	25.2	27.2	25.6	25.3	22.9	26.4	24.9	25.5	28.3	23.5	25.7	23.5
 Corn, sweet	24.0	25.8	24.3	24.1	21.9	25.1	23.7	24.3	26.8	22.5	24.5	22.4
 Cantaloupe	17.2	23.3	20.8	20.8	17.2	22.3	19.1	20.6	26.2	17.9	20.6	16.4
 Potatoes	24.0	30.0	27.1	26.9	20.2	29.3	25.3	25.5	36.2	21.7	26.3	20.5
 Onion	27.6	31.3	28.5	28.6	24.2	30.2	27.5	28.2	34.1	25.3	28.6	24.2
 Small vegetables	22.7	31.5	28,5	28.2	22.7	30.2	25.4	27.0	36.0	24.1	27.0	23.2
 Sorghum, grain	20.9	28,8	25.7	25.6	20.9	27.4	23.4	24.9	32.7	22.2	24.9	21.0
 Soybeans	22.2	26.0	23.2	23.3	18.7	25.0	21.9	23.0	29.7	19.7	23.3	18.2
 Spring grains	22.6	30.6	24.7	25.8	20.6	27.7	23.0	23.4	36.7	24.8	24.3	18.9
 Sugar beets	33.7	37.9	35.0	34.7	27.1	37.3	32.8	34.9	43.6	29.0	35.3	28.4
 Wheat, winter	18.7	19.0	19.0	18,5	17.9	19.1	18.4	19.2	19.8	17.9	19.2	15,5
 Av.
Precipitation	10.3	9.1	6.4	8,3	8,6	9.2	4.6	6.2	8,5	10.9	6.1	10.4
 Summer Crops	8.1	7.8	5.2	7.0	6.5	7.8	3.6	5.1	7.4	8.7	5.1	7.2
 Winter Wheat	6.8	6.3	4.6	6.6	5.4	6.4	5.8	4.9	7.0	6,5	5.2	7.4
 Figure 1: Yield VS.
ET relationship for several irrigated crops.
Figure 2: Generalized Yield VS.
ET and Yield VS.
Irrigation production functions.
eastern Colorado and western Colorado, respectively.
To figure the net irrigation requirement subtract the effective rain  and available stored soil moisture from the net crop water requirement.
The gross irrigation water requirement is the net irrigation requirement divided by the irrigation system efficiency.
For example, corn for grain in Burlington requires 26.2 in.
of water.
Effective precipitation is 8.1 in.
for the season, therefore the net irrigation requirement is 18.1 in.
before soil moisture is accounted
 for.
A silt loam soil will hold 2.2 inches per foot.
Assuming a 3 foot root zone and 50% allowable depletion, 3.3 inches of water are useable and reducing net irrigation requirement to 14.8 inches.
The gross irrigation requirement for a center pivot with 80% irrigation efficiency is 18.5 in.
For a furrow irrigation system with 55% irrigation efficiency the gross irrigation requirement is 26.9 in.
When water supplies are restricted in some way, so that full ET demands cannot be met, limited irrigation results.
Reasons that producers may be limited on the amount of available water include: 1) Limited capacity of the irrigation well In regions with limited saturated depth of the aquifer, well yields can be marginal and not sufficient to meet the needs of the crop; 2) Reduced surface water storage In regions that rely upon surface water, droughts and seasonal fluctuation affect the water allocations available for users.
When producers cannot apply water to meet the crop ET, they must realize that with typical management practices, yields and returns will be reduced as compared to a fully irrigated crop.
To properly manage the water for the greatest return, producers must have an understanding of how crops respond to water, how crop rotations can enhance water availability, and how changes in agronomic practices can influence water needs.
Crop yields increase linearly with the water that is used by the crop.
Crops such as corn, respond with more yield for every inch of water that the crop consumes as compared to winter wheat or sunflower.
High water use crops such as corn require more ET for plant development or maintenance before yields are produced.
Corn requires approximately 10 inches of ET as compared to 4.5 and 7.5 inches of ET for wheat and sunflower.
These crops also require less ET for maximum production compared to corn.
Yield VS.
ET and Irrigation
 In Colorado's semi-arid climate, irrigation is important to increasing ET and grain yields.
Irrigation is used to supplement rainfall in periods when ET is greater than precipitation.
However, not all of the water applied by irrigation can be used for ET.
Inefficiencies in applications by the system result in losses.
As yield is maximized, more losses occur since the soil is nearer to field capacity and more prone to losses such as deep percolation.
Water can be saved by applying less water than is needed for maximum yield.
As seen in Figure 2, a reduction in water applied from point A to point B can save water with little or no yield reduction.
Limited Water Management Reduced Allocations
 When producers are faced with reduced surface water storage, they have three management options that can be utilized.
Producers could 1) reduce irrigated acreage, 2) reduce irrigation to the entire field or 3) include different
 Table 2.
Estimated seasonal water requirement  in western Colorado.
City	Cortez	Mancos	Gunnison	Fruita	Silt	Bedrock	Salida	Walden
 Alfalfa	41.0	37.3	38.4	27.0	44.0	29.3	37.6	36.2	35.1
 Grass hay/pasture	28.0	25.5	26.2	19.1	30.0	21.0	25.5	25.0	24.4
 Dry beans	15.4	18.1	15.4	12.7	18.1	14.6	13.4	14.3	15.1
 Corn, grain	25.5	24.7	24.9	19.5	26.9	20.8	24.6	24.2	23.6
 Corn, silage	24.5	23.7	23.9	18.5	25.9	19.8	23.6	23.2	22.6
 Corn, sweet	22.3	20.3	20.9	14.7	24.0	15.9	20.5	19.7	19.1
 Cantaloupe	17.4	20.3	17.4	12.6	20.3	14.6	16.9	16.3	15.9
 Potatoes	23.1	20.1	20.9	14.2	24.2	16.8	19.0	18.0	19.6
 Onion	26.3	24.7	25.1	19.9	28.0	19.4	24.7	24.4	23.5
 Small vegetables	23.1	26.2	23.1	17.9	26.2	19.8	21.2	21.8	22.5
 Sorghum, grain	21.0	24.5	21.0	16.1	24.5	18.7	20.2	19.5	19.8
 Soybeans	20.7	18.8	19.3	13.6	22.2	14.7	18.9	18.2	17.7
 Spring grains	19.8	18.3	18.4	17.0	22.2	19.0	17.6	19.0	20.3
 Sugar beets	31.6	28.9	29.6	19.4	33.7	19.2	29.3	27.0	25.5
 Wheat, winter	18.8	18.6	18.5	16.1	19.0	9.6	18,9	18.4	16.8
 Av.
Precipitation	6.2	4.0	6.3	4.9	3.6	7.3	9,5	5.3	5.0
 Summer Crops	5.2	3.3	5.2	3.7	3.1	5.5	7.6	4.3	4.2
 Winter Wheat	5.1	5.4	6,9	4.0	4.1	5.2	5,6	4.0	4.6
 ET During Growing Season
 Figure 3: Example of daily ET during the growing season.
crops that require less irrigation.
Option 1 idles potentially productive ground which can be utilized for dryland production, while option 2 reduces yields for the irrigated acres unless precipitation is above normal.
Option 3 incorporates the use of crops that require less irrigation for maximum production and then uses the "saved water" for traditionally irrigated crops.
An example for Wray and a sandy loam soil would be irrigating all corn or irrigating some corn and dry beans.
Corn requires 17.8 inches of irrigation  and dry bean requires 8.6 inches.
If the allocation from the ditch limits a producer to 14 inches of water the producer could raise 80% of their acres to irrigated corn and the remainder in dryland production or idle.
He could also raise 100% of his acres to corn and apply only 80% of the irrigation required for maximum production.
The final option would be that he could raise 40% of his acres to dry bean and 60% of his acres to corn and maintain maximum production on all of his acres.
Limited Water Management Low Capacity Systems
 When managing for maximum production, irrigation systems must have minimum capacities that meet crop water requirements during peak water use periods.
If irrigation system capacities are below what is normally required, reduced yields are expected with normal precipitation.
Management strategies to compensate for low capacity include pre-irrigation and beginning irrigation at higher soil moisture contents.
These strategies may maintain yields in above normal precipitation years but do not help as much in below normal precipitation years.
Management strategies to alleviate this problem include splitting systems into 2 or more crops that have different peak water needs, thus reducing the rate of water requirements during both peak periods.
Crop rotations also spread the irrigation season over a greater time period
 as compared to a single crop.
When planting multiple crops such as corn and winter wheat under irrigation, the irrigation season is extended from May to early October as compared to continuous corn, which is predominantly irrigated from June to early September.
Crops such as corn, soybean and wheat have different timings for peak water use.
With low capacity wells, planting multiple crops with smaller acreages allows for water to be applied at amounts and times when the crop needs the water.
The net effect of irrigating fewer acres at any one point in time is that ET demand of that crop can be better met.
If capacities are increased by splitting acres into crops that have different water timing needs, management can be done to replace stored soil moisture rather than maintaining soil moisture near field capacity in anticipation of crop ET since the system will not meet ET.
Another option is to plant the entire pivot or field to a single crop.
Irrigation management with low capacity systems requires that a producer maintain soil moisture at or near field capacity when ET is less than what the system can apply.
When the ET for the crop is greater than the capacity of the system, plants will use stored soil moisture to maintain ET.
This type of management is necessary to insure that moisture will be available for plants when they reach the reproductive growth phase.
However, if precipitation is less than anticipated, soil moisture may be less than 50% of available water capacity during the reproductive growth stage and yields will be reduced.
Average percent of fields by year fitting into the six categories.
The dry years 2020, 21 and 22 are different than the other years.
In 2020, out of 39 reports, 64% were ranked good, 21% were fair, 0% were wet late, 3% were wet early, 5% were wet all season, and 8% were very wet all season.
The Nebraska Department of Environment and Energy administers chemigator certification.
Individual Natural Resources Districts  inspect and permit the safety equipment that must be in place on an irrigation system before it is used to chemigate.
Chemigation certification lasts for four years.
You can check your certification status online.
EM 8900 Revised March 2013
 Irrigation Monitoring Using Soil Water Tension
 Malheur Experiment Station, Oregon State University: Clint C.
Shock, director and professor; Rebecca Flock, former research aide; Erik Feibert, senior faculty research assistant; Cedric A.
Shock, former research aide; Andre Pereira, visiting professor.
Center for Agricultural Water Research, China Agricultural University, Beijing: Feng-Xin Wang, associate professor
 O ne of the most important tools we have been using at the Malheur Agricultural Experiment Station over the past two decades is the granular matrix sensor , which measures soil moisture.
It is only about 3 inches long and normally is buried vertically in the ground.
Like gypsum blocks, GMS sensors operate on the principle of variable electrical resistance.
The electrodes inside the GMS are embedded in granular fill material above a gypsum wafer.
Additional granular matrix is below the wafer in the fabric tube, where water enters and exits the sensor.
Gypsum dissolved in water is a reasonable conductor of electricity.
Thus, when the sensor contains a lot of water, the electric current flows well.
When there is a lot of water in the soil, there is a lot of water in the sensor.
As the soil dries out, the sensor dries out, and resistance to the flow of electricity increases.
The resistance to the flow of electricity  and the soil temperature are used to calculate the tension of the soil water in centibars.
Soil water tension  is the force necessary for plant roots to extract water from the soil.
Soil water tension reflects the soil moisture status.
The higher the tension, the drier the soil.
Other devices for measuring soil water tension include tensiometers, gypsum blocks, dielectric water potential sensors, and porous ceramic moisture sensors.
What does a granular matrix sensor do for growers?
In the past, growers had to train themselves to guess when the soil was dry enough to warrant irrigation of their crop.
Even with years of experience and well-developed agricultural intuition, it is very difficult to irrigate at the right moment consistently and to apply the ideal amount of irrigation water to maximize crop production.
It would be helpful to have some consistent reference points of SWT for irrigation scheduling.
The digital readout of the GMS
 provides reference points to help growers attain higher yields and better crop quality on their farms.
On a scale of 0 to 100 cb soil water tension, how wet is your field?
Roughly speaking, a GMS reads the following scale of SWT for a medium-texture soil:
 > 80 cb indicates dryness.
20 to 60 cb is the average field SWT prior to irrigation, varying with the crop, soil texture, weather pattern, and irrigation system.
10 to 20 cb indicates that the soil is near field capacity.
0 to 10 cb indicates that the soil is saturated with water.
What new information can a GMS give you?
AGMS can tell you whether the rain last night was really enough to give your onions, for instance, a good drink.
It can tell you whether an overcast day is reducing crop water use in a potato crop enough to delay the next irrigation.
It can tell you whether you will need to irrigate more often in July than in June.
Since the reading comes directly from the crop's root zone, it is a tool designed to provide one more piece of information to your agricultural intuition.
Is scheduling irrigation from SWT really feasible?
We have been using GMS at the Malheur Experiment Station for 26 years, and we can answer with a resounding YES.
There is no replacement for the watchful eye of an experienced grower.
But, imagine a talented stockbroker with great financial logic and intuition.
Does he not excel even more after checking stock quotes on the Internet?
The same is true for the grower.
For example, walking down to your onion field every morning and checking the readout of six or more GMS will help you know when to irrigate the field.
In fact,
 by doing SO you usually can predict irrigations a day or two ahead of time.
Our research has allowed us to determine the threshold SWT of various crops growing on silt loam under different irrigation systems.
We found that irrigating at these critical values has significant benefits to crops.
The SWT irrigation threshold varies not only by crop but also by soil texture, climatic factors, and irrigation method.
The threshold values that maximize marketable yield are known for a wide array of commercial crops growing on different soils under different climatic conditions and irrigation systems.
Let's talk more about how using SWT can MAXIMIZE growers' profits
 Less water used-An irrigation schedule based on a threshold SWT usually results in fewer irrigations per year, as it can help prevent overwatering.
Less pumping energy consumed
 Lower crop stress, which can result in less pest and disease pressure
 Prevention of excessive leaching of mobile plant nutrients, especially nitrogen and boron
 Prevention of groundwater pollution
 Reduced wear and tear on irrigation systems
 From our own experiments, crops that are irrigated according to SWT criteria have higher marketable yield, increased size, and increased produce quality.
How hard is it to collect SWT information?
The GMS can be read in several ways.
One way is with a hand-held Watermark Soil Moisture Meter.
The hand-held meter is used much like a voltmeter and is manually connected to the sensor wires with alligator clips.
It is simple to use, but labor intensive.
You should
 Figure 1.
Variation of soil water tension  over a growing season for furrow-irrigated onions  and sprinkler-irrigated potatoes.
record the data from the meter by hand to make SWT comparisons over time.
For automatic reading and recording of GMS data, dataloggers are available.
Both the Hansen AM400  and the Watermark Monitor  are dataloggers that are installed at the edge of a field.
These dataloggers can be programmed to collect and record data automatically from six or seven GMS and one soil temperature sensor throughout the day.
You can view the data as numbers or graphs on the unit itself, or you can download it to a computer for easy viewing in graphing software or a standard spreadsheet application.
The data from field collection devices can readily be uploaded to the Internet using cell phone modems and graphically displayed in a web portal.
This allows users to view the current soil moisture conditions from any Internetenabled computer, making off-site management easier.
But my field is so BIG and that sensor is so small
 The success of the GMS hinges on how reliably a group of sensors represents the soil moisture of a field.
That is why it is important to install the sensors at points in the field that accurately reflect the average root zone for the average plant.
If part of the field has different water needs, create a second zone and install sensors at representative areas of that zone.
Granular matrix sensors usually are installed in a group of six or seven per irrigation zone.
Each GMS provides information only about soil water tension in the immediate vicinity of the sensor.
Because SWT varies from place to place in a field, and sensors also vary, six or more GMS will provide more reliable estimates of SWT for a field than a single GMS.
The sensors complete a simple electrical circuit.
Thus, you can easily add an "extension cord" using normal electrical wire in order to collect information from many feet into the field.
It is important to maintain clean, dry connections between the extensions and the sensor wires.
What about installation?
Can I do it myself?
Installation is easy and requires few additional tools.
You will need a 7/8" soil sample probe to create the right size hole for the sensor.
Keep in mind that GMS are designed to accurately represent the relative amount of water in the field, SO select an area that is not remarkable.
On page 4, Figure 2  and Figure 3  illustrate the steps involved in installation.
If you have attached a PVC tube to the sensor with glue prior to installation to make it easier to remove the sensors from the field, use the installation method in Figure 2.
The accuracy of the sensor relies on good contact with the soil.
The GMS installation depth depends on the crop's root zone depth, but it also
 Figure 2.
Installation procedure of a granular matrix sensor  in coarse soil at an 8-inch depth in the soil.
Figure 3.
Installation procedure of a granular matrix sensor  in silty soil at 8-inch depth.
can be affected by soil depth and soil texture.
For shallow-rooted crops, sensors installed at less than 12 inches deep are sufficient.
For crops with a deep root system, also install sensors at greater depth within the root zone.
The root zone depth might be greater in well-drained soils and less in clay soils or soils with compacted layers or poor drainage.
To install a GMS sensor, first soak the sensor for several minutes until it reaches saturation.
Then make a hole in the soil using a soil sample probe with an external diameter corresponding to the sensor diameter.
Since the sensitive area of the GMS is centered 0.8 inch above the tip, the hole should have an additional 0.8 inch of depth to provide the desired sensor installation depth.
The next steps depend on the texture of your soil.
For coarser soils that have little tendency to lose their structure when saturated, pour about 2-3 OZ of water into the hole and then place the sensor at the bottom of the hole.
Silty soils tend to lose their structure when saturated and can seal around the sensor, thus impeding the entrance and exit of water.
For silty soils, place the sensor at the bottom of the hole and then add about 2-3 OZ of water to the hole.
Finally, regardless of soil type, backfill the hole with fine soil and use a tube, metal bar, or wooden stick to lightly compact the backfill dirt in order to prevent formation of a preferential path for rain or irrigation water to easily reach the sensor.
Such a path is undesirable because it distorts soil moisture status, thus significantly compromising the reliability of the SWT data obtained by the GMS.
The sensor operates by completing an electric circuit.
It is not uncommon for a frayed wire to "short circuit" the sensor, causing it to read zero continually, or for a cut wire to create an "open circuit," causing an unreasonably high reading.
If sensors are wet and readings should be low, a few common default error numbers include 199 and 250, depending on the datalogger.
Do not
 remove sensors from the soil by pulling on the wire since this can destroy the GMS.
Even with proper maintenance, sensors have a limited lifetime before they physically wear out or their sensitivity is compromised.
Replace the unit at that time.
Check sensors in the spring before use; dry sensors should have high readings, and sensors soaked in water for 1.5 minutes should read between 0 and 4 cb.
What is the bottom line for cost?
Can I really afford this?
GMS systems as a whole are relatively inexpensive.
With yield and quality increases and greater savings on water, energy, fertilizer, and other inputs, costs are quickly recovered.
Funding to help prepare this publication was provided by an Oregon Watershed Enhancement Board grant.
Watermark Soil Moisture Sensor-Irrometer Co., Riverside, CA Dielectric Water Potential Sensor  Decagon Devices, Inc., Pullman, WA Hand-held Watermark Soil Moisture Meter -Irrometer Co., Riverside, CA).
Hansen AM400 Datalogger-Mike Hansen Co., Wenatchee, WA Watermark Monitor Datalogger Irrometer Co., Riverside, CA
 Trade-name products are mentioned as illustrations only.
This does not mean that the Oregon State University Extension Service either endorses these products or intends to discriminate against products not mentioned.
Soil water tension indicates the soil water status and helps a grower decide when to irrigate, thus avoiding underand overirrigation.
Crops that are sensitive to water stress are more productive and have higher quality if they are watered precisely using soil water tension  than if they are underor overirrigated.
The optimum soil water tension for a particular crop depends primarily on crop needs, soil texture, and climate.
Common instruments to measure soil water tension include tensiometers, gypsum blocks, granular matrix sensors, dielectric water potential sensors, and porous ceramic moisture sensors.
Treasure Valley onions on silt loam are irrigated at a SWT of 20 to 25 cb.
Potatoes
 growing on the same site and soil type are irrigated at a SWT of 30 to 60 cb, depending on the irrigation system.
"Soil water potential" is the negative of "soil water tension." A soil water potential of 20 cb is the same as a soil water tension of + 20 cb.
Also, cb  is the same as kPa.
Granular matrix sensors provide good estimates of soil water tension for many soils.
Sensor readings can be conveniently logged, providing a record of soil moisture conditions to aid growers in timing irrigations.
Sensors and wiring need to be checked and loggers require minimal, but necessary, maintenance.
Keep loggers clean and dry and replace their batteries as needed.
Table 1.
Soil water tension  as irrigation criteria for onion bulbs as reviewed by Shock and Wang, 2011.
SWT	Irrigation	Soil moisture sensor depth
 	Location	Soil type	system	
 8.5	Piau, Brazil	Sandy	Microsprinkler	-
 10	Pernambuco, Brazil	-	Flood	-
 15	So Paulo, Brazil	Furrow
 10-15	Malheur County,	Silt loam	Drip	8
 17-21	Malheur County,	Silt loam	Drip	8
 27	Malheur County,	Silt loam	Furrow	8
 30	Texas	Sandy clay loam	Drip	8
 45	Karnataka, India	Sandy clay loam
 Table 2.
Soil water tension  as irrigation criteria for potato as reviewed by Shock and Wang, 2011.
SWT	Irrigation	Soil moisture sensor depth
 	Location	Soil type	system	
 20	Western Australia	Sandy loam	Sprinkler	-
 25	Maine	Silt loam	Sprinkler	-
 25	Luancheng, Hebei Province,	Silt loam	Drip	8
 30	Lethbridge, Alberta, Canada	Sandy loam	Sprinkler	-
 30	Malheur County,	Silt loam	Drip	8
 50	California	Loam	Furrow	-
 50-60	Malheur County,	Silt loam	Sprinkler	8
 60	Malheur County,	Silt loam	Furrow	8
 Table 3.
Soil water tension  as irrigation criteria for cole crops as reviewed by Shock and Wang, 2011.
system or	Soil moisture
 Common	SWT	measurement	sensor depth
 name		Soil type	equipment		Location, season
 Broccoli (Brassica	10-12	Sandy loam	Subsurface drip	12	Maricopa, AZ;
 oleracea var.
italica)	fall-winter
 Broccoli	50, 201	Silt loam	Lysimeters in rain	4	Agassiz, British
 shelter	Columbia, Canada; spring
 Cabbage (Brassica	25	Loamy sand and sand	Lysimeters in rain	4	Tifton, GA; spring
 oleracea var.
capitata)	shelter	and fall
 Cauliflower (Brassica	10-12	Sandy loam	Subsurface drip	4	Maricopa, AZ;
 oleracea var.
botrytis)	fall-winter
 Cauliflower	252	Sandy loam	Furrow and flood	7	Bangalore, India; winter
 Cauliflower	20-40	Sandy loam	-	-	Skierniewice, Poland;
 Collard	9	Sandy loam	Subsurface drip	12	Maricopa, AZ;
 Mustard, greens	6-10	Sandy loam	Subsurface drip	12	Maricopa, AZ;
 Mustard, greens	252	Loamy sand and sand	Lysimeters in rain	4	Tifton, GA; spring
 SWT of 50 cb during plant development, then 20 cb during head development.
2TTWENTY-five cb was the wettest irrigation criterion tested.
Table 4.
Soil water tension  as irrigation criteria for other field and vegetable crops as reviewed by Shock and Wang, 2011.
system or	Soil moisture
 Common	SWT	measurement	sensor depth
 name		Soil type	equipment		Location, season
 Alfalfa grown for seed	200-800	Fine sandy loam,	Sprinkler and	4-72	Logan, UT; summer season
 loam, silt loam	surface flood	of the perennial crop
 Beans, snap	25 superscript	Loamy sand	Lysimeters in rain	4	Tifton, GA; spring and fall
 Beans, snap	45	Sandy clay loam	-	6	Bangalore, India; fall-winter
 Beans, snap	50	Clay loam	Furrow and drip	12	Griffin, NSW, Australia;
 Carrot	30-50	-	Sprinkler	-	Nova Scotia, Canada;
 Carrot	40-50	-	Microsprinkler	6	Nova Scotia, Canada;
 Celery	10	Sandy loam	Drip	8	Santa Ana, CA; fall-winter
 Corn for sweet corn	10-40	Sand	Drip	6	-
 Corn for sweet corn	30	Carstic soils	Drip	12	Champotn, Campeche,
 Corn for sweet corn	50	-	-	-	Utah; spring-summer
 Corn for grain	30	Loamy fine sand	Sprinkler	6	Quincy, FL; spring-summer
 continued Table 4.
Soil water tension  as irrigation criteria for other field and vegetable crops as reviewed by Shock and Wang, 2011.
system or	Soil moisture
 Common	SWT	measurement	sensor depth
 name		Soil type	equipment		Location, season
 Corn for grain	50	-	-	-	Utah
 Cucumber	15-30	Fine sand and	Drip	8	Piikkio, Finland; spring-
 Lettuce, romaine	<6.5	Sandy loam	Subsurface drip	12	Maricopa, AZ; fall-winter
 Lettuce, leaf	6-7	Sandy loam	Subsurface drip	12	Maricopa, AZ; fall-winter
 Lettuce	<10	Red earth	Drip	12	NSW, Australia
 Lettuce	20	Clay loam, sandy	Sprinkler, drip	6	Las Cruces, NM; summer-
 Lettuce, romaine	301	Clay loam	Surface	12	-
 Lettuce, crisphead and	50	Sandy loam	Sprinkler	6	Salinas, CA; spring-summer
 Radish	35	Silt loam	Drip	8	Luancheng, Hebei Province,
 Radish	20	Sandy clay loam	Control basin and	7	Bangalore, India; winter
 Rice	16	Sandy loam	Flood	6-8	Punjab, India; summer-fall
 Spinach	9	Sandy loam	Drip	-	Maricopa, AZ
 Squash, summer	25	Loamy sand and	Lysimeter	-	Tifton, GA; spring, summer,
 Sweet potato	25, then	Loamy sand and	Lysimeters in rain	9	Tifton, GA; summer
 Sweet potato	25-40	Silt loam	Drip	8	Ontario, OR; summer
 Tomato	10	Fine sand	Drip	6	Gainesville, FL; spring
 Tomato	20	Sand	Drip	6	Coruche, Portugal; spring-
 Tomato	12-35	Clay	Drip	4-84	Federal District, Brazil; fall-
 Tomato	50	Silt loam	Drip	8	Yougledian, Tongzhou,
 Watermelon	7-12.6	Sandy loam	Drip	12	Maricopa, AZ; spring-
 'Twenty-five cb or 30 cb was the wettest irrigation criterion tested.
SUTE of 25 cb during plant development, then 100 cb during root enlargement.
3Thirty-five, 12, and 15 cb during vegetative, fruit development, and maturation growth stages, respectively.
4Tensiometer depth was 4" during the vegetative growth stage, 6" in the beginning of the fruit development stage, and 8" from thereon until the irrigations were stopped.
STaylor, S.A., D.D.
Evans, and W.D.
Kemper.
1961.
Evaluating Soil Water.
Utah Agricultural Experiment Station Bulletin 426.
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Using Tensiometers for Vegetable Irrigation Scheduling in Miami-Dade County
 Kati W.
Migliaccio, Teresa Olczyk, Yuncong Li, Rafael Munoz-Carpena, and Tina Dispenza 
 How the Tensiometer Works
 A tensiometer is a simple and relatively inexpensive tool that can be used to schedule irrigation in Miami-Dade County vegetable crops.
Tensiometers continuously measure soil water potential or tension, which is a measure of soil moisture or soil water content.
This is generally expressed in centibars  on a tensiometer vacuum gauge.
If the tension in the soil is high, plants have to use more energy to extract soil water.
If tension in the soil is low, then plants have lower energy requirements to extract soil water.
Figure 1.
Example of a tensiometer's vacuum gauge.
Credits: Tina Dispenza, UF/IFAS
 A typical tensiometer is a water-filled tube with a porous ceramic cup at the lower end.
After it is installed in the soil, water moves from the tensiometer through the cup into the unsaturated soil.
This process continues until the negative pressure inside the tensiometer equals the negative pressure in the surrounding soil.
The pressure inside the tensiometer is then in equilibrium with the pressure in the soil and can be measured by reading a vacuum gauge on the tensiometer.
Figure 2.
Example of a tensiometer.
Credits: Tina Dispenza, UF/IFAS
 2.
Kati W.
Migliaccio, associate professor, Department of Agricultural and Biological Engineering, UF/IFAS Tropical Research and Education Center; Teresa Olczyk, Extension director, UF/IFAS Extension Miami-Dade County; Yuncong Li, professor, Department of Soil and Water Sciences, UF/IFAS TREC; Rafael Munoz-Carpena, professor, Department of Agricultural and Biological Engineering; and Tina Dispenza, engineer, UF/IFAS TREC; UF/IFAS Extension, Gainesville, FL 32611.
Tensiometers can be purchased in different lengths and tensions.
Tensiometer lengths vary from 6 inches to 48 inches.
A tensiometer needs to be long enough SO that the ceramic tip is in the root zone of the irrigated plant, with the top and gauge near the soil surface.
For most vegetable fields in South Dade, a 6-inch tensiometer is appropriate.
However, if root depths are greater than 6 inches, a tensiometer of greater length can be used.
In soil depths greater than 6 inches, tensiometers of various lengths can be used to capture soil tension at different depths.
Tensiometers also are classified by their tension range.
High tension  and low tension  are available commercially, and both are suitable for use in vegetable fields.
Tensiometers require some preparation before being installed in the field.
Each manufacturer will supply specific directions for their device.
Generally, tensiometers must be soaked in clean water overnight.
Then the tensiometers are filled past the rubber stopper seal point, filling the reservoir.
It is recommended that the clean water be mixed with a biocide.
A clean poker should also be used to ensure that the column has filled and air bubbles are not trapped.
Next, pressure is applied to make sure the tensiometers are working correctly.
A pump with a vacuum gauge is ideal to do this SO that the two gauges can be compared.
If the tensiometer can hold pressure and no bubbles appear, the tensiometer is functioning properly.
If bubbles occur, there is an air leak and the tensiometer needs further maintenance.
The tensiometers should be stored with the caps on and ceramic tips in water until they are installed to prevent draining.
Figure 3.
Soaking tensiometers in clean water overnight.
Credits: Tina Dispenza, UF/IFAS
 Figure 4.
Filling tensiometers with water mixed with biocide.
Credits: Tina Dispenza, UF/IFAS
 Figure 5.
Checking for air bubbles trapped in the tensiometer column.
Credits: Tina Dispenza, UF/IFAS
 Figure 6.
Applying pressure using a handheld vacuum pump.
Credits: Tina Dispenza, UF/IFAS
 Tensiometers should be installed at sites that are representative of the soil types and crop conditions in the field.
If soil types vary considerably in the field, you should install a separate tensiometer in each of the soil types.
For example, if you have marl and Krome gravelly soils in the same field, install one tensiometer for each soil type.
Field soil moisture characteristics should also be considered during tensiometer installation.
Fields often have wet spots and dry spots, and they often have areas that typically are wetter or drier than the rest of the field.
Tensiometers should be placed to monitor these extreme areas to prevent yield loss.
If two different crops are planted in the same field, install at least one tensiometer for each crop.
Tensiometers should be located in the active root area in the wetting zone of the irrigation system.
For vegetables grown on beds with drip irrigation, place the tensiometers in the plant row between two plants in the wetting zone of the drip tape.
Proper installation is critical to assure effective contact between the ceramic cup of the tensiometer and the surrounding soil.
Follow these steps to install a tensiometer:
 1.
Remove any grass, weeds, or other obstructions from the soil surface where you will install the tensiometer.
2.
Use a hammer and a steel rod with a diameter slightly larger than the tensiometer's ceramic tip to make a hole deep enough for the ceramic tip to be in the root zone of the plants.
3.
Prepare a thick slurry by collecting soil from the surrounding area and sieving it through a 1/8-inch screen, and then mixing the soil with water.
4.
Place some of the slurry in the bottom of the hole , and then carefully place the tensiometer in the hole.
5.
Add the rest of the slurry around the ceramic cup and the plastic tube of the tensiometer.
Continue adding enough slurry until it overflows.
Gently move the tensiometer back and forth a few times to assure the tensiometer achieves good contact with the soil.
Figure 7.
Rod used to make hole for tensiometer installation in the field.
Credits: Kati Migliaccio, UF/IFAS
 Figure 8.
Hammering in the rod to make a hole for the tensiometer.
Credits: Kati Migliaccio, UF/IFAS
 Taking and Recording Tensiometer Readings
 Tensiometer readings should be taken at the same time each day, ideally in the early morning before irrigation.
Record the readings in a notebook along with the rainfall and irrigation amounts and dates.
Make sure to identify the location of each tensiometer station by recording the site number, the depth of the tensiometer being read, and the date and time of the reading.
Figure 9.
Sieving soil for making the slurry.
Credits: Kati Migliaccio, UF/IFAS
 Figure 12.
Placing tensiometer into hole with slurry.
Credits: Kati Migliaccio, UF/IFAS
 Figure 11.
Pouring slurry into the tensiometer hole.
Credits: Kati Migliaccio, UF/IFAS
 In general, use the following guidelines to interpret tensiometer readings to schedule vegetable irrigation in gravelly or sandy soils.
1.
Readings of 0-5 cbar: Soils are saturated or nearly saturated as a result of irrigation or rain.
Discontinue irrigation to prevent wasting water and leaching nutrients from the root zone.
2.
Readings of 10-15 cbar: Crops should be irrigated as soon as possible.
Irrigation should be initiated at 10 cbar during the flowering and fruit set, and at 15 cbar for the rest of the growing season.
3.
Readings of 25 cbar and higher: Plants probably show symptoms of water stress.
Irrigate immediately!
The tensiometers may soon lose vacuum and require servicing to restore accurate performance.
Figure 10.
Mixing the sieved soil with water to make a slurry.
Credits: Kati Migliaccio, UF/IFAS
 Although tensiometers are simple instruments, they require regular maintenance to provide accurate readings of soil water status.
During the growing season, all tensiometers should be topped off with clean water periodically.
This will prevent losing suction because of low water levels in the plastic tube.
In addition, weekly checks are recommended to ensure that tensiometers have not drained and are operating correctly.
During these inspections, check the water level in the tensiometer, purge any bubbles that may be present , and test the suction with a vacuum pump.
Figure 13.
Servicing a tensiometer in the field; purging bubbles from water column.
Credits: Tina Dispenza, UF/IFAS
 Figure 14.
Servicing tensiometer in the field; applying pressure with vacuum pump.
Credits: Tina Dispenza, UF/IFAS
 When opening a tensiometer for maintenance, hold the bottom portion of the unit steady with one hand while removing the top.
This helps maintain connectivity between the ceramic tip and the soil.
If the bottom portion moves, this can cause air pockets to occur around the ceramic tip, which affects the functionality of the tensiometer.
All tensiometers should be removed from the soil every six months or at the end of the growing season and washed to remove soil, algae, bacteria, and other debris from inside and outside the ceramic cup and plastic tube.
A mild household detergent and small bottle brush can be used for cleaning.
The ceramic cup should be soaked in a chlorine
 solution  to kill bacterial growth.
After cleaning, fill the instrument with clean water and add a mild biocide  to prevent algal growth.
To reinstall, follow the procedures outlined in the preparation section.
1.
The tensiometer gauge always reads zero.
If correct, a zero reading means that the soil is saturated from irrigation, heavy rainfall, or very poor drainage.
1.
There may be no water in the tensiometer, or it lost suction because of a low water level.
Solution: Remove, prepare, and reinstall the tensiometer.
2.
The gauge is faulty.
Solution: Remove and replace the gauge.
Check carefully for air leaks, and then prepare and reinstall the tensiometer.
3.
A connection is leaking.
Solution: Check the general assembly, including the ceramic cup and O-ring seals.
Fix the leak, prepare, and reinstall the tensiometer.
2.
The tensiometer does not seem to record the true soil moisture content.
POSSIBLE PROBLEMS
 1.
There is poor contact between the ceramic cup and the surrounding soil.
Solution: Reinstall the tensiometer following the directions provided.
2.
The gauge is faulty.
Solution: Check the gauge using a vacuum pump with a gauge.
Prepare and reinstall.
3.
The tensiometer needs frequent refilling with water.
POSSIBLE PROBLEMS
 1.
The ceramic cup or seal is leaking.
Solution: Replace the seal or cup.
Check other seals for leaks.
Prepare and reinstall the tensiometer.
2.
The surrounding soil is too dry, and the tensiometer cannot hold water.
If this happens, the tensiometer is likely not in a location that represents field conditions or the plants are severely drought-stressed.
4.
The tensiometer responds too slowly to
 Water is slow to infiltrate between the ceramic cup and the soil.
1.
The ceramic cup may be clogged by salts or algae.
Solution: Clean or replace the cup.
Prepare and reinstall tensiometer.
2.
The gauge sticks.
Solution: Tap to test, and replace the gauge if faulty.
Prepare and reinstall tensiometer.
EVALUATION OF PRESSURE REGULATORS FROM CENTER PIVOT NOZZLE PACKAGES
 Abstract: Performance evaluations of center pivot nozzle packages for uniformity have been conducted as part of the Mobile Irrigation Lab program for a number of years.
These evaluations were performed using a catch can system.
Later the evaluation expanded to spot checking pressure and flow for in-canopy nozzle packages that could not be tested with catch cans.
However, the latter procedure did not measure the pressure drop across the pressure regulator and approximately 80 per cent of Kansas center pivot irrigation systems are pressure regulated.
This study tested pressure regulator performance of regulators from existing center pivot nozzle packages.
Keywords: Center pivot irrigation, pressure regulators
 Center pivot irrigation systems are the dominant irrigation system type in use within Kansas.
Irrigation is also the dominant use of water supplies for the state, but in many areas of the state, water supplies are diminishing.
However, irrigated agriculture makes significant contributions to the economy so improving irrigation water utility has long term benefits to the region.
The Mobile Irrigation Lab  project previously developed a procedure to performance evaluate center pivot nozzle packages for uniformity.
Later, the performance evaluation was expanded to include an evaluation procedure for in-canopy  nozzle packages , although, the performance evaluations did not focus on individual components.
Approximately 80 percent of the nozzle packages were equipped with pressure regulators ; however, the pressure drop across the regulator was not measured in the previous performance evaluation procedure.
By observation, pressure regulator failure has appeared to be either
 excessive leaking at the regulator or clogging with no water passing, but otherwise the regulators were assumed to be functioning.
In this study, pressure regulators from existing systems were collected and laboratory tested for performance.
Two sets of 10 pressure regulators each were initially intended to be removed from various systems in southwest Kansas.
Older nozzle packages were selected.
The samples were normally collected from the third and last span of the system.
In one case, all the pressure regulators from the system were evaluated.
The regulators were subsequently brought to the hydraulics laboratory at the Department of BAE, Kansas State University.
Each regulator was tested at two input pressures  and three nozzles sizes appropriate to the flow rating of the pressure regulator.
Three hundred and nine pressure regulators were collected and tested.
Only one regulator was recorded as failed.
In this case, excessive leakage through the regulator body occurred, which was a part of the GFS3 test.
The average results of this collection are based on the averages of the remaining 9 in the collection sample.
In another case, a regulator had no flow passing through the regulator when it was initially installed on the test stand.
It was removed, at which time debris was noted in the intake side which was then removed by tapping the regulator on a hard surface.
This dislodged the debris, so the regulator was reinstalled and tested.
An example of a pressure regulator performance chart is shown in figure 2.
For the design output pressure or pressure rating, the downstream or output pressure will be slightly less than line  pressure due to friction losses through the regulator.
Once the internal friction loss is overcome, the device will begin to output the approximate design rating.
This value will generally be slightly elevated with increasing input pressure.
The amount of flow through a pressure regulator will also affect the output pressure, with decreasing output pressure with increasing flow.
A summary of the results are in Table 1, where the average output pressure of the collected set are shown as well as the highest and lowest reading from the test set.
The size of the nozzle is also noted in the table.
Pressure regulators were collected from 8 different systems.
On two systems only the outer span regulators were collected and on one system the S3 span had different pressure rated  regulators than the LS span ; making 14 data sets.
Based on figure 2 discussion, it would be expected that as nozzle size  increased, the average output pressure would decrease.
This was the case in 9 of the 14 sets for the 20 psi test.
RKS3, RKLS, GFS3, MGLS, and RBLS did not follow the pattern of decreasing output pressure with increasing flow.
At 30 psi, 8
 of 14 followed the expected pattern with the same sets above and also GFLS breaking pattern.
When comparing test results between 20 and 30 psi pressure tests, only RKS3, RKLS and TLLS did not have higher output pressure at 30 psi input pressure as compared to 20 psi, which would be different than the expected result.
Overall, performance of the regulators seemed very good.
Figures 3 and 4 show the results of Test SFGF S3 and LS which are 6 psi rated regulators and, as noted previously, follow the expected pattern of performance.
For example at 20 psi input pressure, the average S3 output pressure changes from 6.25 to 5.73 to 5.53 psi for the respective nozzle sizes.
Figure 3 shows individual data points to indicate the range of values.
Most test values are relatively close, although in the 20 psi LS test, one regulator had a test value of nearly 8 psi, which is an outlier as compared to the others.
Figure 4 shows a different data presentation.
In this figure, S3 and LS test results were averaged into a combined set.
Note that flow through the nozzle has more impact on the output pressure than does the input pressure.
Figures 5 and 6 show the results of Test UB S3 and LS which are 10 psi rated pressure regulators.
The S3 and LS models are the same but the former is a low flow model while the latter is a high flow model.
As noted previously, they follow the expected pattern of performance.
For example at 20 psi input pressure, the average S3 output pressure changes from 10.25 to 9.74 to 9.20 psi for the respective nozzle sizes.
Figure 5 shows individual data points to indicate the range of values.
Most test values are relatively close, although in the 30 psi LS test, the range of data points was larger than the other ranges.
Figure 6 shows the data presented by nozzle size and the results show the decreasing output pressure with increasing nozzle size.
The output pressures for the 20 and 30 psi input pressures were not as tight as in the SFGF example but still similar; with the average 20 psi LS test was slightly lower than the other average values
 Figures 7 and 8 show the test results from 169 pressure regulators.
These regulators were collected from one center pivot irrigation system in position order and tested at the two pressure and three flow rates as described previously.
The most remarkable feature of either figure 7 or 8 is that the variability of results of the first thirty regulators as compared to the rest of the regulators from the position.
At higher flows , the regulators performed better, although still at higher output pressure as compared to higher numbers of position.
The regulators also performed better at 30 psi  than at 20 psi.
No notable differences in appearance of the regulators during collection or during test installation were noted.
S3 regulators as discussed previously would have been downstream of the variable area noted in this full system analysis.
Pressure regulators collected from a variety of center pivot systems located in SW Kansas were laboratory tested.
Older nozzle packages were targeted.
Although additional analysis of the data is planned, it appears the regulators performed well under the variety of conditions experienced in the region.
One full system analysis was completed.
Regulator performance in the inner part of this system was more variable than the outer part of the system, however no conclusions should be drawn from a single test.
This study was supported in part by The Mobile Irrigation Lab Project GECG 601490, funded by the Kansas Water Plan Fund administered by the Kansas Water Office, USDA Project GEGC 601448 and the Ogallala Aquifer Project GEGC 600468.
This paper was originally presented at the 30th Annual International Irrigation Association Conference, San Antonio, TX.
Dec.
2-4, 2009
 Table 1: Average, highest, and lowest Output Pressure of various pressure regulators for two input pressures and three flow rates.
Pressure	Ave	High	Low	Ave	High	Low
 Regulator	Nozzle	Pressure	Output	Pressure	Pressure	Pressure	Output	Pressure	Pressure
 Size	PSI	PSI	PSI	PSI
 Upstream Test Pressure = 20 psi	Upstream Test Pressure = 30 psi
 RKS3	15	10.21	11	9.5	9.86	10.9	8.4
 10 psi	20	9.63	10.4	9.1	9.68	10.7	9.2
 24	10.26	11.6	9.4	10.47	12	9.1
 RKLS	15	10.34	11.1	9.8	10.13	10.7	9.6
 10 psi	20	9.93	10.5	9.6	9.78	10.7	8.4
 24	10.45	11.7	9.7	10.76	11.2	10.3
 GFS3	15	5.28	6.3	4.2	5.73	6.70	4.60
 6 psi	20	5.6	7.9	4.2	5.67	7.30	3.70
 24	5.47	8.50	4.20	5.51	7.50	3.60
 GFLS	15	5.73	7.6	5.2	5.83	7.1	5.1
 6 psi	20	5.73	7.2	4.9	5.97	7.2	4.7
 24	5.65	7.8	4.6	5.89	7.4	4.8
 MGLS	7	8.91	11.1	7.1	10.09	12.5	6.2
 10 psi	12	7.84	11.1	4.6	7.84	10	5
 15	8.33	10.4	4.8	7.98	11.3	6.5
 RBLS	7	5.79	7.5	5	6.16	7.1	5
 6 psi	12	4.77	6.7	3.6	4.77	6.9	4.1
 15	4.92	6.3	4.2	5.32	6.3	3.7
 SFGFS3	7	6.25	6.6	6	6.54	7	6.1
 6 psi	12	5.73	6.1	5.2	5.98	6.3	5.4
 15	5.53	5.9	4.8	5.6	6.1	5.1
 SFGFLS	7	6.51	7.9	6	6.6	7	6.2
 6 psi	12	6.13	6.7	5.6	6.05	6.5	5.8
 15	5.79	6.3	5.3	5.52	5.9	5.2
 Pressure	Ave	High	Low	Ave	High	Low
 Regulator	Nozzle	Size	Pressure	Output	Pressure	PSI	Pressure	PSI	Pressure	Output	Pressure	PSI	Pressure	PSI
 UBS3	7	10.25	11.1	8.9	10.43	11.5	9.8
 10 psi	12	9.74	10.5	9.2	9.86	10.7	9.2
 15	9.2	10.1	8.1	9.02	9.7	8.1
 UBLS	15	9.7	11	7.7	10.32	12	8
 10 psi	20	8.59	9.8	7.5	9.42	10.5	7.8
 24	8.55	9.7	7.3	8.64	9.2	7.7
 TLS3	7	10.85	11.5	10.3	11.05	11.5	10.5
 10 psi	12	10.24	10.6	9.6	10.39	10.7	10
 15	9.72	10.3	8.7	10.09	10.6	9.6
 TLLS	15	6.51	7.6	5.2	6.34	7.1	5.8
 6 psi	20	6.09	7.5	5.4	5.91	6.7	4.7
 24	5.88	8.2	4.7	5.54	6.6	4.7
 ALS3	7	10.68	11.1	10.2	10.91	11.5	10.1
 10 psi	12	10.21	10.5	9.9	10.12	10.6	8.6
 15	9.97	10.5	9.5	9.97	10.3	9.6
 ALLS	7	10.48	11.1	9.9	10.6	11.3	9.9
 10 psi	12	9.97	10.5	9.6	10.19	11	9.3
 15	9.7	10.1	8.8	9.66	10.1	8
 Figure 1.
Picture of Pressure Regulator Test Stand, including manifold, pressure regulator, pressure shunt, water meter, pressure shunt and flow nozzle.
Figure 2.
Example of Output Pressure verses Input Pressure for a Pressure Regulator.
Input Pressure verses Output Pressure at various flow rates for 6 psi pressure regulator 
 Figure 3.
Input pressure verses output pressure at various flow rates for 10 6 psi pressure regulators for Tests SFGF S3 and LS.
Figure 4.
Average, high and low output pressures for 6 psi pressure regulators for Test SFGF S3 and LS.
Figure 5.
Input pressure verses output pressure at various flow rates for 10 psi pressure regulators for Tests UB S3 and LS.
Figure 6.
Average, high and low output pressures for 10 psi pressure regulators for Tests UB S3 and LS.
Output Pressure of 10 psi Pressure Regulators for Test GF 1-169 for 20 psi input pressure.
Average Pressure N15= 10.18, N20= 9.70, N24 = 9.99
 Figure 7.
Output pressure of 169 pressure regulators tested at three nozzle sizes.
Tests GF 1-169.
Figure 8.
Output pressure of 169 pressure regulators tested at 20 and 30 psi input pressure.
Tests GF 1-169.
I wonder, is it just too easy to turn the irrigation water on?
Many systems today can be started by just touching a button on the smart phone.
If you had to go to the bank and take out eight or ten $100 dollar bills to feed into each pivot before it would start, would you want more information about the available water reserves in the soil?
We all know the reason fast food restaurants started taking credit cards, right?
Because it is well known that people will stop more often and spend more money if they can use plastic.
Therefore, I suggest you consider for yourself: if you had to spend cold, hard cash to start the pivot vs.
paying the cost when the bill comes later on, would you do anything different?
Choose warm-season grasses that require less water like bermudagrass and buffalograss.
Know your soil texture.
Sandy soils require lighter, more frequent watering while clayey soils need heavier, less frequent watering.
Applying water faster than the soil can absorb it will cause water  to run off the landscape.
To save water, do not over-seed warmseason lawns with cool-season grasses, since over-seeded yards require more water than dormant grass.
Install a rain/freeze sensor to prevent water wasted in the landscape.
Water before 10 a.m.
to reduce water loss to evaporation which will reduce disease incidence from allowing water to sit on leaves overnight.
If it's a windy day, skip watering.
Watering in the wind causes needless water loss by moving water away from the lawn.
Do not water hardscapes.
Collect and use rainwater.
Conduct an irrigation audit so you know how much water is being applied to the lawn during an irrigation event.
If you have a clay soil, use the cycle and soak approach.
Turn the water on until it begins to puddle, turn it off and after it soaks in turn the system back on.
This allows water to deeply soak in the soil.
Install a rain garden which allows water to infiltrate into the soil rather than runoff the property.
Learn how to program your irrigation controller so you can update the programs with the changing of the seasons.
Oklahoma City Water Utilities Trust Spring Rain Irrigation Systems Irrigation Station Easton Sod Silver-Line Plastics Green Okie Pergolas and Outdoor Innovative Tree Care Eckroat Seed Company Minick Materials Bentley Turf Farms, Inc Redbud Design and Landscape, Inc.
Midwest Brick & Block Turf Team Outdoor Management Havenyield Tree Farm & Landscape Oklahoma State University-Oklahoma City Oklahoma Cooperative Extension Service Oklahoma State University Department of Horticulture & Landscape Architecture
 Oklahoma State University, in compliance with Title VI and VII of the Civil Rights Act of 1964, Executive Order 11246 as amended, Title IX of the Education Amendments of 1972, Americans with Disabilities Act of 1990, and other federal laws and regulations, does not discriminate on the basis of race, color, national origin, gender, age, religion, disability, or status as a veteran in any of its policies, practices or procedures.
This includes but is not limited to admissions, employment, financial aid, and educational services.
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, the Director of Oklahoma Cooperative Extension Service, Oklahoma State University, Stillwater, Oklahoma.
This publication is printed and issued by Oklahoma State University as authorized by the Vice President, Dean, and Director of the Division of Agricultural Sciences and Natural Resources and has been prepared and distributed at a cost of 2,440.00 for 30,000 copies.
1114 MG
 Oklahoma Cooperative Extension Service Division of Agricultural Sciences and Natural Resources Oklahoma State University
 DO YOUR PART TO SQUEEZE EVERY DROP
 Oklahoma city residents use about 30 to 40 percent of their household water outdoors in the landscape.
The seven principles of a water-wise landscape, or xeriscape, provide simple ways to reduce outdoor water use while maintaining an attractive lawn and garden.
Even though central Oklahoma receives about 35 inches of rain per year, the growing population and variable rainfall across the state creates a need to conserve water in the landscape.
The water conservation garden was provided by the Oklahoma City Water Utilities Trust.
Oklahoma City saw a need to promote proper water use to the public in the midst of persistent drought conditions across the state.
Oklahoma City residents receive water from six surface lakes.
Oklahoma City owns four water supply lakes including Overholser, Hefner, Atoka and Draper and water rights in Lake Canton and McGee Creek Reservoir.
Lakes Overholser, Hefner and Draper are within city limits.
Atoka and McGee Creek Reservoirs are in southeast Oklahoma and Lake Canton is located in northwest Oklahoma.
Making waterwise management decisions reduces water waste and helps support a healthy landscape.
Drought or not, lets work together to squeeze every drop.
PRINCIPLES OF WATER EFFICIENT LANDSCAPES
 Landscape planning and design
 Start with a good design before purchasing plants.
Sketch out your property with considerations for slopes, soils, drainage, turf, sun exposure and recreation areas.
Assess your soil's quality.
Many urban soils are compacted from construction activities so adding organic matter and aerating periodically increases soil water holding capacity, creating healthy plants.
Always take a soil test before fertilizing the landscape.
For information on soil testing go to soiltesting.okstate.ee or visit your local Extension office.
The water conservation garden showcases three warm-season grasses grown in Oklahoma; bermudagrass, zoisiagrass, and buffalograss.
Bermudagrass and buffalograss only need about 1 inch of water or less per week.
Instead of watering on a set schedule, water when the grass begins to show signs of wilt.
If you can see your footprints when you walk across the yard, it's time to water.
Water early in the morning to reduce water loss to evaporation.
Plant selection and placement
 Mulch creates an attractive landscape, controls weeds, prevents erosion, and retains soil moisture.
As organic mulches break down, they help alleviate soil compaction and provide a home for organisms like earthworms.
Maintain a 2 to 4 inch mulch layer around plants and trees.
Replace it as it breaks down or washes away.
Periodically check irrigation systems and fix or replace broken sprinkler heads.
Raise the mower height to reduce evaporation and check the soil before turning on water.
The OSU-OKC Water Conservation Demonstration is located southeast of the OSU-OKC John E.
Kilpatrick Horticulture Center, 400 N.
Portland Avenue.
The garden is open daily during daylight hours and there is free parking available north of the Horticulture Center and west of the garden.
E: Oklahoma native plants
 G: Walk of Fame
Pivot tracks: Fill tracks in the fall so they can firm up over the winter.
Calibrating a Low-Pressure Ground Sprayer: Boom-Mounted Nozzles
 John Long Extension Specialist for Agriculture Machinery Systems
 Calibration is the process of adjusting or modifying spray equipment so it is capable of applying the desired rate of pesticide accurately and uniformly to the target crop area.
The performance of any pesticide depends on the proper application of the correct amount on the target area.
Most performance complaints about agricultural chemicals can usually be traced back to errors in mixing or applying the chemical.
This document will present best practices for reducing application errors.
For mixing refer to PSS-2789, Herbicide Mixing Order.
Variables Affecting Application Rate of Spray Solution
 Three variables affect the amount of pesticide mixture or spray solution applied per acre:
 1) nozzle flow rate.
2) ground speed of the sprayer.
3) effective spray width per nozzle.
To calibrate a sprayer accurately the effect of each of these variables on sprayer output must be understood.
1.
Nozzle Flow Rate The flow rate through the nozzle varies with orifice tip size, nozzle pressure and spray solution characteristics.
Figure 2 shows a cutaway of a typical low-drift air-induction nozzle with identifiable parts labeled.
The size of the nozzle is determined by the size of the pre-orifice for low drift nozzles or the main orifice
 Figure 1.
Calibration is the process of adjusting spray equipment to uniformly apply the desired rate of chemical.
Figure 2.
Cut away model of a TeeJet AIXR nozzle.
White arrows show airflow and blue arrows show liquid flow.
for standard nozzles.
Installing nozzles with a larger or smaller orifice size is the most effective way to change a sprayer's output.
Changes in nozzle pressure also can be used to increase or decrease sprayer output, but not as significantly as changes in orifice size.
Pressure must be increased four times to double nozzle flow rate.
For example, Figure 3 shows a typical catalog chart for a nozzle.
For this particular nozzle, to increase the flow rate of the nozzle from 0.26 gallons per minute  at 30 pounds per square inch  on the low end of the range to 0.52 GPM, pressure would need to be increased to 120 psi.
Pressure adjustment should never be used to make major changes.
Most nozzles have an optimal working pressure somewhere near the middle of the manufacturer suggested range.
Pressures near the low end of the range may distort the spray pattern , while pressures near the upper end of the range tend to produce small droplets and increase physical spray drift.
The pressure range of nozzles vary greatly from model to model but can vary from as low as 15 psi to upwards of 120 psi.
2.
Ground Speed The spray solution application rate varies inversely with the ground speed.
Doubling the ground speed of a sprayer reduces the gallons of spray applied per acre  by one-half.
For example, a sprayer applying 20 GPA at 3 mph would apply only 10 GPA at a speed of 6 mph if all other spray conditions remained the
 Figure 3.
Excerpt from GreenLeaf Technologies Catalog for a TurboDrop XL nozzle.
same.
A sprayer calibrated at 4 mph but actually operated at 3 mph will over spray by 33%, significantly increasing chemical costs and the potential for crop damage.
3.
Effective Spray Width "W" The effective width sprayed per nozzle or cluster of nozzles also affects the spray solution application rate.
Spray width per nozzle is measured differently depending on the nozzle configuration.
Refer to Figure 5 for the best way to measure effective width.
Doubling the effective spray width will decrease the gallons per acre  applied by one-half.
For example, if a broadcast nozzle is applying 40 GPA on a 20-inch spacing, a change to a 40-inch spacing will decrease the application rate of spray solution to 20 GPA.
Typically, this will require changing the nozzles to a wider fan angle or increasing boom height to maintain proper overlap.
Both of these changes can have impacts on drift.
Before calibrating a sprayer, service the entire unit.
Check that all nozzles are the same size and not worn.
Check for uniform nozzle output and pattern and determine exactly how much liquid the sprayer tank holds.
Install a pressure gauge on the boom to determine actual pressure at the nozzles.
Servicing Clean all lines and strainers, making sure the strainers are in good condition and the correct size and
 type for the chemical formulation to be applied.
Inspect all hoses for signs of aging, damage and corroded fittings or leaks.
Check the pressure gauge to determine if it is working properly.
Is the pressure holding constant?
Does it read zero when the pump or boom valve is shut off?
The actual accuracy of the gauge is not as important as is its ability to give the same reading each time the same pressure is produced.
At least once a year, preferably at the beginning of the spraying season, check the gauge against another gauge known to be accurate.
Nozzle Output and Pattern Check for uniformity of nozzle output and the spray angles, spacing and height are consistent.
To check for uniform nozzle output, install the selected nozzle tips and check to be sure the tank is clean.
Then partially fill the tank with clean water and operate the sprayer at a pressure within the recommended range.
Place a container, such as a quart jar, under each nozzle and check to see whether all the jars fill at about the same time.
Replace any nozzle tips with an output that significantly varies compared to the output of the rest of the tips, have an obviously different fan angle or have a non-uniform appearance in spray pattern.
The rule of thumb is nozzles with flow rates greater than 10% above a new nozzle of identical make should be replaced.
An effective way to determine whether a uniform pattern is being produced and whether the boom is at the proper height is to spray some water on a warm, dry, light-colored surface like a concrete pad or gravel drive and observe the drying pattern.
If the pattern is not uniform, some strips will dry slower than others will.
Tank Capacity Checking tank capacity may seem unnecessary, but unless the exact capacity of the sprayer's tank is known, it may lead to serious problems.
This precalibration check should be made at least once, and the data should be recorded.
When determining application rates of spray solution, the use of an inaccurate tank capacity is a common cause of many cases of underand over-application.
A tank thought to hold 200 gallons, but which actually holds 250 gallons, results in a built-in calibration error of 25%.
The best and easiest way to accurately determine tank capacity is to fill the tank using any convenient container for which an exact capacity is known.
Another effective way of measuring tank capacity is to fill or
 Figure 4.
Improper pattern development  vs proper pattern.
Figure 5.
Effective Width Calculation  for broadcast applicators measure the distance between adjacent nozzles,  for banded applications measure the wetted width of the band and  for directed or row crop applicators measure the row spacing and divide by the number of nozzles per row.
drain the tank while measuring with an accurate flow meter.
A third way is to weigh the sprayer both empty and full.
The difference between the two weights is the weight of the water in the tank.
The capacity of the tank in gallons can then be determined by dividing this weight by 8.33 pounds, which is the weight of one gallon of water.
To apply pesticides accurately, a constant ground speed must be maintained.
Field conditions, such as surface roughness, softness and slopes, all affect ground speed due to wheel slip and this can significantly change application rates of spray solution.
Tractor speedometers and tachometers are generally not a good means of determining ground speed because wheel slippage can result in speedometer reading errors of 25% or more.
Changes in tire size also can affect speedometer readings.
The best way to accurately measure ground speed is with a true ground speedometer that utilizes a radar, GPS guidance system or other speed measurement device.
GPS guidance systems are the most common way to determine true ground speed in most situations, but many of the sprayer monitors and rate controllers currently on the market have the ability to accurately measure true ground speed using radar or other devices.
These speedometers are available from a number of spray-equipment manufacturers at reasonable prices and are a good investment if a considerable amount of spraying is done.
If a true ground speedometer is not available, the next best method to assure a constant ground speed is to measure the speed of the sprayer at a variety of throttle and gear settings.
Do this in the field to be sprayed or a field that has conditions and terrain similar to those in the field to be sprayed.
To measure true ground speed, stake out a known distance in the field.
Suggested distances are 100 feet for speeds up to 5 mph, 200 feet for speeds from 5 to 10 mph, and at least 300 feet for speeds above 10 mph.
At the engine throttle setting and gear to be used during spraying, determine the travel time between the measured stakes in each direction.
To ensure the greatest accuracy, the sprayer should be at least half full of liquid.
Average the two travel times and use the following equation or Table 1 to determine the ground speed.
D = the distance between the two stakes in feet.
T = average time in seconds it takes to drive between the stakes.
Figure 6.
Place a container under each nozzle to see if all jars fill in about the same time.
Table 1.
Time to travel distance.
Distance 	3	4	5	6	7	8	9	10	12	15	20
 100	23	17	14	11
 200	45	34	27	23	19	17	15	14
 300	68	51	41	34	29	14	23	20	17	14	10
 The numbers 66 and 88 are used because 1 mph = 88 feet in 60 seconds.
The actual calibration of a field sprayer involves two important steps:
 Step 1.
Determine whether the sprayer is applying the correct number of gallons per acre  of pesticide mixture set by the label.
Step 2.
Using the GPA from Step 1, determine how much pesticide should be added to the sprayer's tank to achieve the desired application rate of spray solution.
The focus will be determining the sprayer output  and making any equipment adjustments necessary to ensure the proper application rate in gallons per acre.
There are many different methods to determine this flow rate and two of those will be discussed in the following sections.
NOTE: Sprayer calibration and nozzle testing is done using only water in the sprayer tank.
For most water-based spray solutions, the addition of chemicals does very little to affect nozzle flow rates.
When using liquid fertilizer solutions as the carrier liquid for chemicals, the nozzle flow rate can vary greatly at higher flow rates.
Refer to BAE-1293, Using Water to Calibrate Sprayers for Fertilizers and Other Liquid Solutions for more information on calibrating for other liquid carriers.
Determining Sprayer Output with the Nozzle Output Method
 One of the easiest and most effective methods to determine whether the sprayer is actually delivering the rate of spray solution  desired is the nozzle output method.
An advantage of this method is it can be completed with the sprayer stationary and does not require the sprayer be driven in the field.
One limitation is ground-driven sprayers cannot be calibrated by this method.
In order to use this method, three pieces of information must be known:
 1.
Operating Pressure will vary by manufacturer but can range from 15 psi to 120 psi, depending on the type of nozzle used.
2.
Ground Speed speed normally ranges from 3 mph to 8 mph for pull-type farm sprayers, 5 mph to 12 mph for most self-propelled farm sprayers, and 10 mph to 20 mph for commercial truck-mounted or floater-type sprayers.
3.
Effective Spray Width "W" varies with the type of nozzle arrangement used, but 15 inches, 20 inches and 30 inches are common.
Step 1.
Fill the spray tank partially with water and operate the sprayer at the selected pressure.
Use a container marked
 in fluid ounces to collect the output of a nozzle for one minute or some convenient fraction of a minute.
Make sure all nozzles are spraying uniformly and determine the average number of fluid ounces per minute  of output for each nozzle.
Step 2.
Convert OPM determined in Step 1 to GPM by dividing OPM by 128.
Step 3.
Select the ground speed  at which the sprayer is to be operated.
This speed will normally be in the 3 mph to 8 mph range for tractor-mounted or pull-type sprayers, 5 mph to 12 mph for self-propelled farm sprayers and 10 mph to 20 mph for truck-mounted floatation sprayers, depending upon field conditions.
Step 4.
Determine the effective spray width  in inches.
For broadcast spraying, "W" will equal the distance between adjacent nozzles.
For banded spraying, "W" will equal the banding width.
For row crop spraying with two or more nozzles per row or band, "W" will equal row spacing or banding width divided by the number of nozzles per row or band.
See Figure 5 for examples.
Step 5.
Once these values are known, the sprayer's output in gallons per acre can be calculated using the following equations:
 OPM GPM = 128
 Speed  = GPM X 5,940 W 
 GPA = the sprayer's output in gallons per acre.
GPM = the nozzle output determined in Step 2 in gallons per minute.
5940 = a constant used to convert inches, gallons per minute and miles per hour to gallons per acre.
Alternatively, using 6,000 instead makes the computation easier and results in an error less than 1%.
MPH = the ground speed selected in Step 3 in miles per hour.
W = the spray width per nozzle which was determined in Step 4 in inches.
128 = the number of fluid ounces per gallon.
For example, a pull-type field sprayer is set up to broadcast spray a herbicide with regular flat fan nozzles spaced 20 inches on center.
A ground speed of 5 mph has been selected.
The average collected nozzle output is 54 OPM.
What is the application rate of spray solution in gallons per acre?
Using Equation.
54 GPM = = 0.4219 gallons per minute 128
 GPA = 0.4219 5,940 = 25.06 gallons per acre 20
 With this set of conditions, the sprayer will apply 25 gallons per acre.
If this is not the application rate of spray solution desired, then one or more conditions will need to be changed.
A small nozzle flow rate change can generally be accomplished by either raising or lowering the pressure within the pressure limitations of the nozzle.
A larger flow rate change can be accomplished by either changing the ground speed or by switching to larger or smaller nozzle tips.
If 20 GPA was the desired application rate of spray solution, a change in ground speed of
 25 GPA = 5.0 MPH = 6.25 MPH 20 GPA
 would provide the desired 20 GPA without nozzle or pressure changes.
From Table 1, this would require that a ground distance of 200 feet be covered in 22 seconds.
Determining Sprayer Output with the 1/128th Acre Method
 In certain cases, nozzle choices may be limited or there is a desire to know what the current application rate of spray solution  is for a particular sprayer setup.
The 1/128th acre method works well in these instances and allows for a simple determination of application rate of spray solution  with very few hand calculations required.
Typically, this method is used for sprayer setups that do not have an accurate true ground speedometer.
In order to use this method, three pieces of information must be known:
 1.
Effective Spray Width "W" varies with the type of nozzle arrangement used, but 15 inches, 20 inches and 30 inches are common.
2.
Operating Gear and Throttle Setting the transmission gear and engine throttle  must be selected.
3.
Calibration Area an area of the field or similar terrain must be available to measure driving times for the sprayer during calibration.
Step 1.
Fill the sprayer tank at least half-full of water.
Choose the proper driving gear and engine throttle position for proper tank agitation and comfortable forward travel speed.
Choose a pressure in the center of the nozzle's recommended range that produces a good pattern.
Step 2.
Determine the Calibration Driving Distance  based upon the effective spray width  for the sprayer nozzle arrangement.
Measure and mark this distance in the calibration area.
Step 3.
Measure the time required by the sprayer to cover the distance laid out in Step 2.
Repeat this process at least two more times and calculate the average time in seconds for all three passes.
Step 4.
With the sprayer stationary and operating at the engine throttle and pressure set during Step 1, use a container marked in fluid ounces to collect the output of one nozzle for the number of seconds calculated in Step 3.
Make sure all nozzles are spraying uniformly and the number of fluid ounces of output are similar for each nozzle.
The application rate of spray solution in gallons per acre  will be the same and the number of fluid ounces collected during this step (e.g.
15
 Table 2.
Calibration distance.
Spray Width 	Calibration Distance 
 fluid ounces collected from each nozzle equals 15 GPA for the sprayer).
Step 5.
Adjust pressure to make minor rate changes and repeat Step 4.
Otherwise, select a new gear and/or throttle position and start back at Step 1.
For example, a pull-type field sprayer is set up to broadcast spray a herbicide with regular flat fan nozzles spaced 20 inches on center.
A gear of A4 and throttle of 2,200 rpm has been selected.
A pressure of 40 psi has been set.
An open field with similar terrain to pasture that will be sprayed has been selected for calibration.
What is the application rate of spray solution in gallons per acre?
Using Table 2, a nozzle spacing of 20 inches along the boom for a broadcast sprayer requires a calibration distance of 204 feet.
This distance is laid out over the calibration area.
After three passes, the average time required to cover 204 feet is 31 seconds.
Water is then collected from one nozzle for 31 seconds resulting in 19 fluid ounces in the measuring jar.
The sprayer will be applying 19 gallons of spray solution per acre covered.
Water also is collected from every other nozzle on the boom.
Any nozzles that vary greatly from 19 fluid ounces should be replaced.
The Oklahoma Cooperative Extension Service WE ARE OKLAHOMA
 The Cooperative Extension Service is the largest, most successful informal educational organization in the world.
It is a nationwide system funded and guided by a partnership of federal, state, and local governments that delivers information to help people help themselves through the land-grant university system.
Extension carries out programs in the broad categories of agriculture, natural resources and environment; family and consumer sciences; 4-H and other youth; and community resource development.
Extension staff members live and work among the people they serve to help stimulate and educate Americans to plan ahead and cope with their problems.
Some characteristics of the Cooperative Extension system are:
 The federal, state, and local governments cooperatively share in its financial support and program direction.
It is administered by the land-grant university as designated by the state legislature through an Extension director.
Extension programs are nonpolitical, objective, and research-based information.
It provides practical, problem-oriented education
 for people of all ages.
It is designated to take the knowledge of the university to those persons who do not or cannot participate in the formal classroom instruction of the university.
It utilizes research from university, government, and other sources to help people make their own decisions.
More than a million volunteers help multiply the impact of the Extension professional staff.
It dispenses no funds to the public.
It is not a regulatory agency, but it does inform people of regulations and of their options in meeting them.
Local programs are developed and carried out in full recognition of national problems and goals.
The Extension staff educates people through personal contacts, meetings, demonstrations, and the mass media.
Extension has the built-in flexibility to adjust its programs and subject matter to meet new needs.
Activities shift from year to year as citizen groups and Extension workers close to the problems advise changes.
CENTER PIVOT IRRIGATION SYSTEM LOSSES AND EFFICIENCY
 Kansas State Research and Extension
 Nearly 85 percent of the irrigated area in the three states of Colorado, Kansas and Nebraska are watered using center pivot sprinkler irrigation systems.
Center pivot irrigation systems have been adopted because of their ruggedness and versatility.
Center pivot systems reduced the amount of labor associated with irrigation as compared to surface irrigation systems and usually apply water to a crop more efficiently and uniformly.
Declining well capacities in many irrigation areas and producer desire to reduce pressure requirements to minimize irrigation pumping costs have prompted development of different water delivery package options for center pivot systems while maintaining the ability to efficiently and to uniformly distribute a limited water supply over a large area.
It is important, when designing a water delivery package for a new system or replacing a water delivery package on an older system, to keep in mind the general performance requirements of the various devices used to distribute water throughout the irrigated field.
If these general requirements are not followed closely, a reduction in the system efficiency could occur which could be due to increased runoff and reduced yields from under-watering due to poor uniformity.
The following will discuss the various options available for use with center pivot irrigation systems and their general performance requirements.
To provide a better understanding of conditions which reduce efficiency, the discussion will cover water losses associated with the various attachment options and configurations.
APPLICATION DEVICES: CHARACTERISTICS AND DESIGN CRITERA
 The water emitting devices that allow the distribution of water to a field from the center pivot system are often called the sprinkler package, even though the water distribution devices may not resemble a traditional sprinkler device.
Sprinkler or water delivery packages can be composed of a range of devices including impact sprinklers, fixed plate spray nozzles and moving plate spray nozzles or other water emission devices such as drag hose and/or drip tube.
The latter application
 devices apply water directly to the soil surface and can be either drag socks or bubble mode spray devices usually associated with Low Energy Precision Application  application packages or Mobile Drip Irrigation  packages that utilize driplines equipped with low flow emitters spaced closely together.
Impact sprinklers were used extensively on early water-drive center pivot irrigation systems.
However, modern impact sprinkler designs now utilize lower pressures and lower angles of water stream trajectories.
Impact sprinklers can have single or double nozzle configurations and have a large wetted diameter.
When properly overlapped, they can provide very uniform application patterns at relatively low water application rates.
The large wetted diameter and low water application rate may be important for tight soils or fields with large slopes to prevent irrigation water runoff.
Fixed plate sprinklers or nozzles spread the water stream emitted from the nozzle orifices by directing the flow against stationary splash pads.
The splash pads deflect the stream of water into the characteristic flow pattern that look like wagon wheel spokes creating usually a doughnut-like wetted pattern on the ground.
The splash pads can be flat, convex or concave, and grooved or nongrooved.
Grooved plates can have coarse to fine grooves.
These various splash plate configurations affect the stream pattern and droplet size.
Moving plate sprinklers or nozzles spread the water stream emitted from the nozzle orifices by directing the flow against splash pads that move.
Some rotate slowly; others spin rapidly; others wobble.
Depending on the speed of the movement, some water patterns develop that look like slowly rotating spokes of water, while others breakup the water streaming into a blur of water droplets.
In addition to the speed of rotation, these devices can also have various grooves and slot configurations to produce various droplet sizes.
The performance of each type of sprinkler nozzle is predictable as flow through the discharge opening or orifice is based on the opening size and the operating pressure.
For a round orifice, the nozzle discharge  can be calculated by:
 Where: q = nozzle discharge is gpm Cd = discharge coefficient  d = nozzle diameter in inches p = pressure in psi.
Since flow varies by the square of diameter, doubling the diameter quadruples the flow whereas doubling pressure would increase flow by about 40 percent as the flow changes by the square root of the pressure.
However, pressure can greatly affect droplet size distribution and wetted diameter.
All nozzles should be operated within the manufacturer's recommended pressure range.
Excessive pressure will result in an increase of small droplet sizes that are more susceptible to wind drift and evaporation losses while under-pressuring will increase the drop size.
Larger droplet sizes may have adverse effects on the soil surface due to higher impact energy or may affect coverage when the sprinkler package is used for chemigation or may affect the uniformity of application when designed with overlap.
Operation outside the recommended pressure range, either high or low, usually decreases the effective wetted diameter.
The wetted diameter of a nozzle refers to
 area of coverage of the nozzle.
There are many sprinkler or water delivery package design considerations, but the following are essential in determining adequate system performance:  application rate,  depth of application,  system irrigation capacity, and  uniformity of application.
APPLICATION RATE.
Application rate is volume of water applied to a location during a specified period of time.
Ideally, the irrigation application rate would be matched to the steady state soil infiltration rate.
Assuming dry soil, the infiltration rate for soil is high at the initiation of water application and decreases as infiltration continues until it reaches a stable  rate.
If the water application rate is less than the soil steady state infiltration rate, the irrigation water should be able to be infiltrated into the soil root zone.
However, this design criterion was developed when the sprinkler packages were primarily high pressure, large wetted diameter impact sprinklers.
The term application rate can also refer to several different measurements.
The instantaneous application rate refers to the rate of water application at any given time.
This value will vary from zero to the peak instantaneous application rate as the water delivery package crosses over a given point.
The peak application rate generally refers to the maximum application rate for a system.
The mean application rate would be volume of water delivered at a given point during the total time of wetting and would be smaller value than the peak application rate.
The application rate for various nozzles must increase with distance from the pivot point as more area is covered by the nozzle with distance.
This is why run off problems are generally associated with the outer edges of a center pivot unless soil or slope conditions are more limiting in an inner portion of the center pivot.
The introduction of fixed plate and moving plate sprinkler nozzle options meant more center pivot sprinkler packages used devices with smaller wetted diameters.
The common use of drop tubes lower the nozzle position closer to the ground surface which also decreases wetted diameter.
These factors mean the system water delivery package design needs to consider the amount of soil surface water storage that is available during the irrigation event to prevent runoff.
The USDA Natural Resources Conservation Service  has determined infiltration rates for most irrigated soils.
Soils with similar infiltration rates were grouped into Intake Families.
Each of these soil intake families has a specific soil intake curve as shown in Figure 1.
The soil type for any field of interest can be determined by referring to soil maps which are available at county extension or NRCS offices and most are now web accessible.
Soil intake curves are a good place to start when determining the maximum application rate.
Average application rates produced by different sprinkler packages, shown in Figure 2, illustrate that sprinkler packages with smaller wetted diameters have higher average application rates and vice versa.
When trying to match the application rate of a system to the intake rate of the soil, it is helpful to put the intake rate curve and the application rate curve on the same figure.
This is shown in Figure 3 with the intake rate curve for the 0.5 NRCS Soil Intake Family and application rate curves for three different wetted radii.
The areas in Figure 3 where the application rate curves extend above the intake rate curve represent water that must be standing on the surface until infiltrated.
Until it is infiltrated, it has a potential to run off or have surface water redistribution.
If this standing surface water does run off, there is a reduction in system efficiency.
Sprinkler packages with a higher wetted radius have a lower application rate and therefore are less likely to produce runoff.
The prevention of runoff should be a major design consideration.
Figure 1.
Infiltration rate curves from the USDA Natural Resources Conservation Service for various soil intake families.
Figure 3.
Potential runoff for a silt loam soil receiving a 1.1-inch water application without surface storage.
DEPTH OF APPLICATION.
The amount of water applied during an irrigation event should not exceed the volume of water that the root zone can hold.
If excess water is applied, water will be lost to deep percolation, thus reducing the overall irrigation efficiency.
Different types of soils have different soil water holding capacities.
For optimal crop growth results, it is best to keep the soil water level between field capacity and about 50 percent of the available water in the crop root zone for the type of soil being irrigated.
These levels are based on the tension required to extract water from the soil.
Field capacity is often defined as the level of water remaining in the soil root zone approximately 3 days after a large irrigation or precipitation event.
Permanent wilting point is defined as the level of soil water at which a plant can no longer extract water from the soil, and thus, the plant can no longer survive.
The soil water between field capacity and the permanent wilting point is the amount of water that is available for plant use.
Application of water above field capacity results in runoff and the soil becomes saturated.
The water that infiltrated will be more likely to be lost to deep percolation.
Applying too little water will result in plant stress.
Irrigation scheduling management procedures can be used to monitor soil water levels.
Table 1 gives typical soil water levels for four soil textures.
The root zone of the crop to be irrigated, along with the available water holding capacity for the soil being irrigated, determines the maximum application amount subject to water supply constraints.
Table 2 summarizes crop water use characteristics for many irrigated crops and includes the root zone for several crops common to the Central Plains region.
Multiplication of the managed root zone depth of the crop by the available water-holding capacity of the soil being irrigated determines the total available water-holding capacity in the root zone.
This is the most water that can be stored without water lost to deep percolation.
The maximum amount that can be applied is less than this since the general irrigation management guideline is to prevent more than 50 percent soil water depletion.
Roots are concentrated in the upper part of the active root zone, so the managed zone is normally limited to no more than 4 feet.
Table 1.
Water-Holding Capacities of Soils.
Soil texture	Water per foot-depth of soil	Water available
 Field capacity	Wilting point	
 	
 Sandy	0.75	0.25	0.50
 Sandy Loam	1.30	0.30	1.00
 Silt Loam	2.00	0.50	1.50
 Clay Loam	3.00	1.00	2.00
 Table 2.
Seasonal Crop Water Use , Typical Average and Daily Peak Water Use Rate, Critical Growth Stages, Typical Root Depth, and Typical Managed Root Depth for Various Crops Common to the Central Plains Region.
MF2384, or Wheat C529; for more specific crop information)
 Seasonal Crop	Average	Generalized	Un-	Typical
 Crop	Water Use 	Water Use	Peak Daily	Peak Water	Single-day	Critical growth	stages	root depth	restricted	root zone	managed
 Rate	Use Rate	depth
 	---	
 Alfalfa	31.5 63.0*	0.40	0.55	after cutting	6 -10	3 4
 Corn	15.6 31.6	0.35	0.50	tasseling, silking	4 6	3 4
 Sorghum	16.0 30.6	0.35	0.40	boot-heading	4 6	3 4
 Soybean	17.4 27.6	0.35	0.40	bloom podding	4 6	3 4
 Sunflowers	16.0 39.4	0.40	0.50	maturity	4 6	3 4
 Wheat	15.4 25.6	0.30	0.40	boot-heading	4 6	3 4
 * *Forage crops such as alfalfa can have use large amounts of water if growing seasons are long.
SYSTEM IRRIGATION CAPACITY.
System irrigation capacity is the average depth of water applied to the entire field if it was watered in one day.
For example, a center pivot may be set to apply a one-inch application as it rotates around a field.
However, it may require four days to complete an irrigation cycle.
The system irrigation capacity is then 1 inch per four days or 0.25 inches/day.
The system capacity can be calculated using the following equation:
 System Irrigation Capacity: IC =  / 
 where: IC = Irrigation Capacity in inches per day
 450 is a conversion factor; 450 gpm = 1 ac-in/hr
 Q = flow rate to irrigation system in gallons per minute A = irrigated area, acres T = Hours of operation per day; usually 24 hours/day
 For example, Eq, 2 indicates that a system irrigating 128 acres with 650 gpm and running continuously will have a system irrigation capacity of 0.27 in/day.
Notice that in this example, the irrigation time is for continuous operation of the system.
Other factors to take into account when calculating the system capacity are possible hours lost to electrical load control or downtime needed for system maintenance or repair.
For the percent of time that the system must be shut down, the capacity will have to be increased to compensate for the lost irrigation time.
Figure 4 shows the relationship between system capacity and system length for three different peak water use rates.
Figure 4.
Impact of design ET rate on system flow rate for various irrigation system lengths.
The crop water use rate is variable from day to day and from season to season, depending on factors such as the type of crop, the stage of growth of the crop, and weather conditions.
Daily peak water use values are shown in Table 2; however, soil water storage provides a buffer so system irrigation capacity is generally less than peak daily use rate.
Deep rooted crops and high water-holding capacity soils will need less irrigation capacity for reliable crop production than shallow rooted crops and sandy soils.
Many irrigation systems have a capacity at much less than the peak use rate.
Systems in Kansas with capacity above 0.25 inches per day are generally low-risk when operated on high water holding capacity soils.
On low water-holding capacity soils, such as sand, the water reserves are much less and system irrigation capacities of 0.3 in/days or greater are needed to prevent yield limiting water stress.
It is worth noting that irrigation capacity could be increased by reducing the total area irrigated.
UNIFORMITY OF APPLICATION.
When designing sprinkler irrigation systems, it is important to provide as uniform application as possible.
A non-uniform application will result in areas of underwatering as well as areas of over-watering.
Either area could result in reduced yield and lead to decreased system efficiency.
The uniformity of the sprinkler or water delivery package design is determined by system package design.
It is affected by the operating conditions and environmental factors, especially wind.
Figure 5 shows the results of a center pivot uniformity test.
Section A of the pivot illustrates a portion of the sprinkler package that was performing well.
This area of the pivot has a coefficient of uniformity of approximately 90 percent.
In section B, a leaky boot connection between two spans was caught in one container.
Section C represents the area covered by the outer two spans of the system that shows an area of over watering and under watering.
This is better illustrated in Figure 6, which shows the test results of this area with the end gun off.
The difference in depth was the result of the nozzles for the two spans being switched at installation.
Section D of Figure 5 demonstrates the effect of an improperly operating end gun.
In this case, the end gun operation angle was improperly set and it was over spraying the nozzles for about one third of the last span and for the overhang of the center pivot.
In this example, all of the causes of the poor uniformity were easily and inexpensively corrected.
Sprinkler Package Uniformity Test with End-gun 'ON' Finney County, Kansas
 Figure 5.
Mobile Irrigation Lab uniformity analysis of a center pivot sprinkler package
 Sprinkler Package Uniformity Test Results of the Outer Two Spans.
Finney County, Kansas
 Figure 6.
Depth of application catch for 2 spans of a center pivot with a reversal of the nozzles between the inner and outer span as indicated by the decreased application depth.
Uniformity is decreased if system pressure is not kept at the design pressure.
Wear of nozzles and incrustation build up can also negatively affect the pattern.
Canopy interference also decreases distribution uniformity.
TYPES OF WATER LOSSES
 From a practical standpoint, water that does not reach or remain in the root zone until it is used by the crop is not available to the plant and is therefore considered lost.
Although an exception may be required if the irrigation water has high salinity or other poor water quality conditions.
Excess water application may be needed to provide a leaching requirement to remove salts from the root zone which is considered a beneficial use.
The reduction in water made available to the plant reduces the water application efficiency of the entire system.
Water losses occur in four areas:  air loss,  foliage loss,  ground loss and  deep percolation, which are illustrated in Figure 7 for several water delivery package configurations.
Figure 7.
Illustration of different types of water losses associated with sprinkler systems.
AIR LOSS.
The two components of air water loss are drift and droplet evaporation.
Droplet evaporation is the water from droplets that evaporates while in flight before reaching the crop canopy or the soil surface.
Drift is the water droplets that move off the field or onto a non-targeted area of the field, usually by wind.
This causes non-uniformity in the water application, and crops located in areas not receiving the proper amount of water may become stressed.
These types of losses can be reduced by selecting nozzles that produce large droplets and moving the discharge point closer to the crop canopy or soil surface.
Irrigation farmers are often very concerned about air losses, referring to the combination of droplet evaporation and drift as simply evaporation.
However, the losses associated with air losses for properly designed and operated nozzles of any type are small as compared to other potential water losses.
Various studies may have contributed to this perception of large air losses associated with sprinkler systems,.
However, recent studies using either improved collection technology or analytical techniques indicated that air losses for properly operated nozzles devices are small.
For example, Thompson et al.
noted that direct evaporation of water droplets was less than1 % of the discharged water.
Minimal direct water droplet evaporation and drift loss is consistent for all types of sprinkler nozzles as long as the droplet sizes produced by the devices are within normal droplet size range.
The number of small droplets can be increased by various design and operational conditions, most commonly by excess operational pressure.
Extremely small droplets can evaporate at a very high rate during flight but only constitute a small portion of the flow volume under normal conditions.
While air losses are relatively unaffected by nozzle type and location, these factors have important impacts on the next category of irrigation water loss-foliage losses.
FOLIAGE LOSS.
Upon entering the canopy of the crop, water can be lost to plant interception or to evaporation.
Interception is water that is "caught" and held on the plant material surfaces, and overtime evaporates into the atmosphere.
Foliage evaporation losses refer to water evaporating from the foliage surface during the time that field location is being irrigated.
To reduce water losses in the canopy, discharge points have been moved closer to the ground to limit the extent of the surface wetting of crop canopy and reduce the total time of irrigation at a given field location.
Interception losses for impact sprinklers and other above canopy nozzles would be consistent and probably not greatly reduced even for in-canopy nozzles, since the nozzles do not stay perfectly horizontal to the ground surface while moving through the crop rows.
However the amount of water lost to canopy evaporation would be related to the time of wetting due to irrigation.
As illustrated previously in figure 2, a low pressure impact sprinkler  might have a wetted radius of 80 feet as compared to a wetted radius of 60 feet for a rotator nozzle ; this would represent a 25% reduction in the time that canopy wetting occurs, therefore a 25% potential reduction in this individual loss component, would represent a positive impact on the overall irrigation efficiency by only a few percent.
Canopy evaporation continues to decrease and can be eliminated with application systems like LEPA and MDI which deliver irrigation water directly to the ground.
LEPA and MDI may have irrigation capacity limitations and require other management techniques, such as circular row planting and in some cases special off-season protection that limit their use.
Reducing canopy evaporation should not be at the expense of creating runoff.
Evaporation from the canopy does suppress crop transpiration while evaporation is occurring as illustrated in Figure 8.
However evaporation occurs more rapidly than transpiration, therefore making evaporation less beneficial than transpiration, and representing a loss of irrigation efficiency.
Figure 8: Water use components for a rotator sprinkler places on top of the pivot lateral..
GROUND LOSS.
Once the water reaches the ground, it can be lost in several ways.
If water application rates are higher than the soil intake rate, water can either be held in surface storage or it can start to move along the soil surface and become runoff.
Runoff water can either leave the field or just move to a different location within the field.
Within field water movement causes nonuniformity in the application, and reduces the efficiency of the application if the soil receiving the runoff as infiltration is over-watered, losing excess water to deep percolation In addition, these areas may also have production decreased due to lack of soil aeration from the ponded water and leaching of nutrients with the deep percolation.
The portion of the field losing water will have less water available to meet crop needs.
Runoff water that leaves the field is a direct irrigation efficiency loss.
Water being held in surface storage will either infiltrate or evaporate.
The stored water lost to evaporation reduces the irrigation amount, and thus the application efficiency.
If the depth of application exceeds the soil water storage capacity within the root zone, water will be lost to deep percolation.
This is when water infiltrates below the crop root zone.
Ground level losses of water can be reduced by using different tillage techniques and reducing the application depth of each irrigation event.
However decreasing the application depth per irrigation event increases the number of events needed to apply the seasonal water needs and subjects the water application to additional foliage water losses.
Soil water evaporation losses are greater during off-season and early season irrigation events when the crop canopy is absent or reduced.
Soil residue also plays a role in the amount of soil evaporation that can occur.
Application packages such as LEPA and MDI that reduce the total wetted surface also have potential to reduce soil water evaporation.
DEEP PERCOLATION LOSS: Deep percolation loss would be water that enters the soil profile that is in excess of the available water storage capacity of the zoot zone, more specifically the managed root zone depth.
Deep percolation losses should be managed by using an appropriate irrigation scheduling method, such as climatic  based irrigation scheduling or soil-based irrigation scheduling.
A combination of these two scheduling methods allows two independent evaluation of the irrigation schedule.
WATER DELIVERY PACKAGE OPTIONS
 There are many different types of nozzles available for selection, each of which can be operated at various pressures, mounted at various heights, equipped with different orifice sizes and spaced at various widths from other nozzles, making hundreds of possible choices among water delivery packages.
If the nozzles are not used within the given specifications, they will not perform as designed, and may reduce application efficiencies significantly.
Table 3 shows the relationships between the nozzle types and their design pressure range.
As might be expected, different nozzles provide different output and application characteristics.
Table 4 gives the rating of output characteristics for Sprinklers 2 through 7 from Table 3.
These characteristics determine the types of water losses to which each nozzle is susceptible.
AVERAGE APPLICATION RATE.
The average application rate is calculated by dividing the application amount by the time of application.
Nozzles operating at different pressures provide a different wetted radius.
It has already been noted that smaller wetted radii  provide a higher average application rate.
Table 4 shows that Nozzle 2, with the lowest operating pressure, has the highest average application rate.
If the average application rate for a nozzle of interest is significantly higher than the intake rate of the soil to be irrigated, the potential for runoff is high.
Table 3.
Minimum end pressures on center pivots and linear move systems for various sprinkler devices..
Spray Nozzles  Rotators  Small Impacts-Modified Nozzles  Small Impacts Round Hole Nozzles  Large Impacts Round Hole Nozzles  Larger Impacts  Round Nozzles  Impact End Gun Modified Nozzle  Impact End Gun Round Hole Nozzle  Gun Type End Gun Modified Nozzle  Gun Type End Gun Round Hole Nozzle
 PEAK APPLICATION RATE.
The peak application rate is the maximum rate at which water is supplied to the soil at a given point in time and at a specified location.
Selecting a sprinkler package with a peak application rate that is too great could cause runoff to develop.
The key is to match the peak application rate to the soil infiltration rate and soil surface water storage capacity.
Three factors that affect the peak application rate are  system length,  system flowrate, and  nozzle wetted radius.
The following equation can be used to calculate the peak application rate:
 =  X Rsp)
 lp = peak water application rate, in/hr K = constant, 122.5 Qp = irrigation system capacity, gpm Rs = system length, ft.
Rsp = wetted radius of outer nozzle, ft.
This equation indicates that as the system length increases the peak application rate increases.
Figure 9 provides a visual representation of how wetted radius impacts the peak application rate as system length increases.
Figure 9.
Impact of sprinkler wetted radius on peak water application rate when designed for 0.35 inch per day ETp.
WETTED RADIUS.
The wetted radius of a sprinkler is the distance water will travel from the nozzle before striking the ground.
Nozzles that have a large wetted radius also tend to have a large droplet size and operate at higher pressures as indicated in Table 4.
Wetted radius is also an indication of the average application rate.
A larger wetted radius will have a lower average application rate, and thus the potential for runoff will be lower.
WATER DROPLET SIZE.
The water droplet size is determined by such things as operating pressure, size and shape of the opening on the nozzle, and what type of pad or arm the nozzle is equipped with.
The important properties of water droplet size to remember are:  large droplets have a high instantaneous application rate that can cause crusting on unprotected soil, which can increase the potential for runoff; and  small droplets are more susceptible to drift and evaporation losses.
Table 4 gives water droplet size comparisons.
Table 4.
Rating of output characteristics of sprinklers 2 through 7 from Table 3..
Average application		
 Instantaneous application rate		
 Wetted radius		
 Water droplet size		
 A trend in recent years has been to use lower pressure nozzles which reduces the overall pressure required for the system and lowers pumping costs.
Since lower pressure nozzles have a smaller droplet size, they have been moved closer to the ground to reduce evaporation and drift losses.
Lower pressure nozzles also increase the average application rate, requiring that special attention being given to reducing the potential for runoff.
LEPA and MDI.
The LEPA nozzle was not included in the above comparisons.
The operating pressure and the position of the nozzle that is close to the ground means the wetted radius for LEPA nozzles are very small.
This also means that the average application rate is very high.
LEPA has been described by some as a traveling flood irrigation system, and because of its characteristics, must be used in conjunction with special management practices.
LEPA packages were developed to serve low irrigation capacity systems on level fields.
LEPA nozzle spacing is usually twice the row spacing  and the rows must be planted in a circle.
In addition, special tillage practices, such as dammer-diking, must be used to control runoff.
MDI uses microirrigation driplines that are attached to the center pivot via drop tubes.
The driplines are designed for this application and feature closely-spaced pressure compensating emitters.
The length of the driplines increase with the distance from the pivot point so that flow rate can be matched to the area of coverage.
These systems were also originally designed for low capacity systems but some have been installed on high capacity systems.
The concept of delivering water directly to the ground would eliminate air and canopy losses and minimize ground losses.
To optimize the benefits of this concept, circular planting is recommended particularly for tall row crops.
Irrigation scheduling is still needed to prevent deep percolation losses.
Center pivot systems are popular because of the ability to provide efficient and uniform application of irrigation water for a wide variety of crops and field conditions when equipped with a properly designed and operated water delivery package.
Center pivot labor requirements also tend to be low as compared to surface irrigation system requirements.
There are many different water delivery package options associated with center pivot irrigation systems, and consideration must be given to the overall system rather than to "fixing" one problem.
A trend in recent years has been to use low pressure nozzles which reduces the overall pressure required for the system, to help reduce operating costs.
Since lower pressure nozzles have a smaller droplet size, they are more susceptible to drift and evaporation losses.
Lower pressure nozzles also increase the average application rate, increasing the potential for runoff.
The capacity needed to effectively water a given field may not be met by a system whose pressure has been reduced solely for the purpose of reducing pumping costs.
This is a good example of how focusing on one aspect of the system can lead to other problems elsewhere on the system.
When designing a new system or converting an older system, consideration should be given to the general nozzle performance requirements as well as to cost reduction and water loss reduction.
USDA NRSC.
1997.
National Engineering Handbook: Irrigation Guide, part 652.
U.S.
Department of Agriculture, Washington, DC.
Pp.
852.
Quantity and Quality of Water for Dairy Cattle
 Michael L.
Looper Professor and Department Head Animal Science
 Arkansas Is Our Campus
 Water constitutes 60 to 70 percent of a livestock animal's body.
Water is necessary for maintaining body fluids and proper ion balance; digesting, absorbing and metabolizing nutrients; eliminating waste material and excess heat from the body; providing a fluid environment for the fetus; and transporting nutrients to and from body tissues.
Dairy cattle get the water they need by drinking and consuming feed that contains water, as well as from metabolic water produced by the oxidation of organic nutrients.
Water loss from the body occurs via urine, feces and milk; through sweating; and by evaporation from body surfaces and the respiratory tract.
The amount of water lost from a cow's body is influenced by the animal's activity, air temperature, humidity, respiratory rate, water intake, feed consumption, milk production and other factors.
This publication covers water intake guidelines and water quality issues for dairy cattle.
Water Intake and Requirements
 Lactating Cows Drinking water or free water intake satisfies 80 to 90 percent of a dairy cow's total water needs.
The amount of water a cow
 Water availability and quality are extremely important for animal health and productivity.
drinks depends on her size and milk yield, quantity of dry matter consumed, temperature and relative humidity of the environment, temperature of the water, quality and availability of the water, and amount of moisture in her feed.
Water is an especially important nutrient during periods of heat stress.
The physical properties of water are important for the transfer of heat from the body to the environment.
During periods of cold stress, the high heat capacity of body water acts as insulation conserving body heat.
Water intake for lactating cows can be predicted from the following equation:
 Water intake, lbs/day = 35.25 + 1.58 X Dry matter intake  + 0.90 X Milk yield  + 0.11 X Sodium intake  + 2.65 X Weekly mean minimum temperature  -
 The equation predicts water consumption will change 1.58 pounds for each 1.0-pound change in dry matter consumed, 0.90 pound for each 1.0-pound of milk produced, 0.11 pound for each gram of sodium consumed and 1.47 pounds for each degree Fahrenheit  change in weekly mean minimum temperature.
Weekly mean minimum temperature typically is 10 to 15F lower than mean daytime temperature.
Table 1 lists the estimated daily water intake for lactating cows using the above equation.
TABLE 1.
Estimated daily water consumption for a 1,500-pound lactating cow producing 40 to 100 pounds of milk daily.
Milk	Estimated	Mean Minimum Temperatureb
 		40F	50F	60F	70F	80F
 40	42	18.4	20.2	22.0	23.7	25.5
 60	48	21.8	23.5	25.3	27.1	28.9
 80	54	25.1	26.9	28.7	30.4	32.2
 100	60	28.5	30.3	32.1	33.8	35.6
 aSodium intake = 0.18% of DM intake.
Mean minimum temperature typically is 10 to 15F lower than the mean daytime temperature.
C1 gallon of water weighs 8.32 pounds.
Dry Cows The major factors affecting free water intake of dry cows are concentration of dry matter in the diet, dry matter intake and amount of protein in the diet.
Water intake of dry cows can be estimated by the following equation:
 Water intake, lbs/day = -22.80 + 0.5062 X Diet dry matter  + 2.212 X Dry matter intake  + 0.0869 X Diet crude protein 2
 For example, a 1,500-pound nonlactating cow that eats 28 pounds of dry matter containing 12 percent moisture and 12 percent crude protein would consume 96 pounds  of water per day at air temperatures between 50F and 80F.
Water intake may be 120 to 200 percent greater during periods of heat stress.
Calves and Heifers During the liquid feeding stage, calves receive most of their water as milk or milk replacer.
However, studies show that calves offered water by free choice in addition to a liquid diet gain faster and consume dry feed earlier than
 calves provided water only in their liquid diet.
Therefore, it is recommended to provide water by free choice to calves receiving liquid diets to enhance growth and dry matter intake.
Weaned dairy heifers consume approximately 1.0 to 1.5 gallons of water per 100 pounds of body weight.
As with all livestock, water should be fresh, clean and always available.
Care should be taken to ensure adequate water supplies during periods of heat stress.
TABLE 2.
Estimated water intake for dairy heifers.
40F	60F	80F
 200	2.0	2.4	3.3
 400	3.8	4.6	6.1
 600	5.4	6.5	8.7
 800	6.8	8.2	11.0
 1000	8.0	9.6	12.7
 1200	9.0	10.8	14.5
 Providing the opportunity for livestock to consume a relatively large amount of clean, fresh water is essential.
Water is consumed several times per day and generally is associated with feeding or milking.
Cows may consume 30 to 50 percent of their daily water intake within 1 hour after milking.
Reported rates of water intake vary from 1 to 4 gallons per minute.
On the basis of farm studies, the length of water troughs should be 2 inches per cow with an optimal height of 24-32 inches.
Reducing the height 2 to 3 inches may be logical for Jerseys.
Water depth should be a minimum of 3 inches to allow the animal to submerge its muzzle 1 to 2 inches.
Provide at least one watering device for every 15 to 20 cows, or a minimum of 2 feet of tank space per 20 cows.
At least two water locations are needed in the loafing area for each group of cows.
For confinement operations, waterers should be allocated at milking parlor exit and within 50 feet of the feed bunk or at every crossover in freestall barns.
Heifers should be provided at least one watering space per 20 animals with a minimum of two waterers per group.
The temperature of drinking water has only a slight effect on drinking behavior and animal performance.
Under most circumstances, responses to chilling water would not warrant the additional cost.
Cows may consume 30 to 50 percent of their daily water intake within 1 hour after milking.
Given a choice, cows prefer to drink water with moderate temperatures  rather than very cold or hot water.
Water quality is an important issue in dairy cattle production and health.
The five properties most often considered in assessing water quality for both humans and livestock are organoleptic properties , physiochemical properties , along with the presence of toxic compounds , excess minerals or compounds  and bacteria and algae.
Research on water contaminants and their effects on cattle performance are sparse.
The following discussion attempts to define some common water quality problems in relation to cattle performance.
Salinity, total dissolved solids  and total soluble salts  are measures of constituents soluble in water.
Sodium chloride is the first consideration in this category.
Other components associated with salinity, TDS or TSS are bicarbonate, sulfate, calcium, magnesium and silica.
A secondary group of constituents, found in lower concentrations than the major constituents, includes iron, nitrate, strontium, potassium, carbonate, phosphorus, boron and fluoride.
Guidelines for TDS in water for dairy cattle are presented in Table 3.
Research has shown feedlot cattle drinking saline water  had lower weight gains than cattle drinking normal water , when the ration's energy content
 TABLE 3.
Guidelines for use of saline waters for dairy cattle.
Less than 1,000	Presents no serious burden to livestock.
1,000 to 2,999	Should not affect health or performance,
 but may cause temporary mild diarrhea.
3,000 to 4,999	Generally satisfactory, but may cause
 diarrhea especially upon initial
 5,000 to 6,999	Can be used with reasonable safety for
 adult ruminants.
Should be avoided for
 pregnant animals and baby calves.
7,000 to 10,000	Should be avoided if possible.
Pregnant,
 lactating, stressed or young animals can
 Over 10,000	Unsafe.
Should not be used under any
 ppm = parts per million
 was low and during heat stress.
High-energy rations and cold environmental temperatures negated the detrimental effects of high-saline water consumption.
Likewise, milk production of dairy cows drinking saline water  was not different from that of cows drinking normal water during periods of low environmental temperature.
But it was significantly lower during summer months.
Cows offered salty water drank more water per day  over a 12-month period than cows drinking normal water.
Hardness is generally expressed as the sum of calcium and magnesium reported in equivalent amounts of calcium carbonate.
Other cations in water, such as zinc, iron, strontium, aluminum and manganese, can contribute to hardness but usually are very low in concentration compared with calcium and magnesium.
Hardness categories are listed in Table 4.
Water hardness has no effect on animal performance or water intake.
TABLE 4.
Water hardness guidelines.
Very hard	> 180
 a1 grain/gal = 17.1 milligrams per liter
 Nitrate can be used in the rumen as a source of nitrogen for synthesis of bacterial protein, but reduction to nitrite also occurs.
When absorbed into the body, nitrite reduces the oxygen-carrying capacity of blood and, in severe cases, results in asphyxiation.
Symptoms of nitrate or nitrite poisoning are labored breathing, rapid pulse rate, frothing at the mouth, convulsions, blue muzzle and bluish tint around eyes, and chocolate brown blood.
More moderate levels of nitrate poisoning have been linked to poor growth, infertility problems, abortions, vitamin A deficiencies, reduced milk production and general unhealthiness.
The general safe concentration of nitrate in water is less than 44 ppm and less than 10 ppm of nitratenitrogen.
In evaluating potential nitrate problems, feed also should be analyzed for nitrate in that the effects of feed and water are additive.
TABLE 5.
Concentration of nitrates  and nitrate-nitrogen  in drinking water and expected response.
0-44	10	No harmful effects.
45-132	11-20	Safe, if diet is low in nitrates and
 133-220	21-40	Could be harmful if consumed
 over a long period of time.
221-660	41-100	Dairy cattle at risk; possible death
 661-800	101-200	High probability of death losses;
 Over 800	Over 200	Do not use; unsafe.
ppm = parts per million
 Sulfate guidelines for water are not well-defined, but general recommendations are less than 500 ppm for calves and less than 1,000 ppm for adult cattle.
When sulfate exceeds 500 ppm, the specific salt form of sulfate or sulfur should be identified, since the form of sulfur is an important determinant of toxicity.
Hydrogen sulfide is the most toxic form, and concentration as low as 0.1 milligram per liter can reduce water intake.
Common forms of sulfate in water are calcium, iron, magnesium and sodium salts.
All are laxative, but sodium sulfate is the most potent.
Cattle consuming water high in sulfates  show diarrhea initially but appear to become resistant to the laxative effect.
Iron sulfate has been reported to be the most potent depressor of water intake compared with other sulfate forms.
Water and
 feed with high sulfate contents have been linked to polioencephalomalacia  in beef calves.
pH is a measure of acidity or alkalinity.
A pH of 7 is neutral, less than 7 is acidic and more than 7 is alkaline.
Little is known about the specific pH's effect on water intake, animal health and production or the microbial environment in the rumen.
The preferred pH of drinking water for dairy animals is 6.0 to 8.0.
Waters with a pH outside of the preferred range may cause non-specific effects related to digestive upset, diarrhea, poor feed conversion and reduced water and feed intake.
Microbiological analysis of water for coliform bacteria and other microorganisms is necessary to determine sanitary quality.
Since some coliform bacteria are soil borne or nonfecal, a fecal coliform test may be used to determine if the source of total coliform is at least in part from feces.
A fecal streptococci test may be run on fresh samples to determine if the contamination is from animal or human sources.
If fecal coliforms exceed fecal streptococci, human sources of pollution may be suspect.
If fecal streptococci exceed fecal coliform, animal sources of pollution are indicated.
For animal consumption, especially young calves, total and fecal coliform counts should be less than 1 per 100 milliliters.
For adult animals, total and fecal coliform counts should be under 15 and 10 per 100 milliliters, respectively.
It is recommended that fecal streptococci counts not exceed 3 or 30 per 100 milliliters for calves and adult cattle, respectively.
Total bacteria count measures virtually all pathogenic as well as noninfectious bacteria that use organic nutrients for growth.
Total bacteria counts in excess of 500 per 100 milliliters may indicate water-quality problems.
Water sources with total bacteria counts in excess of 1 million per 100 milliliters should be avoided for all livestock classes.
Most water supplies will have counts below 200 per 100 milliliters continuously.
Blue-green algae have been reported to cause illness when cattle are allowed to consume water containing this organism.
Although the causative agent has not been identified specifically, cattle should be prevented from drinking water with heavy algae growth.
Symptoms in blue-green algae poisoning include ataxia or incoordination of voluntary muscle movement, bloody diarrhea, convulsions and
 sudden death.
This is an occasional problem in freestanding water, such as farm ponds.
Shading water troughs and frequent sanitation will minimize algae growth.
Other potentially toxic compounds and organisms sometimes are found in water and can pose a health hazard to cattle.
For safe consumption, water contaminants should not exceed the guidelines in Table 6.
However, many dietary, physiologic and environmental factors affect these guidelines and make it impossible to accurately determine the concentrations at which problems may occur.
TABLE 6.
Generally considered safe concentrations of some potentially toxic nutrients and contaminants in water for cattle.
ppm = parts per million
 Water Sampling and Testing
 Typically, 1 or 2 quarts of water from the source in question should be adequate to complete any needed tests.
Samples may be sent to any accredited commercial or state-operated laboratory for analyses.
Producers should consult with their herd veterinarian or state Extension personnel for assistance in selecting a laboratory, as well as for assistance in selecting appropriate tests and interpreting results.
Water availability and quality are extremely important for animal health and productivity.
Limiting water availability to cattle will depress production rapidly and severely.
The most common water-quality problems affecting livestock production include high concentrations of minerals , high nitrogen content , bacterial contamination, heavy growth of blue-green algae and accidental contamination by petroleum, pesticides or fertilizer products.
On the basis of the scientific literature, no widespread specific production problems have been caused by consumption of low-quality water.
Poor water quality might cause reduced production or nonspecific diseases and should be one aspect investigated when there are herd health and production problems.
irrigation in Lodi area
 Vineyard decline-an increasing problem in Tokay vineyards in the Lodi district-results in low yields, large losses due to sunburn damage, small berry size and other low quality factors.
Extensive efforts have been made, in past years, to reduce losses from nematode infestations, dead-arm disease, and poor fertilization practices.
However, no work has been attempted to improve irrigation practices.
Irrigation methods have not been altered over the years to compensate for weakened root systems caused by root pests and a lowering water table.
The most common irrigation method used in Tokay vineyards is a single furrow placed in every other middle between the rows.
The efficiency of the single furrow method is questionable and the application of excessive water causes root damage and weakened vines.
In April, 1960, an intensive, longterm irrigation experiment was established in a Tokay vineyard near Lodi.
The objective of the study is to determine the method of irrigation that will give better distribution of water in the soil and-combined with good cultural practices-improve vine vigor, increase yield, and produce good quality shipping Tokay grapes.
The experimental block of vines selected consisted of 10 rows of 68 vines each, with the rows 10' apart and the vines 10' apart in the rows.
The vines are 50 years old.
The vines in the southern part of the plot are in a weakened condition, but the northernmost vines have good vigor.
The plot was divided into two sections to include the weak vines in one study and the strong vines in the other.
The soil of the plots is deep, relatively well drained Hanford sandy loam.
The soil texture is fairly uniform to a depth of 7', where there is a layer of fine clay.
Hanford sandy loam is the soil type in which the majority of shipping Tokay grapes are grown.
The irrigation method used by the grower is the common single furrow in every other row.
The same furrow loca-
 tions have been used for the past 20 years.
The study is designed to compare three methods of irrigation:
 1.
A single furrow every other vine row.
2.
A single furrow every vine row.
3.
Flooding the entire area on both sides of the vines.
Evaluations are made to determine if and when differences occur in vine vigor and fruit quality from variations in the irrigation methods.
It may be several years before extreme differences occur.
Tensiometers are used to determine the pattern of soil moisture extracted by the vines and the movement of water in the soil following an irrigation.
The locations of the tensiometers and the methods of irrigation are shown in the adjacent diagram.
The tensiometers located at Stations I and IV were installed to study irrigation treatment 1; Stations II and V, treatment 2; and Stations III and VI for treatment 3.
At each station tensiometers were placed at 2', 4' and 6' depths at A, in the west center between vine rows; B, next to the vine; and C, the east center between vine rows.
Rising tensiometer readings indicate decreasing available soil moisture.
In the 1960 trials readings were taken twice weekly, during the growing season, and ranged from zero to 80.
When the average 4' tensiometer reading was between 60 and 70 the plots were irrigated.
Stations I and IV received five irrigations and the other stations four each.
An attempt was made at each irrigation to apply sufficient water to establish a condition of field capacity in the first 6' of soil.
The amount of water and time required to apply it were measured.
For the season an average of about three acrefeet of water was applied.
Observation wells were measured weekly to determine if a water table existed.
After each irrigation, the observation wells near tensiometer stations II and III had standing water.
LODI TOKAY IRRIGATION PLOTS
 The weak vines in the southern portion of the plot showed no moisture extraction and no root activity at the 6' depth.
Following irrigations the water table rose to 7'-8' below the soil surface and stayed there for several days.
In the past when excessive water was applied the lower roots may have been drowned.
moisture throughout the entire root zone.
J.
J.
Kissler is Farm Advisor, San Joaquin County, University of California.
C.
E.
Houston is Irrigation and Drainage Engineer, University of California, Davis.
W.
F.
Clayton is Senior Superintendent of Cultivations, San Joaquin County, University of California.
L.
F.
Werenfels is Irrigation Technologist, University of California, Davis.
A.
N.
Kasimatis is Viticulture Specialist, University of California, Davis,
 The above reported studies were established at the request of the Tokay Marketing Agreement industry committee.
Tokay grape grower James Sanguinetti, of Lodi, also participated in the investigations.
The unirrigated centers had very low soil moisture content after mid-June and the roots remained in dry soil during the rest of the growing season.
The unirrigated centers never received moisture by lateral subbing.
Lateral movement of water from the furrows toward the vines was found to be fair when furrows were placed on both sides of the vine row.
There was little or no lateral movement to the vine row when a single furrow was used in every other middle.
The strong vines in the northern portion of the plot began the growing season with low soil moisture content at the 6' level because of insufficient winter rainfall.
An early spring irrigation would supplement light rainfall in dry years.
Although there has been but one year of work on a long-term project, the results indicate that irrigation of a vineyard by a single furrow in every other vine row does not provide adequate soil
 Tensiometer readings, showing the inadequate irrigation of grapes by use of a single furrow every other vine row.
Plots irrigated June 5, June 27, July 13, July 25, and August 15.
made possible by new technique
 D.
R.
NIELSEN and J.
W.
BIGGAR
 The success or failure of fertilizers, herbicides, and pesticides applied as soil amendments depends on distribution and concentration of the material in the soil.
Fertilizers-the most common amendment-usually are applied by side-dressing or broadcasting, or are dissolved in irrigation water.
Surface application of herb'cides is a common practice but the depth of penetration or lateral movement in the soil must be minimized to protect the crop.
On the other hand, the success of soil fumigants depends upon depth of penetration and uniform distribution.
Whether applied to the soil as a liquid or as a dry material soluble in the soil
 solution, an amendment spreads through the soil as a result of several processes taking place simul:aneously.
The process most commonly considered to cause the spreading of a material through the soil-and the least understood-is the movement of water.
The volume of soil through which water moves is a complicated network of large and small pores resulting in tortuous interconnecting paths that depend upon the average water content of the soil.
The movement of water through small pores is much slower than through the larger pores.
A considerable volume of soil may have pores so small that the soil moisture filling the pores is not
 Schematic diagram illustrating the manner in which soil additives spread through small and large pores.
displaced by applied water.
Because the larger, moisture filled pores conduct the material faster, a substance injected at one point in a soil can be measured very early in the spreading outflow.
Eventually, as the smaller and more tortuous pores are flushed with the material, the concentration measured down-
 Concluded on next page
The following is a brief summary of the irrigation decisions made in each competition this year.
SDI Corn: The SDI irrigation system was first initiated on June 13 by two teams.
Among the 16 teams in the SDI corn competition, irrigation was scheduled by at least two teams on every provided opportunity.
The system was first initiated by Farms 4 and 13 and was concluded on Sept.
15 by Farms 1, 5, 8, 12, 13 and 14.
Three irrigation opportunities were cancelled or reduced due to rainfall events in July.
Except for the control , the total irrigation applied among the SDI corn teams ranged from 7.05  to 17.15 inches , and with an average of 11.03 inches.
This average far exceeded that of the 7.91 inches average in 2021.
Useful information for Hillsborough County homeowners and residents
 * A great resource regarding updating your landscape this season:
 * 2023 Triple Workshops:
 Photo Credit, UF/IFAS 2022
 "We forget that the water cycle and the life cycle are one." Jacques Yves Cousteau
DRY BEAN WATER MANAGEMENT
 The past several years of sustained drought and below average snowpack and summer rains have many in agriculture searching for ways to stretch limited supplies of water.
Not only has stream flow decreased, but ground water levels have declined and in many areas pumping restrictions have been imposed.
At the same time, competition for water outside of agriculture further increases the demand for limited resources.
The combination of drought and the increased demand for water will impose even more challenges for irrigated agriculture.
It will require changing current irrigation practices and incorporation of new ideas to better utilize available water supplies as efficiently as possible.
This means not only using irrigation water efficiently, but also using precipitation and stored soil water for crop production.
Understanding the water needs of a crop will be a key to effective water management.
The amount of water needed for irrigation varies by the crop being grown and the climatic conditions from year to year.
Given in Table 1 are estimated water use rates for regionally grown crops.
Alfalfa	Corn	Drybean	Spring	Soybean	Sunflower	Winter
 31-33	23-26	15-16	18-20	18-20	18-26	18-22
 Table 1.
Seasonal crop water use  for regionally grown crops.
The depth from which corn gets most of its water is generally considered to be in the top 3 to 4 ft of the soil profile.
Corn uses approximately 24 inches of water during the growing season and is often considered a crop that uses a large amount of water.
Yet as we look closer, some of the crops we thought used less water, for example sunflowers and winter wheat, we find can use as much water as corn.
However in the case of sunflowers and winter wheat, these crops can extract more water from the profile than some other crops without adversely impacting yield potential.
Sunflowers also have the ability to effectively extract
 water to depths of up to eight feet.
In this case sunflowers may be viewed as a "drought tolerant" crop when in fact the crop has actually extracted more water from the soil and extracted water from deeper in the soil profile.
Anyone growing sunflowers knows that following this crop the soil can be left in a very dry condition the following spring.
Dry beans use approximately 16 inches of water during the growing season, which is approximately 8 inches less than what corn needs.
This makes dry beans a good crop to grow if irrigation water is limited or if used as part of a crop rotation system to reduce overall irrigation needs.
Dry beans are a shallow rooted crop with the majority of roots found in the top 18 in.
of the soil profile.
Roots can grow deeper into the soil profile to get water but this usually occurs late in the growing season as the plants begin to mature.
The question of when is the best time to apply water to a crop often comes up when water supplies are limited.
Some producers feel that stressing dry beans early in the growing season has little impact on yield and may even improve yield by forcing the roots to grow deeper into the soil profile.
A similar question asked is whether stopping irrigation late in the season reduces yield?
For dry beans, early and late season water stress experiments have been conducted at the Panhandle Research and Extension Center in Scottsbluff, NE.
The results of those experiments are given below.
Figure 1a.
Effect of early season water stress on dry bean yield using sprinkler irrigation.
Figure 2a.
Effect of late season water stress on dry bean yield using sprinkler irrigation.
Figure 1b.
Effect of early season water stress on dry bean yield using furrow irrigation.
Figure 2b.
Effect of late season water stress on dry bean yield using furrow irrigation
 Figures 1a and 1b, show the results of dry bean yield when water is limited during early season growth for sprinkler and furrow irrigation systems, respectively.
The no stress treatment had irrigation starting approximately the last week in June to the first week in July.
For the limited and high stress treatments, the initial irrigation was delayed for one week and two weeks, respectively.
When sprinkler irrigation was used, yield tended to decline more as water stress increased compared to the furrow irrigation system.
This is especially true for the high stress treatment under sprinkler.
Yield loss was greater when water was withheld for two weeks because of the inability of the sprinkler system to replace soil water and meet the future water demand of the crop.
The furrow irrigation system in these experiments refilled the soil profile and thus was able to provide adequate and immediate water for future water use.
Under grower conditions if stress is allowed, furrow irrigation will likely require an extended period of time to irrigate the complete field thus causing further yield reduction similar to the sprinkler trials.
Because the sprinkler and furrow experiments were conducted at different locations, comparisons between the two irrigation systems should not be made.
In figures 2a and 2b, the results of shutting off water late in the season are also shown for both sprinkler and furrow irrigation systems.
The no stress treatment had irrigations throughout the growing season.
Starting August 10, the limited stress treatment received every other irrigation that was scheduled for the no stress treatment while the high stress treatment received no further irrigations.
Similar to the early season water stress results, dry beans irrigated with a sprinkler system showed a slightly steeper decline in yield as water stressed increased.
The decline in yield is again likely related to the inability of the sprinkler irrigation system to supply water in excess to the requirements of the crop.
Once irrigation was reduced or stopped less water was available in the soil profile to meet crop demands.
Once again, the sprinkler and furrow experiments were conducted at different locations and comparisons cannot be made between the two irrigation systems.
When comparing the early and late season experiments, there is a steeper decline in dry bean yield when water stress occurs at the beginning of the season as compared to water stress late in the season.
These results are probably not uncommon and could be expected for most crops.
Early in the season plant root development is limited and therefore water stress can occur rapidly.
The lack of water during initial stages of plant growth likely impacts the majority of the root system.
Late in the growing season, roots are more developed and reach further into the soil profile.
Therefore water stress late in the season will first impact roots high in the soil profile while those deep in the profile may continue to extract some water to meet the needs of the crop.
Finally, because the plant is nearing maturity, the need for water is declining on a daily basis.
As a result, the root system can more easily keep up with the needs of the plant as water in the profile slowly moves to replace the water used by the crop.
These results show for western Nebraska that if water is limited and the irrigator has the ability to choose when water supplies can be used on their bean crop, the choice should be to use water early in the season to maintain plant growth and encourage root development deep into the soil profile.
Reducing irrigation late in the season can result in water stress which will likely reduce yield.
However, compared to water stress early in the season, late season stress can have less of an impact on total production.
Everyone can and should do something to protect groundwater.
Why?
We all have a stake in maintaining its quality and quantity.
Ninety-nine percent of all available freshwater comes from aquifers underground.
Additionally, most surface water bodies are connected to groundwater so how you impact surface water matters too.
Furthermore, many public water systems draw all or part of their supply from groundwater, so protecting the resource protects the public water supply and influences treatment costs.
If you own a well to provide water for your family, farm, or business, groundwater protection is critical to you.
So what is groundwater?
Precipitation that does not quickly run off into streams, is not evaporated by the sun, or does not get taken up by plant roots, slowly infiltrates through layers of soil and rock to become groundwater feeding the springs, streams, and wells of Pennsylvania.
Most of this recharge occurs from rain and melting snow during early spring and late fall when the soil is not frozen and plants are not actively growing.
This infiltrating water eventually reaches a saturated layer of sand, gravel, or rock called an aquifer.
Aquifers may occur a few feet below the land surface, like in Florida, but in Pennsylvania they are more commonly found at depths greater than 100 feet.
Groundwater does not simply remain stagnant under the ground.
Rather, it moves underground from upland to lowland areas.
The direction of groundwater flow underground can be determined by looking at how surface water flows.
Flowing groundwater eventually reaches a discharge point where the water table meets the land surface.
Springs are a classic discharge point where groundwater bubbling to the surface can be seen.
However, streams and lakes are the most likely points of discharge for groundwater.
Groundwater in Pennsylvania is a vast resource and is estimated to be more than twice as abundant as the amount of water that flows annually in the state's streams.
Pennsylvanians have tapped into this important resource and each day more than one billion gallons of groundwater are pumped from aquifers throughout the state for various uses.
More than half of this groundwater is used for domestic drinking-water supplies, which demand high-quality, uncontaminated water.
Groundwater is especially vital to rural areas of the state.
Pennsylvania has more than one million private water wells supplying water to more than three million rural residents.
An additional 20,000 new private wells are drilled each year around the state.
People from many parts of Pennsylvania are concerned about the future availability of adequate groundwater supplies for meeting home and business needs.
In some cases, these concerns are due to increasing local use of groundwater that exceeds the amount of recharge that supplies the aquifer.
More often, groundwater supplies are threatened by increasing impervious cover of the land surface.
Each year, more land area is being covered with roofs, sidewalks, driveways, parking lots, and other surfaces that do not allow rainwater to recharge the underlying groundwater aquifers.
Every acre of land that is covered with an impervious surface generates 27,000 gallons of surface runoff instead of groundwater recharge during a one-inch rainstorm.
Without recharge water feeding the aquifer, groundwater mining or water removal from the aquifer more quickly than it can be recharge, may occur.
Groundwater mining has been documented in parts of southeastern Pennsylvania, where impervious cover has increased rapidly and groundwater withdrawals have also increased.
Water resources planning efforts initiated in Pennsylvania in 2003 aim to document areas where groundwater resources are currently or will be overused.
With this information, local government planning officials can more adequately guide future development based on existing water resources.
The quality of groundwater is also a concern in many areas of the state.
Contrary to popular belief, natural groundwater is not always free of pollutants and impurities.
Some pollutants occur naturally when water interacts with impurities in the rock layers encompassing an aquifer.
Human activities can also pollute groundwater aquifers.
3) Center Pivot The pivot will take a little more time to go through.
Start by checking each tower:  Check tire pressure and condition, check driveline knuckles for wear, drain water from gearboxes and top off with appropriate gear oil, visually inspect the tower box and the alignment system and then check operation.
It is a good idea to make notes of problems that you encountered during the growing season while they are fresh in your mind!
Drain water from all pipe above ground.
Flushing the system: If you have water quality issues or if your well is pumping some sand.
Clean out the sand trap.
Volumetric water content is the volume of water in a given volume of soil.
Some advantages for capacitance probes are that they can be configured to measure multiple depths of soil with one sensor, continuous monitoring capability, and fast response times.
Potential disadvantages are once again the importance of good soil contact and proper installation, higher price, as well as performance can be affected by soil salinity, temperature, and clay content.
Guide to Spring-planted, Cool-season Vegetables
 Guide to Warm-season Vegetables
 Guide to Fall Vegetables
 Insect and Disease Control
 Growing Vegetables in Home Gardens
 Originally developed by David W.
Sams, Professor Emeritus, Plant and Soil Science Revised by Gary Bates, Professor and Extension Coordinator, Plant Sciences
 Gardening can be highly rewarding, but it is not without problems and efforts.
A successful garden requires a good site, careful planning, good management and considerable hard work.
Insects, diseases and weeds require control measures.
Acidic, infertile, poorly drained or sandy soil may have to be improved.
Shade and extremes of moisture and temperature are other problems that must be overcome for a garden to be successful.
For those willing to plan carefully and to perform timely gardening tasks, gardening can be very worthwhile.
A vegetable garden can produce a steady supply of vegetables from spring to fall.
These vegetables can be harvested at optimum maturity and eaten or preserved while fresh.
Fresh vegetables may be higher in flavor and nutritive value and lower in cost than purchased vegetables, which may have been harvested several days earlier.
Vegetable production provides healthful exercise and an interesting outdoor activity for the entire family.
Many gardeners feel the sense of accomplishment, self-sufficiency and security accompanying a successful garden are other significant rewards of gardening.
A good garden site is essential for high vegetable yields.
Poor sites not only produce low yields, but may also be extremely difficult to grow a garden on at all.
Choose a garden site with deep, medium-textured, well-drained, nearly level soil.
Fine-textured, clay soils stay wet late into the spring, are difficult to work and tend to crust badly.
Sandy soils dry out very quickly and require frequent nutrient applications.
Excessive slopes tend to erode.
A slight slope, however, is desirable to prevent cool air from collecting and forming a frost pocket.
Most garden vegetables require six hours of sunlight or more per day to produce well.
The more the garden is shaded, the slower the vegetables will grow and the lower their yields will be.
Trees and large shrubs not only shade gardens, but also use nutrients and water needed for proper vegetable growth.
A site near the house makes it more convenient to care for the garden and to harvest vegetables.
Water is available for transplanting and irrigation.
Children or animals in the garden can be observed, and the garden may be protected from these and other potential problems.
A garden plan will save time, space and money.
Yields will be increased, as will the length of the harvest season.
Begin by making a scale drawing of your available garden area on graph paper.
Divide the drawing into coolseason and warm-season vegetable planting areas.
Cool-season vegetables are those such as onions, cabbage, radishes and English peas.
They require cool weather to grow and mature properly and can withstand some frost.
Cool-season vegetables are planted in the early spring and again in the fall.
Warm-season vegetables require warm weather to grow properly and are planted after the soil has warmed up.
Frost will kill warm-season vegetables.
Examples of warm-season vegetables include okra, sweet potatoes, cucumbers and tomatoes.
The cool-season section of the garden will be planted early and harvested in time to be replanted.
Alternate the cool and warm-season areas of the garden each year to reduce plant pest problems.
Decide which vegetables to grow and the amount of each vegetable you want.
Use Tables 1-3  to estimate the row lengths required to obtain the desired amounts.
Sketch and label the rows of each vegetable on your plan to scale, using the row spacings suggested in Tables 1-3.
Be sure to arrange the rows SO tall vegetables won't shade shorter ones.
Make a note of the planting dates, varieties and amount of seeds required on your plan SO a periodic glance will show what needs to be done.
An efficient garden that's fun to work in requires the correct tools.
It is not necessary to have a lot of tools, but they should be good quality.
All gardeners will require the following:
 1.
A shovel or a spade.
Shovels are long-handled and have wide, rounded blades.
Spades are shorter and
 usually have narrow blades.
Sharpshooter shovels are spades.
Some prefer a long-handled shovel for nearly every gardening task from spading soil to planting and transplanting shrubs.
The shorter spade is stronger but harder to use.
The spade works well to dig a raised bed or a post hole.
It is also a good tool for prying, cutting larger roots and even spading.
All gardeners should have one or the other, and both would be a good investment.
2.
A hoe.
The hoe is a universal gardening tool.
There are dozens of kinds, sizes and shapes.
The standard square-bladed gooseneck hoe is the one to begin with.
It is suitable for removing weeds as well as opening and closing furrows for seeding.
Other hoes can be added if and when you need them.
3.
A rake.
The bow rake is essential for smoothing and leveling seed beds.
It may also be used to cover planting furrows, move mulches, clean up debris and kill emerging weeds.
4.
A trowel.
Buy a good trowel, 3 or 4 inches wide.
Use it to transplant small plants, open short rows, dig small holes and even to weed and cultivate around small plants.
5.
Small supplies.
Use twine and stakes for marking rows, maintaining straight rows and supporting plants.
A bucket for carrying fertilizer and water to the garden and vegetables to the house is very helpful.
A hose is essential for irrigation.
Perhaps the most essential small tool is a good-quality file.
Carry it with you when you work in the garden and use it frequently to keep tools sharp.
Store all tools away from sun and rain.
Weather will deteriorate and roughen handles, as well as rust metal parts.
Rust can be prevented by wiping a light coating of oil on metal after use.
Rough handles can be smoothed with sandpaper.
Well-cared for tools are easier to use and last much longer.
You will want to add additional tools and equipment as your needs grow and finances permit.
The following items will prove useful:
 1.
Watering cans, hoes, nozzles and sprinklers for watering.
2.
A spading fork for soil preparation and harvesting root crops.
3.
A manure fork for turning compost and moving garden residues.
4.
A wheelbarrow or garden cart for hauling large amounts of soil, fertilizer, plant residues or produce.
5.
A rototiller for preparing large areas of soil and controlling weeds.
There are many sizes and types of rototillers.
The large machines with tines in front of the wheels are the standard.
They are less expensive and do a good job breaking up compacted soil, but require considerable physical strength to use.
Large, reartine machines are much easier to use and more suited to large garden areas, but they are also considerably more expensive to purchase.
They do a better job of preparing a seedbed, especially in wet soils.
The last few years have seen the development of small rototillers weighing only about 20 pounds with an effective tilling width of 9 to 12 inches.
These machines are too small for breaking up large gardens or sod, but they are excellent for working up a row in a previously turned garden or to remove weeds.
They are especially good at working wet soil into a suitable seedbed.
Begin soil preparation by removing old plant supports, plastic mulches, excessive vegetative residues and other debris from the garden area several weeks before planting to allow the soil to dry out.
The amount of plant residue that may be turned under depends on how large the pieces are, how the garden will be turned and how long before the area will be worked.
Long cucumber or tomato vines, for example, may be spaded or plowed under but may tangle on the tines of a rototiller.
Cover crops and thick mulch or crop residue should be turned under six weeks or more before planting.
This will promote decay and reduce nutritional and insect and disease problems in the garden.
Adding three pounds of ammonium nitrate per 1000 square feet of soil surface before turning organic materials under will speed decay considerably.
Turning under significant amounts  of plant materials such as compost, organic mulches, leaves or cover crops annually will gradually increase soil organic matter content and improve most garden soils.
The moisture-holding capacity will improve, as will the soil structure and nutrient-holding capability.
Root penetration will improve on clay soils and soil crusting will be reduced.
Figure 1.
Pick up a handful of soil and roll it into a ball.
If the soil sticks together and will not crumble easily, it is too wet to work.
Table 1.
Guide to Spring-planted, Cool-season Vegetables
 Seed or	Inches	Inches	Days to	Length of	Yield range
 Planting	plants per	between	between	first	harvest	per
 Vegetable	interval	100-foot row	rows	plants	harvest	season	100-foot row
 Beets	Mar.
1 to	1/2 oz.
seed	14 to 36	2 to 3	55 to 60	4 weeks	75 to 150 lbs.
Broccoli	Mar.
1 to	80 plants	24 to 36	15	60 to 70	4 weeks	50 to 100 lbs.
Cabbage	Feb.
20 to	80 plants	24 to 36	15	60 to 75	3 weeks	125 to 200 lbs.
Cauliflower	Mar.
1 to	80 plants	24 to 36	15	55 to 65	2 weeks	50 to 100 lbs.
Carrots	Mar.
1 to	1/4 oz.
seed	14 to 36	2 to 3	75 to 85	4 to 6 weeks	50 to 100 lbs.
Collards	Mar.
1/4 oz.
seed	18 to 36	15	65 to 75	4 to 30 weeks	100 to 150 lbs.
Kale	Feb.
1/4 oz.
seed	18 to 36	12 to 15	55 to 65	4 to 20 weeks	100 to 150 lbs.
Kohlrabi	Feb.
or Mar.
1/4 oz.
seed	14 to 36	6	40 to 50	4 weeks	50 to 75 lbs.
Lettuce, Head	Feb.
or Mar.
1/4 oz.
seed	14 to 36	12 to 15	65 to 80	2 to 3 weeks	50 to 100 lbs.
Lettuce, Leaf	Feb.
to Apr.
1/2 OZ.
seed	14 to 36	6	40 to 50	4 to 6 weeks	50 to 75 lbs.
Mustard	Feb.
1/4 oz.
seed	14 to 36	5 to 10	35 to 45	3 to 6 weeks	75 to 100 lbs.
Onions, Bunch	Feb.
or Mar.
400 to 600 sets	14 to 36	2 to 3	30 to 60	3 weeks	30 to 50 lbs.
Onions,	Feb.
or Mar.
200 to 400 sets	14 to 36	3 to 6	100 to 120	2 weeks	50 to 100 lbs.
Peas,	Feb.
1 to	1/2 to 1 lb.
seed	12 to 36	2 to 4	65 to 70	2 to 3 weeks	20 to 30 lbs.
Peas, Snap	Feb.
1 to	1/2 to 1 lb.
seed	12 to 36	2 to 4	65 to 75	2 to 3 weeks	30 to 50 lbs.
Potatoes, Irish	Mar.
14 lbs.
seed	30 to 36	12	90 to 110	4 months	100 to 120 lbs.
Radish	Feb.
15 to	1/2 oz.
seed	14 to 36	1 to 2	25 to 30	3 weeks	50 bunches
 Spinach	Feb.
1 oz.
seed	14 to 36	3 to 4	40 to 50	3 weeks	10 to 30 lbs.
Swiss Chard	Mar.
1/2 oz.
seed	18 to 36	6 to 8	50 to 60	4 to 30 weeks	50 to 150 lbs.
Turnip, Greens	Mar.
1/2 oz.
seed	18 to 36	2 to 4	30 to 40	Several weeks	50 to 100 lbs.
Turnip, Roots	Mar.
1/4 oz.
seed	18 to 36	3	40 to 65	6 months	100 to 150 lbs.
Garden soil should not be worked when it is too wet.
Pick up a handful of soil and roll it into a ball.
If the soil sticks together and does not crumble when dropped, it is too wet to work.
Soil worked too wet forms large, hard clods which are difficult to break up and are completely unsuitable for a seedbed.
Soil should be worked to a depth of at least 6 or 7 inches and smoothed before planting.
Seed should be planted only in moist, finely aggregated soil.
Soils worked into a powdery condition are more likely to crust.
Small seed planted in cloddy soil usually dry out and germinate
 poorly.
Garden soil may be worked with farm equipment, a rototiller or spaded with a shovel.
Vegetable gardens will not reach their potential unless the soil is properly limed and fertilized.
Liming decreases soil acidity, increases fertilizer availability and reduces certain physiological problems such as blossom-end-rot of tomatoes, peppers and watermelons.
A soil test is the only reliable method of determining the optimum amount of lime and fertilizer to apply.
Table 2.
Guide to Warm-season Vegetables
 Seed or	Inches	Inches	Days to	Length of	Yield range
 Planting	plants per	between	between	first	harvest	per 100-
 Vegetable	interval	100-foot row	rows	plants	harvest	season	foot row
 Beans, Bush	Apr.1 to	1/4 lb.
seed	24 to 36	3 to 4	52 to 60	2 weeks or	80 to
 Snap	June 20	more	120 lbs.
Beans, Pole	Apr.
10 to	1/4 lb.
seed	36 to 48	3 to 4	60 to 65	5 to 6 weeks	100 to
 Snap	June 20	150 lbs.
Beans, Bush	May or	1/2 lb.
seed	24 to 36	3 to 4	65 to 75	3 weeks	20 to 30 lbs.
Beans, Pole	May or	1/2 lb.
seed	36 to 48	3 to 4	80 to 90	4 weeks.
25 to
 Lima	June	50 lbs.
Cantaloupe	May	1/4 oz.
seed	72	24	80 to 90	3 weeks	100+ melons
 Corn, Sweet	Apr.
1 to	1/4 lb.seed	36	8 to 12	80 to 95	7 to 10 days	90 to
 June 1	120 ears
 Corn, Super	Apr.
15 to	1/4 lb.seed	36	8 to 12	80 to 95	10 to 15 days	90 to
 Sweet	June 1	120 ears
 Cucumber,	May	1/4 oz.
seed	72	12	50 to 55	3 to 6 weeks	115 to
 Cucumber,	May or	1/4 oz.
seed	72	12	50 to 65	3 to 6 weeks	115 to 250
 Eggplant	May	50 plants	36	24	65 to 80	2 months or	75 to
 Okra	May 5 to	1 oz.
seed	36	6 to 12	50 to 60	7 to 9 weeks	50 to
 May 20	100 lbs.
Peas, Field	May or	1/4 lb.
seed	36	4	65 to 80	3 to 5 weeks	30 to 40 lbs.
Pepper, Sweet	May or	60 plants	36	18 to 24	55 to 80	2 to 3 months	50 to 75 lbs.
Pepper, Hot	May or	60 plants	36	18 to 24	60 to 70	2 to 3 months	10 to 25 lbs.
Potato, Sweet	May	100 slips	36	12	110 to 120	5 months stored	75 to 125 lbs.
Pumpkin	May	1 oz.
seed	120 to 144	48	100 to 120	4 months stored	40 to 50
 Squash,	May or	1 oz.
seed	48 to 60	12 to 24	40-50	6 weeks	100 to
 Summer	June	150 lbs.
Squash, Winter	May or	1 oz.
seed	72 to 96	24 to 36	90-110	4 months stored	50 to 200 lbs.
Tomatoes	Apr.
10 to	50 plants	48	24	70-80	8 weeks or	200-300 lbs.
Watermelon	May	1/4 oz.
seed	120 to 144	48	80-90	3 weeks	20-25 melons
 Table 3.
Guide to Fall Vegetables
 Seed or	Inches	Inches	Days to	Length of	Yield range
 Planting	plants per	between	between	first	harvest	per 100-
 Vegetable	interval	100-foot row	rows	plants	harvest	season	foot row
 Beans, Bush	July 15 to	1/4 lb.
24 to 36	3 to 4	52 to 602	weeks or	80 to 120 lbs.
Snap	Aug.
15	more
 Broccoli	July 15 to	66 plants	24 to 36	18	60 to 70	4 weeks	50 to 100 lbs.
Cabbage	July 5 to	66 plants	24 to 36	18	60 to 75	3 weeks	125 to 200 lbs.
Cabbage	,July 1 to	100 plants	24 to 36	12	40 to 50	4 weeks	200 to 300 lbs.
Cauliflower	July 15 to	66 plants	24 to 36	18	55 to 65	2 weeks	50 to 100 lbs.
Collards	July 1 to Sept.1	1/4 oz.
seed	18 to 36	18	65 to 75	4 to 30 weeks	100 to 150 lbs.
Cucumber,	July 1 to	1/4 OZ.
seed	72	12	50 to 55	3 to 6 weeks	115 to 250 lbs.
Cucumber,	July 1 to	1/4 OZ.
seed	72	12	50 to 65	3 to 6 weeks	115 to 250 lbs.
Kale	July 1 to Sept.
1	1/4 OZ.
seed	18 to 36	12 to 15	55 to 65	4 to 20 weeks	100 to 150 lbs.
Kohlrabi	July 15 to Sept 1	1/4 oz.
seed	14 to 36	3 to 6	40 to 50	4 weeks	50 to 75 lbs.
Lettuce, Leaf	July 1 to Sept.
15	1/2 oz.
seed	14 to 36	6	40 to 50	4 to 6 weeks	50 to 75 lbs.
Mustard	July 1 to Sept.
1	1/4 oz.
seed	14 to 36	5 to 10	35 to 45	3 to 6 weeks	75 to 100 lbs.
Potatoes, Irish	July 1 to	14 lbs.
of	30 to 36	12	90 to 110	4 months	100 to 120 lbs.
July 31	seeds	stores
 Radish	Aug.
1 to	1/2 oz.
seed	14 to 36	1 to 2	25 to 30	3 weeks	50 bunches
 Spinach	Sept.
10 to	1 oz.
seed	14 to 36	3 to 4	40 to 50	3 weeks	10 to 30 lbs.
Squash,	July 15 to	1 oz.
seed	48 to 60	12 to 24	40 to 50	6 weeks	100 to 150 lbs.
Tomatoes	July 1 to Aug.
1	50 plants	48	24	70 to 80	8 weeks or	200 to 300 lbs.
Turnip Greens	Aug.
1 to	1/2 oz.
seed	18 to 36	2 to 4	30 to 40	Several weeks	50 to 100 lbs.
Turnip Roots	Aug.
1 to	1/4 OZ.
seed	18 to 36	3	40 to 65	6 months	100 to 150 lbs.
Instructions for taking soil samples and soil sample boxes are available at your county Extension office.
The samples are sent to the University of Tennessee Soil Testing Laboratory in Nashville.
The returned report indicates the amount of lime and fertilizer recommended.
There is a small fee for this service.
Soil acidity is measured in pH units.
Most vegetables grow best at a pH of 6 to 6.8.
Once this pH is reached, it is generally necessary to check the pH only about every three years.
Lime requires time to dissolve and become be fully effective.
For this reason, it is generally best to apply lime in the fall and to mix it into the soil.
However, spring application of lime is better than no lime at all.
The more finely ground lime is, the more likely a spring application is to produce the desired pH change.
Vegetable gardens require a "complete" fertilizer such as 6-12-12, 10-10-10, 13-13-13 or 15-15-15 for proper growth and development.
The three numbers are referred to as the fertilizer analysis.
The first number is the percentage of nitrogen in the fertilizer by weight.
The second and third numbers are the percentages of phosphate and potash, respectively.
Manure is a complete fertilizer and may be used to supplement chemical fertilizer.
Manure varies considerably in nutrient value, depending on the type of animal, length of storage, amount of bedding material and the moisture contained.
Since most manure has less than 2 percent phosphate and less than 1 percent nitrogen and potash, several times more manure than chemical fertilizer must be applied if only manure is used.
More detail on using manure as a fertilizer may be found in Extension PB 1391, "Organic
 Gardening and Pest Control."
 Apply fertilizer to garden soils in the spring before planting.
Manure is generally broadcast.
Chemical fertilizers may be broadcast, applied in the rows or banded near or under the rows.
If fertilizer is broadcast or applied in
 Figure 2.
Fertilizer analysis numbers refer to the percentage by weight of N, P2O5 and K2O.
the rows, it should be worked into the soil before planting.
Bands are most effective when placed about 2 inches to the side and 2 inches below the seed.
Vegetable plants may be damaged by over-fertilization or fertilizer placed too near them.
Soil test reports give amounts of fertilizer to broadcast in pounds per 1000 square feet and per acre..
To convert the soil test recommendations to amounts per 100 foot of row, use Table 4.
Greens and vegetables with a long growing or production season benefit from additional nitrogen during the growing season.
This is called "sidedressing." Sidedress by applying ammonium nitrate along the row, keeping 4 to 6 inches away from the base of the plants.
Water or work the ammonium nitrate into the soil.
Specific amounts of ammonium nitrate to use and growth stages where sidedressing is most effective are given in Table 5.
Figure 3.
Apply nitrgen sidedressings in bands along rows or circles around plants.
Keep the fertilizer 4 to 6 inches from the plants.
A complete fertilizer may also be used to sidedress vegetables, but the amount required will vary with the percentage of nitrogen in the fertilizer.
Ammonium nitrate is about 34 percent nitrogen.
Adjust the amount of other fertilizers used as sidedressing SO the amount of nitrogen is the same as if ammonium nitrate were used.
Proper spacing among rows and between plants within rows is essential for maximum production of high-quality vegetables.
Use the in row spacings suggested in Tables 1, 2 and 3.
These spacings may be achieved by properly planting high-quality seed and thinning the rows, if necessary, when the seedlings are a few days old.
Tables 1, 2 and 3 also suggest between row spacings.
These spacings assume mechanical equipment, such as a rototiller, is used to work the garden.
If large farm equipment is used, the rows may need to be farther apart.
If only a hoe is used, rows can be closer together.
Figure 4.
Small seeds may be sown directly from the packet ; large seeds should be dropped from the fingers  and carefully spaced.
Do not sow seeds too deeply or thickly.
Be sure to plant in a good seedbed, as described previously under soil preparation.
Planting on ridges will further ensure good stands of cool-season vegetables and make it easier to plant at the proper time.
Ridges promote germination early in the spring because they warm up and dry out quickly.
Ridges also reduce the chance of spring vegetables being flooded during heavy rains.
Later in the season, ridges may reduce germination or plant growth by drying out too quickly.
The soil must not be allowed to crust or dry out before seedlings emerge.
Sand, compost, potting soil or similar materials may be placed over seed to prevent crusting in gardens with heavy clay soils.
It is also important that seed be planted at the correct depth.
As a general rule, seed should be planted at a depth equal to two to four times their diameter.
Plant shallowly early in the spring when the soil is wet and cold and a little deeper in the summer when soils are drier.
Plant shallowly in heavy clay soils and a little deeper in light sandy soils.
Tables 1, 2, and 3 divide vegetables into cool-season, warm-season and fall vegetables.
The recommended planting dates for each type of vegetable are quite different.
There is also considerable variation as to the heat or cold tolerance of each vegetable.
Plant within the recommended planting interval for each vegetable to ensure that the vegetable will have the maximum chance of growing and maturing properly.
Within the planting interval for a crop, you will often have adequate time to stagger several plantings.
With many vegetables, such as lettuce, you may prefer a small but steady supply rather than a lot all at once.
One of the best ways to achieve this is by making several small plantings two or more weeks apart.
The same technique is appropriate for corn.
With corn, the first planting can be larger if you plan to preserve some.
This large initial planting may be followed by one or more smaller plantings made when plants of the previous planting have three fully developed leaves.
Some vegetables are easier to grow from transplants than from seed.
Beginning with transplants rather than seed will also speed vegetable maturity.
Other vegetables, such as sweet potatoes or Irish potatoes, may not be commonly grown from true seed.
Thus, gardens will likely contain vegetables grown from transplants, slips or seed pieces as well as from true seed.
Cabbage, cauliflower, broccoli, tomatoes, peppers and eggplant are usually transplanted into the garden rather than direct-seeded.
Cantaloupe, cucumbers, squash and watermelon may be transplanted if they are grown in individual containers and are transplanted without disturbing their roots.
These vining vegetables should be seeded in containers 3 inches or more across, and transplanted about three weeks after seeding.
Most home gardeners purchase transplants rather than growing them.
Transplant production is discussed briefly later in this publication.
More detailed instructions are contained in SP 291-A, "Growing Vegetable
 Transplants for Home Gardens."
 When buying transplants, select short, stocky, healthy plants without yellowing or dying leaves.
Avoid plants with dead spots or insects on the leaves.
Choose plants in large containers over plants in smaller containers and plants in small containers over bare-root plants.
Do not buy broccoli or cauliflower plants that are already beginning to form heads.
Transplants that are too old may be stunted.
Very large transplants in small containers are often overhardened.
They undergo considerable transplanting shock when set in the garden, because the small rootball has difficulty taking up sufficient water for the large leaf area.
Vine crops should have only one or two sets of true leaves when set in the garden.
Other transplants usually have three or four true leaves.
A small amount of purple color in the veins on the underside of the leaves is an indication of hardening.
Transplants may be injured by sun, wind and cold temperatures if they are set in the garden without some hardening.
You can
 Table 4.
Approximate Pounds of Fertilizer to Apply to 100-Foot Rows to Equal Recommended Rates
 Recommended soil test rate	Fertilizer rates in pounds per 100-foot rows for various row widths*
 Per acre	Per 1000	18 inches	24 inches	30 inches	36 inches	48 inches
 435	10 lbs.
1.5	2.0	2.5	3.0	4.0
 650	15 lbs.
2.3	3.0	3.8	4.5	6.0
 870	20 lbs.
3.0	4.0	5.0	6.0	8.0
 1090	25 lbs.
3.8	5.0	6.3	7.5	10.0
 1305	30 lbs.
4.5	6.0	7.5	9.0	12.0
 * One pint of dry fertilizer will weigh about one pound.
Table 5.
Recommendations for Sidedressing Vegetable Crops
 Crop	Ammonium nitrate	Ammonium nitrate	Time of application
 per 100-foot row	per plant
 Cucumbers, Cantaloupe,	1 to 11/2 pounds	1 tablespoon	When vines are
 Pumpkins, Squash,	1 foot long.
Tomatoes, Pepper,	1 to 11/2 pounds	1 tablespoon	When first fruits are 1
 Eggplant	inch or more in
 Sweet Corn	1 to 11/2 pounds	When 12 to 18 inches
 Okra	After the first picking.
Lettuce	Three to four weeks
 Greens, (Turnips,Spinach,	2 to 3 pounds	Six weeks after
 Collards, Kale, Mustard)	seeding.
Broccoli, Cabbage,	1 to 11/2 pounds	1/2 tablespoon	Three to four weeks
 Cauliflower, Brussels	after transplant.
harden vegetable plants by lowering temperatures 10 degrees for 10 to 14 days.
Allowing the plants to wilt slightly between waterings will also harden them.
However, lowering the temperature or water supply too much will stunt or kill the plants.
If the leaf tissue between the veins is purple, the plant is probably overhardened or stunted.
A stunted plant may never recover and is slow in producing if it recovers.
Never harden cantaloupe or other vine crops.
Set transplants on a cool day or in the evening.
Watering transplants with one-half to one pint of a starter solution per plant will reduce transplanting shock and produce earlier vegetables.
Mix one tablespoon of water-soluble, high-phosphate fertilizer such as 10-50-10 per gallon of water to make a starter solution.
Never set transplants in dry soil without watering them.
Set transplants at the depth they previously grew or slightly deeper.
Leggy tomatoes may be set deeper as the stem will root if buried.
Always be sure the top of peat containers are buried 1/2 to 1 inch below the soil surface or the containers will act as a wick and dry out the rootballs.
Transplants may need initial protection against strong winds, hot sun or freezing temperatures.
Hotcaps can be made from newspapers or gallon milk jugs with the bottoms removed.
Be sure to remove the caps from milk jugs to prevent plants from overheating on sunny days.
A wooden shingle stuck into the ground on the sunny or windy side of a newly set transplant will also provide some temporary
 protection.
More information on protecting transplants is contained under "Protective Devices" on page 16.
Vegetables require 1 to 11/2 inches of water per week for maximum production.
Most years have dry periods when irrigation will greatly increase growth, fruit set, total yield and quality.
The easiest way for most gardeners to irrigate is with a sprinkler.
Apply water slowly to prevent runoff and erosion.
Place several cylindrical containers in the area covered by the sprinkler to measure the water applied.
Apply 1 to 11/2 inches of water, then do not irrigate again for several days.
Frequent shallow waterings promote shallow root growth, which is easily damaged by cultivation or dry periods.
Irrigation early in the day SO plants will dry before night is less likely to spread diseases.
See also the section on trickle irrigation under "Advanced Gardening Techniques."
 Weeds compete with vegetable plants for water, nutrients and sunlight.
Weeds reduce yields and may cause crop failure unless they are controlled.
There are several methods of controlling weeds.
Commercial vegetable growers use a combination of mechanical methods and chemical weed killers called herbicides.
Most herbicides are not recommended for use in home gardens.
They are difficult to use because no one chemical can be
 used on all vegetables and because it is difficult to apply small amounts of chemicals uniformly over the garden area.
Herbicides and other methods of weed control are discussed in more detail in SP291-I, "Weed Control in Home
 Hoeing and cultivating are the most common methods of weed control for home gardeners.
Hoe or cultivate shallowly to avoid the losing soil moisture or cutting the roots of desirable plants.
Hand-pull weeds in or very near the vegetable row.
There will be less damage to vegetable plants if weeds are removed while they are small.
Both plastic and organic mulches may also be used to control weeds.
This is discussed in the mulching section.
Use of proper cultural practices will also help control weeds.
Never allow weeds or vegetable crops to develop mature seed in or near the garden.
Cultivate to prevent weeds from seeding, even if vegetable production is finished.
If erosion is likely to be a problem, the vegetable garden area may be kept mowed when not in use.
Figure 9.
Use very shallow cultivation to prevent damage to vegetable plant roots.
Insect and Disease Control
 Garden vegetables are susceptible to many insect and disease problems.
Unless these problems are effectively controlled, they greatly reduce vegetable quantity and quality.
Begin control of garden insects and diseases by following good cultural and sanitation practices.
Rake and burn or bury insect-infested or diseased plant residues after harvest SO these problems will not overwinter in the garden.
Turning plant residues under in the fall allows them ample time to decay before spring.
Avoid the use of diseased plant material in a compost pile.
Keep weeds and fencerows mowed.
Rotate families of vegetables among different areas of the garden each year.
Grow resistant varieties whenever possible.
Do not save seed if diseases are present.
Other tips concerning cultural control of insects and diseases are found in Extension PB 1391, "Organic Gardening and
 When insect and disease problems occur, they must be identified and treated as soon as possible if damage is to be
 minimized.
County Extension offices can assist with identification.
Extension PB 595, "You Can Control Garden Insects," and PB 1215, "Disease Control in the Home Vegetable Garden," contain recommendations for controlling specific insect and disease problems.
Gardeners should always be careful to apply chemicals according to the instructions on the container.
Some diseases are present every year and are more easily controlled if preventative treatment begins soon after seedlings emerge or transplants are set in the garden.
Other diseases and many insects should be treated as soon as they appear.
Sprays are usually more effective than dusts, because they provide better coverage and are less likely to burn or otherwise harm growing plants.
Compressed air sprayers are superior to other types of home garden sprayers.
Many vegetables must be kept harvested if the plants are to maintain production.
Allowing oversized greenbeans, okra, summer squash or cucumbers to remain on vegetable plants will reduce future yields significantly.
Vegetables which ripen such as tomatoes and peppers will have greater nutritional value if they are harvested when fully ripe.
Information emphasizing vegetables as a potential source of nutrition may be obtained from Extension PB 1228, "Gardening for Nutrition."
 Table 6 contains suggestions as to when to harvest many common vegetables.
Table 6.
When to Harvest Garden Vegetables
 Asparagus	When spears are 6 to 9 inches tall.
Beans, lima	When pods are full but seeds are green.
Beans, snap	While pods snap easily and are still smooth.
Beets	11/2 to 21/2-inch beets have highest quality.
Broccoli	Before flowers show yellow color.
Cabbage	When heads become firm and heavy.
Cantaloupe	When melons can be lifted and the vine slips without pressure.
Carrot	Any time roots are firm and brittle.
Cauliflower	Before curd loosens and discolors.
Collard	When leaves are large but still green and firm.
Corn	When kernel juice is milky, silk begins to dry and ears are full to end.
Cucumber	When seeds are small, flesh is firm and color is green.
Eggplant	Before color begins to dull.
Kale	When leaves are large but before they yellow.
Kohlrabi	When 2 inches or more in diameter but still tender.
Lettuce	When tender and mild flavored.
Before bolting.
Mustard	When leaves are crisp and tender.
Okra	When pods are 21/2 to 31/2 inches long.
Onion	For green onions: when bulb is 3/8 to 1 inch in diameter.
For storing: after the tops have died down.
Parsnip	After cool weather has improved quality.
Peas, English	After pods have filled but before they turn yellow.
Peas, snap	After pods form but before yellowing.
Peas, Southern	For fresh use or freezing: When pods shell easily.
For drying: After pods are dry and brittle.
Pepper, hot	After pods reach full size.
Pepper, sweet	When pods are full size and still firm.
Potato, Irish	For immediate use: After tubers are 1 inch in diameter.
For storage: After vines have died and skin has set.
Potato, sweet	After reaching desired size but before cool fall rains.
Pumpkin	After they are full grown and mature colored.
Before frost.
Radish	When firm and brilliantly colored.
Rutabaga	Before becoming tough.
Spinach	When leaves are crisp and dark green.
Squash, summer	When large end is 1-2 1/2 inches in diameter and skin is still tender.
Squash, winter	When rind is not easily scratched by fingernail.
Swiss, chard	When leaves are crisp, tender and still green.
Tomato	When fully colored but still firm.
Turnip greens	While leaves are green and crisp.
Turnip roots	After 2 inches in diameter but while still tender.
Watermelon	When tendrils adjacent to fruit die and rind on ground becomes yellow.
Gardens will produce more in less area and quality will be higher if certain vegetables are grown vertically rather than horizontally.
Vegetables grown vertically have an extended harvest season and are easier to spray, tend and harvest.
They have fewer disease and insect problems because of improved air circulation and better spray coverage.
English peas, snap peas, cucumbers and pole beans are some of the vegetables that are commonly grown vertically.
These vegetables may be trained on a fence, in a wire cage or on a trellis.
Pole beans may be grouped around individual stakes or stakes may be pulled together at the top and tied for additional strength.
Trellises may be constructed from cane supported by a wire on top, string woven between top and bottom wires or from nylon netting.
Tomatoes respond well to vertical culture, since many of the fruit will rot if they lay on moist soil.
Home garden tomatoes are usually supported by 5or 6-foot stakes or a wire cage.
Use stakes at least 11/2 inches square and drive them a foot or more into the ground.
Plants are pruned to one or two stems and tied loosely to the support at 8to 12inch intervals.
A second method of supporting tomatoes is with wire cages constructed from concrete reinforcing wire.
Cages should be 20 to 22 inches in diameter, which will require a 6-foot length of wire bent into a circle.
Firmly anchor each cage SO it will not blow over.
Cages may be anchored by tying them to individual stakes or by tying them to a wire that is attached to posts at each end of the row of cages.
Set a single indeterminant tomato plant in each cage.
Allow the plants to grow without pruning.
Push the ends back into the cage as they grow.
Harvest fruit by reaching through the mesh.
Figure 11.
Caging tomatoes reduces labor for supporting the plants and increases yield.
Be sure to fasten cages to stakes driven into the ground.
Figure 12.
A double row of English peas 8 inches apart will increase yields and may be supported by a single netting.
Either organic or inorganic mulches may be used in the home garden.
Common organic mulches include straw, grass clippings, leaves, compost and rotted sawdust.
The most common inorganic mulch is black plastic.
Both organic and inorganic mulches reduce weed growth and conserve soil moisture.
Organic mulches also improve soil structure and water-holding ability.
They increase soil organic matter and eventually improve soil nutrient content.
Black plastic mulch also increases soil temperatures.
Apply organic mulches around established plants in a layer 2 to 4 inches deep.
Organic mulches are generally light-colored, reflect sunlight and keep the soil cool longer in the spring.
They work best on cool-season vegetables early in the spring and on warm-season vegetables after soils warm.
Add 1/4 pound of ammonium nitrate fertilizer or its equivalent to each bushel of mulch.
Apply black plastic mulches over freshly fertilized and worked soils several days before planting.
Shape the soil surface SO drainage is toward the plants and use strips of plastic, not sheets.
This will help water to reach the plants.
It is important to thoroughly cover the edges of the plastic with soil to prevent wind damage.
Insert plants or seed through holes or slits cut in the plastic.
Because black plastic absorbs sunlight and warms the soil, warm-season plants such as tomatoes, eggplant, watermelon, peppers and cantaloupe can be set through plastic about a week earlier than they can be planted in bare soil.
The first harvest of these crops will also be earlier when black plastic mulch is used.
Because black plastic mulch warms the soil, it is not well suited to cool-season vegetables.
One disadvantage of black plastic is that it must be removed from the garden and discarded after the growing season.
Another disadvantage is that it is hard to water or to apply nitrogen sidedressings under plastic.
You can lay black plastic over a trickle irrigation tube and water through this tube.
It is also possible to sidedress through irrigation water.
More information on mulches may be obtained from Extension SP 291-H, "Mulching Home Gardens."
 Figure 13.
Apply organic mulches 2 to 3 inches deep around established plants after the soil warms up.
Figure 14.
Spread black plastic before planting.
Plant warm season crops through slits or holes in the plastic.
Compost is a dark, easily crumbled substance that develops from the partial decay of organic material.
Making compost greatly reduces the volume of garden refuse, provides mulching materials for garden plants and contributes organic material to garden soils.
Most gardeners who compost produce compost in a "compost pile." Begin with almost any plant material.
Examples include grassclippings, garden prunings, spent plants, leaves, hay, straw, manure and immature weeds.
Do not compost meat scraps, diseased vegetables or plants or weeds with mature seed.
Start the pile directly on the ground.
Sides of wire, wood or concrete block may be used to keep the pile in place.
Begin the pile with a 6to 8-inch layer of chopped organic material, since chopped materials have greater surface area and will decay more quickly.
Moisten the layer and add 1 to 2 inches of manure or one cup of commercial fertilizer to supply nitrogen.
Lastly, add a small amount of soil or finished compost to supply composting organisms.
Repeat these layers to the height desired.
The compost pile will require six to 12 months before it is dark, crumbly and ready to use.
Turning the pile SO the inside is moved to the outside and vice versa four to 10 weeks after it is begun will speed up the composting process somewhat.
Keeping it moist but not soggy will also speed up the process.
You can also make compost by working organic material directly into the soil.
Simply spread a 2to 4-inch layer of a material such as leaves over the soil and work it in.
Do
 this in the fall or several weeks before planting SO the material will decay before planting.
More information on composting may be obtained from Extension PB 1479, "Composting Yard, Garden and Food Wastes at Home."
 Several systems are designed to increase the number of vegetable plants grown and the produce harvested during a single season in a given area.
These systems increase yields without increasing the area to be fertilized, irrigated or weeded.
Some of them also increase the length of the harvest season.
We have discussed succession planting previously, and now will look at intercropping, double cropping, multiple rows and planting in raised beds.
Intercropping is growing more than one crop in a single area at the same time.
Fast-growing and slow-growing vegetables may be planted together, either by alternating rows or by alternating plants within the row.
The fast-growing vegetable matures and is removed before the slow-growing vegetable needs the space.
For example, radishes and tomatoes, or onions and peppers may be planted in alternate rows, closer together than usual, since the onions and radishes can be harvested in time to provide space for the tomatoes and peppers.
Pole beans are often intercropped with corn in Tennessee.
The bean yield is reduced, but two crops are produced in the space usually required for corn alone.
Another example of intercropping is planting lettuce, radishes or onions early in the spring and setting caged tomatoes or vine crops between the rows in late April or May.
The spring crops will soon be harvested, making room for the tomatoes or vine crops to grow.
With intercropping, the control of insects, diseases and weeds is more difficult.
Many intercropping combinations are difficult to apply in commercial production.
Onions set March 1, harvested June 20
 Tomatoes set May 10
 Lettuce planted March 15, harvested by June 1
 Tomatoes set May 10
 Figure 15.
Intercropping of onions, lettuce and tomatoes.
Double-cropping is growing one crop and harvesting it, before planting and growing a second crop in the same spot the same year.
By grouping cool-season and warmseason vegetables, you can grow spring and summer crops or spring and fall crops in the same space.
warm-season vegetable and then another cool-season vegetable in the same garden area in a single year.
Two rapidly maturing warm-season vegetables, such as green beans or summer squash, may also follow each other in a single year.
Two or more rows of vegetables planted very close together are often called multiple rows.
Vegetables are usually grown in long narrow rows with wide spacings between them.
However, it is possible to increase production of some vegetables by planting two or more rows close together  or by broadcasting seed in a bed.
Vegetables suitable for multiple row or bed plantings are listed in Table 7, while the minimum spacings are contained in Table 8.
Begin by marking off multiple rows or beds.
Beds may be any width as long as you can reach the center.
Four feet is an often-selected width for raised beds.
Leave aisles for walking between the beds or multiple rows.
Beds or rows may be raised in home gardens if desired.
Raised beds may be useful in poorly drained areas, because they will dry out earlier in the spring for planting and be easier to work.
A small garden composed of raised beds can be extremely productive, attractive and may be edged with bricks, railroad ties, landscape timbers or other materials.
Permanently raised beds, however, are very difficult to work with rototillers and other powered equipment.
Space the plants far enough apart SO they will not be crowded, but close enough SO they will occupy all available space when they mature.
Recommended spacings for multiple rows of vegetables are given in Table 6.
Shade from mature vegetable plants reduces weed growth and evaporation from the soil surface.
Because more vegetables are growing in less space, you must maintain a high fertility level and supply moisture during
 Figure 16.
Beds and multiple rows allow greater vegetable production in less space.
periods of drought.
Be sure to fertilize beds as recommended by in your soil test, and apply nitrogen sidedressings as recommended in Table 4.
More information on building and using raised beds may be obtained from Extension SP291-N, "Raised Bed Gardening."
 Figure 17.
Raised beds dry out early in spring.
They may be both attractive and productive.
The most commonly used plant protectors formerly available to home gardeners were buckets and old blankets.
These still work, of course, but protective devices have evolved considerably.
Plants can be covered not only to prevent damage during cold weather, but to modify climates and extend growing seasons.
One-gallon milkjugs are cheap, readily available and highly useful.
Simply cut out the bottoms, take off the caps and push the remainder of the jug 1 inch into the soil directly over the small plants.
The plants will be protected from cold winds and freezing temperatures, and will grow faster.
Protection from cutworms will be an additional benefit.
Remove the milkjugs when the weather moderates.
Your reward will be greater and earlier production.
The jugs can be pinned to the ground with a long wire hairpin if necessary.
The bottoms of the jugs can be used as small platforms to support cantaloupe, pumpkins and winter squash off the ground.
You can protect groups of plants by modifying the climate under an entire row or even several rows.
Spun-bonded or floating row covers, for example, are placed loosely over one or more rows of young plants.
They lie directly on the plants and are lifted as the plants grow.
Floating row covers raise the temperature considerably during the day and offer two or three degrees of frost protection at night.
This results in more rapid plant growth and early harvests.
It is important to apply these covers loosely SO they can be lifted as the plants grow.
Remove them from plants requiring pollination when they flower SO insects can reach the flowers.
The protection of young plants from insects is an important secondary effect of spun-bonded row covers.
Try these covers on cabbage and broccoli where protection from insects is important, and over watermelon and cantaloupe, which respond well to increased heat units.
Be sure
 to use them on weed-free soils or only on small areas, as they will have to be removed to control weeds.
There are also various kinds of small plastic tunnels used to protect plants.
They consist of plastic strips 5 or 6 feet wide.
The plastic may be clear or translucent with numerous slits or holes down the sides, or it may be solid.
The plastic is supported by 6-foot lengths of #10 wire bent into a hoop shape and inserted over the row at 6to 10foot intervals.
The edge of the plastic must be well covered with soil to prevent its removal by wind.
Install plastic row covers immediately after planting or transplanting.
Much of their benefit comes from increased soil temperature, which requires time to achieve.
They are often used with black plastic mulch, which assists in weed control.
Table 7.
Vegetables Suited to Multiple Row or Bed Planting
 Double row only	Multiple row or bed
 Figure 18.
Slitted row cover.
Table 8.
Recommended Spacings for Vegetables Planted in Double or Multiple Rows
 Vegetable	between rows	between plants
 Beans, Bush	10 to 12	3 to 4
 Beans, Pole On Wire	8	3 to 6
 Beets	6	2 to 3
 Carrots	4	2 to 3
 Chard, Swiss	8	6 to 8
 Corn, Sweet	12	8
 Lettuce, Head	12	12 to 15
 Lettuce, Leaf	6	6
 Peas, English	6	3
 Pepper	10 to 12	12
 Radishes	4	1 to 3
 Spinach	6	3 to 4
 Turnip, Greens	4	2 to 3
 Turnip, Roots	6	3
 Row covers provide two or three degrees of frost protection and a considerable increase in heat units.
They can shorten the cantaloupe growing season as much as two weeks and increase both early and total yield.
Like floating row covers, slitted row covers reduce insect infestation.
They must also be removed from plants requiring pollination when they flower and from crops that cannot withstand extreme summer temperatures.
The wires and perhaps even the plastic may be re-used.
Row covers are very conducive to high-yielding small gardens, but difficult to use with some other cultural devices, such as plant supports.
Trickle or drip irrigation systems use a network of water-conducting tubes placed at the side of plant rows to distribute small amounts of water directly to growing plants.
Water emerges through small sprinkler heads, leaks through small emitter holes or soaks through the porous sides of the tubes.
Trickle systems are more costly than sprinkler systems, but they require much less water.
This can be a real advantage to city gardeners who must pay for water, and perhaps for waste water treatment also.
Trickle systems consist of a water source, a backflow valve, a filter, a pressure gauge, header pipes, emitter tubing and possibly emitters  They operate under very low pressure  and are easily installed.
Because the small holes are easily clogged, they require clean water and adequate filtration.
City or well water is suitable for use in a trickle system, but river or pond water will require excellent filters.
Trickle systems use less water, partly because of reduced evaporation.
Water is placed at the base of the plant, not released into the air where it may evaporate or blow
 Figure 19.
Diagram of trickle irrigation system set up to water small garden area.
Plants are set by water emitters.
away.
The aisles between rows are not watered.
Plants remain dry SO diseases are less common and severe.
Growth is rapid because of the constantly available moisture.
Trickle tubes may also be placed under black plastic or used to fertilize vegetables.
Because trickle tubes wet only a portion of the soil, they must run every day or two.
It may be difficult to determine how long they need to run.
Like traditional irrigation systems, they should wet the soil a foot deep.
Gardeners should experiment and see how long this takes.
Most home gardeners purchase vegetable transplants.
There are, however, several advantages to growing your own.
If you grow your own transplants, they will be the size you want when you are ready to plant them.
The container size can be controlled, as can the variety.
There will be less danger of bringing in insects and diseases, and you can properly harden the transplants before planting.
The cost may also be less.
Unfortunately, vegetable transplants are not easy to produce in the home.
Optimum growth requires a heated structure, a greenhouse.
If you grow transplants in the home, you will face two severe problems.
First, vegetable transplants usually grow best with night temperatures 10 degrees below day temperatures.
Second, the light intensity, even in a south-facing window, is not adequate to produce most vegetable transplants.
The first difficulty can be overcome by growing transplants in an unheated room and supplying heat only in the daytime or by simply turning down the thermostat at night.
You can increase the light to suitable levels by building a light box.
A light box is a partial-box with bottom, back and ends only.
Make it about 15 inches high, a little over 4 feet long and about 18 inches from front to back.
Line the inside with foil.
Place the box in front of a south-facing window and set a fluorescent light on the open top.
Attach the light to a timer set to turn on near dawn and to turn off 16 hours later.
The light will not be sufficient to grow plants, but it will supplement the natural light from the south-facing window nicely.
Special plant grow lights are available and work better than ordinary fluorescent lights for growing plants.
Use this plant box to grow a few transplants or to germinate many.
If seedlings are started in this box, they will need to be moved to a more roomy, protected environment when they require additional space.
A coldframe may be used for this.
A coldframe or hotbed may be built according to the design in Extension PB 819, "Vegetable Transplant Production." This frame or bed will suffice to raise seedlings to the transplant stage.
See also Extension SP291-A, "Growing Vegetable Transplants for Home Gardens." See Table 9 to determine ideal germinating and growing temperatures, as well as the time required to produce different kinds of vegetable plants.
You may occasionally acquire vegetable seed that you do not plant immediately.
Sometimes, only part of a seed packet is planted.
You may even wish to preserve a favorite heirloom variety.
How can seed best be stored?
Seed is alive and must remain alive if it is to grow.
The best way to keep it alive is to keep it cool and dry.
Begin by resealing partially filled seed packets with tape.
Place the seed packets in containers such as glass jars with lids, plastic containers or boxes with tight-fitting lids.
Add a small envelope of calcium chloride or powdered milk to the container to absorb moisture, and then refrigerate or freeze the seed.
Seed kept dry and cool will remain free of insects and may remain viable for several years.
Be careful what seed you attempt to collect and save.
Seed of hybrid varieties should never be saved, because plants grown from it may vary considerably from the parent
 plants.
Seed of cross-pollinated plants, such as vine crops, may not grow into plants exactly like the parents either.
Some seed can also carry diseases.
Bean and pea seed are examples that often carry bacterial or viral diseases.
Therefore, saving seed is always risky.
The best way to ensure healthy seed is to purchase fresh seed each year.
If you do have old seed, it may be wise to test it.
Roll 10 to 20 seed in a paper towel and moisten the towel.
Put the moistened towel in a glass jar with a top or in a plastic container with a tight-fitting lid SO the paper towel will not dry out.
Place the container where it will remain warm.
After eight to 10 days, check to see how many seed appear to be vigorously sprouting.
If less than half are sprouting, discard the remaining seed.
If about half are sprouting, you may wish to plant the remaining seed thickly.
If most are sprouting, then the seed may be planted at normal thickness.
Table 9.
Details of Transplant Production
 Vegetable	Approximate growing	Germination	Growing	Conditions for hardening
 time 	temperature	temperature
 	
 Broccoli	5 to 7	70	60 to 65	50 to 55F for 10 days
 Cabbage	5 to 7	70	60 to 65	50 to 55F for 10 days
 Cauliflower	5 to 7	70	60 to 65	50 to 55F for 10 days
 Head Lettuce	5 to 7	70	60 to 65	Lower temperature and
 Cucumber	2 to 3	75	65 to 75	Reduce moisture
 Cantaloupe	2 to 3	75	65 to 75	Reduce moisture
 Eggplant	6 to 8	75	70 to 75	Reduce temperature and
 Pepper	7 to 9	75	60 to 70	Reduce temperature and
 Squash	2 to 3	75	65 to 75	Reduce moisture
 Tomato	5 to 7	75	60 to 70	Reduce temperature and
 Watermelon	2 to 3	80	65 to 75	Reduce moisture
Risk of Early Season Leaching
 Excess irrigation has its own risks.
Generally, when the soil is above field capacity, excess water leaves the root zone, called deep percolation.
This is an essential function of the soil for groundwater recharge.
When deep percolation takes agrichemicals past the root zone, it is called leaching.
May and June are the most critical time for leaching losses all year.
Percent of fields that became wetter moving from August to Sept.
15.
The dry years 2020, 21 and 22 fields are much drier than the other years in the fall.
In 2021, 44% of fields with soil in the 15-25 in zone became wetter from August to Sept.
15, 48% of fields with soil in the 25-36 in zone became wetter from August to Sept.
15, and 37% of fields with soil in both zones became wetter moving from August to Sept.
15.
The Extremely Dry Winter/Spring 2022-23
 Leaving the soil as dry as possible without lowering yields saves money on pumping costs and leaves room to store offseason precipitation.
Most years, adequate precipitation will be received from October through May to refill the soil profile on fields that were fully irrigated the previous year in the entire state.
A lot of years, even in the Panhandle, the two to four inches of recharge that fully irrigated fields can hold will be received from rainfall or snowfall.
In addition to financial savings, leaving the soil drier will help reduce harvest delays due to mud if rain is received in the fall.
Irrigation Water Quality Standards and Salinity Management Strategies
 Irrigation Water Quality Standards and Salinity Management
 Nearly all waters contain dissolved salts and trace elements, many of which result from the natural weathering of the earth's surface.
In addition, drainage waters from irrigated lands and effluent from city sewage and industrial waste water can impact water quality.
In most irrigation situations, the primary water quality concern is salinity levels, since salts can affect both the soil structure and crop yield.
However, a number of trace elements are found in water which can limit its use for irrigation.
*Associate Professor and Extension Agricultural Engineer, Department of Agricultural Engineering, The Texas A&M System, College Station, Texas 77843-2117.
Generally, "salt" is thought of as ordinary table salt.
How-ever, many types of salts exist and are commonly found in Texas waters.
Most salinity problems in agriculture result directly from the salts carried in the irrigation water.
The process at work is illustrated in Figure 1, which shows a beaker of water containing a salt concentration of 1 percent.
As water evaporates, the dissolved salts remain, resulting in a solution with a higher concentration of salt.
The same process occurs in soils.
Salts as well as other dissolved substances begin to accumulate as water evaporates from the surface and as crops withdraw water.
Water Analysis: Units, Terms and Sampling
 Numerous parameters are used to define irrigation water quality, to assess salinity hazards, and to determine appropriate management strategies.
A complete water quality analysis will include the determination of:
 1) the total concentration of soluble salts,
 2) the relative proportion of sodium to the other cations,
 3) the bicarbonate concentration as related to the concentration of calcium and magnesium, and
 Table 1.
Kinds of salts normally found in irrigation waters, with chemical symbols and approximate proportions of each salt.
1 
 Chemical name	Chemical symbol	Approximate proportion
 of total salt content
 Sodium chloride	NaCl	Moderate to large
 Sodium sulfate	Na2SO4	Moderate to large
 Calcium chloride	CaCl2	Moderate
 Calcium sulfate 	CaSO4 2H2O	Moderate to small
 Magnesium chloride	MgCl2	Moderate
 Magnesium sulfate	MgSO4	Moderate to small
 Potassium chloride	KCI	Small
 Potassium sulfate	K2SO4	Small
 Sodium bicarbonate	NaHCO	Small
 Calcium carbonate	CaCO	Very Small
 Sodium carbonate	NaCO3	Trace to none
 Borates	BO-3	Trace to none
 Nitrates	NO-3	Small to none
 1 Waters vary greatly in amounts and kinds of dissolved salts.
This water typifies many used for irrigation in Texas.
Figure 1.
Effect of water evaporation on the concentration of salts in solution.
A liter is 1.057 quarts.
Ten grams is.035 ounces or about 1 teaspoonful.
4) the concentrations of specific elements and compounds.
The amounts and combinations of these substances define the suitability of water for irrigation and the potential for plant toxicity.
Table 2 defines common parameters for analyzing the suitability of water for irrigation and provides some useful conversions.
When taking water samples for laboratory analysis, keep in mind that water from the same source can vary in quality with time.
Therefore, samples should be tested at intervals throughout the year, particularly during the potential irrigation period.
The Soil and Water Testing Lab at Texas A&M University can do a complete salinity analysis of irrigation water and soil samples, and will provide a detailed computer printout on the interpretation of the results.
Contact your county Extension agent for forms and information or contact the Lab at  845-4816.
Two Types of Salt Problems
 Two types of salt problems exist which are very different: those associated with the total salinity and those associated with sodium.
Soils may be affected only by salinity or by a combination of both salinity and sodium.
Water with high salinity is toxic to plants and poses a salinity hazard.
Soils with high levels of total salinity are call saline soils.
High concentrations of salt in the soil can result in a "physiological" drought condition.
That is, even though the field appears to have plenty of moisture, the plants wilt because the roots are unable to absorb the water.
Water salinity is usually measured by
 the TDS  or the EC.
TDS is sometimes referred to as the total salinity and is measured or expressed in parts per million  or in the equivalent units of milligrams per liter.
EC is actually a measurement of electric current and is reported in one of three possible units as given in Table 2.
Subscripts are used with the symbol EC to identify the source of the sample.
ECjv is the electric conductivity of the irrigation water.
ECe is the electric conductivity of the soil as measured in a soil sample  taken from the root zone.
EC is the soil salinity of the saturated extract taken from below the root zone.
EC is used to determine the salinity of the drainage water which leaches below the root zone.
Table 2.
Terms, units, and useful conversions for understanding
 water quality analysis reports.
a.
EC	electric conductivity	mmhos/cm
 b.
TDS	total dissolved solids	mg/L
 a.
SAR	sodium adsorption ratio
 b.
ESP	exchangeable sodium percentage
 Determination	Symbol	Unit of measure	Atomic weight
 calcium	Ca	mol/m3	40.1
 magnesium	Mg	mol/m3	24.3
 sodium	Na	mol/m3	23.0
 potassium	K	mol/m3	39.1
 bicarbonate	HCO	mol/m3	61.0
 sulphate	SO4	mol/m3	96.1
 chloride	CI	mol/m3	35.5
 carbonate	CO3	mol/m3	60.0
 nitrate	NO3	mg/L	62.0
 boron	B	mg/L	10.8
 1 dS/m = 1 mmhos/cm = 1000 umhos/cm 1 mg/L = 1 ppm TDS  = EC  X 640 for EC < 5 dS/m TDS  X 800 for EC > 5 dS/m TDS  = TDS  X 2.72 Concentration  = Concentration  times the atomic weight
 Sum of cations/anions  = EC  X 10
 Key mg/L = milligrams per liter ppm = parts per million dS/m = deci Siemens per meter at 25 C
 Irrigation water containing large amounts of sodium is of special concern due to sodium's effects on the soil and poses a sodium hazard.
Sodium hazard is usually expressed in terms of SAR or the sodium adsorption ratio.
SAR is calculated from the ratio of sodium to calcium and magnesium.
The latter two ions are important since they tend to counter the
 effects of sodium.
For waters containing significant amounts of bicarbonate, the adjusted sodium adsorption ratio (SARad is sometimes used.
Continued use of water having a high SAR leads to a breakdown in the physical structure of the soil.
Sodium is adsorbed and becomes attached to soil particles.
The soil then becomes hard and compact when dry and increas-
 ingly impervious to water penetration.
Fine textured soils, especially those high in clay, are most subject to this action.
Certain amendments may be required to maintain soils under high SARs.
Calcium and magnesium, if present in the soil in large enough quantities, will counter the effects of the sodium and help maintain good soil properties.
Soluble sodium per cent  is also used to evaluate sodium hazard.
SSP is defined as the ration of sodium in epm  to the total cation epm multiplied by 100.
A water with a SSP greater than 60 per cent may result in sodium accumulations that will cause a breakdown in the soil's physical properties.
lons, Trace Elements and Other Problems
 A number of other substances may be found in irrigation water and can cause toxic reactions in plants.
After sodium, chloride and boron are of most concern.
In certain areas of Texas, boron concentrations are excessively high and render water unsuitable for irrigations.
Boron can also accumulate in the soil.
Crops grown on soils having an imbalance of calcium and magnesium may also exhibit toxic symptoms.
Sulfate salts affect sensitive crops by limiting the uptake of calcium and increasing the adsorption of sodium and potassium, resulting in a disturbance in the cationic balance within the plant.
The bicarbonate ion in soil solution harms the mineral nutrition of the plant through its effects on the uptake and metabolism of nutrients.
High concentrations of potassium may introduce a magnesium deficiency and iron chlorosis.
An imbalance of magnesium and potassium may be toxic, but the effects of both can be reduced by high calcium levels.
Table 3.
Recommended limits for constituents in reclaimed water for irrigation.
(Adapted from
 Rowe and Abdel-Magid, 1995)
 Constituent	Long-term	Short-term	Remarks
 use 	use 
 Aluminum 	5.0	20	Can cause nonproductivity in acid soils, but soils at pH 5.5 to 8.0
 will precipitate the ion and eliminate toxicity.
Arsenic 	0.10	2.0	Toxicity to plants varies widely, ranging from 12 mg/L for Sudan
 grass to less than 0.05 mg/L for rice.
Beryllium 	0.10	0.5	Toxicity to plants varies widely, ranging from 5 mg/L for kale to
 0.5 mg/L for bush beans.
Boron 	0.75	2.0	Essential to plant growth, with optimum yields for many obtained
 at a few-tenths mg/L in nutrient solutions.
Toxic to many sensitive
 plants  at 1 mg/L.
Most grasses relatively tolerant at
 2.0 to 10 mg/L.
Cadmium 	0.01	0.05	Toxic to beans, beets, and turnips at concentrations as low as 0.1
 mg/L in nutrient solution.
Conservative limits recommended.
Chromium 	0.1	1.0	Not generally recognized as essential growth element.
Conservative
 limits recommended due to lack of knowledge on toxicity to plants.
Cobalt 	0.05	5.0	Toxic to tomato plants at 0.1 mg/L in nutrient solution.
Tends to be
 inactivated by neutral and alkaline soils.
Copper 	0.2	5.0	Toxic to a number of plants at 0.1 to 1.0 mg/L in nutrient solution.
Fluoride 	1.0	15.0	Inactivated by neutral and alkaline soils.
Iron 	5.0	20.0	Not toxic to plants in aerated soils, but can contribute to soil acidifi-
 cation and loss of essential phosphorus and molybdenum.
Lead 	5.0	10.0	Can inhibit plant cell growth at very high concentrations.
Lithium 	2.5	2.5	Tolerated by most crops at up to 5 mg/L; mobile in soil.
Toxic to
 citrus at low doses recommended limit is 0.075 mg/L.
Manganese 	0.2	10.0	Toxic to a number of crops at a few-tenths to a few mg/L in acid
 Molybdenum 	0.01	0.05	Nontoxic to plants at normal concentrations in soil and water.
Can
 be toxic to livestock if forage is grown in soils with high levels of
 Nickel 	0.2	2.0	Toxic to a number of plants at 0.5 to 1.0 mg/L; reduced toxicity at
 neutral or alkaline pH.
Selenium 	0.02	0.02	Toxic to plants at low concentrations and to livestock if forage is
 grown in soils with low levels of added selenium.
Vanadium 	0.1	1.0	Toxic to many plants at relatively low concentrations.
Zinc 	2.0	10.0	Toxic to many plants at widely varying concentrations; reduced
 toxicity at increased pH  and in fine-textured or organic
 Classification of Irrigation Water
 Several different measurements are used to classify the suitability of water for irrigation, including ECiw, the total dissolved solids, and SAR.
Some permissible limits for classes of irrigation water are given in Table 4.
In Table 5, the sodium hazard of water is ranked from low to very high based on SAR values.
Classification of Salt-Affected Soils
 Both EC and SAR are commonly used to classify salt-affected soils  normally have a pH value below 8.5, are relatively low in sodium and contain principally sodium, calcium and magnesium chlorides and sulfates.
These compounds cause the white crust which forms on the surface
 Table 6.
Classification of salt-affected soils based on analysis of
 saturation extracts.
Criteria	Normal	Saline	Sodic	Saline-Sodic
 ECe 	<4	>4	<4	>4
 SAR	<13	<13	>13	>13
 and the salt streaks along the furrows.
The compounds which cause saline soils are very soluble in water; therefore, leaching is usually quite effective in reclaiming these soils.
Sodic soils  generally have a pH value between 8.5 and 10.
These soils are called "black alkali soils" due to their darkened appearance and smooth, slick looking areas caused by the dispersed condition.
In sodic soils, sodium has destroyed the permanent structure which tends to make the soil impervious to water.
Thus, leaching alone will not be effective unless the high salt dilution method or amendments are used.
Table 4.
Permissible limits for classes of irrigation water.
Concentration, total dissolved solids
 Classes of water	Electrical	Gravimetric ppm
 Class 1, Excellent	250	175
 Class 2, Good	250-750	175-525
 Class 3, Permissible 1	750-2,000	525-1,400
 Class 4, Doubtful	2,000-3,000	1,400-2,100
 Class 5, Unsuitable	3,000	2,100
 *Micromhos/cm at 25 degrees C.
1	Leaching needed if used
 2	Good drainage needed and sensitive plants will have difficulty obtaining
 Water Quality Effects on Plants and Crop Yield
 Table 7 gives the expected yield reduction of some crops for various levels of soil salinity as measured by EC under normal growing conditions, and Table 8 gives potential yield reduction due to water salinity levels.
Generally forage crops are the most resistant to salinity, followed by field crops, vegetable crops, and fruit crops which are generally the most sensitive.
Table 9 lists the chloride tolerance of a number of agricultural crops.
Boron
 is a major concern in some areas.
While a necessary nutrient, high boron levels cause plant toxicity, and concentrations should not exceed those given in Table 10.
Some information is available on the susceptibility of crops to foliar injury from spray irrigation with water containing sodium and chloride.
The tolerance of crops to sodium as measured by the exchangeable sodium percentage  is given in Table 12.
Table 5.
The sodium hazard of water based on SAR Values.
SAR values	Sodium hazard of water	Comments
 1-10	Low	Use on sodium sensitive crops such as avocados
 10 18	Medium	Amendments  and leaching needed.
18 26	High	Generally unsuitable for continuous use.
> 26	Very High	Generally unsuitable for use.
Table 7.
Soil salinity tolerance levels 1 for different crops.
Crop	100%	90%	75%	50%	Maximum ECe
 Barley	8.0	10.0	13.0	18.0	28
 Bean 	1.0	1.5	2.3	3.6	7
 Broad bean	1.6	2.6	4.2	6.8	12
 Corn	1.7	2.5	3.8	5.9	10
 Cotton	7.7	9.6	13.0	17.0	27
 Cowpea	1.3	2.0	3.1	4.9	9
 Flax	1.7	2.5	3.8	5.9	10
 Groundnut	3.2	3.5	4.1	4.9	7
 Rice 	3.0	3.8	5.1	7.2	12
 Safflower	5.3	6.2	7.6	9.9	15
 Sesbania	2.3	3.7	5.9	9.4	17
 Sorghum	4.0	5.1	7.2	11.0	18
 Soybean	5.0	5.5	6.2	7.5	10
 Sugar beet	7.0	8.7	11.0	15.0	24
 Wheat	6.0	7.4	9.5	13.0	20
 Bean	1.0	1.5	2.3	3.6	7
 Beet	4.0	5.1	6.8	9.6	15
 Broccoli	2.8	3.9	5.5	8.2	14
 Cabbage	1.8	2.8	4.4	7.0	12
 Cantaloupe	2.2	3.6	5.7	9.1	16
 Carrot	1.0	1.7	2.8	4.6	8
 Cucumber	2.5	3.3	4.4	6.3	10
 Lettuce	1.3	2.1	3.2	5.2	9
 Onion	1.2	1.8	2.8	4.3	8
 Pepper	1.5	2.2	3.3	5.1	9
 Potato	1.7	2.5	3.8	5.9	10
 Radish	1.2	2.0	3.1	5.0	9
 Spinach	2.0	3.3	5.3	8.6	15
 Sweet corn	1.7	2.5	3.8	5.9	10
 Sweet potato	1.5	2.4	3.8	6.0	11
 Tomato	2.5	3.5	5.0	7.6	13
 Alfalfa	2.0	3.4	5.4	8.8	16
 Barley hay	6.0	7.4	9.5	13.0	20
 Bermudagrass	6.9	8.5	10.8	14.7	23
 Clover, Berseem	1.5	3.2	5.9	10.3	19
 Corn 	1.8	3.2	5.2	8.6	16
 Harding grass	4.6	5.9	7.9	11.1	18
 Orchard grass	1.5	3.1	5.5	9.6	18
 Perennial rye	5.6	6.9	8.9	12.2	19
 Sudan grass	2.8	5.1	8.6	14.4	26
 Tall fescue	3.9	5.8	8.61	3.3	23
 Tall wheat grass	7.5	9.9	13.3	19.4	32
 Trefoil, big	2.3	2.8	3.6	4.9	8
 Trefoil, small	5.0	6.0	7.5	10.0	15
 Wheat grass	7.5	9.0	11.0	15.0	22
 Salinity and Growth Stage
 Many crops have little tolerance for salinity during seed germination, but significant tolerance during later growth stages.
Some crops such as barley, wheat and corn are known to be more sensitive to salinity during the early growth period than during germination and later growth periods.
Sugar beet and safflower are relatively more sensitive during germination, while the tolerance of soybeans may increase or decrease during different growth periods depending on the variety.
Leaching for Salinity Management
 Soluble salts that accumulate in soils must be leached below the crop root zone to maintain productivity.
Leaching is the basic management tool for controlling salinity.
Water is applied in excess of the total amount used by the crop and lost to evaporation.
The strategy is to keep the salts in solution and flush them below the root zone.
The amount of water needed is referred to as the leaching requirement or the leaching fraction.
Excess water may be applied with every irrigation to provide the water needed for leaching.
However, the time interval between leachings does not appear to be critical provided that crop tolerances are not exceeded.
Hence, leaching can be accomplished with each irrigation, every few irrigations, once yearly, or even longer depending on the severity of the salinity problem and salt tolerance of the crop.
An occasional or annual leaching event where water is ponded on the surface is an easy and effective method for controlling soil salinity.
In some areas, normal rainfall provides adequate leaching.
Table 7.
Soil salinity tolerance levels 1 for different crops.
Crop	100%	90%	75%	50%	Maximum ECe
 Almond	1.5	2.0	2.8	4.1	7
 Apple, Pear	1.7	2.3	3.3	4.8	8
 Apricot	1.6	2.0	2.6	3.7	6
 Avocado	1.3	1.8	2.5	3.7	6
 Date palm	4.0	6.8	10.9	17.9	32
 Pomegranate	2.7	3.8	5.5	8.4	14
 Grape	1.5	2.5	4.1	6.7	12
 Grapefruit	1.8	2.4	3.4	4.9	8
 Lemon	1.7	2.3	3.3	4.8	8
 Orange	1.7	2.3	3.2	4.8	8
 Peach	1.7	2.2	2.9	4.1	7
 Plum	1.5	2.1	2.9	4.3	7
 Strawberry	1.0	1.3	1.8	2.5	4
 Walnut	1.7	2.3	3.3	4.8	8
 1	Based on the electrical conductivity of the saturated extract taken from a
 root zone soil sample  measured in mmhos/cm.
a	During germination and seedling stage ECe should not exceed 4 to 5
 mmhos/cm except for certain semi-dwarf varieties.
b	During germination ECe should not exceed 3 mmhos/cm.
Table 8.
Irrigation water salinity tolerances 1 for different crops.
Crop	100%	90%	75%	50%
 Barley	5.0	6.7	8.7	12.0
 Bean 	0.7	1.0	1.5	2.4
 Broad bean	1.1	1.8	2.0	4.5
 Corn	1.1	1.7	2.5	3.9
 Cotton	5.1	6.4	8.4	12.0
 Cowpea	0.9	1.3	2.1	3.2
 Flax	1.1	1.7	2.5	3.9
 Groundnut	2.1	2.4	2.7	3.3
 Rice 	2.0	2.6	3.4	4.8
 Safflower	3.5	4.1	5.0	6.6
 Sesbania	1.5	2.5	3.9	6.3
 Sorghum	2.7	3.4	4.8	7.2
 Soybean	3.3	3.7	4.2	5.0
 Sugar beet	4.7	5.8	7.5	10.0
 Wheat	4.0	4.9	6.4	8.7
 Bean	0.7	1.0	1.5	2.4
 Beet	2.7	3.4	4.5	6.4
 Broccoli	1.9	2.6	3.7	5.5
 Determining Required Leaching Fraction
 The leaching fraction is commonly calculated using the following relationship:
 LF EC ECiw  =
 LF = leaching fraction the fraction of applied irrigation water that must be leached through the root zone
 ECiw = electric conductivity of the irrigation water
 EC = the electric conductivity of the soil in the root zone
 Equation  can be used to determine the leaching fraction necessary to maintain the root zone at a targeted salinity level.
If the amount of water available for leaching is fixed, then the equation can be used to calculate the salinity level that will be maintained in the root zone with that amount of leaching.
Please note that equation  simplifies a complicated soil water process.
ECe should be checked periodically and the amount of leaching adjusted accordingly.
Based on this equation, Table 13 lists the amount of leaching needed for different classes of irrigation waters to maintain the soil salinity in the root zone at a desired level.
However, additional water must be supplied because of the inefficiencies of irrigation systems , as well as to remove the existing salts in the soil.
Table 8.
Irrigation water salinity tolerances  for different crops.
Crop	100%	90%	75%	50%
 Cabbage	1.2	1.9	2.9	4.6
 Cantaloupe	1.5	2.4	3.8	6.1
 Carrot	0.7	1.1	1.9	3.1
 Cucumber	1.7	2.2	2.9	4.2
 Lettuce	0.9	1.4	2.1	3.4
 Onion	0.8	1.2	1.8	2.9
 Pepper	1.0	1.5	2.2	3.4
 Potato	1.1	1.7	2.5	3.9
 Radish	0.8	1.3	2.1	3.4
 Spinach	1.3	2.2	3.5	5.7
 Sweet corn	1.1	1.7	2.5	3.9
 Sweet potato	1.0	1.6	2.5	4.0
 Tomato	1.7	2.3	3.4	5.0
 Alfalfa	1.3	2.2	3.6	5.9
 Barley hay	4.0	4.9	6.3	8.7
 Bermudagrass	4.6	5.7	7.2	9.8
 Clover, Berseem	1.0	2.1	3.9	6.8
 Corn 	1.2	2.1	3.5	5.7
 Harding grass	3.1	3.9	5.3	7.4
 Orchard grass	1.0	2.1	3.7	6.4
 Perennial rye	3.7	4.6	5.9	8.1
 Sudan grass	1.9	3.4	5.7	9.6
 Tall fescue	2.6	3.9	5.7	8.9
 Tall wheat grass	5.0	6.6	9.0	13.0
 Trefoil, big	1.5	1.9	2.4	3.3
 Trefoil, small	3.3	4.0	5.0	6.7
 Wheat grass	5.0	6.0	7.4	9.8
 Almond	1.0	1.4	1.9	2.7
 Apple, Pear	1.0	1.6	2.2	3.2
 Apricot	1.1	1.3	1.8	2.5
 Avocado	0.9	1.2	1.7	2.4
 Date palm	2.7	4.5	7.3	12.0
 Pomegranate	1.8	2.6	3.7	5.6
 Grape	1.0	1.7	2.7	4.5
 Grapefruit	1.2	1.6	2.2	3.3
 Lemon	1.1	1.6	2.2	3.2
 Orange	1.1	1.6	2.2	3.2
 Peach	1.1	1.4	1.9	2.7
 Plum	1.0	1.4	1.9	2.8
 Strawberry	0.7	0.9	1.2	1.7
 Walnut	1.1	1.6	2.2	3.2
 1	Based on the electrical conductivity of the irrigation water  measured
 Very saline, shallow water tables occur in many areas of Texas.
Shallow water tables complicate salinity management since water may actually move upward into the root zone, carrying with it dissolved salts.
Water is then extracted by crops and evaporation, leaving behind the salts.
Shallow water tables also contribute to the salinity problem by restricting the downward leaching of salts through the soil profile.
Installation of a subsurface drainage system is about the only solution available for this situation.
The original clay tiles have been replaced by plastic tubing.
Modern drainage tubes are COVered by a "sock" made of fabric to prevent clogging of the small openings in the plastic tubing.
A schematic of a subsurface drainage system is shown in Figure 2.
The design parameters are the distance between drains  and the elevation of the drains  above the underlying impervious or restricting layer.
Proper spacing and depth maintain the water level at an optimum level, shown here as the distance m above the drain tubes.
The USDA Natural Resources Conservation Service  has developed drainage design guidelines that are used throughout the United States.
A drainage computer model developed by Wayne Skaggs at North Carolina State University, DRAINMOD, is also widely used throughout the world for subsurface drainage design.
Obtaining a satisfactory stand is often a problem when furrow irrigating with saline water.
Growers sometimes compensate for poor germination by planting two or three times as much seed as normally would be required.
However, planting procedures can be adjusted to lower the salinity in the soil around the germinating seeds.
Good salinity control is often achieved with a combination of suitable practices, bed shapes and irrigation water management.
In furrow-irrigated soils, planting seeds in the center of a single-row, raised bed places the seeds exactly where salts are expected to concentrate.
This situation can be avoided using "salt ridges." With a double-row raised planting bed, the seeds are placed near the shoulders and away from the area of greatest salt accumulation.
Alternate-furrow irrigation may help in some cases.
If alternate furrows are irrigated, salts often can be moved beyond the single seed row to the non-irrigated side of the planting bed.
Salts will still accumulate, but accumulation at the center of the bed will be reduced.
With either singleor double-row plantings, increasing the depth of the water in the furrow can improve germination in saline
 soils.
Another practice is to use sloping beds, with the seeds planted on the sloping side just above the water line.
Seed and plant placement is also important with the use of drip irrigation.
Typical wetting patterns of drip emitters and micro-sprinklers are shown in Figure 4.
Salts tend to move out and upward, and will accumulate in the areas shown.
Other Salinity Management Techniques
 Techniques for controlling salinity that require relatively minor changes are more frequent irrigations, selection of more salt-tolerant crops, additional leaching, preplant irrigation, bed forming and seed placement.
Alternatives that require significant changes in management are changing the irrigation method, altering the water supply, land-leveling, modifying the soil profile, and installing subsurface drainage.
The common saying "salt loves bare soils" refers to the fact that exposed soils have higher evaporation rates than those covered by residues.
Residues left on the soil surface reduce evaporation.
Thus, less salts will accumulate and rainfall will be more effective in providing for leaching.
Salt concentrations increase in the soil as water is extracted by the crop.
Typically, salt concentrations are lowest following an irrigation and higher just before the next irrigation.
Increasing irrigation frequency maintains a more constant moisture content in the soil.
Thus, more of the salts are then kept in solution which aids the leaching process.
Surge flow irrigation is often effective at reducing the minimum depth of irrigation that can be applied with furrow irrigation systems.
Thus, a larger number of irrigations are possible using the same amount of water.
Figure 2.
A subsurface drainage system.
Plastic draintubes are located a distance  apart.
Figure 3a.
Single-row versus double-row beds showing areas of salt accumulation following a heavy irrigation with salty water.
Best planting position is on the shoulders of the double-row bed.
Figure 3b.
Pattern of salt build-up as a function of seed placement, bed shape and irrigation water quality.
Table 9.
Chloride tolerance of agricultural crops.
Listed in order
 of tolerance.
without loss in yield
 Rice, paddy	C	30d	1,050
 Clover, strawberry	15	525
 Clover, red	15	525
 Clover, alsike	15	525
 Clover, ladino	15	525
 Sweet potato	15	525
 Broad bean	15	525
 Foxtail, meadow	15	525
 Clover, Berseem	15	525
 Trefoil, big	20	700
 Squash, scallop	30	1,050
 Vetch, common	30	1,050
 Wild rye, beardless	30	1,050
 Sudan grass	30	1,050
 Wheat grass, standard crested	35	1,225
 Beet, red	40	1,400
 Fescue, tall	40	1,400
 Squash, zucchini	45	1,575
 Harding grass	45	1,575
 Trefoil, narrow-leaf bird's foot	50	1,750
 With proper placement, drip irrigation is very effective at flushing salts, and water can be applied almost continuously.
Center pivots equipped with LEPA water applicators offer similar efficiencies and control as drip irrigation at less than half the cost.
Both sprinkler and drip provide more control and flexibility in scheduling irrigation than furrow systems.
Salts often accumulate near the soil surface during fallow periods, particularly when water tables are high or when off-season rainfall is below normal.
Under these conditions, seed germination and seedling growth can be seriously reduced unless the soil is leached before planting.
Changing Surface Irrigation Method
 Surface irrigation methods, such as flood, basin, furrow and border are usually not sufficiently flexible to permit changes in frequency of irrigation or depth of water applied per irrigation.
For example, with furrow irrigation it may not be possible to reduce the depth of water applied below 3-4 inches.
As a result, irrigating more frequently might improve water availability to the crop but might also waste water.
Converting to surge flow irrigation may be the solution for many furrow systems.
Otherwise a sprinkler or drip irrigation system may be required.
In sodic soils , sodium ions have become attached to and adsorbed onto the soil particles.
This causes a breakdown in soil structure and results in soil sealing or "cementing," making it difficult for water to infiltrate.
Chemical amendments are used in order to help facilitate the displacement of these sodium ions.
Amendments are composed
 Table 9.
Chloride tolerance of agricultural crops.
Listed in order
 without loss in yield
 Ryegrass, perennial	55	1,925
 Wheat, Durum	55	1,925
 Barley 	60	2,100
 Wheat C	60	2,100
 Sugar beet	70	2,450
 Wheat grass, fairway crested	75	2,625
 Wheat grass, tall	75	2,625
 These data serve only as a guideline to relative tolerances among crops.
Absolute tolerances vary, depending upon climate, soil conditions and
 bcl concentrations in saturated-soil extracts sampled in the rootzone.
'Less tolerant during emergence and seedling stage.
"Values for paddy rice refer to the CI concentration in the soil water during
 the flooded growing conditions.
of sulphur in its elemental form or related compounds such as sulfuric acid and gypsum.
Gypsum also contains calcium which is an important element in correcting these conditions.
Some chemical amendments render the natural calcium in the soil more soluble.
As a result, calcium replaces the adsorbed sodium which helps restore the infiltration capacity of the soil.
Polymers are also beginning to be used for treating sodic soils.
It is important to note that use of amendments does not eliminate the need for leaching.
Excess water must still be applied to leach out the displaced sodium.
Chemical amendments are only effective on sodium-affected soils.
Amend-ments are ineffective for saline soil conditions and often will increase the existing salinity problem.
Table 15 lists the most common amendments.
The irrigation books listed under the
Fact Sheet No.
4.708
 The purpose of irrigation scheduling is to determine the exact amount of water to apply to the field and the exact timing for application.
The amount of water applied is determined by using a criterion to determine irrigation need and a strategy to prescribe how much water to apply in any situation.
Irrigation Criteria and Irrigation Scheduling
 Irrigation criteria are the indicators used to determine the need for irrigation.
The most common irrigation criteria are soil moisture content and soil moisture tension.
The less common types are irrigation scheduling to maximize yield and irrigation scheduling to maximize net return.
The final decision depends on the irrigation criterion, strategy and goal.
Irrigators need to define a goal and establish an irrigation criterion and strategy.
To illustrate irrigation scheduling, consider a farmer whose goal is to maximize yield.
Soil moisture content is the irrigation criterion.
Different levels of soil moisture trigger irrigation.
For example, when soil water content drops below 70 percent of the total available soil moisture, irrigation should start.
Soil moisture content to trigger irrigation depends on the irrigator's goal and strategy.
In this case, the goal is to maximize yield.
Therefore, the irrigator will try to keep the soil moisture content above a critical level.
If soil moisture level falls below this level, the yield may be lower than the maximum potential yield.
Thus, irrigation is applied whenever the soil water content level reaches the critical level.
How much water to apply depends on the irrigator's strategy.
For example, the irrigator can replenish the soil moisture to field
 capacity or apply less.
If no rain is expected and the irrigator wishes to stretch the time between irrigations, it is advantageous to refill the soil profile to field capacity.
If rain is expected, it may be wise not to fill the soil profile to field capacity, but leave some room for rain.
If the irrigator's goal is to maximize net return, an economic irrigation criterion is needed, such as net return.
This is the income from the crop less the expenses associated with irrigation.
The importance of irrigation scheduling is that it enables the irrigator to apply the exact amount of water to achieve the goal.
This increases irrigation efficiency.
A critical element is accurate measurement of the volume of water applied or the depth of application.
A farmer cannot manage water to maximum efficiency without knowing how much was applied.
Also, uniform water distribution across the field is important to derive the maximum benefits from irrigation scheduling and management.
Accurate water application prevents overor underirrigation.
Overirrigation wastes water, energy and labor; leaches expensive nutrients below the root zone, out of reach of plants; and reduces soil aeration, and thus crop yields.
Underirrigation stresses the plant and causes yield reduction.
Advantages of Irrigation Scheduling
 Irrigation scheduling offers several advantages:
 1.
It enables the farmer to schedule water rotation among the various fields to minimize crop water stress and maximize yields.
2.
It reduces the farmer's cost of water and labor through fewer irrigations, thereby making maximum use of soil moisture storage.
Irrigation scheduling is the decision of when and how much water to apply to a field.
Its purpose is to maximize irrigation efficiencies by applying the exact amount of water needed to replenish the soil moisture to the desired level.
Irrigation scheduling saves water and energy.
All irrigation scheduling procedures consist of monitoring indicators that determine the need for irrigation.
Table 1.
Different methods of irrigation scheduling.
Method	Parameter	Needed	Criterion	Advantages	Disadvantages
 Hand feel and	Soil moisture content	Hand probe.
Soil moisture	Easy to use; simple; can	Low accuracies; field work
 appearance of	by feel.
content.
improve accuracy with	involved to take samples.
Gravimetric soil	Soil moisture content	Auger, caps,	Soil moisture	High accuracy.
Labor intensive including
 moisture	by taking samples.
oven.
content.
field work; time gap
 sample.
between sampling and
 Tensiometers.
Soil moisture tension.
Tensiometers	Soil moisture	Good accuracy;	Labor to read; needs
 including	tension.
instantaneous reading	maintenance; breaks at
 vacuum gauge.
of soil moisture tension.
tensions above 0.7 atm.
Electrical	Electric resistance of	Resistance blocks,	Soil moisture	Instantaneous reading;	Affected by soil salinity;
 resistance	soil moisture.
AC bridge.
tension.
works over larger range	not sensitive at low
 blocks.
of tensions; can be used	tensions; needs some
 for remote reading.
maintenance and field
 Water budget	Climatic parameters:	Weather station or	Estimation of	No field work required;	Needs calibration and
 approach.
temperature, radiation,	available weather	moisture	flexible; can forecast	periodic adjustments,
 wind, humidity and	information.
content.
irrigation needs in the	since it is only an
 expected rainfall,	future; with same	estimate; calculations
 depending on model	equipment can schedule	cumbersome without
 used to predict ET.
many fields.
computer.
The reason for the recommendation is to save money on pumping costs, leave room to store the offseason precipitation, and reduce the potential for leaching nutrients like nitrate nitrogen deeper into the profile.
For most of Nebraska, adequate precipitation will be received from October through May to refill the soil profile on irrigated fields.
In addition, leaving the soil dryer will help reduce harvest delays because of mud in wetter falls.
Other VRI Resources from UNL: Variable rate application of irrigation water with center pivots
 This extension circular  provides an overview of VRI.
Pumpage reduction by using variable rate irrigation to mine undepleted soil water.
Watering Systems for Cattle Ponds
 Dirk Philipp Associate Professor Forages
 Kenny Simon Program Associate Forages
 Arkansas Is Our Campus
 The availability of sufficient quantities of clean water is often overlooked on beef cattle farms; however, it is often the most critical nutrient.
Water may be supplied from various sources such as rural water, water wells, ponds, etc.
While rural water and water wells may be used for watering livestock, they are often limited by availability.
However, most producers have ponds on their properties that can be used for livestock watering.
This document describes two watering devices that can be used for either watering cattle directly from ponds or within close proximity.
Allowing cattle unlimited access to ponds is not ideal from an animal health and environmental perspective.
Cattle may loaf in ponds and may transfer internal parasites as a result.
Foot rot is a common problem of animals lingering in ponds.
Softened hoofs are easily damaged and may become infected with fusobacteria.
One of the more important diseases advanced through the microclimatic conditions around ponds is leptospirosis.
Fever, anorexia and possible calf abortion are possible symptoms of leptospirosis.
Coccidiosis, caused by a protozoan parasite, may cause acute diarrhea, weight loss and the death of animals.
Pond water may also have increased nitrogen or phosphorus levels that may stem from runoff or
 direct manure deposits.
High nutrient levels can result in increased algae and weed growth with the associated reduction in environmental and cattle drinking water quality.
Appropriate pond management helps prevent negative health effects and also negative environmental effects such as erosion of banks and sediment intake that could render the pond unusable in the long term.
Prolonged, unlimited access to ponds by livestock can result in destruction of fish habitat, reduction of pond volume and reduced animal performance.
For many producers, ponds are the only way to provide water for livestock, especially cattle.
There are several ways to water livestock from ponds, some of which are described here.
These pond-watering devices are costeffective, relatively easy to install and low maintenance.
In Arkansas many livestock producers, including those involved with the 300 Day Grazing Program, already use these methods to effectively water livestock.
Limited Access Floating Fences:
 Establishing access to a pond for livestock watering is usually done in conjunction with fencing the entire pond to avoid negative impacts on the structural integrity of the pond and fish habitat.
Fencing around the pond
 helps prevent bank and bottom damage due to cattle traffic.
Since a pond is used to intercept runoff, effort should be made to avoid manure contamination through incoming waterways, spillways and shorelines.
Ponds should be fenced, except the section assigned as cattle access for watering.
An example for the watering access is depicted in Figure 1.
While the exclusion material used depends on what is available, utilizing electric fence wire is a cost-effective solution, given the durability of the material and ease of removal.
The pond exclusion fence should be at least 12 feet away from the shoreline to provide for vehicle access in case of required vegetative control, pond maintenance or recreational activities.
This buffer area also helps maintain vegetation that may filter occurring runoff and provide habitat for wildlife.
Two-inch polyvinyl chloride  pipe is commonly used to construct a floating fence.
Plastic pipes are easy to cut to the desired length and connect to the required shape and length.
The pipes should be sealed airtight so they don't accumulate water.
Electric fence wire may be placed on top of the pipe approximately 20-30 inches above the water surface; 12.5 gauge high-tensile wire may be used to
 obtain a high level of reliability and durability.
The width of the floating fence will depend on the number of livestock watering from the access point.
A floating fence width of 20-40 feet is sufficient for most situations.
For a small herd of cattle, 20 feet appears to be appropriate, while 40 feet is considered sufficient for 200 cattle.
At the access point, the pond should have a slope of about 30 percent and should reach far enough into the pond so that a minimum water depth of 5 feet at the end of the slope is always maintained, even under normal conditions.
A heavy use area should be created within and in front of the floating limited access area.
To construct a heavy use area, install a 6to 12-inch layer of rock and cover with gravel to maintain a firm base and to avoid development of runoff gullies.
The gravel will also discourage livestock from standing for prolonged periods of time.
The rock and gravel materials used for this purpose should feature angular shapes SO they will interlock and provide a firm base.
The gravel pad should be supported by an underlying geoweb or geotextile fabric that prevents sediment from seeping upwards through the pad.
In general, the more solid the entire limited access floating fence construction, the longer it will last.
FLOATING POLYETHYLENE PIPE FOR LIVESTOCK WATER ACCESS AT A FENCED POND
 Figure 1.
Possible design of a floating fence.
Figure 2.
A heavy use area should be created within and in front of the floating limited access area.
Photo courtesy of John Jennings.
There are other examples of temporary low-cost setups similar to a limited access floating fence.
In some instances, a single-strand polywire fence is sufficient to limit cattle access to ponds without the more expensive setup described above.
An example of a temporary floating access across a pond using polywire is depicted in Figures 3 and 4.
If the banks
 Figure 3.
Temporary floating access across a pond using polywire.
of the pond are not steep or cattle can reach the water without walking into the pond most of the time, then a simple fence might be feasible.
The polywire must be raised to a height that will allow the animals to safely draw water.
Overall bank stability and soil type surrounding the pond should also be taken into consideration.
With more shallow and rockier soils in the northern part of the state, this setup might be workable, compared to other parts of the state where deeper soils may quickly lead to the disintegration of the pond banks.
Drawing Water From Ponds: Ponds are well suited for drawing water away to devices from which cattle are watered.
Virtually any watering device can be connected to a pond outlet or modified so that reliable water delivery is achieved.
The products on the market, such as stock tanks or automated waterers, can function just with gravity flow, for which a pond is ideal as it sits mostly on a slight slope and collects runoff from pastures located further up.
Figure 4.
Floating posts can be built from an old paint bucket that is filled with foam and weighted at the bottom to keep the post upright.
Some devices are more suitable than others, and there are a few things that should be considered when using a pond as a water source.
In general, the pond water needs to meet the basic standards to serve as drinking water free from chemical impurities that may affect cattle health and free of pathogens as much as possible.
Ponds used for cattle watering away from the banks are usually clean, as cattle do not loaf in the bank vicinity and thus pathogen loads should be small.
Ponds may serve multiple purposes, such as raising fish, watering livestock and offering recreational opportunities.
Under these circumstances, care should be taken so
 that these different objectives do not conflict and compromise animal health.
Maintaining a pond for fish may include controlling aquatic weeds and algae by adding chemicals that could affect animal health.
Gravity is used in most cases and is a reliable method of channeling water from the pond to the waterers.
Since this happens at low pressure, larger pipes are needed to maintain the required volumes.
A positive side effect is that low-pressure pipes are less expensive than high-pressure pipes.
Care should be taken to maintain an adequate slope that keeps the water flowing and reduces air pockets that cannot be overcome just by back pressure from gravity.
A pump may be used to redistribute water from a pond to water tanks.
Gravity flow can also be used in conjunction with a pump, which can be reduced in size compared to pump-only systems.
Figure 5.
A pump is used to redistribute water from the pond to a water tank.
Photo courtesy of John Jennings.
Stock tanks, tire tanks, freeze-proof tanks and concrete tanks can all be supplied with water drawn from ponds.
The optimal solution will depend on the topographic characteristics of the pasture or the farm.
Normally, the distance between the pond and the watering device is relatively short, as the watering device is located just downslope of the pond.
With large ponds located uphill, water can be piped across pastures to supply several paddocks or several devices.
The installation of pipes is possible after the pond has been built, although it would be ideal to install pipes during pond construction.
A good resource for building fences and laying drainage pipes and pipes that feed water devices is Ponds Planning, Design, Construction, USDA-NRCS, Agriculture Handbook 590.
This manual provides all the details for building ponds, inserting pipes into the pond walls  and keeping debris from being collected at the water entry point.
It is appealing to consider a future expansion of the system if water is piped from ponds.
If the change in altitude is substantial downhill, then pressure
 reducers or safety valves should be considered to avoid damage to pipes, floats and other necessary equipment.
If pipes are installed over long distances, feeding water from a pond with probably inconsistent water supply may not be the best option, as burying the pipe across differences in elevations requires a large construction effort.
For immediate delivery of pond water to a nearby watering device, it is important to build a heavy use area to cope with increased livestock traffic.
These areas do not have to be overly complicated but should feature a layer of gravel that can absorb any water that may overflow or be splashed without creating muddy conditions around the waterer.
Some sources suggest the gravel area be 4 to 6 inches deep and 6 feet around the device at the minimum.
Depending on the soil type and general characteristics surrounding the waterer, the gravel pad may have to be supported by an underlying geoweb or geotextile fabric that prevents sediment from seeping upwards through the pad.
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IRRIGATION MANAGEMENT: WHEN TO TERMINATE CORN IRRIGATION
 While some early corn is starting to be harvested, much of the irrigated crop is still in the R5-R6 stage.
Once corn has passed the dent stage and the milk/starch line progresses down the kernel, daily crop water use is roughly a third of the peak.
Average daily water use after  milkline is typically 0.1-0.12 per day.
The tough question for most farmers is whether additional irrigation will provide a return on the fuel/electric invested.
Soil moisture stress after dent can reduce kernel density and test weight and therefore reduce yield.
If you have missed the scattered rains and the profile is approaching 50% of available water it is advisable to apply another  of irrigation to carry the crop through black layer.
It will typically take 10-11 days to progress from  milkline to black layer and our sandy loam and loamy sand soils should hold enough moisture to carry the crop through this period provided we start with a full profile.
Soil moisture levels below field capacity at R5.5  will need irrigation or rainfall to make it stress free until physiological maturity.
At this point I am unaware of any research-based evidence that irrigation after black layer provides yield benefit.
24-hour rainfall Aug 21  Aug 22
 Irrigated Corn Soil Moisture Report for the UD Warrington Farm Stage R5.5  DIMS Report
 May 2nd planted soybeans at the UD Warrington Irrigation Research Farm are into the R5/R6 stage as of Aug 22nd.
The average daily crop water use for the past week was 0.17 per day and the predicted daily ET for next week is 0.19 per day.
Despite several rain events over the past week, this field required irrigation on Monday 8-18 and without further rain will need irrigating again on Thursday 8-24.
We have observed high rate of water use from the shallow profile; Remember to irrigate in small but frequent doses to avoid pushing water beyond the root zone.
Multiple years of soil moisture sensor data show so use water primarily from the shallow  soil profile.
Double Crop/Late Season Soybeans
 At this point double crop soybeans full canopied.
Once full canopy is achieved, late soybeans will use the same amount of water as the full season beans above.
Basics of Drip Irrigation and Fertigation for Specialty Crops
 Taunya Ernst Program Associate Horticulture
 Amanda McWhirt Extension Specialist Horticulture
 Thomas Zimmerman Program Technician Fruit Research Station
 Erika Henderson Program Associate Fruit Research Station
 Mataya Duncan Graduate Assistant Horticulture
 Amanda Lay-Walters Graduate Assistant Horticulture
 Arkansas Is Our Campus
 Seventy percent of worldwide water use is for agricultural irrigation.
In response to diminishing supplies of irrigation water, many growers have installed and are using irrigation systems that maximize water use efficiency.
Drip systems are often cited as a solution to water shortages.
In Arkansas and other parts of the Southeast drip systems also help minimize leaf wetness, which favors disease development.
Drip or trickle irrigation applies small quantities of water at low flow rates and low pressure rates with frequent irrigation intervals.
This precise system of water delivery can ensure nearly all irrigation water is used by the plant, increasing water use efficiency by 50 percent or more.
In addition, the use of drip irrigation can improve yields and crop quality through the integration of dissolved fertilizer applications, or fertigation, into the irrigation system.
Conventional pre-plant and side-dressing applications of large volumes of fertilizers give plants more nutrients than are needed at the time of application and expose the crop to potential nutrient deficiencies in-between applications.
In contrast, fertigation gives growers increased control over the dosage and
 timing of fertilizer applications.
Fertigation rates can be easily increased to support growing or fruiting plants and then reduced as the growth cycle comes to an end.
The benefits of fertigation are only achieved when the irrigation system can maintain uniform water application across the area.
Windy conditions disrupt water dispersal for overhead sprinkler systems, and fertilizer runoff is a problem in furrow/ flood systems.
The trickle delivery of water and nutrients in a drip system can deliver water and nutrients directly to the root zone of the plants.
This ensures that fertilizer, like water, is used efficiently, reducing cost and waste.
Small scale systems can be built economically and added on to over time.
For these reasons drip irrigation and fertigation are preferred for most fruit and vegetable production in Arkansas.
This fact sheet will cover basic and general considerations for drip irrigation and fertigation system design and construction.
Many irrigation suppliers are good resources for new growers designing a system customized for a specific site and crop.
Parts of the System:
 There are several major components of a drip irrigation system.
Figure 1.
General design and component layout for a drip irrigation system
 These will be outlined in the following sections.
The order in which these components are often placed within the system is shown in Figure 1.
Comparative Energy Costs for Irrigation Pumping
 R.
Scott Fraizer Assistant Professor, Renewable Energy
 One major cost of pumping irrigation water is the cost of energy.
Increasing energy prices require irrigation farmers to consider future availability as well as price when comparing energy alternatives.
Making power cost comparisons between different makes and models of engines and/or between different fuel options is desirable.
By expressing power costs in terms of cost per horsepower-hour , it is possible to make a quick, reliable comparison.
Calculations should be based on derated horsepower  and not on the manufacturers advertised maximum horsepower.
Derating considers the differences between field operating conditions and the manufacturer's testing conditions, which can affect engine performance.
To derate an engine, start with the maximum rated brake horsepower  for the specific speed at which the engine will be operated and make the following deductions:
 1.
Deduct 20 percent for continuous load.
2.
Deduct 3 percent for each 1,000 feet of elevation above sea level.
3.
Deduct 1 percent for each 10F rise of ambient air temperature above 60F.
4.
Deduct 5 percent for accessories.
5.
Deduct 5 percent if a fan and radiator are used.
6.
Deduct 3 percent if a right angle drive is used.
Some manufacturers rate their engines for continuous operation.
In these cases, the deduction for continuous operation has already been made.
For natural gas powered engines a good rule-of-thumb to calculate a rough estimate of an engine's derated continuous horsepower output can be given by:
 HP = Displacement  X Engine Speed  10,000
 As a rule, electric motors do not need to be derated from the horsepower indicated on the nameplate because most manufacturers base this rating on 70F air temperatures and a 10 to 15 percent overload factor.
This is a built-in service factor to compensate for varying temperature and voltage conditions.
If pump power requirements fall between motor sizes, select
 the larger size motor.
For example, if the power required is 32 HP, choose a 40 HP motor rather than 30 HP.
Since power costs are to be calculated in terms of cost per HP-hr or kwh, it is necessary to establish the hours of useful power plant life.
Operator skill, preventive maintenance, and operating conditions greatly affect how long a power unit will remain useful.
Exact data are not available on expected irrigation engine life.
Conferences with service managers at irrigation engine repair shops indicate that with proper maintenance, periodic overhaul, and operation until no longer economically repairable, the following power unit useful life can be expected:
 Automotive engines 20,000 hours Light industrial engines 30,000 hours.
Electric motors 75,000 hours or 25 years.
The typical initial purchase cost per horsepower derated for average Oklahoma conditions is approximately as follows: Natural Gas and LP Gas Engines : Automotive: $75 per derated horsepower.
Light industrial: $180 per derated horsepower.
Diesel Engines : Light industrial: $160 per derated horsepower.
3-Phase Electric Motors : Vertical Hollow-shaft: $90 per nameplate HP.
Solid Shaft: $80 per nameplate HP.
There are four major categories involved in calculating total power unit costs.
These are:
 2.
Repairs and maintenance
 3.
Taxes and insurance
 An economic comparison of power costs must include all four of these categories.
Assuming the power unit is used for its entire useful life at a rate of 2,000 hours per year and has no trade-in value, a capital recovery factor  can be used to determine the annual cost of ownership for the prevailing interest rate.
For a 5 percent interest rate, the CRF is 0.1628 for natural gas, LP gas and diesel engines , and 0.1278 for electric motors.
The annual depreciation cost is:
 Depreciation,  = CRF X ini.
cost  Hours of use/year
 The annual cost of repairs and maintenance  for irrigation power units can vary considerably, depending on the operating conditions, operator skill, and hours of operation.
An accepted practice in estimating these costs is to use a percentage of the initial cost of the unit as the annual cost.
The percentage used depends upon the type of power unit.
For all internal combustion engines, a typical repair and maintenance factor  is 6 percent per year.
For electric motors, the maintenance factor typically is 2 percent of initial cost per year.
Annual maintenance and repair cost is:
 R&M,  = RMF% X initial cost  100% X Hours of use/year
 Taxes and insurance  will vary with time and the depreciated value of the power unit.
Typically they will cost about 1.5 percent of the initial cost of the unit.
Therefore, the annual tax and insurance cost is:
 T&I,  = 1.5% X initial cost  100% X Hours of use/year
 Based on data taken from manufacturer's performance tests and Nebraska Tractor Tests, typical performance efficiencies of 30 percent for diesel engines, and 26 percent for LP gas engines should be expected for irrigation engines in Oklahoma conditions.
Peak efficiencies may range higher or lower than this, but these are reasonable figures for engines that are tuned regularly.
At these performance levels, diesel engines should develop about 16.49 HP-hr of energy per gallon of fuel, while LP gas engines should deliver about 9.39 HP-hr per gallon.
Manufacturer's performance data for natural gas engines have been confirmed by a number of efficiency tests in Oklahoma.
A typical engine efficiency should be about 26 percent.
This means a typical engine should deliver 102 HP-hr per 1,000 cubic feet of natural gas.
Experience has shown that lubricant and filter costs will be about 15 percent of the fuel cost.
Fuel, lubricant, and filter costs in terms of cost per horsepower-hour are:
 Fuel,  = 1.15 X diesel price  16.49
 Fuel,  = 1.15 X LP gas price 
 Fuel,  = 1.15 X natural gas price  102
 These fuel costs do not include either the fuel storage tank costs in the case of LP gas and diesel, or the cost of piping natural gas to the engine.
Electric power schedules are nearly always based on an annual standby charge and a schedule of rates for energy consumed.
The standby charge is based on the horsepower rating indicated on the motor nameplate or the actual measured power demand.
Some power suppliers apply the money collected as standby charges against energy consumed, while other suppliers charge for all energy consumed in addition to the annual standby charges.
Large three-phase electric motors average 85 to 95 percent efficiency in converting electrical energy to mechanical energy depending upon motor size, design, and loading.
Assuming 90 percent motor efficiency, electrical energy per horsepower-hour can be estimated by:
 Energy  = )
 These energy costs do not include any power line construction costs and assume that annual standby charges are applied against energy consumed.
If standby charges are not applied to energy consumed, it is necessary to adjust power costs by dividing the standby charge by the annual hours of operation times rated motor horsepower and adding this value to cost of energy consumed.
Stand-by  = Stand-by charge  Hrs of use X rated HP
 Total power cost  is the sum of depreciation; repairs; taxes, insurance, and interest; and fuel and filter costs.
Using the relationships already established, the total power cost  for a diesel engine operated 3,000 hours per year with diesel fuel costs $3.76 per gallon  would be:
 Depreciation = 0.1278 X $160 =$ 0.00682 3000 R&M = 6% X $160 = $ 0.00320 100% X 3000 T&I = 1.5% X $160 = $ 0.00080 100% X 3000 Fuel cost = 1.15 X $ 3.76 = $ 0.2622 16.49 Total Power Cost  Total = $ 0.2730
 The same procedure can be followed to determine power costs for LP gas and natural gas engines, as well as electric motors.
Rather than making calculations, the nomograph in Figure 1 can be used to estimate total power cost in dollars per horsepower-hour for power units operated approximately
 2,000 hours per year, with a basic interest rate of 10 percent The following example explains the use of the nomograph for comparing relative fuel costs.
Assume an irrigation well is to be equipped with a power unit delivering 100 horsepower after derating, and the well will be pumped 2,000 hours per year.
Natural gas is available at $5.00 per Mcf.
For the 100 HP engine, the total power cost for natural gas would be:
 Adjusting Data to Your Situation
 The data shown on the nomograph are based on certain assumptions.
To estimate more specific power costs, substitute specific information into the appropriate equations from the cost categories section and calculate the cost for a particular situation.
Fuel consumption rates can vary considerably between different makes of engines, as well as between different models of the same make.
There is very little variation in energy consumption between brands of electric motors so long as
 motor type, size, and loading are the same.
Most engine manufacturers publish fuel consumption data on their line of engines.
The gear ratio used in right-angle gear heads should be chosen so that the pump can operate at its rated speed while keeping the engine operating speed at the point where its fuel consumption is most efficient.
If a specific fuel consumption curve is not available for your engine, a good rule-of-thumb is that most economic fuel consumption OCcurs at the speed where the engine produces its maximum torque.
Fuel efficiency tests are usually performed on "bare" engines  with the engine tuned for peak performance.
Under field conditions, the fuel consumption rate will be greater; however, the relative ranking of engines should not change much.
With all other considerations  being comparable, selecting the engine with the lowest fuel consumption rate can reduce total power costs for irrigation pumping.
Considerations other than Fuel
 Fuel selection should not be based on price alone.
Also consider the following: Is the fuel available in the area?
Is the supply dependable?
Is the price relatively stable?
Also, are trained mechanics available for working on power units equipped for the specific fuel?
Answering "no" to anyone of these questions could indicate that another fuel may be more desirable.
Theoretically, a new diesel engine may have a performance efficiency as high as 32 percent in converting the chemical energy of its fuel into mechanical energy.
Natural gas and L.
P.
gas engines may have efficiencies as high as 28 percent, and gasoline engines as high as 27 percent.
As engines age, these performance efficiencies can be reduced significantly by component wear and poor tuning.
It is advisable to keep records of hours of operation, fuel use, and water applied in order to evaluate how the performance of your pumping plant has changed with time.
These records may detect abnormally high fuel consumption and poor efficiency.
If a problem is indicated by the fuel use records, testing can be done to determine if the drop in efficiency is due to the engine or the pump.
Appropriate corrective measures, such as a tune-up or overhaul, can then be taken.
Center pivots comprise three main components: the pump, power unit, and pivot.
Traditionally on leased cropland, the landowner owns the pump and pivot.
Depending on the area of Nebraska and available energy sources, the power unit may be owned by the landowner or tenant.
Ownership of the pump and pivot by the landowner creates greater flexibility for the management of the land when terminating the tenant or selling the property.
Irrigation Management Strategies to Improve Water and Energy-use Efficiencies
 Prepared by: Robert Evans, Extension Agricultural Engineering Specialist R.
E.
Sneed, Extension Agricultural Engineering Specialist J.
H.
Hunt, Extension Agricultural Engineering Specialist
 Published by: North Carolina Cooperative Extension Service Publication Number: AG 452-5 Last Electronic Revision: June 1996 
 Irrigation is practical for many North Carolina farmers.
Because irrigation can be expensive, however, there is much to consider before deciding to irrigate.
Irrigation equipment may cost more than half as much as the land on which it is used.
Irrigation also consumes large quantities of water and energy.
Annual energy costs of $25 per acre are typical in North Carolina, where application rates average about 8 inches of water per acre per year.
When irrigation systems are poorly maintained and operated, energy costs may be two to three times that amount.
One way to reduce irrigation costs is to optimize the use of water and energy, as described in this publication.
How efficiently irrigation systems use water and energy is determined primarily by the type of system and the way it is operated, maintained, and managed.
This publication discusses irrigation decisions that affect water and energy efficiencies.
Comparing the water and energy efficiencies of different systems can be difficult because not all manufacturers use the same terminology.
Some of the more common terms are listed in the box on page 7.
These definitions are helpful in comparing systems and converting efficiencies to consistent units.
Potential water-use efficiency for the types of irrigation systems most frequently used in North Carolina is shown in Table 1.
The word potential means the maximum water-use efficiency that can be achieved when the system is maintained and operated properly.
Many factors influence water-use efficiency.
Irrigation must be scheduled at the proper times to obtain the efficiencies shown.
Irrigation scheduling is the process of determining when to irrigate and how much water to apply.
Scheduling strategies are discussed in Extension Service publication AG542-4, Irrigation Scheduling to Improve Water-and Energy-Use Efficiency.
Other factors affecting water-use efficiency are discussed further in this publication.
Table 4.
Potential Water-Use Efficiencies of Several Types of Irrigation Systems
 Potential Water	Typical Pump
 Type of System		
 Hand-move 	75	60 100
 Hand-move (gun sprinkler]	70	80 130
 Solid-set	80	60 100
 Center plvot 	90	70 110
 Center pivot 	92	40 80
 Linear-move	92	40 80
 Hose-pull traveler	70	30 200
 Drip or trickle	90+	5 75
 Performance data for most agricultural power equipment marketed in the United States are published annually in the Nebraska Tractor Test Report.
The data are obtained by University of Nebraska engineers and can be used to evaluate the energy-use efficiency of irrigation systems.
Performance standards are established for engines and pumping plants properly adjusted according to manufacturer recommendations.
Nebraska performance standards for irrigation pumping plants are shown in Table 2.
Table 1.
Percent of fields that had a lower soil water content on Sept.
15 than in August:
 In 2017, 28% of fields experienced their 15-25 inch soil zone get drier.
In 2017, 26% of fields experienced their 25-36 inch soil zone get drier.
TILLAGE MANAGEMENT AND SPRINKLER-IRRIGATED CORN PRODUCTION
 Tillage management strategies that leave greater amounts of residue on the soil surface are beneficial in sprinkler-irrigated corn production in terms of improving infiltration of both irrigation and rainfall, and in reduction of soil evaporative losses early in the growing season.
Additionally, sometimes early season crop growth is delayed under higher residue conditions and this can result in the shifting of crop evapotranspiration to later in the season for higher residue treatments.
This paper will discuss 4 years  of sprinkler-irrigated corn research under conventional, strip-tillage, and no tillage.
BRIEF DESCRIPTION OF PROCEDURES
 The study was conducted under a center pivot sprinkler at the KSU Northwest Research-Extension Center at Colby, Kansas during the years 2004 to 2007.
Corn was also grown on the field site in 2003 to establish baseline residue levels for the three tillage treatments.
The study area had conventional tillage in 2003.
The soil type was a medium textured, deep, well drained, silt loam soil.
The region has an average annual precipitation of 19 inches with a summer pattern resulting in an average corn cropping season precipitation of 12 inches.
The average seasonal total crop evapotranspiration  for corn in this region is 21 inches.
A corn hybrid of approximately 110-day relative maturity  was planted in 30-inch spaced circular rows on May 8, 2004, April 27, 2005, April 20, 2006 and May 8, 2007, respectively.
The two hybrids differ only slightly with the latter hybrid having an additional genetic modification of corn rootworm control.
Three target seeding rates  were superimposed onto each tillage treatment in a complete randomized block design.
Irrigation was scheduled with a weather-based water budget, but was limited to the 3 treatment capacities of 1 inch every 4, 6, or 8 days.
The weather-based water budget was constructed using data collected from a NOAA weather station located approximately 1800 ft.
northeast of the study site.
The three tillage treatments [Conventional tillage , Strip Tillage  and No Tillage ] were replicated in a Latin-Square type arrangement widths at three different radii.
Planting was in the approximate same row location each year for the Conventional Tillage treatment to the extent that
 good farming practices allowed.
The Strip Tillage and No-Tillage treatments were planted between corn rows from the previous year.
Figure 1.
Physical arrangement of the irrigation capacity  for the nine different pie sectors and tillage treatments  randomized within the outer sprinkler span.
Fertilizer N for all 3 treatments was applied at a rate of 200 lbs/acre.
Phosphorus was applied with the starter fertilizer at planting at the rate of 45 lbs/acre P2O5.
Weekly to bi-weekly soil water measurements were made in 1 ft.
increments to an 8 ft.
depth with a neutron probe.
All measured data was taken near the center of each plot.
Corn yield was measured in each of the 81 subplots at the end of the season by hand harvesting the ears from a 20 ft.
section of one corn row near the center of each plot.
Water use and water productivity  were calculated for each subplot using the soil water data, precipitation, applied irrigation and crop yield.
Weather Conditions and Irrigation Requirements
 In general, conventional tillage treatments were observed to emerge earlier and have improved growth during May and June as compared to the strip and no-tillage treatments, probably because of warmer soil temperatures.
However, by about mid-summer in most of the years the conventional tillage treatments began to show greater water stress, particularly for the reduced irrigation capacities, as
 evidenced by some observed mid-day wilting.
The conventional tillage plots also tended to senesce earlier in most years with the exception of 2004.
Summer seasonal precipitation was approximately 2 inches below normal in 2004, near normal in 2005, nearly 3 inches below normal in 2006, and approximately 2.5 inches below normal in 2007.
Calculated well-watered corn evapotranspiration was near normal in 2004, 2005, and 2006, but was approximately 3 inches below normal in 2007.
Full irrigation needs varied between years with greatest needs in 2005 and 2006 at approximately 15 inches and was lower in 2004 and 2007 at approximately 12 inches.
Corn Yields, Yield Components, Water Use, and Water Productivity
 Average  study wide corn yield, yield components, water use and water productivity are summarized in Table 1 and Figure 2 and 3.
Greatest corn yield was obtained by the fully irrigated treatment  where irrigation was supplied as needed at a capacity limited to 1 inch/4 days.
Average yields decreased approximately 20 bushels/acre for the deficit irrigated treatments.
The greater irrigation capacity was positively reflected in both greater number of kernels/ear and kernel mass , but the number of kernels/ear had the greatest effect.
Table 1.
Summary of average corn yield and water use parameters from a sprinkler-irrigated
 research study, KSU Northwest Research-Extension Center, 2004-2007.
Treatment	Irrigation			Yield	Density	Plant		/Plant	Ears	Kernels	/Ear	Kernel Mass			Water	Use		Productivity	Water
 1 in/4 day	13.8	243	30129	1.00	575	361	25.99	528
 1 in/ 6 day	12.3	224	30137	1.00	546	350	25.05	503
 1 in/ 8 day	10.3	221	30016	1.01	545	347	23.56	526
 Conventional	12.1	221	30016	1.00	534	35.4	24.56	505
 Strip Tillage	12.1	237	30226	1.01	567	35.3	25.15	530
 No-Tillage	12.1	231	30040	1.00	565	35.0	24.88	522
 PD 26,000 p/a	12.1	221	26822	1.01	577	36.2	24.85	501
 PD 30,000 p/a	12.1	232	30145	1.00	556	35.3	24.87	524
 PD 34,000 p/a	12.1	235	33315	1.00	532	34.2	24.88	531
 The strip tillage and no-tillage treatment had greater yields  than the conventional tillage treatment.
The improved tillage schemes were positively reflected in a greater number of kernels/ear.
This nearly 6% greater number of kernels/ear for the two treatments resulted in an approximately 4.5 to 7% greater yield.
Increasing plant density from 26,000 to 30,000 or 34,000 plants/acres increased yield approximately 12 bushels/acre.
Both kernels/ear and kernel mass were reduced for the greater plant densities , but the greater plant densities were able to fully compensate for these lower values by the increased number of plants.
Water use was greatest for the fully-irrigated irrigation treatment  as might be anticipated due to greater irrigation amounts.
However it had the numerically greatest water productivity, although all three treatments had relatively similar values.
There were very little differences in overall crop water use as affected by tillage treatment.
This is to be anticipated as with good irrigation management all treatments either used the provided irrigation or added it to soil water storage.
Due to greater yields, the strip and notillage treatments had greater water productivity.
The range of plant densities from 26,000 to 34,000 plants/acre had no effect on crop water use  with the range of average values differing by less than 0.03 inches.
Much greater water productivity was obtained by the greater plant densities.
The greatest irrigation capacity  had approximately 9% greater yield than the deficitirrigated treatments  due to a greater number of kernels/ear and to a lesser extent greater kernel mass.
All irrigation treatments had relatively similar and high water productivity.
Strip tillage and no-tillage were superior to conventional tillage in terms of grain yield and water productivity.
The number of kernels/ear was greater for the two reduced tillage schemes.
Increasing plant density from 26,000 to 30,000 or 34,000 plants/acre increased grain yield and water productivity although the number of kernels/ear and kernel mass were decreased by the increase in plant density.
Crop water use was not affected over the entire range of plant density.
This paper is part of a center pivot irrigation technology transfer effort is supported by the Ogallala Aquifer Program, a consortium between USDA Agricultural Research Service, Kansas State University, Texas A&M AgriLife Research, Texas A&M AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
Figure 2.
Corn grain yield, kernels/ear, and kernel mass as affect by irrigation capacity, tillage treatment and target plant density in a sprinkler-irrigated research study, KSU Northwest ResearchExtension Center, Colby, Kansas, 2004-2007.
Figure 3.
Corn water use and water productivity as affected by irrigation capacity, tillage treatment and target plant density in a sprinkler-irrigated research study, KSU Northwest Research-Extension Center, Colby, Kansas, 2004-2007.
Figure 4.
Contribution of various yield components to the yield variation for the three irrigation capacities , the three tillage systems  and the three target plant densities.
component variation from zero indicate little effect.
Integrated Controls, Distributed Sensors and Decision Support Systems for Wireless Site-specific Sprinkler Irrigation
 Robert G.
Evans, James Kim and William M.
Iversen Agric.
Engineer, Research Associate and Physical Scientist USDA-ARS, Northern Plains Agricultural Research Laboratory Agricultural Systems Research Unit Sidney, Montana 59270 Voice:406-433-9496 Fax: 406-433-5038 Email: Robert.Evans@ars.usda.gov
 Traditional uniform water applications by self-propelled center pivot and linear move sprinkler irrigation systems ignore within field variations that cause varying crop yield and quality across most fields.
This variability may include topographic relief, changes in soil texture, tillage, fertility and pests as well as various irrigation system characteristics.
These effects on management can be additive and interrelated.
Excessive applications potentially lead to drainage, soil erosion and disease problems as well as excessive energy use, whereas under applications can reduce yields and/or quality with the severity level often depending on management.
Typical management objectives would be to optimize yield and quality goals while maintaining environmental health  and reduce chemical leaching.
Microprocessor controlled center pivot and linear move irrigation systems are particularly amenable to site-specific management approaches because of their current level of automation and large area coverage with a single lateral pipe.
These technologies provide a unique control and sensor platform for economical and effective ways to vary agrichemical and water applications to meet the specific needs of a crop in uniquely defined zones within a field.
Advances in communications and microprocessors have enabled the implementation of site-specific water applications by self-propelled center pivot and linear move sprinkler irrigation systems.
Site-specific irrigation usually involves some type of variable rate application method in combination with georeferenced maps or tables.
These decision maps specify the amount of water applied to each pre-defined management area within a field and are generated using some type of rule base predefined by the producer or a consultant.
Ideally, these management maps or tables are frequently updated based on real time, spatially distributed data on field conditions.
Management areas may be different for irrigation than for chemigation applications, and each may have its own maps.
Recent innovations in low-voltage sensor and wireless radio frequency technologies combined with advances in Internet technologies offer tremendous opportunities for development and application of real-time management systems for agriculture.
Integration of these technologies into the irrigation decision making process can determine when, where how much water to apply in real time; which enables implementation of advanced state-of-the-art water conservation measures for economically viable production with limited water supplies.
Researchers at the USDA-ARS research laboratory in Sidney, Montana have developed and tested an automated closed-loop irrigation system for automated variable-rate linear move sprinkler irrigation system.
This research integrated infield sensor stations distributed across the field, an irrigation control station on the linear move system, and a decision support system on a base computer station.
A site-specific controller and hardware were developed with the capability to switch between either mid-elevation spray application  or low energy precision application  methods as well as to simultaneously vary water application depths by plot as the machines traveled down the field.
The machine was converted to make groups of individual sprinkler nozzles electronically controllable by attaching a programmable logic controller , solenoids, air valves, and a low cost WAAS enabled GPS system.
The linear move irrigation system was modified so that every plot could be irrigated using either MESA or LEPA methods.
The control system was used on fifty-six 15 m X 24.4 m  plots as well as several other smaller research projects in which there were a mix of crops and a prescribed set of management experiments in a single field for a total area of about 12 ha.
All plots were irrigated with an 244 m , 5 span, Valley 1 self-propelled linear move sprinkler irrigation system  including the cart, which was installed in the spring of 2003.
A diesel engine powered an electrical generator set  on the cart that provided electricity for the tower motors, cart motors, pump, air compressor and control valves.
A buried wire alignment system was used with antennas located in the middle of the machine.
The linear move machine used a screened floating pump intake in a level ditch as its water supply.
Nominal operating pressure was about 250 kPa
 1 Mention of a trademark, vendor or proprietary product does not constitute a guarantee or warranty of the product by the USDA and does not imply its approval to the exclusion of other products that may also be suitable.
This type of information is solely provided to assist the reader in better understanding the scope of the research and its results.
.
Two double direction boom backs were installed at each of the towers.
Spans were 48.8 m  in length except for the center span with the guidance system which was a 47.5 m  span.
The machine moved at about 2.1 m min-1 (7 ft min-1 at the 100% setting.
Equivalent depths of water were applied for both irrigation methods for the same crop.
The PLC-based control system activated grouped networks of electric over airactivated control valves.
Thirty 15-meter  wide banks of sprinklers were controlled with this system  Both the depth and method of irrigation were varied depending on the location of each plot in the field.
When not being used, low-cost pneumatic cylinders lifted the LEPA heads above the MESA heads to avoid spray interference when the MESA is operating over a given plot width and length.
Water application depths were varied by modulating pulses of water through the sprinkler nozzles on and off to achieve targeted, variable application amounts on each predefined area  as the machine moved down the field.
The controller, communications and modifications to the water application methods utilized off-the-shelf components as much as possible
 The amount of water applied was adjusted by pulsing nozzle heads on and off to achieve a targeted, variable depth based on a predefined digital map stored in the PLC  of depths for each nozzle location as the machine moved down the field.
As was the case with other site-specific controllers in the literature, machine speed was set by the Valley panel, which established the maximum application depth and the PCL controller managed the sprinkler heads.
Treatments were a percentage of maximum by varying on times in a 60 second cycle time.
However, our software allowed us to easily change the cycle time if we needed to make adjustments.
Distributed Sensor Systems and Control
 A distributed wireless sensor network  was integrated into the existing sitespecific linear move sprinkler irrigation system described above.
Field conditions were monitored by six in-field sensor stations with Campbell CR200 dataloggers  distributed across the field based on a soil property map and monitored soil moisture, soil temperature, and air temperature.
WaterMark soil water sensors  were used in the decision support process and were calibrated with a neutron probe and individually identified for their response ranges at each zone.
All in-field sensory data were sampled on 1 second intervals.
A nearby weather station monitors micrometeorological information on the field, i.e., air temperature, relative humidity, precipitation, wind speed, wind direction, and solar radiation.
Communication signals from the sensor network, weather station and PLC irrigation controller to the base station were successfully interfaced using lowcost Bluetooth wireless radio communication.
A Windows based decision making program was developed with a simple clickand-play menu using graphical user interface , and optimized to adapt changes of crop design, irrigation pattern, and field location.
This system offered stable remote access to field conditions and real-time control and monitoring of both inputs  and outputs.
In-field micrometeorological information was displayed on a geo-referenced field map at the base station screen.
The PLC on the machine provided the current georeferenced location of the machine from an on-board differential GPS.
The base computer recalculated the position of individual sprinkler heads, analyzed soil water status, calculated crop water needs, updated machine instructions and sent control commands to the irrigation controller to site-specifically operate each individual sprinkler group and apply a specified depth of water for every time step  based on criteria in a predetermined management map.
An algorithm for nozzle sequencing was developed as part of the decision support software to stagger nozzle-on operations so as evenly distribute irrigation system flow rates over the 60-sec cycle to avoid hydraulic surges.
Sensor-based closed-loop irrigation was highly correlated to catch can water with r2=0.98.
Automated site-specific sprinkler irrigation system can save water and maximize productivity, but implementing automated irrigation is challenging in system integration and decision making.
Irrigation decisions can be implemented sitespecifically based on feedback from soil water and environmental conditions from distributed in-field sensor stations using wireless radio communications.
The performance of the system was evaluated with the measurement of water usage and soil water status throughout the growing season.
Integration of the decision making process with the controls is a viable option for determining when and where to irrigate, and how much water to apply.
Distributed in-field sensors offer a major advantage in supporting site-specific irrigation management that allows producers to maximize water productivity while enhancing overall profitability.
There are many reasons why site-specific sprinkler irrigation has not generally been a commercial success to date.
These include the fact that servicing hardware and software on advanced, integrated systems can be difficult.
Much hardware troubleshooting could be done via the internet from a central location and defective parts, computer cards or chips changed by on-site technicians, but the support infrastructure is not developed.
Another reason is the lack of decision support applications  that is needed to take full advantage of the capabilities of these systems.
This is likely due to the potential liability inherent in any decision support system, which has delayed their implementation.
Every decision support application would have to be tailored to fit each individual field
 and even simple mistakes can have costly consequences.
Growers usually do not have the interest, knowledge or the time to fuss with software; thus, dealers or consultants would likely have to provide this service.
Specialized, continual training on the hardware, software and advanced agronomic principles would also be needed for dealers, technicians and other personnel to service these systems.
Today, using soil water monitoring equipment provides the most effective method for farmers to make data-driven irrigation scheduling decisions to apply the minimal amount of water while achieving optimal yields.
However, the costs in labor and equipment limit their use.
So, research continues to focus on developing lower-cost methods to schedule irrigation that results in putting on just the right amount of water.
NEW DEVELOPMENTS IN IRRIGATION SCHEDULING
 Although scientific irrigation scheduling techniques have been available for over 30 years, most growers do not use them.
Reasons include complexity, time required, and lack of confidence in the predictions.
The three primary approaches are soil water monitoring, plant stress monitoring, and weatherbased water use predictions.
Soil water monitoring is either labor intensive or equipment intensive.
Many automatic sensors have been developed and marketed in the last few years, but all have shortcomings.
Reliable methods tend to be expensive or labor intensive.
Soil water monitoring is tedious as a primary monitoring technique, but valuable as a periodic check on other methods.
Plant stress based techniques are poorly developed for most crops, although they may become more useful as remote sensing methods and our understanding of plant stress improve.
Weather-based irrigation scheduling remains the most common and practical method.
Direct estimation of water use by a crop using surface energy balance techniques  remain too complex for other than research use.
Exciting new surface energy balance methods using remotely sensed information from satellites is being tested.
These techniques include SEBAL, METRIC, and RESET, which are all based on the same basic concepts.
However, all require thermal infrared data which is not readily available in the frequency or resolution required to schedule irrigations on fields.
The weakest link in this weather based approach to predict crop water use and irrigation requirements is the difficulty in reliably estimating the crop coefficient.
Crop coefficients are commonly estimated based on days since planting or  growing degree days.
A wide variety of irrigated crops are grown under a wide range of conditions, and dependable crop coefficients are not available for many of the crops and growing conditions.
This is especially true for horticultural and other specialty crops that are increasingly important in irrigated areas.
These crops are often not well studied and include widely varying varieties grown under a wide range of planting densities and cultural practices.
Crop water use is related to the interception of incoming solar radiation and the amount of transpiring leaf surface.
Sunlit leaves transpire at a higher rate than shaded leaves.
Both leaf area index  and crop light interception have been related to crop transpiration.
Light interception, as represented either by the portion of the ground surface that is shaded or the crop canopy cover, is much easier to measure than LAI.
Although light interception varies with the crop canopy structure and the sun angle, several studies have found that mid-day shading, or equivalently, canopy cover measured vertically, provides a good relative representation of crop transpiration.
Previous studies have shown that various spectral vegetation indices, calculated from visible and near-infrared reflectance data, are linearly related to the amount of photosynthetically active radiation absorbed by plant canopies.
Related efforts have tried to estimate crop coefficients in specific crop systems by ground-based and airborne spectral data.
Moran et al.
describe the potential and limitations of using satellite imagery for crop management.
Functional relationships between remotely sensed vegetation indices and crop light interception, and light interception and basal crop coefficient, Kcb, allow efficient estimation of crop water use where reference ETo is available.
This could allow estimation of crop water use in near real time for individual fields on a regional scale.
Such a process was proposed in the DEMETER project in southern Europe.
In this paper, I present preliminary relationships between vegetation indices, light interception, and Kcb developed from data collected in the San Joaquin Valley on horticultural crops, and propose a possible structure for an irrigation scheduling system based on remotely-sensed vegetation indices and ETo.
VEGETATION INDEX vs.
CANOPY COVER
 On July 1, 2005, and June 19-20, 2006, canopy cover, CC, of 12 high value crops  in various stages of growth was measured on 33 fields on the west side of the San Joaquin Valley in California.
Most fields were drip irrigated and essentially weed free with a dry soil surface.
These fields were selected to represent a wide range of major SJV perennial and annual horticultural crops with widely varying canopy cover.
Fields were selected that had uniform cropping patterns.
Most fields were at least 200 m in the smallest dimension.
Details of this study are given in Trout et al..
NDVI =  / 
 for each Landsat image pixel.
Figure 1.
Relationship between Landsat NDVI and Camera Canopy Cover, CC, and the linear regression line for the data represented by blue diamonds.
Subsurface Drip Irrigation Systems  Water Quality Assessment Guidelines
 Danny H.
Rogers Extension Agricultural Engineer
 Freddie R.
Lamm Research Irrigation Engineer
 Mahbub Alam Extension Irrigation Specialist
 Kansas State University Agricultural Experiment Station and Cooperative Extension Service Manhattan, Kansas
 Water quality can have a significant effect on subsurface drip irrigation  system performance and longevity.
In some instances, poor water quality, such as high salinity, can cause soil quality and crop growth problems.
However, with proper treatment and management, water with high mineral loading, nutrient enrichment, or high salinity can be used successfully in SDI systems.
However, no system should be designed and installed without assessing the quality of the proposed irrigation water supply.
Water samples should be collected in clean triple-rinsed plastic bottles.
Water samples from wells should be collected after the well has been operating for at least 15 minutes.
Surface water samples should be collected below the water surface.
If the quality varies throughout the pumping season, choose the worst case sample or sample multiple times.
About a half gallon of water is needed to perform the chemical analysis.
The samples need to be analyzed within 3 hours.
If this is not practical, the samples can be frozen or held below 40 degrees Fahrenheit.
Check with the lab for specific collection and handling instructions.
Be certain to let them know the types of tests you need.
These tests are discussed below.
Water Quality Analysis Recommendations
 Prevention of clogging is the key to SDI system longevity.
Prevention requires an understanding of the potential problems associated with a particular water source.
Water quality information should be obtained and made available to the designer and irrigation manager in the early stages of the planning SO suitable system components especially
 the filtration system and management and maintenance plans can be selected.
Recommended water quality tests include:
 1.
Electrical Conductivity  measured in ds/m or mmho/ cm a measure of total salinity or total dissolved solids
 2.
pH a measure of acidity -1 is very acid, 14 is very alkaline, and 7 is neutral
 3.
Cations measured in meq/L, , includes; Calcium , Magnesium , and Sodium 
 4.
Anions measured in meq/L, includes: Chloride , Sulfate  and Bicarbonate 
 5.
Sodium Absorption Ratio  a measure of the potential for sodium in the water to develop sodicity, deterioration in soil permeability, and toxicity to crops.
SAR is sometimes reported as Adjusted  SAR.
The Adj.
SAR value accounts for the effect of the HCO 3 concentration and salinity in the water and the subsequent potential sodium damage.
6.
Nitrate nitrogen 
 7.
Iron , Manganese , and Hydrogen Sulfide  measured in mg/L
 8.
Total suspended solids measured in mg/L of particles in suspension
 9.
Bacterial population a measure or count of bacterial presence in #/ml
 10.
Boron* measured in mg/L
 11.
Presence of oil
 The boron test would be for crop * toxicity concern.
Oil in water would be concern for excessive filter clogging.
It may not be a test option at some labs and could be considered an optional analysis.
The measurement units for reporting concentrations is often milligrams per liter.
Milligrams per liter, when considering irrigation water, is essentially equivalent to parts per million.
Concentrations may also be reported in milliequivalent per liter.
Conversion factors are needed to convert from mg/l to meq/l and vice versa.
Table 1 lists the conversion factors for common constituents.
Tests 1 through 7 will likely be test results included in a standard irrigation water quality test package.
Tests 8 through 11 are generally offered by water labs as individuals tests.
The test for presence of oil may be a test to consider in oil producing areas or if the well to be used for SDI has experienced surging that may have introduced oil into the pumped water.
The fee schedule for tests 1 through 11 will vary from lab to lab.
The total cost for all recommended tests may be a few hundred dollars.
This is still a minor
 Table 1.
Conversion factors: parts per million and milliequivalents per liter 
 Constituent	Convert ppm	Convert meq/l
 to meq/l	to ppm
 multiply by	multiply by
 Na 	0.043	23
 CA 	0.050	20
 Mg 	0.083	12
 CI 	0.029	35
 SO 4 	0.021	48
 CO2 	0.033	30
 HCO3 	0.016	61
 Example: Convert 10 meq/l of SO, to ppm: ppm = 48 X 10 meq/l = 480 ppm
 investment compared to the value of determining the proper design and operation of the SDI system.
Water testing can be done by a number of laboratories in the state.
Be sure to use a certified lab.
Before collecting any sample, remember to check with the lab for the specific collection procedures, test kits, or the handling requirements of the sample that is needed to ensure quality test results.
Table 2 summarizes the water quality
 guidelines for clogging potential.
These guidelines help interpret water quality test results.
Most surface water and groundwater supplies in Kansas are fairly hard, meaning they have a high mineral content.
In addition, many wells, especially older wells, may produce sand when pumping.
These two clogging hazards are classified as chemical and physical
 Table 2.
Water Quality Guidelines for Microirrigation Systems
 Constituent	Level of Concern
 Clogging Potential	Low	Moderate	High
 pH	< 7.0	7 8	> 8.0
 Iron  mg/L	< 0.2	0.2 1.5	> 1.5
 Manganese  mg/L	< 0.1	0.1 1.5	> 1.5
 Hydrogen Sulfide  mg/L	< 0.2	0.2 2.0	> 2.0
 Total Dissolved solids  mg/l	< 500	500 2000	> 2000
 Suspended Solids mg/L	< 50	50 100	> 100
 Bacteria Count 	< 10,000	10,000 50,000	> 50,000
 Crop Effect	Level of Concern
 Potential	Low	Moderate	High
 EC mmho/cm	< 0.75	0.75 3.0	> 3.0
 NO mg/L	< 5	5 30	> 30
 Specific lon	Level of Concern
 Toxicity	Low	Moderate	High
 Boron mg/L	< 0.7	0.7 3.0	> 3.0
 Chloride meq/L	< 4	4 10	> 10.0
 Chloride mg/L	< 142	142 355	> 355
 Sodium 	< 3.0	3 9	> 9
 Table 3.
Example size of various particles.
Coarse sand	0.50 to 1.00
 Fine sand	0.10 to 0.25
 Silt	0.002 to 0.05
 Bacteria	0.0004 to 0.002
 hazards, respectively.
The third clogging hazard is biological, which could be slimes produced by bacterial or algal growth.
As a general rule, filtration requirements are sized to remove particles 1/10 the size of the smallest emitter opening.
Individual silt and clay particles and bacteria can generally pass through the filtration system and even through the drip irrigation emitters.
However, conglomeration of multiple particles is possible, particularly with bonding "glues" provided by biological activity and clogging may result.
It is impractical to filter out all the smaller particles, SO considerations must
 Example: A grower wishes to use household bleach  to achieve a 15 ppm chlorine level at the injection point.
The flow rate of the irrigation system is 700 gpm.
At what rate should the NaOC be injected?
IR = 700 gpm X 15 ppm X 0.006 5.25 = 12 gallons per hour
 At an irrigation flow rate of 700 gpm, the grower is pumping 700 X 60 = 42,000 gph.
The goal is to inject 12 gallons of bleach into 42,000 gallons of water each hour that injection occurs.
If the injector is set for a 300:1 ratio, it will inject 42,000 300 or 140 gallons per hour.
Then, 12 gallons of bleach should be added to 140 gallons of water in the stock solution.
Be careful to use the same time units  when calculating the injection rate.
be given to periodic flushing.
Typical particle sizes are shown in Table 3.
Clogging hazards are discussed in more detail in Filtration and Maintenance Considerations for Subsurface Drip Irrigation  Systems, MF-2361.
Bacteria do not normally live in groundwater until a well allows their introduction, an air exchange, and, in some cases, a source of
 nutrients.
Bacteria can live on iron, manganese, or sulphur.
Their growth process produces a slime that can build up on the well screens and cause well yield declines.
A bacteria-contaminated well will introduce bacteria to the SDI system, which can result in clogging of the filtration system and dripline emitters.
Chlorination of an irrigation well to kill bacteria should be at least an annual practice.
Treat the well with a shock treatment of 500 ppm to
 Table 4.
Notes on Chemical Clogging Hazards
 1.
Bicarbonate concentrations exceeding about 2 meq/L and pH exceeding about 7.5 can cause calcium carbonate precipitation.
2.
Calcium concentrations exceeding 2 to 3 meq/L can cause precipitates to form during injection of some phosphate fertilizers.
Special procedures are necessary for the injection of phosphate fertilizers, and careful injection should be attempted only by experienced personnel.
3.
High concentrations of sulfide ions can cause iron and manganese precipitation.
Iron and manganese sulfides are very insoluble, even in acid solutions.
In this case, frequent acidification or the use of a settling basin for separating iron and manganese precipitants is advisable.
4.
Irrigation water containing more than 0.1 ppm sulfides may encourage growth of sulfur bacteria within the irrigation system.
Regular chlorination may be needed.
5.
Chlorination when manganese is present should be used with caution, as a reaction time delay may occur between chlorination and the development of the precipitate.
This may cause the manganese precipitate to form downstream of the filter and cause emitter clogging.
inject in liquid form  is:
 The general formula for calculating the amount of chlorine to
 IR= xCx0.006 S where:
 IR Chlorine injection rate 
 Q = Irrigation system flow rate 
 C = Desired chlorine concentration 
 S = Strength of NaOC solution used 
 Common household bleach is generally a 5.25 to 7.5 percent solution.
Stronger concentrations of chlorine solutions are available from irrigation dealers and industrial suppliers.
The injected chlorine must travel through the entire system during the injection period.
The propagation time should be calculated or obtained from the installer.
Alternatively, water from the flushline can be tested to see if a free chlorine residual is detected, which would indicate sufficient injection time has elapsed.
Chlorine Injection Rate Formula
 Chlorination of the SDI system is also a practice that would be a routine maintenance procedure, because chlorine will oxidize biological material.
Bacterial growth in driplines can be troublesome due to small clay particles in the water that are smaller than the required level of filtration.
The sticky slime growth may cause these small particles to stick together and clog emitters.
Chlorine can be injected to kill bacteria either continuously with a low dosage base  or periodically at a high dose of 5 to 20 ppm.
Periodic dosage is more common in Kansas systems.
The dosage level should be sufficient that a concentration of 0.5 to 1 ppm of free chlorine should be measured at the end of the system.
Chlorine is more effective in acid waters.
High pH or alkaline waters should be acidified to a pH of 6.5 for effective chlorine treatment.
Acid treatment also can be effective in controlling bacterial growth.
Chemical precipitation hazard guidelines, as shown in Table 1, give some indication of potential clogging hazards.
SDI systems have an advantage over surface drip systems because the emitter level in the driplines are below ground and buffered from sunlight and temperature that could help drive both biological and chemical activity.
Water pH and temperature also play a major role in many reactions.
bicarbonate levels.
The symptom of calcium precipitant is a white film or plating on the dripline or around the emitters or white precipitants in the flush water of the dripline laterals.
Several of the references listed at the end of this publication noted several important chemical precipitation hazards.
These are summarized in Table 4.
The usual treatment for calcium precipitation is to acidify the water by lowering the pH to 7.0 or lower with continuous injection.
Calcium becomes more soluble at low pH.
When using a periodic injection treatment, pH may have to be lowered to 4.0 or less and allowed to sit in the system for up to 60 minutes.
Temperature, pH, and the calcium concentration affect calcium solubility, SO conditions will vary throughout the system.
Litmus paper, colormetric kits, or a portable pH meter can measure the pH at the lower end of the system to determine if free chlorine exists.
Calcium carbonate, commonly known as lime, can be a problem with high pH  and high
 Sulfuric acid or hydrochloric acid can be used to reduce pH.
Muriatic acid  may be the most commonly available acid from hardware or farm supply stores.
Urea sulfuric acid, an acid with nitrogen fertilizer value, can also be used.
This product is safer to use and is marketed as N-pHuric.
Check with your irrigation or fertilizer dealer about its availability in your region.
Caution: Use extreme care in handling acids, and always add acid to water.
Be certain to flush and clean the injection system after an acid treatment because the acid may be corrosive to internal parts.
Treatments need to be done before total emitter blockage occurs.
Remediation, after total blockage, is difficult or impossible because the acid will not come into contact with precipitants in closed passages.
Iron and manganese precipitation can become a problem with concentrations as low as 0.1 ppm.
Most groundwater contains some iron
 and manganese in a soluble state, but when exposed to air, they oxidize and precipitate as a solid.
Irrigators with center pivots, especially center pivots using alluvial groundwater supplies, often see the structures turn red in a short time.
These compounds also can be used as an energy source by bacteria.
They form filamentous slime that can clog filters and emitters, and act as a glue to hold other contaminants together.
Symptoms of iron precipitation are reddish stains and rust particles in the flush water and reddish deposits in the orifices.
Manganese would be similar, but darker or
 black.
Bacterial slimes have a similar color as precipitants, but appear as filamentous sludge in flush water or collected on screens.
Aeration and Settling for Iron and Manganese Treatment
 One effective option for removal of high concentrations of iron and manganese for high flow rate systems is the use of aeration and settling basins, especially for manganese.
The oxidation rate of manganese is much slower than for iron, making manganese removal problematic with some of the other treatment methods.
Aeration of the source water occurs by spraying water into the air or running it over a series of baffles to enhance mixing with oxygen into the water.
There must be sufficient aeration and reaction time; the soluble forms of manganese and iron will oxidize and precipitate.
The disadvantage of this treatment is the need for a second pump.
Total head requirements are not changed when using two pumps, SO energy costs are not a major factor.
Other disadvantages of a settling basin are the space requirement, construction costs, and long-term maintenance needs.
Table 5.
Water treatments to prevent clogging in drip-irrigation systems
 Carbonate precipitation 	1.
Continuous injection: maintain pH between 5 and 7
 HCO3 greater than 2.0 meq/l pH greater than 7.5	2.
Periodic injection: maintain pH at under 4 for 30 to 60
 Iron precipitation 	1.
Aeration and settling to oxidize iron.
(Best treatment for
 Iron concentrations greater than 0.1 ppm	high concentrations 10 ppm or more).
2.
Chlorine precipitation injecting chlorine to precipitate
 a.
use an injection rate of 1 ppm of chlorine per 0.7 ppm
 b.
inject in front of the filter so that the precipitate is
 3.
Reduce pH to 4 or less for 30-60 minutes daily.
Manganese precipitation 	1.
Inject 1 ppm of chlorine per 1.3 ppm of manganese in
 Manganese concentrations greater than 0.1 ppm	front of the filter
 Iron bacteria 	1.
Inject chlorine at a rate of 1 ppm free chlorine continu-
 Iron concentrations greater than 0.1 ppm	ously or 10 to 20 ppm for 30 to 60 minutes daily.
Sulfur bacteria 	1.
Inject chlorine continuously at a rate of 1 ppm per 4 to 8
 sulfide concentrations greater than 0.1 ppm	ppm of hydrogen sulfide, or
 2.
Inject chlorine intermittently at 1 ppm free chlorine for 30
 to 60 minutes daily.
Bacterial slime and algae	1.
Inject chlorine at a rate of 0.5 to 1 ppm continuously or 20
 ppm for 20 minutes at the end of each irrigation cycle.
Iron sulfide 	1.
Dissolve iron by injecting acid continuously to lower pH
 Iron and sulfide concentrations greater than 0.1 ppm	to between 5 and 7.
Chlorination to control algae and bacteria in the basin may be required.
Chlorination and Filtration for Iron and Manganese Treatment
 Injection of chlorine into water will cause the dissolved iron to precipitate SO it can be filtered out.
The reaction occurs quickly, but injections need to be located upstream of the filter.
This treatment method may be best suited for systems with sand media filters.
Chlorine is injected at a rate of 1 ppm for each 0.7 ppm of iron.
Additional chlorine may be required if other contaminants, such as iron bacteria, are present.
This treatment requires continuous injection of chlorine.
Successful treatment also requires complete mixing of the chlorine in the water.
This treatment method is not suited to manganese removal because of its slower oxidation rate.
If manganese and free chlorine remain in the line after
 filtration, precipitation could occur and clog emitters.
Iron is more soluble at lower pH, SO acid can be used as a continuous or periodic treatment as described for calcium carbonate.
In this case, the pH should be lowered to 2.0 or less for 30 to 60 minutes for a periodic or cleaning treatment.
After a periodic treatment, the system must be flushed.
Iron and Manganese Sulfides
 Dissolved iron and manganese, in the presence of sulfides, can form a black, sand-like insoluble precipitant.
The recommended treatment for this combination of compounds is continuous acid injection that lowers pH to between 5 and 7.
Sulfur slime also can be produced by bacteria that can oxidize hydrogen sulfide and produce elemental sulfur.
The symptoms of this condition are white, cottony masses of slime that either clog emitters
 directly or act as glue to collect small silt and clay particles that clump together and clog emitters.
The symptoms and treatments for the various clogging hazards are summarized in Table 5.
Table 6 gives water quality data from the analysis of two irrigation water samples.
Examples 1 and 2 in Table 6 use the water quality data from Table 1 to evaluate the clogging potential of these irrigation waters.
Subsurface Drip Irrigation offers a number of agronomic production and water conservation advantages, but requires proper design, operation, and maintenance to be an efficient, effective, and long-lived irrigation system.
One management change from the current irrigation systems is the need to understand the SDI system
 Table 6.
Water quality analysis of two irrigation water samples 
 EC = 2.51 dS/m pH = 7.4 Ca = 306 ppm Mg = 121 ppm Na = 124 ppm CI = 158 ppm HCO3 = 317 ppm SO4 = 912 ppm Mn = less than 0.1 ppm Fe = less than 0.1 ppm
 Water 2 EC = 0.87 dS/m pH = 7.7 Ca = 44 ppm Mg = 16 ppm Na = 127 ppm CI = 70 ppm HCO3 = 122 ppm SO4 = 226 ppm Mn = 2.6 ppm Fe = 0.65 ppm
 Example 1.
The relatively high total dissolved salts  indicates that Water 1 has some clogging potential.
This is verified by the relatively high bicarbonate concentration.
The calcium concentration and the bicarbonate concentration together suggest that calcium carbonate could clog the emitters, particularly if the pH were to rise as a result of any chemical injection.
The iron and manganese concentrations indicate little potential for clogging from precipitation of those elements.
Example 2.
The analysis of Water 2 reveals little potential for clogging from total dissolved salts , but the pH and bircarbonate concentrations indicate that clogging might result from calcium carbonate precipitation.
The levels of manganese and iron indicate a severe potential for clogging from manganese oxide precipitation and iron oxide precipitation.
sensitivity to clogging by physical, biological, or chemical agents.
Before designing or installing an SDI system, be certain a comprehensive water quality test is conducted on the source water supply.
Once this assessment is complete, the manager should be aware of many of the potential problems that might be caused by the water supply.
The adage "an ounce of prevention is worth a pound of cure" is very appropriate for SDI systems because early recognition of developing problems can prevent hardship.
Developing problems can be easily handled as compared to remediation of a clogged system.
While this may seem daunting at first, as with most new technology, managers will quickly become familiar with the system and its operational needs.
EARLY IRRIGATION FOR ALMONDS
 W.
C.
MICKE H.
C.
MEITH
 K.
URIU P.
E.
MARTIN
 I SOME ALMOND PRODUCING areas of California, under-tree sprinkler irrigation is becoming increasingly popular for frost protection.
Water applied for such frost protection during the early growth period has been observed to also have a marked effect on almond production that cannot be accounted for by frost protection alone.
Among the effects'note have been increased yield, larger kernel  size, greater shoot growth, and delayed nut maturity.
A project was started in 1968 to determine whether these previous observations could be experimentally substantiated, since only limited evidence has been available to show that these factors were related to early-season moisture supply.
The experimental plot consisted of two irrigation treatments, each replicated four times.
The check treatment received the grower's regular irrigation program which consisted of 24 to 30 inches of water applied during the growing season, starting about mid-May and being completed by approximately mid-July.
The other treatment received early irrigation during the frost protection season in addition to the grower's regular irriga.
tion program.
In 1968, the early irrigation treatment received a 7-inch application of water in early March.
Because of wet winters prior to 1969 and 1970 seasons, the early irrigations were delayed until mid-April, with 4 to 5 inches of water applied in a single application each year.
In 1971, the early irrigation treatment was altered to more nearly simulate sprinkler frost protection practices with five applications of 1 to 2 inches each, made over a six-week period from late February through March.
In addition to the irrigation water, about 20 inches of rainfall normally occurs in this area, mostly from October through April.
This study was conducted with the Nonpareil variety on almond rootstock.
The soil was a deep, well drained loam.
Frost protection for both treatments was provided by orchard heaters rather than by sprinklers.
The moisture status of the soil was followed by using gypsum blocks.
As expected, the early irrigation increased the
 soil moisture supply early in the season and generally maintained better soil moisture later into the year as compared with the control treatment.
However, all available soil moisture had usually been extracted by the roots in both treatments to a depth of 9 ft by November 1.
During the first year of this study, yield was not affected by the early application of water.
However, in subsequent years the early irrigation increased yield.
The large increase in 1971 may be due either to the cumulative effect of these irrigations over four years, the extended period of application this year , or possibly both.
Each year, the weight per kernel from early irrigated plots has been 4 to 6% greater than from the control treatment.
Kernels from trees receiving this early irrigation were longer and wider; however, the treatment did not affect kernel thickness.
In almonds, the shell  begins to harden  during May, so by this time the maximum size to which the kernel can grow is essentially established.
Therefore, the effect of soil moisture on kernel size may be greatest early in the season.
The increase in yield in 1969 and 1970 as a result of early irrigation was due mainly to larger kernels; however, in 1971 the increase was due to both larger kernels and greater numbers of nuts per tree.
During the four years of this study, there has been no marked effect of this irrigation treatment on shelling percentage, stick-tights, or worm damage.
The trees receiving the early irrigation have consistently made slightly greater shoot growth each year.
This increased growth could result in a potentially greater bearing surface, particularly with a crop like almonds which is normally lightly pruned, and could explain the increased number of nuts per tree that occurred in 1971.
Each year the nuts from trees receiving the early irrigation have been delayed in maturing.
This result has been noted by several different measurements.
Kernels from these trees developed more slowly, even though their final size was larger.
Secondly, the nuts from early irrigated trees had a greater moisture content throughout the growing season, and even into harvest.
Also, when knocked on the same day, the nuts from
 the early irrigated treatment were often harder to remove from the tree.
Because of the higher moisture content in nuts at harvest from early irrigated trees, either knocking must be delayed a few days, or the nuts allowed to dry on the ground several days longer than usual.
If these precautions are not taken, hulling efficiency can be reduced due to the leathery condition of partially dried hulls; also, excessive foreign matter and/or kernel moisture may be found in deliveries to handlers.
In some years, nut removal can be so difficult that knocking must be delayed a few days to obtain satisfactory nut removal and to prevent excessive damage to the trees.
Most of the observed effects of early water applications have been substantiated by this work and there appears to be considerable potential for this practice with almonds.
Increased yield and larger kernel size have a direct effect on increased production.
Greater shoot growth also could augment production by providing additional bearing surface.
These advantages may not be limited to almonds, but may also apply to other deep.
rooted fruit crops.
W.
C.
Micke is Extension Pomologist, University of California, Davis.
H.
C.
Meith is Farm Advisor, Butte County.
K.
Uriu is Pomologist, and P.
E.
Martin is Staff Research Associate, University of California, Davis, James Pearson, Staff Research Associate, James Yeager, Staff Research Associate, and Ernie Roncoroni, Staff Research Associate, University of California, Davis, also assisted on this project.
Earl Decker, grower and Joe Richter, Durham Pump Shop, Durham, California also cooperated in these tests.
TABLE 1.
ALMOND KERNEL  YIELDS AS AFFECTED BY EARLY IRRIGATION
 1968	1969	1970	1971
 Control	1690	2464	a	2737	1996 a
 Early Irrigation	1684	2561	a	2802	a	2321 b
 Increase over control	-6	97	65	325
 Yields in each column with different letters are significantly different at the 1% level.
TABLE 2.
ALMOND KERNEL  WEIGHT
 AS AFFECTED BY EARLY IRRIGATION
 1968	1969	1970	1971
 Control	1.41	1.32 a	1.41	1.58
 Early irrigation	1.49 b	1.38	1.48	1.67
 control	5.7	4.5	5.0	5.7
 Weights in each column with different letters are significantly different at the 5% level.
A recent article by Dr.
Steve Evett and others traces the history of irrigation in the Great Plains region from a geographical, technical, and political perspective as well as how it has impacted the water resources
HOW THE 2020 DEFINITION OF WOTUS AFFECTS AGRICULTURAL AND SPECIALTY CROP PRODUCERS
 Published: Jun 28, 2020 |  Printable Version  | Peer Reviewed
 Sarah A.
White, Dara Park, Alexander Barrett and Jonathan Jones
 The 2015 Clean Water Rule, now the Navigable Waters Protection Rule, was amended in part because the definition of the Waters of the United States  within it was considered too broad.
The definition of WOTUS in the Clean Water Rule gives the federal government jurisdiction over specific navigable waters.WOTUS is a jurisdictional term used within the Clean Water Act; it pertains to wetland permitting, vessel sanitation devices, the national pollutant discharge elimination system, oil/hazardous spill prevention and control, and countermeasure regulations.1 The WOTUS definition is integral to the Endangered Species Act, as previously regulated water bodies that support threatened and or endangered species may not remain regulated under the 2020 definition.
The United States Environmental Protection Agency and the United States Army Corps of Engineers  co-drafted the definition of WOTUS included within the 2015 Clean Water Rule.
The final rule, published April 21, 2020 in the Federal Register, will be effective as of June 22, 2020.2 This article summarizes the recent history of the Clean Water Rule, including the 2020 Navigable Waters Protection Rule that fulfilled Executive Order 13788,3 amending the definition of WOTUS and providing clarity on the surface water bodies governed by the State versus Federal jurisdiction.
The article also discusses how the new WOTUS definition impacts agricultural and specialty crop producers.
Illustration identifying specific navigable waters the federal government has jurisdiction over.
Figure 1.
Jurisdictional Waters of the U.S.
regulated under the 2020 Navigable Waters Protection Rule are listed in the black text.
Waters excluded from regulatory control are listed in gray italicized text.
Image credit: Sarah A.
White, Clemson University.
Recent History of WOTUS
 In the 2015 update to the Clean Water Rule, many new restrictions were put in place to prevent, reduce, and eliminate pollution.
These restrictions broadened the definition of navigable waters, giving the federal government control over more surface waters, including those that only temporarily hold water.
The term navigable waters granted the government control over waters even if no direct connection to more extensive waterways was apparent.
The 2019 Revised Regulatory Definition of WOTUS: The 2020 Rule
 On April 21, 2020, the agencies published the Navigable Waters Protection Rule , repealing the 2015 Rule and amending the definition of WOTUS as to reflect precedent set by decisions made by the Supreme Court.4
 Per the 2020 Rule, WOTUS are defined as the following2:
 All waters which are currently used, or were used in the past, or may be susceptible to use in interstate or foreign commerce, including all waters which are subject to the ebb and flow of the tide.
All interstate waters including interstate wetlands.
All other waters such as intrastate lakes, rivers, streams , mudflats, sandflats, wetlands, sloughs, prairie potholes, wet meadows, playa lakes, or natural ponds, the use, degradation or destruction of which could affect interstate or foreign commerce including any such waters:
 Which are or could be used by interstate or foreign travelers for recreational or other purposes; or
 From which fish or shellfish are or could be taken and sold in interstate or foreign commerce; or
 Which are used or could be used for industrial purposes by industries in interstate commerce.
All impoundments of waters otherwise defined as WOTUS.
Tributaries of waters identified in  through  above.
Wetlands adjacent to waters  identified in  through  above.
Waters of the United States do not include prior converted cropland.
Notwithstanding the determination of an areas status as prior converted cropland by any other Federal agency, for the purposes of the Clean Water Act, the final authority regarding Clean Water Act jurisdiction remains with E.P.A.
Specific changes, as defined in the 2020 Rule, include organizing WOTUS into four categories:
 Territorial seas and traditional navigable waters: points 1 to 3 above  these include large rivers and lakes and tidally influenced waterbodies used in travel between states or for foreign commerce.
Certain lakes, ponds, and impoundments: point 4 above  lakes, ponds, and impoundments are considered navigable waters if they contribute surface water flow to navigable water or territorial sea either directly through other WOTUS or indirectly through channelized artificial or natural features.
Perennial and intermittent tributaries to those waters: point 5 above  waters are contributing surface flow to traditional navigable waters.
These waters must flow two times or more per year and be connected to navigable waters either directly or via channelized features, whether natural  or artificial.
Ditches are tributaries if they  contribute flow to navigable water more than two times per year,  were constructed to relocate a tributary, or  were constructed in an adjacent wetland.
Wetlands adjacent to jurisdictional waters: point 7 above  wetlands are areas that are inundated or saturated by surface or groundwater frequently enough to support the growth of vegetation adapted for life in saturated soil conditions.2 Wetlands include bogs, Carolina Bays, marshes, swamps, and similar areas.
Adjacent wetlands are wetlands that
 physically touch jurisdictional waters
 are separated by a natural berm, bank, or dune
 are inundated by flooding from a WOTUS
 are separated by an artificial dike, barrier or similar artificial structure that allows direct hydrologic connection 
 is divided by a road or artificial structure that permits direct hydrologic surface connection through or over a structure in a typical year
 Finally, the 2020 Rule more clearly defines bodies of water not included in WOTUS, which are
 groundwater 
 ephemeral features  that flow in response to precipitation
 diffuse stormwater runoff and sheet flow over uplands
 many roadside and farm ditches 
 artificially irrigated areas 
 artificial lakes or ponds constructed in upland areas 
 stormwater control, retention, infiltration, and treatment structures in upland areas
 water-filled depressions in upland or non-jurisdictional water areas 
 groundwater recharge, water reuse, and wastewater recycling structures constructed in upland areas
 contained waste treatment systems  defined to include all components, including lagoons and treatment ponds , designed to either convey or retain, concentrate, settle, reduce, or remove pollutants, either actively or passively, from wastewater or stormwater prior to discharge.2
 One exception to the above bodies of water not included within WOTUS is abandoned, prior converted cropland.
If cropland is abandoned for five or more years and has reverted to a wetland, the wetlands within that cropland are regulated under the 2020 Rule.2
 Groundwater and the Clean Water Act WOTUS Definition
 Groundwater itself is not a jurisdictional WOTUS and is not regulated by the Clean Water Act; the 2020 Rule follows this long-established principle.
However, the Supreme Court recently re-confirmed that the Clean Water Act does protect against the pollution of water that travels through groundwater from a point source  such as a buried pipe  when the discharge through groundwater is the functional equivalent of a direct discharge into a jurisdictional WOTUS.5,6 An example would be an unpermitted discharge of a chemical to a stream from a buried pipe not far from the stream.
Agricultural and specialty crop producers should always think about how applied chemicals move through their farms soils and groundwater, and the proximity of the discharge of chemicals to WOTUS.
It is best practice to follow label recommendations, practice integrated pest management, and consider weather conditions when timing chemical applications to limit the potential for agrichemical movement from/through production areas.
The Impact of the 2020 Ruling on Agricultural and Specialty Crop Stakeholders
 Many agricultural and specialty crop stakeholders use ponds, wells, natural streams, and rivers for irrigation water sources.
Well water is also used to fill some irrigation ponds.
Water withdrawals for irrigation in South Carolina increased by 6.5% from 2017 to 2018.7,8 Water withdrawals will likely continue to increase because new irrigation systems are being continuously installed.
The 2020 Rule respects the rights of States, localities, tribes, and private property owners while protecting the environment and regulating the WOTUS.9 The 2020 Rule ensures that the agencies operate within Congress charge to protect navigable waters and identifies the waters federally protected under the Clean Water Act, Navigable Water Protection Rule.
The 2020 Rule clearly defines the types of water bodies that are considered jurisdictional WOTUS.
This distinction allows farmers to manage non-jurisdictional waters as they desire as long as they comply with all other laws related to water management.
If a farmer/producer is unsure if the Navigable Water Protection Rule regulates water bodies on their land, they should contact their regional Army Corps of Engineers office.
Agencies can identify and classify the types of surface water features using various means, including site visits, remote sensing, maps, surveys, and hydrologic models.8 Agencies will then make WOTUS classification decisions based on the weight of evidence from the most reliable sources of information.
If a water body on a producers land is determined to be a jurisdictional WOTUS, the producer should work with an agency representative to develop a management plan for their water source to comply with Federal rules.
Agricultural and specialty crop producers need to consider a few points, even with the revised WOTUS.
The first is that the Endangered Species Act still protects wetlands that no longer classify as WOTUS  as they provide habitat for endangered species.
Another point of consideration is managing the quality of water leaving their property.
Contaminants  from agricultural sources are considered non-point source pollutants.
Non-point source pollutants can potentially impair WOTUS either by overland flow  or by seepage through soils to groundwater.
Producers need to implement and manage best management practices so that contaminants do not leave their property.
The Environmental Quality Incentives Program  offered by NRCS offers producers assistance in identifying and planning conservation practices and financial aid for their implementation.
PREPLANT IRRIGATION IN THE CENTRAL AND SOUTHERN HIGH PLAINS A REVIEW
 Preplant irrigation has been widely practiced in the semi-arid High Plains since the early expansion of pump irrigation from the Ogallala Aquifer in the late 1930s.
As groundwater storage continues to decline, the common practice of "heavy" water application to fully wet the root zone of graded furrow fields prior to planting is being questioned.
Under some conditions, preplant irrigation is an essential practice for timely stand establishment and high yields.
However, in many situations, the large application depths required for surface irrigation result in inefficient soil water storage and low yield response.
With center pivot sprinkler systems, smaller and more precise preplant irrigation application amounts are possible resulting in more efficient preseason storage.
We conclude that the benefits of preplant irrigation are likely to be greatest  when the soil profile is dry before planting;  when seasonal irrigations are not applied to drought-tolerant crops or are reduced in amount;  when early planting limits soil wetting by precipitation by the desired date; and  when preplant irrigation plus seasonal precipitation on deep, high water storage soils can result in moderately high irrigated yields without seasonal irrigation.
The benefits are likely to be low  when soil profiles are moderately wet at time of irrigation;  when planting dates are flexible and can follow precipitation events for stand establishment; and  when seasonal irrigation provides adequate water to meet plant requirements.
As groundwater decline continues and precipitation becomes more important for supplying crop water requirements, the use of preplant irrigation as an irrigation water management practice will likely decline in importance in the High Plains.
90% of the irrigated area and groundwater pumped for irrigation.
In surface irrigation systems, the preplant irrigation is normally the largest irrigation event and constitutes about one-fourth of the total irrigation applied for corn, about one-third for grain sorghum, and one-half for cotton.
Although preplant irrigation is widely practiced in the semiarid Central and Southern High Plains, it has not previously been the subject of a technical review.
Results of many preplant irrigation tests were reported years ago in Experiment Station reports and other publications that are mostly no longer available.
The significance of this early work along with the more recent work is summarized and interpreted in this review.
Irrigated soils in the High Plains are predominantly gently sloping.
Most surface irrigation is practiced on slopes less than 1%.
Soils are relatively deep with field crop extraction of available soil water  occurring to the 1to 2-m depths.
Graded furrow irrigation is used for 56% of the irrigated crop area in the Texas High Plains in 1989  and for about 50% of the area in the Central High Plains.
Almost all preplant irrigation tests conducted in the High Plains involved water application to graded furrow or level border plots.
Preplant irrigation mostly occurs during April and May for summer crops.
Windy periods of warm, dry air and moderately high evaporative demand are common and contribute to the frequently low profile storage efficiencies.
The High Plains is both a major irrigated and a major dryland crop region.
Long-term precipitation ranges from about 380 mm annually in the southwest to about 600 mm in the northeast.
Precipitation occurs mostly from spring to fall and winters are relatively dry.
The distribution pattern increases in bi-modal tendency from north to south as illustrated by transect data for Colby and Garden City, KS, and Amarillo, Bushland, Lubbock, and Big Spring, TX, in figure 1.
During periods of major drought, very little effective soil water storage occurs from harvest to planting time, whereas in occasional wet periods, precipitation fully rewets the soil profile.
In most years, the profile is partially rewet by preseason precipitation.
Preplant irrigation is widely practiced to avoid the risk of inadequate precipitation prior to planting time which permits timely establishment of crops that are spring planted.
Advantages of preplant irrigation are that it  permits early planting without having to rely on unpredictable rainfall;  delays the need to begin seasonal irrigation and reduces seasonal irrigation water requirements;  improves soil conditions for seedbed preparation and germination of crop volunteer plants and weeds which can be killed by tillage before planting; and  allows
 T he Ogallala Aquifer in the High Plains is a major water resource for irrigation in the Texas High Plains, Oklahoma panhandle, and parts of eastern New Mexico, eastern Colorado, western Kansas, and central and western Nebraska.
The four major field crops,  account for about
 Article was submitted for publication in May 1990; reviewed and approved for publication by the Soil and Water Div.
of ASAE in October 1990.
Presented as ASAE Paper No.
87-2558.
Contribution from the USDA-ARS and Kansas Agricultural Experiment Station, Kansas State University.
Contribution No.
90-419-J.
Figure 1-Average 15-day precipitation moving totals by 3-day periods, January through December, for north to south locations in the Central and Southern High Plains.
The locations and length of record are Colby  and Garden City.
KS, and Amarillo , Bushland , Lubbock , and Big Spring , TX.
Plotting points are centered for the 15-day periods.
additional land area to be irrigated from wells than can be adequately irrigated during the growing season, thus reducing the area in dryland crops and increasing total farm production.
The disadvantages are that it often  increases cost of production;  increases total irrigation water requirements and accelerates depletion of groundwater storage;  reduces the efficiency of irrigation water use for crop production; and  lowers soil temperatures needed for timely stand establishment.
In this review, preplant irrigation is considered in relation to  water intake, storage, and storage efficiency;  field response for the major irrigated crops of grain sorghum, corn, winter wheat, and cotton; and  management in surface and sprinkler irrigation systems.
As groundwater supplies available from the Ogallala Aquifer continue to decline, pumping energy costs remain high or further increase, and the High Plains area continues a transition to dryland agriculture, the advisability of applying large preplant irrigations to fully rewet the soil profile before planting will be increasingly questioned.
Eliminating the preplant irrigation when crops can be established without it is a practical approach to reducing irrigation water requirements.
However, preplant irrigation for soil water storage before planting when the profile is dry or for stand establishment of early planted crops when precipitation is deficient is a practical and efficient management practice.
WATER INTAKE, STORAGE, AND STORAGE EFFICIENCY
 A common disadvantage of preplant irrigation of graded furrow fields is the large application depths compared with
 seasonal irrigations.
Water intake is generally increased due to soil loosening effects of primary tillage, winter freezing and thawing effects on soil structure, and flow retarding effects of crop residues.
In 5 years of tests on Richfield silty clay loam at Garden City, KS, preplant applications for grain sorghum averaged 220 mm compared with 153 mm for two seasonal irrigations.
In 3 years of tests with winter wheat on Pullman clay loam at Bushland, TX, preplant irrigations ranged from 140 to 238 mm applied, whereas seasonal irrigations ranged from 75 to 100 mm.
In a 3-year test of five tillage treatments on Sherm clay loam at Etter, TX, intake during a fall preplant irrigation of a graded furrow field following sorghum harvest and tillage averaged 208 mm, whereas a spring preplant irrigation treatment averaged 462 mm.
During spring preplant irrigation test, intake of water as it advanced across the field in wheel track furrows was onehalf that in non-wheel track furrows.
This indicates the importance of surface soil conditions on water intake.
Also, Musick and Dusek  and Musick et al.
found that deep tillage can greatly increase water intake during a preplant or initial irrigation for emergence.
Practices that have reduced the large preplant irrigation in graded furrow systems are wheel traffic compaction of furrows  and surge flow application.
For sprinkler irrigated fields, a common practice is to apply two to four preplant irrigations for a total depth of about 50 to 100 mm.
Thus, total preplant irrigation depths are usually less than one-half the depths applied in furrow irrigation and profile drainage is substantially reduced.
For crops other than cotton, a widely practiced alternative is to eliminate preplant irrigation and apply one or more small applications after planting for crop emergence.
Emergence irrigation for cotton is not practiced because of adverse effects of lowered soil temperatures for stand establishment.
Without preplant irrigation, sprinkler-irrigated fields frequently have only partially wet profiles as the growing season begins.
For corn, early-season irrigation for profile wetting is applied when plants are small and water use rates are low.
Cotton growth is adversely affected by irrigation at this early stage because of cool temperatures and seedling disease effects associated with wet surface soil.
Irrigation for profile wetting is delayed until warmer growing conditions.
A common practice for sprinkler irrigated cotton is to begin the irrigation season about two weeks earlier than normal.
Soil probes and gypsum blocks are used to some extent to monitor subsoil wetting and the need for additional early-season irrigation for lower-profile wetting.
Planting dates for summer row crops coincide in general with periods of highest annual precipitation probabilities in the High Plains.
Due to flexibility of small applications for emergence when precipitation is inadequate, sprinkler irrigation can be managed to effectively eliminate the preplant irrigation.
This allows increased storage of preseason and early seasonal precipitation on soil that has not been preplant irrigated and allows management flexibility to apply early-season irrigation as needed for
 profile wetting ahead of the rapid plant growth and increasing ET demand period.
It is not uncommon for moderately wet soil profiles to occur after harvest of irrigated crops, either from late season irrigation or irrigation plus late season rainfall.
In the Southern High Plains, corn is adequately irrigated to prevent substantial yield reductions associated with limited irrigation.
Adequate irrigation management normally leaves profile ASW storage in excess of 50% after harvest.
Grain sorghum is grown under both adequate and limited irrigation and the timing of the last irrigation has a major effect after harvest on residual soil water storage,.
Application of the last irrigation at late boot, flower, milk and dough stage of grain sorghum resulted in residual ASW storage in a 1.8-m profile of Pullman clay loam of 71, 118, 142, and 197 mm and deficit storage below field capacity of 156, 109, 85, and 30 mm, respectively.
Sprinkler-irrigated fields usually have drier profiles after harvest than surface-irrigated fields.
Large preplant irrigation depths applied in surface systems and occurrence of average to above average preseason precipitation can dictate that water storage efficiency will be low.
For example, a soil profile that has 100 mm of remaining water storage capacity receives 150 mm preplant irrigation plus an additional 150 mm of precipitation between harvest and planting.
If the soil is fully wet at planting, storage efficiency cannot exceed 33% of the 300 mm of irrigation and precipitation.
Slowly permeable clays, such as Pullman clay loam, are difficult to wet below about 0.6-m depth, and storage efficiencies have been measured in the 20% range.
In the study by Undersander and Regier , storage efficiency of preplant irrigation measured as increased ASW at planting averaged 22% for the fall irrigation and 18% for early spring irrigation.
A soil that is preplant irrigated early in the nongrowing season may lose more water than it gains from scattered rains before the crop season begins.
Musick et al.
measured a net loss in ASW storage for 2 years with 75 and 125 mm of rain after preplant irrigation and before planting.
Gain or loss in ASW from rainfall following preplant irrigation in relation to rainfall amount is illustrated in figure 2.
On deep uniform silt  soil profiles in western Kansas, prolonged soil profile drainage occurs following fall preplant irrigation.
Stone et al.
determined rapid drainage losses from a 1.8-m profile of Ulysses silt loam following irrigation as about 60 mm during a 3-day period to the 640 mm upper limit water content.
Slow drainage losses of an additional 60 mm continued over the extended time period between preplant irrigation and planting the next crop.
Drainage losses equalled or exceeded soil evaporation losses at profile water contents above 80% ASW.
The most efficient condition for preplant irrigation storage is when the profile is relatively dry.
Water applied as preplant irrigation is subject to losses as surface evaporation and deep percolation below the root zone.
Musick et al.
found that storage efficiency of 100 to 150 mm preplant applications to level border plots on five dates from fall to spring decreased in a linear relationship with time.
When evaluated within one or two weeks after irrigation, the highest storage efficiency of 54%
 Figure 2-Precipitation storage after early preplant irrigation for annually grown sorghum compared with storage by nonirrigated plots of Pullman clay loam.
occurred during fall irrigation, and the lowest of 33% occurred during late spring irrigation.
Early preplant irrigation reduced precipitation storage efficiency, and timing of preplant irrigation had little effect on storage efficiency of both preplant irrigation and preseason rainfall.
Average storage efficiencies for the 20 preplant irrigations were 44% for irrigation water and any rainfall occurring following irrigation, 49% for additional soil water storage associated with irrigation, and 29% for irrigation plus precipitation from late fall harvest to sorghum emergence in late June.
These data indicated that storage efficiency of preplant irrigation averaged  more than double the 20% for preseason precipitation reported by Unger  for continuous cropping of dryland grain sorghum on a nearby site, but  less than one-half of the irrigation water applied was stored as ASW for subsequent plant use.
Figure 3-Storage efficiency of preplant irrigation and preplant irrigation plus preseason rainfall for annually grown grain sorghum on Pullman clay loam in relation to preseason irrigation date.
Although storage efficiency of preplant irrigation  is relatively low, additional increments of water storage at planting are efficiently used for yield of grain sorghum that is not irrigated during the growing season.
In 27 years of dryland research at Bushland, TX, grain sorghum yields were linearly related to ASW at planting, with additional storage resulting in an efficient average yield response of 1.5 kg/m.
Stone et al.
concluded from a 3-year study "that the most efficient use of irrigation water is made when water is applied as close as possible to the time of plant need".
preplant irrigation for the next crop.
When the profile ASW appears adequate, shallow tillage can be used to limit surface soil drying and reduce precipitation requirements for adequate rewetting of the surface soil before planting.
Significant relationships have been found between residual ASW storage after harvest and preseason soil water storage from precipitation on Pullman clay loam  and on Keith silt loam.
The use of limited irrigation with an earlier-thannormal cutoff date increases soil water depletion, storage deficit after harvest, and potential storage efficiency of precipitation.
Stone et al.
indicated that on a Ulysses silt loam at Tribune, KS, a range of spring ASW in a 1.8 m profile from 30 to 70% was related to a linear decline in storage efficiency of fall preplant irrigation from 85 to 42%.
In the Texas High Plains, a winter survey of ASW contents to 1.5 m is conducted annually for a 15-county area by the High Plains Underground Water Conservation District No.
1, Lubbock, TX.
Results are made available as contour maps of profile storage deficits in the District newspaper "The Cross Section".
Early awareness of profile soil water deficits is useful information for the farmers in assessing the risk and making decisions concerning
 Figure 4-Effect of preplant irrigation amount for annually grown sorghum  on available soil water, irrigation storage efficiency, and grain yield.
A test of three application depths  of preplant irrigation only for continuous grain sorghum on Pullman clay loam indicated relatively low storage efficiencies at planting of 42 to 32%.
However, the yield response to additional storage without seasonal irrigation was rather high and averaged 2.1 kg/m3.
The data illustrate the decline in storage efficiency as application depths were increased.
The first irrigation water management research for grain sorghum occurred during early irrigation development in the southern part of the Texas High Plains.
This work at Lubbock by Jones and Gaines  emphasized the importance of preplant irrigation to provide a wet soil profile at planting and one seasonal irrigation during boot stage.
This work preceded the introduction of hybrids and the use of fertilizers for grain sorghum; and yields of adequately irrigated crops were relatively low, less than 4 Mg/ha.
Even though yields were relatively low during a period of major drought, irrigation water-use efficiencies  for grain production were rather good, averaging 1.25 kg/m for preplant irrigation, 2.29 kg/m for the boot stage irrigation, and 1.42 kg/m for two seasonal irrigations.
Dryland grain sorghum frequently failed during the major drought years of the 1950s, and Swanson and Thaxton  stated, "A grain sorghum crop can be produced with a preplanting irrigation alone in very dry years when dryland crops are complete failures".
Thus, yield reliability from preplant irrigation was considered important as irrigation developed in the traditional dryland environment of the Texas High Plains.
The use of limited irrigation changed during the 1960s as more emphasis was placed on adequate irrigation for high yields.
However, declining groundwater supplies, low commodity prices, and high pumping energy costs have led to renewed interest in limited irrigation.
In reducing water application, the need for and benefits of preplant irrigation need reevaluation.
As water application for grain sorghum has declined, the production emphasis has shifted from longer maturity, high yield potential hybrids that require high production inputs to medium maturity-length  hybrids that as a group have superior drought tolerance.
These hybrids can be planted two to three weeks later than the medium-late and full season hybrids, which considerably enhances stand establishment reliability from rainfall and reduces the need for preplant irrigation.
The highest yield response to preplant irrigation has occurred for continuous cropping when yield response to preplant irrigation only was compared with dryland yields.
In 7 years of tests at Bushland, TX, dryland yields averaged 2.08 Mg/ha, yields with preplant irrigation only averaged 3.23 Mg/ha, and preplant plus adequate seasonal irrigation averaged 7.98 Mg/ha.
The IWUE of preplant irrigation applied to level border plots without runoff averaged 1.08 kg/m, whereas that of seasonal irrigation averaged 1.81 kg/m3.
The reduced IWUE of preplant compared with seasonal irrigations is associated with the relatively low storage efficiency of preplant irrigation for later use by the crop and reduced storage of rainfall following preplant irrigation and before the beginning of crop growth.
When plant establishment can be obtained without preplant irrigation and a normal irrigation schedule is followed during the season, preplant irrigation may have little influence on yields.
Eliminating the preplant irrigation in a 3-year study by Musick et al.
increased IWUE from 1.26 to 1.68 kg/m in 1964, from 1.44 to 2.25 kg/m in 1966, and 250 mm of precipitation in June 1965 eliminated any soil water storage and yield benefit from the preplant irrigation.
Bordovsky and Hay , in a 3-year study at Colby, KS, found no additional yield benefit from preplant irrigation of grain sorghum when adequately irrigated during the growing season.
When preplant irrigation is not used for grain sorghum, planting in the Southern High Plains can be delayed if necessary from early or mid-May to midor late June for precipitation to rewet the seed zone.
The probability of precipitation depths at Amarillo, TX, for continuous sorghum during preseason and approaching planting during May and May through 15 June are shown in figure 5.
In 35 years of dryland research at Bushland, sorghum stand establishment was possible by late June in all but one season, the major drought year of 1956.
Reduced tillage intensity and shallow operating depths enhance seed zone water content and stand establishment on dryland, and conservation tillage practices may be desirable for stand establishment without preplant irrigation.
When sorghum follows irrigated wheat grown the previous year, a no-tillage system can be successfully used.
The sorghum can be seeded in the old wheat beds which normally have very good soil water contents following fallow and stand establishment does not require preplant irrigation.
The northern part of the Southern High Plains and the Central High Plains have extensive areas of deep, finetextured irrigated soils with silt  subsoils that are high in water storage capacity and have the potential for relatively high yields from preplant irrigation plus seasonal rainfall.
In an early bulletin on irrigation in western
 Figure 5-Probability of exceeding precipitation amounts for annually grown sorghum, Amarillo, TX, for preseason total through 15 June planting and for May and May-15 June in relation to providing surface soil water for planting.
Kansas, Erhart et al.
stated, "It is possible to irrigate additional area in the winter when fields under full irrigation require little or no water.
Such a practice can fill the root zone with water and result in crop yields equal to those under good summer fallow.
Application of 8 to 12 inches  of water may be required to fill the soil to capacity".
In an 8-year test by Erhart  on Ulysses silt loam, yields from about 300 mm of winter irrigation averaged 4.33 Mg/ha compared with 1.88 Mg/ha for dryland after summer fallow in a wheat-sorghum-fallow sequence.
In a 6-year test by Musick and Grimes  on Ulysses clay loam at Garden City, KS, yields from preplant irrigation only averaged 4.80 Mg/ha yields compared with 1.99 Mg/ha for dryland fallow sorghum.
Three of the 6 years occurred during the major drought of the 1950s.
During the three years following the drought, yields with preplant irrigation only averaged 6.37 Mg/ha compared with 2.52 Mg/ha for dryland fallow.
Ratio of grain sorghum yields from preplant irrigation plus precipitation to yields under adequate irrigation increases from south to north across the Southern and Central High Plains for locations having similar seasonal and annual precipitation.
Yield from preplant irrigation as a percent of yield under adequate irrigation at Bushland, TX, averaged 40% during 7 years of tests ; at Garden City, KS, it averaged 66% during 6 years of tests  which included 3 years of major drought, 79% for 3 years after the drought ended, and 57% in 8 years of tests ; at Tribune, KS, it averaged 81% in 3 years of tests on Ulysses silty clay loam ; and at Colby, KS, it averaged 95% in 3 years of tests on Keith silt loam.
At all locations, yields under adequate irrigation were generally similar and were mostly in the 7 to 8 Mg/ha range.
Evapotranspiration demands that require seasonal irrigations for high yields decrease from south to north in the Southern and Central High Plains.
Also, as yields from preplant irrigation without seasonal irrigation increase from south to north, this practice becomes more efficient as the only irrigation applied for soils having major profile storage capacity at the time of irrigation.
Comparative differences were reported for Pullman clay loam at Bushland, TX, and Richfield clay loam at Garden City, KS, by Musick and Sletten.
The corn hybrids grown have longer growing seasons, germinate at cooler soil temperatures, and are planted two to four weeks earlier than the grain sorghum hybrids.
Normal tillage for seedbed preparation frequently results in dry surface soil, and the low precipitation prior to the late April to early May planting dates may necessitate preplant irrigation for germination and stand establishment.
Corn is mostly irrigated and managed for high yields.
Because of critical stage sensitivity to plant water stress, it is seldom grown without seasonal irrigation.
The irrigation cutoff dates used for high yields result in residual storage of ASW which frequently exceeds 50% of available capacity in a 1.5 to 1.8-m profile depth.
A 2-year study of irrigated corn fields in Thomas County, KS, indicated ASW storage to a 1.5 m depth after harvest averaged 80%.
Tests at Colby,
 KS, indicated that irrigation was not needed for stand establishment from early to mid-May planting.
In these tests on Keith silt loam, ASW after harvest averaged about 60%.
They stated, "In most years, fall preseason irrigation is not needed to recharge the soil profile in northwest Kansas".
They further stated that, "Most irrigation systems have excess capacity in June and could add a significant amount of water to a deficit soil profile before the peak water use period of July through August".
Corn is mostly planted following corn or grain sorghum and, to a lesser extent, after harvest of wheat the previous summer.
Preplant irrigation to recharge the profile may not be needed when corn follows corn because of residual ASW after harvest and preseason precipitation and also when corn follows wheat because of fallow season soil water storage.
Preplant irrigation is more likely to be needed following sorghum when irrigation is managed to allow major depletion of ASW by harvest.
Fall or winter irrigation after harvest, following tillage and reforming of bed-furrows, developed as a preplant irrigation practice in western Kansas.
Benefits from fall irrigation for corn in the Central Plains have been debated since the early 1900s.
Knorr  reported yield benefits on sandy loam soils with deep wetting at Scottsbluff, NE, but Farrell and Aune  reported no benefit from moderate wetting depths on Pierre clay at Belle Fourche, SD.
Knapp  recommended winter irrigation for most of western Kansas with the exception of areas with sandy subsoils.
Off-season utilization of labor was one of the major factors in promoting winter irrigation.
More recent studies with corn in the Central High Plains have shown little or no response to preplant irrigation over a wide range of conditions.
Stone et al.
found no significant yield increase from preplant irrigation that substantially increased total water application.
In a 3-year study at Colby, KS, Banbury et al.
found no yield benefit from preplant irrigation over a wide range of treatments from limited to full irrigation.
Lamm and Rogers  found no statistically significant differences in corn yields as affected by preplant irrigation even though average yields were slightly higher for the fall irrigation treatment.
Stand establishment without preplant irrigation can be enhanced by:
 1.
Using fall tillage and reforming bed-furrows to allow a relatively long time interval for the bed seed zone to become rewetted by precipitation.
2.
Delaying planting up to about two weeks in the Central Plains and three weeks in the Southern Plains to enhance surface soil wetting from precipitation.
3.
Planting on summer fallow after irrigated wheat with no-tillage management and seeding into old beds.
4.
Applying, if necessary, a smaller irrigation after planting for rewetting of beds to ensure emergence.
Stone et al.
concluded, "Spring irrigation amounts sufficient for germination and early-season corn growth is obviously a necessary and efficient use of irrigation water.
Beyond this necessary use, and if the irrigation system and capacity can supply sufficient in-season irrigation to com, the application of water in the noncrop season to fill the soil
 profile to field capacity appears to be an inefficient use of water supplies".
Irrigated wheat is mostly grown after wheat, after summer fallow, or to a lesser extent, soon after harvest of a summer crop such as corn.
The time interval for preplant irrigation overlaps the late season irrigation of summer row crops, and the priority for water supplies is normally given to the summer crops.
Therefore, preplant irrigation for wheat is not extensively practiced.
The probability of precipitation at Amarillo, TX, between maturity of one crop and planting time for another and approaching planting time  is shown in figure 6.
Wheat is frequently planted into moist soil after precipitation and may be irrigated for emergence or to improve stand establishment after the crop has partially emerged.
When soil water conditions are adequate for a period of growth after emergence, the initial irrigation may be delayed or deleted.
Preseason precipitation storage, particularly after summer fallow, reduces the need for irrigation until after a period of substantial water use by the crop.
Studies involving preplant irrigation of wheat were conducted on Pullman clay loam at Bushland, TX, by Jensen and Sletten  and on Richland clay loam at Garden City, KS, by Musick et al.
, two locations having similar seasonal and annual precipitation.
At Garden City, seasonal evapotranspiration is about 100 mm lower than at Bushland, and the available water storage to 1.8 m on Richfield clay loam is about 100 mm higher than on Pullman clay loam.
These differences resulted in preplant irrigation only at Garden City yielding 90% of the fully irrigated plots compared with 58% at Bushland.
The tests on Richfield clay loam indicated that preplant irrigation only was an efficient water management practice on a high water storage soil that had major ASW soil water storage capacity at time of irrigation.
However, preplant irrigation contributed to low yield response and water-use efficiency
 Figure 6-Probability of exceeding precipitation amounts for annually grown winter wheat, Amarillo, TX, for preseason totals through 10 October and for September-10 October in relation to providing surface soil water for planting.
from seasonal irrigation.
Stone et al.
in tests of continuous cropping of irrigated wheat at Tribune, KS, concluded that, "Fall irrigation of winter wheat for stand establishment and early growth is a very efficient and worthwhile use of irrigation water.
Additional irrigation in the spring produced yield increases, but the usefulness and profit of the additional irrigations could be questioned".
Winter wheat is planted over a relatively wide range of dates from early September to mid-October.
In many years, precipitation is adequate to provide surface soil water for stand establishment.
When precipitation is inadequate, irrigation after planting to improve stands is more common than preplant irrigation.
If beds and furrows are reestablished following major tillage in July after late June harvest, July-September precipitation in most years is adequate for rewetting of beds and furrows.
Because of previous wetting by precipitation, only a modest amount of precipitation is needed to provide adequate seed-zone soil water at planting.
Irrigation to rewet the soil profile can be delayed until late fall or early spring when it is likely to be used more efficiently for increasing yields.
Because of limitations in heat units and length of growing season, cotton is grown only in a 25-county area in the central and southern parts of the Texas High Plains.
Preplant irrigation is usually applied during late March to early May.
Irrigated cotton is mostly planted during midto late May, whereas dryland cotton is planted during mid-May to early-June following seed zone wetting from precipitation.
Planting dates correspond to the most predictable precipitation period of the year, and in many years, precipitation can be relied upon for stand establishment of irrigated cotton.
Even though stands can be normally established from precipitation, Walker and Onken  stated, "Where available, a preplant irrigation is usually applied to cotton land with subsequent summer irrigations to supplement rainfall".
Cotton is most often grown in monoculture systems, and preplant irrigation is used to rewet the soil profile and to ensure favorable soil water conditions for early planting.
Irrigation inventories conducted by the Soil Conservation Service for the Texas Water Development Board at about 5year intervals since 1958 indicate that groundwater use for cotton has ranged from about 488 mm in the driest season to 196 mm in the wettest season and averaged 299 mm for eight inventory years.
The most common surface application schedules are preplant-only, preplant plus one seasonal application at about peak bloom, and preplant plus two seasonal applications, at about early bloom and late bloom.
Irrigated cotton lint yields in a 25county production area averaged 472 kg/ha during 1968-89, whereas dryland yields averaged 321 kg/ha.
Assuming irrigation water application for cotton has averaged about 300 mm, IWUE for lint yields has averaged about 0.05 kg/m, substantially lower than has been obtained from research field plot tests.
A review of cotton preplant irrigation research at Lubbock, TX, revealed 21 years of test data during 1937-74.
Thaxton and Swanson  concluded
 that, "The preplant irrigation is the most important one".
However, later data indicated that irrigation before planting was less important for yield than irrigation during the critical bloom stage.
For all the preplant irrigation test data, dryland cotton lint yields averaged 285 kg/ha compared with 423 kg/ha for preplant irrigation only and 606 kg/ha for preplant plus one seasonal irrigation during bloom.
Data for 10 years included water application to level plots without runoff, permitting calculation of IWUE values for lint yields.
Dryland lint yields averaged 308 kg/ha compared with 412 kg/ha for preplant irrigation only and 594 kg/ha for preplant plus one seasonal irrigation.
For the first study conducted during 1937-41, IWUE was higher for preplant irrigation than for an additional seasonal water application during bloom, 0.115 kg/m compared with 0.080 kg/m.
As a 10-year average, the IWUE of preplant irrigation only averaged 0.107 kg/m compared with 0.110 kg/m for the additional water applied during bloom.
In a 3-year study by Newman , a seasonal irrigation only during bloom on plots that were not preplant irrigated resulted in a very high IWUE value of 0.235 kg/m, much higher than the 0.062 kg/m for preplant irrigation only.
The study by Newman  is the only one in the literature that reports the response of increased cotton yields to seasonal irrigation applied without preplant irrigation.
The results suggest that the limited groundwater supplies available for irrigation in the Texas High Plains may be used more efficiently for seasonal irrigation during bloom than for preplant irrigation.
W.
M.
Lyle  indicated that the most efficient time to rewet the profile for water use by cotton is prior to the major growth and water use period rather than prior to planting.
Newman  evaluated preplant and seasonal irrigation of cotton in both solid planted and skip-row systems.
In a 3-year test of the popular two-in-and-one out planted skip-row system, the preplant irrigation amount was reduced by one-third and IWUE values were increased to 0.212 kg/m for preplant irrigation only and to 0.270 kg/m for seasonal irrigation only during bloom.
This study indicated that reduced water application in skip-row systems is an efficient use of preplant irrigation and soil water storage at planting.
In the two-in-and-one-out system, irrigation of one furrow between two cotton rows substantially reduces water application compared with solid planting and every-furrow irrigation.
Yield probabilities of dryland and preplant irrigated only cotton by Bilbro  at Lubbock, TX, indicated a declining yield response to preplant irrigation as yield levels increased.
When yields exceeded 600 kg/ha, irrigated and dryland yields were similar.
Production data for a 25-county area since 1968 indicated that irrigated and dryland yields were similar only in 1979, a cooler and wetter than normal season..
Much of the cotton production area has limited groundwater storage and relatively small well yields.
Preplant irrigation can be applied over a longer time period than the normal irrigation season, which is limited to about six weeks because of the short growing season.
Thus, a practical aspect of preplant irrigation is that small wells can be used to irrigate larger land areas than can be irrigated during the growing season.
Drip Irrigation: The Basics
 This micro-tube delivers water to the root zone of the tree.
Under ground, it is attached to an emitter connected to a polyethylene tube.
This drip emitter is connected to micro-tubing which is attached underground to a lateral line..
Laser lines are a type of micro-tubing with emitters embedded inside the tube.
Drip irrigation also known as low-flow, micro, and trickle irrigation is the slow, measured application of water through devices called emitters.
It is the most efficient way to irrigate.
A wide variety of quality products has been developed to make drip irrigation reliable and easy to use for almost any landscape situation.
Drip tape has emitters inside the tubing and is connected to a polyethylene line.
It is used for vegetable gardens or annual flower beds.
Why should I use drip irrigation?
Drip irrigation saves water because little is lost to runoff or evaporation.
This watering method, if implemented correctly, promotes healthy plant growth, controls weed growth, and reduces pest problems.
What types of landscapes are best suited for drip irrigation?
Most of your landscape can be watered with drip irrigation except for turf areas.
Drip systems are particularly well suited for desert landscapes, places where runoff can be a problem, and small, narrow areas such as entryways.
Drip is also a great way to water vegetable gardens, fruit trees, and potted plants.
There is a wide assortment of equipment to suit most budgets and watering needs.
What are the components of a drip irrigation system?
Controllers or timers are also called irrigation clocks.
They are programmed to automatically turn on control valves for a specific amount of time and for certain days.
This determines how often and for how long the irrigation system is turned on.
This prevents water in the irrigation system from flowing back into the potable water supply.
Backflow preventers are required for all irrigation systems and installation is regulated by county, municipal, or local codes.
Valves turn the water in the irrigation system on or off.
They can be manually or automatically operated and are wired to the irrigation controller.
Filters screen particles out of the irrigation lines to maintain a clean water supply.
Even small particles can plug the small openings of emitters and restrict or block water flow.
Drip systems require low pressure of about 20 psi.
A pressure regulator reduces the incoming water pressure which can range from 50 to 75 psi for most water supplies to levels suitable for a drip system.
Rigid PVC  pipe and flexible polyethylene tubing are commonly used for lateral irrigation lines.
These lines are generally buried in the soil.
These lines are also known as '1/4 inch' or 'spaghetti' tubing and deliver water from the lateral lines to the emitters or directly to the plant.
The length of micro-tubing from the lateral line to the plant should not exceed 5 feet.
They deliver water to the plants at slow rates, usually at 0.5, 1, 2, or 4 gallons per hour.
Emitters are either located at the end of the micro tubing or between the polyethylene tubing and micro-tubing.
In drip tape or polyethylene drip lines emitters are located inside the lines spaced at various intervals.
Flush caps are attached to the end of each lateral line.
They are removed periodically to flush particles and debris from the irrigation laterals.
Can I design my own drip irrigation system?
Yes, designing your own drip system is not difficult to do, but it does require some careful planning.
Make a drawing of the final installation design of your system, and keep it for your records.
Group plants with similar water requirements such as trees, shrubs, ground covers and turf on separate valves.
Know the number of plants for each type and their water requirements.
Design with consideration to pipe length, size and elevation changes.
Plan to expand your irrigation system as plants grow.
Move emitters out to the edge of the canopy  where roots will take up water.
Evaluate whether you need more emitters or change existing emitters to deliver more water at a faster rate.
Select quality equipment.
Spending a little money up front will save time and money later.
Local irrigation suppliers are a good source of advice.
Can sprinklers be converted to a drip system?
Yes, there are products that can be installed in place of sprinkler heads.
Keep in mind that sprinklers and drip emitters apply water at different rates.
When converting to a drip system, all sprinklers in the same zone and on the same valve need to be changed.
Sprinkler and drip irrigation apply water at different rates and operate under different pressure, requiring separate valves.
Drip systems need a pressure reducer and a filter to protect drip emitters from high pressure and clogging.
Follow manufacturer's installation recommendations.
Set and change watering schedules according to plant water need, weather and seasons, and soil texture.
Keep filters clean and flush system periodically.
Visually inspect emitters and lines monthly to ensure proper water delivery.
Expand your system as the plants grow.
Keep good records of your installation design.
Winterizing your drip system may be necessary in cold areas to prevent freeze damage.
watered groundcovers have individual drip emitters with low flow rates.
Trees and large shrubs have multiple emitters with higher flow rates  and are This and drip irrigation system has three valves for plants with different water needs.
Vegetables are watered most frequently with drip tape installed in the bed.
Small shrubs deep and infrequent.
For questions about irrigation or water conservation assistance, contact your local Cooperative Extension Office.
Adapted with permission from the Arizona Municipal Water Users Association's "Drip Irrigation" brochure.
COLLEGE OF AGRICULTURE & LIFE SCIENCES Cooperative Extension
 THE UNIVERSITY OF ARIZONA COLLEGE OF AGRICULTURE AND LIFE SCIENCES TUCSON, ARIZONA 85721
 ROBERT E.
CALL Former Extension Agent, Horticulture CADO DAILY Retired Coordinator, Water Resources
 REVISED BY: URSULA SCHUCH Professor and Specialist, Horticulture
 Any products, services or organizations that are mentioned, shown or indirectly implied in this publication do not imply endorsement by The University of Arizona.
IRRIGATION CAPACITY IMPACT ON LIMITED IRRIGATION MANAGEMENT AND CROPPING SYSTEMS
 Joel P.
Schneekloth Regional Water Resource Specialist Colorado State University Extension Akron, Colorado  345-0508 Email: Joel.Schneekloth@Colostate.Edu
 David C.
Nielsen Research Agronomist USDA-ARS Central Great Plains Research Station Akron, Colorado  345-0507 Email: david.nielsen@ars.usda.gov
 Irrigation capacity is an important issue for irrigation management.
Having enough capacity to supplement precipitation and stored soil moisture to meet crop water needs during the growing season to maximize grain yield is important.
However, declines in the Ogallala Aquifer have resulted in decreases in well outputs to the point where systems on the fringe of the aquifer can no longer meet crop water needs during average growing seasons and especially during drought years.
Changing cropping practices can impact the irrigation management by irrigating crops that have different water timing needs so that fewer acres are irrigated at any one point during the growing season and concentrating the irrigation capacity on fewer acres while still irrigating the majority or all acres during the year.
Many producers have not changed cropping practices with marginal capacity systems due to management increases and the potential for an above-average year.
However, the risk of producing lower yields increases.
Crop insurance has been used to offset those lower yields.
However, the frequency of insurance claims has increased to the point where practices need to be changed on these systems.
System capacities are a function of soil type, crop water use and precipitation.
The soil type acts as a bank where moisture reserves can be utilized during times when the irrigation system is not watering between cycles and during time periods when the system capacity is inadequate to meet crop water needs.
Soils such as silt loams have a greater water holding capacity compared to sands
 which decreases the need for larger system capacities.
Crop water use determines the total water utilized daily.
Greater demand by the crop increases the amount of water needed for the crop over any time period.
Precipitation is an important factor in irrigation capacity.
A region with a greater probability of precipitation during the growing season will require less capacity to supplement crop growth.
Heermann  determined the net design capacity for Eastern Colorado along with probabilities of meeting the crop water needs for the growing season for full water needs.
As capacities decline the probability of meeting crop water needs declines.
A 50% probability means that on average, you will meet crop water needs one out of two years and you will not meet crop water needs the other year.
The result will be less than desired yields.
Lamm  found that irrigation capacities of 50% of needed to meet crop water requirements resulted in approximately 40 bu/acre less corn yields.
In above-average precipitation years, the yield difference is less and in drier than average years, the yield difference is greater.
The economics of reducing irrigated acres until the irrigation capacity was equivalent to full irrigation capacities showed that irrigating those fewer acres was economically equal or greater than irrigating all of the acres for a single crop.
Lower capacity systems generally are inadequate for meeting crop water needs during the peak water use growth stages.
This also coincides with the reproductive growth stages and less average annual precipitation during that time period of a summer crop.
Water stress during that time period has more impact upon yield than during the vegetative and late grain-fill growth stages.
Having water stress earlier or later is more desirable than during the reproductive growth stages of tassel, silking and pollination.
Figure 2.
Yield susceptibility to water stress for corn.
The Crop Water Stress Index  normalizes the canopy-air temperature differential for the drying capacity of the air.
It is calculated from measurements of infrared canopy or leaf temperatures, air temperature, and vapor pressure deficit and varies between 0  and 1.
CWSI has been shown to be highly correlated with other measurements of water stress  such as leaf and canopy CO2 exchange rate, leaf and canopy transpiration, leaf water potential, stomatal conductance, and plant available water in the soil profile.
The system capacity research was conducted at the Central Great Plains Research Station near Akron, CO.
Three irrigation capacity strategies and timings were used to determine the response of corn to early season and late season water stress.
The experimental field was divided into three sections and irrigated with a solid set irrigation system with an application rate of 0.42 inches per hour.
The three capacities and timings were: 5 gallons per minute per acre  with season long irrigation , 2.5 gpm/a with season long irrigation  and 6.7 gpm/a with irrigation delayed until 2 weeks prior to tassel
 emergence.
These 3 capacities represent full irrigation capacities, inadequate capacities and growth stage timing with reduced acres for an inadequate capacity.
Three varieties were tested with varying relative maturity.
Irrigation was applied for the full and inadequate capacity if there was allowable storage for the application.
During the early growth stages, irrigation applications were 0.5 inch while later applications were 0.75 inch.
Irrigation for the growth stage was withheld until 2 weeks prior to tassel emergence.
Irrigation applications for growth stage were 1.0 inch per application.
Neutron probe access tubes were installed in the center of each plot  at the beginning of the experiment.
Soil water was measured periodically throughout the growing season with a neutron probe  at depths of 6, 18, 30, 42, 54, and 66 inches.
Irrigation water was applied through a solid set irrigation system equipped with impact sprinkler heads and an application rate of 0.42 inches hr Irrigation amounts were estimated from irrigation run times and sprinkler nozzle flow rates.
Precipitation was measured at a weather station approximately 1000 feet from the plot area.
Water use  was calculated by the water balance method from the changes in soil water, applied irrigation, and precipitation.
Deep percolation and runoff were assumed to be negligible.
Measurements of infrared leaf temperatures were made on one fully sunlit leaf oriented towards the sun in the upper canopy of the corn crop in the center of each of the 36 plots.
Measurements were made using an Optris LS LaserSight infrared thermometer  beginning at 1300 MDT  after acclimating the IRT to ambient conditions for 60 minutes.
Immediately prior to beginning the IRT measurements and following the last reading IRT measurement, the dry and wet bulb air temperatures were taken with an aspirated psychrometer positioned at 1.5 m above the soil surface at the edge of the plot area.
Measurements were taken at approximately weekly intervals on days when the sun was not obstructed by cloud passages.
IRT measurements were corrected for sensor drift by comparing the IRT output to that of a calibration blackbody reference at the beginning and end of the measurement period and at the end of each replication.
The entire measurement sequence was completed in approximately 50 minutes.
Stomatal conductance measurements show the speed at which water vapor transpires from the leaf tissue to the atmosphere.
Water stress results in lower conductance as compared to non-stressed vegetation.
Stomatal conductance measurements were taken with a Decagon Leaf Porometer model SC-1.
Three measurements were taken per plot on the most fully developed leaf in the upper canopy fully exposed to the sun.
Measurements were taken between 1300 and 1600 MDT when water stress impacts on transpiration should be the greatest.
Atmospheric conditions such as temperature and humidity have a significant impact on stomatal conductance so comparisons within a day are relevant as compared to day to day comparisons within a water treatment.
The different irrigation treatments resulted in differential water stress development.
Water stress was generally less in 2009 compared with 2010 due to increased rainfall in 2009.
In both years CWSI values were highest during the vegetative growth stages under the GSL treatment when irrigation was withheld during the vegetative period.
The water stress was relieved after tasseling for the GSL treatment when irrigation was applied on the same schedule as applied for the full treatment (CWSI = 0.11 in 2009 and 0.24 in 2010,
 LIC Corn Yield vs CWSI
 Figure 3.
Corn yield vs crop water stress index.
averaged over hybrids during the reproductive stages).
Because of the greater rain in 2009 the inadequate capacity treatment did not develop the high levels of water stress seen in 2010 (CWSI = 0.09 during vegetative stages and 0.19
 during reproductive stages in 2009 compared with CWSI = 0.32 during vegetative stages and 0.67 during reproductive stages in 2010).
There were no differences in CWSI due to hybrid.
Yield was highly correlated with CWSI averaged over the reproductive period.
Table 1.
Evapotranspiration, yield, and crop water stress index for irrigation capacities and strategies for 2009 and 2010.
ET	Yield	Average	Vegetative	ductive
 Year Irrigation	Hybrid			CWSIt	CWSI#	CWSI 3
 2009	Full	ND4903	26.01	251.6	0.10	0.06	0.07
 EXP151	23.62	213.7	0.11	0.14	0.07
 NC5607	26.61	215.3	0.16	0.08	0.14
 Growth Stage	ND4903	22.37	239.5	0.29	0.58	0.11
 EXP151	22.19	202.4	0.40	0.76	0.16
 NC5607	22.40	216.6	0.23	0.43	0.08
 Inadequate Capacity	ND4903	24.25	218.7	0.27	0.09	0.32
 EXP151	24.73	218.0	0.13	0.05	0.14
 NC5607	25.42	222.9	0.14	0.12	0.12
 Avg.
by Irrigation	Full	25.41	226.9	0.12	0.09	0.09
 GSL	22.32	219.5	0.31	0.59	0.11
 Inad Cap	24.80	219.8	0.18	0.09	0.19
 Averaged by Hybrid	ND4903	24.21	236.6	0.22	0.24	0.17
 EXP151	23.51	211.3	0.21	0.32	0.12
 NC5607	24.81	218.3	0.18	0.21	0.11
 2010	Full	ND4903	22.83	203.8	0.26	0.24	0.30
 TXP151	22.39	209.5	0.24	0.20	0.30
 NE5321	21.98	164.1	0.23	0.22	0.24
 Growth Stage	ND4903	22.6	187.8	0.38	0.48	0.25
 TXP151	22.34	204.9	0.34	0.45	0.22
 NE5321	22.77	203.6	0.39	0.50	0.26
 Inadequate Capacity	ND4903	18.86	140.6	0.51	0.34	0.69
 TXP151	19.02	133.5	0.48	0.33	0.65
 NE5321	19.13	121.9	0.45	0.29	0.65
 Avg.
by Irrigation	Full	22.40	192.5	0.24	0.22	0.28
 GSL	22.57	198.8	0.37	0.47	0.24
 Inad Cap	19.00	132.0	0.48	0.32	0.67
 Averaged by Hybrid	ND4903	21.43	177.4	0.38	0.35	0.41
 TXP151	21.25	182.6	0.35	0.33	0.39
 NE5321	21.30	163.2	0.35	0.34	0.38
 Averaged over all measurements taken: 7/1 to 9/8/2009 and 6/29 to 8/31/2010 Averaged over vegetative development 5 Averaged over reproductive development
 The ET values generally followed the same pattern as CWSI, with greater water use corresponding to lower CWSI.
There were no differences in ET due to hybrid.
Water use was about three inches less in 2010 than in 2009 for the full irrigation treatment, resulting in about 34 bu/a lower yield in 2010 compared with 2009 for the full irrigation treatment.
Under the more favorable growing conditions of 2009, ND4903 produced higher yield than the other two hybrids under full irrigation  and under the growth stage limited irrigation But all three hybrids produced the same yield under the inadequate capacity irrigation treatment.
In 2010 NE5321 had much lower yield  than the other two hybrids  under full irrigation; ND4903 had lower yield  than the other two hybrids  with the growth stage limited treatment.
Yields were lowest in 2010 with the inadequate capacity treatment, with ND4903 yielding highest  and NE5321 yielding lowest.
Irrigation capacities had a significant impact on stomatal conductance during the growing season in 2010.
System capacities less than adequate had lower stomatal conductance as compared to adequate capacities.
Early in the growing season, stomatal conductance for inadequate, growth stage and full irrigation were similar on June 29.
Since irrigation was not initiated until just prior to tasseling on the growth stage treatment, lower stomatal conductance rates were observed in early July as compared to full irrigation while the inadequate capacity was similar to full.
Lack of precipitation during late June and July resulted in reduced stomatal conductance on July 26 for both inadequate and growth stage management as compared to full irrigation.
This water stress for inadequate and growth stage treatments was during tassel emergence.
Irrigation was initiated on the growth stage treatment at this time with application amounts that would be similar to maximum transpiration rates.
Stomatal conductance rates for the growth stage treatment on August 13 were similar to full irrigation while the conductances under the inadequate capacity treatment were less than under both growth stage and full irrigation.
The difference in stomatal conductance between full irrigation and inadequate capacity increased later in the growing season  indicating that water stress levels were increasing in the inadequate capacity management.
Timing and capacity had an impact on grain yield when precipitation was below average.
Grain yields with an inadequate capacity resulted in a 32% reduction in grain yields as compared to full irrigation capacities.
Timing irrigation towards reproductive growth with a higher capacity resulted in similar grain yields.
Reducing irrigation during the vegetative growth stage resulted in higher crop water stress indexes.
However, an irrigation capacity which can meet crop water needs reduced the crop water stress index to values similar to full irrigation capacities and resulted in little or no yield loss.
When capacities are limited on the entire system, management strategies and cropping practices that result in fewer acres of an irrigated crop can alleviate the potential for severely reduced yields as compared to irrigating the entire system with inadequate capacities.
Variety selection is important as the yield potential can vary by water management.
Table 2.
Stomatal conductance for irrigation capacities, strategies and varieties for 2010.
ND4903	EXP151	NE5321	Avg
 6/29	249	194	212	218
 7/12	463	342	446	417
 7/26	200	179	298	226
 8/13	175	197	203	192
 8/20	187	180	214	194
 Avg.
255	218	275	249
 ND4903	EXP151	NE5321	Avg
 6/29	249	277	250	259
 7/12	305	266	336	302
 7/26	165	183	208	185
 8/13	264	296	285	282
 8/20	316	337	277	310
 Avg.
260	272	271	268
 ND4903	EXP151	NE5321	Avg
 6/29	261	237	322	273
 7/12	465	474	480	473
 7/26	316	240	328	295
 8/13	228	284	245	252
 8/20	346	362	369	359
 Avg.
323	319	349	330
Water is one of Nebraskas most valuable resources, said Extension Educator Chuck Burr.
This field day will give those interested in water a chance to learn about irrigation practices and cropping systems on a farm scale that can maintain or increase crop production while conserving water.
Manure irrigation is the process of applying liquid manure  to cropland through sprinkler irrigation.
Because effluent is primarily water with a very small percentage of solids, it can be applied with sprinklers, such as traveling guns or center pivots.
Nor does groundwater respect state borders.
The High Plains Aquifer underlies eight states from Texas to South Dakota.
In Nebraska, the High Plains aquifer underlies approximately 84% of the state.
The High Plains aquifer is a group of aquifers, which include the Ogallala aquifer; the Brule, Arikaree, Broadwater groups and formations; and other younger, unconsolidated units.
Chapter: 54 Using Vertical Financial Analysis to Assess Corn Production Costs
 Corn Enterprise Vertical Analysis
 Is too much money spent on land rent, seed, fertilizers, and pest management?
Vertical analysis may have the answers.
Vertical financial analysis helps pinpoint where the money is spent and it provides a mechanism to compare production costs.
Vertical analysis is done by converting the dollar amounts on a financial statement to percentages.
It compares major expenses to gross revenue.
Seed Knowing that direct expenses per acre are $456 is % revenue = $1100/a $110/a X 100% = 10.0% important, but knowing this represents 64% of gross revenue provides more information.
You can track Fertilizer the percentage over time and compare it to industry % revenue $1100/a X 100% 15.5% $170/a = benchmarks.
Parameters can be set that will serve as an early warning sign of expenses moving out of proportion with revenues.
Key expenses such as seed, fertilizer, rent, machinery costs, and labor/management can be watched, and modification plans can be made and implemented, if necessary.
As gross sales per acre increased from 2006 to 2012, it was assumed that crop expenses would also go up.
But what happens when expenses outpace revenue?
Vertical analysis can help identify this change.
Example 54.1 If your revenue is $1100/acre, your costs of production are $962/acre and your seed and fertilizer costs are $110/acre and $170/acre, respectively, what percentage of your total revenue was spent on seed and how much was spent on fertilizer?
Vertical analysis is conducted by dividing a line item on an income statement by gross revenue.
As an example, if gross revenue is $1,100 per acre and seed is $110 per acre, divide $110 by $1,100 and multiply by 100 to get the percentage.
Guidelines to Using Vertical Analysis
 Vertical analysis is essential to understand how the enterprise is doing financially, reveals inconsistencies, and aids in making astute business decisions.
For example, from 2007 through 2012, the costs for seed, fertilizer, and land rent totaled 43.4% of gross revenue for all farms in the data set.
Historical analysis suggests that it is difficult to be profitable if these key costs increase to > 50% of the gross revenues.
Comparing different expense ratios allows individuals to help target expense reductions where they may have the most impact.
If an expense makes up 16% of gross revenue and another expense makes up 4%, which solution is better: cutting the lower expense by 50% or cutting  the higher expense by 20%?
Focusing management efforts on the higher expense components may increase the return on investment.
Data reported in this report were obtained for cash rented corn enterprise systems located in South Dakota, North Dakota, Minnesota, and Nebraska.
Over 2,000 farms were included in the analysis.
The analysis covers the years 2000 through 2014 and is split into 3 time frames, 2000 through 2006, 2007 through 2012, and 2013 through 2014.
The focus is on key expenses in proportion to gross revenue from the corn enterprise.
The information is presented for all farms in the data set and further broken down
 Table 54.1 The average cost of production, average grain yield, and selling prices for the top 40% of all producers compared with all producers.
$/a	% revenue	$/a	% revenue	$/a	% revenue
 Seed	40	9.8	85	10.6	114	13.1
 Fertilizer	49	11.9	122	14.9	148	17.0
 Machinery	58	14.1	113	14.1	126	14.5
 Other	68	16.5	109	13.9	127	14.5
 Rent	84	20.5	137	17.1	195	22.5
 Corn yield	166	169	165
 Selling price	2.25	4.73	4.33
 $/a	% revenue	$/a	% revenue	$/a	% revenue
 Seed	42	12.3	85	11.1	115	15.8
 Fertilizer	53	15.7	126	14.4	162	22.2
 Machinery	69	20.5	119	15.6	151	20.7
 Other	75	22.6	106	14.3	130	17.8
 Rent	93	27.8	137	17.9	197	27
 Corn yield	155	163	152
 Selling price	2.12	4.66	4.07
 into the group of farms in the top 40 percent of net profit.
These numbers and percentages may be used to further compare to an individual's corn enterprise cost.
Cash Rent Corn Production Systems
 Direct expenses for the corn enterprise include seed, fertilizer, chemicals, crop insurance, repairs, drying, marketing, labor, miscellaneous, operating interest, and land rent.
Land rent has been deducted from direct expenses in this analysis.
Direct expenses without rent ranged from $165to $232 and averaged $193 during 2000 to 2006 for all farms.
In high net profit farms, direct expenses, without rent, ranged from $138 to $226 from 2000 to 2006, with an average of $174 per acre.
For the time period from 2007 to 2012 direct expenses without rent ranged from a low of $238 in 2010 to high of $444 in 2012, with an average of $364 for all farms.
High net profit farms ranged from a low of $249 in 2007 to a high of $443 in 2012 with an average of $354.
The average direct expenses without rent for 2013 and 2014 for all farms is $461 and for high-profit farms is $428.
Direct expenses without rent as a percentage of gross revenue peaked in 2001 at 73% for all farms and reached a low of 40.5% for high-profit farms in 2010.
High-profit farms maintained the direct expense ratio at 40% to 45% of gross revenue for 11 of the 15 years from 2000 to 2014, with only 2009 being above 50%.
High-profit corn producers have been able to remain profitable by keeping direct expenses in the range of 40% to 45% of gross revenues.
From 2000 to 2006, land rents averaged $84/acre.
For all farms, rent doubled from 2007 to 2013.
However, the high-profit farms maintained the land rent in a range of 16% to 20% of gross revenue.
On the high-profit farms, land rent ranged from 16% to 30% of total revenues, whereas the expenses for seed, fertilizer, machinery costs , labor, and management increased from $140 in 2000 to $478 in 2012.
From 2012 through 2014, these costs decreased slightly to $460.
Historically, seed costs ranged from 10% to 11% of gross revenues.
However in 2013 and 2014, seed costs increased to 13% of gross revenues.
For the high-profit group, fertilizers generally range from 13% to 15% of gross revenue.
However, in 2013 and 2014, the percentage of gross revenues increased slightly.
High-profit farms have maintained machinery costs in a range of 13% to 15% of gross revenue.
Table 54.2 Direct expenses without rent and rent for the top 40% of all producers and all producers.
$/a	% revenue	$/a	% revenue	$/a	% revenue
 Direct Expenses w/o Rent	174	42.3	354	44.0	428	49.2
 Rent	84	20.5	137	17.1	195	22.5
 $/a	% revenue	$/a	% revenue	$/a	% revenue
 Direct Expenses w/o Rent	193	57.3	364	48.0	461	63.3
 Rent	93	27.8	137	17.9	197	27.0
Chapter: 53 Corn Storage and Drying
 In many years, corn drying is required to ensure that the crop will be of high quality and available to market in the future.
Harvesting corn with moisture content > 22% requires special precautions, such as providing enough airflow to keep the corn cool and drying within days after harvest.
Prior to storing corn, the bin should be cleaned and potential pest problems controlled.
This chapter discusses corn drying and storage.
Rules of thumb are provided in Table 53.1.
Table 53.1 Corn drying rules of thumb:
 Determine the desired moisture content of the grain, and the short and long-term storage requirements.
Clean all equipment that will contact the grain.
Minimize the number of broken kernels placed into the grain bin.
Grain with high moisture content 22%) needs to be dried prior to storage.
The corn moisture content is a function of air temperature and relative humidity.
If corn will be sold as #2 grain by the spring, it can be stored at 15.5% moisture.
However, if it will be stored for 6-12 months, the moisture content should be reduced to 14%, and if storage is a year or longer, the moisture content should be 13%.
Periodically, at least every two weeks, monitor the grain bin and electronic monitoring devices, if problems are detected, immediately resolve them, waiting will worsen the problem or make the problem uncontrollable.
The most typical problems result from:
 Inadequate monitoring and failure to take immediate action.
Failure in the automatic temperature control system.
High-moisture corn should be dried prior to storage.
If the moisture content is > 22%, the grain should be dried within days after harvest.
In South Dakota, due to low fall temperatures or inadequate airflow, natural air drying may not dry the corn fast enough to complete drying prior to winter.
However, if drying can be delayed until spring, natural drying systems may be adequate.
High-temperture systems can be used to rapidly dry corn grain.
These systems become more efficient as the drying air temperature increases.
During drying it is not recommended to increase the kernel temperature to greater than 140oF.
Details on different drier designs are available in Hellevang and Wilcke.
The length of time that grain can be held before grade loss occurs is dependent on the grain moisture content and grain temperature.
At 60F, corn at 18% moisture can be held for 63 days, whereas corn at 22% moisture can be held only for 16 days.
Corn at 18% moisture can be held for 195 days if it is held at 50F, whereas corn at 22% moisture can be held for 54 days.
If the corn is at 28% moisture, it can be held for 20 days at 40F but only 5 days at 60F.
In South Dakota, grain is placed in grain bins or piles, when the temperature ranges from 20F to 50F.
Each system has unique problems and advantages.
In a grain bin, corn grain should not be stored if the moisture content is > 22%, and any grain peaks should be removed.
Grain bin storage: As temperatures decrease during fall and winter, the cooling process starts near the bin's edges and walls.
Differential cooling can result in water migration from the center of the bin to the edges, and convection currents then occur that cause moisture movement to the top center of the bin.
Even if you have an electronic monitoring system, it is recommend that the bin be checked weekly.
Wet slimy grain, crusting, and condensation on vents, hatches, and the roof can be symptoms of serious problems.
If the surface seals, severe spoilage can result.
If crusting has occurred, stir the surface and in extreme cases remove the spoiled grain.
Use aeration to cool the grain as outdoor temperatures decrease.
Maintain the grain temperature within 15 to 20 degrees of the monthly average temperature during the fall.
Bag storage: Storage of grain in plastic bags is becoming popular.
However, these bags can be susceptible to mold and insect problems.
If the moisture content is high , ensiling can occur if the temperatures are above freezing.
The temperatures in these bags generally mirror the average outdoor air temperatures.
It is not recommend to store high-moisture grain  in these bags until the air temperatures have decreased below 32oF.
To prevent molding, high-moisture corn should be dried prior to spring warm-up.
To prevent problems, the temperatures in the bags should be monitored periodically.
Grain pile storage: Under emergency situations, corn can be stored in piles.
In these systems, water flow should be graded away from the pile, and a plastic sheet should be placed under the pile to prevent water migration from the soil to the pile.
When designing a system, consider how much grain needs to be stored and if the grain will be stored as a conical, windrow, or constrained pile.
Aeration should be provided to control grain temperature.
It may also be possible to store grain in a machine shed.
Table 53.2 Approximate storage time of grains as influenced by moisture content and temperature.
% Moisture	Temperature 
 content	30	40	50	60	70	80
 15	240	125	70
 16	230	120	70	40
 17	280	130	75	45	20
 18	200	90	50	30	15
 19	140	70	35	20	10
 20	90	50	25	14	7
 22	190	60	30	15	8	3
 24	130	40	15	10	6	2
 26	90	35	12	8	5	2
 28	70	30	10	7	4	2
 30	60	25	5	8	3	1
 However, when placing grain in a nonreinforced building it is not recommended to pile the grain higher than a couple feet up the wall.
Grain temperatures can be monitored by placing temperature sensors at various locations in the grain bin, piles, and plastic bags.
Sensors can be placed along the walls of the bin and suspended from the bin rafters.
Problems can be avoided by monitoring temperatures.
Temperatures can be managed by using aeration to change the grain temperature.
Aeration can be used to cool the grain following harvest and equalize the grain temperature in the spring.
Fans that push air into  or remove air from  the chamber can be used.
Fans can be placed at the bottom of the bin.
To avoid moisture migration, aerate the grain to keep the grain temperature within 10 to 15 degrees of the average outdoor temperature during the fall.
When tracking temperatures, smell the exhaust air for odors.
The time required to change the temperature depends on fan size, the season and desired temperature change.
The hours required for one aeration cycle can be estimated by dividing 15 by the airflow rate.
In South Dakota, grain should be cooled to below 35F in the fall.
This process should be started when the average daily temperature is 10 to 15 degrees cooler than the grain temperature.
Cool the grain to 20 to 30 degrees for winter storage.
If hot spots are detected during inspections, aerate the system until differential heating is not observed.
In the summer, the grain should be kept cool.
The goal should be to limit grain temperature to near 40F.
High temperatures increase the risk of mold and insects.
Grain Moisture and Temperature Impact on Storage
 Grain moisture content and temperature have a direct impact on grain storage.
Generally, increasing the temperature or moisture content decreases storage life.
1.
To minimize grain bin problems, ask the question would I let my child do this?
2.
Do not enter a grain bin when unloading a grain bin.
3.
Check to make sure automatic unloading equipment is turned off prior to entering a grain bin.
4.
Use a safety harness when entering a bin if you are not standing on the floor.
5.
Let someone know preferably someone observing that you are entering the bin.
6.
Be careful when stepping on crusts as there may be a void underneath and you could become buried.
7.
Wear a respirator that will remove mold spores and grain dust.
Table 53.3 Troubleshooting guide.
Symptom	Probable cause	Possible solution
 Bad odor	Heating and moisture accumulation	Run the fan; check grain temperature
 problem	and moisture content.
Crust	Spoiled grain	Check to see extent of crust and aerate.
Grain is warming up	Moisture content is high	Run the fan may need to dry grain.
Grain is slimy or wet on top surface	Moisture migration	Run the fan to dry grain and create
 Hard crust	Moisture migration	Remove spoiled grain and aerate.
Water condensation 	Moisture migration grain is warm	Aerate to cool the grain.
No air flow though grain when aerating	Air flow blocked by moldy grain	Determine location and scope of
 problem.
Market or re-bin.
White dust on grain when stirred	Mold on grain	Assess extent of problem remove
 Slow grain cooling	Fines may be blocking aeration	Run the fan longer remove center core.
Nebraska Extension is gearing up to train new and recertifying chemigators in 2023.
Applying agrichemicals through an irrigation system  can be advantageous  it offers a high degree of application uniformity, allows chemicals to be easily incorporated into soil and causes less soil compaction than ground sprayer applications.
However, this practice also comes with risks to health and the environment, especially our water resources.
It is because of this that in Nebraska, a person must be trained and certified to chemigate and cannot chemigate under another persons certification.
Pasture Feeding, Streamside Grazing, and the Kentucky Agriculture Water Quality Plan
 Stephen F.
Higgins, Sarah J.
Wightman, and Carmen T.
Agouridis, Biosystems and Agricultural Engineering
 K entucky's abundant forage makes it well suited for grazing livestock, but the pasturing and pasture feeding of livestock need to be managed.
Otherwise, the land and water that make Kentucky great can quickly degrade.
Allowing cattle to behave as they would naturally can lead to overgrazing, congregation in sensitive areas, buildup of mud, loss of vegetation, compaction of soils, and erosion.
High activity causes manure, urine, and mud to accumulate, which results in high nutrient pathogen and sediment concentrations.
When high activity takes place in or near sensitive areas, surface and ground water quality can be negatively impacted.
Adaptive management and best management practices , particularly those that take into account cattle behavior, can help lessen the effect of livestock grazing on soil and water quality.
This publication is intended to provide an overview of the impacts associated with pasture feeding areas and grazing cattle along Kentucky streams  as well as highlight the Kentucky Agriculture Water Quality Plan  and the BMPs it recommends.
How cattle graze and where they congregate are dictated mainly by cattle preferences.
By having a better understanding of cattle behavior and those preferences, producers can more effectively incorporate BMPs into grazing sysitems SO that cattle behavior is redirected and environmental impact is minimized.
Cattle grazing patterns are controlled largely by the surrounding environment, with topography, water accessibility, forage quality, salt or mineral location, and shade being key factors.
Other contributing factors may include pasture shape,
 Figure 1.
Improper grazing use and lack of nutrient management next to a stream.
direction of prevailing wind, and time of the year.
Cattle prefer to forage on summits and valley bottoms.
Cow-calf pairs especially avoid steep slopes.
Cattle also typically do not travel over 600 feet from a water source and like to congregate near shade and water sources, SO off-stream water and shade sources are recommended to minimize impact to riparian systems.
In Kentucky, pasture-based grazing systems mainly use water from streams, although other natural sources, such as rivers, lakes, and springs, or manmade sources, such as ponds, are also used.
The lands immediately adjacent to these water bodies, where the vegetation is often more lush, green, and abundant, are called riparian areas.
With their thick vegetation,
 gentle slopes, and proximity to water, riparian areas are attractive grazing areas for cattle.
Riparian areas are also more attractive to black-coated cattle and cattle that are experiencing the effects of endophyte in tall fescue.
Endophyte fungus produces alkaloids that become concentrated in the seed head.
When eaten, the fungus restricts blood flow to the extremities of the cattle, making it more difficult for the cattle to dissipate heat.
This effect increases the need for cattle to seek the cooling effects of shade, drinking, or wading in water.
The grazing and congregation of cattle in riparian areas for extended periods of time can cause the denuding of vegetation, loss of soil structure, accumulation of manure and urine, and alteration of stream morphology or shape, all of which contribute sediment, nutrients, and pathogens to surface water.
Although riparian areas often rep-
 resent only a small portion of the total production area, the polluted runoff from overgrazed, over-congregated, and unmanaged riparian areas can contribute a large amount of pollutants such as sediment, nutrients, and pathogens to waterways.
When properly managed, riparian areas provide a number of water quality benefits such as trapping and storing sediments, filtering nutrients and pathogens from runoff, recharging aquifers, providing habitat, and helping reduce the water temperatures through shade.
Grazing Mechanics, High Traffic, and Soil Structure
 Grazing mechanics refers to the method by which cattle bite and ingest forage.
Since cattle have an upper dental pad, they graze by wrapping their tongue around forage and then cutting the forage by jerking their head forward.
While such grazing mechanics mean that cattle cannot graze as close to the ground as horses, they can still remove the entire plant, including the roots and soil attached to the roots.
In addition to grazing mechanics, foot traffic affects soil
 condition.
The amount of force applied to the soil by cattle hooves is approximately 26.8 pounds per square inch.
To put that in perspective, a D9 dozer weighing 52.5 tons applies only 16.1 psi.
The point is that the pressure from cattle hooves can greatly exceed the strength of the soil and can lead to the chipping of dry soils and compaction of moist soils.
That the ability of cattle to tear up an area of soil and vegetation is comparable to the ability of a bulldozer should be no surprise to an experienced cattle producer.
Decreased infiltration rates, low levels of vegetation cover, and inhibited regrowth lead to a loss of soil structure, which can cause increased levels of polluted runoff and soil erosion.
The Kentucky Agriculture Water Quality Act
 In order to protect water quality, the Kentucky Agriculture Water Quality Act  was passed in 1994.
It was written as a guide for reducing water quality impacts associated with agriculture and silviculture activities.
The main focus of the act is to protect surface and groundwater
 resources, primarily through the use of best management practices.
The Kentucky Agriculture Water Quality Plan  is a product of the act and is a statewide guide for developing individual water quality plans for use on individual farms.
All agriculture or silviculture operations on 10 or more contiguous acres of land have been required to have a fully implemented water quality plan since 2001.
KAWQP Best Management Practices
 For pasture feeding areas and grazing operations that include streamside access, producers are encouraged to implement BMPs that restrict or limit cattle access to streams and other water bodies.
At a minimum, livestock producers should implement at least one of the BMPs listed in Table 1 where streamside grazing is practiced; however, trapping, controlling, and preventing pollution usually requires more than one BMP, and producers must consider site-specific conditions when choosing and implementing any BMP.
Table 1.
KAWQP streamside grazing BMPs and recommended resources.
Streamside Grazing BMP	Number	Resources for Implementation
 Planned Grazing Systems	Livestock #1	Rotational Grazing 
 Planned Fencing Systems for Intensive Grazing Management 
 Using a Grazing Stick for Pasture Management 
 Proper Grazing Use	Livestock #2	Planned Fencing Systems for Intensive Grazing Management 
 Using a Grazing Stick for Pasture Management 
 Riparian Area Protection	Livestock #3	Riparian Buffers: A Livestock Best Management Practice for Protecting Water
 Planting a Riparian Buffer 
 Shade Options for Grazing Cattle 
 Limiting Access to Streams by Fencing	Livestock #4	Alternative Water Source: Developing Springs for Livestock 
 with Alternative Water Systems, Limited	Stream Crossings for Cattle 
 Access Points, or Stream Crossings	Drinking Water Quality Guidelines for Cattle 
 Nutrient Management	Livestock	Nutrient Management in Kentucky 
 The Agronomics of Manure Use for Crop Production 
 Managing Liquid Dairy Manure 
 Sampling Animal Manure 
 Potential for Livestock and Poultry Manure to Provide the Nutrients Removed
 by Crops and Forages in Kentucky 
Permanent repairs to the tunnels still have to be completed, the final plans pending approval from the U.S.
Bureau of Reclamation.
Dissolving gypsum in irrigation water using a trough filled with rock gypsum in tests at Fresno State College vineyard.
L.
P.
CHRISTENSEN L.
F.
WERENFELS L.
D.
DONEEN C.
E.
HOUSTON
 Irrigation water infiltration tests were conducted on two typical, slowly permeable vineyard soils on the east side of Fresno County.
Furrow water intake was increased by soil applications of gypsum and sulfur and by adding dissolved gypsum in the irrigation water.
These soil treatments were only of temporary benefit and gave no improvement in late summer.
However, a grass culture or sod treatment, once well established, improved water intake during midsummer and latesummer irrigations.
FURROW WATER INFILTRATION RATES IN VINEYARD STUDY 
 TABLE 1.
ANALYSIS OF SOILS IN EXPERIMENT 
 pH	E.C.
x 10	Sodium	Cation	total	Sodium
 Fresno	7.2	0.63	1.52	6.36	24
 Keorney	6.9	0.47	1.33	4.88	27
 TABLE 2.
ANALYSIS OF WELL WATERS
 E C.
x 103	bonate	Bicar-	Sodium	Cation	total	Sodium
 Fresno	0.41	3.45	0.82	4.44	19
 Keorney 0.21	1.49	0.54	1.94	28
 TABLE 3.
ANALYSIS OF WATER SAMPLES TAKEN AT GYPSUM TROUGH OUTLETS 
 filled with rock gypsum broken to walnut size.
Two vineyard trials were conducted in 1964 and one in 1965 to evaluate various wateror soil-amendment and management practices on representative, slowly permeable soils.
Only the amendments were evaluated the first year, but the second-year study involved soil-management practices as well.
Both vineyards were irrigated with well water, using two wide, flat furrows down the rows.
A permanent furrow system was established at Fresno State after the first irrigation.
Annual grasses had become well established in the furrows by July and were mowed as necessary.
At Kearney, cultivation between each irrigation was practiced except for the second measurement.
1964 soil amendment tests
 Water infiltration rates in furrows were measured during three irrigations for each trial.
Measurements were made by setting tube-orifice plates at the top and bottom of a 300-ft irrigation run.
The head loss at each plate was measured with an electric-point gauge developed by B.
L.
Grover, formerly at U.
C., Riverside.
The difference in rate of water flow between the two plates was then calculated as infiltration rate  into furrow surfaces.
Identically designed trials were established on two different soil series.
One was established on a San Joaquin sandy loam soil in the Fresno State College vineyard.
The other was in a vineyard on a Dinuba fine sandy loam soil at the University of California Kearney Horticultural Field Station near Reedley.
Three waterandsoil-amendment treatments in addition to a check were evaluated.
Each treatment was replicated four times.
Treatments included mid-February applications of gypsum  at 2700 lbs per vineyard acre and soil sulfur  at 500 lbs, confined to a 5-ft-wide strip between the vine rows.
The analysis of the trial soils in table 1 indicates neutral pH values and lack of an alkali  problem.
Both irrigation waters  were low in salts and sodium and had moderate bicarbonate levels, especially at Fresno State College.
The analysis of irrigation waters
 In another treatment, gypsum was dissolved in the irrigation water during each irrigation.
This was accomplished by running the water for each furrow through a wooden trough 96 X 8 X 6 inches deep,
 P OOR WATER INTAKE is one of the most serious irrigation management problems in Fresno County's east-side vineyards.
If the problem is not overcome, dry subsoils may develop by midsummer to late summer, and show typical waterstress symptoms of leaf burn as well as premature leaf fall.
Measuring furrow flow with orifice plate and electric point gauge at Kearney Field Station during studies of water penetration in vineyards.
The problem exists most commonly in the soils customarily described as "whiteash soils"  and "red hardpan soils".
Soil-surface sealing, because of poor soil structure, appears to add to the well-known compaction problems in these soils.
Vineyardists employ various measures to help overcome this condition, including winter covercropping, grass culture in furrows, undervine irrigation, and the practices of subsoiling, cultivating between irrigations, and flattening irrigation runs.
Some vineyardists have also reported promising results from use of gypsum and soil sulfur.
The benefits of using gypsum and sulfur in reclaiming alkali soils are well known.
However, field data on the effects of these amendments to the near-neutral pH  east-side soils are still quite limited.
The soils in Fresno County are irrigated with San Joaquin River and Kings River canal water and/or well water-generally low in total salts and sodium, and containing some bicarbonate.
Such characteristics of water may contribute to poor water intake problems, depending upon analysis.
before and after gypsum addition shows considerable variation in the dissolving rate of gypsum.
This was more of a problem at Kearney where the gypsum had not been SO well crushed into smaller sizes.
All three wateror soil-amendment treatments gave temporary improvement in furrow water intake rates.
At Fresno State College this improvement was noted in both the March and June measurements  However, by Sept.
18, the gypsum and sulfur treatments no longer showed benefits.
Results from the sulfur treatment showed considerable improvement in the June measurement.
The delay may be explained by a lag in microbial change of the sulfur to the soluble sulfate form.
Somewhat similar responses to gypsum and soil sulfur were shown in the Kearney measurements  However, it is not known whether the gypsum-inwater treatment could have been of benefit during the last irrigation had more gypsum been dissolved.
The temporaryonly benefit of soil applications might be explained by the eventual leaching, or loss of much of the soil amendment, from the soil surface through a succession of irrigations.
Only the Kearney station vineyard was used in 1965.
Several cultural practices commonly used to improve water infiltration were compared along with gypsum treatments in this test.
The five treatments included gypsum soil application, grass culture, grass culture plus gypsum, Merced rye winter covercrop, and a check.
The grass-culture treatment consisted of annual rye grass planted in the furrow bottoms on March 2 and mowed as needed thereafter.
The rye winter covercrop treatment was planted in November 1964 and diskedunder March 18, 1965.
Results of this trial  also showed benefits from the gypsum applied earlier in the summer.
The reverse was true of the grass, which gave benefit only later in the summer.
The combination treatment was the best throughout the season.
Peter Christensen is Farm Advisor, Fresno County; Lukas F.
Werenfels was Extension Irrigation Technologist; Lloyd D.
Doneen is Professor of Irrigation; and Clyde E.
Houston was Extension Irrigation Technologist and Drainage Engineer, University of California, Davis.
S IX TO SEVEN THOUSAND acres of direct-seeded celery are grown each year in the central coastal districts of California.
Thinning celery requires approximately 50 man-hours per acreroughly 40% of the labor necessary to produce a crop.
Increasing labor costs and uncertainties concerning quality and supply of labor have prompted growers to look for methods to reduce the time required for thinning.
Coated seed appears to possess many attributes which warrant evaluation in mechanized celery production.
The irregularly shaped and extremely small celery seeds  can be covered with a coating of finely divided Bentonite clay and built up into pellets containing a single seed each.
Coating the seed permits the use of precision planting equipment, which results in a more even distribution of seeds and in a reduction of the number of seeds required to plant a given area than is the case with usual planting methods.
The two degrees of coating studied  included: minimum coating , seed coated to a somewhat irregular shape 4/64 to 5/64 inch in diameter, increasing the weight about 10 times; and spherical coating , seeds coated into a spherical shape 6/64 to 7/64 inch in diameter, increasing the weight nearly 40 times.
Tests were made to determine whether the coating process lowers the capacity of
 the seeds to germinate.
In these tests, the coating was removed by placing the seeds on a sieve and washing away the coating with a stream of water.
Both coated and noncoated seeds were germinated on moist filter paper in petri dishes at temperatures fluctuating between 60 and 70F.
The results indicated that the coating process had no harmful effect upon the seeds-and that the significant depression in germination of the sphericalcoated seed  could be attributed to the presence of the clay coating itself.
To determine the effect of seed coating on rate and percentage of emergence, a greenhouse planting was made in soil that had been pasteurized to eliminate soil insects and pathogenic fungi.
The seeds were planted 1/2 inch deep and 1/2 inch apart in the row.
Daily soil temperatures at the seeding depth fluctuated between 58 and 72F.
The percentage of emergence of spherical-coated seeds was significantly lower than that of either noncoated or minimum-coated seeds.
No significant difference was found in percentage of emergence between noncoated and minimum-coated seeds.
Rate of emergence , here given as the mean emergence period, was adversely affected by the two coating treatments.
The mean emergence periods were 18.7 days for noncoated, 21.8 days for minimumcoated, and 22.3 days for spherical-coated seeds.
Three emergence tests, one each in April, May, and June, were conducted in
 Celery seed appearance in tests: A, noncoated; B, minimum-coated; and C, spherical-coated.
Effects on vegetative soybean: Vegetative growth of soybean during drought is diminished.
Drought stressed soybean are often shorter with smaller leaves due to a lack of water, nutrient availability, and nutrient uptake.
Soybean root growth increases during drought conditions because plant carbohydrates are shifted to root growth.
When adequate rainfall or soil moisture returns, vegetative growth will resume until the mid-seeding filling stage.
Under severe drought stress, soybean flowering may occur earlier than normal in an effort to produce seed before premature death.
Runoff Water Management for Animal Production and Environmental Protection
 Karl VanDevender Professor Extension Engineer
 Arkansas Is Our Campus
 With livestock operations, one of the first considerations when addressing production and environmental practices is the collection, storage and utilization of manure.
One aspect that is often overlooked is the impact of runoff water on manure management.
During a rain, the water will do one of several things.
It may evaporate back into the air.
It may infiltrate into the soil.
Or, it may move as surface runoff.
Vegetation and surface depressions may provide temporary storage or retention of the water, but eventually it will evaporate, infiltrate or run off.
Runoff concerns start when the water comes in contact with animal holding and traffic areas.
Typically, due to heavy use, these areas are not vegetated and have manure on top of or mixed into the surface.
Under these conditions, the runoff water can carry nutrients, sediment and microorganisms from the heavy use area into streams and lakes.
This extra loading of nutrients, sediment and microorganisms raises environmental as well as human and animal health concerns.
Runoff water also increases the amount of mud located in cattle and equipment traffic areas.
Excessive mud not only causes traffic problems for cattle and equipment, it also increases the potential for cattle health problems.
In addition, on farms with manure holding ponds and lagoons, runoff water has the potential to greatly increase the volume of
 liquid manure that needs to be stored and land applied.
This will increase the cost of application and shorten the effective storage time.
To understand the factors that affect runoff volume the equation below is helpful.
Runoff Volume =  X Area of Concern
 This equation shows that less rain and a smaller area of concern will reduce the runoff volume.
Increasing infiltration and evaporation will also reduce the amount of runoff.
Unfortunately, it is usually difficult or impossible to control these factors.
Rain and evaporation are weather conditions that cannot be influenced.
Usually, infiltration is also beyond control.
No infiltration occurs when rain falls on roofs and concrete surfaces.
In vegetated areas, the vegetation serves to slow surface water movement, which increases the time for infiltration and evaporation to occur.
Because of the factors that influence runoff, it is difficult to predict volumes.
However, looking at a couple of example situations can help to provide a feel for potential runoff volumes.
The maximum runoff will be generated when infiltration and evaporation are zero.
Assuming they are zero can be a reasonable assumption for such areas as roofs and concrete surfaces.
Under these conditions, a 1-inch rain generates 0.62 gallon of
 runoff water for each horizontal square foot of surface.
This means that in a 1-inch rain, a 25by 100-foot  roof area can generate 1,550 gallons of runoff water.
If you assumed that half the rainwater falling on grass either evaporated or infiltrated, the same 1-inch rain would generate over 13,000 gallons of runoff water per acre or 0.31 gallon per square foot.
Since very little can be done to reduce runoff volumes, the existing runoff must be managed.
The three basic concepts of runoff management are to keep the clean water clean, manage the heavy use areas and treat the runoff water from heavy use areas.
Key Concepts of Runoff Management
 Keep the clean water clean.
Manage heavy use areas.
Treat the runoff water from heavy use areas.
Keeping the Clean Water Clean
 The idea is to prevent clean runoff water from entering heavy use areas or manure storage units.
The clean water that enters these areas can pick up nutrients, sediments and microorganisms.
Avoiding this is accomplished by redirecting the flow of runoff water.
The runoff water that needs to be redirected comes from roofed areas or ground surfaces up-slope from heavy use areas or manure storage units.
Where water does not enter heavy use areas or manure storage units, it is usually not necessary to redirect runoff.
Diverting Roof Runoff Water
 If the runoff is from a roof, there are two options.
The first is to use gutters to direct the runoff water to downspouts.
At each downspout, the water can be either released to flow away from the heavy use area or enter a pipe or drainage channel to flow to an acceptable release point.
Normally, a gutter system is designed for the heaviest 5-minute rain event that is expected to occur about every 10 years.
In Arkansas, this means the northern counties should design for a 0.6-inch rain.
The southern counties should design for a 0.65-inch rain.
When the gutter system is used to prevent roof water from entering manure storage units, a 25-year 5-minute rain event should be used.
In Arkansas, this means the northern counties should design for a 0.65-inch rain.
The southern counties should design for a 0.75-inch rain.
The second option is to use drainage channels under the roof leaves to catch runoff water and direct it around the heavy use area to an acceptable release point.
Drainage channels under the roof leaves should not be used if they will be located within a heavy use area or there is less than a 12-inch roof overhang.
In addition, if blowing rain is a concern, such as with a free stall barn or feed barn, unguttered roof runoff water may contribute to problems inside the buildings.
Drainage channels may be open surface channels or gravel-filled trenches with perforated pipe in the bottom.
All surfaces beneath roof leaves, including drainage channels, should be designed to move the water away from the building and to avoid standing of water.
In general, they should be sloped at a 1 to 5 percent grade away from the building.
All drainage channels should also be protected from erosion by vegetation, gravel or concrete.
Roof runoff control systems will often contain a combination of gutters and drainage channels as well as areas of unmodified drainage where the runoff water does not need to be redirected.
The decision of where to use gutters and drainage channels is affected by owner preferences and site conditions.
Larger roof areas require larger gutters and larger and/or more downspouts.
Also, there are often concerns about snow and ice damage to gutters.
However, the reduction in the amount of water entering premilk holding areas and free stall barns under windy conditions may justify the additional expense.
With proper placement, the potential for snow and ice damage is reduced.
Situations where a heavy use area is under a roof's drip line will typically require either the use of gutters or the moving of the heavy use area.
Proper gutter placement is important to protect against snow and ice damage.
Steeper pitch roofs require less clearance.
Adapted from WQ322, Roof Gutters for Dairy Barns, Department of Agricultural Engineering, University of Missouri-Columbia.
Diverting Ground Surface Runoff Water
 Surface diversions are usually used to redirect the runoff water from up-slope areas.
These diversions catch the runoff water and divert the flow to an acceptable release point.
They should be vegetated to prevent erosion.
In certain situations, gravel-filled trenches with a perforated pipe may be appropriate.
They are sometimes used in situations where it is desirable to redirect the flow of water that occurs beneath the ground surface.
As indicated previously, steps should be taken to prevent erosion and standing water in the diversions.
When designing surface diversions, care should be used to consider not only the flow of water but also vehicle and animal traffic.
Since large volumes of water and significant flow rates are possible, care should be used where the roof and ground runoff water is released to prevent erosion.
Assistance in the design of both roof and surface water diversions is available through local county Cooperative Extension Service and Natural Resources Conservation Service offices.
Managing Heavy Use Areas
 Proper management of a heavy use area starts with the design of the area itself.
Ideally, it should be no larger than necessary to handle the flow of cattle and equipment.
Excessively large areas take land out of other potentially productive uses and increase the volume of rainwater being exposed to the soil/manure mixture of the heavy use area.
However, areas that are too small or poorly laid out will not meet animal traffic and confinement needs.
In addition, the flow of animal and equipment traffic in the area should be considered when the placement of fences and gates is determined.
One of the biggest problems of heavy use areas is getting them to support cattle and equipment traffic during the wet periods of the year.
Reducing the volume of water and the time of exposure to the water helps the heavy use areas stand up to the traffic.
The clean water diversions discussed earlier reduce the amount of water entering the heavy use area.
Proper surface grading of the heavy use area helps to move the water off the area and prevent standing water.
A cross slope of 1/4 inch per foot should be enough slope to ensure drainage without causing excessive erosion.
Avoid steep slopes as they will cause the runoff to form gullies and washes.
In addition, the distance water flows should be kept to a minimum.
In soils where clean water diversions and proper grading will not be sufficient to avoid excessively
 muddy conditions, practices such as gravel , coal ash products or concrete are options.
Remember that the best approach is to address drainage and clean water diversion problems first.
Then, if necessary, consider constructing surfaces to support cattle and equipment traffic.
After a heavy use area is installed, routine management determines the time cattle are in the area and the frequency of manure removal.
With the exception of total confinement areas, the amount of time cattle are on the heavy use area should be kept to a minimum.
This reduces both manure accumulation and the traffic the area is exposed to.
The frequency of scraping depends on many factors.
Heavy use areas with minimal manure accumulations and earthen surfaces may not need much, if any, scraping.
It may be desirable to scrape some concrete surfaces, such as premilk holding areas, more than once a day.
When scraping earthen and graveled areas, care should be taken not to remove soil or gravel, which will affect surface drainage.
Any low spots should be filled to reestablish a uniform grade.
In earthen areas, a 3to 4-inch layer of soil/manure mix will help to seal the surface and prevent infiltration, which helps to protect groundwater.
In addition, this soil/manure layer tends to help reduce the amount of soil erosion.
However, the retention of moisture increases the importance of good surface drainage.
Assistance in the design and maintenance of heavy use areas is available through local county Cooperative Extension Service and Natural Resources Conservation Service offices.
Treating the Heavy Use Area Runoff
 Since there will always be some runoff water leaving heavy use areas, it should be treated to reduce its sediment and nutrient loading.
One option is to catch and store the runoff water for later treatment by land application.
However, the Arkansas Department of Environmental Quality regulates this approach since it is considered a liquid waste system.
The more common approach is to use vegetative filter strips to treat runoff water.
Filter strips are bands of vegetation down-slope of heavy use areas designed to remove sediment and nutrients from runoff water.
Filter strips operate by causing solids to settle out of the runoff water, allowing water to infiltrate into the soil and providing opportunities for the plants and soil to process and use nutrients.
For filter strips to be effective, the water needs to move as a uniform sheet across the filter strip.
Filter strips lose effectiveness when channelized flows occur.
Filter strips are normally vegetated with grasses that are suitable to the site and that will adequately filter runoff.
A filter strip may require some earthwork before seeding.
Often, however, existing pasture areas with well-established forage can serve as the filter strip.
The width, or length of flow, of a filter strip is based primarily on the slope of the land in the strip.
Steeper slopes require wider filter strips.
Recommended Filter Strip Widths
 0 3%	30 ft
 3 8%	50 ft
 Greater than 8%	100 ft
 Up-slope from such landscape
 features as springs, seeps,
 sinkholes, wells and rock outcrops	100 ft
 Adapted from NRCS Conservation Standard Filter Strip 393-.
Filter strips require some management for successful and continued operation.
The objective is to maintain a uniform stand of vegetation and have the runoff flow as a uniform sheet of water across the surface.
Overgrazing and traffic damage to the vegetation needs to be avoided.
Excessive vegetative growth and sediment deposits may also cause channelized flows to occur.
Fertilizer requirements for filter strips may also be different from surrounding areas.
Therefore, it may be necessary to occasionally mow and remove plant material and sediment that has been deposited in the filter strip.
Assistance in the design and maintenance of vegetative filter strips is available through local county Cooperative Extension Service and Natural Resources Conservation Service offices.
The design and routine management of livestock operations should address rainfall runoff as part of their manure management practices.
With proper design and management, the adverse effects of excessively muddy conditions on production can be minimized.
In addition, the water quality impacts are also minimized.
The key concepts to runoff management are to keep the clean water clean, manage the heavy use areas and treat the runoff water from heavy use areas.
Assistance for all three of these concepts is available through local county Cooperative Extension Service and Natural Resources Conservation Service offices.
Selection and Management of Efficient Low Volume Irrigation System
 CONTROLLED DRAINAGE MANAGEMENT GUIDELINES FOR IMPROVING DRAINAGE WATER QUALITY
 Prepared by: Robert Evans, Extension Agricultural Engineering Specialist J.W.
Gilliam, Professor of Soil Science Wayne Skaggs, William Neal Reynolds Professor Department of Biological and Agricultural Engineering
 Published by: North Carolina Cooperative Extension Service Publication Number: AG 443 Last Electronic Revision: June 1996 
 North Carolina farmers grow crops on over 2 million acres of poorly drained soils.
Thesefields represent nearly 40 percent of the state's cropland.
Cropland drainage has long been one of the most important components of land management in the coastal plain and tidewater regions of the state beginning soon after colonization more than 300 years ago.
*
 Many of these artificially drained soils are adjacent to estuaries and freshwater lakes and streams, areas that are environmentally sensitive and ecologically important.
Agricultural runoff has contributed to the decline of water quality in many of the state's surface water systems.
As shown in Figure 1, agricultural production, tourism, recreation, and fishing contribute more than $10 billion to the state's economy and $4 billion to the economy of coastal counties.
Since these important industries must coexist, future agricultural practices must be designed and managed in a way that will protect water quality.
Restrictions on land development and drainage imposed by the 1985 Food Security Act have limited the possibility of expanding farming operations by clearing and draining land.
Instead, farmers are using more intensive management practices to increase yields and improve production efficiency on land already in cultivation.
*Numbers in parantheses refer to the list of references at the end of this publication.
Figure 1.
Contribution of agriculture, recreation, tourism, and marine fishing to the economy of North Carolina.
Source: MC.
Agricultural Statistics, USDA, 1988; North Carolina Department of Natural Resources, Division of Parks and Recreation; NC.
Department of Commerce, Division of Travel and Tourism; and NC.
Division of Marine Fisheries.
The hydrologic, biological, and chemical cycles in coastal rivers and estuaries are extremely complex.
Although fresh water and nutrients are essential components of these systems , they may become unbalanced as a result of human activities.
These activities include
 damming of rivers and streams;
 discharge of municipal and industrial waste directly into rivers, streams, and estuaries;
 urban and rural development, resulting in more intense stormwater runoff that may carry nutrients and suspended solids from lawns, roads, and other paved areas;
 artificial drainage to promote agriculture and forestry;
 introduction of nutrients from agricultural fertilization and from livestock and domestic waste:
 alteration or conversion of wetlands to other uses such as agriculture, rural and urban development, recreation, and tourism.
The environmental impacts of these activities vary with the status and circulation of the receiving water.
For example, juvenile marine organisms depend on the headwaters of the estuarine system to provide shelter and food.
These areas also provide natural outlets for rural and urban stormwater drains and agricultural drainage systems.
Dilution of seawater by fresh water creates the medium salinity waters that produce most of the economically important species of fish and shellfish.
Some studies have shown, however, that high outflow rates associated with intensive artificial drainage further reduce the salinity of head-waters , sometimes resulting in stress, disease, or depressed production of certain pelagic species .
Other more intensive studies directed specifically at evaluating hydrodynamic effects showed that freshwater out-flow from landbased activities such as artificial drainage have little influence on estuarine salinity.
Rather, salinity fluctuations were dominated by natural circulation patterns caused by tides, wind, and rainfall.
Recently, freshwater outflow was found to stimulate growth of some demersal species .
Nitrogen and phosphorus levels in many tidewater rivers, streams, and estuaries have become high enough that a very delicate balance exists between undesirable species such as blue-green algae  and other desirable flora.
Typically, water bodies receiving excessive nutrient loads are most susceptible to blooms of blue-green algae.
These algae are very prolific when excessive levels of nitrogen, phosphorus, or both are present.
Blue-green algal dominance may alter the aquatic food chains.
The algae blooms are un-sightly  and may pose problems  to recreational users of the water.
They can also consume much of the dissolved oxygen, leaving the water anoxic.
This problem is more acute when the waters are stagnant or have slow circulation.
Anoxic conditions are stressful and sometimes fatal to fish, which depend on oxygen to survive
 .
When fish come to the surface and gasp for air, it often indicates anoxic conditions.
Figure 2.
Blue-green algae mat on surface of Perquimans River near Hertford, North Carolina, July, 1985.
Figure 3.
A fish kill resulting from anoxic conditions  following decomposition of blue-green algae.
Agricultural cropland is a major nonpoint source of nitrogen and phosphorus contributing to the nutrient enrichment of tidewater rivers and estuaries in North Carolina.
Best Management Practices must be adopted to reduce the amount of nitrogen and phosphorus discharged to sensitive surface waters.
Reductions of at least 30 percent in nitrogen and 50 percent in phosphorus have been recommended to minimize blue-green algae blooms in the Lower Neuse River during the summer months.
Agricultural Activities Influencing Water Quality
 Many agricultural practices contribute to environmental problems.
These include tillage practices, fertilizer and pesticide application methods and rates, and drainage and irrigation practices.
For example, typical North Carolina nitrogen fertilization rates for corn have been between 150 and 200 pounds of nitrogen per acre annually.
Although these rates were based on a potential grain yield of 175 to 200 bushels per acre per year, annual corn yields more typically average less than 100 bushels per acre because of soil and climatic conditions.
Therefore, nitrogen fertilization rates exceed yield expectations in many years, resulting in the application of excess nitrogen that is not removed by the crop.
This nitrogen is carried from the field and may cause environmental problems.
Clearly, one very important Best Management Practice is to apply fertilizers at rates consistent with sustainable yields rather than potential yields.
Although several Best Management Practices can be employed to minimize the environmental impacts of crop production, this publication focuses on strategies related to water table management.
Although excessive soil water is often a problem on poorly drained soils, weather conditions are extremely variable, and crops sometimes suffer from drought, which can also reduce yield.
Intensive drainage systems are necessary to ensure access to many fields during wet periods.
But past drainage practices have not always encouraged water conservation.
As a result, these systems have tended to overdrain many areas and increase drought damage during dry growing seasons.
These problems are resulting in a transition from conventional drainage methods to water table management systems.
The latter provide drainage during wet periods but also include control structures to manage the water level at the drainage outlet, making it possible to reduce overdrainage.
In some cases, the system can be used to provide subirrigation during dry periods.
Collectively, these management practices are referred to as water table management  and include any combination of management practices such as surface drainage, subsurface drainage, controlled drainage, or subirrigationthat influence the level of the shallow water table.
Research on the use of subirrigation and controlled drainage to provide water for crops and to meet drainage needs has been conducted in North Carolina since the early 1970s.
Using results of this research, methods and guidelines for designing drainage systems for different soils, crops, and weather conditions have been developed.
Controlled Drainage: A Best Management Practice
 Studies have shown that water table management systems can improve drainage water quality when properly designed and carefully managed.
On the basis of these studies, water table management-in particular, controlled drainage-has been designated a Best Management Practice  for soils with improved drainage.
It therefore qualifies for cost-share assistance under the North Carolina Agricultural Cost Share Program.
As of July 1, 1989, more than 2,500 control structures have been installed to provide controlled drainage on approximately 150,000 acres in eastern North Carolina.
The North Carolina Agricultural Cost Share Program has helped bear the cost of approximately 1,800 of these water control structures.
An additional 1 million acres of cropland in North Carolina are suited for controlled drainage.
This acreage includes most of the cropland in the lower coastal plain and tidewater regions.
Unlike many BMPs, controlled drainage benefits both production and water quality.
The production benefits make it a popular practice with farmers, while the water quality benefits help meet environmental goals.
The North Carolina Agricultural Cost Share Program is not designed to benefit agricultural production but rather to hasten the adoption of BMPs to promote soil and water conservation, provide habitat for wildlife, and protect or restore the environment through improved water quality.
The NCACSP seeks these environmental benefits by providing financial incentives to those who implement controlled drainage systems.
The implementation of controlled drainage, or any other management practice, does not by itself satisfy the objectives of the North Carolina Agricultural Cost Share Program.
The program's purposes are met only after the environmental concerns or problems for a given site have been taken into account and incorporated in a management strategy for that site.
For water table management or controlled drainage practices, this means taking into account any water quality problems of the receiving fresh waters or estuaries and developing management strategies that will minimize the adverse effects of drainage water flowing from agricultural lands.
To do this successfully, it is necessary to know  about any problems in the receiving waters,  the characteristics of the drainage water and how specific management strategies might influence these characteristics, and  the subsequent impact on receiving waters.
Figure 4.
Typical hydrologic cycle for eastern North Carolina.
East of I-95  average annual rainfall ranges from 46 to 56 inches, depending on location.
Actual evaporation ranges from 34 to 36 inches annually.
Therefore, the "excess" rainfall, most of which returns to surface waters, ranges from 12 to 20 inches per year.
Influence of Water Table Management on Drainage Water Quality
 Precipitation and Drainage Outflow
 Rainfall in eastern North Carolina averages from 46 to 56 inches annually, depending on location.
Potential evapotranspiration ranges from 38 to 41 inches, although actual evapotranspiration is typically 34 to 36 inches annually because short-term droughts often occur.
Therefore, excess rainfall  ranges from 12 to 20 inches annually.
A small amount of this excess  percolates through the soil to recharge the deep groundwater aquifer systems.
Most of the excess rainfall, however, eventually returns to the ocean through the surface water system of streams, rivers, estuaries, and sounds.
The rate at which rainfall leaves a site depends on rainfall intensity, topography, infiltration, soil permeability, vegetative cover, the distance from a drainage outlet, and the location of restrictive horizons.
Intense rainstorms often result in surface runoff, whereas rainfall from milder storms usually infiltrates the soil.
Much of eastern North Carolina is underlain by marine clay sediments at depths less than 30 feet from the soil surface.
These sediments restrict the rate of deep
 groundwater recharge.
As a result, excess rainfall that infiltrates the soil moves laterally above them as shallow groundwater flow until it eventually discharges to the surface water system.
This process of rain, surface runoff, infiltration, evaporation, shallow groundwater flow, and deep groundwater recharge is referred to as the hydrologic cycle.
Figure 4 illustrates the hydrologic cycle for eastern North Carolina.
The total annual volume of outflow from a field is about the same for sites that drain well naturally, typical of the upper coastal plain and piedmont, and for those that do not, typical of the lower coastal plain and tidewater regions.
The main difference is in the rate of outflow and the pathway by which excess water leaves the site.
On well-drained sites, outflow occurs soon after rainfall and the flow duration is relatively short, usually a few days.
On poorly drained sites, the outflow is more gradual but may last several weeks.
Artificial drainage tends to convert a poorly drained site into a welldrained site.
Characteristics of Drainage Water
 Excess rainfall leaves a field either as surface drainage  or as subsurface drainage.
This difference is important from a water quality standpoint because the characteristics of the drainage waters differ.
In practice, it is usually difficult to differentiate between surface and subsurface drainage because the outflow in drainage ditches or canals is a combination of the two.
For the remaining discussion, drainage systems in which the majority of outflow has drained through the soil profile are referred to as subsurface drainage systems.
Systems where surface runoff is the primary drainage mechanism are called surface drainage systems.
The following paragraphs summarize the characteristics of drainage water based on approximately 125 site-years of data collected at 14 locations in eastern North Carolina.
Agricultural development using artificial drainage increases total annual outflow at the field edge by 5 to 10 percent , depending on rainfall.
On the average, subsurface drainage increases annual outflow slightly compared to surface drainage, but the increase is usually less than 5 percent.
Peak outflow rates at the field edge are lower by a factor of 1 to 4 , depending on the storm intensity, with subsurface drainage systems than with surface drainage systems.
Drainage waters from surface drainage systems contain higher concentrations of organic nitrogen, phosphorus, and sediment than those from subsurface drainage systems.
Outflow from subsurface drainage systems contains higher concentrations of nitrates than that from surface drainage systems.
Both systems result in increased nutrient concentrations in drainage outflows compared to undeveloped sites , a result of fertilizer use on the developed sites.
Controlled drainage, when managed all year, reduces total outflow by approximately 30 percent  compared to uncontrolled systems, although outflows vary widely depending on soil type, rainfall, type of drainage system and management intensity.
For example, control only during the growing season typically reduces outflow by less than 15 percent.
The effect of controlled drainage on peak outflow rates varies seasonally.
Drainage control reduces peak outflow
 rates during dry periods  but may increase peak outflow rates during wet periods , depending on the control strategy.
Drainage control has little net effect on total nitrogen and phosphorus concentrations in drainage outflow.
Controlled drainage may reduce nitrate-nitrogen concentrations in drainage outflow by up to 20 percent, but total Kjeldahl nitrogen  concentrations are somewhat increased.
Controlled drainage tends to decrease phosphorus concentrations on predominately surface systems but has the opposite effect on predominately subsurface systems.
Seasonal variations may also occur, depending on rainfall, soil type, and the relative contribution of surface or subsurface drainage to total outflow.
Controlled drainage reduces nitrogen and phosphorus transport at the field edge , primarily because of the reduction in outflow volume.
In 14 field studies, drainage control reduced the annual transport of total nitrogen  at the field edge by 9 pounds per acre, or 45 percent , and total phosphorus by 0.11 pound per acre, or 35 percent.
Again, the reductions at individual sites were influenced by rainfall, soil type, type of drainage system, and management intensity.
Figure 5.
Average annual outflows measured from 14 sites in eastetn North Carolina.
The values shown represent approximately 125 site-years of data.
Figure 6.
Average annual nitrogen tranaport  in drainage outflow as measureci at the field edge for 14 soils and sites.
Figure 7.
Average annual total phosphorus transport in drainage outflow as measured at the field edge for 12 soils and sites.
Values shown are for mineral soils only.
Two sites with organic soils were not included.
Figure 8.
Algae bloom in drainage ditch with controlled drainage.
Controlled drainage helps keep agricultural nutrients within the field boundaries and out of sensitive receiving waters.
Effects of Artificial Drainage on Receiving Waters
 Agricultural development slightly increases the total volume of flow reaching the receiving surface water system in coastal areas.
Drainage reduces the time that excess rainfall remains on site before it reaches the receiving system, resulting in higher outflow rates  than from undeveloped sites.
However, in modeling studies  peak outflow rates reaching receiving streams were lower than peak outflow rates at the field edge.
The impact on the receiving waters of these hydrologic changes is still unclear, but it almost certainly depends on the drainage network and circulation of the receiving water.
From a water quality standpoint, the most dramatic effect of agricultural development is a significant increase in nutrient concentrations in drainage water and nutrient transport from fields.
This increase is not a direct consequence of drainage activities; rather, it results from fertilization and other production activities made possible by improved drainage.
The net effect of fertilization combined with artificial drainage is an increase in nitrogen and phosphorus reaching coastal waters.
However, the amounts reaching receiving waters are less than the amounts leaving the field edge  because some of the nitrogen and phosphorus is assimilated and removed en route by natural mechanisms.
Any management strategy that can help keep nutrients on site and prevent them from reaching sensitive receiving surface waters is a positive step.
However, to be effective these strategies must
 reduce nitrogen by 30 to 40 percent and phosphorus at least this much.
Smaller reductions may not adequately improve water quality.
The transport of nitrogen and phosphorus from artificially drained fields can be minimized by applying fertilizers at a rate consistent with sustainable yields, selecting the appropriate water management system , and properly managing that system.
Management Considerations and Guidelines
 The successful management of controlled drainage systems rests on two important objectives.
The first is achieving optimum production efficiency ; the second is attaining maximum water quality benefits.
In selecting the best management strategy from the standpoint of water quality, the characteristics of the receiving surface waters must be considered.
For coastal rivers and streams, the primary concern is eutrophication.
The management strategy should therefore effectively reduce the transport of nitrogen and phosphorus in drainage water.
The condition of the receiving waters will determine whether it is more important to reduce nitrogen or phosphorus, or whether it is necessary to reduce both.
In estuaries, nutrients and freshwater inflow  are the primary concerns.
The question most frequently asked by farmers, yet the one most difficult to answer is: At what depth should the water table be controlled?
In humid regions, there is no "optimum depth because the water table may fluctuate several inches from day to day in response to such variables as rainfall, evapotranspiration, and drainage.
Williamson and Kriz  report that a wide range of water table depths  will result in optimum yields for many crops, depending on soil type, profile layers and their hydraulic properties, weather conditions, type of crop, crop development, and rooting depth.
The starting point recommended for the sandy loam soils of North Carolina is 2 feet.
Most crops can readily tolerate a 6-inch increase or decrease in the water table.
Although not well documented, experience has shown that shortterm fluctuations in the water table will not reduce the yield on most soils provided that the water table depth does not undergo long periods  at a depth less than 1 foot or greater than 3 feet.
Information in earlier sections suggests that total drainage outflow could be decreased  if the control elevation is raised to the soil surface.
Since nutrient transport has been shown to be nearly proportional to drainage outflow, minimizing outflow would minimize the potential transport of fertilizer nutrients.
In addition, very high water table elevations during the growing season may increase the potential loss of nitrogen by denitrification , thus reducing the nitrate levels in drainage outflow.
While this situation might be desirable from a water quality standpoint, it would not be desirable for crop production.
Thus, some compromise in potential water quality benefits is necessary to maintain productivity, although the compromise for water quality is not nearly as severe as might be expected.
Nitrate concentrations in drainage water could be reduced by keeping the water elevation as high as possible in the outlet ditch and subsequently in the field.
However, doing SO would increase the transport of phosphorus by increasing the proportion of surface runoff in total flow.
Although total outflow would be reduced , there would be an increase in peak flows of shorter duration , which would be likely to cause salinity fluctuations near primary nursery areas.
Furthermore, a shallow field water table would restrict root growth and development , thereby reducing evapotranspiration  and nutrient uptake, leading in turn to increased losses in drainage water.
Thus, most water table management strategies aimed at improving production on cropland also have a positive effect on drainage water quality.
The primary difference between the two management objectives is that management during the nongrowing season is also beneficial for water quality.
Another important consideration involving water table management, production, and water quality is trafficability, which is essential for efficient production.
Farmers may severely impair the production potential of their fields by trying to till the soil when it is too wet.
With improved drainage, tillage can begin sooner after rainfall.
For example, the wet spring of 1989 presented serious trafficability problems for many North Carolina farmers.
Because of poor trafficability, less than 50 percent of the acreage planned for corn was actually planted.
However, most fields with good artificial drainage were planted on time.
In some cases, farmers have attempted to resume tillage operations too soon after rains stop.
In doing so, they may damage the soil structure and promote the development of tillage pans , thereby increasing surface runoff and reducing infiltration, root development, and evapotranspiration.
These effects are undesirable for crop production and also adversely affect drainage water quality.
This problem occurs most frequently on soils with a clayey subsoil and a shallow sandy loam or loamy sand surface horizon less than 2 feet thick.
The problem may be compounded by controlled drainage if farmers are reluctant to lower the control elevation.
Many times this problem is not apparent during tillage because there is no immediate trafficability problem, particularly with highflotation equipment.
The interaction between water table management, trafficability, and the development of tillage pans has not been studied extensively.
Farmers in North Carolina have not experienced any apparent trafficability problems when the water table was at least 3 feet deep.
Based on this information, farmers have been encouraged to lower the water control elevation to at least 3 feet deep two days or more before beginning tillage operations.
In some cases, the soil can bear traffic when the water table is about 2 feet deep.
However, the effect on the development of tillage pans or impairment of soil structure is not known.
Controlled drainage in North Carolina has predominantly been practiced with a crop rotation of corn, wheat, and soybeans, although increasing acreages of potatoes, peanuts, and vegetable crops are being included.
Table 1 summarizes a recommended management strategy for a two-year rotation of corn, soybeans, and wheat; this strategy is designed to improve both production and drainage water quality.
The values shown are weir elevations of the control structure relative to average soil surface elevations.
Water table levels in the field may be considerably different from the weir elevation,
 depending on whether the system is in a drainage or recharge cycle; however, the values shown are also the average target elevations of the water table in the field.
Table 1.
General Water Table Management Guidelines to Promote Water Quality and Optimum Crop Yields for a Two-Year Rotation of Corn-Wheat-Soybeans
 Most of the control elevation adjustments shown in Table 1 are related to trafficability and seasonal fluctuations in rainfall.
For example, during a wet spring , the weir elevation should be approximately 1 foot lower than the values shown to improve trafficability; increase potential storage for infiltration; and reduce the potential for surface runoff, sediment and phosphorus transport, and higher peak outflow rates.
During summer months, evapotranspiration will usually cause the water table in the field to decline to an elevation considerably below that of the weir unless water is added to the system by subirrigation.
Intense summer thunderstorms sometimes exceed the infiltration rate of the soil, resulting in loss of much-needed water by surface runoff.
Under these circumstances, the weir elevation can be raised temporarily to retain this water in the field ditches, from which it will then move back into the field by subsurface flow.
However, if the water level in the field ditches has not receded to at least 1 foot within 24 hours, lower the weir elevation to the suggested levels shown in Table 1.
To prevent serious crop damage from heavy rainfall, do not raise weirs in the outlet ditch above 1 foot and leave them unattended for more than 24 hours during the growing season.
When adjusting the weir level to remove excess water, never lower it more than 6 inches within a 12-hour period because the ditch banks will be saturated and may be unstable.
Lowering the water level too quickly may result in sloughing and erosion of the banks.
Also, lowering the weir in small increments minimizes peak outflow rates.
The primary benefit of controlled drainage in lands that discharge to freshwater rivers and streams is a reduction of total outflow and nutrient loading.
These goals can be accomplished by setting the weir at a specified level and making minor adjustments to accommodate production requirements, as shown in Table 1.
Without attentive management, the potential production and water quality benefits of drainage control will not be realized.
Controlled drainage and subirrigation systems are normally designed with closer drain spacing's than conventional drainage systems to provide the drainage capacity needed for trafficability and crop protection when the water table is elevated.
As a result, drainage outflow rates and nutrient transport can be significantly greater than those from conventional systems if the system is not properly monitored.
As discussed earlier, operating a controlled drainage system with a constant weir elevation will reduce outflow rates during recharge periods but will sometimes increase outflow rates during discharge periods.
Thus, if drainage waters are discharged near estuarine areas, the weir elevation must be more intensively managed if peak outflow rates are to be reduced during the critical spring period.
All water table management systems function primarily in the drainage mode during the spring when water table elevations are high and rainfall exceeds evaporation.
Peak outflow rates are usually higher during this period because of the higher water table elevations resulting from controlled drainage.
To
 reduce peak outflow rates and minimize surface runoff by draining the soil between rains, set the weir elevation at or near the soil surface when rainfall is anticipated or forecast.
After the rainfall and as soon as all surface water has infltrated, lower the weir elevation gradually  to its lowest possible elevation or until the next rainfall.
This strategy will allow the soil profile to drain gradually but uniformly and will also provide soil storage capacity in preparation for the next rainfall.
Management at this level of intensity is necessary from late February to May.
During the remainder of the year, the procedures outlined in Table 1 can be followed.
The potential for reducing peak outflow rates by means of this intensive management strategy is not known, but it is believed that outflow rates at the field edge can be reduced to approximately one-half of those for conventional control strategies.
The major disadvantage is the greater attention that must be given to managing the system, especially during the nongrowing season.
The water table elevation in the field may be considerably different from the water level in the outlet ditches or the weir elevation.
From the standpoint of crop production, the water table level in the field is the important consideration.
Intensive management of these systems is required for both production and water quality because many of the management indicators are hidden from view and the response to weir adjustments is not usually immediate.
The response time for water table fluctuations in the field may be several days longer than for similar fluctuations in the outlet ditch.
For example, during the summer the water table in the field sometimes drops below 5 feet.
At this depth, most soils in the tidewater region can store 2 to 4 inches of rainfall.
Yet, as discussed previously, a 2-inch intense thunderstorm may result in surface runoff and outflow.
Based on outflow at the control structure, one would assume that the soil was saturated.
However, after soil moisture redistribution, the water table may rise only to 3 feet, which in many soils is not high enough to supply the crop's water needs.
Thus observation wells that allow the level of the field water table to be observed are essential for proper system management.
Recommendations for the construction, location, and installation of observation wells have been reported, as have suggestions for monitoring frequency.
Be a Steward of Your Soil and Water Resources
 Although agricultural activities have undoubtedly contributed to coastal water problems, they are not the only source of these problems.
Society has been slow to recognize that freshwater and estuarine ecosystems have a limited capacity to absorb waste products produced by human activities.
Likewise, more efficient harvesting methods, especially the non-selective methods practiced over the past two decades, have recognized the production and self-stocking capacity of the estuarine system.
The problems that now exist in coastal waters did not develop overnight; they are the cumulative effects of man's activities over many years.
For example, although nutrient levels in the Chowan River reached levels conducive to blue-green algae blooms by the mid-1950s , the first significant nuisance bloom did not occur until 1972, nearly 20 years later.
Similarly, coastal water problems cannot be corrected overnight.
Nutrient-enriched sediment can now be found at the bottom of many streams, rivers, and estuaries , resulting from many decades of agricultural, municipal, and industrial discharges.
As a consequence, it will take coastal waters several years to cleanse themselves through natural biological, chemical, and flushing processes.
Implementing Best Management Practices on farms may not immediately produce visible improvement in the coastal environment, but it will begin to reverse the damage.
The first step is to reduce inputs SO that the receiving systems can beg in to cleanse themselves.
By integrating good water management with other Best Management Practices, such as reducing fertilization rates to the minimum levels needed for reliable yields, we may be able to achieve drainage water quality similar to that of undeveloped sites.
Equally important, attaining the target yields for which fertilizer rates are chosen also requires proper water management.
Agriculture's harmful impacts on the coastal water environment can be significantly reduced, but only when all landowners and producers exercise stewardship of land and water resources.
Thus far, Best Management Practices for soil and water conservation and environmental protection have been implemented on a voluntary basis, supported by incentive programs such as the North Carolina Agricultural Cost Share Program.
However, with the passage of the swampbuster and sodbuster provisions of the 1985 Farm Bill, Congress demonstrated that it is not deaf to continuing pleas to protect the environment through regulations.
Farmers still have the opportunity to implement practices such as controlled drainage voluntarily.
But without conscientious attention to such practices, future implementation may become mandatory and financial incentives may be removed.
If water quality is to be improved, water control structures must be managed throughout the year, not just during the growing season.
This means raising the weir level to within 12 to 18 inches of the soil surface after the crop has been harvested instead of leaving the flashboards lying on the ditch bank over the winter.
Strategies for water table management are complex.
To ensure maximum production and water quality benefits from controlled drainage, seek professional advice.
Staff members of the North Carolina Agricultural Extension Service and the Soil Conservation Service in each county have been trained in water management and can recommend strategies for efficient operation.
Irrigation: Inspecting and Correcting Turf Irrigation System Problems
 By C.
Swift, Kurt Jones Revised 10/05/2021
 The following can be accomplished when the water is first turned on at the beginning of the irrigation season.
Examine each irrigation sprinkler to determine if:
 Are any pop-up spray heads, impact sprinkler or rotor sprinkler, nozzles, or sprinkler bodies broken?
These need to be replaced with the same size and manufacturer parts.
Are sprinkler filters clean?
Replace missing filters.
Is the sprinkler head above or below grade?
See level sprinkler heads with the top of the lawn.
Use a bulls-eye level to identify tilted sprinkler heads .
Adjust tilted sprinkler heads by removing soil from the high side of the sprinkler body with a curved garden spade.
Adjust the sprinkler body to the level position  and back-fill the void around the sprinkler body to the top of the lawn.
On sloping lawns, the level bubble should be on the up-slope side of the sprinkler.
Sometimes the sprinkler bodies are tilted because a large root is pressing against the body.
A solution is to dig the hole around the sprinkler a little bigger and use a dry-wall saw to cut the root on both sides of the sprinkler body.
Back-fill the hole with the soil that was removed and realign the sprinkler.
Sprinkler heads that are too low do not distribute the water properly as the water is deflected.
All sprinkler riser stems should be at least 4 inches or greater in length.
Sprinkler heads that are too high may be damaged when mowing.
Sprinkler heads that are too high or too low are a tripping hazard.
In order to lift or lower the sprinkler head, you may need to adjust the swing pipe or use a different length nipple extension.
Level the sprinkler body and back-fill with sand.
Remove the nozzle and flush the sprinkler head.
Is the top of the irrigation sprinkler head parallel with the slope of the lawn ?
Are the bodies of impact sprinklers filled with debris?
Debris prevents the inner unit from extending to its full height and restricts the movement of the sprinkler unit.
Removing the inner workings and cleaning out the body and the filter may be required.
A specialized key is available from irrigation supply companies to remove the inner workings of impact sprinkler heads.
Proper maintenance of the irrigation system is critical to ensure uniform application of water in turf areas.
Irrigation sprinkler heads that tilt, are below grade, plugged, or operate at the wrong pressure, etc.
affect the application of irrigation water.
*C.
Swift, former Colorado State University Extension horticulture agent, Tri River Area, Grand Junction, CO., R.D Khalsa irrigation designer, Department of Interior, Bureau of Reclamation.
Photos provided by C.E.
Swift and A.
Blessinger, certified landscape irrigation auditors.
**Kurt Jones, Colorado State University Extension agent, natural resources and agriculture, Chaffee County.
Revised 12/20.
Figure 1 : Types of Irrigation Sprinkler Heads.
Left: Pop-up Spray Head showing the riser stem.
Center Impact Sprinkler Head with maintenance key.
Right: Rotor Sprinkler Head showing the riser stem.
Is the spacing of the sprinklers appropriate for the sprinkler head?
The proper spacing is critical to ensure uniform coverage of the irrigated area.
Using graph paper, sketch a map of the lawn area.
Turn each sprinkler zone on and flag each sprinkler head.
Turn the water off and measure the distance between each sprinkler and log it on the lawn sketch.
The manufacturer's website provides specifications to include appropriate spacing on each of their spray heads or nozzles.
See links below.
Irrigation contractors sometimes take shortcuts when installing systems, increasing the distance between sprinkler heads to reduce their cost by reducing the number of sprinkler heads per zone.
If there is a large variation in sprinkler spacin there are two options.
Either move the sprinklers to improve the spacing or change the sprinkler nozzle size to improve the application uniformity.
Are all the sprinklers on the same zone of the same type and manufacture?
Rotor, impact and spray heads apply different amounts of water per area.
When different
 sprinkler types are on the same zone different amounts of water will be applied resulting in some areas receiving more water than other areas.
The application rate may range from 0.4 inches per hour of water to over 2.0 inches per hour depending on the sprinkler type spacing and nozzle.
If there is a large variation in sprinkler spacing; there are two options.
Either move the sprinklers to improve the spacing or change the sprinkler nozzle size to improve the application uniformity.
Are all the sprinklers on the same zone of the same type and manufacture?
Rotor, impact and spray heads apply different amounts of water per area.
When different
 sprinkler types are on the same zone different amounts of water will be applied resulting in some areas receiving more water than other areas.
The application rate may range from 0.4 inches per hour of water to over 2.0 inches per hour depending on the sprinkler type spacing and nozzle.
Check impact and rotor sprinklers with interchangeable nozzles to ensure they have the proper nozzle.
Impact sprinklers are typically sold with one nozzle color.
These are color coded to identify the amount of water they apply.
Rotor sprinklers are sold with a nozzle tree with all of the nozzle sizes.
The installer must select the proper nozzle for the application.
If two sprinklers have the same nozzle color, and one sprinkler covers 90 degrees, it applies four times the amount of water as the sprinkler that waters 360 degrees.
Replace nozzles to balance the application rate as necessary.
Figure 2: Broken Sprinkler Head
 Figure 3: Sprinkler Head is too high and leaking
 Figure 4: Bulls-eye level on top of a pop-up Sprinkler head
 Figure 5: Tilted sprinkler head.
Figure 7: Swing pipe and nipple extension
 Are nozzles or spray heads damaged?
Are valve boxes too high or too low ?
Too high is a tripping hazard.
Three and 6-inch extension units are available for boxes that are too low.
The high valve box may need to be dug up and reset.
Turn the zone/station on and check the following.
Are the sprinklers applying a uniform pattern of water ?
If not, the nozzles or filter could be plugged.
Nozzles for pop-up sprinklers should have a filter located under the nozzle.
Remove and clean or replace the nozzle and/or filter.
Are there cracks or leaks in each sprinkler head?
Cracked sprinkler heads are often due to improper winterizing of the system or lawn-mower blight.
Replace cracked sprinkler heads.
Do the caps on top of pop-up spray heads leak?
Tighten the cap by hand, or replace the cap and internal parts if necessary.
Figure 6: Water deflected due to the sprinkler
 Do the sprinkler heads at the bottom of a slope continue to drain when the system is turned off?
Replace draining sprinkler heads with check valves or seal-a-matic  sprinkler heads.
If the problem is a check valve or SAM body, unscrew the cap and remove the inner mechanism to determine if the rubber ring or gasket is missing.
If missing, replace the gasket or internal parts of the sprinkler.
Figure 10: Low valve box
 Look for breaks in the pipe.
This will be evident by extremely spongy and/or wet spots, or high water bills.
The turf can even be forced up by the leak creating a bubble of turf.
This is often due to improper winterization.
Always connect the sprinkler head using the bottom inlet not the inlet on the side of the body.
Another way to determine if there is a leak is to count up the nozzles in a zone and determine what the zone flow rate should be.
Turn the zone on and time the water meter to see if the actual flow is close to the calculated flow.
You may need to correct the arc and radius of throw of the water pattern to ensure proper coverage.
Except for sprinkler heads/nozzle providing 360 degrees  of coverage, most heads/nozzles need to be adjusted by lining up the left side of the arc with the left side of the area to be irrigated.
Some brands of rotary sprinkler heads adjust from the left and others adjust from the right.
Rotary and popup spray heads have a ratchet assembly that permits the riser stem to be twisted.
Twist clockwise to avoid screwing the sprinkler body off the barbed elbow or riser nipple.
Some nozzles have a flat spot or mark as the left edge indicator to make it easier to set the left edge.
Once the left side of the water pattern has been adjusted, the sprinkler head or nozzle will most likely need to be adjusted to cover the remaining area.
Figure 8: This sprinkler head is not parallel to the slope
 Figure 9: The inner workings of an impact sprinkler head.
Note filter at the bottom
 Arcthe degrees of water coverage.
i.e.
90 degrees, 180 degrees, 360 degrees etc.
Matched Precipitation Rate  nozzles the precipitation rate is the same regardless of the watering arc and radius of throw.
Nozzle the final orifice that controls the characteristics of the flow of water as it exists the sprinkler.
Precipitation rate the volume of water applied in a specific area, during a specific amount of time.
Radius of throw the distance from the sprinkler head to the furthest point of water application.
Sprinkler Body the casing in which the irrigation mechanism is enclosed.
Riser stem the plastic or metal tube that extends above the sprinkler body where the nozzle is attached.
Stream rotor multiple streams of water rotate around the sprinkler, one stream following the other.
With stream rotor nozzles, the right side of the arc can be adjusted by turning a collar on the nozzle.
With rotary sprinkler heads a special tool may be required to adjust the arc.
Pop-up spray nozzles come in different degrees of arc; 90 degrees, 180 degrees, 360 degrees, etc.
Ensure the nozzles used are 'matched precipitation rate  nozzles.' Variable and adjustable nozzles can be adjusted to cover a greater arc but may not be MPR nozzles.
Impact sprinklers have two wire clips on the riser stem just below the nozzle.
Squeeze the clips and reset them to cover the desired arc.
Some 360-degree rotors and impact sprinklers are non-reversing.
Once the arc is set, adjust the radius.
Rotary and impact sprinkler heads have a variety of nozzle sizes and trajectory angles that can be used to change the flow and radius of throw.
If that is unsatisfactory, sprinkler heads have a screw that protrudes into the stream of water emitted from the nozzle.
Adjusting the screw changes the radius of throw.
The screw on the top of the spray nozzle  is used to change the radius of throw.
When adjusting the screw to increase the radius of throw to the proper distance, the nozzle size or type may need to be changed.
Figure 12: Gaskets in place.
Figure 13: Gasket Missing
 In some cases, a pinched or plugged pipe results in inadequate water at one or more sprinkler heads.
This can be checked by using a pressure gauge..
If the pressure at the sprinkler head is too low, reduce the nozzle size  or change spray nozzles to stream rotor nozzles.
This may solve the problem , but this will reduce the radius of throw on rotors and impact sprinklers.
Too high a pressure results in misting.
Install a pressure regulator on the zone valve or at the back-flow pressure device and adjust the pressure.
These are available from your irrigation
 supply store.
Trouble Shooting the system hydraulics
 A good tool for measuring sprinkler pressure is a 2 1/2 -inch, liquid filled, 100 psi pressure gauge.
Simple pressure testing units are shown in Figures 14 and 15.
An optional method of setting up the pressure gauge is provided in.
Add a 2 foot by 1/4-inch air hose, with an air chuck  on the opposite end from the pressure gauge.
The attachment for a pop-up sprinkler is a specialized tee that threads between the top of the riser stem and the spray nozzle.
A 1/4 -inch Schrader valve is screwed into the leg of the tee.
The air chuck goes on the Schrader valve and the connection is completed.
Turn on the zone valve and read the pressure at the spray head nozzle.
For measuring the pressure at impact and rotor sprinklers, use a pitot-static tube  thread a Schrader valve into the back of the pitot tube, then connect the air chuck to the Schrader valve.
Figure 14: Pressure tester for pop-up spray head
 Figure 15: Pressure tester for rotor and impact sprinkler heads.
Figure 16: From left to right, MP rotator stream nozzle, spray nozzle and RainBird stream nozzle.
Figure 17: Misting due to excessive pressure
 To troubleshoot the hydraulics of the irrigation zone, turn on the water and measure the pressure at the closest sprinkler to the zone valve, and then the farthest sprinkler from the zone valve.
Figure 14 shows the pressure gauge attachment for popup spray heads.
Remove the nozzle and filter, screw on the adapter tee, and replace the filter and nozzle.
To test the pressure of impact and rotor sprinkler heads, insert the pitot tube in the water stream as shown in Figure 20 and read the pressure on the gauge.
Figure 18: Pressure regulator on an irrigation zone valve.
Figure 19: Pressure testing tools.
Note saw for cutting roots.
If the difference in pressure is 10 percent or less, the hydraulics for the zone are good.
If the pressure is between 10 percent and 20 percent, the system hydraulics are fair.
If the difference in pressure is greater than 20 percent, there is a problem.
Measure the pressure at the middle sprinkler in the zone.
If the pressure is between 5 percent to 10 percent of the first sprinkler, the problem is in the downstream pipe.
Figure 20: insert the pilot tube in the water stream
 If the difference in pressure is 10 percent or less, the hydraulics for the zone are good.
If the pressure is between 10 percent and 20 percent, the system hydraulics are fair.
If the difference in pressure is greater than 20 percent, there is a problem.
Measure the pressure at the middle sprinkler in the zone.
If the pressure is between 5 percent to 10 percent of the first sprinkler, the problem is in the downstream pipe.
Figure 22: Slip fitting showing extension fitting.
Compression fittings and slip connections make repairs on PVC pipe easy.
If you make the repairs to any pipes, remove the nozzles from the sprinkler heads downstream of the repair and turn on that zone to flush-out the fillings and dirt resulting from the repair.
Replace the nozzles.
The description of a static VRI irrigation prescription is that this prescription stays the same or changes only a few times during the season.
Considerations include that it is relatively simple to apply.
Does not account for change in spatial variability over a season.
Example uses include avoiding irrigation on uncrossed areas, mining differences in soil available water capacity, and variable rate chemigation.
Management of Iron in Irrigation Water
 Gladis Zinati, Ph.D., Extension Specialist in Nursery Management, & Xiufu Shuai, Ph.D., Postdoctoral Associate in Nursery Management
 Iron is a common trace element in soils and groundwater.
Iron is the fourth most abundant mineral in the earth's crust.
The bulk iron content of soils is typically in the range of 0.5% to 5% , and is dependent upon the source rocks from which the soil was derived, transport mechanisms, and overall geochemical history.
Iron occurs naturally in water in soluble form as ferrous iron (bivalent iron: Fe-2 or non-soluble form as ferric iron (trivalent iron: Fe+3.
During colonial times, bog iron was mined from bogs, streams, and waterways in the New Jersey Pine Barrens.
The Pine Barrens include portions of seven counties: Ocean County, Burlington, Gloucester, Atlantic, Cumberland, Cape May, and Camden County.
The soils are generally sandy and acidic.
Drained water laden with organic acids  from decaying vegetation percolates down to iron-rich clays underlaying much of the Pine Barrens, and in the process leaching out the soluble iron.
Iron in ground water quickly oxidizes to a reddish-brown product  when exposed to air.
Iron is a common water contaminant that is not considered a health hazard; however, its presence at elevated levels can cause aesthetic problems on ornamental plants, buildings and structures, and its accumulation on irrigation equipment can lead to clogged emitters.
Fig.
1.
Iron rust deposits on plant leaves.
Fig.
2.
Rusting of metal structures.
Iron Forms and Levels
 Iron can be present in a water supply in many different forms  and may or may not be apparent to the eye.
These forms include ferrous  or oxidized  iron becomes apparent through precipitation, and usually appears as brownish red colored particles suspended in the water.
Irrigation water with iron levels above 0.1 ppm may cause clogging of drip irrigation emitters and above 0.3 ppm may lead to iron rust stains, and discoloration on foliage plants in overhead irrigation applications.
These levels are generally below the levels that cause toxicities in plant tissue except when iron levels exceed 4 ppm or when the root medium pH is below 5.5.
Iron fixing bacteria, mainly from the filamentous genera such as Gallionella spp., Leptothrix and Sphaerotilus and less from the rod type, such as Psendomonas and
 Enterobacter, react with soluble iron, Fe+2, through an oxidation process that changes the iron to an insoluble form, Fe+3.
When the ferric iron is surrounded by bacteria colonies, a bluish bronze sheen, sticky iron slime gel is created.
The bacteria keeps the iron in the water from settling out and SO when irrigation is applied to plants SO is the bluish iron deposit.
In propagation houses one often observes a slimy yellowish mass that is responsible for clogging the irrigation drippers or nozzles.
Management Methods to Control Iron in Irrigation Water
 Depth of irrigation intake.
Nursery growers can reduce the problem of iron deposits by making sure that their irrigation intakes are located 18 to 30 inches below the surface of the water.
Intakes too close to the bottom pull settled iron sediment off the bottom of the pond.
Those too close to the surface pull more of the oxidized form and other organisms that flourish on iron such as iron fixing bacteria.
Treatment of iron depends on the form  in which it occurs in the untreated water.
Therefore, water testing is needed before considering or selecting the appropriate treatment equipment for effective removal of iron.
Softeners to remove ferrous bicarbonate in water.
The simplest method to remove ferrous bicarbonate iron from the water is to pass it through an air tight water softener containing a resinous cation exchanger: an insoluble
 matrix normally in the form of small  beads, fabricated from an organic polymer substrate with a surface that easily traps and releases ions in a process called ion exchange.
The capacity for removing iron depends on the capacity of resin.
By using a basic softener regenerated with sodium chloride, iron can be removed along with calcium and magnesium.
Oxidation followed by filtration to remove high iron water content.
If well water has a high iron content causing problems, then consider using a basin aeration pump.
This pump keeps the water volume moving , resulting in iron precipitation due to oxidation.
Removal of the precipitated iron can be achieved by filtration.
In aerated water, the redox potential of the water is such that it allows oxidation of the ferrous iron into ferric iron, which precipitates into iron hydroxide, Fe3, thus allowing a natural removal of the dissolved iron.
oxidation precipitation Fe+2 Fe+ Fe,
 The time required for ferrous iron to undergo oxidation to the ferric state is dependent on many factors, the dominant being: pH; temperature; dissolved oxygen level; and the presence of other soluble ions.
The lower the pH and temperature the longer the time required for completion of the oxidation reaction.
Increasing dissolved oxygen decreases the time required for oxidation.
For example:
 At pH 7.0, 90% Fe+2 oxidation requires 1 hour at 21C and 10 hours at 5C.
At pH 8.0, 90% Fe+2 oxidation occurs in 30 seconds.
At pH 6.0 it requires 100 hours.
The critical dissolved oxygen concentration is 2 ppm.
Below that ferrous iron oxidation occurs very slowly.
Allowing complete aeration of the water, then passing the aerated water through a neutralizing filter , permits filtering out the suspended iron and raising the pH before the water is allowed to pass through a water softener.
For this process, the typical filtration requirements are between 20 and 50 microns.
Oxidation and filtration is usually the most economical method for iron removal in terms of operating costs because air is available for free.
However, because large retention tanks may be required, this type of treatment may have higher capital costs.
Oxidation followed by filtration is a relatively simple process.
Oxidants and oxidizing filters.
Other methods of oxidation include the use of oxidants such as chlorine, chlorine dioxide, ozone, and potassium permanganate.
Chlorination is widely used for oxidation of soluble divalent iron.
Chlorine feed rates and contact time requirements can be determined by simple jar tests.
For a complete precipitation of iron, it is recommended to add a base to raise the pH.
Iron precipitates more readily as the pH is raised above neutral.
If aeration is limited by a pressure system and the pH of the water is above 6.8, an oxidizing filter can be an option.
Greensand is a processed material consisting of nodular grains of the zeolite mineral glauconite.
The material is coated with manganese oxide.
The greensand will remove iron better, as manganese zeolite supplements the natural aeration of the water, helping to precipitate the iron.
Chlorination as an oxidizing agent to remove organiciron water.
Organic iron is a compound formed from an organic acid and iron.
This form is often found in water with more than 2 ppm of dissolved organic carbons.
Tannins are natural organics produced by vegetation, which stain water a tea-color.
Organic iron is difficult to remove and therefore, it is important to note its presence in water.
Organic iron and tannins can occur in very shallow wells, or wells being affected by surface water.
A complete analysis of a water sample and initial observation when the sample was drawn will give an indication of their presence.
For example, a sample of water that contains organic iron may be clear when drawn at the pump and the iron may not precipitate, but it appears in a colloidal form.
Organic iron and tannins can slow or prevent iron oxidation, SO water softeners, aeration systems, and iron filters may not work well.
Chemical oxidation followed by filtration may be an option.
Chlorination can be considered as a treatment method, especially when iron exists in organic form.
Chlorination breaks down the organic complexes, and the iron then may be oxidized and precipitated by aeration and pH adjustment.
Chlorinating irrigation water will result in a much faster oxidation rate and it can be injected in gaseous or liquid form.
Commercial irrigation contractors can install these systems.
For additional information on locating irrigation contractors, contact your local Rutgers Cooperative Research & Extension Office.
Gaseous chlorine, injected from cylinders, is more effective and economical over the long run than the liquid form, but it is extremely dangerous when cylinders have to be changed, particularly if the cylinders are housed in a building.
Liquid chlorine , a safer alternative, is injected using a variable ratio injector.
Liquid chlorine losses strength over time and hence, the
 injection rate must be increased.
It is recommended to inject liquid sodium hypochlorite continuously at a rate of 1 ppm for each 1 ppm of iron in the irrigation water.
Mixing liquid sodium hypochlorite in water results in the formation of hypochlorous acid  and hydroxyl ions , a reaction that raises the pH of the water.
The amount of HOCI that will be present in solution, and thus active, will be larger at lower pH levels.
At pH 8, only about 22% of the chlorine injected will be in the active HOCI form, at pH 7, about 73% will be in the HOCI form, and at pH 6, about 96% will be in the HOCI form.
Hypochlorous acid reacts with iron in solution and oxidizes the ferrous iron into the ferric form.
The ferric iron then becomes the insoluble ferric hydroxide as a precipitate.
Chlorine should be injected before the filters SO that these precipitates may be trapped in the filters.
Chlorine may react with some metal and plastic components of irrigation systems.
Therefore, always check with the manufacturer or supplier of system components to identify any potential problems before beginning a chlorine injection program.
The water can be tested for free chlorine using an inexpensive D.P.D.
test kit.
A swimming pool kit at the end of the irrigation line or riser can be used but it should measure free chlorine.
Many pool test kits measure only total chlorine.
Chlorination should be followed by filtration when organic complexes of iron are present in water.
Caution should be exercised when chlorination is selected as a method for iron removal in irrigation water because some plants are sensitive to chlorine, naming a few: crapemyrtle, dogwood, hibiscus, hydrangea, juniper, rhododendron, rose, sugar maple, spruce, and viburnum.
Other products for sequestering iron in water.
Examples known to the authors include: Di-Solv , a negatively charged compound can be added to irrigation water to eliminate mineral buildup, a nourishment source for bacterial growth.
The use of DiSolv reduces plugged emitters due to biological contaminants.
Another product by the same company is AquaSolv a chemical compound that sequesters iron, calcium, and manganese ions.
Similar products may be available from other suppliers.
Effective application depends upon equipment availability and concentration of iron or other problem mineral content.
Iron Testing Kits.
Irrigation water can be tested for iron levels  using a simple test kit.
Examples known to these authors include an inexpensive, simple, easy, and safe CHEMets colormetric iron test kit.
The kit contains 30 individual tests, vaccum-sealed ampules, plus comparators.
Similarly, a multi parameter test kit  such as Hach Model: HA-62A  can
Rainwater Harvesting for High Tunnel Irrigation Using Solar and Gravity Power
 Brian Leib, Professor Wesley Wright, Senior Research Associate Sean Moran, Student Assistant Department of Biosystems Engineering and Soil Science
 High tunnels help extend the growing season of high-value crops, but they always require irrigation because they prevent rain from reaching the crop and soil.
Rainwater harvesting off the high tunnel can alleviate the need for an external source of water to irrigate the crop.
Tank storage of 1.55 gallons per square foot of high tunnel area was able to meet most of the irrigation needs of the crops grown in Tennessee high tunnels.
A supplemental water source may be required during extended periods of drought.
Harvested rainwater can be delivered to the crop using drip tape without an external source of power, keeping a high tunnel off the electricity grid or from using fossil fuel driven pumps.
Three self-contained irrigation delivery systems were tested: 1) gravity power alone, 2) solar-charged battery pumping, and 3) direct-solar transfer pumping to higher-elevation delivery tanks.
It is important to understand the requirements and characteristics of these delivery systems options to determine the best approach for your operation.
Rainwater harveting systems can be very expensive.
Therefore, it is critical to find ways to reduce the cost of water storage to make rainwater harvesting more cost effective in high tunnel production.
High tunnels are simple greenhouse-like structures.
Because they effectively trap solar radiation, the rise in internal temperature allows producers to extend the growing season of high-value crops.
High tunnels are a less expensive alternative to the traditional greenhouse and use plastic films instead of rigid glazing.
Crops are grown in natural soil, and houses do not generally utilize external power for heating and ventilation.
However, high tunnels block out all rainfall making irrigation inside the structure necessary.
Rainwater harvesting is a possible solution for irrigation in high tunnels because it does not require an external source of water or power an important consideration for some producers.
Rainwater harvesting is a common practice on a backyard scale as seen in Figure 1.
In these small-scale systems, rainwater is most often collected using gutters and stored in tanks for hand watering.
UT Extension developed and tested larger scale rainwater harvesting for high tunnels using drip irrigation.
Tanks and gutters were used, but harvested rainwater was delivered to high tunnels by three different methods:
 2.
Solar-charged battery pumping.
3.
Solar-transfer pumping to delivery tanks.
This publication will evaluate the effectiveness of rainwater harvesting for high tunnels in Tennessee while describing these three internally powered irrigation methods.
The characteristics and costs of these approaches will also be compared.
Figure 1: Small-scale rainwater harvesting is becoming more common in residential areas.
Figure 2: Collection tanks that were used to store rainwater.
The holding capacity of these tanks was 1,100 gallons each.
The dark color was chosen to inhibit microbe growth within the tank.
Tank Sizing, Gutters and other Considerations
 An important consideration when designing a rainwater harvesting system is the size of the storage containers.
Container size is determined by rainfall and crop-water use amounts for the surrounding area.
The storage volume needs to be large enough to supply water for an extended period without rainfall.
Local rainfall data indicated that tanks would need to supply irrigation for a two weeks to cover a majority of dry periods in East Tennessee.
Next, a peak evapotranspiration rate for common vegetable crops was estimated at 1.5 inches/week from outside weather data.
However, this rate was considered higher than actual rates because inside a high tunnel, wind, solar radiation and wetting of the soil surface are reduced while drip tape under plastic mulch also inhibits evaporation from the soil surface.
Therefore, an evapotranspiration rate of 1.25 inches/week was multiplied by the two-week dry period to determine a test storage volume of 2.5 inches per high tunnel area.
This equals 1.55 gallons for every square foot of high tunnel footprint.
For a 30-by-48foot-high tunnel, this translates to 2,200 gallons of tank storage as shown in Figure 2.
It should be noted that this criteria was our best estimate for testing rainwater havesting in East Tennessee and more or less water storage may be required depending on actual conditions and the location of the high tunnel.
Initially plastic gutters were used for rainwater harvesting but later changed to heavier metal gutters.
One advantage of using plastic snap together gutters  is that they detach easily from the high tunnel to facilitate snow removal while heavier metal gutters can remain on the high tunnel when snow is dragged off the roof using a loop of rope.
Another snow removal option is a powerful leaf blower that potentially reduces the chances of damage to thin-walled aluminum gutters.
Finally, solid wall plastic tanks were common to all rainwater harvesting systems tested.
Black tanks were used to cut out light and inhibit biological growth in stored water.
Figure 3: Plastic snap together gutters on a high tunnel.
Repair tape was used to fill the gap between the gutter and the structure.
1.
The Gravity Driven System
 Gravity causes water to flow downhill and the same principle can be used to move water from the high tunnel roof to the crop inside without using a pump as shown in Figure 4.
The weight of water also creates water pressure which is highest in the drip system when the tank is full.
In this application, the tanks had to fit under the gutters to capture rainwater and be elevated to ensure water pressure was high enough to operate the drip system as the tanks empty.
Gravity pressure is developed at 1 pound per square inch  for every 2.31 feet of water elevation.
Therefore, the maximum pressure for this high tunnel application was around 2 psi when the tank was full and around 1 psi when the tank emptied.
These pressures were well below recommended pressures to operate drip systems, yet the water distribution was adequately uniform when using short lengths of drip tape on flat to moderate slopes.
At these low pressures, the drip system had to be operated longer than normal to apply the desired amount of water.
The gravity-powered system required minimal maintenance due to its simplicity and because the low-pressure did not create many leaks.
Therefore, the quantity, cost and complexity of repairs was low in comparison to the other systems.
Figure 4c: Gravity from the tank into the high tunnel
 Figure 4d: Gravity into the drip
 2.
The Solar Charged Battery System
 The solar-battery system  was similar to a private well for a home except that the electricity was solar generated instead of connected to an electric utility.
Solar panels charged the batteries, which then provided power to a submersible pump, the pressure switch and the pump controller.
Four 12-volt batteries were connected in parallel and series to create a 24-volt DC system.
The pressure switch was used to signal the pump controller to turn the pump on and off providing automatic operation as valves were opened and closed for irrigation.
The pressure in this system was significantly higher than the other systems due to the pump with the pressure switch set to operate between 35 to 45 psi.
Pressure regulators were used to maintain normal pressure in the drip system at around 12 psi, thus alleviating concerns about water distribution and uniformity.
These high-pressures created many leaks requiring routine maintenance to avoid waste of harvested rain water.
The complexity of the system incurred higher cost and required greater expertise for repairs as compared to the other systems.
3.
The Solar Transfer Pumping System for Gravity Watering
 The solar-transfer system  used a capture tank much like the other two systems.
However, the system was a combination of both gravity flow and solar pumping.
The water was captured and then pumped to the delivery tank at a higher elevation to create higher pressure than the gravity powered system.
Much like the gravity powered system, raising the elevation by just 2.31 feet corresponds to 1 psi of extra static pressure.
Similarly, raising the tank 23.1 feet created 10 psi of static pressure.
This system only transfered water from the capture tank when there was sunlight and the water level in the delivery tank dropped to the point of activating the float switch that allows the pump to turn on.
In essence, this approach was always trying to keep the delivery tank as full as possible and the capture tank as empty as possible.
Opening an irrigation valve allowed automatic operation of the drip system night or day as long as there was water in the delivery tank.
By comparison, the solar-transfer system had a moderate number of leaks and intermediate complexity.
This led to the maintence cost being higher than gravity power alone but lower than solar-battery powered pumping.
The rainwater harvesting systems were evaluated for how well they supplied the irrigation requirements in high tunnels.
Table 1 shows the percentage of rain water applied as compared to the total irrigation amount required when the 1.55 gallons per square foot storage capacity rule was used to determine tank size.
The rainwater harvesting systems met nearly all the irrigation requirements during the fall growing season when crop-water use was very low.
In the spring and summer months, crop-water use peaked at the end of June and beginning of July such that only 80 percent of the irrigation requirement was met in some years.
Of course, the amount of irrigation water provided
 UT-Farm	Farmer 1	Farmer 2
 Spring	Fall	Spring	Fall	Spring	Fall
 2014	83%	100%	98%	100%	100%
 2015	89%	100%	100%	87.5%	91%
 Table 1: Percent of irrigation supplied by RWH.
depended on four main factors: yearly rainfall patterns, seasonality of crop water use, tank size, and operator irrigation habits.
During testing, the tank water lasted at least two weeks.
However, there were some dry periods that lasted long enough to empty the tanks requiring the addition of municipal or well water.
It may not be feasible to continue increasing tank size for these longer dry periods such that rainwater harvesting may require a supplemental source of water.
Still, rainwater harvesting was able to meet a majority of the irrigation requirements for East Tennessee high tunnels.
Tank capacity and dependence on supplemental water will need to be adjusted for rainwater harvesting in different climates.
The overall cost of the different rainwater harvesting systems was dominated by the price of the tanks used to store the water as shown in Table 2.
The cost estimates were based on rainwater harvesting for two 30-by-75-foot high tunnels and will change depending on the size and number of the high tunnels.
The cost of rain gutters and tanks was $12,000 and was the same for each of the alternative delivery systems.
The additional cost for gravity flow, solar-transfer pumping and solar-battery powered pumping were $400, $2,750 and $3,950, respectively.
The high cost of rainwater harvesting shows the importance of evaluating alternate water supplies.
If a less expensive method of water storage were to be adopted, the cost of rainwater harvesting would dramatically decrease in all cases.
Item	RWH type	Description	Cost
 Rain Gutters	GF, STP, SBPP	400 feet of installed aluminum or plastic.
Material only for Galvanized	$2,000
 Storage Tanks	GF, STP, SBPP	9,000 gallons of water, storage from rigid plastic tanks	$10,000
 Elevate Tank	GF	250 concrete blocks to create 0.45 m of lift	$400
 Solar Pumping	STP, SBPP	Solar panels, submersible 24 V solar pump, pump control, wire and conduit	$2,000
 Battery Power	SBPP	4 deep cycle batteries, charge controller, pressure tank and switch, wire, conduit	$1,200
 Water Lines	STP, SBPP	250 feet of 1-inch PVC Pipe with trenching	$750
 Solar Transfer	TOTAL	$14,750
 Solar Battery	TOTAL	$15,950
 Table 2: Cost of the three rainwater harvesting irrigation systems tested during the UT experiment: gravity flow , solar-transfer powered  and solar-battery powered pumping.
When deciding whether to install a rainwater harvesting system, five questions should be asked:
 How important are energy and water sustainability for your high tunnels?
What alternative water sources are possible or already available to you: wells, streams, ponds and municipal?
Will rainwater harvesting be able to provide all or part of your high tunnel water requirements in your location?
What type of rainwater harvesting will work best for your operation: gravity alone, battery-powered solar or solar-transfer pumping?
Do the rainwater harvesting benefits justify the cost when comparing alternative water sources?
In Tennessee, rainwater harvesting was able to supply a majority of the high tunnel irrigation requirement when using the 1.55 gallon per square foot rule.
It did not require an external source of power but did require some supplemental water.
Keep in mind that Tennessee rainfall is substantial and well distributed.
Rainwater harvesting in other regions and climates may require a different design criterion for water storage based on rainfall patterns, crop-water use, soil salinity, operator irrigation habits and the availability of supplemental water sources.
Rainwater harvesting provides high-quality water that could help reduce soil salinity, but it can also harbor biological contamination from roof run-off.
The biggest concern for rainwater harvesting in high tunnels is the large water storage volume that is very expensive when using rigid wall plastic tanks.
Reducing water storage cost would increase the financial feasibility of rainwater harvesting.
Also, different approaches to rainwater harvesting must be considered.
Gravity powered rainwater harvesting is characterized by simplicity, few leaks, lower cost and very low pressure.
The restricted tank placement and low pressure can cause water distribution difficulties with gravity systems.
In contrast, solar-powered battery pumping provides ample pressure to overcome water distribution and irrigation uniformity concerns.
However, this approach is more technically complicated with frequent leaks and the highest cost to install and repair.
Finally, solar-transfer pumping falls in between the other two delivery systems in terms of pros and cons.
Financial support was provided by a USDA-NRCS Conservation Innovation Grant.
High tunnels for testing rainwater harvesting were made available by the East Tennessee AgResearch and Education Center, Organic Crops Unit of the University of Tennessee and by cooperating high tunnel producers in Tennessee.
UTIA.TENNESSEE.EDU Real.
Life.
Solutions.
TM
Support for People Wanting to Improve Their Irrigation Management:
A good strategy to measure pressure on pivots is to install a Schrader valve instead of a pressure gauge.
Get the ones that have  NPT male thread and install it into the port where the gauge was before.
Then attach an air chuck with a grip to a high quality gauge that can be moved between pivots.
Then the pressure can be checked with just one gauge that can be stored inside where it is protected from the weather.
All of these parts can be purchased at the local farm supply store.
Schrader valves can also be installed at the distal end of the machine, which is the most critical point to check the pressure.
Pressure gauges can be easily installed on existing irrigation systems, and new pivots are often equipped with them.
All wireless remote pivot control systems can monitor pressure and send alerts to mobile phones or computers when pressure falls outside a predetermined range.
These data can assist managers in maintaining pivot performance.
However, it should be noted that the accuracy of gauges may decay over time, but replacing gauges is affordable and simple.
DEFICIT IRRIGATION OF GRAIN AND OILSEED CROPS
 Kansas State Research and Extension
 Deficit irrigation is an alternative to full irrigation where water is applied to crops in amounts that are anticipated to support transpiration at less than the maximum potential level.
Under such circumstances, one might expect crop growth and yield to be less than that achieved under full irrigation.
However, profitable production of certain crops can be achieved using deficit irrigation with considerable savings in water used or when the water supply is constrained.
Deficit irrigation of field crops has been discussed in several research papers and reviews.
Since the goal of most irrigation strategies is to optimize net economic returns under the constraints imposed by available resources, it might be wise when examining the deficit irrigation toolbox to allow some variance from the strictest definition of the term.
For example, in some cases, net economic returns may be optimized by growing less land area with a less deficit irrigation strategy.
For the purposes of this discussion, the topic of interest is coping with a deficient or marginal irrigation water supply that might have spatial and/or temporal aspects that must be considered.
So, as the discussion moves forward, it will become evident that in some cases producers are truly applying less than the full irrigation amount to a parcel of land and in other cases the producer is trying to avoid deficit irrigation.
Of course, in many cases the strategy may be a combination of mitigation and partial avoidance of deficit irrigation.
Although there are a number of ways to organize a deficit irrigation toolbox, here we will assume it is organized into these three sections:
 Irrigation management and macromanagement
 Irrigation system and land allocation management
 As is the case with all good mechanics, producers facing deficit irrigation must be able to choose and utilize the best tools for the task immediately at hand and recognize when one or more
 additional tools are needed as the project progresses.
Additionally, some of these deficit irrigation tools have temporal aspects, that is, they may be only available as adjustments for the dormantseason, in-season, or the long-term.
The overall purpose of this paper is to illustrate the concepts of the tools in the tool box and not to exhaustively demonstrate how to use them.
As some of the tools interact with each other, it may be useful to peruse the entire toolbox.
A number of tools to mitigate and/or avoid deficit irrigation reside within the agronomic management section of the toolbox.
A few blank rows are provided to list additional tools that might be in your toolbox.
Table 1.
Primary agronomic management tools to address deficit irrigation for grain and oilseed crops and their temporal availability.
Deficit Irrigation Management Tool	Dormant
 Crop Selection	Yes	No	Yes
 Crop Hybrid or Variety	Yes	No	Yes
 Crop Rotations and Cropping Systems	Yes	No	Yes
 Tillage and Residue Management	Yes	Sometimes	Yes
 Nutrient Management	Yes	Yes	Yes
 Plant Density and/or Row Spacing	Yes	No	Yes
 Weed and Pest Management	Sometimes	Yes	Yes
 Crop selection has long been a tool to cope with deficit irrigation and/or a deficient irrigation water supply.
Some crops are more sensitive to water stress than others and this may be particularly the situation for their economic yield.
However, one is well advised to consider the water sensitivity paradox; a water sensitive crop may have greater water productivity than a less water sensitive crop.
Deficit or limited irrigation presents a challenge for irrigators growing corn.
Corn is sensitive to water stress at all stages of growth and grain yields are usually linearly related to water use from the dry matter threshold  through the point of maximum yield.
Deficit or limited irrigation of corn is difficult to implement successfully without reducing grain yields.
However, some strategies are more successful than others at maintaining corn yields under limited irrigation.
Fully irrigated corn was found to be most profitable and having lowest risk of nine different water allocation schemes in Kansas , but some other scenarios were profitable with some acceptance of risk.
Grain sorghum is relatively tolerant of water stress and can be a good choice for deficit irrigation , but is also less responsive to irrigation.
Irrigated wheat can also be a good choice for deficit irrigation in the southern Great Plains , but in some areas of
 northern Kansas, the response of wheat to irrigation has been minimal.
One of the primary advantages of wheat in coping with deficit irrigation or an insufficient water supply in the US Great Plains is that the wheat growing season has less overall evaporative demand and that the season is temporally displaced from the other principal irrigated crops.
Soybean is somewhat similar to corn in sensitivity to water stress, but typically requires a slightly smaller total amount of irrigation.
Sunflower has a considerably shorter growing period than corn and soybeans and requires less total irrigation, although all three crops' peak evapotranspiration rates are similar.
Summer crop yields were simulated for 42 years of actual weather data  from Colby, Kansas using 1 inch sprinkler irrigation events with an application efficiency of 95%.
Irrigations were scheduled as needed according to the weather-based water budget but were limited to various irrigation capacities.
Figure 1.
Simulated crop yields for corn, grain sorghum, soybean and sunflower as affected by irrigation capacity  and their corresponding response to total irrigation amount  at Colby, Kansas for 42 years  at an application efficiency of 95%.
Note: These are average yield responses.
Yield responses for individual years would vary considerably from those shown
 The graphs indicate that corn benefits from greater irrigation capacities and irrigation amounts, whereas grain sorghum yield plateaus at a lesser irrigation capacity and irrigation amount.
Ultimately, crop selection depends on production costs and crop revenues.
Irrigated land area devoted to grain sorghum in Kansas is actually decreasing and much of this is probably closely tied to economics.
In a cropping simulation, similar to the one above, conducted for the period 19722005, it was concluded that dryland grain sorghum production was more profitable than any of irrigated grain sorghum scenarios.
However, sometimes irrigation capacity is shared across multiple crops to reduce the amount of risk.
For example, maybe a portion of the land is grown in stress-tolerant grain sorghum to effectively increase the irrigation capacity for another portion of the land area growing water-sensitive corn.
Of course, the economics of irrigated crop production vary greatly from year to year.
Producers may wish to compare crop production as affected by the projected water supply using the Crop Water Allocator software developed by faculty at K-State.
Irrigation water requirements of the various crops also vary temporally.
Wheat was already mentioned as a possible crop that could allow shifting of irrigation water when the principal limitation is irrigation capacity.
Similarly, a summer crop's peak water needs vary between months.
Some producers may plant portions of their fields to sunflowers and only irrigate them when irrigation needs of other crops are declining.
Figure 2.
Average fraction of irrigation needs by month for corn, grain sorhum, soybean and sunflower at Colby, Kansas, 1972-2013.
Crop Hybrid or Variety
 Some crop hybrids and varieties are more sensitive than others to water stress.
Although it remains to be seen whether newer drought tolerant hybrids and varieties will actually result in decreased irrigation needs, it does appear that crop yield is better protected from water stress.
Hybrid selection can result in greatly different yields even under the same full irrigation level.
Maximum corn yield averaged 75 bu/acre greater  than the minimum corn yield in crop performance tests conducted from 1996 through 2010 at the KSU Northwest Research-Extension Center at Colby, Kansas.
Producers are advised to choose hybrids and varieties carefully so they can maximize their "crop per drop".
Figure 3.
Variation in corn hybrid yields in KSU-NWREC performance tests during the period 1996 through 2010.
Crop Rotations and Cropping Systems
 Previous crops leave behind residual soil assets, such as soil water, nutrients and increased organic matter, which can be used to offset application of these inputs and their associated costs in the coming year.
For example, irrigated corn requires ample supplies of water and nutrients late in the cropping season to ensure optimum yields, so producers often choose sunflower as a rotational crop after corn in order to utilize the residual soil water and nutrients.
In addition to the economic benefit, producers obtain environmental benefits of reduced usage of scarce water resources and reduced potential of nutrient leaching.
Anecdotally, it has been observed that continuous corn is less common in west central Kansas than in northwest and southwest Kansas where the Ogallala saturated thickness is greater.
Crop rotations also tend to reduce pest problems and to some extent weed pressures often associated with monocultures.
Producers should consider crop rotation as a valuable tool to help manage a deficient or declining water supply.
Tillage and Residue Management
 Residue management techniques such as no tillage or conservation tillage have long been accepted to be very effective tools for dryland water conservation in the Great Plains.
However,
 Klocke  posited that residue management can be even more important in reducing soil water evaporation under irrigation.
Reporting on an earlier two year study from Nebraska, soil water evaporation savings under a corn canopy with straw covering the soil averaged 0.2, 2.6 and 3.8 inches for dryland, limited irrigation, and full irrigation, respectively.
In a later three year study in Kansas, Klocke et al.
reported evaporative ratios  within a corn canopy averaging 0.30, 0.15 and 0.17 for bare soil, corn stover and wheat residue, respectively.
Strip tillage and no tillage had numerically greater corn grain yields  than conventional tillage in all four years of a study conducted at the KSU Northwest Research-Extension Center, Colby Kansas.
The benefits of using strip tillage or no tillage increased as irrigation capacity became more deficit.
Both strip tillage and no tillage should be considered as improved alternatives to conventional tillage, particularly when irrigation capacity is limited.
Figure 4.
Corn grain yield as affected by tillage management and irrigation capacity in a four year study at Colby, Kansas.
Nutrient management can play an important role in increasing the effective use of irrigation and has been the subject of several review articles.
Proper nutrient management increases plant growth and yield response allowing the crop to optimize use of available water supplies.
Appropriate nitrogen fertilization nearly doubled corn yields without much increase in water use  in a two year study of subsurface dripirrigated corn in western Kansas.
Figure 5.
Corn yield as affected by nitrogen fertigation level and irrigation level in a subsurface drip irrigation study, Colby, Kansas, 1990-1991.
Plant Density and/or Row Spacing
 Plant density or plant population can have an effect on water use and water use efficiency.
When irrigation is severely deficit, it may be wise to reduce corn plant density to increase the probability of successful pollination and subsequent growth.
As an example, Roozeboom et al.
recommended corn plant densities for western Kansas of 14,000 to 20,000, 24,000 to 28,000, and 28,000 to 34,000 for dryland, limited irrigation, and full irrigation scenarios, respectively.
After the corn crop reaches a leaf area index  of approximately 2.7, all of the incoming energy is captured  and additional increases in LAI do not result in increased water use.
As LAI for irrigated corn often reaches 5 or greater in the central Great Plains, plant density has to be greatly reduced to actually reduce corn water use.
A key factor in managing corn plant density is assuring that pollination and kernel set are achieved.
Establishing greater kernels/area often requires increased plant density.
Medium to higher plant densities  generally resulted in greater corn yields  in a four year sprinkler-irrigated study in western Kansas.
Adjustments to row spacing and planting geometry may be effective in reducing soil water evaporation losses in some cases for corn and grain sorghum in the central Great Plains.
However, results to date suggest these adjustments are most likely to be advantageous only at the lower end of the range of crop yields.
Figure 6.
Corn grain yield as affected by irrigation amount and plant population, 2004-2007, KSU Northwest Research-Extension Center, Colby Kansas.
Weed and Pest Management
 Weed and pest management is important in coping with deficit irrigation.
Weeds may directly compete for water and nutrients and insect pests may interfere with plant growth and limit the crop's economic yield.
Some pests thrive under deficit irrigation conditions.
For example, spider mites increase under the hotter and drier conditions associated with corn water stress.
Spider mite damage that has occurred to corn's photosynthetic ability cannot be reversed even by substantial precipitation, although a reduction in the number of mites may occur.
Producers coping with deficit irrigation should actively and consistently observe their crop fields managing weed and insect pests as they arise.
IRRIGATION MANAGEMENT AND MACROMANAGEMENT
 A number of tools to mitigate and/or avoid deficit irrigation reside within the irrigation management and macromanagement section of the toolbox.
A few blank rows are provided to list additional tools that might be in your toolbox.
Table 2.
Primary irrigation management and macromanagement tools to address deficit irrigation for grain and oilseed crops and their temporal availability.
Deficit Irrigation Management Tool	Dormant
 Irrigation Scheduling	No	Yes	Yes
 Timing of Irrigation	No	Yes	Yes
 Initiation of the Irrigation Season	No	Yes	Yes
 Termination of the Irrigation Season	No	Yes	Yes
 Dormant Season Irrigation	Yes	No	Yes
 The most common definition of irrigation scheduling is simply the determination of when and how much water to apply.
It is not uncommon to hear a central Great Plains producer indicate that they could not possibly consider irrigation scheduling because they always are in a deficit irrigation condition from the beginning to the end of the cropping season.
Although this may seem intuitively correct, there are actually many years when the irrigation capacity even for marginal systems would not have to be fully utilized.
Often early in the season, a deficit irrigation capacity may exceed the crop evapotranspiration rate.
Simulated irrigation schedules for corn indicate that 80% or more of the maximum observed irrigation requirement is only required in 50 and 60% of the years for severely deficit irrigation capacities of 1 inch/8 days and 1 inch/10 days, respectively.
Additionally, producers using irrigation scheduling can make better decisions about how to handle a triage situation.
Figure 7.
Simulated corn irrigation requirements for Colby, Kansas, 1972-2013 as possible with various irrigation capacities.
Each indicated capacity has the 42 years shown, with some years lying on top of each other.
The percentage of years requiring 80% or more of the maximum possible irrigation is shown below each capacity.
As irrigation capacity increases, the percentage of years requiring 80% or more of the maximum irrigation tends to decrease.
Timing irrigation to the critical growth stages is a deficit irrigation strategy that can be effective in some situations.
This technique may be most applicable when deficit irrigation is limited by total amount of irrigation.
Examples of such scenarios would be an institutional constraint  or when surface water availability constrains the application window.
Timing of irrigation is less applicable for irrigation systems with marginal irrigation capacity and when stretched water resources limit adjustments to the irrigation event cycle.
Since center pivot sprinklers irrigating from marginal groundwater wells are common in the central Great Plains landscape, timing of irrigation is a less applicable tool for many producers.
Initiation of the Irrigation Season
 The determination of when to initiate the irrigation season is an irrigation macromanagement decision that can greatly affect the total irrigation amount.
Ideally, the producer would delay irrigation as long as possible with the hope that timely precipitation would augment the crop water needs.
A recent summary by Lamm and Aboukheira  suggests that corn probably has more inherent ability to handle early season water stress than is practical to manage with the typical irrigation capacities that occur in the central Great Plains.
Producers should use a good method of day-to-day irrigation scheduling during the pre-anthesis period.
To a large extent, the information being used to make day-to-day irrigation scheduling decisions during the pre-anthesis period can also be used in making the macromanagement decision about when to start the irrigation season.
This is because, even though the corn has considerable innate ability to tolerate early season water
 stress, most irrigation systems in the central Great Plains do not have the capacity  or practical capability  to replenish severely depleted soil water reserves as the season progresses to periods of greater irrigation needs.
However, there is some flexibility in timing of irrigation events within the vegetative growth period.
In years of lower evaporative demand, corn grown on this soil type  in this region can extract greater amounts of soil water without detriment.
Timeliness of irrigation and/or precipitation near anthesis appeared to be very important in establishing an adequate number of kernels/area which in this study was greatly correlated with final yield.
Although, timing of irrigation is difficult with typical systems in the central Great Plains, the results suggest that monitoring soil water reserves and evaluating early season evaporative demand may allow for delays in initiating the irrigation season in some years.
Termination of the Irrigation Season
 Irrigators in the central Great Plains sometimes terminate the corn irrigation season on a traditional date such as August 31 or Labor Day  based on long term experience.
However, there can be a large variation on when the irrigation season can be safely terminated.
A more scientific approach might be that season termination may be determined by comparing the anticipated soil water balance at crop maturity to the management allowable depletion  of the soil water within the root zone.
Some publications say the MAD at crop maturity can be as high as 0.8.
Extension publications from the Central Great Plains often suggest limiting the MAD at season's end to 0.6 in the top 4 ft.
of the soil profile.
These values may need to be re-evaluated and perhaps further adjusted downward  based on a report by Lamm and Aboukheira.
They concluded that producers growing corn on deep silt loam soils in the central Great Plains should attempt to limit the management allowable depletion of available soil water in the top 8 ft.
of the soil profile to 45%.
Table 3.
Anthesis and physiological maturity dates and estimated irrigation season termination dates* to achieve specified percentage of maximum corn grain yield from studies examining post-anthesis corn water stress, KSU Northwest Research-Extension Center, Colby, Kansas, 1993-2008.
Note: This table was created to show the fallacy of using a specific date to terminate the irrigation season.
Note: Because there was not an unlimited number of irrigation termination dates, sometimes the date required for a specified percentage of maximum grain yield was the same as the date for the next higher percentage.
After Lamm and Aboukheira.
Date of	Date of	Irrigation Season Termination Date For
 Anthesis	Maturity	80% Max Yield	90% Max Yield	MaxYield
 Average	19-Jul	27-Sep	2-Aug	13-Aug	28-Aug
 Standard Dev.
3 days	6 days	13 days	19 days	13 days
 Earliest	12-Jul	14-Sep	17-Jul	17-Jul	12-Aug
 Latest	24-Jul	10-Oct	14-Sep	21-Sep	21-Sep
 Estimated dates are based on the individual irrigation treatment dates from each of the
 different studies when the specified percentage of yield was exceeded.
Dormant season irrigation for crops such as corn has been advocated for the semi-arid Great Plains since the early 20th century, and the practice has been debated for nearly as long.
Knorr  found that at Scottsbluff, Nebraska, fall irrigation normally increased corn yields.
Farrell and Aune  found opposite results at Belle Fourche, South Dakota.
Knapp  recommended winter irrigation for most of western Kansas with the exception of sandy soils.
The advantages of preseason irrigation  are: 1) provide water for seed germination; 2) delay the initiation of seasonal irrigation; 3) improve tillage and cultural practices associated with crop establishment; and 4) more fully utilize marginal irrigation systems on additional land area.
The disadvantages are that it may: 1) increase production costs; 2) increase irrigation requirements; 3) lower overall irrigation efficiencies; and 4) lower soil temperatures.
Lamm and Rogers  developed an empirical model to aid in decisions concerning fall preseason irrigation for corn production in western Kansas.
Available soil water at spring planting was functionally related to overwinter precipitation and initial available soil water in the fall.
They concluded in most years, fall preseason irrigation for corn is not needed to recharge the soil profile in northwest Kansas, unless residual soil water remaining after corn harvest is excessively low.
A recent survey of sprinkler irrigated corn fields in western Kansas has irrigated that on average, producers are leaving residual available soil water in the 8 ft.
profile at approximately 60% of field capacity.
However, there was large variation between producers  emphasizing the need for each producer to evaluate their own field.
Figure 8.
Effect of western Kansas region on average, maximum and minimum measured plant available soil water  in the 8 ft.
soil profile in irrigated corn fields after harvest for the fall periods in 2010 and 2011.
In a recent field study  at the KSU Southwest Research Extension Center site near Tribune, Kansas, Schlegel et al.
found preseason irrigation to be profitable for corn production with irrigation capacities ranging from 0.1 to 0.2 inches/day.
Preseason irrigation increased grain yields an average of 16 bu/acre.
The crop water productivity was not significantly affected by well capacity or preseason irrigation.
IRRIGATION SYSTEM AND LAND ALLOCATION MANAGEMENT
 A number of tools to mitigate and/or avoid deficit irrigation reside within the irrigation system and land allocation management section of the toolbox.
A few blank rows are provided to list additional tools that might be in your toolbox.
Table 4.
Primary irrigation system and land allocation management tools to address deficit
 irrigation for grain and oilseed crops and their temporal availability.
Deficit Irrigation Management Tool	Dormant
 Irrigation System Selection	Yes	No	Yes
 Managing Water Losses	Yes	Yes	Yes
 Fine Tuning the Irrigation System	Yes	Yes	Yes
 Land/Water Allocation	Yes	Possibly	Yes
 No irrigation system can save water without good management imparted by the producer.
However, some irrigation systems are easier to manage than others.
Additionally, some systems although perhaps more complicated in design and number of components may inherently result in better water management.
This concept can perhaps be considered as "purchasing improved management capabilities upfront".
It has been said that one of the principal reasons that pressurized irrigation systems such as center pivot sprinklers  and subsurface drip irrigation  are considered easier to manage than surface irrigation is because they remove the surface water transport phenomenon from the management.
Many producers in the central Great Plains have converted from surface irrigation to center pivot sprinklers and a few are using SDI, all with a goal of better utilizing a limited and declining water resource.
There is some evidence from the Great Plains that SDI may be able to stabilize yields at a greater level under deficit irrigation than CP assuming both are managed well.
Under deficit irrigation nearly all water losses result in yield reduction.
It is common for the slope of the water production function for corn under deficit irrigation to be 12 to 15 bushels/inch and values of nearly 20 bushels/inch have been reported.
Howell and Evett  characterized the "Big Three" irrigation water losses as deep percolation, evaporation losses from soil, air, or plant, and irrigation runoff.
An excellent tabular discussion of the management of these losses with irrigation systems, tillage management, and irrigation scheduling is provided by Howell and Evett.
Fine Tuning the Irrigation System
 There are some irrigation system adjustments that can be considered "fine tuning" the system but are never-the-less important to deficit irrigation management.
This listing will not be exhaustive but may spur producers to look for that hidden extra capacity.
Here are some system-related practical ways irrigators might use to effectively increase irrigation capacities for crop production :
 Remove end guns or extra overhangs to reduce center pivot system irrigated area
 Clean groundwater well to see if irrigation capacity has declined due to encrustation
 Determine if pump in well is really appropriate for the irrigation system design and operating pressure.
Replace, rework or repair worn pump
 As it was stated in the second paragraph of this paper, deficit irrigation may be avoided by more closely matching the irrigated land area to the available water source.
As economically painful as this may seem, this has always been the design criteria for irrigation systems in arid regions.
Our semi-arid and more humid regions have just been able to successfully gamble with this criterion.
Utilizing this management strategy might be economically painful because:
 it will likely reduce income in years with ample rainfall
 it may negatively affect land values if land is then considered non-irrigated
 it could reduce economic activity in the community as less inputs are bought and less outputs are sold.
However, if water resources and pumping rates continue to decline, the drought persists, and/or climate change imposes drier and warmer conditions, reducing the irrigated land area to avoid deficit irrigation may be the wisest decision.
The previously discussed KSU-NWREC simulation modeling will be used to explore this topic further.
Corn yields were simulated for 42 years of weather data from Colby, KS..
Wellwatered corn ETc ranged from 17.6 to 27.1 inches with average of 23.1 inches for these 42 years of record.
In-season precipitation ranged from 3.1 to 21.2 inches with average of 11.8 inches.
Full irrigation ranged from 6 to 22 inches with average of 15.7 inches.
The marginal water productivity, WP  was 17 bu/acre-in, which might result in an economic benefit of 65 to $85/acre-in.
The yield threshold was 10.9 inches of ETc.
Yields were simulated for irrigation capacities of full irrigation, 1 inch every 4, 6, 8 or 10 days and also for dryland conditions.
As irrigation capacity decreases , corn yields decrease from the fully irrigated yields for some years and the variability in yields also increases.
Typically, crop yields increase with increasing ETc, although this response is not a direct cause and effect.
Rather in many cases, increased ETc is also reflecting better growing conditions.
As irrigation capacity decreases, the positive aspects of greater ETc on yield begins to disappear and the slope is relatively flat for an irrigation capacity of 1 inch/10 days.
Under dryland conditions, corn yields typically decreased over the entire range of increasing ETc experienced at Colby, Kansas during this 42 year period.
Well-watered corn ETc 
 Figure 9.
Simulated corn yields as a function of the calculated well-watered corn evapotranspiration for the 42 year period, 1972-2013, Colby, Kansas as affected by irrigation capacity.
Table 5.
Effect of irrigation capacity on simulated corn yields for the 42-year period, 1972-2013, Colby, Kansas.
Yield variation from full irrigation
 Irrigation	Maximum	Mean	Minimum	for maximum yield at maximum
 capacity	yield	Yield	Yield	well-watered ETc
 Full	273	204	112
 1 inch/4 day	261	202	112	-4.4%
 1 inch/6 day	226	181	112	-17.2%
 1 inch/8 day	216	162	103	-20.9%
 1 inch/10 day	202	148	94	-26.0%
 Dryland	138	77	23	-49.5%
 As water supplies for irrigation become less available due to either hydrological or institutional constraints, irrigation producers and water managers face more uncertainty in production and increase economic risk.
Increased uncertainty and risk can be mitigated through use of improved management practices or management tools.
These tools can only be used effectively if producers know and understand which tool is appropriate to their situation.
Fertilizer-N is a big investment for crop production in Nebraska and elsewhere.
After harvest, growers tend to plan their fertilizer-N management for the next years crop.
But the question is how much nitrogen can they apply to get the most profit from their fertilizer-N investment?
Water, our finite resource has many uses.
Agriculture, domestic, power generation, wildlife and habitat, aesthetics, and recreation are just some of those uses.
Water is life, life is water.
Groundwater use was initially small; however, improvements in well technology made it practical for many producers to be able to access groundwater.
With the invention of the center pivot, the area of irrigated cropland grew to over 22 million acres in the Great Plains.
Irrigation has been a significant factor in the high levels of agricultural production in the region, resulting in the Great Plains being referred to as a bread basket.
EFFECT OF CROP RESIDUE ON SPRINKLER IRRIGATION MANAGEMENT
 Sprinkler irrigation can involve frequent wetting of the soil surface.
Once to twice per week wetting is common.
The largest amount of soil water evaporation occurs when the soil surface is wet.
At this time soil water evaporation rates are controlled by radiant energy.
The more frequently the surface is wet, the more time that the evaporation rates are in the "energy" limited phase.
Crop residues have the capacity to reduce light reaching the soil surface and reduce the soil water evaporation during the "energy" limited phase of evaporation.
As the soil surface dries, the evaporation rate is controlled by soil water movement to the surface.
However, with high frequency of water application from sprinkler irrigation the soil may remain in the "energy" limited phase a large percentage of time.
This produces the opportunity for crop residues to impact soil evaporation rates.
Water applied by irrigation is consumed by two processes: soil water evaporation and plant transpiration.
Transpiration, the process of water evaporating near the leaf and stem surfaces, is a necessary function for plant life.
Transpiration rates are related atmospheric conditions and by the crop's growth stage.
Daily weather demands cause fluctuations in transpiration as a result.
Transpiration provides powerful transformation of this energy into forces for water flow through plants.
It also provides evaporative cooling to the plant.
Transpiration relates directly to grain yield.
As a crop grows, it requires more water on a daily basis until it reaches a plateau at maturity.
Soil water begins to limit transpiration when the soil dries below a threshold which is generally half way between field capacity and wilting point.
Irrigation management usually calls for scheduling to avoid water stress.
Ideally, limited irrigation management reduces plant water stress in critical growth periods such as reproductive and grain fill and allows more stress during less critical growth period such as vegetative growth.
Evaporation from the soil surface has a limited effect on transpiration in the influence of humidity in the crop canopy.
However, the mechanisms controlling evaporation from soil are generally independent of transpiration.
The combined processes of evaporation from soil  and transpiration  are measured together as evapotranspiration  for convenience.
Independent measurements of E and T are difficult but independent measurements are becoming more important for better water management.
Field research in sprinkler irrigated corn has shown that as much as 30% of total evapotranspiration is consumed as evaporation from the soil surface.
These results were from bare surface conditions for sandy soils.
For a corn crop with total ET of 30 inches, 9 inches would involve soil evaporation and 21 inches to transpiration.
This indicates a window of opportunity if the unproductive soil evaporation component of ET can be reduced without reducing productive transpiration.
EVAPORATION FROM BARE SOIL
 Evaporation from bare soil surface after irrigation or rainfall is controlled by the atmospheric conditions and the shading of a crop canopy if applicable.
Water near the soil surface readily evaporates and does so at a rate that is limited by the energy available at the surface.
If water is readily available near the surface, bare soils can evaporate 0.4 in.
during one energy-limited drying cycle.
The time it takes to complete an energy limited cycle depends on the energy in the environment.
Bare soil with no crop canopy on a sunny hot day with wind receives much more energy than a mulched soil under a crop canopy on a cloudy cool day with no wind.
After the energy limited evaporation has been completed, evaporation is controlled by how fast water and vapor can move to the surface.
Rate of evaporation diminishes with time as the drying front moves deeper into the soil.
The soil insulates itself from drying because it takes longer for water or vapor to move through the soil to the surface.
EVAPORATION AND CROP RESIDUES
 For more than 65 years, crop residues in dryland cropping systems have been credited for suppressing evaporation from soil surfaces..
Stubble mulch tillage and Ecofallow systems built on this early work with a progression of innovations in tillage and planting equipment and weed management systems to allow for crop residues to be left on the ground surface.
These crop residue management practices along with crop rotations have increased grain production in the dry Central Plains.
Water savings from soil evaporation suppression has been an essential element.
In dryland management, accumulation of 2-4 inches
 of water during the over-winter/fallow period has been possible.
The presence of standing wheat stubble has captured the precipitation, kept it where it has fallen, stored it, and reduced the evaporation.
Crop residues in dryland culture have reduced energy limited evaporation after rainfall events as long as the soil surface is wet.
Crop residues tend to extend the energy limited evaporation phase with time when compared with bare soils.
The evaporation rate is less under the crop residue.
Given enough time between rainfall events, in dryland culture, accumulated evaporation under crop residue could catch up with evaporation for bare soil.
This could take a time framework of weeks.
The contribution of crop residues for soil water suppression is dependent on the frequency of wetting.
GARDEN CITY, KS STUDIES
 A field study was conducted in Garden City, Kansas during 2003-2005 to test the effectiveness of corn stover and wheat stubble for evaporation suppression in soybean and corn grown in 30-inch rows.
Two twelve inch diameter PVC cylinders that held 6-inch deep soil cores were placed between adjacent soybean or corn rows.
These "mini-lysimeters", which were constructed from 21-inch PVC cylinders were pressed into undisturbed soil.
The soil was bare or covered with no-till corn stover or standing wheat stubble to test the maximum effectiveness of various residues for evaporation suppression.
Crop and mini-lysimeter treatments were replicated four times.
Mini-lysimeters were irrigated once or twice weekly when rainfall did not satisfy crop needs.
The mini-lysimeters were also watered to match rainfall events during 2004 since rains occurred during measurement periods that year.
The mini-lysimeters were weighed daily.
Weight differences were the evaporation amounts.
Plant populations were reduced to match irrigation management in the once per week frequency treatment.
The results should be considered as preliminary.
The statistical comparisons have not been completed.
Only some of the large differences should be noted within each year.
Year-to-year differences will be suggested, but should be considered speculative.
Soil water evaporation measurements began and ended within somewhat different time frameworks for the study years.
Yearly variations in results due to duration of observations are reflected in the total evaporation, evaporation savings from bare soil, and the evaporation as a fraction of evapotranspiration.
The latter factor is due to the growth stage during which the measurements were taken.
During 2003 only the more frequent irrigation treatment for soybean was conducted.
During observation period in 2003, only 8 irrigation events were measured.
During 2004 ample rainfall added to 3 and 7
 measured irrigation events for the two soybean treatments and 4 and 9 measured irrigation events for the two corn treatments.
For 2005, only irrigation events were measured during the observation period.
Table 1.
Soil Water Evaporation Summary-2003-2005
 Surface 1	Total E	Daily Rate	E Savings	E/ET	Watering
 			Events 4
 2003 Soybean	July 18 to September 6 
 Bare 1	3.1	0.06	25	8
 Corn 1	1.8	0.03	1.3	14	8
 Wheat 1	1.5	0.03	1.6	12	8
 2004 Soybean	June 9 to September 20 
 Bare 1	6.5	0.06	33	12
 Bare 2	8.0	0.08	32	19
 Corn 1	3.8	0.04	2.7	19	12
 Corn 2	3.7	0.03	4.2	15	19
 Wheat 1	3.4	0.03	3.1	17	12
 Wheat 2	4.1	0.04	3.8	17	19
 2004 Corn	June 2 to September 20 
 Bare 1	5.8	0.05	32	14
 Bare 2	6.6	0.06	35	22
 Corn 1	3.1	0.03	2.7	17	14
 Corn 2	3.8	0.03	2.8	19	22
 Wheat 1	2.7	0.02	3.1	15	14
 Wheat 2	3.8	0.03	2.9	19	22
 2005 Corn	June 21 to August 11, 2005 
 Bare 1	3.6	0.07	29	5
 Bare 2	3.5	0.07	23	9
 Corn 1	1.9	0.04	1.7	16	5
 Corn 2	2.0	0.04	1.5	13	9
 Wheat 1	2.4	0.05	1.1	20	5
 Wheat 2	2.2	0.04	1.3	15	9
 1 Numbers indicate weekly watering frequency  2 Evaporation savings as the difference from bare soil evaporation 3 Evaporation as a percent of calculated ET from water balance 4 Includes rain events in 2004
 Comparison of 2004 and 2005 is risky.
One year was wet , one year was dry in July.
One year had hail  and the other did not.
One year has a longer record of observed days of data.
The differences in soil water evaporation from covered and bare soil surfaces are consistent despite the variable years.
The crop residues covered the entire surface and reduced evaporation nearly in half during the observation periods.
Differences in evaporation between irrigation treatments with crop
 residues were not evident.
If both irrigation treatments were predominately in energy limited evaporation, evaporation would be similar under the crop residue.
A second set of replicated mini-lysimeters was established in a controlled outdoor, non-cropped setting.
Irrigated clipped grass surrounded the control area.
Measurements were taken between September 6 and October 7, 2005.
The mini-lysimeters were buried in the ground but flush with the surface.
The mini-lysimeters' position was rotated daily to avoid location bias in results.
The 12 experimental treatments included:
 surface cover  X irrigation frequency.
Partial cover corn stover treatments were established by evaluating the residue application with line-transect methods using mesh grids over the mini-lysimeters.
The 100% corn stover and wheat stubble treatment lysimeters were similar to the field plot study treatments.
The partial cover treatments were intended to simulate tillage practices equivalent to one pass chisel, one pass tandem disc, and two pass tandem disc for 75%, 50%, and 25% corn stover cover, respectively.
Figure 1 shows the resulting mass of residue cover on the mini-lysimeters for the control study.
Percent cover and total cover mass did not always correlate well because the leaf and stem densities were not necessarily consistent among treatments.
For example, average residue mass for the 50% corn stover actually exceeded the mass for the 75% corn stover treatment
 Figure 2 combines the results of the cumulative soil water evaporation during September 6 to October 7.
The patterns of evaporation results from bare soil, and the partially covered soil with corn stover are very similar.
Statistical analysis will assist in interpretation of these data.
Only the 100% corn stover and wheat stubble treatments appear to behave differently.
The mass of these residue covers from Figure 1 was quite different.
The reduced cover and mass of the partially covered treatments apparently allowed more radiant energy to reach the soil surface and increased evaporation.
Fig.
1 Crop residue mass on mini-lysimeter surface for partial to full cover treatments.
Surface / Water Frequency 
 Fig.
2 Total soil water evaporation from September 6 to October 7, 2005 for bare, partially covered, and fully covered treatments.
No matter how efficient sprinkler irrigation applications become, the soil is left wet and subject to evaporation.
Frequent irrigations and shading by the crop leave the soil surface in the state of energy limited evaporation for a large part of the growing season.
This research demonstrated that evaporation from the soil surface is a substantial portion of total consumptive use.
We measured up to 30% of ET was E during the irrigation season for corn and soybean on silt loam soils.
We also demonstrated under a variety of conditions that crop residues can reduce the evaporation from soil in half even beneath an irrigated crop canopy.
This puts us closer to our goal to understand how reduce the energy reaching the evaporating surface.
We suggest the potential for a 2.5 to 3 inches water savings due to the wheat straw and no-till corn stover from early June to the end of the growing season.
Dryland research suggests that stubble is worth at least 2 inches of water savings in the non growing season.
In water short areas or areas where water allocations are below full irrigation, 5 inches of water translates into possibly 20 and 60 bushels per acre of soybean and corn, respectively.
This work was partly supported by the US Department of Interior, Kansas Water Resources Institute, the USDA-ARS Ogallala Aquifer Research Initiative, the USDA special water conservation grant, and the Kansas Soybean Commission.
Measuring Discharge in Wadeable Streams
 Whitney Blackburn-Lynch, Carmen Agouridis, and Tyler Sanderson, Biosystems and Agricultural Engineering
 S treams and rivers are plentiful in Kentucky from small mountain brooks to large rivers such as the Mississippi River along the Commonwealth's western border and the Ohio River along its northern border.
Kentucky has more than 90,000 miles of streams and contains more navigable water than any other state except Alaska.
These streams provide important ecological services such as transporting water, sediment and nutrients and providing habitats to aquatic organisms such as fish and macroinvertebrates and terrestrial ones such as deer and birds.
Streams also provide societal services, including drinking water, transportation and recreation.
Careful management of these waterbodies is therefore important.
Figure 1.
Kentucky has thousands of miles of  streams  and  and rivers.
Knowing the amount of water flowing in a stream can improve management practices such as those related to streambank erosion, pollutant loading and transport, and flood control.
Streamflow or discharge is defined as the volume of water moving past a specific point in a stream for a fixed period of time.
In the U.S., discharge is commonly expressed in units of cubic feet per second /s or cfs).
Factors that affect the amount of discharge in a stream include drainage area, weather, and water withdrawals.
As drainage area increases, the amount of discharge also increases as more land contributes runoff to the stream.
Large storm events produce more runoff than smaller ones.
Water withdrawals related to irrigation, industrial uses, or even evapotranspiration by riparian or streamside vegetation can decrease streamflow.
Source: Stephen Patton, Agricultural Communications
 How is Discharge Measured?
To measure a stream's discharge, information on the shape of the stream and the speed of the flowing water is needed.
Discharge  is the product of area  and velocity  as shown in Equation 1.
Area is the product of width w, ft) and depth.
Velocity represents the speed of the flowing water in the stream.
Velocity measurements are typically taken in a straight section of the stream.
Such sections are often stable and uniform in shape which are important factors in determining discharge over longer periods of time.
Discharge measurements are often taken using the velocity-area method, which involves dividing the stream's cross-section into multiple subsections.
Within each subsection, area is determined by measuring the width and depth of the subsection.
The average velocity in each subsection is also measured, which typically involves using a current meter.
For each subsection, the width, depth and velocity measurements are multiplied.
The discharge values for each subsection are summed to arrive at the total discharge for the stream cross-section.
Figure 3.
Velocity is often measured using a current meter.
Source: Alan Fryar, Earth and Environmental Sciences
 Continuously measuring discharge in a stream is not practical.
Instead, it is common to measure water level or stage continuously and relate stage to discharge.
Such a relationship, which is termed the stage-discharge relationship or rating curve, allows for the development of a continuous record of discharge.
Rating curves are site-specific
 Figure 2.
The velocity-area method is used to estimate discharge.
The crosssection is divided into many subsections.
because the relationship between stage and discharge depends on factors such as the shape and size of the stream.
Rating curves developed for one location cannot be used for another.
Because streams are dynamic systems, it is important to regularly check and update stage-discharge relationships.
The USGS develops rating curves for its active stream gages.
These rating curves are available at the USGS Ratings Depot.
Q1 + Q2 + Q15
 For small watersheds, a common method of measuring streamflow is with a weir or flume.
A weir is a structure that is used to obstruct the flow in a stream and direct it through an opening of a defined shape.
A flume is designed to be installed in the channel using a specific shape  that closely matches the shape of the original channel.
The stage behind the weir or within the flume is measured and converted to discharge based on a known stage-discharge relationship for that particular structure.
Figure 4.
Example of a stage-discharge rating curve.
Each circle represents a concurrent stage and discharge measurement.
Stage of 2 ft means discharge is about 17 ft3/s.
Figure 5.
Structures such as  weirs and  flumes are used to measure streamflow.
Source: Carmen Agouridis, Biosystems and Agricultural Engineering
 Source: Matt Barton, Agricultural Communications
 One method to quickly estimate a stream's discharge is measure its width and average depth with a tape measure and estimate velocity using a floating object such as an orange peel.
Measure the width of the channel at the water surface elevation.
Take 3-4 measurements of the water depth and average these measurements.
Velocity is estimated by recording the time it takes the floating object to travel a known distance.
Discharge is the product of width, depth and velocity.
Because velocity varies across the stream channel, this method has a lower level of accuracy.
A simple way to measure velocity is by using a float such as an orange peel, a tape measure, and a stop watch.
1.
Use a tape measure to mark a section of stream at least 20 ft in length.
2.
Drop the orange peel about 5 ft above the start of the marked section.
Try to drop the orange peel in the center of the stream.
3.
When the orange peel reaches the beginning of the marked section, start the stopwatch.
4.
When the orange peel reaches the end of the marked section, stop the stopwatch.
5.
Repeat at least two more times.
6.
Add all of the times and divide by the number of repetitions to obtain an average time.
7.
Divide the length of the marked section by the average time to get an average surface velocity and then multiple by 0.8.
The 0.8 correction accounts for the fact that the velocity of water at the surface is faster than water along the streambed.
A 50 foot distance is marked off along a stream.
The times it takes for an orange peel to travel the marked distance are 12, 10, and 11 seconds giving an average time of 11 seconds.
For a distance of 50 feet and an average time of 11 seconds, using the 0.8 correction, the average velocity is 3.6 feet per second.
All of that depends on what Mother Nature brings.
In the event of higher-than-normal temperatures for an extended time period, the irrigation districts might need to allocate water or cut back on the number of days water is delivered.
The Cornhusker State has more miles of streams and rivers than most other states, and more groundwater in underlying aquifers than any other states.
The High Plains aquifer is an average of 600 feet in thickness under the Sand Hills but can be as much as 1,000 feet thick.
Outside the Sand Hills, its average thickness ranges between 100 and 400 feet.
Partners in Protecting Arkansas' Waterbodies
 From the time Arkansas became a state in 1836, it has followed the riparian doctrine of water allocation.
The basic concept of the riparian doctrine is that private water rights are tied to the ownership of land bordering a natural river or stream.
Thus, water rights are controlled by land ownership.
Beginning in the 1950s, questions of water rights and use began to emerge.
Over time, Arkansas has established a governmental administrative system of water allocation called a regulated riparian system.
Traditional riparian concepts still apply in the state; however, there is a regulatory or permit/administrative structure superimposed on those traditional riparian rights.
Today, there are more than 20 organizations with responsibility for ensuring Arkansas' water quality, water quantity and public health are maintained.
Generally, water quantity is the responsibility of the Arkansas Natural Resources Commission.
Water quality issues fall under the authority of the Arkansas Department of Environmental Quality  and the Arkansas Department of Health.
The Arkansas Natural Heritage Commission  protects unique and rare wetland types.
The Arkansas Game and Fish Commission  monitors wetland-dependent wildlife habitat while the Arkansas Forestry Commission  manages forested wetlands subject to timber harvest.
Partnerships with private organizations such as Ducks Unlimited  and The Nature Conservancy  have been critical to water protection.
The Arkansas Highway and
 Transportation Department  even plays a role in protecting the state's waterbodies by planning transportation projects to avoid negative affects on wetlands.
The Arkansas Natural Resources Commission
 ANRC was established in 1963 "to manage and protect our water and land resources for the health, safety and economic benefit of the State of Arkansas." It has the primary regulatory authority for many of the issues related to water rights, water conservation and water quality.
Registering Water Usage with ANRC
 Arkansas Act 81 of 1957 mandates water users to register annually with ANRC the diversion of surface water by quantity, location and type of use.
ANRC issues Certificates of Registration, which the Commission uses to determine water allocations and for gauging the state's overall water usage and water needs.
Users of groundwater are required to register quantity, location and type of use annually
 There are exemptions to registering water usage with ANRC.
Surface water withdrawals of less than one acre-foot per year, diffused surface water or natural lakes or ponds exclusively owned by one person do not need to be registered.
Groundwater withdrawals from individual household wells used exclusively for domestic use and wells with a maximum potential flow rate of less than 50,000 gallons a day do not need to be registered.
with ANRC.
All users of surface and groundwater are assessed an annual water use fee of $10 per registeredsurface water diversion and $10 per registered well.
The fees collected are utilized for cost-share on water conservation practices, administration and information/education programs.
Arkansas Surface Water Laws
 ANRC has authority for:
 Allocating surface water from streams during times of shortage based on the reasonable use concept
 Determining preferential surface water allocations during times of shortage based on sustaining life, maintaining health and increasing wealth, in that order
 Mandating registration of any diversions of surface water from streams, lakes and ponds and
 Issuing dam construction permits.
In 1991, the state enacted the Arkansas Groundwater Protection and Management Act.
The Act allows ANRC to first designate critical groundwater areas and then, if necessary, to initiate a regulatory program requiring that anyone who wants to withdraw groundwater from an existing well or construct a new well within the area obtain a water right from the Commission.
Before ANRC can make the designation of a critical groundwater area, it must hold public hearings in the affected counties describing the proposed action, the reasons for the action and the recommended boundaries of the identified area.
Laws Specific to Aquifers
 In 1997, the Arkansas General Assembly determined that the Sparta Aquifer was "being depleted and damaged by salt water intrusion." The legislature passed Act 237, which expanded ANRC's authority to enter into negotiations with adjoining states relating to the protection and use of interstate waters to include underground aquifers.
The Commission already had such power relating to streams, lakes, reservoirs, channels and impoundments.
Arkansas Act 1426 of 2001 mandated that any well constructed after September 30, 2001, to withdraw
 groundwater from a sustaining aquifer must be equipped with a properly functioning metering device deemed acceptable by ANRC.
Domestic wells are exempt.
Also exempt from the Act are wells for which a water right was grandfathered under the provisions of the Groundwater Protection and Management Act, unless alternative surface supplies are available.
The Act defines sustaining aquifers as any aquifer "which is used as a significant source for water supply including, but not limited to, the Cockfield, Sparta, Memphis, Cane River, Carrizo, Wilcox, Nacatoch, Roubidoux and Gunter aquifers." The Alluvial Aquifer is not listed in the legislation because it is not considered a sustaining aquifer.
ANRC may consider voluntary reductions, water use efficiencies and implementation of water conservation measures in determining limitations or reduction of withdrawals from a sustaining aquifer.
Data gathered by the metering is incorporated into ANRC's annual water use reports.
Nonpoint Source Pollution Program
Overall, our results indicate that an electric motor running at a constant 1770 rpm will use excess energy for much of the center pivot revolution.
VFD operation includes the installation of a pressure sensor somewhere on the system.
The controller part of the VFD adjusts the motor speed to maintain a set pipeline pressure wherever the sensor is positioned.
Some sensors are placed at the pump outlet, but if the irrigated area has a lot of topography, that position is often the worst location for the sensor.
PRESEASON IRRIGATION OF CORN WITH DIMINISHED WELL CAPACITIES
 Many of the irrigation systems today in the Central Great Plains no longer have the capacity to apply peak irrigation needs during the summer and must rely on soil water reserves to buffer the crop from water stress.
Considerable research was conducted on preseason irrigation in the US Great Plains region during the 1980s and 1990s.
In general, the conclusions were that in-season irrigation was more beneficial than preseason irrigation and that often preseason irrigation was not warranted.
The objective of this study was to determine whether preseason irrigation would be profitable with today's lower capacity wells.
A field study was conducted at the KSU-SWREC near Tribune, KS, from 2006 to 2009.
The study was a factorial design of preplant irrigation , well capacities , and seeding rate.
Preseason irrigation increased grain yields an average of 16 bu Grain yields were 29% greater when well capacity was increased from 0.10 to 0.20 in day-1 Crop productivity was not significantly affected by well capacity or preseason irrigation.
Preseason irrigation was profitable at all well capacities.
At well capacities of 0.10 and 0.15 in day1, a seeding rate of 27,500 seeds a -1 was generally more profitable than lower or higher seeding rates.
A higher seeding rate  increased profitability when well capacity was increased to 0.2 in day1.
Irrigated crop production is a mainstay of agriculture in western Kansas.
However, with declining water levels in the Ogallala aquifer and increasing energy costs, optimal utilization of limited irrigation water is required.
The most common crop grown under irrigation in western Kansas is corn.
Almost all of the groundwater pumped from the High Plains  Aquifer is used for irrigation (97% of the groundwater pumped in
 western Kansas in 1995 [Kansas Department of Agriculture, 1997]).
In 1995, of 3 billion m of water pumped for irrigation in western Kansas, 1.41 million acre-ft  were applied to corn.
This amount of water withdrawal from the aquifer has reduced saturated thickness  and well capacities.
Considerable research was conducted on preseason irrigation in the US Great Plains region during the 1980s and 1990s.
In general, the conclusions were that in-season irrigation was more beneficial than preseason irrigation and that often preseason irrigation was not warranted because overwinter precipitation could replenish a significant portion of the soil water profile.
Much of this research was conducted during a generally wetter climatic period in the Great Plains and also under circumstances of ample inseason irrigation capacity.
The Great Plains drought that occurred during the early part of the last decade  renewed producer interest and has brought new questions about preseason irrigation.
In a more recent study Stone et al.
used simulation modeling to examine the effectiveness of preseason irrigation.
They found the differences in storage efficiency between spring and fall irrigation peaked at approximately 37 percentage points  when the maximum soil water during the preseason period was at approximately 77% of available soil water.
Many of the irrigation systems today in the Central Great Plains no longer have the capacity to apply peak irrigation needs during the summer and must rely on soil water reserves to buffer the crop from water stress.
Therefore, this study was conducted to evaluate whether preseason irrigation would be profitable when well capacity is limited and insufficient to fully meet crop requirements.
A field study was conducted at the KSU-SWREC near Tribune, KS from 2006 to 2009.
Normal precipitation for the growing season  is 13.2 in and normal annual precipitation is 17.4 in.
The study was a factorial design of preseason irrigation , well capacities , and seeding rate.
The irrigation treatments were whole plots and the plant populations were subplots.
Each treatment combination was replicated four times and applied to the same plot each year.
The irrigation treatments were applied with a lateral-move sprinkler with amounts limited to the assumed well capacities.
The preseason irrigations were applied in early April and in-season irrigations were applied from about mid-June to early September.
The in-season irrigations were generally applied weekly except when precipitation was sufficient to meet crop needs.
Corn was planted in late April or early May each year.
The center two rows of each plot were machine harvested with grain yields adjusted to 15.5% moisture
 .
Plant and ear populations were determined by counting plants and ears in the center two rows prior to harvest.
Seed weights  were determined on 100-count samples from each plot.
Kernels per ear were calculated from seed weight, ear population, and grain yield.
Soil water measurements  were taken throughout the growing season using neutron attenuation.
All water inputs, precipitation and irrigation, were measured.
Crop water use was calculated by summing soil water depletion  plus in-season irrigation and precipitation.
Inseason irrigations were 9.6, 12.6, and 19.0 inches in 2006; 7.2, 10.1, 15.6 inches in 2007; 8.2, 11.0, 14.8 inches in 2008; and 8.8, 11.8, 17.9 inches in 2009 for the 0.10, 0.15, and 0.20 in day well capacity treatments, respectively.
In-season precipitation was 6.9 inches in 2006, 8.1 inches in 2007, 9.4 inches in 2008; and 14.4 inches in 2009.
Non-growing season soil water accumulation was the increase in soil water from harvest to the amount at planting the following year.
Non-growing season precipitation was 15.0 inches in 2007, 4.2 inches in 2008, and 8.6 inches in 2009 with an average of 9.3 in.
Precipitation storage efficiency  was calculated as non-growing season soil water accumulation divided by non-growing season precipitation.
Crop productivity was calculated by dividing grain yield  by crop water use.
Local corn prices , crop input costs, and custom rates were used to perform an economic analysis to determine net return to land, management, and irrigation equipment for each treatment.
Preseason irrigation increased grain yields an average of 16 bu a.
Although not significant, the effect was greater at lower well capacities.
For example, with a seeding rate of 27,500 seeds preseason irrigation  increased grain yield by 21 bu -1 with a well capacity of 0.10 in day while only 7 bu a-1 with a well capacity of 0.20 in day-1 As expected, grain yields increased with increased well capacity.
Grain yields  were 29% greater when well capacity was increased from 0.1 to 0.2 in day-1 Preseason irrigation and increased well capacity increased the number of seeds ear-1 but had little impact on seed weight.
The optimum seeding rate varied with irrigation level.
With the two lowest well capacities and without preseason irrigation, a seeding rate of 22,500 seeds a-Superscript was generally adequate.
However, if preseason irrigation was applied, then a higher seeding rate  increased yields.
With a well capacity of 0.2 in day-1, a seeding rate of 32,500 seeds a provided greater yields with or without preseason irrigation.
Crop productivity was not significantly affected by well capacity or preseason irrigation , although the trend was for greater crop productivity with increased water supply.
Similar to grain yields, the effect of seeding rate varied with irrigation level.
With lower irrigation levels, a seeding rate of 27,500 seeds a-1 tended to optimize crop productivity.
It was only at the highest well capacity that a higher seeding rate improved crop productivity.
Crop water use increased with well capacity and preseason irrigation.
Soil water at harvest increased with increased well capacity, but this caused less soil water to accumulate during the winter.
Non-growing season soil water accumulation averaged 2.7 in.
Average nongrowing season precipitation was 9.3 in giving an average non-growing season precipitation storage efficiency of 29%.
Preseason irrigation  increased available soil water at planting by 1.7 in.
Seeding rate had minimal effect on soil water at planting or crop water use but increased seeding rate tended to decrease soil water at harvest and increase over-winter water accumulation.
Preseason irrigation was found to be profitable at all irrigation capacities.
At the two lower well capacities, a seeding rate of 27,500 seeds a was -1 generally the most profitable.
However, the highest irrigation capacity benefited from a seeding rate of 32,500 seeds a-1.
Corn grain yields responded positively to preseason irrigation and increases in well capacity.
This yield increase generally resulted from increases in kernels ear1 Preseason irrigation was profitable at all well capacities.
Seeding rate should be adjusted for the amount of irrigation water available from both well capacity and preseason irrigation.
At well capacities of 0.10 and 0.15 in day1, a seeding rate of 27,500 seeds a-Superscript was generally more profitable than lower or higher seeding rates.
A higher seeding rate  increased profitability when well capacity was increased to 0.20 in day1
Drip irrigation saves money in young almond orchards
 Elias Fereres Donald A.
Martinich Thomas M.
Aldrich Juan R.
Castel Eduardo Holzapfel Herbert Schulbach
 Greatest benefit is in orchard's first five years.
Grower may then want to convert to sprinklers.
T processes are combined in water use by an orchard direct evaporation from the soil surface and tree transpiration.
Together, the processes are referred to as evapotranspiration , or orchard water requirements.
Many studies have been conducted in California to determine the ET of various orchard crops under conventional irrigation techniques.
However, this information is not directly applicable to drip-irrigated orchards, because drip irrigation wets only a fraction of the soil volume.
The potential decrease in ET associated with the use of drip irrigation in orchards has been attributed to a reduction in evaporation losses from the soil surface.
Thus, the ET reductions in drip-irrigated orchards, when compared with ET of orchards irrigated by other methods, must be a function of tree size, with the highest savings presumably OCcurring in orchards in the early stages of growth.
In drip-irrigated young orchards, water can be restricted to the tree root zone as opposed to wetting most of the soil with conventional irrigation techniques.
To evaluate the potential reduction in orchard water requirements, it is necessary to measure the ET of drip-irrigated trees of various ages, relating development of the tree canopy to the ET rates as young orchards grow.
One experiment conducted in San Diego County  provides five years of data on water applied to oneto five-year-old avocado trees under sprinkler and drip irrigation.
the Nickels Soils Laboratory, near Arbuckle, Colusa County.
Information did not exist, however, on ET requirements of deciduous orchards under drip irrigation from the first year to full canopy growth.
Therefore, we conducted a four-year ET experiment in a 40-acre orchard of drip-irrigated young almond trees at
 The trees used when the experiment started in 1978 were three years old and were irrigated by two micro-tube-emitters per tree.
The soil, an Arbuckle gravelly sandy loam over a gravelly clay substratum, has low water storage capacity.
To improve soil physical conditions before planting, a volume of about 6 by 6 by 5 feet for each tree had been excavated, and the soil mixed as it was being returned to the pit.
Root development in the excavated zone was enhanced but also largely restricted to that zone.
This fact simplified our soil-water monitoring efforts, because we were able to use soil-water balance techniques to evaluate ET losses.
A major complication in estimating ET of young orchards from soilwater measurements usually results from uncertainties in determining the extent of the tree root zone.
In 1978, three adjacent trees of the variety Nonpareil were selected; 36 tensiometers and 8 neutron access tubes were installed per tree at depths of 1 to 5 feet and at various distances away from the two emitters.
In 1979 one-year-old and three-year-old Nonpareil trees from successive plantings in the orchard were incorporated into the experiment, and three trees per age class were also selected, replicated three times.
During 1979, 1980, and 1981, measurements were then taken on trees that were one to six years old.
One-year-old trees had only one emitter: twoand three-year-old trees had two emitters about 18 inches away from the trunk.
Two new emitters were installed in the fourth season 3 feet away from the first
 ones.
For the trees instrumented in 1979, neutron access tubes and tensiometers were placed only in the vicinity of the emitter and outside the wetted zones.
Our measurements on trees heavily instrumented in 1978 indicated that the highest rates of soil-water depletion occur a few inches away from the emission point and that they decline with increasing distance from the emitter, becoming negligible outside the zone wetted by the emitters.
This pattern results both-from the poor physical condition of the undisturbed soil and from the lack of available water.
Topographical conditions and the soil intake rate characteristics caused much of the seasonal rainfall  to run off the experimental area.
Soil-water measurements with the neutron probe indicated negligible root activity outside the areas influenced by emitter flow.
Even if the tree root system is restricted to the wetted zones, however, there are still two major limitations to using soil-water balance procedures to determine ET.
The first is uncertainty in estimating the deep percolation component of the water balance.
We chose to reduce soil-water content of the bottom of the root zone to the point that deep percolation could be ignored.
This was achieved by supplying the tree in the spring with less than its required amount of water, depleting soil water in the deeper layers of the root zone.
This restricted the measurement periods from early June onwards but improved the accuracy of our ET estimates for such periods.
The second limitation in computing the water used by the trees from soil-water depletion is that, under drip irrigation, both water availability and root density vary with depth and distance from the emitter.
It is then very difficult to integrate the observed soil-water
 changes over the whole tree root zone.
By frequent monitoring of soil-water content and tension  and by adjusting the volume of applied water, we were able to identify periods  when no measurable changes occurred in soil-water content.
For those periods, we can then assume that the water applied was equal to the ET of the tree.
Applied water was measured by multiplying emitter flows times the hours of operation as well as by placing water meters at the inlet of drip laterals going to the experimental trees.
We found that the most precise method was to measure volumetrically the output of one emitter identical to those used for the experimental trees and located a few feet away from them.
All of the emitter flow rates were checked once to twice a week throughout the experimental periods.
The seasonal records of soil-water content and soil-water tension were screened for periods when content changes near the emitters were small enough to be considered negligible.
For those steady-state periods, assuming that deep percolation was also not significant enough to affect the water balance , the water applied would then be equal to the ET.
Data for those periods were then related to potential evaporation during the same periods as measured with a standard U.
S.
Weather Bureau evaporation pan on bare soil outside the orchard.
The evaporation measurements were corrected to estimate the ET of a mature deciduous orchard using information developed at U.C., Davis, by W.
O.
Pruitt.
The graph presents the ET of the experimental trees expressed as percentages of the estimated ET of a mature orchard in relation to the area shaded by the trees.
The relation is nearly linear but departs markedly from the one-to-one relationship.
Young trees that shaded less than 10 percent of their area at
 TABLE 1.
Seasonal evapotranspiration of drip-irrigated almond trees
 midsummer had more than 20 percent of the estimated ET of a mature orchard.
By the time the six-year-old trees shaded around 42 percent, their ET was between 85 and 88 percent of the ET of a mature orchard.
The ET of any crop is directly related to the available energy and to the aerodynamic conditions that prevail in the area.
For young trees irrigated by drip, where the soil is partially wetted and the tree canopy shades only a fraction of the total area, horizontal energy transfer  from the dry areas surrounding the trees must increase the transpiration rate above that of canopies where the whole soil surface is frequently wetted by rain or irrigation.
This explains why the ET of drip-irrigated young trees is higher than would be expected based on their canopy sizes.
To compute seasonal ET of the experimental trees, we assumed that the relation between tree ET and mature orchard ET during the steady-state periods applies throughout the growing season.
Table 1 presents the calculated seasonal ET of young almond trees.
The water savings potential of drip irrigation is maximum the first two years of the orchard, then declines as trees grow and probably becomes very limited after the sixth year.
In comparison with an irrigation method that would cover all the soil surface , the accumulated water savings over the first six years of a drip-irrigated orchard would approximate 11.5 acre-feet per acre.
On the other hand, some sort of localized irrigation is not uncommon in surface-irrigated young orchards, such as use of only two furrows, one on each side of the tree row.
Under those conditions, water savings brought about by changing to drip would be significantly less.
Growers planting new orchards should carefully consider the potential energy savings of using drip irrigation instead of a fullcover sprinkler system in the trees' early years.
Such savings could be between $50 and $80 per acre for the first year only, depending
 on the source of water and the type of sprinkler system.
It may be possible to use drip irrigation the first five years of an orchard and then, using the same underground pipe network, convert to sprinkler, if desired.
To provide guidelines for good management of drip systems, table 2 presents the water requirements of young almond trees spaced 24 by 24 feet from year one to six.
We assumed an irrigation efficiency of 85 percent, which is characteristic of well-managed drip irrigation systems, except for the first year, where we assumed a 60 percent efficiency.
In the first year it is uncertain where the tree root zone is located, and a greater soil volume must be wetted to supply adequate water to the developing root system at all times.
Our results have been partially tested in another experimental orchard in Fresno County, but these results are only preliminary, since they were all obtained in a single location.
Until more research is conducted to evaluate ET of young deciduous orchards under the various irrigation methods, it would be advisable to monitor soil moisture as an independent check of the normal water requirements of drip-irrigated trees.
In applying this approach to a specific orchard, one should use locally available climatic data to schedule irrigations.
In selecting percent ET from the graph, it is necessary to determine or estimate percent cover or shaded area rather than assuming this information from tree age given in table 1.
Trees of similar age are not always equal in size or shaded area.
TABLE 2.
Gross water requirements for drip-irrigated almond trees spaced 24 by 24 feet*
 Gallons per tree per day
 age	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct
 1	2	3	6	7	8	7	5	3
 2	3	6	7	10	12	10	9	6
 3	7	15	16	23	27	24	20	7
 4	13	21	33	43	48	41	32	13
 5	17	36	40	59	67	58	45	24
 6	23	49	54	79	90	78	60	24
 Mature	24	54	61	95	102	89	65	35
 Based on maximum evapotranspiration of 0.25 inch in July.
Minimizing Risks: Use of Surface Water in Pre-Harvest Agricultural Irrigation; Part III: Peroxyacetic Acid  Treatment Methods
 Jessica L.
Dery, Vijay Choppakatla, Jay Sughroue, and Channah Rock
 What is Peroxyacetic Acid?
Peroxyacetic acid  is a colorless liquid with a low pH and a strong, pungent, vinegar-like odor.
PAA is commonly used as an antimicrobial agent for both non-porous hard surfaces and water in various industries, including agriculture, food processing, beverage, wastewater, hospitals, health care, and pharmaceutical facilities.
It is approved by the US Environmental Protection Agency  for use in agricultural waters as a crop protection tool and is allowed under the National Organic Program  for the production of organic crops, livestock, and food handling.
In Europe and the US, it has been used for many years in wastewater treatment plants  as an alternative to chlorinated compounds, due to concerns of the creation of potentially harmful disinfection by-products  when chlorine-based compounds come into contact with organic matter.
More recently, PAA is quickly gaining interest as a treatment option for agricultural irrigation water to reduce potential pathogens, protect public health, meet new food safety guidelines, and reduce the environmental impact on soils and crops.
PAA is a strong oxidant and fast acting disinfectant with biocidal and viricidal properties.
Commercially available solutions of PAA are a combination of aqueous mixtures of peroxyacetic acid, acetic acid, hydrogen peroxide, and water at various concentrations with an added stabilizer to slow decomposition .
While hydrogen peroxide is also a disinfectant, PAA is a more active and potent antimicrobial agent.
PAA is an excellent bactericide and effective against a variety of microorganisms
 Effective across a wide range of temperatures and pH values encountered in irrigation waters
 Typically used in concentrations of 5 to 10 parts per million  for irrigation water treatment
 Commonly used for post-harvest wash water applications and hard surface disinfection to control human health pathogens and spoilage organisms
 Figure 1.
Chemical makeup of peroxyacetic acid.
Is an effective crop protection tool to control both bacterial and fungal plant pathogens
 PAA does not leave behind toxic DBPs: breaks down into oxygen, carbon dioxide and water
 When using PAA, make sure to follow directions according to the label
 Personal protective equipment  should always be used when handling PAA concentrate as it can cause eye and respiratory problems
 What does PAA treat?
PAA is used to treat pathogenic, or disease-causing microorganisms found in water that concern the fresh produce industry.
While disinfection with PAA is effective across a wide range of microorganisms that pose food safety and health risks, some microorganisms are more resistant to PAA than others.
Mainly used in the food industry, PAA has been utilized since the 1950's to reduce spoilage of fruits and vegetables by removing microorganisms and fungi.
It is currently used as a disinfectant in irrigation water and produce wash water, as a sanitizer for surfaces that come into contact with produce, and to remove deposits and prevent
 biofilm formation on food contact surfaces.
A general ranking of PAA effectiveness on various microorganisms, from most effective to least effective is: bacteria > viruses > bacterial spores > and protozoan cysts .
PAA is least effective at inactivating some parasites such as Giardia lamblia cysts and Cryptosporidium parvum oocysts as well as some viruses.
What happens when PAA is added to irrigation water?
As PAA is added to water, there is a release of active oxygen, which is responsible for the oxidation process and disinfecting properties.
Most disinfection occurs within the first ten or fifteen minutes of contact time.
As PAA degrades, it breaks down into its original components: hydrogen peroxide and acetic acid, which further break down into water, oxygen, and carbon dioxide.
When PAA breaks down, it does not persist or leave behind any residual DBPs, making it an environmentally friendly treatment option.
Table 1.
Log reductions of select pathogens-of-concern to the fresh produce industry from WWTP effluent and surface waters used for agricultural irrigation.
Organism	Water Source		PAA	Contact Time		Reduction	Log	Source
 Clostridium Perfringens	spores	WWTP Effluent	2.0 4.5	20-30	<1 	Briancesco et al., 2005
 E.
coli; Total Coliform
 Bacteria	WWTP Effluent	1.5 2.0	20	5	Stampi et al.
2001
 E.
coli 	Surface a	12.7	5	>3.71	Rock et al., unpublished data 2020
 E.
coli 	Surface b	6	-	>4.99	Rock et al., unpublished data 2020
 E.
coli	Surface C	4,	15, 5	6	LaBorde, 2014
 E.
coli	Surface d	2.5	1.3	3.20	Chang, 2015
 Fecal Coliform Bacteria	WWTP Effluent		15	2.7	Nguyen et al., 2014
 Salmonella enteritidis	WWTP Effluent	1.5 3	10	2-3	Koivunen et al., 2005
 Cryptosporidium oocysts	WWTP Effluent	2.0 4.5	20 30	<1 	Briancesco et al., 2005
 Giardia cysts	WWTP Effluent	2.0 4.5	20 30	<1 (91.6	Briancesco et al., 2005
 Hepatitis A	Produce Wash	100	2	0.7	Fraisse et al., 2011
 Norovirus	Produce Wash	100	2	2.3	Fraisse et al., 2011
 aBench-top trial using Colorado River Water  used for agricultural irrigation at the Maricopa Agricultural Center in Maricopa, AZ; buFF field trial in a continuous flow irrigation system using CRW at the Maricopa Agricultural Center in Maricopa, AZ; cBench-top trial using pond water from Russell E.
Larson Agricultural Research Center, Rock Springs, PA; d Full-scale field trial in a continuous flow irrigation system using pond water from the Plateau AgResearch and Education Center, Crossville, TN.
How are pathogens controlled using PAA?
PAA mechanism for disinfection is through the direct oxidization, or the loss of electrons, of the cell wall of microorganisms.
When electrons are lost from the cell wall, bonds between enzymes and proteins break apart, disrupting the cell structure.
As the cell wall and cell membrane continue to break apart, cellular activities shut down, intracellular components leak out and are further destroyed, and ultimately, cell death occurs.
PAA is a stronger oxidizing agent than all forms of chlorine including sodium hypochlorite, calcium hypochlorite, and chlorine dioxide but weaker than ozone.
Table 2 shows the oxidation capacity of disinfectants commonly used in the agriculture industry based on electron volts , a unit used to measure the potential energy of an electron.
The higher the eV, the higher the oxidation potential, and the more effective the disinfectant.
What factors influence the effectiveness of PAA?
The effectiveness of PAA is influenced by several factors such as the quality of the source water, applied dose, contact time, and characteristics of the microbe.
Water quality characteristics that may affect treatment efficacy include temperature, pH, total suspended solids , biological oxygen demand , and nephelometric turbidity units .
TSS are any solids including salt, plant and animal matter, and waste products; BOD is the amount of oxygen that microorganisms consume as they decompose, or break down, organic matter; and NTU is a measure of the water's clarity, or how much it scatters light.
Parameters such as pH, organic matter content, and temperature may be less of an issue with PAA relative to other treatment chemistries.
PAA is effective over a wide range of temperatures between 0C/32F to 40C/104F.
Additionally, the pH of the irrigation water may also affect the efficacy of disinfection, but very
 minimally.
It has been found that at PAA works best under slightly acidic and neutral conditions where pH values are between 5 to 8..
PAA has the advantage of being a potent disinfectant at low concentrations and short contact times.
Previous studies in WWTPs were successful at reducing E.
coli, Total Coliform bacteria, Fecal Coliform bacteria, and Salmonella concentrations by 2 to 5-logs.
In these trials, PAA concentrations were between 0.8 to 3 ppm and contact times ranged from between 10 to 20 minutes.
Over the last ten years, PAA has been studied more intensely as an option for irrigation water treatment by both university and private researchers.
Several variables have been studied to evaluate their relative importance on the effectiveness of PAA for killing human health pathogens or indicator organisms in irrigation water.
The effective PAA concentrations varied between 1 and 20 ppm depending on the bacteria group and inoculum level, water source, and contact time.
Initial dose concentration and contact time are the two variables with the greatest influence on the effectiveness of PAA to treat irrigation water.
A 2014 study conducted by Laborde  evaluated PAA  for E.
coli control using surface water  collected from the Russell E.
Larson Agricultural Research Center, Rock Springs, PA and inoculated with E.
coli.
Five concentrations of PAA  with different contact times  were evaluated.
The results shown in Figure 2 indicate that the rate of destruction of E.
coli increases with increasing concentration of PAA.
For the negative control  and the 2 ppm treatment, less than a 0.5-log CFU/ reduction of E.
coli occurred after 30 min.
At 4 and 6 ppm PAA, a 6-log reduction occurred after 15 and 5 min, respectively.
However, at 8 and 10 ppm PAA, a 6-log reduction occurred after only 2 min.
Table 2.
Oxidation capacity of selected sanitizers/disinfectants used for agricultural irrigation.
Sodium Hypochlorite 	1.36
 electron-Volts is a unit of energy.
The higher the eV, the greater the oxidation capacity.
Source: NOSB, 2000.
Figure 2.
Effect of PAA concentration in SaniDate 12.0 on the destruction of E.
coli.
More recently, research trials conducted by the University of Arizona in 2019 investigated the effectiveness of various PAA formulations.
Both benchtop and full-scale field trials, using surface water  for agricultural irrigation, found that PAA concentrations between 5-20 ppm were very effective in reducing generic E.
coli and Total Coliform bacteria below detectable levels.
The benchtop study showed a >3.71 log reduction of generic E.
coli using 12.7 ppm at 5 minutes contact time.
The full-scale field trial showed generic E.
coli log reductions of >4.99 with 6 ppm PAA in a continuous flow irrigation system at both the middle and last sprinkler heads.
Table 1 provides a summary of microbial log reductions in both WWTP effluent as well as surface waters used for agricultural irrigation water based on organism, dosing concentrations, and contact times.
Microbial characteristics also play an important role in the disinfection efficacy of PAA.
While studies on the inactivation of human pathogenic viruses in irrigation water are limited, studies on PAA efficacy against some viruses relevant to produce safety have been performed on produce wash water.
These show that viruses may be more resistant to chemical disinfection, including PAA, than bacteria.
Fraisse et al.
found that using 100 ppm of PAA for 2 minutes resulted in log reductions of 0.7 for Hepatitis A and 2.3 for Norovirus, both of which are of food safety concerns.
Studies on WWTP effluents also support these findings: that viruses, as well as parasites , may be more resistant to chemical disinfection.
Giardia cysts and Cryptosporidium oocysts showed less than 1 log reduction at 2.0 to 4.5 ppm at 20 to 30 minutes of contact time.
It should be noted that other chemical disinfectants, such as sodium and calcium hypochlorite, are
 also less effective at reducing some viruses and parasites.
While viruses and protozoans are not mandated to be tested under the Food Safety Modernization Act  Produce Safety Rule  or the Leafy Green Marketing Agreement  metrics, they are a food safety and public health concern.
What are the advantages of using PAA?
There are many advantages of treating irrigation water with PAA.
It is approved by the USEPA, has a long shelf-life, is easy to use, is not considered to be mutagenic or carcinogenic, and is less corrosive to equipment than hypochlorites.
The costs are comparable to sodium and calcium hypochlorite and startup typically requires minimal capital investment; however, this depends on the dosing and concentration needs.
PAA will not contribute to increased sodium or chlorides in the soil profile, unlike chlorine-based chemistries, and there are no measurable effects on pH or BOD.
As PAA breaks down it leaves behind no residual disinfection by-products, making it an environmentally friendly treatment option.
Low concentrations are effective across a wide range of microorganisms and in the presence of organic matter, protein residues, or nitrogen fertilizers , helping to keep production costs down while meeting new regulatory demands and protecting public health.
The risk of phytotoxicity is negligible when treating irrigation water with PAA and the EPA has approved PAA as a fungicide/bactericide used to spray crops at rates 20-30 times stronger than used for irrigation water treatment.
What are the disadvantages of using PAA?
Historically, treating irrigation water with PAA cost slightly more than using sodium hypochlorite but new higher concentrations approved by the EPA for irrigation water treatment are available which significantly reduce the cost.
Another potential disadvantage is that transporting large quantities of PAA require hazmat drivers.
All workers coming into contact with the concentrated and undiluted PAA must be trained as pesticide handlers and must wear the proper PPE as the concentrated solution can cause irritation to the skin, eyes, and respiratory system.
A side-by-side comparison of benefits and drawbacks of using PAA as an irrigation water treatment can be seen in Figure 3.
What are recommended PAA rates and methods for application?
PAA can be applied through any type of sprinkler irrigation system  or drip/micro sprinkles.
PAA is commonly drawn directly from the source container  and injected into the irrigation system via either metering pumps  or venturi type injectors.
Metering pumps, which are controlled by a flow meter, are the most precise method for chemigating PAA.
For vegetable production in Arizona and California, research and grower data has shown that injection rates of between 5-10 ppm are optimal for meeting various food safety requirements by associations, FMSA, or customers.
How do you test irrigation water for PAA during irrigation water treatment?
Testing PAA irrigation water can be easy and inexpensive, and tests are readily available for purchase through multiple online suppliers.
These include methods that rely on a color change to approximate levels of PAA , whereas other  methods require the use of a meter and provide more accurate measurements.
PAA is often measured in ppm, which is equivalent to mg/L.
Most methods, depending on the manufacturer and specific product, are able to measure a wide range of PAA concentrations used in agricultural settings.
Testing at the first sprinkler head, nearest the injection site, will verify the applied dose, while testing at furthest sprinkler head from the injection point will help to determine that sufficient treatment and disinfection is achieved throughout the system.
A side-byside comparison of available testing methods used for testing PAA in agricultural irrigation waters can be seen in Table 3.
Simple colorimetric test strips are the easiest and least expensive option used for the estimation of PAA in a water sample.
The user collects a water sample, dips the test strip in, and compares the color change on the strip to a standard on the product label.
Because the reading is based on a color match, the estimation of PAA concentrations may vary by user.
Testing strips used on a daily basis are relatively inexpensive.
Titration kits are another option, although they are more time consuming and may involve a relatively simple calculation to quantitatively determine concentration.
Reduction of a wide range	Protozoa and some viruses
 of microorganisms	may be resistant
 Organic use requirement of
 breaks down into O2, CO2, &
 Efficacy not greatly affected	Must wear PPE to prevent
 by pH, temperature, OM,	eye, skin, and respiratory
 ammonia, or fertilizers	irritations
 No residuals or DBPs, non-
 Figure 3.
Benefits and drawbacks of PAA as an irrigation water treatment method.
Table 3.
Comparison of testing methods for measuring PAA in irrigation water samples.
Testing Methods, Approximate Cost, & Examples	Advantage	Disadvantage
 Easy to use	User bias to match colors
 No equipment needed	only
 Not suitable for low PAA
 Image credit: LaMotte PAA test strips  & Jay
 Sughroue with Quantofix PAA strips.
Does not require a color	Involves calculations
 match.
May not measure below
 Readings based on	5 ppm
 Image credit: Jay Sughroue, BioSafe Systems
 Easy to use	Higher initial investment
 Eliminates user bias	May be sensitive to light
 Ability to test a multitude	May not measure levels of
 of water quality and	PAA below 5 ppm
 	using specific test strips
 Ability to store data
 Battery powered for use in
 Image credit: Jessica Dery, University of Arizona
 However, the advantage is that the reading is based on a permanent color change, from dark blue to clear, which can eliminate user bias.
Meters are another option for quantitatively measuring PAA in water samples.
They are easy to use, portable, and are able to measure and store various water quality and chemical parameters, depending on the meter.
They eliminate user error, but some meters may be sensitive to light and temperature.
They may require a larger capital investment than qualitative methods.
PAA probes used in other industries, including postharvest fruit and vegetable wash water applications, are now being used to continuously monitor and record PAA residual levels for irrigation water treatment.
Cloud based monitoring and recording provides growers and food safety managers increased real-time accessibility to ensure that
 target parameters are being met.
The cost associated with implementing this new technology is offset by the ability to meet the ever-increasing food safety requirements.
What about plant sensitivities?
PAA is commonly used in both greenhouse settings and produce processing plants, and there is evidence of minimal impact on plant tissue or crop quality.
In a field study conducted at Penn State University strawberry blossoms submerged in PAA solutions  up to 18 hours exhibited no damage to blossoms or fruit development.
Alternatively, studies on hydroponically grown produce have shown conflicting results.
Tomato root systems exposed to PAA demonstrated a decrease in oxygen uptake, but shoots showed no negative effects , whereas exposure of hydroponically grown
 water cress to PAA resulted in increased oxygen uptake, growth, and yield.
Note that because hydroponically grown produce lack soils, which can buffer chemical treatments and reduce root stress, these studies do not adequately mimic in-field applications.
In general, in-field water treatment applications, when managed appropriately, have demonstrated minimal impact on crop health or quality.
Peroxyacetic acid has been used for decades as a highlevel disinfectant/sanitizer in industries that require aseptic environments.
Specifically, PAA is used in agricultural postharvest applications as an antimicrobial agent to control human health pathogens and spoilage organisms in wash water  and on non-porous hard surfaces.
More recently, it is becoming an environmentally friendly treatment alternative for irrigation water treatment as it does not leave behind toxic DBPs and is safe for all crops.
Additionally, it is effective against a variety of microorganisms that are of concern for food safety over a wide range of water temperatures and pH values.
It is cost effective, easy to use, and its disinfection efficacy is not significantly influenced by the presence of organic matter, ammonia, or organic nitrogen fertilizers.
University studies have demonstrated it as an effective treatment option for agricultural irrigation water to help meet new water quality standards and protect public health.
Given the anticipated yield decreases, the residual soil N is expected to be high for rainfed crops.
Growers can credit this residual soil nitrate-N in determining fertilizer-N rates for 2021.
To credit residual nitrate-N, sample soil at 2or 3-foot depth during fall or spring to determine the amount of residual nitrate-N and plug this value into the equation for determining the N rate.
Calculate the N rate according to Nutrient Management Suggestions for Corn or Nutrient Management for Agronomic Crops in Nebraska EC 117.
For alfalfa in the stage 4 crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 1.22 inches and the estimated water use during the week of June 19-25, 2023 is 2.05 inches.
For alfalfa in the maturity crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 1.30 inches.
For alfalfa in the full cover crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 1.18 inches.
Terms and Tables for Water Measurement and Management
 Kevin Heaton, USU Extension Agent, Kane and Garfield Counties Trent Wilde, USU Extension Agent, Millard County Clark Israelsen, USU Extension Agent, Cache County Robert W.
Hill, USU Extension Irrigation Specialist
 Dramatic land development of agriculture operations has resulted in the development of small acreage parcels of 1 to10 acres across Utah.
Often, small acreage owners are faced with water management and water technical terms that they are unfamiliar with.
The goal of this publication is to help the reader become familiar with the most common water measurement and management terms.
Additionally, four tables provide water measurement conversions, water elevation conversions to pressure head, maximum flow rates in PVC pipe, and the volume of water delivered to a field.
Acre foot the volume of water to cover 1 acre to a 1 foot depth.
It is approximately equal to 43,560 cubic feet or 325,851 gallons.
Acre inch the volume of water to cover 1 acre to a 1 inch depth.
It is approximately equal to 3,630 cubic feet or 27,154 gallons.
Cubic foot -7.48 gallons.
Cubic feet per second  is a stream 1 foot wide and 1 foot deep, traveling at the rate of 1 foot per second.
For example, 1 CFS is 448.8  gallons per minute.
This is sometimes referred to as "second feet.'
Inline drip irrigation  systems include emitters embedded within a drip irrigation tubing lateral.
The inline emitters are ideal for irrigating hedges but can also be used for irrigation of individual shrubs where the tubing is snaked between and around shrubs and trees.
In-line emitters have several advantages
 There are a large number of emitters , and thus the watered area is large.
Emitters degrade quickly and it is easy to replace one tube rather than many individual emitters.
The tube can be coiled in areas with increased water requirements in order to concentrate emitters in one location
 In-line emitters have proven to be a reliable watering system in agriculture
 Some irrigation companies are now installing in-line emitters in landscapes.
Figure 1.
In-line emitter tubing.
Because the wetting patterns from the emitters overlap, the in-line emitter drip system can be considered a line source of water rather than a set of point sources.
This makes the irrigation schedule calculation simpler.
The watering schedule for the hedge is a function of the hedge geometry and the wetting pattern geometry.
Instead of calculating a watering time based on the entire hedge, it is simpler to calculate based on a length of hedge equal to the distance along the tubing between two emitters.
Calculate plant water use 
 Where LPD = Liters per day used by the hedge for a distance equal to the emitter spacing.
Calculate soil water storage 
 Where S = volume of usable water  in soil in wetted area for each emitter.
-
 Calculate days between irrigation 
 Calculate irrigation run time 
 Where Q = emitter flow rate 
 The evapotranspiration rate  for a length of hedge equal to the distance between 2 emitters is calculated as follows.
LPD = m m 3 = 
 LPD = evapotranspiration per emitter, liters per day, L = length between emitters, m, H = hedge  width, m, ET = depth of evapotranspiration, mm.
Figure 2.
Parameters used to calculate ET for hedge.
The equation to calculate water storage capacity per emitter is similar to equation 1 except that the width of the wetted area is used instead of the width of the hedge.
Figure 3.
Parameters used to calculate soil water storage.
"MAD" AWHC % 1,000 L =L*W*Z* * MAD * 3 AWHC % * MAD  100% where W = wetted width
 Example.
Calculate the watering schedule for an oleander hedge during summer in Flagstaff.
Oleanders are a medium water use plant SO assume that ET = 3 mm/day.
However, they can survive on very little water SO assume that the MAD is 1.0.
Assume that rooting depth, Z, is 2 m.
The oleander hedge width, H, is 1.5 m.
The distance between emitters, W, is 0.3 m.
Emitter flow rate is 4 LPH.
Wetted width from emitters is 0.8 m Clay loam soil
 Calculate plant water use 
 LPD = ET * H * W = 3 mm/day * 1.5 m * 0.3 m = 1.35 LPD
 Calculate soil water storage 
 S = 10LWZ * AWHC % * MAD = 10*0.3* 0.8 * 2 * 18 * 1 = 86 L
 Calculate days between irrigation 
 Days s=S/LPD=86/1.35= = = 64 days
 Calculate irrigation run time 
 Hours = S /LPH=86L/4LPH = 21 hours.
The system should run for approximately 1 day every 2 months.
Sampling Plant Tissue for Nutrient Analysis
 P lant tissue analysis may be useful to diagnose plant nutritional problems or to monitor effectiveness of a soil fertility program.
It is as simple as taking plant tissue samples from growing crops and sending them to a laboratory for nutrient analysis.
However, if plants are sampled incorrectly, the outcome could be misleading and result in inappropriate fertilizer recommendations.
This publication outlines sampling procedures and recommended nutrient content for Kentucky crops.
Tissue sampling should not substitute for a good soil testing program, but rather it is most effective when used in conjunction with soil testing.
Many factors in addition to low soil fertility influence plant nutrient uptake.
Simply adding more of the deficient element may not alleviate the symptoms.
When tissue results are below optimal, you must determine the cause before attempting to correct the deficiency.
Often plant tissue analysis is most useful when small areas of a field appear stunted or discolored.
The nutrient elements measured in plant tissue depend on the laboratory to which the samples are sent.
Most laboratories analyze for nitrogen , phosphorus , potassium , calcium , magnesium , sulfur , boron , copper , iron , manganese , and zinc.
Testing for these 11 elements may be priced as a package.
Figure 1-Corn.
Seedling : Submit entire plant cutting 1 inch above the soil surface.
Vegetative: Submit uppermost fully developed leaf.
Tasseling: Submit the ear leaf.
Other elements such as arsenic , cadmium , chromium , lead , molybdenum , nickel , selenium , and sodium  may be analyzed on request for an additional fee.
Although many of the latter elements are not essential for plant growth, the results may be important for identifying potentially toxic problems in plants and soil.
Mailing Kit and Other Materials
 The University of Kentucky soil testing laboratory does not offer plant tissue analysis; however, most private soil testing laboratories also offer plant tissue analysis.
Contact the laboratory for test availability, price, submission information, and supplies.
Carefully follow instructions on the information forms, and fill out questionnaires completely.
The questionnaire is an important communication between the producer and the laboratory.
Lack of good or complete information may limit the interpretation of the results.
Figure 2-Soybean.
Seedling : Submit entire plant cutting 1 inch above the soil surface.
Vegetative: For plants between 12 inches and flowering, submit only the uppermost fully developed leaf blades.
Remove the trifoliate blades from the petiole, and sample at least 25 random plants.
Figure 3-Wheat and Forage Grasses.
Seedling : Submit entire plant cutting 1 inch above the soil surface.
Vegetative : Break the top two or three leaves  from the plants.
Flowering: Submit flag leaves only.
What and When to Sample
 Sampling at the latest acceptable stage  gives the best picture of the general nutritional status of the plant because most of the nutrient uptake has occurred.
Nutrient deficiencies could still develop when samples are collected at earlier growth stages.
field, samples from "good" and "bad" areas should be compared.
Make sure you sample the same plant part in each area, and be sure that both areas have been treated the same.
As an aid to proper sampling, diagrams of alfalfa, clover, corn, grain sorghum, wheat and forage grasses, soybean, and tobacco are included in this publication.
The difficult aspect of plant analysis is that nutrient levels within the tissue change as the plant or plant part ages.
For example, corn leaves have a high concentration of nitrogen when they first emerge, but the N concentration can decrease rapidly as the plant grows.
This happens because the plant has the ability to move nitrogen from older tissue to younger tissue.
Therefore, the nitrogen analysis you receive from the lab will vary depending on which leaf was submitted.
In addition, nutrient concentration tends to decrease as the plant grows because nutrients are being diluted with greater amounts of plant tissue.
To account for this variability, sufficiency levels have been determined for specific plant parts at critical times in the crop's life cycle.
That is why useful results require close attention to sampling a specific plant part at a particular growth stage.
If tissue sampling is conducted at a time other than listed in this publication or if it is used as an aid for diagnosing problems in a
 Sample Collection and Handling
 corn silks that are starting to turn brown,
 flowers in soybean above the two or three lowest nodes
 seed head that is fully extended in small grains and forage grasses;
 greater than 10% of alfalfa and clover plants that are showing blooms, etc.
For diagnostic purposes, plant tissue samples can be taken anytime after emergence until the beginning of flowering.
At flowering, the plant changes from vegetative to reproductive stages.
Nutrients then move into the seed, fruit, or grain from other parts.
Therefore, a tissue sample taken after initial flowering is not accurate.
Examples of being too late may include:
 Randomly select the suggested number of plants throughout a field or desired sampling area, and remove the designated plant part.
When a nutrient problem is suspected or there is abnormal growth in part of the area, collect two samples for comparison, one from the normal-appearing area and one from the abnormal area.
Collect the designated plant parts and place in a clean brown paper bag.
Dustor soil-covered plant parts should be avoided.
If sampled parts have a slight dust cover, brush gently with a
 Figure 4-Grain Sorghum.
Seedling : Submit entire plant cutting 1 inch above the soil surface.
Vegetative stages: Sample the uppermost mature leaf.
At flowering, sample the second leaf from the head.
Figure 5-Tobacco.
Select the most recently mature or fully expanded leaf.
This is the first leaf from the growing point that is fully developed.
Cell division is complete, but cell expansion will continue.
Prior to topping, it is generally the fourth or fifth leaf from the bud.
soft brush.
Do not rinse or wash with water as some elements may be leached from the sample.
Sampling for diagnostic purposes usually means that some dead or diseased tissue is associated with abnormal plant growth that should be included.
For best results, either allow the samples to air dry or ship them to the lab using a next-day delivery service.
If samples are to be air-dried, keep the bag open in a clean, dust-free area until the sample reaches a moisture content similar to that of dried hay.
One day in a closed vehicle is usually enough to dry the samples.
Never put the tissue into a plastic bag.
When the tissue is dry, the bag can be folded and stapled shut.
Write the sample number and the producer's name on the outside of the bag, and place into the shipping carton with the completed questionnaire.
Collecting Corn Stalk Samples
 Corn stalk sampling is a special kind of plant tissue analysis because it is conducted at the end of the growing season.
It is used to evaluate nitrogen management practices for future crop years.
Stalk samples should be collected within a three-week period beginning at or just prior to black layer formation.
Nitrate levels in the stalk will remain consistent over this three-week period.
Later sampling may result in unreliable readings because rain can leach nitrogen out of the stalk.
If sampling is delayed, well-fertilized fields can appear deficient.
More information about corn stalk analysis is available in AGR-180, "Corn Stalk Nitrate Test." See Table 3 for interpretation guidelines for the corn stalk nitrate test.
Stalk Nitrate Sampling Procedure
 1.
Select 15 stalks per sample.
2.
Sample fields in a similar manner as with a soil sample.
Take stalks that represent the area being sampled.
3.
Avoid stalks affected by insects or diseases or with small ears or no ears.
4.
Remove leaf sheaths.
5.
Cut an 8-inch sample of stalk beginning 6 inches above the ground and terminating at 14 inches above the ground.
6.
Place the samples in a paper sack, rather than plastic, to avoid mold growth.
7.
Immediately send samples to the laboratory for nitrate analysis.
Table 1.
Macronutrient sufficiency range for crops grown in Kentucky.
Crop	Growth Stage	Plant Part	N	P	K	Ca	Mg	S
 Corn	Seedling 	Whole plant	4.0-5.0	0.4-0.6	3.0-4.0	0.30-0.8	0.2-0.6	0.18-0.50
 Vegetative	Uppermost mature leaf	3.0-4.0	0.3-0.5	2.0-3.0	0.25-0.8	0.15-0.6	0.15-0.4
 Tasseling	Ear leaf	2.8-4.0	0.25-0.5	1.8-3.0	0.25-0.8	0.15-0.6	0.15-0.6
 Soybean Early growth	Uppermost mature trifoliate	3.5-5.5	0.3-0.6	1.7-2.5	1.1-2.2	0.03-0.6	0.30-0.80
 Flowering	Uppermost mature trifoliate	3.25-5.0	0.3-0.6	1.5-2.25	0.8-1.4	0.25-0.7	0.25-0.60
 Small	Seedling 	Whole plant	4.0-5.0	0.2-0.5	2.5-5.0	0.2-1.0	0.14-1.0	0.15-0.65
 Grain*	Flowering	Flag leaf	4.0-5.0	0.2-0.5	2.0-4.0	0.2-1.0	0.14-1.0	0.15-0.65
 Grain	Seedling 	Whole plant	3.9-5.0	0.2-0.5	2.0-4.0	0.3-0.6	0.25-0.6	0.24-0.5
 Sorghum	Vegetative	Uppermost mature leaf	3.0-4.0	0.2-0.4	2.0-4.0	0.3-0.6	0.2-0.5	ND
 Flowering	Flag leaf	2.5-4.0	0.2-0.35	1.4-4.0	0.3-0.6	0.2-0.5	ND
 Burley	Seedling	Whole plant	4.0-6.0	0.2-0.5	3.0-4.0	0.6-1.5	0.2-0.6	0.15-0.6
 Tobacco	Early growth	Uppermost mature leaf	4.0-5.0	0.2-0.5	2.5-3.5	0.75-1.5	0.2-0.6	0.15-0.6
 Flowering	Uppermost mature leaf	3.5-4.5	0.2-0.5	2.5-3.5	0.75-1.5	0.2-0.6	0.15-0.6
 Alfalfa	At 1/10 bloom	Top 4-6 inches 	3.0-5.0	0.25-0.70	2.0-3.5	0.8-3.0	0.25-1.0	0.25-0.50
 Clover,	Prior to bloom	Top 4-6 inches 	3.0-4.5	0.2-0.6	2.2-3.0	2.0-2.6	0.21-0.6	0.26-0.30
 Clover,	Prior to bloom	Top 4-6 inches 	4.5-5.0	0.36-0.45	2.0-2.5	0.5-1.0	0.2-0.3	0.25-0.50
 Orchard	5 weeks after cutting or	Whole plant	2.5-3.5	0.25-0.35	2.5-3.5	0.3-0.5	0.15-0.3	0.2-0.3
 Tall	Actively growing	Whole plant	2.8-3.8	0.26-0.4	2.5-3.5	ND**	ND	ND
 * Small grain includes wheat, oats, barley, and rye.
** A sufficiency range for these elements has not been determined.
Table 2.
Micronutrient sufficiency range for crops grown in Kentucky.
Parts per Million 
 Crop	Growth Stage	Plant Part	Fe	Mn	Zn	Cu	B	Mo
 Corn	Seedling 	Whole plant	40-250	25-160	20-60	6-20	5-25	0.1-2.0
 Vegetative	Uppermost mature leaf	30-250	20-150	20-70	5-25	5-25	0.1-2.0
 Tasseling	Ear leaf	30-250	15-150	20-70	5-25	5-25	0.1-2.0
 Soybean Early growth	Uppermost mature trifoliate	ND**	ND	ND	ND	ND	ND
 Flowering	Uppermost mature trifoliate	25-300	17-100	21-80	4-30	20-60	0.1-2.0
 Small	Seedling 	Whole plant	30-200	20-150	18-70	4.5-15	1.5-4	0.1-2
 Grain*	Flowering	Flag leaf	30-200	20-150	18-70	4.5-15	1.5-4.0	0.1-2.0
 Grain	Seedling 	Whole plant	75-400	13.200	12-150	4-20	3-30	ND
 Sorghum	Vegetative	Uppermost mature leaf	75-200	8-100	12-100	2-15	1-10	ND
 Flowering	Flag leaf	65-100	8-100	12-100	2-7	1-10	ND
 Burley	Seedling	Whole plant	50-300	20-250	20-60	5-10	18-75	0.2-1.0
 Tobacco	Early growth	Uppermost mature leaf	50-300	20-250	20-60	5-10	18-75	0.2-1.0
 Flowering	Uppermost mature leaf	50-300	20-250	20-60	5-10	18-75	0.2-1.0
 Alfalfa	At 1/10 bloom	Top 4-6 inches	30-250	25-100	20-70	4-30	20-80	0.2-4.0
 Clover,	Prior to bloom	Top 4-6 inches 	30-250	30-120	18-80	8-15	30-80	0.5-1.0
 Clover,	Prior to bloom	Top 4-6 inches 	25-100	25-100	15-25	5-8	25-50	0.15-0.25
 Orchard	5 weeks after cutting or	Whole plant	50-250	50-200	20-50	3-10	5-20	ND
 Tall	Actively growing	Whole plant	ND	ND	ND	ND	ND	ND
 * Small grain includes wheat, oats, barley, and rye.
** A sufficiency range for these elements has not been determined.
Figure 6-Alfalfa.
Remove the upper 4 to 6 inches of plant at 10% bloom.
Select at least 50 random plants for sampling.
Figure 7-Red and White Clover.
Remove the upper 4 to 6 inches prior to first bloom.
For red clover, submit leaves, petioles, and stems.
For white clover, submit only leaves.
For diagnostic use, a good representative soil sample should be collected.
When abnormal growth areas exist, take one sample from the normal area and one sample from the problem area.
Take individual soil cores adjacent to plants that are selected for tissue sampling.
Soil should not get on the plant tissue as this will contaminate the sample and alter results for iron and manganese.
Soils contain high amounts of these two elements.
Follow instructions for submission of the soil sample to the soil testing laboratory.
Tables 1 and 2 list the sufficiency ranges for crops commonly grown in Kentucky.
If tissue results fall below the sufficiency range, then further evaluation is needed to determine if the deficiency is caused by a low level of soil nutrient or if it is caused by some other factor.
If fertilizer is required to correct a deficiency, then macronutrients  are generally applied to the soil, while in-season micronutrient  applications are usually applied as a foliar spray.
If foliar
 fertilizers are to be tank-mixed with herbicides, be sure they are compatible because some can reduce the efficacy of certain herbicides.
Nutrient levels above the sufficiency range can occur when another nutrient is deficient or if other growing conditions limit normal growth.
Excessive nutrient levels are not concerning except in a few specific situations.
When soil pH is low, manganese  toxicity can be a problem in corn, soybean, and tobacco.
If the tissue Mn level is above the sufficiency range, a soil sample should be used to determine the appropriate amount of lime needed to raise the soil pH.
Very rarely, nutrient levels can be high enough to affect grazing animals.
If toxicity to animals is suspected, contact your local veterinarian.
Table 3.
Interpretation of corn stalk nitrate analysis.
Status		Interpretation
 Low	0-250	High probability that nitrogen was deficient.
Visual signs of N deficiency
 Marginal	250-700	N availability was close to "optimal," but it was too close to economic
 penalties for good N management.
Optimal	700-2000	High probability that yields were not limited by N availability.
Visual signs
 of N deficiency on lower leaves are often observed in this range.
Excess	More than 2000	High probability that N was greater than needed for maximum yields.
IRRIGATION WATER CONSERVING STRATEGIES FOR CORN
 Jose Payero Queensland Department of Primary Industries and Fisheries 203 Tor Street, Toowoomba, Queensland 4350, Australia Phone +61-7-4688-1513 E-mail: Jose.payero@dpi.qld.gov.au
 Irrigation water management has always been important to the people in southwest Nebraska.
It was evident to the farmer in the area from the earliest days that the land was very productive with adequate water.
Thus, over the years a large portion of the area has had irrigation systems developed.
Today, due to numerous factors, water shortages and allocations have become a reality for the farmers.
Finding a way to conserve irrigation water has been an ongoing research topic since the 1920's at the University of Nebraska West Central Research and Extension Center at North Platte.
The studies have found that corn yield are closely related to crop evapotranspiration  and that usually yields would be lowered if ET is lowered.
Additional studies have found that no significant yield reduction occurred when irrigation was delayed and corn was moderately stressed during the vegetative stage.
However, significant yield reductions were found when stress occurred during the pollination and grain filling stages.
The University of Nebraska-Lincoln Extension started the Republican River Basin Irrigation Management Project in 1996, funded by the US Bureau of Reclamation to help area farmers understand and adopt these water saving methods .
Starting in 2002, line-source irrigation based plots have been used to demonstrate three irrigation strategies on farmers= fields.
The layout makes a good field day site because the three irrigation strategies are all within a few hundred feet.
The line source irrigation system shows full application depth to dryland in a range of just 50 ft.
Fields days were held at each of the sites each year.
Counting these sites, and the other sites demonstrating irrigation scheduling tools, twenty-five field days have been conducted with about 760 people attending over the past five years.
The scope of this paper is limited to showing the yield and water use data generated by the project and some of the keys to making these strategies work on the farm.
The Republican River Basin Irrigation Management Project has been conducted in producer fields growing irrigated corn.
The farmers have planted and cared for the crop, with the timing and quantity of water application being the main variable.
The other changes that were made to the farmer=s crops were created in smaller subplots by thinning the corn stand and creating skip row areas.
The population data will not be discussed in this paper.
The purpose of the plots were to demonstrate and compare three irrigation strategies for west central Nebraska.
They included the traditional fully watered strategy and two that conserve water.
The names and descriptions of the strategies are as follows:
 a.
Fully Watered-the traditional Best Management Practice  irrigation management strategy focused on keeping soil-water at a high enough level to prevent moisture stress from being a limiting factor for yield.
The goal of the strategy was to maintain the plant available soil-water  between field capacity and 50% depletion from planting through maturity.
Usually the soil was kept one-half to one inch below field capacity to allow for rain storage.
After the hard dough stage, the soil was allowed to dry down to 60% depletion.
b.
Water Miser BMP the Water Miser BMP irrigation management strategy focused on saving water during the less sensitive vegetative growth stages and fully watering during the critical reproductive growth stages.
Irrigation was delayed until about two weeks before tassel emergence of the corn, unless soil-water became 70% depleted.
Once the crop reached the reproductive growth stage, the plant available soil-water was maintained in a range between field capacity and 40% depletion.
Usually the soil was kept one-half to one inch below field capacity to allow for rain storage.
After the hard dough stage, the soil was allowed to dry down to 60% depletion.
C.
Deficit Irrigation-The deficit irrigation management strategy focuses on correctly timing the application of a restricted quantity of water, both within the growing season as well as over a several year period.
The intent is to stabilize yields between years by applying irrigation based on soil-water depletion.
Less water will be applied during wetter years, while more will be applied through the drier years, with an average over the years equaling the available quantity of water.
The management strategy is to delay the application of water until about two weeks before tassel emergence for corn, unless soil-water becomes 70% depleted.
Once the crop reaches the reproductive growth stage the plant available soil-water  is maintained in a range between 30 to 60% depletion.
It is allowed to dry down to 70% depleted after the hard dough stage.
The idea is that these depletion numbers should be changed based on the amount of water the producer has to work with.
More research is needed to determine guidelines for differing water use levels.
Cooperators and Site Selection
 The cooperators were picked with the help of the local Extension Educators and irrigation district managers in southwest Nebraska.
They were picked because of their willingness to work with the project, interest in water issues, excellent crop production skills, and location of their fields.
The plots were placed on the edge of the field along a public road to facilitate viewing all season by people traveling past the field.
Big signs explaining the demonstrations were placed at each site.
The demonstrations were conducted at three sites each year with the exception of 2003 when only two sites were harvested because one dropped out at the last minute.
The sites have included farms near the Nebraska towns of Arapahoe, Culbertson, Curtis, Holbrook, and Holdrege.
Plot Layout and Management
 The irrigation demonstration sites used three line-source sprinkler laterals to show the Fully Watered, Water Miser BMP or Deficit Irrigation strategies.
A line-source irrigation system refers to a set of sprinklers that are placed in the field and left in the same location for the season.
The sprinkler spacing within the line was 10 ft and the spacing between the lines was 100 ft.
The sprinkler used had a wetted diameter of 80 ft, creating a 20 ft strip between the lines that does not receive any irrigation to represent dryland conditions.
This configuration creates a watering pattern of the planed application depth next to the sprinkler line and a gradual decrease in the depth of application until about 40 ft from the line where no water is
 applied.
The advantage of the setup is that it gives the planed depth of irrigation plus a gradient from the planed depth to dryland.
The sprinkler lines extended 35 ft past each end of the treatment area to create the correct overlap of the sprinkler pattern.
The plot size including the overall sprinkler line length was 300 ft by 190 ft.
The tillage and cropping methods were the normal practices for that farmer and were primarily conventionally tilled furrow irrigated fields.
The timing and the amount of water applied were the only management variables.
The irrigation scheduling and water application was done by the project manager.
Soil moisture data was gathered every two weeks by the neutron attenuation method.
ET data from the High Plains Regional Climate Center was used to predict irrigation needs in-between.
An irrigation scheduling spreadsheet was
 used to manage the data and calculate the application depth for each week.
The soil types were all silt loam and ranged in water holding capacity from about 1.9-2.5 in/ft.
The water application rate was limited to a net application of 2 inches per week  to simulate a typical system for the area.
The plot yields have been measured each year by either hand harvesting or with a plot combine.
The data has been collected and summarized across the 100 ft width of each of the line-source sprinkler systems.
This represents ten yields points that range from the planed irrigation depth to dryland, eight that received irrigation and two that were dryland.
Table 1 shows the yields and the amount of water that was applied to the three strategies at the farmer=s
 Table 1.
2003-2006 Average of Corn Yields and Water Use by Management Strategy and Site
 Fully Wate Water Mise	Def.
Site	Average Yields 
 Culbertson	150	165	117
 Holdrege	239	244	233
 Curtis	219	223	177
 Arapahoe	192	185	171
 All Sites 1	198	203	174
 Percent of Fully Watered Yield	100	102	88
 Site	Applied Water 
 Culbertson	10.1	9.0	5.6
 Holdrege	6.0	4.7	3.4
 Curtis	9.5	9.5	7.0
 Arapahoe	8.9	8.1	6.9
 All Sites 1	8.9	7.6	5.5
 Percent of Fully Watered Applied Water	100	85	62
 Yield and applied water are weighted by the number of years of data at each site.
irrigated populations.
The data is for the center two plots, one on each side of the sprinkler lines.
The applied water numbers are a net irrigation amount and would need to be increased by five to ten percent to represent a center pivot.
Table 1 contains 10 site years of data, two from Holbrook , two from Culbertson , two from Holdrege , two from Curtis (2005-
 06), and two from Arapahoe.
The data for 2002 is not included in this table because of startup problems.
Yields and Water Usage
 The yields and water usage from 2003-2006 averaged over the five sites are shown in Table 1.
It shows that the Water Miser BMP strategy obtained 102% of the yield, as compared with the Fully Watered strategy, requiring only 85% as much irrigation or 1.3 inches less.
Using the Deficit Irrigation strategies, 88% of the Fully Watered yield was obtained, using only 62% of the irrigation water.
The Water Miser and Fully Watered yields were only four bushels apart and were very close to the farmer=s yield in the rest of the field.
Considering these facts, the Water Miser and the Fully Irrigated strategies produced essentially the same yield and the yields were not limited by a lack of water.
However, the Water Miser strategy reduced the pumping requirement by 1.3 inches.
So the advantage is in saving on pumping costs which range in southwest Nebraska from $2.50 to $15.00 per acre.
Thus, the Water Miser would create a savings of $3.25 to $19.50 per acre in pumping cost.
An economic comparison of the Deficit Irrigation is shown in Table 2 over a range of corn prices and irrigation water pumping costs.
This table is important to study and find where each irrigation system would fall because in southwest Nebraska pumping cost are extremely variable.
Also, with the price change in corn over the past year, the economic returns have changed as well.
An important point to understanding how to interpret this chart is that the corn price is to be the cash price less the harvest, storage, and marketing costs.
This number can easily be $0.40 to $0.50 per bushel less than the cash price.
A second example with higher pumping costs and lower corn prices is worth looking at.
Consider if the price of corn is $2.00 per bushel and the harvest cost would still be $0.50 per bushel or a net price of $1.50 per bushel and the pumping costs were $12.50 per acre-inch.
Looking these numbers up on the
 Table 2.
Sensitivity analysis over a range of water costs and corn prices comparing the Fully Watered to the Deficit Irrigation strategy.
Comparison of Deficit to Fully Watered Strategies
 Cost to apply 1 inch of water/acre, $/a
 $2.50	$5.00	$7.50	$10.00	$12.50	$15.00
 $1.50	-$28.20	-$19.82	-$11.43	-$3.04	$5.34	$13.73
 $2.00	-$40.40	-$32.01	-$23.63	-$15.24	-$6.85	$1.53
 $2.50	-$52.59	-$44.21	-$35.82	-$27.44	-$19.05	-$10.67
 $3.00	-$64.79	-$56.40	-$48.02	-$39.63	-$31.25	-$22.86
 $3.50	-$76.99	-$68.60	-$60.21	-$51.83	-$43.44	-$35.06
 $4.00	-$89.18	-$80.80	-$72.41	-$64.02	-$55.64	-$47.25
 Keys to Making the Water Miser BMP Strategy Work on the Farm
 The Republican River Basin Irrigation Management Project=s original goal was to help farmers use less water in irrigated crop production, not just show that it could be done.
So, lets talk about some of the important things that need to be done by producers to make these strategies work on their farms.
Taking the time to get good information and putting it into an irrigation scheduling system is the key.
Knowing when to start irrigating for the season, what to do after a rain, and when to stop for the season are the main questions to be answered.
The differences between each systems capacity or it=s ability to deliver water to the field varies greatly and is another important point to focus on.
Some systems need to run every hour of every day all
 summer to irrigate the field adequately and others need only run three or four days per week.
Add this to the variability of the rain that each field receives and it emphasizes the importance of recording how much water the field has received.
In almost all cases, the producer's fields received more irrigation water than the Fully Irrigated treatments and yet resulted in essentially the same yields.
The differences were usually that the fields were irrigated earlier in the season and quicker after a rain.
Moreover, the field was wetter when the corn matured.
The advantage that the plot manager had was better soil moisture readings, good rainfall records for each individual field, and accurate irrigation application amounts.
This information was put into an irrigation scheduling program that was used to manage the data and help determine when the next irrigation would be needed and how much to apply.
The biggest advantage of the scheduling program was organizing the data and helping determine the last irrigation.
The four keys to making the Water Miser BMP work are:
 1.
Invest in soil moisture monitoring equipment and use it.
Spending the money to purchase devices that log the readings as they are taken is worth the extra cost.
2.
Critically evaluate when to start irrigating.
Most producers start irrigating before it is needed, particularly with center pivots that can water the entire field in 2-4 days.
The crop should be lowering the soil moisture levels in the second foot of soil  before irrigation is started.
Caution: On low capacity systems, start irrigating as soon as the field can store the irrigation water.
3.
Keep good rain and irrigation application records and compare them to what the ET has been for the field.
The problem is that every irrigation system has a different capacity and every field receives a different amount of rain, so running all system about the same numbers of hours will over water some fields and under water others.
4.
Starting at the dough stage, calculate the amount of rain and irrigation that is needed to get the crop to maturity.
The water levels in the soil depths from 12 to 36 inches should be getting dryer by the start of the dough stage.
The goal is to have the soil moisture level lowered to 40 percent of plant available water by maturity.
Delay the last irrigation with center pivots as long as possible to see if a late rain will provide the needed water.
The Republican River Basin Irrigation Management Project has provided numerous educational opportunities that have helped farmers produce top
 yields while using less water.
It has also generated valuable on-farm real world numbers for the management strategies that conserve irrigation water.
The Water Miser BMP and Deficit Irrigation strategies proved to be valuable water conserving practices at the research level and have now shown to be effective in plots in farmers= fields across south west Nebraska.
Because of a growing concern about manure irrigation, the University of Wisconsin Extension assembled a workgroup to research the concerns.
The workgroup included scientists, public health specialists, state agency experts, farmers, conservationists and others.
Over the course of two years, the group gathered and studied the science of manure irrigation, which culminated in a report that contains findings, responses and recommendations.
The University of Nebraska Institute of Agriculture and Natural Resources, Water for Food Daugherty Global Institute, Nebraska Water Center, and other partners at the local, state and federal level lead the world in water research.
The leadership, research and education these partnerships provide will ensure efficient water use and stewardship of this finite resource for the state and its residents for years to come.
Starter, Banding, and Broadcasting Phosphorus Fertilizer for Profitable Corn Production
 The phosphorus  application methods used in corn production fields can impact yield and net profitability.
The primary benefit from banding P is that it concentrates the P in a small zone near the plant, which can improve P availability.
The objectives of this chapter are to: 1) discuss different P application methods, 2) summarize research comparing P application methods, 3) review the effect of band distance from the seed, 4) discuss safe amounts of P-containing fertilizers that can be placed with the seed, and 5) consider strengths and weaknesses of the application methods.
Plant-available P moves slowly through the soil by diffusion to the root.
Diffusion is the movement of ions from an area with high concentration to an area with low concentration.
Factors that influence P diffusion are soil texture, water content, bulk density, pH, temperature and the distance between higher soil P concentrations zones such as bands and the root.
P diffusion rates are higher for finer textured soil , higher soil water content, lower soil bulk density, soil pH between 5.0 and 6.0, higher soil temperatures, and shorter distances from root to soil zones with higher P concentration.
Crops with finer root systems or those that have been colonized by arbuscular mycorrhizal fungi  may have higher P uptake efficiencies.
Adopting no-till practices that encourage fungi growth and development can encourage AMF colonization.
Figure 26.1 P applied as a broadcast or banded application.
Phosphorus fertilizer application methods include broadcast, banded, or band-applied with the seed.
Liquid or dry fertilizers are used with any of these placement options.
Starter fertilizers, placed at planting, can be located to the side of the row or with the seed.
Usually, only a portion of the total recommended P rate for optimum corn yield is placed as a starter, unless the recommended P rate is low enough to enable full rate application.
The balance of the P recommendation that is not applied as a starter needs to be applied with another method.
Concentrating fertilizer P in a band often improves P availability as there is less opportunity for the fertilizer P to be tied up in the soil, especially at very low or high soil pH.
Rates can sometimes be reduced by one-third or more for band-applied P.
However, reducing rates can result in a decline of soil test P over time, which can reduce yield potential.
Phosphorus can be applied in a variety of forms ranging from liquid to solid products  and the application technique will depend on your goals, your soil test value, and tillage and equipment options.
Tillage system and equipment availability play an important role in determining what choice a corn grower makes when considering P placement.
Equipping a very large planter with fertilizer application equipment can be less than desirable because the added weight can lead to higher soil compaction.
Frequently asked questions regarding P placement for corn:
 1.
What P application method returns the greatest economic return?
2.
What distance from the corn row should P bands be placed?
3.
How much fertilizer can be placed with the seed at planting?
P Application Method Comparisons 
 Choosing the most appropriate P application method is complicated by the many factors that influence plant P uptake efficiency.
Placing the P in a band near the seed may increase plant P uptake efficiency because it concentrates P in a zone easily reached by early root growth.
In addition, P diffusion from the band to the root is high due to a large concentration gradient when compared with broadcast P application.
However, when the bulk soil test P is high, the benefits of banded P are reduced.
Therefore, knowing soil test P level is important when determining placement options.
The optimal balance between P banding and broadcast application is difficult to achieve.
Soil fertility researchers conducted research studies at several land-grant universities between 1970 and 2015 that compared banded and broadcast P applications.
This research suggested that the benefit from banding P increased with yield potential.
For example, at yield less than 100 bu/acre banding and broadcasting P had similar yields, whereas at 200 bu/acre, banding P had a 7.4 bu/acre yield advantage over broadcasting P.
When the P rate was considered, the yield advantage from banding was higher when the P application rate was 40 lbs P,O acre.
Based on these findings, banding is recommended when yields are greater than 150 bu/acre, P rates < 40 lbs 2 O acre, and soil test P is
 Figure 26.2 Band and broadcast P corn grain yield comparison from P placement literature review.
Figure 26.3 Band and broadcast P relative grain yield comparisons across P rates taken from literature review.
at or below the medium category.
These recommendations are contrary to findings from Iowa, where banded and broadcast treatments had similar yields.
Differences between South Dakota and Iowa may be attributed to differences in rainfall, length of growing season, and tillage.
Could higher soil moisture conditions in South Dakota no-till cornfields result in similar conclusions between banded and broadcast P?
Phosphorus placement research projects were conducted in South Dakota between 1998 and 1999 at nine sites located in corn grower no-till fields.
Phosphorus fertilizer was either placed as starter  or broadcast at 40 lbs P,O 2 , /acre.
5 Statistical comparison between the two treatments showed that site year was significant, which is indicative of a wide range of yield environments used in the project.
The banded P treatment  grain yield average was greater than broadcast , but not statistically significant.
A relative grain yield comparison of broadcast and banded P across Olsen P soil test levels showed that banded P resulted in greater yield at the 4-6 ppm soil test range and similar yields when the soil test value was 10 ppm.
Distance of P Band from the Seed
 Phosphorus band distance from the crop root is another factor influencing P uptake efficiency.
Few research studies have investigated the optimal P band distance because it requires specialized research equipment.
Research conducted in 2004 and 2005 near Beresford, SD, and Brookings, SD, evaluated the effect of P band distance from the seed furrow on grain yield.
This research showed that the greatest yield increase occurred when the P band was located 2 inches from the seed.
In some situation, placing the P fertilizer with the seed can improve P uptake efficiency.
Triple super phosphate  was a very common P fertilizer material in the past and was very safe for seed application.
However, for various reasons, this material is not produced to a great extent by the plant food industry.
More recently developed P sources containing nitrogen include ammonium polyphosphate , monoammonium phosphate , and diammonium phosphate.
A number of liquid P sources containing N, P, and K have been developed such as 7-21-7, 4-10-10, 3-1818 and 9-18-9.
In addition, numerous mixed fertilizers have been developed containing secondary and micronutrients as well.
A pop-up fertilizer calculator has been developed for determining safe pop-up
 Figure 26.4 Relative no-till corn grain yield of broadcast and banded P comparisons at 9 locations in SD from 1998 to 1999.
Figure 26.5 P band distance from corn seed furrow influence on relative grain yield at 4 locations in eastern South Dakota during 2004 and 2005.
Soil Moisture at Planting
 gallons/acre 
 Fine/Medium	5.8 	7.8 	11.7 
 Coarse	4.7 	5.8 	7.8 
 fertilizer rates.
This calculator considers the fertilizer source, soil texture, soil moisture, row width, and risk adversity.
The calculator was developed using laboratory method results that were well-correlated to field study data.
There are many different techniques that can be used to apply P to soils.
Each application approach has strengths and weaknesses.
South Dakota has a frigid, semi-arid environment that may influence plant responses to P compared with other corn growing regions.
In our soils and climatic conditions, management practices that encourage early growth may result in higher corn yields.
Different outcomes may be found in more temperate environments.
This paper contains several key summaries including:
 1.
Understanding soil phosphorus, the meaning of soil P test levels, and the factors influencing P movement  to plant roots are very important for optimal P placement.
2.
At lower P,O, application rates , band-placement grain yields were higher than 5 broadcast and generally occurred at research sites with soil test P below the medium level.
3.
In South Dakota no-till corn research, corn grain yield from fertilizer band  applications were higher than broadcast applications at soil test  P levels less than 10 ppm.
4.
P bands placed 4 inches or less from the seed furrow returned the highest grain yield.
Table 26.2 Strengths and weaknesses of P application methods.
Pop-up	Promotes early growth.
Can reduce germination if the rate is too high.
Can increase yields if soil test values are low.
Ammonia contained in the fertilizer can reduce
 Increases P uptake efficiency when soil test P is	germination.
lower.
Extra equipment for planter to carry.
Some liquids are more corrosive and can damage
 Additional P fertilizer may have to be applied to get
 Broadcast	Can be easily applied.
May be less effective than banding for low P rates.
Will increase the bulk soil P level.
May be less effective when soil test P levels are low.
Will increase corn yields.
Could be as effective when compared with banding
 when rates > 40 lbs /acre.
Banded	In high-yield environment can increase yields.
May not be effective for low-yield potentials.
Most effective if the soil P level is in the low to	May not be practical for high P rates.
medium level.
Extra equipment for planter to carry.
Bands should be placed less than 5 inches from the	Some liquids are more corrosive and can damage
 seed.
equipment over time.
Increases P uptake efficiency when soil test P is	Additional P fertilizer may have to be applied to get
 lower.
the recommended rate.
Excellent resources for this series and more information include the ACEN 457/857 Water Law Class, David Aiken, JD, University of Nebraska; Flatwater: A History of Nebraska and Its Water; An Atlas of the Sand Hills; The Groundwater Atlas of Nebraska ; and USGS Estimated Use of Water in the United States.
AVAILABILITY OF CLIMATE DATA FOR WATER MANAGEMENT
 ABSTRACT.
Evapotranspiration from crops causes depletion of soil water reserves and without rainfall or irrigation to replenish the soil moisture serious crop stress can occur.
The Nebraska Automated Weather Data Network  was initiated in 1981 in order to provide information on weather variables that effect crop water use: air temperature, humidity, solar radiation, wind speed/direction, soil temperature, and precipitation.
By 2003 the public access to AWDN and related products reached 12M per year.
This paper describes the Automated Weather Data Network  and the interfaces that provide near real time climate services with emphasis on evapotranspiration  or crop water use.
Currently, automated weather stations are monitored daily at 54 locations in Nebraska and 10 new stations have been purchased with federal drought funds.
There are over 150 stations available in a nine state region.
Several major hurdles must be cleared in order to adequately monitor climate resources.
First, an adequate data collection system is needed to monitor critical variables at an acceptable sampling and delivery frequency.
Second, quality control  and assurance  are necessary.
The QC and QA, when linked to a quick response maintenance and repair capability ensures complete and accurate data for use in summaries and products.
Third, regular client feedback  is needed in order to meet the needs of decision makers and resource managers in the targeted sectors of the economy.
It is essential that the interfaces serve the general consulting communities, so that the private sector can develop and deliver value-added products In some cases, applied research is needed to develop models and other technological tools for the purpose of relating the current climate situation to the area of interest.
Another requirement is adequate technology to deliver the summaries and products in a timely manner.
The use of electronic equipment to automate the collection of measurements from weather-related sensors at remote sites has ushered in a change in the ability to collect weather data and Nebraska was the clear leader in this revolution (Hubbard
 Communication and computer technology have greatly increased the ability of scientists to monitor and disseminate the important climate signals.
The High Plains Regional Climate Center  in the School of Natural Resources engages in applied research necessary to improve climate products including crop water use estimates.
Automated weather stations are maintained at 54 locations in the state.
These stations collect hourly data for variables known to be of importance to agricultural crop and livestock production, including air temperature and humidity, soil temperature, precipitation, wind speed and direction, and solar radiation.
A computer calls each station beginning at 1 A.M.
The data for the previous 24 hours is downloaded, quality controlled, and archived for use by the HPRCC system.
A telephone line or a cell phone is installed at each site.
A flow diagram is shown in Fig.
1.
Software and system components were developed for this system.
Weather stations at remote sites monitor sensors every 10 sec and calculate the hourly averages and where appropriate totals.
The minimum set of sensors is shown in Table 1.
The installation heights shown are standard for AWDN stations.
The AWDN in Nebraska has grown from 5 stations in 1981 to 54 stations in 2003.
Much of the initial growth was due to the interest of researchers who were operating digital weather stations without the benefit of telecommunication or a data management system.
Beginning in 1983, the AWDN began to include sites from surrounding states.
As time passed the interest in additional stations came from the private sector, resource management agencies, and communities.
Maintenance is an important and costly activity.
Replacement of sensor components includes bearings in the cup anemometer and potentiometers in the wind vanes.
Relative humidity sensors are calibrated on an annual cycle.
The tipping bucket is checked for level and calibrated each year by using the volume to mass relationship for a known amount of water.
Leveling screws are adjusted if needed in order to obtain the correct number of tips.
Certain sensors are removed from service for calibration.
The silicon cell pyranometers are calibrated as a group against an Eppley Precision Spectral Pyranometer.
In a similar manner anemometers can be calibrated against a "secondary standard." Thermistors and humidity sensors can be calibrated directly under controlled conditions.
The AWDN facility maintains dry block calibrators and dew point generators for use in calibrating temperature and humidity sensors.
Complete troubleshooting guidelines have been developed.
AWDN repair and calibration
 3.0 DATA MANAGEMENT AND APPLICATIONS PROGRAMS
 A tremendous amount of data can be generated with an hourly weather network.
About 1 Mb of data is produced annually for any three stations.
If this data is to be used effectively it must be easy to access.
Thus, data management is a real concern.
In the case of the AWDN, the approach has been to develop a data management system written entirely in FORTRAN.
This system is indicated as the data base component in Fig.
1.
A suite of utility programs includes tools for data management, quality control, data retrieval, and station selection.
Applications software includes programs  to analyze data and produce summaries for any variable over any desired time period.
Summaries include temperature, precipitation, heating and cooling degree days, growing degree-days, evapotranspiration, leaf wetness, soil water, and crop yield.
On the HPRCC Internet site for on-line subscribers a crop water use report may be generated by selecting inputs from the screen depicted in Fig.
3.
The user is able to choose any combination of crops, maturity groups, and emergence dates.
An example of the ET product is shown in Fig.
4 as it would appear on the computer screen.
The High Plains Automated Weather Data Network has served as a source of data for both research and service efforts.
Some of the research aspects will be covered in this section and the service aspects will be covered in the following section.
Evaporation  at the earth's surface is a major component of the hydrological cycle and is critical to irrigation scheduling from a water balance approach.
Research in the area of evapotranspiration has included efforts to identify the effect of random and systematic errors in measurements used to calculate potential ET  as well as efforts to improve the projections of potential ET.
The AWDN has also been essential to determining appropriate limits for potential ET in the very arid parts of the High Plains region.
Monitoring of drought conditions is another research focal point.
Robinson and Hubbard  evaluated the potential use of network data in the assessment of soil water for various crops grown in the High Plains.
A Crop Specific Drought Index
  for corn has been developed and tested.
Results from the studies indicate that the CSDI for corn will be valuable when applied to drought assessment.
A CSDI for sorghum  was later developed.
Accuracy of interpolation between stations in a network is a topic of research.
The spatial interpolation of potential ET  was examined using AWDN data.
On a related topic, the AWDN data were used to examine spatial variability of weather data in the High Plains.
Another study examined whether it is better to interpolate the weather variables for computing potential ET at a site or to interpolate the potential ET calculated at the surrounding stations.
The AWDN system has been used to collect basic meteorological data for various field experiments.
Data taken by the system are also being used in urban water use studies and in project Storm.
Digital data disseminated by the HPRCC from the new system can be redistributed several times by HPRCC clientele to their user audiences.
The current On-line System offers both opportunities and challenges.
The positive features of the system are:
 accessible via the web
 the computing power of a work station.
clientele have on-line access to the historical data archives that date to the late 1800's.
users can make general summaries according to their own specifications
 up-to-date data is available for decision makers who require it
 an autopilot feature allows users to schedule future summaries, saving the time otherwise required to logon and re-create the summary
 greater simplicity of interface
 navigation by 'mouse' point-and-click
 The combined accesses to HPRCC internet resources is currently about 12M per year.
6.0 NEW APPLIED CLIMATE INFORMATION SYSTEM
 NOAA's National Climatic Data Center  and NOAA's Regional Climate Centers  are developing a new internet based system designed to provide directed access for user specified queries to the entire combined climate data archives.
The new system is called the Applied Climate Information System.
ACIS is a distributed and synchronized system that provides consistent and timely climatic products.
The implementation of the system at multiple centers provides redundancy and ensures timely availability.
The synchronization and standardization ensures that users will receive the same information regardless of the point of contact.
The system was designed with layers of independent modules interconnected by Common Object Request Broker Architecture  to ensure flexibility in both the location and programming language of the modules.
We have used 'open source' and standards based software to reduce any barrier to usage.
ACIS was designed to allow access through three interfaces that provide a different balance of detail, customization, and ease: 1) low-level CORBA, 2) mid-level XMLRPC and 3) high-level web-based interfaces.
Even the low-level interface provides a fairly abstracted and coherent view of the climate data.
Figure 1 shows a series of program steps in the python programming language.
In part A, the program gets the acis_id for a station associated with a Cooperative Observer Network station identifier that reports daily maximum temperature.
The acis_id is an internal id that will define a climatologically coherent record regardless of how the data is reported.
Part B of the program creates a TSVar  that represents the TMAX values from that station.
When a date range is set and data requested, the data server will collect data from local or remote data stores and return it to the client.
The client program does not need to know the data format or location.
These data stores will change dynamically to return the best available data at the time of the request.
To avoid a single point of failure and regulate traffic, redundant ACIS computer
Turfgrass Consumptive Use Values for the Tucson Area
 Consumptive use  curves that provide average rates of turfgrass evapotranspiration  are widely used by irrigation professionals for design and management of turfgrass irrigation systems.
For approximately 35 years, the bermudagrass lawn CU curve developed by the United States Department of Agriculture  has served as the lone published CU curve for turfgrass in Arizona.
While the USDA CU curve has proven useful to the turf industry, turf professionals do question whether ET values obtained from the curve are relevant to turf systems commonly used in Arizona today.
The USDA curve was developed for the summer turf season using a low-maintenance common bermudagrass mowed to a height of 3.8 cm  every four weeks, and watered every two weeks using flood irrigation.
A relevant turf system today consists of hybrid bermudagrass maintained at a height of ~ 2 cm  and watered at frequent intervals using sprinkler irrigation.
The practice of overseeding with ryegrass in the fall to maintain green cover in winter is also common today.
The USDA CU curve does not address the issue of overseeding and provides no information on ET for the period mid-October through mid-April.
A number of research studies have been completed in recent years to quantify the water requirements of turfgrass grown in the low desert regions of Arizona.
Several studies had as their primary objective the development of crop coefficients  that convert reference evapotranspiration  data computed from meteorological data  into estimates of ET.
In this report, we apply Kcs developed from these studies to long-term records of ETo to provide updated CU information for turfgrass grown in the Tucson metropolitan area.
Estimates of ET1 were computed on a daily basis for the period 1987 through 2000 by applying turfgrass Kcs to the historical record of reference evapotranspiration  available for Tucson from the Arizona Meteorological Network.
The mathematical
 Figure 1.
Consumptive use curves for high and acceptable quality turf grown in the Tucson area.
procedure used to produce the ET estimates involved multiplying the appropriate crop coefficients  by ETo:
 ET, = Kcs x ETo
 The Kcs used to estimate ET were developed for a common desert turf system consisting of Tifway
 Turf Irrigation Management Series: IV
 THE UNIVERSITY OF ARIZONA COLLEGE OF AGRICULTURE AND LIFE SCIENCES TUCSON, ARIZONA 85721
 Paul Brown Biometeorology Specialist
 bermudagrass in summer and overseeded ryegrass in winter.
Other assumptions implicit in the use of the Kcs employed include frequent irrigation with sprinklers, mowing heights ranging from 0.625-1.0" in summer and 0.875-1.25" in winter, and two levels of turf quality defined as high and acceptable.
High quality turf areas would include high profile sports turf  and areas where turf appearance is very important.
These areas generally receive high levels of fertilization and maintenance.
Acceptable quality turf would be suitable for lawn or park environments where traffic is low, rapid regrowth is not required and fertilization levels are relatively low.
Crop coefficients appropriate for high quality turf were based on the research results of Brown et al.
and change monthly.
Crop coefficients for acceptable quality turf were derived by subtracting 0.10 from the high quality Kcs.
The resulting 14 years of daily ET, data were averaged by day of the year to produce an average annual ETT data set.
This daily ET1 data set was then summarized into weekly, monthly, and annual totals of ETT.
Consumptive use curves were developed for high and acceptable quality turf from the summarized data sets.
Weekly as opposed to daily values of ET may prove more useful when managing irrigation, especially if irrigation is not being applied each day.
Table 1 provides weekly totals of ET for high and acceptable quality turfgrass grown in the Tucson area.
Evapotranspiration from high quality turf ranges from 0.36" in the first week of January to 1.88" in the last week of June.
The range in weekly ET for acceptable quality turf ranges from 0.30" in early January to 1.62" in late June.
Monthly values of ET1 are useful when planning irrigation budgets for a year.
Table 2 presents monthly ET for high and acceptable quality turfgrass for the Tucson area.
Monthly ET.
for high quality turf ranges
 Table 1.
Weekly consumptive use  in inches for high and acceptable quality turf grown in the Tucson area.
Week	Turf Quality	Week	Turf Quality	Week	Turf Quality	Week	Turf Quality
 Ending	High	Acc.
Ending	High	Acc.
Ending	High	Acc.
Ending	High	Acc.
Jan 7	0.36"	0.30"	Apr 8	1.30"	1.14"	Jul 8	1.75"	1.52"	Oct 7	1.18"	1.02"
 Jan 14	0.44	0.37	Apr 15	1.46	1.27	Jul 15	1.62	1.42	Oct 14	1.16	1.01
 Jan 21	0.46	0.39	Apr 22	1.48	1.29	Jul 22	1.61	1.40	Oct 21	1.00	0.86
 Jan 28	0.51	0.44	Apr 29	1.54	1.34	Jul 29	1.55	1.35	Oct 28	0.85	0.74
 Feb 4	0.58	0.50	May 6	1.66	1.44	Aug 5	1.56	1.37	Nov 4	0.76	0.66
 Feb 11	0.63	0.54	May 13	1.66	1.44	Aug 12	1.54	1.36	Nov 11	0.72	0.62
 Feb 18	0.63	0.54	May 20	1.67	1.45	Aug 19	1.52	1.34	Nov 18	0.63	0.54
 Feb 25	0.70	0.60	May 27	1.69	1.47	Aug 26	1.43	1.26	Nov 25	0.60	0.52
 Mar 4	0.74	0.64	Jun 3	1.77	1.53	Sep 2	1.40	1.23	Dec 2	0.54	0.47
 Mar 11	0.95	0.82	Jun 10	1.75	1.51	Sep 9	1.34	1.17	Dec 9	0.44	0.38
 Mar 18	0.98	0.85	Jun 17	1.79	1.54	Sep 16	1.32	1.15	Dec 16	0.44	0.38
 Mar 25	1.12	0.97	Jun 24	1.81	1.56	Sep 23	1.24	1.08	Dec 23	0.37	0.32
 Apr 1	1.04	0.90	Jul 1	1.88	1.62	Sep 30	1.29	1.12	Dec 31*	0.42	0.36
 * Water use for the week ending December 31 represents an 8-day total for the period December 24-31.
from 1.8" in December to 7.7" in June.
For acceptable quality turf, ET, ranges from 1.6" in December to 6.6" in June.
The last column in Table 2 presents the percentage of annual ET occurring in each month.
These monthly percentages clearly show that the bulk of the annual water use occurs during the summer months.
For example, ET in June accounts for 13% of total annual ET, In contrast, total ET from December through February  represents just 10.9% of annual ET substantially less than ET for June.
Annual CU of high and acceptable quality turf is summarized at the bottom of Table 2.
Consumptive use of high quality turf totals ~58.8" or 4.9' per year while the CU of acceptable quality turf approaches ~51.1' or 4.26' per year.
Table 2.
Monthly and annual consumptive use  in inches for high and acceptable quality turf grown in the Tucson area.
Turf Quality	% of
 January	2.0"	1.7"	3.4
 February	2.6	2.2	4.4
 March	4.4	3.8	7.5
 April	6.2	5.4	10.5
 May	7.4	6.5	12.6
 June	7.7	6.6	13.1
 July	7.2	6.3	12.2
 August	6.7	5.9	11.4
 September	5.6	4.8	9.5
 October	4.5	3.9	7.6
 November	2.8	2.4	4.8
 December	1.8	1.6	3.1
 The CU data presented in this report represent longterm average rates of ET, and should prove useful to individuals involved in the design and management of turf irrigation systems.
It is important to realize that the results presented in this report represent raw ET data that have not been adjusted for precipitation or irrigation system performance.
To use this CU information to determine the amount of water required for irrigation, one must first subtract the amount of effective precipitation  to determine the net water requirement for any period.
Precipitation in the Tucson area averages ~12" or 1.0' per year and should reduce irrigation water requirements substantially.
The final step in determining the irrigation water requirement involves making adjustments to: 1) account for system nonuniformity and 2) ensure leaching is sufficient to maintain soil salinity at acceptable levels.
Adjustments for nonuniformity and salinity management increase the amount of irrigation water required and vary dramatically with location due to differences in irrigation design, topography, local weather conditions, and water quality.
A discussion of these adjustments is beyond the scope of this publication and will be discussed in a subsequent report in the Turf Irrigation Management Series.
North Carolina Cooperative Extension Service
 North Carolina State University
 Land application equipment used on animal production farms must be field calibrated or evaluated in accordance with existing design charts and tables according to state rules that went into effect September 1, 1996.
Technical Specialist certifying waste management plans after September 1, 1996, must also certify that operators have been provided calibration and adjustment guidance for all land application equipment.
The rules apply to irrigation sysitems as well as all other types of liquid, slurry, or solid application equipment.
Information presented in manufacturers' charts are based on average operating conditions for relatively new equipment.
Discharge rates and application rates change over time as equipment ages and components wear.
As a result, equipment should be field calibrated regularly to ensure that application rates and uniformity are consistent with values used during the system design and given in manufacturers' specifications.
Field calibration is a simple procedure involving collection and measurement of the material being applied at several locations in the application area.
This publication contains step-by-step guidelines for field calibration of stationary sprinkler irrigation systems.
Operating an irrigation system differently than assumed in the design will alter the application rate, uniformity of coverage, and subsequently the application uniformity.
Operating with excessive pressure results in smaller droplets, greater potential for drift, and accelerates wear of the sprinkler nozzle.
Pump wear tends to reduce operating pressure and flow.
With continued use, nozzle wear results in an increase in the nozzle opening, which will increase the discharge rate while decreasing the wetted diameter.
Clogging of nozzles or crystallization of main lines can result in increased pump pressure but reduced flow at the sprinkler.
Plugged intakes will reduce operating pressure.
An operating pressure below design pressure greatly reduces the coverage diameter and application uniformity.
Field calibration helps ensure that nutrients from animal waste are applied uniformly and at proper rates.
The calibration of a stationary sprinkler irrigation system involves setting out collection containers, operating the system, measuring the amount of wastewater collected in each container, and then
 computing the average depth of application  and application uniformity.
An in-line flow meter installed in the main irrigation line provides a good estimate of the total volume pumped from the lagoon during each irrigation cycle.
The average application depth can be determined by dividing the pumped volume by the application area.
The average application depth is computed from the formula:
 Average application depth  = Volume pumped  27,154  X Application area 
 The average application depth is the average amount applied throughout the field.
Unfortunately, sprinklers do not apply the same depth of water throughout their wetted area.
Under normal operating conditions, application depth decreases towards the outer perimeter of the wetted diameter.
Stationary sprinkler systems are designed to have overlap of 50 to 65 percent of the wetted sprinkler diameter to compensate for the declining application along the
 outer perimeter.
When operated at the design pressure, this overlap results in acceptable application uniformity.
When operated improperly, well-designed systems will not provide acceptable application uniformity.
For example, if the pressure is too low, the application depth will be several times higher near the center of sprinkler and water will not be thrown as far from the sprinkler as indicated in manufacturers' charts.
Even through the average application depth may be acceptable, some areas receive excessively high application while others receive no application at all.
When applying wastewater high in nutrients, it is important to determine the application uniformity.
Collection containers distributed throughout the application area must be used to evaluate application uniformity.
Many types of containers can be used to collect flow and determine the application uniformity.
Standard rain gauges work best and are recommended because they already have a graduated scale from which to read the application depth.
Pans, plastic buckets, jars, or anything with a uniform opening and cross section can be used, provided the container is deep enough  to prevent splash and excessive evaporation, and the liquid collected can be easily transferred to a scaled container for measuring.
All containers should be the same size and shape.
All collection containers should be set up at the same height relative to the height of the sprinkler nozzle  Normally, the top of each container should be no more than 36 inches above the ground.
Collectors should be located so that there is no interference from the crop.
The crop canopy should be trimmed to preclude interference or splash into the collection container.
Calibration should be performed during periods of low evaporation.
Best times are before 10 a.m.
or after 4 p.m.
on days with light wind (less than 5 miles per hour.
On cool, cloudy days the calibration can be performed any time when wind velocity is less than 5 miles per hour.
General Guidelines for Stationary Sprinklers
 Rain gauges or other collection containers should be spaced in a grid pattern fully enclosing the "effective" wetted area defined by the sprinkler spacing.
The
 most common spacing pattern for stationary sprinklers is a square spacing where the distance between sprinklers is the same as the spacing between laterals.
The spacing between sprinklers and laterals is normally between 50 to 65 percent of the sprinkler wetted diameter specified by the manufacturer.
Collection gauges should be placed one-fourth the lateral line length from the main and no further apart than one-fourth the wetted sprinkler radius or effective sprinkler spacing..
The grid pattern and number of gauges required to complete the calibration depends on the pattern of operating the irrigation system.
The size of the calibration area should be no less than the "effective" area of one sprinkler.
When sprinklers are arranged in a rectangular or square pattern with proper overlap, an "effective area" receives flow from four sprinklers.
Thus, a minimum of four sprinklers should be included in the calibration.
The reliability of the calibration generally improves as more sprinklers are included in the calibration area.
If all sprinklers contributing flow to the calibration area are functioning correctly, it is necessary to include only the minimum number of sprinklers as described in the preceding paragraph.
But, a malfunctioning sprinkler can greatly influence the calibration results.
Its effect on the calibration depends on the calibration setup and number of sprinklers being calibrated, the malfunctioning sprinkler's position within the calibration area, the direction of the prevailing wind, and the nature of the malfunction.
For these reasons, it is extremely important to observe the performance of every sprinkler contributing to the calibration while the calibration is being performed and to record any obvious performance irregularities.
The more sprinklers that can be included in the calibration, the more representative the calibration results will be of the entire field and the less influence one malfunctioning sprinkler will have on the calibration results.
The volume  collected during calibration should be read as soon as a zone or sprinkler is shut off to minimize evaporation from the rain gauge.
Where a procedure must be performed more than once,  containers should be read and values recorded immediately after each different set up.
Operating patterns affect collection container
 STATIONARY SPRINKLER IRRIGATION SYSTEM
 layout and calibration procedures and results.
Typical patterns for stationary sprinklers include:
 1.
Square sprinkler spacing operated as a block  Figure 1 or Figure 2.
The calibration area may be positioned or centered between the two laterals as shown in either Figure 1 or Figure 2.
Four sprinklers contribute flow to the calibration area in the setup shown in Figure 1, while six sprinklers contribute for the setup shown in Figure 2.
If all sprinklers are functioning properly, similar results would be obtained with either setup.
In case 1, with no wind effects, all four sprinklers should contribute equal flow to the calibration area.
If one of the four sprinklers is functioning improperly, the calibration results are not biased by its position within the calibration area.
In case 2, six sprinklers contribute flow to the L3 calibration area, but their contribution is not equal.
S31 Sprinklers S 13 and S 23 contribute much more flow to the calibration area than sprinklers S 12 S 14 S 22 or S24*  The setup shown in Figure 2 provides the advantage of more sprinklers contributing to the calibration, but the disadvantage of the results
 Minimum calibration area = Sprinkler spacing X Lateral spacing
 Figure 1.
Layout of collection containers for calibration of a stationary sprinkler system operated in a block design.
In setup shown, four sprinklers contribute to the calibration.
Figure 2.
Collection container layout for calibration of a stationary sprinkler system operated in a block design.
In setup shown, six sprinklers contribute to the calibration.
potentially being biased by sprinklers 13 and S23 if they are malfunctioning.
For a square sprinkler spacing with collection gauges set at one-fourth the distance of the sprinkler
 spacing, the minimum number of collection gauges required to perform the calibration is 16.
Stepby-step procedures for this pattern are presented in the Case I example on page 6.
2.
One lateral operating at a time with standard overlap from adjacent laterals collection containers must be placed on each side of the lateral, Figure 3, which requires twice as many collectors.
A second alternative is to perform the procedure twice, once on each side of the lateral using 16 containers at a time, Figure 4.
When selecting this alternative, pay attention to changes in operating conditions, such as change in wind speed or direction, that could result in variability.
In either alternative, the amounts collected must be combined to account for overlap.
Step-by-step procedures for this calibration pattern are presented in the Case II example on page 8.
3.
One lateral operating with no overlap between laterals typical case when large gun-type sprinklers are operated in narrow fields, Figure 5.
Calibration procedure is similar to procedure in #2 except outer edges do not receive overlap and must be excluded from the effective area calculations.
Collection gauges may be centered about one sprinkler or positioned between two adjacent sprinklers.
One of two approaches can be used to perform
 Figure 3.
Collection container layout for calibration of a stationary sprinkler system with one lateral operating at a time.
For setup shown, both sides of lateral are calibrated in one operation.
Figure 4.
Collection container layout for calibration of a stationary sprinkler system with one lateral operated at a time.
For the setup shown, the procedure must be performed twice, once for lateral A, once for lateral B.
this calibration.
A general rule in irrigation design is to assume that the width of the effective area is between 50 to 65 percent of the wetted diameter of the sprinkler.
The first
 Figure 5.
Collection container layout to calibrate a single lateral line with no overlap from adjacent lateral.
Either setup shown  may be used.
Figure 6.
Collection container layout to calibrate a stationary gun system when each gun is operated separately.
calibration approach accepts this design guideline that the effective width of the lateral is 60 percent of the wetted diameter of one sprinkler.
Sixteen gauges are set out as shown in Figure 5   with all 16 gauges positioned within the effective sprinkler width.
The outer
 edges are ignored at the onset of the calibration.
Flow from all sprinklers is summed then averaged to compute the average application depth for the effective area.
For the second alternative, the entire width of the field is included in the calibration as shown in Figure 5.
At least 16 gauges should be set out on each side of the lateral.
The calibration can be performed all at once  or the procedure can be performed twice, once on each side of the lateral using 16 gauges at a time.
The "non-zero" volumes collected are averaged to get a "preliminary" average application depth for the wetted area.
Next, the average application depth for each row of gauges is computed.
In this computation, zero values are included.
Those rows whose row average is less than one-half the average from the entire wetted area are then excluded and assumed to fall outside the effective area.
The effective width is the distance from the lateral line to the furthest row from the lateral that is retained.
Step-by-step procedures for this method are
 given in the Case III example on page 9.
4.
Big gun sprinkler operating individually, Figure 6.
Procedure must be repeated for each gun sprinkler or sprinkler position  contributing to the effective area being calibrated.
This operating situa-
 tion results where one or two guns or big sprinklers are moved from hydrant to hydrant throughout the field.
Since stationary big guns should not be operated "head to head." ; the procedure must be repeated several times.
Collection gauges may be centered about one gun
 sprinkler.
This setup requires that the procedure be performed three times, once while Gun 2 operates, again when Gun 3 operates, and a third time when Gun 4 operates.
Collection gauges may also be centered between Gun 2 and 3 or Guns 3 and 4 as shown in Figure 6..
In this setup, the procedure
 CASE I.
Block Pattern with 2 or more laterals operating simultaneously
 
 1.
Determine the effective sprinkler area..
The effective sprinkler area is the minimum area to be included in the calibration area.
Note: The calibration area can be more than the effective area of one sprinkler.
2.
Determine the necessary spacing between collection gauges.
For an effective sprinkler spacing of 80 feet, the rain gauge spacing should not exceed 20 feet..
Gauges closest to the sprinklers should be placed a distance of 1/2 the gauge spacing from the sprinkler.
For a gauge spacing of 20 feet, the first row of gauges should be 10 feet from the lateral line or sprinklers.
3.
Determine the number of gauges required.
Calibration area  Number of gauges = Gauge area 
 Example: Calibration area = 80 ft X 80 ft= 6400 ft2 Gauge area = 20 ft X 20 ft = 400 ft2 gauges GOOD Number of = = 16 gauges
 4.
Set out gauges in a rectangular pattern as shown in Figure 1 or 2, equally spaced at the distance determined in item 2  within the calibration area.
5.
Operate the system for normal operating time for a full cycle.
Record the time of operation.
6.
Immediately record the amounts collected in each gauge.
7.
Add the amounts in #6 and divide by the number of gauges.
This is the average application depth.
Sum of amounts collected in all gauges Average application depth = Number of gauges
 8.
Calculate the deviation depth for each gauge.
The deviation depth is the difference between each individual gauge value and the average value of all gauges.
Record the absolute value of each deviation depth  is dropped and all values are treated as positive).
The symbol for absolute value is a straight thin line.
For example, |2| means treat the number 2 as an absolute value.
It does not mean the number 121.
Because this symbol can lead to misunderstandings, it is not used with numbers in the worksheets at the end of this publication.
The symbol is used in formulas in the text.
Deviation depth = |Depth collected in gauge i average application depth|
 "i" refers to the gauge number
 9.
Add amounts in #8 to get "sum of the deviations" from the average depth and divide by the number of gauges to get the average deviation.
Sum of deviations  Average deviation depth = Number of gauges
 10.
The precipitation rate  is computed by dividing the average application depth  by the application time 
 Average application depth  Precipitation rate = Application time 
 11.
Determine the application uniformity.
The application uniformity is often computed using the mathematical formula referred to as the Christiansen Uniformity Coefficient.
It is computed as follows:
 Average depth  average deviation  U = 100 Average depth 
 12.
Interpret the calibration results.
The higher the index value, the more uniform the application.
An index of 100 would mean that the uniformity is perfect that the exact same amount was collected in every gauge.
An application uniformity greater than 75 is excellent for stationary sprinklers.
Application uniformity between 50 to 75 is in the "good" range and is acceptable for wastewater application.
Generally, an application uniformity below 50 is not acceptable for wastewater irrigation with stationary sprinklers.
If the computed U, C is less than 50, system adjustments are required.
Contact your irrigation dealer or Certified Technical Specialist for assistance.
CASE II.
Single lateral operated at one time but receives overlap from adjacent laterals.
1.
Determine the effective sprinkler area..
2.
Determine the necessary spacing between collection gauges..
Gauges closest to the sprinklers should be placed a distance of one-half the gauge spacing from the sprinkler.
3.
Determine the number of gauges required.
Minimum number is 32 to perform the procedure in one setup, Figure 3; or One side of lateral calibrated at a time requires 16 gauges, procedure performed twice, first operating Lateral A  then repeated without moving gauges and operating Lateral
 4.
The amount collected on one side of the lateral must be added to the amount collected from respective positions on the other side of the lateral.
This is necessary to account for overlap from adjacent laterals.
Therefore, collection gauges should be labeled to indicate their respective positions, such as left or right of the lateral.
5.
Set out gauges in a rectangular pattern as shown in Figures 3 or 4, equally spaced at the distance determined in item 2.
6.
Operate the system for normal operating time for a full cycle.
Record the time of operation.
7.
Immediately record the amounts collected in each gauge..
If only one side of the lateral is calibrated at a time, after recording collection amounts, empty and move the collection containers to the other side and repeat steps 5 through 7 for exactly the same time duration as recorded in item 6.
8.
Collection amounts from pairs of cans should be added to simulate overlap.
Contents should be combined from one side of the lateral to the other side as shown in Figure 3.
Referring to Figure 3, container L1 is combined to R1, L2 to R2, L3 to R3, L4 to R4, L5 to R5, and so on.
9.
Add the amounts from all containers and divide by the number of gauges on one side of the lateral.
This is the average application depth.
Sum of amounts collected in all gauges Average application depth = Number of gauges on one side of lateral
 10.
Calculate the deviation depth for each gauge.
The deviation depth is the difference between combined depth for each position  and the average application depth.
Record the absolute value of each deviation depth.
Absolute value means the sign of the number  is dropped and all values are treated as positive.
The symbol for absolute value is a thin straight line.
Deviation depth = |Depth collected at position i average application depth| "i" refers to the gauge position within the effective calibration area
 11.
Add amounts in #10 to get "sum of the deviations" from the average depth and divide by the number of gauges  to get the average deviation depth.
-Sum of deviations  Average deviation depth =
 Number of gauges on one side of lateral
 12.
Determine the application uniformity.
The application uniformity is often computed using the mathematical formula referred to as the Christiansen Uniformity Coefficient.
It is computed as follows:
  average deviation  U = 100 Average depth 
 13.
Interpret the calibration results.
The higher the index value, the more uniform the application.
An index of 100 would mean that the uniformity is perfect the exact amount was collected in every gauge.
An application uniformity greater than 75 is excellent for stationary sprinklers.
Application uniformity between 50 to 75 is in the "good" range and is acceptable for wastewater application.
Generally, an application uniformity below 50 is not acceptable for wastewater irrigation.
If the computed U is less than 50, system adjustments are required.
Contact your irrigation dealer or Certified Technical Specialist for assistance.
CASE III.
Single Lateral or Gun Sprinkler without overlap from adjacent laterals.
1.
Determine the wetted diameter of a sprinkler or field width.
2.
Determine the necessary spacing between collection gauges.
The spacing in the direction along the lateral should be one-fourth the effective sprinkler spacing.
The gauge spacing perpendicular to the lateral should be 1/8 the wetted diameter or width of the field.
3.
Determine the number of gauges required.
Minimum number is 32 to perform the procedure in one setup.
One side of lateral calibrated at a time requires 16 gauges, procedure performed twice, once on each side of the lateral.
4.
Set out gauges in a rectangular grid pattern as shown in Figure 5, spaced at the distances determined in item 2.
Be sure to label gauges by rows.
The first row of gauges should be located 1/2 the gauge spacing from the lateral.
5.
Operate the system for normal operating time for a full cycle.
Record the time of operation.
Effective sprinkler spacing in feet
 Spacing between collection gauges parallel to lateral =
 Sprinkler wetted diameter in feet
 Spacing between collection gauges perpendicular to lateral =
 6.
Immediately record the amounts collected in each gauge..
If only one side of the lateral is calibrated at a time, after recording collection amounts, empty and move the collection containers to the other side and repeat steps 4 through 6 for exactly the same time duration as recorded in item 5.
7.
Add the "non-zero" amounts collected and divide by the number of gauges with a non-zero amount.
This is the "preliminary" average application depth  within the "wetted" calibration area.
Sum of non-zero amounts collected Average application depth = Number of non-zero gauges
 8.
Determine the average application depth by rows.
Include zero catches in the row computations.
Sum of collection amounts from all gauges on the row Average row application depth = Number of row gauges
 9.
Identify and delete those rows whose average application depth  is less than one-half the preliminary average application depth.
10.
Determine the effective application width.
The boundary is defined as the distance from the lateral to the last row furthest from the lateral that is retained.
11.
Determine the average application depth within the effective area.
Add amounts from all gauges in rows within the effective width.
Sum of amounts collected in rows within effective width Corrected average application depth = Number of gauges within the effective width
 12.
Calculate the deviation depth for each gauge.
The deviation depth is the difference collected in each usable gauge and the average application depth.
Record the absolute value of each deviation depth.
Absolute value means the sign of the number  is dropped and all values are treated as positive.
The symbol for absolute value is a thin straight line.
Deviation depth = |Depth collected at position i average application depth |
 "i" refers to the gauge position within the effective calibration area
 13.
Add amounts in #12 to get "sum of the deviations" from the average depth and divide by the number of gauges.
Sum of deviations  Average deviation depth Number of gauges within the effective width
 14.
Determine the application uniformity.
The application uniformity is often computed using the mathematical formula referred to as the Christiansen Uniformity Coefficient.
It is computed as follows:
 Average application depth  average deviation 
 STATIONARY SPRINKLER IRRIGATION SYSTEM
 15.
Interpret the calibration results.
The higher the index value, the more uniform the application.
An index of 100 would mean that the uniformity is perfect the exact amount was collected in every gauge.
An application uniformity greater than 75 is excellent for stationary sprinklers.
Application uniformity between 50 to 75 is in the "good" range and is acceptable for wastewater application.
Generally, an application uniformity below 50 is not acceptable for wastewater irrigation.
If the computed U, is less than 50, system adjustments are required.
Contact your irrigation dealer or Certified Technical C Specialist for assistance.
WORK SHEET 1.
Example calibration data for a stationary sprinkler system operated in a block pattern.
a.
Effective sprinkler area: 80 ft by 80 ft = 6400 ft2 b.
Spacing between collection containers /4) = 20 ft C.
calibration area  ft2 Number of gauges = = 16 effective gauge area  20 ft x 20 ft d.
Start of Irrigation event 7:15 a.m.
e.
End of Irrigation event 9:30 a.m.
f.
Duration  2.25 hours g.
Operate the system and collect data
 Volume	Deviation from	Volume	Deviation from
 Gauge No.
Collected	Average*	Gauge No.
Collected	Average*
 			
 1	.57	.005	9	.51	.065
 2	.69	.115	10	.26	.315
 3	.83	.255	11	.36	.215
 4	.65	.075	12	.52	.055
 5	.61	.035	13	.79	.215
 6	.38	.195	14	.65	.075
 7	.27	.305	15	.61	.035
 8	.64	.065	16	.86	.285
 Record the absolute value of each deviation, SO all values are treated as positive.
*
 WORK SHEET 1.
0.576 inches
 j.
Precipitation rate =	= 0.26 inches/hour
 k.
Sum of all deviations from the average depth	2.31
 I.
Average deviation from average depth 	0.144
 X 100 = 74.9
 n.
Interpret Results.
Uniformity coefficient is in the good range, so no adjustments are necessary
 h.
Sum of volume collected in all catches 9.20 inches
 WORK SHEET 2.
Example calibration data for a stationary sprinkler system, one lateral operated at a time.
a.
Effective sprinkler area: 80 ft by 80 ft = 6400 ft2
 b.
Spacing between collection containers  / 4) = 20 ft
 C.
Calibration area 	80	ft
 Number of gauges =	=	32
 Effective gauge area 	20 ft x 20 ft
 d.
Start of Irrigation event 7:15 a.m.
e.
End of Irrigation event 9:30 a.m.
f.
Duration  2.25 hours
 g.
Operate the system, collect data, and record on the worksheet on page 13, opposite.
h.
Sum of all catches 10.91 inches
 i.
Average application depth  0.682 inches
 j.
Sum of all deviations from the average depth 1.866
 k.
Average deviation from average depth 0.117
 X 100 = 82.8
 m.
Interpret Results.
Uniformity coefficient is in the excellent range for a stationary sprinkler system.
WORK SHEET 2.
Gauge No.
Collected	Adjustment	from Average*
 L1	.00	.67 	.012  i)
 L2	.15	.64 	.042  i)
 L3	.38	.72 	.038 
 L4	.71	.71 	.028
 L5	.02	.86 	.178
 L6	.20	.79 	.108
 L7	.43	.53	.152
 L8	.78	.80	.118
 L9	.04	.82	.138
 L10	.33	.94	.258
 L11	.51	.74	.058
 L12	.69	.69	.008
 L13	.00	.51	.172
 L14	.11	.44	.242
 L15	.37	.47	.212
 L16	.58	.58	.102
 *Record the absolute value; treat all values as positive.
would be performed twice since only two guns or gun locations contribute to the calibration.
WORK SHEET 3.
Example calibration data for a stationary sprinkler system, one lateral operated at a time, no overlap from adjacent laterals.
a.
Determine the wetted diameter of a sprinkler.
From manufacturers literature, wetted diameter is 160 feet, sprinkler spacing along lateral is 100 feet.
b.
Determine the necessary spacing between collection gauges.
sprinkler spacing	100 [feet]
 parallel to lateral =	=	= 25 feet
 sprinkler wetted diameter	160 feet
 perpendicular to lateral =	=	= 20 feet
 C.
Determine the number of gauges required.
Will calibrate both sides of lateral at one time so need 32 collection gauges
 First row of gauges should be located a distance of 1/2 the gauge spacing from the lateral line.
i.e.,
 if the gauge spacing is 20 feet, first row of gauges should be 10 feet from the lateral.
d.
Start of irrigation event 7:15 a.m.
e.
End of irrigation event 9:30 a.m.
f.
Duration  2.25 hours
 g.
Operate the system and collect data
 h.
Add the non zero amounts collected and divide by the number of gauges with a non-zero amount.
This is
 the average application depth  within the "wetted" calibration area.
Sum of non zero catches in column 3 = 12.59 inches
 Number of gauges with non-zero catch = 28 gauges
 Average catch all non-zero gauges =	= 0.45 inches
 i.
Determine the average application depth by rows.
Include zero catches in the row computations.
Row averages are shown in column 4.
j.
Identify and delete those rows whose average application depth  is less than one-half the average
 Application depth of Row L4 is 0.05 inches and Row R4 is 0.04 inches so discard row 4 values on both
 sides	 of lateral.
k.
Determine the effective application width.
Row 3 is last usable row and is located 50 feet from lateral.
Therefore, effective width is 50
 feet on each side of lateral or 100 feet total.
WORK SHEET 3.
Distance	Volume	Row	Usable	Deviation
 Gauge No.
from	Collected	Average	Values	from Average
 L11	10	.77	.77	.260
 L12	10	.69	.69	.180
 L13	10	.83	.83	.320
 L14	10	.65	.74	.65	.140
 L21	30	.61	.61	.100
 L22	30	.57	.57	.060
 L23	30	.48	.48	.030
 L24	30	.44	.53	.44	.070
 L31	50	.31	.31	.200
 L32	50	.22	.22	.290
 L33	50	.18	.18	.330
 L34	50	.29	.25	.29	.220
 L44	70	.08	.05 
 R11	10	.67	.67	.160
 R12	10	.79	.79	.280
 R13	10	.81	.81	.300
 R14	10	.77	.76	.77	.260
 R21	30	.59	.59	.080
 R22	30	.51	.51	.000
 R23	30	.62	.62	.110
 R24	30	.5	.56	.50	.010
 R31	50	.37	.37	.140
 R32	50	.17	.17	.340
 R33	50	.15	.15	.360
 R34	50	.24	.23	.24	.270
 R44	70	.09	.04 
 WORK SHEET 3.
I.
Determine the average application depth within the effective area.
Add amounts from all gauges in rows
 within the effective width 
 Usable values are shown in column 5 sum of amounts collected in rows within effective width (sum of
 column 5) = 12.23 inches
 Average application depth =	= 0.51 inches
 m.
Calculate the deviation depth for each gauge.
Values shown in column 6.
Deviation depth = |Depth collected at position i average application depth I
 i refers to the gauge position within the effective calibration area
 n.
Sum of deviations  = 4.511 inches
 Average deviation depth =	= 0.188 inches
 O.
Determine the application uniformity.
0.51 inches  0.188 inches 
 Uc = C =	X 100 = 63.1
 p.
Interpret the calibration results.
An index value of 63 percent is acceptable for a stationary sprinkler system.
No adjustments are needed.
Irrigation System Calibration Data Sheet for Stationary Sprinkler
 a.
Effective sprinkler area: Lateral spacing
 ft by spacing along lateral
 b.
Spacing between collection containers (sprinkler spacing
 C.
Number of collection containers
 d.
Start of Irrigation event
 e.
End of Irrigation event
 g.
Operate the system, collect data, and
 record on the worksheet on page 18.
h.
Sum of all catches
 i.
Average application depth 
 Precipitation rate =  =
 k.
Sum of all deviations from the average catch
 I.
Average deviation from average application depth
 U =    100
 Interpret the calibration results.
An application uniformity greater than
 75 is excellent for stationary sprinklers.
Application uniformity between 50 to 75 is in the "good" range and is
 30 acceptable for wastewater application.
Generally, an application uniformity
 31 below 50 is not acceptable for wastewater irrigation.
If the computed UC is less than 50 percent, system adjustments
 32 are required.
Contact your irrigation dealer or Certified Technical Specialist for assistance.
for Animal Wastewater Application Equipment
 Calibration Data Sheet for Stationary Sprinkler 
 Gauge No.
Volume	Overlap	Corrected	Deviation
 Collected	Adjustment	Volume	from Average*
 *Treat all values as positive.
NOTE: While in the field, it may be less confusing to record measured values in the grid above, then transfer these values to the data sheet for calculation and interpretation.
R.O.
Evans, Biological and Agricultural Engineering Extension Specialist J.C.
Barker, Biological and Agricultural Engineering Extension Specialist J.T.
Smith, Biological and Agricultural Engineering Extension Assistant Specialist R.E.
Sheffield, Biological and Agricultural Engineering Extension Specialist
 5,000 copies of this public document were printed at a cost of $3,084, or $.62 per copy.
Published by NORTH CAROLINA COOPERATIVE EXTENSION SERVICE
virus spread has been detected in either the greenhouse or the screenhouse plantings during the last two years.
At the end of the growing period the plants are removed from the boxes and placed in cold storage.
The following spring some of the plants are planted in the screenhouse and others are set out in field plots SO the fruiting performance and vigor of each clone can be evaluated.
This testing is being done at Salinas, Watsonville, and Santa Ana by R.
S.
Bringhurst  and V.
Voth.
The remaining plants are available for planting in a foundation nursery-a plot of fumigated land well isolated from all other strawberry plants.
Data now available indicate that meristemed plants are superior in vegetative vigor to the noncertified commercial stock known to be carrying viruses.
Yield comparisons are not yet available,
 The foundation nursery is indexed by the California Department of Agriculture Nursery Service.
If the foundation nursery meets the requirements of the Regulations for California Certified Strawberry Plants, the plants from the nursery are accepted into the Certification Program for increase and distribution to growers.
To date, one meristemed variety, Fresno, has been certified by the California Department of Agriculture to be free of viruses.
Commercial strawberry plants are the main source of virus inoculum for infecting clean stock.
When varieties are interplanted, viruses spread from infected plants to noninfected plants.
With the increasing trend toward the annual planting systems and the introduction of clean stock of all varieties, losses due to virus can be minimized.
F.
K.
ALJIBURY DONALD MAY
 IRRIGATION and production on the San
 In processed tomatoes production of ripe fruit was significantly affected by irrigation schedules.
Within the range of the test treatments, the longer the period between irrigations, the higher the percentage of ripe fruit and of solids.
However, there was a highly significant reduction in yield and an increase in the amount of sunburn as the irrigation interval increased from 10 to 15 and 20 days.
The 10-day irrigation cycle appeared to be the most suitable practice, yielding the highest tomato tonnage per acre, and consistent with the evapotranspiration and the gypsum block records.
Longer irrigation frequencies depressed yield, stressed the tomato plants, and increased the percentage of sunburned fruits.
Pre-irrigation is a very important practice in the production of tomatoes on the west side of the San Joaquin Valley.
I RRIGATION IS CONSIDERED to be one of the most important practices affecting tomato production on the west side of the San Joaquin Valley.
Previous studies have shown that highest yields were obtained when varieties of processing tomatoes were irrigated when the soil dryness at the 18-inch depth did not exceed 1 bar suction.
When such irrigation programs were used higher tonnages of solids per acre were obtained.
Since most tomato growers in the San Joaquin Valley irrigate by schedule rather than by instruments, this study was based on schedule and evaluated by the use of soil moisture instruments.
The objectives of this study were to evaluate the different irrigation
 schedules and to determine the effect of these schedules on tomato production.
Process tomato variety VF-145-21-4 was seeded March 10 in double row beds.
The beds were 60 inches apart and 1,200 ft long.
The soil was Oxalis silty clay, and was relatively uniform to about 4 ft.
Six irrigation treatments were replicated four times in a randomized block design.
The treatments consisted of three irrigating frequencies, at every 10, 15, and 20 days; and two durations of application, 12 and 24 hours to each frequency.
The treatments are referred to as short and long wet, -medium and -dry, respectively.
The water was pumped from the San Luis Canal and siphoned from a head ditch to the field furrows.
From October, 1968 to April, 1969 over 14 inches of rain fell in the area and in April the soil profile was wet down to 5 ft.
Gypsum blocks were installed at 18-, 30and 60-inch depths to indicate moisture extraction and depth of water penetration.
Thinning was done during the last week of May.
Before thinning, the field was sprinkled with 2.4 inches of water and after thinning all the treatments were irrigated with 2.44 inches of furrow irrigated water.
The plots were harvested July 31, 1969 with mechanical harvesters and the crop was graded and weighed the same day.
The wet treatments, irrigated either for long or short durations, produced the highest yield.
Although the long duration treatment produced a higher yield than the short duration, the yield difference was not significant.
SCHEDULES of PROCESSED TOMATOES Joaquin Westside
 TABLE 1.
EFFECT OF TREATMENTS ON TOMATO YIELD
 Long wet	33.0** a
 Short wet	31.9** a
 Long medium	27.2 b
 Short medium	26.5	b
 Long dry	29.4	ab
 Short dry	27.4	b
 It can be assumed that the yield of the wet plots would have been greater had the field been harvested later  The grower's practice was similar to that in the dry treatment; therefore, the entire field was harvested on July 31.
TABLE 2.
PERCENT GREEN FRUIT AT HARVEST
 Long wet	21.90* C
 Short wet	20.15* c
 Long medium	17.22* bc
 Short medium	17.32* bc
 Long dry	13.87 ab
 Short dry	10.72 a
 The high yield of wet-treatment plots can be attributed to a better fruit set and more vigorous plants.
The gypsum block readings at 18-inch depths indicated that the plants in the medium and the dry treatments were stressed.
The soil moisture stress occurred in the medium and dry treatments, under both durations although there was a consistent trend of increased yield with the long duration  The factor limiting water penetration was the low infiltration rate of the soils.
The infiltration rate of these soils was less than 0.2 inch per hour.
The data showed root activities and moisture extraction down to 5 ft which was the zone of rain moisture penetration.
It is
 apparent that the amount of rain moisture retained in the soil was very important in fulfilling plant moisture needs during the growing season.
Deep cracks which appeared in the bottom of the furrows may have aided water penetration during the irrigation season.
TABLE 3.
PERCENT SOLIDS
 Long wet	5.50 C
 Short wet	5.85 be
 Long medium	5.90 bc
 Short medium	6.50* a
 Long dry	6.25* a
 Short dry	6.45* a
 A similar study conducted on the same ranch and with the same soil type in 1967 showed that the irrigation after thinning never penetrated the profile below 30 inches because of the low rate of water penetration.
A similar trend in crop yield and percent solids to that obtained in this study was also reported.
TABLE 4.
PERCENT OF SUNBURNED FRUIT
 Long wet	1.07* a
 Short wet	1.07* a
 Long medium	1.55 b
 Short medium	1.45 b
 Long dry	1.42 b
 Short dry	1.47	b
 a need for more irrigation than what was provided in the dry treatments of this study.
In the months of May, June, and July, about 22 inches of water was needed to satisfy plant water demands while in the dry treatments, less than 11 inches of irrigation water was added.
TABLE 5.
WATER USE AND IRRIGATION REQUIREMENTS OF THE TREATMENTS
 Number of	Total Inches	Tomato
 Treatments	Post Thinning	Irrigations	of Water	Used	production
 Wet short	5	17.04	31.0
 Wet long	5	20.01	33.9
 Medium short	3	12.16	26.5
 Medium long	3	13.94	27.2
 Dry short	2	9.72	27.4
 Dry leng	2	10.91	29.4
 Significant at 5 per cent level.
Significant at 1 per cent level.
Means followed by common letters are not significantly different.
The production of tomato solids in the dry treatment plots was higher than for the wet treatments.
However, because of higher tomato yields production in the wet treatment plots, the total solids per acre was still higher in the wet treatment plots.
The percentage of sunburned fruit was significantly higher in the medium and dry treatments than in the wet plots.
This was another factor contributing to the higher yield in the wet treatment plots.
F.
K.
Aljibury is Area Technologist, San Joaquin Valley Agricultural Research and Extension Center, Parlier; and Donald May is Farm Advisor, Fresno County.
DRIP IRRIGATION for Plants Grown
 FURUTA R.
A.
COLEMAN T.
MOCK A.
W.
MARSH R.
L.
BRANSON R.
STROHMAN
 D rip and spray irrigation systems permit precise placement of a measured amount of water to soil.
Designed for frequent, slow application of water, these systems make it possible to adjust the volume of water applied to soil in order to replace that which is removed from the soil through evaporation and plant transpiration.
Use of drip and spray irrigation systems should lead to reduced water runoff from soils and more efficient use of water and nutrients needed for plant growth.
Data on evapotranspiration , available water per container, and the influence of irrigation practices on salinity are needed in order to formulate sound management practices for use of drip or spray systems with plants grown in containers.
Experiments were conducted at the University of California South Coast Field Station to obtain this information.
A standard U.S.
Weather Bureau Class A evaporation pan and white and black Livingston atmometers were used to estimate ET.
Actual evapotranspiration for ornamental plants growing in 1-gallon containers was measured by weighing container, plant, and soil before and following irrigation.
These estimates and actual ET measurements were made from June through November 1974.
All tests were with containers on bare ground exposed to full sunlight.
At the beginning and end of each trial, test plants were measured to deter-
 mine their height and widest diameter.
Variations noted.
Evapotranspiration varied according to plant species and position of a plant within its test bed.
Also, considerable variation from plant to plant in similar locations within a test bed was noted.
Data obtained from these trials quantify observations by practical horticulturists for many years.
Differences in ET noted between plant species during the trials cannot be attributed solely to plant size or shape or both.
The results of the first trial, June 3-13, 1974 showed that a hibiscus plant had nearly the same ET as a larger Shamel ash plant.
A shiny leaf coprosma plant had the highest ET but was not the largest in size.
Later, in July, ET from an average upright Monterey pine was the same as that from an average spreading natal plum plant.
Both were almost the same size with respect to exposed area.
The amount of water used daily approached the total water available in the soil.
Available moisture was not determined for each trial.
However, other experiments with the same soil mixture indicate that approximately 400 milliliters of water were available from each 1gallon plant container.
Wind was another factor that affected ET.
Santana winds occurred during some of the experiments in the fall of 1974.
Under santana conditions, ET and evaporation from atmometers in-
 creased dramatically.
For example, for the plant Pyracantha coccinea, the following data were recorded: Evapotranspiration Normal winds 135 ml/container/day Santana winds 280 ml/container/day Ratio santana conditions/normal conditions = 2:1 Evaporation from white atmometer Normal conditions 18 ml/day Santana conditions 68 ml/day Ratio santana conditions/ normal conditions = 8:3.
Similar results were recorded for three other plant species.
Although the ET measured varied with the plant species, the dramatic increase in ET under santana conditions was consistent for all species studied.
Also noted was a greater increase in evaporation from the white atmometer as compared to ET from the plant.
Correlation of ET with evaporation measures.
There was a significant correlation between actual ET and evaporation from the Class A evaporation pan and the white and black atmometers.
Typical coefficients of correlation are reflected by the data obtained for the plant Callistemon citrinus:
 to evaporation pan 0.848 to white atmometer 0.769 to black atmometer 0.736 These correlation coefficients are statistically significant at the 1 percent level.
The same was not true when black minus white atmometer
 For the most efficient use of drip irrigation for plants grown in containers, attention must be paid to evapotranspiration and distribution of and amount of salinity in the soil.
data were used, presumably a measurement only of solar radiation influences.
Significant correlations were noted only during the first trial in June.
In all later trials, this measure did not correlate significantly with the actual ET.
Apparently factors other than light were more important.
Typical data were as follows: Coprosma repens 0.914  Callistemon citrinus 0.392 
 Soil salinity in containers and irrigation method
 Results from earlier work on short-term crops grown in containers indicated that excellent plant growth occurred with drip irrigation.
Analyses of salinity patterns within the soil mass for these crops suggested that salinity might be a potential problem for longer-term crops.
At the South East Field Station, an experiment was begun to study salinity buildup and to answer the following questions:
  Can soil salinity be controlled to a reasonable degree when drip irrigation is used by applying water in excess of that suggested by the standard leaching requirement formula?
Will increases in soil salinity with drip irrigation be sufficient either to injure the plant or to reduce its growth?
Salinity.
Distribution and amount of salinity differed with the irrigation system used.
In containers under overhead irrigation, salinity increased
 from the top to the bottom of the soil ball.
Lateral distribution of salts from the core to the side was about the same.
Under spray and drip irrigation, salinity was least in the core of the soil mass and most in the surface and outer zones of the soil mass.
While the distribution of salts was the same for both spray and drip systems, the amount of salinity was less with spray than with drip.
Increasing the amount of water applied through the drip irrigation system did not materially influence salinity levels.
Thus, the answer to our first question asked seemed to be: for drip irrigation of containers, increasing the amount of water flowing through the soil will not satisfactorily control salinity.
It appears that the rate of application  and distribution of water over the soil surface are more important, as was shown by the lower levels of salinity when overhead sprinkling or spray irrigation were used.
Flushing salts out of the soil appeared to be correlated to the rate and pathway of water flow through the ball of soil in the container.
Plant growth.
Would the buildup of salinity in the soil under drip irrigation, even with daily water applications, result in plant growth inhibition or alteration?
The answer to this question is yes, based on the data from these trials and earlier experiments.
Varietal differences were noted, but, in general, plants under drip irrigation for a lengthy period and without periodic flushing to leach salts from the soil were smaller at the end of 10 months than
 similar plants under overhead or trickle irrigation.
This effect seemed to be due to the retarding effect of high salinity on plant growth, not to nutrient content of the plants.
Visible injury due to high salinity was not noted.
Differences in plant root distribution within the root ball were noted.
In general, under drip irrigation, more roots were found in the center of the root ball.
For plants under overhead irrigation, more roots were found on the edge of the root ball.
Drip irrigation presents horticulturists with a method of precisely controlling the irrigation of plants grown in containers.
The amount of water applied and the timing of irrigation may be controlled by devices such as Livingston atmometers because the evaporation of water from these atmometers correlates closely with ET from the containers.
Allowances for differences in plant species will be necessary.
Control of salinity within the soil poses some problems when drip irrigation is used.
Periodic leaching of the soil will be necessary when drip irrigation is used, because varying the amount of water during normal irrigation will not control salinity adequately.
Leaching appears to be accomplished best by uniformly applying water over the entire soil surface.
The frequency of leaching necessary surely will depend on the salt content of the irrigation water and on the fertilization practices used.
T.
Furuta is Extension Environmental Horticulturist, Cooperative Extension, University of California, Riverside; R.
A.
Coleman is Staff Research Associate, Cooperative Extension, University of California, Riverside; T.
Mock is Staff Research Associate, University of California, South Coast Field Station, Santa Ana; A.
W.
Marsh is Extension Irrigation and Soils Specialist, Cooperative Extension, University of California, Riverside; R.
L.
Branson is Extension Soils and Water Specialist, University of California, Riverside; R.
Strohman is Staff Research Associate, Cooperative Extension, University of California, Riverside.
Best Management Practices For Irrigation Management
 Colorado State R University Cooperative Extension
 Principal author: Reagan M.
Waskom Extension Water Quality Specialist Colorado State University Cooperative Extension
 In association with: Colorado Department of Agriculture and the Agricultural Chemicals and Groundwater Protection Advisory Committee
 The author and the Colorado Department of Agriculture gratefully acknowledge the extensive input and leadership of the Agricultural Chemical and Groundwater Protection Advisory Committee, representing production agriculture, agricultural chemical dealers and applicators, the green industry and the general public.
With cooperation from: Colorado Department of Health and Environment USDA Soil Conservation Service Colorado State Office Colorado State University Department of Soil and Crop Sciences Colorado State University Department of Ag and Chemical Engineering
 Special Acknowledgments to BMP Technical Review Team: G.E.
Cardon, Assistant Professor of Agronomy R.L.
Croissant, Professor of Agronomy J.J.
Mortvedt, Extension Agronomist G.A.
Peterson, Professor of Agronomy L.R.
Walker, Extension Agricultural Engineer D.G.
Westfall, Professor of Agronomy
 Layout and Design by: Colorado State University Publications and Creative Services
 Graphics by: Greg Nelson, Colorado State University Office of Instructional Services
 Best Management Practices for Irrigation Practices
 Colorado's 2.5 million acres of irrigated crop production are extremely important to the state's economy.
However, poorly managed irrigation may cause environmental problems by transporting pesticides, nutrients, and sediments to water supplies.
Concern about irrigation water is nothing new in Colorado, where irrigation uses about 80% of the 1.8 trillion gallons of water diverted annually in the state.
Previously, these concerns centered only on water quantity; now, water quality is an important consideration in managing irrigation.
To reduce nonpoint source pollution caused by leaching and runoff, irrigation systems should be managed SO that the timing and amount of applied water match crop water uptake as closely as possible.
Best Management Practices  for the use of irrigation water can help increase efficiency and uniformity and reduce contamination of water resources.
Because each farm is unique, producers must evaluate their systems to determine which BMPs are suitable for their operations.
Irrigation management BMPs include irrigation scheduling, equipment modification, land leveling, tailwater recovery, proper tillage and residue management, and chemigation safety.
Rather than legislate overly restrictive measures on farmers and related industries, the Colorado Legislature passed the Agricultural Chemicals and Groundwater ProtectionAc  to promote the voluntary adoption of Best Management Practices.
The act calls for education and training of all producers and agricultural chemical applicators in the proper use of pesticides and fertilizers.
Voluntary adoption of BMPs by agricultural chemical users will help prevent contamination of water resources, improve public perception of the industry, and perhaps reduce the need for further regulation and mandatory controls.
BMPs are recommended methods, structures, or practices designed to prevent or reduce water pollution.
Implicit within the BMPs concept is a voluntary, site-specific approach to water quality problems.
This approach does not require replacements of major components of an irrigation system.
Instead, it is suggested that equipment to manage the timing and amount of water applied be acquired as needed, and that the appropriate precautions be implemented during chemigation.
Application Amount and Timing
 Method and Timing of Chemical Application
 Crop Root Zone and Water Use
 Figure 1.
Management and site variables influencing pollutant losses from irrigated fields.
Source: US EPA, 1992.
Proper irrigation scheduling, based on timely measurements or estimations of soil moisture content and crop water needs, is one of the most important BMPs for irrigation management.
A number of devices, techniques, and computer aides are available to assist producers in determining when water is needed and how much is required.
Irrigation scheduling uses a selected water management strategy to prevent the over-application of water while maximizing net return.
In a sense, all irrigations
 are scheduled, whether by sophisticated computer controlled systems, ditch water availability, or just the irrigator's hunch as to when water is needed.
Experienced producers know how long it takes them to get water across their fields and are proficient in avoiding crop stress during years of average rainfall.
The difficulty lies in applying only enough water to fill the effective root zone without unnecessary deep percolation or runoff.
Proper accounting for crop water use provides producers with the knowledge of how much water should be applied at any one irrigation event.
Table 1.
Irrigation scheduling methods and tools
 Method	Tools or parameters used	Advantages/disadvantages
 (Indicates when and how much
 Hand feel and appearance	Hand probe	Variable accuracy, requires experience
 Soil moisture tension	Tensiometers	Good accuracy, easy to read but narrow range
 Electrical resistance tester	Gypsum block	Works over large range, limited accuracy
 Indirect moisture content	Neutron probe/TDR	Expensive, many regulations
 Gravimetric analysis	Oven and scale	Labor intensive
 (Indicates when to irrigate but
 not how much to apply)
 Visual appearance	Field observation	Variable accuracy
 Water stress index	Infrared thermometer	Expensive
 (No field work required, but
 needs periodic calibration since
 only estimates water use)
 Checkbook method	Computer/calculator	Indicates when and how much water to apply
Use: regulatory , VRI type: zone, prescription type: static, management intensity: low.
RESPONSE OF CORN TO DEFICIT IRRIGATION AND CROP ROTATIONS
 Dwindling water supplies for irrigation are prompting alternative management choices by irrigators.
Deficit irrigation, where less water is applied than full crop demand, may be a viable approach.
Application of deficit irrigation management to corn was examined in this research.
A field study was designed to test crop management that  took advantage of delayed irrigation during crop vegetative growth,  reduced irrigation when water applications were unable to supply the full potential of crop yields, and  used no-till practices to reduce soil water evaporation and achieve other soil and water conservation benefits.
Multi-year crop performance results were needed to determine the yield risks for adopting deficit irrigation practices.
The specific objectives of this study were to:  find relationships of irrigation and crop yield,  determine crop evapotranspiration ,  measure soil water gains non-growing season and soil water use during the growing season,  predict the probabilities for achieving grain yields.
Crop rotation research with full irrigation, deficit irrigation, and dryland management was conducted at the West Central Research and Extension Center of the University of Nebraska-Lincoln at North Platte, Nebraska located at 41.1 N, 100.8 W and 2800 feet above sea level.
The semiarid climate in North Platte is characterized by frequent and rapid changes in weather conditions throughout the year.
The average annual precipitation is approximately 19 inches, which is 36% of annual reference ET  using alfalfa as the reference crop.
The soil texture was predominantly Cozad silt loam  with pH of 7.5.
Plant-available soil water holding capacity was 0.17 ft3 ft-3 for volumetric soil water contents from 32% for field capacity to 15% for permanent wilting.
The land slope was less than 1%.
The crop rotations were continuous corn  and wheat-corn-soybean.
Both rotations were managed with no-till practices and non-limiting fertility and pest management.
Corn was planted directly into the previous crop's residue with a no-till planter equipped to apply starter fertilizer.
The rest of the nitrogen was applied near the four to six leaf growth stage.
Pre-emergence and post-emergence herbicides were applied as needed.
Irrigation to meet full crop ET  was scheduled from measurements of soil water deficits in each crop rotation treatment.
An annual water allocation was restricted to 6 inches for the deficit irrigation treatments unless there was sufficient soil water to achieve full ETc.
Deficit irrigation was scheduled to favor applications during critical growth stages for crop development.
For corn, irrigation was reduced or withheld during the vegetative period and concentrated on reproduction and grain fill.
Soil water was measured weekly to a depth of 6 ft.
in 1 ft.
increments with the neutron attenuation method.
Precipitation, net irrigation, and changes in soil water from one measurement to the next were used to calculate weekly ETc.
Drainage was assumed to be minimal within the one-week sampling interval of soil water and was not included in the soil water balance.
Water runoff and run-on to the plots were observed to be zero.
ETr, referenced to alfalfa, was estimated with a Penman combination model, which used maximum and minimum daily air temperatures, relative humidity, solar radiation, and daily wind run as inputs.
Cropping season precipitation  was the sum of all precipitation that occurred from October in the year preceding corn planting through September of the growing season.
Cropping season precipitation as a percentage of long-term average annual precipitation provided a characterization of wetter or drier years.
The criterion for wetter and drier years was +95% of the average cropping season precipitation, which divided the years into two equal groups.
Years 1985, 1989, 1990, 1991, 1994, 1997, and 1998 were considered drier than the long-term average.
Years 1986, 1987, 1988, 1992, 1993, 1995, and 1996 were considered wetter.
Precipitation during the growing season also was a factor for crop yields.
Drier years had less than 12 inches of rain during May through September, while the precipitation in the wetter years for the same time period was 12 to 24 inches.
Another indicator of crop performance was rainfall for April, May, and June because this water accumulated closest to crop water needs was more effective than earlier precipitation.
For example, 1995 was classified as wetter overall; however, adequate early growing season rainfall was followed by very dry months of July and August, which coincided with periods of high ET demand.
Table 1.
Cropping season precipitation  for Oct.
1-Sep.
30.
Drier Years	1985	1989	1990	1991	1994	1997	1998
 Precipitation	17.7	13.8	10.8	14.9	16.7	11.2	17.3
 % of Avg.
89	69	54	74	84	56	86
 Wetter Years	1986	1987	1988	1992	1993	1995	1996
 Precipitation	21.2	20.8	25.7	21.1	20.6	19.4	25.0
 % of Avg.
106	104	129	105	103	97	125
 Average annual irrigation  was less than anticipated.
The first water applications on the deficit irrigation plots often were later than those on the full irrigation plots.
Timely precipitation events during June were more effective for the deficit irrigation when irrigation was delayed.
Table 2.
Average annual irrigation  applied to corn at North Platte, Nebraska, during 1985-1999.
-Deficit Irrigation--	--Full Irrigation--
 CC	WCS	CC	WCS
 Irrigation	4.7	4.6	10.1	9.9
 % of Full	47	47
 Precip.
18.5	18.5	18.5	18.5
 Irr.
23.2	23.1	28.6	28.4
 Cropping season precipitation plus irrigation for the full and deficit irrigation treatments correlated with ETr.
Irrigation plus precipitation was from 23.2 to 28.4 inches during the fourteen years of record, which was 80% to 125% of the mean.
Atmospheric demand for evaporation was predicted by ETr, which ranged from 0.16 to 0.30 inch day and from 61% to 121% of the mean.
Average corn grain yields were 70% to 127% of the mean for 1985-1999.
More or less, corn production followed the pattern of wetter and drier years, except for 1995, which had the least precipitation in July and August.
Corn yields were statistically different among water treatments and increased with additional irrigation.
Corn yields from the WCS rotation were significantly more  than CC during 1985-1999, which could be attributed to more off-season gains in stored soil water and in-season use of stored soil water in the WCS rotation.
Table 3.
Results for corn in the continuous corn  and wheat-corn-soybean  rotations at North Platte, Nebraska, during 1986-1998.
Yield 	IWUE	CS	Net	SW	SW	ETc/day	ETr/day!9
 Precip	Irr.
Gain	[e]	Use
 bu/ac	bu/ac-in	in	in	in	in	in/day	in/day	Etc/ETr
  Irrigation as an independent variable over years and
 Dryland	116 C	--	16.6	0.0	8.1 a	7.6 a	0.19 C	0.25	0.77
 Deficit	158 b	8.9 a	16.6	4.7	6.0 b	5.7 b	0.22 b	0.25	0.88
 Full	175 a	5.9 b	16.6	9.8	4.4 C	3.2 C	0.27 a	0.25	1.06
 LSD0.05	6	1.1	0.8	0.7	0.01	--	0.04
  Rotation as an independent variable over years and
 CC	137 b	---	16.6	7.2	4.5 b	4.9 b	0.22 b	0.25	0.88
 WCS	147 a	---	16.6	7.2	7.8 a	6.1 a	0.23 a	0.25	0.93
 LSD0.05	5	---	--	--	0.7	0.6	0.01	--	0.03
 [a]	Means followed by the same letters in the same column and independent variable are not significantly different.
[c]	IWUE = irrigation water use efficiency /.
[d]	Cropping season precipitation from Oct.
1 of previous year to Sept.
30 of current year.
[e]	Off-season soil water accumulation from previous fall through the current spring.
[f] Growing season stored soil water use.
[g]	ETc and ETr = crop and reference ET during soil water measurement period.
More soil water was accumulated and consumed in the WCS rotation because more time was available to accumulate soil water after winter wheat harvest than after the corn harvest
 Irrigation water use efficiency  was calculated for the deficit and full irrigation treatments.
IWUE was consistently more for deficit irrigation than full irrigation because the first increment of irrigation was used more efficiently than additional irrigation.
Full irrigation had more possibility for more soil water evaporation from more frequent surface wetting.
Growing season use of soil water  tended to correlate with off-season gains in soil water.
Available soil water holding capacity in the deep silt loam soil at the research site contributed to the ability to store water.
Gains and use of soil water increased with less irrigation because roots grew deeper, creating more soil water storage volume to hold off-season precipitation.
Dryland corn extracted water from as much as 7 feet deep into the soil, while fully irrigated corn extracted most of its water from the top 3 feet of soil.
When the CC and WCS rotations were compared, soil water gain and use were significantly different from each other.
More time was available for soil water accumulation in the WCS rotation because corn followed winter wheat rather than corn in the CC rotation.
Stored soil water use was 15%, 27%, and 52% of ETc for full irrigation, deficit irrigation, and dryland, respectively.
Less stored soil water contributed to ETc as more irrigation was added.
Stored soil water was 27% to 32% of ETc across the three crop rotations.
ETc and ETc/ETr  increased significantly for each water treatment from dryland to full irrigation.
However, ETc and ETc/ETr remained nearly constant across crop rotations.
Additional irrigation was used to increase ETc, and more off-season soil water accumulation from dryland management also contributed to more ETc.
Figure 1.
Crop yields as a fraction of fully irrigated yields for the drier years of 1985, '89, '90, '91, '94, '97, and '98 and the wetter years of 1986, '87, '88, '92, '93, '95, and '99.
Deficit irrigation and dryland corn yields were scaled as a fraction of fully irrigated yields from the same year.
Data from all crop rotations were used in this analysis.
The range of relative yields from dryland management  was 0.10 to 1.15 in the drier years and 0.20 to 1.05 in the wetter years, which indicated somewhat more variation in yields from the drier years.
The deficit irrigation applications generally were more during the drier years than the wetter years.
Deficit irrigation increased relative yields compared with dryland yields and decreased the risk for yield results because added irrigation reduced the range of relative yields to 0.2 to 1.2 for the wetter years and 0.75 to 1.15 for the drier years.
The range of full irrigation applications demonstrated that irrigation scheduling was necessary to capitalize on water conservation during the wetter years and match ETc during drier years.
Corn yields were ranked from maximum to minimum by water treatments for all years and crop rotations.
The ranked data were divided into seven groups of probability values by years.
Annual rainfall was 640, 610, 560, 510, 460, 430, and 410 mm for the 14%, 28%, 42%, 56%, 70%, 84%, and 98% probability levels, respectively.
Corn yields for each grouping of vertical bars would be expected to exceed that amount X years out of 100 years.
For the least probability or wettest years , all water treatments had similar yields.
As probability increased from wet to dry years, irrigated corn yields decreased, but the dryland yields decreased more dramatically.
Figure 2.
Percentage of time that crop yields exceed a given amount.
Results based on yield history for the years 1985-1999.
Corn was grown in a no-till cropping system using best management practices to apply water to deficit and full irrigation treatments.
Deficit irrigation was initiated late in the vegetative growth stage or early in the reproductive stage, while full irrigation was applied to meet ETc during the growing season.
The deficit irrigation treatment received no more
 than 6 inches of water, which was timed to favor supplying water during the reproductive and grain fill growth stages.
Continuous corn , and wheat-corn-soybean  crop rotations were grown in the dryland, deficit irrigation, and full irrigation treatments.
Corn yields were statistically different among dryland, deficit irrigation, and full irrigation treatments and increased with added irrigation.
Corn yields were statistically more in the WCS rotation than the CC rotation across water treatments.
ETc was significantly different among water treatments, increasing with additional irrigation, but there was a small crop rotation effect on ETc.
Irrigation water use efficiency , defined as the additional crop yield over dryland production divided by irrigation, was significantly more from deficit irrigation than full irrigation.
From soil water parameter measurements, corn in the WCS was able to use more stored soil water than the CC rotation, which led to less dependence on irrigation.
The dryland treatment accumulated significantly more soil water during the non-growing season than the deficit or fully irrigated treatments because the dryland corn was forced to extract more soil water deeper into the soil profile, leaving more room for water storage.
Dryland yields, as a fraction of fully irrigated yields , varied more than deficit irrigation yields, which decreased the income risk for deficit irrigation compared with dryland.
Over the years of the study, a wide range in water applications to the full irrigation treatment demonstrated the need to schedule irrigations to match crop water needs; otherwise, over and under irrigation could occur.
When crop yields from all years and rotations were ranked from maximum to minimum values within each water treatment, yield results were predicted on the basis of probabilities.
During the wettest years with low probability of occurrence, dryland, deficit irrigation, and full irrigation yields were nearly the same.
As probabilities to achieve yields increased, indicating drier and drier years, dryland yields were 25% of fully irrigated yields, and deficit irrigation yields were 75% of fully irrigated yields at 98% probability of occurrence.
Chapter 2: Troubleshooting Precision Agricultural Equipment
 Even though modern equipment generally operates trouble free, problems still occur.
In some situations, attempting to fix the equipment can void warranties.
The following chapter provides basic troubleshooting guides for precision agricultural equipment, and it does not provide techniques to overcome proprietary defenses.
General GPS Guidance Systems
 A majority of precision agriculture equipment relies on the Differential Global Positioning System  to provide accurate locations during planting, harvesting, and applying precision treatments.
DGPS, which is often referred to as GPS, can provide sub-inch accuracy.
Unfortunately, when the GPS fails, your farming operation may be at a standstill until repaired.
Troubleshooting GPS guidance systems may require contacting the manufacturer's technical support.
However, there are some simple steps that you can follow before calling a technician.
Figure 2.1 A technician calibrates the guidance system on a new tractor.
Problem: Not receiving a GPS signal.
1.
Check for software or firmware updates that may be required by the system.
Not having the current software updates can lead to communication issues between implements and control modules, causing the equipment to malfunction.
2.
Make sure the GPS receiver is not adjacent to buildings, tree lines, or vehicles and that it has a clear view of the sky.
Attempt to install and test the guidance system before the equipment is needed.
In most situations, guidance systems cannot be tested in the shop because GPS signals are transmitted over relatively weak signals and small obstructions can interfere with the signal.
Problem: The vehicle has a clear view of the sky but still does not have a GPS signal.
1.
Check for tight and secure connections, starting at the globe on the roof, to the receiver, to the display cable.
Check all connectors to make sure that the pins have not been pushed sideways.
Loose connections can cause a loss of or a sporadic signal.
2.
Check the indicator lights on the receiver.
If the cab roof receiver's green light is on, the receiver is receiving a GPS signal.
If the receiver has a signal, but the display indicates no connection, there is a problem between the receiver and the display.
3.
Check if the correct differential correction is selected.
For example, the display may be set to utilize WAAS for differential correction when it needs to be set to OmniSTAR or StarFire.
4.
If the GPS light is yellow or blinking , there is an interference with the signal.
Trees or buildings that are blocking the signal between the satellite and the receiver can cause interference.
5.
A red light or amber blinking light on your GPS indicates no communication between satellites and your receiver as you attempt to restart the system.
If the problem persists, contact your local dealer.
6.
Check the baud rate, which is the speed at which the system communicates with satellites.
Baud rate is the rate at which information is transferred from the receiver to the computer, and if it is not set to the correct setting, the GPS system will not work.
Recently purchased systems have baud rates that often are 19,200 or 38,400.
Older systems may have baud rates of 4,800 or 9,600.
Check your manual for correct baud rate settings.
7.
Check the Controller Area Network  bus systems to make sure that the appropriate baud rates for the receiver, wheel-angle sensors, and steering valve are appropriate.
Problem: The location is not correct.
1.
This is a common problem when the GPS system has been off for an extended period of time.
When the system is turned on, the software uses old information to calculate its location.
As the almanac  is obtained, the locations will become more accurate.
Wait until convergence is down to 2"-5" if using a satellite-based correction system.
2.
Poor location accuracy can be caused by the satellite arrangement in the sky.
The satellites may not be evenly distributed in the sky, or close to the horizon rather than overhead.
This can lead to poor Dilution of Precision  values, which can be found in the display.
Typical numbers desired for DOP are: 0-3 good, 3-5 acceptable, and above 5 unusable.
3.
3) Make sure that the receiver is at the highest point on the vehicle.
For example, if you added extensions to the combine's grain tank and the receiver is on top of the cab, the extensions may protrude above the receiver, reducing the number of viewed satellites.
It also could cause a multipath error.
Multipath error occurs when the GPS signal bounces off of an object  and then is picked up by the receiver.
This causes the receiver to receive multiple signals, one directly from the satellite, and one from the signal bouncing off of the bin extension.
Figure 2.2 Grain extensions can cause multipath error, leading to signal degradation.
4.
It is possible that the receiver is communicating with the GPS satellites, but not receiving a correction signal from a WAAS / OmniSTAR/ StarFire satellite.
When this happens, the GPS correction will not be accurate enough for most purposes.
All displays have a screen that indicates the type of GPS correction.
It is important that you are receiving Differential GPS.
5.
An additional frequent problem is the vehicle wandering off course.
Two-way radios and citizens band  radios can interfere with GPS signals, causing loss of satellites.
If the vehicle is wandering off course, change the frequency of the radios and CBs.
Electrical noise from a bad alternator can also cause degradation or loss of GPS signal quality.
Planting and Application Issues
 Problem: The planter shutoffs/startups are producing gaps in the field 
 1.
This can be an issue if the offsets are not correctly entered into the display.
The machine needs to know where everything is in respect to the GPS receiver.
Many companies offer default settings that autopopulate based on the vehicle model and implement model numbers.
These values must be checked.
2.
Check whether the tire size has been changed, the GPS receiver has been moved, or the hitch type has been changed.
3.
Most systems also have a lead-in or turn-on/turn-off time that can be adjusted.
If the product application starts too soon, decrease the turn-on time.
If application starts too late, increase turn-on time.
If product application stops too soon, decrease turnoff time, and if product application stops too late, increase turn-off time.
Figure 2.3 Offsets entered incorrectly can lead to skips and overlaps on the headlands.
Problem: Row does not shut off when entering a headland.
1.
1) The headland or turnrow is the end of each planted field.
These areas are subject to greater compaction than the rest of the field.
To avoid double planting, double fertilizing, and double spraying, farmers often turn off the equipment when entering these areas.
If the wire controlling the row clutch is broken, the planter will default to plant mode.
Check the wiring coming from the individual row clutch and replace if broken.
2.
2) With planters and other application equipment, it is not uncommon to tie one brand of implement to another type of tractor.
This can lead to having multiple displays in the tractor cab, utilizing one for guidance lines and the other to run the planter or application equipment.
a.
Feed GPS from the tractor monitor into the planter monitor for row shutoffs, and variable-rate planting.
b.
Make sure the proper NMEA sentences are being sent to the planter monitor from the tractor display.
i.
i.
Typical message strings are the GGA, VTG and ZDA message strings, depending on the piece of equipment.
ii.
Check with the manufacturer or owner's manual to confirm which NMEA 0183 message strings will be needed for input to the implement prior to planting season.
iii.
If the message strings are correct, set the communication rate in Hertz.
Hertz is the number of times per second the sentence is communicated.
iv.
A typical setting when communicating with application equipment is 5 Hz 10 Hz.
This means the sentences are sent to the implement 5 times per second , meaning the implement is receiving its location information 5 times per second.
A setting of 1 Hz would cause a slower reaction time of the planter.
As an example, if you are V.
planting at 5 mph, you travel at a rate of 7.33' or 88" per second.
The planter would travel 7.33' between rate adjustments.
Problem: The yield map does not make sense.
Yield maps are a powerful resource and contain a vast amount of information when made correctly.
However, if the yield-monitoring system is not calibrated and set up correctly, the data has little value.
To minimize errors, calibrate the system using the prescribed protocols.
Grain yield can be calibrated by measuring combine grain harvested compared with a local elevator's estimates.
Problem: Combine is counting bushels but not showing yield.
Every combine with a yield-monitoring system has a header height sensor that tells the system if the
 header is down  or up.
If you are harvesting and the monitor is counting the bushels but not showing a yield, the problem might be improper header-height calibration.
Check your owner's manual for the correct calibration methods.
This is a common problem when switching from soybeans to corn.
With soybeans, the head rides on the ground, and when switched to corn, the yield-monitoring system may think the header is up.
Problem: The yield displayed is not correct.
Check each of the sensors used to determine yield.
The combine calculates yield using the header width, the combine speed, and measured grain flow.
Make sure speed sensors are communicating properly and that the header width is entered correctly.
Common problems are that the header width is not correct and the vibration calibration was not conducted.
To conduct the vibration calibration, follow the manufacturer's protocols.
Additional suggestions are:
 1.
With an impact sensor yield-monitoring system, harvested grain is deflected by a plate at the top of the clean grain elevator.
As the plate flexes, a voltage signal is produced.
Vibration makes these estimates unreliable.
2.
If the impact plate is dirty or worn, the accuracy of the reported values decreases.
Inspect and clean these plates.
3.
With an optical yield-monitoring system, check the eyes for dirt/dust debris.
Next, check the clearance between the sensor plate and the paddles of the clean grain elevator.
In most systems, this should be approximately one-half inch.
4.
Clean the clean grain elevator speed sensor.
This sensor is used to indicate to the display the speed of the clean grain elevator, which is used to determine the amount of time each paddle is allowed to fill.
Typically, this has a minimum and a maximum speed range, commonly 250 600.
Problem: Which map is correct?
This problem can be avoided by identifying the fields correctly when harvesting.
To minimize errors, identify field names during the winter months and then place a list in each vehicle/machine.
Problem: You have an electrical problem somewhere in the system.
Based on the electrical schematic , a voltmeter can be used to check voltages at specific pins and continuity of wires.
A series of steps are outlined below:
 1.
For all electrical problems, start the diagnosis by checking all fuses.
Check the fuse by touching each end of the leg of the fuse with a lead from the digital multimeter  while set on the continuity setting.
If the DMM beeps, the fuse is good; if the DMM does not react, the fuse is bad.
A blown fuse is an indicator that there is short circuit in the electrical system.
2.
Check the voltage of the system.
Voltage is simply the electrical potential, or electrical pressure.
Think of the voltage as being the equivalent of fluid pressure in a hydraulic system.
A DMM measures the "pressure" and has nearly infinite resistance, like a hose with such a small diameter, no fluid would be allowed to flow.
Volts are comparable to psi, the higher the psi, the more "push" a fluid has.
It is the same for volts, higher volts means more "push."
 3.
Check the battery by setting the DMM to voltage DC in the range that corresponds with the likely voltage of the battery.
For a 12-volt battery, set the range to 20 DCV.
Put the voltmeter probes on the battery terminals.
If the probes are backward, the only consequence is a negative reading.
4.
To measure a voltage drop across a piece of the circuit such as a light bulb, connect the digital multimeter in parallel with the light bulb.
This analysis is useful because it provides information if the circuit is operating correctly.
All sensors typically output a voltage that corresponds to a specific speed, position, and temperature.
For example, if your auto-steer system is not steering correctly, you may want to check the wheel-angle sensor to ensure it is functioning properly.
To do this, connect one probe to the input wire and the other to the ground wire of the sensor.
As you turn the wheels from left to right, you should see the voltage change accordingly (hypothetically -2.5 +2.5
 volts for this example).
If the DMM does not return a smooth voltage signal as the wheel is turned, this could indicate a bad wheel-angle sensor.
If you can't get to a bare wire with your DMM lead, one trick is to poke a hole through the insulation with a thin sharp needle.
When you have completed the assessment, use waterproof silicone to fill the hole.
5.
Current is the electrical flow through a circuit and is usually measured in amps or milliamps.
To measure the current running through a circuit, break the circuit and reconnect the circuit using the probes.
Again, if you hook the probes up backward, you will merely get a negative reading.
The DMM acts as though it has no resistance in this setup, SO it does not change the circuit but it will measure the electrical flow.
Make sure to have the probes plugged into the right ports for current measurement and have the settings at the correct range.
6.
The resistance  is the measurement of resistance to electrical flow.
The resistance of a resistor, section of wire, a switch, or anything can be measured.
A variable resistor, or potentiometer, is usually a dial or slider that changes resistance as it is adjusted to create larger or smaller voltage drop.
Variable resistors are used to set the resistance accordingly.
Unlike measuring current and voltage, a circuit must be disconnected from power when measuring resistance.
To measure resistance, place a probe on each side of the piece you are trying to measure.
7.
Continuity is a test that detects electrical flow through the system.
The DMM will signal a 1 and beep when electricity is flowing.
This is very useful when checking wires, fuses, connections, and switches.
It is also useful in a bundle of wires to match the inputs with the outputs.
Short circuits are identified by testing for continuity between components that should not be connected.
Figure 2.4 Using a voltmeter to test for a voltage drop 
 Figure 2.5 Using a volt meter to test current 
The practicum is planned as part of the USDA-NRCS Conservation Innovation Grant  that the TAPS program received.
MANAGING DIMINISHED IRRIGATION CAPACITY WITH PRESEASON IRRIGATION AND PLANT DENSITY FOR CORN PRODUCTION
 ABSTRACT.
Many of the irrigation systems today in the U.S.
Central Great Plains no longer have the capacity to match peak irrigation needs during the summer and must rely on soil water reserves to buffer the crop from water stress.
Considerable research was conducted on preseason irrigation in the U.S.
Great Plains region during the 1980s and 1990s.
In general, the conclusions were that in-season irrigation was more beneficial than preseason irrigation and that preseason irrigation was often not warranted.
The objective of this study was to determine whether preseason irrigation would be profitable with today's lower-capacity groundwater wells at different levels of corn plant density.
A field study was conducted at the Kansas State University Southwest Research-Extension Center near Tribune, Kansas, from 2006 to 2009.
The study was a factorial design of preseason irrigation , irrigation capacities , and plant density  increased profitability when irrigation capacity was increased to 5.0 mm d1.
Keywords.
Corn, Irrigation capacity, Irrigation management, Preseason irrigation.
I irrigated crop production is a mainstay of agriculture in western Kansas.
However, with declining water levels in the Ogallala aquifer and increasing energy costs, optimal utilization of limited irrigation water is required.
The most common crop grown under irrigation in western Kansas is corn.
Almost all of the groundwater pumped from the High Plains  aquifer is used for irrigation.
In 1995, 3 billion m of water were pumped for irrigation in western Kansas, and 1.71 billion m  were applied to corn.
This amount of water with-
 Submitted for review in August 2011 as manuscript number SW 9347; approved for publication by the Soil & Water Division of ASABE in January 2012.
Presented at the 5th National Decennial Irrigation Conference as Paper No.
IRR108836.
Contribution No.
12-089-J from the Kansas Agricultural Experiment Station, Manhattan, Kansas.
drawal from the aquifer reduced the saturated thickness in some areas by more than 45 m by the year 2003  and has also reduced pumping flow rates.
Similar problems exist in many parts of the High Plains aquifer, particularly in the Southern High Plains.
Considerable research was conducted on preseason irrigation  in the U.S.
Great Plains region during the 1980s and 1990s.
In general, the conclusions were that in-season irrigation was more beneficial than preseason irrigation and that preseason irrigation was often not warranted because overwinter precipitation could replenish a significant portion of the soil water profile.
In a survey from the late 1980s that assessed water management practices of irrigators, 65% of the 455 respondents from western Kansas, western Texas, and the Oklahoma Panhandle reported that they used off-season irrigation.
Preseason irrigation is an irrigation management technique that is relatively unique to the semi-arid Great Plains region; it is not usually needed in the humid and semi-humid regions and is not utilized in the arid region because irrigation systems are typically designed to apply peak irrigation requirements.
The Great Plains also has nearly vertical precipitation isobars , thus
 Table 1.
Irrigation and precipitation amounts in a sprinkler-irrigated corn study, KSU Southwest Research-Extension Center, Tribune, Kansas, 2006-2009.
2006	2007	2008	2009
 Preseason irrigation	Application date	April 4	April 24	April 12	April 17
 In-season irrigation	Initial application date	May 27	June 22	June 13	June 19
 Final application date	Aug.
28	Aug.
31	Sept.
5	Sept.
2
 Total amount applied 
 2.5 mm dtreatment	243	183	209	225
 3.8 mm dtreatment	320	257	278	299
 5.0 mm d-Superscript treatment	483	397	375	453
 Growing season precipitation	Amount 	176	205	238	364
 Non-growing season precipitation	Amount 	__[a]	381	107	217
 [a] Non-growing season precipitation was not measured prior to the 2006 crop.
making preseason irrigation research results more useful over the broad north-to-south expanse of the region.
Much of the previous research was conducted during a generally wetter climatic period in the Great Plains and under circumstances of ample in-season irrigation capacity.
The Great Plains drought that occurred during the early part of the last decade  renewed producer interest and has brought new questions about preseason irrigation.
In a more recent study, Stone et al.
used simulation modeling to examine the effectiveness of preseason irrigation.
They found that the differences in storage efficiency between spring and fall irrigation peaked at approximately 37 percentage points  when the maximum soil water during the preseason period was at approximately 77% of available soil water.
Corn yield is greatly impacted by irrigation capacity when in-season precipitation is limited.
In northwest Kansas, corn yields were increased by approximately 10% when the irrigation capacity was increased from 25 mm every eight days to 25 mm every four days.
In the same study, increasing plant density from 66,300 to 82,300 plants ha increased grain yield  by approximately 6%.
In a study with subsurface drip irrigation at the same site, an irrigation capacity of 2.5 mm d produced approximately 80% of maximum yield even in an extremely dry year, and an irrigation capacity of 4.3 mm d' produced near-maximum yields in most years.
It was also found that increasing plant density from 55,600 to 85,200 plants ha generally increased corn yields, particularly in good corn production years, without a yield penalty when irrigation was severely limited or eliminated.
Many of the irrigation systems today in the Central Great Plains are limited by available water resources.
They can no longer apply peak irrigation needs during the summer and must rely on soil water reserves to buffer the crop from water stress.
Therefore, this study was conducted to evaluate whether preseason irrigation would be profitable when irrigation capacity is limited and insufficient to fully meet crop requirements.
A field study was conducted at the Kansas State University Southwest Research-Extension Center near Tribune, Kansas, from 2006 to 2009 on a deep silt loam soil (Ulys-
 ses silt loam; fine-silty, mixed, superactive, mesic Aridic Haplustolls).
The region is semi-arid with a summer precipitation pattern and an average annual precipitation of 440 mm.
The study was a factorial design of preseason irrigation , irrigation capacity , and plant density  were approximately 36 m long and 18 m wide, and the plant population subplots were approximately 36 m long and 3 m wide.
Corn was planted in late April or early May each year.
The hybrids  were all resistant to glufosinate and/or glyphosate herbicides.
The study area was disked several times in the spring prior to planting to incorporate residue and form a seedbed.
Pre-emergence herbicides were used for weed control along with post-emergence applications of glyphosate  or glufosinate.
Nitrogen fertilizer  of the center two rows of all plots was machine harvested with grain yields adjusted to 0.155 g g-1 moisture.
Plant densities were determined along with the other yield components.
The plots were irrigated with a linear-move sprinkler irrigation system that had been modified to allow water application from different span sections as needed to accomplish the randomization of plots.
The preseason irrigation was applied in approximately 38 mm amounts in two passes several days apart to minimize runoff in April.
The in-season irrigations were initiated in late May to mid-late June.
All plots were irrigated in May after planting each year to aid emergence and incorporate herbicides.
After in-season irrigations were initiated, the 5.0 mm d-Superscript treatment was applied as a weekly irrigation of about 35 mm, the 3.8 mm d-Superscript treatment was applied as a weekly irrigation of about 25 mm, and the 2.5 mm d-Superscript treatment was applied every two weeks as 35 mm  treatment).
When abundant precipitation occurred near the time of planned irrigation events, the scheduled irrigations were not performed.
This occurred once during the summers of 2006, 2007, and 2008.
The final irrigation events
 were in late August to early September.
Corn in this region can extract water from a depth of approximately 2.4 m and will easily utilize water on these deep silt loam soils to a depth of 2 m.
Soil water within the profile was measured throughout the growing season using neutron attenuation , with probe activity centered at 0.3 m depth increments from 0.15 through 2.25 m soil depths.
Care was taken to ensure that access tubes were installed with the appropriate height above ground SO that all measurements were taken at consistent depths.
Available soil water was calculated by subtracting unavailable water  from measured soil water.
All precipitation and irrigation inputs were measured.
Seasonal crop water use was calculated by summing the soil water depletion  plus the in-season irrigation and precipitation.
Non-growing season soil water accumulation was the increase in soil water from harvest to the amount at emergence the following year.
Precipitation storage efficiency  was calculated as non-growing season soil water accumulation divided by non-growing season precipitation.
Storage efficiency from preseason irrigation was calculated as the difference between non-growing season accumulation with preseason irrigation compared with no preseason irrigation  divided by the amount of preseason irrigation.
Crop water productivity  was calculated as the grain yield.
Statistical analyses were performed using the GLM procedure in SAS.
Local crop prices and input costs were used to perform an economic analysis to determine net return to land, management, and irrigation equipment for each treatment.
Custom rates were used for all machine operations.
Input costs, including the cost of seed , were kept uniform for all years.
Although irrigation pumping depths  and energy sources  vary greatly within the region, a representative irrigation cost of $0.157 mm was used in all calculations.
Harvest prices of corn were $0.133, $0.189, $0.156, and $0.136 kg  in 2006, 2007, 2008, and 2009, respectively.
WEATHER CONDITIONS AND IRRIGATION REQUIREMENTS Growing-season precipitation ranged from 176 mm in 2006 to 364 mm in 2009.
Normal growing season precipitation is 245 mm; therefore, 2006 and 2007 were drier than normal years, 2009 was a wet year, and 2008 was about average.
Temperatures were below normal in 2006, near normal in 2007, near normal in 2008 except for a cool August, and slightly above normal in 2009.
In-season irrigations ranged from 183 to 483 mm depending on irrigation capacity and year.
Non-growing season precipitation ranged from 107 mm  to 381 mm , with an average of 235 mm.
CORN GRAIN YIELD RESPONSE
 Preseason irrigation significantly increased grain yields by an average of 1.0 Mg ha.
Although the interaction with irrigation capacity was not significant, the effect tended to be greater at lower irrigation capacities.
For example, with 68,000 plants ha-Superscript preseason irrigation  increased grain yield by 1.3 Mg ha with an irrigation capacity of 2.5 mm d' but only by 0.4 Mg ha with an irrigation capacity of 5.0 mm d-Superscript As might be expected, grain yields increased significantly with increased irrigation capacity.
Grain yields  were 28% greater when the irrigation capacity increased from 2.5 to 5.0 mm d-Superscript This increase was greater than the 10% yield increase in northwest Kansas for a similar increase in irrigation capacity.
Preseason irrigation and increased irrigation capacity increased the number of kernels per ear but had little impact on kernel mass.
The optimum plant density varied with irrigation level.
With the two lowest irrigation capacities and without preseason irrigation, a plant density of 56,000 plants ha was generally adequate.
However, if preseason irrigation was applied, then a higher plant density  increased yields.
With an irrigation capacity of 5.0 mm d1, a plant density of 80,000 plants ha provided greater yields with or without preseason irrigation.
Figure 1.
Average corn grain yields and net returns to land, irrigation equipment, and management as affected by irrigation capacity, plant density  in a sprinkler-irrigated corn study, KSU Southwest Research-Extension Center, Tribune, Kansas, 2006-2009.
Table 2.
Crop parameters as affected by irrigation capacity, preseason irrigation , and seeding rate in a sprinkler-irrigated corn study, KSU Southwest Research-Extension Center, Tribune, Kansas, 2006-2009.
Irrigation	Seed	Grain	Water	Plant	Ear	1000-Kernel
 Capacity	Preseason	Rate	Yield	Productivity	Density	Density	Mass	Kernels
 	Irrigation			per Ear
 2.5	No	56	9.4	16.7	55.3	53.0	317	467
 68	9.7	17.2	66.1	61.0	306	433
 80	9.6	16.8	77.1	71.2	299	371
 Yes	56	10.5	17.4	54.1	53.0	322	520
 68	11.0	18.0	66.0	62.6	316	468
 80	11.2	18.1	77.9	73.1	307	418
 3.8	No	56	10.6	16.8	54.9	52.5	318	531
 68	10.7	17.1	66.6	64.0	310	456
 80	10.5	16.5	76.8	72.2	308	396
 Yes	56	11.3	17.4	55.4	54.2	321	551
 68	12.1	18.6	66.7	64.6	314	501
 80	12.3	18.7	77.6	74.7	307	456
 5.0	No	56	12.3	17.4	55.0	54.3	319	601
 68	13.0	17.8	66.7	66.1	312	532
 80	13.7	18.9	78.5	77.2	306	491
 Yes	56	12.5	17.0	54.7	54.1	326	602
 68	13.4	17.9	66.6	66.2	319	538
 80	14.0	18.8	78.7	77.1	306	505
 Irrigation capacity 	0.001	0.469	0.086	0.001	0.687	0.001
 Preseason	0.002	0.103	0.659	0.107	0.160	0.001
 ICap X Preseason	0.225	0.303	0.452	0.401	0.752	0.140
 Seed rate	0.001	0.001	0.001	0.001	0.001	0.001
 Seed rate X ICap	0.001	0.016	0.012	0.001	0.212	0.185
 Seed rate X Preseason	0.016	0.114	0.089	0.345	0.186	0.242
 Seed rate X ICap X Preseason	0.402	0.623	0.427	0.373	0.518	0.286
 Means	Irrigation capacity	2.5	10.3	17.4	66.1	62.3	311	446
 3.8	11.2	17.5	66.3	63.7	313	482
 5.0	13.1	18.0	66.7	65.8	315	545
 LSD0	0.7	1.1	0.5	1.3	8	21
 Preseason	No	11.0	17.3	66.3	63.5	311	475
 Yes	12.0	18.0	66.4	64.4	315	507
 LSD00	0.6	0.9	0.4	1.1	7	17
 Seed rate	56	11.1	17.1	54.9	53.5	321	545
 68	11.6	17.7	66.5	64.1	313	488
 80	11.9	18.0	77.8	74.2	306	440
 LSD0	0.2	0.4	0.4	0.6	2	10
 Water productivity  was not significantly affected by irrigation capacity or preseason irrigation , although the trend was for greater WP with increased water supply.
This contrasts with previous research , in which WP was less with preseason irrigation.
Similar to grain yields, the effect of plant density varied with irrigation level.
With lower irrigation levels, a plant density of 68,000 plants ha tended to optimize crop water productivity.
It was only at the highest irrigation capacity that higher plant densities improved WP.
Crop water use increased with irrigation capacity and preseason irrigation.
Soil water at harvest increased with increased irrigation capacity, but this resulted in less soil water accumulation during the winter.
Nongrowing season soil water accumulation averaged 69 mm , storing approximately 29% of the average non-growing season precipitation.
When preseason irrigation  was applied, the increase in accumulation of non-growing season water was
 62, 47, and 20 mm for the 2.5, 3.8, and 5.0 mm dirrigation capacities, respectively.
Those values translate into storage efficiencies from preseason irrigation  of 82%, 62%, and 27% for the 2.5, 3.8, and 5.0 mm d-Superscript irrigation capacities, respectively.
The increasing irrigation capacities having increased amounts of available soil water  at harvest  are less efficient at storing the preseason irrigation.
Similarly, on this Ulysses soil, Stone et al.
found storage efficiency from fall preseason irrigation amounts decreased from 80% to 30% as ASW increased from 60% to 80% of the available water capacity.
Available soil water at emergence was 58 mm greater with preseason irrigation from a combination of the storage from preseason irrigation and greater ASW at harvest.
By mid-July , the effect of preseason irrigation on ASW had diminished, and although numerically greater , was not significantly greater than without preseason irrigation.
The effect of preseason irrigation was even further reduced at corn harvest, with only 20 mm greater ASW.
Increasing irrigation capacity significantly increased ASW throughout
 Table 3.
Available soil water in a 2.4 m profile, crop water use, and non-growing season water accumulation for corn as affected by irrigation capacity, preseason irrigation, and seeding rate in a sprinkler-irrigated corn study, KSU Southwest Research-Extension Center, Tribune, Kansas, 2006-2009.
Irrigation	Available Soil Water	Water	Non-Growing Season
 Capacity	Preseason	Seed Rate		Use	Accumulation
 	Irrigation		
 2.5	No	56	212	208	132	541	71
 68	209	191	123	547	69
 80	204	189	118	547	71
 Yes	56	271	237	138	593	128
 68	267	220	124	604	135
 80	275	220	126	610	135
 3.8	No	56	223	210	139	618	69
 68	233	211	154	613	65
 80	230	213	144	620	76
 Yes	56	267	228	157	644	103
 68	266	231	156	644	121
 80	272	232	152	654	128
 5.0	No	56	267	276	230	710	54
 68	253	255	200	726	77
 80	268	269	217	725	72
 Yes	56	341	326	275	739	80
 68	336	316	257	751	93
 80	328	310	250	751	90
 ANOVA 
 Irrigation capacity 	0.010	0.002	0.001	0.001	0.001
 Preseason irrigation	0.001	0.062	0.266	0.001	0.001
 ICap X Preseason irrigation	0.647	0.726	0.587	0.010	0.001
 Seed rate	0.779	0.087	0.076	0.001	0.002
 Seed rate X ICap	0.692	0.368	0.173	0.059	0.156
 Seed rate X Preseason irrigation	0.985	0.818	0.820	0.546	0.424
 Seed rate X ICap X Preseason irrigation	0.389	0.908	0.625	0.749	0.303
 Means	Irrigation capacity	2.5	240	211	127	574	101
 3.8	248	221	150	632	94
 5.0	299	292	238	734	78
 LSD	38	43	45	10	10
 Preseason irrigation	No	233	225	162	627	69
 Yes	291	258	182	666	113
 LSD0.05	31	35	37	8	8
 Seed rate	56	264	247	179	641	84
 68	261	237	169	648	93
 80	263	239	168	651	95
 LSD0.05	9	10	10	5	6
 [a] Fallow accumulation includes only 2007, 2008, and 2009 data.
the growing season.
Seeding rate had minimal effect on ASW at emergence, but increased seeding rate tended to increase crop water use, decrease soil water at harvest, and increase over-winter soil water accumulation.
An increase in ASW in the soil profile at emergence from preseason irrigation occurred below 30 cm to a depth of at least 240 cm  but not in the surface 30 cm.
Lamm et al.
reported no difference in ASW in a 2.4 m soil profile at emergence due to irrigation capacity.
However, in the current study, an increase in irrigation capacity resulted in increased ASW at planting from 60 through 180 cm.
This suggests that drainage losses will be increased when the amount of irrigation is increased either through preseason irrigation or higher irrigation capacity.
The drainage rate for this Ulysses soil was shown to
 be 5, 1, and 0.1 mm d-Superscript at profile available water amounts of 100%, 85%, and 65% of maximum, respectively.
Seeding rate had no effect on ASW at emergence at any depth in the profile, which agreed with earlier reports.
Preseason irrigation was found to be profitable at all irrigation capacities , although the difference was minimal at the 5.0 mm dirrigation capacity.
At the two lower irrigation capacities, a seeding rate of 68,000 seeds ha was generally the most profitable.
However, the highest irrigation capacity benefited from a seeding rate of 80,000 seeds ha
 Table 4.
Available soil water  at emergence in a 240 cm profile as affected by irrigation capacity, preseason irrigation , and seeding rate in a sprinkler-irrigated corn study, KSU Southwest Research-Extension Center, Tribune, Kansas, 2006-2009.
Irrigation Capacity	Preseason	Seed Rate	Soil Depth 
 	Irrigation	(10 3 ha 	0-30	30-60	60-90	90-120	120-150	150-180	180-210	210-240
 2.5	No	56	47	29	25	23	23	23	22	21
 68	45	29	26	24	22	21	21	23
 80	46	26	24	22	21	20	21	24
 Yes	56	49	37	35	32	31	29	29	29
 68	48	38	36	32	29	28	28	28
 80	49	36	35	33	32	29	30	31
 3.8	No	56	47	30	24	25	24	24	25	24
 68	48	30	27	26	25	26	26	25
 80	47	30	26	25	25	26	26	25
 Yes	56	49	38	34	33	31	29	27	26
 68	50	36	34	33	29	27	30	26
 80	50	39	34	33	31	28	28	29
 5.0	No	56	50	36	33	32	30	29	29	29
 68	47	35	32	30	30	29	25	25
 80	49	36	34	32	30	31	29	28
 Yes	56	53	42	45	44	42	41	38	37
 68	52	42	46	43	41	39	38	36
 80	51	43	44	42	40	37	36	34
 Irrigation capacity 	0.270	0.088	0.001	<0.001	0.002	0.009	0.052	0.138
 Preseason	0.116	0.003	<0.001	<0.001	<0.001	0.012	0.008	0.027
 ICap X Preseason	0.934	0.919	0.675	0.685	0.526	0.525	0.476	0.595
 Seed rate	0.519	0.687	0.778	0.765	0.535	0.659	0.991	0.346
 Seed rate X ICap	0.042	0.072	0.837	0.836	0.836	0.945	0.565	0.297
 Seed rate X Preseason	0.387	0.244	0.767	0.932	0.547	0.670	0.664	0.994
 Seed rate X ICap X Preseason	0.223	0.818	0.451	0.513	0.670	0.535	0.569	0.451
 Means	Irrigation Capacity	2.5	47	33	30	28	26	25	25	26
 3.8	48	34	30	29	27	27	27	26
 5.0	50	39	39	37	35	34	32	31
 LSD0.05	4	6	5	4	5	6	6	6
 Preseason	No	47	31	28	27	25	25	25	25
 Yes	50	39	38	36	34	32	32	31
 LSD0.05	3	5	4	4	4	5	5	5
 Seed rate	56	49	35	33	32	30	29	28	28
 68	48	35	33	31	29	28	28	27
 80	49	35	33	31	30	29	28	28
 LSD0.05	1	1	1	1	2	2	2	2
 Table 5.
Net return to land, irrigation equipment, and management  at three irrigation capacities and three seeding rates in a sprinkler-irrigated corn study, KSU Southwest Research-Extension Center, Tribune, Kansas, 20062009.
(mm d-1	Irrigation	56	68	80
 2.5	No	546	561	502
 Yes	672	711	703
 3.8	No	686	670	612
 Yes	758	831	846
 5.0	No	1006	1090	1178
 Yes	1010	1111	1193
 Corn grain yields responded positively to preseason irrigation and increases in irrigation capacity.
This yield increase generally resulted from increases in kernels per ear, suggesting that the grain filling stage was less affected by these two factors.
Grain yield increased 28% by increasing the irrigation capacity from 2.5 to 5.0 mm d-1, which is considerably greater than reported in earlier work (Lamm et
 al., 2009), which showed an increase of 10% with a similar increase in irrigation capacity.
Preseason irrigation increased grain yields by approximately 9% and was profitable at all irrigation capacities, although the differences were small at 5.0 mm d-Superscript irrigation capacity.
Therefore, it may not be prudent to preseason irrigate with irrigation capacities of 5.0 mm d-Superscript or greater SO that the water can be conserved for later use.
Seeding rate should be adjusted for the amount of irrigation water available from both irrigation capacity and preseason irrigation.
At irrigation capacities of 2.5 and 3.8 mm d1 a seeding rate of 68,000 seeds ha was generally more profitable than lower or higher seeding rates.
However, a higher seeding rate  increased profitability when the irrigation capacity was increased to 5.0 mm d-1.
With the anticipated continuing decrease of irrigation capacities above the Ogallala Aquifer, producers will need to consider the benefits from adjustment of plant population and limited use of preseason irrigation for profitable corn production.
This research was supported in part by the Ogallala Aq-
 uifer Program, a consortium between the USDA Agricultural Research Service, Kansas State University, Texas AgriLife Research, Texas AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
KSDA.
1997.
Kansas reported water use summary, calendar year 1995.
Topeka, Kans.: Kansas Department of Agriculture.
KWO.
1997.
1995 Kansas irrigation water use.
Topeka, Kans.: Kansas Water Office.
Irrigation Impact and Trends in Kansas Agricultural1
 Abstract: Total irrigated acreage in Kansas remains at approximately 3 million acres, which is about 15 percent of total annual harvested cropland acres, based on year 2000 data.
This acreage represents over 25 percent of the total value of Kansas crop production.
However, regional analysis show the impact of irrigation is much more significant and in an example county, exceeded over 90 percent of the value of crop production.
Keywords: Kansas, irrigation trends
 Irrigated agricultural remains an important segment of the total Kansas economy, but even more important when irrigation impacts are viewed on smaller regional scales.
Kansas Irrigated Acreage, Crop Value System, Crops, and Water Use
 Irrigated Acreage and Crop Value
 The Kansas irrigated acreage base in 2000 was reported to be almost 3.2 million acres  and produced over 25 percent of the total crop value produced of $2.8 billion.
Irrigated acreage percentage of crop value produced was similar to previous analysis,.
The total value of crop production was less in 2000 than previously.
Center pivot irrigation systems increased their acreage dominance in the state and now represent over 80 percent of all irrigated acreage.
Subsurface Drip Irrigation  is the newest irrigation system option.
While SDI acreage is increasing, SDI still represents less than one percent of all irrigated acres.
Corn remains the most popular irrigated crop, representing 50 percent of all irrigated acreage.
Wheat still remains the second most commonly irrigated crop, but its acreage trend continues downward.
Alfalfa and soybean have been gaining acreage, while grain sorghum acreage has been decreasing.
Alternative crops of cotton, sunflower and dry beans have been increasing in acreage but the number of irrigated acres is not reported separately from dryland production.
However, total acreage of irrigated cotton, sunflower and dry bean are still relatively small.
The total volume of irrigation water reported pumped in 2000 was 3.86 million ac-ft  and reflects the largest volume pumped in five years, and reverses a generally downward trend in applied application depth.
Region 1 of Figure 2 represents the western third of Kansas, Region 2, the middle third, and Region 3 is eastern
 Kansas.
Most of the irrigated acres are in western Kansas and concentrated in southwest Kansas.
The downward use trend is likely attributed to the continued conversion of irrigated lands from surface flood irrigation to center pivot irrigation and relatively favorable climatic conditions during the late 1990's.
Data collected from the Garden City weather station at the Southwest Research and Extension Center shows that annual precipitation and July-August rainfall amounts were above normal during this period.
2000 annual precipitation was above normal but 2000 July-August rainfall was less than normal with high crop water use demand as reflected by the pan evaporation.
Increases in pan evaporation reflect increases in temperature, solar radiation, and wind that also increase crop water use requirements.
Weather data for 2001 and 2002 are also plotted and indicate that high irrigation water use demand is likely for those two years.
Western Kansas: Irrigated Acres and Value of Production
 The western region of Kansas, representing the western 4 or 5 tier of counties  has 2.1 million irrigated acres or about two-thirds of all Kansas irrigated acres.
Within the region, about one-third of all harvested cropland in 2000 was irrigated and produced 61 percent of the total crop value.
Southwest Kansas: Irrigated Acres and Value of Production.
The southwest Kansas region represents a 14 county area.
In 2000, about 48 percent of all harvested acres were irrigated and produced nearly 73 percent of the total crop production value.
Haskell County: Irrigated Acres and Value of Production
 Haskell county is the middle county of southwest Kansas and has the second largest irrigated acreage base in Kansas of 206,000 acres.
Irrigation was applied to 77.4 percent of all harvested acres in 2000 and 92 percent of all crop production value was produced on irrigated acreage.
Irrigated agriculture makes important contributions to the Kansas economy.
These impacts become increasingly significant for heavily irrigated regions.
Planning and Operating Orchard Drip Irrigation Systems
 Components of a typical drip irrigation system.
Drip Irrigation System Layout
 Water Requirements of Pecan Trees
 Capacity of Irrigation Water Source
 Operating Drip Irrigation Systems
 PLANNING AND OPERATING ORCHARD DRIP IRRIGATION SYSTEMS
 Leon New and Guy Fipps*
 Drip irrigation allows precise application of water to plant roots.
Small amounts of water are applied frequently to replace that withdrawn by the plant and lost by evaporation or deep seepage.
Thus, soil moisture in the area around the plant is maintained at a uniform level throughout the growing period.
This increases growth and production potential since plants are not subjected to wet and dry cycles which normally occur with other irrigation methods.
Drip irrigation simplifies irrigation procedures, minimizes distribution and evaporation losses and may reduce labor requirements.
Less of the total soil surface area is wet with drip than with sprinkler and furrow systems.
This significantly reduces the amount of water required for irrigation and simplifies weed control.
The irrigation system can be automatically controlled with a time clock and/or, soil moisture sensors and automatic valves, thereby maintaining optimal soil moisture with minimum labor.
Drip irrigation is used more often for orchard crops than for field crops, primarily because the spacing between emitters and laterals is greater.
This lowers system costs per acre.
DRIP IRRIGATION SYSTEM LAYOUT
 Water is distributed to individual trees through a pipeline system which should be carefully planned for the specific site, orchard size and shape, land slope, tree spacing and water requirements.
The system should provide reasonably uniform pressure at all emitters, require minimum material and achieve maximum operating convenience.
Components of a typical drip irrigation system are illustrated in Figure 1.
The pipeline is composed of a main line which carries water to manifolds and laterals.
Water flow is regulated using manual or automatic valves.
Pressure gauges are located at critical points and are used to ensure proper system operating pressure.
A filter system is installed in the main line SO that all water is filtered.
Injection of fertilizers and other chemicals into the irrigation water often causes minerals to precipitate.
Thus, the fertilizer injector equipment should be installed upstream from the filter SO that precipitates will be filtered.
An anti-siphon unit consisting of a check valve and a vacuum breaker is installed in the main line between the pump and fertilizer injector to prevent backflow of fertilizers or other chemicals back into the water
 source in the event that the irrigation pump stops during injection.
Note that specific chemigation equipment is required by federal regulations.
These requirements are covered in Texas Agricultural Extension Service publication B-1652, "Chemigation Workbook." A lateral pipeline containing emitters is placed along each row of trees.
In larger systems, the orchard may be divided into sections or blocks, with the laterals for each block connected to a separate manifold pipeline.
The main line is normally connected at the center of the manifold as illustrated in Figure 1.
However, topography may dictate placement of the connection at some other point.
An automatic pressure regulating valve or a manual globe type valve with a pressure gauge is installed on the manifold side of the valve to allow for appropriate control of pressure in all blocks.
Valves can be used to equalize pressure variations caused by elevation differences and friction losses, and to maintain sufficient minimum pressure throughout the system.
On moderate to steep slopes, laterals and tree rows generally should be across  the slope to help maintain more uniform pressure at the emitters.
For slight, uniform slopes, proper water pressure in the laterals can sometimes be achieved by placing laterals along the direction of the slope to offset pressure loss caused by friction.
Laterals which direct water flow up the slope should generally be avoided especially when low pressure emitters are used.
Water is released by emitters attached to the laterals near each tree.
Application rates of emitters vary from 1/2 to 2 gallons per hour , while micro-sprinklers may discharge up to 10 gph or sometimes more.
Do not select an emitter which applies water faster than it can be absorbed by the soil.
Most emitters can be installed underground.
However, it is easier to adjust emitter location and to observe and clean clogged emitters when they are on the soil surface.
The size of main lines and manifolds should be carefully selected based on the water flow rate required by mature trees and on pipeline length.
As a general rule, pipe sizes are selected so that velocity of flow is less than 5 feet per second to prevent excessive pressure loss and water hammer.
Polyvinyl chloride  pipe is generally used for the main and manifold pipelines.
Main and manifold pipelines are frequently installed underground with laterals on the surface, although laterals
 Figure 1.
Components of a typical orchard drip system.
also may be underground.
Underground pipelines last longer and do not interfere with field operations.
Main and manifold pipelines are often set 18 to 24 inches below the surface, but site conditions may require other depths.
Underground laterals are usually 12 to 15 inches below the surface, or below plow depth.
Connection joints in underground pipelines should be checked for leaks before covering pipes with soil.
The ditch may be partially backfilled as installation progresses, leaving only the connection joints exposed.
It is best to cover underground pipelines when temperature is coolest, e.g., early morning.
Table 1.
Approximate maximum flow rate  in plastic pipe for drip irrigation.
sizes and flow rates
 Clean water is essential for successful drip irrigation.
Sand, silt, organic and other foreign material can easily clog small emitter openings.
Select a filtration system according to the types and quantity of foreign material in the water and the emitter characteristics, as recommended by the manufac-
 turer.
A filter system in the main pipeline near the pump is more economical and much easier to maintain than several filters located throughout the irrigation system.
Filters with corrosion-resistant stainless steel or bronze screens are available.
These are usually adequate when the irrigation water contains small amounts of sand only.
Two or more filters can be connected in short, parallel manifold pipelines to increase filtering capacity.
Backflushing capability can be provided with an appropriate arrangement of valves.
Be sure that the mesh size of the filtering screen is appropriate for the particular emitter chosen.
Filters with multi-stage screens may be required when water contains moderate to large amounts of sand.
If sand is an extreme problem, settling tanks or sand separators can be installed upstream from the filter to remove a large amount of sand and reduce the filter load.
Dual or oversized filters also will handle extra heavy filter loads, but sand separators or settling tanks may be more economical.
Surface water such as rivers, canals and ponds frequently requires more filtration than water from wells.
It may be necessary to have both a synthetic fiber or metal screen intake filter and a fine-mesh screen or sand filters on the discharge side of the pump.
Settling basins may be needed if the water contains considerable algae.
Sand  filters are commonly used for surface water sources.
These filters are expensive but are very effective and can be equipped for automatic flushing.
Equip filters with cleanout or flush valves so that trapped particles can be easily removed.
Daily flushing is necessary when water contains moderate amounts of sand or other material.
Screens will need periodic, thorough cleaning.
Pressure gauges installed on both sides of the filter provide an indication of filter clogging.
A moderate to high pressure difference indicates the filter needs flushing or cleaning.
Lateral pipelines are usually flexible polyethylene or polybutylene pipe.
Pipe sizes may be given by manufacturers in English or metric units  tubing manufactured specifically for drip irrigation systems.
Be sure pipe, fittings and emitters are compatible.
During installation, heat the end of the pipe in hot water if connections are extremely difficult.
The number of laterals required for each row of trees is determined primarily by tree size or spacing and emitter arrangement at the tree.
For large trees such as pecans, one lateral for each row is normal when micro-sprinklers or tree loops are used.
In-line or attached emitters are often used for smaller trees.
Two laterals of in-line emitters may be best for each row of mature pecan trees.
Three laterals per row may be required for pecan trees spaced 50 feet apart.
Underground lateral pipelines last longer and do not interfere with cultural and harvesting operations.
Place underground laterals approximately 12 inches deep or below plow and freeze depths.
Position single lateral pipelines with in-line emitters 2 feet from the tree trunk.
Where two emitter pipelines are used, locate each pipeline one-fourth of the row spacing on each side of the tree.
Use emitter tubing to apply water within 12 inches of small trees.
Laterals placed on the surface should be "snaked" or left slightly loose along tree rows.
In addition, leave 5 to 10 feet of extra pipe at each end SO that lateral and emitter location can be easily adjusted.
Extra lateral length is especially helpful when emitters are installed in-line.
Flexible pipe also tends to "crawl" as it expands and contracts with temperature changes.
Permissible lateral length is influenced by the diameter of the lateral, tree spacing, quantity of water delivered to each tree, type of emitter and land slope.
Design lateral lines to not exceed the length, pressure loss and flow rates recommended by the manufacturer.
With properly designed drip systems there will be reasonably uniform water application by every emitter in the system.
Many emitters are "pressure compensating," which means that their discharge rate varies little over a wide range of operating pressure.
Other emitters discharge more water as pressure increases and less water as pressure decreases.
Due to the difficulty of achieving absolutely uniform pressure throughout the system, most drip systems are designed for 90 percent uniformity.
This means that the emitter with the lowest discharge rate will apply at least 90 percent as much water as the emitter with the highest discharge rate.
Allowable pressure variation within the system or within a block in a large system can be determined with the pressure-discharge curve for the particular emitter selected.
If a pressure-discharge curve is not available, an
 allowable pressure variation of no more than 20 percent is suggested as the design criterion.
Friction pressure loss in laterals can be determined using friction loss charts for the specific type of plastic pipe used.
These charts are usually available from pipe manufacturers.
Lateral diameter, length and flow rate are needed to determine the pressure loss caused by friction.
Friction pressure loss in a lateral  is about 40 percent of that of a pipe with no emitters.
This is sometimes refered to as the 40 percent rule.
Multiply pressure loss calculated from friction charts by 0.40 to determine pressure loss in the proposed lateral.
Compare the calculated pressure loss with the allowable pressure variation.
If the calculated pressure loss is greater than the allowable variation, lateral length should be decreased or lateral pipeline diameter increased.
Head in feet  can be converted to psi  by dividing by 2.31.
Guidelines for lateral length and flow rate in 1/2-inch lines with emitters are given in Table 2.
In larger orchards, water may be supplied to a "block" of several laterals through a pipeline called a manifold.
The manifold is usually connected to the main line at the midpoint of the manifold in order to provide more uniform pressure to all laterals in the system.
The manifold can be of either polyethylene or polyvinyl chloride  pipe and is usually installed underground.
Plan manifold pipelines to provide as nearly equal pressure at each lateral as possible.
A globe valve or an automatic pressure regulating valve is installed between the main line and manifold to allow for adjustment of pressure SO that all laterals have approximately equal pressure.
Install a pressure gauge immediately downstream from the globe valve to measure pressure at the midpoint of the manifold.
Set the appropriate operating pressure by adjusting the globe valve.
Maximum pressure loss in the manifold plus loss in the lateral should generally be less than 20 percent of the emitter operating pressure.
Select manifold pipe size on the basis of water flow rate and the corresponding friction pressure loss.
Recommended maximum flow rates for some pipe sizes are listed in Table 1.
The 40 percent friction lost rule  applies to manifold as well as laterals pipelines.
Table 2.
Recommended maximum lateral lengths1 for 1/2-inch
 plastic pipe with emitters for various flow rates in gallons per
 Flow rate, GPM	Length, feet
 'Use manufacturer's recommendations when available.
The term emitter is often used to refer to any drip irrigation water discharge oriface.
Various types are available, including in-line and barbed types.
With non-pressure compensating emitters, an increase in pressure increases the emitter discharge rate, while a decrease in pressure decreases the discharge rate.
A pressure compensating emitter will discharge approximately the same amount of water under a wide range of pressures.
Emitter manufacturers provide information on the relationship between pressure and water discharge for their emitters.
Figure 2.
Typical relationships between emitter discharge and pressure for pressure compensating and non-compensating emitters.
Emitters are sometimes classified according to their design operating pressure, either low or high pressure.
Low pressure emitters usually apply 1 to 2 gallons per hour at operating pressures of 2 to 8 psi , while high pressure emitters typically apply 1 gallon per hour at about 15 psi.
The pressure-discharge curves in Figure 3 show that low pressure emitters apply more water at a given pressure than high pressure emitters.
Do not use both high and low pressure emitters in the same drip irrigation system unless pressure-regulating devices are installed upstream from the low pressure emitters.
High and low pressure emitters should not be used in the same lateral pipeline.
The water discharge rate of high pressure emitters is affected less by changes in land elevation within the orchard or friction pressure loss in the pipe than that of low pressure emitters.
Laterals with low pressure emitters cannot be as long as laterals with high pressure emitters.
All of these factors should be considered in selecting emitters and planning drip systems.
The number of emitters needed for each tree is influenced by water movement in the soil as well as the amount of water required by the tree.
A soil that allows limited horizontal movement of water  requires more emitters with lower discharge rates than a soil that will allow greater lateral spreading.
The wetting pattern generally should cover at least 60 percent of the horizontal extent of the tree canopy and root zone.
Diameter of the wetting pattern is affected by soil type, discharge rate and the duration of each irrigation period.
Figure 3.
Pressure discharge relationship for low pressure emitter and high pressure emitter.
Emitter arrangement at each tree should be considered carefully to provide convenient orchard care, easy emitter maintenance and adequate irrigation.
Typical emitter arrangements are shown in Figure 4.
Emitters should be within 1 to 1.5 feet of the trunk of young, newly transplanted trees, but should be moved away from the trunk as the trees grow.
Water quality is a factor in emitter location since salts tend to concentrate at the edges of the wet soil area.
It may be necessary to locate emitters so that wet areas overlap at the tree trunk to prevent harmful accumulations of salt at or near the trunk.
Tree-loops are often used for large trees such as pecans, as shown in Figure 4a.
The loop is connected to the underground lateral pipeline and circles the tree between the trunk and the canopy line.
Tree loops are usually 1/2-inch or 3/8-inch polyethylene pipe, 6 to 10 feet long initially, and contain one or two emitters.
Additional sections of pipe 8 to 12 feet long, containing one emitter, are connected to the initial loop as the tree grows and requires more water.
Large pecan trees typically require tree loops with 6 to 10 or more emitters.
In-line emitter arrangements, as shown in Figure 4b, have been used satisfactorily for smaller trees such as citrus, peaches and apples.
Two to four emitters are installed in the lateral SO that wet areas slightly overlap in a line along the tree row.
When laterals become too long to allow for the addition of emitters without excessive friction pressure loss, a dual-lateral arrangement, as shown in Figure 4c, may be used to supply additional water as the trees grow.
Emitter water discharge rates should be measured periodically using a graduated cylinder or other marked container.
Graduated cylinders are frequently marked to measure volume in milliliters.
Table 3 can be used to convert milliliters per minute to gallons per hour.
Emitter discharge rate should be checked at several locations over the orchard to ensure adequate and uniform irrigation.
Also check operating pressure at the ends of lateral lines at different locations.
Pressure checks should be made immediately if emitter discharge rates are less than planned.
b) single lateral per row
 c) two laterals per row
 Figure 4.
Typical emitter arrangements:  emitters installed in a tree loop,  single lateral with in-line emitters; and  double lateral with in-line emitters.
Figure 5.
Typical wetting patterns of drip emitters and micro sprinklers.
Table 3.
Conversion of flow rate in milliliters per minute 
 to gallons per hour.
Flow rate 	GPH	Flow rate 	GPH
 35	.55	70	1.11
 40	.63	75	1.19
 45	.71	80	1.27
 50	.79	85	1.35
 55	.87	90	1.43
 60	.95	95	1.51
 65	1.03	100	1.59
 Micro-sprinklers  and micro-sprayers  are sometimes preferred over drip emitters.
With these devices, water is discharged into the air and travels some distance before contacting the soil surface.
Micro-sprinklers and micro-sprayers usually have higher flow rates than drip emitters and wet larger soil surface areas in their circular or fan-shaped application patterns.
Figure 5 illustrates typical soil moisture distribution under a micro-sprinkler or sprayer as compared with a drip emitter.
With drip emitters, small areas of nearly saturated soil may occur near the emitter as shown.
Micro-sprinklers and sprayers spread water over a larger surface area and soil saturation is less likely to occur.
Spreading water over larger soil surface areas is particularly advantageous on coarse, sandy soils  and on fine-textured clay soils.
Micro-sprinklers and sprayers are available in a variety of application patterns from a full circle to fan-shaped or part-circle.
Some of the application patterns available are shown in Figure 6.
Some micro-sprinklers and sprayers have interchangable nozzles SO that the spray pattern and dis-
 charge rate can be changed.
Thus, a pattern which concentrates water near the tree can be used when the tree is small.
As the tree grows and the root system expands, the application pattern can be changed to wet a larger soil surface area.
Water droplets traveling through the air from a microsprayer or sprinkler are subject to evaporation loss.
In addition, greater evaporation loss from the soil surface will occur because a larger surface area is wet.
Evaporation losses of 5 to 15 percent can be expected depending upon temperature, wind, humidity, system pressure and orifice size.
Since a larger surface area is wet with micro-sprinklers and sprayers, increased weed germination and growth can be expected.
The rate of water flow to each tree will generally be four to ten times greater from micro-sprinklers or sprayers than from a drip system.
Therefore, larger pipe sizes  will generally be required to obtain uniform water application over the orchard.
Also, it may be necessary.
to divide the orchard into more blocks to route the water supply in sequence from block to block.
Conversion of an existing drip system to a micro-sprayer or sprinkler system may result in unsatisfactory irrigation uniformity unless flow rate requirements and piping system hydraulics are adequately evaluated.
Since salts typically accumulate around the edges of the wet pattern , micro-sprinklers and sprayers may provide better control of soil salinity.
However, drip emitters may be the better choice if the total salt content of the water is high, since the soil is maintained at a higher moisture content near the emitter.
Selection of the emitter and sizing of laterals and mainlines are based on a chosen or available system water capacity, usually expressed as GPM.
Pipelines that make up the irrigation system must be sized initially to provide the water required when the orchard is mature.
For planning purposes, water requirements of
 Figure 6.
Typical application patterns of micro-sprinklers and sprinklers.
orchards can be estimated from National Weather Service Class A evaporation pan rates.
Pan evaporation is influenced by such environmental factors as temperature, relative humidity and wind.
Each of these factors also influences the amount of water that trees require.
Pan evaporation rates are related to tree water usage with a Water Use Factor.
A WUF of 0.7, which means that the water use is 70% of the pan evaporation rate, has been used successfully in planning for orchard irrigation system capacity.
However, experience with citrus orchards in the lower Rio Grande Valley has indicated different values for WUF, as given in Table 4.
Table 4.
Water use factors  for trees for Equations 1 and
 June 1 Aug 31	0.7
 Nov 1 Feb 15	0.5
 remainder of year	0,6
 Source: Dr.
Julian Sauls, Texas Agricultural Extension Service,
 Weslaco.
Citrus values are for the lower Rio Grande Valley.
The other factor used to estimate water requirements is the area covered by the plant canopy.
In orchards the canopy area is based on the diameter of the circle formed by the tree drip line.
The maximum potential size of the tree when mature should be used to calculate canopy diameter for determining irrigation system capacity and in sizing all irrigation pipelines.
The canopy diameter of mature trees can be assumed to be equal to the tree spacing in the row.
For example, the canopy of mature peach trees will be 18 feet in diameter when planted on a spacing of 18 feet by 24 feet.
Pecan trees planted on a spacing of 35 feet by 35 feet will have a canopy diameter of 35 feet when mature.
The daily maximum water requirement for each tree can be projected using the formula:
 Q=AxEx WUF X 0.623
 Where: Q = Daily water requirement in gallons.
A = Area covered by plant canopy in square feet.
E = Class A pan evaporation in inches per day.
0.623 = Constant  WUF = water use factor.
For trees, the area  in equation 1 is the area of a circle with a diameter equal to the diameter of the tree canopy, calculated by:
 Substituting this value for A in equation 1 and combining constant numerical values produces the following equation:
 Equation 3 D x E x WUF X 0.49
 Where: Q = Daily water requirement in gallons per tree.
D = Diameter of area within tree canopy in feet.
E = Class A pan evaporation, inches per day in Table 5.
WUF = water use factor.
Equation 3 can be used to calculate the daily water requirement of trees or other single plants whose canopies cover a circular area.
Average daily Class A pan evaporation rates at various locations in Texas are given in Table 5.
These rates are the daily averages for each month of the year.
Select the daily evaporation rate at the nearest location or average the rates shown for two or three stations nearest the orchard location.
Normally, the maximum daily evaporation for the year occurs in June, July or August.
Use the maximum value to plan irrigation system water capacity.
The value selected from Table 5 is the "E" value used in equations 1 and 3.
Table 6 shows the number of gallons of water required to supply a WUF of 0.7 of daily pan evaporation for trees with canopy diameters of 5 feet to 70 feet.
For a WUF of 0.7, Tables 5 and 6 can be used directly to determine the daily water requirements in gallons.
For example, the maximum average daily evaporation in San Antonio is 0.36 inch and occurs in the months of July and August.
Table 7 shows that 151 gallons of water per day will be required to supply a WUF of 0.7 of pan evaporation for a tree with a canopy 35 feet in diameter.
Note that no allowance has been made for rainfall.
Allowing for normal or expected rainfall often will temporarily reduce the total amount of water that must be supplied by the irrigation system to meet peak water usage.
However, in the event of extended drought, the system should have insufficient capacity to maintain potential yields and prevent tree damage and loss.
Water Requirements of Pecan Trees
 Researchers in the Southeast and Southwest have reported widely differing estimates of the water requirements of pecan trees.
Experience in Texas has indicated that a mature pecan tree will use between 160 and 240 gallons per day during the peak water use period.
Some research has indicated that for short periods during the nut-filling stage, water use increases to almost 100 percent of pan evaporation.
Experience has shown that with systems designed at 0.7 pan evaporation, enough water usually can be stored in the root zone in advance  to supply the requirements of pecan trees during this maximum use period.
Table 5.
Average class A pan evaporation at selected locations*.
LOCATION	JAN	FEB	MAR	APR	MAY	JUN	JUL	AUG	SEP	OCT	NOV	DEC
 Amarillo	11	.15	.24	.32	.36	.44	42	.36	.32	.23	.13	.08
 Angleton	.07	.09	12	16	19	.22	21	20	18	.14	.10	.07
 Austin	.08	.11	17	20	23	28	.30	.31	.23	.17	12	08
 Balmorhea	.18	.20	.29	.36	.40	44	.37	.37	.31	.22	.14	13
 Beaumont	.09	.10	.14	18	.21	.23	22	22	18	.15	.11	08
 Beeville	.10	.12	18	.22	.25	.29	.30	.29	.23	.18	.13	10
 Big Spring	--	--	--	.31	.35	.41	.42	.39	.30	-	--	--
 Buchanan Dam	.09	12	19	.24	.26	.35	.37	.37	26	.20	14	.09
 Chillicothe	.09	.13	.20	.27	30	.37	.39	.37	.27	.18	.12	.08
 College Station	.08	.10	.15	19	.22	.27	.28	.28	.22	.17	.12	.09
 Dalhart	--	--	--	.28	.33	.38	.39	.35	.29	--	--	--
 Del Rio	11	16	.24	.30	33	.40	.44	.41	.31	.22	15	11
 Denison Dam	.11	.13	19	.26	.28	.37	.33	.33	.27	.20	14	.09
 Denton	.07	.10	.16	20	.22	.29	.31	.31	.24	.17	12	.08
 Dilley	.09	.13	.20	.25	.27	.32	.35	35	.26	19	.12	.09
 Dryden	.13	.20	33	42	45	52	52	50	39	.24	.20	.15
 Fort Stockton	13	.17	.29	.36	41	48	44	.40	.30	.23	.17	.13
 Grandfalls	.10	.17	29	.39	42	.47	.44	41	.30	22	15	10
 lowa Park	.06	.09	16	.21	24	.30	.32	.31	.24	17	11	.06
 Lake Kickapoo	--	13	21	.34	35	47	41	.41	.33	.25	.17	.13
 Laredo	18	.22	29	.37	42	.49	.53	.50	.37	.27	.20	.14
 Lubbock	.07	12	19	.27	29	35	.35	.32	.25	.17	.11	.07
 Mansfield Dam	.08	.10	.16	.20	.24	.32	.34	.34	.25	19	13	08
 Nacogdoches	.06	.09	12	16	18	.22	.23	.23	19	.14	.09	.07
 Possum Kingdom Dam	12	18	22	.30	.31	.39	.43	.46	.32	.26	14	.10
 Prairie View	13	14	18	23	26	.32	.30	.31	.24	.20	.14	.11
 Red Bluff Dam	.12	18	.29	.38	.44	.49	44	.42	34	21	15	.10
 San Antonio	.10	.13	18	.23	.26	.32	.36	.36	.28	.20	13	.10
 Sonora	.13	.17	23	.31	.34	.42	.41	.40	.29	.23	.15	.11
 Spur	.10	.13	20	26	.29	36	35	.32	.25	19	.14	.10
 Temple	.08	.11	16	.20	.22	.28	.31	31	24	18	12	.09
 Troup	.06	.10	14	18	.22	.28	.28	.28	22	16	10	.07
 Tyler 	.07	.10	15	19	22	.26	.27	.27	.21	.16	.1	.08
 Weslaco	.10	12	17	.21	23	.27	.28	27	20	.17	.14	.09
 Winter Haven	.08	.11	18	.22	25	.31	.34	33	25	18	.12	.08
 Ysleta	14	17	28	.43	.46	.51	.39	.35	33	22	15	.08
 Adapted from Bulletin 787, "Water Evaporation Studies in Texas, Texas Agricultural Experiment Station Texas Agricultural Extension Service,
 The Texas A&M University System.
For Chihuahua Desert conditions of west Texas, researchers have found that water consumption of pecan orchards can be coorelated to the trunk diameter and the number of trees planted per acre.
For more information contact the Texas Agricultural Experiment Station in El Paso.
Capacity of Irrigation Water Source
 Drip irrigation systems should be planned to deliver the eventual maximum daily water requirement in 1 day  or less.
The required supply of water is calculated by the number of emitters and the discharge rate of each emitter.
Water needs for young orchards are low.
One or two emitters will deliver sufficient water for each small tree.
Emitters must be added as trees grow and require more water.
Each additional emitter increases the amount of water that the irrigation well or other water source must supply.
The rate  that an irrigation well or other water supply source must deliver for each acre irrigated can be calcualted as follows:
 Number of trees per acre X flow rate  GPM/Acre = 60 minutes per hour
 In Table 7, the required water delivery rates calculated with equation 4 are listed for various hourly water application rates and tree spacings.
Three to 6 gallons of water daily will usually supply the water requirement of a tree during the first and second year after planting.
Thus, the irrigation system needs to be operated for only 3 to 6 hours a day or an equivalent amount of time per week during maximum water use months when one 1-gallon-per-hour emitter is used for each tree.
However, as trees grow, additional water must be
 Table 6.
Gallons of water required per tree to supply 0.7 pan evaporation.
Diameter of drip line of tree
 5'	10'	15'	20'	25'	30'	35'	40'	50'	60'	70'
 evaporation 	Gallons of water per tree per day
 .10	0,9	3.4	8	14	21	31	42	55	86	123	168
 .12	1.0	4.1	9	16	26	37	50	66	103	148	202
 .14	1.2	4.8	11	19	30	43	59	77	120	173	236
 .16	1.4	5.5	12	22	34	49	67	88	137	198	269
 .18	1.5	6.2	14	25	39	55	76	99	154	222	303
 .20	1.7	6.9	15	27	43	62	84	110	172	247	336
 .22	1.9	7.5	17	30	47	68	92	121	189	272	370
 .24	2.1	8.2	18	33	51	74	101	132	206	296	404
 .26	2.2	8.9	20	36	56	80	109	143	223	321	437
 .28	2.4	9.6	22	38	60	86	118	154	240	346	471
 .30	2.6	10.3	23	41	64	92	126	164	257	370	505
 .32	2.7	11.0	25	44	68	99	134	175	274	395	538
 .34	2.9	11.7	26	47	73	105	143	186	292	420	572
 .36	3.1	12.3	28	49	77	111	151	197	309	445	605
 .38	3.3	13.0	29	52	81	117	160	208	326	469	639
 .40	3.4	13.7	31	55	86	123	168	219	343	494	673
 .42	3.6	14.4	32	58	90	129	176	230	360	519	706
 .44	3.8	15.1	34	60	94	126	185	241	377	543	740
 .46	3.9	15.8	35	63	98	142	193	252	394	568	773
 .48	4.1	16.5	37	66	103	148	202	263	412	593	807
 .50	4.3	17.1	39	68	107	154	210	274	429	617	841
 .52	4.5	17.8	40	71	111	160	218	285	446	642	874
 .54	4.6	18.5	42	74	116	167	227	296	463	337	908
 Table 7.
Required pumping rate in gallons per minute per acre.
Number of trees per acre X Gallons per hour per tree
 60 minutes per hour
 Gallons per hour per tree
 Trees per acre	0.50	1.0	2.0	3.0	4.0	5.0	6.0	7.0	8.0	9.0	10.0
 27	0.23	0.45	0,90	1.35	1.80	2.25	2.70	3.15	3.60	4.05	6.67
 36b	0.30	0.60	1.20	1.80	2.40	3.00	3.60	4.20	4.80	5.40
 48c	0.40	0.80	1.60	2.40	3.20	4.00	4.80	5.60	6.40
 70d	0.59	1.17	2.34	3.51	4.68	5.85	7.00	8.17
 87	0.73	1.45	2.90	4.36	5.81	7.26	8.70
 109	0.91	1.82	3.63	5.45	7.27	9.08
 1169	0.97	1.94	3.87	5.81	7.74
 145h	1.21	2.42	4.80	7.25
 a	40' X 40' spacing	e	20' X 25' spacing
 b 35' X 35' spacing	f	20' X 20' spacing
 c 30' X 30' spacing	g 15' X 25' spacing
 d	25' x 25' spacing	h	15' X 20' spacing
 1.
Trees are spaced 30 feet X 30 feet in a 100-acre orchard.
The water requirement for mature trees is anticipated to be 8 gallons per hour per tree.
How much water should the irrigation well deliver?
640 GPM.
With the same tree spacing and acreage , what pumping rate is required to apply 1 gallon per hour per tree
 during the first year after transplanting?
80 GPM.
3.
How many acres of trees spaced 35 feet X 35 feet will a 50-GPM well irrigate when the peak water requirement is estimated to be 8 gallons
 per hour per tree?
10.4 Acres.
available to supply daily requirements.
Dry fertilizer broadcast on the soil surface may not be effectively moved into the root zone because only a small area of soil is wet by drip emitters.
However, fertilizer can be effectivly applied through the irrigation system and this method is recommended.
Excellent injection equipment is available.
Usually it can be connected into the main pipeline so that the fertilizer can be selectively routed to all trees in the orchard.
To prevent emitter plugging, fertilizer must be injected upstream from the filter SO that all undissolved fertilizer material and precipitates will be contained by the filter.
Select an injector that operates properly on the electrical voltage, water pressure and water flow rate available in the orchard, and that has adequate capacity to apply the fertilizer needs of mature trees, since this equipment has a normally long lifetime.
Highly soluble nitrogen fertilizers such as potassiun nitrate, calcium nitrate, ammonium nitrate, ammonium polyphosphate and liquid uran and urea nitrogen can be applied by the drip irrigation system.
First dissolve or mix dry fertilizer material in water to make the proper concentrate, making certain that all fertilizer is in solution.
Liquid nitrogen such as uran and urea normally can be applied undiluted by the irrigation system.
Check for formation of a precipitate that can clog the emitters and filter by mixing appropriate amounts of the fertilizer solution and irrigation water prior to injection.
A precipitate is frequently formed when anhydrous ammonia is added to irrigation water.
Other nitrogen fertilizers may also produce precipitates at high concentrations, especially with lower quality water.
Begin fertilizer injection when the irrigation system is applying water at the normal rate.
Check the application rate by timing injection of a specific quantity of material.
Complete injection before the irrigation cycle ends in order to move fertilizer out of the irrigation system and into the root zone.
One to 3 hours may be required to move fertilizer material to trees at the ends of lateral pipelines, especially where only one emitter is used for each tree.
All water from streams and underground sources contains dissolved materials known chemically as salts.
In many areas of Texas irrigation water does not contain enough salt to be injurious to plants.
However, the application of irrigation water does add salt to the soil, where it will accumulate unless it is moved below the root zone by rainfall or excess irrigation water.
When the amount of salt added exceeds the amount removed by leaching, salts may accumulate until the concentration in the soil solution becomes harmful to plants.
High soil salinity interferes with the plants' ability to take up water.
In addition, certain salts or ions can produce specific toxic effects.
Water containing high levels of soduim requires special management since sodium affects soil structure and chemistry.
Irrigation water is considered poor quality when it contains moderate to large amounts of salt.
Poor quality water often can be used more successfully with drip irriga-
 tion than with sprinkler or surface irrigation.
Less total salt is added with drip irrigation since less water is applied.
In addition, a uniformly high soil moisture level is maintained with drip irrigation, which makes more water available to trees and moves or leaches the salts below the root zone.
Even with good irrigation water management, salt will accumulate at the edges of the wet pattern as illustrated in Figure 5, and some artificial leaching  may be required.
Rainfall is normally adequate in the eastern, southern and central areas of the state to accomplish any required leaching of salts.
The addition of extra irrigation water may be required in areas of low rainfall such as in western and High Plains locations.
In most cases, operating the irrigation system when the water requirement of the trees is low can accomplish the required leaching.
When irrigation water contains significant quantities of salt, an annual salinity analysis of soil samples from the root zone is advisable.
Do not guess about water and soil salinity.
Know your water quality by having it laboratory tested and manage it to prevent problems.
This will ensure the longterm productivity of the orchard.
OPERATING DRIP IRRIGATION SYSTEMS
 Continuous irrigation from early spring through the summer is not required.
Orchard water requirements are influenced by tree size and growth stage as well as temperature, relative humidity and wind velocity.
Ideal system operation applies just enough water to replace that used by the trees the previous day.
Uniform soil moisture content is maintained and the volume of moistened soil neither increases nor decreases.
Estimate the daily operating time in hours by dividing the daily water requirement  by the water application rate at each tree in gallons per hour:
 Equation 5 Daily operating = time  Daily water requirement of each tree  Water application rate to each tree 
 The irrigation system is operated for shorter time periods early in the season; operating time increases as evaporation rates and tree use increase as shown in Table 5.
When the operation time calculated with equation 5 exceeds 24 hours per day, additional emitters must be added for each tree.
In new plantings, one emitter often is used to supply the small quantity of water needed by each tree.
As the trees grow, their increased water requirement is provided by longer daily operation until additional emitters are required.
The drip system will have more capacity than needed during the first 3 to 4 years.
Design capacity will be reached when enough emitters have been added to supply the amount of water needed by mature trees.
Continuous operation will likely be required during months of maximum Class A pan evaporation.
Operate the system long enough  early in the season to supply enough water to "fill" the soil root zone.
This is often done when applying fertilizer.
Then
 operate the system to replenish the amount of water removed by the trees.
Also, operate the system 24 to 48 hours following elplanting to wet and settle soil around tree roots.
Applying too much water during the season can hinder tree growth and damage roots by causing poor soil aeration, especially in heavy soils with slow water movement.
Irrigation time can be controlled manually, with time clocks or with moisture-sensing instruments which activate pump controls and automatic valves.
Operate manuallycontrolled or set time clock-controlled systems to apply the required amount of water based on Class A pan evaporation  or estimated water requirement.
Inspect the orchard regularly to determine whether the daily irrigation time should be adjusted.
Soil moisture sensing instruments such as tensiometers and gypsum blocks can help in making irrigation management decisions.
Install instruments to sense soil moisture at two depths, such as 12 and 36 inches.
Use two or more sensing locations for each 20 acres of orchard unless tree size varies within smaller areas or soil types change significantly.
Locate sensors about two-thirds from the center to the outer edge of the wetted pattern.
Irrigation is started when the tensiometer gauge reads between 20 and 40 centibars for most soils.
However, the exact gauge reading can be determined by trial.
Drip irrigation systems can be completely automated with switching tensiometers which activate system controls to start and stop irrigation.
Field experience with automatic systems is limited but promising.
Automatic control is convenient and may conserve irrigation water by preventing over irrigation.
However, all orchards, including those with automatic drip irrigation systems, should be inspected regularly and any necessary maintenance and adjustment of system operation performed promptly.
The greatest potential problem, other than proper system design, for the operator of a drip irrigation system is emitter clogging.
Water passages in emitters are very small, and can easily become clogged by minerals or organic matter.
Clogging can reduce emission rates and cause nonuniform water distribution.
This may cause stress to plants and limit production.
Contaminants are often present in irrigation water.
Contaminants may be soil particles, living or dead organic materials, and scale from rusty pipes.
In some cases, contaminants are trapped in the system during installation.
These include insects, teflon tape, PVC pipe shavings, organic material and soil particles.
Contaminants can grow, aggregate or precipitate in water as it stands in the lines or evaporates from emitters or orifices between irrigations.
Iron oxide, manganese dioxide, calcium carbonate, algae and bacterial slimes can form in drip systems under certain circumstances.
The solution to clogging must be based on the nature of the particular problem.
Emitter clogging can be divided into three groups: physical; biological; and chemical.
Physical clogging is caused by such substances as soil particles , plant material, pipe rust and debris.
Physical clogging is prevented by selecting a filter system
 that is matched to the emitter orifice size and type.
Biological clogging is caused by the growth of algae, bacteria and slime, usually in the drip tubing.
Selecting emitters with large orifices and black pipe may reduce clogging.
In many cases chlorination is necessary.
To treat biological clogging iniatially the system can be flushed with a chlorine concentration of 10 ppm for an hour.
If necessary, concentrations are then increased gradually to about 50 ppm.
If the water pH is high, acid may be injected to lower pH to 7 or below to reduce the concentration of chlorine needed.
Some irrigators recommend routine injection of 1 to 2 ppm chlorine to control algae growth.
Fluid ounces of chlorine needed per 1000 gallons of water is calculated by the following equation:
 Ounces chlorine required ppm chlorine X 13.3 = per 1000 gallons water % chlorine of source
 a) chlorine in bleach is 5.25 percent  or 10 percent  , and b) chlorine content of calcium hypochlorite is 35 percent or 70 percent.
Chemical clogging is caused by the precipitation of calcium, magnesium, iron, fertilizer, etc., from the irrigation water.
Determining the quality of the irrigation water by laboratory analysis is helpful in determining the potential for clogging and the most effective treatment.
Table 8 lists concentrations of some elements which will lead to clogging problems.
Sulfuric and hypochloric acids can be injected to lower the pH of water and reduce the amount of chemical precipitates.
Regular acid treatments are usually necessary to clean emitter passages when concentrations of calcium or magnesium exceed 50 ppm or when water pH is greater than 8.0.
Experimentation is the best method of determining the concentration of acid needed.
First, acid is added to lower the pH to about 6.5.
Expose emitters to this concentration for 30 minutes to 1 hour.
More acid is then added as necessary until the pH is lowered to about 2.
Table 8.
Recommended chemical treatments for selected condi-
 Water quality	Suggested treatment
 Ca > 50 ppm	Hard water, caused by high concentrations of Ca or
 Mg > 50 ppm	Mg, can reduce flow rates by the buildup of
 scales on pipe walls and emitters.
Periodic injection
 of an HCI solution may be required throughout the
 season.
Lower concentrations of Ca and Mg may
 require HCI treatment every 2 to 4 years.
Fe > 0.5 ppm	Iron, sulphur and other metal contaminants
 S 0.5 ppm	create an environment in water that is conducive
 to bacterial activity.
Byproducts of bacteria in
 combination with the fine 
 suspended solids can cause system plugging
 Bacterial activity can be controlled by chlorine
 injection and line flushing on a regular basis
 throughout the irrigation season.
Bacterial
 activity is prevalent in concentrations of Fe and
 S over 0.5 ppm, but also occurs at lower concentra-
 Source: British Columbia Ministry of Agriculture, "Water Treatment Guidelines
MANAGEMENT CONSIDERATIONS FOR CENTER PIVOTS WHEN APPLYING WASTEWATER
 How often in the news today do we ever hear anything positive about a waste water reuse project?
This paper will briefly discuss the relationship of the three elements of a good wastewater reuse project, equipment, agronomic practices and management.
The focus will then be on management concepts to be considered when using center pivots while applying wastewater.
Particularly the paper will focus on the impact of management to the overall project performance.
Examples of wastewater reuse management situations will be presented and discussed.
From the discussion a list of parameters will be developed and discussed which are considered critical to a wastewater project's overall success to not only the livestock and farm but the general public as well.
Only agricultural projects will be included in the discussion but many of the same drivers apply to industrial and municipal wastewater reuse projects.
To begin let's consider that using a center pivot for wastewater reuse is not the same as using a center pivot for crop production.
All stakeholders livestock operation, farm operation, neighbors and the public, must be considered if a project is to be a long term success.
Land application of wastewater with mechanical move irrigation equipment both center pivot and linear has been successfully used for many years.
Mechanized irrigation, due to its characteristics, including limited labor input, application uniformity, ease in handling large volumes of effluent and particularly the ability to apply to an actively growing crop with minimal negative impact to the crop is considered to have advantages for wastewater reuse.
Since the early 1980's the equipment and techniques for irrigating with fresh water have changed dramatically and many of these changes have been incorporated into mechanized equipment used for land application.
While these changes have brought significant improvements, in today's world we must take into account other issues and particularly public perception of a wastewater reuse application system.
Equipment applications are important but equally so are the agronomic practices and management.
If any of these three are not integrated together into the overall package, there is a strong potential for problems and/or project failures.
How the irrigation equipment is selected has been discussed in more detail in a previous paper.
As an example it is possible to have runoff from a field if the equipment application, agronomic practices and management are not all integrated together.
Livestock operations producing meat or milk have little to no interest in crop production except as a possible spot to 'dump' their problem.
In general they want to have no problems and minimize their expense in 'disposing' of their meat and milk production by-product, the wastewater stream.
As stated earlier, to have a successful  wastewater reuse project requires the three key project elements to work together equipment, agronomic practices and management.
Poor application of any of these can lead to project failure and worse the potential for legal implications.
An example would be the wastewater application package of the center pivot is designed so it does not exceed the soil intake rate but the agronomic practices do not maintain any residue on the surface and the farmer decides to apply a depth of 2 1/2 inches per pass.
No matter how well the center pivot equipment options were selected there is the strong potential for runoff and/or excessive wheel tracks leading to the center pivot becoming stuck.
Either of these jeopardizes the overall performance of the wastewater reuse package and potentially could lead to legal action.
Besides the typical irrigation application parameters that need to be considered there are others as well particularly the wastewater storage, nutrient management plan, neighbors and maybe most importantly the expectations of the involved parties.
All of these must be managed and not just casually.
If the livestock owner is also the farm owner the situation is simplified and there is more chance for coordination of management.
But if the livestock owner is not the farm operator, we have a different situation that will impact the management of the center pivot.
Let us now discuss some specific situations.
1) Swine farrowing operation -
 a.
Hog operation does not own the land
 i.
Level of the lagoon in the spring and fall
 1.
The farmer wants to get the field dried out as early as possible in the spring to allow tillage and planting operations and keep the field dry for harvest in the fall
 2.
The hog operator needs to begin pumping as soon as possible in the spring to maintain free board on the lagoon and pump the lagoon down in the fall
 Is this an equipment, agronomic or management problem?
This requires a combination of the all of the above
 Management impact can be:
 In barn management of water and volumes going to a lagoon.
Significant variations in the volumes of wastewater generated per SOW are seen in the field.
Management of communication with the farmer
 Both sides need to be sensitive to the needs of the other
 Structure of financial arrangements so both sides understand the impact.
If the lagoon 'runs over' and reaches a stream this could have significant financial impact to the livestock operation
 Delayed planting and/or harvest may impact the yield potential of the crop
 2) Swine finishing operation -
 a.
Hog operation owns the land
 i.
For the farm Center pivot frequently gets stuck
 Is this an equipment, agronomic or management problem?
Equipment and management probably have the most potential for solutions
 Evaluate the relationship of center pivot options and agronomic practices
 Does the wastewater application package make sense for the agronomic practices?
Try to apply the maximum application depth per pass that does not lead to runoff to maximize the time between wastewater application cycles to allow the wheel tracks to dry.
Consider varying the application depth or even shutting off portions of the center pivot for problem areas
 Be sure to account for this area in the nutrient management plan
 3) Dairy operation -
 a.
Dairy operation owns the land
 i.
For dairy and farm Complaints from neighbors about odor when applying wastewater
 Is this an equipment, agronomic or management problem?
Equipment and management probably have the most potential for solutions
 Use common sense do not apply when the wind is blowing sufficiently to cause drift and the direction is toward the neighbors
 Talk with the neighbors so they understand you are sensitive to their concerns
 Apply at night and early mornings
 4) Beef operation -
 a.
Beef operation does not own the land
 i.
For the feed lot The storage is primarily for storm water runoff and must keep the level in storage low to be able to handle potential storm events
 ii.
For the farm Meeting crop water needs
 Is this an equipment, agronomic or management problem?
Management and agronomic practices probably have the most potential for a solution
 Try to balance wastewater applications as much as possible with the crop needs
 Re-evaluate the storage size and design
 Structure of financial arrangements so both sides understand the impact.
If the storm water storage 'runs over' and reaches a stream this could have significant financial impact to the feedlot operation
 Lack of waste water may impact the yield potential of the crop
 Land application using mechanical move irrigation equipment has proven very beneficial to many reuse projects and can be cost effective over the life of the project.
However not meeting the expectations of all stakeholders can lead to significant problems for the project and long term acceptance.
One of the keys to successful waster water reuse projects is an integrated approach combining equipment, agronomic practices and management.
An analysis of the situations above would indicate some of the issues which management can impact to be:
 If the wastewater producer does not own the land, must manage the communication with the farmer.
Management must be sensitive to the local concerns about odor, impact on visual landscape and other possible concerns.
The management must be reviewed periodically to ensure operation is meeting the design basis and the nutrient management plan as well as any changing operating constraints.
Management must take into account the financial impact to all involved parties.
Key management considerations for the center pivots would be:
 Use some common sense!
Manage closely the soil moisture status and do not exceed what the soil and crop canopy can hold with the application depth.
Manage applications to apply during the night and early morning whenever possible.
Manage applications to avoid windy days that may tend to cause drift.
Manage the center pivot to ensure the wheel tracks in the field have an opportunity to dry as much as possible between irrigation cycles.
Manage the interactions of equipment, agronomic practices and management.
Manage communication between all of the involved parties.
Late Fall Irrigation: Fall frosts have ended the life cycle of many annual plants.
In some cases, below-freezing temperatures have reduced insect numbers and finally ended the harvest challenges of extended green soybean stems and corn plants.
Despite the cold nighttime temperatures, many crops are still growing.
So, the question arises: How much irrigation should be applied in late fall for perennial and winter annual crops like alfalfa, wheat, rye and triticale?
Stay away from pivots if lightning is in the area because they are notorious for being struck.
Better application efficiencies allow for reduced water withdrawals for irrigation by reducing water losses such as deep percolation past the root zone and runoff from the field.
Reduced water losses also reduce negative impacts on water quality.
The estimated crop water use for Nebraska Panhandle crops for the previous week and the upcoming week is shown in this table.
It is based on data gathered and calculations made by Gary Stone, Nebraska Extension educator, and Dr.
Xin Qiao, extension irrigation and water management specialist, both based at the UNL Panhandle Research and Extension Center in Scottsbluff.
IRRIGATION OF OILSEED CROPS
 K-State Northwest Research-Extension Center 105 Experiment Farm Road, Colby, Kansas Voice: 785-462-6281 Fax: 785-462-2315
 Development, water use and yield formation of oilseed crops are inter-related.
Greatest yields are expected with a well-established canopy, a plant population sufficient to support a large number of seeds set per acre and favorable weather conditions for an extended seed fill period.
Oilseed water requirements closely follow canopy formation and evaporative conditions.
Supplemental irrigation scheduled by the water balance method results in higher yields than with irrigation scheduled by growth stage.
A straight-line relationship between yield and water use indicates the yield threshold  and yield response to increased water use.
When precipitation, available soil water and limited irrigation fail to meet crop water requirements, yield reductions depend on the degree of plant water stress at critical stages of growth.
Full-season soybean with full irrigation offers greatest productivity potential.
A smaller yield threshold and extensive rooting system for sunflower provides advantages for limited irrigation or double-crop conditions.
Winter canola can provide good productivity during fall and spring growing seasons when heat stress can be minimized.
Oilseed crops  provide management options for irrigators seeking to reduce irrigation requirements, diversification and/or to reduce input costs.
In 2003, soybeans were planted on 25% of irrigated cropland in Nebraska and on 12% of irrigated acres in Kansas.
Sunflower is emerging as an irrigated crop in W.
Kansas with a substantial increase in doublecropped sunflowers reported in 2005.
Canola, irrigated in the San Luis Valley of Colorado, is an emerging feedstock for biodiesel production.
Irrigated soybean yields range from 55 to over 70 bu/A in variety trials conducted throughout the central Great Plains ; greatest yields occurred in north-central Kansas and the east-central Platte valley of Nebraska.
Varieties with top yields exceeded trial averages by 10%.
Irrigated sunflower yields ranged from 2200 to 2900 lb/A in similar trials located in the central High Plains with greatest yields in NW Kansas.
Top-yielding hybrids exceeded trial averages by
 20% or more.
Irrigated winter canola yields of 2600 lb/A have been recently reported for W.
Nebraska.
Several irrigation guidelines are available for oilseed crops.
This report is intended to integrate these guidelines with recent and regional field studies.
Emphasis is given to crop development, water use and yield responses for irrigated oilseed crops.
DEVELOPMENT, WATER USE, YIELD FORMATION
 Oilseed development, water use and yield formation are inter-related.
Water, nutrients, sunshine and soil conditions must be sufficient, with minimal stress from pests and heat for crop growth to meet potential productivity.
Water requirements and yield formation factors frequently correspond with development stages.
Crop-specific considerations will follow a general discussion of oilseed development, water use and components of yield.
Uniform seedling emergence is favored by soil-seed contact in a firm moist seedbed at a sufficient soil temperature.
Expansive growth of seedling leaves require assimilates, derived from photosynthesis and nutrient uptake, as well as sufficient plant-available water for turgor-driven growth.
Development of new leaves corresponds with plant temperature as well as time.
Thus, leaf appearance is related to degree-days.
For example, new leaves of a standard sunflower hybrid appear in 67 F-d intervals.
Leaf appearance and growth comprise the major processes of canopy formation.
Rapid canopy closure is desirable, because the crop canopy shades the soil and reduces evaporative water losses.
Leaf expansion is typically exponential during early to mid-vegetative growth when supported by sufficient water, nutrients and non-stress conditions.
Crop water requirements increase with canopy formation  because transpiration increases in proportion to leaf area.
Light penetration into lower layers of the crop canopy is desirable.
Photosynthesis can be limited by the amount of light reaching shaded leaves.
Canopy formation nears completion with flowering for some determinant crop types such as sunflower.
However, canopy formation continues with flowering for indeterminant crops such as canola and most soybean varieties of maturity group IV and earlier.
Reproductive development marks the end of the juvenile phase and begins with differentiation of floral buds.
Potential seed number  can be set at this point, for determinant crops.
Development and growth of floral organs proceeds systematically through stages including pollen shed, seed set and seed fill.
Again, sufficiency of water, nutrients and light will support these yield formation processes.
The onset of reproductive development frequently
 varies with thermal time, but may be affected by day-length as well.
Reproductive stages of soybean, sunflower and canola are presented in Tables 1, 2 and 3.
Figure 1.
Sunflower water use and canopy formation  for dryland and irrigated crop.
Table 1.
Description of soybean reproductive stages.
Open flower at any node on main stem.
Indeterminate
 R1	flowering	plants start at bottom and flower upward.
Determinate
 plants start at top four nodes and flower downward.
Open flowers on one of the two uppermost nodes on main
 R3	Beginning	Pod 3/16 inch long at one of the four uppermost nodes on
 Pod 3/4 inch long at one of the four uppermost nodes on
 R4	Full pod	main stem.
R5	Beginning	Seed 1/8 inch long in one of the four uppermost nodes on
 Pod containing a green seed that fills pod cavity on one of
 R6	Full seed	the four uppermost nodes.
R7	Begin	One normal pod on main stem has reached mature pod
 95% of pods have reached mature pod color.
R8	Full maturity	Approximate 5 to 10 days ahead of harvest.
Table 2.
Description of sunflower reproductive stages 
 The terminal bud forms a miniature floral head rather than a cluster of
 R-1	leaves.
When viewed from directly above, the immature bracts form a
 The immature bud elongates 1/4 to 3/4 inch above the nearest leaf
 R-2	attached to the stem.
Disregard leaves attached directly to the back of
 R-3	The immature bud elongates more than 3/4 inch above the nearest leaf.
The inflorescence begins to open.
When viewed from directly above
 immature ray flowers are visible.
This stage is the beginning of flowering.
The stage can be divided into
 R-5	substages dependent upon the percent of the head area 
 that has completed or is in flowering.
[i.e., R-5.3 , R-5.8 , etc.]
 R-6	Flowering is complete and the ray flowers are wilting.
R-7	The back of the head has started to turn a pale yellow color.
R-8	The back of the head is yellow but the bracts remain green.
The bracts become yellow and brown.
This stage is regarded as
 0	Germination: sprouting development
 5	Inflorescence  emergence
 7	Development of seed
 Stand establishment, canopy formation and reproductive development are significant components of the yield formation process.
The crops' capacity to fill seed and achieve yield potential can depend on the active leaf area and number of seeds set per acre.
Greatest yields are expected with well-established canopy, a plant population sufficient to support a large number of seeds set per acre and favorable weather conditions for an extended seed fill period.
Oilseed water requirements closely follow canopy formation and evaporative conditions.
When scheduling irrigation relative to evaporative conditions, crop coefficients can be used to calculate daily crop water use.
Typical crop coefficients, daily water use and development stages for soybean and sunflower are presented in Figure 2.
Lower seasonal water requirements for canola can be expected for the spring growing season,
 which is shorter and with less evaporative demand than the summer growing season of soybean and sunflower.
When soil water reserves are insufficient, actual crop water use is less than evaporative demand  and yield reductions are likely.
Figure 2.
Crop coefficient  and daily crop evapotranspiration  for soybean and sunflower, calculated from 34 years  of weather recorded at Colby, KS.
Reproductive development stages for soybean and sunflower are noted below the graph for reference.
Irrigation is generally required to meet crop water requirements in the central Great Plains.
Two methods of scheduling irrigation are by water budget or by growth stage.
Water budgets seek to maintain available soil water above a minimum value.
Growth stage irrigation seeks to provide sufficient water to meet crop water requirements during specific critical stages.
Studies in west-central Nebraska  and north-central Kansas  indicate greater soybean yields with water budgets than with growth stage irrigation scheduling.
Similar studies are in progress for sunflower.
Figure 3.
Water uptake by sunflower roots  is reduced when the available soil water in the wettest soil layer is less than 60% of available water capacity.
The line approximates an envelope containing observations of water uptake in relation to available soil water.
Water uptake from all soil layers is equivalent to crop evapotranspiration.
For limited irrigation systems, water available to the oilseed crop is likely to be insufficient during canopy formation and/or reproductive development stages.
For example, Figure 4 shows that sunflower canopy formation at flowering  can be limited by available soil water during earlier reproductive growth.
Limited irrigation, while not providing full water requirement of the crop, can improve seed yield.
For example, a one-inch irrigation applied to soybean in SE Kansas at R4 , R5  or R6  increased seed yield by 241 lb/A.
The R4 application increased the number of seeds per plant while the R5 and R6 applications increased seed weight.
When supply of water limits crop water use, seed yields are frequently limited as well.
A straight line can represent the relationship between seed yield and seasonal crop water use.
For example, soybean yield at Colby, KS increased 3.7 bu/A with each additional inch of water use.
The yield threshold  occurred with 7.3 inches of crop water use.
Similar results were reported for west-central Nebraska.
For sunflower, the yield threshold was 4.2 inches and the yield response was 166 pounds per inch of crop water use.
Figure 4.
Sunflower leaf area at flowering  in relation to available soil water at mid-bud  growth stage.
Figure 5.
Soybean yield response to seasonal water use at Colby, KS and central Nebraska sites.
Figure 6.
Sunflower yield response to seasonal water use at Colby, KS.
Under limited irrigation, water can be allocated to minimize the impact of water deficits on yield formation.
For example, soybean yield can be most sensitive to water deficits during flowering and full pod reproductive stages.
The yield response to limited irrigation can be greatest if water is applied to alleviate deficits during stages which are most critical for yield formation.
Critical stages, with maximum crop water use rates, are R3 to R6 for soybean and R1 to R7 for sunflower.
Water stress during these critical stages is expected to reduce yield potential.
However, Table 4 and Figure 4 indicate that sunflower is also susceptible to soil water deficits during vegetative growth.
Additionally, a recent study at Akron, CO showed that delaying limited irrigation until the R4 stage increased oil content of sunflower, though yields were less than that of full irrigation.
Irrigators with limited capacity will benefit from good judgement and additional water use and growth stage information.
Soybean or sunflower can be double-cropped after wheat harvest where growing season temperatures and the length of growing season are sufficient.
Yield potential will be reduced due to the reduced growing period and effects of the yield threshold.
The smaller yield threshold of sunflower may indicate a comparative advantage for double-cropping.
Cooler weather can extend the
 duration of grain fill period but may alter the composition of fatty acids in oil.
Table 4.
Susceptibility of soybean and sunflower to soil water deficits.
Growth Stage	Time period	Susceptibilty	Time period	Susceptibilty
 	Factor		Factor
 Vegetative	38	6.9	53	43.0
 Flowering	33	45.9	17	33.0
 Formation	44	47.2	23	23.0
 A full-season, well-watered soybean crop offers relatively greatest productivity potential for non-calcareous soils with acid to neutral pH.
The nitrogen-fixing crop can require minimal N fertilizer, provided soil is properly inoculated.
Iron chlorosis can limit productivity on calcareous soils with pH exceeding 7.5 ; foliar diseases can also limit productivity.
"Early determinate varieties are recommended for production systems involving narrow rows, high seeding rates, early plantings, good fertility, and a yield potential in excess of 50 bushels per acre".
Photoperiod effects on flower initiation highlight the importance of selecting varieties from maturity groups appropriate for planting period and desired days to maturity.
Sunflower is commonly planted in early June, in the central Great Plains, to avoid stem weevil and sunflower moth pests.
The deep-rooted crop can extract more soil water than other crops.
Combined with the smaller yield threshold, sunflower can give relatively greater yields when water supplies are limited.
The heattolerant crop also tolerates calcareous soil and high pH conditions.
Decreasing daylength  near the R1 stage can reduce the duration of reproductive stages, due to photoperiod effects, when grown at latitudes less than 40.
Winter canola is established in early fall and harvested mid-summer, similar to winter wheat.
The yield advantage of winter varieties over spring varieties is similar to that of winter wheat, approximately 30%.
The small-seeded coolseason crop may be difficult to establish, as well as sensitive to heat stress during yield formation stages.
Oilseed crops tend to produce less yield than feed grain crops.
Less productivity results from differences in photosynthesis and in seed composition.
The C3 physiology of oilseed crops is inherently less effective than the C4 physiology of feed grain crops.
The C3 carbon-fixing enzyme Rubisco, is approximately 2/3 effective when exposed to atmospheric oxygen concentrations.
Plants with C4 physiology also use Rubisco, but it functions in bundle sheath cells where oxygen concentrations are very small, and the enzyme functions at near complete effectiveness, resulting in increased crop productivity.
The second difference between oilseed and feed grain crops involves oil and protein content.
The amount of starch which can be produced from a unit of carbohydrate  is 0.88.
The remaining fraction, 0.12, is consumed in the conversion process.
More carbohydrate is used up in the formation of oil  and protein.
As a consequence, the fraction of carbohydrate converted to oil is 0.33; to protein is 0.35.
Smaller seed yields of oilseed crops is a consequence of greater oil and protein  content, for which a greater fraction of the photosynthetically-fixed carbohydrates are consumed.
The current cost of using sensors on the pivot is high when compared to the increase in profits from reduction of irrigation application and increase in crop yield.
However, the use of pivot-mounted sensors for other aspects of crop production  could also increase the value of the system.
The barriers to adoption will likely diminish as sensors and software for pivot automation become easier to use.
Carefully Consider Decisions to Apply Water in May and June.
Decisions to irrigate in May and June need to be considered very carefully.
Long-term averages show May and June to be two of the highest rainfall months in Nebraska.
The rainfall is usually more than needed to refill the soil profile for fields that were irrigated the previous year.
EM 8900 Revised March 2013
 Irrigation Monitoring Using Soil Water Tension
 Malheur Experiment Station, Oregon State University: Clint C.
Shock, director and professor; Rebecca Flock, former research aide; Erik Feibert, senior faculty research assistant; Cedric A.
Shock, former research aide; Andre Pereira, visiting professor.
Center for Agricultural Water Research, China Agricultural University, Beijing: Feng-Xin Wang, associate professor
 O ne of the most important tools we have been using at the Malheur Agricultural Experiment Station over the past two decades is the granular matrix sensor , which measures soil moisture.
It is only about 3 inches long and normally is buried vertically in the ground.
Like gypsum blocks, GMS sensors operate on the principle of variable electrical resistance.
The electrodes inside the GMS are embedded in granular fill material above a gypsum wafer.
Additional granular matrix is below the wafer in the fabric tube, where water enters and exits the sensor.
Gypsum dissolved in water is a reasonable conductor of electricity.
Thus, when the sensor contains a lot of water, the electric current flows well.
When there is a lot of water in the soil, there is a lot of water in the sensor.
As the soil dries out, the sensor dries out, and resistance to the flow of electricity increases.
The resistance to the flow of electricity  and the soil temperature are used to calculate the tension of the soil water in centibars.
Soil water tension  is the force necessary for plant roots to extract water from the soil.
Soil water tension reflects the soil moisture status.
The higher the tension, the drier the soil.
Other devices for measuring soil water tension include tensiometers, gypsum blocks, dielectric water potential sensors, and porous ceramic moisture sensors.
What does a granular matrix sensor do for growers?
In the past, growers had to train themselves to guess when the soil was dry enough to warrant irrigation of their crop.
Even with years of experience and well-developed agricultural intuition, it is very difficult to irrigate at the right moment consistently and to apply the ideal amount of irrigation water to maximize crop production.
It would be helpful to have some consistent reference points of SWT for irrigation scheduling.
The digital readout of the GMS
 provides reference points to help growers attain higher yields and better crop quality on their farms.
On a scale of 0 to 100 cb soil water tension, how wet is your field?
Roughly speaking, a GMS reads the following scale of SWT for a medium-texture soil:
 > 80 cb indicates dryness.
20 to 60 cb is the average field SWT prior to irrigation, varying with the crop, soil texture, weather pattern, and irrigation system.
10 to 20 cb indicates that the soil is near field capacity.
0 to 10 cb indicates that the soil is saturated with water.
What new information can a GMS give you?
AGMS can tell you whether the rain last night was really enough to give your onions, for instance, a good drink.
It can tell you whether an overcast day is reducing crop water use in a potato crop enough to delay the next irrigation.
It can tell you whether you will need to irrigate more often in July than in June.
Since the reading comes directly from the crop's root zone, it is a tool designed to provide one more piece of information to your agricultural intuition.
Is scheduling irrigation from SWT really feasible?
We have been using GMS at the Malheur Experiment Station for 26 years, and we can answer with a resounding YES.
There is no replacement for the watchful eye of an experienced grower.
But, imagine a talented stockbroker with great financial logic and intuition.
Does he not excel even more after checking stock quotes on the Internet?
The same is true for the grower.
For example, walking down to your onion field every morning and checking the readout of six or more GMS will help you know when to irrigate the field.
In fact,
 by doing SO you usually can predict irrigations a day or two ahead of time.
Our research has allowed us to determine the threshold SWT of various crops growing on silt loam under different irrigation systems.
We found that irrigating at these critical values has significant benefits to crops.
The SWT irrigation threshold varies not only by crop but also by soil texture, climatic factors, and irrigation method.
The threshold values that maximize marketable yield are known for a wide array of commercial crops growing on different soils under different climatic conditions and irrigation systems.
Let's talk more about how using SWT can MAXIMIZE growers' profits
 Less water used-An irrigation schedule based on a threshold SWT usually results in fewer irrigations per year, as it can help prevent overwatering.
Less pumping energy consumed
 Lower crop stress, which can result in less pest and disease pressure
 Prevention of excessive leaching of mobile plant nutrients, especially nitrogen and boron
 Prevention of groundwater pollution
 Reduced wear and tear on irrigation systems
 From our own experiments, crops that are irrigated according to SWT criteria have higher marketable yield, increased size, and increased produce quality.
How hard is it to collect SWT information?
The GMS can be read in several ways.
One way is with a hand-held Watermark Soil Moisture Meter.
The hand-held meter is used much like a voltmeter and is manually connected to the sensor wires with alligator clips.
It is simple to use, but labor intensive.
You should
 Figure 1.
Variation of soil water tension  over a growing season for furrow-irrigated onions  and sprinkler-irrigated potatoes.
record the data from the meter by hand to make SWT comparisons over time.
For automatic reading and recording of GMS data, dataloggers are available.
Both the Hansen AM400  and the Watermark Monitor  are dataloggers that are installed at the edge of a field.
These dataloggers can be programmed to collect and record data automatically from six or seven GMS and one soil temperature sensor throughout the day.
You can view the data as numbers or graphs on the unit itself, or you can download it to a computer for easy viewing in graphing software or a standard spreadsheet application.
The data from field collection devices can readily be uploaded to the Internet using cell phone modems and graphically displayed in a web portal.
This allows users to view the current soil moisture conditions from any Internetenabled computer, making off-site management easier.
But my field is so BIG and that sensor is so small
 The success of the GMS hinges on how reliably a group of sensors represents the soil moisture of a field.
That is why it is important to install the sensors at points in the field that accurately reflect the average root zone for the average plant.
If part of the field has different water needs, create a second zone and install sensors at representative areas of that zone.
Granular matrix sensors usually are installed in a group of six or seven per irrigation zone.
Each GMS provides information only about soil water tension in the immediate vicinity of the sensor.
Because SWT varies from place to place in a field, and sensors also vary, six or more GMS will provide more reliable estimates of SWT for a field than a single GMS.
The sensors complete a simple electrical circuit.
Thus, you can easily add an "extension cord" using normal electrical wire in order to collect information from many feet into the field.
It is important to maintain clean, dry connections between the extensions and the sensor wires.
What about installation?
Can I do it myself?
Installation is easy and requires few additional tools.
You will need a 7/8" soil sample probe to create the right size hole for the sensor.
Keep in mind that GMS are designed to accurately represent the relative amount of water in the field, SO select an area that is not remarkable.
On page 4, Figure 2  and Figure 3  illustrate the steps involved in installation.
If you have attached a PVC tube to the sensor with glue prior to installation to make it easier to remove the sensors from the field, use the installation method in Figure 2.
The accuracy of the sensor relies on good contact with the soil.
The GMS installation depth depends on the crop's root zone depth, but it also
 Figure 2.
Installation procedure of a granular matrix sensor  in coarse soil at an 8-inch depth in the soil.
Figure 3.
Installation procedure of a granular matrix sensor  in silty soil at 8-inch depth.
can be affected by soil depth and soil texture.
For shallow-rooted crops, sensors installed at less than 12 inches deep are sufficient.
For crops with a deep root system, also install sensors at greater depth within the root zone.
The root zone depth might be greater in well-drained soils and less in clay soils or soils with compacted layers or poor drainage.
To install a GMS sensor, first soak the sensor for several minutes until it reaches saturation.
Then make a hole in the soil using a soil sample probe with an external diameter corresponding to the sensor diameter.
Since the sensitive area of the GMS is centered 0.8 inch above the tip, the hole should have an additional 0.8 inch of depth to provide the desired sensor installation depth.
The next steps depend on the texture of your soil.
For coarser soils that have little tendency to lose their structure when saturated, pour about 2-3 OZ of water into the hole and then place the sensor at the bottom of the hole.
Silty soils tend to lose their structure when saturated and can seal around the sensor, thus impeding the entrance and exit of water.
For silty soils, place the sensor at the bottom of the hole and then add about 2-3 OZ of water to the hole.
Finally, regardless of soil type, backfill the hole with fine soil and use a tube, metal bar, or wooden stick to lightly compact the backfill dirt in order to prevent formation of a preferential path for rain or irrigation water to easily reach the sensor.
Such a path is undesirable because it distorts soil moisture status, thus significantly compromising the reliability of the SWT data obtained by the GMS.
The sensor operates by completing an electric circuit.
It is not uncommon for a frayed wire to "short circuit" the sensor, causing it to read zero continually, or for a cut wire to create an "open circuit," causing an unreasonably high reading.
If sensors are wet and readings should be low, a few common default error numbers include 199 and 250, depending on the datalogger.
Do not
 remove sensors from the soil by pulling on the wire since this can destroy the GMS.
Even with proper maintenance, sensors have a limited lifetime before they physically wear out or their sensitivity is compromised.
Replace the unit at that time.
Check sensors in the spring before use; dry sensors should have high readings, and sensors soaked in water for 1.5 minutes should read between 0 and 4 cb.
What is the bottom line for cost?
Can I really afford this?
GMS systems as a whole are relatively inexpensive.
With yield and quality increases and greater savings on water, energy, fertilizer, and other inputs, costs are quickly recovered.
Funding to help prepare this publication was provided by an Oregon Watershed Enhancement Board grant.
Watermark Soil Moisture Sensor-Irrometer Co., Riverside, CA Dielectric Water Potential Sensor  Decagon Devices, Inc., Pullman, WA Hand-held Watermark Soil Moisture Meter -Irrometer Co., Riverside, CA).
Hansen AM400 Datalogger-Mike Hansen Co., Wenatchee, WA Watermark Monitor Datalogger Irrometer Co., Riverside, CA
 Trade-name products are mentioned as illustrations only.
This does not mean that the Oregon State University Extension Service either endorses these products or intends to discriminate against products not mentioned.
Soil water tension indicates the soil water status and helps a grower decide when to irrigate, thus avoiding underand overirrigation.
Crops that are sensitive to water stress are more productive and have higher quality if they are watered precisely using soil water tension  than if they are underor overirrigated.
The optimum soil water tension for a particular crop depends primarily on crop needs, soil texture, and climate.
Common instruments to measure soil water tension include tensiometers, gypsum blocks, granular matrix sensors, dielectric water potential sensors, and porous ceramic moisture sensors.
Treasure Valley onions on silt loam are irrigated at a SWT of 20 to 25 cb.
Potatoes
 growing on the same site and soil type are irrigated at a SWT of 30 to 60 cb, depending on the irrigation system.
"Soil water potential" is the negative of "soil water tension." A soil water potential of 20 cb is the same as a soil water tension of + 20 cb.
Also, cb  is the same as kPa.
Granular matrix sensors provide good estimates of soil water tension for many soils.
Sensor readings can be conveniently logged, providing a record of soil moisture conditions to aid growers in timing irrigations.
Sensors and wiring need to be checked and loggers require minimal, but necessary, maintenance.
Keep loggers clean and dry and replace their batteries as needed.
Table 1.
Soil water tension  as irrigation criteria for onion bulbs as reviewed by Shock and Wang, 2011.
SWT	Irrigation	Soil moisture sensor depth
 	Location	Soil type	system	
 8.5	Piau, Brazil	Sandy	Microsprinkler	-
 10	Pernambuco, Brazil	-	Flood	-
 15	So Paulo, Brazil	Furrow
 10-15	Malheur County,	Silt loam	Drip	8
 17-21	Malheur County,	Silt loam	Drip	8
 27	Malheur County,	Silt loam	Furrow	8
 30	Texas	Sandy clay loam	Drip	8
 45	Karnataka, India	Sandy clay loam
 Table 2.
Soil water tension  as irrigation criteria for potato as reviewed by Shock and Wang, 2011.
SWT	Irrigation	Soil moisture sensor depth
 	Location	Soil type	system	
 20	Western Australia	Sandy loam	Sprinkler	-
 25	Maine	Silt loam	Sprinkler	-
 25	Luancheng, Hebei Province,	Silt loam	Drip	8
 30	Lethbridge, Alberta, Canada	Sandy loam	Sprinkler	-
 30	Malheur County,	Silt loam	Drip	8
 50	California	Loam	Furrow	-
 50-60	Malheur County,	Silt loam	Sprinkler	8
 60	Malheur County,	Silt loam	Furrow	8
 Table 3.
Soil water tension  as irrigation criteria for cole crops as reviewed by Shock and Wang, 2011.
system or	Soil moisture
 Common	SWT	measurement	sensor depth
 name		Soil type	equipment		Location, season
 Broccoli (Brassica	10-12	Sandy loam	Subsurface drip	12	Maricopa, AZ;
 oleracea var.
italica)	fall-winter
 Broccoli	50, 201	Silt loam	Lysimeters in rain	4	Agassiz, British
 shelter	Columbia, Canada; spring
 Cabbage (Brassica	25	Loamy sand and sand	Lysimeters in rain	4	Tifton, GA; spring
 oleracea var.
capitata)	shelter	and fall
 Cauliflower (Brassica	10-12	Sandy loam	Subsurface drip	4	Maricopa, AZ;
 oleracea var.
botrytis)	fall-winter
 Cauliflower	252	Sandy loam	Furrow and flood	7	Bangalore, India; winter
 Cauliflower	20-40	Sandy loam	-	-	Skierniewice, Poland;
 Collard	9	Sandy loam	Subsurface drip	12	Maricopa, AZ;
 Mustard, greens	6-10	Sandy loam	Subsurface drip	12	Maricopa, AZ;
 Mustard, greens	252	Loamy sand and sand	Lysimeters in rain	4	Tifton, GA; spring
 SWT of 50 cb during plant development, then 20 cb during head development.
2TTWENTY-five cb was the wettest irrigation criterion tested.
Table 4.
Soil water tension  as irrigation criteria for other field and vegetable crops as reviewed by Shock and Wang, 2011.
system or	Soil moisture
 Common	SWT	measurement	sensor depth
 name		Soil type	equipment		Location, season
 Alfalfa grown for seed	200-800	Fine sandy loam,	Sprinkler and	4-72	Logan, UT; summer season
 loam, silt loam	surface flood	of the perennial crop
 Beans, snap	25 superscript	Loamy sand	Lysimeters in rain	4	Tifton, GA; spring and fall
 Beans, snap	45	Sandy clay loam	-	6	Bangalore, India; fall-winter
 Beans, snap	50	Clay loam	Furrow and drip	12	Griffin, NSW, Australia;
 Carrot	30-50	-	Sprinkler	-	Nova Scotia, Canada;
 Carrot	40-50	-	Microsprinkler	6	Nova Scotia, Canada;
 Celery	10	Sandy loam	Drip	8	Santa Ana, CA; fall-winter
 Corn for sweet corn	10-40	Sand	Drip	6	-
 Corn for sweet corn	30	Carstic soils	Drip	12	Champotn, Campeche,
 Corn for sweet corn	50	-	-	-	Utah; spring-summer
 Corn for grain	30	Loamy fine sand	Sprinkler	6	Quincy, FL; spring-summer
 continued Table 4.
Soil water tension  as irrigation criteria for other field and vegetable crops as reviewed by Shock and Wang, 2011.
system or	Soil moisture
 Common	SWT	measurement	sensor depth
 name		Soil type	equipment		Location, season
 Corn for grain	50	-	-	-	Utah
 Cucumber	15-30	Fine sand and	Drip	8	Piikkio, Finland; spring-
 Lettuce, romaine	<6.5	Sandy loam	Subsurface drip	12	Maricopa, AZ; fall-winter
 Lettuce, leaf	6-7	Sandy loam	Subsurface drip	12	Maricopa, AZ; fall-winter
 Lettuce	<10	Red earth	Drip	12	NSW, Australia
 Lettuce	20	Clay loam, sandy	Sprinkler, drip	6	Las Cruces, NM; summer-
 Lettuce, romaine	301	Clay loam	Surface	12	-
 Lettuce, crisphead and	50	Sandy loam	Sprinkler	6	Salinas, CA; spring-summer
 Radish	35	Silt loam	Drip	8	Luancheng, Hebei Province,
 Radish	20	Sandy clay loam	Control basin and	7	Bangalore, India; winter
 Rice	16	Sandy loam	Flood	6-8	Punjab, India; summer-fall
 Spinach	9	Sandy loam	Drip	-	Maricopa, AZ
 Squash, summer	25	Loamy sand and	Lysimeter	-	Tifton, GA; spring, summer,
 Sweet potato	25, then	Loamy sand and	Lysimeters in rain	9	Tifton, GA; summer
 Sweet potato	25-40	Silt loam	Drip	8	Ontario, OR; summer
 Tomato	10	Fine sand	Drip	6	Gainesville, FL; spring
 Tomato	20	Sand	Drip	6	Coruche, Portugal; spring-
 Tomato	12-35	Clay	Drip	4-84	Federal District, Brazil; fall-
 Tomato	50	Silt loam	Drip	8	Yougledian, Tongzhou,
 Watermelon	7-12.6	Sandy loam	Drip	12	Maricopa, AZ; spring-
 'Twenty-five cb or 30 cb was the wettest irrigation criterion tested.
SUTE of 25 cb during plant development, then 100 cb during root enlargement.
3Thirty-five, 12, and 15 cb during vegetative, fruit development, and maturation growth stages, respectively.
4Tensiometer depth was 4" during the vegetative growth stage, 6" in the beginning of the fruit development stage, and 8" from thereon until the irrigations were stopped.
STaylor, S.A., D.D.
Evans, and W.D.
Kemper.
1961.
Evaluating Soil Water.
Utah Agricultural Experiment Station Bulletin 426.
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Planting a Riparian Buffer
 Carmen T.
Agouridis and Sarah J.
Wightman, Biosystems and Agricultural Engineering; Christopher D.
Barton, Forestry; and Amanda A.
Gumbert, Agricultural Programs
 What Is a Riparian Buffer?
Streams are dynamic and complex systems that include the active channel as well as its floodplain or riparian zone.
Riparian zones-which are characterized by high levels of interactions between vegetation, soil and water-link terrestrial and aquatic environments.
These areas have high biotic, structural, and functional diversity.
Urban development and agricultural activities can negatively impact stream ecosystems.
Streams draining urban lands often suffer from "urban stream syndrome," which is characterized by flashy hydrology, elevated concentrations of nutrients and contaminants, altered morphology, decreased amounts of organic matter, and poor biotic richness.
Streams draining agricultural lands can also be negatively impacted.
Livestock grazing and crop production can compact soils, remove riparian vegetation, alter stream morphology, and increase pollutant loads to streams.
One way to reduce the impacts of urbanization and agriculture on stream ecosystems is through the use of riparian buffers.
Riparian buffers are vegetation zones located between water bodies such as streams and upland areas such
 as pastures.
These buffers can be composed of one vegetative community but typically consist of three zones planted with native species.
A zone of fastand slow-growing water-tolerant trees  is located adjacent to the water; a zone of shrubs  is located next to the trees, and a zone of grasses and forbs  next to the shrubs.
Ideally, the zones are left undisturbed; however Zone 3 can be mowed or grazed once fully established.
Buffers can consist entirely of grass , but fewer benefits are provided by that approach.
The USDANRCS states that riparian buffers should be 25 ft  wide, at a minimum; however, a buffer width of 200 ft  is recommended.
What Are the Benefits of Riparian Buffers?
Riparian buffers offer a number of ecosystems benefits related to water quality, streambank stabilization, and habitat.
Riparian buffers slow and capture runoff, which can improve water quality by trapping and filtering pollutants such as sediment, nutrients, pesticides, herbicides, road salts, and heavy metals.
The root systems of riparian vegetation help to stabilize streambanks by holding the soil in place.
Leaves and
 Source: Corey Wilson, Landscape Architecture.
twigs serve as a food source for aquatic bugs called benthics that live in the water and are an important part of the food web.
Riparian vegetation can also provide birds and animals with fruits and nuts as well as cover.
The shade provided by the canopy of riparian vegetation helps regulate the water's temperature by keeping it cooler during the summer months.
Maintaining a cooler water temperature helps increase the dissolved oxygen level in the water, thus creating a healthier habitat.
How Do I Create a Riparian Buffer?
Riparian buffers can be created passively  or actively.
Passively creating a riparian buffer is as simple as establishing a no-mow zone.
Over time, plants will become established on the site as seeds are introduced from birds and animals, water from the stream, and the wind.
This method is an easy and cheap way to create a riparian buffer.
However, this passive approach often results in less than optimum conditions, and it can produce a riparian habitat that is harmful.
Dispersal of unwanted plants can be problematic  and can create a riparian area covered with non-native invasive species.
The species that establish, even if native, can be less effective at holding together unstable streambanks or providing valuable wildlife habitats than riparian buffers that are actively created.
Actively creating a riparian buffer typically consists of six steps: site assessment, planting plan development, site preparation, species selection, planting, and protection and maintenance.
Figure 2 shows a planted riparian buffer at the Kentucky Horse Park.
Table 1.
Common invasive species in Kentucky.
Bush honeysuckle 
 Japanese honeysuckle 
 Winter creeper 
 Chinese privet 
 Japanese knotweed 
 Multiflora rose 
 Purple loosestrife 
 Garlic mustard 
 English ivy 
 Common reed 
 Japanese stiltgrass 
 Reed cannarygrass 
 Figure 2.
Newly planted riparian buffer at the Kentucky Horse Park.
When evaluating the location for a riparian buffer, information such as land ownership, permits, site characteristics , utilities, and planned future land use should be gathered.
If stream banks are steep and eroding, re-grading may be necessary prior to planting.
Check on permitting requirements for your selected site prior to performing any earthwork.
Federal, state, and local agencies issue permits for a number of activities in and along streams.
The width of the buffer will depend largely on land availability, but other site characteristics such as slope, infiltration capacity of the soil, soil quality, and site needs  will factor into the buffer design.
For example, if the goal is to filter sediment, a buffer width of 25 ft  may be sufficient for slopes less than 15 percent.
However, if the goal is to reduce soluble nutrient  and pesticide concentrations in runoff, buffer widths of 100 ft  may be needed.
Buffers targeting wildlife habitat or temperature control for fisheries will require wide buffers as well.
Also, buffers located on steeper slopes as well as those with poor-draining soils will likely require greater widths to remove contaminants from runoff.
Soil samples should be collected to determine pH, moisture content, and nutrient content.
Prior to planting and especially before beginning any digging, underground utility lines should be located and clearly marked.
Call 811 to locate underground utility lines.
When developing a planting plan, one of the first things to do is identify the boundaries and constraints of the site.
Clearly note property boundaries, utilities, permit conditions, land use considerations, and budget.
Identify any unique land features such as springs, wet areas, or pedestrian and biking paths.
Determine how many plants are needed.
To achieve streambank stabilization and water quality protection, vegetation should be planted densely and in a tiered fashion.
Streambanks should be planted with trees able to quickly colonize this environment, such as willows, in order to provide protection from the erosive forces of stream flows.
Trees should be planted at a rate of 800 trees per acre using 8by 7foot spacing.
Shrubs should be placed 3 to 5 ft  apart and transplants or plugs of grasses and forbs 1 to 3 ft  apart.
Consider the time of year when planting will occur.
Ideal times to plant trees are late autumn through early winter and late winter through early spring when the ground is thawed.
In Kentucky, this is generally November to December and March to April.
For grasses, consider whether you want cool-season varieties, which should be planted in late autumn to early winter, or warm-season ones that are best planted in late spring, summer or early autumn.
When developing a budget, be sure to include costs associated with land acquisition, permits, streambank stabilization, soil amendments, plants, vegetation protection, labor, and maintenance.
Before the site can be planted, it must be prepared.
If the streambanks are unstable, meaning they are steep and eroding, they should be addressed first.
Re-grading the banks SO that they are less steep may be needed.
Seek advice from an experienced professional and check on permitting requirements if streambank regrading is needed.
Invasive species should be removed.
Removal can typically be done mechanically or using herbicides approved for use in aquatic areas.
If necessary, the approBenefit priate soil amendments Streambank stabilization should be added.
Soil Filtering sediment tests are used to deterFiltering nutrients, pesticides, pathogens mine what amendments Improving aquatic habitat are needed, such as lime
 When selecting plants, consider factors such as water tolerance, project goals, natural succession, plant availability, and aesthetics.
As riparian areas often experience wetting from floods, selected plants must be tolerant of such conditions.
Different vegetation types also have different benefits.
For example, grasses are highly effective at filtering sediment from runoff while trees are best at improving aquatic habitat through water temperature regulation and introduction of debris such as leaves, twigs, and small logs.
In all cases, select native species as these plants will be best adapted to the local climate.
Table 3 contains a listing of some native species that are appropriate for planting in Kentucky riparian buffers.
Consider the anticipated changes in the plant community over time or natural succession.
After preparation, the site may have bare soils and lots of light.
Plant fast-growing
 Table 2.
Vegetation effectiveness for select buffer benefits.
Trees	Shrubs	Grasses	Low
 Improving field  habitat
 pioneer species that are adapted to these conditions as well as slower-growing longer-lived species adapted to more shaded and crowded conditions.
When selecting plants, be sure to find out what plants will be available for purchase during the projected planting period.
Also give consideration to aesthetics by noting plant characteristics such as flowering and seasonal foliage color.
A wide variety of methods may be used for planting different types of vegetation.
For trees, one-year-old bare-root seedlings are often used as they are costeffective and generally available at local nurseries.
Transplanting larger trees is an option but will cost more.
Shrubs such as dogwoods and willows are commonly established from live stakes due to cost,
 Table 3.
Commonly used native species in Kentucky riparian buffers.
Trees	Shrubs and Small Trees	Grasses	Perenial Wildflowers
 American sycamore	Spice bush	Switchgrass	Great blue lobelia
 			
 Pin oak	Arrowwood viburnum	Eastern gamma grass	Purple coneflower
 			
 Swamp white oak	Eastern redbud	Big bluestem	Cardinal flower
 			
 Yellow Buckeye	Buttonbush	River bank wild rye	New England aster
 			
 White oak	Silky dogwood	River oats	Swamp milkweed
 			
 River birch	Rough-leaf dogwood	Deer tongue grass	Grey goldenrod
 			
 Bur oak	Greyheaded coneflower
 	
 Swamp chestnut	Joe Pye weed
 	
 but containerized plants can be used.
Live stakes are dormant, unrooted plant cuttings, generally less than 2 inches  in diameter and 3 ft  in length, that produce roots when planted.
Grasses are generally sowed by hand or with the use of a hand-held broadcaster, but they can be mechanically planted with a seed drill or no-till planter.
Only the most common methods for planting trees, shrubs and grasses will be discussed.
When planting small trees such as seedlings , precautions should be taken regarding timing, transportation, and handling to minimize stress to improve chances of survival.
The ideal time to plant a tree seedling is when temperatures are below 50F  and the ground is thawed.
During transport, seedlings must be kept cool  and moist.
This can be done by wrapping the roots of the seedlings in moist paper towels and storing them in a refrigerator, then transporting them to the project site in coolers.
Seedlings can be planted by hand for rough terrain or small areas using either the slit method  or the wedge method.
Refer to Davis et al.
for specifics regarding the slit and wedge methods.
For large areas, mechanical planters are an option.
Like tree seedlings, live stakes, also known as cuttings, should be planted during the dormant season when the ground is thawed.
Only certain species such as willow or cottonwood can be propagated in this manner.
Fresh cuttings can typically be obtained from nearby existing riparian areas.
Cuttings should be at least 0.5 in.
in diameter and 18 in.
in length.
The top of the cutting should be square and the bottom should be angled to ease planting.
Immediately soak live stakes in water to preserve moisture.
Do not harvest live stakes more than 48 hours prior to planting.
Plant the stakes with the angled  end going into the ground.
For softer soils, a rubber mallet can be used.
For firm soils, create a pilot hole using an iron bar.
Plant live stakes SO that about 80 percent of their length is in the ground.
Be careful not to split the stake or damage the bark when planting.
Live stakes are typically planted 1 ft  on center for dense planting.
If larger trees are desired or if transplantation needs to occur during the growing season, containerized
 or balled and burlapped  plants may be used.
Containerized plants are grown from seed or cuttings in pots of varying size that are usually filled with a soilless media.
The advantage of using containerized stock is that the entire root system is transplanted with the tree which greatly reduces transplant shock.
A disadvantage of containerized plants is that the potting material has a tendency to dry.
Care must be given to ensure that they are watered frequently.
Also, containerized plants can become root-bound in their pots.
Efforts to detangle the roots should occur before planting to ensure proper growth.
Balled and burlapped plants offer the opportunity to plant much larger trees with soils that can be matched to that of the transplantation site.
Unfortunately, use of B&B trees pose some special problems due to their size  and may require large equipment  for successful transplantation.
Planting instructions for containerized and B&B trees are typically provided by the nursery or commercial provider.
If instructions are not provided, the following may be used:
 Dig a hole just as deep as the root ball and two to three times as wide.
Scarify  the soil in the bottom and sides of the hole to encourage root penetration into the native soil.
Remove the moistened root ball from its container.
Loosen the roots from the bottom of the ball.
If root-bound, slice some of the roots from the matted bottom and sides with a knife or pruner until some hang freely.
With B&B trees, remove the string or wire that holds the burlap to the root ball.
It is not necessary to completely remove the burlap, but any plastic wraps covering the burlap  should be completely removed.
Place the plant in the empty hole.
Step back to ensure that the stem is straight, and then check its depth.
The top of the root ball should be even with, or slightly above, the surrounding ground.
Fill the void around the root ball with the soil that was excavated from the hole.
Soil amendments or alternative soil materials should be avoided unless site characteristics dictate otherwise.
Lightly tamp the soil around the buried root ball to remove any air pockets.
Create a watering basin by mounding the soil several inches high just beyond the edge of the planting hole.
The transplanted trees should be watered if dry conditions prevail at the time of planting.
With the use of a bucket, watering can be easily performed in riparian zones due to its close proximity to the stream.
Mulching trees in riparian zones is generally not recommended due to the potential for frequent flooding, which would wash the material away.
Staking of trees may be beneficial.
Staking will help support the tree  until the roots are established enough to properly anchor it in place.
Guying of the tree to the stakes should not be too tight to allow for some movement of the tree.
Remove all support wires once the trees are established to prevent girdling and subsequent mortality.
Native warm-season grasses provide dense root systems and wildlife habitat in riparian buffers.
These grasses can also serve as forage for livestock.
Establishing native warm-season grasses can be challenging, mostly due to competition from already established cool-season grasses.
The most important factor to consider when planting native warm-season grasses is controlling competition, which is generally done using herbicides and site preparation.
The first step when planting native warm-season grasses is to use herbicide to remove weeds.
This step should be done in the year prior to establishment of warmseason grasses before seed formation occurs.
Next, prepare the site by removing as much vegetation as possible during the autumn preceding establishment.
In the spring, apply an herbicide treatment once six inches of cool-season plant growth has occurred.
Seven to ten days before seeding, apply a combination herbicide treatment to kill any remaining cool-season and warm-season plants.
Finally, seed warm-season grasses in mid-May to mid-June when the soil temperature is above 55F.
Grasses should be seeded to a depth no greater than 1/4 inch; otherwise they may not emerge.
Consultation with local Kentucky Department of Fish and Wildlife Resources  and Natural Resources Conservation Service  personnel is recommended when establishing native grass stands.
These professionals can provide guidance and often loan equipment to landowners establishing native grasses for riparian buffers and wildlife habitat.
Some seed companies offer contracting services that include herbicide treatments, site preparation, and seeding of grasses for landowners.
Once the riparian buffer is planted, it faces threats from livestock and wildlife browsing, insects, humans, and unwanted establishment of invasives.
The emerging vegetation should be monitored to ensure that undesired species are identified and quickly removed.
Fencing can help prevent livestock and wildlife from grazing and prevent emerging vegetation from being damaged or destroyed by mowing.
Signage can be used to mark the boundaries of the riparian buffer if fencing is not used.
Tree shelters, which are plastic cylinders that are placed around seedlings to create moist microenvironments, have been shown to not only offer protection from mowers and browsing animals but also to increase tree growth.
Fabric mats are another option for improving tree growth.
Seedlings are placed in the center of a mesh fabric mat , and the ends of the mat are staked into place.
These mats prevent competition from herbaceous vegetation, such as ground cover species and grasses, and prevent competition for water and nutrients, but they do not offer protection from browsing animals.
Figure 3.
Use of tree shelter and fabric mat to for protection from animal browsing and competition.
Minimal maintenance is required for riparian buffers.
The site should be visited yearly during the first three years to check tree survival.
If tree survival is low, additional plantings may be required.
For additional information on riparian buffer planting and maintenance, contact your local University of Kentucky Extension office, Natural Resource Conservation Service  office, or Kentucky Department of Fish and Wildlife Resources office.
The University of Kentucky Arboretum as well as the Bernheim Arboretum and Research Forest are good sources of information.
Funding assistance may be available through programs such as the Environmental Quality Incentive Program , Wildlife Habitat Incentive Program , or Conservation Reserve Program ; contact your local NRCS office for additional information.
For information about planting materials, sources of these materials, and invasive species control useful contacts include:
Nonpoint Source Pollution in the Strawberry River Watershed
 The Strawberry River Watershed is located in northeast Arkansas and includes Independence, Izard, Fulton, Lawrence and Sharp counties.
A "watershed" is an area of land where all of the water that drains from it goes to the same place, SO rainwater or snowmelt in this watershed eventually drains to a common location.
This 769-square-mile watershed is sparsely populated with only about 20,000 people.
1 More than half the watershed, or 57 percent, is covered by forest.
Another 35 percent is considered pastureland.
2 The Strawberry River is popular for recreation, including paddling and fishing.
The river, which starts in Fulton County and flows toward the Black River, is part of the state's Natural and Scenic River System and supports more than 100 species of fish.
3
 Water pollution that comes from multiple sources spread over an area, such as runoff from parking lots, agricultural fields, residential lawns, home gardens, construction, mining, and logging, is known as nonpoint source pollution.
As runoff moves across the landscape, it carries natural and manmade substances that can accumulate in waterways and make them uninhabitable for aquatic species or unusable by people.
Potential pollutants include bacteria, nutrients, sediment, hazardous substances and trash.
4 Given the number of potential sources and variation in their potential contributions these pollutants are not easily traced back to their source.
Strawberry River Watershed Data source: GeoStor.
Map created March 2011.
Major streams: Caney Creek, Coopers Creek, Little Strawberry Creek, North Big Creek, Piney Fork, Reeds Creek, South Big Creek, Strawberry River
 This fact sheet is intended to provide a better understanding of the Strawberry River and its place on the state's priority list of 10 watersheds impacted by nonpoint source pollution.
Strawberry River Watershed Water Quality Issues
 Through water quality monitoring, environmental officials in Arkansas have determined that water quality has been impaired in the watershed because of deteriorating unpaved roads, streambank erosion and agricultural activities on pastureland near waterways.
5
 The primary concerns for this watershed are turbidity, total suspended solids such as sediment,
 fecal coliform bacteria, and phosphorus.
6 The main source of the turbidity and total suspended solids is thought to be from unpaved roads, stream bank erosion and adjacent pastureland.
Turbidity is a measure of the clarity of water and is often the result of excess silt or sediment entering a stream.
High turbidity levels mean the water is murky from a variety of materials, such as soil particles, algae, microbes and other substances.
Turbidity can affect aquatic life in waterways.
Within the watershed, 40 miles of streams are designated as Extraordinary Resource Waters  that do not support aquatic life.
7,8 An ERW is a water resource that is valued for characteristics such as beauty, recreation and social use.
Total suspended solids  can include organic or inorganic solid materials such as sediment, bacteria, algae and industrial wastes that
 Arkansas' Priority Watershed List for Nonpoint Source Pollution
 Arkansas has used a watershed-based approach to nonpoint source pollution management, allowing the public to guide planning to address water quality concerns.
The Arkansas Natural Resources Commission, or ANRC, administers the Nonpoint Source Pollution Management Program.
The program exists to reduce water pollution through the funding of watershed planning and restoration activities, adoption of voluntary best management practices and the development of technologies that assist in water pollution reduction in Arkansas.
Based on public input and the use of a qualitative risk assessment matrix, ANRC has designated 10 priority watersheds as needing the greatest attention.
The current risk matrix 10 identified the following priority watersheds for 2011-2016: Bayou Bartholomew, Beaver Reservoir, Cache River, Illinois River, L'Anguille River, Lake Conway-Point Remove, Lower OuachitaSmackover, Poteau River, Strawberry River and Upper Saline.
in high concentrations can lower water quality by absorbing light.
The source of the fecal coliform bacteria is thought to be related to agricultural practices.
11 In 2006, environmental officials in Arkansas determined the maximum amount of sediment the Strawberry River can receive and meet water quality standards.
This determination is a calculation called Total Maximum Daily Load or TMDL.
12
 These concerns and its border state status led to the Strawberry River watershed being designated as a priority by the Arkansas Natural Resources Commission in the state's 2011-2016 Nonpoint Source Pollution Management Plan.
13
 To encourage continued public input, the University of Arkansas' Division of Agriculture's Public Policy Center facilitated a water quality stakeholder forum for the Strawberry River Watershed in December 2014.
Participants identified runoff from septic and sewer systems, streambank erosion and overall stream sedimentation as local priorities that needed addressing.
People who live, work or recreate in this watershed are encouraged to consider these community priorities when addressing water pollution.
The public is also welcome to attend an annual stakeholder meeting where priority watersheds and nonpoint source pollution are discussed.
For more information about nonpoint source pollution and its impact on the Strawberry River watershed, contact the Cooperative Extension Service, Arkansas Natural Resources Commission or the Arkansas Department of Environmental Quality.
The Arkansas Watershed Steward Handbook is also a good source of information about basic water quality concerns and how the public can get engaged in addressing water pollution.
14
 7 See the Nonpoint Source Pollution Management Plan.
11 See the Arkansas Watershed Steward Handbook to learn more about TSS.
13 See the Nonpoint Source Pollution Management Plan.
14 See the Arkansas Watershed Steward Handbook.
This fact sheet is one in a series of 10 fact sheets on nonpoint source pollution in priority watersheds.
The University of Arkansas Division of Agriculture's Public Policy Center provides timely, credible, unbiased research, analyses and education on current and emerging public issues.
The Arkansas Cooperative Extension Service offers its programs to all eligible persons regardless of race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
Chris G.
Henry Associate Professor Water Management Engineer
 L.
J.
Krutz, Ph.
D.
Director, Mississippi Water Resources Research Institute Mississippi State University
 Drew M.
Gholson, Ph.D.
Assistant Professor & Extension Irrigation Specialist Mississippi State University
 Arkansas Is Our Campus
 What is Surge Irrigation?
Surge irrigation is the intermittent application of water used to improve distribution uniformity along a furrow.
It works on the principle that dry soil infiltrates water faster than wet soil.
When soil is wet, is seals because the soil particles at the surface consolidate.
When water is re-introduced in a furrow that has been wet, the wetting front moves quickly past the wetting zone to dry soil.
At the wetting interface, dry soil slows the advance.
This phenomena allows for a faster advance through the field with less deep percolation and better application uniformity resulting in a more even distribution of water in the rooting zone from the poly-tubing to the tail ditch, and reduced nutrient loss from deep percolation near the poly-tubing.
Surge irrigation is performed through a program of cycle times that account for the advance of the furrow.
These cycle times must be set by the user.
Some tail water is necessary with surge irrigation for it to be effective.
The intermittent application reduces the tail water volume, because the water is moving as a pulse over the sealed furrow to the end of the furrow.
The velocity of the water decreases as it moves along the furrow and has more time to infiltrate before it leaves the furrow.
When set properly, very little tail water leaves the furrow.
A valve that simply moves from one set to another at a uniform or constant time interval is not surge irrigation.
Advance time: Time that is required for wetting front to "advance" from the crown to the end of the furrow.
Recession time: Time for the wave front to recede from the furrow.
Essentially this is when the majority of the tail water has stopped draining from the field.
Opportunity time: Time for water to infiltrate into the soil.
The more time water is in contact with the soil, the more volume is infiltrated.
Soak Time: Time after advance has completed where the remainder of the set time is used to meet the required application depth.
Application depth: The depth of irrigation applied during a surge irrigation.
This depth should be between 2.5 and 3.0 ac-in.
Number of cycles: The number of advance cycles  used to complete a surge advance program.
Generally, surge advance times increase during the surge program, although some surge programs have a longer first advance than second advance before increasing.
On-time: The time water is applied to a given side
 Off-time: The time water is not applied to a given side
 Cycle-time: The time required to complete an on/off cycle 
 Irrigation set time: The total irrigation time, which includes advance and soak times.
The set time for row crops should always be less than 40 hours.
If using a CHS plan, you must add the time for each set together to calculate the irrigation set time.
For example, if a surge is being used on two 24 hour sets, the total time is 48 hours and the sets should be divided into three sets.
Computerized Hole Selection for Surge Irrigation
 To lay out surge irrigation, two irrigation sets must be combined.
For example, if an irrigation set was used to irrigate a 35 acre field or set, then it must be subdivided into two sets of equal size  or similar size.
The time to irrigate each set is combined for the total irrigation set time, and it is recommended not to exceed a total time of 40 hours.
Twenty-four hours is preferred.
Ideally, sets should be reduced to 24-30 hour irrigation times.
When possible, locate surge valves at risers, valves, or bonnets.
It is preferable not to have any lay flat pipe supplying irrigation water to a surge valve due to valve motion.
A surge valve can be used for multiple sets in a field for example, a 40 acre field can be divided into four, 10 acre sets and the valve used for two sets at a time then switched to the other two.
Place a short piece of rigid pipe in the valve and secure with poly pipe tape, to ease the process of connecting pipes.
Use pipe clamps to secure the lay flat pipe to the valve between surge sets.
Anatomy of a Surge Valve
 A surge valve consists of an electronic controller and an aluminum mechanized valve that diverts water from one side to the other.
This is referred to
 as right and left side.
P and R surge valves have advance and soak cycle modes.
The valve started out in the advance mode and then moves into the soak mode after the advance time has been reached.
It continues indefinitely in the soak mode until it is shut off.
The most critical step is programming the advance time correctly in a surge valve.
Once you reach the soak phase in the program you cannot go back to the advance phase.
Set the anticipated time of the advance phase just slightly less than the actual advance time observed in the field from an advance.
In many cases the time that is normally taken to advance through the field will be about half for a surge irrigation.
Use a CHS plan to plan the surge time.
For example, if a CHS plan calls for a 24 hour set time, then expect a 12 hour advance.
However, the advance time is highly variable and the user must determine the advance from experience, so the advance should be monitored during the first irrigation until it is known or can be predicted.
For example, if a 24 hour set is required to put on 2.5 ac-in application depth, and it is observed that the advance is halfway through the field at nine hours, then adjust the advance time down from 24 to 18 hours.
Below is guidance for setting a surge valve for different soils and conditions.
However, there is no hard, fast rule and sometimes the user must experiment with the valve to obtain the best results is necessary.
Surge valves are especially useful in in sandy soils, as the challenge with coarse textured soils is minimizing deep percolation and getting water through the furrow.
Thus set the valve as normal, although expect a longer advance time.
Use default cycle times.
Increasing the number of cycles may improve the irrigation.
Surge valves are useful in silt loam soils, especially those that seal.
In silt loams that do not seal and infiltrate well, use same process as sandy soils.
For silt loams that seal, it will likely be necessary to make substantial changes to the program.
Often in silt loams that seal, the advance will be much less than expected.
For example, for a set time of 24 hours, the advance may be completed in six hours.
Adjust the advance time to five hours, increase the number of advance phases by +1 or +2.
Operate the valve in soak mode for the remainder of the irrigation set, and reduce the flow rate to increase opportunity time.
In cracking soils, the surge valve should be used only in the advance mode.
Set the advance time to the total irrigation set time.
Do not operate in soak mode.
Also reduce the number of advances so that there are only three to four advance cycles.
The surge valve works in a clay soil because in the off cycle, the soil cracks seal up and allow the advance to quickly move through the furrow on the next advance.
Recommended advance settings are shown in Table 1.
Table 1: Surge Valve Star Controller Recommendations for Clay Soils
 Advance	Default Cycles/	Custom Cycles/Side
 Setting	Side Setting	Recommendation
 Input by user	Under custom tab	Use down arrow to adjust
 5	4	4-1  total
 10	5	5-2  total
 15	6	6-2  total
 20	6	6-2  total
 30	6	6-2  total
 It is recommended that the number of cycles per side equals the default setting, minus two.
The total cycles per side should never be less than three.
Two sets of different sizes can still be surge irrigated.
For example, if one set is 15 acres and another is 20 acres, the valve can be adjusted to increase the advance times for each set.
In this example, 43 percent of the time the valve will divert water to the 15 acre set, and 57 percent of the time it will divert water to the 20 acre set.
This can be input directly into the valve through a custom menu.
Surge valves operate on solar power and a battery.
The voltage of the battery and solar panel can be
 checked through the custom menu.
Valve controllers need to be charged and turned off in the off-season.
During the season, they need to be shut off after an irrigation event, or else they will continue to move the valve.
If left unattended, they will drain the battery.
It is highly recommended to use a circle lock or horseshoe clamp to secure the surge valve to a bonnet or hydrant.
The oscillation of the valve can dislodge it from the water source.
When starting an irrigation, the valve can be changed from the right or left side by using the change button it does not advance the program when done during the first advance cycle.
The valve pauses before switching completely over.
This is a setting that can be changed in most valves if water hammer is occurring from high flow rates.
Use of soil moisture sensors or a soil moisture monitoring unit can be useful in evaluating the effectiveness of a surge irrigation program, and to optimize settings.
In some cases surge can reduce the advance time, in other situations it will increase the advance time.
Reducing the advance time will result in a water savings.
An increased advance time typically indicates that more water has been applied to the soil, likely indicating that fewer irrigations will be necessary, overall resulting in less total irrigation water needed to meet crop water demand.
Thus the benefit of surge irrigation is not always apparent from visual observation alone.
Surge Irrigation is the intermittent application of water in furrow irrigation for the purpose of improving down furrow efficiency and reducing deep percolation.
A programmed automated valve is used with lay flat pipe that has been planned with set sizes.
Surge irrigation must be adapted and adjusted to field and soil type conditions.
Plan surge irrigation sets for a total irrigation time of 24 hours and use CHS to determine lay flat pipe hole punch plans.
Acknowledgement: This fact sheet is a joint publication with Mississippi State University.
Printed by University of Arkansas Cooperative Extension Service Printing Services.
CHRISOPHER G.
HENRY is associate professor and water management engineer at the Rice Research and Extension Center, University of Arkansas System Division of Agriculture.
L.
JASON KRUTZ is director of the Mississippi Water Resources Research Institute at Mississippi State University.
DREW M.
GHOLSON is assistant professor and extension irrigation specialist at Mississippi State University.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Director, Cooperative Extension Service, University of Arkansas.
The University of Arkansas System Division of Agriculture offers all its Extension and Research programs and services without regard to race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
Average percent of fields by year fitting into the six categories.
The dry years 2020, 21 and 22 are different than the other years.
In the weighted average dry years, 2020, 2021, 2022, 64% were ranked good, 11% were fair, 3% were wet late, 15% were wet early, 3% were wet all season, and 4% were very wet all season.
Groundwork for this program expansion in Colorado was made possible in part by a multi-state USDA-NRCS Conservation Innovation Grant, as well as a state-level grant from the Colorado Water Conservation Board.
Evapotranspiration demand that exceeds soil water supplies will result in yield reductions at any time during the crop life cycle.
When plant water uptake by the roots is limited so is nutrient availability, uptake, and transport.
Additionally, water stressed plants are more susceptible to insect and disease pathogens and have diminished stem integrity.
Irrigation Water Management Strategies for Drought
 A drought is forecast!
My irrigation water supply will be cut back!
What should I do?
This is never good news.
However, there are a few things you can do to minimize the impact of irrigation water shortages and limit the damage.
This publication is for agricultural irrigation managers and presents ideas for minimizing the impact of drought and getting the most benefit out of the limited water that is available.
Many of these suggestions require additional information and caveats that we will not take time to discuss in the interest of brevity and readability but give references for further reading.
Don't Irrigate When It's Not Needed
 Figure 1 shows some typical variations in crop water use.
In general, the highest irrigation amounts are required during the summer and decrease during the fall and spring.
This is due to changing day lengths, weather, and crop maturity.
However, if the same irrigation schedule is followed all season, then water will be inefficiently used.
In particular, it is easy to lose excess irrigation water to deep percolation during the spring and the fall when crops need less water.
Figure 1.
Crop water use changes drastically throughout the season.
Mean water use estimates for Eastern Washington.
Moderate Water Stress Only has a Small Impact
 As seen in Figure 2, yield increases with additional applied water, but as a crop nears full irrigation the yield response per unit of additional water applied decreases until additional water does not increase yield.
Most crops have yield response
 curves that are very similar.
Because of this, 20-30% cutbacks in applied water usually only result in relatively small yield losses.
Less than 5-10% of yield losses have been reported for water cutbacks up to 30% on cotton, sweet corn, and spearmint.
However, additional water stress beyond that  result in quite large yield losses for each inch of water that cannot be supplied.
In very arid regions some irrigation water must be applied before any yield at all is possible or yields may be SO low that harvesting is not economical.
Because of this, evenly spreading the available water across all acres is often less optimal than completely not irrigating some land.
This leads to optimal land allocation and planting strategies that are discussed below in the "Farm Less Land" section.
Figure 2.
A generalized crop yield response to applied water through irrigation or rainfall.
If there is less water, it often makes sense to just plant fewer acres and leave some fallow for that season.
How much less land to plant is an important consideration.
Consider the yield response to the applied water curve for your crop and area.
As discussed above, applied water reductions of 25-30% often result in only small reductions in yield; however, additional reductions may cause steep yield losses.
Also consider that in many arid areas some irrigation is required to achieve any yield if water is required for germination and growing, and because of this, large areas of partially irrigated land  may not be advisable for these areas.
Therefore, based on the best estimates of available water, it might be advisable to only plant the acreage that can be irrigated at 75-80% of the full irrigation water requirement.
The rest of the land should be left fallow.
Example: You are expecting half of the water you are normally allocated to plant 100 acres.
1.
Calculate the number of fully irrigatable acres: 100 acres / 2 = 50 acres.
2.
Calculate the number of acres if irrigated at 80%: 50 acres / 80% = 50 / 0.8 = 62.5 acres.
This leaves 37.5 acres not irrigated.
Since the goal is often the greatest profit returns to the farm, and because the costs per acre of tilling, planting, spraying, and harvesting are fixed, it may be advantageous to irrigate a bit more  and thus plant fewer acres and hopefully get higher yields on the limited acreage that is planted and irrigated.
In areas with more rainfall, such as Western Oregon or Western Washington where rainfall can be expected to create at least a limited amount of yield without irrigation, planting all of the acreage and then spreading the limited amount of available irrigation water across the whole acreage may be preferable.
In these areas, the combination of rainfall and irrigation would allow crops to grow and be in the linear area of yield-to-water-applied response curve.
For center pivots, an easy way to farm less land, given a lower flow rate delivered, is to simply shut off some of the sprinklers.
Good candidates for this are the sprinklers located towards the center, as this area often has poor yields, is a little harder to farm, and it is difficult to irrigate uniformly anyway.
Water Stress During the Crop's Vegetative Growth Stage Hurts Less
 Try to avoid water stress during flowering or periods of time when the plant is deciding how much to produce such as tuber initiation for potatoes.
Also try to avoid water stress during critical growth stages, such as when the plants are trying to create healthy viable seeds or produce.
Water stress during these times hurts total yield and produce quality significantly.
Conversely, water stress during the vegetative growth stages, when the crop is creating vegetation to capture sunlight to eventually create produce, but is not building grain or produce, has the lowest effect on yield loss.
Water stress during the end-of-season ripening stages often has a lower effect on yield as well.
Because water stress during flowering and yield formation causes the greatest yield losses, it is often best to save the available water supplies for use during these times of crop development.
Unfortunately, these growth stages often coincide with the times of maximum water use demand.
Some Perennial Crops Can Go Dormant with Little Long-Term Damage
 Many perennial crops are adapted to summer deficits and will go dormant during times of drought but will readily regrow when water is again available.
Of particular note is alfalfa and many other forage crops.
In many cases it is better to severely limit the water to these crops allowing them to go into and stay in dormancy until adequate water is again available, which is often the following season.
These crops will turn brown or look bad, but they are still alive.
Although these crops will be using drastically reduced amounts of water, they still use and need at least a small amount of water to survive.
If crops completely run out of water such that the soil is dusty dry  they will die.
This is of particular concern in sandy soils that have lower water holding capacity and for shallow-rooted crops.
Put in a Pond
 On-farm ponds can store water from times of the year that it is more available such as the winter, early spring, and late fall, and make it available during the times of greatest needs or shortages or when the crop is most sensitive to water stress, which is usually during the middle of the summer.
Obviously, the more water that can be stored, the better.
However, bigger ponds can be expensive to build, take up space, and there are sometimes permitting requirements.
Not all soils are suitable for ponds  without being lined with clay or artificial lining materials.
Building a pond may be worth the expense especially if perennial crop loss would require expensive and time-consuming replanting, or if droughts are common and regular.
Use the Soil as Water Storage
 The soil is another great place for on-farm water storage.
Especially on deep soils that have large water holding capacities , it can be possible to fill the soil early in the season to the depth of the roots at times when water supplies are often more available  and then, plan to deplete these soils during times of coming water shortages.
Consider your average winter precipitation and try to maintain space in the soil for that snow melt or spring rainfall to avoid deep percolation water losses over the winter or early spring.
Because deep percolation is more likely when deliberately building up the soil moisture in the early spring, consider applying the fertilizers later or in split applications as leaching and loss of these nutrients is also more likely.
Plant Crops that Use Less Water
 Consider planting crops that have a shorter season  and/or a season that coincides with predicted availability of the water supply.
Figure 1 demonstrates how different crops use water at different times of year and Figure 3 shows differences in the total amount of water that different crops typically use.
Some might use less water due to a shorter growing seasons or use deliberate water stress.
Others require more water to keep them alive, and thus there is less flexibility.
University plant breeders and seed producers have been working hard for many years to develop drought tolerant varieties for many crops.
Make a few phone calls to your seed dealer or university extension specialist to see if there isn't a more drought tolerant variety available.
Figure 3.
Irrigation water requirements estimates  over a typical season and planting scenarios for a few selected crops in Eastern Washington/Oregon
 Plant Different Crops to Take Advantage of Different Seasonal Water Use Timings
 When there is reduced, but constant flow rate delivered throughout the season, it may help to plant a variety of crops that use water at different times.
For example, if water is uniformly limited throughout the season, then a grower might choose to plant spring grains that use water early in the season and then switch the water to potatoes whose water use peaks after spring grains are typically harvested.
The strategy might be different or not applicable if the water supply is shut off completely sometime during the middle of the summer.
All of these strategies depend on the length of the growing season, the time and the amount of water delivered, the weather, and the crop varieties planted.
Figure 4.
Planting a crop that uses water early such as spring grain, followed by crops that can be planted later, such as potatoes or corn, can help spread water supplies.
Out of Sight Shouldn't Mean out of Mind.
The two largest sources of irrigation water losses are both not visible to a farmer.
They are losses via 1) water vaporization and 2) deep percolation.
As the water travels through the air from the sprinkler nozzle, a large portion of that water is evaporated.
It is lost as water vapor and is therefore not visible, but it is a significant amount of water!
Deep percolation occurs when more water is applied to an area of soil than that soil can hold.
Although the water infiltrates into the soil, it will keep moving past the bottom of the crop root zone and will be lost to the farmer.
Again, this is not visible SO is not often considered, but it is significant!
You Can't be Efficient if your Irrigation System is not Uniform.
If the irrigation system inherently applies more water in some areas and less water in others, then some areas will either have excessive water stress and/or others will lose water to deep percolation.
Irrigation uniformity, and therefore your water use efficiency, can be improved significantly by maintaining and operating the irrigation system properly.
This includes operating it at the pressure and flow that it was designed for, making sure nozzles are unplugged, fixing leaks, and replacing sprinklers and hoses that are not operating as intended.
Fix Leaks, Replace Nozzles, Check Pressure Regulators.
Water lost to leaks almost always results in that water being eventually lost to deep percolation.
As sprinkler nozzles and pressure regulators wear, they often result in non-uniform irrigation water application as more water comes out of them than was planned for.
Figure 5.
Water leak in wheel line.
The leak flow rate is over three times that of the sprinkler.
Water Less Frequently with More Water Each Time
 Irrigating frequently results in a greater total amount of time where water is available for evaporation from the wet crop canopy or wet soil surface.
If more water is applied less frequently, then the water is pushed deeper into the soil where it is unavailable for evaporation from the soil surface but is still available for absorption and use by the crop roots.
Be careful to not irrigate too deep such that water is lost to deep percolation!
Figure 6.
On bare soil the same amount of water was applied but one plot was irrigated every day, and one plot was irrigated every five days.
The additional water losses from evaporation from the every-day irrigation are clear.
This also shows how evaporation losses decrease as the weather cools off and the day length shortens.
Reduce Soil Surface Evaporation
 Covering the soil with a plastic or organic mulch or pine bark nuggets can drastically reduce water losses from the soil due to evaporation.
No-till, or strip-till reduces soil surface evaporation, reduces water losses from the tilled soil , and increases the soil surface water storage, all while using less tractor hours and diesel!.
When water stress is unavoidable, another simple way to do irrigation scheduling during times of drought is to simply wait to irrigate until there is visible crop stress.
This will help limit water losses to deep percolation because the grower can be confident that there will be adequate space in the soil to hold the applied irrigation water even if the irrigation system is not perfectly uniform.
Some visible signs of water stress are leaves that are a darker green color, curled or wilted leaves, stunting, and early onset of flowering or reproductive growth stages.
Water at times of lower evaporative loss potential
 If possible, try to avoid watering at times when there is higher evaporative demand.
Sunny, hot, windy, and low humidity conditions increase the evaporation potential and therefore lower irrigation application efficiency, especially for sprinkler irrigation.
At night, the temperatures and wind speeds are often lower, and the humidity is often higher  and thus offers an opportunity for more efficient irrigation.
It is not always possible to only irrigate when the evaporative potential is low, but it can sometimes be
 accomplished when there is water delivery flexibility and when using irrigation systems with high design capacities.
Figure 7.
Irrigating at night.
Considering Variations in Water Delivery During Shortages
 Sometimes growers do not have control over the timing of water supplies and shortages throughout the season and sometimes they do, as when water is stored in an upstream reservoir.
The latter is obviously preferable.
Here are some more things to consider.
Consider Delivery System Losses
 There are often unavoidable water losses in surface water delivery systems.
These losses are not linearly related to the flow rates in these canals and have about the same amount of loss whether they are full or partially full.
Therefore, instead of delivering a constant but reduced amount of water all season, it is often preferable to instead deliver a full, or near-full amount of water, but for limited times.
This reduces the season total delivery system losses.
Of course, every delivery system is different, and these differences must be considered.
If Possible, Take Water Limitations Early or Late in the Growing Season
 These are times of lower crop water demand, and they also coincide with times when the crops are less sensitive to water stress , depending on the crop.
A strategy often employed by irrigation districts is to deliver water early in the spring to allow growers to fill their soil profile, then shut the water off completely for a few weeks during the springtime when ET rates are low, and then deliver water again during the hot part of the summer  when crop water needs are high and at the most sensitive stages to water stress.
If the districts are still short of water in the fall, they can again shut off early when water use rates are low, crops are senescing, or when it is okay for water shortages to induce perennial crops to go dormant early.
Selecting a more efficient irrigation system or making modifications to your existing irrigation system can have large, inherent, and long-lasting impacts to drought readiness.
Water losses from center pivots can be reduced dramatically by lowering the sprinklers much closer to the soil surface.
Figures 8, 9, and 10 below show how the height and operating pressure of the sprinkler packages on a center pivot can greatly affect the overall irrigation application efficiency.
Low energy precision application  and low elevation spray application  have very high irrigation efficiencies especially when the sprinklers are operating below the top of the canopy and are protected from wind drift and evaporation losses.
Additional information on the costs and benefits of converting center pivots to LEPA/LESA is available at Peters et al.
Figure 8.
High pressure impact sprinklers lose 30-40% of their water to wind drift and evaporation and are especially susceptible to increased water losses and on windy days.
When using mid elevation spray application , selecting sprinklers that use lower pressures, and throwing larger drops such as wobblers or nutators are more efficient than sprinkler heads that use high pressure and create lots of smaller droplets.
High pressure impact sprinklers on top of a pivot lateral are sometimes chosen over other methods because they have low instantaneous application rates and can be used in places where soil infiltration rates are very slow to avoid runoff.
However, runoff problems can be fixed in other ways that do not lose as much water to wind drift and evaporation.
These include using boom-backs to spread the water application pattern out or by using tillage practices to increase the soil infiltration and surface water storage, such as reservoir tillage using a dammer-diker implement or creating furrows or rills perpendicular to the slope.
Figure 9.
Mid elevation spray application  losses 10-20% of water to wind drift and evaporation.
Figure 11.
Center pivot irrigation with low elevation spray application  and with mid elevation spray application sprinklers  operating in the background irrigating the spearmint field in Toppenish, Washington.
Figure 12.
Alfalfa irrigation using a center pivot with a mobile drip irrigation  system in Umapine, Oregon.
The MDI systems are extremely efficient and apply water slowly to permit greater infiltration depths per pass..
On hot and windy days and with MESA systems, it may be advisable to simply turn the center pivot system off because not much of that water is getting to the ground due to evaporation and wind losses.
It is also advisable to slow the center pivot down as much as possible.
This results in lower overall losses to evaporation from the wet soil and crop canopy.
More water can be applied per pass when tillage practices are used to increase the soil surface storage, such as using a dammer-diker to create
 furrows or pits in the soil, or when planting rows perpendicular to slopes, or when more organic matter or crop residues are left on the soil surface.
Center pivots can also drag drip tubing.
These systems work well, are extremely efficient, and are better than LEPA or LESA at getting the water into the soil.
However, they are more costly due to the filtration requirements and the additional hardware needed.
More information on these systems is available from Peters.
Figure 13.
Drip irrigation is an inherently efficient system but water losses to deep percolation are still possible due to over-irrigation on nonuniform drip emitter flow rates.
Drip irrigation systems are inherently efficient as there is little opportunity for wind drift, and soil evaporation losses are limited since not all of the soil surface is usually wetted.
Burying the drip lines can increase efficiency by further limiting water losses to soil surface evaporation, but this will probably be only a minor improvement.
The biggest opportunities for improvement with drip irrigation are to do better irrigation scheduling to limit water losses to deep percolation and to increase the irrigation uniformity to ensure that the drip emitters are all flowing the same rate.
Figure 14.
It is very difficult to adequately irrigate the bottom of a surface-irrigated field without over-irrigating the top of the field and creating runoff.
It is difficult to be efficient with surface irrigation since water must commonly infiltrate the soil at the top of the field for many hours before the bottom of the field begins to receive any water.
This results in inherent over-irrigation and water losses to deep percolation at the top of the field and often excessive water losses to runoff at the bottom of the field.
A general rule of thumb to adjust furrow flow rates SO that the water reaches the bottom of the field in half of the irrigation set time.
Another alternative that could be beneficial in water short years is to divide the field to create shorter rows, SO the water reaches the end of the row sooner, and shorter overall set times can be used.
Surge irrigation  or cutback irrigation can also be used to increase surface irrigation efficiencies.
Solid Set, Hand-Lines, and Wheel-Lines
 Leaks are also common on these types of irrigation systems.
In a survey done in Idaho, the average water loss from leaks on wheel lines was 12-16%, and 36% for hand-lines.
Fixing leaks also helps avoid poor uniformity of the system because of inadequate flow and pressure.
Fixing leaks results in water savings and lower pumping power bills.
Over time nozzles wear and the orifice size becomes larger, thus, at any given pressure, the flow increases resulting in non-uniform application and thus lower irrigation efficiency.
Nozzles can be replaced for a low cost.
Figure 15.
A wheel-line irrigation system not uniformly irrigating due to inadequate pressure and leaks.
Big gun sprinklers operate at high pressures and throw water to far distances resulting in large water losses to wind drift and evaporation.
The wind really disrupts the big gun sprinkler patterns creating additional irrigation uniformity problems.
Hence, there are great opportunities to improve the efficiency of big guns sprinklers by operating at night and by avoiding operation on windy days when possible.
Moreover, higher irrigation efficiency and uniformity of big guns can be achieved by decreasing the pressure and increasing the set overlap distance.
However, very low pressures create uniformity problems.
Big gun carts on hose reels can sometimes be replaced with boom carts that have a much higher uniformity and efficiency.
Boom carts can also operate at lower pressures resulting in large pumping energy savings.
Figure 16.
A boom cart being pulled in on a hose reel in a potato field.
Alfalfa is adapted for growth under periodic droughts.
A wide variety of research has shown that during water shortages it is usually best to take the first cutting or two, and then shut the water off completely about the middle of the summer allowing the alfalfa to go dormant.
When alfalfa goes dormant and is brown, it is not necessarily dead.
Above-ground growth will be limited, but it will become active and produce good yields when water becomes available again.
Most grasses grown for hay in the Pacific Northwest  grow best in cool climates and have slower production during the middle of the summer.
During droughts it may be advisable therefore, to fully irrigate in the spring and take the first one or two cuttings and then, deficit irrigate to a level just enough to keep the grass alive during the middle of the summer and not graze or cut it during this time.
Most grasses will go dormant during droughts, but excessive droughts to species that are not adapted for water shortages can cause thinning of the plant population in the field.
As water becomes available again in the fall it can be irrigated and restored to health allowing a possible last cutting or getting it ready for fall and winter grazing.
If droughts are likely to recur regularly, then more drought tolerant species should be selected such as many of the wheatgrass varieties.
As tree fruit are higher value crops, they are usually the last to be chosen for water deficits.
Some evidence is emerging that tree fruit can withstand mild water deficits.
Cover crops are commonly grown in orchards for maintaining soil structure, encouraging water infiltration, and reducing erosion, among other benefits.
However, during droughts, the overall water use rate of the orchard can be reduced by eliminating or not irrigating the cover crop.
Consider selecting cover crops that require minimal maintenance  and that are drought tolerant or have lower water requirements.
Tree fruit also sometimes requires additional water resources for evaporative
 cooling.
There are alternatives to using water for evaporative cooling such as shade netting or some calcium-based products.
Shade netting has also been shown to significantly reduce the overall orchard water use.
Potatoes, Onions, and Other Vegetables
 In general, vegetables do not respond well to water stress and the economic losses from reduced quality, size, and yield are substantial.
Thus, most growers choose to reduce water in other areas besides their vegetable fields.
Strategies during drought conditions may include increasing the planting density and harvesting early.
This will result in more but smaller produce that might be used for seed for vegetatively produced crops like potatoes, or for a specialty market where smaller produce is often preferred.
Some vegetable varieties have more water stress tolerance, and these could be selected for planting.
Because the quality reduction from water stress is clear and causes significant reduction in prices, many growers over irrigate to be safe resulting in water and fertilizer losses to deep percolation.
During a drought irrigation scheduling becomes more important to avoid over irrigating.
Because grains are SO important to the nation's food supply and are largely produced in dryland farming areas with uncertain water supply, many drought tolerant varieties have been developed.
Water stress during the vegetative growth stage limits grain yields the least.
Timing the water cutoff  is also important for water savings and for maximum yield.
Lawns can tolerate significant water stress without dying.
Water stressed lawns look less lush, and many home and business owners prefer to not have this loss in visual appeal.
However reduced irrigation can result in significant water savings especially to municipalities.
Many lawn irrigators should use longer set times and irrigate less frequently.
This pushes roots deeper and reduces evaporative water losses from the wet grass.
Often, irrigating once per week is sufficient.
Irrigating twice per week in dry and hot areas may be necessary during the middle of the summer or when the soil is very sandy or shallow.
Using smart irrigation timers that adjust for the variation in water use throughout the season can save significant amounts of water  and often justify their costs in reduced water bills.
A simple method of irrigation scheduling is to shut your system off, and wait for visible water stress, then irrigate much longer than you normally would.
Poke a shovel or probe into the soil to get an idea of the depth of irrigation water penetration.
Selecting drought tolerant landscaping plants may allow green lawns with the minimum amount of water application.
Using mulch composed of pine bark, gravel, or compost will help reduce water evaporation from the soil surface.
Another strategy is to establish an 'ecolawn', a low input alternative to a conventional perennial grass lawn.
Generally, it consists of a mix of broadleaf and grass species mutually compatible and ecologically stable that stays green through the dry summer months due to its lower water and fertilizer requirements.
Structure: Check sprinkler chart for proper sprinkler placement.
Check for worn or broken components, sprinklers and regulators.
Replace every 7,000  10,000 hours.
Check for boots, gaskets, and mid-drains for leaks.
Roadside Guide to Clean Water: Cover Crops
 Without cover crops, the soil would be bare during the off-season and exposed to rain, snow, and wind.
Cover Crops at a Glance
 A cover crop is grown during the off-season  after the harvest of a primary production crop, like corn or soybean, and before the next production crop is planted.
Typically, cover crops are planted in the fall, after harvest, and they grow over the winter months.
Some cover crops are harvested in the spring, but others are simply killed off, or terminated, before the main crop is planted.
Some farmers may also be able to plant cover crops during summer fallow.
Without cover crops, the soil would be bare at this time and exposed to rain, snow, and wind.
Cover crop plants can include legumes like red clover, small grains like winter rye, and other plants like forage radish.
Cover crops are typically fast-growing and short-lived plants.
Cover crops provide benefits on any barren soil from backyard gardens to large crop fields.
How Cover Crops Work
 Cover crops reduce soil erosion by keeping the soil surface covered.
The leaves of the plants protect the soil from rain drops that otherwise would splash and blast tiny soil  particles from the land.
The roots of the cover crops also assist in holding the soil in place, preventing sediment pollution in nearby streams and other water bodies.
Cover crops also help reduce nutrient pollution by using any fertilizer and manure left over from the last production crop season.
They can even bring nutrients found deeper in the soil back to the soil surface.
After the cover crop is terminated, the nutrients and carbon that are stored in the cover crop will be available to help the next production crop grow.
Cover crops also improve soil health and add organic matter to the soil.
This helps improve water infiltration and storage in the soil, reducing the volume of stormwater running off the field.
Community Benefits of Cover Crops
 Stormwater: Reduces stormwater runoff
 Climate Change: Promotes climate change resiliency
 Habitat: Provides wildlife habitat
 Savings: Provides cost savings
 You can expect to find cover crops in suburban or urban settings.
How to Recognize Cover Crops
 Cover crops planted after plowing a field will quickly establish to reduce soil loss during the fallow period.
Photo by Nicole Santangelo
 Cover crops are often used at the same time as reduced-till or no-till practices where soil isn't plowed between crop plantings.
Photo by Nicole Santangelo
 The taproots of radishes make them a helpful cover crop because they also break up compacted soil before decomposing at the end of winter.
Photo by Nicole Santangelo
 The remnants of a terminated cover crop act as mulch, as seen here under an actively growing tobacco crop.
Photo by Nicole Santangelo
 Ryegrass and cereal rye are both used for cover crops.
Cereal rye, unlike lawn-grass-type ryes, can grow up to 36 feet tall.
Photo by Nicole Santangelo.
Learn more by watching the video: "No-till Farmer to Farmer-Introduction to the Series."
 Cover crops are killed using herbicides or other techniques so that crops can be planted without plowing, reducing soil erosion and sediment pollution.
Photo by Lance Cheung, USDA Natural Resources Conservation Service
 Cover crops aren't just for farmers; they provide many benefits to backyard gardeners, too.
Lets take a look at an example.
We want to apply 0.30 inches of water with the pivot during the chemigation application.
So, by looking on the speed chart, it will take 21.39 hours to complete the circle applying 0.29 inches.
If we know the acres under the pivot  e.g., 121.9 acres  we can determine the acres per hour.
121.9 acres / 21.39 hr = 5.7 acre/hr
 Note  The acres listed on the sprinkler chart assume the end gun  is on the entire field.
Thus, use the irrigated acres from another source if the machine is equipped with an end gun.
Check to see whether the pressure matches the design pressure.
The sprinkler chart will indicate the location the design pressure is to be checked.
It is usually at the base or the top of the pivot point
Cornell Climate Center at Front Line of Drought Response
 For more than a year, as drought spread across the Northeast, agricultural fields went parched, crops withered, wells ran dry.
During the worst drought since the 1960s, irrigated farms in the Northeast suffered crop losses of up to 35 percent; for unirrigated farms, field crops and pasturage losses hit as high as 90 percent across the 12 states in the region.
The drought  which started in April 2016  was declared officially over this month, but its financial impacts may last much longer.
This drought had a big impact on agriculture, especially as it struck right during the growing season, said Jessica Spaccio 04, climatologist with Cornells Northeast Regional Climate Center.
Being in the Northeast, water is usually plentiful, so there arent a lot of irrigation systems in place like in California where droughts are common.
For 35 years, the NRCC, housed in the College of Agriculture and Life Sciences, has been helping farmers and policymakers adapt to the weather.
Led by director Art DeGaetano, professor in the Department of Earth and Atmospheric Sciences, the NRCC monitors climatic conditions and shares the information with the public, part of its mission to inform and apply climate research for economic efficiency and the public interest.
Because scientists anticipate climate change will cause an increase in extreme weather, including more frequent flooding and droughts, the work of the NRCC is proving even more indispensable, according to DeGaetano.
Jessica Spaccio and Samantha Borisoff
 Image Caption ButtonJessica Spaccio 04, left, and Samantha Borisoff, climatologists with Cornells Northeast Regional Climate Center, in Bradfield Hall.
Photo by Matt Hayes / College of Agriculture and Life Sciences.
The NRCC bridges information between national agencies like the U.S.
Drought Monitor and the U.S.
Geological Survey, and the public and private stakeholders whose livelihoods depend on having access to reliable climate data.
For example, the Drought Monitor creates the standards and designations for drought categories nationwide, and USGS monitors groundwater wells to see whether precipitation is restoring underground aquifers or running off into lakes and streams.
The climatologists at the NRCC  Spaccio, Samantha Borisoff and Keith Eggleston  take that data and translate it for individuals, businesses and government agencies who have problems to solve.
We take phone calls and emails from anyone who has a question related to climate data, said Spaccio.
This could be anything from someone at a law firm or an insurance agency dealing with a claim for an accident on a slippery road, to someone at another university doing research, to someone in the agriculture community looking at manure storage, to health agencies working on mosquito control.
The NRCC partners with groups across Cornell to aid research and develop products to meet extension needs.
The NRCC maintains ongoing collaborations with the New York State Integrated Pest Management Program, the New York State Water Resources Institute, the Cornell Institute for Climate Smart Solutions and others.
An unusually mild winter in early 2016 left snowpacks in the Northeast far below average.
As spring came, elevated temperatures and reduced rain stressed plants at the start of the growing season.
By July, the New York Department of Environmental Conservation put the entire state on drought watch, and many counties in the hard-hit Finger Lakes and western New York regions were declared natural disaster areas.
NRCC climatologists hold weekly phone calls with Cornell Cooperative Extension agents throughout the growing season.
During the height of the drought, this network of experts worked to ease the droughts impact on farmers.
The drought was a good test for the climate center, said DeGaetano.
It demonstrated the staffs nimbleness in designing and implementing new and expanded websites, coordinating and developing workshops and webinars, and distributing frequent updates to stakeholders concerned with the droughts status.
Working with Cornells Climate Smart Farming group, the NRCC helped create a tool called the Water Deficit Calculator, which gave farmers estimates of the soil water content accessible by crops.
Part of the work we do is focused on helping people prepare so they can respond more effectively to whatever the weather is going to do, Borisoff said.
Another part is providing context.
When people are struggling and crops are failing, we can say, Yes, it is really bad.
Its the worst drought weve had since the 1960s.
The drought was just as severe in some parts of Massachusetts, Connecticut and New Hampshire.
Some municipalities placed restrictions on water use, while people on private wells saw their water run dry.
Fisheries folks were concerned  the water levels in certain parts of rivers were so low that fish were getting stuck and a few rivers had to be closed to fishing in order to protect the fish, Borisoff said.
Firefighters were being impacted because the dry conditions led to fires that were harder to put out.
In the aftermath of the worst drought in 50 years, climatologists across the Northeast are working to figure out how they can improve response to the next drought.
This could include improving top-down communications, such as creating a drought early warning system, as well as strengthening bottom-up information sharing, such as crowd-sourcing water data from farmers and people on private wells.
We expect with climate change to see these short-term droughts occur more often, Spaccio said.
All it takes is one season, and especially when it hits during the growing season, to have big impacts.
Finally, the article highlights the role of technology in the history of irrigation development and its impact on water resources.
Over the decades, several different types of technology have resulted in increases in irrigation application efficiency, which is the depth of water stored in the root zone divided by the depth of water applied.
EM 8911 Revised January 2013
 Successful Potato Irrigation Scheduling
 Malheur Experiment Station, Oregon State University: Clint Shock, director and professor; Rebecca Flock, former research aide; Eric Eldredge, faculty research assistant; Andre Pereira, visiting professor.
Center for Agricultural Water Research in China, China Agricultural University: Feng-Xin Wang, associate professor
 Oregon State Extension Service UNIVERSITY
 I n the late 1980s, the U.S.
Pacific Northwest potato industry faced a crisis.
Potato tuber quality was inadequate to meet the needs of potato processing companies due to a condition called "sugar ends" or "dark ends" in fried tuber slices.
This defect was common in tubers grown on stressed Russet Burbank plants, but the stresses aggravating the condition were poorly understood.
Growers lost contracted acres.
In 1989, northern Malheur County was declared a groundwater management area due to groundwater nitrate contamination.
The groundwater contamination was linked, at least in part, to furrow irrigation of potato.
All irrigation systems in arid regions require some leaching fraction to avoid salt accumulation.
However, with the high nitrogen  fertilizer rates used through the 1980s, and heavy water applications on furrow-irrigated potato, N and other mobile nutrients were readily lost to deep percolation and in runoff.
In response to these problems, the Malheur Experiment Station began research to determine the soil water requirements for potato production in the Treasure Valley by carefully monitoring soil water status using soil moisture sensors.
As growers modified irrigation and other practices to minimize water stress on potato plants during tuber development, sugar ends became less prevalent.
At the same time, alternative irrigation systems were also tested.
Experiment Station research and grower experience found that sprinkler irrigation could reduce sugar ends and improve tuber grade.
Some growers purchased or leased sprinkler irrigation systems.
Growers regained contracted acreage by learning to schedule irrigation, shifting to less susceptible varieties, and converting from furrow to sprinkler irrigation.
Other growers, however, were unwilling to plant potatoes again.
If potatoes were SO unpredictable, they wondered, how could they consistently produce a quality crop?
However, new understanding of potato development and new information resources have largely taken the mystery out of irrigated potato production in the Treasure Valley.
Irrigation method is an important consideration in irrigation scheduling.
For potatoes, the leading irrigation method is sprinkler irrigation of hilled rows.
Furrow irrigation is still widely used worldwide.
Drip irrigation is an option as the agricultural community has gained familiarity with the system.
Drip irrigation advantages, disadvantages, and methods are discussed in Drip Irrigation Guide for Potatoes, EM 8912.
Potatoes have little tolerance for water stress.
Tuber market grade, tuber specific gravity, and tuber processing quality for French fries are all critically influenced by water stress during tuber bulking.
The incentives for a grower to maintain a precise irrigation schedule to keep the soil water potential within a narrow range of values are significant.
Underirrigation leads to losses in tuber quality, market grade, total yield, and contract price.
Overirrigation leads to erosion, disease susceptibility, water loss, extra energy costs for pumping, N leaching, increased crop N needs, and tuber loss in storage.
In order for an irrigation schedule to be effective, it has to tell us when to water and how much to apply.
Scheduling methods that are successfully used in the Treasure Valley of Oregon and Idaho are:
 Crop evapotranspiration using the checkbook method
 Soil water tension or soil water content using a graph of soil moisture
 A combination of these two methods
 Crop evapotranspiration  is the combined evaporation of water from the soil surface and crop water use (transpiration of water through
 plant tissue).
Crop evapotranspiration values are calculated using weather stations in a production region.
In the Treasure Valley, ET data are available online through AgriMet, a U.S.
Bureau of Reclamation cooperative agricultural meteorological network for the Pacific Northwest.
Other areas are served by public meteorological networks.
Weather stations that estimate evapotranspiration are also sold for farm use.
To illustrate how ET works, think of the soil as a checking account and the water in it as the money in the account.
You keep a record  of all the charges and deposits made to the account.
You can run up your charges only to a certain point; after that you must make a deposit, or get an "overdraft." At this critical balance, although there is still water in the soil, its scarcity places tuber yield and quality at risk.
To use this method of irrigation scheduling, you must have access to the following:
 AgriMet or other local weather station information to estimate potato crop water use  based on the crop coefficient and crop development data.
A rain gauge placed in each production field or group of adjacent fields.
A good estimate for the allowable depletion of water for each soil type.
The allowable soil water depletion for potatoes can be calculated if you know the following:  potato plants' effective rooting depth in a given soil and  the soil's water retention characteristics in the range where the potato plant does not suffer water stress.
Be careful not to overestimate either the root zone depth or the soil's capacity to hold water.
When using this checkbook method, keep the following in mind:
 Spending depletes your account.
Water use by the plant plus losses from evaporation make up the ET estimated by AgriMet or other service.
Table 1.
This sample of an AgriMet table gives ET for Shepody potato  with an emergence date of May 5 , and for Russet Burbank potato  with emergence dates of May 15 and May 23.
Columns entitled Daily Crop Water Use display the calculated value as inches per acre for the past 4 days, while the Daily Forecast predicts water use for the current day.
The last two columns provide the 7and 14-day accumulated ET.
ESTIMATED CROP WATER USE AUG 15, 2005 ONTO
 DAILY	*	*	*	*	*	*
 *	CROP WATER USE-	DAILY *	*	*	*	7	*	14	*
 * CROP START	*	PENMAN ET AUG	* FORE * COVER * TERM * SUM * DAY * DAY *
 *	DATE	*	*	CAST	*	DATE	*	DATE	*	ET	*	USE	*	USE
 *	*	11	12	13	14	*	*	*	*	*
 *	*	*	*	*	*	*	*
 * POTS	505	*	0.29	0.27	0.26	0.20	*	0.24	*	610	*	901	*	25.9	*	1.8	*	3.6	*
 *	*	*	*	*	*	*	*	*
 * POTA	515	*	0.39	0.36	0.35	0.28	*	0.33	*	710	*	920	*	22.7	*	2.4	*	4.6 *
 *	*	*	*	*	*	*	*	*
 * POTA	523	*	0.40	0.37	0.36	0.28	*	0.33	*	710	*	925	*	21.7	*	2.4	*	4.6	*
 Deposits refill the account.
Applied irrigations plus rainfall  are considered deposits.
You can get an "overdraft." Overcharging your bank account or paying a bill late results in a penalty.
The same is true here.
Letting the field get too dry will result in tuber yield and grade penalties.
Keep in mind that water stress can occur by watering only 1 day late.
The soil water account for potato has a limited size.
If there is more rain or irrigation than the soil can hold, the excess is lost.
Table 2 shows an example of the checkbook method of irrigation scheduling by crop evapotranspiration.
In this example, ET is tallied for a potato root zone with an allowable depletion of 1.2 inches of water.
The soil is Owyhee silt loam, a common soil around Ontario, Oregon.
The daily potato evapotranspiration amounts are the August 2005 AgriMet estimates at this arid location, but the rainfall events are hypothetical, for instructional purposes.
Let's suppose that each irrigation supplies 1.2 inches of water, thus replenishing the allowable depletion.
Table 2.
The checkbook method of irrigation scheduling where a silt loam soil has 1.2 inches of allowable depletion for potatoes.
Date	Daily ET	Rain	ET
 Action				
 Irrigate	4	0.32	0.15
 6	0.29	0.08	0.67
 7	0.27	1.45	-0-
 Irrigate	11	0.40	0.20
 Irrigate	15	0.26	0.27
 Irrigate	19	0.25	0.07
 Rainfall is subtracted from the net ET.
If rainfall makes the net ET account negative, the negative balance is dropped, and net ET is set to zero for that day.
The negative balance is dropped because it represents water applied in excess of the root-zone water-holding capacity; this water is lost to runoff or leaching, typically within 24 hours.
Note that the ET for the day of irrigation is also added; thus, net ET accumulated up to the day of irrigation includes the ET for that day.
Irrigation never exceeds 1.2 inches because the extra water would be quickly lost to runoff or leaching.
The grower decides when to irrigate by not allowing net ET to exceed the allowable depletion.
To avoid getting an "overdraft," he must begin irrigation on the day the balance would have exceeded 1.2 inches.
The grower knows how much to irrigate by replacing only the soil's allowable depletion.
There is no mystery here.
We have made clear decisions about when to irrigate and how much water to apply: the result is successful potato irrigation.
The checkbook method on sandy soil?
The checkbook method operates in the same way on a sandy soil, but the irrigation frequency is much higher and irrigations typically are much smaller.
Assume irrigations of 0.33 inch and a 0.5-inch allowable water depletion for potatoes.
Table 3.
The checkbook method of irrigation scheduling where a sandy soil has 0.5 inch of allowable depletion for potatoes.
Date	Daily ET	Rain	ET
 Action				
 Irrigate	2	0.34	0.36
 Irrigate	3	0.34	0.37
 Irrigate	4	0.32	0.36
 Irrigate	5	0.31	0.34
 Irrigate	6	0.29	0.08	0.22
 7	0.27	1.45	-0-
 Irrigate	9	0.31	0.27
 Irrigate	10	0.40	0.34
 Irrigation scheduling by soil water content
 On sandy soils, irrigation scheduling by the checkbook method alone has a narrow margin of error.
Measuring the trend in soil water content in conjunction with the checkbook method can help assure that the field is not getting too dry or too wet.
Regular measurements are made by neutron probe or by other equipment and are plotted over time.
Irrigation scheduling by Soil Water Tension 
 Another effective method for irrigation scheduling is based on soil water tension.
SWT is a measure of how strongly water is held by the soil.
Potato plant performance is closely related to the amount of tension the plant has to exert to move water from the soil into the plant roots.
That force can be measured using tensiometers, Granular Matrix Sensors , or other devices.
GMS  measure SWT using a battery-powered meter.
These measurements are recorded, and they provide information about when to irrigate.
Since 1988, SWT readings from GMS have been used to schedule irrigations in Malheur County growers' fields.
Six or more GMS can characterize the soil water tension in a field, provided they are installed in representative areas and are responsive to ET and irrigations.
The six GMS may be distributed widely across an area with similar irrigation needs.
Sensors are installed 8 inches deep in the potato row between two healthy plants.
Wires from sensors in a given area are brought to a single easily accessible location, such as a field edge, for rapid reading.
Irrigation onset criteria must be developed for each production environment.
Criteria for irrigation onset by SWT depend on the climate, soil, and irrigation system in use.
Studies have determined criteria from 20 to 60 centibars.
The SWT irrigation criteria that optimize potato yield and grade vary by production area and irrigation system.
Based on potato yield and grade responses to irrigation, ideal potato SWT irrigation criteria are as follows:
 50 to 60 cb for sprinklers on silt loam in Oregon 
 60 cb and 30 cb for furrow and drip irrigation, respectively, on silt loam in Oregon 
 50 cb for furrow irrigation on loam in California
 25 cb for sprinklers on silt loam in Maine
 20 cb for sprinklers on sandy loam in western Australia
 When to irrigate on silt loam in the Treasure Valley?
Read sensors daily and plot the data on a graph for immediate interpretation.
On silt loam, tuber growth and grade are maximized when irrigation occurs before the average readings at the 8-inch depth reach 60 cb for sprinkler and furrow irrigation systems or 30 cb for drip systems.
Moderate water stress causes little damage to potatoes before tuber initiation, but during tuber development even small amounts of water stress  can result in decreased tuber grade.
On silt loam, water stress beyond 60 cb
 An SWT scale for potato
 > 80 cb indicates dry soil and water stress for potato plants.
20 to 60 cb is the range that indicates it's time to irrigate, depending on location, soil type, and irrigation system.
10 cb is close to field capacity.
0 to 10 cb indicates the soil is saturated with water.
Figure 1.
Sprinkler-irrigated potato with irrigation criteria of 60 cb on silt loam at Ontario, OR.
Soil water tension drops following each irrigation.
The irrigation on July 12, while replacing ET, did not get the soil wet around the GMS because the previous four irrigations did not refill the root zone.
Figure 2.
Drip-irrigated potato with small drops in soil water tension following irrigations on silt loam at Ontario, OR.
Irrigations are much more frequent.
They maintain an average SWT wetter than 30 cb and do not saturate the soil.
results in decreased specific gravity and increased incidence of dark-end fry colors in susceptible cultivars such as Russet Burbank.
A single, short-duration incident of water stress  can lead to reduced tuber grade and increased dark fry colors.
In one experiment, a single episode of water stress, with GMS readings reaching an SWT of 75 cb or more, resulted in a loss of USDA No.
1 grade tubers, correspondingly more USDA No.
2 grade tubers, and losses in tuber solids.
A single stress episode with GMS readings of 75 cb or drier was associated with increased incidence of the darkest fry colors: USDA No.
3 and No.
4.
Total yield generally is unaffected by one brief episode of stress, but reduced tuber quality can render the crop unprofitable.
Thus, it is critical to maintain SWT at adequate levels.
However, it is very difficult to gauge water stress without a quick, reliable field determination of soil water tension.
GMS provides this capability.
When viewed in graphical form, SWT clearly indicates the current condition of the crop root zone and how rapidly water is being depleted.
Methods for determining crop water needs and installing and managing granular matrix sensors and tensiometers are discussed more thoroughly in Irrigation Monitoring Using Soil Water Tension, EM 8900.
Combining SWT with ET
 A powerful way to schedule irrigation is to combine the ET and SWT methods.
The strong point of SWT is its ability to predict stress before it occurs, while the strong point of ET is its ability to prevent overirrigation.
Combine the two methods by irrigating when the average tensiometer or GMS reading reaches the SWT criterion and applying enough water to replenish ET but not more than needed to refill the root zone.
Dataloggers that automatically read GMS and record SWT can facilitate irrigation management.
The data can be viewed with the push of a button and can be downloaded to a laptop computer or PDA.
Downloaded data can be imported into a spreadsheet and graphed.
The SWT graphs constructed from the stored data make it possible to determine soil moisture trends and to predict or modify irrigation schedules at each GMS location.
The dataloggers also can include soil temperature sensors to correct the SWT data.
Irrometer Co., Inc.
makes the Watermark Monitor, which automatically stores readings from up to eight sensors, including a temperature sensor and pressure switches for recording irrigation events.
Data intervals can be set from once a minute to once every 24 hours.
Data can be downloaded from the Watermark Monitor to a laptop or PDA in the field, or can be transmitted by radio or cellular modem to a remote computer.
The AM400, by M.K.
Hansen Co.
, automatically records readings every 4 or 8 hours from six GMS and a temperature sensor.
Data can be downloaded at the end of the season or as needed.
By pushing a button, the grower can view soil moisture graphs of the recorded data.
Other types of equipment can also be automated.
Potato varieties that express fewer negative characteristics when subjected to stress have been identified.
One of these varieties, Shepody, has become more popular with growers and processors in the past decade.
Other varieties, including Ranger Russet, Umatilla Russet, and other experimental varieties, are discussed in Malheur Experiment Station annual reports and in Shock et al..
Excessively wet soil is conducive to many tuber-rotting pathogens, encouraging the incidence of blights, rots, and wilts that can limit
 yield, tuber quality, tuber size, tuber dry matter content, and crop marketability at harvest or from storage.
Dense canopy growth, long periods of leaf wetness, and high relative humidity create microenvironments that favor disease infection.
Improperly managed irrigation often keeps the vines wet for long periods of time, exacerbating the risk of infection.
Diseases promoted by overirrigation include:
 Late blight 
 Early blight 
 Soft rot 
 White mold 
 Black leg 
 Potato leak 
 Pink rot 
 Rhizoctonia canker 
 Powdery scab 
 Verticillium wilt 
 Prolonged periods of saturation following planting can promote seed piece decay as well as poor and erratic tuber emergence.
Funding to help prepare this publication was provided by an Oregon Watershed Enhancement Board Grant.
Potato is a water-stress-sensitive crop.
Potato plants are more productive and produce higher quality tubers when watered precisely using soil water tension  or soil water content than if they are underor overirrigated.
Potatoes are more sensitive to water stress than are most other crops.
Potatoes have a relatively shallow root system that provides very little margin for irrigation errors.
Yield reductions due to overirrigation can be attributed to poor soil aeration, increased disease problems, and leaching of nutrients from the shallow crop-root zone.
Granular Matrix Sensors provide good estimates of SWT for many soils.
They are particularly effective in silt loam soils typical of much of the Treasure Valley.
SWT provides useful guidelines to avoid water stress by projecting when to irrigate.
A soil water potential of -30 cb is the same as a soil water tension of +30 cb.
Also, cb  is the same as kPa.
In the Treasure Valley, sprinklerand furrowirrigated potatoes on silt loam are irrigated at an SWT of 60 cb.
With drip systems, potatoes are irrigated at an SWT of 30 cb.
Irrigation to replace estimated crop water use  can be an effective way to irrigate potatoes with a sprinkler or drip system.
2013 Oregon State University.
Extension work is a cooperative program of Oregon State University, the U.S.
Department of Agriculture, and Oregon counties.
Oregon State University Extension Service offers educational programs, activities, and materials without discrimination based on age, color, disability, gender identity or expression, genetic information, marital status, national origin, race, religion, sex, sexual orientation, or veteran's status.
Oregon State University Extension Service is an Equal Opportunity Employer.
Trade-name products and services are mentioned as illustrations only.
This does not mean that the Oregon State University Extension Service either endorses these products and services or intends to discriminate against products and services not mentioned.
Use: irrigate each part of the field as needed because of variability caused by precipitation, runoff, evapotranspiration, and/or drainage, VRI type: both, prescription type: dynamic, management intensity: high.
Center pivot irrigation systems have several potential hazards, so personal safety is a priority.
Hazards range from missing driveshaft covers to possible falls from ladders and towers.
The primary safety concern is electrical safety, since many center pivot systems use a high voltage  power supply to pump water and/or to run a number of electrical motors at the towers used to move the system.
If not properly wired and grounded, the combination of metal structure and wet environment will increase the likelihood for electrocution.
For potatoes in the early emergence crop growth stage the estimated water use during the previous week of May 29 June 4, 2023 is 0.12 inches and the estimated water use during the week of June 5-11, 2023 is 0.85 inches.
For potatoes in the vegetative crop growth stage the estimated water use during the previous week of May 29 June 4, 2023 is 0.15 inches.
Chapter 3: IPM Solutions to Pest Management for Corn Production
 Integrated pest management  is not new but has gained interest as growers attempt to reduce production costs while simultaneously reducing the risk of pest resistance to chemical and biological agents.
IPM activities may include using crop rotation, early harvesting, rotating pest control mechanisms, adjusting planting dates and populations, conducting mechanical cultivation, applying appropriate fertilizers, using crop varieties with disease or insect resistance, minimizing planter and chemical application skips, and using biological control agents.
All IPM tactics require using the labeled rate.
The adoption of IPM is important because: 1) pests are becoming resistant to chemical control agents, 2) most of the new chemical control agents are reformulations of old chemistries, and 3) chemical and biological control mechanisms also kill beneficial organisms.
This chapter discusses the role of IPM and how adopting IPM practices can improve long-term sustainability.
Integrated pest management  is a sustainable decision-making process that requires continued assessment of the crop situation and knowledge of the pest being controlled.
A critical component of IPM is the use of a record-keeping system.
A good field record system includes information such as field location, rotation, scouting date, genetics used in the field, fertilizers applied, soil test numbers, current field conditions, previous pest infestations, and previous pesticides applied.
Mapping of the present pest locations in the field makes future management decisions easier.
Enough information should be collected when scouting to make an accurate recommendation.
Scouting should note the plant growth stage, pest growth stage, size of the infestation, type and density of the infestation relative to the economic threshold, health of the pest, and whether the pest population is increasing or decreasing.
In addition, an image of the pest should be collected and placed in the scouting book.
In general, the ability to respond effectively to a pest increases with scouting frequency.
However, the scouting intensity should be balanced against costs.
Scouting information is needed to determine the appropriate control measures.
When the pest population approaches economically damaging levels, the producer will need to monitor more frequently and be prepared to make a decision.
Before applying a pest treatment, the agronomist should ask: is treatment necessary?
The presence of a pest may fall below the economic threshold value.
Most plants have internal mechanisms to control pests.
For example, plants may grow faster in response to shading, whereas other plants may release chemicals that
 attract beneficial insects.
Most plants can tolerate at least some pest damage before economic yield loss occurs.
The point where the control costs are equal to the yield loss is the economic threshold.
If treatment is necessary, does the entire field or just part of the field need to be treated?
Depending on the pest and crop involved, a border treatment may reduce costs while preventing further damage.
And finally, when should an action be taken?
Timing is very important because the damage is different for different growth stages.
IPM is based on Prevention, Suppression, and Eradication
 Prevention: The first line of defense.
In prevention, a treatment is implemented in response to known problem.
Preventative approaches include hybrid selection, rotations, modifying row spacing, adjusting plant populations, using cover crops, using pest-free seed, preventing weeds from reproducing, using insect trap crops, and using maturity dates that avoid pest problems.
Other possible cultural tactics include elimination of alternate hosts or sites for insect pests and disease organisms, such as clearing field borders or waterways, and practicing good sanitation measures, such as cleaning tillage and harvesting equipment when moving from field to field.
Suppression: The second line of defense.
1.
1) In suppression, corrective solutions are used after a problem has been detected.
The goal of suppression is to reduce the economic impact of the problem.
Common examples include cultivation, mowing, flaming, flooding, and plastic mulches.
Keeping a weed from going to seed by mowing, clipping, or plowing the infested area is an example of physical control.
The biological controls work best where the long-term impacts are the primary objective.
2.
2) Chemical control techniques are widely used to reduce pests.
When using chemical control, consider the economic threshold, do not use partial rates, and make sure the applicators are calibrated.
Faulty or worn-out equipment should be replaced.
When applying chemicals it is important to rotate the chemistries if possible.
Pests are resilient, and in many situations, the routine use of any given control mechanism can result in the development of resistant populations.
Precision technology provides the opportunity to reduce this risk by actually applying pesticides to areas of the field where the pest populations usually exist.
Safety of the pesticide being used should always be a concern.
Eradication: The third line of defense.
Eradication is the complete elimination of the pest and generally it is used for exotic pests that produce dire consequences.
Draining a lake to control an invasive plant or fish would be considered eradication.
In most agricultural activities, eradication has produced short-term successes.
An example is Plum Pox virus eradication in plums in Pennsylvania and New York.
The pest monitoring process is referred to as field scouting, and specific scouting methods have been developed for different pests and crops.
Scouting tools include sweep nets, sticky traps, aerial images, and pheromone traps.
The plant growth stage  is a common technique used to assess plant development.
Proper identification of the pest, plant growth stage, soil conditions, and climatic conditions is extremely important in the monitoring process.
Scouting frequency varies with temperature, crop growth, developmental stage, and pest population potentials.
If a pest population is approaching economically damaging levels, the field may require more intense scouting.
Cost of scouting may impact scouting intensity and frequency.
A general guideline is to scout each field at least weekly during the growing season.
A good field-scouting program should provide the following information about the field:
 1.
What pests are present and level of infestation.
2.
Stage of growth of each pest and the crop.
3.
If the pests are parasitized or diseased.
4.
If aphids look mummified.
5.
If pest infestation level is increasing or decreasing.
6.
General physical field conditions.
7.
Insect/weed/disease pocket guidebooks.
8.
Recent pest alert report.
9.
Plastic bag, paper towel.
10.
Notebook and pen/pencil or iPad.
In summary, IPM is not a single product that can be purchased, like a drum of pesticide, and it does not rely on one "silver bullet" method to solve all problems.
Successful IPM programs require planning and knowledge of the crop pests.
Reviewing several soil water logs from central Nebraska, many fields were left a little drier than normal after 2022s harvest.
Plus, with many areas of the state getting very little precipitation from October through May, many fields have needed some irrigation to get the crop established and growing well through the vegetative stage.
It all depends on the amount of water stored in the soil.
Moving effluent from one place to another is expensive because it is very heavy for the amount of nutrients it contains.
If tanker spreaders are used, the volume requires lots of trucks or many trips back and forth from the storage to the field, causing wear and tear on equipment as well as roads.
Whenever the crop-available soil water amount falls below the threshold for irrigation or the crop is under water stress, the program will recommend irrigation if no significant rain is expected in the next three days.
The message is displayed at the top of the screen.
Analyses of Irrigation Water waters of six rivers and nine wells in California studied to establish their usefulness for irrigation
 This is the second of two articles on the quality of water and plant tolerance to salts.
The previous article, in the October issue of California Agriculture, explained the classification of irrigation waters in three groups: Class I.
Excellent to Good-Safe and suitable for most plants under any condition of soil and climate.
Class II.
Good to Injurious-Possibly harmful for certain crops under certain conditions of soil or climate.
Class Injurious to Unsatisfactory-Probably harmful to most crops and unsatisfactory for all but the most tolerant.
Classification of irrigation water into
 three groups is by necessity an arbitrary arrangement and is of value for the purpose of orientation and as a guide.
Analyses of six river and nine well waters in California are given in the accompanying table.
Any of these waters with one constituent falling in a poorer group will automatically be placed in that class, although probably not of as poor a quality water as one having two constituents in the lower class.
The waters in the table are listed in the order of increasing salt concentrations.
The river waters are Class I, except No.
4 which being high in boron, is placed in Class II.
Waters No.
1 and No.
2, very low in total salts, are typical of the river waters flowing from the high Sierra Mountains into the great valleys of California.
The San Joaquin River, No.
5, in the upper reaches has about the same concentration of salt as No.
1 and No.
2, but this sample includes some return flow or drainage water from the valley floor with an increase in salt concentration.
The water is still first class, but indicates contamination.
Colorado River water, No.
6, is near the upper limits of Class I, but the principal salt in this water is calcium sulfategypsum-and is one of the least toxic of the salts occurring in irrigation water.
Many of the wells in California have Class I water.
However, there are some areas and many individual wells that contain high concentrations of certain salts.
The well waters listed in the table are not necessarily typical irrigation waters, but rather have outstanding peculiarities.
No.
7 and No.
10 are representative of the Class I and represent the range of salt concentration that usually occurs in first quality well water.
No.
10 predominates in calcium and magnesium bicarbonates, a form of lime not considered harmful.
Many highly productive western soils are high in lime.
No.
8 is similar to seven except for its high percentage of sodium.
When this type of irrigation water is used, infiltration problems soon develop.
An irrigation water high in sodium percentage has a tendency to seal the surface soil preventing deep percolation.
No.
9 is extremely poor in quality because of the high boron content and high sodium percentage.
The sodium soon would seal the soil and prevent the removal of boron by leaching, and before long the most boron-tolerant plant species would not survive.
No.
12 is classed as a second quality water because of the total concentration of salts-K = 137.
None of the individual ions is extremely high and consequently it is a better water than No.
11 which has a high per cent sodium, although the total concentration of salts are less-K = 109.
Water No.
13 contains sodium chloride-common table salt-with the chloride content sufficiently high to place it definitely in Class III.
Since chloride is
 one of the more toxic elements, its accumulation would be enhanced by sealing of the soil from the high percentage sodium.
Waters No.
14 and No.
15 are placed in Class II and III, respectively, because of their high salt content.
Sulfates, predominating in these waters, are probably harmful to plant growth at the concentration of water No.
15, particularly when accompanied by a high sodium concentration.
Gypsum waters, mainly those containing calcium sulfate are not particularly harmful, and fairly high concentrations of gypsum can be tolerated.
Well water, or underground water, contains minerals in varying proportions, depending upon the type of material through which the water percolates.
Water may enter water-bearing mateContinued on page 14
 Analyses of Selected River and Well Waters Used for Irrigation
 Milligram equivalents per liter
 No.2	K x 105	25C	p.p.m.
B	Anions	Cations	Na	%	Class1
 HCO	CI	so	Ca	Mg	Na
 1	6.4	.06	.55	.05	.03	.30	.11	.22	35
 2	7.7	.03	.70	.10	.31	.37	.16	.58	52	I
 3	15.0	.05	1.22	.13	.12	.63	.51	.26	18	I
 4	40.7	1.24	2.68	.81	.44	1.32	1.75	1.17	32	II
 5	46.7	.12	1.69	2.06	.58	1.26	1.10	2.01	46	I
 6	98.0	.16	2.46	2.05	5.73	4.78	1.74	3.57	34	I
 7	26	.13	1.88	.34	.33	1.41	.44	.89	32
 8	27	.10	1.20	.68	.67	.21	.05	2.42	90	III
 9	79	6.90	2.39	2.47	2.48	.24	.02	7.28	96	III
 10	90	.51	8.87	1.13	1.02	2.49	5.81	2.83	25	I
 11	109	8.10	1.00	2.60	1.20	2.00	8.10	72	II
 12	137	.25	2.46	2.73	4.47	8.30	.75	3.96	30	II
 13	174	.71	1.02	12.04	1.80	2.14	.08	12.67	85	III
 14	255	.50	2.80	2.8	23.00	11.40	5.70	12.90	45	II
 15	433	1.63	2.75	8.55	41.74	12.37	16.71	27.39	49	III
 1 The underlined constituents place waters in Class II or III.
1--Mokelumne River, near Lodi.
2-Kern River, Beardsley Canal.
3-Sacramento River, 35 miles above Sacramento.
4-Cache Creek, Capay Dam.
5-San Joaquin River at EI Solyo.
6-Colorado River, east side canal, Imperial Valley.
7 to 15-Selected wells used for irrigation in California.
WATER Continued from page 6
 rials-generally, coarse sand and gravel strata-and as it slowly flows or percolates through the strata, it dissolves minerals from the rock and soil in varying quantities.
If the minerals dissolved are in the form of calcium and magnesium salts the water is known as hard water, and common soaps do not form suds readily in it.
This type of water is usually considered good for irrigation purposes, as only occasionally do the calcium and magnesium salts reach a concentration toxic to plant growth.
An example of this type of water would be No.
10 of the table.
Soft water, on the other hand, may come from either of two sources: 1, rain water containing very few minerals; this usually will include runoff waters from melting snows or excessive rains, which have not had sufficient contact with the soil or rocks to dissolve appreciable quantities of minerals-such as river waters No.
1, No.
2, and No.
3; 2, water containing a high percentage of sodium salts, such as well waters No.
8 and No.
9.
These salts may reach a concentration toxic to plants, but even at low concentrations they cause a deterioration of the soil structure, and with their continued use the surface soil will seal and prevent the wetting of deeper layers.
When sodium salts in the form of chloride-common salt-and sulfates-glauber salts-accumulate in excessive amounts in the soil they are known as white alkali.
Such accumulations may be possible from waters Nos.
13, 14, and 15.
Some leaching of the surface soil should be provided, either by rainfall or excess irrigation to remove the excess soluble salts.
The accumulation of sodium carbonate or bicarbonate-soda ash-forms black alkali.
Water No.
11 with its high bicarbonate and most of the cations such as sodium, would produce a black alkali if its salts are allowed to accumulate in the surface soil.
Small quantities of these salts are much more toxic to plants than the white alkali.
White alkali is easily detected by the accumulation of white or gray salts on the surface of the soil.
The beginning of a black alkali soil is not easily recognized even though the sodium carbonate salts have produced a deteriorated soil structure, with a reduction in rate of water penetration.
This condition can be caused by a much lower concentration of salt than usually occurs in the formation of white alkali soil.
The plants listed in the next column are divided into three major groups according to their salt tolerance.
In each of these divisions the more sensitive plants are placed first in each group with increasing salt tolerance progressively down the listing.
Plant growth is governed by the concentration and toxicity of the salts dissolved in the soil solution.
These salts may have been originally in the soil, or accumulated there from the salts in the irrigation water.
The plants listed are provisional and subject to revision, as additional information is obtained.
A number of factors may influence the salt tolerance of plants, such as climate, soil type, irrigation practice, and varietal differences and types of salt involved.
Relative tolerance of crop plants to salt constituents in the soil solution arranged in order of increasing tolerance:
 Group I.
Crops which may be grown on soils of weak salinity: Fruit crops: lemon, orange, apple, plum, peach, apricot, almond, pear, grapefruit.
Field and truck crops: green beans, potato, sweet potato, eggplant, artichoke, cabbage, celery, peas, vetch.
Forage crops: burnet, ladino clover, red clover, alsike clover, meadow foxtail, white dutch clover.
Group II.
Crops which may be grown on soils of medium salinity: Fruit crops: olive, grape, fig, pomegranate.
Field and truck crops: wheat, pepper, onion, squash, spinach, carrot, sunflower, lettuce, cantaloupe, rice, oats, rye, barley, sorghum, foxtail, millet, asparagus, tomato, flax, alfalfa.
Forage crops: sickle milk vetch, sour clover, cicer milk vetch, tall meadow oat grass, smooth brome, big trefoil, reed canary, meadow fescue, blue grass, orchard grass, tall fescue, alfalfa, herbam clover, sudan grass, dallis grass, strawberry clover, birdsfoot trefoil, sweet clover.
Group III.
Crops which may be grown on soils of strong salinity: Fruit crops: date palm.
Field and truck crops: cotton, kale, rape, milo, garden beets, sugar beets.
Forage crops: western wheat grass, beardless wild rye, Canada wild rye, fescue grass, rhodes grass, bermuda grass, nuttall alkali grass, salt grass, alkali sacaton.
Tolerance to black alkali-sodium carbonate salt-is not considered in the listing as this salt has a high toxic and corrosive action on the plants.
As a measure of tolerance, it is assumed that fair to good yields will be obtained under favorable conditions of climate, soil, and fertilizer.
Plant Tolerance for Boron
 For convenience plants are divided into three groups according to their tolerance for boron, in the following listing.
The plants that withstand only relatively low concentrations have been designated as sensitive, an intermediate group as semi-tolerant, and a final group as toler-
 ant.
However, in some cases and under certain conditions, there are no sharp lines of demarcation.
Within a group the more sensitive plants have been listed first.
Relative Tolerance of Crop Plants to Boron
 	Group	tolerant)	Group II		Group III
 Lemon	Lima bean	Tobacco
 Grapefruit	Sweet potato	Carrot
 Avocado	Bell pepper	Lettuce
 Apricot	Oat	Broad bean
 Cherry	Barley	Sweet clover
 Persimmon	Olive	Garden beets
 Kadota fig	Rose	Mangel
 Grape	Radish	Sugar beets
 Apple	Sweet pea	Artichoke
 American elm	Sunflower	Asparagus
 Navy bean	Field pea
 L.
D.
Doneen is Lecturer in Irrigation and Associate Agronomist, University of California College of Agriculture, Davis.
Continued from page 2
 period while the over-all production of citrus has declined materially, largely because of unfavorable weather conditions.
Prices of meat animals, dairy products, and poultry and eggs have increased very materially in the last three years, particularly prices of meat animals-cattle, calves, sheep, lambs, and hogs.
The prices in 1948 for these categories were the highest since 1924, the first year for which these indexes were computed.
Production of meat animals in California has increased by about 50% between 1925-1929 and 1942-1946 and has been maintained at about the latter level in the last three years.
During the same period, the production of dairy products and particularly poultry and eggs has increased significantly.
M.
Kuznets is Associate Professor of Agricultural Economics, University of California College of Agriculture, Berkeley.
Index numbers for livestock and livestock products were constructed by Dr.
I.
M.
Lee, Assistant Professor of Agricultural Economics, University of California College of Agriculture, Berkeley.
A more complete technical report of this study-Giannini Foundation Mimeographed Re port No.
102, February 1950-may be obtained by writing to the Giannini Foundation of Agricultural Economics, University of California, Berkeley 4.
BASICS OF IRRIGATION AND INTRODUCTION TO SYSTEMS AND MANAGEMENT IN THE RESIDENTIAL LANDSCAPE
 Brian Leib, Associate Professor, Irrigation Systems and Management Department of Biosystems Engineering and Soil Science Natalie Bumgarner, Assistant Professor and Extension Specialist Department of Plant Sciences
 The central purpose of an irrigation system is to provide adequate water for plant needs, so the discussion on irrigation basics should begin with plants.
All plants have different watering needs, depending on species, season and the environment.
Homeowners and gardeners also need to consider whether the goal is to ensure survival of landscape and garden plants or whether the goal is optimum growth and performance.
For instance, a general statement would be that plants need 0.7 to 1.0 inches of water per week, but this is a figure that applies to loamy soils with good water-holding capacity.
Sandy soils often need more.
In hot weather, these needs may increase to around 1.5 to 2.0 inches per week.
To supplement general watering estimates, it is important that gardeners know the signs signalling that a plant needs water.
Stored soil moisture can provide some of the water needed for plants during hot weather, but most plants need to be watered during extended dry periods.
Gardeners generally do not want to water every day because frequent watering encourages shallow root growth.
So, it is best to add larger amounts of water less frequently.
Sandy soils require more frequent watering than loamy or clay soils that retain water longer.
General signs a plant needs water:
 Leaf color is darker and may have a bluish cast.
Plant wilts, droops or has no upright stature.
Leaves or stems get black spots.
Stems appear dried out or woody on new growth.
Plants experience little or no growth.
Soil is dry more than 4 to 6 inches below the surface.
GUIDELINES FOR DIFFERENT PLANT MATERIALS
 Some rules of thumb were mentioned above for watering requirements, but the following list contains more information on watering specific types of landscape plants.
However, we
 always recognize that plant needs can be highly variable based on environmental conditions, species and plant establishment.
Annuals and vegetables: Water when the top 4 to 6 inches are no longer moist; seedlings and transplants may need to be watered when the top 1 to 3 inches of soil starts to dry out as they are establishing new roots.
Check soil often to ensure it stays moist.
The depth of a shovel in soil can provide a simple way to observe soil moisture within rooting areas.
Be aware of rainfall and consider using general estimates, such as watering three days after light rain events and up to seven days after heavy rainfall events.
Use a natural or organic mulch to maintain more consistent moisture levels.
Perennials: Many native and adapted species that are established  may not require regular watering under relatively normal conditions.
Newly planted perennials should be watered deeply to encourage deep rooting while establishing.
Even established and well-adapted plants likely will need supplemental irrigation under stressful and moderate to long-term low rainfall periods.
Trees and shrubs: Established trees and shrubs should not need to be watered unless conditions are extremely dry.
Trees absorb water best when it soaks to a depth of up to 12 inches.
During warm weather a tree needs 10 gallons of water per inch of tree diameter every one to two weeks.
Using mulch instead of grass under a tree can reduce the competition for water.
It is important to be aware that established trees and shrubs often need little irrigation under relatively normal rainfall.
However, newly planted material should be watered frequently because container media can dry out more quickly than the surrounding soil.
So, moisture should be managed carefully until the plant has root established in the soil.
Other UT Extension publications contain more details on planting and managing trees and shrubs.
Grass: Grass generally needs about 1 inch of water per week.
Water if footprints show after someone has walked on the turf.
However, across the state of Tennessee, there is a wide range of warmand cool-season turfgrass species, and management can differ considerably based on rooting depth of the turfgrass species, soil conditions and establishment.
CALCULATING WATER NEEDS AND WATERING TIME
 To further illustrate watering needs during hotter periods, let's take an example of a 1,000-square-foot garden  on a hot summer day in July in Tennessee.
This garden may use more than 150 gallons of water per day, with the majority of days during July and August around 125 gallons.
Although some rainfall usually will occur during these months, there will often be periods of several days to a few weeks when it will be necessary to supply the total daily water needs from other sources.
To convert these water needs into hand-watering time, let's use a garden hose  as an example, that typically flows at a rate of 2 to 3
 HOW LONG WOULD A GARDENER NEED TO WATER THEIR 1,000-SQUARE-FOOT GARDEN WITH A HOSE IN JULY AND AUGUST?
0.2 inches water per day = 0.0167 ft  7.5 = conversion factor ft3 to gallons 1,000 ft2 0.0167 7.5 = 125 gallons per day 125 7 = 875 gal per week Water hose with spray wand 3 gallons per minute 875 gal / 3 gal/min = 292 minutes Approximately five hours/week, but the garden might be best watered in two or three applications to prevent losses from runoff.
gallons per minute.
Determining the rate of water application can be done simply by timing how fast a 5-gallon bucket is filled.
To provide weekly water needs for this garden, it would require roughly one and a half hours of watering every two to three days; see calculations in the adjacent sidebar.
Regions across Tennessee repeatedly have experienced drought conditions over the last decade.
A drought can simply be defined as an extended period of time when a region experiences below average moisture conditions.
During these periods, certain gardening practices  are particularly important to conserving soil water.
Weeds use water just like desirable plants do.
Controlling weeds through the season when they are small will help reduce total water use.
Mulches help reduce water loss from the soil surface by evaporation.
This is especially true if the plants are small or widely spaced.
The reduced water loss improves uptake of nutrients and may help control some problems that are related to a variable water supply, such as blossom-end rot in tomatoes.
Organic mulches improve infiltration, and black plastic mulches greatly reduce infiltration but reduce evaporation.
Mulches also help in weed control.
Compacted soil layers restrict plant root growth.
This reduces the total soil volume from which plants absorb water.
Soil compaction is most often caused by traffic or tillage on wet soil.
If the soil becomes compacted, tilling to break up the compacted zones will allow more extensive rooting and a reduction in drought stress.
Keep in mind that tilling increases soil moisture losses, so it should not be done during drought conditions.
UNDERSTANDING IRRIGATION SYSTEMS BASICS
 During drier periods, which could be 10-12 days without a soaking rain, most plants need to be watered.
The goal of watering plants or irrigating  is not to water the plants, but to replenish the water in the soil that can be accessed by plants.
In other words, the purpose of irrigating is to supply water for the land, which supplies water to plants.
Two common gardening mistakes are overwatering or adding too little water too late.
If water is ponding on the surface and the soil is waterlogged for several hours after watering, too much is being added.
By observing soils and plants, gardeners will soon develop a good feel for irrigating.
There are many types of irrigation systems available for residential lawns, landscapes and gardens.
Table 1 provides an overview of irrigation systems.
They include sprinklers that distribute water more than 50 feet as well as drippers, which provide water to a small circular area of soil.
For the majority of homeowners, a domestic water supply can limit the design flow rate of an irrigation system.
Municipal residential utilities often have a 3/4-inch meter with a typical flow rate maximum of 10 gallons per minute.
Residential wells often have a rate of flow between 5 and 20 gpm.
Water supplies must provide needed flow in addition to having enough pressure to overcome losses due to friction and differences in elevation.
For example, a sprinkler that sprays more than 25 feet often requires 35 pounds per square inch  of pressure.
To overcome losses in the system, 45 psi is often needed at the faucet.
MEASURING FLOW AND PRESSURE
 A gauge and valve can be used to determine flow rate and pressure.
You will need a pressure gauge that can read between zero psi and 100 psi.
If the plan requires connecting an irrigation system to the main line going to a house, a professional may need to complete the job.
However, useful information can still be gained by making these measurements.
Readings taken generally will be lower than those taken from the city main line.
For a small-acreage system, these readings are sufficient.
First, you need a valve to restrict the flow downstream of the pressure gauge.
A PVC ball valve is easy to use, and all of the fittings can be purchased from a hardware store.
A 3/4-inch pipe to garden hose adapter likely will be needed.
Pressure and flow rate are related, but pressure versus flow rate is different for every system.
The pressure gauge should be connected to the manual valve on a hose bib or a hydrant that is fully open near the point of connection for the proposed irrigation system.
After the hose bib or hydrant is fully open, the ball valve should be opened one position at a time.
Pressure and flow are measured by:
 1) Determining how long it takes to fill a 5-gallon bucket and
 FIGURE 2.
Measuring flow rate and pressure by connecting a pressure gauge to a bib or hydrant.
FIGURE 3.
Pressure and flow rate are related.
then dividing that number by the 5-gallon volume.
Keep in mind that there are 60 seconds in a minute.
For instance, if it takes 30 seconds  to fill up the 5-gallon bucket, the flow rate would be 10 gallons per minute; or
 2) Determining how many times the flow meter needle turns in one minute and calculating gpm.
As flow increases, pressure should drop.
Keep in mind that the pressure versus flow rate relationship is different for every irrigation system.
Therefore, it is important to ensure that a design flow rate maintains enough pressure to operate the desired irrigation equipment.
This may require some research and potential alteration.
The utility can provide potential pressure and flow at a location, and a pressure reducer can often be adjusted to provide more or less pressure as required for irrigation.
On a well system, there can be a pressure gauge on the pressure tank that can be used for rating pressure and flow as a bucket is filled.
The pressure switch that controls when the well pump is turned on and off in conjunction with the pressure tank can be adjusted to better accommodate an irrigation system, but adjusting the pressure switch will not create more flow and pressure if the well pump size is limiting output.
COMMENTS	of irrigation Simplest form	Intensive Labor	be furrows effective in short For runs, can	for of soils.
beds Level easier range are a	application furrow but not evenness are	necessity.
a	efficiency critical Good design is and to	efficacy.
feet.
throw 60 20 Can to water	differences Elevation affect but pressure,	is this small lots.
uncommon many on	models have All almost the same	.
inches 0.45 0.4 to per	for be good replacement May spray a	sprinklers cost).
Examples Nelson Hunter & the are	Rotator.
MP	from 16 feet.
8 Throws to water	for potential has High application rate a	tight slopes soils runoff losses when or on	durations.
for limit long need May to run	minutes.
time 15 to run
 EVAPORATION	POTENTIAL AND	CONSERVATION	EFFICIENCY	Low/Good	Excellent	conservation	potential	Low	Good 	Moderate/Variable	Conservation effi-	depends ciency on	and design use.
Evaporation rate may	10-15%, be which can	higher be than other	types.
efficient be 75% Can	if well designed.
Moderate/Good	delivery Even	improves efficiency.
Moderate/Variable	Depends slope on	infiltration soil and
 REQUIRED PRESSURE FLOW AND	Can done with be bucket, Varies.
sprina	efficiently with hose kler or more cans a	breaker and hose Normal nozzle.
water	from 35 50 is needed psi psi to to pressure	friction of length long loss in overcome a	have hose still and to operate pressure a	barrels Elevated will rain only wand.
spray	of flow and have be 2 slow psi, 1 to out can	of 5/8" will length hose, long there not so	for be breaker.
wand enough pressure or a	Low/Low	be with hose done Can garden and a	with barrel be could rain used systems.
High/High	gallons deliver 30-70 0.5-20 psi to	orifice depending the minute, per on	and size pressure	Moderate/Moderate	30-50 0.2 psi, 4 to gpm	Moderate/Variable	0.25-4 gallons deliver 20-40 psi to	depending orifice minute, the per on	and size pressure
 EXAMPLES PLANT	plants, Container	established newly	shrubs and trees	Vegetable garden	beds	Turfgrass	turf Open low, areas,	similar plant material	similar with beds in	 ft	turf Open areas,	shrub low-growing	beds similar with	material plant and	water usage
 LOCATION/USE	Individual plants	small or areas	 spaced,	Large, open areas	 the	Small-to-	medium areas	Small areas
 DEVICE	watering/garden hose Hand	4)  Furrow	Sprinklers: Rotating constant	discharge and do not	matched automatically have	for precipitation part rates	circles  and 6	Multi-stream SprinRotating	precipitation matched klers:	for radius circles and part	of  	Sprinklers :	for precipitation rate part	circles with sprinklers the in	series same
 COMMENTS	Should purchase compensating pressure	of for and tubes emitters ease use.
lines best, drip last and and work Hoses	longest, if appropriate used at pressures.
filtering if Requires well city water.
not or	Equipment complex expensive, be to can	and require assemble, clean water very	and/or filtering.
extensive	involved maintenance with than More	Avoid sprinkler bare due soil systems.
to	runoff/erosion.
reducing
 EVAPORATION	POTENTIAL AND	CONSERVATION	EFFICIENCY	Low/Good	Applies water at a	long for slow rate a	of period time.
High efficiency water	Moderate/Variable	reduce Can	evaporation and	improve water	into moving	root zone.
efficiency High water	if overwatering.
not
 PRESSURE REQUIRED FLOW AND	Low/Low	deliver gallons 10-25 0.5 psi 2 to to per	hour emitter 0.22 0.6 to gpm per or	ft of drip 100 tape gpm per	Moderate/Variable	deliver gallons hour 15-30 psi 8 to to per	minute gallons 2.5 per
 EXAMPLES PLANT	Herbaceous and	woody ornamental	vegetable beds,	fruit gardens,	plantings	Individual trees,	understory shrubs	herbaceous and	plants
 LOCATION/USE	Direct to root zone	individual of plants	band wetted in or a	drip around tube the	tape or	Small of plant areas	beneath beds, plants	thicker taller,	vegetation
 DEVICE	Trickle/Drip :	Drip with tube 1) external	directed emitters specific to	micro-lines plants and can	with emitter.
used be each	internal with Drip 2) tape	distances emitters at set	.
10	internal with Drip tube 3)	distances emitters at set	.
Bubblers
 FIGURE 4.
The simplest method of overhead watering may be a hose.
It can allow for variation in plant size and water directed at roots to keep leaves dry.
Landscape irrigation can be quite expensive and has three primary areas of cost.
First is the equipment and installation.
Second is the cost of maintenance, including repairing/ replacing emitters damaged by mowing, pipes that break as soil settles, and removing sediment from nozzles and controls.
Third is the cost of operation.
This cost includes modifications to the system as landscape and plant needs change, the amount of energy costs if pumps and other tools are needed, and water.
Water is a significant and ongoing expense.
One thing to consider is whether your water provider will allow you to avoid paying sewer costs on water used for irrigation.
In some situations overall net costs for irrigation may be lessened due to reductions in paying someone to hand water.
It can be helpful to make a drawing of the landscape to scale for planning and also to serve as a record of where irrigation equipment is installed.
Distances don't have to be perfect, and the only things these scale drawings require are graph paper and accurate measuring of distances.
A typical scale equation is 1 inch on paper equals 20 feet in the landscape.
Depending on the size of the lot, several sheets of graph paper may need to be taped together.
Next, using a pencil with a good eraser, lay out the property, structure and hardscape boundaries.
Identify the location of different plant material, beds and gardens.
Additionally, identify water use zones  in the landscape and consider plants with similar requirements.
If making a scale drawing of a residential property seems daunting, consider printing an overhead image of the property using Google Earth, to be used as a template to assess needs and begin planning irrigation systems.
It is important to locate the point of connection where the irrigation system will hook into the existing supply.
If the site is steep, noting the direction and estimated slope is important.
Making note of underground utilities is helpful, but always call 811 and request the utility board to come out and mark the lines directly on the property before any installations are made.
COST FOR IRRIGATING ONE-HALF ACRE
 1 inch of water applied to a half-acre landscape requires 13,500 gallons of water each application.
1 inch/12 = 0.0833 feet.
Therefore, 0.0833 ft 21,780 ft2  = 1,814 ft3
 1814 ft3* 7.5  = 13,500 gallons
 The combined cost for applying 13,500 gallons is $135.00.
If 6 inches of water are required in a growing season, the yearly cost of irrigation is about $810.00 for half an acre.
DESIGNATE GENERAL WATER USE ZONES
 When designing a home landscape, grouping plant material by water needs is very important to enable the irrigation to be optimally efficient and for plants to perform well.
While these techniques may be common in larger commercial plantings, it is not often a high priority for homeowners in selecting plant material.
So, if the goal is to install effective and efficient irrigation, then plant water needs should be considered.
High water use: Plantings that need regular watering and show water stress easily.
Examples include entry to a home, containers and window boxes.
These areas should have accessible water sources.
A rain barrel  could also be an excellent addition to manage high water use areas.
High-to-moderate water use: These moderate-to-high use plant types could include vegetable gardens and turf areas, and water needs will depend on homeowner and gardener preferences and the conditions of the growing season.
To enable optimum garden yields and a high level of aesthetics in turf areas, many summer seasons require supplemental irrigation in these areas.
Moderate water use: Established plants that need watering when showing signs of water stress.
Only half to 1 inch of rainfall per month is sufficient for most established woody ornamentals, assuming this water infiltrates the soil.
Examples include drought-tolerant plants, native plants and plants in mulched beds.
Low water use: Plants that need water only in extreme drought situations, including naturalized or wooded areas with established plants.
GENERAL GUIDELINES FOR RESIDENTIAL IRRIGATION SYSTEMS
 ASSESSMENT OF IRRIGATION NEEDS
 A homeowner should understand the purpose of irrigating ; have a grasp of the concepts and technology of irrigation; and, most importantly, take responsibility for irrigation management.
The following list can be used as a guide when setting up an irrigation system in your own residence or when assisting others through the Tennessee Extension Master Gardener program.
1.
Assess the property and owner's need for irrigation.
2.
Review several additional factors in irrigation:
 Ability to meet plant watering needs in relation to environmental conditions.
Potential physical damage to plants and possible environmental impacts, including runoff, erosion and flooding.
Affordability and maintenance requirements, including time and money.
Water supply issues: the irrigation system must not exceed water supply available in high-use periods and it must be sensitive to water use policies and conservation practices in the area.
3.
Emphasize the importance of proper installation and maintenance.
4.
Address best management practices and the importance of effective irrigation management.
For example, irrigate when water is less likely to be lost as runoff or evaporation.
Effective irrigation management implies:
 Reasonable and attainable goals.
Conscientious planning and design, including the consideration of long-term maintenance costs.
Environmental sensitivity, including knowing local water supply ordinances.
Using equipment suited to the task.
Operations that are matched to needs.
Responsible operation and maintenance.
Careful monitoring and adjustment.
LOCATING AND USING SPRINKLERS, BUBBLERS AND DRIPPERS
 The information below is intended to provide a basic overview of how to maintain a sprinkler system and how to address questions.
It is not intended to provide all the information needed to install a residential irrigation system.
SPRINKLERS IN THE LANDSCAPE
 In general, sprinklers are the least water efficient of irrigation practices outlined in Table 1.
However, they are often the
 only method that can be used in large, open areas and can be designed and operated in a manner that can provide around 75 percent efficiency.
So, homeowners need to understand how to select irrigation systems for their needs and use them most efficiently.
Suggestions for efficiency include:
 Run sprinklers in accordance with rainfall and plant needs and not based solely on timers.
When possible, use sprinklers during the cooler times of day to lower the potential for evaporation losses.
Make sure that sprinklers do not cover streets, sidewalks and other areas where all water applied runs off.
If irrigating by overhead sprinklers, the water must be added slowly enough for the soil to absorb it.
Use caution on clay soils or soils that crust, because sprinklers may exceed the infiltration rate and water may be lost as runoff.
On bare clay soils, this may be a serious limitation, as infiltration rates may be as low as 1/10 inch per hour.
Using mulch to protect the surface will increase infiltration, but on most soils, infiltration will not exceed 3/4 to 1 inch of water per hour.
LOCATING AND USING SPRINKLERS
 Proper location of sprinklers is key to providing even distribution of irrigation water that is not wasteful.
If the distance is too wide, irrigation will be insufficient.
If it is too close, then more water  than is needed will be used and runoff could increase.
If they are placed too far apart, some areas will be too dry.
There are a variety of sprinklers on the market.
Some general suggestions for avoiding overwatering when using sprinklers include:
 Use a rain gauge to check how much water has fallen, check soil moisture and look for signs of drought stress.
Decrease the amount of water by the amount it has rained.
Use average daily temperatures to help predict the rate of evapotranspiration.
Wait until 4 to 6 inches of soil is dry before watering.
Do not water when it is raining.
The following discussion will be focused on the three types of sprinklers presented in Table 1.
These sprinklers have a constant discharge and are best used for large open areas.
Turfgrass is commonly irrigated with these devices.
They require the highest pressure and deliver the highest flow rate of the three types of sprinklers.
Directional sprinklers can be added for corners and odd-shaped areas, but sprinklers do not automatically match precipitation for partial circles.
So, determining the precipitation rate and proper spacing is critical for these sprinklers.
Sprinklers operating correctly actually apply more water close to the sprinkler.
For this reason, proper placement of sprinklers provides an overlap in their patterns to enable even watering.
A sprinkler is placed at the edge of the wetted area of the previous sprinkler so that it will throw water back across the previous sprinkler's pattern.
One simple way to remember this is to place sprinklers with coverage that is head to head, meaning that the area wet by each sprinkler should extend to the next sprinkler.
If there is little wind in the area and rainfall is frequent, this standard can be relaxed somewhat.
These guidelines apply only to sprinklers operating with the specified pressure.
Pressure over the recommendation can result in small droplets that are moved by wind.
Conversely, lower-than-suggested pressure can result in large water drops that don't travel as far as intended, leading to dry areas between sprinklers.
Odd-shaped areas make sprinkler location even more challenging, so these tips can help.
FIGURE 8.
Example of spray sprinkler in small lawn area.
FIGURE 9.
Multi-stream sprinkler.
RULES FOR SPACING SPRINKLERS
 small areas.
This smaller delivery area makes them well suited for smaller lawn areas or landscape beds where the plant material is similar in height and in water needs.
These sprinklers deliver 0.25 up to 4 gallons per minute, and the higher rates over smaller areas have the capacity to increase runoff and erosion if water is delivered faster than it can infiltrate.
Mulches can be an asset in these situations.
Because of these variations in flow, site and use, the efficiency and conservation potential of spray sprinklers varies in the home landscape.
1.
Select a sprinkler that covers the area but doesn't throw water beyond the narrowest areas.
You can break the area into sections and select two or three sprinklers with different sized wetting areas.
2.
Part-circle sprinklers will need to be placed at all corners.
3.
Place part-circle sprinklers evenly along the edges between corners using appropriate headto-head spacing.
4.
Then, add sprinklers with full circles to the middle areas with a similar spacing as used on the edges.
5.
Spacing between sprinklers will not always be exact, so allow for a margin of 10 percent.
6.
Go back and adjust if needed to even out the coverage and prevent any gapping between wetted areas.
7.
Sprinkler layout is an art as much as a science, so adjust over time as needed.
The above discussion focused on traditional rotating and spray sprinklers.
A more recently developed sprinkler design that can be an asset in residential irrigation applications is fixed application rate pressure compensating rotating sprinklers.
These sprinklers are designed to deliver similar precipitation whether being used for a small or large radius area or in part or full circles.
Most models have a similar application rate of around 0.4 to 0.5 inch per hour.
These sprinklers can help homeowners avoid many of the challenges of covering odd-shaped spaces and avoiding dry spots and other inefficiencies in sprinkler irrigation.
Because the design and layout is simpler with these sprinklers, homeowners are more likely to be able to design and install efficient home irrigation systems.
These stream-rotating sprinklers operate at a lower pressure than rotating sprinklers and deliver less flow than spray sprinklers.
They are ideally suited to replace spray sprinklers, producing a much lower application rate, and at the same time can be used in many medium-sized areas that were tradition-
 Spray sprinklers do not rotate and spray out of all sides of the sprinkler at one time, thus reducing their radius of throw  and fitting better into
 FIGURE 10.
Drop tape installed under plastic mulch in crop field.
FIGURE 11.
Close-up view of drip tape showing internal emitter embedded in the plastic.
This tape had emitters at 12-inch spacing.
ally covered by rotating sprinklers.
One drawback is a slightly higher initial cost.
If you have trouble with runoff and erosion of an existing spray sprinkler area, MP rotators can be retrofitted into many types of spray sprinklers by replacing the internal parts.
These sprinklers are well suited for open turf areas  as well as low-growing plant material in landscape beds that require similar amounts of water.
BUBBLER AND DRIP EMITTER CONSIDERATIONS
 Bubbler and drip layouts vary from sprinkler arrangements.
The goal with bubblers is to flood the entire bed or at least make sure that the roots of all plants can reach an area wetted by a bubbler.
With both bubblers and drip systems, the leaves of plants are able to remain dry, which is an important disease management technique for a range of herbaceous and woody plants in the landscape.
There are three main types of driplines.
The first type includes a solid tube that can be run through the bed, and then individual small lines with emitters can be installed on a per-plant basis.
If all the plants are the same size and type and get the same amount of sunlight, their water needs should allow them to have the same number of emitters.
Plants that have a dripline twice as large are often given two emitters unless they are more tolerant of dry conditions.
An asset of this type of irrigation system is that emitters can be added, moved or removed  to provide flexibility as landscapes grow and change.
The second type of drip tubing has internal emitters on set distances.
This tube can be placed at or below the surface to provide consistent water flow along the length of the line.
No punching or installing of emitters and micro lines are needed.
These systems are simpler to install but cannot be adjusted as well to accommodate plants of different sizes together in the same beds.
However, the tube can be snaked through beds to accommodate different plant arrangements.
It can be bent slightly but will kink if bent at too great an angle.
A range of emitter distances are available.
The third type of dripline is often called drip tape, and it is usually installed with one line for every plant row , but sometimes a single dripline can be installed between two close rows of small plants.
It has internal emitters at predetermined spacing, but the line is thin and can kink easily.
Thus, generally it is installed in a straight line to enable water flow.
Drip tape is most common in gardens for individual rows of vegetable plants.
Also because it is thin, it must be operated below 15 to 20 psi to avoid bursting.
A pressure regulator will prevent bursting and control pressure and flow in drip tape.
The thicker walls in driplines and emitters prevent bursting below 60 psi, and pressure-compensating emitters will avoid flow variation caused by pressure differences in these drip products.
THE NEED FOR IRRIGATION ZONES
 Dividing the irrigated area into zones is usually needed to provide uniform water distribution.
Zones are quite simply bubblers, drippers or sprinklers that are controlled by a common valve.
Most water sources do not have enough pressure to run the entire irrigation system properly at the same time.
For example, if a system has 12 gpm at 45 psi but is connected to eight sprinklers that require 3 gpm each, it will not be able to meet the demand.
The result will be dropping pressure, low flow and poor sprinkler operation, causing areas with wet and dry spots.
Irrigation zones ensure that the demand doesn't exceed the supply.
Even if the water supply can provide irrigation for the entire landscape at one time, zones still may be needed if different irrigation products or sprinkler spacings are used.
Different products such as sprinklers, sprayers, bubblers and driplines usually have very different application rates.
If they are operated for the same length of time, they will apply different amounts of water.
If different sprinkler spacings are used, the discharge rate may be the same, but the sprinklers with tighter spacing will have a higher application rate than sprinklers located farther apart.
This means it is important to have different zones so overwatering or poor watering does not occur.
ZONING CONSIDERATIONS FOR DIFFERENT EQUIPMENT
 Zoning also is useful in managing different landscape materials.
Some plants need more water than others, so these areas could be zoned separately to apply the desired amount of water.
Zoning decisions can also improve irrigation uniformity on
 steep slopes by creating zones that follow contours instead of traversing up and down a slope.
Finally, zones should consist of sprinklers or drippers that are near each other, because long pipe runs in a zone can cause high friction loss  that interferes with the uniform operation of irrigation equipment.
Sprinkler specifics: part-circle sprinklers and rotating sprinklers are needed in most landscapes.
When purchased, they have a single nozzle that produces the same flow rate.
half-circle rotating sprinklers can be placed in the same zone if the half-circle is re-nozzled to produce half the flow to create matched precipitation.
The same is true for halfand quarter-circle sprinklers in the same zone, but this practice is not recommended for fulland quarter-circle sprinklers re-nozzled to one-fourth the flow rate because the radius of throw is significantly reduced, preventing proper overlap of sprinklers.
If necessary, leave the corner sprinklers at half the flow of the full-circle sprinklers.
In contrast, spray sprinklers and stream rotators of the same model already produce matched precipitation when located at the same spacing, and full circles can be mixed with part circles in a zone without modifying the nozzles.
A new generation of stream rotators named MP rotators or R-VAN maintains matched precipitation with different models, operating pressures and radius adjustments, making them much easier to place in a landscape  and maintain good uniformity with a known application rate.
Drip irrigation can be treated differently with respect to application rate, because emitters can be located on a plant canopy basis instead of a land area basis.
For instance, one emitter could be placed to supply water to every 9 square feet of canopy such that bigger plants would have more emitters than smaller plants, and all sizes of plant material can be widely scattered within a bed.
To summarize, zones should only contain irrigation equipment that has similar application rates, either on a land area basis for sprinklers or on a plant canopy basis for drip.
Pressure is lost in an irrigation system due to the friction of water moving along the pipe walls and passing through each piece of irrigation equipment.
Friction losses require that the pipe size corresponds to the flow rate in each segment of pipe.
Pipe that is too small will create excessive pressure drop and water will not be applied uniformly, or some equipment may fail to operate at extremely low pressures.
On the other hand, pipe that is too large will unnecessarily add to the cost of the irrigation system.
The higher the velocity of water, the higher the friction loss and pressure drop in a pipeline.
For example, if 20 gpm is carried by a 1.5-inch PVC pipe, the velocity is 2.65 feet per second and the pressure drop will be 0.71 psi per 100 feet of pipe, while the same 20 gpm flow in a 1-inch pipe would cause the velocity to be 5.71 feet per second and the pressure drop to be 4.59 psi per 100 feet of pipe.
To keep pressure loss due to friction at acceptable levels, a simple three-step method has been devised.
1.
Route the mainline pipe from the water source to the zones and route pipe to sprinklers within the zone.
2.
Total the flow in gpm for each pipe section based on the expected flow rate per sprinkler.
3.
Choose the smallest pipe that will keep the flow velocity below 5 ft/sec in each section.
Manufacturers provide pipe charts that show the friction loss and water velocity for different pipe types, pipe sizes and flow rates.
Using the manufacturer's literature and the 5 ft/sec rule, a simplified pipe chart showing the pipe size that correlates with a flow range can be created.
Remember that different pipes have different hydraulic characteristics.
Make a chart for each pipe type because the material roughness and the inside diameters differ.
Using the simplified pipe chart, assign a pipe size to each pipe section based on flow.
Many homeowners will discover that their water supply is often limited to less than 15 gpm, so they can simply use a 1-inch PVC pipe for their entire system.
AN INTRODUCTION TO VALVES AND AUTOMATION
 Valves controlling irrigation can be manual  or electric solenoid valves that will be needed for an automatic system.
In a manifold, the main water supply is connected to all valves, and the valves control the flow to the individual zones or laterals in a zone.
Valves can be placed subsurface to protect from freezing and lawn equipment that can be accessed through a valve box.
Automation is accomplished by means of electronic solenoid valves and a controller.
Solenoid valves are placed at the
 FIGURE 13.
Irrigation box showing an automatic controller and one irrigation zone.
Additional zones could be added if required.
head of every zone.
Each valve requires a common wire and power  wire that connect to a central controller.
Most solenoid valves have a manual override that allows operation of the zone when power is not available.
Any electrical system used around the home should be installed and maintained using sound electrical practices.
Once the valves and the controller are properly wired, the controller program can be set up.
The controller program has three main settings: the length of time to operate each valve, the start time to initiate the valve sequence, and the days that the valve sequence will operate.
Controllers come in all makes and models but fall into three basic categories: electromechanical, solid-state electronic and hybrids.
Electromechanical controllers were the first type of controllers with settings made on rotating dials with trip pins.
Later, solidstate controllers were introduced with all settings entered on a keypad within a program loop.
Presently, hybrid controllers are the most popular, because a limited number of dials helps the user enter the settings without having to enter a long programming loop.
Even with automation, a manual valve should be installed at the beginning of the irrigation system so that all components can be maintained with the water turned off.
A normal timer program is set for the days of the week to water  and the starting time to initiate the valve sequence with a valve run timer for each zone.
The optional features available to manage water are rain delays, rain gauge shutdown and soil sensor shutdown.
If you don't use one of these features to help you manage irrigation, remember to turn off your controller when it is raining.
Choosing manual or automatic operation of the irrigation system depends on personal preference.
However, with either system, backflow prevention is required.
Backflow prevention is necessary on many landscape irrigation systems to keep stagnant or contaminated water out of the water supply.
It is especially important for protecting drinking water but can also be important in other situations.
Backflow can occur when a pump is turned off , when there is major pipe break, or when there is a large demand for water for another use, such as a fire truck pumping from a municipal water system.
Backflow occurs when pipes are full and when there is an upstream pressure drop causing water in the pipe to change direction.
When this happens, the vacuum in the pipes can pull soil, debris or other materials into the water stream.
So, backflow prevention is needed if you use utility water to prevent the water or other contaminants from flowing into the water supply line if pressure is lost in the system.
Homeowners with wells should consider backflow prevention to protect their own water supply.
There are many backflow prevention devices.
They range from a simple check valve, like a foot valve used in pumping from a pond or stream, to a Reduced Pressure Backflow Device.
A RPBD provides the most protection, has the highest cost, causes the greatest loss in pressure, and is required for hook up to domestic water by many municipalities.
The RPBD can be used in most situations, but it cannot be located where it will be submerged.
A pump is required if the intended water supply is a stream, a pond, a well or a domestic supply that does not provide enough pressure to operate the irrigation system.
The pump type  can be chosen based on the location and type of water supply, the flow that it will deliver, and the height of the pump above the water supply.
Pump flow can be determined from the zone with the highest flow.
The required pressure or head is a summation of pipe friction to the most distant
 RECOMMENDATIONS FOR DRIP PRODUCT USAGE
 Water must be cleaned with 120-200 mesh filters, depending on the drip product.
Screen filters should be used for well and utility water.
Disc filters should be used for surface water irrigating a small area.
Sand media filters are best suited for surface water and large drip projects.
Water pressure must be within the appropriate range.
Pressure regulators should be used to protect the drippers and ensure operation at a designated flow.
Pressure compensating emitters should be used when operating under a greater range of pressures.
location, friction loss through all equipment , elevation gain from the water source to the highest water emission point, and the pressure needed to operate the highest pressure sprinkler, sprayer, bubbler or dripper in the system.
It is advisable to seek the aid of an irrigation professional in making the calculations needed to size a pump.
Even if using a pressurized source, such as municipal drinking water, it is important to subtract the friction losses and the elevation gain from the existing pressure to ensure there is enough pressure to operate the sprinklers, bubblers, and/or drippers.
Excess pressure can also damage an irrigation system.
A pressure-reducing valve will maintain pressure at an acceptable level, and a pressure relief valve will release water when a high-pressure threshold is reached.
A pressure reducer is usually required to control high pressure in the utility main line before it is released into your home.
A pressure reducer can be adjusted to meet the needs of a home irrigation system in most situations.
If water is pumped, a system can be designed to operate at acceptable pressures.
Class 160 or schedule 40 PVC pipe is rated to operate at pressures up to 160 psi and is commonly used in landscape irrigation.
Normal operating pressures will be exceeded temporarily when flow starts and stops in a pipeline, resulting in pressure spikes known as water hammer.
These pressure surges can be excessive and break pipe when the flow velocity exceeds 5 feet per second and air is not purged from the pipeline.
Airflow in a pipeline needs to be controlled in addition to water.
Air release/vacuum relief valves allow air to evacuate when filling the pipe and also allow air to enter the line when the pipe is drained.
A continuous-acting air relief valve allows air to be purged from high points in the pipeline once the system is under pressure.
In many instances, sprinklers allow for proper air management; the devices described above often are not needed for small landscape systems.
In addition to the valves, some equipment is related to specific irrigation products.
For sprinklers, a swing joint is a flexible connection between a sprinkler and the lateral pipe that allows easy adjustment of the sprinkler height, protecting the sprinkler head from mower damage.
This flexible connector also protects the lateral pipe when vehicles run over the sprinkler heads, allows the sprinkler to be moved deeper if the soil settles, and facilitates removal/replacement when a sprinkler is damaged.
For drip irrigation, filtration is needed to keep the emitters from plugging.
Municipal and well water are often clean enough to use without filtration, but a screen filter is still recommended to protect the emitters from debris caused by pipe breaks and the sand that is sometimes carried in well water.
A disc filter is a better choice if surface water is used on a small drip area.
If an extensive area is drip irrigated with surface water, a sand filter is a better choice than a disc filter.
Filters for drip irrigation will be in the 120to 160-mesh range; the manufacturer's literature for the actual requirement should be checked.
When sprinkler and drip are used in the same landscape, small pressure regulators will help reduce the pressure for use in the drip-irrigated zones.
Ar = application rate in inches per hour
 Q = flow or discharge in gallons per minute
 A = area into which flow is applied in feet2
 Conversion factor = 96.3
 Example: A full-circle sprinkler discharges 2.4 gpm and the sprinkler spacing is 30 by 30 feet.
Ar =  /  = 0.25 inches per hour
 DETERMINING IRRIGATION TIMING IN THE LANDSCAPE
 Once an irrigation system that uniformly applies water within each zone is designed and installed, it is important to know how to operate the system so the landscape always looks its best and neither water nor money is wasted by overirrigating.
The first step in determining how long to operate each zone is to calculate the rate water is applied to each zone.
An application rate is calculated by dividing the flow into the area irrigated  and multiplying by the conversion factor, 96.3, to determine the inches of water applied in one hour.
For sprinklers, this can be done by dividing the flow rate of a single sprinkler by the area of the individual sprinkler spacing or by dividing the flow of the entire zone by the total area of the zone.
For drip irrigation, the flow for one emitter can be divided by the plant canopy area.
For drip tape, the flow per 100 feet is divided by the area between drip lines.
Some may prefer to place rain gauges or vertical-sided baking pans in a zone, run the zone for an hour , and measure the depth of water caught in inches to determine the inches applied in an hour.
However, this method will not work very well for bubblers and drip.
Once the application rate for each zone has been obtained, the operation time is calculated by dividing the irrigation amount by the application rate.
For instance, during peak water-use periods, apply 0.5 inches of water two times per week if there is no rainfall.
If a zone's application rate is 1.0 inch per hour, the zone would need to be operated for 30 minutes.
Once the peak operation times for each zone have been calculated, program the valves on the controller to operate for the desired time.
Next, program the days of the week the zones or valves will operate and the start time that initiates the sequential operation of all valves on a program.
Often there is no need to operate your zones for the full length of time.
Peak water use generally occurs in June, July and August when solar radiation and temperatures are high.
Even during potential peak water-use times, plants may not use water
 at a peak rate when the weather conditions are cool, cloudy and humid with little or no wind.
Also, during the spring and fall, landscapes will not use as much water.
Therefore, operation time should be reduced by shortening the valve run times or by skipping days when the program is scheduled to operate.
As mentioned earlier, in addition to periods of lower water use, rainfall can meet the landscape water requirements.
The controller should be turned off during periods when rainfall exceeds water-use rates.
Some controllers have a rain delay feature that allows the controller to be turned off for a specified time period before resuming normal operation.
For instance, after a 1-inch rainfall, a rain delay may be set so that normal operation of the controller will be suspended for seven days.
Some controllers are equipped with rain gauges  that automatically suspend controller operation for different lengths of time depending on the rainfall amount.
Finally, some controllers are equipped with soil moisture sensors  that will not allow the controller to operate until the soil dries to specified soil moisture.
This type of control will respond both to rainfall and a change in the landscape water-use rate.
Although automation and sensors can help manage water more efficiently, it always pays to observe what is happening in the landscape.
A zone on an exposed, south-facing slope will dry out faster than a shaded area on a north slope, causing a need
 HOW DEEP SHOULD YOU WATER?
Determining how deep to water depends on several factors: soil texture, soil structure, plant type, age and size, and watering practices.
A mature plant needs a certain amount of water to survive, whereas young plants need water to continue to grow and develop.
Compacted or shallow soils inhibit deep rooting, and plants may not be able to be watered deeply.
Consider the following when watering:
 Leafy vegetables and annual bedding plants: 6 inches to 1 foot.
Small shrubs, cool-season turfgrass, corn and tomatoes: 1 to 2 feet.
Large shrubs, trees, warm-season turfgrass: 1.5 to 5 feet.
to increase the valve run time on the former while decreasing the time on the latter.
Runoff may be observed on sloping ground or on heavy, more clayed soil.
To prevent this loss of water leading to dry soil conditions, shorten the run time and operate more often.
Sandy soils show signs of stress sooner than silt or clay soil.
Since sands hold less water, irrigate more often than once or twice per week and reduce the run time accordingly, because long irrigations on sandy soils are liable to percolate water through the root zone where the plant cannot access the water.
UMA INSTITUTE OF AGRICULTURE THE UNIVERSITY OF TENNESSEE
 AG.TENNESSEE.EDU Real.
Life.
Solutions TM
Home Sprinkler Systems: Backflow Prevention Devices
 By C.
Swift and M.
Higgins*  Revised by K.M.
Jones**
 Backflow prevention devices protect the drinking water system from contamination due to backflow of non-potable  water into the potable  water supply.
Backflow is of two types, back-siphonage and backpressure.
Any drop in pressure in the main city water line can result in back-siphonage backflow of fertilizers, pesticides, manures and other contaminants through sprinkler heads and the irrigation piping system into the potable water supply.
This same contamination may occur through a hose-attached sprinkler, spray nozzle or pesticide sprayer.
This presents a serious threat to public health.
This drop in pressure can result from a break in the line or by lowered mainline pressure due to high water withdrawal, as may occur during fire fighting operations.
Improper installation of a lawn sprinkler pump or injector system may force contaminants back into the potable water supply.
In this case, the pressure exerted by the pump is greater than the pressure in the potable water system.
This is known as backpressure backflow.
If properly installed, an approved backflow prevention device will prevent back-siphonage and/or back-pressure backflow.
Not all devices are designed to handle both types of backflow.
Backflow prevention devices are designed for installation on sprinkler systems connected to potable  water supplies only.
Sprinkler systems only connected to irrigation water  do not require backflow protection.
Some parts of the state of Colorado have dual irrigation systems that apply irrigation and potable water through the same irrigation system.
These systems require a reduced pressure principle assembly to protect the domestic water supply.
Permits normally are required for systems that require backflow prevention devices prior to the installation of a
 Backflow prevention devices must be installed on all sprinkler systems  using potable  water.
Backflow prevention devices are designed to prevent contamination of the potable water system from pesticides, feces and other hazardous materials.
Hose connection backflow prevention devices may provide protection for the system when insecticides, other pesticides or fertilizers are applied by means of a hose-end spray attachment.
C.E.
Swift, former Colorado State University Extension, Horticulture Agent, Tri River Area.
M.
Higgins, Grand Junction Pipe and Supply, Grand Junction, Colo.
**Revised by Kurt Jones, Colorado State University Extension agent, natural resrouces and agriculture, Chaffee County.
5/20.
sprinkler system.
The installation design, to include the type and placement of backflow prevention devices will be approved during the permit review process.
Permits are available from city/county building departments.
Types of Backflow Prevention Devices
 A mechanical backflow prevention device allows water to flow in only one direction.
Pressure vacuum breakers , and the reduced pressure principle device , are the ones commonly used in residential sprinkler systems.
The RP device must be used for more hazardous back-pressure situations.
These are effective only against backsiphonage.
These mechanical backflow preventers are not to be used when backpressure problems may exist.
There are two types, the atmospheric vacuum breaker  and the pressure vacuum breaker.
The atmospheric vacuum breaker  is gravity operated and must be installed in the unit.
This device must always be installed at least six  inches  above all downstream piping and outlets.
The pressure vacuum breaker  is designed to open after long periods of continuous water pressure.
This type of device may be installed under a constant pressure upstream of all control valves.
This device must be installed in a vertical position and at least twelve  inches above all downstream piping.
While more expensive than the AVB or combination device, only one PVB is needed for an entire sprinkler system.
The PVB is equipped with test cocks and must be tested yearly by a backflow technician.
Figure 1: Atmospheric vacuum breaker.
Figure 2: Plastic  and brass  combination AVB units are available.
Figure 3: Pressure Vacuum Breaker.
Figure 4: Reduced Pressure Device.
The reduced pressure  backflow device is the highest level of protection available.
This device protects from backflow and back pressure.
When installing the device, a minimum of 12 inches of access and clearance between the lowest portion of the device and grade, floor or platform must be provided.
There must be adequate clearance around the assembly so that testing and repairs can be accomplished.
Reduced pressure backflow devices are often used when pressure vacuum breakers cannot be used.
Sprinkler attachments, spray nozzles and other items attached to a hose connected to the potable water supply must be protected by the use of an approved hose connection vacuum breaker.
These devices are designed for hose threaded outlets.
Backflow prevention is critical when using a hose-end sprayer connected to the potable water supply.
Backflow can easily suck an insecticide or other chemical back into the domestic water system.
A hose connection vacuum breaker should be used as minimum protection when fertilizers, insecticides or other pesticides are applied with a hose-end sprayer.
Figure 5: Hose connection vacuum breaker.
Backflow prevention devices are designed with the degree of health hazard in mind.
Unless prohibited in your area, lawn sprinkler systems using potable water can be used with either an
 AVB or PVB device unless a higher degree of hazard exists.
The injection of fertilizers, pesticides or other contaminants through the irrigation system represents a higher degree of hazard and requires the use of a device such as the reduced pressure principle backflow assembly  to ensure safety.
Backflow prevention devices will be damaged by freezing during the winter unless drained of all water.
See 4.719, Home Sprinkler Systems: Preparing your Sprinkler System for Winter for details.
Hose connection vacuum breakers are best removed, drained and stored for the winter.
ENERGY SAVINGS USING VARIABLE FREQUENCY DRIVES ON CENTRIFUGAL PUMPING APPLICATIONS
 Dan Bodenhamer Power Control Area Mgr.
Rockwell Automation Kansas City, MO 913-577-2513
 Modern Electric Motor Starting Means
 There are three primary methods used to start and operate induction AC motors: Full voltage direct across the line starters, reduced voltage soft starts, and Variable frequency drives.
The three methods all have distinctly different effects on both the mechanical system but also the power distribution networks.
Both the full voltage and reduced voltage starting means are only capable of running AC motors at the motor's synchronous speed of 60Hz.
Full voltage cross the line starters allows the utility's full wave form to start the motor.
This method will see a 600% to 800% of full load current in-rush during the starting of the motor.
Many utility providers have begun to limit this starting means to only smaller motor loads due to the effects of the high in-rush current required to start the motor.
Reduced Voltage soft starts will allow for more control of starting ramp rates of the system, but will have a typical in-rush current during starting of 350% to 450% of the motor's full load current and not allow for speed control.
Both of these starting means do not allow for power factor correction within an induction AC motor system.
However, a variable frequency drive allows an induction AC motor to have virtually no in-rush current and is capable of reduced operating speeds of the motor.
As a mode of operation, a variable frequency drive rectifies the incoming AC power to a DC bus first.
It then switches the DC bus power to create a modified AC waveform to the motor.
This technology allows for smoother starts, infinite control of a pump's flow, and significant avoidance of water hammer.
A variable speed drive is also capable bringing an oversized system closer to unity power factor as well.
199
 Affinity's Law Effects on Power consumption
 Affinity's law is the phenomena that a centrifugal pump typically follows as the system's speed is reduced to control flow rather than throttling.
A cubed root relationship allows for significant reductions in energy consumption as the system's speed is lowers.
Typically a reduction in speed by 10% can net an energy saving of 27%.
These savings often justifies the additional cost of the more sophisticated variable frequency drives.
Comparing the Cost to Traditional Engines
 The three popular power sources for irrigation today are Natural Gas fired internal combustion engines, Diesel cycle engines, and Electric AC induction motors.
The more traditional methods of power are far less energy efficient than an AC motor.
These typically run at 50% or less efficient.
Their efficiency will dramatically decrease as their operating speeds are reduced which can negate the benefit of running a system at slower speeds.
However, an AC motor with an applied variable frequency drive system is capable of reducing its energy consumption at slower speeds while maintaining the system's efficiency in excess of 90%.
During this session we will cover the basic calculations for power consumption, speed's effects on a centrifugal pumping system, and a look at the total cost of ownership comparing traditional power means versus AC motors applying variable frequency technology.
The Nebraska Pumping Plant Criteria
 The University of Nebraska established a performance criteria for pumping plants, based on field tests of pumping plants, lab tests of engines and manufacturer data on three-phase electric motors.
The criteria is commonly referred to as the Nebraska Pumping plant Criteria.
A pumping plant meeting the NPC is delivering the expected amount of useful work, measured as water horsepower hours , for the amount of energy consumed.
The NPC should be thought of as a reasonable target for every new pumping plant.
It is possible for a well-designed pump coupled to an efficient power unit to exceed the NPC.
In fact, large scale pump testing projects have found around 10% of pumping plants in the field that are performing over 100% of the NPC.
The NPC  is stated in terms of horsepower-hours of work input into the pump shaft and in terms of the water horsepower hours  produced per unit of energy consumed.
Stating performance in these terms makes it possible to compare the performance of all pumping plants using a given energy source, regardless of pumping rate, lift, and system pressure.
Table 1.
The Nebraska Pumping Plant Performance Criteria 
 Energy Source	hp-h / energy unit	whp-h/energy unitb	Energy units
 Diesel	16.66	12.5	Gallons
 Gasoline	11.50	8.66	Gallons
 Propane	9.20	6.89	Gallons
 Natural gas d	82.2	61.7	MCF
 Natural gas 	8.9	6.67	Therm 
 Electricity	1.18	0.885	kWh
 The author personally conducted over 200 pumping plant tests in Kansas and Nebraska from 1978 to 1981.
The most surprising finding was producers generally did not know when a pumping plant was inefficient until they received the test results, even when the pumping plant test showed it was using 30 to 50 percent more energy than expected by the NPC.
The reason producers couldn't recognize poorly performing pumping plants is they almost never have two pumping plants operating under the same pumping conditions of volume, lift and system pressure.
They therefore didn't have any way to judge the relative performance of a given pumping plant vs.
others.
How to use long term records to locate inefficient pumping plants
 Four large-scale pumping plant studies in the 1950s, 60s, 70s and 80s found fairly consistent results.
The average performance rating was between 76% and 81% of the NPC.
Discussing average performance ratings is useful when thinking about the energy wasted within the irrigation industry as a whole.
But individual producers need to identify which specific pumping plants are highly efficient, average or poor.
The primary purpose of this paper is to demonstrate how a producer can use existing records to identify pumping plants that should be tested by a professional so those with low performance ratings can be adjusted, repaired or replaced with a better design.
This involves a five step calculation procedure.
Step 1.
Calculate the water horsepower output of the pumping plant.
whp-h = acre-inches pumped X total head  / 8.75 whp-h / ac-in x ft
 whp-h = water horsepower hours
 acre-inches = volume of water necessary to cover an acre one inch deep.
27,154 gallons.
total head  = lift  + system pressure 
 lift = distance  from the water level inside the well casing to the discharge head while pumping.
system pressure  = psi X 2.31 ft/psi
 Step 2.
Performance = whp-h / fuel used for the test period
 Step 3.
Performance rating =  X 100%
 Step 4.
Potential fuel savings =  / 100) X fuel used for the test period
 Step 5.
Potential Dollar Savings = Fuel savings X Fuel price
 f Conversion to acre-inches
 If the water meter totalizer registers in gallons, divide gallons by 27,154.
If the water meter totalizer registers in acre-feet, multiply acre-feet by 12.
If the water meter totalizer registers in cubic feet, divide cubic feet by 3,630.
Test period: Entire irrigation season
 System: Center pivot sprinkler system with a diesel engine.
Pumping water level: 140 feet
 Pressure at the discharge head: 40 psi
 Ac-in of water pumped : 1,415
 Total fuel used for test period = 3,571 gallons of diesel
 Diesel fuel price: $2.20 /gallon
 Step 1.
whp-h = acre-inches pumped X total head  / 8.75
 = 1415 X ) / 8.75
 = 1415 X  / 8.75
 = 1415 X  / 8.75
 Step 2.
Performance = whp-h for the test period / fuel used for the test period
 = 37,518 whp-h / 3,571 gallons
 = 10.5 whp-h / gallon
 Step 3.
Performance rating =  X 100%
 =  X 100% = 84%
 Step 4.
Potential fuel savings =  / 100) X fuel used for the test period
 =  /100) X 3,571 gallons of diesel
 = 0.16 X 3,571 gallons
 Step 5.
Potential Dollar Savings = Fuel savings X Fuel price
 = 571 gallons X $2.20 per gallon = $1256.20
 For those with a computer and access to the internet, the author has created an Excel workbook to simplify the calculations.
Results include: performance, performance rating, potential energy savings and potential dollar savings using records.
The program can be run on-line in most popular internet browsers or it can be downloaded to the user's computer and opened in Excel.
The Diesel Example worksheet is represented by the lower screen capture.
Notice the tabs at the bottom of the worksheet.
Click on the tabs to see examples or to open and use the Worksheet to calculate the performance of your pumping plants.
accompanies the Crop Watch articles above.
Microsoft Internet Explorer TM is able to open the file on-line, if desired.
To download the Excel worksheet to your computer, right click on the link below and select "save as" to save the file to the folder of your choice on your computer.
To use the file, start Excel, browse to the file and open it normally.
Long_Term_Pump.xls Excel worksheet to calculate long-term pumping plant performance from your records
 Cost of Owning and Operating an Irrigation System
 2	Estimate Pumping Plant Performance Rating and Potential Energy Savings
 3	From Your Records
 4	Developed by Tom Dorn and Randr Pivor, UNL Extension Educators 1/20/2006	Revised 1/16/2007
 6	Note: This is an example worksheet and cannot be editied.
Click on Worksheet tab at bottom to enter your values.
8	Step 1.
Select energy type:	Energy	NPC	Energy Units
 9	Choices: Diesel, Electricity, GasolineJNat Gas, NG Therm, or Propane	Diesel	12.5	Gallons
 11	Step 2.
Input energy price per unit In cell E11	Energy $/unit	$2.2000
 14	Water Meter Readings
 15	Step 3.
Select Water meter totalizer units	Units	Beginning	Ending
 16	Choices: Gallons, Ac-In, Ac-ft Dr No meter	Acre-In	27123.0	28623.0
 17	Step 4.
Type beginning reading in D16 and ending reading in E16
 23	Please input the following:
 24	Step 5.
Pumping water level	160	Feet
 25	Step 6.
Pressure at the discharge head	45	PSI
 26	Step 7.
Total fuel used for test period	4700	Gallons
 30	Ac-In of water pumped 	1600.0	ac-Inches
 31	Water horsepower hours  for test period	45248.6	whp-h
 32	Estimated performance of this pumping plant	9.63	whp-h per unit of fuel
 33	Performance rating, % of the NPC	77.0	Percent
 35	Potential Fuel Savings over test period	1080	Gallons
 37	Potential Fuel Cost Savings over test period	$2,376
 39	Based on 75% pump efficiency
 40	Hat Gas is priced SMCF assumed 925 BTU/cubic Foot, 
 41	HG Therm is priced by the Therm 
 H	1	Worksheet Mesel Ehample Electric Example No Water Mater
eight times at 24 to 36 inches, and averaging nearly six times for the soil profile as a whole.
Not surprisingly, the dependence of soil Cl on applied water Cl shows a similar relationship to that of Na , though the increases in soil Cl at applied water values greater than about 5.5 meq/L across the soil subprofiles are less than those for Na.
This likely reflects the greater mobility of Cl in the soil compared to Na.
It is of major concern that at applied water Cl values more than 5.5 meq/L, soil Cl concentrations increased across all depths.
Soil SAR values roughly match those of the applied water SAR values up to about 4, after which soil SAR values are about 1.5 times greater than the values of the applied water, though the correlation of soil SAR and applied water SAR was less than significant.
These results indicate that the effect of the quality of applied water on soil salinity is dependent on the level of salts present in the applied water.
It is important to note that there may be other factors responsible for the variation in soil salinity parameter values, including growers' use of soil amendments, and the combined effects of applied water and winter rainfall leaching must be considered.
A second paper in this issue contains an analysis of the data from the perspective of soil water balance and addresses these effects.
As competition for water supplies intensifies and associated sea water intrusion affects the use of well water in coastal California areas, the long-term effects on soil salinity from use of recycled water are important to investigate.
Our primary objective was to quantify the changes in salinity in Monterey County fields under intensive production and determine whether the long-term use of recycled water there has been deleterious to the types of soils in the area.
Our analysis of study data from 2000 to 2012 supports the general conclusions of the MWRSA in the 1980s: The use of recycled water has caused an increase in soil salinity in the area; however, SAR values are not deleterious and Na has shown little accumulation in the rooting zone.
Can irrigation with municipal wastewater conserve energy?
Water conservation and energy costs were concerns 35 years ago, just as they are today.
This study looked at whether reuse of wastewater on farmland would require less energy than discharging it to the ocean.
If so, would it require more or less energy than importing fresh water for irrigation?
In 1977, the energy costs came out about even.
Would today's energy costs and irrigation/wastewater technologies yield a different result?
1977 "Approximately 80 percent of the potential for reclamation in California is in basins where wastewater is being discharged to brackish or saline water mainly the Pacific Ocean.
"One of the expected benefits of wastewater reuse is energy savings in those situations where reuse is an alternative to importation of fresh water.
Two important questions, then, are:  Would reuse of wastewater on farmland require less energy than discharge to the ocean?
If so, would it require more or less energy than importation of fresh water for irrigation?
"Municipal wastewater discharged to the Pacific Ocean requires considerable energy for secondary treatment  and pumping through a long ocean outfall.
Since wastewater reused for irrigation of fodder, fiber, and seed crops requires only primary treatment , each acre-foot reused could save about 200 KWH in direct energy requirements compared to ocean disposal by eliminating the secondary treatment and ocean outfall pumping.
"Under current health regulations wastewater reused for pasture irrigation and surface irrigation of food crops requires secondary treatment.
Therefore reuse instead of ocean disposal would save only the approximately 50 KWH otherwise required for outfall pumping.
Wastewater reused for sprinkler irrigation of food crops requires secondary treatment plus chemical coagulation and filtration.
Such reuse would require slightly more direct energy possibly 10 KWH/AF than ocean disposal of the wastewater.
"When only these direct energy requirements are considered, it appears that irrigation with wastewater could save very large amounts of energy compared with importing fresh water.
However, elevation and quality differences tend to offset the benefits."
 Roberts EB, Hagan RM.
1977.
Energy: Can irrigation with municipal wastewater conserve energy?
Calif Agr 31:45.
Robert Hagan served the UC Davis community as professor of water science from 1948 until his retirement in 1987.
In addition to his expertise on agricultural water use under arid conditions, Hagan sought to increase constructive communication between growers and environmental groups on issues of water and 100 resource use.
The UC Davis Robert M.
Hagan Endowed Chair in Water Management and Policy was established in his honor.
Co-author Edwin B.
Roberts served as a staff research associate at UC Davis, working with Professor Hagan.
An Overview of Systems-based Pest Management for Nursery Production
 Diana R.
Cochran, former Postdoctoral Scientist, Plant Sciences Amy Fulcher, Assistant Professor, Plant Sciences Frank A.
Hale, Professor, Entomology and Plant Pathology Alan S.
Windham, Professor, Entomology and Plant Pathology
 Want to know the most inexpensive way to control pests?
Prevent them!!
Benefits of Using Systems-based Pest Management
 Systems-based pest management is just that preventing pests at each step in the production system.
By using a systems-based approach to pest management, growers can reduce the spread of pests, better understand the source of pests, safeguard their nursery from accepting infested liners from suppliers, and ensure that only pest-free plants are shipped to their customers.
Systems-based pest management also equips a nursery to track plant and pest movement if a regulated pest is detected within the nursery.
Financial Risk From Pests
 Pests  can pose a risk during nursery production by reducing plant growth or plant quality.
Reduced growth or quality can decrease nursery profits by lengthening production cycles, lessening the number of marketable plants, or lowering sale prices.
Pests can also cause plant death or halt sales altogether if they are regulated pests.
The discovery of a regulated pest such as Phytophthora ramorum, the organism that causes sudden oak death and a foliar blight of many ornamental plants, can lead to quarantines, forced plant destruction and a subsequent loss of significant revenue.
Nursery growers who adopt a systems-based approach to pest management reduce the risks associated with the movement of plants through the production cycle and improve their ability to respond to and recover from the detection of pests, especially those that are regulated.
Figure 1.
Common critical control points to prevent the introduction or spread of pests within generalized nursery production cycles 
 What Is Systems-based Pest Management?
Unlike conventional pest management, systems-based pest management is a proactive approach.
Owners or managers invest time up front preventing pest-related problems rather than solely responding to problems as they arise.
Systems-based pest management starts with tracing the production path and identifying high-risk or vulnerable points during the production chain when pests could be introduced or easily spread throughout the nursery.
These high-risk points are called "critical control points" and are the most effective places to prevent, control, contain, reduce or eliminate risk due to pests.
Common critical control points include receiving areas, propagation houses, container storage areas, substrate piles, irrigation water, cull piles, etc.
Once these critical control points are identified, a set of practices is put into place that collectively provides overlapping and cumulative pest prevention as well as early detection and control.
Adopting a Systems-based Pest Management Approach
 Adopting new practices throughout a nursery can be daunting.
If you are uncomfortable adopting an entirely new approach to pest management at one time, try adopting one or two key practices each year over a fourto-five-year period until the entire production chain has transitioned to systems-based pest management.
For example, begin sanitizing used containers in year one, monitor pest population levels on susceptible plants in year two, etc.
Each year you can focus on mastering that specific strategy and reap the associated benefits.
At the end of the four-to-five-year period, your nursery will start receiving the benefits of cumulative practices and strategies by having a fully implemented systems-based pest management program.
Irrigation Timing during Drought Corn, Cotton, and Sorghum Furrow Systems
 Juan Enciso, Charles Hillyer, Dana Porter, and Guy Fipps*
 When water is limited, farmers must make several difficult decisions about how many times to irrigate, when to apply the water, and how much to apply.
They also must accept that their crop may have some deficit, depending on the amount of water available.
In districts where water is allocated per irrigation, farmers need to decide how many irrigations to apply and when to apply them.
The guidelines below can help you plan irrigations to minimize yield reductions in corn, cotton, and sorghum.
Reducing the number of irrigations
 If the water supply is limited, first determine whether to irrigate part of the field or to practice deficit irrigation on all of it.
The type of irrigation system greatly influences this decision:
 Sprinkler systems give irrigators better control of the amount and timing of irrigations, enabling the water to be distributed evenly over the entire field according to the irrigation plan.
Surface irrigation systems require that the irrigators depend on their knowledge of and ability to manage the system.
Because surface irrigation lacks the flexibility of sprinkler systems, those irrigators must consider other strategies for managing drought, such as:
 Associate Professor and Extension Agricultural Engineer; Assistant Professor and Extension Agricultural Engineer; Associate Professor, Extension Program Leader, Biological and Engineering Department; and Professor and Extension Agricultural Engineer, The Texas A&M University System
 Delaying the first irrigation of the season
 Reducing the number of irrigations
 Forgoing the last irrigation
 The goal of delaying irrigation is to take a chance on rainfall during the waiting period.
This strategy requires that you carefully consider weather forecasts and current soil moisture.
At times, farmers must reduce the number of irrigations but carefully control where to apply them.
In some growth stages, the crop is more sensitive, and yield losses may be higher.
If the soil has moisture for the crop, the irrigator may be able to avoid the last application.
After maturity, rainfall does not affect yield.
Irrigating in critical growing stages
 Crops grown with limited water need deep soils that retain moisture well.
These include medium to heavy soils with textures such as clay loams and silty clay loams.
If water is limited, plant more drought-tolerant crops such as dry-land sorghum, dry-land cotton, and sunflower.
Irrigation strategies differ by levels of water reduction.
Following are plans for corn, cotton, and sorghum.
Irrigation needed at this growth stage
 Figure 1.
Timing and number of irrigations for corn in drought conditions.
Maize tolerates water deficits fairly well during its vegetative and ripening periods.
Yields drop the most when the deficits occur in the flowering periods.
Target your irrigation during flowering and, if water is available, during yield formation.
Five irrigations: Apply water according to the first row in Figure 1.
In many situations, if soil moisture is good at planting, you may delay irrigation and end it at physiological maturity without affecting crop yields.
Four irrigations: If water is lacking, monitor the soil moisture content and consider the rainfall received during the season.
With adequate rainfall, you may be able to delay and even conserve one irrigation.
Three irrigations: If you expect a wet year and decide to irrigate corn, but only three irrigations are available, try to pre-irrigate to establish good
 moisture for germination.
The critical stages for irrigation are before the tasseling and silking stages, when the yield potential is determined.
Two irrigations: Apply water to establish the crop, and apply the second irrigation before tasseling.
You will be taking the risk of relying on rainfall to supplement that irrigation.
Cotton must have adequate soil water during germination and establishment.
An irrigation will be needed if not enough moisture is available to establish the crop and obtain good stand.
If water for two additional irrigations is available, apply one irrigation before squaring and the second before peak flowering.
If only two irrigations are available, apply one before or just after planting to obtain a uniform stand.
Apply the second irrigation before the first white bloom.
Irrigation needed at this growth stage
 Figure 2.
Timing and number of irrigations for cotton in drought conditions
 Sorghum requires about 17 to 19 inches of water.
Rainfall supplements part of these needs.
The growth periods of sorghum are:
 1.
Establishment, from planting to fifth leaf visible 
 2.
Vegetative, from fifth leaf visible to head emergence or boot ; in the boot stage, the head has developed nearly to full size and is enclosed in the flag-leaf sheath
 3.
Flowering, from emergence to seed set 
 4.
Yield formation, from seed set to physiological maturity 
 5.
Ripening, from physiological maturity to harvest  for a total of 92 to 120 days during the season
 Sorghum is more drought resistant than are other crops such as corn.
Sorghum has an extensive root system that helps the plant recover quickly after periods of water stress.
Sorghum requires from one to four irrigations, depending on climatic conditions, soil type, and tillage operations such as residue management.
For optimum production when water is limited, irrigation must be timed appropriately.
If only one irrigation is available and the soil lacks enough moisture to germinate the seed, the best strategy is to apply water at pre-plant or just after planting to germinate the seed.
If only two irrigations are available, it is usually best to apply one at pre-plant and a second during the boot stage.
The plant will achieve bigger gains in productivity per unit of water with these two irrigations.
After the third irrigation, the productivity per unit of water will start to drop.
If a third irrigation is available, apply it during the filling heading stage.
This stage is when the peduncle grows rapidly, extending the head through the flag leaf sheath.
About half of the plants in a field are in some stage of bloom and two-thirds of the time from planting to physiological maturity.
The plant has produced about half the total dry weight, and grain formation begins.
If moisture is limited and the plant is stressed, the heads will fill poorly.
Irrigation needed at this growth stage
 Figure 3.
Timing and number of irrigations for sorghum in drought conditions
 If four irrigations are available, the best strategy is to apply the last one during the soft dough stage, when the grain fills rapidly.
About half of the dry weight accumulates in this period.
Some of the strategies to irrigate furrow irrigation systems are:
 Take advantage of this drought period to level your land if it is not leveled.
To improve efficiencies, retouch the land already leveled.
Block the furrows at the lower end.
Supervise irrigations to avoid spills and runoff.
Use pump-back systems to help save runoff water.
Irrigate using gated and flexible plastic pipes.
To increase uniformity and reduce deep percolation losses:
 Irrigate the tractor wheel rows.
Use packers and smothers on the rows to advance the water faster to the end of the row.
Have a good flow rate per furrow to advance water as fast as possible in the row without eroding the soil.
A low flow rate
 will increase percolation at the upstream end, and will lixiviate  the fertilizer.
Shorten the wetting length of the rows.
Block the rows at the lower end.
Supervise irrigation closely to avoid runoff.
This publication was funded by the U.S.
Department of Agriculture-Natural Resource
 Conservation Service as part of the Conservation Innovation Grants Number 69-3A75-1382 and the financial support of the Texas Water Development Board as part of the Agricultural Water Conservation Demonstration Initiative , also known as the Texas Project for Ag Water Efficiency.
Most farmers I work with try very hard to keep the cost of production as low as possible without compromising yield.
So why do some spend extra money pumping more water than needed?
Well, they apparently do not think they are pumping more water than needed.
Every farmer has hundreds of decisions to make each day and when to start the next irrigation can become just another decision that needs to be made quickly before moving on.
But think about this: if your fuel delivery guy pumped 500 gallons of diesel in your tank to fill it, and then pumped an extra 100 gallons that overflowed the tank, just to make sure it was full, how happy would you be with him?
At a very real level, that is what many irrigators are doing when pumping water into the soil profile.
In general, about one-third of the irrigators in the study on the normal to wet years are doing a good job of applying the correct amount of water to minimize deep percolation of water and nutrients and save pumping costs while producing top yields.
The other two-thirds could have saved money and water without lowering yield.
In fact, about one-third could have saved a lot!
On the other hand, about 60% to 80% are doing a good job during the dry years as shown in Table 1.
We should always keep adequate soil moisture levels to maximize yield on irrigated fields if we have the water.
During peak water use, UNL recommends maintaining soil water storage levels above 50% of plant available water in the top three feet of soil.
Watering the Emerald Triangle: Irrigation sources used by cannabis cultivators in Northern California
 Reported subsurface water use among North Coast cannabis cultivators is widespread and may become increasingly common.
by Christopher Dillis, Theodore E.
Grantham, Connor McIntee, Bryan McFadin and Kason Grady
 Water use by cannabis cultivators represents an emerging threat to surface flows in Northern California's sensitive watersheds.
To date, however, no data has been available to formally assess where cannabis sites source their water.
This study analyzed data from annual reports, covering the year 2017, submitted by 901 cannabis cultivators enrolled in the Cannabis Waste Discharge Regulatory Program administered by the North Coast Regional Water Quality Control Board.
The analysis identified cannabis cultivators' most common sources for water extraction, monthly patterns for each water source and differences between sites compliant and not compliant with the cannabis program.
The most commonly reported source of water was wells , with most extraction from wells occurring during the growing season.
Surface water diversions  and spring diversions  were the most common sources after wells, with extractions from these sources distributed much more evenly across the year.
Although nearly one-third of noncompliant sites  used wells, this source was more than twice as frequently reported among compliant sites , indicating that wells may become increasingly common as more sites become part of the regulated cannabis industry.
A ssessing the environmental impacts of the cannabis industry in Northern California has been notoriously difficult.
The federally illegal status of cannabis has prevented researchers from obtaining funding and authorization to study cultivation practices.
Fear of federal enforcement has also driven the industry into one of the most sparsely populated and rugged regions of the state , further limiting opportunities for research.
The result has been a shortage of data on cultivation practices and their environmental risks.
An improved understanding of cannabis cultivators' water use practices is a particularly pressing need.
Given the propensity of cannabis growers to establish farms in small, upper watersheds, where streams that support salmonids and other sensitive species are vulnerable to dewatering , significant concerns have been raised over the potential impacts of diverting surface water for cannabis cultivation.
The
 environmental impacts of stream diversions are likely to be greatest during the dry summer months , which coincide with the peak of the growing season for cannabis.
Further, because cannabis cultivation operations often exhibit spatial clustering , some areas with higher densities of cultivation sites may contain multiple, small diversions that collectively exert significant effects on streams.
An important assumption underlying these concerns, however, is that cultivators rely primarily on surface water diversions for irrigation during the growing season.
Assessments of water use impacts on the environment may be inaccurate if cultivators in fact use water from other sources.
For instance, withdrawals from wells may affect surface flows immediately, after a lag or not at all, depending on the well's location and its degree of hydrologic connectivity with surface water sources.
Documenting the degree to which cannabis cultivators extract their water from aboveground and belowground sources is therefore a high priority.
In 2015, the North Coast Regional Water Quality Control Board , one of nine regional boards of the State Water Resources Control Board, developed a Cannabis Waste Discharge Regulatory Program  to address cannabis cultivation's impacts on water, including streamflow depletion and water quality degradation.
A key feature of the cannabis program is an annual reporting system that requires enrollees to report the water source they use and the amount of water they use each month of the year.
Enrollees are further required to document their compliance status with several standard conditions of operation established by the cannabis program.
These include a Water Storage and Use Condition, which requires cultivators to develop off-stream storage facilities  to minimize surface water diversions during low flow periods, among other water conservation measures.
Reports that demonstrate noncompliance with the Water Storage and Use Standard Condition indicate that enrollees have not yet implemented operational changes necessary for achieving regulatory compliance.
In this research, we analyzed data gathered from annual reports covering 2017 to gain a greater understanding of how water is extracted from the environment for cannabis cultivation.
We addressed three main questions:
 1.
From what sources do cannabis cultivators most commonly report extracting water for cannabis cultivation in the North Coast region and do patterns of extraction differ across the region?
2.
How does reliance on each water source differ from one month to another?
3.
Do sites that report compliance with the Water Storage and Use Standard Condition, and sites
 that report noncompliance, rely on different water sources?
The data used to answer these questions was selfreported.
Individuals providing data were not required to use standardized, controlled collection procedures or calibrated instrumentation.
Authors of this research took steps to increase the dataset's integrity, but the data should be used and interpreted with a recognition that uncertainty and various potential biases are involved.
The data used in this study was collected from cannabis sites enrolled for regulatory coverage under the cannabis program.
The program was adopted in August 2015, with the majority of enrollees entering the program in late 2016 and early 2017.
The data presented in this article was collected from annual reports submitted in 2018 , which reflected site conditions during the 2017 cultivation year.
The data therefore represents, for the majority of enrollees in the cannabis program, the first full season of cultivation regulated by the water quality control board.
Because the data was self-reported, we screened reports for quality and restricted the dataset to reports prepared by professional consultants.
Most such reports were prepared by approved third-party programs that partnered with the board to provide efficient administration of, and verification of conformity with, the cannabis program.
Additional criteria for excluding reports included claims of applying water from storage without any corresponding input to storage, substantial water input from rain during dry summer months and failure to list a proper water source.
Reports containing outliers of monthly water extraction amounts were also identified and excluded due to the likelihood of erroneous reporting or the difficulty of estimating water use at very large operations.
Extreme outliers were defined as those values outside 1.5 times the bounds of the interquartile range (25th percentile through 75th
 Wellhead at a permitted cannabis cultivation site.
Withdrawals from wells may affect surface flows immediately, after a lag or not at all.
Cannabis growers often establish farms in small, upper watersheds, where streams that support sensitive species such as coho, pictured, are vulnerable to dewatering.
percentile range of all values).
Farms were not required to use water meters, and those without meters often estimated usage based on how frequently they filled and emptied small, temporary storage tanks  otherwise used for gravity feed systems or nutrient mixing.
The final dataset included 901 reports.
Parcels of land where cannabis was cultivated including multiple contiguous parcels under single ownership constituted a site, and this is the scale on which reporting was conducted.
The spatial extent of the cannabis program included all of California's North Coast region ; however, only a subset of the counties in this region allow cannabis cultivation and therefore reports were only received from the following counties: Humboldt , Trinity , Mendocino  and Sonoma.
Because Sonoma County contributed relatively little data, we combined Sonoma County's enrollments with those from Mendocino County when making county-level comparisons.
FIG.
1.
Map of study area.
Humboldt, Trinity and Mendocino counties together comprise the "Emerald Triangle," entirely contained within the North Coast region of California.
Additional reports were collected from sites in Sonoma County but, due to the small size of that sample, the reports were combined with Mendocino County's for analysis.
The data used for this analysis included the source and amount of water that cultivators added to storage each month as well as the source and amount of water applied to plants each month.
We did not analyze absolute water extraction rates.
Rather, we used the amount of water extracted each month whether water was added to storage or applied to plants directly from the source to analyze seasonal variation in each water source's share of total water extraction.
Water sources included: surface , spring , rain , well , delivery  and municipal .
The two external sources delivery and municipal were consolidated into a single category.
Because staff from the water quality control board were not able to corroborate the accuracy of reported data, enrollees may have classified water sources erroneously.
A well placed in proximity to a stream, for example, might properly qualify as a diversion of surface water; SO might rainwater catchment ponds or spring diversions that are hydrologically connected to a watercourse.
We attempted to minimize these potential errors by restricting the dataset to reports prepared by professional consultants.
As mentioned, enrollees were required to assess several standard conditions in their site reports, including water storage and use requirements.
To encourage cultivators to join the regulated industry, and because many cultivation sites existed prior to adoption of the cannabis program, existing sites were not required to comply with standard conditions as a prerequisite for enrollment.
Rather, cultivators unable to comply with the standards when they enrolled were required to indicate their lack of compliance and develop a plan for achieving compliance.
Such sites were not held in violation of regulations, thus removing a potential motivation to falsely report site conditions.
More than one-quarter  of enrollees in the dataset  reported noncompliance with the Water Storage and Use Standard Condition.
Analysis of water sources
 To address question 1 from which sources cannabis cultivators most frequently extract water across the North Coast region, and if extraction patterns differ across the region we calculated the percentage of sites that reported use of each water source.
We also calculated, for sites using each source, the percentage of sites that also used at least one other source category.
Directly applying water to plants and also placing water in storage did not constitute use of multiple extraction sources if the water was drawn from the same source category.
Additionally, sites that used multiple inputs from the same category for example, multiple wells were not considered users of multiple sources, as this classification was reserved for extraction from multiple categories of sources.
We performed all elements of
 our analysis for the entire dataset and for each county individually.
To address question 2 how reliance on each water source differed from one month to another we divided each site's monthly water extraction total by its annual extraction total to calculate the relative percentage of water extracted in each month, and performed similar calculations for each source category.
The median amount of water extracted and interquartile range were calculated for each month both for overall extractions and for each source category individually.
To address question 3 whether sites reporting compliance with the Water Storage and Use Standard Condition relied on different water sources than those reporting noncompliance we compared water source extraction patterns for sites of both types.
Specifically, we calculated for each compliance status the percentage
 of sites that extracted water from each source category and made comparisons accordingly; and did likewise for monthly extraction patterns, following procedures similar to those described in regard to question 2.
The purpose of this comparison was strictly qualitative, and no inferential statistics were performed to determine statistically significant differences.
Instead, this element of our analysis was performed for exploratory purposes, with the intention of identifying broad trends that warrant future attention.
Water sources varied across counties
 The most commonly reported water source was wells.
Over half the sites  reported at least some reliance on wells for their irrigation water.
FIG.
2.
Examples of water sources.
Subsurface water well.
Well casing with associated power box and piping, used to convey water to storage or used for direct application.
Spring diversion.
Spring box installed to consolidate flow, which is then directed through PVC piping.
Surface water diversion.
Example of a typical stream used for surface water diversion.
Streams may vary from perennial watercourses to seasonal drainages.
Rainwater catchment.
Storage tanks with filtered tops are one of many means for collecting rainwater.
FIG.
3.
Percentage of sites extracting water from each source, overall and in each county analyzed.
Shaded portions of bars depict the percentage of sites using each respective source that also used additional sources.
The shaded portion depicting percentage corresponds to the length of each bar individually, rather than the x-axis.
Surface water  and springs  were the next-most common sources.
Rainwater catchment and off-site water were the least commonly used water sources.
Sites using wells and off-site sources were the least likely to use additional sources.
In contrast, sites using rain catchment systems most frequently reported using an additional source category , followed by sites reporting use of spring diversions  and surface diversions.
To determine if the observed high frequency of well use was due to bias associated with examining only reports prepared by consultants, we reincorporated sites without consultants and reran the analysis on this dataset.
Reported well use was slightly more common among sites not using consultants  than among sites using consultants.
Counties displayed notable variation in the frequency with which cannabis cultivators used particular water sources.
Compared to all sites in the dataset, sites in Humboldt County relied more on surface water  and spring diversions , with fewer relying on wells.
The pattern was reversed in Trinity County, with a high percentage of sites there reporting well use  and relatively few using surface  and spring  diversions.
A large number of sites  in Trinity County were located in a single watershed known for a high concentration of similar cultivation practices, so we recalculated the percentages with these sites excluded.
The resulting totals for Trinity County were closer to the overall results: wells , surface , spring , rain  and off-site.
Mendocino and Sonoma counties  reported a similar pattern of extraction sources per site: wells , surface , spring , rain  and off-site.
Patterns of using multiple sources varied among counties.
Sites in Humboldt County using well water extraction much more commonly used additional sources of water  than did similar sites in Trinity  and Mendocino/Sonoma  counties.
Use of additional sources was also more common among Humboldt County sites extracting surface water  and spring water  than among sites using surface and spring water in Trinity County  and Mendocino/Sonoma counties.
Wells were a prominent water source for cannabis cultivators during the summer months.
Extraction from wells generally peaked in August and declined in off-season months.
The pattern was reversed for rainwater use, with most extraction OCcurring in off-season months.
Spring water use was generally even across the year, with slightly higher use
 FIG.
4.
Relative monthly water extraction.
Boxes depict the interquartile range, with black lines at median values for each month.
Monthly values reflect the sum of water placed in storage and directly applied to plants.
during the growing season.
Surface diversions occurred throughout the year, but declined late in the growing season, likely reflecting declining availability of surface water.
The pattern exhibited in off-site water use closely matched that of well water; the former, however, was a less substantial source of water in general.
There appeared to be differences in the extraction sources reported by compliant and noncompliant sites.
Although nearly one-third of noncompliant sites  used well extraction, this source was more than twice as frequently reported among compliant sites.
In contrast, noncompliant sites reported surface diversion  and spring diversion  more commonly than did compliant sites.
Rain and off-site sources were the least commonly used for both compliant sites  and noncompliant sites.
Use of additional alternative sources was lower for compliant sites with wells  than for noncompliant sites with wells.
The seasonal extraction patterns of compliant and noncompliant sites were generally similar , following the overall pattern discussed above.
We found that well water is the most commonly reported source of extracted water for cannabis cultivation in the North Coast region of California.
Furthermore, among the source categories, wells are least frequently supplemented with alternative sources.
Spring and surface water diversions together are also important water sources, with seasonal patterns of use that are distinct from well water extraction.
Reported timing of well water extraction closely tracks the water demand patterns of plants, indicating that cultivators are applying well water directly to plants, rather than storing it.
In contrast, the timing of extractions of spring water and surface water remains relatively consistent throughout the year, suggesting that water from these sources may be diverted to storage in the winter, reducing the need for extraction in the summer months.
These seasonal extraction patterns and the relative predominance of each source may inform assessments of cannabis cultivation's impacts on water availability.
The use of well water for cannabis cultivation, in comparison to other water sources, presents both potential threats and benefits for instream flow.
In upper reaches of small watersheds, streams are dependent throughout the summer months on subsurface water flows from the landscape into the stream.
Well water extraction may reduce cold water inputs limiting streamflow or, in extreme conditions, dewatering stream channels.
The extent to which use of subsurface water affects streamflow and water temperature depends on the degree to which well water sources are hydrologically connected to streams.
When wells are shallower and closer to streams, and
 when soil conductivity is greater, subsurface water pumping is more likely to directly capture streamflow.
However, if wells are less hydrologically connected to streams, the effects of extraction will be attenuated, resulting in smaller-magnitude and temporally lagged streamflow depletions.
With sufficient groundwater recharge in wet months, well water extractions may affect streamflow less than surface water diversions, which were previously assumed to be cannabis cultivators' predominant means of obtaining water in the region.
Further analysis is necessary to understand the potential impacts of well use on streamflow depletion.
Such an analysis would incorporate information on well locations and depths and would consider the underlying geology and soil properties at cultivation sites.
Meanwhile, the prevalence and distribution of wells relative to other water sources are influenced by broader geospatial characteristics such as topography and precipitation patterns.
Understanding these issues will also be important for assessing the threats and benefits associated with subsurface water extraction.
Variation between counties in well extraction patterns demonstrates that, although subsurface water may be the most common source of water in North Coast cannabis cultivation, the availability of alternative  sources may play an important role.
Humboldt County watersheds included in this study consistently receive more average annual precipitation  than do those in Trinity , Mendocino  and Sonoma  counties.
This difference translates into more available surface and spring water in Humboldt County over the course of the growing season.
The observation that fewer sites in Humboldt County report well use, compared to other counties in the study, suggests that if surface or spring water is available, cultivators are likely to use it.
Conversely, the potential necessity of groundwater use in counties that receive less rainfall holds particular importance in consideration of emerging areas of
 FIG.
5.
Percentage of sites extracting water from each source, organized according to reported compliance status.
Shaded portions of bars depict the percentage of sites using each respective source that also used additional sources.
The shaded portion depicting percentage corresponds to the length of each bar individually, rather than the x-axis.
industry growth throughout California.
Further analysis is needed to understand how likely cultivators are to rely on wells if other sources of water are available to them.
The winter preceding the 2017 growing season was the wettest on record.
It is important to understand how cultivators may source their water during years in which summer water availability is not as abundant.
These findings suggest that cultivators may utilize wells both as insurance against surface water scarcity in the summer drought months and as a means of achieving regulatory compliance.
The observation that nearly one-third of noncompliant sites reported well extraction indicates that use of subsurface water may be a common means to avoid water scarcity in the late growing season.
While Northern California receives considerable seasonal rainfall, there is also
 significant spatial variability in rainfall totals and in corresponding summer flow persistence of small streams.
Considering the ephemeral nature of surface water in many areas , the increasing frequency of drought due to climate change  and cannabis cultivation's consistent demand for irrigation water as crops near harvest , cultivators are strongly motivated to secure reliable water sources for the entirety of the growing season.
Therefore, it is likely that water extraction from wells is a common practice for cultivators, beyond those seeking participation in the regulated industry.
Although cannabis regulations place no explicit restrictions on where water is sourced, those currently within or seeking to
 FIG.
6.
Comparison of relative monthly water extraction for compliant and noncompliant sites.
Boxes depict the interquartile range, with black lines at median values for each month.
Monthly values reflect the sum of water placed in storage and directly applied to plants.
join the regulated cannabis industry will be subject to a restriction on diversions of spring and surface water during the growing season.
This requirement  is already in place for permits issued by the California Department of Fish and Wildlife and will also be enforced by the State Water Resources Control Board beginning in 2019.
The data provided in this study indicates that, in order to meet the forbearance period requirement, cultivators may be more inclined to drill a well to achieve compliance than to develop water storage for spring and surface water.
Determining cultivators' capability to store the water they need for the growing season may shed further light on the likelihood that growers will seek subsurface water.
If compliance necessitates drilling a well, it will be important to account for the impacts of this potential shift in cultivation practices.
Successful protection of freshwater resources in Northern California will require a more complete accounting of where cannabis cultivators source their water and the amount and timing of water extracted.
Study of cannabis as an agricultural crop has been notoriously inadequate, but data provided by the water quality control board's cannabis
 program offers critical new insights into the water use practices of cultivators entering the regulated industry.
In this initial analysis, we found that subsurface water may be much more commonly used in cannabis cultivation than previously supposed.
Further analyses of cannabis cultivation's water extraction demand, as well as of geospatial variation in water demand, may help elaborate the ramifications of this finding.
Ultimately, a better understanding of cannabis cultivation's water demand will be useful for placing the cannabis industry in the greater context of all water allocation needs in the North Coast and throughout California.
Nonpoint Source Pollution in the L'Anguille River Watershed
 The L'Anguille River Watershed is located in northeast Arkansas and includes communities in Craighead, Cross, Lee, Poinsett, St.
Francis and Woodruff counties.
A "watershed" is an area of land where all of the water that drains from it goes to the same place, SO rainwater or snowmelt in this watershed eventually drains to a common location.
This Delta watershed is long and narrow and is named for the major waterway in the area, the L'Anguille River.
Beginning just south of Jonesboro, the river flows southward for 98 miles until it reaches the St.
Francis River near Marianna.
The watershed spans 973 square miles and is home to an estimated 33,166 people as of 2011.
Nearly 71 percent of the land in this watershed is used for row crops.
Water pollution that comes from multiple sources spread over an area, such as runoff from parking lots, agricultural fields, residential lawns, home gardens, construction, mining and logging, is known as nonpoint source pollution.
As runoff moves across the landscape, it carries natural and manmade substances that can accumulate in waterways and make them uninhabitable for aquatic species or unusable by people.
Potential pollutants include bacteria, nutrients, sediment, hazardous substances and trash.
3 Given the number of potential sources and variation in their potential contributions, these pollutants are not easily traced back to their source.
L'Anguille River Watershed Data source: GeoStor.
Map created March 2011.
Major streams: Brushy Creek, First Creek, L'Anguille River, Larkin Creek, Second Creek
 Second Creek, a tributary of the L'Anguille River, was designated by the state as an "Extraordinary Resource Water" or a water resource that is valued for characteristics such as beauty, recreation and social use.
4
 This fact sheet is intended to provide a better understanding of the L'Anguille River Watershed and its place on the state's priority list of 10 watersheds impacted by nonpoint source pollution.
L'Anguille River Watershed Water Quality Issues
 Through water quality monitoring, environmental officials in Arkansas have determined that the entire length of the L'Anguille River has problems supporting some aquatic species because of high turbidity levels.
5,6 Turbidity is a measure of the clarity of water.
High turbidity levels mean the water is murky from a variety of materials, such as soil particles, algae, microbes and other substances.
7
 Essentially all streams in the watershed have high turbidity and silt issues that may be a result of the clearing and channelization of streams for agricultural irrigation.
8 Additionally, development and property management practices can influence the amount of sediment that runs off properties along Crowley's Ridge.
Other major nonpoint source pollution
 Arkansas' Priority Watershed List for Nonpoint Source Pollution
 Arkansas has used a watershed-based approach to nonpoint source pollution management, allowing the public to guide planning to address water quality concerns.
8 The Arkansas Natural Resources Commission, or ANRC, administers the Nonpoint Source Pollution Management Program.
The program exists to reduce water pollution through the funding of watershed planning and restoration activities, adoption of voluntary best management practices and the development of technologies that assist in water pollution reduction in Arkansas.
Based on public input and the use of a qualitative risk assessment matrix, ANRC has designated 10 priority watersheds as needing the greatest attention.
The risk matrix9 identified the following priority watersheds for 2011-2016: Bayou Bartholomew, Beaver Reservoir, Cache River, Illinois River, L'Anguille River, Lake Conway-Point Remove, Lower Ouachita-Smackover, Poteau River, Strawberry River and Upper Saline.
concerns for this watershed are low oxygen levels, total dissolved solids, chlorides and sulfates, according to the Nonpoint Source Pollution Management Plan.
10
 These concerns led to the L'Anguille River Watershed being designated as a priority by ANRC in the state's 2011-2016 Nonpoint Source Pollution Management Plan.
To encourage continued public input, the University of Arkansas Division of Agriculture's Public Policy Center facilitated a water quality stakeholder forum for the L'Anguille River Watershed in August 2015.
Participants identified erosion as their watershed's priority concern that needed addressing but also expressed concern over sedimentation and water velocity.
Forum participants reviewed a long list of stakeholders who should be engaged in addressing water quality concerns.
Participants said the people who live near Crowley's Ridge, as well as developers of the properties, aren't aware of the impact they have on water quality downstream or do not see it as an issue.
They recommended educating people living near Crowley's Ridge and the developers about the dual benefits of managing property aesthetics and water quality.
People who live, work or recreate in this watershed are encouraged to consider these community priorities when addressing water pollution.
The public is also welcome to attend an annual stakeholder meeting where priority watersheds and nonpoint source pollution are discussed.
For more information about nonpoint source pollution and its impact on the L' Anguille River Watershed, contact the Cooperative Extension Service, Arkansas Natural Resources Commission or the Arkansas Department of Environmental Quality.
The Arkansas Watershed Steward Handbook is also a good source of information about basic water quality concerns and how the public can get engaged in addressing water pollution.
11
 6 See the Nonpoint Source Pollution Management Plan.
8 Integrated Water Quality Monitoring and Assessment Report , 2008.
Arkansas Department of Environmental Quality: Little Rock, Arkansas.
See the Nonpoint Source Pollution Management Plan.
10 Learn about these water quality issues in the Arkansas Watershed Steward Handbook.
11 See the Arkansas Watershed Steward Handbook.
This fact sheet is one in a series of 10 fact sheets on nonpoint source pollution in priority watersheds.
The University of Arkansas Division of Agriculture's Public Policy Center provides timely, credible, unbiased research, analyses and education on current and emerging public issues.
Colorado State University Extension
 Subsurface Drip Irrigation 
 Fact Sheet No.
4.716
 Subsurface drip irrigation is a lowpressure, high efficiency irrigation system that uses buried drip tubes or drip tape to meet crop water needs.
These technologies have been a part of irrigated agriculture since the 1960s; with the technology advancing rapidly in the last three decades.
A subsurface system is flexible and can provide frequent light irrigations.
This is especially suitable for arid, semi-arid, hot, and windy areas with limited water supply, especially on sandy type soils.
Since the water is applied below the soil surface, the effect of surface irrigation characteristics, such as crusting, saturated conditions of ponding water, and potential surface runoff  are eliminated when using subsurface irrigation.
With an appropriately sized and wellmaintained system, water application is highly uniform and efficient.
Wetting occurs around the tube and water typically moves out in all directions.
Subsurface irrigation saves water and improves yields by eliminating surface water evaporation and reducing the incidence of weeds and disease.
Water is applied directly to the root zone of the crop and not to the soil surface where most weed seeds germinate after cultivation.
As a result, germination of annual weed seeds is greatly reduced which lowers weed pressure on cash crops.
In addition, some crops may benefit from the additional heat provided by dry surface conditions, producing more crop biomass, provided water is sufficient in the root zone.
When managed properly with a fertilizer injector, water and fertilizer application efficiencies are enhanced, and labor needs are reduced.
Field operations are also possible, even when irrigation is applied.
The degree to which one is willing to invest in subsurface irrigation technology and maintenance determines its suitability for certain crops.
Although it can be tailored to work with almost all crops across a wide spectrum of enterprise types, it is mostly used for high-value vegetable crops, turf and landscapes.
In addition, strawberry, tomato, potato, cantaloupe, onions and other vegetables have also shown improvements, both in yield and quality, with melon crops maturing earlier and more uniformly.
The improvements on these crops are enhanced when subsurface irrigation is used in conjunction with plastic mulches.
Soils with low infiltration rates, like many on the Colorado western slope soils, pose a challenge for subsurface irrigation and drip tube spacing needs to be adjusted for clayey type western slope soils.
Apart from depth, spacing of drip tubes will also impact crop health.
It is also important to know characteristics of the soil type for your crop to optimize irrigation scheduling with subsurface irrigation.
Contact your county CSU Extension or USDA-NRCS office for assistance.
Alfalfa germination may need to be done with hand-set sprinklers before using the subsurface irrigation-then many benefits are available; such as:
 1.
subsurface irrigation tubing can be semi-permanently installed, eliminating most of the annual replacement cost;
 2.
irrigation can occur much closer to cutting dates since the surface can remain dry for machinery; also
 3.
alfalfa regrowth after a cutting may be enhanced by subsurface irrigation since it does not contribute to the germination and emergence of shallow-rooted weeds.
Subsurface drip irrigation is a low-pressure, high efficiency irrigation system that uses buried drip tubes or drip tape to meet crop water needs.
Subsurface irrigation saves water and improves yields by eliminating surface water evaporation and reducing the incidence of weeds and disease.
A subsurface drip system may require higher initial investment than a gated pipe/furrow system and cost will vary due to water source, water quality, filtration needs, choice of material, soil characteristics and degree of automation desired.
*D.
Reich, former Colorado State University Extension water resource specialist; R.
Godin, CSU Agricultural Experiment Station and Extension research scientist; reviewed by Jos L.
Chvez, CSU irrigation specialist; original author, former Colorado State University Extension irrigation specialist.
8/2014
 A large variety of drip tubes are available on the market.
The spacing and the flow rate of the emitters in subsurface drip tubes vary according to the product and soil type and should match the water needs of the crop grown.
The polyethylene tubes have built-in emitters that can vary from 4 to 24 inch spacing, operating at low nominal pressure , to dribble water into the soil at a consistent and predictable rate (0.07-2.5 g Pressurecompensating emitters means subsurface irrigation is suitable to distribute water uniformly in sloping fields.
Furthermore, research has shown that emitter discharge of subsurface irrigation systems resulted in greater irrigation uniformity than surface drip irrigation, due to the interaction between effects of emitter discharge and soil pressure.
Drip tubes vary in wall thickness.
The higher the "mil" number the thicker the wall , which extends the life of the tube.
The cost tends to increase with increases in wall thickness.
However, for semi-permanent systems such as alfalfa, more robust tubing is key to minimizing maintenance and rodent problems.
If burrowing rodents are common in your area you should consult with your county CSU Extension or USDA-NRCS office prior to moving forward with a subsurface irrigation system.
Also consult with your county CSU Extension or USDA-NRCS office or subsurface irrigation supplier about emitter spacing or tube thickness combination works best for your soils and operation.
A typical system layout consists of a settling pond , pumping unit, pressure relief valve, check valve or back flow prevention valves, a sand media filter , chemical injection unit, filtration unit equipped with back-flush control solenoid valves, pressure regulators, air vent valves, and PVC pipe lines delivery system to carry the water to the field.
lateral drip tubes are attached.
Items such as a flow meter and pressure gauges are essential to monitoring the performance of the system and providing warning of leaks and blockages.
The delivery system is composed of main, sub-main and manifold, to which the
 It is essential to provide an air release/ vacuum breaker valve at the manifold for easy drainage of the tubes when the pump is shut off.
This will allow the release of trapped air that can damage the pump  and disrupt irrigation.
Install the valve at the highest point in the pump's discharge piping, but in a manner that makes it safely and easily accessible.
These vacuum breakers help maintain line pressure when shutting down after an irrigation.
A rapid drop in line pressure can cause tubes to collapse or flatten.
This is one of the drawbacks in a newly installed system, loose soil may settle around a collapsed tube, making it difficult for the tube to regain its shape, at the commencement of the next irrigation.
Drainage valves at the end of each tube at the end of the field are also essential for clearing small soil particles that have passed through the filter system and for draining the tubes at the end of the irrigation season.
The tubes are inserted below the soil surface, using an attachment pulled by a tractor.
The placement depths vary from 6 to 24 inches, depending on the soil, top soil depth and crop.
Shallow-rooted crops, like strawberries, may require placement as shallow as 3 to 4 inches below the surface.
Laying tape or tube higher in the soil profile depends on the capillary action or "wickability" of the soil.
Some soils, such as quick draining sandy or gravel soils, do not wick moisture evenly out from emitters, with the soil above the emitters
 Figure 1: A typical subsurface microirrigation field layout.
typically receiving less water.
In these instances, place tape or tube closer to the surface to germinate seeds and sustain seedlings.
Otherwise, a portable sprinkler system should be available for seed germination.
Placing subsurface irrigation deeper in the soil also enhances soil tillage benefits.
In all cases, face the emitters on the tubes upward at installation.
Once an emitter depth is decided on, consistent depth placement of tubing or tape is helps to achieve uniform soil-water content throughout the field but is not necessary if tubing has pressure-compensating emitters.
It is essential to have a filtration unit that will filter all the particles that are bigger than the emitter openings.
As a rule of thumb, filters should remove particles four times smaller than the emitter opening, or as small as economically feasible; since particles my group and clog emitters.
A filtration system mainly consists of sand media filters; however, a combination of screen and disk filter with sand media filters is highly desirable.
A screen filter installed before sand media filters  will remove larger organic and inorganic debris  before the suspended material reaches the sand filter, however, with large amounts of early season debris mesh filters may not be feasible as labor is needed to flush almost hourly.
A 200 mesh filter is adequate for most types of emitters although some drip tapes require only 100 mesh.
Filtration can be viewed as the heart of a subsurface irrigation system and should be designed properly by agencies mentioned above or your professional system supplier, to fit the level of contamination in the water source.
Filtration may not be a concern for subsurface irrigation in urban areas where domestic or higher quality well water is used.
The performance and life of any system depends on how well it is designed, operated and maintained.
Whether automatically controlled or otherwise, inspect the system regularly.
What's more,
 since subsurface irrigation is under the surface, repairing tubes is difficult and cumbersome.
Another drawback is that plugged emitters are not noticeable until the plants are wilted.
Also, rodents tend to chew the tubes, therefore use precaution to prevent rodent damage, or do not use a buried system where rodents are common.
The filtration back-flush system needs to be well maintained and the laterals flushed at regular intervals  are needed at the end of the lateral line as mentioned earlier).
Clogging is also not readily apparent, SO you may choose to use acid solutions  and/or chlorine  that often boost flushing effectiveness.
In Colorado, acid is most often used for flushing since it will also eliminate algae and carbonate  build up.
Cleanout valves installed at the end of the tube lines are important to remove blockages and draining the system.
The quality of water affects the system.
High pH water will tend to precipitate a white calcium salt residue, especially with pressure changes that occur across subsurface irrigation emitters.
Calcium and iron precipitates are a problem with most well waters.
High salinity or iron concentrations in the water will also cause precipitates; which are aggravated by the presence of organic matter, bacteria and algae.
These will require more frequent flushing measures.
Deep well water may be free of scum, but check the pH to avoid precipitate buildup.
Other sources of emitter clogging can be plant roots that tend to grow into the small emitters.
Emitter blockage is often a function of poor subsurface irrigation design, consult with CSU Extension or NRCS staff to ensure you have sized pumps, lines, filters and zones correctly.
drip tubes and emitters with acid solutions.
Never mix acid and chlorine!
Be sure to flush lines thoroughly with untreated water in between chemical flushes.
N-phuric, a commercial mixture of acid and N-fertilizer available in the market, is useful.
In addition to lowering the pH to reduce precipitate formation, the product will provide nitrogen fertilizer to the crop.
However, caution should be used and N-phuric should not be used late in the growing season as it will delay maturity and delay dormancy in perennial crops.
It is essential to winterize the system at the end of the cropping season by thoroughly draining all pipes and ancillaries.
An air compressor may help blow out the residual water, especially from the above ground fixtures.
Polyethylene tubes are flexible and won't typically break due to freeze.
It is essential to have a filtration unit for a drip system, irrespective of whether the dripper is used above ground or below the ground surface.
Contaminants can be controlled with chemical flushes or injection.
Chemicals to consider are acid, acid-forming chemicals or chlorine.
Contact your local CSU Extension office for advice on flushing
 A subsurface drip system may require higher initial investment and cost will vary due to water source, water quality, filtration needs, choice of material, soil characteristics and degree of automation desired.
System cost, including installation, may range from $2000 to $4000 per acre, however, economies of scale do also apply to subsurface drip.
Research consistently shows yield and quality of produce improves when a subsurface irrigation system is used.
Normal life expectancy of a system is considered to be 12 to 15 years.
Some systems have been reported to last 20 years with good maintenance, and could last longer provided good quality water is used.
The system remains buried in the ground for many years.
Cost-share programs such as the Environmental Quality Incentives Program  also exist to assist with improvements.
For additional information on irrigation management and scheduling, see Colorado State University Extension fact sheets:
 4.707, Irrigation Scheduling: The Water Balance Approach
 4.702, Drip Irrigation for Home Gardens
 4.703, Micro-Sprinkler Irrigation for Orchards
 Additional information on the Web:
Irrigated Agriculture in Oklahoma
 Mukesh Mehata Research Assistant
 Saleh Taghvaeian Extension Specialist in Water Resources
 Irrigation plays a vital role in fostering the economic viability of agricultural production in Oklahoma, especially in the arid and semi-arid western parts of the state.
In recent years, irrigated agriculture has been challenged by prolonged droughts and strong competition from industrial, urban and environmental sectors over limited freshwater resources.
These constraints along with the increasing demand in food, feed, fiber and fuel necessitate the urgent need to provide Oklahoma producers with tools to improve irrigation management and maximize water productivity.
This task, however, is not possible without understanding the current situation of irrigated agriculture and investigating its potential weaknesses and opportunities.
This fact sheet provides an overall picture of the state of irrigated agriculture in Oklahoma.
The information and analysis are based on the data published in the Irrigation and Water Management Survey  conducted in 2018 by the National Agricultural Statistics Service of the USDA.
Irrigation and Water Management Survey, 2018
 The 2018 Irrigation and Water Management Survey adds detailed irrigation-related information to the basic data collected from all agricultural operations in the 2017 Census of Agriculture.
Some of the 2018 data are not comparable with previous survey reports conducted in 1997, 2003, 2008 and 2013, since the definition and reporting of some operations  has changed.
Comparisons in this fact sheet are made keeping this point in mind to avoid misleading conclusions.
According to the 2018 survey, Oklahoma has 1,835 farms containing irrigated lands.
The total area of land in these farms exceeds 3.4 million acres, with an actual irrigated area of 601,492 acres.
This shows a 41% increase compared to the total irrigated acres in 2013 survey and a 30% increase compared to the 2008 survey.
The larger increase compared to 2013 is probably due to the severe drought of 2011-2014, which resulted in many farms losing their ability to irrigate in those years.
In terms of actual irrigated acres, Oklahoma is ranked 22nd among all 50 states.
All our neighboring states have significantly larger
 2018 Irrigation and Water Management Survey Volume 3 Special Studies Part 1
 United States Department of Agriculture Sonny Perdue, Secretary National Agricultural Statistics Service Hubert Hamer, Administrator
 Figure 1.
The 2018 survey cover page.
irrigated areas, ranging from New Mexico with about 675,300 acres  to Arkansas with 4.25 million acres.
The total amount of irrigation water applied in the survey year was 662,063 acre-feet, which is equal to more than 215 billion gallons.
This shows a 27 and 26% increase compared to 2013 and 2008 estimates, respectively.
The increase in the total amount of applied water seems to be caused by the expansion of irrigated area and not necessarily a change in the amount of irrigation applied to a unit of land.
Less than 0.1% of the total amount was applied to operations under protection  and the remaining  was applied to operations in the open.
Eighty-five percent of the total water applied in the open in 2018 was supplied from groundwater resources and the remaining 15% from surface resources.
This indicates a smaller
 Figure 2.
An irrigation canal taking water from Lake Altus in southwest Oklahoma to agricultural fields.
reliance on groundwater compared to 2013, when groundwater accounted for 92% of irrigation water applied in the open.
The larger dependence on groundwater in 2013 was probably a result of the 2011-2014 drought, which severely limited surface water resources.
The share of groundwater in supplying irrigation was about 83% in 2008, like 2018.
However, the volume of groundwater withdrawn for irrigation in 2018 was 30% larger than 2008 and 17% larger than 2013.
This increase in the total amount of groundwater extraction could shorten the life of those aquifers that have a limited recharge capacity, such as the Ogallala aquifer in Oklahoma Panhandle.
It should be noted that the reported amount of applied water is based on irrigators' best estimate and not metered flow rates.
Reclaimed water, defined as the wastewater that has been treated for non-potable reuse purposes, could be an important source of water when freshwater resources are scarce.
In 2018, only two farms in Oklahoma reported the use of reclaimed water for irrigation.
This number was 40 farms with total irrigated acres of 3,775 and 18 farms with total irrigated acres 2,205 in 2008 and 2013, respectively.
These statistics suggest there is a significant potential for reuse of reclaimed water in irrigated agriculture in Oklahoma.
According to the survey, 5,702 irrigation wells were in use on Oklahoma irrigated lands in 2018, which is 16% more than 2013 and 53% more than 2008.
Among all wells surveyed in 2018, 19% had meters to monitor groundwater withdrawal, up from 16 and 13% in 2013 and 2008, respectively.
In addition, 35% of wells did not have a backflow prevention device , which is necessary to prevent the flow of potential contaminants into aquifers; especially if chemigation is practiced.
Chemigation is the injection of chemicals such as fertilizers and pesticides into irrigation systems.
The 2018 average well depth was 194 feet in Oklahoma, smaller than the average depth in 2013  and 2008.
The average depth to water estimated at the beginning of the growing season was 87 feet in Oklahoma, according to the 2018 survey.
Compared to 2013 survey, only 9% of Oklahoma wells showed an increase in depth to water, while 45% reported no change.
However, the 2018 average pumping capacity was 368 gallons per minute , which was 10% less than 2013 and 27% smaller than 2008.
The decline in pumping capac-
 ity over time is consistent with increase in total groundwater withdrawal mentioned before.
The national average pumping capacity in 2018 was 708 gpm.
Irrigation Pumps and Energy Costs
 Regardless of water source , many irrigated farms rely on pumps to either raise the water to a desired level or to pressurize it for distribution through sprinkler and drip systems.
In 2018 Oklahoma producers spent about $21.5 million in energy expenses to power 6,530 pumps.
Though producers powered more pumps in 2018 compared to 2013 and 2008, they expended 3% less compared to 2013 and 31% less than 2008.
Taking irrigated acres into account, the amount of energy expenditure in 2018 translates into $42 and $18 per acre for groundwater and surface water irrigation, respectively.
Electricity was the main source of pumping energy, supplying water to 46% of all irrigated acres in state.
The second major energy source was natural gas, which contributed 39% in 2018.
The third most-used energy source was diesel, which powered pumps to irrigate 15% of the remaining irrigated acres in 2018.
Figure 3.
A natural gas engine extracts groundwater for irrigation.
In addition to the energy expenses mentioned above, Oklahoma producers spent another $38.2 million on irrigation equipment, facilities, land improvement and computer technology.
This was about two times more than 2013 in terms of the total amount, but slightly smaller when translated to average expenditure per affected acre.
A large portion of this money  was spent for scheduled replacement and maintenance.
About one-third  of the total expenditures was dedicated to new expansion.
Only 2% was used for water conservation, significantly smaller than the corresponding percentages in 2013  and 2008  and the 2018 national average.
Only 3% of irrigated acres where mentioned expenditures were made received financial assistance from EQIP or other USDA programs.
Oklahoma producers paid above $7.8 million of total labor expenses in 2018, which was around 1.7 times larger than 2013 and four times larger than 2008.
Out of this amount, about $5.5 million was spent on hired labors and over $2.3 million on contract labor.
Furthermore, the average hired labor expenses per farm was $19,1 188, whereas contract labor per farm expenses was $15,022.
Out of all irrigated acres in Oklahoma, only 2% experienced an irrigation interruption in 2018 that resulted in diminished crop yield.
One of the leading causes for irrigation interruption was equipment failure, affecting 45% of all acres that reported interruption.
Groundwater shortage was another reason for irrigation interruption, reported by 12% of total interrupted acres.
According to the 2013 survey, which was conducted during drought, groundwater shortage was responsible for irrigation interruption at 32% of irrigated acres.
Deciding When to Irrigate
 Improving irrigation management is not possible without implementing state-of-the-art methods in deciding when to irrigate.
In Oklahoma, the main method for determining irrigation timing was the "condition of crop" in 2018, mentioned by 84% of irrigated farms.
The next most common method was the "feel of soil," used by 36% of all irrigators.
The third most common method was based on "personal calendar," implemented in 10% of all farms.
Smart methods such as soil moisture sensing devices, plant sensing devices and computer models had a low adoption rate, with each one of them being mentioned by less than 5% of irrigated farms.
Among these smart methods, the use of soil moisture sensing devices in Oklahoma lags the national average and many neighboring states.
The percentage of farms that used these sensors was 12% across the nation, 10% in Texas, 11% in Arkansas, and 19% in Kansas.
Nebraska was the leading state, with about one-third of all irrigated farms having adopted the soil moisture sensing devices in their irrigation scheduling.
Surprisingly, the use of soil moisture sensors in Oklahoma was two times larger back in 2013 at 11%, similar to the national average.
It is not clear why the adoption rate has declined dramatically in the 2018 survey.
Figure 4.
Installing soil moisture sensors at a cotton field near Altus.
Despite the availability of the Oklahoma Mesonet as an extensive and well-maintained network of weather stations, the use of daily evapotranspiration  products in determining when to irrigate was reported by only 3% of Oklahoma farmers.
This is less than the U.S.
average  and several other states such as Kansas  and Nebraska.
This information suggests that there is a great potential to improve irrigation scheduling in Oklahoma by promoting the use of advanced approaches such as sensors, Mesonet products and computer models.
It should be noted that percentages reported for mentioned methods do not add up to 100%, since many irrigators use more than one method to decide about irrigation timing.
Barriers Toward Water and Energy Conservation
 Identifying the barriers that prevent producers from improving water and energy conservation is the first step toward achieving conservation goals.
According to the 2018 survey, a major barrier was related to financial challenges.
Thirty-five percent of farmers said that they could not finance improvements, up from 26% mentioning this barrier in both 2013 and 2008 surveys.
Twenty-five percent of producers mentioned that improvements would not reduce costs enough to cover installation costs and 26% noted that landlord would not share in costs.
Only 16% of producers mentioned that water and energy conservation was simply not their priority, which shows a decline when compared to 19% in 2013 and 29% in 2008.
Simplified Irrigation Scheduling on a Smart Phone or Web Browser
 Keywords.
Irrigation Scheduling, weather networks, checkbook, mobile apps, crop coefficients.
Figure 1.
Login Page.
Figure 2.
Bookmark or add to your home screen.
After logging in click "Add New Field"  to bring up the screen in Figure 4 where you can give the field a descriptive name, chose the growing year , choose the weather network from your state, select the weather station in that network that is nearest or best represents your field's growing climate, and select the crop grown and the soil texture.
Click "Add Field" and you're done with the setup!
Follow the on-screen instructions.
Help is available for each page by clicking the "Help" link on that page.
Additional information is available below in the Using the Model / In-Depth Descriptions section.
Verizon 3G 3:54 PM 93%
 The Irrigation Scheduler lets you view, store, and analyze your irrigation water usage based on crop type, soil type, and historical water use data from a chosen weather network.
This can help you make informed decisions on when, and how much water to apply for maximum crop yields and quality.
To get started, click Add New Field, and then select your crop type, soil type and closest weather station.
We'll do the rest by filling in information based on your choices.
Later, if you wish, you can use 'Field Settings' to personalize or refine the default field settings for the selected crop and soil type.
Check box to start with existing field: Field Name: Block C3 Field Year: 2013 Network: AgWeatherNet  Station: WSU HQ Field Crop: Grass  Field Soil: Fine Sandy Loam Add Field
 Privacy About Us Contact Us Logout Desktop Website Help
 Figure 4.
Add a New Field
 Irrigation scheduling is finding the answers to two basic questions: "When do I turn the water on?" and, "How long do I leave it on?" Improved irrigation scheduling has tremendous public and private benefits.
It has been shown in various studies to decrease irrigation water use by 10-30% while resulting in equivalent or better crop yields and quality.
Since irrigation is responsible for 80-90% of the consumptive water use in most arid areas, the total water and energy savings from improved irrigation management is tremendous.
Irrigation scheduling has the following benefits:
 Benefits to the grower:
 Lower pumping energy costs,
 Lower irrigation-related labor costs, and
 Decreased loss of expensive fertilizers to runoff or leaching.
Benefits to the environment:
 Less movement of fertilizers and pesticides with the water off of farms fields into streams, water-bodies, and groundwater , and
 More water remains available in groundwater and in streams for alternative uses including fish and wildlife habitat.
Benefits for energy supply:
 Decreased irrigation energy pumping costs , and
 Water remains in rivers to drive power-generation turbines at multiple dam sites.
There are many irrigation scheduling tools available including paper-and-pencil versions , spread sheet versions , compiled program versions , and online versions.
However these tools are not widely used and most of them are not readily adaptable to the Pacific Northwest State.
The most common reason cited for not using these tools is that they are difficult to learn, time consuming to use, and that the grower does not feel that it is worth this time and effort required.
Agricultural producers are also rarely in the office and don't get many chances for, and tend to not enjoy doing "desk-work." A simple and user-friendly irrigation scheduling tool that is accessible from a smart phone that is already in most producer's pocket is needed to increase the adoption of data-based irrigation scheduling.
Irrigation Scheduler Mobile is a soil water balance model that meets these requirements.
It is a free irrigation scheduling tool developed by Washington State University that is designed for use on a smart phone or on a desktop web browser for doing simplified check-book style irrigation scheduling.
It is a basic soil water budget model.
In addition Irrigation Scheduler Mobile has the following features:
 It is simple to set up and intuitive to use.
There are integrated help menus on each page.
It uses tables of default crop and soil parameters to simplify setup
 It automatically pulls daily crop water use  estimates from a chosen weather station in a fairly expansive number of agricultural weather networks.
It readily displays useful charts and tables for visual evaluation of soil water status and model inputs.
It is flexible enough to allow modifications by educated users for improved accuracy.
The model can be corrected using soil water measurements or estimates.
It includes a one-week forecast of crop water use and soil water status for irrigation decision planning.
It works with cutting dates to model forage regrowth.
Growers can interact with it in terms of hours of irrigation run time or in inches of water applied.
Simple calculators are included to help calculate irrigation application rate if required.
A correction for the smaller active soil volume due to un-irrigated inter-rows is included.
Soil water can be displayed as a percent of the total available water , or as volumetric soil water content  for better comparison with soil moisture sensors.
It can send out push notifications to growers in the form of an email or as a text message.
When adding a new field you can copy settings from an existing field.
Since it is designed as a web application, it can be run on any mobile phone platform with internet access, or directly from a full sized computer web browser.
You can download all of the data to a comma-separated variable  file for more detailed analysis.
It can do use reporting of the number of days each field was viewed and or edited by month.
This was requested for cost-share documentation.
It is possible to set up different crop defaults for different climatological regions.
Background Information and Model Assumptions
 Soil serves as a reservoir to store water and nutrients for use by the plant.
Knowing when to irrigate and how much water to apply requires knowledge of three things:
 1.
How much water can the soil hold?
2.
How much water is the plant using?
3.
At what point  will the plant begin to experience water stress?
Let's discuss each of these separately.
How Much Water Can the Soil Hold?
Water is held in the empty spaces between soil particles.
When these empty spaces are completely filled, the soil is said to be saturated.
Excess water will drain out over time until a point where the soil can hold a certain amount of water indefinitely against the downward pull of gravity.
This soil water content is the soil's full point called field capacity  and in this application is measured in inches of water per foot of soil depth.
The excess water that drains will move down to lower soil layers.
Applying more water than a soil can retain in the plant's managed root zone results in water loss to deep percolation  or "deep water loss".
Water loss to deep percolation wastes water, pumping energy, and vital plant nutrients that are held in the soil water solution.
Figure 5.
The various components of the soil water content.
As a plant's roots remove water from the soil, the soil dries out to the point where the suction or pull of the soil on the water is greater than the plant's ability to absorb water.
At this point the plant will wilt and die.
Although there is water left in the soil, from the plant's
 perspective the soil is empty.
This soil water content is referred to as the permanent wilting point  and is also measured in inches of water per foot of soil depth.
The difference between field capacity and permanent wilting point is known as the available water-holding capacity  again given in inches of water per foot of soil depth.
AWC = FC PWP
 Different soils have different available water-holding capacities.
For example, sand cannot hold as much water as a silt soil.
The default values of FC, PWP, and AWC that are used in this model for different soil textures are given in Appendix A.
A plant's rooting depth is also an important consideration.
A plant with deeper roots has access to much more soil and consequently has a larger reservoir of soil water to draw upon compared to plants with shallower roots.
The FC, PWP, and AWC are multiplied by the rooting depth to get the amounts of water held at those points in inches.
Rooting zone depths change over time as the plant and its roots grow.
Root growth in Irrigation Scheduler Mobile is assumed to increase linearly from a beginning depth at the planting or emergence date and is assumed to reach their maximum depth at the same time the crop canopy reaches full cover or covers  70-80% of the field area.
After this time the root depth is assumed to remain constant until the end of the growing season.
Default values for the parameters that define the changing root zone depth for the various crops are given in Appendix B.
Figure 6.
Parameters that define the changing root zone depth.
Defaults values for these parameters are set based on the crop chosen, but can be modified in "Advanced Field Settings."
 How Much Water is the Plant Using?
The amount of water required to grow a crop consists of the water lost to evaporation from a wet soil surface and leaves, and transpiration of water by the plant.
Together these are called evapotranspiration  and are also referred to as crop water use.
ET is measured in inches of water used per day.
The crop evapotranspiration  is calculated as:
 where ET, is the estimated evapotranspiration of a reference surface of full grown alfalfa that is calculated from measured weather data.
The weather data used to calculate ETr include solar radiation, air temperatures, humidity, and wind speed data.
Irrigation Scheduler Mobile uses alfalfa reference ET, as calculated by the ASCE standardized Penman-Monteith Equation.
Kc is a crop coefficient specific to a crop and that crop's growth stage over the season.
Crop coefficients Irrigation Scheduler Mobile are mean crop coefficients and defined as in the FAO-56 publication.
Default dates and crop coefficient values for different crop S are given in Appendix B.
Figure 7.
Parameters that define the crop coefficient curve.
At What Point Will the Plant Experience Water Stress?
As water is removed from the soil through ET there is a point below which the plant experiences increasing water stress.
This point is known in this model as the first stress point or more generally as the management allowable depletion.
To manage the soil water for maximum crop growth, depletion below this point is undesirable.
As the soil water content decreases below MAD the stomata in the plant leaves will begin to close, the leaves will often
 curl or droop, and the plant will use less water and the growth will decrease.
The model estimates this decrease in water use according to Figure 8.
Daily crop water use is proportionately decreased as the % of available water decreases below MAD towards the PWP.
This follows the water stress coefficient  concept as described by Allen et.
al..
Irrigation scheduling for maximum crop growth requires maintaining the soil water content between field capacity and the MAD.
Different plants are more resistant to water stress than others and therefore the MAD for each crop may be different.
The default MAD values for the various crops are given in Appendix B.
Figure 8.
Water use is proportionately decreased as the % of available water goes below the MAD.
Yield is also assumed to decrease in the same pattern.
Defaults values for MAD is set based on the crop chosen, but can be modified in "Advanced Field Settings."
 The following additional assumptions are made by this soil water balance model.
All water entered as an irrigation amount infiltrates into the soil.
Water in the plant's root zone is equally available to the plant regardless of depth.
The season begins with a full soil profile.
This can be modified by using the "Reset/ Correct Soil Water Availability" option on the first day in the Daily Budget table.
Plant roots grow into soil at field capacity.
Water moves quickly into the soil and excess water is lost quickly to deep percolation.
All rainfall goes towards satisfying the calculated ET demand.
Using the Model / Page Descriptions
 7-Day Daily Budget Table
 The Daily Budget Table screen  shows the most relevant values from a daily soil water budget and allows the user to edit the inputs for each day using the "Edit" link.
The data in each column is described below:
 Water Use : This is the daily crop water use  estimated from measured weather parameters from the selected weather station, and the entered crop coefficients.
This model uses alfalfa reference evapotranspiration calculated using the standardized ASCE Penman-Monteith method.
The model gets the weather data from the weather network when the model is first opened, if it has been greater than two hours since the data was pulled, or after a change is made in Field Settings.
Because of this, if the weather network managers make corrections to the historical data for that weather station, these changes are reflected in the model.
Rain& Irrig.
: This is the sum of the measured rainfall at the weather station for that day and/or and the irrigation amount.
Irrigation events must be entered using the Edit link.
This is net irrigation, not gross.
Some applied irrigation water is lost to evaporation.
Therefore gross irrigation amounts must be discounted for irrigation efficiency.
Typical irrigation efficiency values are: drip-95%, center pivot-85%, wheel/hand lines/lawn sprinklers-70%, big guns-60%.
For example a gross depth of 1 inch of water is applied by a center pivot, enter 0.85 here.
If you use measured application depths, don't correct for efficiency.
For surface irrigation, a reasonable assumption is that you completely refill the soil to field capacity, or replace the soil water deficit.
Soil Water : This is the calculated daily soil water content expressed as a percent of the available soil water.
100% is equivalent to field capacity, and 0% is equivalent to wilting point.
Entering a measured or estimated soil moisture value here  will correct the model to the entered value from that day forward.
Volumetric soil water content for comparison with soil moisture sensor readings is available in the expanded information.
Water Deficit : The soil water deficit in the root zone.
This is the amount of "space" in the soil, or the depth of irrigation water that can be applied before the soil is full again.
Edit Data: Use this link at each line to add irrigation amounts or correct the model for measured soil water contents.
Some descriptions of how the page operates:
 Line Colors: When the calculated soil water content is well above the MAD point and the plant growth should be at maximum, then the row is highlighted green.
When the soil water content gets close to the MAD line 
 then the row turns yellow.
And when the soil water content goes below the MAD line the row is highlighted red as a warning of crop water stress.
The Most Important Number: The most important value for irrigation scheduling is this morning's soil water deficit.
This is the amount of water that I need to apply today to completely refill my soil profile.
If I apply more water than this, some will be lost to deep percolation because the soil can't hold it all.
It is highlighted in red.
Navigation: You can navigate to other dates in the growing season using the buttons at the bottom of the table.
The date button in the middle is used to go to the week starting with the chosen date.
Note that you cannot navigate outside of the growing season as defined by the crop's planting date and end-of-season or harvest date as defined in Field Settings.
The and buttons takes you to the beginning of the growing season and to today  respectively.
The and >>> buttons navigation you forward or backwards respectively in time by one week.
Figure 9.
Daily Budget Table screen
 Figure 10.
Choose first date of week to view.
Forecast: The last day on the Budget Table represents very early this morning.
A seven-day forecast is available.
This forecast is based on the projected maximum and minimum temperatures from the National Weather Service  for those days at the latitude and longitude of the chosen weather station.
The Hargreaves equation is used with these temperature data to estimate grass reference ETo which is then multiplied by 1.2 for alfalfa reference ETr which is used in the model.
If the model is viewed late in the day, the 7th
 forecasted day is from the NWS.
However before 6 PM the 6th forecasted day is repeated for the 7th forecasted day.
Irrigations can be entered in the future to do planning.
These irrigation events will remain as time passes from the future to the past.
Historical ET information always overwrites forecasted values.
Forecast values are pulled when the field is first viewed, once every two hours, or after a change is made in Field Settings.
Edit Data: Clicking the Edit link on that day expands the screen to accept inputs for that day as shown in Figure 11.
From here you can add or edit irrigation amounts, or reset or correct the soil water availability to make it better match reality based on observations or soil moisture measurements.
Click Cancel closes the table up again.
You must click Save for these changes to be applied.
Figure 11.
Edit button expands table for inputs.
Figure 12.
Reset/Corrective Soil Water Availability
 Irrigation: Enter the net amount of irrigation applied to the field on this date.
If you chose to use hours instead of inches in Field Settings then you can enter this value in hours of irrigation run time.
Some applied irrigation water is lost to evaporation.
Therefore gross irrigation amounts must be discounted to account for irrigation inefficiency.
This is done by multiplying by the irrigation efficiency as a decimal.
Typical irrigation efficiency values are: drip-95%, center pivot-85%, wheel/hand lines/lawn sprinklers-70%, big guns-60%.
For example, a gross depth of 1 inch of water is applied by a center pivot, enter 0.85 here.
If you
 use measured application depths, don't correct for efficiency.
For surface irrigation, either use a very large number  or a reasonable assumption is that you completely refill the soil to field capacity to 100% Available Water, or completely replace the soil water deficit.
Reset/Correct Soil Water Availability: Check this box to overwrite the calculated percent of available soil water with an entered number.
You might want to do this to correct the model to make it better match observations or a soil moisture measurement.
The model will use your entered value as the new value and will calculate the estimated soil water content from that point on.
Unchecking this box will make model return to the calculated value.
Correcting Rainfall : Measured rainfall is automatically included from the weather station.
If you measured rainfall at your field and it differs significantly from the existing value, you can correct it by adding the difference as an irrigation.
If you measured less rainfall than the weather station reported, you can subtract the difference by adding this difference as a negative irrigation value.
It makes the soil water chart look funny to plot that negative value, but the math works correctly.
Additional Details: Additional details of the daily soil water budget are available by clicking on the date.
This will expand the table to show these details.
The table can be returned to normal again by clicking the date again.
Verizon 3G	5:46 PM	75%
 Date Water Rain& Avail.
Water	Edit
 Use	Irrig.
Water	Deficit	Data
 			
 08/14	0.12	0	97.8	0.1	Edit
 08/15	0.13	0	95.4	0.3	Edit
 08/16	0.13	0	93	0.4	Edit
 Day of Year:	227	Measured Available Water:	0%
 Irrigation:	0 in.
Modeled Available Water:	93%
 Precipitation:	0 in.
Field Capacity:	10 in.
Determining the Amount of Irrigation Water Applied to a Field
 Arizona Water Series No.29
 Critical to any irrigation management approach is an accurate estimate of the amount of water applied to a field.
Too often, growers apply water to make the fields and rows "look good"  or continue irrigating until the water reaches the end of every furrow.
However, quite often they never realize just how much water they have applied.
When growers do not take their system's efficiency into account, they may apply too little or too much water.
Too little water causes unnecessary water stress and can result in yield reductions.
Too much water can cause water logging, leaching, and may also result in loss of yield.
How Much Did I Apply?
Estimating the amount of water applied to a field or to a set is fairly easy for surface systems.
The Irrigator's Equation, Qxt=dxA, can be used to estimate the depth of water applied.
In the equation:
 Q is the flow rate, in cubic feet per second ; t is the set time or total time of irrigation ; d is the depth of water applied  and A is the area irrigated.
If you are working with a pump, remember that 450 gallons per minute equals 1 cfs.
Also, there are 40 miners-inches per 1 cfs.
However, miners-inches change from region to region.
Make sure you check which type of miners-inches you are working with.
Table 1 has some useful conversions.
To determine how much water was applied, use the Irrigator's Equation and solve for the unknown value, d, depth of water applied in inches.
For example, suppose you irrigated a set 320 ft.
wide ; 800 ft.
long with a head of 6 cfs.
Your set time was about 6.5 hours.
How much water have you applied?
First, calculate the area irrigated:
 Solving for d  we get: d  =  / 5.9 = 6.6 inches
 The total amount of water applied to the field was 6.6 inches in depth.
How Long Should My Set Time Be?
The Irrigator's Equation can also be used to estimate how long your set times should be.
By choosing a target amount of water to apply, you can use the same equation but solve for time instead of depth of application.
For example, suppose you estimated that your soilwater deficit was 4.0 inches.
You want to refill the soil and apply the full 4.0 inches.
Your set size is 150 feet wide , 1100 feet long, and you are running 5 cfs.
How long should your set time be?
Again, first calculate the total area to be irrigated.
In this case, we have:
 150 ft.
X 1100 ft.
= 165,000
 To convert to acres:
 Now using the Irrigator's Equation, we get:
 5.0   = 4  X 3.8 
 Solving for t we get:
 The set time should be three hours to apply 4.0 inches of water.
The Irrigator's Equation can be used to determine any of the four variables in the equation, providing you know the other three.
Don't Forget the Efficiency
 The one factor in irrigation that is most often overlooked is the efficiency of the irrigation system itself.
There are many different types of efficiency and many different ways to define it.
Efficiency here refers to the overall system's ability to apply an equal amount of water to all parts of the field.
A system with 100% efficiency would be able to
 Table 1.
Conversion from cubic feet per second  to gallons per minute  to Miners inches.
Flow Rate Conversion Table
 Cubic Feet per Second 	Gallons per Minute 	Miner's Inches
 apply the same amount of water to every inch of the field, head end, tail end, center, side, etc.
No system is 100% efficient.
Drip systems are the most efficient and they are usually near 95% efficient.
Surface systems are notorious for inefficiency, but properly maintained fields can achieve efficiencies as high as some sprinkler systems.
Table 2 gives the range of efficiencies normally associated with different types of irrigation systems.
In order to apply the proper amount of water to a field, first you must decide what efficiency to use in your calculations.
The table gives a range of values for seasonal and peak use periods.
These are provided because some systems are better equipped to handle large applications and during times of peak water use, when water demand is high, the system's efficiency is increased.
For example, all of the surface systems have an increase in their efficiency from seasonal to peak use periods because surface systems can apply large amounts of water more efficiently than smaller amounts.
During the early part of the season, these systems are inefficient because they over-water.
Overall, seasonal efficiency is relatively low compared to the efficiency during peak use.
Sprinkler and drip systems , on the other hand, maintain their efficiencies regardless of seasonal or peak use periods.
This is because these systems apply large and small quantities of water at about the same efficiency.
Taking the average of the ranges in Table 2 is probably a good start, although many surface systems operate at the very low end of the ranges given.
Also, many sprinkler systems with LEPA  systems and drop nozzles achieve even higher efficiencies than those given.
You can contact your local Natural Resources Conservation Service office or local consultant who may be able to perform an analysis on your system to determine the irrigation efficiency.
Once the efficiency has been determined, use that to adjust your irrigation amounts.
Let's take the second example where the grower was determining how long the set time should be to irrigate 4.0 inches.
If he has a system that is 75% efficient, then the target amount would be increased from 4.0 inches to 5.3 inches.
In order to account for the system's inefficiency, the
 efficiency must be divided into the targeted amount.
In the example above, the efficiency of 75%  is divided into the target amount of 4 inches:
 This gives the actual amount of water that needs to be applied to assure that the entire field receives at least 4 inches of water.
Of course, some of the field will receive more water, but that is the cost of the system's inefficiency.
To determine the set time for the example above, we use the Irrigator's Equation and calculate for 5.3 inches instead of 4.0 inches:
 Solving for t we get: =  / 5 = 4 hours
 The set time should be four hours to assure that all parts of the field receive at least 4.0 inches of water.
Proper calculation and keeping records of irrigation amounts and set times, as well as a realistic estimate of system efficiency, will help to assure that your crop receives all the water it needs.
The information provided in this bulletin is also available in an Irrigation Slide Chart , which helps to determine set times and flow rates.
The slide chart is written in both English and Spanish and is easy to use.
The slide chart is available through your local Cooperative Extension office.
When the ratio of the end gun throw  to the pivot length  is 0.02, the the pivot speed with the end gun on  compared to the speed with the end gun off  is 0.96.
When the ratio of the end gun throw  to the pivot length  is 0.03, the the pivot speed with the end gun on  compared to the speed with the end gun off  is 0.94.
When the ratio of the end gun throw  to the pivot length  is 0.04, the the pivot speed with the end gun on  compared to the speed with the end gun off  is 0.92.
When the ratio of the end gun throw  to the pivot length  is 0.05, the the pivot speed with the end gun on  compared to the speed with the end gun off  is 0.91.
When the ratio of the end gun throw  to the pivot length  is 0.06, the the pivot speed with the end gun on  compared to the speed with the end gun off  is 0.89.
When the ratio of the end gun throw  to the pivot length  is 0.07, the the pivot speed with the end gun on  compared to the speed with the end gun off  is 0.87.
When the ratio of the end gun throw  to the pivot length  is 0.08, the the pivot speed with the end gun on  compared to the speed with the end gun off  is 0.86.
When the ratio of the end gun throw  to the pivot length  is 0.09, the the pivot speed with the end gun on  compared to the speed with the end gun off  is 0.84.
When the ratio of the end gun throw  to the pivot length  is 0.1, the the pivot speed with the end gun on  compared to the speed with the end gun off  is 0.83.
When the ratio of the end gun throw  to the pivot length  is 0.11, the the pivot speed with the end gun on  compared to the speed with the end gun off  is 0.81.
When the ratio of the end gun throw  to the pivot length  is 0.12, the the pivot speed with the end gun on  compared to the speed with the end gun off  is 0.8.
When the ratio of the end gun throw  to the pivot length  is 0.13, the the pivot speed with the end gun on  compared to the speed with the end gun off  is 0.78.
When the ratio of the end gun throw  to the pivot length  is 0.14, the the pivot speed with the end gun on  compared to the speed with the end gun off  is 0.77.
When the ratio of the end gun throw  to the pivot length  is 0.15, the the pivot speed with the end gun on  compared to the speed with the end gun off  is 0.76.
When the ratio of the end gun throw  to the pivot length  is 0.16, the the pivot speed with the end gun on  compared to the speed with the end gun off  is 0.74.
When the ratio of the end gun throw  to the pivot length  is 0.17, the the pivot speed with the end gun on  compared to the speed with the end gun off  is 0.73.
When the ratio of the end gun throw  to the pivot length  is 0.18, the the pivot speed with the end gun on  compared to the speed with the end gun off  is 0.72.
When the ratio of the end gun throw  to the pivot length  is 0.19, the the pivot speed with the end gun on  compared to the speed with the end gun off  is 0.71.
When the ratio of the end gun throw  to the pivot length  is 0.2, the the pivot speed with the end gun on  compared to the speed with the end gun off  is 0.69.
Monitoring soil moisture helps refine irrigation management
 Soil moisture sensors can be used to determine the appropriate interval between irrigation, depth of wetting, depth of extraction by roots and adequacy of wetting.
We tested the performance of soil moisture sensors in different crops.
Sensors that read on a continuous basis, such as the Enviroscan device, can provide valuable information that may not be readily evident from periodic measurements.
The Watermark blocks responded well throughout the wetting and drying cycles, indicating that they function more consistently over a wider range of soil moisture contents compared with tensiometers and gypsum blocks.
Irrigation scheduling addresses the questions of when to irrigate and how much water to apply.
Determining when to irrigate requires estimating the irrigation timing so that yield reductions will not occur due to ex-
 Enviroscan soil moisture sensors like the one shown, that monitor on a continuous basis, provide more information that can be valuable.
cessive soil moisture depletions.
One method for irrigation scheduling is to measure or monitor soil moisture content.
This paper discusses methods for estimating when to irrigate and presents case studies of using various soil moisture sensors for irrigation scheduling.
When should you irrigate?
Available soil moisture is the water that plants can use.
It is the difference between the field capacity moisture content and that at 15 bars , sometimes referred to as the permanent wilting point.
Table 1 lists typical moisture contents at field capacity and at 15 bars for various soil textures and their available soil moisture.
Two methods are recommended for determining when to irrigate.
One method recommends irrigating when the soil moisture tension reaches a recommended value , which depends on crop type.
The second method recommends irrigating when the available soil moisture is depleted to an allowable value, called the allowable depletion.
Recommended allowable depletions  are expressed as a percentage of the available water.
For most crops, an allowable depletion of 50% is used.
TABLE 1.
Soil moisture contents in inches of water per foot of soil
 15 Bar	Available moisture
 Soil texture	Field capacity		content
 Sand	1.2 *	0.5 	0.7 
 Loamy sand	1.9 	0.8 	1.1 
 Sandy loam	2.5 	1.1 	1.4 
 Loam	3.2 	1.4 	1.8 
 Silt loam	3.6 	1.8 	1.8 
 Sandy clay loam	4.3 	2.4 	1.9 
 Sandy clay	3.8 	2.2 	1.7 
 Clay loam	3.5 	2.2 	1.3 
 Silty clay loam	3.4 	1.8 	1.6 
 Silty clay	4.8 	2.4 	2.4 
 Clay	4.8 	2.6 	2.2 
 *Numbers in parentheses are the volumetric moisture contents in percent.
Source: Ratliff et al.
1983
 Normally, recommended soil moisture tensions and allowable depletions are presented independent of climate and soil texture.
However, research has shown that for cool, humid conditions, relatively large allowable depletions can occur before transpiration and yield are reduced.
For warm, dry conditions, allowable depletions may be relatively small for the same soil type.
For sand/loamy sand, consider using allowable depletions as the criterion for irrigating.
Use of soil moisture tension may result in soil moisture depletions greater than allowable depletions.
For sandy loam/loam/silty loam soils, either method may be appropriate.
Compatibility between the two methods is more likely for these soils.
For clay loam/clay soils, consider using allowable depletion as the criterion for irrigating.
Use of soil moisture tension may result in small depletions.
These recommendations are appropriate for low-frequency surface and sprinkler irrigation, where irrigation intervals are such that large soil-moisture depletions occur between irrigations.
For high-frequency irrigation , small irrigation intervals recommended for these systems result in very small soil moisture depletions between irrigations.
Therefore these recommendations do not apply for high-frequency irrigation.
Which irrigation scheduling method is the best?
The best method is that which maximizes crop yield.
The recommended values in tables 2 and 3 reflect site-specific conditions, and thus some adjustment may be necessary for other soil types, salinity, climate, cultivars and cultural practices.
Site-specific conditions under which recommendations were developed are not known, and thus any adjustments may require some trial-and-error.
Some incompatibility may exist between the two methods.
A recommended tension of 70 centibars may deplete 60% to 70% of the available soil moisture in sandy soil, based on generic soil moisture release curves.
In contrast, the 70centibar recommendation may deplete only 15% to 20% of the available soil moisture in clay soil.
However, a 50% allowable depletion in this soil may cause a soil moisture tension of 150 centibars.
Methods of monitoring/measuring soil moisture include tensiometers, electrical resistance blocks, neutron moisture meter and dielectric soil moisture devices.
Advantages of measuring/monitoring soil moisture include determining soil moisture depletions, adequacy of wetting from irrigation, patterns of soil moisture extraction due to root uptake of water and trends in soil moisture content with time during the irrigation season.
This information can also be used to validate other irrigation scheduling techniques.
The following examples illustrate the type of information that can be obtained from monitoring/measuring soil moisture.
contents were also measured with a neutron moisture meter  to help interpret the readings of these instruments for this article.
We used Watermark blocks, gypsum blocks and tensiometers to evaluate flood or border irrigations of a walnut orchard planted on sandy loam.
Soil moisture
 We developed the following guidelines using the recommended values in tables 2 and 3 and the generic moisture release characteristic curves:
 Tensiometer readings were lowest just after an irrigation.
Minimum readings were less than 20 centibars at the 6-inch depth; between 20 and 30 centibars at the 18-inch depth; and between 25 and 50 centibars at the 24-inch depth.
Readings increased with time after an irrigation to a
 TABLE 2.
Recommended soil moisture tensions
 *The smaller values are recommended for a warm, dry climate and the larger values for a cool, humid climate.
Intermediate climate should use intermediate values.
TABLE 3.
Recommended allowable depletions
 Crop	Allowable depletion	Crop	Allowable depletion
 Alfalfa	55	Melon	35
 Barley	50-55	Olive	65
 Bean	45-50	Onion	25
 Beet	50	Pasture	50-60
 Broccoli	50	Pea	35
 Cabbage	45	Pepper	25
 Carrot	35	Potato	25
 Cauliflower	50	Safflower	60
 Celery	20	Sorghum	55
 Citrus	50	Soybean	50
 Clover	35	Spinach	20
 Corn	50-60	Strawberry	15
 Corn 	50-60	Sugarbeet	50-80 
 Cotton	50-65	Sunflower	45
 Date	50	Sweet Potato	65
 Deciduous tree	50	Tomato	50-60
 Lettuce	30	Wheat	55
 Source: Doorenbos and Pruitt 1977
 Fig.
1.
Tensiometer readings , Watermark block readings , gypsum block readings  and NMM volumetric soil moisture contents  with time during Irrigation season for a flood-irrigated walnut orchard grown in a sandy loam soil.
Fig.
2.
Watermark block readings  and NMM volumetric soil moisture contents  with time during the Irrigation season for furrow-irrigated processing tomatoes grown in a silty clay soil.
maximum reading of about 80 centibars, the maximum reading that can be obtained with tensiometers at or near sea level.
The tensiometer at the 12-inch depth did not respond with time, possibly due to a leaking instrument.
Watermark block readings also increased as soil moisture depleted after an irrigation.
Maximum readings ranged between 100 and 180 centibars, indicating that Watermark blocks operate under drier conditions than tensiometers.
Readings just after an irrigation were less than 20 centibars for all depths except 24 inches, where minimum block readings ranged between 30 and 50 centibars.
Gypsum block readings exceeded 90 just after an irrigation , to between 5 and 25 just before an irrigation.
However, little change in readings occurred for about 1 week after an irrigation.
Thereafter, large changes in readings occurred over the next 2 weeks.
NMM soil moisture contents ranged between 30% and 40% for the
 6and 12-inch depths just after an irrigation.
Just before irrigations, soil moisture contents were about 15%.
Lower moisture contents occurred at the deeper depths, indicating less wetting at those depths.
Little change in moisture content occurred 30 inches deep, indicating that irrigation water was not reaching this depth.
All devices responded to changes in soil moisture content between irrigations.
However, as the soil dried, soil moisture tensions exceeded the tensiometer's maximum reading of about 85 centibars.
Thus the tensiometers were not effective in monitoring soil moisture in this field.
The gypsum blocks also responded to soil moisture changes, but they changed little during the week following an irrigation.
By the time they started responding, soil moisture tensions were nearly 60 to 70 centibars.
The Watermark blocks responded well throughout the wetting and drying cycles, indicating that they function more consistently over a wider range of soil moisture contents compared with tensiometers and gypsum blocks.
For this crop, the recommended allowable depletion is 50%, and the recommended soil moisture tension is about 70 centibars.
Both Watermark block readings and NMM soil moisture contents indicate that intervals between irrigations were too long.
Watermark readings greatly exceeded 70 centibars.
Soil moisture contents ranged from field capacity to nearly the 15-bar moisture content , indicating that most of the available soil moisture was used between irrigations instead of the recommended 50%.
For this soil type, however, the recommended soil moisture tensions were compatible with the recommended allowable depletion.
Watermark and NMM data showed about a 50% depletion at about 70 centibars of tension.
Just after an irrigation, NMM soil moisture contents for furrow-irrigated
 processing tomatoes grown on silty loam soil were about equal to field capacity  for all depths of measurement.
Watermark block readings were less than 20 centibars.
Between irrigations, moisture contents decreased to about 35%, while block readings increased to between 70 and 85 centibars.
After the irrigation cutoff date of Aug.
19, moisture contents decreased over time to less than 30%, a practice designed to increase soluble solids of the fruit.
Watermark block readings generally increased to more than 100 centibars.
These measurements indicate that optimal irrigation water management was used at this site.
Between irrigations about 50% of the available soil moisture was depleted, the allowable depletion recommended for this crop.
Depth of wetting was adequate.
Watermark block readings were made in an alfalfa field irrigated with a center pivot sprinkler machine.
To help interpret the block readings, we also measured soil moisture contents with an NMM.
Measurements were made at 1-foot intervals down to 5 feet.
Irrigations occurred every several days.
Soil texture ranged from loam at 1 foot to loamy sand at 3, 4 and 5 feet.
Initially, Watermark readings were between 10 and 20 centibars, about field capacity for this soil.
However, NMM soil moisture contents varied with depth, reflecting soil variability, with the largest moisture content near the surface and the smaller contents about 3 feet deep.
This variability was not detected from the Watermark block readings because they measure soil moisture tension only.
Block readings at 1 foot started increasing on about May 6 as crop evapotranspiration increased.
At the same time, soil moisture content started decreasing at that depth.
Block readings periodically showed
 large readings followed by smaller readings, after which readings increased with time.
The large readings occurred when the grower quit irrigating before cutting the alfalfa.
Irrigations following the cutting decreased soil moisture tension.
Watermark readings at the deeper depths initially lagged the 1-foot readings.
The deeper the depth, the greater the lag.
Readings at the 1-, 2and 3-foot depths increased to about 100 centibars at the end of May, the time of the first cutting.
However, no decrease occurred after the irrigation in early June.
Instead, the Watermark readings continued to increase with time, indicating that soil moisture depletion occurred at those depths, but applied water was inadequate to rewet that deep.
The soil moisture depletions at the deeper depths indicate that more water per irrigation was needed.
Watermark block readings from an alfalfa field irrigated with a wheel-line sprinkler system generally remained less than about 40 centibars at all depths.
This indicates that the field is irrigated too frequently, thus too much irrigation water was applied.
The irrigation frequency and/or duration of irrigation should be reduced to correct the problem.
We installed Watermark blocks in an irrigated pasture at 1-foot intervals down to 4 feet.
An addi-
 Fig.
3.
Watermark block readings  and NMM volumetric soil moisture contents  with time during the irrigation season for center-plvot-irrigated alfalfa.
Fig.
4.
Watermark block readings with time during the irrigation season for sprinklerirrigated pasture.
Fig.
5.
Enviroscan readings with time during the Irrigation season for furrowirrigated garlic.
tional block was installed at 0.5 feet in early July to better monitor soil moisture of this shallow-rooted crop.
In early March, Watermark block readings ranged between 10 and 20 centibars, except at 4 feet.
The 1-foot readings increased slightly with time until near the end of May.
Watermark blocks at both the 0.5and 1-foot depths showed a periodic behavior of increasing readings with time, followed by a large decrease and then an increase.
Maximum readings for the 0.5-foot depth were much larger than for the 1-foot block.
At the deeper depths, Watermark readings increased slightly until about mid-July.
These readings were generally between about 10 and 30 centibars, indicating little soil moisture depletion at those depths.
These readings show that much of the soil moisture depletion was occurring at less than 2 feet deep.
The wetting and drying cycles reflect the cutting and irrigation schedule of the pasture.
NMM soil moisture contents  revealed that most of the available moisture was depleted during the cutting/drying periods.
These readings differed considerably compared with the alfalfa readings.
Moisture extraction occurred down to at least 5 feet deep for the alfalfa, but occurred only in the upper 2 feet for pasture, which shows the smaller root depth of the pasture.
Therefore pasture should be irrigated more frequently, with smaller water application per irrigation, compared with alfalfa.
In some soil types, the Enviroscan readings were inaccurate.
and 36 inches.
Although the Enviroscan system is designed to directly measure soil moisture content, some of the readings were not realistic for this soil type.
Nevertheless, the continuous measurements provided useful information on the irrigation water management.
At 4 inches deep, large changes in readings caused by irrigations and rainfall occurred between days 80 and 90.
Readings at 12 inches also changed, but only a slight change occurred at 20 inches.
No change was found at the other depths.
We used an Enviroscan system in a garlic field that was furrow irrigated weekly until cutoff.
Soil type was silt loam.
The sensors, which read every hour, were installed in a plant row at depths of 4, 12, 20, 28
 Between days 90 and 110, readings at 4 inches deep steadily decreased, showing little response to the weekly irrigations.
This behavior reflected inadequate wetting due to very nonuniform infiltration of irrigation water along the furrow length.
The uniformity problem was corrected by increasing the furrow inflow rate of the subsequent irrigations.
Thereafter, substantial changes in Enviroscan readings occurred.
These continuous measurements clearly showed the lack of wetting caused by inadequate infiltration.
This behavior was less obvious from the weekly measurements made with an NMM.
Monitoring soil moisture tension or soil moisture content can help identify problems in irrigation water management that might affect crop yield or water use.
Problems identified in these examples include excessive intervals between irrigations , inadequate wetting , too-frequent irrigations  and differences in soil moisture extraction patterns between alfalfa and pasture.
Tensiometers and electrical resistance blocks can be used to determine when to irrigate, trends in soil moisture content, and adequacy of wetting.
They cannot be used to estimate changes in soil moisture content unless they have been calibrated for a particular soil type, a process that is difficult and time consuming.
Dielectric soil moisture sensors can be used to measure soil moisture contents, provided that they are reasonably accurate.
Continuous monitoring of soil moisture content can identify trends that might not be readily detectable from weekly measurements, even though the instrument may not be accurate.
B.R.
Hanson is Extension Irrigation and Drainage Specialist and D.
Peters is Staff Research Associate, Department of Land, Air and Water Resources, UC Davis; S.
Orloff is Farm Advisor, UC Cooperative Extension, Siskiyou County.
Micro-Sprinkler Irrigation for Orchards
 Fact Sheet No.
4.703
 by R.
Godin and I.
Broner*
 Micro-sprinkler irrigation has become established and widely used in Colorado orchards in recent years because of its potential to increase yields but more importantly because of the increased irrigation efficiency and decreased labor requirements.
However, there is an increase in the amount of time required to manage the system properly to realize the gains in efficiency compared to gated pipe/furrow irrigation.
Micro-sprinkler irrigation applies water directly to the soil surface area allowing water to dissipate under low pressure and infiltrate orchard soils in a wetted profile that uniformly meets water demand throughout the orchard block.
Compared to gated pipe/ furrow irrigation, water use on orchards with micro-sprinklers is typically 30% less, and can be as much as 50% less with close attention being paid to irrigation system management.
All else being equal, this increased irrigation efficiency can mean the difference between small or medium sized fruit and crop, and a good or full sized fruit and crop in 'water-short' years.
Some of the additional advantages of micro-sprinkler irrigation systems are: the potential for reducing frost damage, greater control over water application times and amounts to more closely match local evapotranspiration  rates to maintain optimum soil moisture.
The lower susceptibility to clogging due to larger orifice sizes than drip irrigation systems also reduces the need for extra fine filtration.
Orchard micro-sprinkler irrigation systems operate under low pressure, typically 20 to 35 psi, with wetting patterns of 10 to 30 feet, and a variety of discharge flows of 8 to 90 gph, to more closely match soil infiltration rates, orchard size, tree maturity and spacing and the depth of the rooting system.
Timing irrigations to only irrigate to the maximum depth of the tree root zone can also increase
 fertilizer efficiency by significantly reducing or eliminating leaching of nutrients below the tree root zone.
System Layout and Equipment
 Micro-irrigation systems consist of a system 'head' and a distribution network.
A pump, filter, flow meter , pressure gauges, fertilizer injector , pressure regulator, and controller  generally make up a system head.
The meter and acid injector are optional equipment but highly desirable because they help monitor system performance  and add flexibility to the system.
The distribution network consists of pipes usually made of polyethylene , pipe fittings, sprinklers and valves.
Valves can be actuated electrically by a controller connected to a solenoid valve in the case of an automated system or manually.
When sediment is found in irrigation water, typically ditch systems; water filtration is essential for protecting sprinkler nozzles from clogging and the irrigation system from rapid wear.
Two basic types of filters are sand media filters and screen/spin filters.
At least one stage of filtration is needed for micro-irrigation systems, though micro irrigation sprinkler systems usually require less filtration than drip irrigation systems, filtration is a must if not using well water.
The bigger the orifice of the sprinkler, the less filtration is needed.
In western Colorado's fruit growing areas, early season irrigation  water is usually sediment laden and controllers with automatic filter back flushing cycles are a must to reduce labor costs as non-self flushing systems typically have to be manually cleaned hourly or more often early in the season.
The required screen size or sand filter size is determined by the sprinkler type, orifice size, and amount of contaminants in the water source.
Micro-sprinkler irrigation is a low pressure, low to medium volume irrigation system suitable for high value crops such as tree fruits.
If managed properly, micro irrigation can increase yields and decrease water use and fertilizer and labor requirements when compared to gated pipe/ furrow irrigation systems.
Micro-sprinkler irrigation saves water because of the high application efficiency and high water distribution uniformity with little if any waste if managed properly.
Micro-sprinkler irrigation is ideal for irrigating sloping or irregularly shaped orchard blocks that cannot be flood/ furrow irrigated.
An additional increase in efficiency can be obtained by the addition of fertilizer injection to the system.
Water-soluble fertilizers can be injected through a microirrigation system thereby significantly reducing cost compared to traditional fertilizer applications.
Ron Godin, Colorado State University Extension, TriRiver Area.
I.
Broner, former Colorado State University Extension irrigation specialist.
11/2013
 Figure 1: Typical micro-sprinkler irrigation system "head." Controller can detect differences between inlet and outlet pressure and activate automatic filter back flush systems.
Each sprinkler manufacturer specifies a minimum mesh size or filtration needed for each of their particular sprinklers in order to minimize wear on sprinkler and maximize sprinkler efficiency.
Micro-sprinkler irrigation systems operate at relatively low pressure compared to large sprinkler irrigation systems.
For this reason, pumping costs are substantially less.
A pressure regulator is used to control the line pressure as sprinklers have a maximum operating pressure for optimal efficiency.
Multiple pressure regulators may be desirable for locations with large elevation changes, as pressure increases with elevation drops.
Small diameter polyethylene pipe  is generally used for the in-row laterals that are laid on the soil surface with risers or suspended on wire and T-posts in the tree row with drop down sprinklers nozzles, typically sprinklers are connected to the poly pipe with spaghetti tubing.
Irrigation lines are buried between rows to facilitate tractor operations.
The lateral is connected to a manifold that is supplied with water through a main and/or sub-main connection.
Manifolds, sub-mains and mains are usually buried with control valves either above or below ground.
for each sprinkler.
Once sprinklers are selected and installed, lateral pressure is controlled by a pressure regulator valve to match sprinkler size and capacity.
It is important that all sprinklers being fed from a common lateral are selected for the same pressure.
Sprinkler dealers can size and design complete sprinkler irrigation systems for the exact needs of your orchard and your water supply.
The purpose of the lateral is to supply water to sprinklers located in the tree row and the lateral should be sized for the maximum flow rate of water application.
Sprinklers are chosen for flow rate at the tree but are dependent on lateral pressure to perform correctly.
Sprinkler manufacturers specify minimum and maximum pressure ranges to maximize system efficiency
 Micro-sprinkler irrigation can be configured in one of two ways; with either drop down sprinklers from suspended irrigation lines or risers mounted on stakes from surface irrigation lines.
Both methods connect sprinklers to in-row irrigation lines with 'spaghetti' tubing.
Drop down sprinklers allow for mowing between trees since no moving of sprinklers is required to mow, unlike with riser mounted sprinklers.
Micro-irrigation systems are also useful and suitable for sloping or irregularly-shaped pieces of land that are otherwise impractical to furrow irrigate.
Micro-sprinkler systems usually have a sprinkler between every other tree and are staggered  in adjoining tree rows to maximize irrigation coverage and efficiency, and minimize costs.
The size of the sprinkler emitter, or orifice and working pressure, determines application rate.
Maximum application rates are in turn dependent on soil characteristics such soil texture and maximum water infiltration rates for given soils, SO as not to apply water at a faster rate than the soil can absorb in a given time.
When irrigation water contains
 sediment, typically ditch or reservoir water, micro-sprinkler systems usually make use of an in-line filter system to prevent emitter clogging and reduce wear.
Micro-irrigation systems can apply water on a short-set, high-frequency basis, optimal for younger trees with a smaller root mass, or long-set, lower frequency irrigations to providing a more consistent and optimal soil moisture environment for mature trees, depending on your particular orchard and water supply situation.
Soil moisture monitoring devices, such as composite gypsum blocks or Watermark sensors, can help improve overall irrigation system performance by allowing the irrigator to monitor and manage soil moisture more conveniently and accurately.
Consult with your local Extension office for guidance on installing and reading soil moisture sensors for your soil type; typically maximum soil moisture depletion for fruit trees is 30 to 40 KPa2 of soil vacuum during flowering and 50 to 60 KPa2 post flowering until the fruit sizing stage where maximum soil moisture depletion returns to 30 KPa2.
Where uninterrupted water delivery is available, micro-sprinkler systems can be setup to operate irrigations automatically, triggered on and off by the same soil moisture monitoring devices.
Since micro-sprinkler irrigation systems apply water in a manner that can be very precise at meeting your crops water needs, it is recommended that irrigators practice the 'water balance approach' regardless of irrigation frequency.
The water balance approach involves calculating the daily water use by the crop  and replenishing it on an as needed basis depending on soil water holding capacity and the orchard's age, top soil depth, rooting depth, and water availability schedule.
For example, if you have water available every 8 days and the daily ET is 0.3 inches, you would apply 2.4 inches of water to refill your soil profile.
Even if soil moisture sensors are in place, the water balance approach is a good tool for monitoring the condition of the tree/ root/water system and the accuracy of sensors.
The water balance approach is described in Extension fact sheet 4.707, Irrigation Scheduling: The Water Balance Approach.
The crop  concept is described in fact sheet 4.715, Crop Water Use and Growth Stages.
Different water management methods are also described
 Soil and Water Quality
 If your orchard has been diagnosed with high salt levels, this can be mitigated by leaching  salts below the tree root zone.
You should consult your local Extension specialist before attempting any large scale leaching as leaching done incorrectly or at the wrong time can worsen your salt situation.
Irrigation water with high pH also impairs the trees' ability to absorb key micronutrients such as iron, zinc and manganese, but high soil and/or water pH can be neutralized by the injection of acid into the irrigation water with a fertilizer injector in order to lower irrigation water and soil pH and induce a more healthy growing environment for the trees, you should consult with your local Extension agent about these practices.
In western Colorado's tree fruit growing areas, irrigation water pH typically starts at approximately pH = 7.6 at the beginning of the growing season and increases to a high of pH = 8.3 near harvest, due to increasing carbonate levels in the irrigation water.
The pH of the soil tends towards the pH of the irrigation water, SO
 irrigating with high pH water can in and of itself increases soil pH, which in turn reduces micro-nutrient availability to trees.
All orchardist should know the pH of their orchard soils and actively work to lowering and maintaining soil pH at levels of pH = 7.4 or less, to optimize micro-nutrient availability in our alkaline soils.
Lowering the soil pH to less than pH = 7.4 is not economically practical in the short-term due to the high rate of free lime in area soils.
More on irrigation water quality is described in Extension fact sheet 0.506, Irrigation Water Quality Criteria and on salinity in Extension fact sheet 0.521, Diagnosing Saline and Sodic Soil Problems.
In all fruit growing areas of western Colorado, there may be cost-sharing money available to install a micro-sprinkler irrigation system.
Fertilizer injection or 'fertigation' is also possible with micro-sprinklers but is highly dependent on soil type and if cover crops are already providing some of the tree nutrients.
Cover crops grown in the orchard alleyways have the potential to reduce erosion, keep orchard temperatures cooler thereby reducing overall ET and may supply much of the orchard's required fertility depending on the species mix.
Healthy soils and good water quality are integral parts of a productive orchard and successful micro-sprinkler irrigation management program.
Soil and water testing are the best tools for determining if there are salinity, pH or nutrient problems present in your orchard or irrigation water.
For more information on soil and water testing refer to Extension fact sheet 0.520, Selecting an Analytical Laboratory.
Research and Canal Update: Dr.
Xin Qiao gave a research update on the irrigation water management program he is conducting with area producers called PLAN.
The group of growers and ag businesses will be working to create a platform for learning more about technology with support on using it.
INTRODUCING THE WEB-BASED VERSION OF KANSCHED: AN ET-BASED IRRIGATION SCHEDULING TOOL
 Irrigation scheduling is a process of determining when and how much water to apply to a crop to meet specific management goals generally to prevent yield limiting crop water stress.
Evapotranspiration  or crop water use information can be used for irrigation scheduling and is often described as being similar to a checkbook accounting procedure except in this case, root zone soil water content, rather than money, is the account balance.
Deposits to the account would be effective rainfall and irrigation and withdrawal is the crop water use One notable difference is that the water balance can become too large and the additional deposits would be lost to surface water runoff or deep percolation as well as being too low or deficient for optimal crop growth.
The upper limit of root zone soil water is determined by the soil water holding capacity which for irrigation water management purposes is known as field capacity and the managed crop root zone.
The desired lower limit for optimal crop growth can be a more variable value depending on the crop, the stage of growth, and management goal.
Often it is referred to as the managed allowable deficit or MAD.
A common MAD is 50 percent of the total available soil water holding capacity.
The normal goal of the irrigation scheduling procedure is to help the irrigation manager keep track of the amount of water in reserve above a minimum soil water balance level to prevent water stress to the growing crop
 The irrigation manager also considers the irrigation system capacity, the application amount that can be efficiently applied, the soil intake rate, and other factors when making the final irrigation scheduling decision, so irrigation scheduling tools that can be customized to a field's characteristics can greatly facilitate the irrigation scheduling decision process.
Irrigation scheduling procedures can help eliminate unnecessary irrigation water applications, although even the most rigorously followed schedule cannot prevent all losses since large rainfall events can exceed soil water storage capacity by themselves.
The benefits of irrigation scheduling generally translate into increased net returns through several possible avenues, such as reducing irrigation labor and equipment operation pumping cost, and may also result in improved yields due to less water stress or less loss of fertilizer due to leaching.
One of the early obstacles to adoption of on-farm irrigation scheduling had been the time management problem of gathering, processing, and implementing scheduling on a daily irrigation cycle period.
Computer technology presents the opportunity for information gathering, transferring, and processing to be done much more easily, efficiently, and sometimes automatically.
Scheduling software, communication, and control technology exists that can provide management recommendations which could then be remotely implemented.
In the early 1990's, an excel spreadsheet program was introduced by Kansas State University Research and Extension to help facilitate ET based irrigation scheduling.
This eventually evolved into KanSched.
KanSched features have been described in previous CPIC programs and shown to be useful to a variety of climatic conditions and irrigation capacities.
KANSCHED THE WEB BASED VERSION
 This text introduces the next version of KanSched which will be a web-based.
For the sake of clarity in this paper it will be referred to as KanSched3.
As a web based program, users will have to set up their own user accounts and identities.
However, once the user accesses the account, KanSched3 will appear very similar to the KanSched2 stand-alone version.
Figure 1 shows the initial field set up page, the user can not advance in the field until the field characteristics are entered.
Figure 1.
Initial field set up page for KanSched3
 The field set up information is the same entires as in KanSched2, crop and crop growth information, reference ET source and crop coefficients , soil and system efficiency.
In KanSched3, a new feature will allow the user to select a climatic zone that will further custimize the crop coefficients to their location, although custimized Kcos can still be entered as in KanSched2.
KanSched Mobile Irrigation Lab
 Enter the general information for the field below.
Once completed, click the Save Field button to save your progress.
Field Name:	KanSched Demo Field
 Crop & Growth Information
 Crop Type:	Corn	change	i
 Emergence Date:	Apr 15, 11
 Season Length:	168	days
Review and Operational Guidelines for Portable Ultrasonic Flowmeters
 Blessing Masasi Research Assistant
 R.
Scott Frazier Associate Professor and Extension Specialist, Energy Management
 Saleh Taghvaeian Assistant Professor and Extension Specialist, Water Resources
 Having an accurate estimate of any input used for agricultural production is the first step towards increasing the efficiency of utilizing that input and maximizing yield per unit input.
This is especially true in case of irrigation water, as this precious resource is limited in availability and the competition over its use is growing rapidly from various sectors.
Knowing the amount of water applied to agricultural fields is a prerequisite in evaluating how an irrigation system is performing and if any improvements are required.
This information also allows for determination of pumping plant efficiency, which is required for improving energy conservation and reducing pumping costs.
Ultrasonic flowmeters provide the capability of measuring water flowrate accurately, by utilizing the dynamics of ultrasonic energy transmission.
A compact marvel of modern engineering, the portable ultrasonic flowmeter enables one to determine water flowrate through a pipe without having to interrupt the flow.
These devices are becoming more common as improvements continue to be made to the technology.
The popularity of portable ultrasonic flowmeters has been largely attributed to their convenient size, weight and ease of use.
The weight of most commercially available units is less than 13.0 pounds , which is a major advantage for set up and transportation to remote areas.
Portable ultrasonic flowmeters generally come with a built-in rechargeable battery, which can last up to 18 hours when fully charged.
This attribute makes them the flowmeter of choice in cases where more time is spent in the field, for example when evaluating many irrigation systems in remote areas.
The equipment can also be used while the battery is being charged, if a power source such as a generator is available.
Depending on the brand and model, portable ultrasonic flowmeters can operate on pipe diameters from 0.5 inch to 20 feet; flow velocities from 1.0 to more than 50 feet per second; and a wide range of fluid temperatures.
They have excellent accuracy, ranging between 1 and 5 percent, when set up and operated properly within their range of flowrates.
On the other hand, portable ultrasonic flowmeters are relatively expensive
 compared to other types of flowmeters.
The price depends on the type and range of flows that can be measured.
At the time of preparation of this fact sheet, the price for a single unit ranged between $2,000 and $13,000.
Ultrasonic flowmeters consist of clamp-on transducers that are attached on the outside wall of the pipe with flowing water.
These transducers transmit and receive ultrasonic signals that result in the computation of corresponding flowrate, which is displayed by the meter.
The digital display showing the water flowrate is the device to the left sitting on top of the pipe.
Portable ultrasonic flowmeters are programmed to measure and display flow in most of the commonly used water flow units such as gallons per minute, liters per second and cubic meters per second.
Several types of ultrasonic flowmeters exist in the market.
They vary in setup, signal type, application and price.
This fact sheet describes the general characteristics and principles behind two main types of portable ultrasonic flowmeters currently available in the market and used for both laboratory and field applications: transit-time and doppler ultrasonic flowmeters.
The operation of transit-time ultrasonic flowmeters is based on the principle of phase shift flow measurement.
According
 Figure 1.
Ultrasonic flowmeter installed on a pump outlet pipe.
to this principle, ultrasonic signals  moving in the direction of flow require less time to travel between the two transducers as compared to signals moving against the flow.
The more common transit-time ultrasonic flowmeters consist of two transducers mounted on the outside wall of the pipe.
These two transducers act alternatively as transmitter and receiver.
The first transducer sends out an ultrasonic signal and the second transducer receives it.
Immediately after, the second transducer sends a signal back to the first transducer.
The transit times between the up-stream and down-stream signals are estimated and their difference is used to compute the velocity of the flowing water.
Transit-time ultrasonic flowmeters are reported to work very well with relatively clean water that allows good signal transmission.
Doppler ultrasonic flowmeters measure the frequency change  of a signal sent into the flowing liquid stream across the pipe.
The injected signal bounces off of bubbles or particles in the stream and this echo is returned to the transducer.
The frequency of the signal is shifted lower in case of flow moving away from the sensor.
The device compares the frequency shift to the original signal and computes the flow velocity.
For accurate flow measurement with the doppler-type ultrasonic flowmeter, the fluid should contain sufficient concentration of particles and/or bubbles to reflect the signal adequately.
Doppler ultrasonic flowmeters work well with suspension flows where particle concentration is more than 100 parts per million and particle size is larger than 100 micrometers, but less than 15 percent in concentration.
Thus, these flowmeters are not recommended for use in clean water.
Doppler flowmeters typically have just one transducer, therefore setup for measuring may be easier than the transit-time flowmeters.
Figure 2.
Doppler ultrasonic arrangement.
Selecting Portable Ultrasonic Flowmeters
 There are a number of important factors to consider when choosing a good portable ultrasonic flowmeter.
One factor is the sediment properties of the water in terms of quantity and size.
Generally, when water to be measured has sediment particles more than 100 parts per million and larger than 100 micrometers , the doppler type should be considered.
On the other hand, in the case of clear and clean water without sufficient sediments, the transit-type works better.
The desired level of accuracy should be considered when selecting the best portable ultrasonic flowmeter for the job.
Between the two types of ultrasonic flowmeters discussed in this fact
 sheet, the transit-time was reported to be more accurate as compared to the doppler type.
The pipe size and flow range for which the flowmeter is intended to be used should also give guidance on choosing the right flowmeter to purchase.
Maintenance of Portable Ultrasonic Flowmeters
 As with any piece of equipment, portable ultrasonic flowmeters require routine inspection and maintenance to ensure efficiency and accuracy.
Major maintenance recommendations are generally included in the respective manuals.
In general, these devices require less maintenance compared to other flowmeters because they have no moving parts.
After use, dust and transmission gel should be adequately wiped from the transducers and other electronics before housing in the carrying case.
When not in use, meter components should be kepti carrying case and stored where it will not be exposed to excessive dust and other contaminants.
The equipment should be stored away from high temperature and humidity and not exposed to direct sunlight and rain.
Replacement of components like the built-in battery and electronics should be done based on the manufacturer's recommendation.
The lifetime of components is generally stated in the equipment manuals and guidelines.
Nebraska is a groundwater-rich state, thanks in part to the High Plains Aquifer.
Many people are familiar with the High Plains Aquifer , but fewer people know that there are other aquifers in the state.
In fact, Nebraska has seven secondary aquifers, which are much smaller in areal extent than the High Plains Aquifer and generally have poorer water quality, but are nonetheless important in places where the High Plains Aquifer and shallow sand gravel deposits are absent.
Interest on subsurface drip irrigation  to irrigate row crops has been increasing in Nebraska in recent years.
This increased interest has been due in part by limited irrigation water supplies in parts of the state.
In places where water supplies are limited, some farmers have been experimenting with SDI as an alternative to surface irrigation, to produce crops with less water and to reduce labor.
This is specially the case in small, odd-shaped field where installing a center pivot system in not practical.
Another common use of SDI in Nebraska is to irrigate center pivot corners, which are commonly non-irrigated.
To put SDI in Nebraska in the right prospective, it should be stated that, even thought irrigated acreage in Nebraska is only second to California, only 33% of its cropland is irrigated.
At the same time, center pivots irrigate most of the irrigated land in Nebraska.
Although reliable information on acreage irrigated by SDI in Nebraska are not currently available, it is safe to say that the number a acres currently irrigated by SDI is insignificant as compared with those irrigated by center pivot and surface systems.
At the time of this writing, the Nebraska Department of Agricultural Statistics did not have any information on acres irrigated by SDI in the state, and the Nebraska Department of Environmental Quality  is just starting to keep records on SDI systems installed in the state.
In 2001, however, the Irrigation Journal published the result of an irrigation survey, which included irrigated acreages by different irrigation systems by state and nationwide.
Results for Nebraska shown in fig.
2 indicate that low-flow systems, which include systems like SDI, surface drip systems and micro-sprinklers, only represent approximately 0.04% of all irrigated acreage.
By comparison, the same source indicates that in the entire United States low-flow systems represent approximately 4.9% of irrigated acreages.
Irrigated Acreages in Nebraska
 Figure 2.
Irrigated acreages by irrigation method in Nebraska.
Figure 3.
Percent irrigated land by irrigation method in The United States.
As suggested above, Nebraska has been slower in the adoption of low-flow system, including SDI, as compared with the national average.
This may be due to a variety of factors.
First, the high cost of SDI is difficult to recuperate by growing low-value crops like those commonly grown in Nebraska.
This contrasts with places like California, where SDI is used to grow high-value crops, like fruits and vegetables.
Although the cost per acre of an irrigation system can vary widely depending on field size and desired level of automation, researchers in Texas have published the cost comparison for different irrigation systems shown in Table 1.
It shows that an SDI system cost approximately twice as much as a center pivot.
For a crop like corn, the advantages of SDI as compared with center pivots, in terms of labor and water savings, are not as significant as to justify paying approximately twice as much for an SDI system.
For surface irrigators, on the other hand, even though the water and labor savings that can be realized by switching to SDI can be significant, the logical step would, however, be to switch to a center pivot if field size and shape allow.
Researchers in Kansas, however, have done economic comparison between SDI and Center pivots for row crops.
They have shown that as the field gets smaller, the economic feasibility of SDI becomes more attractive.
The farm size at which a break-even point is reached, however, depends on a variety of factors, some of which are not well documented, such as:
 Live expectancy of the SDI system,
 Expected yield increase with SDI over center pivot,
 Expected water savings with SDI,
 Value of the water saved using SDI.
Table 1.
Irrigation investment cost for different irrigation systems.
Irrigation System	Cost 
 Conventional furrow	165	153	142
 Center pivot	367	268	252
 SDI	832	615	570
 1.
Assuming tax rate of 15% and discount rate of 6%.
2.
Assuming tax rate of 28% and discount rate of 6%.
A second factor that drives the adoption of more efficient irrigation systems like SDI is water scarcity, which until recent years, have not been much of a problem in Nebraska.
Nebraska is sitting on top of a large portion of the High Plains Aquifer and has far more ground water than any other High Plains state.
The volume of groundwater stored in the Nebraska portion of the aquifer has been estimated at 2,000 million acre-feet.
Despite the large quantity of groundwater available in Nebraska, decreases in water table due to over-pumping are now a big problem in South West Nebraska and in Box Butte County.
At the same time, due to several years of drought, surface water resources stored in reservoirs and in the soil profile in the area are at all-time lows.
This situation has motivated many surface irrigators to install center pivots,
 and others to consider SDI.
The groundwater depletion problem, however, is not yet as widespread and severe in Nebraska as it is, for instance, in Texas, Kansas, Oklahoma, Colorado, and New Mexico.
Another factor limiting SDI in Nebraska has been the fact that information for farmers wanting to install SDI systems has been very limited.
For instance, even though research with SDI has been carry out for decades in California, and for over 12 years in Kansas, no similar programs have been established in Nebraska.
Only now is Nebraska establishing SDI research and extension programs as a reaction to farmer's demands for information.
Innovative farmers have mainly been leading the introduction of SDI to the state.
Without the benefit of independent information sources, other than that provided by the industry and irrigation dealers, a share of SDI system failures have occurred.
Initially, farmers started experimenting with "leaky hose" type of systems, with disappointing results, and now thin-wall drip tapes are commonly used.
Also, other than cost, the main problem limiting the adoption of SDI in Nebraska is the lack of a viable solution to potential rodent problems.
What follows is a description of demonstrations, extension, and research efforts that have been made or are currently underway to either generate and/or provide information related to SDI in Nebraska.
UNL SDI RESEARCH FACILITIES
 In recent years, the University of Nebraska-Lincoln  has been in the process of establishing SDI research and extension programs.
So far, SDI research facilities have been installed at North Platte, Scottsbluff, Lincoln, and there are plans to install another facility at Clay Center.
A Brief description of these facilities follows.
SDI Research Facility at North Platte
 In 2003, installation of a SDI research and demonstration facility was completed at the UNL West Central Research and Extension Center located in North Platte, NE.
Funding for this facility was obtained through grants from the Nebraska Foundation and from the US Bureau of Reclamation.
The facility covers 12 acres, divided into 72 individual plots.
This number of plots can accommodate 18 treatments, replicated four times.
Each plot is 30 ft X 237 ft, which can accommodate 12 rows of crop planted at a 30-inch spacing.
A drip tape was installed every other row  at a depth of approximately 16 inches.
The drip tape installed was a T-Tape TSX 515-12-340, with a wall thickness of 15 mil, an inside diameter of 0.625 inch and a nominal flowrate of 0.34 gpm/100 ft at 8 PSI of pressure.
The tapes in each plot are connected to an individual supply line at the head of the plot, and to an individual flushing line at the downstream end of the plot.
The
 supply line of each plot is connected to a manifold.
The manifold has an air vent, electric valve, flowmeter, and pressure regulator for each plot.
The electric valves are then connected to a SDM-CD16AC relay controller  system that is controlled by a CR10X datalogger.
Eight of the plots are instrumented with ECH20 Dielectric Aquameters  to continuously monitor soil moisture at five depths in the soil profile, to a depth of five feet.
The system can be automated by programming the datalogger to respond to environmental inputs, such as soil moisture or weather information.
The water supply for the system is a 720 GPM well.
A Cycle Stop Valve , pressure switch, and pressure thank combination was installed at the pump to allow irrigating a reduced number of plots at one time.
A chemigation system to allow injecting fertilizer, chlorine, and acid with the irrigation water was also installed.
The chemigation system was designed and installed with all the safety devices to meet NDEQ regulations.
During the 2003 growing season, the system was used to irrigate a silage corn crop.
The system operated as expected, with very few problems.
Before installation, Rozol pocket gopher bait  was applied all around the field, with the purpose of preventing rodent damage.
No rodent problems were detected during 2003.
During the next three years, the facility will be used to conduct an experiment in which several irrigation amounts, nitrogen rates, and methods of nitrogen application for corn will be evaluated.
Funding has already being secured to install an additional 72 plots in an adjacent field.
SDI Research Facility at Scottsbluff
 The installation of the SDI Research and demonstration facility in Scottsbluff, NE, was completed in 2003.
Funding for this facility was obtained from the US Bureau of Reclamation.
The facility covers approximately 8 acres and is divided into 34 plots.
Each plot is 400 ft X 22 ft, which accommodates 12 rows of crop spaced 22 inches.
The system has Netafim Typhoon 630-12.5 mil tapes with drippers spaced every 24 inches and a nominal dripper flowrate of 0.25 gallons per hour at 10 PSI of pressure.
The tapes were installed every other row  at a depth of 10-12 inches.
Irrigation to each plot can be controlled using a control manifold installed in each plot.
Each control manifold is instrumented with a flowmeter, pressure regulator, electric valve, manual valve, and air vent.
The electric valves are connected to a programmable control panel.
A flushing manifold was also installed at the downstream end of each plot.
The water source for the system is canal water.
Water is filtered using a Netafim DiscKleen disc filter.
The system is also set up to be able to apply chemicals with the irrigation water.
The system was designed to grow corn and dry beans.
Sugar beet, which is another important crop in the area, may also be grown with the SDI system in the
 future.
The system will be used for demonstration and, in the next 3 years, an irrigation frequency trial will be conducted.
Even though irrigation research could not be started with the system in 2003, the system was used to irrigate a corn crop.
Leaks were the main problem detected during the 2003 growing season.
Approximately 50 to 60 leaks in the tapes were found, which seemed to be caused by field mice.
Digging out the tapes to repair those leaks was a very timeconsuming and difficult task.
SDI Research Facility at Lincoln
 The objective of installing this SDI research facility was to conduct an experiment to evaluate corn yield potential under intensive management.
In 1999 and 2000, the experiment was irrigated to replenish daily crop evapotranspiration via a surface drip system, with the tape placed next to the plants in each row.
In 2001, a permanent SDI system was installed with drip tapes in alternate rows at a depth of about 12 to15 inches.
SDI Research Facility at Clay Center
 Funding to install a SDI research facility at the UNL South Central Research and Extension Center  has been secured since about two years ago.
Delays in installing this facility, however, have occurred because of two reasons.
First, the Irrigation Engineer leading the effort took a different job and move to another state.
Second, because of budget cuts to UNL by the state, the SCREC was closed down and the tenured faculty was moved to Lincoln.
The research farm at SCREC, however, will remain in operation and under the control of UNL faculty and some on-site support staff.
Therefore, the plans to install the SDI research facility at Clay Center are still underway.
Currently, a 40-acre farm is available for this purpose, and a new Irrigation Engineer has recently been hired, who is expected to lead this effort.
Current plans are to start the installation during spring of 2004 and initiate a research project in 2005.
Initially, a threeyear experiment will compare nitrate leaching under SDI and surface irrigation.
The experiment will also evaluate different irrigation levels and nitrogen fertigations scheduled using weekly chlorophyll meter readings.
SDI EXTENSION PROGRAMS IN NEBRASKA
 In the last few years, a series of extension programs dealing with SDI have been taken place in Nebraska.
The University of Nebraska Cooperative Extension, in collaboration with other partners, has been the main institution organizing these programs.
Partners have included the Natural Resource Districts , the Natural Resource Conservation Service , the Nebraska Department of Environmental Quality , and the irrigation industry, among others.
Several of the SDI extension programs that have been conducted in Nebraska include, among others:
 In 2001, the NRCS organized a one-day SDI meeting directed to provide information for NRCS personnel.
This included speakers from the SDI industry, including NETAFIM, T-Tape, and Agricultural Products, Inc.
In 2001, a coalition of groups organized an SDI meeting.
Groups represented included the NRCS, the Tri-Basin Natural Resources District, the Lower Republican NRD, and the Harlan County UNL Cooperative Extension.
The meeting was held in Alma, Nebraska to discuss SDI and the impact it can have to agriculture.
Speakers were invited to share their knowledge and a farmer panel was presented to discuss real life experiences with the 65 people who attended.
In 2001, UNL Cooperative Extension and NRCS organized a Farmer's Panel on SDI, as part of the Central Plains Irrigation Conference, which was conducted at Kearney, NE.
The purpose of the panel was to discuss local farmer's experiences with SDI.
Approximately 40 people attended the farmer's panel.
Displays from the SDI industry were also presented at this conference.
In 2001, the Nebraska Fertilizer and Agricultural Chemical Institute conducted and educational program for crop consultants, in Omaha, NE.
This program included a presentation on SDI as an emerging technology by a UNL faculty.
In 2002, a half-a-day SDI meeting was conducted at North Platte, NE.
Speakers came from Kansas State University, NRCS, and NDEQ.
Also, industry displays were presented.
This was an informational meeting covering design, management, advantages and disadvantages of SDI, and legal requirements for SDI.
The information was directed to farmers and crop consultants.
Approximately 30 people attended this meeting, which included farmers, crop consultants, and agency personnel.
In 2002, a two-day SDI informational meeting was conducted at Hastings, NE.
This meeting presented speakers from the SDI industry  and from the NRCS.
It was mainly directed to educate UNL extension educators, UNL faculty, and personnel from the NRD, NRCS, and other local agencies.
Approximately 25 people attended this program.
In 2002, a field day was conducted at the South Central Research and Extension Center at Clay Center.
A presentation on SDI by UNL faculty was included as part of this field day.
Approximately 200 people attended this presentation.
In 2003, UNL Cooperative Extension faculty conducted a series of educational programs focusing on irrigation related issues important to
 farmers in the state.
One of the topics of this program was a discussion of advantages and disadvantages of SDI.
It also included the presentation of displays by the SDI industry.
The program was offered at five different locations across Nebraska.
Approximately a total of 200 people participated in this educational program.
In addition to educational meetings on SDI, written material and TV spots have produced to educate Nebraskans about SDI.
NRCS has helped SDI in Nebraska by providing cost share funds through the EQIP program and by providing technical assistance for farmers.
Following is a description of some examples of SDI demonstrations that NRCS has been involved with.
Leaky Pipe System in Phelps County, NE.
An evaluation of a 67-acre leaky pipe system installed in Phelps County, Nebraska, was conducted by a group of institutions during 1995 and 1996.
Funding for the evaluation was provided by a NDEQ 319 non-point Source Water Pollution grant.
Institutions involved in the evaluation included the NRCS, UNL Cooperative Extension, Central Nebraska Public Power & Irrigation District  and the Tri-basin Natural Resource District.
The purpose of the evaluation was to help state and federal agencies determine if the practice was eligible for cost sharing through the Farm Service Agency  and the Great Plains Conservation Program.
In this farm, a 3/8-inch diameter leaky pipe was installed at 18-inch depth, a 6-ft spacing, and run length of 960 ft.
The soil was a Holdredge silt loam with a 0-1% slope.
The water source was surface water, which was filtered using a sand-andgravel medium filter.
The system was also instrumented with a venturi fertilizer injection system.
Access points were installed to measure flow and pressure changes at 5 points along three randomly selected laterals.
Access tubes were also installed for weekly monitoring of soil moisture at 6-inch increments to a depth of 6 feet.
Nitrogen fertigations were scheduled based on chlorophyll meter readings.
During the 1995 evaluation, it was found that the individual line Distribution Uniformity  was poor.
The three line tested emitted water a different rates.
Section of the line with the higher pressure did not emit the most water.
The average seasonal DU for the three lines was only 54%.
It was determined that by the end of the growing season the smaller holes on the leaky pipe had become plugged.
The average daily application for 1995 had dropped to 0.11 in/day from
 0.17 in/day measured in 1994.
Chemical treatment applied in 1995 did not improve flows.
In August 1995, the water source was changed to well water.
Chemical treatment applied in spring of 1996 was able to improve flowrates from 0.11 in/day, measured in 1995, to 0.20 in/day.
On July 2, 1996, a pressure switch installed at the filter was causing the filter to continuously flush.
On this date the subsurface system was abandoned and a gated pipe system was used for the remainder of the season.
SDI System in Gosper County
 In 2002, an SDI system was installed in a 22.8-acre field located in Gosper County, Nebraska, which was previously irrigated by conventional gravity without reuse.
In this farm, a 1 3/8 inch diameter T-Tape with a 24-inch emitter spacing was installed every other row.
The field was 2000 ft in length in the West site and 2500 ft in the East site.
The soil was a Holdrege Silt Loam with 0-1% slope.
The system was designed to irrigate corn and soybean using a groundwater well.
Filtration is accomplished with a Fresno filter with 200-mesh screen.
From the producer's prospective, the goals for installing the system were:
 To save irrigation water
 After two seasons operating the system, the producer feels that 2100 feet of length is the maximum length that can be irrigated with a 1 3/8-inch tape on 0-1% slopes.
He feels that half-mile length is too long.
In 2003, soil moisture was monitored.
It was found that soil moisture stayed pretty consistent in the first 2000 feet of row length and decreased in the 2000-2500 feet section.
The producer has had very little problems with gophers.
To prevent gopher problems, after harvesting in 2002 he irrigated to get the area around the tape wet for the winter.
He also ran a gopher machine around the borders of the field.
So far, he has only had to repair 2 holes.
After the 2003 season, he just watered and is still waiting to see the results.
Regarding the quality of the well water, an iron bacteria problem was detected.
Because of this, in the second season he chlorinated the well using 100 gallons of chlorine bleach in the spring and chlorinated again with 25 gallons just prior to irrigating.
There were no problems during the 2003 growing season.
The producer doesn't know if chlorination helped with the iron bacteria or if it was just one of those years where the iron bacteria wasn't around much.
At the end of the season, the producer chlorinated the system, not the well.
This will be flushed out in spring 2004.
Based on his experience, the producer advice is:
 Know your installer to make sure he knows what he is doing.
Test your water so you know what water problems you may have to address, if any.
Regarding the original goals, he has found that labor has been reduced and he is pretty sure that there have been water savings in this field, as compared to the previous system, even though water use has not been rigorously measured.
He has found, however, that with SDI the problems/headaches are not really decreased or increased, they are just different.
From the NRCS prospective, the purpose in 2004 is to use this field as a demonstration site and to compare irrigation water savings between the SDI and conventional gravity irrigation with reuse system.
SDI in the Aurora, NE, Area
 In this area there have been quite a bit of interest in SDI, but few have actually installed SDI systems.
In 2002 a farmer converted a 15-acre field, located southwest of Aurora, to SDI.
According to NRCS personnel in the area, the producer seems to be getting along well with the system.
It was a system cost shared by the EQIP program, so NRCS was involved in making sure he had the proper design and installation to meet NRCS specifications.
Another farmer, North of Aurora, has also been converting to SDI without NRCS assistance.
He has so far installed approximately 50 acres.
There have been several others who started the process of applying for help through the EQIP program but then backed out.
One of them backed out because he couldn't get anyone to install the system.
The others probably just were unsure or became fearful of the unknowns about this fairly new system.
There have also been some installations in nearby counties.
The Central Nebraska Public Power & Irrigation District , in cooperation with The Nebraska Environmental Trust established three SDI demonstration sites in the spring of 2002.
The sites are 7-9 acre pivot corners, installed in a single corner of three different pivots across the Irrigation District.
CNPP&ID has the following two primary questions to resolve with SDI research:
 Can surface water be used successfully in these systems?
and,
 How does water use efficiency  of SDI compare to the other types of irrigation systems used in the District?
The SDI systems performed well in the 2002 and 2003 seasons; yields on the center pivot corners have met or surpassed yields under the pivot at each of the sites.
In particular, higher yields on all SDI corners were noted in 2002 when extended periods of high winds and temperatures, coupled with record low relative humidity and precipitation levels, stressed plants under the pivots for several hours of each pivot rotation.
In 2003, adjusted yields for one of the Phelps County fields were 205, 220, and 29 bu/Ac for the pivot, SDI, and dryland, respectively.
In-depth study of the WUE question will start in 2004 since cooperators have become familiar with system operation, and soil disturbance around the tape laterals is not as pronounced as in 2002 when the tapes were
 laid down behind a deep shank chisel.
Plans for the future include looking into nutrient applications, relative differences in root development, and further automation of the SDI systems.
Legal requirements for SDI in Nebraska
 An aerial photograph of the section in which the SDI system is to be installed, indicating where all wells are located.
Average flow rate of the SDI system
 Depth to groundwater where the SDI system is to be located.
Construction details of the water wells.
Design details of the SDI system.
Also, before chemigating, producers need to be certified by NDEQ.
This is done by attending an applicator's certification training and passing a written test.
In addition to this, NDEQ requires the SDI system to comply with a series of safety regulations.
This is done by obtaining a Chemigation Permit from the local NRD.
The NRD has to make sure that all chemigation safety measures have been included in the irrigation system before it can issue a permit, which requires a field inspection.
The chemigation permit is valid for one year, which means that the NRD has to re-inspect the system every year.
System safety requirements have been described by Vitzthum.
Information for this paper was provided by Dean.C.
Yonts , Ben Hardin, David Kohls, Kevin Breece, Curtis Scheele, Marcia Rompke and David Miesbach.
Bruce Johnson, Cornhusker Economics, June 20, 2001
While these mechanized systems are highly efficient in applying irrigation, they should be supplemented with scientific irrigation scheduling  methods to compute crop water requirements precisely for different parts of the field.
If every field reduced seasonal irrigation application by one inch, this would have a significant positive impact on our water resources.
The key to early water management is to apply irrigation only when it is needed to get the crop off to a good start, while keeping in mind over-irrigation enables crop input losses.
Precision water and nitrogen management can help guide your early season irrigation decisions.
THE BASICS OF IRRIGATION RESERVOIRS FOR AGRICULTURE
 Published: Oct 13, 2021 |  Printable Version  | Peer Reviewed
 Debabrata Sahoo, Mohammad Nayeb Yazdi, James S.
Owen, Jr.
and Sarah A.
White
 Agricultural and specialty crop producers, crop advisors, and extension agents can use this introductory guide on irrigation reservoirs as an overview of irrigation reservoir design basics, water quality and quantity considerations, and routine monitoring and management.
Also discussed are funding opportunities through the Environmental Quality Incentives Program  for agricultural and specialty crop growers who use or are considering installing an irrigation reservoir as primary or supplemental sources of water for their operations.
In the United States, irrigated agricultural acreage has increased yearly.1 In South Carolina specifically, irrigated acreage has increased from 95,642 acres in 2002 to 210,437 acres in 2017.1 Water for irrigation typically comes from ground or surface sources, including stormwater and recycled water.
Competition for ground and surface water sources is increasing.
Water availability can be restricted when regions are impacted by drought.
Growers can use a reservoir  to hold captured storm runoff and contain irrigation return water  that have traveled through production areas and could contain chemical and biological contaminants.2 Water in irrigation reservoirs is often supplemented by water from municipal sources, pumped from wells, or diverted from other surface waters.
Appropriate design of the reservoir is important to meet the water security needs of the farm.3 Additionally, reservoirs should be designed to manage both water and sediment.4,5 The design of irrigation reservoirs is comparable to stormwater detention ponds found in urban areas.6 The size of the reservoir varies with the type of operation.
Irrigation reservoirs are typically a minimum of 10 ft deep, unless restricted by shallow groundwater depth, and should be large enough to hold the volume of water necessary for the operation for a specific period of time.
Historical weather data, including extreme events, can help growers account for water generated during storm events and the frequency of storm events throughout the year when planning for the volume of water to store.
Appropriate reservoir design should consider  the volume of water entering and leaving the reservoir,  the time water resides in the reservoir before exiting or reuse to ensure optimal hydraulic retention time , and  the depth to groundwater.
The HRT is defined as the average amount of time that water stays in the reservoir and is estimated by dividing the reservoir volume by inflow rate or outflow rate to the reservoir.
In general, HRT quantifies the amount of time it takes for water introduced to the pond to flow out again.
Longer HRTs aid in efficient contaminant removal, improving desired quality parameters when recycled for irrigation.7 Increasing HRT is most easily accomplished by increasing the storage capacity of the reservoir and maximizing the distance between where water enters the reservoir  and where water leaves the reservoir.
A irrigation reservoir with trees around it.
Figure 1.
Irrigation reservoir at a plant nursery.
Image credit: Sarah A.
White, Clemson University.
If installing a new reservoir, consider sizing based on the volume of water needed to irrigate crops during a prolonged drought cycle, when the use of other water sources may be regulated or restricted.8 Develop a drought contingency plan for the reservoir to better meet  water applications during droughts.9,10,11
 When determining how to size a reservoir, consider the volume of irrigation return water after an irrigation event,2 current and future water requirements, stormwater runoff during growing and dormant seasons,12 and losses due to evaporation and seepage.6 A reservoir should be sized to contain a minimum of 90% of daily applied irrigation water.3 If an operation irrigates with overhead sprinklers for 1 hour, between 40%-55% of the water applied becomes irrigation return water.2 Irrigation return rates vary with the type of delivery system: overhead , capillary , and drip.12 The Reservoir Refill Calculator  calculates how much irrigation water returns to a reservoir after an irrigation event.13
 Several other factors, such as the location of the reservoir, distance from the production sites, elevation, slope, groundwater table depth, wildlife, soil type, and proximity to the electrical power supply, should also be considered while designing a reservoir.4,6 For instance, the bottom of a reservoir should be at least 1 m above the groundwater table.
Local Natural Resources Conservation Service  conservationists can help growers to apply the basic principles and design techniques for reservoirs, and landscape architects can provide additional information and special designs.14 The operator of the farm should consider fencing a reservoir to secure it for safety reasons.
Reservoirs can have multiple inlets, an outlet, and an emergency spillway, in addition to a water withdrawal mechanism.
While inlets and outlets help water get into and out of the reservoir, emergency spillways aid in safely conveying excess water without jeopardizing reservoir structural integrity during extreme events that produce extraordinary volumes of water.
The inlets can be earthen, gravel, vegetated, plastic-lined, concrete channels, or pipes routing irrigation return water from the production area to the reservoir.
The slope of the reservoir sides should be chosen to minimize the potential for bank erosion, which could destabilize the reservoir.
The slope of the reservoir sides is a function of the soil characteristics, and typically slope can be 3:1 or 4:1 to minimize bank erosion.14,15,16 Additionally, shoreline vegetation could also be selected to minimize bank erosion and better protect reservoir structural integrity.
Top left plastic lined ditch to direct water.
Middle images vegetated ditches, top right reservoir with three concrete inlets, bottom right shows a ditch with a porous paver, and bottom right shows a pipe with water flowing into a reservoir.
Figure 2.
Types of inlets that direct water into irrigation reservoirs  plastic-lined,  vegetated,  concrete,  modified pavers,  vegetated with riprap for sediment control, and  pipe.
Image credit: Sarah A.
White, Clemson University.
Water Quantity and Quality
 Availability of adequate quality water for crop production is becoming more challenging due to the changes in climatic patterns, urbanization, population growth, drought, saltwater intrusion, aquifer depletion, and changes in policies.17 Care and appropriate water conservation efforts must be taken within agricultural operations to extend water supply to meet crop demand.
Growers need to develop resilient, on-farm water management practices to remain profitable during water-scarce conditions.
Water-resilient management includes implementing efficient irrigation systems and practices, reducing water use, increasing onsite water storage, including retention reservoirs, and identifying an alternate or backup water source.6 Growers will need to invest in infrastructure to recapture, treat, and reuse irrigation return water.18,19,5,20 The primary sources of water for irrigation reservoirs include stormwater and recycled irrigation water  supplemented by groundwater, surface water, or municipal reclaimed water.6 Most surface waters are considered Waters of the United States, and withdrawals from or releases into them need to comply with South Carolina regulations.21,22 Please refer to the How the 2020 Definition of WOTUS Affects Agricultural and Specialty Crop Producers publication for more information on identifying surface waters that constitute Waters of the United States.21 Please refer to Water Withdrawal Regulations Every Agricultural User in South Carolina Should Know publication for more information on water withdrawal regulations specific to agricultural water.18
 Diagram of on farm-water types include surface, ground, operational , and non-contaminated stormwater.
Figure 3.
On-farm water classifications.
Image credit: Sarah A.
White, Clemson University and Mohammad N.
Yazdi, The Ohio State University.
Water quality is critical for healthy crop production.
Different sources of water within a production area may have different concentrations of agrichemicals, which include nutrients, metals, pesticides, herbicides, insecticides in addition to pathogens, weed seeds, cations, anions , and sediment.
Depending on the nature of the operation, stormwater could be considered clean  or contaminated.
For example, water runoff from a greenhouse or building that does not come into contact with production areas is considered clean.
Conversely, water that has been in contact with the crop or production area in which ground has been altered or agrichemicals applied would be considered operational water.
Whether generated during a storm or irrigation event, operational water could contain contaminants of concern to growers and negatively impact the surrounding ecosystem including surface waters.5,6 Proper management of operational water plays a pivotal role in controlling the fate and transport of agrichemicals and limiting their escape off-farm.18 The majority of operational water meets recommended irrigation water quality standards and can be reused for irrigation without treatment.23
 In some cases, operational water will need to be treated  before reapplication to the target crop or release off-farm to mitigate risk.18 The article by Majsztrik et al.18 provides an in-depth discussion of the various treatment technologies available and the relative costs of each treatment.
Some treatment occurs in the reservoir if the residence time  in the reservoir before either reusing the water for irrigation or releasing it into the receiving water bodies is adequate.
Since many contaminants are sediment-bound, managing sediment movement within the operation also helps to manage water quality.24,25 Water quality can also be improved by designing reservoirs in series to effectively increase the HRT within each reservoir and enhance contaminant  removal.26 Operators should consider installing various best management practices  to minimize erosion and control sediment losses.
Vegetated buffer strips and grass swales are generally regarded as inexpensive BMPs that help control sediment prior to the reservoir.27 Forebays, a small settling reservoir or structure in front of the larger reservoir , and turbidity curtains  are examples of reservoir-related control measures that minimize sediment movement into the reservoir.
Other BMPs that reduce the amount of sediment or agrichemical movement into the reservoir include smart irrigation , control release fertilizers, and targeted pesticide applications.
A concrete square designed to trap sediment with water in the middle.
Figure 4.
Sediment forebay installed in the operational water flow path to facilitate sediment removal prior to an irrigation reservoir.
Note the sloped edge to facilitate easy sediment removal.
Image credit: Sarah A.
White, Clemson University.
Irrigation reservoir with a a dock, backflush pipe, and floating white tube from which turbidity curtains can be suspended.
Figure 5.
Turbidity curtain installed onfarm to limit sediment movement in the irrigation reservoir.
Image credit: Sarah A.
White, Clemson University.
Reservoir Monitoring and Management
 Regular reservoir management and monitoring are needed to meet the water demands of an operation in terms of both water quantity and quality.
Plan to collect a water sample for water quality analysis at least once a season  until consistency over time of the water quality parameters is determined.28 For a detailed step-by-step guide on how to collect a water sample, please refer to the Collecting Samples for Agricultural Irrigation Water Testing publication.
When collecting a sample, collect water away from the bank at the same depth as the irrigation pump intake  to best characterize the quality of water directly applied to the crops.28 If an extreme  storm event occurs, it is wise to test water quality  to guarantee that desired quality standards are being met.
Various management technologies are available to support water quality reservoir functionality and storage capacity.
Inspect the reservoir inlets, outlets, and spillway regularly to ensure structural integrity remains.29 Remove floating debris from the reservoir periodically, particularly after storm events.
If aquatic weeds or algae are problematic , consult with your local extension agent or specialist to develop a management plan to mitigate their presence.
Aerators can be used to mix the water column  and transfer oxygen throughout the water column while disrupting algal community growth.30 Floating wetlands can be employed to compete with algal communities for nutrients in the water to limit the potential for algal blooms.
They may even be useful for limiting plant pathogen survival in water.31 Sediment catch basins or vegetation-based filtration systems at the inlet of the reservoir can reduce sediment and associated contaminants.
Periodically , test the depth of the reservoir to assess sediment accumulation within the structure, especially after an intense storm event using sonar-based monitoring technologies.
The depth measurements could help you decide when reservoir dredging is needed to restore storage volume.
If water quality issues are present in the reservoir, various treatment technologies could be deployed to overcome them.
Ultra-violet  light can disinfect water containing various bacteria and viruses.
Sedimentation tanks could be used to minimize sediment in irrigation water.
Flocculants could be used to cluster fine particles and enhance their settling from water.
Please refer to Majsztrik et al.18 for detailed information on water treatment technologies, the order of treatment technologies to maximize treatment efficacy, and estimates on cost.
For growers who must comply with Food Safety Modernization Act  requirements, consult the Food and Drug Administrations Food Safety Modernization Act webpage for further information guidance on testing and compliance requirements.
The Natural Resources Conservation Service , as part of the 2018 Farm Bill, has allocated funds through the Environmental Quality Incentives Program  to provide technical and financial assistance to producers to address natural resource concerns and deliver environmental benefits such as improved water and air quality, conserved ground and surface water, increased soil health and reduced soil erosion and sedimentation, improved or created wildlife habitat, and mitigation against drought and increasing weather volatility.32,33 The technical and monetary assistance through EQIP helps producers voluntarily implement various BMPs.
Producers are encouraged to contact their local NRCS office to request assistance and develop a plan to implement BMPs and apply for funding.
Cost-share for all projects is not guaranteed, but technical assistance is.
However, beginning in 2020, States may provide increased payment rates for high-priority practices.
In consultations with the State Technical Committee, State Conservationists may designate up to 10 practices to be eligible for increased payments.32 National and South Carolina priorities related to the installation of a reservoir include reducing non-point source pollution  and conserving ground and surface water resources to mitigate drought.33 If you are interested in applying to the EQIP, contact your local service center listed on the Service Center Locator website, and visit the USDA NRCS website to start your application.
Irrigation retention reservoirs are critical infrastructure for agricultural producers, especially specialty crop growers.
Reservoirs ensure water availability during drought and manage operational water quality.
When installing a reservoir, consider designing for the minimum volume capacity you need to enable irrigation during an extended drought scenario  whatever the duration.
When using water from a reservoir, monitor for contaminant presence and determine if the water should be treated prior to use for irrigation.
The EQIP through NRCS can provide technical and financial assistance for infrastructure improvements, like reservoirs, but the process requires a time investment to develop a plan in line with NRCS priorities.
Extension Brief, EBR-42 January 2016
 Good Agricultural Practices : Irrigation Water Treatment for High E.
coli
 What should you do if your water test results show that levels of generic E.
coli exceed the maximum recommended amount?
Before investing in a system to clean and sanitize your irrigation water, do a visual survey of your water sources to investigate what is causing the elevated microbial counts.
Below are several strategies to consider.
Check Surface Water for Environmental Contamination
 While performing a survey of your water sources, ask yourself:
 Is there evidence of animal intrusion into the water source ?
Is it possible to fence animals out or prevent birds from landing?
Are animal pastures, buildings, or manure storage located uphill from water sources?
Is it possible to build a berm to divert runoff away from the water source?
Has it been unusually rainy?
Although it seems like rain would dilute bacterial counts in water sources, high amounts of precipitation can increase E.
coli counts.
Are backflow prevention devices installed and properly functioning?
Is the irrigation intake valve floating above the sediment?
If the intake is pulling up sediment, it may lead to higher bacterial counts.
If Your Water is from a Well, Check the Structural Integrity of all Parts
 Inspect the well casing:
 Is it cracked or corroded?
Are there any areas that allow leaking and contamination into the well?
If so, can the cracked areas be patched?
Is the well cap broken or missing?
Do any seals appear to be broken or missing?
What Can You do When Microbial Counts are High?
If possible, switch to an alternative water source with acceptable test results while bacterial counts remain high in the original source.
If there is not an alternative water source, is it possible to switch to a less-risky irrigation method?
For example, you can use trickle/drip irrigation instead of overhead irrigation.
After making any changes to reduce contamination, give the water source a few weeks to settle out, then take another water test.
If you survey the water sources and cannot identify a potential source of contamination, and a resulting test does not show a decrease in levels of E.
coli bacteria, then mitigation measures might be necessary.
The analysis focused on dividing the fields into one of six categories based on the soil water levels in the heart of the season  and on Sept.
15.
The six categories were developed based on the readings from the Watermark sensors.
The sensors generate data reported in centibars and have a range from 0  to 240  centibars.
Centibar is a unit of measure that refers to the force required by the plant to pull the water out of the soil and into the plant.
Typically, installations use a set of three sensors, with one sensor installed at six to 12 inches, one at 18-24 inches, and one at 30-36 inches.
Can farmers use water more effectively?
Two on-farm demonstrations compare irrigation methods
 Cotton under irrigation in the San Joaquin Valley.
High water tables and associated high salinity now hamper farm production across 400,000 acres of farmland in Fresno, Kings, Tulare and Kern Counties in the San Joaquin Valley.
The two following reports describe farm demonstration projects undertaken to reduce drainwater volume while maintaining profitability.
Performed at different sites under differing conditions, the projects yielded different results.
An analysis of the combined results appears on page 11.
Reducing drainwater: Furrow VS.
subsurface drip irrigation
 Allan E.
Fulton Claude J.
Phene
 J.D.
Oster Blaine R.
Hanson David A.Goldhamer
 Cotton was produced using conventional furrow irrigation, an upgraded continuous-flow furrow design, surge irrigation, and subsurface drip irrigation in 1987 and 1988.
We found that the most economical method of reducing potential drainage at this site was to reduce the furrow length by half and decrease the set time by more than one-half during preirrigation.
A subsurface drip system reduced potential drainage most effectively and increased production, but caused an overall profit loss.
Subsurface drip systems may be profitable if properly designed and managed; however, a substantial yield increase or reduction in drainage disposal costs must be achieved.
Otherwise, profitability of subsurface drip would be less than that for furrow irrigation systems.
Southern San Joaquin Valley growers must often apply excess water to alleviate soil salinity or to compensate for nonuniform infiltration.
This practice contributes to the expansion of the high water table.
Meanwhile, annual saltimportation withirrigation water amounts to 3 million tons.
Soils also contain minor elements such as selenium, arsenic, molybdenum, uranium, vanadium, and boron that increase the environmental hazards of drainage disposal.
Disposal options such as reuse of saline drainwater, discharge into underlying geologic strata or evaporation ponds, or proposed discharge into the ocean are either expensive or controversial due to possible adverse effects on crop production and the environment.
Whatever combinations of disposal options are ultimately selected, judicious use of irrigation water is a logical first step to minimize drainage volumes requiring disposal.
In 1986, the San Joaquin Valley Salinity and Drainage Workgroup  concluded that there was a need for on-farm demonstra-
 tions of irrigation methods that had the potential of reducing drainage volumes.
Several demonstrations are currently underway using funds and equipment provided by the University of California Salinity and Drainage Task Force, the U.S.
Department of Agriculture's Agricultural Research Service , the California Department of Water Resources , the State Water Resources Control Board, irrigation industries, and farm cooperators.
This paper, and the one following, report results obtained from two of these projects, which involve both furrow and pressurized irrigation systems.
Field site.
The field data reported here were obtained from a 320-acre site located 10 miles southwest of Stratford, California.
Continuous furrow, surge furrow, and subsurface drip irrigation systems were used to irrigate cotton on side-by-side 10-acre plots.
The existing furrow system consisted of 40inch beds and furrow lengths with 0.16 slope.
The soil was a Westhaven clay loam; irrigation water was from the California Aqueduct.
Soil salinity averaged 1.5 decisiemens per meter  near the surface and increased to about 11 dS/m at a depth of 6 feet.
The water table depth, which ranged from 5 to 9 feet, was nearer the surface on the east half of the field.
Continous furrow irrigation.
In 1987, inflow and outflow were measured with broadcrested weir flumes installed in replicated sets of furrows to evaluate the amount of water infiltrated during the preirrigation and the first and last crop irrigations.
The "two-point" volume balance method was used to develop an equation describing cumulative infiltration for each furrow.
Data required for this method included field slope, wetted cross-sectional furrow area, water inflow and advance rates, and furrow length.
Results from these evaluations were used to plan improvements of the conventional furrow irrigation system in 1988.
During preirrigation in 1988, furrow length was reduced from 2,500 feet to 1,250 feet by laying a second line of gated pipe 1,250 feet from the head ditch.
Irrigation set times were reduced from 24 to about 11 hours and inflow rates were 36 gallons per minute.
The furrow length was converted back to 2,500 feet for the crop irrigations and the inflow rate was increased to 43 gpm.
Set times for the crop irrigations were 12 hours.
The first crop irrigation and subsequent crop irrigations were scheduled -16 bars and -18 bars leaf water potential, respectively, using the pressure chamber.
Surge irrigation.
In 1987, surge irrigation was used during the crop irrigations in June, July, and August.
Inflow and outflow were measured for replicate sets of furrows
 Four-inch sub-mainline is shown in a trench which runs across the furrows.
Lines of drip tubing which have been shanked under the center of each 40-inch cotton bed are connected to the sub-mains before burying the line.
The cotton crop is shown above exposed drip tubing.
Circled area shows type of root distribution found when cotton is grown with drip system.
to determine the amount of infiltrated water for each irrigation.
The resulting data were used to develop a management plan for 1988.
In 1988, furrow lengths were also reduced to 1,250 feet during preirrigation.
Four surge cycles  were used to pulse the water to the furrow ends: average cycle times were 50, 87, 94, and 128 minutes to advance water to 310, 620, 930, and 1,250 feet, respectively.
The average cutback phase  was slightly under 10 hours.
Furrow length was converted to 2,500 feet for the crop irrigations.
Six surge cycles  were used to advance water across the field: cycle times were 44, 73, 104, 147, 171, and 135 minutes to advance water to 420, 840, 1,260, 1,680, 2,100, and 2,500 feet, respectively.
The duration of the cutback phase  was about 9 hours.
The crop irrigations were scheduled using the pressure chamber.
Subsurface drip.
The operation pad included a water holding tank with inflow from the district valve controlled by an au-
 tomatic float valve, a 35 horsepower electrical pump, two sand media filters with a backflush line, a fertilizer injection pump, a water meter, and an electronic controller.
A 6-inch-diameter polyvinylchloride  mainline extended 1,800 feet downfield and was buried at a depth of 36 inches.
Four-inch PVC submains were connected 615 feet down the main line and at its end.
The submains were buried at 30 inches, perpendicular to the beds.
Drip tubing  was shanked into the soil about 15 inches below the bottoms of alternate furrows  and connected to the submains.
The drip tubing extended 615 feet off both sides of the submains and was connected into 2-inchdiameter PVC drainlines with manual flushing valves.
The pressure-compensated ram emittors in the drip tubing were spaced 39.3 inches apart and discharged water at the rate of 1 gallon per hour.
Furrow irrigation was used to preirrigate in 1987 because of the wide drip-tube spacing.
Irrigations were applied daily with the drip system beginning in May and ending
 September 15.
Daily application rates were calculated from real-time estimates of grass reference evapotranspiration  and crop coefficients  for SJ-2 cotton developed by the USDA-ARS Water Management Research Laboratory, Fresno.
The entire plot was irrigated at the same time.
Prior to the 1988 season, additional drip tubing was installed under the unused furrow to achieve 40-in spacing between drip lines.
The cotton beds were moved SO that the tubing was located beneath the bed.
An electric flow valve was installed at the inlet into each 4-inch submain to divide the system into two 5-acre parcels with flexibility for separate operation.
The 40-inch tube spacing along with rainfall allowed adequate preirrigation.
The irrigation scheduling method was the same as that used in 1987 except irrigation was cut off on August 30.
Management of other cultural practices.
Land preparation, pest control, defoliation, and harvest were managed by the cooperator in all plots.
Rates of fertilizers were managed by the cooperator in the furrow systems.
Fertilizer and soil fumigant were applied through the subsurface drip system at rates based upon results from subsurface drip research in cotton monoculture at the Westside Field Station.
Nitrogen, phosporus, and zinc fertilizers were applied in the furrow-irrigated treatments at rates of 113, 40, and 5 pounds per acre, respectively, in 1987 and at rates of 129, 40, and 5 pounds per acre, respectively, in 1988.
In the subsurface drip treatment, nitrogen, phosphorus, and potassium were applied at rates of 220, 63, and 63 pounds per acre, respectively, in 1987, and at rates of 176, 253, and 176 pounds per acre, respectively, in 1988.
Zinc fertilizer was not applied in the subsurface drip plot in either year.
Vapam soilfumigant was applied each season during preirrigation at 30 gallons per acre to prevent root intrusion and control verticillum wilt and at 5 gallons per acre to assist defoliation.
Water infiltrated predominantly through cracks in the fine-textured soil during the initial stage of infiltration.
The initial water intake rate was very high, but declined to a much slower, steady rate after only 3 hours of infiltration.
The steady state infiltration rate  was highest during preirrigation; by the last irrigation the rate was about eight times lower.
As a result, the preirrigation and the first crop furrow irrigation were targeted for improved irrigation to reduce the amount of infiltrated water in the 1988 season.
The depth of water infiltrated during 1988  preirrigation and first crop irrigation with the upgraded continuous-flow furrow system decreased by 2.3 and 1.8 acreinches per acre, respectively, when compared to the infiltrated depths applied with
 the original furrow system in 1987.
Similarly, corresponding reductions for surge were 2.1 and 2.0 acre-inches per acre.
We recognize that climatic conditions which affect crop evapotranspiration , thereby affecting drainage, were not identical between the preirrigation and the first crop irrigation in 1987 and 1988.
However, we believe the reductions in infiltrated water and potential for drainage in 1988 can be compared to the infiltrated amounts in 1987 for the following reasons: 1) the infiltration rates and potential for drainage were highest for preplant and first crop irrigations and 2) cumulative ETc prior to the first crop
 furrow irrigations was 3.58 and 3.24 inches in 1987 and 1988, respectively.
Preirrigation with the drip system and rainfall provided adequate water for cotton germination and seedling establishment in 1988.
The amount infiltrated, 2.2 to 2.3 acreinches per acre, indicates potential to achieve additional drainage reduction with an irrigation system that provides sufficient control SO that the applied water approximately equals the water depletion.
Cropyield in 1987 were uniformly higher than 1988, irrespective of the irrigation system.
This reflects more favorable climatic conditions in 1987.
Production for
 TABLE 1.
Description of system performance for the conventional one-half mile furrow irrigation method in 1987
 Water advance	Steady-state	Depth
 times to end	infiltration	infil-
 of furrows	rate	trated
 Preirrigation	16	0.15	7.7
 First crop	8	0.07	6.9
 Last crop	6	0.02	4.0
 TABLE 2.
Depth of infiltrated water with the upgraded continuous flow furrow, surge flow furrow, and subsurface subsurface drip systems in 1988
 Irrigation	Upgraded	Surge	East	West
 Preplant	5.4	5.6	2.2	2.3
 First crop	5.1	4.9	NA	NA
 subsequent crop	13.6	14.0	18.8*	20.5*
 Rainfall	3.4	3.4	3.4	3.4
 Total	27.5	27.9	24.4	26.2
 *Water was applied daily.
Number in parentheses gives the number of post-plant irrigations.
NA denotes non-applicable.
TABLE 3.
Machine-harvested cotton yields for upgraded continuous flow, surge, subsurface drip, and conventional irrigation by grower
 method	Year	acreage	Lint yield	Turnout
 average	1987	280	3.4	31
 furrow	1988	280	2.6	32
 furrow	1988	5.7	2.6	32
 furrow	1988	5.7	2.6	32
 Subsurface	1987	5.7	3.7	28
 drip	1988	5.7	2.9	31
 *496 pounds per bale
 both the furrow and subsurface drip systems was not reduced when infiltrated water during preirrigation and the first crop irrigation were decreased.
Crop yields for the upgraded continuous and surge flow were equal to the grower average.
In 1988, lint yields were 0.3 bale per acre higher for subsurface drip.
More timely water application due to daily irrigation, a possible response to higher fertilizer rates, or more uniform water applications across the field were all factors that could have caused the increased production.
A similar increase occurred in 1987.
The lower gin turnout  in 1987 likely reflects poor defoliation due to the late irrigation cutoff date of September 15.
In 1988, the gin turnout for subsurface drip was similar to the other treatments, which we attribute to the earlier irrigation cutoff date of August 30 and improved defoliation.
Irrigation system costs.
In 1988, production costs excluding land  totalled $631, $642, and $643 per acre for the original grower furrow design, upgraded furrow design, and surge furrow system, respectively.
We used gated pipe rather than
 siphon tubes to reduce furrow length, increasing system costs about $12 per acre.
Shorter irrigation set times increased labor costs $6 per acre.
Water savings reduced costs about $7 per acre.
The annualized costs of the system, fertilizer and fumigant were the primary factors that inflated the total production costs for the subsurface drip system to $1,555 per acre.
The applicability of the fertilizer and fumigant costs for the subsurface drip to a larger farm scale are questionable.
The fertilizer costs were high, in part due to the small quantity purchased and the premixed formulation.
Based on individual prices for liquid sources of nitrogen, phosphorus, and potassium, the same amount of nutrients could have been purchased for about $87 and $160 per acre in 1987 and 1988, respectively.
Phosphorus fertilizer rates in 1988 may have been reduced.
However, it is possible that phosphorus may be less available to plants irrigated by subsurface drip systems, which promotes root growth in less fertile subsoils.
Fumigant is not needed for disease control if cotton is grown in rotation with
 TABLE 4.
Total annual costs for subsurface drip, surge, and the upgraded continuous flow
 Grower	Upgraded	Surge	Drip
 System	18	30	31	352
 Water	42	35	35	50
 Irrigation labor+	12	18	18	13
 Cultural	442	442	442	473
 Fertilizer	36	36	36	331
 Fumigant	0	0	0	255
 WWD assessment	34	34	34	34
 Depreciation$	47	47	47	47
 Total	631	642	643	1,555
 *System cost using capital recovery factor over 10 years at 10% interest.
+From UC Committee of Consultants Report, "Associated Costs of Drainage Water Reduction."
 Cultural costs include land preparation, pest control, harvest, taxes, insurance, repair, and management.
Calculated as 5% per year of initial capital cost of system.
TABLE 5.
Profitability of the original grower furrow system, upgraded continuous flow or surge furrow
 systems, and subsurface drip in 1988
 Original	Upgraded	Subsurface drip
 grower	continuous/surge	40-in.
80-in.
Lint value	967	967	1,069	1,069
 Production costs	631	643	1,555	962
 Seed credit	77	77	97	97
 Return [loss]	413	401	[389]	204
 *Costs of land ownership or land leasing were not deducted from return.
other crops.
Other economical alternatives such as injections of acids, chloride, and use of emitters that are made of materials pretreated with herbicides may control root intrusion.
Eliminating ripping and reducing herbicide use saved $69 per acre but taxes, maintenance and repairs increased the total cultural costs $31 per acre.
Pressurization added $15 per acre to the cost of water.
Profitability.
In the assessment of profitability, we added an alternative subsurface drip irrigation system based on the 80-inch spacing used in 1987 and revised fertilizer and fumigant costs.
Returns were $12 per acre less for the upgraded continuous-flow furrow system compared to the original grower furrow system.
On the cracking soils at this site, there was no economic benefit from water savings by using surge irrigation over the upgraded continuous-flow furrow system.
At this location, where rising water tables and increased soil salinity are expected in the future, costs to improve the conventional furrow system and increase control of drainage would be less than costs associated with disposal of the additional drainwater generated from the conventional furrow system.
increased system costs and increased fertilizer and fumigant costs resulted in a substantial loss of $389 per acre for the 40inch drip system.
Using 80-inch tube spacing would reduce the annual system costs to $200 per acre with a further reduction to $170 per acre being possible if less expensive, in-line emitters were used as was done at the DWR site described in the next paper.
The corresponding costs for taxes, insurance, and maintenance would be reduced $53 per acre.
Reduction or elimination of fumigation and use of higher analysis fertilizer materials would lower the total annual production costs about $250 per acre.
To assure drainage water control and adequate seed bed water content, an alternativemethod of preirrigation, such as handmove sprinklers, would be required with the 80-inch system to achieve the same level of drainage reduction as with the 40-inch drip system.
Preirrigation with a furrow system would not reduce potential drainwater as much due to the high water infiltration rates.
Ultimately, the estimated annual production costs could bereduced to $965 per acre, excluding land costs.
Assuming similar yields could be achieved with an 80-inch subsurface drip system, as is indicated with the 1987 production results , a modified subsurface drip system could potentially generate a profit of approximately $204 per acre.
This is about $200 per acre less return to land and management than achieved during a single year of cotton production with a well-designed and managed
 furrow irrigation system at this site.
Either a direct and sizeable cost for disposal of added drainwater generated from the furrow sysitems, substantially higher yields, or changes in crop rotations to higher-value crops may increase the economic viability of subsurface drip at this site.
Future on-farm demonstration needs.
Additional commercial demonstrations are now underway within drainage problem areas, supported by the DWR, the USDAARS, Cooperative Extension, and the U.S.
Soil Conservation Service.
Future needs to be addressed include: overcoming incovenient set times for furrow systems with shortened furrow lengths; developing drainage reduction methods for surge flow irrigation of sandier soils; determining fertilization and chemigation requirements of subsurface drip irrigation; learning the ominallifespan of subsurface dripsystems;
 managing salinity with subsurface drip sysitems, particularly where water tables are shallower than those encountered in this field project, and optimizing subsurface drip system design  for use with alternative crop rotations.
Allan E.
Fulton is Soils and Water Farm Advisor, Kings County; J.D.
Oster is Soils and Water Extension Specialist, UC Riverside; Blaine R.
Hanson is Irrigation and Drainage Extension Specialist, UC Davis; Claude J.
Phene is Soils and Irrigation Scientist, USDA-ARS; David A.
Goldhamer is Irrigation Extension Specialist, Kearney Agricultural Center.
Subsurface drip produced highest net return in Westlands area study
 Richard B.
Smith J.
D.
Oster Claude Phene
 Cotton was produced using subsurface drip, low-energy precision application , scheduled furrow, and conventional furrow irrigation systems in 1989.
Subsurface drip irrigation produced the highest net return to the grower through increased cotton yields.
Significant water conservation was achieved with both pressurized irrigation systems.
However, computeraided scheduling of furrow irriga-
 Editor's note: In the process of developing irrigation projects such as the one described in the previous article, a UCsponsored work group recommended increasing the scale of demonstration projects and studying pressurized irrigation systems more intensively.
The California Department of Water Resources agreed to fund these projects, one of which was the following.
tion did not result in significant water savings.
Pressurized irrigation systems may offer the flexibility and control necessary to significantly limit unnecessary water additions to the shallow groundwater table.
In evaluating how drainwater disposal costs affect farm profits, the University of California Committee of Consultants on Drainwater Reduction concluded that maximum profits are achieved with furrow irrigation systems where there is no cost associated with drainwater disposal.
Profitability decreased with increasing disposal costs; the rate of decrease was dependent on the infiltration uniformity achievable for each system.
The lower the uniformity, the greater the rate of decrease.
Where drainwater disposal costs exceeded about $75 per acrefoot, two pressurized irrigation systems subsurface drip and low-energy precision application  were projected to be more profitable than furrow systems.
Boyle Engineering Corporation, under contract with the California Department of
 Water Resources Water Conservation Office, is testing this economic analysis.
The objective of this on-farm demonstration is to evaluate the effectiveness of subsurface drip and LEPA irrigation systems on reducing deep percolation losses and increasing grower profitability.
These pressurized irrigation systems are also compared to existing and scheduled furrow irrigation systems.
This paper summarizes data obtained during the first year  of this project and compares them to those reported in the previous paper.
The DWR project site is located at Harris Farms in Westlands Water District, about 6 miles southwest of Five Points.
The site consists of about 160 acres equally divided into four irrigation treatments.
Soils are fine-textured with average soil profile salinity  generally less than about 4 decisiemens per meter.
The project site is underlain by a shallow saline water table.
Depth to groundwater ranges from about 24 to 30 inches in spring and early summer to about 72 to 84 inches in fall and early winter.
The average shallow water table salinity ranges from about 4 to 11 dS/m.
The site was planted to cotton  in 1989.
Subsurface Drip.
The subsurface drip system uses 0.4 gallon-per-hour in-line emitters spaced at 40 inches along 0.52-inch inside diameter x0.62-inch outside diameter polyethylene tubing.
Spacing between tubing laterals is 80 inches.
Tubes were buried 18 inches deep  in nonwheel rows to minimize compaction problems.
Two buried PVC submains supply irrigation water to the laterals.
Each submain is regulated by a 4-inch pressure-regulating valve.
The drip tube is connected to the buried PVC pipe with a polyethylene hose riser.
The riser is connected to a saddle glued onto the PVC pipe.
Lateral runs are approximately 450 feet.
The ends of each lateral are connected to a PVC pipe flush manifold.
Each manifold has two manually operated flush valves.
A 30-horsepower booster pump supplies water to the system from a small reservoir.
Filtration is performed by media filters filled with No.20 crushed silica media.
The media has an approximate filtration capability of 200to 250-mesh.
The filtered water is metered before going into the PVC mainline.
Nitrogen and phosphorus fertilizers, and sulfuric acid to prevent root intrusion, are injected with a venturi connected across the discharge and inlet of the booster pump.
The pressure-regulating valves at the submain inlets are set to regulate pressure at 25 psi.
This corresponds to a system average discharge of 0.56 gallon per hour per emitter.
The average application rate is 0.04 inches per hour.
Overall calculated emission uni-
Pipe Systems for Irrigation
 hydraulic characteristics of pipe systems for irrigation enterprises under investigation
 A.
F.
Pillsbury and E.
H.
Taylor
 Semiclosed pipe systems for distribution of water by irrigation districts appear to be superior to other systems in operating characteristics.
Higher cost of water, high value land, and need for more efficient delivery and usage dictate increasing attention to the efficiency of concrete pipe water distribution systems.
Analyses and model studies under way are investigating the several possible types of systems to determine to what extent each provides a certain flexibility required by the farmer; whether or not a high load-factor is possible for reasons of economy; the characteristics of each system as to operational economy; and, the hydraulic characteristics from the viewpoints of design and steadiness of flow.
The closed or pressure system-conventional for the distribution of domestic water-is rarely designed for irrigation service, although there are many combination domestic and irrigation systems in southern California.
Costs of the pressure pipe required by this system have generally precluded its use.
In some instances the use of a closed system might involve water hammer problems.
To avoid overload, the number of deliveries open at any one time can be regulated.
Deliveries, however, with anything like a high load-factor on the system, would be subject to considerable fluctuation.
Downstream control
 Scale model of an open system used in laboratory studies.
float valves might correct this, and could be installed to give the farmer more flexibility in his delivery.
Open systems have an overflow stand at periodic intervals.
Deliveries are made from the upstream portion of each stand, presumably at a near constant head and hence at steady flow.
For good service, there must be provision to discharge regulatory waste at the end of each lateral.
Otherwise, the last delivery absorbs all regulatory fluctuations.
Such systems have an inherent instability associated with the entrainment of air.
Portion of an open system showing overflow stand at periodic intervals.
Deliveries are normally made from the upstream portion of each stand.
A scale model of an open systemfitted with plastic parts-permits laboratory observation of the entrainment of air, the initiation of surge, and a venting design which corrected the surge initiation encountered.
The incidence of surge, observed in the model, resulted from the gradual build-up of an air pocket in the extreme upstream reach of pipe, which periodically blew back into the stand.
The surge initiated was not serious, but the amplification in successive reaches downstream was.
In the model, placement of large size vents immediately downstream from each overflow stand prevented any surge initiation.
The diameter of these vents should be at least two thirds the diameter of the pipe line.
However, when surge was imposed upon the system from outside by any change in flow rateboth rates being steady-surge was amplified as before venting, but dampened out in about two minutes.
Although vents were successful in preventing all surge initiation observed in the model, they were not completely successful in preventing the carrying of considerable air into the system at high flows, which appears to adversely affect the friction loss.
In such cases a supplemental vent may be necessary a short distance downstream.
The semiclosed system simply substitutes a float valve with downstream control for the baffle in each overflow stand of an open system.
The semiclosed system has the essential operating characteristics of the closed system, except that pipe line pressures never exceed the value established by the water surface in the next stand upstream.
Thus low pressure pipe can be used.
Only the water which is delivered flows down the system; so there is no regulatory waste involved-provided there is storage or control all the way upstream.
Deliveries can be kept at essentially a constant rate unless the capacity of the system is exceeded.
If desired, farmers can vary their flows at will without causing operating Concluded on next page
 slight encouragement in trials hindered by climatic conditions
 One species of grass, among the 11 varieties of legumes and grassesplanted in December 1952-in test plots in the southern San Joaquin Valley, showed promise in December 1953.
Trial plantings of grasses and legumes, in rows about 1,300' long, have been made each year beginning in the autumn of 1951.
Poor plant growth because of lack of rainfall in two seasons out of three has prevented any significant observations on grazing.
The test plots-of about 500 acres each, and fenced-were established in Fresno, Kings, and Kern counties to introduce plants and develop management practices to alleviate the Westside dust problem.
In 1952, adequate rainfall produced good plant growth and the rows fertilized with ammo-phos-16-20-0-applied at the rate of about 44 pounds per acreresponded very satisfactorily.
Schismus arabicus, a grass native to the Mediterranean area, was first noticed on the Westside Plains some seven or eight years ago.
The plant seems to root firmly in the soil and is therefore resistant to wind action.
Stockmen reported
 that stock liked the grass and it seemed to be a good forage plant.
No extensive stands of Schismus were found but plants were scattered over much of the Westside area.
Seeds of the new grass were collected and in early December, 1952-after good early rains-the three test plots were planted with:
 Schismus arabicus invaiding slick spots.
The plants are growing where the soil had cracked the previous summer.
Hence the tile-like appearonce.
Schismus arabicus Crested wheat, Agropyron cristatum Tall wheat, A.
elongatum Intermediate wheat, A.
intermedium Pubescent wheat, A.
tricophorum Stipa rosengurtii Indian ricegrass, Oryzopsis hymenoides Wimmera ryegrass, Lolium subulatum Smilo, Oryzipsis miliacea Rose clover  and bur clover  -inoculated with nitragin-were seeded at the rate of two pounds per acre each in rows one through 18.
Apparently none of the perennials in the 1951 or 1952 test plot plantings survived the summer of 1953.
Growth in the test plots started very well and good stands were obtained.
However, subsequent rains were light and the plots-along with the native cover on the Westside-dried up in March.
The plants did not mature enough to produce seed.
In the fall of 1953 Schismus plants were found to have invaded slick spots where the soil contains more alkali than adjoining vegetated areas.
Apparently the seed produced by the 1952 plantings had been broadcast by the wind to lodge in cracks in the soil-caused by its dry.
ing out-and had taken root.
Lloyd Brown is Soils Specialist, University of California, Berkeley.
James L.
Myler, Assistant Director, Field Stations, and Farm Advisors, Richard G.
Jones, Fresno County; Herbert S.
Etchegaray, Kings County; and Roy V.
Parker, Kern County, University of California, participated in the studies reported above.
Continued from preceding page
 problems as far upstream as the automatic feature is provided.
Operation can be completely automatic.
There is no opportunity for air entrainment.
Without air entrainment, and with correct design, the semiclosed distribution system provides positive stability in operation.
The hunting of float valves in series is a very real possibility if design is not correct.
If the oscillatory properties of the float and valve happen to be matched in just the right way to the characteristics of the pipe and stands, serious surging can result.
Successful conversions of open sysitems to semiclosed systems have been made on a number of farms on the steeper slopes in southern California.
Some valves used had hunting difficulties but most installations were remarkably successful.
Air bubble forming below an overflow stand.
The vent shown is closed.
The question of water hammer has been raised in regard to semiclosed sysitems.
The factors which make for stability cause a lag in response of the valves for which a foot or two freeboard must be provided in the stand, but as observed in the field, there appears to be no appreciable hammer.
Opportunity for hammer would occur with fast closing manual valves on deliveries.
Such valves can well be avoided except where deliveries are made directly from a stand.
The storage in the stand can absorb most of the shock.
The analyses and model studies currently under way indicate that material improvements can be made in the operation of all three systems.
A.
F.
Pillsbury is Professor of Irrigation, University of California, Los Angeles.
E.
H.
Taylor is Associate Professor of Engineering, University of California, Los Angeles.
The above progress report is based on Research Project No.
860A.
Keeping Trash Out of Streams Rachel E.
Williams and Carmen T.
Agouridis, Biosystems and Agricultural Engineering
 F resh water is an essential natural resource that is used every day for drinking, bathing, cooking, cleaning, and recreation.
In Kentucky, the water used for these tasks mainly comes from streams and rivers, but it can also come from groundwater.
Because our streams, rivers, and aquifers are SO vital to our daily lives, it is important that we protect them from trash, debris, and other pollutants found in stormwater.
What happens to the land around these water sources affects their condition and health.
How does trash reach streams?
One of the most common ways trash reaches streams is through the stormsewer system, although some trash is blown in by the wind or illegally dumped along the stream banks.
The storm sewer system is a series of gutters, curbs, and pipes that rapidly routes runoff from impervious surfaces such as roads and parking lots to nearby streams, rivers or lakes.
When stormwater flows across a parking lot, for example, it picks up trash, debris, and other contaminants as it flows to a storm-sewer inlet, such as a storm drain or a gutter.
The stormwater and all of these pollutants then travel through the storm-sewer system and eventually end up in nearby streams, lakes or reservoirs.
So unless someone picks it up, an empty soda bottle that is left in a parking lot will eventually make its way to a stream.
Whose trash is it?
Most of the trash found in streams comes from the average citizen.
The U.S.
Environmental Protection Agency estimates that 80 percent of trash in marine systems is land-based in origin, with cigarettes, plastic beverage bottles, plastic bags, and food wrappers and containers topping the list.
The Anacostia Watershed Society found that as much as 85 percent of the trash found in its local streams was associated with eating and
 Figure 1.
Trash can enter the storm sewer systems through curb inlets, located in parking lots and along roads.
Figure 2.
Floatables, such as this plastic bottle, are a common site in urban streams.
drinking.
The most common items in the streams were plastic bags, aluminum cans, plastic and glass bottles, Styrofoam, and snack wrappers , although other items such as tires, appliances, and clothing were found as well.
This phenomenon is not isolated.
A 100-foot stretch of stream in an urban area can have 50 or more pieces of trash along the streambed and banks.
How does trash affect stream health?
Trash affects streams by altering the flow and impacting wildlife.
Large pieces of trash can block the flow of water in
 Figure 3.
Large pieces of trash, such as this shopping cart, can direct flows and cause stream-bank erosion.
streams, resulting in ponding, or bigger pieces can redirect flow into stream banks, causing them to erode.
Small pieces of trash are easily caught in vegetation along the stream banks.
If enough smaller trash accumulates on roots, limbs, or rocks in the stream, a portion of the stream flow can be blocked or altered.
Trash can also clog stormwater inlets and culverts, which worsens flooding.
Ingestion and entanglement are the two main ways trash negatively impacts wildlife.
Wildlife can mistake smaller pieces of floatable trash, such as cigarette butts or plastic bags, for food.
If ingested, wildlife can suffer from malnutrition or
 Figure 4.
Stream-bank vegetation often catches small pieces of trash.
even internal injuries.
Sharp objects can cut the mouth and puncture the digestive tract.
Wildlife also can become injured when they are entangled in trash while swimming through it, sitting on it, or even playing with it.
How does trash affect human health?
People who come into contact with trash in streams should exercise caution.
Trash containing fecal matter, such as diapers or pet waste bags, can expose people to pathogens.
Glass and other sharp objects, such as metal or even hypodermic needles, can result in cuts and punctures.
What can you do to help?
Properly dispose of your trash in a waste bin or a recycling bin.
If you see litter on the ground, pick it up.
Keep a small waste bag in your car to collect loose trash that might easily fall out.
Opt out of plastic bags.
Instead, shop with reusable bags.
Drink from a refillable bottle rather than single-use bottles.
Volunteer for a stream cleanup.
All these trends prompt us to manage our water more precisely.
Specifically, irrigationthe largest user of freshwater in Nebraska and worldwidecan be applied more precisely.
Besides improving when irrigation is applied , where irrigation is applied  can be improved as well.
Appendix B: Seasonal Hazards Frost, Hail, Drought and Flood
 Corn is usually safe from frost up to the two-leaf stage  because the growing point is below the soil surface.
Soil temperatures can be different than air temperatures.
Soil water content and residue cover affect soil warming and cooling.
Damage can occur if temperatures dip below freezing.
If frost damage is suspected, an assessment can be conducted by slicing the plant in half vertically.
If the innermost part of the plant  appears mushy or discolored , the plant will likely not recover.
An assessment for frost damage should not be attempted until at least 3 days of warm temperatures following a frost event.
Warm temperatures encourage the plant to resume growth, but cool temperatures will not.
If an attempt at damage assessment is made before the plant has had time to recover, the assessment may not be accurate.
Assessments conducted 3 to 10 days after frost are common.
Frost damage can be spotty in a field, with the most severe damage in low-lying areas of fields and little to no damage in even slightly higher elevations.
Hail can defoliate the crop and cause breakage or bruising of the stalk, creating entry sites for insects and diseases.
The severity of the damage caused by hail is related to the size and duration of the hail.
In most hail cases, the crop will recover; yield loss depends on the growth stage at the hail event and the
 Figure B.1.
Frost damage on corn.
Figure B.2.
Corn seedling damage due to frost.
severity of the damage.
A hail event occurring when the growing point is belowground may only strip the emerged leaves.
As the crop develops, it becomes more vulnerable to leaf stripping.
Damage to leaves and stalks can reduce yield if the movement of sugars from the leaves to the ears is restricted.
Hail during ear development may result in a barren crop.
Water is essential to crop growth and development, but it must be available within an optimal range.
Too much water can kill plants from lack of soil O 2 or can result in disease problems.
As with frost, flooding may be site-specific in the low-lying areas of a field.
Drainage may be an option for frequently flooded areas.
However, to determine the legality of drainage, local USDA-NRCS offices must be contacted prior to installing artificial drainage systems.
Drought also restricts corn yield.
Dry conditions during silking will reduce kernel set and pollination.
In a field that has both high and low landscape positions, drought will be noticed on hilltops and summits before the lower-lying areas are affected.
Weather conditions such as frost, hail, flood, or drought can severely reduce yields.
Effects from these events are manageable to a certain extent, but loss can be expected when these events occur.
The degree of loss depends on the severity of the event.
Crop insurance has become a common component of corn production in the U.S.; the insurance provides the producer economic protection for uncontrollable events.
Producers should consider crop insurance based on the consequences of crop loss.
Figure B.3.
Hail damage to corn.
Figure B.4.
Drought stress prior to silking.
Saleh Taghvaeian Assistant Extension Specialist, Water Resources
 The term "surface irrigation" refers to systems that deliver water to crops using a gravity-fed, overland flow of water.
Surface irrigation conveyance and distribution systems are among the first engineering innovations of humans, dating back to more than 6,000 years ago.
This Fact Sheet provides general information on key aspects of this historic technology that is still in use in many parts of the world.
Types of Surface Irrigation Systems
 Surface irrigation systems can be classified into three major types: basin, border, and furrow systems.
The basin system consists of level, diked areas that receive undirected flow of water.
Basins range widely in size from only a few square feet  to a few hundred square feet.
The soil surface inside large basins may be corrugated to facilitate a more uniform water distribution.
The dikes surrounding the basin should be stable enough and well-maintained to prevent breaching.
However, it is always a good design practice to include spill structures in dikes in case heavy rainfalls and/or mistakes in irrigation cut-off time occurred.
Due to their near-zero surface slope and closed boundaries, basin irrigation is appropriate for crops that can tolerate inundation.
Border irrigation is different than basin because the borders are rectangular in shape, have a sloping surface, and are not diked at the tail end.
Borders are appropriate for irrigating almost all crops, except those that require ponding conditions.
The inflow rate should be identified carefully as large enough to allow water front advancement, but not too large to erode the fertile top soil out of the field.
Figure 1.
Basin irrigation in central Utah.
In furrow irrigation, the soil surface is channeled and furrows are formed to direct the flow and avoid flooding the entire field.
Water moves in these furrows and seeps through their walls and bottom.
Each furrow receives an inflow of water, which could be provided by means of hand-
 Figure 2.
Furrow irrigation using siphon tubes, Northern Colorado.
Figure 3.
Furrow irrigation using gated pipes, Northern Colorado.
dug checks, gated pipes or siphons tubes.
Furrow irrigation provides better control of water management, but it also has several disadvantages compared to basin and border irrigation.
The first disadvantage is the increased risk of salt build-up on beds, where water does not reach.
Secondly, a larger volume of surface runoff is generated in furrow systems.
Finally, they are more labor-intensive because farm equipment needs to be moved among numerous furrows.
Surface vs.
Pressurized Systems
 Compared to pressurized systems , surface irrigation systems require smaller capital investment.
The main capital expense is the cost of land grading, which is required in order to achieve a uniform distribution of water across the field.
The maintenance costs are also usually less, as structures for control and for regulating water flow are made with inexpensive and readily-available material.
Another advantage of surface irrigation systems is that they are less sensitive to weather variables and water quality.
For example, the efficiency of water application in sprinkler systems diminishes quickly under high wind conditions.
Or in drip systems, low quality of irrigation water can result in emitter clogging and poor distribution uniformity.
A disadvantage of surface systems is the complexity of designing components to achieve efficient water application.
This is mainly due to the high variability of soil properties, which serves as the conduit for water transfer across the field.
Another disadvantage is the high cost of labor required to operate the system.
In addition to the starting and stopping of the flow done manually water advancement in the field needs to be closely monitored.
Finally, surface systems are usually less efficient.
This topic is discussed in more detail in the next section.
Surface irrigation systems are believed to have low efficiencies, averaging about 60 percent.
This means that only 60 percent of the delivered water is stored in the top layer of the soil, where crop roots can extract it for beneficial use.
The remaining 40 percent escapes the field through deep percolation below the root zone or through surface runoff at the tail end of the field.
However, the efficiency can be increased significantly implementing a precise land grading, regulating the inflow, optimizing irrigation timing, and reuse of surface runoff.
For example, efficiencies as high as 92 percent were reported for furrow irrigation systems in a cotton production area in eastern Australia.
Higher efficiency rates will not only help producers to save on labor and conveyance costs, but will also reduce the load of salts, sediments, and nutrients leaving the field.
Although improving irrigation efficiency has several benefits, it should be noted that the "lost" portion of water at one field is usually a source of water for another user somewhere downstream.
As a result, increasing efficiency by reducing return flows  may negatively affect downstream users.
That is why capturing surface runoff and reusing it at the same field is not allowed by the water law in several western States.
Figure 4.
Furrow irrigation of cotton in Southern California.
Higher efficiency in surface irrigation systems can be achieved through:  ensuring that the field of interest is appropriate for surface irrigation, and  adopting technologies that provide a better control over water management.
A field is appropriate for surface irrigation if it has the following conditions:
 Ground slope is less than 3 percent and is uniform across the field.
Soil texture is heavier.
These soils have lower infiltration rates, which facilitate fast advancement of water and consequently less deep percolation losses.
They also have a high water-holding capacity, which is appropriate for applying infrequent, large amounts of water through surface irrigation.
Water supply and flow rate are large enough to push the stream down the field at a fast, yet non-erosive velocity.
If a field does not have the above characteristics, a large portion of applied water will escape the field, even if advanced technologies for controlling water management are implemented.
Once these requirements are met, several available technologies can be adopted to improve water application efficiency at the field level.
The next section provides a brief introduction to these technologies, ranging from simple to more complex options.
A significant portion of water is lost in the water delivery network and head ditches before it reaches the field.
Earthen canals and ditches lose large amounts of water due to seepage.
Use of concrete and/or plastic lining can reduce the seepage.
Using low-pressure aluminum and/or PVC pipes not only eliminates seepage, but also minimizes evaporation losses.
Knowing the irrigation requirement is a key to improving efficiency.
Applying water in excess of what can be stored in the root zone or what can be extracted by the crop at a given growth stage and weather conditions leads to wasted time, money, and nutrients, not to mention the adverse effects on soil salinization and weed growth.
But in areas where irrigation
 water and/or soil are high in salinity, irrigation depth should be increased in proportion to the salinity level to leach the salts below the root zone and maintain a more favorable condition for water extraction by crop roots.
In the case of furrow irrigation, improving water advancement results in less deep percolation losses and higher irrigation efficiency and uniformity.
Weeds are a major source of slowing or blocking water stream in furrows.
Thus, weed control is more important with furrow irrigation regimes.
Cultivation and leaving loose soil in furrows can also significantly slow water advancement.
A major challenge in surface irrigation is to balance the trade-off between deep percolation and surface runoff.
Deep percolation can be reduced by increasing the inflow to the highest levels that do not result in soil erosion.
This reduces the infiltration at the head end of the field, but increases the runoff at the tail end at the same time.
In contrast, applying a small inflow would reduce the volume of runoff, but increases the deep percolation at the head end.
A hybrid solution is to start with a large non-erosive flow to push water down the field, and then reduce the inflow once the water front reaches the tail end.
This approach, known as cutback, can be achieved by adjusting the water delivery equipment.
In case of furrow irrigation with siphons, for example, two or three siphons can be used during water advancement.
The extra siphons can be removed once the water reaches the tail end, leaving only one siphon in the furrow to supply a reduced stream.
Figure 5.
The trade-off between deep percolation and surface runoff.
Runoff Capture and Reuse
 Actual field measurements indicate the runoff from furrows could account for a large portion of the water turned in at the head of the furrow.
During the past several years, many irrigators have constructed reuse pits to capture this runoff.
Basically, one of two concepts can be followed relative to the utilization of the captured runoff.
First, the water can be collected and stored until there is a sufficient amount to irrigate the same field  or another area.
Second, runoff water can be added to the regular water supply and used for irrigation of the same or following sets.
The choice of concept to follow will be dictated by the cropping system, available irrigable land, and amount of runoff water involved.
Some general rules of thumb regarding runoff reuse systems are:
 Reuse pit capacity should be adequate to store the runoff occurring from one irrigation set.
Keep in mind the percentage of runoff is greater for later season irrigation.
Design capacity of the reuse pump must be greater than the average anticipated runoff rates into the pit.
The reuse pit should be emptied at the end of the last set of the irrigation cycle.
This will provide limited storage in the event rainfall produces significant runoff between irrigation cycles.
Surge flow irrigation is an innovative advancement in surface irrigation management that was developed more than three decades ago at Utah State University.
With this regime, water is applied in pulses , as opposed to applying a continuous flow.
Applying intermittent pulses reduces the water infiltration rate into the soil and allows for faster movement of water down the field.
Pulses of water can be applied using gated pipes with solar/battery powered valves and controllers.
The valve alternates the flow between two sets of irrigation, directing it to one set for a period of time  and then switching it to another set for the same period.
During this time, the first set is dewatered, the sediments are settled, and the infiltration rate is reduced.
The cycles are repeated until the water reaches the tail end of the field, when a cutback continuous or surge flow could be maintained to fill the root zone.
With surge flow, water reaches the tail end at approximately the same time as continuous flow, but with only 50 percent to 60 percent of volume applied in continuous flow.
Previous field research in Colorado, Oregon and Washington has demonstrated surge flow regime results in higher uniformity/efficiency and lower nitrogen loss and fertilizer cost.
Surge flow irrigation is also advantageous when light and frequent irrigations are required, such as during the early season for main agricultural crops or during the entire season for vegetables.
The Oklahoma Cooperative Extension Service Bringing the University to You!
The Cooperative Extension Service is the largest, most successful informal educational organization in the world.
It is a nationwide system funded and guided by a partnership of federal, state, and local governments that delivers information to help people help themselves through the land-grant university system.
Extension carries out programs in the broad categories of agriculture, natural resources and environment; family and consumer sciences; 4-H and other youth; and community resource development.
Extension staff members live and work among the people they serve to help stimulate and educate Americans to plan ahead and cope with their problems.
Some characteristics of the Cooperative Extension system are:
 The federal, state, and local governments cooperatively share in its financial support and program direction.
It is administered by the land-grant university as designated by the state legislature through an Extension director.
Extension programs are nonpolitical, objective, and research-based information.
It provides practical, problem-oriented education
 for people of all ages.
It is designated to take the knowledge of the university to those persons who do not or cannot participate in the formal classroom instruction of the university.
It utilizes research from university, government, and other sources to help people make their own decisions.
More than a million volunteers help multiply the impact of the Extension professional staff.
It dispenses no funds to the public.
It is not a regulatory agency, but it does inform people of regulations and of their options in meeting them.
Local programs are developed and carried out in full recognition of national problems and goals.
The Extension staff educates people through personal contacts, meetings, demonstrations, and the mass media.
Extension has the built-in flexibility to adjust its programs and subject matter to meet new needs.
Activities shift from year to year as citizen groups and Extension workers close to the problems advise changes.
Irrigation is used in Kentucky for both specialty and row crops.
Irrigation systems reduce risks of low profitability from low yields and crop stress.
Drip irrigation, essential for producing many specialty crops, is used throughout the state on farms of all sizes.
Overhead irrigation systems are concentrated in western Kentucky, where farms of 1,000 or more acres account for most of the annual acreage changes in Kentucky's irrigated farmland.
This fact sheet focuses on drip irrigation, which increased in use as more Kentucky farms began specialty crop production.
According to the Census of Agriculture, irrigated acreage increased from 2002 to 2012 on Kentucky farms of 10 to 99 acres, a farm size more likely to focus on specialty crop production.
Drip irrigation is also widely used on larger farms, orchards and nurseries for both watering and fertigation.
Water Source Irrigation water may be sourced from wells and municipal water systems as well as surface water such as lakes, ponds, streams and springs.
Filters are required for irrigation systems using surface water systems, and backflow prevention devices are required for municipal water.
Testing of irrigation water for bacterial contamination, hardness, and chemical properties such as pH, iron and sulfur is advised both as a Good Agricultural Practice to promote food safety and prevent clogging of drip systems.
The University of Kentucky Soil Laboratory in the College of Agriculture, Food and Environment
 Above: Drip irrigation and plastic mulch are common on staked tomatoes in Kentucky.
Below: Irrigation is essential for high-value crops.
If you can't irrigate it don't plant it.
Equipment Planning Advance planning is important to
 Both gravity and a small solar-powered DC electric pump are used in this rainwater catchment system for drip irrigating this high tunnel in Kentucky.
design a system that meets crop and soil requirements.
Equipment and supplies required for effective drip irrigation depend on several factors, including size of the fields to be irrigated, crop water requirements and soil types.
In most cases an irrigation professional will be needed to help plan the most efficient system.
Pumps and related equipment such as filters, pressure regulators, valves and gauges are installed on a system-specific basis.
Soil moisture sensors  should be used to help determine water needs.
Although water pressures of 8-12 pounds per square inch  are generally required for drip, recent onfarm demonstrations in Kentucky have shown that it is also possible to use very low-pressure  gravity-fed drip systems for high tunnels and other small plots up to about 1/4 acre.
These low-pressure systems have also been coupled with small solarpowered DC pumps and battery systems for drip.
Irrigation System Management and Labor Properly timed irrigation applications are essential in both drip and overhead irrigation systems.
In larger systems, sensor and remote technologies are available to reduce risks from either missing irrigation or applying improper amounts of water.
Proper drip irrigation system design will help producers manage much of the risk associated with improper applications.
Producers should also budget an adequate amount of time for managing systems for specialty crops.
For small farms, inexpensive tensiometers or moisture meters can help best determine when crops need
 water and when the water should be shut off.
Although uncommon in Kentucky, irrigation systems can also be fully or partially automated using sensors, solenoid valves, etc.
Nursery and Greenhouse Irrigation
 Advanced greenhouse irrigation technology utilizes computer-controlled irrigation systems, and laborsaving irrigation technologies are available across the entire range of greenhouse sizes.
The buildup of soluble salts in the soil or growing medium from fertigation is a concern in nursery, high tunnel, and greenhouse applications.
Following irrigation best management practices can mitigate such concerns.
Costs of Drip Irrigation
 Drip irrigation systems generate positive returns on investment by 1) dramatically increasing yields and horticultural product quality 2) minimizing risk of crop failure and/or yield loss from drought and irregular watering 3) efficiently delivering nutrients through fertigation 4) reducing the amount of water and energy needed to produce high-yielding crops 5) reducing risk from foliar fungal and bacterial diseases.
Drip irrigation has been shown to provide the most yield benefits when combined with plastic mulch on commercial vegetables; however, drip tape alone is also used in some annual crops, as well as in perennial fruit crops.
In 2015, the initial equipment cost for a 1-acre drip irrigation system was estimated at $2,585, including drip tape and plastic mulch.
There is a $400 cost for each additional acre of drip irrigation, up to about 10 acres.
Installation Cost Estimate for Drip Irrigation in Kentucky
 Source: 2016-17 Vegetable Production Guide for Commercial Growers
 2 in.
centrifugal pump and 163cc engine	$700
 Single filter backflush valve	$260
 Layflat, 2" 	$105
 Suction hose and strainer	$95
 Fittings, valves, gauges	$100
 Total Equipment Cost for Installation	$2,185
 Plastic mulch and drip tape, per acre	$400
 Total Cost for 1-acre drip irrigation system	$2,585
 *Cheaper disc filters  can also be used on small farms in place of sand filters, although sand filters may be needed for surface water.
Small farm bed-shaper/plastic layer forms raised beds, lays plastic mulch, and installs drip irrigation tubing in one operation.
Growers using plastic mulches will also need a plastic mulch layer/bed shaper costing from $1,200 to $5,000, depending on size and model.
A waterwheel setter, for transplanting into plastic mulch, is also commonly used, costing approximately $2,000 to $2,500.
Many Kentucky counties have purchased mulch layers and waterwheel setters to rent or loan to farmers.
The expense of renting or sharing this equipment reduces the farm-level investment needed for drip irrigation, making the practice more feasible for small farmers.
The cost estimate below uses a 10-year depreciation expense for these two pieces of equipment, or $400 annual cost.
Simple Economic Evaluation of the Value of Drip Irrigation in Tomatoes
 Drip irrigation systems are easily justified for smallscale producers because of the potential yield and quality losses from inadequate watering.
Hundreds of demonstrations promoting drip and plastic mulch systems on small farms in Kentucky have shown that, in most cases, marketable yields are doubled compared with rain-fed production.
Based on the sample annual costs of a drip irrigation system , a tomato producer would need to generate
 Sample Annual Costs of Drip Irrigation System
 Plastic mulch and drip tape	$400
 Total Annual Variable Cost	$400
 Fixed Cost of Irrigation System (5-year
 Fixed Equipment Cost (10-year depreciation
 Total Annual Fixed Cost	$837
 $1,237 more in the value of production to justify installation and utilization of an irrigation system for an acre of tomatoes.
This value represents the gross revenue from approximately 600 to 1,000 pounds of production.
Inadequate irrigation or non-irrigated tomatoes can result in yield losses of 5,000 to 10,000 pounds or more per acre.
The case for investing in an adequate irrigation system is easily justified.
Drip irrigation tubing or "tape" is thin-walled plastic tubing with builtin emitters for slow and precise water application.
Drip irrigation wets the soil around the roots and permits application of nitrogen fertilizers directly to the root zone.
Above left: Sand filters are often used with surface water sources.
Above right: Disc filters are commonly used for specialty crops on small farms in Kentucky.
"Irrigation Water Volume and Soluble Salt Levels in Two PNP Irrigation Delivery Systems," (UK
 Thick-walled tubing and layflat is often used for main and submains for drip irrigation on small farms in Kentucky.
Reviewed by Brent Rowell, UK Extension Professor Photos courtesy of Brent Rowell
For pasture grass in the actively growing crop growth stage the estimated water use during the previous week of May 29 June 4, 2023 is 0.90 inches and the estimated water use during the week of June 5-11, 2023 is 1.45 inches.
Appendix A: Corn Planting Guide
 Obtaining maximum profit from a corn crop depends on the timely planting of an appropriate hybrid, at the proper depth, with a planter that evenly spaces the seed.
The success of a corn crop is dependent on equipment maintenance, seedbed preparation, the development of a sound fertility and pest management program, and planting the seed.
Early planting is best, but tempertures should be warm enough to assure quick germination and emergence, and late enough to avoid hard frosts.
Planting opportunity windows can be narrow due to spring rains or a late warm-up.
Time spent in the off-season maintaining equipment and planning tentative season-long schedules can increase efficiency in the spring.
This section discusses planter maintenance, planting date, replanting considerations, seeding rate, and planting depth.
Planter Maintenance and Preparation
 A corn planter is a piece of precision equipment, with each component working together to place the seed in the ground at a uniform depth and with a uniform distance between seeds.
Research has shown that the uniform spacing of seed can increase yields up to 20 bu/acre.
Although they are conducted too late to correct an in-season problem, stand counts and population surveys can be useful for determining if a planter should be calibrated prior to the next use.
Growing conditions should also be evaluated as poor seed quality, or problems such as soil crusting, areas that are too wet or too dry, or cold soil temperatures for extended periods, may be responsible for non-uniform stands.
Potential yield losses due to uneven stands can be estimated.
If planter calibration is necessary, always follow the manufacturer's instructions for calibrating seed metering equipment.
Assistance is available from local Extension educators, crop consultants, or seed dealers.
Table A.1.
Planter Maintenance Checklist
 Calibrate planter fertilizer and pesticide applicators.
Check down pressure springs.
Maintain even and recommended tire pressure.
Lubricate bearings and other moving parts.
During planting, it is important to place seed at the proper depth and ensure that the walls of the furrow are not smeared by the opener.
Down pressure tension should be adjusted if seed is not placed at the desired depth .
Closers or packing wheels should apply enough pressure for good seed-to-soil contact; too much pressure
 Table A.2.
Suggested and historical dent corn planting dates in South Dakota by region
 Approximate planting dates by reporting region	South Dakota
 Suggested planting dates*	Historical acres planted, 1970 1994**	Reporting
 Earliest	Latest	Desired range	10%	50%	90%	Region
 May 4	Jun 5	May 12 -26	May 10	May 26	Jun 9	Northwest
 5	5	May 10 24	9	20	5	North Central
 6	5	May 10 24	6	18	4
 Apr 29	Jun 8	May 12 24	May 12	May 25	Jun 10	West Central
 May 3	5	May 6 26	9	20	5	Central
 6	5	May 6 26	4	16	3
 May 4	Jun 3	May 7 24	May 7	May 20	Jun 2	Southwest
 Apr 29	8	May 3 17	10	22	7	South Central
 27	10	May 1 15	6	15	2
 * Dates are best estimates obtained from historical and research data within a reporting region ** Adapted from National Agricultural Statistics Service  South Dakota Field Office
 will compact the seedbed.
Adjust down pressure tension in consideration of soil moisture and residue conditions.
As no-till and reduced-till systems become increasingly popular, the planter takes on the additional task of manipulating soil and crop residue.
Hence, there are more parts to wear out and maintain.
Implements that manage residue on the planter are critical in no-till and other high-residue systems, as crop residue can interfere with openers and closures.
The spring planting window generally ranges from late April to mid-June.
Historically, 10% of the corn acres in South Dakota are seeded by mid-May and continuing to mid-June.
Seed germination depends on soil moisture and temperature.
Care should be taken to avoid Average tillage and planting operations when soil is wet.
Yields may or may not be reduced due to delayed planting.
However, due to problems associated with compaction, "mudding" the seed in will reduce the yield both of the current years' crop and of those crops grown in the future.
As a general rule, corn should not be planted Emergence 110 110 110 until the soil temperature  1100 1250 1400 between 7 and 8 a.m.) approaches 50F.
In R6  1900 2200 2500 cold soil conditions , seeds will readily absorb water but will not initiate root or shoot growth; this leads to seed rots and poor emergence.
If circumstances force planting before soil temperatures reach 50F, it is recommended to consult with a reputable seed dealer or agronomist to select
 Table A.3.
Yield response of corn to planting date
 Average planting date	Daily yield
 Maturity	April 17	April 27	May 7	May 17	May 27	May 7
 Average yield 	
 	130	132	131	132	119	0.06
 	143	145	141	131	109	1.6
 137	139	136	131	114	1.1
 *No data for 1995 or 2000 Yield data collected from 1986 to 2001  Southeast South Dakota Experiment Station, Beresford SD 
 Table A.4.
Estimated accumulated GDUs required for corn
 RM* 80 days	RM* 95 days	RM* 110 days
 Growth Stage			
 * Relative Maturity  of hybrid in days
 an appropriate hybrid.
Delayed Planting or Replanting Considerations
 Delayed planting reduces the number of growing degree units  accumulated during the season, hindering the crop from maturing before the first fall killing frost.
Corn killed by frost before maturity may not have completely filled kernels and has a slower dry-down rate, which can lead to excessive drying costs.
If planting is delayed, late-maturing hybrids can lose up to 1.1 ou/Acre* per day compared to earlier-maturing hybrids that can be planted later in the season without realizing a loss.
Often, the trade-off is that earlier hybrids may inherently have a lower yield potential.
The number of GDUs that a hybrid needs to reach physiological maturity is related to maturity ratings.
Since GDUs are based on temperature, the amount of GDUs accumulated in the spring and fall are less than during the peak summer months.
Available GDUs decline with later planting dates.
However, corn will usually emerge quicker if soil temperatures are warmer.
If planting is delayed, an earlier maturing hybrid should be considered.
A rule of thumb is to plant 20% of fields with a full season hybrid, 60% with a mid-season hybrid, and the remaining 20% with a short-season hybrid.
If planting is delayed, growers are urged to consult their seed dealer to determine if an earlier-maturing hybrid is warranted.
The optimal population for an area is influenced by available water, nutrients, and overall soil productivity.
Even within a field, optimal populations may vary by soil type or landscape position.
Low populations can lead to increased weed pressure , whereas higher plant populations increase seed investment with little return.
Achieving an optimal population throughout the field gives corn a competitive edge over weeds and can optimize grain dry-down time in the fall.
Optimal corn populations vary from 24,000 to 32,000 plants per acre.
Higher-productivity soils with sufficient drainage and available water can support higher populations.
Data in table 3.5 provides a guide for selecting optimal population rates.
Some overall recommendations for seeding rate include:
 Increase populations by =10% for silage crops.
Set seeding rates higher than target population to account for less than 100% germination and seedling mortality.
Increase seeding rate by = 2000 seeds/acre in no-till systems.
Increase seeding rate by = 2000 to 3000 seeds/acre in irrigated fields.
Depth and Planting Operations
 Depending on field conditions at the time of planting, depth can vary from 1-1/2 to 3 inches.
Under optimal conditions, seed is commonly placed 1-1/2 to 2 inches below the soil surface.
In dry conditions, it may be advantageous to plant deeper  to place the seed into a higher-moisture area.
If soil is very dry and rain is not expected, seed may be placed up to 3 inches deep.
Planting deeper than 3 inches is not recommended because placing the seed too deep  will not allow emergence.
Although soil conditions may be dry, consider the probability of rain in the near future.
Rain can seal the surface of the soil, making it difficult for the developing plant to emerge.
Shallower depths  should be targeted if rain is likely.
Crop residue can affect seeding date.
Seed can be left on the surface when seed openers "ride-up" over residue.
When seeding into areas with heavy residue, plant at least 1-1/4 inches but no more than 1-1/2 inches deep if moisture conditions are favorable.
Check seed depth often in high-residue situations to make sure that seed is placed at the proper depth.
These measurements should not include any surface residue.
Seed left on the surface or in the residue layer will not grow or properly develop.
If residue is problematic, consider residue management planter attachments.
A review of soil water data logs from farmers in the Upper Big Blue Natural Resources District indicates irrigators tend to overwater more in wetter years than dry ones.
On very dry years like 2022, many farmers apply about the right amount of water.
However, some still over irrigate, and some tend to under-irrigate.
EM 8782 Revised March 2013
 Drip Irrigation: An Introduction
 Drip irrigation tubing used to irrigate wine grapes.
Drip irrigation provides slow, even application of low-pressure water to soil and plants using plastic tubing placed in or near the plants' root zone.
It is an alternative to sprinkler or furrow methods of irrigating crops.
Drip irrigation can be used for crops with high or low water demands.
Why consider drip irrigation?
Drip irrigation can help you use water efficiently.
A well-designed drip irrigation system loses practically no water to runoff, evaporation, or deep percolation in silty soils.
Drip irrigation reduces water contact with crop leaves, stems, and fruit.
Thus, conditions may be less favorable for disease development.
Irrigation scheduling can be managed precisely to meet crop demands, holding the promise of increased yield and quality.
Growers and irrigation professionals often refer to "subsurface drip irrigation," or SDI.
When a drip tape or tube is buried below the soil surface, it is less vulnerable to damage due to UV radiation, cultivation, or weeding.
With SDI, water use efficiency is maximized because there is even less evaporation or runoff.
Agricultural chemicals can be applied more efficiently through drip irrigation.
Since only the crop root zone is irrigated, nitrogen already in the soil is less subject to leaching losses, and applied fertilizer can be used more efficiently.
In the case of insecticides, less product might be needed.
Make sure the insecticide is labeled for application through drip irrigation, and follow the label instructions.
Additional advantages of drip irrigation include the following.
Drip systems are adaptable to oddly shaped fields or those with uneven topography or soil texture; these specific factors must be considered when designing the drip system.
Drip systems also can work well where other irrigation systems are inefficient because parts of the field have excessive infiltration, water puddling, or runoff.
Drip irrigation can be helpful if water is scarce or expensive.
Because evaporation, runoff, and deep percolation are reduced, and irrigation uniformity is improved, it is not necessary to "overwater" parts of a field to adequately irrigate the more difficult parts.
Precise application of nutrients is possible using drip irrigation.
Fertilizer costs and nitrate losses can be reduced.
Nutrient applications can be better timed to meet plants' needs.
Drip irrigation systems can be designed and managed SO that the wheel traffic rows are dry enough to allow tractor operations at any time.
Timely application of herbicides, insecticides, and fungicides is possible.
Proven yield and quality responses are possible through careful irrigation scheduling made possible with drip irrigation.
Yield and quality benefits have been observed in onion, hops, broccoli, cauliflower, lettuce, melon, tomato, cotton, and other crops.
A drip irrigation system can be automated.
For an example of automated drip irrigation, see Shock, et al., 2011.
There are some disadvantages to drip irrigation.
For example:
 Drip irrigation systems typically have initial costs of $1,200 to $1,700 per acre.
This cost range does not include the equipment to install or retrieve the drip tape or hose in nonpermanent systems.
A drip system for use on an annual vegetable crop such as onion will cost about $1,200 per acre, with approximately $900 in capital costs for pumps, filtration, and water distribution, and $300 in recurring annual costs for drip tape.
A drip system using drip tubing with in-line emitters is more often used for grapes, hops, orchards, etc.
It will cost about $1,700 to $2,100 per acre and can last 12 to 15 years.
Part of the large variability in the per-acre cost of drip tubing is related to the distance between
 plant rows.
For example, grapes are planted in rows closer than hops, SO more tubing is used per acre, leading to greater cost.
Hard hose with plug-in emitters is most frequently used for landscape and nursery applications.
The cost per acre of these systems varies widely, depending on their complexity.
Systems can be more elaborate and costly than necessary.
Growers new to drip irrigation might want to start with a simple system on a small acreage.
Drip tape or tubing must be managed to avoid leaking or plugging.
Drip emitters are easily plugged by silt or other particles not filtered out of the irrigation water.
Emitter plugging also can be caused by algae growing in the tape or by chemical deposits at the emitter.
Filtration, acid injection, and chlorine injection remedies to these problems are addressed in "System management and maintenance," page 5, and "Standard maintenance," page 6.
Also see the website Maintenance of microirrigation systems.
You might need to redesign your weed control program.
Drip irrigation might be unsatisfactory if herbicides need rainfall or sprinkler irrigation for activation.
However, drip irrigation can reduce weed populations or reduce weed problems in arid climates by keeping much of the soil surface dry.
Tape depth must be chosen carefully to accommodate crop rotations and for compatibility with operations such as cultivation and weeding.
Except in permanent installations, drip tape causes extra cleanup costs after harvest.
You'll need to plan for drip tape disposal, recycling, or reuse.
Despite all of drip irrigation's potential benefits, converting to drip irrigation can increase production costs, especially where an irrigation system already is in place.
Ultimately, there must be an economic advantage to drip irrigation to make it worthwhile.
Table 1.
Types of drip irrigation systems.
Internal	Wall	Emitter	Emitter
 diameter	thickness	spacing	flow rate
 System type				
 Drip tape	0.375-1.375	4-35	2-36	0.07-0.84
 Tubing (drip	0.410-0.800	23-47	12-60	0.40-1.80
 Hard hose with	0.125-1.5*	29-125	custom	0.50-4.0*
 *Larger diameter hose and higher rate microsprinkler emitters are available for hard hose systems.
A wide range of components and system design options is available.
The Digital Drip Directory  lists equipment and suppliers.
Drip tapes, tubes, and emitters vary greatly in their specifications, depending on the manufacturer and product use.
The distribution system, valves, and pumps must match the supply requirements of the tape.
Tape, depth of tape placement, distance between tapes, emitter spacing and flow, and irrigation management all must be chosen carefully based on crop water requirements and the soil's properties.
Drip tubing, rather than drip tape, usually is used for perennial crops such as grapes or poplar trees.
The wetting pattern of water in the soil from the drip irrigation tape or tube must reach plant roots.
Selection of emitter spacing and tape depth depends on the crop root system and soil properties.
Seedling plants such as onions have relatively small root systems, especially early in the season.
Drip irrigation system design requires careful engineering.
Design must take into account the effect of the land's topography  on pressure and flow requirements.
Plan for water distribution uniformity by carefully considering the tape, irrigation lengths, topography, and the need for periodic flushing of the tape.
Design vacuum relief valves into the system as needed.
When designing a drip system, first identify fairly similar irrigation zones.
Irrigation zones are based on factors such as topography, field length, soil texture, optimal tape run length, and filter capacity.
Irrigation system designers use computer programs to analyze these factors to design efficient drip systems.
Once the drip system is designed and installed, it is possible to schedule irrigations to meet the unique needs of the crop in each zone.
Consider power and water source limitations.
Have your water analyzed by a laboratory that is qualified to evaluate emitter plugging hazards.
Water quality might create limitations and increase system costs.
Filters must be able to handle worst-case scenarios.
For excellent resources on water quality assessment and filter maintenance, see Filtration and Maintenance Considerations for Subsurface Drip Irrigation  Systems.
Finally, be sure to include both injectors for chemigation and flow meters to confirm system performance.
Every trickle counts when you are battling a water shortage.
An ineffective or improperly managed filter station can waste a lot of water and threaten a drip system's fitness and accuracy.
In the western U.S., sand media filters have been used extensively for microirrigation
 Figure 1.
Drip irrigation system with a prefilter, pump station with backflow prevention, and chemical injection site.
A pressure control valve is recommended to adjust the water pressure as desired before it enters the drip lines.
A water meter can be placed after the pressure control or between a solenoid valve and each zone.
An air vent provides vacuum relief.
Vacuum relief is necessary between the solenoid valve and the drip tapes to avoid suction of soil into the emitters when the system is shut off.
systems.
Screen filters and disk filters are common as alternatives or for use in combination with sand media filters.
Sand media filters provide filtration to 200 mesh, which is necessary to clean surface water and water from open canals for drip irrigation.
These water sources pick up a lot of fine grit and organic material, which must be removed before the water passes through the drip tape emitters.
Sand media filters are designed to be selfcleaning through a "back-flush" mechanism.
This mechanism detects the drop in pressure due to the accumulation of filtered particles.
It then flushes water back through the sand to dispose of clay, silt, and organic particles.
Sand used for filters should be between sizes 16 and 20 to prevent excess back flushing.
Because clean water from one filter is needed to back flush another filter, at least two sand media filters are generally used.
In addition to a sand media filter, a screen filter can be used as a prefilter to remove larger organic debris before it reaches the sand media filter, or as a secondary filter before the irrigation water enters the drip tube.
For best results, filters should remove particles four times smaller than the emitter opening, as particles may clump together and clog emitters.
Screen filters can act as a safeguard if the main filters fail, or may act as the main filter if a sufficiently clear underground water source is used.
System management and maintenance
 If a drip hose system is used on the soil surface for perennial crops over a number of years, the drip hose should be lifted periodically SO that leaves, soil, and debris do not cover the hose.
If the drip hose is not lifted, roots can grow over the hose, anchor it to the ground, and eventually pinch off the flow of water.
Place a water flow meter between the solenoid valve and each zone and record its gauge daily.
This provides a clear indication of how much water was applied to each zone.
Records of water flow can be used to detect deviations from the standard flow of the system, which may be caused by leaks or clogged lines.
The actual amount of water applied recorded on the meter can be compared with the estimated crop water use  to help assure efficient water management.
Leaks can occur unexpectedly as a result of damage by insects, animals, or farming tools.
Systematically monitor the lines for physical damage.
Leaks in buried hose or tape are generally difficult to detect.
Ponding on the surface often indicates a leak.
Also, pressure drop and/or flow increase can indicate leaks.
It is important to fix holes as soon as possible to prevent uneven irrigation.
Chlorine clears clogged emitters
 If the rate of water flow progressively declines during the season, the tubes or tape may be slowly plugging, resulting in severe damage to the crop.
In addition to maintaining the filtering stations, regular flushing of the drip tube and application of chlorine through the drip tube will help minimize clogs.
Once a month, flush the drip lines by opening the far ends of a portion of the tubes at a time and allowing the higher velocity water to flush out the sediment.
Because algae growth and biological activity in the tube or tape are especially high during
 warmer months, chlorine usually is applied at 2-week intervals during these months.
If drip lines become plugged in spite of maintenance, many cleaning products are available through irrigation systems suppliers.
Choose a product appropriate for the specific source of contamination.
Manage irrigation and fertilization together to optimize efficiency.
Chemigation through drip systems efficiently delivers chemicals in the root zone of the receiving plants.
Because of the precision of application, chemigation can be safer and use less material.
Several commercial fertilizers and pesticides are labeled for delivery by drip irrigation.
Make sure injected products are compatible with water to prevent chemical precipitation and subsequent plugging of emitters.
Injection pumps with backflow prevention devices are necessary to deliver the product through the drip lines.
These pumps allow for suitable delivery rate control, while backflow prevention protects both equipment and the water supply from contamination.
Remember that in Oregon water belongs to the public, not to the landowner.
Other safety equipment may be required; contact a drip irrigation system supplier for details.
Soil microorganisms convert nitrogen  fertilizers to nitrate.
Nitrate is water soluble, available to plants, and subject to leaching loss.
One of the benefits of drip irrigation is reduction or prevention of nitrate loss.
Typically, when irrigation is monitored closely, less N fertilizer is needed with drip irrigation systems than with furrow irrigation systems because the fertilizer is spoon-fed to the root system and little is lost due to leaching.
For example, if a field is converted from furrow irrigation to drip irrigation and the amount of N fertilizer is not reduced, the crop may become excessively leafy, which can inhibit curing and
 increase harvest costs as well as losses.
Plant tissue analysis performed by a qualified analytical lab can help you determine crop nutrition needs during the season and tailor N fertilizer applications to actual crop needs.
Fertilizer can be injected through the drip system.
Fertilizers containing sulfate, phosphate, calcium, or anhydrous or aqua ammonium can lead to solid chemical precipitation inside the drip lines, which can block emitters.
Obtain chemical analysis of your irrigation water and seek competent technical advice before injecting chemical fertilizers into drip systems.
Plan for seed emergence.
The drip tape must be close enough to the surface to germinate the seed if necessary, or a portable sprinkler system should be available.
A tape tube 4 to 5 inches deep has successfully germinated onion seeds in silt loam soil.
Tape at 12 inches failed to uniformly germinate onions.
Tape placement is often deeper in other row crops.
The total irrigation water requirement for crops grown with a drip system is greatly reduced compared to a surface flood system because water can be applied much more efficiently with drip irrigation.
For example, with furrow irrigation, typically at least 4 acre-feet/acre/year of water are applied to onion fields in the Treasure Valley of eastern Oregon and southwestern Idaho.
Depending on the year, summer rainfall, and the soil, 20 to 32 acre-inches/acre of water have been needed to raise onions under drip irrigation in the Treasure Valley.
Applying more water than plants need will negate most of drip irrigation's benefits.
The soil will be excessively wet, promoting disease, weed growth, and nitrate leaching.
To determine application rates, use measurements of soil water and estimates of crop water use.
For shallow-rooted crops, irrigate only to replace the
 soil moisture deficit in the top 12 inches of soil.
It usually is not necessary to exceed ET.
Local daily crop evapotranspiration estimates are available for some U.S.
Pacific Northwest locations on the AgriMet website.
For measuring soil water, see Instrumentation for soil moisture monitoring  and Irrigation Monitoring Using Soil Water Tension.
For planning irrigation scheduling, see Irrigation Scheduling..
Add chlorine or other chemicals to the drip line periodically to kill bacteria and algae.
Acid might also be needed to dissolve calcium carbonates.
Be sure to follow chemical labels for safe handling instructions.
Acids and chlorine can be very hazardous.
Filters must be managed and sand changed as needed.
Even with filtration, drip tape must be flushed regularly.
The frequency of flushing depends on the amount and kinds of sedimentation in the tape.
Root intrusion must be controlled for some crops.
Rodents must be controlled, especially where drip tape is buried.
OSU Extension Service publications
 Funding to help prepare this publication was provided in part by an Oregon Watershed Enhancement Board grant.
MAINTAINING DRIP IRRIGATION SYSTEMS
 Drip irrigation systems are becoming more widely used for horticultural crop production, especially vegetable crops.
The system must function efficiently during the entire growing season.
Failure at a critical point in the crop production cycle can cause loss of the entire crop.
System failures are often due to inadequate maintenance of the system especially if fertigation is being utilized to supply nutrients to the plant's root zone.
Maintenance of the drip irrigation system does take time and understanding; however, maintenance is critical for successful use of drip irrigation systems.
This article should help one understand how to maintain drip irrigation systems.
Water for drip irrigation can come from wells, ponds, rivers, lakes, municipal water systems, or plastic-lined pits.
Water from these various sources will have large differences in quality.
Well water and municipal water is generally clean and may require only a screen or disc filter to remove particles.
However, no matter how clean the water looks, a water analysis/quality test prior to considering installation of a drip irrigation system should be completed to determine if precipitates or other contaminants are in the water.
This water quality analysis should identify inorganic solids such as sand and silt; organic solids such as algae, bacteria, and slime; dissolved solids such as iron, sulfur, and calcium; and pH of the water.
Water testing can be done by a number of laboratories in the state.
Your local Cooperative Extension Service  County Agent can supply a list of laboratories or suggest a local lab that can do water quality analysis.
Check with the lab first to obtain a sample kit containing a sampling bottle that is clean and uncontaminated.
Use: apply extra water to sloping areas to compensate for runoff after a heavy rain, VRI type: both, prescription type: both, management intensity: medium/high.
Each year, the Upper Big Blue NRD requires each farmer in six zones across the district that have high nitrates in the groundwater to use soil water monitoring equipment in at least one irrigated field and to turn the data into the NRD at the end of the year.
The study focused on the fields that used a Watermark system, which includes three sensors placed at different depths to represent the root zone of corn and soybeans and a data logger to automatically record the data.
Water Supply and Conservation Education Programs
 Gene R.
Taylor, II, Assistant Professor and Extension Turfgrass Specialist Richard H.
White, Associate Professor Turfgrass Physiology, Texas Agricultural Experiment Station Scott Abernathy, Former Turfgrass Extension Assistant David Smith, Former Extension Associate-Integrated Landscape Management The Texas A&M University System
 W ater is rapidly becoming a limited
 resource in Texas and will become more limited as the population increases.
Unless water conservation efforts are strengthened, water rationing programs will become more prevalent across the state and water prices will increase drastically.
Water conservation must be considered by anyone working in turf and grounds maintenance.
Athletic field managers must know how to conserve water, yet provide a safe and aesthetically pleasing facility for recreational use.
As an athletic field manager, you must know how your irrigation system performs and understand all the factors that affect turfgrass water use in order to develop a sound irrigation management program.
You must be able to answer the following questions.
How does your irrigation system operate?
Know how to program your irrigation controller.
Know how much water is applied in a given amount of time for each zone.
Know the distribution pattern of the system.
What is the soil type?
What is the rooting depth of the turf?
What are the water requirements of the turfgrass as determined by the specific turf species and varieties, the specific use of the grass, and the level of management?
What environmental conditions affect turf water use rates?
HOW does your irrigation system operate?
To develop an efficient watering program, the first key is to understand the performance and capabilities of your irrigation system.
Thoroughly understand the features of your controller including options such as dual programming, multiple start times and sensor override capabilities.
The controller should be frequently modified for seasonal changes in turfgrass growth and variable environmental conditions.
It is vital to know the application rate and distribution pattern of each sprinkler zone, and the soil type and the rooting depth to establish an effective and efficient irrigation schedule.
A Texas A&M certified landscape irrigation auditor can evaluate your system and provide a detailed report containing this information.
Your county Extension agent should have a directory of certified irrigation auditors in your area.
If you choose to perform your own irrigation audit, simply follow the 18-step procedure in "Performing an Irrigation Audit."
 Besides performing a complete irrigation audit, you should routinely check your system to ensure that each sprinkler head operates properly.
Record any problems on the report form.
Look for broken sprinkler heads, misaligned heads, sunken heads, high water pressure, low water pressure, leaks in the lines, and improper rotation.
PERFORMING an irrigation audit
 1.
To obtain the most accurate results, perform the audit at the same time of day the system normally operates.
Avoid extremely windy or rainy conditions.
2.
Determine the square foot area of irrigated turf and record this value on the audit report.
Draw the area on graph paper to scale.
3.
Turn the irrigation system on and flag each sprinkler head in individual zones.
Use a different color flag to represent separate zones to eliminate confusion.
Plot each sprinkler head on the graph and label it with a letter.
4.
Measure and record the distance between each sprinkler head.
5.
Use a soil probe to pull multiple soil samples from across the irrigated area.
6.
Examine the soil samples and determine the effective rooting depth.
The plant's effective rooting depth is the depth of soil, in inches, that contains a large number of live, growing roots.
Find an average rooting depth from all soil samples.
Record the average rooting depth on the report form.
7.
Determine the soil type using the "feel method." A clay soil will feel sticky and form a ribbon when squeezed between the fingers.
A sandy soil will feel gritty, and a loamy soil will be a mixture of sand, silt and clay.
Record this information for later use.
8.
Conduct the remaining steps of the audit individually on each irrigation zone, beginning with zone 1.
9.
You will need 15 to 20 catch cans or devices to perform the irrigation audit.
Straight-sided containers such as coffee cans, tuna and cat food cans work well, or rain gauges can be used.
10.
Place the catch cans at each sprinkler head and halfway between heads.
This simple placement pattern requires the least number of catch cans while providing adequate coverage of the tested area.
When placing catch cans at each head, make sure the cans are far enough away from the heads SO as not to interfere with the spray pattern.
Plot the location of each catch can on the graph and label with a number.
11.
Irrigate the zone for a short period of time.
The run time should be long enough to allow for five to 10 rotations of a geared rotor or impact sprinkler head.
Normally, testing run times range from 10 to 30 minutes for large sprinklers.
While shorter testing run times permit faster auditing, running the system longer will lead to more accurate results.
Record the run time.
12.
While the system is running, use a pressure gauge to check and record the water pressure at each sprinkler head.
13.
After the zone designated run time is completed, measure and record the depth of water caught in each catch can.
A ruler can be used to accurately determine the depth.
14.
Record all individual catch depths and head pressures to their appropriate locations on the graph.
15.
Average all catch can depths for the zone.
Record this value.
16.
Look for distribution problems within the system.
Keep in mind that other heads not on that particular zone could add to the depth of some catch cans, especially those cans near each head.
17.
If problems exist, determine the cause.
18.
Repeat steps 10 through 17 for the remaining zones.
Measure the area to be irrigated by a zone.
WHAT is the soil type?
To develop an effective irrigation schedule, it is crucial to know and understand the characteristics of your specific soil type.
Soil type influences how often you need to water and how much water you need to apply per application.
Soil types have different water holding capabilities.
As soils dry, they hold onto their remaining water more tightly.
Eventually water is held SO tightly by the soil that the turfgrass roots are unable to extract it for use.
The remaining water is unavailable to the grass.
Available water is the fraction of water held by the soil that can be extracted by plant roots.
When there is a high loss of water from the soil both by evaporation and by transpiration from the plants , a percentage of the available water might not be available rapidly enough to prevent drought stress.
Therefore, for irrigation scheduling, it is important to have readily available water, or a volume of water in the soil that will effectively prevent drought stress injury regardless of environmental conditions.
Table 1 gives general approximations of the amount of readily available water held in each soil type.
With the irrigation audit, you determined your soil type.
Locate your soil type in Table 1 and record the volume of readily available water for your soil type on the Auditing Report.
Table 1.
Estimates of readily available water for different soils.
Soil Texture	Readily Available Water 
 WHAT is the rooting depth of the turf?
To establish an effective irrigation schedule, you must know the effective rooting depth, or the depth of actively growing roots.
Use this depth to determine how deeply to water each time you irrigate.
Deeper water within the effective root zone results in less frequent irrigation.
Water to a depth just below the effective rooting depth.
Irrigation water below this depth is unavailable to the roots, and is wasted.
Shallow irrigation significantly less than the effective rooting depth can lead to a decrease in rooting depth and will require more frequent irrigation to prevent drought stress.
During the irrigation audit, an average effective rooting depth for the irrigated area was determined.
This information will be used when establishing your irrigation schedule.
Check your system to ensure that each sprinkler head is working.
WHAT are the water requirements?
Water requirements of turf can vary significantly depending on species and variety, specific use of the grass and its level of management.
Grass species and even varieties within each species can vary significantly in their water use rates.
Table 2 gives a general ranking of the water use rates for the more common turfgrass species
 used on Texas athletic fields.
Record on the Auditing Report which ranking your turfgrass species is given.
For more specific information, contact your county Extension agent.
Table 2.
Rankings of turfgrass water use rates by species.
High	Perennial Ryegrass, Annual Ryegrass,
 Poa trivialis, Kentucky Bluegrass
 Medium	Tall Fescue, Hybrid Bermudagrass
 The specific use of the grass determines the level of management and directly influences the water use rates of turf and its irrigation requirements.
An athletic field that receives heavy traffic or is a high priority field will require a high level of management to maintain an appropriate turfgrass quality.
The intensity of traffic also will affect the level of management.
College football causes more stress and injury to turf than high school baseball, and thus would require a higher level of management.
Fertilization, mowing and management of thatch and soil compaction are all management practices that influence the water requirements of a turfgrass area.
Specific use of the field and the financial operating budget dictate the frequency at which you perform each of these tasks.
A good fertilization program provides all essential nutrients to the turf in the required amounts.
Proper fertilization helps promote optimum shoot and root development.
A deep root system enables a plant to use water held deep in the soil, significantly reducing the frequency of irrigation.
Fertilization programs that supply excess nutrients, especially nitrogen, promote shoot growth at the expense of root development.
This results in turf with a short, weak root system.
Nutrient deficiencies are equally as bad, increasing a turf's susceptibility to stresses such as disease, insects, weed invasion and drought.
Therefore, practice moderation when developing a fertilization program.
Table 3 provides recommended nitrogen rates for most common athletic field turfgrass species used in Texas.
Determine the soil type by feeling soil in the palm of your hand.
Table 3.
Yearly nitrogen fertilizer requirements for common Texas athletic field turfgrass species.
Grass Species	Maintenance Needs
 
 Mowing also affects root and shoot development.
Turf that is maintained at a higher mowing height normally has a deeper, more extensive root system.
However, as the leaf area increases, transpiration can increase and result in higher water use rates.
Therefore, moderate mowing heights should be used during high stress periods.
Mowing frequency should be determined using the "one-third" rule.
No more than one-third of the leaf area should be removed at any one time.
Frequent mowing leads to thicker, denser turf.
The higher the density, the lower the evaporative water loss from the soil.
Also, dense turfgrass is more competitive against weed invasion.
Table 4 gives recommended mowing heights for common athletic field turfgrass species.
Flag each sprinkler head.
Use a different color of flag for each zone.
Table 4.
Recommended mowing heights for turfgrasses used on athletic fields in Texas.
Grass Species	Mowing Height
 Hybrid Bermudagrass	0.5 1.5
 Common Bermudagrass	1.0 1.5
 Zoysia japonica	1.0 2.0
 Tall Fescue	1.5 2.0
 Kentucky Bluegrass	1.0 2.0
 Perennial Ryegrass	0.5 2.0
 Annual Ryegrass	1.0 2.0
 Poa trivialis	0.5 2.0
 Thatch, the layer of nondecomposed organic matter found between the soil surface and the base of the leaves, can slow water movement into the soil and lead to runoff.
Thatch accumulation results from heavy fertilization, improper mowing and overwatering.
Certain management practices used during low stress periods help control thatch development.
They are topdressing, vertical mowing and aeration.
Soil compaction limits both water and air movement into the soil profile, and reduces shoot and root development.
A good aeration program, which significantly increases air exchange and water infiltration rates, should be established to break up compacted layers.
The frequency of aeration for a specific turf area is dictated by the intensity of traffic the area receives.
Areas that receive heavy traffic require frequent aeration.
Consider the overall management level of the turfgrass area by noting how often and at what rates you fertilize and how often you aerate and topdress.
Give your personal management level a ranking of high, medium or low and record this on the Auditing Report.
WHAT environmental conditions affect turf water use rates?
Environmental conditions influence irrigation requirements.
Low humidity, high temperatures,
 Check for obstructions to spray.
While performing the audit, look for broken or damaged heads.
and/or high wind speeds can significantly increase water lost from the soil and plants by potential evapotranspiration.
When PET is high, soil water is lost more rapidly and irrigation must be more frequent.
PET rates and, therefore, the frequency of irrigation are much lower when conditions are cool, humid and/or calm.
The time of year also impacts irrigation frequency.
During the summer, when temperatures are high and days are long, supplemental irrigation requirements are high.
During late fall, winter and early spring, temperatures are cool, days are short, and rain is frequent, thus irrigation requirements are low.
PUT it all together.
Now that you have considered the components that influence irrigation scheduling and how they apply to your situation, put it all together to generate an irrigation schedule that is specific to your situation.
To determine the run time for your irrigation system, you need to know:
 average effective rooting depth,
 volume of readily available water for your soil type, and
 average depth of water caught in each catch can per zone.
Your goal is to thoroughly wet the soil to a depth at or just below the effective rooting depth.
To do this, you need to determine how much water to apply and how long the system needs to run to put out that volume of water.
1.
Convert the average effective root depth from inches to feet by dividing by 12.
6 inches 12 inches per foot = 0.5 foot
 2.
Multiply that number by the depth of readily available water for your soil type.
This gives the total volume of readily available water for the effective root zone or the total depth of water that must be applied.
0.5 foot x 1.4 inches per foot of sandy loam = 0.7 inches
 3.
The precipitation rate for zone 1 is the average depth of water from all catch cans in zone 1 divided by the run time.
For example, if the system runs for 5 minutes with an average depth of 0.25 inch, then you have applied 0.25 inch per 5 minutes.
4.
Convert this number to inches per hour by multiplying the number by 60 minutes and then dividing by 5 minutes.
This gives an average precipitation rate, in inches per hour, for that particular zone.
0.25 in.
X 60 minutes per hour = 15 inches = 3 inches per hour 5 minutes 5 minutes
 5.
To determine the actual irrigation run time for the zone, divide the total depth of water that must be applied  by the average precipitation rate .
This gives the run time in hours for that particular zone.
Record this value.
0.7 3 = 0.23 hour
 6.
To convert this value to minutes multiply by 60.
0.23 x 60 = 13.9 minutes
 7.
Repeat for all other zones.
8.
Set the controller to run each zone for its specified time.
You may need to use split applications to prevent runoff.
To determine the irrigation frequency, you need to know:
 the depth of readily available water for your soil type;
 the ranking of the water use rate of your grass species;
 the ranking of your level of management; and
 the effects PET has on irrigation frequency.
Your goal is to irrigate as infrequently as possible without causing severe drought stress injury to the turf.
This will produce
 Place the catch can far enough away from the sprinkler head to avoid obstructing the spray pattern.
higher quality turfgrass while saving water and money.
To meet this goal, you must determine how long the water applied during irrigation will sustain the grass.
This will vary significantly with changing environmental conditions.
There are two methods-visual assessment and PET based irrigation-to determine irrigation frequency.
Both work and are wellaccepted methods.
Choose the method that best serves your purposes.
Visual Assessment for Irrigation Needs
 This system is very simple but slightly more time intensive than the PET based method.
After watering, do not irrigate again until the grass begins to show symptoms of drought stress: grass leaves turning a dull, bluish color; leaf blades rolling or folding; or footprints that persist for an extended period of time after you walk across the turf.
When drought stress symptoms develop, irrigate using the appropriate run times and then wait for symptoms to redevelop before the next irrigation.
This method requires routine checks  of the field for signs of drought stress.
When conditions are hot, dry , and/or windy, pay closer attention because symptoms will develop more rapidly.
The longer you use this system, the easier it will become.
You will begin to "get a feel" for how long the field will go between irrigations, and what areas will show stress first.
This method allows you to spend less time checking your field, but does require some math and access to daily PET data.
The premise behind PET based irrigation scheduling is simple.
After irrigation, you know how much readily available water is in your effective root zone.
PET is an estimate of the depth of water lost from the soil each day.
Therefore, you irrigate when the depth of water lost by PET equals the depth of readily available water you originally applied.
To use this method, you first need to determine a crop coefficient.
To do this, you will use the ranking of water use rate of your grass species  and the level of management.
Use Table 5 to determine the crop coefficient, then follow the steps to develop a PET based irrigation program.
Table 5.
Estimating crop coefficient based on grass species and level of management.
Water use rate	Level of	Crop
 of grass species	management	coefficient
 Check water pressure at each sprinkler and record pressure problems.
Setting up a PET based irrigation program
 1.
After the soil has been thoroughly watered to the appropriate depth, start recording daily PET rates.
2.
Multiply each daily PET value by the crop coefficient.
This new value is called the irrigation index.
3.
The first irrigation index value is the day following irrigation.
Each subsequent day is added to this value until they total the depth of readily available water.
Then, irrigate.
The following day, start again.
Measure and record the depth of water collected in each cup.
Wednesday Irrigated = 1" applied Thursday PET X Crop coefficient = 0.25" Friday PET X Crop coefficient = 0.20" Saturday PET X Crop coefficient = 0.15" Sunday PET X Crop coefficient = 0.25" Monday PET X Crop coefficient = 0.10" Time to irrigate again = 0.95" For information on obtaining daily PET data, contact your county Extension agent.
Early morning is considered the best time to water.
Wind speed and temperatures are low, and water pressure is usually good, which allows irrigation to be applied uniformly.
Watering late in the evening or at night maintains wet leaves for an extended period of time and significantly increases the chance for disease.
Midafternoon watering with high wind speeds can lead to nonuniform distribution.
Water movement into some soils, especially the finer textured clays and loams, can be very slow.
If a sprinkler head applies water faster than it can move down into the soil, significant amounts of water can be lost as runoff.
To avoid this problem, use sprinklers with low application rates and/or irrigate to a point just before runoff, and then stop watering.
Let the surface dry and then begin watering again.
Repeat this process until the desired volume of water is applied.
Multiple cycle irrigation controllers can be programmed to do this automatically.
Available Readily Water	Loam Silt
  Depth Ave.
Sandy Loam
 Square Foot Area	Sample Soil	Depths Rooting	Soil Type
 Noted Problems	Comments or
 Type Head	 rotor,
 1	2	3	4	5	6	7	8	9	10	11	12
 Ranking-Turfgrass Rate Water Use	Management Ranking-Level of	Coefficient Crop
 Irrigation Auditing Report 
 Available  Readily Water	Silt Loam
  Depth Ave.
inches 5.8	Sandy Loam
 Square Area Foot	Sample Soil	Rooting Depths	Soil Type
 E	40	33	34	a9	30
 D	30	33	32	30	34
 C	38	36	35	33	33	34
 B	36	38	36	32	29	30
 A	40	35	33	34	31	33
 Problems Noted	Comments or	 Head Leaky	spraying Head C11 too high	 Rotation Poor	 Head Leaky
 Head Type	 rotor,	rotor	rotor	rotor	rotor	spray	spray
 	20.0	20.3	20.0	20.4	20.0	21.0
 1	2	3	4	5	6	7	8	9	10	11
 Ranking-Turfgrass Water Rate Use	Ranking-Level Management of	Coefficient Crop
 Sample Graph Irrigation Area
 Irrigation Audit Step 6
 a) 6.0 + 5.5 + 6.3 + 5.0 + 6.1 = 28.9 inches b) 28.9 inches 5 samples = 5.8 inches of roots
 a).16 +.10 +.17 +.17 +.12 +.18 +.20 +.13 +.19 +.17 +.10 +.18 = 1.87
 Determining the Run Time
 Step 1 5.8 inches 12 inches per foot =.483 feet
 Step 2.483 feet X 1.8 inches of water per foot of soil =.87 inches of available water = total depth water that must be applied
 Step 4 a).16 X 60 = 9.6 b) 9.6 5 = 1.9 inches of water per hour = precipitation rate
 Step 5.87 1.9 =.46 hour
 Step 6.46 X 60 = 28 minutes
Turfgrass Consumptive Use Values for the Phoenix Area
 Consumptive use  curves that provide average rates of turfgrass evapotranspiration  are widely used by irrigation professionals for design and management of turfgrass irrigation systems.
For approximately 35 years, the bermudagrass lawn CU curve developed by the United States Department of Agriculture  has served as the lone published CU curve for turfgrass in Arizona.
While the USDA CU curve has proven useful to the turf industry, turf professionals do question whether ET values obtained from the curve are relevant to turf sysitems commonly used in Arizona today.
The USDA curve was developed for the summer turf season using a low-maintenance common bermudagrass mowed to a height of 3.8 cm  every four weeks, and watered every two weeks using flood irrigation.
A relevant turf system today consists of hybrid bermudagrass maintained at a height of ~ 2 cm  and watered at frequent intervals using sprinkler irrigation.
The practice of overseeding with ryegrass in the fall to maintain green cover in winter is also common today.
The USDA CU curve does not address the issue of overseeding and provides no information on ETT for the period mid-October through mid-April.
A number of research studies have been completed in recent years to quantify the water requirements of turfgrass grown in the low desert regions of Arizona.
Several studies had as their primary objective the development of crop coefficients  that convert reference evapotranspiration  data computed from meteorological data  into estimates of ET.
In this report, we apply Kcs developed from these studies to long-term records of ETo to provide updated CU information for turfgrass grown in the Phoenix metropolitan area.
Estimates of ET were computed on a daily basis for the period 1987 through 2000 by applying turfgrass Kcs to the historical record of reference evapotranspiration  available for the Phoenix area from the Arizona Meteorological Network.
Specific
 Figure 1.
Consumptive use curves for high and acceptable quality turf grown in the Phoenix area.
data used in this analysis were obtained from two Phoenix area AZMET stations located on golf courses: Phoenix Greenway  and Phoenix Encanto.
The mathematical procedure used to produce the ET, estimates involved multiplying the appropriate crop coefficient  by ETo:
 ET.
= Kcs x ETo =
 Turf Irrigation Management Series: V
 THE UNIVERSITY OF ARIZONA COLLEGE OF AGRICULTURE AND LIFE SCIENCES TUCSON, ARIZONA 85721
 Paul Brown Biometeorology Specialist
 The Kcs used to estimate ET1 were developed for a common desert turf system consisting of Tifway bermudagrass in summer and overseeded ryegrass in winter.
Other assumptions implicit in the use of the Kcs employed include frequent irrigation with sprinklers, mowing heights ranging from 0.625-1.0" in summer and 0.875-1.25" in winter, and two levels of turf quality defined as high and acceptable.
High quality turf areas would include high profile sports turf  and areas where turf appearance is very important.
These areas generally receive high levels of fertilization and maintenance.
Acceptable quality turf would be suitable for lawn or park environments where traffic is low, rapid regrowth is not required and fertilization levels are relatively low.
Crop coefficients appropriate for high quality turf were based on the research results of Brown et al.
and change monthly.
Crop coefficients for acceptable quality turf were derived by subtracting 0.1 from the high quality Kcs.
The resulting 14 years of daily ET data from the two AZMET sites were first averaged by day of the year to produce an average annual ET data set for each location.
These location specific ETT values were in turn averaged to produce a Phoenix-area annual
 ET data set.
This Phoenix-area daily ET data set was then summarized into weekly, monthly, and annual totals of ET Consumptive use curves were developed for high and acceptable quality turf from the summarized data sets.
Annual CU curves for high and acceptable quality turfgrass grown in Phoenix area are presented in Figure 1.
Turfgrass ET varies nearly 5-fold over the course of the year, reflecting the annual fluctuation in atmospheric evaporative demand.
The ET of high quality turf ranges from a low of ~0.05" day in December to ~0.25" day in June.
Evapotranspiration from acceptable quality turf runs about 15% below that of high quality turf and ranges from ~0.04" / day in December to ~ 0.22" / day in June.
Weekly as opposed to daily values of ET may prove more useful when managing irrigation, especially if irrigation is not being applied each day.
Table 1 provides weekly totals of ET for high and acceptable quality turfgrass grown in the Phoenix area.
Evapotranspiration from high quality turf ranges from 0.31 in the first week of January to 1.83" in the first week of July.
The range in weekly ET1 for acceptable quality turf
 Table 1.
Weekly consumptive use  in inches for high and acceptable quality turf grown in the Phoenix area
 Week	Turf Quality	Week	Turf Quality	Week	Turf Quality	Week	Turf Quality
 Ending	High	Acc.
Ending	High	Acc.
Ending	High	Acc.
Ending	High	Acc.
Jan 7	0.31"	0.26"	Apr 8	1.23"	1.07"	Jul 8	1.83"	1.59"	Oct 7	1.13"	0.98"
 Jan 14	0.37	0.31	Apr 15	1.40	1.22	Jul 15	1.73	1.51	Oct 14	1.04	0.90
 Jan 21	0.41	0.35	Apr 22	1.43	1.24	Jul 22	1.71	1.49	Oct 21	0.92	0.80
 Jan 28	0.43	0.37	Apr 29	1.53	1.33	Jul 29	1.71	1.49	Oct 28	0.75	0.65
 Feb 4	0.52	0.44	May 6	1.59	1.38	Aug 5	1.78	1.56	Nov 4	0.70	0.60
 Feb 11	0.53	0.45	May 13	1.63	1.41	Aug 12	1.72	1.52	Nov 11	0.62	0.54
 Feb 18	0.56	0.48	May 20	1.65	1.43	Aug 19	1.68	1.48	Nov 18	0.56	0.49
 Feb 25	0.67	0.57	May 27	1.67	1.45	Aug 26	1.58	1.39	Nov 25	0.53	0.46
 Mar 4	0.71	0.61	Jun 3	1.71	1.48	Sep 2	1.42	1.24	Dec 2	0.48	0.41
 Mar 11	0.83	0.72	Jun 10	1.68	1.45	Sep 9	1.37	1.20	Dec 9	0.39	0.34
 Mar 18	0.90	0.78	Jun 17	1.73	1.49	Sep 16	1.33	1.16	Dec 16	0.38	0.33
 Mar 25	1.03	0.89	Jun 24	1.72	1.48	Sep 23	1.24	1.08	Dec 23	0.33	0.28
 Apr 1	0.93	0.81	Jul 1	1.81	1.56	Sep 30	1.22	1.06	Dec 31*	0.38	0.33
 * Water use for the week ending December 31 represents an 8-day total for the period December 24-31.
ranges from 0.26" in early January to 1.59" in early July.
Monthly values of ET are useful when planning irrigation budgets for a year.
Table 2 presents monthly ETT for high and acceptable quality turfgrass for the Phoenix area.
Monthly ET for high quality turf ranges from 1.6" in December to 7.7" in July.
For acceptable quality turf, ET ranges from 1.4" in December to 6.7" in July.
The last column in Table 2 presents the percentage of annual ET occurring in each month.
These monthly percentages clearly show that the bulk of the annual water use occurs during the summer months.
For example, ET in July accounts for 13.4% of total annual ETTIn contrast, total ET from December through February  represents just 9.9% of annual ET substantially less than ET for July.
Annual CU of high and acceptable quality turf is summarized at the bottom of Table 2.
Consumptive use of high quality turf totals -57.7" or 4.8' per year while the CU of acceptable quality turf approaches ~49.9" or 4.16' per year.
Table 2.
Monthly and annual consumptive use  in inches for high and acceptable quality turf grown in the Phoenix area.
Turf Quality	% of
 January	1.7"	1.4"	3.0
 February	2.4	2.0	4.1
 March	4.0	3.4	6.9
 April	5.9	5.2	10.3
 May	7.3	6.3	12.7
 June	7.4	6.4	12.8
 July	7.7	6.7	13.4
 August	7.3	6.4	12.7
 September	5.6	4.8	9.6
 October	4.2	3.6	7.2
 November	2.5	2.1	4.3
 December	1.6	1.4	2.8
 The CU data presented in this report represent longterm average rates of ET, and should prove useful to individuals involved in the design and management of turf irrigation systems.
It is important to realize that the results presented in this report represent raw ET data that have not been adjusted for precipitation or irrigation system performance.
To use this CU information to determine the amount of water required for irrigation, one must first subtract the amount of effective precipitation  to determine the net water requirement for any period.
Precipitation in the Phoenix area averages ~7" or 0.6' per year and should reduce irrigation water requirements to some degree.
The final step in determining irrigation water requirements involves making adjustments to: 1) account for system nonuniformity and 2) ensure leaching is sufficient to maintain soil salinity at acceptable levels.
Adjustments for nonuniformity and salinity management increase the amount of irrigation water required and vary dramatically with location due to differences in irrigation design, topography, local weather conditions, and water quality.
A discussion of these adjustments is beyond the scope of this publication and will be discussed in a subsequent report in the Turf Irrigation Management Series.
In addition, the IRTs in the full and over-irrigation levels detected crop water stress at multiple days  but did not result in yield loss.
At the full irrigation level, the common method prescribed the largest irrigation depth for three of four cases, with sensor-based methods prescribing reduced irrigation applications.
In Scenario 3, a corner extension was added.
When the added pipeline is fully extended into the corner, the flow rate changes substantially.
The additional flow rate required by the 350+ foot extension results in increased friction loss in the main portion of the pivot.
In most cases the corner extension is totally functional for only about 20 degrees in each corner or 22% of the revolution.
LIMITED IRRIGATION OF CONVENTIONAL AND BIOFUEL CROPS
 Declining ground water is not a new dilemma in Nebraska or throughout the Great Plains.
The drought across the High Plains and inter-mountain west from 1999 to 2008 magnified the seriousness of the problem, however.
The passage of Nebraska legislation to conjunctively manage groundwater and surface water has changed ground and surface water management.
In many areas it simply means less water for producers.
The economic reality is that irrigation provides more stability and income than dryland farming.
UNL research suggests that applying limited water to an optimum number of acres provides more profit potential and has less impact on the local economy than converting some land to dryland.
Under limited irrigation, less water is applied than is required to meet full ET demand and the crop will be stressed.
The goal is to manage cultural practices and irrigation timing such that the resulting water stress has less of a negative impact on grain yield.
Previous NE research on the concepts of moisture conservation from dryland no-till ecofallow  and the timing of limited irrigation  were combined in a project at North Platte, NE in the 1980's.
Yields with 6 inches of irrigation for winter wheat , corn  and soybean  were 99%, 86% and 88% of the fully irrigated yields.
The western portion of the Central Great Plains is defined as the High Plains region.
It presents challenges when converting to limited irrigation compared to eastern portions of the Great Plains because of lower rainfall, sandier soils and higher elevation.
Alternative crops that use less water than corn and are adapted to this region include winter wheat, chickpea, canola, camelina, crambe, dry beans, sunflower, dry or forage pea, and millets and forage sorghums.
Grain sorghums often do not perform because of lack of cold tolerance or inability to mature before killing frost.
These crops use 16 to 18 inches of ET versus 23 to 25 inches for corn in the NE panhandle.
Based on earlier research with limited irrigation at North Platte, NE experiments were initiated at Scottsbluff, NE in 2005.
The soil is a Tripp very fine sandy loam  with a pH of 7.8 and an organic matter content of 1.2%.
Slope ranges from 0.8 to 1.5%.
Plant available water holding capacity of this soil is 1.5 in/ft for the 0 to 4 foot normal rooting depth.
The 30-yr average precipitation at Scottsbluff  is 15.5 in with a mean annual temperature of 48 F.
The frost-free period  is 125 days.
The primary objectives of this experiment were  to determine yields from limited-irrigated corn, winter wheat, dry beans and canola grown in a no-till cropping system versus full irrigation and  to determine the agronomic feasibility and problems encountered in using no-till on crops that have primarily been grown under conventional full tillage in this area.
The cropping system initially included winter wheat, corn, and dry beans  grown under no-tillage.
In 2006, spring canola  was added following wheat.
This provided a cropping system with two grass crops and two broadleaf crops.
Inclusion of canola also allowed for more timely planting of winter wheat.
Canola is harvested in August.
Planting winter wheat after dry beans is a challenge some years due to late maturity of the beans which delays wheat planting beyond optimum time  and affects wheat stand and ultimate yield potential, especially under full irrigation.
Each phase of the rotation is present each year under a linear move sprinkler irrigation system.
A randomized complete block design with four replications was used.
The irrigation levels for the crops were 4, 8 and 12 inches per crop per growing season.
In 2007, the irrigation levels for the corn were changed to 5, 10 and 15 inches.
The highest irrigation level was designed to be near the longterm average non-ET limiting irrigation.
Individual plots are 40 ft by 70 ft.
All crops were surface planted with no-till equipment.
A Monosem planter fitted with finger-spoke disk furrow openers and a single-disk starter fertilizer attachment 2 in to the side of the row were used for corn and dry beans.
A no-till drill was used to plant winter wheat and canola.
Plant populations for dry beans , canola  and winter wheat  were the same for all water levels, but were modified for corn based on prior research.
Corn plant populations for the low, medium and high irrigation levels were 16,000/ac, 24,000/ac and 32,000/ac.
The lowest level limited irrigated corn was usually not irrigated until tassel emergence based on conclusions from Maurer et al.
but in extremely dry years  some water was applied earlier.
Irrigations of 1 to 2 in per week approximating farmer practice were applied from late vegetative stage until water was used.
For the medium irrigation level, irrigation was started earlier in the vegetative period.
Similar strategies were used for winter wheat.
For canola at the lowest water level, irrigation was applied during flowering and
 early pod-fill as noted periods of stress sensitivity.
For higher levels irrigation began earlier and was extended through pod-fill.
For dry bean, the lowest irrigation level presented a management challenge as there was not published information on irrigation timing for limited water.
After our first two years, we learned that we could not withhold water until the reproductive period because it slowed development and delayed maturity which significantly reduced yield.
After 2007, we applied limited amounts of irrigation  beginning about 50% cover to keep the crop growing and developing with limited stress.
Irrigation was usually completed just as pod-fill began.
Irrigation scheduling was modified depending on rainfall, but during this experiment with drought in 2006 through 2008, that was not a consideration during the high water use periods except during 2005 and 2009.
Rainfall for the five years was: 2005: 19.6 in; 2006: 13.3 in; 2007: 8 in; 2008: 11" and 2009: 19.76 in.
Herbicides were selected to provide optimum weed control in the current crop without carryover that would injure the next crop.
Roundup@-ready corn and canola were used.
Plots were routinely scouted during the summer for insect problems.
Helix seed treatment was required for canola to protect against flea beetle but no other insects were a problem.
Because of the crop rotation there were not major insect problems in the other crops and plant diseases were not a problem.
There was some spider mite infestation on corn, but it did not reach economic thresholds that required treatment.
Winter wheat yields are shown in Table 1.
For the initial year  spring wheat was planted as the plot area was in corn during the fall of 2004 so winter wheat could not be planted.
Spring wheat was planted early, stands were excellent but the low yields compared to what we can grow using winter wheat show why irrigated spring wheat is not an economically viable option for the panhandle.
Table 1.
Wheat yields at Scottsbluff.
2005*	2006	2007	2008	2009*
 Irrig	Bushels per acre
 0 in	40	45	20	25	50
 4 in	53	83	45	55	58
 8 in	58	91	75	78	72
 12 in	57	100	100	99	72
 *Spring wheat yields, winter wheat 2006 and later.
**Sooty mold and black point reduced yields due to wet conditions
 The 0 inch irrigation data is provided only as a comparison and in most cases is
 a county-average from NE Agricultural Statistic or represents data from companion studies in the plot area that are true dryland.
The 0 inch irrigation yields also show that continuous dryland yields in this environment are very low many years, ranging from 0 to only 25% of fully irrigated yields.
The average relative yields for the four years of winter wheat were 67% for the 4 in treatment and 88% for the 8 in treatment.
Because both 2006 and 2007 were so dry, maximum yields were not attained unless full irrigation was applied.
In an 'average' year or wetter year such as 2005 or 2009, the 8 inch irrigation or less would produce near maximum yields.
Relative yield levels were calculated each year and are presented in Figure 1.
Over the course of the experiment we have established an upper and lower boundary that hopefully encompasses the range of wet to dry conditions we might see.
This information can be used to check against current optimization programs as verification and provide information for economic analysis.
2006-09 Relative Wheat Yields
 Figure 1.
Relative winter wheat yields 2006 through 2009.
Table 2 shows corn yields for the five years.
During 2007, a late freeze on June 8 caused severe damage, but plants did recover.
Maturity was not affected, but overall yield potential was decreased.
Table 2.
Corn grain yields at Scottsbluff.
Irrigation	2005	2006	2007	2008	2009
 0 in	81	30	30	60	90
 5 in	133	139	97	115	149
 10 in	153	172	139	165	185
 15 in	174	188	172	183	194
 The average relative yields over five years were 69% for the low irrigation treatment and 90% for the medium treatment.
Good yield increases were obtained for the last increment of water for corn which is why most producers try to fully irrigate.
Relative corn grain yields are shown in Figure 2.
2005-09 Relative Corn Yield
 2005 2006 2007 2008 2009
 Figure 2.
Relative corn grain yields 2005 through 2009.
Dry bean yields are shown in Table 3.
During 2006, herbicide damage decreased plant vigor and delayed maturity but because of a warm and late fall beans did mature before frost.
Maturity was not affected, but overall yield potential was decreased compared to other years.
Table 3.
Dry bean yields at Scottsbluff.
Irrigation	2005	2006	2007	2008	2009
 0 in	1,000	400	300	300	1500
 4 in	2,140	1,310	1,050	1562	2280
 8 in	2,580	1,560	1,640	1783	2660
 12 in	2,560	1,800	2,265	2160	2950
 For dry beans, average relative yields over five years were 71% for the 4 in treatment and 87% for 8 in irrigation.
As with winter wheat, in more normal years, the 8 in application would normally produce 90% of maximum yields.
Relative yields are shown in Figure 3.
2005-09 Relative Dry Bean Yields
 Figure 3.
Relative dry bean yields for 2005 through 2009.
Spring canola yields are shown in Table 4.
Canola was not grown until 2006.
Canola is a new crop for the area and yields did improve after our first learning year determining appropriate cultural practices, especially planting date and irrigation.
Yield levels are good for this area and compared to major canola regions in the southern Canadian provinces and the Northern Great Plains but are not as high as could be obtained with winter canola grown in climates with
 less extreme winters.
The problem with winter canola is that it does not fit these rotations well.
The only crop it can follow is winter wheat as it must be planted in mid-August.
It also is subject to winter-kill about 50% of the time in this area.
Table 4.
Spring canola yields.
Irrigation	2006	2007	2008	2009
 0 in	1,000	1,000	300	2450
 4 in	2,050	2,040	1562	2650
 8 in	2,110	2,485	1783	2630
 12 in	2,140	2,740	2160	2650
 The average relative yields for canola over four years were 82% for the low irrigation treatment and 92% for the medium treatment.
These higher yields reflect the ability of canola to use residual soil moisture from the 3 to 4 foot depths not used by the previous dry bean crop.
Soil water data shows that canola effectively roots to 5 feet at this site.
Canola has the potential to fit in limited irrigated rotations and is a viable oil seed crop for this region as it produces about twice as much oil per acre than soybean.
Relative yields are shown in Figure 4.
2006-09 Relative Canola Yields
 Figure 4.
Relative canola yields for 2006 through 2009.
The data confirm much of the previous research on limited irrigation in higher rainfall regimes.
The shape of the irrigation response functions  was generally curvilinear but they were much steeper than those at North Platte.
Because three of the five years of this experiment received precipitation that was on average only 66% of the 30-year average, it was a severe test and there were much higher responses between the medium and high irrigation level than in the North Platte research.
Winter wheat is a drought tolerant crop, but in this environment  it has a 20% higher yield potential and will respond to additional water to reach that maximum yield level.
At the lowest irrigation levels, most crops yields were only 45-50% of maximum yield except canola which produced at 76%.
At the medium irrigation level corn, dry beans and wheat produced 7075% of maximum yield whereas canola produced 90%.
The data provide an excellent basis for determining the economic value of irrigation water and show the potential of no-till limited irrigated systems to sustain higher levels of productivity than most producers would deem possible with much less water than they have become accustomed to.
Dr.
Brent Black, USU Extension Fruit Specialist, Dr.
Robert Hill, USU Extension Irrigation Specialist, and Dr.
Grant Cardon, USU Extension Soils Specialist
 Proper irrigation is essential to maintaining a healthy and productive peach orchard.
Over irrigation slows root growth, increases the potential for iron chlorosis in alkaline soils, and leaches nitrogen, sulfur and boron out of the root zone leading to nutrient deficiencies.
Over irrigation can also induce excessive vegetative vigor.
Excessive soil moisture also provides an environment ideal for crown and collar rots.
Applying insufficient irrigation water results in drought stress and reduced fruit size and quality.
Peach fruit development occurs in three phases.
In the first phase, fruit size increases primarily due to cell division.
During the second "pit hardening" phase, there is little increase in fruit size.
The third phase from pit hardening to harvest is marked by rapid fruit growth which results from cell expansion.
This third phase cell expansion requires ample available water, and occurs during the hottest and driest summer conditions.
Properly managing irrigation is analogous to managing money.
In addition to knowing your current bank balance , it is important to track both expenses  and income.
Bank Balance 
 How big is my bank account?
Water holding capacity
 Field Capacity is the amount of water that can be held in the soil after excess water has percolated out due to gravity.
Permanent Wilting Point is the point at which the water remaining in the soil is not available for uptake by plant roots.
When the soil water content reaches this point, plants die.
Available Water is the amount of water held in the soil between field capacity and permanent wilting point.
Allowable Depletion  is the point where plants begin to experience drought stress.
For peaches, the amount of allowable depletion, or the readily available water represents about 50% of the total available water in the soil.
The goal of a well-managed irrigation program is to maintain soil moisture between field capacity and the point of allowable depletion, or in other words, to make sure that there is always readily available water.
Figure 1.
Soil water content from saturated to dry.
Optimal levels for plant growth are between field capacity and allowable depletion.
The amount of readily available water is related to the effective rooting depth of the plant, and the water holding capacity of the soil.
The effective rooting depth depends on soil conditions, variety and rootstock.
Although peach roots can grow to several yards depth, nearly all of the roots of a mature tree are typically in the top 2 feet.
The water holding capacity
 within that rooting depth is related to soil texture, with coarser soils  holding less water than fine textured soils such as silts and clays.
A deep sandy loam soil at field capacity, for example,
 would contain 1.8 to 2.25 inches of readily available water in an effective rooting depth of 3 feet.
Table 1.
Available water holding capacity for different soil textures, in inches of water per foot of soil.
Available water is the amount of water in the soil between field capacity and permanent wilting point.
Readily available water is approximately 50% of available.
Soil Texture	Available	Readily available 
 	2 ft root depth	3 ft root depth
 Sands and fine sands	0.5 0.75	0.5 0.75	0.75 1.13
 Loamy sand	0.8 1.0	0.8 1.0	1.2 1.5
 Sandy loam	1.2 1.5	1.2 1.5	1.8 2.25
 Loam	1.9 2.0	1.9 2.0	2.85 3.0
 Silt loam, silt	2.0	2.0	3.0
 Silty clay loam	1.9 2.0	1.9 2.0	2.85 3.0
 Sandy clay loam, clay loam	1.7 2.0	1.7 2.0	2.6 3.0
 Figure 2.
The amount of allowable depletion, or the readily available water, represents about 50 percent of the total available water.
What's in the bank?
Measuring Soil Moisture
 In order to assess soil water content, one needs to monitor soil moisture at several depths, from just below the sod layer or cultivation depth , to about 70 percent of effective rooting depth.
One of the more cost effective and reliable methods for measuring soil moisture is by electrical resistance block, such as the Watermark sensor.
These blocks are permanently installed in the soil, and wires from the sensors are attached to a handheld unit that measures electrical resistance.
Resistance measurements are then related to soil water potential, which is an indicator of how hard the plant roots have to "pull" to obtain water from the soil.
The handheld unit reports soil moisture content in centibars, where values close to zero indicate a wet soil and high values represent dry soil.
The relationship between soil water potential and available water differs by soil type.
The maximum range of the sensor is 200 centibars, which covers the range of allowable depletion in most
 soils.
The sensors are less effective in coarse sandy soils, and will overestimate soil water potential in saline soils.
Remember that allowable depletion is 50% of available water, which roughly corresponds to soil water potentials of 50 centibars for a loamy sand soil, and 70 centibars for a loam.
Table 2.
Recommended WatermarkTM sensor values at which to irrigate.
Soil Type	Irrigation Needed
 Loamy sand	40 50
 Sandy loam	50 70
 Silt loam, silt	70 90
 Clay loam or clay	90 120
 TM Watermark is a registered trademark of Irrometer, Co., Riverside, CA.
Water is lost from the orchard through surface runoff, deep percolation , evaporation from the soil surface, and transpiration through the leaves of the plant.
Of these, the biggest losses are typically due to evaporation and transpiration, collectively known as "evapotranspiration" or ET.
Deep percolation from excess irrigation can be another large loss.
Estimates of ET are based on weather data, including air temperature, relative humidity and wind speed.
Some weather stations in Utah are programmed to calculate and report the ET estimates for alfalfa as a reference crop (ETref or ET2.
The ET of your crop can be determined by multiplying the ET, by a correction factor
 or crop coefficient  that is specific to your crop and its stage of development.
ETcop =ET, x Kecop
 The Kcrop for peach is shown in Figure 3.
At full bloom , a peach orchard is using about 20% of the amount of water used by the alfalfa reference crop.
Water use increases gradually as the canopy develops until the full canopy is established  when water use is 95% of a reference alfalfa crop.
Water use increases slightly during fruit ripening, then drops below 90% after fruit harvest.
Water use increases again during the late season then declines during leaf senescence.
Typical weekly ET, values are shown in Table 3.
Calculated ET, for your location can be determined by accessing weather data from a nearby weather station at the following Web site:
 Table 3.
Typical weekly alfalfa reference evapotranspiration  values for Utah locations.
Location	May	June	July	August
 Logan	1.38	1.83	1.94	1.68
 Ogden	1.48	1.98	2.10	1.80
 Spanish Fork	1.48	1.94	2.08	1.74
 Santaquin	1.47	1.92	2.03	1.67
 Moab	1.63	2.08	2.19	1.87
 Cedar City	1.57	1.95	2.04	1.74
 St.
George	1.95	2.40	2.53	2.02
 Figure 3.
Crop coefficients for peach, based on an alfalfa reference ET.
Adapted from Johnson et al..
Income Irrigation and Rainfall
 In Utah's high elevation desert climate, rainfall contributes a small fraction of the in-season water requirements of the crop.
Therefore, regular irrigation is needed to supply orchard water needs.
This irrigation water can be supplied by flood, furrow, impact sprinklers, drip lines or microsprinklers.
Whichever irrigation system you utilize, it is important to calibrate your system SO that you know precisely how much water is being applied.
With sprinklers and microsprinklers, the simplest way to do this is to place catch cans in multiple locations in your planting and collect water for a set period of time.
The amount of water collected over time will give you an application rate , and differences in water collected among the catch cans will tell you how uniform the application is within your planting.
When trying to determine application uniformity, it is best to measure output at both ends of your irrigation system.
Also, if your planting is on a slope, you should measure output at the highest and lowest points of your field.
Elevation differences and the distance the water travels through the irrigation lines both affect water pressure, and consequently the flow rate at the nozzle.
If you have trickle irrigation, you can place catch cans under the emitters and determine flow rate for each emitter.
Flow rate from each emitter and emitter spacing can be used to calculate rate per area.
The efficiency of your system is a measure of how much you have to over water the wettest spots in the orchard to get adequate water to the dry spots.
Efficiency is related to the uniformity of application and to the amount of evaporation that occurs before the water can move into the soil.
A well-designed microsprinkler or drip system can be 70 to 90% efficient.
Overhead sprinkler systems are typically 60 to 75% efficient, while flood and furrow irrigation is typically 30 to 50% efficient.
Following is an example of how to calculate water needs for a mature peach orchard just prior to fruit harvest.
The orchard is on a deep sandy loam soil with row middles planted to grass cover.
ETr values are 2.10 inches per week.
Crop coefficient is 0.98.
= ET, X Kcrop
 crop = 2.10 inches/week * 0.98=2.06 inches/week
 Soil storage capacity 
 The total storage capacity for readily available water over the 2-foot effective rooting depth is 1.5 inches.
1.5 inches / 2.06 inches per week = 0.73 weeks or 5.1 days between irrigations
 Restated, the soil moisture in the rootzone will go from field capacity to plant stress levels in 5 days.
To recharge the soil profile, you will need to add 1.5 inches of water.
Assuming a microsprinkler irrigation system with an efficiency of 80%, 1.9 acre inches of water application will be required per acre for each watering.
Good irrigation management requires:
 1.
An understanding of the soil-plant-water relationship
 2.
A properly designed and maintained irrigation system, and a knowledge of the efficiency of the system
 3.
Proper timing based on
 a.
Soil water holding capacity
 b.
Weather and its effects on crop demand
 C.
Stage of crop growth.
Each of these components requires a commitment to proper management.
Proper management will lead to the maximum yields per applied irrigation water, and will optimize the long term health and productivity of your orchard.
A new Web tool uses the science of crop simulation crop modeling and information technology to help make smarter irrigation decisions with less effort from producers.
MOBILE DRIP IRRIGATION RESULTS FROM FARM DEMONSTRATION SITES
 The High Plains Aquifer of western Kansas is in decline.
Each producer usually has different points of view in addressing this issue since they have different economic situations, management philosophies and locations.
However, one thing is common, many producers are seeking new methodologies and technologies to extend the useable aquifer life and limit the economic impact of loss of aquifer pumping capacity, such as improved soil water conservation practices, more efficient irrigation applications and deficit irrigation management strategies.
These methodologies include new mobile drip irrigation  technology systems, irrigation scheduling tools such as soil moisture sensors, and telemetry in the monitoring equipment, among others.
The producers were looking for visible proof as to which of these methodologies were going to work for their particular objectives and locations.
Several producers stepped up and offered their farms to demonstrate the methodologies that they are seeking to adopt in order to address a specific objective in their operation.
These producers approached the K-State Research Extension , Kansas Water Office and other government and private entities
 to help them in the design, installation, and monitoring of the demonstration farms also known as the Water Technology Farms.
Thus, in 2016 cropping season three WTFs were established which also corresponds with objectives of the Kansas Water Vision.
They are demonstration farms that allow the installation and testing of the latest irrigation technologies on a whole field scale.
The concept of using driplines on center pivot  system is not new.
T-L Irrigation, Inc.
experimented with this idea in the early 2000s, calling it precision mobile drip irrigation.
However, based on the studies of Olson and Rogers , no yield differences between the PMDI and CP were found.
They associated the lack of discernible impact to the relatively wet years of the study and inherent high variability in the field caused by factors beyond the control of the investigators.
The MDI was developed with the concept of combining the high efficiency but expensive subsurface drip irrigation  technologies and the relatively low-cost simple operation and maintenance of center pivot irrigation technologies.
Although, MDI should increase irrigation efficiency, a previous study on a similar product found more negative management issues than positive efficiency advantages.
However, a recent study using new MDI product lines in corn reported no significant differences in yield between MDI and in-canopy spray nozzles but better soil water storage under MDI.
In addition to potential irrigation efficiency improvement with MDI, there is producer interest in MDI as a potential water application system to help alleviate wheel track rutting issues,  which in turn would reduce erosion and improve field conditions.
The Water Technology Farms
 T&O Farms, LLC in Finney County  consists of 10 sprinkler systems, four equipped with MDI, and four equipped with low pressure spray nozzles.
There are four circles planted to sorghum and alfalfa that are set-up as paired field comparison of MDI and spray nozzles.
Each field has a soil water sensor.
The systems are fully automated with water use, groundwater levels, moisture sensor data and weather station data tied to a real-time website.
Other notable set-up and technology in the farm includes sorghum seeding rate plots, application of soluble polyacrylamide on soybean and corn, circular planting and the use aerial imageries for thermal and plant health assessment.
The Garden City Company/Dwane Roth Farm in Finney County  north of Holcomb consists of a circle with multiple modes and spacing of water application packages on its four outer spans.
These application packages include MDI on 30and 60-in spacing, i-Wob spray nozzle, and bubbler on 30and 60-in spacing.
The farm is unique as the water source is both ground and surface water.
The circle is planted circle to corn managed with a precision soil zoning package, uses soil water sensors and has aerial imageries for thermal and plant health assessment.
The ILS Farm in Pawnee County  is comparing MDI with regular spray nozzles on a higher utilizing volume irrigation wells than those wells being studied in Finney County.
Two corn circles are involved with the spray nozzles planted in typical straight rows with the other field is planted in circle.
Irrigation scheduling using weather-based and soil water sensors was utilized at this farm.
Figure 1.
The location of the three water technology farms in south central and southwest Kansas.
North of Finney county is The Garden City Co./Roth Farm and South of it is the T&O Farm.
The ILS Farm is in Pawnee County in the south central region.
Each of the farms had specific objectives when these WTFs were created.
Part of the principle was that each of these farms addresses a certain farming situation operating under a specific hydrologic condition.
The T&O Farm has a general objective of identifying the irrigation technologies that will help them conserve and extend the life of the Ogallala aquifer.
The GCC/Roth farm aims to evaluate the effectiveness of spray nozzles, i-Wob and MDI under its current water supply conditions.
The ILS Farm is about finding the most efficient irrigation water application package that will work well with an irrigation scheduling tool.
It is worth noting that the T&O and Roth Farms also have a very personal objective, to pass on the farming operations to the next generation of family members with the assurance that there is sufficient water for them to use to irrigate the crops.
T&O Farms, LLC is located 10 miles south of Garden City, KS and consists of 10 sprinkler systems, four equipped with MDI, and the rest are equipped with low pressure spray nozzles.
The systems are fully automated with water use, groundwater levels and soil water sensor data are transmitted to a real-time website.
Each field has at least one telemetric soil moisture sensor that is being monitored by a crop consultant.
For 2016, only seven of these field were directly monitored for its agronomic performance.
There are four circles in a section which are planted to sorghum and alfalfa.
These fields are set-up as paired field comparisons of MDI and spray nozzles.
Each circle has commercial soil water sensor and KSRE installed 5-ft access tubes for weekly manual soil water monitoring using CPN Neutron Probe.
This particular section has its aerial image taken at least eight times during the season in the thermal and the NDVI bands for a general health assessment.
One field of corn is planted in a circle and is irrigated with spray nozzle.
Soluble polyacrylamide  is applied throughout the irrigation systems on the east half of the circle and the other half is just water without PAM.
Both sections of the circle have separate soil water sensor and neutron access tubes.
Adjacent and similar to the corn field is a soybean field also planted in a circle irrigated with MDI.
Soluble PAM is applied by means of the irrigation systems on the east half of the circle and only irrigation water on the west.
Both sections of the circle also have separate soil water sensor and neutron access tubes.
One of the sorghum fields has several seeding rate population plots of 40,000, 60,000, 80,000, and 100,000 seeds per acre.
The Garden City Company/Dwane Roth Farm is located 5 miles north of Holcomb in Finney County and consists of a circle with multiple modes and spacing of water application packages on its four outer spans.
These application packages include MDI on 30and 60-in spacing, i-Wob spray nozzle, and bubbler on 30and 60-in spacing.
Telemetric soil water sensors and neutron access tubes were installed and monitored in each of the spans.
The farm is unique as the water source is both ground and surface water when there is water delivered through the canals.
The field is planted in circle to corn using a GPSequipped tractor.
The ILS Farm in Pawnee County is comparing MDI, to regular spray nozzles on a higher volume well than those wells being studied in Finney County.
Two corn circles were involved; the South circle was fitted with spray nozzles and planted in typical straight rows and the North circle has its three outer spans fitted with two sets of application packages and planted in circle.
Half of the spans has MDI and the other half has spray nozzles.
To verify the discharge, four drops in each span has water meters installed.
Irrigation scheduling using weather-based and soil water sensors was implemented on this farm.
The farm has significantly reduced the water used for 2016.
At the end of the season, they used 1151 ac-ft of water against their allocated 1511 ac-ft or around a 23% reduction.
The combination of all the technologies and management practices they employed probably helped in optimizing their use of water.
The producer expressed that when they are making a decision, they had higher confidence in their decision if they could see all the parameters in one location, i.e.
they could see in real time the water use, soil water status, static water level and weather conditions from their computer and mobile device.
As of writing of this report, not all yield data and other farm information has been shared by the producer yet.
In particular, we do not have the data yet in the paired field comparing the two water
 application packages.
Based on our ocular observations, there seems to be no difference in the general stand, growth and yield of both crops in the field.
Part of the reason is that the area received a relatively high amount  of rainfall last year.
Nonetheless, this also suggests that at the least both application packages are performing well as designed.
The field with soluble PAM showed significantly higher soil water content from 3ft below the surface and deeper.
Apparently, the water applied with PAM infiltrates better and deeper into the soil.
After the last irrigation, we took hand samples from both sides of the field to estimate corn yield.
There was significant difference between the two, with the PAM side yielding 259 bu/ac while the other side has only 235 bu/ac.
However, it was reported to us by the producer that by the time the field was harvested with a tractor combine, they only got a field average of 218 bu/ac.
They noticed that there were some nematode issues in certain parts of the field.
The yields from the seeding rate plots were almost identical across the different rates.
As expected with a sorghum plant, seeds per head tend to compensate depending on the density of the plants.
The 40,000 seeding rate was not significantly different from 100,000 or any other seeding rates.
However, we observed a notable weed pressure in the 40,000 seeding rate plots but not on any other plots.
Figure 2.
Soil water content  at the circle at different depths for with and without liquid polyacrylamide  application.
Red  bars are without PAM on the west of the circle and the blue  bars are with PAM.
Figure 3.
Grain yield of sorghum at different seeding rates.
The Garden City Company/Dwane Roth Farm
 The farm received a total of 25.2 inches of rainfall during the cropping season which is more than 7 inches above normal.
That factor alone made it impossible to detect any differences in soil water content and yield between the different application packages.
With that amount of rainfall, the effect of water quality was also masked.
Only 11 inches of irrigation was applied to the field.
The field average yield was 228 bu/ac.
The producers reported to us that they learned a lot in using the technologies during the first year.
They were highly impressed at the information they received from the soil water sensors which gave them confidence to shut down their system for several days when they saw adequate soil water.
They noted difficulty in circular planting and despite all the adjustments that they made, the MDI driplines were still getting caught in the canopy of the corn plants.
The farm received a total of 17 inches of rainfall during the cropping season.
The total depth of irrigation they applied was 13.5 inches to the South field and 14.1 inches to the North field.
The yields from both fields and treatments were not significantly different  whose values ranged from 222 bu/ac in the South field and 235 bu/ac for the MDI in the North field.
The average yield from the tractor combine was 200 bu/ac for both fields.
Looking at the soil water on both fields, it appears that irrigation applied by spray nozzles on the South field was deeper into the soil profile.
However, when we checked into our notes, this disparity could be associated with the change in soil type at this depth.
We noted that during the installation of the neutron access tubes, the soil changed from sandy loam to loamy sand at the depth of 3 ft and below.
We decided to install the tube anyway because it was a lot better than having a completely loamy sand from top to bottom observed at several other spots of the field.
Figure 4.
Corn yields at the different treatments at the ILS farm.
Figure 5.
Water content  at the MDI and Spray treatments in the ILS farm measured using a neutron probe.
The Water Technology Farm concept is a great way to showcase and assess the performance of the new technologies and management practices in the vicinity of the producers' own farms.
If proven effective, producers are more receptive to change and adopt the new technologies or practice if they see it working in their area at the scale that they are operating.
As researchers and extension specialists, we see water technology farms as an expansion of the research going on at our research plots and an opportunity to educate the producers about the science behind the technology and practices.
As part of the establishment of the water technology farms a field day was held on each farm as part of its educational component.
Field days was deemed very successful on these farms because in addition to the large attendance, there was a general atmosphere of inquisitive attitude among all the people who were there.
The field days fostered good conversation between producers and managers to the point that many remained talking in the field an hour or two after conclusion of the program.
One year of data is not enough to make conclusive statements since all three fields received normal to above normal rainfall.
It is evident that all the technologies tested are performing as expected under last year's condition.
But again, nothing conclusive could be said.
However, one year is long enough to start identifying their advantages as well as the challenges that may have to be addressed.
For example, it is imperative that to maximize the full potential of an MDI in tall row crops, fields must be planted in circles.
We are seeing that despite the GPS technology installed in many tractors, some of them are not yet capable of planting precisely in a perfect circle.
Improvements have to be made either on the MDI system or the GPS guided tractor, or both.
Donors to the water technology farms: Kansas Water Office; United Sorghum Check-Off Program; Kansas Corn Commission; Seaman Crop Consulting, SW KS GMD No.
3; Kansas Department of Agriculture; Conestoga Energy Partners; Teeter Irrigation; MDI; Helena; Kansas Geological Survey; Ogallala Aquifer Program; Syngenta; Hortau; Servi-Tech Expanded Premium Services, LLC; Kansas Farm Bureau; KSU Mesonet; K-State Research and Extension; AquaSpy; Kansas Grain Sorghum Commission; Crop Metrics; Netafim; Valley Irrigation; Garden City Coop; American Irrigation; WaterPACK; Pioneer HiBred International; Western Irrigation Supply House and Ag Systems, Inc.; and Presley Solutions.
EM 8901 Revised January 2013
 Drip Irrigation Guide for Onion Growers
 Malheur Experiment Station, Oregon State University: Clint C.
Shock, director and professor; Rebecca Flock, former research aide; Erik Feibert, senior faculty research assistant; Cedric A.
Shock, former research aide
 S ince 1992, the Oregon State University Malheur Agricultural Experiment Station in Ontario, Oregon, has evaluated drip irrigation on onion.
As pioneers in onion drip irrigation, we have investigated crop response to irrigation intensity and flow rate, bed configuration, subsurface chemigation, nitrogen fertilizer rates, microirrigation criteria, and plant population.
As a result of this research, distinct advantages of drip irrigation have become available to growers.
These advantages include lower fertilizer costs; significant reductions in water use and nitrate leaching; increased control of insects, iris yellow spot virus, and weeds; and increased onion size and marketable yield.
Drip irrigation is expected to exceed 50 percent of Treasure Valley onion crop acres in 2013.
Clearwater Supply, Ontario, Oregon: Jim Klauzer
 Drip systems are tailored to each crop and field.
Growers have many options for custom fitting a drip system to their specific situation.
It is difficult to describe in a brief publication all of the factors that affect irrigation.
Thus, this publication provides a framework, general recommendations, and rationales to aid onion growers interested in maximizing their land use and crop yield through drip irrigation.
Consult your local extension agent or other agricultural professional for additional information.
In 1989, northern Malheur County was declared a groundwater management area due to groundwater nitrate contamination.
The groundwater contamination was linked, at least in part, to furrow irrigation of onion.
In arid regions, all irrigation systems require some leaching fraction to avoid salt accumulation.
However, the high nitrogen fertilizer rates used through the 1980s, combined with heavy water applications to furrow-irrigated onion, allowed nitrate and other mobile compounds to be lost readily to deep percolation.
Surface erosion also posed a problem.
In an effort to find an alternative method of irrigating crops with high water demands in an
 arid region, we considered drip irrigation.
Drip irrigation is the slow, even application of lowpressure water to soil and plants using plastic tubing placed directly at the plants' root zone.
This method allows very little evaporation or runoff, saves water by directing it more precisely, reduces the transmission of pathogens, and produces fewer weeds.
High onion yields are feasible with furrow irrigation on level, even-textured fields without investment in drip irrigation.
However, variable topography or soil textures make furrow or sprinkler irrigation difficult.
Drip irrigation can irrigate these difficult fields uniformly, thus maximizing land use and crop yield.
When designing a drip system, first identify fairly similar irrigation zones.
Irrigation zones are based on factors such as topography, field length, soil texture, optimal tape run length, and filter capacity.
Many irrigation system suppliers use computer programs to easily analyze these factors and design drip systems.
Once the zones are assigned and the drip system designed, it is possible to schedule irrigations to meet the unique needs of each zone.
Because onions have very strong positive yield and grade responses to wet soil, yet exhibit increased risk of decomposition in overly wet soil, it is indispensable that the drip system be carefully designed to apply water uniformly.
Yield is lost in excessively dry areas, while disease and nitrate leaching are promoted in excessively wet areas.
The minimum water application uniformity for onion is 90 percent.
The bed configuration used in many of our studies has proven effective for Sweet Spanish onion.
Two double rows per 34to 44-inch bed
 Figure 1.
Typical bed configuration for dripirrigated onions.
On 44-inch beds, two double rows are centered 18 inches apart.
Double rows consist of two onion rows spaced 3 inches apart.
Drip tapes are installed 3 to 4 inches deep in the bed center.
Tape emitters are 12 inches apart.
are planted in late March at 150,000 seeds/acre.
The 44 inches is the distance between the furrows.
Double rows are centered 18 inches apart and consist of two onion rows spaced 3 inches apart.
Drip tapes are installed 2 to 3 inches deep in the bed center, between the two double rows, at the time of planting.
The tape emitters are spaced 8 to 12 inches apart.
This bed configuration minimizes tape use and cost per acre.
However, this configuration can be problematic if the water fails to "sub" or move over to the onion rows.
Alternative bed configurations have been used successfully, especially in soils where the water will not wick to the side sufficiently for one tape to serve a conventional bed.
The use of three drip tapes with six double rows of onions on 78to 88-inch beds is locally called "intense bed." One double row is planted on either side of each tape SO that the onion rows are closer to the drip tapes.
Closely related to bed configuration is the issue of plant spacing and population.
Over the past few decades, the advent of larger market size classes-colossal  and super colossal -has led to new considerations in plant population and spacing.
Because the entire top of the onion bed is wetted under drip irrigation, growers initially assumed that more onions could be planted per acre by spacing them closer together.
This approach succeeds in increasing the total number of onions, but the crowded spacing can result in a greater number of smaller, lower value onions.
To optimize financial returns, one must consider the influence of plant population on bulb size.
Research at the Malheur Experiment Station showed that onion bulb size distribution is closely related to plant population.
Colossal and super colossal onion yields are favored by low plant population and less plant competition.
In our research, comparatively higher populations resulted in greater numbers of medium and jumbo onions, as well as greater total marketable onion yield.
It is difficult to predict the optimum onion plant population in any year due to price variability.
Onion prices vary by size class depending on availability, which depends on weather in several production areas.
Onion prices can increase with increasing bulb size.
However, when the market does not favor super colossal and colossal onions, gross returns are correlated more with total marketable yield.
Every trickle counts when you are battling a water shortage.
An ineffective or improperly managed filter station can waste a lot of water and threaten a drip system's fitness and accuracy.
In the West, sand media filters are used extensively for drip irrigation systems.
Screen filters and disk filters are common alternatives or for use in combination with these filters.
Sand media filters provide filtration to 200 mesh, which is necessary to clean surface water and water from open canals for drip irrigation.
These water sources pick up a lot of fine grit and organic material, which must be removed before the water passes through the drip tape emitters.
Sand media filters are designed to be selfcleaning through a "back flush" mechanism.
This mechanism detects an increase in the pressure differential between input and output of the filter due to the accumulation of filtered particles.
It then flushes water back through the sand to remove clay, silt, and organic particles.
Some back flush mechanisms are based on elapsed time or a combination of elapsed time and pressure differential, rather than on pressure differential alone.
Sand used for filters should be between size 16 and 20 to prevent excessive back flushing.
It may be better to use several smaller sand media filters rather than a few larger tanks SO that clean water is available for the flush.
Sand media needs to be replaced every two or three seasons.
In addition to a sand media filter, a screen filter can be used as a prefilter to remove larger organic debris before it reaches the sand media filter, or as a secondary filter before the irrigation water enters the drip tape.
For best results, screens should filter out particles four times smaller than the emitter opening, as particles may clump together and clog emitters.
Screen filters can act as a safeguard if a problem occurs with the main filters.
They also may act as the main filter if a sufficiently clean underground water source is used.
However, some groundwater contains enough particulate matter to require a sand media filter.
Secondary filters often are omitted if the drip tape is replaced annually.
Figure 2.
Drip irrigation system with a prefilter, pump station with backflow prevention, and chemical injection site.
The chemical injection site should be after the main filter station.
A pressure control valve is recommended to adjust the water pressure as desired before it enters the drip lines.
A water meter can be placed after the pressure control.
Vacuum relief is necessary between the solenoid valve and the drip tapes to avoid suction of soil into the emitters when the system is shut off.
A water flow meter should be an integral part of the system, and each zone's gauge should be recorded regularly.
This provides a clear indication of how much water was applied to each zone.
Water flow records can be used to detect deviations from the standard flow, which may be caused by leaks in the system or by clogged lines.
Leaks can occur unexpectedly as a result of damage by insects, animals, weeding crews, or farming tools.
Systematically monitor the lines for physical damage.
It is important to fix holes as soon as possible in order to maintain system uniformity.
Chlorine clears clogged emitters
 If the rate of water flow progressively declines during the season, the tape may be slowly plugging, resulting in severe damage to the crop.
The application of chlorine through the drip tape will help minimize clogging.
Because algae growth and biological activity in the tape are especially high during June, July, and August, chlorine usually is applied at 2-week intervals during these months.
Buffering the irrigation water to below pH 5.0 increases chlorine activity significantly.
Use chlorine applications in moderation SO that the chlorine cleans the emitters without affecting the soil environment.
If drip lines become plugged in spite of maintenance, many cleaning products are available through irrigation system suppliers.
Choose a product appropriate for the specific source of contamination.
In addition to the use of chlorine and maintaining the filtering stations, flush the drip lines once a month by opening the bottom ends of a portion of the tapes at a time and allowing the higher velocity water to wash out the sediment.
Daily crop water use
 Irrigation application must reflect crop water use.
Therefore, it is crucial to plan how much water to apply and when to apply it to optimize efficiency.
Water applied at any one irrigation should not exceed the soil's water-holding capacity.
Different combinations of intensity, frequency, and flow rates can be customized to meet varying irrigation needs within a field.
During each irrigation the wetting pattern needs to reach or pass the base of the onion plants most distant from the drip tape.
The first irrigation of the season establishes the wetting pattern and often is 24 to 36 hours long.
Fine silts or salts in the soil can be moved laterally with the initial wetting front, and they can become fixed when the water ceases to move outward.
Expanding a wetting pattern beyond this initial boundary can require an excessive amount of water.
Once growers monitor the initial irrigation for the desired wetting pattern, subsequent irrigation sets should maintain the previously established wetting pattern.
Onion plants growing beyond the wetting front usually have smaller bulb size.
The use of automated zone control greatly aids in maintaining an adequate wetting zone.
By pulsing the water in shorter sets, many times a limited amount of water can establish a larger wetted sphere than longer sets.
Water applied per irrigation and irrigation frequency
 Low-application, high-frequency irrigation has been identified as the ideal irrigation strategy for maximizing plant growth.
Growers can expect to irrigate drip-irrigated fields more frequently than furrow-irrigated fields.
The typical range for drip irrigation frequency is 1 to 2 days.
One reason for the need for more frequent irrigation with drip systems is simply that less water is applied per irrigation cycle.
Also, moisture may be wicked away from the root zone as the irrigated plots and surrounding dry soil equilibrate.
Since irrigations are small, drip irrigation causes significantly less erosion, less deep percolation, and less leaching than furrow irrigation.
Drip irrigation permits greater control and precision of irrigation timing and the amount of water applied.
This flexibility to tailor a schedule based on local soil water tension , thus precisely matching crop needs, may be the greatest advantage of drip irrigation.
Irrigation frequency depends on the water applied: the lower the amount, the higher the frequency.
The amount of water applied per irrigation is governed by the duration of the irrigation and the flow rate.
The irrigation application and frequency should be planned to keep the SWT at an optimal level without excessive leaching.
An onion irrigation amount and frequency study in 2002 and 2003 showed that the optimum amount on silt loam was no less than 1/2 inch per irrigation.
Amounts of 1/8, 1/4, and 1/16 inch per irrigation offered little or no advantage and slightly reduced the yield of colossal and super colossal onions.
Practical limitations of the highfrequency, low-application principle include
 excessive mainline drainage from very frequent irrigations and the need to dedicate water sources to one field.
The duration of the irrigations should be shortened if the second foot of soil is becoming very wet.
The duration of the irrigations should be lengthened if the wetting front is not reaching from the drip tape all the way to the base of the onion plants.
The drip tape emitters determine the flow rate of water into the plot.
Drip tapes with lower water application rates make low-intensity, high-frequency irrigations more feasible by improving wetting pattern and uniformity.
Low flow.
Ultra-low-flow emitters reduced the yield of the largest bulb size class compared to low-flow emitters.
Ideal emitter flow rates depend on the soil type.
Coarser soils usually require higher emitter flow rates.
Why measure soil water tension?
Soil water tension  is the measure of how strongly water is held in the soil.
Onion yield and grade are related to the amount of energy needed for plant roots to remove water from the soil.
SWT also provides information on soil saturation, which can help growers avoid saturating the soil, thereby maintaining aeration of plant roots and reducing leaching losses of water or nutrients.
These factors make irrigation by SWT economically and environmentally important.
Viewed in graphical form, the SWT clearly indicates the relative condition of the root zone of the crop over time.
The use of granular matrix sensors and tensiometers to determine crop water needs is
 discussed in Irrigation Monitoring Using Soil Water Tension, EM 8900.
Based on a 2-year study at the Malheur Agricultural Experiment Station , it is recommended that drip-irrigated onion in the Treasure Valley on silt loam be irrigated when SWT at the 8-inch depth reaches 20 centibars.
Note that lower numbers indicate wetter soil.
This recommendation is based on several factors.
Research has shown that onion yield, size, and therefore profit, increase with decreasing soil water tension.
In 1998, the highest yield and profit were in plots irrigated when the SWT was 10 cb.
However, in 1997, onions irrigated at 10 cb displayed increased decomposition during storage.
Depending on the year, onions irrigated at the lowest  soil water tension could be subject to longer periods of excessively wet soil, thereby promoting disease.
Furthermore, fields irrigated at soil water tensions wetter than 17 cb exhibited deep percolation of water and increased risk of nitrate leaching.
Thus, the optimum SWT for maximizing profit and yield for the Treasure Valley grower producing onion on silt loam should be closer to 20 cb.
This threshold takes into account the difficulty of predicting effects on storage quality and on the environment.
Irrigation at 20 cb or slightly drier minimizes decomposition in storage.
A pattern of water use
 Onions use very little water from the time they are planted through May.
Water use slowly increases until early July, at which time the irrigation frequency must be increased to meet onion plant water needs.
At some time in early August, water use starts to decrease, SO the frequency of irrigations needs to start decreasing to avoid over-irrigation.
Irrigation and fertilization should be managed together to optimize efficiency.
Chemigation through drip systems efficiently deposits chemicals in the root zone of the receiving plants.
Because of its precision of application, chemigation can be safer and use less material.
Several commercial fertilizers and pesticides are labeled for delivery by drip irrigation.
Injection pumps with backflow prevention devices are necessary to deliver the product through the drip lines.
These pumps allow for suitable delivery rate control.
Backflow prevention protects both equipment and the water supply from contamination.
Other safety equipment may be required; contact a dripirrigation system supplier for details.
Soil microorganisms convert nitrogen  fertilizers to nitrate.
Nitrate is water soluble, available to plants, and subject to leaching loss.
Since nitrate loss management was one of the initial reasons for exploring drip irrigation, it is appropriate that we revisit this topic.
When growers observed very high onion yields under drip irrigation, many assumed that greater yields would require increased N fertilizer.
In fact, no more N than usual is required.
Typically, less is needed because the fertilizer is spoon-fed to the root system with very limited loss.
Nitrogen fertilizer normally is applied at a little more than half the customary rate because it is supplied directly to the root system and is not leached immediately from the root zone.
Furthermore, studies on furrowand dripirrigated onion have shown that N often is not the most limiting factor in Treasure Valley onion growth and therefore is not required to the extent that was previously thought.
In a 3-year drip-irrigated study, N rate had no significant effect on onion yield, grade, or gross
 returns, but the irrigation water contained some nitrate.
Consult Nutrient Management for Sweet Spanish Onions in the Pacific Northwest  to calculate whether N fertilization is needed to fully meet the onion crop's needs.
Root tissue sampling allows for initially conservative N applications followed by N application via chemigation as needed.
This has proven to be an effective means of achieving high yields.
Systemic insecticides sometimes are used in drip systems for enhanced insect and nematode control.
Normally, the product is introduced in the middle of the irrigation set, allowing a clean water period to push the product out of the drip tape and closer to the crop.
In some instances, a pH-buffering agent is needed to enhance the effectiveness of insecticides.
A second injection pump is required for a pH-buffering agent.
Funding to help prepare this publication was provided by a grant from the Oregon Watershed Enhancement Board Grant.
Drip irrigation is the slow, even application of low-pressure water to soil and plants using plastic tubing placed near the plants' root zone.
Drip irrigation systems facilitate water management in fields that are difficult to irrigate due to variable soil structure or topography.
Onion yield and grade respond very sensitively to irrigation management.
Recommended soil water tension for irrigation onset for drip-irrigated onion is 20 centibars  on silt loam.
Seasonal water needs for drip-irrigated onion are 28 to 32 inches, depending on the year.
"Soil water potential" is the negative of "soil water tension." A soil water potential of -20 cb is the same as a soil water tension of +20 cb.
Also, cb is the same as kPa.
Drip systems require careful design and maintenance.
2013 Oregon State University.
Trade-name products and services are mentioned as illustrations only.
This does not mean that the Oregon State University Extension Service either endorses these products and services or intends to discriminate against products and services not mentioned.
Orange Sizes and Irrigation
 tests in Riverside County indicate irrigation practices may have influence on fruit size
 The most important single factor that an orange grower can control and utilize to improve fruit sizes is the application of irrigation water.
Other factors which affect the size of oranges-such as air temperatures, winds, rain or the lack of it and time of bloomare uncontrollable for the most part and there is little a grower can do about them.
There are certain other factors, however, such as irrigation, cultivation, and fertilization over which the grower does have some degree of control.
There are many conditions in irrigation which affect the fruit sizes in an orchard.
Penetration of water into the soil is one of the most important, and the length of the irrigation run and methods of applying water have a decided effect upon penetration-particularly in the lower part of the orchard.
Length of the irrigation run must be considered when applying water to an orchard.
If a long irrigation run is not handled properly, the result will be small sizes on the bottom half of this run.
The longer the run, the longer it takes the water to reach the end of the rows, and therefore, the less time it has to penetrate the soil.
If water is held on the end of the run long enough to penetrate to a desirable depth, trees near the irrigation stands will receive more water than is needed, and usually leaching and loss of water occur below the root zone.
In cases where fertilizer is applied in the water, less fertilizer would be received by trees at the end of the run.
Fruit measurements were made in a series of studies to determine the effect on size of oranges on trees near the irrigation stand at the head of the row, and on trees near the end of the row.
Great differences were found in some groves during the experiment.
One grove near Corona had a 22-tree440 feet-irrigation run.
The fruit was measured on trees down the irrigation run, and then the average value by size was determined to give an average return per packed box.
Fruit Measurements Made in Orange
 Tree No.
Distance	Size	Per Packed
 from	from	Oranges	Box Based	on 1948
 Pipeline	Pipeline	Per Box	Prices by
 2	20 Ft	252	$1.63
 12	220	288	1.39
 21	400	344	1.21
 The above table shows that the difference between Tree 2 and Tree 21 was 42c a box.
This indicates improvement in water application would be desirable to bring up returns on the bottom half of the orchard.
Differences of two to three sizes were found on many groves between the top and the bottom of irrigation runs of 11 to 12 trees in length.
In another grove in the Corona area the fruit was measured on trees at the top and at the bottom of the irrigation run.
The average difference between sizes of fruit was about.25 of an inch, or about two packing sizes.
It was observed that there was a smaller number of fruits on the trees at the lower end of the irrigation run.
One of the best ways to shorten the irrigation runs is by adding additional pipelines; particularly on long runs of 15 trees or more.
Many growers use runs from six to 10 trees in length to improve water distribution and to get better water penetration.
Another method that can be used is the cut-back system, although it requires a little more hard labor and effort.
Where four or more furrows are used and after adequate penetration is secured in the tree furrow-for example, five to six trees down from the pipeline-the water can be run down the center furrows and then cut back into the tree furrow past the fifth or sixth tree.
The water runs easier with less loss from penetration in the center furrows, and therefore, excessive water loss around the top few trees is avoided.
This enables a grower to get the water to his trees farthest from the
 pipeline quicker and without excessive loss.
A pointed rod or probe can be used to measure the depth the water has penetrated in the tree furrow so that it can be determined when to switch the water to the center furrows.
A third method used to increased fruit size at the bottom of a run where water deliveries permit, is to use the alternate middle irrigation system.
If the irrigation time is normally 30 days, for example, one half of the water is applied every 15 days.
Every other middle between the trees is irrigated on one irrigation, then 15 days later the other, or dry middles, are irrigated.
By this method the soil is irrigated no more often than before, but the trees receive water twice as often.
This prevents stress upon the trees during hotter periods when the soil would normally dry out before a scheduled irrigation.
Fruit on trees at the upper end and at the bottom of the irrigation run were measured in a grove in Moreno Valley in which the grower used the alternate middle irrigation system.
The irrigation run was 15 trees long.
Fruit on trees on the bottom of the run in this particular case happened to be slightly larger than on the trees at the top, although the difference is not too significant.
The trees at the bottom of this run received sufficient water to prevent stress and loss of fruit sizes.
From the results of these studies it would seem that adequate penetration of moisture should be obtained on the lower half of an irrigation run.
With few exceptions, a better job of applying water usually can be done after a careful analysis of each individual situation.
At the present differential of price by size of citrus fruit, the improvement of one size can often make as high as 50 to $1.00 a box to the grower, particularly in the smaller size range.
C.
P.
Teague is Assistant Farm Advisor, Riverside County.
Tom Samples, Professor and John Sorochan, Associate Professor Plant Sciences
 Although water vapor accounts for less than 2 percent of the atmosphere's total volume, it is of utmost importance from the standpoint of weather and climate.
It is the primary absorber of solar energy and radiant energy from the earth.
It is also the source of all forms of precipitation and condensation.
Water vapor contains energy important for atmospheric circulation and affects the rate that water moves through plants into the atmosphere.
Turfgrasses vary in water-use rate, or the total amount of water required for growth, plus the amount of water transpired from the plant and evaporated from both the plant and soil surfaces.
The water-use rate is usually reported as evapotranspiration, or ET, and is measured in millimeters per day.
For example, bermudagrass, centipedegrass and Zoysia have a relatively low ET rate  compared to annual ryegrass, creeping bentgrass, Kentucky bluegrass and tall fescue.
Generally, the higher the air temperature and the drier the air, the greater the ET.
Wind accelerates water loss from turf.
Growth rate, aerial shoot
 density, leaf area and leaf position influence the resistance of a turf canopy to water loss.
Turfgrass ET = crop coefficient X pan evaporation
 The crop coefficient, with a value most often less than 1, varies among turfgrasses and geographic locations.
If, for example, the pan evaporation rate is a reported 1.9 inches / week and the tall fescue crop coefficient is an estimated 0.8, the weekly water requirement of a tall fescue turf is 1.9 inches X 0.8 or 1.52 inches.
One and one-half inches  of irrigation or rainfall are required to replace the amount of water lost through evapotranspiration during the week.
How Often?
Many variables deserve consideration when deciding how to set an automatic irrigation system.
These include turfgrass species, season and soil texture.
Actively growing turfs generally contain more than 70 percent water and, depending on species, may use from 1/10 inch to 3/10 inch or more of water daily.
In Tennessee, precipitation during early spring may meet the
 water requirement of actively growing, coolseason turfgrasses and warm-season turfgrasses recovering from winter dormancy.
However, turfgrasses most often require supplemental irrigation to maintain growth and color during hot, dry summer months.
Fine-textured, clayey soils usually hold more water for a longer period of time than coarse-textured, sandy soils.
One irrigation philosophy is to water thoroughly and infrequently in an effort to encourage turfgrass plants to develop deep roots.
The soil is moistened to a depth of at least 6 inches and the turf is not irrigated again until symptoms of drought stress begin to appear.
Many industry professionals managing turfgrasses in loam soil keep this philosophy in mind and set irrigation systems to apply 1/2 inch  of water no more than twice each week.
When thoroughly irrigating turfs maintained on slopes or in heavy clay soils, it may be necessary to activate sprinkler heads in each zone several times to avoid runoff.
Another irrigation philosophy, based, in part, on research conducted at Michigan State University, is to irrigate lightly and often  during the summer.
A goal is to meet the daily water requirement of shallowly rooted turfgrasses while conserving water by preventing runoff and the percolation of water below the turfgrass root zone.
Damage from certain diseases and insects may be reduced when water is applied by light, frequent rather than deep, infrequent irrigation.
Moisture Sensors.
Several manufacturers market soil moisture sensors that, when installed below the soil surface, can automatically activate an irrigation system before the turf becomes droughtstressed and shut the system off before the soil becomes saturated.
Monitoring Soil Moisture and Turfgrass
 Drought Stress.
The relative moisture status of a soil can be estimated by using a pocket knife to probe the soil, noting the resistance to penetration by the blade.
Many soils contain large amounts of
 clay and become very hard as they dry.
Wilting of plants and footprinting signal the need to irrigate.
Turfs often appear bluish-gray as they wilt and may fail to spring back when compressed by foot-traffic.
When Is the Best Time of Day to Irrigate?
Since excessively wet turfs are prone to disease, watering at night should be avoided whenever possible.
Turfs irrigated during midday often dry quickly; however, much of the applied water may evaporate.
The compromise is to irrigate during early morning hours.
Irrigating in the morning will reduce evaporative water loss and limit the amount of time the turf canopy is wet.
Crop Water Use and Growth Stages
 Fact Sheet No.
4.715
 by M.M.
Al-Kaisi and I.
Broner* Revised by A.A.
Andales**
 Crop water use, also known as evapotranspiration , is the water used by a crop for growth and cooling purposes.
This water is extracted from the soil root zone by the root system, which represents transpiration and is no longer available as stored water in the soil.
Consequently, the term "ET" is used interchangeably with crop water use.
All these terms refer to the same process, ET, in which the plant extracts water from the soil for tissue building and cooling purposes, as well as soil evaporation.
The evapotranspiration process is composed of two separate processes: transpiration  and evaporation.
Transpiration is the water transpired or "lost" to the atmosphere from small openings on the leaf surfaces, called stomata.
Evaporation is the water evaporated or "lost" from the wet soil and plant surface.
Significant evaporation can take place only when the soil's top layer  or when the plant canopy is wet.
Once the soil surface is dried out, evaporation decreases sharply.
Thus significant evaporation occurs after rain or irrigation.
Furthermore, as the growing season progresses and canopy cover increases, evaporation from the wet soil surface gradually decreases.
When the crop reaches full cover, approximately 95 percent of the ET is due to transpiration and evaporation from the crop canopy where most of the solar radiation is intercepted.
Crop water use  is influenced by prevailing weather conditions, available water in the soil, crop species and growth stage.
At full cover, a crop will have the maximum ET rate  if soil water is not limited; namely, if the soil root
 zone is at field capacity.
Full cover is a growth stage at which most of the soil is shaded by the crop canopy.
In a more technical term, the crop is at full cover when the leaf area is three times the soil surface area under the canopy.
At this growth stage, the crop canopy intercepts most of the incoming solar radiation, thereby reducing the amount of energy reaching the soil surface.
Different crops reach full cover at different growth stages and times after planting.
In order to standardize ET measurements and calculations, a reference crop ET  is used to estimate actual ET for other crops.
In humid and semi-humid areas where water usually is not a limiting factor, grass is used as a reference ET crop.
In arid or semi-arid areas, alfalfa is more suitable as a reference ET crop because it has a deep root system, which reduces its susceptibility to water stress resulting from dry weather.
Actual evapotranspiration  is the water use of a particular crop at a given time.
ET of an annual crop reaches its maximum at full cover, and can be higher or lower than ET, depending on the crop.
In Colorado, alfalfa is used as the reference crop.
Corn at full cover has a maximum water use rate, ET, of 93 percent of alfalfa ET, while sugar beets have a maximum ET rate of 103 percent of alfalfa ET.
Estimating Crop Water Use
 Actual crop water use, ET, can be measured directly by using several research methods or indirectly by measuring changes in soil water content with time.
However, these methods are expensive, tedious and can
 Water stress during critical growth periods reduces yield and quality of crops.
Crop water use  at critical growth stages can be used in irrigation scheduling to avoid stressing crops.
Crop water use  is weather dependent as well as soil, water and plant dependent.
Periodically check soil water at different depths within the root zone and at different growth stages to avoid stressing the crop during critical growth stages.
*M.M.
Al-Kaisi, former Colorado State University regional water management specialist; and I.
Broner, former Extension irrigation specialist and associate professor , bioresource and chemical engineering.
**A.A.
Andales, Colorado State University associate professor.
12/2014
 be done only in research settings.
Therefore, ET is theoretically and empirically correlated to weather parameters to generate ET models that estimate ET from weather parameters.
ET equations most often used in Colorado are the Penman and JensenHaise models.
These models were checked and calibrated for local conditions and give reliable estimates of ET.
The JensenHaise equation uses temperature and solar radiation measurements, while the Penman equation uses temperature, solar radiation, wind run and humidity.
Actual evapotranspiration, ET, can be calculated from reference ET by multiplying ET by the crop coefficient.
A crop coefficient is the ratio between ET of a particular crop at a certain growth stage and ET.
If the crop coefficient is smaller than one, the crop uses less water than reference ET and vice versa.
Crop coefficients depend on the stage of growth and usually are presented as a function of time following planting.
Crop coefficients are measured using lysimeters for different crops and are shown in fact sheet 4.707, Irrigation Scheduling: The Water Balance Approach.
These coefficients represent average conditions namely average weather.
In years that are significantly different from the average year, actual crop development may exceed or lag behind the average crop development rate.
Therefore, when using crop coefficients in an irrigation scheduling scheme, some adjustments of the average curve to actual crop development may be needed.
The crop coefficient of an annual crop is small at the beginning of the growing season, gradually increases as the crop develops, and may decline as the crop matures.
Effect of Soil Water on ET
 Crop water use also is influenced by the actual soil water content.
As soil dries, it becomes more difficult for a plant to extract water from the soil.
At field capacity , plants use water at the maximum rate.
When the soil water content drops below field capacity, plants use less water.
This phenomenon is described by the soil coefficient , which is a function of soil water content.
The soil coefficient often is used in irrigation scheduling schemes to adjust the actual ET to reflect soil water conditions.
After rain or irrigation, actual ET is higher than when the soil or crop surface is dry.
When the soil or crop surface is wet, the evaporation portion of ET increases significantly, resulting in a higher actual ET, especially early in the growing season.
This actual ET rate can be larger than reference ET.
This phenomenon is described in irrigation scheduling schemes as an additional evaporation coefficient.
This coefficient adjusts actual ET  to reflect wet soil surface conditions.
Each soil type can hold different amounts of water while acting as a water reservoir for plants.
Estimating the soil water content and information on maximum water holding capacities of different soils are given in 4.700, Estimating Soil Moisture.
Managing Irrigation According to Growth Stages
 Crops are different in their response to water stress at a given growth stage.
Crops summarized according to their sensitivity to water stress at various growth stages  reveal the importance of these stages in making the irrigation decision.
Crops that are in the sensitive stage of growth should be irrigated at a lower soil water depletion level than those that can withstand water stress.
If a crop is last in the irrigation rotation and is at a sensitive stage of growth, the recommended strategy may be to apply partial or lighter irrigations in order to reach the end of the field before the sensitive crop is subjected to water stress.
Such a strategy can be used with sprinkler systems, but this may lead to unfavorable soil moisture conditions at the lower soil depths.
When soil is repeatedly watered to only shallow depths, the lower soil depths tend to develop a soil moisture deficit that exceeds the allowable soil moisture depletion level at that particular growth stage.
Therefore, quick soil moisture assessment at various soil depths to determine the actual water use is essential in irrigation scheduling as related to growth stages.
Crop appearance is considered one of many field indicators that can be used in irrigation scheduling.
A crop suffering from water stress tends to have a darker color and exhibits curling or wilting.
This is a physiological defense mechanism of the crop that is evident on hot, windy
 afternoons when the crop cannot transpire fast enough, even if the water is readily available in the soil.
If the crop does not recover from these symptoms overnight, the crop is suffering from water stress.
Any changes in crop appearance due to water stress may mean a reduction in yield.
However, using this indicator alone for irrigation scheduling is not recommended if a maximum yield is desired.
This indicator is inferior for modern agriculture due to the inability to determine the actual crop water use.
However, ignoring it at the critical growth stages may lead to yield reduction.
Using the growth stage as a field indicator in irrigation scheduling should be coupled with more sensitive and accurate methods of determining the crop water use, such as soil moisture measurements and ET data.
The main advantage of this indicator is to provide direct and visual feedback from the crop.
Different crops have different water requirements and respond differently to water stress.
Crop sensitivity to water stress varies from one growth stage to another.
Table 1 is a summary of critical growth stages during which major crops in Colorado are especially sensitive to water stress.
A good irrigation scheduling scheme should consider sensitivity of the crop to water stress at different growth stages.
This is accomplished by using a coefficient termed the Management Allowable Depletion , which is the amount of water allowed to be depleted from the root zone before irrigation is scheduled.
The MAD is usually given as a percentage of maximum water holding capacity of the soil.
At the time of irrigation, the soil water deficit should be less than or equal to the MAD.
The goal of any irrigation scheduling scheme is to keep the water content in the root zone above this allowable depletion level.
This ensures that the crop will not suffer from water stress and will produce maximum potential yield.
In Table 2, suggested MADs for selected crops are given for different growth stages.
This information can be used in an irrigation scheduling scheme by using the appropriate MAD for each growth stage to trigger irrigation.
Table 1.
Critical growth stages for major crops1.
Crop	Critical period	Symptoms of water stress	Other considerations
 Alfalfa	Early spring and immediately after	Darkening color, then wilting	Adequate water is needed between
 Corn	Tasseling, silk stage until grain is fully	Curling of leaves by mid-morning,	Needs adequate water from germination
 formed	darkening color	to dent stage for maximum production
 Sorghum	Boot, bloom and dough stages	Curling of leaves by mid-morning,	Yields are reduced if water is short at
 darkening color	bloom during seed development
 Sugar beets	Post-thinning	Leaves wilting during heat	Excessive full irrigation lowers sugar
 content of the day
 Beans	Bloom and fruit set	Wilting	Yields are reduced if water short at bloom
 or fruit set stages
 Small grain	Boot and bloom stages	Dull green color, then firing of lower	Last irrigation at milk stage
 Potatoes	Tuber formation to harvest	Wilting during heat of the day	Water stress during critical period may
 cause cracking of tubers
 Onions	Bulb formation	Wilting	Keep soil wet during bulb formation and
 Tomatoes	After fruit set	Wilting	Wilt and leaf rolling can be caused by
 Critical period for seed production is boot
 Cool season	Early spring, early fall	Dull green color, then wilting	to head formation
 Fruit trees	Any point during growing season	Dulling of leaf color and drooping of	Stone fruits are sensitive to water stress
 growing points	last two weeks prior to harvest
 1Taken from Colorado Irrigation Guide, Natural Resources Conservation Service.
Table 2.
Management allowable depletion  at the root zone of selected crops at different growth stages.
Crop	Growth stages	MAD in root zone	Effect of water stress
 Alfalfa	Emergence-1st cut	65	Yield reduction
 1st cut-2nd cut	50
 2nd cut-3rd cut	40
 3rd cut-4th cut	60-70
 Pinto beans	Emergence-aux.
budding	60-70	Yield reduction
 Potatoes	Early veg.
period	40-60	Many jumbo and lower yield
 Tuber bulking period	30-40
 Corn	Emergence-12 leaf	60-70	Yield reduction of 11.5 bu/A-in water deficit
 Small grains	Emergence-first node	65-70	Yield reduction of 6-8 bu/A-in of water deficit
 Soybeans	Before flowing	65-70	Yield reduction
 First flower-first pod	60-65
IMPROVEMENTS IN IRRIGATION EFFICIENCY
 Efficiency is the name-of-the-game these days.
We are constantly reminded that we must be more efficient with our time, our money, our skills, and our resources.
Yet, the working definitions of the various efficiencies that each of us use may be quite different.
Sometimes the correctness of the appropriate use of an efficiency term is entirely related to one's perspective.
The topic of this presentation is irrigation, so let's look at two important efficiency terms in irrigation and look at how the terms interact.
WATER USE EFFICIENCY 
 Water use efficiency  is typically defined as the crop yield divided by the amount of water used.
Algebraically it can be expressed as
 WUE = Mcrop/Vwuse Eq.
1.
where Mcrop is equal to the mass of the crop and Vwuse is equal to the volume of water used.
It is easy to see that increases in WUE can be accomplished either by increases in Mcrop relative to Vwuse or by decreases in V wuse relative to Mcrop.
Whereas both techniques increase the beneficial use of water, only the second technique results in water conservation directly.
It is important to note that manipulation of either term must be relative to the other term in the equation.
Reducing water use is not beneficial if crop yield is reduced to the same extent.
WATER APPLICATION EFFICIENCY 
 The water application efficiency  definition as reported by Heermann et al.
is algebraically expressed as
 Ea = Vsoil / Vfield Eq.
2.
where Vsoil is equal to the volume of irrigation water needed for crop evapotranspiration to avoid undesirable water stress and Vfield is equal to the volume of water delivered to the field.
Ea is often incorrectly confused with the water storage efficiency which is the fraction of an irrigation amount stored in the remaining available crop root zone following an irrigation event.
The use of water storage efficiency is discouraged by Heermann et al.
because of the difficulty of determining the crop root zone and because the water storage efficiency can still be quite low while sufficient water is provided for crop production.
It is easy to manipulate Vfield so that Ea can be equal to 1 or 100%.
It should be noted that any irrigation system from the worst to the best can be operated in a fashion to achieve 100% Ea if Vfield is low.
Increasing Ea in this
 manner totally ignores the need for irrigation uniformity.
For Ea to have practical meaning, Vsoil needs to be considered to avoid undesirable water stress.
INTERACTION OF WUE AND E
 Algebraically it has been shown that either efficiency term can be maximized through manipulation of the various terms in the equations.
However, some of these manipulations are not beneficial to the irrigator and perhaps, also not beneficial to the economic vitality of the state.
Consideration of both terms is necessary to optimize beneficial use of water for crop production.
In a thorough review of crop yield response to water, Howell et al.
enumerated four methods of increasing water use efficiency: 1) increasing the harvest index ; 2) reducing the transpiration ratio ; 3) reducing the root dry matter amount and/or the yield threshold required to initiate the first increment of economic yield; or 4) increasing the transpiration component relative to the other water balance components, for example, through reductions of evaporation, drainage, and runoff.
Clearly, some of these four methods are more difficult than others.
Tanner and Sinclair  in a review of studies from the early 1900's to the 1980's conclude that there is very little hope for appreciably improving the transpiration ratio.
Some say that plant breeders and agronomists have made great strides in increasing the harvest index  for many of the more important crops.
Corn yields have increased an average of 2.5 bu/acre annually for the last 40 years in Thomas County, Kansas due to improvements in corn hybrids and cultural practices.
The actual water used by the corn has not changed appreciably although the water use efficiency has increased.
The yield threshold  varies somewhat depending on the locale and the annual weather conditions.
However, it does not appear practical that it can be manipulated to an appreciable extent.
Improved irrigation systems and practices can increase both WUE and Ea by Method 4, increasing the transpiration component relative to the other water balance components.
Crop yield is linearly related to transpiration for many field crops from the point of the yield threshold through the point of maximum yield.
However, the relationship of crop yield and total water use is usually curvilinear.
The region between the dotted line and the curve represents the inefficiencies caused by the irrigation system and/or inappropriate irrigation/precipitation timing or amounts.
Use of irrigation water beyond the point where the dotted line and the curve join at maximum yield represents wasteful overirrigation and should be eliminated immediately.
All of the points on the rising dotted line have equal WUE, so all are equally beneficial in terms of WUE.
However, most irrigators are practicing irrigation for the beneficial purpose of increasing crop yields and economically need to produce near the top of the rising leg.
Lamm et al.
analyzed 9 different resource allocation schemes for irrigated corn ranging from full irrigation to severely deficit irrigation.
Full irrigation was found to be the most economical operating point.
They concluded,
 Irrigators wishing to continue to grow corn when irrigation is limited by physical  or institutional constraints should seriously consider reducing irrigated land area to match the severity of the constraint.
Only reductions in the area between the dotted line and the curve  and obviously elimination of overirrigation should be considered as opportunities where improved irrigation systems and practices can increase WUE and Ea.
Many irrigators are already upgrading irrigation systems and management of their present systems to stretch water.
There are considerable opportunities for further water use reductions, but the ultimate reductions cannot be economically obtained overnight.
The irrigation sector continues to search for economical ways to reduce inefficient water use in a manner that can optimize both WUE and Ea.
Figure 1.
Hypothetical crop yield response to total water use and transpiration.
Area between dotted line and curve is inefficiency.
Use of irrigation water beyond where dotted line and curve rejoin  is wasteful overirrigation.
Starting point for both lines is yield threshold.
Numbers shown for example only, actual values will vary.
This paper was first presented at the 12th Annual Water and the Future of Kansas Conference, Feb 28 March 1, 1995, Kansas State University, Manhattan Kansas.
Some updates were made in April 2011.
Additionally, we need to factor in the cost to pump the irrigation water and the danger of leaching nitrogen and sulfur below the root zone, so irrigation can get expensive very quickly.
One inch of water that moves below the root zone, whether from rain or irrigation, will take at least five to 10 lbs.
of nitrogen with it.
This illustrates that putting nitrogen fertilizer on closer to when the plant will use it with a sidedress application or through chemigation should be considered a best management practice.
Figure 6: Ratio of simulated to design nozzle discharge for a simulated center pivot at a location in a field with a 1% slope increasing away from the pivot point.
An inlet pressure at the pivot point less than the design pressure for the pivot point results in an uneven distribution of irrigation depth.
Figure reprinted from Martin et al..
Drip and Furrow Irrigation of Fresh Market Tomatoes on a Slowly Permeable Soil:
 PART 2.
WATER RELATIONS
 D.
W.
GRIMES V.
H.
SCHWEERS P.
L.
WILEY
 Frequent furrow irrigation of fresh market tomatoes, on a sandy loam soil, caused the soil surface to seal, greatly restricting water penetration into the plant root zone.
Water penetration in furrows was adequate throughout the season if the frequency of irrigation was lowered.
A drip irrigation system maintains not only a desirable soil moisture distribution, but also the cultural advantage of a dry surface area for foot traffic of harvesters that improves their efficiency and reduces soil compaction.
W later penetration slows during the growing season in furrowirrigated, fresh market tomato fields on eastern San Joaquin Valley
 soils.
Such slowing has been shown also in preliminary experiments at the Lindcove Field Station in 1973 and 1974.
In 1975, an experiment was conducted at the Lindcove Field Station, on a Vista sandy loam soil, to examine the influence of furrow irrigation frequency on surface penetration capability, and to determine whether drip irrigation  could maintain adequate water penetration throughout the season.
Four irrigation treatments consisted of the furrow and drip methods, each at two intervals: infrequent  and frequent  furrow treatments, and infrequent  and frequent  drip treatments.
The four treatments were replicated three times in field plots 50 feet long.
Each plot comprised three rows, 5' 4" apart.
Early-season irrigations were scheduled on the basis of tensiometer readings, but poor water penetration on the most frequently irrigated furrow treatment soon rendered this impractical.
The irrigation treatments are described in more detail in part 1 in this issue, along with other procedures and the resulting production trends.
The frequent irrigations were initiated in late April , the infrequent irrigations in early May.
As shown in graph 1, water penetration was becoming a problem on the frequently irrigated furrow treatment  by mid-May.
The tensiometer readings at 12 inches of
 Biwall drip irrigation tubing placed at the base of tomato plants.
Note the wetted area around the outlet.
two adjacent plots furrow-irrigated at different frequencies illustrate the striking influence of irrigation frequency on water penetration.
A final cultivation at the end of May failed to improve penetration significantly.
The restriction to water penetration caused by frequent furrow irrigation is believed to be a relatively shallow surface pheonomenon on this soil, related to particle dispersal, orientation, and a possible biological growth-reducing effective pore volume.
Rate of water penetration may vary considerably in a short radial distance in this soil.
An adjacent tensiometer-monitored replication of the frequent furrow treatment showed adequate water penetration at both 12and 24-inch tensiometer placement depths through mid-June.
Thereafter, however, no irrigation penetrated to the 12-inch depth.
Graph 1 compares plots that were side by side in the study.
The less frequent furrow treatment , irrigated at weekly intervals throughout the season, showed good water penetration during the entire irrigation season.
No tendency was observed toward the high degree of surface sealing resulting from the high frequency treatment.
Water intake rates for the two furrow irrigation frequencies were determined at two dates in late season.
The volume of water shown represents the difference in volume between inflow measurements and outflow at the end of the 50-foot rows.
Tabular values are averages of the three replications and four measurements at 90minute intervals on July 16.
Three measurements were made at twohour intervals on July 23.
The average intake water volume for W-1, 4.14 cubic feet per hour, is equivalent to a water penetration rate of 0.19 inch per hour, considering the entire soil surface.
This compares with 0.05 inch per hour for the frequently irrigated plot, about one-fourth as fast.
lier irrigations had been less frequent because water demand was lower.
The low frequency, W-3 plot was irrigated for 12 hours on Wednesday of each week, the same as for W-1.
The high frequency drip treatment delivered slightly more water than the expected demand.
Drip and furrow methods compared
 Tensiometers at a 12-inch depth in the row for the W-4 treatment had an average reading of 10 centibars after June 1.
The corresponding value for a 24-inch depth was 20 centibars.
Tensiometers at 12 inches for the W-3 treatment consistently approached 80 centibars the day before irrigation and occasionally exceeded the air entry value.
The water volume added with this treatment consistently rewet the 12-inch in-row depth but was not always sufficient to reach the 24-inch depth.
As expected, this treatment allowed an appreciable water deficit and reduced yield correspondingly.
The high frequency treatment  may have allowed a small water loss by drainage below the root zone, but achieved high production.
Drip irrigation was through biwall tubing  immediately adjacent to plants in the row.
After June 1, the high frequency plot  was irrigated for 12 hours three times weekly , the same as for the high frequency furrow treatment.
Ear-
 To evaluate both vertical and lateral water distribution, soil samples were taken from the center replication on July 17, the day after
 each treatment was irrigated, at 6inch intervals to a depth of 5 feet.
Samples were collected directly in the row, at half the distance from the row to midway between rows, and midway between rows, respectively referred to in graph 2 as row, 1/2, and center.
The measured water contents were converted to matric potential from laboratory-measured waterrelease curves.
Most of the water that plants can use from this soil is held at a value not lower than -1 bar.
Little or no water is available for plants at values lower than -15 bars.
Graph 2 shows that the infrequently irrigated furrow treatment had good vertical and lateral water distribution following irrigation.
The surface 6 inches is very dry midway between rows, but below two feet the water is evenly distributed horizontally.
Except in an approximate 6-inch radial zone around the furrow, the entire cross-sectional profile of the frequently irrigated treatment is quite dry.
Because this small zone was kept wet, production was reasonably good.
The most droughty treatment was the infrequent drip.
While the soil volume immediately near the row was rewetted to a depth below 12 inches, this volume of water was not adequate to avoid excessive stress.
Probably the most favorable water
 distribution is with the frequently irrigated drip treatment.
A large amount of available water was maintained in soil near the row to a depth of two feet.
Below two feet the soil water was held at -1/3 bar and decreased to slightly lower values at greater depth.
This distribution of soil water should adequately meet plant demands with minimal deep percolation losses.
The water relations evident from this study show reduced water penetrability from surface sealing by high frequency furrow irrigation materially influencing the water volume available for plant use.
This, in turn, was reflected in total yield and production trends.
A lower frequency  on this sandy loam soil gave a much improved water condition by maintaining an adequate penetra-
 tion rate through the season.
A desirable soil moisture distribution was provided by drip irrigation if sufficient water was added to meet plant demands throughout the season.
A cultural advantage of the drip system is that the soil surface area for foot traffic is kept dry, resulting in less soil compaction and greater harvest efficiency.
The economics of this system will be examined in greater detail.
D.
W.
Grimes is Lecturer and Associate Water Scientist and P.
L.
Wiley is Staff Research Associate, San Joaquin Valley Agricultural Research and Extension Center, Parlier; V.
H.
Schweers is Farm Advisor, Tulare County, Visalia.
The assistance of personnel at the Lindcove Field Station is gratefully acknowledged.
Table.
Water intake rates at two dates for infrequently and frequently furrow-irrigated tomato plots at the Lindcove Field Station in 1975.
Water intake/50' of row
 
 Infrequent	4.39 b	3.90 b
 Frequent	1.55 a	0.91 a
 Graph 1.
Tensiometer readings at 12 inches for the infrequent  and frequent  furrow irrigation treatments during May on a Vista sandy loam at the Lindcove Field Station.
Graph 2.
Soil wetting profiles on tomatoes the day after water addition for two irrigation methods, each at two frequencies.
SOIL WATER MATRIC POTENTIAL 
Determining Irrigation Run Times with Drip Tape on Specialty Crops
 By Adrian Card & Troy Bauder*
 Drip irrigation is well suited for most vegetable crops because these crops typically require frequent, shallow irrigations due to their shallow rooting depths.
Drip irrigation is designed to apply relatively low volumes of water more efficiently than other irrigation systems.
However, when not properly managed, any increase in irrigation efficiency provided by a drip system can be lost.
Applying irrigation water at the right time and in the right amount for optimal plant health is one important factor for consistently high yields.
While in salt affected soils growers may need to over irrigate to flush salts out of the root zone, excessive water application has the potential to reduce yields by leaching nitrate-nitrogen below the depth of the root zone and cause plant health problems due to less air and more water in soil pores.
Conversely, water shortage also reduces plant health and thus crop yields.
A key point to remember, particularly with buried drip tape versus drip tape on the soil surface, is that the emitted water from the tape will immediately move down in the soil due to gravity at the same time it moves up.
With buried drip tape, irrigating until the moisture is seen in a wide band on the soil surface will often cause a portion the applied water to move below the root zone, resulting in lost water and nutrients.
Specialty crop irrigation scheduling with drip tape can be done effectively with six pieces of information: 1) Available Water Capacity  per foot of soil based on soil texture, 2) Management Allowed Depletion  for a specific crop, 3) current crop rooting depth and Maximum Rooting Depth , 4) soil water depleted, 5) drip tape flow rate, and 6) estimated drip
 tape efficiency.
For related information see fact sheet 4.707.
Available Water Capacity  "How much do you have?"
 Soil is like a sponge.
It can be filled only to a maximum volume of water and then water drains downward due to gravity.
This state is called field capacity and reflects total soil water.
Field capacity can be measured in inches of water and varies by soil texture.
Plants can extract the water in the soil until the point at which the soil holds the water with more force than the plants can exert to extract it, thus only a portion of the total soil water is available to plants.
When no water is available for plant root uptake this is referred to as permanent wilting point and results in plant death.
AWC is the inches of field capacity that plants can readily extract and is calculated as field capacity minus wilting point.
AWC also varies by soil texture.
Refer to charts below or have your soil tested to determine AWC per foot of soil for your soil texture.
Figure 1: Graphic representation of soil water concepts
 Drip irrigation is designed to apply relatively low volumes of water more efficiently than other irrigation systems.
When not properly managed, any increase in irrigation efficiency provided by a drip system can be lost
 Crops extract about 70% of plant available water from the upper half of their root system.
Application efficiency of drip irrigation is approximately 90%.
*Adrian Card, Agriculture Agent, CSU Extension and Troy Bauder Assistant Deputy Director, CSU Agricultural Experiment Station
 Figure 2: Management Allowed Depletion  and Maximum Rooting Depth  values by crop
 The chart below shows average percent MAD of soil moisture for various crops with MRD in inches.
Plant growth stage and compacted layers affect rooting depth.
NOTE: adjust MRD based on plant growth stage and local soil conditions.
Forage crops are shown for comparison.*
 Crop	% MAD	MRD 	Crop	% MAD	MRD 
 Alfalfa	55	48 72	Kale	30	18 24
 Apples	50	39 78	Leek	30	12 18
 Asparagus	40	46 70	Lettuce	30	12 20
 Beans 	45	20 27	Melons 	40	31 59
 Beets	50	23 39	Onions	25	12 23
 Broccoli	50	16 23	Okra	30	18 24
 Brussel sprouts	30	16 23	Parsnip	40	18 24
 Cabbage	45	20 31	Peaches	50	24 36
 Cantaloupe	40	24 48	Peas	35	12 24
 Carrots	35	20 39	Peppers	25	20 39
 Cauliflower	50	16 27	Potatoes	25	16 24
 Celery	20	12 20	Pumpkin	40	36 48
 Chard	50	18 24	Radishes	30	12 20
 Cucumber	50	18 24	Raspberries	50	12 24
 Chinese cabbage	30	12 18	Rhubarb	80	18 24
 Collards	50	12 18	Spinach	20	12 20
 Corn 	50	31 47	Strawberries	20	12 24
 Eggplant	45	18 24	Summer squash	30	12 24
 Grapes 	35	36 60	Sweet potato	65	24 36
 Grapes 	45	36 60	Tomatoes	40	24 48
 Grass 	50	18 30	Watermelon	40	24 36
 Hops	50	36 60	Winter squash	40	36 48
 Management Allowable Depletion  "How much can you lose?"
 MAD is the plant tolerated loss of AWC and varies for specialty crops.
MAD can be expressed as a percent or in inches.
Growers should not exceed the MAD for each crop and need not wait to irrigate until the MAD "red line" is reached.
A yield loss will be incurred when MAD is exceeded.
For different crops in the same irrigation zone, use the crop with the smallest MAD value to represent the entire zone.
For example, a sandy clay loam holds 1.8 inches of water per foot of soil.
The MAD for peppers is 25%, thus this soil can be depleted by 0.45 inches below AWC.
Rooting Depth "Where is it?"
 Crops extract about 70% of plant available water from the upper half of their root system.
Sample soil moisture for fully rooted crops from half the depth of the Maximum Root Depth  to determine when to irrigate (how
 close to MAD) and how much water to apply based on inches of soil water depleted.
If unsure, a generic sample from about 9 inches deep should be representative for most fully rooted vegetable crops in Colorado.
Sample shallower than half the MRD if the crop is not fully rooted.
Samples should represent the average soil moisture conditions for crop roots and should be taken 4 6 inches away from both the crop and the drip tape.
Water Depletion "How much is there now?"
 There are several methods to determine current inches of soil water depleted.
Once soil texture is known, a low tech and less accurate method to determine current soil water depletion with a soil sample is the feel and appearance method.
Take a sample with a soil probe to the appropriate depth based on crop rooting.
Refer to the NRCS publication "Estimating Soil Moisture by Feel and Appearance" and note images and description for AWC and percent soil water available and inches depleted.
Another method utilizes soil water sensors that remain in the field to determine soil dryness in units of centibars.
Centibars are a unit of measure for soil tension, or how strongly the soil is holding soil water.
For example and based on Figure 3, a sandy clay loam holds 1.8 inches of water.
At 40 centibars that soil has 1.3 inches of water available and is 28% depleted.
Once MAD is known for an irrigation zone monitored by these sensors, doing the calculation once to determine the MAD equivalent centibars will help with irrigation management by establishing that "red line".
Figure 3: Approximate soil moisture tension and available water for sandy and loamy soils
 Moisture	Fine Loamy Sandy Fine sandy
 Tension	sands	sand	loam	loam
 cb	Inches of water per foot of soil
 0	Wet	1,00	1,10	1,40	1,80
 10	1.00	1.10	1,40	1.80
 15	0,90	1,10	1.40	1,80
 20	0.50	0.90	1.20	1.80
 25	0,70	0,80	1.10	1,60
 30	0,60	0.70	1.00	1,50
 35	0.50	0,70	0,90	1,30
 40	0,40	0,60	0.90	1.20
 45	0.40	0,60	0,80	1.10
 50	0,40	0,50	0,80	1.00
 55	0.30	0,50	0,70	1.00
 00	0,30	0,40	0,70	0,90
 65	0.30	0,40	0.00	0.00
 70	0,20	0.40	0.60	0,80
 75	0,20	0.30	0,60	0,70
 80	Drier	0,20	0,30	0,50	0.70
 clay loam Clay loam loams Loams
 cb	Available Soil Water
 Wet	Inches per foot of soil
 0	1.8	1.8	2.2	2.4
 10	1,8	1.7	2.0	2.4
 20	1.7	1.6	1.9	2.3
 25	1.6	1.4	1.8	2.1
 30	1.5	1.3	1.7	2
 35	1,4	1.3	1.6	1,9
 40	1,3	1.2	1.5	1,8
 45	1.2	1.1	1.5	1.7
 50	1.1	1.1	1.4	1.6
 55	1.0	1,0	13	1.5
 60	0,90	1.0	1.2	1,4
 70	0.80	0,00	1,1	1,3
 75	0.70	0,85	1.0	1.2
 80	Drier	0.60	0.80	0,95	1.1
 Some vendors provide wireless Refer to pages 19 and 20 in the "Irrigated Field Guide and Record Book" sensors, allowing growers to set a MAD for a soil water sensor report and view hourly soil water graphs via internet connected devices.
This allows growers to see both soil water increases  and decreases  and making it simple to see when decreases are nearing the MAD value.
Remote sensing of soil moisture greatly reduces monitoring effort and expedites irrigation management.
Drip Tape Flow Rate
 Many are familiar with sprinkler irrigation and the measurement of water applied in inches while drip output is given in gallons.
It is possible to figure inches of water applied with drip tape given two variables:
 1.
Flowrate of drip tape used measured in gallons/minute per 100 ft of tape 
 2.
Tape spacing inches between tapes on or between planted beds, not emitter spacing in the tape
 Figure 4: Inches of water per hour for various drip tape flow rates and tape spacings
 Refer to the following chart to determine the output of inches per hour from your irrigation system.
Application efficiency of drip irrigation is approximately 90%.
This efficiency must also be factored in the calculation to determine run time.
Tape	Drip Tape Flow Rate 
 Spacing	0.2	0.25	0.3	0.35	0.4	0.45	0.5	0.55	0.6	0.65	0.7	0.75
 12	0.19	0.24	0.29	0.34	0.39	0.43	0.48	0.53	0.58	0.63	0.68	0.73
 14	0.17	0.21	0.25	0.29	0.33	0.37	0.41	0.46	0.50	0.54	0.58	0.62
 16	0.14	0.18	0.22	0.25	0.29	0.32	0.36	0.40	0.44	0.48	0.52	0.56
 18	0.13	0.16	0.19	0.22	0.26	0.29	0.32	0.35	0.38	0.41	0.44	0.47
 24	0.10	0.12	0.14	0.17	0.19	0.22	0.24	0.27	0.29	0.32	0.34	0.37
 30	0.08	0.10	0.12	0.13	0.15	0.17	0.19	0.21	0.23	0.25	0.27	0.29
 60	0.04	0.05	0.06	0.07	0.08	0.09	0.10	0.11	0.12	0.13	0.14	0.15
 Adapted with permission from "Drip Irrigation for Row Crops", Blaine Hansen, et al., UC Davis, 1997
 Run Time Calculation Example
 Soil texture is a sandy clay loam with AWC of 1.8 inches per foot of soil.
MRD for peppers is 20 inches deep.
Soil samples are taken from 9 inches deep.
Soil moisture assessment indicates soil is approximately 37 centibars and 25% depleted.
MAD for peppers is 25% so the soil is at MAD.
Time to irrigate as further drying will reduce plant health and yields.
1.8 inches of water per foot of soil X 0.25 depletion = 0.45 inch of water to be replaced in the top foot of soil
 Drip tape has flowrate of 0.35 gallons of water/minute per 100 feet of tape and tapes are spaced 12" inches apart on the bed, giving a conversion of 0.34 inch of water per hour based on the table above.
0.45 inches of water to be replaced divided by 0.34 inches of water per hour = 1.32 hours 1.32 hours X 60 minutes/hour = 79 minutes.
Initial run time is 79 minutes.
Initial run time of 79 minutes divided by 0.90 application efficiency = 88 minutes to replace 0.45 inches of water to 12 inches deep.
CORN PRODUCTION IN THE CENTRAL GREAT PLAINS AS RELATED TO IRRIGATION CAPACITY
 In arid regions, it has been a design philosophy that irrigation system capacity be sufficient to meet the peak evapotranspiration needs of the crop to be grown.
This philosophy has been modified for areas having deep silt loam soils in the semi-arid US Central Great Plains to allow peak evapotranspiration needs to be met by a combination of irrigation, precipitation and stored soil water reserves.
Corn is the major irrigated crop in the region and is very responsive to irrigation, both positively when sufficient and negatively when insufficient.
This paper will discuss the nature of corn evapotranspiration rates and the effect of irrigation system capacity on corn production and economic profitability.
Although the information presented here is based on information from Colby, Kansas  for deep silt loam soils, the concepts have broader application to other areas in showing the importance of irrigation capacity for corn production.
Corn evapotranspiration  rates vary throughout the summer reaching peak values during the months of July and August in the Central Great Plains.
Long term  July and August corn ET rates at the KSU Northwest Research Extension Center, Colby, Kansas have been calculated with a modified Penman equation  to be 0.266 and 0.249 inches/day, respectively.
However, it is not uncommon to observe short-term peak corn ET values in the 0.35 0.40 inches/day range.
Occasionally, calculated peak corn ET rates may approach 0.5 inches/day in the Central Great Plains, but it remains a point of discussion whether the corn actually uses that much water on those extreme days or whether corn growth processes essentially shut down further water losses.
Individual years are different and daily rates vary widely from the long term average corn ET rates.
Corn ET rates for July and August of 2002 were 0.331 and 0.263 inches/day, respectively, representing an
 approximately 15% increase over the long-term average rates.
Irrigation systems must supplement precipitation and soil water reserves to attempt matching average corn ET rates and also provide some level of design flexibility to attempt covering year-to-year variations in corn ET rates and precipitation.
Figure 1.
Long term corn evapotranspiration  daily rates and ET rates for 2002 at the KSU Northwest Research-Extension Center, Colby Kansas.
ET rates calculated using a modified Penman approach.
The USDA-NRCS National Engineering Handbook  and through its state supplements for Kansas  offer some suggested guidelines for center pivot sprinkler irrigation capacities.
A complete description of the calculation procedures used to arrive at these guidelines lies beyond the scope of this paper.
However, the minimum gross irrigation capacities in inches/day can briefly be summarized as the net irrigation requirement  for the July-August  period for 80 or 50% chance
 rainfall adjusted for the application efficiency divided by the 62-day period.
A summary of this information and its resultant minimum gross irrigation capacities for corn at Colby, Kansas  is shown in Table 1.
Table 1.
Summary of USDA-NRCS irrigation capacity guiding parameters and values for corn in Colby, Kansas.
Adapted from USDA-NRCS-KS, 2000, 2002.
Parameter	Value	Tab.
or Fig.
Source
 80% chance rainfall	15.4	Table KS4-1	KS Guide, Feb 2000
 50% chance rainfall	13.5	Table KS4-2	KS Guide, Feb 2000
 Irrigation Zone for Colby, KS.
2	Figure KS4-1	KS Guide, Feb 2000
 Irrigation Design Group	5	I D Group 5	KS Guide, Feb 2000
 for Keith silt loam, Colby, KS.
Monthly distribution of NIR, %
 July % with 80% chance rainfall	40.9%	Table KS4-3	KS Guide, Feb 2000
 August % with 80% chance rainfall	32.5%	Table KS4-3	KS Guide, Feb 2000
 July % with 50% chance rainfall	43.1%	Table KS4-4	KS Guide, Feb 2000
 August% with 50% chance rainfall	33.9%	Table KS4-4	KS Guide, Feb 2000
 Minimum center pivot sprinkler
 gross irrigation capacity, in/day,
 at stated application efficiency 
 85% Ea and 80% chance rainfall	0.21	Table KS4-10	KS Guide, Apr 2002
 90% Ea and 80% chance rainfall	0.20	Table KS4-11	KS Guide, Apr 2002
 85% Ea and 50% chance rainfall	0.20	Table KS4-10a	KS Guide, Apr 2002
 90% Ea and 50% chance rainfall	0.19	Table KS4-11a	KS Guide, Apr 2002
 The calculation of minimum gross irrigation capacities in this manner violates long standing irrigation design philosophies as is stated in the Irrigation Guide.
However, the rationale is given that center pivot sprinklers in the region typically do not satisfy the peak crop ET without either  relying on major withdrawal of root zone soil water rationale for these guidelines or  allowing application rates to exceed soil intake rates thus producing excessive runoff.
An argument can be made against this rationale in that irrigation runoff might best be handled through sprinkler package selection and the subsequent management of that package rather than through reducing irrigation system capacity.
The USDA-NRCS-KS 2002 guidelines do list the caveat that for dryer-thanaverage years this design criterion will likely result in plant water stress and reduced yields unless stored soil water reserves can buffer the irrigation system capacity deficiency.
However, there might be another point of discussion about the procedure used to calculate the minimum gross irrigation capacity.
The calculation procedure uses the July and August monthly distributions of seasonal NIR to determine minimum capacities.
The monthly distribution tables also include planning values for the month of May of approximately 1.5 to 4% of NIR.
These May planning values might be of good value for preseason planning, but may be detrimental to design of good irrigation management in July and August.
Allocation of some monthly distribution to May would result in some reductions of irrigation distributions in June, July and August.
Simulation of corn irrigation schedules for Colby, Kansas
Irrigation Scheduling with the Feel Method
 Craig A.
Storlie, Ph.D., Extension Specialist in Agricultural Engineering
 Monitoring soil moisture is one of the most important management procedures available for irrigation management.
Estimating soil moisture using the feel method is one of the easiest methods available for monitoring soil moisture, and can be used to determine the proper frequency of irrigations.
Proper irrigation depth can be determined from known plant and soil characteristics.
Determining when to irrigate and how much water to apply with each application are the goals of the management practice termed irrigation scheduling.
Soil Water-Holding Capacity and Available Water
 Soil in the plant root zone acts as a reservoir for water.
Soil texture is the primary factor influencing the amount of water that the soil reservoir can store.
Available water is defined as amount of water that plants are able to withdraw from the soil and use.
Fine textured soils, such as clays, silt loams, or loams, are able to hold much more available water than sandy, coarse-textured
 TABLE 1.
Influence of Soil Texture on Available Water-Holding Capacity
 
 Loamy sand	0.75 1.50
 Sandy loam	1.25 1.75
 Loam and Silt loam	2.00 2.75
 Clay loam	1.75 2.50
 soils.
Soil water-holding capacity is an important factor to consider in determining the proper irrigation depth.
The water storage capacity of soils is also influenced by soil depth.
Nearly all vegetables and agronomic crops grown under irrigated conditions extract water from the top 2 feet of the soil profile, even though the roots of some crops can extend much deeper.
In fact, in most crops, 75%-95% of the roots are in the top 12 inches of the soil profile.
For this reason, manage irrigation events with the top 12 inches of the root zone in mind.
Water which seeps beyond this depth may not be used by the crop.
Together, soil water-holding capacity and plant rooting depth can be used to determine the appropriate irrigation depth.
The appropriate irrigation frequency is influenced by soil water-holding capacity and by the rate at which plants use water, and can be determined by monitoring soil moisture.
The feel method is a simple and inexpensive procedure which can be used to monitor soil moisture.
Soil Sampling and Evaluation
 Samples evaluated using the feel method can be extracted from the plant root zone using a soil probe, auger, or spade.
Be certain to evaluate a number of samples from between 3 inches and 9 inches below the soil surface.
This is likely to be the most active root zone.
Test samples from various locations in the field where soil texture, plant size or vigor, or plant species are different.
Sample a minimum of four sites from a single management zone.
Remove a small handful of soil from your sampling tool and squeeze the soil firmly.
Open your hand and observe the condition of the soil.
For fineor medium-textured soils, try to ribbon the soil by working it between your thumb and forefinger.
Use Table 2 to estimate the amount of
 available moisture remaining in the soil.
Field capacity is the moisture content at which a soil is holding the maximum amount of water it can against the force of gravity.
Wilt point is the moisture content at which plants wilt and are adversely affected by moisture stress.
The water that a soil releases to plants between field capacity and wilt point is termed available water.
Irrigate when 50% of available water has been depleted.
Allowing the soil to dry below this moisture level may jeopardize obtaining maximum yields.
Learning to accurately predict soil moisture with the feel method requires practice.
To learn the feel of your soil at particular moisture contents, start early in the spring when soils are wet, or start a day or two after a saturating rain or irrigation.
Soil sampled under these conditions will be at or near field capacity.
Likewise, sample soil in which plants are growing that are beginning to wilt.
Soil at this moisture content is at the wilt point.
Knowing the feel of soil at these endpoints will help you estimate soil moisture at points between these moisture contents.
As an example of how to schedule irrigations using the feel method, assume tomatoes are being grown on soils of fine sand texture, and that the plants have a 1-foot root zone depth.
Use Table 1 to determine that these soils have an available water-holding capacity of 1 inch per foot of soil depth.
After using the feel method and estimating that available soil moisture in the crop root zone is at 50% and that irrigation is required, determine the appropriate irrigation depth by multiplying the root zone depth by the available water-holding capacity of the soil and by the percent available water depletion.
In this case:
 Irrigation depth = 1 in.
available water 1-ft root zone depth X X 50% = 1/2 inch foot of soil
 TABLE 2.
Irrigation Guidelines for Using the Feel Method
 Moisture Depletion	Sand,	Sandy loam, Loam,	Clay loam,
 Loamy sand	Silt loam	loam
 0%	forms ball, wet outline	forms ball, wet outline	forms ball, wet outline
 	of ball is left on hand,	of ball is left on hand,	of ball is left on hand,
 will not ribbon	ribbons easily	ribbons easily
 50%	breaks easily when	forms ball, will ribbon	forms ball, will easily
 	bounced in hand, will	with some difficulty	ribbon
 crumbly, but will hold
 	100%	crumbles into small	will not form ball,	pressure, will not	together under	holds together under	somewhat pliable,
  2004 by Rutgers Cooperative Research & Extension, NJAES, Rutgers, The State University of New Jersey.
Desktop publishing by Rutgers-Cook College Resource Center
 RUTGERS COOPERATIVE RESEARCH & EXTENSION N.J.
AGRICULTURAL EXPERIMENT STATION RUTGERS, THE STATE UNIVERSITY OF NEW JERSEY NEW BRUNSWICK
Schader valves can be installed at the distal end of the machine, which is the most critical point to check the pressure.
In this instance, the pressure should be a minimum of 17 psi.
On these projects, they are large.
If irrigation districts have some large projects available, they could join together on a cooperative basis and apply for one or two of these grants.
It might be a smart avenue to secure funds for their project, Wilson said.
Economics of Surface to Sprinkler Irrigation System Conversion for Lower Capacity Systems
 R evised February 4, 2000
 The profitability of converting from furrow surface irrigation to a center pivot sprinkler irrigation system depends upon a number of factors.
These include a) the pumping capacity of the irrigation well, b) the cost of converting to the sprinkler irrigation system and loan repayment period, c) changes  in irrigated acreage, and d) comparative irrigated crop yields for the old and new systems.
Labor savings are also commonly thought to be a major consideration in switching from furrow surface irrigation to center pivot irrigation systems.
Other factors considered include long run crop prices, production costs, and tax-related depreciation and interest deductions for the pivot system investment.
A number of studies have been performed to analyze the profitability of irrigation system conversion.
These studies have typically relied on a number of assumptions about initial furrow irrigated field size and crop yields, irrigation well capacity and irrigation system water application efficiencies, crop yields and net returns, labor use for alternative irrigation systems, and sprinkler irrigation system investment and pump repair costs.
Lamm, et.al.
1997, focused on the impact of sprinkler irrigation capacity on corn yield potential and economics.
Lower irrigation pumping capacities were shown to affect both crop yields and net returns under western Kansas conditions, particularly in high water use years when limited irrigated water applications were unable to fulfill crop needs.
This study focuses on the impact of differing irrigation well pumping capacities and weather conditions upon irrigated corn yields and the
 profitability of converting from furrow surface irrigation to center pivot irrigation systems.
The analysis concentrates on irrigation system capacities of 700 gallons/minute  and less.
The value of labor savings gained by switching from furrow surface irrigation to center pivot irrigation systems are also examined.
The results of this analysis are presented on an annual basis over the life of the alternative irrigation systems, accounting for the impact of tax deductions and debt repayment on annual cash flows.
This analysis assumes that a crop producer with a furrow surface-irrigated quarter section of farmland is determining whether or not to convert to a center pivot irrigation system.
The existing furrow surface irrigation system produces 160 acres of irrigated corn and is assumed to have an improved furrow irrigation application efficiency of 70%.
The center pivot sprinkler irrigation system will produce 125 acres of irrigated corn.
The remaining 35 acres in the corners of the 160 acre field will no longer be irrigated, but instead are placed in a wheat-corn-fallow rotation.
Alternative center pivot sprinkler irrigation system application efficiencies of 85% and 100% are examined in this study.
Center Pivot Sprinkler Investment Costs & Tax Deductions
 Current budget estimates from KSU Farm Management Guide MF-836  as well as irrigation industry cost projections are used to estimate the purchase cost of a sprinkler irrigation system.
An additional $4,500 is budgeted to modify the existing well pump for the higher pressure requirements of sprinkler irrigation.
The total cost of the pivot sprinkler system is projected to be $45,209, including a standard 7 tower pivot system with drops, low drift nozzles, underground pipe from the field edge to the
 Table 1.
Capital Requirements for a Center Pivot irrigation System.
Item	Feet	Price/ft	Costs
 Standard 7 Tower Center Pivot
 System Base Price	1,320	$28,000
 Drops on 80" Spacing	2,100
 Low Drift Nozzles	2,400
 38" X 11.2 Tires	3,000
 8" Underground Pipe	1,320	$2.52	3,326
 Electrical Wiring	1,320	$1.90	2,508
 12 KVA Generator	2,375
 Total Cost of Center Pivot System	$45,209
 Pump Modification Cost	$4,500
 Total System & Pump Cost	$49,709
 pivot point, electrical wiring and connectors and an electric generator.
The total system and pump modification costs are $49,709.
The MACRS 150% Declining Balance method  is used to calculate tax depreciation.
Both principal and interest payments are calculated for a 5 year amortized note at 9% interest, with the total payment for each of the 5 years equaling $12,780 per year.
The combined federal , state  and self employment  tax rate used here is 36.30%.
In the final after-tax profitability calculations this same combined total tax rate is used.
Water Application Rates and Well Pumping Capacities
 A key aspect of this analysis involves the comparison of irrigated corn yields and net returns across a range of five different gross irrigation pumping capacities for alternative irrigation systems.
Irrigation schedules  are simulated for the 1972-1998 period using climatic data from the KSU Northwest Research-Extension Center in Colby, Kansas.
Irrigation is scheduled as needed according to the climatic conditions, but is limited to the frequencies for the two systems as indicated in Table 2.
The irrigation season is limited to the 90 day period between June 5 and September 2.
The first furrow surface irrigation event in each year is on June 15, reflecting a typical date of first irrigation following the final furrowing process.
After that, furrow irrigation events are scheduled as the capacity limitation allows and if the calculated irrigation deficit exceeds 3 inches.
Center pivot sprinkler irrigation events are scheduled during the 90-day period as the capacity limitation allows and if the calculated irrigation deficit exceeds 1 inch.
Table 2.
Equivalent Irrigation Frequencies and Pumping Capacity for Furrow Surface and Center Pivot Sprinkler Irrigation Systems.
Center Pivot	Furrow Surface
 Gross Irrigation	Frequency	Flowrate	Frequency	Flowrate
 Capacity	& Amount	Gpm per	& Amount	Gpm per
 Inches per Day	Applied	125 acres	Applied	160 acres
 0.250"	1" in 4 days	589	3" in 12 days	754
 0.200"	1" in 5 days	471	3" in 15 days	603
 0.167"	1" in 6 days	393	3" in 18 days	503
 0.125"	1" in 8 days	295	3" in 24 days	377
 1" in 10 days
 3" in 30 days
 Irrigated corn yields for the various alternative irrigation systems and irrigation capacities are also simulated for the same 27 year period using the evapo-transpiration  estimates from the irrigation schedules and using a yield production function developed by Stone et al..
In its simplest form, the model results in the following equation,
 Yield = -184 + 
 with yield expressed in bushels/ acre and ET in inches.
Further application of the model reflects weighting factors for specific growth periods.
These additional weighting factors are incorporated into the simulation to better estimate the effects of irrigation timing for the various systems and capacities.
The weighting factors and their application to the model are discussed in detail by Stone et al..
Crop Revenues, Costs, and Net Returns
 In these profitability projections, the long term corn selling price is assumed to be $2.36 per bushel in western Kansas.
USDA Production Flexibility Contract payments on irrigated corn acres are assumed to be $35/ acre.
The long term wheat selling price is assumed to be $3.18 per bushel with wheat yields assumed to average 44 bushels per acre.
Dryland no-till corn yields are assumed to average 82 bushels per acre.
Farm program Production Flexibility Contract  payments on dryland wheat and corn acres are assumed to be $10 per acre.
The fuel, oil and maintenance cost of applying irrigation water through a center pivot is assumed to be $3.02 per acre-inch, and $2.62 per acre-inch for surface irrigation systems.
No land costs are assumed in these budgets to avoid the effects of varying land rental or purchase market conditions in the High Plains region.
These analyses are performed both with and without KSU labor cost estimates included for the alternative crop enterprises.
By paying special attention to labor costs it may be possible to determine the degree to which claims of labor savings from system conversion are valid or not.
In the following analyses, profitability estimates that represent returns to land, labor and management do not include labor cost estimates.
When labor cost estimates are accounted for, profitability measures represent returns to only land and management.
The time period for this analysis is 15 years.
This time span is a conservative approximation of the expected life span of a newly purchased center pivot system.
No inflation or deflation in crop prices or input costs is assumed during the 15 year period.
Long term average crop selling prices and production costs were taken from KSU Farm Management Guide Budgets.
Specific budgets used included those for Center
 Pivot Irrigated Corn In Western Kansas , Flood Irrigated Corn in Western Kansas , Wheat in a W-S-F Rotation in Western Kansas , and No-Till Corn in a W-C-F Rotation in Western Kansas.
Long term planning prices for western Kansas for corn and wheat were taken from Prices for Crop and Livestock Cost-Return Budgets.
Specific information on the seed, fertilizer, herbicide, insecticide, fuel, oil, machinery, crop insurance, operating interest, and other costs used here are found in the KSU Farm Management Guide budgets, and are available from either the authors or through county extension offices in Kansas and other states.
Long Term Average Irrigation Requirements and Corn Yields
 The simulated irrigation schedules an d corn yield model are use d to generate estimates of the irrigation requirement and corn yields for the various irrigation systems and capacities for each year.
This data is summarized into averages, standard deviations, and maximum and minimum values of irrigation requirements and corn yields.
Standard deviation is used here as a measure of yield variability.
The higher the standard deviation of a particular value the higher the variability of the estimate and vice versa.
The 1 inch/4 days  gross irrigation capacity generates average yield estimates of 196 and 192 bu.
per acre for the 100% efficient center pivot system  and the 85% efficient center pivot , respectively.
For the 70% efficient furrow surface irrigation system  the equivalent application of 3 inches/12 days  leads to an average yield estimate of only 174 bu.
per acre.
Gross average irrigation requirements for the three systems, CP100%, CP85% and FS70% are 13.3, 14.6 and 16.4 inches per acre, respectively.
As gross irrigation system capacity declines further, the projected yields for each of the three irrigation systems decline.
However, CP100% yields decline less than CP85% yields.
Yields for FS70% trailed both CP100% and CP85%, declining from 174 to 118 bu.
per acre.
Yield results for FS70% are most variable across the alternative irrigation capacities.
Water application amounts per acre are higher for FS70% than for CP85%, which in turn are higher than for CP100%.
Corn yields are also simulated for full irrigation.
Under the full irrigation scenario, adequate irrigation water is supplied to meet the crop's evapo-transpiration needs without potential timing delays caused by inadequate irrigation system pumping capacity.
In essence, irrigation water is being optimally supplied to the crop at the same rate in which the crop is using it.
The analysis results show that if full irrigation is possible for all three systems  equal corn yields of 197 bushels per acre would be obtained.
The average irrigation water application for the three systems would
 be 13.9, 16.5, and 20.2 inches for the CP100%, CP85%, and FS70% systems, respectively.
Table 3.
Average Irrigated Corn Yields and Irrigation Application Amounts for 1972-1998
 Irr.
Cor	Irr.
Cor	Irr.
Cor	Irr.
Cor	Irr.
Cor	Irr.
Cor
 n	n	n	n	n	n
 Amou	Amou	Amou	Amou	Amou	Amou
 nt	Yiel	nt	Yiel	nt	Yiel	nt	Yiel	nt	Yiel	nt	Yiel
 d	d	d	d	d	d
 						(bu/
 a	a	a	a	a	a
 A.
Center Pivot Sprinkler System @ 100% Application Efficiency on 125
 Frequen	1" in 4 days	1" in 5 days	1" in 6 days	1" in 8 days	1" in 10	Full
 GPM	589 gpm	471 gpm	393 gpm	295 gpm	236 gpm
 Average	13.3	196	12.0	188	10.7	177	8.6	156	7.2	140	13.9	197
 Std	3.9	43	3.1	36	2.4	4.2	1.7	24	1.2	25	4.2	44
 Minimu	5 111	5 111	5	5	4 103	4	92	5	111
 Maximu	20 261	17	254	14	21	11	188	9	174	21 269
 B.
Center Pivot Sprinkler System @ 85% Application Efficiency on 125
 Frequen	1" in 4 days	1" in 5 days	1" in 6 days	1" in 8 days	1" in 10	Full
 GPM	589 gpm	471 gpm	393 gpm	295 gpm	236 gpm
 Average	14.6	192	12.9	179	11.4	166	9.0	145	7.4	130	16.5	197
 Std	3.9	39	2.9	30	2.1	25	1.6	25	1.2	27	5.1	44
 Minimu	6	111	6 111	6 108	5	94	4	74	6 111
 Maximu	20	259	17	235	14	201	11	182	9 174	25	269
 C.
Furrow Surface Irrigation System @ 70% Application Efficiency on 160 acres 
 Frequen	3" in 12	3" in 15	3" in 18	3" in 24	3" in 30	Full
 cy	days	days	days	days	days	Irrigation
 GPM	754 gpm	603 gpm	503 gpm	377 gpm	302 gpm
 Average	16.4	174	14.4	160	13.0	149	10.6	132	8.4	118	20.2	197
 Std	4.2	32	3.4	28	2.9	27	2.1	28	1.5	30	6.2	44
 Minimu	6 103	6	88	5	75	4	60	3	50	6 111
 Maximu	21	233	18 203	15	181	12	171	9 162	30	269
 a.
Based on 1972-1998 climatic conditions at the Northwest Research Extension Center in Colby, Kansas, and on the Stone et al.
corn yield prediction model.
Regression equations are generated for yields as related to irrigation capacity.
This allows for the calculation of corn yields for specific irrigation well capacities ranging from 200 to 700 gpm for the three alternative irrigation systems.
This perspective is important to decision makers in the Central Great Plains of Kansas who often are dealing with wells that have pumping capacities in this range.
Projected annual average corn yields for CP100% ranged from 3 to 11 bu.
per acre higher than for CP85% corn yields across of the range of well capacities considered here  on 125 acre fields.
However, average corn yields for FS70% on 160 acre fields are from 28 to 33 bu.
per acre lower than CP85% yields for wells in the 300 to 600 gpm pumping capacity range.
The impact of lower furrow surface-irrigated corn yields on this analysis of conversion profitability depends in part on how profitable the nonirrigated crop production on the 35 acres in the center pivot corners is.
No 200 gpm yield outcomes are presented for FS70%, and no 700 gpm yield outcomes are presented for CP100% and CP85% because this would require extrapolation beyond the range of the generated equations.
Figure 1.
Irrigated Corn Yields as affected by Well Pumping Capacity, Irrigation System and Application Efficiency.
Annual After-Tax Net Returns
 Regression equations are also generated for annual after-tax net returns to land, labor and management as related to irrigation capacity for the three irrigation systems.
The results are shown in Table 4 and Figure 2.
These findings indicate that it is profitable to convert from furrow surface irrigation to center pivot irrigation systems, given the yield results and cost-return assumptions used in this study.
At 600 gpm well pumping capacities, both the center pivot irrigation systems examined have $6 to $12 per acre annual net returns advantages over the furrow surface irrigation system.
As well pumping capacity declines to 300 gpm, the advantage of center pivot systems over furrow surface irrigation increases to $25 per acre and $12 per acre for 100% and 85% efficient center pivots, respectively.
Table 4.
After-tax Net Returns for Alternative Irrigation Systems.
Center Pivot	Center Pivot	Furrow Surface
 100% Efficiency	85% Efficiency	70% Efficiency
 Pump Capacity	Total Net	Net Per	Total Net	Net Per	Total Net	Net Per
 	Revenue	Acre	Revenue	Acre	Revenue	Acre
 200	$2,063	$13	$408	$3
 300	6,566	41	4,516	28	$2,519	$16
 400	9,783	61	7,716	48	5,602	35
 500	11,714	73	10,009	63	8,253	52
 600	12,360	77	11,396	71	10,473	65
 The inclusion of labor costs based on K-State Research and Extension budget estimates for these crop enterprises causes furrow surface irrigation net returns to be even lower relative to the center pivot sprinkler system returns.
The addition of labor costs leads to a $15/acre decline in center pivot after-tax annual net returns, and a $22/acre decline in furrow surface irrigation after-tax annual net returns in comparison to the results presented in Table 4 and Figure 2.
Figure 2.
After-tax Net Returns for Alternative Irrigation Systems Per Acre 
 This study shows that it is economically profitable to convert from furrow surface irrigation to center pivot sprinkler irrigation systems.
These findings are dependent upon this study's assumptions about production, costs, and returns fo the alternative irrigation systems.
These results hold true in spite of the irrigator having to pay principal and interest costs for the debt associated with the purchase of the center pivot sprinkler irrigation system and pump modification costs, and having to switch 35 acres of
 previously irrigated cropland out of irrigated corn production and placing it in an intensive dryland cropping system.
Decreased irrigation well pumping capacity has a negative affect upon both the production and the profitability of an irrigated corn enterprise.
For a 160 acre field, annual average irrigated corn yield estimates under furrow surface irrigation are dramatically reduced  as irrigation well capacity declines from 700 to 300 gpm.
To deal with this problem, producers typically reduce irrigated acreage to the level that they can still provide adequate water for irrigated crop growth.
A future direction of this analysis may be to provide better information on how many acres of irrigated crop production can be adequately irrigated under these reduced well capacity scenarios, given the climate of the region.
The associated economic analysis would be driven primarily by changes in irrigated corn yield levels and declines in irrigated acreage as producers seek to find the most productive and profitable irrigated acreage level given their limited water pumping capacities.
These findings support the claims of irrigators that labor savings are a factor that encourages them to convert from furrow surface irrigation to center pivot irrigation systems.
When labor costs were accounted for in this analysis, the relative profitability of furrow surface irrigation system is made even worse in comparison to the profitability of investing in a center pivot irrigation system.
While labor is an important consideration, this analysis suggests that actual corn production levels with furrow surface irrigation versus a center pivot system are more important than labor considerations in the system conversion decision.
Earlier studies typically found that the high initial investment costs for the center pivot irrigation systems typically made them less profitable relative to the existing furrow surface irrigation system.
However, most of these studies were based on the expectation that furrow surface-irrigated corn yields would be approximately equal to those under center pivot irrigation.
This analysis shows that as pumping capacity declines below moderate levels, furrow irrigation of larger fields becomes less profitable relative to investing in a center pivot system.
Dhuyvetter, Kevin C.
1996.
"Converting from Furrow Irrigation to Center Pivot Irrigation Does It Pay?".
Proceedings of the Central Plains Irrigation Short Course and Exposition, pp.
13-22.
Nitrogen and Irrigation Management
 Fact Sheet No.
0.514
 Nitrogen is the plant nutrient most frequently deficient for maximum crop production.
Discontinuing N fertilizer or manure applications typically decreases crop yields.
Following the 4R nutrient approach to nitrogen management helps identify practices to improvement nitrogen efficiency.
The four R's include applying the nitrogen source at the Right rate, at the Right time, in the Right place, and using the Right source.
This fact sheet focuses on the first three of these concepts.
The following practices are a part of a responsible nitrogen management plan.
Choose a realistic yield expectation.
A yield average of five successful crop years
 plus five percent is a recommended yield goal.
Use soil analysis to assess N needs.
If a soil contains high amounts of residual N, decrease N fertilizer accordingly.
For more accurate assessment of N needs, use in-season soil sampling for nitrate testing to complement preplant testing.
Use a reputable soil testing laboratory that provides recommendations consistent with your goals.
Check laboratory provided fertilizer recommendations against university recommendations.
Give N credit for manure and previous legumes.
See Colorado State University Extension bulletins XCM 172 and 568A for determining the correct credits.
Analyze irrigation water to determine if it contains nitrate-N.
Multiply parts per million  of nitrate-N by 0.23 to get pounds of nitrate-N per acre-inch of water.
Credit irrigation water applied during vegetative  growth stages.
Use plant tissue testing, the pre-sidedress soil nitrate test, or chlorophyll meter to assess the N status of the field and the need for additional N fertilizer when making in-season applications.
Recommended N Application Techniques Right Time and Place
 Split N applications to improve uptake efficiency and yield return for fertilizer investment.
Apply one-third at or prior to planting and the balance before the critical growth stage for that crop.
This is especially important for sandy soils that are vulnerable to nitrate leaching.
Avoid application of high rates of N in the fall or at planting time.
Rates can be adjusted during the season if conditions warrant more N fertilizer.
Good nitrogen and irrigation management practices increase yields while reducing fertilizer and irrigation costs.
Best management practices for nitrogen and irrigation management preserve water quality.
Incorporate urea, urea ammonium nitrate, ammonium sulfate, and manure into the soil to prevent volatilization losses of ammonia gas.
Volatilization reduces N efficiency and necessitates higher N application rates.
Use ammonium N fertilizers, such as anhydrous ammonia, to reduce nitrate leaching, especially for fall applications.
Place N and phosphorus in the same band to increase yields, as well as N and phosphorus uptake efficiencies.
Only apply N in irrigation water where irrigation efficiency and uniformity is high.
Fertigation is not recommended in systems with runoff that is not captured in a lined tail-water pond for later reuse.
Do not apply manure to frozen land, especially on slopes, to prevent N loss in runoff waters.
Use slowor controlled-release N fertilizers, such as sulfuror polymercoated urea or urea formaldehyde, on golf courses, lawns, or high-value crops where it is economical.
Keep good records of N fertilizer and manure applications to help make N management decisions later.
Over-irrigation results in leaching of nitrate to the groundwater, surface runoff losses and reduces the efficiency of N fertilizers.
Therefore, irrigation water management is essential for profitable yields and protecting water quality.
Schedule irrigation according to the guidelines below.
Obtain information about your crop's water needs and critical growth stages, soil characteristics and irrigation system efficiency to properly schedule irrigations.
See 4.715, Crop Water Use and Growth Stages.
Table 1: Typical application efficiencies of irrigation systems.
Micro sprinklers and drip	85-95
 Low pressure center pivots	80-90
 High pressure center pivots	75-85
 Side roll/hand move sprinklers	60-70
 Furrow no cutback	40-60
 Furrow with cutback	60-80
 Furrow with surge	70-90
 Use a soil probe to monitor soil moisture.
Probe the field during and after irrigation to determine depth of water penetration.
Determine the soil's moisture content in the effective root zone and its maximum water-holding capacity by measurement or the feel method.
See 4.700, Estimating Soil Moisture.
Determine the application efficiency of your irrigation systems.
Consult a qualified irrigation technician to assess irrigation system performance.
If feasible, use irrigation systems that give higher application efficiencies.
Use measuring devices such as flumes and water meters to determine how much water you apply.
When using siphon tubes or gated pipes, multiply the stream flow rate by the irrigation duration.
With surface irrigation, use cutback practices to reduce deep percolation and runoff.
Operate sprinklers to apply water rates that match intake rates of soil.
Agricultural Crop Water Use
 Danny H.
Rogers Professor, Extension Irrigation Engineer, Biological and Agricultural Engineering
 Jonathan Aguilar Assistant Professor, Water Resources Engineer, Southwest Research Extension Center
 Isaya Kisekka Assistant Professor, Irrigation Research Engineer, Southwest Research Extension Center
 Philip L.
Barnes Associate Professor, Water Quality, Biological and Agricultural Engineering
 Freddie R.
Lamm Professor, Irrigation Research Engineer, Northwest Research and Extension Center
 Crop water use, also referred to as evapotranspiration , is the water used by a crop for growth and cooling.
Crop water use, or crop water requirement, is the total amount of water needed for evapotranspiration from planting to harvest for a given crop in a specific climate, when adequate soil water is maintained by rainfall and/or irrigation SO it does not limit plant growth and crop yield.
Only a small fraction of the water a plant takes in is used for growth, often only about 1 percent; the majority of water is needed to allow the plant to cool itself.
The movement of water into the plant is important, since this water carries essential nutrients needed by the plant for growth processes.
Both evaporation and transpiration processes require energy or heat.
This heat energy comes from the sun  or from advective heat, which is heat moved by air masses.
Since this is a physical process, it can be predicted for a known crop using weather information.
The common procedure for estimating the crop water use for a specific crop is to input weather data into an equation developed to predict the water use for a reference crop.
The reference crop is often
 Evapotranspiration is the combination of two words: evaporation and transpiration.
Evaporation refers to the water that moves from a wetted soil or leaf surface directly to the atmosphere, while transpiration refers to the water that the plant to be used in the growth process or released into the atmosphere.
The term evapotranspiration was coined since the two processes can occur simultaneously and are difficult to measure separately.
either grass or alfalfa of a specific height.
The reference crop ET is often designated ETo for grass or ETr for alfalfa.
The reference crop ET is then modified to the actual crop water use using a crop coefficient , which is unique for each crop species.
The Kco's vary by crop and by the stage of growth of the specific crop.
This process is more fully discussed in K-State Research and Extension publication MF2389, What is ET?.
Crop Water Use Fluctuations
 Diurnal/Nocturnal Crop Water Use
 Since crop water use is an energy-driven process, crop water use has a diurnal  cycle.
The most commonly reported crop water use is the daily  crop water use.
Daily use can have significant variation driven by the weather conditions, such as a hot and windy day versus cool and cloudy day.
Seasonal crop water use varies for a given crop based on the summation of the growing season conditions.
During drought, reference crop ET rates are higher because the daily weather conditions are hotter and with clear skies, allowing more solar radiation to reach the crop leaf surface as contrasted with cooler and cloudy days.
During drought, crop water use may be suppressed if the plants are stressed due to lack of adequate soil water from the lack of precipitation events and no irrigation.
The processes occurring internally in the plant are photosynthesis and respiration.
Photosynthesis is unique to plants because chloroplasts in the plant cells give them
 the ability to capture light energy and produce sugar  when carbon dioxide and water are available.
Photosynthesis allows plants to convert light energy into a form that can be used to fuel plant growth.
This growth process is called respiration, which is the metabolizing  of sugar for plant growth and other life processes.
Both plants and animals respire.
Plants release oxygen during photosynthesis but require oxygen to complete respiration.
Photosynthesis can only occur in the presence of light, while respiration can occur whether dark or light.
In a similar manner to respiration, soil water evaporation can occur throughout a 24-hour period; however, the rate of evaporation would likely increase with the additional solar radiation energy of the daytime hours.
Soil evaporation also decreases as the soil surface dries.
It also decreases under a crop canopy that shields the soil surface from sunlight and wind.
Figure 1 shows the generalized relationship between soil evaporation and transpiration for a location with wet soil and a crop canopy.
The figure also shows the effect of irrigation on the transpiration and evaporation process.
Notice that canopy evaporation greatly increased the water flux as soon as the canopy was wetted by sprinkler irrigation and stayed high until the irrigation ceased and the leaves dried.
There was also a small water flux associated with droplet evaporation during the irrigation event.
Transpiration through the plant occurs at a lesser rate than does direct evaporation from the plant canopy.
Daily Crop Water Use Fluctuations
 Daily ET for a crop varies throughout the growing season as driven by two factors:  the weather conditions  and  the stage of the crop's growth.
These two factors are illustrated in Figure 2: the top line represents the typical crop water use rate for a reference crop as influenced by weather conditions of wind, temperature, solar radi-
 ation, and humidity.
During the typical growing season in Kansas, the weather conditions cause ET demands to increase as spring turns into summer and then start decreasing as fall approaches.
However, the crop also has to advance through its growth stages, SO in the early season when the crop is small, its actual water use rate is also small, as represented by the lower line in Figure 2.
Water use increases as plants add leaves and increase the total leaf area.
It then gradually begins to
 Figure 1.
Water use for a rotator sprinkler placed on top of the pivot lateral irrigating at noon for 50 minutes.
The figure illustrates, in addition to how water is lost during irrigation, that crop transpiration occurs during daylight hours, while soil water evaporation occurs throughout the entire day.
Irrigation in the U.S.
is primarily mechanized, with more than 57% of the irrigated land equipped with center pivot irrigation systems.
Nebraska has 8.3 million irrigated acres, which account for 14.9% of the total irrigated acreage in the U.S.
Nebraska uses approximately 90% of its water for irrigation, having over 80,000 center pivot irrigation systems.
With this in mind, we can set up some trigger dates to assess moisture levels and pasture conditions, informing the implementation of a drought management plan.
May 20 to June 10: Assess earlier precipitation levels.
If March-May precipitation was 50-75% of the long-term average, reduce stocking rates 30-40% or more depending upon grass species and plant health;
Soil Water Recharge Function as a Decision Tool for Preseason Irrigation
 F IELD plot soil water data collected at Colby, Kansas from 1979 through 1982 were used to develop an empirical model to predict available soil water content after corn planting  from fall soil water content and fall through spring precipitation.
Soil water storage and storage efficiency were both found to be negatively linearly related to fall soil water content.
The overall 3-yr storage efficiency equation had a high correlation, R2 = 0.87 at significance level P > 0.01.
The soil water recharge function is centered around a water storage efficiency equation developed over wide ranges of fall through spring precipitation and fall soil water contents.
Decision tools predicting the need for fall preseason irrigation based on estimates of fall soil water and the fall through spring precipitation probabilities are presented.
This model's simplicity makes it practical as a criterion for determining the need for fall preseason irrigation for corn on the silt loam soils of western Kansas.
Rising concern about declining water supplies and high pumping costs has focused attention on the efficiency of various irrigation management techniques.
Preseason irrigation for corn is one management option that has been questioned.
There is still a considerable amount of preseason irrigation for corn conducted in the fall in western Kansas, despite the fact that in many years overwinter precipitation will recharge the crop root zone to field capacity.
Practical criteria for evaluating the need for preseason irrigation in western Kansas are needed.
Previous studies have indicated that a negative correlation exists between the initial soil water content and soil water storage from precipitation.
Power et al.
in a North Dakota study found that nearly all winter precipitation was lost when fall irrigation was practiced, while dryland plots stored
 Article was submitted for publication in February, 1985; reviewed and approved for publication by the Soil and Water Div.
of ASAE in July, 1985.
Contribution from the Colby Branch Experiment Station and the Northwest Kansas Area Extension Office, Kansas State University, Manhattan, KS, Contribution No.
85-336-J.
significant amounts of precipitation as soil water.
Willis et al.
observed that fall irrigation subsequently increased runoff during precipitation, thus contributing to inefficient water storage.
Mathews and Army  reported soil water storage during fallow was negatively correlated with initial water content at 25 research stations in the Great Plains.
Wittmuss and Yazar , from an analysis of winter soil water storage for 3 years at Lincoln, NE, found storage efficiency varied from 0 to 77% depending on initial soil water, winter precipitation and tillage system.
Musick  at Bushland, TX found a negative linear relationship between soil water after grain sorghum harvest and winter-precipitation storage.
Winter storage efficiency, the fraction of winter precipitation stored in the soil profile, reached a maximum of 55% when clay loam soils were initially near the wilting point and decreased to nearly zero when initially at field capacity.
Similar results have been reported at northern locations.
Timmons and Holt  reported a negative linear relationship between soil water after corn harvest and winter soil water recharge at 10 locations in the northern United States during the mid-1960's.
Hobbs and Krogman  also observed, that for a number of crops in Alberta, Canada, winter soil water storage and fall soil water content had a negative linear relationship.
Stone, et al.
analyzed 3 years of data from Tribume, KS, finding a negative curvilinear relationship between the rate of soil water storage and fall soil water.
However, plots of each year's data suggest linear relationships with different slopes and intercepts among years.
This report will discuss the development of a model to evaluate soil water storage in terms of two variables, initial soil water content  and winter precipitation.
The model can be used as a criterion for decisions concerning fall preseason irrigation for corn.
Although the equation may be specific to northwest Kansas, the developmental procedure is applicable elsewhere.
The study was conducted from 1979 through 1982 at the Colby Branch Experiment Station, Colby, KS, on a deep well-drained Keith silt loam.
This medium-textured loessial soil, typical of many western Kansas soils, is described in more detail by Bidwell et al..
A 1.5 m crop root zone is typically considered for irrigation management, although some water may be extracted from deeper depths in dryland production.
This 1.5 m soil profile will hold approximately 250 mm of plant available soil water
 at field capacity.
This corresponds to a volumetric soil moisture content of approximately 0.30 cm/cm and a profile bulk density of approximately 1.3 g/cm.
The climate can be described as semi-arid with a continental-type precipitation distribution.
The 70-year average annual precipitation at Colby is 473 mm.
Annual lake evaporation is approximately 1400 mm.
The four treatments in the main study consisted of preseason irrigations applied in the fall, spring, late summer or no preseason irrigation, each replicated three times in a randomized complete block design.
All irrigations were applied by furrow irrigation using cutback procedures.
Irrigation flow-rates to individual furrows were evenly matched across the field with a hand-held flow measuring device, but no efforts were made to measure total inflows and runoff.
However, for the purposes of this report data from each soil water sampling location is considered as point data, without regard to treatment or replication and there will be no further discussion of individual treatments.
The data from the spring irrigation treatment was excluded from the regression analysis as the irrigation occurs between the period of interest, fall-spring.
The data base was extended by including data from two additional fallspring fallow studies conducted in 1979-80 on nonirrigated soils.
The plots, approximately 90 m by 9 m with approximate land slope of 0.5%, were chiseled, double disked and corrugated in the fall.
Soil water contents were determined gravimetrically in 30 cm increments to 1.5 m at two sites in each plot in the fall of 1979 and the spring of 1980.
Soil water measurements were made before and after fall irrigation, before and after spring irrigation, and after corn planting.
Results from 1979-1980 indicated the need for more frequent monitoring of soil water, so in the fall of 1980 and again in 1981 neutron probe access tubes were installed to a depth of 1.5 m at two locations in each plot.
Volumetric soil water contents were measured at each site on at least six dates during the fall-spring fallow period.
Irrigation water management for corn production often results in residual available soil water in the profile after harvest.
Correct decisions concerning the need for preseason irrigation involves knowing the effects the initial soil water content and preseason precipitation will have on the final available soil water at planting , expressed by the following equation,
 FASW = IASW + A ASW [1]
 where IASW is the initial available soil water content
 after harvest and A ASW the change in soil water storage during the fallow period.
The initial fall available soil water content, IASW, can be measured or estimated, but the change in soil water content, A ASW must be predicted.
Since A ASW is negatively correlated with IASW, linear and polynomial regressions were used to evaluate the relationship between ASW and IASW.
Equations derived from each year's results were different, but all were linear of the form,
 A ASW = a + b IASW [2]
 where A ASW is defined as above, IASW is the measured available soil water content to a 1.5 m soil profile depth after corn harvest, a is the intercept, and b is the slope of the line.
The regression statistics for the soil moisture storage function are shown in Table 1.
The difference in regression coefficients between years suggests that other factors influenced soil water storage, such as amount and distribution of snow and rainfall.
For example, Musick  reported striking contrasts in soil water storage due to precipitation in 3 very different years.
The equations as presented in Table 1 are of little use for prediction of future soil water storage because they change significantly with the year of study.
Clearly, more than initial soil water  must be used to evaluate soil water storage, A ASW.
Storage efficiency,  has been used to explain the effects of precipitation  on A ASW as in equation [3].:
 EFF = A ASW / P [3]
 The boundary conditions for this equation are undefined EFF for P=0, and EFF= as P approaches infinity.
However, for regression equations, caution should be used when approaching the boundaries which may be beyond the range of data.
It is also possible for A ASW to be negative due to long-term drainage or evaporation losses.
As suggested by some, A ASW might increase curvilinearly with P, especially at low precipitation rates.
If so, EFF might vary appreciably with yearly variation in precipitaiton.
However, Stone et al.
indicated the curvilinear response of storage efficiency to precipitation amount was slight.
Also, their period of investigation was November through March, typically a period of low precipitation in western Kansas.
Musick et al.
found soil water storage to be linearly related to precipitation in the range 70 to 350 mm.
This suggests that a certain amount of precipitation would be lost to evaporation before any net soil water storage occurs.
This linear relationship indicates storage efficiency to be fairly constant over a considerable range of precipitation values.
TABLE 1.
LINEAR REGRESSION STATISTICS FOR SOIL WATER STORAGE EQUATIONS OF THE FORM, A ASW = a + b , WITH A ASW AND IASW IN mm.
Sampling dates	Number of	Intercept	Slope	Correlation	of estimate,
 observations	a	b	R2	mm
 11/28/79	6/5/80	54	244	-0.925	0.943	16
 11/19/80	5/11/80	18	235	-0.787	0.947	13
 1/26/82	5/20/82	18	165	-0.615	0.619	21
 All years	90	221	-0.814	0.858	22
 TABLE 2.
LINEAR REGRESSION STATISTICS FOR STORAGE EFFICIENCY EQUATIONS OF THE FORM, EFF = c + d , WITH EFF IN % AND IASW IN mm.
Sampling dates	Standard error
 and	Number of	Intercept	Slope	Correlation	of estimate,
 precipitation, mm*	observations	c	d	R2	%
 11/28/79	6/5/80	210	54	116	-0.44	0.944	8
 11/19/80	5/11/81	266	18	88	-0.30	0.952	5
 1/26/82	5/20/82	119	18	139	-0.52	0.621	17
 All years	198	90	116	-0.43	0.865	11
 *Precipitation between fall and spring soil water sampling.
From equation [3], it follows that if ASW is functionally related to IASW, then EFF must also be related to IASW.
Regression analysis of EFF with IASW has indicated the following equation fits all three series of data:
 EFF = C + d IASW [4]
 where EFF is expressed in percent, c is the intercept, and d is the slope of the line.
The regression statistics and the fall to spring precipitation for the 3 years are shown in Table 2.
Some yearly variation occurred but the overall equation has a good correlation with an R2 = 0.87 at a significance level of P > 0.01.
However, this equation should not be used when analyzing dry soils beyond the range of the data, because a storage efficiency of more than 100% will be predicted where IASW is zero.
Predicted storage efficiencies greater than 100% for dry soils may be a limitation of the linear model or inaccuracy in measurements of soil water contents or snowfall.
Typically corrugated field plots collect more snow than standard rain gages.
Storage efficiencies for the driest plots were generally in the 60 to 75% range, somewhat higher than the 55% maximum value reported by Musick.
Infiltration differences between the Pullman clay loam at Bushland, TX and the Keith silt loam of this study might explain much of that difference.
Percolation may have lowered the efficiencies cited by Musick, as the 1.2 m depth was the profile under consideration.
Also evaporation during
 Fig.
1-Relationship of storage efficiency  to fall available soil water content.
this part of the year is probably higher at Bushland than at Colby.
Winter storage efficiencies of approximately 31% on dry soils in Canada reported by Hobbs and Krogman  were much less than efficiencies found in this study.
Their values may have been lower because of reduced infiltration on frozen soils, sublimation of snow, or losses by percolation.
On the other hand, Timmons and Holt  reported storage efficiencies as high as 77% for areas in the northern United States.
Stone et al.
reported maximum storage efficiencies of approximately 45% at Tribune, KS.
However, for their 3-year study the maximum cumulative preseason precipitation amount was less than 90 mm.
Precipitation between November to March typically occurs in small events and evaporation might have reduced their reported storage efficiencies.
Kuska and Mathews  in a 25-year study at Colby, KS, found approximately 80% of the winter precipitation was stored in soils of wheat stubble fields left undisturbed until May.
They reported considerable yearly variation, with overwinter storage decreasing in years when the soil was wet after harvest.
The undisturbed wheat stubble traps snow and can reduce evaporation.
Similarly, the corrugated fields in our study can trap snow through generally not as well as stubble.
Fall corrugation is a common practice on tilled fields to reduce wind erosion in western Kansas.
Storage efficiencies of our study, though higher than some reported in the literature, are reasonable.
Storage efficiency was negative for some plots in 1979-1980 because of initial soil water contents above "field capacity".
Over time, drainage continued and the spring soil water amounts were less than the fall amounts.
This is not unusual because "field capacity" is a somewhat arbitrary point where rapid drainage ceases.
It is often defined as the amount of water in the soil 3 days after a large rain or irrigation.
Though deep drainage is not a total loss from the soil profile, as it may return to the aquifer, it is a loss in this storage efficiency equation, since we are concerned only with the top 1.5 m.
This deep drainage is also soil water which is unlikely to be recovered by plant roots where irrigation is practiced.
As noted earlier, EFF will approach zero as P approaches infinity because a given soil profile does not have infinite storage capacity.
In our study, "field capacity" was approximately 250 mm, although more water can be stored on a short-term basis.
Indeed, storage efficiencies for 1980-1981 were low due to excessive precipitation.
Storage efficiencies for November through March 31 , compared with those of November through May 11 , are shown in Fig.
2.
Many of the plots were approaching "field capacity" on March 31.
The additional 153 mm of precipitation between March
 Fig.
2-Storage efficiency as a function of fall available soil water compared during periods of limiting and unlimiting precipitation.
Fig.
3-Predicted available soil water  at planting in relation to fall soil water and total DecemberMay precipitation.
31 and May 11 exceeded the remaining available storage in the profile of even the drier plots, and as a result storage efficiencies decreased.
Some of this decreased efficiency can be attributed to runoff and evaporation, but most was probably loss to profile drainage below 1.5 m, the depth to which soil water content was measured.
The preceding discussion emphasizes the need to "calibrate" a storage efficiency equation with data from years when the precipitation does not grossly exceed the storage capacity.
When precipitation is abnormally high, high amounts of storage may be indicated by such a "calibrated" equation, but these storage amounts can be easily truncated back to values comparable to storage capacity of the soil.
During the period 1979-1982, fall to spring precipitation did not grossly exceed storage capacity of the drier soils, at least for a significant portion of the fallow period.
As a result, our equation should be reasonably valid over a considerable range of precipitation amounts.
Rearrangement of equation [3] and substitution into equation [1] yields:
 FASW = IASW +  [5]
 and substituting the overall 3-year relationship of EFF to IASM  into equation [5] yields:
 FASW = IASW +  X P) [6]
 where all variables are expressed in mm.
Now FASW can be predicted from two variables, IASW and P.
Fig.
3 shows how various IASW and precipitation amounts can affect FASW.
This figure illustrates that even when soil water is low in the fall, with average December through May precipitation, FASW will exceed 90% of field capacity.
In addition some storage is likely to occur in June when the corn evapotranspiration rate is less than the precipitation.
The resulting FASW for P = 0 is likely to be reduced somewhat from the 1:1 relationship shown due to evaporation and percolation depending on the IASW level and the water contents of the different depths.
Although the fall through spring precipitation can not be predicted in advance, probability values of
 precipitation can be used for predicting FASW.
Fig.
4 shows the cumulative December-May precipitation amounts for Colby, KS, based on exceedance probabilities using a Log Pearson Type III distribution.
Using the exceedance probabilities in Fig.
4 and the relationship expressed in equation [6], the probability of needing preseason irrigation to reach a specified percentage of "field capacity" can be determined.
With a fall available soil water content  of 150 mm there is a 60% chance of needing irrigation to reach 100% of "field capacity".
Accepting 80% of "field capacity" and an IASW of 150 mm, the probability of needing irrigation is only 5%.
In addition to determining if the irrigation is needed, it is useful to know the amount of preseason irrigation required.
Many surface irrigation systems do not have the ability to apply a small irrigation amount evenly across a recently corrugated field.
In this case, a decision needs to be made whether to accept a lower level of soil water at planting and not irrigate in the fall, or whether to apply a larger irrigation amount realizing that some of the fall through spring precipitation may be lost to deep drainage.
Fig.
6 shows the net irrigation required at various IASW to achieve a desired certainty of reaching field capacity.
Net irrigation in this case implies the increase in IASW over the non-irrigated value.
The equations are handled as before with the new IASW reflecting the increase due to irrigation.
The efficiency of the irrigation process itself
 Fig.
4-Probability of exceedance for total December through May precipitation at Colby, Kansas  using a Log Pearson Type III distribution and the associated statistics.
Fig.
5-Probability of needing fall preseason irrigation to reach a specified percentage of field capacity by June 1 as affected by fall soil water content  at Colby, KS.
will be related to system type and design.
With IASW at 150 mm, a fall net irrigation amount of 50 mm will give an approximately 60% probability of reaching 100% of "field capacity".
An increase to 80% probability is possible if a 75 mm irrigation amount is applied.
Regardless of what level of probability the producer is willing to accept, in some years soil water content at planting will be deficient, which could have a significant impact on crop yield.
The probability of not having sufficient soil water in the seed zone for germination is very low due to high probabilities of some precipitation in late April or early May.
In some years germination may be delayed beyond the optimum date due to insufficient precipitation.
However, fall preseason irrigation is no guarantee there will be sufficient seed zone soil water in the spring.
The deficiencies below the seed zone might be reason for concern.
However, most irrigation systems have excess capacity in June and could add a significant amount of water to a deficient soil profile before the peak water use period of July through August.
Fig.
6-Probability of reaching field capacity by June 1 with various initial fall soil water contents  as affected by net preseason irrigation amounts at Colby, KS.
A model has been developed to be used as a tool in the decision-making process concerning fall preseason irrigation of corn on the silt loam soils of northwest Kansas.
This model can help the irrigator make a decision about whether or not to irrigate in the fall to insure adequate soil water for the next crop season.
Using probability, the irrigator can determine the need for irrigation as well as determining what irrigation amount is necessary to reach a desired soil water content at planting.
The procedure used to develop this model could be used in other regions, even though the coefficients are likely to be site specific.
The model suggests that in most years fall preseason irrigation for corn is not needed to recharge the soil profile in northwest Kansas.
A rational approach, such as this model provides, could result in the largest single water savings an irrigator could obtain in a single season.
elaborate on what criteria are important in the decisionmaking process and to provide an approach for evaluating the need for fall preseason irrigation.
Preseason irrigation is a tool that should be used wisely to minimize unnecessary costs and water use.
Table II shows the typical amount of water that will be in the different soils types and can be used to help estimate the volume of water.
Remember to use the top 4 ft of soil for the active root zone and plan to use the soil water down to 40% of plant available water  after the dough stage for corn/sorghum and the R5 stage for soybeans/dry beans.
The amount of irrigation applied last year or the year before may have very little to do with the amount needed this year.
The long-term average of irrigation application depth and timing is relatively meaningless for the decisions producers need to make on any given day in the current growing season.
However, without any additional data, all an irrigator can do is put on about the same amount of water as in the past and make slight adjustments if the weather is dry or wet.
EVALUATING ENERGY USE FOR PUMPING IRRIGATION WATER
 ENERGY USE IN IRRIGATON
 Irrigation of 13.8 million acres of cropland accounts for a large portion of the energy used in Colorado, Nebraska, and Kansas.
Analysis of data from the 2008 USDA Farm and Ranch Irrigation Survey shows that the average energy use for irrigating crops in Nebraska alone would be equivalent to about 340 million gallons of diesel fuel annually if all pumps were powered with diesel engines.
While use varies depending on annual precipitation, average yearly energy consumption in Nebraska is equivalent to about 40 gallons of diesel fuel per acre irrigated.
The cost to irrigate a field is determined by the amount of water pumped and the cost to apply a unit  of water.
Factors that determine pumping costs include those that are fixed for a given location  and those that producers can influence.
The factors that producers can influence include: irrigation scheduling, application efficiency, efficiency of the pumping plant, and the pumping pressure required for center pivot system.
Pumping costs can be minimized by concentrating on these factors.
Irrigators may also consider changing the type of energy used to power irrigation if they determine that one source provides a long-term advantage.
Irrigation scheduling can minimize the total volume of water applied to the field.
Demonstration projects in central Nebraska have indicated that 1.5-2.0 inches of water can be saved by monitoring soil water and estimating crop water use rates.
The goal is to maximize use of stored soil water and precipitation to minimize pumping.
Improving the efficiency of water application is a second way to conserve energy.
Water application efficiency is a comparison between the depth of water pumped and the depth stored in the soil where it is available to the crop.
Irrigation systems can lose water to evaporation in the air or directly off plant foliage.
Water is also lost at the soil surface as evaporation or runoff.
Excess irrigation and/or rainfall may also percolate through the crop root zone leading to deep
 percolation.
For center pivots, water application efficiency is based largely on the sprinkler package.
High pressure impact sprinklers direct water upward into the air and thus there is more opportunity for wind drift and in-air evaporation.
In addition, high pressure impact sprinklers apply water to foliage for 20-40 minutes longer than low pressure spray heads mounted on drop tubes.
The difference in application time results in less evaporation directly from the foliage for low pressure spray systems.
Caution should be used so that surface runoff does not result with a sprinkler package.
Good irrigation scheduling should minimize deep percolation.
Figure 1.
Diagram of factors affecting irrigation pumping costs.
Energy use can also be reduced by lowering the operating pressure of the irrigation system.
One must keep in mind that lowering the operating pressure will reduce pumping cost per acre-inch, but reducing the pressure almost always results in an increased water application rate for a center pivot.
The key is to ensure that the operating pressure is sufficient to eliminate the potential for surface runoff.
Field soil characteristics, surface roughness, slope and tillage combine to control how fast water can be applied to the soil surface before surface runoff occurs.
If water moves from the point of application, the savings in energy resulting from a reduction in operating pressure is counterbalanced by the need to pump more water to ensure that all portions of the field receive at least the desired amount of water.
Finally, energy can be conserved by ensuring that the pumping plant is operating as efficiently as possible.
Efficient pumping plants require properly matched pumps, systems and power sources.
By keeping good records of the amount of water pumped and the energy used, you can discover if extra money is being
 spent on pumping the water and how much you can afford to spend to fix components that are responsible for increased costs.
This document describes a method to estimate the cost of pumping water and to compare the amount of energy used to that for a well maintained and designed pumping plant.
The results can help determine the feasibility of repairs.
The cost to pump irrigation water depends on the type of energy used to power the pumping unit.
Electricity and diesel fuel are used to power irrigation for about 76% of the land irrigated in the region.
Nebraska uses electricity or diesel fuel to power pumping plants used to irrigate approximately 7.58 million acres of cropland.
Natural gas and Propane are used on about 20 and 4% of the land in the 3-state region, respectively.
Kansas leads the region in the use of natural gas for pumping plant power with approximately 1.4 million acres irrigated.
Very little land is irrigated with gasoline powered engines.
The cost to pump an acre-inch of water depends on:
 The work produced per unit of energy consumed,
 The distance water is lifted from the groundwater aquifer or surface water source to the pump outlet,
 The discharge pressure at the pump outlet,
 The performance rating of the pumping plant, and
 The cost of a unit of energy.
The amount of work produced per unit of energy depends on the source used to power the pump.
One gallon of diesel fuel will generate about 139,000 BTU of energy if completely burned.
The energy content can also be expressed as the horsepower-hours of energy per gallon of fuel.
Not all of the energy contained in the fuel can be converted to productive work when the fuel is burned in an engine.
The Nebraska Pumping Plant Performance Criteria  was developed to provide an estimate of the amount of work that can be obtained from a unit of energy by a well designed and managed pumping plant.
Values were developed from testing engines and motors to determine how much work  could be expected from a unit of energy.
An average efficiency for the pump and drive system for well designed and maintained pumping plants was used to provide the amount of work that could be expected from a "good" pumping plant.
The overall performance of the engine/motor and pump system is expressed as water horsepower hours.
Research conducted to develop the NPPPC showed that diesel engines produced about 16.7 hp-hr of work per gallon of diesel fuel and that good pumping plants would produce about 12.5 whphr/gallon of diesel fuel.
The performance of the engine and pumping plant systems can also be expressed as an efficiency, i.e., the ratio of the work done
 compared to the energy available in the fuel.
Results show that a diesel engine that meets the Nebraska Pumping Plant Criteria is only about 30% efficient and that the overall efficiency is only about 23%.
Diesel engines are more efficient than spark engines.
Figure 2.
Diagram of pumping lift and discharge pressure measurements needed to assess pumping efficiency.
The amount of energy required for a properly designed and maintained pumping plant to pump an acre-inch of water can be determined from Tables 2 and 3.
Table 1.
Energy Content of Fuels for Powering Irrigation Engines
 Average Energy	Nebraska Pumping Plant
 Engine or	Pumping	Engine or	Pumping
 Motor	Plant	Motor	Plant
 Energy Source	Horsepower	Performance	Performance	Efficiency	Conversion
 BTU	hour	hp-hr/unit	whp-hr/unit	%	%
 1 gallon of diesel fuel	138,690	54.5	16.7	12.5	31	23
 1 gallon of gasoline	125,000	49.1	11.5	8.66	23	18
 1 gallon of liquefied petroleum gas 	95,475	37.5	9.20	6.89	25	18
 1 thousand cubic foot of natural gas	1,020,000	401	82.2	61.7	21	15
 1 therm of natural gas	100,000	39.3	8.06	6.05	21	15
 1 gallon of ethanol	84,400	33.2	7.80	5.85	X	X
 1 gallon of gasohol (10% ethanol, 90%
 gasoline)	120,000	47.2	11.08	8.31	X	X
 1 kilowatt-hour of electrical energy	3,412	1.34	1.18	0.885	88	66
 I Conversions: 1 horsepower = 0.746 kilowatts, 1 kilowatt-hour = 3412 BTU, 1 horsepower-hour = 2,544 BTU t Assumes an overall efficiency of 75% for the pump and drive.
Nebraska Pumping Plant Criteria for fuels containing ethanol were estimated based on the BTU content of ethanol and the performance of gasoline engines.
For example, a producer who has a system with a pumping lift of 150 feet and operates at a pump discharge pressure of 60 pounds per square inch  would require 2.63 gallons of diesel fuel to apply an acre-inch of water.
If the producer uses electricity the value of 2.63 should be multiplied by the factor in Table 3 to convert energy units.
So, for electricity  = 37 kilowatt-hours would be needed per acre inch of water from a well with a pumping lift of 150 feet and an outlet pressure of 60 psi.
The amount of energy required for an actual pumping plant depends on the efficiency of the pump and power unit.
If the pumping plant is not properly maintained and operated, or if conditions have changed since the system was installed, the pumping plant may not operate as efficiently as listed in Table 2.
The energy needed for an actual system is accounted for in the NPPPC.
Table 4 can be used to determine the impact of a performance rating less that 100%.
For a performance rating of 80% the multiplier is 1.25, so the amount of energy used would be 25% more than for a system operating as shown in Table 2.
The amount of diesel fuel for the previous example would be  = 3.29 gallons per acre-inch of water.
Table 2.
Gallons of diesel fuel required to pump an acre-inch at a performance rating of 100%.
Lift	Pressure at Pump Discharge, psi
 feet	10	20	30	40	50	60	80
 0	0.21	0.42	0.63	0.84	1.05	1.26	1.69
 25	0.44	0.65	0.86	1.07	1.28	1.49	1.91
 50	0.67	0.88	1.09	1.30	1.51	1.72	2.14
 75	0.89	1.11	1.32	1.53	1.74	1.95	2.37
 100	1.12	1.33	1.54	1.75	1.97	2.18	2.60
 125	1.35	1.56	1.77	1.98	2.19	2.40	2.83
 150	1.58	1.79	2.00	2.21	2.42	2.63	3.05
 200	2.03	2.25	2.46	2.67	2.88	3.09	3.51
 250	2.49	2.70	2.91	3.12	3.33	3.54	3.97
 300	2.95	3.16	3.37	3.58	3.79	4.00	4.42
 350	3.40	3.61	3.82	4.03	4.25	4.46	4.88
 400	3.86	4.07	4.28	4.49	4.70	4.91	5.33
 Table 3.
Conversions factors for other energy sources.
Energy Source	Units	Multiplier
 Natural Gas	1000 cubic feet	0.2026
 Table 4.
Multiplier when pumping plant performance rating is less than 100%.
Rating, %	100	90	80	70	50	30
 Multiplier	1.00	1.11	1.25	1.43	2.00	3.33
 Producers can use Tables 2-4 and their energy records to estimate the performance rating for their pumping plant and the amount of energy that could be saved if the pumping plant was repaired or if operation was adjusted to better match characteristics of the pump and power unit.
Producers can also use hourly performance to estimate how well their pumping plant is working.
For the hourly assessment an estimate of the pumping lift, discharge pressure, flow rate from the well and the hourly rate of energy consumption are required.
The acre-inches of water pumped per hour can be determined from in Table 5.
Table 5.
Volume of water pumped per hour.
Pump	Water Pumped	Pump	Water Pumped
 Discharge	per Hour	Discharge	per Hour,
 gpm	acre-inch/hr	gpm	acre-inch/hr
 250	0.55	1250	2.76
 300	0.66	1300	2.87
 350	0.77	1350	2.98
 400	0.88	1400	3.09
 450	0.99	1500	3.31
 500	1.10	1600	3.54
 550	1.22	1700	3.76
 600	1.33	1800	3.98
 650	1.44	1900	4.20
 700	1.55	2000	4.42
 750	1.66	2100	4.64
 800	1.77	2200	4.86
 850	1.88	2400	5.30
 900	1.99	2600	5.75
 950	2.10	2800	6.19
 1000	2.21	3000	6.63
 1050	2.32	3200	7.07
 1100	2.43	3400	7.51
 1150	2.54	3600	7.96
 1200	2.65	3800	8.40
 The performance of the pumping plant  in terms of energy use per acre-inch of water is then the ratio of the hourly energy use divided by the volume of water pumped per hour:
 fuel use rate  -
 For example, suppose a pump supplies 800 gallons per minute and the diesel engine burns 5.5 gallons of diesel fuel per hour.
A flow rate of 800 gpm is equivalent to 1.77 acre-inches per hour.
The pumping plant performance is computed as 5.5 gallons of diesel per hour divided by 1.77 acre-inches of water per hour.
This gives 3.11 gallons of diesel per acre-inch.
Suppose that the pumping lift is 150 feet and the discharge pressure is 60 psi for this example.
If the system operates at the Nebraska Pumping Plant Performance Criteria only 2.63 gallons of diesel per acre-inch would be required.
The pumping plant performance rating  would be:
 from Table 2 100 x 2.63 Pp 3.11
 For this case the performance rating is 85 meaning that the system uses about 18% more diesel fuel than required for a system at the Nebraska Criteria.
The multipliers in Table 2 can also be used with the hourly method for other energy sources.
Energy savings from repairing the pumping plant should be compared to the ability to pay for the repairs.
The money that can be paid for repairs is determined by the length of the repayment period and the annual interest rate.
These values are used to compute the series present worth factor.
The breakeven investment is the value of the annual energy savings times the series present worth factor.
The series present worth factor represents the amount of money that could be repaid at the specified interest rate over the repayment period.
For example, for an interest rate of 7% and a repayment period of 10 years each dollar of annual savings is equivalent to $7.02 today.
Only $4.10 could be invested today for each dollar of savings if the investment was to be repaid in 5 years rather than 10 years.
Suppose a pivot was used on 130 acres to apply 13.5 inches of water.
The pumping lift was about 125 feet and the discharge pressure was 50 psi.
Energy use records for the past season show that 5500 gallons of diesel fuel were used.
The average price of diesel fuel for the season was $3.00 per gallon.
Using the value of 2.19 gallons of diesel fuel per acre-inch from Table 2, an efficient
 pumping plant would require about 3843 gallons of diesel fuel for the year.
The annual records show that 5500 gallons were used to pump the water, then the performance rating would be  X 100 = 70%.
This shows that 1657 gallons of diesel fuel could be saved if the pumping plant performance was improved.
The annual savings in pumping costs would be the product of the energy savings times the cost of diesel fuel; i.e., $3/gallon times 1657 gallons/year = $4971/year.
If a 5-year repayment period and 9% interest were used, the series present worth factor would be 3.89 from Table 6.
The breakeven repair cost would be $4971 X 3.89 = $19,337.
If repair costs were less than $19,337 then repairs would be feasible.
If costs were more than $19,337 the repairs may not be advisable at this time.
Table 6.
Series Present Worth Factor
 Repayment	Annual Interest Rate
 years	6%	7%	8%	9%	10%	12%
 3	2.67	2.62	2.58	2.53	2.49	2.40
 4	3.47	3.39	3.31	3.24	3.17	3.04
 5	4.21	4.10	3.99	3.89	3.79	3.60
 6	4.92	4.77	4.62	4.49	4.36	4.11
 7	5.58	5.39	5.21	5.03	4.87	4.56
 8	6.21	5.97	5.75	5.53	5.33	4.97
 9	6.80	6.52	6.25	6.00	5.76	5.33
 10	7.36	7.02	6.71	6.42	6.14	5.65
 12	8.38	7.94	7.54	7.16	6.81	6.19
 15	9.71	9.11	8.56	8.06	7.61	6.81
 20	11.47	10.59	9.82	9.13	8.51	7.47
 25	12.78	11.65	10.67	9.82	9.08	7.84
 The optimal type of energy for powering irrigation engines depends on the long-term relative price of one energy source compared to another.
Energy prices have varied considerably over time.
The nominal cost of energy per million BTUs is illustrated in Figure 3 for the types used to power irrigation systems for the period from 1970 through 2006.
These results show that electricity was expensive relative to other energy sources from about 1983 through about 2000.
Electricity has become more favorable especially recently when fossil fuels prices have increased rapidly.
While diesel fuel once was very economical the situation has recently changed.
Two methods can be used to analyze power source alternatives for irrigation.
The previous section illustrated how to determine the amount one could afford to pay
 Results of using the spreadsheet to compare the total annual cost of an electrically powered and a diesel powered irrigation system are shown in Table 7 for a range of electricity and diesel fuel prices.
The annual savings is the difference between the annual costs for diesel minus the cost for an electrically powered system.
The results show that electricity is generally preferred except when diesel is less than $2.25 /gallon and electrical rates are above 8c/kWh.
If the price of electricity is 6c/kWh and diesel fuel is $2.25 per gallon then switching to electricity could save over $3,000 annually as long as service can be brought to the field.
Again, these are representative costs and producers should analyze their unique situation.
Figure 3.
Historical energy prices since 1970.
Annualized Cost of Owning and Operating an Irrigation System
 Center Pivot with Electric Pump Mot	Written by: Tom Dorn, Extension Educator UNL-IANR Lancaster County, NE revised 02/02/2009
 Select Distribution System	Pivot	Note: Users are encouraged to replace values in blue font
 Acres Irrigated	130	with values that represent their unique situation.
Pumping water level, ft.
150
 System Pressure, PSI	50
 Gross Depth applied, inch	12	Select Distribution system and energy source for the pump motor from pull down menus.
Select Power Unit Type	Electricity
 Labor Chrg, $/hour	$15.00
 Irrigation District, $/ac-ft	0
 Return on Invest.
, 9	6
 Drip Oil, $/gal	$4.50
 Increase in Property Tax Due to Irrig.
Development, $/ac	$0.00
 Annual Elec Hookup Cost	$2,500	HP=	100	$/HP=	$25.00
 Component	Ownership Costs	Operating Costs
 Initial Cost	Life	Salvage4	R.O.I.
Insurance + tax	Depr	Repairs2	Oper.
labor	Electricity	Energy $1	Total Costs
 Irrigation Well	$16,500	25		$491	$165	$693	$215	$23	Kw-hour	kW+Hookup	$1,587
 Irrigation Pump	$11,163	18	$558	$369	$112	$589	$340	$94	$/kW-h	$1,504
 Gear Head	$0	15	$0	$0	$0	$0	$0	$0	$0.11	$0
 Pump Base, etc.
$1,100	25	$55	$36	$11	$42	$17	$23	$129
 Electric Motor& Switches	$8,500	30	$425	$276	$170	$269	$550	$351	53,182	$5,691	$7,307
 Center Pivot System	$52,000	20	$2,600	$1,712	$1,040	$2,470	$2,028	$702	$70	$8,022
 $0	$0	$0	$0	$0	$0	$0	$0
 Add'l Property Tax	$0	$0
 Totals	$89,263	$2,813	$2,884	$1,498	$4,063	$3,150	$1,193	$5,761	$18,549
 1 Energy Cost assumes operating at 100% of the NPC.
Hookup charge	Ownership Costs	Operating Costs
 added for Electric Units.
Total Costs
 2 Drip oil added to repair costs.
For internal combustion engines, 5% o	Total annual $	$8,445	$10,104	$18,549
 energy costs added to repair costs for oil, filters, and lube.
Annual $/ Acre	$64.96	$77.72	$142.68
 3 Energy Cost for Center Pivot assumes 7/8 hp-h per acre inch of water	$/ac-in	$5.41	$6.48	$11.89
 delivered.
Other systems require no additional energy for distribution
 4 End of life salvage value 5% of purchase price except for irrigation well.
End of life cost for well = 5% to plug the well.
Figure 4.
Detailed analysis for an electrically powered center-pivot irrigated field with the conditions shown.
Annualized Cost of Owning and Operating an Irrigation System
 Center Pivot with Diesel Engine	Written by: Tom Dorn, Extension Educator UNL-IANR Lancaster County, NE revised 02/02/2009
 Select Distribution System	Pivot	Note: Users are encouraged to replace all values in blue font
 Acres Irrigated	130	with values that represent their unique situation.
Pumping water level, ft.
150
 System Pressure, PSI	50
 Gross Depth applied, inches	12	Select Distribution system and energy source for the pump motor from pull down menus.
Select Power Unit Type	Diesel
 Labor Chrg, $/hour	$15.00
 Irrigation District, $/ac-ft	0
 Return on Invest.
, %	5
 Drip Oil, $/gal	$4.50
 Increase in Property Tax Due to Irrig.Development, $/ac	$0.00
 Component	Ownership Costs	Operating Costs
 Initial Cost	Life	Salvage4	R.O.I.
nsurance + tax	Depr	Repairs2	Oper.
labor	Diesel	Energy $ 1	Total Costs
 Irrigation Well	$16,500	25		$409	$165	$693	$215	$23	Gallons	$1,505
 Irrigation Pump	$11,163	18	$558	$308	$112	$589	$340	$94	$1,442
 Gear Head	$2,800	15	$140	$78	$28	$177	$36	$23	$343
 Pump Base, etc.
$1,100	25	$55	$30	$11	$42	$17	$23	$123
 Diesel Engine & Tank	$11,500	12	$575	$325	$230	$910	$782	$351	3,765	$8,472	$11,070
 Center Pivot System	$52,000	20	$2,600	$1,427	$1,040	$2,470	$2,028	$0	$185	$7,150
 $0	$0	$0	$0	$0	$0	$0	$0
 Add'l Property Tax	$0	$0
 Totals	$95,063	$3,103	$2,576	$1,586	$4,882	$3,419	$515	$8,657	$21,634
 1 Energy Cost assumes operating at 100% of the NPC.
Hookup charge	Ownership Costs	Operating Costs
 added for Electric Units.
Total Costs
 2 Drip oil added to repair costs.
For internal combustion engines, 5% of	Total annual $	$9,044	$12,591	$21,634
 energy costs added to repair costs for oil, filters, and lube.
Annual $/ Acre	$69.57	$96.85	$166.42
 3 Energy Cost for Center Pivot assumes 7/8 hp-h per acre inch of water	$/ac-in	$5.80	$8.07	$13.87
 delivered.
Other systems require no additional energy for distribution
 4 End of life salvage value 5% of purchase price except for well.
End of life cost for well = 5% to plug the well.
Figure 5.
Detailed analysis for a center-pivot irrigated field powered with diesel fuel for the field conditions shown.
Table 7.
Annual Savings by Using Electricity
 Diesel Fuel Cost, $ / gallon
 Electricity	1.75	2.00	2.25	2.50
 Price,	Total Annual	$19,616	$20,625	$21,634	$22,643
 $ / kWh	Costs
 0.06	$18,549	$1,067	$2,076	$3,085	$4,094
 0.07	$19,119	$497	$1,506	$2,515	$3,524
 0.08	$19,689	-$73	$936	$1,945	$2,954
 0.09	$20,259	-$643	$366	$1,375	$2,384
 0.10	$20,829	-$1,213	-$204	$805	$1,814
 This publication demonstrates methods to estimate the potential for repairing pumping plants to perform at the Nebraska Pumping Plant Performance Criteria and the annual cost for varying energy sources.
Producers frequently have several questions regarding the procedures.
First they want to know "Can actual pumping plants perform at a level equal to the Criteria".
Tests of 165 pumping plants in the 1980's indicated that 15% of the systems actually performed at a level above the Criteria.
So producers can certainly achieve the standard.
Recent evaluations in Nebraska have identified pumping plants that were operating at above 100% of the NPPPC, but many were between 80 and 100% of the NPPPC.
The second question is "What level of performance can producers expect for their systems?" Tests on 165 systems in Nebraska during the 1980s produced an average performance rating of 77% which translates to an average energy savings of 30% by improving performance.
Tests on 200 systems in North Dakota in 2000 produced very similar results.
These values illustrate that half of the systems in the Great Plains could be using much more energy than required.
The simplified method can help determine if your system could be inefficient.
The third issue focuses on "What should I do if the simplified method suggests that there is room for improving the efficiency?" You should first determine if the irrigation system is being operated as intended.
You need to know if the pressure, lift and flow rate are appropriate for the irrigation system.
For example, some systems were initially installed to deliver water for furrow irrigation and are now used for center-pivot systems.
If the pumping plant is not redesigned, conditions for the new system are likely not appropriate and you need to work with a well driller/pump supplier to evaluate the design of the system.
USING THE K-STATE CENTER PIVOT SPRINKLER AND SDI ECONOMIC COMPARISON SPREADSHEET
 In much of the Great Plains, the rate of new irrigation development is slow or zero.
However, as the farming populace and irrigation systems age, there has been a continued momentum for conversion of existing furrow-irrigated systems to modern pressurized irrigation systems.
These systems, including center pivot sprinkler irrigation  and subsurface drip irrigation , can potentially have higher irrigation efficiency and irrigation uniformity while at the same time reducing irrigation labor.
SDI is a relatively new irrigation system alternative for corn production on the Great Plains.
Corn producers converting from furrowirrigated systems to a pressurized system are faced with economic uncertainty about whether to convert to center pivot sprinklers  or SDI.
In the spring of 2002, a free Microsoft Excel1 1 spreadsheet template was introduced by K-State for making economic comparisons of CP and SDI.
Since that time, the spreadsheet has been periodically updated to reflect changes in input data, particularly system and corn production costs.
The spreadsheet also provides sensitivity of these comparisons to key factors.
Efforts are underway to expand the spreadsheet capabilities to other crops and regions within the Great Plains, but those templates are not ready for distribution at this time.
This paper will discuss how to use the spreadsheet and the key factors that most affect the comparisons.
The template has five worksheets , the Main, CF, Field size & SDI life, SDI cost & life, Yield & price tabs.
Most of the calculations and the result are shown on the Main tab.
ANALYSES METHODS AND ECONOMIC ASSUMPTIONS
 There are 18 required input variables required to use the spreadsheet template, but if the user does not know a particular value there are suggested values for each of them.
The user is responsible for entering and checking the values in the unprotected input cells.
All other cells are protected on the Main worksheet.
Some error checking exists on overall field size and some items  are highlighted differently when different results are indicated.
Details and rationales behind the input variables are given in the following sections.
Type a question for help
 This template determines the economics of converting existing furrow-irrigated fields to
 center pivot sprinkler irrigation  or subsurface drip irrigation  for corn production.
Version 06, modified by F.R.
Lamm, 2-01-06
 Field description and irrigation system estimates 4
 Non-cropped field area , acres
 Cropped dryland area, acres 
 Irrigation system investment cost, total $
 Irrigation system investment cost, $/irrigated acre
 Irrigation system life, years
 Interest rate for system investment, %
 Annual insurance rate, % of total system cost
 Total variable costs, $/acre 
 Additional SDI variable costs  or savings , $/acre
 Yield and revenue stream estimates
 Corn grain yield, bushels/acre
 Corn selling price, $/bushel
 Net return to cropped dryland area of field 
 Advantage* of CP over SDI, $/total field each year
 Advantage in Net returns to land and management 22
 You may examine sensitivity to Main worksheet  assumptions on three of the tabs listed below.
23
 Field size & SDI life
 SDI cost & life
 Figure 1.
Main worksheet  of the economic comparison spreadsheet template indicating the 18 required variables  and their suggested values when further information is lacking or uncertain.
Field & irrigation system assumptions and estimates
 It is assumed that an existing furrow-irrigated field with a working well and pumping plant is being converted to either center pivot sprinkler irrigation or SDI.
The pumping plant is located at the center of one of the field edges and is at a suitable location for the initial SDI distribution point.
Any necessary pump modifications  for the CP or SDI systems are assumed to be of equal cost and thus are not considered in the analysis.
Land costs are assumed to be equal across systems for the overall field size with no differential values in real estate taxes or in any government farm payments.
Thus, these factors "fall out" or do not economically affect the analyses.
An overall field size of 160 acres  was assumed for the base analysis.
This overall field size will accommodate either a 125 acre CP system or a 155 acre SDI system.
It was assumed that there would be 5 noncropped acres consumed by field roads and access areas.
The remaining 30 acres under the CP system are available for dryland cropping systems.
Irrigation system costs are highly variable at this point in time due to rapid fluctuations in material and energy costs.
Cost estimates for the 125 acre CP system and the 155 acre SDI system are provided on the current version of the spreadsheet template, but since this is the overall basis of the comparison, it is recommended that the user apply his own estimates for his conditions.
In the base analyses, the life for the two systems are assumed to be 25 and 15 years for the CP and SDI systems, respectively.
No salvage value was assumed for either system.
This assumption of no salvage value may be inaccurate, as both systems might have a few components that may be reusable or available for resale at the end of the system life.
However, with relatively long depreciation periods of 15 and 25 years and typical financial interest rates, the zero salvage value is a very minor issue in the analysis.
When the overall field size decreases, thus decreasing system size, there are large changes in cost per irrigated acre between systems.
SDI costs are nearly proportional to field size, while CP costs are not proportional to field size.
Quadratic equations were developed to calculate system costs when less than full size 160 acre fields were used in the analysis:
 CPcost% = 44.4 +    SDIcost% = 2.9 +   
 where CPcost% and CPsize%, and SDIcost% and SDIsize% are the respective cost and size % in relation to the full costs and sizes of irrigation systems fitting within a square 160 acre block.
The annual interest rate can be entered as a variable, but is currently assumed to be 8%.
The total interest costs over the life of the two systems were converted to an average annual interest cost for this analysis.
Annual insurance costs were assumed to be 0.25% of each total system cost, but can be changed if better information is available.
It is unclear whether insurance can be obtained for SDI systems and if SDI insurance rates would be lower or higher than CP systems.
Many of the SDI components are not subject to the climatic conditions that are typically insured hazards for CP systems.
However, system failure risk is probably higher with SDI systems which might influence any obtainable insurance rate.
Figure 2.
CP and SDI system costs as related to field size.
Production cost assumptions and estimates
 The economic analysis expresses the results as an advantage or disadvantage of CP systems over SDI in net returns to land and management.
Thus, many fixed costs do not affect the analysis and can be ignored.
Additionally, the analysis does not indicate if either system is ultimately profitable for corn production under the assumed current economic conditions.
Production costs were adapted from KSU estimates.
A listing of the current costs is available on the CF worksheet   and the user can enter new values to recalculate variable costs that more closely match their conditions.
This sum would become the new suggested Total Variable Costs on the Main worksheet , but the user must manually change the input value on the Main worksheet  for the economic comparison to take effect.
The user may find it easier to just change the differential production costs between the systems on the Main tab rather than changing the baseline assumptions on the CF tab.
This will help maintain integrity of the baseline production cost assumptions.
The reduction in variable costs for SDI is attributable to an assumed 25% net water savings that is consistent with research findings by Lamm et al..
This translates into a 17 and 13 inch gross application amount for CP and SDI, respectively.
The current estimated production costs are somewhat high considering the gross revenues are only approximately $550/irrigated acre.
This may be reflecting the overall
 profitability issue during these trying economic conditions, but producers might also try to reduce these variable costs somewhat to cope with low crop prices.
This fact is pointed out because a lowering of overall variable costs favors SDI, since more irrigated cropped acres are involved, while higher overall variable costs favors CP production.
The variable costs for both irrigation systems represent typical practices for western Kansas.
X	File	Edit	View	Insert	Format	Tools	Data	Axum	Window	Help	Adobe PDF	Type a question for help
 e	21	10	B	I	.00	.00
 A	B	C	D	E	F	G	H
 1	Factors for Variable Costs	CP	Suggested	SDI	Suggested	Version 06, modified by F.R.
Lamm, 2-01-06
 2	Seeding rate, seeds/acre	$/1000 S Suggested	34000	34000	34000	34000
 3	Seed, $/acre	$1.49	$1.49	$50.66	$50.66
 4	Herbicide, $/acre	$30.55	$30.55	$30.55	$30.55
 5	Insecticide, $/acre	$38.70	$38.70	$38.70	$38.70
 7	Nitrogen fertilizer, lb/acre	$/lb	Suggested	225	225	225	225
 8	Nitrogen fertilizer, $/acre	$0.29	$0.29	$65.25	$65.25
 9	Phosphorus fertilizer, lb/acre	$/lb	Suggested	45	45	45	45
 10	Phosphorus fertilizer, $/acre	$0.25	$0.25	$11.25	$11.25
 12	Crop consulting, $/acre	$6.50	$6.50	$6.50	$6.50
 13	Crop insurance, $/acre	$0.00	$0.00	$0.00	$0.00
 14	Drying cost, $/acre	$0.00	$0.00	$0.00	$0.00
 15	Miscellaneous costs, $/acre	$0.00	$0.00	$0.00	$0.00
 16	Custom hire/machinery expenses, $/acre	$124.79	$124.79	$124.79	$124.79	Assumes all tillage, cultural and harvesting operations.
17	Other non-fieldwork labor, $/acre	$0.00	$0.00	$0.00	$0.00 Assumed covered by custom hire.
18	Irrigation labor, $/acre	$5.00	$5.00	$5.00	$5.00
 20	Irrigation amounts, inches	17	17	13	13	Assumes approximately 25% savings with SDI.
21	Fuel and oil for pumping, $/inch	$6.75	$6.75	$6.75	$6.75 Assumes equal operating pressures at pump site.
22	Fuel and oil for pumping, $acre	$114.75	$87.75
 23	Irrigation maintenance and repairs, $/inch	$0.33	$0.33	$0.33	$0.33
 24	Irrigation maintenance and repairs, $/acre	Suggested	$5.61	$4.29
 26	1/2 yr.
interest on variable costs, rate	8%	8%	$18.12	$16.99
 28	Total Variable Costs	$471.18	$441.73	These values are suggested values on Main tab.
14	.
Main	CF	Field size & SDI life	SDI cost & life	Yld & Price	<
 start	Pegasus Mail	CPSDI06.doc	x	Microsoft Excel		10:48 AM
 Figure 3.
CF worksheet  of the economic comparison spreadsheet template and the current production cost variables.
Note that the sums at the bottom of the CF worksheet are the suggested values for total variable costs on the Main worksheet.
Yield and revenue stream estimates
 Changes in the economic assumptions can drastically affect which system is most profitable and by how much.
Previous analyses have shown that the system comparisons are very sensitive to assumptions about
 Size of CP irrigation system
 Shape of field 
 Life of SDI system
 with advantages favoring larger CP systems and cheaper, longer life SDI systems.
The results are very sensitive to
 any additional production cost savings with SDI.
The results are moderately sensitive to
 and very sensitive to
 higher potential yields with SDI
 with advantages favoring SDI as corn yields and price increase.
The economic comparison spreadsheet also includes three worksheet  that display tabular and graphical sensitivity analyses for field size and SDI system life, SDI system cost and life, and corn yield and selling price.
These sensitivity analysis worksheets automatically update when different assumptions are made on the Main worksheet.
SOME KEY OBSERVATIONS FROM PREVIOUS ANALYSES
 Users are encouraged to "experiment" with the input values on the Main worksheet  to observe how small changes in economic assumptions can vary the bottom line economic comparison of the two irrigation systems.
The following discussion will give the user "hints" about how the comparisons might be affected.
Smaller CP systems and systems which only complete part of the circle are less competitive with SDI than full size 125 acre CP systems This is primarily because the CP investment costs  increase dramatically as field size decreases  or when the CP system cannot complete a full circle.
Increased longevity for SDI systems is probably the most important factor for SDI to gain economic competitiveness with CP systems.
A research SDI system at
 the KSU Northwest Research-Extension Center has been operated for 17 years with very little performance degradation, so long system life is possible.
However, a short SDI system life that might be caused by early failure due to clogging, indicates a huge economic disadvantage that would preclude nearly all adoption of SDI systems.
The sensitivity of CP system life and cost is much less because of the much lower initial CP cost and the much longer assumed life.
In areas where CP life might be much less than 25 years due to corrosive waters, a sensitivity analysis with shorter CP life is warranted.
This tab determines the CP and SDI economic sensitivity to field size, shape, and SDI system life.
The elements in the table  represent the CP advantage in net returns per acre.
Field size	160	127	95	64	32	80
 CP Size	125	100	75	50	25	64	Wiper 1/2 circle
 CP Cost	$456.00	$531.88	$641.96	$836.40	$1,368.27	$890.63
 CP Dry	30	24	18	12	6	14
 SDI Size	155	124	93	62	31	78
 SDI Cost	$900.00	$920.03	$941.70	$974.25	$1,050.30	$955.29
 SDI life	Note: This sensitivity valid only if full-sized CP  and
 years	SDI  costs exist on Main worksheet  !!!!!!!!
5	$144.82	$145.77	$144.13	$137.74	$121.32	$130.26
 10	$57.63	$55.94	$51.94	$43.36	$19.58	$37.12
 15	$28.57	$26.00	$21.21	$11.90	-$14.34	$6.07
 20	$14.03	$11.02	$5.85	-$3.83	-$31.30	-$9.45
 25	$5.32	$2.04	-$3.37	-$13.27	-$41.47	-$18.77
 Figure 4.
The Field size & SDI life worksheet  sensitivity analysis.
Note this is one of three worksheets  providing tabular and graphical sensitivity analyses.
These worksheets automatically update to reflect changing assumptions on the Main worksheet.
The present baseline analysis already assumes a 25% water savings with SDI.
There are potentially some other production cost savings for SDI such as fertilizer and herbicides that have been reported for some crops and some locales.
Small changes in the assumptions can make a sizable difference.
Combining a higher overall corn yield potential with an additional small yield advantage for SDI can allow SDI to be very competitive with CP systems.
AVAILABILITY OF FREE SOFTWARE
 1 Mention of tradenames is for informational purposes and does not constitute endorsement by Kansas State University.
This paper was first presented at the 18th annual Central Plains Irrigation Conference, February 21-22, 2006, Colby, Kansas.
Contribution No.
06-208-A from the Kansas Agricultural Experiment Station.
The correct citation is
CORN PRODUCTION WITH LIMITED WATER SUPPLIES
 Crop yield response to irrigation has been measured since the early years of irrigated agriculture research.
Field research on this topic has continued because irrigation systems, management techniques, and crop genetics have improved.
Field research from the Great Plains research indicates that as irrigation applications to corn decrease, yields do not decrease at the same rate.
Yield response to irrigation can be location specific and can vary by years due to differences in precipitation and stored soil water.
Economic studies can use average yield responses over years to find overall trends but year to year variations in yields are needed for risk analysis.
Testing and validation of crop production models need robust data sets that may include reference evapotranspiration , soil water measurements, crop grain yields, dry matter accumulation, harvest index, growth stage dates, maximum leaf area index, plant population, and crop residue coverage of the soil surface.
These parameters were measured in this study to find the response of corn to a range of irrigation application amounts.
The corn was grown in a no-till environment with best management practices for weed and insect control.
Crop productivity , yield/irrigation ratio, soil water accumulation during the non-growing season, and soil water use during the growing season were also derived from field data.
Therefore, the objectives of this study were to:  build a robust data set of parameters for testing crop models over a range of irrigation;  find the relationships of grain and dry matter yields to ETc and irrigation; and  carry out the study over multiple years to find year to year variability in yield responses.
The cropping systems project was located at the Kansas State University, Southwest Research-Extension Center near Garden City, Kansas.
The soil type was a Ulysses silt loam  with pH of 8.1 and organic matter content of 1.5%.
The soil had an available water capacity of 1.92 in/ft between field capacity  and permanent wilting.
Long-term average climatic data for Garden City are: annual precipitation, 18.7 inches; mean temperature,
 54C; open-pan evaporation , 71 inches; and frost-free period, 170 days.
Corn was grown in a five year rotation of corn-corn-wheat-sorghumsunflower.
Two consecutive years of corn were planted, the first after sunflower and the next after corn.
All crops were planted in 2004 and the irrigation treatments were imposed so all crops were in rotation in 2005 and the initial soil water content included the effects of the irrigation variable from the previous 2004 crop.
High through low water treatments were maintained on the same individual plots during all years and crops.
Each crop was present every year in five cropping blocks, which were replicated over years.
Irrigation treatments were randomized and replicated four times within each of the crop blocks in a randomized complete block design.
The irrigation plots were 45 feet wide and 18 feet long.
Cultural practices, including hybrids, no-till planting techniques, fertilizer applications, and weed control, were the same across irrigation treatments.
Cultural practices followed the requirements of no-till management and fertilizer and weed management were carried out so they would not limit crop production.
Seeded plant populations increased across the six irrigation treatments with increasing levels of irrigation  based on past research to be appropriate for the yield expectations of each irrigation treatment.
Grain yield was measured by hand harvesting two adjacent rows 10 feet long.
Biomass was harvested from one row 10 feet long.
Leaf area was measured by removing five plants from the field and passing the leaves through an optical scanner.
Crop residue coverage from the previous crop was measured shortly after planting using the line-transect method described by Dickey et al.,.
Growth stages were recorded from field observations during the season.
A commercial four-span  model 8000 Valley  linear move sprinkler system was modified to deliver water in any combination of irrigation treatments simultaneously to each of the four replications.
Application depth for every irrigation event was 1 inch.
Six irrigation treatments, replicated four times received from 13 inches  to 3 inches  of water during the growing season.
If rainfall was sufficient to fill the soil profile to field capacity in treatment 1, water was not applied.
To achieve the irrigation frequency variable, plots were irrigated or skipped during each pass of the irrigation system to achieve the target frequency.
Each plot received no more than 2 inches of water per week to simulate the common commercial system capacity of 0.22 in/day.
Table 1.
Average irrigation frequency and irrigation amounts for 2005-2009.
Field trials show the fertilizer value of nitrogen in irrigation water
 by Michael Cahn, Richard Smith, Laura Murphy and Tim Hartz
 Increased regulatory activity designed to protect groundwater from degradation by nitrate-nitrogen  is focusing attention on the efficiency of agricultural use of nitrogen.
One area drawing scrutiny is the way in which growers consider the NO3-N concentration of irrigation water when determining N fertilizer rates.
Four dripirrigated field studies were conducted in the Salinas Valley evaluating the impact of irrigation water NO3-N concentration and irrigation efficiency on the N uptake efficiency of lettuce and broccoli crops.
Irrigation with water NO3-N concentrations from 2 to 45 milligrams per liter were compared with periodic fertigation of N fertilizer.
The effect of irrigation efficiency was determined by comparing an efficient  and an inefficient  irrigation treatment.
Across these trials, NO3-N from irrigation water was at least as efficiently used as fertilizer N; the uptake efficiency of irrigation water NO3-N averaged approximately 80%, and it was not affected by NO3-N concentration or irrigation efficiency.
C alifornia agriculture faces increasing regulatory pressure to improve nitrogen  management to protect groundwater quality.
Groundwater in agricultural regions, such as the Salinas Valley and the Tulare Lake Basin, has been adversely impacted by agricultural practices, with nitrate-N  in many wells exceeding the federal
 drinking water standard of 10 mg/L.
The threat to groundwater is particularly acute in the Salinas Valley, where the intensive production of vegetable crops has resulted in an estimated net loading  of > 100 lb/ac  of N annually.
Levels of NO3-N in irrigation wells in the Salinas Valley commonly range from 10 to 40 mg/L.
Given the typical volume of irrigation water applied to vegetable fields, NO3-N in irrigation water
 could represent a substantial fraction of crop N requirements, provided that crops can efficiently use this N source.
Indeed, the concept of "pump and fertilize"  has been suggested as a remediation technique to improve groundwater quality in agricultural regions.
Cooperative Extension publications from around the country  agree that the fertilizer value of irrigation water NO3-N can be significant, but they differ as to what fraction of water NO3-N should be credited against the fertilizer N recommendation.
There is a paucity of field data documenting the efficiency of crop utilization of irrigation water N.
Francis and Schepers  documented that corn could use irrigation water NO3-N, but in their study N uptake efficiency from irrigation water was low, which they attributed to the timing of irrigation relative to crop N demand and the availability of N from other sources.
Martin et al.
suggested that uptake efficiency of irrigation water NO3-N could actually be higher than from fertilizer N, but their conclusion was based on a computer simulation, not on field trials.
An injection system generated irrigation water with NO3-N concentrations of 12, 25 and 45 mg/L.
which irrigation water NO3-N can substitute for fertilizer N.
Two questions commonly asked by growers are whether plants can effectively use N at the low concentrations common in irrigation water, and to what degree irrigation inefficiency reduces water NO3-N availability.
We undertook this study to document the agronomic value of irrigation water NO3-N in the production of vegetable crops under field conditions representative of the Salinas Valley.
Irrigation water NO3-N trials
 Four field trials were conducted at the U.S.
Department of Agriculture Agricultural Research Service  facility near Salinas between 2013 and 2015.
The soil was a Chualar sandy loam.
Before planting, fields were sprinkler-irrigated to leach residual soil NO3-N SO that all trials were conducted with low background soil N availability.
The well water used for pre-plant leaching as well as for all in-season irrigation ranged between 2 and 4 mg/L NO3-N over the course of this study.
The experimental design for each trial was a randomized complete block, with four replications.
Individual plots consisted of four beds, each 40 inches  wide and 40 feet  long, with all data collected from the middle two beds.
Crisphead lettuce 'Telluride' was seeded on May 16, 2013, in two rows per
 bed and germinated using sprinklers.
A soil anticrustant solution containing 17 lb/ac  of N was applied to all treatments at planting to improve germination.
After plants were thinned to a final in-row spacing of approximately 12 inches , drip tape was installed on top of the beds and the field was drip-irrigated for the rest of the season.
Crop growth and N uptake were compared across a range of treatments simulating different irrigation water NO3-N
 concentrations during the drip-irrigated phase of the crop.
The different NO3-N concentrations were achieved by using water-powered proportional injectors to enrich all drip-applied water to 12,2 25 or 45 mg/L NO3-N.
Injected NO3-N was a blend of Ca2 and NaNO3 to maintain a cation balance similar to groundwater.
A water sample was collected from each treatment during each irrigation to confirm that the target NO3-N concentrations were achieved.
Additionally, an unfertilized control and a fertilized control treatment were included; both were irrigated using water containing only 2 mg/L NO3-N.
The fertilized control received five fertigations of ammonium nitrate solution  totaling 150 lb/ac  of N.
Also, all treatments were fertilized with potassium thiosulfate  in two fertigations of 30 lb/ac  of K each.
Each N treatment was evaluated at two levels of irrigation to observe the interaction between irrigation efficiency and crop uptake of irrigation water NO3-N.
The lower level of irrigation, 110% of crop evapotranspiration , was chosen to represent efficient management with minimal leaching.
The higher level of irrigation, 160% of ETc, was chosen to represent less efficient irrigation management; we have observed a number of Salinas Valley vegetable fields in which irrigation reached as high as 200% of ETc (Smith et
 Calculating the N in irrigation water
 C alculation of the amount of nitrogen in irrigation water requires knowledge of both the N concentration and the volume of water applied.
Laboratory analysis for nitrate in water is commonly reported as milligrams per liter  or parts per million ; these units are numerically the same: 1 mg/L equals 1 ppm.
Labs may report concentration either as nitrate  or nitrate-N ; the conversion between the two is
 NO3 4.43 = NO3-N
 To convert NO3-N concentration to mass of N applied, this equation can be used:
 mg/L NO3-N = lb of N/ac-in of water
 Nitrate is usually the only form of N present in irrigation water in an agronomically significant amount, SO it is the only N form reported on the typical water test.
However, recycled municipal wastewater, which is increasingly being used for irrigation in California, can contain more ammonium N  than NO3-N, as well as some organic forms of N that become relatively quickly available in soil.
Wastewater treatment plants routinely test for these other N sources in addition to NO3-N, and this information is publicly available.
One should consider all forms of N when estimating the amount of plant-available N in recycled water.
al.
2016).
Applying 160% of ET generated an estimated leaching fraction of 37%.
ETc was estimated by multiplying reference evapotranspiration  values obtained from the CIMIS weather station located on the USDA-ARS facility by crop coefficients calculated by the method described by Johnson et al..
Irrigation was applied twice weekly.
Data on ETc and irrigation volume are given in table 1.
Precipitation was an insignificant factor, with < 0.2 inches  received in any trial.
A second trial of the same structure was conducted in 2014.
Broccoli 'Patron' was seeded on Aug.
18 in two rows per bed and germinated with sprinkler irrigation following an anticrustant application containing 23 lb/ac  of N.
After crop establishment and bed cultivation, the trial was converted to surface drip irrigation.
The irrigation levels evaluated were 110% and 190% of ETc.
The fertilized control treatment received three fertigations of AN-20 totaling 220 lb/ac kg/ha) of N.
All treatments were also fertigated with KTS in two applications of 25 lb/ac 8kg/ha) of K.
Two trials were conducted in 2015 to directly compare the uptake efficiency of irrigation water NO3-N to that of fertilizer N.
In the spring trial, crisphead lettuce 'Telluride' was seeded and germinated as previously described.
After converting the field to drip irrigation, four levels of fertigation (a seasonal total of 0, 20, 60
 TABLE 1.
Inches of crop evapotranspiration (ETc and irrigation applied
 during the drip-irrigated portion of the field trials
 Irrigation applied	Leaching fraction t
 Year	Crop	ETc	Low*	High	Low	High
 2013	Lettuce	6.3	7.0	10.1	10	37
 2014	Broccoli	6.0	6.8	11.5	12	48
 2015	Lettuce	3.6	4.0	6.6	10	45
 2015	Broccoli	8.5	10.2	16.8	17	49
 Low = 110% to 120% of ETc high = 160% to 200% of ETc.
t Calculated by the method of Cahn and Bali 2015.
and 150 lb/ac [0, 22, 67 and 168 kg/ha] of N from AN-20, applied in three equal fertigations) were compared at each of two irrigation levels.
In each irrigation treatment, three concentrations of irrigation water NO3-N  without any AN-20 fertigation were also evaluated.
In the fall trial, broccoli 'Patron' was grown.
The treatments were similar to the lettuce trial, with the exception that the seasonal AN-20 fertigation levels were 0, 40, 80 and 200 lb/ac  of N.
The irrigation levels evaluated were 120% and 200% of ETc.
In all trials, plots were harvested when the highest fertilizer N rate treatment reached commercial maturity.
Aboveground fresh and dry biomass and whole-plant N concentration were determined.
From these data, crop N uptake was calculated.
Uptake efficiency of irrigation water NO3-N was calculated as the
 increase in crop N uptake above the unfertilized control divided by the amount of NO3-N in the applied water.
Uptake efficiency of NO3-N
 Lettuce biomass and crop N uptake increased linearly with increasing irrigation water NO3-N concentration in the 2013 trial.
Across the NO3-N enrichment levels, uptake efficiency of irrigation water NO3-N was 85%, and it was similar between the levels of irrigation.
The amount of N applied in the 45 mg/L water treatment at 160% of ET  was sufficient to maximize crop productivity, producing fresh biomass equivalent to the biomass of the fertilized control receiving 150 lb/ac  of N from AN-20.
An on-site CIMIS weather station provided accurate evapotranspiration data.
Each N treatment was evaluated at two levels of irrigation 110% and 160% of ET
 Recycled municipal wastewater contains nitrate as well as other forms of plant-available nitrogen.
Results of the 2014 broccoli trial were similar, with crop biomass and N uptake increasing linearly with increasing irrigation water NO3-N concentration.
Uptake efficiency of irrigation water NO3-N was again high  across NO3-N concentrations and irrigation levels.
However, given the much higher N requirement of broccoli compared to lettuce, even the 45 mg/L NO3-N water treatment was insufficient to maximize crop productivity.
The 2015 trials clearly demonstrated that irrigation water NO3-N was at least as effectively used by the crop as fertilizer N.
The regression lines in figures 3 and 4 indicate the crop response to fertigation with AN-20 at the two levels of irrigation; all regressions were highly significant.
The fact that the irrigation water NO3-N treatments generally placed above the fertilizer response line for their respective irrigation regimes suggested
 The 2015 trials clearly demonstrated that irrigation water NO3-N was at least as effectively used by the crop as fertilizer N.
that a higher N uptake efficiency was achieved with irrigation water NO3-N than with N from fertigated AN-20.
This was most pronounced in the broccoli trial , where the N uptake efficiency for fertilizer was substantially lower under the high irrigation level (200% of ETd.
Averaged across all field trials, the N uptake efficiency of irrigation water NO3-N was remarkably high, averaging approximately 80%.
Neither NO3-N concentration nor irrigation level significantly influenced N uptake efficiency.
It must be noted that the high N uptake
 efficiency in these trials was attributable to the fact that residual soil NO3-N in these fields had been deliberately minimized by heavy preplant leaching in order to maximize the uptake efficiency of both fertilizer N and water NO3-N.
In typical production fields, higher levels of residual soil NO3-N are common, and N uptake efficiency of applied N, whether from irrigation water or fertilizer, would likely be lower.
These field trials unequivocally demonstrated that vegetable crops can effectively use NO3-N from irrigation water, even at relatively low concentration.
The important question is how can growers safely estimate an appropriate fertilizer credit for irrigation water NO3-N.
In answering that question, it is important to distinguish between N uptake efficiency and a
 Fig.
1.
Effect of irrigation water NO3-N on lettuce biomass and aboveground N uptake, 2013 trial; water NO3-N concentrations were 2, 12, 25 and 45 mg/L.
Fig.
2.
Effect of irrigation water NO3-N on broccoli biomass and aboveground N uptake, 2014 trial; water NO3-N concentrations were 2, 12, 25 and 45 mg/L.
fertilizer credit.
N uptake efficiency refers to the fraction of applied N taken up by the crop.
N uptake efficiency from either fertilizer or irrigation water is affected by overall soil N availability (all sources,
 including residual soil NO3-N and soil N mineralization); as total N availability increases, N uptake efficiency from either fertilizer or irrigation water will decline.
A fertilizer credit is the comparison of the
 relative availability of N from irrigation water and from fertilizer N.
Several factors need to be considered in calculating a fertilizer credit.
First, the stability of the irrigation water NO3-N concentration over time is important.
In general, surface water sources have reasonably low but stable NO3-N, typically <5 mg/L.
Water districts usually have historical records that provide good estimates of NO3-N concentration for the current season.
Nitrate concentration in irrigation wells may be more variable, SO periodic monitoring within a growing season may be appropriate.
Growers who use several wells of differing NO3-N concentration to irrigate a field would need to monitor the NO3-N concentration of the blended water.
This can be accomplished by collecting water in a covered bucket using a drip emitter connected to the irrigation main line; this sample can be tested using nitrate-sensitive colorimetric test strips.
Drip irrigation increases irrigation efficiency and simplifies the determination of the "fertilizer credit" for irrigation water NO3-N.
Fig.
3.
Comparison of lettuce response to N fertilizer  with crop response to irrigation water NO3-N, 2015 trial; water NO3-N concentrations were 14, 25 and 45 mg/L.
Fig.
4.
Comparison of broccoli response to N fertilizer  with crop response to irrigation water NO3-N, 2015 trial; water NO3-N concentrations were 14, 25 and 45 mg/L.
Second, it may be necessary to consider irrigation inefficiency when calculating a fertilizer credit, depending on the details of the irrigation management.
In this study, drip irrigation was used, with frequent irrigation at relatively low volume, typically < 0.6 inches  per application; even in the high irrigation treatment , the volume of leachate from individual irrigations was small.
Under these conditions, N uptake efficiency was similar in the high and low irrigation regimes, indicating that the crops were able to remove a substantial amount of NO3-N even from the fraction of applied water that eventually leached.
This phenomenon may relate to the residence time of applied water within the active root zone.
With low volume leaching events, it may take several irrigation cycles before water moves below the root zone, giving the crop the opportunity to take up applied NO3-N.
In a fertigation trial with bell pepper, Scholberg et al.
found that increasing fertilizer retention time from 1 to just 3 days quadrupled fertilizer N uptake efficiency.
Conversely, when irrigation management features large leaching events, particularly early in the season when crop N uptake is slow and before a substantial root system has developed, crop access to and use of irrigation water NO3-N would be limited, and this should be considered in the fertilizer credit calculation.
In the context of vegetable production, irrigation to germinate seeded crops or to establish transplants would be particularly vulnerable to inefficiency.
It may be appropriate not to credit any of the irrigation water NO3-N applied during crop establishment.
Presidedress soil nitrate testing
 Fig.
5.
Influence of irrigation water NO3-N concentration  and irrigation level  on the mean N uptake efficiency of irrigation water NO3-N across the four field trials.
Bars represent the 95% confidence interval of the measurement.
would capture any N contribution from irrigation water still in the root zone following establishment.
From that point forward, crediting 100% of irrigation water NO3-N against the assumed fertilizer N requirement would be a reasonable practice if in-season irrigation were managed efficiently.
Where in-season irrigation results in large leaching events, a smaller fertilizer credit could be justified.
However, it should be acknowledged that large leaching events may similarly restrict crop recovery of fertilizer N.
These field trials documented that NO3-N in irrigation water is effectively used by crops.
Growers can confidently
 adjust their fertilization practices to reflect the agronomic value of this N source.
In doing SO they will reduce the potential for N loading to groundwater.
M.
Cahn is UC Cooperative Extension  Farm Advisor in Monterey County; R.
Smith is UCCE Farm Advisor in Monterey County; L.
Murphy is Staff Research Associate with UCCE in Monterey County; and T.
Hartz is UCCE Specialist in the Department of Plant Sciences at UC Davis.
This project was funded by a grant from the California Department of Food and Agriculture's Fertilizer Research and Education Program  and the Fertilizer Inspection Advisory Board.
We thank Sharon Benzen and David Lara of the USDA-ARS in Salinas, California, for assistance with the field trials.
Value of Using Sensors to Manage Irrigation and Tips for Proper Installation: With planting wrapping up across the state, now is an excellent time to turn attention to soil water sensor and ETgage installations if they havent already been completed.
Timely installation is important to gain the true benefits of sensors, leading to reduced irrigation costs, reduced chances of overwatering leading to anaerobic soil conditions, and less nutrient leaching.
Many of you already use soil water monitoring equipment or ET data to make good decisions.
The only thing you need to do is continue what is working and hone your analysis skills.
Chapter: 11 Soil Tillage
 Historically, tillage was used to manage residues, diseases, insects, weeds, excess water, and soil compaction with little consideration given to its impact on soil health, water quality, and erosion.
The extreme drought during the 1930s helped change this perception.
Tillage was and is still used to prepare a seedbed.
Today, innovations in production tools  provide an opportunity to replace moldboard plows  with conservation-tillage systems.
Alternate tillage systems are listed in Table 11.1.
When considering tillage systems, it is important to consider that compaction can be caused by all systems as well as by grain wagons, combines, and trucks driving across the field.
Field traffic should be minimized to minimize compaction.
Excessive tillage can increase soil crusting and compaction.
Moldboard plowing or excessive tillage is not considered a Best Management Practice  for South Dakota production systems because of erosion and compaction risks.
Additional information on compaction is provided in Chapter 14.
Clean-tillage involves inverting the soil SO that most of the residue is buried.
Moldboard plowing followed by preplant disking is a common clean-till procedure.
Because crop residue is mostly buried, the soil surface is exposed to wind and rain, increasing the potential for erosion and a loss of soil moisture.
Of the tillage systems discussed, clean-tillage carries the greatest wind and water erosion risks.
Clean-tillage
 Figure 11.1 Moldboard plowing wheat stubble in South Dakota.
Table 11.1 Tillage systems for corn production:
 1.
Clean-till, <30% residue cover
 Not considered a Best Management Practice.
2.
Conservation-till, >30% residue
 Chisel plow followed by a disk.
3.
Ridge-till, >30% residue cover
 Requires special equipment for ridgebuilding.
4.
No-till or strip-till, >30% residue
 Requires special equipment and a residuemanagement plan.
is not considered a conservation tillage system.
The advantages and disadvantages of clean-till systems are shown in Table 11.2.
Clean-tillage may be best-suited for bottomland or poorly drained soils because it speeds soil heating and reduces soil water content, and water erosion risks are low.
However, moldboard plowing can result in a plow pan that can restrict plant root growth.
The use of deep rippers to overcome a plow-pan problem will provide only temporary relief.
Conservation-tillage systems leave at least 30% or more crop residue on the soil surface following planting.
Directions for calculating residue were prepared by McCarthy et al..
There are a number of implements that can be used in conservation-till.
The most common conservation tillage-systems are spring disking and chisel plowing.
Different systems provide different amounts of surface residue.
Advantages and disadvantages are provided in Table 11.3.
Increasing the residue on the soil surface decreases the potential for erosion and soil water loss.
Crop residues create a barrier between the soil, water, and wind that reduces erosion.
The amount of residue left on the soil surface is directly related to available water, and the length of time needed for the soil to warm.
The amount of residue remaining on the soil surface can be increased by:
 1.
Including a high-residue-producing crop in the rotation.
2.
Conducting tillage operations in the spring.
3.
Reducing the number of tillage passes.
4.
Using cover crops.
5.
Driving slower during tillage.
6.
Setting chisels and disks to a shallower soil depth.
7.
Using straight shanks and sweeps rather than curved implements.
Ridge-tillage is a conservation-tillage system where crops are grown on permanent beds.
With ridgetillage, the planter must be able to cut residue, penetrate the soil to the desired depth, and in many situations, clear the ridge of the previous years' crop residues.
Following planting, cultivators are used to control weeds, and rebuild and shape the ridges.
Ridge-tillage is well-suited to relatively flat landscapes and is often furrow irrigated in arid climates.
Advantages and disadvantages are provided in Table 11.4.
Table 11.2 Advantages and disadvantages of clean-till:
 Suited for many soils	High erosion risk
 Pest control	Fuel and labor
 Soil warmer	Soil-moisture loss
 Mixed nutrients	Increased runoff
 Figure 11.2 Chisel plowing wheat stubble.
Table 11.3 Advantages and disadvantages of conservation-till:
 Reduced erosion	May require stalk
 Reduced cost	Increased compaction
 Mixes nutrients	Can delay planting
 Table 11.4 Advantages and disadvantages of ridge-till:
 Reduced erosion	Crusting in light textured soils
 Saves water	Must match wheel spacing
 Lower fuel costs	Not suited to rotation that
 includes alfalfa or small grains
 Increased snow catch	High labor requirement
 In ridge-tillage, crop residue and organic matter tend to accumulate between the ridges.
If mechanical cultivation and ridge-building take place during the growing season, these materials are generally mixed
 into the upper portion of the soil profile.
Relative to conventional-tillage, ridge-tillage generally increases water infiltration and reduces surface runoff.
Banding the fertilizer into the ridge can reduce nitrogen leaching.
Herbicides may be applied to the ridge, with cultivation used between the rows for weed control.
Two disadvantages of ridge-tillage are 1) specially designed equipment is needed, and 2) it is labor intensive.
In ridge-tillage, it is recommended that the soil samples for nutrient analysis be collected halfway between the center of the row and the crop row.
When applying fertilizers into the ridge, care should be taken to minimize direct contact with the seed.
For sandy soils, the amount of N plus K2C applied with the seed should not exceed 5 lbs/acre.
This limit increases to 10 lbs/acre for fine-textured  soils.
The effectiveness of P and K applications is often improved by banding.
Figure 11.3 Corn in a ridge-tillage system.
Strip-tillage is a conservation-tillage system where the seedbed  is tilled and cleared of residue and the rest of the area is not disturbed.
Strip-till systems prepare a seedbed that is relatively free of residue, even in a corn-following-corn rotation.
The spreading of residue at harvest can reduce residue interference at planting.
Strip-tillage may be conducted in the fall or spring.
Spring strip-till uses a tillage tool that tills strips ahead of the seed openers on the planter.
If strips are prepared in a separate operation: 1) it can be challenging to consistently follow the strip with the planter, and 2) it is recommended to follow the same direction with the planter.
Failing to follow the strips with the planter can affect fertilizer placement with respect to the seed.
Figure 11.4 Strip-tilled corn in South Dakota.
In this image strip-tillage was conducted down a slope.
The strip can provide a conduit for water transport.
If P or K fertilizers are needed, they can be fall banded into the strips.
As with any tillage system, N fertilizer should not be fall-applied until soil temperatures are below 50F.
Starter fertilizer can be used; however, the total amount of N + K2O applied in contact with the seed should not exceed 5 pounds in a sandy soil and 10 pounds in fine-textured soils.
Many producers have problems when attempting to plant into fall-created strips in rolling terrain.
Plant growth can be compromised if the seed rows are too close or too far away from the fertilizer band.
Soil in the strip-tilled systems tends to warm faster than areas where residue is present.
Strip-tillage does not eliminate erosion and, following rainfall, erosion can occur down the strip.
Contour strip-tillage should be considered in high-slope situations.
In some strip-till systems, when strips are tilled in the fall or spring, fertilizer is applied in a band.
Properly managed no-till systems leave the most residue on the soil surface.
This residue conserves soil water and can increase yields and profitability.
Compared with other systems, no-tillage has higher water infiltration rates and less potential for erosion.
Lower erosion losses are attributed to increased water infiltration and reduced runoff, resulting from the development of macropores.
Considering the potential conservation and production benefits, no-tillage should be strongly considered by South Dakota producers.
Advantages and disadvantages are provided in
 No-tillage requires the optimization of planting and residue-management systems.
A common misconception is that residue managers can compensate for nonuniform residue distribution.
Residue management begins at harvest.
Using stripper headers for harvesting wheat and other crops allows straw to remain upright and attached, and prevents residue from being moved by wind or water.
In corn, this is accomplished by adjusting the combine to keep the stalk intact and upright.
Uniformly spreading chaff is particularly difficult when using large headers.
Straw and plant stems that are chopped into small pieces are difficult to distribute uniformly and have a tendency to be moved into piles by wind or water.
Residue managers work best in situations where residue is uniform.
However, in situations when residue is not uniform, it is almost impossible to properly adjust residue managers.
Single-disc fertilizer openers placed at the same depth and 2 to 3 inches to the side of the seedopener path can serve a dual purpose, cutting residue and placing the sideband fertilizer.
When compared with conservation tillage, no-till soils generally remain cooler in the spring.
Cooler soil temperatures can slow nitrogen  and sulfur  mineralization.
Placing nutrients such as N and S as a sideband improves early season plant vigor.
The planter is the most important implement in a notill system.
Germination can be improved when seeds are covered with loose material and firmly planted at the right depth in warm, moist soil.
The basic corn planter was designed for use in well-tilled seedbeds.
Consequently, modifications are needed to assure optimal seed placement.
Almost all row-crop planters have openers that utilize two discs to open the seed slot.
The seed-opener discs are often arranged SO that the blades touch evenly at the front and have discs of equal size.
Some manufacturers offset these discs SO that one disc leads the other.
Wiper/depth wheels can limit the problem of mud being brought to the surface and interfering with seed-opener depth wheels.
South American openers use offset double-disc openers with discs of different sizes; this design results in a differing angular momentum between the blades that is thought to improve the slicing action.
All disc openers require sharp blades; if they are not sharp, the residue can be pushed  into the trench, resulting in uneven germination and growth.
Hair-pinning is worse when residue is cut into short lengths and soil structure is poor.
Continuous long-term no-till systems have less of a problem with this issue.
Once the seed is placed in the trench, it needs to be pressed into the soil and covered.
In no-tillage systems, the best method is to separate the firming  and covering operations.
Several companies make devices designed to press or lock the seed into the bottom of the trench.
This speeds the rate at which the seed imbibes water and anchors it to the bottom of the trench.
The lack of root penetration is
 Figure 11.5 No-till corn in South Dakota.
Table 11.5 Advantages and disadvantages of notill:
 Reduced erosion	Specialized equipment
 Saves water	Nutrient stratification
 Lower fuel costs	Reliance on herbicides
 Increased snow catch	Cool spring temperatures
 May require more N
 Figure 11.6 Planting corn in a no-till system.
often blamed on "sidewall" compaction, which can be traced to a poorly anchored seed.
There are several companies that make aftermarket devices designed to press the seed into the bottom of the trench.
In general, vertical wheels work better in most conditions; however, they are more expensive and harder to mount than the type that uses a sliding piece of plastic.
Once the seed is firmly pressed into the bottom of the trench, it needs to be covered.
Standard closing systems on corn planters are designed to work in tilled seedbeds by packing the area under and around the seed, while leaving loose material above the seed.
Standard rubber or cast-iron closing systems normally do not function well in no-till systems because they have difficulty properly closing the trench in wellstructured or wet soils.
If the soil over the seed is packed too firmly, the corn plant may set its growing point too shallow.
This makes it prone to damage from herbicides and late frosts.
If the soil covering the seed is too loose, the seed trench may dry too fast, leading to stand loss.
Many companies (e.g., Martin, May-Wes, Exapta, Yetter make attachments designed to loosen the soil in the seed trench and place it over the seed.
One reason that strip-till may appear superior to no-till is that the seed is planted into loose soil created by the strip-tillage operation, which allows for optimal operation of standard closing wheels.
Other attachments needed for conversion of a standard planter to a no-till planter are fertilizer openers and residue managers.
The best fertilizer opener designs are single-disc openers with a depth-gauging and/ or wiping wheel.
These openers cut the residue and place fertilizer 2 to 3 inches to the side of the seed.
In fine-textured soils, most of the N and P can be band-applied using this approach.
However, in irrigated or sandy fields, limit the amount of N applied to one-third to one-half of the seasonal N requirement.
The likelihood of planter plugging in heavy residue can be reduced by using residue managers that cut residue before it is moved and by replacing wide-depth wheels with narrow-depth wheels.
Using a residue manager with a backswept design helps keep residue from wrapping.
Cutting the residue allows the residue managers to split the mat of residue without tearing it apart, which is especially important under damp conditions.
Cutting residue reduces soil disturbance because residue managers do not have to engage the soil, reducing problems with surface sealing or crusting, weed growth, and erosion.
July13, 2021.
Irrigation is in full swing for the North Platte Valley in the Panhandle of Nebraska.
Resources to Navigate Drought Successfully
 My well ran dry.
My livestock might need hay this winter.
The lawn is dying.
What do I do?
By Cathryn Kloetzli, Extension Professional, and Erin Roche, Crop Insurance Education Program Manager, University of Maine Cooperative Extension
 As a farmer, gardener or landowner, there are steps and management practices you can implement to reduce or eliminate threats caused by water shortages and damaging weather events.
This collection of resources has been gathered for you to successfully navigate the impacts caused by drought.
Drought happens so rarely in Maine.
Why bother with any of this?
While the cost to implement preventative measures is often minimal, the potential loss by not implementing these measures can be great.
Although it is uncommon for drought to significantly impact Maine, this does not mean that Maine is immune to water shortages.
A drought from 1999-2002 caused 17,000 private wells to run dry in the 9 months prior to April 2002, and farmers lost more than 32 million dollars in crop production between 2001 and 2002 ).
The resources below provide several low-cost, simple to implement measures that every business and home can take to help lessen or avoid the impact of drought.
Take the opportunity to protect, and even enhance, your investments  often just by planning ahead.
How do I monitor Maines drought status?
The Palmer Drought Severity Index   provides a PDSI Map.
Northeast Drought offers weekly updates of current conditions and impacts.
U.S.
Drought Monitor updates its drought disaster map weekly.
My well ran dry.
What do I do?
Call 2-1-1 to report your dry well.
This action allows the state to see how widespread the problem is.
For moderate water use purposes, consider tapping into local roadside springs.
Contact the Drinking Water Program to see if the spring is regulated and tested.
Contact Licensed Well Drillers and Pump Installers  to discuss options such as well replacement, or lowering an existing pump deeper into the water table.
For homeowners  Resources are available to qualifying homeowners: Maine State Housings Home Repair Program or USDAs Single Family Housing Loans and Grants.
We need water for the farm.
Where do we turn?
Check with bulk water haulers or your local fire department to see if they are able to assist you.
Use a water storage system, not a well, that protects the water until needed.
Estimate water use on the farm and at home to gauge how much water you will need to haul in.
Consider Rainwater Harvesting  from barrels to cisterns.
I dont have enough hay to feed my livestock due to the drought?
What can I do?
Check the Maine Hay Directory or the national Hay Exchange.
Plan for transport costs.
For a rough approximation on what to pay for hay prices, check out the Hay Report.
Scroll down and click on Pennsylvania Weekly Hay Report, which has the closest market information for Maine.
Do You Have Enough Forage This Year?
helps you calculate the amount of forage you need, take stock of how much forage you currently have, and develop a plan going forward.
Our hay crop is very short.
Fields we got 28 round bales off last year we got 7 this year.
We usually sell a third of what we put up for hay and this year were looking to buy.
Maine farmer, 2016
 My crops/pasture/yard/wildlife didnt have enough water this year.
How can I make sure that doesnt happen again?
Start now to implement these practices to use your water supply efficiently and avoid future shortages.
Stretch short water supplies.
Prepare your farm before drought strikes.
Invest in irrigation.
For more information, see Small Scale Solutions for Your Farm  and Irrigation for Fruit and Vegetable Production, which includes a chart of crops critical watering times.
Trickle irrigation can be useful for home gardens.
See Northeast Irrigation Supply and Design for a listing of irrigation providers and products.
Natural Resources Conservation Service  helps farmers lessen the impacts of drought through conservation practices such as irrigation pipeline, cover crops, mulching and more.
For technical and financial assistance, contact your local NRCS office.
Improve soil health to prevent drought impacts.
Learn more about the Water Source Development Grant, Environmental Quality Incentives Program, Agricultural Management Assistance, and Conservation Stewardship Program.
What are some crop-specific techniques I can use to help minimize damage from drought?
FORAGES: Forage Management in Drought , includes shortand long-term approaches.
TURF/LANDSCAPERS: Resources for Landscapers, Keeping Landscape Plants Alive , and Managing Lawns.
Is crop insurance worth it for Maine farmers?
Will it work for us?
Where can I learn more?
Crop insurance protects farmers crop yield or revenue from a wide range of adverse weather conditions such as drought, excess moisture, frost, freeze, etc.
Failure of irrigation or water supply due to drought is also an insured type of loss.
The best things farmers can do is be proactive and sign up for crop insurance ahead of time.
If you wait until after the loss has occurred, recovery options and coverage are more limited.
Go here to learn more about crop insurance.
Crop insurance is purchased through private agents serving Maine.
Locate an agent.
Farmers get a free premium quote from a crop insurance agent or county Farm Service Agency.
Crop insurance helps me sleep better at night.
The few years it was a real disaster, the money we received certainly helped our bottom line.
Maine farmer, 2016
 What crops are covered by crop insurance policies for weather-related loss?
Most crops grown in Maine are eligible for some type of risk management program coverage through the Federal crop insurance program or the FSA Non-insured Crop Disaster Assistance Program.
For more information, refer to the resources given in the Is crop insurance worth it?
question above.
Will there be natural disaster assistance after the drought has occurred?
It depends.
Federal farm programs may be available through the FSA to help farmers recover from drought.
For example, the Emergency Assistance for Livestock, Honeybees, and Farm Raised Fish and the Livestock Indemnity Program provide assistance to farmers suffering from grazing and livestock losses.
Also, depending on the extent and severity of the drought, assistance to qualifying farmers in the form of low-interest emergency loans may be available.
Contact your county FSA office for details.
What else can our farm do to protect itself?
Fill out a risk management checklist  or do a SWOT analysis  to identify areas for improvement.
Modify your management practices or integrate a new technology.
Consider purchasing crop insurance to provide additional protection.
Stay informed about climate and agriculture in Maine, visit the Maine Climate and Ag Network.
Once established, yucca plants can increase on drier rangeland sites.
They produce a deep taproot that competes aggressively for the limited water in these soils.
With sharp leaves protecting the plant, cattle rarely eat it during summer.
Modeling identifies optimal fall planting times and irrigation requirements for canola and camelina at locations across California
 Sufficient rainfall and appropriate soil temperatures during the canola planting window occur statewide on average 1 in 3 years, but camelina is significantly more drought and cold tolerant.
by Nicholas George, Lucia Levers, Sally Thompson, Joy Hollingsworth and Stephen Kaffka
 In California, Brassica oilseeds may be viable crops for growers to diversify their cool-season crop options, helping them adapt to projected climate change and irrigation water shortages.
Field trials have found germination and establishment problems in some late-planted canola, but not camelina at the same locations.
We used computer modeling to analyze fall seedbed conditions to better understand this phenomenon.
We found seedbeds may be too dry, too cold, or both, to support germination of canola during late fall.
Based on seedbed temperatures only, canola should be sown no later than the last week of November in the Central Valley.
Camelina has broader temperature and moisture windows for germination and can be sown from October to December with less risk, but yields of camelina are lower than canola yields.
In areas without irrigation, growers could plant canola opportunistically when seedbed conditions are favorable and use camelina as a fallback option.
D iversifying crops can improve farm economic performance, aid with weed and pest management, better utilize soil and water resources, and, in the case of Brassica oilseeds, provide benefits for pollinators.
Growers have relatively few economically viable cool season crop options in California , but diversifying winter crop options may become more valuable if summer production of irrigated annual or short-term perennial species is limited by shortage of irrigation water, and potentially by climate change.
On an area basis, wheat is the dominant cool-season crop in California.
There has been long-standing interest in the potential of canola , and other Brassica oilseed species, to diversify cereal-based cropping in California.
In a recent review, Angus et al.
concluded that canola can have synergistic
 effects on the productivity of wheat-dominated cropping.
It benefits subsequent wheat crops by acting as a disease break, suppressing weed growth and providing more flexibility in herbicide choices.
Canola seed is used for the production of edible oil and high protein oilseed meal used for livestock feed.
It is also used for biodiesel production.
At present, the demand for these products in the United States is larger than domestic production.
Camelina  is another cool-season oilseed crop of interest to California growers.
Currently, camelina is not widely used as a food for either humans or livestock, but it has been used for this in the past, and there is recent research directed towards this use.
At present, canola and camelina are not important crops in California.
If used to diversify cool-season cropping, however, they could help sustain the longterm viability of California agriculture.
Under rain-fed production, the mean yield of canola in the Sacramento Valley  is predicted to be over 3,100 pounds per acre .
This should make canola, given suitable market development, economically competitive with wheat in the region.
Mean rain-fed yields of current camelina varieties are around 890 pounds per acre .
Camelina is therefore unlikely to be economically competitive with wheat or
 canola, but it is regarded as a hardy crop, with low input requirements , and recent field studies in California have shown it to be more cold and drought tolerant than canola.
Camelina may therefore have a niche in production situations where canola and wheat are not viable due to low water availability or cold temperatures, especially if larger yields can be achieved reliably.
Sowing time, establishment issues
 The development of a cool-season oilseed industry in California will require locally appropriate agronomic practices for reducing production risks and maximizing yield.
In Mediterranean climates like California's, the appropriate fall sowing time is an important consideration for rain-fed production.
It involves a trade-off between sowing late enough to reduce the risk of dry conditions during germination and establishment, and sowing early enough to optimize canopy leaf area at flowering, necessary for a high yield potential, and avoiding flowering and seed development during late spring, when hot and dry conditions are common.
Timely establishment in fall therefore increases the likelihood of a high yield for canola, assuming average rainfall and temperatures and suitable agronomic management.
The ideal planting time for cool-season canola in California has been identified as between late October and early November , although the optimal time within this
 A variety trial of canola several weeks after sowing at UC Davis.
Researchers predict that canola yield in the Sacramento Valley could be over 3,100 pounds per acre under rain-fed production, which would make it economically competitive with wheat in the region.
TABLE 1.
The study assessed cool-season growing conditions in three agricultural regions in California
 coldest month	Mean rainfall	Mean rainfall
 Years in climate		Oct-Dec	Oct-May
 Region	Site	Latitude	Longitude	record	F 	inches 	inches 
 Central	Atascadero	35.47	-120.65	13	46 	1.0 	12 
 San Luis Obispo	35.31	-120.66	27	54 	2.2 	19 
 Sacramento	Durham	39.61	-121.82	31	45 	2.3 	21 
 Colusa	39.23	-122.03	31	45 	1.5 	16 
 Davis	38.60	-121.54	31	45 	2.0 	17 
 Lodi	38.13	-121.39	14	46 	1.3 	14 
 San Joaquin	Los Banos	37.10	-120.75	25	45 	0.8 	9 
 Firebaugh	36.85	-120.59	16	45 	0.7 	10 
 Parlier	36.60	-119.50	31	45 	0.9 	11 
 Five Points	36.34	-120.11	31	46 	0.9 	8 
 Kettleman City	35.87	-119.90	31	46 	0.8 	8 
 period is unclear.
Furthermore, poor establishment, and even total stand failure, of some but not all laterplanted canola crops has been an episodic problem observed in California.
The reason for this has been unclear.
In contrast, camelina sown at the same locations and times has not displayed establishment problems.
Canola seed can exhibit high germination percentages at soil temperatures as low as 40F  , but under field conditions, sustained temperatures below 50F  commonly result in low or delayed germination and subsequent poor establishment.
In terms of water availability, over 90% germination of canola seed is generally achieved at a soil matric potential of -0.4 MPa or greater, and germination percentages then decline to zero between -0.4 MPa and -1.5 MPa.
By contrast, camelina is considered cold tolerant during germination , with studies finding almost 100% germination and emergence at temperatures below freezing although time to germination increases from approximately 9 days at 50F  to 68 days at 30F .
Camelina also tolerates lower soil water during germination than canola, 90% germination of camelina has been observed at matric potentials as low as -3.0 MPa, although seedling growth is more vigorous  at water potentials over -1.5 MPa.
The establishment problems occasionally observed in California for canola, but not camelina, may therefore be due to fall seedbed conditions being episodically
 suboptimal for canola germination but usually suitable for camelina.
To test this hypothesis, we examined the temperature and moisture conditions of seedbeds in potential oilseed production areas of California which largely overlap with current cereal cropping areas of the state and assessed the frequency with which conditions suitable for germination of canola and camelina occur during the fall planting window for these crops.
The goal of the study was to identify risks associated with establishing canola and camelina in California under rain-fed conditions, suggest the best times and conditions for oilseed sowing and stand establishment in the region, and provide directions for future research.
Our analysis was designed to estimate the proportion of seasons in which soil moisture and soil temperature conditions were simultaneously suitable for the germination of canola or camelina at 11 locations throughout the Sacramento Valley , San Joaquin Valley  and Central Coast of California.
These regions currently support cereal production and could incorporate canola or camelina production in the future.
We considered data from a 31-year period , when suitable data  were available from the California Irrigation Management Information System.
Previous work has found that the ideal sowing time for oilseeds in California is between October and November , so the time period we used for our analysis
 was Oct.
1 to Dec.
31, with December being the mean coldest month throughout most of the region.
Some locations had climate records for fewer than 31 years.
Analyses excluding these locations produced similar results to those including them, SO all the locations were used in the final results.
Soil temperature and moisture modeling
 Soil temperature and soil moisture information was not directly available for the regions of interest.
We therefore used established modeling frameworks to estimate temperature and moisture time series at each location.
Soil water  was modeled using the Hydrus-1D Richards' equation solver.
Richards' equation describes the flow of water through a variably saturated soil.
The implementation of Richards' equation in Hydrus-ID has been extensively tested in representative soils from the Central Valley of California and shown to reproduce observed shallow soil water dynamics.
Evaporative demand was estimated within the model using climate data.
The evaporative data were then used to provide an atmospheric boundary condition to Richards' equation, which was solved to estimate soil water content.
Hydrus-1D soil moisture computations described above.
All calculations were conducted in R.
The U.S.
Department of Agriculture Natural Resources Conservation Service  soils website was used to determine the most common soil types at each location.
Loam soils were the dominant soil types, SO soil matric potential was estimated to a depth of 1 inch  for loam soil variants  using the van Genuchten soil water retention model , with standard soil parameters available in Hydrus from Carsel and Parrish.
Initial soil moisture was set to the wilting point, assuming complete drying of the top 1 inch  of the surface soil by the end of summer.
The model did not account for soil cover or fieldscale variation in topography or microclimate, which have acknowledged effects on soil moisture and temperature dynamics, and which, consequently, could be influential at specific sites.
Results are therefore idealized predictions of likely germination and emergence behavior of canola and camelina in response to the variety of climate and soil conditions experienced throughout likely production regions in California.
Canola and camelina seed are most commonly planted within 1 inch  of the soil surface in flat fields with no soil cover.
No-till systems with residue cover were not modeled.
Seedbed temperatures were estimated at the same study locations used for soil moisture estimation.
We used the method proposed by Ktterer and Andrn  and tested in California by Thompson et al..
In this method, soil temperatures follow air temperatures, and their fluctuations lag with depth and soil thermal conductivity.
With these assumptions, temperatures at 1 inch  below the soil surface were estimated.
Thermal conductivity of the soil was adjusted for changes in water content , using the parallel
 To relate the modeled time series of soil moisture and temperature to seed germination and emergence likelihood, temperature and moisture ranges that support germination were identified from the literature.
Based on these literature values, the minimum soil water threshold for canola germination was set to -0.4 MPa, and to -1.5 MPa for camelina.
Minimum soil temperature requirements for germination of canola and camelina were set to 50F  and 40F , respectively.
To explore the likelihood of optimal seedbed conditions occurring in the October to December planting window at each site, we counted the number of years in which temperature and moisture (treated both
 A field of canola in full bloom at West Side Research and Extension Center.
A high canola yield is more likely if it is sown at the right time it must be late enough in the fall that the risk of dry conditions during germination and establishment is low, and early enough to optimize canopy leaf area at flowering.
independently and jointly) exceeded the germination thresholds identified, for each day of the planting window.
This enabled us to estimate the probability of optimal seedbed conditions occurring before the cutoff date in any given season.
A joint analysis of these conditions was undertaken because temperature and moisture are correlated in the winter rainfall-dominated Mediterranean climate of California.
Across all sites, suitable temperature and moisture conditions for canola germination were met jointly in only 36% of years.
Probability of good germination
 At the Central Valley locations, soil temperatures were predicted to drop below the 50F  canola germination threshold by mid-November, and at coastal locations this threshold was crossed by December.
Based on seedbed temperature criteria alone, canola sown after the end of November in the Central Valley
 is likely to germinate well in fewer than 30% of years.
Camelina, by contrast, is likely to experience acceptable temperatures for germination to the end of November in most years, and through the end of December in 70% to 80% of years.
The probability of soil moisture exceeding the minimum canola threshold for germination is less than 50% until early November in the Sacramento Valley, and until early December in the San Joaquin Valley and Central Coast.
The probability of soil moisture exceeding the minimum camelina threshold for germination exceeds 50% by October.
The joint probability of meeting temperature and moisture conditions simultaneously is shown in figure 1D.
There is a relatively low probability that a seedbed on an arbitrarily selected day in the period from October to December will meet both temperature and moisture requirements for canola germination.
Across all sites, suitable temperature and moisture conditions for canola germination were met jointly in only 36% of years.
The probability of meeting the conditions simultaneously peaks around Nov.
15.
Optimal conditions
  Estimated seedbed temperatures
  Probability of seedbed temperature being above germination threshold
 Fig.
1.
The estimated mean seedbed temperature, adjusted for moisture content, for different regions of California, relative to approximate minimum temperatures for germination of canola and camelina.
The probability of seedbed temperature being above the minimum temperature for germination for canola and camelina for different regions of California.
The probability of seedbed moisture being above the minimum water content for canola and camelina germination.
The joint probability of seedbeds meeting both the minimum matric potential and temperature requirements for germination of canola and camelina in different regions of California.
for camelina are achieved in approximately 85% of years, and the probability of meeting both moisture and temperature conditions peaks on approximately Dec.
1.
Our modeling work supported the hypothesis that episodic problems with the establishment of some later-planted canola crops, and the acceptable establishment of camelina at the same locations, are due to seedbed conditions that are suboptimal for canola but not camelina.
The Sacramento and San Joaquin Valleys showed similar temporal trends in temperature, moisture and the probability of jointly meeting moisture and temperature germination requirements.
The Sacramento Valley has a higher probability of achieving minimum soil moisture thresholds than does the San Joaquin Valley, reflecting the earlier onset and higher average winter rainfall in that region.
The Central Coast and San Joaquin Valley locations have a lower likelihood of achieving suitable soil moisture levels than the Central Valley but are predicted to stay warmer later in the season.
Based on seedbed temperatures only, canola should be sown no later than the end of November in the Central Valley and no later than the third week of November near the Central Coast.
The number of growing degree-days following sowing needed for the emergence of canola is 80C  , therefore a more conservative sowing date would be approximately a week earlier than those times.
Under a best-case scenario, in approximately 50% of years in the Sacramento Valley and in the majority of years in the San Joaquin Valley and Central Coast, supplemental irrigation will be needed to ensure successful stand establishment.
In production situations with either water supply constraints or no ability to irrigate, canola should be planted opportunistically under conditions of both sufficient rainfall and warm seedbed conditions.
These conditions may exist only 1 in every 3 years, which requires growers to quantitatively monitor soil moisture and temperature during the planting season.
Under rain-fed farming conditions, camelina poses fewer risks during establishment than canola.
The germination requirements of camelina, in terms of temperature and soil moisture, are likely to be met from October to December throughout the Central Valley and Central Coast.
There may be a yield penalty associated with later sowing , but this is not demonstrated in the research literature or empirically for California at present.
Camelina is not economically competitive with canola in California, due to its lower mean yields , but our analyses suggest that in locations or seasons where canola cannot be planted due to prevailing conditions,
 camelina represents a lower-risk oilseed option, particularly if yields can be increased reliably to the higher range of potential yields observed in field trials.
Irrigation, new varieties, no-till
 The establishment challenges for canola identified here could be addressed through several approaches.
Irrigation reduces risk during crop establishment and extends the growing season by permitting earlier sowing which may be useful even in areas where the mean winter rainfall may be sufficient to support relatively high yields.
Crop simulation modeling suggests irrigation is also important for increasing yields and minimizing variability for canola production in California.
Total irrigation requirements of canola and cool-season cereals are similar , and lower than the irrigation needs of many current warm-season crops.
Using canola varieties that germinate reliably under either drier  or colder 50F/10C) soil conditions could make planting viable earlier or later in the season.
This would potentially broaden the planting window and increasing the number of years in which rain-fed production of canola is viable.
Screening for varieties that germinate reliably at lower temperatures or at deeper sowing depths, where
 Although camelina has lower yields, it is more drought tolerant than canola and is a less risky option when canola cannot be planted as a result of suboptimal seedbed conditions.
At Rossier Family Farm in Paso Robles, this field of camelina  produced a harvestable crop, while an adjacent field of canola  failed due to a lack of rain.
soil temperatures will remain higher later in the season, would be valuable.
Agronomic management methodologies that increase soil water and temperature in early fall could also be considered as part of a canola production system.
For example, canola could be produced using minimumor no-tillage methods, which have been shown to preserve soil moisture in California.
N.
George is Project Scientist and S.
Kaffka is Assistant UC Cooperative Extension Agronomist in the Department of Plant Sciences at UC Davis; L.
Levers is Postdoctoral Researcher in the Department of Environmental Sciences at UC Riverside; S.
Thompson is Assistant Professor in the Department of Civil and Environmental Engineering at UC Berkeley; and J.
Hollingsworth is Staff Research Associate at Kearney Agricultural Research and Extension Center, Parlier.
Chapter: 15 Cover Crops in Rotations Including Corn
 Cover crops are noncash crops grown with or after a cash crop.
Benefits from cover crops may include: 1) reduced wind and water erosion, 2) reduced nitrate leaching, 3) increased soil organic matter and water infiltration, 4) improved nutrient recycling, 5) improved water quality, 6) improved soil health, 7) enhanced weed suppression, 8) remediation of saline and sodic soil problems, and 9) increased forage for livestock and wildlife.
Establishing cover crops in the region's semi-arid, frigid soils can be challenging.
Viable options for planting cover crop seed include: planting after wheat harvest, planting in-season after the critical weed-free period , and in the fall, following corn harvest.
When deciding to plant cover crops, caution must be used to ensure that cover crops do not void your crop insurance and that your weed-control and cover-crop objectives are aligned.
The purpose of this chapter is to discuss the strengths and weaknesses of including cover crops in South Dakota cropping systems.
Figure 15.1 Brassicas  planted into spring wheat stubble in mid-August harvest.
Photo taken in November, about 10 weeks after planting.
This cover-crop mix provided fall forage for livestock and helped reduce soil compaction.
Table 15.1 Steps for integrating cover crops into your rotation:
 1.
Identify specific objectives and agronomic requirements the desired cover crop.
Determine the season when cover crops are desired and fit the rotation.
a.
b.
Determine if the cover crop will exacerbate pest problems.
Determine if herbicides used during the cropping season allow establishment and growth of the choosen cover C.
crops.
2.
Select a cover-crop mixture  and seeding rates, planting date, and seeding method that are compatible with the applied herbicides and landscape position to obtain the greatest benefits with no loss to the cash crop.
3.
Determine costs  and expected returns.
If carefully chosen, cover crops will not overwinter and cause problems in the following spring.
Herbicides, application timing,and labor costs must be considered if the cover crop does overwinter or produces viable seed.
Successful cover crops require planning and a clear identification of goals.
For example, if the purpose is to utilize excess nutrients, then a cover crop should be established after the cash crop has met most of its nutrient needs.
However, if the purpose is to provide cattle forage or increase water filtration, then the cover crop should be seeded as early as possible in the season to maximize fall growth.
Table 15.2 Matching the cover-crop objective to the plant species.
Grazing	turnips, lentils, canola, radish, rye, oat
 Reducing compaction	radish, canola, sugar beets, sunflower, turnip
 Soil moisture management	canola, clover, winter wheat, rye
 N fixation	clovers, vetches, lentils, cowpeas, chickling vetch
 Residue cycling	brassicas 
 Nutrient cycling	sunflower, sugar beets, brassicas, small grains
 Salinity remediation	sugar beets, barley, winter or spring canola
 Cover Crops and Compaction
 Cover-crop cocktails that include brassicas  can be used to reduce soil compaction.
These plants produce a taproot that can penetrate soils down to 2 feet or more.
The plant roots can rapidly decompose leaving large pores in the soil.
These old root channels aid in water infiltration and soil aeration, and provide root pathways for following crops.
Cover Crops and Soil Health
 Cover-crop mixtures can help provide food for beneficial soil organisms such as earthworms, bind the soil together, and speed up the mineralization of crop residues.
Crop residues with high C to N ratios such as wheat straw or corn stover generally mineralize slowly, whereas those with low C to N ratios, such as brassicas , peas or soybeans, generally mineralize rapidly.
The mineralization rate influences how much of the nitrogen contained in residue will be available to the following crop.
Figure 15.2 Beneficial isopods associated with a decomposing radish root.
Soil Residue Cover, Trapping Nutrients and Managing Salts
 When determining a cover-crop blend to plant, consideration should be made for the current soil-residue cover.
If the desired outcome is crop-residue retention, cover crops with high C:N ratios should be considered.
However, if the goal is to improve soil nutrient recycling from one crop to the next, then crops with low C:N ratios should be seeded.
The decomposition rate of surface residues will increase if brassicas are used in the cover-crop mixture.
Cover crops can be useful in salt management by increasing water loss through transpiration instead of evaporation, and reducing capillary movement of water and salts into surface soil.
In South Dakota, barley, sugar beets, rape, rye, canola, and western wheatgrass can be seeded into salty soil zones.
Cover Crops and Rotational Sequences
 Selecting the appropriate cover-crop species and seeding rates is critical for achieving your goals.
Mixing multiple species allows for several goals to be addressed by a single planting, and often enhances the opportunity for successful establishment.
Care must be taken not to plant at too high a rate, as cover crops can use water needed for the following crop and act as a weed that limits cash-crop yield.
If many species are planted together, the rate of each must be evaluated because competition among these plants can impact survival.
In South Dakota, considerable success has been achieved by seeding a cover crop after winter or spring
 wheat wheat harvest  that allows for fall growth.
In this system, the cover crop is planted after the short-season crop and before next season's corn planting.
Care in selecting the cover crop should be taken.
Crops such as winter rye or hairy vetch are often suggested, as these plants usually overwinter.
However, roller crimping or herbicide application may be required to kill them before corn planting.
Another risk is that seed shattering from cover crops that matured in the fall or spring may behave as weeds in the next crop.
Other opportunities for seeding cover crops include following a failed crop  or after corn's weed-free period.
Our research at SDSU indicates that if cover crops are planted at or just before corn planting, the cover crop can be an ideal weed.
In this example, even though the cover crop was a legume , this species at this planting time outcompeted corn for N, resulting in N-deficiency and a corn-yield loss at the end of the season.
However, if a cover crop was planted during the middle or near the end of corn's critical weedfree period , the cover crop did not reduce the corn yield.
In SDSU research, drilled and broadcast planting techniques were compared.
Drilling the cover crop into the interrow of corn had superior stand establishment and growth compared with any type of broadcast seeding.
Even if rains followed the broadcast application of seed, the seed remained on the soil surface, sprouted, and most died before establishment.
Drilled seeds, on the other hand, became well-established and provided green forage in the fall, even though planted in July.
In addition, if drilled between rows, the distance from the corn can be maximized to lessen the cover crop's impact as a weed, whereas broadcast applications are imprecise and may negatively influence corn growth and development.
Cover-crop Composition: WarmVS.
Cool-Season Plants
 The ideal cover-crop mixture is dependent on the covercrop goals, weed-control program, planting time, and soil characteristics.
Cover-crop mixtures need to be developed for each unique situation.
For example, cool-season grazing blends often consist of turnips, radishes, and grasses, whereas cowpeas, millet, and sudangrass can be used for warmseason grazing.
Selecting an appropriate seeding mixture is critical.
Cover-crop cocktail composition could be warmor
 Figure 15.3 An example of cover crop drilled into the interrow area of a cornfield.
Cover-crop mix  was planted at V3 and photo taken at V6 of corn at Aurora, SD.
Figure 15.4 Crimson clover drilled into corn at V6 on June 30, 2011, with photo taken Sept.
15, 2011, near Trail City, SD.
Figure 15.5 An example of cover crop broadcast into a crop at Aurora, SD.
Note many seeds on the soil surface did not germinate.
cool-season plants or a mixture depending on when the cover crop is seeded.
Cool-season plants grow best in cool temperatures.
Cool-season species start growth when air and soil temperatures are cool and will continue to grow during the spring and fall but go dormant or quickly die when temperatures are warm.
Cool-season broadleaves can be divided into  brassicas, and  legumes.
Cool-season grasses include barley, oats, winter wheat, and rye.
In a South Dakota fall, a cool-season cover-crop mixture is often blended with broadleaf and grass species.
Warm-season plants grow best in warm temperatures.
Warm-season species typically start growth in late spring when soil and temperatures are warm.
These plants thrive during the warm summer weather.
Examples of warm-season plants are big bluestem, corn, and sorghum.
Warmseason species typically do not tolerate frost and will die quickly as fall temperatures decrease.
Match Herbicides and Cover Crops
 The use of pre-emergence herbicides with residual activity reduces the germination and growth of covercrop seeds and seedlings.
For example, if grass herbicide was broadcast-applied in May, it may be difficult to establish hearty stands of rye in August.
The solution is planning.
Many herbicides have activity for a relative long period of time.
For example, Roundup  has no residual soil activity and no restrictions to planting any crop after application.
In comparison, Maverick  has a long residual activity , and planting to anything except small-grain crops is not recommended.
Matching the herbicide rotation to the desired cover crop is critical for cover-crop success.
ingredient	Trade name or premix name	Examples of rotational crop restrictions
 Atrazine	Aatrex	Second cropping season after application
 Premix products with similar restrictions	alfalfa, barley, canola, beans, wheat, flax, lupines, oat, peas,
 as atrazine: Buctril + atrazine; Bullet;	rye, sugar beet
 Degree Extra; Expert; Field Master;
 Fultime; Guardsman; Harness Xtra;
 Keystone Premix types; Lumax;
 Clopyralid;	Accent Gold	26 months canola, lupines, flax, sugar beet
 flumetsulam;	18 months sunflower
 nicosulfuron;	10 months alfalfa, bean, pea
 rimfulsuron	8 months barley, spring wheat, oat, rye
 4 months winter wheat
 Rimfulsuron;	Basis	18 months alfalfa, canola, flax, pea, sugar beet
 nicosulfuron	10 months bean, sunflower
 9 months barley, spring wheat, oat
 4 months rye, winter wheat
 Rimfulsuron;	Basis Gold	18 months alfalfa, barley, canola, bean, wheat, flax,
 nicosulfuron;	lupines, oat, pea, rye, sugar beet
 Atrazine;	Bicep Lite II Magnum	Second cropping season alfalfa, barley, bean, lupines, oat,
 s-metolachlor	pea, rye, spring wheat, sugar beet
 15 months canola, flax, winter wheat
 s-metolachlor;	Camix	Next cropping season barley, oat, rye
 mesotrione	18 months alfalfa, canola, bean, flax, lupine, pea, sugar
 4.5 months winter and spring wheat
 Diflufenzopyr;	Celebrity Plus	Dependent on soil pH and rainfall; generally 10 to 18
 dicamba; nicosulfuron	months for crops
 ingredient	Trade name or premix name	Examples of rotational crop restrictions
 Diflufenzopyr;	Distinct	One month alfalfa, barley, canola, bean, flax, lupine, oat,
 dicamba	pea, rye, sugar beet
 Foramsulfuron;	Equip	18 months alfalfa, canola, bean, flax, lupine, pea, rye
 iodosulfuron	8 or 9 months barley, wheat, oat, spring wheat, sugar beet
 2 months winter wheat
 acetochlor	Harness 
 Clopyralid;	Hornet 
 Acetochlor; atrazine	Keystone premixes (see atrazine
 Bentazon; atrazine	Laddok 
 Imazethapyr; imazapyr	Lightening	40 months canola, sugar beet
 9.5 months alfalfa, barley, bean, lupine, pea
 4 months rye, wheat
 aother restrictions apply, see label for details
 s-metolachlor;	Lumax 
 Dicamba; atrazine	Marksman 
 Primisulfuron;	Northstar	18 months canola, flax, lupine, sugar beet
 dicamba	8 monthsalfalfa, barley, oat, pea, spring wheat
 3 months rye, winter wheat
 Atrazine; 2,4-D	Shotgun 
 Nicosulfuron;	Steadfast	10 months alfalfa, canola, bean, lupine, pea
 rimfulsuron	8 months barley, spring wheat, oat, rye
 4 months winter wheat
 Nicosulfuron;	Steadfast ATZ	18 months barley, canola, bean, flax, lupine, oat, pea, rye,
 rimfulsuron; atrazine	spring wheat, sugar beet
 10 months alfalfa, winter wheat
 Halosulfuron; dicamba	Yukon	36 months sugar beet
 9 months alfalfa, lupine, pea
 2 months barley, bean, oat, spring wheat, winter wheat
 Table 15.4.
Cover-crop blends for grazing.
Grazing blend	Type	Full rate	Option 1	Option 2	Grazing warm	Season	Grazing compaction
 Species	lbs/a	%	lbs/a	%	lbs/a	%	lbs/a	%	lbs/a
 Lentils	Cool/broad	30	30	9	40	12
 Turnip	Cool/broad	4	30	1.2	30	1.2	20	0.8
 Radish	Cool/broad	8	10	0.8	20	1.6
 Rapeseed	Cool/broad	5	30	1.5
 Oat	Cool/broad	70	30	21
 Copea	Warm/broad	30	40	12	30	9
 Millet	Warm/broad	25	60	15	20	5
 Sudangrass	Warm/broad	25	20	5
 Table 15.5 Cover crops that may aid in reducing compaction.
Grazing blend	Type	Full rate	Compaction	Grazing/comp.
Residue/comp.
Species	lbs/a	lbs/a	lbs/a	lbs/a
 Lentils	Cool/broad	30	9	12
 Radish	Cool/broad	8	4.8
 Canola	Cool/broad	5	0.5	1.5
 Cowpea	Warm/broad	30	12
 Millet	Warm/broad	25	15
 Turnip	Cool/broad	4	1.2	1.2
 Table 15.6 Cover crops that may enhance residue-cycling compaction.
Grazing blend	Type	Full rate	Residue cycling	Compaction present
 Species	lbs/a	lbs/a	lbs/a
 Lentils	Cool/broad	30	15	9
 Canola	Cool/broad	5	2.5	2
 Radish	Cool/broad	8	2.4
 Table 15.7 Cover crops that may potentially germinate under saline conditions.
Grazing blend	Type	Full rate	Option 1	Option 2	Option 3
 Species	lbs/a	lbs/a	lbs/a	lbs/a
 Sugar beet	Cool/broad	4	2	2.4	1.2
 Barley	Cool/broad	50	25	20
 Canola	Cool/broad	5	2	1.5
 Table 15.8 Cover crops that may reduce soil moisture and enhance nitrogen cycling.
Grazing blend	Type	Full rate	Option 1	Option 2	Option 3
 Species	lbs/a	lbs/a	lbs/a	lbs/a
 Hairy vetch	Cool Broad	15	7.5	7.5
 Canola	Cool Broad	5	2.5
 Rye	Cool grass	100	50	50
 Triticale	Cool grass	60	30
 The cover crop should be matched to the drainage characteristics of the soil.
For example, annual rye is a cool-season grass that grows under wet soil conditions and tends to grow better in heavy clay soils than cereal rye, whereas cereal rye grows better in wellto moderately well-drained sites.
Cereal and annual rye overwinter like winter wheat.
The major problems with cereal rye are that if excessive spring growth is not controlled: 1) soil moisture can be depleted, and 2) it can produce stands up to 6 feet tall, Figure 15.6 Fungi  decomposing a corn root.
which may be too much biomass for no-till planting.
Typically, herbicide is used in spring to burn down annual rye when its growth is 8 to 16 inches tall.
However, during cool spring weather, glyphosate may have limited effectiveness against annual rye.
Under these conditions, annual rye seeds can become a future weed problem.
Cover crops may reduce available moisture for the cash crop, but they also increase water infiltration and snow catch.
Depending on the situation, our research suggests that they can reduce or increase available moisture for the row crop.
Cover crops increase plant diversity, which can in turn increase soil biological diversity.
Depending on which species is seeded, cover crops may increase or decrease mycorrhizae.
Cost share programs may be available for cover-crop seeding from county USDA-NRCS offices.
EQIP and CSP are programs that typically allow some cost-share benefits for cover crops.
The best way to take advantage of the programs is to check early with your county NRCS office for applications and deadlines.
Center pivot irrigation systems are designed and managed to apply water as uniformly as possible to enhance crop production.
Uniformity has a direct effect on the systems overall application efficiency, which is a measure of how well an irrigation system delivers water to a crops root zone.
Updating the Nebraska Pumping Plant Performance Criteria
 Collaborators: Derrel Martin, Dean Patterson, Jerry Hudgins, Simon van Donk, and Dean Yonts
 Irrigation water is removed from groundwater storage using deep well turbine pumps powered by electric motors or diesel, gasoline, propane, ethanol, or natural gas internal combustion engines.
For best operating efficiency irrigation power units are selected to specifically meet the requirements of the irrigation system that include how deep the water in the well is under pumping conditions, the water pressure required at the pump outlet, and the system flow rate.
Since each component of the irrigation pumping plant  is a mechanical device, wear and tear can reduce its operating efficiency making the motor use extra power to pump the water.
As some components of the irrigation system are replaced, such as replacing a sprinkler package, the original pumping plant may no longer match the new requirements.
These factors cause the energy use efficiency of irrigation pumping plants to be lower than optimum.
The evaluation of pumping plants to establish pumping plant performance dates back into the 1950's when researchers at the University of Nebraska were unable to directly compare the operation of an electrically powered pump installation to that powered by a diesel or other internal combustion engine.
The solution to this issue was to develop performance criteria for each energy source that would be based upon the amount of work  operators could expect if the system were well-designed and well-maintained.
This performance criterion was referred to as the Nebraska Pumping Plant Performance Criteria  that is cited by irrigation design engineers worldwide.
Defining the original criteria involved manufacturer's and Nebraska Tractor Test data and field evaluations of pumping installations.
Since 1959, the diesel fuel standard was updated by Fischbach and Dorn,.
The 3-state area has approximately 110,000 active irrigation wells  The University of Nebraska conducted a statewide pumping plant efficiency study in the late 1970's.
In this study, they tested 180 farmer-owned pumping plants.
When the performance ratings of all pumping plants tested were
 tallied, the average pumping plant in the study was found to be operating at 77% of the NPPPC.
Some pumping plants were found to be very efficient, and 15% of the systems tested actually exceeded the NPPPC.
Engineers from Minnesota, North Dakota and South Dakota were involved in irrigation pumping plant efficiency tests during 1978, 1979 and 1980.
Performance characteristics were determined for 249 electric powered installations.
The average performance rating was 77% of the NPPPC.
More recent tests confirm that pumping plant performance ratings remain well below the NPPPC.
Pumping plant evaluations conducted on 244 units in Texas during the early 1990's.
In their work, diesel powered units averaged 80.4%, natural gas engines averaged 87.5% and electric motors averaged 72.5% of the NPPPC.
Hla and Scherer,  reported on 37 units tested in North Dakota and found the average performance rating for center pivot based systems was about 80% of the NPPPC.
Based on Nebraska Tractor Test data, significant improvement has been made in the brake horsepower output per unit of fuel for internal combustion engines.
However, pumping costs continue to increase due to rising fuel costs which have overshadowed improvements in pumping plant components.
That said, more efficient irrigation pumping plants still could save an average of 25-30 percent of the energy used to pump irrigation water through properly matching and adjusting the pump and motor to current operating conditions.
In Nebraska alone, improvement in pumping plant performance will reduce energy costs by up to $40 million per year.
Frequently cited causes of pumping plant inefficiency are the following:
 1.
The pipeline is valved back at the well to meet pressure requirements;
 2.
Well screen is plugged due to mineral incrustation and/or iron bacteria resulting in extra pumping lift;
 3.
Worn pump impeller due to wear from pumping sand or extended use;
 4.
Improper impeller adjustment on deep well turbine pumps;
 5.
Alteration of the irrigation application system without redesigning the pumping plant;
 6.
Mismatched system components such power unit too large ;
 7.
The power source may not be operating at the specified speed  for maximum efficiency;
 8.
The engine may need a tune-up; and
 9.
Improperly sized discharge column.
Nebraska survey results indicate that 32.7% of the power units used to pump irrigation water are diesel engines, 42.6% are electric motors, 17% are natural gas engines, 7.6% are powered by propane and 0.02% are powered by gasoline
 engines.
The average irrigation system in Nebraska operates for 774 hours, pumping water at a rate of 839 gallons per minute, from a depth of 143 feet, with a pump outlet pressure of 42 pounds per square inch.
Based on the NPPPC, the average system would require 57.4 kilowatt-hours of electricity per hour of operation or 44,464 kilowatt-hours per year.
The equivalent annual energy use would be 3149 gallons of diesel fuel, 5,712 gallons of propane, or 6,380 MCF of natural gas.
Assuming an average performance rating of 80% of the NPPPC, if the performance rating were improved by 10% percent, the average annual energy savings would be equivalent to 5,560 kilowatt-hours of electricity.
When multiplied by 92,000 wells in Nebraska, the potential savings could reach nearly $100 million per year in energy savings.
The NPPPC is based upon the assumption that the pump efficiency is 75% and on the energy contained in fuel for internal combustion engines.
Likewise, the assumed efficiency of an electric motor is 88%.
Other assumptions are included in the footnotes in Table 1.
Based on these assumptions, the existing pumping plant performance criteria are listed in Table 1.
Table 1.
The current Nebraska Pumping Plant Performance Criteria.
Energy Source	Energy Unit	Bhp-hr/unit 	Whp-hr	2//unit	
 Electric	Kilowatt-hr	1.185	0.885
 Diesel	Gallon	16.6	12.5
 Natural Gas	1000 cu.
Ft.
88.97	66.7
 Propane	Gallon	9.2	6.89
 Gasoline 6	Gallon	11.5	8.66
 1 Horsepower hours  is the work accomplished by the power unit including drive losses 2 Water horsepower hours  is the work produced by the pumping plant per unit of energy at the NPPPC 3 The NPPPC are based on 75% pump efficiency 4 Criteria for diesel revised in 1981 to 12.5 whp-hr/gal 5 Assumes 88% electric motor efficiency 6 Taken from Test D of Nebraska Tractor Test Reports.
Drive losses are accounted for in the data.
Assumes no cooling fan 7 Manufacturers' data corrected for 5 percent gear-head drive loss and no cooling fan.
Assumes natural gas energy content of 1000Btu per cubic foot.
The key factors affecting pumping plant performance are typically recorded using a procedure developed by the University of Nebraska.
The test involves accurate measurement of pump discharge pressure, pumping water level, water flow rate, and fuel consumption.
These data are entered into Equation 1 to determine the water horsepower-hours produced by
 the pumping plant.
When divided by the fueled consumed during the testing period, the outcome is the pumping plant performance.
WHP HR = [ +  * Flow Rate 1) 3960 WHP-HR = water horsepower-hours of work produced by the pumping plant Pressure = pump outlet pressure, psi Lift = water level in the well during pumping, ft.
Flow Rate = pump flow rate measured at the outlet, gpm
 Figure 1 shows a schematic of a pumping plant with some performance variables that are recorded during a pumping plant test.
Figure 1.
Schematic of factors affecting the pumping plant performance of a deep well turbine pump powered by an electric motor.
Additional information recorded during the test include the number and type of impellers, pump speed of rotation, power-take-off torque, motor manufacturer, and motor model number.
Where necessary, an electric current meter is used to record incoming power in each leg of 3-phase power line.
Recent Nebraska tests have included monitoring gas emissions from the engine exhaust to gain additional insight into how well the engine is adjusted.
In the winter of 2008-2009, we received a grant through the Water Energy and Agriculture Initiative to conduct pumping plant evaluations across the state of Nebraska with the overall goal of helping to reduce the energy consumption by irrigation pumping plants powered by electricity, natural gas, propane, gasoline, ethanol, and diesel fuel.
Specific objectives are to:
 1) Identify pumping plant components that do not match current operating requirements;
 2) Determine the potential maximum brake-horsepower output per unit of energy for new irrigation power plants;
 3) Develop a revised Nebraska Pumping Plant Performance Criteria for diesel, natural gas, propane, electricity, ethanol, and gasoline power units.
Testing protocol varied slightly depending on the type of power unit and the ability to install instrumentation to the system.
However, the general protocol is listed below.
Irrigation Pumping Plant Test Sequence:
 1.
Record information about pump and motor on the data sheet that was not available via the well registration or producer.
Contact well driller if necessary to identify pump impellers.
2.
Record static water level in the well if system has been shut down for several hours.
3.
Install monitoring equipment including: engine/motor and pump speed, engine exhaust gas analyzer, pump outlet pressure, ultrasonic flow meter, and fuel use with scale or electric meter.
4.
Start the pumping plant and bring the system to normal operation speed.
Allow to run for a minimum of 30 minutes.
5.
Switch engine fuel source to the test can on the scale.
6.
Manually record all data onto data sheet to start the test sequence.
During the test period record the outlet pressure, motor and pump rpm, flow rate , fuel use rate, pumping water level and exhaust gas concentrations a minimum of once every 5 minutes for a minimum of 30 minutes.
7.
Manually calculate system performance to ensure the accuracy of recorded data.
8.
Save data files in separate file folder on the laptop.
9.
If the test is acceptable, turn off the motor/engine and remove equipment.
1.
The pumping plant evaluation must be conducted with all conditions nearly constant throughout the testing sequence.
Recorded information during the test sequence should change less than the following:
 Pump speed + 0.5%
 Pumping water level + 1%
 Fuel use rate + 0.5%
 Pump flow rate + 1%
 2.
Pumping water level, flow meter, fuel use, and engine exhaust gases should be recorded nearly simultaneously.
3.
Engine speed should not be changed once the test has been initiated since engine speed impacts flow rate, outlet pressure, and fuel use rates.
4.
At least one test sequence should be conducted with and without power use by the center pivot, volume gun, or other irrigation system components.
Initial year testing began in July of 2009 and the results of the tests are presented in Table 2.
Nearly all of the units tested were less than 3 years old.
Though at least one unit in each of the energy sources was above the NPPPC, overall results indicated that extra energy is still being used to pump irrigation water in Nebraska.
The electric units were the closer to the NPPPC than the other power types.
Table 2.
Average test results for pumping plant tests conducted in 2009.
Energy	Flow Rate	Pumping	Outlet	Energy	Performance	% of
 Type	Level	Pressure	Use	NPPPC
 gpm	feet	psi	Unit/hr	Whp-hr/unit	%
 Electric	794	146	37	46.1	0.84	95
 Diesel	668	105	46	35.6	10.8	82
 Propane	513	39.5	52	3.58	5.77	84
 Ethanol	1689	191	1	9.3	8.89	??
A new pumping plant testing program is under way to update the Nebraska Pumping Plant Performance Criteria for all energy types.
Average pumping plant test results conducted previously in Nebraska and elsewhere have been near 80% of the NPPPC.
Tests conducted on relatively new installations in 2009 produced results that ranged from 82% for Diesel powered units to 92% for electric units.
The project will continue in 2010 and the update of the NPPPC will be based on data collected by the UNL and other entities across the country.
Fipps, Guy, and Bryon Neal.
1995.
Texas Irrigation Pumping Plant Efficiency Testing Program.
Texas Energy Office Final Report.
Hla, Aung K., Thomas F.
Scherer.
2001.
Operating efficiencies of irrigation pumping plants.
American Society of Agricultural Engineers Paper No.
01-2090.
St.
Joseph, MI 49085.
Effects on vegetative corn: Drought stress during vegetative stages results in reduced stem and leaf cell expansion.
The effect of drought stress on leaf morphology is much larger than that of photosynthesis.
When drought stress is combined with heat stress vegetative development will progress more rapidly.
Any stress that occurs during the sixth to eighth leaf stage  can result in fewer kernel rows, whereas stress from eighth leaf to seventeenth leaf stage  can result in fewer kernels per row.
Chemigation Equipment and Safety
 L.
Leon New and G.
Fipps
 Chemigation is the process of injecting an approved chemical into irrigation water and applying it through the irrigation system to a crop or field.
Chemigation is not a new concept, but has been used for years.
Recent progress in chemigation equipment and know how allows for more effective chemigation through drip and sprinkler irrigation systems, particularly center pivots.
The earliest work applying chemicals through sprinklers was with fertilizers, known as fertigation.
Herbigation soon followed, which is the application of herbicides through an irrigation system.
Next came insectigation with insecticides, fungigation with fungicides and nematigation with nematicides.
The term chemigation describes the application of all these chemicals through the irrigation system.
Uniformity of application With a properly designed sprinkler irrigation system, both the water and chemicals can be uniformly applied, resulting in excellent distribution of the water-chemical mixture.
Precise application Chemicals can be applied where they are needed and in the correct concentrations.
Economics Applying chemicals through chemigation is usually less expensive than conventional application methods.
Often, the amount of chemicals needed can be reduced.
Timeliness Chemicals can still be applied when other methods cannot be used due to wetness, excessive wind, applicator availability or other factors.
Reduced soil compaction and crop damage Conventional in-field spray equipment is not needed, often
 resulting in less soil compaction from tractor wheels and crop damage.
Operator safety Because the operator is not continuously in the field during applications, reduced human contact with the chemicals from drift, frequent tank fillings and other exposures occur.
High management Chemical application requires safe use of chemicals, skill in calibration, knowledge of the irrigation and chemigation equipment and understanding of irrigation scheduling concepts.
Additionalequipment Proper injection and safety devices are essential.
Legal equipment requirements have been established and must be used.
The U.S.
Environmental Protection Agency's Label Improvement Program  became effective in April 1988.
Pesticide labels must now state whether the product is approved to be applied through the irrigation system.
If so, application instructions are provided.
In addition, the label improvement program requires the use of specific safety equipment and devices designed to prevent accidental spills.
These requirements also aid the grower by providing for consistent, precise and continuous chemical injection, thus reducing the amounts  of chemicals applied.
Figure 1 illustrates some of the required safety equipment.
A summary of chemigation pumping and safety equipment requirements is shown in Table 1.
A list of alternate chemigation equipment approved by EPA is provided in Table 2.
CHEMICAL INJECTION SAFETY CONNECTIONS
 Figure 1.
Chemical injection equipment for chemigation, showing some of the approved safety connections.
Table 1.
Summary of Chemigation Equipment Requirements.
a.
Check valve between well and injection points.*
 b.
Vacuum relief valve between check valve and well.
C.
Low pressure cut off.
d.
Low pressure drain.*
 a.
Anti-back flow injection valve 10 psi.
b.
Normally closed solenoid valve between injection pump and chemical tank.*
 C.
A metering type injection pump.*
 a.
Interlock injection pump and water pump power.
b.
Interlock normally closed solenoid valve and injection pump power.
Alternative safety equipment may be substituted according to regulations approved by the EPA in March 1989.
See Table 2.
The check valve in the irrigation pipeline prevents chemicals from going into the well if the irrigation pump inadvertently stops.
The vacuum relief valve prevents a vacuum from being formed that could draw chemicals through the check valve.
Small amounts of chemicals that may leak by the check valve are disposed of through the low pressure drain.
The power
 supply of the injection and irrigation pumps must be interlocked.
When properly interlocked, the low pressure cut off will stop the injection pump should the irrigation pump's power fail.
The anti-back flow injection valve prevents water from flowing backward into the chemical tank should the injection pump fail.
The 10 psi spring prevents gravity flow of the chemical into the irrigation pipeline when both the injection pump and irrigation pump are shut down.
The normally closed solenoid valve, or other alternatives, further ensure that no water will flow into the chemical tank and that no chemical will leave the tank unless it is pumped.
Power interlocks ensure that all other power will be shut down should any equipment fail, including the center pivot.
Management Practices for Chemigation
 Flushing injection system Flush the injection system with clean water after use to prevent accumulation of precipitates and contamination of the equipment, and to support future operation.
Flushing irrigation system After injection is completed, operate the irrigation pump for at least 15 minutes to flush the chemical from the irrigation system.
If the irrigation system stops automatically, flush the system as quickly as possible after the shutdown is
 A.
Original Device Functional normally closed, solenoid-operated valve located on the intake side of the injection pump.
Alternative Device 1 Functional spring-loaded check valve with a minimum of 10 psi cracking pressure.
Notes: The valve must prevent irrigation water under operating pressure from entering the pesticide injection line and must prevent leakage from the pesticide supply tank on system shutdown.
This valve must be constructed of pesticidal resistant materials.
Alternative Device 2 Functional normally closed hydraulically operated check valve.
Notes: The control line must be connected to the main water line such that the valve opens only when the main water line is adequately pressurized.
This valve must prevent leakage from the pesticide supply tank on system shutdown.
The valve must be constructed of pesticidal resistant materials.
Alternative Device 3 Functional vacuum relief valve located in the pesticide injection line between the positive displacement pesticide injection pump and the check valve.
Notes: This alternative is appropriate for only those chemigation systems using a positive displacement pesticide injection pump and is not for use with venturi injection systems.
This valve must be elevated at least 12 inches above the highest fluid level in the pesticide supply tank and must be the highest point in the injection line.
The valve must open at 6 inches water vacuum or less and must be spring loaded or otherwise constructed such that it does not leak on closing.
It must prevent leakage from the pesticide supply tank on system shutdown.
The valve must be constructed of pesticidal resistant materials.
B.
Original Device Functional main water line check valve and main water line low pressure drain.
Alternative Device 1 Gooseneck pipe loop located
 in the main water line immediately downstream of the irrigation water pump.
Notes: The bottom side of the pipe at the loop apex must be at least 24 inches above the highest sprinkler or other type of water emitting device.
The loop must contain either a vacuum relief or combination air and vacuum relief valve at the apex of the pipe loop.
The pesticide injection port must be located downstream of the apex of the pipe loop and at least 6 inches below the bottom side of the pipe at the loop apex.
C.
Original Device Positive displacement pesticide injection pump.
Alternative Device 1 Venturi systems including those inserted directly into the main water line, those installed in a bypass system, and those bypass systems boosted with an auxiliary water pump.
Notes: Booster or auxiliary water pumps must be connected with the system interlock such that they are automatically shut off when the main line irrigation pump stops, or in cases where there is no main line irrigation pump, when the water pressure decreases to the point where pesticide distribution is adversely affected.
Ventures must be constructed of pesticidal resistant materials.
The line from the pesticide supply tank to the venturi must contain a functional, automatic, quick closing check valve to present the flow of liquid back toward the pesticide supply tank.
This valve must be located immediately adjacent to the venturi pesticide inlet.
This same supply line must also contain either a functional normally closed solenoid-operated valve connected to the system interlock or a functional normally closed hydraulically operated valve which opens only when the main water line is adequately pressurized.
In bypass systems as an option to placing both valves in the line from the pesticide supply tank, the check valve may be installed in the bypass immediately upstream of the venturi water inlet and either the normally closed solenoid or hydraulically operated valve may be installed immediately downstream of the venturi water outlet.
D.
Original Device Vacuum relief valve.
Alternative Device 1 Combination air and vacuum relief valve.
discovered, and extend the flushing period to a minimum of 30 minutes.
Monitoring Periodic monitoring of the irrigation system and chemical injection equipment helps assure proper operation during any chemical application.
Calibration check The pivot should be checked for uniform application and overall flow rate to make
 sure the pivot system is performing as specified.
A high uniformity coefficient is needed to ensure even coverage and to prevent either excessive or inadequate concentrations of chemicals in certain areas of the field.
Drive units High speed center pivot drive units are desirable with some chemicals SO lighter applications of water can be made.
Chemical compatibility Check compatibility of the chemical with the water supply to prevent precipitate that could clog nozzles on the system.
End guns Check the uniformity and application under the end gun, and shut it off if it is not desirable.
Uniformity should match the system.
However, in most cases, it is recommended to shut off the end gun during injections.
Chemical labels Follow the label directions.
Use only chemicals that are specifically labeled for chemigation.
If a failure occurs, the user is liable.
Runoff Manage the irrigation system to prevent runoff of the water-chemical mixture.
If runoff occurs, take precautions to prevent it from leaving the field.
With a given sprinkler package on a center pivot, reducing the amount or depth of application  reduces the potential for runoff.
Application to surface water Avoid application of chemicals on fields with permanent or semi-permanent surface water areas.
Such applications may affect wildlife, other nontarget plants and animals and groundwater quality.
Three types of injection units are used for chemigation.
The two types of mechanical units are piston  pumps and diaphragm pumps.
Both can be powered by belt drive or an electric or hydraulic motor and can be adjusted for various flow rates within a designed range.
Chemigation pumps should be selected SO that chemicals can be applied at the appropriate rate.
Injection pumps are commonly purchased with two heads, one for injection of low applications of insecticide and herbicide, and the other one for injection of 20 to 30 pounds of nitrogen per acre.
With proper plumbing, both heads can be used simultaneously.
Usually a single injection pump with two heads is available to apply appropriate quantities of two chemicals.
A single pump with two heads costs less than two injection pumps.
When dual head pumps are used for simultaneous injection of two chemicals, install an injection and automatic check valve and injection hose for each head.
Positive displacement pumps are typically used to inject nitrogen fertilizer and usually cannot be easily adjusted to inject appropriate quantities of insecticide, fungicide and herbicide.
There are various size pistons and pump arm assemblies available that can be
 used to inject the correct amount of chemical and to accommodate the desired travel speed of the center pivot.
Piston sizes 1/4 to 5/8 inch are more appropriate for low-rate injection and sizes 3/4 inch to 1 1/4 inches for intermediate and high chemical injection rates.
Positive displacement pumps are stopped when changing injection rates, SO more time may be required to set the accurate rate.
Diaphragm pumps are used extensively for low-rate chemical injection.
Changes in injection rates can be made while running SO accurate injection can be more conveniently established.
In some cases, diaphragm pumps can be added to existing higher capacity injection units.
The third unit, the venturimeter is a tube with a reduced diameter in the throat.
Velocity changes in the throat create a vacuum that pulls the chemical into the water stream.
Venturi meters require a constant water supply from an external water source, or may be equipped with a bypass and a small booster pump for use of water from the system.
An additional pump or booster pump must be used for maintaining steady flow through the venturi at a higher pressure than the pivot.
A small valve is used on the suction line to regulate the injection rate.
Any variations in flow rate from the water supply will change the vacuum and the rate of injection.
All three pumps are satisfactory for injection of chemicals.
Each should be calibrated and set for the volume of chemical to be injected and rechecked periodically.
Clean carefully after use.
If chemicals stay in the pumps, their useful life is short, and there are problems from failure of valves, seals, hoses or other mechanical parts.
Diaphragm pumps are more popular because of ease of calibration, maintenance and the lack of external leaks.
Some important characteristics and components of chemigation pumps include:
 1.
Accuracy to within + 0.5 percent
 3.
Adjustable while running
 4.
Durable stainless steel valve balls
 6.
Accessibility of repairs
 7.
Appropriate size chemical tank/tanks
 Injection pumps should operate within + 0.5 percent accuracy, utilize stainless steel and other non corrosive material where there is direct contact with chemicals.
Repair should be accessible.
Appropriate
 size chemical tanks equipped for agitation and a calibration tube are important to successful chemigation.
Complete chemigation units that provide these features are available.
Many pump injection rates are available.
It is essential that the pump selected has capacity to apply the appropriate amount of chemical.
Injection pumps are usually rated in gallons per hour.
The pump rating is the maximum injection rate.
Typically, the minimum adjustable injection rate of a single pump is approximately 10 percent of the maximum rating.
It is usually worthwhile to project the range of probable injection rates of likely chemicals prior to purchasing an injection pump.
Accurate calibration of injection equipment is essential for safe and proper application.
Small differences in injection rates can make large differences in the total amount of chemical applied and could cause insufficient or excessive application.
The following conversions and equations are useful for calibration of chemigation equipment:
 450 gallons/minute = 1 acre-inch/hour 27,000 gallons = 1 acre-inch
 Amount of Irrigation Water
 The amount of water applied during a single irrigation is determined by three factors:
 a.
the water pumped or system flow rate in gallons per minute 
 b.
time pumped in hours
 c.
acres on which water is pumped during time , expressed as:
 depth of irrigation system flow rate  X time  =  450 X acres irrigated
 Conversely, the amount of time to apply a given amount of water is:
 Equation 2  hours =  X 450 acres
 Correct injector calibration is necessary SO that the chemical solution is injected at a rate that ensures that the proper amount of chemical will be applied.
The total amount of chemical solution  is first calculated by multiplying the amount of chemical solution needed per acre  by the total number of acres; or
 total chem ical solution =  of chem needed  solution per acre)
 The injection rate  is then based on the total solution needed  divided by the irrigation time  necessary to apply the targeted depth calculated in Equation  and ; or
 injection rate total solution chemical and mix  =  revolution or irrigation time 
 To set calibration, use a stopwatch and a tube or other container of known-volume graduations.
Usually a graduated cylinder marked in milliliters or ounces is used.
Convert the injection rate from gallons per minute using the following formulas:
 If using a milliliter graduated cylinder:  X 63.09 = ml per min
 If using an ounce graduated cylinder:  x 2.133 = oz per min
 Use 32 percent urea ammonium nitrate to apply 10 pounds N per acre through a 1320 foot center pivot covering 125.5 acres at 900 gallons per minute.
The fertilizer is applied with 0.50 inches of water.
Note: 32 percent urea ammonium nitrate weighs 11.06 lb/gal and has 3.54 1b N/gal.
Step 1.
Compute time to make one circle and apply 0.5 inches with equation.
X 450> 125.5 ac 900 gpm 31.4 hours per circle
 Step 2.
Convert pounds of N per acre to gallons per acre: 10 lb N/ac + 3.54 lb N/gal = 2.82 gal solution/ac
 Step 3.
Calculate total chemicals needed with equation.
125.5 ac X 2.82 gal N solution/ac = 353.9 total gal fertilizer solution
 Step 4.
Calculate injection rate with equation.
353.9 g gal + 31.3 hours = 11.3 gal/hour injection rate
 Step 5.
Identify injection rate in ounces per minute with equation.
11.3 X 2.133 = 24.12 oz/min of fertilizer solution
 Step 6.
Set pump injection rate to 24.12 oz/min.
Step 7.
Set center pivot speed control to 31.4 hours/per revolution or circle
 More detailed information on chemigation regulations and calibration are given in TAEX publication B-1652, Chemigation Workbook.
Funding for this publication was provided by the Extension Service USDA under the USDA Water Quality Initiative.
Educational programs conducted by the Texas Agricultural Extension Service serve people of all ages regardless of socioeconomic level, race, color, sex religion, handicap or national origin.
Growers of fresh market tomatoes frequently attribute an increase in small fruit during the growing season to poor water relations.
In studies on a Vista sandy loam soil, greater numbers of small fruit were produced by drought-stressed plants.
A high frequency of furrow irrigation caused the soil surface to "seal" greatly restricting water penetration and lowering the production of large tomatoes.
Production was best when water was added through a drip hose placed at the base of plants in the row or by less frequent furrow irrigation.
G rowers of tomatoes for the fresh market often report that there are more small tomatoes as the season progresses.
The general feeling is that productivity is related to the ability to move adequate irrigation water into the soil.
Preliminary studies at the Lindcove Field Station in 1973 and 1974 indicate that yield and size of fresh market tomatoes are indeed influenced when soil penetration by furrow-applied water is reduced.
A soil surface that is constantly moist from frequent water addition while daily picking is going on leads to soil compaction by harvest laborers walking over the moist soil.
Reduced water penetration may lead to increased frequency of irrigation,
 further compounding the problem.
In 1975 an irrigation trial was established at the Lindcove Field Station on a Vista sandy loam soil with the fresh market tomato variety 6718.
Tomato transplants were set 2 feet apart in the row, 25 plants per row.
Each plot was 3 rows spaced 5.33 feet apart.
Each treatment was replicated three times.
Before the plants were set, two bands of fertilizer were placed 14 inches apart at a depth of 5 inches.
The transplants were then set midway between the fertilizer bands.
The fertilizer was ammonium sulfate at 80 pounds of nitrogen per acre.
Transplants were set on February 20 and covered with plant protectors  for frost protection.
On two occasions, May 23 and July 2, 20 pounds of nitrogen  were dissolved and applied through the drip hose or applied in the furrow bottom near the row, followed by irrigation.
Two methods of irrigation were used: furrow and drip, each at two frequencies.
The furrow system consisted of a conventional furrow placement 1 foot on each side of the row.
A return-flow system was used.
For the drip method, 8-mil biwall tubing was used  with outlets 12 inches apart on the outside wall and 72 inches apart on the inside wall.
Outflow rate at various pressures was measured at the experimental site.
From this calibration it was determined that a pressure of 10 psi at the sub main would provide the flow rate desired.
A pressure gauge and regulator  were installed for each 3-row plot.
Soil water status was monitored throughout the season with tensiometers placed within the tomato row at 12and 24-inch depths in all treatments of two replications.
In early season  the infrequently and frequently furrowirrigated treatments, respectively designated W-1 and W-2, were irrigated when the 12-inch tensiometer reached values of 70 and 30 centibars.
Scheduled the same way during this time were the infrequent  and frequent  drip irrigation treatments.
Irrigations were started for W-2 and W-4 on April 30, but W-1 and W-3 were delayed until May 2.
Before that time, spring rains kept the soil adequately wet on all treatments.
During May, the dry treatments  were irrigated at weekly intervals for 6 to 7 hours, whereas the wet treatments (W-2
 Furrow and drip irrigation systems of the study.
Graph.
Production trends of four size groupings of fresh market tomatoes from furrow and drip irrigation each at two frenquencies.
and W-4) were irrigated at 3-day intervals for 6 to 7 hours.
After May, water penetration became so slow for the frequently irrigated furrow treatment  that scheduling by tensiometer reading was impractical.
In early June, when increased foliage and radiation increased the water demand, a new schedule was established for all treatments which continued for the duration of the experiment.
The infrequent treatments  were still ir rigated weekly , but for 10 hours ntl innicated
 Table 1.
Size designation of fresh market tomatoes.
Trial	USDA	Los Angeles	Diameter size
 Designation	designation	lug size	range 
 Size 1	Extra-small	7x8	1 28/32 2 4/32
 Size 2	Small	7x7	2 4/32 2 9/32
 Size 3	Medium	6x7	2 9/32 2 17/32
 Size 4	Large	6x6	2 17/32 2 28/32
 Size 5	Extra-large	5x6,	2 28/32 3 15/32
 Size 6	Maximum-large	4x5	3 15/32 over
 duration of water application.
The frequent drip irrigation sequence was established to provide about 20 percent more water  than the expected demand, whereas the infrequent drip treatment  was expected to induce considerable drought stress during fruit development.
Harvest dates were June 20 and 26, and July 3, 8, 11, 15, 18, 23, and 25, with the peak harvest at about July 8.
On each harvest date all tomatoes with more red color than the "breaker" stage were picked and divided into sizes.
It developed that the total yield of extra-small, small, and mediumsized fruits was a relatively small part of total yield, contributing less than 100 lugs per acre at the peak picking dates.
The extra-small, small, and medium sizes are normally packed in 3-layer lugs.
As shown in the graph, the yield of extra-small, small, and medium sizes was highest for treatment W-3.
The low volume of water available from this treatment caused the greatest plant stress throughout the season.
Next highest for those tomato sizes were the frequent  and infrequent  furrow treatments.
The frequent drip treatment  provided an optimum soil water condition  and produced the least amount of small tomatoes.
The large, extra-large, and maximum-large sizes are all packed in two-layer flats and contributed most of the total production.
For
 size 4  the yield at the peak pick date was highest for the W-1 treatment, followed by the W-2 and W-4 treatments.
The low water available from the W-3 treatment resulted in the lowest peak pick yield.
Total yield of size 4  tomatoes showed no statistically significant separation by treatment, but was highest for the W-1 treatment followed by W-3, W-2 and W-4 in that order.
Size 5  had a peak pick yield and total yield that followed the same pattern, but with a statistical separation by treatment.
Again, the infrequent furrow treatment  gave the highest peak yield, though total production was not significantly better than for either W-4 or W-2.
The low water availability of the W-3 treatment gave the lowest yield of the size.
Peak pick yield of size 6  was also achieved with the W-1 treatment.
Peak production of 496 flats per acre  was about twice that observed for W-3.
Peak
 yields from W-2 and W-4 were intermediate between those from W-1 and W-3.
However, high production over a longer period characterized the optimum moisture conditions of the W-4 treatment, producing a substantially higher total season yield.
Severe water penetration problems developed during the growing season on the wet-furrow treatment plots.
Soil surface sealing prevented the frequent furrow irrigation from reflecting the amount of water applied to the soil surface.
Water availability was governed more by penetration rate than by irrigation frequency for the furrow method.
Productivity directly reflected the soil water conditions.
The trial confirmed the observations that water penetration markedly influences total yield, fruit size, and peak harvest yield of fresh market tomatoes.
Application of irrigation water through a drip hose placed immediately at the base of plants in the row could improve water penetration and avoid compaction from foot traffic of the harvest crew.
V.
H.
Schweers is Farm Advisor, Tulare County, Visalia; D.
W.
Grimes is Lecturer and Associate Water Scientist, San Joaquin Valley Agricultural Research and Extension Center, Parlier.
Assistance of personnel at the Lindcove Field Station and P.
L.
Wiley at the Kearney Field Station is gratefully acknowledged.
Table 2.
Total-season fresh market tomato yield as influenced by frequency and method of irrigation at the Lindcove Field Station in 1975.
Furrow,	Drip,	Furrow,	Drip,
 Tomato size	infrequent	infrequent	frequent	frequent
 			
 1	96.75 a	199.05 a	92.75 a	68.09 a
 2	75.69 a	114.54 a	61.89 a	60.82 a
 3	156.96 a	241.28 a	176.85 a	149.61 a
 4	688.36 a	590.18 a	529.68 a	485.79 a
 5	1184.73 b	673.60 a	822.21 ab	1010.26 ab
 6	1499.79 b	758.69 a	1294.00 b	1633.16 b
 Total	3702.28b	2577.34 a	2977.38 ab	3407.73 ab
 Sizes 1, 2, and 3 are 3-layer lugs, while 4, 5, and 6 are 2-layer flats.
Numbers not followed by the same letter within a size class or for the total of all sizes, differ at a 5% probability level according to Duncan's multiple-range test.
Preventive Maintenance for Irrigation Equipment
 Craig A.
Storlie, Ph.D., Extension Specialist in Agricultural Engineering
 Irrigation system maintenance is an important management practice which can prevent costly repairs from occurring during the growing season.
Late winter and early spring are appropriate times to perform maintenance duties.
In developing plans for the upcoming growing season, avoid future problems by allotting time to perform these duties.
Drip irrigation systems are more likely to develop problems than other irrigation system types.
For this reason, it is important to treat drip systems with extra care.
Clogging of emitters is the most serious problem associated with drip systems and is caused by physical, biological, and chemical contaminants.
Physical contaminants consist mainly of sediment and other materials that are carried by the irrigation water.
Clogging by these materials is prevented through filtration.
Biological contaminants, such as algae and bacteria, are removed through treatment with a chemical biocide and are either filtered or flushed from the system.
Chemical reactions can occur and cause chemical contaminants to precipitate from the irrigation water and clog emitters.
These reactions are usually avoided through water treatment.
In describing appropriate irrigation system maintenance procedures, it is convenient to divide the irrigation system into three sections: the pumping plant, the water treatment system, and the distribution system.
The pumping plant consists of the pump, motor, and coupling system.
The water treatment system include filters, pressure regulators, and chemical injectors.
The distributions system consists of mains, submains, valves, pressure gauges, and backflow prevention devices.
Each of these sections are maintained in different ways.
Pumping plant maintenance is used to maximize pumping plant efficiency and prolong pump and motor life.
Internal combustion engines should be maintained to operate at peak performance.
Oil, coolant, filters, and lubricants should be checked and changed as specified by the manufacturer.
Engines should also be kept clean SO that they can dissipate heat effectively and sheltered to reduce weathering.
Regular tune-ups will insure that engines run efficiently.
Electric motors require little service.
Protective rodent screens should be cleaned to provide proper air circulation and replaced if they are damaged.
An overhead shelter will also insure that electric motors are properly cooled and that rainfall does not cause corrosion or electrical shorts.
Insuring proper lubrication of the line shaft is an essential part of deep-well turbine pump maintenance and is usually the only upkeep required for these pumps.
Pump adjustment might also be appropriate but must be performed by a trained professional.
Pump impellers normally wear very slowly over their life.
This causes pumping efficiency to slowly decrease.
A system that pumps sand will wear much quicker and should be adjusted every 3-5 years by a trained professional, who will optimize the setting of the impellers in the pump bowls.
A decreased flow rate or operating pressure are signs that a pump has lost efficiency.
However, changes in the distribution system also influence system operating characteristics.
A professionally performed pumping test is the only way to accurately assess the condition of the pumping plant.
Centrifugal pumps are also relatively maintenance free.
Most centrifugal pumps have a packing gland where the drive shaft exits the volute case.
Occasion-
 ally, these must be tightened or replaced if leakage through them is excessive.
Care must be taken not to over-tighten the packing gland.
This could lead to pump failure.
Coupling systems are used to connect the motor to the pump or line shaft.
Gear heads, belts, pulleys, and PTO shafts require lubrication and adjustment to insure peak performance.
Belts, pulleys, and PTO's are typically used in systems using internal combustion engines.
The speed at which a pump is operating can be adjusted by adjusting motor speed or coupling drive ratio.
Use caution in adjusting the speed of the pump.
A pump operates at peak efficiency under a narrow range of flow rates and pressures.
Irrigation water treatment components are used to filter water, inject chemicals, and reduce system pressure.
Filters are used to remove sediment from irrigation water.
Screen filters should be taken apart and inspected for rips or holes in the filter element.
Filters are damaged when they are allowed to operate under heavy sediment loads without regular flushing.
Clean filter elements by spraying them with water.
Media filters may occasionally require that additional media be added to replace material that is slowly lost in the back-flush process.
Electric and hydraulic lines and controls should also be inspected.
Pressure regulators should be inspected for physical damage.
Hoses can rip and regulator bodies can crack.
Diaphragms may also crack or split and should be inspected for wear.
Pressure gauges are used to monitor system pressure and should be used at all locations in the system where a pressure change is expected.
Placing them immediately upand downstream of filters and regulators is particularly useful to monitor the operation of these devices.
In addition, they can be used to trouble-shoot the distribution system.
A higher-than-normal pressure might indicate that a valve that should have been opened is broken or stuck shut, or that sprinklers or driplines are clogged.
A low system pressure could be an indication that there is a leak somewhere in the system or that a valve to a zone that should have been closed was left open.
Pressure gauges are fragile and should be replaced annually or calibrated.
A simple manifold can be constructed from PVC to calibrate gauges.
Use a tire pump to pressurize the manifold and check that all gauges read nearly the same as a high quality gauge that remains permanently on the manifold.
Chemical injectors require service to insure their proper operation.
Seals and fittings become worn through abrasion and corrosion and should be inspected, cleaned, and replaced as necessary.
Some materials cause certain rubber and plastic fittings to soften or expand.
Always dilute materials, particularly pesticides and acids, at a ratio of 10:1 or greater.
Maintenance of injectors might also include calibration to determine injection rates.
Maintenance of the water distribution system is simple, but very important.
Inspect non-permanent pipes for animals or debris before installing in the field.
Inspect mains if possible, and at least flush all mains and submains prior to connecting sprinklers or driplines.
Flushing requires that the system be installed and ready to operate early in the season.
Prevent disappointment later by getting the system ready early and run it once just to flush, inspect, and repair.
Valves, fittings, and back-flow prevention devices can also be checked by running the system prior to the first time irrigation is needed.
A final preventative maintenance practice that is appropriate if problems with the water source are suspected or if a new water source is being used is to have a sample of irrigation water tested by a laboratory.
Certain water quality characteristics give strong clues about problems that may arise.
A local county extension agent can help you in determining which types of tests are appropriate and how results of these tests should be interpreted.
2004 by Rutgers Cooperative Research & Extension, NJAES, Rutgers, The State University of New Jersey.
Economic Feasibility of Solar Photovoltaic Irrigation System Use in Great Basin Forage Production
 Kynda R.
Curtis, Associate Professor and Extension Specialist, Department of Applied Economics, Utah State University
 The Great Basin is primarily located in Nevada, western Utah, and small sections of southern Oregon and Idaho.
The Great Basin is noted for its arid conditions and high percentage of publically owned land.
The potential for solar energy generation in the Great Basin is vast.
In Utah for example, a recent report released by the Utah Renewable Energy Zone Task Force  estimates that Utah's potential for generating concentrating solar power  is approx.
826 Gigwatts  spread across 16,500 potential sites and 6,300 square miles.
The report states that CSP in Utah could generate over 1.5 million GW hours per year or equivalent to the electricity used by 150 million average households.
In Nevada the 250 days of annual average sunshine has led to its recognition as the U.S.
leader in per capita solar energy production.
Nevada has the highest solar energy generation potential.
For example, the Department of Energy  estimates 100 square miles of commercial solar development in Nevada could supply all U.S.
electricity needs.
Solar energy applications in agriculture are numerous, but primary examples include space and water heating, greenhouse heating, crop and grain drying, as well as powering electric fencing, lighting and water pumping.
The use of solar energy to generate electricity for power is performed with the use of a solar photovoltaic  system.
Solar PV systems can be an efficient source of energy in rural areas, as PV systems have been shown to be more cost effective than installing new electrical lines and transformers.
Additionally, solar PV systems do not have moving parts or require fuel, making them more convenient to operate and maintain than traditional fuel based generators.
Due to the prevalence of cattle grazing and alfalfa hay production in the Great Basin, solar PV systems may be most useful in bringing water to cattle and pumping water for irrigated crop purposes, especially in remote areas.
This fact sheet examines the potential economic feasibility of implementing
 solar PV systems for irrigation pumping in Great Basin forage production.
Solar PV systems use semiconducator technology to convert sunlight directly into electricity.
They can be used in conjunction with the existing electricity grid through net metering and interconnections with the local utility.
Solar PV systems can also provide electricity independent of the electricity grid, known as an "off-grid" system, with batteries typically providing the needed storage and backup for times when the sun is not shining.
On-grid systems can also be equipped with batteries to provide electricity when the grid goes down.
Photovoltaic systems come in a range of sizes and types and are commercially available.
Source: Utah Clean Energy
 Feasibility of Solar System Use in Great Basin Forage Production
 To evaluate the potential economic feasibility of using solar PV systems for irrigated forage production in the Great Basin we use the production cost and returns study for alfalfa production in Humboldt County, Nevada  and the production cost and returns study for forage
 production in Eureka County, Nevada.
Both areas consist of an average farm size of 500 acres, four pivots in forage production.
The primary difference between the two areas is the production of cool season grasses in addition to alfalfa in Eureka County.
As the published studies are several years old, the studies were updated to reflect conditions in 2010.
The updated studies now constitute Scenario 1, production using standard power.
The annual irrigation pumping cost in both areas is $45,000 per year.
For Scenario 2, use of a solar PV system for irrigation pumping, we include the investment in a solar PV system to run all four pivots.
The cost of the initial PV system was based upon a 2009 study completed in Humboldt County by Sustainable Energy Solutions.
The solar PV system for each pivot is $420,000 installed or $1,680,000 for the entire farm.
This cost can be reduced by taking advantage of a 25% USDA REAP grant of $420,000 and a 30% tax credit of $378,000, resulting in a total initial investment of $882,000.
The annual maintenance cost for the PV system is estimated at 0.893% of the initial cost  and the useful life of the PV system is estimated at 30 years.
Keep in mind that the cost of the solar PV system implementation will vary with irrigation system requirements, such as well depth and pump and piping system productivity.
The energy demands for each system may vary and hence the size of the PV system will also vary.
As shown in Table 1 , Scenario 2 lowers the initial establishment cost of the alfalfa stand, decreases annual operating costs, but increases annual ownership costs.
Annual farm net returns to production also increase from $1,395.17 to $5,449.10, or $10.90 per acre.
A similar result is found in Table 2 for Eureka County, but the magnitude of decrease in establishment costs and increase in annual farm net returns is less than that of Humboldt County.
Table 1: Scenario Comparison for Forage Production in Humboldt County, Nevada
 Annual Operating	Annual Ownership
 Scenario	Establishment Cost	Cost	Cost	Annual Net Returns
 1 Standard Power	$	80,004.46	$	197,077.16	$	101,527.68	$	1,395.17
 2 Solar PV System	$	76,457.26	$	158,988.20	$	135,562.70	$	5,449.10
 Table 2: Scenario Comparison for Forage Production in Eureka County, Nevada
 Annual Operating	Annual Ownership
 Scenario	Establishment Cost	Cost	Cost	Annual Net Returns
 1 Standard Power	$	101,933.73	$	288,118.24	$	111,573.26	$	308.50
 2 Solar PV System	$	98,386.54	$	250,029.28	$	145,405.59	$	4,565.13
 In the above analysis we assume stable energy costs for Scenario 1.
However, it is more likely that energy costs will increase over the life of the solar PV system.
If we increase the cost of irrigation pumping by 20%, annual farm net returns in Scenario 1 for Humboldt County fall to -$9,157.09, SO the use of the solar PV system results in higher annual net returns of $14,607.08.
If we conduct the same analysis for Eureka County, annual farm net returns in Scenario 1 fall to -$10,772.30 and hence the use of the solar PV system results in higher annual net returns of $15,337.43.
Keep in mind that these results are based on point estimates and do not includes changes or variability in costs and revenues other than those related to irrigation pumping.
Based upon the assumptions used, the implementation of the solar PV irrigation system led to increased annual farm net returns in forage production both in Humboldt County and Eureka County.
Forage producers facing increasing energy costs, large distances to existing lines and/or grids may find the implementation of solar PV irrigations systems a cost effective alternative.
Information on determining PV system size and current state and national rebates and incentive programs can be found in the resources section below.
Rain to Drain: Slow the Flow Adaptation
 Tips for using the Rain to Drain: Slow the Flow Curriculum at fairs and community events when time is limited.
Rain to Drain: Slow the Flow is easily adapted to a demonstration activity at community events, fairs, and other fast-paced environments when time is limited.
Rain to Drain: Slow the Flow can be adapted from a full educational curriculum into a fast-paced demonstration activity.
This adaptation is appropriate for events where you only have a few moments to reach your audience  The demonstration will provide a visual and interactive way to explain how stormwater moves in natural and developed communities and how green infrastructure allows for a more natural flow.
3 Community Models  as prepared in the curriculum
 Three trays to work on 
 At least 1 rain bottle
 1 set of laminated development cards, plus one extra rooftop card 
 1 set of laminated green infrastructure cards, green felt, plastic canvas and rocks to represent green infrastructure on the model
 1 set of green infrastructure photo pages 
 You will set-up three communities, side-by-side, for quick transitions.
Just like in the full curriculum, the muffin tin will represent a model community.
You will set up one muffin tin as a natural community , one as a developed community , and one as a green community.
You could call these three models your community in the past , present , and future.
First Model 
 Rain to Drain Natural Community Set-up
 1.
Explain to those doing the activity how the sponges represent the Earth's surface before people developed it.
Q.
What do you think our community looked like before people lived here?
A.
Trees, forests, meadows, Penn's Woods, etc.--Make sure they conclude that there were a lot more plants.
2.
Explain that this model represents our community over 500 years ago, when it was in its natural state.
Each well of the muffin tin is a property in your neighborhood.
Q.
What do you think the blue muffin well represents?
A.
Water 
 Q.
What do cups under each property represent?
3.
Have a volunteer make it rain on this model.
Hand them the rain bottle and pour a cup of water in while they move the bottle over the tray.
Q.
Where did most of the rain water go when it rained in our community 500 years ago?
A.
Underground and soaked up by the soils in the forest
 4.
Have the audience observe how there was very little runoff into the water body.
Second Model 
 Rain to Drain Developed Communities Set-up
 1.
Transition the audience's attention from the natural community to the developed community model.
Q.
What do you see when you look around your community today, is it all forest?
A.
No.
We have roads, houses, sidewalks, etc.
2.
Point out the development cards on the model and explain what each represents.
Q.
Where do you think the rainwater will go now that the natural community is covered in developed surfaces?
A.
It will roll downhill instead of infiltrating into the ground
 3.
Ask for a volunteer to make it rain on the developed community model.
Q.
Where did most of the stormwater go in this community?
A.
Into the blue water body cup
 Q.
Is there enough groundwater in this community to support plant life and wells for drinking water or farming?
A.
No, the water wasn't able to infiltrate and recharge the groundwater
 Q.
What else might be carried over the surface of roads and concrete in the stormwater that will end up in the water body?
A.
Pollutants like fertilizers, leaky car oil, pet waste, and other dirt
 Q.
Do we need houses, roads, and these other developed surfaces?
A.
Yes, we need these for our way of life.
Third Model 
 Rain to Drain Green Community Set-up
 1.
Explain to those doing the activity that we need to find a way to compromise.
Ask them if they know what "Going Green" is.
We can go green with our buildings as well.
Q.
What can we do to get stormwater to infiltrate like it did in the natural community, but still be able to build the surfaces we need?
A.
Use green infrastructure.
2.
Show the audience the types of green infrastructure on the cards  and show the modifications on the model that are associated with each.
Explain how these types of development reduce stormwater runoff while providing the surfaces we need in our community.
3.
Ask for a volunteer to make it rain on the green community model.
Q.
Where did the stormwater end up in the green community?
A.
Less runoff into the body of water, more infiltration into the ground
 Q.
Did the body of water flood this time
 Q.
Is there groundwater available for use by plants and people?
4.
Ask the audience to consider where each of these and other green practices could be used in your community.
Effects of Weather on Irrigation Requirements
 Fact Sheet No.
4.721
 The irrigation requirements of a crop are affected by weather variability.
The amount and timing of precipitation  and evapotranspiration  demand are the two main weather-related variables that determine irrigation requirements.
The ET demand of a crop is a measure of how much water can be consumed via soil evaporation and plant transpiration assuming that plant-available water is adequate.
The ET demand varies from day-to-day depending on crop growth stage and weather variables such as solar radiation, air temperature, humidity, and wind conditions.
The daily ET demand of a crop can be estimated from daily measurements of the weather variables previously mentioned.
Assuming that all other growth factors are non-limiting meaning conditions are such that these factors remain favorable to crop growth a crop will attain its yield potential as long as its ET demand is satisfied throughout the growing season.
Yield reductions occur when the ET demand is not satisfied, especially during critical growth stages.
The ET demand can be satisfied by precipitation, stored soil moisture in the root zone, and/or irrigation.
Irrigation becomes necessary when natural precipitation and stored soil moisture are not adequate to satisfy all of the ET demand.
period of record.
Instructions for using this online tool are available on the website above.
For this example, corn ET demand was calculated assuming a May 1 planting date each year.
There were 17 years between 1992 and 2008.
However, 24 days of data were missing from the 2003 seasonal record at ARDEC and no nearby weather station could be used in its place.
Therefore, 2003 was excluded from the analysis.
Also, 28 days of data were missing from the 2008 seasonal record because of tornado damage of the weather station.
A complete record for 2008 from a nearby weather station  was used instead.
For the 16 years of usable record available from CSU-ARDEC, the average seasonal  corn ET demand was 20.2 inches while average precipitation for the same period was only 6.5 inches.
This meant that the average shortfall  was 13.7 inches, which would have had to be satisfied by stored soil moisture and/or irrigation.
The quantity ET P  can also be used as a rough estimate of irrigation requirement.
Actual stored soil moisture at planting must be subtracted from this quantity to get a better estimate of the seasonal irrigation requirement.
It is also important to note that not all precipitation amounts are effectively available to the crop because of runoff and deep percolation losses from the root zone.
Figure 1 shows that ET demand, precipitation, and irrigation requirements can vary greatly from year-toyear.
This figure shows how the weather in each year  affects irrigation requirement.
The water shortfall was highest in 2006  and lowest in 1995.
Variability in evapotranspiration demand and precipitation causes irrigation requirements to change from year to year.
Past records of seasonal evapotranspiration and precipitation can be used to plan ahead for irrigation requirements that will probably occur.
The amount and timing of precipitation  and evapotranspiration  demand are the two main weather-related variables that determine irrigation requirements.
A crop will attain its yield potential as long as its ET demand is satisfied throughout the growing season and all other growth factors are non-limiting.
Figure 1: Total corn evapotranspiration  demand per season  at CSU-ARDEC near Fort Collins from 1992 to 2008.
The year 2003 was not included because of missing data.
Part of the ET demand can be satisfied by precipitation  while the remainder  must be satisfied by stored soil moisture or irrigation.
It is difficult to say with certainty what a crop's irrigation requirement will be for the coming season.
This is because weather, specifically precipitation and ET demand, are difficult to predict.
However, past records of P and ET can be used to estimate the probability  that certain amounts of P, ET, and corresponding shortfalls  will occur at a location.
Then, depending on the level of risk we are willing to take; we can select a level of probability  and determine the corresponding crop ET demand that will likely occur.
We can then plan ahead to ensure that we have enough water to supply the ET demand that will likely occur.
Simple frequency analysis of P and ET can be performed to estimate the chances based on past weather records.
Hydrology, McGraw-Hill, Inc., New York, p396]: Pe
 where m is the rank of a value in a list arranged from highest to lowest and n is the total number of observations or values.
For instance, the highest value will have a rank of 1 while the lowest value will have a rank of n.
As with any statistical procedure, having more data  is better than having few data.
As an example, the data from CSUARDEC  was plotted versus their probabilities of exceedance.
Table 1 shows the ranking of seasonal corn ET demand from highest to lowest.
The probabilities in the right-most column were calculated using the Weibull formula.
The same procedure was applied  to seasonal precipitation and water shortfall.
Figure 2 shows that the relationship between corn ET demand and exceedance probability can be approximated by a straight line.
The straight line accounts for about 94 percent of the variability of corn ET demand depending on exceedance probability.
From the graph, one can see that 50 percent of the time, seasonal corn ET demand was equal to or greater than 20 inches of water.
Seasonal corn ET demand was at least 17 inches 80 percent of the time while it was at least 22.5 inches 20 percent of the time.
From the graph, one can get an estimate of how often a certain value of corn ET demand at CSU-ARDEC was equaled or exceeded.
For example, if we want to be 80 percent sure that our water supply  will be enough to satisfy corn ET demand, then we should determine the seasonal corn ET that is exceeded only 20 percent of the time.
Corn ET with 20 percent exceedance probability means that it will
 Figure 2: Probabilities  of exceeding different values of seasonal corn ET  at CSU-ARDEC for the period 1992-2008.
It is difficult to say with certainty what a crop's irrigation requirement will be for the coming season.
This is because weather, specifically precipitation and ET demand, are difficult to predict.
not be exceeded 80 percent of the time.
From Figure 2 at 20 percent probability of exceedance, the expected seasonal corn ET is 22.5 inches.
Therefore, we should make plans to have a total of 22.5 inches of water available for the season.
In this example, we are taking a 20 percent chance  that our water supply will not be enough to satisfy corn ET demand.
Producers who are willing to take more risks can select a higher probability of exceedance.
Likewise, seasonal precipitation  was plotted against probability.
In this case, precipitation versus probability was not linear, SO the horizontal axis was converted to a logarithmic scale.
This means that the probability changes rapidly as seasonal precipitation varies.
In hydrology, a logarithmic scale is often used to make the probability graph appear linear.
Sometimes, we are interested in unknown values between two adjacent observations.
Interpolation is the process of estimating unknown values between actual observations based on observed trends.
Converting data to their logarithmic
 Table 1.
Ranked values of seasonal  corn ET demand at CSU-ARDEC and their assigned probability values.
Year	Corn ET 	Rank, m	exceedance, %
 2006	23.07	1	5.9
 2000	23.01	2	11.8
 2002	22.88	3	17.6
 2001	21.80	4	23.5
 1994	21.60	5	29.4
 1998	21.58	6	35.3
 2007	20.92	7	41.2
 1999	20.91	8	47.1
 1993	20.77	9	52.9
 2008	20.75	10	58.8
 2005	19.37	11	64.7
 1996	17.84	12	70.6
 1995	17.49	13	76.5
 1997	17.27	14	82.4
 1992	17.22	15	88.2
 2004	16.39	16	94.1
 values makes interpolation easier, since a straight trend line is much simpler than a curved trend line.
From Figure 3, it can be estimated that seasonal  precipitation at CSU-ARDEC was at least 5.5 inches 50 percent of the time.
The plot shows that seasonal precipitation was at least 4 inches 80 percent of the time while it was at least 9 inches 20 percent of the time.
As mentioned earlier, the water shortfall represented by  can be a rough estimate of irrigation requirements.
The probability graph of this requirement for
 corn at CSU-ARDEC is linear.
Half of the time , the water shortfall was at least 13 inches.
The water shortfall was at least 8.5 inches, 80 percent of the time, while it was at least 18 inches 20 percent of the time.
Caution Needed in Interpreting Probabilities
 Probability graphs, like the ones given previously, are only as reliable as the individual data points used to make them.
At times, there may be outliers data points that are extremely high or low because of errors in data collection.
Outliers may need to be excluded from the data series to get a more reliable probability plot.
Also, having more data points in time gives more credibility to the probability graph.
In the above example, the year 2003 was excluded because it had 24 days of missing records, which would have caused an under-estimation of ET and P for that year.
As more years are added to the historical record of ET and P at CSUARDEC , these can be included in updated versions of the probability graphs.
There is a danger in estimating
 probabilities outside of the available
 Figure 3: Probabilities  of exceeding different values of seasonal precipitation  at CSU-ARDEC for the period 1992-2008.
Figure 4: Probabilities  of exceeding different values of seasonal  water shortfalls  at CSU-ARDEC for the period 1992-2008.
data range.
For example, estimating the probability of 16 inches of seasonal precipitation from Figure 3 would not be a good idea.
Probability plots are most reliable in the middle of the data range, where more data have been recorded or observed.
That is why longer periods of record are better, because more extreme  values would have been recorded.
Statisticians use statistical tests of the data to improve the reliability of probability plots and to fit appropriate lines through the data points.
Only a simplistic approach is given here to illustrate how weather variability can affect irrigation water requirements.
A field can be managed with uniform irrigation by mounting two IRT sensors in the outer two spans of the pivot.
Since most center pivots can vary the irrigation application across the field using either speed control or zone control, the SIS methods can be used to implement variable rate irrigation more effectively and on a greater number of systems.
For management of variable rate irrigation, two pairs of sensors  on the pivot would be helpful for sensing additional field area.
The SIS methods reduced irrigation applications as compared with the common practice method, with potential benefits for water quality by reducing nitrate leaching.
Table 1.
Percent of fields that had a lower soil water content on Sept.
15 than in August:
 In 2019, 46% of fields experienced their 15-25 inch soil zone get drier.
In 2019, 46% of fields experienced their 25-36 inch soil zone get drier.
These six categories were determined because the soil water level where deep percolation losses of water and nutrients slows to a low rate in a silt loam soil is about 70 cb; thus, it is recommended to keep at least one of the sensors in the second or third foot in this range or dryer.
Yield losses would not be expected until all the sensors were approaching 140 cb, making the 70 cb level very achievable without any chance of causing yield loss.
Field capacity in a silt loam is about 30 cb, so the goal is not to refill the soil above this level with irrigation in the second or third foot.
The Dakota aquifer  is by far the largest of these secondary aquifers, supplying all of the water to more than 3,400 wells in eastern Nebraska.
Seventy-five percent of these wells are domestic, although in places the aquifer is capable of supplying a sufficient volume of water for irrigation and commercial use.
The biggest limitation to using the Dakota aquifer is potentially high salt concentrations.
Geologists think the salty water probably moves into the Dakota aquifer from underlying rocks, a hydraulic condition that is increased by heavy pumping.
When the tenant owns the pivot, the rental rate charged should be discounted, to compensate the tenant for higher ownership and repair expenses.
The Nebraska Farm Real Estate Market Developments 2017-18 Report evaluated common rent discounts for this scenario.
The results are shown in Table 1 below.
Best Management Practices for Waterbirds on Agricultural Lands
 Rebecca McPeake Professor Wildlife
 Waterbirds occupy an important niche in streamside and wetland habitats.
Their presence indicates a healthy ecosystem and can add value to agricultural lands.
Agricultural
 FIGURE 1.
Mallards resting at a farm pond.
Arkansas Is Our Campus
 producers with water resources on their land can fine-tune their management practices to enhance wildlife and waterbird populations.
Water resources may include a river or stream bank, flooded field, reservoir, shallow water area or farm pond.
Best management practices for agricultural production will improve water quality and reduce soil erosion as well as improve waterbird habitat.
As with any changes in production practices, it is beneficial to modify a small portion of your operation first to test and refine the practice before applying to your entire farm.
Waterbirds is a term used to describe a group of birds which depend on rivers, lakes, ponds or streams for food and cover.
Species
 include waterfowl, loons, grebes, pelicans, cormorants, anhingas, gulls, terns, wading birds, shorebirds, marshbirds and a few land birds such as Bald Eagles and Belted Kingfishers.
FIGURE 2.
The secretive King Rail is a type of waterbird found in Arkansas which nests in weedy rice fields and adjacent ditches.
To improve waterbird and wildlife habitat on your farming operation, you will most likely need to make only minor modifications to your practices.
Consider the following best management practices which will be described in more detail: Nutrient Management, Tillage Management, Integrated Pest Management, Field Harvest Management, and Field Border and Edge Management.
As nutrient costs continue to rise, producers are paying closer attention to the cost of nutrient application and return.
Good nutrient management practices for growing a profitable crop are very similar to those needed for improving waterbird habitat.
Nutrient management that ensures good water quality will benefit waterbirds.
1.
Have a written nutrient management plan.
Plans can be obtained by contacting your local USDA Service Center or Conservation District Office.
This is a starting point for your crop management plan.
In addition to the conventional nutrient management considerations, the plan should also include how nutrients affect ground and surface waters and wildlife populations.
2.
Use soil testing and manure analysis in making nutrient recommendations.
Apply only the nutrients that are needed by the crop.
3.
Apply nutrients when and where they can be most effectively used by the crop.
A system that allows applications based on nutrient needs will save money and benefit yield as well as improve waterbird habitat.
4.
Focus on all important nutrients, not just nitrogen or phosphorous.
Potassium as well as micronutrients need to be part of a nutrient management plan.
Excessive phosphorous will have a negative effect on surface water quality.
5.
Use management practices that prevent movement of nutrients into ground or surface waters.
These practices include filter and buffer strips.
Tillage systems vary widely across most production systems and crops.
However, any tillage practice that leaves crop residue, reduces erosion, and
 maintains and protects the water and soil will benefit waterbirds.
Commitment to long-term reduced tillage systems not only will benefit wildlife, but improve soil health and in many instances crop productivity.
Therefore, consider the following when evaluating your tillage systems:
 1.
Consider a tillage system that will leave residue and waste grains.
The residue will protect the soil, and the grains can be used by wildlife as a food source.
2.
If tillage needs to be done, conduct it at a time that will have minimal effect on bird populations.
This generally means avoiding tillage during the nesting season, which can be until late July or early August, to leave food and cover for brooding chicks.
3.
When possible, use a no-tillage system that will reduce trips in the field and soil disturbance.
Fewer trips across the field will leave better nesting and resting locations for waterbirds.
Integrated pest management  involves using the best management practice that benefits both the cropping system and wildlife habitat.
In many cases, IPM uses multiple methods of control that are based on economic and pest thresholds.
Prudent use of agrichemicals will benefit the economics of production and waterbirds.
1.
Have a written IPM plan for your crops.
This plan should include all possible alternatives for pest management, how pest monitoring will be conducted, what thresholds will be used and costs for control activities.
You may consider including a section on reducing agrichemical effects on wildlife.
Contact your local county Extension agent for details.
2.
When using agrichemicals, make sure to follow the label directions, apply the correct rate and use only what is needed.
This means using proper calibration and making applications under the right weather conditions to reduce drift.
Many times agrichemicals can drift into nontarget areas that will destroy waterbird habitat along field edges.
3.
Use the safest practice that will have the least impact on waterbird habitat.
For many pests, crop rotations offer the most economical and effective method of control.
When possible, avoid
 using liquid or granular insecticides.
Choose herbicides, insecticides and fungicides with low toxicity and good environmental profiles.
Since many bird populations depend on insects for food, it is important to select those with minimal effects on beneficial insects.
4.
Adopt proactive, ecological pest management solutions such as crop rotation, planting pest-resistant cultivars, creation of habitat for beneficial organisms and maintaining healthy, biologically active soils.
5.
Monitor pest levels, set threshold levels and keep detailed records of IPM practices for future evaluation.
Today's harvesting machinery is much more efficient than even the equipment that was used 10 or 15 years ago.
It is important for producers to manage and set up this equipment to be as efficient as possible.
However, there are a few simple practices that a producer may consider that can benefit waterbirds and wildlife as well as improve agronomics.
1.
Leaving crop residue will protect the soil, and the grains can be used by wildlife as a food source.
FIGURE 3.
Soybeans growing in wheat stubble.
2.
Increase crop harvest height  so that more residue remains during overwintering and early nesting.
An exception is rice stubble in which increased height could have a negative effect and limit food accessibility for waterbirds.
Rice stubble is poor nesting habitat.
In early spring some birds might nest in taller stubble that will be disturbed for field preparation.
3.
If a portion of a field is damaged by flood, drought, weeds, etc., and the grain is difficult to harvest or is of poor quality, consider leaving
 some of this crop for wildlife.
Always check with your crop insurance provider to determine the feasibility of leaving unharvested crops.
Additionally, these crops may serve to attract waterfowl.
Check with your county wildlife officer or local county Extension agent for rules and regulations for hunting waterfowl over agricultural fields.
Field Border and Edge Management
 Waterbirds and other wildlife can be found in areas surrounding fields.
Field edges are critical habitat for many species.
Some simple management can be used to enhance these environments.
1.
Avoid or delay burning and mowing field borders, ditches and other habitat surrounding fields if possible.
Unmowed borders and ditches provide nesting habitat and escape cover for rails and other birds that are flushed by the combine.
If the borders need to be mowed, attempt to delay mowing until after nesting in late July.
Note that delayed mowing could contradict your IPM plan for stink bugs, which is to keep the borders mowed during the cropping season, particularly for rice.
Waiting until August to mow could cause stink bugs to move from the weeds in the border to the rice at the stage of growth that rice is most susceptible.
However, if stink bugs are not a consideration, consider this option.
2.
Manage herbicide drift around field borders.
Avoid spraying these borders with herbicides when making applications to fields.
3.
Areas of waste grain can be left near borders.
Field borders can be enhanced with food plots.
4.
Identify and manage wetlands, marshes and moist soil units to encourage waterbird use.
If the area is consistently unproductive, consider enrolling in a farm bill conservation program.
A conservation buffer is a type of field edge where small areas or strips of land are left in permanent vegetation.
Buffers are designed to intercept pollutants and manage other environmental concerns.
Strategically placed buffer strips can effectively mitigate the movement of sediment, nutrients and pesticides within farm fields.
These same buffers provide food and cover for waterbirds and wildlife.
Types of buffers are riparian buffers, filter strips, grassed waterways, shelterbelts, windbreaks, contour grass strips, shallow water areas for wildlife, field borders, alley cropping and vegetative barriers.
A general, multi-purpose streamside buffer design consists of a 50-foot-wide strip of grass, shrubs and trees between the normal bank-full water level and cropland.
Trees spaced 6 to 10 feet apart occupy the first 20 feet nearest the stream, shrubs spaced 3 to 6 feet apart dominate the next 10 feet, and grass extends 20 feet further out to the edge of the crop field.
Planting trees and shrubs in well-spaced rows makes maintenance activities, such as mowing, easier to do.
This design requires 6 acres per mile of stream bank, or 12 acres if installed on both sides of the stream.
FIGURE 4.
A streambank stabilization project at various stages of plant growth with cost-share funding through the Wildlife Habitat Incentives Program.
Investigate the potential of establishing buffers around fields using one of the many programs from the Natural Resources Conservation Service , Farm Service Agency  or other conservation group.
There are many programs that pay producers to establish field buffers, filter strips or restore and enhance wetlands and streamside areas.
These programs provide financial incentives and technical assistance for establishing properly managed wildlife habitat.
Crop-Specific Best Management Practices
 Corn is an important crop for waterbirds.
The energy found in corn is helpful for migrating waterbirds as well as overwintering birds.
Farmland can also be a good source of invertebrates that birds eat, such as earthworms, larval insects and flying insects.
Avoid nutrient management practices that harm earthworm populations.
In some cases, applications of soil insecticides and anhydrous ammonia can harm earthworms.
Use a reduced-tillage or no-till system.
Use an insect and weed management program that meets the needs for production purposes but allows some insect and weed survival for waterbirds.
Maintain shallow water areas and wetlands, and use filter and buffer strips when feasible.
If your farm has temporary wet areas, consider enrolling these in a farm bill conservation program.
Soybeans are an important protein source for waterbirds and wildlife.
Leave waste grain following harvest.
Low areas and seasonal wetlands in soybean fields can also provide valuable resting and nesting habitats for waterbirds.
Use a reduced-tillage or no-till system to improve water quality and leave more waste grain for migrating and nesting birds.
Long-term no-till systems will improve invertebrates and overall soil health.
When managing soybean insects, such as the soybean aphid, treat only when thresholds have been reached and, if possible, use a mild form of insecticide such as pyrethroid.
Avoid drift into field borders and edge habitats where waterbirds can thrive.
If you are using a rice rotation or want to improve waterfowl habitat, flood soybean fields in the fall using variable water depths.
Dabbling ducks and other waterbirds can be supported by just 6 inches of water.
Maintain shallow water areas and wetlands, and use filter and buffer strips when feasible.
If your farm has temporary wet areas, consider enrolling these in a farm bill conservation program.
Wheat can be an important resource for waterbirds.
Waste wheat seed is a good food source for nesting and resting waterbirds.
Winter wheat seedlings are eaten during migration.
Straw left in wet areas can improve invertebrate populations.
Many waterbirds can benefit from a straw height of 12 to 19 inches.
Reduced and no-till systems will leave more waste grain, improve water quality and provide habitat.
These systems will help invertebrates thrive by providing a food source for waterbirds.
Use sound nitrogen management to avoid issues with water quality.
Split nitrogen applications may have economic and agronomic benefits, especially on soil types with high leaching characteristics.
Good soil equals good wildlife habitat.
Too many waterbirds, particularly snow geese, can negatively affect wheat production.
If this is a problem, hunting can be an effective deterrent when in season.
Propane cannons and flagging are options for protecting winter wheat from goose damage.
For more information, contact your local county Extension office, a regional office of the Arkansas Game and Fish Commission  or USDA Wildlife Services.
Cotton does not provide a meaningful food source for waterbirds.
However, it is an important component of the landscape where many waterbirds overwinter.
The best management practices for cotton reflect good stewardship of crop management.
No-till and reduced-till systems have a positive effect on water quality.
These systems will affect soil health and can increase invertebrate habitat.
Nutrient management should follow a plan that takes into consideration water quality and wildlife.
Agrichemicals should be managed according to your IPM plan.
Since insects are a potential food source for waterbirds, practices for insect control should be based on insect thresholds.
When selecting an insecticide, choose one with minimal environmental effects.
Properly managed rice has the greatest potential for producing quality habitat for waterbirds.
Rice
 production benefits waterbirds by providing feeding, resting and nesting habitat throughout the year.
Waterbirds can benefit rice production by eating weed seeds and insect pests and speeding straw decomposition.
Rice production practices are compatible with attracting waterfowl, which provides a recreational resource and possibly income from duck hunters.
Waterbirds and rice plants have one thing in common both require good water management.
Winter flooding conserves soil and soil nutrients, increases the quality of runoff water, retards winter weed growth and contributes to rice straw decomposition, thus providing economic and environmental benefits.
Irrigate using surface water by installing a tailwater recovery system and by pooling rainwater.
Surface water is cheaper to pump than groundwater.
Gradual, staggered flooding of rice fields will provide new feeding opportunities throughout the winter period and a range of water depths for waterbirds.
Areas of exposed moist soil are beneficial for birds, too.
Drawdown of fields that were flooded during the winter should be delayed to late February to provide habitat for late-wintering waterfowl, early-migrating shorebirds and early-migrating wading birds.
Drawdowns should be gradual or partial to continually expose new habitat throughout migration.
If feasible, plant later-maturing rice varieties to allow more time for rice-nesting birds to finish nesting before harvest.
A later harvest also means more waste grain is available later in the winter for waterfowl.
TABLE 1.
Calendar for applying best management practices for rice and bird activity.
Note that flooding rice fields can benefit waterbirds at any time of year.
FIGURE 5.
Irrigation ditches provide habitat for waterbirds.
For helping waterbirds, a conventional harvester is recommended over a stripper-header because the former leaves more waste grain.
Roll or burn straw after harvest.
Use nutrient management practices as specified in a nutrient management plan.
Use a tillage system that leaves crop residue and waste grain such as conservation till or no-till.
Use an IPM plan.
Minimize pesticide drift into adjacent habitats.
Manage impoundments and drainage ditches as permanently flooded habitat with native emergent vegetation.
Allow field borders and ditches to grow to provide cover and food for waterbirds.
If you must mow, ideally delay mowing until late July or early August.
Do not burn or mow after May 1.
Enhance buffer strips and riparian areas for wildlife using farm bill conservation programs.
As with any new practice, there will be a considerable learning curve on how to implement best management practices for your farm and its associated wildlife habitat.
Here are a few simple suggestions for implementing these practices:
 1.
Set clear goals and objectives.
Determine what you would like to accomplish and why.
FIGURE 6.
Geese are attracted to water and open areas.
2.
Be patient.
Do not try to change too many things at once.
Try a few things and evaluate their effectiveness.
Establishing wildlife habitat often takes longer than establishing a crop.
For example, native warm-season grasses take several years before they are properly established.
Orchard Sprinkler Irrigation studies show supply of readily available soil moisture more important for fruit growth than type of irrigation
 A.
H.
Hendrickson and F.
J.
Veihmeyer
 Sprinkler irrigation has many advantages in deciduous orchards, but also presents problems not found with surface irrigation.
In general, sprinkler irrigation is well adapted to areas of sandy or shallow soils, and where the hilly nature of the area makes it difficult to secure uniform distribution of water by surface methods.
It is useful in some areas where erosion presents a serious problem.
Sprinkling is advantageous in almond and walnut orchards, where it can smooth and firm the soil surface for mechanical harvesting.
One problem encountered with a sprinkling system is the moving of the pipe on some soils, where the surface layer tends to remain wet and soft for a considerable time after sprinkling.
Lowhanging branches which interfere with uniform distribution of water with undertree sprinklers present another problem.
Where the sprinklers are above the level of the tree tops wind is a factor that tends to prevent uniform water distribution.
Incidence of fungus diseases has not been serious even where the sprinklers
 Low-hanging branches prevent uniform distribution of water.
wet a considerable portion of the foliage.
Up to the present time, the tendencyamong users of sprinkler irrigation-has been to apply too little rather than too much water at each irrigation.
Many problems dealing with the rate of application and the length of the sprinkling
 Soil moisture contents in a mature Duarte plum orchard, showing an excellent irrigation program.
The available soil moisture, shown by the portion of solid bars above the dotted line, representing the wilting percentage-5%-indicate some moisture left from rain and previous irrigations, when water was applied.
period remain to be worked out.
Experimental results, however, indicate that the growth and fruiting of sprinkled trees are the same as those where surface applications are used, provided the supply of readily available moisture is maintained in the soil containing most roots.
Growth of fruit is a sensitive index of soil-moisture conditions because a decrease in the rate of growth of the fruit coincides with the exhaustion of the readily available soil moisture.
Experiments with Santa Rosa plums and Bartlett pears were carried out in sprinkled and in furrow irrigated orchards.
The soil, a Holland sandy loam, with a field capacity of 12% and a permanent wilting percentage of five, was the same in all of the plots.
The interval between irrigation was 12 days which was short enough to maintain a supply of readily available moisture.
Neither the furrow irrigated nor the sprinkled plots reached the permanent wilting percentage before the fruit was picked.
The results obtained with the Santa Rosa plums on peach root showed that increases in fruit size were essentially equal under both furrow and sprinkler irrigation.
The fruits in both plots grew rapidly from about the middle of April until the middle of May when they slowed down slightly during the pit-hardening period, and then resumed rapid growth until picked.
The Bartlett pears in the furrow and sprinkler plots grew at the same rates from -late in May until picked shortly after the middle of July.
The results from the tests with the Santa Rosa plums and the Bartlett pears show that the method of applying the water is without effect on the growth of the fruit-provided the soil moisture is not reduced to the permanent wilting percentage during the growing period.
Ideal irrigation practice consists of the maintenance of readily available moisture in the root zone.
The soil moisture record of a mature Duarte plum orchard, on a Holland sandy loam-represented by the bar graph on page 3-shows how this ideal program was approximated in 1951.
The trees were about 15 years old at the time the record was obtained.
They are planted on 20-foot triangles and in
 Continued on page 12
 Continued from page 3
 a healthy vigorous condition with the branches of adjoining trees coming together in many cases.
The orchard is in a permanent cover crop, principally grass which is mowed several times a year.
The sprinklers are supplied from an underground pipe system and are moved in a regular rotation that provides each tree with a watering every 12 days.
The sprinklers are run about 12 hours and apply a little over 3" of water at each setting.
The soil holds about 1.25" of available water per foot of depth.
The bar graph shows the percentages of soil moisture around a recently irrigated tree, and one just before the water was applied.
The open bar of each pair shows the average soil moisture content a few hours after sprinkling, and the solid bar, the moisture content a few hours before the end of the 12-day interval.
The dry tree-solid bar-was brought up to about the same moisture content as the sprinkled one within the next 24 hours.
The length of the solid bar indicates that, in the early part of the season, while there was some moisture left from the winter rains and the previous irrigations, the soil moisture could be maintained above the permanent wilting percentage easily.
Later in the season, however, the amounts of water applied were barely adequate to maintain readily available moisture during the 12-day interval.
The last irrigation-October 15-wet down only about 2'.
The difference between the amount of moisture found at the end of each 12-day period and the amount applied at the beginning, indicates that the average daily use of a mature plum orchard in permanent cover crop in the foothills of central California is closer to 0.3" per day than to amount sometimes used.
A study of the distribution of water by sprinkling was made in a pear orchard where many branches hung down and touched the ground.
The orchard was left unirrigated for several weeks until the soil moisture was reduced to the permanent wilting percentage-5%-to a depth of 4'.
The orchard was then irrigated.
Soil samples were taken to a depth of 4' at eight compass points about 8' from the trunk of a tree with low-hanging branches.
The sprinkler position was on the east side of the tree.
No water reached the northwest and the west sides of the tree in the top foot of soil.
Water penetrated the second foot in four of the sampling places, the third foot in three, and the fourth foot in only one sample.
The total amount of water at the eight sampling points is shown in the bottom unit of the diagram on this page.
Distribution of soil moisture from sprinklers in a pear orchard where low branches interfered with uniform delivery.
Observation throughout the orchard showed dry areas behind each tree when the position of the low-hanging branches interfered with the distribution of water.
Moving the pipeline to change the relative position of the sprinklers with regard to the trees would change the position of the unsprinkled area, so that the same area would not remain dry all season.
These studies showed that whether irrigation of deciduous orchards is by sprinklers or by surface methods, the growth of the fruit is the same-provided the supply of readily available soil moisture is maintained.
A.
H.
Hendrickson is Lecturer in Pomology, University of California, Davis.
F.
J.
Veihmeyer is Professor of Irrigation, University of California, Davis.
The above progress report is based on Research Project No.
633A.
Continued from page 5
 yards were killed after 43-hour exposure to DDT-treated leaves.
On leaves treated with malathon-dipped in a suspension one fifth as concentrated as the DDTtreated leaves-the leafhoppers from both vineyards were all dead in 24 hours.
In this test the cages were cloth covered on opposite sides.
This lessened the possibility that malathon killed leafhoppers by fumigant action.
Malathon is a new organic phosphate insecticide of much lower toxicity to humans and animals than most of the other organic phosphates.
It is less persistent than DDT-especially in warm weather-and part of its effectiveness appears to result from its fumigant action.
Probably the fumigant effect is less during the cooler weather of spring, so in the pre-bloom dust applications good coverage is most important.
As compounded during the 1952 seascn, malathon dusts possessed an unpleasant odor which, however, could not be detected in the vineyard the day after treatment.
Taste tests conducted with grapes either sprayed or dusted with normal dosages have shown no off-flavors.
As presently licensed for use on grapes, malathon may be applied not later than two weeks before harvest.
Although field tests and grower experience during the 1952 season showed malathon to be outstanding for leafhopper control where DDT resistance is present, some questions as to dosage and timing still await solution.
Further tests with malathon are planned for 1953.
E.
M.
Stafford is Associate Professor of Entomology, University of California, Davis.
Frederick L.
Jensen is Farm Advisor, Tulare County, University of California.
The above progress report is based on Research Project No.
962.
Continued from page 7
 be high enough to prevent serious infestations of cyclamen mite.
In most fields, however, TEPP applications against red spider destroy the predators and earlyseason or mid-season infestations of cyclamen mite are the natural result.
Populations of these predators recover fairly soon from a single early spring treatment but applications of TEPPwhere no real red-spider threat existsare likely to do more harm than good.
Three or more repeated applications over an interval of time may so reduce the predator population that it will not reappear in sufficient numbers to regain control of the cyclamen mite until serious loss has resulted.
Pesticide applications to adjoining crops may drift into fields under natural predator control and destroy the predators throughout a wide margin of a field and disrupt an achieved control.
This has been observed where dust applications of adjacent crops by airplane were made.
Research is in progress to develop methods of mass-rearing this predator or of harvesting it from clipped strawberry tops, cold-storing them, and distributing them in developing infestations of earlyseason 2nd-year, or late-season 1st-year fields.
C.
B.
Huffaker is Associate Entomologist in Biological Control, University of California, Berkeley.
C.1 Kennett is Principal Laboratory Technician in Biological Control, University of California, Berkeley.
The above progress report is based on Research Project No.
1490.
Arkansas Water Primer Series: Arkansas State Water Plan Compliance Certification
 In 1969, the Arkansas General Assembly passed Act 217, which made the Arkansas Natural Resources Commission  responsible for water planning at the state level and the development of the Arkansas State Water Plan.
The first plan was published in 1975.
In 1985, the legislature enacted Act 1051, which directed ANRC to update the plan SO it would remain a valid and reliable document.
Components of the Arkansas State Water Plan
 The Arkansas State Water Plan consists of 12 basin reports and an executive summary.
Each basin report contains a:
 Land resource inventory 
 Surface water identification  and
 Groundwater identification.
Water Plan Compliance Certification 1
 Section 3 of Arkansas Act 469 of 1989 mandates that all water development projects
  obtain a certification of compliance with the Arkansas Water Plan from ANRC.
Applicable projects include those:
 Involving the development of a new water supply source
 Utilizing a new or different place of withdrawal
 Increasing water treatment plant capacity
 Involving system expansion that would result in an aggregate increase of existing and additional water demand being greater than 80 percent of existing water treatment capacity
 Involving an expansion that would result in an increase of more than 20 percent of the current average water usage and
 Involving flood control or drainage.
Additionally, an applicant of any proposed water project that will have any part of its structure near enough to an existing system to cause that system concern must send the neighboring system notice that it has applied to ANRC for Water Plan Compliance Certification.
This provides the notified system an opportunity to file an objection to the proposed water project with the Commission.
To receive certification, a project proposal and narrative, a preliminary engineering report and an application fee must be submitted to ANRC.
All applications must contain the following information:
 General nature of improvements
 Once the required information and fees are received, ANRC staff review the project proposal to determine the accuracy of the data contained in the
 application.
A public hearing is conducted in order to receive additional information and comments concerning the proposal.
If the project is approved by ANRC staff, the applicant receives a final determination letter stating the project complies with the Arkansas State Water Plan.
Applicants may also receive an exemption letter for projects that do not require Water Plan Compliance Certification.
Such projects may include:
 Local drainage facilities for recreational developments of less than five acres
 Drainage facilities associated with street construction or improvements or
 Installation of new water services from existing mains.
Fact Sheet 109  Glossary of WaterRelated Terms contains a comprehensive list of terms used in the Arkansas Water Primer Fact Sheet Series.
1 Arkansas Natural Resources Commission Rules Governing Water Development Project Compliance with the Arkansas Water Plan.
The University of Arkansas Division of Agriculture's Public Policy Center provides timely, credible, unbiased research, analyses and education on current and emerging public issues.
The Arkansas Water Primer Fact Sheet Series was funded by a grant from the U.S.
Department of Agriculture with additional financial assistance from the University of Arkansas Division of Agriculture.
Original research for the Series was provided by Janie Hipp, LL.M., and adapted by Tom Riley, associate professor and director of the University of Arkansas Division of Agriculture's Public Policy Center, and Lorrie Barr, program associate, University of Arkansas Division of Agriculture's Public Policy Center.
Chapter: 46 Mycotoxins in Corn
 Mycotoxins are secondary metabolites produced by some fungi that are highly toxic to humans and animals.
Consequently, the presence of mycotoxins can raise serious concerns if allowed to enter the food chain.
Some fungal pathogens infect corn ears and cause ear rots/ molds and in addition to reducing corn yield, produce the mycotoxins.
Mycotoxin consumption in livestock can lead to reduced intake or feed refusal, altered endocrine system, suppressed immune function, and other effects.
Corn showing symptoms of fungal infections that produce mycotoxins should be sampled and sent for laboratory analysis.
Production of mycotoxins starts in the field, and may continue during the storage period, depending on storage conditions.
Mycotoxin levels never decrease during storage, but concentrations may increase if grain is not stored correctly.
To minimize mycotoxins in the food supply, the Food and Drug Administration has established action and advisory levels for these compounds.
Mycotoxins and their level of toxicity vary by fungal pathogens producing them.
Therefore, each mycotoxin has a different acceptable maximum level, depending on the end-use product or the animal consuming the product.
The purpose of this chapter is to discuss mycotoxins in corn production.
Figure 46.1 Aspergillus ear rot.
There are several mycotoxins that can contaminate corn.
These include: aflatoxins produced by Aspergillus spp ; fumonisins, deoxynivalenol  and zearalenone produced by Fusarium spp.; and ochratoxins produced by Penicillium verrucosum.
The level of mycotoxin contaminating grain is dependent on many factors, including: the incidence and severity of ear rot in the field; the amount of damage on corn kernels during combining; the prevailing weather conditions ; and the adoption of cultural practices that minimize yield-limiting factors.
The fungus Aspergillus flavus produces aflatoxins in corn.
This fungus is abundant in nature, but
 Table 46.1 FDA action levels for aflatoxins in human food, animal feed, and animal feed ingredients.
Intended Use	Feed or Other Products	Aflatoxin Level 
 Human consumption	Milk	0.5 ppb
 Human consumption	Foods, peanuts and peanut products,	20 ppb
 brazil and pistachio nuts
 Immature animals	Corn, peanut products, and other	20 ppb
 animal feeds and ingredients, excluding
 Dairy animals, animals not listed above,	Corn, peanut products, cottonseed, and	20 ppb
 or unknown use	other animal feeds and ingredients
 Breeding cattle, breeding swine and	Corn and peanut products	100 ppb
 Finishing swine 100 pounds or greater	Corn and peanut products	200 ppb
 Finishing  beef cattle	Corn and peanut products	300 ppb
 
 infection in corn is favored by dry and hot weather during grain fill, and at or after physiological maturity.
Aflatoxins are highly toxic and carcinogenic.
Consumption of aflatoxins by livestock can cause feed refusal, reduced growth rate, and rough hair coat among other symptoms.
The FDA-established action level for aflatoxin in grain is 20 ppb in lactating dairy cows.
The level of aflatoxin for beef cattle, swine, or poultry is 100 ppb.
In combination with drought, other stress factors such as insect injury, nematode infestation, and fertility stress can increase chances for this mold to develop.
Fumonisins are a family of mycotoxins produced by many species of Fusarium including the corn pathogens Fusarium verticillioides and F.
proliferatum.
Corn ears with Fusarium ear rot typically have scattered infected kernels on ears.
Kernels with moisture levels > 18% have increased chances for Fusarium infection.
Fumonisin consumption in animals affects the liver of cattle and immune system in pigs and poultry.
Allowable amount of fumonisins varies by animal type and the age of the animal.
Table 46.2 FDA guidance levels for fumonisin in animal feed.
Total Fumonisins  Levels in
 Class of Animal	Grain or Grain Byproducts and 
 [parts per million ]
 Horses and Rabbits	Corn and corn byproducts	5 ppm 
 not to exceed 20% of diet**
 Swine and Catfish	Corn and corn byproducts	20 ppm 
 not to exceed 50% of diet
 Breeding Ruminants, Breeding Poultry	Corn and corn byproducts	30 ppm 
 and Breeding Mink*	not to exceed 50% of diet
 Ruminant > 3 months old being raised	Corn and corn byproducts	60 ppm 
 for slaughter and mink being raise for	not to exceed 50% of diet**
 Poultry being raised for slaughter	Corn and corn byproducts	100 ppm 
 not to exceed 50% of diet**
 All Other Species or Classes of livestock	50% of diet**	10 ppm 
 Livestock and Pet Animals	10 ppm 
 *Includes lactating dairy cattle and hens laying eggs for human consumption
 
 Table 46.3 FDA advisory levels for vomitoxin.
Vomitoxin levels in grains or grain
 Intended Use	Grain or Byproducts	byproducts and complete diet
 Human Consumption	Finished products	1 ppm
 Swine	Grain and grain byproducts not to	5 ppm **
 exceed 20% of diet
 Chickens	Grain and grain byproducts not to	10 ppm **
 exceed 50% of diet
 Ruminating beef and feedlot cattle older	Grain and grain byproducts *	10 ppm **
 Ruminating dairy cattle older than 4	10 ppm **
 Distillers grains, brewers grains, gluten	Ruminating beef and feedlot cattle older	30 ppm
 feeds, and gluten meals *	than 4 months, and ruminating dairy
 cattle older than 4 months
 All other animals	Grain and grain byproducts not to	5 ppm **
 exceed 40% of diet
 * 88 percent dry matter basis ** Complete diet figures shown within parentheses 
 Deoxynivalenol  or Vomitoxin
 Deoxynivalenol is produced by Gibberella zeae.
This compound is sometimes called vomitoxin because it can cause vomiting in swine, especially young pigs.
The main negative effect of this mycotoxin is feed refusal and reduced feed intake.
Gibberella-infected ears when peeled back have pinkish-red kernels covered with the fungal mycelium.
Levels of DON acceptable in animal feeds vary by animal type, but generally beef cattle and poultry can tolerate higher levels than swine.
Infection by this fungus is favored by temperatures between 70-80F after silking.
This disease is more prevalent in fields of continuous corn.
Grain moisture content of greater than 20% is also conducive for this ear rot and mycotoxin problem to develop.
Zearalenone is a second mycotoxin produced by Gibberella zeae.
Zearalenone interferes with reproduction hormones in animals.
Often found with DON.
The FDA does not have recommended action or advisory levels for zearalenone, but levels over 560 ppb is of concern.
Ochratoxins are produced by Penicillium verrucosum.
This fungus usually colonizes corn in storage if grain has > 18% moisture.
However, Penicillium ear rots also can develop in the field, especially on ears with mechanical or insect damage.
Unlike other ear rot pathogens, Penicillium attacks only mature kernels.
The fungus may invade and discolor the embryo resulting in "blue eye." Ochratoxin A is the most common ochratoxin, and swine are the most sensitive.
No FDA guidelines for this toxin are available at this time.
Sampling for Ear Rots and Mycotoxins
 Scouting fields before harvest is important to determine the amount of ear rot in a field and consequently if there is a risk of mycotoxin contamination of grain.
Scout fields by peeling back the husks and inspecting at least 10 ears and at least 5 random stops throughout the field.
If > 10% of ears in a field have > 1020% moldy kernels, the field should be scheduled for harvest as early as possible.
Care should be taken not to damage kernels during harvest.
The grain should be cooled and dried to < 15% moisture content immediately after harvest.
Grain from fields where ear rot was a problem should be stored in a separate bin to grain from fields where the ears were healthy.
To sample grain for mycotoxin testing from a moving grain stream, take a composite sample of 10 lbs using a diverter-type mechanical sampler.
If a mechanical sampler is not available, take a fistful of seeds carefully from the grain stream  and collect 10 lbs.
For stationary corn, use a grain probe, and sample the load at several locations until a composite sample of 10 lbs is collected.
With any sampling method, care should be taken to obtain a representative sample of the entire load.
Representative samples can be sent to diagnostic labs for mycotoxin analysis.
The South Dakota State University Plant Disease Clinic performs these tests and seed can be mailed to: SDSU Plant Disease Clinic SPSB 153 Jackrabbit Drive, Box 2108 Brookings, SD 57007.
Reducing Mycotoxin Development in Grain
 All ear rot pathogens are abundant in the environment and therefore development of ear rots is driven by favorable conditions.
Many ear rot pathogens also survive on infested residue.
The following practices can reduce chances of mycotoxin development on corn.
Use crop rotation to reduce ear rot fungal pathogens inocula.
Minimize yield-limiting factors by selecting an appropriate hybrid for the field, timely seeding, planting at suitable population, using adequate fertility, and controlling pests and diseases.
Manage insect pests to minimize insect injury to ears and kernels.
Scout fields before harvesting to determine the level and type of ear rots.
Minimize kernel damage during harvest by adjusting combine settings to prevent damage.
Harvest early to avoid continued development of ear rots, and consequently mycotoxin production, when risk of disease and contamination are high.
If mycotoxin problems are suspected, screen the kernels to remove cracked kernels.
Dry grain to < 15% moisture immediately after harvest  and before storage.
Clean combines, carts, augers, and bins with pressurized air to avoid cross-contamination.
Regularly check bins during storage to ensure molds are not developing during storage.
Apricot Irrigation tests indicate one irrigation not enough for best results
 A.
H.
Hendrickson and F.
J.
Veihmeyer
 An irrigation before harvest, one about the last week in July and probably one in early September would be a rational irrigation program for apricot trees on deep soil-such as that at Winters.
The treatments were designated by the letters A, B, C, and D.
Soil samples to a depth of six feet at biweekly intervals provided a soil moisture record of each plot.
Typical apricot tree from an irrigated treatment showing an abundance of blossoms.
Treatment plot A was irrigated often enough to keep the soil moisture content above the permanent wilting percentage in the top six feet throughout the growing season.
Four irrigations, including one in May before picking, were usually applied.
The harvest period occurred in late June and early July.
Treatment plot B was irrigated immediately after harvest and thereafter whenever the soil moisture in the top three feet was reduced to about the permanent wilting percentage.
Because of the harvest period, when irrigation was not possible, this plot was generally subjected to lack of readily available moisture in the top three feet for one or two weeks in late June and early July.
Treatment plot C was irrigated once immediately after harvest and not thereafter.
Like plot B, it was subjected to dry soil condition for a relatively short period during harvest.
Dry soil conditions prevailed again, beginning about the middle of August, and continuing until the fall rains.
Treatment plot D was not irrigated during the growing season.
The soil moisture in this plot was reduced to about the permanent wilting percentage late in June and was without readily available moisture, after about the first of July, until the moisture was replenished by fall rains.
The importance of the continuity of the supply of readily available soil moisture was a striking feature of the results obtained in a continuing study of the responses of apricot trees to different irrigation treatments.
An experiment in differential irrigation treatment was started in 1947 with a block of apricot trees in the Wolfskill experimental orchards.
The orchard consists of trees of the Royal variety on apricot root plantedin 1939-24 feet apart on the square system.
The soil is classified as a Yolo silty clay loam.
The experiment was planned in such a way that the trees were brought into full bearing under a system of uniform treatment as regards irrigation and other cultural practices.
Growth and yield records prior to differential irrigation treatment showed that the trees were remarkably uniform.
The orchard was then divided into sixteen suitable plots, and four different irrigation treatments started.
The plots contained either eight or ten experimental trees surrounded by guards that received the same irrigation treatment.
in 1948 and were significantly smaller in 1949 and 1950.
The cumulative yields of treatment D were significantly less than those of A, B, or C in 1948, 1949, and 1950.
Plot D has yielded less than any of the other three and treatment C, with but a single irrigation during the summer, is falling behind the leaders, A and B.
No significant differences in yields were obtained the first year.
Beginning with 1948 the yields in certain plots showed effects of the irrigation treatments and continued to do so through 1950.
The results obtained during the first four years were graphed as cumulative yields-the 1948 average yields were added to the 1947 yields and so on.
Treatment D produced a very light crop, averaging 41 pounds per tree in 1948, following the first summer when it was subjected to dry soil conditions after late June.
Some trees in this treatment did not produce a single fruit.
The increase in size of trees, as measured by gains in cross-section areas of tree trunks presents a slightly different picture, in that certain responses were obtained during the first season of differential irrigation treatment.
The average gain in cross-section area of tree trunks for the three years before the experiment started ranged from 41 to 46 square centimeters.
In 1947, the gains in cross-section areas of the trees
 Typical apricot tree from an unirrigated treatment showing absence of blossoms.
Continued on page 13
 Climatic conditions in 1948 were different from 1947.
The season was late and cool and had more than normal rain in May.
As a result the readily available soil moisture in D plot was not exhausted until early in August or about a month later than usual.
The combination of light crop and the cool season apparently favored the formation of fruit buds in the summer of 1948 and a satisfactory set of fruit in the spring of 1949.
In 1949 the trees under treatment D exhausted the readily available soil moisture about the middle of June and a light crop followed in 1950.
Nearly every tree in this plot showed pronounced alternation in bearing.
No significant differences in cumulative yields between treatments A and B were obtained during the four-year period.
The cumulative yields from treatment C were slightly less than those of A and B
 Summer Weight Gain Brafords, Herefords compared for seasonal gains in Imperial Valley
 Brafords gained more during the summer in tests at the Imperial Valley Field Station; yielded more meat when slaughtered but usually brought a little less money per pound than Herefords.
Most of the data obtained in the tests indicate that the Brafords do not grade out quite as high as Herefords do when both are fed similar rations for the same length of time.
Brafords and Herefords usually make excellent gains on the Imperial Valley's spring pasture and during early summer, but show a drop in daily gain during August when both days and nights are extremely hot.
Several tests were conducted over a three-year period to determine the rates of gain of Hereford and Braford cattle during the different seasons of the year at the Imperial Valley Field Station of the University of California.
Six Hereford steers, six Hereford heifers, six Braford steers, and six Braford heifers were purchased in Bakersfield and received at the station on December 7, 1948.
All the calves were from good grade Hereford cows.
The animals were fed as a group, so comparative food consumption rates on the four lots are not available but feed records on the whole lot were kept.
Cold weather and muddy pastures
 made it necessary for the animals to be fed in the dry lot from December 7 to March 4.
During that period all groups made good gains; the average daily gain for the four lots was 1.47 pounds per head per day.
The ration for this phase of the test was mostly alfalfa hay with a little grain hay.
During the pasture season, the animals were on good alfalfa pasture and received about 3.5 pounds of alfalfa and grain hay per head per day.
The Braford steers gained 2.15 pounds per head per day during the spring pasture period-March 5 to June 13-while the Hereford steers gained 1.82 pounds.
Summer pasture gains-June 14 to September 14-for the Braford steers averaged 2.05 pounds per head per day while the Herefords gained an average of 1.58 pounds.
Although the summer gains for all lots are good, there was a drop in daily gain from August 5 to September 14.
During this period both the days and the nights were hot.
Hereford and Braford steers made an average daily gain of 2.03 pounds and 2.60 pounds respectively, from June 14 to August 4 but gained only 1.02 pounds and 1.
35 pounds during the August and September period.
All lots made good
 gains during the 37-day grain feeding period.
The test animals were shipped to the Los Angeles Union Stock Yards on October 23 and sold by lots on October 24.
The Hereford steers brought 261/2c per pound and the Braford steers 251/4c per pound, while the heifer lots were both sold for 24c per pound.
Dressing percentages for the Brafords were 2% to 4% higher than the Herefords.
Other data collected has shown this same difference.
N.
R.
Ittner is Associate Specialist in Animal Husbandry, University of California College of Agriculture, El Centro.
The Herefords that gained 0.8 pound per day were brought into the valley during July.
Observations indicate that Herefords will do better if they are brought into the valley during the spring and are permitted to become adjusted to the hot weather gradually.
Consideration should be given to selecting Herefords from warmer areas for summer feeding rather than from our cooler states such as Colorado and Montana.
Animals on good alfalfa pasture in the valley make excellent gains and do well during the first part of the summer.
There is a definite drop in gains during the latter part of the summer in both Braford and Hereford cattle.
The Braford steers made 0.5 pounds more gain per pound during the summer-June 14 to September 14-than the Hereford steers.
Other summer tests have shown differences in daily gains between Brafords and Herefords to range from 0.4 to 1.1 pounds.
During the summer, different groups of Herefords on good pasture, with shade, water, and a little hay during the day have gained 0.8 pound to 1.58 pounds per day.
Continued from page 5
 in plot A were 43 square centimetersthe largest-and were 21 square centimeters in plot D-the smallest.
The gains in treatment A were significantly larger than in B, C, and D while those in D were significantly smaller than the other three, The differences between B and C were not significant.
The responses to the change in irrigation were noticeable in increases in growth the first year after differential treatment was started but did not appear in yields until the second year.
The trends in both cases have continued through 1950.
The results obtained from treatment A, which did not reach the permanent wilting percentage at any time, showed con-
 sistently good production and growth during the test.
Treatment B, which reached the permanent wilting percentage and remained there for a short period before being irrigated, produced slightly less than treatment A but the difference in cumulative yields between A and B was not significant.
The gains in cross-section of B, however, were significantly less than those of A.
The irrigation treatment of B has apparently been adequate as far as yields are concerned, but increase in growth was less than in A because of the drought during the picking season.
Treatment C, with only a single irrigation, had significantly smaller cumulative yields than either A or B and grew less than A.
Treatment D with no irrigation is far below the other three treatments both in yield and growth.
A short period without readily avail-
 able moisture as occurred in treatment B apparently did not affect the crop which was essentially mature before the dry soil conditions prevailed, but did affect the increase in growth which was not completed before the readily available moisture was exhausted.
Treatment C, although it bore and grew fairly well, shows that one irrigation, under conditions of this experiment was not enough for best results.
On the average, treatment C was without available soil moisture after early September.
Treatment D responded by low yields and a relatively small amount of new growth.
A.
H.
Hendrickson is Lecturer and Pomologist, University of California College of Agriculture, Davis.
F.
J.
Veihmeyer is Professor of Irrigation, University of California College of Agriculture, Davis.
The above progress report is based on Research Project No.
633C.
Nonpoint Source Pollution in the Cache River Watershed
 The Arkansas portion of the Cache River Watershed is located in northeast Arkansas and includes communities in Clay, Craighead, Cross, Greene, Jackson, Lawrence, Monroe, Poinsett, Prairie, Randolph, St.
Francis and Woodruff counties.
A "watershed" is an area of land where all of the water that drains from it goes to the same place, SO rainwater or snowmelt in this watershed eventually drain to a common location.
This watershed is long and narrow and is named for the major waterway in the area, the Cache River.
The watershed spans 1,956 square miles and is predominantly used as cropland.
About 20 percent of the watershed is forested.
1
 This fact sheet is intended to provide a better understanding of the Cache River Watershed and its place on the state's priority list of 10 watersheds impacted by nonpoint source pollution.
Water pollution that comes from multiple sources spread over an area, such as runoff from parking lots, agricultural fields, residential lawns, home gardens, construction, mining and logging, is known as nonpoint source pollution.
As runoff moves across the landscape, it carries natural and manmade substances that can accumulate in waterways and make them uninhabitable for aquatic species or unusable by people.
Potential pollutants include bacteria, nutrients, sediment, hazardous substances and trash.2 Given the number of potential sources and variation in their potential contributions, these pollutants are not easily traced back to their source.
Cache River Watershed Data source: GeoStor.
Map created March 2011.
Major streams: Bayou De View, Beaver Dam Ditch, Big Creek, Big Gum Lateral, Black Creek, Buffalo Creek, Cache River, Cow Left Ditch, Cypress Creek, Gum Slough, Hill Bayou, Housman Creek, Locust Creek, Poplar Creek, Swan Pond Ditch, Willow Ditch.
Cache River Watershed Water Quality Issues
 Through water quality monitoring, environmental officials in Arkansas have determined that different portions of the watershed have distinct pollution concerns.
The upper section of Bayou DeView and Lost Creek Ditch did not support some aquatic species because of elevated levels of metals including aluminum, beryllium, copper, lead and zinc.
In addition, these sections have historical challenges with excessive levels of
 chlorides and total dissolved solids.
Past water quality testing by the Arkansas Department of Environmental Quality found elevated levels of lead in several segments of the Cache River and Bayou DeView, and current agriculture practice is a suspected source of the lead.
Upon further investigation by the Ecotoxicology Research Facility researchers at Arkansas State University, other potential sources of this lead contamination may be attributable to historical agricultural and industrial practices that influenced lead levels distributed in stream sediments.
In recent years, the Arkansas Natural Resources Commission  has funded local projects to help landowners better manage discharge from agricultural fields and reduce sediment from entering waterways.
ANRC associates these efforts with reduced lead levels found in recent years in Bayou DeView.
3
 Metals can come from natural or manmade sources, including geologic formations, atmospheric depositions, runoff/leaching from mining operations and discharges from industrial or city water treatment
 Arkansas' Priority Watershed List for Nonpoint Source Pollution
 Arkansas has used a watershed-based approach to nonpoint source pollution management, allowing the public to guide planning to address water quality concerns.
The Arkansas Natural Resources Commission, or ANRC, administers the Nonpoint Source Pollution Management Program.
The program exists to reduce water pollution through the funding of watershed planning and restoration activities, adoption of voluntary best management practices and the development of technologies that assist in water pollution reduction in Arkansas.
Based on public input and the use of a qualitative risk assessment matrix, ANRC has designated 10 priority watersheds as needing the greatest attention.
The current risk matrix4 identifies the following priority watersheds: Bayou Bartholomew, Beaver Reservoir, Cache River, Illinois River, L'Anguille River, Lake Conway-Point Remove, Lower Ouachita-Smackover, Poteau River, Strawberry River and Upper Saline.
plants.
High concentrations of metals can be hazardous to the environment because of how they accumulate in aquatic species and build up in soils.
These concentrations can negatively affect people and animals that eat contaminated fish.
Copper and zinc are naturally occurring metals that in excess can be poisonous.
Total dissolved solids and chlorides, which are a mixture of chlorine and other compounds, can originate from natural geological sources such as dissolving rocks.
Other sources of chlorides include salts used for de-icing, runoff from urban and agricultural land and soaps and water softeners found in sewage.
High chloride concentrations can interfere with species' biological processes and affect their salt and fluid levels.
These concerns and its border state status led to the Cache River Watershed being designated as a priority by ANRC in the state's 2011-2016 Nonpoint Source Pollution Management Plan.
5
 To encourage continued public input, the University of Arkansas Division of Agriculture's Public Policy Center facilitated a water quality stakeholder forum for the Cache River Watershed in Newport in October 2014.
Participants identified sedimentation as their watershed's priority concern that needed addressing.
Participants also expressed concern over how water quality issues can impact their economy and about the effects of flooding.
People who live, work or recreate in this watershed are encouraged to consider these community priorities when addressing water pollution.
The public is also welcome to attend an annual stakeholder meeting where priority watersheds and nonpoint source pollution are discussed.
For more information about nonpoint source pollution and its impact on the Cache River Watershed, contact the Cooperative Extension Service, Arkansas Natural Resources Commission or the Arkansas Department of Environmental Quality.
The Arkansas Watershed Steward Handbook is also a good source of information about basic water quality concerns and how the public can get engaged in addressing water pollution.
6
 This fact sheet is one in a series of 10 fact sheets on nonpoint source pollution in priority watersheds.
The University of Arkansas Division of Agriculture's Public Policy Center provides timely, credible, unbiased research, analyses and education on current and emerging public issues.
Trigger Dates: As we head into the growing season following last years dry conditions, assessing pasture conditions at the correct time is critical to successful planning.
How can trigger dates complement your drought planning this year?
COLORADO CROP WATER ALLOCATION TOOL
 Many farmers in Colorado face limited irrigation water supplies.
Limitations are imposed by a variety of circumstances including declining groundwater levels, significantly higher energy costs, evolving water case law and decreasing return flows in river systems.
Regardless of the circumstance, farmers face the same question: what is the "best" allocation of limited water resources?
A Farm's Changing Financial Position
 Under full irrigation, farm managers purchase inputs and choose crops in order to maximize profits with existing resources.
As available irrigation water decreases, the manager's original input purchases and crop choices will not maximize profits.
This is reasonable because when making a whole farm plan, the farm manager chooses equipment, land, and financial capital jointly, and all of these choices assume adequate irrigation supplies.
Farm managers shifting from full to limited irrigation need to reconsider strategic choices if facing perpetual water limitations.
One approach to making these decisions is to consider the farm's asset efficiency, cost efficiency and ability to use borrowed funds when maximizing profits.
Limited Irrigation and Asset Efficiency
 Farm profits rely importantly on the ability to generate revenues from the existing asset base.
A convenient way to measure this ability is the asset turnover ratio :
  ATR = Gross Revenues Total Farm Assets
  Gross Revenues = Yield per acre X Acres Cropped X Crop Price
 The asset turnover ratio summarizes how well the farm's resource inputs  generate gross revenues.
Note that expenses are not included in the asset turnover ratio; rather only farm sales  are present.
Limited irrigation reduces the ATR of a typical farm by reducing the level of gross revenues.
Gross revenues are the product of the farm's yield per acre times cropped acres times the selling price of the crop as indicated by equation.
Yields decrease as irrigation is limited because less water is available for consumptive use, and gross revenues fall with decreased yields.
In equation , the gross revenues are decreased which makes the ATR smaller.
A lower ATR means the farm is less efficient in producing revenues from its existing asset base.
The farm may adopt several strategies to mitigate this shortcoming.
One strategy is to time irrigations in order to reduce the vegetative growth of a row crop saving water for the important grain fill period.
This mitigates the impact of reduced yields for the fixed cropping area shown in equation.
The farm manager might also choose a crop whose price and yield combination are higher than other crops.
The Colorado Crop Water Allocation Tool reduces gross revenues to reflect decreasing yields that follow limited irrigation.
In addition, the spreadsheet user can adjust prices according to market conditions.
Alfalfa is an interesting alternative when mitigating ATR reduction.
When alfalfa is stressed with insufficient water supplies, the relative feed value of the crop actually increases.
The feed value is important to dairies and feedlots, and alfalfa with a greater relative feed value garners a higher price.
As a result, farm managers can partially offset ATR reductions by marketing a hay crop's quality more effectively.
Long term water shortages may lead to using some assets more intensively and culling less productive assets.
As an example, a farm manager may choose to fully irrigate a portion of the farm and allow the rest to lie fallow.
This "rotational" fallow approach leaves other resources, namely equipment and farm labor, underutilized.
Taking advantage of a slack resource, the farm manager can lease
 the farm's equipment to another operation, or might consider performing custom work for other operations.
Gross revenues are increased when slack resources are put to use, so the limited irrigation ATR will increase by using the same asset base more intensively.
Culling the least productive assets might also improve the ATR ratio.
However, selling assets, such as underutilized equipment, reduces the opportunity for the farm to expand operations if circumstances change.
Selling equipment might also alter the farm's cost structure as the manager may need to hire custom work or lease equipment occasionally.
Limited Irrigation and Cost Efficiency
 In the previous section, asset efficiency described the farm's ability to generate revenues from its available resources.
The farm's efficiency in retaining these revenues as profits is its cost efficiency.
Operating profit margin  measures cost efficiency and is calculated as:
  OPM = Operating Income Gross Revenues
  Operating Income = Gross Revenues Operating Expenses
 In equation , gross revenues become operating income once expenses have been differenced.
Operating income represents the funds available for paying creditors and income taxes with the remainder compensating owners.
The OPM calculated in equation  can be no greater than 1.0; after all, operating income cannot exceed gross revenues.
An increase in OPM implies improved cost efficiency because the farm is retaining more of its gross revenues as operating income.
A reduction in farm's gross revenues, or a sudden increase costs, will alter the OPM.
Limited irrigation will reduce the gross revenues of the farm operation as discussed previously.
Operating expenses will change too.
Expenses that decline are those closely tied to production levels including harvesting costs, irrigation energy costs, and irrigation labor expense.
Additionally, fertilizer rates are reduced to match a lower target yield, and managers may limit seeding rates of row crops like corn.
Yet, herbicide and insecticide costs may increase under limited irrigation because a water stressed crop is more susceptible to pests.
In contrast, overhead expenses, such as general farm labor, depreciation and insurance, do not change even though irrigation amounts are reduced.
For this reason, cost efficiency generally suffers when limited irrigation is compared to full irrigation under the same cropping pattern.
Evidence of this effect is found in
 equation , where OPM declines as operating income is reduced at a proportionally greater rate than gross revenues.
Changing the crop rotation might save irrigation water and alter the farm's cost structure.
As an example, managers may seek to adopt a corn-wheat rotation in place of continuous corn to conserve water.
The rotation also reduces costs significantly as wheat requires fewer inputs than corn.
The Colorado Crop Water Allocation Tool is designed so that the user can change the expected allocation to reflect differing input levels including fertilizer, chemical, seed and tillage operations well as differing crop rotations.
The operating return per acre is calculated for each operation so that limited irrigation alternatives can be compared.
Asset Efficiency, Cost Efficiency and Profits
 Farm profitability is a direct result of the efficiency with which the farm uses its assets and manages it costs.
Indeed, the following mathematical relationship is true:
  Rate of Return to Farm Assets  = ATR X OPM
  ROFA = ATR X OPM = Operating Income Total Farm Assets
 Operating income divided by total farm assets is the rate of return to farm assets  as written in equation.
More simply, the ROFA represents the percent rate of return that a farm can generate with its assets a percent that can be compared against similar farms.
Those farms with higher ROFA's are said to be more efficient in deploying and using farm assets to generate operating income.
ROFA is a product of the farm's asset efficiency and cost efficiency as shown in equation.
If a farm seeks to increase its profitability, it may adopt a strategy that generates a greater revenue stream from its resources  or improves its cost efficiency.
Unfortunately, reduced water supplies typically decrease both ATR and OPM by reducing gross revenues and operating income.
As a result, the ROFA of a limited irrigation farm declines.
A declining ROFA is especially problematic for a firm whose interest expense is relatively high.
The operating income used to calculate the ROFA also represents the funds available to compensate the lender for the use of borrowed capital.
If ROFA consistently falls below the average interest rate on borrowed capital, then the farm will have to find another means in order to make payments to the lender.
The relationship between borrowed capital and limited irrigation is considered in the next section.
Limited Irrigation and Borrowed Funds
 Borrowed capital permits farmers grow their business more quickly and control a larger asset base than if the owner were to grow based solely on retained earnings.
In order to secure borrowed capital, farms often pledge their land as collateral.
Shifting from full to limited irrigation impacts the farm's ability to secure borrowed funds in two ways: it limits the ability to repay debt by restricting cash flow and it undermines the security of the farm's collateral by decreasing the market value of its assets.
Each effect will be discussed in turn.
Limited Irrigation and Repayment Capacity
 Repayment capacity is an important measure of the cash available to make existing term debt payments and/or to seek additional financing.
Lenders calculate repayment capacity according to:
  Repayment Capacity = Operating Income + Depreciation + Contributions
 Repayment capacity reflects the available cash in the farm operation; therefore, depreciation is added to operating income in equation..
Likewise, off farm income might represent an important cash contribution to the farm operation, so it is added to operating income to reflect the ability to repay.
Operating income declines with limited irrigation reducing the funds available to repay scheduled principal and interest payments.
Increasing off-farm contributions, custom farming and expanding the operation may enhance repayment capacity by increasing cash flow.
Yet, declining repayment capacity will limit opportunities to buy or lease additional farm acres.
Furthermore, limited irrigation reduces farm's collateral.
Limited Irrigation and Loan Collateral
 Market values for farmland change with expected profits farmland that is more productive and profitable is in greater demand fetching higher prices and cash rents.
A farm evolving from full to limited irrigation will experience a decrease in the market value of its land.
Land is often pledged as collateral for the farm operation.
Lenders are acutely aware of circumstances that alter expected farming profits and may attach more stringent covenants to loans on land that adopts limited irrigation cropping in place of full irrigation Example covenants include the use of crop insurance and
 maintaining a specific working capital level in the farm business bank account.
Farm manages should communicate frequently with their lender when examining limited irrigation alternatives.
Farms transitioning from full to limited irrigation will find their financial position is altered.
Assets, especially land and equipment, may not be used to their full potential so that gross revenues are reduced.
The cost efficiency of the farm operation will suffer, in a large part because overhead costs remain the same but the revenues available to compensate are reduced.
Farm managers may be able to improve efficiency by carefully examining and reducing inputs such as fertilizer and the seeding rate.
Finally, farm managers adopting limited irrigation practice should recognize shrinking cash flows will limit repayment capacity, and the declining values of farm assets decrease opportunities to grow the business with borrowed funds.
Farm managers can address the changes with a variety of activities that range from timing irrigations to expanding the farm operation.
The Colorado Crop Water Allocation Tool is one resource to assist in choosing among limited irrigation alternatives.
When a center pivot is running below the designed operating pressure, decreases in water application uniformity can occur, which, in turn, decrease yields.
Interpreting Irrigation Water Tests
 Basic interpretation of how various water quality parameters can influence plant growth during irrigation.
Greenhouse and crop producers across Pennsylvania utilize a variety of sources of water for irrigation.
Data from U.S.
Geological Survey show that each day over 34 million gallons of water are used for irrigation of about 78,000 acres in the state each day.
Over 19,000 acres of irrigation occurs in micro-irrigation systems commonly found in greenhouses.
Unfortunately, the quality of these water supplies is often overlooked as a potential source of plant growth issues.
Water quality is most important for crops grown in small amounts of growth media  or hydroponically.
Greenhouse and high tunnel growth environments also increase the importance of water quality because irrigation is the only source of water.
Crops grown outside are less affected by irrigation water sources if they experience dilution from natural rainfall.
In any case, water testing should be the first step when considering the use of irrigation water to ensure that maximum crop yield will be realized and disastrous plant toxicity issues will not develop.
All irrigation water sources should be tested for pH, alkalinity, conductivity, hardness, chloride, and sodium at a minimum since these are common issues in Pennsylvania water supplies.
A more thorough test is ideal and should also include total dissolved solids, boron, calcium, magnesium, sodium adsorption ratio , nitrate-nitrogen, ammonium-nitrogen, phosphorus, potassium, sulfur, iron, manganese, copper, molybdenum, and zinc.
Most test results will be expressed as milligrams per Liter  which is the same as parts per million  in aquatic solutions.
Water test results should be considered in combination with soil or growth media test results.
The table below includes parameters in the Penn State Agricultural Analytical Services Laboratory irrigation test kit.
Approximate levels of concern for each parameter are provided where applicable and discussed further in the text that follows the table.
However, some plant species have water quality tolerances that differ from the general levels discussed.
Growers are urged to research the specific water quality tolerances of their crops, especially if they are noticing growth or health problems in response to irrigation.
The pH of water is measured on a scale of 0 to 14.
A pH of 7.0 is neutral while pH levels below 7.0 are acidic and levels above 7.0 are basic.
Each whole number difference represents a ten-fold difference in acidity.
The pH of water along with alkalinity affects the solubility and availability of nutrients and other chemical characteristics of irrigation water.
In general, most plants prefer slightly acidic conditions in a pH range of 5.0 to 7.0.
Problems with low or high pH are exacerbated in plants grown in soil-free or small growing systems since growth media can often act to buffer pH problems.
Higher water pH levels can be tolerated if the water alkalinity is not excessive.
High pH  may reduce the availability of various metals and micronutrients causing deficiency symptoms.
High pH is often accompanied by high alkalinity.
High pH problems can be corrected by acid injection or in some cases by using an acid fertilizer.
Rainwater in PA is acidic.
Less commonly, low pH  may result in toxic high levels of metals like iron and manganese; this is usually found in combination with low alkalinity.
Low pH problems can be corrected by switching to a basic fertilizer or liming the growing medium.
Total Alkalinity, Bicarbonates, And Carbonates
 Perhaps the most important water quality parameter to affect irrigation waters in Pennsylvania is alkalinity.
Alkalinity is a measure of the dissolved materials in water that can buffer or neutralize acids.
These include carbonates , bicarbonates , and hydroxides.
Alkalinity is typically reported as mg/L of calcium carbonate.
Alkalinity can originate from carbonates or bicarbonates that dissolve from the rock where the groundwater is stored.
While the separate carbonate and bicarbonate alkalinity test results are helpful in understanding the source of the alkalinity and the potential for other contaminants in the water, from an irrigation perspective the total alkalinity is the most important water test result.
The ideal range for total alkalinity is approximately 30 to 100 mg/L but levels up to 150 mg/L may be suitable for many plants.
High alkalinity above 150 mg/L tends to be problematic because it can lead to elevated pH of the growth media which can cause various nutrient problems.
Low alkalinity  provides no buffering capacity against pH changes.
This is especially problematic where acid fertilizers are used.
Alkalinity in pond water can vary a great deal throughout the day if photosynthetic algae and plants are present.
Hardness is determined by the calcium and magnesium content of water.
Since calcium and magnesium are essential plant nutrients, moderate levels of hardness of 100 to 150 mg/L are considered ideal for plant growth.
These levels of hardness also inhibit plumbing system corrosion but are not high enough to cause serious clogging from scale formation.
High concentrations of hardness above 150 mg/L will build up on contact surfaces, plug pipes and irrigation lines and damage water heaters.
These levels can also cause foliar deposits of scale.
Removal of hardness by using a water softener is necessary only if the water is causing problems.
Extremely soft water below 50 mg/L may require fertilization with calcium and magnesium as discussed below.
Calcium concentrations in water are most often a reflection of the type of rock where the water originates.
Groundwater and streams in limestone areas will have high calcium levels while water supplies from sandstone or sand/gravel areas of the state will typically have low calcium concentrations.
Calcium levels below 40 mg/L will typically need fertilizer additions of calcium to prevent deficiency while high levels of calcium above 100 mg/L may lead to antagonism and resulting deficiency in phosphorus and or magnesium.
High levels of calcium may also lead to clogged irrigation equipment due to scale formation.
Water softening  is typically used to reduce calcium levels in water but softening for irrigation should use potassium for regeneration rather than sodium to prevent damage by excess sodium in the softened water.
Like calcium, magnesium in water tends to originate from the rock and generally only causes problems when it is below 25 mg/L necessitating the addition of magnesium in fertilizer.
Magnesium can also cause scale formation at high concentrations which may require softening.
Electrical Conductivity 
 Electrical conductivity is a measure of electrical current carried by substances dissolved in water.
Conductivity is also often referred to as "soluble salts" or "salinity".
As more salts are dissolved, water will better conduct electricity resulting in a higher conductivity reading.
Conductivity is usually reported in millimhos per centimeter  or milliSiemens per centimeter  which are equivalent units.
Elevated conductivity levels in water can damage growth media and rooting function resulting in nutrient imbalances and water uptake issues.
The conductivity of typical clean water is 0 to 0.6 mmhos/cm.
Conductivity of fertigation solutions varies with the fertilizer concentration and salt, but generally ranges from 1.5 to 2.5 mmhos/cm.
To avoid problems from excessive salts, raw water before fertilizer additions should be below 1 mmhos/cm for plugs and below 1.5 mmhos/cm for other growing conditions.
Raw water conductivity above 3 mmhos/cm can be expected to cause severe growth effects on many plants.
While excessive water conductivity is a common problem in the western United States, water supplies in Pennsylvania rarely reach levels of concern unless the same soil or media is irrigated repeatedly without winter exposure to rain and snow.
Treating water with high conductivity typically requires either dilution with another lower conductivity water source  or advanced treatment with reverse osmosis or distillation.
Total Dissolved Solids 
 TDS is a measure of all of the dissolved substances in water.
TDS and conductivity levels in water are typically closely correlated and a conversion factor of approximately 640 is often used to predict TDS from conductivity which is easier to measure.
The formula is TDS  = 640 * EC.
Using the conductivity levels of concern above, TDS levels should be below about 640 mg/L to avoid problems in plugs and below about 960 mg/L to avoid problems with other plant growing conditions.
TDS levels above about 2,000 mg/L are very likely to cause plant growth problems.
As with conductivity issues, high TDS waters will need advanced treatment or dilution to make the water useable for irrigation.
Boron is a trace mineral that is rarely a problem in Pennsylvania irrigation waters.
Boron is a micronutrient needed in small amounts.
Boron toxicity may occur if the concentration in irrigation water or fertigation solution exceeds 0.5 to 1.0 mg/L, particularly with long-term slow-growing crops.
High boron levels can be treated using anion exchange or reverse osmosis treatment systems but pH adjustment is sometimes needed to improve treatment efficiency.
Chloride can occur in water supplies naturally or from various activities.
Chloride can damage plants from excessive foliar absorption  or excessive root uptake.
Most plants can tolerate chloride up to 100 mg/L although as little as 30 mg/L can be problematic in a few sensitive plants.
Chloride is difficult to remove from water so advanced treatment using membranes  or distillation is necessary.
Dilution with low chloride water can also be used.
Sodium has many sources in water including road salt applications, wastewaters, water softening wastes and naturally high pH waters dominated by sodium bicarbonate.
High levels of sodium can damage the growth media and cause various plant growth problems.
If water with excess sodium and low calcium and magnesium is applied frequently to clay soils, the sodium will tend to displace calcium and magnesium on clay particles, resulting in breakdown of structure, precipitation of organic matter, and reduced permeability.
Sodium in excess of 50 mg/L may cause toxicity in sensitive plants, particularly in recirculating irrigation systems.
Sodium can be further evaluated based on the sodium adsorption ratio  which is described below.
Sodium is difficult to remove from water requiring reverse osmosis, distillation or dilution.
Sodium Adsorption Ratio 
 SAR is used to assess the relative concentrations of sodium, calcium, and magnesium in irrigation water and provide a useful indicator of its potential damaging effects on soil structure and permeability.
Typically a SAR value below 2.0 is considered very safe for plants especially if the sodium concentration is also below 50 mg/L.
Nitrogen is a critical plant nutrient so nitrate in water can be beneficial for irrigation but should be accounted for in the overall fertilization program.
Nitrate-nitrogen in water does represent broader concerns for both human consumption and surface waters.
The drinking water standard for nitrate-nitrogen is 10 mg/L.
Typical values for clean water are 0.3 to 5 mg/L.
Discharged waste water from greenhouses or nurseries entering surface waters or streams should be lower than 10 mg/L.
The acceptable range for fertigation of most crops is 50 to 150 mg/L.
The ammonium-N concentration in typical clean water ranges from 0 to 2 mg/L.
The typical fertigation range is 0 to 75 mg/L.
See comments, above, for fertilizer nitrogen.
Toxicity in sensitive plants may occur when ammonium is used in fall, winter, or early spring.
Toxicity symptoms include stunting, root death, leaf yellowing and distortion of growing points which can be corrected by switching to nitrate fertilizer.
Phosphorus levels in groundwater and unpolluted surface waters are usually very low  in Pennsylvania.
Higher levels often indicate contamination from fertilizer or manure runoff.
Levels above 5 mg/L may cause antagonism and deficiencies in other nutrients.
Waste water to be discharged to surface waters should be as low as possible  to reduce environmental impact.
Phosphorus levels in water need to be considered in the overall fertilization program.
High potassium is generally not a concern for plant growth.
Levels above 10 mg/L may indicate water contamination from fertilizers or other man-made sources.
Water concentrations are useful simply for determining the overall fertilization requirements for plants receiving the irrigation water.
Sulfur is an essential plant nutrient.
High concentrations are rarely a concern other than in coal mining regions where extremely high levels are occasionally observed.
More often, sulfur levels are tested to determine if sulfur addition is needed in fertilizer.
Very low sulfur levels below 10 mg/L are common in most of the state.
Iron can be a complex water quality problem that not only affects plant growth but also can clog irrigation equipment.
For micro-irrigation systems, iron levels need to be below 0.3 mg/L to prevent clogging.
Levels above 1.0 mg/L can cause foliar spotting in overhead irrigation systems.
Very high iron above 5.0 mg/L can cause severe staining and plant toxicity in sensitive species.
Iron toxicity problems are most likely to occur where growth media is acidic.
Induced iron deficiency can also occur in sensitive species if pH is greater than 7.0 to 7.5.
Iron treatment is most easily accomplished by using a settling pond to aerate and settle the iron sediment before the water is used for irrigation.
Various forms of oxidizing filters can also be used to oxidize and filter iron but these can be costly for large volumes of irrigation water.
In cases where iron is clogging drip irrigation systems, acidification treatment can be used to keep iron in solution or chlorination/filtration can be used to remove iron and prevent clogging.
Manganese presents many of the same issues as iron in irrigation water.
It can clog irrigation equipment and cause foliar staining.
The recommended drinking water standard for manganese is 0.05 mg/L which is also the level where black staining and irrigation clogging may occur.
Concentrations above 2.0 mg/L can be directly toxic to some plant species.
Removal of manganese utilizes the same treatment described for iron above, but manganese removal efficiency is generally lower than iron and may require pH adjustment.
Copper in water most often originates from corrosion of copper plumbing lines, especially by acidic, low TDS water.
It very rarely occurs in significant concentration in groundwater or surface water.
Unfortunately, even low concentration of copper above 0.2 mg/L can be toxic to some plants.
If copper is found in irrigation water, corrosion of metal plumbing should be investigated as a cause and replacement with plastic plumbing should be considered.
The use of copper algaecides should be avoided in irrigation ponds.
Molybdenum is a trace mineral which can also cause plant toxicity in rare cases.
Molybdenum concentrations above 0.05 can be problematic but are very rare in Pennsylvania irrigation water sources.
Removal of molybdenum is difficult on a large scale for irrigation.
Zinc is another trace mineral that rarely occurs in groundwater or surface water.
When zinc is found in irrigation water, corrosion from galvanized pipes in the irrigation plumbing should be investigated as a possible source.
Mine drainage can also be a source of zinc in western Pennsylvania.
Levels above 0.3 mg/L can be toxic to some plants especially in low pH growth media.
Fully appropriated basins in Nebraska are river basins  where water coming into the basin is equal the amount of water taken out or otherwise leaving the basin.
These areas are closed to both new high-capacity wells  and to new appropriations.
Fully appropriated basins are designated by the Nebraska Department of Natural Resources.
EXAMINING THE TOOLBOX FOR DEFICIT IRRIGATION OF GRAIN AND OILSEED CROPS
 Deficit irrigation is an alternative to full irrigation where water is applied to crops in amounts that are anticipated to support transpiration below the potential level.
Under such circumstances, one might expect crop growth and yield to be less than that achieved under full irrigation.
However, profitable production of certain crops can be achieved using deficit irrigation with considerable savings in water used.
Deficit irrigation of field crops has been discussed in several research papers and reviews.
Since the goal of most irrigation strategies is to optimize net economic returns under the constraints imposed by available resources, it might be wise when examining the deficit irrigation toolbox to allow some variance from the strictest definition of the term.
For example, in some cases, net economic returns may be optimized by growing less land area with a less deficit irrigation strategy.
For the purposes of this discussion, maybe the topic of interest is coping with a deficient or marginal irrigation water supply that might have spatial and/or temporal aspects that must be considered.
So as the discussion moves forward, it will become evident that in some cases producers are truly applying less than the full irrigation amount to a parcel of land and in other cases the producer is trying to avoid deficit irrigation.
Of course, in many cases the strategy may be a combination of mitigation and partial avoidance of deficit irrigation.
Although there are a number of ways to organize our deficit irrigation toolbox, here we will assume it is organized into these three sections:
 Irrigation management and macromanagement
 Irrigation system and land allocation management
 As is the case with all good mechanics, producers facing deficit irrigation must be able to choose and utilize the best tools for the task immediately at hand and recognize when one or more additional tools are needed as the project progresses.
Additionally, some of these deficit irrigation tools have temporal aspects, that is, they may be only available as adjustments for the dormantseason, in-season, or the long-term.
The overall purpose of this paper is to illustrate the concepts of the tools in the tool box and not to exhaustively demonstrate how to use them.
As some of the tools interact with each other, it may be useful to peruse the entire toolbox.
A number of tools to mitigate and/or avoid deficit irrigation reside within the agronomic management section of the toolbox.
A few blank rows are provided to list additional tools that might be in your toolbox.
Table 1.
Primary agronomic management tools to address deficit irrigation for grain and oilseed crops and their temporal availability.
Deficit Irrigation Management Tool	Dormant
 Season	In-Season	Long Term
 Crop Selection	Yes	No	Yes
 Crop Hybrid or Variety	Yes	No	Yes
 Crop Rotations and Cropping Systems	Yes	No	Yes
 Tillage and Residue Management	Yes	Sometimes	Yes
 Nutrient Management	Yes	Yes	Yes
 Plant Density and/or Row Spacing	Yes	No	Yes
 Pest Management	Sometimes	Yes	Yes
 Crop selection has long been a tool to cope with deficit irrigation and/or a deficient irrigation water supply.
Some crops are more sensitive to water stress than others and this may be particularly the situation for their economic yield.
However, one is well advised to consider the water sensitivity paradox that a water sensitive crop may also have greater water productivity than a less water sensitive crop.
Deficit or limited irrigation presents a challenge for irrigators growing corn.
Corn is sensitive to water stress at all stages of growth and grain yields are usually linearly related to water use from the dry matter threshold  up to the point of maximum yield.
Deficit or limited irrigation of corn is difficult to implement successfully without reducing grain yields.
However, some strategies are more successful than others at maintaining corn yields under limited irrigation.
Fully irrigated corn was found to be most profitable and having lowest risk of nine different water allocation schemes in Kansas , but some other scenarios were profitable with some acceptance of risk.
Grain sorghum is relatively tolerant of water stress and can be a good choice for deficit irrigation , but is also less responsive to irrigation.
Irrigated wheat can also be a good choice for deficit irrigation in the southern Great Plains , but in some areas of northern Kansas the response of wheat to irrigation has been minimal.
One of the primary advantages of wheat in coping with deficit irrigation or an insufficient water supply in the US Great Plains is that the wheat growing season has less overall evaporative demand and that the season is temporally displaced from the other principal irrigated crops.
Soybean is somewhat similar to corn in sensitivity to water stress, but typically requires a slightly smaller total amount of irrigation
 .
Sunflower has a considerably shorter growing period than corn and soybeans and requires less total irrigation, although all three crop's peak evapotranspiration rates are similar.
Summer crop yields were simulated for 42 years of actual weather data  from Colby, Kansas using 1 inch sprinkler irrigation events with an application efficiency of 95%.
Irrigations were scheduled as needed according to the weather-based water budget but were limited to various irrigation capacities.
Figure 1.
Simulated crop yields for corn, grain sorghum , soybean and sunflower as affected by irrigation capacity  and their corresponding response to total irrigation amount  at Colby, Kansas for 42 years  at an application efficiency of 95%.
Note: These are average yield responses.
Yield responses for individual years would vary considerably from those shown here.
The graphs indicate that corn benefits from greater irrigation capacities and irrigation amounts, whereas grain sorghum yield plateaus at a lessor irrigation capacity and irrigation amount.
Ultimately, crop selection depends on production costs and crop revenues.
Irrigated land area devoted to grain sorghum in Kansas is actually decreasing and much of this is probably closely tied
 to economics.
In a cropping simulation similar to the one above conducted for the period 19722005, it was concluded that dryland grain sorghum production was more profitable than any of irrigated grain sorghum scenarios.
However, sometimes irrigation capacity is shared across multiple crops to reduce the amount of risk.
For example, maybe a portion of the land is grown in stress-tolerant grain sorghum to effectively increase the irrigation capacity for another portion of the land area growing water-sensitive corn.
Of course, the economics of irrigated crop production vary greatly from year to year.
Producers may wish to compare crop production as affected by water using the Crop Water Allocator software developed by faculty at KState.
Irrigation water requirements of the various crops also vary temporally.
Wheat was already mentioned as a possible crop that could allow shifting of irrigation water when the principal limitation is irrigation capacity.
Similarly the summer crop's peak water needs vary between months.
Some producers may plant portions of their fields to sunflowers and only irrigate them when irrigation needs of other crops are declining.
Figure 2.
Average fraction of irrigation needs by month for corn, grain sorhum, soybean and sunflower at Colby, Kansas, 1972-2013.
Crop Hybrid or Variety
 Some crop hybrids and varieties are more sensitive than others to water stress.
Altough it remains to be seen whether newer drought tolerant hybrids and varieties will actually result in decreased irrigation needs, it does appear that crop yield is better protected from water stress.
Hybrid selection can result in greatly different yields even under the same full irrigation level.
Maximum corn yield averaged 75 bu/acre greater  than the minimum corn yield in crop performance tests conducted from 1996 throug 2010 at the KSU Northwest Research-Extension Center at Colby, Kansas.
Producers are advised to choose hybrids and varieties carefully so they can maximize their "crop per drop".
Figure 3.
Variation in corn hybrid yields in KSU-NWREC performance tests during the period 1996 through 2010.
Crop Rotations and Cropping Systems
 Previous crops leave behind residual soil assets, such as soil water and nutrients which can be used to offset application of these inputs and their associated costs in the coming year.
For example, irrigated corn requires ample supplies of water and nutrients late in the cropping season to ensure optimum yields, so producers often choose sunflower as a rotational crop after corn in order to utilize the residual soil water and nutrients.
In addition to the economic benefit, producers obtain environmental benefits of reduced usage of scarce water resources and reduced potential of nutrient leaching.
Anecdotally, it has been observed that continuous corn is less common in west central Kansas than in northwest and southwest Kansas where the Ogallala saturated thickness is greater.
Crop rotations also tend to reduce pest problems often associated with monocultures.
Producers should consider crop rotation as a valuable tool to help manage a deficient or declining water supply.
Tillage and Residue Management
 Residue management techniques such as no tillage or conservation tillage have long been accepted to be very effective tools for dryland water conservation in the Great Plains.
However, Klocke  posited that residue management can be even more important in reducing soil water evaporation under irrigation.
Reporting on a earlier two year study from Nebraska, soil water evaporation savings under a corn canopy with straw covering the soil averaged 0.2, 2.6 and 3.8 inches for dryland, limited irrigation, and full irrigation, respectively.
In a later three year study in Kansas, Klocke et al.
reported evaporative ratios  within a corn canopy averaging 0.30, 0.15 and 0.17 for bare soil, corn stover and wheat residue, respectively.
Strip tillage and no tillage had numerically greater corn grain yields  than conventional tillage in all four years of a study conducted at the KSU Northwest Research-Extension Center, Colby Kansas.
The benefits of using strip tillage or no tillage increased as irrigation capacity became more deficit.
Both strip tillage and no tillage should be considered as improved alternatives to conventional tillage, particularly when irrigation capacity is limited.
Figure 4.
Corn grain yield as affected by tillage management and irrigation capacity in a four year study at Colby, Kansas.
Nutrient management can play an important role in increasing the effective use of irrigation and has been the subject of several review articles.
Proper nutrient management increases plant growth and yield response allowing the crop to optimize use of available water supplies.
Appropriate nitrogen fertilization nearly doubled corn yields without much increase in water use  in a two year study of subsurface dripirrigated corn in western Kansas.
Figure 5.
Corn yield as affected by nitrogen fertigation level and irrigation level in a subsurfacd drip irrigation study, Colby, Kansas, 1990-1991.
Plant Density and/or Row Spacing
 Plant density or plant population can have an effect on water use and water use efficiency.
When irrigation is severely deficit, it may be wise to reduce corn plant density to increase the probability of successful pollination and subsequent growth.
As an example, Roozeboom et al.
recommended corn plant densities for western Kansas of 14,000 to 20,000, 24,000 to 28,000, and 28,000 to 34,000 for dryland, limited irrigation, and full irrigation scenarios, respectively.
After the corn crop reaches a leaf area index  of approximately 2.7, all of the incoming energy is captured  and additional increases in LAI do not result in increased water use.
As LAI for irrigated corn often reaches 5 or greater in the central Great Plains, plant density has to be greatly reduced to actually reduce corn water use.
A key factor in managing corn plant density is assuring that pollination and kernel set are achieved.
Establishing greater kernels/area often requires increased plant density.
Medium to higher plant densities  generally resulted in greater corn yields  in a four year sprinkler-irrigated study in western Kansas.
Figure 6.
Corn grain yield as affected by irrigation amount and plant population, 2004-2007, KSU Northwest Research-Extension Center, Colby Kansas.
Adjustments to row spacing and planting geometry may be effective in reducing soil water evaporation losses in some cases for corn and grain sorghum in the central Great Plains.
However, results to date suggest these adjustments are most likely to be advantageous only at the lower end of the range of crop yields.
Pest management is important in coping with deficit irrigation.
Weed pests may directly compete for water and nutrients and insect pests may interfere with plant growth and limit the crop's economic yield.
Some pests thrive under deficit irrigation conditions.
For example, spider mites increase under the hotter and drier conditions associated with corn water stress.
Spider mite damage that has occurred to corn's photosynthetic ability cannot be reversed by an easing of drought conditions, although a reduction in the number of mites may occur.
Producers coping with deficit irrigation should actively and consistently observe their crop fields managing weed and insect pests as they arise.
IRRIGATION MANAGEMENT AND MACROMANAGEMENT
 A number of tools to mitigate and/or avoid deficit irrigation reside within the irrigation management and macromanagement section of the toolbox.
A few blank rows are provided to list additional tools that might be in your toolbox.
Table 2.
Primary irrigation management and macromanagement tools to address deficit irrigation for grain and oilseed crops and their temporal availability.
Deficit Irrigation Management Tool	Dormant
 Irrigation Scheduling	No	Yes	Yes
 Timing of Irrigation	No	Yes	Yes
 Initiation of the Irrigation Season	No	Yes	Yes
 Termination of the Irrigation Season	No	Yes	Yes
 Dormant Season Irrigation	Yes	No	Yes
 The most common definition of irrigation scheduling is simply the determination of when and how much water to apply.
It is not uncommon to hear a central Great Plains producer indicate that they could not possibly consider irrigation scheduling because they always are in a deficit irrigation condition from the beginning to the end of the cropping season.
Although this may seem intuitively the situation, there are actually many years when the irrigation capacity even for marginal systems would not have to be fully utilized.
Often early in the season, a deficit irrigation capacity may exceed the crop evapotranspiration rate.
Simulated irrigation schedules for corn indicate that 80% or more of the maximum observed irrigation requirement is only required in 50 and 60% of the years for severely deficit irrigation capacities of 1 inch/8 days and 1 inch/10 days, respectively.
Additionally, producers using irrigation scheduling can make better decisions about how
 to handle a triage situation.
Figure 7.
Simulated corn irrigation requirements for Colby, Kansas, 1972-2013 as possible with various irrigation capacities.
Each indicated capacity has the 42 years shown, with some years lying on top of each other.
The percentage of years requiring 80% or more of the maximum possible irrigation is shown below each capacity.
As irrigation capacity increases, the percentage of years requiring 80% or more of the maximum irrigation tends to decrease.
Timing irrigation to the critical growth stages is a deficit irrigation strategy that can be effective in some situations.
This technique may be most applicable when deficit irrigation is limited by total amount of irrigation.
Examples of such scenarios would be an institutional constraint  or when surface water availability constrains the application window.
Timing of irrigation is less applicable for irrigation systems with marginal irrigation capacity and when stretched water resources limit adjustments to the irrigation event cycle.
Since center pivot sprinklers irrigating from marginal groundwater wells are common in the central Great Plains landscape, timing of irrigation is a less applicable tool for many producers.
Initiation of the Irrigation Season
 The determination of when to initiate the irrigation season is an irrigation macromanagement decision that can greatly affect the total irrigation amount.
Ideally, the producer would delay irrigation as long as possible with the hope that timely precipitation would augment the crop water needs.
A recent summary by Lamm and Aboukheira  suggests that corn probably has more inherent ability to handle early season water stress than is practical to manage with the typical irrigation capacities that occur in the central Great Plains.
Producers should use a good method of day-to-day irrigation scheduling during the pre-anthesis period.
To a large extent the information being used to make day-to-day irrigation scheduling decisions during the pre-anthesis period can
 also be used in making the macromanagement decision about when to start the irrigation season.
This is because even though the corn has considerable innate ability to tolerate early season water stress, most irrigation systems in the Central Great Plains do not have the capacity  or practical capability  to replenish severely depleted soil water reserves as the season progresses to periods of greater irrigation needs.
However, there is some flexibility in timing of irrigation events within the vegetative growth period.
In years of lower evaporative demand, corn grown on this soil type in this region can extract greater amounts of soil water without detriment.
Timeliness of irrigation and/or precipitation near anthesis appeared to be very important in establishing an adequate number of kernels/area which in this study was greatly correlated with final yield.
Although, timing of irrigation is difficult with typical systems in the central Great Plains, the results suggest that monitoring soil water reserves and evaluating the early season evaporative demand may allow for delays in initiating the irrigation season in some years.
Termination of the Irrigation Season
 Irrigators in the central Great Plains sometimes terminate the corn irrigation season on a traditional date such as August 31 or Labor Day  based on long term experience.
However, there can be a large variation in when the irrigation season can be safely terminated.
A more scientific approach might be that season termination may be determined by comparing the anticipated soil water balance at crop maturity to the management allowable depletion  of the soil water within the root zone.
Some publications say the MAD at crop maturity can be as high as 0.8.
Extension publications from the Central Great Plains often suggest limiting the MAD at season end to 0.6 in the top 4 ft of the soil profile.
These values may need to be re-evaluated and perhaps further adjusted downward  based on a report by Lamm and Aboukheira.
They concluded producers growing corn on deep silt loam soils in the central Great Plains should attempt to limit the management allowable depletion of available soil water in the top 8 ft of the soil profile to 45%.
Table 3.
Anthesis and physiological maturity dates and estimated irrigation season termination dates* to achieve specified percentage of maximum corn grain yield from studies examining post-anthesis corn water stress, KSU Northwest Research-Extension Center, Colby, Kansas, 1993-2008.
Note: This table was created to show the fallacy of using a specific date to terminate the irrigation season.
Note: Because there was not an unlimited number of irrigation termination dates, sometimes the date required for a specified percentage of maximum grain yield was the same as the date for the next higher percentage.
After Lamm and Aboukheira.
Date of	Date of	Irrigation Season Termination Date For
 Anthesis	Maturity	80% Max Yield	90% Max Yield	MaxYield
 Average	19-Jul	27-Sep	2-Aug	13-Aug	28-Aug
 Standard Dev.
3 days	6 days	13 days	19 days	13 days
 Earliest	12-Jul	14-Sep	17-Jul	17-Jul	12-Aug
 Latest	24-Jul	10-Oct	14-Sep	21-Sep	21-Sep
 Estimated dates are based on the individual irrigation treatment dates from each of the
 different studies when the specified percentage of yield was exceeded.
Dormant season irrigation for crops such as corn has been advocated for the semi-arid Great Plains since the early 20th century, and the practice has been debated for nearly as long.
Knorr  found that at Scottsbluff, Nebraska, fall irrigation normally increased corn yields.
Farrell and Aune  found opposite results at Belle Fourche, South Dakota.
Knapp  recommended winter irrigation for most of western Kansas with the exception of sandy soils.
The advantages of preseason irrigation  are to 1) provide water for seed germination; 2) delay the initiation of seasonal irrigation; 3) improve tillage and cultural practices associated with crop establishment; and 4) more fully utilize marginal irrigation systems on additional land area.
The disadvantages are that it may 1) increase production costs; 2) increase irrigation requirements; 3) lower overall irrigation efficiencies; and 4) lower soil temperatures.
Lamm and Rogers  developed an empirical model to aid in decisions concerning fall preseason irrigation for corn production in western Kansas.
Available soil water at spring planting was functionally related to overwinter precipitation and initial available soil water in the fall.
They concluded in most years, fall preseason irrigation for corn is not needed to recharge the soil profile in northwest Kansas, unless residual soil water remaining after corn harvest is excessively low.
A recent survey of sprinkler irrigated corn fields in western Kansas has irrigated that on average, producers are leaving residual available soil water in the 8 ft profile at approximately 60% of field capacity.
However, there was large variation between producers  emphasizing the need for each producer to evaluate their own field.
Figure 8.
Effect of western Kansas region on average, maximum and minimum measured plant available soil water  in the 8 ft soil profile in irrigated corn fields after harvest for the fall periods in 2010 and 2011.
In a recent field study  at the KSU Southwest Research Extension Center site near Tribune, Kansas, Schlegel et al.
found preseason irrigation to be profitable for corn production with irrigation capacities ranging from 0.1 to 0.2 inches/day.
Preseason irrigation increased grain yields an average of 16 bu/acre.
The crop water productivity was not significantly affected by well capacity or preseason irrigation.
IRRIGATION SYSTEM AND LAND ALLOCATION MANAGEMENT
 A number of tools to mitigate and/or avoid deficit irrigation reside within the irrigation system and land allocation management section of the toolbox.
A few blank rows are provided to list additional tools that might be in your toolbox.
Table 4.
Primary irrigation system and land allocation management tools to address deficit
 irrigation for grain and oilseed crops and their temporal availability.
Deficit Irrigation Management Tool	Dormant
 Irrigation System Selection	Yes	No	Yes
 Managing Water Losses	Yes	Yes	Yes
 Fine Tuning the Irrigation System	Yes	Yes	Yes
 Land/Water Allocation	Yes	Possibly	Yes
 No irrigation system can save water without good management imparted by the producer.
However, some irrigation systems are easier to manage than others.
Additionally, some systems although perhaps more complicated in design and number of components may inherently result in better water management.
This concept can perhaps be considered as "purchasing improved management capabilities upfront".
It has been said that one of the principal reasons that pressurized irrigation systems such as center pivot sprinklers  and subsurface drip irrigation  are considered easier to manage than surface irrigation is because they remove the surface water transport phenomenon from the management.
Many producers in the central Great Plains have converted from surface irrigation to center pivot sprinklers and a few are using SDI, all with a goal of better utilizing a limited and declining water resource.
There is some evidence from the Great Plains that SDI may be able to stabilize yields at a greater level under deficit irrigation than CP assuming both are managed well.
Under deficit irrigation nearly all water losses result in yield reduction.
It is common for the slope of the water production function for corn under deficit irrigation to be 12 to 15 bushels/inch and values of nearly 20 bushels/inch have been reported.
Howell and Evett  characterized the "Big Three" irrigation water losses as deep percolation, evaporation losses from soil, air, or plant, and irrigation runoff.
An excellent tabular discussion of the management of these losses with irrigation systems, tillage management, and irrigation scheduling is provided by Howell and Evett.
Fine Tuning the Irrigation System
 There are some irrigation system adjustments that can be considered "fine tuning" the system but are never-the-less important to deficit irrigation management.
This listing will not be exhaustive but may spur producers to look for that hidden extra capacity.
Here are some system-related practical ways irrigators might use to effectively increase irrigation capacities for crop production :
 Remove end guns or extra overhangs to reduce center pivot system irrigated area
 Clean groundwater well to see if irrigation capacity has declined due to encrustation
 Determine if pump in well is really appropriate for the irrigation system design and operating pressure.
Replace, rework or repair worn pump
 As it was stated in the second paragraph of this paper, deficit irrigation may be avoided by more closely matching the irrigated land area to the available water source.
As economically painful as this may seem, this has always been the design criteria for irrigation systems in arid regions.
Our semi-arid and more humid regions have just been able to successfully gamble with this criterion.
Utilizing this management strategy might be economically painful because:
 it will likely reduce income in years with ample rainfall
 it may negatively affect land values if land is then considered non-irrigated
 it could reduce economic activity in the community as less inputs are bought and less outputs are sold.
However, if water resources and pumping rates continue to decline, the drought persists, and/or climate change imposes drier and warmer conditions, reducing the irrigated land area to avoid deficit irrigation may be the wisest decision.
The previously discussed KSU-NWREC simulation modeling will be used to explore this topic further.
Corn yields were simulated for 42 years of weather data from Colby, KS..
Wellwatered corn ETc ranged from 17.6 to 27.1 inches with average of 23.1 inches for these 42 years of record.
In-season precipitation ranged from 3.1 to 21.2 inches with average of 11.8 inches.
Full irrigation ranged from 6 to 22 inches with average of 15.7 inches.
The marginal WP  was 17 bu/acre-in, which might result in an economic benefit of 65 to $85/acre-in.
The yield threshold was 10.9 inches of ETc.
Yields were simulated for irrigation capacities of full irrigation, 1 inch every 4, 6, 8 or 10 days and also for dryland conditions.
As irrigation capacity decreases , corn yields decrease from the fully irrigated yields for some years and the variability in yields also increases.
Typically, crop yields increase with increasing ETc, although this response in not a direct cause and effect.
Rather in many cases, increased ETc is also reflecting better growing conditions.
As irrigation capacity decreases, the positive aspects of greater ETc on yield begins to disappear and the slope is relatively flat for an irrigation capacity of 1 inch/10 days.
Under dryland conditions, corn yields typically decreased over the entire range of increasing ETc experienced at Colby, Kansas during this 42 year period.
Through reductions in irrigated land area, a producer could regain irrigation capacity, increase crop yield, and reduce their own risk.
The short term marginal benefits to the individual producer
 should increase due to less input costs being associated with the non-irrigated acres.
The Crop Water Allocator software may be useful to producers in determining the optimum cropping scenario.
Well-watered corn ETc 
 Figure 9.
Simulated corn yields as a function of the calculated well-watered corn evapotranspiration for the 42 year period, 1972-2013, Colby, Kansas as affected by irrigation capacity.
Table 5.
Effect of irrigation capacity on simulated corn yields for the 42-year period, 1972-2013, Colby, Kansas.
Yield variation from full irrigation
 Irrigation	Maximum	Mean	Minimum	for maximum yield at maximum
 capacity	yield	Yield	Yield	well-watered ETc
 Full	273	204	112	-
 1 inch/4 day	261	202	112	-4.4%
 1 inch/6 day	226	181	112	-17.2%
 1 inch/8 day	216	162	103	-20.9%
 1 inch/10 day	202	148	94	-26.0%
 Dryland	138	77	23	-49.5%
Salvatore S.
Mangiafico, Environmental and Resource Management Agent Christopher C.
Obropta, Extension Specialist in Water Resources
 Rainwater harvesting at privately owned businesses and farms is primarily used for reducing runoff during rain events and to conserve potable water resources.
Collected water is often used for supplemental ornamental plant irrigation, for which purpose it is generally suitable.
While most collected rainwater could be treated and disinfected to make it of potable quality, in New Jersey collected rainwater typically cannot be used legally in public or non-public water systems.
This publication does not address all the considerations that would be necessary for using harvest rainwater as a potable water source.
Potential Contaminants in Harvested Rain Water
 In general, rainwater is a relatively pure source of water when compared with surface water, reclaimed water, or, in some cases, groundwater.
However, it should be noted that harvested rainwater will contain a variety of constituents that may be considered contaminants.
The rain itself may pick up a variety of contaminants suspended in the air, and may also carry away substances deposited on the roof and collecting surfaces during dry weather.
Additional contaminants can come from the materials of the collecting surfaces themselves, or come from animal droppings or plant debris on the collecting surfaces.
Also, algaecides or waterproofing materials added to roofing materials may leach into collected water.
Some contaminants could be considered natural, while others are clearly human-contributed.
While some contaminants are deposited from the atmosphere from wet or dry deposition, other contaminants may be released from the materials used for the collection equipment.
Deposition onto collection surfaces, though, is probably the largest factor in influencing what contaminants will be found in collected water.
Contaminants found in harvested rain water will likely be influenced by the surrounding area.
In agricultural areas, soil particles and pesticides
 may be present, whereas in urban areas heavy metals and hydrocarbons from industry or vehicle traffic may be present.
The amounts of contaminants will also vary based on weather patterns, since contaminants can build up on roof surfaces during dry weather, and then be found in high concentrations during the beginning of the next rain, an effect know as "first flush."
 Consideration should also be given to the materials used in the roof and water collection system.
While polyvinyl chloride , aluminum, and galvanized steel surfaces contribute few pollutants themselves, glues, sealants, or lead solder can contribute contaminants to collected water.
Metal surfaces may contribute metals; for example, water in contact with galvanized materials may leach out zinc.
Typical composite or asphalt shingles may leach other compounds.
Potential contaminants of most concern include heavy metals , polycyclic aromatic hydrocarbons , pesticides, and pathogenic bacteria.
Because each of these contaminant categories have chemicals with known health effects to humans, drinking untreated harvested rain without further treatment is not recommended.
Common sense sanitation measures, such as washing hands after handling collected water, should also be followed.
Each of these contaminant categories has chemicals with potential toxicity in environmental systems, particularly aquatic environments.
Considering this, it may be a better conservation practice to collect roof runoff and use it on-site rather than allow any potential contaminants to move into the local stormwater system.
Many contaminants will preferentially associate chemically with particles and organic matter; therefore, separating out any particles from collected water before use or discharge may be beneficial.
Water Quality For Irrigation
 Even though harvested rainwater may have elevated concentrations of certain contaminants, the general chemical properties of rainwater in New Jersey will be acceptable for plant irrigation.
Recommendations for crop specific water quality should be followed when available.
Irrigation water should have suitable chemical parameters, including pH, alkalinity, salts, and concentrations of specific elements.
Rainwater in New Jersey is typically acidic, with annual averages ranging from 4.3 to 4.9 pH units.
Electrical conductivity is typically below 0.1 mmhos/ cm , and concentrations of specific ions are typically relatively low.
Specific water quality parameters are important in ensuring water will not clog drip emitters or sprinklers with fine nozzles.
These include water hardness, suspended solids, bacteria, and specific metal concentrations.
In general, harvested rainwater should not be problematic for these applications.
Typically, hardness of rainwater will not exceed recommended levels.
Suspended solids and bacteria can be controlled with proper collection design and maintenance.
Depending particularly on the materials used in the water collector, harvested water may have elevated levels of certain metals which might contribute to clogging of irrigation emitters, such as iron and manganese.
Filtration of water may be necessary if it contains particulates that could clog irrigation systems.
Similarly, iron, manganese, and bacteria could be removed with a combination of filtration and water treatment if necessary.
Because harvested rainwater may have elevated concentrations of a variety of contaminants, caution should be used in using it for edible crops.
It is safer to use harvested water for ornamental plants that will not be eaten.
For edible crops, where possible, water should be applied to soils rather than to the edible parts of plants.
In the soil, many contaminants including metals may become bound to soil particles and organic matter, making them less available for plant uptake or runoff.
Whenever handling harvested rainwater, basic good hygiene practices should be followed.
Wash hands after handling water, or preferably wear impermeable gloves.
Avoid getting harvested water into eyes, mouth, or open wounds.
Potential For Heavy Metal Contamination of Soils
 Because of potential elevated levels of metals such as copper or lead in roof runoff, it is possible over the long term to load soils with metals to the point where they may be of concern for plant health.
Recommended limits for applying water with significant heavy metal concentrations are expressed in two ways.
One approach is to evaluate the concentrations of metals in the water itself.
USEPA  follows this approach, basing recommended limits on typical amounts of water applied to plants and chemistry of the metal ions in soil.
Limits for select metals are given in Table 1.
Table 1.
Recommended maximum concentrations of selected metals in irrigation water to prevent plant toxicity.
Maximum level in water
 *Adapted from USEPA 2004, Table 2-7.
A longer list of constituents can be found there.
Concentrations are based on 20 years of use in soils.
Higher concentrations may be permissible for shorter term use.
+Toxicity will vary by plant species, and environmental concern will vary by constituent and soil properties.
A second approach is to evaluate the concentration of a metal in the soil.
It is important to note that the metal concentration in the soil may be reported as either the total or available concentration.
The total concentration is where virtually all of the metal is extracted from the soil and reported.
The total concentration generally exceeds what a plant can remove from the soil.
The available concentration is an estimate of the amount of metal in the soil which would be available for plant uptake.
Table 2 lists regulatory limits for total concentration of some metals for land application and also cautionary limits for plant health of available metals.
Comparing data from studies of roof runoff concentrations of metals in the U.S.
to recommended maximum concentrations in water , both copper and zinc in roof runoff were sometimes recorded at concentrations that could lead to phytotoxic soil concentrations in some cases.
Clark et al.
suggested that zinc concentrations may be particularly high from roofs made of galvanized metal or
 aluminum-zinc-coated materials, and that copper concentrations may be particularly high from wood products which use copper compounds as preservatives.
Lead concentrations reported by Clark et al.
and DeBusk et al.
for roof runoff in the U.S.
ranged from non-detectable to 0.3 mg/L.
Considering this range, soils would probably have to be irrigated for decades to build up lead concentrations greater than those considered "background levels" for children's health for New Jersey soils .
However, since the results of this calculation will depend on the actual irrigation rate and soil properties, prudence suggests soil should be tested periodically when applied water has lead concentrations in the tenths of mg/L, if there is concern of exposure to lead-contaminated soils.
Where elevated levels of zinc or copper in soil are suspected, plant health can be promoted by liming the soil to correct pH, maintaining optimum phosphorus levels in the soil, and adding compost or other organic matter to soils with low organic matter.
Recommendations from soil tests should be followed.
A similar approach
 could be followed in the case of suspected elevated concentrations of lead, though additional precautions may be warranted if children are in contact with the soil in these cases.
In most cases, water collected from the roofs of buildings should be acceptable for use in irrigating ornamental plants.
Rain water in New Jersey tends to have chemical qualities that make it acceptable to use for irrigation.
However, roof runoff may contain a variety of impurities deposited on the roof during dry times or carried in the rain itself.
Small amounts of most common impurities are unlikely to be a concern.
However, in some cases the water may have elevated concentrations of metals either deposited from the atmosphere or leached from materials in the roof or water collection system.
Additionally, it should be kept in mind that roof runoff may have animal dropping or other organic debris that can carry bacteria.
Employing a device that diverts away the first flush of roof runoff-which is likely to contain the bulk of impurities collected on the roof during dry times-can reduce the amount of pollutants in collected water.
Similarly, prudence suggests using good personal hygiene when handling collected water.
If there are pollutants of concern in water, application to ornamental rather than edible crops is recommended.
If edible crops are irrigated with collected water, applying water to the soil may be preferable to applying it to the edible portions of plants.
Table 2.
Recommended maximum concentrations of selected metals in soil.
Maximum total concentration in soil	Cautionary available concentration in soil
 Constituent	Symbol		 t
 Cadmium	Cd	13	_t
 Copper	Cu	500	20
 Lead	Pb	140	-
 Zinc	Zn	900	50
 Figures are for total concentrations in soil.
Based on U.S.
regulatory limits for land application of sludge and wastes.
Adapted from NRCS , using the rough conversion: kg/ha = mg/kg X 3.
A longer list of constituents can be found there.
t Based on cautionary limits for plant health.
Figures are for available metal concentrations by Melich extractant.
Adapted from Rutgers Soil Testing Laboratory.
# Data not available.
RECOMMENDED PROCEDURES FOR A DRIP IRRIGATION SYSTEM
 Subsurface Drip Irrigation  is a drip irrigation system where the dripline is permanently buried below the soil surface, supplying water directly to the roots.
SDI is more than an irrigation system, it is a root zone management tool.
Fertilizer can be applied to the root zone in a quantity when it will be most beneficial resulting in greater use efficiencies and better crop performance.
A number of crop protection chemicals are also available  for application through the drip system making it a powerful crop protection tool.
The longevity of the system will depend on factors such as initial water quality, proper operation, regular maintenance and the quality of the dripline.
Netafim has sub-surface drip irrigation systems with more than 20 years of continuous operation.
This publication details the procedures Netafim recommends to ensure the longest possible life for your SDI system.
Figure 1 is a schematic layout of the components which make up an SDI system:
 Dripline the heart of the system  can be either pressure compensating  or nonpressure compensating.
Filters  is the best choice to protect the dripline.
Fertilizer Injector injects fertilizer chemicals into the system for maximum crop performance and to maintain the dripline over the long term.
Pipeline headers, control and air release vents complete the system.
Our intent is not to describe the process of system design in detail.
Your Netafim USA Dealer is trained to design and install quality SDI systems.
It is important to understand how the system is put together and why certain design elements are specified.
Figure 1.
Schematic layout of drip system components
 The following dripline recommendations are meant as guidelines only soil type, topography and water quality will affect the final design.
Your Netafim USA Dealer is familiar with the local conditions and will recommend a dripline that is appropriate for your area.
The dripline should be installed with a GPS where possible so that its position can be determined as necessary.
Depending upon local conditions the dripline can either have pressure compensating  or non-compensating drippers.
Factors such as length of run, topography, zone size and water quality play an important role in choosing the right dripper.
Regardless of the type of dripper used there are several basic guidelines to follow:
 1.
The distance between driplines is determined by the crop.
For corn crops with rows every 40" the typical spacing between
 rows of driplines is 80", with the dripline located in the furrow and one dripline in every other row.
With this layout one dripline irrigates two rows of corn with one irrigated row followed by a dry row.
This arrangement has implications for measuring the moisture content of the soil.
The measurement should never be taken in the dry row.
Some growers have been increasing the density of their corn plantings by moving to 20" rows and in this case the dripline is placed on 40" centers.
In all cases the water application rate is set by design to meet the crop needs given the water availability.
2.
Driplines are generally buried at a depth of 12" to 18".
The crop being grown, the soil texture and the presence of rodents are the main considerations for determining the burial depth of the dripline.
Sandy soils generally require a more shallow burial.
In areas with a large rodent population deeper burial of the dripline is less likely to cross paths with rodent's teeth.
In general rodents are not fond of sandy soil so the shallower depth is not a concern.
However, deeper placement may make it difficult to germinate the crop with the drip system unless there is sufficient residual moisture in the soil.
The following should be taken into consideration when designing the SDI system:
 The distance between drippers and the dripper flow rate selected to achieve the appropriate application rate given the water availability.
Dripline wall thickness 13 to 35 mil is usually recommended, with 15 to 25 mil most commonly used.
The volume output of the pumping station dictates the amount of area that can be irrigated.
A simple formula has been derived converting the maximum required evapotranspiration rate  in inches of water per day per acre into gallons per minute per acre.
ET  *18.86  = GPM/acre
 Using this formula an ET of 0.25 inches per 24 hours per acre would require 4.72 GPM/acre.
This calculation is for a pump running 24 hours.
More commonly as a safety factor, systems are sized for 20 hours of operation.
To accomplish this use the following formula:
 24 /  X  24/20X 4.72=5.66 GPM/acre
 On flat land the pressure output required of the pump stations is mainly dictated by the flushing requirements of the filters and pipes.
On hilly terrain the pressure required to lift water to the highest point must also be considered.
Most automatic filters require a minimum of 30 psi to self-clean properly.
This is generally the pump's minimum operating pressure to operate a drip system.
The filter system protects the drip system from sand and other small particles which can plug the dripline's drippers.
A well designed filter system maximizes the performance and longevity of your SDI system.
Two types of filters are recommended:
 1.
Sand media filters
 2.
Netafim disc filters 
 In general, screen filters are suitable only for very clean water sources.
Sand media and disc filters which utilize depth filtration are most effective at removing suspended particles from the water.
The filter system should be setup to automatically clean when the pressure differential across the media is too large.
A pressure differential switch in combination with a flushing controller is a common approach for automation of filter cleaning.
Figure 2.
Example of a Netafim Apollo Disc-Kleen Filter
 Pressure control valves  are recommended for non-pressure compensated dripline to achieve the correct working pressure in the drip system.
Pressure regulating valves must be adjustable to accommodate higher pressures required during flushing.
Air vacuum vents  prevent soil suction into the drippers at system shut-down.
For every 50 laterals there should be one anti-vacuum vent at the highest elevation and one mounted on the flushing manifold's highest elevation.
A double-purpose automatic air vent must be installed at the pump and is usually required in the mainline.
The system  is designed to supply fertilizer to all irrigation blocks using either an automated system or a simple injection pump.
Please consult a Netafim USA Dealer to determine which fertilizers may be safely applied through the drip system.
It is essential to monitor flow in order to monitor the operation of your system and crop's water use.
Your SDI system is designed to produce a specific flow rate at a given pressure.
Changes in the flow rate may indicate leaks in the system, improperly set pressure regulating valves or even changes in the well and pumping plant.
On the following pages, use of a water meter and a pressure gauge to determine system problems is detailed.
Figure 3.
Example of a field installation of pressure regulating valves and air vents
 Figure 4.
Fertilizer Injection system
 Use pressure gauges to ensure that the drip system, filter system and pump operate at the correct pressure.
Pressure gauges are also critical to assess potential problems with the system.
Most permanent SDI systems use flush manifolds to flush entire zones at a single time.
A manifold at the end of the field also improves system uniformity.
The use of flush manifolds is highly recommended to reduce the labor required to properly maintain the system.
Whether you have just installed a new system or are starting the system up after sitting through the off season, these simple steps, taken before irrigation will help to ensure optimum system performance.
1.
Flush the well before operation through the filter.
A new well or one that has been sitting during the off-season, may discharge sand at startup.
This "plug" of particles can overwhelm the filtration system causing it to repeatedly trigger an unproductive backflush cycle.
If the well discharges sand on a regular basis it may be necessary to install a sand separator before the regular filtration system.
Consult your Netafim USA Dealer for more information on sand separators.
2.
Thoroughly flush the laterals and mains before system operation.
In new systems, during installation, it is possible that dirt and PVC pieces accumulated in the system these need to be flushed out properly.
During the season, systems need to be flushed on a regular basis.
Filters do not filter 100% of particles, often fine silt enters.
This will settle in lines and must be flushed especially from the driplines.
Debris also can get into the lines after a break has occurred and should be flushed after any repairs.
3.
Check for leaks in dripline laterals.
Laterals are occasionally damaged during installation.
System start-up is the right time to check for leaks, before the crop canopy expands making repairs difficult.
1.
Open flush manifolds on line ends.
2.
If possible, run the pump station for a few minutes with the discharge to waste  to flush out any sand.
3.
Open mainline flush valves, with submain valves closed, and operate your system until discharge water runs clear for 5 minutes.
Check the flow rate and whether and how often the filter system backflushes during operation.
4.
Open submain valves with flush manifolds still open to clear the submains of debris.
5.
For each submain, open the control valve until discharge water at the end of the lateral runs clear.
If the capacity of the water supply is insufficient to flush all laterals simultaneously, then flush a few laterals at a time.
Close the submain valve.
6.
Close the flush manifolds on lateral ends.
7.
Operate the system until it is fully pressurized and all air is discharged.
8.
Check system for leaks and repair.
9.
Re-flush the lines after leaks are repaired.
10.
Check pressure gauges and adjust all pressure regulators, or regulating valves as necessary.
11.
Check for proper operation of all system components: pumps, controllers, valves, air vents, pressure regulators, gauges, water meters, filter system and fertilizer injectors.
12.
Record readings from all pressure gauges and flow meters and check on the frequency of backflush cycle of your filters.
If backflushing is frequent  consult your Netafim USA dealer.
SYSTEM PRESSURE AND FLOW TESTS
 Upon initial startup it is best to evaluate the uniformity of your drip system.
This is accomplished by:
 1.
Measuring the pressure in the system at various points and comparing this to the design pressure.
2.
Reading the water meter or calculating the system flow and comparing the result to the designed flow rate.
These evaluations should be conducted as part of system startup and as an ongoing part of system maintenance.
Consult the maintenance section of this guide for a complete program for system care.
Drip systems are typically designed to operate between 10 and 15 psi.
Measuring the pressure at several points in your drip system is the simplest way to evaluate the performance.
A good evaluation will include pressure measurements at a minimum of three points along the header end of the field and three points at the far end of the field.
Pressure measurements at more points in the field including along the length of the laterals will give a more complete picture of system uniformity but are usually not necessary if the end pressures are within one psi of the header pressure.
A water meter is an important component of every drip system.
It gives the operator a quick indication of the operational performance of their system and is used to determine proper water application rates.
Every new system should be designed with a water meter.
Older systems without water meters should be retrofitted with one.
The system design should include an estimated system flow rate and the measured flow rate should be within +/5% of the designed rate.
To calculate the flow rate expected for each zone use the following formula:
 CONVERTING SYSTEM FLOW RATE TO INCHES OF APPLIED WATER
 Irrigation schedules are usually based on evapotranspiration  rates which are expressed in inches of water evaporated over a given time period, usually a day or week.
It is simple to convert a flow rate in GPM, either read from a meter or calculate as outlined on previous page, to inches of water applied per hour by using the following formula.
MONITORING YOUR DRIP SYSTEM
 To achieve the highest yields and water savings possible with a drip irrigation system, it is necessary to monitor your system and make adjustments.
In addition, regular system monitoring may give advance warning of potential problems.
MONITORING SYSTEM PRESSURE AND FLOW RATES
 As presented earlier, measurements of system flow and pressure give a good picture of the system's performance.
Because of the large number of variables at play in an irrigation system the measured water application rate may not exactly match the predicted rate.
Still large differences in calculated versus measured values may indicate a problem with your calculations or a physical system problem such as a broken or clogged line.
Over the growing season changes in the flow rate or pressure in your system can be used to diagnose problems with the system.
Table 2, details some of the problems that can be diagnosed by monitoring system pressure and flow rate.
This is by no means a comprehensive list but is a good place to start.
The maintenance of your SDI system centers on identification of the factors which can lead to reduction of the performance of your drip system and procedures to mitigate these negative impacts.
Factors that can slow or stop flow through the drip system include: suspended material, chemical precipitation, biological growth, root intrusion, soil ingestion and crimping of the dripline.
To ensure maximum system life reduce or eliminate the impact of the negative factors.
This may require water treatment and a systematic program for regular maintenance.
In this section we outline the various potential issues that can adversely affect the drip system and offer procedures to mitigate the potential damage.
Gradual decrease in flow rate	Dripper plugging
 Possible pump wear 
 Sudden decrease in flow rate	Stuck control valve
 Gradual increase in flow rate	Incremental damage to dripperline by pests
 Sudden increase in flow rate	Broken lateral, submain, main line
 Large pressure drop across filters	Debris buildup in filters
 Inadequate flushing of filters
 Gradual pressure decrease at filter inlet	Pump wear or water supply problems
 Sudden pressure decrease at filter outlet	Broken lateral, submain, main line
 Pressure regulator or water supply failure
 Gradual pressure increase at filter outlet	Dripper plugging
 Sudden pressure increase at filter outlet	Stuck control valve
 Sudden pressure decrease at submain	Damaged or broken lateral
 Table 2.
Problems diagnosed from system flow rates and pressures
 The potential for dripper plugging problems will vary with the source of the irrigation water, either surface or ground water.
In general, algae and bacterial growth are usually associated with the use of surface water.
Whole algae cells and organic residues of algae are often small enough to pass through the filters of an irrigation system.
These algae cells can then form aggregates that plug the drippers.
Residues of decomposing algae can accumulate in pipes and drippers to support the growth of slime-forming bacteria.
Surface water can also contain larger organisms such as moss, fish, snail, seeds and other organic debris that must be adequately filtered to avoid plugging problems.
Groundwater, on the other hand, may contain high levels of minerals that can challenge dripper function.
Water from shallow wells  often will produce plugging problems associated with bacteria.
Chemical precipitation is more common with deep wells.
A water quality analysis can give the grower a "heads up" on potential trouble areas for the drip system.
This test should be accomplished before the final design of the system to ensure that proper components are installed to address any problem areas.
Many laboratories around the United States have Water Quality Analysis services available which are able to conduct a "Drip Irrigation Suitability Test".
The analysis should include testing for pH, dissolved solids, manganese, iron, hydrogen sulfide, carbonate and bicarbonates.
Table 3 lists the more common water quality issues that can affect drip irrigation systems.
Having a water analysis in the moderate or even severe category does not mean drip irrigation cannot be used but only that special precautions must be applied to prevent problems.
Consult your local Netafim USA Dealer for more information on water quality and drip irrigation.
TYPE OF FACTOR	MINOR	MODERATE	SEVERE
 INORGANIC	<10	10 100	>100
 IRON 	0,0 0.1	0.1 0.4	0.4+
 MANGANESE 	0.0 0.2	0.2 0.4	0.4+
 SULFIDES 	0.0 0.1	0.1 0.02	0.2+
 CALCIUM CARBONATE	0,0 50.0	50.0 100.0	150.0+
 BACTERIA POPULATIONS	10,000	10,000 50,000	50,000+
 Table 3.
Common water quality issues with drip irrigation
 Suspended solids in the incoming water are the most common stress impinging upon the drip system and the easiest to control.
Each and every Netafim dripper has a large filter built into the unit to keep suspended particles from being trapped in the labyrinth.
This filter is located at the bottom of dripper and points toward the center of the drip tubing so that it can be cleaned by flushing the dripline.
This built-in filter plays an important role in the longevity of the SDI system.
Thus, most water used for drip irrigation must be filtered to remove suspended solid particles that can lodge in the drippers and reduce or even stop the flow.
These particles can be either organic such as algae or inorganic such as sand.
Each manufacturer recommends a filtration level based on the technology of the dripper device.
The Netafim drippers commonly require 120 mesh filtration.
This is the lowest filtration requirement of any commercial drip irrigation product.
That means that the drippers are more reliable ensuring long service even under harsh conditions.
Surface water generally contains a combination of organic and inorganic suspended particles.
These include algae, moss, aquatic animals as well as suspended sand, silt and clay particles.
Filtering this mix of material is a challenge that is best accomplished using three-dimensional filtration, such as disc or sand media.
Well water generally has lower levels of suspended solids which can be handled using disc filtration or in cases of very low contaminant levels screen filters.
If large quantities of sand are being generated by the well a sand separator may be installed before other filters.
Filters for SDI should automatically clean  during operation when the contaminant levels get high enough.
Chemical plugging usually results from precipitation of one or more of the following minerals: calcium, magnesium, iron, or manganese.
The minerals precipitate from solution and form encrustations  that may partially or completely block the flow of water through the dripper.
Water containing significant amounts of these minerals and having a pH greater than seven has the potential to plug drippers.
Particularly common is the precipitation of calcium carbonates, which is temperature and pH dependent.
An increase in either pH or temperature reduces the solubility of calcium in water, and results in precipitation of the mineral.
When groundwater is pumped to the surface and discharged through a micro-irrigation system, the temperature, pressure and pH of the water often changes.
This can result in the precipitation of calcium carbonates or other minerals to form scale on the inside surfaces of the irrigation system components.
A simple test for identifying calcium scale is to dissolve it with vinegar.
Carbonate minerals dissolve and release carbon dioxide gas with a fizzing, hissing effervescence.
Figure 5.
Dripper with calcium precipitate.
The black pieces in the picture are pieces of the cut-away plastic dripline and not contaminants.
Iron is another potential source of mineral deposit that can plug drippers.
Iron is encountered in practically all soils in the form of oxides, and it is often dissolved in groundwater as ferrous bicarbonate.
When exposed to air, soluble ferrous bicarbonate oxidizes to the insoluble or colloidal ferric hydroids and precipitates.
The result is commonly referred to as 'red water, which is sometimes encountered in farm irrigation wells.
Manganese will sometimes accompany iron, but usually in lower concentrations.
Hydrogen sulfide is present in many wells.
Precipitation problems will generally not occur when hard water, which contains large amounts of hydrogen sulfide, is used.
Hydrogen sulfide will minimize the precipitation of calcium carbonate  because of its acidity.
Fertilizers injected into a drip system may contribute to plugging.
This may be the result of a chemical reaction that occurs when different fertilizers are mixed or because the fertilizer in question is not completely soluble.
This type of plugging is completely preventable.
To determine the potential for plugging problems from fertilizer injection, the following test can be performed:
 1.
Add drops of the liquid fertilizer to a sample of the irrigation water so that the concentration is equivalent to the diluted fertilizer that would be flowing in the lateral lines.
2.
Cover and place the mixture in a dark environment for 12 hours.
3.
Direct a light beam at the bottom of the sample container to determine if precipitates have formed.
If no apparent precipitation has occurred, the fertilizer source will normally be safe to use in that specific water source.
A micro-irrigation system can provide a favorable environment for bacterial growth, resulting in slime buildup.
This slime can combine with mineral particles in the water and form aggregates large enough to plug drippers.
Certain bacteria can cause enough precipitation of manganese, sulfur and iron compounds to cause dripper plugging.
In addition, algae can be transported into the irrigation system from the water source and create conditions that may promote the formation of aggregates.
Dripper plugging problems are common when using water that has high biological activity and high levels of iron and hydrogen sulfide.
Soluble ferrous iron is a primary energy source for certain iron-precipitating bacteria.
These bacteria can attach to surfaces and oxidize ferrous iron to its insoluble ferric iron form.
In this process, the bacteria create a slime that can form aggregates called ochre, which may combine with other materials in the micro-irrigation tubing and cause dripper plugging.
Ochre deposits and associated slimes are usually red, yellow or tan.
Sulfur slime is a yellow to white stringy deposit formed by the oxidation of hydrogen sulfide.
Hydrogen sulfide  accumulation in groundwater is a process typically associated with reduced conditions in anaerobic environments.
Sulfide production is common in lakes and marine sediments, flooded soils, and ditches; it can be recognized by the rotten egg odor.
Sulfur slime is produced by certain filamentous bacteria that can oxidize hydrogen sulfide and produce insoluble elemental sulfur.
Figure 6.
Filamentous sulfur slime completely clogging a small water meter.
The sulfur bacteria problem can be minimized if there is not air-water contact until water is discharged from the system.
Defective valves or pipe fittings on the suction side of the irrigation pump are common causes of sulfur bacteria problems.
If a pressure tank is used, the air-water contact in the pressure tank can lead to bacterial growth in the tank, clogging the dripper.
The use of an air bladder or diaphragm to separate the air from the water should minimize this problem.
Plan roots tend to grow toward soil areas with the highest water content.
Because of this tendency, roots can clog subsurface drip systems by growing into the dripper openings.
Plant roots tend to "hunt" for water when it is in short supply thus, the problem seems to be more acute when irrigation is not sufficient for the plant needs.
This is a particular problem in systems that are left unused for part of the season.
Several strategies can be employed to reduce the possibility of root intrusion:
 1.
Short frequent irrigations keep adequate water in the root zone so the roots have no need to look for water.
2.
Acid injection that lowers the pH to less than four will discourage root growth and can be used to clean roots out of drippers with small amounts of root intrusion.
High concentrations of chlorine , N-pHURIC, phosphoric or metam sodium  will also destroy roots in the drippers.
3.
In areas where it is allowed, trifluralin is an effective inhibitor of root growth and can be used to prevent root intrusion.
4.
Seamed dripline encourages roots to grow along the seam and into the dripper.
Netafim products are designed without a seam to discourage this intrusion.
Soil ingestion is not a problem in properly designed SDI systems.
Soil injection occurs when soil is sucked into the dripline.
When a drip system is shut off the water continues to flow to the low end of the field creating a vacuum at the higher end, sucking saturated soil into the line.
A properly designed drip system will minimize this potential problem.
The supply manifold must be equipped with vacuum relief vents, these vents allow air to flow into the driplines when the system is shut off.
Netafim air/vacuum relief vents will allow sufficient air into the system.
Insufficient air will create a vacuum.
This is not a good place to skimp.
CRIMPING OF THE DRIPLINE
 Pinching of the dripline can occur as the result of soil disturbance by equipment or drying out.
Because it is difficult to correct crimping in an SDI system many growers are setting up their system so there is minimum traffic on the driplines.
The lines are installed using GPS and the field is laid with specific traffic rows.
Follow the standard instructions for the maintenance of your filter system.
Filters are the first line of protection for your drip system and they need regular maintenance to operate at a high level.
On a bi-weekly basis observe the system as it completes a backflush cycle.
Make sure all pressures are within the system limits before and after backflushing.
Check the operation of backflush valves, pressure differential switches and controller.
Make sure you clean the command filter.
At the end of the season check the media level in media tanks.
Scum can build up on disc filters and the discs may need to be cleaned with acid.
In areas that experience a freeze, drain all water from the filter, valves and command system.
To minimize sediment build up, regular flushing of drip irrigation pipelines is recommended.
The system design should be such that a minimum flush rate of 1.0 ft/sec can be obtained in the lines.
Valves large enough to allow sufficient velocity of flow should be installed at the ends of mains, submains and manifolds.
Also, allowances for flushing should be made at the ends of lateral lines.
Flushing of the drip lateral lines should continue until clean water runs from the flushed line for at least two minutes.
A regular maintenance program of inspection and flushing will help significantly in preventing dripper plugging.
Chemical treatment is often required to prevent dripper plugging due to microbial growth and/or mineral precipitation.
The attachment of inorganic particles to microbial slime is a significant source of dripper plugging.
Chlorination is an effective measure against microbial activity.
Use chlorine and all other chemicals only according to label directions.
Acid injection can remove scale deposits, reduce or eliminate mineral precipitation and create an environment unsuitable for microbial growth.
Chlorination is the most common method for treating organic contaminants.
Active chlorine is a strong oxidizer and as such, is useful in achieving the following:
 A.
Prevent clogging and sedimentation of organic substances.
B.
Destroy and decompose sulfur and iron bacteria, as well as accumulated bacterial slime in the system.
C.
Improve performance of filtration systems while reducing backflush water.
D.
Clean systems of organic sediments.
If the micro-irrigation system water source is not chlorinated, it is a good practice to equip the system to inject chlorine to suppress microbial growth.
Since bacteria can grow within filters, chlorine injection should occur prior to filtration.
Liquid sodium hypochlorite --laundry bleach--is available at several chlorine concentrations.
The higher concentrations are often more economical.
It is the easiest form of chlorine to handle and is most often used in drip irrigation systems.
Powdered calcium hypochlorite , also called High Test Hypochlorite , is not recommended for injection into micro-irrigation systems since it can produce precipitates that can plug drippers, especially at high pH levels.
The following are several possible chlorine injection schemes:
 Inject continuously at a low level to obtain one to two ppm of free chlorine at the ends of the laterals.
Inject at intervals  at concentrations of 20 ppm and for a duration long enough to reach the last dripper in the system.
Inject a slug treatment in high concentrations  weekly at the end of an irrigation cycle and for a duration sufficient to distribute the chlorine through the entire piping system.
The method used will depend on the growth potential of microbial organisms, the injection method and equipment and the scheduling of injection of other chemicals.
When chlorine is injected, a test kit should be used to check to see that the injection rate is sufficient.
Color test kits  that measure 'free residual' chlorine, which is the primary bactericidal agent, should be used.
The orthotolidine-type test kit, which is often used to measure total chlorine content in swimming pools, is not satisfactory for this purpose.
D.P.D.
test kits can be purchased from irrigation equipment dealers.
Check the water at the outlet farthest from the injection pump.
There should be a residual chlorine concentration of one to two ppm at that point.
Irrigation system flow rates should be closely monitored, and action taken  if flow rates decline.
Chlorination for bacterial control is relatively ineffective above pH 7.5, so acid additions may be necessary to lower the pH to increase the biocidal action of chlorine for more alkaline waters.
Since sodium hypochlorite can react with emulsifiers, fertilizers, herbicides and insecticides, bulk chemicals should be stored in a secure place according to label directions.
Recipe for Chlorine Injection
 WARNING: Active chlorine solutions are dangerous to human beings and animals the manufacturers' instructions must be followed very carefully.
When using chlorine, proper protection for the eyes, hands and body parts must be worn, i.e.
glasses, gloves, shoes, etc.
Chlorine contact with the skin can cause serious burns, contact with the eyes can cause blindness and swallowing may be fatal.
Prior to filling any tank with chlorine solution, be sure it is absolutely clean of fertilizer residue.
Direct contact between chlorine and fertilizer can create a thermo reaction, which can be explosive.
This is extremely dangerous.
The direct contact of chlorine and fertilizer in the irrigation water after it has been injected into the system is not hazardous.
The contact of free chlorine in water and nitrogenous  fertilizer creates the combination of chlor amine which is called "combined chlorine".
If possible, avoid any application of ammonium or urea fertilizers together with chlorination.
In the case that chlorination is required, it is recommended to ask your local Farm Extension Service for assistance in the computation and application methods.
Sodium hypochlorite is transported by tanks.
It should be stored in a clean tank without any remnants of fertilizers.
The tanks should be painted white and placed in a shaded area.
In the field, storage should not exceed 20 days.
In case of gas chlorine, transportation, storage and general handling should be carried out in accordance with the manufacturers' specific instructions under supervision of the relevant authorities.
CHLORINATION OBJECTIVE	APPLICATION METHOD	
 SYSTEM HEAD	SYSTEM END
 PREVENT	CONTINUOUS CHLORINATION	3 5	0.5 1
 SEDIMENTATION	INTERMITTENT CHORINATION	10	1-2
 SYSTEM CLEANING	CONTINUOUS CHLORINATION	5 10	1-2
 INTERMITTENT CHORINATION	15 50	4 5
 CONCENTRATION AND INJECTION POINT
 It is important to remember that chlorine concentration decreases as time and distance from the injection point increases.
The lowest concentration will always be found furthest from the injection point.
The injection point should be as close as possible to the treated system.
The required concentration of active chlorine is a result of the chlorination objective.
When the purpose of chlorination is improving filtration performance, the injection point should be close to the filtration system to assure even distribution throughout the filters.
Chlorine concentration downstream of the filter battery should be no less than one to two ppm for constant chlorination and three times more for intermittent chlorination.
For continuous chlorination, the injection should start after pressurizing the system.
For intermittent chlorination, the procedure should be as follows:
 START	By flushing the system.
Inject required amount over time, preferably at the beginning of the
 CONTACT TIME	Preferably one hour, but not less than thirty minutes.
At the end of the process, open the end of the line, flush out and run
 fresh water for an hour.
Use the following worksheets to determine the proper injection rate of chlorine in terms of GPH for liquid and lbs./hr for gas.
1.
Choose the proper chlorine solution factor:
 5% Chlorine Solution: The factor is = 2.00
 10% Chlorine Solution: The factor is = 1.00
 15% Chlorine Solution: The factor is = 0.67
 2.
Multiply the solution factor by the treated flow in terms of GPM.
3.
Multiply by the desired chlorine concentration in terms of ppm.
4.
Multiply by the factor of 0.0006.
5.
The result will be the required injection rate of chlorine in terms of GPH
 The chlorine solution is 10%.
The flow is 100 GPM.
The desired chlorine concentration is 10 ppm.
Chlorine Flow Desired Chlorine Chlorine Injection Solution Factor GPM X concentration  X 0.0006 = Rate GPH 10 X 100 X 10 X 0.0006 = 0.6
 The injection rate of chlorine solution will be 0.6 GPH
 1.
Determine the flow of the treated zone in terms of GPM.
2.
Multiply the flow by the desired chlorine concentration in terms of ppm.
3.
Multiply it by the factor of 0.0005.
4.
The result will be the injection rate of the gas in terms of lbs.
per hour.
The flow is 100 GPM.
The desired chlorine concentration is 10 ppm.
Flow Desired Chlorine Chlorine Injection GPM X Concentration  X 0.0005 = Rate  100 X 10 X 0.0005 = 0.5
 The injection rate of the gas will be 0.5 lbs./hr.
Acid can be used to lower the pH of irrigation water to reduce the potential for chemical precipitation and to enhance the effectiveness of the chlorine injection.
Sulfuric, hydrochloric and phosphoric acid are all used for this purpose.
Acid can be injected in much the same way as fertilizer; however, extreme caution is required.
The amount of acid to inject depends on how chemically base  the irrigation water is and the concentration of the acid to be injected.
One milliequivalent of acid completely neutralizes one milliequivalent of bases.
If acid is injected on a continuous basis to prevent calcium and magnesium precipitates from forming, the injection rate should be adjusted until the pH of the irrigation water is just below 7.0.
If the intent of the acid injection is to remove existing scale buildup within the micro-irrigation system, the pH will have to be lowered more.
The release of water into the soil should be minimized during this process since plant root damage is possible.
An acid slug should be injected into the irrigation system and allowed to remain in the system for several hours, after which the system should be flushed with irrigation water.
Acid is most effective at preventing and dissolving alkaline scale.
Avoid concentrations that may be harmful to drippers and other system components.
Phosphoric acid, which is also a fertilizer source, can be used for water treatment.
Some microirrigation system operators use phosphoric acid in their fertilizer mixes.
Care should be used with the injection of phosphoric acid into hard water since it may cause the precipitation of calcium carbonate.
For safety, dilute the concentrated acid in a non-metal, acid-resistent mixing tank prior to injection into the irrigation system.
When diluting acid, always add acid to water, never water to acid.
The acid injection point should be beyond any metal connections or filters to avoid corrosion.
Flushing the injection system with water after the acid application is a good practice to avoid deterioration of components in direct contact with the acid.
Acids and chlorine compounds should be stored separately, preferably in epoxy-coated plastic or fiberglass storage tanks.
Acid can react with hypochlorite to produce chlorine gas and heat; therefore, the injection of acid should be done at some distance , prior to the injection of chlorine.
This allows proper mixing of the acid with the irrigation water before the acid encounters the chlorine.
Hydrochloric, sulfuric and phosphoric acids are all highly toxic.
Always wear goggles and chemical-resistant clothing whenever handling these acids.
Acid must be poured into water; never pour water into acid.
Recipe for the Treatment of Drip Irrigation Systems with Acid
 SAFETY PRECAUTIONS: Contact of the acid with the skin can cause burns.
Contact with the eyes could be extremely dangerous.
During treatment and especially when filling containers with acid, wear protective goggles, clothes and boots.
Follow the instructions on the Material Safety Data Sheet  attached to the delivered acid.
PROBLEMS OF CORROSION: Polyethylene and PVC tubes are resistant to acid.
Aluminum, steel,  and asbestos-cement pipes are damaged by corrosion.
In every case, resume normal water flow through the system after completion of treatment for at least one hour in order to flush any remaining acid.
The importance of flushing cannot be over emphasized when the pipes used are particularly sensitive to corrosion.
METHOD OF OPERATION: Acid can be applied through the drip irrigation system by a fertilizer pump resistant to acids or by conventional control head with a fertilizer tank.
APPLICATION OF ACID BY FERTILIZER PUMP: The goal of acid treatment is to lower the pH level of the water in the irrigation system to values between two to three for a short time.
This is achieved by injection of a suitable quantity of acid into the system.
1.
Clean the filters.
2.
Flush the system with clean water as follows: flush the main pipes then the distribution pipes and finally the drip laterals.
Use the highest pressure possible for flushing.
Deactivate the pressure regulators and flush the laterals, a few at a time.
Flushing with clean water will prevent blockages during treatment.
3.
Ascertain the discharge of the water from the system through which the acid will be injected, and the discharge of the fertilizer pump.
4.
Calculate the required amount of acid that should be injected into the system in order to get 0.6% of acid concentration in the irrigation water.
5.
Inject the acid into the system within fifteen minutes only after the system has reached maximum operation pressure.
NOTE: Acids suitable to be injected in 0.6% concentrations are: Nitric acid 60% Phosphoric acid 75%85% Sulfuric acid 90% 96% Hydrochloric acid 30% 35%
 In many cases the most economical acids are sulfuric acid  and hydrochloric acid.
Sulfuric acid 90% and system flow is 100 GPM.
Because the acid is to be injected only 15 minutes the total acid required is 10 gallons
 NOTE: Under certain conditions, i.e., hard water with a very high pH, there might be a need to raise the acid concentrate in the system to 1%.
Please consult a Netafim USA Representative prior to such a treatment.
IRON CONTROL SYSTEM FOR DRIP IRRIGATION
 Iron deposits create severe clogging problems in drip systems.
Iron deposit is described as a filamentous amorphous gelatinous type of brown-reddish slime, that precipitates from water that contains iron.
Iron deposits get stuck in drippers and can cause complete plugging of the system.
The problem exists in well water areas where the groundwater aquifers are formed mainly of sandy soils or organic muck soils  usually with a pH of below 7.0 and in the absence of dissolved oxygen.
These waters contain ferrous iron  which is chemically reduced, 100% water soluble and serves as the primary raw material for slime formation.
Iron bacteria, mainly from the filamentous genuses like Gallionella Sp.
Leptolhris and ,Sphaerotihus and less from the rod type like Pseudomonas and Enterobacter, when present in the water, react with the ferrous iron  through an oxidation process.
This changes the iron form to ferric iron  which is insoluble.
The insoluble Ferric iron is surrounded by the filamentous bacteria colonies that create the sticky iron slime gel that is responsible for clogging the dripper.
Concentrations of ferrous iron as low as 0.2 ppm are considered a potential hazard to drip systems.
Between 0.2-1.5 ppm dripper clogging hazard is moderate.
Concentrations above 1.5 ppm are described as severe.
Practically any water that contains concentrations higher than 0.5 ppm of iron cannot be used in drip systems unless they are treated chemically or otherwise.
Experiments in Florida indicate that chlorination successfully controls iron slime when iron concentrations were less than 3.5 ppm and the pH was below 6.5.
It is also stated that long term use of water with a high level of iron, may not be suitable for drip irrigation.
The literature mentions that water containing more than 4.0 ppm cannot be efficiently chemically treated and it should undergo a pond sedimentation process before pumping it back to a drip system.
There are several ways to control iron slime problems.
The common denominator of all treatments is prevention of the formation of slime.
Basically there are two preventive treatments:
 1.
STABILIZATION  Stabilization treatments keep the ferrous iron in solution by chelating it with sequestering agents.
Such agents include various poly phosphates and phosphonate.
2.
OXIDATION SEDIMENTATION FILTRATION This type of treatment oxidizes the soluble "invisible" ferrous iron into the insoluble "visible" ferric iron.
It then will precipitate, so it can be physically separated from the water by means of filtration.
The second procedure is generally the less expensive for the severe iron problems in supply water.
The various means to oxidize iron include chlorination and aeration.
There are also other oxidizers but they are generally more expensive.
Chlorine injection for iron control is normally handled in the same manner as continuous chlorine injection outlined above, with residual chlorine levels of one to two ppm.
Aeration is most often applied to settling ponds using sprayers or agitators to react the Iron with the air.
In this case the pond becomes a pre-filtration component.
A sand media filter is the most appropriate filter for settling down the oxidized iron and filtering it from the water.
When designing a filtration system for iron removal it is good practice to oversize the filter units.
Larger units with slower water velocity will allow oxidized iron to settle and the resultant water will be easier to filter.
This is the same principle as exhibited in settling ponds.
Scale inhibitors, such as chelating and sequestering agents, have long been used by other industries.
A number of different chemicals are being marketed for use in micro-irrigation systems to prevent plugging.
Many of these products contain some form of inorganic polyphosphate that can reduce or prevent precipitation of certain scale-forming minerals.
These inorganic phosphates do not stop mineral precipitation, but keep it in the sub-microscopic range by inhibiting its growth.
Probably the most commonly used of these materials is sodium hexametaphosphate as little as 2 ppm can hold as much as 200 ppm calcium bicarbonate in solution.
Sodium hexametaphosphate is not only effective against alkaline scale, but also forms complexes with iron and manganese and can prevent depositions of these materials.
Although the amount of phosphate required to prevent iron deposits depends on several factors, a general recommendation is two to four ppm phosphate for each ppm of iron or manganese.
These phosphates are relatively inexpensive, readily soluble in water, nontoxic and effective at low injection rates.
Algae problems which often occur with surface water sources such as a pond can be effectively treated with copper sulfate.
Dosages of one to two ppm  are sufficient and safe to treat algae growth.
Copper sulfate should be applied when the pond water temperature is above 60F.
Treatments may be repeated at two to four-week intervals, depending on the nutrient load in the pond.
Copper sulfate should be mixed into the pond.
The distribution of biocides into surface water must be in compliance with EPA regulations.
Copper sulfate can be harmful to fish if alkalinity, a measure of the water's capacity to neutralize acid, is low.
Alkalinity is measured volumetrically by titration with H2S0 and is reported in terms of equivalent CaCO Repeated use of copper sulfate can result in the buildup to levels toxic for plants.
Irrigation Scheduling: The Water Balance Approach
 Fact Sheet No.
4.707
 The water requirement of a crop must be satisfied to achieve potential yields.
The crop water requirement is also called crop evapotranspiration and is usually represented as ET.
Evapotranspiration is a combination of two processes evaporation of water from the ground surface or wet surfaces of plants; and transpiration of water through the stomata of leaves.
The water requirement can be supplied by stored soil water, precipitation, and irrigation.
Irrigation is required when ET  exceeds the supply of water from soil water and precipitation.
As ET varies with plant development stage and weather conditions, both the amount and timing of irrigation are important.
The water balance  method of irrigation scheduling is one method of estimating the required amount and timing of irrigation for crops.
This method can be used if initial soil water content in the root zone, ET, precipitation, and the available water capacity of the soil are known.
The soil in the root zone has an upper as well as a lower limit of storing water that can be used by crops.
The upper limit is called the field capacity , which is the amount of water that can be held by the soil against gravity after being saturated and drained; typically attained after 1 day of rain or irrigation for sandy soils and from two to three days for heavier-textured soils that contain more silt and clay.
The lower limit is called permanent wilting point , which is the amount of water remaining in the soil when the plant permanently wilts because it can no longer extract water.
The available water capacity , or total available water, of the soil is the amount of water between these two limits  and is the maximum amount of soil water
 As the crop grows and extracts water from the soil to satisfy its ET requirement, the stored soil water is gradually depleted.
In general, the net irrigation requirement is the amount of water required to refill the root zone soil water content back up to field capacity.
This amount, which is the difference between field capacity and current soil water level, corresponds to the soil water deficit.
The irrigation manager can keep track of D, which gives the net amount of irrigation water to apply.
On a daily basis, D can be estimated using the following accounting equation for the soil root zone:
 DE=DA T-P-Irr-U+SRO+DP [1] where D is the soil water deficit  in the root zone on the current day, D is the soil water deficit on the previous day, ET is the crop evapotranspiration rate for the current day, P is the gross precipitation for the current day, Irr is the net irrigation amount infiltrated into the soil for the current day, U is upflux of shallow ground water into the root zone, SRO is surface runoff, and DP is deep percolation or drainage.
The last three variables in equation 1  are difficult to estimate in the field.
In many situations, the water table is significantly deeper than the root zone and U is zero.
Also, SRO and DP can be accounted for in a simple way by setting L to zero whenever water additions  to the root zone are greater than D + ET.
Using these assumptions, equation 1 can be simplified to:
 The water balance approach to irrigation scheduling keeps track of the soil water deficit by accounting for all water additions and subtractions from the soil root zone.
Crop water consumption or evapotranspiration accounts for the biggest subtraction of water from the root zone while precipitation and irrigation provide the major additions.
Crop evapotranspiration can be obtained from the Colorado Agricultural Meteorological Network  or by using atmometers.
The soil in the root zone has an upper as well as a lower limit of storing water that can be used by crops.
As the crop grows and extracts water from the soil to satisfy its ET requirement, the stored soil water is gradually depleted.
Atmometers are designed to simulate the water use of a well-watered reference crop.
*A.A.
Andales, Colorado State University Extension irrigation specialist and assistant professor, soil and crop sciences; J.L.
Chvez, Extension irrigation specialist, assistant professor, civil and environmental engineering; T.A.
Bauder, Extension water quality specialist, soil and crop sciences.
1/2015
 Table 1.
Soil texture and plant available water capacity 
 Soil Texture	Available water capacity
 inch of water / inch of soil -
 Coarse sands	0,05	0.07	0.06
 Fine sands	0.07	0.08	0.08
 Loamy sands	0.07	0.10	0.08
 Sandy loams	0.10	0.13	0.12
 Fine sandy loams	0.13	0.17	0.15
 Sandy clay loams	0.13	0.18	0.16
 Loams	0.18	0.21	0.20
 Silt loams	0.17	0.21	0.19
 Silty clay loams	0.13	0.17	0.15
 Clay loam	0.13	0.17	0.15
 Silty clay	0.13	0.14	0.13
 Clay	0.11	0.13	0.12
  [2]
 Take note that D is set equal to zero if its value becomes negative.
This will occur if precipitation and/or irrigation exceed  and means that water added to the root zone already exceeds field capacity within the plant root zone.
Any excess water in the root zone is assumed to be lost through SRO or DP.
The amounts of water used in the equations are typically expressed in depths of water per unit area.
Equation 2 is a simplified version of the soil water balance with several underlying assumptions.
First, any water additions  are assumed to readily infiltrate into the soil surface and the rates of P or Irr are assumed to be less than the long term steady state infiltration rate of the soil.
Actually, some water is lost to surface runoff if precipitation or irrigation rates exceed the soil infiltration rate.
Thus, equation 2 will under-estimate the soil water deficit or the net irrigation requirement if P or Irr rates are higher than the soil infiltration rate.
Knowledge of effective precipitation , irrigation, and soil infiltration rates  are required to obtain more accurate estimates of D.
Secondly, water added to the root zone from a shallow water table  is not considered.
Groundwater contributions to soil water in the root zone must be subtracted from the right hand side of the equation in case of a shallow water table.
Equation 2 will overestimate D if any actual soil water additions from groundwater are neglected.
It is a good practice to occasionally check  if D from
 equation 2 is the same as the actual deficit in the field.
Remember that D is the difference between field capacity and current soil water content.
Therefore, the actual deficit in the field can be determined by subtracting the current soil water content from the field capacity of the root zone.
If D from equation 2 is very different from the observed deficit, then use the observed deficit as the D value for the next day.
These corrections are necessary to compensate for uncertainties in the water balance variables.
Field measurements of current soil water content can be performed using the gravimetric method  or using soil water sensors like gypsum blocks.
In irrigation practice, only a percentage of AWC is allowed to be depleted because plants start to experience water stress even before soil water is depleted down to PWP.
Therefore, a management allowed depletion  of the AWC must be specified.
Refer to fact sheet number 4.715  for values of MAD for selected crops.
Ranges of rooting depth for selected crops are given in Table 2.
The rooting depth and MAD for a crop will change with developmental stage.
The MAD can be expressed in terms of depth of water  using the following equation.
where MAD is management allowed depletion , AWC is available water capacity of the root zone , and is depth of root zone.
The value of dMAD MAD can be used as a guide for deciding when to irrigate.
Typically, irrigation water should be applied when the soil water deficit  approaches , then the irrigator should not wait for D to approach dMAD' but should irrigate more frequently to ensure that D does not exceed MAD However,
 Table 2.
Irrigation management depths  in inches for selected crops.
Annual crop	Seedling	Vegetative	Flowering	Mature
 Soil depth or D  -
 Corn	12	24	30	36 to 48
 Potatoes	12	18	24	24 to 48
 Small grain	12	18	24	36 to 48
 Field beans	12	18	24	24 to 30
 Sugarbeets	12	18	24	36 to 48
 Vegetables	6 to 12	18	18	18 to 24
 Perennial crop	Seedling	Establishment	Mature
 Alfalfa	6 to 12	24 to 36	48 to 72
 Turf and lawns	6	12	12
 Grass and pasture	6	12	24
 keep in mind that more frequent irrigations increase evaporation of water from the soil surface, which is considered a loss.
In addition, when rainfall is in the forecast, the irrigator might want to leave the root zone below field capacity to allow for storage of forecasted precipitation.
Crop evapotranspiration , in inches per day, is estimated as: ET =ET,xKxK, [4]
 where ET, is the evapotranspiration rate  from a reference crop , K is a crop coefficient that varies by crop development stage , and K is a water stress coefficient.
At any given point in the growing season, the K for a crop is simply the ratio of its ET over the reference crop ET.
The K can be thought of as the fraction of the reference crop ET that is used by the actual crop.
Values of K typically range from 0.2 for young seedlings to 1.0 for crops at peak vegetative stage with canopies fully covering the ground.
In some instances, peak K might reach 1.051.10, for crops showing similar biomass characteristics as alfalfa, when the soil and canopies are wet.
A typical crop coefficient curve  is shown in Figure 1.
Crop coefficient values for commonly grown crops are given in Table 3.
If D remains less than d MAD' K may be assumed to be 1.
A K of 1 means that the crop is not experiencing water stress.
The Colorado Agricultural Meteorological Network  provides daily values of ET for common crops assuming that K = 1.
CoAgMet calculates K internally, based on planting date and weather data.
Refer to fact sheet 4.723, The Colorado Agricultural Meteorological Network  and Crop ET Reports, to obtain daily ET values at many locations around the state.
In cases when water availability is limited  rate.
The water stress coefficient is calculated by : K TAW-D [5] where TAW is total available water in the soil root zone , D is the soil water deficit , and MAD is management
 Figure 1.
Example crop coefficient curve that shows K values that change with crop development.
allowed depletion.
The value of TAW can be calculated from: TAW=AWC*D [6]
 where AWC is available water capacity of the root zone  and is the total depth of the root zone rz.
In equation 5, MAD is specifically defined as the fraction of AWC that a crop can extract from the root zone without suffering water stress.
Note that K should be set equal to one when D is less than dMAD The ET obtained from CoAgM should be multiplied by K calculated from equation 5 to get an "actual"  ET value that can be used in equation 2.
An alternative to obtaining ET values from CoAgMet is to obtain onsite measurements using a field instrument called an atmometer.
This device can estimate reference crop ET at locations that don't have a CoAgMet weather station, have unusual micro-climate characteristics, or when a user doesn't have access to CoAgMet data.
An atmometer can give reasonable estimates of alfalfa reference ET
  but may underestimate ET during periods of rain or high wind.
An atmometer basically consists of a wet, porous ceramic cup mounted on top of a cylindrical water reservoir.
The ceramic cup is covered with a green fabric that simulates the canopy of a crop.
The reservoir is filled with distilled water that evaporates out of the ceramic cup and is pulled through a suction tube that extends to the bottom of the reservoir.
Underneath the fabric, the ceramic cup is covered by a special membrane that keeps rain water from seeping into the ceramic cup.
A rigid wire extending from the top keeps birds from perching on top of the gauge.
A site tube on the front of the instrument allows the user to observe and record the water level, similar to a rain gauge.
The ET rate for a given time period is the difference in water level between two time periods.
Atmometers are designed to simulate the water use of a well-watered reference crop, which is either alfalfa  or clipped grass  that is fully covering the ground.
In Colorado, alfalfa reference  is commonly used.
Actual ET from a specific crop can be estimated using equation 4, following a similar procedure described in the previous section.
The atmometer provides an estimate of ET, which must be multiplied by the appropriate K and K  values to obtain ET.
Crop coefficients for commonly grown crops are provided in Table 3.
For most non-water-stressed forage and grain crops at full canopy, water loss from an
 Table 3.
Representative crop coefficients  of commonly grown crops for use with alfalfa reference ET.
Days from planting	green-up	or	Corn	Beans	Dry	Potatoes	Winter	Wheat	Transplant	onions	Grains	Sugar	Beets	Alfalfa	Pasture
 5	0.25	0.23	0.22	0.30	0.38	0.20	0.19	0.25	0.33
 10	0.25	0.30	0.21	0.33	0.38	0.25	0.20	0.43	0.33
 15	0.26	0.33	0.26	0.44	0.39	0.32	0.20	0.61	0.45
 20	0.27	0.44	0.33	0.52	0.40	0.40	0.21	0.82	0.56
 25	0.27	0.57	0.40	0.65	0.42	0.50	0.22	1.00	0.68
 30	0.29	0.71	0.50	0.74	0.43	0.60	0.27	1.00	0.79
 35	0.35	0,89	0,59	0.82	0.45	0.69	0.30	1.00	0.79
 40	0.41	1.00	0.70	0.89	0.46	0.78	0.33	1.00	0.79
 45	0.49	1.00	0.73	0.95	0.47	0.88	0.36	1.00	0.79
 50	0.58	1.00	0.81	1.00	0.48	0.96	0.38	1.00	0.79
 55	0.67	1.00	0.87	1.00	0.50	1.00	0.43	1.00	0.79
 60	0.73	1.00	0.94	1.00	0.52	1.00	0.50	0.33*	0.79
 65	0.78	1.00	0.95	1.00	0,56	1.00	0.55	0.45
 70	0.86	1.00	0.95	1.00	0.59	1.00	0.60	0.77
 75	0.91	0.92	0.95	1.00	0.61	1.00	0.66	1.00
 80	0.94	0.85	0,95	1.00	0,65	0,93	0.77	1.00
 85	1.00	0.79	0.95	0.92	0.67	0.85	0.84	1.00
 90	1.00	0.73	0,95	0,85	0.74	0.77	0.92	1.00
 95	1.00	0.66	0,95	0.72	0.78	0,61	1.00	1.00
 100	1.00	0.59	0.95	0.58	0.81	0.45	1.00	1.00
 105	0.98	0.52	0,95	0.48	0.81	0.29	1.00	*after cutting
 110	0.96	0.45	0,95	0,35	0.81	0.23	1.00
 115	0.91	0.38	0.95	0.22	0.81	0.20	1.00
 120	0.85	0.95	0.22	0.81	0.20	1.00
 125	0.78	0.95	0.22	0.81	0.20	1.00
 130	0.69	0.95	0.22	0.81	0.20	1.00
 135	0.64	0.95	0.22	0.81	0.20	1.00
 140	0.58	0.95	0.22	0.80	0.20	0,96
 atmometer will be practically equal to actual crop ET.
detailed instructions on how to install and maintain their instrument.
The dry beans were planted on May 31, 2008 and the initial soil water was assumed
 to be at field capacity.
This meant that the soil water deficit  was zero at the start of the growing season.
This assumption was reasonable because actual precipitation from January 15 to May 30, 2008 was 2.56 inches, which was greater than AWC for the top foot of soil.
Water requirements of dry beans change throughout the season because rooting depth  and the rate of ET change as the crop develops and weather varies.
Table 4 shows the assumed management rooting depths and corresponding values of root zone AWC and MAD for different growth phases of dry beans.
Before using equation 2, an irrigator must pre-determine the depth of
Irrigation Water for Greenhouses and Nurseries
 James A.
Robbins Extension Specialist/ Professor Ornamental Horticulture
 Arkansas Is Our Campus
 Both the quality and quantity of water are critical to the successful production of plants in a greenhouse or nursery.
While considered a critical parameter, water issues are frequently overlooked by most growers.
Parameters deemed suitable for drinking water purposes are not necessarily acceptable for growing plants.
Appropriate tests should be conducted prior to selecting a greenhouse or nursery site.
Water quality properties can be divided into three categories: physical, biological and chemical.
Critical physical properties include suspended solids and temperature.
Suspended solids such as soil particles are potential problems since these particulates can clog irrigation nozzles and cause abrasion of irrigation equipment.
Water temperature can be an important consideration, particularly when growing foliage plants where high or low temperature water can cause leaf spotting that reduces the value of these plants.
Important biological properties include algae, microbes and disease organisms.
Algae and microbes are a concern since they may cause clogging of irrigation system components.
Chemical properties are typically given the most focus when dealing with irrigation water.
From the grower's standpoint, the most critical
 chemical water quality parameters are soluble salts, hardness, sodium and chloride concentration and pH.
In a few cases, elements such as iron, boron and fluoride are also considered critical parameters.
Chemical properties, like physical and biological, may change significantly during a year, particularly as the demand increases on a ground well and the water table is lowered.
Table 1 includes general guidelines for irrigation water used in plant production.
A more detailed discussion on several of these parameters is required.
In general terms, pH is a measure of the hydrogen ion concentration.
The pH can vary on a scale from 0-14 with a pH of 7 being neutral, less than 7 considered acid and above 7 called basic or alkaline.
Irrigation water with a pH of 4 might be termed very acid and water with a pH of 8.5 very alkaline.
The pH is an important parameter to know since it will influence the relative solubility of certain nutrients and can impact the solubility of certain chemicals or pesticides used in grower operations.
The pH of irrigation water is not generally as critical a measurement as the pH of the media.
While the term pH is often used interchangeably with alkalinity, these are two totally different parameters.
Table 1.
General Guidelines for Irrigation Water Used in Plant Production
 Parameter*	Units	Upper Limit	Optimum Range
 EC	umho/cm ****	750 plugs; 1,250 greenhouse;	0-300
 TDS**	ppm	480 plugs; 800 greenhouse; 960 nursery	0-192
 	
 pH	---	possibly 8.0 upper; 4.5 lower	5.2-6.8
 Alkalinity	ppm CaCO	200 	0-60 plugs
 	0-100 greenhouse
 Bicarbonate 	ppm	150	30-50
 ***	meq/l	2.4	0.5-0.8
 Hardness	ppm CaCO	200	20-150
 Na 	ppm	50 	0-30
 SAR	---	4 greenhouse; 6 nursery	0-3
 Ca 	ppm	120	40-100
 Mg 	ppm	50	5-25
 Nitrate-N 	ppm	50	0-10
 P	ppm	5	0-1
 K 	ppm	10	1-10
 Sulfate 	ppm	240	25-200
 SO4	meq/l	5	0.5-4.2
 Fe	ppm	5 	1-3
 Mn	ppm	1	0.2-1
 B	ppm	2	0.2-0.5
 CI 	ppm	140	1-50
 F	ppm	1	0-1
 Al	ppm	5	0-5
 Mo	ppm	0.07	0-0.05
 Zn	ppm	2	0-0.2
 Cu	ppm	0.2	0.05-0.15
 * Play the charge balance game.
Express the concentrations of the four major cations  and the four major anions  in meq/l.
Add the cations up, then add the anions up.
The cation total should be very close to the anion total if the analysis is correct.
While pH is a measure of the hydrogen ion concentration, alkalinity is a relative measurement of the capacity of water to resist a change in pH or the ability of the water to change the pH of the growing media.
You may wish to think of alkalinity as the buffering capacity of the water how well it resists or causes a change in pH.
It is not uncommon to have irrigation water with a pH of 7.5  but with a low alkalinity value that is quite acceptable for growing plants.
Alkalinity is a measure of the total carbonates , bicarbonates  and hydroxyl ions.
Alkalinity increases as the amount of dissolved carbonates and bicarbonates rises.
Irrigation water with high alkalinity  will tend to raise the pH of the growing media over time and will require more acid to lower the pH of the water to an acceptable level should a grower wish to do that.
Water with a high alkalinity  will require that a grower consider using acid-type soluble fertilizers rather than calcium-based fertilizers.
Acid injection is commonly used to manage water with high alkalinity.
Notice that the term alkaline  is entirely different from the term alkalinity.
The term hardness refers to the combined concentration of Ca and Mg in the water.
Hardness can be used as an indicator of alkalinity.
"Hard" water, water with a high concentration of Ca and Mg, should be checked for high alkalinity.
Hard water is a potential problem since the calcium and magnesium can combine with bicarbonate to form insoluble calcium and magnesium carbonate salts.
These salts can impact media pH and reduce the amount of sodium available to a plant.
Irrigation water, particularly if the source is from groundwater, usually contains some amount of dissolved salts.
Some of these dissolved salts, particularly sodium, chloride, boron, fluoride and iron, are of greater concern to growers than others.
Soluble salts are a concern in that they are either directly toxic to the plant, impede the uptake of water by the roots or cause foliar spotting that lowers the overall value of the plants.
Water high in soluble salts may be referred to as saline.
Total soluble salts are easily measured by monitoring the electrical conductivity  of the solution.
Note that soluble salts may disassociate in water to form charged ions.
If the ion
 carries a positive charge , it is called a cation; if it carries a negative charge , it is called an anion.
The most common cations of interest in water are calcium , magnesium  and sodium ; the most common anions are bicarbonate , chloride  and sulfate.
An electrical conductivity meter simply measures the total relative amount of either the dissolved anions or the dissolved cations.
Pure water, with few or no dissolved salts, would be a poor conductor of electrons so the electrical conductivity value would be very low or approaching zero.
Interestingly enough, urea when dissolved in water to make a fertilizer solution does not disassociate so it cannot be monitored adequately using an EC meter.
Electrical conductivity measurements DO NOT indicate the relative amounts of any specific salt or ion.
Additional specific tests typically run by outside laboratories must determine concentrations of specific ions.
Units most frequently used when reporting concentrations of ions are ppm or mg/l; however, they are sometimes reported in units of meq/l.
The units meq/l can be calculated from the ppm by dividing the ppm by the equivalent weight  of the respective ion.
For example, with sodium, the EW is 23.
If the concentration of sodium was 100 ppm, the concentration expressed in meq/l would be 4.3.
Na : High sodium is a concern to growers since it can contribute to salinity problems, interfere with magnesium and calcium availability in the media and cause foliar burns.
Sodium and chloride problems are observed when irrigation water is run through a water softener that is using sodium chloride to "soften" or exchange the calcium and magnesium in the water.
"Softened" water is generally not recommended for greenhouse or nursery irrigation purposes.
Cl (chlorine is the element; chloride is the ion,
 Cl-): Elevated chloride is often associated with an elevated sodium concentration.
Chloride, like sodium, can be directly toxic to the plant.
Water is generally not a major source for chloride problems; however, certain fertilizer salts  can be.
Fe : Elevated iron levels generally cause aesthetic problems on plants and greenhouse structures, but high levels can also cause an accumulation on irrigation equipment that leads to plugged emitters.
Levels that cause this discoloration are generally below the levels that cause toxicities in plant tissue.
B : Like sodium and chloride, boron can sometimes be found in high concentrations which are toxic to plants.
High boron levels are commonly associated with alkaline soil formations in areas of low rainfall and are, therefore, frequently found in many western states.
Like other nutrients, crop sensitivity to boron varies so certain species may be susceptible to damage at a concentration of 0.5 ppm while others tolerate levels up to 4 ppm.
Plant age also influences susceptibility or degree of problem.
Seedlings will generally be more susceptible than mature plants of the same species.
Management strategies to minimize boron problems when the water source is high include eliminating boron from the fertilizer sources, increasing the leaching fraction, increasing the media pH and increasing the calcium level.
F (fluorine is the element; fluoride is the ion,
 F-): Several important floriculture crops including Easter lilies, freesias, spider plant , Maranta and Dracaena are known to be extremely sensitive to even low levels of fluoride in irrigation water.
Fluorine is not considered an essential element for plants, but it can be a concern for greenhouse growers since it is routinely added to drinking water to prevent tooth decay.
A fluoride analysis is highly recommended if the greenhouse water is provided by a city water source that is fluoridated.
Zn  or Cu : Problems associated with Zn or Cu toxicities are generally not associated with water systems; however, in a few cases acid water transported through galvanized or copper pipes may result in toxic levels of these elements in the irrigation water.
These elements are a concern if using an acid growing media.
Sodium Adsorption Ration or SAR
 It has already been suggested that sodium concentrations need to be evaluated in terms of the amounts of calcium and magnesium because of the close potential interaction of the three nutrients.
To quantify this relationship, the sodium adsorption ratio  is calculated.
Generally, the higher the SAR value, the greater the potential for problems.
The type of irrigation method also needs to be considered.
High SAR water applied using an overhead irrigation system in a climate with low humidity  can cause leaf injury.
The same water applied using surface or drip irrigation may not be a problem.
Some laboratories provide results as an "Adjusted SAR." This value is more difficult to calculate and requires special tables and knowledge of the carbonate and bicarbonate concentrations.
An adjusted SAR has the advantage in that it takes into account the tendency of high bicarbonate/carbonate
 water to precipitate calcium into calcium carbonate, which reduces the calcium content and increases the potential for a sodium problem.
While certain parameters can be tested adequately by a grower, most choose to send water samples out for laboratory analyses.
Those parameters that can be tested easily and inexpensively by growers in-house include pH, alkalinity and total soluble salts.
pH can be measured by a grower using an inexpensive pH meter or "pen" or by using indicator test strips.
Alkalinity can be measured using test kits available from some grower supply firms or swimming pool supply companies.
These test kits usually rely on adding a color indicator to the water sample and then adding acid dropwise to reach a final color that translates into a specific alkalinity value.
Soluble salts are easily measured using an inexpensive electrical conductivity meter with automatic temperature compensation.
Several laboratories, including one affiliated with the University of Arkansas System Division of Agriculture Cooperative Extension Service, are capable of analyzing water samples.
Most laboratories will offer a flat fee for a standard package of tests , or they will offer a cafeteria plan for you to pick and choose specific tests.
It is critical that you indicate you are submitting an irrigation water sample rather than a domestic drinking water sample.
It is best to collect the water sample in a clean plastic bottle.
Collect the specified volume after running the tap for a few minutes.
It is suggested that you fill the bottle to the top to avoid any room for air.
If a nitrate analysis is required, the sample should be shipped to the laboratory quickly or significant changes in concentration can occur over time.
An example University of Arkansas Irrigation Water Report can be found on page 6.
Working with water quality issues is technical in nature and may require addition of expensive equipment or chemical treatment of the water.
Before developing a major water treatment system for your growing operation, you are encouraged to contact your local Cooperative Extension agent for guidance.
Scenario: Water with an alkaline pH and high alkalinity
 This scenario is corrected by using the appropriate acid and usually an acid injector.
Phosphoric acid is used more frequently than sulfuric acid or nitric acid since it is considered safer; however, handling any of these concentrated acids is to be considered dangerous.
Strict safety guidelines must be followed.
Nitric and sulfuric acids should be considered when the alkalinity is high  since phosphoric acid might supply excessive amounts of the nutrient phosphorus.
Acid injection is usually considered when the alkalinity is over 100 ppm.
Tables are available that calculate the amount of a specific acid required based on the starting pH, the amount of alkalinity, the amount of change in pH required and type of acid used.
An online "Alkalinity Calculator"  is available through the University of New Hampshire.
The amount of acid required to neutralize the alkalinity of water can also be determined from the following equation.
AxB x C = the ounces of acid/1,000 gallons of water to lower the pH to 6.4
 A is a cofactor determined by the current or starting pH:
 Water pH	A	Water pH	A
 6.7	0.249	7.7	0.475
 6.9	0.342	7.9	0.484
 7.1	0.4	8.1	0.49
 7.3	0.437	8.3	0.494
 7.5	0.46	8.5	0.496
 B is the sum of the bicarbonate and carbonate expressed in meq/l.
C is a cofactor determined by the type of acid used.
Starting pH of the water = 7.5 carbonate + bicarbonate = 3.4 meq/l using 75% phosphoric acid
 0.460 X 3.4 X 10.6 = add 16.5 ounces of 75% phosphoric acid/1,000 gallons of water
 Scenario: Water with a high EC
 There are probably two common approaches to dealing with saline water.
The first remedy is to simply blend the higher EC source with water from a lower EC source, usually a surface retention pond.
The other approach involves careful management of the irrigation volume being applied.
While the ideal scenario is to minimize leaching to avoid wasting fertilizer and water, increasing what is called the leaching fraction  can improve the usability of high EC water.
Leaching fraction is simply the volume of water leached divided by the volume of water applied and that result multiplied by 100.
Here is a simple example.
A general rule of thumb is that if the EC of the irrigation water is >2,000 umho/cm, it would require a leaching fraction of 40 percent or higher.
If the EC of your irrigation source is 1,000 umho/cm, you can leach with a smaller volume or percentage.
A grower faced with high EC water would also not want to let pots dry out.
Simply stated, the concentration of salts will increase around roots as the media dries out.
Growers would also want to use fertilizer products with a lower salt index if possible.
The final resolution is expensive and rarely used.
Growers can install expensive reverse osmosis or deionization equipment to reduce the soluble salt concentration in their water source.
Scenario: Water with high concentration of suspended solids
 Filtration is the standard method for removing suspended solids.
You may wish to work with an irrigation supplier or engineer so the appropriate equipment is selected and positioned within your irrigation system.
A general rule of thumb used by irrigation designers suggests that a minimum of 1 acre-inch  of water capacity is required per acre of nursery stock per day of irrigation.
Assuming a grower might irrigate for 180 days during a year in Arkansas, it would require 4.86 million gallons of water per acre of container stock per year.
Another common recommendation suggests an estimated
 annual use of 13 acre-feet of water per acre of container nursery stock.
Greenhouse operations also use an impressive amount of water.
One rule of thumb is a requirement for 1-2 quarts per square foot of growing area per day.
One acre of growing space would require approximately 11,000-22,000 gallons of water per day.
This does not include water requirements for evaporative cooling systems or other non-crop uses.
Example of University of Arkansas Irrigation Water Report
 Arkansas Cooperative Extension Service in a Cooperative Effort with Arkansas Water Resources Center Water Quality Laboratory
 DRIP OR TRICKLE IRRIGATION WATER REPORT FORM
 Cooperative Extension Service  671-2000
 Name : Joe Extension Address : 9999 University Road City : Fayetteville County : Washington
 Date : 04/09/18 State : AR Zip : 72701 Date Received : 04/01/18
 Lab #: 999901 Sample ID:
 Fe, Total	0.68 mg/l
 HCO	3	2.20 meq/l
 NO3-N 	0.00 mg/l
 NO3 	0.00 mg/l
 Hardness, Total	82.20 mg/l as CaCO
 Suspended Solids, Total	1.70 mg/l
 Acknowledgment is given to DR.
GERALD L.
KLINGAMAN, former Extension horticulture specialist ornamentals, as an original co-author of this fact sheet.
Printed by University of Arkansas Cooperative Extension Service Printing Services.
DR.
JAMES A.
ROBBINS is Extension specialist/professor ornamental horticulture with the University of Arkansas System Division of Agriculture in Little Rock.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Director, Cooperative Extension Service, University of Arkansas.
The University of Arkansas System Division of Agriculture offers all its Extension and Research programs and services without regard to race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
Example Calculations of Late Season Crop Water Need:
 1.
Determine the amount of water needed by the plants based on growth stage as shown in Table 1.
2.
Determine the date plants will reach maturity.
3.
Determine the amount of expected rainfall.
4.
Calculate the amount of required irrigation to maturity
Another objective is to create a database for growers, researchers and businesses to learn from each other with common data on crops and soils to guide research on practical issues, Qiao said.
The network is growing with interest and will eventually include growers and ag businesses outside the panhandle.
Many locations had triple digit heat during September and several records were broken.
The highest statewide temperatures were above 105F.
There were five days at or above 100F for Curtis, Scottsbluff, Chadron and Valentine, and above 95F for five or more days for much of western Nebraska.
A few scattered below freezing temperatures were observed at high elevations of the western panhandle, elsewhere the lowest temperatures were in the 30s and low 40s.
The average monthly temperature of 67.4F was 3.6F warmer than normal.
September temperatures have been trending warmer over time, gaining nearly 4F since 1991.
Chemigation Training: Chemigators who are either seeking certification for the first time or renewing their existing certification can do so through an online training program or a face-to-face training session.
There is no cost for chemigation training.
Western Ohio Cropland Values and Cash Rents 2016-17.
Ohio cropland values and cash rental rates are projected to decrease in 2017.
According to the Western Ohio Cropland Values and Cash Rents Survey, bare cropland values in western Ohio are expected to decrease from 4.4 to 8.2 percent in 2017 depending on the region and land class.
Cash rents are expected to decline from 1.4 percent to 4.2 percent depending on the region and land class.
OHIO CROPLAND VALUES AND CASH RENT
 Ohio cropland varies significantly in its production capabilities and, consequently, cropland values and cash rents vary widely throughout the state.
Generally speaking, western Ohio cropland values and cash rents differ from much of southern and eastern Ohio cropland values and cash rents.
The primary factors affecting these values and rates are land productivity and potential crop return, and the variability of those crop returns.
Soils and drainage capabilities are the two factors that most influence land productivity, crop return and variability of those crop returns.
Other factors impacting land values and cash rents are field size and shape, population density, ease of access, market access, local market prices, potential for wildlife damage, field perimeter characteristics, and competition for rented cropland in a region.
This fact sheet summarizes data collected for western Ohio cropland values and cash rents.
The Western Ohio Cropland Values and Cash Rents study was conducted from February through April in 2017.
The opinion-based study surveyed professionals with a knowledge of Ohios cropland values and rental rates.
Professionals surveyed were farm managers, rural appraisers, agricultural lenders, OSU Extension educators, farmers, landowners, and Farm Service Agency personnel.
The study results are based on 120 surveys returned, analyzed and summarized.
Respondents were asked to group their estimates based on three land quality classes: average, top and poor.
Within each land-quality class, respondents were asked to estimate average corn and soybean yields for a five-year period based on typical farming practices.
Survey respondents were also asked to estimate current bare cropland values and cash rents negotiated in the current or recent year for each land-quality class.
Survey results are summarized below for western Ohio with regional summaries  for northwest Ohio and southwest Ohio.
The measures shown in the following tables are the summary of the survey responses.
The measures shown are the average , standard deviation indicating the variability of the data from the average measure and range.
Range identified in the tables consists of two numbers: The first is the average plus the standard deviation and the second is the average minus the standard deviation.
WHY RANGE IS IMPORTANT
 Range represents the spread of land values and cash rents.
When farmers and landowners consider a parcel, its helpful to compare not only the average, but also the range measure.
The range in these tables represents two-thirds of the responses in the survey, which provides reliable data.
Also, farmers and landowners need to realize land in a given region does not fall neatly into thirds of each land-quality class.
Typically, only a small percentage of acreage in a given county or region will fall into the top land category, which is usually large tracts of land with highly productive soils.
Average land will typically be the majority of land in a given region or county while poor land will tend to have lower productivity soils, steeper slopes, poor drainage, smaller tracts, or a combination of these characteristics.
FACTORS AFFECTING CASH RENTAL RATES
 Ultimately, supply and demand of cropland for rent determines the cash rental rate for each parcel.
The expected return from producing crops on a farm parcel and the variability of that return are the primary drivers in determining the rental rates.
Many of the following factors contribute to the expected crop return and the variability of that return.
Secondary factors may exist and could affect potential rental rates.
These secondary factors are also listed.
Rent will vary based on expected crop return.
The higher the expected return, the higher the rent will tend to be.
VARIABILITY OF CROP RETURN
 Land that exhibits highly variable returns may have rents discounted for this factor.
For example, land that is poorly drained may exhibit variability of returns due to late plantings during wet springs.
FACTORS AFFECTING EXPECTED CROP RETURN AND VARIABILITY OF CROP RETURN:
 Land  Quality: Higher quality soils translate into higher rents.
Fertility Levels: Higher fertility levels often result in higher cash rents.
Drainage or Irrigation Capabilities: Better surface and sub-surface drainage of a farm often results in better yields and higher potential cash rent.
Likewise, irrigation equipment tied to the land will allow for higher yields, profits and rents.
Size of Farm/Fields: Large farms/fields typically command higher average cash rent per acre due to the efficiencies gained by operators.
Shape of Fields: Square fields with fewer point rows will generally translate into higher cash rents as operators gain efficiencies from farming fields that are square.
Previous Tillage Systems or Crops: Previous crops and tillage systems that allow for an easy transition for new operators may enhance the cash rent value.
Field Border Characteristics: Fields surrounded by tree-lined fence rows, woodlots or other borders affecting crop growth at the field edge will negatively impact yield and therefore should be considered in rental negotiations.
Wildlife Damage Potential: Fields adjacent to significant wildlife cover including woodlots, tree-lined fencerows, creeks and streams may limit production potential to border rows and should be considered in rental negotiations.
SECONDARY FACTORS AFFECTING RENTAL RATES:
 Buildings and Grain Storage Availability: Access to machinery and grain storage may enhance the value of the cropland rental rate.
Location of Farm : Proximity to prospective operators may determine how much operators are willing to bid for cash rents.
Good road access will generally enhance cash rent amounts.
USDA Farm Program Measurables: Farms that participate in the USDA Farm Program and have higher program yields may command higher cash rents than non-program farms.
Services Provided by Operator: Operators that provide services such as clearing fence rows, snow removal and other services may be valued by the landowner.
This may even be a partial substitute for cash rent compensation.
Conditions of Lease: Conditions placed on the lease by the landowner may result in fewer prospective operators and a lower average cash rent.
Payment Dates: Leases that require part or all of the rent to be paid early in the year  may result in lower rental rates due to higher borrowing or opportunity costs for the operator.
Reputation of Landowner or Operator: Reputations of the parties may play a part in the cash rental negotiations.
A landowner with a reputation of being difficult to work with may see cash rents negatively affected by this reputation.
Farmers with a similar negative reputation may have to pay higher rents.
Special Contracts: Farms with special contract commitments may restrict the operator from changing crops based on market conditions.
This may negatively impact cash rents.
There may also be contracts that positively affect cash rents such as high value crop contracts or contracts for receiving livestock manure.
The following sections of the fact sheet detail the 2017 survey results divided into western, northwest and southwest Ohio.
The western Ohio summarized data is simply the entire data set which includes both the northwest and southwest regions.
Tables 1 through 3 also detail projected changes for long-term land value and cash rents, which will be explained later in the fact sheet in the Additional Survey Results section.
Survey results from western Ohio are summarized in Table 1.
See Figure 1 for counties included in this region.
Additional results, including year-over-year percentage change, rent per bushel of corn, and rent as a percentage of land value, are summarized in Tables 4 and 5.
Figure 1: Western Ohio
 Survey results for average producing cropland showed an average yield to be 171.8 bushels of corn per acre.
Results showed that the value of average cropland in western Ohio was $7,702 per acre in 2016.
According to survey data, average producing cropland is expected to be valued at $7,327 per acre in 2017.
This is a projected decrease of 4.9 percent.
Average cropland rented for an average of $198 per acre in 2016 according to survey results.
Average cropland is expected to rent for $192 per acre in 2017 which amounts to a 3.0 percent decrease in cash rent year-over-year.
This 2017 rental rate projection of $192 per acre equates to a cash rent of $1.12 per bushel of corn produced.
Rents in the average cropland category are expected to equal 2.6 percent of land value in 2017.
Survey results indicate top performing cropland in western Ohio averaged 203.2 bushels of corn produced per acre and the average value of top cropland in 2016 was $9,143 per acre.
According to this survey, top cropland in western Ohio is expected to be valued at $8,675 per acre in 2017.
This is a projected decrease of 5.1 percent.
Top cropland in western Ohio rented for an average of $250 per acre in 2016 according to survey results.
Top cropland is expected to rent for $240 per acre in 2017  which equates to a cash rent of $1.18 per bushel of corn produced.
Rents in the top cropland category are expected to equal 2.8 percent of land value in 2017.
The survey summary showed the average yield for poor performing cropland to be 139.7 bushels of corn per acre, with the average value of poor cropland as $6,191 per acre in 2016.
According to survey data, this poor producing cropland is expected to be valued at $5,698 per acre in 2017.
This is a decrease of 8.0 percent.
Poor cropland rented for an average of $154 per acre in 2016 according to survey results.
Cash rent for poor cropland is expected to average $150 per acre in 2017 which amounts to a 2.3 percent decrease in cash rent year-over-year.
This 2017 rent projection of $150 per acre equates to a cash rent of $1.07 per bushel of corn produced in 2017.
Rents in the poor cropland category are expected to equal 2.6 percent of land value in 2017.
Survey results from northwest Ohio are summarized in Table 2.
See Figure 2 for counties included in this region.
Additional results, including year-over-year percentage change, rent per bushel of corn, and rent as a percentage of land value, are summarized in Tables 4 and 5.
Figure 2: Northwest Ohio
 Yields for average producing cropland averaged 164.9 bushels of corn per acre or 51.4 bushels of soybeans per acre.
Results showed the value of average cropland in northwest Ohio was $6,834 per acre in 2016.
According to survey data, this average producing cropland is expected to be valued at $6,480 per acre in 2017.
This is a projected decrease of 5.2 percent.
Average cropland rented for an average of $180 per acre in 2016 according to survey results and is expected to rent for $177 per acre in 2017, which is a year-over-year decrease of 1.4 percent.
The 2017 rental rate of $177 per acre equaled $1.07 per bushel of corn produced.
Rents in the average cropland category are expected to equal 2.7 percent of land value in 2017.
Survey results indicated top performing cropland in northwest Ohio averaged 197.2 bushels of corn per acre or 60.9 bushels of soybeans per acre.
Results also show the average value of top cropland was $8,357 per acre in 2016.
According to this survey, top producing cropland in northwest Ohio is expected to be valued at $8,023 in 2017.
This is a projected decrease of 4.0 percent.
Top cropland in northwest Ohio rented for an average of $228 per acre in 2016 and is expected to rent for $223 per acre in 2017  according to survey results, which equals $1.13 per bushel of corn produced.
Rents in the top cropland category are expected to equal 2.8 percent of land value.
The survey summary showed the average yield for poor performing cropland in northwestern Ohio equaled 136.0 bushels of corn per acre or 40.5 bushels of soybeans per acre.
Results also show the average value of poor cropland was $5,253 per acre in 2016 and is expected to average $4,821 per acre in 2017.
This is a projected decrease of 8.2 percent.
Poor cropland rented for an average of $139 per acre in 2016 and is expected to average $137 per acre in 2017 according to survey results  which equals $1.01 per bushel of corn produced.
Rents in the poor cropland category are expected to equal 2.8 percent of land value in 2017.
The northwest region for the purposes of this survey includes: Williams, Fulton, Lucas, Ottawa, Defiance, Henry, Wood, Sandusky, Paulding, Putnam, Hancock, Seneca, Van Wert, Allen, Hardin, Wyandot, Crawford, Marion, and Morrow counties and parts of Richland, Huron and Erie Counties, as shown in Figure 2.
Counties bordering this region to the south will also contain land parcels with cropland value and rental rate characteristics similar to northwest Ohio data.
Survey results from southwest Ohio are summarized in Table 3.
See Figure 3 for counties included in this region.
Additional results, including year-over-year percentage change, rent per bushel of corn, and rent as a percent of land value, are summarized in Tables 4 and 5.
Figure 3: Southwest Ohio
 Yields for average cropland were 177.2 bushels of corn per acre or 55.3 bushels per acre of soybeans according to the survey data.
Results showed the value of average cropland in southwest Ohio was $8,512 per acre in 2016.
According to survey data, average producing cropland is expected to be valued at $8,134 per acre in 2017.
This is a projected decrease of 4.4 percent.
Average cropland rented for an average of $212 per acre in 2016 and is expected to rent for $203 per acre in 2017 according to survey results  which equals $1.15 per bushel of corn produced.
Rents in the average cropland category are expected to equal 2.5 percent of land value in 2017.
Survey results indicate top performing cropland in southwest Ohio averaged 208.4 bushels of corn per acre or 67.4 bushels of soybeans per acre.
Results also showed that the average value of top cropland was $10,036 per acre in 2016.
According to this survey, top producing cropland in southwest Ohio is expected to be valued on average at $9,435 per acre in 2017.
This is a projected decrease of 6.0 percent.
Top cropland in southwest Ohio rented for an average of $268 per acre in 2016 and is expected to rent for $255 per acre in 2017 according to survey results which is a year-over-year decrease of 5.1 percent.
The 2017 rental rate of $255 per acre equaled $1.22 per bushel of corn produced.
Rents in the top cropland category are expected to equal 2.7 percent of land value in 2017.
The survey summary shows the average yield for poor cropland in southwestern Ohio was 143.4 bushels of corn per acre or 42.7 bushels of soybeans per acre.
Results also showed that the average value of poor cropland was $7,255 per acre in 2016.
According to survey data, poor producing cropland is expected to be valued at $6,721 per acre in 2017.
This is a decrease of 7.4 percent.
Poor cropland rented for an average of $168 per acre in 2016 and is expected to average $163 per acre in 2017 according to survey results  which equals $1.14 per bushel of corn produced.
Rents in the poor cropland category are expected to equal 2.4 percent of land value in 2017.
The southwest region for the purposes of this survey includes: Mercer, Auglaize, Shelby, Logan, Union, Delaware, Darke, Miami, Champaign, Clark, Madison, Franklin, Preble, Montgomery, Greene, Clinton, Fayette and Pickaway counties and parts of Butler, Warren, Brown, Highland and Ross counties as shown in Figure 3.
Counties bordering this region to the north will also contain land parcels with cropland value and rental rate characteristics similar to southwest Ohio data.
For the entire survey area , survey respondents estimated the average value of transition land, or land being held for sale for residential, commercial or industrial uses, to be $13,924 in 2016, and is expected to be $14,932 in 2017.
It should be noted that there is a very wide range in this survey data.
PROJECTED ESTIMATES OF LAND VALUES AND CASH RENTS
 Survey respondents were asked to give their best estimates for long-term land value and cash rent change.
The average estimate of cropland value change in the next five years for western Ohio  is a decrease of 6.02 percent.
Responses for the five-year cropland value change ranged from an increase of 10 percent to a decrease of 30 percent.
The average estimate of cash rent change in the next five years is a decrease of 5.16 percent.
The cash rent change also had a large range, with responses ranging from an increase of 20 percent to a decrease of 30 percent.
These estimates are summarized in Table 1 for the entire survey area and in Tables 2 and 3 for the survey sub-regions.
Survey respondents were asked to estimate interest rates for 2017 for two borrowing terms: 20 year fixed-rate mortgage and operating loan.
The average estimate, according to survey respondents, of 20 year fixed-rate mortgage borrowing is 5.51 percent for 2017.
According to the same respondents, the average estimate of operating loan interest rates is 4.69 percent for 2017.
PASTURE LAND VALUE AND RENTAL RATES
 According to the survey, pasture cash rents are projected to average $112 per acre in western Ohio in 2017, while the average value of pasture land is expected to average $5,227 per acre.
The summary of these responses is presented in Tables 1 through 3 and includes:
 Five year projected percent change in cropland value
 Five year projected percent change in cash rent
 Mortgage interest rate20 year fixedprojected 2017
 Operating loan rateprojected 2017
 Pasture cash rentprojected 2017, improved, non-rotation
 Pasture land valueprojected 2017, improved, non-rotation
Pivots are long machines making it impossible to always see if someone is working on it.
So always lock the disconnect in the OFF position when servicing the machine to prevent another person from turning it back ON and injuring or killing you.
Classification of Irrigation Water Quality
 Hailin Zhang Director, Soil, Water and Forage Analytical Lab
 All irrigation waters contain some dissolved salts.
Dissolved salts are present because some chemical elements have a strong attraction for water and a relatively weak attraction for other elements.
Two such chemical elements, for example, are sodium and chloride.
The amounts of these elements contained in water must be very high before sodium will combine with chloride to form the solid material sodium chloride, common table salt.
The total amount and kinds of salts determine the suitability of the water for irrigation use.
Water from some sources may contain so much salt that it is unsuitable for irrigation because of potential danger to the soil or crops.
Irrigation water quality can best be determined by chemical laboratory analysis.
The Oklahoma State University Soil, Water and Forage Analytical Laboratory has developed chemical procedures for determining water quality.
Test results, their interpretation, and a general recommendation on suitability of the water for irrigation use are reported.
Measurements of Water Quality
 The two most important measures for determining irrigation water quality are:
 1.
The total amount of dissolved salts in the water.
2.
The amount of sodium  in the water compared to calcium  plus magnesium.
The total dissolved salt content is estimated by measuring how well the water conducts electricity.
Salty water is a good conductor of electricity.
Electrical Conductivity  is measured in units of micromhos/cm.
The ppm salt concentration of the water is estimated by multiplying 0.66
 times the EC value.
For example, water having an electrical conductivity of 1000 micromhos/cm would contain about 660 ppm salt.
Other analytical procedures are used to measure the amounts of individual chemicals, such as sodium, in the water.
The list of chemicals  routinely measured to determine irrigation water quality follow:
 Electrical Conductivity  Chloride  Sodium  Nitrate  Calcium  Carbonate  Magnesium  Bicarbonate  Sulfate (SO4
 Classification of Water Quality
 The most damaging effects of poor-quality irrigation water are excessive accumulation of soluble salts and/or sodium in soil.
High soluble salts in the soil make soil moisture more difficult for plants to extract, and crops become water stressed even when the soil is moist.
When excessive sodium accumulates in the soil, it causes clay and humus particles to float into and plug up large soil pores.
This plugging action reduces water movement into and through the soil, thus crop roots do not get enough water even though water may be standing on the soil surface.
These two aspects of irrigation water  are grouped in relation to the levels present and their effects on crops and soils.
This classification system is based on research conducted in Oklahoma, other states,
 Figure 1.
Diagram for classifying irrigation water in Oklahoma.
and by the USDA Salinity Laboratory at Riverside, California.
The diagram in Figure 1 illustrates the classification system.
Since the degree to which sodium is damaging to soil is strongly influenced by the amounts of calcium and magnesium present, the sodium adsorption ration  is also used.
Figure 1 is used by taking the percent sodium reported on the water test and locating that value on the left side of the figure.
Draw a line across the figure at this point.
Next, find the value for the electrical conductivity along the bottom of the figure and at that point draw a line straight up and down.
The water class is indicated where the two lines cross.
Interpretation of Water Classes
 Oklahoma irrigation waters are grouped into six classes on the basis of soluble salt content and sodium percentage.
Interpretation of these classes in relation to their use follows:
 Class 1.
Excellent.
The total soluble salt content and sodium percentage of this water are low enough that no problems should result from its use.
Class 2.
Good.
This water is suitable for use on most crops under most conditions.
Extensive use of Class 2 water on clay soils where little or no leaching occurs may eventually cause a saline or sodic soil problem.
Normal rainfall will usually dilute the soluble salts and eliminate the risk of salt accumulation.
If the water's sodium percentage is high , gypsum can be used periodically to remedy the problem.
Class 3.
Fair.
This water can be used successfully for most crops if care is taken to prevent accumulation of soluble salts including sodium, in the soil.
Good soil management and irrigation practices must be followed.
Class 3 water can be used with little danger on permeable, well-drained soils.
The water table should be at least 10 feet below the surface to allow accumulated salts to be leached below the root zone by adequate irrigation when rainfall is limited.
Class 4.
Poor.
Use of this water is restricted to welldrained permeable soils for production of salt tolerant crops.
Irrigation practices must receive careful attention to avoid salt accumulation.
Excess water must be applied when rainfall is not adequate to cause periodic salt leaching.
Good soil management practices must be used to maintain good physical condition of the soil.
Soil fertility levels must be maintained at adequate levels.
Use of this water on medium textured soils may cause soil salinity problems if good practices are not followed.
This water is not recommended for use on fine textured soils.
Class 5.
Very Poor.
Use of this water is restricted to irrigation of sandy, well-drained soils in areas of the state which receive at least 30 inches of rainfall.
This water should not be used without advice from a trained in irrigation water use.
Class 6.
Unsuitable.
Water of this quality is not recommended for crop irrigation.
Modification of Water Quality Class
 The diagram of Figure 1 uses the primary criteria for classifying irrigation water, however, other components of the water which are less commonly a problem must sometimes be considered.
Residual Sodium Carbonate.
When total carbonate levels exceed the total amount of calcium and magnesium, the water quality may be diminished.
When the excess carbonate  concentration becomes too high, the carbonates
 combine with calcium and magnesium to form a solid material  which settles out of the water.
The end result is an increase in both the sodium percentage and SAR.
The USDA has established guidelines  for modifying water quality classifications based on residual sodium carbonate  expressed in units of milliequivalent.
Residual carbonate levels less than 1.25 meq are considered safe.
Waters with RSC of 1.25-2.50 meq are within the marginal range.
These waters should be used with good irrigation management techniques and soil salinity monitored by laboratory analysis.
Risk is lowest with waters for which the RSC is at the low end of the range and which are being applied to permeable, well-drained, coarse-textured soils in high rainfall areas.
RSC values of 2.50 meq or greater are considered too high making the water unsuitable for irrigation use.
Modification of RSC by soil applied gypsum may permit use of waters with RSC values above the safe level.
Boron.
Boron is present in water as boric acid and in this form may be toxic to plants even at very low concentrations.
Plant species differ in their tolerance to boron as identified in Table 1.
Classification of irrigation water in relation to its boron content and crop tolerance is shown in Table 2.
Boron toxicity is not common in Oklahoma although boron is routinely analyzed in our irrigation water test.
Conditional Use of Low Quality Water
 Water of undesirable quality may be used successfully when the undesirable aspects of the water are off-set by certain desirable aspects of the water or positive conditions of its use.
These aspects include the following:
 1.
Gypsum content of the water and/or soil
 4.
Water table level
 5.
Type of crop
 Gypsum.
When water contains high concentrations of calcium and sulfate, some of these two chemicals will combine in the soil and form gypsum.
Therefore, the harmful soluble salts left in the soil will be reduced somewhat, and there will be less risk in using this water.
Water which is high in gypsum can be used on clay textured soils.
Table 1.
Plant Tolerances to Boron.
Pecan	Sunflower	Sugar beet
 Black Walnut	Cotton	Garden beet
 Navy Bean	Radish	Alfalfa
 Pear	Field Pea	Onion
 Table 2.
Classification of Irrigated Water Based on Boron Concentration In Relation to Plant Tolerance
 Classification	Sensitive	Semi-Tolerant	Tolerant
 Excellent	< 0.3	< 0.6	< 1.0
 Good	0.4-0.6	0.7-1.3	1.0-2.0
 Fair	0.7-1.0	1.4-2.0	2.1-3.0
 Poor	1.1-1.3	2.1-2.5	3.1-3.8
 Unsuitable	> 1.3	> 2.5	> 3.8
 Irrigation water which has a high sodium hazard  may be used if the soil contains gypsum or if gypsum can be added to the soil.
The amounts of gypsum required will depend on the excess sodium or residual carbonate in the water and how much water is applied.
The amount of gypsum needed to off-set residual sodium carbonate in an acre-foot of water can be calculated using the formula:
 lbs gypsum per acre = 232 lbs X RSC
 The value of RSC, given in meq, is reported on the irrigation water analysis report.
For example, if 24 inches  of water is applied during the growing season and the water has a RSC level of 2 meq, the gypsum required per acre-foot of water would be:
 232 lbs X 2 = 464 lbs gypsum per acre.
For the 2 acre-feet of water applied, twice as much would be needed.
464 lbs gypsum per acre-foot X 2 acre-feet = 928 lbs gypsumper acre.
The gypsum could be added every four years at the rate of two ton per acre.
Many soils and waters in western Oklahoma contain native gypsum.
Water which is of low quality because it contains excess residual sodium carbonate or excess sodium may be used on these soils with less risk.
Water high in total salts, however, has more risk and should not be used on these soils.
Soil Characteristics.
Sandy textured soils are less likely to accumulate salts or sodium and generally more water can be applied to them than fine textured soils.
Because of this, there is less hazard in irrigating coarse textured soils with low quality water.
Also, salts and sodium can be leached much easier from coarse textured soils if that becomes necessary.
Water Table.
It is extremely important that the water table be at least 10 feet below the surface when low quality water is used.
This allows water movement below the root zone if leaching becomes necessary and it eliminates movement of salts from the water table to the soil surface.
Effective Rainfall.
The risks of using low quality water are lessened as effective rainfall increases.
Rain dilutes the salt and sodium in the soil.
Therefore, areas which normally receive more than 30 inches of rain have less risk in using low quality water than areas receiving less rain.
Type of Crop.
Crops vary in their tolerance to salts as reported in Fact Sheet 2226.
Low quality water may be used on tolerant crops after they are established.
Using low quality water during germination and seedling development should be avoided, however, since most plants are very sensitive to salts at this stage of growth.
The Oklahoma Extension Service offers an irrigation water test through a County Extension Office, about one pint of water in a clean container is required.
A small fee is charged to cover testing costs.
Testing and reporting the results generally takes about three to five working days.
A brief interpretation is provided on the report.
More detailed interpretation can be found from an online interactive program at: soiltesting.okstate.
edu/water-test-interpretation-program.
The Oklahoma Cooperative Extension Service Bringing the University to You!
The Cooperative Extension Service is the largest, most successful informal educational organization in the world.
It is a nationwide system funded and guided by a partnership of federal, state, and local governments that delivers information to help people help themselves through the land-grant university system.
Extension carries out programs in the broad categories of agriculture, natural resources and environment; family and consumer sciences; 4-H and other youth; and community resource development.
Extension staff members live and work among the people they serve to help stimulate and educate Americans to plan ahead and cope with their problems.
Some characteristics of the Cooperative Extension system are:
 The federal, state, and local governments cooperatively share in its financial support and program direction.
It is administered by the land-grant university as designated by the state legislature through an Extension director.
Extension programs are nonpolitical, objective, and research-based information.
It provides practical, problem-oriented education for people of all ages.
It is designated to take the knowledge of the university to those persons who do not or cannot participate in the formal classroom instruction of the university.
It utilizes research from university, government, and other sources to help people make their own decisions.
More than a million volunteers help multiply the impact of the Extension professional staff.
It dispenses no funds to the public.
It is not a regulatory agency, but it does inform people of regulations and of their options in meeting them.
Local programs are developed and carried out in full recognition of national problems and goals.
The Extension staff educates people through personal contacts, meetings, demonstrations, and the mass media.
Extension has the built-in flexibility to adjust its programs and subject matter to meet new needs.
Activities shift from year to year as citizen groups and Extension workers close to the problems advise changes.
The difference in cost between the two scenarios is $14.61 per acre.
With 130 acres irrigated the total annual savings from using sensors would equal $1,899.30.
From this total we would have to subtract the cost of the sensors.
A typical range for sensor prices is as low as $175 for systems with NRD cost share up to $1,500 per year for subscription based services.
Therefore, the net savings from using sensors for a 130 acre center pivot could range from $400 to $1,700 per year.
CROP PRODUCTION COMPARISON UNDER VARIOUS IRRIGATION SYSTEMS1
 P.
D.
Colaizzi, Ph.D.
Agricultural Engineer USDA-ARS P.O.
Drawer 10 Bushland, Texas 79012-0010 Phone: 806-356-5763 FAX: 806-356-5750 pcolaizzi@cprl.ars.usda.gov
 S.
R.
Evett, Ph.D.
Soil Scientist USDA-ARS P.O.
Drawer 10 Bushland, Texas 79012-0010 Phone: 806-356-5775 FAX: 806-356-5750 srevett@cprl.ars.usda.gov
 Studies on crop productivity for major irrigated crops in the Great Plains were reviewed for different types of modern pressurized irrigation systems.
Crops included corn, cotton, grain sorghum, winter wheat, and preliminary data on soybean and sunflower.
Irrigation systems consisted of spray and LEPA devices commonly found on center pivots, and drip irrigation.
Spray, LEPA, and SDI were compared at Halfway and Bushland, TX, and simulated LEPA and SDI were compared at Colby, KS.
Nearly all studies involved varying the irrigation capacity  or irrigation rate.
Yield response in terms of irrigation method could usually be described as SDI LEPA SPRAY for low irrigation capacities , and SPRAY LEPA SDI for full  capacities or rates.
In some cases, yield response was more consistent across irrigation rates.
Although additional data are lacking that would explain these differences, it appears that LEPA, and to a greater extent SDI, result in greater partitioning of
 1 Joint contribution from the USDA-Agricultural Research Service and Kansas Agricultural Experiment Station.
Contribution No.
06-193-A from the Kansas Agricultural Experiment Station.
The mention of trade or manufacturer names is made for information only and does not imply an endorsement, recommendation, or exclusion by USDA-Agricultural Research Service or the Kansas Agricultural Experiment Station.
water to plant transpiration relative to spray for low irrigation rates.
At greater irrigation rates, the yield depressions observed for SDI and/or LEPA relative to spray were less clear, although these may be the result of poor aeration and nutrient leaching by deep percolation.
The U.S.
Great Plains produces a major portion of the nation's corn, wheat, sorghum, soybeans, sunflower, and in the southern and central portions, cotton.
High yields are possible with irrigation, and roughly 8 Mha  are presently irrigated in an eight state area that includes South Dakota, Nebraska, southeastern Wyoming, eastern Colorado, Kansas, the Oklahoma Panhandle, northwestern Texas, and eastern New Mexico.
The region is mostly semiarid, with extremely variable precipitation , high evaporative demand due to high solar radiation, high vapor pressure deficit, and periods of high regional advection, especially in the southern portion.
The primary water resource for this eight state area is the Ogallala Aquifer, one of the largest freshwater aquifers in the world.
The Ogallala has been declining in most areas because withdrawals have exceeded recharge after intensive irrigation began in the late 1930s, when internal-combustion engines and rural electrification first became widely available for pumping.
However, the rate of decline has abated in some areas such as the High Plains of Texas  due to either reductions in irrigated area, conversion to more efficient irrigation systems, or both.
The earliest irrigation systems in the Great Plains were generally graded furrow, and these were most suitable for land with small slopes.
Musick et al.
mentions improvements in sprinkler systems after World War II allowed expansion of irrigation to land otherwise unsuitable for furrow systems.
This was followed by center pivots in the 1960s and 1970s.
Earlier center pivot sprinkler configurations were high-pressure impact, but these were replaced by lowpressure spray and low-pressure precision applicators  since the 1980s.
Spray heads are commonly positioned above the crop  or within the crop canopy.
In the mid-1980s, surface and subsurface drip irrigation  became adopted by cotton producers in the Trans Pecos region of Texas , and SDI has been used successfully for corn production in Kansas.
Center pivots with modern sprinkler packages  can be highly efficient in terms of uniformity and application efficiency , as can SDI , and numerous studies have documented high crop productivity using either type of system.
With declining water resources and escalating energy costs, total irrigated area in the Great Plains will likely
 decrease; however, remaining irrigated land will likely see greater adoption of efficient irrigation technology and techniques, including deficit irrigation, irrigateddryland rotations , and careful irrigation scheduling.
Studies in Texas, Kansas, and elsewhere indicate that relative performance of different irrigation systems in terms of crop productivity often changes with irrigation rate  and climate, among other factors, which should be considered in selecting an irrigation system.
The objectives of this paper are to review studies of crop productivity under various irrigation systems, with an emphasis on how crop productivity is affected by types of systems across a range of irrigation rates.
The scope will be limited to major crops irrigated in the Great Plains, including corn, cotton, grain sorghum, winter wheat, and some preliminary data on soybean and sunflower.
Data presented will be limited to pressurized irrigation systems  from studies conducted at the USDA-Agricultural Research Service in Bushland, TX, the Texas Agricultural Experiment Station in Halfway, TX, and the Kansas State University Northwest Research-Extension Center in Colby, KS.
Soils at these locations are generally deep, well drained, and loam to clay loam in texture.
Consequently, results presented herein may not be applicable to locations having coarser or finer soils, or for shallow-rooted crops.
Some additional references are given for studies conducted outside the Great Plains, and a few involve comparisons with furrow irrigation.
This review is by no means comprehensive and does not contain rigorous statistical analyses, but is intended to highlight major findings that appear common to different crops at the three locations.
SOME EFFICIENCY AND ECONOMIC ASPECTS OF SPRAY, LEPA, AND SDI
 Schneider  reviewed published research of application efficiencies and uniformity coefficients for spray and LEPA systems.
Reported application efficiencies for spray methods generally exceeded 90% and were from 95% to 98% for the LEPA methods.
Reported uniformity coefficients in the direction of travel ranged from 0.75 to 0.90 for spray and from 0.75 to 0.85 for LEPA; along the mainline  these were from 0.75 to 0.85 for spray and from 0.94 to 0.97 for LEPA.
The review noted that measured application efficiencies for spray were sensitive to the device used, and because of the start and stop movement of most irrigation systems, measured uniformities of LEPA were sensitive to the length of basin checks, irrigation system span alignment, and distance from the tower where system speed was controlled.
Water is usually applied to alternating interrows with LEPA; thus, the high reported LEPA uniformities along the mainline are the result of measuring water only where it is actually applied, disregarding the rows and nonirrigated interrows.
The review
 also discussed potential water loss pathways and concluded that runoff is generally the greatest potential loss for both LEPA and spray; hence, some form of runoff control such as basin tillage  or reservoir tillage is required to achieve these high efficiencies and uniformities.
Schneider and Howell  measured surface runoff from a slowly permeable Pullman clay loam soil with a 0.25% slope over two seasons of irrigated grain sorghum production.
Treatments consisted of the spray and LEPA methods with and without basin tillage  for five levels of soil water replenishment, or irrigation rate IR.
They observed no runoff for the spray method using furrow dikes for all IR, and no runoff for any sprinklertillage method combination for the 40% IR.
Grain yields and water use efficiencies were significantly reduced with increasing runoff.
For 100% IR, runoff losses averaged 12% for spray without dikes, 22% for LEPA with dikes, and 52% for LEPA without dikes.
They noted that as the seasons progressed, the furrow dikes eroded, decreasing soil water storage capacity on the soil surface and increasing the potential for runoff.
Howell et al.
reported that furrow dikes improved corn yield for both full and limited spray irrigation compared to flat and bed tillage , but did not observe runoff due to dike erosion.
Schneider  discussed other potentially large water loss pathways, including deep percolation, wind drift, and surface evaporation  and emphasized that both LEPA and spray can be highly efficient, provided that these pathways are carefully evaluated in order to select the most appropriate sprinkler package.
Water loss pathways described for spray and LEPA can potentially be eliminated with SDI through proper design, maintenance, and management, which is likely to also conserve expensive fertilizer and chemicals commonly injected into irrigation water.
We further postulate that furrow dikes may be more effective for rainfall capture for SDI than LEPA or spray because of reduced erosion.
Camp  reviewed published research on SDI and noted that crop yields were equal to or exceeded those of other irrigation systems, and water use was significantly less.
However, adoption of SDI in the Great Plains remains low relative to center pivots primarily because of capital costs but also due to greater maintenance and management requirements, among other factors.
If preplant rainfall is sparse and unreliable, crop germination can be difficult with SDI.
O'Brien et al.
showed that SDI can be more economical than center pivots for decreased field sizes , provided system life was at least 10 years  for continuous corn production.
SDI is particularly suited to small and oddly-shaped fields; furthermore, center pivots quickly lose their cost advantage where they cannot make a complete circle.
On the other hand, Segarra et al.
reported that SDI was not always competitive with LEPA for continuous cotton, despite SDI having greater lint yields.
But they noted
 that economic outcomes were also sensitive to system life, as well as installation costs, pumping lift requirements, and hail damage to crops.
Enciso et al.
reported that net returns of SDI in a cotton production system were sensitive to lateral spacing , lateral installation depth, and crop germination, where lateral spacing  was a tradeoff between capital cost and risks assumed in crop germination.
These varying results illustrate the difficulty in making general guidelines for SDI , and suitability of SDI should, at minimum, be assessed on a crop-, site-, and producer-specific basis.
The following sections review productivity for different pressurized irrigation systems according to crop, and selected publications are summarized for corn, cotton, grain sorghum, and winter wheat in Tables 1, 2, 3, and 4, respectively.
CORN, SOYBEAN, AND SUNFLOWER
 Subsurface drip irrigation  research has been conducted at the Kansas State University Northwest Research-Extension Center in Colby, KS since 1989 on a deep, medium textured, well-drained Keith silt loam soil.
Lamm  compared seven years  of corn productivity at this location for SDI and simulated LEPA, where the effects of LEPA were mimicked by delivering precise amounts of water to furrow diked basins through pressure regulated flow dividers and flexible supply tubes.
Irrigation capacity for simulated LEPA was varied by applying 25 mm  of water at 4, 6, and 8 day intervals.
Irrigation was applied daily with SDI at 2.5, 3.3, 4.3, and 6.4 mm per day.
This resulted in a range of seasonal irrigations applied relative to meeting the full irrigation requirement.
Grain yield VS.
seasonal irrigation were grouped for years having average or greater rainfall  or significant drought  for simulated LEPA and SDI, where yield and seasonal irrigations were averaged for each group of years.
For average to wet years, grain yield with SDI was slightly greater than simulated LEPA, but vice versa for drought years.
In average to wet years, differences in grain yields were primarily due to kernel weight, but in drought years, this was due to the number of kernels per ear.
Soybean and sunflower production were also compared between simulated LEPA and SDI at Colby, KS.
Irrigation rates  were varied according to 60%, 80%, and 100% of meeting the full irrigation requirement.
For both crops, relative yields between simulated LEPA and SDI again varied by IR, with SDI resulting in greater production at the lower IR, but less production at the higher IR.
Although only a single season is represented for each crop, it is interesting that production patterns were somewhat similar to corn in that 2005 received less rainfall than 2004.
We presently do not have data
 Table 1: Selected studies of crop productivity with pressurized irrigation systems for corn.
Subsurface drip irrigation  controlled annual weeds more effectively than sprinkler  or furrow irrigation in plots not treated with herbicides.
Weed control by subsurface drip irrigation
 Stephen R.
Grattan Lawrence J.
Schwankl W.
Thomas Lanini
 M ost California growers on irrigated farmland rely on the application of synthetic chemicals to control weeds.
Although these chemicals are effective, there are increasing concerns about the longterm effects such materials may have on the quality of soil and water.
Various nonchemical methods have been suggested as alternative means of weed control.
These include:  mulching, the use of plastic films or residual organic matter layered on the soil surface;  cultivation, mechanical removal of weeds before they reproduce;  interspecific competition, growth suppression of weeds through crop competition for nutrients, water, and light; and  heat,
 the use of solar energy and clear plastic films over the soil surface to produce heat and reduce weed-seed germination.
These methods have effectively reduced weed growth and vigor.
In this article, we discuss water management as an additional ecologically sound and effective method to control annual weeds in summer row crops.
Drip-irrigation tape or tubing buried 10 to 18 inches below the soil surface for several consecutive years is a new irrigation practice that several growers have adopted.
Farm managers using this system have noticed that it reduces weed infestation, but this effect of subsurface drip irrigation had not been experimentally
 tested or quantified.
We designed a field experiment at the University of California, Davis, to evaluate the effect of the irrigation method on weed control.
Three irrigation methods were selected: furrow, sprinkler, and subsurface drip.
The laterals of the drip system were buried in the plant row, 10 inches below the surface of the bed.
Since each method would produce different soil surface wetting patterns, we tested our hypothesis that weed infestation is related, in part, to the soil water content of the top inch of the soil surface.
Weed growth was studied in a field of processing tomatoes.
A 2-acre site was divided into 15 randomized plots.
Each plot contained six , 60-inch-wide beds 150 feet long.
Before the irrigation treatments began, annual weed seeds  were sown evenly on all plots to ensure uniform weed infestation.
One row of tomato seeds was sown in the middle of each bed in the first week of May 1987.
Half of each plot was randomly selected and then sprayed with two herbicides-Devrinol  at 2 pounds and Tillam  at 6 pounds per acre.
The other half remained unsprayed.
The tomato stand in all plots was established by sprinkler irrigation until plants were nine inches tall.
Weeds were manually removed in the plant rows of each plot.
On June 24, one day before beginning the various irrigation methods, the entire field was cultivated to remove all weeds.
Each plot received equal amounts of water to replace estimated losses from evapotranspiration.
Sprinkler and furrow plots were irrigated weekly; drip irrigation plots were watered daily.
No effective rainfall was recorded during the experimental portion of the season-June 25 until September 23.
All plots received their last irrigation three weeks before harvest.
A block of weeds and tomato plants, two beds wide and 15 feet long , was harvested from the center of each of the 30 plots on September 23.
The tomato fruit was separated into reds, greens, and rots and were weighed.
The weeds were dried, weighed, and characterized according to species.
Influence of irrigation method
 The total weight and distribution of weeds were related, in part, to the water content  of the surface inch of soil.
Fig.
1.
In furrow and sprinkler irrigation plots not treated with herbicides , weed growth was most vigorous in the furrow area where the water content was highest.
Subsurface drip irrigation without herbicides was at least as effective in controlling annual weeds as herbicides were under furrow or sprinkler irrigation.
This zone was monitored because it is generally considered to be the optimal depth for weed germination.
In the case of furrow irrigation, the water content was greater and weed growth was more vigorous in the furrow than in the plant row.
Although herbicides largely reduced weed growth, the relationship between soil water and weed growth was the same as in plots with no herbicide.
Under sprinklers, the surface soil water content 24 hours after irrigation was uniform within the plot, yet more weeds were found in the furrow than in the bed.
This result indicates that weed distribution under furrow and sprinkler irrigation is related not only to the surface soil water content but also to crop density.
The total mass of weeds produced per surface area in fields irrigated by subsurface drip were several orders of magnitude less than were produced under the two other irrigation methods.
This is not surprising since, under buried drip irrigation, most of the soil surface remained dry during the season except for a moist strip about 10 inches wide in the plant row.
A few annual weeds were able to overcome crop competition and flourish in this strip.
Unlike sprinklerand furrow-irrigated plots, there was no difference in weed growth between herbicide-treated and untreated subsurface drip plots.
This indicates that herbicides were not needed to control weeds with this method, at least in the absence of rain.
Growth of field bindweed was not influenced by the irrigation method.
This result was not unexpected, since bindweed does not need to propagate from seed but can sprout from storage roots.
Establishment of perennial weeds like bindweed is generally not directly related to moisture in the upper portion of the soil profile.
Field bindweed is notorious as a difficult-to-control weed with a deep root system.
In our study, there was no relationship between field bindweed growth, herbicide treatment, and location across the bed.
Field bindweed, however, represented only a small proportion of the total weed biomass.
Fruit yield and quality
 The yields of red tomato fruit  were inversely related to the biomass of weeds.
The irrigation method did not influence the yield, providing weed density was reduced by herbicides.
In the absence of herbicides, the yield was significantly higher with subsurface drip than with the more conventional methods of irrigation.
The yield suppression in the furrow and sprinkler plots that were not treated with herbicides was probably caused by weed competition for light, nutrients, and water.
Previous studies have shown that irrigation can affect tomato fruit quality.
The fruit in our study appeared to mature more rapidly under subsurface drip than by the other methods.
This observation is based on a smaller quantity of green fruit and, to some extent, larger amounts of rotten fruit produced in the subsurface drip plots.
We believe this difference is related to a late-season outbreak of mites and powdery mildew which was first noticed in the subsurface drip plots.
The soluble solid content  in the tomato fruit was influenced by the irrigation method.
Fruit from subsurface drip plots contained significantly lower solids than fruit from either furrow or sprinkler plots.
This difference may be due to a reduced cumulative water stress experienced by drip-irrigated plants.
There is potential for improving soluble solids in
 TABLE 1.
Yield of tomatoes under furrow, sprinkler, and subsurface drip irrigation
 method	Reds	Greens	Rots
 No herbicide	35 a 3 a 2 a
 Herbicide	45 b 7 b 3 bc
 No herbicide	35 a 4 a 4 bc
 Herbicide	47 b 7 b 3 b
 No herbicide	53 b 2 a 4 C
 Herbicide	52 b	2 a	4 bc
 Values followed by same letter are not significantly different as determined by LSD test at 5% confidence level.
drip-irrigated processing tomatoes as this crop-water management practice is studied further.
There are several concerns related to adopting subsurface drip irrigation to control weeds.
First, growers are uneasy about not being able to visually determine if their irrigation system is working properly.
The system has to be designed SO that line pressure can be monitored.
Second, the initial costs of materials  and installation are high.
Individuals who use this system, however, claim that costs are offset in subsequent years by reduced traffic demands in the field and labor savings.
Buried drip tubing should last for several years.
Third, the system requires careful management to avoid problems with filtration, orifice clogging, leaks, and the like.
Fourth, the depth and spacing of the tube must be determined for each situation according to soil type, slope, cropping sequence, and equipment.
It would be desirable to bury the tape or tubing deep enough in row crops to avoid cultivation damage but shallow enough to subirrigate without using large quantities of water, particularly early in the season.
Furthermore, sequential crops must accommodate a fixed spacing of buried drip tubes.
This may require changes in cultural practices.
Irrigation management can play a large role in the control of annual weeds in summer crops.
In this experiment, subsurface drip irrigation without herbicides was at least as effective in controlling weeds as herbicides under sprinkler and furrow irrigation.
At present, this irrigation method as an ecologically sound alternative for controlling weeds would be most attractive to small growers who produce crops without pesticides or by transitional growers moving from strong to reduced chemical dependence.
Stephen R.
Grattan is Extension Plant-Water Relations Specialist, and Lawrence J.
Schwankl is Extension Irrigation Specialist, Department of Land, Air and Water Resources, and W.
Thomas Lanini is Extension Weed Ecologist, Department of Botany.
All are with the University of California, Davis.
The authors extend their appreciation to Inge Bisconer of Hardie Irrigation for donation of the drip irrigation material and to Brenda Lanini of Campbell Soup for donation of the tomato seeds.
They also thank Kent Kaita, Wilbur Bowers, Lee Smith, Jeff Mitchell, and Alan Dong for their assistance.
New plastic drain  compared with excavated clay and bituminous fiber drains installed in 1964.
Drainage system performance after 20 years
 Mark E.
Grismer lan C.
Tod Frank E.
Robinson
 As part of a study of the longevity and effectiveness of clay, bituminous fiber, and concrete drainage pipes, several pairs of these pipes were installed in a heavy clay soil at the Imperial Valley Agricultural Center at El Centro, California in January 1964.
Drain lines were laid at a depth of 7 feet and a spacing of 120 feet.
Bituminousfiber drains were installed in a fiberglass envelope; washed gravel was used to enclose the clay and concrete pipes.
Observations on the effectiveness of the three materials were begun in the spring of 1966 by University of California researchers Frank E.
Robinson and James N.
Luthin.
They found no real difference in the performance of the different pipe materials and reported that variability in drain water discharge and quality was due primarily to variability of soil water transmission properties, especially along the trenches made during drainline installation.
Though one of the original intents was to study the effectiveness of these "lines periodically to show how flow changes with time," drain discharge measurements were discontinued until recently.
Also, periodic examination of drainline "segments to see how they stand up under a long period of use" was part of the original study.
Over 20 years have elapsed since the subsurface drain discharge and drain wa-
 ter salinity were originally measured.
We investigated the performance of the old drainage system, comparing it with a newly installed system, and examined the status of the original drainline materials as part of a larger study related to infiltration and drainage of cracking clay soils.
This investigation was conducted to address some of the concerns of the original study.
We conducted our study on the heavy clay quarter of the field used in the original trial.
The area was tiled with two bituminous fiber and one clay drainline.
Drain discharge and water quality were measured on the three drainlines following irrigation during the spring and summer of 1986 and 1987.
In June 1987, three new corrugated plastic drainlines were installed with gravel envelopes.
The new drains were placed within 10 feet of the old drains.
To eliminate effects of the old drains on performance of the new ones, the old drains were partially excavated and plugged with earthen backfill.
After installation of the new drains, drain discharge and water quality were measured throughout the summer and fall.
Durability of old drains
 Excavation of the original drainage pipes revealed that the gravel envelope
With the kickoffs for the competitions held at the West Central Research, Extension and Education Center  in North Platte and the Stumpf International Wheat Center in Grant, Nebraska, now in the history books, participants are busy setting up their online TAPS portals, researching and making their first decisions of the 2023 season.
The TAPS team is greatly looking forward to this seventh year of farm management competitions.
Black Mission fig production improved by heavier irrigation
 An analysis of tree-water relations and fruit yield indicates that Black Mission fig production responds favorably to a higher volume of water applied during the summer than is currently used by most of the industry.
Larger fruit size was the primary yield component responsible for the improved production and profit.
Based on historical reference crop evapotranspiration rates and the crop coefficients determined using data from this study, summerapplied water should be about 36 inches for maximum Black Mission fruit production and grower profit in the Madera area.
Figs have been produced in the San Joaquin Valley for more than a century.
During the last few decades, much of the production has been displaced from the flat topography in
 Fresno County to more undulating land in Madera County.
Flood irrigation has been largely replaced by drip irrigation, which offers much better control of irrigation timing and amounts.
However, realization of potential production benefits from drip irrigation while using minimum irrigation amounts requires knowledge of tree response to different levels of applied water.
Since little work has been done in California on fig irrigation requirements, we studied the response of the two primary varieties Calimyrna and Black Mission to various irrigation regimes in 1994-95.
This paper reports on our results for Black Mission and presents irrigation scheduling recommendations.
This work took place in a commercial 20-year-old Black Mission orchard located just east of Madera.
The soil is a shallow sandy loam with a 2-to-3-
 Trees in the foreground received a total of 10.7 inches of water  while trees in the background were irrigated with 33.3 inches of water.
Photo was taken during the harvest period.
foot root zone with relatively low infiltration rates.
We established seven irrigation regimes, based on applying various percentages  of the grower/cooperator's irrigation rate during the summer.
This grower's irrigation regime was typical of that used by much of the fig industry in California.
There were six replications of each irrigation treatment.
Since the irrigation amounts between the progressive treatments were small, single tree rows served as replications; there were no "guard" rows between the adjacent treatments, which minimized the size of the project.
Each replication  contained seven trees, and the interior five trees were monitored.
The grower generally irrigated for 12-hour durations, one to four times per week.
To facilitate the differential irrigation, we modified the existing singleline drip irrigation system by adding another drip line to each replication.
Each irrigation treatment was imposed by varying the number and discharge rates of drip emitters per tree.
The original drip line was maintained in each replication and used during fertilizer application.
Manifold valving on each replication allowed easy switching of drip lines.
Dual pressure regulators were installed on each replication to maintain desired operating pressures.
In-line meters were used to
 Fig.
1.
Summer-applied water with time during 1995 for seven irrigation regimes.
measure applied water.
Table 1 shows mean 1994-95 summer-applied water.
Rainfall and winter irrigation filled the soil moisture reservoir at the start of the season with an estimated 5 inches of available soil water.
Both predawn  leaf water and midday  stem water potentials were measured monthly in 1994.
Midday stem-water potential appeared to be more sensitive to the various irrigation regimes.
Therefore, stem water potential was monitored more frequently in 1995 as an indicator of tree stress.
The procedure involved placing a foil-covered polyethylene bag over a shaded leaf close to the tree trunk at about 10 AM.
At about 1 PM, the leaf and bag combination was removed with a small knife and immediately placed in a pressure chamber for stem water potential determination.
Single leaves on one tree in each of three replications per irrigation treatment were sampled every week or two.
On Aug.
18, 1995, we conducted a diurnal study of stem water potential and stomatal behavior on one replication of each irrigation treatment.
Single interior canopy leaves close to the trunk on each of three trees per irrigation treatment were used to determine stem water potential every 2 hours from 4 AM to 8 PM.
To determine stomatal conductance, we used a steady-state porometer on three fully sunlit leaves on each of three trees per irrigation treatment every 2 hours from 8 AM to 6 PM.
Fruit growth, yield components
 Beginning in early July, we randomly sampled four fruit per tree on each of the five monitored trees per replication each week.
We determined fresh and oven-dry weights and measured the diameter of the fresh fruit with electronic calipers.
There were five harvests Aug.
23, Sept.
2, 14 and 22, and Oct.
3.
To avoid interfering with the grower's harvest, we handracked the fruit in each replication just prior to the grower's normal mechanical sweeping and removed it from the orchard.
The fruit was placed on paper trays and airdried 4 to 6 days.
The fruit was then collected and weighed to determine gross yield.
All fruit was then placed in cold storage.
Following the last harvest, all fruit was removed from cold storage and
 Stomatal conductance is measured with a porometer by Dan Howes.
TABLE 1.
Mean 1994-95 summer-applied water, yield components and trunk growth
 Summer	"Product"	"Product"	Total	"Product"	Cull	Total	Increase in
 Irrigation	applied	fruit	fruit	fruit	fruit	fruit	fruit	primary scaffold
 treatment	water	value	fruit wt.
load	yield	yield	yield	X.S.
area
 inches	$/ton	gm/fruit	no./tree	lb/acre	lb/acre	lb/acre	cm
 T1	10.7	1,130 a	6.72 a*	4,245	4,635	277 a	4,913 a	13.1 ab
 T2	15.3	1,160 abc	7.53 bc	4,314	4,997	286 a	5,282 ab	8.5 a
 T3	19.8	1,154 abc	7.05 ab	5,236	5,537	328 a	5,866 ab	13.2 ab
 T4	23.6	1,151 ab	7.24 ab	4,958	5,333	444 ab	5,778 ab	17.7 ab
 T5	26.7	1,183 C	8.14 cd	4,625	5,817	509 ab	6,326 ab	33.6 c
 T6	30.4	1,178 bc	8.46 d	4,632	5,891	695 b	6,586 ab	24.1 bc
 T7	33.3	1,182 bc	8.54 d	4,666	5,957	666 b	6,623 b	21.0 abc
 *Values not followed by the same letter are statistically different using Fisher's Protected Least Squares Difference at the 95% confidence level; ns = no significant
 Fig.
2.
Midday stem-water potential with time during 1995 for the first six irrigation regimes.
T7 was similar to T6 and has been omitted for clarity.
Fig.
3.
Diurnal measurements of stemwater potential and stomatal conductance on Aug.
18, 1995, for the first six irrigation regimes.
T7 was similar to T6 and has been omitted for clarity.
transported to a commercial sorting operation.
Each fruit was characterized as "product"  or "cull" , based on visual appearance.
Total "product" and "cull" fruit were weighed and a subsample of the "product"  taken.
This sample was analyzed by a commercial laboratory to determine industry size categories, which was necessary to calculate tonnage value.
During the winter of 1994, trees in three of the replications of each irrigation treatment were inadvertently mechanically topped.
This influenced not only canopy size but fruit size.
There-
 fore the data reported in this paper is mean values  from the three of the original six replications that were not topped.
The circumference of one primary scaffold on each of the five trees per replication was measured before and after the study.
These values were used to determine the increase on scaffold cross-sectional area.
Tree-water status and stomatal behavior can be used as indicators of water stress.
Seasonal stem water potential is shown in Figure 2.
The more negative the stem water potential, the greater the water stress.
Through midJune, treatment values were -0.3 to -0.5 megapascal , with no clear differences between irrigation regimes.
This reflects the fact that the soil water reservoir was fully refilled by rainfall and winter irrigation, and this reservoir must be depleted before summer irrigation treatment differences become apparent.
The stem water potential for all treatments declined from mid-June to early July.
This is consistent with inadequate water being applied to even the most heavily irrigated treatment, and possibly to increased evaporative demand.
In mid-July, trees with lower amounts of applied water began to diverge from the more well watered trees.
Although the more heavily irrigated trees recovered to -0.5 to -0.6 MPa from mid-July through midAugust, treatment differences remained.
By late August, treatments that applied 19.8 inches or less of mean 1994-95 summer-applied water  had an average stem
 Mario Salinas prepares to measure stem water potential with a pressure chamber.
water potential of -1.4 MPa compared with -0.9 MPa for the treatments with at least 23.6 inches of 1994-95 mean summer-applied water.
Again, it appears that inadequate water was applied from late August through mid-September to all treatments.
Another approach for using treewater relations to identify stress is with diurnal measurements.
We conducted a diurnal study on Aug.
18, 1995, where stem water potential  and stomatal conductance  were monitored every 2 hours beginning at 4 AM and 8 AM, respectively.
Although the lower applied water treatments had lower stem water potential values predawn, these differences narrowed in the early morning hours.
By 10 AM, the lower irrigation treatments diverged from the more well watered regimes, and treatment differences generally reflected the levels of applied water.
However, T5 had the least
 negative stem water potential in the late afternoon.
The largest treatment differences occurred at the noon and 2 PM readings.
This greater sensitivity of midday stem water potential compared with predawn leaf water potential was observed throughout the season.
Stomatal conductance diurnal patterns also reflected applied water amounts.
Although the deficit irrigated treatments had lower stomatal conductance throughout the day, maximum stomatal conductance occurred at midday in all treatments.
Higher stomatal conductance results in higher photosynthesis, the process that produces the sugars necessary for vegetative and reproductive growth.
Yield and yield components
 Fruit load was not significantly different between treatments even though primary scaffold growth tended to be less for the lower irrigation treatments.
Therefore, total fruit production differences were due almost entirely to differences in fruit size.
Cull fruit was directly related to irrigation amounts and ranged from 277 to 666 lb/acre for the lowest and highest irrigation treatments, respectively.
This was due to the larger wetted surface area in the higher irrigation regimes.
Fruit that dropped on wet soil was subjected to conditions much more likely to promote fungal disease.
This was the primary factor that resulted in the fruit
 Black Mission figs that fall on wet soil are more likely to develop a fungal disease than those on dry soil.
Diseased figs are culled out at the fruit processor.
TABLE 2.
Mean 1994-95 fruit size expressed as industry standard grades
 Irrigation	Extra Fancy	Fancy	Extra Choice	Choice	Standard
 T1	0.07 at	2.23 a	18.9 a	44.0	34.7 a
 T2	0.23 ab	4.70 ab	29.4 ab	43.6	22.1 b
 T3	0.53 ab	3.20 a	27.7 ab	44.9	23.7 b
 T4	0.37 ab	3.30 a	25.4 ab	47.2	23.8 b
 T5	0.70 ab	8.23 ab	35.1 b	40.7	15.2 b
 T6	0.90 b	7.10 ab	33.7 b	42.1	16.1 b
 T7	0.73 ab	9.90 b	30.3 b	42.6	16.5 b
 *Extra Fancy is largest fruit and Standard is smallest fruit.
+Values not followed by the same letter are statistically different using Fisher's Protected Least Squares Difference at the 95% confidence level; ns = no significant difference.
TABLE 3.
Summer water use of mature clean-cultivated Mission figs for an average weather year near Madera.
Values based on crop coefficients developed in this study and long-term historical reference crop water use 
 Daily	Crop	Daily	Cumulative	Daily
 Date	ETo	coefficient	ETc	ETc	ETc
 inches/day	Kc	inches/day	inches	gal/tree/day*
 Apr 1-15	0.17	0.18	0.03	0.5	5.3
 Apr 16-30	0.21	0.34	0.06	1.3	10.1
 May 1-15	0.23	0.49	0.11	3.0	19.6
 May 16-31	0.25	0.65	0.15	5.4	26.0
 Jun 1-15	0.26	0.82	0.21	8.6	37.1
 Jun 16-30	0.28	0.97	0.25	12.4	43.9
 Jul 1-15	0.28	1.02	0.28	16.6	48.9
 Jul 16-31	0.27	1.02	0.28	21.1	48.9
 Aug 1-15	0.26	1.02	0.27	25.1	46.2
 Aug 16-31	0.23	1.02	0.27	29.3	46.2
 Sept 1-15	0.20	0.88	0.18	32.0	30.7
 Sept 16-30	0.17	0.77	0.15	34.3	26.8
 Oct 1-15	0.14	0.64	0.09	35.6	15.6
 *Assumes 14 x 20 ft spacing.
Can be calculated using the following equation:
 ETc  = ETc  x tree spacing  x 0.622 
 being characterized as culls.
We must emphasize that the experimental orchard had soil with relatively poor infiltration, which aggravated the problem of large wetted areas in the tree row.
Even though the lower irrigation regimes had less cull fruit, they also produced less product yield, again mostly the result of the aforementioned smaller fruit size.
Larger fruit size resulted in higher product tonnage prices for the higher irrigation treatments.
This was the main factor in the gross revenue differences.
Seasonal irrigation with 26.7 inches or more T5 and greater had gross revenue of about $3,400/acre compared with about $2,600/acre with 10.7 inches.
Based on the tree-water relations and production data, we selected T5 as the optimal irrigation treatment.
However, we also recognized the aforementioned deficit irrigation during mid-June through early July and during late August through midSeptember.
We adjusted the T5 applied water data accordingly and determined mean applied amounts in 1994-95 for each 2-week period from April through mid-October.
These adjusted applied water amounts were divided by the mean reference crop water use values  from a nearby CIMIS station to generate crop coefficients for each 2-week period.
The maximum crop coefficient was 1.02 from July through August.
Crop coef-
 Fig.
4.
Mean 1994-95 gross revenue from harvested marketable fruit versus summer-applied water.
ficients and long-term historical ETo for Madera were used to determine normal-weather-year Black Mission fig orchard evapotranspiration.
This resulted in 35.6 inches of summerapplied water and a maximum orchard water use value of 49 gallons/ for mature Black Missions on a 14-foot-by-20-foot spacing.
Analysis of tree-water relations and fruit yield components indicates that Black Mission fig production responds favorably to higher levels of summerapplied water than is currently used by most of the industry.
Greater fruit size was the primary yield component responsible for the improved production and profit.
Based on historical ETo and the crop coefficients determined using data from this study, which we believe are transferable for Black Missions in the San Joaquin Valley, summer-applied water should be about 36 inches for maximum fruit production and grower profit in the Madera area.
The disadvantage of applying more water is more cull fruit due to higher fungal disease from fruit dropped on wet soil, especially if the soil has poor infiltration.
We are currently working on using buried drip irrigation to eliminate surface wetting and thus minimize cull fruit even when high irrigation rates are applied during the harvest period.
D.A.
Goldhamer is UC Cooperative Extension Water Management Specialist and M.
Salinas is Research Associate, Kearney Agricultural Center, Parlier.
The authors gratefully acknowledge the cooperation of Richard De Benedetto of De Benedetto Ag., Inc., Paul Mepsle of RiPaul Sorting, Inc., and Ron Klamm and the Fig Research Institute, who provided funding.
They also express appreciation to the following field assistants: Cindy Greene, Dan Howes, Jesus Salinas, Lino Salinas, Heraclio Reyes, Raul Resendez and Julio Villegas.
Goldhamer DA, Snyder RL.
1989.
Irrigation Scheduling: A Guide for Efficient On-Farm Water Management.
UC Division of Ag and Nat Res Publication 21454.
Schwankl L, Hanson B, Prichard T.
1996.
Micro-Irrigation of Trees and Vines.
UC Irrigation Program Water Management Series Publication 94-01.
A goal of every dairy producer is to raise fast-growing, healthy heifers to replace older cows in the milking herd, while minimizing costs.
Most calf-rearing facilities are labor and capital intensive and must be well managed to minimize death loss and disease.
Unfortunately, newborn heifer calves often receive insufficient colostrum immunoglobulins, predisposing them to illness.
Rearing immunodeficient calves in groups on pasture  from birth offers dairy producers an opportunity to reduce production costs with no greater risk of mortality while improving animal performance.
In this pilot study, feed costs were 48% lower for mob-reared calves from birth up to 165 days of age.
Additionally, the rate of gain for mob calves was greater immediately following weaning, and the risk of mortality was 40% less for mob calves than for calves reared in individual pens with limited calf-to-calf contact.
Also, high-speed center pivot systems are now available on the market, which are capable of moving around the field in about four hours.
This high speed makes it possible for all data  to be collected during peak daylight hours , when the crop is most likely to experience stress.
The 10-page whitepaper outlines those situations where soil health best management practices dont improve water quality, for example when high water infiltration capacity in soil with limited depth to bedrock can lead to rapid delivery of nutrients to groundwater or when no-tillage practices can result in more runoff and overall phosphorus losses from frozen sloping fields relative to fall chiseling.
What does the prediction for a field look like?
Upon logging into your account, all the corn and soybean fields youve entered will be shown on a Google map with either green or red colors: green indicates no need for irrigation while red indicates a need for irrigation.
To see detailed predictions for a field, users can click the symbol for that field.
A new screen will open and display a graph of estimated soil water status and crop water stress for that field.
LAND APPLICATION OF ANIMAL WASTE ON IRRIGATED FIELDS
 Animal wastes are routinely applied to cropland to recycle nutrients, build soil quality, and increase crop productivity.
This study evaluates established best management practices for land application of animal wastes on irrigated corn.
Swine  and cattle  wastes have been applied annually since 1999 at rates to meet estimated corn P or N requirements along with a rate double the N  requirement.
Other treatments were N fertilizer  and an untreated control.
Corn yields were increased by application of animal wastes and N fertilizer.
Over-application of cattle manure has not had a negative effect on corn yield.
For swine effluent, over-application has not reduced corn yields except for 2004, when the effluent had much greater salt concentration than in previous years, which caused reduced germination and poor early growth.
All animal waste and N fertilizer treatments increased soil solution NO3-N concentration  compared with the untreated control.
Application of animal wastes on a N requirement basis resulted in similar NO3-N concentrations as fertilizer N applied at 180 lb/a.
The 2xN application caused NO3N concentrations to about double for both swine and cattle wastes.
Application of swine effluent based on P requirement produced similar NO3-N concentrations as the 2xN rate because of the relatively low P content in the effluent.
This study was initiated in 1999 to determine the effect of land application of animal wastes on crop production and soil properties.
The two most common animal wastes in western Kansas were evaluated; solid cattle manure from a commercial beef feedlot and effluent water from a lagoon on a commercial swine facility.
The rate of waste application was based on the amount needed to meet the estimated crop P requirement, crop N requirement, or twice the N requirement.
The Kansas Dept.
of Agriculture Nutrient Utilization Plan Form was used to calculate animal waste application rates.
Expected corn yield was 200 bu/a.
The allowable P application rates for the P-based treatments were 105 lb PO5/a since soil test P levels were less than 150 ppm Mehlich-3 P.
The N recommendation model uses yield goal less credits for residual soil N and previous manure applications to estimate N requirements.
For the N-based swine treatment, the residual soil N levels after harvest in 2001, 2002, and 2004 were great enough to eliminate the need for additional N the following year.
So no swine effluent was applied to the 1xN treatment in 2002, 2003, or 2005 or to the 2xN requirement treatment since it is based on 1x treatment.
The same situation occurred for the N based treatments using cattle manure in 2003.
Nutrient values used to calculate initial applications of animal wastes were 17.5 lb available N and 25.6 lb available P2O5 per ton of cattle manure and 6.1 lb available N and 1.4 lb available P2O5 per 1000 gallon of swine effluent.
Subsequent applications were based on previous analyses.
Other nutrient treatments were three rates of N fertilizer  along with an untreated control.
The N fertilizer treatments also received a uniform application of 50 lb/a of P2O5.
The experimental design was a randomized complete block with four replications.
Plot size was 12 rows wide by 45 ft long.
The study was established in border basins to facilitate effluent application and flood irrigation.
The swine effluent was flood-applied as part of a pre-plant irrigation each year.
Plots not receiving swine effluent were also irrigated at the same time to balance water additions.
The cattle manure was hand-broadcast and incorporated.
The N fertilizer  was applied with a 10 ft fertilizer applicator.
The entire study area was uniformly irrigated during the growing season with flood irrigation in 1999-2000 and sprinkler irrigation in 2001-2005.
The soil is a Ulysses silt loam.
Corn was planted at about 33,000 seeds/a in late April or early May each year.
Grain yields are not reported for 1999 because of severe hail damage.
Hail also damaged the 2002 and 2005 crop.
The center four rows of each plot were machine harvested after physiological maturity with yields adjusted to 15.5% moisture.
Nitrate concentration in the soil solution at the 5 ft depth was determined periodically through the growing season in 2003 and 2004.
The 5-ft depth is below the effective rooting depth of corn, so any nitrate movement past this depth is assumed non-recoverable by the corn plant.
Suction-cup lysimeters  are used to collect the soil water samples.
The first samples are collected shortly after corn planting and then every 1-2 week intervals during the growing season as long as sufficient water is present at the 5-ft depth to allow
 collection.
The samples are kept refrigerated after collection until delivered to the KSU Soil Testing laboratory for nitrate-N analysis.
Corn yields were increased by all animal waste and N fertilizer applications in 2005, as has been the case for all years except in 2002 where yields were greatly reduced by hail damage.
The type of animal waste affected yields in 4 of the 6 years with higher yields from cattle manure than from swine effluent.
Averaged across the 6 yr, corn yields were 13 bu/a greater following application of cattle manure than swine effluent on an N application basis.
Over application  of cattle manure has had no negative impact on grain yield in any year.
However, over-application of swine effluent reduced yields in 2004 because of considerably greater salt content  causing germination damage and poor stands.
No adverse residual effect from the over-application was observed in 2005.
The concentrations of NO3-N in the soil solution at the 5-ft depth for eight sampling periods in 2003 are shown in Table 4.
The NO3-N concentrations were stable between time periods but quite variable among replications.
All animal waste and N fertilizer treatments increased solution NO3-N concentration compared with the untreated control.
Application of animal wastes on a N requirement basis resulted in similar NO3-N concentrations as fertilizer N applied at 180 lb/a.
Although for both cattle and swine wastes, no fresh applications were made in 2003 for the N based treatments because of sufficient residual soil N.
The 2x N application caused NO3-N concentrations to more than double for both swine and cattle wastes.
Application of swine effluent based on P requirement produced similar NO3-N concentrations as the 2x N rate because of the relatively low P content in the effluent.
Compared with the 2001 values , some treatments showed considerably higher NO3-N concentrations in 2003.
The three treatments  that had soil solution concentrations >100 mg kg) -1 of NO3-N in 2001 showed increases in NO3-N concentrations in 2003 indicating continual accumulation of NO3-N at the 5-ft depth.
It would be expected that over-application of cattle manure  could result in increased soil solution NO3-N concentrations.
Similarly, since the swine effluent used in this study was relatively low in P, the application rates necessary to meet P requirements over-supplies N as shown by the elevated soil solution NO3-N concentrations.
However, for the 2xN swine effluent treatment there was no effluent applied in 2002 or 2003.
With no additional effluent applied since the 2001 water samples were collected, the higher concentration of NO3-N at the 5-ft depth in 2003 indicates movement of NO3-N from the upper profile rather than from fresh applications.
Table 5 shows the NO3-N concentrations in the soil solution at the 5-ft depth for eight sampling periods in 2004.
Soil solution NO3-N concentrations were similar for the untreated control and the low rate of N fertilizer, but increased by all other treatments.
In general, soil solution NO3-N concentrations were greater in 2004 than 2003.
It would be expected that the soil solution NO3-N concentrations for the N based swine effluent treatments would be greater because of the higher N content of the effluent in 2004.
However, soil solution NO3-N concentrations were also greater following applications of cattle waste based on N requirement and the higher rates of N fertilizer.
Project supported in part by Kansas Fertilizer Research Fund and Kansas Dept.
of Health and Environment.
Table 1.
Application rates of animal wastes, Tribune, KS, 1999 to 2005.
1999	2000	2001	2002	2003	2004	2005
 P req.
15.0	4.1	6.6	5.8	8.8	4.9	3.3
 N req.
15.0	6.6	11.3	11.7	0	9.8	6.8
 2XN req.
30.0	13.2	22.6	22.7	0	19.7	13.5
 1999	2000	2001	2002	2003	2004	2005
 P req.
28.0	75.0	61.9	63.4	66.9	74.1	73.3
 N req.
28.0	9.4	37.8	0	0	40.8	0
 2XN req.
56.0	18.8	75.5	0	0	81.7	0
 * The animal waste applications are based on the estimated requirement of N and P for a 200 bu/a corn crop.
Table 2.
Analysis of animal waste as applied, Tribune, KS, 1999 to 2005.
1999	2000	2001	2002	2003	2004	2005
 Total N	27.2	36.0	33.9	25.0	28.2	29.7	31.6
 P2O5	29.9	19.6	28.6	19.9	14.6	18.1	26.7
 1999	2000	2001	2002	2003	2004	2005
 Total N	8.65	7.33	7.83	11.62	7.58	21.42	13.19
 P2O5	1.55	2.09	2.51	1.60	0.99	2.10	1.88
 Table 3.
Effect of animal waste and N fertilizer on irrigated corn, Tribune, KS, 20002005.
Rate	2000	2001	2002	2003	2004	2005	Mean
 Cattle	P	197	192	91	174	241	143	173
 manure	N	195	182	90	175	243	147	172
 2 X N	195	185	92	181	244	155	175
 Swine e	P	189	162	74	168	173	135	150
 effluent	N	194	178	72	167	206	136	159
 2 X N	181	174	71	171	129	147	145
 N fertilizer	60 N	178	149	82	161	170	96	139
 120 N	186	173	76	170	236	139	163
 180 N	184	172	78	175	235	153	166
 Control	0	158	113	87	97	94	46	99
 LSD0.05	22	20	17	22	36	16	12
 Treatment	0.034	0.001	0.072	0.001	0.001	0.001	0.001
 Control VS.
treatment	0.001	0.001	0.310	0.001	0.001	0.001	0.001
 Manure VS.
fertilizer	0.089	0.006	0.498	0.470	0.377	0.001	0.049
 Cattle vs.
swine	0.220	0.009	0.001	0.218	0.001	0.045	0.001
 Cattle 1x vs.
2x	0.900	0.831	0.831	0.608	0.973	0.298	0.597
 Swine 1x VS.
2x	0.237	0.633	0.875	0.730	0.001	0.159	0.031
 N rate linear	0.591	0.024	0.639	0.203	0.001	0.001	0.001
 N rate quadratic	0.602	0.161	0.614	0.806	0.032	0.038	0.051
 Rate of animal waste applications based on amount needed to meet estimated crop P requirement, N requirement, or twice the N requirement.
No yields reported for 1999 because of severe hail damage.
Hail reduced corn yields in 2002 and 2005.
Table 4.
Nitrate concentration in soil solution at the 5-ft soil depth in 2003 following application of animal wastes and N fertilizer.
Nutrient source Application	Time of Sampling
 Basis*	May 21	May 29	June 10	June 18	June 23	July 2	July 9	July 16	Mean
 Soil solution NO3-N, ppm
 Cattle manure	P	45	31	46	38	41	43	45	44	42
 N	75	69	68	62	64	52	61	49	63
 2 X N	322	375	375	348	375	310	371	378	357
 Swine effluent	P	264	280	281	280	283	278	296	299	283
 N	106	112	122	103	99	89	94	100	103
 2 X N	272	306	264	288	299	281	290	291	286
 N fertilizer	60 N	23	20	22	19	21	18	22	22	21
 120 N	48	41	40	23	31	35	36	24	35
 180 N	102	98	105	84	86	64	71	73	85
 Control	0	8	5	7	3	3	4	4	4	5
 Treatment	0.001	0.001	0.001	0.001	0.001	0.001	0.001	0.001
 Control VS.
treatment	0.028	0.034	0.019	0.020	0.012	0.014	0.006	0.005
 Animal waste VS.
fert.
0.003	0.003	0.001	0.001	0.001	0.001	0.001	0.001
 Cattle VS.
swine	0.139	0.145	0.188	0.090	0.109	0.038	0.070	0.047
 Cattle 1x VS.
2x	0.003	0.001	0.001	0.001	0.001	0.001	0.001	0.001
 Swine 1x VS.
2x	0.038	0.032	0.070	0.018	0.008	0.006	0.004	0.004
 N rate linear	0.306	0.371	0.278	0.380	0.367	0.488	0.432	0.406
 N rate quadratic	0.833	0.805	0.719	0.653	0.709	0.907	0.849	0.647
 * The animal waste applications are based on the estimated requirement of N and P for a 200 bu/a corn crop.
Table 5.
Nitrate concentration in soil solution at the 5-ft soil depth in 2004 following application of animal wastes and N fertilizer.
Nutrient source Application	Time of Sampling
 Basis*	May 26	June 4	June 8	June 15	June 23	June 27	July 7	July 14	Mean
 Soil solution NO3-N, ppm
 Cattle manure	P	108	109	111	102	111	99	105	111	107
 N	321	335	344	358	306	282	293	294	317
 2 X N	322	418	421	300	454	402	424	405	393
 Swine effluent	P	355	366	357	505	476	446	546	531	448
 N	145	127	128	219	146	141	169	170	156
 2 X N	203	303	327	325	247	395	540	307	331
 N fertilizer	60 N	14	4	5	7	4	4	4	3	6
 120 N	116	119	109	129	111	120	139	135	122
 180 N	170	183	180	177	201	211	218	234	197
 Control	0	8	5	4	4	2	2	1	1	3
 Treatment	0.005	0.002	0.003	0.008	0.001	0.001	0.002	0.001
 Control VS.
treatment	0.006	0.005	0.007	0.009	0.007	0.003	0.024	0.001
 Animal waste VS.
fert.
0.005	0.002	0.002	0.004	0.003	0.001	0.001	0.001
 Cattle VS.
swine	0.795	0.753	0.772	0.241	0.993	0.285	0.063	0.258
 Cattle 1x VS.
2x	0.995	0.409	0.465	0.642	0.185	0.248	0.294	0.249
 Swine 1x VS.
2x	0.663	0.248	0.213	0.547	0.535	0.039	0.015	0.217
 N rate linear	0.064	0.060	0.078	0.122	0.059	0.036	0.069	0.013
 N rate quadratic	0.728	0.748	0.834	0.686	0.921	0.883	0.779	0.822
 * The animal waste applications are based on the estimated requirement of N and P for a 200 bu/a corn crop.
MEASURING WATER FLOW AND RATE ON THE FARM
 Proper water management involves two basic considerations: when and how much irrigation water to apply.
The timing of an irrigation event  involves utilizing information on plant needs and soil water conditions.
How much depends primarily on the soil's water holding capacity, the depletion level and the rooting depth of the crop.
Once you have calculated how much water to apply, how can you be sure that you have accurately applied that amount?
Or, if you miss your target amount, how do you determine how much water you actually applied?
The amount of water applied to a field is a function of time, flow and area.
The time of an irrigation is easily recorded.
The amount of area irrigated is also easily calculated.
However, estimating flow rate in an open ditch is often guess work, at best.
In this bulletin we shall discuss ways to measure water flow in an open ditch.
Considerations in Selecting a Measuring Device
 Selecting the proper device for measuring water flow is often difficult due to several factors.
Possibly the most limiting factor for most growers is cost.
This includes the cost of the device itself as well as costs for installation and maintenance.
Quite often, the materials needed to construct the device are less expensive than the cost of installation.
Accuracy is another important factor, although most may say that "some information is better than none." Growers should be aware that many devices yield great accuracy in a laboratory setting, yet fail in the field.
Be sure to ask about the field accuracy of the device.
The flow range of the device must also be taken into account.
Devices such as sharp-crested weirs, shortthroated flumes or submerged orifices do not operate well in high flow situations.
Head loss is another consideration when choosing a water flow measurement device.
Sharp-crested weirs usually require more head loss than do broad-crested weirs or acoustic flow meters.
However, sharp-crested weirs cost less and can measure much lower flows.
The condition of your site is also a factor.
Is the canal or ditch that you are measuring lined or unlined?
Is it concrete or plastic?
Is the ditch geometry common or was it custom designed for your farm?
Ultrasonic meters, for example, do not work well when the geometry of the ditch is irregular, but portable flumes can often be installed with acceptable results.
Different devices yield different types of information.
Instruments such as weirs and flumes are used to measure the flow rate, but do not include volume.
Most meters measure total volume.
Some new ultrasonic devices give accurate measurements of both rate and volume.
Decide whether you want rate or volume.
The quality of the water needs to be considered when choosing a water measurement device.
The device's ability to pass sediment and debris can become critical when working with open channel flows.
Although flumes and weirs pass debris easily, they often have difficultly with sediment.
Sediment can build up in the flume or weir, giving a false reading.
Another component in measuring water flow is operation and maintenance.
All too often, devices are installed properly poorly maintained.
Poorly maintained equipment yields poor measurements and erroneous information.
Factors to be considered include the need for electricity and the number of moving parts that may wear after time.
Construction and installation are always integral concerns, as equipment varies greatly.
Installation of flumes does not require a high level of precision, but proper installation of an ultrasonic meter may take time and patience.
Having the ability to verify your device in the field can be very important.
Slight differences in installation procedures often cause these devices to be misread and require field calibration.
Also, be sure to check on the ease of troubleshooting and repair when choosing a measurement device
 Finally, consider how many of these devices you need and then decide which one will give you the best repeatability.
It is difficult to obtain an instrument that gives you the same standard error from one device to another.
Devices vary from one another, each requiring it's own calibration.
However, with proper installation and maintenance, most devices will yield acceptable results.
There are other aspects that also need to be considered.
Consider the potential for vandalism in your area.
Devices such as ultrasonic meters have high replacement costs; SO you will want to protect these as much as possible.
Flumes and weirs that are built into a ditch are less likely to be vandalized because there isn't a great deal of equipment to attract vandals.
You may also want to weigh environmental concerns against longevity, maintenance, construction, field verification and standardization.
For example, some devices require high maintenance and frequent visits.
If the site is located in a pristine wildlife area, you may opt for a device that requires fewer maintenance trips in order to rminimize impact to the surrounding area.
All of these factors have been consolidated into a table developed by the Bureau of Reclamation.
This table summarizes how various devices compare with each other in terms of cost, accuracy, flow, etc.
The table is presented on two pages.
The first page lists the devices and some of the considerations previously mentioned.
The second page is a continuation of the same table.
The same devices are listed, but with additional information.
To use the table effectively, you need to know what flow rates you will have, what you want to measure and whether you are measuring in an open ditch or closed conduit.
For example, what would be a good device for measuring flow rate in a concrete ditch on a farm that usually carries about 5 cfs?
The sharp-crested and broad-crested weirs work well in this flow range, as do the long-throated flumes and submerged orifices.
The "differential head meters for pipe" also work well, but are intended for pipe.
Next, consider the canal type.
The canal is concrete lined and both the broad-crested weir and the long-throated flumes perform best.
Both devices have similar accuracy, but the broad-crested weir is less expensive.
Table 1-Part 2 illustrates that both devices will measure rate but not volume.
Both pass debris and have similar maintenance needs.
In fact, these two devices are the same in Table 1-Part 2 except for construction where the broadcrested weir is considered to be easier to construct.
The decision is now left to you.
If you want to save money, install the broad-crested weir.
If you want to save time and effort in construction, install the long-throated flume.
Either way, you will be helping yourself by measuring the amount of water flowing into your fields.
With this information, you will be able to determine how much water you have applied and/or how long your irrigation set time should be.
For information on these aspects of irrigation, contact your local Cooperative Extension office.
If the use of sensors results in savings of 2 inches of water, the same operating costs of $7.31 per acre would apply, but ownership costs would change to $11.68 per inch since we are spreading the costs over fewer inches of water and a total cost of $19.00 per acre inch.
Over the course of a year, this would result in a total annual cost of $113.97 per acre.
Now that summer range is going dormant for the winter, grazing will do little harm to your grasses.
This might be a good year to reclaim some of your rangeland back from yucca.
Winter grazing is your best tool.
SUMMER CROP PRODUCTION AS RELATED TO IRRIGATION CAPACITY
 In arid regions, it has been a design philosophy that irrigation system capacity be sufficient to meet the peak evapotranspiration needs of the crop to be grown.
This philosophy has been modified for areas having deep silt loam soils in the semi-arid US Central Great Plains to allow peak evapotranspiration needs to be met by a combination of irrigation, precipitation and stored soil water reserves.
The major irrigated summer crops in the region are corn, grain sorghum, soybean and sunflower.
Corn is very responsive to irrigation, both positively when sufficient and negatively when insufficient.
The other crops are less responsive to irrigation and are sometimes grown on more marginal capacity irrigation systems.
This paper will discuss the nature of crop evapotranspiration rates and the effect of irrigation system capacity on summer crop production.
Additional information will be provided on the effect of irrigation application efficiency on irrigation savings and corn yields.
Although the results presented here are based on simulated irrigation schedules for 33 years of weather data from Colby, Kansas  for deep silt loam soils, the concepts have broader application to other areas in showing the importance of irrigation capacity for summer crop production.
SUMMER CROP EVAPOTRANSPIRATION RATES
 Crop evapotranspiration  rates vary throughout the summer reaching peak values during the months of July and August in the Central Great Plains.
Long term  July and August corn ET rates at the KSU Northwest Research Extension Center, Colby, Kansas have been calculated with a modified Penman equation  to be 0.267 and 0.249 inches/day, respectively.
However, it is not uncommon to observe short-term peak corn ET values in the 0.35 0.40 inches/day range.
Occasionally, calculated peak corn ET rates may approach 0.5 inches/day in the Central Great Plains, but it remains a point of discussion whether the corn actually uses that much water on those
 extreme days or whether corn growth processes essentially shut down further water losses.
Individual years are different and daily rates vary widely from the long term average corn ET rates.
Corn ET rates for July and August of 2004 were 0.245 and 0.229 inches/day, respectively, representing an approximately 8% reduction from the long-term average rates.
In contrast, the corn ET rates for July and August of 2003 were 15% greater than the long term average rates.
Irrigation systems must supplement precipitation and soil water reserves to attempt matching average corn ET rates and also provide some level of design flexibility to attempt covering year-to-year variations in corn ET rates and precipitation.
Figure 1.
Long term corn evapotranspiration  daily rates and ET rates for 2004 at the KSU Northwest Research-Extension Center, Colby Kansas.
ET rates calculated using a modified Penman approach.
Simulation of irrigation schedules for Colby, Kansas
The new extension publication, Impact of Irrigation Technologies on Water Use, is available online.
The NebGuide was reviewed by Xin Qiao, Chuck Burr and Aaron Nygren.
CROP SELECTIONS AND WATER ALLOCATIONS FOR LIMITED IRRIGATION
 Steven Briggeman Software Developer, Sprout Software Manhattan, Kansas
 Irrigators choose crops on the basis of production capabilities, economic returns, and crop adaptability to the area, government programs, crop water use, and their preferences.
When full crop evapotranspiration demand cannot be met, yield-irrigation relationships and production costs become even more important inputs for management decisions.
Under full irrigation, crop selection often is driven by the prevailing economics and production patterns of the region.
Crops that respond well to water, return profitably in the marketplace and/or receive favorable government subsidies are usually selected.
These crops still can perform in limited irrigation systems, but management decisions arise as water is limited: should fully watered cops continue to be used; should other crops be considered; what proportions of land should be devoted to each crop; and finally,
 how much water should be apportioned to each crop?
The outcome of these questions is finding optimal economic return for the available inputs.
Determining the relative importance of the factors that influence the outcome of limited-irrigation management decisions can become complex.
Commodity prices and government programs can fluctuate and change advantages for one crop relative to another.
Water availability, determined by governmental policy or by irrigation system capacity, may also change with time.
Precipitation probabilities influence the level of risk the producer is willing to assume.
Production costs give competitive advantage or disadvantage to the crops under consideration.
The objective of this project has been to create a decision tool with user interaction to examine crop mixes and limited water allocations within land allocation constraints to find optimum net economic returns from these combinations.
This decision aid is for intended producers with limited water supplies to allocate their seasonal water resource among a mix of crops.
But, it may be used by others interested in crop rotations and water allocation choices.
CWA  calculates net economic return for all combinations of crops selected for a rotation and water allocated to each crop.
Subsequent model executions of land-split  scenarios can lead to more comparisons.
Individual fields or groups of fields can be divided into in the following ways: 100%; 50%-50%; 25%-75%; 33%-33%-33%; 25%-25%-%50; 25%-25%-25%-25%.
The number of crops eligible for consideration in the crop rotation could be more than the number of land splits under consideration.
Optimum outcomes may recommend fewer crops than selected land splits.
Fallowing part of the field is a valid option.
Irrigation system parameters, production costs, commodity prices, yield maximums, annual rainfall, and water supplied to the field were held constant for each model execution, but can be changed by the user in subsequent executions.
The model examines each possible combination of crops selected for every possible combination of water allocation by 10% increments of the water supply.
The model has an option for larger water iteration increments to save computing time.
For all iterations, net return to land, management, and irrigation equipment is calculated:
 Net return =   where:
 Field research results have been used to find relationships between crop yields and amounts of irrigation.
Yields from given irrigation amounts multiplied by commodity prices are used to calculate gross income.
Grain yields for corn, grain sorghum, sunflower, and winter wheat were estimated by using the "Kansas Water Budget" software.
Software development and use are described in Stone et al..
Yield for each crop was estimated from irrigation amount for annual rainfall and silt loam soils.
Figure 1.
Yield-irrigation relationship for corn with annual rainfall from 11-21 in.
The resulting yield-irrigation relationship for corn  shows a convergence to a maximum yield of 220 bu/ac from the various combinations of rainfall and irrigation.
A diminishing-return relationship of yield with irrigation applied was typical for all crops.
Each broken line represents normal annual rainfall for an area.
CROP SELECTION WITH RESTRICTED IRRIGTION
 In 2012 irrigators need to tailor their water management to have the expectation of producing at least their irrigated proven yield to qualify for crop insurance as an irrigated practice.
If they do not have enough water to produce their proven yield on the whole field, they may need to reduce irrigated acreage to fully irrigate the planted area.
They need to know how much water it will take to produce their proven yield.
Each row in the yield table is for the available soil water on October 1, 2011 and April 1, 2012.
The change in soil water from October 1 through April 1 is based on the average annual precipitation expected during the dormant season.
Water accumulates if there is room enough to store it, depending on how much evaporation occurs at the soil surface, and how much water drains below the expected root zone.
KSU researches  measured available soil water  after the 2011 harvest in producer irrigated fields in southwest Kansas.
They found a minimum of 17% ASW and a maximum of 95% ASW among the sampled fields.
This demonstrates that producers need to determine ASW in their own fields.
Within each row in the table, there are columns for the amount of irrigation it will take to produce the predicted yield.
An irrigator can find his/her proven yield on the table for each value of ASW  and applied irrigation.
The volume of irrigation, available for that field in 2012, needs to be determined in units of acre-inches, This volume divided by the inches of irrigation required to produce the proven yield  is the acreage that can be planted (see example.
These tables are provided by Kansas State University for producers as information for determining possible strategies for 2012.
They were not derived by the Risk Management Agency.
Crop insurance underwriters should be contacted for additional information.
Table 1.
Predicted corn yields for annual precipitation of 17 inches.
Available	Available	Applied Irrigation
 Water	Water	5"	8"	11"	14"	17"	20"	23"	26"
 1-Oct	1-Apr	Yield	Yield	Yield	Yield	Yield	Yield	Yield	Yield
 %	%	bu/ac	bu/ac	bu/ac	bu/ac	bu/ac	bu/ac	bu/ac	bu/ac
 10	20	92	124	149	168	184	198	210	220
 30	35	120	148	169	186	200	213	220	220
 50	50	148	171	189	203	215	220	220	220
 70	60	164	184	200	213	220	220	220	220
 Corn from table1; annual precipitation = 17 inches; available water on April 1= 20%; proven yield = 168 bu/ac; irrigation needed = 14 inches; irrigation volume available = 1200 ac-inches ; Irrigated acres to produce proven yield = /14 inches) = 88 acres
 Table 2.
Predicted corn yields for annual precipitation of 21 inches.
Available	Available	Applied Irrigation
 Water	Water	5"	8"	11"	14"	17"	20"	23"	26"
 1-Oct	1-Apr	Yield	Yield	Yield	Yield	Yield	Yield	Yield	Yield
 %	%	bu/ac	bu/ac	bu/ac	bu/ac	bu/ac	bu/ac	bu/ac	bu/ac
 10	25	135	165	183	193	205	217	220	220
 30	45	156	182	197	206	216	220	220	220
 50	60	172	194	207	214	220	220	220	220
 70	70	178	197	210	217	220	220	220	220
 Table 3.
Predicted sorghum yields for annual precipitation of 17 inches.
Available	Available	Applied Irrigation
 Water	Water	5"	8"	11"	14"	17"	20"	23"	26"
 1-Oct	1-Apr	Yield	Yield	Yield	Yield	Yield	Yield	Yield	Yield
 %	%	bu/ac	bu/ac	bu/ac	bu/ac	bu/ac	bu/ac	bu/ac	bu/ac
 10	20	108	125	139	149	158	160	160	160
 30	35	123	137	149	158	160	160	160	160
 50	50	136	148	158	160	160	160	160	160
 70	60	144	154	160	160	160	160	160	160
 Table 4.
Predicted sorghum yields for annual precipitation of 21 inches.
Water	Water	5"	8"	11"	14"	17"	20"	23"	26"
 1-Oct	1-Apr	Yield	Yield	Yield	Yield	Yield	Yield	Yield	Yield
 %	%	bu/ac	bu/ac	bu/ac	bu/ac	bu/ac	bu/ac	bu/ac	bu/ac
 10	25	123	139	147	155	160	160	160	160
 30	45	139	148	155	160	160	160	160	160
 50	60	146	154	160	160	160	160	160	160
 70	70	148	156	160	160	160	160	160	160
 This work was partly supported by the US Department of Interior, Kansas Water Resources Institute, and the USDA-ARS Ogallala Aquifer Program.
Home Sprinkler Systems: Preparing Your Sprinkler System for Winter
 Fact Sheet No.
4.719
 by M.
Higgins and C.
Swift Revised by Kurt Jones
 The concept of preparing your sprinkler system for winter must be done correctly to assure there are no costly repairs and replacements to make in the spring at system start-up.
The process consists of expelling all the water from the irrigation system and equipment.
This is necessary because water freezing in the irrigation system will break pipes, fittings, valves, sprinklers, pumps, and other system components.
Most substances contract as they get cold; however, when water cools, it contracts only until it reaches a temperature of 39 degrees Fahrenheit.
Upon further cooling to 32 degrees Fahrenheit, water expands as it turns to ice.
Water expands and increases in volume by one-eleventh, SO 11 cubic feet of water will form approximately 12 cubic feet of ice.
This expansion force is sufficient to cause pipes and fittings to burst valves to crack, and sprinkler and pump cases to split open.
Draining the system may be accomplished by the use of either manual or automatic drain valves which rely on gravity to purge water from the system.
These valves rely on a properly-installed system laid to grade with no humps in the pipe to trap water in low areas.
This method is not recommended since sub-surface pipes have a tendency to shift with time, and there is no way to visually inspect lines once draining is complete.
The only positive way to be sure enough water has been expelled from the system is by using compressed air to "blow" the water out.
Systems with electric valves must be blown out with pressurized air.
There is no other way
 to drain the water off the top of the diaphragm of the valve.
Air volume is as critical as air pressure.
If an insufficient volume of air is used, after forcing some water out, the air will ride over the top of the water.
This will result in the remaining water draining into low spots and subjecting the system to freeze damage.
Ideal pressures are in the range of 40 to 80 pounds per square inch  for the air compressor with 80 psi being the maximum for rigid PVC pipe and 50 psi for polyethylene pipe.
Set the pressure regulator on the air compressor accordingly.
If the pressure is in excess of what the nozzles are rated, the excessive pressure will blow the sprinkler nozzles off and could cause other damage.
The rating of the nozzles is available at the manufacturer's home web page.
Rule of thumb: If the sprinkler heads stay up after the water is blown out and compressed air continues to flow through the system, you are using the right size compressor.
The idea is to "blow" your system out using only the volume of air necessary.
If you normally run one zone at a time when irrigating, the system should blow out the same way.
If you try to do more, the excess velocity of flow and added friction will heat up the pipe and fittings to a point where they could possibly melt.
If the pipe and fittings do not burst during this operation, they could be damaged, reducing their life.
To figure out the best sized compressor for the system, you need to know the gallons per minute  that flow through each zone in the system.
When the system was designed it should have had a GPM rating for each zone marked on the irrigation plan.
If this information is not available, a quick estimate of GPM per zone can be made by adding up the GPM rating for each sprinkler head nozzle on the zone.
GPM data is available on the manufacturer's web site.
Prepare your sprinkler system for winter by expelling all the water from the irrigation system and equipment.
Do not trust manual or automatic drain valves.
The system should be blown out with pressurized air.
To determine the best sized compressor for your system, know the gallons per minute  that flow through each zone.
If your irrigation system is attached to domestic water, it is required to have a backflow prevention device.
*M.
Higgins, Grand Junction Pipe and Supply, Grand Junction, CO.; C.E.
Swift, former Colorado State University Extension, horticulture agent.
**Kurt Jones, Colorado State University Extension, agent, natural resources and agriculture, Chaffee County.
10/2014
 Divide GPM by 7.5 to determine the cubic feet per minute  needed.
This is the ideal sized compressor to "blow out" your system.
GPM divided by 7.5 gallons = CFM needed
 For example, if the system is designed for 30 PSI and 20 gallons per minute per zone, divide 20 by 7.5.
The answer is 2.66 cubic feet per minute.
A compressor capable of providing 2.66 CFM  at 30 PSI  will be required.
Under-sized compressors
 Figure 1: Stop and Waste.
Figure 2: Stop and Waste with a key.
will take longer and work a lot harder to deliver the required volume to pressure to purge your system.
Larger compressors stand the risk of pressurizing too quickly and causing damage to the system, though an air pressure regulator on the outlet of the compressor can overcome this problem.
Turning off the Water Supply
 Start by turning off the water supply to your system.
A stop and waste valve or drain of some type should have been installed between the water supply and the backflow device.
Turn this off.
This may be located in a basement, crawlspace, or valve box underground.
In many cases, a stop and waste valve will be installed below ground.
The stop and waste may be 5 feet down, SO a long key may be necessary.
Do not force this valve while opening or closing it.
If the system has a pump, it should be drained, removed from the system and stored inside.
If this is not possible, drain the pump and wrap it to insulate it from the weather.
Winterizing the Backflow Device
 If your irrigation system is attached to domestic water, it is required to have a backflow prevention device.
Atmospheric Vacuum Breaker  devices are installed downstream of each valve and are winterized with compressed air when the zone is blown out.
AVBs may
 not be legal in your area.
Check with your water district, planning/building department or county health department.
Pressure Vacuum Breaker  or Reduced Pressure  backflow prevention devices must never be blown out with compressed air.
The rubber seals inside can easily melt from the heat of the air.
1.
A properly designed and installed PVB should drain easily if both the riser before and after the backflow preventer are empty of water.
After the system is blown out, both ball valves and test cocks  should be exercised back and forth several times.
Leave these in a half-open position for the winter.
Ball valves that
 Figure 4: Both ball valves and test cocks should be exercised back and forth several times.
are either fully closed or fully open tend to trap water, expand and cause damage.
In the spring, close the test cocks and ball valves before pressurizing the system.
Once the water supply to the PVB is turned on open the ball valves slowly to pressurize the rest of the irrigation system.
Opening the ball valves slowly will prevent damage to the system which can be caused by water hammer.
Draining an RP Device
 The internal passages of the Reduced Pressure device must be drained of all water.
There are two check valves in an RP that need to be drained separately.
This is accomplished as follows:
 Figure 3a: Left Photo Pressure vacuum backflow device.
Figure 3b: Right Photo Reduced Pressure back flow device.
Blue handles designate isolation ball valves.
Note blowout fittings  on either side of the device.
1.
Slowly close the main shutoff valve upstream of the device.
Figure 5: Open test cocks  and remove the check cap.
2.
Drain the system of all water upstream of the device.
This will require opening the stop and waste or other drain.
3.
For the first check zone , open test cocks #2 and #3.
This will drain all the water between the first and second check valves.
4.
For the second check zone  remove the check cap, spring and disk holder.
All water downstream of the second check will drain through the body.
Replace disk and spring.
Check cap.
5.
If the device is equipped with optional drain plugs, remove the plugs and test cocks #2 and #3.
6.
Leave the isolation ball valves approximately 45 degrees while draining the assembly.
Leave the ball valves in this position for the winter.
7.
The ball valves should be fully closed when the system is pressurized in the spring.
Always open and close the ball valves slowly to prevent damage to the system caused by water hammer.
Winterizing the Rest of the Irrigation System
 To blow out the irrigation system, connect the compressor to the downstream blowout fitting.
Ensure the isolation ball cock on the downstream side of the backflow device is closed.
Remember to turn it back to the half-open, half-closed position after blowing out the irrigation system.
Start one or more of the zones/stations at the irrigation controller, turn on the compressor to the proper pressure and blow out the system.
If the backflow device does not have a blowout fitting on the downstream side, one will need to be added before the irrigation system can be blown out.
Each zone/station should be blown out twice to make sure all the water is purged from the system.
It is better to use two short cycles per station/zone than to have one long cycle.
Once a zone is "blown out," avoid blowing that zone out again.
Compressed air moving through dry pipes causes friction and heat which could cause damage.
After purging the system of all water, leave all the valves on your backflow preventer half open.
This will help keep the backflow preventer from freezing and splitting during the winter.
If the PVB test cocks are left open, be sure to close them before turning the system on in the spring.
Connecting the compressor's air line to a metal fitting instead of PVC will help dissipate some of the heat during the blowout process.
The irrigation controller should remain powered during the winter.
Do not unplug the controller.
Heat from the transformer can help reduce moisture and protect components in the controller from corrosion.
The controller should be programmed to run through a minimum cycle once a week to help keep solenoid plungers from sticking.
Blowing out sprinkler systems can occasionally upset pets due to "whistling." Care should be taken to protect your pets from running off during winterization.
Final Thought and Warning
 It is important to remember it is much less costly and much less labor intensive to properly and efficiently prepare the system in the fall than to repair damaged fittings, piping, valves, sprinklers and other components in the spring.
Caution!
Wear Proper Eye Protection!
Coconut Oil and Coconut Water: Are Coconuts the New Superfood?
Jamie I.
Baum, PhD Assistant Professor Nutrition
 Rosemary Rodibaugh, PhD Professor Nutrition
 Arkansas Is Our Campus
 Products containing coconut continue to increase in popularity.
Products such as coconut oil and coconut water are flooding the market.
It is difficult to walk into a grocery store without seeing a coconut-containing product on display.
There are hundreds of blogs and diets that sing the praises of health benefits they claim are linked to coconut products, including weight loss, cancer prevention and improved brain function in Alzheimer's disease.
Does this mean that coconuts are the next superfood?
Coconut oil is an edible oil extracted from the "meat" of matured coconuts.
It has several applications in the food industry.
It is used in processed foods because it is relatively inexpensive and can provide crisp texture to foods.
Coconut oil has a high smoke point, the temperature where it starts to break down, which makes it shelf stable and ideal for foods that need a longer shelf-life.
Hydrogenated and partially hydrogenated coconut oil are found in cereals, baked goods, biscuits, salty snacks, soaps, cosmetics and moisturizers.
According to some health food promoters and celebrity doctors, coconut oil is the latest miracle food, claiming it can cure everything from heart disease to obesity and cancer.
However, the effects of coconut oil on health have not been well studied.
These health claims tend to be based more on personal testimonials than on scientific evidence.
In fact, there are very few studies in people showing benefits of coconut oil most of these studies are epidemiology studies
  that show a link between high coconut-consuming countries and longevity [1-2].
Coconut oil is considered a saturated fat and contains 9 calories per gram.
There are two basic types of fats saturated and unsaturated.
Unsaturated fats are healthy fats and include plant-based fats  and fish oils.
These fats should be the primary fats in your diet because they either do not affect cholesterol levels or they raise HDL  cholesterol without raising LDL  cholesterol.
Saturated fats found in animal fats and tropical oils, including coconut oil, should be consumed only in small amounts because they raise both HDL  and LDL  cholesterol.
The U.S.
2010 Dietary Guidelines recommend that saturated fat should be limited to 7 to 10 percent of total calories because it can increase risk for heart disease.
The fat in pure virgin coconut oil is about 92 percent saturated, the highest amount of saturated fat of any edible fat, which means it doesn't take much of it for you to reach your daily saturated fat limit [2].
However, some of the saturated fatty acids found in coconut oil, lauric acid and myristic acid, have been linked with some positive health benefits [3-6].
For example, lauric acid has been shown in many studies to increase HDL cholesterol and decrease LDL cholesterol, but when taken as an isolated fatty acid, not as part of coconut oil [6].
Coconut oil is unique because it also contains a high level of medium chain triglycerides , which are metabolized differently
 than long chain fatty acids such as lauric and myristic acids.
MCTs are transported directly from the intestinal tract to the liver, where they are burned off as fuel, which may raise the metabolic rate slightly [4-5].
With MCT going through this metablolic pathway, less fatty acids are available to be circulated throughout the body and deposited in fat tissues.
Since the effect of MCT oil on weight loss is modest, it is not likely that coconut oil, which is only about half MCTs, will have much effect on weight loss.
Only one study has been conducted on the effect of coconut oil on weight loss, a master's thesis in Brazil, and there was no significant effect [3].
Because the saturated fat in coconut oil is from lauric acid, coconut oil may be better for you than butter and other animal fats.
Although coconut oil doesn't contain cholesterol, some studies show that it raises both LDL and HDL cholesterol [6].
If you choose to use coconut oil, choose "virgin" or unrefined coconut oil and use it in moderation.
Many health care organizations such as the U.S.
Food and Drug Administration, the Academy of Nutrition and Dietetics and the American Heart Association advise against the consumption of high amounts of coconut oil due to its high levels of saturated fat.
One tablespoon of coconut oil contains 117 calories, 14 grams of fat, 12 grams of saturated fat and is generally more costly than healthier fats.
If you are looking for real health benefits, liquid vegetable oils like soybean, canola, corn or olive oil are better choices.
Coconut water is the clear fluid from young, still-green coconuts.
Coconut water is believed by many consumers to have a variety of health benefits.
However, to date, there is no scientific literature available to support these claims.
One popular claim related to coconut water is that it is more hydrating than water.
A recent study compared bottle water, coconut water, coconut water from concentrate and a carbohydrate-electrolyte sports drink [7].
The study found no difference between beverages on hydrating abilities and support of exercise following beverage consumption [7].
Coconut water does contain a high amount of potassium ,
 which is why it is often used for rehydration by athletes.
Coconut water has about 45 calories per 8-ounce serving and those calories can add up quickly if you are not mindful of the amount you drink.
If you enjoy the taste of coconut oil and coconut water, include small amounts of it in your diet, but don't expect big rewards.
There is no strong scientific evidence that proves eating coconut oil or drinking coconut water has any great health benefits.
Chapter: 21 Precision Soil Sampling
 In South Dakota, the N, P, and K fertilizer recommendations are adjusted based on the amount of each nutrient contained in the soil.
However, soilbased recommendations are only as good as the sample collected.
Precision soil-nutrient information can be collected using many different techniques, including grid-soil sampling, management-zone sampling, mappingunit sampling, and grid-cell sampling.
This chapter discusses soil sampling, laboratory accuracy, and submitting the soil samples to an appropriate soil testing laboratory.
Figure 21.1 Black and white photograph of a quarter section collected in 1956 and a soil P grid map collected in 2001.
Note: In 2001 there was no visible trace of a farm site on this quarter section of land.
Collecting a Composite Soil Sample
 1.
Soil sampling protocols are site, nutrient, and crop specific, and they can be collected following a wide variety of approaches, including grid cell, whole field, grid point, and management zone.
2.
Soil sampling date can influence the soil test results.
Soil test results are often lower following harvest than prior to seeding because of plant uptake during the growing season and mineralization of organic matter.
However, sampling in the fall has the advantage of allowing more time to collect and interpret the results.
3.
Early spring sampling provides time for moisture to replenish the soil profile, thus making sampling easier.
4.
Soil samples can be collected with a soil probe or auger.
Probes and buckets should be cleaned prior to use.
Collecting representative samples is difficult if soil conditions are too wet or too dry.
5.
The soil sampling strategy should consider how fertilizer was previously applied.
a.
Sampling banded fields is much more difficult than sampling fields where fertilizers were broadcast-applied.
6.
Sample areas where animals were confined separately from the rest of the field.
Guess rows as they may contain 0 or 2 fertilizer bands.
a.
b.
Exclude field entrances, field discontinuities , headlands and boarders, old homesteads, and animal confinement areas from the bulk sample.
8.
In reduced-tillage fields where the location of the fertilizers are known:
 a.
Avoid old P bands, unless adequate samples are collected.
For P recommendations, if the rows are spaced 30 inches apart, collect 1 core from the old fertilizer band for every 20 outside the band.
b.
If N was band-applied between the crop rows in the previous year, collect 15 to 30 cores halfway between the fertilizer band and crop row.
9.
In tilled fields where N and P fertilizer were broadcast, randomly collect 15 to 30 cores from each sampling zone.
10.
If the N and P band locations are unknown, collecting representative samples is difficult, and undersampling  a field can result in misleading recommendations.
11.
Soil from all cores should be crushed and thoroughly mixed before a subsample is removed for analysis.
a.
Typically, a pound of soil is adequate for most chemical analysis.
b.
The samples should be frozen or air-dried and submitted to the laboratory for analysis.
However, drying soil samples can influence the soil test results.
Drying and grinding soil samples can result in the release of trapped K that was not plant-available.
When selecting a soil testing laboratory, consider the reliability of the results as well as the turnaround time.
Opportunities for Precision Nutrient Management
 In South Dakota, the primary soil nutrients that limit corn yields are nitrogen  and phosphorus.
However, fundamental differences between N and P make it difficult to manage these nutrients using a common solution.
One difference is that P stays where it is placed since it is chemically attached  to the soil solids.
Alternatively, applied nitrogen can be lost to denitrification , leaching , and volatilization.
Chemical differences between N and P result in:
 1.
N being an annual cost, whereas P is a capital cost.
2.
A portion of P applied 50 years ago still being available today.
3.
N recommendations that are based on the amount of nitrate contained in the surface 2 feet, whereas P recommendations are based on the concentration of P in the surface 6 inches.
4.
Different opportunities to capture a return on the sampling investment exist for N and P.
For example:
 a.
The greatest opportunity to increase profitability with precision P management occurs when the whole-field composite soil Bray-1 P concentrations range between 12 and 30 ppm, and prior manure applications may have increased nutrient variability.
This opportunity exists because even though the field average value is greater than the optimum value , 50% to 70% of field may have soil test values that are below this value.
b.
The greatest opportunity for precision N management exists when the field has relatively high variability, prior manure applications increased variability, split N applications are an option, and there is a high likelihood that the soil contains a significant amount of NO-N.
3
 5.
Whether you use traditional or precision soil sampling, soil sampling is a time-tested approach to increase profitability.
If you are composite sampling and the year-to-year composite results have a significant amount of variability, this field is a good candidate for grid sampling.
Selecting a Sampling Protocol
 A one-size-fits-all soil sampling protocol is not recommended and it is important to remember that the starting point for your fertilizer investment is the soil sample.
The strengths and weaknesses of the different sampling approaches are summarized in Table 21.1.
In spite of soil sampling protocols that generally recommend that sampling areas should be less than 40
 Table 21.1 Sampling approach and the skill required to implement them.
Sampling approach	Protocols	Fertilizer errors
 Follow "good" protocols for collecting
 Whole field	samples.
Do not collect composite samples	Moderate to high	Low	High
 from entrances or old homesteads.
Samples are randomly collected from
 Grid cell	predetermined cells.
Low	Low	Moderate
 Use an offset pattern to collect 10 to 15
 cores located 8 to 10 feet  from
 Grid point	the grid-point center.
The location of this	Low	High	Moderate to low
 point should be determined with GPS.
Composite soil samples collected from
 Soil type	NRCS defined soil map.
Moderate to high	Moderate	High to moderate
 Soil samples collected from management
 Management zone	Moderate	High	HiModerate
 Locate old homesteads on old USDA-
 Prior management	NRCS photos and sample the homesteads	Moderate	Low	High to moderate
 separately from the rest of the field.
Best guess	No soil sample collected.
Low	Low	Extremely high
 acres, many agronomists collect a single, composite sample from a quarter section.
If wholefield samples are collected follow good sampling protocols.
In grid-cell sampling, the field is split into uniform cells where a single, composite soil sample is collected from each cell.
Prior research has shown that recommendation errors are reduced by using a 10-acre or smaller grid cell.
Cells generally are rectangular in shape and a composite soil sample is collected from each cell.
These samples should be collected using "good" soil sampling protocols.
Samples are then mixed to create a composite sample.
If the field contains old homesteads or old animal confinement areas, these zones should be separated from the rest of the field.
The zones can be any size and they can be changed to match the expected variability.
This technique is easy to implement, well-suited for today's equipment, and does not require extensive training.
One of the most commonly used techniques for collecting precision soil-nutrient information is gridpoint sampling.
In this technique, samples are collected at specified grid points.
A commonly used spacing density is 2.5 acres.
The grid points should be offset and their locations should be marked with a differentially corrected GPS.
Grid-point sampling is useful when several fields are combined and when manure has been extensively applied.
At each grid point, 15 to 20 cores should be collected from an 8to 10-foot radius surrounding the point.
The major drawbacks to this approach are the labor and analysis costs.
Grid-point sampling can be used as a baseline measurement.
In soil type-based sampling, composite soil samples should be collected from each soil mapping unit.
Assessments of this sampling approach have been mixed.
Management-zone sampling is where the field is split into zones based on soil and crop-yield variability.
This approach has value if the data layers show consistent yield patterns over multiple years.
Management zones can be developed based on apparent electrical conductivity, yield-monitor data sets, remote sensing, historical records, field scouting, and personal preferences.
In this approach, computer classification of the various data layers is used to identify management zones.
Geographic information systems  software
 is routinely used to process the data.
Once a zone is identified, a single, composite sample, containing 15 to 20 individual cores, should be collected.
This approach is not recommended for fields with recent manure application histories.
In this sampling approach, the field is split into different zones based on the prior management.
For example, including a subsample from an old homestead in a whole-field sample increases the soil test P value and reduces the fertilizer recommendation.
In this approach, areas previously enrolled in CRP, tile drained, and/or including animal confinement areas should be sampled separately from the rest of the field.
Management practices implemented 50 years ago can still impact soil test P values today.
Selecting a Reputable Laboratory
 Submitting the Sample for Analysis
 Once the laboratory has been selected, follow its recommendations for submitting samples.
Contact information for the different laboratories is available below.
Many soil testing laboratories recommend that the samples be cooled and submitted for analysis as soon as possible.
Do not leave moist samples in the truck.
If they cannot be submitted within 24 hours, they should be air-dried or frozen after collection.
Composite soil samples should be dried by spreading them out on a clean table for 2 or 3 days.
Once the analytical results are obtained the data should be archived for future reference.
Choices for longterm storage include:
 1.
Printed hard copies of all data from a given field.
2.
On-farm storage of the digital records.
This is complicated by computer systems that routinely change.
3.
Off-farm storage by a data management company.
In summary, fields are a mosaic of habitats, each having unique characteristics that influence soil properties and crop yields.
The effectiveness of matching solutions to problems rests on the ability to identify problems, characterize the site, and develop appropriate solutions.
To conduct an assessment of a field's fertility program, regular soil samples should be collected from targeted locations.
This information needs to be stored for future use.
Additional information for conducting an assessment is available in Chapter 29.
Precision soil sampling can be used for many purposes, including improving your understanding of your field and increasing profits.
Precision farming by itself does not guarantee a return for your investment.
Your return on investment depends on how well you use the information.
IRRIGATION GUIDELINES FOR OILSEED CROPS IN THE U.S.
CENTRAL GREAT PLAINS
 K-State Northwest Research-Extension Center 105 Experiment Farm Road, Colby, Kansas Voice: 785-462-6281 Fax: 785-462-2315
 Development, water use and yield formation of oilseed crops are inter-related.
Greatest yields are expected with a well-established canopy, a plant population sufficient to support a large number of seeds set per acre and favorable weather conditions for an extended seed fill period.
Oilseed water requirements closely follow canopy formation and evaporative conditions.
Irrigation scheduled by the water balance method results in higher yields than with irrigation scheduled by growth stage.
A straight-line relationship between yield and water use indicates the yield threshold  and yield response to increased water use.
When precipitation, available soil water and limited irrigation fail to meet crop water requirements, yield reductions depend on the degree of plant water stress at critical stages of growth.
Full-season soybean with full irrigation offers greatest productivity potential.
A smaller yield threshold and extensive rooting system for sunflower provides advantages for limited irrigation or double-crop conditions.
Winter canola can provide good productivity during fall and spring growing seasons when heat stress can be minimized.
Oilseed crops  provide management options for irrigators seeking to reduce irrigation requirements, diversification and/or to reduce input costs.
In 2003, soybeans were planted on 25% of irrigated cropland in Nebraska and on 12% of irrigated acres in Kansas.
Sunflower is emerging as an irrigated crop in W.
Kansas with a substantial increase in doublecropped sunflowers reported in 2005.
Canola, irrigated in the San Luis Valley of Colorado, is an emerging feedstock for biodiesel production.
Irrigated soybean yields range from 55 to over 70 bu/A in variety trials conducted throughout the central Great Plains ; greatest yields occurred in north-central Kansas and the east-central Platte valley of Nebraska.
Varieties with top yields exceeded trial averages by 10%.
Irrigated sunflower yields ranged from 2200 to 2900 lb/A in similar trials located in the central High Plains with greatest yields in NW Kansas.
Top-yielding hybrids exceeded trial averages by
 20% or more.
Irrigated winter canola yields of 2600 lb/A have been recently reported for W.
Nebraska.
Several irrigation guidelines are available for oilseed crops.
This report is intended to integrate these guidelines with recent and regional field studies.
Emphasis is given to crop development, water use and yield responses for irrigated oilseed crops.
DEVELOPMENT, WATER USE, YIELD FORMATION
 Oilseed development, water use and yield formation are inter-related.
Water, nutrients, sunshine and soil conditions must be sufficient, with minimal stress from pests and heat for crop growth to meet potential productivity.
Water requirements and yield formation factors frequently correspond with development stages.
Crop-specific considerations will follow a general discussion of oilseed development, water use and components of yield.
Uniform seedling emergence is favored by soil-seed contact in a firm moist seedbed at a sufficient soil temperature.
Expansive growth of seedling leaves require assimilates, derived from photosynthesis and nutrient uptake, as well as sufficient plant-available water for turgor-driven growth.
Development of new leaves corresponds with plant temperature as well as time.
Thus, leaf appearance is related to degree-days.
For example, new leaves of a standard sunflower hybrid appear in 67 F-d intervals.
Leaf appearance and growth comprise the major processes of canopy formation.
Rapid canopy closure is desirable, because the crop canopy shades the soil and reduces evaporative water losses.
Leaf expansion is typically exponential during early to mid-vegetative growth when supported by sufficient water, nutrients and non-stress conditions.
Crop water requirements increase with canopy formation  because transpiration increases in proportion to leaf area.
Light penetration into lower layers of the crop canopy is desirable.
Photosynthesis can be limited by the amount of light reaching shaded leaves.
Canopy formation nears completion with flowering for some determinant crop types such as sunflower.
However, canopy formation continues with flowering for indeterminant crops such as canola and most soybean varieties of maturity group IV and earlier.
Reproductive development marks the end of the juvenile phase and begins with differentiation of floral buds.
Potential seed number  can be set at this point, for determinant crops.
Development and growth of floral organs proceeds systematically through stages including pollen shed, seed set and seed fill.
Again, sufficiency of water, nutrients and light will support these yield formation processes.
The onset of reproductive development frequently
 varies with thermal time, but may be affected by day-length as well.
Reproductive stages of soybean, sunflower and canola are presented in Tables 1, 2 and 3.
Figure 1.
Sunflower water use and canopy formation  for dryland and irrigated crop.
Table 1.
Description of soybean reproductive stages.
Open flower at any node on main stem.
Indeterminate
 R1	flowering	plants start at bottom and flower upward.
Determinate
 plants start at top four nodes and flower downward.
Open flowers on one of the two uppermost nodes on main
 R3	Beginning	Pod 3/16 inch long at one of the four uppermost nodes on
 Pod 3/4 inch long at one of the four uppermost nodes on
 R4	Full pod	main stem.
R5	Beginning	Seed 1/8 inch long in one of the four uppermost nodes on
 Pod containing a green seed that fills pod cavity on one of
 R6	Full seed	the four uppermost nodes.
R7	Begin	One normal pod on main stem has reached mature pod
 95% of pods have reached mature pod color.
R8	Full maturity	Approximate 5 to 10 days ahead of harvest.
Table 2.
Description of sunflower reproductive stages 
 The terminal bud forms a miniature floral head rather than a cluster of
 R-1	leaves.
When viewed from directly above, the immature bracts form a
 The immature bud elongates 1/4 to 3/4 inch above the nearest leaf
 R-2	attached to the stem.
Disregard leaves attached directly to the back of
 R-3	The immature bud elongates more than 3/4 inch above the nearest leaf.
The inflorescence begins to open.
When viewed from directly above
 immature ray flowers are visible.
This stage is the beginning of flowering.
The stage can be divided into
 R-5	substages dependent upon the percent of the head area 
 that has completed or is in flowering.
[i.e., R-5.3 , R-5.8 , etc.]
 R-6	Flowering is complete and the ray flowers are wilting.
R-7	The back of the head has started to turn a pale yellow color.
R-8	The back of the head is yellow but the bracts remain green.
The bracts become yellow and brown.
This stage is regarded as
 0	Germination: sprouting development
 5	Inflorescence  emergence
 7	Development of seed
 Stand establishment, canopy formation and reproductive development are significant components of the yield formation process.
The crops' capacity to fill seed and achieve yield potential can depend on the active leaf area and number of seeds set per acre.
Greatest yields are expected with well-established canopy, a plant population sufficient to support a large number of seeds set per acre and favorable weather conditions for an extended seed fill period.
Oilseed water requirements closely follow canopy formation and evaporative conditions.
When scheduling irrigation relative to evaporative conditions, crop coefficients can be used to calculate daily crop water use.
Typical crop coefficients, daily water use and development stages for soybean and sunflower are presented in Figure 2.
Lower seasonal water requirements for canola can be expected for the spring growing season,
 which is shorter and with less evaporative demand than the summer growing season of soybean and sunflower.
When soil water reserves are insufficient, actual crop water use is less than evaporative demand  and yield reductions are likely.
Figure 2.
Crop coefficient  and daily crop evapotranspiration  for soybean and sunflower, calculated from 34 years  of weather recorded at Colby, KS.
Reproductive development stages for soybean and sunflower are noted below the graph for reference.
Irrigation is generally required to meet crop water requirements in the central Great Plains.
Two methods of scheduling irrigation are by water budget or by growth stage.
Water budgets seek to maintain available soil water above a minimum value.
Growth stage irrigation seeks to provide sufficient water to meet crop water requirements during specific critical stages.
Studies in west-central Nebraska  and north-central Kansas  indicate greater soybean yields with water budgets than with growth stage irrigation scheduling.
Similar studies are in progress for sunflower.
Figure 3.
Water uptake by sunflower roots  is reduced when the available soil water in the wettest soil layer is less than 60% of available water capacity.
The line approximates an envelope containing observations of water uptake in relation to available soil water.
Water uptake from all soil layers is equivalent to crop evapotranspiration.
For limited irrigation systems, water available to the oilseed crop is likely to be insufficient during canopy formation and/or reproductive development stages.
For example, Figure 4 shows that sunflower canopy formation at flowering  can be limited by available soil water during earlier reproductive growth.
Limited irrigation, while not providing full water requirement of the crop, can improve seed yield.
For example, a one-inch irrigation applied to soybean in SE Kansas at R4 , R5  or R6  increased seed yield by 241 lb/A.
The R4 application increased the number of seeds per plant while the R5 and R6 applications increased seed weight.
When supply of water limits crop water use, seed yields are frequently limited as well.
A straight line can represent the relationship between seed yield and seasonal crop water use.
For example, soybean yield at Colby, KS increased 3.7 bu/A with each additional inch of water use.
The yield threshold  occurred with 7.3 inches of crop water use.
Similar results were reported for west-central Nebraska.
For sunflower, the yield threshold was 4.2 inches and the yield response was 166 pounds per inch of crop water use.
Figure 4.
Sunflower leaf area at flowering  in relation to available soil water at mid-bud  growth stage.
Figure 5.
Soybean yield response to seasonal water use at Colby, KS and central Nebraska sites.
Figure 6.
Sunflower yield response to seasonal water use at Colby, KS.
Under limited irrigation, water can be allocated to minimize the impact of water deficits on yield formation.
For example, soybean yield can be most sensitive to water deficits during flowering and full pod reproductive stages.
The yield response to limited irrigation can be greatest if water is applied to alleviate deficits during stages which are most critical for yield formation.
Critical stages, with maximum crop water use rates, are R3 to R6 for soybean and R1 to R7 for sunflower.
Water stress during these critical stages is expected to reduce yield potential.
However, Table 4 and Figure 4 indicate that sunflower is also susceptible to soil water deficits during vegetative growth.
Additionally, a recent study at Akron, CO showed that delaying limited irrigation until the R4 stage increased oil content of sunflower, though yields were less than that of full irrigation.
Irrigators with limited capacity will benefit from good judgement and additional water use and growth stage information.
Soybean or sunflower can be double-cropped after wheat harvest where growing season temperatures and the length of growing season are sufficient.
Yield potential will be reduced due to the reduced growing period and effects of the yield threshold.
The smaller yield threshold of sunflower may indicate a comparative advantage for double-cropping.
Cooler weather can extend the
 duration of grain fill period but may alter the composition of fatty acids in oil.
Table 4.
Susceptibility of soybean and sunflower to soil water deficits.
Growth Stage	Time period	Susceptibilty	Time period	Susceptibilty
 	Factor		Factor
 Vegetative	38	6.9	53	43.0
 Flowering	33	45.9	17	33.0
 Formation	44	47.2	23	23.0
 A full-season, well-watered soybean crop offers relatively greatest productivity potential for non-calcareous soils with acid to neutral pH.
The nitrogen-fixing crop can require minimal N fertilizer, provided soil is properly inoculated.
Iron chlorosis can limit productivity on calcareous soils with pH exceeding 7.5 ; foliar diseases can also limit productivity.
"Early determinate varieties are recommended for production systems involving narrow rows, high seeding rates, early plantings, good fertility, and a yield potential in excess of 50 bushels per acre".
Photoperiod effects on flower initiation highlight the importance of selecting varieties from maturity groups appropriate for planting period and desired days to maturity.
Sunflower is commonly planted in early June, in the central Great Plains, to avoid stem weevil and sunflower moth pests.
The deep-rooted crop can extract more soil water than other crops.
Combined with the smaller yield threshold, sunflower can give relatively greater yields when water supplies are limited.
The heattolerant crop also tolerates calcareous soil and high pH conditions.
Decreasing daylength  near the R1 stage can reduce the duration of reproductive stages, due to photoperiod effects, when grown at latitudes less than 40.
Winter canola is established in early fall and harvested mid-summer, similar to winter wheat.
The yield advantage of winter varieties over spring varieties is similar to that of winter wheat, approximately 30%.
The small-seeded coolseason crop may be difficult to establish, as well as sensitive to heat stress during yield formation stages.
Oilseed crops tend to produce less yield than feed grain crops.
Less productivity results from differences in photosynthesis and in seed composition.
The C3 physiology of oilseed crops is inherently less effective than the C4 physiology of feed grain crops.
The C3 carbon-fixing enzyme Rubisco, is approximately 2/3 effective when exposed to atmospheric oxygen concentrations.
Plants with C4 physiology also use Rubisco, but it functions in bundle sheath cells where oxygen concentrations are very small, and the enzyme functions at near complete effectiveness, resulting in increased crop productivity.
The second difference between oilseed and feed grain crops involves oil and protein content.
The amount of starch which can be produced from a unit of carbohydrate  is 0.88.
The remaining fraction, 0.12, is consumed in the conversion process.
More carbohydrate is used up in the formation of oil  and protein.
As a consequence, the fraction of carbohydrate converted to oil is 0.33; to protein is 0.35.
Smaller seed yields of oilseed crops is a consequence of greater oil and protein  content, for which a greater fraction of the photosynthetically-fixed carbohydrates are consumed.
Liquid polymers keep drip irrigation lines from clogging
 J.
L.
Meyer M.
J.
Snyder L.
H.
Valenzuela A.
Harris R.
Strohman
 Clogging from lime (CaCO precipitation can be prevented by injecting a homopolymer of maleic anhydride into buried drip systems.
Investigators prevented drip tubing from clogging in coastal strawberry plots by using this polymer and chlorine for high-bicarbonate waters.
Drip irrigation is practiced on one-half million  of California's 9 million irrigated acres, and is mostly used with annual crops.
Drip systems use 3 to 15 mil thick polyethylene formed into multi-chambered 1/2-inch tubing with laser-drilled orifices every 8 to 16 inches.
Discharge rates vary from 0.4 to 0.7 gallons per minute for 100 feet of tubing, at line pressures that range from 5 to 15 pounds per square inch.
Clogging is a problem common to all drip irrigation systems, and to some extent to drip emitters and low-flow minisprinklers.
The degree of seriousness is a combined function of the specific contaminants in the irrigation water and the orifice size.
Clogging is the result of particles in water, biological clogging from fungal, bacterial, or algal growth, or lime and iron precipitation.
Irrigation waters, particularly the well waters of coastal and southern California, contain varying amounts of soluble salts that may precipitate in drip lines or emitters.
As water evaporates, temperatures change in the lines, the concentrations of solutes increase, and some solutes can precipitate with increased temperature.
High levels of calcium, magnesium, bicarbonate, and sulfates are of particular concern in the West.
Calcium, together with bicarbonates and sulfates, can form precipitates of lime and gypsum downstream from a filter, clogging drip orifices.
Clogging may be partial or complete.
In the case of a partial clog, the only apparent change is a small increase in
 line pressure.
In fact, that change in pressure can indicate a substantial decrease in water emission.
Injection of fertilizers into the drip system can enhance clogging.
Fertilizers that contain calcium and phosphates have the greatest potential to clog.
In contrast, liquid fertilizers containing acids can help prevent lime deposition.
The traditional method for controlling calcium and magnesium carbonate deposits has been to inject acid into the system either continuously or intermittently to reduce the pH of waters.
The compound used most commonly to lower the of water has been sulfuric acid.
Hydrochloric and phosphoric acids have also been used, but they are more expensive and pose severe handling hazards.
The search for a calcium and magnesium carbonate inhibitor led researchers to examine several commercial products.
One of these is the patented homopolymer of maleic anhydride that we studied in 1989 in a strawberry drip system.
In November 1988, we selected Gold Coast Farms of Santa Maria for the January-toAugust 1989 trial.
Their well water contained bicarbonate levels in the 4.0 to 4.5 Meq/L range.
Within the farm, we divided a 10-acre Chandler strawberry field into four plots of 2.5 acres each.
Two plots used the maleic anhydride polymer injected at 2 mg/L (2
 This apparatus injects an experimental polymer into drip lines, inhibiting the buildup of lineclogging sediments.
Fig.
1.
Drip tubing flow rates decrease as the season progresses.
Extra clogging in the lines not treated with the liquid polymer significantly reduces their capacity to transport water to plants.
ppm) and continuous chlorine at 1 mg/L, and the other two plots used only continuous chlorine injection.
The 10-acre field was set up SO each of the four sections would irrigate separately.
Each section consisted of one hundred 300-footlong rows.
Water meters were installed for each plot.
The grower continuously injected chlorine into each irrigation system from February 1, 1989 through August 8, 1989.
The treated plots also received a continuously injected polymertreatment.
The grower used soil matrix potential tensiometers to determine irrigation scheduling.
Irrigation was initiated when tensiometers reached 15 cb readings at depths of 4 or 6 inches.
TABLE 1.
Applied water and reference
 Month	Treated	Untreated	ETot
 ave.
inches applied	inches
 March	3.26	3.33	3.62
 April	2.92	2.92	5.08
 May	4.81	4.33	5.83
 June	4.30	4.41	4.94
 July	4.09	4.00	5.84
 Total	19.38	18.99	25.31
 *ETaw = the evapotranspiration of applied water.
tETo = reference evapotranspiration from CIMIS stations.
TABLE 2.
Irrigation hours to meet crop water requirement  for strawberry at Santa Maria, 1989
 Month	Treated	Untreated	Difference
 March	20.45	20.45	.00
 April	27.75	28.12	.37
 May	29.16	33.61	4.46
 June	27.40	35.74	8.34
 July	28.36	37.16	8.80
 Total	133.12	155.08	21.97
 TABLE 3.
Strawberry yield, measured in 12pound crates per 2.5 acres, Gold Coast, 1989
 3/3 to	5/20 to	Total
 Treatment	5/19	8/20	for year
 Treated 1 East	4,797	2,661	7,458
 Treated 2 West	4,264	2,365	6,629
 Untreated 1 East	4,165	2,310	6,475
 Untreated 2 West	4,120	2,288	6,408
 We read the water meters about once a week.
Emitter flow and uniformity were measured on March 21, June 21, and August 7.
Yield data were taken for each plot from March through May.
Weekly and monthly reference evapotranspiration  data were obtained from the CIMIS weather stations in Santa Maria.
The applied water data  showed a trend of lower flow rates in the untreated plots.
Figure 1 shows the flow rates of polymer-treated and untreated waters on March 1, March 21, June 21, and August 7.
Emission evaluations of polymertreated water show only slight decreases over the 6-month growing period, but untreated well waters show a decrease of nearly 50% by August.
A linear regression of flow rate versus time was fitted for both treated and untreated plots.
The test for equality of slopes demonstrated that the decrease in flow rate over time for untreated water was significantly greater than for treated water at the 1% level.
A shoppers' survey: California nuts and produce, food quality, and food safety
 The results  indicate that the system injected with 2 mg/L maleic anhydride polymer supplied the actual amount of water required for plant needs, while the untreated tubing's output decreased as the season progressed.
The crop water requirement  for strawberries and the flow rate differences are shown as hours of irrigation in table 2.
The hours of irrigation needed to apply a given amount of seasonal water are much greater for the untreated than the treated system.
795 consumers interviewed at 53 California markets gave a variety of reasons for buying the way they do.
Many had their own ideas about what indicates good quality in produce, but had trouble putting those ideas into words.
Consumer ideas about food safety were easier to articulate.
The yield from each individual plot was obtained for the period from March 1989 to May 19, 1989, and the yields from the aggregated plots , from May 20 to August 20, 1989.
A yield increase of about 300 12-pound trays per 2.5 acre plot was obtained in the early season.
Assuming this trend continued, an overall yield increase of about 600 trays would result where the aggregated yield was assigned to each 2.5 acre plot and added to the early season results.
This suggests that the plots treated with 2 mg/L maleic anhydride polymer received the appropriate amount of irrigation water.
Yields were increased and drip efficiency improved where we injected the polymer into drip irrigation lines.
J.
L.
Meyer is Irrigation and Soils Specialist and R.
A.
Strohman is Staff Research Associate, UC Riverside; M.
Snyder is Farm Advisor, Santa Barbara County; L.H.
Valenzuela is Farm Advisor, Santa Barbara County; and A.
Harris is with Ciba-Geigy, Manchester, United Kingdom.
The authors wish toacknowledge the valuable assistance provided by growers Ronald Burkand Robert Espiola of Gold Coast Farms, and by Olocco Ag Services, Santa Maria, California.
Consumer interest in fresh produce is high.
Researchers report that people are changing their eating habits to increase their intake of produce, and this attitude is reflected in different purchasing patterns.
The guiding factors in food choice are quality, nutritive value, and safety.
Consumer concerns about produce safety primarily with respect to pesticide and chemical residues have been the focuses of recent research.
When specifically asked, about 80% of consumers in a nationwide survey considered residues to constitute a serious hazard.
In the past two years, almost 20% of consumers have transformed their concern into action, and have altered their purchasing patterns to include the purchase organicor certified "residue-free" produce.
Little research focusing on consumers' perception of quality has been completed.
Consumers have identified products that are "inconsistent" in quality, but their criteria for quality have not been identified.
Although brand-name produce has been available for some time, consumers do not
 place a lot of emphasis on brands when it comes to purchasing.
Fewer than half of consumers consider a brand-name item to be superior in quality to those without brands.
Other researchers have not measured the influences of consumer identification and use of other indicators of produce quality, such as color, texture, and stage of maturity.
We undertook this study to determine the selection criteria of California consumers and their attitudes toward specific California specialty crops.
The first author personally interviewed 795 consumers in an open-ended questionnaire at 53 sites throughout California.
Cities were selected at random within population parameters.
Six stores were selected as interview sites in each of five cities with populations over 50,000.
We selected three stores from each of five cities, unincorporated areas, or polling districts with populations between 500 and 50,000.
We also selected one store in each of eight cities or unincorporated areas with populations under 500.
Stores were randomly selected from the telephone directory.
We conducted interviews in the produce department of each store between February and July 1987.
Fifteen consumers were randomly selected for interview at each survey site.
Consumers were asked to recall the number of times they had purchased selected
CRITERIA FOR SUCCESSFUL ADOPTION OF SDI SYSTEMS
 Subsurface drip irrigation  systems are currently being used on about 15,000 acres in Kansas.
Research studies at the NW Kansas Research and Extension Center of Kansas State University begin in 1989 and have indicated that SDI can be adapted for efficient, long-term irrigated corn production in western Kansas.
This adaptability has been demonstrated on other deep-rooted irrigated crops grown in the region by demonstration plots and producer experience.
Many producers have had successful experiences with SDI systems; however most experienced at least some minor technical difficulties during the adoption process.
However, a few systems have been abandoned or failed after a short use period due to problems associated with inadequate design, inadequate management, or a combination of both.
Both research studies and on-farm producers experience indicate SDI systems can result in high yielding crop and water-conserving production practices, but only if the systems are properly designed, installed, operated and maintained.
SDI systems in the High Plains must also have long life to be economically viable when used to produce the relatively low value field crops common to the region.
Design and management are closely linked in a successful SDI system.
A system that is not properly designed and installed will be difficult to operate and maintain and most likely will not achieve high irrigation water application uniformity and efficiency goals.
However, proper design and installation does not ensure high SDI efficiency and long system life.
An SDI system must be operated at design specifications and utilize good irrigation water management procedures to achieve high uniformity and efficiency.
An SDI is also destined for early failure without proper maintenance.
This paper will review important criteria for successful adoption of SDI for Kansas irrigated agriculture.
MINIMUM SDI SYSTEM COMPONENTS FOR WATER DISTRIBUTION AND EFFICIENT SYSTEM OPERATION
 Design considerations must account for field and soil characteristics, water quality, well capabilities, desired crops, production systems, and producer goals.
It is difficult to separate design and management considerations into distinct issues as the system design should consider management restraints and goals.
However, there are certain basic features that should be a part of all SDI systems, as shown in Figure 1.
Omission of any of these minimum components by a designer should raise a red flag to the producer and will likely seriously undermine the ability of the producer to operate and maintain the system in an efficient manner for a long period of time.
Minimum SDI system components should not be sacrificed as a design and installation cost cutting measure.
If minimum SDI components cannot be included as part of the system, serious consideration should be given to an alternative type of irrigation system or remaining as a dryland production system.
Figure 1.
Minimum components of an SDI system.
K-State Research and Extension Bulletin MF-2576, Subsurface Drip Irrigation  Component: Minimum Requirements.
The water distribution components of an SDI system are the pumping station, the main, submains and dripline laterals.
The size requirements for the mains and submains would be similar to the needs for underground service pipe to center pivots or main pipelines for surface flood systems.
Size is determined by the flow rate and acceptable friction loss within the pipe.
In general, the flow rate and acceptable friction loss determines the dripline size  for a given dripline
 lateral length.
Another factor is the land slope.
An SDI system consisting of only the distribution components would have no method to monitor system performance and the system would not have any protection from clogging or any methods to conduct system maintenance.
Clogging of dripline emitters is the primary reason for SDI system failure.
The actual characteristics and field layout of an SDI system will vary from site to site, but often irrigators will want to add additional capabilities to their system.
For example, the SDI system in Figure 2 shows additional valves that allow the irrigation zone to be split into two flushing zones.
The ability to flush SDI systems is essential.
Filter systems are generally sized to remove particles that are approximately 1/10 the diameter of the smallest emitter passageway.
However, this still means small particles pass through the filter and into the driplines.
Overtime, they can clump together and/or other biological or chemical processes can produce materials that need removal to prevent emitter clogging.
The opening of the flushline valves and allowing water to pass rapidly through carrying away any accumulated particles flushes the driplines.
A good design should allow flushing of all pipeline and system components.
If the well or pump does not have the capacity to provide additional flow and pressure to meet the flushing requirements for the irrigation zone, splitting of the zone into two parts may be an important design feature.
The frequency of flushing is largely determined by the quality of the irrigation water and to a degree, the level of filtration.
A good measure of the need to flush is to evaluate the amount of debris caught in a mesh cloth during a flush event.
If little debris is found, the flushing interval might be increased but heavy accumulations might mean more frequent flushing is needed.
The remaining components, in addition to the water distribution components of Figure 1, are primarily components that allow the producers to monitor the SDI system performance, to protect or maintain performance by injection of chemical treatments, and to allow flushing.
The injection equipment can also be used to provide additional nutrients or chemicals for crop production.
The backflow preventive device is a requirement to protect the source water from accidental contamination should a backflow condition occur.
The flow meter and pressure gauges are essentially the operational feedback cues to the manager.
In SDI systems, all water application is underground.
In most properly installed and operated systems, no surface wetting occurs during irrigation, so no visual cues are available to the manager concerning the system operating characteristics.
The pressure gauges at the control valve of each zone allow the measurement of the inlet pressure to driplines.
Decreasing flow and/or increasing pressure can indicate clogging is occurring.
Increasing flow with decreasing pressure can indicate a major line leak.
The pressure gauges at the distal ends of the dripline laterals are especially important in establishing the baseline performance characteristics of the SDI system.
Flowrate and pressure measurement records can be used as a diagnostic tool to discover operational problems and determine appropriate remediation techniques.
Figure 2.
An example layout for a well designed SDI system.
Anomaly A: The irrigator observes an abrupt flowrate increase with a small pressure reduction at the Zone inlet and a large pressure reduction at the Flushline outlet.
The irrigator checks and finds rodent damage and repairs the dripline.
Anomaly B: The irrigator observes an abrupt flowrate reduction with small pressure increases at both the Zone inlet and the Flushline outlet.
The irrigator checks and finds an abrupt bacterial flare-up in the driplines.
He immediately chlorinates and acidifies the system to remediate the problem.
Anomaly C: The irrigator observes an abrupt flowrate decrease from the last irrigation event with large pressure reductions at both the Zone inlet and Flushline outlet.
A quick inspection reveals a large filtration system pressure drop indicating the need for cleaning.
Normal flowrate and pressures resume after cleaning the filter.
Anomaly D: The irrigator observes a gradual flowrate decrease during the last four irrigation events with pressure increases at both the Zone inlet and Flushline outlet.
The irrigator checks and find that the driplines are slowly clogging.
He immediately chemically treats the system to remediate the problem.
Figure 3.
Hypothetical example of how pressure and flowrate measurement records could be used to discover and remediate operational problems.
The heart of the protection system for the driplines is the filtration system.
The type of filtration system needed will depend on the quality characteristics of the irrigation water.
Clogging hazards are classified as physical, biological or chemical.
The illustration in Figure 1 depicts a pair of screen filters, while Figure 2 shows a series of sand media filters.
In some cases, the filtration system may be a combination of components.
For example, a well that produces a lot of sand in the pumped water may require a cyclonic sand separator in advance of the main filter.
Sand particles in the water would represent a physical clogging hazard.
Another common type of filtration system is the disc filter.
Biological hazards are living organisms or life by-products that can clog emitters.
Surface water supplies may require settling basins and/or several layers of bar screen barriers at the intake site to remove large debris and organic matter.
Sand media filtration systems, which consist of a bank of two or more large tanks with specially graded filtration sand, are considered to be well suited for surface water sources.
Water sources that have a high iron content, can also be vulnerable to biological clogging hazards, such as when iron bacteria flare-up in a well.
Control of bacterial growths generally requires water treatment in addition to filtration.
Chemical clogging hazards are associated with the chemical composition or quality of the irrigation water.
As water is pulled from a well and introduced to the distribution system, chemical reactions can occur due to changes in temperature, pressure, air exposure, or also by the introduction of other materials into the water stream.
If precipitants form, they can clog the emitters.
The chemical injection system is often considered to be a part of the filtration system but it can also be used to inject nutrients or chemicals to enhance plant growth or yield.
There are a variety of types of injectors that can be used; the choice of unit depends on the desired accuracy of injection of a material, the rate of injection, and the agrochemical being injected.
There are also state and federal laws that govern the type of injectors, required safety equipment , appropriate agrochemicals and application amounts that can be used in SDI systems.
Always follow all applicable laws and labels when applying agrochemicals.
Many different agrochemicals can be injected, including chlorine, acid, dripline cleaners, fertilizers, and some pesticides.
Producers should never inject any agrochemical into their SDI system without knowledge of the agrochemical compatibility with the irrigation water.
For example, many phosphorus fertilizers are incompatible with many water sources and can only be injected using additional precautions and management techniques.
If a wide variety of chemicals are likely to be injected, then the system may require more than one type of injection system.
The injection systems in Figures 1 and 2 are depicted as a single injection point, located upstream of the main filter.
Some agrochemicals might require an injection point downstream from the filter location to prevent damage to the filter system.
However, this should only be done by experienced irrigators or with an expert consultant, since the injection bypasses the protection of the filter system.
Positive Displacement Pump Injection System
 Figure 4.
Typical layout for an injection system showing many of the safety interlocks and backflow prevention devices required to prevent contamination of the environment..
Chlorine is commonly injected to disinfect the system and to minimize the risk of clogging associated with biological organisms.
Acid injection can also lower the pH chemical characteristic of the irrigation water.
For example, high pH water may have a high clogging hazard due to a mineral dropping out of solution in the dripline after the filter.
The addition of a small amount of acid to lower the pH to slightly acidify the water might prevent this hazard from occurring.
Water quality can have a significant effect on SDI system performance and longevity.
In some instances, poor water quality, such as high salinity, could cause soil quality and crop growth problems.
However, with proper treatment and management, water with high mineral loading, water with nutrient enrichment or water with high salinity can be used successfully in SDI systems.
However, no system should be designed and installed without first assessing the quality of the proposed irrigation water supply.
WATER QUALITY ANALYSIS RECOMMENDATIONS
 Prevention of clogging is the key to SDI system longevity and prevention requires understanding of the potential problems associated with a particular water source.
Information on water quality should be obtained  and made available to the designer and irrigation manager in the early stages of the planning process so that suitable system components, especially the filtration system, and management and maintenance plans can be selected.
Table 1.
Recommended water quality tests
 1.
Electrical Conductivity  measured in ds/m or mmho/cm a measure of total salinity or total dissolved solids;
 2.
pH a measure of acidity where 1 is very acid, 14 is very alkali, and 7 is neutral;
 3.
Cations measured in meq/L, , includes; Calcium , Magnesium , and Sodium ;
 4.
Anions measured in meq/L, includes: Chloride , Sulfate , Carbonate , and Bicarbonate ;
 5.
Sodium Absorption Ratio  a measure of the potential for sodium in the water to develop sodium sodicity, deterioration in soil permeability and toxicity to crops.
SAR is sometimes reported as Adjusted  SAR.
The Adj.
SAR value better accounts for the effect on the HCO concentration and salinity in the water and the subsequent potential damage by sodium to the soil.
6.
Nitrate nitrogen  measured in mg/L;
 7.
Iron , Manganese , and Hydrogen Sulfide  measured in mg/L;
 8.
Total suspended solids a measure of particles in suspension in mg/L;
 9 Bacterial population a measure or count of bacterial presence in # / ml, ;
 10.
Boron* measured in mg/L;
 11.
Presence of oil**
 * The boron test would be for crop toxicity concern.
** Oil in water would be concern for excessive filter clogging.
It may not be a test option at some labs, and could be considered an optional analysis.
Results for Tests 1 through 7 are likely to be provided in a standard irrigation water quality test package.
Tests 8 through 11 are generally offered by water labs as individual tests.
The test for presence of oil may be a test to consider in oil producing areas of the state or if the well to be used for SDI has experienced surging, which may have mixed existing drip oil in the water column into the pumped water.
The fee schedule for Tests 1 through 11 will vary from lab to lab and the total cost for all recommended tests may be a few hundred dollars.
This is still a minor investment in comparison to the value offered by the test in helping to determine proper design and operation of the SDI system.
As with most investments, the decision lies with the investor.
Good judgments generally require a good understanding of the fundamentals of the particular opportunity and/or the recommendations from a trusted and proven expert.
While the microirrigation  industry dates back over 40 years now and its application in Kansas as SDI has been researched since 1989, a network of industry support is still in the early development phase in the High Plains region.
Individuals considering SDI should spend time to determine if SDI is a viable systems option for their situation.
They might ask themselves:
 What things should / consider before / purchase a SDI system?
1.
Educate yourself before contacting a service provider or salesperson by
 C.
Visit other producer sites that have installed and used SDI.
Most current producers are willing to show them to others.
2.
Interview at least two companies.
a.
Ask them for references, credentials  and sites  of other completed systems.
b.
Ask questions about design and operation details.
Pay particular attention if the minimum SDI system components are not met.
If not, ask why?
System longevity is a critical factor for economical use of SDI.
C.
Ask companies to clearly define their role and responsibility in designing, installing and servicing the system.
Determine what guarantees are provided.
3.
Obtain an independent review of the design by an individual that is not associated with sales.
This adds cost but should be minor compared to the total cost of a large SDI system.
Subsurface drip irrigation offers a number of agronomic production and water conservation advantages but these advantages can only be achieved with proper design, operation, and maintenance, so that the SDI system can have an efficient, effective, and long life.
One management change from current irrigation systems is the need to understand the SDI system sensitivity to clogging by physical, biological and/or chemical agents.
Before designing or installing an SDI system, be certain a comprehensive water quality test is conducted on the source water supply.
Once this assessment is complete, the system designer can alert the manager of any potential problems that might be caused by the water supply.
The old adage "an ounce of prevention is worth a pound of cure" is very appropriate for SDI systems.
Early recognition of developing problems and appropriate action can prevent larger problems.
While this may seem daunting at first, as with most new technology, most managers quickly will become familiar with the system and its operational needs.
The SDI operator/manager also needs to understand the function and need for the various components of an SDI system.
There are many accessory options available for SDI systems that can be included during the initial design and installation phases, and even added at a later time, but more importantly, there are minimum design and equipment features that must be included in the basic system.
SDI can be a viable irrigation system option, but should be carefully considered by producers before any financial investment is made.
The SDI operator/manager should monitor and record zone flowrates and pressures during ever irrigation event so that through observation of short and long term performance trends, operational problems can be discovered and remediated immediately.
The above discussion is a very brief summary from materials available through K-State.
The SDI related bulletins and irrigation-related websites are listed below:
 This paper was first presented at the 19th annual Central Plains Irrigation Conference, February 27-28, 2007, Colby, Kansas.
Permeable Pavement for Stormwater Management
 Carmen T.
Agouridis, Jonathan A.
Villines, and Joe D.
Luck, Biosystems and Agricultural Engineering
 M anaging runoff in urban areas offers many challenges for engineers, landscape architects, and planners.
As cities grow, the amount of impermeable surfaces-those that do not allow water to infiltrate into the ground-increases.
Examples of impervious surfaces are asphalt roads, concrete sidewalks, parking lots, building roofs, and areas of highly compacted soils such as in subdivisions.
If not properly managed, the stormwater runoff produced by these impermeable surfaces can have negative effects on nearby surface waters.
When waters from storm events do not infiltrate the soil, the stormwater management system, consisting of stormwater structures and pipes, quickly directs them to streams, rivers, and lakes.
Such increases in stormwater runoff can have detrimental effects on nearby lands and receiving streams resulting in flooding, increased peak flows, groundwater or stream baseflow reductions, increased stream velocities and streambank erosion, increased water temperatures, and reduced water quality.
Stormwater must be managed in such a way as to prevent or minimize these negative impacts from urban growth.
One method of stormwater management is to reduce runoff by increasing infiltration through the use of permeable or pervious pavement.
Permeable pavement allows stormwater to percolate through the pavement and infiltrate the underlying soils thereby reducing runoff from a site, unlike standard pavement which prohibits infiltration.
Permeable pavement looks similar to standard asphalt or concrete except void spaces are created by omitting fine materials.
Compacted gravel is not considered permeable pavement.
When properly designed, installed, and maintained, permeable pavement is an effective stormwater best manage-
 Figure 1.
Used to construct the parking spaces , sidewalks , and roadways  at the fire department in Georgetown, Ky., permeable pavement allows stormwater to infiltrate to the underlying soils.
Figure 2.
Permeable pavement  has large void spaces to allow water to infiltrate, unlike traditional asphalt.
ment practice  that can last for decades.
The purpose of this publication is to explain the benefits of permeable pavement, review the types of permeable pavement available, and discuss design considerations and maintenance requirements.
Types of Permeable Pavement
 Numerous types of permeable pavement are available.
Pervious concrete is most common today, but porous asphalt, interlocking concrete pavers, concrete grid pavers, and plastic reinforced grids filled with either gravel or grass are also available.
Other types and variations exist, but these are the most popular and versatile designs.
The pavement type itself typically refers only to the surface layer of a structure consisting of multiple layers.
Beneath the permeable pavement or surface layer, typically lies a filter course comprised of finer aggregate.
This filter course overlays a stone reservoir , the thickness of which depends on
 the stormwater storage needs and load bearing requirements.
Below the stone reservoir, a layer of filter fabric rests on the undisturbed soil.
The filter fabric prevents soil particles from entering the stone reservoir due to fluctuations in the water table or any pumping action from repeated loadings.
Filter fabric should also be used along the sides or perimeter of the permeable pavement system to prevent soil from entering at those locations.
Figure 3 shows a typical cross-section of a permeable pavement installation.
To prevent clogging, only cleaned, washed stone that meets municipal roadway standards should be used.
Depending on design needs, perforated pipes can be added near the top of the stone reservoir to discharge excess stormwater from large events.
Also, instead of allowing stormwater to infiltrate into the underlying soil or where the permeability of the underlying soil is not optimal, perforated underdrain pipes can be installed to route water to an outflow facility structure.
It is recommended that an observation well be installed at the down-gradient end of the permeable pavement to monitor performance.
Figure 3.
Typical cross-section of permeable pavement.
Adapted from City of Rockville, MD.
Pervious concrete is a mixture of Portland cement, coarse aggregate or gravel, and water.
Unlike conventional concrete, pervious concrete contains a void content of 15 to 35 percent  that is achieved by eliminating the finer particles such as sand from the concrete mixture.
This empty space allows water to infiltrate the underlying soil instead of either pooling on the surface or being discharged as runoff.
Sidewalks and parking lots are ideal applications for pervious concrete.
The structural strength of pervious concrete, although typically less than standard concrete mix designs, can easily withstand the relatively light loads generated by pedestrian and bicycle traffic.
The loads placed on pervious concrete in parking lots can be much more substantial and require consideration when selecting the concrete mix and pavement thickness.
While the structural strength of porous concrete can be increased by adding larger amounts of cement, the porosity will decrease, thus decreasing infiltration rates.
Porous asphalt is a standard asphalt mixture of both fine and coarse aggregate bound together by a bituminous binder except it uses less fine aggregate than conventional asphalt.
The void space in porous asphalt is similar to the 15 to 35 percent of pervious concrete.
The surface appearance of porous asphalt is similar to conventional asphalt, though porous asphalt has a rougher texture.
The surface layer of asphalt is usually thinner than a comparable installation of pervious concrete.
While the compressive strength of pervious concrete is usually less than that of conventional concrete, the compressive strength of porous asphalt is comparable to that of conventional asphalt.
Porous asphalt can be used for pedestrian applications such as greenways and low volume, low speed vehicular traffic applications such as parking lots, curbside parking lanes on roads, and residential or side streets.
Permeable interlocking concrete pavers  and clay brick pavers  as well as concrete grid pavers  are similar in installation and function but are made from different materials.
PICPs are solid concrete blocks that fit together to form a pattern with small aggregate-filled spaces in between the pavers that allow stormwater to infiltrate.
These spaces typically account for 5 to 15 percent of the surface area.
PICBP as the same as PICPs except the material is brick instead of concrete.
With CGPs,
 Figure 4.
Pervious concrete was used to construct a portion of the Legacy Trail in Coldstream Park in Lexington, Ky.
Figure 5.
Porous asphalt is very similar in appearance to conventional asphalt except it has a rougher texture.
Figure 6.
Permeable interlocking concrete pavers ,  permeable interlocking clay brick pavers , and  concrete grid pavers.
large openings or apertures are created by the CGPs lattice-style configuration.
These openings, which can account for 20 to 50 percent of the surface area, usually contain soil or grass, though small aggregates can be used.
While CGPs have larger openings than PICPs and PICBPs, they are not designed for use with a stone reservoir but instead can be placed directly on the soil or an aggregate base.
As such, the infiltration rate of PICPs and PICBPs is much higher than that of CGPs.
reduced hydroplaning on roadways, and resistance to freeze/thaw conditions.
Evaporation from beneath the permeable pavement can produce a cooler surface helping reduce the heat island effect often experienced in urban settings.
Permeable pavement can also aid in the health and development of urban trees by providing root systems with greater access to water and air.
Plastic turf reinforcing grids  are made of interlocking plastic units with large open spaces.
PTRG are generally used to add structural strength to topsoil and reduce compaction.
Typically grass fills the open spaces, although small aggregate can be used as well.
Infiltration is improved when grass is used as the plant roots help increase the permeability of the underlying soil.
Benefits of Permeable Pavement
 Permeable pavement offers a number of environmental benefits.
Increasing the amount of stormwater infiltrated can result in lower stream flow levels after storm events, increased stream baseflow due to increased groundwater recharge, and increased stream stability through reduced stream velocities and peak flows.
The benefits of providing stream stability range from erosion control to maintaining the habitat necessary for aquatic life.
As permeable pavement eliminates standing water, other noticeable benefits include improved braking,
 benefiting aquatic habitats.
Permeable pavement also reduces the temperature of waters entering surface and groundwater bodies thus reducing thermal pollution.
The materials used in permeable pavement and its foundation  are capable of retaining soluble and fine particulate nutrients, sediments, heavy metals, and other pollutants from stormwater runoff thus improving the quality of water that enters surface waters and groundwaters.
Coarse particulate removal is not advised due to issues with clogging, SO some pretreatment may be required in addition to regular maintenance.
Some stormwater pollutant loads may also be reduced as permeable pavements can act like a biofilter where microorganisms break down contaminants.
Studies have reported reductions in sediment , total nitrogen , phosphorus , BOD , bacteria , and metals.
Additionally, using permeable pavement can lessen the need for treatment chemicals.
For example, permeable pavement has been shown to reduce the need for road salt applications by up to 75 percent due to improved drainage conditions.
Reducing road salt and chemical applications leads to a reduction in chloride levels in receiving waters thus
 Uses of Permeable Pavement
 Permeable pavement can be installed in most places that conventional concrete or asphalt pavement is presently used.
However, some properties of most permeable pavements limit their applicability.
Permeable pavements are not generally used in applications where high traffic loads, in terms of volume and weight, and/or high rates of speed are encountered.
Their use should be limited to pedestrian and light to medium vehicle traffic.
Greenways, sidewalks, driveways, and overflow parking lots are ideal locations.
Permeable pavement has also been used in agricultural facilities such as horse washing pads.
To reduce the potential for groundwater contamination, consideration should be given to the pollutant loads carried in the stormwater runoff because permeable pavement promotes infiltration.
Permeable pavement should not be used near "hotspots" or areas generating significant concentrations of pollutants.
Examples of such hotspots include vehicle service areas, industrial chemical storage facilities, and gas stations.
Permeable pavement is typically designed to absorb only the stormwater that falls directly on it, although stormwater from rooftops or adjacent parking lots can sometimes be directed to permeable paved areas.
Typically, drainage
 from adjacent areas should be managed separately.
If permeable pavement is to receive stormwater runoff from off-site areas, pre-treatment  may be needed to remove coarse particulates, even if the contributing area is 100 percent impervious.
A variety of BMPs are available to manage stormwater runoff from adjacent lands.
Refer to the Resources section to locate additional information.
Consideration of site conditions is also important.
Permeable pavement is most applicable on sites with slopes of 0.5 percent or less SO that stormwater runoff is evenly distributed and has a chance to infiltrate.
Permeable pavement has been used on sites with slopes up to 5 percent.
The underlying soils should be carefully evaluated.
Soils should have a minimum field-verified permeability rate of 0.5 inches per hour, although the U.S.
Environmental Protection Agency lists 0.27 in/hr as the minimum acceptable infiltration rate.
If underlying soils do not meet the permeability requirement, then modification using gravel and/or sand and/or the use of an underdrain is required.
For these low permeability soils, a high ratio of bottom surface area to storage volume is needed.
Installing permeable pavement at sites with soils not meeting the minimum infiltration rate of 0.27 in/hr should be approached with caution.
If the combined silt/clay content exceeds 40 percent and/or the clay content exceeds 30 percent, frost-heave is likely and percolation is poor.
Permeable pavement should not be used over uncompacted fill soils as this material can be unstable.
The depth to bedrock or the seasonally high water table from the bottom of the system should be at least 2 feet, although 4 feet is more desirable.
Permeable pavement should not be installed within 100 feet of drinking water wells to avoid groundwater contamination.
If possible, permeable
 pavement should be located away from building foundations to prevent damage from seepage.
A minimum distance of 100 feet up-gradient and 10 feet downgradient is recommended.
Cost considerations generally limit the application of permeable pavement to sites less than 10 acres.
To design permeable pavement, consideration must be given to both structural and hydraulic Clay components.
The manufacturer should be consulted to determine the appropriate structural design process for the type of permeable pavement selected.
The intended use of the permeable paved surface will impact the needed thickness of the pavement and the underlying layers.
Both must be sized to support anticipated traffic loads, storm volume storage, drain times, and water quality needs.
Permeable pavement has been successfully used in karst environments.
The large surface area over which infiltration occurs helps reduce the potential for sinkhole development.
However, a detailed geotechnical investigation may be needed to address concerns about sinkhole formation and/or groundwater contamination.
It is recommended that the stone reservoir be carbonate to aid in buffering capacity.
The stone reservoir is sized to hold the desired stormwater volume generated from the design storm.
Specifications of duration and return period for the design storm should be obtained from the locality.
Stormwater stored in the stone reservoir should ideally exfiltrate within 24 to 48 hours following rainfall, but no less than 12 hours and no more than 72 hours, to provide sufficient storage for subsequent storm events.
The ability of the soil to infiltrate stormwater depends
 Table 1.
Estimated soil infiltration rates.
Soil Texture*	Soil Group	
 Loamy sand	A	2.41
 Sandy loam	B	1.02
 Silt loam	C	0.27
 Sand clay loam	C	0.17
 Clay loam	D	0.09
 Silty clay loam	D	0.06
 Sandy clay	D	0.05
 Silty clay	D	0.04
 *Silt loam, sand clay loam, clay loam, silty clay loam, sandy clay, silty clay, and clay soils have infiltration rates below the recommended minimum of 0.5 in/hr.
Silt loam at 0.27 in/hr is listed by the U.S.
EPA as acceptable but not recommended.
on its permeability.
Infiltration rates should be tested in the field.
Table 1 shows ranges of infiltration rates for hydrologic soil groups.
It is recommended that infiltration rates are tested in the field and that a design factor of safety of 2 is used.
The design factor of safety accounts for any soil compaction that may occur during construction as well as clogging over time.
The thickness of the stone reservoir depends largely on structural requirements.
The thickness can be increased to accommodate water storage needs, but it should not be decreased from what is structurally required.
Decreasing the thickness would compromise structural stability.
Design of the stone reservoir storage area is generally completed through one of two methods: minimum depth method or minimum area method.
The minimum depth method determines the depth of the stone reservoir given a specific area for the permeable pavement.
The minimum area method computes the needed surface area of the permeable pavement given a design depth for the stone reservoir.
The method described in this publication does not provide guidance on underdrain design.
1.
Compute the depth of the stone reservoir.
dp = depth of stone reservoir 
 Q = runoff from contributing area 
 A = contributing area 
 Ap = permeable pavement surface area 
 P = design rainfall 
 f = infiltration rate 
 T = fill time 
 Vr = void ratio of stone reservoir
 Not that void spaces typically range between 30 and 40 percent, although it is recommended that the exact value be obtained from the supplier.
2.
Compute the maximum allowable depth of the stone reservoir.
dmax= = dmax = Maximum allowable depth of stone reservoir  Ts = Maximum allowable storage time 
 Check the design feasibility:
 Is the bottom of the aggregate at least 2 ft above the seasonal high water table?
If no to either, reduce design storm depth or increase permeable pavement surface area.
1.
Compute the maximum allowable depth of the stone reservoir.
2.
Select dp so that it is less than or equal to dmax and bottom of aggregate is at least 2 ft above seasonal high water table.
3.
Compute the minimum required surface area.
Following either method, complete the following:
 1.
Determine the minimal structural base thickness.
2.
Check for minimum separation between bottom of structural base and seasonal high water table.
3.
Select the geotextile filter fabric for soil separation.
Example: Minimum Depth Method
 Local regulations require capture of the 2-year 24-hour storm, which is 3.1 inches for Lexington, Kentucky.
The goal is to capture runoff from building roofs and access roads and convey stormwater runoff to a permeable pavement system in the parking lot.
Since the contributing area has a CN = 98, all of the flow from the design storm will flow to the permeable pavement.
Contributing area  is 30,000 ft2, and permeable pavement area  is 40,000 ft2.
The field tested infiltration rate  is 0.64 in/hr.
With a design factor of safety of 2, f=0.32 in/hr.
The voids ratio  supplied by the quarry is 0.4.
T is assumed to be 2 hours.
A maximum allowable storage time of 24 hour is the design criteria.
dp is less than d max"
 The structural base thickness.
In this example, assume a structural base thickness of 16 in.
is required for expected loadings and frost conditions.
This is thicker than the 12.0 in.
required.
The bottom of the structural base is at least 2 ft from the seasonal water table.
The total thickness of the permeable pavement system will consist of the thickness of the permeable pavement surface, filtering layers, and the structural base.
If a leveling course is used with permeable pavers, include this in the total thickness.
Based on a sieve analysis of the soil subgrade, use the U.S.
Highway Administration  geotextile filter criteria to select the appropriate geotextile.
Maintenance should be performed on a regular basis.
To prevent clogging, the permeable pavement surface should be vacuum swept followed by high-pressure jet hosing at least four times per year.
Do not apply sand or ash to permeable pavement for snow removal purposes.
Signage should be posted at locations where permeable pavement is installed to advise maintenance crews of this requirement.
Openings in the surface of permeable pavements are susceptible to clogging by sediment from passing vehicles, wear of the pavement surface, and runoff from nearby disturbed soils.
It is therefore essential to ensure that nearby soils are adequately secured prior to, during, and after installation of permeable pavement.
Pretreatment systems may be required to help prevent clogging.
Legally binding easements or covenants may be needed to ensure proper maintenance techniques are followed.
The permeable pavement should undergo regular inspection.
Inspection should occur several times within the first few months after construction to check that pretreatment systems, such as vegetative filter strips, are functioning properly in addition to the permeable pavement.
Afterwards, inspection can occur on a quarterly to annual basis depending on performance.
It is also recommended that following large storms permeable pavement be inspected for evidence of clogging.
If spot clogging is identified on pervious concrete or porous asphalt, drilling half-inch holes into the pavement every few feet may help.
For permeable pavers, select pavers can be replaced.
Another option is to design a perimeter stone filter inlet as a backup.
Extending the stone base several feet outside the perimeter of the permeable pavement offers a means of infiltrating stormwater should the system clog.
If the subsoil or subsoil-filter cloth becomes clogged, complete replacement will be required.
One possibility is to include additional capped underdrains in the design as a backup system.
This way, the system can still provide a level of stormwater storage and treatment.
A number of factors affect the cost of permeable pavement, such as the availability of materials, transport, site conditions, stormwater management requirements, project size, contractor experience, and, in the case of pavers, method of installation.
Consideration should also be given to long-term maintenance costs.
However, using permeable pavement as part of a larger stormwater management effort can yield substantial long-term savings.
The most obvious savings come in the form of land that would otherwise have to be used for retention ponds and other traditional stormwater infrastructure.
Since permeable pavement and other low-impact development  stormwater management methods can reduce or eliminate the need for surface ponds, the space saved can be used for incomegenerating property development.
In addition, curb and gutter systems now being used in conventional parking lots can be reduced in size or eliminated entirely.
The EPA conducted a series of case studies across the U.S.
which revealed that total capital costs of comprehensive LID stormwater management installations  were actually 15 to 80 percent less than conventional retention and drainage facilities.
For Water Quality Protection in Arkansas
 BEEF CATTLE MANAGEMENT For Water Quality Protection in Arkansas
 MANAGEMENT OF HEAVY USE AREAS
 Managing Specific Heavy Use Areas
 Dirk Philipp, Associate Professor-Forages, University of Arkansas System Division of Agriculture Katherine Teague, County Extension Agent-Agriculture/Water Quality, University of Arkansas System Division of Agriculture
 Karl VanDevender, Extension Agriculture Engineer, University of Arkansas System Division of Agriculture
 T he beef industry is a major part of Arkansas' economy.
Cattle are produced on approximately 23,000 farms, of which over 90 percent are family-owned and operated.
The total economic impact of our state's beef industry was over $600 million in 2016.
Arkansas is also rich in water resources that provide drinking water for communities, irrigation for agriculture, transportation, and recreational benefits including swimming and fishing.
The state's rivers and streams tributaries typically originate in rural, forested areas and drain large watersheds encompassing both urban and rural areas, including livestock operations.
Therefore, it is crucial to minimize environmental disturbances in all parts of the watershed, as water resources are shared by a growing population.
The main objective of livestock management for water quality is to minimize manure-contaminated runoff entering waterways.
Through environmentally sound management of animals and manure, the quality of our state's water resources can be protected.
Conversely, improper livestock and
 result in manure accumu-
 and loss of desirable
 serious water quality impairments.
Prevention is a more cost-effective approach than remediation to protecting water quality.
The goal of pollution prevention in livestock agriculture is to avoid the contamination of ground and surface waters with undesirable bacteria and excess nutrients from manure.
The two primary nutrients of concern are phosphorus and nitrogen.
While both elements are essential nutrients for living organisms, excessive amounts in water bodies can cause eutrophication, a process in which aquatic plant growth is accelerated.
The resulting microbial decomposition causes the depletion of dissolved oxygen, essentially depriving other organisms of this crucial element.
In turn, populations of desirable fish such as crappie and bass may decline, while more low-oxygen tolerant species such as carp may increase.
Furthermore, livestock manure can be a source of disease-causing organisms.
These pathogens can infect humans and animals alike through contact with a contaminated water source.
of which may lead to
 The objective of this publication is to help beef producers recognize management practices that protect water quality while enhancing their operations economically.
If these practices are implemented voluntarily, environmental concerns can be addressed on the farm with the freedom and flexibility not available through regulation.
S oil compaction from overstocking is a common problem that results in reduced infiltration rates and increased runoff risk.
This is particularly the case in fields that are designated for hay feeding during the colder and wetter periods of the year.
There is rarely only one soil type or topographic feature found on any property; therefore, different areas of the farm should be managed accordingly to minimize environmental impacts while maximizing utilization for the production goals that the producer wants to achieve.
In general, loamy and clayey soils are more susceptible to compaction than soils with gravely or sandy textures.
Moreover, soils around riparian zones can easily be compacted due to the higher amount of organic matter and moisture content found there in comparison to upland pastures.
Producers should recognize the location of particularly wet areas that might be excluded from grazing or protected with special measures.
Soil compaction is primarily caused by cattle hoof action, and several factors can influence the magnitude of compaction.
Among these are:
 1.
STOCKING DENSITY This has been shown to affect infiltration rates and vegetative growth, but depending on the grazing method used, the impact of high stocking densities can be acceptable if animals graze through an area quickly and at times with low soil moisture present.
2.
GRAZING MANAGEMENT Continuous stocking should be avoided in areas where cattle have the opportunity to loaf or socialize in areas such as riparian zones or streams.
With rotational grazing or strip grazing, producers have control over how long animals will remain in a particular paddock, thus reducing the risk of soil compaction and over-, underor spot grazing.
FIGURE 2.
Beef production is a vital contributor to the Arkansas agriculture.
The total impact of the state's beef industry is over $1.4 billion.
3.
VEGETATIVE GROWTH Pasture should be kept in good condition, that is, maintaining ground cover, sufficient forage growth, and avoiding overgrazing.
The pasture canopy helps reduce the impact of rain and, therefore, helps retains oil particles in place to minimize erosion.
In addition, pasture canopy and roots help with water movement into the soil and therefore help reduce runoff.
As previously indicated, the main concern in maintaining water quality standards is the potential addition of N, P, sediment and pathogens to surface waters.
These additions may occur from direct deposits or when those elements are subject to leaching or runoff from pastures.
The concentration of nutrients and microorganisms in manure deposits is high; therefore, the challenge is to keep manure on pastures and away from waterways through suitable grazing management and/or appropriate placement of filter strips.
Manure distribution on good pastures is usually not a problem; however, uneven distribution of manure is more likely to contribute to water quality impairments.
Regardless of grazing method,
 the major problem is overgrazing, which occurs when too many animals are kept on too few acres for prolonged periods of time.
This can result in reduced production of desirable forage species in a pasture, increased potential for internal parasite infestations, decreased animal performance and pasture damage due to compaction, especially on wet soils.
Grazing animals can have either a positive or negative effect on water quality, depending on the way their grazing patterns are controlled.
Proper grazing management favors pasture productivity and reduces the potential for soil erosion and manure runoff.
Healthy and vigorous canopy cover protects and enhances water quality by lessening the impact of precipitation which dislodges soil particles, thereby reducing the amount of sediment in surface runoff as well as the volume of runoff water.
FIGURE 3.
The challenge for beef producers is to utilize manure without impacting water quality.
This is achieved through appropriate management strategies, particularly maintaining pasture canopy height and applying suitable grazing methods.
Possible stocking rates depend upon the land's carrying capacity.
Factors affecting the carrying capacity include soil productivity, forage yield potential, species composition, animal age, soil type and the physical characteristics of the pasture.
When implementing a forage plan, the advantages and disadvantages of possible grazing methods should be considered.
A grazing method is a defined procedure or technique of grazing management designed to achieve a specific objective.
These methods can impact environmental quality to a larger or smaller extent based on their specific nature.
Some of the more common grazing methods are:
 This grazing method allows livestock unrestricted and uninterrupted access to a specific area.
No subdivision fences are used during this period.
To respond to changes in forage supply, producers can add or remove livestock, increase the total size of the area being grazed or provide supplemental feed.
In northwest Arkansas, many producers utilize this grazing method due to relatively low input requirements such as labor and fencing material.
Because farms in the region are relatively small and most producers or their spouses are required to seek off-farm income, this is the preferred grazing method.
However, one single method of grazing-particularly continuous stocking-rarely fits an overall forage plan.
Moreover, given the topography, weather patterns and soil conditions, this method may be disadvantageous from the viewpoint of environmental stewardship.
Some studies have shown that continuous stocking increases the runoff potential, simply because of greater soil compaction through cattle hoof action compared with other grazing methods or haymaking.
Overgrazing can frequently occur and results in poor groundcover and low infiltration rates.
In addition, forage utilization is lower at about 55 to 65 percent with continuous grazing in comparison with more advanced methods such as rotational grazing.
Grazing pressure under continuous grazing may be low and thus cattle may avoid certain pastures areas, resulting in weed development and encroachment in the long term.
Rotational stocking implies recurring periods of grazing among two or more paddocks with periods of rest and regrowth of forage between grazing events.
During periods with high forage production, some paddocks can be used for hay before the forage becomes too mature.
Under normal circumstances, a paddock or cell is grazed until 70 to 80 percent of the available forage has been utilized.
Rotational stocking is particularly important for pastures that contain species that benefit from rest periods.
Legumes such as clovers and alfalfa should be grazed rotationally to provide times for replenishment of root and shoot carbohydrates.
A grazing system comprised of rotational stocking as a grazing method is more labor intensive, but there are advantages in terms of environmental sustainability.
There is evidence that nutrient concentration in runoff may be reduced
 under rotational stocking compared with continuous stocking.
Additionally, a rotational stocking scheme gives the producer the flexibility to react to changes in forage production and to take advantage of differences in pasture species maturity of warmand cool-season forages.
Strip grazing confines animals to an area that is grazed during a relatively short period of time.
Utilization is high with this grazing method, up to 80 to 90 percent, because grazing takes place quickly on a small area, thereby reducing waste due to trampling.
Stocking density is set high enough to remove available forage as completely and quickly as possible.
This practice allows juvenile animals to graze areas that their dams cannot access at the same time.
Therefore, the impact on environmentally sensitive areas can be reduced by avoiding trampling of heavier animals yet giving access to forage for smaller animals with a requirement for higherquality forage.
In a grazing system using continuous stocking, buffer grazing is an approach to adjust forage supply by using temporary fencing to exclude livestock from certain areas that can be harvested either as hay or grazed during a time when environmental impacts are minimized.
This grazing method is well-suited to make use of sensitive riparian areas by providing only infrequent access for grazing livestock yet allowing extra forage when needed.
The stability of streambanks is of utmost importance for maintaining a high degree of on-farm water quality protection.
Numerous studies have shown that livestock can damage streambanks in the process of seeking access to water and shade.
This is especially critical with widespread use of toxic endophyte-infected tall fescue forage that may induce elevated body temperatures that lead cattle to seek water cooling, particularly during spring and summer.
Besides trampling of streambank vegetation resulting in sediment loss, water quality may be impaired through defecation in streams, both of
 which can result in a transfer of nutrients from pasture to waterway.
Definition of Riparian Zones
 Riparian zones are vegetated corridors adjacent to streams that provide a transition zone between aquatic and upland ecosystems.
For many livestock producers, riparian zones are also economically important as forage quantity and quality tends to be greater in these areas than on upland pastures.
If managed properly, riparian zones can protect waterways while simultaneously enhancing forage supplies.
Riparian areas serve a variety of functions which help protect water quality:
 Riparian vegetation including trees and understory species help maintain stream bank structure by holding soil in place and slowing the erosive power of water flow.
Through reduced erosion, less sediment is transported away, keeping fish habitat intact while minimizing nutrient loss.
Riparian vegetation can filter runoff and hence reduce the amount of sediments and nutrients reaching the stream.
Nutrients that are transported from higher upland areas can be taken up by riparian plants.
Riparian vegetation provides shade to maintain cooler water temperatures.
Algae growth is limited in shaded water bodies due to reduced solar radiation.
Woody debris can help create spawning areas for fish.
Smaller organic debris such as twigs and leaves provide a food source for many aquatic organisms.
Riparian vegetation helps reduce stream velocity that, in turn, helps reduce bank erosion and sediment loss.
The stream velocity reduction is the combined result of vegetation reducing surface flow into the stream, increasing inflitratiton into to the soil and slowing of the stream flow itself.
THE STREAMSIDE FOREST BUFFER
 FIGURE 4.
Schematic design of a stream buffer.
There are usually several zones between the stream and the crop or pasture land.
Illustration courtesy of Arkansas Water Resources Center, University of Arkansas.
Original source USDA Forest Service.
There are many management options to improve the functionality of riparian zones through proper livestock management.
Even in cases where riparian zones have been degraded to a high degree, vegetation will re-establish soon after stress factors which diminished vegetation in the first place have been removed.
Complete livestock exclusion is an effective way to let bank vegetation recover; however, adoption has been limited due to various reasons, and there are other opportunities to achieve desired results.
Stream Crossings and Partial Livestock Exclusion
 In many instances, intermittent streams cross farmers' land or serve as property boundaries.
These streams drain pastures and serve as tributaries for larger rivers or lakes further downstream.
Therefore, any kind of water quality impairment occurring at that level should be avoided.
Good grazing management is especially important whenever paddocks are intersected by a larger drainage channel.
Often, cattle are given free choice of where to cross.
However, establishment of designed stream crossings is preferred due to their environmental and potential production benefits.
One of the simpler solutions is to cover the stream bottoms with coarse gravel at specific crossing sites which prevent further channel erosion and excluding cattle from sites along the stream that are already heavily eroded.
In doing so, temporary fences made of polyor high-tensile wires can be set up relatively inexpensively and allow for flexibility when they have to be moved.
Another type of livestock crossing for intermittent creeks or small permanent creeks is comprised of an approximately 8-foot-wide concrete slab that is lined with large rocks on either side.
These rocks prevent cattle from walking into the stream, while catching debris and sediments during runoff events.
Many NRCS financial incentive programs include stream crossings as approved practice.
Fencing of streams is recommended whenever degradation reaches a point where temporary, or for some stream sections permanent, livestock exclusion is warranted.
One management strategy is one-sided exclusion of a stream with a temporary fence.
This will allow cattle access on one side, but animals are discouraged from crossing the entire stream.
Therefore, the fence should be placed close to the edge of the streambank.
To make this option workable, livestock need to be rotated frequently to avoid overuse of one or the other side of the streambank.
Fencing along both sides of the stream is recommended when bank damage has progressed to an extent that complete exclusion is the only option for sufficient soil protection and vegetation recovery.
In this case, cattle can still be given infrequent access to graze forage inside the fenced area.
Livestock need to be rotated frequently to avoid overuse of one or the other side of the streambank.
Fencing along both sides of the stream is recommended when bank damage has progressed to an extent that complete exclusion is the only option for sufficient soil protection and vegetation recovery.
In this case, cattle can still be given infrequent access to graze forage inside the fenced area.
Providing watering devices off-stream has been shown to be an effective alternative to stream access.
Examples such as nose water pumps can provide clean water to animals while minimizing trampling of streambanks.
When given the choice, cattle drank from an off-stream water trough 92 percent of the time VS.
the time spent
 FIGURE 6.
Healthy banks surrounding an intermittent stream in a pasture setting.
Photograph courtesy of John Pennington, University of Arkansas Division of Agriculture.
FIGURE 5.
Damage to an intermittent stream caused by uncontrolled access of cattle.
The streambanks recovered rapidly after access for livestock was limited.
FIGURE 7.
Example of a well-constructed cattle crossing.
These structures help maintain streambank stability by allowing cattle to cross the water at certain locations only.
Stream crossings vary in design and costs.
Photograph courtesy of NRCS.
in the creek in an experiment conducted in Virginia.
During this study, streambank erosion was reduced by 77 percent and in-stream total suspended solids were reduced by 90 percent, total nitrogen by 54 percent, and total phosphorus by 81 percent.
During typical, hot Arkansas summers, cattle may still prefer the cooler stream areas, but nutrient transport into streams from feces should be avoided.
Time spent by cattle in streams can be minimized by providing shade that is located away from streams.
If no other option is available than watering cattle from streams, livestock access points should be protected with gravel similar to a stream crossing, SO that animals do not linger, trample banks or otherwise damage the channel structure.
For additional information on watering options, refer to Extension Fact Sheet
 Grazing Management in Riparian Zones
 Total livestock exclusion may provide the quickest results in terms of vegetation recovery in eroded riparian zones, but appropriate grazing management can greatly reduce negative impacts in riparian zones.
In general, grazing practices that have negative effects on soil stability and plant vigor should be avoided.
Grasses and forbs can be grazed in riparian areas as long as an approximate minimum canopy height of 4 inches is maintained.
While most producers focus on grazing practices for cattle, an increasing number of farmers own goats and sheep, which have somewhat different grazing habits than large ruminants.
Goats are browsers and can select individual leaves and strip bark of woody plants, which needs to be taken into consideration when stocking these animals in newly reforested areas.
Sheep graze close to the ground but tend to do less damage in riparian areas since these animals do not congregate in low-lying areas as they feel vulnerable to predation.
Riparian zones should be grazed whenever conditions allow for minimal environmental impact.
The following recommendations should be considered whenever livestock is utilized to graze riparian vegetation:
 FIGURE 8.
Off-stream watering devices can reduce cattle damage to pond banks and ensure the availability of water in a safe manner.
In the picture above, the soil surrounding the water access point is protected with coarse gravel to prevent the development of muddy conditions.
Photograph courtesy of NRCS.
Monitor soil moisture content close to streams.
If moisture content is high, soil is more sensitive to compaction, resulting in increased runoff during following precipitation events.
Graze pastures to a height of no less than 4 inches.
Avoid moving cattle to riparian zones during hot summer days.
Cattle will linger in streams and may damage streambanks.
Avoid cattle grazing during periods of flowering of native grass species.
Avoid excessive grazing of woody species that build the underbrush in a riparian ecosystem.
Grazing methods utilized depend on the situation, but rotational stocking will likely be more beneficial from an environmental standpoint than continuous stocking.
Furthermore, other methods such as strip grazing can be used to move cattle through sensitive areas quickly.
Creep grazing can be used to give calves access to lush vegetation that usually develops in riparian zones due to generally higher soil moisture in these areas.
H eavy use areas are those areas where livestock tend to congregate.
Apart from watering devices and stream crossings that were previously covered, examples emphasized here include feeding areas, shade loafing areas, travel lanes, working facilities and holding pens.
The typical site has little or no vegetative cover and substantial manure accumulation.
Emphasizing soil, vegetation and animal management in these areas can reduce the potential for water impairment.
Much of the needed management relates to whether the heavy use area is permanently located, like working facilities, or temporarily located, like hay rings.
Regardless if the heavy use area is of a permanent or temporary nature, the basic design and management principles are keep the clean water clean, minimize the amount of water exposed to the heavy use area and treat the water exiting the heavy use area.
In practice this usually is accomplished with upslope diversions as needed, minimizing the size of heavy use area and vegetated filter strips downslope.
Heavy use areas are generally characterized by a lack of vegetative cover, compacted soil and a concentration of manure.
Cattle cannot graze these areas because little if any forage is produced there.
Heavy use areas cannot be completely avoided, but the size can be minimized.
Travel lanes should be no wider than necessary to provide movement of cattle and equipment from one part of the farm to another.
Holding pens and working facilities should be designed to make maximum use of a minimum of space.
The location of a heavy use area can impact management efficiency and water quality.
Select sites with higher elevation and slight to moderate slope to promote drainage and reduce the amount of standing water.
Uniform slopes are less likely to puddle.
Avoid steep slopes that increase the chance of nutrient runoff and erosion.
Studies of settling channels for unpaved drylot runoff showed an accumulation of about 2 yd 3 of solids/head-year from a 340-foot-long lot with a 15 percent slope.
From a shorter, 7 percent slope, the settled solids were only 0.6 3/head-year.
Berms or grassed waterways may be necessary to direct water away from heavy use areas.
When determining the location of heavy use areas, avoid environmentally sensitive areas.
These areas include creeks, ponds, wells, sinkholes or any access to surface or ground water.
Constant action and movement of cattle can cause erosion problems and premature destruction of pond and creek banks.
Water quality can be lowered by the increase in sediments due to erosion and the addition of bacteria and nutrients from manure.
Fencing is the most effective management tool for limiting access to these areas.
If fencing is not economically feasible, other options include:
 Providing shade in an environmentally safe area.
Reviewing the external parasite control program used on the farm.
Perhaps fly pressure is driving cattle to the pond for relief.
Refer to grazing management practices that limit adverse health effects in cattle, such as replacing endophyte-infected tall fescue with an alternative.
FIGURE 9.
Cattle should be managed in ways that limit access to ponds and creeks.
Fencing is the most effective option, but other options exist.
The advantages of a well-maintained heavy use area are reduced amount of mud and standing water, and increased animal comfort, health and safety.
Beef producers usually find that heavy use areas require little routine management or maintenance.
Filling in low spots and maintaining a uniform grade help minimize areas of standing water and mud.
Concrete, gravel, or gravel over a geotextile mat may be needed to prevent excessively muddy conditions.
In most cases, scraping the area to remove excess manure is not needed.
If scraping becomes necessary, excess manure collected from these sites can be used as an excellent fertilizer.
The nutrient value will vary with the production phase and the ration being fed.
It is estimated that one ton of manure from beef cattle would provide about the equivalent of 100 pounds of 11-7-10 fertilizer.
Manure analysis is available through your local Cooperative Extension Service Office.
To avoid stockpiling or manure storage problems as well as adverse interactions with neighbors or regulatory agencies, be sure to land-apply excess manure as it is collected.
Apply in accordance with a nutrient management plan or at a proper agronomic rate when no rain is in the forecast.
Filter strips are an important tool in nutrient management and are maintained to reduce the nutrient and bacterial content of runoff from the entire farm.
Locating vegetative filter strips downslope from heavy use areas helps protect water resources.
Quite often, pasture forage found downslope of the heavy use area serves as an effective filter strip.
Research at the University of Arkansas demonstrates that, with adequate vegetative cover, a filter strip's effectiveness is determined by the width and slope of the filter.
The wider the filter strip, the better the filtering action.
A filter strip on a flatter slope will be more effective than on a steeper slope.
As the slope increases, SO should the width of the filter strip.
Assistance is available from the Cooperative Extension Service, University of Arkansas and the Natural Resources Conservation Service  for the proper design of filter strips in accordance to a specific land type.
TABLE 1.
VEGETATIVE FILTER STRIPS
 % SLOPE	LENGTH OF FLOW
 0% 3% Slope	30 ft
 3% 8% Slope	50 ft
 Over 8% Slope	100 ft
 Managing Specific Heavy Use Areas
 Cattle tend to defecate near where they are fed; therefore, management of the feeding area is a major portion of the manure management aspects of a beef program.
The point has already been made that the feeding site should be located away from any environmentally sensitive areas.
When feeding grain or a mixed ration, use feed bunks or troughs.
Permanent bunks or feeding sites may need to be on a concrete or geotextile mat.
Move portable feeders as needed to allow these areas to recover.
Beef producers should also rotate hay feeding areas throughout the feeding season.
Portable hay rings can be used to help reduce waste, but they do not totally eliminate it as cattle tend to pull hay out of the ring and tromp it into the ground.
Waste can be reduced by limiting the number of COWS fed at one time.
Two feet of space is needed for each mature cow to access hay in a ring.
This limits the number of cattle that one hay ring can efficiently feed to approximately 15 head.
Moving the portable rings on a regular basis to reduce excessively muddy conditions, spreading the manure over a large area and minimizing long-term damage to the pasture are important.
Unrolling round bales is another hay feeding option.
This enables more cattle to feed at one time and allows small calves to have a better chance to compete for hay.
It also spreads the feeding area resulting in cattle distributing manure over a larger area.
The disadvantage to unrolling hay is that daily feeding is required and that it is not suitable for all producers.
After the hay feeding season is over, producers should drag and smooth the feeding areas.
A tire drag is an inexpensive and quite effective tool for this job.
It does not clog up with debris but rather breaks up clods, spreads cow patties and helps level rough areas.
Spreading the cattle manure smoothes the ground and helps reduce spot grazing.
Travel lanes are designed to ease movement of cattle on the farm.
The use of well-designed lanes increases the producer's control of cattle movement and helps to limit the damaging effects of cattle movement to smaller areas.
Keep travel lane size to a minimum, allowing just enough room for maintenance and equipment transport.
The amount of time cattle spend in the travel lane should be kept to a minimum, reducing the amount of manure deposited in this area.
Careful planning of shade and feed locations helps in the movement of animals along the travel lane.
Travel lanes should not be placed on steep slopes.
A travel lane on a 15 percent slope generates more than twice the solids in runoff than a travel lane on a 7 percent slope.
Shade is important to cattle productivity and should be managed properly.
Cattle may select natural shade as a loafing area, or producers may provide artificial shade to provide heat relief for their cattle.
If cattle use the shade a few hours a day, manure accumulation and loss of vegetation will result.
Move portable shade on a regular basis to allow for vegetative regrowth.
Rotate pastures or use electric fencing to keep cattle from concentrating in one small area if they are loafing under natural shade.
This reduces the potential for damage to trees and vegetation.
FIGURE 10.
Shade is important to cattle productivity and should be managed to reduce potential non-point source pollution.
Cooking for swine food
 Normally, a beef or dairy producer is limited by practicality to composting or burial, with composting being the recommended method.
The other methods require specialized equipment or unavailable outside services.
With both composting and burial, location is important with remote sites away from water and out of drainage ways being an important consideration.
It is usually easier to find a suitable site for composting due to its absorbent base layer of carbon material.
In contrast, many Arkansas soils are not suitable for burial due to some combination of physical characteristics and depth to bedrock or ground water.
In general, for assistance selecting suitable burial sites, contact your local Natural Resource Conservation Service  office.
It is advisable to contact NRCS and make a location determination before the need arises.
For information on large animal mortality composting refer to Extension Fact
 In Arkansas, an animal feeding operation  is defined as a lot or facility where cattle are confined for at least 45 days a year and vegetation is not maintained over a significant portion of the normal growing season.
A concentrated animal feeding operation  is an AFO where potential for environmental concerns is greater usually due to a larger number of animals.
Due to the concentration of animals and the absence of vegetation in these facilities, proper manure management is critical to preserve water quality.
These facilities should be designed to allow for the collection, storage and utilization of the manure generated.
Confined operations may require a permit from the Arkansas Department of Environmental Quality.
Several factors determine if a permit is required, including the number of head at the facility, whether the stockpiled manure is protected from the weather and the location and topography of the facility.
General information is available from the Cooperative Extension Service though your local county extension agent.
For details about permit requirements and the permitting process, contact the Arkansas Department of Environmental Quality.
If a confined operation is in use or is being planned, your local conservation district office and the Natural Resources Conservation Service can assist in developing one or more alternative facility design and associated manure management plans.
During this process, the Cooperative Extension Service is available to provide information on various agricultural and environmental practices.
he practices covered in this publication promote a sound manure management for Arkansas beef producers.
By following these practices, cattlemen can improve herd health, forage production and overall management efficiency while protecting the quality of Arkansas' water resources.
A well-managed grazing system is essential to good cattle manure management.
Use stocking rates that do not exceed the pasture's carrying capacity.
Include minimal size, upslope water diversion and downslope vegetative water treatment in heavy use area designs and management.
Select sites for heavy use areas that have good drainage and minimum slope.
Avoid environmentally sensitive areas.
Limit cattle access to bodies of water.
Maintain a vegetative filter strip downslope of all heavy use areas.
Maintain proper widths corresponding to the slope of the site.
Rotate feeding sites to allow recovery from heavy use.
Move temporary structures, such as feeders, hay rings or mineral boxes, on a regular basis.
Water cattle from tanks when possible.
Dispose of dead animals properly.
MidWest Plan Service, Livestock Waste Facilities handbook, MWPS-18, Iowa State University, Ames, IA.
For example, if the standard speed of the electric motor is 1770 rpm and you wanted the motor to run at 1650 rpm, you would adjust the frequency of the electric supply from 60 hertz down to 56 hertz [1650 rpm  1770 rpm x 60 hertz].
Center Pivot Operation and Evaluation Field Checks
 Charles Hillyer, Troy Peters, Xin Qiao, Jake LaRue, Sandeep Bhatti, Derek Heeren
 This is meant as a simple guide to new irrigators on what to check for to ensure efficient center pivot and linear move irrigation system operation for maximum economic productivity and water effectiveness.
Please spend some time to read the pivot safety checklist!
All sprinklers are operating?
Any plugged nozzles?
Pressure and flow rate of each sprinkler spray pattern looks good?
Are Rotators rotating?
Are iWobs wobbling?
Are spinners spinning?
End gun operating over the angles as per the sprinkler chart?
Is there surface runoff?
Water ponding in low spots?
Can be due to leaks.
If runoff is everywhere, consider speeding the pivot up.
Visual observation of any non-uniform water application areas.
Water stressed areas?
Stripes in field?
If using surface water and filter, check the filters.
If you have a flow meter, is the weekly flow total close to expectations?
If flow rate or well drawdown changes during the season, update the percent timer on panel based on current well flow rates
 If using aerial imagery to identify uniformity issues 
 Rings indicate nozzle/leak issues?
Spoking?
It may occur at light application depths, if low pressure setting in the panel is incorrect or if the pump is surging.
Bank of nozzles lost because of a failed controller in VRI?
Systems with Telemetry or Remote Operation
 Pressure at design pressure or higher?
Pivot location where expected?
End-gun state is as expected
 Aux ports state is as expected
 Pivot travel speed based on telemetry is as expected for the applied water depth
 Last time it communicated seems reasonable?
Can you find the current sprinkler chart?
If you have a flow meter.
Does the flow rate match the sprinkler chart?
If part-circle or wiper pivot.
Bumper bars in place and functional?
Has the pivot point bearing been greased?
With the power off , check for loose connections or loose cord grips in the control panel and tower boxes.
Do contactors show signs of arcing?
Electrical grounding conductors solidly connected?
Clean or tighten as required.
Check the tire pressure.
Check wheel lug nut torque.
Check for leaks at tower joints, goosenecks, and at sprinkler and hose couplings
 Does the operating pressure match the design pressure ?
Check the oil level in the gear boxes.
Is there water in the oil?
If so, drain the water.
Are the drive shaft U-joint inserts still in good condition?
Are the drive shaft safety shields in place?
Gearbox noise indicating wear or problems?
Is the filter for the hydraulic tubes for hydro-valves actuators clean?
Does the pivot alignment look straight when it is operating?
Rodent damage to wiring?
Walk the entire system while it is operating to look closely for problems.
If you have remote-control or telemetry, is it still operational and communicating?
System starts/stops on command
 Is it time to replace the sprinkler nozzles, sprinklers, or regulators?
Because of non-uniform sprinkler operation
 Sprinkler spray pattern isn't uniform
 Usually recommended every 5-10 years depending on water quality.
Prepare water use report
 Hours of operation for the season seem reasonable?
Will you need to budget for winter maintenance?
Was the system flushed?
Are the sand traps clean?
Is the pivot and connections to the well completely drained of water?
Is the power off?
Do a pumping plant performance audit
 Seriously consider replacing the sprinkler package.
Does the package need redesigning or updating?
Compare installed nozzles to sprinkler chart.
Are pressure regulators working as expected or need to be replaced?
Do pressure gauges and flow meters need replacement?
Change the gearbox oil at the interval recommended by the manufacturer.
Check structural bolts, chains, and nuts.
Are they still tight?
Inspect the tower drive motor contactors and replace if necessary.
Do a pumping plant performance audit
 Electrician do an inspection for electrical safety
 Catch can test to check application uniformity
Estimating Irrigation Water Requirements to Optimize Crop Growth
 Why Estimate Water Needs?
Predicting water needs for irrigation is necessary for developing an adequate water supply and the proper size equipment.
The value of irrigation is significantly reduced if the water supply or the irrigation equipment cannot deliver the amount of water your crops need during a drought.
Irrigation supplements probable rainfall so a crop's seasonal water needs are satisfied.
Water should be delivered at a rate sufficient to meet the crop's peak water use rate.
Seasonal water needs and peak use rates are directly related to yield goal.
High-yield goals have a high water demand.
A water supply that restricts either the seasonal amount or rate of application limits the potential yield.
Amount of Water Needed During Growing Season Depends on Many Factors
 The crop, yield goal, soil, temperature, solar radiation, and other cultural factors determine the amount of water needed during the growing season.
Long-season crops require more water than short-season crops.
Some crops such as corn require irrigation during the entire growing season and use more water than other crops such as soybeans, which benefit mostly from additional water at specific critical stages of maturity.
High-yield goals require more water than lower-yield goals for the same crop.
Table 1 lists some typical Maryland crop yield goals and growing season lengths.
The amount of irrigation required for crop production depends on the particular season's useful rainfall, the soil's water-holding capacity and the crop water needs.
Useful rainfall is the portion of the rain that is stored in the soil root zone.
Table 1.
Yield goals and season lengths for common crops vary
 Crop	Yield goal	Growing
 Grain corn	180	240	120
 Soybeans	50	70	120
 Cantaloupes	4	6	90
 Cucumbers	6	10	60
 Lima beans	1.5	2.5	80
 Peas	2.5	4	100
 Sweet corn	6	8	90
 Sweet potatoes	8	10	120
 Tomatoes	20	30	100
 Watermelons	20	30	110
 a	Although a 120-day crop, soybeans are irrigated
 primarily from flowering to maturity.
Fine-textured soils  can store more water than coarse-textured soils .
Therefore, coarse-textured soils dry faster and require more frequent irrigation than fine-textured soils.
If corn is grown on coarse sand with a 1.5-foot root zone, rainfall amounts over 1.88 inches are not beneficial since only 1.25 inches of water are held per foot of soil.
Table 2.
Clays, silts and loams can store more water than coarse-textured soils
 Soil texture	total moisture	available
 Coarse sand	1.25	0.9
 Fine sand	1.75	1.2
 Loamy Sand	2.25	1.4
 Sandy Loam	2.5	1.6
 Fine sandy loam	2.75	1.8
 Silt loam	3.0	1.9
 Silty clay loam	3.25	2.0
 Silty clay	3.5	2.1
 a Some of the moisture held in the soil is not available to plants as it is held tightly to the soil particles.
Sands do not have high water-holding capacity, but most of it is available.
Small rainfall events are not beneficial to crops on heavy soils when they are severely dry because the unavailable portion is replaced first.
Using long-term average rainfall amounts, table 3 gives estimated irrigation requirements.
Table 3.
Corn has highest estimated irrigation water requirement to grow
 Field Corn	10	15
 Sweet Corn	6	8
 Short season Vegetables	4	5
 Based on light textured soils.
Heavier soils will require less.
Severe drought years will require more and rainy years will
 *an acre inch of water = 27,154 gallons
 Water Use Rates by Plants  Change with Environmental Conditions and Plant Maturity
 Plants have specific critical periods when they need more water.
Hot, dry, and windy conditions will cause rapid water loss from the soil and plant.
If the soil becomes excessively dry during critical water-need periods, yield can be significantly reduced.
Irrigation must be able to supply water at the expected peak water use in order to be of the greatest benefit to crops during rain-deficient periods.
The peak water use rate for vegetables and most grain crops falls between 0.2 and 0.25 inches per day per acre.
The peak water use rate for high-yielding grain corn can reach 0.33 inches per day.
Table 4.
Crops have different critical periods of water needs
 Alfalfa	Start of flowering and before
 Apples	Bud stage and fruit enlargement
 Beans, lima	No particular period
 Corn*	Tasseling through ear
 Cucumbers	Flowering through harvest
 Melons	Blossom to harvest
 Peaches	Final fruit enlargement and pit
 Peas	Flowering and seed enlargement
 Peppers	Planting to fruit set
 Potatoes, Irish	Blossom to harvest
 Potatoes, sweet	At transplant
 Soybeans*	Flowering to seed enlargement
 Strawberries	Fruit enlargement and bud set,
 Tomatoes	Early flowering, fruit set, and
 * see figure 1
 Daily Peak Water Use Rates Translate into Pumping Rates Based on Total Hours of Time Available for Operating Irrigation System
 As pumping time decreases, the flow rate of the pump must increase to provide the necessary daily volume of water.
Table 5.
To meet peak irrigation water demand, use rates must increase as pumping hours decline
 Daily	Water use	I	ate 
 pumping hours	0.2	0.25	0.33
 24	3.8	4.8	6.3
 20	4.6	5.7	7.6
 15	6.1	7.6	10.1
 10	9.1	11.4	15.1
 a Gallons per minute per acre
 For example, if you irrigated your entire 20 acres of sweet corn  for 24 hours every day, the application rate would be 4.8 gpm  per acre.
If you irrigated only 15 hours per day, every day, the application rate would be 7.6 gpm per acre.
Water losses occur between the water source and the plant through leaks, runoff, and evaporation.
These losses are variable depending on the irrigation equipment.
High-efficiency pivots  may lose 10 percent of total irrigation water, while drip systems may lose less than 5 percent.
However, hand-move sprinkler and aluminum pipe irrigation systems could lose 25 percent or more.
To ensure that plants receive the necessary amount of water, the water supply would have to provide for the peak use plus the expected loss.
Table 6 lists typical systems and water loss factors.
Table 6.
Typical water loss factors depend on the type of irrigation system
 Low pressure spray	1.07
 -pivots with efficient nozzles
 High pressure spray	1.1
 If you used a traveling gun to irrigate sweet corn that required 0.33 inches/day, you would actually need to pump almost a half-inch more per week-0.4 inches/day -to account for water loss.
An irrigated area may be so large that it takes several days to irrigate the entire field.
In this case, calculate the pumping rate using the area irrigated each day.
For example, a center pivot system that completes a circle every 3 days irrigates, one-third of the total field area daily.
The irrigation frequency for any part of the field is once every 3 days.
The application rate of water should not exceed the ability of the water to enter the soil.
However, the amount of water in the soil should not decline below 50 percent of the maximum amount stored.
These conditions, related to soil properties and plant rooting depth, determine the frequency of water application and are an important part of irrigation system design.
Regardless of irrigation frequency, the cumulative daily peak water use must be satisfied.
Some Farms Must Manage with a Minimal Water Supply
 Due to high crop prices, there is interest in installing irrigation on farms with minimal water supplies.
Suppose you have a 100-acre field with a water supply of 300gpm.
If you are growing corn, 3gpm/ac is not sufficient in most years.
There are a couple strategies that you could adopt to manage reduced supplies:
 1) Plant half the field in one crop and the other half in a crop that has a different daily maximum water use time.
For example, plant corn that will require 0.3 inches/day in July/early August and beans that will need 0.3 inches/day late August/September.
2) Plant half the field with a short-maturity variety and the other half with a longseason variety  the same day.
This will enable you to concentrate irrigation on the early maturing variety at a different time than the late one.
3) Plant crops with the same maturity a few weeks apart 
 4) Practice "water banking;" that is, irrigate more than necessary when the crop is not at peak water use to build soil moisture reserves to be used later.
This works well with heavier soils that will hold more water.
For example, irrigate 0.25" per day when corn is young and only using 0.15" per day in order to build soil reserves to be used when it needs 0.35" per day.
The other important management strategy is to start irrigating before the soil moisture reserves are completely depleted.
This is especially important with large pivots, since it may take two days for them to make a circle or irrigate the entire field.
Volume of Water Used for Irrigation is Highly Variable and Depends on Soil, Crop, Yield Goal, and Weather
 Irrigation needs will vary from year to year depending on rainfall.
If corn is grown on a sandy soil with no rainfall in a hot, dry and windy summer, 25 acre inch  would be needed.
Conversely, in a wet year, no irrigation may be necessary to obtain high yield.
The in-between years are harder to predict, as are yield expectations with minimal water supplies.
The information in this fact sheet will facilitate the computation of needed seasonal water volumes and peak pumping rates.
If you cannot develop water supplies to meet these needs, establish a different crop or a lower-yield goal or reduce the acres irrigated.
Figure 1.
Seasonal water needs and peak water use rates are directly related to yield goal
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EVALUATING CENTER PIVOT, NOZZLE-PACKAGE PERFORMANCE
 One definition of performance is: "operation: process or manner of functioning or operating." The manner of functioning of a center pivot nozzle package is to deliver irrigation water to a targeted area.
Good or successful performance in an irrigation setting with a growing crop most often implies that the application of irrigation water accomplished the goal of making the irrigation water available to the crop, usually by being distributed across the soil surface and infiltrated into the crops root zone where it can be accessed by the individual plants equally and, for the case of full irrigation capacity, in sufficient quantities to prevent yield limiting water stress.
Another factor related to good performance is minimization of losses associated with the irrigation application, i.e.
high irrigation efficiency.
Distribution uniformity is discussed by Rogers et al.
1997 and illustrated in Figure 1.
It and can either indicate the degree of evenness in the depth of irrigation water applied to the soil or in the amount of the water infiltrated into the soil.
The former may be associated with depths applied at the surface, based on catch-can measures for sprinkler systems.
The latter associated with soil water measurements after infiltration, which are much more difficult to collect than surface measurements.
This concept for uniformity was originally developed by Christiansen in 1942 for sprinkler systems.
Generally, high uniformity is associated with the best crop growth conditions since each plant has equal opportunity to use applied water.
Non-uniformity results in areas that are underwatered or overwatered.
In particular, overwatered areas may cause a decrease in irrigation efficiency if the water moves below the crop root zone and therefore is lost for crop water use.
Figure 1: Illustration of a sprinkler package water distribution uniformity verses infiltrated water distribution uniformity in the soil.
Irrigation efficiency can be defined as the percentage of water delivered to the field that is used beneficially.
This definition is a broad definition in that irrigation water may have more uses than simply satisfying crop water requirements.
Other beneficial uses could include salt leaching, crop cooling, pesticide or fertilizer applications, or frost protection.
However, most Kansas irrigation systems are single-purpose, which is to supply water for crop use.
Water diverted in Kansas for beneficial use, except for domestic water use, is subject to the terms and conditions of the Kansas Water Appropriation Act.
This appropriation act allows the transfer of water use from one type of use to another as long as it does not increase the use of water beyond the original consumptive use.
Consumptive use is the amount of water actually consumed while it is being applied to a beneficial use.
The amount of consumptive use for various types of users can be large.
For example, the consumptive use of water diverted for use in a cooling tower, where it is evaporated, is essentially 100 percent, while water passing through a turbine of a hydroelectric power plant has essentially zero consumptive use.
The range of consumptive use for irrigation can be very large as well.
For example, large-scale irrigation systems from a river diversion and canal system may have return flows to the river of up to 50 percent whereas a deficit-irrigated field in from a groundwater well in a low rainfall area may have little or no return of water to the groundwater.
For many properly-designed and
 operated irrigation systems in low rainfall areas, consumptive use is often used  to be crop-water use.
An accepted method of estimating crop-water use is through the use of evapotranspiration  which is calculated using weather information.
The term evapotranspiration is the combination of two terms, evaporation and transpiration.
Evaporation is water which returns to the atmosphere directly from wetted plant surfaces, wetted soil surfaces, or wetted residue cover.
Transpiration refers to the water which is transported from soil water reserves through the root system, stems and leaves of a plant before being released to the atmosphere.
A primary function of transpiration is cooling of the plant.
An additional small amount  of the water absorbed by the plant is used as part of the photosynthetic process.
Nutrients are also transported as water moves from the soil into the plant.
Evapotranspiration  is the combination of evaporation and transpiration.
Evaporation is water movement from wet soil and leaf surfaces.
Transpiration is water movement through the plant.
Figure 2: Illustration of evaporation and transpiration.
It is difficult to measure evaporation  and transpiration  separately, hence, the combined term, ET.
In conventionally-tilled irrigated crops, the E portion of ET is generally about 30 percent of the seasonal crop water budget, but might be cut in half when high, surface-residue tillage systems are used.
Early in the season, when the crop is small and does not cover or shade the soil surface, more sunlight and wind energy reaches the soil surface and a higher portion of the ET is the E portion.
After the canopy closes, almost all ET becomes T.
Evaporation can be suppressed in irrigated agriculture by increasing planting
 density to encourage rapid ground cover and by minimizing the frequency of canopy wetting by irrigation events when using sprinkler systems.
The yield of a crop is generally proportional to the amount of crop-water use.
Modern center pivots and linear-move nozzle packages with proper design and installation and under good irrigation management tend to minimize irrigation losses by reducing the wetted radius of the nozzles and reducing the height of the nozzles above the crop canopy while also selecting and operating the systems to eliminate surface run off.
The systems would also be managed to minimize deep percolation.
Surface water movement of irrigation water under a center-pivot irrigation system should be eliminated with either a change in the operating procedures or a change in the nozzle-package design.
Deep percolation of irrigation can be minimized with proper depth of application and irrigation scheduling; although, total elimination of deep percolation or drainage is not always possible due to the occurrence of large rainfall events.
The remaining losses are due to water evaporation while the irrigation water is in flight, on the plant, or on the soil surface.
These losses are, in essence, consumed.
Water evaporation from a plant surface will suppress transpiration as the evaporation process will serve to cool the plant as illustrated in Figure 3.
Canopy evaporation greatly increases during the period of irrigation, so evaporation from surfaces should not be encouraged as the evaporation process occurs much more rapidly than plant transpiration.
As much as 0.20 inches of water may be needed to wet a crop canopy.
This amount of water could evaporate in several hours while on some days that same amount of water may have been sufficient for the entire day, if it were available for transpiration to the plant via the soil root zone.
Therefore, many nozzle-package designs attempt to minimize evaporation losses using various nozzle configurations and placement strategies.
Irrigation water losses, as shown in Figure 4, can be divided into air losses, canopy losses, and soil losses.
The center-pivot nozzle package system design and management should minimize  surface runoff and deep percolation.
Percolation losses may still occur due to unusual precipitation events.
Although surface runoff and or water redistribution within a field still occur on some individual fields; in general, surface water losses have decreased over time due to sprinkler package designs which are better matched to field conditions.
Also, changing cultural practices such as more adoption of noor limitedtillage on fields result in high crop-residue covers that reduce the potential for surface run off and early season soil evaporation losses.
Deep percolation losses have also been minimized as more irrigators adopt irrigation scheduling as a part of their management practice.
There is also an increase in the number of low-irrigation capacity systems.
Over 90 percent of Kansas irrigated acreage is watered by center-pivot irrigation systems which could, with proper package design and operation, eliminate irrigation water runoff.
Deep percolation losses should be minimized
 Figure 3.
Water use for the rotator sprinkler placed on top the pivot lateral..
with proper irrigation scheduling.
The remaining irrigation losses as shown in Figure 4 occur either in the air, from the crop canopy, or from the soil.
These losses occur as evaporation to the atmosphere, so the irrigation water is consumed just as the water used in the crop transpiration process.
The implication of this discussion on water losses for a single irrigation event during the growing season, assuming the system is properly designed and operated  and properly scheduled , then essentially all the water applied would be used consumptively.
This implication for a single irrigation event, however, can be different when viewed on a longer time scale, as will be discussed in a later section.
Figure 4: Illustration of where irrigation water losses can occur for a center pivot nozzle package.
An example of how irrigation losses can be affected by design criteria is illustrated in Figure 5.
Three water-use scenarios are shown for two irrigated conditions and a non-irrigated condition.
Note for the non-irrigated condition, no losses of water occurred due to canopy or drop evaporation since no irrigation occurred.
There was still some soil evaporation contribution, but there was a high level of transpiration.
For the two irrigated conditions, a small sliver is shown to represent droplet evaporation, the evaporation that occurs while the water droplet is in flight.
The soil evaporation was greater in the irrigated condition as compared to non-irrigated due to the recently-wetted soil surface from the irrigation.
Between the two irrigated conditions, note that the spray just about the crop canopy had less canopy evaporation than the impact sprinkler.
Spray nozzles would have a much smaller wetted diameter than the impact sprinkler, and therefore a specific location in a field would have been wetted for less time, resulting in less time for canopy evaporation to occur at that location.
Figure 5: Evaporative losses for impact and spray nozzle devices  Data was collected at Bushland, TX; 90 F, 15-mph windspeed, and dry.
Example of a Center Pivot Uniformity Test
 
 When designing sprinkler irrigation systems, it is important to provide as uniform of an application as possible.
A non-uniform application will result in areas of under-watering as well as areas of over-watering.
This will result in reduced yields as well as decreased system efficiency.
The uniformity of the sprinkler nozzle package design is determined by package design.
It is affected by the operating conditions, and environmental factors, especially wind.
Figure 6 shows the results of a center-pivot uniformity test.
Section A of the pivot illustrates a portion of the sprinkler package that was performing well.
This area of the pivot has a coefficient of uniformity of almost 90 percent.
In section B, a leaky boot connection between two spans was caught in one container.
Section C represents the area covered by the outer two spans of the system that shows an area of over watering and under watering.
Section D of Figure 6 demonstrates the effect of an improperly-operating end gun.
In this case, the operation-angle of the end gun was improperly set and it was over spraying the nozzles of about one third of the last span and the overhang of the center pivot.
In this example, all of the causes of the poor uniformity were easily and inexpensively correctable.
Uniformity is decreased if system pressure is not kept at the design pressure.
Wear of nozzles and incrustation buildup can also affect the pattern.
Canopy interference also affects distribution uniformity.
Sprinkler Package Uniformity Test with End-gun 'ON' Finney County, Kansas
 Figure 6: Uniformity test results for a Mobile Irrigation Lab uniformity evaluation.
Irrigation Efficiency Impact on Irrigation Schedules and Crop Water Use
 Table 1 illustrates the effect of improving irrigation efficiency on the water budget for an example year with average seasonal ET and rainfall for a corn crop.
The water budgets were made using KanSched, an ET-based, irrigation-scheduling program.
While the rainfall was near normal for the growing season, it was less than normal early in the season and heavier than normal late in the season.
The non-water-stressed ET for the year is 21.13 inches, which would be associated with "full" yield.
Three water budgets are shown in Table 1 using a low-capacity irrigation system.
All field and crop characteristics were identical.
All irrigation water was scheduled whenever 1.00 inches of root-zone, soil-water deficit existed and the previous irrigation was completed.
The only difference between schedules was irrigation efficiencies which were selected to be, 70 percent, 80 percent, or 90 percent.
At 70-percent irrigation efficiency, there were 5 days where the root-zone, soilwater content dropped below the recommended managed-allowable deficient  of 50 percent.
Actual ET was 21.00 inches, which is only slightly suppressed, as compared to "full" ET of 21.13 inches; however, the most severe stress occurred during the pollination period which is the most water-sensitive stage of growth for corn.
The lowest predicted root-zone, soil-water level was 39.7 percent of available water.
But, since this occurred at pollination, grain yield reduction would likely occur.
When irrigation efficiency was increased to 80 percent irrigation efficiency, there were 3 days below MAD and crop ET was increased to 21.09 inches.
The lowest predicted root-zone, soil-water level was 46.7 percent of available water.
This stress still occurred at pollination, so grain yield reduction might occur, but not to the degree of the previous example.
The length and severity of the stress was not as great as the previous example.
"Full" ET was still not achieved at 80-percent efficiency but the gross amount of irrigation water was reduced.
For the 70percent efficiency level, 11.00 inches of gross irrigation water was applied as compared to 10.00 inches for the 80percent efficiency level.
When irrigation efficiency is improved to 90 percent, the crop ET increases to 21.13 inches, which is the maximum for the climatic conditions and maturity length of corn used in this example.
This is indicated  by noting zero days of soil-water levels below 50 percent MAD.
The gross irrigation application dropped to 8.00 inches as compared to the 11.00 or 10.00 inches of the previous examples.
It is possible, however, to have examples where increasing irrigation efficiency would not result in reduced gross irrigation application, but it would result in an increase in the amount of water used beneficially by the crop.
The drop of 2.00 inches of gross irrigation pumping occurred in this example because the increase in efficiency resulted in more net irrigation water being available to the crop with each irrigation to such a degree that the crop's full-water requirement was met with a lower gross-irrigation amount.
The data shown in Table 2 represents the case where an increase in irrigation efficiency did not result in a drop in gross irrigation application depth.
It uses the same weather record as the example in Table 1; the only change is the soil type and rooting depth.
At 70-percent irrigation efficiency, there were 9 days where root-zone, soil-water dropped below the recommended managed allowable deficient  of 50 percent and the gross irrigation application was 11.00 inches.
Increasing efficiency to 80 percent still resulted in 11.00 inches of gross irrigation application, but the number of stress days was reduced to 5 and the level of stress was lower.
There was not a reduction in gross irrigation application with an increase in efficiency since all the "saved" water went into meeting the crop-water-use demand.
When irrigation efficiency was increased to 90 percent, one day of crop-water stress was still predicted, even with high efficiency; however, recall the example system is a low-capacity system that can only apply 1.00 inches every six days
 which could not meet the crop water needs during the extended dry period of this actual weather record.
For the entire season, however, more net irrigation water was available due to the higher efficiency resulting in less gross pumping for the season.
In Example 2, increasing irrigation efficiency did not result in a decrease in overall pumpage because both the 70-percent and 80-percent systems pumped 11.00 inches of water.
However, the water-use efficiency or water used productively should be improved as the net irrigation application increased from 7.70 inches to 8.80 inches and reduced the number of days that the crop experienced stress.
Since the irrigations were scheduled, meaning the water was not applied unless sufficient root zone storage was available, the applied irrigation water should not be lost to deep percolation.
This means the loss would be associated with soil, canopy, or air losses which are evaporation processes and the water returned to the atmosphere.
This would be "consumed" from the groundwater water source.
In this sense, increasing irrigation efficiency did not change the amount of water consumed from the aquifer as the pumped water was either consumed  by the crop or consumed  by the inefficiencies of the irrigation system.
Historically, when the majority of irrigation systems were surface  irrigation systems, large application depths were required to advance the water across the field in the furrows to ensure the crop root zone was filled along the entire length of the field.
This often resulted in deep percolation losses in the upper part of the field and a zone of deep percolation at the end of the field if excess water was diked at the bottom end.
Deep percolation losses may have been eventually be returned to the groundwater aquifer.
As irrigators in Kansas switched from gravity-flood to sprinkler systems , the losses associated with irrigation has switched from deep percolation to surface evaporation losses.
These evaporative losses are now considered consumed since these evaporation processes transfer water to the atmosphere and not back to the original water source.
Table 1: Effect of improving irrigation efficiency on gross irrigation requirement for corn under a low-capacity irrigation system.
Irrigation	Crop	Effective	Gross	Net	of days	Soil
 Efficiency	ET	Rain	Irrigation	Irrigation	< 50%	Water
 %	Inches	Inches	Inches	Inches	MAD	Value
 No Irr	17.23	12.57	0.00	0.00	51	16.1%
 70	21.00	11.60	11.00	7.70	5	39.7%
 80	21.09	11.49	10.00	8.00	3	46.7%
 90	21.13	11.52	8.00	7.20	0	52.2%
 Table 2: Effect of improving irrigation efficiency on gross irrigation requirement for corn under a low-capacity irrigation system.
Irrigation	Crop	Effective	Gross	Net	of days	Soil
 Efficiency	ET	Rain	Irrigation	Irrigation	< 50%	Water
 %	Inches	Inches	Inches	Inches	MAD	Value
 70	20.80	12.10	11.00	7.70	9	38.4
 80	21.04	11.44	11.00	8.80	5	44.5
 90	21.12	11.45	10.00	9.00	1	49.8
 Analysis of irrigation consumptive use on an annual basis.
A simulation model was used to examine the effects of several irrigation schedules for two soil types.
The average results using multiple years of actual weather data for each of the water-budget components on an annual basis are shown in Table 3.
High water-holding capacity, silt-loam soils were used for the northwest Kansas location, while sandy soils were used for the south central Kansas location.
The application amounts used for each site were selected as typical for the region.
Irrigation was limited to the frequency shown, but it was scheduled based upon available soil moisture  of 50, 60, and 70 percent, so a range of the total irrigation application amount was applied.
A base-line crop was needed to be able to determine how the different water-budget components would change with the addition of irrigation water and what portion of the irrigation water was associated with each change.
For the northwest Kansas location , the average ET for the simulation period was 14.40 inches for the base-line dryland corn crop.
The average amount of runoff for dry-land corn was estimated to be 0.94 inches, with zero predicted percolation and 3.90 inches of interception.
As irrigation is added, water budget components increase.
Using the three irrigation schedules, irrigation amounts ranged from 13.90 to 16.71 inches and ET values increased according in various amounts above the baseline dry-land value of 14.40 inches.
The dry-land water budget components were then subtracted from the corresponding irrigated-condition, water-budget component and are shown in the lower portion of Table 3.
For example, for the 50-percent schedule, run off was estimated to be 1.42 inches, however 0.94 inches occurred under dry-land conditions, therefore the increased runoff contribution due to irrigation is 0.48 inches.
In the same example, ET increased by 12.34 inches due to the 13.90 inches of irrigation.
Dividing these two numbers would be an estimate of the seasonal irrigation efficiency; calculated, in this case, to be 89 percent.
The amount of water consumed is estimated by adding ET and interception, since these two amounts are returned to the atmosphere.
Percolation could be returned to groundwater.
The fate of runoff is less certain, it still might be lost to evaporation, but it was not consumed within the field.
Dividing the amount consumed by the irrigation amount would be an estimate of consumptive use  efficiency, in this example the value is 94 percent.
As additional irrigation water added, both seasonal irrigation efficiency and CU efficiency decrease.
Since soil-water levels in the crop root zone are increased, the likelihood of losses to runoff and percolation increase due to occasional large precipitation events within the irrigation season and during the non-irrigation portion of the year.
The results for the south central location  on sandy soil follow the same trend as the silt loam example for both seasonal irrigation efficiency and CU efficiency, but the efficiencies are considerably lower.
Sandy soils have less water storage capacity and therefore are more prone to have deep percolation losses.
Also, the greater annual precipitation south central Kansas provides more opportunities for percolation losses.
Table 3: Water budget comparisons using POTYLDR  comparisons for two soil types.
Silt Loam Soil in	Sandy Soil in
 Northwest Kansas	South Central Kansas
 	1.00	1.00	1.00	Corn	0.75	0.75	0.75	Corn
 days, if needed	3	3	3	2	2	2
 @ ASM, %	50	60	70	50	60	70
 Irrigation, in.
13.90	15.69	16.71	None	9.39	10.99	12.24	None
 Runoff, in.
1.42	1.45	1.52	0.94	1.20	1.27	1.33	1.05
 Percolation, in.
0.22	0.44	1.21	0.00	6.38	7.12	8.02	4.05
 Intercept., in.
4.68	4.77	4.85	3.90	3.51	3.65	3.74	2.64
 ET, inches	26.74	28.18	28.26	14.40	24.33	24.98	25.18	18.34
 Additional amounts as compared to Dry-land Corn
 Amount of Gross Irrigation	Amount of Gross Irrigation
 Runoff, in.
0.48	0.51	0.58	0.15	0.22	0.28
 Percolation, in.
0.22	0.44	1.21	2.33	3.07	3.97
 Interception,	0.87	1.01	1.10
 in.
0.78	0.87	0.95
 ET	12.34	13.78	13.86	6.03	6.68	6.88
 Eff., % 	89	88	83	64	61	56
 CU 	13.12	14.65	14.81	7.77	7.69	7.98
 CU eff, %	94	93	89	73	70	65
 Center pivot irrigation systems can be equipped with a variety of nozzle packages that can effectively deliver irrigation water to crops.
Proper design and operation of the systems are essential for high efficiency and good distribution uniformity.
Irrigation application depths, total seasonal application amount, soil type, and precipitation all have an effect on seasonal irrigation efficiency and consumptive use of water.
The remainder of the circle experiences a gradual change in flow rate as the extension moves into and out of the corner.
Thus, the pump impeller selection is based on a flow rate requirement for less than 22% of the system rotation.
With the corner extension, use of a VFD conserved about $1.60 per hour of operation.
RESOURCE ALLOCATION IN CORN PRODUCTION WITH WATER RESOURCE CONSTRAINTS
 I irrigated agriculture in the Central Great Plains improves net farm income and provides more economic stability for a region often subject to drought.
Irrigation development in the Central Great Plains occurred in areas with little municipal or industrial use of the water.
Irrigation management generally provided water for fully irrigated crop production.
As irrigation development continued, more marginal water resources were developed, and overdevelopment of some sources occurred.
During the same time, other water uses have become more important as urban areas seek to meet water needs.
Article was submitted for publication in December 1992; reviewed and approved for publication by the Soil and Water Div.
of ASAE in April 1993.
Presented as ASAE Paper No.
92-2606.
Irrigation systems and management techniques have responded to conserve limited water supplies and maintain economic productivity.
Changing physical and institutional constraints continue to require new or different methods to allocate water.
Scientists and water planners have examined many different methods for using water efficiently.
Many factors can affect management schemes, such as water supply, irrigation capacity, crop yield potential, crop-marketing opportunities, dryland cropping alternatives, structure of individual state water law, federalfarm programs and even farmer preference.
When irrigation water supply is the major constraint, management takes into account the available cropping system alternatives, available land area to be irrigated, and any peculiarities imposed if the constraint is institutional.
Constraints on water use can be single-season or multiseasonal.
Contribution No 93-221-J from the Kansas Agricultural Experiment Station.
The mention of trade names or commercial products does not constitute their endorsement or recommendation by the authors or by the Kansas Agricultural Experiment Station.
Bernardo et al.
, using a multiseasonal simulation model to simulate a surface-irrigated farm in the Columbia River Basin, reported a 40% reduction of annual water allocation could be imposed without a severe impact on net farm income.
Martin et al.
developed a dynamic programming model to annually allocate a limited water supply over a multiseasonal period.
This model can also be used to help producers choose the correct mix of crops and balance of irrigated and nonirrigated land.
A water-banking system implemented in southwest Nebraska, limiting the amount
 of water utilized in a five-year period, provides an excellent opportunity to utilize this model.
Martin and van Brocklin  reported multiseasonal allocation decisions depend on whether the objective is to maximize net income or to maximize the lowest annual net income during the period.
Maximizing net income will favor using the water earlier in the period.
Reducing the risk of a low net income will favor saving some of the water for a drier than normal year.
Crop rotations can result in more efficient use of limited irrigation supplies.
Rotation of a higher irrigation-use crop, such as corn, with a lower irrigation-use crop, such as wheat, allows efficient use of residual soil water and increases the effective storage of overwinter precipitation.
Rotations also permit a higher ratio of irrigated to nonirrigated area.
The advantage is reduced yield variation due to drought because a larger area receives some irrigation.
In western Kansas, corn yields have increased dramatically over the last 20 years and at a much higher rate than grain sorghum yields.
Grain sorghum production can be marginal because of cool nighttime temperatures at the higher elevations.
Corn is a major feed grain for the large red meat industry in Kansas.
These factors, coupled with federal farm programs, make corn the irrigated crop of choice for most western Kansas producers.
However, deficit irrigation of corn is a questionable enterprise.
Yields usually decrease when irrigation is less than required to meet the full evapotranspiration requirements of corn.
In an irrigated-corn study in the Southern High Plains, Eck  found water stress reduced yields but did not increase water-use efficiency.
He concluded deficit irrigation of corn was not feasible for that area.
Musick and Dusek  in a study at Bushland, Texas, reached a similar conclusion, stating "limited irrigation of corn should not be practiced." Stewart et al.
, although not thoroughly discounting the practice, admitted that limited irrigation of corn is much more complex than limited irrigation of grain sorghum.
They concluded water stress during the reproductive and early grain-filling stages should be avoided, unless there was a conditioning or stress-hardening period during the vegetative stage.
Rhodes and Bennett  reported after reviewing numerous studies, that water stress imposed at any growth stage on corn will generally lower the efficiency of the water used in transpiration.
Still, western Kansas irrigators desire to grow corn and, in many cases, are practicing deficit irrigation.
Producers are familiar with corn production techniques and are sometimes reluctant to change to alternative cropping systems.
Kansas water law ties an irrigation water right to a parcel of land, so there are some practical concerns to using irrigated and nonirrigated rotations on the same parcel of land.
A three-year study was initiated in the fall of 1985 to determine the potential for deficit irrigation of corn, by not only managing the allocation of irrigation, but also nitrogen fertilization and plant population.
The study did not determine the optimum fertilization and plant population within a given irrigation constraint.
Rather it sought to evaluate several possible management schemes in terms of net income.
Fertilizer and seeding rates
 incorporated into the various irrigation management schemes were based on previous experience with corn production in northwest Kansas.
The project was conducted from 1985 to 1988 at the KSU Northwest Research-Extension Center at Colby, Kansas, on a deep, well-drained, loessial Keith silt loam.
This medium-textured soil, typical of many western Kansas soils, is described in more detail by Bidwell et al..
The 1.5-m  soil profile will hold approximately 250 mm  of available water at field capacity corresponding to a volumetric soil water content of approximately 0.30 and a profile bulk density of approximately 1.3 gm/cm 1 lbs/ft3.
The climate is semi-arid with an average annual precipitation of 474 mm  and approximate annual lake evaporation of 1400 mm.
Daily climatic data used to schedule irrigation were obtained from a weather station located approximately 250 m  east of the study site.
The study was conducted in a 0.6 ha  dead level irrigation basin, approximately 180 m long 30 m wide  with plots 4.6 m wide and 30 m long ft) running perpendicular to the level basin length.
The plots accommodated six corn rows spaced 76  apart.
Small dikes were constructed around each plot to prevent runoff between plots.
The study treatments were replicated three times in a randomized complete block design.
The reference evapotranspiration  was calculated using a modified Penman combination equation similar to the procedures outlined by Kincaid and Heerman.
The specifics of the ET, calculations used in this study are fully described by Lamm et al..
Basal crop coefficients  were generated by equations developed by Kincaid and Heerman  based on work by Jensen  and Jensen et al..
The basal crop coefficients were calculated for the area by assuming 70 d from emergence to full canopy for corn with physiological maturity at 130 d.
This method of calculating actual evapotranspiration  as the product of K cb and ET, has been applied in past studies at Colby and it has been found to accurately estimate AET.
In constructing the irrigation schedules, no attempts was made to modify AET with respect to soilevaporation losses or soil-water availability as outlined by Kincaid and Heerman.
Nine treatments were devised to examine several reasonable irrigation schemes within three given constraints on total water allowance.
The irrigation season ceased for a particular treatment when the irrigation constraint was reached.
All plots started the season with a full soil water profile and any applied preseason irrigation was not considered a part of the allowance.
Preseason irrigation is not typically needed in northwest Kansas.
The treatments or management schemes were as follows,
 Water allowance not to exceed 455 mm
 100% of calculated AET
 75% of calculated AET
 50% of calculated AET
 Water allowance not to exceed 305 mm
 100% of calculated AET
 75% of calculated AET during vegetative stage, 100% thereafter
 50% of calculated AET during vegetative stage, 100% thereafter
 Water allowance not to exceed 150 mm.
100% of calculated AET
 75% of calculated AET during vegetative stage, 100% thereafter
 50% of calculated AET during vegetative stage, 100% thereafter
 Irrigation water was metered separately onto each plot through gated pipe according to the following criteria:
 Set allowable calculated depletion in the corn root zone to be 75 to 100 mm.
Add rainfall and irrigation amounts as deposits to the water budget.
If depletion amount is negative, set to zero.
Calculate daily actual water use or AET for corn.
Multiply AET amount by treatment level percentage to obtain modified AET value for the particular treatment.
Subtract modified AET value from water budget for each treatment.
Irrigate a treatment with an amount equal to the calculated root-zone depletion when the treatment reaches the allowable calculated depletion.
Application efficiency for the small basins was assumed to be 100%.
The maximum irrigation rate in the corn study was not allowed to exceed 7.5 mm/day  or a 75 mm  irrigation in a 10-d period.
This maximum irrigation rate reflected the typical capacity of irrigation systems in northwest Kansas.
If the cumulative AET by the corn exceeded the maximum irrigation rate in a given time period, the calculated depletion would not be returned to zero after irrigation.
Tassel initiation was used as the point at which to shift from the initial AET factor to the final AET factor for treatments 5, 6, 8, and 9.
The corn was grown using standard regional production practices for furrow-irrigated corn with the exception of three production inputs, nitrogen fertilizer, seeding rate, and irrigation.
Different fertilizer rates and plant populations were used with the different irrigation schemes to minimize production costs.
The nitrogen fertilizer  was broadcast applied in mid-October of each year preceding planting in the following spring.
Irrigation treatments with an initial AET factor of 100%  received an actual nitrogen amount of 235 kg/ha  and were seeded at a rate of 56,800 seeds/ha.
The 75% AET factor treatments  received a nitrogen amount of 200 kg/ha  and were seeded at a rate of 51,600 seeds/ha.
Those treatments scheduled with an AET factor of 50%  received a nitrogen amount of 170 kg/ha  and were seeded at a rate of 42,300 seeds/ha.
Corn  was planted on 2 May, 28 April, and 29 April for 1986, 1987, and 1988, respectively.
Figure 1-Summer precipitation during the study period and the long-term mean  precipitation at Colby, Kansas.
An approximately 6-m  length of one corn row from the center of each plot was hand harvested in the fall  for yield determination.
RESULTS AND DISCUSSION CLIMATIC CONDITIONS
 Seasonal precipitation  was 324 mm  in 1986, 352 mm  in 1988 which was slightly above the average seasonal amount  of 321 mm.
In each year one or more of the principal growth months,  had considerably less than the long term mean  precipitation.
The cumulative calculated actual evapo-
 Figure 2-Cumulative calculated water use  of corn for 1986 to 1988 and the long term mean  at Colby, Kansas.
transpiration  was approximately 10% greater than the 20-year mean for both 1987 and 1988 and was near normal for 1986.
The timing of precipitation events and evapotranspiration resulted in net irrigation requirements for fully irrigated corn of 380, 305, and 457 mm  for 1986, 1987, and 1988, respectively.
The net irrigation requirement for corn in Thomas County, Kansas, where the study was conducted, is 391 mm  with 80% chance precipitation.
CORN YIELDS AND IRRIGATION
 Corn yields varied widely among treatments  for the three years of the study, ranging from a low of 3.95 Mg/ha  for Treatments 3 and 7 in 1988, the year with the highest irrigation requirements, to a high of 10.61 Mg/ha  for Treatment 4 in 1986, the year with lowest, cumulative, seasonal AET.
An irrigation constraint of 455 mm  of net irrigation generally will not limit corn production in northwest Kansas, as was the case in this study.
Averaged over the three years, fully irrigated  Treatment 1, fertilized with 235 kg/ha  of nitrogen and using a seeding rate of 56,800 seeds/ha , had the highest yield of 9.98 Mg/ha.
Averaged over the three years, Treatment 1 had significantly higher  yields than all treatments except for Treatment 4 and 5.
Results for Treatment 3 illustrate the effect of season-long restrictions in irrigation.
Yields for Treatments 3 were consistently lower than those of Treatments 6 and 9, in which irrigation was restricted only during the vegetative stage.
A similar comparison could be made for Treatment 2 and 5.
Seasonlong restriction of irrigation resulted in lower amounts of irrigation but also usually resulted in a substantial yield reduction.
Tassel initiation, the end of the vegetative stage, occurred on 19 July 1986, and on 15 July for both 1987 and 1988.
All treatments with the 305-mm  irrigation constraint  had statistically similar yields in the range of 8.66-9.23 Mg/ha.
These data indicate a good balance in matching the three resources of
 Table 1.
Resource management schemes and their effects on irrigation requirements and yields of corn, KSU Northwest Research-Extension Center, 1986 to 1988, Colby, Kansas
 Irrigation	Fertilizer	Nitrogen	Seeding	Rate	Irrigation Amount--mm 	Corn Grain Yield Mg ha 
 Constraint	kg/ha	seeds / ha
 Trt ET Factor		mm	acre)		1986	1987	1988	Mean	1986	1987	1988	Mean
 1.
1.00ET	455	235	56800	380	305	455	380	10.0	10.1	9.9	10.0
 										
 2.
0.75ET	455	200	51600	230	230	305	255	9.7	7.6	7.8	8.3
 										
 3.
0.50ET	455	170	42300	75	75	150	100	7.8	6.4	4.0	6.1
 										
 4.
1.00ET	305	235	56800	305	305	305	305	10.6	9.2	7.5	9.1
 										
 5.
5/1.00ET	305	200	51600	305	230	305	280	10.2	9.5	8.0	9.2
 										
 6.
50/1.00ET	305	170	42300	230	230	305	255	9.2	9.0	7.8	8.7
 										
 7.
1.00ET	150	235	56800	150	150	150	150	7,7	7.0	4.0	6.2
 										
 8.
/1.00ET	150	200	51600	150	150	150	150	8.7	8.5	4.6	7.3
 										
 9.
0.50 / 1.00ET	150	170	42300	150	150	150	150	8.7	7.5	6.4	7.5
 										
 Mean	9.2	8.3	6.7	8.0
 			
 LSD	0.05	1.4	2.1	1.6	1.3
 			
 Table 2.
Irrigation dates and amounts for the various treatments, 1986 to 1988
 Date	Trt 1	Trt 2	Trt 3	Trt 4	Trt 5	Trt 6	Trt 7	Trt 8	Trt 9
 Jul	109	78	109	78	109	78
 					
 Jul 25	110	74	76	110	74	76	110	74	76
 								
 Aug 7	76	76
 Aug 13	86	86	76
 Aug 20	76	76
 Aug 28	76	76
 Total	380	230	75	305	305	230	150	150	150
 								
 Jul 22	76	76	76
 Jul 29	76	76	76	76	76
 				
 Aug 4	76	76	76	76
 			
 Aug 13	76	76	76	76	76
 -					
 Aug 15	76	76
 Aug 25	76	76	76	76
 			
 Total	305	230	75	305	230	230	150	150	150
 								
 Jun 22	76	76	76
 Jun 27	76	76	76
 			-
 Jul 5	76	76	76	76	76	76
 					
 Jul 18	76	76	76	76	76	-
 				
 Jul 29	76	76
 Jul 31	76	76	76
 Aug 10	76	76
 Aug 13	76	76	76
 Sep 2	76	76
 Total	455	305	150	305	305	305	150	150	150
 								
 irrigation, nitrogen fertilizer and seed within the irrigation constraint.
Although the average yields for these three treatments were considerably lower than for the fully irrigated Treatment 1, relatively high yields were obtained except in 1988, the year with the highest irrigation needs.
A comparison of the irrigation schedules for 1986 to 1988  shows that Treatment 1 and 4 were identical until the 305-mm  limit was reached in mid-August.
This
 Figure 3-Production costs and total income for the various resourceallocation management schemes for corn.
Net income is the difference between total income  and production costs.
late date was within approximately two weeks from the end of the irrigation seasons for all three years.
Average yields for treatments limited to receiving 150 mm  of irrigation ranged from 6.21 to 7.53 Mg/ha.
Under this severe constraint, the highest yields were obtained when the limited amount of irrigation was shifted toward the critical reproductive and grain filling stages.
Limiting irrigation during the vegetative stage  generally delayed the last irrigation to about 20 d later than when full irrigation  was applied.
EFFECT OF RESOURCE ALLOCATION ON NET INCOME
 An enterprise analysis was performed to determine the effect of resource-allocation on net income.
Cash corn prices, farm program payments and fixed costs were held constant.
The total costs of the irrigation energy, nitrogen fertilizer and seed among treatments ranged from $88 to $156/ha.
Other variable costs among treatments ranged from approximately $440 to $460/ha  with the small differences being the interest costs associated with the three changing inputs.
Total income was calculated as the sum of the federal farm deficiency payment and the product of corn yield and cash market price.
Net income was calculated as the difference between total income and total fixed and variable costs.
Net income is influenced by the effect of resource allocation on both production costs and crop production.
Although minimizing costs is desirable, it is more important to manage and balance the resource inputs to obtain high crop yields, as illustrated in figure 3.
The height difference between the total income  and total costs  equals net income.
The amplitude of the total income line varies much more than the amplitude of the cost bars.
Therefore, changes in total income caused the greatest shift in net income.
Proper resource management, resulting in high production and, therefore, high total income, had a greater effect on net income than the differential costs of the resources.
The highest net income  was obtained when resources were not limited.
However, Treatments 4 to 6, in which irrigation was limited to
 Figure 4-Effect of different grain prices and the presence  or absence  of farm deficiency payment on net income for the various resource-allocation management schemes for corn.
Figure 5-Mean annual and standard deviation of net income for the various resource-allocation management schemes for corn.
EFFECT OF CORN GRAIN PRICE AND DEFICIENCY PAYMENTS ON NET INCOME
 Further economic analysis was performed to illustrate the effect different grain prices and deficiency payments had on net incomes of the various management schemes.
Farm deficiency and production costs were calculated as described in the previous section.
Corn can be grown with a 150-mm  water allocation at a low profit potential when the deficiency payment is included but requires careful management of irrigation, nitrogen fertilizer and seed.
When irrigation allocations are restricted and result in low yields below the farm program yield, a paradox can occur, higher cash market grain prices can result in less net income.
As the market price approaches the federal target price the
 deficiency payment rate is reduced.
Thus when the market price is high and the crop yield is below the program yield, the reductions in deficiency payments are not fully offset by the increases in market sales.
MEANS AND STANDARD DEVIATIONS OF NET INCOME
 The means and standard deviations of net income were calculated  to examine the average profit potential and the variation of profit  for the various treatments.
Annual irrigation requirements and corn yields for the treatments varied and were reflected in the individual calculations  of the means and standard deviations of net income.
The standard cash grain price, deficiency payment and production costs, as previously described, were used in this portion of the analysis.
Risk-aversion techniques strive to maximize the mean net income, while minimizing the standard deviation of net income.
Analysis of the means and standard deviations of net income revealed that the best management scheme was the fully irrigated Treatment 1.
Both maximum mean and minimum standard deviation of net income were obtained by Treatment 1.
Treatments 3, 7, 8, and 9 should be avoided because they have the lowest means and highest standard deviations of net income.
In these schemes, the standard deviation of net income is greater than the mean.
When mean net income is positive, a producer should survive financially in the long run.
However, many producers would not survive because of the large variations in annual cash flow.
Risk-averse producers should not practice marginal management schemes.
Treatments 2 and 4, although possessing mid-range mean net incomes compared to the other treatments, have standard deviations higher than the mean.
This would classify them as relatively risky management schemes, especially when compared to Treatments 1, 5 and 6.
The analysis revealed that Treatment 5 was best when irrigation was constrained to 305 mm.
In essence, though the differences are not great, Treatment 5 manages a better balance of resources than Treatments 4 and 6 as
 indicated by the higher mean and lower standard deviation.
Fully irrigated corn using the standard recommended seeding rate and full fertilization was found to be a more profitable enterprise than any of the other resourceallocation schemes for deficit-irrigated corn examined in this study.
Irrigators wishing to continue to grow corn when irrigation is limited by physical  or institutional constraints should seriously consider reducing irrigated land area to match the severity of the constraint.
This should not be construed to mean that no opportunities exist to reduce the amount of water typically used to fully irrigate corn.
Many irrigators are already upgrading irrigation systems and management of their present systems to "stretch" water.
This does not result in more corn production for each unit of water transpired, but because inefficiencies, such as evaporation and percolation are reduced, more water is available for plant transpiration.
If the irrigation amount for a given land area is constrained at a deficit amount, moderate periods of stress hardening during the corn vegetative stage with proper matching of the fertilizer and seeding rate will stretch the irrigation season.
This may result in more water being available for irrigation during the critical reproductive and grain-filling stages.
Such stretching of the irrigation season increased corn yields by 20%  when the water allocation was restricted to 150 mm.
Net income is influenced by the effect of resourceallocation on both production costs and crop production.
However, at the price levels used in this study, producers should allocate irrigation, nitrogen fertilizer and corn seed to ensure high production rather than to obtain significant production cost savings.
Crop production variations affected net income much more than variations in resource costs.
Analysis of the means and standard deviations of net income for the nine management schemes revealed that full irrigation with the standard recommended amounts of nitrogen fertilizer and seed was best.
This scheme not only maximized the mean net income but also minimized the standard deviation of net income.
Risk-averse producers should not practice the severely restricted irrigation management schemes because the standard deviation of net income is greater than the mean net income, which means large variations in annual cash flow.
Comparison of the profitability of these management schemes for corn production to other enterprises, such as irrigated wheat or irrigated grain sorghum production, lies beyond the scope of the study, so no conclusions in this area can be drawn or should be inferred.
This article  conducted a case study for a method of mapping soil water properties when the required accuracy exceeds what is provided by the NRCS soil survey.
Soil water properties were first determined at sparse sampling locations and then predicted throughout a field using a regression relationship with densely  sampled variables such as elevation or apparent soil electrical conductivity.
The analysis found that soil water properties do not relate closely to ECa on every field.
Still irrigation timing is important, and adequate subsurface moisture can help control weeds.
If irrigation occurs before the alfalfa plants have begun to regrow after cutting though, weed growth will be promoted instead.
When summer heat arrives, alfalfa plants will likely draw moisture from their eight feet rooting depths to maintain full forage production.
Conversely, lower spring irrigation amounts may result in shallower rooting decreasing summer irrigation efficiency.
For early season irrigation, the target is to refill the top six feet of subsoil profile for the late spring and summer.
More information is available on our UNL Extension website and our free NebGuide G1778, Irrigation Management and Crop Characteristics of Alfalfa.
Important Agricultural Soil Properties
 Danny H.
Rogers Professor, Extension Irrigation Engineer, Biological and Agricultural Engineering
 Jonathan Aguilar Assistant Professor, Water Resources Engineer, Southwest Research Extension Center
 Isaya Kisekka Assistant Professor, Irrigation Research Engineer, Southwest Research Extension Center
 Philip L.
Barnes Associate Professor, Water Quality, Biological and Agricultural Engineering
 Freddie R.
Lamm Professor, Irrigation Research Engineer, Northwest Research and Extension Center
 Soil itself is not essential to a growing plant.
Soil serves as a storage reservoir for nutrients and water needed for plant growth.
These soil properties are essential to crop production.
Crop production potential is greatly influenced by the physical and chemical properties of soils.
These same properties also influence related activities such as tillage, erosion, drainage, and irrigation.
Important agronomic soil properties include the soil water-holding capacity, infiltration rate, aggregation, temperature, organic matter content, and nutrient availability.
The definitions of soil from the Soil Science Society of America is: soil:  the unconsolidated mineral or organic material on the immediate
 surface of the earth that serves as a natural medium for the growth of land plants.
The unconsolidated mineral or organic matter on the surface of the earth that has been subjected to and shows effects of genetic and environmental factors of: climate , and macroand microorganisms, conditioned by relief, acting on parent material over a period of time.
A product, soil differs from the material from which it is derived in many physical, chemical, biological, and morphological properties and characteristics.
As a material medium for plant growth, a given volume of soil is composed of three parts: solids, air, and water, as illustrated in Figure 1.
The solid portion can be further divided into mineral and organic matter, while the air and water portion of the soil is called the pore volume.
Under normal farming practices, the ratio of solid to pores remains constant and for a given environmental condition, the organic matter remains stable.
Organic matter can be altered by changing conditions such as
 Figure 1.
Soil composition components.
erosion or cultural practices.
Most soils have an organic matter content of less than 1 percent to about 5 percent by volume.
Organic matter consists of decaying plant and animal material, largely microbes and insects.
Although it is only a small fraction of the total soil volume, organic matter's role in serving as the primary storage receptor for plant nutrients is extremely important.
The balance between water and air in the soil is important.
The ratio of water to air in the pores of the soil volume varies greatly; as one increases, the other must decrease.
Soils that are completely filled with water, or saturated, have all air displaced from the soil pores.
Without air, or oxygen in particular, root respiration is disrupted, which is an integral part of the plant growth process.
There are three classes of soil particles sand, silt, and clay and their relative proportions determine the soil textural class, as shown in Figure 2.
Texture is a way to describe a soil by feel.
For example, coarse sand may feel gritty, while a silt loam has the feel of flour.
The relative sizes of the three soil particles are shown in Figure 3, while the size classification ranges are depicted in Figure 4.
The soil texture is determined using a laboratory analysis that determines the fractions of sand, silt, and clay.
Primary soil particles can be combined into secondary arrangements called peds, which can be of various sizes and shapes.
Unlike most soil particles, which are too small to be seen without magnifica-
 Figure 2.
A soil textural classification triangle.
tion, most peds can be seen and are important to maintaining soil tilth and crop productivity.
Unlike soil texture, soil structure can be affected by crop cultural practices.
The soil structure develops over time as the result of root penetration, freezing and thawing cycles, the presence of organic and inorganic binding agents, and biological activities.
Soil structure is affected by cultural practices that can accelerate the loss of organic materials or destroy aggregates through improper tillage practices.
Generally, productive agricultural soils have a soil structure that allows good root penetration and allows a good exchange of air and water within the soil profile.
Soils classified in the same series are soils that have been formed from the same parent material and are similar in profile arrangement and characteristics, except in the A horizon (upper-
 Figure 3.
The relative sizes of soil particles.
On the series level, one of the properties defined is the soil depth of the various layers, which typically consists of three levels: A , B, and, C.
Progressively downward, each layer is less affected by the five soil forming factors of parent material, climate, topography, biota, and time.
Biota refers to the biological organisms and activities.
The layers can be distinctive parent material, such as when a different material is overlain on an existing soil, such as wind-deposited loess on flood sedimentation.
The
 depth of soil and the corresponding thickness of various textural layers have an important influence on irrigation management decisions.
The density of a substance is defined as the mass per unit volume.
In soils, this value is called the bulk density: Bulk density  = M/ = mass of dry soil/volume of soil sample Bulk density is typically expressed in grams/cm3.
Typical soil bulk densities range from 1.1 to 1.7 g/cm.
Another soil density term is particle density, which is defined as the mass of the dry soil particles divided by the volume of the soil particles.
For all practical purposes, the mass of dry soil particles is the same as the mass of the dry soil, as the weight of air is the only difference.
Figure 4.
USDA soil classification of primary soil particles by size.
Particle density  = M&/Vs = mass of dry soil/volume of the soil particles or solids
 The space between soil solids or particles is called the pore space.
Soil porosity describes this portion of the soil volume that can hold either air or water.
Porosity is generally expressed as a percentage.
Porosity  = volume of pores/volume of soil
 Particle density is typically expressed in grams/cm3 and the ranges for typical soils is 2.6 to 2.7 cm.
A Pp value of 2.65 g/cm is used for most soils.
The particle density of a soil is typically constant, changing only slightly if the organic matter content changes, whereas bulk density depends on the amount of pore space in a soil.
Soil pore space can be altered.
In agricultural settings, increasing bulk density indicates compaction is occurring, which could cause detrimental growing conditions, such as limiting root penetration or decreasing the soil aeration process.
tion water over a given time.
The infiltration rate of a soil is not constant and depends on many factors, including the surface conditions, such as residue cover and surface roughness; soil water content; and slope.
Most agricultural soils have a porosity of about 50 percent, but if they become compacted, porosity decreases, which limits the space available for water and air and restricts root development.
Porosity  = )x 100
 The infiltration rate for soils is high at the initiation of infiltration and decreases as the infiltration process continues.
The elapsed time between the initiation of infiltration and the current time of an event is called the opportunity time.
Soil infiltration and permeability describe the movement of water in soils.
Infiltration is the movement of water into the soil from the soil surface.
The infiltration rate, also called the intake rate, is a measurement of the ability of a soil to absorb rainfall or applied irriga-
 The infiltration rate relationship with time is shown in Figure 5 for the various soils.
As the opportunity time increases, the infiltration rate decreases until it becomes relatively constant.
The infiltration rate for this condition is called the basic infiltration rate or steady state infiltration rate.
Soils that have similar intake rates are classified as being from the same intake family.
Soils with high clay content tend to have low intake rates, silt soils have higher intake rates than clay, and sands tend to have the highest intake rates.
After water has entered a soil, the term to describe the water movement within the soil profile is permeability.
Soils with larger and connected pore spaces are more permeable than soil with small, disconnected pore spaces, even if the porosity values are similar.
The downward movement of water within a soil profile is called percolation.
The measure of the rate of water movement is called hydraulic conductivity and measured in units of inches/hour.
These rates can be quite variable.
The amount of water in a soil available for plant use is one of the most important measurements needed for proper irrigation management.
While the porosity of most agricultural soils is similar, the amount of plant-available water varies greatly.
This is due to size of the pore space in a soil and the way water is held within the pores of a soil.
Figure 6 illustrates that for a given soil volume, larger particle sizes are associated with larger pore size.
Since all soils have about the same porosity, this means smaller-sized particle soils will have smaller, but more, pore spaces.
Soils can be a mixture of particle sizes and this also affects the size and number of pores.
Soil geometry is also much more complex than these circular depictions.
Four important terms are used to describe the water level within a soil.
When all the soil pores are filled with water, the soil is said to be saturated.
However, the gravitational pull on the water causes some of it to drain.
While this water could be used by plants, the gravitational drainage is generally too rapid to allow plants to capture much of this water.
Figure 5.
Infiltration rate curves from the Natural Resources Conservation Service.
Soil permeability is grouped into classes ranging from very slow to very rapid, as shown in Table 1.
Table 1.
Soil Permeability Classes
 Classification	Infiltration Rate 
 Very Slow	< 0.06
 Moderately Slow	0.2 0.6
 Moderately Rapid	2.0 6.0
 Very Rapid	> 20.0
 Illustration of the effect of particle size on the size and number of pore spaces within a fixed soil volume.
Illustration of the effect of a mixture of soil particle size on the number and size of pores within a given soil volume.
Figure 6.
The effect of soil particle size and particle mixture on pore space.
Water retained by the soil after gravitational drainage is held in place by capillary and adsorption forces.
This occurs due to the surface tension  of water and the attraction of the water to the soil particle by adhesion.
Some of the water is available to plants
 The amount of water retained in the soil after gravitational drainage is the field capacity of the soil.
As plants extract water, the remaining water is held more tightly until eventually the plant cannot extract additional water.
The soil water content at this point is called the wilting point.
The film of water that remains around the soil particles is held by adsorption forces and is called hygroscopic water.
It is not available for plant use.
Several of these conditions are illustrated in Figure 8.
The amount of water between field capacity and wilting point is called plant available water.
Average water-holding capacities for various soil textural classes are shown in Tables 2 and 3.
Table 2 values tend to be larger for the surface layers than for the Table 3 subsoil layers.
Of course, the holding capacity can vary from site to site.
The effect of different water holding capacities for three soil types is illustrated in Figure 9.
Even though all three soils hold over 5 inches of water at saturation, the sand only holds about 1 inch of plant available water.
The silty clay loam soil has the largest amount of water in storage but has a larger amount not plant available, SO the loam soil ends up with the most plant available water.
Figure 10 graphically illustrates typical field capacity and wilting point values for 11 soil textures.
At field capacity, the available water is said to be 100 percent available in reference to plant use, while at wilting point, the available water to plants is 0 percent available.
Calculating Soil Water Content
 The amount of water in a soil can be measured directly using the gravimetric method, which is simply the weight of the water in a soil sample in proportion to the dry soil sample weight.
See Formula A.
The soil water content by volume is volume of water in a soil
 Illustration of water levels within a soil
 Figure 7.
Illustration of water levels within a soil.
sample in proportion to the volume of the soil sample.
See Formula B.
It is relatively easy to collect samples and measure the gravimetric water content of a soil, but the more useful value is the volumetric water content.
The gravimetric water content is related to the volumetric content by the following relationship shown in Formula C.
Example calculations: Determine the gravimetric water content for a silt loam soil sample collected from the surface 12-inch layer and weighing 105 grams.
After drying, the sample weighs 85 grams.
The gravimetric water content is 24%.
Soil bulk density values are given in tables 2 and 3.
The density of water is 1.0 gram/cm3 or 62.4 pounds/ ft3.
Determine the volumetric water content for the same sample.
The bulk density from Table 2 for a silt loam is 1.40.
The volumetric water content is 34%, as shown in Formula E.
X 100
 Gravimetric water % =
  X 100
 Volumetric water % =
 
 
 Volumetric water % =
 Gravimetric water % =
 Volumetric water % =  / Density of water
 Table 2.
Average available water capacity for Kansas soils in the 0to 12-inch layer.
Percentage by Mass	Fraction by Volume
 Soil	Bulk Density	Field	Wilting	Available	Field	Wilting	Available
 Texture	Capacity	Point	Water	Capacity	Point	Water
 Sand	1.60	8.7	3.5	5.2	0.14	0.06	0.08
 Loamy Sand	1.60	11.9	4.5	7.4	0.19	0.07	0.12
 Sandy Loam	1.55	15.4	5.8	9.6	0.24	0.09	0.15
 Fine sandy Loam	1.50	19.5	7.5	12.0	0.29	0.11	0.18
 Loam	1.45	23.6	9.2	14.4	0.34	0.13	0.21
 Silt Loam	1.40	27.2	10.9	16.3	0.38	0.15	0.23
 Silty Clay Loam	1.35	28.8	13.0	15.8	0.39	0.18	0.21
 Sandy Clay Loam	1.40	27.0	13.5	13.5	0.38	0.19	0.19
 Clay Loam	1.40	27.3	15.1	12.2	0.38	0.21	0.17
 Silty Clay	1.30	28.7	18.0	10.7	0.37	0.23	0.14
 Clay	1.25	29.4	20.1	9.3	0.37	0.25	0.12
 Source: NRCS Kansas Irrigation Guide
 Table 3.
Average available water capacity for Kansas soils for depth greater than 12 inches.
Percentage by Mass	Fraction by Volume
 Soil	Bulk Density	Field	Wilting	Available	Field	Wilting	Available
 Texture	Capacity	Point	Water	Capacity	Point	Water
 Sand	1.70	7.0	3.0	4.0	0.12	0.05	0.07
 Loamy Sand	1.70	10.0	4.2	5.8	0.17	0.07	0.10
 Sandy Loam	1.65	13.4	5.6	7.8	0.22	0.09	0.13
 Fine sandy Loam	1.60	18.2	8.0	10.2	0.29	0.13	0.16
 Loam	1.55	22.6	10.3	12.3	0.35	0.16	0.19
 Silt Loam	1.50	26.8	12.9	13.9	0.40	0.19	0.21
 Silty Clay Loam	1.45	27.6	14.5	13.1	0.40	0.21	0.19
 Sandy Clay Loam	1.50	26.0	14.8	11.2	0.39	0.22	0.17
 Clay Loam	1.50	26.3	16.3	10.0	0.39	0.24	0.15
 Silty Clay	1.40	27.9	18.8	9.1	0.39	0.26	0.13
 Clay	1.35	28.8	20.8	8.0	0.39	0.28	0.11
 Source: NRCS Kansas Irrigation Guide
 Since the sample represents the 12-inch soil layer, the depth of water in the layer can be calculated by multiplying the soil depth by the volumetric soil water content fraction or:
 Depth of water in the soil layer = 12 inches X  = 4.08 inches
 Similarly, the depth of water in the 12-inch soil layer at field capac-
 ity can be calculated using the field capacity value from Table 2 as Depth of water in soil at field capacity = 12 inches X  / 1.0 = 4.56 inches
 The amount of plant available water in the soil sample can be estimated by subtracting the amount of water in the soil at wilting point.
mass, which is 0.15 by volume.
From Table 2 silt loam soil water content at wilting point is 10.9% by
 The plant available portion of the water content from the sample is therefore 34% minus 15% or 19% by volume.
The plant available water depth in the 12 inch soil layer is 12 inches X  = 2.28inches.
Direct measurement of soil water content by gravimetric sam-
 Figure 8.
Illustration of gravitational and capillary held water in the soil pore spaces.
pling is an accurate and reliable method to determine soil water content, and the sampling can be done at multiple locations within a field.
However, it is not commonly used as it is labor intensive and, because of the sample drying requirements, there is a time delay between collection and the results.
A specific site also cannot be resampled since a physical sample is removed.
Other indirect measurement methods to determine soil water content are discussed in other publications.
More discussion on crop water requirements and how plants extract water are in publication L934, Agricultural Crop Water Use.
Figure 9.
Illustration of soil water levels for three soil types.
Figure 10.
Illustration of percentage term definitions for available water by volumetric measure and as a percentage of available water for soil textures.
Corn is a major irrigated crop in the U.S.
Great Plains with a large irrigation requirement making efficient, effective irrigation technology important.
The objective of this paper was to compare corn productivity for different irrigation methods and irrigation rates in 2009 and 2010 at Bushland, Texas.
Irrigation methods included mid-elevation spray application , low elevation spray application , low energy precision application , and subsurface drip irrigation.
Each irrigation method was evaluated at four irrigation rates, which were 25, 50, 75, and 100% of meeting the full crop water requirement.
There were no significant differences in grain yield and water use efficiency for MESA, LESA, and SDI for the 100% irrigation rate in 2009 and for all irrigation rates in 2010.
In 2009, SDI resulted in significantly greater grain yield and water use efficiency compared with all other methods at the 50 and 75% irrigation rates; little measurable grain yield resulted for all methods at the 25% rate.
However, 2009 was not a typical production year because an irrigation system failure occurred just before anthesis, and unusually high atmospheric demands followed, resulting in soil water shortages in all plots during the most watersensitive development stages, with consistent lowering of grain yield.
In both years, LEPA resulted in lower yield, soil water content, and water use efficiency compared with the other methods at the 75 and 100% rates, which was partially attributed to furrow dike erosion and plot runoff.
The relative response of corn to MESA, LESA, LEPA, and SDI was much different compared with other crops that were evaluated in previous experiments; these included grain sorghum, soybean, and cotton.
Grain corn is a major irrigated crop in the U.S.
Great Plains that has been mostly produced for beef cattle feed and more recently as a feedstock for ethanol.
In the semiarid Southern High Plains, nearly all corn production requires irrigation and is dependent on pumping from the Ogallala Aquifer, which has been declining since large-scale development of irrigation in the region because pumping has exceeded recharge.
Within the Texas portion of the Southern High Plains, approximately 75 percent of the irrigated area is with center pivot sprinklers, with the remaining 20 and 5 percent comprising gravity  and subsurface drip irrigation , respectively.
Most SDI has been installed in the cotton producing region centered around Lubbock, Texas.
For both full and deficit irrigation rates, cotton lint yield and water use efficiency have been shown to be consistently greater for full and deficit irrigation rates under SDI compared with sprinklers, including both mid elevation spray application  and low elevation spray application  configurations.
Cotton response to low energy precision application  has also been more favorable compared with MESA or LESA, but still not as favorable as SDI.
This is thought to be related to SDI maintaining warmer soil temperatures near the surface because less evaporative cooling occurs relative to MESA, LESA, or LEPA, which apply water directly to the soil surface and/or plant canopy.
Sufficiently warm soil and plant microclimate is critical for cotton production in semiarid regions with high elevations because cool nighttime temperatures usually occur throughout the year.
Other studies have shown that SDI resulted in greater grain yield and water use efficiency for grain sorghum  and soybean  at deficit irrigation rates because lower evaporative losses for SDI relative to sprinklers resulted in greater soil water being available for plant transpiration, which was also observed for cotton.
As irrigation well capacities decline, Great Plains producers are increasingly being forced to adopt deficit irrigation strategies.
Since SDI has been shown to increase crop water productivity relative to MESA, LESA, and LEPA at deficit irrigation rates for some crops, there has been continued adoption of SDI in the Great Plains.
Corn response to various rates of deficit and full irrigation has been evaluated in the Great Plains using sprinkler irrigation , LEPA , and SDI.
However, it appears that only Schneider and Howell  and Lamm  directly compared corn response to different irrigation methods, where the irrigation system itself was a randomized and replicated treatment.
Schneider and Howell  compared spray and LEPA, and Lamm  was limited to SDI VS.
simulated LEPA, where water for the simulated LEPA treatment was applied by stationary tubing into furrow basins.
No study has directly compared corn production under SDI with moving spray or LEPA packages commonly used with center pivots in the Great Plains.
The objective of this research was to compare corn water productivity using MESA, LESA, LEPA, and SDI across a range of irrigation rates.
This research was conducted at the USDA Agricultural Research Service Conservation and Production Research Laboratory at Bushland, Texas.
The soil is a Pullman clay loam  with slow permeability due to a dense B21t horizon that is 6 to 20
 inches below the surface.
A calcic horizon begins at approximately 4 ft below the surface.
The relative performance of MESA, LESA, LEPA, and SDI were compared for irrigation rate treatments ranging from near dryland to meeting full crop evapotranspiration  in a strip-split block design.
The irrigation rate treatments were designated lo, l25, 50, l75, and 100, where the subscripts were the percentage of irrigation applied relative to meeting full ETc.
The lo plots were similar to dryland production, in that they received only enough irrigation around planting to ensure crop establishment; but irrigated fertility and seeding rates were used.
Each rain event was measured manually by a gauge located at the field site.
Each plot was 30 ft wide by 39 ft long and contained 12 raised beds with east-west orientation and 30-inch centers, with the crop planted in the centers of the raised beds.
Dikes were installed in all furrows following emergence to control run on and runoff of irrigation water and rain.
The MESA, LESA, and LEPA methods  were applied with a hose-fed, three-span lateral-move irrigation system, where each span contained a complete block , resulting in three replications for each treatment.
The LEPA method used double-ended drag socks in 2009; however, the drag socks were sometimes caught by plants and pulled off as the drop moved through after plants reached heights of about 5 ft, resulting in excessive furrow dike erosion.
Several attempts to lower the height and strengthen the drag sock connection were not successful.
Therefore, the LEPA treatment used low-impact bubblers without socks in 2010.
Irrigation rate treatments were imposed by varying the speed of the lateral-move.
The SDI method consisted of drip laterals installed with a shank injector beneath alternate furrows at the 12-inch depth, where irrigation treatments were imposed by varying emitter flow rates and spacing.
Corn.
Volumetric soil water was measured by gravimetric samples to the 6-ft depth in 1-ft increments at planting and harvest.
Soil water was also measured during the crop season by neutron probe  to the 10-ft depth in 8-inch increments  using a depth control stand, which allowed accurate measurement of soil water at shallow  depths.
The NP meters were field-calibrated and achieved accuracies better than 0.005 in.
3 in.
-3 , including the 4-inch depth near the surface.
Both gravimetric and NP were measured near the center of each plot  and in the center of the raised bed.
Table 1.
Sprinkler irrigation application device information [a]
 Applicator	Model [b]	Options	
 LEPA,	Super Spray head	Double-ended drag	0
 LEPA,	Quad spray	Bubbler	1.0
 LESA	Quad IV	Flat, medium-	1.0
 MESA	Low-drift nozzle	Single, convex,	5.0
  spray head	medium-grooved
 [a] All sprinkler components manufactured by Senninger Irrigation, Inc., Orlando, Fla., except where noted.
[b] All devices equipped with 10 psi pressure regulators and No.
17  plastic spray nozzles, giving a flow rate of 6.5 gpm.
[c] Manufactured by A.
E.
Quest and Sons, Lubbock, Tex.
Table 2.
Subsurface drip irrigation  dripline information [a]
 Irrigation	Emitter Flow	Emitter	Application
 rate	Rate 	Spacing 	Rate (in.
h-1
 25	0.18	36	0.019
 50	0.24	24	0.038
 75	0.24	16	0.057
 100	0.24	12	0.076
 [a] All SDI dripline manufactured by Netafim USA, Fresno, Calif.
[b] Smooth tubing, no emitters
 Irrigations were scheduled based on NP measurements, usually at weekly intervals during the irrigation season.
Early in the season, irrigation water was applied when the average soil water deficit in the root zone of the 100 treatment reached 1.0 inch below field capacity, where field capacity was 4.0 inches per ft  of the soil profile.
From about the middle of the vegetative stage  to termination of irrigations, the appropriate irrigation amount was applied on a weekly basis in 1.0-inch increments to avoid over-filling the furrow dike basins.
All sprinkler plots were irrigated on the same day, with the deficit  treatments receiving proportionately less water by increasing the speed of the lateral move system.
The SDI plots had the same amount of water
 applied as the sprinkler plots except the duration of each irrigation event was longer.
Table 3.
Agronomic and irrigation data for the 2009 and 2010 seasons.
Fertilizer applied	150 lb ac 1 preplant N	150 lb ac 1 preplant N
 130 lb ac preplant P	65 lb ac-1	preplant P
 240 lb ac 1 irr N 	[a]	150 lb ac-1	irr N  [a]
 90	lb	ac- preplant S
 Herbicide applied	2.0 qt ac-1 -1 Bicep	1.5 lb ac -1 Atrazine
 Insecticide applied	NONE	NONE
 Corn variety	Pioneer 33B54 BT, RR	Pioneer 33B54 BT, RR
 Plant density	35,000 seeds ac -1	35,700 seeds ac -1
 Planting date	29-Apr	12-May
 Harvest date	15-Sep	15-Sep
 Preplant irrigation	3.0 inches	0.8 inches
 First treatment irrigation	-Jun	11-Jun
 Last irrigation	28-Aug	26-Aug
 lo irrigation	[b]	3.0 inches	1.8 inches
 l25 irrigation	[b]	7.2 inches	7.1 inches
 150 irrigation	[b]	11.4 inches	12.2 inches
 l75 irrigation [b]	15.6 inches	17.5 inches
 100 irrigation [b]	19.7 inches	22.8 inches
 Precipitation	10.0 inches	8.7 inches
 [a] Liquid urea 32-0-0 injected into irrigation water; deficit irrigation treatments received proportionately less.
[b] Includes preplant irrigation
 Grain yield, final plant population, kernel mass, number of ears, and kernels per ear were determined by hand harvesting two adjacent rows along a 21.5 ft length in the center of each plot.
Ears were shelled by hand and kernels were oven dried at 160F for 5 days.
Dry yield mass was converted to 15.5 percent moisture , and reported as volume.
Kernel mass was determined from three 500kernel subsamples, and kernels per ear was calculated as yield mass per area divided by kernel mass divided by ears per area.
Yield components, seasonal water use , and water use efficiency were compared using the SAS PROC MIXED procedure.
Water use efficiency  to seasonal water use .
Any differences in these parameters were tested using least squared differences (a
 0.05), and means were separated by letter groupings using a macro by Saxton.
The 2009 season began with planting on April 29, reaching anthesis on July 8, and black layer by September 3.
Hand samples used to determine yield and yield components were obtained on September 15.On June 3 , some hail damage occurred, which the plants appeared to have outgrown in two weeks.
The tassel and silk stages coincided with high temperatures, high wind speeds, and low relative humidity, resulting in crop evapotranspiration approaching almost 0.50 in.
d-Superscript 1 for several days.
The unusually high temperatures during silking are believed to have affected pollen viability.
Rainfall during the 2009 season totaled 10.0 inches , which was somewhat below the 12.3-inch average from April 29 to September 15.
In 2010, planting was delayed until May 12 because of cold and wet conditions during the El Nio winter and spring.
Very warm conditions during May and June resulted in rapid growing degree day accumulation, and the 2010 crop reached anthesis near the same time as the 2009 crop.
The 2010 crop reached black layer by September 8, and hand samples were obtained on September 15.
Total rainfall during the season was 8.7 inches , which was also below average.
Table 4.
Dates and cumulative growing degree days  for corn development stages, where GDD were computed using baseline and maximum temperatures of 50 and 86 F, respectively.
Date	GDD 	GDD 
 Plant	29-Apr	0	12-May	0
 Emerged	13-May	158	28-May	258
 4-leaf	21-May	277	3-Jun	387
 5-leaf	25-May	339	5-Jun	433
 6-leaf	28-May	378	8-Jun	515
 8-leaf	3-Jun	484	11-Jun	591
 10-leaf	12-Jun	668	14-Jun	664
 12-leaf	15-Jun	739	17-Jun	737
 14-leaf	4-Jul	1206	5-Jul	1184
 Tassel	8-Jul	1298	10-Jul	1290
 Silk	15-Jul	1481	15-Jul	1422
 Blister	21-Jul	1626	23-Jul	1630
 Milk	30-Jul	1817	28-Jul	1753
 Dough	4-Aug	1929	6-Aug	1981
 Dent	11-Aug	2109	12-Aug	2137
 Black layer	3-Sep	2623	8-Sep	2758
 Grain yields in 2009 were much lower than expected except for the MESA, LESA, and SDI methods at the 100 irrigation rate.
There was essentially no yield for all irrigation methods at the lo and l25 rates, and only SDI resulted in more than 10 bu ac at the 50 rate.
At the 75 rate, MESA, LESA, and LEPA resulted in less than 100 bu ac-1, and SDI only 188.8 bu ac-1.
Previous studies at our location using LEPA at the 180 rate and SDI at the 167 rate resulted in 200 to 235 bu ac-1.
Grain yield was reduced in 2009 mainly from failure of ears to produce kernels, as numerous blank cobs were observed.
Final plant population and kernel mass, however, were as expected and were similar to those reported at Bushland, Texas  and at Colby, Kansas.
Seasonal water use was less for SDI at 25 and 150 compared with the other methods, resulting in greater water use efficiency.
At l75, there were no differences in seasonal water use; at 100, LEPA used 1.5 to 2.0 inches more than the other methods.
Overall, seasonal water use was similar to that reported in previous studies , but since grain yield was relatively low, water use efficiency was also relatively low except for MESA, LESA, and SDI at 100 and SDI at 75.
In 2010, most grain yields were similar to previous studies  at the 75 and 100 rates, and greater than expected at the 25 and 50 rates.
However, grain yield using LEPA was significantly less compared with the other methods at the l75, and 100 rates.
The low grain yield using LEPA was inconsistent with previous studies at our location.
As discussed later, although soil water depletion in the LEPA method was greater compared with the other methods, it did not appear to be enough in the 100 rate to cause yield-reducing water stress.
At 50, grain yield for MESA was similar to LEPA.
Grain yield differences were related to both kernel mass and kernels per ear; these yield components were within the expected ranges.
Plant population was slightly greater for LEPA at 150, l75, and 100 rates.
For each irrigation rate, there were no differences in seasonal water use among irrigation methods.
Therefore, water use efficiency followed nearly the same trends as grain yield, with LEPA having less water use efficiency compared with the other irrigation methods.
The kernel set failure observed in 2009 was likely the result of water shortages in the soil profile during anthesis, which coincided with very high atmospheric demand and high temperatures.
The soil water shortages were due to irrigation system operational problems followed by unusually high crop water demand.
The combination of greater sensitivity to water stress during anthesis  and greater atmospheric demand would both serve to decrease the readily available soil water in the root zone , as defined by FAO 56.
If soil water depletion in the root zone exceeds RAW, the crop experiences water stress, which may reduce yield.
This is illustrated by comparing RAW with measured soil water depletion in the root zone during the season.
Also shown is the total available soil water in the root zone
 Table 5.
Corn response for 2009 season.
Irrig.
Irrig.
Grain yield	Final	Kernel	Kernels	Seasonal	Water use
 rate [a]	method	15.5% wb [b]	plant pop.
mass	per ear	water use	efficiency
 bu ac -1	plants ac-1	mg	inches	bu ac-1 in-1
 25	MESA	0.0	a	[c]	34,143 a	0 b	0 b	15.3	ab	0.0	a
 	LESA	0.0	a	33,603	a	0 b	0 b	15.7	ab	0.0	a
 LEPA	0.3	a	32,793	a	0 b	0 b	16.6	a	0.0	a
 SDI	3.6	a	33,198	a	105	a	567	a	14.8	b	0.2	a
 50	MESA	7.5	b	33,333	a	322	a	26	b	19.9	ab	0.4	b
 	LESA	8.8	b	32,928	a	307	a	29	b	20.7	ab	0.4	b
 LEPA	8.9	b	34,008	a	301	a	50	b	21.4 a	0.4	b
 SDI	70.9	a	33,738	a	310	a	186	a	19.8	b	3.6	a
 75	MESA	37.5	C	34,278	a	341	a	89	C	24.1	a	1.5	C
 	LESA	77.3	b	32,659	a	347	a	186	b	24.7 a	3.1	b
 LEPA	30.1	C	33,873	a	312	a	96	C	25.2 a	1.2	C
 SDI	188.8	a	33,468	a	357	a	433	a	25.4 a	7.4 a
 100	MESA	214.9	a	34,683	a	348	a	477	ab	28.0	b	7.7	a
 	LESA	235.5	a	33,873	a	349	a	525	a	28.5	b	8.3	a
 LEPA	103.0	b	33,198	a	349	a	256	b	30.2	a	3.4	b
 SDI	233.0	a	34,413	a	348	a	527	a	28.5	b	8.2	a
 lo 	0.0	C [d]	30,769	b	0	C	0 b	10.5	e	0.0	C
 125 	1.0	C	33,434	a	26	C	142	b	15.6	d	0.1	C
 150 	24.0	C	33,502	a	310	b	73	b	20.4	C	1.2	C
 75 	83.4	b	33,570	a	339	a	201	b	24.8	b	3.3	b
 100 	196.6	a	34,042	a	349	a	446	a	28.8	a	6.9	a
 MESA	65.0	bc	[e]	34,109	a	253	ab	148	b	21.8	b	2.4	bc
 LESA	80.4	b	33,266	a	251	ab	185	b	22.4	ab	3.0	b
 LEPA	35.5	C	33,468	a	240	b	100	b	23.3	a	1.3	C
 SDI	124.1 a	33,704	a	280	a	428	a	22.1	b	4.9	a
 [a] Numbers in parenthesis are seasonal irrigation totals for each irrigation rate.
[b] Yields were converted from dry mass to 15.5 percent moisture content by mass  and 56.0 lb bu
 [c] Numbers followed by the same letter are not significantly different  within an irrigation rate.
[d] Numbers followed by the same letter are not significantly different <0.05) between irrigation rate averages.
[e] Numbers followed by the same letter are not significantly different  between irrigation method averages.
Table 6.
Corn response for 2010 season.
Irrig.
Irrig.
Grain yield	Final	Kernel	Kernels	Seasonal	Water use
 rate [a]	method	15.5% wb [b]	plant pop.
mass	per ear	water use	efficiency
 bu ac	plants ac-1	mg	inches	bu ac-1 in-Superscript
 25	MESA	90.1	a	[c]	35,088 a	207	bc	328	a	18.2 a	5.0	a
 	LESA	101.9	a	34,548	a	217	ab	363	a	18.2 a	5.6	a
 LEPA	90.7	a	35,088	a	228	a	309	a	18.1 a	5.0	a
 SDI	82.6	a	34,008	a	193	C	349	a	17.8 a	4.7	a
 50	MESA	180.1	b	35,223	a	274	b	484	a	22.6 a	8.0	ab
 	LESA	196.9	ab	34,683	a	284	ab	522	a	22.4 a	8.8	a
 LEPA	175.1	b	35,493	a	276	b	461	a	23.0 a	7.6	b
 SDI	202.3	a	34,278	a	296	a	522	a	22.6 a	9.0	a
 75	MESA	233.5	a	33,603	b	316	a	574	a	27.7 a	8.5	a
 	LESA	231.0	a	34,008	ab	322	a	556	a	27.1 a	8.5	a
 LEPA	194.3	b	36,167	a	309	a	453	b	28.0 a	7.0	b
 SDI	237.5	a	35,088	ab	316	a	562	a	26.9 a	8.8	a
 100	MESA	246.7	a	34,008	ab	326	b	575	a	31.6 a	7.8	a
 	LESA	235.4	a	32,659	b	348	a	557	ab	32.1 a	7.3	a
 LEPA	195.3	b	35,762	a	291	C	489	b	32.2 a	6.1	b
 SDI	249.1 a	34,278	ab	333	ab	565	a	32.1 a	7.8	a
 lo 	18.5	d	[d]	33,828	a	194	C	140	C	13.3 e	1.4	d
 125 	91.3	C	34,683 a	211	C	337	b	18.1	d	5.1	C
 150 	188.6	b	34,919	a	282	b	497	a	22.6	C	8.3	a
 75 	224.1	a	34,717	a	316	a	536	a	27.4	b	8.2	a
 100 	231.6 a	34,177	a	325	a	547	a	32.0	a	7.2	b
 MESA	187.6	a	[e]	34,481	a	281	ab	490	ab	25.0 a	7.3	a
 LESA	191.3	a	33,974 a	293	a	500	a	24.9 a	7.6	a
 LEPA	163.9	b	35,628	a	276	b	428	b	25.4 a	6.4	b
 SDI	192.9	a	34,413	a	284	ab	500	a	24.8 a 7.6	a
 [a] Numbers in parenthesis are seasonal irrigation totals for each irrigation rate.
[b] Yields were converted from dry mass to 15.5 percent moisture content by mass  and 56.0 lb bu-
 [c] Numbers followed by the same letter are not significantly different  within an irrigation rate.
[d] Numbers followed by the same letter are not significantly different  between irrigation rate averages.
[e] Numbers followed by the same letter are not significantly different  between irrigation method averages.
e.
f.
Figure 1.
Soil water depletion, total available soil water , and readily available soil water  in the root zone for  2009 150;  2010 50;  2009 l75;  2010 l75;  2009 I 100,  2010 I 100-
 .
Assuming a maximum root depth of 6 ft, the Pullman clay loam soil at the study location has about 10.0 inches of maximum TAW, with the lower and upper limits of plant extractable water at 14.0  and 24.0 inches  respectively.
RAW is generally around 50 percent of TAW for most crops including corn during the growing season.
However, RAW depends on crop species and the soil water matric potential relationship, and varies with time according to crop growth stage and atmospheric demand.
RAW can be adjusted from a base value in terms of ETc, which accounts for the crop growth stage and atmospheric demand.
The FAO 56 procedure recommends that RAW be increased if ETc exceeds 0.20 in.
d-Superscript and decreased if ETc is below this value.
The resulting RAW was computed using a daily soil water balance based on FAO 56 procedures, and shown on days when soil water contents were measured in 2009 and 2010.
Soil water depletion and RAW were different in the two seasons evaluated.
In 2009, soil water depletion generally increased throughout the season.
Soil water depletion in the 100 irrigation rate was below RAW until around silking , but then increased.
At that time, high temperatures  and winds  resulted in ETc reaching almost 0.50 in.
d.
Consequently, the adjustment to RAW using the FAO 56 procedure resulted in RAW decreasing from almost 4.0 to 2.5 inches.
Since soil water depletion was greater than RAW, the crop would have experienced water stress that likely reduced yield, especially since the water stress occurred during anthesis.
Later in July, the unusually high atmospheric demand abated, and soil water depletion fell below RAW in all irrigation methods except LEPA.
As expected, soil water depletion in the 75  and 150  irrigation rates were even greater compared with 100.
In 2010, soil water depletion in the 100 irrigation rate was well below RAW throughout the season except for LEPA.
In contrast to 2009, RAW increased to over 5.0 inches around anthesis  in 2010 due to low atmospheric demand from relatively cool and wet conditions.
Soil water depletion at 100 in 2010  generally varied about the 1.0-inch level until irrigations were terminated.
This reflected the intended full irrigation treatment, which unfortunately was not achieved in 2009 due to irrigation system operational problems followed by high atmospheric demand coinciding with anthesis.
Total rainfall plus irrigation for the 100 rate in 2009 and 2010 was 29.7 and 31.5 inches, respectively.
The LEPA grain yield and water use efficiency depressions relative to the other methods may have resulted from runoff from the hand sample areas in the l75 and 100 rates, which were sometimes indicated by increases in LEPA soil water depletion.
In 2010, the LEPA soil water contents declined below the other methods from July 14 to the end of the season ; as noted previously, LEPA grain yields were also significantly less than the other methods
 at l75 and 100.
Greater furrow dike erosion was observed for the LEPA bubblers  compared with the drag socks.
In 2009, initial soil water content for the 100 LEPA treatment was greater than the other methods, but this fell below the other methods  by August.
Also as noted previously, seasonal water use was significantly greater, but grain yield was significantly less than the other methods.
This may have also resulted from runoff from the hand sample and neutron access tube areas of the plots.
Drag socks were sometimes caught on plants and were pulled from the applicator as the lateral move passed through, resulting in erosion of furrow dikes.
Differences in grain yield and water use efficiency were sometimes correlated to differences in soil water content.
The SDI method resulted in the least soil water depletion compared with the other methods for the l75 rate in 2009 and the 150, 75, and 100 rates in 2010, which was not surprising since losses to evaporation should be minimized with SDI.
However, SDI resulted in significantly greater grain yield compared with the other methods only for 50 and 75 in 2009, and SDI grain yield was similar to MESA and/or LESA for 50 and 75 in 2010 and 100 in 2009 and 2010.
One anomalous result that could not be explained in terms of soil water content occurred in 2009 for the 50 rate.
Here, soil water depletion was the least for LEPA during most of the season, but soil water depletion for SDI was similar to or greater than MESA and LESA.
However, only SDI had appreciable grain yield.
Also, at the l25 rate in 2010 , there were no significant differences in grain yield or water use efficiency among irrigation methods, and SDI resulted in numerically the least grain yield and water use efficiency compared with the other methods as kernel mass was significantly the least.
The only apparent differences in soil water depletion for the l25 rate were observed for MESA, which was around 0.75 inches greater than the other methods by the end of the season.
This was in sharp contrast to other crops, where SDI consistently resulted in greater yield and water use efficiency compared with other methods at the 25 rate, as described next.
Corn response to different irrigation methods was vastly different from the responses of grain sorghum, soybean, and cotton, which were evaluated in previous experiments.
To review, there were three main aspects of grain yield differences for corn, including 1) yield being much lower than expected in 2009 for deficit irrigation rates; 2) yield depressions for LEPA relative to the other irrigation methods; and 3) yield being much greater for SDI compared with the other methods for 50 and 75.
These differences could be explained mostly in terms of differences in soil water contents and the timing of soil water shortages.
Four seasons of cotton were also evaluated in a previous experiment.
At all irrigation rates, SDI consistently resulted in the largest lint yield compared with all other methods, and LEPA consistently outyielded MESA and LESA.
For three seasons of grain sorghum and one season of
 soybean , SDI also resulted in significantly greater yield and water use efficiency compared with all other methods, but only at the l25 and 50 rates.
Also at these rates, grain sorghum and soybean responses were nearly the same for MESA and LEPA, but numerically less for LESA.
At the l75 and 100 rates, however, grain sorghum yield was greater for MESA and LESA compared with LEPA and SDI, which appeared to be related to over irrigation in some years.
The grain sorghum, soybean, and cotton evaluations all used LEPA drag socks, and no consistent yield depressions were observed for LEPA compared with the other irrigation methods as were observed for corn.
Furthermore, the yield depressions were inconsistent with previous studies of corn irrigated with LEPA at our location.
The consistently greater lint yield response of cotton for SDI was most likely related to reductions in evaporative cooling of the soil surface compared with the spray methods, as indicated by near-surface soil temperature measurements.
The greater grain yield for sorghum and soybean with SDI compared with the other methods at low  irrigation rates was more likely related to reductions in evaporative losses, as SDI resulted in greater soil water content that could be partitioned to plant transpiration, and these crops are not as thermally-sensitive as cotton.
Finally, although SDI did not result in consistently better corn water productivity compared with the other irrigation methods, it should be noted that small plot studies have limitations in that they cannot represent every situation inherent in large-scale operations.
For example, there is anecdotal evidence from producers, extension personnel, and crop consultants that SDI results in field environments less favorable to weeds, pests, and other diseases, which may greatly reduce the costs of herbicides, pesticides, and other inputs, which are significant, especially in light of increasingly stringent environmental regulations.
Therefore, although crop water productivity is a key criterion in selecting the most profitable irrigation method, numerous other factors apply.
In addition, the results of this study were based on only two seasons using a single corn variety, and the first season clearly represented a worst-case scenario in terms of the sequence of irrigation, crop development, and weather events.
As new seed varieties are introduced that are more drought tolerant and disease resistant, it is plausible that they will have different responses in terms of crop water productivity, which will warrant continued field studies in irrigation system comparison.
Corn grain yield and water use efficiency were not significantly different among mid-elevation spray application , low elevation spray application , and subsurface drip irrigation  for the full irrigation rate in 2009 and all irrigation rates  in 2010.
The SDI method sometimes resulted in greater soil water content compared with MESA or LESA, but this did not always translate to differences in grain yield, apparently because in some cases the soil water
 contents were sufficient to avoid water stress.
The SDI method resulted in significantly greater grain yield and water use efficiency compared with all other irrigation methods only for the 50 and 75 rates in 2009; however, the 2009 season was not representative of typical conditions because several events resulted in soil water shortages during anthesis, and crop yields were much lower than expected.
The low energy precision application  method resulted in reduced yield, soil water contents, and water use efficiency compared with the other methods at the l75 and 100 rates, which appeared to result from furrow dike erosion and runoff from the hand sample and soil water measurement areas of the plots.
Corn response to the different irrigation methods was very different from other crops evaluated in previous experiments, which included grain sorghum, soybean, and cotton.
In particular, cotton lint yield and water use efficiency were significantly greater for all irrigation rates for SDI compared with all other methods, and LEPA also resulted in consistently better response compared with MESA or LESA.
This research was supported by the USDA-ARS Ogallala Aquifer Program, a consortium between USDA-Agricultural Research Service, Kansas State University, Texas AgriLife Research, Texas AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
We thank Mr.
M.
D.
McRoberts, Mr.
B.
Ruthhardt, Mr.
E.
Hutcherson, and the numerous student workers for their meticulous and dedicated efforts in executing experiments and obtaining and processing data.
Pockets of southwestern Nebraska and the Panhandle saw minor groundwater level declines, but the latest Groundwater-Level Monitoring Report shows a wealth of increases in groundwater supply across the rest of the state from spring 2018 to spring 2019.
On average, wells measured in spring 2019 saw a 2.63-foot increase in groundwater levels statewide.
Early installation helps to minimize root and leaf damage and makes it easy to get around the field with the pickup or ATV to install the equipment.
Water deliveries by the four major irrigation districts  are expected to be near normal.
The districts hope to deliver water to growers through the first week in September.
Water Resources of Beaver Lake
 Trish Ouei County Extension Agent Stormwater Educator Benton County
 Mike Daniels Professor and Extension Water Quality and Nutrient Management Specialist
 Beaver Lake is a manmade reservoir located in Northwest Arkansas.
The lake has more than 487 miles of shoreline, and its surface covers 31,710 acres.
Beaver Lake is the first  in a series of three U.S.
Army Corps of Engineers reservoirs on the White River in Arkansas and Missouri.
The Beaver Lake/White River headwaters originate in the Boston Mountains southsoutheast of Fayetteville near the community of Boston and flow northnortheast into Beaver Lake before discharge from Beaver Dam into the backwaters of Table Rock Lake near Eureka Springs, Arkansas.
The lake
 Arkansas Is Our Campus
 Used with permission of Beaver Water District
 itself lies within Benton, Washington and Carroll counties.
The full Beaver Lake watershed extends into three more counties, with the largest portion in Madison County and extends into small portions of Franklin and Crawford counties as well.
The watershed encompasses 766,026 acres almost 1,200 square miles.
As one of the fastest economic and population growth regions in the state and nation, Beaver Lake is crucial to meeting Northwest Arkansas's increasing demands for abundant high-quality water.
In May 1927, over 14 percent of Arkansas was under water due to flooding.
In 1928, Congress delegated the U.S.
Army Corps of Engineers to develop a plan to control the Mississippi River.
The Corps began a study of the White River basin the next year.
The Flood Control Act of 1938 authorized construction of dams in the White River basin at the discretion of the Corps for flood control.
In 1954, the proposed Beaver Dam, then located at Beaver, Arkansas , was authorized; however, it very quickly looked like Beaver Dam would not become a reality because the benefits versus costs were not favorable.
Looking ahead, Northwest Arkansas residents saw a need to establish a long-term, dependable drinking water supply for the region.
The Beaver Dam Association requested that Congress add municipal and industrial water supply to the authorized purposes of Corps reservoirs.
Congress passed the Water Supply Act of 1957 that would allow these uses for the lake to be determined in uses versus costs ratio.
With the benefit-to-cost ratio now favorable, Beaver Dam was to be built.
Because geologic conditions at Beaver, Arkansas, were not favorable for construction, the dam site was moved about 6 miles upstream near the town of Busch, Arkansas, but the name Beaver was retained.
Construction of Beaver Dam began in 1959 and was completed in May 1965.
At a cost of $60 million, the dam project included a powerhouse with two 56-MKW hydroelectric power generators.
More than 1.7 million cubic yards of earth were moved, and 780 thousand cubic yards of concrete were poured.
The multipurpose project provides flood control, hydroelectric generation, drinking water supply  along with recreation to Northwest Arkansas.
After adding water supply to the purposes for the dam, the water suppliers helped contribute funds to construct the dam.
The drinking water suppliers continue to contribute yearly along with the U.S.
Army Corps of Engineers and Southwestern Power Administration to the annual maintenance and operation of the dam.
The primary reason for constructing Beaver Dam was to provide flood control.
The U.S.
Army Corps of Engineers is completely responsible for flood control of the reservoir.
The conservation pool, which is the normal or target level, is between 1,077 and 1,121.43 feet above sea level.
Typically, excess rainfall and runoff are captured in the flood pool to prevent flooding downstream.
The lake may rise into the flood pool, which is 1,120.43 to 1,130 feet.
Water in the flood pool is then released over time through hydroelectric power generation, opening the flood gates or through the emergency spillway to return.
This returns the lake level to the top of the conservation pool.
The release of waters from the flood pool of Beaver Lake is dependent upon the ability of downstream reservoirs to receive the water.
By law, the electricity generated at Beaver Lake is sold to rural electric cooperatives, municipal utilities and military installations.
Southwestern Power Administration , a Department of Energy agency, markets power to approximately 100 power utilities in Arkansas, Kansas, Missouri, Oklahoma, Texas and Louisiana.
Nearly 7 million people and businesses receive power from these utilities.
Two generating units each produced 56,000 kilowatts of power in 2015.
The actual generation at Beaver Dam was over 185,264 megawatt-hours, bringing in roughly $9.14 million to the U.S.
Treasury.
Hydroelectric power is very economical and environmentally sound.
According to SWPA, the energy marketed by the entire Southwestern Power Administration in an average year saves the American people the equivalent of 9.5 million barrels of oil, 2.9 million tons of coal or 47.5 billion cubic feet of natural gas.
This cost-based energy also prevents
 Beaver Lake is the primary source of fresh water for most of Northwest Arkansas.
The Beaver Water District, the Carroll-Boone Regional Water District, the Madison County Regional Water District and the Benton/Washington Regional Public Water Authority all use Beaver Lake as their source of water.
Beaver Lake now provides water to one of every seven Arkansans.
Beaver Water District is the largest of the four water suppliers.
With a current maximum production capacity of cleaning 140 million gallons of water per day , Beaver Water District also has a longterm plan of 220 MGD.
The district is a wholesale provider of drinking water selling to four customer cities Fayetteville, Springdale, Rogers and Bentonville that in turn provide water to more than 320,000 people.
Since the 1990s, the demand on Beaver Lake as a public water supply source has increased dramatically.
The long-term planning of Beaver Water District will continue to benefit the expected population growth of the area.
The lake hosts a variety of recreational activities, such as boating, fishing, camping, waterskiing and picnicking, and is vital to the tourism industry of Northwest Arkansas.
It is important to note that while recreation is allowed on the lake, it was not one of the recognized cost benefits that allowed construction of the dam.
Each year thousands of people take to the shores and waters of the lake to pursue the many species of fish that thrive in it, including bream, crappie, largemouth bass, catfish, white bass and the king of the lake, the striped bass.
The lake is also a key draw in the area for other water sports.
In 2015 alone, more than 2 million people used Beaver Lake for recreation.
Thousands of pleasure boaters, water skiers and personal watercraft owners took advantage of the lake.
There are also 11 Army Corps of Engineers parks along the lake's shores for people to enjoy.
With 673 overnight campsites available, visitors will find everything from tents to motor-home sites around the lake.
Many parks also have day-use facilities.
In addition, seven commercial marinas operate along the lake providing fuel and supplies.
Recreation makes a significant contribution to the area's economy.
In 2015 camping and day-use fees generated more than $1 million in revenue.
It is estimated that the economic benefits of Beaver Lake include over $30 million in visitor spending within 30 miles of the lake.
A MULTIPURPOSE RESERVOIR ON THE WHITE RIVER CONSTRUCTED AND MANAGED BY THE U.S.
ARMY CORPS OF ENGINEERS 
 Used with permission of Beaver Water District
 Protecting Beaver Lake for Future Generations
 In our society, water quality must be considered from many different points of view.
For example, water that may be fine for swimming may not be desirable for showering, or water that can be consumed by livestock may not be safe for humans to drink.
Beaver Lake provides fresh water to meet many different needs.
The water quality in Beaver Lake is good; however, there are always yearly fluctuations in the quality of the lake's waters.
Heavy rains will cause large amounts of soil to increase turbidity  of the lake.
Individual swimming areas have been temporarily closed on occasion due to excessive bacteria levels usually caused by polluted runoff and animal waste.
Nutrients like fertilizers and manure also promote increased algae growth, which in turn causes taste and odor issues to the public drinking water supply.
There are two types of water pollution point source and nonpoint source.
Point source pollution can be attributed to a specific source such as a factory or wastewater treatment plant.
Point sources of pollution are typically under governmental control or regulation.
Nonpoint source pollution cannot be attributed to any one specific, identifiable source, and the most significant reduction in this type of pollution is by responsible stewardship of individuals.
Nonpoint source pollution is caused by contaminants that are spread across the landscape and delivered to water bodies through runoff from storm events.
Polluted runoff can come from many different land surfaces including agriculture or farming operations, soil erosion/runoff from construction sites, poorly maintained septic systems, improper use of fertilizers and pesticides on lawns, oiland chemical-laced
 impervious surfaces like highways and parking lots and uncollected pet or animal waste along trails, homes and farms just to name a few.
Beaver watershed land use is dominated by forest and agricultural lands, especially in the north and east parts of the watershed.
However, as the population of the area has grown, the watershed has undergone rapid changes in land use, beginning with the conversion of forested land to pastures and agricultural land to urban areas.
This is most apparent in the southwest area and along the western edge of the watershed boundaries, and it is forecasted to continue.
It is estimated that low density residential development will cover 18 percent of the watershed by 2055.
That development will come at the loss of forest and pasture lands.
Without proper educational efforts, planning and development, these changes could result in potential contamination of our streams and lake.
Primary sources of contamination include agricultural runoff, unpaved roads, urban stormwater runoff, septic systems and waste water treatment, streambank erosion and land clearing operation needs for new construction.
As the population increases, the potential for pollution increases as well.
Activities within the watershed impact the quality of the lake.
This must be considered as the population within the watershed grows and the use of the reservoir increases.
We must monitor the water quality of streams and lakes to ensure that alterations in land use and development do not adversely impact this precious resource and impair any of the intended uses.
The waters of Beaver Lake must be protected and preserved if we are going to maintain the quality of life that exists today.
In 2012 the U.S.
Environmental Protection Agency agreed to the watershed protection strategy put forth by the Beaver Watershed
 Alliance for the Beaver Lake watershed.
If this is to be accomplished, everyone including farmers, landowners, industry leaders, volunteer organizations and government officials, will need to work together.
The University of Arkansas System Division of Agriculture Coopertive Extension Service partners with many organizations  to promote good stewardship practices to help protect the lake and promote research on the water quality of this essential resource.
With nonpoint sources of pollution being the largest threat to the Beaver Lake watershed, the actions of individuals can make a difference.
To better protect our area's water supply, please consider the following options for pollution prevention and runoff control.
1 Be water wise conserve!
Eliminate habits that waste water and create runoff.
Install drip irrigation to water outdoor plants in the morning or evening only.
Use rain barrels.
Plant drought tolerant native plants when possible.
Educate yourself on ways water can be conserved around the house.
Properly design, install and maintain your septic system.
Septic systems should be pumped every three to five years as solids accumulate.
Improperly maintained systems can cause ground and surface water contamination.
3 Properly maintain your automobiles, boats and other equipment.
If you change your own oil, take used oil to a recycling center.
If your car or truck leaks oil or antifreeze, you should fix the problem.
Fluids from leaking automobiles are washed from pavement or concrete when it rains.
Leaking gas or oil from boats can pollute lake waters.
Soil test lawns, gardens and pastures.
Applying excessive amounts of fertilizers or animal manures can lead to nutrient runoff into area streams and lakes.
Soil test results provide a complete soil nutrient profile with recommendations for fertilizer applications.
Following soil test guidelines will save you money while maximizing lawn, garden, and pasture growth and prevent runoff of fertilizer into streams, rivers and lakes.
5 Dispose of household hazardous wastes properly.
Many household hazardous waste collection sites are located in Northwest Arkansas.
Very small amounts of some chemicals can pollute large amounts of waters and even kill fish.
6 Recycle.
Recycling can significantly reduce the load placed on area landfills, which in turn can decrease the potential for water pollution.
Recycling also decreases the amount of water that is required for manufacturing new products.
Limit livestock access to streams and rivers.
Livestock entering and leaving streams can weaken the banks, causing soil erosion and increasing the sediment load on lakes.
In addition, allowing livestock to wade in streams increases the risk of bacterial contamination of the water due to discharge of fecal matter.
8 Limit the amount of runoff caused by your residence.
Turn downspouts onto grassy surfaces instead of pavement.
Reduce impervious surface area by installing pavers/stepping stones.
Use mulch to cover bare soils.
Consider installing a rain garden to capture runoff and recharge the groundwater supplies.
9 Take a stand.
Don't wait until area streams or rivers turn green with algae or become contaminated with toxic chemicals.
Don't wait for other people to take up the cause of protecting your water.
Get involved and encourage others to get involved in community efforts to protect our water resources.
Actively participate in educational programs that will improve your knowledge about water quality.
As population grows, potential for contamination of an area's water supply also grows.
The old saying, "An ounce of prevention is worth a pound of cure," is especially true when it comes to protecting our water resources, which include Beaver Lake.
As water quality in the lake decreases, the costs associated with making it fit for drinking increase.
It makes good sense to do everything we can to protect our water resources and not wait until a problem exists before doing something about it.
Beaver Lake has met the water needs of Northwest Arkansas for over 50 years.
Residents of Northwest Arkansas need to act now if the lake is to continue to serve future generations.
Special thanks to Robert Morgan, Ph.D., P.E., Manager of Environmental Quality at Beaver Water District, for his contributions.
Printed by University of Arkansas Cooperative Extension Service Printing Services.
TRISH OUEI, county Extension agent stormwater educator at Bentonville in Benton County, and DR.
MIKE DANIELS, professor and Extension water quality and nutrient management specialist in Little Rock, are employees of the University of Arkansas System Division of Agriculture.
This is where tools such as an ETgage and soil water sensors come into play.
An ETgage will give you potential crop water use and the soil water sensors will give you an idea of how much water is stored in the soil profile.
Then you will be able to determine how much water the crop will need in either irrigation or precipitation to finish out the year.
For more information on this topic, see NebGuide G1871, Predicting the Last Irrigation of the Season.
The analysis found that all the fields in 2017, 18 and 19 were irrigated to a level preventing water stress all season, however 15% to 20% of the fields may have been underwatered late into the season just a little bit  late in the season in the dry years of 2020, 21 and 22.
Does Wetter Water Make Fatter Wallets?
Using Soil Wetting Agents
 R.
Troy Peters, Tamara Mobbs, and Joan Davenport
 Various soil wetting agents are marketed to improve water penetration and distribution uniformity, moisture retention, water use efficiency, and drainage.
Commonly referred to as surfactants, their manufacturers claim these products make water "wetter." The question is, are they worth the money?
The answer, as usual, is "it depends."
 Water Repellency at the Molecular Level
 The polar nature of water makes it want to stick together.
Since a water molecule would rather be in with other water molecules, it exhibits an apparent repulsion of anything that is non-polar at the water surface interface, including air.
This repulsion is referred to as surface tension.
Most soil particles have negatively charged surfaces that attract the positively charged end of water molecules  and cause water to stick to it.
This makes most soils hydrophilic or "having an affinity for water." The combination of this attraction and surface tension creates capillary forces that draw water up into the cracks and spaces between soil particles and therefore enables soil to hold water in reserve for plant use.
Soil particles that have non-polar coatings become hydrophobic, or water repellent.
Most of these coatings form from organic processes and compounds within the soil.
Sandy soils , soils with high organic matter, and soils that cycle from wet to very dry are more susceptible to water repellency.
Soils that are dry and/or have high organic matter are more prevalent near the soil surface, which is therefore where the related water repellency issues exist.
Soils in fields or forests that have been burned also tend to exhibit water repellency issues.
Problems with Water-repellent Soils
 Because water doesn't stick to hydrophobic soil particles as readily as hydrophilic soil particles, water tends to bead up on hydrophobic soil surfaces instead of going into the soil.
This results in higher runoff and poor water distribution uniformity.
The water that does go into the soil tends to move in concentrated fingers of flow instead of uniform distribution throughout the soil profile.
This causes localized dry spots in some places and deep percolation in others resulting in poor irrigation efficiency and crop performance.
How Soil Wetters/Penetrants Help
 Surfactants or soil wetters/penetrants help overcome water repellency problems by adding molecules to water that have both a polar, hydrophilic  end and a non-polar, hydrophobic end; the non-polar end sticks to the water-repellent coatings on the soil and draws the water in behind it, encouraging the problem soil to become wet.
The large number of different soil surfactants available vary greatly in their molecular weight, size, shape, structure, methods used to bind soil, recommended application rates, and length of time they are effective in the soil.
Be sure to read the label carefully to compare these different products.
In order to test the efficacy of surfactants, two common southeastern Washington soils were obtained that had no known water repellency issues.
Four different surfactants were compared to a plain water control: 1 non-ionic, 2 block polymer, and 1 anionic.
Laboratory tests were performed where untreated water and the 4 surfactants were applied at the labeled rate to measure the infiltration rate , soil water-holding capacity , unsaturated hydraulic conductivity , and capillary rise.
These tests were performed with basic soil physics methods using 6 inch-diameter clear soil columns and micro infiltrometers.
Each test was replicated 4 times.
No significant differences were found in infiltration rate, water content, unsaturated hydraulic conductivity, or capillary rise rates between the surfactant treatments and plain water for the tested soils.
Although there are demonstrated benefits of using soil surfactants on water-repellent  soils, such exhibits fail to substantiate claims that surfactants or soil penetrants/wetters provide any benefit for normal, non-water-repellent soils.
The simplest way to determine the degree of a soil's water repellency is to place several droplets of water on a sample of air-dried, disturbed  soil.
If it takes longer than 5 seconds for the water droplets to penetrate the soil, the soil may have some degree of water repellency and a surfactant or soil penetrant/wetter may provide some benefits.
If the water droplets flatten out and go into the soil within 5 seconds, the soil can be considered normal, with no water repellency issues that use of a surfactant or soil penetrant/wetter would likely provide any improvement.
Other Solutions to Water Repellency
 Low infiltration rates may be due to heavy textured soils , compaction, poor tillage practices, and/or very dry soils.
Water repellency issues can also be managed to a certain degree by not allowing soils to get excessively dry , good tillage practices , and not burning fields.
An interstate compact is an agreement negotiated between states, adopted by their state legislatures, and then approved by Congress.
Once an allocation of interstate water is determined by such a means, each individual state may then issue water rights to its share of the water through its normal administrative process.
Interstate compacts have been traditionally used in making water allocations in the western states.
Irrigation Pump System Testing
 Robert Scott Frazier, PhD, PE, CEM Assistant Professor
 Carol Jones, PhD, PE Associate Professor
 Pumps are widely used in a variety of locations by rural operations.
Agricultural producers can use considerable amounts of water transported by pumping.
In some locations with heavy irrigation operations, the pumping systems can comprise the majority of the energy costs.
For this reason, these systems should be inspected and improved if possible.
The pump system curve describes the relationship between the pump flowrate  and the head pressure  for the actual pump.
The system curve describes the overall irrigation system pressure and flow needs while the performance curves for the pump describe the relationship between the head pressure and the capacity flow rate of the pump based on different impeller diameters.
Usually these curves reflect the performance at a constant and specific driver speed, rpm.
The intersection of the system curve and the pump performance curve will be the optimum operating conditions  of the pump for the system.
Best design practices prefer this intersection to be located close to the best efficiency point  of the pump performance curve.
This also is the most energy efficient point for the pumping system to operate.
Figure 1 gives an example of a system curve and pump performance curve intersecting at the operation or "best efficiency point".
It is somewhat rare to find older water pumping systems operating at optimal efficiency.
Often these systems were not designed properly and they have degraded over time.
Impellers corrode, wear and even break.
Pump systems and pipes can become clogged with dirt, sediment, and mineral buildup.
Often the impeller size is not properly matched to motor power or desired flow rate.
The end result is wasted energy and money.
By conducting a pump test, one is able to see how far from optimal  the actual pump performance is.
In gen-
 Figure 1.
Example pump performance and system curves.
eral, pumping systems that are above 60 percent in pumping efficiency  are considered to be in excellent condition.
Pumping systems that are 49 percent or below, are either designed incorrectly, in poor condition, or both, and need to be replaced or repaired.
A long term study  showed the average centrifugal well pump efficiency was 55.4 percent in Southern California.
It is anticipated that the same poor efficiency average could be found in many regions of the United States.
This indicates that many pumping systems are at or below this value, and therefore, in the poor efficiency range.
Pumps should be tested every three to five years to ensure no loss of efficiency.
"You can't improve what you can't measure" is an old but accurate statement.
The total efficiency of a fluid pumping system is a function of the flow rate which can be measured, the specific gravity of the fluid , the total "dynamic head"  and power input  which is usually the electrical power to an electrical motor.
Let's examine this relationship and how we might determine the efficiency.
The calculated efficiency will, in turn, tell us something about the status of our pumping system and what opportunities we have to save energy and money.
Begin by looking at the required horsepower  to pump water at a certain pressure  and at a certain flow rate.
This relationship is:
 HPw = TDH X GPM
 HPw is the horsepower needed to pump the water TDH is the total dynamic head measured in feet 
 GPM is the flow rate of the water in gallons per minute 
 The flow rate of the water  can be measured maybe not easily though.
In some cases, ultrasonic velocity measuring devices that clamp onto the outside of the piping are used and do not interfere with the water flow.
In other cases a measuring device is used in the water stream.
Once the fluid velocity is determined, multiply by the pipe inside cross-sectional area to get an estimate of the flow rate.
If this flow rate is what is needed and is satisfactory, move to the next task.
That is, the flow we want is right now, is it producing that flow efficiently?
Total dynamic head  is a measure of the amount of resistance to flow in the system.
This is usually measured in terms of "feet"2 Total head pressure usually comes from three things: amount of elevation change, length and shape of piping system, and end-use pressure requirements.
There are various tables and methods of determining TDH.
If pulling water from a well, the well depth is given in feet.
Charts
 and tables can be used to estimate the TDH for lengths and diameters of pipes due to friction losses in the pipes.
Turns and valves in the pipe system add "feet" to the TDH as they resist flow also.
Finally, the end uses such as nozzles, spray heads, and drip irrigation add their own pressure requirements.
Of the parameters to be measured, TDH is one of the most difficult and is often estimated to some degree instead of achieving a precise measurement.
Pressure requirements are also often over-estimated and a "just in case" over-design is often used.
This can lead to lower pump performance and high costs over time.
Once there is the power needed to pump the water  at the actual present flow rate, measure the actual electrical power  being used to currently pump the water at the GPM measured.
A comparison ratio of actual to theoretical optimum power reflects the pumping system's actual efficiency via the following relationship:
 x0.746 = KW MEASURED
 Notice that the measured power will always be greater than the theoretical power, therefore the efficiency will always be less than 1.0.
In reality it will never get close to even 0.8  because of the combined pump and motor's efficiencies in the kW measured.
Typically, the pumping system's total efficiency will be between 0.4 and 0.7.
The system efficiency will also tend to be better as the pumping system gets larger.
This is because large electric motors and pumps are generally more efficient than smaller motors and pumps.
Table 1 shows a range of pump system efficiencies for different motor horsepower.
Notice the general increase in efficiency as equipment gets bigger.
This does not imply you should purposely oversize equipment however.
To see what the energy cost implications of this are, the following calculations for one 30 HP pump will help illustrate the costs involved.
Let's say the efficiency of the example pump in question is determined to be 45 percent using the techniques mentioned above.
This could be an old pump that is seriously clogged with sediment and has wear on the impeller.
This low efficiency example is not uncommon.
What if we could rework the system to be 61 percent efficient?
If the current pump system calculated at 45 percent pumping efficiency is improved to 61 percent efficiency, and the pump is assumed to be running 85 percent of the time:
 2 In water systems, "feet" of pressure correspond directly to psi pressure.
It is an old measurement system still in wide use.
Power Savings :
 Table 1.
Typical pump system efficiencies.
Motor HP	Low	Fair	Good	Excellent
 3-7.5	44.0	44-49.9	50-54.9	>54.9
 10	<46.0	46-52.9	53-57.9	>57.9
 15	<47.1	48-53.9	54-59.9	>59.9
 20-25	<48.0	50-56.9	57-60.9	>60.9
 30-50	<52.1	52.1-58.9	59-61.9	>61.9
 60-75	<56.0	56-60.9	61-65.9	>65.9
 100	<57.3	57.3-62.9	63-66.9	>66.9
 150	<58.1	58.1-63.4	63.5-69.9	>68.9
 200	<59.1	59.1-63.8	63.9-69.4	>69.4
 250	<59.1	59.1-63.8	63.9-69.4	>69.4
 300	<66.0	60-64.0	54.1-69.9	>69.9
 Energy Savings = Power Savings X Run Time = kW X  X 0.85  savings Cost Savings:
 C = $1,404 + $5,808 = $7,212/yea = savings
 As can be seen, this is not a small amount of savings!
Multiply this by several pumping systems with similar efficiencies over several years and you get tens of thousands of dollars of opportunity cost.
Achieving a 61 percent pumping
 efficiency might require extensive rework of the current system but the cost savings over time can be attractive.
Acquiring the data needed for the pump efficiency calculations can sometimes prove difficult.
The depth of the well is needed, as well as, an accurate estimate of the system distribution head pressure.
Well openings are sometimes not accessible and so water level is often guessed.
The flow rate of the pump system can sometimes be difficult to measure for a variety of reasons.
If air or solids are in the water flow, faulty velocity measurements can result.
Possibly the biggest problem for average cost calculations is that most systems do not operate at one constant load.
Determining the average or actual load may require multiple measurements with equipment.
Without actual system data, average loads over long time periods are often over estimated.
While you may not have the equipment or means to perform the pump tests, if your operation has several large pumps running for long periods of time, it may be worth the expense to have these systems tested by a professional.
Companies that often have this service include: irrigation, well drilling and pump supply companies.
If the efficiencies are reported to be low, the companies may also be able to help you service or redesign the systems.
You might test a sample of pumps and determine if further testing is justified.
It is also doubtful that electrical utility costs will decrease in the future.
Remember, if pump system run times are long the payback time may be short and very attractive for addressing the problems.
Figure 3.
Examples of avoidance zones that could be implemented with VRI: uncropped or killed areas , surface water , and wet spots.
Depending on the geometry, zone control may be best suited to avoid application in some areas , while speed control may be an adequate solution for other situations.
tests on influence of irrigation on the productive life of French prune on myrobalan root in Yolo loam soil
 A.
H.
Hendrickson and F.
J.
Veihmeyer
 Three irrigations a year-between June and September-of 7.5 acre inches each seemed to constitute an adequate irrigation program for French prunes in Yolo loam during a 16-year test at Davis.
The investigation was conducted with French prune trees on Myrobalan root planted 24 feet apart on the square system.
The soil is classified as a Yolo loam, having a field moisture capacity of about 22%, and a permanent wilting percentage of 11%.
Differential irrigation treatment was started when the trees were 10 years old and had received uniform treatment prior to that time.
Circumference measurements of the trunks had been obtained each year, and yields were recorded as soon as the trees began to bear.
The measurements obtained during the four years preceding the test were used in the layout of the various plots.
Each plot consisted of three rows of 10 trees each.
Eight trees in the center row-guarded on both sides and both ends by trees receiving the same treatment-were used in obtaining the experimental results.
Average yields of prune trees arranged by two-year periods.
The downward trends in 1931-32 and 1935-36 were due to severe frosts.
Five treatments of either three or four replications were used.
Treatment A kept the range of readily available moisture high.
The plot was irrigated when the soil in the top three feet was reduced to about 15% except in a few cases, when other orchard operations, such as picking, did not permit applying water exactly on time.
However, the soil moisture was not allowed to fall below about 13%.
Under treatment B the plot was irrigated when the soil moisture in the top three feet reached the permanent wilting percentage.
Here again, because of harvesting operations, the trees could not always be irrigated on time and sometimes
 were subjected to dry soil conditions for periods that did not exceed about three weeks.
Treatment C-in effect-was the intermediate of the five treatments.
The plot was irrigated the same as in treatment A until about the middle of July, after which no water was applied.
This plot was therefore subjected to dry soil conditions in late summer but this dry period was not so long as those in treatments D and E.
The plot under treatment D was not irrigated during the growing season.
On a number of occasions it was necessary to irrigate plot D in early spring when the soil was not wetted to a depth of six feet by the winter rainfall.
This treatment subjected plot D to dry soil conditions beginning late in June or early in July each year.
Treatment E was similar to D, except in that it provided one irrigation, usually in September, after the crop was picked.
The plot was subjected to dry soil condi-
 Average increase in cross section areas of trunks of prune trees and average yields during four age periods.
Following the initiation of differential irrigation treatment, the yields for the 4-year period-represented by the second block in the lower row remained about stationary in the A, B and C treatments, while the D and E treatments were considerably less.
The next period-third block in the lower row-yields from A and B were about equal, and far ahead of the dry plots, D and E.
Treatment C was intermediate.
The last period indicates a downward trend in all treatments.
The trees in treatment D were removed half way through this period.
A French prune tree in an irrigated plot, left, at 11 years of age, center, the same tree in its prime at 17 years and, right, at 26 years.
tions from about the first of July to the middle or last of September.
The above soil moisture conditions were attained by the following number of irrigations of about 7.5 acre inches at each application: A, four or five; B, three; C, two; D, none and E, one, after harvest.
In the first four-year period under differential irrigation plots receiving treatments A, B, and C, produced about as much fruit as they did during the fiveyear period before the treatments were started-when the average yield was 133 pounds of fresh fruit per tree.
The dry plots, D and E, which were not irrigated while the crop was on the trees, dropped considerably below the irrigated ones in yield.
The lack of readily
 available soil moisture during the growing season was shown immediately after differential treatment started by a reduction in crop in treatments D and E.
During this period all treated trees continued fairly vigorous growth as indicated by the average increase in crosssection areas.
Trees under treatment A made the largest increase, averaging about 27 square centimeters gain.
Treatment B trees were second with approximately 22 square centimeters.
Trees receiving treatments C, D, and E increased, on the average, about 18 square centimeters.
The amount of new growth was associated with the soil moisture conditions during the growing season.
The trees with treatment A, which kept the soil moisture above the permanent wilting percentage, made the largest growth.
In the plot under treatment B
 where the soil moisture was allowed to reach the permanent wilting percentage before the supply was replenished but on several occasions-particularly during harvest when it was not practical to irrigate-dry soil conditions prevailed for short periods.
The plot with treatment C, while irrigated twice a season, reached the permanent wilting percentage early enough in the season to affect the growth of the trees.
Plots D and E were without readily available soil moisture usually after the first week in July.
In general this period was characterized by medium sized crops and continued growth of the trees.
During the next 10-year period, the trees were in their prime.
Following the vigorous growth up to that time, the trees yielded heavily.
Treatments A and B were essentially equal in production, and far Continued on next page
 A French prune tree in an unirrigated plot, left, at 10 years of age, center, the same tree at 17 years and, right, at 26 years of age, just before its removal from the orchard.
Continued from page 9
 from 1.4 to 4.6 per box, while administrative and office costs range from 3.5 to 5.9c per box.
Fixed costs for land, buildings, and equipment range from 7.8c to 14.4c per box even under the assumptions of current replacement values and of a uniform length of season.
As the tables suggest even the best op-
 erated houses can improve efficiency in some operations and, conversely, houses with relatively high total costs usually are fairly efficient in some practices.
Plant volume is an important factor, and is one of the aspects of efficiency covered by the current studies.
Each plant consists of many small operations and improving efficiency requires change and adjustments in these small operations.
A reduction in shipping point costs will result, not from a single sweeping
 adjustment, but from a step-by-step approach and the combination of these steps into well-integrated totals.
Following reports in this series will compare house operations, methods, equipment, and arrangements.
The comparisons may be used to establish standards for efficient operation.
With minor modifications, the results of these studies can be applied to many of the problems of packing and processing other fruits and vegetables.
R.
G.
Bressler is Professor of Agricultural Economics, University of California College of Agriculture, Berkeley.
Selected Costs of Handling Cannery Fruit in 11 California Pear Packing Plants, 1950
 Cost per ton of cannery fruit-dollars
 hour b	and dump	Receive	Grade	truck and	Package,	load	and miscel-	Supervision	laneous	Subtotal	operating	General	and admin-	istration	Office	costs	Fixed	Grand	total
 L	1.9	1.42	1.99	3.60	0.91	7.92	1.93	2.44	2.49	14.78
 M	5.4	0.94	0.76	2.49	0.43	4.62	0.46	1.54	1.93	8.55
 N	2.0	1.29	1.38	2.09	0.45	5.21	1.36	1.89	2.88	11.34
 P	2.1	0.78	1.52	1.25	0.54	4.09	1.70	1.47	4.08	11.34
 R	9.9	0.90	1.02	1.30	0.79	4.01	0.60	2.04	2.09	8.74
 S	7.3	0.81	1.25	2.55	0.55	5.16	1.29	1.82	1.55	9.82
 T	13.9	0.90	0.52	1.26	0.70	3.38	1.28	1.82	1.61	8.09
 U	3.9	0.85	1.05	1.05	0.43	3.38	1.18	1.80	2.36	8.72
 V	10.7	0.45	0.89	1.10	0.30	2.74	1.02	1.56	2.18	7.50
 W	12.0	0.68	0.93	1.41	0.76	3.78	1.22	1.99	2.24	9.23
 Computed on the basis of 8-hour days with typical hourly rates of output.
As such, these cost estimates will differ from average costs for a season.
Typical hourly rotes of output, in tons of connery fruit.
Adjusted to reflect uniform wage rates typical for the industry.
Includes general supplies, fuel, power, light, and miscelloneous costs.
Based on thirty 8-hour days of operation per season, current replacement values for building and equipment, and uniform methods of allocating plant and equipment costs between fresh and cannery fruit.
Continued from preceding page
 ahead of the dry plots, D and E.
Treatment C was intermediate.
During this period-while the trees were 15 to 24 years old-the average yields were remarkably consistent, within each of the five treatments, when analysed in consecutive two-year periods.
Plot A averaged 357 pounds; B, 350 pounds; C, 295 pounds; D, 230 pounds, and E, 240 pounds.
The plots, A, B, and C, retained the averages through the entire 10 years, but D and E showed a tendency to decline in yields after the eighth year.
On the whole this period was characterized by maximum yields for the various treatments and relatively small increases in cross section areas.
In the last period while the trees were in their 25th to the 28th years, yields on all plots were materially reduced.
Treatments A and B still yielded best with an average of 262 and 238 pounds respec-
 tively; C was third with 193 pounds; D dropped to 66 pounds; and E produced 141 pounds.
Because of low yields and the death of trees, treatment D was discontinued after the first two years of the final period, and the trees were removed.
Thus, after 16 years of no irrigation during the growing season, this part of the experiment ended.
From a commercial standpoint, the trees had probably ceased to be profitable several years before their removal.
In growth, treatments A and B averaged slightly less than in the previous period, while treatments C, D, and E were about the same.
During the period of the first four years of differential treatment the irrigated plots showed marked increases in growth, but not in yields.
The differences in growth and yields, between the irrigated and unirrigated treatments, or those without readily available water for considerable periods, were due to the slower growth and smaller yields of the
 dry plots.
Increased yields from the irrigated plots followed, after the trees had attained large size.
The trees in all treatments seemed to be in their prime-during the 10-year period from 15 to 24 years old-although there was a tendency for the yields from the treatments to decrease a few years before the end of this period.
In this period the trees in treatments A and B seemed to reach a maximum average production-when averaged at two-year intervals to reduce the great variability due to alternate bearing-of 357 and 350 pounds per year respectively.
When studied in the same way, the average maximum yield for treatment C was 295 pounds.
Treatments D and E reached considerably lower average maximums.
A.
H.
Hendrickson is Lecturer in Pomology, University of California College of Agriculture, Davis.
F.
J.
Veihmeyer is Professor of Irrigation, University of California College of Agriculture, Davis.
The above progress report is based on Research Project No.
633 C.
Chapter 6: Corn Seed Testing
 Optimizing corn profitability starts with purchasing high-quality hybrid seed.
Seed-testing information is critical in making this decision.
This chapter discusses the standard tests that are required on seed offered for sale, and the additional tests that might provide insights into the seed quality.
Key components are provided in Table 6.1 and an image of germinated seeds are in figure 6.1.
Table 6.1 Key components in producing and testing seed quality:
 1.
Inspect the label to make sure it meets your goals.
2.
Adjust the seeding rate based on information contained in the label.
3.
Different tests provide different information about your seed.
4.
Carryover seed not planted last year most likely will have lower seed quality than new seeds.
Seed tests can be conducted at the SDSU Seed Testing Lab.
Seed sample envelopes may be obtained from Extension Service offices or by contacting the SDSU Seed Testing Lab.
Samples being submitted to SDSU should be sent to:
 SDSU Seed Testing Lab Box 2207-A Brookings, SD 57007 
 Figure 6.1 Corn seedlings evaluated after 7 days in a germination test.
The two on the left are considered "normal seedlings," capable of producing a productive plant in the field, whereas the three on the right are "abnormal seedlings" and are not capable of producing a productive plant.
Samples can also be submitted to other laboratories.
Information about these laboratories is available at the Association of Official Seed Analysts or the Society of Commercial Seed Technologists.
In South Dakota, it is required that all purchased seed must be tested for purity, noxious weeds seeds, and seed germination.
The Association of Official Seed Analysts Rules for Testing Seeds  defines the protocols for these tests.
Seed tests provide information needed to determine seeding rates.
For example, a seed lot with 80% labeled germination rate requires more seed per acre than a seed lot with a 90% germination rate.
Not having a current seed label or seed-testing information puts producers and their investment at risk.
Germination rates are valid in South Dakota only for 9 months from the time of testing, and company carryover seed requires a new germination test.
Selected tests, purposes, analysis times, and advantages/ disadvantages are provided in Table 6.2.
Additional Seed Tests that Provide Useful Information Herbicide/insect Tolerance/resistance Trait Test
 Most commercial corn varieties on the market today are tolerant to at least one of the commonly used herbicides  and have at least one form of BT  insect resistance.
Seed bioassay, lateral flow strips, enzyme-linked immunosorbent assay  tests, and polymerase chain reaction  tests can assess herbicide/insect trait resistance.
This test exposes corn seed to a green chemical stain that is subsequently rinsed off.
Damage to the pericarp is readily apparent as any cracks or breaks will stain green.
Damage will be classified as light, medium, and severe.
The test is very useful in seed-conditioning facilities to maximize output while minimizing damage to the seed from machinery.
Hybrid corn seed is always tested after production to check the hybridity, self's, and outcross levels.
Each company has developed a quality specification for acceptable levels of hybridity that must be achieved to market the seed.
These quality specifications must meet or exceed the minimum requirements of the Federal Seed Act.
Electrophoresis or PCR testing methods are commonly used for evaluating hybridity level.
Corn seed is produced  and conditioned primarily by seed companies with the proper seed handling and cleaning equipment.
Farmer producers who produce, dry, and process their own corn seed are extremely rare.
Fertility and Moisture Content
 High quality corn seed production begins in the field.
Soil fertility plays a crucial role in ensuring the proper nutrients are present for quality seed/grain production.
Nutrient deficiencies can result in small seeds with low emergence rates.
The seed moisture content at harvest may influence seed quality.
Corn seed will be harvested anywhere from 25% to almost 40% moisture content and carefully dried down to 12-13% moisture to minimize seed deterioration.
Seed vigor and viability can be decreased by mechanical damage during the harvest and post-harvest seed-handling processes.
Table 6.2 The time and purpose of the different seed tests.
Test	Purpose of the test	complete analysis
 This is not a required test but is crucial in determining seeding
 rates.
Seed counts in corn will vary by genetics and kernel size
 .
Corn seed when
 sold in "bushel" bags is sold in units of 80,000 seeds.
The percentage of seeds that can be expected to grow and
 produce plants.
Laboratory germination tests are conducted
 Corn germination test	under favorable conditions, which do not always occur in the	6-7 days
 This test provides information about the physical makeup of
 Purity analysis	the seed lot.
1-3 days
 It is prohibited to sell corn if the seed lot contains prohibited
 Noxious weed exams	noxious weed seeds.
1 -3 days
 This is a rapid  chemical viability test that can
 Tetrazolium  test	be used to estimate germination.
It can also be used to assess	1-2 days
 vigor and mechanical damage.
Not all viable seeds are capable of completing their life
 cycle, and a vigor test provides information on this issue.
Vigor test	Although not required by law, this test provides important
 Below are a several	information for seed-corn marketing decisions.
A vigor test
 vigor tests available for	is recommended for carryover seed.
Not all vigor tests are
 hybrid seed corn	equivalent.
When selecting a test to use, consult with your
 seed adviser, agronomist or the seed lab staff on what works
 best for your needs.
This test is conducted under high humidity and temperature,
 and it provides an excellent indicator of corn seed vigor.
This
 test simulates less than optimum field conditions and it should
 aging test 	be conducted in conjunction with a standard germination test.
10 days
 The AA test results should be within 15% of the germination
 test results.
For example, if your germination is 90%, the
 acceptable AA would be > 75%.
This rapid test is conducted using cold temperatures.
Even
 though the cold test is not as consistent and reliable as the
 accelerated aging  test, it is more useful than the AA
 Corn cold test	test.
The cold test is considered a direct vigor test and results	12-14 days
 are correlated to field emergence under less than optimal
 conditions.
For acceptable quality, the cold test results should
 This test is conducted using saturated conditions and cold
 Saturated cold test	temperatures.
The test is used to assess how well the seed will	10-15 days
 do under constant saturated soil conditions.
There are many companies that produce and sell corn hybrids.
There is also a growing market for nonGMO corn and/or organic corn seed, and a small market for open-pollinated corn.
Check with your local agronomist for a variety with the appropriate maturity and traits for your region.
Almost all the corn seed sold is protected under the Plant Variety Protection Act  and/or has a utility/plant patent , which means that seed cannot be saved after harvest for replanting or sold by the farmer except as grain.
These protections virtually eliminate the legal ability of farmers to plant seeds harvested on their farm.
Conventional open-pollinated varieties are one exception that can be saved and replanted.
However, over 90% of the seed currently sold and planted in South Dakota is GMO seed with some herbicide/insect resistant trait.
Seed quality is crucial and it is recommended that you purchase seed from reputable dealers.
Often a producer purchases more seed than he/she plants, or the weather causes a change in planting plans that results in some unplanted seed.
Most corn seed sold has been treated with a fungicide/insecticide and, therefore, cannot be sold as grain.
Due to the lifespan of corn, any unused seed should be kept in a cool, dry environment, if not returned to the source of purchase.
One to three months prior to planting, a vigor test, at minimum, should be conducted.
If the vigor has dropped, the seeding rate should be increased.
If the seed vigor is too low, the seed must be disposed of using appropriate disposal methods.
Substandard seed may be donated or planted to food plots for wildlife.
Planting low-quality seed can result in stand failures, while overplanting or underplanting rates can also cause lower yields.
In addition, low-quality seed deteriorates rapidly and may produce poor stands.
Corn seed has a longer lifespan  than soybeans  and can usually be carried over for a year without a significant loss of germination or vigor if stored in a dry, cool location.
Irrigation in the Central Plains began in the 1930's and 1940's when farmers began drilling wells.
The 1960's saw rapid irrigation development, as the center pivots became a proven technology.
The growth has been quite slow since the 1980's when the drilling of wells has been controlled.
There is a continual increase in drawdown of the water table in many areas of the Central Plains.
McGuire, 2004 published a Fact Sheet presenting the water-level changes in the High Plains Aquifer.
Two periods were highlighted, predevelopment to 2003 and 2002 to 2003.
McGuire reported that in 1949 there was 2.1 million irrigated acres compared to 13.7 million acres in 1980.
The irrigated area peaked at 13.9 million acres in 1997 and reduced to 12.7 million acres in 2002.
Ground water withdrawals increased from 4 to 19 million acre-feet from 1949 to 1974.
The withdrawals exceed the recharge and the pumping lifts are continuing to increase.
The objective of this paper is to discuss the effect the continuing decrease on water levels have on center pivot irrigation systems.
Area weighted average water level changes are -1.0, -1.7, and -1.3 feet in the states of Colorado, Kansas and Nebraska.
The 2002-2003 water level changes varied from a rise of 9 feet to a decline of 14 feet.
There were significant areas that had ground water declines in excess of 5 feet in a one-year period.
Southwest Kansas had areas of greater than 50 feet decline in water levels from the predevelopment to 2003.
Obviously, much of this occurred in the later years with the increased irrigation development.
Pumping of air is a major problem that is readily observed.
It is the gradual decline in the water table and the decrease in irrigation uniformity that is not as easily observed.
ANALYSIS OF INCREASED PUMPING DEPTHS
 The analysis of center pivot performance is made using a computer simulation program.
Presentations of the use of CPED were given at the previous two Central Plains Irrigation Conferences.
The program simulates the application
 depths for the center pivot irrigation system.
The input to the program includes the pump characteristics, the sprinkler package and lateral dimensions.
The pumping level or total dynamic lift  is input to the program.
The program solves the hydraulics of the center pivot system and pumping plant to determine the total discharge and pressure on the center pivot system.
The problem of pumping air cannot be analyzed with the simulation analysis.
It is assumed that the pump has sufficient net positive suction head to prevent air entrainment as it is lifted from the ground water and pressurized for the center pivot.
The increase in TDL is assumed to be at least 10 feet and that it could easily approach 50 feet over just a few years, much less than the life of a center pivot system.
CENTER PIVOT AND PUMP SYSTEMS
 Four center pivot systems are used to illustrate the characteristics of various pump and sprinkler packages.
Table 1 summarizes the variables of each of the systems simulated.
Assuming a change in the number of pump stages are used to illustrate their effect on the adequacy of an existing system All the systems with pressure regulators had big guns with booster pumps at the end of the lateral.
Changes in the pressure and operating point on the pump curve with changes in TDL are a function of the unregulated sprinkler head until the pressure was below the regulator pressure.
The analysis assumes that the sprinkler packages provide uniform irrigations when adequate pressure is maintained.
The data are from systems installed in the Great Plains.
Table 1.
A brief description of the systems used for illustrating the effect of changes in the total dynamic lift.
System	H	P	B	K
 Towers	7	7	8	14
 Length, ft.
1287	1260	1491	2584
 Sprinkler type	Iwob	Impact	Rotator	Spray
 No.
of Sprinkler	123	42	170	206
 Sprinkler spacing, ft	18/9	30	9	18/9
 Pressure Regulator	Yes	No	Yes	Yes
 Pump stages, no.
3/2	7/3/2	1/2	4/3
 Topography, differential ft.
20	0	0	3
 TDL, ft	90190	90-350	20-150	78-128
 The first system simulated is a low pressure system with inverted wobbler1 nozzles.
Pressure regulators are installed on all application devices except for
 the big gun on the end of the system.
There is 20 feet of elevation change along the 1300 foot lateral.
The system was installed with a three stage pump that can accommodate a 100 foot increase in TDL and still maintain sufficient pressure.
This example demonstrates an over-design where one stage could be removed and still meets the demands with the existing sprinkler package.
Figure 1 illustrates the elevation and pressure head distribution at each of the towers.
The minimum elevation and pressure head requirements at the end of the system is approximately 213 feet which is at least 10 feet less than provided with a 190 ft.
TDL.
System H 3 stage pump
 Figure 1.
Lateral pressure head curves for System H  as installed with increases in total dynamic lift from 90 to 190 feet.
Elevation and pressure head at end of system must equal 231 feet to meet minimum pressure requirements for installed sprinkler package.
Figure 2 is the same center pivot system but with one stage removed from the pump.
The lower curve is the elevation of the center pivot pad and each of the towers.
The difference between this and the elevation and pressure head distribution in the curves for the different TDL's, demonstrates the need for pressure regulation.
The curves for the TDL of 90 and 110 meet the minimum pressure along the entire length of the system.
However, with the increase in drawdown of 50 feet , the pressure is no longer sufficient to meet the required minimum.
Table 2 and 3 summarize the operating conditions for the three and two stage pumps, respectively.
For the three stage pump the change in total discharge is a result of the big gun without pressure regulation.
The reduced application depth is due to the reduced application with the big gun at the outer end of the pivot.
The KW demand decreases with an increase in TDL.
This is due to a lower pivot
 pressure and decrease in the big gun discharge.
The KW demand and the head/stage is nearly the same for all conditions.
System H 2 stage pump
 Figure 2.
Lateral pressure head curves for System H  with increases in total dynamic lift from 90 to 140 feet.
Elevation and pressure head at end of system must equal 231 feet to meet minimum pressure requirements for installed sprinkler package.
Table 2.
Simulated operating characteristics for System H with three stage pump as was installed.
TDL, feet	90	110	140	190
 Discharge,gpm	829	823	812	793
 Pivot Pressure, psi	71	63	50	30
 Irrigation depth, in.
0.77	0.77	0.76	0.75
 Big gun, gpm	135	129	119	99
 Head/stage, feet	88.0	88.5	88.9	89.8
 KW	58.9	58.8	58.3	57.5
 Table 3.
Simulated operating characteristics for System H with two stage pump.
TDL, feet	90	110	140
 Discharge,gpm	797	788	692
 Pivot Pressure, psi	34	25	15
 Irrigation depth, in.
0.75	0.74	0.66
 Big gun, gpm	103	94	85
 Head/stage, feet	89.6	89.8	92.2
 KW	38.4	38.1	34.3
 However, when one stage is removed,  the big gun discharge is reduced as well as the application depth.
A larger booster pump for the big gun could easily correct this.
The head/stage is approximately the same as for the three stage pump.
The final incremental increase in drawdown of 50 feet to a TDL of 140 does result in the pressure not being met at the outer end of the lateral.
The discharge decreased and the application depth decreased from 3/4 inch to 2/3 inch.
The major benefit of the two stage pump is the reduction of power requirements.
Assuming a pump efficiency of 70%, the demand is reduced from 59 to 38 KW.
Operating with the three stage pump will obviously provide for a larger safety factor that can accommodate a larger increase in TDL.
However, the two stage pump can easily accommodate a 20 foot increase in drawdown, with the current design conditions.
The irrigator can still consider a change to a three stage pump when water levels decline further
 System P is similar in length to System H but the sprinklers are high pressure impact heads.
The system is assumed to have no topography change along the lateral.
The system is simulated with three pump configurations having 7, 3, and 2 stages.
It is the only system in this study that does not have pressure regulators along the lateral.
The seven stage pump has TDL range from 300 to 350 feet.
The TDL range for the two and three stage pumps is 90 to 100 feet.
Figure 3 illustrates the pump curves for the 3, 4, and 7 stage pumps.
The system operating points for the simulation are plotted on the pump curves.
The discharge range for all simulations is between 600 to 800 gpm.
The system without pressure regulators does exhibit a drop in the irrigation depth even with an increase in TDL by 10 feet.
The Christiansen uniformity for each of the different pump configurations is 89 to 90%.
An increase of 10 feet in the TDL for the four stage pump had a 0.02 in.
decrease in application depth with a decrease in CU from 90 to 80%.
The decrease in uniformity is primarily caused by the change in discharge and the pattern radius of the big gun.
Comparing the three stage pump with TDL=90 and the seven stage pump with TDL=350 illustrates this fact.
The pivot pressures are only 2% different but the CU is 11% different.
Examining the depth data shows that the big gun has a major influence on the CU.
CPEDlite used by the NRCS for EQIP funding does not include the big gun in the uniformity calculations.
It is included here only to see the effect of changing TDL on the system performance.
The take home message is that the increase in TDL can decrease the application depth by 10 15%.
Figure 3.
The pump curves for the different number of stages for System P.
The operating points are for the one included in the simulation analysis of this system.
Table 4.
Simulated operating characteristics for System P with seven stage pump as was installed.
TDL, feet	300	310	350
 Discharge,gpm	729	712	642
 Pivot Pressure, psi	55	53	43
 Irrigation depth, in.
0.77	0.75	0.68
 Big gun, gpm	32	31	28
 Head/stage, feet	63	63.6	66.1
 KW	86.5	85.3	79.9
 CU	89	89	78
 Table 5.
Simulated operating characteristics for System P with three and four stage pump to illustrate the lower power requirement.
Pump stages	3	4	4
 TDL, feet	90	90	100
 Discharge,gpm	630	769	751
 Pivot Pressure, psi	41	61	59
 Irrigation depth, in.
0.67	0.81	0.79
 Big gun, gpm	27	33	33
 Head/stage, feet	66.3	61.4	62.3
 KW	33.7	50.8	50.4
 CU	89	90	80
 System B is a pressure regulated system with a rotator sprinkler package.
Both a single and double stage pump are used in the simulations.
The system is also assumed to be operating on a level field.
Figure 4 shows the pump curves and simulated operating points for the single and double stage pumps.
Again the two pump curves are used to illustrate the effect of TDL changes over different ranges.
The one and two pumps used a TDL range from 0-50 feet and 90-150 feet, respectively.
The one stage pump with TDL=0 feet and the two stage pump with TDL=90 are equivalent for the center pivot system.
The pivot pressures vary only by 1 psi.
In each case the head/stage is equal to 86.7 feet, thus the pressure difference is the difference between the TDL and the head/stage.
The simulations demonstrate that a delta change in TDL has the same effect on the center pivot pressures whether the TDL is small or much larger.
The increased TDL requires additional stages be added to the pump.
The pump head for a two stage pump is double that of the single stage and the KW is linearly related to the number of stages.
This conclusion assumes that the same pump characteristic for the single stage is used as stages are added.
This is often the case where the discharge is used to select the pump.
Figure 4.
System B operating with single and two stage pump shown with simulated system points.
Table 6.
Simulated operating characteristics for System B with a single and two stage pump.
One stage pump	Two stage pump
 TDL, feet	0	20	40	50	90	110	130	150
 Discharge,gpm	855.1	841.8	827.1	767.7	853	840	816.9	704.5
 Pivot Pressure, psi	33.9	25.5	17.2	13.7	32.5	24.4	16.3	11.1
 Irrigation depth, in.
0.6	0.6	0.6	0.6	0.6	0.6	0.59	0.51
 Big gun, gpm	134	121	106	103	132	119	105	100
 Head/stage, feet	86.7	87.3	88.1	90	86.7	87.4	88	92
 KW	20.0	19.8	19.6	18.6	39.8	39.5	38.7	34.9
 Another observation that can be illustrated with this system is the effect of pressure regulators.
Figure 5 shows the center pivot hydraulic characteristics for System B assuming there are no pressure regulators with the same sprinkler package.
Different pivot pressures were used to simulate the four points on the curve.
The regulated system point  has the same discharge as the first point on the curve.
This emphasizes the influence of pressure regulators on a system.
Regulators control the nozzle pressure for all heads when the pressure exceeds the regulator pressure along the lateral.
The pivot pressure for the unregulated system is one-half that of the regulated system and the application depth decreases with distance from the pivot.
The effect of drawdown on a regulated system is best observed by decreased pivot pressure as TDL increases.
Systems with big guns are affected by a decrease in discharge as TDL increases.
The big gun discharge decreased approximately 10% when the TDL increased 50-60 feet.
Figure 5.
System B center pivot system hydraulic demand curve operating without pressure regulators
 System K is an illustration with a much longer lateral length  than previous systems.
The topography change is about 3 feet along the entire lateral.
Three and four stage pumps were used for the simulations comparing TDL's of 78 and 128 feet.
Figure 6 shows the three and four stage pump curves and the simulated operating points.
The discharges are almost double from the previous systems to irrigate the larger area.
The operating characteristics are show in Table 7.
The pivot pressure for the three stage pump and a TDL=128 feet is below that required for the lateral pressure to exceed the pressure regulator settings.
The average irrigation depth is reduced by 8%.
Figure 7 shows the application depths for each of the simulations.
The depth is the same for all simulations to the 1600 feet from the pivot.
The reduction in depth results from the smaller depths from this point on to the end of the pivot lateral.
The system is not meeting the design but would be difficult to evaluate with catch
 cans.
The application depth is 13% less at the outer end of the system.
The best procedure for monitoring systems would be to measure the pivot pressure and compare to minimum pressure required at the time of design.
Figure 6.
System K operating with three and four stage pumps shown with simulated system points.
Table 7.
Simulated operating characteristics for System K with a single and two stage pump.
four stage pump	three stage pump
 TDL, feet	78	128	78	128
 Discharge,gpm	1617	1596	1583	1465
 Pivot Pressure, psi	94	73	61	43
 Irrigation depth, in.
0.38	0.39	0.39	0.36
 Big gun, gpm	156	135	122	105
 Head/stage, feet	78.3	78.8	79.3	81.2
 KW	136.3	135.4	101.3	96.0
 Figure 7.
Simulated depths for the System K for the combinations of TDL and pump stages.
The continual increase in drawdown in the Central Great Plains requires that producers monitor their water table depths and center pivot system operation.
The data used for the simulation analysis indicated that many systems are designed to have considerably more pumping capacity than needed.
This will automatically provide a factor of safety as the water table drops.
The cost of operation of these systems is more expensive since many systems operate with pressure regulators.
The excess pressure is dissipated in the regulator before reaching the nozzle and the energy is wasted.
It is recommended that each system be analyzed to assure a pumping capacity that meets current needs plus an estimated increase in future water table depths.
Monitoring wells in an area provides some guidance for the amount of anticipated increase in TDL requirements.
McGuire, V.L., 2004, Water-Level Changes in the High Plains Aquifer, Predevelopment to 2003 and 2002 to 2003.
Fact Sheet 2004-3097, U.S.
Geological Survey.
Enterprise Budgets Durum Wheat, Following Cotton, Flood Irrigated, Southern Arizona Blase Evancho, Paco Ollerton, Trent Teegerstrom and Clark Seavert
 This enterprise budget estimates the typical economic costs and returns to grow durum wheat after a cotton crop using flood irrigation in southern Arizona.
It should be used as a guide to estimate actual costs and returns and is not representative of any farm.
The assumptions used in constructing this budget are discussed below.
Assistance provided by area producers and agribusinesses is much appreciated.
As of the date of this publication, the price for labor, fuel, fertilizer, and chemicals is increasing dramatically, which makes developing a long-term budget difficult.
Therefore, a sensitivity analysis shows the net returns per acre as these inputs increase by 10 and 20 percent.
This budget is based on a 1,500-tillable acre farm.
As Arizona is experiencing irrigation water shortages, approximately 40 percent  of the total farm tillable acres are fallowed.
This fallowed land will allow adequate water to irrigate the following crops: 271 acres in cotton, 45 acres in silage corn, 90 acres in spring barley, 181 acres in durum wheat, and 316 acres of alfalfa hay.
The costs to fallow land are allocated to each crop based on its water use.
All crops are grown using flood irrigation.
Tractor driver labor cost is $17.89 per hour and general labor $14.55 per hour; both rates include social security, workers' compensation, unemployment insurance, and other labor overhead expenses.
For this study, owner labor is valued at the same rate as tractor driver rates, and all labor is assumed to be a cash cost.
Tractor labor hours are calculated based on machinery hours, plus ten percent.
Interest on operating capital for harvest and production inputs  is treated as a cash expense, borrowed for 6-months.
An interest rate of six percent is charged as an opportunity to the owner for machinery ownership.
The machinery and equipment used in this budget are sufficient for a 1,500-acre farm with 1,000 acres in crops.
The machinery and equipment hours reflect producing cotton, silage corn, spring barley, durum wheat, and alfalfa hay.
A detailed breakdown of machinery values is shown in Table 2.
Estimated labor, variable, and fixed costs for machinery are shown in Table 3, based on an hour and per acre basis.
The machinery costs are calculated based on the total farm use of the machinery.
Off-road diesel is $4.00 per gallon.
The cultural operations are listed approximately in the order in which they are performed.
A 175-hp tractor is used to pull the v-ripper, heavy offset disk, moldboard plow, landplane, lister, and planter.
A 125-hp tractor is used to pull the shredder/root puller, drill, cultivator, fertilizer spreader, and boom sprayer.
A charge for miscellaneous and other expenses is five percent of production costs, including additional labor, machinery repairs and maintenance, supplies and materials, tax preparation, memberships in professional organizations, and educational workshops not included in field operations.
In this budget the price of durum wheat is $18 per cwt, with an average yield of 66 cwt, resulting in a gross income of $1,188 per acre.
Variable costs are $916 per acre and fixed cash costs of $285 per acre, giving a net return above variable cash costs of -$14 per acre.
Total fixed costs are $46 per acre and total costs of $1,248 per acre, when all variable and fixed costs are considered.
The gross income minus total costs results in a -$60 per acre return.
A breakeven price of $18.20 per cwt would be required to cover variable and fixed cash costs and $18.91 per cwt to cover total costs.
Tables 4 and 5 show the baseline net returns per acre for cash and total costs at various yields and prices as in this study.
Tables 6, 7, 8, and 9 show a sensitivity analysis of returns per acre as the price for labor, fuel, fertilizer, and chemicals are increased an additional 10 and 20 percent.
NOTE: Not included in these budgets are family living withdrawals for unpaid labor, returns to management, depreciation and opportunity costs for vehicles, buildings and improvements, inflation, property and crop insurance, and local, state, and federal income and property taxes.
Table 1.
Economic and Cash Costs and Returns of Producing Durum Wheat Following Cotton, $/acre.
Returns	Unit	$/Unit	Quantity	Value
 Durum Wheat	CWT	$18.00	66.00	$1,188.00
 Variable Cash Costs	Price	Quantity	Unit	Labor	Machinery	Materials	Total
 Land Preparation and Maintenance
 V-Ripper	1.00	acre	$13.53	$34.60	$0.00	$48.13
 Offset Disk	2.00	acre	9.43	23.76	0.00	33.19
 Drill	1.00	acre	5.41	10.13	58.50	74.04
 Seed	$0.39	150.00	pounds
 Ferlilizer Spreader	1.00	acre	1.88	3.73	340.50	346.11
 Nitrogen	$273.00	1.00	acre
 Phosphorus	$67.50	1.00	acre
 Boom Sprayer	1.00	acre	1.19	1.82	17.00	20.01
 Herbicides	$17.00	1.00	acre
 Irrigation	50.93	0.00	192.50	243.43
 Irrigation Water, Flood	$55.00	3.50	ac ft
 Irrigation Labor, Flood	$14.55	3.50	hours
 Harvest, Custom 	$25.00	3.30	tons	0.00	0.00	82.50	82.50
 Other Expenses	5.0%	0.00	0.00	42.37	42.37
 Interest on Operting Capital	6.0%	0.00	0.00	26.69	26.69
 Total Variable Cash Costs	$82.37	$74.05	$760.06	$916.48
 Fixed Cash Costs	Unit	$/Unit	Value
 Fallow Costs	acre	$115.39	$115.39
 Annual Cash Rent Payment	acre	170.00	170.00
 Total Fixed Cash Costs	$285.39
 Total Returns minus Total Varialbe and Fixed Cash Costs	-$13.87
 Fixed Non-Cash Costs	Unit	$/Unit	Value
 Power Units, Machinery & Equipment, depreciation & interst	acre	$45.88	$45.88
 Total Fixed Non-Cash Costs	$45.88
 Total Annual Costs	$1,247.75
 1	Returns Cost includes minus cutting Total Annual nating Costs wheat from field to a market within a round trip of 20 miles..
-$59.75
 Table 2.
Whole Farm Machinery Cost Assumptions.
Width	Market	Annua	Life
 Machine		Value	Use	
 175 HP Tractor	N/A	$180,000	1,365	10
 125 HP Tractor	N/A	80,000	495	15
 V-Ripper	8.0	22,000	459	10
 Offset Disk	18.0	30,000	517	15
 Moldboard Plow	9.3	35,000	138	15
 Landplane	16.0	18,000	78	15
 Lister	10.0	6,500	99	15
 Cotton Shredder/Root Puller	20.0	12,000	41	15
 Row Planter	24.0	40,000	72	15
 Row Cultivator	24.0	22,000	103	10
 Drill	20.0	25,000	97	15
 Fertilizer Spreader	40.0	18,000	109	20
 Boom Sprayer	60.0	9,500	145	20
 Table 3.
Machinery Cost Calculations, on a per hour and per acre basis.
-Variable Costs-	Fixed Cost
 Fuel &	Repairs &	Deprec.
Total Cost
 Machie	Lube	Maint.
& Interest
 175 HP Tractor	$36.80	$7.37	$17.20	$61.37
 125 HP Tractor	23.00	1.78	18.31	43.09
 V-Ripper	0.00	6.16	6.19	12.35
 Offset Disk	0.00	5.40	6.48	11.88
 Moldboard Plow	0.00	18.20	28.29	46.50
 Landplane	0.00	3.24	25.80	29.04
 Lister	0.00	1.78	7.32	9.10
 Cotton Shredder/Root Puller	0.00	2.76	32.57	35.33
 Row Planter	0.00	14.02	64.48	78.50
 Row Cultivator	0.00	3.90	27.10	30.99
 Drill	0.00	12.06	30.14	42.20
 Fertilizer Spreader	0.00	14.31	19.02	33.34
 Boom Sprayer	0.00	5.36	7.51	12.87
 Acre/	Operator	Variable	Fixed	Total
 Field Operation	Hour	Labor	Costs	Costs	Costs
 175 HP Tractor & V-Ripper	1.45	$13.53	$34.60	$16.08	$64.21
 175 HP Tractor & Offset Disk	4.17	4.72	11.88	5.68	22.27
 175 HP Tractor & Moldboard Plow	2.55	7.73	24.50	17.87	50.11
 175 HP Tractor & Landplane	5.09	3.87	9.31	8.45	21.62
 175 HP Tractor & Lister	3.18	6.18	14.44	7.71	28.33
 175 HP Tractor & Shredder	6.64	2.97	4.15	7.67	14.78
 175 HP Tractor & Planter	4.36	4.51	13.34	18.72	36.56
 175 HP Tractor & Cultivator	6.55	3.01	4.38	6.94	14.32
 175 HP Tractor & Drillr	3.64	5.41	10.13	13.32	28.87
 175 HP Tractor & Fertilizer Spreader	10.47	1.88	3.73	3.56	9.18
 175 HP Tractor & Boom Sprayer	16.55	1.19	1.82	1.56	4.57
 Table 4.
Estimated Per Acre Returns Over Cash Cost at Varying Yields and Prices at Full Production.
Change in Prices/Lb	60.00	62.0	64.0	66.0	68.0	70.0	72.0
 $16.50							
 $17.00							22
 $17.50						23	58
 $18.00					22	58	94
 $18.50				19	56	93	130
 $19.00			14	52	90	128	166
 $19.50		7	46	85	124	163	202
 Table 5.
Estimated Per Acre Returns Over Total Cost at Varying Yields and Prices at Full Production.
Change in Prices/Lb	60.00	62.0	64.0	66.0	68.0	70.0	72.0
 $16.50							
 $17.00							
 $17.50							12
 $18.00						12	48
 $18.50					10	47	84
 $19.00				6	44	82	120
 $19.50			0	39	78	117	156
 Table 6.
Estimated Per Acre Returns Over Cash Cost at Varying Yields and Prices at Full Production with a 10 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Change in Prices/Lb	60.00	62.0	64.0	66.0	68.0	70.0	72.0
 $16.50							
 $17.00							
 $17.50							4
 $18.00						4	40
 $18.50					2	39	76
 $19.00					36	74	112
 $19.50				31	70	109	148
 Table 7.
Estimated Per Acre Returns Over Total Cost at Varying Yields and Prices at Full Production with a 10 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Change in Prices/Lb	60.00	62.0	64.0	66.0	68.0	70.0	72.0
 $16.50							
 $17.00							
 $17.50							
 $18.00							
 $18.50							30
 $19.00						28	66
 $19.50					24	63	102
 Table 8.
Estimated Per Acre Returns Over Cash Cost at Varying Yields and Prices at Full Production with a 20 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Change in Prices/Lb	64.5	65.0	65.5	66.0	66.5	67.0	67.5
 $16.50							
 $17.00							
 $17.50							
 $18.00							
 $18.50							22
 $19.00						20	58
 $19.50					16	55	94
 Table 9.
Estimated Per Acre Returns Over Total Cost at Varying Yields and Prices at Full Production with a 20 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Change in Prices/Lb	64.5	65.0	65.5	66.0	66.5	67.0	67.5
 $16.50							
 $17.00							
 $17.50							
 $18.00							
 $18.50							
 $19.00							12
 $19.50						9	48
 THE UNIVERSITY OF ARIZONA Cooperative Extension
 BLASE EVANCHO Area Agent, Arizona Cooperative Extension, University of Arizona
 Paco OLLERTON Producer in Pinal County
 TRENT TEEGERSTROM Ag Econ Extension Specialist, Department of Agriculture and Resource Economics, University of Arizona
 CLARK SEAVERT Agricultural Economist, Department of Applied Economics, Oregon State University
IMPROVEMENTS IN IRRIGATION EFFICIENCY
 Efficiency is the name-of-the-game these days.
We are constantly reminded that we must be more efficient with our time, our money, our skills, and our resources.
Yet, the working definitions of the various efficiencies that each of us use may be quite different.
Sometimes the correctness of the appropriate use of an efficiency term is entirely related to one's perspective.
The topic of this presentation is irrigation, so let's look at two important efficiency terms in irrigation and look at how the terms interact.
WATER USE EFFICIENCY 
 Water use efficiency  is typically defined as the crop yield divided by the amount of water used.
Algebraically it can be expressed as WUE = Mcrop/Vwuse Eq.
1.
where Mcrop is equal to the mass of the crop and wuse is equal to the volume of water used.
It is easy to see that increases in WUE can be accomplished either by increases in Mcrop relative to Vwuse or by decreases in Vwuse relative to McropWhereas both techniques increase the beneficial use of water, only the second technique results in water conservation directly.
It is important to note that manipulation of either term must be relative to the other term in the equation.
Reducing water use is not beneficial if crop yield is reduced to the same extent.
WATER APPLICATION EFFICIENCY 
 The water application efficiency  definition as reported by Heerman et al.
is algebraically expressed as
 Ea = Vsoil/Vfield Eq.
2.
where Vsoil is equal to the volume of irrigation water needed for crop evapotranspiration to avoid undesirable water stress and Vfield is equal to the volume of water delivered to the field.
Ea is often incorrectly confused with the water storage efficiency which is the fraction of an irrigation amount stored in the remaining available crop root zone following an irrigation event.
The use of water storage efficiency is discouraged by Heerman et al.
because of the difficulty of determining the crop root zone and because the water storage efficiency can still be
 quite low while sufficient water is provided for crop production.
It is easy to manipulate Vfield so that Ea can be equal to 1 or 100%.
It should be noted that any irrigation system from the worst to the best can be operated in a fashion to achieve 100% Ea if Vfield is low.
Increasing E in this manner totally ignores the need for irrigation uniformity.
For Ea to have practical meaning, Vsoil needs to be considered to avoid undesirable water stress.
INTERACTION OF WUE AND Ea
 Algebraically it has been shown that either efficiency term can be maximized through manipulation of the various terms in the equations.
However, some of these manipulations are not beneficial to the irrigator and perhaps, also not beneficial to the economic vitality of the state.
Consideration of both terms is necessary to optimize beneficial use of water for crop production.
In a thorough review of crop yield response to water, Howell et al.
enumerated four methods of increasing water use efficiency: 1) increasing the harvest index ; 2) reducing the transpiration ratio ; 3) reducing the root dry matter amount and/or the dry matter threshold required to initiate the first increment of economic yield; or 4) increasing the transpiration component relative to the other water balance components, for example, through reductions of evaporation, drainage, and runoff.
Clearly, some of these four methods are more difficult than others.
Tanner and Sinclair  in a review of studies from the early 1900's to the 1980's conclude that there is very little hope for significantly improving the transpiration ratio.
Plant breeders and agronomists have made great strides in increasing the harvest index  for many of the more important crops.
Corn yields have increased an average of 2.5 bu/acre annually for the years 1968-1991 in Thomas County, Kansas due to improvements in corn hybrids and cultural practices.
The actual water used by the corn has not changed appreciably although the water use efficiency has increased.
The dry matter threshold  varies some depending on the annual climatic conditions.
However, it does not appear practical that it can be manipulated to a significant extent.
Improved irrigation systems and practices can increase both WUE and Ea by Method 4, increasing the transpiration component relative to the other water balance components.
Crop yield is linearly related to transpiration for many field crops from the point of the dry matter threshold through the point of maximum yield.
However, the relationship of crop yield and total water use is usually curvilinear.
The area between the dotted line and the curve represents the inefficiencies caused by the irrigation system and/or inappropriate irrigation/precipitation timing or amounts.
Use of irrigation water beyond the point where the dotted line and the curve join at maximum yield represents wasteful overirrigation and should be eliminated immediately.
All of the points on the rising dotted line have equal WUE, so all are equally beneficial in terms of WUE.
However, most irrigators are practicing irrigation
 for the beneficial purpose of increasing crop yields and economically need to produce near the top of the rising leg.
Lamm et al.
analyzed 9 different resource allocation schemes for irrigated corn ranging from full irrigation to severely deficit irrigation.
Full irrigation was found to be the most economical operating point.
They concluded,
 Irrigators wishing to continue to grow com when irrigation is limited by physical  or institutional constraints should seriously consider reducing irrigated land area to match the severity of the constraint.
Only reductions in the area between the dotted line and the curve  and obviously elimination of overirrigation should be considered as opportunities where improved irrigation systems and practices can increase WUE and E.
Many irrigators are already upgrading irrigation systems and management of their present systems to stretch water.
The opportunity for water use reductions is significant but the ultimate reductions can not be economically obtained overnight.
The irrigation sector continues to search for economical ways to reduce inefficient water use in a manner that can optimize both WUE and E.
Figure 1.
Hypothetical crop yield response to total water use and transpiration.
Area between dotted line and curve is inefficiency.
Use of irrigation water beyond where dotted line and curve rejoin  is wasteful overirrigation.
Starting point for both lines is dry matter threshold.
Numbers shown for example only, actual values will vary.
This paper was first presented at the 12th Annual Water and the Future of Kansas Conference, Feb 28 March 1, 1995, Kansas State University, Manhattan Kansas.
The purpose of this work was to evaluate whether the innate variability of manures and the difficulty in achieving a uniform spread negate the recommendations often made by land-grant universities to sample manure and calibrate manure spreaders.
The objectives of this study  were 1) to measure the variability within stockpiles of various animal manures and determine the number of subsamples needed to characterize the nutrient content within a 10% probable error and 2) to compare Colorado manure analyses to the table values we have been using in our publications, which come from Midwestern data.
Ten sub-samples  from each of five manure stockpiles  were collected.
Each stockpile was sampled from a different farm.
Two samples were taken from the top and two from each side of each stockpile.
For each pair of samples, one was taken shallowly , and one was taken more deeply ft).
For the side samples, one of each sample pair was taken from the middle and one from near the bottom of the stockpile.
Each sub-sample was analyzed separately for dry matter , total nitrogen , ammonium , nitrate , phosphorus , and potassium  to determine the variability within the pile.
Collected data and the following equation were used to determine the number of sub-samples needed.
n = tCV/p2 where t=Student's t value , CV=coefficient of variation expressed as a decimal, and p=probable error expressed as a decimal.
Beef, dairy, horse, sheep, and chicken manures were sampled in order to compare Colorado manure analyses to Midwestern table values.
Six to ten different livestock operations were sampled for each manure type.
Each sample
 was a composite of six 0.5 qt sub-samples taken from different locations and depths within the stockpile.
The D.M., total N, NH4, P2O5, and K2O values measured in these samples and manure sample means from each farm tested in the within-stockpile variability experiment described above were combined into a database.
Results were compared to values previously used in Colorado extension publications which came from Midwestern manure samples.
The objectives of this study  were 1) to compare the Tarp Method and the Swath Width and Distance Method for manure spreader calibration, 2) to measure the variability among tarps in the Tarp Method and to calculate how many tarps would be required to achieve 10% probable error, 3) to evaluate the uniformity of the spread patterns and measure the swath widths of the manure spreaders, and 4) to compare the measured application rates from both the Tarp Method and the Swath Width and Distance Method with the stated goals of the operators.
We worked with ten different operators of manure spreaders.
All of the spreaders were truck-mounted.
We used eight tarps, three 10 X 12 ft tarps lined up in a row in the direction of travel for the Tarp Method and five 5 X 10 ft tarps lined up side-by-side perpendicular to the direction of travel.
The tarps were each weighed with a hanging scale prior to laying them out.
After laying the tarps out, we measured the weight of the full manure spreader using a set of four wheel-load scales or a drive-on scale at the feedlot source.
Then, the operator drove over the tarps while spreading manure.
Each tarp was weighed with the manure on it using a hanging scale, and the tarp weight was subtracted from the manure plus tarp weight to calculate the net weight.
The empty manure spreader was also weighed, and the manure weight was calculated by subtracting the empty spreader weight from the full spreader weight.
The average capacity of the trucks was 15.4 tons of manure, but the capacity ranged from 12.3 to 20.6 tons.
For the Tarp Method, the net weight in lbs was divided by the area of the tarp , multiplied by 43,560 sq ft/acre and divided by 2000 lbs/ton to calculate the application rate in tons/acre.
The coefficient of variation was calculated for the three tarps, and the number of tarps required to achieve 10% probable error was calculated using the equation shown above.
The lb per tarp measurements were graphed as a function of tarp location as part of the Swath Width and Distance Method.
Using the graph, we did a field estimate of swath width by predicting the location where the application rate would be 50% of the maximum.
Swath width was subsequently calculated based on determination of the slope of the line from the middle tarp to the inner tarps, and then calculating the distance from the center which would receive 50% of the
 maximum application rate.
We used a measuring wheel to measure the distance that manure was spread on from each truck load.
The average travel distance per load was 0.45 miles, with a range of 0.31 to 0.56 miles.
Then we calculated application rate by dividing the weight of the manure in tons by the receiving area in square feet  and then converting to tons/acre by multiplying by 43,560 sq ft per acre.
We defined an off-center spread pattern as one where the difference between the inner tarps was greater than 50% of the lower weight, and calculated which manure spreaders resulted in off-center spread patterns.
The Tarp Method, Swath Width and Distance Method, and operator goals were compared using analysis of variance and the Least Significant Differences Mean Separation Test at p<0.05.
The average spread pattern and comparison of field estimated and calculated swath width were evaluated similarly.
The variability of samples within a manure stockpile differed for the various constituents.
Ammonium and nitrate had the greatest coefficients of variation due to their relatively low concentrations.
The greater the coefficients of variation, the greater the number of sub-samples required for useful analysis.
For example, to achieve probable error within 10% for a beef manure stockpile, one would need 17 sub-samples to characterize total N, 20 sub-samples for P, 32 for K, 121 for NH4-N, and 692 sub-samples for NO3-N.
For solid manures, it seems possible to estimate the total N, P, and K in a stockpile within 10% probable error with a moderately intensive sampling plan.
However, to characterize the NH4-N and NO3-N levels in order to predict N availability to crops, the required sub-sample number becomes impractical.
In addition to CVs, another measure of similarity is the confidence interval , which is a measure of the probability that a sample will fall within an upper and lower limit.
For the one case in which we had over 100 samples , the 90% C.I.s were quite narrow.
For example, the mean total N content was 23 lb/ton, with a C.I.
of 21-24 lb/ton.
We can interpret this to mean that nine out of ten beef manure stockpiles will have a N content between 21 and 24 lb/ton.
Based on our information, we recommend a minimum of 25 farms for manure database creation in the Mountain West in order to achieve 90% C.I.
ranges of 10% D.M.
and 10 lb/ton for the nutrients.
Including 72 farms in each database
  would reduce the ranges in the 90% C.I.s to 5% D.M.
and 5 lb/ton for each of the nutrients.
The solid manures sampled from Colorado operations differed in comparison with those we previously used in our extension publications, which originated from sources in the Midwest.
The dry matter contents of the Colorado manures were consistently higher than those reported from the Midwest.
On a wet weight or "as is" basis, the Colorado manures had higher total N contents in four out of five cases.
Ammonium was lower in all of the Colorado manures on a wet weight basis.
Colorado P2O5 and K2O contents were higher than Midwestern data for all manure types, when evaluated on a wet weight basis.
The semi-arid and windy climate of Colorado probably leads to greater evaporation of water and volatilization of NH3 from manure stockpiles, resulting in the higher dry matter values and lower contents of NH4-N in all of the manures.
Phosphate and K2O contents are probably greater in Colorado manures because of the concentration effect from the greater loss of water.
This concentration effect also occurs with organic N, causing the increase in total N content in most of the manures.
The Swath Width and Distance Method resulted in significantly higher measured application rates than the Tarp method.
When a spreader truck was driven over the tarps, the tarp width was effectively reduced due to being pulled in by the weight of the truck.
The data was corrected for this shrinkage, and the Tarp Method still resulted in lower measured values.
The coefficient of variation  for the weights on the three tarps used in the Tarp method ranged from 17-56%, with an average CV of 30%.
We used relatively large tarps for the Tarp method, because the larger the tarp, the lower we expect the CV to be.
Only two of the ten test cases had CVs > 40%.
We calculated that three tarps result in 39% probable error, and five tarps result in 30% probable error.
In other words, if the goal of the operator is to spread 20 tons manure/acre, three tarps would result in measured values from 12-28 tons/acre, and five tarps would result in measured values of 14-26 tons/acre.
Since using five or less tarps results in so much error, we do not have sufficient confidence in the Tarp Method.
We determined that 46 tarps would be required to achieve 10% error in measured application rate by the Tarp method.
On average, the spread patterns were centered.
However, seven out of ten spreaders had patterns which were off-center.
One of these seven cases could potentially be attributed to strong winds.
Another one of the spreaders had one side with 7.5 times the amount of manure on it than the other side.
Some of the trucks did not seem to be loaded evenly, but trucks were loaded according to
 common procedure; therefore, the unevenness of the spreading could be partially attributed to asymmetrical loading and partially attributed to the need for adjustment and improvement of manure spreaders.
Calculated swath widths ranged from 7.5 ft to 16.1 ft, with an average of 11.1 ft.
With swath widths less than 10 ft, using 10 ft X 10 ft tarps would be inadequate for swath width determination.
The calculated swath widths were not significantly different from those estimated in the field.
On average, neither the Tarp method nor the Swath Width and Distance method were significantly different from the application rate goal of the operator.
Three of the operators stated their goals in ranges of 5 tons/acre, and, in these cases, we used the middle of the range for the comparison.
Nonetheless, the operators are generally achieving their stated application rates, with p<0.05.
Both of the methods tested here were too variable to be useful.
Of course, manure spreading is innately variable, and evaluating a large area from small tarps whether for swath width determination or actual application rate calculation only works if the spreading is uniform.
Although we did not evaluate the Loads per Field Method , since this method encompasses the entire spreading area and does not involve the use of small tarps, we would expect the variability to be less with this method.
Rather than emphasizing spreader calibration, we should focus on improving manure spreader design to be more uniform and checking spread patterns and overlap distances in order to improve uniformity of applications.
Manure varies within and among livestock operations due to different feeding and management practices.
Table values can replace site-specific sampling if enough , local sample numbers were used to develop those table values.
Otherwise, if you are uncertain of the source of the table values, site-specific manure sampling remains valuable.
Be sure to take a minimum of six subsamples per stockpile  in order to have some level of confidence in the analysis.
Manure spreading is also a variable process.
The Tarp Method for spreader calibration does not adequately capture that variability.
The Swath Width and Distance Method is usefully for determining necessary overlap distance to reduce application variability.
It is important to weigh manure loads, load spreaders evenly, overlap properly, and count loads applied per field to get a decent estimate of application rate.
Although agronomic manure application rate can be done very precisely, the innate variability of manure and manure spreading require us to be reasonable in
 our expectations.
Annual soil sampling provides a critical feedback loop to adjust manure utilization practices from year-to-year.
Declining water supplies, drought, increased competition from other users, and either existing or anticipated restrictions on the amount of water that can be applied over a specified time period, are encouraging many producers to improve the irrigation efficiency of their irrigation systems.
To most people, irrigation efficiency, Eirr, is a general term that indicates how well a water resource is used to produce a crop.
Although Eirr can be looked at from several perspectives, this paper deals with it at the field level of a producer.
Typically a producer is concerned primarily about making most effective use of water on his farm and does not pay much attention to how individual fields or his farm affects the water budget of an entire watershed.
Water that is applied but not beneficially used to produce a crop, is referred to as a loss even though that water may still be physically observed as runoff, etc.
Irrigation efficiency, Eirr, is mathematically defined as:
 Eirr= Vol beneficial / Vol gross where: Vol beneficial is the volume of water used to produce a crop Vol gross is the volume of water taken from the water resource
 Sometimes the volume of water delivered to a field, Vol delivered is used instead , of Vol gross.
In situations where there are no significant losses from the water source to the irrigation system such as a center pivot with a well/pump near the pivot, Vol gross = Vol delivered In other situations such as a long, leaky conveyance ditch leading to a field, there are significant losses so that Vol delivered is less than Vol gross Depending on your perspective or area of interest, it may make sense to include conveyance losses when talking about improving irrigation efficiencies.
Fig.
1 illustrates how the soil water in the root zone varies over time as the evapotranspiration  of the crop withdraws water and periodic irrigations or rains replace water in the root zone.
Good water management applies irrigations before the soil moisture level reaches the management allowable depletion  with an applied depth that just refills the soil profile to field capacity.
The MAD is a management decision of the producer that will vary by crop and his willingness to accept risk of yield reducing stress.
If irrigations are too far apart, yielding-reducing water stress will occur.
If the applied depth from irrigation or rain causes soil moisture to exceed FC, the excess water either runs off or percolates below the root zone and hence is not beneficially used by the crop.
Fig.
1 Schematic of soil water in profile over time
 It is important to measure the amounts of water beneficially used and delivered to a field in order to document improvements in irrigation efficiency due to management changes and/or upgrades in the irrigation system.
Careful measurements of crop water use make it possible to determine the volume of water beneficially used.
Other conference papers cover this topic very well.
Accurate measurement of applied water requires properly installed and well maintained equipment.
Flumes, such as the Parshall flume, are adequate for open channel flow, unless the headloss through the flume is too great.
Another option is to pour a raised concrete sill in an existing concrete ditch.
The as-built dimensions can be input into Winflume, an easy-to-use computer program, to create an accurate rating curve for each installation.
Flow meters are typically used for obtaining flow data in the pipelines of pressurized irrigation systems, although other methods can be used.
Propeller meters are probably the most common but require periodic maintenance to make sure the propellers turn freely and produce accurate measurements.
Ultrasonic flowmeters are non-invasive and very accurate but more expensive.
Because they are temporarily attached to the outside of the pipe, they are portable making it possible to measure many irrigation systems with a single piece of equipment.
The key to getting accurate measurements from this equipment, is to pay close attention to installation procedures, such as locating the sensors where flows are uniform and the pipe is flowing full.
IMPROVEMENTS TO REDUCE LOSSES
 From the definition given above, the closer Eirr is to 1.0, the more efficient is the water use.
The most obvious way for increasing Eirr is to reduce losses so Volgross is as small as possible.
A list of possibilities is given below.
1.
Significant conveyance losses in an open channel can be reduced by ditch lining, ditch realignment, or installing a closed pipeline.
2.
Improve application uniformity to reduce deep percolation
 For surface systems, quicker furrow advance to reduce the differences in infiltration opportunity time along a furrow.
Options include land leveling, surge irrigation, furrow firming, etc.
For sprinkler systems, options include changing sprinkler types, renozzling the system or changing nozzle spacings to improve the overlap between heads.
3.
Modify the timing and amount of an irrigation to match the WHC of the soil profile better, thereby reducing percolation and runoff losses.
4.
Convert to a more efficient irrigation system  to reduce application losses.
If the new system is well designed and managed, applications are more uniform reducing deep percolation and runoff.
The implicit assumption is that if a physical change is made in the irrigation system, management also changes appropriately.
For example, converting from surface to sprinkler irrigation can greatly reduce water application depths, but if irrigation management does not change as well, then it is still possible to apply as much water as with a surface system.
IMPROVEMENTS TO USE WATER MORE EFFECTIVELY
 The previous discussion assumes that available water supply is not limited, so the goal is apply water uniformly at the right time and amount so percolation and
 runoff are minimal.
This may be an ideal situation where the field is managed as a uniform block of soil.
The actual situation is likely to be more variable with some water stressed areas where yields are depressed.
With the recent interest in adopting new technologies site-specific management of fields, there are additional opportunities for improving Eirr by increasing Vol beneficial in the water stressed areas.
In many irrigated fields, there are significant differences in soil texture that have a large effect on the water holding capacities of the soils.
Accurate delineation of these differences is difficult if the only resources available are the USDA-NRCS soil survey and a few soil cores taken across the field.
However, recent research has shown that soil texture correlates very well with the bulk electrical conductivity  of soil when the salinity levels are low.
The Veris 3100 EC system equipped with global positioning system  equipment, makes it possible to map the bulk soil EC at a rate of 30-40 ac/hr.
Depending on the soil variability, 6 to 12 soil cores are taken, and analyzed for soil texture and other soil properties of interest.
The EC values at the sample sites are statistically correlated with the various soil parameters to estimate soil texture and water holding capacity over the entire field.
Using this map, the producer can identify the sizes of areas that are of particular concern when he is making management decisions about when and how much water to apply.
Since summer precipitation is generally unpredictable in the western part of the Great Plains, most irrigators do not consider possible rain when they make decisions about irrigation timing and amount.
By scheduling irrigations according to the water needs in areas of the field with the lowest water holding capacities, significant water stress affecting yield can be avoided across the entire field.
If water stress affecting yield is detected using remote sensing, yield map from previous year, or some other method, it may be possible to make some changes in the irrigation system or management to reduce the stress and resultant yield reduction in low WHC areas.
The course of action with the least cost is to increase the irrigation frequency and decrease the applied depth so the soil water depletion does not exceed the MAD in the low WHC areas.
Unless there are very unusual circumstances, the frequency should not be less than 2 days because of the inherent inefficiencies of applying very small depths.
Obviously, if adequate water is unavailable because of diminished well yields, management changes cannot increase the available supply.
However, if the well yield is sufficient but system capacity is insufficient, redesign with different applicators and/or renozzling the system could increase the available water and reduce stress in the crop.
Obtaining and analyzing a good quality yield map is a good starting point for quantifying the extent and magnitude of yield depressions.
Since depressed yields can have various causes, additional information is needed to determine whether irrigation is the primary cause.
Aerial images in color and/or infrared wavebands, can be very useful in identifying variability in biomass throughout the
 season.
In-depth field observations are usually very helpful in ground-truthing aerial images.
If there is good evidence that the irrigation regime has caused yield depressions in certain areas of the field, operational changes during an irrigation should be made to best satisfy the irrigation needs over the entire field.
If the available water is limited and water is being applied to minimize waterstressed areas with minimal losses, then increasing Vol beneficial is the only way to improve irrigation efficiency.
A clear understanding of what beneficial means is crucial in considering various options.
Since a primary objective of irrigation is to optimize crop production for the available water supply, management decisions must consider the how much water is required to achieve at least reasonable economic production.
If taken to the extreme where all of the available water supply is applied over a large enough area so there is no percolation or runoff, there could be very little economic production  even though the irrigation efficiency approaches 1.0.
However, a forage crop could be at an economic production level so Vol beneficial is greater than 0, although the optimum balance would probably have more water applied on a smaller area.
This example illustrates two options for management changes that would increase Vol beneficial One possibility is to change the irrigated area so the seasonal application depth would produce an economical production level so Volbeneficial approaches Vol gross Another option would be to grow different crops so Vol beneficial could match the available water supply.
Although there are a lot of possible scenarios for managing a limited water supply, Eirr will probably be high  and may not change even if the crops grown are changed to produce a larger economic return per unit of water beneficially used.
Other conference papers discuss these options in much more detail.
Numerous factors will continue to encourage improvements in on-farm irrigation efficiencies.
The trend to convert from surface to pressurized systems will continue, in part at least, to lower labor requirements.
Although this conversion enables the producer to apply less water over the season and reduce runoff and deep percolation, there is probably very little reduction in the amount of water used by the crop.
The reduction in runoff and percolation translates into fertilizer and chemical savings, has very positive environmental implications, and makes it possible to maintain good production in areas where legal restrictions limit the amount of water that can be withdrawn over time.
However, in areas where applied depths are not restricted by law, it is unclear whether there are significant financial benefits from just reducing the amount of water diverted or pumped for irrigation.
MISSISSIPPI STATE UNIVER EXTENSION
 Extending Knowledge.
Changing Lives.
Irrigation FAQs I Mississippi State University Extension Service
 How much yield benefit do we get from irrigation in Mississippi?
Any yield response depends on the management and timeliness of the irrigation.
The following table displays accepted yield data for the major irrigated crops in Mississippi.
Accepted Yield Responses By Crop
 Cotton	180 pounds of lint
 Corn	50 to 180 
 Grain Sorghum	No good data.
How much water does it take for different irrigation systems?
Furrow--A minimum of 10 GPM per acre.
Flood--, 15-20 GPM per acre.
Border--A minimum of 10 GPM per acre.
Center Pivots--A minumum of 4.5 GPM per acre to put out a gross of 1 inch in 4 days..
Towable Privots and Traveling Guns--A minumum of 5 GPM per acre total to by irrigated.
Irrigation, Soil and Water Home
 How many acres of Mississippi crops are irrigated?
Other Crops	100,000 acres
 When do you start to irrigate?
When you feel like an inch of rain would do some good and when soil moisture in the root profile reaches 50 percent depletion.
The critical stages for the different crops are:
 Corn	Eight leaf stage and very critical at tassel and silk
 Grain Sorghum	Boot stage
 Mississippi succeeding in irrigation efficiency efforts
 Filed Under: Irrigation, Water May 2, 2023
 Technology allows Jeremy Jack to implement management practices on Silent Shade Planting Co.
in Belzoni that were impossible 15 years ago, and water use efficiency is just one way his operation has improved.
Water conservation is high agricultural priority at MSU
 Filed Under: Irrigation, Water April 20, 2023
 Agriculture is the world's single largest consumer of fresh water, making the water shortages expected over the next 10 years in at least 40 states -Mississippi included -critically important.
MSU Extension survey seeks farmer feedback
 STARKVILLE, Miss.
-Delta-based agricultural producers in a four-state region are invited to participate in a survey designed to gauge opinions and identify current practices related to water use.
The online "Delta Region Irrigation Producers' Survey," or DRIPS, also includes questions related to how producers prefer to receive educational information, which will help the Mississippi State University Extension Service design future programs.
Survey results are confidential, and participants remain anonymous.
Extension irrigation specialist receives national award
 STONEVILLE, Miss.
-An irrigation specialist with the Mississippi State University Extension Service has gained national recognition for his outreach related to water conservation practices.
Agriculture, Crops, Irrigation, Remote Sensing Technology, Soils, Soil Health, Soil Testing, Healthy Soils and Water, Healthy Water Practices, Water Volume 8 Number 2
 Brian Andrus irrigated exactly zero times on his Sunflower County farm in 2021.
He didn't even turn on his well.
New Ways to Water
 Soybeans, Irrigation Volume 2 Number 3
 Delta soybean producer irrigates his fields, increases yields
 Most of the Delta is already irrigated, but not all farmers are taking advantage of the latest irrigation technologies.
However, agents with the Mississippi State University Extension Service are increasing Delta producers' knowledgeand application-of new, more efficient ways to water the rows.
The More Things Change
 Catfish, Corn, Rice, Soybeans, Wheat, Farming, Irrigation, Soils Volume 2 Number 1
 Delta farmer Travis Satterfield reflects on 40+ years in the fields
 The price of rice hasn't increased much since Travis Satterfield of Benoit began growing it in 1974, but nearly everything else in the world of production agriculture has changed.
2020 Pearl River Clean Sweep removes thousands of pounds of trash
 Since it began 4 years ago, the Pearl River Clean Sweep has removed more than 135,000 pounds of trash from the Pearl River Basin, including the Pearl, Strong, and Bogue Chitto Rivers across 15 Mississippi counties and two Louisiana parishes.
The Clean Sweep offers an opportunity for volunteers to participate in a coordinated effort organized by like-minded leaders.
Many people affiliated with the Mississippi State University Extension Service participated in the 2020 cleanup, and lead organizer Abby Braman is an Extension-certified Master Naturalist volunteer.
Volume 5 Number 2
 In this "What's New in Extension," Extension agents implement better safety standards, train to deliver Mental Health First Aid, and receive national recognition.
Also, new irrigation and specialists join the Extension family.
Sprinklers Cool Birds and Conserve Water
 Yi Liang Assistant Professor, Extension Engineer
 Susan E.
Watkins Professor, Extension Poultry Specialist
 G.
Thomas Tabler Former Project Manager, Poultry Science
 David McCreery Project/Farm Manager, Poultry Science
 Arkansas Is Our Campus
 Keeping birds comfortable during hot, humid weather is critical for optimizing weight gains, feed conversion and livability.
Improved growth rates and the trend to heavier average market weights contribute to greater heat loads in modern broiler barns.
While the poultry industry has made significant strides to minimize seasonal effects, even the best housing design can still result in birds settling with lighter weights when nature turns up the temperature.
Current methods used by the industry to overcome heat stress include tunnel ventilation that uses exhaust fans to rapidly move air along the length of the barn.
When wind speed alone no longer provides adequate bird cooling, water is circulated over the cooling pads to cool the
 air entering the house.
The final stage of cooling involves the use of interior foggers that saturate the air with a fine mist to increase air cooling.
In both cases, the air temperature is reduced by water evaporation, absorbing heat from the air.
Unfortunately both systems tend to saturate the barn air with moisture , which is counterproductive to the bird's own natural ability to cool itself by evaporative heat loss through the air that it breaths out.
A second challenge with recirculating cool-cell systems is the significant water usage that is directly correlated to outside temperature and how rapidly the air moves through the house.
Figure 1 shows that a single 40 by 400 foot barn with 120 feet of pads used as much as 2,500 gallons of
 FIGURE 1.
Daily cooling water usage by cool-cell systems and the corresponding daily maximum ambient temperature.
water per day with 38-day-old birds present.
Cooling water consumption could be even higher under 100F days with the same age of flock.
Drought conditions during the 2012 summer were a wake-up call for many producers regarding the need to better conserve water yet maintain good bird performance.
An alternative to the traditional cool cells and foggers is the sprinkler system which works by cooling the birds instead of the air.
Cattle and hogs are often cooled in hot weather by sprinkling with water.
Only a few years ago poultry producers avoided catastrophic losses by hosing birds with water during extremely hot weather.
Lowpressure water sprinkling does not cool the barn air but rather works by wetting the birds' feathers.
Heat is then absorbed directly from the birds as these water droplets evaporate and are carried away by the tunnel fans.
The natural response of any producer or live production manager is the thought that sprinklers will soak the litter causing terrible conditions.
This is proving to simply not be the case; sprinkler houses are actually drier than cool-cell and fogger houses.
The computerized sprinkler control systems take into account bird age and barn air temperature to determine how much water will be "sprinkled" and at what intervals less water is used via sprinklers when birds are young than when birds are older, covering more floor space and generating more heat.
As more cooling is required, there is less opportunity for the water to fall on the floor.
Sprinkler systems use intermittent spraying of controlled water volumes followed by sufficient time for the water to evaporate and be removed by 500+ feet per minute wind speeds.
As a result, litter conditions in the sprinkler houses, as measured on the day of sell, were similar to those in the cool-cell houses.
One significant difference with sprinklers as compared to cool cells is the air temperature inside a chicken house with sprinkler cooling is either the same as or only slightly lower than the outside air.
As a result, the humidity of the air in a sprinkler house
 is similar to the outside air, but consistently lower than that of the air in a cool-cell house as shown with the dotted lines in Figure 4.
It is important to note that when barn temperatures are at or below the set point, birds readily give up the extra heat they generate to the "dry" air that moves over them.
As barn temperature rises above the desired set point, birds no longer cool themselves by the air carrying or "convecting" the heat away  and additional evaporative heat removal is needed.
With sprinkler systems, the controller utilizes bird age and temperature information to increase the amount of water as needed for bird cooling.
Increasing the sprinkler run time or decreasing the time between sprinklings will compensate for the higher temperature so birds stay comfortable.
While sprinkler houses may have higher air temperatures than cooling pads or fogger houses, adequate cooling is still achieved by direct evaporative heat loss from the feathers and increased respiration losses from the birds' lungs due to lower air relative humidity.
Due to the focus of water evaporation at each individual bird's surface, the cooling water used by sprinkler houses averaged 70% less than the cooling water used by the cool-pad-only houses.
In tests conducted at the Applied Broiler Research Farm of the University of Arkansas over five summer flocks, the sprinkler houses  used in the range of 4,000 to 10,000 gallons of cooling water per flock per house , compared to the pad-cooling houses .
Results from three summer flocks when sprinklers and cooling pads were used in combination  show that the combination-cooling house saved 40% of cooling water compared to its paired pad-cooling house.
Supplementing the sprinklers with the cool cells under extremely hot conditions may be necessary to gain the best flock performance and water savings.
FIGURE 2.
More sprinkled water is used when the house is warmer during the day or with older age of birds.
FIGURE 3.
Litter moisture conditions in sprinkler houses and in cool-pad houses on the market day of flocks.
FIGURE 4.
Inside temperature and relative humidity on a typical summer day using either sprinklers or cooling pads.
FIGURE 5.
Cooling water used by sprinkler-only, cooling pads-only and the combined use of the two systems from 40 by 400 foot houses of five summer flocks.
General Layout and Operation for Sprinkler Systems
 The sprinkler system in a typical broiler house includes two or three lateral PVC lines with low-pressure  sprinklers, depending on the width of the house.
No booster pump is needed.
Sprinklers should be evenly placed 20 feet apart and staggered on adjacent lines to ensure uniform floor coverage.
The sprinklers should be grouped into zones with up to 20 nozzles in each zone.
This allows the water to be activated by zone to avoid overwhelming the water supply on the farm.
All existing temperature sensors inside the house should be shielded from water drops to avoid erroneous readings due to the chilled effect of water evaporation.
Aluminum foil or pie plates are used as easy and inexpensive shields.
Sprinklers are typically recommended for use after flock age of 21 days  to minimize the possibility of most of the water ending up on the litter due to low floor coverage by the birds.
Overhead sprinklers together with tunnel ventilation can successfully cool broiler chickens with substantially less water.
Cooling is achieved by intermittently spraying large water droplets uniformly into the house, typically beginning flock age of 21 days under normal stocking density.
The amount of water spray varies according to the total live weight of the birds and the thermal condition inside the house.
The relatively dry and fast-moving air inside the house helps to remove heat from birds' respiratory pathways to keep them comfortable and gives a chance for moisture to escape from the litter.
Cooling water is significantly reduced since the birds are the cooling target instead of the air.
Printed by University of Arkansas Cooperative Extension Service Printing Services.
DR.
YI LIANG is assistant professor Extension engineer with the Biological and Agricultural Engineering Department and DR.
SUSAN E.
WATKINS is professor and Extension poultry specialist with the Poultry Science Department located at the University of Arkansas in Fayetteville.
DAVID McCREERY is project/farm manager, Poultry Science, located in Savoy.
Liang, Watkins and McCreery are employees of the University of Arkansas Division of Agriculture.
DR.
G.
THOMAS TABLER was formerly project manager, Poultry Science, with the University of Arkansas and is currently a professor at Mississippi State University.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Director, Cooperative Extension Service, University of Arkansas.
The Arkansas Cooperative Extension Service offers its programs to all eligible persons regardless of race, color, national origin, religion, gender, age, disability, marital or veteran status, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
Denitrification in Seepage-Irrigated Vegetable Fields in Florida
 Eric H.
Simonne, Guodong Liu, and Benjamin Morgant2
 Vegetable crops such as tomato , bell pepper , watermelon  Mat.
& Nakai), summer squash , green bean , potato , and eggplant  are widely grown in Florida in the winter and spring seasons.
The main irrigation methods used for vegetable production are drip irrigation , sprinkler irrigation  including center or linear pivot irrigation, and seepage irrigation .
Drip irrigation consists of delivering water to each plant through a network of pipes and drip tubing.
Overhead irrigation is made up of pipes, sprinklers, and pivots.
Irrigation scheduling of both drip and overhead irrigation can be precisely managed to meet crop demands and maximize crop yields and quality.
Seepage irrigation is the most common irrigation method in Florida on muck and sandy soils and consists of maintaining a water table perched on an impermeable layer.
The top of the water table is typically maintained at between 18 and 24 inches  deep.
While drip irrigation and overhead irrigation have been gaining popularity in the last twenty years, seepage irrigation remains a very common production system in Florida.
In the field, the distinction between seepage irrigation and drip irrigation or overhead irrigation is not always clear, as in most cases, a perched water table is maintained in dripor
 overhead-irrigated fields.
Because of the sandy soils low water-holding capacity, "true" drip or overhead irrigation  is rare in Florida.
For example, growers provide two thirds of irrigation water through center pivot irrigation and the other one third through seepage irrigation for potato production in southwest Florida.
Figure 1.
Vegetable crops grown in Florida with seepage irrigation and drip irrigation; a) water moves laterally when it reaches the spodic layer on an Acona fine sand, b) holes in the plastic are made by the fertilizer injection wheel, c) water control structures, and d) cantaloupe grown with drip irrigation.
Credits: Eric Simonne, UF/IFAS
 Figure 2.
Overhead irrigation through center pivot for potato production in southwest Florida.
Credits: Guodong Liu, UF/IFAS
 These vegetable crops are also grown with intensive fertilization with UF/IFAS N fertilizer recommended rates ranging from 150 to 200 lb/acre  N.
For crops grown with drip or overhead irrigation, current recommendations are to use the results of a soil test and to apply a third to a half of the N and K and all the P and micronutrients preplant.
The remaining N and K are injected throughout the growing season.
When drip or overhead irrigation is used, nutrients move with the water by gravity until the water encounters the impermeable layer.
When irrigation water reaches the impermeable layer, lateral water movement occurs.
For crops grown with seepage irrigation, all nutrients recommended by the soil test results are applied preplant before the plastic is laid.
Approximately a third of the N and K and all the P are applied broadcast in the bed , and the remaining N and K are applied in 2 bands located on the bed shoulders.
In this system, water moves upward by capillarity and slowly solubilizes nutrients in the root zone.
Heavy rains are common in Florida and may leach nutrients out of the root zone.
A leaching rain occurs when it rains at least 3 inches  in 3 days or 4 inches in 7 days.
After a leaching rain, drip-, overhead-, and seepage-irrigated fields may become flooded.
Vegetable crop growth and yield are reduced when anaerobic conditions are maintained for more than 24 hours.
To reduce the incidence of flooding, a network of ditches and canals conveys the water to large pumping stations that can rapidly move it out of the farmed land and into an enclosed retention area where denitrification may occur.
Hence, the N fertilizer applied to vegetable fields may be taken up by the crop, denitrified , volatilized , or moved off site by leaching rains where, because water is typically pumped into an enclosed retention area, denitrification may also occur.
Vegetable crop fertilizer application rates are often greater than the UF/ IFAS recommended rates to ensure adequate fertilization
 and economical productivity despite these possible N losses.
In response to public awareness of environmental issues, section 303 of the Federal Clean Water Act of 1977  requires that states identify impaired water bodies and establish total maximum daily loads  for pollutants entering these water bodies.
Best Management Practices  were defined as specific cultural practices aimed at reducing the negative environmental impact of agricultural production while maintaining or increasing yield and productivity.
In 1987, the Florida legislature passed the Surface Water Improvement and Management  Act requiring the development, by the five Florida water management districts of plans to clean up and preserve Florida lakes, bays, estuaries, and rivers.
The modification made in 1994 to the Florida Fertilizer Law  known as the Nitrate Bill  established a mechanism to fund projects aiming at protecting the state's water resources by improving fertilizer management practices.
In 1999, the Florida Watershed Restoration Act defined a process for the development of TMDLs.
The Florida Department of Agriculture and Consumer Services released the "Water Quality/Quantity BMPs for Indian River Area Citrus Groves" in 2000  and the "Florida Vegetable and Agronomic Crop Water Quality and Quantity BMP Manual" in 2015.
Both manuals define the BMPs that will apply to these industries in Florida.
Current nutrient BMPs focus on soil testing, plant analyzing, and irrigation scheduling.
The practical impact of fertilization practices on water quality in Florida is not fully understood.
It is possible that all the N fertilizer used above the UF/IFAS recommended rate directly contributes to the degradation of water quality.
It is also possible that N fertilization rates above current UF/IFAS recommendations are needed in seepage-irrigated soils  to offset N loss by denitrification.
However, the occurrence and rate of denitrification in vegetable fields is not known.
Preservation of water quality through improved N management in vegetable production requires an understanding of the fate of N in vegetable fields, including denitrification.
The objectives of this article are to
 1.
describe denitrification and the factors known to affect its rate,
 2.
present current methods available for the measurement of denitrification rate,
 3.
summarize available estimates of denitrification rate, and
 4.
attempt to provide guidelines on how to account for potential denitrification losses in fertilizer programs.
Factors Affecting Denitrification Rate
 The N cycle is a set of transformations that affect N in the biosphere, by which N passes from air to soil, to soil organisms, and back to air.
Denitrification is defined as the reduction of nitrate  to gaseous dinitrogen  by a series of reactions in which N goes from NO 3 to NO, 2  to NO  to N20 , and finally to N,.
Denitrification can be described as: 4 H+ + 5  + NO N 2 + 5 CO 2 where NO is in the soil solution and N, is a gas released into the atmosphere.
The most prevalent denitrifying bacteria in soils are species of Pseudomonas  and Alkaligenes , but approximately 30 genera have been confirmed to be capable of denitrification.
In the absence of oxygen , these heterotrophic bacteria use nitrate as a terminal electron acceptor in their cellular respiration.
The main factors that affect the activity of the denitrifying bacteria are nitrate concentration , soil organic matter content , moisture level , oxygen concentration , pH , and soil temperature.
In field conditions, these factors tend to act together, and it is often difficult to measure the specific effect of each of them.
The simultaneous occurrence of favorable factors for the growth of the denitrifying bacteria will result in a bacterial population increase and a subsequent increase in denitrifying activity.
Nitrate concentration does not limit denitrification at concentrations greater than 1.4 grain/gallon .
Denitrification rate increases with increasing NO, supply to a maximum and then declines with further increase in NO The decline may be resulted from high NO content inhibiting the enzymatic reduction of NO to N2O.
Nitrate is the preferred N-form by most vegetables and the optimum NO3-N NHratio is 3:1.
Hence, the presence of NO3 in a field (from the application of
 NO containing fertilizer or from the conversion of NH to NO by nitrification) may stimulate denitrification in situations where N supply was the factor limiting denitrification.
In soils, denitrifying activity is highly correlated with waterextractable organic carbon and is frequently stimulated by the addition of exogenous carbon.
Different organic compounds which support equal rates of denitrification may give different fractions of N2O in the products, suggesting that they may exert different effects on the enzymes involved.
Denitrification studies in columns on soils from Florida have found that when soil organic matter content is less than 0.91%, it becomes the limiting factor for denitrification, when NO 3 supply is not limiting.
In Florida, soil organic matter content may range from 1% to 2% in sandy soils to 40% to 60% in organic muck soils.
Hence, soil organic matter content is not likely to limit carbon availability for the growth of denitrifying bacteria in sandy soils..
The incorporation of crop residues from vegetables or cover crops, or the application of manure or compost amendments increased soil organic matter content.
However, increasing C:N ratio of the organic matter source tends to reduce the denitrification rate.
In incubation studies, denitrification rate was highest with vetch  residues  than with soybean  , corn  , and wheat  residues .
Information on the effect of crop residue from cover crops used in Florida such as sorghum Sudangrass  Moench) or sunhemp  on denitrification rates is currently limited.
Denitrification cannot occur in aerobic conditions.
Concentrations of dissolved oxygen above 0.2 parts per million, ppm  suppressed denitrification.
With constant soil water content, denitrification rate increases with decreasing oxygen concentration.
With constant oxygen concentration, denitrification rate increases with water content because bacteria must use oxygen in NO 3 instead of soluble O2.
In soils, the presence of oxygen and moisture content are linked because soil pores are either filled with water  or air.
Hence, soil texture and soil compaction affect denitrification by influencing the tortuosity of soil pore space, hence, the diffusion of substrates to, and products from, the microsites where
 denitrification occurs.
An increase of the water-filled pore space causes a decrease of the oxygen concentration level in the soil, which favors anoxic conditions and hence, an increase in denitrification rate.
Denitrification was reported to occur at low levels when soil moisture content was below 60%  and was reduced when soil moisture content was below 90%.
In the absence of rain, the seepage-irrigated soils of Florida can be characterized by decreasing water content from the impermeable spodic layer  to the surface of the soil.
Hence, the soil just above the impermeable layer is constantly saturated and anaerobic, which favors denitrification.
Alternating or contiguous aerobic and anaerobic conditions stimulate concurrent nitrification and denitrification, which may result in greater total N loss from the soil than would be found under continuous anaerobic conditions.
unmulched green bean or potato fields may be lower than those in adjacent mulched fields.
Soil fumigants are often used in vegetable production to reduce soilborne pathogens.
Broad-spectrum fumigants such as Telone C-35  or chloropicrin also reduce all the levels of denitrifying bacteria.
During the three weeks following fumigation, denitrification may occur at reduced rates, or may not occur at all.
During most of the growing season, the conditions in Florida's irrigated soils are overall conducive to denitrification:
 Nitrogen and nitrate levels are high.
Organic matter is incorporated in the tillage zone thereby supplying a carbon source.
The water gradient above the impermeable layer creates aerobic and anaerobic conditions in proximity to one another.
Soil pH is between 6 and 7.
Soil temperature is between 60F and 80F  during most of the year.
pH affects denitrification rate and the type of N form released.
Denitrification rate was very low at pH = 4.1, increased with increasing pH, and was very rapid in the pH range of 7.5 to 8.2.
As pH decreases below 7, nitric  and nitrous oxides  become the dominant by-product, while N2O and N, are the dominant by-products at pH above 7.
Hence, liming of agricultural soils or using alkaline irrigation water favors the activity of denitrifying bacteria.
While all these factors contribute to denitrification, spatial and temporal variability of these factors affect the actual denitrification rate.
Moreover, the actual denitrification rate cannot exceed the rate allowed by the most limiting factor.
Therefore, actual denitrification rates and potential denitrification rates may be different in the field.
Methods for Measuring Denitrification Rate
 The Association of Official Analytical Chemists  has yet to approve a method to measure denitrification in soils.
Current methods used to quantify denitrification come from different scientific domains, such as ecology, agriculture, and industrial engineering, and reflect different interests in different aspects of denitrification.
Studies comparing different methods to determine denitrification reported different denitrification rates based on methodology used.
Hence, the appropriate method should be identified and selected before measurements begin.
Methods used to measure denitrification may be grouped in two types: the indirect methods and the direct methods.
The three most used indirect methods are based on nitrate disappearance, nitrate/chloride ratios, and N balances.
The direct methods used to determine denitrification activity in fields include isotopic methods , acetylene inhibition , gaseous diffusion ,
 prediction models that use micrometeorological data  or simple field measurements , and computer simulation.
Among these direct methods, the acetylene inhibition technique  is the most widely used with agricultural soils and can be used in the laboratory as well as in the field.
The enzyme nitrous oxide reductase normally catalyzes the conversion of N2O into N2.
When its activity is inhibited by acetylene , N2O accumulates.
As N,O concentration in the air is much lower than that of N2, it can then be quantified by gas chromatography with negligible background interferences.
The protocol for the AIT includes:
 1.
fabrication of a denitrification potential solution ,
 2.
mixing the soil sample with the denitrification potential solution in an air-tight capped Erlenmeyer flask,
 3.
adding ethylene into the flask,
 4.
calculating the volume of the headspace in the flask,
 5.
keeping the flask continuously agitated to prevent effects of diffusion,
 6.
taking air space samples with a syringe, and
 7.
injecting the head-space sample in a gas chromatograph.
The advantages of the AIT include an increase in sensitivity compared to other methods, the use of natural nitrate substrate pool, the possibility to automate and analyze large number of samples, and a relatively low cost compared to the other methods.
While simple and versatile, the AIT has some limits:
 Acetylene is a poor nitrous-oxide reductase inhibitor at low nitrate concentrations.
Acetylene may inhibit nitrification.
Acetylene may be metabolized by soil microorganisms.
Contaminants may be present in the acetylene.
Therefore, the AIT method is better suited for short-term measurements of denitrification.
Direct and indirect methods may be used to measure denitrification in the field or in the laboratory.
However, it is accepted that three conditions should be met to make valid estimates of field denitrification rates from laboratory measurements.
First, the internal environment of the experimental apparatus should be subjected for the duration of the experiment to the same episodic or seasonally cyclical changes that occur in the external environment of the field site.
Also, the soil substrate being studied should have inherent heterogeneity and natural properties like those of the soil at the field site.
Finally, the monitoring and measuring devices and sampling methods should not produce artifacts or create artificial conditions that may alter soil processes.
Progress in understanding and quantifying denitrification has been limited by the lack of uniformity in approaches and standardization in units used to report denitrification rate.
Singunga  proposed that soil samples for estimation of potential denitrification should be taken under saturated conditions , in the presence of excess NO 3 and C, and on undisturbed soil cores; soil temperature  and pH should also be cited.
The reporting unit for denitrified N should be expressed in parts per million, ppm,  N per hour.
Soil mass should be reported on a dry weight  basis.
Compilation of Available Estimates of Denitrification Rates
 Denitrification estimates found in the literature from short-term studies  from worldwide ecosystems are overall in good agreement.
Short-term studies reported denitrification rate in soils from unfertilized areas of 57.6 ppm per day  N in a hardwood forest  and 0.03 to 0.07 ppm  N for uncultivated land.
Other short-term studies reported denitrification rates in highly fertilized agricultural fields  ranging from 0 to 1 ppm per day  N.
However, no consensus may be found in published denitrification estimates when all estimates are converted to the same unit and on a yearly basis.
By compiling and transforming 94 denitrification rates found in the literature, the average yearly denitrifcation rate  was 171.4 + 272.3 lb/acre/year  N.
These results show that reliable daily estimates of denitrification are available, but their occurrence on a year-round basis is poorly represented by the
 extrapolation of short-term estimates.
There is no guarantee that a denitrification rate measured over a short period will be sustained over a long period of time.
Few denitrification estimates are available from vegetable fields in Florida.
Due to the differences of the environment, N rate, soil organic matter content, and the crop tested, the estimates from different sources are usually not comparable.
There are research data available in the literature.
Approximately 23% of the N fertilizer was unaccounted for in an N balance made on bell pepper grown in lysimeters.
The N not accounted for was assumed to be lost by denitrification.
As the fertilizer rate used in this experiment was 300 lb N/ acre , the potential denitrification estimate from this study was 25.7 ppm  per season.
In another study, denitrification rate was measured every two weeks on undisturbed soil cores from an EauGallie fine sand with the acetylene inhibition technique.
Soil cores were collected from a field where two tomato crops  were grown with seepage irrigation and fertilized each with an N rate of 200 lbs/acre.
Actual denitrification rates ranged between 1.012 to 0.016 ppm per day.
Actual denitrification measurements were consistently greater than the ones predicted by the LEACHN model.
However, these two denitrification estimates are of limited practical use to help predict the importance of denitrification in designing fertilizer programs for vegetables.
The denitrification estimate from lysimeter-grown bell pepper was obtained by difference  and is likely to over-represent denitrification rate in the field due to the accumulation of error in the fraction determined by difference.
The depth of soil sampling in the tomato field was 0-8 inches .
A shallow sampling depth was used in this study to assess the effect of sludge amendment incorporated in the top 8 inches  of soil on denitrification.
Air content, and thereby oxygen availability in surface soil is much greater than that of the deeper soil layers.
Hence, the denitrification estimate was largely underestimated from the tomato field.
These results have some implications on fertilizer recommendation and nutrient management.
First, denitrification estimates currently available in the literature were made in studies in which the focus was not fertilization management.
Hence, it is unlikely that any of them truly represent field-scale denitrification rates for a whole growing season.
Therefore, there is no basis for systematically increasing fertilizer applications by amounts that poorly represent denitrification.
The second consequence is that
 fertilizer recommendations need to be based on fertility trials conducted under conditions like those of production.
Even if denitrification rate is not determined, it is at least factored into the recommendation.
Hence, fertilizer recommendations may be higher in denitrification-prone areas  than in other areas  for similar varieties, production seasons, and yield goals.
In addition, improved N management may be achieved through regular monitoring of crop nutritional status by using whole-leaf analysis or fresh petiole-sap testing.
With the difficulties associated with long-term field measurement of denitrification, denitrification may be indirectly determined through complete N balances that would include measurement of the different N fractions.
Another implication of denitrification on fertilizer management is temporary flooding during the off season.
Summer rains often result in the complete flooding of the vegetable fields.
Although specific data are not available, it is likely that residual N may be denitrified at that time.
As it reduces the potential for N loss to the ground and surface water, maintaining conditions favorable for denitrification during non-cropped periods could become a possible BMP on flatwood soils.
Table 1.
Indirect methods for measuring denitrification in soils.
Chapter 5: Corn Growth and Development
 As the corn plant develops, it undergoes physical and biochemical changes, which impact its response to different management decisions.
By understanding these changes, management inputs can be made more efficient.
The purpose of this chapter is to highlight corn growth stages.
The rate that corn grows and develops changes during the season.
Young corn plants increase in weight slowly, but as more and more leaves are produced, the rate of dry-matter accumulation increases.
Under normal growing conditions, the rate of plant development is largely dependent on temperature.
Environmental factors, such as water and nutrient deficiencies, can alter the relationship between plant growth and temperature.
In South Dakota, water and nitrogen  are important resources that limit corn growth and development, and ultimately influence yield.
If water, nitrogen, or other resources become limiting, especially when the plant is rapidly growing, yield is often reduced.
Other factors can also stress corn plants, thereby limiting growth and reducing yield.
Disease and insect infestations can interfere with water and nutrient uptake or severely damage the plant to the point of yield loss.
Weeds have many effects on corn growth, including causing the down regulation  of many genes during the weed-free period and creating direct competition for water, nutrients, and light.
Stress from temperature and water impacts nutrient availability and susceptibility to pests.
Many management decisions consider the stage of growth and development of the crop.
For example, some pesticide products are labeled for use only at
 Figure 5.1 Dry-matter accumulation in corn plant over time.
certain stages because of potential for crop damage or other undesirable effects.
Fertilizer applied at the right time can provide a greater crop response; however, if fertilizer is applied at the wrong growth stage, benefits can be reduced or negative responses can occur.
Water stress at certain stages is more critical than at other stages.
Management efficiency can be improved by matching the crop's need to the treatment.
Understanding how a corn plant grows and develops is important for maximizing efficiency.
A number of classification approaches can be used to identify a corn plant's growth stage.
However, in South Dakota the most widely used system is the Iowa State classification approach.
This system divides corn growth and development into vegetative  and reproductive  stages.
The VE  occurs when the coleoptile pushes through the soil surface.
After emergence, the vegetative stages are designated numerical subdivisions as V1, V2, V3; through Vn where n is the number of leaves with collar visible until the tassel emerges.
The collar is where the leaf blade visually breaks away from the sheath and the stalk of the corn plant , and vegetative growth stages are based upon the number of visible leaf collars.
Leaves within the whorl, not
 Figure 5.2 Corn 1st, 2nd, and 3rd leaf collars.
Figure 5.3 Corn growth stages typically observed in South Dakota.
Table 5.1 Growth and development stages in corn.
Vegetative Stages	Reproductive Stages
 VE	Emergence	R1	Silking silks visible outside the husks
 V1	First leaf collar	R2	Blister kernels are white and resemble a blister in shape
 V2	Second leaf collar	R3	Milk kernels are yellow on the outside with a milky
 V3	Third leaf collar	R4	Dough milky inner fluid thickens to a pasty consistency
 V	nth leaf collars visible	R5	Dent nearly all kernels are denting
 VT	Tasseling last branch of tassel is completely visible	R6	Physiological maturity the black abscission layer has
 fully expanded and with no visible leaf collar are not included.
For example, a plant with 3 collars would be called a V3 plant, although more than 3 leaves may be showing on a plant.
It is important to note that the number of leaves vary depending on the corn hybrid and environmental conditions.
In South Dakota, early season  can begin reproductive development after the V12 stage.
It is not uncommon for late maturing hybrids  to develop more leaves after the V12 growth stage.
At about V6 stage, the small lower leaves are torn from the plant due to increasing stalk and nodal root growth.
This loss of lower leaves needs to be taken into consideration when determining the vegetative stage.
Reproductive stages begin at silking  and end at maturity or "black layer".
Under warm, moist conditions, corn will germinate and emerge 4 to 6 days after planting.
Optimal temperature and soil water are critical at this time.
Germination and emergence are delayed when soil water is limiting because the seed needs to imbibe water to germinate.
Alternatively, too much water also delays emergence and root development.
In residue-covered soils or if spring air temperatures are low, germination may be slow due to cool soil temperature.
Temperatures below 50F may delay seed germination.
Ideally, corn should be planted at a depth of 1.5 to 2.0 inches.
Shallow planting 1.5 inches) into warmer soil can accelerate emergence but may result in poor root development.
Planting deeper than 2 inches may result in first leaves emerging below the soil surface.
The first leafy structure that appears aboveground is the coleoptile , followed by true leaves.
Warm, moist, and well-aerated soil conditions promote vigorous growth and development.
New leaves are produced at a single "growing point" near the tip of the stem.
The "growing point" is below the soil surface for up to 4 weeks after planting.
When the growing point is below the soil surface, the crop usually survives light frost or minor hail.
However, corn plants are most susceptible to flood damage during this stage and flooding can results in severe yield losses.
Corn roots do not explore a significant volume of soil during early growth stages but develop rapidly as the plant develops.
Corn has seminal and nodal roots.
Seminal roots emerge immediately after germination, cease growth at V3, but continue to function throughout the life of the plant.
Nodal roots are initiated at formation of the first node  and continue to develop until kernel blister.
By the V6 growth stage, nodal roots become the major supplier of water and nutrients.
Nutrient deficiencies, especially phosphorus , are common early in the growing season if soil is cool and wet.
The application of starter fertilizer will usually prevent this problem.
If fertility levels are sufficient, early season nutrient deficiencies often disappear and usually do not reduce yield.
Scouting fields for weeds are crucial during early growth.
Figure 5.4 Corn seedling showing seminal and nodal roots.
Six-Leaf  to Seven-Leaf  Stage
 In South Dakota, corn is usually at V6 in early to mid-June.
At the V6 stage, rapid stem elongation begins and ear shoots begin to develop.
A new leaf emerges about every three days, while lower leaves begin to degenerate.
The growing point is above the soil surface and frost or hail can cause significant damage.
The root system is well-developed and distributed in the soil, and the plant has an improved capacity to absorb nutrients.
Scouting to determine whether additional fertilizer is needed is critical at the V6 growth stage.
Sidedressing nitrogen  is most effective when applied between V6 and V8.
In addition, scouting for corn rootworm and other root-pruning insects is also critical.
Because control options for these insects are limited, the best option is to plant resistant or genetically modified hybrids.
Eight-Leaf  to Eleven-Leaf  Stage
 At this stage many ear shoots, which are potential ears, are present.
Eventually, only one or two upper shoots form harvestable ears.
The number of ears formed depends on the corn hybrid, with prolific hybrids forming more than one ear when planted at low plant populations.
At this stage, deficiencies in macronutrients and micronutrients can start to show.
If not corrected, nutrient deficiencies can seriously restrict leaf growth.
By V10, the plant is growing rapidly, with new leaves appearing every 2 to 3 days.
The plant requires substantial amounts of water and nutrients to maintain this growth rate.
Stress from pests, heat, lack of nutrients, and/or water can slow development.
Twelve-Leaf  to more leaves
 The number of leaves on a plant is dependent on the plant's maturity rating and the type of corn.
For example, silage corn may have more leaves than corn designed to produce grain.
The higher the maturity rating, the higher the number of leaves.
The potential number of kernels per ear and ear size are determined at the V12 growth stage.
The rate of corn plant development at the V12 stage is influenced by hybrid maturity.
Earlier-maturing hybrids progress through these stages in a shorter time, resulting in smaller ears compared to later-maturing hybrids.
If water and nutrient availability can support a higher population, yield differences between early and late hybrids can be equalized by increasing plant density or population.
Stress at the V12 stage can reduce kernel numbers and ear size.
The plant has a peak water demand during this growth stage and it can use one-quarter of an inch per day.
The corn plant also needs and utilizes large amounts of nitrogen, phosphorus, and potassium at this stage.
Severe hailstorms that strip leaves and break tassels can result in complete crop loss.
The tasseling stage occurs 2 to 3 days before silking.
At this stage, the plant has reached full height and the last branch of the tassel is fully visible, but silks have not yet emerged from the ear shoot.
The length of time between VT and R1  varies depending on the corn hybrid and environmental conditions.
Pollen shed usually takes place from late morning to early evening.
At this stage, the impact of a hailstorm can be very severe compared to any other corn growth stage, since all leaves have emerged.
Any damage to or complete loss of the tassel may result in very poor to no grain formation.
The emergence of silk  marks the first stage of the reproductive period.
Every potential kernel  on the ear grows its own silk.
Silks begin to elongate soon after the V12 stage.
At the R1 stage, the silks emerge and capture pollen shed from the tassel.
Pollen captured by the silks fertilizes ovules on the cob within 24 hours, which then develop into kernels.
Pollen shed typically occurs during early or mid-morning, when moisture and temperature conditions are favorable.
This stage is one of the most crucial reproductive stages and unfavorable environmental conditions can severely reduce yield.
Dry  and hot 95F) conditions result in reduced fertilization because of the drying of the exposed
 silks and killed pollen.
With no fertilization, ears are barren.
Silks grow at a rate of approximately 1.5 inches a day.
The silks continue to grow until pollen is captured and germinate or until they degrade as they mature.
Environmental conditions such as drought stress can result in delayed silk elongation and emergence.
Generally, silks remain receptive to pollen for up to 10 days after silk emergence, though they start to deteriorate only five days after emergence.
Under favorable environmental conditions, there is synchrony between pollen-shed and silk emergence making silk receptivity of little concern.
Insect pests, such as corn rootworm destroy silks through feeding and can produce reduced yields.
To minimize losses, fields should be scouted for corn rootworm beetles at silking  and controlled if populations exceed the economic threshold.
Potassium  uptake is complete at silking, but nitrogen  and phosphorus  uptake continues.
If N and P are limiting, the plant will attempt to compensate by moving these nutrients from older leaves into upper leaves or the developing grain.
At this stage, Nand P-deficiency symptoms can be observed in lower leaves.
Unfortunately, nutrient application either at this time or later in development will not make up for these deficiencies.
Kernel Blister Stage 
 After pollination, kernel formation begins.
The kernels at the R2 stage are whitish and shaped like blisters.
They appear approximately 10 to 14 days after silking.
At this stage, silks turn brown and dry rapidly.
Starch begins to accumulate in the kernel as the plant initiates a period of kernel fill.
At the R2 growth stage, the radicle, coleoptile, and the first embryonic leaf have formed in the embryo.
The kernel moisture content at the R2 stage is about 85%.
Any severe stress at pre-blister and blister stage can result in aborted kernels and reduce the number of kernels on the cob.
At this stage, the plant will need 960 growing-degree days , also called growing-degree units, to reach physiological maturity.
Additional water at or after R2 does not enhance yield, slows dry-down, and may encourage stalk and grain diseases.
Kernel Milk Stage 
 The kernel milk stage occurs approximately 22 days after silking.
At this stage, kernels are mostly yellow on the outside, starch accumulation occurs rapidly, kernels contain a milky white fluid, and cell division in the endosperm is complete.
Observable kernel growth is mainly due to cell expansion and starch accumulation, severe stress can cause kernel abortion.
The kernel moisture content is about 80%, and approximately 880 GDD are required to reach physiological maturity.
Although not as critical as the R1 growth stage, stress at this time can reduce kernel size and weight.
Kernel Dough Stage 
 As the kernels mature to the dough  stage, they change from a milky consistency to soft and sticky.
At R4, the kernels have accumulated nearly half of their mature weight and the cob has a color ranging from light red to pink.
At this stage, four embryonic leaves are formed and the kernel moisture content is approximately 70%.
Unfavorable environmental conditions or nutrient deficiencies can reduce kernel weight.
Kernel Dent Stage 
 At the R5 growth stage, nearly all of the kernel crowns are denting, the moisture content is approximately 55% , and a distinct horizontal line called the milky line can be seen between the yellow (starchy-
 solid) and white  areas on the kernel.
As the kernel matures and starch hardens, this line slowly progresses to the tip end of the kernel.
A hard frost at R5 can kill the plant, thus reducing yield and kernel development.
Corn plants killed at this stage generally have low test weight and a slower drydown rate.
Selecting a hybrid that matures 2 to 3 weeks before fall frost reduces these risks.
If early frost kills the plant, the crop can be harvested and ensiled as high-moisture grain for animal feed.
The corn plant is at physiological maturity  about 55 to 65 days after silking.
At this stage, kernel dry-weight has reached its maximum, the kernels are physiologically mature and safe from frost damage, the moisture content ranges from 30% to 35%, the starch line has advanced to the kernel tip, and a black layer has formed at the base of the mature kernels.
The black layer forms from the tip of the kernels to the basal kernels.
Severe stress after this stage has little effect on grain yield, unless the integrity of the stalk or ear is compromised by disease such as stalk rots or insect feeding.
At this time, allowing the crop to dry in the field reduces drying costs if the crop is to be harvested for grain.
Moisture content of 15% allows corn to be stored safely for less than six months.
For long-term storage, corn should be dried to 12% moisture to avoid spoilage.
Hybrids have subtle differences in growth and development.
Early harvest is rarely profitable because of drying costs or dockage.
Corn can be left in the field if stalks maintain strength, ear drop is not a problem, and there is limited risk of ear and kernel rots especially under hot, dry conditions.
Harvest loss from lodging and ear drop can be significant in fields damaged by European corn borer or Western bean cutworm.
In these situations, early harvesting to reduce harvest losses should be weighed against drying costs.
Scouting to assess stalk condition, ear retention, ear rots, and grain moisture is recommended.
Growing-degree Days: Rating Corn Hybrids
 Regional differences in the corn growing season have resulted in multiple methods to match hybrid characteristics to environmental conditions.
Corn growth rate is controlled primarily by temperature, and this is often characterized by a calculation called growing-degree days.
Most seed corn companies rate hybrid maturity based on GDD or heat units.
The GDD accumulation for a single day is the average of the low and high temperature, minus 50F.
The calculation subtracts 50F because corn plants have limited growth below 50F.
If the low temperature for any given day is < 50F, the low temperature is defined as 50F, and if the temperature is > 86F, the high temperature is defined as 86F.
This method of calculating GDD is often referred to as the  system.
Different pests or crops have different critical values.
Example calculations are provided in Chapter 10.
GDD are calculated for each day beginning with the day after planting.
The GDD accumulation for the growing season varies depending on the location and year.
The number of GDD required for the corn plants to reach a particular stage of development is fairly consistent.
Tables 5.2 and 5.3 show the GDD needed for a plant to reach a certain vegetative or reproductive stage.
The duration of the growing season for corn hybrids is directly related to their GDD requirements, with late-maturing hybrids or long-season hybrids requiring more GDD than shorter-season hybrids.
The U2U  Project website can be used to calculate the date of different growth stages based on the hybrid and planting date.
Table 5.2 Comparison between leaf collar and FCIC1 corn growth staging systems for a 120-day  hybrid
 FCIC	Leaf Collar	Description	Days/Stage	GDUs/Stage	Days after	Seeding	GDUs after	Seeding
 -	V0	Seeding to Germination	5 10	100 150	5 10	100 150
 -	VE	Coleoptile Opens	2 4	66	7 14	166 216
 V2	V1	1st Leaf Collar	3	66	10 17	232 282
 V2	2nd Leaf Collar	3	66	13 20	298 348
 V4	V3	3rd Leaf Collar	3	66	16 23	364 414
 V5	V4	4th Leaf Collar	3	66	19 26	430 480
 V6	V4	4th Leaf Collar	3	66	19 26	430 480
 V7	V5	5th Leaf Collar	3	66	22 29	496 546
 V8	V6	6th Leaf Collar	3	66	25 32	562 612
 V9	V7	7th Leaf Collar	3	66	28 35	628 678
 V10	V7	7th Leaf Collar	-	-	-	-
 V11	V8	8th Leaf Collar	3	66	31 38	694 744
 V12	V9	9th Leaf Collar	3	66	34 41	760 810
 V13	V10	10th Leaf Collar	3	66	37 44	826 876
 V14	V11	11th Leaf Collar	3	66	40 47	892 942
 V15	V12	12th Leaf Collar	3	66	43 50	958 1,008
 V16	V13	13th Leaf Collar	3	66	46 53	1,024 1,074
 V17	V14	14th Leaf Collar	3	66	49 56	1,090 1,140
 V18	V15	15th Leaf Collar	2	48	51 58	1,138 1,188
 V17	17th Leaf Collar	2	48	55 62	1,234 1,284
 V18	18th Leaf Collar	2	48	57 64	1,282 1,332
 V19	19th Leaf Collar	2	48	59 66	1,330 1,380
 V20	20th Leaf Collar	2	48	61 68	1,378 1,428
 V	nth Leaf Collar
 -	-	-	-
 VT	Tassel Extended No Silks	4	100	65 72	1,478 1,528
 All values are approximations, as the values may vary over years, production environments, and locations.
1 Federal Crop Insurance Corporation , operated by the United States Department of Agriculture, Risk Management Agency
 2 Relative maturity 
 Table 5.3 Comparison between leaf collar and FCIC1 corn growth staging systems for a 120-day  hybrid
 Silked	R1	Silked Pollen Shed	4	100	69 76	1,578 1,628
 Silks Brown	Silks 75% Brown	5	125	74 79	1,703 1,753
 Pre-Blister	No Fluid in Kernels	4	100	78 85	1,803 1,853
 Blister	R2	Kernels are watery	4	100	82 89	1,903 1,953
 Early Milk	Kernels Begin to Yellow	4	100	86 93	2,003 2,053
 Milk	R3	Kernels Yellow, No Solids	5	100	91 98	2,103 2,153
 Late Milk	Kernels Contain Semi-Solids	4	100	95 102	2,203 2,253
 Soft Dough	R4	Kernels Pasty	5	100	100 107	2,303 2,353
 Early Dent	Kernels Begin to Dent	5	100	108 115	2,403 2,453
 Dent	R5	Kernels Soft but Dented	5	125	113 120	2,528 2,578
 Late Dent	Kernels Dented but Drying	5	125	118 125	2,653 2,703
 Nearly Mature	Kernel Embryo not Hard	5	125	123 130	2,778 2,828
 Mature	R6	Black Layer	5	125	128 135	2,903 2,953
 All values are approximations, as the values may vary over years, production environments, and locations.
1 Federal Crop Insurance Corporation , operated by the United States Department of Agriculture, Risk Management Agency
 2 Relative maturity 
Drip irrigation controls soil salinity under row crops
 Keeping soil salinity low in the root zone is crucial to growers of salt-sensitive crops.
This study investigated patterns of soil salinity under surface and subsurface drip irrigation.
High soil salinity occurred midway between drip laterals for both irrigation methods and above the drip tape for subsurface drip irrigation.
Rainfall leached the salts from the zones of high salinity for both irrigation methods.
Drip irrigation of row crops is increasing in California's coastal valleys and along the west side of the San Joaquin Valley.
In some coastal areas, the salinity of the irrigation water exceeds
 Salt accumulation is apparent In the white lines on the soil surface along row crops irrigated with subsurface drip.
Salts above the drip tape are driven toward the surface, whereas salts below the tape continue to move down.
1 decisiemen per meter.
Because salt-sensitive and moderately salt-sensitive crops such as lettuce, broccoli, cauliflower, tomatoes, onions, celery, garlic and strawberries are grown in these areas, salinity management is necessary to prevent yield reductions.
A number of studies have been conducted on soil salinity under surface drip irrigation.
Researchers at the U.S.
Salinity Laboratory investigated salt distributions under a traveling trickle irrigation system before and after simulated rainfall.
The irrigation water salinity was 2.2 dS/m.
Water was applied at rates to provide leaching fractions of 5%, 10% and
 25%.
Results showed that before the rainfall, soil salinity was low near the drip laterals and high near the soil surface midway between laterals.
The zone of low salinity was the largest for the highest leaching fraction and the smallest for the lowest leaching fraction.
Small changes in soil salinity occurred with depth below the lateral for all three leaching fractions.
Midway between laterals, salinity rapidly decreased with depth for the top 6 inches , and then gradually decreased with depth.
After 1.2 inches  of simulated rainfall, soil salinity decreased near the soil surface midway between laterals.
The initially high salt concentrations near the sur-
 Fig.
1.
Salt patterns under surface drip irrigation before and after rainfall for leaching fractions of 5% and 25%.
face were driven downward by the rainfall.
Changes in soil salinity caused by rainfall near the emitter were small.
Another research project, conducted in Israel, studied root distributions with respect to soil salinity under surface drip irrigation for row crops.
This study showed patterns of soil salinity similar to those in figure 1.
Maximum soil salinity near the soil surface occurred at about 8 inches  from the emitter.
However, maximum root density occurred near the emitter, where soil salinity was the lowest.
Another Israeli project studied salt and water distributions under surface drip irrigation for lateral spacings of 39 and 79 inches.
Water applications were 75% and 100% of the amount applied to an adjacent sprinkler-irrigated plot.
Soil type was a loam.
The 39-inch spacing was one lateral per cotton row ; the 79-inch spacing was one lateral every second row.
Again, the results showed salt patterns similar to those in figure 1.
Salt accumulation occurred above the 12inch  depth for all treatments except near the emitters.
Below 12 inches, little change in soil salinity occurred with depth.
However, nearsurface soil salinity between laterals of the 39-inch spacing was three to four times higher than that of the 79inch spacing.
Both soil water content and soil salinity data showed that leaching was occurring below the emitters for the 100% water treat-
 ment.
The maximum depth of salt and water movement under the emitter was about 39 inches for the 75% treatment.
Sampling in Santa Maria Valley.
A literature review revealed little information on salt patterns for subsurface or buried drip irrigation of row crops under field conditions.
For this study, we sampled two locations in the Santa Maria Valley to determine the patterns and magnitudes of soil salinity under drip irrigation of vegetables.
Sampling occurred over about 12 months to evaluate changes in the distributions.
Soil types were a clay loam and a fine sand.
We took samples in the clay loam soil during stand establishment of a lettuce crop , just before harvest , after a winter of rainfall , and after the following lettuce crop.
Samples were taken in a grid across the bed perpendicular to the drip tape.
During the September sampling, we also took samples parallel to the drip tape.
Cauliflower was grown at the fine-sand site.
Sampling in the fine sand was done on
 Fig.
2.
Salt pattern, August 1992.
Fig.
3.
Salt pattern, October 1992.
Fig.
4.
Soil salinity after 14 inches  of rainfall.
Fig.
5.
Salt pattern, September 1993.
the same dates as for the clay loam, with no regard to stage of growth.
The salinity of the irrigation water at the clay loam site was 2.5 dS/m; at the fine-sand site it was 2.2 dS/m.
Depth of the drip tape was 5 inches.
Bed and lateral spacing was 38 inches.
Emitter spacing was 12 inches.
Two plant rows per bed were used for the lettuce, and one plant row per bed for cauliflower.
Due to the difficulty of measuring flow rates, we did not measure the water applied to each field.
Salinity low near tape.
In August 1992, soil salinity near the drip tape was less than 1.5 dS/m at the clay loam site.
Soil salinity ranged between 1.5 and 2.0 dS/m throughout the soil profile at depths below the drip tape except near the edge of the bed.
At horizontal distances less than about 6 inches  from the drip tape and at the depth of the tape, soil salinity changed slightly with distance from the tape.
Beyond 6 inches, soil salinity increased considerably, particularly near the edge of the bed.
Soil salinity increased rapidly above the drip tape as depth decreased, and was highest near the soil surface.
This pattern of very high salinity occurred across the bed, where salinity exceeded 5 dS/m.
The depth interval of the high-salinity zone was smallest directly above the drip tape and largest near the furrow.
The soil salinity near the drip tape was less than 1.5 dS/m, which is less than the salinity of the irrigation water.
This is a consequence of the standard method used to measure soil salinity.
Soil samples are dried and ground, then distilled water is added to make a saturated paste.
The salinity of the extract of the saturated paste is the measure of soil salinity.
Because of the dilution effect, the salinity of the extract can be less than the salinity of the irrigation water under high-frequency irrigation if the soil sample is taken close to the water source.
We found a similar pattern of soil salinity for the October 1992 sampling, except that salinity levels were higher in the vicinity of the drip tape.
The soil salinity of the soil
 profile within 6 inches  of the drip tape was between 2.0 and 2.5 dS/m, compared to between 1.0 and 1.5 dS/m for the August sampling.
The reasons for this increase are not clear, but it may reflect either a soil salinity still increasing toward an equilibrium value or a decrease in the leaching fraction compared to the earlier crop.
Soil salinity near the soil surface had also increased.
Soil salinity of the depth interval that earlier was between 3 and 5 dS/m was now between 5 and 10 dS/m.
Differences in sample processing can cause variations in soil salinity monitored over time.
Saturation percentages that differ considerably  between sampling dates could account for some of the salinity differences with time.
Average saturation percentages, however, ranged between 33.6 and 34.2, indicating that salinity differences with time were unaffected by sample processing.
These salinity patterns show that no leaching of salts occurred above the drip tape during irrigation, as expected.
Salt in the water flowing upward above the drip tape, in response to evapotranspiration, accumulated in the top 2 to 3 inches.
Near and below the drip tape, leaching was considerable compared to the rest of the root zone as indicated by the low soil salinity and small changes with depth.
As horizontal distance from the drip tape increased less leaching occurred, and consequently high soil salinity OCcurred near the edge of the bed and
 beneath the furrow.
Similar patterns and magnitudes were found at the fine-sand site.
In March 1993, after nearly 14 inches  of winter rainfall, the salinity near the surface was reduced considerably.
Uniform salinity was found throughout the soil profile, except under the furrow, where soil salinity was higher.
Interestingly, soil salinity near the drip tape was similar to that shown in figure 3, suggesting little leaching from rainfall.
However, these salinity levels may reflect the downward movement and dispersion of the near-surface salts due to multiple rainfall events.
The higher soil salinity under the furrow suggests less leaching compared to the rest of the profile.
This may be due to furrow compaction from wheel traffic , which may have resulted in surface runoff of rainfall.
A different behavior was found at the fine-sand site for the March samples.
Soil salinity throughout most of the soil profile generally was between 1 and 1.5 dS/m.
Under the furrows, soil salinity ranged between about 0.4 and 0.6 dS/m.
Infiltration of water from rainfall ponding in the furrow may have caused lower salinity under the furrow than elsewhere in the profile.
In September 1993 the salt pattern shown in figure 5 occurred at the clay loam site.
After one crop season, salinity had again increased to very high levels near the soil surface.
Salinity in the vicinity of the drip tape was similar to that in figure 2.
Near
 Greater than 10 dS/m
 20 in.
40 inches 
 Fig.
6.
Salt pattern along lateral length, September 1993.
and below the drip tape, soil salinity decreased compared to the March salinity.
This indicates that leaching from the drip irrigation occurred during this crop season.
By September 1993 near-surface soil salinity increased at the fine-sand site to levels exceeding 6 dS/m.
Salinity under the furrows also increased.
However, soil salinity in the fine-sand near and below the drip tape changed little from the March levels.
Figure 6 shows a uniform salt pattern near the surface with distance along the lateral.
No pattern reflecting salt accumulation midway between emitters was found.
This probably reflects the small emitter and plant spacings.
Similar behavior was found at the fine-sand site.
Methods of salinity control
 Salinity control requires the application of sufficient water during irrigations to leach salts below the root zone.
Under subsurface drip irrigation of row crops, wetting patterns during irrigation allow leaching of salts near the drip tape.
During irrigation, little leaching occurs midway between laterals, and no leaching OCcurs above the drip tape.
Thus salinity control under drip irrigation requires leaching by rainfall or with another irrigation method, such as sprinkler irrigation, if rainfall is insufficient.
The leaching water must leach the salts below the drip tape.
Once those salts are carried below the drip tape, irrigations with the drip system continue to move the salts downward.
Salts not initially carried below the drip tape accumulate above the drip tape.
Prior to planting, some growers control the salinity above the drip tape by building up the bed and then operating the drip system to carry the accumulated salts up into the builtup bed.
The built-up bed is then pushed into the furrow before planting.
This approach is justified because most of the very high soil salinity is concentrated in the top 2 to 3 inches  of the soil profile.
The saline soil displaced into the furrow should cause little problem because operation of
 the drip system prevents those salts from moving laterally toward the drip tape.
Little root development of shallow-rooted crops should occur near the edge of the bed and beneath the furrow.
Studies of root distribution suggest that little root development may occur beyond 6 to 8 inches  from the drip tape.
One concern is that small amounts of rainfall during the cropping season may move the accumulated salts near the surface down into the part of
 Fig.
7 A.
Pattern of soil water content  under a leaching fraction nearly equal to zero.
B.
Pattern of soil water content  under a leaching fraction of about 50%.
the root zone with the highest root density.
This highly saline soil water could affect crop growth; however, little or no information is available on any potential effect.
Some growers operate the drip system during rainfall in an attempt to prevent the downward movement and to dilute the highly saline soil water.
At one sampling location at the clay loam site, the drip tape was not centered in the bed, but instead was offset to one side.
This offset caused the zone of high soil salinity near the furrow of the far side to shift toward the center of the bed.
Salinity levels in the soil profile below the plant row on the far side were higher than OCcurred where the tape was centered between plant rows.
As in surface drip, the higher the leaching fraction, the larger the volume of low-salinity soil in the vicinity of the emitter.
Patterns of soil water content, as described by the soil matrix potential, were determined in a tomato field near Davis for a very small leaching fraction  and for a leaching fraction of about 50%.
The smaller the matrix potential, the higher the soil water content.
The leaching fractions were calculated using potential evapotranspiration data and amount of water applied to the field.
A relatively small volume of very wet soil OCcurred in the vicinity of and below the emitter for the small leaching fraction , whereas a much larger volume of very wet soil OCcurred under the higher leaching fraction.
Soil salinity was not measured at this location, but it would be expected that more leaching would occur around the emitter for the large volume of very wet soil.
Under other irrigation methods, the average root-zone salinity can be related to the leaching fraction and irrigation water salinity.
This approach assumes a certain soil-water uptake pattern by the plants.
This approach may be difficult to apply under drip irrigation because leaching and thus soil salinity vary greatly throughout the soil profile.
Near and below the emitter, actual leaching may be very high, reflected by the
 low soil salinity.
Above the drip tape no leaching occurs, and little leaching may occur near the furrow.
Plant uptake of soil water may also be highly variable throughout the profile, reflecting the pattern of soil water.
Therefore relating leaching fraction and average root-zone salinity may not be possible.
We can only conclude that the higher the leaching fraction, the larger the zone of relatively low-salinity soil around the drip tape.
The salinity of this zone reflects that of the irrigation water.
The depth of the drip tape may also be a factor in controlling soil salinity under subsurface drip irrigation.
The shallower the tape, the smaller the amount of rainfall or sprinkler-applied water needed to carry the salts below the drip tape.
Salts leached below the drip tape continue to be leached by the drip system.
Also, the shallower the tape, the more root zone of shallow-rooted crops in the low-salinity soil.
The shallower the drip tape, the smaller the amount of rainfall or sprinkler-applied water needed to carry the salts below the drip tape.
Also, a shallower tape leaves more root zone of shallow-rooted crops in low-salinity soil.
In some coastal areas with salinity problems, growers are under pressure to decrease deep percolation to reduce groundwater contamination from fertilizers leached from the root zone.
However, where salinity can affect crop production, some minimum amount of deep percolation is necessary for salinity control.
This minimum amount is the leaching fraction needed to prevent any yield reductions.
Studies conducted at the U.S.
Salinity Laboratory revealed that for surface drip irrigation with an irrigation water salinity of about 2 dS/m, minimum leaching fractions were 26% for lettuce, 17% for cauliflower, 14% for celery and 21% for tomatoes.
This means that 14 to 26% of the water applied by drip irrigation should percolate below the root zone to prevent crop yield reductions from excessive soil salinity.
tion.
This could also be a problem along the lateral between emitters, although no such pattern was found at these sites, where the emitter spacing along the lateral was 12 inches.
Zones of low salinity occur near the drip emitter for both types of drip irrigation.
This suggests that salt-sensitive and moderately salt-sensitive crops should be planted as close as possible to the drip lateral to provide a low-salinity environment for the roots.
The larger the leaching fraction, the larger the zone of low-salinity soil.
3.
Rainfall during the crop season can carry salts accumulated near the soil surface downward into the soil profile.
These salts move as a zone of highly concentrated soil water.
This zone of salinity may not be a problem under surface drip if the plant row is close to the lateral, since most of the root growth is near the lateral and the high-salinity water is midway between laterals.
However, this zone could be a problem under subsurface drip irrigation, where salt accumulation occurs above the drip tape.
4.
Leaching fractions of 14 to 26% may be needed under drip irrigation to prevent yield reductions of vegetable crops for an irrigation water with electrical conductivity equal to 2 dS/m.
Minimum leaching fractions are less with lower-salinity irrigation water.
2.
Under subsurface drip irrigation, a zone of very high salinity can occur above the drip tape.
This is caused by salt accumulation from the evapotranspiration of water flowing upward from the drip tape.
This zone of high salinity must be removed for stand establishment of salt-sensitive crops.
One method of salinity control includes leaching with rainfall or sprinkler irrigation to move the salts downward below the drip tape.
Another method consists of building up the bed, operating the drip system to carry the accumulated salts into the built-up bed, and then removing the built-up soil before planting.
B.R.
Hanson is Irrigation and Drainage Specialist, Department of Land, Air and Water Resources, UC Davis; and W.E.
Bendixen is Farm Advisor, Santa Barbara County, uc Cooperative Extension.
For additional information about the studies cited in this article, contact Blaine R.
Hanson.
1.
Zones of high soil salinity occur midway between laterals under both surface and subsurface drip irriga-
 The results of this study led to the following conclusions and recommendations for salinity management under drip irrigation of row crops.
Enterprise Budgets Silage Corn, Flood Irrigated, Southern Arizona Blase Evancho, Paco Ollerton Trent Teegerstrom and Clark Seavert
 This enterprise budget estimates the typical economic costs and returns to grow silage corn using flood irrigation in southern Arizona.
It should be used as a guide to estimate actual costs and returns and is not representative of any farm.
The assumptions used in constructing this budget are discussed below.
Assistance provided by area producers and agribusinesses is much appreciated.
As of the date of this publication, the price for labor, fuel, fertilizer, and chemicals is increasing dramatically, which makes developing a long-term budget difficult.
Therefore, a sensitivity analysis shows the net returns per acre as these inputs increase by 10 and 20 percent.
This budget is based on a 1,500-tillable acre farm.
As Arizona is experiencing irrigation water shortages, approximately 40 percent  of the total farm tillable acres are fallowed.
This fallowed land will allow adequate water to irrigate the following crops: 271 acres in cotton, 45 acres in silage corn, 90 acres in spring barley, 181 acres in durum wheat, and 316 acres of alfalfa hay.
The costs to fallow land are allocated to each crop based on its water use.
All crops are grown using flood irrigation.
Tractor driver labor cost is $17.89 per hour and general labor $14.55 per hour; both rates include social security, workers' compensation, unemployment insurance, and other labor overhead expenses.
For this study, owner labor is valued at the same rate as tractor driver rates, and all labor is assumed to be a cash cost.
Tractor labor hours are calculated based on machinery hours, plus ten percent.
Interest on operating capital for harvest and production inputs  is treated as a cash expense, borrowed for 6-months.
An interest rate of six percent is charged as an opportunity to the owner for machinery ownership
 The machinery and equipment used in this budget are sufficient for a 1,500-acre farm with 1,000 acres in crops.
The machinery and equipment hours reflect producing cotton, silage corn, spring barley, durum wheat, and alfalfa hay.
A detailed breakdown of machinery values is shown in Table 2.
Estimated labor, variable, and fixed costs for machinery are shown in Table 3, based on an hour and per acre basis.
The machinery costs are calculated based on the total farm use of the machinery.
Off-road diesel is $4.00 per gallon.
The cultural operations are listed approximately in the order in which they are performed.
A 175-hp tractor is used to pull the v-ripper, heavy offset disk, moldboard plow, landplane, lister, and planter.
A 125-hp tractor is used to pull the shredder/root puller, drill, cultivator, fertilizer spreader, and boom sprayer.
A charge for miscellaneous and other expenses is five percent of production costs, including additional labor, machinery repairs and maintenance, supplies and materials, tax preparation, memberships in professional organizations, and educational workshops not included in field operations.
In this budget the price of silage corn is $60 per ton, with an average yield of 30 tons, resulting in a gross income of $1,800 per acre.
Variable costs are $1,160 per acre and
 fixed cash costs of $351 per acre, giving a net return above variable cash costs of $289 per acre.
Total fixed costs are $84 per acre and total costs of $1,595 per acre, when all variable and fixed costs are considered.
The gross income minus total costs results in a $205 per acre return.
A breakeven price of $50.37 per cwt would be required to cover variable and fixed cash costs and $53.17 per cwt to cover total costs.
Tables 4 and 5 show the baseline net returns per acre for cash and total costs at various yields and prices as in this
 study.
Tables 6, 7, 8, and 9 show a sensitivity analysis of returns per acre as the price for labor, fuel, fertilizer, and chemicals are increased an additional 10 and 20 percent.
NOTE: Not included in these budgets are family living withdrawals for unpaid labor, returns to management, depreciation and opportunity costs for vehicles, buildings and improvements, inflation, property and crop insurance, and local, state, and federal income and property taxes.
Table 1.
Economic and Cash Costs and Returns of Producing Silage Corn, $/acre.
Returns	Unit	$/Unit	Quantity	Value
 Corn Silage	ton	$0.08	22,000.00	$1,760.000
 Variable Cash Costs	Price	Quantity	Unit	Labor	Machinery	Materials	Total
 Land Preparation and Maintenance
 V-Ripper	1.00	acre	$13.53	$34.60	$0.00	$48.13
 Offset Disk	1.00	acre	4.72	11.88	0.00	16.60
 Chisel	0.00	acre	0.00	0.00	0.00	0.00
 Landplane	1.00	acre	3.87	9.31	0.00	13.18
 Listen	1.00	acre	6.18	14.44	0.00	20.63
 Row Planter	1.00	acre	4.51	13.34	50.00	67.85
 Seed	$50.00	1.00	acre
 Ferlilizer Program	1.00	acre	1.88	373	379.50	385.11
 Nitrogen	$312.00	1.00	acre
 Phosphorus	$67.50	1.00	acre
 Boom Sprayer	2.00	acre	2.38	3.64	110.0	116.02
 Herbicides	$90.00	1.00	acre
 Insecticides	$20.00	1.00	acre
 Row Cultivator	3.00	acre	9.02	13.14	0.00	22.16
 Irrigation	80.03	0.00	302.50	382.53
 Irrigation Water, Flood	$55.00	5.50	ac ft
 Irrigation Labor, Flood	$14.55	5.50	hous
 Harvest expenses paid by buyer	1.00	acre	0.00	0.00	0.00	0.00
 Other Expenses	5.0%	0.00	0.00	53.61	53.61
 Interest on Operting Capital	6.0%	0.00	0.00	33.77	33.77
 Total Variable Cash Costs	$126.11	$104.10	$929.38	$1,159.59
 Fixed Cash Costs	Unit	$/Unit	Value
 Fallow Costs	acre	$181.33	$181.33
 Annual Cash Rent Payment	acre	170.00	170.00
 Total Fixed Cash Costs	$351.33
 Total minus Total Variable and Fixed Cash Costs
 Fixed Non-Cash Costs	Unit	$/Unit	Value
 Power Units, Machinery & Equipment, depreciation & interst	acre	$84.12	$84.12
 Total Fixed Non-Cash Costs	$84.12
 Total Annual Costs	$1,595.04
 Returns minus Total Annual Costs	$204.96
 Table 2.
Whole Farm Machinery Cost Assumptions.
Width	Market	Annua	Life
 Machine		Value	Use	
 175 HP Tractor	N/A	$180,000	1,365	10
 125 HP Tractor	N/A	80,000	495	15
 V-Ripper	8.0	22,000	459	10
 Offset Disk	18.0	30,000	517	15
 Moldboard Plow	9.3	35,000	138	15
 Landplane	16.0	18,000	78	15
 Lister	10.0	6,500	99	15
 Cotton Shredder/Root Puller	20.0	12,000	41	15
 Row Planter	24.0	40,000	72	15
 Row Cultivator	24.0	22,000	103	10
 Drill	20.0	25,000	97	15
 Fertilizer Spreader	40.0	18,000	109	20
 Boom Sprayer	60.0	9,500	145	20
 Table 3.
Machinery Cost Calculations, on a per hour and per acre basis.
-Variable Costs-	Fixed Cost
 Fuel &	Repairs &	Deprec.
Total Cost
 Machie	Lube	Maint.
& Interest
 175 HP Tractor	$36.80	$7.37	$17.20	$61.37
 125 HP Tractor	23.00	1.78	18.31	43.09
 V-Ripper	0.00	6.16	6.19	12.35
 Offset Disk	0.00	5.40	6.48	11.88
 Moldboard Plow	0.00	18.20	28.29	46.50
 Landplane	0.00	3.24	25.80	29.04
 Lister	0.00	1.78	7.32	9.10
 Cotton Shredder/Root Puller	0.00	2.76	32.57	35.33
 Row Planter	0.00	14.02	64.48	78.50
 Row Cultivator	0.00	3.90	27.10	30.99
 Drill	0.00	12.06	30.14	42.20
 Fertilizer Spreader	0.00	14.31	19.02	33.34
 Boom Sprayer	0.00	5.36	7.51	12.87
 Acre/	Operator	Variable	Fixed	Total
 Field Operation	Hour	Labor	Costs	Costs	Costs
 175 HP Tractor & V-Ripper	1.45	$13.53	$34.60	$16.08	$64.21
 175 HP Tractor & Offset Disk	4.17	4.72	11.88	5.68	22.27
 175 HP Tractor & Moldboard Plow	2.55	7.73	24.50	17.87	50.11
 175 HP Tractor & Landplane	5.09	3.87	9.31	8.45	21.62
 175 HP Tractor & Lister	3.18	6.18	14.44	7.71	28.33
 175 HP Tractor & Shredder	6.64	2.97	4.15	7.67	14.78
 175 HP Tractor & Planter	4.36	4.51	13.34	18.72	36.56
 175 HP Tractor & Cultivator	6.55	3.01	4.38	6.94	14.32
 175 HP Tractor & Drillr	3.64	5.41	10.13	13.32	28.87
 175 HP Tractor & Fertilizer Spreader	10.47	1.88	3.73	3.56	9.18
 175 HP Tractor & Boom Sprayer	16.55	1.19	1.82	1.56	4.57
 Table 4.
Estimated Per Acre Returns Over Cash Cost at Varying Yields and Prices.
Price/Ton	27.0	28.0	29.0	30.0	31.0	32.0	33.0
 $51.00				$19	$70	$121	$172
 $54.00		1	55	109	109	217	271
 $57.00	28	85	142	199	199	313	370
 $60.00	109	169	229	289	289	409	469
 $63.00	190	253	316	379	379	505	568
 $66.00	271	337	403	469	469	601	667
 $69.00	352	421	490	559	559	697	766
 Table 5.
Estimated Per Acre Returns Over Total Cost at Varying Yields and Prices.
Price/Ton	27.0	28.0	29.0	31.0	32.0	33.0
 $51.00					$37	$88
 $54.00				79	133	187
 $57.00		1	58	172	229	286
 $63.00	106	169	232	358	421	484
 $66.00	187	253	319	451	517	583
 $69.00	268	337	406	544	613	682
 Table 6.
Estimated Per Acre Returns Over Cash Cost at Varying Yields and Prices with a 10 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Price/Ton	27.0	28.0	29.0	31.0	32.0	33.0
 $51.00					$45	$96
 $54.00				87	141	195
 $57.00		9	66	180	237	294
 $63.00	114	177	240	366	429	492
 $66.00	195	261	327	459	525	591
 $69.00	276	345	414	552	621	690
 Table 7.
Estimated Per Acre Returns Over Total Cost at Varying Yields and Prices with a 10 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Price/Ton	27.0	28.0	29.0	30.0	31.0	32.0	33.0
 $51.00							$12
 $54.00					3	57	111
 $57.00				39	96	153	210
 $60.00		9	69	129	189	249	309
 $63.00	30	93	156	219	282	345	408
 $66.00	111	177	243	309	375	441	507
 $69.00	192	261	330	399	468	537	606
 Table 8.
Estimated Per Acre Returns Over Cash Cost at Varying Yields and Prices with a 20 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Price/Ton	27.0	28.0	29.0	30.0	31.0	32.0	33.0
 $51.00							$20
 $54.00					11	65	119
 $57.00				47	104	161	218
 $60.00		17	77	137	197	257	317
 $63.00	38	101	164	227	290	353	416
 $66.00	119	185	251	317	383	449	515
 $69.00	200	269	338	407	476	545	614
 Table 9.
Estimated Per Acre Returns Over Total Cost at Varying Yields and Prices with a 20 percent Increase in Fuel, Labor, Fertilizer and Chemical Costs.
Price/Ton	27.0	28.0	29.0	30.0	31.0	32.0	33.0
 $51.00							
 $54.00							34
 $57.00					19	76	133
 $60.00				52	112	172	232
 $63.00		16	79	142	205	268	331
 $66.00	34	100	166	232	298	364	430
 $69.00	115	184	253	322	391	460	529
 THE UNIVERSITY OF ARIZONA Cooperative Extension
 BLASE EVANCHO Area Agent, Arizona Cooperative Extension, University of Arizona
 Paco OLLERTON Producer in Pinal County
 TRENT TEEGERSTROM Ag Econ Extension Specialist, Department of Agriculture and Resource Economics, University of Arizona
 CLARK SEAVERT Agricultural Economist, Department of Applied Economics, Oregon State University
Turfgrass Consumptive Use: Prescott, Arizona
 Paul W.
Brown and Jeff Schalau
 Turf Irrigation Management Series
 Irrigation of turfgrass is an issue of growing concern in northern Arizona cities and towns as population growth places increasing demands on limited water supplies.
Understanding the water requirements of turfgrass is essential if we are to improve irrigation management and better plan for future urban growth.
Consumptive use  tables and curves that provide average rates of turfgrass water use  was developed in conjunction with the University of Arizona TRIF Water Sustainability Program that also funded the installation and operation of an automated weather station to improve future estimates of turfgrass CU.
This bulletin provides revised estimates of turfgrass CU developed from data sets collected by this weather station.
Turfgrass CU values  were estimated by applying crop coefficients  appropriate for acceptable  and high quality  turf to daily values of standardized reference evapotranspiration :
Groundwater Conservation Districts: Success Stories
 Dana Porter, Russell Persyn and Juan Enciso*
 The aquifers in Texas have different quantities of groundwater, recharge characteristics, and susceptibility to contamination.
Demand for water from these limited resources is increasing, so our aquifers must be conserved and protected for the benefit of the state's economy, our natural ecosystems, and our quality of life.
The Texas Water Code, Chapter 36, calls for the creation of Groundwater Conservation Districts "in order to provide for the conservation, preservation, protection, recharging, and prevention of waste of groundwater, and of groundwater reservoirs or their subdivisions, and to control subsidence caused by withdrawal of water from those groundwater reservoirs or their subdivisions." In Texas, local decision making through Groundwater Conservation Districts has been the rule and not the exception.
In fact, Groundwater Conservation Districts are the state's preferred method of groundwater management.
Texas diverse climatic systems, aquifers, water use patterns, population growth projections, and economy make planning for water use a complex issue.
Groundwater Conservation Districts are formed according to local needs; therefore, the roles of the districts reflect differences in local needs.
Some districts serve primarily to protect water quality; others work mainly to promote conservation of limited supplies, or to combat subsidence.
Groundwater Conservation Districts are carrying out a number of successful programs to protect and conserve the state's water supplies.
At special conferences, demonstration projects, field days, and public events, districts showcase conservation practices, demonstrate best management practices, and distribute educational materials.
For example, the South Plains Underground Water Conservation District sponsors an annual South Plains Water and Soil Conservation Conference and Trade Show, which includes agricultural water conservation practices updates and water level measurement reports for the area.
This conference targets agricultural producers, offers continuing education units, and fosters communication among agricultural producers, irrigation industry representatives, and conservation proccess fessionals.
Success Stories Success Stories
 Purpose of Groundwater Districts
 Groundwater Conservation Districts have assigned duties, and they may invoke authorized powers necessary to fulfill their duties.
A Groundwater Conservation District is required to:
 Develop and adopt a comprehensive management plan for efficiently using groundwater and preventing its waste.
The plan also must include measures for preventing land subsidence.
This plan must be submitted to, and certified by, the Texas Water Development Board and filed with other districts within a common groundwater management area.
Adopt rules necessary to implement the management plan.
Require permits for drilling, equipping, completing, or substantially altering the size of water wells.
A Groundwater Conservation District may also:
 Make and enforce rules necessary to implement the water management plan.
Make surveys of the groundwater resources.
Regulate the spacing of wells and/or production of wells.
Require that unused or abandoned wells be capped or plugged.
The common goal of all Groundwater Conservation Districts is to conserve groundwater resources through local management in order to ensure adequate water for their districts in the future.
Promoting Water Conservation through Education and Public Awareness
 Groundwater Conservation Districts use a variety of programs and media to inform the public about water issues and to raise public awareness of the need for water conservation.
News releases and public service announcements distributed through newspapers, radio
 This Cessna 340 aircraft, equipped with belly racks and wingtip generators, is used for cloud seeding by three Groundwater Conservation Districts in the Texas High Plains.
stations and television stations offer timely information to large general audiences.
Some districts publish bulletins and fact sheets with in-depth information on a variety of topics.
These materials are distributed at local offices and exhibits at area events.
Some districts use Internet sites to make information even more widely accessible.
In several districts, newsletters keep subscribers informed of issues, programs and activities in the district.
Assisting in Water Conservation through Technical Services
 Groundwater Conservation Districts can provide a range of technical support services to help water users with conservation.
Such services include monitoring precipitation and aquifer water levels.
Several districts test wells, pump plant efficiency, and irrigation system efficiency.
Water quality testing can vary from biological evaluations  to more complete water quality analyses  In some districts, water analysis is offered free of charge to residents of the district, and may be offered on a fee basis to residents outside the district.
For specific information on water analysis services and fees, residents should contact their districts.
Using agricultural water conservation techniques, such as low energy precision application  center pivot sprinklers and furrow diking, improves irrigation efficiency and conserves groundwater.
Success The Santa Rita Underground Water Conservation District has a program to plug more than 350 abandoned wells to prevent contamination of groundwater.
Success To help prevent contamination of their limited water resources, the Mesa Underground Water Conservation District sponsors a Used Oil and Filter Collection Program.
Approximately 40,000 gallons of waste oil have been collected and recycled each year since 1993.
Success Stories Success Stories Success Stories Success Stories
 To help farmers implement water conservation practices, some districts make the necessary equipment available for loan.
Laser land leveling equipment and furrow dikers, for instance, may be made available for improving agricultural irrigation efficiency.
Districts also may participate in the Agricultural Water Conservation Equipment Loan Program through the Texas Water Development Board.
Through this program, the districts can make low interest loans available to farmers and ranchers to help them install highly efficient irrigation systems  Some districts offer funding and technical assistance for plugging unused or abandoned water wells.
Permitting and Rulemaking Activities
 Groundwater Conservation Districts are granted the authority to make and enforce rules for conserving, preserving, protecting, and recharging groundwater, and for controlling subsidence.
According to the Texas Water Code, the districts must require permits for drilling, equipping, or completing wells or substantially altering the size of wells or well pumps.
Districts may require that unused or abandoned wells be capped or plugged.
Districts may regulate well spacing and/or pumpage rates in order to control subsidence and to prevent excessive water table drawdown or reduction of artesian pressure.
Financing Alternatives: Funding for District Activities
 Groundwater Conservation Districts vary in size, from partial county or single county districts to multiple county districts.
Staffing levels vary from one part-time position to several full-time positions, depending upon the goals of the Boards of Directors and the contributions of the local taxpayers.
This open, abandoned irrigation well is well hidden on CRP land.
Groundwater Conservation Districts work to make sure abandoned wells are properly capped to prevent accidents and aquifer contamination.
A moisture meter is used to collect pre-plant soil moisture data.
This information helps producers know how much to irrigate before planting.
The Texas Water Code, Chapter 36, allows groundwater districts to levy property taxes to pay maintenance and operating expenses at a rate not to exceed 50 cents on each $100 of assessed valuation.
Most district activities are funded through these ad valorem taxes, for which the maximum tax rates are set by local election.
Districts surveyed reported ad valorem tax rates of $0.0045 to $0.0575 per $100 valuation.
Hence, the annual tax paid on property valued at $100,000 ranges from $4.50 to $57.50.
Some districts are financed through user fees, which are assessed on the basis of the volume of water pumped or the volume permitted/allocated.
Other sources of revenue include permitting fees, permit application fees, and fees for services  provided outside district boundaries.
Some districts are able to provide special services and programs funded by grants for special projects from the Texas Water Development Board and the United States Environmental Protection Agency , through the Texas Natural Resource Conservation Commission.
Special Projects and Research Efforts
 Groundwater Conservation Districts conduct special projects, often in cooperation with other agencies and districts, to address special needs.
These special projects include groundwater modeling, groundwater recharge through infiltration and injection, area subsidence measurements, groundwater mapping, enhancement of recharge, and weather modification programs.
Such projects may be cooperatively funded by federal, state and/or local agencies.
Success Weather modification/rainfall enhancement programs use cloud seeding to augment normal rainfall, particularly during the peak irrigation season, in order to reduce pumpage and increase aquifer recharge.
Programs include the West Texas Weather Modification Association, High Plains Precipitation Enhancement Program, South Texas Weather Modification, Southwest Texas Rain Enhancement Program, and the Edwards Aquifer Authority Precipitation Enhancement Program.
These programs are funded jointly by the districts and the state through the Texas Natural Resource Conservation Commission.
Water quantity and quality have been improved through the Recharge Enhancement Program of the Barton Springs/Edwards Aquifer Conservation District.
Recharge into the aquifer through caves in Onion Creek is enhanced by a structure that prevents debris from plugging the cave entrance.
The quality of the recharge water is improved by a feature that allows the relatively dirty "first flush" water to bypass the cave entrance.
After this "first flush," a valve on the structure is opened to allow clean recharge water to enter the cave entrance to the aquifer.
Other activities of the District include cave cleanup programs and household hazardous waste collection programs to remove potential sources of contamination.
Stories Success Stories Success Stories
 L-5240, "Groundwater Conservation Districts," Texas Agricultural Extension Service.
B-1612, "Managing Texas' Groundwater Resources Through Groundwater Conservation Districts," Texas Agricultural Extension Service.
Water for Texas: A Consensus-Based Update to the State Water Plan.
1997.
Texas Water Development Board, Austin, Texas.
These examples predicted that there is enough water available in both cases.
However, these numbers assume you have a soil at full soil water storage and we will get average rainfall amounts until crop maturity.
Keep in mind that if the soil water level is more than 1.15 inches below full capacity at the Platte County or 2.47 inches at the Hitchcock County, and average rainfall is not received, additional irrigation will be required.
Types of Drive Systems
 Wheel and Drive Options
 The center pivot is the system of choice for agricultural irrigation because of its low labor and maintenance requirements, convenience, flexibility, performance and easy operation.
When properly designed and operated, and equipped with high efficiency water applicators, a center pivot system conserves three precious resources-water, energy and time.
Manufacturers have recently improved center pivot drive mechanisms , control devices, optional mainline pipe sizes and outlet spacings, span lengths, and structural strength.
The first pivots produced in the 1950s were propelled by water motors.
They operated at high pressures of 80 to 100 psi and were equipped with impact sprinklers and end guns that sprayed water toward the sky, resulting in significant evaporation losses and high energy use.
Today, pivots are driven by electric or oil hydraulic motors located at each tower and guided by a central control panel.
Pressures as low as 10 to 15 psi  are usually adequate for properly designed LESA  and LEPA  pivots that are 1/4 mile long operating on level to moderately sloping fields.
Water application efficiency with such systems is 85 to 98 percent.
When purchasing a center pivot system one must select:
 mainline size and outlet spacing;
 length, including the number of towers;
 application rate of the pivot; and
 the type of water applicator.
These choices affect investment and operating costs, irrigation efficiency, and crop production.
Wise decisions will result in responsible water management and conservation, flexibility for future changes, and low operating costs.
Switching from furrow to pivot irrigation can save water and money.
For example, on the Texas High Plains, field measurements show that corn is irrigated an average of 16 to 17 hours per acre per year with furrow irrigation.
With center pivot MESA irrigation , similar corn yields are pro-
 duced with 12 to 13 hours per acre per year.
LEPA and LESA applicators further reduce irrigation to an average of 10 to 11 hours per acre per year.
A quarter-mile  system that irrigates about 120 acres typically costs $325 to $375 per acre excluding the cost of groundwater well construction, turbine pumps and power units.
Longer systems usually cost less on a per-acre basis.
For example, half-mile systems  that irrigate approximately 500 acres cost about $200 to $250 per acre.
This relatively high cost is often offset by a number of advantages, including reduced labor and tillage, improved water distribution, more efficient pumping, lower water requirements, more timely irrigation, and convenience.
Programmable control panels and remote control via phone lines or radio can start and stop irrigations, identify location, increase or decrease travel speed, and reverse direction.
Fertilizers and certain plant protection chemicals can be applied through the center pivot, which increases the value and use of the system.
Programmable injection unit control, monitoring, and safety are compatible with center pivot control sysitems.
Towable pivot machines are available, so that additional tracts of land can be irrigated with the same machine.
When considering a towable machine, remember that sufficient water is needed to irrigate all tracts.
Plan the irrigated circle and position the pivot so that it can be moved to drier soil at the location from and in the path in which it is to be towed.
Types of Drive Systems
 In electric drive pivots, individual electric motors  power the two wheels at each tower.
Typically, the outermost tower moves to its next position and stops; then each succeeding tower moves into alignment.
Thus, at any time a tower can be in motion.
The rotation speed  of the pivot depends on the speed of the outermost tower and determines the amount of water that is applied.
The operator selects the tower speed using the central power control panel, normally located at the pivot point.
At the 100 percent setting, the end tower moves
 Figure 1a.
Electric drive.
continuously.
At the 50 percent setting, the outer tower moves 30 seconds and stops 30 seconds each minute, etc.
The speed options on most central power control panels range from approximately 2 to 100 percent.
With oil hydraulic drive systems, all towers remain in continuous motion.
The outermost tower speed is the greatest, and each succeeding tower moves continuously at proportionally reduced speeds.
As with electric drive machines, the center pivot travel speed is selected at a central control.
It is a master control valve that increases or decreases oil flow to the hydraulic motor/s on the last tower.
Two motors per tower are used with the planetary drive, one for each wheel.
One motor per tower powers the
 Figure 2.
Hydraulic move.
Figure 1b.
Electric drive.
optional worm drive assembly.
The required hydraulic oil pressure  is maintained by a central pump usually located near the pivot pad.
The central pump may be powered by natural gas, diesel or electricity.
The number of towers and maximum travel speed determine the hydraulic oil flow and the central pump power requirement, which usually ranges from 7.5 to 25 horsepower for quartermile systems.
Additional site specific travel speed options are available.
Theoretically, continuous move systems provide greater irrigation uniformity.
However, other factors influence uniformity, including travel speed , system design, type of water applicator, and operator management, in combination with the amount of water  the machine is nozzled to deliver.
In field tests, both electric and hydraulic drive systems work well.
The choice is often guided by available power sources, personal preference in servicing and maintaining the system, the service history of local dealers, what is being sold in the local market and why, purchase price, and dependability.
Wheel and Drive Options
 The travel speed is determined by the wheel size in combination with the power drive mechanism, and is set at the central control panel.
The speed of the pivot determines the amount of water applied as specified on the corresponding system design precipitation chart.
(See the following discussions on the system design precipitation chart and system management as related to travel speed.
Gear drives should be checked
 for proper oil levels and any water in the gear boxes removed at least once each year.)
 Electric power drive has two gear reductions.
One gear reduction is in the drive shafts connecting the electric motor to a gear box located at each of the two tower wheels.
The second gear reduction is the gear box driving each wheel.
The maximum center pivot travel speed depends on the:
 electric motor speed or rotation in revolutions per minute ;
 speed reduction ratios in both the center drive shafts and gear boxes; and
 Table 1 gives examples of electric center drive and gear box reductions, wheel circumference, travel distance for each revolution, and representative maximum travel speed in feet per hour.
Hydraulic drive pivots have one gear reduction.
Two configurations are used-a hydraulic motor in each wheel hub, or a single motor located at one wheel coupled to a right angle gear drive with a connecting drive shaft that also powers the second wheel.
A hydraulic valve meters oil flow to each set of drives at each tower to maintain system alignment.
Total oil flow is determined by the travel speed, number of drive units , gear reduction, and tire size.
Table 1 lists typical hydraulic drive center pivot oil pump horsepower, tire size, and end tower travel speed.
The design computer printout provides required information about the center pivot and how it will perform on a particular tract of land.
A portion of a typical design printout is shown in Figure 3.
It includes:
 the pivot design flow rate  in GPM;
 irrigated acreage under the pivot;
 elevation changes in the field as measured from the pivot point;
 operating pressure and mainline friction losses;
 the pressure regulator rating in psi ;
 the type of water applicator, spacing and position from the mainline;
 nozzle size for each applicator;
 water applicator nozzle pressure;
 maximum travel speed; and
 A sample precipitation chart is shown in Figure 4.
It identifies irrigation amounts  for optional travel speed settings, gear reduction ratios and tire size.
It corresponds with Figure 3.
Table 1.
Typical gear reduction, wheel drive RPM and maximum end tower travel speed.
Center	Gear	Wheel diam.-inch	End tower
 Motor	drive	box	Rim & tire	Last wheel	feet
 Drive	RPM	ratio	ratio	Rim	Rim & tire	circum.
ft.
drive RPM	per hour
 Electric	1740	58:1	52:1	24	40	10.47	.5769	362
 Electric	1740	40:1	50:1	24	40	10.47	.8700	546
 Electric	3450	40:1	52:1	38	54	14.13	1.6586	1406
 No.
Hydraulic pump	Tire size	Rim & tire	Last wheel	End tower
 towers	drive HP	circum.
ft.
drive RPM	feet per hour
 Hydraulic	8	10	16.9 X 24	10.47	.5730	360
 Hydraulic	8	15	14.9 X 24	10.47	.9312	585
 Hydraulic	8	25	11.2 X 38	14.13	1.5723	1333
 Hydraulic	18	25	11.2 38	14.13	.6286	533
 J J Farms & Section 130 625.00 GPM 4.00 PSI 13.67 PSI identification Pivot location Pivot flow Design rate end the Design Pressure at pivot Pressure at
 ft 1309.00 ft 12.50 ft 12.00 ft ft, +7.0 -8.0 0 length Overall length tube Drop mainline) (from position Regulator elevation of Design end tower End GPM gun
 ACRES	1.84	5.53	9.23	12.92	16.61	20.30	23.99	27.68	5.41	123.51
 6	6	6	6	6	6	6	6	6
 DROP 1st	POSITION		36.60	3.335	3.335	3.335	3.335	3.335	3.335	3.335	3.335
 DROP	DIAMETER		0.75	0.75	0.75	0.75	0.75	0.75	0.75	0.75	0.75
 DROP	SPACING		6.67	6.67	6.67	6.67	6.67	6.67	6.67	6.67	6.67
 19	24	24	24	24	24	24	24	5	192
 MAINLINE	DIAMETER		6.38	6.38	6.38	6.38	6.38	6.38	6.38	6.38	5.78
 SPAN	LENGTH		160	160	160	160	160	160	160	160	29	1309
 SPAN	NO.
1	2	3	4	5	6	7	8	9	Total
 Brand size and/or and applicator of  flow capacity LF often (low expressed as	if is Plug plugged outlet number, 11.
from furro Distance 12.
applicator, in to arm	LENGTH
 (when should nozzle the the the regulators 7.
Pressure used, nozzle at at pressure pressure are	DROP
 12	150	156	156	162	144
 size by applicator's applicator based delivered GPM and the nozzle Actual the 5.
operating on pressure	Applicator mainline number position 9.
on or	flow), flow), (high HF etc.
11	PLUG	NO.
1
 than of be rating) the less the regulator's psi no	by inches) either in number actual size or	10	REG	SIZE	6LF	6LF	6LF	6LF	6LF
 9	SPRK	NO.
1	2	3	4	19
 mainline 6.
the the in in psi Pressure outlet at	LABEL SPRINKLER	SIZE NOZZLE &
 8	4.0	4.0	4.0	4.0	6.5
 based by needed applicator GPM the the covered 4.
area on
 7	NOZZLE	PSI	6.66	6.66	6.66	6.66	6.66
 between feet 2.
length between Distances outlets in towers span or	from feet pivot Distance 3.
in point outlet tower to or
 6	PIPE	PSI	13.27	13.20	13.13	13.05	11.86
 5	GPM	DEL.
0.29	0.29	0.29	0.29	0.76
 4	GPM	NEED	0.18	0.21	0.24	0.27	0.76
 Mainline pivot point from number 1.
outlet
 3	DISTANCE	PIVOT TO	6.08	36.60	43.27	49.94	56.61	156.66
 2	LAST	OUTLET	36.60	6.67	6.67	6.67	6.67
 1	1	2	3	4	5	20
 144	144	150	150	156	144	144	144
 6LF	6LF	6LF	6LF	6LF	6LF	6LF	6LF
 20	21	22	23	24	43	44	45
 6.5	7.0	7.0	7.0	7.0	9.5	9.5	9.5
 6.66	6.66	6.66	6.66	6.66	6.66	6.66	6.66
 11.79	11.72	11.65	11.58	11.50	10.20	10.03	9.96
 0.76	0.88	0.88	0.88	0.88	1.61	1.61	1.61
 0.79	0.82	0.85	0.89	0.92	1.53	1.56	1.59
 160.00	163.33	170.00	176.67	183.84	190.01	316.67	320.00	323.33	330.00
 160.00	6.67	6.67	6.67	6.67	6.67	6.67	160.00	6.67	6.67
 1 Tower	21	22	23	24	25	44	2 Tower	45	46
 Sample Figure chart.
4.
precipitation
 XXXXX IRRIGATOR 1 SIZE  MOTOR = 1745 RPM LOADED MOTOR = 58T01 GEAR RATIO BOX CENTER =
 50T01 RATIO GEAR WHEEL BOX = 11.2 24.0 SIZE TIRE X = 5.90 SPEED MAX.
LAST TOWER =
 water of 1.
applied Total amount this inches speed in setting at
  setting the control on indicated of usually percentage as a speed the maximum
 hours Time complete in make 3.
to a this circle speed setting at
 22.70	28.38	32.44	37.84	45.41	56.76	75.68	90.82	113.53	126.14	151.37	189.22	227.06
 % SETTING TIMER -
 80	70	60	50	40	30	25	20	18	15	12	10
 0.25	0.32	0.36	0.42	0.51	0.64	0.85	1.02	1.27	1.42	1.70	2.12	2.55
 It is essential that correct information about available water supply  and changes in field elevation are used in designing the pivot so that accurate irrigation amounts, operating pressure requirements, and the need for pressure regulators can be determined.
Give this information to your dealer, and then inspect the resulting computer design printout before placing your order to ensure that the system is designed to accommodate your site conditions and will perform as expected.
Always look at the design mainline operating pressure at the pad to determine if it is what you want.
If not, inquire about ways to lower it.
System irrigation capacity is determined by the gallons per minute  and the number of acres irrigated.
System capacity is expressed in terms of either the total flow rate in GPM or the application rate in GPM per acre.
Knowing the capacity in GPM per acre helps in irrigation water management.
Table 2 shows the relationship between GPM per acre and irrigation amounts.
These irrigation amounts apply for all irrigation systems with the same capacity in GPM per acre.
The amounts do not include application losses, and are for systems operating 24 hours a day.
To determine your system's capacity, select the desired irrigation amounts in inches and multiply the corresponding GPM per acre by the number of acres you are irrigating.
For example, if you irrigate 120 acres with 4 GPM per acre, 480 GPM  are required to apply 0.21 inches per day, 1.50 inches per week, and 6.40 inches in 30 days.
Mainline pipe size influences the total operating cost.
Smaller pipe sizes, while less expensive to purchase, may have higher water flow friction pressure loss, resulting in higher energy costs.
Plan new center pivots to operate at minimum operating pressure to
 Table 2.
Daily and seasonal irrigation capacity.
minimize pumping cost.
For a pivot nozzled at 1,000 GPM, rules of thumb are as follows.
Each additional 10 psi pivot pressure requires approximately 10 horsepower.
Each additional 10 psi pivot pressure increases fuel costs about $0.35 per hour  at natural gas costs of $3.00 per MCF.
At $0.07 per KWH for electricity, the cost is $0.60 per hour  for each additional 10 psi pressure.
It costs $0.48 per hour  for each additional 10 psi pressure for diesel priced at $0.80 per gallon.
GPM/	Inches in irrigation days
 acre	Inch/day	Inch/week	30	45	60	80	100
 1.5	.08	.55	2.4	3.8	4.8	6.4	8.0
 2.0	.11	.75	3.2	4.8	6.4	8.5	10.6
 3.0	.16	1.10	4.8	7.2	9.5	12.7	15.9
 4.0	.21	1.50	6.4	9.5	12.7	17.0	21.2
 5.0	.27	1.85	8.0	11.9	15.9	21.2	26.5
 6.0	.32	2.25	9.5	14.3	19.1	25.4	31.8
 7.0	.37	2.60	11.1	16.7	22.6	29.7	37.1
 8.0	.42	2.97	12.7	19.1	25.4	33.9	42.4
 
 Table 3 lists friction pressure losses for different mainline sizes and flow rates.
Total friction pressure in the pivot mainline for quarter-mile systems  on flat to moderately sloping fields should not exceed 10 psi.
Therefore:
 For flows up to approximately 750 GPM, 6 5/8-inch diameter mainline can be used.
Friction pressure loss exceeds 10 psi when more than 575 GPM is distributed through 6-inch mainlines.
Some 8-inch spans should be used when 800 GPM or more are delivered by a quarter-mile system.
For center pivots 1,500 feet long , 6 5/8-inch mainline can be used for 700 GPM while keeping friction pressure loss under 10 psi.
Some dealers may undersize the mainline in order to reduce their bids, especially when pushed to give the best price.
Check the proposed design printout.
If operating pressure appears high, ask the dealer to provide another design using proportional lengths, usually in spans, of larger pipe, or to telescope pipe  to reduce operating pressure.
Table 3, section C shows how friction and operating pressure for half-mile systems can be reduced with size 8and 10-inch mainline pipe.
Saving money on the initial purchase price often means paying more in energy costs over the life of the system.
Telescoping involves using larger mainline pipe at the beginning and then
 Table 3.
Approximate friction loss  in center pivot mainlines.
Mainline pipe diameter, inches
 6	6 5/8	8	10
 Flow rate, GPM	Mainline pressure loss, psi
 800	18	11	4
 900	23	14	5
 1000	28	17	7
 1100	33	20	8
 1200	39	24	9
 600	13	8	3
 700	16	10	4
 800	21	13	5
 900	26	16	6
 1600	134	83	31	10
 2000	125	48	15
 smaller sizes as the water flow rate  decreases away from the pivot point.
Typical mainline sizes are 10, 8 1/2, 8, 6 5/8 and 6 inches.
Mainline pipe size governs options in span length.
Span length options are usually:
 100 to 130 feet for 10-inch;
 130 to 160 feet for 8 1/2and 8-inch; and
 160 to 200 feet for 6 5/gand 6-inch.
Telescoping mainline pipe size is a method of planning a center pivot for minimum water flow friction loss and low operating pressure, and thus, lower pumping costs.
Telescoping uses a combination of pipe sizes based on the amount of water  flowing through.
Telescoping is usually accomplished in whole span lengths.
Its importance increases with both higher flow rates  and longer center pivot lengths.
Dealers use computer telescoping programs to select mainline pipe size for lowest purchase price and operating costs.
If your dealer does not offer this technology, request it.
Table 4 shows examples of telescoping mainline size to manage friction pressure loss.
Example 1 shows that for a center pivot 1,316 feet long, fric-
 Table 4.
Telescoping to reduce mainline friction pressure with outlets spaced at 60 inches.
Feet of mainline size
 GPM	10-inch	8 1/2-inch	8-inch	6 5/8-inch	Total feet	Friction pressure PSI
 1100	0	0	0	1316	1316	19
 1100	0	0	640	676	1316	10
 2500	0	0	1697	927	2624	73
 2500	0	897	800	927	2624	63
 2500	897	o	800	927	2624	48
 2500	1057	640	540	387	2624	32
 2500	1697	0	540	387	2624	25
 tion pressure loss is reduced from 19 to10 psi by using 640 feet of 8-inch mainline rather than all 6 5/8-inch to deliver 1,100 GPM.
Example 2 lists friction pressure losses for various lengths and combinations of mainline pipe size for the delivery of 2,500 GPM by a 2,624-foot system irrigating 496 acres.
Friction pressure loss is reduced from 73 to 25 psi by using more 10and 8and less 6 5/8-inch mainline pipe.
When designing your system, compare the higher cost of larger mainline pipe to the increased pumping costs associated with smaller pipe.
Pressure regulators are "pressure killers." They reduce pressure at the water delivery nozzle so that the appropriate amount of water is applied by each applicator.
Selection of nozzle size is based on the rated delivery psi of the pressure regulators.
Nozzles used with 10 psi regulators are smaller than those used with 6 psi regulators when the same amount of water is applied.
Low rated  pressure regulators, if used, allow center pivot design to be appropriate at minimum operating pressure.
Pressure regulators require energy to function properly.
Water pressure losses within the regulator can be 3 psi or more.
So, entrance  water pressure should be 3 psi more than the regulator rating.
Six-psi regulators should have 9 psi at the inlet; 10-psi regulators, 13 psi; 15-psi regulators, 18 psi; and 20-psi regulators, 23 psi.
Regulators do not function properly when operating pressure is less than their rating plus 3 psi.
Pressure regulator operating inlet pressure should be monitored with a gauge installed upstream adjacent to the regulator in the last drop at the outer end, and should be checked when the machine is upslope.
Another gauge located in the first drop in span Elevation change one will monitor operating pressure Feet when the center pivot is located on 2.3 downslope terrain.
Pressure regulator psi rating influences system design, appropriate operating pressure, the total energy requirements, and the costs of pivot irrigation.
As with other spray and sprinkler systems, pressure regulators are not necessarily needed for all sites.
Table 5
 shows how variations in terrain elevations influence mainline operating pressure.
Elevation changes in the field have the largest impact with lower design pressures.
From the first to last drop on a pivot, the operating pressure at the nozzle should not vary more than 20 percent from the design operating pressure.
Without regulators, operating pressure and pumping cost usually will not increase significantly if the elevation does not change more than 5 feet from the pad to the end of the pivot.
Where elevation changes are greater than 5 feet, the choice is to increase operating pressure  or to use pressure regulators.
This decision is site specific and should be made by comparing the extra costs of pressure regulators to the increased pumping costs without them..
Where the water flow rate, and thus the operating pressure, vary significantly during the growing season, perhaps from seasonal variations in groundwater pumping levels, the design flow rate  and the use of pressure regulators should be evaluated carefully.
If water pressure drops below that required to operate the regulators, then poor water application and uniformity will result.
In contrast, if the design operating pressure is high, pumping costs will be unnecessarily high.
When operating pressure decreases to less than required, the solution is to renozzle for the reduced gallons per minute.
The amount of water flow in the mainline decreases or increases operating pressure for the nozzles installed.
Table 5.
Percent variation in system operating pressure created
 by changes in land elevation for a quarter-mile pivot.
Maintain
 less than 20 percent variation.
System design pressure *
 6	10	20	30	40
 1	16.5	10.0	5.0	3.3	2.5
 4.6	2	33.0	20.0	10.0	6.6	5.0
 6.9	3	50.0	30.0	15.0	10.0	7.5
 9.2	4	40.0	20.0	13.3	10.0
 11.5	5	50.0	25.0	16.6	12.5
 13.9	6	30.0	20.0	15.0
 16.2	7	23.3	17.5
 18.5	8	26.6	20.0
 *pressure at the nozzle
 There are various types of spray applicators available, each with pad options.
Low-pressure spray applicators can be used with flat, concave or convex pads that direct the water spray pattern horizontally, upwards and downwards at minimum angles.
Spray applicator pads also vary in the number and depth of grooves they have, and, thus, in the size of water droplets they produce.
Fine droplets may reduce erosion and runoff, but are less efficient because of their susceptibility to evaporation and wind drift.
Some growers prefer to use coarse pads that produce large droplets, and control runoff and erosion with agronomic and management practices.
There is little published data on the performance of various pad arrangements.
In the absence of personal experience and local information, following the manufacturer's recommendations is likely the best strategy in choosing pad configuration.
Pads are very inexpensive.
Some growers purchase several groove configurations and experiment to determine which works best in their operation.
High-pressure impact sprinklers mounted on the center pivot mainline were prevalent in the 1960s when energy prices were low and water conservation did not seem so important.
Now, high-pressure impacts are recommended only for special situations, such as the land application of wastewater, where large nozzles and high evaporation can be beneficial.
Impact sprinklers are usually installed directly on the mainline and release water upward at 15 to 27 degrees.
Undistorted water pattern diameters normally range from 50 to more than 100 feet.
Water application losses average 25 to 35 percent or more.
Lowangle, 7-degree sprinklers reduce water loss and pattern diameter somewhat, but do not significantly decrease operating pressure.
End guns are not recommended because they are higher volume  impact sprinklers with lower application and distribution efficiencies and high energy requirements.
Very few center pivots in Texas are now equipped with impact sprinklers.
There are improved applicators and design technology for more responsible irrigation water management.
These new applicators operate with low water pressure and work well with current center pivot designs.
Low-pressure applicators require less energy and, when appropriately positioned, ensure that most of the water pumped gets to the crop.
The choice is which low-pressure applicator to use and how close to ground level the nozzles can be.
Generally, the lower the operating pressure requirements the better.
When applicators are spaced 60 to 80 inches apart, nozzle operating pressure can be as low as 6 psi, but more applicators are required than with wider spacings.
Water application is most efficient when applicators are positioned 16 to 18 inches above ground level, so that water is applied within the crop canopy.
Spray, bubble or direct soil discharge modes can be used.
Field testing has shown that when there is no wind, low-pressure applicators positioned 5 to 7 feet above ground can apply water with up to 90 percent efficiency.
However, as the wind speed increases, the amount of water lost to evaporation increases rapidly.
In one study, wind speeds of 15 and 20 miles per hour created evaporative losses of 17 and 30+ percent, respectively.
In another study on the southern High Plains of Texas, water loss from a linear-move system was as high as 94 percent when wind speed averaged 22 miles per hour with gusts of 34 miles per hour.
Evaporation loss is significantly influenced by wind speed, relative humidity and temperature.
The following sections describe three types of lowpressure application systems that can significantly reduce operating pressure and deliver most of the water pumped for crop production.
With Mid-Elevation Spray Application , water applicators are located approximately midway between the main-
 on tall crops such
 as corn and sugar
 extend down to the
 should be used in
 on the type of
 Figure 5.
Drop arrangement.
ment selected.
While some applicators require 20 to 30 psi operating pressure, improved designs require only 6 to10 psi for conventional 8 1/2to 10-foot mainline outlet and drop spacing.
Operating pressures can be lowered to 6 psi or less when spray applicators are positioned 60 to 80 inches apart.
With wider spacings, such as for wobbler and rotator applicators, manufacturers' recommended nozzle operating pressure is greater.
Research has shown that in corn production, 10 to 12 percent of the water applied by above-canopy irrigation is lost by wetting the foliage.
More is lost to evaporation.
Field comparisons indicate that there is 20 to 25 percent more water loss from MESA abovecrop-canopy irrigation than from LESA and LEPA within-crop-canopy center pivot systems.
Low Elevation Spray Application  applicators are positioned 12 to 18 inches above ground level, or high enough to allow space for wheel tracking.
Less crop foliage is wet, especially when planted in a circle, and less water is lost to evaporation.
LESA applicators are usually spaced 60 to 80 inches apart, corresponding to two crop rows.
The usual arrangement is illustrated in Figure 6.
Each applicator is attached to a flexible drop hose, which is connected to a gooseneck or furrow arm on the mainline.
Weights help stabilize the applicator in wind and allow it to work through plants in straight crop rows.
Nozzle pressure as low as 6 psi is best with the correct choice of water applicator.
Water application efficiency usually averages 85 to 90 percent, but may be less in more open, lower profile crops such as cotton.
LESA center pivots can be converted easily to LEPA with an applicator adapter that includes a connection to attach a drag sock or hose.
Figure 6.
Drops with LESA applicators.
Figure 7.
LESA applicator.
The optimal spacing for LESA drops is no wider than 80 inches.
With appropriate installation and management, LESA drops spaced on earlier, conventional 8 1/2to 10-foot spacing can be successful.
Corn should be planted in circle rows and water sprayed underneath the
 primary foliage.
Some growers have been successful using LESA irrigation in straight corn rows at conventional outlet spacing when using a flat, coarse pad that sprays water horizontally.
Grain sorghum and soybeans also can be planted in straight rows.
In wheat, when plant foliage causes significantly uneven water distribution, swing the applicator over the truss rod to raise it.
Low Energy Precision Application  irrigation discharges water between alternate crop rows planted in a circle.
Water is applied with:
 applicators located 12 to 18 inches above ground level, which apply water in a "bubble" pattern; or
 drag socks or hoses that release water on the ground.
Socks help reduce furrow erosion; double-ended socks are designed to protect and maintain furrow dikes.
Drag sock and hose adapters can be removed from the applicator and a spray or chemigation pad attached in its place when needed.
Another product, the LEPA "quad" applicator, delivers a bubble water pattern  that can be reset to optional spray for germination, chemigation and other in-field adjustments.
LEPA applicators typically are placed 60 to 80 inches apart, corresponding to twice the row spacing.
Thus, one row middle is wet and one is dry.
Dry middles allow more rainfall to be stored.
Applicators are arranged to maintain a dry row for the pivot wheels when the crop is planted in a circle.
Research and field tests show that crop production is the same whether water is applied in every furrow or in alternate furrows.
Applicator nozzle operating pressure is typically 6 psi.
Field tests show that with LEPA, 95 to 98 percent of the irrigation water pumped gets to the crop.
Water application is precise and concentrated, which requires a higher degree of planning and management, especially with clay soil.
Center pivots equipped with LEPA applicators provide maximum water application efficiency at minimum operating pressure.
LEPA can be used successfully in circles or in straight rows.
It is especially beneficial for low profile crops such as cotton and peanuts, and even more beneficial where water is limited.
Converting Existing Pivots to LEPA
 Water outlets on older center pivot mainlines are typically spaced 8 1/2 to 10 feet apart.
Because LEPA drops are placed between every other crop row, additional outlets are needed.
For example, for row spac-
 Figure 8.
Double-ended sock.
Figure 9.
LEPA bubble pattern.
ings of 30 inches, drops are needed every 60 inches.
Likewise, for 36-inch row spacings, drops are placed every 72 inches.
Two methods can be used to install additional drops and applicators: 1) converting the existing outlets with tees, pipe and clamps; or 2) adding additional mainline outlets.
Installation is quicker if a platform is placed underneath the pivot mainline.
The platform can be planks placed across the truss rods or the side boards of a truck.
A tractor equipped with a front end loader provides an even better platform.
Using Existing Outlets.
First, the existing gooseneck is removed and crosses, tees or elbows are connected to the mainline outlets as needed.
Galvanized or plastic pipe is cut to extend from the outlet point to the drop location.
A galvanized elbow is used to connect the drop to the extension pipe.
This elbow should be clamped to the mainline to maintain the drop position.
Figure 10.
Multi-functional LEPA head.
Figure 11.
Adding drops.
Adding Outlets.
It is less costly to convert to LEPA by adding outlets than to purchase the tees, plumbing, clamps and labor required to convert existing outlets.
New mainline outlets can be installed quickly using a swedge coupler made of metal alloy.
An appropriate size hole is drilled into the pivot mainline at the correct spacing.
The swedge coupler is then inserted into the hole.
The manufacturer recommends that a small amount of sealant be used with the coupler to ensure a leak-proof connection.
A standard hydraulic press  is attached to the coupler with a special fitting that screws into the coupler.
The press is used to compress the coupler against the inside of the mainline pipe to make a water-tight seal.
The swedge coupler compresses quite easily; be careful not to over-compress the coupler.
Regular goosenecks or furrow arms are then screwed into the coupler.
Figure 12.
Drilling for swedge coupler.
Figure 13.
Installing swedge coupler.
Figure 14.
Swedge coupler installed.
Outlets also can be added by welding threaded 3/4inch female couplings into the existing mainline.
Since welding destroys the galvanized coating, welded couplings should be used only on ungalvanized main lines.
As with the swedge coupler, goosenecks and drops can be used with the welded couplings.
Other Conversion Tips.
When water is pumped into a center pivot, it fills the mainline and drops.
The weight of the water causes the pivot to "squat." With 160-foot spans, the pivot mainline will be lowered approximately 5 inches at the center of the span.
Likewise, a 185-foot span will be about 7 inches lower at the center when filled with water.
The length of the hose drops should be cut to account for this change so that all LEPA heads are about the same height above the ground when the system is running.
Center pivot manufacturers can provide appropriate drop hose cut lengths.
Goosenecks or furrow arms and drops are installed alternately on each side of the mainline to help equalize stresses on the pivot structure for high profile crops.
Also, when crops are not planted in a circle, having drops on both sides of the mainline helps prevent all the water from being dumped into the same furrows when the system parallels crop rows.
A permanently installed, continuously functioning flow meter measures the actual amount of irrigation water applied, and is highly recommended.
It is used in conjunction with the design printout for irrigation water management.
In addition, properly located pressure gauges monitor system performance and, in combination with the flow meter, provide immediate warning of water deficiency and other system failures.
Two pressure gauges are needed on the center pivot, one at the end of the system, usually in the last drop upstream from the applicator or regulator, and one at the pivot point.
A third one in the first drop of span one will monitor operating pressure when the machine is downslope in relation to the pivot point.
On older equipment, conventional mainline outlet spacings were 8 1/2 to 10 feet.
New center pivots should have 60or 80-inch mainline outlet spacings, even if this reduced spacing is not required by the water applicator initially selected.
Manufacturers continue to develop more efficient applicators designed to be spaced closer together to achieve maximum irrigation efficiency and pumping economy.
Ordering your pivot with a closer mainline outlet spacing will ensure that it can be quickly and inexpensively equipped with a new applicator design in the future.
Retrofitting mainline outlet spacing typically costs $5,000 to $7,000 more than when the spacing is specified with the initial purchase.
As with any other crop production investment, a center pivot should be purchased only after careful analysis.
Compare past crop production per acre-inch of irrigation applied to the projected production with center pivot ; also consider how much water is available.
Then answer the question: Will a center pivot cost or make money in my operation?
Remember, personal preference is one of the most important considerations.
Pivot management is centered around knowing how much water is applied in inches.
The system design printout includes a precipitation chart that lists total inches applied for various speed settings on the central control panel.
If a precipitation chart is not provided , contact the dealer who first sold the pivot to obtain a copy.
Dealers usually keep copies of the computer design printout indefinitely.
When a precipitation chart is not available, use Table 6 to identify the irrigation amount based on flow rate and time required to complete a circle.
For other sizes of pivots or travel speeds, irrigation inches can be calculated using the first equation below.
Keep in mind that the equations assume 100 percent water application efficiency.
Reduce the amounts by 2 to 5 percent for LEPA, 5 to 10 percent for LESA, 20 percent for MESA, and 35 to 40 percent for impact sprinklers.
Calculations for other length pivots can be made using the formulas below.
1.
Inches applied = Pivot GPM X hours to complete circle 450 X acres in circle
 2.
Acres per hour =
 Acres in circle Hours to complete circle
 3.
End tower speed in feet per hour = Distance from pivot to end tower in feet X 2 X 3.14 Hours to make circle
 4.
Number of feet the end of machine must move per acre = 87,120
 Distance  from pivot to outside wetting pattern
 Runoff from center pivot irrigation can be controlled by changing the optional speed control setting to match water application to soil infiltration.
Agronomic methods of runoff control include furrow diking , farming in a circular pattern, deep chiseling of clay sub-soils, main-
 Table 6.
Inches of water applied by a 1,290-foot center pivot*
 with 100 percent water application efficiency.
Pivot	Hours to complete 120-acre circle
 GPM	12	24	48	72	96	120
 400	0.09	0.18	0.36	0.53	0.71	0.89
 500	0.11	0.22	0.44	0.67	0.89	1.11
 600	0.13	0.27	0.53	0.80	1.06	1.33
 700	0.16	0.31	0.62	0.93	1.24	1.55
 800	0.18	0.36	0.71	1.07	1.42	1.78
 900	0.20	0.40	0.80	1.20	1.60
 1000	0.22	0.44	0.89	1.33	1.78
 1100	0.24	0.49	0.98	1.47	1.95
 feet/hour	667	334	167	111	83
 Acres/hour	10	5	2.5	1.7	1.3
 *1,275 feet from pivot to end tower + 15-foot end section
 taining crop residue, adding organic matter, and using tillage practices that leave the soil "open."
 Farming in the round is one of the best methods of controlling runoff and improving water distribution.
When crops are planted in a circle, the pivot never dumps all the water in a few furrows as it can when it parallels straight rows.
Circle farming begins by marking the circular path of the pivot wheels as they make a revolution without water.
The tower tire tracks are then a guide for laying out rows and planting.
If the mainline span length  does not accommodate an even number of crop rows, adjust the guide marker so that the tower wheels travel between crop rows.
Furrow diking is a mechanical tillage operation that places mounds of soil at selected intervals across the furrow between crop rows to form small water storage basins.
Rainfall or irrigation water is trapped and stored in the basins until it soaks into the soil, rather than running off.
Furrow diking reduces runoff and increases yields in both dryland and irrigated crops.
A similar practice for permanent pastures, called chain diking, involves dragging a chain-like implement that leaves depressions to collect water.
Maximum crop production and quality are achieved when crops are irrigated frequently with amounts that match their water use or ET.
Irrigating twice weekly with center pivots is common.
Texas has three PET 
 weather station and crop water use reporting networks, located at Amarillo, College Station and Lubbock.
They report daily crop water use based on research.
One strategy used by growers is to sum the daily crop water use  reported during the previous 3 to 4 days and then set the pivot central control panel to apply that amount of water.
2.00 The daily crop water use reported by the PET networks is for full irriga2.22 tion.
Most center pivots operating on 2.44 the Texas South and High Plains are planned and designed for insufficient capacity  to supply full daily 67 crop water use.
Growers with insuffi1 cient capacity should use a high water management strategy that ensures that the soil root zone is filled with water, by either rainfall, pre-watering or early-season irrigation, before daily crop water use exceeds the irrigation capacity.
Most soils, such as Pullman, Sherm, Olton and Acuff series soils, can store approximately 2 inches of available water per foot of topsoil.
Sandy loam soils typically store 1 inch or more of available water per foot of topsoil.
Sandy soils store less.
The County Soil Survey available from the Natural Resources Conservation Service contains the available water storage capacity for most soils.
Be sure to use the value for the soil at the actual center pivot site.
Soil moisture monitoring is highly recommended and complements ET-based scheduling, particularly when there is rainfall during the irrigation season.
Soil moisture monitoring devices such as tensiometers and watermark and gypsum block sensors can identify existing soil moisture, monitor moisture changes, locate the depth of water penetration, and indicate crop rooting depths.
These three types of sensors absorb and lose moisture similar to the surrounding soil.
Gypsum block and watermark sensors are read with resistance-type meters.
Tensiometers have gauges that indicate soil moisture by measuring soil moisture pressures in units of centibars.
Tensiometers are very accurate, but are most useful in lighter soils that are irrigated frequently.
Watermark sensors respond more quickly and are more accurate than gypsum blocks, but cost more.
Readings may be taken weekly during the early growing season.
During the crop's primary water use
 periods, readings should be taken two or three times each week for more timely management.
Plotting sensor readings on a computer spreadsheet or graph paper is the best method of tracking and interpreting sensor readings and managing irrigation.
An example is shown in Figure 15.
It describes soil moisture measured with gypsum blocks in wheat production.
A single block or tensiometer installed at a depth of 12 to 18 inches will measure moisture in the upper root zone; another installed at 36 inches will measure deep moisture.
Sensors usually are installed at three depths-12, 24 and 36 inches-and at a representative location in the field where the soil is uniform.
They should not be placed on extreme slopes or in low areas where water may pond.
Select a location within
 Figure 15a.
Soil moisture measurements in a wheat field.
Soil moisture should not fall below a reading of 40 to 60 for most soil types.
Figure 15b.
Cumulative ET and total water supplied to the wheat field in Figure 15a.
the next to the last center pivot span but away from the wheel tracks.
Locate sensors in the crop row so they do not interfere with tractor equipment.
Follow manufacturers' recommendations on preparing sensors.
It is essential to have the sensing tip in firm contact with undisturbed soil to obtain accurate readings.
The soil auger used to install sensors must be no more than 1/8 inch larger than the sensing unit.
Chemigation is the application of an approved chemical  with irrigation water through the center pivot.
Chemigation is an improved, advanced concept.
Pesticide and other chemical labels must state whether the product is approved for application in this way.
If so, application instructions are provided on the label.
EPA regulations require the use of specific safety control equipment and devices designed to prevent accidental spills and contamination of water supplies.
Using proper chemigation safety equipment and procedures also aids the grower by providing consistent, precise and continuous chemical injection, thus reducing the amounts  of chemicals applied.
As in Texas, state regulatory agencies may have their own requirements in addition to those of the EPA.
For more information contact your county Extension office or state Department of Agriculture.
Uniformity of application.
With a properly designed irrigation system, both water and chemicals can be applied uniformly, resulting in excellent distribution of the water-chemical mixture.
Precise application.
Chemicals can be applied where they are needed and in the correct concentrations.
Economics.
Chemigation is usually less expensive than other application methods, and often requires a smaller amount of chemical.
Timeliness.
Chemigation can be carried out when other methods of application might be prevented by wet soil, excessive wind, lack of equipment, and other factors.
Reduced soil compaction and crop damage.
Because conventional in-field spray equipment may not be needed, there could be less tractor wheel soil compaction and crop damage.
Operator safety.
The operator is not in the field continuously during applications, so there is less human contact with chemical drift, and less exposure during frequent tank fillings and other tasks.
Skill and knowledge required.
Chemicals must always be applied correctly and safely.
Chemigation requires skill in calibration, knowledge of the irrigation and chemigation equipment, and an understanding of the chemical and irrigation scheduling concepts.
Additional equipment.
Proper injection and safety devices are essential and the grower must be in compliance with these legal requirements.
The application of fertilizers with irrigation water, or fertigation, is often referred to as "spoon-feeding" the crop.
Fertigation is very common and has many benefits.
Most fertigation uses soluble or liquid formulations of nitrogen, phosphorus, potassium, magnesium, calcium, sulfur and boron.
Nitrogen is most commonly applied because crops need large amounts of it.
Keep in mind that nitrogen is highly soluble and has the potential to leach; it needs to be carefully managed.
There are several nitrogen formulations that can be used for fertigation, as shown in Table 7.
Be sure a solid formulation is completely dissolved in water before it is metered into the irrigation system.
This may require agitating the mixture for several hours.
Continue agitating throughout the injection process.
Nutrients can be applied any time during the growing season based on crop need.
Mobile nutrients such as nitrogen can be carefully regulated in the soil profile by the amount of water applied so that they are available for rapid use by the crop.
Nutrients can be applied uniformly over the field if the irrigation system distributes water uniformly.
Some tillage operations may be eliminated, especially if fertilization coincides with the application of herbicides or insecticides.
However, do not inject two chemicals simultaneously without knowing that they are compatible with each other and with the irrigation water.
Groundwater contamination is less likely with fertigation because less fertilizer is applied at any given time.
Application can correspond to maximum crop needs.
There is minimal crop damage during fertilizer application.
Table 7.
Amount of fertilizers needed to apply specific amounts
 Pounds of N per acre
 Kind of fertilizer	20	40	60	80	100
 Pounds per acre of fertilizer needed
 for rate of N listed above
 	60	120	180	240	300
 	98	196	294	392	488
 	44	89	133	177	222
 Gallons per acre of fertilizer needed
 for rate of N listed above
 	6.7	13.4	20	26.8	33.4
 	5.7	11.4	17	22.8	28.5
 	8.9	17.8	26.7	35.6	44.5
 Table 8.
Relative corrosion of various metals after 4 days of immersion in solutions of commercial fertilizers.*
 Fertilizer	PH of	Kind of metal
 solution	Galvanized	Sheet	Stainless	Bronze	Yellow
 iron	aluminum	steel	brass
 Calcium nitrate	5.6	Moderate	None	None	Slight	Slight
 Sodium nitrate	8.6	Slight	Moderate	None	None	None
 Ammonium nitrate	5.9	Severe	Slight	None	High	High
 Ammonium sulfate	5.0	High	Slight	None	High	Moderate
 Urea	7.6	Slight	None	None	None	None
 Phosphoric acid	0.4	Severe	Moderate	Slight	Moderate	Moderate
 Di-ammonium phosphate	8.0	Slight	Moderate	None	Severe	Severe
 Complete fertilizer 17-17-10	7.3	Moderate	Slight	None	Severe	Severe
 *Solutions of 100 pounds of material in 100 gallons of water.
Fertilizer distribution is only as uniform as the irrigation water distribution.
Use pressure gauges to ensure that the center pivot is properly pressured.
Lower cost fertilizer materials such as anhydrous ammonia often cannot be used.
Fertilizer placement cannot be localized, as in banding.
Ammonia solutions are not recommended for fertigation because ammonia is volatile and too much will be lost.
Also, ammonia solutions tend to precipitate lime and magnesium salts, which are common in irrigation water.
Such precipitates can form on the inside of irrigation pipelines and clog nozzles.
The quality of irrigation water should be evaluated before using fertilizers that may create precipitates.
Besides ammonia, various polyphosphates  and iron carriers can react with soluble calcium, magnesium and sulfate salts to form precipitates.
Many fertilizer solutions are corrosive.
Chemigation injection pumps and fittings constructed of cast iron, aluminum, stainless steel and some forms of plastic are less subject to corrosion and failure.
Brass, copper and bronze are easily corroded.
Know the materials of all pump, mixing and injector components that are in direct contact with concentrated fertilizer solutions.
Table 8 describes the corrosion potential of various metals when in direct contact with common commercial fertilizer solutions.
B-1670, "Soil Moisture Management."
 L-2422, "Chemigation Equipment and Safety."
 L-2218, "Pumping Plant Efficiency and Irrigation Costs"
 Actual lowest and highest field elevation irrigated in relation to the pivot point was used in the computer design printout.
Actual measured or reduced flow rate and pressure available by pump or water source was used in the computer design printout.
Friction loss in pivot mainline for quarter-mile-long systems is no greater than 10 psi.
Mainline size is telescoped to achieve selected operating pressure.
Mainline outlets are spaced a maximum of 60 to 80 inches or, alternately, two times the crop row spacing.
Gauges are included at the pad and last drop to monitor operating pressure.
For non-leveled fields, less than 20 percent variation in system design operating pressure is maintained when pivot is positioned at the highest and lowest points in the field.
Pressure regulators were evaluated for fields with more than 5 feet of elevation change from pad to the highest and the lowest point in the field.
Tower wheels and motor sizes were selected based on desired travel speed, soil type and slope, following manufacturer's recommendations
 Operation control provides expected performance.
The dealer provided a copy of the pivot design printout.
Educational programs of the Texas Agricultural Extension Service are open to all people without regard to race, color, sex, disability, religion, age or national origin.
Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 30, 1914, in cooperation with the United States Department of Agriculture.
Chester P.
Fehlis, Deputy Director, Texas Agricultural Extension Service, The Texas A&M University System.
Over-appropriated basins in Nebraska are river basins  where water coming into the basin is less than the amount of water taken out or leaving the basin.
These areas are closed to new high-capacity wells.
Over-appropriated basins are designated by the Nebraska Department of Natural Resources.
One approach to data collection is that the center pivot itself can be used as a platform to mount crop canopy sensors  which inform the SIS methods.
As the pivot is moved around the field, the sensors can monitor the crop and collect essential data across the field.
Wyoming Small Acreage Irrigation
 Caleb Carter, Kristi Hansen, Windy Kelley, Lucy Pauley; Ed.
J.
Thompson
 Steve Miller, editor, Tana Stith, graphic designer
 Issued in furtherance of extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture.
Glen Whipple, director, University of Wyoming Extension, University of Wyoming, Laramie, Wyoming 82071.
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Are you considering irrigating your small acreage?
Owning and managing a small acreage in Wyoming is exciting but can present some challenges.
Precipitation variability in an arid climate and a short growing season can make growing a crop difficult.
Generally, using some form of irrigation to produce a crop  is necessary.
Whether purchasing a property or already an owner, you may have irrigation questions: Can I use the water from the ditch running across the property?
What is a water right?
Does the property have one?
What is the best method to irrigate my property?
How often should I irrigate?
What are some ways to deal with conflicts with my neighbor over water?
This document is organized into four sections to help answer these questions.
The first is, "Can I irrigate?" This section explains how to determine if a property has a water right, how much water does the water right entitle the irrigator to use, how water rights may work within a subdivision, and a brief description of Wyoming water law.
The next section, "How can I irrigate?," discusses various irrigation methods used across Wyoming.
The third section, "Should I irrigate?," then discusses how to determine when to irrigate and how much water to apply.
The last section, "Irrigation Conflicts in Your Neighborhood," gives some points to consider if you find yourself in a water conflict.
With that, welcome to Wyoming small acreage irrigation.
We hope you find this a valuable resource as you start exploring the intricacies of irrigation in Wyoming.
A BRIEF HISTORY OF WYOMING WATER
 In the early history of the United States, anyone living in riparian areas  was allowed reasonable use of the waters that flowed past their private lands.
This "riparian rights" doctrine had been adopted from English common law and was appropriate in the eastern United States where water was relatively plentiful.
Pioneers in the western United States quickly realized the riparian rights doctrine was not feasible where water was scarce and large portions of the landscape were federally owned.
Early settlers found they needed to supplement rainfall with water transported through ditches and canals to provide sufficient water for crops.
Mining operations based on public lands needed water to extract gold and other minerals, but they could not assert riparian rights on lands they did not own.
The doctrine of prior appropriation developed in the West: the first to put water to beneficial use has a continued right to the water regardless of proximity to a waterway and land ownership.
As is the case in other western states, Wyoming water law has been developed over the past 130 years with these conditions in mind.
In the late 1800s, homesteaders laid claim to 160-acre units of land and secured water rights from the state for irrigating.
These original homesteads, with their ditch and canal systems and prior appropriation water rights, became the large farms and ranches that now characterize agriculture in Wyoming.
Some of these farms and ranches have gradually been subdivided since the 1970s, as demand for housing and rural small-acreage parcels has increased.
This creates challenges for new landowners seeking to understand how their water rights fit into a Wyoming water law created with a different ownership structure in mind.
For more information on western water law and the history of water in Wyoming, please see Getches  and Board of Control.
SECTION 1.
CAN I IRRIGATE?
Are you a landowner with a ditch running across your property?
Interested in irrigating crops or pasture?
Before doing anything with water on your land, the first question to ask is: Do I have a water right?
What is a water right?
The Wyoming Constitution declares all waters within the boundaries of Wyoming belong to the state; however, permitted water rights are issued by the state to individuals and entities that put the water to beneficial use.
Beneficial uses are defined by Wyoming statute or are determined at the discretion of the state engineer and include  agricultural, municipal, industrial and domestic use, and stock watering.
A water right grants the holder a legal right to use a certain amount of water for a specified use at a specific place.
The Wyoming State Engineer's Office and the Wyoming Board of Control supervise these appropriations.
In Wyoming, water rights for irrigation use are attached to the land.
For other uses, the right is attached to the purpose for which it is acquired this is the case in most, but not all, western states.
Wyoming water law is based upon the doctrine of prior appropriation.
Under prior appropriation, the first to claim a right to water on a particular waterway has the most senior right to use the water.
Under this "first in time, first in right" approach, senior rights on a waterway are fully satisfied before a junior right holder receives any water.
A right holder's seniority is based on the date they file an application with the State Engineer's Office for a water permit.
The oldest water rights in Wyoming are "territorial" water rights that pre-date statehood in 1890; an application for a water permit filed today would have a present day priority date.
In Wyoming, a basic water right for irrigation from a surface water source is 1 cubic foot per second  for 70 acres of land.
One cfs is the rate of flow of water that will supply 1 cubic foot of water in one second.
One cfs delivered continuously for 1 day is equivalent to 1.98 acre-feet of water.
An acre-foot is the volume of water to cover an acre of land 1-foot deep, about enough water to provide two households with water for one year.
A water right holder must put their water to beneficial use continuously to maintain the water right.
Under Wyoming state law, a water right not used for five successive years, when water was available for diversion, is deemed forfeited and could be subject to abandonment.
How are water rights administered in Wyoming?
The Wyoming State Engineer is responsible for issuing permits for the use of water in Wyoming.
Water commissioners, or hydrographer/commissioners, working for their division superintendent and ultimately the state engineer, are responsible for day-to-day activities related to administering water rights in Wyoming.
The Board of Control, comprised of the state engineer and four water division superintendents, adjudicates water rights and approves petitions to modify adjudicated water rights, such as allowing existing water right holders to change the point of diversion from the waterway, the place of use, or the type of use.
The Wyoming Board of Control meets four times per year, generally in Cheyenne.
Their meetings are open to the public.
Do I have water rights?
Determining whether or not water rights are associated with your property is important.
You should not assume you have rights to an irrigation ditch or the associated water even if it crosses your land, as that water could be allocated to someone else's property.
Contact the State Engineer's Office or your local water commissioner, use the State Engineer's Office e-Permit online database, or visit the county clerk's office of where your property resides to determine if water rights are associated with the property.
Water rights are not connected to a residential subdivision lot number, but rather to the property's public land survey system legal description.
Provide the property public land survey system legal description to the county clerk's office to ensure information for the correct property is accessed.
The public land survey system legal description of a property is defined as the quarter-quarter , section, township, and range referenced to a principal meridian and base line.
The public land survey system legal description of your property may or may not be printed on your property tax assessment notice or tax bill.
Your property deed will contain the legal description of your property but not necessarily a public land survey system legal description.
This information can often be found on a 7.5 minute United States Geological Service  topographic map.
You can buy a topographic map of your area from a number of sources, such as an outdoor or hunting/fishing shop, or you can visit the USGS website and purchase them online.
Additionally, several counties  offer online maps for their county free to the public.
Typically, the web-based maps have layers a user can add to or remove from the base map, which often includes the legal description.
A county assessor's office should be able to tell you whether or not an irrigation district administers your water rights and, if so, the name of the district.
Many irrigation districts assess fees for operation, maintenance, and rehabilitation expenses from landowners whose properties have water rights associated with them.
The county assessor's office collects this annual fee.
If an irrigation district doesn't exist, and you have water rights, a less formal "entity" may have formed to deliver water.
Examples include ditch companies, corporations, and homeowner associations.
You may not be in any kind of organized district, ditch company, or association at all.
Your water right may simply be a single diversion out of a creek or stream or a ditch shared with several common landowners.
You've determined you have water rights now what?
Wyoming statutes  govern water rights and responsibilities associated with those rights; however, the state allows flexibility for specifics at a more local level, such as how/when water will be delivered.
If you have water rights, understanding state laws and local bylaws/rules governing your use of water is important, as is understanding the extent to which you share water rights with neighbors.
Lay of the land post-subdividing
 New housing developments are often constructed on lands formerly part of a farm or ranch with irrigation water rights.
Unless the party that subdivides the land completes the legal process of severing water rights from a parcel of land with an irrigation appropriation, which requires approval from the State Engineer's Office or Board of Control, these sub-divided lands will most likely have water rights associated with them.
In some instances, when land is subdivided, a water distribution plan is developed and recorded.
These plans include information such as which properties have water rights associated with them, the location of delivery and catch ditches , and easements for ditch maintenance, among other information.
Even if you determine you have a water right, you may not be able to access the water when and how you want, even if you see it flowing on or next to your land.
There may be local rules established by your subdivision association, irrigation district, or ditch company that indicate how and when you can access the water.
For example, you may need to request permission from your subdivision association, irrigation district, or ditch company before you can activate your ditch.
How much water you are able to receive may also vary from year-to-year depending on water availability regardless of the size of your right, because small-acreage water rights are typically part of a larger, shared water right.
Small-acreage landowners usually combine their individual irrigation water allocations "to create a larger volume and then rotate that volume from one acreage to the next in a sequence that provides water to each tract on a regular and timely basis".
If this is not done, there is a good probability the water connected to the water right of a single parcel would be too small in volume to make it from the water source to the parcel of land.
Figure 1.
Example with a subdivision  with half the parcels having water rights, a subdivision  without any water rights, and a ranch  with water rights.
Each landowner should contact a local official  to learn about laws and local bylaws/rules to better understand how to appropriately access their water rights.
The following checklist will get you started.
Note this is a general list and, depending on the answers, you might want to ask additional questions and/or ask for clarification.
Do I belong to an irrigation district or ditch company?
Does the district/company have bylaws or other written rules?
Does the district/company meet if so, when do they generally meet?
Is there a map that shows the irrigation ditch system?
If so, where can I get a copy?
Does the irrigation district/company have a fee?
If so, how much is it, when will I be billed, and who do I pay?
What are the fees used for?
How is water allocated among the landowners with water rights?
Are water allocations combined and rotated among landowners?
If so, who is responsible for rotating the water?
What happens if I use up my allotment of water before the water is turned off for the year?
Is the irrigation water automatically turned on each year, or do I have to request water when I want to irrigate?
If the former, what is the general timeline for when water is turned on/off each year?
If the latter, who do I contact to receive water?
How will I know when I will receive water and for how long do I get to keep the water?
There is a lot to know and understand as a small-acreage irrigator.
Not all irrigation districts and ditch companies are structured the same.
Different water management structures in Wyoming
 The reality is much variability exists throughout Wyoming for how small-acreage/subdivision irrigation water rights are managed.
For example, there are different structures at the local level varying from county-assessed irrigation districts to less formal entities that handle their assessment fees internally.
This flexibility has many advantages, such as allowing areas to customize how they will manage shared irrigation water; however, it also has the potential to introduce a number of challenges and user conflict.
Following are a few key ways irrigation districts and ditch companies differ from each other in Wyoming.
This section provides an example of how your irrigation water rights might be administered and to help you be better prepared when talking to your neighbors or officials about irrigating.
Governance.
An irrigation district is a court-established assessment district organized under Wyoming Statutes to deliver water to the lands within its boundaries that have water rights.
A district usually has one large diversion canal and several smaller distribution ditches, called laterals, which carry water from the diversion canal to individual parcels of land with water rights.
The State Engineer's Office generally monitors and regulates an irrigation district's diversion at the canal headgate  but leaves internal distribution of water to irrigated lands to the district.
State law gives irrigation districts authority to collect assessment fees from water users within its boundaries.
These fees are generally collected through the county at the same time as property taxes.
Irrigation districts are generally formed when irrigators need borrowing authority under state law to
 help them construct or improve canals, reservoirs, or other infrastructure that make accessing their water rights easier.
An elected board of directors governs an irrigation district.
A ditch company is a corporation formed to construct a ditch to convey irrigation water.
Ditch company assessments are handled internally rather than through the county.
Irrigation districts and ditch companies may hire managers, ditch riders, and/or attorneys.
These employees are authorized through company bylaws to enter properties within the boundaries of the district/companies to conduct business of the district.
When a subdivision is within the boundaries of an irrigation district or ditch company, the district/company may require the subdivision association to appoint a watermaster.
This watermaster is the point of contact between the district/company and landowners.
All decisions and communications about water delivery timing and quantity go through the watermaster.
This structure is intended to facilitate more efficient communication between the irrigation district and landowners.
Whether a subdivision is created within or outside the boundaries of an irrigation district or ditch company, there may also be provisions in the subdivision homeowner associations for the collective operation and maintenance of ditches.
Like ditch companies, homeowner associations also have the authority to assess themselves and establish rules for members.
Assessment fees.
Most irrigation districts and ditch companies charge an assessment fee to cover administrative costs and maintain canals and laterals.
Ditch riders are a primary expense of many irrigation districts.
Ditch riders help maintain the system and open headgates for customers who have called for water.
Assessment fees vary greatly depending on the size, complexity, and age of the system.
Most irrigation districts charge a per-acre fee.
Many districts also charge an additional per-customer fee.
Water delivery.
An irrigation district can have difficulties delivering water to the small acreages created by subdivisions when there is not enough water after
 IRRIGATION AND DRAINAGE PLANS
 Under state law, a subdivision of five lots or more must address water rights in some fashion.
The subdivider may petition to move the rights to other lands, request cancellation of the rights, or develop an irrigation and drainage plan.
An irrigation and drainage plan specifies how and where each lot is going to get water and where wastewater goes.
The plan must be approved by the State Engineer's Office.
In 2009, all seven irrigation districts in Park County petitioned the county planning and zoning commission to change their rules to require that any piece of land being subdivided must have an irrigation and drainage plan approved by the local irrigation district.
Platte County has implemented a similar regulation.
People often think once water leaves their property it is no longer their concern.
But people are responsible for their wastewater until it returns to a natural waterway.
Even with irrigation plans and drainage plans in place, there is still potential for conflict if subdivision landowners are not aware of easements on their properties.
Sometimes, easements are not even defined on an irrigation plan.
By state law, if a ditch has been in place for over 10 years, an leasement may exist, whether recorded or not.
Landowners can acquire information on the irrigation and drainage plan for their subdivision either from the county or from their irrigation district.
SOME EXAMPLES OF HOW IRRIGATION ARRANGEMENTS CAN FUNCTION
 Example 1.
Producer Irrigation District
 Producer Irrigation District has a service area of over 35,000 acres.
Although approximately 40 percent of its 1,200 customers are small-acreage landowners, they comprise less than 10 percent of this total acreage.
Farmers in this irrigation district tend to grow alfalfa hay, barley, sugarbeets, and dry beans.
An elected five-member board of directors governs the Producer Irrigation District.
Irrigation district customers vote on a per-acre basis.
For example, someone with water rights on 4 of their 5 acres has four votes.
Producer Irrigation District has an assessment fee of $22/acre.
They have an additional assessment of $75 per landowner.
Irrigation districts in Wyoming have taxing authority under state law.
The Producer Irrigation District assesses its membership once per year, on the same timeline as county property taxes.
The irrigation district does not provide water to customers who have not paid their assessments.
Watermaster: the Producer Irrigation District requires subdivisions within its service area elect a watermaster to be the single point of contact between individual landowners and the irrigation district.
The watermaster coordinates delivery of water, collects assessment fees, and resolves problems that arise between landowners within the subdivision.
headgate.
If somebody within a subdivision is not taking care of a ditch, or somebody is flooding their neighbor's property, then the irrigation district may simply shut off the headgate to the subdivision until the problem is resolved.
Generally speaking, each subdivision has a single headgate served by Producer Irrigation District.
The irrigation district's responsibility to serve a subdivision stops at the
 Ordering water.
Farmers and subdivisions submit water order cards to the irrigation district when they want to irrigate.
The ditch rider, an employee of the irrigation district, then divides available water for the day among those who have ordered it on a per-acre basis.
The irrigation district requires 48 hours notice to turn on water and 24 hours notice to turn it off.
The subdivision watermasten orders water for a subdivision.
The irrigation district ditch rider turns the water into the subdivision's ditch.
From that point, the subdivision watermaster and landowners must coordinate water deliveries among themselves.
Subdivision landowners have to be organized and communicate among themselves to take the water in rotation when it's their turn.
Example Water Order Card
 WATER ORDER RECORD ONE CARD PER TURNOUT
 ON-48 HOURS NOTICE OFF-24 HOURS NOTICE
 SUBMITTED	&	CUBIC FEET PER SECOND
 NUMBER	TURN-ON	CHANGE	TURN-OFF
 LAT.
AMOUNT	FROM	TO
 T.O.
DATE	DATE	DATE
 NOTICE: BY PLACING THIS ORDER YOU ACKNOWLEDGE YOUR RESPONSIBILITY FOR THE CONTROL OF YOUR WATER AND MAINTENANCE OF YOUR WASTE DITCHES.
Example 2.
Ranchland Irrigation District
 The next irrigation district example is in western Wyoming.
The district was formed in the 1990s from an old irrigation system.
The district provides water to one ranch and to two subdivisions comprised of lands with adjudicated water.
The majority, if not all, of landowners grow grass hay.
The Ranchland Irrigation District encompasses more than 2,129 adjudicated acres of which 97 percent are irrigated by subdivision landowners.
The Ranchland Irrigation District landowners meet a minimum of once a year to address annual business, including electing one new water commissioner.
The Ranchland Irrigation District is divided into three sub-districts, each of which has an elected commissioner.
The landowners who have water rights within the Ranchland boundaries govern the district by electing the commissioners.
Each landowner gets one vote for each whole adjudicated acre in their name.
Commissioners are volunteers who serve three-year terms and receive a minimum stipend to offset costs for fuel and time.
The commissioners have a number of responsibilities, including determining the amount of water required, when the primary headgates will be opened, and how the water will be rotated among landowners for their sub-districts.
They work with the watermaster to maintain ditches of their sub-districts.
The Ranchland Irrigation District has two part-time employees: an accountant and a water/ditch master.
The accountant is responsible for maintaining the Ranchland Irrigation District's ledger and ensuring due diligence is complete for grants the district has received.
The commissioners appoint a watermaster annually to serve a one-year term as an officer of the Ranchland Irrigation District.
The watermaster is responsible for the Ranchland irrigation system, managing the system as directed by the commissioners, and enforcing the rules or contacting the appropriate authority, among other duties.
A commissioner fills the role of the watermaster when he/she is unavailable.
The other two appointed officers are the president, which is one of the three elected commissioners, and a secretary-treasurer.
Additionally, each sub-
 district/lateral designates a contact person who works with the watermaster and/or commissioner to coordinate irrigation needs.
The Ranchland Irrigation District administers an annual fee for water rights, which is billed and collected through the county assessor's office.
At the time of print, each landowner pays a $25/year fee plus an approximately $9/acre fee.
The Ranchland Irrigation District uses the funds to pay commissioner stipends, part-time employees, and to maintain the main ditches and associated laterals.
As noted earlier, the commissioners determine how the water will be rotated among landowners.
In two of the Ranchland sub-districts, the landowners follow a rotation call schedule.
The rotation starts with the first person along the ditch.
They receive and can use the water for up to 24 hours per 10 acres they own per rotation.
They notify the next person on the ditch , and the landowners can discuss who and when the water will be moved to the next property.
Once the water reaches the last person on the ditch, the first person will receive the water again.
The call rotation allows flexibility among the landowners; however, it requires much communication.
For example, if there are 10 landowners in a sub-district and one owns 20 acres, two own 30 acres, and the other seven each own 10 acres, a given landowner can expect to receive water every 15 days.
However, sometimes a landowner elects not to keep the water the entire time for any number of reasons, which shortens the time the rotation will start over.
The third sub-district follows a calendar and assigns dates when a landowner can irrigate.
In other words, if landowner X is assigned the 4th, 12th, 20th, and 28th, those are the dates of the month they can irrigate.
The time they start and stop irrigating is set, for example, start and stop at 6:30 a.m.
of a given rotation.
The calendar method minimizes the need for communication among landowners; however, the system tends to be less flexible.
ditch losses  to push the water all the way to the end of the ditch.
Some districts/companies may continue to deliver water just to the original headgate of the pre-subdivided ranch and leave internal administration of the water to the homeowner association.
In particularly arid areas of Wyoming where there is little hope of receiving much water in any year, the irrigation district may make a single annual delivery to ensure sufficient water left after ditch losses to make the delivery.
In less arid areas, irrigation districts have established protocols for sharing water.
Check with your district to see if it has procedures in place for rotating water in water-short years.
Districts/companies often establish rules for how often  landowners can irrigate.
For example, a district might have an established rule each landowner will get 24 hours of irrigation water per 10 acres per rotation.
A person who owns 20 acres would be allowed to irrigate up to 48 hours each time they receive irrigation water.
The number of times they receive water in a given season is contingent on how many acres are irrigated above and below them and the length of the irrigation season.
What if there is no ditch company or subdivision managing the irrigation water?
In some cases, a ditch company, subdivision, or other entity has not been formed to manage irrigation water.
Hopefully, the small-acreage landowners can mutually agree to maintain and operate the ditch to ensure the ditch remains operational.
Irrigators who share a private ditch and/or pipeline that is not part of a formal group  can assess themselves a fee and develop rules to maintain the order among themselves.
Occasionally, landowners won't agree when to turn water on/off.
The general rule of thumb in non-districts/companies is that no person can deny another person access to their water.
This said, a person/group of people can deny access to water if granting it would result in "unpreventable" harm, and/ or the person who desires water is "in violation of a rotation that all parties are engaged in".
Note that the ditch and headgate issues within the boundaries of an irrigation district, ditch company, or subdivision are civil matters and are not within the purview of the State Engineer's Office.
Please see Section 4, "Irrigation Conflicts in Your Neighborhood," for ideas on minimizing conflict.
Irrigation ditch and easement 101
 Understanding the separation between water rights and ditch rights, which occurred in 1912 in the state of Wyoming, is important.
Considering irrigation ditches are the "vessels" for providing water to irrigators, it is understandable why water and ditch rights are murky.
In Wyoming, ditch and easement disputes are civil issues, which means the State Engineer's Office has little to no authority.
New subdivisions are often built near existing ditches, canals, and laterals.
Many homeowners want to park on easement roads, which may be their right as the underlying property owner.
However, when irrigation district employees need access to an easement road, those cars need to be moved.
Who is a ditch owner?
A person is considered an owner of a ditch, entirely or partially, if a ditch is used to deliver water to their property or the ditch serves to move runoff away from their property.
Ditches crossing properties that do not have water rights associated with them are not uncommon.
In this situation, someone else  owns the ditch, and they have an easement to access the ditch.
An easement allows an individual to rightfully enter the real property of someone else for a specific reason in a specific area.
Additionally, an easement permits a ditch to exist in its current location, and sufficient room along the ditch for the ditch owner to perform routine and necessary maintenance.
Wyoming receives an average of 16 inches of precipitation annually.
Because of the state's high elevation and mountainous terrain, there is significant variability in precipitation levels from one basin to the next.
One basin can be experiencing drought, while another basin is experiencing above-average precipitation.
Wyoming is a headwaters state that provides water to four major river basins.
Although its precipitation level is relatively low , Wyoming's large land area means it actually receives a fairly large volume of water in total: approximately 17 million acre-feet annually.
One acre-foot is the amount of water it takes to cover 1 acre of land 1-foot deep in water.
One acre-foot is approximately enough water to provide two households with water for one year.
Much of Wyoming's precipitation occurs in the mountains over the winter months as snow and enters Wyoming's rivers, canals, and reservoirs during the spring months when temperatures rise.
Agriculture uses approximately 80 percent of water in the state.
Of this amount, the single largest crop
 by far is alfalfa and grass hay, primarily used for livestock feed.
The remaining water in the state goes to municipal and industrial users and is depleted by evaporation from the state's many reservoirs.
Wyoming water users do not have a right to all the precipitation that falls within the state's borders.
Downstream states in all four directions have a right to water from Wyoming through a mix of legal compacts, court decrees and, in the case of the Upper Green River Basin in southwestern Wyoming , an international treaty with Mexico.
ADMINISTRATION OF WYOMING WATER AND SMALL-ACREAGE IRRIGATION
 Large tracts of land were once a part of the same irrigation system likely owned by one ranch.
A previous owner decided to subdivide the land, which resulted in many private landowners with connected water rights.
The structure of Wyoming water and small acreages is similar to the original structure with a few additions, such as a subdivision spokesperson.
The following is a schematic of the administrative positions of Wyoming's water and small-acreage irrigation and the role of each level.
Chief administrator of Wyoming water regulation
 Job: Supervision and protection of Wyoming waters
 Appropriation, distribution, and application of water to beneficial use
 Administers water for each of their divisions [See Figure 2] with assistance from hydrographer commissioners and water commissioners below.
Division 1: North and South Platte River drainages, and the Niobrara and Little Snake River drainages 
 0 Division 2: includes all drainages north of the North Platte and Niobrara River drainages and east of the Bighorn Mountains 
 0 Division 3: Big Horn and Clark's Fork River drainages 
 D Division 4: Green, Bear, and Snake River drainages, and most of the Great Divide Basin 
 Wyoming Board of Control is comprised of the state engineer and the four division superintendents
 Supervision and protection of Wyoming waters
 0 Adjudication of water rights
 Approval of modifications of adjudicated and some unadjudicated water rights
 Assists division superintendent in administering water duties may include:
 Routine administration of surface water sources following a "call for regulation"
 Measuring streamflow, reservoir content, and operation and maintenance of stream gauging stations and networks
 Inspecting water structures and land under water rights permits for compliance and adjudication
 Meets with and advises water resource users
 An organized group that acts to provide water to its shareholders on a proportionate basis
 Public, mandatory, and fee collecting entity
 Water is allocated by acre
 Can create rules/bylaws for handling water within their boundaries without outside oversight 
 An organized group that acts to supply and deliver water to its shareholders on a proportionate basis
 Private, voluntary, and fee-collecting entity
 Holds and manages water rights for shareholders who have pro-rata interest 
 An organized group that acts to provide water to its shareholders and maintains the lateral ditch system
 Generally smaller and separate legal entities from mutual ditch companies 
 Hired by a ditch company or irrigation district to maintain a ditch and open and close headgates as necessary
 Calculates ditch volumes and oversees ditch operations
 Coordinates water diversions and "calls" with the water commissioner/hydrographer commissioner during irrigation season
 Note: sometimes smaller ditch companies use a rotating "ditch captain" to coordinate efforts with the water commissioner
 Can create rules/bylaws for handling irrigation water within their boundaries without outside oversight
 An appointed person who speaks with the irrigation district, water commissioner, and/or ditch rider on behalf of the ditch co-owners
 Individual, small-acreage landowners who have equal water rights and use the same water delivery system
 Share the operation and maintenance responsibilities and expenses
 Source: Wyoming Water Resources Data System.
Figure 2: Administrative Water Divisions of Wyoming
 HOW IS GROUNDWATER REGULATED DIFFERENTLY THAN SURFACE WATER?
Groundwater in Wyoming is also managed under the doctrine of prior appropriation, so an earlier right has a higher priority to water from an aquifer during periods of limited supply.
One distinction related to irrigation is that groundwater permits are not based on the 1 cfs/70 acres duty of water that defines issuance of surface water irrigation permits.
Those wanting to drill a well need to follow the same procedures one would to apply for a permit to divert from a surface water source on your land.
The first step is to file an application with the state engineer.
Your application must be approved before drilling can begin.
The required forms to begin this process are available at the State Engineer's Office, offices of water division superintendents, water commissioners, and county clerks.
A permit to construct a well will generally be approved by the state engineer unless the well is in a groundwater control area.
Typically, the Board of Control designates groundwater control areas where groundwater withdrawals are approaching or have exceeded the recharge rate.
In these locations, a permit to drill will receive greater scrutiny from the state engineer and the local control area board.
There are three groundwater control areas in Wyoming Goshen, Laramie, and Platte counties.
If there is an older well on your land used solely for stock and/or domestic purposes, you might not have a permit on file with the state engineer.
Wells drilled for these purposes before 1969 are exempt from permitting.
If you want to change the location of an existing well or drill an existing well deeper, you might be able to do so without loss of priority under certain conditions.
For example, a change is likely to be approved if the new well location is in the same aquifer and the same general vicinity as the old one.
Contact the State Engineer's Office before moving a well or drilling deeper.
So which ditch and how much maintenance are you responsible for?
You have some level of responsibility to maintain a ditch if it is used to deliver water to your property or carries run-off water away from your property, including catch-ditches.
Each ditch owner is responsible for their proportionate ownership of the ditch, which is the "ratio between the water right of each water user to the total water rights adjudicated under such irrigation works".
The proportionate ownership of a common ditch includes not only the delivery ditch to an irrigator's property, but the stretch of ditch from the point runoff leaves a person's property until the water enters a natural waterway or enters an area under the authority of another entity.
Not using your water rights?
Are you still responsible for ditch maintenance and assessed fees?
The short answer is yes; however, there is more to the story.
Contact the State Engineer's Office for more information.
Ditch embankments are among the most important aspects of ditch maintenance.
Proper maintenance of embankments, including removal of trees and shrubs, ensures water from a ditch does not flood or damage the property of others.
A ditch owner is liable for damage due to
 "negligence or unskillfulness of constructing, maintaining, or operating" their ditch.
Thinking about moving dirt?
We all have visions of what we will do with our properties, how we will change and improve them over time.
Someone's vision might be to fill in and/or reroute a ditch to better irrigate a corner of their property.
Although possible, investigate this option thoroughly and only proceed with great caution and care.
Subdivisions may collect a small fee from each landowner to cover ditch maintenance rather than requiring everybody to maintain the portion of the ditch on their property.
Requiring everybody maintain the portion of the ditch that is on his or her property can lead to conflict.
The person at the top of the ditch is maintaining for everybody; the person at the end of the ditch does not have to maintain their ditch at all.
Another recipe for conflict is if someone new comes to the area and is second on the ditch but doesn't maintain their ditch.
The lay of the land can be deceptive to the naked eye.
An area that appears flat or to slope in one direction could have a slope great enough, or in multiple directions, to let gravity take over.
The outcome is water in unintended locations, which could result in significant destruction.
Imagine accidently flooding your home or neighbors due to rerouting an irrigation ditch with the good intention of better irrigating a corner of your property.
Dirt mover beware!
State law prohibits a person from wrongfully changing the location of a ditch, which inhibits or eliminates the ability of a co-owner from receiving their water.
Many ditches appear to wander across a property rather than proceeding in a straight line.
There are often reasons for this, including the need for the ditch to follow a particular slope to deliver the water to the spot where needed.
Straightening or deepening a ditch can lead to it not delivering the water as desired or other undesired consequences, such as physical degradation of the system by erosion or down cutting.
The possibilities of what can occur when filling-in or rerouting a ditch are endless.
Again, you are encouraged to proceed with caution prior to moving dirt.
The following is a short list of resources that might help ensure the success of your ditch project.
Wyoming State Engineer's Office or Board of Control
 USDA Natural Resources Conservation Service
 University of Wyoming Extension
 Land survey and engineering firms
 811 Call Before You Dig
 I want more or less water to flow down the main ditch can I adjust the amount of water from the natural watercourse into an irrigation delivery system?
The short answer is "maybe." When a river is under administrative regulation, the local water commissioner or other authorized State Engineer's Office representative are the only individuals who may, either directly or indirectly, alter the amount of water leaving the natural watercourse into an irrigation delivery system..
When the watercourse is under "free river" conditions , water users typically adjust their own diversions from the watercourse.
The water commissioner from your area will know if the river is under administrative regulation or not.
However, your water access may still be restricted by an irrigation district, irrigation company, or homeowner association rules.
Dry pockets were found in much of the west at an inch or less, which is half or less of normal.
There was a daily precipitation record set at Norfolk of 0.79 inch on Sept.
17.
After the third driest summer on record, sixth driest year-to-date , and long-term dryness plaguing portions of the state, drought conditions generally worsened after another dry month.
Interpretation of Soil Moisture Content to Determine Soil Field Capacity and Avoid Over-Irrigating Sandy Soils Using Soil Moisture Sensors
 Lincoln Zotarelli, Michael D.
Dukes, and Kelly T.
Morgan
 Capacity of the Soil to Store Water
 Soils hold different amounts of water depending on their texture and structure.
The upper limit of water storage is often called "field capacity" , while the lower limit is called the "permanent wilting point".
Following an irrigation or rainfall event that saturates the soil, there will be a continuous rapid downward movement  of some soil water due to gravitational force.
During the drainage process, soil moisture decreases continuously.
The velocity of the drainage is related to the hydraulic conductivity of the soil.
In other words, drainage is faster for sandy soils compared to clay soils.
After some time, the rapid drainage becomes negligible and at that point, the soil moisture content is called "field capacity." The permanent wilting point is determined as the soil moisture content at which the plant is no longer able to absorb water from the soil causing the plant to wilt and die if additional water is not provided.
However, most plants will undergo substantial water stress before this point, and vegetables will likely sustain substantial yield reductions long before the permanent wilting point is reached.
The total amount of water available for plant uptake is the "plant available water" , which is the difference between FC and PWP  and is often expressed as a percent by volume (volume of water/volume of soil
 sample).
The "available water holding capacity"  is determined by multiplying the PAW by the root zone depth where water extraction occurs.
Depletion of the water content to PWP adversely impacts plant health and yield.
Thus, for irrigation purposes, a "maximum allowable depletion"  or fraction of AWHC representing the plant "readily available water"  is the ideal operating range of soil water content for irrigation management.
Theoretically, irrigation scheduling consists of initiating
 Figure 1.
General relationship between plant available water , soil field capacity, permanent wilting point, soil unavailable water and soil texture class.
Credits: UF/IFAS
 2.
Lincoln Zotarelli, assistant research scientist; Michael D.
Dukes, associate professor; Department of Agricultural and Biological Engineering; and Kelly T.
Morgan, assistant professor, Department of Soil and Water Science; UF/IFAS Extension, Gainesville, FL 32611.
irrigation at low soil water contents, corresponding to the given MAD, and irrigating until depleted water has been replaced without exceeding FC, otherwise drainage and/or deep percolation will occur.
Irrigation scheduling is simply applying water to crops at the right time and in the right amount and is considered an important best management practice.
Typically, irrigation scheduling is most often determined by grower judgment or using a pre-determined calendar schedule of irrigation events based on previous seasons' water requirements.
Several factors such as plant evaporative demand, soil characteristics and root distribution are taken into account as well, in order to establish proper irrigation scheduling.
A wide range of irrigation scheduling methods is used in Florida with corresponding levels of water management.
The recommended method for scheduling irrigation  for vegetable crops is to combine,  the crop water requirement method that takes into account plant stage of growth;  a measurement of soil water status; and  guidelines for splitting irrigation.
Practical Determination of Soil Field Capacity for Sandy Soils Using Soil Moisture Measurements
 Figure 2 shows volumetric soil water content at depth of 0-6 inches measured by a capacitance sensor during a period of 4 days.
There were 2 irrigation events on 11/06 and 11/09 at 7:00 am.
For the soil field capacity point
 determination, we intentionally applied an irrigation depth that resulted in saturation of studied soil depth layer, in this particular case 0-6 inches.
Figure 2.
Example of practical determination of soil field capacity for sandy soil after irrigation event.
Credits: UF/IFAS
 The depth of irrigation applied was 0.17 in.
After both irrigation events, there was a noticeable increase in soil moisture content.
The degree to which the soil moisture content increases, however, is dependent upon the volume of irrigation, which is normally set by the duration of irrigation event.
For plastic mulched drip irrigation in sandy soils, long irrigation cycle times result in a relatively large increase in soil moisture in the area below the drip emitter.
In Figure 2, the spike in soil moisture appears to only be temporary, as the irrigation water rapidly drains down beyond the 6 inch zone.
This rapid spike in soil water content indicates that the soil water content, as measured by the SMS probes, rapidly reached a point above the soil water holding capacity and the water percolated down to deeper soil layers.
Between 11/06 at 6:00 pm and 11/07 at 7:00 pm , the rate of decrease of soil water content slowed to a constant rate due to slower soil water extraction by drainage, which occurred during the day and night.
Evapotranspiration, also reduced the soil water content, that occurred exclusively during the daytime.
For sandy soils, the point at which the slope of drainage and extraction lines changes from a rapid to a slower decrease in soil water content can be assumed as the field capacity point.
At this point, the water has drained out from the large soil pores , and has been
 replaced by air.
The remaining pore spaces  are still filled with water and will supply the plants with needed moisture.
It is very important the irrigation manager understands this concept of "field capacity" to establish an irrigation control strategy with goals of providing optimum soil moisture for plant growth, productivity, and reduction of fertilizer nutrient leaching.
Examples of Irrigation Management of Vegetable Crops in Sandy Soils
 Figures 3 and 4 show examples of over-irrigation and proper management of drip irrigation, respectively.
In Figure 3, the irrigation was applied once per day with a depth of 0.18 in, equivalent to 4,718 gal/ac with drip irrigation.
After each irrigation event there was an increase in the soil water content followed by rapid drainage.
Large rainfall events may lead to substantial increases in soil moisture content.
On 10/29, right after the irrigation, a large rainfall of 0.44 in, which resulted in a second spike of soil water content in the same day.
Irrigation the following day  began when the volumetric soil water content was above field capacity and could have been skipped safely.
Figure 3.
Example of over-irrigation on volumetric soil moisture content of 0-6 inches depth under plastic mulched conditions for sandy soils.
Credits: UF/IFAS
 Between 10/31 and 11/02, no irrigation was applied to the crop.
The volumetric water content decreased from 0.14 to 0.08 in/in.
Due to the very low water holding capacity of the sandy soils, skipping irrigation for several days could lead to unneeded crop water stress especially during very hot or very windy days , or during the flowering stage of growth.
Between 11/02 and
 11/06, large daily irrigation events were repeated, exceeding the "safe irrigation zone," and leading to water drainage and nutrient leaching.
Figure 4.
Example of adequate irrigation management on volumetric soil moisture content of 0-6 inches depth under plastic mulched conditions for sandy soils.
Credits: UF/IFAS
 This document summarized guidelines for determining soil field capacity and optimum irrigation schedules for sandy soils using soil moisture sensor measurements.
Soil moisture sensors have shown potential for soil moisture monitoring and supporting irrigation decisions in vegetable crops.
In the past, soil moisture sensors have not been widely used by growers because of costs, the level of technical skill required, and sensor maintenance required.
Advances in soil moisture sensors have made them easier to use and the cost of energy has made these sensors a more viable option.
Continued restrictions aimed at reducing nutrient leaching and recent increases in energy costs have increased grower interest in use of improved technologies.
This information is supplied to help the irrigation system manager schedule and operate the system to optimal capacity.
With proper management and operation, microirrigation systems can apply precise amounts of water to the crop for maximum effectiveness at high levels of efficiency.
Using Flexible Pipe  with Surface Irrigation
 Juan Enciso and Xavier Peries*
 Aimed at farmers and irrigators who want to irrigate their crops using flexible plastic pipes , this publication highlights  advantages of using poly-pipe,  factors to consider in selecting such pipe, and  considerations for installing it.
Advantages of Using Pipes to Deliver Irrigation Water
 Using pipe systems  to convey and distribute water to fields has several advantages:
 Increases in on-farm irrigation efficiency, by avoiding water loss due to deep percolation from earthen conveyance ditches.
Better irrigation control.
Fluctuations in irrigation-canal water levels are common.
Using earthen ditches and siphon tubes requires intensive labor to avoid water spillage as a result of such fluctuations.
In contrast, a pipe-irrigation system needs only to have an outlet opened to deliver water through the pipe to furrows; irrigation can be left unattended, even when fluctuations in water levels occur.
Labor savings.
In the Rio Grande Valley, water is distributed through canals coming from the river and is delivered at different outlets.
Systems are designed to deliver one "head" of water at each turnout.
One turnout is installed for each 40-acre field.
Farmers may have field-blocks larger than 40 acres, and sometimes farmers may irrigate several fields at the same time.
With pipe-irrigation sysitems, one irrigator can control six to eight irrigation fronts.
Types of Pipes Used to Deliver Water
 Both gated pipes and poly-pipes can convey and deliver irrigation water.
Gated pipes are rigid, made of aluminum or PVC, and generally less than 12 inches in diameter.
Poly-pipes are expensive but are flexible and expand when full, are made from polyethylene resins, and generally are used for the larger pipe diameters needed to irrigate furrow crops.
Selecting the Correct Type of Poly-pipe
 The most important of several pipe-selection characteristics are thickness and diameter.
Thickness determines pipe durability.
Some farmers prefer thinner poly-pipe mil); because poly-pipe is sold by weight, they can save money by economizing on thickness.
Poly-pipes also come in larger thicknesses , allowing more pressure to be contained.
*Assistant Professor and Extension Agricultural Engineering Specialist ; Extension Associate Biological and Agricultural Engineering Department; Texas AgriLife Extension Service, The Texas A&M System
 Pipe diameter should be selected based on irrigation flow-rate.
Table 1 provides some approximate diameters and thicknesses needed for selected flow-rates.
Larger diameters will yield less friction with less head loss, permitting longer runs.
Pipe outlets for discharging water to fields are made with a hole puncher after the poly-pipe has been laid out , with outlet size influencing furrow stream-size.
The most common outlet sizes are 1/2, 1 and 2 inches.
Table 1.
Poly-Pipe Characteristics.
Diameter	Thickness	Maximum	Maximum	Gallons/
 		pressure	head	Minute
 		
 8	10	1.30	3	400
 10	6	0.86	2	500
 10	10	1.30	3	600
 12	6	0.86	2	800
 12	10	1.30	3	1,000
 16	6	0.86	2	1,800
 16	10	1.30	3	2,000
 18	6	0.86	2	2,500
 18	10	1.30	3	2,700
 22	10	1.30	3	3,800
 Economics of Poly-Pipe Irrigation
 The main expense associated with poly-pipe is its initial cost.
Labor costs are minimal, since installation takes two workers just half a day.
Once installed, poly-pipe remains in position for an entire season.
Poly-pipe can be used for as many as three irrigation seasons if it is handled carefully to avoid damage and stored between seasons in a dry place out of direct sunlight.
Poly-pipe prices vary according to manufacturer and depending on characteristics such as UV-resistance, diameter and thickness.
Price also varies depending on amount of pipe purchased.
Prices reported in Table 2 represent 2005 averages for three different
 Table 2.
Prices for different poly-pipe diameters and thickness.
Diameter	Thickness	Price/1,320 ft unit
 		
 manufacturers and are based on standard tubing length of 1,320 feet.
Polypipe generally comes in one of two colors, white or blue.
Plugs are used to stop water discharge from pipe outlets.
Plug prices vary according to opening size, rang-
 ing from 4 cents per unit for 1/2-inch plugs to 20 cents per unit for 2-inch plugs.
Gate holes also are available  and permit better irrigation control.
Larger outlet sizes allow larger stream-size and faster advance and may be preferable for irrigating long, sandy furrows or furrows containing considerable harvest residue.
Materials required for poly-pipe installation include
 Tractor with furrower tool and unspooling bracket
 Pump or valve for connection
 Clamps, rubber straps, or duct tape
 PVC connectors 
 Hole puncher with plugs
 Prior to poly-pipe installation, fields should be leveled.
Poly-pipe should be installed only on flat surfaces or down-hill, never up-hill.
A minimum of 6 inches of water head  is required for poly-pipe use.
Poly-pipe installation steps are as follows:
 1.
Open the box containing the poly-pipe roll and check pipe condition.
2.
Use a furrower to dig a trench.
The furrow should be deep enough to accommodate about 50% of the polypipe's diameter and 100% of its width to avoid any rolling to the side.
The trench should be built up to an elevation slightly higher than that of the irrigated furrows to avoid water return.
If the field block is curved along its edge, the curve should be no sharper than 70, preferably with an 8-foot radius.
Figure 1.
Making the trench with a furrower.
3.
Mount poly-pipe on an unspooling bracket SO it is ready to roll out.
Figure 2.
Poly-pipe set with an unspooling bracket.
4.
Stretch the poly-pipe gently into its trench , while someone holds onto it at the supply-pipe end.
Use a shovel to place dirt on top of the poly-pipe at 10-foot intervals  to keep it in place and prevent it from being moved by the wind..
Allow a few extra inches of poly-pipe at any curves to avoid excessive tension as the pipe fills with water.
Figure 3.
Placing dirt on poly-pipe at 10-foot intervals.
5.
Use clamps, rubber straps, string, or even duct tape  to connect the poly-pipe tightly to valves or supply-pipe fittings.
Discharge-pipe diameter does not have to match that of the poly-pipe, which can be larger.
If the pipe supplying water is at a higher elevation than the ground on which the polypipe will rest, build a soil ramp to support the polypipe at the connection point SO that the poly-pipe does not hang freely in the air.
At the point where the poly-pipe connects to the supply pipe, turn the polypipe tubing back onto itself for a distance of about a foot.
Pressure inside the poly-pipe is likely to be greatest at this connection point, SO the extra tubing will provide resistance to prevent the poly-pipe from separating from the clamp.
Whenever more than one
 Figure 4a.
Poly-pipe connected tightly to the supplying pipe.
Figure 4b.
Using rubber straps to connect the poly-pipe to the supplying pipe.
roll of poly-pipe is needed, connect the rolls with a corrugated pipe.
Be sure to roll each end back on itself  before strapping it to the supply pipe.
Figure 5a.
Connecting two rolls of poly-pipe.
Figure 5b.
Using a corrugated PVC pipe to connect two rolls of poly-pipe.
Figure 5c.
Making a tight connection to avoid water leaks.
At the end of the poly-pipe, build a mount  up to 2 feet high to stop water flow; that way, if too many poly-pipe outlets are closed, developing pressure, the water will just flow over the elevated mount without damaging the pipe.
6.
Filling can now begin.
Open valves slowly and gradually.
As the poly-pipe fills with water, create a vent 10 feet from the discharge-pipe connection point by punching a small hole with a pencil in the top of the poly-pipe; additional holes may be necessary at spots further along the poly-pipe to avoid air build-up, which can limit water flow and increase pressures inside pipes.
7.
Once the poly-pipe is completely full and has expanded, then the hole puncher can be used to punch holes in front of each row to be irrigated , at points between the 2 and the 3 o'clock
 Figure 6.
Hole puncher, plugs, and gates for poly-pipe.
positions.
If necessary, increase water flow in order to make the last holes.
8.
To make new holes, install plugs in old holes, then continue to punch new holes until they all have been finished.
When a set of new furrows needs to be irrigated, the holes used in previous irrigations should be closed with plugs.
When irrigation is finished, leave plugs inserted in the poly-pipe.
Always use plastic plugs larger than the poly-pipe holes.
Figure 7.
Using poly-pipe hole puncher.
Figure 8a.
Inserting plugs in poly-pipe.
Figure 8b.
Gate holes used to irrigate sugarcane.
Texas A&M AgriLife Extension Service
Water Quality and Nutrient Management at Home
 Brad Lee, Suzette Walling, and Gregg Munshaw, Plant and Soil Sciences; and Rick Durham, Horticulture
 F ertilizers and other lawn amendments benefit the residential landscape by providing or supplementing the essential nutrients for plant growth and maintenance.
Commercial fertilizers are commonly formulated based on three major nutrients: nitrogen , phosphorus , and potassium.
Each nutrient plays an important role in plant development; however, improper application of fertilizers and amendments may increase the risk of non-point source pollution of surface and ground waters.
In a balanced system, the major nutrients  contribute to soil health and plant growth.
However, runoff of surplus nutrients  to freshwater bodies can result in eutrophication, creating a nutrient rich water body for algae growth.
This process can lead to hazardous or nuisance algal blooms.
These blooms may appear as a green scum on the water surface or as thick mats below the surface.
Large growths of algae  can decrease oxygen levels in water and limit light to plants that provide food and shelter for aquatic organisms, and may produce toxins that are harmful to aquatic and terrestrial organisms.
Some of the toxins are known to cause skin irritation, rashes, or even more serious damage in humans and their pets.
Natural P in Kentucky
 The amount of P in soils is strongly related to the naturally occurring amount in the soil's parent material.
For example, the limestone parent material from which soils in the Bluegrass region form is naturally high in phosphate.
However, there are other parts of the state, such as the western Pennyrile region, where the limestone parent materials and soils are naturally low in phosphate.
Many
 Figure 1.
A.
Satelite image of a toxic Lake Erie algal bloom which resulted in a "do not drink" advisory for Toledo's drinking water system in August 2014.
B.
Photo of algae bloom in Lake Erie from a boat, July 2017.
Figure 2.
Average soil test P levels of approximately 1 million samples collected from urban and agricultural soils between 1990 and 2014.
Kentucky farmers are knowledgeable about the level of P in their soils and most apply only when fertilizer is needed or when fertilizer is affordable.
However, in the urban areas of Kentucky, landowners are much less knowledgeable about soil nutrient levels and often apply P fertilizer without knowing how much
 their plants actually need.
In addition, many homeowners over apply fertilizer because they do not know the amount of nutrients needed nor do they realize the concentration of nutrients within different fertilizer sources.
This problem is compounded by marketing campaigns by fertilizer vendors suggesting that a
 particular brand of fertilizer is required for a successful lawn or garden.
Soil test results over the past 25 years show that most Kentucky urban soils already have more than enough P and no additional applications are required.
The agricultural sector has responded to government incentives and economic drivers to reduce Papplications, resulting in soil P levels that have decreased over time.
However, results from home and garden soil tests show the opposite trend, with soil P levels increasing over time  The high level of P in lawn and garden soils indicates that many of these soils are at a high risk for P becoming soluble, indicating a higher likelihood of being transported downstream by runoff.
It is important that the urban sector reduce P applications to avoid increased risk to our lakes and streams.
Soil Testing for Ohio Lawns, Landscapes, Fruit Crops, and Vegetable Gardens
 Soil tests provide more helpful information on soils than any other resource.
It is an inexpensive way to maintain good plant health in lawns and landscapes, and to maximize productivity of vegetable gardens and fruit crops.
Soil test results pinpoint plant nutrient needs and soil test lab recommendations guide fertilizer applications so just the right amount is used.
Test results also provide information for making plant selection decisions based on the right plant in the right place and a soil test can help diagnose what went wrong if good plants go bad.
Soil samples are sent to a soil testing lab.
Results will be sent back to you along with recommendations for taking corrective actions if needed.
This includes the amount of fertilizers and other additives needed to support healthy plants.
Reliable fertilizer recommendations can help horticulture professionals and gardening enthusiasts make decisions that support good plant health and save money!
A standard soil test will provide information on soil pH, cation exchange capacity , lime requirement index and base saturation.
The soil test will also provide the status of phosphorus , potassium , calcium  and magnesium.
For additional fees, soil testing labs will provide information on iron , manganese , zinc  and copper  as well as a few other elements depending on the soil testing lab.
Soil testing labs can also provide information on soluble salts, nitrates, soil texture and the organic matter content of the soil.
The extra fees for these analyses may be justified if you are trying to solve a diagnostic problem by gaining information not provided through a standard soil test.
WHY DO I NEED TO SOIL TEST?
The guidance provided by soil tests to horticulture professionals and gardening enthusiasts is sometimes compared to the guidance that blood tests provide to physicians.
In this vein, a soil test is like a blood test for the soil.
Soil tests can be used for four purposes: maintaining proper soil fertility; guiding plant selection; performing plant problem diagnostics; and for conforming to industry approved standard practices.
1.
Maintaining Proper Soil Fertility.
Healthy plants need certain levels of soil nutrients to thrive.
Soil nutrients and fertility may fluctuate during the growing season.
This is influenced by the quantity and availability of plant nutrients that are altered by the addition of fertilizers, manure, compost, mulch, and lime or sulfur, in addition to nutrient loss through leaching.
Furthermore, large quantities of plant nutrients are removed from soils as a result of plant growth and development, and the harvesting of crops.
A soil test will determine the current fertility status and provide the necessary information to maintain optimum fertility year after year.
Soil tests take the guesswork out of fertilization and are very cost effective; they eliminate wasteful spending on fertilizer products.
Test results and recommendations help protect our environment by discouraging the overapplication of plant nutrients.
Excess nutrients not used by plants may escape into groundwater, streams and lakes where they can contribute to environmental problems, such as algal blooms.
2.
Guiding Plant Selection.
Some plants will grow in a wide range of soil pH levels, while others require a narrow range of pH.
Most turfgrasses, flowers, ornamental shrubs, vegetables and fruits grow best in slightly acid soils which represent a pH of 6.1 to 6.9.
Plants such as rhododendron, azalea, pieris, mountain laurel and blueberries require a more acidic soil to grow well.
A soil test will determine whether the soil is acidic or alkaline.
It is the most cost effective way to match the pH requirements of plants that you select with the pH of the soil in which you are planting.
Figure 1: Colorado blue spruce showing a nutrient deficiency symptom.
Photo by Joe Boggs, Ohio State University Extension.
3.
Performing Plant Problem Diagnostics.
Soil tests are an important tool for learning why plants lack vigor or are showing symptoms of other plant health issues.
For example, Figures 1, 2 and 3 show a symptom, called chlorosis, that is typical of a nutrient deficiency in the foliage.
If trees are exhibiting yellowing  leaves or needles during the growing season, a soil test may reveal whether the symptom is caused by a lack of an essential nutrient, a problem with the soil pH or both!
4.
Conforming to Industry Approved Standard Practices.
The American National Standards Institute  is a private, non-profit organization that oversees the development process and approval of voluntary consensus standards for the private sector in the United States.
The Tree Care Industry Association  is accredited by ANSI to develop the actual standards known as ANSI A300 Tree Care Management standards.
They are the generally accepted industry standards for tree care practices.
Following are recommendations from the ANSI standards specific to soil testing:
 A300 -2011 SOIL MANAGEMENT
 14.4.4: Soil testing should be done prior to designing, plant selection, planting and/or developing management plans for landscapes.
15.2: Soil and/or foliar nutrient analysis should be used to determine the need, formulation and rate of fertilizer.
15.6.3: When new plants are specified, they should be tolerant of the native soil pH.
A300 -2012 PLANTING AND TRANSPLANTING
 63.3 Plant and site inspections for transplanting.
63.3.5 Soil at the installation site should be analyzed and tested for pH, structure, texture, density, nutrients and percolation.
Figure 2: Oak showing a nutrient deficiency symptom.
Photo by Joe Boggs, Ohio State University Extension.
Figure 3: Red maple showing a nutrient deficiency symptom.
Photo by Joe Boggs, Ohio State University Extension.
WHEN DO I SOIL TEST?
A soil test is used as a planning tool and the first step in learning what you need to do, or not do.
Soil samples can be taken any time of the year, as long as the soil is workable.
However, you should allow plenty of time to receive and evaluate your soil test results, and then take action to improve your soil fertility.
Any recommended adjustments, such as a fertilizer application, should be made at the appropriate time of the year.
For example, fall is the best time of the year to make a lime application to raise the soil pH, while spring is the most appropriate time of the year for a sulfur application to lower the pH.
HOW FREQUENTLY SHOULD I SOIL TEST?
A soil test every two to three years is usually adequate for maintaining soil fertility.
Sample more frequently if you desire a closer monitoring of the fertility levels, or if you grow plants that require more nutrients.
Soil tests for diagnostic purposes can be made as needed.
WHAT SOIL SAMPLING TOOLS DO I NEED?
Figure 4: Soil probes provide a simple method for collecting soil samples Photo by Joe Boggs, Ohio State University Extension.
A soil probe is the easiest tool for taking soil samples.
Soil probes quickly extract samples to a consistent depth simplifying the job of taking soil samples, especially when taking multiple composite samples.
Soil probes are also useful for assessing soil moisture to monitor irrigation needs and for evaluating other physical properties of the soil such as compaction.
Purchasing a soil probe is a good investment for horticulture professionals and serious gardeners.
Figure 4 shows examples of some typical soil probes available for purchase.
Others are also available.
The T-handle step probe is recommended for more compacted soils or when collecting samples in a large area such as a lawn.
The longer length and welded step reduces back and shoulder strain from bending over and applying pressure to insert the probe into the soil.
Figure 5 shows how a soil probe is used to collect a soil sample beneath turfgrass.
Garden Spade, Knife or Hand Trowel
 A garden spade, heavy gauged knife , or hand trowel as shown in Figure 6 can also be used to take thin slices or sections of soil for gathering soil samples.
These tools require more time, effort and skill for taking precise soil samples compared to a soil probe.
However, they are simple and effective if you are sampling loose soil, such as in vegetable gardens and flowerbeds.
They are also cost effective for lawns and landscapes if you are only performing plant nutrient maintenance tests over small areas every few years.
Figure 5: Using a soil probe for soil sampling in turfgrass.
Photo by Joe Boggs, Ohio State University Extension.
Figure 6: Using a hand trowel for soil sampling.
Photo by Joe Boggs, Ohio State University Extension.
Soil samples should be collected in a clean plastic bucket or box as shown in Figure 7.
Metal buckets, such as aluminum or zinc plated buckets, should never be used as the metals may contaminate the samples and influence the test results.
Figure 7: Soil samples should be collected in a clean plastic bucket.
Photo by Joe Boggs, Ohio State University Extension.
Figure 8: This graphic shows five zones that will be soil tested.
The stars in the graphic show where the subsamples should be taken.
The subsamples should be taken in a zig-zag pattern, shown by the yellow-dotted lines.
Graphic by Joe Boggs, Ohio State University Extension.
HOW DO I TAKE SOIL SAMPLES?
The validity of soil test results and recommendations depend on the quality of the samples taken and sent to a testing lab.
Soil fertility varies throughout a lawn, landscape, fruit planting or vegetable garden.
Because of this, the soil sample sent to the lab must be representative of the entire area.
Submitting a composite sample reduces the influence of soil fertility variations.
A composite sample is a number of individual subsamples randomly collected over the entire test area.
The subsamples are mixed together and a small amount of soil, about 1 pint in volume, is sent as a representative sample to the testing lab.
Figure 8 shows examples of subsample numbers and patterns to create a composite sample.
The number of subsamples depends upon the size of the area being tested.
In general, 5 to 10 subsamples are sufficient for small areas such as flowerbeds and 10 to 15 samples are recommended for larger areas such as lawns.
Subsamples should be taken at random in a zigzag pattern over the entire area and each subsample should be taken to the same depth and soil volume.
Separate soil tests should be used for:
  Areas that have received different applications for soil fertility programs.
Soils distinguishable by color , drainage or other factors.
Different types of plant cultivation.
Figure 8 shows different zones for soil sampling.
Sample when soils are suitable for spading or plowing.
Organic matter on top of the soil should not be included in soil test samples.
Organic matter can affect the soil test results.
This includes plants , the typical 1 inch or less organic layer typically found over Ohio soils, mulch, thatch, etc.
Coarse organic matter, such as mulch or thatch, should be removed before taking a soil sample.
The organic layer included in soil probe  or hand trowel  samples should be removed prior to dropping the sample into a plastic bucket.
Soil should be sampled to root depth, which typically means 5 to 8 inches for trees, shrubs, flowerbeds and vegetable gardens, and 3 to 4 inches for lawns.
Of course, root depth may vary based on soil type and other conditions.
Sample a vegetable garden between rows to avoid fertilizer bands where applications were made directly to plants.
HOW TO PREPARE SOIL SAMPLES FOR SUBMISSION
 Figure 9: A typical soil test kit you will receive from the soil-testing lab.
Contact a soil-testing lab for instructions, soil test kits and appropriate forms.
A list of testing labs is at the end of this fact sheet.
Break up lumps and air dry the soil on parchment or butcher paper  at room temperature with no artificial heat.
Dry until the lumps can be crushed to the size of wheat grains or smaller.
Mix well and remove roots and other large pieces of organic debris as well as small stones or rock pieces.
Take about one pint of the composite sample and place it in the sample bag associated with the kit.
Figures 9 through 13 below illustrate a typical soil test kit that you will obtain from the lab.
Make sure the information on the forms is complete so you receive recommendations for your lawn, landscape, fruit or vegetable needs.
Photos by Joe Boggs, Ohio State University Extension.
Figure 10: Complete all forms required by the testing lab.
Figure 11: Take about one pint of the composite sample to be sent for testing.
Figure 12: The bag is filled and ready to be sent to the testing lab.
Figure 13: The form is completed and ready to be mailed with the filled bag.
WHERE DO I SEND MY SOIL SAMPLE?
Table 1 at the end of the fact sheet shows a list of soil testing labs in Ohio and neighboring states as well as the types of materials they will test.
The labs listed belong to the North American Proficiency Testing  program that is operated under the supervision of the Soil Science Society of America.
For a fee, these labs will provide basic soil testing.
Some labs also offer more advanced testing such as an analysis of soilless media, compost, plant tissue, and water as well as tests for soluble salts and the amount of organic matter found in the soil.
Contact the soil-testing lab before collecting the soil samples.
Generally, soil-testing labs will provide a complete set of instructions, either with sample kits or upon request.
Follow the instructions carefully.
You will need to mail soil sample, completed sample form, and appropriate payment to the soil-testing lab selected.
HOW LONG DOES THE SOIL TEST TAKE?
Soil test results and fertilizer recommendations are usually mailed in two weeks, depending on the testing lab.
Make sure you read and follow the directions for filling out the soil testing form accurately and completely; incomplete forms may cause delays in receiving results and recommendations.
For example, unless you fill out the form for the types of plants you grow or will be growing, no recommendations will be given.
WHAT KINDS OF SOIL TESTS ARE AVAILABLE?
The kinds of available tests vary with different soil and tissue testing labs.
Some of the common soil tests are lawn and garden, horticultural, agronomic, and soilless media test.
Refer to Table 1 for a suggested partial list of soil and tissue testing labs and the types of tests available in Ohio and neighboring states.
Please note the types of tests that individual labs offer may change without notice.
Contact the lab for current tests available.
The inclusion of a lab on this list does not necessarily imply any endorsement by The Ohio State University, nor does the exclusion of a lab imply any condemnation.
Hence, The Ohio State University does not assume any liabilities associated with the selection and use of these labs.
WATER WITHDRAWAL AMOUNTS IN SOUTH CAROLINA
 Published: Feb 9, 2023 |  Printable Version  | Peer Reviewed
 Heather B.
Nix and Mani Rouhi Rad
 Access to plentiful, clean water is critical for life and economic activity.
South Carolina has typically been considered a water rich state, and surface and ground freshwater supplies have supported rapid population and economic growth for many years.
However, the state faces challenges, including significant population growth, rapid land-use change, and variability in weather patterns attributed to climate change that can threaten the availability of water resources for sustainable future use.1 The late 1990s through early 2000s brought about one of the worst droughts in South Carolinas history, which had long-term impacts on agriculture and timber industries, municipal water supply, and waterway health.2 As a result of drought events, coupled with growing demand for water resources, SC water managers anticipate future state-wide water shortages,3 which can have lasting impacts on South Carolinas economy and residents.
This article describes the main water use sectors in the state and provides an overview of recent annual water withdrawals.
Understanding how water is used and how much water is withdrawn from various sources will help sustainably manage water supplies into the future.
Water is commonly used in South Carolina for drinking water; irrigation of crops and golf courses; production of electricity; manufacturing, mining, recreation; and support of aquatic ecosystems.
South Carolina regulates both surface and groundwater withdrawals greater than three million gallons  in any month and requires annual reporting to the SC Department of Health and Environmental Control.
For a complete overview of South Carolinas water use regulations, please see the Land-Grant Press publication Water Withdrawal Regulation in South Carolina.
The main sectors that use water or rely on water availability in South Carolina include
 Aquaculture: Water is used for raising organisms that live in the water, whether for food, sport, or conservation.
Golf Courses: Water is used specifically to maintain golf course turf, including tee boxes, fairways, putting greens, associated practice areas and periphery aesthetic landscaping.4
 Irrigation : According to SCDHEC, encompasses water used for agricultural and landscaping purposes including turf farming and livestock management.4 Agricultural water use is mainly used to support plant growth and can also include water use for pre-irrigation, frost protection, chemical application, weed control, field preparation, dust suppression, and leaching salts from the root zone.5
 Manufacturing or Industrial: This category includes self-supplying manufacturing facilities and industries that withdraw water directly from a water body to use in their facility.
Water can be used for various needs, such as processing, cooling, dilution, in-plant conveyance, or cleaning, and may be consumed or discharged into a waterway.
Mining: Water is used for the extraction of minerals and other mining operations, such as dust control on roads.
In January 2021, SCDHEC listed permitted active mining operations for the following: clay/sand, granite, river sand, vermiculite, lime, shale, soil, gold, and sericite.6
 Other: Water used for any purpose not specifically identified in any other category.4
 Power Generation: Electricity generation nearly always requires water.
Hydroelectric uses the potential and kinetic energy of stored and flowing water, and thermoelectric uses water mainly for steam generation and cooling purposes.
Water may also be used in air emissions control equipment at power plants.
Water Supply: Water is withdrawn by public or private suppliers for distribution to other water users.4 According to the US Environmental Protection Agency, a public water system provides water for human consumption through pipes or other constructed conveyances to at least fourteen service connections or serves an average of at least twenty-five people for at least sixty days a year.
7 Water suppliers provide water for indoor or outdoor use by residential , commercial, and industrial users.
Residential Self-Supply: Over 20% of SC residents depend on individual groundwater wells for drinking and other household uses.8 While the water use of individual homes is minor, collectively, this sector could be responsible for significant groundwater withdrawals.
Instream Flow: South Carolinas waterways provide environmental flows, assimilative capacity for wastewater, and recreational opportunities, such as boating, water skiing, fishing, and swimming.
Water-based recreational activities typically do not involve water withdrawals but rather depend on water availability in a river or lake.
The 2016 Economic Contributions of Natural Resources report indicates that water-related recreation is directly responsible for more than 75,000 jobs and more than $6.9 billion in revenue for South Carolina.9
 SCDHEC compiles an annual Water Use Report utilizing data reported by surface and groundwater users that withdraw greater than 3 MG in any month.
Water withdrawals below the 3 MG threshold are typically not included in the Water Use Reports.
With the exception of hydropower generation and mining, water withdrawals over the 3 MG threshold are typically regulated, regardless of if any portion of the water is returned near the source  or if the water is removed from the source water permanently.
Many water use sectors return a portion of the water withdrawn near the source.
A forthcoming article in the Journal of South Carolina Water Resources, An Introduction to Consumptive Use of Water in South Carolina, provides more information regarding consumptive and non-consumptive use in South Carolina.
From 2017 to 2021, facilities reporting a water withdrawal to SCDHEC increased from 1,004 to 1,209, with agricultural irrigation facilities outnumbering all other major users combined.10 However, a much different picture emerges when assessing the total volume of water withdrawn.
By far, hydropowers reported withdrawals outpace all other uses.10 Because hydropower does not technically remove water from a river, it is commonly excluded to allow evaluation of physical water withdrawals.
When hydropower is removed from the evaluation to consider only physical withdrawals , thermoelectric power generation withdraws the largest volume of water.
Annual withdrawals are not reported for Residential Self Supply; estimates of the number of private drinking water wells and estimated total annual usage for South Carolina are provided in table 2.
Overall, water users in South Carolina withdraw significantly more surface water than groundwater.4 For example, in 2021, more than 99% of the 1,699,387 MG total combined withdrawal reported for thermoelectric was from surface water sources.
While many water users may rely on a combination of surface and groundwater sources, the only water use categories that withdrew a larger volume of groundwater than surface water in 2021 were irrigation , residential self-supply, and other.8,10,14-16
 Table 1.
Number of water withdrawers and reported annual water withdrawals  per water sector.
All data from SCDHEC Annual Water Use Reports.
Understanding current water use and planning for future needs for water provision is critical for the well-being of South Carolinians.
A basic understanding of water withdrawals is an essential first step toward sustainable water management.
Most of the water withdrawn from South Carolinas water supply is for energy production.
Overall, water users throughout the state rely heavily on surface water sources.
Additional evaluations should further consider the consumptive use of surface and groundwater withdrawals in South Carolina.
Smart Irrigation Technology: Controllers and Sensors
 Malarie Gotcher Extension Associate
 Saleh Taghvaeian Irrigation Extension Specialist
 Justin Quetone Moss Turfgrass Research and Extension
 Rainfall in Oklahoma is variable across the state and fluctuates by year.
During dry periods, irrigation may be needed to preserve landscape quality.
Overor under-irrigating a landscape can possibly increase disease incidence, waste water and decrease overall landscape condition.
Irrigation system efficiency is dependent upon several factors including design, installation and specific site conditions.
Water applied to a landscape can account for a significant portion of a property's water use.
In Oklahoma, outdoor water use accounts for approximately 30 percent to 50 percent of household water use.
A substantial amount of water is lost to evaporation, wind and runoff as a consequence of improper watering methods.
Reducing or eliminating this loss decreases utility bills and creates a more water efficient, healthy landscape.
Outdoor water savings can be achieved using smart irrigation technologies.
Smart irrigation controllers and sensors have been developed to reduce outdoor water use by irrigating based on plant water need compared to traditional automatic system timers, which irrigate on a user-determined fixed schedule.
This technology exists as a complete controller or as a sensor that can be added to an existing irrigation timer to create a smart controller.
Smart irrigation technology uses weather data or soil moisture data to determine the irrigation need of the landscape.
Smart irrigation technology includes:
 These products maximize irrigation efficiency by reducing water waste, while maintaining plant health and quality.
Incorporating smart irrigation technology in the landscape can potentially reduce outdoor water consumption.
This technology is appropriate for small, residential landscapes as well as large, managed landscapes.
The following sections describe how each product functions and the advantages and disadvantages of each product.
Irrigation managers and homeowners should be aware that smart irrigation technology will need to be periodically adjusted and maintained for maximum water savings.
Smart Irrigation Technology: New Controllers
 There is a broad spectrum of smart irrigation technology that consumers can benefit from utilizing.
Choosing the correct technology for the situation is essential to achieve potential water savings.
Watering restrictions exist in some areas of Oklahoma, so the irrigation timer may be adjusted for allowed watering days.
Irrigation controllers can be separated into two main categories: Climate based controllers and soil moisture based controllers.
Climate-based controllers also referred to as evapotranspiration  controllers use local weather data to adjust irrigation schedules.
Evapotranspiration is the combination of evaporation from the soil surface and transpiration by plant materials.
These climate-based controllers gather local weather information and make irrigation run-time adjustments so the landscape only receives the appropriate amount of water.
There are three basic types of ET controllers:
 Signal-based controllers use meteorological data from a publicly available source and the ET value is calculated for a grass surface at the site.
The ET data is then sent to the controller by a wireless connection.
Historic ET controllers use a pre-programmed water use curve, based on historic water use in different regions.
The curve can be adjusted for temperature and solar radiation.
On-site weather measurement controllers use weather data collected on-site to calculate continuous ET measurements and water accordingly.
Figure 1.
Evapotranspiration based controller.
Photo courtesy of Rainbird.
Evapotranspiration controllers have been shown to reduce outdoor water use.
In Las Vegas, Nev., homes with ET based controllers saw an average of 20 percent irrigation reduction compared to homes with homeowner-scheduled irrigation.
Additionally, a study conducted on St.
Augustine turfgrass showed an average irrigation savings of 43 percent in the summer compared to homeowner-scheduled irrigation, with no reduction in turfgrass quality.
The accuracy of ET controllers depends on the equation parameters.
Most ET controllers cost between $250 and $900.
Professional grade ET controllers range between $900 and $2,500.
Soil Moisture Sensor Controllers
 The second type of smart irrigation controllers includes soil moisture sensor controllers.
Instead of using weather data, soil moisture sensor controllers utilize a soil moisture sensor placed belowground in the root zone of lawns to determine water need.
The soil moisture sensor estimates the soil volumetric water content.
Volumetric water content represents the portion of the total volume of soil occupied by water.
The controllers can be adjusted to open the valves and start irrigation once the volumetric water content reaches a user-defined threshold.
The appropriate threshold value depends on soil and vegetation type and usually ranges from about 10 percent to 40 percent.
Soil moisture sensors must be installed in a representative area of the turf; far enough from sprinkler heads, tree roots, sidewalks and walls.
Similar to ET controllers, soil moisture controllers have been shown to reduce irrigation, while maintaining turfgrass quality.
Compared to homeowner irrigation schedules, soil moisture controllers had an average 72 percent irrigation savings and a 34 percent water savings during drought conditions.
In some cases, studies have shown smart controllers will increase water use at sites that typically use less than the theoretical irrigation requirement.
Figure 2.
Example of a soil moisture controller.
Typically, soil moisture sensor controllers range from $280 to $1,800.
Difference in pricing depends on product manufacturer and end user, either residential or commercial customers.
Smart Irrigation Technology: Add-on Sensors
 In many cases, a scheduling irrigation controller is already in use on a property and upgrading to a smart controller is impractical.
To increase efficiency of automatic irrigation systems a soil moisture, rain, wind or freeze sensor can be added to upgrade the existing system.
Some manufacturers produce devices capable of measuring multiple environmental elements using one apparatus.
Many sensors are compatible with existing systems, easy to install and produce similar results to smart irrigation controllers.
The add-on sensors are generally more affordable than smart irrigation controllers, assuming a compatible irrigation timer is already installed on site.
Soil moisture sensors can be connected to an existing irrigation system controller.
The sensor measures the soil moisture content in the root zone before a scheduled irrigation event and bypasses the cycle if the soil moisture is above a specific threshold.
Different types of soil moisture sensors are available and the consumer should ensure system compatibility before purchasing a sensor.
Some soil moisture sensors include a soil freeze sensor that will interrupt the irrigation cycle if temperatures fall below 32 F.
Soil moisture sensors are available as wired or wireless systems.
Typical cost for a soil moisture sensor can range from $99 to $165.
Rain and Freeze Sensors
 Although these sensors are not considered smart technology, rain and freeze sensors interrupt the irrigation cycle during a rain or freeze event when irrigation is unnecessary.
Watering during the rain wastes water, money and causes unnecessary runoff.
Three different types of rain sensors are available and each function is based on separate concepts.
Figure 3.
Ideal locations for soil moisture sensor placement.
The original type of rain sensor still in use today works with a small cup or basin that collects water, once a predetermined amount is collected, the weight of the cup interrupts the irrigation cycle.
Debris in the cup can also interrupt the irrigation cycle and should be checked and cleared of litter periodically.
The second type of rain sensor uses a dish with two electrodes that are a specific distance from the bottom of the cup.
The distance can be adjusted to allow for small rain events and similar to the first type of rain sensor, debris can reduce accuracy by displacing water in the cup.
When the water reaches the electrodes, the irrigation cycle is interrupted.
The third type of rain sensor does not have a rain catch cup, which makes it low maintenance and reliable.
Instead, the sensor uses several disks that expand as they get wet.
The expanded disks trigger the switch and interrupt the cycle.
The system will resume the scheduled cycles once the disks dry out.
The disks should be checked at least once a year to determine if
 they need to be replaced.
All of the devices should be mounted in an open area where they will receive rainfall.
Potential water savings depends on the amount of rainfall in any given year.
During years with average to above average rainfall, water savings are more significant than during dry years.
Rain sensors have shown payback periods of less than a year, but should be monitored for optimum performance.
As an example, if a homeowner's irrigation system waters a 1/4-acre yard and applies 1 inch of water each irrigation cycle, then each cycle applies 6,789 gallons of water.
If water costs $5.00 per 1,000 gallons, the monetary savings will be $33.95 each time the irrigation cycle is interrupted during a rainfall event.
Considering each rainfall event, the homeowner could expect substantial water and money savings.
Most wireless rain sensors are more expensive and range from $120 to $200, while wired rain sensors cost approximately $30 to $50.
Freeze sensors interrupt an irrigation cycle when air temperatures fall below 32 F.
Eliminating irrigation during freezing temperatures can potentially extend irrigation system life and prevent sidewalks and streets from icing over, causing dangerous situations.
Many rain sensors include a freeze sensor and homeowners should account for sensor capability when considering price.
Oklahoma has an average wind speed of 16 miles per hour  with wind gusts from 20 mph to 30 mph.
Watering during windy conditions reduces irrigation distribution uni-
 Figure 4.
Rain sensor with a small basin to collect rainfall.
Figure 5.
Rain sensor attached to a gutter  and the inside of an expanding disc rain sensor.
Photos courtesy of Hunter Industries.
formity across the landscape and decreases the amount of water infiltrating into the soil profile.
Wind sensors interrupt the irrigation cycle if wind speed exceeds a specific threshold.
Smart irrigation technology may help reduce water waste, while also providing a healthy, attractive landscape.
Irrigation system owners should provide regular maintenance and ensure the irrigation system is only watering the landscape when needed.
Many wind sensors are around $80 to $100 dollars or are packaged with other sensors.
Figure 6.
Irrigating during windy conditions wastes water and reduces system efficiency.
Figure 7.
Example wind sensor for use in the landscape.
Photo courtesy of Hunter Industries.
Practical Use of Soil Moisture Sensors for Irrigation Scheduling
 Good irrigation water management will increase yields, improve crop quality, conserve water, save energy, decrease fertilizer requirements, and reduce non-point source pollution.
Using soil moisture measurements is one of the best and simplest ways to get feedback to help make improved water management decisions.
However, the installation, calibration, and interpretation of the data from these instruments is often overwhelming for most busy growers.
Here's an attempt to provide practical recommendations for using these sensors to improve your operation.
The major types of soil moisture sensors are listed in Table 1 and grouped according to the technology used to measure soil moisture.
Research continues to show that these sensors are not always accurate.
However, they all give trend lines that can be usable for irrigation scheduling.
Although the technologies used by each sensor type are quite different, these sensors can be roughly categorized into two groups: those that give the soil water content, and those that give the soil water tension.
Table 1.
Major types of soil moisture sensors and their relative advantages and disadvantages.
Sensor Type	Advantages	Disadvantages
 Neutron Probe	Accurate.
Repeatable.
Government required
 (Campbell Pacific	Samples a relatively large	paperwork and regulations.
Nuclear; CPN)	area.
One sensor for all	Can't leave in field.
Relatively
 sites & depths.
expensive.
Time Domain	Less expensive	Samples small area.
Transmissivity	.
Easy to log
 Capacitance	Easy to set up to log and/or	Highly affected by soil
 Sensors	transmit data.
conditions immediately next
 (Enviroscan, Echo	to the sensor.
High
 Probes, Acclima,	variability.
More expensive
 Vernier, etc..)	.
Tensiometers	Less expensive	Maintenance issues.
Granular Matrix	Inexpensive 	Highly variable output.
Less
 Sensors	accurate.
Sensitive to
 	temperature and soil salinity.
Soil Water Content-based soil moisture sensors: 
 Soil water content measurements are much more meaningful for irrigation scheduling when they are compared to the maximum amount of water that the soil can hold long term, or field capacity.
The simplest way to determine your soil's field capacity is to use the sensor to take a soil water content
 measurement at a time when you are confident that the soil is full of water, yet free water has had time to drain through.
Good times to take these measurements are in the spring as soon as soil thaws , or 12 to 24 hours after a heavy irrigation.
Remember that the soil content measurement must be multiplied by the depth of soil in the root zone that it represents to give the total water content in that soil depth.
Table 2.
Ranges of available water by soil texture.
Soil Texture	Avail.
Water	Total Water in 3.5 ft	Max.
Depletion at
 Capacity  in/ft	Root Zone 	50% of AWC 
 Coarse Sand	0.2 0.8	0.7 2.8	0.4 1.4
 Fine Sand	0.7 1.0	2.5 3.5	1.2 1.8
 Loamy Sand	0.8 1.3	2.8 4.6	1.4 2.3
 Sandy Loam	1.1 1.6	3.9 5.6	1.9 2.8
 Fine Sandy Loam	1.2 2.0	4.2 7.0	2.1 3.5
 Silt Loam	1.8 2.5	6.3 8.8	3.2 4.4
 Silty Clay Loam	1.6 1.9	5.6 6.7	2.8 3.3
 Silty Clay	1.5 2.0	5.3 7.0	2.6 3.5
 Clay	1.3 1.8	4.6 6.3	2.3 3.2
 Peat Mucks	1.9 2.9	6.7 10.2	3.3 5.1
 Using this method the absolute accuracy of the sensor is less important because we are just comparing it to itself.
Also the periodic measurements throughout the season now take on meaning as we can determine the soil water deficit  and the amount of water that can be depleted before water stress occurs.
Good irrigation managers will maintain the water content well between field capacity and this stress point.
Tension-based soil moisture sensors: 
 When using tension-based soil moisture sensors, the soil's field capacity, wilting point, and the maximum depletion point are mostly irrelevant.
A soil that is full of water will have a measured soil water tension near zero.
Fruit trees and vines should be irrigated before they reach 40-50 centibars.
For regulated deficit irrigation, this could be increased to 80 centibars.
Again, since these measurements can be inaccurate and soil specific, refine your limits using crop observations over time.
For example, note the measured soil water tension at the earliest indications of water stress , and be sure to irrigate before you reach that point in the future.
Also take some readings right after an irrigation.
If the bottom sensor goes to zero, then it's possible you put too much water on.
If it shows no movement at all, apply more water next time to push water a bit deeper.
Avoid preferential flow of water to the sensor due to installation process.
Flag the sensor well so that it can be easily found.
Graphical representation of the data greatly helps with data interpretation.
Use soil water measurements with irrigation scheduling tools such as Kansched and daily water use data from AgWeatherNet or AgriMet for much better water management.
Keep records.
Correlate readings with observations.
Stay away from both the field capacity, and water stress points if possible.
Realize that soil and sensors have a lot of variability.
Be patient and stick with it.
It may take a year or two before you are good at interpreting your sensor readings.
New commercial and noncommercial applicators must pass at least two state exams: one covering the general standards that all applicators have in common, and at least one category exam covering information specific to the type of work an applicator will be doing.
B.C.
SPRINKLER IRRIGATION MANUAL
 Prepared and Web Published by
 BRITISH COLUMBIA Ministry of Agriculture
 LIMITATION OF LIABILITY AND USER'S RESPONSIBILITY
 The primary purpose of this manual is to provide irrigation professionals and consultants with a methodology to properly design an agricultural irrigation system.
This manual is also used as the reference material for the Irrigation Industry Association's agriculture sprinkler irrigation certification program.
While every effort has been made to ensure the accuracy and completeness of these materials, additional materials may be required to complete more advanced design for some systems.
Advice of appropriate professionals and experts may assist in completing designs that are not adequately convered in this manual.
All information in this publication and related materials are provided entirely "as is" and no representations, warranties or conditions, either expressed or implied, are made in connection with your use of, or reliance upon, this information.
This information is provided to you as the user entirely at your risk.
The British Columbia Ministry of Agriculture and the Irrigation Industry Association of British Columbia, their Directors, agents, employees, or contractors will not be liable for any claims, damages or losses of any kind whatsoever arising out of the use of or reliance upon this information.
When using the term "sprinkler irrigation", reference to stationary irrigation systems with flow rates ranging from 1/2 to 12 gpm per sprinkler head is usually intended.
The selection of an appropriate sprinkler and nozzle combination requires knowledge on system types, sprinkler spacing, operating pressures and soil conditions.
5.1 Sprinkler Nozzle, Pressure and Spacing Selection
 Efficient irrigation system design requires the selection and matching of the sprinkler equipment and spacing to the crop, soil and field shape.
An appropriate sprinkler spacing is determined by the type of nozzle used and the operating pressure selected.
Every sprinkler-nozzle combination has a specific operating pressure range.
Too much pressure will disperse the water stream into a very fine spray resulting in increased evaporation losses or poor distribution.
Wind effects on sprinkler distribution patterns are more pronounced on fine droplet sizes.
Conversely too little pressure will not sufficiently break up the water stream and may result in puddling, runoff, poor distribution patterns and crop damage.
Sprinkler irrigation system spacings are usually denoted by the sprinkler spacing along the lateral and lateral spacing along the mainline.
Therefore, 40 X 60 denotes a 40 ft sprinkler spacing and a 60 ft lateral spacing.
The actual layout of the system may be square or rectangular.
See Figure 5.1.
Handlines and wheellines usually accommodate a square or rectangular spacing while solid set systems can be triangular, rectangular or square.
Triangular spacings may increase application efficiency for undertree systems in orchard plantings.
Triangular spacings allow the designer to minimize the interference effect of tree trunks and lower branches on application uniformity.
In situations where there is a predominant wind direction, the irrigation system should be designed SO that the sprinkler lateral is perpendicular to the wind.
A closer sprinkler spacing than normal may be required for these situations.
The distribution by a sprinkler irrigation system can be checked by determining the coefficient of uniformity.
Appendix E explains this term and how it can be calculated.
Figure 5.1 Sprinkler Layouts
 The maximum spacing of a sprinkler system is determined by the wetted diameter of the sprinkler and the wind speed.
The wetted diameter of a sprinkler is a function of nozzle size and operating pressure.
Sprinkler manufacturer's charts will provide wetted diameter information.
Sprinklers and laterals should be spaced no futher than the maximum percentage of wetted diameter based on various wind speeds as shown in Table 5.1.
Lateral lines are often spaced slightly further apart than 50% of the wetted diameter but this is then made up by a sprinker spacing along the lateral that is slightly closer.
Table 5.1 Sprinkler Spacing Recommendations
 Wind Speed	Spacing as a Percentage of Wetted Diameter
 Up to 6.5 km/hr	60%
 6.5 13 km/hr	50%
 Over 13 km/hr	40%
 To obtain good uniformity, sprinkler systems must provide sufficient overlap.
The minimum coefficient of uniformity should not be less than 80%.
Following the recommended spacings as shown in Table 5.1 should allow the irrigation system to achieve a coefficient of uniformity of 80% under normal operating conditions.
Application efficiency is an indication of the percentage of water applied by the irrigation system that is actually available to the crop.
Lower efficiencies mean more water is lost during the application process to evaporation, wind drift or runoff and is not available to the crop.
Efficiencies of irrigation systems can vary due to wind, operating pressure, sprinkler trajectory, time of day, and hot or cool weather.
The efficiency can also be affected by the design, operation and maintenance of the irrigation system.
Typical application efficiencies can be found in Table 3.1 in Chapter 3.
Irrigation Interval  is the number of days that it takes the irrigation laterals to cover the field.
This is calculated by determining the number of lateral settings in a field and dividing this by the number of sets operated each day.
Equation 5.1 Irrigation Interval 
 Number of Sets in Field II = Number of Sets per Day
 where II = Irrigation Interval 
 Net Water Required 
 Net Water Required  is the amount of water required by the crop to be able to sustain optimum growth over the irrigation interval.
It is determined by multiplying the daily evapotranspiration  rate by the irrigation interval .
Equation 5.2 Net Water Required 
 NWR = Net Water Required 
 II = Irrigation Interval 
Minimizing Risks: Use of Surface Water in Pre-Harvest Agricultural Irrigation; Part II: Sodium and Calcium Hypochlorite  Treatment Methods
 Jessica L.
Dery, Daniel Gerrity and Channah Rock
 Chlorine is a water-soluble chemical disinfectant that is commonly used for microbial disinfection because it is effective, economical, and approved by the Environmental Protection Agency  for water treatment.
Chlorine-based compounds have been used as 'primary' disinfectants for drinking water, wastewater, and agricultural irrigation water  for decades.
Primary disinfection kills or inactivates bacteria, viruses, and other potentially harmful organisms.
Chlorine is also an effective 'secondary' disinfectant for prevention of bacterial and fungal growth or re-growth in distribution systems.
Secondary disinfection provides long-lasting, residual water treatment as the water moves through pipes, including irrigation pipes and sprinklers with prolonged retention times.
In general, chlorine can be applied to irrigation water in three forms:  as solid calcium hypochlorite [Ca,],  as liquid sodium hypochlorite , or  as gaseous chlorine  (USDA NRCS; Schwankl et
 Figure 1.
Chlorine treatment for agricultural irrigation.
Image credit Jessica Dery, UA.
al., 2012).
Table 1 provides a brief overview of these three forms of chlorine.
Each form varies in concentrations of 'available' chlorine, levels of effectiveness, characteristics, and advantages.
It is therefore important to understand
 Table 1.
Overview of three forms of chlorine available for disinfection of water.
Form	added to water	Action when	chlorine	Available	Points of interest
 Most hazardous 
 	Decreases pH and alkalinity	100%	Extensive training required
 May be preferred in alkaline waters because it decreases pH
 Not recommended for injection into drip irrigation (calcium
 Solid calcium	Increases pH, hardness, and	65-75%	precipitates may clog emitters)
 hypochlorite ,)	alkalinity	Less corrosive than liquid form
 Less stable in normal storage conditions
 Liquid sodium	Increases pH	Generally safe to use
 hypochlorite 	and alkalinity	10-15%	Should be stored in a shaded area and away from fertilizers	No special training required
Chapter: 37 Combine Adjustments to Reduce Harvest Losses
 Grain yield losses can be classified as: 1) preharvest ear losses, 2) ear losses from the header, 3) kernel shatter loss from the header, 4) threshing losses, and 5) separation and cleaning losses.
Chapter 36 provided directions and calculations to determine the magnitude of these losses during harvest.
This chapter provides a discussion of combine adjustments and settings that can be made to reduce losses that occur as the combine gathers and processes the crop.
Water is a critical factor in maintaining agricultural lands at optimal yield and crop capacity.
Because the most valuable crops grown in Colorado require irrigation, the quality of applied irrigation water is highly influential in determining which crops can be grown.
Crop selection may be limited, or yields may decrease as salinity levels of irrigation water exceed critical levels, or if irrigation water is applied at the wrong crop stage.
Salinity is an ongoing concern among Colorado growers.
As more information is gathered, it is apparent that the problem is spreading.
The Northern Colorado Water Conservancy District , in cooperation with the U.S.
Bureau of Reclamation, has undertaken a multi-year study assessing salinity levels throughout the Lower South Platte Basin.
This study involves monitoring the surface waters of the Lower South Platte River and its tributaries, assessing salinity and water levels at several groundwater observation wells, and mapping soil salinity levels throughout the District boundaries.
The monitoring began in the spring of 2001 and has continued to expand in its scope.
Currently, there are twenty-six automated and twenty-eight manual stations recording salinity levels along the South Platte and its tributaries.
Additionally, nine agricultural irrigation systems, a number of natural returned flows and forty-three groundwater observation wells are being monitored.
Northern Water has also gathered soil salinity data from several fields.
CENTER PIVOT SPRINKLER PACKAGE SURVEY RESULTS
 A road survey of center pivot irrigation systems was conducted in select counties across Kansas on two separate occasions.
A county road map for the selected counties was divided into three transects north/south and three transects east/west.
The survey was conducted in the fall of 2003 in Barton, Edwards, Pawnee, and Stafford counties.
The counties surveyed in 2006 were Finney, Ford, Grant, Gray, Haskell, Scott, Stevens, and Thomas.
The purpose of the survey was to obtain useful information in order to characterize the types of center pivot nozzle packages currently being used and to gather baseline data for future surveys.
The survey information consisted of observations on field location, degree of rotation, number of spans, nozzle type, pressure regulation, general nozzle type, nozzle height, number of spans and overhang, outlets on overhang, and end gun presence and type.
Since the surveyor made observations from the road and not directly from the field, the exact type of nozzle packages could not always be determined.
Therefore, they were generally characterized as impact sprinklers, fixed plate nozzles, or moving plate nozzles, which were recognizable configurations.
The results of the survey are presented in two groups: the south central survey and the western survey.
South Central Kansas Center Pivot Survey Results
 The summary of observations from the south central region of Kansas is shown in Table 1.
Most of the 325 systems that were observed were typical quarter section center pivots and 95% of those systems could make a complete revolution, as shown in Table 1a.
The most common type of nozzle package in the area was moving plate nozzles , as outlined in Table 1b, and each nozzle package was likely to be pressure-regulated, as shown in Table 1c.
Observations on the nozzle spacing and heights were divided into three height categories and five height locations.
Table 1d reveals that the most common nozzle spacing was medium  and Table 1e shows that the most common nozzle height was a mounting just below the center pivot truss.
The observations of primary interest for this region were the number of end guns used on the sprinkler systems.
Table 1f reveals that over one-third  of the systems were equipped with a big gun or traditional end gun, which requires a booster pump.
On the other hand, 48.9% of the systems were equipped with either double or single large impact sprinklers which are pressurized by using existing system pressure.
Almost 13% of the systems did not have a different nozzle at the outer end as compared to the rest of the center pivot system.
Table 1 : Summary of Pivot Nozzle Package Survey for Barton, Edwards, Pawnee, and Stafford Counties surveyed in 2003.
Table 1a: Survey Results of Rotation Degree for Center Pivot Systems in South Central Kansas
 Degree of	Number of observations	Percentage
 Full Circle	309	95
 Partial Circle	16	5
 Table 1b: Survey Results of Types of Sprinkler Nozzles on Center Pivot Systems in South Central Kansas
 Nozzle Type	Number of observations	Percentage
 Fixed Plate	19	5.8
 Moving Plate	244	75.1
 Table 1c: Survey Results of Pressure Regulators on Center Pivot Systems in South Central Kansas
 Pressure	Number of observations	Percentage
 Table 1d: Survey Results of Nozzle Spacing on Center Pivot Systems in South Central Kansas
 Nozzle Spacing	Number of	Percentage
 Close 	64	19.7
 Medium 	187	57.5
 Table 1e: Survey Results of Nozzle Height on Center Pivot Systems in South Central Kansas
 Nozzle Height	Number of	Percentage
 < 4 ft above ground	25	7.7
 > 4 ft above ground	42	12.9
 Truss to 2 ft below truss	221	68.0
 Within truss	1	0.3
 Top of pivot	27	8.3
 Table 1f: Survey Results of End Gun Type on Center Pivot Systems in South Central Kansas
 End Gun Type	Number of	Percentage
 Big Gun	122	37.5
 Double Large Impact	78	24.0
 Single Large Impact	81	24.9
 Western Kansas Center Pivot Survey Results
 The total number of systems observed in the western Kansas survey was 659.
Center pivots larger than the typical quarter section system are more common in western Kansas, so the survey results of the number of spans ranged from 4 to 19, as shown in Table 2.
Out of the total number of observations in western Kansas, 483 were either 7 or 8 spans in length, and only 10 systems were less than 6 spans in length.
Seventy-six systems were either 9 or 10 spans in length,
 and almost 15% of the observed systems were 15 spans or larger.
Approximately 50% of the systems that were 11 spans or larger were operated as partial circles, as compared to about 7% for systems of 10 spans or smaller.
Table 2: Center Pivot Survey Results of Number of Spans and Degree of Rotation
 Number of Spans	Number Observed	Number of Partial	Percent
 4	1	1	<1
 5	2	0	0
 6	10	2	<1
 7	276	18	2.7
 8	207	19	2.9
 9	26	2	<1
 10	50	1	<1
 11	1	1	<1
 12	2	1	<1
 13	4	0	0
 14	4	2	<1
 15	6	4	<1
 16	28	14	2.1
 17	20	11	1.7
 18	16	10	1.5
 19	6	1	<1
 As Table 3 shows, 78% of the observed systems were pressure regulated and 89% used a fixed plate nozzle package.
Table 3: Center Pivot Survey Results for Pressure Regulation Use and Nozzle Type
 Pressure	Number	Percentage	Nozzle Type	Number	Percent
 Yes	515	78.2	Fixed Plate	589	89.4
 No	136	20.7	Moving Plate	62	13.6
 Unknown	8	12.1	Impact	2	<1
 End guns, defined either as traditional big guns or impact sprinklers, accounted for only slightly more then 15% of the systems, as shown in Table 4.
Table 4: Center Pivot Survey Results of Use of End Guns
 End Gun Type	Number	Percent
 Big gun	7	1.1
 Single large impact sprinkler	22	3.3
 Double large impact sprinkler	73	11.1
 None 	557	84.5
 Observations were also made on the placement of the nozzle for both spacing and height, as shown in Table 5.
The most common observation was a mixed spacing configuration, which means that the first several spans had wider spacing than the outer spans.
Only three systems were observed to have wide spacing.
The majority of the systems were shown to use drop nozzles located at less than a 4 foot height, followed by systems that had heights above 4 feet but more than 2 feet below the truss.
Table 5: Center Pivot Survey Results for Nozzle Spacing and Nozzle Height
 Nozzle	Number	Percent	Nozzle	Number	Percent
 Close 	214	32.7	Less than 4	385	58.4
 Medium (8-	197	29.9	Greater	212	32.2
 12 ft)	than 4 foot
 Mixed	245	37.2	Truss to 2	55	8.3
 Wide	3	<1	Within truss	4	<1
 Top of	3	<1
 Survey information was also collected on the ability of the center pivot to make a full revolution.
Table 6 shows that 88 systems, or 13%, could only make partial revolutions.
Table 6: Center Pivot Survey Results for Rotations
 Degree of Rotation	Number	Percent
 Full 	571	88.6
 Partial 	88	11.4
 Additional analysis looked at various combinations of observations.
Table 7 shows nozzle type versus nozzle spacing, Table 8 outlines nozzle height versus nozzle type, Table 9 compares nozzle height and nozzle spacing, and Table 10 shows the number of spans versus the degree of rotation.
Table 7: Center Pivot Survey Results for Nozzle Type and Nozzle Spacing
 Nozzle Type	Nozzle Spacing	Observation	Percent
 Fixed Plate	Close 	196	33.3
 Medium 	155	26.3
 Wide 	1	<1
 Fixed Plate	Total	589
 Impact	Close 	0
 Medium 8-12 ft)	0
 Wide 	2	100
 Mixed	Medium 	1	100
 Moving Plate	Close 	18	29.0
 Medium 	38	61.3
 Moving Plate	Total	62
 Unknown	Medium 	3	60
 Table 8: Center Pivot Survey Results for Nozzle Height and Nozzle Spacing
 Nozzle Height	Nozzle Spacing	Number of Observation
 < 4 ft	Close 	131
 Medium 	41
 < 4 ft	Total	385
 > 4 ft above ground	Close 	64
 Medium 8-12 ft)	118
 Wide ( > 12 ft	29
 > 4 ft above ground	Total	212
 Truss to 2 ft below truss	Close 	18
 Medium 	35
 Truss to 2 ft below truss	Total	55
 Within truss	Close 	1
 Medium 	2
 Within truss	Total	4
 Top of Pivot	Medium 8-12 ft)	1
 Wide 	2
 Top of Pivot	Total	3
 Table 9: Center Pivot Survey Results for Nozzle Height and Nozzle Type
 Nozzle Height	Nozzle Type	Observation	Percent
 < 4 ft	Fixed Plate	371	96.4
 Moving Plate	12	3.1
 < 4 ft	Total	385
 > 4 ft above ground	Fixed Plate	183	86.3
 Moving Plate	27	12.7
 > 4 ft above ground	Total	212
 Top of Pivot	Impact	2	67
 Fixed Plate	1	33
 Top of Pivot	Total	3
 Truss to 2 ft below truss	Fixed Plate	41	74.5
 Moving Plate	13	23.6
 Truss to 2 ft below truss	Total	55
 Within truss	Fixed Plate	4	100
 Within truss	Total	4
 Table 10: Center Pivot Survey Results for the Number of Spans versus the Degree of Rotation
 Number of	Number	Number with	Partial	Partial
 Spans	Observed	Full Rotation	Rotation
 4	1	0	1	<1
 5	2	2	0	0
 6	10	8	2	<1
 7	276	258	18	2.7
 8	207	188	19	2.8
 9	26	24	2	<1
 10	50	49	1	<1
 11	1	0	1	<1
 12	2	1	1	<1
 13	4	4	0	0
 14	4	2	2	<1
 15	6	2	4	<1
 16	28	12	14	2.1
 17	20	9	11	1.7
 18	16	6	10	1.5
 19	6	5	1	<1
 Ninety percent of the observed systems had nozzles which were placed in the two lower placement categories: "less than 4 feet" or "greater than 4 feet but less then 2 feet below truss." Sixty-three percent of all fixed plate nozzles were within 4 feet of the ground, while only 12% of moving plate nozzles fit that category.
Sixty-two percent of the moving plate nozzles were observed in the "greater than 4 feet" category, as compared to 29% of the fixed plate nozzles.
Observation results revealed that moving plate nozzles tend to use higher and wider spacing configurations than the fixed plate nozzles.
Approximately threefourths of the fixed plate nozzles utilized a mixed spacing configuration.
Sixty-one percent of the moving plate nozzles use medium spacing, and another 10% fit into the mixed spacing category.
The large center pivots, which have a greater number of spans, are more likely to be associated with partial rotations.
For systems with 11 spans or less, only 7% did not have full rotation.
For span numbers greater then 11, approximately half of the systems could do full circles.
These results are expected, due to the likelihood of physical constraints in larger fields, water-right and land ownership constraints, and irrigation capacity issues for large systems.
A three-way observation of nozzle spacing, nozzle height, and nozzle type is shown in Table 11.
Fixed plate nozzles are usually spaced closer and lower to the ground than moving plate nozzles, as is necessary because of the operational characteristics of the two nozzle types.
Moving plate nozzles are most commonly used with medium spacing in the "greater than 4 feet" height category.
Table 11: Center Pivot Survey Results for Nozzle Spacing, Height, and Type.
Nozzle Spacing	Nozzle Height	Nozzle Type	Number	Percent
 Close < 8 ft.
< 4 ft	Fixed Plate	126	98.5
 Moving Plate	5	1.5
 < 4 ft	Total	131
 > 4 ft above ground	Fixed Plate	55	85.9
 Moving Plate	9	14.1
 > 4 ft	Total	64
 Truss to 2 ft below truss	Fixed Plate	14	77.8
 Moving Plate	4	22.2
 Truss to 2 ft below truss	18
 Within Truss	Fixed Plate	1	100
 Moving Plate	0	0
 Within Truss	Total	1
 Close <8 ft.
Total	214
 Medium 	< 4 ft	Fixed Plate	36	87.8
 <4 ft	Moving Plate	5	12.2
 < 4 ft	Total	41
 > 4 ft above ground	Fixed Plate	90	76.3
 Moving Plate	26	22.0
 > 4 ft above ground	Total	118
 Truss to 2 ft below truss	Fixed Plate	26	74.2
 Moving Plate	7	20.0
 Truss to 2 ft below truss	Total	35
 Within Truss	Fixed Plate	2	100
 Moving Plate	0	0
 Within Truss	Total	2
 Top of Pivot	Fixed Plate	1	100
 Top of Pivot	Total	1
 Medium 	Total	197
 Mixed	< 4 ft above ground	Fixed Plate	209	98.1
 Moving Plate	2	<1
 < 4 ft above ground	Total	213
 > 4 ft above ground	Fixed Plate	26	89.6
 Moving Plate	3	10.4
 > 4 ft above ground	Total	29
 Truss to 2 ft below truss	Fixed Plate	1	50
 Moving Plate	1	50
 Truss to 2 ft below truss	Total	2
 Within Truss	Fixed Plate	1	100
 Moving Plate	0	0
 Truss to 2 ft below truss	Total	1
 Mixed Spacing	Total	245
 Wide 	> 4 ft above ground	Fixed Plate	1	33.3
 Top of Lateral	Impact	2	66.7
 Wide 	Total	3
 Regional Survey Comparisons and Contrasts
 The south central and western Kansas results were similar in that both regions predominately used systems with lengths of 7 or 8 spans.
Approximately 21% of the systems in either region had span lengths of 8 or greater.
However, in the south central region only two systems were greater then 10 spans in length, whereas 13% of the western systems were greater than the 10 spans.
These results are expected since the terrain of the south central area requires systems that have a higher irrigation capacity for serving sandy soils.
These systems are often problematic, though, because of friction losses and limitations of well capacities.
In addition, more of the south central systems  completed full circles than the western systems , although this trend is likely related to the number of larger systems in the west.
The most common type of sprinkler package in the south central survey was a moving plate type nozzle as compared to the fixed plated nozzle in western Kansas.
Higher capacity systems and sandy soils both make the use of moving plate nozzles and higher nozzle placement a preferred design selection for the general soils and slopes of south central Kansas.
End guns are commonly used on sprinkler systems in south central Kansas.
Only approximately 13% of the systems in south central Kansas did not have some type of end nozzle.
On the other hand, only 15% of western Kansas systems actually used an end gun on their sprinklers.
Over one-third  of the south central systems were equipped with a big gun  and about half  were equipped with either double or single large impact sprinklers.
The dominant center pivot nozzle package of western Kansas is a fixed plate nozzle positioned near to the ground using a drop tube as compared to a moving plate nozzle positioned near truss height in south central Kansas.
Here are some terms and concepts related to sharing water among states:
 An Interstate water compact is an agreement between two or more states regarding competing demands for a water resource that are beyond the legal authority of one state alone to solve.
States administer water rights within their own political boundaries; however, the process becomes more complicated when involving an interstate body of water.
Under these conditions, there are three possible ways to achieve an interstate allocation of water: a suit for equitable apportionment brought by the states in the U.S.
Supreme court; a congressional act; and an interstate compact.
The first-year Popcorn TAPS Competition, sponsored by Zangger Popcorn Hybrids, held a separate kickoff event remotely on March 28.
The eight competitors hail from Nebraska and a couple of other states, as well as one international participant from France.
Participants in this competition will make slightly different decisions than the sprinkler corn participants, although held in the same field.
One aspect of beet armyworm behavior that can be exploited to curb infestations is adult flight activity.
Pheromone traps, an effective way to monitor beet armyworm populations, have shown that population density fluctuates with seasonal temperature patterns; infestations are more prevalent during the summer, when temperatures are high.
Pheromone traps may also provide early warning of an infestation, preventing an outbreak if control is successful.
Laboratory assays indicated that the beet armyworm can develop resistance to Lannate.
A Florida  strain was shown to be moderately resistant to Lannate, and evidence indicates that resistance may still be increasing.
Resistance to Lannate in the California strain , however, could not be detected.
Several steps can be taken to suppress the development of resistance:  insecticide rotation,  localized treatment of infestations, and  use of microbial agents.
There are presently several insecticides registered for use against the beet armyworm on ornamentals in California, including Dursban, Lannate, and Pounce.
Each may be incorporated into the present chemical control program and used on a rotational basis.
A rotation scheme of this nature will prevent the beet armyworm from being repeatedly exposed to a single insecticide, a situation conducive to the rapid development of insecticide resistance.
Another measure that may deter development of resistance is localized treatment of infestations.
Beet armyworm infestations are often clumped or aggregated, apparently because of the egg-laying patterns of the adult female.
Treatments confined to these areas reduce the amount of insecticide needed and preserve natural enemies, as well as reducing resistance development.
Bacillus thuringiensis compounds hold great potential for control of lepidopterous pests.
In addition to the conventional broad-spectrum insecticides used against the beet armyworm, the inclusion of BT compounds in a control program may delay the occurrence of resistance.
BT has a different mode of action, which may help to decrease the probability of resistance development.
Furthermore, BT is virtually nontoxic to mammals, very compatible with most natural enemies, and relatively harmless to plants.
BT is registered for this use on ornamentals.
Thuringiensin, however, is not currently registered.
Harvey A.
Yoshida is a graduate student, and Michael P.
Parrella is Associate Professor of Entomology, Department of Entomology, University of California, Riverside.
This research was supported, in part, by the American Florists Endowment, The Fred C.
Gloeckner Foundation, the California Association of Nurserymen, and Statewide Critical Applied Research Funds from UC Riverside.
The authors thank Dr.
Joe Begley, Yoder Brothers, Alva, Florida, for supplying beet armyworm.
Activated sludge, secondary treatment of municipal wastewater.
Using reclaimed municipal wastewater for irrigation
 Takashi Asano G.
Stuart Pettygrove
 The risks are proportional to the degree of human contact and the adequacy and reliability of treatment.
application of municipal wastewater is a well-established practice in many arid and semiarid regions of the world.
In some regions, 70 to 85 percent of such water is used for agricultural and landscape irrigation.
As demand for water increases in this country, irrigation with reclaimed municipal wastewater has become a logical and important component of total water resource planning and development.
In California, about 220,000 acre-feet of municipal wastewater from 240 cities and towns are used each year, principally for agricultural and landscape irrigation.
In addition, about 610,000 acre-feet per year of treated wastewater is incidentally reused after it is discharged and enters surface or ground waters.
Over half of the intentionally reclaimed municipal wastewater  is used to irrigate fodder, fiber, and seed crops, a use not requiring a high degree of treatment.
About 7 percent is used to irrigate orchard, vine, and other food crops.
Irrigation of golf courses and landscape areas makes use of about 14 percent of reclaimed wastewater each year, and these uses are increasing.
There are several reasons for the growing use of reclaimed municipal
 wastewater, including:  the lack of fresh water at a competitive price;  the potential use of plant nutrients in reclaimed municipal wastewater;  the availability of high-quality effluents;  a need to establish comprehensive water resource planning, including water conservation and reuse; and  the avoidance of more stringent water pollution control requirements, including advanced wastewater treatment facilities at municipalities.
Although irrigation with municipal wastewater is in itself an effective form of wastewater treatment, some additional treatment must be made before such water can be used for agricultural or landscape irrigation.
The degree of treatment is an important factor in the planning, design, and management of wastewater irrigation systems.
Preapplication treatment is necessary to protect public health, to prevent nuisance conditions during application and storage, and to prevent damage to crops, soils, and groundwater.
The quality of reclaimed water depends to a great extent on the quality of the municipal water supply, the nature of the wastes added during use, and the de-
 gree of treatment the wastewater receives.
Wastewater quality data routinely measured and reported at treatment plants mostly pertain to biochemical oxygen demand and suspended solids that are of interest in water pollution control.
In contrast, the water quality characteristics of greatest importance in irrigation use the salt content and concentration of specific chemical elements that affect plant growth or soil permeability are not routinely measured.
Consequently, it is often necessary to sample and analyze the wastewater for those constituents to determine its suitability for agricultural and landscape irrigation.
Historically, the quality of irrigation water has been determined by the quantity and kind of salt present.
As salinity in the reclaimed wastewater increases above a certain level, the probability of soil, water, and cropping problems also increases.
Potential problems are related to the total salt content, to the types of salt, or to excessive concentrations of one or more elements.
These problems are no different from those caused by salinity or specific ions in fresh water and are of concern only if they restrict the use of the water or require special management to maintain acceptable crop growth and yields.
For irrigation with reclaimed wastewater, therefore, the suitability of a water is judged against the level of management needed to cope successfully with the water-related problems that are expected to develop during use.
Salinity, measured by electrical conductivity, is the single most important factor in determining the suitability of a water for irrigation.
Plant damage from both salinity and specific ion concentration is usually tied closely to an increase in salinity.
Establishing a net downward movement of water and salt through the root zone is the only practical way to manage a salinity problem.
Under such conditions, good drainage is essential to
 Fig.
1.
Generalized flow sheet for municipal wastewater treatment and use for irrigation.
allow a continuous movement of water and salt below the root zone.
Long-term use of reclaimed wastewater for irrigation is not possible without adequate drainage.
Toxicity occurs when a specific ion is taken up by the plant and accumulates in amounts that result in damage or reduced yield.
The ions of most concern in wastewater are sodium, chloride, and boron.
The most prevalent toxicity from the use of reclaimed municipal wastewater is caused by boron originating from discharges of household detergents or from industrial plants.
Chloride and sodium also increase during domestic use of water, especially where water softeners are used.
With sensitive crops, toxicity is difficult to correct without changing the crop or the water supply.
The problem is usually accentuated by hot and dry weather.
Besides its direct effect on the plant, sodium in irrigation water may affect soil structure, reducing the rate at which water can move into the soil as well as soil aeration capacity If the infiltration rate is greatly decreased, it may be impossible to supply the plant with enough water for good growth.
In addition, reclaimed wastewater irrigation systems are frequently on less desirable soils or those already having soil permeability and management problems.
It may be necessary in this case to modify soil profiles by excavating and rearranging the affected land.
A permeability problem usually occurs in the surface layer of the soil and is mainly related to a relatively high sodium or very low calcium content in the soil or in the applied water.
At a given sodium adsorption ratio , the infiltration
 TABLE 1.
Laboratory analyses needed to evaluate common irrigation water quality problems
 Measurement	Symbol	Unit	irrigation water
 Electrical conductivity	ECw	mmho/cm or dS/m	0.1	3
 Total dissolved solids	TDS	mg/L	10 2,000
 Calcium	Ca2+	meq/L	0.2	20
 Magnesium	Mg2+	meq/L	0.1	5
 Sodium	NA+	meq/L	0.1	40
 Carbonate	CO32-	meq/L	0	0.1
 Bicarbonate	HCO	meq/L	0.1	10
 Chloride	CI-	meq/L	0.1	30
 Sulfate	S042-	meq/L	0	20
 Boron	B	mg/L	0.1	2.0
 pH 	pH	unit	6.5	8.5
 Sodium adsorption ratio	SAR or RNa	-	0.1	15
 rate increases or decreases with the salinity level.
Therefore, SAR and electrical conductivity of applied water  should be used in combination to evaluate the potential permeability problem.
Reclaimed municipal wastewaters are normally high enough in both salt and calcium, and there is little concern for the water dissolving and leaching too much calcium from the soil surface.
Sometimes reclaimed wastewaters are relatively high in sodium; the resulting high SAR is a major concern in planning wastewater irrigation projects.
The nutrients in reclaimed municipal wastewater provide fertilizer value to crops or landscapes but in certain instances are in excess of plant needs and cause excessive vegetative growth, delayed or uneven maturity, or reduced quality.
Nutrients occurring in significant quantities include nitrogen and phosphorus, and occasionally potassium, zinc, boron, and sulfur.
The most beneficial and the most frequently excessive nutrient in reclaimed municipal wastewater is nitrogen.
Treated wastewater typically contains 90 pounds per acre-foot  of total nitrogen.
Most of this is in the ammonium or quickly available organic form, with little present as nitrate.
The actual economic value of the nitrogen depends on amount of water applied, crop requirement, and other factors; in many situations, the reclaimed water contains at least the total crop requirement for nitrogen as well as for several other elements.
Clogging problems with sprinkler and drip irrigation systems have been reported.
Slimes and bacteria in the sprinkler head, emitter orifice, or supply line cause plugging, as do heavy concentrations of algae and suspended solids.
The most frequent clogging problems occur with drip irrigation systems From the standpoint of public health, however, such systems are often considered ideal, because they are totally closed and avoid the problems of worker safety and spray drift.
Excessive residual chlorine in treated effluent due to chlorine disinfection causes plant damage when sprinklers are used, and the effluent is sprinkled on foliage.
Residual chlorine at less that 1 mg/ L should not affect plant foliage, but when it exceeds 5 mg/L, severe plant damage can occur.
Water quality case studies
 We have used a brief report of case studies by Ayers and Tanji  to guide the reader through some of the de-
 tailed irrigation water quality criteria presented in table 2.
Table 3 contains chemical analyses of representative waters in California: relatively unpolluted water from the Sacramento River at Keswick; a moderately saline groundwater from Vernalis in San Joaquin County; and two treated municipal wastewater effluents from Fresno and Bakersfield.
The Fresno municipal wastewater treatment plant is designed for 60 million gallons per day  and is now operating at 38 mgd.
Land treatment of effluent includes both percolation ponds  with 21 recovery pumps for export of recovered water, and a 600-acre on-site farm using effluent directly for irrigation.
Crops grown with both direct effluent delivery and percolated-recovered water include cotton, corn, alfalfa, almonds, sorghum, beans for seed, wine grapes, and winter cereals.
The Bakersfield treatment plant #2 is designed for 19 mgd and is now operating at 7 to 16 mgd.
It provides primary treatment followed by aerated lagoons covering 51 acres and reservoirs to provide up to 90 days of storage if needed.
The effluent is used to supply 5,100 acres of crop-
 land with a 55-inch depth of water.
Crops grown include cotton, corn, alfalfa, sorghum, rice and irrigated pasture.
Effluent is blended with low-nitrogen water to control growth of nitrogen-sensitive crops such as cotton.
The quality of reclaimed water from Fresno and Bakersfield can be evaluated by following the guidelines in table 2.
Although the water quality is such that "slight" to "moderate" permeability, toxicity, and miscellaneous problems can be expected from use of these two wastewaters, Ayers and Tanji concluded that good normal farming practices used in the area should allow full production of adapted crops.
Table 4 summarizes their evaluation of the suitability of reclaimed wastewater for irrigation.
Health and regulatory considerations
 There is some risk of human exposure to pathogens in every wastewater reclamation and reuse operation, but the health concern is in proportion to the degree of human contact with the reclaimed water and the adequacy and reliability of the treatment processes.
TABLE 2.
Guidelines for interpretation of water quality for irrigation 
 Degree of restriction on use
 Potential irrigation	Slight to
 problem	Units	None	moderate	Severe
 ECW	dS/M or	< 0.7	<	0.7	3.0	>	3.0
 TDS	mg/L	<450	450 2,000	2,000
 water into the soil.
SAR 03	and ECW =>0.7	0.7 0.2	<	0.2
 3 6	=>1.2	1.2 0.3	<	0.3
 = 6 12	>1.9	1.9 0.5	<	0.5
 12 20	>2.9	2.9 1.3	<	1.3
 1 20 40	>5.0	5.0 2.9	<	2.9
 Surface irrigation	SAR	< 3	3	9	>	9
 Sprinkler irrigation meq/l	< 3	> 3
 mg/l	< 70	> 70
 Surface irrigation	meq/l	< 4	4 10	>	10
 mg/L	< 140	140 350	> 350
 Sprinkler irrigation meq/L	< 3	> 3
 mg/L	<100	> 100
 Boron 	mg/L	< 0.7	0.7 3.0	>	3.0
 Nitrogen 	mg/L	< 5	5 30	>	30
 sprinkling only)	meq/L	< 1.5	1.5 8.5	>	8.5
 mg/L	< 90	90 500	500
 pH	unit	normal range 6.5 8.4
 Residual chlorine	mg/L	< 1.0	1.0 5.0	>	5.0
 A secondary clarifier in which sludge settles before effluent undergoes dual-media filtration.
TABLE 3.
Analyses of representative waters in California
 Sacramento	Vernalis area	Wastewater effluent
 River	San	Fresno	Bakersfield
 Keswick	Joaquin Co.
May	(date
 Constituent	May 1978	June 1979	1978	unknown)
 Electrical conductivity	0.11	1.25	0.69	0.77
 pH	7.1	7.7	8.6	7.0
 Calcium 	0.50	5.0	1.2	2.35
 Magnesium 	0.41	2.72	1.05	0.41
 Sodium 	0.26	4.00	3.48	4.74
 Potassium 	0.04	0.10	0.35	0.66
 ratio 	0.4	2.0	3.3	4.0
 Bicarbonate 	0.69	3.11	3.87	3.57
 Sulfate 	0.15	2.29	1.29
 Chloride 	0.06	5.63	1.97	3.01
 Nitrate + ammonia-N 	0.08	5.9	14 *	0.5
 Boron 	-	1.4	0.43	0.38
 Total dissolved solids (mg/
 	72	800	442	477
 Cadmium 	0.002	<0.01
 SOURCE: R.S.
Ayers and K.
Tanji.
1981.
"Agronomic Aspects of Crop Irrigation with Wastewater," Proceedings of the Specialty Conference, Water Forum '81.
American Society of Civil Engineers.
*TKN = total Kjeldahl nitrogen.
TABLE 4.
Evaluation for the suitability of reclaimed wastewater for irrigation 
 Problem area	Fresno	Bakersfield
 Salinity	No problem	No problem
 Toxicity 
 Surface irrigation	Slight	No problem
 Sprinkler irrigation	Slight to moderate	Slight to moderate
 Surface irrigation	No problem	No problem
 Sprinkler irrigation	No problem	No problem
 Boron	No problem	No problem
 Heavy metals	No problem	No problem
 Miscellaneous 
 Nitrogen	Slight to moderate	-
 Bicarbonate	Slight to moderate	Slight to moderate
 The contaminants in reclaimed water that are of health significance may be classified as biological and chemical agents.
For most of the uses of reclaimed water, pathogenic organisms pose the greatest health risks, and water quality standards for pollution control are properly directed at these agents.
Bacterial pathogens, helminths, protozoa, and viruses are removed in wastewater treatment processes in varying degrees.
The most important treatment process from the standpoint of pathogen destruction is chlorine disinfection.
The inactivation of viruses by chlorine is, however, highly variable.
To protect public health without unnecessarily discouraging wastewater reclamation and reuse, many regulations include water quality standards and requirements for treatment, sampling and monitoring, treatment plant operations, and treatment process reliability.
To minimize health risks and aesthetic problems, tight controls are imposed on the delivery and use of reclaimed water after it leaves the treatment facility.
Regulations for a specific irrigation use are based on the expected degree of contact with the reclaimed water and the intended use of the irrigated crops.
Land application of municipal wastewater is common in many regions of the world.
According to a 1984 California State Department of Health Services survey, approximately 220,000 acre-feet of municipal wastewater are reclaimed annually in California by 240 wastewater treatment plants that supply water to more than 380 users.
One approach to evaluating the suitability of reclaimed wastewater is to consider it the same as any other freshwater source and appraise its suitability for irrigation using the criteria in table 2.
These criteria, when applied to the reclaimed water quality of Fresno and Bakersfield, suggest that there will be no serious potential agronomic or public health problems in the use of reclaimed municipal wastewater from those cities.
In fact, both projects have been operated for many years with few problems stemming from poor water quality.
Takashi Asano is Water Reclamation Specialist, California State Water Resources Control Board, Sacramento, and Adjunct Professor, Department of Civil Engineering, University of California, Davis; and G.
Stuart Pettygrove is Cooperative Extension Soils Specialist, Department of Land, Air and Water Resources, UC Davis.
Protect from cattle: If grazing cattle on stalks, protect the system and pumping plant from cattle.
Forests and Urban Stormwater
 Kyle Cunningham Associate Professor of Forestry
 Arkansas Is Our Campus
 Trees and forests are important to water management in all settings in Arkansas.
Most people recognize the valuable role forests play in stormwater management in rural settings, but often the role trees play in assuring healthy water supplies and in stormwater management for urban areas goes unrecognized.
This fact sheet will focus on the functions and uses of trees in stormwater management in urban areas.
Arkansas' landscape is changing.
As we enter the 21st century, urban areas are spreading rapidly.
As urbanization of the landscape increases, stormwater management problems increase.
Existing stormwater facilities in some places are being swamped by the volume of stormwater generated by new development.
Many past management practices have proven inadequate to handle current stormwater volume and also have proven detrimental to the environment.
Clearly, we need to change our thinking and view our existing landscape and forests as part of our stormwater infrastructure.
Stormwater management is evolving in that direction as traditional management costs increase and we learn to reduce costs by retaining stormwater for utilization on-site rather than transporting it off-site to the nearest body of water.
Stormwater is the flow of water that results from precipitation and which occurs immediately following rainfall or as a result of snowmelt.
When a rainfall event occurs, several things can happen to the precipitation.
Some of the precipitation infiltrates or soaks into the soil surface, some is taken up by plants and some is evaporated into the atmosphere.
Stormwater is the remaining portion of the precipitation that drains from the land surface and from soils.
In urban and suburban areas, much of the land surface is covered by constructed and impervious surfaces, such as buildings and pavement, which do not allow rain to soak into the soil surface as it does in naturally vegetated areas, so more of the rainfall becomes stormwater runoff.
Most developed areas rely on storm drains to carry large amounts of runoff from roofs and paved areas to nearby waterways.
Why is stormwater a problem?
Storm sewer systems concentrate runoff into smooth, straight conduits.
This runoff gathers speed and erosional power as it travels underground.
When this runoff leaves the storm drains and empties into a stream, its excessive volume and power blast out stream banks, damaging streamside vegetation and wiping out aquatic habitats.
Figure 1.
Excessive stormwater results in erosional damage to stream channels.
The stormwater carries sediment from construction sites and other denuded surfaces.
Water from streets, roof tops and parking lots is often warmer than that from other surfaces, which can be harmful to the health and reproduction of aquatic life.
Not only does stormwater volume and peak flow increase, but storm flow from urban areas carries more pollutants into streams than stormwater from forests.
Many homeowners use pesticides and fertilizers on their lawns.
Some of these homeowners ignore recommendations and use more, or far more, than necessary.
These materials, along with grass clippings, pet wastes and petroleum wastes from streets and driveways, directly enter streams or enter through municipal stormwater systems.
Since stormwater is not treated, anything that enters a storm sewer system is discharged directly into the waters we use for swimming, fishing, and as drinking water.
Where it enters drinking water sources, the cost of municipal water treatment is increased.
If water treatment is inadequate, this can affect human health.
Household hazardous wastes like pesticides, paints, solvents, used motor oil and other auto fluids can poison aquatic life.
Debris such as plastic bags, sixpack rings, bottles, cups and cigarette butts which enter water bodies can choke, suffocate or disable aquatic life like ducks, fish, turtles and birds.
Bacteria and other pathogens in stormwater can wash into swimming areas and create health hazards.
Land aimals and people can become sick or die from eating diseased fish or drinking polluted water.
Figure 2.
Aquatic wildlife can be injured or killed by debris washed into streams with stormwater.
The sediments in stormwater can cloud the streams and lakes and make it difficult or impossible for aquatic plants to grow.
Sediment also fills in the spaces around rocks and woody debris in streams.
These spaces are critical habitats for aquatic organisms which are the foundation of the aquatic food web.
Excess nutrients can cause algal blooms.
When algae die, they sink to the bottom and decompose in a process that removes oxygen from the water.
Fish and other aquatic organisms can't survive in water with low dissolved oxygen levels.
How do trees fit into the stormwater picture?
Wild forests  are ideal settings for stormwater management; however, they are incompatible with some human activities.
For example, one would not want to play football in a forest.
Also, light automobile traffic, or even heavy foot traffic, can compact soil, which can kill tree roots.
Urban forests, because of their lower stand density, are less effective at stormwater management than wild forests, but they still provide many benefits in stormwater management.
Let's look at the value of trees in stormwater management, starting with the point where rain first contacts the tree the canopy.
The canopy of a tree is the layer of leaves and twigs that forms the top of the tree.
Because urban trees are frequently solitary, the crown may form a shell that covers the upper half or more of the trunk.
Raindrops fall at a speed of 5 to 20 mph, depending upon size of the raindrop.
An individual raindrop won't pack much wallop, but what about a rain storm?
A one-inch rain can deliver about 45 foot-pounds of energy per square foot of soil.
That's enough energy to break soil into fine particles which are easily transported.
Some of those particles are transported down slope while others clog pores in the soil, reducing infiltration and increasing runoff.
Raindrops falling through a forest canopy impact leaves and twigs and dissipate energy into the tree rather than the soil.
Much of this water will be retained on the leaves and twigs for a time.
Some of the water retained on the tree drips off the leaves or runs down the limbs and trunk to the soil over a period of time.
That time lag delays and reduces the volume of peak storm flow, which reduces the impact of stormwater on stream channels.
Some of the water which is retained on the leaves and twigs never reaches the ground.
It evaporates directly from the leaves and twigs and does not contribute to stormwater.
Research in forests similar to those found in Arkansas indicates that 12% to 18% of rainfall that falls over mature forests never reaches the ground.
A 15% reduction in stormwater doesn't sound like much, but think about it this way.
If we assume a storm dropping one inch of rain, a modest storm, this reduces stormwater by more than 4,000 gallons per acre of watershed.
Obviously, urban forests are less dense than wild forests, so stormwater reduction will be less.
Both deciduous and evergreen forests annually drop leaves which accumulate on the forest floor as leaf litter.
Leaf litter absorbs the energy of the falling rain that gets through the canopy without striking a leaf or twig.
Leaf litter also slows surface flow of stormwater and traps much of the sediment and other pollutants carried by stormwater.
Most
 homeowners remove leaf litter in urban areas, leaving the soil vulnerable to erosion and compaction.
Dense grass can substitute for some of these benefits; however, grass cannot provide all of the benefits provided by urban forests.
Figure 3.
Manicured lawns mitigate some stormwater but are not as effective as urban forests.
Trees also use a substantial volume of water.
This water is absorbed from the soil by the roots and released through the leaves to the atmosphere in a process called transpiration.
A mature tree can transpire around 50 gallons of water per day, every day through the summer.
This is more water than will evaporate from nonforested soils.
This process provides two benefits.
First, some of the water from storm events is transpired by trees before it reaches streams.
That's 50 gallons per tree per day that doesn't enter streams as stormwater.
Even well after a storm event, trees continue to extract water from soil.
By reducing soil water content below the saturation level, trees make room in the soil for even more water from the next storm event.
Tree roots provide another benefit, as well.
Roots are not permanent.
Trees continually lose and replace some of the roots.
As these dead roots decay, they provide larger channels for water infiltration into the soil.
Some evidence indicates that water moving along the root surfaces may infiltrate even dense soil layers.
As a result of these processes, less water is available for overland flow and some water infiltrates deeply enough to enter groundwater.
Tree roots also absorb some of the pollutants, such as fertilizers, present in stormwater.
Forests provide many benefits in stormwater management.
They intercept rain before it becomes stormwater and return part of the rain to the atmosphere.
Forests also return water to the atmosphere through transpiration.
Forests deposit mulch, which protects the soil from rain impact, and their roots create infiltration channels and absorb some pollutants.
How can we use trees to manage and mitigate stormwater?
When we discuss using trees in urban stormwater management, we really need to discuss two separate situations.
First, we need to consider some of the issues we will deal with when wild lands are newly converted to urban or industrial uses.
Second, we need to consider some of the issues associated with areas long ago converted to urban or industrial uses.
These differences are important because areas which have not been in urban use have a much more dense forest than those which have been in urban use for many years.
Often when wild land is converted to urban uses, the site is first cleared of all vegetation to facilitate regrading the site to improve construction efficiency.
Ornamental trees may be added to the site afterwards.
The reduction in forest cover that comes with development will increase the stormwater runoff from the site and change the character of the runoff.
Figure 4.
Save as many trees as possible on land under development.
Protect trees during construction.
Clearing the vegetation from the site has several negative effects.
First, the volume of stormwater increases dramatically.
Only about 10% of rain from moderate storms enters streams as stormwater from an intact forest.
The remaining 90% is returned to the atmosphere through evapotranspiration or percolates into the soil and is held there until it is taken up by plant roots.
In contrast, 40% to 55% of rain falling on lawns runs off as stormwater.
The percentage is even higher for impervious surfaces such as streets or roofs.
This increase in storm flow erodes stream channels.
When this stormwater is diverted away from natural systems and into storm drains, a significantly greater load is placed on municipal stormwater systems.
Stormwater volume isn't the only thing that changes.
Stormwater runs off lawns more quickly
 than off forests, so the stormwater from a rain event is delivered to the stream over a shorter period of time.
Since a greater volume of water is being discharged during a shorter time period, peak storm flow is greater, which causes higher water levels, more erosion in stream channels and potentially more flooding.
Several general guidelines will be helpful for planning stormwater management before development begins.
First, leave buffers of undisturbed forest along streams.
Thirty-five feet on each side of the stream channel should be considered the minimum.
Wider buffers should be considered on sloped sites.
It may be tempting to incorporate these buffers into parks, but this should not be done because most parks are raked clean to facilitate usage.
Leaf litter is important to the function of buffer strips.
Removing the leaf litter and the foot traffic associated with park uses results in soil compaction and greater runoff.
Light foot traffic will not harm buffer strips, but heavy foot traffic should not be encouraged.
Don't set up picnic tables in the buffer strips.
Paved walking trails through the buffer strips will not greatly impede buffer function; however, care should be taken to preserve water flow through the buffer strip.
Do not place walking trails within 25 feet of the stream channel.
Trees in buffer strips should not be removed unless absolutely necessary.
Removing a few hazardous trees will not impair the function of the buffer strip, but do not remove more trees than necessary.
Trees absorb water from the soils of the buffer strip before that water reaches the stream channel.
Fewer trees result in more water delivered to the stream.
Trees also provide the leaf litter which protects the soil from overland flow and erosion.
All of the trees on the site are important to stormwater management; however, development cannot take place without removing some of the trees.
Developers must balance the need to remove trees for safe and efficient development with leaving trees for stormwater management.
Remove only trees which must be removed to safely accomplish development.
To the extent possible, the healthiest trees should be left on the site.
In general, healthy trees will be part of the upper forest canopy on the site.
Seek the advice of a consulting forester to determine which trees should remain after development.
Construction activities around trees can severely damage root systems.
See UACES fact sheet FSA5011, Ten Easy Ways to Kill a Tree , for more information about protecting trees during construction.
The fact sheet is available from the Cooperative Extension Service web site or your county extension agent.
Also, consider planting trees after development is complete.
Don't forget to look for tax breaks and conservation easements to
 help offset some of the cost of leaving trees for stormwater management.
Peak storm flows can be delayed and reduced by holding stormwater in detention or infiltration basins.
Detention basins can take the form of constructed wetlands which hold water permanently and serve as sinks for stormwater.
Detention basins usually have wetland vegetation, including trees, around the edges and may have an outlet to a creek or other drain for excess stormwater.
Infiltration basins serve a similar function; however, they do not hold water permanently.
They are dry most of the time and are designed to hold water only immediately after a storm event.
Infiltration basins have no surface outlet.
As the name implies, water soaks into the soil from infiltration basins.
Infiltration basins contain vegetation which may include shrubs and trees which can tolerate flooding for short periods.
While it is relatively easy to plan stormwater management before development is conducted, changing stormwater management practices in existing urban areas is much more difficult.
Streams have already been moved to surface or underground concrete conduits, buffer zones have been covered with lawns or impervious surfaces, and almost all available land has been put to residential or commercial use.
Little land is available to manage stormwater on-site in these situations.
Municipalities can maintain the health of existing trees and plant new trees where opportunities are available.
Isolated trees still catch rainfall before it enters the stormwater stream and help remove soil water before it enters streams.
Sometimes opportunities may be found in existing urban landscapes.
Most urban areas contain at least some land suitable for urban forests.
These areas include lawns, parks, athletic complexes, schools, road medians and cemeteries.
While some parks and athletic complexes will not be suitable for trees because of the type of use, often parts of these public lands can support an urban forest.
Public lands are the easiest to incorporate into a stormwater management system because they are publicly owned and already under control of the local government.
Protect existing trees on these properties and plant trees where they are appropriate.
Cemeteries and lawns, even though privately owned, could be incorporated into stormwater management systems through offering incentives to maintain or establish tree cover.
Tree protection ordinances can be used to maintain forest canopies on private properties where incentives produce inadequate results, but these ordinances often are unpopular.
Many private citizens and businesses are eager to participate in green redevelopment.
Those who own land adjacent to
 streams may be willing to donate easements along streams so that buffer strips can be installed where none currently exist.
Citizens are often willing to help plant trees, as well.
When urban sites are redeveloped, opportunities arise to install stormwater management systems.
Soils under parking lots, roads and sidewalks can be used to temporarily store stormwater.
Engineered soils are available that provide greater water storage capacity than compacted soils typically found under parking lots without a loss in soil strength.
Stormwater should be directed to the storage under the parking lot instead of being directed into stormwater drains.
These systems should be used in conjunction with trees to dispose of stormwater on-site.
The trees are important to making this system work because the trees reduce the stormwater volume entering the system and remove stormwater from the engineered soils through transpiration.
The tree roots penetrate compacted subsurface soils and provide channels for infiltration to further remove water from the engineered soils.
Trees must be carefully matched to local rainfall patterns to provide a good balance between tolerance to flooding and tolerance to drought.
Urban soils are often compacted enough to reduce stormwater infiltration.
Compaction results in poor plant growth and increased stormwater runoff.
In the long term, trees can remediate compacted soils and improve water infiltration.
Tree roots growing through the soil create open channels for air and water infiltration.
Besides increasing infiltration, the increase in soil porosity will improve plant growth and further increase the value of the site for stormwater management.
Stormwater management is a significant cost for many cities and can have a significant impact on our environment; however, the costs and impacts can be reduced.
Appropriate planning at the time of development or redevelopment greatly reduces the cost of stormwater management in terms of dollars and environmental impact.
Even when redevelopment is not an option in the near future, proper management of the urban forest can reduce stormwater costs and impacts.
The concept of Low Impact Development  and other sustainable stormwater management techniques is gaining popularity.
Increased awareness of "green development and construction" in urban areas is causing urban planners to develop new approaches to stormwater management.
TENSIOMETER USE IN SCHEDULING IRRIGATION
 Mahbub Alam Extension Specialist, Irrigation and Water Management
 Danny H.
Rogers Extension Irrigation Engineer
 Tensiometers continuously monitor soil water status, which is useful for practical irrigation scheduling, and are extensively used on high-value cash crops where low water tension is desirable.
Tensiometers are ideal for sandy loam or light-textured soils.
Measurement range is limited to less than one bar tension.
Clay soils will still have plant available water past this limit, although the most readily available water is gone.
Tensiometers may be used in clay soils for crops that need low soil water tension for maximum yield or high crop quality.
Kansas State University Agricultural Experiment Station and Cooperative Extension Service
 Tensiometers are soil water measuring devices that are sensitive to soil water change and useful for irrigation scheduling.
Irrigation scheduling is a process to determine when to irrigate and how much water to apply.
Applying too little or too much water in an untimely manner can result in yield reductions.
Over irrigation wastes water, costs money to pump, and may leach nutrients beyond the root zone.
Irrigation scheduling is important and can be achieved by monitoring soil water status with tensiometers.
Plant roots undergo tension as they pull the water out of a soil matrix.
Tensiometers are devices that measure the soil water tension by acting like a mechanical root.
This mechanical root is equipped with a gauge that continu-
 ously registers how hard the root must work to extract water from soil.
Tensiometers are particularly accurate at low tensions, which is the wettest part of the soil water range.
They are popular with growers of high-value crops, such as vegetables and fruits on sandy soils.
A tensiometer is a sealed, waterfilled tube equipped with a vacuum gauge on the upper end and a porous ceramic tip on the lower end.
The basic components are a reservoir and cap, body tube, vacuum dial gauge, and a ceramic tip.
Reservoir and cap.
The reservoir acts as a water supply for the body tube.
The cap on the reservoir must provide an airtight seal for the tensiometer or the device will not work.
Some models do not have an enlarged reservoir; the body tube works as a reservoir, and the cap directly seals the system.
Body tube.
The body tube provides support and a liquid connection between the porous tip and the vacuum gauge.
Tensiometers come in various lengths.
Standard lengths are 6, 12, 18, 24, 36, 48, and 60 inches.
Ceramic tips.
The ceramic tip is porous, but the openings are SO small that when saturated with water, air cannot pass through within the range of soil water tensions to be measured.
Water moving out through the porous tip causes the vacuum dial gauge reading to change indicating the suction, or tension, at which the water is being pulled by the surrounding soil.
Vacuum gauges.
The vacuum gauge  is calibrated in centibar or hundredths of one "bar." A bar is the unit of pressure, either positive
 Figure 2.
Vacuum dial gauge.
Table 1.
Interpretation of Tensiometer readings
 0	Saturated	Soil is saturated regardless of soil type.
If readings persist,
 there is possible danger of waterlogged soils, a high water
 table, poor drainage and soil aeration; or the continuity of the
 water column in the tube may have broken.
5-10	Surplus water	Indicates a surplus of water for plant growth.
Drainage contin-
 ues and persistent reading indicates poor drainage.
10-20	Field Capacity	Field capacity for all types of soils.
Additional water will drain
 as deep percolation carrying nutrients without opportunity for
 plant use.
Sandy soils, however, have very little storage capa-
 city, and suction values increase rapidly as water is removed by
 plants past 15 to 20.
For sensitive crops, like potato, rapid
 irrigation may be required before damaging stress can develop.
20-40	Irrigation range Available water and aeration good for plant growth in fineand
 medium-textured soils.
Irrigation is not required for these soils
 at this range.
Coarse-textured soils may require irrigation in the
 20 to 30 range and finer sandy soils at 30 to 40 centibar ranges.
40-60	Usual range for starting irrigation.
At 40 to 50 centibar, irriga-
 tion may need to be started for loamy soils.
On clay soils (silty
 clay loams, silty clays, etc.) irrigation usually starts from 50 to
 60.
Heavy clay soils still have some available water.
Irrigation,
 however, ensures maintaining readily available soil water.
The
 stage of growth and type of crop will influence the decision.
70	Dry	Stress range.
However, crop is not necessarily damaged.
Some
 soil water is available in clay soils but may be low for maxi-
 80	Top range of tensiometer accuracy; higher readings are pos-
 sible, but tension within the water column inside tensiometer
 will break between 80 to 85 centibar.
This has relationship to
 elevation of the area compared to mean sea level.
At higher
 elevation, the water inside the tube may break at a lower read-
 ing according to atmospheric pressure.
or negative, that has been adopted for the expression of soil suction.
The bar is an international unit of pressure in the metric system and is equivalent to 14.5 psi  or 0.987 atmospheres.
One centibar is also equal to 1 kPa.
A reading of zero corresponds to a completely saturated condition, regardless of the type soil.
A reading of 80 indicates a very dry condition for sandy soils or sensitive crops.
This also is the functional upper limit for tensiometer readings.
A tension higher than 80 will cause the water column inside the tube to break rendering it nonfunctional.
A depth label is usually placed on the vacuum gauge or on the side of the tube to indicate the depth at which the ceramic tip will be set when installed.
This is important for identification purposes.
The soil suction reading on the vacuum gauge dial is an indication of soil water availability for plant use
 and does not require calibration for salinity or temperature.
The readings have different meaning in terms of use for irrigation scheduling depending on soil type.
Table 1 and Figure 3 suggest interpretation of tensiometer readings in relation to soil texture.
Each situation is different, SO irrigators should monitor crop conditions, such as wheel track compaction or plow pans, that can affect root development and water movement in the soil.
TENSIOMETERS WITH ELECTRONIC READER
 Electronic technology has been added to the tensiometers to be remotely read and used to automatically start irrigation.
The manufacturers have developed equipment that will read the tensiometer and turn on an irrigation controller or solenoid valve to initiate irrigation.
prised of an electronic switch that can be mounted on the vacuum gauge dial of the tensiometer and set to start irrigation at a certain reading.
As the soil water tension rises, the gauge needle, which has a magnetic property, moves to a set reading and coincides with the eye of the switch.
At this point the electric circuit closes and establishes a current flow to the controller or the solenoid valve, which turns the system on for irrigation.
With the progress of irrigation, the soil water gets recharged.
The tensiometer is very sensitive to soil water change, and the increase in soil water reduces the tension.
The gauge needle falls back, electric current flow is discontinued, and the system automatically shuts down.
These switches are normally operated by alternating current  flow.
The need for a direct  current system should be specified at the time of ordering.
Follow the manufacturer's instructions for installation.
There are two systems currently available.
One of the systems is com-
 The other automatic system operates by using a pressure transducer.
In this system, the vacuum gauge is replaced by a pressure transducer, which senses any change in pressure and modifies the electric current flow to reflect that change.
The reading is continuous.
By directly attaching it to the tensiometer body in place of the vacuum gauge, it is connected to the tensiometer system.
The transducer is read by an ammeter or voltmeter, which may be interfaced with a data logger or computer.
The reading is translated into soil water tension.
This information can be used to make decisions for controlling the irrigation system.
The computer may be programmed to start an irrigation system at a certain value.
The power requirement for the transducer input may vary, but many have requirements of less than 10 volts.
The automated versions of tensiometers enable remote system operation.
The irrigation systems now can be controlled based on the soil water content.
Soil water exists primarily as thin films around and between soil particles and is bound to soil particles by strong molecular forces.
As the soil dries, the water films become thinner and more tightly bound to soil
 Figure 3.
Interpretation of tensiometer readings.
matrixes.
This increase in tension within the films now in contact with the tensiometer causes water to be drawn from the ceramic tip.
The withdrawal of water from the ceramic tip creates a partial vacuum in the tensiometer.
Water continues to be drawn until the vacuum created inside the tensiometer equals the tension of the water films outside.
At this point equilibrium is reached and water ceases to flow.
The vacuum gauge reading indicates the amount of suction or tension.
As water is added to the soil from rainfall or irrigation, the soil suction is reduced.
The higher vacuum in the tensiometer causes soil water to be drawn into the tensiometer, and the vacuum will be reduced until a balance in tension is reached.
The tensiometer continuously responds and maintains a balance with the soil water suction or tension and the vacuum gauge indicates the amount of tension, hence the name tensiometer.
As with any measurement device, proper care and maintenance are required.
Check the tensiometer before installation in the field.
If the tensiometer was used previously, begin by washing and rinsing it inside and out.
Residues on the porous ceramic tip that were not removed by washing may be removed by sanding
 the finer pores.
Allow the tensiometer to stand upright, soon the tip will wetup and free water will appear like a sweat.
Refill as necessary to dispel all the air from the tensiometer.
After letting it stand in a bucket of water overnight, seal the tensiometer and set it upright in the air.
The air will start drying the tip.
The gauge should read 70 when air dried.
Periodic checking of the gauge reading will indicate if it is functioning properly.
Repeat the wetting and drying cycle with the tensiometers that do not respond correctly the first time.
lightly.
Fill the reservoir and body tube with distilled water, taking care that the ceramic tip is wetted from one direction to avoid air entrapment in
 Distilled water treated with three to five drops of chlorine bleach per gallon may be used to inhibit algae growth.
Manufacturers also provide solutions for water treatment that may be used according to direction.
Distilled water available in a grocery store has been found adequate.
If excessive air bubbles are noticed, boiling may be helpful, but the remaining waters need to be stored in an airtight container.
Some manufacturers provide a
 Figure 4.
Zone of soil water control with a two-tensiometer station.
hand-operated vacuum pump to help remove air from the tensiometer.
Operating the pump when the tensiometer is filled with water and the tip is submerged in water helps remove gases from the pores of the ceramic tip and solution.
After each pumping, refill the tensiometer completely with water and repeat until no more bubbles are observed.
The tensiometer is then sealed by screwing the reservoir cap down securely.
If tensiometers are not to be installed immediately, cover the tips with a plastic bag to prevent evaporation or let them stand in a bucket of water until installed.
Depth selection.
The number of tensiometer installation sites required will depend on the crops grown and field conditions.
Fewer stations of tensiometers are needed when a single crop is grown in large blocks of uniform soil.
If the soils are varied or different crops are to be grown, more stations are necessary.
Stations need to be selected to represent an area, and care should be taken not to cause excessive compaction or destruction of plants around during installation, which may alter the condition.
Except for very shallow-rooted crops, tensiometers are normally installed in groups of two or more to characterize the soil in the top half to three quarters of the root zone.
If the potential root zone is less than 12 inches, a single tensiometer may be installed in the center of the zone at 6 inches deep.
With deeper-rooted crops, one tensiometer should be placed at the upper one quarter of the rooting depth and another at the lower quarter point or three quarters of the depth.
In deeply rooted crops or situations where there is a distinct break in soil textures, three or more tensiometers may be needed.
An example might be 18 inches of sand overlying a silty soil growing corn where 3 to 4 feet of the root zone is to be managed.
One tensiometer might be placed at 6 inches, a second at 18 inches and a third at 2 to 3 feet.
The differences in tension readings would make it possible to
 Figure 5.
Furrow system station arrangement.
better assess the soil water conditions.
Almost 70 percent of crop water is supplied by the top half and only 10 percent from lower one fourth of the rooting depth.
Irrigators, therefore, often manage only the top half or threefourths of the root zone.
Tensiometers should be long enough to reach the desired depth and diaphragm vacuum gauges not touching the ground.
They should never be set in a hole.
Site selection.
Location of the tensiometers in the field generally depends on the type of irrigation system used.
For large fields, generally, there will be at least four stations or locations in each field.
If the tensiometers are installed in a flood-irrigated field, stations will be located at the top and bottom of the first and last sets.
Each station should be far enough in from the top or bottom of the field SO it is not affected by initial wetting effects or by ponding of water.
Under a sprinkler system, use two stations on each side of the pivot when it is in its normal stop position.
Set one station on each side near the middle of the pivot, and
 Figure 6.
Center pivot station arrangement
 one station on each side near the outer tower of the pivot, usually about the middle of the outer span.
The stations on each side should be far enough away from the pivot SO the sprinklers will not wet them when the system is stopped or until after the system is moving.
This system of positioning stations on flood or sprinklers will give start and stop indicators for the irrigation sequence.
Tensiometers may be installed using a soil auger or a probe.
Manufacturers also provide simple coring tubes.
Placement should be in a crop row to avoid traffic.
Where furrow irrigation is used, the tensiometers may be angled slightly to place the tip under the furrow.
The electronic tensiometers may require a cover to safeguard the electric connections from sprinkler or rain water.
If a valve cover box is used, the tensiometer tips need to be slanted out to be in the crop area.
The hole should be small enough to create resistance to insertion of the tensiometer and shaped to form close soil contact at the tip.
This may be accomplished by returning a little loosened portion of the soil from the depth of placement back into the hole and adding a little water.
When the tensiometer is pushed for placement, the soft soil will move around the tip to conform to the rounded shape and make a good contact.
Tensiometers must be handled with carethe tips may break if handled roughly.
Ceramic tips of the tensiometers must be kept wet until installed.
Steady and firm pressure may be applied while inserting the tensiometer until it reaches the desired depth.
The depth label on the tensiometer will identify the root zone being monitored as either deep or shallow.
Tensiometer locations need to be marked both in the row and at the edge of the field.
A brightly painted wooden stake or a metal rod with a colored flag attached are good markers.
Locating tensiometers in tall crops can be a problem.
A written log of the station locations also is recommended.
Tensiometers are weatherproof, except for freezing, and generally require very little service.
When first installed, there may be tiny air bubbles
 clinging to the sides of the body tube.
However, after one cycle of soil water use, which creates a high vacuum, the bubbles will rise to the top and can be eliminated by refilling.
The amount of bubbles will depend on the gas originally present in the vacuum gauge and the amount dissolved in the water.
Servicing is best done soon after irrigation.
Tensions are low and air that may have been drawn into the cup at high tensions can be eliminated by refilling.
Tensiometers return to equilibrium rapidly at low tensions.
They also respond quickly to a very minute withdrawal of water from the system.
If much air is drawn into a tensiometer at low tensions, the porous cup may be defective, and the tensiometer may need to be replaced.
Some air entry is unavoidable.
When using a number of tensiometers, watch for tensiometers that accumulate abnormal amounts of air.
The colored fluid concentrate supplied by the manufacturer for control of algae helps to spot collected air bubbles in the tensiometer.
Some tensiometers may require gauge adjustments.
The pointers may be adjusted to read zero at the atmospheric pressure of the location of use by opening a screw provided to let air enter into the seal gauge.
This may be needed to take care of the difference of pressure due to elevation change.
In others, this is accomplished by adjusting to zero with the tensiometer cup standing in a bucket of water.
The depth of water outside of the tensiometer in the bucket must not stand too high to avoid outside pressure.
pump to remove air.
The tensiometer may have been empty because of dry soil.
If the tip was dry, fine air bubbles will rise rapidly for several minutes and then cease.
If larger bubbles rise and continue, a leak is indicated, and the source should be determined.
If the bubbles rise from the bottom, remove the tensiometer and replace the tip.
If the bubbles enter from the side, the body tube may be cracked and should be fixed.
If bubbles rise from the gauge, the leak may be in the gauge or the threaded connection.
A leaky gauge needs to be replaced, but a threaded connection can be resealed.
If no large bubbles rise, yet the reading remains at zero, the reservoir cap may be cracked or the seal may be defective.
Inspect for an 'O' ring.
There needs to be one for a proper seal.
In most cases, the trouble is easily corrected.
A damaged vacuum gauge may stick in one position or may not respond smoothly with changes in soil water.
Check a suspect gauge against one known to be in good working order, or replace the suspect gauge with a new one.
Readings higher than expected, especially after irrigation, are generally not tensiometer failure.
The irrigation water may not have penetrated to the depth of the tensiometer tip.
Tensiometers should be removed from the field before freezing.
The water can freeze and break the ceramic tip or the body or damage the vacuum gauge.
Tensiometers need to be emptied before long-term storage.
This prevents salt deposition in the porous material with evaporation or rusting of the gauge.
A tensiometer that is out of water or leaking will remain at zero on the gauge, or the reading will fluctuate in the low suction range.
Two or more successive zero readings may be a sign of a malfunction and should be investigated.
If the gauge remains at zero, refill with water and use a hand
 The major criticism of the tensiometer is that it functions reliably only in the wet range of soil water at readings of about 80 centibars or less.
At higher readings, the porous tip may leak air, and the gases will be drawn out of the water.
At low pressure, the water will vaporize causing discontinuation of the tension column or vacuum.
The gauge reading will fall to zero.
This is not as serious as it may seem because most of the available water in coarse-textured soils and about 50 percent or more in fine-textured soils have already been used at this range.
seasons making it cost-effective.
Finally, the ceramic tip may gradually fill with precipitates because of soil water movement through the pores.
This slows water transfer through the tip and increases the time required for the tensiometer to respond to a change in soil-water conditions.
Some slowing does no harm, but if the response time becomes too slow, a new tip should be installed.
The response time may be improved by rubbing the exterior of the tip with fine sandpaper or soaking the tip in a mild acid solution.
The amount of plugging depends on the soil water chemistry and the manner of use.
Another criticism is the price, which ranges from $45 to $60.
When used in large quantities, the cost may seem prohibitive.
Irrigation scheduling, however, has been shown to easily pay for itself through increased yields or reduced pumping.
Proper handling may extend the useful life, and the cost may be spread over many
 Where tensiometers can be left in the ground, the tip porosity remains satisfactory for several years in most soils.
But each time the tensiometer is removed from the soil, tip life is reduced.
This is particularly true if the soil is calcareous or saline.
In extreme cases, where the tensiometer is installed and removed several times per season, the tip may need to be replaced after one year of use.
To minimize this damage, a tip that is removed from the soil should be protected from drying until the tensiometer has been emptied, cleaned, and dried.
Before winter storage, the tensiometer needs to be cleaned and flushed with distilled water.
Flushing is done by filling the tube and letting the water drain out of the tip by gravity.
If stored where frost protection is not available, make certain all the water from the system had been drained.
The gauges will hold some water that is not readily visible.
The vacuum pump may be used to remove the water by holding the tube horizontal with the gauge in upright position.
At the time of reuse, the preparation process should be repeated.
Place two or more tensiometers of different lengths near one another , usually in the crop row.
Two stations may be enough in a small field with uniform soil and slope, but four stations is the usual minimum recommendation.
The location of stations will depend upon the type of irrigation system.
With furrow irrigation, this may be at the upper and lower quarter
 points of the first and last set in the field.
For a center pivot, it may be in the outer and middle spans, with pairs of stations at the start point and at the end point of the pivot.
Tensiometer stations should be located in representative areas of the field.
Do not position tensiometers in low spots or on knobs, and place them where the plant population is representative of the field.
Wait 24 hours after installing the tensiometer to obtain reliable readings.
If the soil was dry at in-
 Tensiometer installation depth is determined by the active root zone of the crop.
For example, for a corn crop on a deep soil, three tensiometers, installed at depths of 12, 24, and 36 inches, are recommended at each station.
OTHER AVAILABLE IRRIGATION PUBLICATIONS
 Considerations for Sprinkler Packages on Center Pivots L908 Efficiencies and Water Losses of Irrigation Systems MF2243 Evaluating Pumping Plant Efficiency L885 Guidelines for Use of Propeller-Type Irrigation Water Methods L896 Irrigation Water Measurement L877 Large Acreage Center Pivot Systems L902 LEPA Irrigation Management for Center pivots L907 Managing Furrow Irrigation Systems L913 Managing LEPA Bubblers and Flat Sprays on Corn L879
 stallation, irrigation or rainfall may be needed before obtaining satisfactory readings.
Tensiometers should be left in the field for the duration of the growing season.
The roots of the crop must grow around the porous tip for reliable readings.
Moving the tensiometer during the growing season is not recommended.
Predicting the Final Irrigation for Corn, Grain Sorghum, and Soybeans MF2174 Scheduling Irrigations by Electrical Resistance Blocks L901 Soil Water Measurement: An Aid to Irrigation Water Management L795 Soil, Water and Plant Relationships L904 Sprinkler Package Effects on Runoff L903 Subsurface Drip Irrigation for Field Corn: An Economic Analysis L909 Surge Irrigation L912 Tensiometer Use In Scheduling Irrigation L796
 Kansas State University Agricultural Experiment Station and Cooperative Extension Service, Manhattan, Kansas
If pollination is good, manage the field as normal.
If pollination is poor, those kernels will develop normally with reduced yield potential.
These field may be considered for forage or silage harvest.
If there is no pollination, there are two options;  harvest as near to pollination as possible for the highest quality forage possible or  leave the crop as a living cover crop until the fall before mowing or chopping.
Continual leaf rolling of the plant in the weeks leading up to pollination can result in a yield loss of 1-5 percent per day.
During pollen shed and silking severe stress can reduce yields by up to nine percent per day.
In the weeks following pollination drought stress can reduce yield by up to six percent per day.
Statewide Estimates of Potential Groundwater Recharge
 Briana Wyatt Graduate Research Associate
 Saleh Taghvaeian Assistant Professor and Extension Specialist, Water Resources
 Tyson Ochsner Sarkey's Distinguished Professor, Associate Professor of Applied Soil Physics
 Groundwater is water that is found naturally in aquifers, which are underground layers of permeable rock or unconsolidated materials.
The depth at which these water reservoirs occur varies by location  as well as with time , and can range from the soil surface to many hundreds of feet below ground.
There are three types of aquifers: 1) confined aquifers, 2) unconfined aquifers and 3) perched aquifers.
Confined aquifers have a confining layer both above and below a saturated zone.
A confining layer is any layer of material that restricts the movement of water.
An unconfined aquifer is one that has a confining layer only at the bottom of the formation.
Perched aquifers are unconfined aquifers of limited areal extent that retain water due to some restricting layer, such as a clay layer.
For more information on the basics of groundwater hydrology, see Extension Fact Sheet WREC-104, "Introduction to Groundwater Hydrology and Management."
 Groundwater aquifers are important sources of water for agricultural, municipal and household use across the world, sustaining one-fourth of the human population.
It is estimated that there are more than 390 million acre-feet of groundwater in Oklahoma, most of which is held in the state's 22 major aquifers.
These aquifers supply nearly half of all water used in Oklahoma and more than 70 percent of water used for agricultural irrigation.
To sustainably manage groundwater resources, it is necessary to know an aquifer's recharge rate, or the rate at which water is being returned to the aquifer.
Understanding an aquifer's recharge rate allows water managers to know whether more water is being returned to or lost from the aquifer, either by pumping or by natural discharge.
Rates of groundwater loss often exceed the rate of recharge due to excessive pumping or drought, which causes water levels in aquifers to drop.
This disparity between recharge rates and groundwater losses led to water level declines during 2001-
 Figure 1.
Water-level declines in Oklahoma aquifers from 2001-2006.
Source: Oklahoma Water Resources Board, 2007.
2006, ranging from 0.6 to more than 21 feet in many major Oklahoma aquifers, as shown in Figure 1.
Many prior studies have estimated recharge rates for individual Oklahoma aquifers.
However, factors such as data availability, climate during the study period  and the duration of the study  can impact study results and can make comparing recharge rates between studies difficult.
In contrast to aquiferspecific studies, very few state-wide estimates of groundwater recharge have been made.
The most recent state-wide recharge rates were published nearly 40 years ago .
Because of the importance of groundwater in the state, accurate and up-to-date recharge rates are essential for the sustainable management and longevity of groundwater resources.
Groundwater recharge is often limited by the amount of water that drains from a soil profile, and the drainage rate is strongly influenced by soil moisture conditions.
Because drain-
 Table 1.
Summary of previously published recharge rates for select Oklahoma aquifers.
Source: Oklahoma Comprehensive Water Plan 2012 Executive report.
Name	Type	Recharge Rate
 Arbuckle-Timbered Hills	Bedrock	0.3-0.6
 Elk City	Bedrock	2.8
 Rush Springs	Bedrock	1.8
 Arkansas River	Alluvial	5.0
 Canadian River	Alluvial	2.0
 Cimarron River	Alluvial	2.3
 Enid Isolated Terrace	Alluvial	2.3
 Gerty Sand	Alluvial	1.0
 North Canadian River	Alluvial	1.0-5.0
 North Fork of the Red River	Alluvial	2.3
 Red River	Alluvial	2.5
 Salt Fork of the Arkansas River	Alluvial	2.3
 Tillman Terrace	Alluvial	2.9
 Washita River	Alluvial	2.65-4.41
 age limits the amount of recharge an aquifer may receive, it is helpful to think of the drainage rate as a potential recharge rate, or as an upper limit on actual recharge.
Assuming water flow in soil is gravity-driven, it is possible to estimate the amount of drainage from the soil profile using soil moisture data from monitoring stations and soil property data.
The Oklahoma Mesonet has provided daily soil moisture data at three depths  for more than 100 stations since 1996.
These data were used to estimate annual drainage at 78 locations from 1998-2014.
Using soil moisture data to estimate drainage rates has three distinct advantages over previous methods: 1) it incorporates long-term meteorological and soil moisture data that have been collected since 1996, including the effects of several extreme climatic events, 2) results can be updated any time as long as the soil moisture monitoring system is intact and 3) in addition to site-specific estimates of drainage, the large number of point measurements available may be used to indicate the spatial distribution of recharge across the entire state of Oklahoma, as opposed to single-aquifer studies that have been done in the past.
Long-term mean annual drainage  estimates found using soil moisture data from the Oklahoma Mesonet are shown in Figure 3.
Soil moisture-based drainage rates generally followed the precipitation gradient of the state, as expected, decreasing from east to west.
Mean drainage estimates for the period from 1998-2014 agreed well with prior recharge estimates, with drainage rates ranging from 0.2 inch
 Figure 2.
Mesonet site name abbreviations and locations for sites where drainage estimates were made.
Labels for three sites  were excluded for clarity.
Adapted from Wyatt et al..
Figure 3.
Statewide mean annual soil moisture-based drainage rates for the years 1998-2014.
Drainage rate labels for the Stillwater, Oklahoma City East, Porter, and Marena sites were excluded for clarity, but were 8.4, 3.2, 6.5 and 2.6 inches per year, respectively.
Figure 4.
Prior state-wide groundwater recharge estimates published by Pettyjohn.
per year at Boise City in the Oklahoma Panhandle to 10.5 inches per year at Bristow in northeast Oklahoma.
This is similar to the range of recharge values found by prior studies in Oklahoma, with reported recharge rates ranging from 0.03 to 10.5 inches per year.
The median drainage rate for the study period was 2.64 inches per year, which is approximately 7.7 percent of the median state-wide rainfall of 34.3 inches per year for the same period.
This means, on average, approximately 8 percent of rainfall falling in Oklahoma became drainage from 1998-2014.
Soil moisture based drainage rates correspond fairly well with the most recent prior state-wide estimates of groundwater recharge.
Although Pettyjohn et al.
used a different method and data from the 1970's, the maps
 are similar in several ways, including the trend that drainage and recharge rates decrease from east to west.
Additionally, the maximum soil moisture-based drainage rate in this study  and maximum Pettyjohn et al.
recharge rate  are comparable.
However, there are also some differences between the two maps.
For instance, calculated drainage rates in the Oklahoma Panhandle range from 0.2 to 1.1 inches per year and are higher than the recharge rate of 0.1 inch per year or less estimated for this region by Pettyjohn et al.
Soil moisture-based drainage estimates summarized by aquifer compare well with previous recharge estimates for major Oklahoma aquifers.
These drainage values were found by computing the median value of the mean annual drainage rate for aquifers with a minimum of three Mesonet sites above them, resulting in aquifer-scale drainage rate estimates for six Oklahoma aquifers.
Aquifer-scale drainage rates fall within the range of previous recharge estimates, with the exception of the Arkansas River alluvial aquifer, which has only one prior recharge estimate.
Though only one other study has estimated recharge for the Arkansas River alluvial aquifer, the soil moisture-based drainage estimate is within 30 percent of the estimated recharge rate found by that study.
These results provide strong evidence that drainage estimates from a large-scale soil moisture monitoring network can be indicative of potential recharge rates at the spatial scales of an individual aquifer and an entire state.
Soil moisture-based drainage estimates can be made by applying a simple unit-gradient assumption to daily soil moisture data from long-term in situ monitoring stations.
The primary weaknesses of this approach in the present study
 Table 2.
Summary of soil moisture-based drainage rates by aquifer.
Aquifer name, number of Mesonet sites located above the aquifer, median value of the mean annual soil moisture-based drainage rate, a range of previous recharge estimates, and the number of publications contributing to that range.
ASSESSMENT OF PLANT AVAILABLE SOIL WATER ON PRODUCER FIELDS IN WESTERN KANSAS
 Water shortage is the primary factor limiting crop production in the USA's westcentral Great Plains, and agricultural sustainability depends on efficient use of water resources.
Precipitation is limited and sporadic with mean annual precipitation ranging from 16 to 20 inches across the region, which is only 6080% of the seasonal water use for corn.
Yields of dryland crops are limited and variable and some producers have used irrigation to mitigate these effects.
Continued declines within the Ogallala Aquifer will result in a further shift from fully irrigated to deficit or limited irrigation or even dryland production in some areas.
As this occurs, producers will desire to maintain crop production levels as great as possible while balancing crop production risks imposed by constraints on water available for production.
Efficient utilization of plant available soil water  reserves is important for both dryland and irrigated summer crop production systems.
In western Kansas, dryland grain sorghum yield was linearly related to PASW at emergence and sorghum yields increased 501 lbs/acre for each additional inch of PASW.
When the experimental effects of tillage were considered, grain sorghum yield response to water supply  was greater with no-tillage than with conventional tillage.
With conventional tillage at
 Bushland, Texas, grain sorghum yield increased 385 lbs/acre-inch of PASW at planting.
Evaporative demands increase from north to south  in the Great Plains and this can reduce overall yield response to water.
Precipitation increases from west to least in the Great Plains and in Kansas the average increase is approximately 1 inch for each 18 miles.
Research is needed to characterize the amounts of PASW available to producers in the spring before planting of summer crops.
The research results can be used to develop better cropping recommendations for producers based on their geographical location within western Kansas when used with information about their anticipated summer precipitation.
Preseason irrigation  is a common practice in central and southern sections of the western Great Plains on the deep soils with large water-holding capacity that are prevalent.
The residual soil water left in irrigated corn fields has a strong effect on the amount of preseason irrigation and precipitation that can be stored during the dormant period.
Although preseason irrigation is common, research has shown it is often an inefficient water management practice.
Measured water losses from marginal preseason irrigation capacities during the 30-45 day period prior to planting in a Texas study were extremely high, ranging from 45 to 70%.
While several reasons are given by producers for the use of preseason irrigation, Musick et al.
stated its primary purpose is to replenish soil water stored in the plant root zone.
From an analysis of soil water data from producer fields with silt loam soils near Colby, Kansas, Rogers and Lamm  concluded that irrigation above the amount required to bring soil water to 50% PASW water would have a high probability of being lost or wasted.
They found in a three-year study  of 82 different fields that on average producers were leaving residual PASW in the top 5 ft of the soil profile at 70% of field capacity.
Since that time, groundwater levels have continued to decline and more irrigation systems have marginal capacity.
Research is needed to both assess the current amounts of residual PASW producers are leaving in the field after irrigated corn harvest and how much PASW is replenished during the period before spring planting of the next corn crop.
The primary objectives of this project were to characterize the fall residual profile PASW after irrigated corn production and the PASW in dryland wheat stubble following the winter period and prior to dryland summer crop production in producer fields in three distinct regions of western Kansas [southwest , west central  and northwest ].
Secondary objectives were to characterize aspects of the overwinter precipitation storage for the two crop residues.
The ongoing study was initiated in the fall of 2010 on the deep silt loam soils in western Kansas.
Fifteen fields from each of the three regions  were sought for each crop residue type  for sampling of PASW.
In general five fields of each residue type were selected in each county.
In a few cases, additional fields  were selected when it was deemed useful in gaining a better geographical distribution.
Another selection criterion for the irrigated corn fields was irrigation system capacity.
Attempts were made to find one or two fields in each county with capacities equivalent to less than 400, 400 to 600, and over 600 gpm for a 125 acre field.
++	Shermant	#	+	+	Thomas	+	+	# Sheridan	++
 +	#	+	+
 + Greeley	+	+	Wichita	#	+	Scott	++	Lane
 +	+	+	#	+++
 +	I	+	+	+	+	+++	Gray
 +	Stanton	+	+	+	#	Grant + +	+	Haskell	+	+
 Figure 1.
Geographical distribution of soil water measurements in producer fields in western Kansas, 2010.
Each symbol represents a GPS-referenced producer field.
Although a broad geographical representation was a primary desire , an attempt was made to select producers using good management practices and for which realistic weather conditions could be obtained from public sources.
Fields in NW Kansas were selected in Sheridan, Thomas and Sherman counties.
Fields in WC Kansas were selected in Scott, Wichita and Greeley counties.
There was increased difficulty finding producers with continuous  irrigated corn fields in WC Kansas, particularly in Wichita and Greeley Counties.
The Ogallala aquifer in this region of Kansas is more marginal and severely depleted, so producers appear to be using more crop rotation to utilize residual soil water better, thus conserving more aquifer water for future years.
Fields in SW Kansas were selected in Haskell, Grant and Stanton counties.
There were 96 total fields in 2010 fall sampling and 91 fields in 2011.
The GPS-referenced neutron access tubes  were installed in an equilateral triangular-shaped pattern.
Initial volumetric soil water content was determined in these fields after installation of tubes and again in late spring prior to summer crop initiation in one-foot increments to a depth of 8 feet.
Published soil type and soil characteristics were used to estimate PASW within the profile.
The data from the three sampling points was examined for uniformity between readings and to remove any anomalies.
A few tubes were lost due to damage by producer field operations between the fall and spring measurement periods.
Less than 1% of the data was lost due to measurement anomalies or damaged tubes.
The study is ongoing and some of the more complex interrelationships of producer practices with residual soil water have not been quantified or evaluated yet.
Although it should be noted that the results may vary widely from what may be occurring on your or other fields located within these counties, the soil water results may still be indicative of some of the irrigation capacities and practices, climatic, soil, and cropping conditions of these three distinct regions of western Kansas.
Weather conditions in nearly all of western Kansas were excessively dry from early August 2010 through mid-April of 2011.
The western portion of WC and NW Kansas began to get more normal precipitation in late April 2011 and ended the cropping season with normal amounts of precipitation or greater.
However, SW Kansas remained under severe drought conditions through the summer and much of the fall.
For example, Grant County received less than 30% of normal annual precipitation for the period September 1, 2010 through September 1, 2011.
In SW Kansas, dryland summer crops resulted in almost total failure and even many of the irrigated crops were severely stressed.
The western edge of WC Kansas  and for nearly all of NW Kansas experienced near-
 to above-normal precipitation for most of the summer period.
A particularly wet weather multi-day period in early October 2011 that tracked across some counties in WC Kansas and the eastern half of NW Kansas with those areas receiving between 2 and 4 inches of precipitation.
Because of the multi-day nature of this precipitation, much of the water infiltrated into the soil profile.
Soil Water as Affected by Location and Residue Type
 In general, sprinkler irrigated corn fields had greater PASW than the dryland wheat fields  as might be anticipated.
Additionally, it should be noted that in many cases in SW Kansas, some fall dormant season irrigation  had been practiced prior to the soil water measurements to facilitate easier strip tillage operations.
In 2010, NW Kansas had slightly more PASW  in wheat fields  than in the other two regions.
The coefficient of variation  of PASW in wheat fields was least in NW Kansas and greatest in SW Kansas, probably reflecting the higher evaporative demand and worse drought conditions affecting SW Kansas.
The irrigated corn fields residual PASW averaged 160% that of the dryland wheat fields  and also had less variability.
The average PASW in irrigated corn fields for the three regions only varied about 1 inch  and with an average value of 10.30 inches would approximate a profile at 60% of field capacity, which would suggest overall adequate irrigation management.
However, there was a large amount of field to field variation.
The maximum PASW for the irrigated corn fields averaged nearly 16.4 inches which would be very wet unless there was considerable late season precipitation or fall dormant season irrigation.
At the other end of the spectrum, the minimum average PASW was approximately 4.3 inches, which would be only about 25% of field capacity.
There was on average slight losses or very small accumulations in the dryland wheat residue fields by late spring 2011 , with the exception of NW Kansas which saw an average increase of 2.05 inches of PASW.
This reflects some appreciable late April 2011 precipitation events in NW Kansas that the other regions had missed or had lesser amounts.
In contrast, NW Kansas had only minimal increase in PASW in the irrigated corn fields while PASW in the WC and SW Kansas fields increased approximately 2 inches.
This reflects that many of the WC and SW Kansas fields had received additional dormant season irrigation to better cope with the drought before spring planting.
The maximum PASW for the sprinkler irrigated corn fields averaged 12.15, 20.06, and 18.65 inches for NW, WC and SW Kansas, respectively.
These values in WC and SW Kansas would be considered extremely wet  and would be subject to high deep
 percolation rates.
Close examination of the individual field data revealed that these high maximum values in the spring 2011 also were very high on the same fields in the fall of 2010, suggesting that these irrigators should cut back on late and/or dormant season irrigation.
In contrast, the minimum values of PASW in the spring of 2011, on the producer fields averaged only 5.51 inches in the 8 ft profile.
These producers with such low values of PASW might have greatly benefited had they used more dormant season irrigation, particularly in such a dry summer.
The irrigated corn fields had approximately 160% of the PASW of the wheat fields, similar to the results from the fall of 2010 and again with less variability in PASW.
In fall of 2011, because of the continuing drought in SW Kansas, it was anticipated that producer fields would be much drier than in 2010.
Although this turned out to be true for SW Kansas for dryland wheat fields , overall the irrigated corn fields were wetter  in 2011, with only SW Kansas having slightly drier irrigated fields in fall 2011.
The wetter summer period in portions of WC Kansas  and NW Kansas no doubt had some effects on the amounts of residual PASW.
The October 2011 multi-day wet period resulted in some very wet wheat residue fields in Thomas and Sheridan Counties in northwest Kansas.
Discussion of Annual Differences in Corn Residual PASW
 Although record or near-record drought conditions existed in southwest Kansas for the entire period from the middle of the summer of 2010 through the fall of 2011, there were only minimal differences in fall irrigated corn PASW for the 31 fields that were available for PASW measurements in both years.
Part of the rationale might be that drought conditions were similar between the two years.
However, the irrigated corn residual soil water is still relatively high on the average for SW Kansas.
So, the presence of severe drought may not be a good indicator of the amounts of residual soil water left after irrigated corn harvest.
Sometimes, crop damage is caused by system capacity  at the critical stages, rather than what irrigation amounts can be applied during the total season.
Insect damage such as spider mites is exacerbated by high canopy temperatures and drought.
Producers recognizing the drought and crop damage may continue to irrigate hoping to mitigate further crop damage and this sometimes increases profile PASW as the damaged crop is no longer transpiring typical amounts of water.
One caveat, in some cases the PASW results are probably reflecting the effects of some fall dormant season irrigation that occurred before the PASW sampling.
However, in most cases the fall irrigation amounts were not large.
Table 1.
Plant available soil water  in producer fields in western Kansas in fall 2010.
Residue Type	number of fields	Average	Maximum	Minimum	CV*
 Northwest Kansas, Sheridan, Thomas and Sherman Counties
 Dryland Wheat	Sheridan 	7.64	11.40	4.49	0.33
 Thomas 	8.58	11.08	6.16	0.19
 Sherman 	5.48	8.26	3.86	0.31
 All 3 Ctys 	7.39	11.40	3.86	0.30
 Irrigated Corn	Sheridan 	10.50	11.10	8.57	0.06
 Thomas 	10.79	15.55	6.76	0.22
 Sherman 	8.35	11.64	6.56	0.24
 All 3 Ctys 	9.99	15.55	6.56	0.24
 Irrigated to Dryland Ratio	Sheridan	1.37	0.97	1.91	0.19
 Thomas	1.26	1.40	1.10	1.12
 Sherman	1.52	1.41	1.70	0.77
 All 3 Ctys	1.35	1.36	1.70	0.79
 West Central Kansas, Scott, Wichita and Greeley Counties
 Dryland Wheat	Scott 	5.11	8.97	2.48	0.50
 Wichita 	5.10	9.31	3.03	0.48
 Greeley 	6.13	11.08	2.07	0.53
 All 3 Ctys 	5.43	11.08	2.07	0.48
 Irrigated Corn	Scott 	11.98	16.57	8.20	0.27
 Wichita 	9.31	11.78	6.54	0.20
 Greeley 	8.78	10.63	3.96	0.32
 All 3 Ctys 	10.02	16.57	3.96	0.29
 Irrigated to Dryland Ratio	Scott	2.34	1.85	3.31	0.54
 Wichita	1.83	1.27	2.16	0.42
 Greeley	1.43	0.96	1.91	0.60
 All 3 Ctys	1.85	1.50	1.91	0.60
 Southwest Kansas, Haskell, Grant and Stanton Counties
 Dryland Wheat	Haskell 	5.39	10.19	1.50	0.72
 Grant 	3.43	6.08	1.70	0.50
 Stanton 	10.88	14.41	7.39	0.29
 All 3 Ctys 	6.57	14.41	1.50	0.66
 Irrigated Corn	Haskell 	9.82	17.06	2.37	0.61
 Grant 	9.06	13.86	6.28	0.37
 Stanton 	13.83	16.71	11.50	0.14
 All 3 Ctys 	10.84	17.06	2.37	0.41
 Irrigated to Dryland Ratio	Haskell	1.82	1.67	1.58	0.84
 Grant	2.64	2.28	3.69	0.74
 Stanton	1.27	1.16	1.56	0.47
 All 3 Ctys	1.65	1.18	1.58	0.62
 * Coefficient of variation is defined as the standard deviation of PASW divided by the mean PASW.
Table 2.
Plant available soil water  in producer fields in western Kansas in spring 2011.
Residue Type	number of fields	Average	Maximum	Minimum	CV*
 Northwest Kansas, Sheridan, Thomas and Sherman Counties
 Dryland Wheat	Sheridan 	9.66	12.55	7.78	0.19
 Thomas 	9.67	11.47	7.34	0.13
 Sherman 	8.77	10.80	7.07	0.20
 All 3 Ctvs 	9.44	12.55	7.07	0.16
 Irrigated Corn	Sheridan 	11.21	12.15	10.67	0.05
 Thomas 	11.02	15.69	8.23	0.22
 Sherman 	8.74	11.84	6.37	0.24
 All 3 Ctys 	10.41	15.69	6.37	0.21
 Irrigated to Dryland Ratio	Sheridan	1.16	0.97	1.37	0.26
 Thomas	1.14	1.37	1.12	1.69
 Sherman	1.00	1.10	0.90	1.21
 All 3 Ctys	1.10	1.25	0.90	1.28
 West Central Kansas, Scott, Wichita and Greeley Counties
 Dryland Wheat	Scott 	6.26	10.92	3.74	0.46
 Wichita 	5.06	7.22	3.63	0.30
 Greeley 	6.44	11.36	2.43	0.50
 All 3 Ctys 	5.92	11.36	2.43	0.43
 Irrigated Corn	Scott 	14.51	20.06	9.70	0.27
 Wichita 	11.12	13.87	7.51	0.23
 Greeley 	10.60	13.60	4.47	0.34
 All 3 Ctys 	12.08	20.06	4.47	0.30
 Irrigated to Dryland Ratio	Scott	2.32	1.84	2.59	0.58
 Wichita	2.20	1.92	2.07	0.78
 Greeley	1.65	1.20	1.84	0.67
 All 3 Ctys	2.04	1.77	1.84	0.70
 Southwest Kansas, Haskell, Grant and Stanton Counties
 Dryland Wheat	Haskell 	6.25	11.03	2.09	0.64
 Grant 	4.02	6.91	2.28	0.45
 Stanton 	8.76	11.93	5.28	0.34
 All 3 Ctys 	6.34	11.93	2.09	0.54
 Irrigated Corn	Haskell 	12.10	18.65	5.70	0.43
 Grant 	11.50	15.74	7.05	0.30
 Stanton 	13.64	16.13	10.24	0.18
 All 3 Ctys 	12.39	18.65	5.70	0.31
 Irrigated to Dryland Ratio	Haskell	1.94	1.69	2.73	0.67
 Grant	2.86	2.28	3.10	0.67
 Stanton	1.56	1.35	1.94	0.53
 All 3 Ctys	1.95	1.56	2.73	0.56
 * Coefficient of variation is defined as the standard deviation of PASW divided by the mean PASW.
Table 3.
Plant available soil water  in producer fields in western Kansas in fall 2011.
Residue Type	number of fields	Average	Maximum	Minimum	CV*
 Northwest Kansas, Sheridan, Thomas and Sherman Counties
 Dryland Wheat	Sheridan 	13.95	17.81	7.03	0.29
 Thomas 	7.11	9.14	6.19	0.16
 Sherman 	6.85	8.70	3.76	0.31
 All 3 Ctys 	9.30	17.81	3.76	0.46
 Irrigated Corn	Sheridan 	13.77	15.60	10.45	0.14
 Thomas 	13.07	16.86	8.94	0.22
 Sherman 	8.31	11.69	5.95	0.28
 All 3 Ctys 	11.85	16.86	5.95	0.28
 Irrigated to Dryland Ratio	Sheridan	0.99	0.88	1.49	0.49
 Thomas	1.84	1.84	1.44	1.32
 Sherman	1.21	1.34	1.58	0.89
 All 3 Ctys	1.27	0.95	1.58	0.61
 West Central Kansas, Scott, Wichita and Greeley Counties
 Dryland Wheat	Scott 	8.08	10.96	5.44	0.25
 Wichita 	8.36	10.05	6.46	0.20
 Greeley 	8.57	10.76	6.63	0.18
 All 3 Ctys 	8.34	10.96	5.44	0.20
 Irrigated Corn	Scott 	13.00	17.85	9.75	0.23
 Wichita 	12.59	14.21	10.74	0.11
 Greeley 	11.73	12.25	10.98	0.04
 All 3 Ctys 	12.46	17.85	9.75	0.16
 Irrigated to Dryland Ratio	Scott	1.61	1.63	1.79	0.90
 Wichita	1.50	1.41	1.66	0.57
 Greeley	1.37	1.14	1.66	0.22
 All 3 Ctys	1.49	1.63	1.79	0.80
 Southwest Kansas, Haskell, Grant and Stanton Counties
 Dryland Wheat	Haskell 	5.98	10.30	2.73	0.46
 Grant 	3.26	6.74	0.16	0.90
 Stanton 	5.57	8.16	4.63	0.26
 All 3 Ctys 	4.94	10.30	0.16	0.52
 Irrigated Corn	Haskell 	10.40	15.58	2.94	0.59
 Grant 	8.76	16.49	3.13	0.66
 Stanton 	11.11	14.30	8.65	0.20
 All 3 Ctys 	10.15	16.49	2.94	0.46
 Irrigated to Dryland Ratio	Haskell	1.74	1.51	1.08	1.30
 Grant	2.69	2.45	19.02	0.74
 Stanton	2.00	1.75	1.87	0.76
 All 3 Ctys	2.06	1.60	17.84	0.88
 * Coefficient of variation is defined as the standard deviation of PASW divided by the mean PASW.
Fall 2010 PASW (inches/8 f
 Figure 2.
Similarity of plant available soil water  in the 8 ft soil profile in irrigated corn fields after harvest for the fall periods in 2010 and 2011 in western Kansas producer fields.
These data represent 31 fields that producers made available for PASW measurements in both years.
Effect of Regional Characteristics on Corn Residual PASW
 Although intuition might suggest that less saturated thickness of the Ogallala and more marginal irrigation system capacities  would result in less residual PASW in the irrigated corn fields of WC Kansas, there was no strong evidence of that in the data from 2010 and 2011.
This might be because producers with lower capacity irrigation systems have adjusted to their limitation by using longer pumping periods.
Their goal by pumping later into the crop season would be to minimize crop yield loss, but sometimes those later irrigation events also increase residual PASW.
Effect of Field Type on Overwinter Change in PASW
 Overwinter accumulation or loss of PASW could be affected by precipitation, initial PASW, residue type, and any applied dormant season irrigation, so the following results are being discussed in terms of field type, rather than just crop residue type.
The corn fields on average accumulated approximately 2 inches of soil water overwinter when the fall 2010 PASW was very low and only about 1 inch of accumulation when the PASW was high.
In contrast, the wheat
 fields accumulated only about 1 inch of soil water overwinter when the fall 2010 PASW was very low and tended to lose up to 2 to 3 inches of PASW when PASW was higher.
These differences are probably due to dormant season irrigation slightly increasing PASW in the corn fields while the drought conditions were not favorable for much overwinter accumulation in the dryland wheat fields.
Figure 3.
Effect of western Kansas region on average, maximum and minimum measured plant available soil water  in the 8 ft soil profile in irrigated corn fields after harvest for the fall periods in 2010 and 2011.
Fall 2010 PASW 
 Figure 4.
Effect of field type on accumulation of plant available soil water  in the 8 ft soil profile for the period fall 2010 through spring 2011 for producer fields in western Kansas.
Effect of System Capacity on Fall PASW in Irrigated Corn Fields
 There were only small differences in PASW  as affected by low , medium  or high  irrigation system capacity  in 2011.
Further analysis of the effect of capacity on fall PASW will be done by incorporating more precise information about system capacity and also from information to be provided by the producers about actual aspects of their irrigation cropping season and irrigation schedule.
These results suggest a few very important aspects for irrigated crop production in western Kansas:
 1.
Irrigation not only increases the water available for crop production, but also reduces the variability in ASW in the field.
2.
Average PASW may not be indicative of an individual field, so it is wise to check your each field after harvest.
3.
Each year is different, so irrigating to average conditions is very risky and may be less profitable.
4.
Science-based irrigation scheduling can help to better manage your water resources in-season and between seasons.
Cost-sharing programs may be available to help individuals implement science-based irrigation scheduling.
This research was supported in part by the Ogallala Aquifer Program, a consortium between USDA Agricultural Research Service, Kansas State University, Texas AgriLife Research, Texas AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
Contribution no.
12-311-A from the Kansas Agricultural Experiment Station.
This paper was first presented at the Central Plains Irrigation Conference, February 21-22, 2012, Colby, Kansas.
It can be cited as
 Soil water sampling process on producer fields in western Kansas, 2010-2011.
ETgage Install Tips: As with soil sensors, early installation of atmometers or ETgages is important, so remember to take the time to get them out now.
By installing early, we will make sure that everything is working properly during less critical growth stages and reinforces the importance of reading the ET gage every week.
Remember to use distilled water when you are setting up your ETgage.
Usually by mid to late August, corn and soybeans have progressed enough in maturity that we have a good handle on how much water it will take to finish the crop out.
Depending on soil type, some fields may have enough stored soil water to get the crop to maturity without additional irrigation or rainfall.
So just how much water do we need to finish out the growing season?
This chart gives you a good idea of water needed based on the growth stage of the crop.
B.C.
SPRINKLER IRRIGATION MANUAL
 Prepared and Web Published by
 BRITISH COLUMBIA Ministry of Agriculture
 LIMITATION OF LIABILITY AND USER'S RESPONSIBILITY
 The primary purpose of this manual is to provide irrigation professionals and consultants with a methodology to properly design an agricultural irrigation system.
This manual is also used as the reference material for the Irrigation Industry Association's agriculture sprinkler irrigation certification program.
While every effort has been made to ensure the accuracy and completeness of these materials, additional materials may be required to complete more advanced design for some systems.
Advice of appropriate professionals and experts may assist in completing designs that are not adequately convered in this manual.
All information in this publication and related materials are provided entirely "as is" and no representations, warranties or conditions, either expressed or implied, are made in connection with your use of, or reliance upon, this information.
This information is provided to you as the user entirely at your risk.
The British Columbia Ministry of Agriculture and the Irrigation Industry Association of British Columbia, their Directors, agents, employees, or contractors will not be liable for any claims, damages or losses of any kind whatsoever arising out of the use of or reliance upon this information.
CENTRE PIVOT SYSTEM DESIGN
 Centre pivot systems have become more popular as a replacement for existing irrigation systems or for a new installation due to the lower operating costs and reduced labour.
In the Province of British Columbia, it is more common to see part circle pivots than full circle units.
This is due to the topography of the land and field shapes.
Pivot systems travel while irrigating and therefore must apply sufficient water during a short application time, resulting in higher application rates.
See section 3.3 for more information on centre pivot systems.
During each successive pass, a centre pivot system must apply an equal amount of water to the soil along the length of the pivot.
To accomplish this, the outside radius of the pivot must apply as much water as is applied near the pivot point, but in a much shorter time period.
Application rates at the end of the pivot are therefore much higher than near the pivot point.
For example, a centre pivot with a wetted radius of 1,320 ft is often used to irrigate a quarter section or 160 acres.
The pivot will irrigate only 125 acres out of the 160 acre quarter section unless a corner system is used.
Starting from the pivot point,
 The first 660 ft irrigates 31.4 acres
 The next 273 ft irrigates 31.4 acres
 The next 210 ft irrigates 31.4 acres
 The next 177 ft irrigates 31.4 acres
 The last 177 ft of the pivot's wetted radius, which is only 13.4% of the total radius, must irrigate 25% of the area.
Figure 7.1 compares the application rate for two locations along the pivot lateral to the intake rate of the soil.
Figure 7.1 Centre Pivot Application and Soil Intake Rate Patterns Source: Design and Operation of Irrigation Farm Systems.
ASABE 2007
 Where the system application rate exceeds the soil intake rate, puddling and runoff can occur.
System design and sprinkler selection must take into account soil, crop, climate and application rate to achieve the best performance.
The maximum application rate applied by a centre pivot system can be determined from Equation 7.1.
Equation 7.
1 Maximum Application Rate
 PAR = 122.5 Rxr X Q
 where R = L+rx 0.75
 where	PAR = Maximum application rate of centre pivot 
 Q = Centre pivot flow rate 
 R = Effective wetted radius of pivot 
 r =	Wetted radius of the large sprinklers near the end of the pivot 
 L =	Physical length of the pivot 
 The effective wetted radius of the centre pivot, R, is the nominal radius of the field that is to be irrigated.
It is calculated using the distance from the centre point to the terminal sprinkler on the pivot, plus 75 percent of the wetted radius of that terminal sprinkler.
It does not include the end gun.
The maximum application rate can also be determined graphically from Figure 7.2.
Figure 7.2 Determination of Maximum Application Rates for Centre Pivots
 A systematic procedure for centre pivot design can be achieved by the following steps:
 1.
Determine the effective wetted radius of coverage  by dividing the shortest dimension of the field by two.
The physical length of the pivot is often less than this due to the radius of throw of the terminal sprinkler on the pivot.
This does not include the end gun.
2.
Determine the peak evapotranspiration and irrigation efficiency.
The peak evapotranspiration can be obtained from Table 4.5 or by actual climatic data for peak conditions.
The irrigation efficiency will vary depending on the type of sprinklers used.
Table 7.1 Pivot Application Efficiency
 Sprinkler Type	Application Efficiency
 3.
Determine the irrigated area.
The irrigated area is calculated for the pivot lateral minus the end gun.
The area is used to determine the pivot flow rate.
Equation 7.2 Irrigated Area 
 A = Area irrigated  R = effective wetted radius of pivot  P = Percentage of full circle irrigated 
 4.
Determine the pivot flow rate using Equation 7.3.
Equation 7.3 Pivot Flow Rate
 where	Q = Pivot flow rate 
 ET = Peak Evapotranspiration 
 A = Area irrigated 
 AE = application efficiency 
 If the pivot has an end gun, the flow rate for the end gun needs to be calculated separately.
To determine the end gun discharge, the flow rate is based on the extra radius covered for the entire arc of the pivot even if it only operates periodically.
This is done SO that the end gun application rate matches that of the pivot.
If the end gun flow rate was only designed for the actual area covered, the application rate would be low and under watering would occur.
Equation 7.4 End Gun Flow Rate
 2 where QE = End gun flow rate  Q = Pivot flow rate  RE = Pivot radius with end gun  R = Effective wetted radius of pivot 
 Source: Design and Operation of Farm Irrigation Systems
 Warning Pivot System Design
 Much like a travelling gun system or a stationary gun system, care should be taken in designing a pivot system near electrical transmission lines.
Many pivots have an end gun to increase the pivot coverage and the operator must be very careful that the gun stream does not contact the power line.
High voltage power lines can arc over to an irrigation stream if sufficient stream break up has not occurred.
Section 6.7 provides information on the minimum clearances between the gun jet stream and high voltage power lines that should be met for safety reasons.
5.
Determine the minimum travel design speed of the centre pivot lateral at which potential runoff starts.
The duration of application is a critical factor in determining the minimum design speed.
The maximum design application rates shown in Table 4.4 are based on set times exceeding four hours.
Most soils permit a higher system application rate during the first one or two hours of application as compared to an eight or twelve hour set time.
Table 7.2 can be used as a guide in determining an appropriate application rate for short duration applications.
Table 7.2 Maximum Application Rate Adjustment for Short Durations
 Duration of Water Application [min]	Multiplication Factor
 The minimum travel speed of the last tower is determined by Equation 7.5.
Equation 7.5 Minimum Travel Speed
 where S = Minimum travel speed of wetted area at the end of the pivot  r= Wetted radius of sprinklers near the end tower , not end gun Tm= Maximum duration of application 
 The maximum duration of water application  is determined from Table 7.2.
The multiplication factor  can be calculated by using Equation 7.6.
Equation 7.6 Multiplication Factor
 where F = Multiplication factor PAR = Maximum application rate of centre pivot  Equation 7.1 MAR = Maximum application rate accepted by the soil  
 6.
Determine the rotation speed  of the pivot.
This calculation of N will determine the maximum rotation speed.
If the pivot moves any slower, then runoff may occur.
Equation 7.7 Rotation Speed
 II R $ 30 S
 where N = Rotation speed of pivot  R = Effective wetted radius of pivot  S = Minimum travel speed of wetted area at the end of the pivot 
 7.
Determine the gross water applied  by the pivot per revolution.
Equation 7.8 Gross Water Applied per Revolution
 where GWAr = Gross water applied per revolution 
 Q = Centre pivot flow rate 
 N = Rotation speed of pivot 
 A = Area irrigated 
 Table 7.3 can be used to determine the GWAr by a centre pivot system for a rotation time of 24 hours.
Table 7.3 Amount Applied per Day by Centre Pivot Systems 
  = 24 hr)
 Effective	Area	Pivot Flow 
 	200	300	400	500	600	700	800	900	1000	1100	1200
 200	2.9	3.67	5.52	-	-	-	-	-	-	-	-	-
 300	6.5	1.63	2.45	3.27	4.09	4.90	5.72	-	-	-	-	-
 400	11.5	0.92	1.38	1.84	2.30	2.75	3.22	3.68	4.14	4.60	5.06	5.52
 500	18.0	0.59	0.88	1.18	1.47	1.76	2.06	2.35	2.65	2.94	3.24	3.53
 600	26.0	0.41	0.62	0.82	1.02	1.23	1.43	1.63	1.84	2.04	2.25	2.45
 700	35.3	0.30	0.45	0.60	0.75	0.90	1.05	1.20	1.35	1.50	1.65	1.80
 800	46.2	0.23	0.34	0.46	0.57	0.69	0.80	0.92	1.03	1.15	1.26	1.38
 900	58.4	0.18	0.27	0.36	0.45	0.54	0.64	0.73	0.82	0.91	1.00	1.09
 1000	72.1	0.15	0.22	0.29	0.37	0.44	0.51	0.59	0.66	0.74	0.81	0.88
 1100	87.3	0.12	0.18	0.24	0.30	0.36	0.43	0.49	0.55	0.61	0.67	0.73
 1200	103.9	0.10	0.15	0.20	0.26	0.31	0.36	0.41	0.46	0.51	0.56	0.61
 1300	121.9	0.09	0.13	0.17	0.22	0.26	0.30	0.35	0.39	0.44	0.48	0.52
 1400	141.4	0.08	0.11	0.15	0.19	0.23	0.26	0.30	0.34	0.38	0.41	0.45
 1500	162.3	0.07	0.10	0.13	0.16	0.20	0.23	0.26	0.29	0.33	0.36	0.39
 1600	184.6	0.06	0.09	0.11	0.14	0.17	0.20	0.23	0.26	0.29	0.32	0.34
 8.
Calculate the net water applied as per equation 7.9.
Equation 7.9 Net Water Applied 
 NWA = Net water applied  GWAr = Gross water applied per revolution  AE = Application efficiency  Table 7.1
 Clarification Center Pivot Design Maximum Irrigation Interval
 The maximum irrigation interval for a centre pivot is not calculated as the pivot is applying water daily to meet the peak evapotranspiration rate.
Much like a drip irrigation system that replenishes the soil moisture daily to match the amount withdrawn by a crop, a centre pivot system operates the same way.
The maximum irrigation interval is therefore only one day or slightly longer.
Using the design principles outlined in this manual, the net water applied  on a 24 hour basis will likely closely match the peak ET rate used in the design.
If the net water applied is significantly less than the peak ET rate then the design should be re-evaluated.
Clarification Center Pivot Design Peak Flow Rate
 The peak flow rate of a center pivot can be calculated two ways.
If Equation 7.3 is used the center pivot system efficiency is incorporated into the calculation.
For example 7.1 the flow rate using equation 7.3 is 466 gpm.
An efficiency of 80% is used in the example.
The information from Table 4.6 indicates a flow rate of 5.25 gpm/acre at a peak ET rate of 0.21 in/day.
The 94 acres covered by the pivot would require a flow rate of 493 gpm.
Since the efficiency used in the table is 72%, a higher flow is determined using this methodology.
Helpful Tips Irrigation Design Parameters
 The centre pivot irrigation design plan shown here is also provided in Appendix C with the corresponding design parameters shown on the adjacent page.
The design parameter summary is useful for evaluating the irrigation system design and performance characteristics.
This information should be included with every irrigation system plan.
Example 7.1 Centre Pivot Irrigation in Armstrong
 A farmer near Armstrong intends to grow alfalfa on a deep, sandy loam soil.
The area to be irrigated will accommodate a pivot with an effective wetted radius of 1,320 ft.
The pivot will operate over a three quarter circle.
The end gun will operate in the corners only.
For a centre pivot irrigation system, what flow rate, rotation speed, and amount of water applied will be required?
Drop tube rotator sprinklers will be used in this application.
Maximum soil water deficit  
 in Maximum application rate  
 in/hr Peak evapotranspiration  
 in/day Effective wetted radius  without end gun
 ft Effective wetted radius  with end gun
 ft Percentage of full circle irrigated 
 7 Application efficiency 
 1.
Calculate the irrigated area for the pivot
 2.
Calculate the system flow rate.
a).
Calculate the pivot flow rate.
b).
Calculate the end gun flow rate.
3.
Determine the minimum design travel speed of the centre pivot lateral at which potential runoff starts.
a).
Select sprinkler type.
Wetted radius of the largest sprinkler at the end of pivot  35 12 ft
 b).
Calculate the maximum application rate applied by the pivot.
Determine the rotation speed.
Calculate the maximum duration of application.
With the F factor, duration of water application  
 d).
Calculate the minimum travel speed.
3.14 X	1,320	5	ft
 30 X	4.7	16	ft/min
 =	29.4	17	hr/rev
 5.
Determine the maximum gross amount applied per revolution.
The actual rotation speed of a centre pivot system should be determined by field measurements during operation.
The design procedure given above is useful in determining whether the type of pivot selected can be made to match the crop and soil parameters that exist.
Helpful Tips Centre Pivot Operation
 Pivot operators often do not apply sufficient water to keep up with crop demand during the peak of the irrigation season.
There are a few reasons for this.
First, for forage crops the pivot system is not operating while the crop is being cut, dried and removed from the field.
Since the pivot is applying water that matches peak conditions it is difficult to gain on the water lost during the harvesting period if weather conditions are at peak.
Secondly the pivot is applying a relatively small amount of water during every revolution.
The water applied does not have an opportunity to move down into the root zone during peak climatic conditions.
The lower part of the soil profile can therefore dry out.
Crops need moisture through their entire root zone to ensure that all of its roots can help support the crop's growth during peak conditions.
Thirdly, an operator could be fooled that there is plenty of moisture available to the crop as the soil surface may appear moist but there actually is very little moisture further down in the root zone.
Earlier in the season, when there is usually plenty of water available due to spring freshet, centre pivots should be operated to build up soil moisture to within 75% 90% of field capacity.
The pivots should then be operated on a schedule for the rest of the season that keeps the soil moisture at a level around 75% of field capacity.
During harvest periods or should water shortages occur later in the season the soil storage that has been built up is then available to offset the potential shortfalls that may occur due to interruptions in pivot operation.
94.2 IRRIGATED PIVOT  AREA BY
 9  GUN END IRRIGATED AREA BY
 103,2  TOTAL IRRIGATED AREA
 555 FLOW 
 197  HEAD TOTAL DYNAMIC
 1320 LENGTH  OF PIVOT
  MAXIMUM ROTATION SPEED 32
 4,7  SPEED TRAVEL MINIMUM
 466 FLOW PIVOT RATE 
 89 
How to use Watermark Soil Moisture Sensors for Irrigation
 Chris Henry Ph.D., Associate Professor and Water Management Engineer Rice Research and Extension Center
 P.B.
Francis Ph.D., Professor University of Arkansas at Monticello
 L.
Espinoza Ph.D., Soil Scientist Crop, Soil and Environmental Science
 Arkansas Is Our Campus
 This is the second in a series of three fact sheets on Watermark TM Soil Moisture Sensors.
The first fact sheet details "How to Make a Watermark TM Sensor." This fact sheet discusses how to use Watermark Soil Moisture Sensors, and the third fact sheet provides additional detail about "Predicting the Last Irrigation of the Season using Watermark TM Soil Moisture Sensors."
 Soil moisture sensing is an invaluable tool for understanding agronomic practices and improving irrigation water management.
Soil moisture sensors provide a measure of plant available water.
Sensor trends can also provide information about irrigation efficiency problems, infiltration, deep percolation, and water stress.
A cost effective and popular sensor used for irrigation is the granular matrix potential sensor or WatermarkTI sensors.
Tensiometers also measure the soil matric potential; however, they measure it directly using a ceramic tip, gage and fluid.
Watermarks are easy to use and deploy.
They are comprised of two electrodes, a ceramic disk, granular material, fabric and a stainless steel mesh fashioned to form a 7/8-inch diameter cylinder and tip.
They can be attached to polyvinyl chloride  tubing and placed in the soil at various depths.
As water enters the granular matrix, the resistance of the electrodes changes/ this change in electrical resistance is proportional to the change in the matric potential or soil tension.
It is important to understand that the
 value reported by a granular matric potential sensor is based on electrical resistance not on a direct measure like a tensiometer.
However, their simplicity, range and the maintenance-free operation make them a very popular sensor for use in agricultural irrigation.
These sensors are installed in the plant row between plants.
When installed, the sensor equilibrates to the surrounding moisture content generally within a day.
The sensor measures the electrical resistance of the ceramic material and is converted to matric potential.
The range of a WatermarkTM sensor is from 0-239 kPa or centibars.
The sensors report soil water as matric potential or vacuum, which is a measure of the energy that the plant exerts to draw available water from the soil, referred to as the "soil water potential." Soil matric potential is measured in pressure, usually either centimeters of water, bars, or kilopascals, although several other units can also be used.
Soil matric potential measurements are inherently a negative value of pressure, however it is common and appropriate to use the inverse positive term of "tension." When soil is saturated, the soil pores are full and the tension is near zero.
As gravity pulls the gravitational water from the soil matrix, air is replaced creating a small amount of tension.
This threshold is field capacity, typically around 15-35 centibars , dependent on soil type.
As plants extract water beyond field capacity, they do so until the wilting point, or 1500 centibars.
Figure 1.
Manual reader and WatermarkTM sensors installed on CPVC pipe for installation and different depths.
Soil water content of soils varies by texture, soil organic matter and compaction.
Therefore, field capacity and the soils ability to hold water vary and must be determined for each installation.
In general, clayey soils contain smaller pores and have a greater ability to retain moisture in the matrix because it takes more energy to extract the water from the matrix.
In sandy soils, the pore spaces are large and since water is easily extracted from large pores, less water is available once the pores have been emptied.
Watermark sensors are best used by gluing them to PVC or CPVC pipe at several depths to represent the rooting zone of the crop.
The use of the rubber washer help seal the sensor to the soil has been found to improve potential problems from installation.
Press the washer down tightly and place soil on top of the washer to provide a good seal.
The seal prevents water from migrating down to the sensor between the soil and PVC interface.
The use of 6, 12, 18 and 30 inch deep sensors is recommended for soybeans, peanuts, corn and cotton.
For furrow irrigated rice, 4, 8, 12 and 18 inches is rec-
 ommended.
The 6, 12, 18 and 30 inch spacing has proved to be a very reliable and representative spacing for Arkansas silt loam soils.
The 6 and 12 inch represent the top foot, where most of the water movement takes place.
Using two sensors for the top foot of the profile provides redundancy, good resolution, and minimizes sensor to sensor variation.
Also many times the 12 inch sensor is near a tillage pan, which can create some erroneous readings.
The 18 inch sensor represents the second foot of the profile and the 30 inch sensor represents the third foot.
Sensor installation at 36 inches is also acceptable, but at this depth sensor extraction in some soils can be challenging.
This arrangement also allows for good representation of the profile should one sensor fail or readings are questionable.
The soil moisture profile can still be estimated with the other three.
Another configuration is 6, 12, and 24 inches, representing the profile down to 30 inches.
This can also work well, but loss of one sensor, especially the 24 inch makes it difficult to rely on the sensors to schedule irrigation.
Scheduling irrigation with only two sensors is not recommended.
Interpretation of the 30 inch sensor should be done with caution.
In most situations this water is available but severe compaction has been observed to limit water movement.
Less often this subsoil is replenished, so irrigators should use this available water before the end of the season.
However, early subsoil moisture depletion before the reproductive stages indicates inadequate irrigation.
If available subsoil water remains unchanged it generally indicates either a pan, a fragipan, or excessive irrigation.
Users should monitor trends to observe water use patterns during the year and use their observations to establish acceptable thresholds for their particular situations.
As long as sensors are showing movement, plants are extracting water.
When this movement stops, plants are not extracting water, this is likely due to excessive or deficit soil moisture conditions.
When above field capacity, air is pushed out of the soil matrix, roots are starved for oxygen and cannot extract soil water.
This can often be seen when rain follows an irrigation.
It may take several days for enough air to re-enter and for transpiration to resume.
Sensor responses will flat-line in these situations indicating plants are experiencing  water stress.
The rate of change of a tension is non-linear.
Near field capacity, tension is low near 33 cb, and plants can extract water easily and water is plentiful.
Tension may only change a few centibars in a day when at peak water demand.
As soil tension increases above 90 cb in silt loam and clay soils tension may change 5-10 cb in a day when experiencing peak water demand.
Sensor trends may have a steep slope and then gradually flatten out indicating that extraction is decreasing and the plants are accumulating stress units.
When this occurs it is the maximum allowable depletion  for that soil type and situation.
Another trend that is commonly observed in sealing soils, is that as irrigation is applied, the sensor responses do not change much or level out after an irrigation.
While sometimes sensors responses will go to zero centibars, soils that seal restrict water entry and the sensor responses will decrease or level out rather than show saturated conditions.
This is normal and indicates infiltration issues.
Soil management practices such as winter cover crops, deep tillage, reduced tillage, no-till, and gypsum may help improve water infiltration in soils.
In addition to soil matric potential sensors, there are many other types of sensors.
The most common are dielectric, total domain reflectometry and capacitance  probes.
Generally these are used in conjunction with a telemetry system of some sort so the cost is much higher than WatermarkTM sensors.
These sensors typically report volumetric water content.
The sensors generally use the dielectric properties of soil and water to correlate sensor signals to water content.
Capacitance sensors report relative values, and calibration of the resulting values while they may be called volumetric water content are not absolute.
Thus capacitance sensors require calibration at every location and soil type to actual response of the crop and water content.
Therefore, irrigators should use the trends to determine field capacity and stress levels and manage between the reported values for the sensor.
Shallowing of the trend in water content in a layer is an indication of water stress by the crop.
Saturation can often be seen after a significant rainfall, where the upper soil layer is brought to a high water content and then equilibrates to field capacity after gravity draws the free water from the matrix.
This usually occurs within a few hours to a day.
Once stabilized, this should represent field capacity for the sensor.
When stress is observed in a soil layer by shallowing of the moisture content change, this indicates the lower threshold for all of the sensors.
Thus once these points are observed and recorded, the irrigator can maintain an average soil water content within this zone.
This is applicable to all types of sensors including WatermarksTM
 A mobile app is currently available on the Apple App store.
It is strongly recommended to use the mobile app with Arkansas crops, soil types and WatermarkTM sensors.
Search for the "Arkansas Soil Sensor Calculator" on the Apple App Store.
Use of the app simplifies the calculations and water retention curve information provided in this fact sheet and simplifies irrigation decision making.
An Android version of this app is not available.
To effectively use Watermark TM sensors, one must know the effective rooting zone.
Sheffield and Wein-
 dorf  report effective rooting depths for crops in Louisiana.
Irmak and Rudnick  report effective rooting depth for crops in Nebraska.
One main challenge when moving from a calendar scheduling method  to a sensor-based scheduling method is that when ample water in the upper root zone, to plants during the vegetative stage, they may not develop a deep rooting system.
This may depend on soil, environmental conditions and crop varieties.
It is also important to keep in mind that the most effective roots at extracting water and nutrients from the soil are very small and fine and difficult to visually see.
Simply pulling up a plant from the soil may only reveal the very large root masses.
Use Table 1 and visual observations of the sensor changes to gauge the effective root zone to use for scheduling irrigation.
Heavy rains early in the season, compaction and tillage pans, and fragipans can limit rooting depth, so using sensors can be used to judge the effective root zone where water is being depleted.
Table 1.
Effective Rooting Depths
 Crop	Effective Rooting Depth1	Effective Rooting Depth2
 It is recommended to interpret sensor reading at 18-24 inches or 1.5-2 feet early in the season for corn, cotton and soybeans when the plants are small and in the vegetative stages, unless a pan or other restrictive layer shows the subsoil is not being depleted.
Often it is not until the reproductive stage that the 2-3 feet sensor depths show depletion.
Allowable Depletion or Managed Allowable Depletion 
 There are three critical points in the soil water balance: saturation, field capacity and the permanent wilting point.
Field capacity is defined as the point at which all of the water the soil can hold after gravity takes effect.
When soil is saturated, water is taking the place where air occupies part of the soil matrix when at field capacity.
This occurs near 33 centibars in silt loams and clays, but is soil texture specific.
When the soil matric potential reaches 1500 centibars, plants wilt perma-
 nently and death occurs.
The difference between field capacity and wilting point is called total plant available water.
Allowable depletion or managed allowable depletion is the percent or point in the plant available water that is available to plants before potential yield limiting stress occurs.
It is a percent of the total plant available water the soil can hold.
At least half of the total plant available water is held as a reserve.
The other half or less, referred to as the allowable depletion, is readily available water for plants.
Once 50% of the total plant available water is used by plants, stress may begin to accumulate because it takes more effort for the plants to extract water from the soil.
For center pivots where planned application rates are near an inch of water, a more conservative allowable depletion is used; 30-35% is recommended.
This provides a buffer or additional margin of safety should an unexpected delay occur.
Also there is less water applied and so the soil only needs to be depleted just enough to store the irrigation event and any potential rainfall.
For furrow irrigation system, a higher allowable depletion should be used.
In furrow irrigation application, depths should be between 2-3 ac-inches/ac.
Thus more soil storage is needed to store this amount of water and smaller irrigation applications are not possible.
Thus for furrow irrigation systems an allowable depletion of 40-50% is recommended.
For the last irrigation of the season, a 50% allowable depletion should be used.
Allowable depletion can range between 30% and 50%, SO use an allowable depletion that provides enough margin of safety for the irrigation system but also allows enough room to store an irrigation and any potential rainfall.
For example, a furrow irrigation system that has limited capacity should use a lower allowable depletion.
A center pivot irrigator could use a 40% allowable depletion if there is a strong chance of rain in the near future or has a machine with a short turn time.
Figure 2.
Total Plant Available Water and the relationship between Saturation, Field Capacity, Permanent Wilting Point, and Allowable Depletion.
Shown is a 35% Allowable Depletion.
Determining Plant Available Water
 There is a known relationship between the soil water content and soil matric potential.
It is different for every soil type and varies by region.
Relationships have been developed and generalized for many of the soil types in Arkansas.
Use Tables 1 and 2 to convert WatermarkTM reading for the effective root zone and allowable depletion desired for the conditions present.
First, average the WatermarkTM readings for the effective root zone.
Second, determine the plant available water for the soil type and average sensor reading.
Take this value times the effective rooting depth in feet.
The result is the plant available water in inches in the profile.
For example, consider a furrow irrigated corn crop on a silt loam soil with a pan, where the 6, 12, and 18 inch sensors read 10, 25, and 55 centibars.
Take the average  of the readings.
Using Table 2, read 30 cb for the silt loam soil with a pan, to find 0.72 in/ft.
Multiply 0.72 in/ft times the effective rooting depth for corn of 2 feet.
This is the amount of plant available water in the profile for an allowable depletion of 45%.
Table 3 shows the available water for a 35% allowable depletion.
Table 4 shows the plant available water for an allowable depletion of 50%.
Plants exposed to an average tension in the effective rooting zone at higher levels than 50% allowable depletions are expected to begin to accumulate stress.
While some sensors will exceed these levels, the average soil tension for the effective root zone should not reach these levels.
Visu-
 Table 2.
Plant Available Water for in  for Soil Types versus Watermark Readings in centibars at a 45% MAD.
Tension	Sand	Sandy	Loam	Silt Loam	with Pan	Silt Loam	Clay
 	1.0 in/ft)				
 0	1.72	1.44	1.03	1.71	1.30
 5	1.67	1.44	1.03	1.71	1.28
 10	0.69	0.93	0.93	1.53	1.01
 15	0.30	0.67	0.93	1.41	0.83
 20	0.09	0.51	0.93	1.29	0.70
 25	0.39	0.80	1.17	0.60
 30	0.30	0.72	1.07	0.52
 35	0.22	0.73	1.02	0.45
 40	0.16	0.64	0.88	0.39
 45	0.11	0.56	0.77	0.34
 50	0.07	0.49	0.68	0.29
 55	0.03	0.42	0.59	0.25
 60	0.37	0.51	0.22
 70	0.27	0.38	0.15
 80	0.18	0.27	0.10
 90	0.13	0.17	0.05
 100	0.05	0.10	0.01
 al observation should be used with sensor readings to confirm that the readings align with plant progress.
Soil moisture within a field can be variable and placement of the soil sensors cannot always be assumed to be representative of the field they are being used to monitor.
Confirm readings by sampling the soil profile  and the feel method when in doubt.
fall is highly variable and is a function of the depth and intensity.
Generally, it is assumed that small storm events of less than half an inch are completely retained.
The more intense the precipitation event the more runoff occurs and less of the rainfall is captured by the soil.
Tension	Sand	Sandy	Loam	Silt Loam	with Pan	Silt Loam	Clay
 					
 0	1.62	1.30	0.87	1.47	1.14
 5	1.57	1.30	0.87	1.47	1.12
 10	0.59	0.79	0.77	1.29	0.85
 15	0.20	0.53	0.77	1.17	0.67
 20	0.37	0.77	1.05	0.54
 25	0.25	0.64	0.93	0.44
 30	0.16	0.56	0.84	0.36
 35	0.08	0.57	0.79	0.29
 40	0.02	0.49	0.64	0.23
 45	0.40	0.54	0.18
 50	0.33	0.44	0.13
 55	0.26	0.36	0.09
 60	0.21	0.27	0.06
 Sand	Sandy	Loam	Loam	Loam	Silt	Clay
 			with Pan		
 	25	70	123	134	120
 Determining the Next Irrigation
 Table 3.
Plant Available Water for in  for Soil Types versus Watermark TM Readings in centibars at a 35% MAD.
The water use by crop growth stage for corn and soybeans is shown in Tables 5 and 6.
Once the amount of plant available water in the profile has been determined, use these tables to determine crop water use.
Divide the available water in the soil by the daily crop water use to determine when the plants will consume the available water.
Next, subtract the time for the irrigation set.
If rainfall occurs after readings were taken, add effective rainfall to the plant available water.
Effective rainfall is the depth of rainfall that infiltrated into the field.
The depth of effective rain-
 Table 4.
Soil Tension where no readily Plant Available Water Remains 
 Days to initiate = Plant Available Water  + effective  Irrigation set irrigation Daily crop water use  time 
 For example, given no rainfall, if the plant available soil water is 2.14 inches and crop water use is 0.25 inches per day, irrigation will need to be completed by.
If 48 hours is required to complete the irrigation, then irrigation needs to be initiated in 6.5 days.
See the fact sheet "Predicting the Last Irrigation of the Season using WatermarkTM Soil Moisture Sensors" to determine the last irrigation.
Table 5.
Daily Corn Water Use by Growth Stage
 Growth Stage	Crop Water Use 
 R3 Milking R4 Dent	0.33
 R5 Full Dent	0.25
 Table 6.
Daily Soybean Water Use by Growth Stage
 Late Vn	Late Vegetative stages	0.20
 R1 to R3	Flowering to beginning pod	0.20
 R4 to R6	Pod development to pod fill	0.25-0.35
 Printed by University of Arkansas Cooperative Extension Service Printing Services.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Director, Cooperative Extension Service, University of Arkansas.
The University of Arkansas System Division of Agriculture offers all its Extension and Research programs and services without regard to race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
Nutrients and Water Quality Concerns
 Mike Daniels Environmental Management Specialist Agriculture
 Karl VanDevender Extension Engineer
 Tommy Daniel Professor Water Quality
 Arkansas Is Our Campus
 One of the primary goals of nutrient management planning is to minimize any detrimental effects that nutrients can have on the environment.
Maintaining the quality of surface and groundwater is a key concern.
On livestock farms, the proper management of nutrients in manure is an important environmental issue, since managing nutrients in manure can be more challenging than in commercial fertilizer.
Manure contains nutrients and organic matter that normally benefit the environment but, if improperly managed, can reduce water quality.
Nitrogen in manure can be in different forms, but under the right environmental conditions, most forms will eventually be converted to the nitrate  form.
Nitrate is highly soluble, and since it is negatively charged, it is not readily absorbed by soil particles.
This makes it susceptible to leaching through the soil and accumulating in groundwater.
Groundwater quality can be reduced if contaminated by nitrates.
High nitrate levels  in drinking water may lead to health problems such as methemoglobinemia , especially in young infants.
In this case, elevated nitrates in humans interfere with the body's ability to transport oxygen in the blood stream.
Excessive nitrate in groundwater originating from livestock operations is possible for a variety of reasons:
 manure storage facilities are not properly sealed,
 nutrients are applied too closely to sinkholes or rock outcroppings,
 excessive nitrogen applications beyond the crop's needs,
 nitrogen application just prior to large runoff-production storm event
 One purpose of nutrient management planning is to develop management practices that minimize the risk of these things happening.
Due to the human health concerns from nitrates, nutrient management plans, until recently, have historically focused on managing nitrogen with little regard to other nutrients, with respect to water quality.
One major consideration in Northern Arkansas that can affect nitrate contamination is karst topography.
This geographical feature is defined as limestone formations characterized by sinkholes, springs, caves, fractured rocks, etc.
The concern here is that karst formations often have direct pathways from surface features to groundwater with very little treatment potential from soil.
In severe cases, it can be like pouring the nitrates through a pipe directly into the groundwater or introducing them directly into a well.
Much of Northern Arkansas is karst topography, and special attention needs to be given when developing nutrient management plans in this region.
Phosphorus  is a naturally occurring element in the environment.
It is an essential nutrient for plant and animal life.
Over the past 20 years, P has become an increasing environmental concern as it can accumulate in and degrade the quality of freshwater streams and lakes.
Phosphorus is not considered a human health issue, and it would not be a problem, except that P is the nutrient that limits biological activity in most of our clear water lakes and streams.
Nitrogen and potash generally occur naturally in the environment in sufficient quantities to support algae and plant growth in water bodies.
Insufficient P in most inland water bodies keeps the clear water lakes and streams from being congested with algae and aquatic vegetation.
The P requirement for aquatic plants is, in order of magnitude, smaller than for terrestrial plants.
Very small increases in P in freshwater can trigger unwanted algae and vegetative growth.
This can lead to the acceleration of eutrophication, the natural aging process of a lake that is characterized by excessive biological activity.
Consequences of accelerated eutrophication include degradation of recreational benefits and drinking water quality.
Excessive algal growth and decay can cause drinking water to have a foul odor and an "off flavor" taste, which raises treatment costs to correct for human consumption.
Advanced eutrophication can also reduce aquatic wildlife populations and species diversity by lowering dissolved oxygen and increasing the biological oxygen demand.
Eutrophication from excessive P has not generally been considered a public health issue like other contaminants derived from agricultural runoff, such as nitrates or pathogenic bacteria.
However, there are toxic algae that can flourish with increases in available nutrients, which is causing researchers to focus more attention on the isolated events that have occurred in other states.
The Fate of Phosphorus Applied to Pastures
 Most forms of phosphorus are readily adsorbed by soil particles in a very stable chemical bond.
For this reason, phosphorus has been considered historically to be immobile in runoff unless it moved with soil particles during soil erosion.
The conventional wisdom was that if good ground cover was maintained, then phosphorus should not move and would not harm water quality.
Since most non-legume forage crops require much more nitrogen than phosphorus , nutrient management plans have been based on nitrogen needs of the crop rather than phosphorus needs.
Repeated application of manure based on nitrogen needs causes P to accumulate in the soil.
In some cases, ten years of repeated application have caused very high soil test phosphorus  levels, particularly on pasturelands where crops have not been removed.
Phosphorus in pastures that are grazed is generally recycled through the grazing animal and deposited back on the pasture.
In the
 Figure 1.
The Nitrogen Cycle
 Figure 2.
Research and water quality monitoring is helping to assess the impact of nutrients derived from animal manures on water quality of streams and rivers.
past, this buildup has not been a cause for concern.
Phosphorus is a naturally occurring nutrient and, even at high levels, is not detrimental to crop production.
For some sites with high STP levels, it is now known that appreciable amounts of soluble P can be removed from pastures in runoff water, even in the absence of additional manure applications.
Looking at the top one inch of the soil profile, recent research has shown that the concentration of P in runoff increases as STP increases.
However, it should be noted that factors other than STP may influence P movement.
More recent research has shown that phosphorus losses from pastures can be dominated by soluble P losses from freshly applied poultry litter in runoff from storm events soon after application.
These losses from the litter can be up to five times more than soil-derived phosphorus losses even on extremely high soil P levels.
These research findings along with water quality monitoring  have led to increased focus on developing and implementing management practices that reduce phosphorus inputs to streams and lakes.
Reducing P in runoff from confined animal operations has become of primary concern with state and federal agencies.
In fact, both new state and federal regulations that require nutrient management plans require and that these plans will be based on P rather than nitrogen.
Phosphorus-Based Nutrient Management Plans
 Historically, nutrient management plans were based primarily on nitrogen to optimize forage production and to minimize nitrate contamination of groundwater.
For example, most nutrient management plans written in Arkansas to date have been based on nitrogen since forage crops need much more nitrogen than P.
In nitrogen-based plans, the long-term use of poultry litter as fertilizer on forages may lead to the buildup of soil P.
Due to the sensitivity of water quality to P and the excessive P applications in nitrogen-based plans, nutrient management plans are now being written based on P as the first consideration.
Phosphorus-based plans do not necessarily mean that application rates will be based on phosphorus instead of nitrogen.
If it is determined during the planning process that minimal environmental impact from P exists, then the application rates may well be based on nitrogen.
The production ramifications of Pbased application rates when using manure are that more acreage will be needed to spread the same amount of manure and that nitrogen needs from the manure itself will be insufficient to meet high production goals.
Corn management and yield loss: Management depends on the remaining yield potential.
Each field provides a unique combination of soil, management, hybrid, and water supply so not all the fields will have the same yield reduction.
After pollination a key is to determine how successful pollination was; that is how many kernels per ear were attained.
This can be determined by performing a shake test to see if silks are still attached to the ovules ; silks will easily drop from fertilized ovules.
Or wait until seven to ten days after pollination when the ear is in the blister stage  to see how many kernels are expanding.
Precision mobile drip irrigation is an irrigation system where drip hoses are attached to a center pivot sprinkler and drug on top of the ground.
The placement of water by the hoses on the ground could potentially increase irrigation efficiency over a standard drop nozzle system.
In addition, problems associated with wet wheel tracks should be reduced.
However, drag hoses lying on the ground could cause more management concerns for farmers.
One example would be animal damage to the drip hoses which disrupts uniform water distribution.
The objectives of this study were to compare yield from corn irrigated using precision mobile drip irrigation  to sprinkler irrigation with drops.
The second objective was to discern if the emitters have a reduction in water flow over the season due to clogging.
Figure 1 is a sprinkler with the drag hoses attached.
The study was initiated on a center pivot sprinkler located seven miles north and three miles west of Hoxie, KS.
Cooperation from DLS Farms was very important to evaluating these two application methods.
Three spans, spans 4, 5, and 7, of an eight span center pivot sprinkler were divided into two sections.
Each section had either the PMDI system installed or the standard drop nozzle system.
With this configuration, three replications of each method were achieved for a total of six plots.
The center pivot sprinkler is nozzled to apply 300 gpm.
Drag hose spacing on the PMDI system was 60 inches while the spacing on the drop nozzle system was 120 inches.
The entire flow to the center pivot was screen filtered to 50 mesh.
For the 2004 growing season, the farmer strip-tilled the field the previous fall and applied 75 lbs/A of N as anhydrous ammonia and 7-25-0 lbs/A as 10-34-0.
The field was planted on May 2, 2004 in circular rows with Mycogen 2E685 treated with Cruiser at 26,000 seeds/A with 50 lbs/A of N as 32% UAN applied in a 2x2.
Appropriate pest management measures were taken to control weeds and insects.
For the 2005 growing season, manure was applied to the field, and then the field was strip-tilled in the fall.
On April 28, 2005 Mycogen 2E762 treated with Cruiser was seeded in straight noncircular rows at 26,000 seeds/A with 50 lbs/A of N as 32% UAN applied in a 2x2.
Appropriate pest management measures were taken to control weeds and insects.
Emitter water flow at the end emitter and then the 5, 10, and 15 emitter from the end of two drag hoses from each plot were captured for one minute on May 26, August 4, and September 13 in 2004 and May 27, July 29, and September 8 in 2005.
Water flow for the entire drag hose was also collected for the two drag hoses along with the water flow from two drop nozzles on the same span.
Corn yield was collected in two ways.
First, samples were hand harvested from forty feet of each plot.
Samples were then dried, threshed, weighed, and yield was calculated on a bu/a basis.
Yield was also collected at harvesting using a Green Star yield monitoring system for the entire field.
Weather conditions over the summer brought supplemental rainfall which allowed for respectable yields to be achieved at the site for both years.
When comparing hand harvest yields, there was no significant difference between the PMDI treatment and the drop nozzle treatment in either year or when combined across years.
When looking at the 2004 field map  or the 2005 field map  generated by a yield monitor, no discernable pattern was evident between the two systems.
Table 1.
Yield  as influenced by irrigation treatment 
 Treatment	2004	2005	Combined Results
 PMDI	233	239	236
 Drop Nozzle	236	236	236
 LSD 	NS	NS	NS
 Fig.
2 2004 Field Map DLS Farms
 Harvested Acres: 59.99 Date: 11/5/04 Yield: 234.58 bpa Moisture: 15.40% Harvest Hours: 4.33
 Fig.
3 2005 Field Map
 Yield Map  Client: Owner Farm: Dave Up North Field: E PivotW/2 DLS-2 SE 12-7-29 Harvested Acres: 61.89 Date: 10/5/2005-10/6/2005 Yield: 227.73 bpa Moisture: 15.73% Harvest Hours: 4.61
 GREENSTAR JOHN DEERE AG MANAGEMENT SOLUTIONS
 In 2004, the average emitter output over the summer declined from 214 ml/min.
on May 24 to 209 ml/min on August 4 to 180 ml/min on September 13.
Output from the emitters decreased by an average of 16% through the summer.
Output from the nozzles from span 4, 5, and 7 also decreased from an average of 2.51 gpm on May 26 to 2.48 gpm on August 4 to 2.28 gpm on September 13.
The average reduction in flow was 9%.
The 9% reduction in flow indicates that the overall pumping capacity of the well was reduced.
However, the additional 7% reduction in flow rate from the emitters is likely due to emitter clogging.
In 2005, the average emitter output over the summer declined from 180 ml/min.
on May 27 to 168 ml/min on July 29 to 158 ml/min on September 8.
Output from the emitters decreased by an average of 14% through the summer.
Output from the nozzles from span 4, 5, and 7 actually increased from an average of 2.13 gpm on May 27 to 2.17 gpm on July 29 to 2.49 gpm on September 8.
The average increase in flow was 17%.
Why there was an increase in flow over this time is difficult to explain, but it may be related to a difference in field evaluation for the locations where the sampling was conducted.
However, there was a greater difference in 2005 compared with 2004 in the flow between the average output of the emitters and the average output of the nozzles which implies increased clogging of the emitters.
In conclusion, as with any field evaluation, variability is inherently higher due to factors outside of the parameters that can be controlled by the investigators.
However, there was no positive or negative impact on yield from those plots that were irrigated with the PMDI system versus a standard drop nozzle system.
Emitter flow was decreased in both years when compared with nozzle flow which was likely due to emitter clogging.
Clogging of the emitters over the life of the system along with puncturing of the hoses from wildlife appear to be two negatives of the system, while one benefit of the system was the reduced wheel pivot tracks when the PMDI system is used to water crops near the pivot wheel.
The authors of this paper would again like to thank DLS farms for their cooperation on this project.
Fig.
5.
Emitter response from 2004 and 2005
 Fig.
6.
Nozzle Response from 2004 and 2005
Historically, the center pivot has been used by a farmer/operator to apply a selected depth of water uniformly across the entire field.
Changes in technology have occurred that give growers the ability to apply differing amounts of water and products carried in the water to different zones along the pivot and sectors around the field.
This paper will discuss results from the summer of 2010 of a commercial center pivot equipped with the Valley Variable Rate Zone Control package.
The paper will also review potential payback.
It will close with a discussion of future needs for variable rate irrigation.
Since the introduction of the center pivot in the mid-1950s, the mechanical move industry has continued to improve and develop products to better meet the needs of production agriculture.
The overall goal has been to provide cost-effective, uniform irrigation across the field with a specific application depth
 With the introduction and acceptance of precision agriculture, suddenly more information has become available for a particular field and areas in the field, including yield, soil and gird sampled fertility maps.
Farmers now have data indicating the variability across the field, which was already suspected but not proven.
The challenge then became how to use this data and how to make changes that would impact different areas of the field.
Fertilizer and chemical application equipment, as well as planters, have been equipped to make changes in rates or volumes across the field.
Research into variable rate, or "site specific," irrigation has been conducted at a number of locations across the United States by both Universities and USDA-ARS.
These include, but are not limited to Universities of Georgia, Idaho, Nebraska and Texas A&M, and the USDA-ARS at Florence, SC, Ft.
Collins, CO and Sidney, MT.
The first commercial, marketed variable rate irrigation package was jointly developed by the University of Georgia, FarmScan and Hobbs and Holder.
These units have primarily been installed in the southeastern United States.
The goal of this project was to demonstrate on a commercial field the viability of using a Valley Variable Rate Irrigation  Zone Control package to solve a farmer's challenges while maximizing returns from a center pivot irrigated field.
The VRI Zone Control package consists of a Valley Pro2 control panel, VRI tower boxes and a sprinkler control valve package.
Information is sent between the control panel and the VRI tower boxes using a power line carrier  through the existing center pivot span cable.
No additional control wires are required to use the product.
Due to durability, reliability and experience, the sprinkler control valve used is the AquaMatic brand, which has been used for more than thirty years on corner machines for sprinkler control.
A tubing harness connects the AquaMatic valve to the solenoid on the VRI tower box.
This hardware allows the center pivot to be broken into a maximum of thirty Pivot Zones.
Below is a conceptual drawing of the Valley VRI Zone Control package components.
A prescription that is specific for the field is created with the VRI Prescription Software, which resides on an external computer.
The prescription is then loaded into the Pro2 control panel.
The VRI Prescription Software allows prescriptions to have up to 180 sectors around the field, each sector as small as two degrees.
In the spring of 2010, Valmont Irrigation began to review commercial field sites to validate the lab and field testing that had been done with the Valley VRI Zone Control package.
A possible field was identified near Dyersburg, Tennessee, owned by Jimmy Moody; the center pivot was a Valley Model 8000 that was
 installed in 1997.
The machine's configuration was a total length of 1,148 ft: five spans of 180 ft and one span of 185 ft with a 64 ft overhang.
The flow rate was 800 gpm and pipeline coupler spacing was 108 in.
The control panel was mechanical.
The sprinklers were fixed-pad sprays with a medium groove pad and regulator.
End pressure was 10 psi at the nozzle; the center pivot had pressure regulators.
The drive train was high speed with 14.9x24 tires.
The pump was a deep well turbine with a fixed-speed motor.
Based on the manufacturer's data, it was determined that the flow rate should not drop below 450 gpm to maintain good efficiency and minimal pressure rise.
Mr.
Moody described his challenges with this field.
Parts of the field were either being overwatered or under watered, and uniform crop production was not being achieved across the field.
His goal was to have more uniform crop production across the field.
To accomplish, this he believed he needed to be able to adequately water the light soils without flooding the heavy soils.
To evaluate the field to determine both the number of Pivot Zones needed along the pivot and sectors around the field, the NRCS soil maps  were reviewed; however, they did not seem to match the situation Mr.
Moody had described.
Bw Bowdre clay CM Commerce loam CR Crevasse loamy sand CS Crevasse sandy loam Ro Robinsonville fine sandy loam
 Mr.
Moody did not have a series of annual yield maps to average in order to help define the appropriate VRI package.
Mr.
Moody had done grid soil sampling, but, while this data was valuable and interesting, it did not help to lay out the VRI package.
In a conversation with Dr.
Earl Vories of USDA-ARS about VRI and how to determine the layout of Management Zones, it was suggested by Dr.
Vories that apparent electrical conductivity  of the soil profile be used.
ECa is a sensor-based measurement that provides an indirect indicator of important soil physical and chemical properties.
Dual EM was used to determine ECa, as shown on the map below in Figure 2.
This data seemed to match Mr.
Moody's perception of the field's characteristics.
The decision was thus made to use this information as a starting point to help define the VRI Zone Control package.
Rice was the crop for the 2010 growing season.
Based on the shallow root system of rice, it was decided to use the shallow ECa information to both define the VRI Zone Control hardware and to develop the initial prescription.
A decision was made to maintain the same area in the zones in order to simplify management decisions and to make it easier to determine the impact on the hydraulics, as each Pivot Zone along the center pivot would have the same flow rate.
The center pivot was split into ten Pivot Zones with the length of the Pivot Zones and number of sprinklers as:
 Zone 1 363 feet 40 sprinklers Zone 2 150 feet 17 sprinklers Zone 3 115 feet 13 sprinklers Zone 4 97 feet 11 sprinklers Zone 5 86 feet 10 sprinklers Zone 6 78 feet 9 sprinklers Zone 7 71 feet 8 sprinklers Zone 8 66 feet 7 sprinklers Zone 9 62 feet 7 sprinklers Zone 10 59 feet 7 sprinklers
 Each Pivot Zone along the center pivot represents 9 1/2 acres and had a flow of 80 gpm.
The sectors around the field were in four-degree increments, which totaled 900 Management Zones, or "blocks." Figure 3 below illustrates the initial prescription used.
The VRI Zone Control hardware was installed along with a new sprinkler package, pressure regulators and sprinkler control valves.
One AquaMatic valve was used for each hose drop.
Once the hardware was installed and the VRI software was uploaded to the Pro2 control panel, the constants for the VRI Zone Control were entered and the prescription uploaded.
The pivot was then run to test the package.
During the growing season, base application depths ranged from 0.25 in to 0.45 in.
A significant portion of the nitrogen for the rice crop was applied through the center pivot with an Inject-O-Meter pump.
The nitrogen was liquid with an analysis of either 32-0-0-0 or 28-0-0-5.
The VRI Zone Control package was used as the heavier soils had much better fertility than the lighter textured areas, so the nitrogen application amounts were cut back based on the EM map.
Since the injector pump was a fixed speed, a separate prescription was created to compensate as much as possible for the fixed pump.
The goal was to reduce nitrogen as in the areas that received less irrigation.
One area of particular interest was how to validate the performance of the VRI Zone Control during the growing season, while not just waiting for the yield results.
The VRI Zone Control package "pulses," or cycles, the valves off and on, which then turns the sprinklers off and on to achieve the desired change to the base application depth.
The problem was approached in three ways:
 Visual observation of the Pivot Zones and Management Zones
 Soil moisture monitoring in one of the areas with the light textured soils where the prescription always called for 100% of the base application depth, and in heavy soils area where the base depth was reduced by up to 40%.
For example, if the base application depth was 1.00 in, then an area of 40% reduction would only apply 0.60 in
 Aerial imageryinfrared and color spectrum
 One of the first observations was the cycle time was too long when a Pivot Zone was operating in an area where there was to be a reduction in the application depth.
It was observed the drive unit was moving so far during a pulse that sufficient overlap of the sprinkler package in the direction of travel was not being achieved.
To correct this, the cycle time was changed in the constants something easily done at the control panel.
The soil moisture data was tracked remotely; it looked for drying trends in the area where the prescription called for a reduced application depth.
Below is an example of the data sets for a sample time period.
The top set of data is an area with clay loam soil that received 60% of the base application depth.
The bottom data set is an area of fine sand that always received 100% of the base depth.
Along the X axis is time, from June 15th to September 28th.
The y axis is in centibars, which ranges from 0 to 100.
Most important from this data is that over time, the top graph did not show a drying trend; for most of the crop season it paralleled the soil moisture status of the area that received 100% of the base application depth.
In addition, visual observations and use of a soil probe indicated the soil moisture was adequate in the area receiving 60% of the base application depth.
The following were a series of infrared images taken during the growing season.
In the images above, there was gradual improvement in the ground cover and, in general, the crop appeared "good" across the field with no particular weak areas except for the areas where the crop was blown out by wind in the early season.
Harvest was a challenge due to a wind storm part-way through harvest that lodged the crop badly in the south-central part of the field, which traditionally was believed by Mr.
Moody to have the best yields.
Overall, the field variability was significantly reduced and the light textured soils yielded well in a very dry year; a total of 19.4 in per acre were applied to the crop in 61 passes of the center pivot.
19.4 in was calculated based on the hours of center pivot operation and the flowrate.
This is interesting because it is incorrect if there had been no VRI, then it would have been correct.
Some sections of the field received 19.4 in because they had a prescription of 100% of the base application depth.
However, the areas with a 60% prescription  received 11.6 in per acre.
Applying the prescription across the field to the total pumped inches indicates that, overall, 12% less irrigation was actually applied, which illustrates a significant water and energy savings.
Total applied nitrogen was also reduced by using the VRI prescription.
The reduction in nitrogen was 15% another significant amount.
The farmer was pleased with the performance, and based on savings and overall yield increase estimates the payback for the unit to be just over three years.
Historically, center pivot irrigation has treated the entire irrigated field the same and the goal has been to make uniform applications across the field.
With variable rate irrigation, the farmer now has the ability to apply specific amounts of water to specific locations within the field.
Based on the information collected in 2010, there are a number of areas requiring additional work and evaluation:
 Better tools to determine economic number and size of Management Zones.
With the recent cooperation developed with CropMetricsTM TM this is one solution to overcome this.
Better tools to determine prescriptions.
This is now easy with the CropMetrics solution.
Methods to obtain easy feedback from the Management Zones and to incorporate into the farmer's decision-making tools.
Validation of VRI Zone Control performance
 Quantify possible benefits, such as water savings, yields increase and nitrogen use, and impact on the payback.
Explore sprinkler package performance and how it relates to VRI.
Management of the hydraulic issues associated with a fixed-speed pump.
Use of variable rate chemigation pumps.
Another factor is how one thinks of center pivot irrigation.
The overall goal may not be to achieve general field uniformity, but rather to apply specific amounts of water and other crop inputs to particular areas of the field.
Irrigation Variable Rate Development, Marek, Thomas and Auvermann, Brent, 2004, TAES-Amarillo, Texas Agricultural Experiment Station
 Personal communication Valmont Irrigation Engineering and Application departments
 Using Precision Agriculture Methods to Predict Soil Suitability for Rainfed Corn Production, Vories, Earl, Kitchen, Newell, Sudduth, Ken, Sadler, John, Griffin, Terry and Stevens, Gene, 2008 ASABE Annual International Meeting, Rhode Island, American Society of Agricultural and Biological Engineers, paper 084437
Drip irrigation provides the salinity control needed for profitable irrigation of tomatoes in the San Joaquin Valley
 by Blaine R.
Hanson, Don E.
May, Jirka Simunek, Jan W.
Hopmans and Robert B.
Hutmacher
 Despite nearly 30 years of research supporting the need for subsurface drainage-water disposal facilities, the lack of these facilities continues to plague agriculture on the San Joaquin Valley's west side.
One option for coping with the resulting soil salinity and shallow water-table problems is to convert from furrow or sprinkle irrigation to drip irrigation.
Commercial field studies showed that subsurface drip systems can be highly profitable for growing processing tomatoes in the San Joaquin Valley, provided that the leaching fraction can achieve adequate salinity control in the root zone.
Computer simulations of water and salt movement showed localized leaching fractions of about 25% under subsurface drip irrigation, when water applications equaled the potential crop evapotranspiration.
This research suggests that subsurface drip irrigation can be successfully used in commercial fields without increasing root-zone soil salinity, potentially eliminating the need for subsurface drainage-water disposal facilities.
T he lack of widespread subsurface drainage-water disposal facilities
 Subsurface drip irrigation is allowing San Joaquin Valley tomato growers to apply water precisely and uniformly, increasing yields and reducing the runoff of saline drainage water.
A UC study  concluded that a salt balance must be maintained in the root zone for productive cropping systems to continue, and irrigation without improved management practices cannot be sustained in the San Joaquin Valley.
The only options available to address salinitv and drainage problems without
 as a result, subsurface drip irrigation is commonly used in salt-affected soils for processing tomato production.
The second option has been proposed, but little information exists on its use by growers.
The California Department of Water Resources is promoting the third option, but its use is limited and still in an experimental stage
 Subsurface drainage systems and drainage-water disposal methods are not needed for properly designed and managed drip irrigation systems.
tion and maintenance of drip systems.
The main disadvantage of drip irrigation is its high installation cost, which ranges from $600 to $1,000 per acre.
Subsurface drip irrigation, commonly used for processing tomatoes, involves placing drip lines 8 to 12 inches below the soil surface directly below the plant row; surface drip irrigation involves placing the drip lines on the soil surface.
In the late 1980s, two large-scale comparisons of subsurface drip and furrow irrigation were conducted in cotton under saline, shallow groundwater conditions.
Drip irrigation consistently resulted in higher cotton yields with less water application than furrow irrigation.
However, the profit with furrow irrigation was much higher at one location, and drip irrigation was only slightly more profitable at the other.
The cost of the drip systems played the major role in their profitability.
As a result, growers who convert to drip ir-
 rigation of cotton assume an additional economic risk.
In 2008, the Westlands Water District which encompasses more than 600,000 acres of farmland in western Fresno and Kings counties reported 37,396 acres of cotton and 86,011 acres of processing tomatoes, now the largest single crop acreage; cotton production has decreased substantially in recent years.
Because processing tomatoes are a higher value crop than cotton, subsurface drip irrigation offers potentially higher profits.
However, unlike cotton, tomatoes are moderately sensitive to soil salinity, and reduced tomato yields can result.
The threshold electrical conductivity , which represents the maximum root-zone soil salinity at which yield is not reduced, is 2.5 deciSiemens per meter  for tomato compared to 7.7 dS/m for cotton.
Between 1998 and 2003, experiments in commercial fields in the Westlands Water District, on the San Joaquin Valley's west side, evaluated subsurface drip irrigation of processing tomatoes under saline, shallow groundwater conditions.
In addition, starting in 2006, computer simulations using the HYDRUS-2D model  evaluated leaching with subsurface drip irrigation under these conditions.
This model has been used previously in studies of water and chemical movement under drip irrigation.
We present a review of this research.
Specialized equipment  is used to install drip tape 8 to 12 inches below the soil surface, at a cost of about $600 to $1,000 per acre.
Despite this price, studies show that improved irrigation efficiency and yield benefits increase profits for growers in the San Joaquin Valley, compared with sprinkle or furrow irrigation.
Experiments in three commercial fields  compared subsurface drip irrigation to sprinkle irrigation.
Drip systems ranged from 40 to 80 acres each in area, and sprinkle irrigation was used for the rest of the fields.
Water table depths ranged from 2 to 6 feet.
Electrical conductivity ranged from 0.3 dS/m for irrigation water from Westlands Water District to 1.1 dS/m for well water, and from 4.0 to 16.4 dS/m in the shallow groundwater.
A small-scale, randomized, replicated experiment was conducted in each drip-irrigated field to investigate the relationship between yield, soluble solids  and applied water.
The soil type was clay loam at the three experimental sites.
We found that subsurface drip irrigation was highly profitable for processing tomatoes under these shallow, saline groundwater conditions compared to sprinkle irrigation.
Average yields were 40.5 tons per acre for subsurface drip irrigation versus 33.9 tons per acre for sprinkle irrigation, with $484 per acre more profit on average for drip than sprinkle irrigation.
The average difference in soluble solids between the two irrigation methods was not significant.
The small-scale experiments showed increased yield and decreased soluble solids as applied water increased.
Yields of the drip-irrigated fields were monitored for 2 more years after
 the first year.
Yields remained high except for one site, which had 2 years of reduced yields due to late plantings.
We did not find any trends toward yield reductions with increased soil salinity near the drip lines, which ranged from values less than, to higher than, the threshold electrical conductivity of 2.5 dS/m for tomatoes.
At a fourth commercial field , a small-scale, randomized-block, replicated experiment evaluated the response of tomato and cotton yields to different amounts of applied water under very shallow groundwater conditions of 18 to 24 inches.
The soil type was clay loam.
Tomato yields ranged from 34.6 tons per acre for 15.6 inches of applied water to 42.8 tons per acre for 23.2 inches, even though nearsaturated, highly saline soil occurred at only 18 inches deep.
At 23.2 inches, water application is about equal to the seasonal evapotranspiration or crop water use for tomatoes.
However, cotton yields did not respond when water was applied at amounts equal to or greater than about 40% of the potential seasonal evapotranspiration.
The electrical conductivity of the irrigation water was 0.5 dS/m and of the ground-
 TABLE 1.
Seasonal applied water, evapotranspiration and leaching fractions calculated from a water balance for four commercial sites
 Year*	applied water	ETt	fraction#
 1999	16.0	20.3	0
 2000	16.8	21.4	0
 2001	20.5	22.9	0
 1999	22.2	25.1	0
 2000	29.0	25.2	13.1
 2001	22.9	26.6	0
 2000	28.8	24.2	13.6
 2001	22.1	23.1	0
 2002	23.2	24.3	0
 BR, DI, DE and BR2 are site designations for the commercial fields.
# Zero values indicate no leaching, which occurred because seasonal applied water values were smaller than seasonal evapotranspiration.
water was 8 to 10 dS/m.
At all commercial sites, tomato yields increased as applied water increased.
Factors contributing to this finding included higher soil-water content and reduced root-zone soil salinity due to larger zones of low salt around the drip lines as more water was applied.
Cotton yields, however, were unresponsive to the amount of applied water, reflecting cotton's salt tolerance and ability to utilize saline, shallow groundwater.
Consequently, contributions by the saline, shallow groundwater to crop evapotranspiration should be minimized for tomato and maximized for cotton.
Soil salinity levels around the drip lines depended on the depth to groundwater, salinity of shallow groundwater, salinity of irrigation water and amount of applied water.
For a water table depth of about 6 feet, relatively uniform soil salinity occurred throughout the profile, with values smaller than the threshold electrical conductivity of tomato.
For water table depths less than about 3 feet, relatively low levels of soil salinity occurred near the drip line, but values increased to high levels beyond the wetting pattern due to the upward flow of shallow groundwater.
Higher soil salinity occurred near the drip line when the salinity of the irrigation water increased.
Larger amounts of applied water increased the zone of low-salt soil near the drip line, even when shallow water tables had depths of less than 2 feet.
At all sites, water table depth showed little response to drip irrigation, except when overirrigation OCcurred during one year at site BR.
A subsequent reduction in applied water at that site caused the water table to decline due to reduced percolation and the natural drainage of shallow groundwater.
Salinity control is needed in the root zone to maintain profitable subsurface drip irrigation of tomatoes in salt-affected soils.
This can be achieved by leaching or flushing salts from the
 Fig.
1.
Soil salinity/electrical conductivity  around the drip line for water depth of about  6 feet, EC irrigation water = 0.3 dS/m, EC groundwater = 8 to 11 dS/m;  2 to 3 feet, EC irrigation water = 0.3 dS/m, EC groundwater = 5 to 7 dS/m; and  2 to 3 feet, EC irrigation water = 1.1 dS/m, EC groundwater = 9 to 16 dS/m.
Fig.
2.
Soil salinity/electrical conductivity  around the drip line for water depth of about 18 to 24 inches, EC irrigation water = 0.5 dS/m, EC groundwater = 8 to 10 dS/m, for water applications of  23.2 and  15.6 inches.
Fig.
3.
Soil-water salinity/electrical conductivity  around the drip lines at  start of simulation period ,  just after first irrigation ,  just before second irrigation  and  just after last irrigation.
Applied water = 100% evapotranspiration; EC irrigation water = 0.3 dS/m.
root zone applying irrigation water in amounts exceeding the soil moisture depletion.
The leaching fraction is used to quantify leaching adequacy, and is derived from the ratio of the amount of water that drains below the root zone to the amount of water applied.
Leaching fractions can be determined several ways.
One approach is to measure the average salinity of the root-zone soil and irrigation water, and then use appropriate charts or equations to determine the leaching fraction.
However, soil salinity, soil-water content and root density all vary around the drip line, resulting in uncertainty about the accuracy of root-zone soil salinity.
A second approach commonly used is the water balance method, by which a fieldwide amount of leaching is calculated as the difference between the seasonal amount of applied water  and evapotranspiration.
Because actual evapotranspiration in a given field is usually unknown, it is frequently estimated using crop coefficients and a reference crop evapotranspiration value obtained from the California Irrigation Management Information System.
We calculated fieldwide leaching fractions for the commercial fields using the water balance method.
Evapotranspiration was determined using canopy growth rates and a calibrated computer model.
These calculations showed little or no fieldwide leaching at most of the sites , which suggests inadequate salinity control and raises questions about how
 long drip irrigation can be sustained under saline, shallow groundwater conditions.
The soil salinity data, however, clearly showed that because of the wetting pattern under drip irrigation, leaching was highly concentrated near the drip line.
The soil salinity data also indicated that the water balance approach is not appropriate for drip irrigation and that estimating actual or localized leaching fractions under drip irrigation may be difficult and also inaccurate.
It is reasonable to expect that the salinity patterns reflect long-term behavior, as long as adequate salinity-control measures  prevent salts from accumulating in the root zone.
Because of the difficulties in estimating actual leaching fractions for the drip-irrigated commercial fields, we used the computer model HYDRUS-2D  to simulate the movement of water and salt in soil under drip irrigation for a 42-day period and quantify drainage below the root zone.
Simulations were conducted for water table depths of 20 and 40 inches; irrigation water salinities of 0.3, 1.0 and 2.0 dS/m; and applied water at 80%, 100% and 115% of potential evapotranspiration.
For 0.3 dS/m irrigation water, we conducted an additional simulation of applied water at 60% of potential evapotranspiration.
The depth of application per irrigation was based on
 a daily evapotranspiration rate of 0.29 inches per day, but the actual simulations varied by applied water amounts and irrigation frequency.
The application rate was constant during the simulation period for a particular scenario consisting of a water table depth, an irrigation water salinity and an applied water amount.
We simulated two irrigations per week for a 40-inch water table depth, and daily irrigations for the 20-inch depth.
These frequencies reflect those used in the commercial field experiments.
The drip line was 8 inches deep, and electrical conductivity of the shallow groundwater was 10.0 and 8.0 dS/m for the 20and 40-inch water table depths, respectively, based on measured levels in the commercial fields.
The initial soil-water salinity levels at the start of the simulation period were based on samples collected in spring, prior to drip irrigation.
The simulated root distribution was based on field data of rooting patterns for drip-irrigated tomatoes at the UC West Side Research and Extension Center.
Simulated reclamation  of soil near the drip line was rapid, and the simulated salinity patterns were consistent with those found in the commercial fields .
The simulations predicted that the volume of reclaimed soil would increase over time, with most reclamation occurring below the drip line, and that salts would accumulate near the soil surface.
Large seasonal applications of water would increase the zone of lower-salinity soil near the drip lines, consistent with our field data.
But the larger amounts would have little effect on the volume of reclaimed soil above the drip line.
As expected, salinity near the drip line would increase as irrigation water salinity increased.
The root uptake of soil water would decrease as applied water decreased, suggesting the potential for decreased yields with decreasing water applications, as was found in our commercial field data for processing tomatoes.
The actual or localized leaching fractions for the 40-inch water table
 scenarios were 7.7% for the 60% water application treatment, 17.3% for the 80% treatment, 24.5% for the 100% treatment and 30.5% for the 115% treatment.
As irrigation water salinity increased, the actual leaching fraction increased as a result of reduced root-water uptake.
Even for water applications equal to or smaller than 100% of potential evapotranspiration, drainage occurred below the root zone due to the spatially variable wetting under drip irrigation.
In both studies , considerable localized leaching occurred around the drip lines, due to the wetting patterns of subsurface drip irrigation.
The localized or actual leaching fractions determined from the computer simulations were about 25% to 30% for a water application equal to 100% of potential evapotranspiration.
increased as the amount of applied water increased, and soil salinity around the drip line increased as salinity of the irrigation water increased.
Leaching and efficient drip systems
 The field research and computer simulation modeling demonstrated that subsurface drip irrigation of processing tomatoes is highly profitable compared to sprinkle or furrow irrigation under saline, shallow groundwater conditions.
Tomato yields increased as applied water increased, and cotton yields were unaffected.
These tomato yield results suggest that root uptake of saline, shallow groundwater should be minimized to prevent yield reductions, while the cotton yield results indicate that substantial root uptake of the saline groundwater can occur without yield reductions.
Under subsurface drip irrigation of processing tomatoes, localized leaching is highly concentrated near the drip line, resulting in relatively low soil-salinity levels in areas where root density is highest.
The water balance approach for estimating leaching amounts is inappropriate for drip irrigation because of such localized leaching.
The computer simulations showed that reclamation around drip lines in saline soil would be rapid.
Predicted reclamation was faster for relatively infrequent large water applications per irrigation than for smaller applications.
The low-salt zone around the drip line
 We found that very high irrigation efficiencies under drip irrigation can only be obtained by substantial deficit irrigation, in contrast to the frequent assumption that drip irrigation is nearly 100% efficient for water applications equal to about 100% of potential evapotranspiration.
A common assumption is that applying water at amounts equal to 100% of potential evapotranspiration results in irrigation efficiency of 100%, defined as the ratio of cumulative root-water uptake to applied water.
In cases of drip irrigation at 100% of potential evapotranspiration, little drainage below the root zone is assumed to occur.
However, the computer simulations showed that this assumption is not true.
Because of spatially varying soilwater wetting around the drip lines, irrigation efficiency was 74.6% and 69.7% for the 40and 20-inch water table scenarios, respectively, with the 100% water application.
Very high irrigation efficiencies occurred only under conditions of severe deficit irrigation.
The key to sustained subsurface drip irrigation of processing tomatoes in salt-affected soils is profitability, which in turn depends on salinity control in the root zone.
This requires irrigating with relatively low-salt water; applying sufficient irrigation water for adequate localized leaching; leaching salts that accumulate around the drip line; and preventing saline, shallow groundwater intrusion into the root zone.
The following are recommenda-
 Because of high-frequency irrigation, the volume of drainage per irrigation was small and drainage was distributed evenly over the irrigation season.
As a result, natural subsurface drainage in the commercial fields was sufficient to prevent groundwater intrusion into the root zone.
To minimize the uptake of shallow, saline groundwater which can affect tomato yields sufficient irrigation water must be applied in the root zone to ensure adequate leaching.
Above, filters, pumps and fertilizer tanks are part of drip irrigation systems.
tions for subsurface drip irrigation of processing tomatoes under conditions of the San Joaquin Valley's west side:
 Water applications.
Seasonal water applications should be about equal to the seasonal evapotranspiration, which is 25.5 inches in the San Joaquin Valley.
This provides sufficient localized leaching.
Higher applications could raise the water table, causing saline, shallow groundwater intrusion into the root zone.
Smaller applications reduce tomato yields.
Salinity of irrigation water.
The electrical conductivity of irrigation water should be about 1.0 dS/m or less; higher levels may reduce yields.
Irrigation frequency.
From daily to two or three irrigations per week should occur after the start of drip irrigation.
Daily irrigations are recommended for very shallow, saline groundwater conditions.
The amount of water application per irrigation should be determined using appropriate crop coefficients  and the reference crop evapotranspiration from CIMIS.
Salt leaching.
Periodic leaching of salt accumulated above buried drip lines will be necessary with sprinkle irrigation for stand establishment, if winter and spring rainfall is insufficient.
System maintenance.
Drip irrigation systems should be designed for a high uniformity of applied water, and should be properly maintained to prevent emitter clogging.
Can drip irrigation eliminate the need for expensive subsurface drainage systems and drainage-water disposal methods?
We believe the answer is yes, since no subsurface drainage systems were used at our sites.
Subsurface drip irrigation continues to be used at these sites along with many other fields along the San Joaquin Valley's west side.
Drip irrigation resulted in little change to the water table at these sites , and the computer simulations revealed that drainage or percolation below the root zone would occur.
The field data indicated that small ap-
 plications of water per irrigation and relatively uniform distribution of irrigations over time, coupled with natural subsurface drainage, prevented groundwater intrusion into the root zone.
This finding suggests that, for the conditions in these fields, subsurface drainage systems and drainage-water disposal methods are not needed for properly designed and managed drip irrigation systems.
These results indicate that subsurface drip irrigation of processing tomatoes a higher value, moderately salt-sensitive crop compared to cotton is sustainable in the salt-affected soils that we studied.
Similar results might be expected for crops of similar value that are moderately salt sensitive and suitable for drip irrigation, such as melon.
Drip irrigation of salt-tolerant crops such as cotton, sugar beets and grain may not be profitable because of their relatively low cash value.
While
 little research has been conducted in the San Joaquin Valley on drip irrigation of salt-sensitive crops under saline conditions, a literature review of numerous studies on drip irrigation of vegetable crops  showed that drip irrigation may be a sustainable practice for salt-sensitive crops.
B.R.
Hanson is Irrigation and Drainage Specialist, Department of Land, Air and Water Resources, UC Davis; D.E.
May is Farm Advisor Emeritus, UC Cooperative Extension; J.
Simnek is Professor of Soil Physics and Hydrologist, Department of Environmental Sciences, UC Riverside; J.W.
Hopmans is Professor of Water Management, Department of Land, Air and Water Resources, UC Davis; and R.B.
Hutmacher is Extension Cotton Specialist, Department of Plant Sciences, UC Davis, and Director, UC West Side Research and Extension Center.
Support for this project was provided by the UC Prosser Trust Fund; the Westlands Water District; and Farming D and Britz Farming Company, both of Five Points, Calif.
Irrigation Tips to Conserve Water and Grow a Healthy Lawn
 Gregg Munshaw and Brad Lee, Plant and Soil Sciences
 T urfgrasses are composed of thousands of cells, all containing water, in which metabolic processes such as photosynthesis and respiration take place.
Water makes up 80 to 90 percent of the total plant mass.
If this level drops below 60 percent, these processes may slow and wilting will occur.
Water is critically important for:
 Maintaining turgidity, which keeps plants standing upright
 Transporting nutrients and sugars through the plant
 Transpirational cooling when water moves out of the leaves and evaporates
 Water is also very important for moving pesticides and fertilizer into the root zone.
Although water is essential for grass survival, because we have a limited fresh water supply, we must find a balance between keeping grass alive and conserving water.
The Importance of Water Conservation
 Although 70 percent of the earth's surface is covered with water, only about 1 percent of it is available for our use.
As the human population continues to increase, our limited water resources will become even more taxed.
Concern also exists that global warming will cause more frequent droughts.
Due to need, overuse, lack of additional resources, and the potential for climate change to limit rainfall, water conservation should be something that every one of us takes seriously.
The Environmental Protection Agency's  WaterSense program estimates that the average household uses 320 gallons of water each day in the United States.
Of this, 96 gallons are used outdoors for things like irrigation and washing cars.
Landscape irrigation alone accounts for nearly 9 billion gallons of fresh water used in the United States each day.
Figure 1.
Footprinting on a cool-season grass indicates the need for watering.
The goal of water conservation in the landscape does not need to be as drastic as eliminating all irrigation, but we should choose plant material wisely and decide if and when irrigation is necessary.
This publication is designed to promote a healthy lawn through watering while promoting water conservation through best management practices.
climate.
If you are not sure whether a certain plant is a good choice, contact your local extension office for clarification.
The options for lawn choices are simple.
Some grasses native to North America use very little water , but unfortunately they are either not suitable as a lawn surface or they are not adapted to our climate.
Warm-season grasses such as bermudagrass and zoysiagrass have excellent drought tolerance , but you must be prepared for a dormant  lawn from late fall through spring.
The best choice for an attractive lawn throughout the entire year as well as one that will require less water during the summer is turf type tall fescue.
This grass has much better heat and drought tolerance than Kentucky bluegrass, which means the sprinklers can stay off longer.
Is it time to water?
Look for the following clues:
 Footprints remain in the grass long after being made.
Soil from the root zone is dry or powdery.
No rain has occurred for at least a week during hot, dry, sunny, or windy weather.
Turf on high spots and/or south slopes starts to show some yellowing or turns bluish gray.
The right grass is a good start, but when it comes to watering, there are several other factors that need to be considered.
Table 1 lists the drought tolerance rankings of lawn grasses commonly grown in Kentucky.
Table 1.
Drought tolerance rankings of lawn grasses grown in Kentucky
 Warm-	bermudagrass	Very good
 Cool-	tall fescue	Medium
 Season	Kentucky blue-	Fair
 perennial rye-	Very poor
 Does the Lawn Need Water?
The first approach to watering lawns is to water as needed.
Most lawn soils in Kentucky have adequate water-holding capacity and do not require water every day to sustain turfgrass growth.
If you have to water, wait until the lawn is dry enough that footprints are left after walking on it.
Footprinting will let you know that the lawn is just beginning to wilt.
Once the first signs of wilt are apparent, water long enough to allow puddles to begin forming on the surface.
At this point you have reached the maximum percolation rate of the soil.
Before rewatering, allow the soil to dry again until footprints are visible after walking on it.
This method will create the deepest possible root system and the healthiest plants in terms of drought tolerance.
This type of irrigation scheduling is considered "deep and infrequent."
 Another method to determine when water is needed is to attempt to insert a screwdriver into the soil.
If the soil is suf-
 Figure 2.
Unwatered Kentucky bluegrass  and tall fescue  lawns during drought.
ficiently moist, inserting the screwdriver will be fairly easy.
As the soil becomes increasingly dry and hard, inserting the screwdriver will become more difficult.
When you cannot insert the screwdriver and the soil in the top inch or two appears dry, consider turning on the water.
Moisture probes are also available to let you know when the soil becomes dry enough to water.
The second philosophy regarding watering lawns is to not water them at all.
In many years rainfall is frequent enough that supplemental water is not required.
However, in some years, the effects of drought may be visible on lawns.
Kentucky bluegrass lawns will become dormant during lengthy droughts and will turn brown.
More often than not, these lawns are not dead and will recover when rain and cooler temperatures return in the fall.
Tall fescue, however, has a much deeper root system and will remain green and growing longer than Kentucky bluegrass.
A concern with drought dormant lawns is that they are not competitive against weeds, thus attention may be needed to guard against invading weeds.
Further, if the drought period is extensive, there is a chance that these cool-season lawns will not recover.
Traffic, including mowing, should be strictly avoided when cool-season grasses are under drought stress.
Permanent damage can occur when traffic is applied
 to severely drought stressed grasses.
Traffic during drought will also encourage warm-season weed species.
Whenever possible, water lawns in the very early morning hours.
Watering in early morning will greatly reduce losses to evaporation by allowing time for infiltration before sunrise.
Watering at this time will also have the largest effect on reducing the daily leaf wetness period by knocking off dew that has formed overnight.
Conversely, watering in the evening will prolong the leaf wetness period.
Reducing the length of the daily leaf wetness period will have a very positive impact on reducing summer disease problems.
Watering during the day is not recommended as the water droplets from the sprinklers are often affected by wind and end up in areas other than where desired.
Further, irrigation water during the day is lost to evaporation, which leads to the need for more water and higher water bills.
Excessive watering is just as bad as not watering enough.
Too much soil moisture causes all the pore spaces in the soil to be filled with water, reducing space for air.
Roots require oxygen to grow.
If soil oxygen levels are low, the root system will become shallow.
An unhealthy root
 system will lead to problems with the aboveground portion of the plant, and shallow roots can be a concern if irrigation water becomes limited.
Overwatering can kill your lawn.
Kentucky receives an average of about 1 inch of precipitation per week during the summer, SO watering should supplement rainfall rather than providing all the moisture that the lawn needs.
Automatic irrigation systems should not be programmed daily or even every other day.
Besides causing shallow roots, overwatering causes nutrient loss, disease-susceptible turf, and severe problems with weeds such as nutsedge, nimblewill, bentgrass, annual bluegrass, oxalis, and crabgrass.
Most Kentucky soils can hold about two thirds of an inch of plant extractable water in the surface 4 inches where most turfgrass roots persist.
Although this amount is less than the turf will likely use during a week, it is equivalent to about 400 gallons of water per 1,000 square feet of lawn.
The difference between the total amount needed for evaporation and transpiration per week and the amount of plant extractable soil water plus weekly rainfall is approximately equal to the amount of irrigation needed to maintain maximum growth, e.g.:
 total amount required  = irrigation required
 A rule-of-thumb is that turf needs about 1 inch of rainfall or irrigation water per week from May through September.
Long-term weather data relating water loss and rainfall indicate that most Kentucky lawns need an average of less than one quarter inch of irrigation water per week.
However, such long term weather averages mask the increased need for irrigation during periods of obvious drought.
So how do you determine how long to run the sprinklers to apply one quarter inch of water per week?
The easiest way is to push a soil probe or screwdriver into the soil as described above.
Another more exact method is using catch cans.
To check the irrigation rate and uniformity, place cups, soup cans, or pie pans in several areas of the lawn.
Run your sprinklers for 15 minutes, then measure the depth of water in each can.
The amount should be roughly the same in each can-ifi it is not, adjust the sprinklers.
Multiply the average amount in the cans by four to give you the precipitation rate per hour.
The result is the exact amount of time you will water to supply one quarter inch of water per week.
Sloped areas will typically require shorter and more frequent periods firrigation to refill the soil because water runs down the slope before it has a chance to enter the soil.
Water sloped areas until runoff occurs, and repeat every few hours until you can easily insert a screwdriver into the soil.
Good Judgment with In-Ground Irrigation Systems
 Although you may set an automatic timer to irrigate several times each day-DON'T.
Instead, use the instructions above to decide when irrigation is needed.
Then use one of the following methods:
 Manually set the clock pautomatically rotate through the different stations.
Program the system for one irrigation to occur.
Set the automatic timer to provide one or two irrigations per week with either automatic or manual cutoff if significant rainfall or mild weather occur.
Factors that Cause Short Root Systems
 Nitrogen at wrong time of year
 Acidic soil conditions 
 Root injury 
 Cultural Practices to Promote Lawn Health and Reduced Water Use
 Because tall fescue is a deeper rooted plant than Kentucky bluegrass, by selecting tall fescue for your lawn you are already promoting water conservation.
There are several other maintenance practices that will promote deep rooting and help reduce water consumption.
Fall fertilization.
Most cool-season lawns only require 2 to 3 pounds of nitrogen per 1,000 square feet of lawn per year to remain healthy.
This fertilizer should be applied in the fall only.
Fertilizing in the spring and summer and heavy rates of nitrogen promote shallow roots and a greater need for irrigation.
Proper mowing.
By mowing taller during the summer months when coolseason lawns can be under heat stress, rooting is promoted and plants are able to seek out available water in the soil.
Compacted soils.
Hard soils will limit how much water is able to infiltrate the soil and will promote runoff.
Compacted soils should be aerified to promote infiltration into the soil and percolation through it.
Cool-season lawns should be aerified in the fall or spring.
Thatch reduction.
Thatch layers thicker than half an inch can promote shallow rooting and summer heat stress due to elevated crowns.
Dethatching or aerification should be performed to reduce thatch.
Kentucky bluegrass, zoysiagrass, and bermudagrass are all high-thatch producing species..
Limit traffic.
Although not a maintenance practice, keeping pets and kids off the lawn, especially during the heat of the summer, will promote a healthier lawn.
Lawns that are stressed from traffic require increased irrigation for recovery.
Taking proper care of your lawn using the above maintenance practices will result in a more dense lawn.
As density increases, water lost to evaporation from the soil decreases, which results in more water savings.
The following guidelines will help you use your irrigation system effectively:
 in lawn will need the same frequency of irrigation.
If, for example, you are watering a flowerbed under a oofoverhang, you may need irrigation even during rainy spells, especially on the east and north sides of buildings.
Probe the soil to find out.
When irrigation is necessary, apply about two thirds of an inch of water.
If surface occurs before irrigation is complete, apply only one half of the amount in future irrigations and let the system recycle after a few hours.
An efficient irrigation wets only the turfgrass zone without saturating the soil or causing run-off.
More frequent irrigation is usually required on the hotter, south-facing slopes where a half inch or more of thatch is present, when growing Kentucky bluegrass rather than tall fescue, when mowing at 11/2 inches in height rather than 21/2 inches in height, and certainly during the hottest time of year.
During summer vacations and other summer periods when close attention cannot be given to irrigation, consider not watering or setting the irrigation clock to apply about two thirds of an inch of water each week.
During fall and spring, since temperatures are cooler, the lawn can usually go 2 to 3 weeks without significant rainfall or irrigation.
Do not water according to a clock.
Be sure that sprinklers are adjusted so they are not watering sidewalks.
Do not water until the lawn needs water.
Fertilize only in the fall to promote drought tolerance.
Fix leaky hoses/spigots so water is not being wasted.
Water in the early morning.
Water can be applied anytime during the day without damaging turf.
However, evaporative water loss during irrigation is much higher during the heat of day.
Early morning watering is often advantageous since it removes dew and guttation water, which often encourage disease problems.
If a turf disease is evident, avoid late evening watering that would prolong leaf wetness.
Otherwise watering during late evening or night causes no problems.
Kentucky's continuously changing environment provides a challenge to planning an efficient turfgrass irrigation program.
However, by observing the lawn for signs of drought and performing cultural practices to promote plant health, over time your lawn can become a good mix of aesthetics and function while promoting water conservation.
Other Extension Publications Detailing Water Conservation
 Saving Water at Home  Saving Water Saves Energy: Tips for Conserving Water at Home 
David Franzen, Extension Soil Science Specialist, Professor Caley Gasch, Assistant Professor of Soil Health Christopher Augustin, Extension Soil Health Specialist, North Central REC Thomas DeSutter, Professor, School of Natural Resource Sciences, Soil Science Naeem Kalwar, Extension Soil Health Specialist, Langdon REC Abbey Wick, Extension Soil Health Specialist, Associate Professor, Soil Science
 Saline soils contain salts in great enough abundance that crop yields suffer and sometimes makes successful crop production impossible.
Excessive salts injure plants by disrupting plant water uptake and interfering with the uptake of nutrients essential for plant growth and development.
Saline soils often are referred to as "salty," "sour" or "alkali" by farmers and landowners; however, the proper name for these soils is "saline." The soil test used to characterize saline soils from nonsaline soils is the soil EC test.
The EC is the acronym for "electrical conductivity," which is the laboratory method relating electrical conductivity of a current through a soil with salts in the soil solution, called "soluble salts."
 Nearly all North Dakota soils have salt EC values greater than zero.
Recent North Dakota experiments indicate that soils with an EC value greater than 0.2 millimho per centimeter  the common term of electrical conductance used by soil scientists-have a negative effect on most North Dakota crops.
A mmho/cm is equivalent to a deci-siemen/meter , so 0.2 mmho/cm is equivalent to 0.2 dS/m.
A salt is any compound that is a product of the reaction of an acid with a base.
Sodium chloride  is a salt.
Gypsum , epsom salts
  and glauber salts  are salts.
Calcium chloride , magnesium chloride  and lime  also are salts.
Of this list, all are soluble salts except for lime.
Calcium carbonate is weakly soluble-about 100 times less soluble than gypsum-so it is not characterized as a soluble salt and does not contribute to salinity in soils.
In general, chloride salts are most active with respect to their negative effect on crop production.
A soil with EC dominated by chloride salts will result in lower crop yield, compared with a soil with similar EC dominated by sulfate salts.
Salts are the product of the mineral geology of North Dakota, the semiarid climate has lasted for thousands of years, and mineral weathering.
The underlying bedrock in North Dakota is shale.
Shale is a sedimentary rock developed from ancient muds released through regional soil erosion and deposited millions of years ago in shallow seas.
Nearly all of North Dakota was covered by a shallow ocean within the past 100 million years, and the erosion of the surrounding landscapes deposited clays into the ocean to great depths.
With time and pressure from overburden, the mud, along with all the minerals that were a part of the sediment deposits, including a great deal of sodium from the ocean saltiness, turned to rock.
North Dakota has experienced several glaciations within the past 100,000 years.
Each of these glaciers has moved ground limestone and granite from rocks from what is now Canada into North Dakota and left these materials behind.
Clays, silts, sands, gravel and rocks are the product of glacier deposition.
A glacier may appear to be like a bulldozer, but the ice is so deep and the pressures within it so extreme that the ice slowly churns internally, mixing disturbed sediments within the glacial ice.
From a distance, a glacier looks pristine and clear blue, but close-up, the ice is very dirty.
After the ice age glacial melt, this region has become semiarid, with annual precipitation ranging from about 22 inches in the east to as low as 14 inches in the west.
The lack of precipitation, particularly during the summer months of high evaporation, has resulted in many closed-basin landscapes with limited surface runoff into major streams and rivers.
The frequency of streams and rivers in the state is very low, compared with that of regions to our east.
The lack of clear drainage paths results in locally high water tables, which are expressed as "potholes" in the central region of North Dakota.
The dominant soluble salts in North Dakota are sulfatebased: calcium sulfate, magnesium sulfate and sodium sulfate.
In some areas, chloride salts are dominant.
That is particularly the case west of Grand Forks, where artesian flows from deep geologic sediments contain high levels of sodium chloride and other chloride salts due to their ancient ocean origins.
A soil continuously is changing.
Salts are brought to the soil surface  or leached to deeper depths  as a result of evapotranspiration and the amount and timing of rainfall.
This may seem counterintuitive, but salinity becomes worse in years of wetter-than-normal weather, and it is the worst when the weather turns dry immediately following a series of wet years.
The extent of salinity is reduced if dry weather persists for years.
For example, in a survey of farmers from Hettinger County who experienced a series of wetter-than-normal years immediately before a 1968 survey, 51% of the farmers reported that saline soils appeared since 1960.
More recently, many North Dakota farmers have noted severe salinity that developed in their fields since the most recent wet period that began in 1992.
A water table is defined as the depth of soil where the soil is saturated with water.
This is usually not the depth of water where one might drill a well, but it is the layer that has potential to feed water into the root zone or even to the soil surface, depending on the depth.
The water table depth is important because most of the ground water in North Dakota immediately at and below the water table has high levels of dissolved salt.
During periods of dryness, particularly in this region where the summer evapotranspiration is greater than seasonal rainfall, the water moves via capillary action upward.
The upward distance the groundwater can travel is directly related to the size of sediments  it travels through, but it also is restricted by soil cracks when present.
Figure 1 illustrates the relative rise of groundwater in soils from sands to silt loams.
In loams and clay loam soils, the capillary rise can be as much as 15 feet above the water table (Knuteson et al.,
 1989).
In silt loam soils, the capillary rise can be as much as 9 feet from the water table, while in sands it may rise only 2 feet.
Clay texture theoretically would have the greatest capillary rise, but in the field, clay-textured soils , crack when dry, and the cracks are a barrier to capillary rise.
Therefore, in North Dakota, the greatest capillary rise is usually in silt loam to very fine sandy loam soils because they have small pore sizes and they do not crack substantially.
Development of soil salinity is a product of soil water movement from "recharge" areas to "discharge" areas.
Recharge areas are where water soaks into soil in greater quantities than other nearby areas, and recharge soils tend to be leached of salt because the general movement of water is downward.
Discharge areas are soils where the salts reach the surface through upward capillary water flow or lateral flow along a soil matrix discontinuity in rolling terrain.
The patterns of saline soils in fields can be categorized as:
 Roadside or pond-side salinity 
 General salinity development in relatively flat landscapes on higher elevations 
 Hillside seeps due to water movement impeded by a limiting layer 
 Salinity develops along roadsides because the sediments under the roads are compact and do not allow surface
 water or groundwater to move to the opposite side of the water movement direction.
The water "stacks up" on the "waterward" side of the road.
Also, road ditches are common alongside roads, even if the water in the ditches flow to nowhere.
Road ditches hold water for days and sometimes weeks.
The ditches act like a long, narrow pond.
The water moves down the ditch bottom, and because it cannot move under the road, it moves through capillary action back into the field, and then capillary rise moves the water toward the soil surface with the salts it collects from the soil along the way.
The water evaporates near or at the surface and salinity results.
Figure 3.
Saline development in a nearly level landscape with a shallow, saline water table.
Continuous cropping will help decrease development.
Figure 2a.
Saline soil development near shallow streams, road ditches and sewage lagoons.
Figure 2b.
Use of a 30-foot alfalfa strip along borders of shallow stream, road ditch or sewage lagoon prevents fringe salt deposition.
Figure 4.
Saline development on a high clay content, subtly undulating landscape.
Salt accumulates on high clay content ridges, while the low spots are leached of salts.
Continuous cropping will help lower water table and stop salinity development.
Figure 5.
Saline seep development.
In coarser-textured soils, the salinity develops closer to the ditch.
In loam soils, the salinity develops 30 to 50 feet from the ditch, and in finertextured soils, the salinity develops 50 to 100 feet from the ditch.
A relatively low-salinity strip usually occurs immediately next to the ditch, and the salinity develops further into the field.
The movement of water from ditch to field is an arc , which results in the ditch lowEC/high-EC progression.
A management technique to remediate roadside salinity is to establish alfalfa at least 30 feet wide along the road or ditch in the lower-EC area.
Alfalfa is a "water hog," using up to 25 inches of soil water every year and rooting at least 8 feet deep two years after establishment.
Alfalfa roots act as a dam, so water moving from the ditch into the field is intercepted by the alfalfa.
Any water moving into the field beneath the reach of the alfalfa root will be too deep to move upward into the cropping root zone.
This technique is very effective but requires that the soil next to the road/ditch is not subject to flooding because alfalfa is not tolerant of flooded conditions.
In the Red River Valley and other parts of the state where the landscapes are dominated by ancient lakebed sediments , higher elevations that rise above the surrounding depressions, usually less than 6 inches difference in elevation, become saline due to lateral water movement from subtle depressions.
The depressions accumulate runoff from rainfall too intense to infiltrate the higher elevations.
Accumulation of water in depressions happens often because movement through clay soils, such as the Fargo silty clay loam series, is at most 1/3 inch of water infiltration per day.
Evidence for the pattern of water recharge in depressions and discharge on the "bumps" in the Red River Valley lies in the pattern of iron deficiency chlorosis  in soybean seeded in these fields.
The IDC results from the difficulty of soybean to take up iron in soils with a pH greater than 7 that have free carbonates.
The carbonates are present because although lime is not classified as a soluble salt, it is slightly soluble, and through the centuries, the lime is deposited in the landscape "bumps" just as soluble salts are deposited for much shorter time periods.
West of the Red River Valley, saline seeps are common in hilly landscapes.
Glacial soils exhibit "discontinuities" of
 Figure 7.
A saline seep along U.S.
Highway 83 in North Dakota.
The discharge area is where salts have accumulated.
Water needs to be managed between the discharge and recharge area.
textures within the soil matrix and parent material.
Glaciers did not melt in a day, but for years and maybe centuries.
When water moved fast beneath the melt, sands fell out of the water.
When the water moved more quickly, finer sands and silts were deposited, together with some clay that might have been fixed to the sands or silts.
When the water ponded and was still, clays were deposited.
The result is that many hill sediments have layers of sediments of varying textures.
When water moves downward through soil, it moves as a response to gravity.
If the water encounters a different texture-from loam to clay, clay to loam or sandy to
 loamy-the water does not move immediately into the new texture.
It has to reach 100% pore saturation before it can move into the new texture.
Once it approaches 100% pore saturation, the water tends to move along the texture change surface downward.
If the discontinuity is near the hillside, the water, along with the salts it carries, comes out of the hill, and the hillside discharge develops a saline soil that we call a "saline seep".
Soil Testing for Salinity
 Soils that are severely salt-affected usually have a bright white, crusty appearance when dry.
However, the severity of salinity extends well beyond the obvious area.
In soils that are wet, the white crust is not seen.
This is because the salts are in the soil solution.
Soils also can have high enough EC values just below the soil surface to reduce crop production severely without having the white surface appearance.
The extent and severity of salinity only can be diagnosed and mapped using soil testing, or an EC sensor or EM  sensor proxy.
Some laboratories, and nearly all scientific soil salinity publications, use the saturated paste method of salt analysis.
This method can be at least 10 times more
 expensive to use, and the method is more time-consuming to perform.
Recent NDSU studies have shown that for many soils, we have a reasonable conversion formula from the 1:1 EC values to a saturated paste EC value.
The r2  values of the relationships below in North Dakota were 0.90, but the relationship from South Dakota samples was 0.82 when outliers to the data were removed.
Saturated Paste ECe = ~~2.2 X EC1:1 EC1:1 = 0.45 X Saturated Paste ECe
 Personal handheld EC sensors are available through farm supply catalogues.
The handheld EC sensors are easy to use in the field for quick diagnosis.
Values from handheld EC sensors should be calibrated with lab results to directly relate their values to published values from lab methods.
A great variability occurs in the EC readings from different hand-held EC meters.
Differences also occur with soil temperature in EC values from hand-held instruments.
These instruments probably are best used qualitatively to demonstrate soil EC differences within fields to confirm that salinity is the issue affecting crop production.
To improve accuracy, handheld EC meters should be calibrated routinely with a standard calibration solution.
When testing soils, distilled water should be used because tap or well water likely has salts that can falsify the soil test.
However, they are not a substitute for laboratory analysis if one doesn't put the effort into calibrating the instrument with laboratory results.
Other qualitative instruments for mapping field EC ranges are the Veris 3100 soil EC sensor  and the Geonics Ltd.
EM-38.
The Veris 3100 measures
 Figure 8.
Veris 3100 EC sensor in use.
Figure 9.
EM38 in use.
EC, and the results may be calibrated to laboratory EC analysis with measurement of soil moisture at the time of sensing.
The EM38 maps EC through electro-magnetic conductance.
Electricity and magnetism are mathematically related, so the maps developed from each will be similar.
The Veris has to penetrate the soil and the EM38 does not.
Salinity management is water management.
Practices should dry the soil so capillary rise is minimized and leaching is maximized.
Cultivating increases soil salinity by turning a field darker in color, increasing capillary rise and decreasing leaching from destroying macropores.
Practices include planting salt-tolerant cash crops, full-season salttolerant cover crops and late-season cover crops ; perennial cropping; and drainage.
The goal of salinity management should be to reduce soil salinity to a level that allows profitable crop production.
Ignoring acres affected by salinity in a field results in wasteful expense for seed, fertilizer and pesticides, and the profitability of the field as a whole is reduced.
Therefore, the first step to salinity management is to map the field for EC.
The best sampling strategy is to sample in zones.
A good template for a zone map may be multiyear yield maps and satellite/aerial imagery.
Crops are good indicators of relative EC levels, and the patterns of reduced yields can be used to guide zone sampling effectively.
Also, soil EC or EM sensor maps are effective if the equipment is available for use or hire.
The reason high soil salinity is present is because of water tables too close to the soil surface.
As soil EC increases, its effects are amplified and the area affected grows larger because crop water use decreases as crop growth decreases.
The problem "feeds on itself" because salinity breeds more due to low crop water use at the fringes of the area of high salinity.
The importance of having something growing that is tolerant to the salinity present cannot be overemphasized.
Great advances have been made recently in our understanding of the tolerance of North Dakota-adapted wheat, corn and soybean cultivars to soil EC.
The values that appear in this publication are meant as a general guide.
A variability of tolerance to soluble salts occurs within each crop type.
Spring wheat, durum and winter wheat have a similar tolerance for salinity.
The soil salinity work in North Dakota has focused on spring wheat.
As Figure 10 illustrates, some yield reduction occurs with 1:1 EC greater than 0.2.
The yield reduction continues to about 85% of maxiumum at EC 2 and 70% at EC 4, but the reduction in productivity is very large at EC values greater than 5.
From about 60% yield potential at EC 5, productivity falls to less than 20% at EC 8.
Figure 10.
Relationship of spring wheat relative yield and soil 1:1 EC values.
Corn is more sensitive to soil salinity, compared with wheat.
At an EC of 0.2 , relative yields average about 100%, with considerable variability greater and less than 100% of about + 15%.
That level of tolerance persists until the soil reaches EC 1.
At EC values from 1 to 2, relative yields decrease about 10%.
From EC 2 to 3, relative yields decrease about 10%, and at EC greater than 3, for every 1 EC unit, yields continue to decrease about 15%.
At EC 5, yields decline to 20%.
Figure 11.
Relationship of field corn relative yield and soil 1:1 EC values.
Soybean is more sensitive to salinity than corn, canola, sunflower or wheat..
From EC 0.2  to 0.8, the average relative soybean yield is about 95%.
At an EC value of 1.5, relative yield falls to about 80%.
At an EC of 2.2, relative yield declines to 60%.
Producers have little hope of raising a profitable soybean crop at EC values greater than 3.
In addition, the presence of iron deficiency chlorosis  reduces yields more than indicated on Figure 12.
Soils with greater than 10% free lime at the surface, with EC values of 2 and favorable environment for IDC  have resulted in less than 20% relative yield in field trials.
Considerable variability in tolerance occurs in IDC and soil EC in soybean cultivars.
Generally, cultivars tested in this region with high IDC tolerance also tend to be more tolerant to high EC because North Dakota cultivar screening trials evaluate both simultaneously in the field and in greenhouse studies.
Barley has greater salt tolerance, compared with most other crops adapted to the North Dakota environment.
Recent work in Canada and Spain shows that barley yield response is similar to the relationship in Figure 13.
Yields of barley are almost unaffected by salinity until 1:1 EC of 2 in sulfate-dominated systems.
However, in chloridedominated systems, yield decreases with EC values greater than 1.
Most soil EC in North Dakota, with the exception of the area west of Grand Forks, is sulfate dominated.
Figure 13.
Relative six-row barley yields from two experiments in a chloride-dominated system.
[Experiment 1 Steppuhn and Raney ; Experiment 2 Bole and Wells ]
 Canadian research indicates that oats are nearly as salt tolerant, and depending on cultivar, sometimes superior to that of barley.
Oat productivity was at 50% that of yield in a nonsaline soil at 1:1 EC of 11.
Barley productivity was slightly greater at EC values greater than 8.
Figure 12.
Relationship of soybean relative yield and soil 1:1 EC values.
Figure 14.
Relative yields of spring/winter wheat, cereal rye, flax, barley and oats in a Saskatchewan experiment comparison.
Canola salt tolerance is similar to barley except at EC greater than 2.5.
Considerable variation occurs in salt tolerance among cultivars, however.
Communication with the seed company technical staff would be helpful in avoiding those cultivars with less tolerance than required.
Of the state-grown, nonsoybean annual legumes of greatest acreage, field pea is the least tolerant to salinity.
Based on threshold salinity from studies in Canada, field pea suffers little yield loss at 1:1 EC  From 0.6 on, field pea yield loss is about 15% for each unit of EC, as shown in Figure 17.
Figure 17.
General relationship of field pea yield and soil EC.
Sunflower usually is referred to as moderately salt tolerant, yet it successfully competes with higher EC-rated barley for acres that are grown to yield.
The initial response of sunflower to soil salinity is a low-threshold salinity.
This means that with an EC of 1, the potential yield drops by 5%.
The general relationship between sunflower seed yield and soil EC is shown in Figure 16.
Sunflower may be helpful in saline soil management once the EC is reduced through the use of more salt-tolerant crops because it will dry the soil to deeper depths.
However, it would not be the first crop to seed on soils with EC greater than 5.
Figure 16.
General relationship between sunflower seed yield and soil EC.
Much variation occurs among cultivars from this relationship.
The threshold salinity for lentil is about 0.6 mmho/cm .
This varies with cultivar from about 0.35 to 1 mmho/cm.
The EC for 50% yield is about 1.5, and can vary from about 1.25 to 1.75.
The genetic variability of salt tolerance among lentil cultivars is much less than in chickpea and faba bean.
Chickpea and Faba Bean
 The threshold salinity for chickpea and faba bean is about 0.75 mmho/cm .
The EC for 50% yield of chickpea is about 2.3, while 50% yield of faba bean is about 2.5 mmhos/cm.
A great genetic variability occurs in salinity tolerance within faba bean and chickpea cultivars.
Figure 18.
Average relationships of lentil, faba bean and chickpea cultivars with soil salinity in a Syrian experiment.
The threshold salinity for alfalfa in terms of a 1:1 EC is 1 mmho/cm .
The relationship of alfalfa to increasing salinity is 100% 14.5 , or about 14.5% yield reduction for each additional unit of EC.
New "salt tolerant" alfalfa varieties are available commercially.
These varieties do grow better in more saline areas than normal varieties.
However, if the EC1:1 is greater than 3 mmhos/cm, growth likely will be severely limited and a salt-tolerant perennial  would grow better in that area.
Figure 19.
Relative alfalfa yield with soil salinity, California.
Pinto Bean/Dry Edible Bean
 Pinto bean and all dry edible bean are very sensitive to soil salinity.
The threshold salinity is about 0.5 mmhos/cm, and for each 0.5 increment greater EC, the reduction in yield potential is about 20%.
There is variation in EC tolerance between cultivars.
Profitable yield of dry bean is unlikely at EC's greater than 1.5 mmhos/cm.
Figure 20.
Relative pinto bean yield with soil salinity,
 Colorado.
Recent cover crop experiments support the previous findings that cereal rye is tolerant of moderate to severe salinity.
Work by Francois et al.
indicated that a threshold salinity for rye would be a 1:1 EC value of about 3.8 mmhos/cm.
Relative yield still was about 30% at an EC of 7.
A zero yield would be predicted by their work at an EC of 10.
The work by Fowler and Hamm  indicates that rye is similar to oats and barley in salt tolerance until the soil EC reaches about 6.
The reduction in productivity with EC greater than 6 with each unit increase in EC is much greater in rye than in barley and oats.
Safflower is remarkably adapted to highly saline soils.
In a California experiment , researchers found no differences in seed yield up to at least a 1:1 EC value of 3.5 mmhos/cm , although plant height was reduced.
The crop was able to compensate for the higher salinity by reducing some parameters of growth, but the salinity did not affect yield.
Other studies have noted that once soil EC  reaches 5, yield reductions are quite large.
An EC of 6.5 had a yield reduction of 25%, compared with lower EC values.
Although flax is a Middle Eastern crop, its salt tolerance is less than it is for field corn.
Perhaps this is because flax was grown for millennia in the Nile Valley, where low-salt water  leached out salts from field soils before seeding.
The threshold salinity for flax is about 0.5 mmho/cm.
The percent of relative yield with 1:1 EC is 10% with 0.6 mmho/ cm , 25% with 1 and 50% at 1.5.
The experiments performed by Fowler and Hamm  indicate a greater tolerance to salts, with similar productivity to an EC of 3 , and 50% productivity to about EC 9.
North Dakota field observations generally support its general intolerance to salt, as indicated in Table 1.
If the EC1:1 is greater than 4 mmhos/ cm, salt tolerant forages provide a much greater chance of success than cash crops or salt tolerant alfalfas.
However, the salt tolerant grasses may be slow to establish as by the time these are planted are in July or August and the grasses should be planted in May.
Table 1.
Approximate threshold salinity values for field crops and percent reduction in yield due to salinity.
% Yield reduction due to salts
 1:1 EC,	10	25	50	100
 Crop	mmhos/cm	mmhos/cm necessary to reduce relative yield
 Alfalfa	1	1.6	2.5	4.2	7.9
 Barley	2	3	4.5	6	12
 Canola	1.5	2	3	4	7.5
 Chickpea	0.75	1	1.6	2.3	4
 Corn	1	2	3	4	5.5
 Dry bean	0.5	0.8	1.3	1.7	3
 Faba bean	0.75	1	1.75	2.5	4.5
 Field pea	0.3	1	1.8	3.75	7
 Flax	0.5	0.6	1	1.5	3
 Lentil	0.6	0.75	1.25	1.5	3
 Oats	2.3	3	4	6	8
 Rye	3.8	5.4	6.3	7.2	10
 Safflower	3.5	4.5	6.5	8	14
 Soybean	0.6	1	1.75	2.3	4
 Sugarbeet	3	4	6	8	12
 Sunflower	0.75	1	2.2	5	10
 Wheat	1	2	3.5	5.5	11
 Table 2.
Approximate threshold salinity values for forage grasses and percent reduction in yield due to salinity.
% Yield reduction due to salts
 salinity,	10	30	100
The major drawback to all of this is that much of the water in storage in mainstem reservoirs in Wyoming will be used up this year, leaving a lesser amount in the reservoirs for the 2022 growing season.
An above-normal snowpack and runoff in the mountains will be needed to fill the reservoirs.
The report, created at the Conservation and Survey Division in the School of Natural Resources, was written, researched and produced by Young, Mark Burbach, Leslie Howard, Susan Lackey and Matt Joeckel.
When the university reopens, the report will be available for $7 from the Nebraska Maps and More Store, 3310 Holdrege St.
Phone orders will be accepted at 402-472-3471.
Download the free PDF.
Plant transpiration increases as corn leaf area increases.
Transpiration is the mechanism by which water moves from the soil through the plant into the atmosphere.
The greatest water demand for corn occurs from the late vegetative stages through the blister stage and for soybean from the early pod set through the mid seed fill stages.
In other words, the greatest demand for transpiration occurs during periods of rapid growth.
Table I.
Normal water requirements for corn, grain sorghum, soybeans, and dry beans between various stages of growth and maturity in Nebraska.
For Soybeans R4 crop stage, the stage of growth is known as end of pod elongation, the approximate days to maturity is 37, and the water use to maturity is 9.0 inches.
For Soybeans R5 crop stage, the stage of growth is known as beginning of seed enlargement, the approximate days to maturity is 29, and the water use to maturity is 6.5 inches.
For Soybeans R6 crop stage, the stage of growth is known as end of seed elongation, the approximate days to maturity is 18, and the water use to maturity is 3.5 inches.
For Soybeans R6.5 crop stage, the stage of growth is known as leaves begin to yellow, the approximate days to maturity is 10, and the water use to maturity is 1.9 inches.
For Soybeans R7 crop stage, the stage of growth is known as beginning maturity, the approximate days to maturity is 0, and the water use to maturity is 0.0 inches.
IN-CANOPY SPRINKLER APPLICATION FOR CORN: WHAT WORKS AND WHAT DOESN'T
 In-canopy sprinkler application in fully developed corn after tasseling is affected by nozzle spacing, nozzle height, row orientation with respect to center pivot travel, and nozzle type.
Incorrect combinations can lead to poor in-canopy uniformity.
In general, as nozzle spacing increased from 5 to 10 ft, in-canopy uniformity decreased.
The 4 ft nozzle height was worse than the 2 and 7 ft nozzle heights in terms of in-canopy uniformity.
Circular  rows almost always have better in-canopy uniformity than straight  rows.
Spinner nozzles had better incanopy uniformity than plate nozzles at the 2 and 7 ft heights.
In-canopy center pivot sprinkler irrigation is gaining popularity in much of the Great Plains region.
However, uniformity of applied irrigation can be greatly affected by canopy distortion of the sprinkler pattern.
Some irrigators are experimenting with wide-spaced in-canopy sprinklers for irrigation of corn as a means of reducing investment costs.
However, there is little research information available on the effectiveness of this strategy.
The height of the sprinklers also has a direct bearing on the magnitude of the distortion.
Redistribution of the applied water within the crop canopy is also affected by the orientation of the corn rows with respect to the center pivot sprinkler travel direction.
Nozzle type  may also influence distribution of in-canopy sprinkler application.
This report summarizes the 1996 in-canopy sprinkler application research conducted at the KSU Northwest Research Extension Center at Colby, Kansas.
The results are from fully developed corn plants after tasseling.
It should be noted that the canopy conditions roughly represent the last 30-40 days of the irrigation season.
The results do not represent the whole corn growing season, but do represent a time when irrigation needs are critical.
The study was conducted on a fully developed corn canopy from August 1-3, 1996 at Colby, Kansas.
Corn was planted in 30 inch rows at a plant population of 33, 100 plants/acre  in both circular and straight rows under a center pivot sprinkler irrigation system.
This resulted in separate plot areas with rows parallel or perpendicular to the center pivot travel direction.
The plot areas were centered at radii of 277, 327 and 377 ft on a two tower center pivot.
Throughfall is water that reaches the soil surface by falling through the leaves of the plant canopy.
Stemflow is water that reaches the soil surface by flowing down the plant stem.
Both components must be measured to get estimates of water distribution at the soil surface.
Throughfall was measured in pans 16 inches long by 26 inches wide  and 4.5 inches in height.
Throughfall was converted to an equivalent depth by dividing the measured amount by the pan area with appropriate conversion factors.
Stemflow was measured with special collection units made from a 6 inch section of split 2 inch PVC pipe taped around the base of the corn stalks.
Stemflow was converted to an equivalent depth by relating the measured amount to the land area represented by an individual plant.
Trials were replicated at three radii  with a single nozzle at each location.
Flowrates at the three radii were 5.08, 5.80 and 6.85 gpm using #30, #32 and #35 Nelson 1 nozzles with 10 psi pressure regulators.
Treatments variables were nozzle height  and nozzle type.
Each height and nozzle type combination was replicated at each radii.
The location of the throughfall and stemflow collection units are fixed at the three radii, so the replication is made by repeating irrigation events.
The six events  were conducted over a three day period.
Stemflow and throughfall was also measured for a coincidental 1.2 inch rainfall event that occurred the evening of July, 31, 1996.
Stemflow and throughfall was measured from a single nozzle at each of the three radii for the left half of each pattern for both parallel and perpendicular rows.
Preliminary tests indicated a potential in-canopy wetted radius of 20 ft for the highest sprinkler height.
Collection units were dispersed over the 20 ft distance with one throughfall pan for each interrow and one stemflow collection unit for each row.
This translates into 54 stemflow and throughfall collection units each.
Each throughfall pan was further divided into three equal size compartments 
 to give better breakdown of water distribution.
A single event could potentially consist of 162 measurements of throughfall and 54 measurements of stemflow, although distorted sprinkler patterns reduced some of the amounts to be measured to zero.
The single nozzle arrangement was used to facilitate the use of superpositioning to "mirror" the amounts catched.
This allowed the simulation of various nozzle spacings.
The center pivot sprinkler for these trials was operated at a speed that would apply 1.5 inches if all nozzles were operating on a 5-ft spacing.
For this system, it is operating at a linear speed of 0.88 ft/minute for 3% of the 1 minute cycle at the 377 ft radius.
This slow speed allows for larger measured sample and therefore more accuracy as measurement errors would constitute a smaller fraction of the sample.
The applied amount does not affect the relative sprinkler water distribution pattern, only the magnitude of the amounts.
The collected data was analyzed using appropriate statistical procedures.
The under-canopy water distribution was calculated for various simulated nozzle spacings.
The unadjusted Christiansen Uniformity Coefficient was calculated for each treatment and row orientation as a index of performance.
These are not truly the CU for these in-canopy systems because they are using "mirrored" data, but these values do serve as a relative index between the comparisons in this study.
Water application pattern as affected by row orientation and nozzle spacing
 As outlined in the procedures, the concept of superposition was used to mirror the application from the single nozzle to get the resultant water pattern for nozzle spacings of 5, 7.5 and 10 ft.
Figure 1 shows the water application patterns at the ground surface from the Nelson Spinner nozzle applying water from a height of 2 ft for both the circular corn rows  and the straight corn rows.
It is helpful to remember in interpreting the data, that a flatter pattern for a given nozzle spacing represents the best water distribution.
For example, in Figure 1, the circular rows with the 5 ft nozzle spacing  have a better water distribution pattern than the perpendicular rows with the 5 ft nozzle spacing.
Application variation [ Avar = 100 X / Maximum amount) ] was 20% for the circular parallel rows and 54% for the straight perpendicular rows.
This is a considerable difference between the two row orientations.
Normally for
 sprinkler applications on bare soils, it is considered desirable to limit the variation to less than 10% along the sprinkler lateral.
However, there are other factors affecting distribution for in-canopy application and the 10% rule is probably not acceptable.
Figure 1.
Water application pattern as affected by row orientation and nozzle spacing for spinner nozzles at the 2 ft height in a fully developed corn canopy after tasseling.
The differences in Avar for the two orientations with the 5 ft nozzle spacing is considerable, but it should be noted that it occurs over a distance less than 2.5 ft.
In some cases, depending on field slope, soil type, tillage practices and residue levels, soil water infiltration differences may buffer out the water application differences over this short distance.
Hart  concluded from computer simulations that differences in irrigation water distribution occurring over a distance of approximately 3 ft were probably of little consequence and would be evened out through soil water redistribution.
However, if chemigation  is a consideration, these differences might be
 very significant.
If field characteristics encourage runoff or ponding in low areas, these differences would probably be unacceptable.
Perfectly perpendicular rows only exist for two locations in a center pivot sprinkler field with straight rows, so for straight rows the application varies from parallel to perpendicular.
In ridge-till situations when the rows are perpendicular, a large percentage of the center pivot capacity  is being applied to just a very few furrows in in-canopy application.
Figure 1 also shows the effect of wider nozzle spacings on the water distribution pattern.
It is helpful to remember in interpreting this aspect of the data, that even if the magnitude of the variation in application amounts are similar that the shorter the trend line the better the potential distribution.
For example, the circular rows with the 10 ft nozzle spacing has a somewhat similar Avar to the perpendicular rows with the 5 ft nozzle spacing.
However, for the 10 ft spacing, there is a trend of decreasing water application over a much longer distance, and so potentially larger areas would have incorrect application amounts.
The differences between Avar for the circular parallel and perpendicular rows for the 10 ft.
nozzle spacing are 69 and 92%, respectively.
It is highly probable that these amounts of application variation over the distance of 5 ft would lead to runoff or ponding in the locations with over application and crop water stress in the locations with under application.
Figures 2 and 3 show the water application patterns for circular parallel and straight perpendicular rows for all three simulated nozzle spacings, 5, 7.5 and 10 ft for the spinner nozzle at the 2 ft height.
Acceptable nozzle spacings/row orientation combinations for the spinner nozzle at 2 ft height are probably limited to 5 and 7.5 ft spacings with circular rows and to the 5 ft nozzle spacing with perpendicular rows.
Avar for these combinations were 20, 44 and 54%, respectively.
This conclusion assumes chemigation is not being used  and that runoff is controlled to a small  localized area with tillage management  or by residue management.
In-canopy uniformity as affected by sprinkler height and nozzle type
 Another way of characterizing the performance of in-canopy sprinkler distribution would be to calculate the Christiansen Uniformity Coefficient, CU.
For those familiar with CU values, it should be re-noted that the in-canopy uniformity values expressed in this paper are not true CU values because they are using "mirrored" data, but they do serve as a relative index between the comparisons in this study.
In addition, these values are not adjusted using
 the techniques of Heermann and Hein, 1968) for the center pivot radius since they are over a very short distance.
For these reasons, the values in this paper are referred to as in-canopy uniformity, to distinguish them from true CUs.
Figure 4 shows the in-canopy uniformity for spinner nozzles at heights of 2, 4 or 7 ft at nozzle spacings of 5, 7.5 or 10 ft for both circular parallel and straight perpendicular rows.
It can be seen that the 4 ft height is always the worst height for a given nozzle spacing and row orientation.
This may not be surprising since this is about the corn ear height, an area of high leaf density at this portion of the season.
Distortion of the sprinkler pattern is very high at the 4 ft height.
For the circular parallel rows, the 2 ft height is better than the 7 ft height, but the opposite is true for the straight perpendicular rows.
This may seem confusing.
However, some previously unmentioned factors are beginning to have an influence.
As the nozzle is raised in the canopy, the flowpath to the soil surface changes from almost equal amounts of stemflow and throughfall to larger amounts of stemflow.
This is indicated by the "spikes" in the 4 and 7 ft height lines in Figure 5.
The spikes correspond to the locations of the corn rows and are stemflow amounts.
Because these spikes affect the in-canopy uniformity, the 7 ft height is worse than the 2 ft height for the circular rows.
For the perpendicular rows, there are some spots in the center pivot travel that give a relatively straight path of throughfall that is not heavily distorted by the nearby plant row.
The in-canopy uniformity at 7 ft can be better than at the 2 ft level for the straight perpendicular rows because of less distortion.
Figure 2.
Water application pattern for circular parallel rows at various nozzle spacings for spinner nozzles at the 2 ft height in a fully developed corn canopy after tasseling.
Figure 3.
Water application pattern for straight perpendicular rows at various nozzle spacings for spinner nozzles at the 2 ft height in a fully developed corn canopy after tasseling.
Spinners had considerably better in-canopy uniformity than plates at the 2 ft height  This may not be surprising since the spinner has a rotating water impingement plate that has multiple angles for the diffused water.
Conversely, the plate nozzle is static and has only one angle of water diffusion.
In essence, the spinner nozzle allows searching of the crop canopy for holes to better diffuse the water.
At the 4 ft level, the plate nozzle showed better in-canopy uniformity than the spinner nozzle.
One possible reason is that the plate nozzle may be diffusing water at a higher kinetic energy which may allow better penetration.
Another possibility may be that the multiple diffusion angles of the spinner may be causing more partitioning of the sprinkler application into stemflow as the height is raised in the canopy.
At the 7 ft height there was not great differences in in-canopy uniformity as affected by nozzle type but the spinner did have higher values.
Figure4.
In-canopy uniformity as affected by nozzle spacing and row orientation for spinner nozzles at various heights in a fully developed corn canopy after tasseling.
The uniformity between corn rows was calculated from closely spaced containers.
Figure 5.
Water application patterns showing evidence of spiking due to stemflow increases as nozzle height increased from 2 to 4 to 7 ft in a fully developed corn canopy.
Figure 6.
In-canopy uniformity as affected by nozzle spacing and nozzle type for circular parallel rows at various heights in a fully developed corn canopy after tasseling.
The uniformity between corn rows was calculated from closely spaced containers.
Table 1 shows the some of the application characteristics for all the comparisons in this study.
Examining the rainfall event shows that even Mother Nature can present uniformity differences.
The rain storm in this case was driven by a 17 mph  wind from the East-Northeast.
This resulted in nearly perpendicular application for the circular rows and nearly parallel application for the straight rows, resulting in in-canopy uniformities of 65 and 86%, respectively.
In reviewing of this table and additional water application patterns not shown, it is the author's belief that in-canopy uniformities can be characterized by the following categories:
 Good to Excellent 80-100% Fine for most application scenarios
 Fair to Good 70-80% Chemigation may require symmetry
 Marginal to Fair 60-70% Probably will cause some problems
 Unacceptable < 60% There are better methods
 Summarizing this section, the worst height in terms of in-canopy uniformity for a spinner nozzle is at 4 ft in a fully developed corn canopy.
Row orientation makes a large difference in in-canopy uniformity at the 2 and 7 ft height.
Spinners performed better than plates at the 2 and 7 ft heights.
In-canopy uniformities as high as 93% are possible with circular rows using spinners with a 5 ft spacing.
Planning To Irrigate: A CHECKLIST
 Tom Scherer, Extension Agricultural Engineer
 installing an irrigation system on a piece of land requires a great deal of planning and a significant financial investment.
Before any irrigation equipment, including drilling the production well, can be placed on the land you will need a water permit from the North Dakota State Department of Water Resources.
On most farms, the number of irrigated acres is usually much less than the dryland acreage.
Therefore, irrigation must be integrated into the total farm enterprise.
Irrigation requires intensive fertility management, improved weed and insect control, timely identification of disease problems and above all accurate record keeping.
Allocating the time for managing the irrigation system is a key factor in the success of any irrigation project.
The need for information and assistance from both public and private sources becomes more critical under irrigation.
When considering an investment in irrigation, one of the first questions to be asked is, "Why do I want to irrigate?" The primary reason should be to increase net farm income over dryland production.
Increased income may result from the ability to grow longer-season crops or a high value specialty crop, provide an assured forage supply for animal operations or improve crop rotations.
Irrigating as insurance against insufficient rainfall, just because the water is available or because you have fields with irrigable soils are poor reasons.
The higher yields possible with irrigation require greater management skills and inputs in the form of fertilizer, seed and possibly pest control.
When you have decided that irrigation will fit into your farming enterprise, use the checklist below to guide the irrigation development process.
1.
Determine if your soils are irrigable.
2.
Determine the quantity and quality of water required.
3.
Determine the availability of power and type of irrigation equipment.
4.
Does irrigation pay in your farm enterprise?
5.
Can you can obtain financing?
6.
Select and manage your irrigated crops.
Step 1: Determine if Your Soils are Irrigable
 Not all soils can be irrigated due to various physical problems such as too much slope, low infiltration rates or poor internal drainage that may cause salt buildup.
Soils are classified as either irrigable, conditional or non-irrigable and are defined in the following way:
 Irrigable soils have no restrictions for sustained irrigation using proper application rates, amounts and water quality.
Conditional soils have restrictions for sustained successful irrigation due to such factors as water table elevation, layers of low permeability, potential for salinization, steep slopes and other problems.
Some restrictions can be corrected with drainage.
Conditional soils should have a detailed field level soil survey conducted, ideally by a registered soil classifier, before irrigation is developed.
Nonirrigable soils have severe restrictions to irrigation and should only be developed where they are minor inclusions into irrigable soils.
Installing a Subsurface Drip Irrigation System for Row Crops
 The success of a subsurface drip irrigation  system for row crops depends on its design, installation, operation, management and maintenance.
All phases are equally important.
This publication describes the components and installation of an SDI system.
Steps in the installation process are:
 installing the mainlines, manifolds  and flush lines;
 connecting the tape with the manifolds and flush lines;
 Components of the irrigation system
 The main components of an irrigation system are the filters, mainlines, manifolds , field blocks, flush lines, drip lines  and accessories.
All the drip lines  connected to the same submain make up a field block.
Several field blocks can be grouped together as one station and operated simultaneously.
Water is supplied to drip lines in the field blocks by the manifold.
In some permanent systems, the drip lines are also connected to a flush line so that accumulated sediments can be flushed from the drip lines using a
 Figure 1.
Typical layout of a drip irrigation system.
single valve.
The flush line is also called a collector line.
In some field blocks, particularly those with longer lateral lengths , the flush line may also be connected to the mainline by a separate valve and manifold, so that water can be supplied to both ends of the drip line.
This prevents excessive pressure loss in longer drip lines.
The flush line should always contain a flush-out valve, even if it is also used as a supply line.
Seasonal systems do not use flush lines; their tapes last only a season or two before needing to be replaced.
The drip lines may be connected to the manifold in several ways as shown in Figure 2.
The manifold can be placed at the soil surface or buried.
Figure 2.
Typical connections from manifold to drip lines or laterals.
In this case the manifold is connected to the drip line with a stainless steel wire.
The injector consists of a roll that holds the tape and a shank that opens the soil to bury the tape.
As the shank opens the soil, the tape is guided into the soil, usually through a curved pipe mounted behind the shank.
The shank must be durable enough to resist the impact of rocks and other obstructions in the soil.
The pipe that is mounted behind the shank should be smooth and curved so it does not tear the tape.
Drip line injection is shown in Figures 4 and 5.
The steps for injecting the tape are:
 1.
Mark the locations where the manifold and flush lines will be installed, using flags or lines of gypsum on the field.
2.
If the tape will be more than 8 inches deep or the soil is rocky, pre-rip the rows using the shank alone without the tape.
Pre-ripping makes depth and spacing more uniform and helps to clear away rocks that could damage the tape.
Pre-ripping is not necessary on easily plowed fields.
Figure 3.
Toolbars with drip tape injector.
Figure 4.
Installing the drip tape.
Figure 5.
Changing a roll of drip tape in the middle of the field.
Figure 6.
Drip line splicing.
3.
Be extremely careful not to cut the tape when unwrapping the plastic that covers the roll.
Careless or rough handling of the tape may lead to major leaks after installation.
4.
Lay the tape down with the emitters facing upward to avoid soil plugging.
The rolls have indicators showing the direction of the emitters.
5.
Just before lowering the shank, anchor the tape temporarily by hand or with a stake SO it can be pulled into the soil.
Stakes can be made of welding rods or rigid wire.
6.
The depth of the tape will depend on the crop.
Tape has been installed 12 to 14 inches deep for permanent SDI systems in crops such as cotton and alfalfa in the St.
Lawrence, Trans-Pecos and Lubbock areas.
In the Lower Rio Grande Valley, tape has been installed 2 to 6 inches deep for vegetable crops such as onions and melons.
Check to see that the tape is at the correct depth and adjust the control roller if necessary.
7.
If the drip tape runs out in the middle of the field it must be spliced.
A 3to 4-inch-long PVC tube can be used to splice the old and new rolls together by securing the tape to the ends of the tube using two stainless steel wires or special connections.
Trenching may be necessary for mainlines, manifolds and flush lines.
Manifolds and flush lines sometimes can be installed above the soil surface, with a trench only for the mainline.
Trenching can be done with a rotary trencher or a backhoe.
A rotary trencher is recommended.
The steps are as follows:
 1.
Before trenching, pack the tape on the field with a tractor, passing a wheel on each side of the tape.
2.
Trenches should be 2 feet wide or the size of the bucket on the backhoe.
The trenches for the submains should be at least 16 inches below the depth of the drip line and 1 foot below the flushing line.
3.
Expose the tape from the ditch forming a triangle.
Leave enough space to work with the hands and tie the drip line to the PVC pipe.
4.
Level and pack the ditch bottoms with soil that falls from exposing the tape.
5.
Place some flags where each station ends.
Figure 7.
Pack the soil with a tractor tire on each side of the ditch.
Figure 8.
Cross-section of the drip tape connection to the PVC manifold.
Figure 9.
Drilling the manifold , inserting the grommet and the PVC hose , and connecting the PVC hose to the drip tape.
Connecting drip lines with manifolds and flush lines
 If manifolds and flush lines are below the soil surface:
 There are several ways to make the connections.
The following example uses grommets and barb fittings.
1.
Drill a hole in the top of the manifold or flush line just where the tape is to be connected..
Use a 13/16-inch drill bit for #700 grommets.
Use a 9/16-inch drill bit for #400 grommets.
2.
Clean the hole with a knife to remove all plastic residue.
This plastic could produce leaks later in the season.
3.
Insert the grommets in the hole.
4.
Pre-assemble the insertion to the PVC hose, using glue.
5.
Soak the insertion with soapy water so it will fit easily into the grommet.
6.
Insert the PVC hose into the tape, being careful not to bend the hose.
7.
Tie a stainless steel wire around the tape.
If submains and flush lines are above the soil surface:
 The most common connection method is to insert small-diameter PE tubing  into the PVC, PE or lay flat hose as shown in Figure 10A.
A hole is then made on the drip line and the tubing is inserted in the drip line.
The tubing is attached to the drip line with a piece of folded tape.
Another method is to use connections as shown in Figure 10b.
Figure 10.
Connecting the drip tape to a manifold above the soil surface with tubing  and with a fitting.
Run each station for 4 hours and check for leaks.
If there are leaks in the middle of the field, make a hole and splice the tape.
If there is a leak in the manifold, the connection between the tape and manifold needs to be redone or the plastic remnants need to be removed from the hole drilled in
 Figure 11.
Typical layout of the pumping station showing the filtering equipment.
the manifold.
If there are no leaks, GENTLY push some loose soil into the ditch.
Then add water to the ditch so the soil will settle around the pipe to hold it and prevent it from moving.
Do not move too much soil at once, as this can damage rigid pipe and connections.
Pack the soil, then add more soil and water until the ditch is filled.
The filters should be installed over solid surfaces, preferably concrete bases.
A typical set up of the filtering equipment and its components is shown in Figures 11 and Filtration Process Back-Flushing Process 12.
Filters remove the solid matter suspended in the water to keep the drip emitters from clogging.
The most Inlet Inlet common filtration size for subsurface Back-Flush Valve drip irrigation is 200-mesh , which represents an -> opening of about 0.003 inches.
Centrifugal filters, media or
 sand filters, and screen and disk filters are commonly used, often in combination.
For example, if water comes from an aquifer and some sand is being pumped, a centrifugal filter can be used to trap the sand, followed by a disk or sand media filter.
When water comes from a canal, it is common to have both a media filter and a screen filter.
Media filters need the most adjustment during installation.
Media filters consist of several tanks that filter the water, and each tank needs to be back-flushed.
This is done by passing clean water through a tank in a reverse direction; the clean
 Figure 12.
Filtration and back-flushing process.
water comes from the other tanks that are not being back-flushed.
Tanks must be backflushed when they are dirty, a condition that is usually indicated by an increase of pressure of about 10 psi.
A sand media filter has some pressure loss-about 3 to 5 psi.
Incorrect installation can increase the loss to about 10 to 25 psi.
Follow these steps to install a sand media filter:
 1.
Order only pre-washed gravel.
2.
Install the gravel and the sand at the depths recommended by the manufacturer.
3.
Close all the valves downstream of the tanks.
4.
Open the main valve.
5.
Open completely the back-flush valve of one of the media tanks.
Then open the back-flush flow rate adjustment valve slowly.
Remember that the back-flush flow rate adjustment valve should be calibrated just one time.
The back-flush flow rate should be determined from visual observation.
The back-flush flow rate should be sufficient to expand the media bed and separate the sand into individual particles.
The smaller particles and those with lighter specific gravity than the media need to be carried out of the tank.
The back-flush flow rate should not be excessive to limit the amount of sand removed from the tank.
The first time a tank is back-flushed it is normal to remove some sand.
Use a 100-mesh screen at the discharge to catch the sand discharged.
6.
Repeat the process, opening the back-flush valve of each tank.
7.
Adjust the frequency and the time of the back-flushing operation.
It is important to back-flush at least once per day and to control the back-flushing automatically by triggering it with a differential pressure switch.
This switch is usually set to start when the differential pressure increases to 5 to 8 psi.
Figure 13.
Filtration equipment.
WATER LOSSES ASSOCIATED WITH CENTER PIVOT NOZZLE PACKAGES
 T.A.
Howell, Ph.D., P.E.
Research Leader  USDA-Agricultural Research Service P.O.
Drawer 10 Bushland, Texas 79012-0010 Voice: 806-356-5646 Fax: 806-356-5750 Email:tahowell@cprl.ars.usda.gov
 Sprinkler packages that are available and used in the Great Plains of the United States are widely varied from older impact heads to more modern spray heads or various rotator designs and have an assortment of application and/or placement modes.
This paper will address common sprinkler packages in use on center pivot sprinklers.
Sprinkler packages are designed and selected  for a variety of reasons.
Often high irrigation uniformity and application efficiency are cited as priority goals in selecting a particular sprinkler package or sprinkler application method.
In practice, many sprinkler packages can achieve the desired design and operational goals equally well at or near the same costs.
Management, maintenance, and even installation factors can be as important as the selection of a package or application method.
This paper discusses the desired traits of various sprinkler packages and sprinkler application modes and discusses the anticipated water losses that might impact both irrigation uniformity and efficiency.
In most cases "generic" descriptions are used rather than individual commercial names of sprinkler manufacturers.
End-gun effects are not discussed or addressed to a significant degree.
TYPES OF SPRINKLER PACKAGES
 The first sprinklers used on center pivots were impact heads adopted from hand-move, portable sprinkler lines that had a large angle  of discharge to maximize the water jet trajectory.
Many of these were single nozzle types, but some used double nozzles to improve the uniformity for the pattern.
Early center pivot design sprinkler spacing was about 32 ft  with impact sprinklers while some later designs used a variable spacing (closer
 towards the outer end of the pivot).
Two principal design modes were commonly used for these packages 1) constant  spacing with variable nozzle diameters along the center pivot to vary the sprinkler discharge or 2) almost constant nozzle discharge and head selection with variable spacing.
It was common to mount larger sprinklers on the ends of the pivot  to cover more land area with a fixed pivot length.
A third design mode called the semiuniform spacing  is a combination of these two other design modes.
The variable spacing mode is easier to apply to rotator-spinnerspray heads but greatly complicates the center pivot pipeline design and the sprinkler package installation and maintenance.
The constant outlet spacing is quite common, particularly for closely spaced systems  used with LEPA , LESA , or LPIC  methods of application.
The sprinkler outlet spacing for non LEPA/LESA type systems with the constant spacing are often spaced up to 10 ft  apart.
This spacing type is still used for pipeline mounted low angle impact sprinklers or spray heads on drops.
One concern with this spacing design can be the larger sprinkler discharge rate at the outer end requiring large nozzles with larger droplets.
Additionally, it can result in the requirement for higher operating pressures in some cases.
These two factors larger nozzles and higher operating pressures can cause infiltration problems due to soil crusting and/or runoff difficulties from the high instantaneous application rates.
When LEPA and LESA are not used, the semiuniform spacing can rather conveniently be used with a 10 ft  outlet spacing uniformly along the pivot pipeline.
Allen et al.
suggested that the first third of the pivot length might use a 40 ft  sprinkler spacing, the middle third might use a 20 ft  sprinkler spacing, and the outer third might use a 10 ft  sprinkler spacing with the unused outlets plugged.
This concept would also work with a 5 ft  outlet sprinkler spacing along the pipeline that might offer conversion options to LEPA, LESA, or LPIC application methods.
This semiuniform spacing mode avoids many of the problems with larger nozzles.
The application uniformity will depend on many factors of the design and several operational factors , effect on pressure at the outlet, etc., soil type, etc.) The main sprinkler factors affecting uniformity are the sprinkler spacing, the sprinkler device type -its diameter of throw, application pattern type, operating pressure, nozzle and spray plate design, the elevation of the application device above the ground, and any crop canopy interference.
Center pivot sprinklers can be classified generally into two broad types -impact sprinklers and spray heads.
Within the impact type, nozzle angles can vary from the older type heads with higher trajectory angles  to lower angle impact sprinklers  that are typically mounted on top of the center pivot pipeline.
Impact sprinklers are usually constructed using brass or plastic materials.
They operate with a spring and heavy jet deflector arm with each arm return  imparting a momentum to rotate the nozzle jet slightly.
It might take up to 100 or more deflector arm returns to cause the impact sprinkler head to make a full rotation.
The rotation speed depends on several design factors of the deflector arm; its mass and the bearing in which the sprinkler rotates.
Nozzles can be simple "straight bore" types  or various design types that provide flow controls by compensating the nozzle discharge -pressure relationship to provide a more constant discharge independent of the operating pressure.
The operating pressure of most impact sprinklers is in the range of 25 to 40 psi , but the operating pressure is higher for larger sized nozzles.
Impact sprinklers typically have a 3/4 in.
NPT male end , but some larger nozzles may require a 1 in.
NPT  size to reduce pressure losses across the pipeline mounting coupling.
Impact sprinklers have an advantage because they typically have a large radius of "throw", thereby having a larger wetted area and smaller instantaneous application rate  that can nearly match the soil infiltration rate with fewer runoff and erosion difficulties.
Because they must rely on the hydrodynamics of the water jet and its breakup for the irrigation application, transport mechanism, they are affected to a greater degree by winds and subject to greater pattern distortions because of their higher application elevation above the ground or crop.
Also, they might have a higher pumping cost due to their greater operating pressure.
Spray heads are a much more diverse classification.
They can range from simple nozzles and deflector plates to more sophisticated designs involving moving plates that slowly rotate or types with spinning plates to designs that use an oscillating plate with various droplet discharge angles and trajectories.
The rotator types are similar to small, low angle impacts sprinklers, except the sprinkler rotation is controlled by the nozzle jet with a hydraulic "motor." Most spray heads have a near 360 degree coverage and can have deflector plates designed with differing groove sizes to affect the spray streams , and they can have streams that are ejected almost horizontal , upward  and/or downward  with downward orientated spray heads.
They can be designed with plates that direct water
 streams upward at various angles for chemigation of tall or short crops.
Spray heads can have partial coverage , which are often used near towers to minimize track wetting.
Spray heads can be mounted upward on the center pivot pipeline itself.
Typically, spray heads are mounted on "drops" from "goose-neck" fittings that make a 180-degree bend from the upper side of the center pivot pipeline and longer "goose-necks"  may be used to allow matching LEPA or LESA drops to the rows.
The drops are usually flexible hoses.
For longer drops , the drop hose will typically have a weight  to minimize swaying from the wind.
Usually, the "goose-necks" and drops are installed on alternating sides of the center pivot pipeline.
Figure 1.
Typical example of a LESA system with spray heads on drops spaced 5 ft  apart).
Note that the furrow arms and drop hoses alternate from one side to the other along the truss.
Spray heads typically operate at pressures from 10 to 30 psi , but some LEPA or LESA systems operate at pressures as low as 6 psi.
Lower pressure systems or ones with significant elevation changes are usually equipped with pressure regulators to achieve higher uniformities.
Spray heads are often constructed from plastic, and the various nozzle sizes are color-coded.
Allen et al.
describes many of the common types of spray heads from several manufacturers and their characteristics.
Table 1 provides a summary of some of the typical sprinkler heads used on center pivots.
The list of advantages and disadvantages is intended solely as a guide, and individual situations may have unique situations not characterized here.
Readers are encouraged to seek local advice from technical advisors  before making any sprinkler design selection or changes.
Figure 2 conceptually illustrates the relative application rates under various sprinkler types after.
The peak application rate linearly increases along the center pivot radius and is a maximum at the outer end.
The X-axis presented as a distance scale in Fig.
2 can be converted to a time scale based on the speed of the center pivot at that point  to achieve the time course of the application as the pivot passes a particular point).
The area under each of the transformed curves will be a constant along the center pivot's length representing the application amount.
The application modes for center pivot "sprinkler packages" can be described as either 1) overhead or over-canopy methods or 2) near-canopy or in-canopy methods.
The sprinkler type selected is influenced by the mode of the desired application method.
The mode and sprinkler type may influence the required spacing.
So these are not independent alternatives.
Hence, they have been called "sprinkler packages" because all aspects of design, installation, maintenance, and management affect the "package" performance.
The overhead or over-canopy methods are those application types mounted on the center pivot pipeline itself or those mounted on drops that are typically just below the truss rod elevation above ground.
Of course these descriptions are still arbitrary depending on the system height and the crop height.
One of the main decision factors for this mode is whether only overhead or over-canopy chemigation is desired or if no chemigation option is desired.
Impact sprinklers, spray heads, and rotators are typically considered for this application mode.
This mode and application method is well suited to rolling topography, low intake soil types, and crops tolerant of overhead wetting.
The overhead or over-canopy methods are those application types mounted on the center pivot pipeline itself or those mounted on drops that are typically just below the truss rod elevation above ground.
Of course these descriptions are still arbitrary depending on the system height and the crop height.
One of the main decision factors for this mode is whether only overhead or over-canopy chemigation is desired or if no chemigation option is desired.
Impact sprinklers, spray heads, and rotators are typically considered for this application mode.
This mode and application method is well suited to rolling topography, low intake soil types, and crops tolerant of overhead wetting.
Table 1.
Characteristics of common center pivot sprinkler types
 Sprinkler	Type	Range	psi	Height	ft	Advantages	Disadvantages
 Impact, high angle		25-50		6-15	Low application rate.
High energy requirement.
Exposure to wind effects.
Impact, low angle		25-35		6-15	Low application rate.
High energy requirement.
Still impacted by winds.
360 spray head,	10-30	6-15	Lower energy	High application rate.
rotator, spinner;	high location			requirement.
Closer	spacing.
Only over canopy	chemigation.
360 spray head,	10-30	1-6	Less wind effect.
Close
 LESA or LPIC	low location			spacing.
Some have	LEPA drag hose	High application rate.
Varied	requirement.
Lower drift
 Low drift and	10-30	Pipeline	and wind effects.
Many
 multiplate spray		Truss	configurations.
Some	High application rate.
heads	Level.
have LEPA drag hose
 LPIC	adapters and chemigation
 Pipeline.
Larger wetted diameter,	Can have higher energy
 Rotators		15-50	Truss	Level.
Good resistance to wind	lower application rate.
requirement.
Limited in-	canopy chemigation
 Spinners		10-20	Rotators	Varied.
See	Low energy requirement.
Gentler droplet	applications.
chemigation applications.
Limited in-canopy
 Low misting from small
 Oscillating/Rotating	10-20	3-6	droplets.
Low application	Limited in-canopy
 Spray Plates			rate and gentler	chemigation applications.
applications and less	Extremely high
 LEPA Bubble		6-10		1-3	purpose (convertible from	spray to bubble to drag	evaporation.
Multi	application rate.
Requires	storage (~1-2 in., 15-50	furrow dikes or surface
 sock).
Excellent in-	mm of water volume).
LEPA Drag Sock		6-10		0	See LEPA Bubble.
Less	erosion of furrow dikes.
See LEPA Bubble.
Figure 2.
Illustration of the relative application rates for various sprinkler types under a center pivot.
Modified and adopted from King and Kincaid.
The LEPA application rate is difficult to show because it is essentially a "point" discharge, and its peak was illustrated to exceed the rate range of this graph.
The nearcanopy or in-canopy application methods are always mounted on drop tubes from the center pivot pipeline.
The main difference is whether the sprinkler devices are mounted near the ground , within the crop canopy or the mature crop canopy , or just above the maximum height of the crop.
Of course, a LPIC system designed for a tall crop may not be a LPIC system in a shorter crop.
For that reason, we  have preferred to use the names LESA for a system with the spray heads mounted 1-2 ft  above the ground or MESA  for a system with spray heads mounted 5-8 ft  above the ground.
The name LEPA should only be used for a system with bubblers  or drag socks mounted on a flexible hose.
LEPA hoses can be attached with commercial adapters to many types of spray heads whether the spray heads are mounted low near the ground like LESA or at a higher elevation like a LPIC or MESA system.
Although Lyle and Bordovsky  originally used LEPA in every furrow, subsequent research  demonstrated the superiority for alternate furrow LEPA.
The reasons aren't always evident, but they may result from the deeper irrigation
 penetration , possible improved crop rooting and deeper nutrient uptake, and less surface water evaporation.
LEPA and LESA work best with either LEPA heads or 360 spray heads.
Some of these systems  also have flexibility to chemigate either a tall crop  or shorter crops.
LPIC and MESA systems have the conversion potential to LEPA, but they don't have the under canopy chemigation potential of LEPA or LESA systems.
LEPA and LESA systems are typically located in or above alternate furrows or between alternate rows if furrows are not used.
LEPA requires a furrow with furrow dikes according to the concepts described by Lyle and Bordovsky  while LESA can be effective without furrows in no-till or conservation till systems.
This doesn't imply LEPA heads cannot be used without furrow dikes, but it shouldn't be described as "LEPA".
LPIC or MESA systems are typically spaced for a desired uniformity and may not be bound by the row spacing.
LPIC systems may require a narrower spacing to compensate for crop interference.
Figure 3.
Illustration of the LEPA, LESA, LPIC, and spray application concepts in tall and short crops.
The illustration has drops in each furrow to conserve space while actual systems typically use drops in alternate furrows either 60-in.
or 80-in.
apart depending on the crop row spacing.
Lyle and Bordovsky  developed the LEPA concept as a "system" comprising irrigation combined with furrow diking.
In fact, all advanced center pivot sprinkler application packages need to be incorporated into a complete agronomic package involving tillage, controlled traffic, residue management, fertility, harvesting, etc..
Table 2 summarizes several of the typical center pivot "sprinkler packages" and their "system" components.
LESA / LPIC System [irrigation, tillage, traffic, fertility]
 Figure 4.
Illustration of the "agronomic system" concept involving irrigation, controlled tillage, fertility, etc.
The efficiency of an irrigation application depends on many factors.
The water losses depend on the application technology and operation and include other agronomic cultural aspects.
The interpretation and characterization of water loss estimates or measurements involves the conservation of mass applied to sprinkler irrigation as outlined by Kraus.
He presented the components as
 where Qs is the sprinkler discharge, Qae is the droplet evaporation during travel from the nozzle to the target surface, Qad is the water drift outside the target area, Qfi is the intercepted water on the foliage, and Qgi is the water reaching or
 intercepting the ground.
The units for these components can be expressed on a rate, mass, or volume basis.
Qfi represents the sum of water evaporated from the foliage during the irrigation  and the amount of water remaining on the foliage at the end of then irrigation.
The water reaching the ground  can be partitioned into its components characterized as
 where Qsi is the infiltrated water, Qge is the water evaporated from the ground during the irrigation, Qgs is the water stored on the ground during the irrigation, Qgwe is the water evaporated from the water stored on the ground prior to infiltration during irrigation, Qgri is the water that runs onto the unit area, and Qgro is the water that runs off the unit area.
In its simplest case, irrigation application efficiency is equivalent to the ratio Qsi/Qs because percolation beneath the root zone can usually be ignored.
Percolation beneath the root zone depends on irrigation scheduling and other water management issues.
Percolation can be significant in low lying areas in the field that accumulate runoff from upland areas.
Generally for a center pivot, drift outside the area is small and is often ignored; however, it could be more significant with systems equipped with end guns or in extremely high wind situations.
Typically, irrigation application efficiency can only be measured after the water application has been completed and after the evaporative processes that affect the Qae, Qfe, and Qge components.
For methods that wet the foliage, transpiration will decline, and generally the "net" evaporation  is the component of interest.
Also, the movement of the water vapor downwind humidifies the drier air reducing the crop evapotranspiration rates, even before the area is wetted by the irrigation.
In addition evaporation continues after the completion of the irrigation event from the foliage intercepted water  and surface storage water  and the evaporation from the ground during the irrigation  and following the event.
At the typical observation time, the intercepted water on the foliage and the ground will already have evaporated and these amounts are largely unknown, except by some inference methods.
Table 3 outlines the possible water loss components common for various sprinkler packages.
Table 2.
Example sprinkler packages with desired tillage and agronomic systems.
Impact sprinklers	Any	Any
 MESA or spray	Any.
Controlled traffic desired.
Basin tillage	Any
 with ridge-till, reservoir tillage with or without
 beds.
No-till, ridge-till, or conservation till
 LPIC	Any.
Controlled traffic desired.
Basin tillage	Any
 360 Spray head	with ridge-till, reservoir tillage with or without
 Low drift head	beds.
No-till, ridge-till, or conservation till
 LESA	Any.
Controlled traffic desired.
Basin tillage	Any, circular
 360 Spray head	with ridge-till, reservoir tillage with or without	rows desired
 Low drift head	beds.
No-till, ridge-till, or conservation till
 LEPA 	Controlled traffic desired.
Basin tillage with	Circular rows
 ridge-till, reservoir tillage with beds.
LEPA 	Controlled traffic desired.
Basin tillage with	Circular rows
 ridge-till, reservoir tillage with beds.
(basin
 tillage is more effective)
 Howell et al.
reviewed many of the studies that had measured evaporative losses from sprinkler systems, especially those using lysimeters.
They noted the great difficulty in making measurements of evaporative losses, but they found major differences in the application losses for differing sprinkler methods low angle impacts, LEPA, and over canopy spray  due to their different wetted times, differing wetted surfaces.
Tolk et al.
, using measured corn transpiration, found net canopy evaporation of intercepted water was 5.1 to 7.9% of applied water for a one-inch  application volume.
McLean et al.
reviewed several past evaporation studies and evaluated above canopy evaporation losses from center pivots using the change in electrical conductivity of sprinkler catch water as an indicator of evaporation.
They reported impact and spray losses from -1 to 3%.
The negative losses were attributed to atmospheric condensation on the droplets due to the cool
 groundwater temperatures that were less than the atmospheric dew point temperature.
Schneider  reviewed the evaporation losses from LEPA and spray systems.
He summarized the limited studies reporting "net" canopy evaporation that had values ranging from 2 to 10%.
Evaporation from LEPA systems ranged from 1 to 7% of the applied amounts with application efficiencies ranging from 93 to 100%.
His review of evaporation losses from spray irrigation studies had values that ranged from 1 to 10%, while their mean application efficiencies ranged from 85 to 100%.
Table 3.
Water loss components associated with various sprinkler packages.
Water Loss	MESA or	LESA
 Component	Overhead	Spray	LPIC	LEPA
 evaporation	Yes	Yes	Yes	No
 Droplet drift	Yes	Yes	No	No
 evaporation	Canopy	Yes	Yes		Yes,	
 water	No	Yes	Yes	Yes, 
 evaporation	Yes	Yes	Yes	Yes, 
 Surface water	No,	Yes,	Yes	Yes,
 movement			
 Runoff		Yes	Yes	unless surface
 Percolation	No	No	No	No
 Surface water redistribution  and field runoff should not occur in most cases.
Yet, they regularly happen and affect the infiltration uniformity, deep percolation, and ultimately the efficiency of the application.
Spray systems  or LEPA systems  are most prone to runoff problems.
Soil type and slope play a central role in the surface water redistribution and runoff potential of a particular site in addition to the sprinkler package and system capacity .
Either surface storage (basin or reservoir
 tillage) or crop residues from no-till or profile modification tillage  may be needed to reduce or eliminate surface water redistribution and runoff.
Increasing the system speed  generally reduces the potential runoff volume.
Both water redistribution and field runoff occur from rainfall that can further impact irrigation water requirements.
Few studies are published on rainfall runoff from sprinkler-irrigated fields or that have measured the total season water balance components.
Figure.
5 Illustration of runoff or surface water redistribution potential for impact sprinkler and spray  center application packages for an example soil.
represents the start of the irrigation,  is the peak application rate , and  is the completion of the irrigation.
The first intersection point of the infiltration curve and the application rate curve represents the first ponding on the soil surface.
Schneider  reviewed many of the previous studies on irrigation runoff and surface storage as influenced by tillage systems for LEPA and spray application methods.
Runoff or water redistribution without basin or reservoir tillage ranged from 3 to over 50% in several studies with the greatest runoff losses occurring from LEPA modes without basin tillage.
LEPA applications in alternate furrows may require twice the storage volume needed for equivalent LESA or LPIC systems (representing full wetting like rain or
 MESA).
Runoff from LESA or LPIC systems may be critical on steeper slopes , low intake soils , and higher capacity systems.
The sprinkler package is a combination of the sprinkler applicator, the application mode, and the applicator spacing.
The system capacity determines the peak application rate of the particular sprinkler application package.
The sprinkler package should be designed together with the tillage and agronomic system.
The particular soil and slope conditions will define the infiltration rate.
The intersection area between the infiltration curve and the application rate curve illustrates the "potential" runoff or surface water redistribution that might require surface storage from basin or reservoir tillage needed to reduce or eliminate runoff from LESA, LESA, or LPIC systems.
The type of sprinkler applicator and the mode of application determine the particular components of water losses.
"Net" canopy evaporation may be in the 5-10% range.
Overall evaporation losses in several cases were between 10-20%.
Irrigation efficiency of LEPA systems without runoff were in the 93 -99% range, but without basin tillage LEPA systems in several cases had large runoff  amounts.
LESA or LPIC systems can be efficient with evaporative losses less than 10% in most cases, particularly with basin or reservoir tillage or with a no-till system.
McLean, R.K., R.
Sri Ranjan, and G.
Klassen.
2000.
Spray evaporation losses from sprinkler irrigation systems.
Can.
Agric.
Engr.
42:1-8.
Table 1.
Crop water use for the remainder of the growing season for corn and soybean.
For corn in the R4 Dough stage of growth, it needs approximately 34 days to maturity and 7.5 water use to maturity.
For corn in the R4.78 Beginning dent stage of growth, it needs approximately 24 days to maturity and 5.0 water use to maturity.
For corn in the R5 1/4 milk line stage of growth, it needs approximately 19 days to maturity and 3.75 water use to maturity.
For corn in the R5 1/2 milk line stage of growth, it needs approximately 13 days to maturity and 2.25 water use to maturity.
For corn in the R5 3/4 milk line stage of growth, it needs approximately 7 days to maturity and 1.0 water use to maturity.
For corn in the R6 Physiological maturity stage of growth, it needs approximately 0 days to maturity and 0 water use to maturity.
Both methods require the basic information for the pivot.
All the needed details can be found on the sprinkler chart for the center pivot.
The sprinkler chart is the documentation that came with the sprinkler package for the pivot and describes the basic layout of the pivot, water flow rate, pressure, size of each sprinkler, etc.
If the current sprinklers on the pivot came with the machine when it was new, the pivot dealer should be able to provide a copy.
Otherwise, ask the company that sold the current sprinkler package for it.
If you do not have the sprinkler chart, then you will need to determine the needed data by measuring the pivot.
Chapter: 39 Selected Broadleaf Weeds in South Dakota Corn Fields
 Table 39.1 Relative competiveness of common South Dakota weeds.
Yield loss due to weeds varies by species, weed density, and time of emergence.
Weeds that emerge early tend to cause more yield loss than those that emerge after crop establishment.
All weeds have the potential to cause 100% yield loss, however, some are relatively more competitive with corn than others.
This table gives a relative rating of different weed species and their ability to cause a 5% yield loss.
Highly competitive weeds 
 Common cocklebur	Common sunflower	Common waterhemp	Giant ragweed
 Moderately competitive weeds 
 Canada thistle	Field bindweed	Switch grass	Velvetleaf
 Hedge bindweed	Horseweed	Volunteer corn	Giant foxtail
 Common lambsquarters	Woolly cupgrass	Redroot pigweed	Russian thistle
 Kochia	Wild proso millet
 Low competitive weeds 
 Wild buckwheat	Green foxtail	Yellow foxtail	Longspine sandbur
 Large crabgrass	Witchgrass	Venice mallow	Barnyardgrass
 Corn Yield Losses 
 Weeds present in the field from V2 to V8 can irreversibly reduce corn yields.
This period is often called the weed-free period.
This loss often occurs before the weeds compete with the corn plant for water, nutrients, and light.
The factor responsible for this loss is unknown, although light quality, volatile compounds, and/or other mechanisms have been examined.
Different weed species have different emergence and
 growth rates.
In general, weeds that emerge early in the growing season have greater impact on corn yields than weeds that emerge later.
Perennial plants can germinate from seed, or may produce new shoots from buds on roots, rhizomes , stolons , crowns, etc..
The new shoots can emerge very early in the spring and grow quickly because of carbohydrate storage in the perenneating structures.
These plants are often found to prosper in no-till or minimum-tillage systems due to the lack of disturbance to the perenneating structures.
In most cases, tillage should not be used as the major control mechanism because structures with the buds may be moved to new areas to form new infestations.
Examples of perennials include: Canada thistle, field bindweed, hedge bindweed, dandelion, and Jerusalem artichoke.
In addition, all seven South Dakota Noxious Weeds are perennials, with descriptions included at the end of this chapter.
Herbicide applications should be timed for summer just before flowering to kill flowers and potential seed, and fall after the first light frost  to move herbicide to the plant's roots.
Frequent mowing or plant disruption without herbicides is needed to keep the plant from flowering and producing seed.
In addition, frequent disturbance can help deplete carbohydrates in the roots, rhizomes, etc., which can weaken the plant.
Unfortunately, if new shoots form from buds, the leaves can begin sending carbohydrates to the roots soon after emergence, SO nonchemical weed control can be a long-term task.
These plants germinate from seed in the spring and form a rosette that, if undisturbed during the first season, overwinters.
The second year, the plant produces flowers and seeds.
Examples of biennial weeds include: musk thistle, bull thistle, biennial wormwood, and common mallow.
Chemical and nonchemical control can be effective against biennial weeds.
Nonchemical control approaches for biennial weeds include: tillage, high-quality seed corn, crop rotations, mulches, and cover crops.
The chemical control of the rosette form of biennial weeds is often very effective in the fall.
Herbicide effectiveness generally increases with temperature.
Daytime temperatures of 50F or higher are desirable.
Annual weeds are those that germinate from seed every year and live only for a single season.
Annual weeds can germinate at different time periods.
Winter annuals will germinate and emerge in fall or very early spring and flower early, usually before corn planting.
Winter annual weeds include: field pennycress, horseweed or marestail, and evening primrose.
Winter annuals can be more of a problem in no-till systems as the undisturbed residues provide overwinter protection for the germinated weeds.
In addition, these weeds may set seed even before any spring field operations occur.
Early emerging spring annual weeds  include: common sunflower, Pennsylvania smartweed and ladysthumb, common lambsquarters, and giant ragweed.
Early emerging spring annual weeds may be controlled with preplant burndown applications of herbicides.
These plants cause interference and the greatest yield losses if they remain undisturbed because they are already growing before corn emergence.
Weeds that emerge at or soon after corn planting include: common ragweed, velvetleaf, Russian thistle, redroot pigweed, common cocklebur, wild mustard, black nightshade, Venice mallow, wild buckwheat, and kochia.
These weeds are targeted with a pre-emergence herbicide application.
Weeds that emerge after corn emergence and into midsummer include: common waterhemp, biennial wormwood, Palmer amaranth, and buffalobur.
Weeds not controlled by pre-emergence applications are typically the targets of postemergence control operations.
Canada thistle 
 Canada thistle  is a South Dakota Noxious Weed and it typically emerges before or at corn planting.
Plant Description: This perennial has a deep, extensive root systems and spreads by seeds or pieces of root transported from one location to another.
The emerging plants are very small and the leaves are opposite.
The plants are very dark green, and leaves have a crinkled appearance with sharp spines on the leaf margins and stem.
The stems are erect, may have green or red stripes, and can grow to almost 6 ft tall under certain conditions.
Flowers are imperfect, with colonies of male and female plants.
Areas of Infestation and Yield Loss Potential: This weed is often found in disturbed sites and may thrive in no-till systems.
Canada thistle can produce a 30% yield reduction with 4 shoots or more per ft2.
Tillage, in mature stands, will spread rhizomes and increase areas of infestation.
Herbicides can control seedlings, but older plants should be treated with herbicide when plants are in the bud stage or in the fall after the first frost.
Herbicide Resistance: Biotypes of Canada thistle have been reported to be resistant to synthetic auxin herbicides.
Perennial sowthistle 
 Perennial sowthistle  is a South Dakota Noxious Weed that typically emerges early from rhizomes, whereas young plants can start from creeping roots almost any time during the year.
Seeds can germinate throughout the season if moisture is adequate.
Plant Description: This perennial reproduces by seeds and regrows from tap and creeping roots.
This plant has a dandelionlike rosette and produces a flower stalk that has yellow, dandelionlike flowers.
The plant has a smooth stem with milky juice, and it has long, lobed leaves with spiny edges.
The leaves have a whitish coating on the leaf surface.
Areas of Infestation and Yield Loss Potential: This weed generally escapes from roadside areas, and infestations often start at field margins.
Perennial sowthistle is a problem in no-till and minimum-till fields.
This plant can form dense colonies, however, little research has been done to examine harvest losses.
Herbicide Resistance: To date, herbicide resistance has not been reported in perennial sowthistle, but other species of sowthistle have been reported to be
 resistant to ALS-inhibitor herbicides.
Wild four o'clock 
 Wild four o'clock  typically emerges before or at corn planting, and this perennial plant reproduces primarily from seed and shoots that arise from the taproot.
Plant Description: The leaves are opposite, ovate with no or few hairs, and the stems are erect.
Inflorescence is an umbel with pink or red-purple sepals.
Flowers open late in the afternoon, hence the name four o'clock.
Areas of Infestation and Yield Loss Potential: This plant often grows in sandy, dry soils.
If growing in more fertile sites, it usually has poor growth because of other plant competition.
It has a large taproot and it is not aggressive.
It rarely is observed at densities high enough to produce significant yield losses.
Herbicide Resistance: As of 2015, herbicide resistance has not been reported, although the plant is tolerant to 2,4-D .
Curly dock 
 Curly dock  typically emerges before or at corn planting.
This perennial plant reproduces mainly by seed, but once established, new rosettes form at the top of the taproot in late fall or early spring.
Plant Description: Curly dock, a member of the buckwheat  family, is erect and grows from 2to 5-ft tall.
It has an ocrea  at the leaf base.
Leaves are hairless, and stems are often unbranched below the flower head.
Leaves are alternate along the stem.
The fruits and stems turn rusty brown at the end of the season.
Areas of Infestation and Yield Loss Potential: This plant is often found in wet areas of the field.
This plant is not aggressive and rarely observed in densities high enough to produce large yield losses.
However, yield loss may occur due to wet soil conditions.
Herbicide Resistance: As of 2015, herbicide resistance has not been reported.
However, plants in the Polygonum family are tolerant of synthetic auxin herbicides.
Swamp smartweed 
 Swamp smartweed  typically emerges before or at corn planting This perennial plant reproduces primarily from seed, but once established, shoots arise from rhizomes, stolons, and rooting stems.
Plant Description: Swamp smartweed is erect and grows from 1to 3-ft tall.
It is a member of the
 buckwheat  family.
This plant has an ocrea  at the leaf base.
Leaves are oblong and alternate along the stem.
The inflorescence is spike with pinkor rose-colored flowers.
Areas of Infestation and Yield Loss Potential: This plant is often found in low-lying, wet areas of the field.
This plant can be observed in high densities in wet soils and yield losses may be due to poor corn growing conditions.
Herbicide Resistance: As of 2015, herbicide resistance has not been reported.
However, plants in the Polygonum family are tolerant of synthetic auxin herbicides.
Common milkweed 
 Common milkweed  typically emerges before or at corn planting, and this perennial plant reproduces from seed, root buds, and crown buds.
Several stems can arise from a single crown.
This plant is being reintroduced in many areas due to its importance to the larvae of the monarch butterfly.
Plant Description: This plant has an erect plant habit that grows from 2to 6-ft tall.
Leaves are opposite, oblong and hairy.
Stems are hairy and contain milky sap.
The flowers are arranged in umbellate cyme and flowers have pinkto rose-colored petals.
Areas of Infestation and Yield Loss Potential:
 Common milkweed prefers dry, open sites.
This plant can be aggressive with densities high enough to result in significant yield loss.
Harvest problems may occur if high densities are present because of the sticky sap from cut stems.
Herbicide Resistance: This plant has always been tolerant of glyphosate  due to sticky sap in the plant.
Hemp dogbane 
 Hemp dogbane  typically emerges before or at corn planting but new shoots can emerge throughout the season.
This perennial plant reproduces from seeds and a spreading root system.
Plant Description: It has an erect plant habit, but unlike milkweed, often is bushy with many stems.
Plants can grow up to 3 ft tall.
Leaves are opposite, oblong, and the upper leaf surfaces typically are hairless.
Stems contain milky sap.
The flowers are arranged in a cyme and have white to white-green petals.
Areas of Infestation and Yield Loss Potential: Hemp dogbane prefers dry, open sites and is an aggressive plant that is difficult to control.
Crop rotations with a hay crop for several years with several cuttings per year help reduce infestations.
Herbicide Resistance: This plant is tolerant to glyphosate.
Ground cherry 
 Ground cherry  typically emerges before or at corn planting, but new shoots can emerge throughout the season.
This perennial plant reproduces from seed and it develops a thick, underground root system.
Plant Description: Ground cherry has an erect habit but often becomes bushy with many stems.
Plants can grow up to 3 ft tall.
Leaves are alternate, oval with a toothed margin.
Leaf surfaces have glandular hairs, and single yellow-green flowers develop papery, conical seedpods.
Areas of Infestation and Yield Loss Potential: This aggressive plant prefers dry, open sites and can be difficult to control.
Sticky seeds can adhere to crop seeds during harvest if corn is cut short.
Herbicide Resistance: As of 2015, herbicide resistance has not been reported.
Jerusalem artichoke 
 Jerusalem artichoke  typically emerges early from tubers with many plants appearing in a small area.
This perennial plant reproduces from seed, tubers, and rhizomes.
Plant Description: Jerusalem artichoke has a sunflowerlike rosette and the leaves are opposite.
The plant has pale yellow, disk flowers, and it can grow up to 10 ft tall.
Areas of Infestation and Yield Loss Potential: High populations can be found in wet sites and in no-till or minimum-till fields.
This plant can be extremely aggressive due to its tall stature, and corn yield losses of almost 100% have been reported.
Herbicide Resistance: Herbicide resistance has not been reported.
Field bindweed 
 Field bindweed  emerges in late spring to early summer.
Plant Description: This perennial plant can grow from rhizomes or seed and it has arrow-shaped leaves on a twining stem.
The root system can be extensive and deep-rooted.
Flowers are white to pink and bellor trumpet-shaped.
Areas of Infestation and Yield Loss Potential: This plant grows well in dry soils and it can produce a 50% yield reduction in corn.
In addition, the vining nature of the plant can cause problems with harvest equipment.
Herbicide Resistance: This plant is tolerant of glyphosate , and biotypes are resistant to cell-membrane disruptor   herbicides.
Hedge bindweed 
 Hedge bindweed  typically emerges before or at corn planting.
This perennial, vining plant reproduces by seed and rhizomes.
Plant Description: Hedge bindweed can be confused with field bindweed.
However, the leaves have a long petiole and a pointed tip.
The flowers are large, funnel-shaped, and white to pink in color.
Areas of Infestation and Yield Loss Potential: Found
 in disturbed sites.
This plant is not as aggressive as field bindweed, although the vines may cause problems during harvest.
Herbicide Resistance: As of 2015, herbicide resistance has not been reported.
Dandelion  typically emerges early, before corn planting, and the seeds can germinate throughout the season if moisture is adequate.
This perennial reproduces by seeds and regrows from the taproots.
Plant Description: Dandelion has a basal rosette with long, lanceolate, lobed leaves.
Milky juice can be found throughout the plant and exudes when cut.
Bright yellow infloresence with flowers arranged in heads.
Areas of Infestation and Yield Loss Potential:
 Dandelions can be a problem in no-till and minimum-till fields.
This plant is not as aggressive as other perennials due to the low growing rosettes.
Herbicide Resistance: As of 2015, herbicide resistance has not been reported, although some are tolerant to synthetic auxin herbicides.
Common Mallow  
 Common mallow  generally is a biennial plant that reproduces from seeds.
However, it can behave as an annual, winter annual, biennial, or short-lived perennial if winters are mild or it is located in a protected site.
Seedlings emerge in several flushes throughout the season.
Plant Description: The leaves are alternate and ovalto kidney-shaped with wavy, lobed edges.
The plant is prostrate to the ground, rarely getting taller than 1.5 ft but may have long vines.
Leaf surface is hairy.
Fruit is disk-shaped and flattened with a cheese-wheel appearance.
Areas of Infestation and Yield Loss Potential: Dense infestations are rarely observed in cultivated fields, but they may occur.
The plant has a deep taproot that can help it survive drought and cold temperatures.
Common mallow may not reduce corn yields, however, it can cause problems during harvest.
Herbicide Resistance: As of 2015 herbicide resistance has not been reported, although it is tolerant to glyphosate.
Bull thistle 
 Bull thistle  is a biennial plant that reproduces from seeds with a rosette  formed in the first year.
In the second year if the plant is not disturbed it bolts and sends out many erect stems with flowers starting to form in July.
This plant is the symbol of Scotland, as it saved the country from invaders.
Plant Description: The rosette leaves are elliptical to ovate in shape covered in cobweb-like hairs.
Leaf margins can be unlobed  to finely lobed but all are tipped with spines.
Leaf surface is hairy.
In the second year, stalks range from 3 to 6 ft in height with alternate, spiny leaves and spines on the stalk.
Flower bolls are covered with spines and cobweb-like hairs.
Areas of Infestation and Yield Loss Potential: This plant prefers moist  sites but will grow on drier, sandy sites.
In South Dakota, corn yield reductions have not been assessed.
Herbicide Resistance: As of 2015, herbicide resistant biotypes have not been reported, although it is tolerant of glyphosate.
Musk thistle 
 Musk thistle  reproduces from seeds with a rosette  formed the first year with emergence in the fall or early spring.
In the second year, if not disturbed, the plant bolts and sends out many erect stems with flowers forming as early as May.
Plant Description: The rosette leaves are elliptical and smooth  with leaf margins deeply toothed to pinnately lobed.
Leaf veins extend beyond the leaf margin to end as spines.
Second-year stalks range from 2 to 4 ft in height, with alternate, spiny leaves and stalks with spiny wings.
Flower color ranges from rose-purple to white.
The inflorescences are disklike and nodding.
Areas of Infestation and Yield Loss Potential: This plant prefers moist  sites but will grow in drier, sandy sites.
Musk thistle impact on corn yields is often not assessed, however, areas with heavy infestations may not be suitable for harvest.
Herbicide Resistance: This plant may be resistant to synthetic auxin herbicides.
Biennial wormwood 
 Biennial wormwood  typically emerges in late-June to early July after corn planting and the plant may behave as an annual, flowering later in the first year of growth.
Reproduction is from seed.
Plant Description: The first true leaves of seedlings are finely divided and often mistaken for common ragweed.
Biennial wormwood has sharp leaf edges and leaves are hairless, whereas common ragweed has rounded leaf edges with hairs.
Vegetative plants are rosettes.
Flower stalks can grow up to 6 ft tall and a plant can produce over 400,000 seeds/plant.
Areas of Infestation and Yield Loss Potential: This plant grows well in disturbed, poorly drained soils and yield reduction can be up to 40% with 1 plant per ft2.
If the infestation is dense, areas may not be harvested because of the height of biennial wormwood, effectively reducing yield by 100% in these areas.
Figure 39.17 Biennial wormwood seedling, inflorescence, and mature plant.
Herbicide Resistance: Herbicide applications must be done before the plant is 3" tall, as tolerance to all herbicides becomes an issue.
As of 2015, herbicide resistant biotypes have not been reported.
Annuals Germinating in the Fall or Early Spring
 There are 20 species of eveningprimrose  in the Great Plains.
These plants will emerge in the fall, overwinter as a rosette, or emerge in the early spring prior to planting.
This biennial, winter annual, or early spring emergence plant reproduces only from seed.
Plant Description: The plant has numerous hairy leaves that are lancelike to oblong.
Plants can grow up to 6 ft tall, and the flowers are yellow to reddishyellow.
The fruit is a cylindrical capsule tapering at the tip.
Areas of Infestation and Yield Loss Potential: High infestations can be found in reduced-tillage systems, and this plant is tolerant of drought conditions and sandy soil types.
This plant is being explored as an alternative oil seed crop.
Historically, the populations are less than the economic threshold.
Herbicide Resistance: As of 2015, herbicide resistance has not been reported, but the plant is difficult to control with herbicides typically used in corn.
Prickly lettuce 
 Prickly lettuce  is an annual or winter annual erect plant that reproduces from seeds germinating in fall or early spring.
Plant Description: The cotyledons  are oval or oblong with spiny margins and spines along the midrib of the leaf.
The young plant is a basal rosette  with stem elongation during flower development.
The plant, when cut, exudes milky sap.
Leaves on the elongated stem are alternate and leaf bases clasp the stem.
Flowers are yellow in color and petals have a toothed margin.
Areas of Infestation and Yield Loss Potential: This plant is often found in disturbed sites.
Its impact on corn yields is unknown.
Herbicide Resistance: Prickly lettuce biotypes in the United States have been reported to be resistant to ALS-inhibitor herbicides  and synthetic auxin herbicides.
Flixweed  is an introduced erect winter annual or biennial that germinates from seeds in the fall or spring.
Figure 39.18 Eveningprimrose rosette, flower, and seed capsule.
Plant Description: The leaves are finely divided and pinnately compound, grayish-blue in color.
Juvenile plants have ovate-shaped leaves in a rosette arrangement, deeply lobed margins, and the leaves are covered in star-shaped hairs.
Flower petals are very small and yellow or greenish-yellow.
Flixweed is distinguished from other mustards because of its finely dissected leaves and very long, thin siliques.
Areas of Infestation and Yield Loss Potential: This plant is often found in disturbed, dry sites.
The impact of this plant on corn yields is unknown.
Herbicide Resistance: Flixweed biotypes in Kansas winter wheat fields have been reported to be resistant to ALS-inhibitor herbicides.
Tansy Mustard 
 Tansy mustard  is a native winter annual that germinates from seeds in the fall or spring.
Plant Description: The leaves are finely divided and pinnately compound, greener in color than flixweed.
Juvenile plants have ovate-shaped leaves in a rosette arrangement, deeply lobed margins, and leaf surface has a gray to whitish pubesence.
Flower petals are very small and yellow or greenish-yellow.
It blooms earlier than flixweed.
The fruits  of tansy mustard are siliques.
Tansy mustard and flixweed can be distinguished by examining the seed and seedpods.
Tansy mustard seeds are 1/2-inch long and arranged in two rows along the pod, whereas flixweed seeds are 1to 1 1/2-inches long and are arranged in a single row.
Areas of Infestation and Yield Loss Potential: Dry, disturbed sites.
Tansy mustard impact on corn yields is not known, and herbicides are most effective if they are applied prior to the plant bolting.
Herbicide Resistance: Herbicide resistance has not been reported.
Shepherds Purse 
 Shepherds Purse  is a winter annual that germinates from seeds in fall or spring.
Plant Description: The basal leaves are in a rosette and deeply lobed, and could be confused with dandelion.
The seed stalk, when bolting, has narrow, alternate leaves that wrap around the stem and have irregular margins.
The stem can be up to 1.5 ft tall with branches near the top.
It has small white flowers and the seedpod is a silicle that is flat and triangular.
Area of Infestation and Yield Loss Potential: The impact of sheperdspurse on corn yields is unknown and it can be controlled by a wide variety of herbicides if applied before bolting.
Herbicide Resistance: There are biotypes that are resistant to ALS-inhibitor herbicides  and Photosystem II inhibitors   herbicides.
Field pennycress 
 Field pennycress  is an erect winter annual that may germinate from seeds in the fall or spring.
Plant Description: The cotyledons are oval or oblong.
The young plant is a basal rosette , and stem elongation occurs during flower development.
Young leaves are generally oval and without hair.
Leaves on the elongated stem become more narrow and lancelike toward the top of the plant, but all have a toothed margin.
Seeds are in silicles, which have the pennyshaped appearance, giving the plant its common name.
Areas of Infestation and Yield Loss Potential: This plant is often found in disturbed sites.
This plant may not reduce yield but may cause problems during harvest or result in dockage due to off flavor of grain.
This plant is being considered as an alternative oilseed crop, SO fields are being planted to this species.
Herbicide Resistance: Biotypes have been found to be resistant to ALS-inhibitor herbicides.
Horseweed  may overwinter as a rosette and bolt in the spring or emerge in the spring at or before corn planting.
Plant Description: This winter or summer annual reproduces from seed, and it has numerous linear, hairy  leaves crowded on the stem.
The plant has numerous dotlike glands that secrete terpenes, releasing an unpleasant odor when the plant is crushed or cut.
Typically the stem below the inflorescence is unbranched unless injured.
Plants can grow up to 5 ft tall.
The flowers are very small and are generally white.
Seed is dispersed by wind with seeds having small white bristles.
The plant can tolerate drought conditions.
Figure 39.24 Image of horseweed..
Areas of Infestation and Yield Loss Potential: This plant generally has populations that are less than the economic threshold, however, high densities in row crops have been reported to cause > 80% yield loss.
Herbicide Resistance: There are biotypes resistant to Photosystem II inhibitors  , glyphosate , ALS-inhibitors , and cell-membrane disruptor   herbicides.
Rotating herbicides or other control methods is necessary to minimize selection of herbicide resistant biotypes.
Black medic 
 Black medic  is a winter or summer annual that reproduces from seed.
Plant Description: This plant has a prostrate growth habit with multiple branches radiating from a central taproot forming a mat.
The leaves are compound having 3 leaflets with sharply toothed margins and prominent veins.
Small yellow flowers form dense heads at the stem ends.
A single large seed develops in each flower.
This weed seldom has a high enough density to warrant control and it has been suggested as a possible cover crop.
Areas of Infestation and Yield Loss Potential: If uncontrolled early, moderate to high densities can result in significant yield loss.
This plant can outcompete corn for nitrogen early in the season.
This weed typically has been sparse in fields.
Herbicide Resistance: Biotypes have been reported that are resistant to Photosystem II inhibitors  , as well as, glyphosate , ALS-inhibitors , and cellmembrane disruptor   herbicides.
Rotating herbicides or other control methods is necessary to minimize selection of herbicide resistant biotypes.
Low-growing or Vinelike Annual Broadleaf Weeds
 Prostrate knotweed  Prostrate knotweed  is an annual plant reproducing from seeds that germinate early in the spring at or before corn planting.
Plant Description: Plants grow near flat to the ground and form a mat from a central taproot.
Leaves are small, alternate and often covered with white mildew.
Flowers are in the leaf axil, with 3 to 6 flowers per axil.
This plant is a member of the buckwheat  family, SO there is a papery brown or tan sheath  at the nodes.
There are other plants similar to prostrate knotweed, including erect knotweed , which tends to be more upright, and common knotweed , which as 1 to 3 flowers per leaf axil.
Areas of Infestation and Yield Loss Potential: This plant can grow in compacted, dry, salty soils.
Historically, this weed has seldom been dense enough to warrant control.
However, mats of the plant can cause problems.
Herbicide Resistance: There are European biotypes that are resistant to photosystem II inhibitors .
Plants in the Polygonum family are difficult to control with synthetic auxin herbicides .
Spotted spurge 
 Spotted spurge  is an annual plant that germinates from seeds in the spring at or before corn planting.
Plant Description: Similar to knotweed, spotted spurge grows as a mat to cover the ground.
Stems are pink and covered with hair and leaves are small and opposite, with some having a distinct purple spot in the leaf center.
Flowers are in the leaf axil, and seeds are borne in a three-parted seedpod.
This plant contains a sticky, milky white sap that is exuded when the stems are cut.
Areas of Infestation and Yield Loss Potential: This weed has seldom been dense enough to warrant control.
However, mats of the plant can cause problems.
Herbicide Resistance: Herbicide resistance has not been reported, although due to the milky sap, glyphosate  may provide poor control.
Prostrate pigweed 
 Prostrate pigweed  is annual plant that has seeds that germinate in early spring at or before corn planting.
Plant Description: Similar to knotweed and spotted spurge, it grows as a mat to cover the ground.
This plant has pink stems that, unlike spotted spurge, do NOT contain milky juice.
Stems are pink, sparsely hairy, and leaves are oblong and alternate.
Small flower clusters are produced in the leaf axil.
Shiny black seeds can be shaken from the plant.
Areas of Infestation and Yield Loss Potential: This weed has seldom been dense enough to warrant control.
However, the plant mats can cause problems.
Herbicide Resistance: Biotypes of prostrate pigweed have been reported to be resistant to ALS-inhibitor  and Photosystem II inhibitors  herbicides.
Common purslane 
 Common purslane  is an annual with seeds that germinate in the spring at or before corn planting.
Plant Description: Common purslane has pink stems that are fleshy and leaves are succulent.
These plants are drought-resistant and grow best in hot, dry
 weather.
These plants grow as a mat to cover the ground and can re-root from stems following disturbance.
Stems are pink, leaves are oblong and alternate, but clustered at the ends of branched stems.
Small yellow flowers are produced in the leaf axil.
Very tiny, shiny black seeds can be shaken from the plant.
Areas of Infestation and Yield Loss Potential: This weed has seldom been dense enough to warrant control.
However, mats of the plant can cause problems.
Herbicide Resistance: Biotypes of common purslane have been reported to be resistant Photosystem II inhibitors.
Wild buckwheat 
 Wild buckwheat  is an annual vining broadleaf with seeds that germinate at or prior to corn seeding.
However, depending on soil temperatures and moisture, seeds can also germinate later.
Plant Description: Wild buckwheat is a member of the buckwheat  family.
This plant has an ocrea  that is located at the base of the leaf on the stem.
This plant is often confused with the perennial field bindweed  and is known as black bindweed in some areas.
Triangular seeds, the ocrea, very small flowers, leaf shape, and root structure all help distinguish wild buckwheat from field bindweed.
Herbicide Resistance: Biotypes can be resistant to ALS-inhibitor  and Photosystem II inhibitors , and it is difficult to control with either glyphosate  or 2,4-D .
Tall morning glory 
 Tall morning glory  is an annual, vining plant that has seeds that germinate at or just after corn planting.
This plant can also reproduce from rhizomes.
Plant Description: Tall morning glory has heartshaped leaves with entire margins.
The stems have erect hairs and can climb up a plant.
The flowers are large, funnel-shaped, and can be purple, blue, white, or red.
This plant has been used as an ornamental but can escape into crop fields.
Areas of Infestation and Yield Loss Potential: Tall morning glory grows best in moist places.
Buried seed can stay viable for a long time.
It is important to
 control as a seedling before the plant twines up the crop.
This plant is not as aggressive as field bindweed, although the vines can reach 16 ft in length and may cause problems during harvest.
Herbicide Resistance: To date, herbicide resistance has not been reported.
Broadleaf Annuals with an Erect  Growth Habit
 Palmer amaranth  In South Dakota, Palmer amaranth  is an annual plant that is a new invasive weed.
It is thought that the seeds will germinate late in the season after corn emergence.
HOWEVER, this is unsubstantiated.
Plant Description: The first true leaves of seedlings are more linear than cotylendons of waterhemp, and the leaf surfaces are not hairy.
Palmer amaranth has male and female plants and can grow up to 10 ft tall.
The inflorescence of the female plant  is more highly branched and has more spines than the male.
The female plant has been reported to produce over 1 million shiny black seeds.
Areas of Infestation and Yield Loss Potential: This plant is often found in fertilized, disturbed areas.
The impact of Palmer amaranth in South Dakota is unknown.
However, it is VERY aggressive in Southern states with yield losses of 100% reported.
Herbicide Resistance: Biotypes of this plant have been reported to be resistant to 5 different herbicide types in Southern regions and may have multiple resistances to two or more herbicides in the same plant.
These include ALS-inhibitor  and Photosystem II inhibitors , glyphosate , and PPO type  herbicides.
Redroot pigweed 
 Redroot pigweed  is an annual plant with seeds that germinate at or during corn planting.
Plant Description: The cotyledons are thin and linear, and the leaves are lancelike with alternate arrangement.
The lower surface is hairy.
Stems are stout and the lower portion is reddish.
The plant is monoecious, with a single plant having both male and female flowers present.
Seeds are black, shiny, and numerous with a large plant producing over 800,000 seeds per plant.
Plants may hybridize with other Amaranthus species.
Figure 39.32 Seedling of Palmer amaranth vs.
common waterhemp.
Figure 39.33 Palmer amaranth seedling displaying white and purple markings, some plants will have no distinguishing watermarks on the leaves.
Note that the leaf petioles of the older leaves are very long.
When compared with the length of the leaf blade, the petiole of Palmer amaranth will be longer than the blade.
Areas of Infestation and Yield Loss Potential: This plant typically is found in disturbed areas usually with high fertility.
Depending on weed density, yield losses as high a 55% have been reported.
Herbicide Resistance: Redroot pigweed biotypes have been shown to be resistant to Photosystem II inhibitors  and ALS-inhibitor  herbicides.
Common waterhemp 
 Common waterhemp  is an annual plant that has seeds that germinate late in the season after corn emergence.
Plant Description: The first true leaves of seedlings are more lancelike  than the oval  leaves as seen on redroot pigweed.
Leaf surfaces are not hairy.
This plant has male and female plants.
The inflorescence of the female plant is more highly branched than the inflorescence of the redroot pigweed.
The female plant has been reported to produce over 1 million shiny black seeds.
Areas of Infestation and Yield Loss Potential: This plant is often found in disturbed areas with high fertility.
Depending on density yield losses of up to 55% have been reported.
Herbicide Resistance: Biotypes of this plant have been reported to be resistant to ALS-inhibitor  and Photosystem II inhibitors , glyphosate , and PPO  type herbicides.
Toothed Spurge 
 Toothed spurge  is an annual plant that has seeds that germinate after corn emergence.
Plant Description: The leaves are opposite, blades ovate or lancelike, leaf tip sharply pointed.
Short hairs are on upper and lower leaf surfaces.
Stems have short bristly hairs, erect, and when cut, exude sticky, milky juice.
Flowers are in terminal clusters, green, with seeds borne in capsules.
Areas of Infestation and Yield Loss Potential: The yield loss potential is unknown, however, the milky sap can cause problems with harvest.
Herbicide Resistance: Herbicide resistance has not been reported at this time.
Due to the milky sap in the plant, toothed spurge is not well controlled with glyphosate.
Volunteer soybean is an annual plant that has seeds that can germinate after corn emergence.
The plants look like the crop soybean but are growing from seed from previous crops.
High densities can reduce corn yields 20% to 30%.
Herbicide Resistance: The volunteer soybean herbicide resistance will depend on the stacked traits from previous plantings, including glyphosate  and, when available, synthetic auxin herbicides.
Smartweed sp.
Smartweed sp.
is a native, annual plant that has seeds that germinate prior to seeding corn.
Plant Description: This plant has a linearto oarshaped cotyledon, and the leaves are alternate in arrangement with the leaf surface smooth to slightly hairy.
Nodes on the stem are swollen  with a papery sheath at each node.
Flowers are pink and the inflorescence type is a raceme.
Areas of Infestation and Yield Loss Potential:
 This plant is adapted to the wetter areas of a field.
Smartweeds can reduce yield 15% at high densities.
Herbicide Resistance: Smartweed biotypes have been reported to be resistant to Photosystem II inhibitors herbicides.
Giant Ragweed 
 Giant ragweed  is an annual plant with seeds that first germinate when corn is being planted.
Germination can continue if the temperatures remain cool.
Plant Description: The cotyledons are spatulate  and the leaves are opposite and divided into 3 to 5 lobes.
The stems are erect, branched, and can grow to almost 6 ft tall under favorable conditions.
The flowers are nonshowy and without petals.
Areas of Infestation and Yield Loss Potential: Giant ragweed is often found in disturbed sites with moist soil.
If not controlled, early emerging plants at densities of 0.5 plants/ft2 can reduce corn yield up to 40%.
Herbicide Resistance: Biotypes of this plant have been reported to be resistant to ALS-inhibitors  in many states, and glyphosate  has been reported in some populations in Minnesota, Iowa, and Nebraska.
Biotypes resistant to both ALS and glyphosate have also been reported.
Common Ragweed 
 Common ragweed  is an annual plant with seeds that germinate when corn is seeded.
Figure 39.38 Smartweed seedling, young ladysthumb plant , ocrea , and raceme inflorescence with pinkish flowers.
Plant Description: This plant has cotyledons that are spatulate , and leaves that are opposite in the lower stem and alternate on the upper stem.
The leaves are finely divided.
The stems are erect,
 branched, and grow to 1 to 2 ft.
The flowers are nonshowy and without petals.
Areas of Infestation and Yield Loss Potential: This weed is typically found in disturbed sites.
At moderate densities, it can reduce corn yields by 10%.
At high densities yield losses can be severe.
Herbicide Resistance: Biotypes of this plant have been reported to be resistant to ALS-inhibitors  in many states.
In South Dakota, glyphosate  resistant biotypes have been documented.
Velvetleaf  is an annual plant with seeds that germinate shortly after corn seeding.
Plant Description: The seedlings have round cotyledons and alternate, heart-shaped leaves.
Leaves are covered with soft hairs giving it a "velvet" feel.
The plant can reach 6 ft in height.
Areas of Infestation and Yield Loss Potential: This plant is often found in crop production fields and roadsides.
In moderate infestations , 20% corn yield reductions have been reported.
Figure 39.40 Common ragweed seedlings at several growth stages and mature plant above a soybean canopy.
Herbicide Resistance: Biotypes in Minnesota and other areas have been reported to be resistant to Photosystem II inhibitors  herbicides.
Figure.
39.41 Velvetleaf seedling and mature plant.
Black nightshade  Black nightshade  is an annual plant with seeds that germinate when corn is emerging.
Plant Description: The cotyledons of the seedling are ovate, green on upper surface and purple on lower surface.
Leaves are alternate and oval in shape with few hairs.
Leaves are often holey because of flea beetle feeding.
Flowers are white to bluish.
Seeds are in berries with 50 to 100 seeds per berry.
The juice of the berry stains seeds and reduces crop value.
Areas of Infestation and Yield Loss Potential: This plant can often be found in disturbed sites.
With high to moderate infestations (> 1 plant/ft2 yield losses can be 80%.
Juice of berries also mixes with chaff and this combination can plug combines.
Herbicide Resistance: Black nightshade biotypes have been reported to be resistant to ALS-inhibitor  and Photosystem II inhibitors , as well as cell-membrane disruptor   herbicides.
Figure 39.42 Blacknightshade cotyledon, underside of young plant, and plant with flowers.
Venice mallow 
 Venice mallow  is an annual plant with seeds that typically germinate after corn emergence.
Plant Description: The cotyledons of the seedlings are round and the leaves are alternate with 3 to 7 distinct lobes.
The leaf surface has hairs and the flowers are white to pale yellow.
Fruits are an inflated capsule.
Areas of Infestation and Yield Loss Potential: This plant can often be found in disturbed sites and it is drought-tolerant and can grow in gravely and acid soils.
Corn yield losses are generally < 5% with moderate infestations, although season-long competition can increase this loss.
Herbicide Resistance: As of 2015, herbicide resistance has not been reported.
Buffalobur  is an annual plant where the seeds typically germinate after corn emergence.
Plant Description: The first true leaves of seedlings are lance-shaped and the leaves are many-lobed, and alternate along the stem.
Leaf surfaces and stems are spiny with long yellow spines.
Spiny capsules hold the fruit.
Areas of Infestation and Yield Loss Potential: Buffalobur thrives in well-drained, disturbed soils.
Depending on density and emergence date, yield losses are generally low to moderate.
Herbicide Resistance: As of 2015, herbicide resistance has not been reported.
Common sunflower  Common sunflower  is an annual plant and has seeds that germinate during or shortly after corn planting.
Plant Description: The plant cotyledons are oval with toothed-shaped margins on alternating leaves.
The stems become multi-branched and covered with stiff hairs as the plant matures, and also has characteristic yellow flowers.
This plant may be confused with Jerusalem artichoke, a perennial.
Common sunflower will not have creeping rhizomes.
Areas of Infestation and Yield Loss Potential:
 Infestations typically occur in drier soils.
At moderate densities, this plant can reduce corn yields 70%.
Herbicide Resistance: Some biotypes of common sunflower are resistant to ALS-inhibitor  herbicides.
Common Cocklebur 
 Common cocklebur  is an annual plant with seeds that germinate after corn seeding.
Plant Description: The cotyledons of the seedlings are linear, thick, and shiny green.
Leaves are alternate and large with wavy margins.
Seeds are in burs that stick to animal coats.
Areas of Infestation and Yield Loss Potential: This plant can often be found in wet, poorly drained soils.
At high densities, it can reduce yields 70%.
Herbicide Resistance: Biotypes of cocklebur have been reported to be resistant to ALS-inhibitor  herbicides in some Midwestern states.
Russian thistle 
 Russian thistle  is an annual plant that typically emerges before or at corn planting.
Plant Description: The seedlings resemble small pine trees with threadlike leaves.
Older plants become spinelike with the leaf surface from smooth to hairy with nonshowy flowers.
The entire plant breaks off at the base and disperses seed as it tumbles in the wind.
Areas of Infestation and Yield Loss Potential: This very droughtand salt-tolerant plant can be found in many areas.
Depending on density and time of emergence, this plant can reduce corn yields 50%.
If Russian thistle comes up even 1 week after the crop, yield losses may not be measurable.
Herbicide Resistance: Biotypes have been reported to be resistant to ALS-inhibitor  herbicides.
Common lambsquarters 
 Common lambsquarters  is an annual plant and it has seeds that generally germinate at or slightly before corn planting.
Plant Description: Emerging plants are very small, and the leaves are opposite and covered with a mealy powder, especially on the underside.
The stems are erect, may have green or red stripes, and can grow to almost 6 ft tall under certain conditions.
The flowers are nonshowy and without petals.
Areas of Infestation and Yield Loss Potential: Found in disturbed sites.
Depending on density yield losses can be 30%.
Herbicide Resistance: Biotypes of this plant have been reported to be resistant to ALS-inhibitor  and Photosystem II inhibitors.
Reduced sensitivity to glyphosate  has been reported in some populations.
Kochia  is an annual plant that reproduces from seeds.
Kochia emerges at or before corn planting.
Plant Description: Seedlings can be very small with over 1000 present in a 1-ft2 area.
Leaf margins are fringed with hair.
Leaf surfaces range from being without hairs to very hairy.
Wind-blown plants will disburse seed in the fall.
Areas of Infestation and Yield Loss Potential: Kochia is often found in disturbed sites.
Depending on density, yield losses can be 40%.
Herbicide Resistance: Some kochia biotypes in South Dakota have been reported to be resistant to Photosystem II inhibitors  , ALSinhibitors , and synthetic auxin herbicides.
Wild Mustard 
 Wild mustard  is an erect annual plant with seeds that germinate before or at corn planting.
Plant Description: The cotyledons are kidneyshaped, and the leaves are alternate with hairs on the bottom of the leaf.
Lower leaves are deeply lobed, whereas upper leaves are coarsely toothed.
Flowers are yellow and seeds are found in a thin pod, known as a silique.
Areas of Infestation and Yield Loss Potential: This plant is often found in disturbed sites.
Yield losses are dependent on density.
For example, 1 and 4 plants/ft2 can reduce yield 10% and 50%, respectively.
Herbicide Resistance: Biotypes have been found to be resistant to ALS-inhibitor  herbicides.
South Dakota Noxious Weeds
 Noxious Weeds of South Dakota 
 Canada thistle	1.6 million
 There are many weeds in the state that have been listed as Local  Noxious Weeds.
These plants can be annual, biennial, or perennial.
Before the plant can be placed on the local  noxious weed list, the county has to petition the South Dakota State Weed and Pest Board.
If approved for listing, the plant remains on the list for a maximum of 5 years.
Saltcedar  was introduced into the United States in the 1820s for ornamental and windbreak purposes.
This perennial shrub or small tree reproduces from seeds, root sprouts, and buried stems.
Plant Description: The leaves are alternate and scalelike, blue-green to gray-green.
Stems are erect or bushy, and can be up to 20 ft tall.
Flowers are pink arranged on a raceme inflorescence.
Millions of seeds can be produced per plant.
Flowering can start in early April and continue through September.
Areas of Infestation: Often found in wet, disturbed sites, with the first infestations seen along the outside of potholes or along riverbanks.
When the plants continue to invade, the infestation can be found in drier sites in very dense stands.
Saltcedar is difficult to control.
This plant has been found in western and southern South Dakota along rivers and streams and a few eastern South Dakota sites along lakes shores.
Leafy Spurge 
 Leafy spurge  is a perennial, erect plant reproducing by seed, crown buds, and rhizomes.
Plant Description: The leaves are alternate and narrow.
Stems are erect up to 2.5 ft tall, branched
 above and without hair.
When cut, stems exude a milky latex.
Creeping rhizomes can extend about 10 ft from the original plant and have many buds on the lateral root.
Flowers are greenish-yellow in small clusters.
Seeds are in capsules that can split when ripe and shoot seed up to 20 ft.
Flowering can start in May and continue through September.
Areas of Infestation: Often found in disturbed sites in very dense stands and the plant is difficult to control.
Pasture areas of eastern South Dakota both north and south have dense leafy spurge infestations.
Scattered plants can be found along roadsides.
Purple Loosestrife 
 Purple loosestrife  is a perennial, erect plant, reproducing by seed and rhizomes.
This plant is an escaped ornamental.
Plant Description: The stems are erect, not highly branched, four-angled, and hairless.
Leaves are opposite or in whorls.
Leaf blades are lanceolate with sharply pointed tips.
Leaves have no petioles  and leaves are covered with hairs.
Crown buds and short creeping rhizomes.
Flowers are purple and arranged on spikes.
Flowering can start in July and continue through September.
Areas of Infestation: Often infestations start in very wet sites, but can then invade drier areas.
The stands are too dense for waterfowl nesting and wet areas go dry because of this infestation.
It spreads rapidly and is aggressive.
This plant can be found along the shores and sandbars in the Missouri River.
The eastern South Dakota pothole region may be highly vulnerable to invasion.
The plant is difficult to control even with biocontrol agents that have been released in some areas.
Russian knapweed 
 Russian knapweed  is a perennial, erect plant, reproducing by seed and rhizomes.
Do not hand-pull as plant contains toxins that cause problems.
Horses that eat this plant may get "chewing disease" from toxins in the plant.
Plant Description: Russian knapweed stems are erect, sparsely hairy, forming dense colonies.
The plant has creeping rhizomes that produce adventitious shoots.
Leaves are alternate with lower leaves lobed and upper leaves linear.
Inflorescence type is a head with flowers that are pink to purple and numerous.
Flowering can start in June and continue through September.
Areas of Infestation: Often found in disturbed sites in very dense stands and the plant is difficult to control.
This plant has the greatest acres of infestation in Hutchinson County with scattered reports in other eastern and western South Dakota counties.
Hoary cress 
 Hoary cress  is a perennial, erect plant, reproducing by seed and rhizomes.
Plant Description: Hoary cress leaves, which clasp the stem, are alternate with lower leaves oblong and upper leaves more lance-shaped.
Stems are erect, sparsely hairy.
Creeping rhizomes that can extend about 10 ft from the original plant.
Flowers are white on corymbs of numerous racemes.
Flowering can start in early April and continue through August.
Areas of Infestation: Often found in disturbed sites in very dense stands.
The plant is difficult to control once established.
The plant is found in scattered infestations throughout western South Dakota with the highest infested areas reported in Butte County.
Irrigation Systems for the Garden
 A recap of a Granite State Gardening interview on irrigating the garden with Jeremy DeLisle
 Micro-sprinklers, drip irrigation, and soaker hoses are all low-volume and highly efficient irrigation techniques when used correctly.
Plants in your garden will grow better with even soil moisture and irrigation can be a great way to not only conserve water, but also reduce stress to your plants and physiological issues like cracking and blossom end rot.
Other advantages are reduced runoff when irrigating on a slope, adaptability as your garden changes and grows, and the opportunity to automate and optimize watering.
These systems are also increasingly accessible and affordable for home gardeners, and many suppliers carry products specifically designed for small scale use, even as small as raised beds and containers.
There are a few ways of irrigating a garden:
 Overhead watering with a sprinkler system: oscillating or impact sprinklers
 There are also a few sources of water for irrigating the garden:
 Surface water like streams or ponds
 Rainwater, captured with a rain barrel.
When using a rain barrel, the rainwater is often collected from a roof.
Keep in mind there may be bird excrement or substances on the roof that may impact the safety of using collected rainwater on crops you plan to eat.
If you are going to use this type of water, preferably use it in a drip system and ensure the drip tape is under mulch so that the water isn't wetting the foliage of your food crops.
A typical practice is to utilize screening to prevent debris from entering the barrel, while also preventing insects such as mosquitoes from utilizing the water source as a breeding location.
Some barrels come with rings that can be screwed on to the top of the barrel.
These typically have a few larger holes cut out for water to enter from gutters, or whatever the surface is that will collect the water to be diverted into the barrel.
Screening can be laid over the top of the barrel before the ring is screwed on to trap it in place and filter out large debris.
If you are using water from a well, you will want to measure the output of your well.
There is significant variation.
To find out what your flow rate is, see how long it takes to fill a 5-gallon bucket at full pressure and then go from there to do your calculations.
The math is simple.
You need to convert seconds to minutes, so divide the number of seconds it took to fill the bucket by 60, and then plug that into the formula of gallons / minutes = gallons per minute.
For example, if it took 10 seconds to fill your 5-gallon bucket, the equation is 5 /  = 29.4 gallons per minute.
Your drip tape will list a maximum flow rate.
If that maximum flow rate is.5 gallons per minute per 100 feet, which is a common maximum flow rate, then you use the formula of  x 100 feet to calculate how much drip tape you can use in a zone.
Each zone has its own submain pipe, and you do these calculations to ensure that you dont exceed the capacity of your system and can control how much water goes through your system to your plants in a given time.
You will only run water into one zone at a time.
Learn more about these calculations from the fact sheet Simple Calculations for Small Drip Irrigation Systems from the University of Kentucky Cooperative Extension Service.
Understanding what your maximum flow rate is from your water source, what flow rate can be supported by your irrigation system, and critically how much water you need to provide for your crops, you can hone in on how long you want to run your system at a given time.
If there is elevation change, Colorado State Extension says that a general rule of thumb is to add 5 psi to the operating pressure for every 10-foot rise in elevation above the point of connection to the water source.
Your soil profile is a factor in determining how much irrigation to provide.
A loamy soil with a higher organic matter content will have good water holding capacity and good drainage, whereas a clay soil will hold water with poor drainage and sandy soil will have poor water holding capacity.
With sandy soil, you will want to water more frequently for short bursts, whereas a loamy soil will be better suited to less frequent, deeper watering.
A soil moisture sensor is a helpful tool to guide your irrigation rates.
Regularly monitoring soil moisture levels and adjusting the frequency and volume of your irrigation makes a significant difference, and should be done throughout the growing season as your crops develop and weather changes.
Generally, crops need more frequent watering when they are less developed, and less frequent, deeper watering as they are further developed.
In a garden setting, a moisture meter will likely show your levels on a dry to moist scale and come with a guide to where you want moisture levels to be for different crops.
An alternative or supplement to a moisture meter can be the use of a rain gauge or rainfall monitoring data from a source like NEWA.
If you utilize a water softener, you will need to install a hose spigot before the water reaches the softener so you can divert that water to your garden and landscape before it goes through the water softener.
The sodium-based salts used by water softeners are toxic to plants, so you should never water plants with softened water.
Filtration to remove algae, sand and other materials is important.
If using surface water or well water, you may need to use more elaborate filters, and frequent cleaning may be necessary if you are not using self-cleaning emitters.
Filters with a higher mesh count have greater screening capacity.
Look for Y or T filters that do not require dismantling to clean, as opposed to in-line filters.
The basic components of a drip irrigation system are as follows:
 The distribution system, consisting of the hose bibb, filter assembly and feeder lines we recommend a backflow prevention device and a pressure reducing valve, and a timer can also be incorporated between the hose bibb and the filter body.
The feeder lines, with drip tape attached to quarter turn valves
 The drip tape, folded over several times at the end
 Drip tape is an efficient way of irrigating your plants that enables a high degree of control over how much you are irrigating your crops and how it is spaced to provide optimal irrigation for your garden's design.
Drip tape is most suitable for annual crops being grown in rows.
It is important to properly space emitters.
If placed poorly or too far apart, plants can suffer.
Another mistake to avoid is using more than 200 feet of mainline for a single zone.
If you are just using drip tape for irrigation, you should be able to get several seasons out of the tape if stored properly over winter.
If you are feeding fertilizer through the tape, it may only last a season.
If your tape has suffered damage or clogging, it may be worthwhile to replace the tape instead of trying to get another season out of it.
Drip tubing is another technique for drip irrigation.
Tubing is more rugged and can be left in the ground over the winter, so is better suited to perennial plantings such as perennial vegetables, fruits, trees, and shrubs.
The tubing needs to be drained of water at the end of fall but can be left over winter.
If you are gardening in raised beds, some additional plumbing is necessary with a few more fittings to create the necessary angles.
For maintenance, you should regularly monitor for leaks.
If you have a timer with a flow meter, you will notice a spike in flow that might signal a leak.
Another way you might notice a leak is if plants in an area start to struggle.
In that case, the irrigation system should be checked in that area for clogs or leaks.
Nuisance wildlife can be an issue, so look for chewing on lines and respond accordingly with needed repairs and wildlife management as needed.
Goof plugs can be used to plug holes in the mainline that are not needed.
When you harvest crops, we recommend turning off water flow to that area.
Store your feeder lines with vales open and one end cap removed.
Ensure all water has drained out and attach the lines to a wall or fence with the opened end at the lowest point.
Ensure that you remove your filter assembly from the hose bibb and feeder lines as well.
In the spring, check for leaks and cracks with closing all your valves and pressurizing the system.
Soaker hoses are perforated rubber hoses with either small holes that slowly release water into the soil or that exude water along the entire length of the hose.
Soaker hoses can be placed in a curved orientation and then be buried in mulch, proving optimum irrigation hidden from sight.
Soaker hoses are well suited to plantings in irregular shapes and can also be a good option for raised beds.
Soaker hoses are a great entry level option for a gardener that wants to move away from overhead irrigation.
We will caution that soaker hoses can get plugged up and suffer from declining flow as the hose gets filled up with bacterial iron, calcium deposits, sand, and other debris.
Moisture levels should be regularly monitored to ensure the soaker hose is working properly, and the hoses themselves should also be regularly inspected to ensure they are emitting water as intended.
Micro-sprinklers, which are also called micro-sprayers, can be a good option for certain crops, and are an excellent option for raised beds.
These systems will provide excellent coverage and come in a variety of sizes and patterns to meet your needs.
Micro-sprinklers may be a great option for leafy greens in particular.
Upgrading your sprinkler is another great option.
Oscillating sprinklers that are sturdy, adjustable, and made with quality materials can make a significant difference.
For overhead irrigation, limit your watering to the early morning rather than during the day or in the evening.
How to Calibrate Your Sprinkler System 
 Knowing the amount of water your sprinkler system applies to your landscape is an important step in efficient water use.
Most people irrigate their landscape for a given number of minutes without knowing how much water they are really applying.
This may lead to overor under-watering, neither of which will benefit the landscape nor the environment.
Calibrating will help you to apply the correct amount of water to your landscape.
Whether you have an in-ground system or a hose and a sprinkler, the following steps will calibrate your system:
 Figure 1.
Calibrating a Sprinkler System
 1.
Obtain several  coffee cans, tuna fish cans, or other straight-sided containers to catch the irrigation water.
Containers need to be the same size and should be from 3 to 6 inches in diameter.
2.
If you have an in-ground irrigation system, place the containers in one zone at a time.
Scatter the cans at random within the zone.
Repeat the entire procedure in every zone because there may be differences in the irrigation rates.
If you use a hose-end sprinkler to water your landscape, place the containers in a straight line from the sprinkler to the edge of the watering pattern.
Space the containers evenly.
3.
Turn the water on for 15 minutes.
4.
Use a ruler to measure the depth of water in each container.
Note: The more precise the measurement, the better your calibration will be.
For most cases, measurements to the nearest 1/8 inch are adequate.
5.
Look for large differences in water amounts between cans.
For example, if one has 1/2 inch or more and other cans are nearly empty, you
 2.
L.E.
Trenholm, Associate Professor, Turfgrass Specialist, Department of Environmental Horticulture, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611, J.
Bryan Unruh, Associate Professor, Turfgrass Specialist, West Florida Research and Education Center, Institute of Food and Agricultural Sciences, Jay, FL 32565, J.L.
Cisar, Professor, Turf Specialist, Ft.
Lauderdale Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida, Ft.
Lauderdale, FL 33314.
The Institute of Food and Agricultural Sciences  is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations.
U.S.
Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A.
& M.
University Cooperative Extension Program, and Boards of County Commissioners Cooperating.
Millie Ferrer, Interim Dean
 know that your coverage is not uniform and your system needs to be inspected further.
6.
Find the average depth of water collected in the containers.
7.
To determine the irrigation rate in inches per hour, multiply the average depth of water times four.
For example, if you collect an average of 1/4 inch in 15 minutes, and your target application rate is 1/2 inch, you will need to run your irrigation system for 30 minutes.
Refer to Table 1 for additional calculations.
To calculate the time of irrigating for rates not listed in Table 1, use equation 1.
Calibrate the sprinkler system during the same time it is normally run, SO that water pressure is similar.
Low water pressure can significantly reduce the amount and coverage of water applied by a sprinkler system.
Application rates normally should not exceed 1/2 to 3/4 inch of water per irrigation.
Most irrigation controllers can be adjusted for accurate time settings.
Consult your operating instructions or local sprinkler company for details.
If you use a hose-end sprinkler, a mechanical timer and shut-off switch that attaches to the faucet will help make watering more efficient.
Avoid mixing sprinkler head types within the same zone.
Mist heads apply more water than impact or rotary heads.
Match sprinkler heads for uniform coverage.
Most rotary heads come with several different nozzles to choose from.
Make sure that the nozzles are matched.
Check the sprinkler system regularly.
Replace broken sprinkler heads, clear clogged nozzles, and adjust the direction of spray as needed.
Be sure that irrigation water is not thrown on driveways, sidewalks, or roadways.
Use water efficiently; do not waste it.
For more specific information on turf irrigation, see factsheet ENH 9, "Watering Your Florida Lawn."
 Figure 2.
Hose-End Sprinkler
 Amount of water to be applied X 60 Minutes required to run each zone = Your calibrated irrigation rate
 Equation 1.
Use this equation to calculate the time required to apply water for rates not listed in Table 1.
Table 1.
Time required to apply water for a given irrigation rate.
Irrigation Rate (Amount of water
 1/2"	1"	1 1/2"	2"
 Total water to	Minutes to run each zone
 1/2"	60	30	20	15
 3/4"	90	45	30	23
In a dry year, aerial imagery can be a useful tool to help identify systematic patterns  within a field as a result of water stress from poor uniformity.
However, in high rainfall areas  aerial imagery may not be able to visually identify differences in the crop canopy.
In these instances, it's recommended that catch cans be used to evaluate application uniformity.
Evenly distribute cans of equal size across the system, measure the depth of water applied, and compare to identify areas of nonuniform water application.
EFFECTS OF IRRIGATION ON SAFFLOWER SAN JOAQUIN
 B.
B.
FISCHER H.
YAMAD.
Highest yields of safflower were obtained when a medium pre-irrigation of 18 inches and two supplemental 8-inch crop irrigations were applied, according to the trial reported here.
When approximately the same total amount of water was applied in one pre-irrigation or in a pre-irrigation and one supplemental crop irrigation, the yields were significantly lower.
This study strongly suggests that maximum safflower yields  depend on readily available soil moisture in the top 4 feet of soil during bud and flowering periods.
S AFFLOWER IS widely grown on the west side of the San Joaquin Valley.
Yields vary greatly from season to season and from field to field, ranging from as low as 1000 lbs per acre to as high as 3500 lbs.
This great fluctuation can be minimized by providing the plants with moisture especially during the bud and flowering stages of development
 This experiment was conducted on a Panoche clay loam soil at the Boston Ranch Company, Westhaven, Fresno County.
The objective was to determine yield responses to varying amounts of water applied in pre-irrigation and supplemental crop irrigations.
All plots were uniformly fertilized, prior to the pre-irrigation (in mid-
 TABLE 1.
SOIL MOISTURE MEASUREMENTS BEFORE AND AFTER PRE-IRRIGATION, AND FOLLOWING HARVEST
 Soil	S1	S2	S3	S4
 depth	Before	After	After	After	After	After	After	After	After
 pre-irr.
pre-irr.
harvest	pre-irr.
harvest	pre-irr.
harvest	pre-irr.
harvest
 Feet	Inches	Inches	Inches	Inches	Inches	Inches	Inches	Inches	Inches
 0-4	6.11	16.45	6.39	17.81	7.60	18.50	7.39	17.04	6.74
 4-8	7.33	16.95	6.67	10.31	7.09	9.51	6.61	11.13	7.26
 8-12	11.79	14.50	12.14	12.71	10.98	13.52	12.48	12.59	12.19
 0-12	25.23	47.90	25.20	40.83	25.67	41.53	26.48	40.76	26.19
 TABLE 2.
CALCULATION OF EVAPOTRANSPIRATION FOR THE VARIOUS IRRIGATION TREATMENTS
 treatments	Irrigation	Total water	applied	evapotranspiration	Calculated	water applied	E.T.
of total	Used by	Water leached	beyond 12 ft.
after pre-irr.
after horvest	remained in	soil profile
 Inches	Inches	%	%	%
 S1	30.2	22.7	75.2	24.8
 S2	33.6	30.9	92.0	6.8	1.3
 S3	25.1	22.3	88.8	6.4	5.0
 S4	16.3	14.6	84.5	4.9	5.9
 TABLE 3.
EFFECT OF IRRIGATION ON YIELD AND BUSHEL WEIGHT OF SAFFLOWER
 Treatment	Pre-irr.
Crop irr.
Yield	Stat.
Bushel	Stat.
Oct.
63	Apr.
14	May 28	lbs/A	notation*	weight	notation*
 S1	30.2	2,413	b	41.1	b
 S2	17.9	7.9	7.8	3,039	a	41.8	a
 S3	17.9	7.2	2,476	b	39.0	bc
 S4	16.3	1,803	C	38.2	C
 C.V.
9.33%	C.V.
3.31%
 October) by injecting NH3 gas into the soil to a depth of 9 inches, with a 16-inch spacing, at the rate of 100 lbs nitrogen per acre.
Fifteen pounds of U.S.
10 safflower variety  were drilled in two rows on each 40-inch bed, spaced 20 inches apart on December 5, 1963.
The rainfall total from planting until harvest was approximately 2.5 inches.
Yields and bushel weights having the same letters are not significantly different at the 1% probability level.
Individual plots were 24 ft wide and 600 ft long, replicated five times.
The amount of water applied in the pre-irrigation and crop irrigations was measured through siphon tubes for each plot.
The treatments and the amounts of water applied were as follows: S1, 30.2-inch pre-irrigation; S2, 17.9-inch pre-irrigation plus 7.9 inches at bud stage  and 7.8 inches at first bloom  : S3, 17.9-inch pre-irrigation plus 7.2 inches at bud stage  inch pre-irrigation.
The field had been cropped and treated uniformly for the previous two years.
To determine the initial moisture content of the field, eight locations were selected at random, and soil samples were taken to a depth of 12 ft in one-foot increments, prior to the pre-irrigation.
The moisture percentages were then converted to inches of water in the soil by multiplying the bulk density  times inches of soil.
The bulk density was determined by taking core samples from two 12-foot pits dug in the field with a back hoe.
Soil sampling before the pre-irrigation, after pre-irrigation, and again after harvest made it possible to account for all the water applied through siphon tubes on the plots  In the soil samples following the pre-irrigation, it
 was found that 7.5, 2.3, 1.6 and 0.8 inches of moisture percolated beyond the depth of sampling for S1, S2, S3 and S4 treatments, respectively.
The soil samples taken after harvest indicated that not all the moisture applied in the 12-foot soil profile was used.
The S1 treatment had the same moisture content as the initial soil samples before the pre-irrigation, and S2, S3 and S4 had 0.4, 1.2 and 0.9 more inches of moisture, respectively, than the initial soil samples.
Therefore, not all the moisture that was added to the soil profile was used by the safflower plants.
The evapotranspiration , or the amount of moisture extracted from the various depths, is summarized in tables 1 and 2.
The percentage of E.T.
of the total water applied was highest for the S2 treatment.
The amounts of moisture extracted from the top 4 ft of soil , in treatments S2 and S3 indicate that the bulk of the roots were in that zone.
Treatment S2 suggests that to obtain maximum yields, adequate moisture
 Progress Reports of Agricultural Research, published monthly by the University of California Division of Agricultural Sciences.
PRACTICES YIELD IN VALLEY
 William W.
Paul Manager Agricultural Publications Jerry Lester Editor Chispa Olsen Assistant Editor California Agriculture
 Articles published herein may be republished or reprinted provided no advertisement for a commercial product is implied or imprinted.
Please credit: University of California Division of Agricultural Sciences.
California Agriculture will be sent free upon request addressed to: Editor, California Agriculture, 207 University Hall, University of California, Berkeley, California 94720.
To simplify the information in California Agriculture it is sometimes necessary to use trade names of products or equipment.
No endorsement of named products is intended nor is criticism implied of similar products which are not mentioned.
needs to be available in the top 4 ft of soil during the reproductive stages of the safflower development.
To follow the depth-of-wetting and extraction patterns by the safflower roots, electrical resistance gypsum blocks were installed on March 11.
The blocks were set at 2-, 4-, 6-, 8-, 10-, and 12-foot depths at 1/3 the distance from each end of each plot in three of the five replications.
Readings were taken at weekly intervals during the growing season and the block readings were averaged for each treatment.
The 2and 4-, 6and 8-, and 10and 12-foot depths were averaged and plotted on graphs 1, 2, 3, and 4.
The higher the reading, the more moisture that was available to the plants.
The highest yield was obtained in treatment S2, where two crop irrigations were applied.
The lowest yield was harvested in treatment S4, where only a 16" pre-irrigation was applied.
Yields were obtained by harvesting a 14ft swath through the full length of each plot in the five replications.
The grain was transferred from the combine into a portable scale for weighing, and subsamples were obtained for bushel weight determinations.
Yields in treatments S1 and S3 did not significantly differ and their consumptive use of water was approximately the same.
Bushel weight was significantly higher in treatment S2.
Safflower is a deeply rooted crop and will extract moisture from as deep as 12 ft as shown in this study; for maximum yields , supplemental crop irrigations are essential.
Many growers have been reluctant to irrigate safflower because of fear of root rot.
Recent studies indicate that, with presently available varieties, root rot injury can be minimized by growing the plants on raised beds and irrigating before any drought symptoms appear.
In other words, irrigation is necessary before plants show visible stress.
No root rot was observed in any of the treatments reported in this study.
B.
B.
Fischer is Farm Advisor, Fresno County; H.
Yamada is Laboratory Technician IV, University of California West Side Field Station, Five Points; and C.R.
Pomeroy was Irrigation Specialist and Superintendent, West Side Field Station,.
Don A.
Patterson and Jim Fisher of Boston Ranch, Westhaven, assisted in conducting this experiment.
AVERAGE GYPSUM BLOCK READINGS FOR S1, S2, S3, AND S4 TREATMENTS, SAFFLOWER IRRIGATION TRIAL, FRESNO COUNTY
IMPACT OF WIDE DROP SPACING AND SPRINKLER HEIGHT FOR CORN PRODUCTION
 Bill Kranz Northeast Research and Extension Center University of Nebraska Norfolk, NE 68701
 Freddie Lamm Northwest Research-Extension Center Kansas State University Colby, KS 67701-1697
 Derrel Martin Biological Systems Engineering Department University of Nebraska Lincoln, NE 68583
 Jose Payero West Central Research and Extension Center University of Nebraska North Platte, NE 69101
 Using center pivot sprinkler nozzles below the top of the corn crop canopy presents unique design and management considerations.
Distortion of the sprinkler pattern can be large and the resultant corn yield can be reduced.
In many areas, water available for irrigation is being limited due to reduced supply of both ground and surface water.
During periods of drought, uniformity problems associated with center pivot irrigation become quite visible.
Many times water stress on the crop is not evident until late in the season when the crop has nearly matured.
In many cases aerial observations of fields have revealed concentric rings that corresponded to sprinkler spacing.
Figure 1a.
Height reduction in corn caused by drops spaced too wide.
igure 1b Concentric rings in corn field caused by having drops spaced too wide.
The impact of sprinkler spacing on water distribution and corn yield was the focus of University of Nebraska and Kansas State research studies.
Researchers conducted field experiments along with on-farm evaluations to gain a better understanding of operating sprinkler devices within the corn canopy.
The results from these experiments will be discussed.
Field Evaluation of Changes in Soil Water Content
 In a Nebraska study soil water content was measured as a method to evaluate the uniformity of water distribution.
Soil water content was measured in the top 12 in.
of soil before and after irrigation.
Spinners 1 were spaced 12.5 ft apart and located at a height of 42 inches in a mature corn crop.
Sprinklers were moving parallel to the corn rows but not necessarily between the corn rows.
Figure 2 shows the location of the sprinklers in the corn rows and the change in soil water content measured before and after irrigation.
Soil water content increased nearly 12% in the rows nearest the sprinkler device.
Soil water content averaged less than a 2% increase at locations directly between the sprinkler devices.
The small change in soil water content indicates the rows between the sprinkler devices received little or no water during the irrigation event.
In-Canopy Water Distribution Pattern
 Figure 2.
Changes in water content following irrigation with sprinkler nozzles located in a corn canopy.
1 Mention of trade name is for information only and does not imply endorsement
 Variation in Corn Yield as Affected by Sprinkler Height
 When the sprinkler pattern is distorted and the nozzle spacing is wide enough to prevent some corn rows from getting equal opportunity to water, yields can be reduced.
A study was conducted at the KSU Northwest Research-Extension Center from 1996-2001 to examine the effect of irrigation capacity and sprinkler height on corn production when the spray nozzle spacing was too wide for adequate in-canopy operation.
Performance of the various combinations was examined by measuring row-torow yields differences  Corn rows were planted circularly allowing the nozzle to remain parallel to the corn rows as the nozzle traveled through the field.
As might be expected, yield differences were greatest in dry years and nearly masked out in wet years.
For the purpose of brevity in this report, only the 6 year average results will be reported.
Even though the average yield for both corn rows was high, there is a 16 bu/acre yield difference between the row 15 inches from the nozzle and the corn row 45 inches from the nozzle for the 2 ft nozzle height and 10 ft nozzle spacing.
At a four ft nozzle height the row-torow yield difference was 9 bu/acre and at the 7ft height the yield difference disappeared.
This would be as expected since pattern distortion was for a shorter period of time for the higher nozzle heights.
It should be noted that the circular row pattern probably represents the least amount of yield reduction, since all corn rows are within 3.75 ft of the nearest nozzle.
For straight corn rows, the distance for some corn plants to the nearest nozzle is 5 ft.
KSU-NWREC, 1996-2001 Spinner Nozzle with 10ft spacing Note: 10 ft spacing not recommended
 Figure 3.
Row-to-row variation in corn yields as affected by sprinkler height in a study with a nozzle spacing too wide  for in-canopy irrigation, Colby, Kansas.
Data averaged across 4 different irrigation levels.
Note: The average yield for a particular height treatment would be obtained by averaging the two row yields.
On-Farm Evaluation of Sprinkler Spacing
 Many center pivot sprinkler systems are designed with wide sprinkler spacing as a method to reduce equipment cost.
For outer spans closer sprinkler spacing is needed in order to meet the water application requirements.
Although concentric rings were showing up in Nebraska fields, the outer portions of the fields showed no such pattern.
To evaluate the rings, a series of samples were collected to determine crop yield and soil water content.
Samples were collected from both sprinkler spacings where the spacing transition occurred to insure similar soil type and cultural conditions.
The location of sprinklers were first identified in relation to the wheel tracks.
Then the location of sprinklers were superimposed in that area of the field where the center pivot sprinkler devices run nearly parallel with the planted rows of corn.
All corn rows between two sprinkler devices were sampled to determine soil water content and grain yield.
Yield was determined by harvesting 10 feet of row.
Soil water content was measured to a depth of 4 feet at one location in each row.
The results given are the average of two yield and soil water content samples.
Field measurements were collected for two different center pivot fields represented in figures 4 and 5.
Sprinklers were located at a height of 7 ft.
and at either a 9 or 18 ft.
spacing.
Corn rows were planted 30 in.
apart.
Figures 4a and 5a shows the results for the narrow spacing of the two fields while figures 4b and 5b show results for the wide sprinkler spacing.
Generally, there were no reasonable patterns for either yield or soil moisture content for the 9 ft.
sprinkler spacing in figures 4a and 4b.
However, corn yield did decline when the sprinkler spacing increased to 18 ft.
in figures 5a and 5b.
Because soil water data was collected at the end of the season when the crop was mature, some of the difference, or lack of difference, in soil water content may have been eliminated with late season precipitation or added irrigation.
It should also be noted that soil water content is extremely low and most likely approaching wilting point.
Figure 4a.
Corn yield and soil water content for sprinkler devices spaced 9 ft apart at 7 ft height.
Figure 4b.
Corn yield and soil water content for sprinkler devices spaced 18 ft apart at 7 ft height.
Figure 5a.
Corn yield and soil water content for sprinkler devices spaced 9 ft.
apart at 7 ft height.
Figure 5b.
Corn yield and soil water content for sprinkler devices spaced 18 ft.
apart at 7 ft height.
Effect of sprinkler height and type on corn production
 Another study conducted from 1994-95 at the KSU Northwest ResearchExtension Center examined corn production as affected by sprinkler height and type and irrigation capacity.
Spray nozzles on the span , spray nozzles below the truss rods  and low energy precision application  nozzles  were compared under irrigation capacities limited to 1 inch every 4, 6, 8 or 10 days.
Corn yields averaged 201, 180, 164, and 140 bu/a for irrigation capacities of 1 inch every 4, 6, 8, or 10 days, respectively.
No statistically significant differences in corn yields, or water use efficiency were related to the sprinkler package used for irrigation.
There was a trend for the  package to perform better than spray nozzles at limited irrigation capacities and worse than the spray nozzles at the higher irrigation capacities.
Figure 6.
Corn grain yields as affected by sprinkler height and type at four different irrigation levels, KSU Northwest Research-Extension Center, Colby, Kansas, 1994-1995.
The first observation is supported by research from other locations, which shows that LEPA can help decrease evaporative water losses and thus increase irrigation efficiency.
The second observation indicates that LEPA may not be suited for higher capacity systems on northwest Kansas soils, even if runoff is controlled as it was in this study.
It should be noted that this study followed the true definition of LEPA with water applied in bubble mode to every other row.
The term LEPA is often misused to describe in-canopy spray nozzle application.
The reason that LEPA is not performing well at the higher irrigation capacities may be puddling of the surface soils, leading to poor aeration conditions.
However, this has not been verified.
In 1995 with a very dry late summer, LEPA performed better than the other nozzle orientations at the lower capacities and performed equal to the other orientations at the higher capacities.
Averaged over the two years, the trend continued of LEPA performing better at the lower irrigation capacities.
Overall, spray nozzles just below the truss rods performed best at the highest two capacities, but LEPA performed best when irrigation was extremely limited.
As the cost of pumping increases and water supplies become more restricted, irrigation schedules that more closely match water application to water use will exaggerate the nonuniform application of water due to sprinkler spacing and incanopy operation of sprinkler devices with similar results to what we have shown here.
It has been a common practice for several years to operate drop spray nozzles just below the center pivot truss rods.
This results in the sprinkler pattern being distorted after corn tasseling.
This generally has had relatively little negative effects on crop yields.
The reasons are that there is a fair amount of pattern penetration around the tassels and because the distortion only occurs during the last 30-40 days of growth.
In essence, the irrigation season ends before severe deficits occur.
Compare this situation with sprinklers operated within the corn canopy that may experience pattern distortion for more than 60 days of the irrigation season.
Assuming a 50% distortion for sprinklers beginning 30 days earlier, it would result in irrigation for some rows being approximately 40% less than the needed amount.
These experiments have shown that significant yield reductions do occur because of the extended duration and severity of water stress.
In-canopy center pivot sprinkler irrigation is gaining popularity in much of the Great Plains region.
Physical and institutional constraints have resulted in lower system capacities that have encouraged irrigators to get the maximum benefit from their water application.
However, using center pivot sprinkler nozzles below the top of the corn crop canopy presents unique design and management considerations.
Let's see if you really want to be an in-canopy irrigator!
The rules for the game are:
 1.
Use the provided answer sheet to choose your answer.
2.
Author will provide rationale for correct answer.
3.
Assume you are irrigating a western Kansas corn field.
4.
There might be more than one answer, but choose the best
 5.
Purpose of game is education and to encourage conceptual thinking.
6.
Answers are author's opinion based on his scientific understanding.
7.
Some questions are easier than others.
8.
You can still be an in-canopy irrigator if you fail, but are hopefully wiser.
So, now that you know the rules,
 WHO WANTS TO BE AN IN-CANOPY IRRIGATOR?
1 Any opinions, findings, conclusions, or recommendations expressed in this paper are those of the author and do not necessarily reflect the views of Kansas State University.
ANSWER SHEET FOR WHO WANTS TO BE AN IN-CANOPY IRRIGATOR?
Question	My answer	Lamm's answer
 QUESTIONS FOR WHO WANTS TO BE AN IN-CANOPY IRRIGATOR?
Question 1.
What do the letters LEPA stand for?
A.
Lone Elm Protection Association
 B.
Low Energy Precision Application
 C.
Low Elevation Projected Aperture
 D.
Low Efficiency Puddled Application
 Question 2.
Which of the following is a traditional design criteria for sprinkler irrigation systems?
A.
Always place sprinkler nozzles at a height below the corn ear height
 B.
When irrigating, use a timer setting not more than 7%
 C.
Apply water at a rate less than the soil intake rate
 D.
Use lower capacity sprinklers on sandier soils
 Question 3.
Which of the following is not an advantage of in-canopy sprinkler application?
A.
Higher uniformity due to application closer to soil surface
 B.
Lower wind evaporation losses
 C.
Less canopy interception losses
 D.
Insecticides may be applied to crop canopy
 Question 4.
You are experiencing runoff on your typical Kansas farm when applying 1 inch with in-canopy irrigation.
What solution should you try first?
A.
Speed the system up by reducing cycle time
 B.
Slow the system down by increasing cycle time
 C.
Accept some runoff while reducing evaporation losses
 D.
Raise the outside span of nozzles above the canopy
 Question 5.
Which of the following is the most effective in-canopy management scheme?
A.
Space nozzles 10 ft apart at a height of 4 ft.
B.
Plant corn in circular rows and space nozzles at twice the row spacing
 C.
Replace nozzles annually
 D.
Use short duration cycles later in the crop season
 Question 6.
The father of LEPA is considered to be
 Question 7.
In deficit irrigation situations, a lower value of application uniformity is of more importance.
Question 8.
K-State research has shown in-canopy irrigation can
 A.
Result in 50% water savings when compared to above-canopy irrigation
 B.
Help improve soil structure due to less crusting
 C.
Help reduce nitrogen costs
 D.
Reduce corn yields when nozzle spacing is 10 ft
 Question 9.
Which of the following is not a guiding principle of LEPA sprinkler irrigation?
A.
Pressure at the end tower must be less than 20 psi
 B.
Be capable of conveying and discharging water into a single crop furrow
 C.
Each plant has equal opportunity for irrigation water
 D.
Result in zero runoff from irrigation water application point
 Question 10.
K-State research has found in-canopy sprinkler distortion to be affected by
 A.
Crop row orientation with respect to center pivot sprinkler travel
 B.
Time of the irrigation season
 C.
Height of the nozzles
 D.
All of the above
 Question 11.
Which of the following are true about stemflow, the amount of water reaching the soil by flowing down the stem?
A.
Is a small portion of the total delivered water from the top of a corn canopy
 B.
Is the predominate flow path for a fully developed corn canopy
 C.
Increases with decreased plant spacing
 D.
Both B and C
 Question 12.
K-State promotes use of in-canopy sprinkler irrigation
 A.
For all corn production systems due to high corn water use
 B.
On all sandy soils but less frequently on silt loam soils
 C.
When properly designed and managed
 D.
Both B and C
 CORRECT ANSWERS AND RATIONALE FOR WHO WANTS TO BE AN IN-CANOPY IRRIGATOR?
Question 1.
What do the letters LEPA stand for?
The correct answer is B.
Low Energy Precision Application.
Low energy refers to a guiding principle that nozzle pressures should be in the low range.
Precision application refers to guiding principles related to conveying water equally to the crop furrow, reducing evaporation losses, and eliminating runoff.
Question 2.
Which of the following is a traditional design criteria for sprinkler irrigation systems?
The correct answer is C.
Apply water at a rate less than the soil intake rate.
Traditionally, sprinkler irrigation systems have been designed to uniformly apply water to the soil at a rate less than the soil intake rate to prevent runoff from occurring.
These design guidelines need to be either followed or intentionally circumvented with appropriate design criteria when designing and managing a center pivot irrigation system using LEPA and other in-canopy sprinklers.
Answer A  is incorrect because it ignores the fact that impact sprinklers might be the most appropriate selection in many cases.
Answer B  is incorrect because timer settings are changed as needed to adjust irrigation amount.
Answer D  is incorrect because lower soil water holding capacities for sands generally increase the need for higher capacity sprinklers that can more closely match peak water needs.
Question 3.
Which of the following is not an advantage of in-canopy sprinkler application?
The correct answer is A.
Higher uniformity due to application closer to soil surface is not an advantage of in-canopy sprinkler application.
Distortion
 Question 4.
You are experiencing runoff on your typical Kansas farm when applying 1 inch with in-canopy irrigation.
What solution should you try first?
Figure 1.
Typical soil intake and sprinkler application patterns as related to time to complete the whole application pattern.
Note: Increasing or decreasing the center pivot sprinkler travel speed would not change the peak application rate for either sprinkler type.
Thus runoff would likely still occur.
Increasing or decreasing the travel speed would change the duration of the pattern and thus would decrease or increase the total amount of runoff.
Question 5.
Which of the following is the most effective in-canopy management scheme?
The most effective scheme is B  because it allows water to be applied relatively uniformly to the cropped area and reduces the potential for runoff.
Straight planted corn rows will distort the pattern severely when corn rows are parallel to center pivot sprinkler travel.
Nearly all the center pivot sprinkler capacity will be applied to a few irrigation furrows when the corn rows are perpendicular to sprinkler travel direction.
Nozzles at twice the row spacing still allow plants equal opportunity for the irrigation water.
Answer A  is incorrect because K-State research  has shown 4 ft.
to be the worst height because of the large ear and leaf mass at this location.
Answer C  is generally not required every year.
Nozzle wear is most often associated with heavy pumping of sand.
Answer D  is incorrect because earlier in the season is generally the time period shorter duration cycles are utilized to firm wheel tracks.
Question 6.
The father of LEPA is considered to be
 Question 7.
In deficit irrigation situations, a lower value of application uniformity is of more importance.
The correct answer is B.
False.
In some cases, where irrigation is limited, a lower value of uniformity can be acceptable.
For example, if the maximum water application amount still falls upon the upward sloping line of the yield production function, a crop area deficient of water will be compensated for by an area receiving a larger amount of water.
The example of nonuniform deficit irrigation has the same average application amount as the uniform irrigation amount.
Overall, production under the two systems would be identical because the production function is linear over the range of water applications.
Figure 2.
Hypothetical relationship of relative crop yield and relative water needs for nonuniform deficit irrigation  and for uniform deficit irrigation.
Average relative water need is the same for both irrigation schemes, and, consequently, the average relative yield would also be the same.
Question 8.
K-State research has shown in-canopy irrigation can
 The correct answer is D.
Reduce corn yields when nozzle spacing is 10 ft.
In 1997, corn yields for rows halfway between 10-ft spaced nozzles were reduced as much as 40 bu./acre as compared to corn rows next to the nozzle.
1997 data averaged over irrigation capacities of 1 inch every 4, 5, 6 or 8 days, KSU-NWREC, Colby, Kansas.
FIGURE 3.
Row-to-row variation in corn yields as affected by sprinkler height when in-canopy sprinklers are too widely spaced at 10 ft.
Note: Field average yield for a particular sprinkler height would be the average of the two side-byside bars rather than the higher yield that could be obtained with properly spaced in-canopy sprinklers.
Answer A  is incorrect.
Savings in the 5-15% are more realistically possible.
Answer B  is incorrect because the typically higher peak application rates associated with in-canopy irrigation would tend to degrade the soil surface, leading to more soil crusting.
Answer C  is incorrect.
Nitrogen fertigation has been successfully used with LEPA
 fertigation in some K-State research, but there isn't evidence at the present time indicating it would be more efficient than traditional sprinkler irrigation methods.
Question 9.
Which of the following is not a guiding principle of LEPA sprinkler irrigation?
The correct answer is A.
Pressure at the end tower must be less than 20 psi.
It is not a guiding principle, because the pressure should be less than 10 psi.
Answers B, C, and D  are all guiding principles.
Question 10.
K-State research has found in-canopy spray pattern distortion to be affected by
 The correct answer is D.
All of the above which included crop row orientation with respect to center pivot sprinkler travel, time of the irrigation season and height of the nozzles.
Circular crop rows which result in sprinkler nozzles traveling parallel to corn rows will result in less distortion of the spray pattern.
Spray patterns for widely spaced spray nozzles at a two ft.
height are distorted for approximately 60 days, while spray nozzles just below the truss rod are distorted for only about 30 days.
This difference in time periods for the different heights can ultimately reduce corn yields for rows furthest from the spray nozzle.
This is also noted in Figure 3 where the yield reduction effect for distant rows was greater for the lower heights.
Question 11.
Which of the following are true about stemflow, the amount of water reaching the soil by flowing down the stem?
The correct answer is D.
Both B and C: Is the predominate flow path for a fully developed corn canopy and Increases with decreased plant spacing.
Although most people would think that water falling through the plant leaves would be the primary way water reaches the soil, the fully developed corn plant is actually a very good funnel and channels the water along the stem.
Higher plant population results in more "funnels." At a typical irrigated corn plant spacing of 7.9 inches, stemflow accounts for 53% of the water reaching the soil after tasseling when being irrigated near the top or above the
 corn canopy.
This flow mechanism conceivably could affect application of crop amendments when using the center pivot sprinkler.
Question 12.
K-State promotes use of in-canopy sprinkler irrigation
 The correct answer is C.
When properly designed and managed.
Answer A  is incorrect because sometimes runoff on tight soils and/or sloping ground can easily exceed any possible evaporation savings.
Answer B  is incorrect because system flowrates, which are higher on sandy soils to meet peak water needs, may exacerbate runoff problems.
Furrow irrigation, using siphon tubes and earthen head ditches and tailwater ditches, is the most common method of irrigating field crops in the San Joaquin Valley.
Its operation requires only one irrigator.
Farmers describe irrigation costs, benefits
 Labor costs may offset water savings of sprinkler systems
 In recent years San Joaquin Valley farmers have improved irrigation methods to reduce subsurface drain water and make more efficient use of limited water supplies.
Water-saving methods include sprinklers and gated pipe.
However, these methods involve higher labor and energy costs, which may exceed the value of water saved when switching from surface irrigation methods, such as furrow irrigation with siphon tubes.
Although more expensive, when sprinklers are used correctly they provide better leaching of salts while generating less subsurface drain water than surface methods.
Public policies that reduce the capital cost of investing in sprinkler systems, and research to develop better surface irrigation methods, will assist farmers in continuing their efforts to improve irrigation water management while maintaining economic viability.
State and federal agencies significantly reduced water deliveries to the San Joaquin Valley from 1990 through 1992 due to persistent statewide drought.
In 1993, environmental regulations further reduced surface water supplies, restricting the volume of water that could be pumped into supply canals from the Sacramento Delta.
It is likely that these environmental regulations, and the increasing demand for water among all users in California, will continue to cause reductions in the volume of surface water delivered annually through the Delta to federal and state water agencies.
Many San Joaquin Valley farmers have improved their irrigation practices in recent years to maximize the benefit of water, which is higher priced and in shorter supply.
Higher prices for irrigation water and the desire to reduce subsurface drainage water have also motivated farmers to manage surface irrigation more intensively and to use sprinkler systems for some irrigation events.
The improved
 Sprinklers irrigating a cotton field on the west side of the San Joaquin Valley.
It is possible to improve water distribution by using sprinklers, which also leach salts more uniformly through the soil profile.
Above, tomatoes irrigated in every other furrow using siphon tubes and an earthen head ditch.
Below, tomatoes irrigated using gated pipe with erosion socks.
Gated pipe irrigation systems have a higher capital cost, but reduce the seepage losses that occur in earthen head ditches.
management of surface irrigations and the use of sprinklers allowed farmers to plant more acres of field crops during the drought than they could have irrigated using traditional methods.
However, most of the farm-level improvements have been more costly
 to implement than traditional irrigation methods.
Often, the increased costs of capital, labor and energy exceed the savings that result from a reduction in the water volume purchased for irrigation.
This is particularly true when comparing well-
 managed surface irrigation methods such as siphon tubes to sprinkler systems.
Farmers who use sprinkler systems often derive additional benefits that are not easily quantified, such as improvements in distribution uniformity or the enhanced leaching of salts through the soil profile.
However, the cost of purchasing and operating sprinkler systems significantly increases the average annual cost of irrigating.
We collected detailed information about irrigation practices and costs by interviewing 10 farmers in the 9,000acre Broadview Water District, located in northwestern Fresno County, during August 1992 and May 1993.
The farmers were interviewed individually by three researchers and the manager of the water district.
The interviews, which lasted between 1 and 2 hours, were recorded on audiotape to preserve details about water management practices and costs.
The tapes assisted researchers in constructing consistent descriptions of irrigation practices.
Preliminary cost information developed from the interviews was presented to the farmers and the district manager for verification.
We selected Broadview Water District for this research because its farmers have made significant improvements in water management practices in recent years and their experience is helpful in describing both the benefits and costs of implementing those improvements.
The farmers described their current water management practices and the labor requirements for four irrigation methods  and four field crops.
Additional cost data were obtained from actual invoices for the purchase of sprinkler and gated pipe systems by Broadview farmers during 1992 and 1993.
Typical costs to purchase and maintain irrigation systems have been estimated using the Broadview information.
Capital costs have been amortized over the expected useful life of each system, using a real interest rate
 of 4%.
Wage rates, water prices, and energy costs are those reported in the farmer interviews.
The specific irrigation methods, the number of irrigation events, and the labor requirements for each crop and technology combination have been developed using the information obtained during farmer interviews and the irrigation data compiled for all farmers in the district from 1990 through 1993.
The most common method of irrigating field crops in the San Joaquin Valley is furrow irrigation, using siphon tubes and earthen head ditches and tailwater ditches.
Water flows by gravity through furrows that are typically either 1/4-mile or 1/6-mile long in 150-acre fields.
In previous years, 1/2mile furrows were very common in the valley, but these have been replaced by 1/4-mile and 1/6-mile furrows on most crops.
Most cotton fields are now irrigated using 1/4-mile furrows; many tomato and melon fields are irrigated using 1/6-mile furrows.
The shorter furrows allow farmers to achieve greater distribution uniformity, while reducing deep percolation and surface runoff.
However, 1/4-mile furrows require one additional head ditch and tailwater ditch, and 1/6-mile furrows require two additional sets of ditches.
place it in the gated pipe system.
The capital cost of a gated pipe system increases significantly when furrow lengths are reduced from 1/2 mile to 1/4 mile or 1/6 mile because of the pipe that is required for each additional line.
Some farmers in the San Joaquin Valley have begun using a combination of gated pipe and siphon tubes in the same field, to reduce the capital cost of a gated pipe system while still achieving many of the benefits.
These farmers use an earthen head ditch and siphon tubes at the high end of a field and use gated pipe to deliver water to the lower portion of the field.
One line of gated pipe is used if the field is divided into 1/4-mile furrows and two lines are used if the field is divided into 1/6-mile furrows.
This reduces the amount of gated pipe required to irrigate a 150-acre field by 2,640 feet, which represents a saving of about $10,000 at current pipe prices.
day and night to minimize surface runoff.
The irrigator also moves the siphon tubes or opens and closes the gates, as necessary, when changing the irrigation set from one portion of a field to another.
In addition, some farmers report that the labor requirement for opening and closing earthen ditches is similar to the labor requirement for placing gated pipe in the field and then removing it later in the year.
Labor requirements are similar when irrigating with siphon tubes or gated pipe.
Both systems require supervision by one irrigator during both
 Many farmers who use surface irrigation methods laser level their fields every 10 or 12 years to improve distribution uniformity.
Typical costs of laser leveling range from $60 per acre to $350 per acre in the San Joaquin Valley.
The cost depends on the volume of soil that is cut and filled throughout a field during the leveling procedure.
Fields that have been leveled in recent years require less work than fields that are being leveled for the first time.
Because many of the fields in the region have been leveled in recent years, a laser-leveling cost of $60 per acre is used in this analysis.
TABLE 1.
Estimated annual capital and maintenance costs of irrigation systems
 Gated pipe irrigation systems reduce the seepage losses that occur in earthen head ditches.
Water is delivered to furrows through sliding gates in aluminum pipes that transport water from a turnout or canal.
Gated pipe systems can be designed to deliver water in 1/2-mile, 1/4-mile or 1/6-mile furrows, by placing additional lines of gated pipe in each field.
Some farmers prefer gated pipe systems when using shorter furrows, because there is no loss of crop area caused by the second and third sets of ditches that are required when using a siphon tube system.
However, additional labor is required to place the gated pipes in each field before irrigations begin and to remove the pipe following the final irrigation event.
In addition, farmers who receive their water in canals or open ditches must use a booster pump to lift water from the canal or ditch and
 capital	maintenance	annual	Annual
 System	cost	cost	cost	cost
 1/2-mile furrows	2,065	1,938	4,003	13.34
 1/4-mile furrows	2,139	2,007	4,146	13.82
 1/6-mile furrows	2,194	2,059	4,253	14.17
 1/4-mile furrows	7,728	6,268	13,996	46.65
 1/6-mile furrows	9,185	7,450	16,635	55.45
 1/4-mile furrows	6,524	5,292	11,816	39.39
 1/6-mile furrows	7,982	6,474	14,456	48.19
 Sprinklers and siphon tubes
 1/4-mile furrows	8,222	6,941	15,163	50.54
 1/6-mile furrows	8,277	6,993	15,270	50.90
 Sprinklers and gated pipe
 1/4-mile furrows	13,811	11,202	25,013	83.38
 1/6-mile furrows	15,268	12,384	27,652	92.17
 Sprinklers	6,083	4,934	11,017	73.45
 Notes: The amortized capital costs are estimated using a real interest rate of 4% and a useful life of 12
 years for siphon tube systems and 10 years for sprinkler and gated pipe systems.
Annual maintenance
 costs are estimated to be 10% of the initial cost of the system.
The total annual cost is divided by 300 acres to determine the annual cost per acre, assuming the system
 can be used on two fields.
When sprinklers are used alone, it is assumed the system is used on one
 Many farmers have begun using sprinkler systems to irrigate field crops in response to rising water prices and reductions in water supply.
It is possible to improve distribution uniformity by using sprinklers if the systems are operating correctly and if wind conditions are favorable.
Sprinklers are also preferred by some farmers for pre-irrigations because they leach salts more uniformly through the soil profile.
The initial cost of pipe and components for a sprinkler system is significantly higher than the initial cost for a siphon tube or gated pipe system.
However, farmers using sprin-
 klers for all irrigation events may be able to avoid the cost of laser leveling because field characteristics are not the primary determinant of distribution uniformity when using sprinkler sysitems.
Sprinkler system design, component wear and operating conditions have a greater influence on distribution uniformity than do field conditions.
Sprinkler systems require a pressurized water delivery in order to move water through the pipelines, risers and nozzles.
Farmers who receive water delivery from a water district canal must install booster pumps to lift water from the canal and to pressurize their sprinkler systems.
The initial cost
 TABLE 2.
Typical row spacings and the days per irrigation event, using siphon tubes or gated pipe
 Days per irrigation event
 Crop and irrigation event	spacing	per set	24-hour sets	12-hour sets
 Pre-irrigation	40	40	20	10
 Seasonal irrigations	40	60	13	7
 Pre-irrigation	40	40	20	10
 Early irrigations	80	40	10	5
 Later irrigations	80	60	7	4
 Early irrigations	60	40	13	7
 Later irrigations	60	60	9	5
 Early irrigations	40	40	20	10
 Later irrigations	40	60	13	7
 Notes: There are 792 rows in a 150-acre field when the row spacing is 40 inches.
There are 528 rows when
 the spacing is 60 inches and there are 396 rows when the spacing is 80 inches.
Cantaloupe fields are pre-irrigated on 40-inch rows, but the crop is later planted on 80-inch beds.
TABLE 3.
Typical labor costs for a single irrigation event on a 150-acre cotton field
 Hours per set	Hours per set
 Irrigation method	12	24	12	24
 Siphon tubes, 1/4-mile furrows
 Day and night irrigators	12.48	24.96	12.48	24.96
 Open and close ditches	3.12	3.12	0.63	0.63
 Total labor cost	15.60	28.08	13.11	25.59
 Gated pipe, 1/4-mile furrows
 Day and night irrigators	12.48	24.96	12.48	24.96
 Open and close one ditch	0.52	0.52	0.11	0.11
 Deliver pipe to the field	5.20	5.20	1.04	1.04
 Total labor cost	18.20	30.68	13.63	26.11
 Sprinklers, 6 lines per field
 Day and night irrigators	7.49	14.97	7.49	14.97
 Line movers	12.48	12.48	12.48	12.48
 Deliver pipe to the field	10.40	10.40	2.08	2.08
 Total labor cost	30.37	37.85	22.05	29.53
 Note: These examples pertain to a field that is planted on 40-inch rows.
Each irrigation set includes 40
 rows during pre-irrigations and 60 rows during seasonal irrigations, when using siphon tubes or gated pipe.
Sprinkler systems deliver water to 60 rows per set during all irrigation events.
Irrigators are paid $7.80 per
 hour and line movers are paid $26 per line, including wages and payroll taxes.
of a booster pump and diesel engine is about $18,000, and the variable cost of pumping water is about $10 per acrefoot at current energy prices.
Sprinkler systems require significantly more labor than surface irrigation methods because the sprinkler lines must be moved at regular intervals to irrigate large fields.
In the San Joaquin Valley, it is common to operate a sprinkler system for 12 hours or 24 hours, then move the sprinkler lines to the next portion of the field.
A typical sprinkler system that includes six lateral lines must be moved 11 or 12 times when irrigating a 150-acre field because each lateral line delivers water to a 37-foot-wide portion of the field.
Line movers are often hired for that task only, and they move lines in the early morning and early evening.
Typically a separate person is hired to supervise the operation of the sprinklers and the booster pump during the day, and another person is hired to monitor the booster pump during the night.
Many farmers have begun using sprinklers for pre-irrigations and early irrigations of cotton and tomatoes, while using surface methods for late-season irrigations.
These farmers achieve better leaching of salts during pre-irrigations and are able to use less water during early irrigations, when plants are small and root systems are not extensive.
Some farmers use sprinklers to irrigate cotton throughout the season, but many prefer surface methods during July and August.
Farmers must switch to surface methods on tomatoes to prevent damage that can be caused by placing water directly on the plants and fruit.
Cost-effective combinations of irrigation systems are achieved when irrigation strategies permit one set of sprinklers or gated pipe to be used on more than one crop in the same year.
For example, the same sprinkler system that is used to pre-irrigate cotton fields from November through February can be used to irrigate young tomato plants in April and May.
The same system can also be used for the first and second cotton irrigations in June and July.
Many farmers have de-
 veloped irrigation strategies that minimize the average cost of using sprinkler systems in combination with surface methods.
The estimated annual capital costs of siphon tube irrigation systems range from $13.34 per acre, for a traditional system with 1/2-mile furrows, to $13.82 per acre, for 1/4-mile furrows, and $14.17 per acre, for 1/6-mile furrows.
The largest component of the capital cost is the expenditure for laser leveling.
The siphon tubes, tarps and wooden stakes are relatively inexpensive, but more of these are required when using the shorter furrow lengths.
The estimated annual capital cost, without laser leveling, is $1.43 per acre when using 1/4-mile furrows and $1.78 per acre when using 1/6-mile furrows.
The estimated annual capital cost of a gated pipe system is $46.65 per acre when using 1/4-mile furrows and $55.45 per acre when using 1/6-mile furrows.
One mile of gated pipe and 1/4 mile of transportation pipe are required when using 1/4-mile furrows, while 1.5 miles of gated pipe and 1/3 mile of transportation pipe are required when using 1/6-mile furrows.
The cost of laser leveling accounts for 29% of the total annual capital cost of gated pipe systems.
Without laser leveling, the estimated annual capital cost of a gated pipe system would be $33.25 per acre when using 1/4-mile furrows and $42.05 per acre when using 1/6-mile furrows.
Several farmers in Broadview reduce the capital cost of gated pipe sysitems by using an earthen head ditch, rather than gated pipe, to irrigate the highest portion of a field.
This practice reduces the amount of gated pipe required by 1/2 mile, while still providing many of the benefits of using gated pipe in other portions of the field.
The estimated capital cost of a gated pipe system with an earthen head ditch is $39.39 per acre when using 1/4-mile furrows and $48.19 per acre when using 1/6-mile furrows.
The initial cost of a gated pipe system that can be used to irrigate 300 acres is reduced by $7.25 per acre when
 one of the lines is replaced by an earthen head ditch.
The estimated purchase price of a sprinkler system that can be used to irrigate a 150-acre field is $49,341.
This system includes 3/4 mile of transportation pipe and 3 miles of lateral pipe that are used to deliver water in six sprinkler lines per field.
The six 1/2mile lines must be moved 11 or 12 times to irrigate the 150-acre field.
The estimated capital cost also includes a booster pump and diesel engine for lifting water from a delivery canal and adding sufficient pressure to operate the sprinklers.
Most farmers use sprinkler systems to irrigate more than one field each year by scheduling irrigations sequentially and by using sprinkler systems on more than one crop.
The estimated annual capital cost of a sprinkler system that can irrigate a 150acre field is $73.45 per acre.
The
 average cost is reduced when farmers are able to irrigate more than one field with one sprinkler system.
The largest component of labor costs for siphon tube and gated pipe irrigation systems is the expense for day and night irrigators to manage each irrigation event.
The estimated cost of an irrigator is $7.80 per hour, or $93.60 per 12-hour shift, including wages and payroll taxes.
Therefore the cost of day and night irrigators is $187.20 per 24-hour day, or $1,872  for a 10-day irrigation event.
In the past, most farmers hired only day irrigators and did not monitor water deliveries closely during the night.
In recent years many farmers have hired night irrigators, even though this doubles their expenditure for irrigation labor.
TABLE 4.
Crop-specific annual irrigation costs
 Cotton	Cantaloupes	tomatoes	seed
 Siphon tubes, traditional	13.34	13.34	13.34	13.34
 Siphon tubes, improved	13.82	14.17	14.17	13.82
 Gated pipe	46.65	55.45	55.45	46.65
 Sprinklers and siphon tubes	50.54	50.90	50.90	50.54
 Sprinklers and gated pipe	83.38	92.17	92.17	83.38
 irrigators and line movers
 Siphon tubes, traditional	43.06	27.46	32.45	24.65
 Siphon tubes, improved	86.11	51.17	67.39	49.30
 Gated pipe	91.31	56.99	64.90	51.90
 Sprinklers and siphon tubes	94.85	58.65	135.82	61.15
 Sprinklers and gated pipe	97.45	60.01	138.74	63.75
 Cost of water and energy
 Siphon tubes, traditional	130.00	110.00	130.00	100.00
 Siphon tubes, improved	120.00	100.00	128.00	88.00
 Gated pipe	150.00	125.00	160.00	110.00
 Sprinklers and siphon tubes	117.50	97.50	122.00	78.00
 Sprinklers and gated pipe	137.50	112.50	140.00	90.00
 Siphon tubes, traditional	186.40	151.28	175.79	137.99
 Siphon tubes, improved	219.93	165.34	209.56	151.12
 Gated pipe	287.96	237.44	280.35	208.55
 Sprinklers and siphon tubes	262.89	207.05	308.72	189.69
 Sprinklers and gated pipe	318.33	264.68	370.91	237.13
 Sprinklers	344.05	-	-	-
 Notes: The annual capital and maintenance costs are presented in Table 1.
Traditional siphon tube irrigation includes 1/2-mile furrows  or 1/4-mile
 furrows , with no night irrigator.
Improved siphon tube irrigation includes 1/4-mile furrows (cot-
 ton and alfalfa seed) or 1/6-mile furrows  and a night irrigator.
Labor costs are estimated using $7.80 per hour for irrigators and $26 per line for line movers, including
 wages and payroll taxes.
The cost of water is $40 per acre-foot and the cost of energy is $10 per acre-foot
 Young cotton plants irrigated with sprinklers.
Sprinkler systems require significantly more labor than surface irrigation methods because the sprinkler lines must be moved at regular intervals to irrigate large fields.
The cost per day for an irrigator is the same when using siphon tubes, gated pipe or sprinklers.
However, the total cost of irrigators for an irrigation event is determined by the number of days required to irrigate a 150-acre field.
As shown in table 2, the number of days required for an irrigation event using siphon tubes or gated pipe is determined by the crop row spacing and the number of rows irrigated in each set.
For example, 20 days may be required to pre-irrigate a cotton field that is planted in 40-inch rows, if 40 rows are irrigated in each 24-hour set.
Only 10 days may be required if the field is irrigated in 12-hour sets.
Some late season irrigations of cantaloupes are completed in 4 to 5 days, if 40 to 60 rows are irrigated in each 12-hour set.
Farmers using sprinkler systems can usually complete an irrigation event more quickly than farmers using siphon tubes or gated pipe.
A typical sprinkler line irrigates an area 37 feet wide, which is equivalent to 11 rows of cotton planted in 40-inch rows.
A six-line sprinkler system irrigates 66 rows of cotton in each set.
Therefore a farmer using sprinklers and 24-hour sets can irrigate a 150-acre cotton field
 in 12 days.
Only 6 days are required if 12-hour sets are used.
The second largest component of labor costs for siphon tube systems is the labor required to open and close earthen ditches before and after a set of irrigation events.
The ditches are closed to permit cultivation of fields between irrigations.
A siphon tube system with 1/4-mile furrows requires two head ditches and two tailwater ditches in each 150-acre field.
The estimated cost of labor to open and close these ditches is $468.
A field that is irrigated using 1/6-mile furrows requires one additional set of ditches, and the estimated cost to open and close ditches is $655.20.
A field that is irrigated with gated pipe and 1/4-mile furrows may require only one tailwater ditch and no head ditches.
The estimated cost to open and close the tailwater ditch is $78.
A field that is irrigated with gated pipe and 1/6-mile furrows may require one or two tailwater ditches.
The labor required to transport gated pipe and sprinkler systems from storage areas to fields is a significant portion of the total labor cost.
For example, the estimated cost of delivering
 gated pipe to a field, attaching the pipes and connecting them to the booster pump is $780 when using 1/4mile furrows and $1,014 when using 1/6-mile furrows.
These estimates include the cost of picking up the pipe at the end of the irrigation season and returning the pipe and pump to a storage area.
The cost is higher when using 1/6-mile furrows because there is 47% more pipe to be delivered and returned.
The estimated cost to deliver, assemble and return a sprinkler system on a 150-acre field is $1,560.
Sprinkler systems include more than 4 miles of pipe that must be transported and assembled.
The line movers hired to move sprinkler systems between each irrigation set are typically compensated for each line moved, rather than for the number of hours worked.
Many farmers in the San Joaquin Valley pay $26 per sprinkler line, including wages and payroll taxes.
Therefore the estimated cost to move a six-line system one time is $156, and the estimated cost to irrigate a 150-acre field  is $1,872.
Table 3 presents three examples of typical labor costs for a pre-irrigation and a single seasonal irrigation event.
As noted earlier, the total cost of irrigators for an irrigation event is the same for siphon tubes and gated pipe but lower for sprinklers, because fewer days are required to irrigate a field with sprinklers.
The total labor cost for gated pipe is slightly higher than the labor cost for siphon tubes because the cost of labor required to deliver and remove pipe from the field is greater than the cost of opening and closing ditches.
The estimated labor cost is highest for sprinklers, due to the costs of delivering and returning the sprinkler system and moving sprinkler lines across the field.
Cotton.
San Joaquin Valley cotton fields are usually pre-irrigated in late fall or early winter, prior to planting in March or April.
Seasonal irrigations of cotton occur in June, July and August.
The estimated cost of pre-irrigating and irrigating a 150-acre cotton field
 using siphon tubes for all irrigation events is $186.40 per acre when using 1/2-mile furrows and $219.93 per acre when using 1/4-mile furrows and hiring a night irrigator.
This scenario includes five seasonal irrigations in addition to the pre-irrigation.
The cost of hiring night irrigators  is only partially offset by the $10per-acre reduction in water cost when using the 1/4-mile furrows.
Gated pipe systems generate a higher annual capital cost and they require more labor and energy than siphon tube systems, resulting in an annual irrigation cost of $287.96 per acre.
The estimated annual cost of using sprinklers for both the pre-irrigation and all seasonal irrigations of cotton is $344.05 per acre, with a labor component of $145.60 per acre.
This cost can be reduced significantly by using sprinklers for the pre-irrigation only and using surface methods for all seasonal irrigations.
For example, the estimated cost of using sprinklers followed by siphon tubes is $262.89 per acre, while the cost of using sprinklers followed by gated pipe is $318.33 per acre.
The high cost of labor for moving sprinkler lines, and concerns about the availability of reliable line-moving crews, are often cited by farmers as principal reasons for using surface methods for seasonal irrigations.
Cantaloupes.
Cantaloupe fields are also pre-irrigated in late fall or early winter to establish deep moisture in the root zone prior to planting the crop in March or April.
The estimated total cost of pre-irrigating and irrigating a 150-acre field using siphon tubes is $151.28 per acre when using traditional 1/4-mile furrows and $165.34 per acre when using 1/6-mile furrows and hiring a night irrigator.
This scenario includes the pre-irrigation and three seasonal irrigations.
The value of water saved when using 1/6mile furrows and a night irrigator does not justify the additional cost of irrigation labor.
However, most farmers use 1/6-mile furrows for irrigating cantaloupes because yields respond positively to the improved distribution uniformity that is achieved when using shorter furrow lengths.
The estimated annual costs of using gated pipe or sprinklers to irrigate cantaloupes are significantly higher than the costs of using siphon tubes.
Much of the increase is due to the amortized capital cost of the systems, but there is also an energy cost for lifting water from delivery canals and pressurizing the system.
The additional cost of using sprinklers or gated pipe must be justified by improvements in distribution uniformity, reductions in drain water volume or the improved leaching of salts.
Processing tomatoes.
In the San Joaquin Valley, it is common to irrigate processing tomatoes soon after planting to moisten the seed bed for germination.
A pre-emergent irrigation is then delivered to minimize soil crusting that can inhibit seedling emergence and to provide moisture for the young plants.
The volume of water delivered during the germination and pre-emergent irrigations is relatively small, because the goal is to provide moisture in the upper root zone without overwatering the plants.
The estimated annual cost of using siphon tubes for all irrigations on tomatoes is $175.79 per acre when using 1/2-mile furrows and $209.56 per acre when using 1/4-mile furrows and hiring a night irrigator.
This scenario includes one germination, one pre-emergent, and six seasonal irrigations.
The estimated cost of conducting the same irrigations using gated pipe and 1/6-mile furrows is $280.35 per acre.
Several Broadview farmers have begun using sprinklers for the germination, pre-emergent, and first two seasonal irrigations of tomatoes, while using siphon tubes or gated pipe for the remaining seasonal irrigations.
The estimated annual cost of this irrigation strategy is $308.72 per acre, while the estimated cost of using sprinklers followed by gated pipe is $370.91 per acre.
The labor cost of irrigating tomatoes with sprinklers is significantly higher than for other crops in table 4 because the sprinklers are used for four irrigation events.
Alfalfa seed.
Alfalfa seed is usually planted during late fall in the San
 Joaquin Valley and the young plants are often able to utilize rainfall in late fall, winter and spring.
During the summer, farmers irrigate alfalfa seed as needed to maintain the optimal balance between vegetative growth and blossom development.
If the plants receive too much water, blossom development and yield are reduced.
Alfalfa seed fields are often retained for 2 or 3 years before replacement with another crop.
Older fields of alfalfa seed develop deep roots that are able to extract water from a high water table.
Farmers must adjust water deliveries appropriately, to avoid causing excessive vegetative growth.
As a result, many farmers irrigate alfalfa seed only two or three times per year.
The estimated annual cost of irrigating alfalfa seed three times with siphon tubes is $137.99 per acre when using 1/2-mile furrows and $151.12 per acre when using 1/4-mile furrows and hiring a night irrigator.
The estimated cost of conducting the same irrigations using gated pipe and 1/4-mile furrows is $208.55 per acre.
Some farmers use sprinklers for the first irrigation of alfalfa seed and surface methods for later irrigations.
The estimated annual cost of using sprinklers for the first irrigation and siphon tubes for later irrigations is $189.69 per acre, while the estimated cost of using sprinklers followed by gated pipe is $237.13 per acre.
It is less costly to use sprinklers followed by siphon tubes than to use gated pipe for all irrigations because less water is delivered when using sprinklers, and less energy is required when using siphon tubes.
The cost of irrigating field crops using siphon tubes and 1/4-mile furrows or 1/6-mile furrows is significantly less than the cost of using gated pipe or sprinkler systems, which require additional labor and energy costs that may not be recovered by savings in water deliveries.
In recent years, many farmers have begun managing surface irrigations intensively and they have achieved average water deliveries that are similar to those recorded for sprinkler systems.
Sprinklers provide more
 uniform leaching of salts during preirrigations, and many farmers now use sprinklers for that task before switching to surface methods during the season.
Some farmers combine gated pipe with earthen head ditches to reduce the capital cost of improved surface methods while reducing the number of ditches required in each field.
These improvements in irrigation methods are partly responsible for increases in the yield of cotton and other crops that respond to improvements in irrigation distribution uniformity.
They have also helped to reduce deep percolation and the volume of drain water collected in subsurface drainage systems.
Farmers will continue to implement improvements in surface irrigation methods, and they will purchase gated pipe and sprinklers when these systems can be justified economically.
Public policies that provide low-interest loans or other incentives for the purchase of higher technology systems reduce the farm-level annual capital cost of these systems significantly.
However, the labor and energy requirements of gated pipe and sprinkler systems will continue to limit the adoption of these irrigation methods for field crops.
Many farmers have discovered that the most cost-effective strategy for reducing irrigation costs is to manage surface irrigation systems more intensively.
Research that develops further improvements in surface methods will enhance farm-level efforts to improve water management and reduce subsurface drain water while maintaining economic viability.
Silverleaf whiteflies show no increase in insecticide resistance
 Steve Castle Nilima Prabhaker
 Tom Henneberry Steve Birdsall
 Nick Toscano a Dick Weddle
 This research was supported by the California and Rhode Island Agricultural Experiment Stations, the USDA Cooperative State Research Service and the Water Conservation Office in the California Department of Water Resources.
D.
Wichelns is Associate Professor, Department of Resource Economics, University of Rhode Island; L.
Houston is Natural Resource Economist, Kingston, Rhode Island; D.
Cone is Manager, Broadview Water District, Firebaugh, CA; Q.
Zhu was Graduate Student, University of Rhode Island, and now is Research Scientist, California Health Foundation, Sacramento; and J.
Wilen is Professor, Department of Agricultural Economics, UC Davis.
The silverleaf whitefly  continues to be a difficult pest to control in California's desert valleys.
To gain a better understanding of the possible role that insecticide resistance plays in its annual outbreaks, a resistance monitoring program was established to document susceptibilities of whiteflies to various insecticides through time.
Continuous monitoring during 1993 and 1994 detected no trend toward higher resistance levels.
Higher toxicities of insecticide mixtures compared to single insecticides were regularly observed in bioassay results.
Various factors including diverse insecticide use and altered cropping patterns may have helped to avoid serious insecticide resistance problems in the Imperial Valley so far.
The silverleaf whitefly became the predominant pest of agriculture in the Imperial Valley with its initial major outbreak in 1991.
Although there are good indications that this new whitefly species had been present on melons and cole crops the previous year, it wasn't until the summer and fall of 1991 that its full destructive potential was realized.
The damage to agriculture was perhaps unprecedented in terms of the breadth of crops attacked and the losses incurred.
Since 1991, the silverleaf whitefly has continued to ruin many crops despite intense efforts to manage populations by all methods, including reducing crop acres, using insecticides and practicing good crop sanitation.
In 1992 planted cotton acreage was reduced to half of the previous year's 12,370 acres, fall melon production was eliminated, and dry-down of thousands of acres of alfalfa was implemented, all in voluntary cooperation to limit whitefly population.
Never-
Roadside Guide to Clean Water: Grassed Waterways
 Grassed waterways are wide, shallow channels installed where water runoff usually concentrates in an agricultural field.
Grassed Waterways At a Glance
 Grassed waterways  are wide, shallow channels that are installed where water runoff usually concentrates in an agricultural field.
They are planted with permanent vegetation, meaning they might be mowed, but the plants are never plowed or killed intentionally.
They are designed to carry water down a hill while also preventing erosion.
The plants growing in these contoured pathways help slow the flow of water and the plant roots help to hold the soil in place.
How Grassed Waterways Work
 As water flows downhill, it tends to gather in natural depressions in the land.
Over time, this concentrated flow of water can chisel away at the land, forming small channels called rills, or larger channels called gullies.
Oftentimes this happens when there are not enough plants growing to hold the soil in place.
Grass waterways are planted in the natural depressions where water tends to flow.
They can either prevent erosion before it happens or fix minor erosion that has already started.
They are broad, rounded swales that are planted permanently in grass instead of rotated through crops like corn and soybeans.
This year to year grass acts as a stable pathway for runoff water to follow.
The wide, sloping channel spreads water out as it flows.
This reduces the force of the water over the land and therefore reduces erosion.
Water quality is improved because less soil and sediment is moved from the field to to nearby streams and water enters those streams more gently.
Community Benefits of Grassed Waterways
 Climate Change: Promotes climate change resiliency
 Habitat: Provides wildlife habitat
 Savings: Provides cost savings
 You can expect to find grassed waterways in rural settings.
How to Recognize Grassed Waterways
 Grassed waterways are used to reduce the impacts of surface water that flows on agricultural fields.
Photo by Sarah Xenophon
 Grassed waterways are planted with a mixture of grasses and legumes that are adapted to the local climate and will withstand flowing water.
Photo by Lynn Betts, USDA Natural Resources Conservation Service
 Sometimes stone may be placed along the center of the waterway to promote drainage and prevent erosion.
Photo by U.S.
Department of Agriculture
 Natural grass waterways are established where the farmer simply avoids plowing an area and allows permanent vegetation to establish.
Photo by Jeff Vanuga, USDA Natural Resources Conservation Service
Afterward, tour participants regrouped with other attendees, totaling nearly 60 people, at the Doniphan Event Center for dinner and the official kickoff of the 2023 TAPS competitions, which include sprinkler corn, subsurface drip irrigated  corn, and sorghum.
Changes to these competitions this year include the moving of the sorghum competition plots to the Stumpf International Wheat Center in Grant, Nebraska, and the addition of cover crops to the pivot field in the offseason, although this will not require additional participant decision-making, just an awareness, as this may cause a reconsideration of best management practices for competitors.
Additionally, participants were introduced to the new web platform, where they will submit their management decisions.
Vegetable production is increasingly popular for Tennessee residents.
Home vegetable gardening benefits include financial and nutritional value resulting from providing fresh vegetables as well as enhancing personal health and well-being through gardening activities.
However, a basic understanding of soils, site selection, and crop maintenance is required before a gardener can take full advantage of the many benefits of home vegetable production.
To meet these needs, this series of fact sheets has been prepared by UT Extension to inform home gardeners and propel them to success in growing vegetables.
TOMATOES THE HEART OF THE HOME GARDEN
 As the most popular crop grown by home gardeners in the United States, tomatoes  are certainly king of the garden.
This is definitely because of the number of participating gardeners, but it is also due to gardeners' passion about their home-grown tomatoes.
The number and variety of tomatoes currently on the market and maintained through personal seed saving is a testament to the importance of this botanical fruit that is most often referred to as
 a vegetable.
Tomatoes are a great source of vitamins C and A, as well as lycopene, which has been shown to be beneficial to cardiovascular health.
There is both art and science in producing the home-grown tomato.
In this factsheet, we will focus on the science and detail some of the most common and useful practices for growing tomatoes in the home garden.
Figure 1.
Tomatoes come in an amazing and beautiful variety of shapes and colors.
SELECTING TOMATO TYPES AND PLANTS
 TOMATO TYPES AND CULTIVARS
 Gardeners must make two important decisions related to the types and cultivars of tomatoes for the home garden.
The first is related to the determinate or indeterminate habit of the plant.
Determinate tomatoes are those that will "top themselves." This means that the primary growing tip is genetically programmed to form a flower at a certain point, and the plant does not grow any taller.
Determinate tomatoes are typically shorter and can be easier to manage in the garden.
Tomato fruit are set over a relatively short period of time and then ripen
 over a concentrated harvest interval.
Indeterminate varieties continue to grow and produce both new leaves and new flowers from their primary growing point.
This continued growth means they will be taller and continue to set and mature fruit through the summer and fall.
Unless damaged by insects, disease or environmental stress, indeterminate tomatoes will produce until killed by low temperatures in the fall.
So, they will require taller stakes to provide good support.
When choosing between determinate and indeterminate tomato plants, consider your intended use.
Determinate plants may be best for more concentrated yield for canning while indeterminate plants may produce over a longer period of time
 for fresh eating.
Also consider the time available to invest in plant support, training, disease and pest control, and picking throughout the season.
The second decision important in selecting tomatoes for the home garden is the specific tomato cultivar.
Hundreds of tomato cultivars are commercially available to home gardeners with many more saved by residents for personal production.
The most important considerations are the disease resistance and the gardener's preference in terms of fruit color, size, shape, taste and days to harvest.
Table 1 provides some examples of tomatoes that have performed well in trials in the region.
Another good source of information is the All-America Selections website.
This site details vegetable cultivars that have been
 Growth habit	Cultivar**	Days to harvest	Fruit type, color, estimated size	Disease resistances***
 Determinate	Early Girl F1	58	Slicer, red 	V, F1, F2
 Determinate	Celebrity F1	75	Slicer, red 	F1, F2, V, N, TMV
 Determinate	Plum Dandy F1	76	Paste, red	F1, V, EB
 Determinate	Plum Crimson F1	80	Paste, red 	VI, F1, F2, F3, EB
 Determinate	Mountain Fresh F1	77	Slicer, red 	VI, F1, F2, EB-tolerant
 Determinate	Plum Regal F1	80	Paste, red 	V, F1, F2, TSWV, LB, EB
 Determinate	Carolina Gold F1	71	Slicer, gold 	V, F1, F2
 Determinate	Valley Girl F1	65	Slicer, red 	V, F1, F2
 Indeterminate	Big Beef F1	70	Large slicer, red 	F1, F2, V, N, TMV, LS
 Indeterminate	Cherokee Purple OP	72	Large slicer, purple 
 Indeterminate	Pink Girl F1	72	Slicer, pink 	AC, F1, LS, V
 Indeterminate	Better Boy F1	75	Slicer, red 	F1, N, V
 Indeterminate	Brandywine OP	78	Large slicer, many colors 
 Indeterminate	Mountain Magic F1	72	Cherry, red 	EB, V, F1, F2,LB
 Indeterminate	Matt's Wild Cherry OP	60	Cherry, red 	EB, LB
 Indeterminate	Cupid F1	71	Grape, red 	AC, F1, LS, BS
 Indeterminate	Supersweet 100 F1	65	Cherry, red 	F1, V
 Indeterminate	Sungold F1	65	Cherry, gold 	F1, TMV
 Indeterminate	Juliet F1	60	Grape, red 	Cracking, EB
 Indeterminate	Jolly F1	75	Pear, pink 
 Table 1.
Tomato cultivars* suggested for home garden production
 * Cultivar information from University of Kentucky Extension publication ID133.
** F1 denotes hybrid cultivars, OP denotes open pollinated cultivars  *AC=Alternaria stem canker, BS=bacterial speck, EB=early blight, Ex=Fusarium wilt races 1,2,3, LB=late blight, LS=gray leaf spot, N=root knot nematode, TMV=tomato mosaic, TSWV=tomato spotted wilt virus, V=Verticullium wilt, VI=viruses
 Figure 2.
'Matt's Wild Cherry' tomatoes.
Tomato cultivar selection is important, but the selection or production of highquality plants is also crucial.
Tomato fruit yield and garden performance begin with high quality plants.
Tomatoes can be direct seeded, but due to the 90-120 days from seeding to harvest, transplants are common for garden tomatoes to reduce the time to harvest.
Because of this convention in both commercial and garden production, the time to harvest listed in cultivar information  will be estimates of time from transplant to harvest of ripe fruit.
Tomato plants can be produced by the gardener or purchased.
Starting your own transplants can enable the largest selection of cultivars, but it can be a challenge to maintain appropriate conditions.
Whether grown or purchased, tomato plants
 should be stocky with strong root systems.
Plants that have been grown with suboptimum light or improper temperature conditions will often be "leggy" or have thin stems with larger distances between leaves.
Also look for transplants that have a healthy green color and are free from damaged or yellowed leaves that indicate insects or plant stress.
Inspect leaves for any sign of disease.
Avoid purchasing transplants grown out of state, as these have been a major source of disease problems in Tennessee gardens.
Purchase locally grown transplants, if possible.
Transplant-borne diseases such as bacterial spot are difficult or impossible to control once introduced into the garden.
Tomato plants are commonly 6 to 8 weeks old when ready for garden planting.
All transplants should be "hardened off" before planting.
This term refers to slowly subjecting plants to outdoor conditions to lessen their stress at transplant and help them to better handle the sun, wind and temperatures they will experience in the garden.
Many garden centers will have plants that have been through these conditions to enable them to have the best chance of transitioning well to your garden environment, but it can be a good idea to ask what the recent conditions have been when buying plants.
Heirloom is a term that commonly is used to describe cultivars that are expected to deliver characteristic homegrown tomato flavor.
Many heirloom tomatoes have qualities that may not be present in commercial cultivars, such as softer texture or thinner skin.
These traits may make fruit preferable for home eating.
However, issues in handling and the lack of disease resistance are drawbacks of heirloom tomatoes, such as Cherokee Purple and Brandywine.
In more precise terms, commercial heirloom cultivars are those that were introduced by seed companies before 1940 while family heirlooms are maintained and distributed by
 home gardeners or farmers.
Heirlooms are able to be maintained by seed collection.
This means that they are open-pollinated or non-hybrid cultivars that produce plants from seed that are identical to the parent.
Hybrid refers to a tomato cultivar produced specifically to combine traits from two parents.
Most of the new cultivars released are hybrids because the crossing of specific parents enables cultivars to have distinct and desirable disease resistance, taste, shape, color and other traits.
However, a cross of two distinct lines means seeds from a hybrid tomato fruit will not produce a plant that is genetically similar to the parent.
Therefore, hybrid seeds or plants must be purchased each year rather than grown from seeds saved from a previous crop.
Grafting refers to the shoot  of one cultivar being placed on the lower stem and roots of another .
They then
 Figure 3.
A recently grafted tomato with the scion seen above the clear clip and the rootstock below the clip.
A clear plastic clip tightly holds the scion and rootstock together as plant tissue grows and connects the two plants.
Credits: Ken Chamberlain and Vegetable Production Systems Lab OSU OARDC
 grow together to become one plant.
Grafting is a mechanism that allows desirable fruit traits of one tomato cultivar to be combined with desirable growth or disease resistance traits of another.
It most commonly is used to provide resistance to soil-borne diseases or nematodes, but it can provide increased stress resistance as well.
Grafting also can be a means to improve yield through strong root growth or plants that last longer in the field or garden.
Grafting is costly because it initially requires two plants and extra handling and care in seedling production and during healing of the graft union.
Grafted plants are available for sale by many seed companies and transplant producers.
They may be an asset to your garden, but the conditions at your site will determine whether the benefits of yield or disease resistance are worth the extra time or cost of grafted plants.
SELECTING AND PREPARING THE GARDEN SITE
 SITE CONSIDERATION AND CROP ROTATIONS
 Tomato production is best carried out in a garden site with mediumtextured, well-drained soil with a good level of organic matter and supply of nutrients.
If a suitable in-ground site is not available, many tomato cultivars can be grown in raised beds  and containers.
Soil tests should be taken to determine the pH and nutrient level of the soil.
Tomato gardens should have at least a 6.1 soil pH with an optimum target range of 6.5 to 6.8.
Keeping
 the pH in these ranges is important for nutrient utilization and can lessen the impact of some soil diseases, such as Fusarium wilt.
Follow lime recommendations on the soil test report to attain this level.
Many diseases and pests that infect vegetable plants can be reduced if specific crops are not grown in the same location in consecutive years.
Diseases and pests often impact specific crop families, and it is best to grow tomatoes in a site only once every three to four years.
Vine crops, such as pumpkins and squash, sweet corn, or beans and peas are good crops to grow in the intervening years.
Rotation does not eliminate problems, but it can be a good step in helping to reduce disease and nematode issues.
Garden soil should be prepared in a similar fashion as for other garden vegetables.
A fine, but not powdery, seedbed 6 to 8 inches deep is ideal.
Remember to incorporate any plant residue or cover crop biomass a few weeks before planting to allow time for breakdown of that material.
Lime also should be applied in the fall or applied and incorporated several weeks before spring planting to allow time to alter the soil pH.
Tomatoes produce a significant plant and fruit biomass and require relatively large amounts of nutrients to achieve optimum productivity.
Fertilizer will generally be applied before planting and during crop growth.
The preplant fertilizer application often uses a complete fertilizer , such as 10-1010 or 6-12-12.
Your soil test report will suggest fertilization materials and rates according to the balance of nutrients in the soil.
Fertilizer should be evenly spread and incorporated or banded near transplant roots.
Make sure not to apply chemical fertilizer where it can directly contact young plants because the high salt level can burn young roots or stems.
OPTIONS FOR PREVENTATIVE WEED CONTROL
 Weeds are one of the largest challenges in the home garden, so a combination of control measures is best.
Cultural practices to prevent weed issues rely on removing annual weeds before they have a chance to mature and produce seeds.
Likewise, perennial weeds may be physically pulled and should be completely removed to ensure that rhizomes  are not able to remain and cause additional problems.
Other practices that can reduce weed pressures in the home garden are mulching  and appropriate uses of cover crops which can cover the ground and outcompete weeds.
Solarization, or the heating of soil by covering with plastic sheeting, can also be a tool to reduce weed seeds and subsequent weed and disease issues.
All of these tactics are presented in more detail in W 346-D "The Tennessee Vegetable Garden: Plant Management Practices."
 Herbicides are not often used in home gardens because of the low number of products available to consumers and the challenge in using these products in gardens where many crops are being produced across several seasons.
Some pre-emergence  herbicide products may be useful if application rate and timing are carefully followed.
See UT Extension publication W 245 "Common Herbicides for Fruit and Vegetable Weed Control" for more details.
Post-emergence products are more challenging to use because of their broad range of activity and the risk of overspray or drift onto garden vegetables.
Additionally, tomato plants are one of the most sensitive crops to herbicide damage and can be severely harmed by small amounts of herbicide drift that may not damage other
 nearby crops.
Use caution in managing any nearby lawn or garden area where there is any chance that spray drift or herbicide residue in soil could contact garden tomatoes.
Mulching materials, such as straw, leaves, grass clippings or compost can be applied after planting.
When applied 3 to 6 inches thick, these mulches provide weed control for most annual weeds, moderate soil moisture levels, and reduce some disease problems.
Organic mulches  are often not applied at planting because they can cool early season soil temperatures by blocking sunlight from warming the soil.
It may be best to apply them after the plants are established and soil temperatures have warmed.
Organic mulches can be an asset in the heat of summer by moderating and cooling soil temperatures.
See W 346-D for additional information on mulching.
Inorganic or plastic mulches can also provide benefits to home garden tomato production.
Black is the most common plastic color because it prevents weed growth while warming up the soil in the early season to aid in early growth.
As with organic mulches, plastic mulches moderate soil moisture levels and also reduce some risks of leaf diseases by reducing soil splashed on leaves from precipitation.
Install 4-foot-wide strips of plastic in the row area and seal the edges with about 6 inches of soil about two weeks before the planned transplanting date.
Plastic mulch is a great addition to raised beds because the two methods increase early season drainage and soil warming.
Install plastic after lime and fertilizer applications have been completed.
It is essential to also install drip irrigation under the plastic mulch because it is impermeable to rainfall.
Tomatoes are planted through slits cut in the plastic.
Tomato stakes also can be driven through the plastic, but be careful to avoid the underlying drip line.
It is best to plan the planting arrangement and measure distances between rows and plants ahead of time.
The distance between plants in the row  depends on the type of tomatoes being grown and the pruning methods that will be used.
Determinate varieties do not grow as tall as indeterminate and can normally be spaced closer in the row.
Gardeners can chose to plant at a wider in-row
 Tomato type	In-row spacing	Between-row spacing
 Determinate	18-24 inches	48-60 inches
 Indeterminate	24-36 inches	60-72 inches
 Table 2.
Plant spacing estimates for garden tomatoes.
Figure 4.
These young tomatoes in a 2015 trial at the UT Plateau AgResearch and Education Center illustrate different mulching techniques used with drip irrigation and the Florida weave support system.
spacing to allow easier access.
Pruning will be discussed in detail below and is commonly used to manage growth in indeterminate tomatoes.
Betweenrow spacing can be related to the type of tillage equipment being used and can be wider if needed.
Keep in mind, though, that wider plant and row spacing will also mean more space open for weed growth.
When soil is properly prepared and the threat of spring frost is passed , tomatoes transplants can be planted in the garden.
Young plants should be around 6 to 10 inches tall and properly hardened off at transplanting.
In well-prepared soil, a hole is dug deep enough to cover the root ball of the plant.
If transplants have been grown
 in fibrous containers that are planted rather than removed, make sure that all parts of the container are covered with soil to prevent water loss from exposed edges.
Often, a soluble starter fertilizer will be added to the planting hole to provide moisture and nutrition for the young transplant.
Tall, leggy plants are a challenge in the home garden.
It may be best to install the support system  at planting to support the tall plants and plant them at a normal depth.
Some gardeners make a trench to lay a portion of the stem horizontally under the soil or they bury the plant extra deep.
While roots will emerge from these buried stems, such practices can lead to stem breakage or lower soil temperature, aeration or nutrients for the deeply planted roots.
Additionally,
 both of these practices will negate the impact of grafted rootstocks if grafted plants are used.
The best practice is to select and plant healthy and appropriately sized tomato plants.
For best growth, keep the soil in the root zone moist enough to prevent wilting of tomatoes.
This is especially important soon after transplanting when the plant is transitioning to garden conditions.
Garden tomatoes will generally require 1 to 1.5 inches of water per week, but this number can change according to environmental conditions and plant size.
Managing
 Location	Bristol	Chattanooga	Clarksville	Crossville	Jackson	Knoxville	Memphis	Mountain	Nashville
 Last spring	May 3	April 17	April 27	May 10	April 19	April 28	April 9	May 26	April 21
 Table 3.
Spring planting dates with only a 10 percent chance of temperatures lower than 32 F after that date as determined by 30-year NOAA weather data from local stations.
Figure 5.
Florida weave support system being used on garden tomatoes.
Three layers of twine have been installed in this image.
water in garden tomatoes is based on knowing the rainfall received on your site and then applying water if rainfall is not sufficient.
Most years in Tennessee there will be periods of the spring, summer and early fall when rainfall is insufficient or inconsistent for the best tomato plant growth.
Tracking the volume over the season will help make irrigation practices more precise.
When irrigating, it is best to apply 1/2 to 3/4 inch of water twice a week rather than the full amount in one irrigation event.
This will reduce runoff and provide more consistent soil moisture but provide enough water to wet the soil for several inches.
Likewise, it is best to deliver irrigation to the root zone of the plants through trickle or drip irrigation rather than overhead watering.
Drip irrigation will be more efficient in water use and will keep the plants leaves dry.
Soaker hoses are also common in the home garden and deliver water directly to plant roots.
They can be purchased or constructed from used garden hose.
Soaker hoses can be cost-effective and versatile in the garden, but they
 do not deliver water as evenly as drip irrigation lines.
If sprinkler irrigation is the only option, apply at a time when leaves will dry before nightfall to lower the risk of leaf disease.
PLANT MANAGEMENT SUPPORT AND PRUNING
 Proper plant management and support are needed to produce both the best yield and the best quality tomatoes.
An added bonus of good plant management and support is that it can save time during picking.
Tomatoes are normally supported with stakes or cages.
Staking can be carried out for individual tomato plants or installed and tied as a row.
If stakes are used, they should
 be durable hardwood about 4 to 5 feet tall for determinate types or 6 to 8 feet for indeterminate tomatoes.
Aim to have about 1 foot of the stake length in the ground for stability.
For individual staking, tie plants loosely to the stakes at 8to 10-inch intervals.
Make sure to use cloth or a string material that will not damage the stems as the plant weight increases.
Stakes also can be placed every two plants and twine woven around them to form a basket that supports all the plants in the row.
This method is sometimes called the "Florida Weave." String is tightly stretched horizontally along both sides of the stakes at the same height, with plants held between the string layers.
Twine is wound around each middle stake to maintain tension and tied off at the end stakes.
These layers of support are repeated every 8 to 10 inches vertically as the plant grows.
When cages are used for support, they must be strong enough to support the plant for the entire growing season.
Cages can be purchased or constructed at home with materials
 Figure 6.
This image shows two large lateral branches  that can be removed to maintain a single stem on an indeterminate tomato plant.
Notice that the bloom and young fruit are clearly on the main stem of the tomato.
such as concrete reinforcing wire.
As a guide in cage construction, a 6-foot length of wire will form a cage about 21 inches in diameter.
Cages should be well anchored in the soil to support the weight of the plants and fruit and allow access to ripe fruit for removal without damage.
The method of pruning and plant management depends on the type of tomato and the method of support.
Indeterminate tomatoes that produce fruit clusters and leaves throughout the season are commonly trained to a single stake or grown in a cage.
If stakes are used, lateral branches  are often removed to create a plant with a single main stem.
Suckers can compete for plant resources and be a challenge to support on a single stake.
The removal of suckers is less commonly practiced if tomato cages are used.
Yields per plant are usually higher in a cage than when supported by stakes because fruit is harvested from both the main stem and lateral branches.
Fruit may ripen slower in cages, but sunscald  is often reduced.
Determinate tomato plants are generally pruned less than indeterminate plants, and some gardeners chose not to prune them
 at all.
Because their main stem stops growing at a certain point, many of the fruit of a determinate tomato are produced on lateral branches.
Sometimes a few leaves and lateral branches are removed below the first flower cluster because it can increase early yield and fruit size.
It is best to leave one or two suckers below the first flower to avoid leaf curling, stunting and reduced yield.
Determinate plants can be challenging to train to a single stake because of lateral branches, but cages and the Florida Weave system work well.
NUTRIENT MANAGEMENT AND FERTILIZATION
 In addition to initial fertilization discussed above, tomatoes need adequate nutrition throughout the growing season to produce well.
"Sidedressing" is the application of fertilizer in a small furrow 2-4 inches to the side of the row during plant growth because all the nutrient needs of tomatoes cannot be well supplied by only a pre-plant fertilizer application.
The timing of this is application of fertilizer is often made after the first cluster of fruit has set and young tomatoes are the size of a golf ball or
 slightly smaller.
Timing is important because young tomatoes that are supplied with too much nitrogen will produce much stem and leaf growth which can slow or reduce fruit set and yield.
Often these sidedressings are repeated once a month while the plant is bearing.
One of the most important concepts for home tomato growers is calculating fertilizer needs across the whole season.
The most common nutrients applied in a sidedressing are nitrogen and potassium.
Nitrogen is needed for many plant growth processes while potassium is important for many reactions in the plant and for high fruit quality.
An example is provided below.
Common targets for nitrogen and potash  over a season are often around 0.5 lb/100 sq.
ft.
and 0.7 lb/100 sq.
ft, respectively.
If 3 lbs.
of 10-10-10  was added at planting to 100 sq.
ft., then 0.3 pounds of N and K20  were applied.
Two subsequent monthly sidedressings of 1.5 lbs.
of 6-12-12  per 100 sq.
ft.
beginning after the fruit set on the first cluster would provide a total of 0.18 lb N and 0.36 lb.
K20 to come quite close to N and K20 seasonal targets.
Recommendations in the soil test report also provide fertilization tactics throughout the growing season.
COMMON CHALLENGES IN HOME TOMATO PRODUCTION
 Blossom end rot  involves the death of cells at the flower end of the fruit followed by decay.
This condition is related to inadequate calcium levels in the developing fruit.
Maintaining proper pH can reduce BER risk because lime 
 supplies calcium while increasing the pH and making it easier for the plant to take up calcium.
Calcium nitrate fertilizer can also be added to the soil as a means of preventing BER and should be applied as a sidedressing three to four weeks after transplanting, but use caution due to the possibility of oversupplying nitrogen as presented above.
Providing uniform soil moisture by using irrigation and mulches is also a benefit because calcium must dissolve in soil water to be taken up by plants.
Tomatoes may also have less BER if they are not pruned too heavily or excessively fertilized.
Sometimes, BER affects only the early fruit and clears up without action.
Misshapen fruit is often related to poor pollination, which can lead to different growth rates in areas of the fruit.
Examples include catfacing, puffiness and odd fruit shapes.
Temperatures that are cool , especially at night can lead to poor pollination, but warm temperatures, fertilization or humidity issues can also impact pollination.
Cracking  can appear as concentric rings around the top of the
 fruit or cracking down the fruit.
It can be related to variety characteristics, but is most often linked with irregular patterns in growth and/or water issues.
Swings in moisture or nutrition can both lead to cracking, which is best prevented by maintaining optimum and consistent moisture.
Modern varieties are less prone to cracking than heirlooms.
HARVEST, HANDLING AND STORAGE
 Most home garden tomatoes are harvested fully ripe.
This practice will enable full flavor development but also reduces shelf life and produces fruit that are more susceptible to damage during handling.
Fruit harvested at 60-80 percent full color will ripen well in the home if handled correctly.
Cherry tomatoes are often picked slightly before full maturity to prevent cracking that can occur quickly after ripening.
Most gardeners removes the fruit from the vine while leaving the calyx (small
 green leaves and stem) on the plant.
Removing the calyx and stem can reduce fruit punctures during picking and handling.
Tomatoes are best picked into shallow boxes and placed one to two layers deep to prevent damage.
Fully ripe tomatoes are generally of the highest quality when stored at room temperatures in the home and eaten within 2 to 3 days.
So, it is best to harvest tomatoes from the garden when they will be consumed in a few days.
Tomatoes are chilling sensitive and refrigeration can cause flavor loss.
It is common for newer hybrid cultivars to retain a firmer texture and avoid decay for longer periods after harvest than many heirloom cultivars.
If frost is on its way at the end of the season and tomato fruit is still on the plants, they can be harvested green to slowly ripen in the home.
They may not be quite as flavorful as an August garden tomato, but they can be an excellent addition to a fall salad, providing a final taste of summer for the year!
ADDITIONAL RESOURCES AND REFERENCES
 Contact your county Extension office with questions about managing soil or plants in the home garden.
UMA INSTITUTE OF AGRICULTURE THE UNIVERSITY OF TENNESSEE
 Real.
Life.
Solutions.
TM
 W / 346-H 10/16 17-0033
The manufactures have done an excellent job of producing safe equipment, which are by in large installed by qualified dealers and electricians.
However, the fact that 3-phase, 480 V power is being used, safety must always be a top priority because it can be fatal.
The following is a partial list of some important safety and maintenance tips for center pivot irrigation systems: one him
Initial irrigation practices in Kansas emerged around 1650 in a Taos Indian village in what is currently the Scott County State Park.
The "modern" era of irrigation began in the 1880's with the organization of irrigation ditch companies which built diversion works and canal systems along the Ark River.
Following World War II, Kansas irrigation rapidly expanded due to political/societal will, technology and readily available energy.
The1945 Water Appropriation Act, which provides the basis of current Kansas water law, was designed to encourage the development of water resources.
The development of the Hugoton natural gas well field and improved irrigation well drilling and pumping equipment following WWII contributed to the rapid increase in the irrigated area of Kansas, particularly over the Ogallala Aquifer.
Irrigation system types have evolved from primarily surface flood irrigation to predominately sprinkler irrigation.
In 1970, approximately 18 percent of the 1.8 million irrigated acres were sprinkler irrigated.
In 1989, there was a change in the water use reporting procedures  and this is responsible for the abrupt change in total irrigated area in that year.
The rapid increase of an irrigated land area  during the 1970's was a result of the adoption of center pivot irrigation.
By 1990, approximately 50% of the total area used center pivot sprinkler irrigation and that percentage has increased to nearly 92% today, though the total irrigated area has remained relatively stable at approximately 3 million acres.
Figure 1.
Progression of irrigated land area through time for Kansas.
Early estimates are based on various surveys.
Since 1989, the actual irrigated land area has been reported on annual water use reports submitted to the Kansas Department of Agriculture.
In 1989, subsurface drip irrigation  research plots were developed at the Northwest Research and Extension Center of K-State in Colby, Kansas.
Surveys for SDI systems began in 1992 with an initial estimate of the existing systems of approximately 5,000 acres  and small, steady increases for each year thereafter.
Concerns with the accuracy of these estimates led to a review of the annual water use reports in 2003, resulting in SDI estimates of just over 14,000 acres.
In 2004, the DWR/KWO Annual Water Use Report began reporting SDI land area and systems combining multiple irrigation system types.
A typical example would be SDI being used in the corners of a field irrigated with center pivot sprinkler system.
In 2008 and 2009, SDI data include both SDI and SDI combo acres.
SDI systems continue to be installed in Kansas but still represent less than 1 percent of the total irrigated land area.
Figure 2.
Progression of total irrigated land area, sprinkler systems, and flood Irrigation system Kansas.
Figure 3.
Increase in subsurface drip irrigation systems in Kansas.
The abrupt changes in SDI area are due to survey and reporting methods and not due to abandonment of SDI systems.
SDI has been increasing steadily in Kansas.
Corn is currently produced on nearly 50% of the irrigated land in Kansas  with a peak land area of about 1.7 million acres in 1999.
The area in corn production trended downward during the droughty and low crop price years of the early 2000's, but has rebounded beginning in 2005.
Figure 4.
Irrigated area devoted to the five major irrigated crops in Kansas.
The total amount of annual water diversions and also the amount of water pumped on a given land area has decreased over time  although there are annual fluctuations caused by differences in precipitation and crop water use needs.
For example, the 1990's were relatively wet years, while the early 2000's were extremely dry.
Crop year 1993 was one of the highest rainfall years on record, while 2002 was one of the lowest and this is reflected in the corresponding valley and peak in water use, respectively.
Part of the rationale for the decrease in water use may be more accurate reporting, but the conversion of flood irrigated land to center pivot sprinklers was also rapid during this time period, changing from roughly 50 percent to 90 percent center pivot sprinkler irrigated land.
When appropriately managed, center pivot sprinkler systems typically have greater application efficiency than surface flood irrigation systems.
Figure 5.
Total irrigation water diverted and average application depth by year for Kansas.
Reduced total water diversion can also be attributed to the continuing decline of water table levels and the subsequent decrease in well yield, and to the shifting of tillage practices.
Reduced tillage also enhances precipitation capture and reduces soil water losses that are caused by disturbance of the soil surface layers.
Greater residue also reduces early-season soil evaporation losses.
Increase pumping costs and the adoption of improved irrigation management practices, such as irrigation scheduling, also contribute to less overall water diversions.
Application depth varies  considerably across Kansas.
Since, the majority of the irrigated acres are located in Region 1 and because it has the largest net irrigation requirements, the state total and Region 1 values are very similar.
Figure 6.
Regional average irrigation application depths by year for Kansas
 The four major grain crops grown in Kansas  have experienced upward trends in yield.
Corn yield has had the most dramatic increase for both irrigated and dryland production with irrigated corn yield improvements of approximately 2.5 bushels/acre for the each year of record, This result is more than twice the dryland rate of 1.1 bushels/acre.
The average irrigated yield increase is 0.59 bu/ac, 0.60 bu/ac and 0.31 bu/ac for soybean, grain sorghum and wheat respectfully.
Irrigated yield increase trends have been larger than for dryland.
Figure 7.
Kansas corn yield trends since 1974.
Figure 8.
Kansas soybean yield trends since 1984.
Figure 9.
Kansas grain sorghum yield trends since 1974.
Figure 10.
Kansas wheat yield trends since 1974.
IRRIGATION WATER USE EFFICIENCY
 Irrigation water use efficiency  has sometimes been defined as the yield of a crop divided by the amount of irrigation water applied.
Because yield has increased over time  and the average application depth has been trending downward , IWUE has been increasing.
Southwest Kansas yield, irrigation application, and IWUE for corn are shown in Figure 11.
IWUE has increased by 0.16 bushels/inch for each year of record, although there is considerable year-to-year variability.
Figure 11.
Corn yield, irrigation application depth, and irrigation water use efficiency trends for Southwest Kansas.
The four major energy sources for pumping irrigation water in Kansas are natural gas, electricity, diesel and propane  with natural gas being the most common energy source.
The use of electricity has been increasing since the mid 1990s  partially because its costs compared to the other sources has become more competitive.
Figure 12.
Kansas irrigation pumping plant energy source.
Figure 13.
Kansas irrigation pumping costs by energy source.
According to the 2007 Census of Agriculture , the First Congressional District of Kansas ranked as the leading Congressional district in the U.S.
for the market value of agricultural products sold.
All of western Kansas and much of the irrigated region in South Central Kansas are part of this Congressional district.
Approximately 15 percent of Kansas' cropland area harvested each year is irrigated but contributes about 30 percent of the total value of crops produced.
Kansas irrigated land area and irrigation water usage for three selected years, 1993 , 2000 , and 2002  are shown in Table 1.
The area irrigated is relatively stable as compared to the value of production share produced by irrigation.
In general, a higher percentage from irrigation is associated with dry conditions resulting in loss of dryland yield productivity.
The total crop value is dependent on both the yield and crop price.
Table 2 shows total production, value, and price for the major crops of Kansas in 2000 and 2009.
On a percentage basis, irrigated agriculture for Western Kansas produced about 25 percent of the total Kansas crop value in both years, even though the value of total production was nearly twice as high in 2009 as compared to 2000.
Figure 14: Kansas irrigation percentage of cropland harvested acres and total crop value for the five major crops.
Table 1.
Selected example years of Kansas cropland, irrigated acreage, and irrigation water use.
Year	 Acres	Total Cropland	Total Irrigated	Acres	Total Cropland	Percentage of	Irrigation Water	Use 
 1993	20,454,400	2,841,000	13.9%	2,828,973
 2000	21,656,900	3,183,983	14.7%	3,885,805
 2002	20,230,400	3,211,859	15.9%	4,228,410
 Table 2.
Irrigated crop production and value for Kansas in 2000 and 2009.
Crop	Production 	Farm value 	Crop price
 2000	2009	2000	2009	2000	2009
 Alfalfa	1.45**	0.96**	0.1414	0.1041	$97/ton	$108/ton
 Total farm value	0.9202	1.639
 Total farm value of all Kansas crops	3.6233	6.5430
 Irrigation percentage of total farm value*	25.4%	25.1%
 * Irrigation values only include the three Western Kansas crop reporting districts.
Alfalfa yields in millions of tons, all other crops in millions of bushels.
Kansas irrigation is concentrated primarily in the Ogallala region of Western Kansas, thus resulting in increased economic impact.
Harvested cropland acres, crop value produced and the irrigation percentage for 2002 and 2009 is shown in Table 3 for western Kansas.
As compared to 2009, dryland crop failures resulted in fewer harvested acres in 2002.
Consequently, the percentage of acres harvested and crop value produced by irrigation was much higher.
Table 3 also shows 2009 data for Southwest Kansas and demonstrates the high concentration of irrigated agriculture in the region since over 70 percent of the crop value produced came from irrigated acres.
The impact of irrigation in a single county in Table 3 shows 2002 and 2007 county data for Haskell County in Southwest Kansas.
In 2002, a dry year, almost 95 per cent of all crop value came from irrigated land, while in 2007 still over 80 percent of the crop value comes from irrigated agriculture.
Haskell County is used as an example as the county has been part of several social/economic studies that were initiated in the early
 1940's.
Six communities across the US were selected originally to study issues of social and economic instability.
Williams and Bloomquist  noted that irrigated agriculture had played a key role in providing the foundation of stability for the county.
Table 3.
Western Kansas crop production statistics for wheat, grain sorghum, corn, soybeans, and alfalfa*.
Total of Irrigated	Irrigated and	Irrigation	Irrigation
 Location	and Dryland	Dryland	Percentage of	Percentage of
 	Production	Total Area	Total Value
 2002	2009	2002	2009	2002	2009	2002	2009
 Western KS	5,372	6,899	905,163	2,333,500	36.7%	28.3%	70.2%	48.3%
 Southwest KS	2,532	3,042	565,555	1,120733	53.5%	44.0%	85.8%	70.4%
 2000	2007	2000	2007	2000	2007	2000	2007
 Haskell County	224.2	274	63,783	134,174	74.9%	62.0%	94.3%	81.6%
 * Other crops not included are silage, sunflower, cotton, and dry beans.
IRRIGATION WATER WITHDRAWAL IMPACT
 While some areas of the Ogallala have substantial water in storage , many areas have been depleted to levels that make large scale irrigation no longer possible.
Using a minimum threshold criterion of the aquifer being able to support a well with a 400 gpm pumping rate for a 90 day pumping season, some areas have been depleted and other areas have a projected lifespan of less than 25 years.
New technologies and cropping systems have allowed producers to adapt to declining well yield associated with the declining aquifer water table, but the irrigated land area in Kansas will eventually decrease.
Average 2009 2011 Saturated Thickness, Kansas High Plains Aquifer
 Figure 16.
Average saturated thickness for the High Plains Aquifer in Kansas.
Estimated Usable Lifetime for the High Plains Aquifer in Kansas 
 Figure 17.
Estimated usable lifetime for the High Plains Aquifer in Kansas 
 Irrigated agriculture initially developed using surface flood irrigation systems but has shifted to using center pivot irrigation systems.
The land area irrigated has been relatively.
Crop yield and irrigation water use efficiency have continued to improve even as average application depths have declined.
Unfortunately, improvements in systems, irrigation management, and cultural practices have not been sufficient to overcome excess water withdrawals in many areas of the High Plains aquifer system, especially the Ogallala.
The economic impact is considerable for the state of Kansas, in general, and is dramatic in areas of high irrigation concentration.
This research was supported in part by the Ogallala Aquifer Program, a consortium between USDA Agricultural Research Service, Kansas State University, Texas AgriLife Research, Texas AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
Contribution no.
12-313-A from the Kansas Agricultural Experiment Station.
USDA NASS.
Various Years.
Kansas Farm Facts.
In cooperation with Kansas Department of Agriculture.
Kansas Irrigation Water Use Report.
Various Years.
Prepared in cooperation by the Kansas Water Office and the KDA, Division of Water Resources.
Kansas Geological Service.
2012.
Gray scale maps provided by request for conference proceedings.
This paper was first presented at the Central Plains Irrigation Conference, February 21-22, 2012, Colby, Kansas.
It can be cited as
Economic implications of drip irrigation
 Margriet Caswell David Zilberman George E.
Goldman
 The profit potential is greatest on lower quality land
 D rip irrigation technology from Israel was introduced into California orchards in 1969.
Don Gustafson, Farm Advisor in San Diego County, who initially experimented with drip irrigation of avocados, found that orchards could be planted on slopes of up to 60 degrees and that water savings of 30 to 50 percent could be made.
As a result, extensive areas in the San Diego foothills were converted to growing avocados, enlarging the agricultural land base in the area.
Bernarr Hall, another Farm Advisor in San Diego, combined the use of drip irrigation with plastic mulching to grow strawberries on marginal land.
By 1974, there were 40,000 drip-irrigated acres in California and, by 1980, 300,000 acres.
The technology is used mostly for tree crops  and high-value row crops ; some attempts have been made to use it
 The adoption of drip irrigation, however, has not been geographically uniform in the state.
It seems to be more prevalent in regions with marginalquality lands and high water costs, and it has been more readily accepted in southern than in northern California.
These uneven adoption patterns prompted our study of the economic implications of drip irrigation.
To analyze how this technology has spread in California, we developed a conceptual framework based on the premise that drip irrigation increases the value of land as a production input and that the magnitude of this increase varies across lands of different qualities.
time.
On land with low water-holding capacity, such as sandy soil or an uneven slope, a significant amount of the applied water is not used by the crop because of percolation beyond the root zone or runoff of water from the land.
Modern low-volume irrigation technologies, in particular, drip irrigation apply smaller amounts of water per unit of time than do traditional methods.
Modern irrigation methods can thereby reduce runoff or excess percolation, or both, increasing the portion of applied water available to the crop.
These methods can thus improve the effectiveness of land as a medium for crop production.
This relative advantage of drip irrigation and other modern methods over traditional methods is greater for lower quality land.
We developed an economic model for the analysis of crop production in a region with different land qualities and two irrigation technologies traditional and modern.
Assuming that farmers want to earn as much money as possible, that profits per acre are not related to farm size for the range of farms considered here, and that modern technology costs more per acre, this model indicates that: Under both technologies, better land produces greater yields per acre.
Land can be considered a medium for the interaction between variable inputs , resulting in the production of a crop.
One important dimension of land quality is the capacity to hold the inputs that are applied and to ensure their use by the plant.
In the case of water, this quality is called water-holding capacity.
Under traditional irrigation technollogies , large amounts of water are applied in a short period of
 Fig.
1 The most profitable irrigation method depends on land quality.
Adopting drip irrigation would make poor-quality land  profitable; better-quality land  could be converted to drip irrigation; higher quality land would continue with traditional methods.
On better land, more water is used per acre when an increase in irrigation has a relatively strong impact on yield, whereas less water is applied per acre when the added yield resulting from an increase in irrigation is relatively small.
Yields per acre are greater under the modern technology than under the traditional technology.
Experiments in Israel have shown increases in production, and work on bell peppers in San Diego County had similar results.
Drip irrigration does not necessarily reduce water consumption per acre.
Since this method increases water effectiveness, using more water may be justified if it will substantially increase yield.
Only when the traditional system obtains most of the crop's yield potential will drip irrigation use less water per acre.
The water-use efficiency under drip irrigation will always be better.
The modern technology should be adopted and used first on lower quality land, where the profit potential is greater.
Later, if the cost of the modern technology declines, its adoption on higher quality land may be profitable also.
High capital expenditures are associated with the use of low-volume methods, such as drip irrigation.
The disadvantage of higher costs for the new technology, as compared with costs of traditional systems, would be greater on the better quality land and less on poorer quality land.
Terracing a steep slope to flood-irrigate would be too expensive.
The profit a farmer can earn with each irrigation system depends on land quality.
Since the value of land in its agricultural use is directly related to profitability, its price will depend on the most profitable irrigation method  as well as its quality.
Before introduction of the new technology, it would be profitable to floodirrigate all land qualities greater than B in figure 1.
With the adoption of drip irrigation, more land qualities would become profitable for farming; below a certain land quality, a farmer should change from traditional to drip irrigation methods.
Land qualities between A and B would be added to the agricultural land base; those between B and C would be converted from traditional to drip methods; and those greater than C would continue with former methods.
Profitability for each irrigation system obviously changes when economic factors vary.
Farmers depending on groundwater are affected by escalating energy prices and a dropping water table.
Figure 2 shows the conditions under which a particular farmer would be expected to switch irrigation technollogies.
Under some circumstances, neither method would be profitable.
If the farmer had a shallow well , energy prices would have to go above 50 cents per foot of lift before a technology change would be recommended.
With wells deeper than 500 feet, any energy price greater than 20 cents would prompt a change from flood irrigation to a drip system.
Fig.
2 Rising energy prices and dropping water tables might justify a switch to drip irrigation, but under some circumstances, neither drip nor other types of irrigation would be profitable.
Although the land-augmenting characteristic is the most important feature, drip irrigation also reduces preharvest labor, limits weed growth, promotes early and even ripening, and allows irrigation during cultivation and harvesting.
All of these advantages have to be considered in the economic analysis for selection of the proper irrigation
 technique at each location.
The introduction of drip irrigation also has implications for members of an industry  as a whole.
Farmers may face declining prices for their product as their aggregate output increases.
This would be particularly true for growers of specialty crops.
They may also face rising water prices as the amount used by the industry increases.
If these conditions are true, then the adoption of drip irrigation may affect output or water prices.
These price changes, in turn, could have secondary effects on the tendency to adopt drip irrigation.
We analyzed the outcome in these cases and concluded:
 The adoption of drip irrigation could increase total production and reduce product price.
It would increase total water use and water price when an increase in irrigation had a strong yield effect but might reduce water price and total water use when an increase in application had a relatively small impact on yield.
The introduction of drip irrigation, by lowering crop price and/or raising water costs, would reduce the land rent and value of high-quality land in the region.
If owners of the better land had strong political influence and considered drip irrigation to be against their interests, they might object to research and development efforts that would lead to the adoption of such technollogies.
Therefore, these technologies would be likely to be developed in regions with predominantly marginal land.
Although it is most likely that the introduction of drip irrigation would increase the potential amount of land available for a crop, the long-run effects due to changing prices might, in somecases, reduce the amount of land used to grow that crop.
California farmers face many difficult decisions in the next few years as a result of population pressures, uncertain water availability, unstable crop prices, environmental constraints, and increases in the costs of energy and labor.
This study has indicated several variables affecting profitability.
Government policies supporting the adoption of new technology may directly or indirectly change these parameters.
Among the new technologies, drip irrigation will have an important effect on California's agriculture in the coming years.
Margriet Caswell is Assistant Professor, Department of Economics, University of California, Santa Barbara; David Zilberman is Associate Professor, Agricultural and Resource Economics, and George E.
Goldman is Economist, Cooperative Extension, UC Berkeley.
A Review of Center Pivot Irrigation Control and Automation Technologies
 Written for presentation at the 5th National Decennial Irrigation Conference Sponsored jointly by ASABE and the Irrigation Association Phoenix Convention Center Phoenix, Arizona December 5 8, 2010
 Abstract: Electronic sensors, equipment controls, and communication protocols have been developed to meet the growing interest in site-specific irrigation using center pivot and lateral move irrigation systems.
Onboard and field-distributed sensors can collect data necessary for real-time irrigation management decisions and transmit the information directly or through wireless networks to the main control panel or base computer.
Equipment controls necessary to alter water application depth to meet the management criteria for relatively small management zones are now commercially available from irrigation system manufacturers and after-market suppliers.
Selection of the communications system for remote access depends on local and regionaltopography and cost relative to other methods.
Communication systems such as cell phones, satellite radios, and internet based systems allow the operator to query the main control panel or base computer from any location at any time.
Recent developments in the center pivot industry have led to contractual relationships between after-market suppliers and irrigation system manufacturers that should support further development of site-specific application of water, nutrients and pesticides in the future.
Keywords: site-specific irrigation, distributed sensor networks, wireless communication, variable rate irrigation,
 Agricultural fields are variable in terms of production for many reasons.
This variability may include topographic relief, changes in soil texture, tillage and compaction, fertility differences, localized pest distributions and various irrigation system characteristics.
The effects of different sources of variability on management can be additive and interrelated.
Fortunately, recent advances in communications and microprocessors have enabled the general implementation of site-specific water applications by self-propelled center pivot and linear move sprinkler irrigation systems.
The design of a suitable site-specific irrigation system can be complex because of the need to address the numerous causes of the variation that may exist in each field, the system capabilities that may be needed to achieve the desired management level, constraints inherent in the currently existing equipment and the general management philosophy of the owner/operator.
These considerations are not mutually exclusive, but they do not lend themselves well to categorization.
These issues are discussed in more detail by Buchleiter et al., 2000; Evans et al., 2000; McCarthy et al., 2010; Sadler et al., 2000; and Perry et al., 2004.
McCarthy et al  developed a predictive-adaptive control model for sitespecific irrigation water application of cotton using a center pivot.
Various simulation models were used to evaluate alternative irrigation control options across a range of crop management and environmental conditions.
The authors concluded that while the VARlwise framework accommodated a range of system control strategies, further work is necessary to explore procedures for using data with a range of spatial and time scales.
Decision support systems should be holistic approaches to irrigated crop management within a single field.
Within the decision support program structure, the irrigator predefines the criteria and guidelines to be used by the software structure and simulation models in making basic decisions to be implemented by a microprocessor-based control system.
Results of georeferenced grid sampling of soils, yield maps and other precision agriculture tools can also be major components in defining rules for these management systems.
These "rules" are used as the basis for analysis and interpreting the data from real time data networks, remote sensing, irrigation monitoring systems, agronomic and other information used to provide direction and implement the basic commands.
Decision support systems can also include instructions for chemigation  and provide alerts  to the grower based on output from established models using real-time environmental data.
In short, decision support provides more management flexibility by implementing short term, routine commands to direct irrigation schedules and other basic operations, which frees the irrigator to concentrate on managing other areas to minimize risk and reduce costs.
These integrated approaches will require the integration of a mix of various sensor systems , hardware, GPS, controllers and computing power.
The maximum benefits will be derived from a decision support system when the plant condition in selected areas of a field is monitored by some means to improve overall system management.
Monitoring systems can be field-based measurements or remotely sensed or an integrated mix of several sensor systems.
Existing center pivot systems span the evolution of technology from water to electric and hydraulically driven machines.
Due to their design, center pivots are operating on varying topography, and often have a range in soil textures present under a single machine.
Low infiltration rate soils challenge managers of standard machines with the need to provide little or no irrigation water to some areas while fully irrigating others.
Each of these factors represents a reason for using some sort of monitor/controller to manage water applications based upon need.
Precision application, variable rate irrigation and site specific irrigation are terms developed to describe water application devices with the goal of maximizing the economic and/or environmental value of the water applied via a moving irrigation system.
The most basic method to alter the water depth applied with a center pivot is to adjust the center pivot speed of travel based upon field soils or more frequently based upon field topographic features or different crops.
Early developments provided a very limited set of controls to turn end guns on and off based upon field position.
Other features included edge of field stops and stop-in-slot controls to cease irrigation due to obstructions or the completion of a complete rotation.
Programmable control panels allow adjusting the speed of travel multiple times during an irrigation event.
This is accomplished by entering the field position in a 360 circle where the speed will be changed to apply more, less or no irrigation water.
This approach could be used where portions of the field were planted to a different crop, but it lacked the flexibility necessary to supply water at rates required to meet management objectives of relatively small field areas with irregular shaped boundaries.
Individual sprinkler control of water application depth can be accomplished by using a series of on-off time cycles or as it has become known as "pulsing" the sprinkler through on-off cycles.
Reducing the on-time is effective at reducing both the application depth and the water application rate.
Later efforts in Washington State involved equipping a center pivot with a custom built electronic controller to activate water operated solenoid valves in groups of 2-4 nozzles.
Normally open solenoids allowed system control with the assurance that irrigation water was applied even if the control system failed.
Chvez et al.,  reported that a remote irrigation monitoring and control system installed on two different linear move irrigation systems performed well.
The systems proved to be highly flexible and capable of precision irrigation using a series of in-field and onboard wireless monitoring spread spectrum radios/sensors networks.
Individual nozzle/solenoid valves were pulsed according to prescription maps.
Deviations related to positioning of nozzles when irrigating were on average 2.5 + 1.5 m due mainly to inherent DGPS inaccuracy.
A variable flow sprinkler was developed for controlling irrigation water application by King and Kincaid  at Kimberly, ID.
The variable flow sprinkler uses a mechanically-activated pin to alter the nozzle orifice area which adjusted the sprinkler flow rate over the range of 35 to 100% of its rated flow rate based upon operating pressure.
The pin was controlled using either electric or hydraulic actuators.
The main issue is that the wetted pattern and water droplet size
 distribution of the sprinkler changed with flow rate which created water application uniformity issues due to a change in sprinkler pattern overlap.
Controlling irrigation water application depth can also be accomplished through the use of multiple manifolds with different sized sprinkler nozzles to vary water and nitrogen application.
These systems included 2-3 manifolds where simultaneous activation of one or manifolds served to adjust the water application rate and depth across a range of depths that is not possible with a single sprinkler package.
Control of each manifold was accomplished using solenoid valves similar to those described for the pulsing sprinkler option above.
As with any new technology, there are positives and negatives associated with each of these methods of controlling sprinkler flow rates.
Certainly long term maintenance by producers is an issue.
However, the biggest factor limiting their use is their installation cost that ranges from around $2000 for a system monitor to over $20,000 for control of individual sprinklers.
Center pivot position is the most basic use of sensors for center pivot control systems.
Until recently, alignment systems typically had an accuracy of +0.5 to 1.5 of the location of the first tower.
At a distance of 390 m from the pivot point, the position of the last sprinkler could be off by 3 to 10 m.
Research conducted by Peters and Evett  found that resolver determined position errors could be up to 5 degrees or over 30 m on a 390 m long center pivot.
Consequently, commercially available center pivots now employ a Wide-Area Augmentation System  enabled GPS antenna option to identify the position of the end tower to < 3 m accuracy.
The stop-start cycle of the center pivot typically allows determination of system position to less than 1 m accuracy.
The net effect of being able to accurately determine the pivot lateral location is that management zone size can be reduced without increasing the potential for a misapplication of water, nutrients, or pesticides.
Recent innovations in low-power sensors, battery and wireless radio frequency technologies combined with advances in Internet technologies offer tremendous opportunities for development and application of real-time management systems for agriculture.
Wireless sensor networks  are preferred because they can eliminate problems and costs associated with stretching and maintaining wires across a field; however, power requirements of the field wireless systems can be a concern.
Decision support frameworks will necessarily rely on WSNs for real-time, automated, low power soil water and micro-meteorological instrumentation, infrared thermometers monitoring of plant temperatures or other sensors that are strategically distributed to provide continuous feedback of field conditions.
Various sensors systems can also be mounted on the machine and provide real-time feedback for decision support as the machines move across a field (Peters and Evett,
 2008; O'Shaughnessy and Evett, 2010).
These field-based data may also be integrated with various remotely sensed data to help differentiate between various biotic and abiotic stresses.
Integrated data sources and networks provide needed information to re-calibrate and check various simulation model parameters for on-the-go irrigation scheduling and adjustments.
Integration of these technologies into the irrigation decision making process can determine when, where, and how much water to apply in real time; which enables implementation of advanced water conservation measures for economically viable production with limited water supplies, conserve energy, and enhance environmental benefits.
Local field-based sensor systems are generally a combination of an automated agricultural weather station providing meteorological data and WSNs that directly indicate localized field conditions from either one or multiple sensor types.
Field sensors can include soil water levels, air temperatures and humidity, precipitation  and other information such as infrared  surface radiometric measurements.
The Smart Crop system  is a recent example of an in-field wireless system commercialized for canopy temperature monitoring.
These sensor stations can transmit data wirelessly to a datalogger for either direct use by the grower  or base computer for decision support programs.
Wireless communications allow the base computer to be located with the control system on the irrigation machine or in a remote location.
Satellite and aerial imagery, GIS mapping services and GPS are becoming commonplace throughout the agricultural industry around the world.
Remotely sensed information can be photometric , thermal or multispectral acquired by aircraft and satellites in a variety of formats and resolutions.
There are a number of ways that multispectral data can be used to enhance water and energy conservation by helping to determine the exact causes of the nonuniform appearance  of the crop.
Advanced pattern recognition software and other tools for multispectral or other remotely sensed data can be used to detect many problems in agriculture.
However, two barriers to the widespread adoption and use of these integrated technologies in today's agriculture are the cost of these services and the difficulty for producers to understand and use the output in a timely manner.
The timeliness of this type of information is critical to producers because it is much better for their bottom line if they can make adjustments as the problems develop, not after the fact.
New analysis tools and interpretation aids as part of a comprehensive decision support system are needed for growers to take full advantage of these technologies.
Spectral and thermal ground-based remote sensors mounted on self-propelled irrigation systems are capable of providing information to farmers in a more timely manner than aircraft or satellite sources.
Infrared thermocouple thermometers mounted on a moving pivot lateral provide radiometric temperature measurements of in-field crop canopy.
Software to control drip and moving sprinkler systems has been integrated with this plant-feedback information and the Time-Temperature Threshold  algorithm , patented as the Biologically Identified Optimal Temperature Interactive Console  for managing irrigation by the USDA under Patent No.
5,539637.
Briefly, the TTT technique
 can be described as comparing the accumulated time that the crop canopy temperature is greater than a crop-specific temperature threshold with a specified critical time developed for a well-watered crop in the same region.
The TTT technique has been used in automatic irrigation scheduling and control of plant water use efficiency for corn in drip irrigated plots, and soybean and cotton in LEPA irrigated plots.
Peters and Evett  demonstrated that remote canopy temperatures could be predicted from a contemporaneous reference temperature and a pre-dawn temperature measurement.
IRT measurements made from a moving sprinkler can then be used to provide spatial and temporal temperature maps that correspond to in-field water stress levels of crops.
General, broad-based and easily modified software for managing these decision support systems for a multitude of crops, climatic conditions, topography, and soil textures are not currently available from manufacturers, government or consultants.
Development and updating of management maps for these irrigation systems is currently a painstaking and specialized process that is currently done only once a year or less.
Distributed Wireless Sensor Networks
 Distributed in-field sensor-based irrigation systems offer the potential to support site-specific irrigation management that allows producers to maximize their productivity while saving water.
However, the seamless integration of sensors, data interface, software design, and communications for site specific irrigation control using wireless sensor-based irrigation systems can be challenging.
Power needs are often a major consideration and solar panels are often used.
Researchers have addressed the issues of interfacing sensors and irrigation control using several different approaches.
Shock et al.
used radio transmission for soil moisture data from data loggers to a central data logging site where decisions were made and manually changed.
Miranda et al.
used a closed-loop control system and determined irrigation amount based on distributed soil water measurements.
Wall and King  explored various designs for smart soil moisture sensors and sprinkler valve controllers for implementing "plugand-play" technology, and proposed architectures for distributed sensor networks for sitespecific irrigation automation.
They concluded that the coordination of control and instrumentation data is most effectively managed using data networks and low-cost microcontrollers.
It is often not feasible or desired to have in-field sensing stations that use wires to connect to a base station because of the cost, labor and maintenance, especially if the distances are greater than 10 m.
Wires can also be damaged by farm equipment and small animals; and wires create more opportunity for lightning damage.
Wireless data communication systems avoid many of these problems and provide dynamic mobility and easy relocation and replacement of stations.
Radio frequency technology has been widely adopted in consumer's wireless communication products and provided opportunities to deploy wireless signal communication in agricultural systems.
Adopting a standard interface for sensors and actuators allows reuse of common hardware and communication protocols such as communication interface and control algorithm software.
Instrumentation and control standards for RS232 serial  and RS485  communication protocols have been widely applied and well documented for integrating sensors and actuators, particularly in industrial applications.
Two wireless protocols that are commonly used for this purpose are Bluetooth   and ZigBee .
Bluetooth and ZigBee  are designed for radio-frequency  applications for mobile applications that require a relatively low data rate, long battery life, and good network security.
These are "line-of-sight"  systems and crop canopies, small trees, and fences can interfere with transmissions.
ZigBee is a low-cost, nonproprietary wireless mesh networking standard, which allows longer life with smaller batteries, and the direct-sequence spread spectrum  mesh networking provides high reliability.
Bluetooth is a faster but more expensive standard than ZigBee, and uses spread spectrum modulation technology called frequency hopping  to avoid interference and ensure data integrity.
ZigBee has lower power needs than Bluetooth, but it also transmits effectively over less distance.
Enhanced Bluetooth transmitters are available that can transmit up to 1 km.
Bluetooth wireless technology has been adapted in sensing and control of agricultural systems.
Zhang  evaluated Bluetooth radio in different agricultural environments, power consumption levels, and data transmission rates.
He observed 1.4 m as an optimal radio height for maximum 44 m radio range and reported limitations of significant signal loss after 8-hours continuous battery operation and 2-3 seconds of transmission latency with the increase of communication range.
Oksanen et al.
used a PDA with Bluetooth to connect a GPS receiver for their open, generic and configurable automation platform for agricultural machinery.
Lee et al.
explored an application of Bluetooth wireless data transportation of moisture concentration of harvested silage and reported a limitation of 10-m short range.
However, the limitations reported by reviewed publications about Bluetooth applications in agricultural systems can be solved or minimized by system design optimization.
The power shortage can be solved by using solar power that recharges the battery.
The radio range and transmission latency can also be extensively improved by using an upgraded power class and antenna.
The same techniques can be applied to Zigbee-based systems.
Drawbacks in using wireless sensors and wireless sensor networks include provision for ample bandwidth, existing inefficiencies in routing protocols, electromagnetic interference, interference by vegetation, radio range, sensor battery life , and synchronous data collection.
An immediate limiting factor in self-powered WSN operations is battery life, which can be addressed to some degree by decreasing the duty cycle of the sensor nodes.
Researchers are also concentrating on RF communication protocols to increase the energy efficiency of a WSN by investigating algorithms for multi-path routing, data throughput and energy consumption  and by reducing idle listening and collisions that occur during the medium access to realize power conservation.
However, reducing quiescent current draw is typically a significant method for impacting battery longevity.
Other identified challenges specific to WSNs and agriculture include interference with radio propagation due to crop canopy height.
Andrade-Sanchez et al.
determined that power consumption and power output varied
 significantly among transceivers, and the average measure of signal strength as a function of distance resembled the shape of the theoretical prediction of path loss in free space.
In addition, the received signal strength indication  was influenced by the spatial arrangement of the network in both the vertical and horizontal planes in tests with line-of-sight Signal obstruction issues relating to crop height and in-field equipment are inherently reduced when the moving sprinkler is used as the sensor platform; but infield sensors require manual adjustment above crop canopy.
Remote Communications with Self-Propelled Irrigation Systems
 There are several methods for remotely communicating with self-propelled sprinkler irrigation systems.
Many of these are being marketed by the manufacturers of this equipment and include cell phones, RF radios, and satellite radio communications for relatively basic monitoring and control of the systems.
Hybrid systems relying on internet to connect computers at or near the site are combined with wireless RF systems for the link to the machine.
Each manufacturer has developed unique hardware and software that allow the owner to access the main control panel to determine system status including travel direction, speed of travel, application depth, and field position.
More sophisticated software provided by an office base station uses visualization software to allow the owner to see year-to-date summaries of water and chemical application events.
All information can be archived for record keeping purposes.
Selection of the communications system for remote access depends on topography and cost relative to other methods.
Cell phone systems with modems at the control panels are the least costly and probably the most common.
Satellite radio communications are often preferable when there are large topographic differences that limit cell phone service.
Higher powered, licensed, radio systems  with data modems may also be an option but may also be affected by topographic relief.
Repeater stations for LOS radio frequency systems can also be quite expensive, especially if there is a need to communicate long distances over diverse topography.
Recent developments in the center pivot industry have resulted in contractual arrangements with developers of after-market control and monitor systems such as FarmScan, AgSense, and PivoTrac.
These additions to the existing onboard control capabilities of center pivot panels make site-specific irrigation a reality for irrigation zones less than the 100 m The main considerations remaining include the development of decision support systems that maximize the value of the applied water or chemical based on field-based information and the cost recovery potential of the cropping system since system costs up to $20,000 are possible when there is a large number of management zones along the system length.
Table 1.
Monitor, control, communication, and data reporting capability of center pivot control panels.
Reinke	T-L	Valmont	Zimmatic
 Position in field and travel direction	Y	Y	Y	Y
 Speed of travel	Y	Y	Y	Y
 Wet or dry operation	Y	Y	Y	Y
 Pipeline pressure	Y	Y	Y	Y
 Pump status	Y	Y	Y	Y
 Auxiliary components'	Y 	Y 	Y 	Y 
 Stop-in-slot and auto restart	Y	Y	Y	Y
 Wind speed	Y	N	Y	Y
 Start and Stop	Y	Y	Y	Y
 Speed of travel	Y	Y	Y	Y
 Auto restart and auto reverse	Y	Y	Y	Y
 End gun	Y	Y	Y	Y
 High and Low voltage shutdown 	High and Low pressure shutdown	N/Y	Y	N/Y	Y	Y/Y	Y	N/Y	Y
 System stall shutdown	Y	Y	Y	Y
 Auxiliary components	Y	Y	Y	Y
 System guidance	Maximum control points per circle IT	3600	Y	180	Y	72	Y	180	Y
 Sprinkler application zones	2	3	30	NL
 Cell phone	Y	Y	Y	Y
 Radio	Y	Y	Y	Y
 Computer	Y	Y	Y	Y
 Subscription required	Y	Y	Y	Y
 Data Collection and Reports
 Soil water content	Y	Y	Y	N
 Precipitation per season	Y	Y	Y	Y
 Application date and depth	Y	Y	Y	Y
 Irrigation events per season	Y	Y	Y	N
 Chemical application rate	N	N	N	Y
 Chemical application per season	N	N	N	Y
 System position by date	Y	Y	Y	Y
 N/Y indicates no automatic shutdown for high voltage is provided but the panel does provide  automatic shutdown for low voltage.
Y indicates that up to 7 auxiliary components  can be controlled by the panel.
System guidance provided by above ground cable, below ground cable, furrow or GPS.
Number of positions in a revolution where set points may be changed.
II
 Electronic sensors, equipment controls, and communication protocols have been developed to meet the growing interest in site-specific irrigation using center pivot and lateral move irrigation systems.
Onboard and field-distributed sensors can collect data necessary for real-time irrigation management decisions and transmit the information through wireless networks to the main control panel or base computer.
Equipment controls necessary to alter water application depth to meet the management criteria for relatively small management zones are now commercially available from irrigation system manufacturers and after-market suppliers.
But decision systems for automatic control are incomplete.
Selection of the communications system for remote access depends on local and regional topography and cost relative to other methods.
Communication systems such as cell phones, satellite radios, and internet based systems allow the operator to query the main control panel or base computer from any location at any time.
Recent developments in the center pivot industry have led to contractual relationships between after-market suppliers and irrigation system manufacturers that should support further development of site-specific application of water, nutrients and pesticides in the future.
Drip Irrigation for Vegetable Production
 Drip or trickle irrigation is a very efficient method of applying water and nutrients to crops.
For many crops, the conversion from sprinkler to drip irrigation can reduce water use by 50 percent.
Crop yields can increase through improved water and fertility management and reduced disease and weed pressure.
When drip irrigation is used with polyethylene mulch, yields can increase even further.
These benefits are only possible when a drip irrigation system is properly designed, managed, and maintained.
Irrigation system design is complex and is beyond the scope of this publication.
You should consult with a qualified agricultural engineer or irrigation equipment dealer to design your drip irrigation system.
However, by understanding the various design factors, you can help ensure that your drip irrigation system is properly designed and operated.
System components, basic design principles, practical applications, and operating guidelines are discussed in this publication.
Advantages of drip irrigation
 1.
Lower-volume water sources can be used because trickle irrigation may require less than half of the water needed for sprinkler irrigation.
2.
Lower operating pressures mean reduced energy costs for pumping.
Drip irrigation of bell peppers
 3.
High levels of water-use efficiency are achieved because plants can be supplied with more precise amounts of water.
4.
Disease pressure may be less because plant foliage remains dry.
5.
Labor and operating costs are generally less, and extensive automation is possible.
6.
Water applications are made directly to the plant root zone.
No applications are made between rows or other nonproductive areas, resulting in better weed control and significant water savings.
7.
Field operations, such as harvesting, can continue during irrigation because the areas between rows remain dry.
This publication was developed by the Small-scale and Part-time Farming Project at Penn State with support from the U.S.
Department of Agriculture-Extension Service.
8.
Fertilizers can be applied efficiently through the drip system.
9.
Irrigation can be done under a wide range of field conditions.
10.
Compared to sprinkler irrigation, soil erosion and nutrient leaching can be reduced.
Disadvantages and limitations of drip irrigation
 1.
Initial investment costs per acre may be higher than those of other irrigation options.
2.
Management requirements are somewhat higher.
Delaying critical operation decisions may cause irreversible crop damage.
3.
Frost protection is not possible with drip systems; if it is needed, sprinkler systems are necessary.
4.
Rodent, insect, and human damage to drip lines are potential sources of leaks.
5.
Water filtration is necessary to prevent clogging of the small emitter holes.
6.
Compared to sprinkler irrigation, water distribution in the soil is restricted.
Because vegetables are usually planted in rows, drip tape with prepunched emitter holes is used to wet a continuous strip along the row.
Most vegetables are grown for only one season, SO thin-walled disposable tape  is generally used for only one season.
Less emphasis is placed on buried mainlines and sub-mainlines to allow the system to be dismantled and moved from season to season.
Costs may be high, SO you should develop a functional system that allows for maximum production with minimal costs.
You may purchase an entire system from a drip irrigation dealer or adapt your own components.
Proper system design will help you avoid problems later.
Irrigation water may come from wells, ponds, lakes, rivers, streams, or municipal water suppliers.
Groundwater is fairly clean and may only require a screen or disk filter to remove particles that can clog emitters.
However, a water quality test should be conducted to check for precipitates or other contaminants before a drip system is installed.
Surface water from streams and ponds contain bacteria, algae, and other aquatic life, making more expensive sand filters an absolute necessity.
Municipal water suppliers will generally provide water quality test results, making it easier to spot potential problems.
However, you can expect to pay a high price for this water.
Drip irrigation system components
 A drip irrigation system has six major components:
 1.
Delivery system Mainline distribution to field Sub-mainline  Feeder tubes or connectors Drip lines
 2.
Filters Sand Screen Disk
 3.
Pressure regulators Fixed outlet Adjustable outlet
 4.
Valves or gauges
 Positive displacement injectors Pressure differential injectors Water-powered injectors
 How these components are put together for your application, and which options you choose, will depend on the size of the system, the water source, the crop, and the degree of automation you desire.
Mainline distribution to field: Underground polyvinyl chloride  pipe or above-ground aluminum pipe is used to deliver water from its source  to the sub-mainline.
Irrigation mainline with screen filter, pressure regulator, pressure gauge, and water meter connected to submain
 Sub-mainline : It is common to use vinyl "lay flat" hose  as the sub-mainline.
This hose is durable and long lasting, and it lies flat when not in use SO that equipment can be driven over it.
The lay flat hose, connectors, and feeder tubes are retrieved after each growing season and stored until the following year.
Since polyethylene pipe is somewhat rigid, it is not easily rolled up at the end of the season.
Vinyl lay flat hose with connector and drip tape
 Connectors/couplings: Plastic connectors or couplings are used to connect the drip line to the sub-main.
Drip tape and wetting pattern
 Drip lines: Two basic types of drip lines are used for commercial vegetable production, with turbulent flow drip tape most commonly used.
This polyethylene product is thin-walled, collapses when not pressurized, and has emitters formed into its seam during manufacturing.
Drip tapes are operated at pressures ranging from 6 to 15 psi.
Drip tubes with internally attached emitters are an alternative to turbulent flow drip tapes.
Products with in-line or internally attached emitters tend to be more expensive, but they often have better water distribution uniformity and better clogging resistance.
Understanding the water flow rate, emitter spacing, wall thickness, diameter, and pressure compensation ability of the drip line you choose is very important.
Water flow rate is typically specified in gallons per minute per 100 feet of tape  or by the emission rate of a single emitter in gallons per hour.
Tape flow rates typically range from 0.2 to 1.0 gpm per 100 ft.
For vegetable production, tapes with flow rates around 0.5 gpm are often used.
Maturing vegetables grown in the northeastern United States require about two to three hours of irrigation during hot summer days when a 0.5 gpm per 100 ft tape is used.
Emitter spacing refers to the distance between emitters along the drip line.
For vegetables, emitter spacings of 8 to 16 inches are common.
On very sandy soils, a closer spacing may be required to ensure adequate water distribution.
However, closer emitter spacings translate to higher emission rates.
Higher emission rates increase the system flow rate and require a larger pump and pipe size, leading to a higher overall system cost.
A 12-inch emitter spacing works well on many soils and is very common in the northeastern United States.
Wall thickness of drip tapes is specified in mils.
Manufacturers produce drip tapes with wall thickness ranging from 4 to 25 mil.
Wall thickness selection should be based on user experience, the number of seasons a product will be used, and the potential for damage by insects, animals, and machinery.
Inexperienced users needing a single-season product should begin with a 10 mil tape to minimize the stretching and breaking commonly experienced when installation procedures are first being learned.
Experienced users of single-season tapes often prefer 8 mil products.
Tape cost is influenced by wall thickness, SO thin-walled tapes cost less than thicker tapes.
A drip line installed on the soil surface is much more likely to be damaged by birds, animals, and insects than one buried 1 to 3 inches in a bed covered with plastic mulch.
Buried lines will also not move around on the bed.
Drip lines laid on the soil surface can move, as a result of wind and the expansion and contraction of the polyethylene.
Drip lines on the soil surface are also prone to damage by tractors and foot traffic.
Although drip tubes can be reused, commercial vegetable growers rarely reuse them.
Reusing drip tape is an ecologically sound practice, but the cost of retrieval, storage, and repair is high.
Diameter of the drip tape is important to consider in system design and is chosen based on row length.
Row length directly affects both the flow rate through the tape and pressure loss in the tape.
A tape diameter of 5/8 inch is the industry standard and is common where rows range from 300 to 600 feet.
For rows ranging from 600 to 1,500 feet, 7/--inch-diameter tape is available.
As with wall thickness, the cost of tape is proportional to tape diameter.
Pressure compensation refers to a drip line's ability to maintain a specified emission rate over a range of pressures.
A pressure compensating line emits water at the same flow
 rate over a range of pressures.
A non-pressure compensating line emits water at a rate that increases linearly with pressure.
Commonly used drip lines fall somewhere in the middle and are called partially pressure compensating.
For example, many drip lines will experience a 10 percent increase in emission rate when pressure is increased 20 percent.
Drip tubes with internally attached emitters are fully pressure compensating, but they are more complicated to manufacture and are more expensive.
The cost of drip lines varies with diameter, wall thickness, emitter design, and pressure compensation capability.
Turbulent flow tapes  with a wall thickness of 8 mil cost $1.50 to $2.50 per 100 ft.
Tubes with internally attached emitters and a wall thickness of 8 mil cost from $2.50 to $4.00 per 100 ft.
Filters are essential to the operation of a drip system.
Many devices and management techniques are available for cleaning irrigation water.
Depending on the water source, settling ponds, self-cleaning suction devices, sand separators, media filters, screen filters, and disk filters are used with drip irrigation systems.
Keeping a drip system free of debris is critical because most clogs will irreparably disable a system.
Media, screen, and disk filters are characterized by the size of the holes the water passes through in the filter element.
The size of the openings is specified by the filter's mesh size.
Mesh size is inversely related to the size of the filter openings.
For example, a 200-mesh filter will capture smaller particles than a 100-mesh filter.
For most drip tapes, 150 to 200 mesh filtration is required.
For clog-resistant tubes with internally attached emitters, 100-mesh filtration is sufficient.
Settling ponds use gravity to allow particulate matter to settle to the bottom of the pond.
However, other techniques are more suitable and practical, since settling is not efficient for removing suspended matter.
Although sand-sized particles will settle in seconds, siltand clay-sized particles can take hours, weeks, or months to settle.
Ponds also support aquatic life that often contributes to clogging problems.
Media, screen, or disk filters are preferred for removing physical material from water.
The location of the suction inlet is an important decision as it affects the quality of the water entering the filtration system.
Ideally, the inlet should be located some distance from the edge of the pond, 1 to 2 feet below the pond surface.
Attaching the inlet of the suction pipe to the bottom of a sealed, partially water-filled 55-gallon drum can serve as a self-adjusting inlet depth regulator.
However, it is often impractical to locate the inlet away from the shoreline.
Near the pond edge, weeds and algae are often drawn into the inlet.
A self-cleaning suction device can reduce the amounts of weeds and algae drawn into the system.
This device has a screened, barrel-shaped rotating basket around the inlet of the suction pipe.
A pressurized water return line from the irrigation system sprays water against the inside of the
 screen basket, cleaning the basket and forcing weeds and algae away from the inlet.
Sand separators are sometimes used in front of media, disk, or screen filters.
These devices separate sand and heavy particulate matter by swirling the water passing through them.
Sand separators must be sized according to the flow rate to operate properly and will not remove siltor clay-sized material.
Media filters are the most common filters used in commercial vegetable production.
Ranging from 14 to 48 inches in diameter, they are usually installed in pairs.
Media filters are expensive, heavy, and large, but they can clean poor-quality water at high flow rates.
In a media filter, 12 to 16 inches of media  act as a threedimensional filtering agent, trapping particles within the top inch or two of media.
As the media fills with particulate matter, the pressure drop across the media tank increases, forcing water through smaller and fewer channels.
This will eventually disable a media filter, requiring that clean water from one tank be routed backwards through the dirty tank to clean the media.
This "backwashing" requires exact flow rates to make the media "dance" and be thoroughly cleaned.
Large, commercial-sized filters require electronic controls and hydraulic valves to route the water.
Typically, the pressure drop across a clean media tank is 2 to 3 psi.
When the pressure differential across the media filters reaches a given level, typically 5 to 8 psi higher than when the tanks are clean, it is time to blackflush the filters.
Sand filter, pump, and fertigation unit
 Screen filters are used widely in commercial vegetable production and are the most common irrigation filter used by small operations if the water source is relatively clean.
Screen filters can remove debris efficiently like a media filter, but they are not capable of removing as much debris as a media filter before cleaning is required.
Compared to media filters, screen filters are often oversized because they only have a relatively small, two-dimensional cleaning surface.
Screen filters are sometimes used as secondary filters, located downstream from media filters.
Regular cleaning of screen filters is very important.
If they are neglected, a portion of the screening element will become caked and clogged, forcing water through a smaller area.
This can push debris through the screening element and under extreme conditions rupture it.
Upstream and downstream pressure gauges can help you judge when a filter requires cleaning.
A pressure drop of 1 to 3 psi is normal for a screen filter.
Screen filters should be cleaned when the pressure drop is 5 to 8 psi compared to when the filter is clean.
Many screen filters contain a flushing valve, making it extremely easy to clean the filter.
Disk filters are devices that possess traits of both media and screen filters.
The screening element of a disk filter consists of stacks of thin, doughnut-shaped, grooved disks.
The stack of disks forms a cylinder where water moves from the outside of the cylinder to its core.
Like a media filter, the action of the disk filter is three dimensional.
Debris is trapped on the cylinder's surface while also moving a short distance into the cylinder, increasing the capacity of the disk filter.
Cleaning a disk filter requires removing the disk cylinder, expanding the cylinder to loosen the disks, and using pressurized water to spray the disks clean.
Although disk filters have a cleaning capacity between media and screen filters, disk filters are not recommended where organic matter load is high.
Both disk and screen filters can be configured with electronic controls, hydraulic valves, and special devices to operate as self-cleaning filters.
With these attachments, self-cleaning disk and screen filters can be used in place of media filters if the organic matter load is not high.
These devices have the advantage of being smaller and lighter but cost about the same as media filters.
Pressure regulators reduce the water pressure in the irrigation system manifold  to the working pressure of the drip lines.
Both fixed outlet and adjustable outlet pressure devices are available for a wide range of flow rates.
Globe valves regulate pressure by constricting the water flow path.
However, they are not
 recommended because any change in the system flow rate or operating pressure also affects downstream pressure.
This could happen when water is routed to a different zone or when a system begins to experience some clogging.
The danger in having an unreliable pressure regulator is that the system could become over-pressured.
Drip tape may deform or burst at pressures as low as 30 psi.
Screen filters, pressure regulators, and pressure gauges
 Watering several fields or sections of fields from one water source can be accomplished by using automatic or manually operated valves to open and close various zones.
Either hand-operated valves  or automated electric solenoid valves  can be used to control irrigation zones.
It is also recommended that a water meter be installed to monitor total water usage and flow rate in the system.
A backflow/ anti-siphon valve is also necessary if you use a well or municipal water source or when injecting 3009320 fertilizers or chemicals into the system.
Chemigation is the practice of injecting and applying fertilizers, Water meter pesticides, and anticlogging agents with a drip irrigation system.
Fertilizers are routinely injected; the ability to "spoon-feed" nutrients is partially responsible for the yield increases resulting from drip irrigation.
Systemic pesticides are also frequently injected into a drip irrigation system to control insects and protect plants from disease.
Chemicals that prevent or repair clogging problems can also be injected.
Chlorine is used to kill algae, and acids are used to modify water pH and dissolve certain precipitate clogs.
The type of chemical being injected is a key consideration in determining the appropriate chemical injector.
For fertilizers, maintaining an accurate injection rate is not critical, unless fertilizer is injected on a continuous basis.
The most important feature of a fertilizer injector is that it has a high-enough injection rate to complete the injection cycle in a reasonable period.
An injector with a capacity of 1 gpm is likely to be sufficient for injecting fertilizer into irrigation zones of less than 10 acres.
In contrast, injecting chemicals to prevent clogging requires an accurate and very low injection rate.
Since these materials are usually injected continuously at concentration rates of 1 to 10 ppm, a separate injector is often used.
Pesticide injection is similar to fertilizer injection, but the volume of material required is usually small compared to the volume of fertilizer required.
For this reason, most pesticides can use injectors suited to either fertilizers  or clogging prevention.
The type of power available at the injection site will affect your choice of injectors.
Injectors can be powered by gasoline engines, the PTO shaft of a tractor, electric motors, or the water pressure of the irrigation system.
Positive displacement, pressure differential, and waterpowered injectors make up the majority of injectors used for chemigation.
Externally powered diaphragm, piston, gear, lobe, and roller  pumps are all positive displacement injectors.
These injectors are typically powered by gas, diesel, or electric, have a high chemical resistance, and are medium to high in cost.
The injection rate of diaphragm pumps can be adjusted, but piston pumps must be stopped to adjust the injection rate.
A piston pump is more chemically resistant than a diaphragm pump, and its injection rate is less affected by downstream pressure.
Many growers purchase an expensive, high-quality diaphragm or piston pump for injecting fertilizers.
With the higher cost comes reliability, durability, and peace of mind.
Pressurized mixing tanks and venturi injectors are two common pressure differential injectors.
These devices often have no moving parts and tend to be very simple because they use the difference in pressure between two different locations on an irrigation system to power the injection process.
Pressure tanks are the simplest types of injectors and work well for fertilizers because delivery accuracy is not critical.
The venturi injector is more efficient and more accurate than a pressurized mixing tank.
Both require that the injector be plumbed parallel to the irrigation mainline and that a constriction be placed in the mainline between the line delivering water to the injector and the line returning to the mainline.
Venturi injectors can deliver chemicals very accurately and can be sized for a particular injection rate.
They can be used either for injecting fertilizers or for anticlogging agents.
Water-powered injectors are driven by the pressure of the irrigation system.
Thus, their principal advantage is they
 do not require an external power source.
Both piston and diaphragm types are available.
Their injection rate is either proportional to the system pressure or to the flow rate through the injector.
Proportional injectors insert chemicals in proportion to the flow rate.
They are particularly useful where chemicals are injected for clogging prevention and a fixed concentration of chemical is required.
Changing the system flow rate  does not change the concentration of material injected with proportional injectors.
Irrigation scheduling is the process of determining how often to irrigate and how much water to apply.
The appropriate irrigation frequency depends on the rate at which crops use water and on the water-holding capacity of the soil.
The amount of water to apply for each irrigation application can be calculated from known soil and plant characteristics.
Drip wetting pattern with plastic mulch
 Soil in the root zone acts as a reservoir for water.
Soil texture is the primary factor influencing the amount of water stored.
Available water is defined as the amount of water that plants can easily withdraw from the soil and use.
Fine-textured soils, such as clays, silt loams, and loams, hold much more water than coarse-textured soils.
Thus, coarse-textured soils must be irrigated more frequently.
For most crops, an appropriate goal is to irrigate when 50 percent of the available water is depleted.
Table 1.
Available water-holding capacity for different soil textures.
AVAILABLE WATER HOLDING CAPACITY
 SOIL TEXTURE	
 Loam and silt loam	2.00-2.75
 C.
A.
Storlie, 1995.
Water-storage capacity is influenced by soil depth.
Nearly all irrigated vegetable and agronomic crops extract water from the top two feet of the soil profile, even though the roots may extend much deeper.
In fact, 75 to 95 percent of most plant roots are in the top 12 to 18 inches of the soil profile.
Proper irrigation results in this plant root zone being refilled, but not overfilled.
Filling the root zone beyond its capacity results in leaching.
The proper duration can be calculated from the plant root zone depth, soil texture, and water flow rate.
Tensiometers indicate available soil moisture by measuring soil tension.
Soil tension indicates how tightly water is held by the soil and increases as moisture in the soil is depleted.
This force draws water out of a tensiometer through its porous tip, creating a vacuum inside the tensiometer.
This negative pressure, or tension, is registered on a vacuum gauge.
However, tensiometers do not work well in finetextured soils and require constant maintenance.
Because of this, most vegetable growers rely on their experience to determine critical periods of plant water demand and proper irrigation.
Clogging is the most serious threat to a drip irrigation system and arises from physical, biological, and chemical contaminants.
Filtration can remove physical contaminants, and chemical water treatment is often necessary to eliminate or remove biological and chemical contaminants.
Tapes buried under plastic mulches are much less apt to become clogged from mineral deposits.
Bacteria, algae, and slime in irrigation lines can be removed with chlorine or commercial bacterial control agents injected through the fertilizer injection system.
A 2-ppm chlorine daily rinse at the end of the irrigation cycle or a 30-ppm "shock treatment" can be used if slime becomes a problem in the system.
Consult your irrigation system dealer for dilution rates for commercial cleaning products.
Periodic flushing of the mainline, sub-mainline, and drip tape is an excellent maintenance practice.
Adapters are available for the ends of each drip tape to automatically flush lines at the end of each irrigation cycle, or they can be manually opened to allow a few gallons of water to flush from the end.
This will prevent any buildup of particles or slime at the end of the drip line.
Checking filters daily and cleaning if necessary.
A clogged screen filter can be cleaned with a stiff bristle brush or by soaking in water.
Backwashing sand filters to remove particulates and organic contaminants.
Checking drip lines for leakage.
A large, wet area in the field indicates a leaking drip line.
Leaking lines can be repaired by splicing with an inline connector or bypassed with a short piece of feeder tube.
Using water treatment chemicals to dissolve excessive mineral deposits and remove buildup of organic contaminants in water supply lines.
Drip irrigation as part of a plasticulture system
 Table 2.
Component list for a one-acre plastic mulch drip irrigation system.*
 COMPONENT DESCRIPTION	TOTAL PRICE 
 Engine and pump (5.5-hp engine and
 24-inch stainless steel media filter  and
 Lay flat, header pipe 2"	$150
 Drip tape 	$150
 Plastic mulch 	$300
 Valves (pressure regulation, gauges, and
 Lay flat connectors and hole punch	$200
 *Only plastic mulch and drip irrigation components are included.
The field is assumed to be level with an adjacent surface water supply.
The filters designed in this system are capable of irrigating one acre at one time.
The system contains media filters, a venturi injector, and a 5.5-hp engine and pump.
Additional equipment to consider includes water meters.
Although the base equipment used in this example will sufficiently handle more than one acre, carefully consider the number of zones and the time required to irrigate additional zones before purchasing equipment.
No sales tax, freight, or field labor was included in these estimates.
Laying plastic mulch and drip tape
 Prepared by William J.
Lamont Jr., professor of vegetable crops, Michael D.
Orzolek, professor of vegetable crops, Jayson K.
Harper, professor of agricultural economics, Lynn F.
Kime, senior extension associate in agricultural economics, and Albert R.
Jarrett, professor of agricultural engineering
 An OUTREACH program of the College of Agricultural Sciences
 Penn State College of Agricultural Sciences research and extension programs are funded in part by Pennsylvania counties, the Commonwealth of Pennsylvania, and the U.S.
Department of Agriculture.
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Yucca plants, which are also called soapweed, can be quite common on rangeland in western and central Nebraska.
In some areas, they can be quite thick and significantly reduce grass production.
There are ways, though, to reclaim those grazinglands.
Tailwater Recovery and On-Farm Storage Reservoir: Nutrient Runoff Mitigation and Reuse Potential
 Tailwater recovery  systems are a combination of financially assisted USDA Natural Resource Conservation Service  conservation practices aimed at collecting runoff and storing that water for irrigation.
This surface-water storage structure is a viable option for
 capturing and recycling precipitation and irrigation runoff.
In addition to storing water for irrigation, these systems have the potential-and have been funded-to reduce nutrient runoff leaving the agricultural landscape.
Figure 1.
Water movement through a TWR system.
Note that not all TWR systems have the same components.
Some TWR systems are comprised of only a large TWR ditch and no on-farm storage reservoir.
Top left: Nutrientand sediment-laden water running off a field in the Mississippi Delta region.
Top right: Runoff water being captured by a TWR ditch.
Bottom left: Nutrientand sediment-laden water being pumped into an on-farm storage reservoir.
Bottom right: Surface water being irrigated from a TWR/OFS system.
Preventing Nutrients from Leaving the Farm Biological
 Plant and microbial activity impact the water leaving agricultural fields.
Biological activity occurs naturally in agricultural drainage ditches and also may occur in TWR systems.
Plants and algae take up nutrients required for their growth.
Microorganisms also play a central role in nutrient transformation and removal.
When oxygen is not present, microorganisms in the soil can carry out a process called denitrification to reduce nitrogen in the water and return it to the air.
Holding water on the landscape in a TWR system allows the heavier sediment and sediment-bound phosphorus to settle out of the water.
This also allows time for biological processes to take place to reduce nitrogen.
Finally, by recycling this water onto the landscape, TWR systems prevent sediment and nutrients from leaving the farm landscape.
Table 1.
Annual mean loads leaving fields and running off
 into TWR systems and amount captured (prevented from
 leaving farms) by TWR systems in the Delta.
Runoff 	550,911	449	1,972
 Captured 	270,579	179	1,087
 Source: Omer et al.
Figure 2.
Plant and algal growth in TWR ditches in Mississippi's Delta region.
Sediment and Nutrient Runoff
 Sediment and nutrient runoff from agricultural fields occurs year-round with precipitation and irrigation events.
However, there are times of the year when more sediment and nutrient loss occurs.
Figure 3 shows sediment, phosphorus, and nitrogen field runoff occurring from March to July each year.
Most of the field runoff coincides with precipitation in the Mississippi Delta region.
Runoff events occurring in March to July also overlap with the primary growing season in the region.
Figure 4.
Runoff leaving a field after a precipitation event in the Mississippi Delta region.
The small building on the bottom left houses water-quality sampling equipment used to monitor runoff leaving the field and entering the TWR system.
Figure 3.
Sediment and nutrient loads leaving fields and running off into TWR systems annually.
Six TWR systems were monitored.
The systems were within watersheds ranging from 141 to 385 acres and were all tilled land.
Solid lines represent the trend over the 2-year monitoring period.
TWR System Sediment and Nutrient Capture Performance
 Results show that TWR systems do not reduce concentrations of sediment and nutrients in captured runoff; however, loads of sediment and nutrients are reduced .
The impact TWR systems have on load reductions is substantial and is comparable to nutrient-loading goals of state and federal agencies.
Captured nutrients are available in TWR system water for irrigation; however, the loads of nutrients are too little to reduce fertilizer application rates.
Figure 5.
Mean percent load reductions from TWR systems in the Delta.
Nutrients Available for Irrigation Reuse
 Runoff captured by a TWR system is stored and reused as irrigation water, allowing potentially available nutrients to be put back into the field to meet crop needs.
Results from this study showed relatively low nutrient values available per acre in TWR water stores.
The available amount of nutrients will fluctuate throughout the year with changes in temperature, precipitation, and fertilizer inputs in the field.
Figure 6.
Rice irrigation with water from a TWR system in the Mississippi Delta region.
Table 2.
Mean loads of nutrients available (in the TWR sys-
 tem's water) to irrigate back onto crops during the irrigation
 2014 	0.9	9.0	1.4
 2015 	0.7	4.0	1.3
 Mean 	0.8	6.5	1.3
 Source: Omer et al.
Cost of Production and Equitable Leasing Arrangements for Center Pivot Irrigated Corn in Central Nebraska
 The focus of this paper is to provide an economic analysis of the profitability of center pivot irrigated corn enterprises in central Nebraska in 2007.
An analysis of equitable crop share leasing arrangements and breakeven cash rental rates for irrigated corn producers follows from the estimates of irrigated corn enterprise profitability.
Currently  grain futures and expected 2007 harvest prices for U.S.
corn are appreciably higher than at almost any other time since the early 1970s.
The reasons for these high grain futures prices have to do with bioenergy-related market demand and other related factors affecting grain markets but that is not the focus of this paper.
Here, we are concerned about the impact of expected high corn prices upon not just the gross revenue but also the expected net profitability of the irrigated corn enterprise for 2007.
This analysis is based on grain and fertilizer market prices and conditions as they existed in late January, early February, 2007.
With heightened expectations for corn prices in 2007 and for gross/net revenues for irrigated corn enterprises, there is much interest on the part of both farm operator/tenants and landowners regarding the impact of these market factors upon cropland leasing arrangements.
In this paper the equity and returns of irrigated crop share and cash rent leasing arrangements for landowners and tenants are examined for irrigated corn enterprises in central Nebraska.
2007 Irrigated Corn Production, Revenue and Cost Assumptions
 Historically high expected corn prices for the 2007 crop have unquestionably raised expectations about the profitability of raising irrigated corn under center pivot sprinkler systems in central Nebraska.
An expected harvest cash price of $3.50 per bushel for corn is used in this analysis.
Other key assumptions and information sources used in this analysis are as follows:
 Crop Yields and Direct Crop Production Costs: The UNL Extension publication "Nebraska Crop Budgets 2006" , edited by UNL Extension Specialists Roger A.
Selley and Robert N.
Klein, was the primary source of yield and direct crop cost of production information used in these budgets.
Three  alternative cost-return budgets are presented for irrigated corn in Nebraska:
 A.
Center pivot irrigated corn in a conventional-till continuous corn rotation: 175 bu/acre yield, 13 acre inches of irrigation water applied
 B.
Center pivot irrigated corn in a no-till continuous corn rotation: 180 bu/acre yield, 9 acre inches of irrigation water applied
 C.
Center pivot irrigated corn in a no-till corn-soybean rotation: 190 bu/acre yield, 9 acre inches of irrigation water applied
 Assumptions about yield goals and actual yields, the amounts and costs of corn seed, herbicide and insecticide treatments, the amount of fertilizer applied, the number and types of field operations, and other management expenses are all taken from UNL Crop Production budgets.
Drying, harvesting and hauling operation costs was also taken from this same source.
Fertilizer prices are obtained from retail fertilizer sales contacts in Central Nebraska.
Farm Program Payments: USDA farm program payments on irrigated cropland in central Nebraska are assumed to be $35 per acre .
Crop Revenue Coverage Insurance: Crop Revenue Coverage  insurance premium costs for irrigated corn in Buffalo County, Nebraska are estimated using the USDA Risk Management Agency online insurance premium calculator.
Chicago Board of Trade December 2007 corn futures prices on January 31 st were used in estimating the CRC insurance premiums.
Custom Field Operation and Harvesting Costs: Expenses for field operations and harvesting are estimated using the most recent state-wide custom rate averages for Nebraska.
This approach is a departure from field operation cost estimates in UNL Extension publication EC872, but consistent with the approach used in K-State Research and Extension crop budgets to estimate field crop cost of production.
Labor cost estimates associated with field operation custom rates are calculated in the manner used in K-State budgets.
Irrigation Equipment and Pumping Costs: K-State Research and Extension estimates of irrigation equipment costs are used to represent the cost of the center pivot irrigation system , power unit , and well, pump and gearhead.
Straight-line  depreciation methods are used to allocate the cost of the system over its lifespan.
An interest rate of
 Table 1.
Irrigated Corn Cost Return Budget
 Center Pivot Irrigated Corn Cost-Return Budget in Nebraska
 Daniel O'Brien, Agricultural Economist NW Kansas, K-State Research & Extension
 Nebraska Crop Budgets for 2006 , EC872
 Tillage System:	Conv'l.
Till	No-Till	No-Till
 Crop Rotation:	Corn-Corn	Corn-Corn	Corn-Soyb.
INCOME PER ACRE	Yield Level, bu/ac
 A.
Actual Yield bushels per acre	175	180	190
 Yield Goal bushels per acre	190	195	205
 B.
Price per bushel	$3.50	$3.50	$3.50
 C.
Net government payment	$35.00	$35.00	$35.00
 D.
Indemnity payments	$0.00	$0.00	$0.00
 E.
Miscellaneous income	$0.00	$0.00	$0.00
 F.
Returns/acre  + C + D + E)	$647.50	$665.00	$700.00
 1.
Seed	$58.90	$60.80	$63.65
 2.
Herbicide	27.03	27.59	38.45
 3.
Insecticide / Fungicide	4.65	4.64	1.86
 4.
Fertilizer and Lime	51.37	53.37	45.37
 5.
Crop Consulting	12.50	12.50	12.50
 6.
Crop Insurance	11.66	11.63	11.52
 7.
Drying	45.50	46.80	24.70
 8.
Miscellaneous	20.04	31.02	26.59
 9.
Custom Hire / Machinery Expense	119.33	85.80	88.29
 10.
Non-machinery Labor	13.48	9.70	9.98
 a.
Labor	5.00	5.00	5.00
 b.
Fuel and Oil	64.61	44.73	44.73
 C.
Repairs and Maintenance	4.29	2.97	2.97
 d.
Depreciation on Equipment and
 Well	53.10	53.10	53.10
 e.
Interest on Equipment and Well	43.52	43.52	43.52
 12.
Land Charge / Rent	139.00	139.00	139.00
 G.
SUB TOTAL	$673.97	$632.17	$611.22
 13.
Interest on 1/2 Nonland Costs	17.68	15.74	15.79
 H.
TOTAL COSTS	$691.65	$647.91	$627.01
 I.
RETURNS OVER COSTS 		$17.09	$72.99
 J.
TOTAL COSTS/BUSHEL 	$3.95	$3.60	$3.30
 K.
RETURN TO ANNUAL COST /G	-3.93%	5.19%	14.53%
 TABLE 2.
Production Inputs -Center Pivot Irrigated Corn Central NE
 ITEM	175	180	190
 Seed, 1,000/acre* Bt Seed	31.0	32.0	33.5	$1.90	/1000
 N 	200	210	170	$0.20	/lb
 N	7	7	7	$0.15 /lb
 P	24	24	24	$0.43 /lb
 Bicep II Magnum	2.10	2.10	2.10	$11.25	/qt
 Exceed	0.25	0.25	0.50	$12.40	/oz
 + Crop Oil Concentrate	0.50	0.50	0.50	$0.60	/pt
 2,4-D Ester 4#	0.00	0.30	0.00	$1.88	/pt
 Gramoxone Inteon	0.00	0.00	1.50	$5.03	/pt
 NIS	0.00	0.00	6.00	$0.13	/oz
 Regent 4 SC	0.83	0.83	0.00	$3.46	/oz
 Lorsban 15 G	0.10	0.10	0.10	$2.00	/lb
 Capture 2 EC	0.51	0.51	0.51	$1.74	/oz
 Mustang Max	0.40	0.40	0.40	$1.71	/oz
 Capture 2 EC	0.00	0.00	0.05	$1.74	/oz
 Irrigation water, inches	13	9	9	$4.97	/in
 Yield Level 	Custom
 ITEM	175	180	190	Rate
 Chopping stalks	1	0	0	$8.77 /ac
 Disk	1	0	0	$9.28 /ac
 Field cultivate	1	0	0	$7.97	/ac
 Row crop cultivation	1.25	0	0	$7.59	/ac
 Hoe	0	0	0.1	$5.00	/ac
 Planting conventional row crop	1	0	0	$12.65	/ac
 Planting no-till	0	1	1	$12.81	/ac
 Anhydrous application	1	1	1	$8.53	/ac
 Fertilizer application	0	0	0	$5.29	/ac
 Herbicide application	1	1.2	1	$5.13 /ac
 Insecticide ground rig application	0.25	0.25	0.5	$5.12	/ac
 Insecticide airplane application	0.32	0.32	0.34	$6.59	/ac
 Base charge	1	1	1	$26.12	/ac
 Grain cart custom charge	175	180	190	$0.060	/bu
 Hauling with truck	175	180	190	$0.100	/bu
 Non-machinery labor	1.35	0.97	1.00	$10.00
 Land charge/rent	$139.00	$139.00	$139.00
 Interest on capital	9.0%
 Irrigation Equipment	Investment, $/ac	Years	Salvage value
 Well, pump and gearhead value	$398.00	25	0%
 Power unit and meter	$94.00	7	0%
 Irrigation system	$475.00	20	0%
 9% is used on the irrigation equipment to represent the economic cost of paying for and eventually replacing the irrigation equipment.
Pumping cost acre inch of water applied are calculated using current diesel fuel prices and irrigation system assumptions relevant to central Nebraska.
Land Charge / Rent: An irrigated farmland rental rate of $139 per acre for central Nebraska is assumed in these cost-return budgets, as reported in the 2006 Nebraska survey of farmland and rental values .
Interest on Operating Costs: A 9% interest rate on operating costs is used in these budgets, consistent with K-State cost of production budgets.
Expected Profitability of Center Pivot Irrigated Corn in 2007 in Central Nebraska
 Expected net returns over all costs except management for the 175 bu., 180 bu.
and 190 bu.
per acre yield scenarios are , $17.09, and $72.99 per acre, respectively.
As stated earlier, these budgets are based on expected harvest cash corn prices of $3.50 per bushel and cash rental rates of $139 per acre for irrigated corn in central Nebraska.
Equitable Crop Shares for Irrigated Corn Leases
 An analysis of equitable crop share leasing arrangements for irrigated corn illustrates the marked impact of alternative irrigation equipment ownership situations.
Specifically, equitable irrigated cropland leasing arrangements differ depending on whether farm operator/tenants or landowners own the center irrigation systems and power units involved.
Two irrigation equipment ownership scenarios are examined for each of the three corn yield/crop rotation regimes in this analysis.
Scenario #1: The first irrigate crop share lease scenario represents situations where the farm operator/tenant owns the center pivot sprinkler system and the power unit, pays 67% of herbicide, drying and crop insurance costs, and contributes 100% of all other crop inputs.
In this scenario, the landowner contributes the land, well, pump and gearhead, and pays 33% of herbicide, drying and crop insurance costs.
Scenario #2: The second lease scenario represents situations in which the farm operator/tenant pays 67% of herbicide, drying and crop insurance costs, and contributes 100% of all other crop inputs.
The landowner contributes the land, center pivot sprinkler system, power unit, well, pump and gearhead, and pays 33% of herbicide, drying and crop insurance costs.
Table 3.
Equitable Crop Shares for Irrigated Corn Leases
 Corn after Corn	Corn after Corn	Corn after
 Actual Yield:	Actual Yield:	Actual Yield:
 175 bu./acre	180 bu./acre	190 bu./acre
 Operator' Contribution: Pivot System + Power Unit; 2/3 Herbicides, Drying & Crop Insurance
 Landowner's Contribution: Land; 1/3 Herbicides, Drying & Crop Insurance
 Expenses 	Operator $	$475	$432	$438
 Landowner $	$210	$211	$209
 Calculated Equitable	Operator %	69%	67%	68%
 Crop Shares 	Landowner %	31%	33%	32%
 Returns to Management	Operator $		$15	$36
 Operator's Contribution: 2/3 Herbicides, Drying & Crop Insurance
 Landowner's Contribution: Land, Pivot System + Power Unit; 1/3 Herbicides, Drying & Crop Insurance
 Expenses 	Operator $	$413	$370	$375
 Landowner $	$273	$274	$272
 Calculated Equitable	Operator %	60%	57%	58%
 Crop Shares 	Landowner %	40%	43%	42%
 Returns to Management	Operator $		$12	$31
 Landowner's and tenant's total expenses, equitable shares, and profit/loss are reported for these two scenarios for each of the three yield/cropping system regimes.
Equitable share percentages  for crop share leases are the focus of these analyses.
University of Nebraska-Lincoln Extension personnel indicate that the most common terms for irrigated crop share leasing arrangements in central Nebraska are 1/3-2/3 leases  with herbicides, crop insurance and drying costs shared or paid for  by the landowner.
Ownership of the center pivot systems and pumping plants will likely vary from farm to farm and may affect the proportional revenue shares between operator/tenants and landowners in irrigated crop share leasing arrangements.
Scenario #1 Results: Under Scenario #1  the calculated equitable crop shares for the tenant for the 175 bu., 180 bu.
and 190 bu.
scenarios are 69%, 67% and 68%, respectively.
These calculated equitable crop share percentages are nearly identical to the most common 33%-67% landowner-tenant crop share arrangement for irrigated crop share leases in central Nebraska.
Scenario #2 Results: Under Scenario #2  the calculated equitable crop shares for the tenant for the 175 bu., 180 bu.
and 190 bu.
scenarios are 60%, 57% and 58%, respectively.
These downward adjustments in equitable crop share percentages for the operator/tenant reflect greater contributions of financially valued resources by the landowner to the irrigated crop share leasing arrangement in the form of the center pivot irrigation system and power unit.
Cash Lease Equivalents and Breakevens
 This part of the analysis is intended to address some of the current questions raised by farm operator/tenants and landowners about cash rental rates in the current environment for grain prices.
Two measures of financial returns in cropland leasing arrangements are calculated.
The first measure is "risk adjusted crop share equivalent returns to landowners".
The second is "tenant's breakeven returns to land and management".
Risk Adjusted Crop Equivalent Returns: The landowner's risk adjusted crop equivalent returns are calculated in the following manner.
The returns per acre a landowner would receive with an equitably adjusted crop share lease arrangement are reduced by a risk adjustment or percentage.
This risk adjustment is applied to account for the additional financial risk assumed by tenants in cash rental arrangements as opposed to crop share lease arrangements where tenants and landowners share more financial risk from the irrigated corn enterprise.
A 3% risk adjustment factor is used in this analysis.
Breakeven Returns to Land: The farm operator/tenant's breakeven returns to land indicate the maximum amount that could be paid for irrigated cash rent under these corn production and irrigation equipment ownership scenarios before the operator/tenant begins losing money.
Returns to management are not quantified or specifically accounted for in this crop budget analysis.
If a tenant is paying the breakeven / maximum cash rent amount for irrigated cropland as indicated in this analysis, then they are not allowing for any return to management from this irrigated corn enterprise.
Two alternative corn prices  are used to illustrate the impact of higher grain price and revenue expectations for irrigated corn in 2007.
The impact of alternative irrigation ownership scenarios  is also illustrated.
Table 4.
Cash Lease Equivalents & Breakeven Land Costs
 Conv.
Tillage	No-Till	No-Till
 175 bu./acre	180 bu./acre	190 bu./acre
 I.
Cash Rent Equivalents & Breakevens @ $3.00 / bushel Corn Price:
 Scenario #1: Operator: Pivot System + Power Unit, Crop Expenses / Landowner: Land*
 Landowner's Equivalent Share Rent 	$131 /ac	$146 /ac	$155 /ac
 Tenant's Breakeven Land Cost 	$48 /ac	$105 /ac	$131 /ac
 Scenario #2: Operator: Crop Expenses / Landowner: Land, Pivot System + Power Unit*
 Landowner's Equivalent Share Rent 	$180 /ac	$200 /ac	$211 /ac
 Tenant's Breakeven Land Cost 	$111 /ac	$167 /ac	$194 /ac
 II.
Cash Rent Equivalents & Breakevens @ $3.50 / bushel Corn Price:
 Scenario #1: Operator: Pivot System + Power Unit, Crop Expenses / Landowner: Land*
 Landowner's Equivalent Share Rent 	$156	$175 /ac	$184 /ac
 Tenant's Breakeven Land Cost 	$135 /ac	$195 /ac	$226 /ac
 Scenario #2: Operator: Crop Expenses / Landowner: Land, Pivot System + Power Unit*
 Landowner's Equivalent Share Rent 	$214/ac	$237 /ac	$250 /ac
 Tenant's Breakeven Land Cost 	$198 /ac	$257 /ac	$289 /ac
 * Assume operator/tenant pays 67% fertilizer, drying and crop insurance expenses, 100% remaining crop costs.
Discussion of Results: For $3.00 /bushel corn, a landowner's equivalent risk adjusted financial returns under an equitable share rent arrangement are greater than operator/tenant's breakeven returns to cover land and management for all scenarios considered.
For $3.50 /bushel corn, this remains true for the 175 bu/acre scenario, but not for the 180 bushel and 190 bushel per acre budgets, although the returns are similar.
The tenant's breakeven returns to land and management in the $3.50 per bushel examples are markedly higher than the current or highest historic cash rental rates charged for irrigated cropland in the Nebraska-Kansas region.
The comparable returns to landowners under equivalent equitable irrigation share leases with higher corn prices offer a reasonable alternative to cash rental arrangements in these examples.
The expected profitability of irrigated corn and the expected returns to operator/tenants and landowners in alternative crop leasing arrangements are markedly affected by expectations of higher corn prices for 2007.
Whether all the adjustments in 2007 crop input prices for irrigated corn production have been fully realized to date is an open question.
It is also unknown to what degree the higher selling price expectations for the 2007 corn crop will be actually realized at harvest time, although corn futures prices are other industry and governmental policy indicators are supportive of that perspective at the current time.
This analysis indicates that landowner's returns under risk adjusted crop share leasing arrangements are expected to be of similar to operator/tenant's breakeven cash rental rates for irrigated cropland in 2007.
Given the uncertainty about both corn selling prices and the cost of production inputs for corn in 2007, it may be advisable for farm operator/tenants and landowners to consider equitably designed crop share leasing arrangements as opposed to cash rent leases for irrigated cropland in the coming year.
Alternatively, existing cash rental arrangements could be adjusted to include both fixed  and flexible  components to share higher crop revenues should historically high actual 2007 harvest prices for corn and expected crop yields  actually come to fruition in fall 2007.
A focus on grain prices in this analysis and these decisions is only partially adequate.
Instead, the focus of local crop leasing arrangements for any particular farm operation or piece of irrigated farmland would more appropriately placed on net crop enterprise revenues instead of on crop prices alone.
In the risky, uncertain environment for irrigated corn production in 2007, crop share leasing arrangements are a viable and reasonable option to cash lease arrangements.
They are a mechanism that may help farm operator/tenants manage their financial risk in high cost irrigated corn enterprises while allowing landowners to means to participate is potentially 2007 higher crop revenues.
Is Your Irrigation System Ready for the Season?
It has been another wet spring here in Nebraska.
This creates a challenge for the local farmers to get in the field and get all the spring work wrapped up.
As wet as it has been, most producers have probably not started thinking about the irrigation equipment.
Irrigation Water Management  A Simple Analogy
 Brian Leib, Associate Professor, Irrigation Systems and Management Tim Grant, Extension Assistant, Soil and Water Resources Department of Biosystems Engineering and Soil Science
 Irrigation water management  can seem complicated and much of the equipment used is of a technical nature; however in reality, the concepts that govern IWM are simple.
For example, why do most of us keep track of the gasoline in our cars?
The self-evident answer is that most of us do not want to run out of gas and be stranded.
Similarly, we irrigate SO our crops do not run out of water and strand us with less than desirable yields.
Let's take the analogy of irrigation management and fuel management a little further.
Just as gas tanks are limited in the amount of fuel they can store , soils are likewise limited.
The rooting depth also limits water storage.
A crop with 4-foot roots in a silt loam soil that has a water holding capacity of 2 inches per foot will be able to store 8 inches of water for the plant to use.
It is not advisable to allow the crop to use all the available moisture  before irrigating because the crop would be severely stressed.
A rule of thumb value is that yield reduction starts when about 50 percent of the total available water  is depleted.
A better understanding of how soils store water and specific water holding capacities for Tennessee soils are available.
1
 If we overfill a tank during refueling, gas shoots out of the tank, onto the ground, and possibly onto ourselves.
No one likes wasting gas that has been paid for, contaminating the environment, and reeking with the smell of gasoline.
The effects of over-irrigation are similar, if not as dramatic.
Full irrigation  followed by an unexpected rainfall event can result in runoff with soil erosion from the soil surface and/or deep percolation with leaching through the crop-root zone.
Both are a waste of water that create the potential to wash ag chemicals into streams and groundwater.
Water and Fuel Management
 In a humid region like Tennessee, managed depletion irrigation  can leave storage capacity in the soil to capture rainfall.
The uncertainty of rainfall amount and timing in a humid region like Tennessee would be like having a generous neighbor who liked to put free gas in vehicles at unknown times and in unknown amounts without any regard for the level of gas already in a tank.
Even though this is an unrealistic situation for refueling, it is the reality of irrigating in the humid Southeast.
If this were a realistic situation, the logical response would be to keep your fuel tank partially full: perhaps 1/3 full.
This would leave room to store any free gas  that the generous neighbor might put in your tank yet still maintain a buffer against running empty if no free gas  arrived.
This principle of maintaining a managed depletion of water from the soil profile can be applied to most crops, and has been applied specifically to cotton 2 and soybean crops 3 in Tennessee.
We have several tools to assist us with MDI similar to those used in fuel management.
A smartphone and navigation app can be used to plan a trip.
If we
 wanted to drive to Miami from Memphis, we would look up the mileage and find out it is approximately 1,000 miles.
If the vehicle gets 20 mpg, we could calculate how much gas we would need, and knowing there may not always be a gas station available, we may decide to refill the tank after 10 gallons are used from the 16-gallon tank.
With this approach, we would expect to refuel five times during our trip.
Similarly, historical crop-water use and rainfall can help us plan how to irrigate a crop.
Historically, for West Tennessee, corn is expected to use 20 inches of water.
The average effective rainfall during the same period is 14 inches , and 3 inches of soil water can safely be depleted in a silt loam soil.
Therefore, the irrigation requirement would be 3 inches.
If an irrigation system applies 0.5 inches per application, then on average the field will need to be irrigated six times during the growing season to maximize yield.
Historic crop-water use and rainfall can be found in the MOIST  Tables for "Corn," "Cotton" and "Soybean." In a humid region like Tennessee, not all rainfall is effectively stored for plant use and rain rarely falls according to yearly averages.
Therefore, irrigation will need to be adjusted accordingly.
Another tool used in fuel management is the trip odometer.
Many of us zero the trip odometer after refueling to estimate gas mileage and gas usage.
If the trip odometer reads 120 miles since refueling and the vehicle gets 20 mpg, then 6 gallons of gas have been used and up to 6 gallons could be added at the pump without overfilling or more gas could be utilized before refueling.
In this scenario, we are keeping track of actual usage because real trips do not always turn out the way they are planned.
In the same way, actual crop-water use can be calculated from weather stations maintained by UT's Department of Biosystems Engineering and Soil Science.
4 For example, a crop has used 1.5 inches of water in a week based on the growth stage and weather conditions.
If 1 inch of rain occurred during this week, only 0.5 inches of irrigation are required to keep soil moisture at the same level.
Programs like the MOIST Spreadsheet can help calculate actual crop-water use and balance water use with rainfall and irrigation to maintain an appropriate MDI level of soil moisture.
5
 Of course, the most popular method of tracking fuel supply is measuring the tank level with a fuel gauge.
Similarly, soil moisture levels can be measured by a variety of sensors.
Without going into the details of how different soil water sensors work, it is im-
 portant to remember your own experience with fuel gauges in different vehicles.
One vehicle may read E for empty and mean it is safe to drive for another 75 miles, while another vehicle at E means it is time to refuel immediately.
Likewise, soil moisture sensors vary in calibration and also have different characteristics and costs.
Spending some time understanding a sensor's characteristics and hands-on experience with MDI levels for triggering irrigation are required to get the most out of any soil water sensor.
The University of Tennessee has tested many types of sensors and can provide guidance on how to use different types.
6 The MOIST+ APP  incorporates the use of sensors that measure soil tension.
7
 Finally, gas pumps can be compared with irrigation systems.
A gas pump meters fuel into the tank as an irrigation system delivers water to the soil at a known rate.
However, gas pumps are fairly universal and there are many distinct types of irrigation systems with a wide range of application rates and characteristics requiring different operation times to apply the same amount of water.
For example, drip irrigation forces the effective soil moisture storage tank to be small because it can't supply water to the entire soil profile, leading to frequent smaller irrigations.
Center pivot irrigation can supply water to the entire soil profile, but its high potential for runoff forces light and frequent irrigation similar to buying a few gallons worth of gas every couple of days.
Very few irrigation systems have been successfully engineered to turn off automatically when soil moisture has reached the desired level, as a gas pump does when the tank is full or the dollar amount is reached.
Therefore, irrigators need to understand how their systems apply water to effectively implement a managed depletion of soil water.
8
 1.
How Soils Hold Water, a Home Experiment.
2.
The Basics of Cotton Irrigation in Tennessee.
3.
The Basics of Soybean Irrigation in Tennessee.
4.
How Much Water Is Your Crop Using?
5.
Using a Water Balance to Make Irrigation Decisions: MOIST.
6.
Using Soil Moisture Sensors for Irrigation Management in Tennessee.
7.
The MOIST+ APP
 8.
Understanding Application Characteristics of Center Pivot Irrigation.
Figure 2.
Examples of overlapping pivots.
Over-application in the dark green areas could be reduced by using zone control on the large pivot in  or either pivot in.
North Carolina Cooperative Extension Service
 North Carolina State University
 Irrigated Acreage Determination Procedures for Wastewater Application Equipment
 Irrigation continues to be the most practical and cost effective method of applying wastewater to fields so that the nutrients contained in the wastewater can be used by IRRIGATION SYSTEM growing crops.
However, irrigation systems have inherent application limitations that make field calibration, irrigation scheduling, and determination of irrigated acreage critical for proper use of the nutrients contained in the applied wastewater.
Irrigation systems are normally designed to satisfy equipment specifications provided in manufacturers' charts.
Information presented in manufacturers' charts are based on average operating conditions for relatively new equipment.
Discharge rates and precipitation rates change over time as equipment ages and components wear.
Poor designs and/or improper operation can also cause poor performance.
As a result, equipment should be field calibrated regularly to ensure that application rates and uniformity are consistent with values used during the system design and given in manufacturers' specifications.
Field calibration is a simple procedure that involves collecting and measuring the material being applied at several locations in the application area.
Step-by-step guidelines for field calibration of hard hose traveler irrigation systems are given in Extension publication AG-553-2, Field Calibration Procedures for Animal Wastewater Application Equipment: Hard Hose and Cable Tow Traveler Irrigation System.
Irrigation must be scheduled when fields are dry enough to retain all of the applied liquid within the root zone.
If soils are too wet during irrigation, some of the applied wastewater may run off the field or leach below the root zone and become unavailable to the crop.
These unused nutrients could contaminate surface or ground water supplies.
Determining when and how much wastewater to apply for the prevailing conditions is referred to as irrigation scheduling.
Irrigation scheduling techniques and procedures are outlined in Extension publication AG-452-4 Irrigation Scheduling to Improve Waterand Energy-Use Efficiencies.
Sprinkler irrigation systems do not apply water uniformly throughout their entire wetted radius.
Application depths tend to be higher near the sprinkler and decrease gradually within the first 60 to 70 percent of the wetted radius.
Beyond this point, the application depth declines quickly, dropping to zero at the outer edge.
Irrigation design guidelines take equipment limitations into account in establishing recommended overlap ranges to optimize uniformity of coverage.
Determining the uniformly irrigated area for traveler systems can be difficult for travel lanes along the perimeter of the field, for non-uniform travel lane spacings, or for excessive travel lane spacings with improper overlap.
This publication contains step-by-step guidelines for determining irrigated acreage of hard hose traveler irrigation systems.
Travel lane spacing and design guidelines have been developed primarily for freshwater irrigation with the primary goal of ensuring that those areas of the field receiving the least amount of water receive enough to sustain the crop and achieve yield goals.
To achieve minimum desired application depths within the "lighter application zones," travel lane spacings of 70 to 75 percent of the wetted sprinkler diameter have been determined to be "optimum" to compensate for the declining application along the perimeter.
Closer lane spacings are sometimes economically justified for higher value crops; however, closer spacings may also result in some overlap zones receiving more water than necessary, and certainly more than the average.
A good irrigation design considers these factors and uses a travel lane spacing that achieves a balance between the relative proportion of "under" and "over" irrigated area in order to achieve the most uniform application possible.
The application uniformity can be quantified using one of several uniformity indices.
The uniformity index recommended for wastewater application is the Christiansen Uniformity Coefficient, Uc.
Step-by-step computational procedures are outlined in Extension publication AG-553-2, referenced in the previous section.
An application uniformity index of 60 is the minimum acceptable for wastewater application using hard hose traveler systems.
Irrigation systems should be field calibrated regularly to ensure that application uniformity is within the acceptable range.
Field calibration can also be used to determine the area within a field receiving a uniformly acceptable application.
In an effort to answer technical specialists' questions and to provide uniform interpretations of the state's animal waste management rules, the North Carolina General Assembly formed an interagency committee in
 1996.
The SB 1217 Interagency Committee is composed of two representatives of each of the five agencies with responsibilities for the development and/or enforcement of animal waste management rules.
The committee recently adopted guidelines and procedures for determining the acreage that can be counted toward the "irrigated area" in satisfying the Certified Animal Waste Management Plan.
The committee considered many factors including recommendations from irrigation engineers, certified irrigation designers, and industry representatives before arriving at these guidelines.
The irrigated acreage determined by these procedures is intended to "reasonably and practically" account for physical limitations of the application equipment.
The "irrigated acreage" computed by the procedures presented below must equal or exceed the acreage requirement specified in the CAWMP for proper nutrient use.
The irrigated area determination includes two broad categories: existing irrigation systems -those systems installed before the guidelines were finalized-and new systems or expanded systems installed after the SB 1217 committee released the third revision of the Sixth Guidance Document.
Future updates and revisions may occur, SO you should refer to the most recent Guidance Document for the latest interpretation and effective dates.
For the purpose of computing the irrigated acreage available to satisfy the CAWMP, the SB 1217 Interagency Committee adopted the term "CAWMP wettable acre" to be applied to existing systems.
This term applies to existing systems that satisfy minimum specifications as outlined below.
The irrigated acreage for new or expanded irrigation systems should continue to be based on standard irrigation design guidelines, which are based on the effective design area.
The term expanded irrigation system applies to new irrigation components that wet an area of a field that was not wetted before adoption of the new guidelines.
These terms are defined below.
Irrigated Acreage Determination Procedures for Wastewater Application Equipment
 Figure 1.
Area "wetted" during a single pull of a hard hose traveler.
Existing irrigation systems-For hard hose traveler systems designed and installed in accordance with minimum overlap guidelines  and laid out with multiple overlapping lanes, the CAWMP wettable acre allowance is the entire "net wetted area" in the field.
The net wetted area is the part of the field that gets "wetted" during two or more parallel pulls of the gun when operated during normal conditions, i.e., wind speed
 Figure 2.
Shaded area shows net wetted area for a field irrigated with a hard hose traveler with mutiple lanes.
The "wetted area" for a single pull without overlap is the area inscribed within the wetted diameter and length of pull as shown in Figure 1.
For multiple pulls such as shown in Figure 2, the wetted area is also the entire shaded area; but, in this publication, this area is referred to as "net wetted area." Due to the overlap, some of the same areas are wetted during adjacent pulls.
These overlap areas cannot be counted twice, hence the term "net" is used.
For a hard hose traveler system, there are two travel lane designations within the field that affect determination of irrigated acreage.
An interior travel lane is any lane that receives overlap on both sides of the pull as shown in Figure 3.
The center lane is an interior lane.
Travel lanes along the perimeter of the field receive overlap on just one side and are referred to as exterior travel lanes.
Figure 3.
CAWMP wettable acre allowance for existing systems based on net wetted area for exterior  and interior travel lanes.
Figure 4.
Shaded area shows allowable "irrigated area" for existing single pull hard hose traveler.
Note that the net wetted area allowance for an exterior lane is larger than the net wetted area allowance for an interior lane.
This is due to overlap.
In single travel lanes with no overlap, the outer wetted edge cannot be counted under CAWMP wettable acre rules.
In this case, the net wetted area is computed based on 90 percent of the verified wetted diameter as shown in Figure 4.
For any system in which the lane spacing exceeds 90 percent of the verified wetted diameter, each lane should be treated as a "single lane" case.
The system layout, including determination of lane spacing and the number of interior and exterior lanes, must be determined in order to compute the CAWMP irrigated acreage of an existing system.
The CAWMP wettable acre rules distinguish between existing systems with two or more overlapping travel lanes
 Figure 5.
Normalized application depth versus distance from a gun or sprinkler.
and existing systems with only one travel lane without overlap.
For multiple lanes, the CAWMP wettable acre allowance is "all" of the area wetted, whereas only 90 percent of the area wetted can be counted for single pulls.
New or Expanded Irrigation Systems-New or expanded irrigation systems must follow recommended design standards, which base the allowable irrigated area on the effectively irrigated area, referred to in this publication as the "design area."
 The effective irrigated area is the wetted area that receives at least 50 percent of the target application amount.
From field calibration measurements, this has been determined to be the area that falls within 78 percent of the wetted radius as shown in Figure 5.
Note that application depths remain within 90 percent of the target amount out to 60 percent of the wetted radius.
Between 60 and 70 percent of the wetted radius, application amounts still remain within 80 percent of the target application amount.
But beyond 70 percent of the wetted radius, application amounts drop off quickly, declining to 50 percent by 78 percent of the wetted radius.
At 90 percent of the wetted radius, the application depth drops below 20 percent.
Traditional design spacing guidelines established by the North Carolina Cooperative Extension Service for traveling gun systems have been for 60 to 75 percent of manufacturers' published wetted diameter.
These recommendations are strongly collaborated by the data shown in Figure 5.
A multi-travel lane system , operated under light wind with exactly a 78 percent lane spacing, would result in a nearly perfect application uniformity.
Even if the lane spacing were stretched out to 85 percent of the wetted diameter, the minimum application amount would be 50 percent of the target amount along the overlapped zone, which would still result in acceptable uniformity.
It should be noted that the results shown in Figure 5 are based on field-verified wetted
 diameters.
Recent measurements on more than 50 systems determined that field-measured wetted diameters averaged 10 percent less than values published in manufacturers' literature.
A spacing based on 85 percent of field-verified wetted diameter is roughly the same as a spacing based on 77 percent of manufacturers' values.
Thus, a design spacing recommendation of 60 to 75 percent of manufacturers' values  is a conservative recommendation to ensure that enough wastewater is applied in the lighter application zones.
The Extension recommendations should continue to be applied to new or expanded systems.
Spacings greater than 85 percent of the verified wetted diameter or 75 percent of the wetted diameter published in manufacturers' literature are considered excessive and result in unacceptable uniformity.
For existing irrigation systems involving a single pull or excessive lane spacing, the CAWMP wettable acre should be based on no more than 90 percent of the verified wetted gun diameter as shown in Figure 4.
When using new systems with single pulls or excessive lane spacing, base the CAWMP wettable acre on no more than 75 percent of the manufacturer's published wetted gun diameter as shown in Figure 6.
To accurately calculate the irrigated area, determine the wetted diameter or radius of the gun.
There are two methods for determining the wetted diameter, and both require operating the system:
 Figure 6.
Shaded area shows allowable irrigated area based on "effective design area" for new or expanded systems.
Directly measure the wetted diameter , or
 Measure gun pressure, then read the wetted diameter from manufacturers' charts for the observed pressure.
The recommended procedure is to determine the wetted diameter  rather than rely on pressure and manufacturers' tables.
Values given in manufacturers' charts tend to be about 10 percent higher than values measured in field calibrations.
Regardless of the method used, collect field data and record it on the Field Data Worksheet provided at the end of this publication.
Footprint measurement-Footprint measurement involves observing, marking, and measuring the farthest distance from the gun that gets wetted.
Field data should be collected on the lane farthest from the pump.
Measuring two or more different lanes improves the reliability of the field procedures.
Measurements should be made during very light wind.
The wetted distance from the gun should be determined on both sides of the lane along the perimeter as indicated in Figure 7.
The system should be operated long enough for all air to be purged from the system before starting to make measurements.
With the system operating at normal pressure:
 1.
Standing just outside the wetted perimeter, observe and flag the farthest point getting wetted for each of three consecutive passes of the gun.
2.
Select one flag to mark the average distance of the three observations.
Remove the other two flags.
3.
Move to the other side of the lane  and repeat steps 1 and 2.
The wetted perimeter should be flagged on two sides of the gun as shown in Figure 7.
Figure 7.
Field measurements to determine "wetted diameter" of a hard hose traveler.
4.
Measure and record the distances from the gun  to each flag.
5.
Compare the two measurements and if the values are within 5 percent, compute the average of the two; this will be the wetted radius.
If the difference between the measurements is more than 5 percent, repeat steps 1 through 4 at another location along the lane or along a different lane.
6.
If the difference between the second set of measurements is also greater than 5 percent, the wind speed may be too high, resulting in excessive drift; or, the gun may be functioning improperly.
Once you have eliminated or corrected the cause of the variability, repeat, beginning with step 1.
If you cannot correct the problem, contact an irrigation technical specialist.
Pressure measurement-The wetted diameter can also be estimated from pressure measurements at the gun.
Pump pressure is NOT an acceptable substitute.
Collect field data when the system is operated on the lane farthest from the pump.
You should operate the system long enough for all air to be purged from the system before measuring the pressure.
Figure 8.
Pressure gauge installed on a traveling gun.
Gun type sprinklers have a port for installing a pressure gauge, shown in Figure 8.
A glycerin-filled gauge is recommended.
Permanently installed gauges are likely to foul, SO it is also recommended that you install a shut-off valve between the gauge and gun.
The valve can be opened long enough to read the pressure, then closed to extend the life of the gauge.
It is also necessary to determine the exact size of the nozzle opening.
Most manufacturers stamp the nozzle size on the end of the nozzle.
If the nozzle opening cannot be read, a precise measurement using calipers is required.
Figure 9.
Area components of traveler pull required to compute total irrigated area for a lane.
Once you measure the operating pressure and nozzle a opening, estimate the wetted diameter from the manufacturer's a=330 literature.
When using tables in this publication to determine irrigated acreage, reduce the
 Figure 10.
Recommended arc angle of gun for use with hard hose traveler.
value taken from manufacturers' charts by 10 percent.
The gun pressure can sometimes be estimated based on direct pressure measurements at the reel if pressure losses in the flexible hose and drive mechanism are properly accounted for.
This procedure should be used only when footprint measurement or pressure measurement at the gun cannot be completed.
Once you collect the necessary field data and determine the wetted radius or diameter, compute the CAWMP wettable acres.
Computations are not difficult; but they can become cumbersome for nonuniform lane spacings, lane spacings with improper overlap, and pulls along the perimeter of the field.
To simplify the determination of irrigated acreage, computations have been tabulated for the end areas of the pull for typical lane spacings and patterns.
Use of these tables requires precise determination of wetted diameter, system layout, and the number of interior and exterior travel lanes as defined earlier.
Step-by-step computational procedures are outlined in the Computational Worksheet provided at the end of this publication.
A flowchart for using the tables is shown in Figure 14.
Existing systems with multiple lanes:
 Determining the irrigated area for each pull
 involves doing calculations for three area components of the pull-"start-end" area, "middle" area, and "stopend" area.
These areas are shown in Figure 9.
Start-end area-Start-end areas have been computed for lane spacings between 60 to 90 percent of wetted diameter and are shown in column  in Tables EE60 to EE90 for Existing Exterior  lanes and Tables EI60 to EI90 for Existing Interior  lanes.
Middle area-The middle area must be computed based on the net wetted width and the length of pull.
There are endless combinations of "length of pull," SO it is not practical to tabulate these values.
Instead, you should compute this area by multiplying the length and width of the rectangular area shown in Figure 9.
Stop-end area-The stop-end area is influenced by the wetted diameter of the gun and the angle of gun rotation referred to as "gun arc angle," shown in Figure 10.
Gun arc angles commonly range from 180 to 330 degrees.
Typical arc angles are shown in Figure 11.
Stop-end areas based on several common arc angles are tabulated in columns C through G of Tables EE60 to EE90 for existing exterior lanes and Tables EI60 to EI90 for existing interior lanes.
Existing system with single lane or lane spacing greater than 90 percent.
Irrigated acreage determination for fields with a single pull or where the lane spacing exceeds 90 percent of the wetted diameter involves determination of the three area components just as in the previous section.
However, only 90 percent of the wetted area is used in computing the irrigated area.
Use Table E90+ for existing systems with single pulls or when lane spacings exceed 90 percent of wetted diameter.
New or expanded systems: Determination of irrigated area for new or expanded systems involves determination of the three area components-startend, middle, and stop-end areas.
But irrigated acreage
 Figure 11.
Typical gun arc angles used for traveling gun systems.
for new or expanded systems is based on the effective design area, which is computed based on 78 percent of the wetted diameter.
These values are given in Tables NE60 to NE75 for New Exterior  lanes and Tables NI60 to NI75 for New Interior  lanes.
Values for new single lane systems are shown in Table N75+.
You should follow these general guidelines in using the tabulated values presented in this publication.
Make decisions on a field-by-field basis as referenced in the CAWMP.
1.
Determine the number of interior and exterior lanes for each field.
2.
Determine whether the system in each field satisfies the existing or new designation.
3.
Obtain the lane spacing from the Field Data Worksheet.
4.
Determine whether the system satisfies the multiple lane or single lane definition.
If the lane spacing exceeds 90 percent of the verified wetted diameter, treat the system as an existing system with single pulls and read the irrigated acreage from Table E90+.
5.
Read or compute the irrigated area per lane for the given wetted diameter from the appropriate column based on gun position, lane spacing, and lane position.
Read the irrigated area for the start-end of the pull from column B of the appropriate table based on lane spacing and position.
Rectangular area  Compute the area of the rectangular component using the formula:
 Middle area = length of pull X /43,560
 Interior lane Middle area = /43,560
 Read the irrigated area for the stop-end of the pull from the appropriate table based on lane spacing and position  and gun arc angle, columns C through G.
If the lane spacing falls between the tabulated values, interpolate or round down and use
 the table for the next lowest value shown.
For example, if the computed spacing is between 70 and 74 percent, use the 70 percent table.
6.
Add the area components for each pull, then add all of the pulls.
This is the total irrigated acreage for the field.
Determining Irrigated Acreage EXAMPLES
 Case I: Multiple lanes
 Figure 12 shows a typical lane spacing and pattern for a hard hose traveler system.
This existing system has five pulls laid out in the field.
The travel distance of the gun is 820 feet and the gun angle is 330 degrees.
1.
Determine the number of interior and exterior lanes for each field.
In Figure 12, lanes 1 and 5 are exterior lanes; lanes 2, 3, and 4 are interior lanes.
Number of exterior lanes = 2 Number of interior lanes = 3
 2.
Determine whether the system in each field satisfies the existing or new designation.
System satisfies existing designation.
3.
Using the Field Data Worksheet, determine the lane spacing.
The lane spacing  is 220 feet.
The wetted diameter  is 290 feet.
Lane spacing as a percentage of wetted diameter is: 220 feet / 290 feet = 75.9 percent
 4.
Determine whether the system satisfies the multiple lateral or single lateral definition.
System satisfies the multiple lateral system definition with lateral spacing equal to 75.9 percent of wetted diameter.
Figure 12.
Hard hose traveler irrigated area determination.
5.
Read the irrigated area per lane for the given wetted diameter from the appropriate column based on gun position, lane spacing, and lane position.
For a wetted diameter of 290 feet and lane spacing of 75 percent:
 Exterior lane, Table EE75
 Start-end area = 0.70 acres Middle area = 820 feet X /43,560 = 4.80 acres
 Stop-end area  = 0.51 acres Total for exterior = 0.70 + 4.80 + 0.51 =
 HARD HOSE TRAVELER IRRIGATION SYSTEM
 Interior lane, Table EI75 Start-end area = 0.65 acres
 Middle area =  /43,560 = 4.14 acres
 Stop-end area  = 0.46 acres
 Total for interior = 0.65 + 4.14 + 0.46 = 5.25 acres
 6.
Multiply the areas from step 5 by the number of lanes in each category.
Add these.
The sum is the total irrigated acreage for the field.
2 exterior lanes X 6.01 acres/lane = 12.02 acres
 3 interior lanes X 5.25 acres/lane = 15.75 acres
 Total irrigated area of field 12.02 ac + 15.75 ac = 27.77 acres
 Case II: Single lane.
Figure 13 shows a typical field situation that would result in a single lane.
Data and irrigated area must be reported on a field-by-field basis.
These fields are surrounded by drainage ditches spaced 330 feet apart.
This existing system has one lane per field and uses a model 150 gun.
The travel distance of the gun is 900 feet, and the gun angle is 270 degrees.
1.
Determine the number of interior and exterior lanes for each field.
In Figure 13, there is only one pull per field.
Number of lanes per field = 1
 2.
Determine whether the system in each field
 System satisfies existing designation.
3.
Using the Field Data Worksheet, determine the lane spacing.
Not applicable since there is only one lane per field.
4.
Determine whether the system satisfies the multiple lane or single lane definition.
System satisfies single lane.
5.
Read the irrigated area per lane for the given wetted diameter from the appropriate column based on gun position, lane spacing, and lane position.
For a wetted diameter of 290 feet and single lane system:
 satisfies the existing or new designation.
Figure 13.
Typical field layout where only one pull occurs in each field.
Start-end area = 0.61 acres
 Middle area = 900 feet X /43,560 = 5.39 acres
 Stop-end area  = 0.31 acres
 Total irrigated area for field = 0.61 + 5.39 + 0.31 = 6.31 acres
 6.
Multiply the areas from step 5 by the number of lanes in each category.
Add these.
The sum is the total irrigated acreage for the field.
Since there is only one lane per field and irrigated acres must be reported on a field-by-field basis, the irrigated area for the field is the same as computed in step 5.
Animal waste management operations that rely on spray irrigation systems may be required to have a wettable acre determination completed to ensure nutrients contained in the wastewater are applied to adequate land at agronomic rates.
All CAWMP will be reviewed by state Division of Water Quality or Division of Soil and Water field inspectors to determine whether a wettable acre determination is indeed required.
If so, the Field Data Worksheet and Computational Worksheet that follow will have to be completed for traveling gun systems and added to the CAWMP.
A wettable acre  designated technical specialist must complete and sign the Computational Worksheet to certify that the irrigation system can be operated SO that the wastewater nutrients are applied to appropriate areas.
Step-by-step procedures for completing the CAWMP wettable acres determination have been developed along with tables from which irrigated acreage can be determined for various irrigation system designs.
Figure 14.
Flowchart showing decision-making process for identifying which tables to use to determine CAWMP wettable acres for traveling gun irrigation systems.
CAWMP Wettable Acre Terms
 CAWMP wettable acre-the irrigated acreage that the SB 1217 Interagency Committee allows to be counted toward the land application area requirement of the Certified Animal Waste Management Plan  for existing irrigation systems.
Effective design area-the portion of the wetted area that receives at least 50 percent of the target application amount.
Land application acreage for new or expanded irrigation systems must be based on effective design area.
Excessively spaced travel lane-parallel travel lane spacing that exceeds allowable spacing recommendations.
For existing traveling gun systems, this refers to spacings in excess of 90 percent of the verified wetted diameter.
For new or expanded traveling gun systems, it refers to spacings in excess of 75 percent of the manufacturer's published wetted diameter.
Existing irrigation system-an irrigation system that was installed before release of the third revision of the Sixth Guidance Document.
Multiple lane irrigation system-an existing irrigation system with two or more parallel lanes equally spaced between 60 and 90 percent of the verified wetted diameter.
Net wetted area-the part of the field that gets wetted when two or more sprinklers are operated with overlapping radii.
New or expanded irrigation system-any component of an irrigation system that wets a portion of a field that was not wetted before release of the third revision of the Sixth Guidance Document.
Single lane irrigation system-an existing irrigation system with only one travel lane per field or one with excessively spaced lanes.
For existing systems, lane spacings greater than 90 percent of the verified wetted diameter are considered excessive.
For new or expanded systems, lane spacings in excess or 75 percent of the manufacturer's published wetted diameter are considered excessive.
Verified wetted diameter-field-measured distance from one side of the wetted width of a pull to the opposite side of the wetted width of the pull.
Wetted area-the area that becomes wetted as a traveling gun is pulled toward a reel.
Wetted diameter-the distance from one side of a wetted perimeter through the point of gun rotation to the opposite side of the wetted perimeter.
Wetted diameter is twice the wetted radius.
Wetted radius-the distance from the gun to a point along the edge of the wetted perimeter.
Wetted radius is the distance the gun throws water.
Hard Hose Traveling Gun System FIELD DATA WORKSHEET*
 Make and model number
 [feet] and hose inside diameter 
 Gun make and model number
 Number of exterior hydrants
 Number of interior hydrants
 based on gun chart.
observed at working gauge,
 determined from gun charts,
 Operating pressure at hose reel
 observed at working gauge or
 [inch] 
 feet 
 Pump make and model number
 Engine make and model number
 Electric motor horsepower and rpm
 Note: It is strongly recommended that you field determine wetted diameter and operating pressure at the reel and gun.
Locate each hydrant on a copy of the map.
Indicate the start and stop of the sprinkler cart * for each travel lane and show the distance traveled.
Show the location of the supply line.
Irrigated acres are determined by the travel lane.
Optional data, furnish where possible.
Signature of owner or facility representative
 Signature of technical specialist
 Printed name of owner or facility representative
 Printed name of technical specialist
 *** Only the person or people collecting the data should sign the Field Data Worksheet.
Hard Hose Traveling Gun System COMPUTATIONAL WORKSHEET
 1.
Farm number 
 Field number  2.
Irrigation system designation
 New/expanded irrigation system 3.
Number of travel lanes
 feet] Length of pull 1
 [feet] Length of pull # Interior lanes
 [feet] Length of pull
 [feet] from Field Data Worksheet 5.
Spacing
 [as a percentage of wetted diameter] 6.
Hydrant layout
 Excessively spaced hydrants 7.
Read the irrigated area per travel pull for the given wetted diameter from the appropriate table and column based on pattern, spacing, and travel lane location.
Travel lane length 
  Acres start end of pull from
 Column  Acres middle portion of pull  {Pull length
 [feet] X Wetted width
 [feet]} / 43,560  Acres stop end of pull from
 Total acres for travel lane length  
 Travel lane length 
  Acres start end of pull from
 Column  Acres middle portion of pull  {Pull length
 [feet] X Wetted width
 [feet]} / 43,560  Acres stop end of pull from
 Total acres for travel lane length  
 Travel lane length 
  Acres start end of pull from
 Column  Acres middle portion of pull  {Pull length
 [feet] X Wetted width
 [feet]} / 43,560  Acres stop end of pull from
 Total acres for travel lane length  
 8.
Multiply the tabulated irrigated acreage value per travel pull by the number of pulls of each category in the field.
Add all of these, and this is the total irrigated acreage for the field.
Acres per travel lane length  X
 Acres  Acres per travel lane length  X
 Acres  Acres per travel lane length  X
 Total CAWMP wettable acres for field 
 Wettable Acre Computational Worksheet Completed by:
 Table EE60.
Area Allowances for Existing Hard Hose Traveler Systems Exterior lane in fields with multiple overlapping lanes: Hydrant spacing based on 60 percent of verified wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.17	0.00	0.03	0.07	0.12	0.14
 160	0.20	0.00	0.04	0.08	0.14	0.16
 170	0.22	0.00	0.04	0.09	0.16	0.18
 180	0.25	0.00	0.05	0.11	0.18	0.20
 190	0.28	0.00	0.06	0.12	0.20	0.22
 200	0.31	0.00	0.06	0.13	0.22	0.25
 210	0.34	0.00	0.07	0.14	0.24	0.27
 220	0.37	0.00	0.08	0.16	0.27	0.30
 230	0.41	0.00	0.08	0.17	0.29	0.33
 240	0.45	0.00	0.09	0.19	0.32	0.36
 250	0.48	0.00	0.10	0.21	0.34	0.39
 260	0.52	0.00	0.11	0.22	0.37	0.42
 270	0.56	0.00	0.11	0.24	0.40	0.45
 280	0.61	0.00	0.12	0.26	0.43	0.49
 290	0.65	0.00	0.13	0.28	0.46	0.52
 300	0.70	0.00	0.14	0.30	0.49	0.56
 310	0.74	0.00	0.15	0.32	0.53	0.60
 320	0.79	0.00	0.16	0.34	0.56	0.64
 330	0.84	0.00	0.17	0.36	0.60	0.68
 340	0.89	0.00	0.18	0.38	0.63	0.72
 350	0.95	0.00	0.19	0.40	0.67	0.76
 360	1.00	0.00	0.20	0.43	0.71	0.81
 370	1.06	0.00	0.21	0.45	0.75	0.85
 380	1.12	0.00	0.22	0.47	0.79	0.90
 390	1.18	0.00	0.24	0.50	0.83	0.95
 400	1.24	0.00	0.25	0.53	0.88	1.00
 410	1.30	0.00	0.26	0.55	0.92	1.05
 420	1.36	0.00	0.27	0.58	0.97	1.10
 430	1.43	0.00	0.29	0.61	1.01	1.15
 440	1.50	0.00	0.30	0.64	1.06	1.21
 450	1.57	0.00	0.31	0.67	1.11	1.26
 460	1.64	0.00	0.33	0.70	1.16	1.32
 470	1.71	0.00	0.34	0.73	1.21	1.38
 480	1.78	0.00	0.36	0.76	1.26	1.44
 490	1.86	0.00	0.37	0.79	1.32	1.50
 500	1.93	0.00	0.39	0.82	1.37	1.56
 Table EE65.
Area Allowances for Existing Hard Hose Traveler Systems Exterior lane in fields with multiple overlapping lanes: Hydrant spacing based on 65 percent of verified wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.18	0.00	0.04	0.08	0.13	0.15
 160	0.20	0.00	0.04	0.09	0.15	0.17
 170	0.23	0.00	0.05	0.10	0.16	0.19
 180	0.26	0.00	0.05	0.11	0.18	0.21
 190	0.29	0.00	0.06	0.13	0.21	0.23
 200	0.32	0.00	0.07	0.14	0.23	0.26
 210	0.35	0.00	0.07	0.15	0.25	0.28
 220	0.39	0.00	0.08	0.17	0.28	0.31
 230	0.42	0.00	0.09	0.18	0.30	0.34
 240	0.46	0.00	0.09	0.20	0.33	0.37
 250	0.50	0.00	0.10	0.22	0.36	0.40
 260	0.54	0.00	0.11	0.23	0.39	0.44
 270	0.58	0.00	0.12	0.25	0.42	0.47
 280	0.62	0.00	0.13	0.27	0.45	0.51
 290	0.67	0.00	0.14	0.29	0.48	0.54
 300	0.72	0.00	0.15	0.31	0.51	0.58
 310	0.76	0.00	0.16	0.33	0.55	0.62
 320	0.81	0.00	0.17	0.35	0.58	0.66
 330	0.87	0.00	0.18	0.38	0.62	0.70
 340	0.92	0.00	0.19	0.40	0.66	0.75
 350	0.97	0.00	0.20	0.42	0.70	0.79
 360	1.03	0.00	0.21	0.45	0.74	0.84
 370	1.09	0.00	0.22	0.47	0.78	0.88
 380	1.15	0.00	0.24	0.50	0.82	0.93
 390	1.21	0.00	0.25	0.53	0.87	0.98
 400	1.27	0.00	0.26	0.55	0.91	1.03
 410	1.34	0.00	0.27	0.58	0.96	1.08
 420	1.40	0.00	0.29	0.61	1.01	1.14
 430	1.47	0.00	0.30	0.64	1.05	1.19
 440	1.54	0.00	0.32	0.67	1.10	1.25
 450	1.61	0.00	0.33	0.70	1.15	1.31
 460	1.68	0.00	0.34	0.73	1.21	1.37
 470	1.76	0.00	0.36	0.77	1.26	1.43
 480	1.83	0.00	0.38	0.80	1.31	1.49
 490	1.91	0.00	0.39	0.83	1.37	1.55
 500	1.99	0.00	0.41	0.87	1.43	1.61
 Table EE70.
Area Allowances for Existing Hard Hose Traveler Systems Exterior lane in fields with multiple overlapping lanes: Hydrant spacing based on 70 percent of verified wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.18	0.00	0.04	0.08	0.13	0.15
 160	0.21	0.00	0.04	0.09	0.15	0.17
 170	0.24	0.00	0.05	0.11	0.17	0.19
 180	0.26	0.00	0.06	0.12	0.19	0.22
 190	0.29	0.00	0.06	0.13	0.21	0.24
 200	0.33	0.00	0.07	0.15	0.24	0.27
 210	0.36	0.00	0.08	0.16	0.26	0.29
 220	0.40	0.00	0.08	0.18	0.29	0.32
 230	0.43	0.00	0.09	0.19	0.31	0.35
 240	0.47	0.00	0.10	0.21	0.34	0.38
 250	0.51	0.00	0.11	0.23	0.37	0.42
 260	0.55	0.00	0.12	0.25	0.40	0.45
 270	0.60	0.00	0.12	0.27	0.43	0.49
 280	0.64	0.00	0.13	0.29	0.46	0.52
 290	0.69	0.00	0.14	0.31	0.50	0.56
 300	0.74	0.00	0.15	0.33	0.53	0.60
 310	0.78	0.00	0.16	0.35	0.57	0.64
 320	0.84	0.00	0.18	0.37	0.61	0.68
 330	0.89	0.00	0.19	0.40	0.64	0.73
 340	0.94	0.00	0.20	0.42	0.68	0.77
 350	1.00	0.00	0.21	0.45	0.72	0.82
 360	1.06	0.00	0.22	0.47	0.77	0.86
 370	1.12	0.00	0.23	0.50	0.81	0.91
 380	1.18	0.00	0.25	0.53	0.85	0.96
 390	1.24	0.00	0.26	0.56	0.90	1.01
 400	1.31	0.00	0.27	0.59	0.95	1.07
 410	1.37	0.00	0.29	0.62	0.99	1.12
 420	1.44	0.00	0.30	0.65	1.04	1.18
 430	1.51	0.00	0.32	0.68	1.09	1.23
 440	1.58	0.00	0.33	0.71	1.14	1.29
 450	1.65	0.00	0.35	0.74	1.20	1.35
 460	1.73	0.00	0.36	0.77	1.25	1.41
 470	1.80	0.00	0.38	0.81	1.31	1.47
 480	1.88	0.00	0.39	0.84	1.36	1.54
 490	1.96	0.00	0.41	0.88	1.42	1.60
 500	2.04	0.00	0.43	0.91	1.48	1.67
 Table EE75.
Area Allowances for Existing Hard Hose Traveler Systems Exterior lane in fields with multiple overlapping lanes: Hydrant spacing based on 75 percent of verified wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.19	0.00	0.04	0.09	0.14	0.15
 160	0.21	0.00	0.05	0.10	0.16	0.18
 170	0.24	0.00	0.05	0.11	0.18	0.20
 180	0.27	0.00	0.06	0.12	0.20	0.22
 190	0.30	0.00	0.06	0.14	0.22	0.25
 200	0.33	0.00	0.07	0.15	0.24	0.27
 210	0.37	0.00	0.08	0.17	0.27	0.30
 220	0.40	0.00	0.09	0.19	0.30	0.33
 230	0.44	0.00	0.09	0.20	0.32	0.36
 240	0.48	0.00	0.10	0.22	0.35	0.40
 250	0.52	0.00	0.11	0.24	0.38	0.43
 260	0.57	0.00	0.12	0.26	0.41	0.46
 270	0.61	0.00	0.13	0.28	0.45	0.50
 280	0.66	0.00	0.14	0.30	0.48	0.54
 290	0.70	0.00	0.15	0.32	0.51	0.58
 300	0.75	0.00	0.16	0.35	0.55	0.62
 310	0.80	0.00	0.17	0.37	0.59	0.66
 320	0.86	0.00	0.18	0.39	0.63	0.70
 330	0.91	0.00	0.20	0.42	0.67	0.75
 340	0.97	0.00	0.21	0.45	0.71	0.79
 350	1.02	0.00	0.22	0.47	0.75	0.84
 360	1.08	0.00	0.23	0.50	0.79	0.89
 370	1.15	0.00	0.25	0.53	0.84	0.94
 380	1.21	0.00	0.26	0.56	0.88	0.99
 390	1.27	0.00	0.27	0.59	0.93	1.04
 400	1.34	0.00	0.29	0.62	0.98	1.10
 410	1.41	0.00	0.30	0.65	1.03	1.15
 420	1.48	0.00	0.32	0.68	1.08	1.21
 430	1.55	0.00	0.33	0.71	1.13	1.27
 440	1.62	0.00	0.35	0.75	1.18	1.33
 450	1.69	0.00	0.36	0.78	1.24	1.39
 460	1.77	0.00	0.38	0.82	1.29	1.45
 470	1.85	0.00	0.40	0.85	1.35	1.52
 480	1.93	0.00	0.41	0.89	1.41	1.58
 490	2.01	0.00	0.43	0.93	1.47	1.65
 500	2.09	0.00	0.45	0.96	1.53	1.72
 Table EE80.
Area Allowances for Existing Hard Hose Traveler Systems Exterior lane in fields with multiple overlapping lanes: Hydrant spacing based on 80 percent of verified wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.19	0.00	0.04	0.09	0.14	0.16
 160	0.22	0.00	0.05	0.10	0.16	0.18
 170	0.25	0.00	0.05	0.12	0.18	0.20
 180	0.28	0.00	0.06	0.13	0.20	0.23
 190	0.31	0.00	0.07	0.15	0.23	0.25
 200	0.34	0.00	0.08	0.16	0.25	0.28
 210	0.38	0.00	0.08	0.18	0.28	0.31
 220	0.41	0.00	0.09	0.20	0.30	0.34
 230	0.45	0.00	0.10	0.21	0.33	0.37
 240	0.49	0.00	0.11	0.23	0.36	0.41
 250	0.53	0.00	0.12	0.25	0.39	0.44
 260	0.58	0.00	0.13	0.27	0.43	0.48
 270	0.62	0.00	0.14	0.29	0.46	0.51
 280	0.67	0.00	0.15	0.32	0.49	0.55
 290	0.72	0.00	0.16	0.34	0.53	0.59
 300	0.77	0.00	0.17	0.36	0.57	0.63
 310	0.82	0.00	0.18	0.39	0.60	0.68
 320	0.88	0.00	0.19	0.41	0.64	0.72
 330	0.93	0.00	0.21	0.44	0.69	0.77
 340	0.99	0.00	0.22	0.47	0.73	0.81
 350	1.05	0.00	0.23	0.49	0.77	0.86
 360	1.11	0.00	0.24	0.52	0.82	0.91
 370	1.17	0.00	0.26	0.55	0.86	0.96
 380	1.23	0.00	0.27	0.58	0.91	1.02
 390	1.30	0.00	0.29	0.61	0.96	1.07
 400	1.37	0.00	0.30	0.65	1.01	1.13
 410	1.44	0.00	0.32	0.68	1.06	1.18
 420	1.51	0.00	0.33	0.71	1.11	1.24
 430	1.58	0.00	0.35	0.75	1.16	1.30
 440	1.65	0.00	0.37	0.78	1.22	1.36
 450	1.73	0.00	0.38	0.82	1.27	1.43
 460	1.81	0.00	0.40	0.85	1.33	1.49
 470	1.89	0.00	0.42	0.89	1.39	1.56
 480	1.97	0.00	0.43	0.93	1.45	1.62
 490	2.05	0.00	0.45	0.97	1.51	1.69
 500	2.14	0.00	0.47	1.01	1.57	1.76
 Table EE85.
Area Allowances for Existing Hard Hose Traveler Systems Exterior lane in fields with multiple overlapping lanes: Hydrant spacing based on 85 percent of verified wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.20	0.00	0.04	0.09	0.15	0.16
 160	0.22	0.00	0.05	0.11	0.17	0.18
 170	0.25	0.00	0.06	0.12	0.19	0.21
 180	0.28	0.00	0.06	0.14	0.21	0.23
 190	0.31	0.00	0.07	0.15	0.23	0.26
 200	0.35	0.00	0.08	0.17	0.26	0.29
 210	0.38	0.00	0.09	0.19	0.28	0.32
 220	0.42	0.00	0.09	0.20	0.31	0.35
 230	0.46	0.00	0.10	0.22	0.34	0.38
 240	0.50	0.00	0.11	0.24	0.37	0.42
 250	0.54	0.00	0.12	0.26	0.40	0.45
 260	0.59	0.00	0.13	0.28	0.44	0.49
 270	0.63	0.00	0.14	0.31	0.47	0.53
 280	0.68	0.00	0.15	0.33	0.51	0.56
 290	0.73	0.00	0.16	0.35	0.54	0.61
 300	0.78	0.00	0.18	0.38	0.58	0.65
 310	0.84	0.00	0.19	0.40	0.62	0.69
 320	0.89	0.00	0.20	0.43	0.66	0.74
 330	0.95	0.00	0.21	0.46	0.70	0.78
 340	1.01	0.00	0.22	0.49	0.75	0.83
 350	1.07	0.00	0.24	0.51	0.79	0.88
 360	1.13	0.00	0.25	0.54	0.84	0.93
 370	1.19	0.00	0.27	0.58	0.88	0.99
 380	1.26	0.00	0.28	0.61	0.93	1.04
 390	1.32	0.00	0.30	0.64	0.98	1.10
 400	1.39	0.00	0.31	0.67	1.03	1.15
 410	1.46	0.00	0.33	0.71	1.09	1.21
 420	1.54	0.00	0.34	0.74	1.14	1.27
 430	1.61	0.00	0.36	0.78	1.19	1.33
 440	1.69	0.00	0.38	0.81	1.25	1.40
 450	1.76	0.00	0.39	0.85	1.31	1.46
 460	1.84	0.00	0.41	0.89	1.37	1.52
 470	1.92	0.00	0.43	0.93	1.43	1.59
 480	2.01	0.00	0.45	0.97	1.49	1.66
 490	2.09	0.00	0.47	1.01	1.55	1.73
 500	2.18	0.00	0.49	1.05	1.61	1.80
 Table EE90.
Area Allowances for Existing Hard Hose Traveler Systems Exterior lane in fields with multiple overlapping lanes: Hydrant spacing based on 90 percent of verified wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.20	0.00	0.05	0.10	0.15	0.17
 160	0.23	0.00	0.05	0.11	0.17	0.19
 170	0.26	0.00	0.06	0.13	0.19	0.21
 180	0.29	0.00	0.07	0.14	0.21	0.24
 190	0.32	0.00	0.08	0.16	0.24	0.27
 200	0.35	0.00	0.08	0.17	0.26	0.29
 210	0.39	0.00	0.09	0.19	0.29	0.32
 220	0.43	0.00	0.10	0.21	0.32	0.36
 230	0.47	0.00	0.11	0.23	0.35	0.39
 240	0.51	0.00	0.12	0.25	0.38	0.42
 250	0.55	0.00	0.13	0.27	0.41	0.46
 260	0.60	0.00	0.14	0.29	0.45	0.50
 270	0.64	0.00	0.15	0.32	0.48	0.54
 280	0.69	0.00	0.16	0.34	0.52	0.58
 290	0.74	0.00	0.18	0.36	0.55	0.62
 300	0.80	0.00	0.19	0.39	0.59	0.66
 310	0.85	0.00	0.20	0.42	0.63	0.71
 320	0.91	0.00	0.21	0.44	0.68	0.75
 330	0.96	0.00	0.23	0.47	0.72	0.80
 340	1.02	0.00	0.24	0.50	0.76	0.85
 350	1.08	0.00	0.26	0.53	0.81	0.90
 360	1.15	0.00	0.27	0.56	0.85	0.95
 370	1.21	0.00	0.29	0.59	0.90	1.01
 380	1.28	0.00	0.30	0.63	0.95	1.06
 390	1.35	0.00	0.32	0.66	1.00	1.12
 400	1.42	0.00	0.33	0.69	1.06	1.18
 410	1.49	0.00	0.35	0.73	1.11	1.23
 420	1.56	0.00	0.37	0.77	1.16	1.30
 430	1.64	0.00	0.39	0.80	1.22	1.36
 440	1.71	0.00	0.40	0.84	1.28	1.42
 450	1.79	0.00	0.42	0.88	1.34	1.49
 460	1.87	0.00	0.44	0.92	1.40	1.55
 470	1.95	0.00	0.46	0.96	1.46	1.62
 480	2.04	0.00	0.48	1.00	1.52	1.69
 490	2.12	0.00	0.50	1.04	1.58	1.76
 500	2.21	0.00	0.52	1.08	1.65	1.84
 Table EI60.
Area Allowances for Existing Hard Hose Traveler Systems Interior lane in fields with multiple overlapping lanes: Hydrant spacing based on 60 percent of verified wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.15	0.00	0.02	0.05	0.09	0.11
 160	0.17	0.00	0.02	0.05	0.11	0.13
 170	0.19	0.00	0.02	0.06	0.12	0.14
 180	0.21	0.00	0.03	0.07	0.14	0.16
 190	0.23	0.00	0.03	0.07	0.15	0.18
 200	0.26	0.00	0.03	0.08	0.17	0.20
 210	0.28	0.00	0.04	0.09	0.18	0.22
 220	0.31	0.00	0.04	0.10	0.20	0.24
 230	0.34	0.00	0.05	0.11	0.22	0.26
 240	0.37	0.00	0.05	0.12	0.24	0.28
 250	0.40	0.00	0.05	0.13	0.26	0.31
 260	0.44	0.00	0.06	0.14	0.28	0.33
 270	0.47	0.00	0.06	0.15	0.31	0.36
 280	0.51	0.00	0.07	0.16	0.33	0.39
 290	0.54	0.00	0.07	0.17	0.35	0.42
 300	0.58	0.00	0.08	0.19	0.38	0.45
 310	0.62	0.00	0.08	0.20	0.40	0.48
 320	0.66	0.00	0.09	0.21	0.43	0.51
 330	0.70	0.00	0.09	0.22	0.46	0.54
 340	0.75	0.00	0.10	0.24	0.48	0.57
 350	0.79	0.00	0.10	0.25	0.51	0.61
 360	0.84	0.00	0.11	0.27	0.54	0.64
 370	0.88	0.00	0.12	0.28	0.57	0.68
 380	0.93	0.00	0.12	0.30	0.61	0.71
 390	0.98	0.00	0.13	0.31	0.64	0.75
 400	1.03	0.00	0.14	0.33	0.67	0.79
 410	1.08	0.00	0.14	0.35	0.70	0.83
 420	1.14	0.00	0.15	0.36	0.74	0.87
 430	1.19	0.00	0.16	0.38	0.78	0.91
 440	1.25	0.00	0.17	0.40	0.81	0.96
 450	1.31	0.00	0.17	0.42	0.85	1.00
 460	1.36	0.00	0.18	0.44	0.89	1.05
 470	1.42	0.00	0.19	0.46	0.93	1.09
 480	1.49	0.00	0.20	0.48	0.97	1.14
 490	1.55	0.00	0.21	0.50	1.01	1.19
 500	1.61	0.00	0.21	0.52	1.05	1.24
 Table EI65.
Area Allowances for Existing Hard Hose Traveler Systems Interior lane in fields with multiple overlapping lanes: Hydrant spacing based on 65 percent of verified wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.16	0.00	0.02	0.05	0.10	0.12
 160	0.18	0.00	0.03	0.06	0.12	0.14
 170	0.20	0.00	0.03	0.07	0.13	0.16
 180	0.22	0.00	0.03	0.08	0.15	0.17
 190	0.25	0.00	0.04	0.09	0.17	0.19
 200	0.28	0.00	0.04	0.10	0.19	0.22
 210	0.30	0.00	0.04	0.11	0.20	0.24
 220	0.33	0.00	0.05	0.12	0.22	0.26
 230	0.36	0.00	0.05	0.13	0.25	0.29
 240	0.40	0.00	0.06	0.14	0.27	0.31
 250	0.43	0.00	0.06	0.15	0.29	0.34
 260	0.47	0.00	0.07	0.16	0.31	0.36
 270	0.50	0.00	0.07	0.18	0.34	0.39
 280	0.54	0.00	0.08	0.19	0.36	0.42
 290	0.58	0.00	0.08	0.20	0.39	0.45
 300	0.62	0.00	0.09	0.22	0.42	0.49
 310	0.66	0.00	0.10	0.23	0.45	0.52
 320	0.71	0.00	0.10	0.25	0.48	0.55
 330	0.75	0.00	0.11	0.26	0.51	0.59
 340	0.80	0.00	0.12	0.28	0.54	0.62
 350	0.84	0.00	0.12	0.30	0.57	0.66
 360	0.89	0.00	0.13	0.31	0.60	0.70
 370	0.94	0.00	0.14	0.33	0.64	0.74
 380	1.00	0.00	0.15	0.35	0.67	0.78
 390	1.05	0.00	0.15	0.37	0.71	0.82
 400	1.10	0.00	0.16	0.39	0.74	0.86
 410	1.16	0.00	0.17	0.41	0.78	0.91
 420	1.22	0.00	0.18	0.43	0.82	0.95
 430	1.27	0.00	0.19	0.45	0.86	1.00
 440	1.33	0.00	0.19	0.47	0.90	1.04
 450	1.40	0.00	0.20	0.49	0.94	1.09
 460	1.46	0.00	0.21	0.51	0.98	1.14
 470	1.52	0.00	0.22	0.54	1.03	1.19
 480	1.59	0.00	0.23	0.56	1.07	1.24
 490	1.66	0.00	0.24	0.58	1.11	1.29
 500	1.72	0.00	0.25	0.61	1.16	1.35
 Table EI70.
Area Allowances for Existing Hard Hose Traveler Systems Interior lane in fields with multiple overlapping lanes: Hydrant spacing based on 70 percent of verified wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.16	0.00	0.03	0.06	0.11	0.13
 160	0.19	0.00	0.03	0.07	0.13	0.15
 170	0.21	0.00	0.03	0.08	0.15	0.17
 180	0.24	0.00	0.04	0.09	0.16	0.19
 190	0.26	0.00	0.04	0.10	0.18	0.21
 200	0.29	0.00	0.05	0.11	0.20	0.23
 210	0.32	0.00	0.05	0.12	0.22	0.26
 220	0.35	0.00	0.06	0.14	0.25	0.28
 230	0.39	0.00	0.06	0.15	0.27	0.31
 240	0.42	0.00	0.07	0.16	0.29	0.34
 250	0.46	0.00	0.07	0.18	0.32	0.36
 260	0.49	0.00	0.08	0.19	0.34	0.39
 270	0.53	0.00	0.08	0.20	0.37	0.42
 280	0.57	0.00	0.09	0.22	0.40	0.46
 290	0.62	0.00	0.10	0.24	0.43	0.49
 300	0.66	0.00	0.10	0.25	0.46	0.52
 310	0.70	0.00	0.11	0.27	0.49	0.56
 320	0.75	0.00	0.12	0.29	0.52	0.60
 330	0.80	0.00	0.13	0.31	0.55	0.63
 340	0.85	0.00	0.13	0.32	0.59	0.67
 350	0.90	0.00	0.14	0.34	0.62	0.71
 360	0.95	0.00	0.15	0.36	0.66	0.75
 370	1.00	0.00	0.16	0.38	0.69	0.80
 380	1.06	0.00	0.17	0.41	0.73	0.84
 390	1.11	0.00	0.18	0.43	0.77	0.88
 400	1.17	0.00	0.19	0.45	0.81	0.93
 410	1.23	0.00	0.20	0.47	0.85	0.98
 420	1.29	0.00	0.21	0.50	0.89	1.03
 430	1.35	0.00	0.22	0.52	0.94	1.08
 440	1.42	0.00	0.23	0.54	0.98	1.13
 450	1.48	0.00	0.24	0.57	1.03	1.18
 460	1.55	0.00	0.25	0.59	1.07	1.23
 470	1.62	0.00	0.26	0.62	1.12	1.28
 480	1.69	0.00	0.27	0.65	1.17	1.34
 490	1.76	0.00	0.28	0.68	1.22	1.40
 500	1.83	0.00	0.29	0.70	1.27	1.45
 Table EI75.
Area Allowances for Existing Hard Hose Traveler Systems Interior lane in fields with multiple overlapping lanes: Hydrant spacing based on 75 percent of verified wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.17	0.00	0.03	0.07	0.12	0.14
 160	0.20	0.00	0.03	0.08	0.14	0.16
 170	0.22	0.00	0.04	0.09	0.16	0.18
 180	0.25	0.00	0.04	0.10	0.18	0.20
 190	0.28	0.00	0.05	0.12	0.20	0.22
 200	0.31	0.00	0.05	0.13	0.22	0.25
 210	0.34	0.00	0.06	0.14	0.24	0.27
 220	0.37	0.00	0.06	0.16	0.26	0.30
 230	0.41	0.00	0.07	0.17	0.29	0.33
 240	0.44	0.00	0.08	0.18	0.31	0.36
 250	0.48	0.00	0.08	0.20	0.34	0.39
 260	0.52	0.00	0.09	0.22	0.37	0.42
 270	0.56	0.00	0.10	0.23	0.40	0.45
 280	0.60	0.00	0.10	0.25	0.43	0.49
 290	0.65	0.00	0.11	0.27	0.46	0.52
 300	0.69	0.00	0.12	0.29	0.49	0.56
 310	0.74	0.00	0.13	0.31	0.52	0.60
 320	0.79	0.00	0.14	0.33	0.56	0.64
 330	0.84	0.00	0.15	0.35	0.59	0.68
 340	0.89	0.00	0.15	0.37	0.63	0.72
 350	0.94	0.00	0.16	0.39	0.67	0.76
 360	1.00	0.00	0.17	0.42	0.71	0.81
 370	1.06	0.00	0.18	0.44	0.75	0.85
 380	1.11	0.00	0.19	0.46	0.79	0.90
 390	1.17	0.00	0.20	0.49	0.83	0.94
 400	1.23	0.00	0.21	0.51	0.87	0.99
 410	1.30	0.00	0.22	0.54	0.92	1.04
 420	1.36	0.00	0.24	0.57	0.96	1.10
 430	1.43	0.00	0.25	0.59	1.01	1.15
 440	1.49	0.00	0.26	0.62	1.06	1.20
 450	1.56	0.00	0.27	0.65	1.11	1.26
 460	1.63	0.00	0.28	0.68	1.16	1.31
 470	1.70	0.00	0.30	0.71	1.21	1.37
 480	1.78	0.00	0.31	0.74	1.26	1.43
 490	1.85	0.00	0.32	0.77	1.31	1.49
 500	1.93	0.00	0.33	0.80	1.37	1.55
 Table EI80.
Area Allowances for Existing Hard Hose Traveler Systems Interior lane in fields with multiple overlapping lanes: Hydrant spacing based on 80 percent of verified wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.18	0.00	0.03	0.08	0.13	0.15
 160	0.21	0.00	0.04	0.09	0.15	0.17
 170	0.23	0.00	0.04	0.10	0.17	0.19
 180	0.26	0.00	0.05	0.12	0.19	0.21
 190	0.29	0.00	0.05	0.13	0.21	0.24
 200	0.32	0.00	0.06	0.14	0.23	0.26
 210	0.36	0.00	0.07	0.16	0.26	0.29
 220	0.39	0.00	0.07	0.17	0.28	0.32
 230	0.43	0.00	0.08	0.19	0.31	0.35
 240	0.47	0.00	0.09	0.21	0.34	0.38
 250	0.50	0.00	0.10	0.22	0.36	0.41
 260	0.55	0.00	0.10	0.24	0.39	0.44
 270	0.59	0.00	0.11	0.26	0.42	0.48
 280	0.63	0.00	0.12	0.28	0.46	0.52
 290	0.68	0.00	0.13	0.30	0.49	0.55
 300	0.73	0.00	0.14	0.32	0.52	0.59
 310	0.78	0.00	0.15	0.34	0.56	0.63
 320	0.83	0.00	0.16	0.37	0.60	0.67
 330	0.88	0.00	0.17	0.39	0.63	0.72
 340	0.93	0.00	0.18	0.41	0.67	0.76
 350	0.99	0.00	0.19	0.44	0.71	0.81
 360	1.05	0.00	0.20	0.46	0.75	0.85
 370	1.11	0.00	0.21	0.49	0.80	0.90
 380	1.17	0.00	0.22	0.52	0.84	0.95
 390	1.23	0.00	0.23	0.54	0.89	1.00
 400	1.29	0.00	0.24	0.57	0.93	1.05
 410	1.36	0.00	0.26	0.60	0.98	1.11
 420	1.42	0.00	0.27	0.63	1.03	1.16
 430	1.49	0.00	0.28	0.66	1.08	1.22
 440	1.56	0.00	0.29	0.69	1.13	1.27
 450	1.64	0.00	0.31	0.72	1.18	1.33
 460	1.71	0.00	0.32	0.76	1.23	1.39
 470	1.78	0.00	0.34	0.79	1.29	1.45
 480	1.86	0.00	0.35	0.82	1.34	1.51
 490	1.94	0.00	0.37	0.86	1.40	1.58
 500	2.02	0.00	0.38	0.89	1.46	1.64
 Table EI85.
Area Allowances for Existing Hard Hose Traveler Systems Interior lane in fields with multiple overlapping lanes: Hydrant spacing based on 85 percent of verified wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.19	0.00	0.04	0.09	0.14	0.16
 160	0.22	0.00	0.04	0.10	0.16	0.18
 170	0.24	0.00	0.05	0.11	0.18	0.20
 180	0.27	0.00	0.06	0.13	0.20	0.22
 200	0.34	0.00	0.07	0.16	0.25	0.28
 210	0.37	0.00	0.08	0.17	0.27	0.30
 220	0.41	0.00	0.08	0.19	0.30	0.33
 230	0.44	0.00	0.09	0.21	0.33	0.36
 240	0.48	0.00	0.10	0.22	0.35	0.40
 250	0.53	0.00	0.11	0.24	0.38	0.43
 260	0.57	0.00	0.12	0.26	0.42	0.47
 270	0.61	0.00	0.13	0.28	0.45	0.50
 280	0.66	0.00	0.13	0.31	0.48	0.54
 290	0.71	0.00	0.14	0.33	0.52	0.58
 300	0.76	0.00	0.15	0.35	0.55	0.62
 310	0.81	0.00	0.17	0.37	0.59	0.66
 320	0.86	0.00	0.18	0.40	0.63	0.71
 330	0.91	0.00	0.19	0.42	0.67	0.75
 340	0.97	0.00	0.20	0.45	0.71	0.80
 350	1.03	0.00	0.21	0.48	0.75	0.85
 360	1.09	0.00	0.22	0.50	0.80	0.89
 370	1.15	0.00	0.24	0.53	0.84	0.94
 380	1.21	0.00	0.25	0.56	0.89	1.00
 390	1.28	0.00	0.26	0.59	0.94	1.05
 400	1.34	0.00	0.27	0.62	0.98	1.10
 410	1.41	0.00	0.29	0.65	1.03	1.16
 420	1.48	0.00	0.30	0.69	1.08	1.22
 430	1.55	0.00	0.32	0.72	1.14	1.28
 440	1.63	0.00	0.33	0.75	1.19	1.34
 450	1.70	0.00	0.35	0.79	1.24	1.40
 460	1.78	0.00	0.36	0.82	1.30	1.46
 470	1.86	0.00	0.38	0.86	1.36	1.52
 480	1.94	0.00	0.40	0.90	1.42	1.59
 490	2.02	0.00	0.41	0.93	1.48	1.66
 500	2.10	0.00	0.43	0.97	1.54	1.72
 Table EI90.
Area Allowances for Existing Hard Hose Traveler Systems Interior lane in fields with multiple overlapping lanes: Hydrant spacing based on 90 percent of verified wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.20	0.00	0.04	0.09	0.14	0.16
 160	0.22	0.00	0.05	0.11	0.16	0.18
 170	0.25	0.00	0.06	0.12	0.19	0.21
 180	0.28	0.00	0.06	0.14	0.21	0.23
 190	0.31	0.00	0.07	0.15	0.23	0.26
 200	0.35	0.00	0.08	0.17	0.26	0.29
 210	0.38	0.00	0.08	0.18	0.28	0.32
 220	0.42	0.00	0.09	0.20	0.31	0.35
 230	0.46	0.00	0.10	0.22	0.34	0.38
 240	0.50	0.00	0.11	0.24	0.37	0.41
 250	0.54	0.00	0.12	0.26	0.40	0.45
 260	0.59	0.00	0.13	0.28	0.43	0.49
 270	0.63	0.00	0.14	0.30	0.47	0.52
 280	0.68	0.00	0.15	0.33	0.50	0.56
 290	0.73	0.00	0.16	0.35	0.54	0.60
 300	0.78	0.00	0.17	0.38	0.58	0.65
 310	0.83	0.00	0.19	0.40	0.62	0.69
 320	0.89	0.00	0.20	0.43	0.66	0.73
 330	0.95	0.00	0.21	0.45	0.70	0.78
 340	1.00	0.00	0.22	0.48	0.74	0.83
 350	1.06	0.00	0.24	0.51	0.79	0.88
 360	1.12	0.00	0.25	0.54	0.83	0.93
 370	1.19	0.00	0.26	0.57	0.88	0.98
 380	1.25	0.00	0.28	0.60	0.93	1.04
 390	1.32	0.00	0.29	0.63	0.98	1.09
 400	1.39	0.00	0.31	0.67	1.03	1.15
 410	1.46	0.00	0.32	0.70	1.08	1.21
 420	1.53	0.00	0.34	0.74	1.13	1.27
 430	1.60	0.00	0.36	0.77	1.19	1.33
 440	1.68	0.00	0.37	0.81	1.24	1.39
 450	1.76	0.00	0.39	0.84	1.30	1.45
 460	1.84	0.00	0.41	0.88	1.36	1.52
 470	1.92	0.00	0.43	0.92	1.42	1.59
 480	2.00	0.00	0.44	0.96	1.48	1.65
 490	2.08	0.00	0.46	1.00	1.54	1.72
 500	2.17	0.00	0.48	1.04	1.61	1.79
 Table E90+.
Area Allowances for Existing Hard Hose Traveler Systems Fields with single pull or multiple pulls and Hydrant spacing greater than 90 percent of verified wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.16	0.00	0.04	0.08	0.12	0.14
 160	0.19	0.00	0.05	0.09	0.14	0.16
 170	0.21	0.00	0.05	0.11	0.16	0.18
 180	0.24	0.00	0.06	0.12	0.18	0.20
 190	0.26	0.00	0.07	0.13	0.20	0.22
 200	0.29	0.00	0.07	0.15	0.22	0.24
 210	0.32	0.00	0.08	0.16	0.24	0.27
 220	0.35	0.00	0.09	0.18	0.27	0.29
 230	0.39	0.00	0.10	0.19	0.29	0.32
 240	0.42	0.00	0.11	0.21	0.32	0.35
 250	0.46	0.00	0.11	0.23	0.34	0.38
 260	0.49	0.00	0.12	0.25	0.37	0.41
 270	0.53	0.00	0.13	0.27	0.40	0.44
 280	0.57	0.00	0.14	0.29	0.43	0.48
 290	0.61	0.00	0.15	0.31	0.46	0.51
 300	0.66	0.00	0.16	0.33	0.49	0.55
 310	0.70	0.00	0.18	0.35	0.53	0.58
 320	0.75	0.00	0.19	0.37	0.56	0.62
 330	0.80	0.00	0.20	0.40	0.60	0.66
 340	0.84	0.00	0.21	0.42	0.63	0.70
 350	0.89	0.00	0.22	0.45	0.67	0.75
 360	0.95	0.00	0.24	0.47	0.71	0.79
 370	1.00	0.00	0.25	0.50	0.75	0.83
 380	1.05	0.00	0.26	0.53	0.79	0.88
 390	1.11	0.00	0.28	0.56	0.83	0.93
 400	1.17	0.00	0.29	0.58	0.88	0.97
 410	1.23	0.00	0.31	0.61	0.92	1.02
 420	1.29	0.00	0.32	0.64	0.97	1.07
 430	1.35	0.00	0.34	0.68	1.01	1.13
 440	1.41	0.00	0.35	0.71	1.06	1.18
 450	1.48	0.00	0.37	0.74	1.11	1.23
 460	1.55	0.00	0.39	0.77	1.16	1.29
 470	1.61	0.00	0.40	0.81	1.21	1.34
 480	1.68	0.00	0.42	0.84	1.26	1.40
 490	1.75	0.00	0.44	0.88	1.32	1.46
 500	1.83	0.00	0.46	0.91	1.37	1.52
 Table NE60.
Area Allowances for New or Expanded Hard Hose Traveler Systems Exterior lane in fields with multiple overlapping lanes: Hydrant spacing based on 60 percent of wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.12	0.00	0.03	0.05	0.08	0.09
 160	0.13	0.00	0.03	0.06	0.10	0.11
 170	0.15	0.00	0.03	0.07	0.11	0.12
 180	0.17	0.00	0.04	0.08	0.12	0.14
 190	0.19	0.00	0.04	0.09	0.14	0.15
 200	0.21	0.00	0.04	0.10	0.15	0.17
 210	0.23	0.00	0.05	0.11	0.17	0.19
 220	0.25	0.00	0.05	0.12	0.18	0.20
 230	0.27	0.00	0.06	0.13	0.20	0.22
 240	0.30	0.00	0.06	0.14	0.22	0.24
 250	0.32	0.00	0.07	0.15	0.24	0.26
 260	0.35	0.00	0.08	0.16	0.25	0.29
 270	0.37	0.00	0.08	0.17	0.27	0.31
 280	0.40	0.00	0.09	0.19	0.29	0.33
 290	0.43	0.00	0.09	0.20	0.32	0.35
 300	0.46	0.00	0.10	0.22	0.34	0.38
 310	0.49	0.00	0.11	0.23	0.36	0.41
 320	0.53	0.00	0.11	0.24	0.39	0.43
 330	0.56	0.00	0.12	0.26	0.41	0.46
 340	0.59	0.00	0.13	0.28	0.43	0.49
 350	0.63	0.00	0.14	0.29	0.46	0.52
 360	0.67	0.00	0.14	0.31	0.49	0.55
 370	0.70	0.00	0.15	0.33	0.51	0.58
 380	0.74	0.00	0.16	0.35	0.54	0.61
 390	0.78	0.00	0.17	0.36	0.57	0.64
 400	0.82	0.00	0.18	0.38	0.60	0.68
 410	0.86	0.00	0.19	0.40	0.63	0.71
 420	0.91	0.00	0.20	0.42	0.66	0.74
 430	0.95	0.00	0.21	0.44	0.70	0.78
 440	0.99	0.00	0.22	0.46	0.73	0.82
 450	1.04	0.00	0.23	0.48	0.76	0.85
 460	1.09	0.00	0.24	0.51	0.80	0.89
 470	1.13	0.00	0.25	0.53	0.83	0.93
 480	1.18	0.00	0.26	0.55	0.87	0.97
 490	1.23	0.00	0.27	0.57	0.90	1.01
 500	1.28	0.00	0.28	0.60	0.94	1.05
 Table NE65.
Area Allowances for New or Expanded Hard Hose Traveler Systems Exterior lane in fields with multiple overlapping lanes: Hydrant spacing based on 65 percent of wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.12	0.00	0.03	0.06	0.09	0.10
 160	0.13	0.00	0.03	0.06	0.10	0.11
 170	0.15	0.00	0.03	0.07	0.11	0.13
 180	0.17	0.00	0.04	0.08	0.13	0.14
 190	0.19	0.00	0.04	0.09	0.14	0.16
 200	0.21	0.00	0.05	0.10	0.16	0.17
 210	0.23	0.00	0.05	0.11	0.17	0.19
 220	0.25	0.00	0.06	0.12	0.19	0.21
 230	0.28	0.00	0.06	0.13	0.21	0.23
 240	0.30	0.00	0.07	0.15	0.22	0.25
 250	0.33	0.00	0.07	0.16	0.24	0.27
 260	0.36	0.00	0.08	0.17	0.26	0.29
 270	0.38	0.00	0.09	0.18	0.28	0.32
 280	0.41	0.00	0.09	0.20	0.31	0.34
 290	0.44	0.00	0.10	0.21	0.33	0.37
 300	0.47	0.00	0.11	0.23	0.35	0.39
 310	0.51	0.00	0.11	0.24	0.37	0.42
 320	0.54	0.00	0.12	0.26	0.40	0.45
 330	0.57	0.00	0.13	0.27	0.42	0.47
 340	0.61	0.00	0.14	0.29	0.45	0.50
 350	0.65	0.00	0.15	0.31	0.48	0.53
 360	0.68	0.00	0.15	0.33	0.50	0.56
 370	0.72	0.00	0.16	0.35	0.53	0.60
 380	0.76	0.00	0.17	0.36	0.56	0.63
 390	0.80	0.00	0.18	0.38	0.59	0.66
 400	0.84	0.00	0.19	0.40	0.62	0.70
 410	0.89	0.00	0.20	0.42	0.65	0.73
 420	0.93	0.00	0.21	0.45	0.69	0.77
 430	0.97	0.00	0.22	0.47	0.72	0.80
 440	1.02	0.00	0.23	0.49	0.75	0.84
 450	1.07	0.00	0.24	0.51	0.79	0.88
 460	1.11	0.00	0.25	0.53	0.82	0.92
 470	1.16	0.00	0.26	0.56	0.86	0.96
 480	1.21	0.00	0.27	0.58	0.90	1.00
 490	1.26	0.00	0.29	0.61	0.94	1.05
 500	1.32	0.00	0.30	0.63	0.97	1.09
 Table NE70.
Area Allowances for New or Expanded Hard Hose Traveler Systems Exterior lane in fields with multiple overlapping lanes: Hydrant spacing based on 70 percent of wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.12	0.00	0.03	0.06	0.09	0.10
 160	0.14	0.00	0.03	0.07	0.10	0.11
 170	0.16	0.00	0.04	0.08	0.12	0.13
 180	0.17	0.00	0.04	0.09	0.13	0.14
 190	0.19	0.00	0.05	0.10	0.14	0.16
 200	0.22	0.00	0.05	0.11	0.16	0.18
 210	0.24	0.00	0.06	0.12	0.18	0.20
 220	0.26	0.00	0.06	0.13	0.19	0.22
 230	0.28	0.00	0.07	0.14	0.21	0.24
 240	0.31	0.00	0.07	0.15	0.23	0.26
 250	0.34	0.00	0.08	0.16	0.25	0.28
 260	0.36	0.00	0.09	0.18	0.27	0.30
 270	0.39	0.00	0.09	0.19	0.29	0.33
 280	0.42	0.00	0.10	0.21	0.31	0.35
 290	0.45	0.00	0.11	0.22	0.34	0.38
 300	0.48	0.00	0.11	0.24	0.36	0.40
 310	0.52	0.00	0.12	0.25	0.39	0.43
 320	0.55	0.00	0.13	0.27	0.41	0.46
 330	0.59	0.00	0.14	0.29	0.44	0.49
 340	0.62	0.00	0.15	0.30	0.46	0.52
 350	0.66	0.00	0.16	0.32	0.49	0.55
 360	0.70	0.00	0.16	0.34	0.52	0.58
 370	0.74	0.00	0.17	0.36	0.55	0.61
 380	0.78	0.00	0.18	0.38	0.58	0.64
 390	0.82	0.00	0.19	0.40	0.61	0.68
 400	0.86	0.00	0.20	0.42	0.64	0.71
 410	0.90	0.00	0.21	0.44	0.67	0.75
 420	0.95	0.00	0.22	0.46	0.71	0.79
 430	0.99	0.00	0.23	0.49	0.74	0.83
 440	1.04	0.00	0.25	0.51	0.78	0.86
 450	1.09	0.00	0.26	0.53	0.81	0.90
 460	1.14	0.00	0.27	0.56	0.85	0.94
 470	1.19	0.00	0.28	0.58	0.89	0.99
 480	1.24	0.00	0.29	0.61	0.92	1.03
 490	1.29	0.00	0.30	0.63	0.96	1.07
 500	1.34	0.00	0.32	0.66	1.00	1.12
 Table NE75.
Area Allowances for New or Expanded Hard Hose Traveler Systems Exterior lane in fields with multiple overlapping lanes: Hydrant spacing based on 75 percent of wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.12	0.00	0.03	0.06	0.09	0.10
 160	0.14	0.00	0.03	0.07	0.10	0.12
 170	0.16	0.00	0.04	0.08	0.12	0.13
 180	0.18	0.00	0.04	0.09	0.13	0.15
 190	0.20	0.00	0.05	0.10	0.15	0.16
 200	0.22	0.00	0.05	0.11	0.16	0.18
 210	0.24	0.00	0.06	0.12	0.18	0.20
 220	0.26	0.00	0.07	0.13	0.20	0.22
 230	0.29	0.00	0.07	0.14	0.22	0.24
 240	0.31	0.00	0.08	0.16	0.24	0.26
 250	0.34	0.00	0.08	0.17	0.26	0.28
 260	0.37	0.00	0.09	0.18	0.28	0.31
 270	0.40	0.00	0.10	0.20	0.30	0.33
 280	0.43	0.00	0.11	0.21	0.32	0.36
 290	0.46	0.00	0.11	0.23	0.34	0.38
 300	0.49	0.00	0.12	0.24	0.37	0.41
 310	0.52	0.00	0.13	0.26	0.39	0.44
 320	0.56	0.00	0.14	0.28	0.42	0.47
 330	0.59	0.00	0.15	0.30	0.45	0.50
 340	0.63	0.00	0.16	0.31	0.47	0.53
 350	0.67	0.00	0.16	0.33	0.50	0.56
 360	0.71	0.00	0.17	0.35	0.53	0.59
 370	0.75	0.00	0.18	0.37	0.56	0.62
 380	0.79	0.00	0.19	0.39	0.59	0.66
 390	0.83	0.00	0.20	0.41	0.62	0.69
 400	0.87	0.00	0.22	0.43	0.65	0.73
 410	0.92	0.00	0.23	0.46	0.69	0.76
 420	0.96	0.00	0.24	0.48	0.72	0.80
 430	1.01	0.00	0.25	0.50	0.76	0.84
 440	1.06	0.00	0.26	0.53	0.79	0.88
 450	1.11	0.00	0.27	0.55	0.83	0.92
 460	1.16	0.00	0.28	0.58	0.87	0.96
 470	1.21	0.00	0.30	0.60	0.90	1.00
 480	1.26	0.00	0.31	0.63	0.94	1.05
 490	1.31	0.00	0.32	0.65	0.98	1.09
 500	1.37	0.00	0.34	0.68	1.02	1.14
 Table NI60.
Area Allowances for New or Expanded Hard Hose Traveler Systems Interior lane in fields with multiple overlapping lanes: Hydrant spacing based on 60 percent of wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.11	0.00	0.02	0.05	0.08	0.09
 160	0.12	0.00	0.02	0.05	0.09	0.10
 170	0.14	0.00	0.02	0.06	0.10	0.11
 180	0.15	0.00	0.03	0.07	0.11	0.13
 190	0.17	0.00	0.03	0.07	0.12	0.14
 200	0.19	0.00	0.03	0.08	0.14	0.15
 210	0.21	0.00	0.04	0.09	0.15	0.17
 220	0.23	0.00	0.04	0.10	0.17	0.19
 230	0.25	0.00	0.05	0.11	0.18	0.20
 240	0.28	0.00	0.05	0.12	0.20	0.22
 250	0.30	0.00	0.05	0.13	0.21	0.24
 260	0.32	0.00	0.06	0.14	0.23	0.26
 270	0.35	0.00	0.06	0.15	0.25	0.28
 280	0.37	0.00	0.07	0.16	0.27	0.30
 290	0.40	0.00	0.07	0.17	0.29	0.33
 300	0.43	0.00	0.08	0.18	0.31	0.35
 310	0.46	0.00	0.08	0.20	0.33	0.37
 320	0.49	0.00	0.09	0.21	0.35	0.40
 330	0.52	0.00	0.09	0.22	0.37	0.42
 340	0.55	0.00	0.10	0.24	0.39	0.45
 350	0.59	0.00	0.10	0.25	0.42	0.47
 360	0.62	0.00	0.11	0.26	0.44	0.50
 370	0.65	0.00	0.12	0.28	0.47	0.53
 380	0.69	0.00	0.12	0.29	0.49	0.56
 390	0.73	0.00	0.13	0.31	0.52	0.59
 400	0.76	0.00	0.14	0.33	0.55	0.62
 410	0.80	0.00	0.14	0.34	0.57	0.65
 420	0.84	0.00	0.15	0.36	0.60	0.68
 430	0.88	0.00	0.16	0.38	0.63	0.71
 440	0.93	0.00	0.17	0.39	0.66	0.75
 450	0.97	0.00	0.17	0.41	0.69	0.78
 460	1.01	0.00	0.18	0.43	0.72	0.82
 470	1.06	0.00	0.19	0.45	0.75	0.85
 480	1.10	0.00	0.20	0.47	0.79	0.89
 490	1.15	0.00	0.21	0.49	0.82	0.93
 500	1.20	0.00	0.21	0.51	0.85	0.97
 Table NI65.
Area Allowances for New or Expanded Hard Hose Traveler Systems Interior lane in fields with multiple overlapping lanes: Hydrant spacing based on 65 percent of wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.11	0.00	0.02	0.05	0.08	0.09
 160	0.13	0.00	0.03	0.06	0.09	0.11
 170	0.15	0.00	0.03	0.07	0.11	0.12
 180	0.16	0.00	0.03	0.07	0.12	0.13
 190	0.18	0.00	0.04	0.08	0.13	0.15
 200	0.20	0.00	0.04	0.09	0.15	0.17
 210	0.22	0.00	0.04	0.10	0.16	0.18
 220	0.24	0.00	0.05	0.11	0.18	0.20
 230	0.27	0.00	0.05	0.12	0.19	0.22
 240	0.29	0.00	0.06	0.13	0.21	0.24
 250	0.32	0.00	0.06	0.14	0.23	0.26
 260	0.34	0.00	0.07	0.16	0.25	0.28
 270	0.37	0.00	0.07	0.17	0.27	0.30
 280	0.40	0.00	0.08	0.18	0.29	0.32
 290	0.42	0.00	0.08	0.19	0.31	0.35
 300	0.45	0.00	0.09	0.21	0.33	0.37
 310	0.49	0.00	0.10	0.22	0.35	0.40
 320	0.52	0.00	0.10	0.24	0.38	0.42
 330	0.55	0.00	0.11	0.25	0.40	0.45
 340	0.58	0.00	0.12	0.27	0.43	0.48
 350	0.62	0.00	0.12	0.28	0.45	0.51
 360	0.65	0.00	0.13	0.30	0.48	0.54
 370	0.69	0.00	0.14	0.32	0.50	0.57
 380	0.73	0.00	0.15	0.33	0.53	0.60
 390	0.77	0.00	0.15	0.35	0.56	0.63
 400	0.81	0.00	0.16	0.37	0.59	0.66
 410	0.85	0.00	0.17	0.39	0.62	0.69
 420	0.89	0.00	0.18	0.41	0.65	0.73
 430	0.93	0.00	0.19	0.43	0.68	0.76
 440	0.98	0.00	0.19	0.45	0.71	0.80
 450	1.02	0.00	0.20	0.47	0.74	0.84
 460	1.07	0.00	0.21	0.49	0.78	0.87
 470	1.12	0.00	0.22	0.51	0.81	0.91
 480	1.16	0.00	0.23	0.53	0.85	0.95
 490	1.21	0.00	0.24	0.55	0.88	0.99
 500	1.26	0.00	0.25	0.58	0.92	1.03
 Table NI70.
Area Allowances for New or Expanded Hard Hose Traveler Systems Interior lane in fields with multiple overlapping lanes: Hydrant spacing based on 70 percent of wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.12	0.00	0.03	0.06	0.09	0.10
 160	0.13	0.00	0.03	0.06	0.10	0.11
 170	0.15	0.00	0.03	0.07	0.11	0.13
 180	0.17	0.00	0.04	0.08	0.13	0.14
 190	0.19	0.00	0.04	0.09	0.14	0.16
 200	0.21	0.00	0.05	0.10	0.16	0.17
 210	0.23	0.00	0.05	0.11	0.17	0.19
 220	0.26	0.00	0.06	0.12	0.19	0.21
 230	0.28	0.00	0.06	0.13	0.21	0.23
 240	0.30	0.00	0.07	0.15	0.22	0.25
 250	0.33	0.00	0.07	0.16	0.24	0.27
 260	0.36	0.00	0.08	0.17	0.26	0.29
 270	0.38	0.00	0.08	0.18	0.28	0.32
 280	0.41	0.00	0.09	0.20	0.31	0.34
 290	0.44	0.00	0.10	0.21	0.33	0.37
 300	0.47	0.00	0.10	0.23	0.35	0.39
 310	0.51	0.00	0.11	0.24	0.37	0.42
 320	0.54	0.00	0.12	0.26	0.40	0.45
 330	0.57	0.00	0.13	0.28	0.42	0.47
 340	0.61	0.00	0.13	0.29	0.45	0.50
 350	0.65	0.00	0.14	0.31	0.48	0.53
 360	0.68	0.00	0.15	0.33	0.51	0.56
 370	0.72	0.00	0.16	0.35	0.53	0.60
 380	0.76	0.00	0.17	0.37	0.56	0.63
 390	0.80	0.00	0.18	0.38	0.59	0.66
 400	0.84	0.00	0.19	0.40	0.62	0.70
 410	0.89	0.00	0.20	0.43	0.66	0.73
 420	0.93	0.00	0.21	0.45	0.69	0.77
 430	0.97	0.00	0.22	0.47	0.72	0.81
 440	1.02	0.00	0.23	0.49	0.76	0.84
 450	1.07	0.00	0.24	0.51	0.79	0.88
 460	1.12	0.00	0.25	0.54	0.83	0.92
 470	1.16	0.00	0.26	0.56	0.86	0.96
 480	1.21	0.00	0.27	0.58	0.90	1.00
 490	1.27	0.00	0.28	0.61	0.94	1.05
 500	1.32	0.00	0.29	0.63	0.98	1.09
 Table NI75.
Area Allowances for New or Expanded Hard Hose Traveler Systems Interior lane in fields with multiple overlapping lanes: Hydrant spacing based on 75 percent of wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.12	0.00	0.03	0.06	0.09	0.10
 160	0.14	0.00	0.03	0.07	0.10	0.12
 170	0.16	0.00	0.04	0.08	0.12	0.13
 180	0.18	0.00	0.04	0.09	0.13	0.15
 190	0.20	0.00	0.05	0.10	0.15	0.16
 200	0.22	0.00	0.05	0.11	0.16	0.18
 210	0.24	0.00	0.06	0.12	0.18	0.20
 220	0.26	0.00	0.06	0.13	0.20	0.22
 230	0.29	0.00	0.07	0.14	0.22	0.24
 240	0.31	0.00	0.08	0.16	0.23	0.26
 250	0.34	0.00	0.08	0.17	0.25	0.28
 260	0.37	0.00	0.09	0.18	0.27	0.31
 270	0.40	0.00	0.10	0.20	0.30	0.33
 280	0.43	0.00	0.10	0.21	0.32	0.35
 290	0.46	0.00	0.11	0.23	0.34	0.38
 300	0.49	0.00	0.12	0.24	0.37	0.41
 310	0.52	0.00	0.13	0.26	0.39	0.43
 320	0.56	0.00	0.14	0.28	0.42	0.46
 330	0.59	0.00	0.14	0.29	0.44	0.49
 340	0.63	0.00	0.15	0.31	0.47	0.52
 350	0.67	0.00	0.16	0.33	0.50	0.55
 360	0.70	0.00	0.17	0.35	0.53	0.59
 370	0.74	0.00	0.18	0.37	0.56	0.62
 380	0.78	0.00	0.19	0.39	0.59	0.65
 390	0.83	0.00	0.20	0.41	0.62	0.69
 400	0.87	0.00	0.21	0.43	0.65	0.72
 410	0.91	0.00	0.22	0.45	0.68	0.76
 420	0.96	0.00	0.23	0.48	0.72	0.80
 430	1.01	0.00	0.24	0.50	0.75	0.84
 440	1.05	0.00	0.26	0.52	0.79	0.88
 450	1.10	0.00	0.27	0.55	0.82	0.92
 460	1.15	0.00	0.28	0.57	0.86	0.96
 470	1.20	0.00	0.29	0.59	0.90	1.00
 480	1.25	0.00	0.30	0.62	0.94	1.04
 490	1.31	0.00	0.32	0.65	0.98	1.09
 500	1.36	0.00	0.33	0.67	1.02	1.13
 Table N75+.
Area Allowances for New or Expanded Hard Hose Traveler Systems Exterior or Interior lane in fields with single pull or: Hydrant spacing greater than 75 percent of wetted diameter 
 wetted	start end	stop end wetted area 
 d	area	arc angle	arc angle	arc angle	arc angle	arc angle
 		180 degrees	225 degrees	270 degrees	315 degrees	330 degrees
 						
 150	0.12	0.00	0.03	0.06	0.09	0.10
 160	0.14	0.00	0.04	0.07	0.11	0.12
 170	0.16	0.00	0.04	0.08	0.12	0.13
 180	0.18	0.00	0.04	0.09	0.13	0.15
 190	0.20	0.00	0.05	0.10	0.15	0.17
 200	0.22	0.00	0.05	0.11	0.16	0.18
 210	0.24	0.00	0.06	0.12	0.18	0.20
 220	0.27	0.00	0.07	0.13	0.20	0.22
 230	0.29	0.00	0.07	0.15	0.22	0.24
 240	0.32	0.00	0.08	0.16	0.24	0.26
 250	0.34	0.00	0.09	0.17	0.26	0.29
 260	0.37	0.00	0.09	0.19	0.28	0.31
 270	0.40	0.00	0.10	0.20	0.30	0.33
 280	0.43	0.00	0.11	0.22	0.32	0.36
 290	0.46	0.00	0.12	0.23	0.35	0.38
 300	0.49	0.00	0.12	0.25	0.37	0.41
 310	0.53	0.00	0.13	0.26	0.40	0.44
 320	0.56	0.00	0.14	0.28	0.42	0.47
 330	0.60	0.00	0.15	0.30	0.45	0.50
 340	0.63	0.00	0.16	0.32	0.48	0.53
 350	0.67	0.00	0.17	0.34	0.50	0.56
 360	0.71	0.00	0.18	0.36	0.53	0.59
 370	0.75	0.00	0.19	0.38	0.56	0.63
 380	0.79	0.00	0.20	0.40	0.59	0.66
 390	0.83	0.00	0.21	0.42	0.63	0.70
 400	0.88	0.00	0.22	0.44	0.66	0.73
 410	0.92	0.00	0.23	0.46	0.69	0.77
 420	0.97	0.00	0.24	0.48	0.73	0.81
 430	1.01	0.00	0.25	0.51	0.76	0.85
 440	1.06	0.00	0.27	0.53	0.80	0.88
 450	1.11	0.00	0.28	0.56	0.83	0.93
 460	1.16	0.00	0.29	0.58	0.87	0.97
 470	1.21	0.00	0.30	0.61	0.91	1.01
 480	1.26	0.00	0.32	0.63	0.95	1.05
 490	1.32	0.00	0.33	0.66	0.99	1.10
 500	1.37	0.00	0.34	0.69	1.03	1.14
 Robert 0.
Evans, PE; Biological and Agricultural Engineering Associate Professor Ronald E.
Sneed, PE, CID; Biological and Agricultural Engineering Professor, Emeritus Ron E.
Sheffield, Biological and Agricultural Engineering Extension Specialist Jonathan T.
Smith, Biological and Agricultural Engineering Extension Assistant
 2,000 copies of this public document were printed at a cost of $5805.70 or $2.90 per copy.
NC STATE UNIVERSITY A&T STATE UNIVERSITY COOPERATIVE EXTENSION Helping People Put Knowledge to Work
 Published by NORTH CAROLINA COOPERATIVE EXTENSION SERVICE
The main objective with these calculations is to approach the end of the growing season using the stored soil water without affecting crop yields, while also creating room to store the offseason precipitation by lowering the soil water to 40% plant available water.
These calculations will be improved if refigured weekly with updated irrigation and rainfall data.
For more information on this topic, see NebGuide G1871, Predicting the Last Irrigation of the Season.
Table I.
Normal water requirements for corn, grain sorghum, soybeans, and dry beans between various stages of growth and maturity in Nebraska.
For Grain Sorghum stage 6 crop stage, the stage of growth is known as half bloom, the approximate days to maturity is 34, and the water use to maturity is 9.0 inches.
For Grain Sorghum stage 7 crop stage, the stage of growth is known as soft dough, the approximate days to maturity is 23, and the water use to maturity is 5.0 inches.
For Grain Sorghum stage 8 crop stage, the stage of growth is known as hard dough, the approximate days to maturity is 12, and the water use to maturity is 2.0 inches.
For Grain Sorghum stage 9 crop stage, the stage of growth is known as physiological maturity, the approximate days to maturity is 0, and the water use to maturity is 0.0 inches.
The producer will then select their soil texture from the dropdown list.
Once the soil texture is selected it will tell you the available water holding capacity for the soil in inches per foot.
Next select the number of sensors you are using at this location.
You can then enter your sensor readings and select your Allowable Water Depletion percentage.
Subsurface irrigation has been around since the 1860s, but drip irrigation was not a practical choice until Chapin developed lay-flat twin-wall drip tape in the late 1960s.
Early problems with clogged lines, slime, and an inability to run nutrients through the lines have basically been solved as long as growers use a few precautionary tools to guard against problems.
A well designed drip irrigation system benefits the environment by conserving water and fertilizer.
A properly installed drip system can save as much as 80% of the water normally used in other types of irrigation systems.
Water is applied either on the surface, next to the plant, or subsurface, near the root zone.
In dry years, fewer weed seeds germinate between rows because there is less water available beyond the plant root zone.
Another advantage to drip irrigation is that there is less evaporation from the soil, especially when drip irrigation is used with plastic mulch.
Water is applied more evenly throughout the field, thus eliminating the need to run the irrigation longer to wet the whole field.
It requires some expertise to install and operate a drip system and consultation with a knowledgeable professional is wise.
A less than adequate system can result in yield variability in the field due to areas of over-or underwatering and clogged lines.
Pumps, filters and tape may not last as long.
Trying to save money by cutting costs of initial equipment purchases will usually cost more money in the long run.
Any or all of these problems can completely offset the potential cost savings from using drip.
This is by no means a comprehensive review of all materials used for drip irrigation.
The references listed at the end of this article are useful resources to use in learning more about drip irrigation and in designing a system.
The complexities of the system are related to the size of the farm, water quality, slope of the land, and the value of the crop.
The system should be compatible with the growers cultural practices, such as bed width, crop rotation, access to the field, unless he/she is willing to change them.
The economic benefit of drip irrigation will only be realized if an increase in production potential or a decrease in operating costs outweighs the increased cost of setting up the system.
If the cost of the system can be spread over multi-crops and uses, then the cost is easily justified.
Thicker-walled drip tape can be used for three or more years, thus spreading the initial cost of tape over more than one year.
The emitters in a drip system have small diameters that can easily become clogged if the wrong filters are used in the system.
Therefore it is critical that a water test is taken prior to designing the system.
Organic materials, such as plant materials, algae, small living organisms and inorganic sand, silt, and clay are the primary concern if the source of water is from surface water such as a pond or stream.
Surface water might have contaminants from runoff.
Inorganic materials such as salts are usually the primary concern if the water comes from groundwater.
A water analysis should be done before the system is designed.
Any reputable water testing lab will work as long as some specific tests are done.
The water should be tested for at least the following: calcium, magnesium, pH, carbonates and bicarbonates, iron, living organisms, and size of the particulate matter.
The test should be taken at a time that is representative of the poorest water quality in the growing season because the filter is chosen based on this analysis.
If water will be pumped into a holding tank before it enters the field, then the water sample should be taken from the tank as it could add contaminants to those coming from the water source.
The results of the water test determine the type of filtration system used.
The pH, calcium, and magnesium concentration will affect the solubility of certain fertilizers.
Fertilizer can precipitate out and clog either the filter system or the emitters in the drip tape.
A good rule of thumb is to premix a small amount of the fertilizer you plan to use in the water that will be used in the drip system, before adding it to the tank.
If any precipitation occurs after 24 hours, then another fertilizer or a lesser concentration should be used.
Further details about fertigation will be covered in another section.
Slope of the Land
 A slope of 2% or less is the ideal for drip irrigation.
An elevation change of 2 ft can cause a 1 psi change in pressure.
Very little land in New England fits this criteria.
The length and number of lateral lines, the pump size, and pressure regulators are chosen based on the slope.
Different emitter sizes or spacing between emitters can be adjusted to accommodate slopes.
One of the advantages to drip irrigation is that it can be adapted to various soil types.
The soil type determines the soil wetting patterns.
Soil wetting patterns in turn influence depth of the drip tape and the distance between premitters.
The duration and frequency of irrigation are also determined by the soil type.
Over watering can move fertilizer away from the root zone.
On sandy soils, the water never moves laterally more than 10 inches.
In sandy soils, irrigate more frequently, but run the water for a lesser amount of time.
In heavier soils, irrigate less often, but run the water for a longer duration.
In both cases, this should lessen the chance of leaching fertilizers away from the root zone.
Before buying one roll of tape, pump, or filter, the entire system should be drawn out on paper.
The main components of a typical drip system are the pump, flowmeters, main and sub-main lines, drip tape, pressure valves, filters, fertilizer injectors, and flushing manifolds.
Before purchasing any component, a number of questions need to be answered:
 Is the tape going to be laid on the surface or buried beneath the soil?
Is plastic going to be used with the tape?
What crop or crops will be planted/rotated in the field?
Will the tape be used to germinate seeds or will another irrigation method be used?
Will fertilizers be injected into the water?
Two goals for a drip irrigation system are to apply water uniformly over the field and to have the water running through the system only as long as necessary to properly wet the field.
The uniformity of the water flow depends on the spacing and the type of emitters used with the tape.
Drip tape should have a coefficient of manufacturing variation  number which reveals how much variation in uniformity there is from one emitter to the next.
A CV of 0.05 is considered excellent and a CV between 0.05 and 0.1 is acceptable.
It is worth the initial expense of buying quality tape and emitters because of the reduced costs later on, such as the cost of pumping water.
The length of the drip lines is another important consideration.
The length is determined by the pump size, the field size, and the slope of the land.
Any one of these factors will influence wetting uniformity because the emitters will discharge water at different rates if there are changes in pressure along the line.
Because of variation in water pressure, tape is rarely laid out longer than a length of 400 feet.
The choice of tape thickness, measured in millimeters , is based on how long you want the tape to last and the expected highest water pressure in the lines.
The longer the tape is in the ground, or the higher the pressure in the lines, the thicker the tape should be.
Tape thickness is usually between 4 and 10 mil though thickness of up to 25 mil can be purchased.
Tape life is usually 2 to 3 years depending on how well the system is managed in the field.
Thicker tapes  have been used in alfalfa fields where the tape may be in the ground up to 5 years.
Placement of Drip Tape
 There are three decisions to be made regarding placement of the drip tape:
 the distance from the plant in the row,
 whether to bury the tape or place it on the soil surface, and
 the depth to bury the drip tape.
Whether the tape is laid on the surface or buried beneath the soil, there are a few general guidelines to follow.
The tape should be placed as close to the plant as is practical for the specific crop.
Twelve inches is the maximum distance away from the plant row most tape is placed between 6 and 12 inches away.
A little further away is possible in soils that have good lateral movement or when other means of irrigation is used to germinate seed or establish seedlings.
The tape should be placed so that the emitters are pointed upward so that soil, silt and clay will settle away from the emitters after the water stops flowing.
Tape can be laid on the surface, especially if it is used in conjunction with black plastic.
The advantages are that it is easy to install and to make repairs.
The disadvantages are that there is greater evaporation in the initial stages of the crops growth and the tape is more likely to be damaged by production practices, wind, and animals.
Drip tape is usually buried between 6 and 10 inches deep, though with some root crops, the tape can be buried a little deeper.
Tape is buried 18 to 24 inches deep in some alfalfa fields.
How deep the tape should be buried in a given field is determined by the crop, the soil type, the root pattern of the crop, soil wetting patterns, and the tilling practices used in the field.
Water moves upward and laterally from the tape better in a loam soil than in a sandy soil, therefore, tape should be buried at shallower depths in sandy soils than loam soils.
The purpose of a pump is to deliver water evenly at the correct flowrate and pressure.
There are usually two kinds of pumps sold centrifugal pumps and deep well turbines.
The pump capacity needed and the discharge pressure should be determined prior to purchase.
The capacity is determined by the crops water requirements, the efficiency of the whole system, and the largest acreage to be irrigated by the pump at a given time.
The discharge pressure is determined by the desired operating pressure through the drip tape, the pressure loss due to friction, and the various changes in elevation within the system.
There is a rule of thumb that the larger the capacity of the pump, the more efficient it is.
However, there is a point where efficiency levels off and more capacity does not bring any benefit.
As previously mentioned, the choice of filter is based on the quality of the water passing through the system.
It is usually the greatest expense in a drip system.
Growers may try to cut costs by buying a less than adequate filter for the worst case scenario on the farm.
This usually leads to more costs down the road.
If the water is loaded heavily with suspended solids, then a sedimentation tank is recommended.
This would allow some of the coarse materials to settle out before it reaches the filter.
However, a sedimentation tank should not be the only method of filtration for the system.
If the sediment load is high, than it is a good idea to prefilter the water with a vortex sand separator before running the water through another filter.
A sand separator causes the water to swirl in a vortex.
This forces sediments to drop to the bottom of the container.
These separators can remove as much as 98% of the contaminants that would not pass through a 200 mesh screen, but are not as effective at removing organic materials.
Screen filters are inexpensive and easy to install.
Mesh filters work well if there are moderate to low contaminants in the water such as those coming from a well.
Screen filters have a limited ability to store contaminants.
Thus, if the water comes from a river or a holding pond, the screens will have to be flushed often.
This could result in considerable down time in the system.
Clean water must be used to clean the system!
Mesh screen sizes are between 20 and 200 mesh.
The larger the number, the smaller the particle the screen will filter out.
The screens are made from stainless steel, nylon, or polyester.
The maximum flow rate through a screen is 200 gpm/sq.
ft.
of screen.
Sand filters are more effective than screen filters if the contaminant load is moderate to heavy or there are sources of heavy inorganic or chemical substances in the water.
A sand filter can run longer than a screen filter before it needs to be cleaned.
There is less down time in the system.
The filters can be set up in pairs so that clean water from one filter is used to flush the other filter.
The correct filter size is critical to the failure or success of the system.
Under-sizing will increase pressure loss and there is considerable down time for cleaning.
It is better to be too big than too small.
For most systems the average size filter is 20 gpm/sq.
ft.
The type of sand filter used in the system is based on how much the water needs tobe cleaned.
It is made up of crushed, sharp edged silica or granite.
The sand never needs replacing unless it is contaminated by oil or other chemicals.
Sand filters can remove particles smaller than those that can be removed from a 200 mesh screen filter.
Another popular type of filter is a disc filter.
It consists of a series of disks that are stacked on top of each other.
The disks are made up of microscopic grooves that serve as the filters.
Equivalent mesh sizes are between 40 and 600 mesh.
They require less water for cleaning than do sand filters.
Cartridge filters are used if contaminant concentrations are less than 5 ppm and there is low flow volume through the system.
The filters are usually replaced rather than cleaned.
The filters are made out of paper, cotton, fiberglass, or other synthetic material.
Paper will deteriorate over time and may clog the system.
Cartridge filters, though inexpensive and popular, are not recommended for drip irrigation.
The main reason for properly managing a drip irrigation system is so that the water is not wasted and fertilizer does not leach.
Managing the system requires that
 the operator knows how much water the crop used since the last irrigation or rainfall event and
 the operator applies a specific amount of water during any one irrigation.
A flowmeter measures the volume of water passing through the system.
The system can be programmed to shut down as soon as the flow meter registers that a predetermined volume of water has passed through it.
This saves water over the long run and decreases the likelihood of nutrients leaching from the root zone.
The flow volume for a single irrigation event is determined by the needs of the crop and the size and efficiency of the system.
There are several types of flowmeters.
The most commonly used flowmeter is the propeller meter.
It requires installation in a straight section of pipe and for the pipe to flow at full capacity in order to register accurately.
Propeller meters can become clogged if there is debris in the water.
Variation in water pressure will alter the amount of water registered on the meter.
Magnetic flowmeters do not have an obstruction in the pipe so there is no opportunity for debris to get clogged in the meter.
Also, there is no pressure loss as the water flows through it.
Magnetic meters remain accurate for a longer time than propeller meters.
The initial cost is higher and they require an external power supply.
The need for an external power supply to run the meter is a disadvantage since flowmeters are usually placed right in the field and not always within easy access of a power supply.
Mainlines are made of either PVC pipe or lay-flat hose.
Their purpose is to deliver water to the submains and laterals.
The diameter of the pipe is determined by the distance the water needs to travel and the pressure requirements of the system.
The wider the diameter of the pipe, the more expensive it is.
The longer the pipe and the more elbows or junctions, the more loss due to friction, which then causes a gradual loss in pressure.
A design engineer will help determine the appropriate pipe size for the system.
Care showed be taken when laying the pipe to prevent soil or debris from getting into the system and clogging the lines.
The lines should be flushed before the tapes is connected to flush out any dirt that got into the lines during installation.
It is a good idea to bury the lines at least deep enough to allow equipment to roll over them with out damaging the pipe.
Check Valves And Pressure Regulators
 Valves control the direction of water flow.
They are used to prevent water from flowing backward into a well after the system is shut off.
Pressure regulators help maintain a constant pressure as the water flows through the system.
Pressure relief valves prevent sudden changes in pressure from damaging pipes or tape.
Vacuum-relief valves are installed to prevent soil from being sucked into the emitters when a vacuum is created after the system is shutoff.
Once the system has been properly designed, the next most important step is to operate the system correctly.
No matter how well the system is built, if it is used improperly, then the cost of the system will be greater than the benefit.
Every crop requires different amounts of water to grow.
The amount of water the crop needs for optimal production depends on the crop, the region of the country the crop is grown in, and the weather patterns for the growing season.
Calculating how much water to apply depends on the evapotranspiration rate of the crop and the soil moisture content.
An important point to remember with drip irrigation is that the water is applied near the plant and that there is very little available moisture outside of the root zone.
The root zone of a specific crop is much closer to the plant under a drip system than with other types or irrigation or where there is significant rainfall during the growing season.
Soil moisture should be measured in the root zone, not in the furrows away from the plant.
During periods of warm weather, the moisture in the root zone can be rapidly depleted even though there is sufficient moisture next to the plant.
One of the reasons for using drip irrigation is to decrease the amount of water applied to the field.
This aids in weed control and decreases surface run-off.
But you must still apply enough water for the crops needs.
This factor never changes.
The way to measure the amount of water that a plant has used is to measure the evapotranspiration rate, also called crop water use.
Either term means the amount of water used by the crop in a given period of time.
This includes the amount of water that has evaporated from the soil surface and the amount of water that had transpired  from the leafs surface.
Yields are limited if the plant receives less water than required for optimum growth.
If no reliable evapotranspiration data is available, then monitoring the soil moisture is the next best way to determine how much water is required for the next irrigation event.
It is also useful to monitor soil moisture to determine if the field overall is getting too wet or too dry, both indications that the irrigation system is not functioning properly.
The usual devices for measuring soil moisture are tensiometers or gypsum blocks.
A tensiometer is the most common tool used by growers.
A tensiometer is a plastic pipe with a ceramic cup at one end and a vacuum gauge at the other.
They can be purchased through several field equipment suppliers.
The cup is wetted to saturation; then the pipe is filled with water.
The pipe is inserted into the ground at the root zone.
A rule of thumb is to place the tensiometer about six inches from the drip tape at a depth of one-third the entre root zone.
As the soil becomes wet or dry through irrigation or rain, the change in the water level of the pipe is registered on the gauge.
The higher the reading on the tensiometer, the drier the soil.
If the tensiometer reading is getting higher as the season progresses, then the soil is too dry; if the reading is decreasing as the season progresses, then the soil is too wet.
A gypsum block is less commonly used by growers.
It measures the soil moisture by measuring electrical resistance.
After the gypsum is saturated with water, it is embedded in the soil.
Soil water moves in and out of the gypsum block as the soil is wetted or dried through irrigation or rain.
The gypsum dissolves and moves with the water.
As the concentration of the gypsum changes, the electrical resistance changes.
The block needs to be replaced after all the gypsum dissolves.
The soil should be irrigated often enough to keep the soil moisture level at a constant level.
Some water all the time is better than putting the plant through a water stress-no water stress cycle.
Generally, the plant should never be water stressed.
Irrigation is more frequent under drip irrigation than more conventional irrigation because the roots remain close to the emitters.
An irrigation schedule is based on the climate, the plant, and the soil.
The table below shows the rule of thumb for irrigation.
Fertigation is the word used to describe the injection of chemical fertilizer into irrigation water.
Nitrogen and potassium, are available in liquid or soluble solid form and can be applied through a drip system, though phosphorus is usually broadcast at the beginning of the season.
Anything injected into the water must go into solution or the system can become plugged.
As mentioned earlier, a water test is a critical component of a properly designed system.
Injection should always occur upstream of the main filters so that undissolved materials can be screened out.
Fertilizer should be injected into the system during the last phase of a scheduled irrigation event with three quarters of an hour to an hour of water with no fertilizer after that.
This is to insure that all the fertilizer is applied and none remains in the tubing.
Fertilizer in the tubing can encourage the growth of algae and other organisms.
There are several ways to inject chemicals into the system and there are advantages and disadvantages to each method.
The five main types of injectors are: Chemical injection pumps, venturi applicators, pressure differential tanks, gravity injectors and bladder tanks.
It is best to consult with an irrigation specialist to determine the right type for your operation.
University of Nebraska Extension irrigation scheduling recommendations encourage irrigators to allow the crop to continue using more and more of the stored soil water starting in August and continuing into September when the crop matures.
The recommendation is to lower the soil water level from the usual summer water condition of a minimum of 50% plant available water in the top three feet of soil to 40% in the top four feet after the dough stage  is reached.
Thus, the stored soil water content should be significantly lower when the crop matures in September than earlier in August.
10 gallons/acre x 5 acre/hr = 50 gph
 The calculation is just this simple, but it takes some effort to determine the acres per hour the pivot will irrigate.
Use: Avoid application in uncrossed areas , VRI type: zone, Prescription type: static, management intensity: low.
What Is Surge Irrigation?
Surge irrigation is the intermittent application of water along a furrow to improve distribution uniformity.
It works on the principle that dry soil infiltrates water faster than wet soil.
When soil is wet, the surface soil particles consolidate and form a seal.
When water is re-introduced in a wet furrow, the wetting front moves quickly past the wetting zone to dry soil.
At the wetting interface, dry soil slows the advance.
This phenomenon allows for a faster advance through the field with less deep percolation and better application uniformity.
The result is a more even distribution of water in the rooting zone from the polytubing to the tail ditch, and reduced nutrient loss from deep percolation near the poly-tubing.
Surge irrigation works through a program of cycle times that account for the advance of the furrow.
These cycle times must be set by the user.
A valve that simply moves from one set to another at a uniform or constant time interval is not surge irrigation.
Some tailwater is necessary for surge irrigation to be effective.
The intermittent application reduces the tailwater volume because the water is moving as a pulse over the sealed furrow to the end of the furrow.
Its velocity decreases as it moves along the furrow, SO it has more time to infiltrate before it leaves the furrow.
When set properly, very little tailwater leaves the furrow.
Advance time: Time required for the wetting front to advance from the crown to the end of the furrow.
Recession time: Time for the wave front to recede from the furrow.
Essentially, this is when the majority of the tailwater has stopped draining from the field.
Opportunity time: Time for water to infiltrate into the soil.
The more opportunity time water has contact with the soil, the more volume is infiltrated.
Soak time: Time after the advance has completed when the remainder of the set time is used to meet the required application depth.
Application depth: The depth of irrigation applied during surge irrigation.
This depth should be between 2.5 and 3.0 ac-in.
Number of cycles: The number of advance cycles  used to complete a surge advance program.
Generally, surge advance times increase during the surge program, although some surge programs have a longer first advance than second advance before increasing.
On-time: The time water is applied to a given side.
Off-time: The time water is not applied to a given side.
Cycle-time: The time required to complete an on/off cycle.
Irrigation set time: The total irrigation time, which includes advance and soak times.
The set time for row crops should always be less than 40 hours.
If using a CHS plan, you must add the time for each set together to calculate the irrigation set time.
For example, if a surge is being used on two 24-hour sets, the total time is 48 hours, SO the sets should be divided into three sets.
Computerized Hole Selection for Surge Irrigation
 To lay out surge irrigation, two irrigation sets must be combined.
For example, if an irrigation set was used to irrigate a 35-acre field or set, then it must be divided into two sets of equal size  or similar size.
Combine the irrigation time for each set to get the total irrigation set time.
It is recommended not to exceed a total time of 40 hours; 24 hours is preferred.
Ideally, sets should be reduced to 24to 30-hour total irrigation set times.
When possible, locate surge valves at risers, valves, or bonnets.
It is preferable not to have any lay-flat pipe supplying irrigation water to a surge valve due to valve motion.
A surge valve can be used for multiple sets in a field.
For example, a 40-acre field can be divided into four 10-acre sets and the valve used for two sets at a time, then switched to the other two.
Place a short piece of rigid pipe in the valve; secure with poly pipe tape to make it easier to connect pipes.
Use pipe clamps to secure the lay-flat pipe to the valve between surge sets.
Anatomy of a Surge Valve
 A surge valve consists of an electronic controller and an aluminum mechanized valve that diverts water from one side to the other.
P & R Surge Systems valves have advance and soak cycle modes.
The valve starts out in the advance mode and then moves into the soak mode after the advance time is reached.
It continues indefinitely in the soak mode until it is shut off.
Programming the advance time in a surge valve is critical.
Once you reach the soak phase in the program, you cannot go back to advance phase.
Set the anticipated time of the advance phase slightly less than the actual advance time observed in the field.
In many cases, surge irrigation advance time is about half the normal time.
Use CHS to plan the surge time.
For example, if a CHS plan calls for a 24-hour set time, then expect a 12-hour advance.
However, the advance time is highly variable, SO use your experience to determine the advance; monitor the advance during the first irrigation until you know or can predict it.
For example, if a 24-hour set is required to put on 2.5 ac-in application depth and you observe that the advance is halfway through the field at 9 hours, then adjust the advance time down from 24 to 18 hours.
Guidance on setting a surge valve for different soils and conditions is provided below.
However, there is a no hard-and-fast rule; experiment with the valve to get the best results.
Surge valves are especially useful in sandy soils, as the challenge with these soils is minimizing deep percolation and getting water through the furrow.
Set the valve as normal, but expect a longer advance time than 50 percent of the irrigation set time.
Use default cycle times.
Increasing the number of cycles may improve irrigation.
Surge valves are especially useful in silt loams that seal.
In silt loams that do not seal and infiltrate well, use the same process as for sandy soils.
For silt loams that seal, you likely will need to make substantial changes to the program.
In the sealing silt loams, the advance is often much less than expected.
For example, for a set time of 24 hours, the advance may be completed in 6 hours.
Adjust the advance time to 5 hours and increase the number of advance phases by one or two.
Operate the valve in soak mode for the remainder of the irrigation set.
Reduce the flow rate to increase opportunity time.
In cracking soils, the surge valve should be used only in the advance mode.
Set the advance time to the total irrigation set time.
Do not operate in soak mode.
Reduce the number of advance cycles to only three or four.
The surge valve works in clay soil because, in the off-cycle, the soil cracks seal up and allow the advance to quickly move through the furrow on the next advance.
Table 1 lists recommended advance settings.
Table 1.
Surge valve STAR Controller recommendations for clay soils.
Advance setting	Default cycles/side	Custom cycles/side
 Input by user	Under custom tab	to adjust
 5	4	4-1  total
 10	5	5-2  total
 15	6	6-2  total
 20	6	6-2  total
 30	6	6-2  total
 The number of cycles per side should equal the default setting minus two.
Total cycles per side should never be less than three.
Two sets of different sizes can still be surge irrigated.
For example, if one set is 15 acres and another is 20 acres, the valve can be adjusted to increase the advance times for each set.
In this example, the valve will divert water to the 15-acre set 43 percent of the time, and it will divert water to the 20-acre set 57 percent of the time.
This setting can be input directly into the valve through a custom menu.
Surge valves operate on solar power and a battery.
Check the voltage of the battery and solar panel through the custom menu.
Valve controllers need to be charged and turned off in the off-season.
During the season, shut them off after an irrigation event, or else they will continue to move the valve and drain the battery.
The oscillation of the valve can dislodge it from the water source, SO use a circle lock or horseshoe clamp to secure it.
When starting irrigation, change the valve from the right or left side using the change button; this does not advance the program when done during the first advance cycle.
The valve pauses before switching completely over.
This setting can be changed in most valves if high flow rates cause a water hammer.
The benefits of surge irrigation are not always apparent from visual observation alone.
Soil moisture
 sensors or monitoring units can be useful in evaluating effectiveness and optimizing surge irrigation program settings.
Surge reduces the advance time in some situations and increases it in others.
Reducing the advance time results in water savings.
An increased advance time typically indicates that more water has been applied to the soil; likely, fewer irrigations will be necessary, which means less total irrigation water will be needed to meet crop water demand.
Surge irrigation is the intermittent application of water in furrow irrigation to improve down-furrow efficiency and reduce deep percolation.
It uses a programmed, automated valve with lay-flat pipe that is planned with set sizes.
Surge irrigation must be adapted and adjusted to field conditions and soil type.
Plan surge irrigation sets for a total irrigation time of 24 hours, and use CHS to determine lay-flat pipe hole-punch plans.
Acknowledgement: This is a joint publication with the University of Arkansas.
U/A DIVISION OF AGRICULTURE RESEARCH & EXTENSION University of Arkansas System
 By Drew M.
Gholson, PhD, Assistant Professor and Irrigation Specialist, Delta Research and Extension Center, MSU; Chris G.
Henry, Associate Professor and Water Management Engineer, Rice Research and Extension Center, University of Arkansas System Division of Agriculture; and L.
Jason Krutz, Director, Mississippi Water Resources Research Institute, MSU.
Produced by Agricultural Communications.
Extension Service of Mississippi State University, cooperating with U.S.
Department of Agriculture.
Published in furtherance of Acts of Congress, May 8 and June 30, 1914.
GARY B.
JACKSON, Director
Crop water use will vary across the Panhandle due to variations in temperature and precipitation events.
Crop water use will assist growers with irrigation scheduling and efficient water use.
Potential economic impacts of irrigation-water reductions estimated for Sacramento Valley
 This article is drawn from a longer Agricultural Issues Center report, "Economic Impacts of Irrigation Water Cuts in the Sacramento Valley." The full report may be ordered for $12 from AIC by calling  752-2320.
In the Sacramento Valley, irrigation water is vital to agriculture and agriculture is vital to local economies.
This study investigates these relationships by asking: If surface irrigation water were cut by 25%, what would be the economic impacts on farmers and on communities?
The study results indicate that the effects would not be uniform across crops and the eight counties in the Sacramento Valley.
In most regions and for most crops, a cut in irrigation water would cause a modest acreage reduction of up to 3%.
Overall crop-revenue losses for core regions would total $8 million while the loss for the entire Sacramento Valley would be $11 million.
About 80% of those losses would take place in poorer counties that depend most heavily on agriculture, and particularly on rice.
However, in response to surface-water reductions, farmers and others would mitigate their losses by making adjustments such as conserving water, changing cropping patterns or implementing new technologies.
W e all know that water is important.
In particular, water is an essential input for farm production, and California farmers have faced some severe shortages.
As water becomes more scarce, farmers act to minimize their losses by adopting water-conserving technologies, shifting from more water-intensive crops to less water-intensive crops, or increasing their reliance on groundwater.
These agricultural effects translate through the rest of the economy.
This paper analyzes the effects of reduced irrigation water supply on the economies of the Sacramento Valley region.
The specific economic variables examined are changes in acre allocations, farm revenues and general economic health of the county, including personal income and employment.
The study area includes Butte, Colusa, Glenn, Sacramento, Sutter, Tehama, Yolo and Yuba counties.
All these counties have large farming industries and, except for Sacramento and Yolo counties, agriculture is a dominant industry.
The importance of agriculture throughout the region underscores the importance of irrigation water supply.
Reducing the supply of irrigation water will be felt first at the farm.
In response to less available and probably more costly water, farmers alter their production patterns by adjusting their input use and output production.
Fewer acres cropped and lower farm revenue reduce the region's commercial activities and overall county personal income.
By calculating these "multiplier effects," we trace the impact of potential irrigation water reductions through to the broader regional economy.
Although some calculated impacts, such as on crop acreage and county revenue, are in the single-digit percentages, such declines can have broad economic implications for an entire region.
Economy of Sacramento Valley
 The eight Sacramento Valley counties contain almost 7% of the state's geographic area and 5% of its population.
The population is denser in the two more urban counties, Yolo and Sacramento.
These counties also domi-
 nate the region's economy.
Personal income in Sacramento County accounts for 70% of the Sacramento Valley's total personal income, $31 billion, and together with 10% for Butte County and 9% for Yolo County, accounts for almost 90% of the Valley's total personal income.
Colusa and Glenn counties account for only 1% each, the lowest share.
personal incomes ranking 56th and 57th out of 58 counties.
Wide variations in per capita personal income also exist between counties.
Although per capita personal incomes of all eight counties are below the state average of $21,348, Sacramento and Yolo counties closely follow the state level.
The rest of the counties fall between 60% and 90% of the state's average.
In fact, Tehama and Yuba counties are among the poorest in California with per capita
 From the perspective of our study, it is useful to know each county's economic reliance on agriculture.
For this measure, the sales value of farm products is calculated as a ratio of personal income in that county.
Colusa and Glenn counties, with shares of 54% and 46%, show the largest relative scale of farm economy and Sacramento County, with 1%, the lowest share.
The rest of the counties range between 6% and 17%.
In general, the counties characterized by higher agricultural shares in their personal incomes are the lower per capita personal income counties.
Therefore, any disruption of agricultural production may have relatively greater impacts on the economies of counties that rely heavily on agriculture.
Crop production and irrigation
 The Sacramento Valley is endowed with natural water resources.
The sur-
 TABLE 1.
Water use by source and overall water reduction under a 25% surface-water cut and 10% maximum groundwater increase
 Water use in 1992
 Total water	Groundwater	Surface water	hypothetical scenario*
 1,000 aft	1,000 af	% share	1,000 af	% share	%
 Region 2: Far North	543	396	0.73	147	0.27	0.0
 Region 3: Northwest	1,234	402	0.33	832	0.67	13.6
 Region 4: Sacramento River	958	304	0.32	654	0.68	13.9
 Region 5: Northeast	2,040	900	0.44	1,140	0.56	9.6
 Region 6: Yolo-Solano	1,029	634	0.62	395	0.38	3.4
 Region 7: Southeast	651	269	0.41	382	0.59	10.5
 Region 8: Sac-San Joaquin 1,124	943	0.84	181	0.16	0.0
 Our analysis of a hypothetical surface-water reduction utilizes an economic simulation model based on past behavior and profit-seeking by farmers.
We consider a scenario of an arbitrarily chosen 25% cut in surface irrigation water to which one response is a 10% increase in groundwater use.
Finally, the time period considered in our model to adjust from one equilibrium to another is regarded as an intermediate run with the length of 2 to 3 years.
*Numbers represent the impact of reducing surface water by 25% and increasing groundwater by 10%.
For regions 2 and 8, zero reduction is shown because 10% of groundwater is more than 25% of surface water.
+Acre-feet.
Source: DWR 1994, with reported aggregate numbers constructed by authors.
TABLE 2.
Acreage response to a 25% cut in surface-water availability
 Region 2	Region 3	Region 4	Region 5	Region 6	Region 7	Region 8
 Far North	Northwest	Sac.
River	Northeast	Yolo-Solano	Southeast	Sac.-S.J.
Pasture	-1.2	-27.2	-9.7	-0.05	-13.6	-6.9	0.5
 Alfalfa hay	of	-4	-0.8	1.4	-2	-0.7	0.3
 Sugarbeets	-0.1	-1	-0.6	0	-0.6	-0.3	0
 Nongrain field crops*	-0.5	-2.7	0.6	2.4	-1.9	0.1	-0.3
 Rice	-0.4	-4	-3.1	-1.1	-2.2	-1.4	-0.1
 Vegetables	0	-0.1	0	0.1	-0.1	0.04	0
 Tomatoes	-t	-0.6	-0.2	0.2	-0.4	-0.1	0.01
 Fruits, nuts	-0.6	-0.3	-0.1	0	-0.2	-0.1	0
 Small grains#	-	-0.6	6.3	8.5	-1.9	2.4	-0.4
 Subtropical orchards	0	-0.2	-	0.01	-	-	-
 Total	-0.4	-3.1	0	0	-2.1	-2.5	0
 *Nongrain field crops include field corn, dry beans, oilseeds and miscellaneous hays.
t"0" means no change; means not relevant or no production.
Small grains include wheat, barley, etc.
Subtropical orchards include kiwifruit and olives.
rounding mountains and its five major rivers provide abundant water supplies.
With these natural advantages, this area has developed major agricultural industries.
The Sacramento Valley grows a wide variety of crops including the two most important, rice and orchard crops , as well as wheat, alfalfa hay and vegetables.
Rice.
Rice accounts for almost 30% of the crop acreage and provides 25% of total crop revenue in the Sacramento Valley.
Except for Tehama and Sacramento counties, the Valley is one of the nation's major rice-producing areas with more than 90% of California's rice land.
The rice crop is the single largest irrigation water user in the state, and also the most intense user on a per-acre basis.
Rice uses 6.7 acre-feet while some crops such as grapes use as little as 1.3 acre-feet.
Orchards.
Orchards account for 22% of all crop acreage in the Valley.
The economic significance of orchard crops is substantial in all counties.
The farm revenue share of orchard crops ranges from 91% in Tehama County to 16% in Yolo County, with an overall 44% share in the Sacramento Valley.
Vegetables.
Vegetables, which supply 18% of the Sacramento Valley's crop revenue, are economically important in Colusa, Yolo and Sutter counties.
Yolo County, the most important vegetable producer in the Valley, receives more than 50% of county crop revenue from vegetable production, primarily from processing tomatoes.
Agriculture in the Sacramento Valley is relatively more irrigationintensive compared with the rest of the state's farmland, accounting for about 30% of the state's entire agricultural water use over roughly 23% of its total irrigated crop area.
Irrigation water is supplied to the Sacramento Valley mainly from five sources :
 Groundwater supplies almost half of the irrigation water in the Sacramento Valley.
Local surface supplies, including natural rainfall and captured runoff, are the second largest source.
To identify the water sources in the Valley, we use seven hydrologic regions, as defined by the California Department of Water Resources .
Groundwater and local supplies are the major sources for almost all regions.
The CVP and state project deliveries are relatively less important, except for region 5, which receives all its water supply from this state source.
These five supply sources are further combined into two broadly defined sources, surface water and groundwater.
These sources supply 51% and 49%, respectively, of the Sacramento Valley's irrigation water.
Our model of a 25% cut in surface water first alters the way farm resources are allocated among competing crops.
Importantly, cropland is reallocated and irrigation water is redistributed in order to minimize the reduction in profits.
To investigate these links, we adopted the Central
 Valley Project Model  that was initially developed by DWR for such analyses.
This model is based on an optimization technique known as positive mathematical programming.
The most important aspect of the PMP technique is that it allows marginal conditions to vary while average conditions calibrate to the base-year data.
In other words, PMP uses the observed acreage allocation to derive a net revenue relationship that has a decreasing return per acre as the crop acreage expands in a given region.
This decreasing return calculation is based on what we know from experience to be actual returns in this region.
Decreasing crop profitability is mostly caused by the decreasing availability of quality land.
The model assumes that farmers are fully aware of land effects and that they allocate crops to maximize expected profits from a farm.
This changing profitability is contrasted to other optimization models that assume a fixed profitability.
The model used for our analysis consists of an objective func-
 Orchards account for about one-fifth of the crop acreage in the Sacramento Valley, but are not expected to cause major revenue losses following an irrigation water cut.
tion, resource constraints and an irrigation technology equation.
The objective function maximizes the sum of net producer revenue and net consumer benefits.
Net revenue is defined as total sales revenue minus irrigation costs and other variable costs.
Resource constraints consist of two sets, constraints on total irrigation water available and constraints on total cropland available.
A variety of crops are aggregated into 10 categories.
Because of their dominance and economic importance, individual crops such as rice and tomatoes are separated out as individual categories.
Water transfers.
The model allows water transfers within a region, but allows no transfer across the region boundary.
These regions are relatively homogeneous, but may include several water districts and parts of more
 than one county.
In reality, water is in general not fully transferable within a local region and may be partly transferable across regional boundaries.
While our two assumptions on transferability may be offsetting, we think the economic impacts may be underestimated slightly due to our configuration of a region that encompasses many water districts.
Water trading is also an important assumption.
Zilberman et al.
examined the economic impact of water cuts in the Central Valley under the scenario of water trading and showed that the economic loss due to a water cut can be reduced more than 50%.
Efficiency improvements.
The analysis allows for the fact that farmers can adjust to a water shortage by increasing efficiency of their irrigation systems but only at a significant cost.
Irrigation systems in the Sacramento Valley have been steadily improved in recent years, and the model assumes that additional gains are possible and would be made if water were even more scarce.
In our model, farmers respond to the water cut by adjusting irrigation-systems costs and associated applied water or irrigation efficiency.
However, these two water-associated inputs are related through a technical constraint, a constant elasticity of substitution isoquant that governs the trade-offs between system costs and water efficiency.
Subject to this constraint, farmers choose water-related inputs  to maximize their profits.
Prices.
Output and input prices are treated as constants.
Possible price effects of changes in crop output resulting from the 25% cut in water supply are not included.
For example, even though the study area produces much of the national output of japonica rice, projected effects on global and local rice prices are expected to be small because supply shifts are limited to only 1% or 2%.
The consequence of the constant price assumption in our application is that net consumer effects are quite small.
CVPM regions.
The CVPM is based on geographical units, called CVPM regions, that are configured by DWR in accordance with water distribution channels and the construction of DWR's water data.
The Sacramento Valley includes:
 Region 2, Far North.
Region 3, Northwest.
Region 4, Sacramento River.
Region 5, Northeast.
Region 6, Yolo-Solano.
Region 7, Southeast.
Region 8: Sacramento-San Joaquin.
Scenario.
In our model, we hypothesize the following water-reduction scenario.
Surface water  is reduced by 25%, but this reduction is accompanied by an increase in groundwater use by a maximum of 10% from 1992 levels.
We chose 1992 as a base year because  cuts in irrigation water represent policy options that may be more likely considered and adopted during the drought periods, and  1992 represents the most recent drought year.
One reaction to a surfacewater cut may initially be increased use of groundwater.
However, avail-
 ability of groundwater for further pumping is limited.
In order to reflect this situation, the scenario allows the additional supply of groundwater but is limited to a maximum of 10%.
We believe our 10% assumption is reasonable, but it may exclude the situation that prevails under a severe extended drought  considers an alternative base period.
Altering the base period causes no major changes in results.
Model responses to reductions
 In our model, each region responds to the surface-water cut in an optimal way depending on its water situation and pattern of agriculture.
In general, there are three ways that a farmer can respond.
First, the farmer can alter the crop mix, toward a higher proportion of less water-intensive crops or higher value crops.
Second, the farmer can apply less water.
Third, the farmer can make an investment in technology that improves water efficiency.
These responses are all aimed at minimizing the reduction in farm net income resulting from the irrigation water cut.
Our model allows all three options and finds a combination of responses that minimizes the net income loss.
Table 2 presents our model results on the changes in acreage under the 25% water-cut scenario.
Some effects are dramatic.
In the Northwest region, irrigated pastureland falls by 27%.
There are also cases where acreage increases.
In most regions and for most crops, a cut in irrigation water causes an acreage reduction of up to 3%.
However, this rate of reduction seems to be relatively modest, given the 13.6% water cut.
Farmers are, therefore, likely to respond to a water cut mainly by adjusting their cropping patterns, rather than retiring acreage.
Among all crops, pastureland has the largest proportional acreage cut.
Crops such as vegetables and orchard crops, with high value per unit of water, experience little acreage reduction.
Furthermore, increases in area planted
 tend to occur more often with field crops and small grains that require relatively little water.
These adjustments are consistent with profit maximization.
When there is a constraint placed on input, in this case water, production tends to shift from more water-intensive crops to less waterintensive crops.
Our model also allows for an adjustment of irrigation systems.
As surface water becomes scarce, farmers improve irrigation systems, increase water efficiency and apply less irrigation water.
For most crops, the optimal input mix is higher systems costs with lower water applications.
Among all crops, rice shows the largest proportional increase in water-systems costs, simultaneously with the substantial cut in applied water per acre.
The impact of the surface-water reduction depends on the region's groundwater availability.
As expected, improvement in irriga-
 tion systems is more pronounced in regions 3, 4, 5 and 7 where surface water is a more important source than groundwater, while smaller adjustments are realized in regions that rely more heavily on groundwater.
The Far North and Sacramento-San Joaquin regions rely heavily on groundwater in their irrigation water supplies.
This implies that the effect of the 25% surface-water cut in these regions is relatively small and we may expect smaller impacts on agriculture than in other regions.
We do not present regional farmrevenue for effects by crop here, but the major revenue loss in most counties occurs with rice; the Northwest region loses $4.2 million of rice revenue, and regions 4, 5 and 6 also experience large losses.
As expected, vegetable, fruit and nut revenues are harmed the least by the surface-water cut across regions, and in some cases revenues actually increased for these crops.
TABLE 3.
Percent changes in water-related variables in response to a 25% cut
 Alfalfa	Sugar-	field	Vege-	and	Small	tropical
 Pasture	hay	beets	crops	Rice	tables	Tomatoes	nuts	grains	orchards
 Appl.
water	-1.1	-1.3	0.5	-0.9	-1.2	0.4	-	-1.1	-1.4	-1
 Region 2	IS cost	2.1	2.6	-1	1.7	6	-1	-	2.4	5.1	2.4
 Far North	Water effi.1	1.1	1.3	-0.5	0.9	1.2	-0.4	-	1.1	1.4	1.1
 W-rel costs	-0.3	-0.2	-0.2	0.2	-0.6	-0.3	-	0.8	3.2	0.9
 Appl.
water	-4.5	-10.3	-6.5	-7.4	-10.9	-9.6	-7.2	-9	-6.6	-8.8
 Region 3	IS cost	9.4	23.9	16.1	15.8	64.3	28.2	20.4	24	29.6	24.1
 Northwest	Water effi.
4.7	11.4	7	8	12.3	10.6	7.7	9.8	7	9.7
 W-rel costs	-0.7	0.9	5.8	4	3	11.6	5.8	10.1	19.7	11.2
 Appl.
water	-21.9	-22.4	-13.1	-15	-15.4	-19.7	-14.6	-16	-5.4	-
 Region 4	IS cost	64.4	67.4	41.4	41	97.6	74.4	52.9	51.2	23.2	-
 Sac.
River	Water effi.
28	28.8	15.1	17.7	18.2	24.5	17	19	5.7	-
 W-rel costs	17.9	24.3	26.4	22.7	8.5	48.4	30.1	34.4	18.4	-
 Appl.
water -18	-17.9	-10.7	-11.9	-15.4	-15.7	-11.6	-14.6	0.3	-14
 Region 5	IS cost	48.5	48.7	30.4	29.2	97.6	53.3	38.1	45	-1	43.7
 Northeast	Water effi.
21.9	21.8	11.8	13.5	18.2	18.5	13.1	17.1	-0.3	16.3
 W-rel costs	10.4	14.5	17.9	14.5	6	32.4	19.7	28.5	-0.8	28.9
 Appl.
water	-3.5	-6	-3.8	-4.3	-6	-5.5	-4.2	-5.2	-5	-
 Region 6	IS cost	7.1	12.9	8.6	8.5	32.5	14.8	10.9	12.7	21.5	-
 Yolo-Solano Water effi.
3.6	6.4	4	4.5	6.4	5.8	4.3	5.5	5.3	-
 W-rel costs	-1.2	-1	2.1	1.1	-2.9	4.7	1.9	4	13.4	-
 Appl.
water	-9.2	-10.1	-6	-7	-11.2	0.5	-6.3	-5.9	-4.5	-
 Region 7	IS cost	20.6	23.4	15	14.9	62.1	-1	19.2	16.4	17.1	-
 Southeast	Water effi.
10.1	11.3	6.4	7.6	12.6	-0.5	6.8	6.3	4.7	-
 W-rel costs	1	2.9	7.6	6.1	0.5	-0.3	9.2	11	12.5	-
 Appl.
water	-0.1	-0.1	0	0	0.2	0.4	0	0	-0.3	-
 Region 8	IS cost	0.2	0.1	0	0	-1	-1	0	0	0.9	-
 Sac-S.J.
Water effi.
0.1	0.1	0	0	-0.2	-0.4	0	0	0.3	-
 W-rel costs	-0.1	0	0	0	0.1	-0.3	0	0	0.5	-
 *For each region, the values reported are % changes in applied water , irrigation-systems costs
 , water efficiency  and water-related costs.
+Measured as a ratio of evapotranspiration to applied water per acre.
Across our core area, regions 2 through 5, the major losses were seen in rice, field crops and pastureland.
Overall crop-revenue losses for these core regions amount to $8 million while the loss for the entire Sacramento Valley is $11 million.
More than three-quarters of total revenue losses occur in rice.
The loss in farm revenue is mitigated by the adjustments farmers and others make in response to surface-water reductions.
Importantly, water is moved to its highest valued use and water-use efficiency is improved to maximize net farm revenue.
The result is a smaller percentage decline in farm revenue than the 25% cut in surface water.
Finally, it is worth noting that farmland values are closely tied to net revenue changes from production.
Even though further discussion on farmland value is beyond our scope, with relatively active land markets, land prices should move together in proportion to changes in the net income stream.
We now broaden our focus from the agricultural sector to the overall economy by examining how the declines in farm revenue may trigger a further decline in revenue in the Sacramento Valley.
We quantitatively evaluate the effects of a cut in irriga-
 tion water on the overall local  revenue as well as the effects on the local job market using income and job multipliers.
The economic assessment is made at the county level by first allocating regional agricultural effects across counties.
The conversion from region to county is based on crop acreage, with a region's acreage being distributed among the counties of which it is comprised.
We developed conversion acreage formulas from region to county based on acreage data collected by California Agricultural Statistics Service, other crop maps, and county agricultural commissioner reports.
Revenue effects include revenue generated  over the entire local economy due to agricultural revenue changes that are measured at the farm-gate level.
This includes revenue from packing and shipping, brokerage, and retail activities as well as farm-input-industry activities.
Multiplier effects differ across crops, depending on the extent of postharvest activities and whether or not the product is processed.
For example, fresh produce such as fruits and vegetables has relatively large income multipliers compared to feed grains such as corn and wheat, because fresh produce re-
 quires additional local packing and shipping.
Activities that take place outside the county are not included in our multiplier impacts.
For example, economic activity generated from crop output in another county is not shown in the revenue totals used here.
This suggests that the overall multiplier effect in the Sacramento Valley is likely to be larger than our estimates.
We used income multipliers developed by Goldman at UC Berkeley.
The multipliers are specific to crops and counties, and take into account various offfarm activities for each crop category as well as the scale of other activities in each county.
They range from 1.2 to 2.5, meaning that a $1.00 change in farm-gate revenue results in a $1.20 to $2.50 revenue change in the overall county economy.
Fruits have the highest multiplier among all crop categories.
Sacramento County tends to have the highest multipliers across almost all crop categories, which may be due to its large economy as compared to other counties and the fact that many farm-related activities occur there.
As expected, aggregate county revenue effects are generally negative.
Under all scenarios, the smallest revenue loss occurs in Tehama County, and the largest OCcurs in Colusa County, which alone makes up almost 32% TOTAL of the total revenue loss for the Sacra16 -687 mento Valley.
Glenn 12 and Yolo counties also 14 -897 experience substantial 10 0 -217 revenue losses.
Rev0 enues from water22 -633 intensive crops such 16 -13,056 as rice, pasture and alfalfa, are reduced by a -17 substantial margin.
-
 TABLE 4.
County revenue effects of a 25% surface-water cut
 Butte	Colusa	Glenn	Sacramento	Sutter	Tehama	Yolo	Yuba
 Pasture	56	-40	-300	-30	-134	7	-262
 35*	-30	-220	-18	-90	5	-177
 Alfalfa hay	32	-180	-167	76	7	-16	-663
 20	-136	-123	45	5	-12	-448
 Sugarbeets	0	-71	-38	-3	-22	0	-83
 0	-48	-27	-2	-14	0	-54
 Nongrain field crops	48	-112	-238	-34	357	-30	-646
 28	-76	-165	-20	229	-23	-425
 Rice	-1,516	-4,879	-3,067	-126	-2,051	-3	-754	-660
 -837	-3,360	-2,100	-63	-1,291	-2	-465	-457
 Vegetables	1	-27	-	-1	57	0	-47
 1	-16	-	-1	32	0	-30
 Tomatoes	-	-143	-	11	-30	-	-466	-	-628
 -	-87	-	5	-17	-	-295	-
 Fruits, nuts	192	-69	-65	9	9	60	-75	36	97
 90	-39	-39	4	5	37	-45	22
 Small grains	277	383	-52	57	701	-21	-334	99	1110
 199	317	-41	39	522	-16	-252	69
 Subtropical orchards	2	-	-6	-	1	-3	-	1	-5
 1	-	-4	-	-	-2	-	1
 Total	-908	-5,138	-3,933	-41	-1105	-6	-3330	-472	-14,933
 -464	-3,475	-2,719	-11	-619	-13	-2191	-328
 *Nonbold numbers are revenue changes at the farm-gate level that induced the county-level changes.
Revenue from rice decreases the most, accounting for almost 90% of total revenue losses.
This occurs in part because rice tends to be particularly dependent on surface water and be-
 cause it is the most important crop in most counties.
Rice revenues have the largest share of revenue in Butte, Colusa, Glenn, Sutter and Yuba counties.
However, the 90% share is a very high ratio given that rice contributes only 16% of total crop revenue in the Sacramento Valley.
This implies that a reduction in surface irrigation water affects rice production much more severely than other crops, and the economic impact would be greater in counties that have more intense rice production.
The major rice-growing counties of Colusa and Glenn are the hardest hit.
However, Yolo County is not among the major rice-producing counties but its total revenue losses are almost as high as in Glenn County.
This is because Yolo County has high total crop revenue compared to other counties.
Unlike other counties, Yolo County's losses are spread among various crops.
Lee et al.
demonstrate that effects are much larger where the percentage water cut is from a "normal" year base and when groundwater substitution does not occur.
In the most extreme scenario, the water cut would cost $46 million in total revenue and more than 300 jobs across the eight counties.
Again the losses are largest in Colusa and Glenn counties.
The largest revenue loss in Colusa County among all scenarios is more than 5% of the county personal income.
To illustrate what the revenue losses mean more broadly, the total revenue effect for each county is calculated as a percentage of the county personal income.
Colusa County is the hardest hit, not only by losing the largest amount of revenue, but also by losing the largest percentage  of personal income.
The next hardest hit was Glenn County.
These two counties have the lowest personal income among all Sacramento Valley counties, as well as the highest economic reliance on agriculture.
For the remaining counties, total revenue effects are
 less than 1% of county personal income.
Agriculture, water and economies
 Each of the counties we examined has a large agricultural industry.
Except for Sacramento and Yolo counties, farming itself primarily irrigated agriculture is the dominant contributor to the local economy.
The importance of agriculture as a primary industry in this region underscores the importance of irrigation water supply.
Results of this study indicate at least three general conclusions.
Adjustments that occur within the agricultural production system in response to reduced water supply are crucial.
These adjustments are generally found by  substituting away from intensive water use by adopting more efficient irrigation technologies, and  switching to crops that use less water or earn more dollars per unit of water.
Our results show that farmers tend to switch away from water-intensive crops such as rice, pastureland or alfalfa to less water-intensive crops such as small grains.
A reduction in water supply results in relatively greater economic impacts on those counties that are more dependent on agriculture.
As expected, revenue losses are highest in absolute and relative terms for those counties with more agricultural output.
Colusa County is one of the most reliant on agriculture in its economy ; therefore, its economy loses the largest overall amount of revenue as well as
 Yolo County receives more than half of its crop revenue from vegetables, primarily processing tomatoes, above.
Orchard crops such as stone fruits, olives, walnuts and almonds, below, are among the most important crops in the Sacramento Valley.
Growers would adjust to a loss of irrigation water by adopting more efficient technologies and switching to less waterintensive crops.
the largest percentage of personal income, exceeding $5 million per year, or about 1.6%.
The next hardest hit is Glenn County, at about 1% of county personal income; Glenn County is next to Colusa County in its reliance on agriculture in its economy.
Counties that depend heavily on agriculture for their economic livelihoods are also the poorest in the Sacramento Valley.
All of the counties that have large agricultural industries tend to have lowest per capita personal incomes.
This suggests that the counties with the least economic resources would be hardest hit if the water supply were reduced.
The second reason is to help prevent extended harvest delays because of rain.
If the field is kept at field capacity, any rain can cause delays and lead to soil compaction from harvest equipment.
Irrigation plots in the above photo are receiving a pre-plant irrigation which will wet the soil profile to a depth of six feet to field capacity.
IRRIGATION AND NITROGEN FOR COTTON
 a yield surface and optimum combinations on a Panoche loam soil
 D.
W.
GRIMES L.
DICKENS W.
ANDERSON H.
YAMADA
 Studies on Panoche clay loam soil showed the effectiveness of irrigation water and nitrogen fertilization for cotton to be highly interdependent.
A lint yield equation was calculated to determine the combination of irrigation water and nitrogen that would minimize costs for specific yield levels and input cost conditions.
T MANAGEMENT OF IRRIGATION water and nitrogen fertilization influences cotton production on any soil in the San Joaquin Valley.
In past years most of the data obtained have come from studies where only one of the two factors was included as a variable treatment, while the other was held at some presumably "optimum" level.
However, developments in economic-agronomic studies have recently demonstrated the feasibility of using empirical crop yield equations which facilitate the use of production economics principles.
These principles greatly assist in the determination of optimum use levels and least-cost combinations of resources used in production.
During 1966 an experiment was conducted on a soil classified as Panoche clay
 loam at the West Side Field Station to determine the influence of different irrigation and nitrogen fertilization levels on the production characteristics of two varietal strains of Acala cotton.
Irrigation 11-Pre-plant + 7/22-23  Total water applied in addition to pre-plant.
12-Pre-plant + 6/10  + 7/22  Total water applied in addition to pre-plant.
Is-Pre-plant + 6/10  + 7/1  + 7/15  + 8/1  + 8/22  Total water applied in addition to pre-plant.
Nitrogen Nitrogen rates were 0, 50, 100, 200, and 400 pounds of nitrogen per ocre.
Irrigation water was measured on each plot from gated pipe.
Sufficient water was added at the pre-plant irrigation to wet the soil to field capacity to a minimum depth of 6 ft.
Seasonal irrigations  rewet the soil to the 6-ft depth.
Nitrogen was side-dressed as ammonium sulfate on May 25.
Because the varietal strains  did not differ appreciably in their yield response to the imposed treatments, data from both varieties were composited to better evaluate the effects of irrigation and nitrogen fertilization.
An empirical yield equation was determined from the data obtained in this study and is shown graphically.
The surface "grid" shows the calculated lint yield associated with any combination of seasonal irrigation water and nitrogen fertilization-within the amounts of these factors included as treatments in the study.
Additional increments of seasonal irrigation water resulted in proportional or "straight line" increases in cotton lint yields at given levels of nitrogen fertilization.
For example, where no nitrogen was added, increasing the seasonal irrigation water from 11 to 27.5 acre-inches increased lint yields from 553 to 711 lbs of lint per acre, an over-all increase of 158 lbs of lint per acre.
Where plots received 300 lbs of nitrogen per acre, increasing the seasonal water from 11 to 27.5 acre-inches increased yields from 850 to 1300 lbs of lint per acre, or an over-all increase of 450 lbs.
of lint per acre.
From these data it is evident that, on soils of this nature, a maximum yield response to increased water availability is possible only when adequate nitrogen is also supplied.
Within the treatment range of nitrogen additions, the highest yield increase per unit of nitrogen was obtained at the lowest level of added nitrogen.
Where only 11 acre-inches of seasonal irrigation water were added, the highest yield was obtained when 250 lbs of nitrogen was
 Graph 1.
Yield surface for lint yields as influenced by seasonal irrigation water and nitrogen fertilization.
Graph 2.
Yield surface showing isoquants or the combinations of water and nitrogen required to produce a specific yield.
applied.
At this level of N-fertilization, an increase of 315 lbs of lint per acre over plots receiving no additional nitrogen occurred.
On the other hand, where 27.5 acre-inches of water were added, the maximum yield resulted from the addition of 332 lbs of nitrogen per acre.
This level of fertilization increased lint yield by 594 lbs per acre over plots receiving no additional nitrogen-demonstrating that the yield level obtained from either additional irrigation water, or nitrogen, is dependent upon the level of availability maintained for the other factor under consideration.
The studies show that the production of a given yield is possible by several different combinations of irrigation water and applied nitrogen  In this illustration the "grid" of the yield surface in graph 1 is replaced by a series of curved lines connecting the many different combinations of irrigation water and nitrogen which produced a given indicated level of lint.
For example, the 1000.
lb-per-acre yield level can be obtained from the combination of 27.5 acre-inches of water and 90 lbs of nitrogen per acre, from the combination of 16.3 acre-inches of water and 270 lbs of nitrogen per acre -or from an infinite number of combinations intermediate between them.
The lines connecting points of equal yield are called isoquants and their calculation makes it possible to determine the combination of water and nitrogen at which a designated yield can be obtained at the lowest cost to the producer.
The different combinations of water and nitrogen given by the curved lines for a specific or constant yield are more
 easily seen in graph 3.
The fact that a given yield can be produced by different combinations of water and nitrogen can be thought of in terms of substitution of one factor for another.
There is, of course, no substitution in terms of the chemical or physiological role of these factors; nevertheless, there is substitution in terms of lint yield.
As shown in the graph, increasing amounts of nitrogen are required to "substitute" for a given quantity of water at lower levels of water addition.
Conversely, at lower levels of nitrogen fertilization, more water is required to "substitute" for a pound of nitrogen while maintaining a constant yield.
The yield equation resulting from this study does not have a determinate solution in terms of establishing an optimum quantity of irrigation water.
Previous studies have shown that maximum or near-maximum lint yields were attainable in this area by the addition of 25 to 30 acre-inches of water during the season  Conditions during the 1966 season were such that the water requirements were increased above normal, and the addition of 27.5 acre-inches was therefore insufficient to establish an optimum level with certainty.
Cost-minimizing combinations of irrigation water and nitrogen for specific yield levels and price conditions are shown by the straight diagonal lines in graph 3.
These lines are called isoclines and are obtained from the yield equation and prevailing cost of irrigation water  and nitrogen fertilizer.
Assuming a nitrogen cost of $0.12 per pound , and irrigation water costing $2.50 per acre-inch ($30.00 per acre-
 OPTIMUM RATES AND COMBINATIONS OF WATER AND NITROGEN FOR SPECIFIED YIELD AND COST CONDITIONS
 Yield	Price per unit	Ratio	Optimum quantity
 Pounds	of lint	Acre-inch	Pound of	Pn	Acre-inches	Pounds	of
 per acre	of water	nitrogen	Pw	of water	nitrogen
 1200	$1.68	$0.12	0.072	27.4	192
 2.50	"	0.048	25.7	222
 "	3.33	"	0.036	25.0	240
 "	4.16	"	0.029	24.6	250
 1100	1.68	"	0.072	23.7	177
 2.50	"	0.048	22.0	205
 "	3.33	"	0.036	21.3	222
 "	4.16	"	0.029	20.9	232
 1000	0.83	"	0.145	25.4	108
 "	1.68	"	0.072	19.7	162
 "	2.50	"	0.048	18.0	188
 "	3.33	"	0.036	17.3	205
 4.16	0.029	17.0	215
 Graph 3.
Yield isoquants and isoclines.
The isoclines connect points of equal slope on the isoquants and show combinations of water and nitrogen having the least cost for different price combinations.
foot), a Pn/Pw ratio of 0.048 is obtained, making the diagonal line designated by this ratio.
Starting at the bottom and following the line upward and to the right, the line passes through levels of increased lint production.
At the 1100-lb lint-yield level, the cost-minimizing combination of 22 acre-inches of water and 205 lbs of nitrogen per acre is indicated by the connecting dashed lines.
At the 1200 pound lint yield level, the cost-minimizing combination  of 25.7 acre-inches of water and 222 lbs of nitrogen is illustrated for the same prevailing cost conditions.
The table shows a series of optimum rates and combinations of water and nitrogen for yield levels of 1200, 1100, and 1000 lbs of lint per acre for several different cost conditions.
The Pn/Pw ratios were obtained by varying irrigation water costs.
However, the ratios may be obtained by varying either the cost of water or nitrogen.
The optimum amounts of nitrogen shown in the table are somewhat greater than those normally recommended for these soils.
Cotton grown in 1966 was preceded by safflower in 1965 with minimal fertilization; therefore, very little nitrogen carryover from the previous application was in evidence.
Previous studies have shown that cotton may grow excessively vegetative or "rank" on many soils when more than adequate amounts of either water or nitrogen are added.
The "rankness" may depress yields by creating an unfavorable fruiting pattern.
Under the soil and climatic conditions of this study, yields were depressed only by relatively high rates of nitrogen addition.
These investigations are being continued with some changes to place greater emphasis on obtaining a more generalized yield equation covering a greater variety of soil types.
Donald W.
Grimes is Assistant Water Scientist, and Lamar Dickens is Laboratory Technician, Department of Water Science and Engineering, University of California, Davis, and at the U.S.
Cotton Research Station, Shafter.
Wayne Anderson and Hidemi Yamada are Laboratory Technicians, Department of Agronomy and Field Stations, University of California, Davis, and at Shafter and the West Side Field Station, Five Points, respectively.
Research from which this progress report was prepared was supported in part by a grant from the California Planting Cotton Seed Distributors.
Adult western flower thrips, Frankliniella occidentalis Perg.
Cloth cages enclosing sesame flowers, into which thrips were introduced.
Studies of both the flower thrips and lygus bug indicate that they caused no serious sesame plant injury, reduction of pod set, or seed loss at the populations existing under the conditions of these experiments.
It appeared that much larger population densities of these pests would be necessary to contribute to the poor pod set and low yields observed recently on untreated field plants.
The green peach aphid caused up to 27% seed loss when present in moderate to large numbers, however.
The aphid was effectively controlled by use of two applications of either oxydemetonmethyl or endosulfan.
T HE PREVALENT lack of pod set and low yields experienced in the production of an indehiscent strain of sesame  prompted this evaluation of the effect of a few pest insects on this plant in California.
A preliminary survey made in 1963 showed that the most plentiful insect pests were lygus bugs, Lygus hesperus Knight, western flower thrips, Frankliniella occidentalis , and the green peach aphid, Myzus persicae  Later in the growing season, a striped flea beetle, Systena sp.
nr.
bitaeniata Lec.
was present.
The ability of these pests to damage sesame was studied the following year.
During 1964, flower thrips  were introduced onto flower buds enclosed by fine-mesh cloth cages  at 5, 10, and 20 adults per bud.
Thrips were introduced July 28, and produced young for the next 13 days while the flowers were blooming.
A maximum of 90 nymphs were produced on one flower, as determined by hand counting an extra set of caged flowers to which thrips had been
Subsurface Drip Irrigation in the Southeast
 Subsurface drip irrigation is the practice of installing drip irrigation  below the ground surface.
The potential exists to use SDI below planting and tillage operations even in standard row-crop production systems.
The advantages of SDI include the potential for more precise management of water near the roots of crops, minimizing losses due to evaporation, installation of systems in fields with irregular shapes, allowance for spoon-feeding nutrients  and zoning of irrigation areas based on limited water supplies and differing water needs of soils and crops.
What makes the humid and sub-humid region different from other regions  where SDI has been used for many years?
Humid and sub-humid regions must deal with significant rainfall and temporary excess soil-water conditions that are not typical of arid and semi-arid regions.
The site selection, soils, tillage requirements and management of moisture-related problems  may be quite different from those in arid regions.
Several of the most important considerations for SDI are the same for any type irrigation system; however, some additional considerations are necessary when using SDI in humid and sub-humid areas.
SDI systems are not cheap to design, install and maintain, especially if the entire water supply system must also be developed.
The potential for row crops or other non-specialty crops to help pay for the system needs to be carefully assessed before a decision is made to invest in SDI.
Selected SDI systems have been shown to function for long periods ; however, an increased level of management and care is required if the system is to be in place and functional for a long period of time.
Water supply: quantity and quality
 Sufficient water from ground, surface or reuse sources must be available to meet the required pumping rates for the system and total supply needs for an irrigation season.
Pumping capabilities  should be based on the peak water demand for the highest water-use crop expected to be grown over the system and the flushing requirements.
The water supply should be free of particulates and biological materials.
Source water pH that is slightly acidic is preferred since higher pH levels  tend to precipitate minerals within the irrigation system.
Basic filtering is usually required for any water supply used in SDI systems.
If the water supply does not meet the criteria above, advanced filtering or even chemical treatment may be required because of the high potential for clogging of drip emitters.
SDI systems can be designed for wastewater disposal/treatment; however, proper care must be taken to include proper filtration and chemical injection treatment to prevent emitter plugging.
Irrigation systems require an energy source to pump water and maintain the water pressure.
An electrical, diesel, natural gas or other energy source is selected based on availability, cost and accessibility; however, SDI systems do have operational controllers that may be less desirable for use with a fossil fuel-based power system because the controllers may not be on all the time.
Like other drip irrigation systems, SDI systems can be zoned to reduce the pumping rate, pump and power unit size, and energy requirements.
As a result, the rate of energy use is lower; however, the time of operation will be extended due to the low water-application rates.
SDI systems do not have strict soil restrictions, except under the condition that a plow pan or other semi-impervious zone is located near the drip emitters.
The desired distribution of water can be negatively affected by semi-impervious zones above or beside the emitters.
There is some potential for benefit if the semi-impervious zone is below the emitters by reducing potential deep seepage and encouraging lateral movement of water.
Soils that are prone to develop plow pans can use SDI and reduced  tillage.
Cropping operations that require periodic soil turning can quickly destroy an SDI system that is too shallow.
Soils that typically require deep sub-soiling are less amenable to subsurface drip irrigation.
Under conditions where soils must be deep sub-soiled, the depth and location of the SDI laterals must be mapped extensively so the lateral lines are not damaged.
Very sandy soils may have a limited capillary  movement of water from the emitters that may result in difficulties to provide sufficient amount of water during germination or plant establishment.
A supplemental irrigation system may be necessary to assure plant establishment if rainfall is insufficient during the plant-establishment period.
If the topography is complicated, SDI systems are available with pressure-compensating emitters.
These emitters are designed to discharge a similar flow rate as the elevation and slope changes; however, SDI systems require a relatively low operating pressure typical for any drip system.
Significant changes in slope can affect the available pressure to different parts of the field.
High pressures can cause drip lines to rupture, and low pressure can reduce the water output across a portion of the field.
One advantage of SDI systems is they can be more easily adapted to field sizes and shapes when compared to other types of irrigation systems.
Field areas are not always circular  or rectangular  area.
The potential exists for an SDI system to irrigate only the best soils.
One disadvantage of SDI compared to other types of irrigation is that the infrastructure is permanent in the field.
As such, for leased land it may not be economical to install SDI.
Costs for SDI can be high, especially if irrigation lines are placed below each row.
Care must be taken to maintain a consistent depth, spacing and location to reduce the potential for damage from mechanical operations.
The depth of tubing required for crops that have their fruit below the ground  may be too deep for effective early-season irrigation.
What will you need for your SDI system?
Figure 1 shows the essential components of a well-designed SDI system.
Care and maintenance of all these components are essential for long-term and reliable operation.
For additional information on site selection criteria, the reader is referred to Site Selection for Subsurface Drip Irrigation in Humid Areas.
Other Design and Installation Considerations
 Operational system components should be located in an easily accessible area for improved management.
Any components that are to be located above ground should be strategically located away from potential traffic.
All high points in the system should have air relief valves installed.
Designs should include good flushing capabilities for laterals and mains.
For SDI systems to function for a number of years, flushing capabilities are absolutely essential.
There are a number of critical design steps for creating an effective SDI system.
The reader is referred to the document on Design of Subsurface Drip Irrigation Systems in Humid Areas or other similar documents for details.
There are a number of questions that need to be answered before an adequate design can be completed:
 Will the same crop be grown each year, or will crops be rotated?
Do all crops to be grown have similar water use characteristics?
Will the entire field be planted, or will the field be divided into smaller areas of different crops?
Does the field area grade from lighter soils  to heavier soils ?
Will field crops  be grown in rotation to row crops?
Is sub-soiling a part of the production system?
Are nutrient applications a critical part of the production system?
Do you currently use an irrigation system that is not time intensive?
Are you willing to spend more time on maintaining and operating an irrigation system like SDI?
Is your available labor force willing and able to work with a new system that requires more care and effort?
Each of the above questions generates a different set of design parameters from water supply to pumping requirements, location of components, depth of installation, spacing of drip laterals, automation requirements, etc.
Soliciting input from trained personnel with SDI experience is a must if you anticipate using your system for 10+ years.
Installation of the designed system is critical to the performance expectations.
How many times have corners been cut  in hopes of saving installation dollars?
If the design does not take into account specific details of the field site, the designer should be consulted about appropriate modifications.
If connectors or other components are replaced due to availability issues, the system owner should have assurance of the lifespan of these replacement components.
Proper field layout prior to installation, proper equipment for installation to ensure depth precision and permanent marking of buried lines after installation will all encourage a more efficient system.
Timing of installation is one of the most critical factors in humid areas.
Soil water characteristics  during installation are critical.
Installation of an SDI system is similar to a chiseling operation.
If the soil water content is not acceptable for chiseling, it is likely not acceptable for drip installation.
Fall is usually the best time for drip installation because of drier conditions  and sufficient time for soil settling prior to planting.
If you are planning to install your own SDI system, please take time to consult Installation Considerations for Subsurface Drip Irrigation in Humid Areas, check other resource materials and visit with your local irrigation expert and others with SDI experience.
Local Cooperative Extension Service representatives, NRCS personnel and irrigation dealers are good starting points for obtaining recommendations and information.
What irrigation scheduling technique do you expect to use for your subsurface drip irrigation system?
This is one of the first important considerations to encouraging efficient water use no matter what irrigation technique is proposed.
In the humid and sub-humid region, irrigation scheduling is critical because rainfall can greatly influence the water in soils and the need for irrigation.
What irrigation scheduling technique is best for you?
The one you will use.
Whether techniques are weather-based, rely on soil water measurement or use another approach to determine crop water needs, they must meet your management interest and capability.
Since SDI applies water below the ground, soil water sensing approaches seem logical.
Placement of such sensors is critical to ensure proper measurement of the soil water conditions below plants.
SDI systems are not typically limited to a particular time-of-day operation based on evaporation losses.
However, cost-saving energy-management systems may dictate the time when the irrigation system is not allowed to operate.
Chemigation and fertigation are logical approaches to delivering chemicals  and plant nutrients to the root zone of crops through an irrigation system.
Manufacturers' labels should be followed closely to ensure effective application, proper use and system life.
The types of chemicals required for different situations should be understood from the beginning.
SDI has the potential to deliver low fertilizer rates over a long period, thus reducing the potential for leaching losses  and providing appropriate fertilizers when needed by the plants.
Preventative maintenance is a key to system longevity.
Once a problem develops, it is often impossible to correct, especially when the problem is associated with buried drip tubing.
Testing of the quality of the water supply, routine flushing and cleaning of the system  and continuous monitoring of system flow and pressure are essential to proper operation.
Be aware that source-water quality can change during the season and over years, so periodic testing is essential.
The system components described in Figure 1 include a flow meter and pressure gauges.
Maintaining good records of baseline pressures and flow rates for each zone is essential.
Without such records, it is difficult to determine if a problem exists.
Decreased pressures and higher flow rates are indications of possible holes in the irrigation system.
Increased pressure and lower flow rates are indications of possible plugging of emitters.
SDI is a relatively new technology in humid areas.
There is a great deal of research and development in the application of such systems.
Some of these references can be found in the document Introduction to Subsurface Drip Irrigation Applications for Humid and Sub-humid Areas.
If you are considering SDI for your operation, make sure you understand the site, system and management requirements to ensure that your system will be in operation for a long period of time.
Subsurface drip irrigation  technologies have been a part of irrigated agriculture since the 1960s, but have advanced at a more rapid pace during the last 20 years.
In the summer of 1988, K-State Research and Extension issued an in-house request for proposals for new directions in research activity.
A proposal entitled Sustaining Irrigated Agriculture in Kansas with Drip Irrigation was submitted by irrigation engineers Freddie Lamm, Harry Manges and Dan Rogers and agricultural economist Mark Nelson.
This project led by principal investigator Freddie Lamm, KSU Northwest Research-Extension Center , Colby, was funded for the total sum of $89,260.
This project financed the initial development of the NWREC SDI system that was expressly designed for research.
In March of 1989, the first driplines were installed on a 3 acre study site which has 23 separately controlled plots.
This site has been in continuous use in SDI corn production since that time, being initially used for a 3year study of SDI water requirements for corn.
In addition, it is considered to be a benchmark area that is also being monitored annually for system performance to determine SDI longevity.
In the summer of 1989, an additional 3 acres was developed to determine the optimum dripline spacing for corn production.
A small dripline spacing study site was also developed at the KSU Southwest Research-Extension Center  at Garden City in the spring of 1989.
In the summer of 1989, further funding was obtained through a special grant from the US Department of Agriculture.
This funding led to expansion of the NWREC SDI research site to a total of 13 acres and 121 different research plots.
This same funding provided for a 10 acre SDI research site at Holcomb, Kansas administered by the SWREC.
By June of 1990, K-State Research and Extension had established 25 acres of SDI research facilities and nearly 220 separately controlled plot areas.
Over the course of the past 20 years, additional significant funding has been obtained to conduct SDI research from the USDA, the Kansas Water Resources Research Institute, special funding from the Kansas legislature, the Kansas Corn Commission, Pioneer Hi-Bred Inc., and the Mazzei Injector Corporation.
Funding provided by the Kansas legislature through the Western Kansas Irrigation Research Project  allowed for the expansion of the NWREC site by an
 additional 5.5 acres and 46 additional research plots in 1999.
An additional 22 plots were added in 2000 to examine swine wastewater use through SDI and 12 plots were added in 2005 to examine emitter spacing.
Two research block areas originally used in a 1989 dripline spacing study have been refurbished with new 5 ft spaced driplines to examine alfalfa production and emitter flowrate effects on soil water redistribution.
The NWREC SDI research site comprising 19.5 acres and 201 different research plots is the largest facility devoted expressly to smallplot row crop research in the Great Plains and is probably one of the largest such facilities in the world.
Since its beginning in 1989, K-State SDI research has had three purposes: 1) to enhance water conservation; 2) to protect water quality, and 3) to develop appropriate SDI technologies for Great Plains conditions.
The vast majority of the research studies have been conducted with field corn because it is the primary irrigated crop in the Central Great Plains.
Although field corn has a relatively high water use efficiency, it generally requires a large amount of irrigation because of its long growing season and its sensitivity to water stress over a great portion of the growing period.
Of the typical commodity-type field crops grown in the Central Great Plains, only alfalfa and similar forages would require more irrigation than field corn.
Any significant effort to reduce the overdraft of the Ogallala aquifer, the primary water source in the Central Great Plains, must address the issue of irrigation water use by field corn.
Additional crops that have been studied at the NWREC SDI site are soybean, sunflower, grain sorghum, alfalfa and demonstration trials of melons and vegetables.
This report summarizes several studies conducted at the KSU Northwest and Southwest Research-Extension Centers at Colby and Garden City, Kansas, respectively.
A complete discussion of all the employed procedures lies beyond the scope of this paper.
For further information about the procedures for a particular study the reader is referred to the accompanying reference papers when so listed.
These procedures apply to all studies unless otherwise stated.
The two study sites were located on deep, well-drained, loessial silt loam soils.
These medium-textured soils, typical of many western Kansas soils, hold approximately 18.9 inches of plant available soil water in the 8 ft profile at field capacity.
Study areas were nearly level with land slope less than 0.5% at Colby and 0.15% at Garden City.
The climate is semi-arid, with an average annual precipitation of 17 inches.
Daily climatic data used in the studies were obtained from weather stations operated at each of the Centers.
Most of the studies have utilized SDI systems installed in 1989-90.
The systems have dual-chamber drip tape installed at a depth of approximately 16-18 inches with a 5-ft spacing between dripline laterals.
Emitter spacing was 12 inches and the dripline flowrate was 0.25 gpm/100 ft.
The corn was planted so each dripline lateral is centered between two corn rows.
Figure 1.
rows.
Physical arrangement of the subsurface dripline in relation to the corn
 tillage and to match bed spacing to dripline spacing with spacing the studies, was not practical conducted at both locations.
In these dripline dripline it A inches modified apart, ridge-till system on was used in corn production with two corn planted perpendicular harvesting equipment.
Additionally at Garden City, corn available grown with to the driplines in the dripline spacing rows were spacing studies grown a 5-ft wide bed.
Flat planting was used for the rows, 30 confined conventional production practices for each location.
study.
Wheel All corn traffic was was to the furrows.
TARGETED, PRECISION IRRIGATION FOR MOVING PLATFORMS: SELECTED PAPERS FROM A CENTER PIVOT TECHNOLOGY TRANSFER EFFORT
 center pivot irrigation tech transfer
 Center-pivot and lateral-move irrigation systems are used on over 85% of the irrigated area in the U.S.
Great Plains.
Low-energy precision application  from mobile lateral irrigation platforms was first developed in 1978.
Various in-canopy and near-canopy application technologies are widely practiced in the U.S.
Great Plains.
Adding advanced irrigation management technologies to moving platforms can optimize water and energy use.
Uniformity of application is a key performance factor in evaluating moving irrigation platforms.
ABSTRACT.
This article is an introduction to an ASABE Special Collection of ten articles concerning center pivot  technology transfer that appears in this issue of Transactions of the ASABE and in Applied Engineering in Agriculture.
The year 2018 marked the 40th anniversary of research and development of low-energy precision application  for use with CP sprinkler irrigation systems.
Since 1978, researchers, extension specialists, and industry have continued development of multiple technologies that are suitable for mobile lateral irrigation platforms.
A two-year technology transfer effort with funding from the USDA-ARS Ogallala Aquifer Program  was initiated in January 2017 to promote adoption of advanced and efficient irrigation technologies and to highlight recommended practices for mobile irrigation platforms, including both CP and lateral-move  systems.
The articles in this Special Collection address five major topic areas: in-canopy and near-canopy irrigation application from moving platforms, site-specific variable-rate irrigation  and associated sensor technologies for moving platforms, the use of variable-frequency drives  with CP systems, and uniformity evaluations for CP systems.
While these ten articles are not inclusive of all the important advances in irrigation from moving platforms since 1978, they illustrate that continued improvement in irrigation management occurs by combining engineering and agronomic sciences.
Pressurized irrigation from moving platforms is increasing in the U.S.
and will be an important tool for meeting global food and water challenges.
In addition to introducing and summarizing the Special Collection, this article provides additional rationale for the CP technology transfer effort.
Submitted for review in February 2019 as manuscript number NRES 13371; approved for publication as part of the Center-Pivot Irrigation Tech Transfer Collection by the Natural Resources & Environmental Systems Community of ASABE in September 2019.
Mention of company or trade names is for description only and does not imply endorsement by the USDA.
The USDA is an equal opportunity provider and employer.
Keywords.
Center pivot, Irrigation uniformity, Lateral-move sprinkler, LEPA, Linear-move sprinkler, Low-energy precision application, Site-specific irrigation, Sprinkler irrigation, Variable-frequency drives, Variable-rate irrigation, VFD, VRI.
C enter-pivot  and lateral-move  systems are currently the predominant irrigation methods in the U.S..
This is particularly the case in the U.S.
Great Plains , which includes four of the top ten states in terms of irrigated area; an average of 85% of the irrigated area in those four states uses CP systems.
The Kansas and Texas High Plains / Southern Ogallala Aquifer region, as part of the U.S.
Great Plains, is noted for limited and declining groundwater resources  and a relatively high adoption rate of efficient advanced irrigation technologies.
One of the earliest advanced mobile sprinkler irrigation technologies, low-energy precision application , was first studied near Halfway, Texas, by William Lyle and James Bordovsky be-
 Figure 1.
Time series  of the extent of center-pivot  irrigation in the U.S..
ginning in 1978.
Lowpressure CP irrigation, including , low-elevation spray application , mid-elevation spray application , and other variations have become the most widely practiced irrigation methods in the region.
This is due in large part to the suitability of the technologies to the crop production systems in the region, relevant applied research programs, collaborations among research and extension programs and with industry, the effectiveness of cost-share programs, and the willingness of agricultural producers in the region to adopt technologies and best management practices  to adapt to limited water conditions.
From the early work on LEPA that began in 1978, to LESA and MESA, and most recently to the new integrated sensor and control systems mounted on CP and LM systems, research and extension programs that are now affiliated with the USDA-ARS Ogallala Aquifer program  have made important contributions to the advancement of irrigation using mobile platforms.
While low-pressure CP irrigation is widely practiced in the U.S.
Great Plains, applied research continues to refine the technologies and recommendations.
Thus, a CP technology transfer effort was designed to provide opportunities for end-users to hear up-to-date recommendations to aid in their irrigation decisions.
There is a need to improve understanding by non-practitioner audiences (e.g., absentee landlords,
 ag lenders, crop insurance agents, and policymakers) of the most appropriate uses of these technologies, SO this CP technology transfer effort has helped to improve their understanding of the state of the art, considerations for irrigation management, and appreciation for the advances in irrigation technology, management, and efficiency.
Additionally, the CP technology transfer effort provided an opportunity for engineers and scientists to collaborate and synthesize current knowledge into more accessible publications and media as well as to provide a venue to brainstorm additional improvements to systems and technologies.
In the spring of 2017, a broad range of U.S.
irrigation engineers, scientists, USDA-NRCS specialists, and industry representatives associated with CP technologies were invited to participate in a brainstorming retreat sponsored by the OAP CP Technology Transfer Project held in Amarillo, Texas, on March 28-29.
A total of 39 individuals from 16 U.S.
states  participated in the retreat.
The retreat's several goals included networking opportunities for both more-experienced and lessexperienced individuals, electronic distribution of large bodies of CP-related publications from the Central Plains Irrigation Conference and the USDA-ARS Conservation and Production Research Laboratory, discussion of past and current research, identification of research, extension, and educational needs, and discussion of industry status and information gaps.
Although it is impossible to fully capture the richness and value of this two-day event in this brief report, an attempt was made to tabulate the key topics, their status, and important knowledge gaps.
No attempt to prioritize any of the topics was intended with this tabulation, nor should it be considered inclusive of all the topics discussed during the twoday event.
The articles included this ASABE Special Collection address at least four of the issues listed in table 1 and are discussed in the following sections.
IN-CANOPY AND NEAR-CANOPY IRRIGATION APPLICATION FROM MOVING PLATFORMS
 As table 1 suggests, there is much maturity in our under-
 Figure 2.
Extent of center-pivot irrigation in the ten U.S.
states with the greatest areas of irrigation in 2013.
Table 1.
Key topics, comments and information status, and knowledge and/or implementation gaps identified at a center-pivot irrigation brainstorming retreat in Amarillo, Texas, on 28-29 March 2017.
This list is meant to portray the wide range of topics and some gaps that were identified.
The order of this listing does not indicate priority, nor is it inclusive of all the ideas discussed during the two-day event.
Topic	Comments and Information Status	Knowledge and/or Implementation Gaps
 Variable-rate	Emerging technology, uncertainty remains about extent of future	Hardware development has outpaced development of management
 irrigation 	needs and adoption.
information.
and site-specific	Three types identified (sector control, speed control, and VRI	Although many teams are working on dynamic prescriptions, con-
 irrigation 	zone or individual sprinkler control).
tinued work is needed to remove this impediment.
Many current, commercially available CP systems have more ca-	Uncertainty about producer expectations.
pabilities than recognized by system end-users.
Abandonment can be high without appropriate support from indus-
 VRI is not needed by all producers, and implementation is not	try, universities, consultants, or USDA-NRCS.
economically feasible for all operations.
Continued need for research and education.
Sprinkler	As a maturing technology, many different packages are provided	A maturing technology, but there are still many implementation
 packages and	by industry to meet the needs of producers.
mistakes.
application	Selection should consider crop, soil, water source and quality,	"One size fits all" mentality ignores available knowledge.
systems	and energy.
Runoff must be controlled first for any realistic success with in-
 LEPA, LESA and MESA have specific requirements that need	canopy and near-canopy sprinkler application.
consideration.
Educational needs of producers still remain.
Greater interest and adoption of in-canopy and near-canopy ap-
 plication when evaporative losses are higher, irrigation capacity
 is lower, and land slope is lower.
Sprinkler	Hydraulics can be modeled, but catch can results are still instruc-	Uncertainty of continued status of some modeling efforts.
uniformity	tive and can point out hardware and implementation problems.
CPED is now available from USDA-NRCS in a MS-Excel format.
Catch can tests are still time and labor intensive.
Producers still need to monitor and respond to the basic infor-
 Mismatch of nozzles and operating pressure is common.
mation of system flow rate and pressure.
The crop can integrate some minor uniformity problems.
Mobile drip	An emerging technology with just a few research studies to date.
Scope of appropriate applicability of the technology (e.g., soil
 irrigation	Can reduce wheel track problems.
type, slope, crops) is still unknown.
Rodents can be a problem.
Forces applied on CP systems  are of concern.
Maintenance issues, filtration needs, and other concerns.
Wheel tracks,	Primarily anecdotal or industry-held information.
Need for generic  publication or guidance on
 rutting, and	May negatively affect irrigation management, such as early end-	span selection and wheel/flotation system selection.
getting stuck	of-season irrigation termination.
Chemigation	A maturing technology, and perhaps not as much recent research	Sprinkler packages and sprinkler spacings.
effort by the public sector and universities.
VRI interactions with chemigation.
Uncertainty of the audience (i.e., end-users, regulators, or chemi-	Safety, industry standards, and associated education are needed.
cal industry) may result in inertia.
Microbursts,	No known information resources identified.
What direction to park CP to reduce risk of damage?
tornadoes, and	Could this be a student project or modeling effort?
Loaded with water for downforce or not?
Center pivot	A maturing knowledge base.
Producers and installers still need education.
safety	USDA-NRCS has some materials and trains its own staff about	Need for lay-oriented publications.
safety concerns with CP systems.
Who has expertise for presentations?
Remote	An emerging area with large amount of interest.
Many approaches are necessary for research, but the large number
 sensing	Can interface with VRI research needs and with standalone re-	of options makes selecting an approach difficult for producers.
search as well.
Hardware offerings may outpace development of management in-
 UAVs are of considerable interest to producers.
formation.
Remote sensing could encompass weather, soil, or plant infor-	Continued need for research and education.
mation and combinations of the three types.
Variable-frequency	The technology is maturing and interest is growing due to wider	Some evaluations have been done in the region, but more are
 drives 	use of electricity as the sole energy source for CPs.
needed.
Still not economical for many cases.
More modeling is needed.
Economic feasibility depends on field slopes and changes in pres-	VRI will further complicate the need for VFDs
 sures, time of operation, and price of energy.
Publications	Mature, yet continuing evolving topic area.
How well are we targeting audiences?
and information	Fewer attendees at traditional university-led workshops, tours,	Do we adjust to the audience (i.e., professionals, producers, regu-
 needs	and field days.
lators, industry, legislators, urban, gender, and age)?
Not just an agricultural problem, based on attendance, and land-	Could public/private partnerships be used to greater advantage?
scape management has similar issues.
Individual companies may have material that could be packaged
 Grower panels can be useful when sufficiently unbiased and sci-	for industrywide education.
entifically sound.
Technology farms or large-plot research may be better for infor-
 Younger audiences are more open to electronic media.
mation delivery.
Fewer, better, regional conferences may be an option for sound-
 ing the knowledge but may still have attendance issues.
University	Small and decreasing numbers of agricultural irrigation programs	Industry needs well-educated staff who are willing to live in agri-
 degree programs	in the U.S.
are attracting fewer U.S.-born students.
cultural regions.
and certificate	The importance of agriculture is not always reflected.
Universities need well-trained faculty and funding to retain good
 programs	Community colleges may be able to fill some staffing needs.
faculty.
USDA-NIFA may be helpful in providing irrigation fellowships	Universities need to develop students to find food and fiber solu-
 to help build capacity.
tions for 9.6 billion people by 2050.
standing of sprinkler packages, application systems, and their appropriate application, but there are still major gaps in the implementation by end-users.
Efforts are warranted to improve education of end-users of the conceptual requirements of these systems and to point out operation-specific applicability.
The original development of LEPA coincided with a period of relatively high energy costs and concerns about energy availability in the late 1970s; thus, low energy use was a key objective of LEPA development.
In Texas, where LEPA was originally developed in semi-arid conditions, air and canopy evaporative losses from sprinkler irrigation can be appreciable, reducing crop yields in water-limited operations with low-capacity irrigation systems, SO reduction or elimination of these losses was an advantage of LEPA.
Scientifically, LEPA has always been considered to be a system of technologies, with both CP hardware and adoption of specific farming practices.
The required elements of LEPA irrigation systems are discussed in a Special Collection article by Bordovsky  that provides a fortyyear review of LEPA.
In addition to discussing the required elements for successful LEPA, this article discusses the historical development and efforts to establish design and operating criteria.
A considerable amount of early research was concentrated on design and operating criteria, such as applicator spacing, irrigation intervals, and irrigation amounts.
Research results for LEPA on various crops are also presented, along with comparisons of LEPA with other irrigation systems.
As continued progress was made with LEPA, research conducted at Texas A&M University examined possibilities for using LEPA as a platform for more complex systems or operations, such as application of chemicals within crop canopies or planting crops by incorporating seeds into the irrigation stream before the LEPA applicator.
LEPA continues to be an important water conservation tool that provides an energy-efficient and economical method of irrigating row crops.
Industry has also promoted its adoption through development of brand-specific applicators.
As far back as 1998, the worldwide annual economic benefit of LEPA was estimated to be greater than USD $1.1 billion.
Following the development of LEPA, other low-pressure in-canopy and near-canopy sprinkler application technologies were developed, such as LESA, MESA, low-pressure in-canopy , LEPA with drag sock, and precision application residue managed.
A Special Collection review article by Lamm et al.
discusses in-canopy and near-canopy sprinkler application.
The authors list seven guiding principles for LEPA, provided by Lyle , and focus a considerable portion of their article on the need to match the guiding principle that all plants should have equal opportunity to the applied irrigation water.
They discuss how partitioning of the sprinkler irrigation amount in fully developed corn canopies is affected by sprinkler type and corn row location.
Symmetry of sprinkler application, spatial orientation of the sprinklers with respect to the corn rows, and the seasonal duration of the sprinkler pattern distortion are all concluded to be important factors in plants achieving equal opportunity to the applied water.
One of the reasons
 that producers are interested in LEPA and other low-pressure systems is to reduce evaporative losses.
However, because the wetting patterns for these systems are much smaller than for impact sprinklers, runoff losses can easily surpass any reductions in evaporative losses.
Runoff and surface water redistribution are also discussed by Lamm et al.
, with research and anecdotal results indicating their potential magnitude and consequences.
In a Special Collection article by Evett et al.
, MESA and subsurface drip irrigation  are compared for corn and grain sorghum production in the Texas Panhandle in terms of measured crop evapotranspiration using large weighing lysimeters, grain yield, and water use efficiency.
Evaporative losses were generally less with SDI than with MESA, particularly in the early season before the crop canopy covered the soil surface and during any preplant irrigation when the soil was bare.
Differences were greater for corn than for grain sorghum.
Evaporative differences became smaller as the plant height increased, suggesting that LEPA or LESA could further decrease sprinkler evaporative losses in this semi-arid region.
Corn grain yield was up to 19% greater with SDI compared to MESA in two separate years, while sorghum yields were equal to or 15% less with SDI in two other years.
WUE was greater with SDI in both years for corn but only in one year for grain sorghum.
Evett et al.
conclude that SDI would be successful for corn production, but that MESA might be preferable to SDI for grain sorghum.
Similarly, grain yield for grain sorghum was greater with LEPA than with SDI in northwest Kansas with irrigation regimes designed to replace 60%, 80%, or 100% of ET minus rainfall.
Increased WUE with SDI is one reason why SDI has become a significant technology in west Texas, despite its greater capital cost compared with CP.
Briefly summarized, the science and conceptualization of low-pressure CP irrigation technologies has led to multiple adaptations of the technology that have been adopted on a wide scale in the U.S.
Great Plains and are beginning to be adopted in other areas.
However, when the implementation knowledge gained in earlier studies is ignored or discarded, much of the potential water and energy savings is not realized.
SITE-SPECIFIC VARIABLE-RATE IRRIGATION AND ASSOCIATED SENSOR TECHNOLOGIES
 Site-specific VRI was identified as an important emerging topic in the U.S.
in the 2017 CP technology brainstorming retreat discussed earlier , and the consensus was that hardware development has often outpaced the development of management information.
Special Collection articles addressing site-specific VRI for CP systems and associated sensors for monitoring and/or control are provided by Colaizzi et al.
, ''Shaughnessy et al.
, and Stone et al..
A current review of the advantages and disadvantages of VRI is the focus of O'Shaughnessy et al..
The listed advantages focus on economic, environmental, and agronomic aspects generally related to greater productivity and efficiency resulting from improved resource management
 while enhancing risk management.
The listed disadvantages concern the high upfront costs when additional VRI hardware is required and the complexity of management and risk, particularly in the case of matching VRI to variable spatiotemporal crop needs within the field.
The authors conclude that a number of advances have occurred in recent years to further develop VRI, and that multiple teams across the U.S.
are taking multiple approaches to address VRI management.
The authors propose a design protocol for a VRI system that includes delineation of management zones , addressing both spatial and temporal variability in plant water status through information from sensor networks, establishing fundamental irrigation management rules for VRI, and recognizing that VRI requires timely updating of robust prescription maps frequently during the crop season.
Although the current number of VRI systems in the U.S.
is small, this number is anticipated to increase, and those working in the VRI area will need to identify where VRI can be beneficial and where it will likely not be beneficial.
Inherent to successful VRI application is the ability to monitor crop status in real-time or near real-time to allow dynamic updating of prescriptive irrigation schemes.
In a Special Collection article by Colaizzi et al.
, a comparison of stationary and moving  infrared thermometer  measurements is discussed.
The authors found that temperature measurement errors and noise were generally similar between moving and stationary platforms and that addition of more expensive hardware to decrease errors due to CP movement does not appear justified.
They indicate that the addition of low-cost imaging radiometers might improve the interpretation of IRT temperature measurements.
In a Special Collection article by Stone et al.
, the potential for water conservation with site-specific VRI is examined through simulation modeling.
Water requirements for a highly variable field site  with 12 soil mapping units were simulated over a 21-year period under irrigation scenarios consisting of various numbers of management zones with either fixed 12.5 mm irrigation events or full irrigation replacement to field capacity.
The authors conclude that VRI design should not be based entirely on the average weather conditions and that greater VRI effectiveness can be obtained by identifying management zones based on actual or anticipated weather conditions.
They point out that VRI, as compared to uniform irrigation, can either increase or decrease the total amount of irrigation water required for adequate irrigation, depending on the different management zones within the field.
This may be instructive for understanding why there have been mixed results when assessing water savings under VRI and why water use efficiency, rather than water saving, may be the key point of VRI.
Current marketing of drought-tolerant  corn hybrids has generally focused on developing hybrids that can tolerate moderate levels of plant water stress and sustain grain yield, without suffering yield suppression when conditions are favorable for high grain yield.
Generally, this requires development of hybrids specific to a target region with its inherent climatic conditions.
A Special Collection article by
 'Shaughnessy et al.
examines the productivity of DT hybrids at varying levels of irrigation in the semi-arid Texas High Plains.
The authors report a greater grain yield for a 101-day early-maturity DT hybrid than for a 96-day early-maturity DT hybrid when seasonal crop water use exceeded approximately 675 mm, but the 96-day early-maturity DT hybrid had greater yields for lower crop water use.
In a drier year, the authors found that a 115-day mediummaturity DT hybrid compared to a 101-day early-maturity hybrid had greater yield and greater yield response to seasonal crop water use.
Summarizing additional years of studies with both conventional and DT hybrids, they conclude that current DT hybrids have greater yields than previous older conventional hybrids and have yields similar to today's conventional hybrids in the Texas High Plains.
When corn was severely deficit-irrigated, the DT hybrid response was not improved over conventional hybrids.
These data suggest that corn hybrid selection will remain an important factor for both deficit irrigation and VRI scenarios.
VARIABLE-FREQUENCY DRIVES WITH CP IRRIGATION SYSTEMS
 The addition of an end gun  or a corner extension allows a circular CP system to irrigate a greater proportion of a square field.
However, these systems increase the complexity of CP operation and management, and they require the capability to manage power requirements due to the changing flow rates and pressure.
Additionally, large elevation changes within CP irrigated fields can affect power requirements.
VFDs are a new technology in irrigated agriculture that increase and decrease the speed of electric pump motors.
VFDs can help manage the changing flow rates and pressure for CP systems.
A Special Collection article by Brar et al.
discusses the potential for energy conservation and economic benefits with VFDs by simulating VFD use on 1,000 CP systems in ten counties across Nebraska.
The authors found that the resulting energy savings and net returns were greatly influenced by topographical changes within the CP field, the characteristics of the corner attachment operation, and the electrical energy costs.
In some cases, although energy savings were achieved, the payback period for the VFD exceeded its expected life.
The results illustrate realistic scenarios in which VFDs can have a positive effect.
UNIFORMITY EVALUATIONS FOR CP IRRIGATION SYSTEMS
 Sprinkler application uniformity was also an important topic discussed at the 2017 CP brainstorming retreat.
Catch can diameter and placement can have an effect on spray catch and on the resulting uniformity values for some newer sprinkler applicators , as discussed by Rogers et al..
The authors compared four collector diameters  using a Latin-square study design.
To minimize catch variability, they recommend 100 or 147.5 mm catch cans for spinning plate sprinklers, but the can size is less important for the other types of sprinklers.
Increasing the number of collectors to five to ten in a partic-
 ular measurement area decreased the variability to less than 5% for all sprinkler applicators.
These results add value to an earlier study by O'Shaughnessy et al.
of wind effects on irrigation distribution across and between VRI zones managed to apply different amounts of water.
The earlier study found that the orientation and pattern of 200 mm catch cans, along with a mechanism for catch can leveling, were important for accurately assessing wind effects on VRI distribution.
A series of CP uniformity evaluations on fields in Kansas is the subject of a Special Collection article by Rogers et al.
The 53 tests were conducted over multiple years to provide information about the typical performance of CP sprinkler packages on Kansas farms, although the systems were not randomly selected but rather were selected according to voluntary participation in the program.
The average Christiansen uniformity coefficient with the Heermann-Hein modification  for all tested systems was 79, with a range from 53 to 92.
Early tests tended to be on producer fields participating in a demonstration project and tended to have higher CUHH values, which indicates that good values are achievable.
Later tests, conducted at the request of producers, tended to be for systems suspected of having uniformity problems.
Many of the sprinkler package deficiencies could have been identified and corrected with visual inspection and/or a comparison to the design specifications.
Information from these tests has been used in meetings and publications to inform producers of the importance of uniformity and sprinkler package design, installation, and maintenance.
Further work summarized by Rogers et al.
examined the effect of collector size on catch amount and variability.
In general, collector sizes of 10 cm or greater did not substantially affect accuracy, as long as a sufficient number of collectors was used.
Some CP technologies are relatively mature and have a rich and robust knowledge base, but it is important to periodically review the history and conceptual requirements that brought about and constrain these technologies.
This is particularly important as efforts are made to extend these technologies into new regions or new circumstances with differing constraints.
The Special Collection articles by Bordovsky  and Lamm et al.
focus on providing such reviews, while Evett et al.
compares a low-pressure CP application system to subsurface drip irrigation.
Other CP technologies can be categorized as emerging and represent promising opportunities to advance targeted, precision irrigation, such as site-specific VRI and associated sensor technologies, which are the subject of four Special Collection articles.
These articles present important information for characterizing and monitoring VRI and discuss how VRI technologies must also consider additional factors, such as weather, plant water stress information, and cultivar characteristics.
The use of VFDs was the focus of a large simulation study
 for 1,000 CP systems across Nebraska in a Special Collection article by Brar et al..
Their results suggest that this emerging technology can result in energy savings and economic benefits, but the benefits greatly depend on field topography, CP characteristics, and operation.
Although CP sprinkler application uniformity has a mature knowledge base, producers still have difficulty implementing or maintaining uniform designs in commercial settings.
Catch can tests, as discussed in Special Collection articles by Rogers et al.
, are an important tool for documenting the uniformity of both effective and ineffective sprinkler designs and for encouraging producers to improve their CP sprinkler uniformity.
This Special Collection is not an exhaustive discussion of the needs for CP technology transfer but rather a part of the continuing effort to help practitioners use and advance targeted, precision irrigation from moving platforms.
Emerging public policy, along with declining aquifers, improved technologies, and changing climate, will continue to play an important role in the future of irrigation practices and the importance of continued technology transfer.
This article is part of a CP irrigation technology transfer effort supported by the Ogallala Aquifer Program, a consortium of the USDA-ARS, Kansas State University, Texas A&M AgriLife Research, Texas A&M AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
Contribution No.
19-224-J from the Kansas Agricultural Experiment Station.
Some of the research reported here was supported by the USDA National Institute of Food and Agriculture under Award Nos.
2016-67021-24420 and 2016-68007-25066.
46-50).
Great Plains Foundation.
Effect of Late Season Water Stress on Corn in Northwest Kansas
 Abdrabbo A.
Aboukheira, Research & Extension Water Scientist
 Written for presentation at the 2012 ASABE Annual International Meeting Sponsored by ASABE Hilton Anatole Dallas, Texas July 29 August 1, 2012
 Mention any other presentations of this paper here, or delete this line.
Abstract.
Four separate studies were conducted over the years 1993 through 2008 at the Kansas State University Northwest Research Extension Center at Colby, Kansas to examine the effects of post-anthesis  water stress on field corn.
Prior to anthesis, all treatments in each of the studies were fully irrigated according to their need.
The results of these studies suggest that corn yield is nearly linearly related to the amount of crop water use during the post-anthesis period and that total crop water use amounts during the period may average nearly 430 mm.
Producers should plan for crop water use during the last 30 and 15 day periods that may average nearly 125 and 50 mm, respectively, to avoid yield reductions.
Management allowable depletion during the postanthesis period should be limited to 45% of the available soil water for a 2.4 m profile on the deep silt loam soils of this climatic region.
Keywords.
Corn, irrigation, water management, management allowed depletion, production function.
When to terminate the irrigation season is an important irrigation macromanagement decision that can potentially save water and increase net income when made correctly, but can have negative economic consequences when made incorrectly.
Much of the established literature on irrigation management during the late corn growth stages is 40-50 years old and was written at a time when irrigated corn yields were much lower  than they are today.
It is quite possible that some of the numerous yieldlimiting stresses  that were tolerable at the lower yield level are less tolerable today.
On the other side of the issue, there has been much improvement in corn hybrids during the period with incorporation of traits that allow water stress tolerance and/or water stress avoidance.
The post-anthesis grain filling stage in corn is considered to be highly sensitive to water stress with only the flowering  and early reproductive period being more sensitive.
Plant water stress can cause kernel abortion if it occurs early enough in the post-anthesis period but is more often associated with poor grain filling and thus reduced kernel weight.
Grain kernel weight is termed as a very loosely restricted yield component , meaning that it can be manipulated by a number of factors.
The final value is also set quite late, essentially only a few days before physiological maturity.
The rate of grain filling is linear for a relatively long period of time from around blister kernel to near physiological maturity.
Yield increases of over 0.25 Mg/ha for each day are possible during this period.
Providing good management during the period can help to provide a high grain filling rate and, in some cases, may extend the grain filling period a few days thereby increasing yields.
Availability of water for crop growth and health is the largest single controllable factor during this period.
However, the rate of grain filling remains remarkably linear unless severe crop stress occurs.
This is attributed to remobilization of photosynthate from other plant parts when conditions are unfavorable for making new photosynthate.
Irrigators in the Central Great Plains sometimes terminate the corn irrigation season on a traditional date such as August 31 or Labor Day  based on long term experience.
However, a more scientific approach might be that season termination may be determined by comparing the anticipated soil water balance at crop maturity to the management allowable depletion  of the soil water within the root zone.
Some publications say the MAD at crop maturity can be as high as 0.8.
Extension publications from the Central Great Plains often suggest limiting the MAD at season end to 0.6 in the top 1.2 m of the soil profile.
These values may need to be re-evaluated and perhaps adjusted downward.
Lamm et al.
found subsurface drip-irrigated corn yields in northwest Kansas began to decrease rapidly when available soil water in the top 2.4 m was lower than 56-60% of field capacity for extended periods in July and August.
Lamm et al.
permitted small daily deficits to accumulate on surface-irrigated corn after tasseling, and subsequent analysis of those data showed declining yields when available soil water levels approached 60% of field capacity for a 1.5 m soil profile at physiological maturity.
Four studies were conducted at the KSU Northwest Research-Extension Center at Colby, Kansas, USA on a productive, deep, well-drained Keith silt loam soil  during the sixteen-year period, 1993-2008.
In general, the 1990s were a much wetter period than the
 2000s.
The summers of 2000 through 2003 would be considered extreme droughts.
The climate for the region is semi-arid with a summer pattern of precipitation with an annual average of approximately 480 mm.
The average precipitation and calculated corn evapotranspiration during the 120-day corn growing period, May 15 through September 11 is 300 mm and 587 mm, respectively.
The corn anthesis period typically occurs between July 15 and 20.
The corn was planted in late April to early May, and standard cultural practices for the region were used.
Irrigation was scheduled as needed by a climate-based water budget except as modified by study protocols that will be discussed in the Specific Procedures section that follows.
Calculated crop evapotranspiration  was determined with a modified Penman equation for calculating reference evapotranspiration  multiplied by empirical crop coefficients suitable for western Kansas.
Precipitation and irrigation were deposits into the crop water budget and calculated ETc was the withdrawal.
Soil water was measured in each plot on a weekly or biweekly basis with a neutron probe to a depth of 2.4 m in 0.3-m increments.
These data were used to determine crop water use and to determine critical soil water depletion levels.
Water use values were calculated as the sum of the change in available soil water to the specified profile depth, plus the irrigation and precipitation during the specified period.
This method of calculating crop water use would also include any deep percolation or rainfall runoff that may have occurred.
Corn yield and yield components of plants/area, ears/plant, and kernel weight were measured by hand harvesting a representative 6 m row sample.
The number of kernels/ear was calculated with algebraic closure using the remaining yield components.
Four separate studies were conducted over the years 1993 through 2008 to examine the effects of post-anthesis water stress on corn.
Prior to anthesis, all treatments in each of the studies were fully irrigated according to their need.
A two-year study  consisting of six irrigation treatments with three replications in a complete randomized block design was conducted in small level basins consisting of 6 corn rows each  approximately 27 m long.
Surface irrigation was used to provide irrigation amounts for each event that were between 60 to 75 mm to help achieve higher distribution uniformity than smaller applications would have provided.
The six irrigation treatments were termination of the irrigation season on either August 5, 10, 15, 20, 25 or 30.
The corn hybrid was Pioneer 3183.
The year 1993 was an extremely poor corn production year characterized by very cool and wet conditions while 1994 was a good year for corn production.
A four-year study  consisting of nine irrigation treatments with four replications in a complete randomized block design was conducted in small level basins consisting of 8 corn rows each  approximately 27 m long.
Surface irrigation was used in this study with event irrigation amounts of approximately 60 to 75 mm.
The nine irrigation treatments were termination of the irrigation season at either anthesis, anthesis plus 6, 12, 18, 24, 30, 36, 42 or 48 days.
The corn hybrid was Pioneer 3183.
Corn yields in 1995 were somewhat depressed due to a hail storm but were good in 1996 through 1998.
The two studies conducted after 1998 utilized subsurface drip irrigation to more closely control soil water levels and distribution uniformity of irrigation water.
Both studies utilized the same field site that had a subsurface drip irrigation  system installed in 1999 with 1.5-m dripline
 spacing and an emitter spacing of 0.6 m.
The 1.5 m spaced corn rows were planted parallel and centered on the driplines such that each corn row would be 0.38 m from the nearest dripline.
The nominal emitter discharge was 1.1 L/h for the 0.6 m emitter spacing.
In a study conducted from 1999 through 2001, seven irrigation treatments were replicated three times in a complete randomized block with plot size of 8 corn rows  by approximately 85 m.
In this study, irrigation during the post-anthesis period was managed for two distinct periods.
Four of treatments began at anthesis with one treatment receiving no irrigation after anthesis and the other three treatments only receiving irrigation if the available soil water in the top 1.5m of profile fell below approximately 68, 48 or 27% of field capacity.
Three additional treatments were no irrigation after two weeks following anthesis and soil water maintenance level treatments of either 48 or 27% of field capacity beginning also at that time.
After anthesis, irrigation amounts were generally not greater than 13 mm for each required event and were conducted daily as needed to return the available soil water to the required treatment level.
The year 1999 had above normal precipitation but 2000 and 2001 were extreme drought years.
The corn hybrid was Pioneer 3162.
The final post-anthesis water stress study  was conducted on the same SDI field site as the 1999 through 2001 study but the seven irrigation treatments were the irrigation season being terminated at one week intervals beginning one week after anthesis.
This typically meant that the first irrigation treatment ceased about July 20 to 27 and the last irrigation treatment ceased about August 31 to September 7.
The crop was fully irrigated until the irrigation termination date occurred and irrigation event amounts were generally not greater than 13 mm.
The seven irrigation treatments were replicated three times in a complete randomized block design.
The corn hybrid was Pioneer 3162.
Post anthesis water productivity was calculated as the crop yield in Mg/ha divided by the post-anthesis crop water use in mm.
Tabular data analysis for post-anthesis water stress studies
 Results from 16 years  of studies indicate that anthesis for corn in Northwest Kansas varies from July 12 to July 24 with an average date of July 19.
Physiological maturity ranged from September 14 through October 10 with an average date of September 27.
The average length of the post-anthesis period was approximately 70 days.
Using the corn grain yield results from the study and the individual treatment irrigation termination dates responsible for those yields, Table 1 was created to indicate the problems with using inflexible dates for determining the irrigation season termination date.
Additionally, the corn grain yield results and the treatment irrigation dates were used to estimate the date when a specified percentage of maximum grain yield would occur.
Because there was not an unlimited number of irrigation treatment dates there are years when the date required for a specified percentage of maximum grain yield was the same as the date for the next higher percentage.
The average estimated termination date to achieve 80, 90 and 100% of maximum corn grain yield was August 2, 13, and 28, respectively, but the earliest dates were July 17, July 17 and August 12, respectively, while the latest dates were September 14, 21, and 21, respectively.
Irrigators that use average or fixed dates to terminate the corn irrigation season are not realistically considering the irrigation needs of the corn that may be greater or smaller in a particular year, and thus, often will neither optimize corn production, nor minimize water pumping costs.
Table 1.
Anthesis and physiological maturity dates and estimated irrigation season termination dates* to achieve specified percentage of maximum corn grain yield from studies examining post-anthesis corn water stress, KSU Northwest Research-Extension Center, Colby, Kansas, 1993-2008.
Note: This table was created to show the fallacy of using a specific date to terminate the irrigation season.
Note: Because there was not an unlimited number of irrigation treatment dates, there are years when the date required for a specified percentage of maximum grain yield was the same as the date for the next higher percentage.
Year	Date of	Date of	Irrigation Season Termination Date For
 Anthesis	Maturity	80% Max Yield	90% Max Yield	MaxYield
 1993	20-Jul	30-Sep	5-Aug	5-Aug	15-Aug
 1994	20-Jul	15-Sep	5-Aug	15-Aug	15-Aug
 1995	20-Jul	29-Sep	5-Aug	13-Aug	18-Aug
 1996	20-Jul	3-Oct	17-Jul	17-Jul	29-Aug
 1997	23-Jul	1-Oct	23-Jul	23-Jul	27-Aug
 1998	20-Jul	28-Sep	20-Jul	20-Jul	24-Aug
 1999	23-Jul	6-Oct	24-Jul	13-Aug	20-Sep
 2000	12-Jul	20-Sep	14-Sep	20-Sep	20-Sep
 2001	16-Jul	29-Sep	30-Jul	22-Sep	22-Sep
 2002	22-Jul	30-Sep	4-Aug	30-Aug	7-Sep
 2003	22-Jul	23-Sep	3-Aug	3-Aug	18-Aug
 2004	19-Jul	28-Sep	8-Aug	21-Aug	27-Aug
 2005	20-Jul	28-Sep	2-Aug	9-Aug	29-Aug
 2006	17-Jul	25-Sep	30-Jul	13-Aug	13-Aug
 2007	18-Jul	19-Sep	14-Aug	21-Aug	28-Aug
 2008	24-Jul	10-Oct	31-Jul	6-Aug	27-Aug
 Average	19-Jul	27-Sep	2-Aug	13-Aug	28-Aug
 Standard Dev.
3 days	6 days	13 days	19 days	13 days
 Earliest	12-Jul	14-Sep	17-Jul	17-Jul	12-Aug
 Latest	24-Jul	10-Oct	14-Sep	21-Sep	21-Sep
 *	Estimated dates are based on the individual irrigation treatment dates from each of
 the different studies when the specified percentage of yield was exceeded.
Maximum corn yields  during the 16-year period in the various studies averaged 16.2 Mg/ha with a range of 9.7 to 18.7 Mg/ha.
Extremely poor growing conditions  greatly reduced yields in 1993 and hail suppressed yield in 1995.
The post-anthesis water use that occurred for the irrigation treatment that maximized yield  averaged 430 mm with a range of 378 to 513 mm.
Assuming that yield formation for the corn crop started at anthesis, the average post-anthesis water productivity  was 38 kg/ha-mm and the range of post-anthesis water productivity over the years was 20 to 49 kg/hamm.
Table 2.
Maximum corn yields and post-anthesis water use data from studies examining post-anthesis corn water stress, KSU Northwest ResearchExtension Center, Colby, Kansas, 1993-2008.
Year	Maximum		Yield	PAWUMY*		PAWUMY		during last	30 days		during last 15	days 	PAWU	MY
 1993	9.7	488	7.3	7.3	4.5
 1994	15.4	394	7.0	5.5	4.5
 1995	10.7	463	7.2	5.1	4.4
 1996	17.6	391	5.6	4.1	3.5
 1997	15.4	410	5.8	4.1	3.8
 1998	16.4	420	6.0	3.9	3.5
 1999	17.1	470	6.3	3.4	2.1
 2000	16.3	514	7.3	7.0	7.7
 2001	16.8	494	6.6	4.1	4.1
 2002	17.8	422	6.0	3.5	0.4
 2003	16.9	384	6.1	2.3	2.7
 2004	17.8	413	5.8	4.6	4.2
 2005	18.5	414	5.9	2.2	0.9
 2006	16.8	419	6.0	2.5	2.6
 2007	17.1	413	6.6	2.6	2.7
 2008	18.7	377	4.8	2.9	2.3
 Average	16.2	430	6.3	4.1	3.4
 Standard Dev.
2.5	42	0.7	1.5	1.7
 Minimum	9.7	377	4.8	2.2	0.4
 Maximum	18.7	514	7.3	7.3	7.7
 PAWUMY is the post-anthesis water use occurring for the irrigation treatment that
 achieved maximum corn grain yield within the specified year.
PAWUMY averaged 6.3 mm/day during the approximately 70-day period between anthesis and physiological maturity and remained at 65 and 53% of that value  during the last 30 and 15 days of the season, respectively.
This emphasizes that although crop water use is tapering off during the latter part of the season, due to maturing crop canopies and also due to lower reference evapotranspiration , it must be considered an important factor in late season crop management.
Producers should also be aware that irrigation systems with marginal or insufficient capacity may have allowed considerable soil water depletion  during the pre-anthesis period.
Graphical data analysis for post-anthesis water stress studies
 The corn grain yield results within a given year were normalized to the maximum value occurring in that particular year to give the relative yield.
The post-anthesis water use within a given year was then normalized with respect to the water use that occurred for the irrigation treatment that maximized corn grain yield in that particular year.
This allowed
 treatments receiving excessive irrigation to have relative post-anthesis water use  values greater than one.
There was a strong relationship between relative corn yield  and relative post-anthesis water use  as shown in Figure 1.
Figure 1.
Relative corn grain yield  as affected by relative post-anthesis water use  for various studies examining the effect of post-anthesis water stress, KSU-NWREC, Colby, Kansas, 1993-2008.
The dotted line represents a unity relationship between RY and RPAWU MYNote: RPAWUMY values can exceed one because some treatments received irrigation water in excess of the amount required to maximize corn grain yield.
This excessive water may have been lost in deep percolation but would have been included in the calculation procedures of postanthesis water use.
Although there are a number of curves that can be drawn through the data , there was a large portion of the data in the efficient range of RPAWUMY  that can be adequately characterized by a one-to-one relationship between RY and RPAWUMYThe subtle differences between assuming a curvilinear or linear relationship in the efficient range of post-anthesis water use might become important when trying to optimize corn production using water resource and economic constraints.
There was a reasonably good relationship between relative corn grain yield  and the minimum post-anthesis available soil water  within the 2.4 m soil profile  Corn yield tended to decrease for treatments having less than a minimum available soil water of approximately 55% of field capacity for any point-in-time within the post-anthesis period.
Thus, the management allowable depletion  in these studies was approximately 45% as compared to the traditionally larger values often quoted in the literature.
However, the 45% MAD value is consistent with the results of Lamm et al.
and Lamm et al.
from irrigated corn studies on the same soil type.
Figure 2.
Relative corn grain yield  as affected by the minimum value of available soil water  within the 8 ft soil profile occurring during the post-anthesis period.
Data are from various studies examining the effect of post-anthesis corn water stress, KSU-NWREC, Colby, Kansas, 1993-2008.
There was also a relatively good relationship between RPAWUMY and MPAASW.
RPAWUMY tended to decrease for treatments with MPAASW less than 55% of field capacity.
This is to be as expected because of the strong relationship between RY and RPAWUMY but does provide additional evidence and rationale for a MAD value of approximately 45% for this soil type in this region as compared to the higher values in the literature.
Mininum Post-Anthesis Available Soil Water
 Figure 3.
Relative post-anthesis water use  as affected by the minimum value of anthesis period.
Data are from various studies examining the effect of available soil water  within the 2.4 m soil profile occurring during the postpost-anthesis corn water stress, KSU-NWREC, Colby, Kansas, 1993-2008.
justified has in comparing the MPAASW values for different soil profile depths to see which depth regions  where MPAASW is less than 0.55.
Additionally, further efforts are Further data analysis should focus on determining the cause of increased scatter in the graph the greatest correlation and also to determine the inaccuracy associated with choosing alternative depths.
Recommendations for managing post-anthesis corn water stress
 yield.
Producers growing corn on deep silt loam soils in the Central Great Plains should attempt to limit management allowable depletion of available soil water in the top 2.4 m of the soil profile water use during the last 30 and 15 days of the season might average nearly 125 and 50 mm, post-anthesis water use will result in nearly a one-to-one percentage decrease in corn grain should not be based on an average or fixed date.
Producers in the Central precipitation and irrigation.
When irrigation losses are minimized, a percentage decrease in Great Plains should plan for post-anthesis water use needs of approximately 432 mm and that Producers should use a good method of day-to-day irrigation scheduling during the postanthesis period.
The macromanagement decision about when to terminate the irrigation season respectively.
This water use would need to come from the sum of available soil water reserves, to 45%.
Macromanagement decisions at the seasonal boundaries should always be made in the context of having implemented appropriate day-to-day irrigation scheduling.
Proper day-to-day scheduling will provide much-needed information about the crop and soil water status and evaporative demand being experienced within the given year.
Corn yield formation was primarily linearly related to the water use during the post-anthesis period for cases when irrigation was limited to the amount required for maximum yield.
Limiting available soil water depletion to approximately 45% during the period is important in achieving maximum grain yields.
Minimizing Risks: Use of Surface Water in Pre-Harvest Agricultural Irrigation
 Part I: Understanding Water Quality & Treatment Options
 Jessica L.
Dery, Natalie Brassill, and Channah M.
Rock
 Why treat agricultural irrigation water?
Irrigation water can act as a vector, or carrier, that can transport or spread pathogens to crops, where they have the potential to cause illness.
Decisions to treat irrigation water can be driven by buyer requirements, for product marketing or branding, or because the water quality exceeds the FDA Food Safety Modernization Act  regulations or the Leafy Green Marketing Agreement  standards for generic Escherichia coli.
For example, the quality of surface waters may be more impaired or have higher pathogen contamination compared to ground water.
This is because they are directly exposed to external influences and therefore may require treatment.
To ensure irrigation water is at a quality sufficient to meet grower needs, it is important to understand how water quality affects treatment methods and associated challenges and solutions.
If the quality of the water source is unknown, there are many labs recommended by the Arizona Department of Health Services that offer U.S.
EPA approved testing methods.
Links to testing labs, EPA registered sanitizers, and approved testing methods are provided at the bottom of this fact sheet.
This publication is a general overview of water quality and common treatment methods.
It is the first of a series covering specific treatment options for pre-harvest agricultural irrigation such as chlorination, Ultra Violet , and peroxyacetic acid.
Various water treatment methods or technologies can be used for agricultural irrigation based on the water quality parameter of concern.
Such methods include chemical treatment, physical treatment, and biological treatment, and are illustrated in Figure 1.
It is important to remember each method has advantages
 Irrigation Canal, Yuma, AZ Photo by Natalie Brassill
 Figure 2.
Factors affecting effectiveness of irrigation water treatment methods.
and disadvantages.
Integrated approaches incorporating treatment technologies, sanitary surveys, and good agricultural practices  should be implemented as a more effective and comprehensive way to mitigate risks to fresh produce.
What factors affect treatment effectiveness?
The effectiveness of treatment methods is influenced by the background quality of the irrigation water and includes physical, chemical, and biological parameters.
In deciding which treatment method, or methods, to implement, your water's quality profile should be assessed.
Each of these factors can impact which water treatment is best suited to meet your water quality needs.
Organic matter are organic substances broken down from plants, animals, microorganisms, and from geological origins that can be found in water sources, either settled or in suspension.
Organic matter consumes disinfectants, requiring increased concentrations of the disinfectant to be effective.
These organic substances also contribute to the turbidity of the water supply, which is a measure of the water's clarity, or how much light is scattered by the material in the water.
The more turbid a water source is, the more light is scattered, and the more difficult it is to see through.
Turbidity provides food and a 'hiding' place for organisms and pathogens, shielding them from disinfection treatments such as ozone, UV, and chlorine.
This results in a need for increased concentrations of chemicals necessary to achieve the desired level of water quality, or inclusion of a 'pre-treatment' step, such
 Factors affecting effectiveness of treatments include:
 as filtration, to remove sediment.
The concentration of microbes in irrigation water, or the microbial load and the characteristics of the microbes can also affect treatment effectiveness.
Different types of microbes may require different treatment methods, disinfection concentrations, or contact time.
Temperature is another important factor that can impact water treatment.
Because chemical reactions often increase at higher temperatures, chlorine treatments, for example, are less effective at low temperatures.
In addition, temperature affects other water quality parameters such as pH, or the measurement of how acidic or alkaline  the water is.
As the temperature of the irrigation water increases, pH decreases.
The pH of the irrigation water also affects the efficiency of certain treatments.
For example, ozone treatments require different dosages based on pH and chlorination is more effective in water with lower pH.
Excess calcium and magnesium in a water source contribute to the hardness of water and can lead to scaling of irrigation lines.
This buildup can decrease the effectiveness of water treatment
 processes such as UV, making it important to minimize scale deposits in the irrigation system.
Because these factors affect treatment methods differently, they will be discussed in more detail for each treatment method in this series
 How long does it take a disinfectant to work?
Disinfectants and sanitizers do not kill, or inactivate, microbes immediately upon contact.
They take time to work.
There are several factors influencing how fast a disinfectant works, known as the inactivation rate.
This rate is dependent on the type of pathogen, as some microbes are more resistant to disinfection than others and may require increased disinfectant concentrations or contact time.
The chemical disinfectant concentration  and the time  in which the chemical disinfectant is in contact with the water is known as the 'contact time'.
This also affects this rate of inactivation.
It is important to remember that an increase in chemical concentration can decrease the amount of contact time  needed to kill or inactivate pathogens, and vice versa.
When treating irrigation water with chlorine, it is important to understand breakpoint disinfection, or breakpoint chlorination.
This occurs when there has been enough chlorine added to the irrigation water to satisfy the chlorine demand.
At this point, the water begins to build up residual and free  chlorine, the form of chlorine with the most disinfecting power.
This is an important concept for monitoring chlorine levels for maximum disinfection efficiency and will be further discussed in Part II of this series covering chlorination treatment.
Temperature and pH are also important in determining the rate of disinfection.
For example, ideal temperatures for chlorine treatment are between 65 and 99F, and ideal pH is between 6-7.5.
Figure 2 provides an example of factors that influence treatment effectiveness.
Temperature is not included in this figure as the effects are variable between treatment methods.
Factors affecting inactivation rates of disinfectants:
 Chemical concentration, C 
 Contact time, CT 
 Types of irrigation water to be tested:
 Water that directly contacts the edible portion of harvested crop.
Water used for sprout irrigation
 Treating Agricultural Irrigation Water
 When treating your irrigation water with sanitizers/ disinfectants, it is important to follow specific guidelines and remember to:
 Use sanitizers and disinfectants approved by the EPA to determine if it will be effective.
Sanitizers and disinfectants are to be used in accordance with label specifications and guidelines.
Each sanitizer may have different specifications.
Always remember to follow directions on all sanitizer labels.
Use an accepted testing method.
FDA BAM  method.
U.S.
EPA approved or AOAC accredited method for quantitative monitoring of water for generic E.
coli.
Presence/absence testing.
Must have a similar limit of detection as quantitative monitoring.
Document all test results and remedial actions.
These must be available for verification and kept for a twoyear period.
Certain agricultural water must either be required to meet the proposed FDA FSMA or LGMA metrics for Maximum Contaminant Level  Goal for E.
coli, set by the EPA, OR it must contain approved disinfectant at sufficient concentrations to prevent contamination.
This fact sheet is part of the 'Minimizing Risks: Use of Surface Water in Pre-Harvest Agricultural Irrigation series.
Additional information detailing specific treatment methods for agricultural irrigation waters is available as part of this series.
Table 1.
Example corn yield loss estimates when stress occurs for four or more consecutive days.
Adapted from Classen and Shaw, 1970; Rhoads and Bennet, 1990; and Shaw, 1988.
The Corn Development stage known as early vegetative  has an estimated Yield Loss per Day of Stress of 1-3.
The Corn Development stage known as Late vegetative  has an Estimated Yield Loss per Day of Stress of 2-5.
The Corn Development stage known as Pollination to Blister  has an Estimated Yield Loss per Day of Stress of 3-9.
The Corn Development stage known as Milk  has an Estimated Yield Loss per Day of Stress of 3-6.
The Corn Development stage known as Dough  has an Estimated Yield Loss per Day of Stress of 3-5.
The Corn Development stage known as Dent  has an Estimated Yield Loss per Day of Stress of 2-4.
The Corn Development stage known as Maturity  has an Estimated Yield Loss per Day of Stress of 0.
ThinkWater, a part of the Oklahoma Cooperative Extension Service, works to educate Oklahoma residents about water conservation and smart irrigation.
Our mission is to promote conscious water use and drought awareness.
Learn more about us !
The City of OKLAHOMA CITY Utilities Department
 Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Director of Oklahoma Cooperative Extension Service, Oklahoma State University, Stillwater, Oklahoma.
This publication is printed and issued by Oklahoma State University as authorized by the Vice President, Dean, and Director of the Division of Agricultural Sciences and Natural Resources and has been prepared and distributed at a cost of $,550.00 for 30,000 copies.
1015
 Seven Water-wise Landscape Principles
 Water-wise landscaping  is a landscape practice designed to provide effective water management strategies for outdoor landscapes.
These strategies are based in water conservation and the efficient use of water in all aspects of the landscape from design to maintenance.
Xeriscape is a term applied to low maintenance and efficient landscapes.
The term often is misunderstood to mean "zero" or no landscaping.
Xeriscapes may look like a traditional landscape, but are established with a set of principles that save water and maintenance time.
The term water-wise landscape is used to emphasize the relation to water conservation.
Water-wise landscaping is not the exclusive use of rocks and cactus, or the elimination of turfgrass.
Water-wise landscapes are designed to save water and can be creative, and attractive.
Water-wise landscapes may look different, depending on where they are located.
Plants appropriate for Oklahoma will differ from those appropriate for Arizona or other places.
However, the same principles apply no matter the location.
Figure 1.
Buffalograss: A native Oklahoma turfgrass that does well in the state's climate.
Plan and Design: The best landscapes start with planning and design.
Take time to plan out your landscape and consider shade, drainage and other factors that may impact new landscape features.
Improve Soil: Start with a soil test.
Healthy soil holds more water and provides better growing conditions for plants.
Improve soil by adding compost and organic matter.
Practical Use of Turf: Turf serves important functions in the landscape, but can require significant amounts of water to maintain.
Select turfgrass species well-suited to Oklahoma's climate, water infrequently and deeply, and implement functional turfgrass species.
Use of Mulch: Mulch covers the soil and retains moisture.
A layer of mulch can be a great way to conserve water, limit weeds and reduce the amount of maintenance required.
Efficient Use of Irrigation: Irrigation can be an important tool.
However, it is important to implement efficient irrigation technologies to maximize the efficiency of water use.
Select Appropriate Plants: There are many native plant species available that are well-suited to Oklahoma's climate.
It is important to select a plant that is adapted to the local moisture and temperature conditions.
Implement Good Maintenance Practices:
 Maintenance preserves the beauty of a landscape and contributes to water savings.
Practices such as correct mowing height, pruning and weeding all help to save water.
Much of Oklahoma receives good average annual rainfall.
However, it often doesn't fall during hot, summer months when plants need it most.
Oklahoma's rainfall is highly variable from year to year and, when coupled with population growth in Oklahoma's urban areas, can create stress on water supplies.
During hot summer months, as much as 50 percent of all water is used on outdoor landscapes.
Oklahoma water-wise landscape practices establish colorful and attractive landscapes that require less water and maintenance than conventional landscaping.
Water-wise landscapes are designed to work with periods of natural rainfall and to be hardy enough to withstand long periods of drought.
Consider implementing the seven water-wise landscape principles in your landscape!
Figure 2.
Pervious pavers: Consider the installation of pervious hardscapes that allow water to infiltrate rather than run off.
Figure 3.
Soil test bag: Perform a soil test to ensure the soil has the nutrients required to maintain a healthy landscape.
Nonpoint Source Pollution in the Beaver Reservoir/Upper White River Watershed
 The Arkansas portion of the Beaver Reservoir watershed is located in northwest Arkansas and includes communities in Benton, Boone, Carroll, Crawford, Franklin, Johnson, Madison, Newton and Washington counties.
The watershed includes areas of southern Missouri.
A "watershed" is an area of land where all of the water that drains from it goes to the same place, SO rainwater or snowmelt in this watershed eventually drains to a common location.
Referred to sometimes as the Upper White River Watershed, the Beaver Reservoir Watershed spans 2,219 square miles and is predominantly comprised of forest, including a national forest.
1 This watershed includes Beaver Lake, the region's source of drinking water and a popular recreation spot for fishing, boating and swimming.
At the start of the decade, more than 176,000 people lived in the watershed, and the population is expected to continue growing.2
 Water pollution that comes from multiple sources spread over an area, such as runoff from parking lots, agricultural fields, residential lawns, home gardens, construction, mining and logging, is known as nonpoint source pollution.
As runoff moves across the landscape, it carries natural and manmade substances that can accumulate in waterways and make them uninhabitable for aquatic species or unusable by people.
Potential pollutants include bacteria, nutrients, sediment, hazardous substances and trash.
3 Given the number of potential sources and variation in their potential contributions, these pollutants are not easily traced back to their source.
Beaver Reservoir/Upper White River Watershed Data source: GeoStor.
Map created March 2011.
Major streams: Brush Creek, Clear Creek, Dry Creek, Dry Fork Creek, Holman Creek, Indian Creek, Keels Creek, Kings River, Lollar Creek, Long Creek, Mill Creek, Osage Creek, Piney Creek, Richland Creek, Terrapin Creek, War Eagle Creek, White River, Yocum Creek
 The population of Benton and Washington counties grew 44.3 percent and 28.8 percent, respectively, from 2000-2010.
4
 This fact sheet is intended to provide a better understanding of the Beaver Reservoir Watershed and its place on the state's priority list of 10 watersheds impacted by nonpoint source pollution.
Beaver Reservoir Watershed Water Quality Issues
 Past water quality monitoring by Arkansas environmental officials shows that portions of the watershed have distinct pollution concerns.
5 Total suspended solids, silt, turbidity, a lack of oxygen, and nutrients have all been identified as issues in this watershed.
The region's historical use of animal manure as a fertilizer has contributed to the state designating the region including this watershed as a "nutrient surplus area." There are regulations on applying poultry litter or commercial fertilizer products to land in the area.
6
 Nitrogen and phosphorus are essential nutrients that support the growth of algae and plants.
Nutrients can threaten water quality when people do not follow best management practices, such as applying the right amount of phosphorus as a fertilizer or using grassy buffers to prevent it from entering runoff water or nearby waterways.
Phosphorus can also enter waterways as part of discharge from water treatment plants, which are regulated by the state and have permits that allow specific amounts of nutrients to be discharged.
Turbidity is a measure of the clarity of water and is often the result of excess silt or sediment entering a stream.
High turbidity levels mean the water is murky from a variety of materials, such as soil particles, algae, microbes and other substances.
Turbidity can affect aquatic life in waterways.
Total dissolved solids can originate from natural geological sources such as dissolving rocks.
There are wastewater treatment plants that discharge in this watershed.
However, phosphorous levels in the Kings River and Osage Creek have decreased significantly in recent years.
In this watershed, the majority of
 Arkansas' Priority Watershed List for Nonpoint Source Pollution
 Arkansas has used a watershed-based approach to nonpoint source pollution management, allowing the public to guide planning to address water quality concerns.
The Arkansas Natural Resources Commission, or ANRC, administers the Nonpoint Source Pollution Management Program.
The program exists to reduce water pollution through the funding of watershed planning and restoration activities, adoption of voluntary best management practices and the development of technologies that assist in water pollution reduction in Arkansas.
Based on public input and the use of a qualitative risk assessment matrix, ANRC has designated 10 priority watersheds as needing the greatest attention.
The risk matrix7 identified the following priority watersheds for 2011-2016: Bayou Bartholomew, Beaver Reservoir, Cache River, Illinois River, L'Anguille River, Lake Conway-Point Remove, Lower OuachitaSmackover, Poteau River, Strawberry River and Upper Saline.
phosphorus entering waterways comes from nonpoint sources, including runoff from farms and urban developments.
The rapid population growth and increased construction in Benton and Washington counties over the past two decades could contribute to the concern for nonpoint source pollution.
8
 Despite new development, unpaved roads continue to be a source of excessive sediment in area waters, as well as streambank erosion.
Sections of the White River downstream of West Fork have been found to not support some species of aquatic life because of excessive sediment and high turbidity, or cloudy water.
In the past, the middle fork of the White River and the river itself have had oxygen levels too low to support some species.
These concerns and its border state status led to the Beaver Reservoir Watershed being designated as a priority by the Arkansas Natural Resources Commission in the state's 2011-2016 Nonpoint Source Pollution Management Plan.
9
 To encourage continued public input, the University of Arkansas Division of Agriculture's Public Policy Center facilitated a water quality stakeholder forum for the Beaver Reservoir Watershed in August 2015.
Unlike many of Arkansas' watersheds, the Beaver Reservoir Watershed has a history of active watershed groups working to restore waterways or prevent further pollution.
Forum participants identified funding as their watershed's priority concern, saying that more money is necessary to meet the needs already identified by stakeholder groups.
Participants also expressed two other priorities continued focus on educating the public about nonpoint source pollution and sediment reduction by way of erosion control and streambank stabilization.
People who live, work or recreate in this watershed are encouraged to consider community priorities when addressing water pollution.
The public is also welcome to attend an annual stakeholder meeting where priority watersheds and nonpoint source pollution are discussed.
For more information about nonpoint source pollution and its impact on the Beaver Reservoir Watershed, contact the Cooperative Extension Service, Arkansas Natural Resources Commission or the Arkansas Department of Environmental Quality.
The Arkansas Watershed Steward Handbook is also a good source of information about basic water quality concerns and how the public can get engaged in addressing water pollution.
10
 This fact sheet is one in a series of 10 fact sheets on nonpoint source pollution in priority watersheds.
The University of Arkansas Division of Agriculture's Public Policy Center provides timely, credible, unbiased research, analyses and education on current and emerging public issues.
The Arkansas Cooperative Extension Service offers its programs to all eligible persons regardless of race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or
 veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
USING THE K-STATE CENTER PIVOT SPRINKLER AND SDI ECONOMIC COMPARISON SPREADSHEET 2009
 In much of the Great Plains, the rate of new irrigation development is slow or zero.
Although the Kansas irrigated area, as reported by producers through annual irrigation water use reports, has been approximately 3 million acres since 1990, there has been a dramatic shift in the methods of irrigation.
During the period since 1990, the number of acres irrigated by center pivot irrigation systems increased from about 50 per cent of the total irrigated acreage base to about 90 percent of the base area.
In 1989, subsurface drip irrigation  research plots were established at Kansas State University Research Stations to investigate SDI as a possible additional irrigation system option.
Early industry and producers surveys have indicated a small but steady increase in adoption.
Field area as reported by the 2006 Kansas Irrigation Water Use Report indicated that 10,250 acres were exclusively irrigated by SDI systems and an additional 8,440 acres were irrigated partly by SDI in combination with another system type such as an irrigated SDI corner of a center pivot sprinkler or a surface gravityirrigated field partially converted to SDI.
Although Kansas SDI systems represent less than 1 percent of the irrigated area, producer interest still remains high because SDI can potentially have higher irrigation efficiency and irrigation uniformity.
As the farming populace and irrigation systems age, there will likely be a continued momentum for conversion to modern pressurized irrigation systems.
Both center pivot sprinkler irrigation  and subsurface drip irrigation  are options available to the producer for much of the Great Plains landscape.
Pressurized irrigation systems in
 general are a costly investment and this is particularly the case with SDI.
Producers need to carefully determine their best investment options.
In the spring of 2002, a free Microsoft Excel 1 spreadsheet template was introduced by K-State Research and Extension for making economic comparisons of CP and SDI.
Since that time, the spreadsheet has been periodically updated to reflect changes in input data, particularly system and corn production costs.
The spreadsheet also provides sensitivity analyses for key factors.
This paper will discuss how to use the spreadsheet and the key factors that most strongly affect the comparisons.
The template has five worksheets , the Main, CF, Field size & SDI life, SDI cost & life, Yield & price tabs.
Most of the calculations and the result are shown on the Main tab.
Field description and irrigation system estimates
 Total	Suggested	CP	Suggested	SDI	Suggested
 Field area, acres	160	160	125	125	155	155
 Non-cropped field area , acres	5	5
 Cropped dryland area, acres 	30	0
 Irrigation system investment cost, total $	$73,450	-$73,450	$186,000	$186,000
 Irrigation system investment cost, $/irrigated acre	$587.60	$1,200.00
 Irrigation system life, years	25	25	20	20
 Interest rate for system investment, %	8.0%	8.0%
 Annual insurance rate, % of total system cost	1.60%	1.60%	0.60%	0.60%
 Production cost estimates	CP	Suggested	SDI	Suggested
 Total variable costs, $/acre 	$585.92	$585.92	$559.29	$559.29
 Additional SDI variable costs  or savings , $/acre	Additional Costs	$0.00	$0.00
 Yield and revenue stream estimates	CP	Suggested	SDI	Suggested
 Corn grain yield, bushels/acre	Suggested	220	-220	220	220
 Corn selling price, $/bushel	$4.00	$4.00	KSTATE
 Net return to cropped dryland area of field 	$36.00	$36.00	Kania State University
 Advantage of SDI over Center Pivot Sprinkler
 *	$/total field each year	$1,065.25
 *	Advantage in net returns to land and management	$/acres each year	$6.66
 You may examine sensitivity to Main worksheet  assumptions on three of the tabs listed below.
Figure 1.
Main worksheet  of the economic comparison spreadsheet template indicating the 18 required variables  and their suggested values when further information is lacking or uncertain.
ANALYSES METHODS AND ECONOMIC ASSUMPTIONS
 There are 18 required input variables required to use the spreadsheet template, but if the user does not know a particular value there are suggested values for each of them.
The user is responsible for entering and checking the values in the unprotected input cells.
All other cells are protected on the Main worksheet.
Some error checking exists on overall field size and some items  are highlighted differently when different results are indicated.
Details and rationales behind the input variables are given in the following sections.
Field & irrigation system assumptions and estimates
 Many of the early analyses assumed that an existing furrow-irrigated field with a working well and pumping plant was being converted to either CP or SDI and this still may be the base condition for some producers.
However, the template can also be used to consider options for a currently center pivot irrigated field that needs to be replaced.
The major change in the analysis for the replacement CP is that the cost for the new center pivot probably would not have to include buried underground pipe and electrical service in the initial investment cost.
The analysis also assumes the pumping plant is located at the center of one of the field edges and is at a suitable location for the initial SDI distribution point.
Any necessary pump modifications  for the CP or SDI systems are assumed to be of equal cost and thus are not considered in the analysis.
However, they can easily be handled as an increased system cost for either or both of the system types.
Land costs are assumed to be equal across systems for the overall field size with no differential values in real estate taxes or in any government farm payments.
Thus, these factors "fall out" or do not economically affect the analyses.
An overall field size of 160 acres  was assumed for the base analysis.
This overall field size will accommodate either a 125 acre CP system or a 155 acre SDI system.
It was assumed that there would be 5 noncropped acres consumed by field roads and access areas.
The remaining 30 acres under the CP system are available for dryland cropping systems.
Irrigation system costs are highly variable at this point in time due to rapid fluctuations in material and energy costs.
Cost estimates for the 125 acre CP system and the 155 acre SDI system are provided on the current version of the spreadsheet template based on discussions with dealers and Dumler et al.
, but since this is the overall basis of the comparison, it is recommended that the user apply his own estimates for his conditions.
In the base analyses, the life for the two systems is assumed to be 25 and 20 years for the CP and SDI systems, respectively.
No salvage value was assumed for either system.
This assumption of no salvage value may be inaccurate, as both systems might have a few components that may be reusable or available for resale at the end of the system life.
However, with relatively long depreciation periods of 20 and 25 years and typical financial interest rates, the zero salvage value is a very minor issue in the analysis.
System life is a very important factor in the overall analyses.
However, the life of the SDI system is of much greater economic importance in analysis than a similar life for the CP system because of the much higher system costs for SDI.
Increasing the system life from 20 to 25 years for SDI would have a much greater economic effect than increasing the CP life from 20 to 25 years.
When the overall field size decreases, thus decreasing system size, there are large changes in cost per irrigated acre between systems.
SDI costs are nearly proportional to field size, while CP costs are not proportional to field size (Figure
 2).
Quadratic equations were developed to calculate system costs when less than full size 160 acre fields were used in the analysis :
 CPcost% = 44.4 +  	
 SDIcost% = 2.9 +  	
 where CPcost% and CPsize%, and SDIcost% and SDIsize% are the respective cost and size % in relation to the full costs and sizes of irrigation systems fitting within a square 160 acre block.
Figure 2.
CP and SDI system costs as related to field size.
The annual interest rate can be entered as a variable, but is currently assumed to be 8.0%.
The total interest costs over the life of the two systems were converted to an average annual interest cost for this analysis.
Annual insurance costs were assumed to be 1.6% of the total system cost for the center pivot sprinkler and 0.6% for the SDI system, but can be changed if better information is available.
The lower value for the SDI was based on the assumption that only about 40% of the system might be insurable.
Many of the SDI components are not subject to the climatic conditions that are typically insured hazards for CP systems.
However, system failure risk is probably greater with SDI systems which might influence any obtainable insurance rate.
The cost of insurance is a minor factor in the economic comparison when using the current values.
Production cost assumptions and estimates
 The economic analysis expresses the results as an advantage of SDI or alternatively CP systems in net returns to land and management.
Thus, many fixed costs do not affect the analysis and can be ignored.
Additionally, the analysis does not indicate if either system is ultimately profitable for corn production under the assumed current economic conditions.
Production costs were adapted from KSU estimates.
A listing of the current costs is available on the CF worksheet   and the user can enter new values to recalculate variable costs that more closely match their conditions.
The sum of these costs would become the new suggested Total Variable Costs on the Main worksheet , but the user must manually change the input value on the Main worksheet  for the economic comparison to take effect.
The user may find it easier to just change the differential production costs between the systems on the Main tab rather than changing the baseline assumptions on the CF tab.
This will help maintain integrity of the baseline production cost assumptions.
Factors for Variable Costs	CP	Suggested	SDI	Suggested
 Seeding rate, seeds/acre	$/1000 S Suggested	34000	34000	34000	34000
 Seed, $/acre	$2.24	$2.24	$76.16	$76.16
 Herbicide, $/acre	$28.68	$28.68	$28.68	$28.68
 Insecticide, $/acre	$35.30	$35.30	$35.30	$35.30
 Nitrogen fertilizer, lb/acre	$/lb	Suggested	242	242	242	242
 Nitrogen fertilizer, $/acre	$0.40	$0.40	$96.80	$96.80
 Phosphorus fertilizer, lb/acre	$/lb	Suggested	50	50	50	50
 Phosphorus fertilizer, $/acre	$0.35	$0.35	$17.50	$17.50
 Crop consulting, $/acre	$6.50	$6.50	$6.50	$6.50
 Crop insurance, $/acre	$37.00	$37.00	$37.00	$37.00
 Drying cost, $/acre	$0.00	$0.00	$0.00	$0.00
 Miscellaneous costs, $/acre	$0.00	$0.00	$0.00	$0.00
 Custom hire/machinery expenses, $/acre	$150.14	-$150.14	$150.14	-$150.14
 Other non-fieldwork labor, $/acre	$0.00	$0.00	$0.00	$0.00
 Irrigation labor, $/acre	$6.50	$6.50	$6.50	$6.50
 Irrigation amounts, inches	17	17	13	13
 Fuel and oil for pumping, $/inch	$5.80	$5.80	$5.80	$5.80
 Fuel and oil for pumping, $acre	$98.60	$75.40
 Irrigation maintenance and repairs, $/inch	$0.60	$0.60	$0.60	$0.60
 Irrigation maintenance and repairs, $/acre	Suggested	$10.20	$7.80
 1/2 yr.
interest on variable costs, rate 8.0%	8.0%	$22.54	$21.51
 Total Variable Costs	$585.92	$559.29
 Figure 3.
CF worksheet  of the economic comparison spreadsheet template and the current production cost variables.
Note that the sums at the bottom of the CF worksheet are the suggested values for total variable costs on the Main worksheet.
The reduction in variable costs for SDI is attributable to an assumed 25% net water savings that is consistent with research findings by Lamm et al..
This translates into a 17 and 13 inch gross application amount for CP and SDI, respectively.
The current estimated production costs are somewhat high reflecting increased energy and other related input costs, but fortunately crop revenues have also increased due to high demand for corn for ethanol production.
This fact is pointed out because a lowering of overall variable costs favors SDI, since more irrigated cropped acres are involved, while higher overall variable costs favors CP production.
The variable costs for both irrigation systems represent typical practices for western Kansas.
Yield and revenue stream estimates
 Changes in the economic assumptions can drastically affect which system is most profitable and by how much.
Previous analyses have shown that the system comparisons are very sensitive to assumptions about
 Size of CP irrigation system
 Shape of field 
 Life of SDI system
 with advantages favoring larger CP systems and cheaper, longer life SDI systems.
The results are very sensitive to
 any additional production cost savings with SDI.
The results are moderately sensitive to
 and very sensitive to
 higher potential yields with SDI
 with advantages favoring SDI as corn yields and price increase.
The economic comparison spreadsheet also includes three worksheet  that display tabular and graphical sensitivity analyses for field size and SDI system
 life , SDI system cost and life , and corn yield and selling price.
These sensitivity analysis worksheets will automatically update when different assumptions are made on the Main worksheet.
The elements in light blue of the sensitivity tables indicate cases where CP systems are more profitable while elements with negative signs in reddish brown are cases where SDI is more profitable.
This tab determines the CP and SDI economic sensitivity to field size, shape,
 and SDI system life.
The elements in the table  represent the CP advantage in net returns per acre.
Field size	160	127	95	64	32	80
 CP Size	125	100	75	50	25	64	Wiper 1/2 circle
 CP Cost	$587.60	$685.38	$827.22	$1,077.78	$1,763.15	$1,147.66
 CP Dry	30	24	18	12	6	14
 SDI Size	155	124	93	62	31	78
 SDI Cost	$1,200.00 $1,226.70 $1,255.60 $1,299.00 $1,400.40 $1,273.72
 SDI life	Note: This sensitivity valid only if full-sized CP  and
 years	SDI  costs exist on Main worksheet  !!!!!!!!
5	$167.72	$168.06	$164.71	$154.55	$127.31	$146.23
 10	$51.47	$48.29	$41.79	$28.71	-$8.36	$22.05
 15	$12.72	$8.36	$0.82	-$13.24	-$53.58	-$19.35
 20	-$6.66	-$11.60	-$19.66	-$34.21	-$76.19	-$40.05
 25	-$18.28	-$23.58	-$31.96	-$46.80	-$89.75	-$52.47
 Figure 4.
The Field size & SDI life worksheet  sensitivity analysis.
Note this is one of three worksheets  providing tabular and graphical sensitivity analyses.
These worksheets automatically update to reflect changing assumptions on the Main worksheet.
SOME KEY OBSERVATIONS FROM PREVIOUS ANALYSES
 Users are encouraged to "experiment" with the input values on the Main worksheet  to observe how small changes in economic assumptions can vary the bottom line economic comparison of the two irrigation systems.
The following discussion will give the user "hints" about how the comparisons might be affected.
Smaller CP systems and systems which only complete part of the circle are less competitive with SDI than full size 125 acre CP systems This is primarily because the CP investment costs  increase dramatically as field size decreases  or when the CP system cannot complete a full circle.
It should also be pointed out that part of the economic competitiveness of the higher priced SDI systems with lower priced CP systems occurs simply because less land area of the field is in dryland crop production.
Increased longevity for SDI systems is probably the most important factor for SDI to gain economic competitiveness with CP systems.
A research SDI system at the KSU Northwest Research-Extension Center in Colby, Kansas has been operated for 20 years with very little performance degradation, so long system life is possible.
There are a few SDI systems in the United States that have been operated for over 25 years without replacement.
However, a short SDI system life that might be caused by early failure due to clogging, indicates a huge economic disadvantage that would preclude nearly all adoption of SDI systems.
Although SDI cost is an important factor, long SDI system life can help reduce the overall economic effect.
The CP advantage for SDI system lives between 15 and 20 years is greatly diminished as compared to the difference between 10 and 15 year SDI system life.
The sensitivity of CP system life and cost is much less because of the much lower initial CP cost and the much longer assumed life.
Changing the CP system life from 25 to 20 years will not have a major effect on the economic comparison.
However, in areas where CP life might be much less than 25 years due to corrosive waters, a sensitivity analysis with shorter CP life is warranted.
The present baseline analysis already assumes a 25% water savings with SDI.
There are potentially some other production cost savings for SDI such as fertilizer and herbicides that have been reported for some crops and some locales.
For example, there have been reports from other regions of less broadleaf and grassy weed pressure in SDI where the soil surface remains drier less conducive to germination of weed seeds.
Small changes in the assumptions can make a sizable difference in the economic analysis because there are more irrigated acres under the SDI system.
This tab determines the CP and SDI economic sensitivity to SDI system life and SDI system cost.
The elements in the table  represent the CP advantage in net returns per acre.
SDI Cost	SDI system life, years
 $/acre	5	10	15	20	25	30
 900	$96.22	$9.04	-$20.03	-$34.56	-$43.28	-$49.09
 1000	$120.05	$23.18	-$9.11	-$25.26	-$34.95	-$41.40
 1100	$143.89	$37.32	$1.80	-$15.96	-$26.61	-$33.72
 1200	$167.72	$51.47	$12.72	-$6.66	-$18.28	-$26.03
 1300	$191.55	$65.61	$23.63	$2.64	-$9.95	-$18.35
 1400	$215.38	$79.75	$34.55	$11.94	-$1.62	-$10.66
 1500	$239.21	$93.90	$45.46	$21.24	$6.71	-$2.98
 Figure 5.
The SDI cost and life worksheet  sensitivity analysis.
Note this is one of three worksheets  providing tabular and graphical sensitivity analyses.
These worksheets automatically update to reflect changing assumptions on the Main worksheet.
It has already been stated that higher corn yields and higher corn prices improve the SDI economics.
These results can be seen on the Yield and Price sensitivity worksheet  on the Excel template.
This result occurs because of the increased irrigated area for SDI in the given 160 acre field.
The significance of yield and price can be illustrated by taking one step further in the economic analysis, that being the case where there is a yield difference between irrigation systems.
Combining a greater overall corn yield potential with an additional small yield advantage for SDI on the Main tab can allow SDI to be very competitive with CP systems.
This tab determines the CP and SDI economic sensitivity to corn yield and corn price assuming that corn yields are equal for both irrigation systems.
The elements in the table  represent the CP advantage in net returns per acre.
Corn cash price, $/bu
 Corn Yield	$2.80	$3.20	$3.60	$4.00	$4.40	$4.80	$5.20
 160	$74.34	$62.34	$50.34	$38.34	$26.34	$14.34	$2.34
 170	$69.09	$56.34	$43.59	$30.84	$18.09	$5.34	-$7.41
 180	$63.84	$50.34	$36.84	$23.34	$9.84	-$3.66	-$17.16
 190	$58.59	$44.34	$30.09	$15.84	$1.59	-$12.66	-$26.91
 200	$53.34	$38.34	$23.34	$8.34	-$6.66	-$21.66	-$36.66
 210	$48.09	$32.34	$16.59	$0.84	-$14.91	-$30.66	-$46.41
 220	$42.84	$26.34	$9.84	-$6.66	-$23.16	-$39.66	-$56.16
 230	$37.59	$20.34	$3.09	-$14.16	-$31.41	-$48.66	-$65.91
 240	$32.34	$14.34	-$3.66	-$21.66	-$39.66	-$57.66	-$75.66
 250	$27.09	$8.34	-$10.41	-$29.16	-$47.91	-$66.66	-$85.41
 260	$21.84	$2.34	-$17.16	-$36.66	-$56.16	-$75.66	-$95.16
 270	$16.59	-$3.66	-$23.91	-$44.16	-$64.41	-$84.66	-$104.91
 Figure 6.
The Yield and Price worksheet  sensitivity analysis.
Note this is one of three worksheets  providing tabular and graphical sensitivity analyses.
These worksheets automatically update to reflect changing assumptions on the Main worksheet.
AVAILABILITY OF FREE SOFTWARE
 Contribution No.
09-242-A from the Kansas Agricultural Experiment Station.
1 Mention of tradenames is for informational purposes and does not constitute endorsement by Kansas State University.
Example Savings from Using Sensors for an Irrigation System: To illustrate the potential savings from using sensors, lets use an example irrigation system irrigating 130 acres with a pumping lift of 150 feet and a system pressure of 45 psi and diesel fuel at $2.00 per gallon.
Discount on Cash Rent per Acre When Tenant Owns Pivot for Irrigation System in Nebraska:
 2.4% of respondents have a $0 discount on cash rent per acre when the tenant owns pivot for irrigation system.
30.6% of respondents have a $10-$25 discount on cash rent per acre when the tenant owns pivot for irrigation system.
58.5% of respondents have a $26-$50 discount on cash rent per acre when the tenant owns pivot for irrigation system.
8.5% of respondents have a $51+ discount on cash rent per acre when the tenant owns pivot for irrigation system.
IRRIGATION SCHEDULING WITH PLANNED SOIL WATER DEPLETION
 ABSTRACT.
A two-year study was initiated in the spring of 1990 on a Keith silt loam soil  in northwest Kansas to determine if irrigation scheduling with planned soil water depletion could be used successfully for irrigated corn  as a method of conserving and protecting groundwater resources without reducing yields.
The study was conducted using surface irrigation in small dead-level basins.
Planned soil water depletion was attempted by allowing a small additional daily deficit  to accumulate in irrigation amounts as scheduled by an evapotranspiration -based water budget.
The daily deficit amounts were imposed on three irrigation levels, heavy , normal , and deficit  which represented a range of management by irrigators.
The plant-available soil water at physiological maturity was related linearly to irrigation amounts.
However, the plantavailable soil water at physiological maturity was reduced by only 25 mm for each 100 mm reduction in irrigation.
Imposition of a small daily deficit of 1 mm/day after tasseling resulted in yield reductions of 7, 1, and 3% for the heavy, normal, and deficit irrigation management levels, respectively.
The 1 mm/day deficit resulted in irrigation savings of approximately 12, 9, and 0% for the three respective irrigation management levels and generally resulted in slight reductions in available soil water at physiological maturity.
In some cases, the imposition of the 1 mm/day deficit had little effect on the total seasonal irrigation amount, but simply shifted the irrigation event to a later date.
The larger 2 mm/day daily deficit after tasseling reduced yields by 7, 9, and 15% for the three respective irrigation levels and reduced irrigation amounts by 19, 26, and 25%.
Yields were related linearly to irrigation and water use with a reduction in irrigation or water use reflected by yield reductions.
Water use efficiencies were similar whether planned soil water depletion was used or not.
Therefore, from a water conservation standpoint, irrigation scheduling with planned soil water depletion was not justified.
Keywords.
Irrigation, Soil water depletion, Corn, Water use efficiency.
D eclining groundwater supplies, increased competition for available water resources, and irrigation-induced, water-quality problems have resulted in an increased need for waterconserving irrigation practices.
Irrigation practices for corn production in western Kansas usually extend watering until late in the season, resulting in high levels of soil water remaining in the profile in the fall after harvest.
Rogers and Lamm  found in a survey of 82 producer fields in northwest Kansas that plant-available soil water contents after corn harvest averaged 70% of field capacity for a 1.5-m-depth soil profile.
One method of conserving water would be to mine the plant-available soil water gradually during the irrigation season, in anticipation of recharge from precipitation during the off season.
This concept of irrigation scheduling
 Article was submitted for publication in February 1994; reviewed and approved for publication by the Soil and Water Div.
of ASAE in June 1994.
Presented as ASAE Paper No.
93-2583.
The mention of trade names or commercial products does not constitute their endorsement or recommendation by the authors or by the Kansas Agricultural Experiment Station.
Contribution No.
94-288-J from the Kansas Agricultural Experiment Station.
with planned soil water depletion was developed by Woodruff et al.
under semi-humid conditions in Missouri.
Further experimental testing of the concept  found it could be used successfully on deep soil profiles with high water holding capacity, provided irrigation frequency was sufficient to maintain adequate soil water in the most active zone of water and nutrient uptake.
Martin et al.
reported that mining of 50% of the soil water may be acceptable if off-season precipitation is sufficient to fully recharge the crop root zone.
Drier soil profiles at harvest result in greater opportunity for capturing winter precipitation and also reduce the potential for overwinter drainage losses and leaching of chemicals to groundwater.
Research in Kansas by Rice  found that nitrate leaching during the growing season was minimal and that the overwinter period was of greater concern because the evapotranspiration  then is usually lower than the precipitation.
Mining plant-available soil water to a low level would be acceptable and even desirable if corn yields could be maintained.
However, deficit irrigation of corn is difficult to implement successfully without incurring yield reductions.
After reviewing numerous studies, Rhodes and Bennett  reported, that water stress imposed at any growth stage on corn will generally lower the efficiency of the water used in transpiration.
Mining the soil water may be possible by allowing a slight deficit in irrigation amounts to accumulate over the latter part of the season.
The difficulty in this approach is that this period also coincides with the most critical crop growth stages.
In simulation studies, Gilley et al.
found that for several locations in Nebraska, replacing 90 and 80% of the cumulative ET during the reproductive and grain filling stages for corn, respectively, resulted in near maximum yields.
Using an ET-based water budget, an irrigator may be able to avoid yield reductions by allowing a small, daily deficit in supplying ET needs to occur over a long period of time.
2 mm/day beginning after tasseling were superimposed on the three management levels.
For example, assuming a 40-day period between tasseling and the last irrigation and with no drainage below the root zone, one would expect the normal  irrigation treatment with a 2 mm/day daily deficit to have an additional 80 mm of soil water deficit at the end of the irrigation season compared to the normal treatment with the 0 mm/day daily deficit.
Actual amounts would vary considerably, depending on timing and amounts of irrigation and precipitation.
Summarizing the nine irrigation treatments:
 Three irrigation management levels were included in the study, heavy , and deficit (0.75 representing the range of management that occurs among irrigators.
One of three daily deficits, 0, 1, or
 Heavy irrigation ET) Treatments
 1.
Daily deficit of 0 mm/day after tasseling 
 2.
Daily deficit of 1 mm/day after tasseling 
 3.
Daily deficit of 2 mm/day after tasseling 
 Field studies were conducted at the Kansas State University  Northwest Research-Extension Center, Colby, Kansas, during 1990 and 1991 on a deep, welldrained, loessial, Keith silt loam soil.
This medium-textured soil, typical of many western Kansas soils, is described in more detail by Bidwell et al..
The 1.5-m soil profile will hold approximately 300 mm of available water at field capacity and has a profile bulk density of approximately 1.3 gm/cm.
This corresponds to a volumetric soil water content of approximately 0.34.
The reference evapotranspiration  was calculated using a modified Penman combination equation similar to the procedures outlined by Kincaid and Heerman.
The specifics of the ET, calculations used in this study are fully described by Lamm et al..
Basal crop coefficients  were generated by equations developed by Kincaid and Heerman  based on work by Jensen  and Jensen et al..
The basal crop coefficients were calculated for the area by assuming 70 days from emergence to full canopy for corn and physiological maturity at 130 days.
This method of calculating actual evapotranspiration  as the product of and ET, has been applied in past studies at Colby, Kansas, and it has been found to estimate AET accurately.
In constructing the irrigation schedules, no attempt was made to modify AET with respect to soil-evaporation losses or soil-water availability as outlined by Kincaid and Heerman.
4.
Daily deficit of 0 mm/day after tasseling 
 5.
Daily deficit of 1 mm/day after tasseling 
 6.
Daily deficit of 2 mm/day after tasseling 
 Deficit irrigation  Treatments
 7.
Daily deficit of 0 mm/day after tasseling 
 8.
Daily deficit of 1 mm/day after tasseling 
 9.
Daily deficit of 2 mm/day after tasseling 
 The continental climate can be described as semi-arid, with an average annual precipitation of 474 mm and approximate annual lake evaporation of 1400 mm.
Daily climatic data used to schedule irrigation were obtained from a NOAA weather station located approximately 350 m northeast of the study site.
The study was conducted each year in a different 0.6-ha, dead-level irrigation basin approximately 180 m long X 30 m wide with plots 4.6 m wide and 30 m long running perpendicular to the level basin length.
The plots accommodated six corn rows spaced 76 cm apart.
Small dikes were constructed around each plot to prevent runoff onto adjacent plots.
The study treatments were replicated three times in a randomized complete block design.
The treatments were analyzed as a single-factor design.
Irrigation was scheduled using a water budget to calculate the root zone depletion with precipitation and irrigation water amounts as deposits and calculated daily corn water use  as a withdrawal.
Irrigation efficiencies were assumed to be 100% in the small deadlevel irrigation basins.
Modification of the individual treatment irrigation schedules to simulate the various management levels, heavy, normal, or deficit irrigation, was accomplished by multiplying the calculated AET value by 1.25, 1.00, or 0.75, respectively.
Planned soil water depletion was accomplished by reducing the calculated AET value by the daily deficit  after tasseling.
If the root-zone depletion became negative, it was reset to zero.
Treatments were irrigated to replace 100% of their calculated root-zone depletion, when the depletion was within the range of 65 to 100 mm.
Most irrigations were applied at a depletion of approximately 65 mm.
Irrigation water was metered separately onto each plot.
All plots started the season with a nearly full soil water profile.
All treatments received an initial irrigation of 64 mm after the layby furrowing was performed  to alleviate water stress caused by root pruning during the furrowing process.
A neutron probe was used to measure volumetric soil water contents in 30-cm increments to a depth of 1.5 m on an approximately weekly basis during each season.
Access tubes were located near the center of each plot in-line with the corn row.
The plant-available soil water was calculated from these data using wilting point values determined from long-term dryland research for the soil type.
The soil water measurements were used to evaluate the treatment responses, but were not used to periodically update or adjust the irrigation schedules.
The seasonal water use for each treatment was calculated as the sum of precipitation, irrigation, and
 measured soil water depletion between the initial  and the final  soil water measurements.
Water use, as expressed here, included any deep percolation that occurred.
Water use efficiency was calculated as the corn grain yield in milligram per hectare divided by the calculated water use in millimeters.
Conventional tillage was used in corn production.
The previous crop  residue was shredded and doubledisked in the fall for increased residue decomposition.
Nitrogen  at a rate of 245 kg/ha of N and phosphorus  at a rate of 45 kg/ha of P2O5 was broadcast applied as a solution in mid-October.
Following fertilization, the area was furrowed to prevent overwinter wind erosion and to provide 76-cm-spaced ridges for planting in the spring.
Corn  was planted at a seeding rate of 65,500 seeds/ha on 23 April 1990 and 8 May 1991.
The corn emerged on 15 May each year.
An approximately 6-m length of one corn row from the center of each plot was hand harvested at physiological maturity on 18 September of each year for yield determination.
EFFECT OF CLIMATIC CONDITIONS
 Seasonal precipitations  were 309 and 332 mm for 1990 and 1991, respectively, which was very near the long-term  mean of 321 mm.
However, in both years, May precipitation was significantly greater than the 99-year mean.
The corn emerged on 15 May in each year so crop water use from the available May precipitation was low.
In 1990, all months except May had precipitation amounts less than the long-term average.
In 1991, both August and September had lower than average precipitation amounts.
The cumulative calculated AET for the 120-day period beginning on 15 May was 592 and 600 mm for 1990 and 1991, respectively, as compared to the 20-year mean of 587 mm.
The net irrigation requirement for corn in Thomas County of northwest Kansas is 391 mm with 80% chance precipitation.
In 1990, extremely high AET during the mid-June to mid-July period, coupled with low precipitation, resulted in greater irrigation needs than most irrigation systems in northwest
 Figure 1-Seasonal precipitation at KSU Northwest ResearchExtension Center, Colby, 1990-1991.
Figure 2-Cumulative AET for corn calculated from climatic data, KSU Northwest Research-Extension Center, Colby, 1990-1991.
Kansas could provide.
Nearly 63% of the seasonal irrigation requirement of 363 mm for the normal fully irrigated condition  was applied before the corn tasseled on 20 July.
Seasonal irrigation amounts for the various treatments ranged from a high of 499 mm to a low of 202 mm.
Fortunately, deep soils with available water buffered the corn from excessive water stress during the period.
The crop year 1991 was characterized by slightly above-normal precipitation in June and July but appreciably below-normal precipitation in August and September, resulting in 84% of the seasonal irrigation amount of 410 mm for the normal fully irrigated condition  being applied after the corn tasseled on 20 July.
Seasonal irrigation amounts for 1991 were relatively similar to those of 1990 ranging from a high of 530 mm to a low of 191 mm.
Table 1.
Irrigation dates and amounts  for the various treatments, 1990-1991
 Date	Trt 1	Trt 2	Trt 3	Trt 4	Trt 5	Trt 6	Trt 7	Trt 8	Trt 9
 19 Jun	64	64	64	64	64	64	64	64	64
 29 Jun	66	66	66
 3 Jul	89	89	89	64	64	64
 9 Jul	97	97	97
 17 Jul	76	76	76
 19 Jul	74	74	74	74	74	74
 8 Aug	70	70	70
 10 Aug	64	64
 22 Aug	64	64
 27 Aug	64	64	64
 29 Aug	64	64
 30 Aug	64	64
 Total	499	435	429	363	357	293	266	266	202
 2 Jul	64	64	64	64	64	64	64	64	64
 15 Jul	83	83	83
 18 Jul	84	84	84
 29 Jul	64	64	64	64
 2 Aug	64	64	64	64
 12 Aug	64	64	64
 16 Aug	64	64
 21 Aug	64	64	64	64	64
 26 Aug	64	64	64
 28 Aug	63	63	63	63	63
 4 Sep	70	70	70
 6 Sep	64	64	64
 Total	530	466	409	410	346	274	255	256	191
 The climatic conditions for the two years can be summarized overall as being near normal.
Irrigation amounts were also near normal, but the seasonal distributions were very dissimilar because of the timing of precipitation and high ET periods.
UTILIZATION OF PLANT-AVAILABLE SOIL WATER Contribution of Various Soil Profile Layers.
The soil
 profile depth an irrigator manages for irrigation scheduling purposes varies with soil type and climatic conditions.
In previous studies at Colby, a depth of 1.5 m has been considered adequate for fully irrigated corn.
The average seasonal change in plantavailable soil water for the 1.5 m profile between 6 June through 17 September 1990 and 28 May through 18 September 1991 is shown in figure 3.
The change in soil water as related to soil profile depth was nearly linear over the wide range of irrigation treatments, meaning that all layers contributed somewhat similar amounts of water.
This contradicts the classical textbook theory of increased crop water use from the surface layers, but is indicative of the ability of this particular deep soil profile to buffer the effects of dry surface layers with water from lower depths.
However, this buffering effect may not be as beneficial as frequent small irrigations of the surface layers, which should contain more nutrients for plant uptake.
There were significant differences in soil water depletion among treatments  with a general trend towards increased depletion with decreasing amounts of irrigation.
One noteworthy exception to the trend was Treatment 7 , which decreased soil water to a greater degree than Treatments 8 and 9, although not significantly.
Although Treatments 7 and 8 received similar amounts of total irrigation in both years, Treatment 7 received the last irrigation early enough to be effectively used in grain production.
As the irrigation treatments became more limited there was a greater reliance on the deeper parts of the soil profile for soil water utilization, as indicated by the decreasing line slopes.
Time Series Progression of Plant-available Soil Water.
Analysis of the time series progression of plantavailable soil water in the 1.5 m soil profile 
 Figure 3-Average cumulative change in soil water during the periods 6 June through 17 September 1990 and 28 May through 18 September 1991 as a function of depth in the soil profile for the various irrigation treatments.
Numbers to the right of graphed lines represent the least-significant-difference for the indicated depth at P = 0.05.
Figure 4-Time series progression of plant-available soil water in the 1.5-m-depth soil profile for the various irrigation treatments, 1990.
shows some of the distinct climatic characteristics for the two years.
In 1990, a sharp decrease in plant-available soil water occurred until about 3 July  which was reflective of the excessively high ET from mid-June through early July  and the low June precipitation.
Treatments 6, 7, 8, and 9 had soil water depletions of over 100 mm on 16 July.
This implies the water use model was slightly underestimating AET under the extreme climatic conditions because irrigation events should have kept depletions under 100 mm.
Because over 60% of the irrigation had been applied by the time the daily deficits were initiated in 1990, less separation occurred in plant-available soil water levels for the various daily deficit treatments than in 1991.
Another sharp decline began in late August 1990, following the last irrigation for the various treatments.
Unusually high temperatures and winds in early September 1990 caused another high ET period, which resulted in low soil water levels at physiological maturity, even for the heavy irrigation treatments.
Plantavailable soil water levels for the 1.5-m profile ranged from 97 to 150 mm.
In 1991, relatively high irrigation needs after tasseling , when the daily deficits were initiated, resulted in appreciable separation of soil water levels for the various treatments.
There were significant differences in plant-available soil water levels for the 1.5 mm profile at physiological maturity ranging from 98 to 232 mm.
Figure 5-Time series progression of plant-available soil water in the 1.5-m-depth soil profile for the various irrigation treatments, 1991.
Table 2.
Summary of corn yield and water use data, Northwest Research-Extension Center, 1990
 Yield	Water Use	WUE:	Soil Water
 Daily	1990	1991	Mean	1990	1991	Mean	1990	1991	Mean	1990	1991	Mean
 ET Factor*					(mm/1.5
 1.
1.25	0	13.1a	13.9a	13.5a	808a	820a	814a	0,016a	0,017a	0.017a	128abc	232a	180a
 2.
1.25	1	11.5ab	13.8a	12.6abc	747b	803a	775b	0.015a	0.017a	0.016a	114bcd	174b	144bc
 3.
1.25	2	12.1ab	13.2ab	12.6abc	732b	754b	743c	0.017a	0.018a	0.017a	136ab	161bc	149b
 4.
1.00	0	12.1ab	13.7ab	12.9ab	671c	767b	719d	0.018a	0.018a	0.018a	150a	149c	150b
 5.
1.00	1	12.5ab	13.0abc	12.8abc	676c	716c	696e	0.019a	0.018a	0.018a	124bc	142c	133c
 6.
1.00	2	11.2b	12.3bcd	11.7bcd	622d	665d	644f	0.018a	0.018a	0.018a	108cd	117d	112d
 7.
0.75	0	11.2b	11.7cde	11.5cd	592e	668d	630g	0.019a	0.018a	0.018a	97d	98d	97e
 8.
0.75	1	11.3ab	11.2de	11.2d	594e	635e	615h	0.019a	0.018a	0.018a	112cd	116d	114d
 9.
0.75	2	9.3c	10.4e	9.8e	528f	587f	558i	0.018a	0.018a	0.018a	100d	105d	102e
 Within columns, means followed by the same letter are not significantly different according to LSD means separation at P 0.05.
* Daily deficit amount applied to scheduling treatments after 20 July.
Water use efficiency is defined as yield in Mg/ha divided by total water use in mm.
Plant available soil water in a 1.5-m soil profile at corn physiological maturity on 17 September 1990 and 18 September 1991.
Irrigation and Plant-available Soil Water at Physiological Maturity.
The plant-available soil water at physiological maturity for the corn  was linearly related to the applied irrigation amount.
Linear regression of the 18 data points from both years resulted in an equation for ASW in
 where IRR is expressed in millimeters.
Overall, the equation does not have a very good fit as expressed by the relatively high standard error of the estimate  and the relatively low RSQUARE.
However, the results show that to leave the soil profile drier at harvest by a given amount, irrigation needs to be reduced on the average by four times that amount on this soil type.
The relationship holds over a fairly broad range of irrigation levels which further implies that only slight decreases of ASW, m are possible with good surface irrigation practices on this soil.
Although the primary purpose of irrigation is to provide water for crop use, another purpose is to maintain a conducive soil environment for nutrient uptake.
Excessive depletion of soil water also can have the effect of reducing nutrient
 availability.
Plant-available soil water was lower than 50% of field capacity for Treatments 6 to 9.
The 50% depletion level of plant-available soil water is the critical point of many soils where yields are reduced.
Although the response  was linear over a fairly wide range of treatments for these two years, the response would approach the asymptotes of upper and lower limits of plant-available soil water as irrigation was further increased or decreased.
Figure 6-Plant-available soil water, ASW in a 1.5-m soil profile at corn physiological maturity as a function of cumulative seasonal irrigation amount, 1990-1991.
The imposition of the daily deficits after tasseling generally decreased plant-available soil water at maturity.
In many cases, these decreases were statistically significant, particularly for the heavy and normal irrigation treatments in 1991.
Planned soil water depletion  on the heavy irrigated treatments.
This occurred in both years for Treatments 7 and 8.
A portion of the last
 Figure 7-Average measured plant-available soil water, ASW in a 1.5-m soil profile at corn physiological maturity and cumulative seasonal irrigation for the various irrigation management levels and daily deficits, 1990-1991.
irrigation amount for Treatment 8 in both years probably went to increasing plant-available soil water at maturity rather than to crop production.
Use of a small, 1 mm/day deficit after tasseling reduced overall irrigation amounts for the heavy, normal, and deficit irrigation management levels by 63, 35, and 0 mm, respectively.
The larger 2 mm/day deficit resulted in savings of 95, 102, and 64 mm.
CORN YIELDS AND IRRIGATION
 Corn yields varied widely among treatments  for the two years of the study, ranging from a low of 9.3 Mg/ha for Treatment 9 in 1990 to a high of 13.9 Mg/ha for Treatments 1 in 1991.
Although early seasonal crop water use  was higher than normal in 1990, the pollination and grain filling stages of the corn occurred during periods characterized by extremely mild temperatures.
These mild climatic conditions reduced plant water stress during the critical growth stages and resulted in overall excellent grain yields.
Although 1991 irrigation requirements for the fully irrigated condition  were higher which would generally indicate less favorable growing conditions, more consistent and less severe growing conditions resulted in higher yields in 1991 than obtained in 1990.
Imposition of a small daily deficit  after tasseling did not have a statistically significant effect on yields within a given management level.
However, the imposition of the larger 2 mm/day deficit did appreciably affect yields for the normal  and deficit  management levels.
The deficit-irrigated treatment with a daily deficit of 2 mm/day  had a significantly lower yield.
No significant differences in water use efficiencies  occurred among treatments in either year, indicating that irrigation amounts even for the heavy irrigated treatments were relatively efficient.
Reductions in irrigation imposed by the daily deficits for the deficit treatments thus would reduce yields by 0.018 Mg/ha for each millimeter reduction in irrigation.
Statistically significant linear relationships for yield as a function of irrigation amount and water use were determined  with regression of the 18 data points
 Figure 8-Average corn yields and cumulative seasonal irrigation amounts for the various irrigation management levels and daily deficits, 1990-1991.
Figure 9-Corn yield as functions of cumulative seasonal irrigation amount  and measured water use , 1990-1991.
from both years resulting in equations for yields, Y in Mg/ha:
 Y 8.61 +  Y = 2.98 +  
 where irrigation  and water use  are expressed in millimeters.
The equations fit the overall data fairly well, with standard error of the estimates equal to 0.74 and 0.55 Mg/ha, respectively.
The RSQUAREs of equations 2 and 3 were 0.65 and 0.81, respectively.
The absence of significant differences in water use efficiencies among treatments indicates that no benefits occurred in terms of water resource conservation by imposition of the daily deficits after tasseling.
The savings in water by using planned soil water depletion were directly offset by yield reductions.
Water saved in one year would have the same yield production potential in a future year.
The water use efficiencies were slightly lower for the heavy irrigation treatments indicating that some deep percolation losses were occurring for these treatments.
It is possible that the daily deficits would have had less effect on yields if the frequency of irrigation events had been higher.
Stegman et al.
reported that an irrigation interval of seven days or less should be used when scheduling irrigation with planned soil water depletion.
Reducing the soil water level at harvest may have additional economic benefits such as reduced leaching of chemicals that traditionally have not been accounted for in analyses.
Overall, the two years of this study had near normal precipitation and evapotranspiration, resulting in near normal irrigation requirements.
However, the seasonal distribution of irrigation was dissimilar.
Soil water was utilized to a depth of 1.5 m in this study, and all layers contributed somewhat similar amounts of water, as evidenced by the linear relationships of seasonal soil water changes and profile depth.
This characteristic of this deep soil profile would be beneficial in irrigation scheduling with planned soil water depletion, because water stress caused by dry surface layers could be buffered
 with water from lower depths.
However, some reduction in nutrient availability could occur because of dry surface layers.
The plant-available soil water at physiological maturity was related linearly to the irrigation amount over the wide range of irrigation treatments.
However, the plant-available soil water at physiological maturity was reduced by only 25 mm for each 100 mm reduction in irrigation.
Yields were related linearly to irrigation and water use with a reduction in irrigation or water use reflected by a reduction in yield.
Using irrigation scheduling with planned soil water depletion resulted in yield reductions.
Water use efficiencies were similar whether planned soil water depletion was used or not.
Therefore, from a water conservation standpoint, irrigation scheduling with planned soil water depletion was not justified.
From a water quality standpoint, irrigation scheduling with planned soil water depletion might be advantageous.
Drier soils at harvest would reduce the potential for overwinter chemical leaching.
Smaller, more frequent irrigations as might be accomplished by surge, sprinkler, or drip irrigation might have helped maintain yields, while allowing planned soil water depletion.
1985a.
Soil water recharge function as a decision tool for preseason irrigation.
Transactions of the ASAE 28:15211525.
1985b.
Corn yield response to different irrigation regimes.
ASAE Paper No.
MCR 85-131.
St.
Joseph, Mich.: ASAE.
PARTITIONING OF SPRINKLER IRRIGATION WATER BY A CORN CANOPY
 ABSTRACT.
The total sprinkler irrigation amount is partitioned by the crop canopy into three major components: stemflow, throughfall, and interception storage.
A study of the partitioning process by a fully developed corn canopy under low wind conditions was conducted.
Nearly 3000 measurements of stemflow were made over the course of 23 irrigation/precipitation events using 240 different plants during the two years of the study.
At the same time, nearly 300 measurements of the throughfall were made.
The objectives were to determine if the process varies between sprinkler types, to determine what factors affect the partitioning process, and to develop models for the process.
The partitioning process was examined at three plant spacings and six irrigation amounts under high-pressure impact sprinklers , lowpressure spray heads on drop tubes at a 2.2 m height , low-pressure spray heads at a 4.1 m height , and also under natural precipitation.
Stemflow decreased linearly with plant spacing and increased linearly with irrigation amount.
Throughfall increased linearly with both plant spacing and irrigation amount.
After tasseling, stemflow is the predominate flow path for sprinkler irrigation water, accounting for 53% at a typical plant spacing of 20 cm.
Throughfall accounted for 43% of a typical irrigation amount.
Interception storage, estimated by algebraic closure, was 1.8 mm when averaged over all events.
Comparisons of the developed models with previous research indicates reasonable stability of the partitioning process even though corn production systems and corn plant structure have changed over time.
Statistically significant differences occurred in the partitioning process between the LS, LS-4.1 and the HI systems, with the LS-4.1 and HI systems being more similar to natural precipitation.
The similarities in stemflow between the LS-4.1 and the HI systems suggests that the differences in stemflow for the LS system may be caused by the height and angle at which applied water intercepts the crop canopy.
The average stemflow percentages for the three plant spacings was 46, 43, and 43% for the LS, LS-4.1, and HI systems, respectively.
Keywords.
Irrigation, Stemflow, Throughfall, Interception, Partitioning, Crop canopy, Sprinkler pattern.
C enter pivot sprinkler designs can be classified into two major types, impact sprinkler and spray head systems.
Impact sprinkler systems typically have significantly higher operating pressures than spray head systems.
A large percentage of the center pivot sprinkler irrigation systems currently being placed on southern and central Great Plains farms are classified as low-pressure spray systems.
The peak application rate from low-pressure spray heads is significantly higher than that from high-pressure impact systems.
Because low-pressure spray heads have a much smaller diameter of applied water, they must apply water at a much higher rate to apply similar amounts of irrigation.
Article was submitted for publication in December 1999; reviewed and approved for publication by the Soil & Water Division of ASAE in May 2000.
This is contribution No.
00-214-J from the Kansas Agricultural Experiment Station.
The mention of trade names or commercial products does not constitute their endorsement or recommendation by the authors or by the Kansas Agricultural Experiment Station.
The total sprinkler irrigation amount is partitioned by the crop canopy into four components: stemflow, throughfall, interception storage, and in-canopy evaporation.
Stemflow is the amount of irrigation water that flows down the leaves to the leaf-stalk node and then down the stem to the soil surface.
Numerous researchers have pointed out the significance of stemflow for corn.
Throughfall represents any irrigation water that reaches the soil surface by directly or indirectly falling through the plant leaf structure.
Interception storage is the amount of water temporarily remaining on the plant after irrigation.
This includes water on leaf and stem surfaces and water trapped in the leaf sheath area.
Most interception storage eventually evaporates.
In-canopy evaporation is the amount of evaporation occurring within the canopy during the irrigation event.
It often is considered negligible.
Wesenbeeck and Kachanoski  measured soil water in the tillage layer around corn plants with time domain reflectometry methods.
They found an increase in soil water recharge around plants, which they attributed to stemflow.
Warner and Young  reported stemflow as high as 40% of the incident rainfall for mature corn and considerable plant-to-plant variation.
They also found significant preferential flow immediately beneath the corn
 row.
The interrelationship between stemflow and preferential flow may be of considerable importance for a crop such as corn.
Indeed, Glover and Gwynne  reported that stemflow was an important mechanism in survival of corn plants in East Africa.
They found wetter soils in a 20 cm band around the plants extending up to 10 cm into the profile as compared to just a few mm in the interrow.
Soil sampling also showed a much higher concentration of roots in the areas associated with the deeper wetting fronts.
Quinn and Laflen  reported that, for corn, up to 49% of the incident rainfall was partitioned into stemflow.
It was calculated as the difference between incident rainfall and the amount of throughfall collected in troughs beneath the canopy.
Stemflow increased as canopy cover increased and tapered off as the crop matured.
Increasing the row width from 50 to 75 cm decreased the stemflow percentage from 57 to 43%.
Increasing the row width increased the fraction of throughfall percentage from 44 to 57%.
Plant spacing was held constant at 30.5 cm.
Steiner et al.
reported direct measurements of stemflow varying from 35 to 64% of incident irrigation amount and a mean of approximately 47% for fully tasseled corn with a leaf area index greater than three.
Proportions of stemflow were reported to be similar regardless of whether the water was applied as sprinkler irrigation using low-angle impact sprinklers or received as rainfall.
Throughfall ranged from 31 to 55% and averaged 43% of the irrigation amount.
Haynes  measured throughfall for several crops including corn and found that the distribution was influenced by the character of the vegetative growth.
The canopy structure for corn tends to pass precipitation toward the plant stem with a "funneling" effect.
Haynes found throughfall to be about 70% of the incident precipitation for corn on a seasonal basis.
Its distribution was more uniform under drilled crops than under row crops.
Armstrong and Mitchell  measured the distribution of transformed rainfall under corn and soybean.
They pointed out that the redistribution methods are appreciably different.
Soybean tends to concentrate the water near the canopy edge, indicating a "shingle" effect.
In corn, throughfall is redistributed across the row interspace in an approximately periodic distribution.
In a related article, Armstrong and Mitchell  pointed out that peak throughfall amounts could be as much as 47 times the precipitation amount for discrete locations in the crop canopy.
However, the average amount is much less.
They attributed this periodicity in throughfall amounts to the periodicity of openings in the canopy or of leaf characteristics.
Steiner et al.
reported interception storage for fully tasseled corn of approximately 2.7 mm.
This value compares well with values reported by Seginer  and Smajstrla and Hanson  of 2.5 mm for corn canopies.
In visual observations of center pivot sprinkler-irrigated corn, Lamm  noted significantly more erosion at the base of corn plots irrigated with spray heads on drop tubes than with impact sprinklers.
He attributed this to differences in stemflow between the two system types, hypothesizing that stemflow was higher for the spray head system.
Differences in the canopy partitioning process between sprinkler types may have physical and economic importance.
Knowledge of differences in stemflow could be important in developing chemigation techniques that call for precise application to the target area that could be either the soil or the foliage.
Engineers and sprinkler designers could use partitioning information in design to limit soil erosion and surface sealing by sprinklers.
Differences in the partitioning process ultimately could affect infiltration and redistribution of the water in the soil profile.
Nonuniform infiltration recently has become an important water quality issue.
One objective of this research was to document if such differences in the partitioning process within a fully developed corn canopy truly exist among center-pivot sprinkler designs and natural precipitation.
Other objectives were to determine what factors affect the partitioning process and to develop models for the process.
The study was conducted at the Kansas State University Northwest Research-Extension Center at Colby, Kansas, during the summers of 1987 and 1988.
In 1987, the partitioning process was examined for two irrigation amounts  under two sprinkler types: high-pressure impact sprinklers  and lowpressure spray heads on drop tubes at a 2.2 m height.
The process was examined at three radii from the center pivot point representing three application intensities.
In addition, the process was examined for three corn plant spacings replicated at each radii.
A 126-m, three-span, electric drive, center pivot sprinkler system was used in this study.
The center pivot was designed to allow for either high-pressure 310 kPa impact sprinklers or low-pressure 103 kPa spray heads.
The HI and LS sprinklers, and pressure regulators were manufactured by Senninger Irrigation Inc., Orlando, Florida.
The 360 spray heads  with convex medium serrated impingement pads were mounted on drop tubes leaving the sprinkler approximately 2.2 m above the soil surface which would be down into the upper levels of fully tasseled corn.
The resultant impingement angle on fully tasseled corn was approximately 20 from horizontal.
The HI sprinklers with a 12 exit trajectory were 4.1 m above the soil surface.
The largest concentration of water droplets from these sprinklers struck the crop canopy at approximately 70 from the horizontal.
Switching between sprinkler types was accomplished manually.
No change was made in the actual center-pivot line pressure, and the LS sprinkler pressure was reduced by regulators.
The center pivot sprinkler irrigation system covered 5 ha directly under the lateral and had a total cropped area of approximately 5.3 ha on a land slope of approximately 0.5%.
This study was superimposed onto a larger study area examining tillage and sprinkler type effects.
Design of the existing sprinkler-tillage study allowed for this irrigation amount partitioning study to be superimposed in the northeast corner of the southern half of the center pivot sprinkler-irrigated area.
This site allowed for separate irrigation of the partitioning study under the LS sprinklers and concurrent irrigation with the sprinkler-tillage study under the HI sprinklers.
The study area was located
 between the second and third towers of the center pivot  and was buffered by at least 10 m of corn planted on all sides.
Because of the prevailing southwest wind direction, the sprinkler lateral usually was nearly perpendicular to the wind as it crossed the study area.
The four combinations of sprinkler type and irrigation amount in 1987 were replicated randomly at least four times, with minor exceptions, within each four-event block at the start of each time block.
The irrigation schedule for the larger sprinkler tillage study was made to make projections of anticipated irrigation dates for the HI sprinklers.
The HI sprinkler treatments had to be scheduled concurrently with irrigation for the sprinkler-tillage study.
In most cases, this did not present a problem; however, if the first randomization seriously delayed a needed irrigation event, the events were re-randomized to provide a more reasonable schedule.
The partitioning process was studied in fully tasseled corn for 19 events during the period 23 July through 19 August 1987.
The first five events were excluded from analysis because of severe leakage from the stemflow collection units.
Stemflow and throughfall were measured for the one precipitation event during the period.
The partitioning process was examined for five irrigation amounts  in 1988 at two radii from the center pivot point.
Each combination of sprinkler type and irrigation amount was conducted once during the season.
The partitioning process was studied in fully tasseled corn for 14 events during the period 29 July through 18 August 1988, which included three significant precipitation events.
An additional LS event, with the spray heads located above the canopy at a height of 4.1 m, was conducted to examine the effect of LS sprinklers height on the partitioning process.
The 1988 combinations of sprinkler type and irrigation amount were assigned randomly during the study period, but no attempt was made to block the five combinations.
As in 1987, the HI sprinkler treatments had to be scheduled concurrently with irrigation for the sprinkler-tillage study.
Application intensity increases with distance from the center of the center-pivot system.
The partitioning process was studied at the three intensities in 1987 obtained at distances 81.7, 93.9, and 106.1 m from the pivot point.
These distances coincided with location of LS devices.
The LS sprinklers were 3.05 m apart, and the HI sprinklers were 12.2 m apart.
There was a 1.5 m offset between the two sprinkler types, resulting in HI locations at 83.2, 95.4, and 107.6 m.
In 1988, only the first two intensity sites were studied.
The actual intensities were computed from data obtained during the irrigation events.
The intensity factor is tied to the distance from the pivot point, SO any other differences in plot areas will be included in the intensity factor results.
Corn hybrid Pioneer 3377 was planted in 76 cm rows on 24 April 1987, and 27 April 1988.
Six corn rows were precisely centered and circularly planted at the desired radius, such that a LS sprinkler would pass between two corn rows.
Three plant spacings of 20, 30, and 41 cm were obtained by hand thinning and were randomized within each intensity site.
At each intensity-plant spacing subsite, primary data collection was made on two adjacent corn rows located 38
 Figure 1-General layout of the three intensity sites in relation to the location of the sprinklers.
Only the first two intensity sites were used in 1988.
and 114 cm from the corresponding LS sprinkler.
Because the LS sprinkler effectively irrigates 4 rows, by symmetry, the two-row arrangement gave satisfactory representation.
It was assumed that the location of the data collection site was not critical for the HI sprinklers, because of their wide rotating pattern and the contribution from adjacent HI sprinklers.
Plant characteristics were measured after the corn was fully tasseled  during a four-day period, 20-23 July 1987 and during a two-day period, 27-28 July 1988.
The actual plant spacing was defined as the average of the distances to the nearest adjacent plants and was measured to the nearest centimeter.
The circumference of each plant stalk at the first node was measured to the nearest millimeter.
Corn stem diameter is often linearly related to leaf area.
Plant spacing and circumferences of the plants used in the partitioning measurements was recorded in both years.
In 1987, plant and leaf heights were measured to the nearest 5 cm to the tip of the tassel for each plant selected for measurement of the partitioning process.
In 1988, 10 plants adjacent to each intensity-plant population subsite were selected for measurement.
This was done to minimize the stress from human traffic to the leaf structure in the measurement area.
Leaf length and width were measured to the nearest centimeter and millimeter, respectively, for each plant in 1987.
In addition, a set of five plants from the general field area was cut and brought into the lab for leaf area measurement.
The leaf areas, leaf lengths and leaf widths from these five plants were used to develop an equation to compute leaf area in cm:
 where the sum total of the product of all leaf lengths  in cm and leaf widths  in cm is multiplied by 0.76.
This equation compares favorably with one reported by Steiner et al.
for which the slope was 0.79.
In 1988, 10 plants adjacent to each intensity-plant population subsite were selected for measurement.
Equation 1 was used to calculate the leaf area for these 10 plants, and the mean was used as the average value for the subsite.
Leaf area index  is defined as the ratio of leaf area to land area.
For an individual plant, this equation would be:
 where leaf area  is expressed in cm, and actual plant spacing  and row width  are expressed in cm.
Standard rain gages were used to measure the abovecanopy irrigation amounts.
They were located at ground level at the edge of each intensity site in a bare area, so they did not measure a true above-canopy amount.
However, it was the only practical way to estimate the quantity under the two different types of sprinklers.
Rain gages at a height close to the LS sprinklers will not provide an accurate catch.
The method used in this study should provide a good estimate of the SG amount because actual within-canopy droplet evaporation is considered negligible.
The SG amount was measured at only one location for each intensity site but repeated samples  were taken to reduce measurement errors.
The commercial rain gages with a 10 cm opening and 280 mm capacity provided accurate readings to the nearest 0.25 mm.
An electronic tipping bucket rain gage also was used to measure the SG amount at each intensity site and provided the basis for computation of irrigation intensity.
The electronic rain gages had 22-mm diameter openings and each tip of the bucket represented 0.25 mm.
Stemflow was collected on 16 individual plants at each intensity-plant spacing subsite  with special collection units fabricated at the research center.
The collection tube was
 Figure 2-Stemflow collection unit attached to a corn plant.
constructed from approximately an 18 cm section of 5 cm ID SDR 26 PVC pipe with a full length slot cut with a jigsaw.
The slot allowed the collection tube to be pried open enough to fit around a growing corn plant stem.
A small metal tube was glued in a hole near the base of the collection tube opposite the slot.
A transfer hose connected to the metal tube was used to drain the water from the stemflow collection tube to the reservoir jug that held accumulated stemflow until it could be measured.
The corn plants were stripped of the lower two leaves, which were fully mature at this date, to provide a smooth surface for mounting the stemflow collection unit.
The stem area was dried with a cloth to facilitate the taping and sealing of the stemflow collection unit just above the second node.
Small quantities of carpenter's glue and dry masonry cement were added to the collection tube to help prevent water leakage through the tape.
A small spacer prevented the top of the collection tube from touching the corn plant.
A sample schematic drawing of a typical intensity-plant spacing subsite is shown in figure 3.
Not all subsites would have a SG measurement site immediately adjacent.
The volumetric stemflow amount was modified for the actual land area represented by a plant  to give a stemflow amount in depth which would be a more practical comparison to the SG amount.
The stemflow amounts were measured within h of the irrigation event, except for night time precipitation events.
In this case, stemflow was measured commencing at 8:00 A.M.
the following day.
Throughfall was collected at each intensity-plant spacing subsite with specially constructed pans, 230 mm in height and 66 cm in length, just fitting between the 76-cm corn rows.
Pan width was a multiple of plant spacing  and thus ensured that a pan covered a ground area representative of the plant spacing.
General measurements of throughfall were made rather than specific measurements related to stemflow of certain plants.
This was because of the physical limitations of putting the stemflow collection units and throughfall collection gages in the same location.
Throughfall was measured at two locations at each intensity-plant spacing subsite.
One pan was centered beneath the LS sprinkler between the rows, and the other was centered in the adjacent two rows.
The throughfall volume was divided by the land area to express the actual throughfall amount as a depth.
Figure 3-Schematic of a typical intensity-plant spacing subsite showing how the various measurement units were situated.
Hourly weather data were recorded at an automated weather station located approximately 1000 m from the study site.
Data collected included air temperature, relative humidity, wind direction, wind speed , and solar radiation.
Generally, the irrigation events were conducted before dawn to avoid adverse wind conditions.
RESULTS AND DISCUSSION WEATHER CONDITIONS
 Weather conditions varied from year to year, event to event, and sometimes during the event.
In 1987, the first few events were conducted after sunrise.
However, weather conditions change rapidly on the High Plains after sunrise, SO later events were conducted before dawn whenever possible to minimize experimental error.
The events were of different duration because of the differences in sprinkler types and irrigation amounts.
Sometimes the wind would be high before dawn and the event had to be canceled or postponed to later in the day.
However, when the wind speed increased during an event, the event would continue.
In 1987, the events used in the analysis were characterized by low average wind speeds, which were often below the 0.5 m/s sensor threshold.
The relative humidity was fairly low during the events, which would tend to increase evaporative losses.
However, since the wind speed was low and most events were conducted early in the morning, evaporative losses due to advection would be low.
In 1988, nearly all of the events were conducted before dawn or late in the evening.
The relative humidity was fairly high during nearly all of the events.
The high relative humidities would have resulted in lower evaporative demands.
The average wind speeds were higher than in 1987, but the wind speed exceeded 4.5 m/s in only one event when the speed reached 5.5 m/s.
The weather factors during the events in both years should have had relatively minor effects on the partitioning process because of the timing of most of the events, and because events were canceled on windy days.
MODELING OF STEMFLOW AMOUNT
 Analysis of Covariance.
The study included five class variables: sprinkler type, irrigation amount, intensity site, nominal plant spacing, and row.
Two of these have continuous variable counterparts.
There were two nominal class amounts, 13 mm and 38 mm, in 1987.
The effects of these classes or the actual amounts can be examined in regression.
Similarly, the three nominal plant spacings had continuous actual plant spacing counterparts.
Analysis of covariance  was performed on the 1987 data to broadly establish the importance or lack of importance of the class variables in the prediction of stemflow amount.
A previous graphical analysis had shown that the stemflow amount was related linearly to the covariates, SG, and PS.
So these terms, when appropriate, would be logical covariates in the AOCs.
The AOC revealed significant differences between the event types.
The stemflow amount was significantly higher for the LS sprinkler than the other two event types.
There was not enough information at the P = 0.05 significance level to conclude that the stemflow amounts were different for the HI and the precipitation 
 events.
From this analysis, it was concluded that a model for each sprinkler type is warranted, and that HI affects the stemflow part of the partitioning process somewhat similarly to natural rainfall.
The AOC did not show enough evidence to suggest that the corn row affected the stemflow amount for either the HI event or the single  event in 1987.
However, the row did have a significant effect on stemflow amount for LS sprinklers.
The LS sprinkler pattern was distorted by nearby row  1.1 m distance from the LS sprinkler.
Averaged over the two rows, the LS sprinklers resulted in the highest stemflow amount for a given irrigation event.
This means that the distortion of the pattern by Row 2 increased the overall average stemflow amounts for the LS events, even though less stemflow was occurring on Row 3.
The conclusion to be drawn from this analysis is that the data can be pooled across row location for the HI and R events.
However, for the LS events, a better fit can be obtained if row location is considered.
For a single event at the end of the study in 1988, the LS sprinklers were raised to a height of 4.1 m, the same height as the HI sprinklers.
This configuration  was used to determine if the row effect that was SO prominent for the LS events was more related to the sprinkler type or the sprinkler pattern distortion caused by Row 2.
An AOC did not show enough evidence at the 0.05 significance level to conclude that row affects stemflow amount for the LS-4.1 configuration.
From this analysis, one could conclude that the row effect for the LS sprinklers was related more to pattern distortion by the row than to the properties of the LS sprinkler.
The LS-4.1 configuration was similar to HI and R events in the way it affected stemflow amount.
This suggests that the differences in stemflow for the LS system may be caused by the LS sprinkler height and/or the angle that water strikes the crop canopy.
Statistically significant differences in stemflow amounts occurred between the intensity sites.
The trend was toward lower stemflow amounts for the higher intensity sites.
This trend held even for the R event, which could reasonably be expected to have the same intensity for the three locations.
Other differences in the sites, such as plant factors, were probably more important than the sprinkler application rate.
It was concluded that the experimental design did not allow a clean separation of intensity effects.
The data were pooled across intensity site, and no further speculation on the effect of intensity on the partitioning process was made.
Regression Analysis.
An overall regression model to predict stemflow amount, S for the sprinklers in 1987 was constructed.
Averaging across intensity sites, rows, and individual plants resulted in 36 data points in the model.
Each data point represented 48 measurements, provided there were no missing data.
For the 12 sprinkler events in 1987, there were 1728 possible measurements, with only 16 missing.
For the purposes of regression, a full model was constructed including the five plant variables, actual plant spacing , plant height , stem diameter , leaf area , and leaf area index.
The above-canopy irrigation amount  was also included as was its square term.
One cross effect was included , which seemed appropriate based on a preliminary graphical analysis.
The full model was:
 = f(PS, THT, DIA, LA, LAI, SG,
 Some of the plant variables are related to each other and, therefore, are not independent.
Leaf area index is related inversely to plant spacing by definition.
Some of the variables that affect stemflow are not required in the model because of these interrelationships.
For this reason, a backwards selection procedure was used in the regression analyses, and nonsignificant independent variables were removed.
The only plant characteristic that remained in the model was PS, which was incorporated in the cross product, PS X SG.
Other factors, such as LAI are still highly correlated with stemflow but can be accounted for with the inclusion of PS in the model.
The intercept was removed from the model to satisfy the boundary condition of no stemflow with no irrigation.
Rearranging the variables and parameter estimates resulted in the 1987 equation:
 Sa=x SG 
 for PS in cm and S and SG in mm.
The model fit the overall data very well with a standard error of the estimate, SE , of 1.41.
This is an estimate of the variance about the regression line.
The RSQUARE of the model is no longer valid because the intercept of the model has been removed.
Similarly, regression was performed on the 10 sprinkler events in 1988.
Averaging across intensity sites, rows, and individual plants resulted in 30 data points in the model.
Each data point represented 32 measurements, provided there were no missing data.
In 1988 there were 960 possible measurements, with only 22 missing.
Regression using the backwards selection procedure yielded a model with independent variables identical to those in the final 1987 model.
The parameter estimates varied only slightly from those in 1987.
Though the equations look slightly different, there is little difference in the predicted values over the range of variables studied.
The overall data for both years were combined for an overall prediction equation , which fit the measured stemflow amount well.
The AOC showed differences in the amounts of stemflow between event types.
The stemflow amount was greater for LS than for HI, R, and LS-4.1 events.
The AOC also showed a difference in stemflows between rows for the LS system.
Therefore, regression equations
 Table 1.
Summary of regression equations to predict stemflow amount using the model form S = f(SG, PS
 Equation for Stemflow	in
 Event Type	Year	Amount  in mm*	mm
 All sprinklers	87	S =  SG	1.41
 All sprinklers	88	S =  SG	1.26
 All sprinklers	87-88	S =  SG	1.69
 HI, R, and LS-4.1 event	87-88	S = (0.710 0.00885 SG 1.39
 LS Row 2	87-88	S =  X SG	1.77
 LS Row 3	87-88	S =  X SG 1.79
 LS sprinklers	87-88	S =  X SG 1.63
 Plant spacing  is in cm and irrigation amount SG) is in mm.
*
 Figure 4-Relationship of measured and predicted stemflow amounts for all sprinkler events in 1987-1988.
Each data point represents the average of 48 measurements in 1987 and 32 in 1988.
for the individual event type and rows for the LS system are warranted.
A regression was performed on the combined HI, R, and LS-4.1 data from 1987 and 1988 to predict stemflow amount using a model of the form:
 similar to the form of the overall 1987-1988 equation.
The resulting regression equation  gives essentially equal predictions to the overall combined 1987-1988 equation.
The distortion of the spray pattern for the LS events by the nearby row  resulted in higher stemflow amounts for this row than for the row 1.14 m farther away.
Row 2 also showed a greater effect of plant spacing.
Individual regression equations for stemflow amount were generated for each corn row for the LS events.
Over the entire range of plant spacings, Row 2 had approximately 19% higher stemflow amounts compared to Row 3.
However, at the 20-cm plant spacing, Row 2 had approximately 35% greater stemflow amounts than Row 3.
At the 41-cm plant spacing, the predicted stemflow amounts for the two rows were almost equal.
This is a logical result.
As the plant spacing increased, there was less distortion of the spray pattern by Row 2, and the row effect disappeared.
An overall regression equation for the LS events was generated by averaging across both rows.
This equation is useful for predictions of the aggregate field average stemflow.
It underestimated the stemflow amount for Row 2 by approximately 40% and overestimated the amount for Row 3 by approximately 17% at the 20-cm plant spacing.
Over the entire range of plant spacings, this overall LS equation predicted stemflow amounts about 7% higher than those predicted by the combined HI, R, and LS-4.1 equation.
However, at the 41-cm spacing, the difference was approximately 10%.
The several regression equations to predict stemflow amount that have been presented are summarized in table 1.
The overall two-year sprinkler equation generally shows a good fit with either data set.
This is encouraging, because it indicates stability in the parameter
 estimates at least for this center-pivot sprinkler system and corn variety.
Most of the popular corn varieties presently being marketed have similar canopy structure.
The highpressure impact center pivot sprinkler system  is still used widely on areas with high runoff potential.
The lowpressure spray system on drops  is also very common in the southern and central Great Plains.
The equations were developed under relatively stable weather conditions usually before dawn.
Therefore, these equations might need to be modified before being used under other conditions.
Windy conditions that cause the plant leaves to move probably would reduce stemflow amounts and increase throughfall amounts.
Gusty wind conditions would likely cause more plant-to-plant variability in stemflow amounts.
Hot, sunny conditions might increase interception losses, but probably would not appreciably affect stemflow amounts under the high application rates of the outer spans of center pivot sprinklers.
Stemflow and Its Consequences.
The practice of placing the LS sprinklers down into the top 30 cm of the corn canopy is promoted widely in the southern and central Great Plains as a means of reducing evaporation.
However, these potential water savings must be balanced against lower distribution uniformity caused by the spray pattern distortion.
Some of the uniformity problems, in terms of less water for crop use, are buffered by the deep silt loam soils in the area.
Higher or lower irrigation amounts at some points on the soil surface may be buffered partially by the infiltration and soil water redistribution processes.
In addition, the distortion occurs only after tasseling, so the irrigation uniformity problem probably does not cause large yield differences on these deep soils, as long as the LS sprinkler spacing is fairly close.
On most of the systems in northwest Kansas, the LS sprinkler spacing is typically 240 to 300 cm.
The combined sprinkler equation gives a relatively good estimate of the stemflow amount for the LS events when only an aggregate field estimate is needed.
However, much row-to-row variation occurs, and a better prediction can be obtained for a particular row by using the appropriate row equation.
Figure 5-Stemflow as a percentage of a typical irrigation amount  as related to the corn plant spacing for the various regression equations for 1987-1988.
The stemflow as a percentage of the irrigation amount is presented in figure 5 for the two-year overall equations.
At a typical irrigated corn plant spacing of 20 cm, the average stemflow was approximately 53% of a typical 25-mm irrigation amount.
This value is slightly higher than the values of 49% and 44% reported by Quinn and Laflen  and Steiner et al.
, respectively.
The stemflow percentage decreased linearly with increased plant spacing over the range of spacings examined.
Leaf area index decreases with increased plant spacing  and thus the "funneling" surface decreases resulting in less stemflow.
The prediction equations seemed to give reasonable results compared to the limited data in the literature.
The stemflow percentages for the two rows under the LS system varied by approximately 16% at the typical 20cm plant spacing; the value is 62% more for Row 2 and 46% for Row 3.
This may have considerable significance to the process of chemigation.
If the target area of the chemical is the foliage, these variations in stemflow may be unacceptable.
In many situations, the crop producer will plant the rows parallel to the field boundary rather than circularly.
In this case, although the row effect might disappear, one would expect more plant-to-plant variation.
The stemflow amount would vary depending on the proximity of a plant to a LS sprinkler and would be higher for closer plants.
The aggregate field average stemflow amount probably would be similar to the case of the circular rows in this study.
Wind direction also could skew the uniformity of stemflow amounts, depending upon the row orientation in relation to the sprinkler location.
If the wind direction is perpendicular to the sprinkler lateral and parallel to the corn rows, the uniformity should be similar to the results of this study.
If the wind direction is parallel to the sprinkler lateral and perpendicular to the row, the row-to-row differences might be reduced, because the wind would alter the travel distance of the spray.
Buschman et al.
measured European corn borer control under chemigation for the two sprinkler types  at both Colby and Garden City, Kansas.
The HI system gave much better control at both locations.
They did not indicate whether the entire LS spray pattern was sampled for efficacy of the chemicals.
Some rows could have shown higher efficacy because of the differences in stemflow.
If drop tubes are not used, the LS sprinklers are the same height as the HI sprinklers.
This would be similar to the case where the LS sprinklers were raised to truss height.
This configuration performed similarly to the HI system in terms of the amount of stemflow recorded.
In addition, no row effect occurred.
This suggests that the LS sprinklers at truss height may be better than when on drop tubes, if distribution uniformity is a critical factor, such as for a chemigation event.
Kiesselbach  reported that approximately 3 L of water run down the outside of a fully developed corn plant for each 25 mm of irrigation water.
The plant spacing was not indicated, and the data likely were collected from an isolated potometer.
However, the overall 1987-88 prediction equation for all sprinkler events predicted 2.94 for a 25-mm irrigation event for the 41-cm plant spacing after proper conversion of the equation to predict a volumetric amount.
Little interaction occurred among plants at this higher plant spacing, SO the situation might be
 similar to the case of plants grown in isolated potometers.
The overall equation also gives an upper limit of the stemflow amount at approximately 3 L for each 25 mm of irrigation as plant spacing is increased further.
The throughfall amount , stemflow amount , and interception storage amount  add up to the above canopy irrigation amount.
Because T and S a are the two major addends that result in SG, it would follow that factors affecting stemflow also would affect throughfall.
It was assumed that there was no need to perform separate AOC for T and that it could be predicted by a regression model of the form:
 Averaging across intensity sites and row location for the 12 sprinkler events in 1987 resulted in 36 data points, each representing six measurements.
In 1988, there were five HI events and five LS events.
Averaging across the two intensity sites and two row locations resulted in 30 data points, each representing the average of four measurements.
Separate regression equations were developed for throughfall using the 1987 and 1988 data.
The effect of plant spacing on T was insignificant in 1988 over the range of plant spacings examined.
The factor was left in the equation for the purposes of consistency with the 1987 and combined results.
The combined data  were used to
 Table 2.
Summary of regression equations to predict throughfall amount using the model form T = g
 Equation for Throughfall	in
 Event Type	Year	Amount  in mm*	mm
 All sprinklers	87	T2 = (0.373 + 0.00457 PS SG 1.90
 All sprinklers	88	Ta (0.387 + 0.00068 PS X SG 0.88
 All sprinklers	87-88	T  X SG 2.33
 HI, R, and LS-4.1 event	87-88	Ta = (0.332 + 0.00457 X SG 2.25
 LS Row 2	87-88	T =  : X SG 3.49
 LS Row 3	87-88 T =  X SG 1.53
 LS sprinklers	87-88 Ta =  X SG 2.17
 Plant spacing  is in cm and irrigation amount  is in mm.
*
 Figure 6-Relationship of measured and predicted throughfall amounts for all sprinkler events in 1987-1988.
develop an overall throughfall equation.
Note that the slope of the plant spacing effect for the T is positive; whereas, the slope was negative for the S As PS increases, S approaches zero.
As S approaches zero, T2 approaches 100% of SG.
The predicted throughfall expressed as a percentage of a typical 25-mm irrigation amount  increased from 43.4% at the 20-cm plant spacing to 50.0% at the 41-cm plant spacing.
Similar to the regression analysis of stemflow, T was expected to vary with event type.
Regression equations  for the various event types were generated using the model expressed in equation 6.
Regression analysis of the HI, R, and LS-4.1 event data for both 1987 and 1988 resulted in an SEv.x of 2.25.
However, the coefficient of variation of the model was 21%, indicating considerable variation.
Throughfall amounts were appreciably different between Rows 2 and 3 for the LS events, with more modeling variation for Row 2.
Over the range of plant spacings examined, T for Row 2 was approximately 28% higher than for Row 3.
The row effect for S disappeared at the high 41-cm plant spacing.
This was not true for the T, because the difference was approximately 23% at the 41-cm plant spacing.
This is probably because the spray pattern was distorted by both rows for the throughfall collection unit for Row 3.
An overall LS equation can be used for prediction of an aggregate field average T for the LS system.
Throughfall and Its Consequences.
The throughfall as a percentage of irrigation amount is presented in figure 7 for the two-year overall equations.
At a typical 20-cm plant spacing, the throughfall is 43% of the irrigation amount.
This value compares well with the two-year average value of 47.6% reported by Steiner et al..
Quinn and Laflen  reported the throughfall to be 57% for corn at the 12th week stage with a 30-cm plant spacing and a 75-cm row spacing.
The overall equation predicted 47% for this spacing.
However, the data of Quinn and Laflen were collected under a rainfall simulator, and characteristics of throughfall could differ from a center pivot.
The throughfall percentages for the two rows under the LS system were 50.4 and 38.1% for Row 2 and Row 3, respectively.
Stemflow was also higher for Row 2.
This
 Figure 7-Throughfall as a percentage of a typical irrigation amount  as related to the corn plant spacing for the various regression equations for 1987-1988.
means that the spatial distribution uniformity of irrigation was poor under the LS system.
Throughfall was less under the HI system than under the LS system at the 20-cm plant spacing.
However, at the larger spacings, throughfall for the HI system was higher than that for the LS system.
This may be related to how the systems deliver the irrigation water.
The HI system delivers water in fairly large periodic pulses; whereas, the LS system delivers the water in a continuous stream of water droplets.
The periodic loading of the plants by the HI system can cause the leaves to bounce up and down during the pulse.
This movement of the leaves might be restricted at the 20-cm spacing.
However, at the larger spacings, this movement might cause much of the water to leave the leaf surface as throughfall rather than as stemflow.
ESTIMATION OF INTERCEPTION STORAGE AMOUNT
 This study did not directly measure the interception storage amount , but it can be estimated from algebraic closure: Ia=SG
 SG, and T are all measured variables containing experimental error and of considerably larger magnitude than I.
As a result, the variation in I estimates can be easily larger than I itself.
The residual I from equation 7 was calculated for all the events and plant spacings during the two-year study.
The average interception storage from these 81 estimates was 1.8 mm; however, the standard deviation was 2.0 mm.
The maximum residual was 11.0 mm; whereas, the minimum was -3.2 mm.
Because the estimates of I were highly variable, no regression models will be presented.
The I2 was 1.85 mm for the LS events versus 2.06 mm for the HI events, which may indicate a slight reduction in evaporation losses.
The R events had the lowest interception, 1.13 mm.
This may be related to the weather conditions during the storms or to the fact that most of the precipitation amounts were relatively small.
For the single LS-4.1 event, the average interception storage, 2.03 mm, is comparable to that of the HI event.
The differences among all three event types are small giving further credibility to the assumption that within-canopy evaporation losses are small or negligible.
The interception storage estimates were obtained from data often collected before dawn under relatively low wind conditions.
They do not include appreciable canopy evaporative losses that might occur during the irrigation/precipitation event.
The problem of estimating I is not new.
Whether the estimates are made by watering plants and then weighing, calculation of the residual as done in this study, or using a microclimate model, they are open to discussion.
Probably for this reason, a range of 1.5 to 2.5 mm covers most of the estimates in the literature.
Methods were developed for predicting the stemflow and throughfall components of the irrigation partitioning process.
The data used to develop the models were obtained under low or no wind conditions usually before dawn.
Therefore, the equations may need to be modified
 for windy conditions.
These models do a relatively good job of predicting the components on an aggregate basis.
The regression analyses revealed that stemflow and throughfall amounts were related most highly to plant spacing and irrigation amount.
The stemflow amount decreased linearly with plant spacing  and increased linearly with irrigation amount.
The throughfall increased linearly with both increased PS, and SG.
Other plant factors such as height, leaf area, stem diameter, and leaf area index did not significantly  add precision to the model.
At the three nominal plant spacings of 20, 30, and 41 cm, the predicted stemflows expressed as a percentage of the irrigation amount for all sprinkler types were 53.4, 45.9, and 37.6%, respectively.
The predicted throughfall expressed as a percentage of the irrigation amount was 43.5, 46.6, and 50.0%, for the three plant spacings, respectively.
At typical irrigated corn plant spacings, stemflow is the predominate flow path for irrigation water after tasseling, and throughfall is slightly lower.
The partitioning process differed considerably between the low-pressure spray heads on drop tubes  events and the high-pressure impact sprinkler  events.
The LS events not only had higher stemflow amounts but also had large differences between row location.
The distortion of the spray pattern that occurs when the LS sprinklers are placed on drop tubes down into the canopy heavily influenced the partitioning process.
This factor should be considered in designing multipurpose center pivot sprinkler systems.
The stemflow amounts in the HI events were more similar to those in the precipitation events than to those in the LS events.
Raising the LS sprinklers above the crop canopy resulted in stemflow amounts similar to those with the HI events and eliminated the row effect.
These facts should be considered when chemigation procedures are being developed, when point data for irrigation amounts under crop canopies are being examined, and in cases where uniform soil water redistribution is crucial.
Interception was estimated by subtracting the stemflow and throughfall amounts from the irrigation amount.
Assuming that in-canopy evaporation is negligible during the events, the residual was an estimate of interception storage.
Because stemflow, throughfall, and irrigation amount are all measured variables containing experimental error, the error associated with this method of estimating interception storage is high.
The mean interception value based on 81 separate estimates was 1.8 mm with a standard deviation of 2.0 mm.
1987b.
A comparison of rainfall distribution under different plant canopies.
ASAE Paper No.
87-2509.
St.
Joseph, Mich.: ASAE
 AOC = analysis of covariance
 DIA = stem diameter
 HI = high pressure impact sprinkler
 I = interception storage amount
 LA = leaf area
 LAI = leaf area index
 LL = leaf length
 LS = low pressure spray head
 LS-4.1 = low pressure spray head at 4.1 m height on top of sprinkler lateral
 LW = leaf width
 PS = actual measured plant spacing between adjacent plants
 R = rainfall event
 RW = corn row width
 S = stemflow amount
 SG = above-canopy irrigation amount caught in standard rain gages.
Ta = throughfall amount
 THT = plant height
IRRIGATION OF SMALL GRAINS IN ARIZONA
 Steve Husman and Michael J.
Ottman
 Water Use and Irrigation Requirement
 Wheat and barley use about 2 ft of water in Arizona, but 3 to 3.5 ft of applied water is often required with surface flood irrigation due inefficiencies in the irrigation system.
Less irrigation water is required with more efficient irrigation systems such as sprinkler or drip.
If 6 inches of water is applied per irrigation, then six or seven irrigations are required during the season.
The first postemergence irrigation is generally needed by the 5 leaf stage and the last irrigation by soft dough.
An example irrigation schedule is presented in Table 1.
For an explanation of small grain growth stages and heat units to attain these stages see Ottman.
Small grains can be produced successfully with a variety of irrigation systems.
Drip and sprinkler irrigation systems can apply smaller amounts of water than surface flood systems, and therefore, less applied water moves past the root zone.
Surface flood systems are more efficient at leaching salts, which is a consideration if salts are a problem.
Small grains can be grown equally well on beds or flat ground.
Beds have an advantage if infiltration is a problem, the field has substantial sidefall, or a sufficient head of water can not be delivered.
Growing small grain plants in furrows in a bed system can slow the advance of surface irrigation water, increase water infiltration, but result in less efficient irrigation.
Season Water Use by Small Grains
 Water use in small grains is negligible during early development, increases rapidly during jointing, peaks during grain fill, and falls steeply during senescence as the crop turns color.
Water use is most affected by developmental stage before the crop fully covers the soil surface and after the crop turns color.
Otherwise, water use increases as the season progresses due to increased solar radiation and temperature.
Water use can be greater than the longer term average on windy days especially.
Water stress at any stage can reduce yields of smallgrains.
However, small grains are most susceptible towater stress during jointing, least susceptible during grainfill, and intermediate in susceptibility during tillering.
Yield is reduced by water stress duringtillering by reduced tiller number.
Water stress duringjointing reduces plant height and susceptibility to lodging, but also reduces kernels per head andyield potential.
Water stress during grain fill can reducekernel weight and result in unacceptable grain test weight.
The first post-emergence irrigation for wheat and barleyis usually needed by about the 5-leaf stage.
Applying thefirst irrigation earlier may temporarily increase cropgrowth but not
 Table 1.
Example irrigation schedule for durum planted on December 10 at Maricopa on a sandy loam soil.
2 nodes	Feb 27
 Heading to flowering	Mar 30
 Soft dough	Apr 22
 Table 2.
Average daily water use of durum planted at Maricopa on December 10.
Month	Days	Average daily water use inches/day
 increase grain yield, or may actually reducecrop growth through waterlogging or cooling of the soil.Rainfall often allows the first irrigation to be delayed.
Thefirst irrigation may be applied early to help in the germina-tion of the seed if the soil crusts or to prevent seedlingdesiccation in cracking soils.
The first irrigation may alsobe applied early if the crop has a critical need for nitrogenfertilizer.
The price or availability of water is a factor thatmay warrant applying the first irrigation early.
Applyingthe first irrigation too early can result in loss of soilnitrogen by leaching or denitrification.
Waterlogged conditions also hinder nitrogen uptake fromthe soil since plant roots need oxygen to take up nitrogen.
The symptoms of waterlogged soil conditions are yellow-ing and lack of growth of the plants.
Delaying the firstirrigation as long as possible with the intention of promot-ing root development and improving the ability of the cropto extract deep soil moisture is a questionable practice.
Plant wilting is usually a sign thatthe first irrigation is needed or should have been appliedsometime earlier.
The timing of the last irrigation for wheat and barley isusually a difficult decision.
Applying an unnecessaryirrigation at the end of the season wastes water and cancause lodging.
Conversely, water stress at the end of theseason may reduce kernel weight, test weight, and yield.
On a sandy loam soil, the last irrigation is needed at softdough.
About 3 to 4 inches ofwater is needed to carry the crop from soft dough tomaturity.
The average sandy loam soil holds about thisamount of plant available water in the active rooting zone.
On sandier soils, the last irrigation may be needed betweensoft dough and hard dough, and on heavier soils, the lastirrigation may be applied before soft dough.
Obviously, the timing of last irrigation depends on soil type, theirrigation system, the growth stage of the crop, expectedweathe conditions, and other factors.
Nevertheless, noirrigation water is needed once the heads have completelyturned color from green to tan since the crop is mature
 Table 3.
Grain yield of barley and wheat as affected by soil moisture depletion fraction at irrigation.
This research was conducted atMaricopa and the data is an average of two varieties and two years.
Soil moisture depletion	Barley	Wheat
 fraction% of available water
 Table 4.
Rooting depth of small grains at various growth stages.
Rooting Depth	Growth Stage
 3.0	Flag leaf collar visible
 or kernel milky 
 atthis point and the kernels cease to accumulate dry weight.
Do not confuse the gradual color change of the cropbetween flowering and hard dough with the tan color ofthe head that occurs at maturity.
It usually is not economi-cal to apply a final irrigation to benefit a few green tillers ina mature crop.
A final irrigation is sometimes applied atmaturity not for crop water requirements but to soften thesoil for tillage after harvest.
Critical Soil Moisture Depletion
 Small grains should generally be irrigated when 50% ofthe available water is depleted.
However, grain yield wasincreased by 786 lbs/ acre for barley and 837 lbs/ acre fordurum if irrigations were applied at 35% rather than 50%depletion in a study conducted at the Maricopa Agricul-tural Center.
The cost of producing this addi-tional grain yield includes one or two additional surfaceflood irrigations, an additional 34 lbs N/ acre, and in-creased harvesting and hauling costs.
Therefore, whetheror not irrigating at 35% depletion is economical dependson the difference between the increased costs and increased revenue.
Another consideration is the irrigationsystem utilized, since irrigating at 35% depletion ratherthan 50%
 depletion can be achieved without applyingmore water with drip or sprinkler irrigation, but not withsurface flood irrigation.
Irrigations can be scheduled using set calendar dates ordays between irrigations based on grower experience,methods that directly measure soil moisture or crop stress,or the soil water balance method.
Grower experience isuseful in scheduling irrigations under average conditions, but it is difficult to adjust for unusual weather or variationsin irrigation water supply.
Soil moisture and crop waterstress can be measured in a variety of ways  )and calibrated at certain critical levels to trigger irrigation.
However, these techniques are more often used in highervalue crops than small grains.
The soil water balancemethod can estimate soil moisture and impending cropstress without the investment in sensors and collection ofthe data they provide, but some accuracy may be lost.
Soil Water Balance Method
 The soil water balance method of irrigation schedulingtreats soil water as a "bank" from which water is "with-drawn" by the
 Available Water Holding Capacity
 Sandy clay loam	1.73
 Silty clay loam	1.94
 crop and water is "deposited" by irrigationwhen withdrawals reach a critical level.
The critical level is referred to as a maximum allowable depletion, and is theproduct of the acceptable depletion fraction , and the available water holdingcapacity of the soil :
 Maximum allowable depletion  = Depletion fraction X Rooting depth  X Available water 
 As an example, if we assume a depletion fraction of 50%,a rooting depth of 3 ft., and available water of 1.73 inches/f then an irrigation is triggered when 2.6 inches of waterare used.
If daily crop water use is 0.20inches per day, then 2.6 inches of water is used in 13 days, and the irrigation intervalis 16 days since water use calculation begins 3 days afterthe previous irrigation to allow for drainage or use ofexcess water.
Arizona Meteorological Network, AZMET
 Water use = ETo Kc
 An example of reference evapotranspiration  pro-vided by AZMET is shown in Table 6.
The crop coeffi-cient  converts evapotranspiration of the grass refer-ence crop  to evapotranspiration  or water use ofthe crop of interest.
Crop coefficients  at variousgrowth stages are provided for wheat and barley in Table 7.
Arizona Irrigation Scheduling System, AZSCHED
Available water is the volume of water stored between field capacity, which is the amount of water held by a soil after it has been saturated and allowed to drain for 24-48 hours, and permanent wilting point, which is the point where plants can no longer extract any water and will wilt and die.
Therefore, available water is simply the amount of water a soil can supply to plants.
Nursery Irrigation System Checklist
 Tom Yeager and Shawn Steed2
 Irrigation is a very important aspect of container plant production and must be intensively managed to achieve optimal production times for plants of superior quality.
Inadequate irrigation often results in plants that exhibit slow growth, abnormal leaf color, and sparse foliage compared to plants that receive adequate water.
While the symptoms of inadequate water seem distinct, excessive water might result in similar symptoms.
Thus, there must be a balance between excessive and inadequate irrigation.
Producers use irrigation control devices and experience to achieve the balance; however, many potential pitfalls can occur when delivering or applying irrigation.
This publication provides a checklist to assist producers with delivering water efficiently.
A few simple checks can make a big difference in efficient and uniform delivery of the appropriate amount of water.
Check the irrigation system for missing components before turning it on.
Determine if nozzles or other water-emitting devices, such as stakes or drip tubes, are missing.
Missing nozzles not only result in wasted water, but they alter the pressure of the system, disrupting nozzle function.
Nozzles and orifices should have the same specifications as those of the original design.
A properly functioning nozzle is designed to operate or deliver a specified amount of water per unit of time at a predetermined operating pressure.
Within an irrigation zone or area controlled by a single valve, the same nozzles and orifices with specific flow and pressure should be used.
If nozzles with different-sized orifices use the same pressure as existing nozzles, then output changes and delivery is not uniform.
However, exceptions could be
 made to equalize delivery between nozzles with different areas of rotations or to compensate for pressure differences due to elevation changes.
Pressure changes one pound per square inch for each two and one-third foot change in elevation.
Pressure-compensating nozzles may be used to help ensure uniform irrigation.
Nozzles should be positioned and oriented appropriately without obstruction to ensure water delivery at the proper angle.
For example, nozzles on risers or those hanging above the crop are positioned vertically SO that water distribution is perpendicular to the riser or hanger and uniform across the surface of the containers.
Microirrigation nozzles are positioned SO that water is delivered onto or into the container substrate.
In addition, ensure that water delivery is not obstructed by algae, plant foliage, or anything that will interfere with nozzle operation or water exiting the nozzle.
Before turning on the irrigation, look for leaks or leak indicators.
A small flow of water is obvious, but indicators of leaks where water is not flowing require careful examination.
Areas of inadequately irrigated plants or plants that are tipped from sudden high flow discharge can be indicative of malfunctions or burst pipes.
Stains, the presence of algae or weeds, and substances or surfaces that remain moist are also leak indicators.
Also before irrigation events check fuel supply for pumps powered by diesel.
For irrigation events triggered by timer clock, check valve wires and time function on digital or
 analog clocks especially after thunderstorms or power outage events.
Figure 1.
Algal growth is present on a nozzle that remains moist when the system is not operating.
Credits: Tom Yeager, UF/IFAS
 During irrigation start, operation, and shutdown, watch the nozzles, water flow, and distribution.
As pipes fill with water, friction retards water movement.
Pressure or force exerted by water works to overcome the friction and propel water along the length of pipe.
The longer a pipe or distance the water travels, the greater the loss in water pressure from friction.
A small-diameter pipe has more friction or pressure loss per unit length of pipe than a larger-diameter pipe.
Therefore, an irrigation system must be designed with proper pipe sizes.
Not only does a long distance result in the opportunity for a lot of friction, it also means that nozzles close to the water source are likely to begin operating before nozzles farther away from the water source.
Consequently, those plants at the beginning of water delivery or nearest the water source receive irrigation before those farther away.
This scenario is difficult to manage because plants close to the water source may receive too much water, and plants farther away may not receive enough water.
A properly designed system with pressure regulators  or pressure-compensating nozzles can minimize differences in irrigation volume applied throughout the irrigated area.
The differences in water applied throughout the area are measured by conducting a uniformity test.
See the reference section of this publication for resources detailing the procedure for conducting uniformity tests.
It can be expensive to replace or retrofit an existing irrigation system to achieve uniform delivery.
An option is to place small plants with low daily water requirements in locations where small irrigation volumes are applied and place large plants with high daily water requirements in locations where large volumes are applied.
Figure 2.
Appropriate nozzle operating pressure is achieved with a pressur regulator mounted below the sprinkler.
Credits: Tom Yeager, UF/IFAS
 During system operation, irregular flow or irregular patterns of water delivery are an indication of improper system function.
These irregularities could be because of inherent differences in water pressure related to system design, clogged orifices, obstructions, or worn, irregularshaped orifices that result in variable water pressure.
Orifice size may be checked with the blunt end of a drill bit of appropriate caliber.
A pitot tube with pressure gauge can be used to check pressure as the water flows from the orifice.
During system operation, watch the arc or angle of water delivery to ensure it is appropriate.
Irrigation should adequately cover the edges of benches or beds of plants.
Rotating nozzles should move consistently with the same number of rotations per minute.
Also, check for leaks while the system is pressurized and operating.
If nozzles are mounted on risers, checks should be performed to make sure that risers are not loose, have movement, or are leaning from the vertical position.
Risers that are not vertical will reduce the efficiency of the system and result in excess or inadequate water application to the surrounding plants.
Loose risers usually result in broken or cracked pipes eventually resulting in wasted water SO continual maintenance is essential.
As the system shuts down, watch the pattern of water exiting the nozzles and note the duration of flow.
Nozzles located at lower elevations may continue to emit water for several minutes with a concentrated stream rather than a dispersed pattern.
In addition to the excess water applied, this concentrated stream can damage tender plants and displace substrate from containers.
Low-pressure drains on the ends of pipes at the lowest elevations allow pipes to drain rapidly so that duration of water delivery is minimized after irrigation ceases.
Antidrip nozzles perform a similar function.
each volume.
Volumes should be similar to those calculated based on the nozzle manufacturer's output specification for the amount of time the system operated.
The volume collected per unit of time is the irrigation application rate and should be consistent in time if operated under the same conditions.
Figure 3.
The blunt end of a drill bit with appropriate caliber is used to check orifice wear.
Credits: Tom Yeager, UF/IFAS
 Figure 4.
A pitot tube with pressure gauge is used to monitor pressure as water flows from the orifice.
Credits: Tom Yeager, UF/IFAS
 Figure 5.
A low-pressure drain on the end of a pipe allows the pipe to drain rapidly when irrigation ceases.
Credits: Tom Yeager, UF/IFAS
 During system operation or water delivery, monitor the amount of water applied.
This can be done with meters or reservoirs  for collecting water.
Reservoirs should be placed strategically throughout the irrigated area.
Ensure that reservoirs are not obstructed by plants or other objects.
Measure and record water volume shortly after irrigation.
An ideal approach is to note the location of
 Figure 6.
Reservoirs are used to monitor the irrigation application amount.
Credits: Tom Yeager, UF/IFAS
 The amount of water applied or the operation time should be adjusted to minimize the volume of leachate or water exiting the container.
Reservoirs that exclude direct entry of overhead sprinkler water are placed under containers and used to collect leachate.
One can quickly look to see if there are obvious differences in the leachate amount in the reservoirs.
Leachate volumes should be similar for plants that are small relative to container substrate
 surface area.
However, differences in leachate volumes do not indicate lack of uniform delivery.
Leachate volumes may vary because plants extracted different amounts of water from the substrate, the substrate physical properties varied with time, or canopies of large plants influenced the amount of water entering the container substrate.
Simple checks performed before and during irrigation can make a difference in the effectiveness of irrigation and result in more efficient use of personnel time.
A checklist is provided below.
Irrigation Checklist Before Irrigation
 Check for missing components.
Determine that nozzles and orifices have the same specifications as original design.
Ensure that nozzles are positioned and oriented appropriately, without obstruction.
Look for indications of leaks.
Check power or fuel supply to pumps and irrigation timer clocks.
Watch nozzles operate to determine appropriate function.
Conduct tests to verify uniform water delivery.
Determine if flow from nozzles ends immediately when operation terminates.
Note volume applied per unit of time because that is the application rate.
Check that volume applied is consistent with each similar irrigation event.
Adjust operational time to achieve minimal leaching.
Continual maintenance is necessary for optimal performance.
Figure 7.
A plastic sleeve secured around a container with a rubber band prevents irrigation water from entering the reservoir along the container sidewall.
Credits: Tom Yeager, UF/IFAS
 Overtime irrigation delivery pipes may start to fill with biological contaminates or dirt and debris from irrigation sources and system repairs.
You may notice less outflow from furthest nozzles or emitters visually or with catchreservoir or leaching fraction test.
In freezing conditions, algae that was growing along the length of deliver pipes might die and slough-off, causing widescale plugging of nozzles or emitters.
In these cases, careful monitoring of the irrigation event will alert operators to problems.
System wide flushes by removing the furthest nozzles and running irrigation can help alleviate these symptoms.
In some instances chemical intervention may be needed to keep delivery pipes clean from biological growth.
See irrigation further reference section at the end of the article for more information.
For larger containers using spray stakes, irrigation application can be monitored with catch pans using the leaching fraction method.
See the reference section of this publication for resources detailing the procedure for conducting leaching fraction tests.
The Role of Nonpoint Source Models in Watershed Management
 The U.S.
Environmental Protection Agency  considers nonpoint sources of sediment, nutrients and pesticides as one of the leading causes of water quality impairments.
By definition, nonpoint source contaminants are much harder to identify and thus, more difficult to manage than point sources.
This is confounded by the fact that landscape hydrology is highly variable both spatially and temporally.
Consequently, efforts by the USEPA to address nonpoint sources occur at a watershed scale.
A watershed is the area of land where all of the water that is under it or drains off of it goes into the same water body.
Models integrate information over a watershed to identify Best Management Practices and critical source areas most likely to affect watershed-scale nutrient losses.
Because of the time and expense involved in monitoring water quality response to implementation of conservation measures and the growth and accessibility of computer capacity, simulation models are increasingly used to estimate the effects of watershed management.
Computer simulation models represent mathematical descriptions of scientific understanding about chemical, physical and biological processes that influence both point and nonpoint source contaminant loads within a watershed.
In their most comprehensive form, models can integrate information over a watershed scale to evaluate Best Management Practices.
As such, models can suggest where BMPs are most likely to decrease watershed-scale nutrient losses.
In the case of TMDL  development, models can allocate load reduction targets among the model's identified contaminant sources.
Thus, use of nonpoint source models provides a method of simulating long periods to estimate the relative effects of changes in climate, land use and land management practices on sediment and nutrient loadings from large, complex watersheds.
As a result, models yield
 numerical results with which to gauge progress.
This numerical ranking simplicity provides strong appeal to policymakers and managers; however, this appeal can sometimes bring false confidence and misconceptions.
"All models are wrong; some models are useful." George Box
 Model credibility can be achieved through a careful process of calibration, verification and validation.
The definitions used here are derived from the work of Thomann and Mueller.
Calibration is an iterative process of fine-tuning the model to a set of field data, preferably data that were not used in the model construction.
Verification is the statistical comparison of the model output to additional data collected under different forcing and boundary conditions.
Finally, validation is achieved through calibration and verification SO that the model is an accurate representation of the real system or watershed being assessed.
There are many models available; selecting the right one for the job is critical.
Shirmohammadi et al.
provided a comprehensive discussion of water quality models.
They provide a list of models with their practical attributes in terms of their complexity, scale, purpose and level of validation.
Shirmohammadi et al.
also provide a long list of proper and improper uses of water quality models and conclude that one has to keep in mind the uncertainty associated with model simulations and use the results with caution, especially when applying a model outside the conditions used in calibration and verification.
It is of critical importance that model developers clearly define what the model is useful for and what it is not designed to do.
Likewise,
 users must decide what they want to accomplish with a model.
For example, one must consider the scale , time  and level of accuracy  that needs to be simulated, as well as the amount and quality of data available.
It is incumbent on the modeler to explicitly express the assumptions made in representing the system which is being modeled.
These assumptions affect the model outcome.
Violation of these assumptions may ultimately affect decisions based upon modeled results.
Models play an important role in making watershed management and policy decisions to identify critical source areas and target BMPs.
Despite such cautionary realities, the role of models will be more and more important over the next decade in making watershed management and policy decisions to identify critical source areas and target BMPs.
However, as Silberstein  points out, the use of models to evaluate scenario outcomes often results in use outside the tested boundaries of models, with little or no data to constrain the scenarios.
It is, therefore, critical that any use of nonpoint source models must be associated with data collection and monitoring to further verify model estimates.
Silberstein  best summarized the role of nonpoint source models in watershed management assessment and prioritization of future actions, and rather than paraphrase his text, it is quoted below.
"Models are enormously useful as test beds for ideas and for exploring the implications of our understanding of natural systems.
They are extremely valuable as data processing and analysis aids, often showing up data errors and inconsistencies that might otherwise have gone unnoticed.
Models are also useful for exploring scenarios that cannot be tested in the real world.
However, while this last use is a rapidly expanding one, it is also the most dangerous.
As high level managers appreciate the nice graphics and, possibly, simplistic sets of options, it can be easy to lose sight of the limitations of the process that generated them.
It is in this mode that models are often run outside their tested bounds, and by definition little or no data are available to constrain the scenario results.
If we are to continue to learn about and improve our management of our environment, we must continue to observe it, and that means collecting data.
Modeling is an important accompaniment to measurement but is no substitute for it.
Science requires observation, and without that we will cease to progress in understanding our environment and, therefore, in managing it appropriately."
 Uncertainty arises because of an imperfect representation of the physics, chemistry and biology of the real world, because of numerical approximations, because of inaccurate parameter estimates, and data input.
Causes of model uncertainty can be broadly classified into model uncertainty  and input uncertainty.
For example, there is a cumulative uncertainty associated with water quality monitoring used for model calibration.
This uncertainty is derived from stream flow measurement, sample collection, sample preservation and storage, and analysis.
Standardized methods to quantify this uncertainty involve forcing the model to "fit" historically measured data, if available, with predetermined limits of performance.
This will assist modelers in quantifying the "quality" of calibration and verification data, determining model accuracy goals and evaluating model performance.
Whenever possible, the uncertainty should be represented in the model output  or as confidence limits on the output of a time series of concentrations or flows.
In many cases, the knowledge of the cause and effects of uncertainty, as well as the measurement of uncertainty, is as or more important than the model output in making "real-world" management decisions.
Inherent uncertainty in model estimates should be clearly stated.
The tendency described earlier for decision makers to "believe" models because of their presumed deterministic nature and "exact" form of output must be tempered by responsible use of the models, such that model computations or "estimates" are not oversold or given more weight than they deserve.
Above all, model users should determine that model computations are "reasonable" in the sense of providing output that is physically realistic and based on input parameters that are within accepted ranges.
Modelers should use all available measurements and multiple levels of comparison to evaluate if model estimates are physically realistic.
Consider spending more time and money to get good data and analyze it to make great irrigation scheduling decisions.
Pumping water is the largest energy bill on most irrigated farms in Nebraska.
In addition, over irrigating can carry some of your valuable inputs below the root zone.
This is a leading cause of increasing nitrate level in the groundwater and can lower crop yields.
For more information on yield losses take time to read the following NebGuide: Plant Growth and Yield as Affected by Wet Soil Conditions Due to Flooding or Over-Irrigation
Poultry Litter Management in the Illinois River Watershed of Arkansas and Oklahoma
 Sheri Herron Research Associate
 Andrew Sharpley Professor Soil and Water Quality Management -
 Susan Watkins Professor Poultry Specialist
 Mike Daniels Professor Water Quality and Nutrient Management
 Arkansas Is Our Campus
 During the past decade, ongoing lawsuits between Oklahoma and several entities in Northwest Arkansas have focused attention on water quality impairment by upstream wastewater treatment facility discharges and the application of poultry litter as a fertilizer.
The main concerns center on phosphorus  levels in streams in Northwest Arkansas that flow into Eastern Oklahoma.
The lawsuit settlement in the EuchaSpavinaw Watershed, adjacent to the Illinois River Watershed , requires users of poultry litter to have a nutrient management plan that determines appropriate rates of application based on the potential for P loss in runoff.
The court case covering the IRW is still awaiting final rule.
However, the application of poultry litter to pastures is now regulated by the States of Arkansas and Oklahoma and requires that litter be applied by a state-certified applicator and according to a P-based nutrient management plan.
Thus, both in-house and land management of poultry litter is of importance to this area, as well as other areas of the U.S.
with localized concentrations of livestock production; for example, the Delmarva Peninsula, Coastal Plains of North Carolina and the North Bosque River area of Texas.
This fact sheet describes how poultry litter is utilized and managed in the Illinois River Watershed, how poultry producers have adapted to P-based nutrient management and how this has affected litter export programs, all of which are helping to reduce the risk of water quality impairment.
Poultry litter is a mixture of manure and bedding material, typically rice hulls, wood shavings or a combination of the two.
Fresh bedding is placed in the house following clean-out.
The objectives of in-house poultry litter management include maximizing bird health, maintaining air quality and reducing energy costs.
Some factors influencing litter management are beyond the control of the producer and include weather, specifically temperature and humidity, and feed content, which is controlled by the integrator company for which the producer raises birds.
Other factors, such as in-house environmental controls and litter conditioning practices, can be managed by the producer.
Between flocks of broiler chickens, producers in this region often remove the top layer of the litter known as "cake." Periodic removal of this "cake" has the benefit of reducing in-house moisture and ammonia, both of which can decrease broiler productivity and bird weight gains.
Instead of removing the "cake," some producers choose to till the litter to mix the wetter upper layer in with the drier lower layer.
For optimum results with tilling, the "cake" needs to be broken into small particles and blended with the remaining litter to create a uniform mixture.
With some types of equipment it may take three to four passes to get the desired blend.
After this, the house is usually well ventilated to remove excess moisture and ammonia.
A newer practice being supported by some of the integrator companies is windrowing litter between flocks.
Litter is formed into two rows the length of the poultry house, with each row being at least 3 to 4 feet high for best results.
With proper conditions, windrowing litter can result in biological activity and heat production that partially composts the litter.
If the heat production reaches 130F in the piles, it can reduce pathogen populations that are a threat to bird health.
For optimum effectiveness, the rows are turned after 72 hours and allowed to heat a second time.
Following the second cycle, windrowed litter is redistributed in the house for the next flock of birds.
Ideally, temperatures should reach 130F both times.
Again, it is important to ventilate the house well after windrowing to avoid ammonia-induced health problems for the next flock of birds.
Windrowing necessitates a downtime between flocks of at least 10 days, with additional days needed to prepare the house for the next flock.
Example of windrowed poultry litter
 Broiler producers utilize one or a combination of the practices above for in-house litter management between flocks and typically remove all of the litter from the house once per year.
Turkey producers typically remove the cake or remove all of the litter between flocks, as their grow-out periods are much longer than for broiler chickens.
Chicken hen and pullet producers generally remove all of the litter between flocks.
When birds are present, litter moisture and ammonia are managed using heaters and ventilation fans to maintain ideal in-house conditions for bird health.
Outdoor weather conditions influence the moisture and temperature of the incoming ventilation air and greatly impact the intensity of this management, determining the need for either heating or cooling.
Nutrient Content and Fertilizer Value
 Poultry litter is not typically managed to increase its fertilizer value; however, in-house management does affect the nutrient content of litter and its value as a fertilizer for pastures and crops, when removed
 from the house.
Thus, determining the nutrient content of litter is an important consideration when using litter as a fertilizer.
Determining nutrient content requires collecting a litter sample either in-house before clean-out or from stacked litter after clean-out  and submitting the sample to the University of Arkansas Diagnostic Testing Laboratory or the Oklahoma State University Soil, Water and Forage Analytical Laboratory in Oklahoma through your local county Extension office.
Poultry litter that is used in the Arkansas IRW as a fertilizer for pastures, haylands and crop fields must be analyzed for nutrient content every 5 years, as required by state law.
In Oklahoma, state law requires that litter be analyzed annually.
Litter that is exported off the farm is analyzed each time it is hauled.
The nutrient content of litter varies with feed management, which is controlled by the integrators along with in-house feeder pan, brood feeding and litter management, as mentioned above and by Sharpley et al.
and Zhang et al..
As feed and litter management can vary from year to year, values used to estimate total nutrient production, current fertilizer value and pricing for markets are based on the previous year's litter analyses averages by bird type.
Table 1 lists the averages for 2011 based on litter analyzed by the University of Arkansas Soil Testing Laboratory and provided by Nathan Slaton, director of the University of Arkansas Division of Agriculture's Soil Testing Program.
TABLE 1.
Mean nutrient content of poultry litter analyzed by the University of Arkansas Diagnostic Testing Laboratory in 2011.
Bird Type	N	P2O5	K2O	Moisture	%
 lb/ton on an as is basis
 Broiler	64	55	58	25.8
 Hen	47	60	43	27.0
 Pullet	49	66	42	26.1
 Turkey	65	63	49	26.4
 Similar trends and nutrient contents of poultry litter were obtained for prior years.
Based on average nutrient content, the value of poultry litter, as compared to commercial fertilizer prices, can be estimated.
Table 2 lists the values as of January 15, 2012.
TABLE 2.
Average value of poultry litter based on its nutrient content and commercial fertilizer prices from four fertilizer dealers in Eastern Oklahoma as of January 15, 2012.
Litter Type	N	P2O5	K2O	Total
 $/ton on an as is basis
 Broiler	$25	$26	$31	$82
 Hen	$19	$29	$23	$71
 Pullet	$19	$32	$22	$73
 Turkey	$26	$30	$26	$82
 1N value is based on 70% availability.
Management of Poultry Litter Removed From Houses
 Average litter production by bird type is influenced by many factors and is most accurately documented based on the quantity removed annually as cake and clean-out.
Table 3 lists watershed-based estimates of the annual quantity of litter generated by bird type and removed from the house.
These estimates were based on the current number of houses provided by the poultry industry.
Average tons of litter removed per house annually were estimated from data based on individual load weights provided from poultry litter trucking companies gathered during 2006 through 2011 and compiled by BMPs Inc.
TABLE 3.
Estimated annual litter production in the IRW.
# Houses	Per House	Removed
 Bird Type	in IRW	Annually	Annually
 Broiler	1,133	1951	220,935
 Hen	211	120	25,320
 Pullet	195	100	19,500
 Turkey breeder	27	75	2,025
 Turkey growout	53	132	7,000
 1 Average tons removed per broiler house annually is the sum of 140 tons of clean-out and 55 tons of cake litter.
Removed litter that cannot be immediately land applied or exported from the watershed is stored temporarily on-site beneath litter stacking sheds, which keep litter stored on top of concrete and under cover as a means of containment and keeping the litter dry.
Poultry litter stacking sheds provide safe, temporary on-site storage of litter by keeping the litter dry and contained.
Poultry litter is ultimately land applied as fertilizer or exported via trucking out of the watershed.
Land application of poultry litter in the IRW in Arkansas and Oklahoma is regulated by state laws, both requiring analyses of soil and litter to determine application rates, which minimize the risk of P loss in runoff.
Arkansas tracks litter application in the IRW through the nutrient management
 planning process, which is supervised by Washington and Benton County Conservation Districts.
Nutrient management data has been compiled by the Arkansas Natural Resources Commission , dating back to 2007, to evaluate the impact of using the Arkansas Phosphorus Index  on litter application rates in the IRW.
The index was recently updated and planners began using the newly revised version in 2010.
Since 2007, almost 740 nutrient management plans have been developed, covering 46,920 acres.
The average litter application rate prior to the implementation of the revised ARPI was 2.3 tons/acre.
If all the planned acres received litter at the average rate, it would amount to 107,920 tons utilized annually in the Arkansas portion of the IRW.
Starting in 2010, the average litter application is 1.6 tons/acre using the revised ARPI, resulting in 75,080 tons planned for application annually in the Arkansas portion of the IRW.
Oklahoma tracks litter application in the IRW through required records submitted by Oklahoma Registered Poultry Feeding Operations and licensed waste applicators.
Current data is for 2009 and 2010, as compiled by the Oklahoma Department of Agriculture, Food and Forestry.
Land application of litter in the Oklahoma IRW dropped from 31,660 tons in 2009 to 7,770 tons in 2010.
While reductions in litter application rates have occurred, it is difficult to create an accurate mass balance due to the difference in the methods used by each state to collect litter utilization data.
In 2005, the five primary poultry integrator companies in Northwest Arkansas committed to the Oklahoma Scenic Rivers Commission  to export 202,500 tons out of the IRW over a 3-year period.
This commitment was the catalyst for the creation of the coordinated litter export program, which now transports over 100,000 tons annually from the IRW.
This litter is transported to nonnutrient sensitive watersheds, mainly in Oklahoma and Kansas, for use primarily on cropped fields.
To assist with meeting the commitment to OSRC, both Oklahoma and Arkansas committed EPA 319h funds to offset a portion of the trucking costs and pay poultry producers for their litter, in the amount of $1.3 million in grants and matching funds.
The grants were administered by BMPs Inc, a nonprofit corporation established in 2004 for the purpose of
 creating a poultry litter export industry.
Following the grant projects, ANRC administered an additional $300,000 of federal, state and local funding for the export program in Arkansas.
Through this grant funding process, a coordinated, large-scale litter hauling system was created, including scheduling, marketing and transportation.
Although grant subsidies are no longer available, local independent trucking companies continue to operate today, transporting litter in 23-ton capacity semi-trailers.
Litter exports are tracked using certified scales to weigh each load.
Table 4 summarizes the tonnage documented by independent haulers and poultry integrators as exported out of the watershed since 2006 and may not be a total accounting.
TABLE 4.
Tons of litter exported out of the IRW.
Responses to environmental, legal and livestock production concerns, as well as increasing costs of bedding materials, have resulted in changes to poultry house and poultry litter management.
Producers are implementing litter management practices to improve the quality of their bedding material.
Nutrient management plans are reducing the maximum litter and therefore P application rates.
This, combined with a successful litter export program, has resulted in a significant reduction in the amount of litter applied in the watershed.
Printed by University of Arkansas Cooperative Extension Service Printing Services.
SHERI HERRON is research associate and DR.
ANDREW SHARPLEY is professor soil and water quality management with the Crop, Soil and Environmental Sciences Department at the University of Arkansas, Fayetteville.
DR.
SUSAN WATKINS is professor poultry specialist with the Center of Excellence for Poultry Science at the University of Arkansas, Fayetteville.
DR.
MIKE DANIELS is professor water quality and nutrient management with the Crop, Soil and Environmental Sciences Department, University of Arkansas Division of Agriculture, in Little Rock.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S.
Department of Agriculture, Director, Cooperative Extension Service, University of Arkansas.
The Arkansas Cooperative Extension Service offers its programs to all eligible persons regardless of race, color, national origin, religion, gender, age, disability, marital or veteran status, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
evidence indicates asparagus on sedimentary soil can utilize about 20" of irrigation in addition to a normal 16" rainfall
 G.
c.
Hanna and L.
D.
Doneen
 Frequency of irrigation in relation to yield of asparagus on sedimentary soil was the subject of an eight-year experiment at Davis.
Before 1930, the major part of the asparagus production in California was confined to the Sacramento-San Joaquin Delta area where the peat and peat-sediment soils have a permanent water table of from 3' to 8' below the soil surface.
However, because old asparagus land can not be replanted where there has been a buildup of Fusarium wilt during the life of the original planting-as has occurred in many Delta plantings-there has been a shift to the San Joaquin area.
A major portion of suitable land in the Delta area has been, or is, in asparagus and as the industry is forced to move to the upland the absence of a high water table causes irrigation-amount and frequency-to become a problem.
The eight-year experiment was initiated with a planting of one year old asparagus of a strain of the Washington variety.
Six treatments replicated six times were arranged in a Latin square.
The plots consisted of three rows each 30' long.
The roots were planted 8" deep, l' apart in the row.
The space between rows was 6'.
Guard rows separated the plots.
To establish the crop, all plots were given the same irrigation treatments the first year.
The following year, differential irrigation treatments were established to maintain soil moisture through various levels of availability for the cutting and vegetative seasons.
After the first year, the dry plotsTreatment A-were not irrigated.
The wet plots-Treatment B-were irrigated when approximately half of the available moisture was used from the soil permeated by roots.
The intermediate plots -Treatment C-were irrigated when most of the available moisture had been used by the plant.
Under Treatment D the plots were kept dry during the cutting season and wet in the vegetative season.
In Treatment E the cutting season was dry and the vegetative season was intermediate.
In Treatment F the cutting season was intermediate and the vegetative season, wet.
The differential treatments during the cutting season were unnecessary because the soil moisture was in the upper half of available moisture range due to winter rainfall.
So, essentially, the three irrigation treatments prevailed only during the vegetative season.
The spears were harvested when they were approximately 41/2" or more above the soil surface.
They were trimmed to 7" in length, counted and weighed.
Termination of the season varied from year to year, depending on age of the bed and the general appearance of the spears.
The first year of the experiment the annual rainfall was 31.5" as compared to the normal of 16.3".
Rainfall the second season was also well above normal resulting in a temporary or perched water table about 6' below the soil surface in the first spring after the study was started.
The perched water table was caused by a heavy compact bluish clay layer at the 14'-16' depth.
Thus a huge reservoir of water was stored in ac least a part of the root zone, and it was evident from frequent soil sampling that roots
 of the asparagus plant in the dry plots utilized all the available moisture to the depth of the bluish clay layer-14 feet.
By the second spring the water table had receded to a depth of 10', and a few months later, had entirely disappeared from the soil profile.
The perched water table probably accounts for the high yields in the first and second years of the dry plot, and the mean weight of spears for the same two years.
The number of inches of water applied to the treatments B, C, D, E, and Continued on page 14
 Accumulated yields irrigated asparagus expressed as percent of dry treatment.
Applied during the vegetative season of asparagus for various Irrigation treatments
 Treat-	ment	gation	irri-	No.
1	2	3	Year	4	5	6	7	Mean
 A	0	31.5	21.2	17.8	15.5	15.5	15.4	12.7	18.5
 Irrigation water, depth inches
 B	4	19.4	20.1	17.1	19.4	17.1	21.3	17.6	18.9
 C	2	12.8	11.2	10.5	15.5	11.8	15.5	13.5	13.0
 D	4	19.2	20.1	17.1	19.4	17.1	21.3	17.6	18.8
 E	2	12.8	11.2	10.5	15.5	11.8	15.5	13.1	12.9
 F	4	19.1	20.1	17.1	19.4	17.4	21.3	17.6	18.8
 The Effect of Differential Irrigation on Asparagus
 Treat-	ment	Harvest	season	Growing	season	yield/	Total		plot		spear	Mean	wt./	spears/	Mean	plant	no.
Yield	Mean	spear	wt./
 A	Dry	Dry	448.8	21.3	15.0	B-A	B-A
 B	Wet	Wet	548.3	26.1	14.4	B-C	B-C*
 C	Inter.
Inter.
511.8	24.2	14.3	B-D	B-D
 D	Dry	Wet	547.5	25.6	14.6	B-E	B-E
 E	Dry	Inter.
515.0	23.9	14.7	B-F	B-F
 F	Inter.
Wet	551.0	24.6	15.3	C-A	C-A*
 L.S.D = 5%	39.2	1.48
 Significant difference at the 1% level.
Significant difference at the 5% level.
Continued from preceding page
 they produced the largest yields, although in comparison with yields from trees on some of the rootstocks, not significantly so.
Significant yield differences among the various rootstocks were, generally, a reflection of differences in tree size and were less pronounced with the Sevillano scion variety than with Mission and Manzanillo.
Fruit size-in the Manzanillo and Sevillano varieties-was greater for trees on their own roots than on other rootstocks.
Only in some comparisons were such differences significant.
In the Mission variety, fruit size showed little variation among the rootstocks.
In all three varieties the weight of the pit was little influenced by the rootstock.
In all three scion varieties, two rootstocks-0.
verrucosa and O.
ferruginea -caused a significant reduction in length-width ratios in comparison with fruit from trees on most of the other rootstocks.
Fruit from own-rooted trees of the Manzanillo and Sevillano varieties was not significantly different in shape from that on the other stocks.
However, in Mission, fruit from own-rooted trees had a greater length-width ratio-significantly so in some comparisons-than fruit from trees on other rootstocks.
Shotberry production-with all rootstocks-was the greatest by far in the Sevillano variety, followed by Manzanillo, then Mission.
In Sevillano and Mission, the occurrence of shotberries was greatest-the differences being significant in most comparisons-when O.
verrucosa and O.
ferruginea were the rootstocks.
Shotberry production in Man-
 zanillo seemed to have little relation to the rootstock used.
There seemed to be no consistent relationship between rootstock and rate of fruit maturity, except in the Manzanillo variety, where the three Olea species as rootstocks significantly delayed the rate of fruit maturity.
In determinations of the percentage of potassium, calcium, magnesium, sodium, phosphorus, and nitrogen in the dry matter of leaves of the three scion varieties studied, no consistent relationships appeared between any of the rootstocks and the mineral nutrient level of the trees.
Although differences in individual tree growth were encountered with clonal stocks, this effect was much more evident with seedling rootstocks.
Seedlings of the Ascolano varietywhich itself has a vigorous tree growth
 Effect of Rootstock on Tree Size After 4 years' Growth.
Sevillano Scion Variety.
Corning and Lindsay.
Average of 10 Trees.
cuttings	8.4 sq cm	72.5 sq cm
 -1% level	11.6	40.1
 -5% level	8.7	30.2
 Effect of Rootstock on Tree Size and Yields of Three Olive Scion Varieties After 8 Years' Growth.
Winters.
Average of 5 Trees.
Rootstock	sq.
cm.
section	Trunk	cross	lbs.
per	Yields	aver.
4 yr.
tree	section	sq.
cm.
Trunk	cross	lbs.
per	Yields	aver.
4 yr.
tree	section	sq.
cm.
Trunk	cross	lbs.
per	Yields	aver.
4 yr.
tree
 cuttings	285	67	542	140	365	86
 cuttings	376	50	251	85	202	31
 seedlings	456	50	252	58	20
 seedlings	418	62	236	51	312	44
 seedlings	345	49	410	85	302	46
 seedlings	369	51	374	72	243	40
 seedlings	220	53	204	49	88	15
 seedlings	184	30	184	44	112	36
 seedlings	279	40	226	42	192	41
 seedlings	341	21	260	49	266	31
 -1% level	269	34	168	41	149	39
 -5% level	200	25	125	31	111	29
 when used as rootstocks-proved to have a rather uniformly dwarfing influence on all three varieties, but much more so on Manzanillo than Mission or Sevillano.
The clonal stock, Oblonga, had a pronounced dwarfing effect on Manzanillo and somewhat less on Mission, but an invigorating influence on Sevillano.
It is apparent that the behavior of each scion-rootstock combination must be tested individually.
Any given influence of a rootstock on the vigor of one variety can not necessarily be expected to hold true for another scion variety.
In commercial olive production there are situations where either a dwarfing or an invigorating rootstock would be useful.
In the Tulare County olive district especially, the trees are vigorous and tend to grow excessively tall, making picking difficult and slow, resulting in high harvesting costs.
Under such conditions, a dwarfing stock would be of great benefit.
Smaller trees, planted closely together, may give higher yields per acre and have much lower harvesting costs.
On the other hand, in some areas it is often difficult to obtain adequate tree growth.
In such cases, the use of invigorating rootstocks should prove to be very desirable.
Some individual seedlings used as rootstocks in the present study have shown dwarfing effects and some have had an invigorating influence.
Cuttings taken from suckers arising from such selected seedling rootstocks have been rooted and grafted.
Large-scale tests of such trees are now underway to determine if these stocks will have consistently dwarfing or invigorating effects so that they can be developed as clonal rootstocks for commercial use.
H.
T.
Hartmann is Associate Professor of Pomology, University of California, Davis.
The above progress report is based on Research Project No.
1301.
Continued from page 8
 F-in addition to the rainfall-are given in the upper table on page 8.
The intermediate irrigation treatment was considered to be about the amount of water growers would apply, while the wet plots probably received more water than is usually applied.
The results as shown in the lower table and in the graph on page 8 indicated that both the intermediate and wet treatments had significantly higher yields than the dry plots.
The difference in yield between the intermediate and wet plots was not significant at the 5% level but approached significance.
The difference in mean weight per spear between the intermediate and wet plots was significant at the 5% level.
However,
EM 8783 Revised March 2013
 Strategies for Efficient Irrigation Water Use
 Figure 1.
Furrow-irrigated onion grown at Ontario, Oregon, receives about twice as much water as the crop actually uses.
Malheur Experiment Station, Oregon State University: Clint C.
Shock, director and professor
 Scientific Ecological Services, Ontario, Oregon: Byron M.
Shock
 Wild Iris Communications, Corvallis, Oregon: Teresa Welch
 Oregon State Extension Service UNIVERSITY
 W hen water is plentiful, growers usually schedule irrigation practices around other farming activities.
For example, most growers change furrow irrigation sets at 12to 24-hour intervals because this timing is convenient and uses labor efficiently.
However, long irrigation sets can waste water.
When water is in short supply, you need to rethink some practices to obtain maximum benefit from available water.
After all, next to the land itself, water is a grower's second most important resource.
It makes sense to exchange management and labor for water use efficiency.
Because irrigation districts must keep their systems charged with water, these practices have a greater impact as more growers use them.
Even when water is more plentiful, there are compelling reasons to use less.
Excessive water use can waste soil and fertilizer in water runoff.
Excessive irrigation results in deep percolation and leaching of nitrates, nitrites, and other farm chemicals.
These contaminants contribute to the total daily load of chemicals carried by aquifers.
Self regulation by growers typically benefits all parties interested in clean, plentiful water, including you and other growers.
See Shock and Welch, 2011b, TMDLs and Water Quality in the Malheur Basin: A Guide for Agriculture.
Approaches to using less water
 You can improve irrigation efficiency by irrigation scheduling, adopting practices such as deficit irrigation and conservation tillage, and installing more efficient irrigation systems.
Sprinkler and drip irrigation systems are more efficient than furrow irrigation.
Some of these strategies entail additional costs, but they can also lead to higher market value of crops.
This sounds simple, but it isn't.
Many growers err on the side of excess.
Too much water has less visual impact than too little, but it wastes soil and fertilizer as well as water.
Eliminate deep watering of shallow-rooted crops such as onions and beans.
Frequent, light irrigations help keep water and mobile nutrients in the root zone where plants can use them.
Schedule irrigations based on evapotranspiration 
 There is a seasonal demand pattern for water, which varies by crop.
The optimal time to irrigate a particular field also depends on when the crop last received water and the soil waterholding capacity.
Use ET charts from the Bureau of Reclamation AgriMet system or other source.
The charts show fairly accurate estimates of crop water use and can help you decide when and how to irrigate.
Know the water-holding capacity of your soils.
A sandy loam soil will not hold as much water as a silt loam; thus, it must be irrigated more frequently with less water per irrigation.
Extra water is lost to runoff and deep percolation.
Schedule irrigations based on soil water content or soil water tension
 Irrigation scheduling can be done based on soil water content or soil water tension.
Use soil-moisture monitoring equipment to measure how much moisture is in the soil.
There are several types of sensors available.
The soil water content sensors used most commonly in the Pacific Northwest are neutron probes and capacitance sensors.
The most common soil water tension sensors are granular matrix sensors and tensiometers.
These instruments, when used with ET charts, provide a fairly accurate estimate of irrigation needs.
Graph soil moisture readings.
The most important aspect of soil-moisture monitoring is graphical presentation of the readings over time in order to improve your irrigation accuracy.
Even if you measure soil moisture with a shovel and your fingers, you can graph the readings.
Figure 3 shows a card used for recording soil water tension.
Figure 2.
Using hypothetical AgriMet crop water use data.
1	ESTIMATED CROP WATER USE JULY 16, 2012 ONTO
 2	3	4	5	6	7	8	9	10
 CROP WATER USE-	7	14
 PENMAN ET JULY	Daily	COVER	TERM	SUM	DAY	DAY
 Forecast	DATE	DATE	ET	USE	USE
 12	13	14	15
 ONYN	401	0.32	0.3	0.29	0.31	0.32	710	820	20.6	2.16	4.3
 POTS	501	0.33	0.32	0.3	0.32	0.34	610	820	19.7	2.3	4.28
  = Location of weather station: ONTO = Ontario, Malheur Experiment Station
  = Crop: ONYN = Onions; POTS = Shepody potatoes
  = Start date: Crop emergence date
  = Amount of water used by the crop each day for the past 4 days
  = Estimated water use for the date on the chart, i.e., July 16
  = Cover date: Date the crop reached full canopy
  = Term date: Date irrigation stops or crop is harvested
  = Sum ET: Total estimated water use from the beginning of the growing season to the current date
  = 7 day use: Prediction of water needed by crop for the next 7 days
  = 14 day use: Prediction of water needed by crop for the next 14 days
 Figure 3.
Sample soil water tension recording card.
For more information on measuring soil moisture and using soil moisture observations to inform irrigation decisions, see Shock, et al., revised 2013b, Irrigation Monitoring Using Soil Water Tension.
Deficit irrigation is irrigation that applies less water than the crop needs for full development.
Some crops lose little yield and quality with modest irrigation deficits, saving water.
Deficit irrigation works with deep-rooted crops such as wheat and corn.
Wheat and corn have been successfully grown with carefully controlled deficit irrigation, but they do lose test weight and yield.
Know each crop's tolerance of drought stress, and irrigate accordingly.
Some plants handle drought stress much better than others, with yield and quality positively related to some water deficit during part of the growing season.
Almonds, wine grapes, and alfalfa seed are such crops.
Sugar beets and alfalfa can extract moisture from a greater depth than most crops, SO they can continue growth without irrigation as long
 as water reserves are available deeper in the soil profile.
Deficit irrigation is less successful with crops for which the proportion of the crop yield that is monetizable and/or the quality is depressed by water stress.
Examples include potatoes and vegetable crops such as onions.
Russet Burbank potatoes suffer greatly in quality when drought stressed, losing tuber grade and fry color consistency.
Umatilla and Shepody potato varieties suffer less quality reduction than Russet Burbank, but still more than other crops.
Total yield is reduced when Shepody and Umatilla Russet varieties are drought stressed.
Potato plants can be stressed lightly very early, but not after setting tubers.
Water stress on onions affects yield and grade and reduces the percentage of bulbs that have single centers.
For many seed and grain crops, water stress at the flowering stage is most damaging.
Plan your acreage under irrigation
 Know the water-use requirements of the crops you intend to grow, and make sure you have enough water to get an economic yield.
When water supplies are short, plant crops that require less water.
Figure 4.
No-till wheat requires less fuel and water inputs.
Reduce irrigated acreage: Leave some ground idle, and apply the saved water to highvalue crops.
Conservation tillage practices such as minimum tillage, no till, and strip till help conserve soil water.
Tillage is reduced and crop residue from the previous crop is at least partially retained on the soil surface.
The retention of crop residues reduces water loss from the soil to the air and cools the soil.
Each time that the soil is tilled, it is exposed to drying; conversely, reductions in tillage help conserve soil water.
For strip tillage, cultivate only within the row zone and leave the inter-row zone undisturbed.
This usually leaves at least 30 percent of the previous crop residue on the surface after planting.
Soil infiltration capacity of the inter-row zone is increased, allowing water to go where it's needed.
See Foley, et al., 2012b, Making Strip Tillage Work for You: A Grower's Guide.
Figure 5.
Strip tillage saves water and helps protect sugar beet seedlings from being blown out of the soil by wind.
Figure 6.
Strip tillage of beans for seed helps to conserve soil moisture and cools the soil.
Carefully manage surface irrigation
 Surface irrigation systems are inherently inefficient.
They bring a heavy flow of water in direct contact with your soil, dislodging soil particles.
Fully surface irrigating a field from top to bottom often results in a field where the top is over-irrigated and the bottom is underirrigated.
To save water with furrow irrigation, change irrigation sets soon after the water reaches the end of the furrow rather than at a specified time of day.
Over-watering the top of the field stresses plants and causes nitrogen deficiency as nitrogen leaches below the root zone.
Slightly
 drought stressing the bottom of the field often causes production losses similar to those caused by over-watering the top of the field.
Mulch the bottom of the field with straw SO the water that gets there soaks in.
Use PAM  or straw mulch to improve water infiltration in tight soils.
See lida and Shock, 2008, Make Polyacrylamide Work for You!.
Use sedimentation basins with pump-back systems to collect runoff and reuse it.
Sometimes this involves pumping water to the top of the field or to the next field.
Analyze the cost of pumping to see whether this strategy is effective.
See Shock and Welch, 2011a, Tailwater Recovery Using Sedimentation Ponds and Pumpback Systems.
Use surge irrigation or at least use a modified surge program during the first annual furrow irrigation.
The wetting-drying cycle of surge irrigation reduces water loss to deep percolation, which is particularly important on the first irrigation when the soil is friable and takes a lot of water.
For a modified surge
 Figure 7.
Sprinkler systems can apply less water per acre than furrow flood systems while fully meeting crop water needs.
irrigation program, alternate siphon tubes between rows every couple of hours on the first irrigation.
This method can save water and reduce nitrogen loss through leaching.
See Shock and Welch, 2010, Surge Irrigation.
Use alternate-row irrigation; irrigate one side of a bed on one irrigation and the other row or side on the next.
This practice works well on crops that are less sensitive to moisture stress.
Another strategy is to irrigate only compacted rows; since water infiltrates wheeltraffic rows more slowly than soft rows, water is less likely to move below the root zone.
Compact the soft, non-traffic rows in furrowirrigated fields SO their infiltration rate is similar to that of the wheel-traffic rows.
Consider switching to sprinkler irrigation or drip irrigation.
Both allow you to manage water more efficiently and apply it to the depth needed.
Both often increase yields.
Some crops might have more disease problems under sprinklers because the foliage stays wet.
Also, there are increased power costs unless the water intake is high enough above the rest of your farm to allow you to set up a gravity flow system.
Drip irrigation can save a lot of water, in many cases 30 percent to more than half of the amount used for furrow irrigation.
A drip irrigation system is costly to set up, but is practical for onions and promising for seed alfalfa.
See Shock, revised 2013a, Drip Irrigation: an Introduction; Shock, et al., revised 2013c, Drip Irrigation Guide for Onion Growers, and Shock, et al., revised 2013e, Drip Irrigation Guide for Potatoes.
Maintain and update sprinkler and drip irrigation systems
 The Malheur Experiment Station is investigating ways to leave the tape in the ground through several cropping cycles.
Sustainable Agriculture Techniques series
 Funding to help prepare this publication was provided by an Oregon Watershed Enhancement Board grant.
For winter wheat in the boot/heading crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 1.30 inches and the estimated water use during the week of June 19-25, 2023 is 1.50 inches.
For winter wheat in the soft dough crop growth stage the estimated water use during the previous week of June 12-18, 2023 is 1.18 inches.
OVERHEAD IRRIGATION OF VEGETABLES
 Irrigation is a critical management tool for producing high yielding and high quality vegetable crops.
Scheduling irrigation for different vegetables grown under center pivot, travelling gun, or solid set overhead systems involves knowledge of the soil water holding capacity, the effective rooting depth of the crop , how efficiently water is being delivered , how much water is being used by the crop  and how much water is being lost from the soil and wetted surfaces directly.
The combination of transpiration and evaporation losses is termed evapotranspiration.
To schedule irrigation, the goal is to replace water lost through evapotranspiration without excessive runoff or excessive loss through percolation out of the root zone.
Another factor to consider is the permissible water depletion; how much will you allow the soil to dry down between irrigations.
For most crops we set this at 50% of the water holding capacity of the soil.
However, for some shallow rooted crops you may want to keep that value lower.
By knowing how much water is being lost and how much is left in the soil, you can determine when to irrigate and how much to irrigate.
In classic work done by the University of Delaware Agriculture Engineering Department in the 1970s and 1980s, water use estimates were developed for a number of vegetable crops.
These values remain useful guides for irrigating these crops.
A summary follows:
 Sweet Corn: Water use 40 days after planting was 0.10 inches per day, water use 60 days after planting was 0.23 inches per day and water use at peak  was 0.26 inches per day.
Potatoes: Water use 40 days after planting was 0.15 inches per day, water use 60 days after planting was 0.27 inches per day and water use at peak  was 0.37 inches per day.
Peas: Water use 40 days after planting was 0.16 inches per day and water use 60 days after planting was 0.33 inches per day.
Lima Beans: Water use 20 days after planting was 0.13 inches per day, water use 40 days after planting was 0.25 inches per day, water use 60 days after planting  was 0.33 inches per day and water use 80 days after planting was 0.23 inches per day.
Cucumbers: Water use 20 days after planting was 0.13 inches per day, water use 40 days after planting was 0.27 inches per day, and water use at peak  was 0.30 inches per day.
Watermelons: Water use 20 days after planting was 0.10 inches per day, water use 40 days after planting was 0.23 inches per day, water use 60 days after planting  was 0.30 inches per day, water use 80 days after planting was 0.28 inches per day and water use 100 days after planting was 0.22 inches per day.
Tomatoes: Water use 20 days after planting was 0.15 inches per day, water use 40 days after planting was 0.27 inches per day, water use 60 days after planting  was 0.33 inches per day, water use 80 days after planting was 0.28 inches per day and water use 100 days after planting was 0.25 inches per day.
In future articles information on irrigation scheduling aids , soil moisture sensors, and irrigation scheduling under plastic mulch will be presented.
The use of dry grass mulch in cotton furrows substantially increased irrigation efficiency in recent tests at the U.
S.
Cotton Field Station, Shafter.
The millet and sudangrass used in these tests was seeded in 8-inch bands down the furrows and then desiccated by oil-spraying when growth reached 10 to 18 inches high.
Time required for irrigation water to flow down the furrows was nearly doubled by the sudangrass mulch.
Infiltration rates were substantially increased by the grass mulches and a greater soil water content, following irrigation, was obtained.
While cotton seed yields showed no significant differences in these tests, data indicated that both crop uniformity and yield improvements could result from use of grass mulches on soils with low infiltration rates.
H.
YAMADA JOHN MILLER JOHN STOCKTON
 Desiccated Grass Mulch Irrigation Efficiency for
 T HIS STUDY on the use of a desiccated grass mulch in furrows for improving efficiency of irrigation for cotton was conducted at the U.
S.
Cotton Field Station, Shafter, California, in 1959.
Water infiltration rates drop to low values following layby  on the cotton soils used for this investigation.
This coincides with the period of maximum water use by the cotton crop.
Surface roughness of furrow bottoms is considered to be an important factor in determining infiltration rates.
Increasing surface roughness delays the rate of advance and may increase the wetted perimeter in the furrow.
The increased time and wetted surface increased the total water penetrating into the soil, as well as the measured rate of infiltration.
Alternate solutions to the problem involve reducing the rate of application or using tailwater systems and increasing the time per irrigation.
These approaches, however, do not increase the infiltration rate.
The desiccated grass mulch was investigated as a method of increasing surface roughness in irrigation furrows and improving irrigation efficiency.
Cotton was planted on high beds to facilitate early development of the furrow profile needed for irrigation.
After the second cultivation in mid-June, when the cotton was 4 to 6 inches high, German millet and Piper sudangrass were planted at rates of 64 and 82 pounds per acre, respectively, in 8-inch bands in the furrows.
A grass-free treatment was included in the experiment.
All treatments, including the grass-free check, were given a
 light irrigation for germination of the grass seed.
No cultivations were made after the grass was planted.
The grass was allowed to grow until the sudan was 15 to 18 inches tall and the millet was 10 to 12 inches tall.
The grass was then killed with an oil spray.
Shields were used to protect the cotton.
Within a few days after oiling, a dense mat of desiccated grass, still rooted to the furrow bottom, formed a mulch for reducing the rate of advance of irrigation water.
The rate of advance of water after the mulches were established was measured at each irrigation.
The time required for the irrigation stream to reach the lower end of the field was nearly doubled by the sudan and significantly increased by the millet, as shown in the graph.
Decreasing the rate of advance of water during post layby irrigations can be helpful in improving irrigation efficiency on soils with low infiltration rates or on excessive slopes.
Sudan, before oiling, grown in irrigation furrows between cotton rows.
The infiltration rate of irrigation water in these furrows was determined by measuring the rates of intake and runoff for individual furrows.
The difference between these two measurements, reported as inches per hour, represents the rate that water enters soil during the irrigation.
Infiltration measurements were made four times during the season and average values are reported in the table.
The infiltration rates for the mulched treatments were significantly greater than
 for the grass-free treatment.
The mulches probably increased the wetted perimeter in the furrow-which would increase the infiltration rate of irrigation water.
The water content of the soil profile immediately after irrigation is a reflection of the infiltration rate.
Soil water was measured to a depth of four feet by collecting soil samples after each of three irrigations.
The data in the table are means for the three dates of sampling.
The greater soil water content for the sudan and millet plots is an indication of an improvement in irrigation efficiency and would permit a longer interval between irrigations.
Sudan appeared to be more effective than millet in improving irrigation efficiency.
The improved efficiency is probably due to the better growth of sudan.
The sudan was 5 to 6 inches taller than the millet at the time the grasses were
 INFLUENCE OF DESICCATED GRASS MULCHES ON INFILTRATION RATE OF IRRIGATION WATER, SOIL WATER CONTENT, AND COTTON YIELDS
 Mulch	Infiltr.
rate	Soil water	content	Seed cotton	yield
 treatment			
 Grass-free check	0.170	6.96	2480
 German millet	0.230	7.83	2420
 Piper sudan	0.303	8.23	2250
 LSD	.05	0.031	0.95	N.S.
.01	0.047	N.S.
N.S.
Millet, before oiling, grown in irrigation furrows between cotton rows.
Rate of advance of water in irrigation furrows with 7.6 gpm as influenced by desiccated grass mulches.
killed, as indicated in the photos.
The greater growth of sudan resulted in a more dense mat of dead grass that was more effective in slowing the rate of advance of water.
The yield of seed cotton on September 22, as reported in the table, shows no significant difference in production.
This lack of a yield increase from the mulch treatments compared with no mulching may be due to the nearly adequate irrigation efficiency for the grass-free check or to the competitive effects of the grass.
Improved cotton yields and crop uniformity could result from the use of mulches on soils with low infiltration rates of irrigation water.
Progress Reports of Agricultural Research, published monthly by the University of California Division of Agricultural Sciences.
William W.
Paul Manager Agricultural Publications Jerry Lester Editor California Agriculture
 Articles published herein may be republished or reprinted provided no advertisement for a commercial product is implied or imprinted.
Please credit: University of California Division of Agricultural Sciences.
California Agriculture will be sent free upon request addressed to: Editor.
California Agriculture, 207 University Hall, 2200 University Avenue, Berkeley 4, California.
To simplify the information in California Agriculture it is sometimes necessary to use trade names of products or equipment.
No endorsement of named products is intended nor is criticism implied of similar products which are not mentioned.
Another factor besides knowing how much water the crops will use between now and maturity is determining the amount of water stored in the soil.
A fine sand soil, for example, holds about one inch per foot of soil or four inches on the top four feet of soil.
A silt loam soil, on the other hand, holds two inches per foot of soil or eight inches on the top four feet of soil.
Assuming both soils are at field capacity, the maximum amount of water that can be used is 2.4 inches  for the fine sand soil and 4.8 inches  for the silt loam soil.
MONSANTO TECHNOLOGY PIPELINE FOR CENTRAL PLAINS CONFERENCE
 While corn is widely grown in the United States, from the central Corn Belt to the Western Great Plains, its yield potential is directly related to the amount of available water.
From 1984 to 1992, according to the USDA, 67 percent of major crop losses were due to drought.
Roughly 85 percent of corn grown in the U.S.
suffers from varying degrees of drought during the growing season.
About 6,800 gallons of water are required to grow a day's food for a family of four.
Water availability is already a major issue in several parts of the world and becoming a growing problem in others.
Now, more than ever before, it is critical that farmers have a tool to combat the impact of water shortage on their crops.
In 2003, Monsanto successfully completed its first tests that demonstrated that some of the genes in its discovery program could enhance the drought tolerance of corn hybrids.
These observations of enhanced yield and plant health were confirmed with greater precision in 2004 thru 2007.
During 2008 field trials in the Western Great Plains, drought-tolerant corn showed a six to 10 percent yield enhancement a gain of 7-10 bushels on an average of 70-130 bushels per acre.
In December 2008, the company made the first regulatory submission to the Food and Drug Administration for droughttolerant corn the first-ever biotech crop with that trait.
Further submissions to the USDA and to other importing countries will be made in the coming months.
The crop is now in Phase 4 of the R&D pipeline, the last phase before commercialization.
This phase includes development and testing of the best trait and germplasm combinations for commercial launch.
In general, the drought-tolerance gene works by mitigating the impact of low soilmoisture content on the plant's physiology.
In response to inadequate water, corn plants typically begin to shut down their metabolism, slowing photosynthesis and growth-rate.
The gene we have submitted for regulatory approval enables the corn plant to maintain metabolism for a longer period of time during drought stress.
Ongoing testing has shown that the crop experiences no negative impact in conditions of adequate moisture.
Beyond the Great Plains, Monsanto's drought-tolerant technology is expected to also help improve on-farm productivity in other parts of the world like Africa where rainfall is insufficient or irregular.
Monsanto's drought-tolerant technology shows promise to give corn crops worldwide a better opportunity to achieve their yield potential.
In addition to drought tolerance, Monsanto also has other corn technologies in its pipeline.
SmartStax contains multiple modes of action, for insect-resistance management against above and below ground insects, and offers the company's most comprehensive weed-control system.
The company expects a 2010 commercial launch for SmartStax pending regulatory approval.
These technologies as well as others in our pipeline or already on the market reflect Monsanto's commitment to help farmers boost on-farm productivity through established and new advancements in plant breeding and biotechnology.
The company's investment in breeding and biotechnology research is key to meeting these commitments with more than $2.6 million per day spent on leading agricultural research.
In June 2008, Monsanto announced an ambitious plan to double yields in its three core crops corn, cotton and soybeans by 2030 compared to a base year of 2000 as part of a three-point pledge called the Sustainable Yield Initiative.
The company also committed to conserving more of the world's precious natural resources by reducing by a third, the aggregate amount of key inputs such as water, land and energy, required to produce each unit.
Monsanto plans to do this by providing choices for modern agricultural technology to its stakeholders and has also committed to helping resource-poor farm families.
The Lake Conway-Point Remove Watershed is located in central Arkansas and includes communities in Conway, Faulkner, Perry, Pope, Pulaski, Van Buren and Yell counties.
A "watershed" is an area of land where all of the water that drains from it goes to the same place, SO rainwater or snowmelt in this watershed eventually drains to a common location.
The Lake Conway-Point Remove Watershed is actually two separate watersheds that are considered as one set by the U.S.
Geological Survey.
The conjoined watershed spans 1,144 square miles and is mostly forested or used for pastureland.
Very little of the watershed is used for row crop farming.
1 The population is increasing at an accelerated rate, with Faulkner County growing 31.6 percent over the last 10 years.
2 More than 88,000 people lived here as of 2011.3
 Nonpoint Source Pollution in the Lake ConwayPoint Remove Watershed
 Water pollution that comes from multiple sources spread over an area, such as runoff from parking lots, agricultural fields, residential lawns, home gardens, construction, mining and logging, is known as nonpoint source pollution.
As runoff moves across the landscape, it carries natural and manmade substances that can accumulate in waterways and make them uninhabitable for aquatic species or unusable by people.
Potential pollutants include bacteria, nutrients, sediment, hazardous substances and trash.
4 Given the number of potential sources and variation in their potential contributions, these pollutants are not easily traced back to their source.
Lake Conway Point Remove Watershed Data source: GeoStor.
Map created March 2011.
Major streams: Arkansas River, Beardy Branch, Brock Creek, Clear Creek, Galla Creek, Gum Log Creek, Harris Creek, Hill Creek, Isabell Creek, Overcup Creek, Palarm Creek, Point Remove Creek, Rocky Cypress Creek, Stone Dam Creek, Tupelo Bayou, White Oak Creek
 This fact sheet is intended to provide a better understanding of the Lake Conway-Point Remove Watershed and its place on the state's priority list of 10 watersheds impacted by nonpoint source pollution.
Lake Conway-Point Remove Watershed Water Quality Issues
 Through water quality monitoring, environmental officials in Arkansas have determined that the primary nonpoint source pollution concerns for this watershed are turbidity, silt and total dissolved solids.
Turbidity is a measure of the clarity of water.
High turbidity levels mean the water is murky from a variety of materials, such as soil particles, algae, microbes and other substances.
White Oak Creek and Stone Dam Creek have experienced high turbidity and silt issues, and unknown sources have contributed sediment to White Oak Creek, according to the Arkansas Department of Environmental Quality.
In 2006, environmental officials in Arkansas determined the maximum amount of turbidity White Oak Creek can receive and still meet water quality standards.
This determination is a calculation called Total Maximum Daily Load, or TMDL 5,6
 These concerns and the watershed's rapid urbanization led to the Lake Conway-Point Remove Watershed being designated as a priority by ANRC in the state's 2011-2016 Nonpoint Source Pollution Management Plan.
7
 Arkansas' Priority Watershed List for Nonpoint Source Pollution
 Arkansas has used a watershed-based approach to nonpoint source pollution management, allowing the public to guide planning to address water quality concerns.
The Arkansas Natural Resources Commission, or ANRC, administers the Nonpoint Source Pollution Management Program.
The program exists to reduce water pollution through the funding of watershed planning and restoration activities, adoption of voluntary best management practices and the development of technologies that assist in water pollution reduction in Arkansas.
Based on public input and the use of a qualitative risk assessment matrix, ANRC has designated 10 priority watersheds as needing the greatest attention.
The current risk matrix9 identifies the following priority watersheds for 2011-2016: Bayou Bartholomew, Beaver Reservoir, Cache River, Illinois River, L'Anguille River, Lake Conway-Point Remove, Lower OuachitaSmackover, Poteau River, Strawberry River and Upper Saline.
To encourage continued public input, the University of Arkansas Division of Agriculture's Public Policy Center facilitated a water quality stakeholder forum for the Lake Conway-Point Remove watershed in August 2015.
Participants identified water quality issues such as sedimentation, regulations and erosion as local priorities that need addressing.
A group of stakeholders has worked with the University of Arkansas since 2013 to develop a Lake Conway-Point Remove Watershed plan to address nonpoint source pollution.
A draft plan has been reviewed by the Environmental Protection Agency.
Stakeholders are in the process of addressing EPA recommendations for finalizing the plan.
People who live, work or recreate in the Lake Conway-Point Remove Watershed are encouraged to consider these community priorities and the watershed plan when addressing water pollution.
The public is also welcome to attend an annual stakeholder meeting where priority watersheds and nonpoint source pollution are discussed.
For more information about nonpoint source pollution and its impact on the Lake Conway-Point Remove watershed, contact the Cooperative Extension Service, Arkansas Natural Resources Commission or the Arkansas Department of Environmental Quality.
The Arkansas Watershed Steward Handbook is also a good source of information about basic water quality concerns and how the public can get engaged in addressing water pollution.
10
 This fact sheet is one in a series of 10 fact sheets on nonpoint source pollution in priority watersheds.
The University of Arkansas Division of Agriculture's Public Policy Center provides timely, credible, unbiased research, analyses and education on current and emerging public issues.
Printed by University of Arkansas Cooperative Extension Service Printing Services.
The Arkansas Cooperative Extension Service offers its programs to all eligible persons regardless of race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
New in Nebraska this year, the competition offerings will include a sprinkler irrigated popcorn competition, in addition to the sprinkler corn, Subsurface Drip Irrigated  corn and sorghum competitions that have been hosted previously.
The Basics of Soybean Irrigation in Tennessee
 Brian Leib, Associate Professor, Irrigation Systems and Management Tim Grant, Extension Assistant, Soil and Water Resources Department of Biosystems Engineering and Soil Science
 Angela McClure, Professor and Extension Specialist, Corn and Soybean Avat Shekoofa, Assistant Professor, Crop Physiology Water Stress and Irrigation Department of Plant Sciences
 Financial support from the Tennessee Soybean Promotion Board, the Southern Soybean Research Project and USDA NRCS Conservation Innovation Grant
 1.
The four essential factors for making effective irrigation decisions in soybean are growth stage, water-use rate, soil type and rainfall pattern.
2.
On silt loam soils, in most years consider irrigating soybeans at first pod  and full pod  when water use first peaks.
Monitor soil water status during first seed , as this is one of the most sensitive growth stages for drought stress in soybean.
3.
In high rainfall years, yield reduction in soybean has been observed in silt loam and poorly drained soil when irrigation was added during late vegetative and early reproductive stages.
4.
In sandy soils, soybeans are more likely to require irrigation in late vegetative and early reproductive stages  with the later reproductive stages  being even more critical for providing adequate soil moisture.
5.
Since variable rainfall can create soil conditions too wet or too dry for optimal soybean yield, a managed depletion irrigation  approach is recommended.
MDI prescribes a significant withdrawal of soil water before initiating irrigation to create storage capacity for capturing rainfall that alleviates crop stress from water logging while maintaining a buffer of easily available soil water to prevent drought stress.
6.
Once the MDI level is reached, water should be applied at a rate equal to crop-water use from rainfall and supplemental irrigation.
7.
Center pivot application amounts should be set as high as possible without creating significant run-off: 0.3 to 0.5 inches per revolution on sloping fields and 0.5 to 0.8 inches per revolution on flatter river bottoms.
8.
Soybean irrigation should be terminated by early to middle full seed.
Adequate soil moisture and/or rainfall can allow termination before R6.5.
Slight but consistent yield loss has been observed when irrigating up to beginning maturity.
9.
MDI can be implemented by a water balance method that keeps track of both the water added to the soil by rainfall and irrigation as well the amount used and removed by the crop.
10.
MDI also can be implemented by soil sensor methods that are a direct measurement of soil water status at a specific locations and depths.
Soybean irrigation recommendations for Tennessee are based on more than five years of AgResearch and Education Center trials and farm demonstration sites.
A more detailed understanding of these recommendations is provided in the remainder of the publication.
Water Use, Soil Type, Rainfall and Irrigation Approach 1
 Figure 1: Historic average weekly crop-water use of soybean shown as a solid red line.
Crop-water use of any given time period can vary from this line by up to 15 percent, as the weather conditions vary from normal.
Soybean water use varies by growth stage and weather conditions.
The rate of water use is an important factor for deciding when and how much to irrigate.
As shown in Figure 1, water use is 0.5 inches per week during most of the vegetative growth stages, increasing to almost 1.0 inch per week by first flower.
From first flower  to first pod , water use increases rapidly from 1.0 to 1.5 inches per week.
Thereafter, water-use averages almost 1.5 inches per week through first seed  to full seed.
Note that these are historic averages, and a sunny, hot week could require up to 15 percent more water while a cloudy, cool week could require up to 15 percent less water.
2
 Soil type is also an important consideration when making irrigation decisions.
A soil profile that is deep silt loam could contain 3 inches of readily available water in a soybean root zone when it is at
 field capacity.
However, a soil profile that is sandy throughout may only contain around 1.0 inches of readily available water when it is at field capacity.
If a deep silt loam and a sandy soil are refilled to field capacity by a large rain event after pod formation , how long would it be before we would need to irrigate each soil?
Since water use is averaging 1.5 inches per week at this point, we can expect the sandy soil to need water in five days.
On the other hand, the deep silt loam soil can provide enough readily available water to supply that crop for two weeks before the crop starts losing yield potential.
The differing abilities of soils to hold water can have implications on irrigation management across fields and even within the same field.
3
 Adjusting to rainfall in combination with cropgrowth stage and soil type is the key to good irrigation management in soybean.
Yet, this can be complex since rain is extremely variable in a humid region like Tennessee.
To illustrate the impact of highly variable rainfall patterns, consider this question that is faced by Tennessee irrigators: What is coming next a four-week drought, a 4 inch rain, or something in between?
If we knew a four-week drought was coming, we would irrigate frequently to keep soil moisture close to field capacity to avoid stress and ensure high yield.
If we knew a 4-inch rain
 was coming, we would let the soil dry out in order to utilize that rainfall and avoid overly wet conditions that could harm yield.
Since we do not know what weather is on the horizon with a high degree of accuracy, we need to allow soil moisture to deplete to a reasonable level that will facilitate the capture and use of rainfall yet not lose yield potential.
Since center pivots are usually designed to "keepup" with crop-water use during peak demand periods with no rain, and cannot "catch up" and return the profile to field capacity once significant depletion has occurred, these systems are best managed by maintaining a desired level of soil water depletion.
A guiding principle of our irrigation approach is to allow a significant but safe soil water depletion to develop according to soil type and crop-growth stage, and then use center pivot irrigation to maintain a "managed depletion" of soil water that facilitates rainfall capture while preserving some readily available water to prevent crop stress.
We are calling this approach managed depletion irrigation or MDI.
Tennessee-based research has verified the importance of irrigating during seed fill  as consistent yield responses have been noted in silt loam soils  even in wet years.
In higher than average rainfall years, 1 to 2 inches of irrigation during R5 where able increase
 yield by 10 percent to 25 percent in silt loam soil.
Soybean irrigation will be necessary before R5 and in higher amounts during drier years and in sandier soils with lower water holding capacity.
However yield loss has occurred from irrigating during vegetative growth stages and early reproductive stages in silt loam soil during some wet years.
Over-irrigation, either too early or too much, can certainly lead to yield loss in poorly drained soils.
In most years on silt loam soils, we would recommend beginning to consider irrigation in R3 and R4 when water use first peaks, and especially monitor soil water status during R5.
Irrigation will be needed at earlier growth
 stages in lower water holding soils and we have just initiated soybean irrigation trials in sandier soil to provided better recommendations on when to initiate irrigation under these conditions.
4
 We have discussed the impact of soil textural differences on irrigation initiation, but much of our soybean acres are grown on rolling loess hills where the texture is consistently silt loam.
In this case, we expect topography to be the primary driver of irrigation decisions with side slopes requiring earlier irrigation than hilltops and low lying areas due to soil erosion limiting the rooting depth on the side slopes.
However, from 2013 to 2017 in several fields across West Tennessee, this pattern has not appeared, and, in fact, the opposite has most often been true with higher soil moisture measured on the sloping ground due to the fragipan impeding drainage of water in wetter years.
Yield maps tell us that in a dry year, sloping ground can certainly become water-limited, and in those years the sloping ground could benefit from either earlier irrigation or more irrigation.
In wet years, though, there does not appear to be much merit to irrigating sloping grounds differently than level ground on the loess hills of Tennessee.
5
 Another important part of irrigation decisions is how much water to apply and rates of 1.5, 1.0 and 0.5 inches per week were tested as a combination of rain plus irrigation.
In silt loam soils with higher than average rainfall, soybean yield was sometimes optimized with supplemental irrigation lower than the 1.5 inches per week rate during seed fill  while it should be noted the 1.5 inch per week rated did not diminish yield when irrigation was delayed allowing for a significant but safe depletion of soil water.
In drier years and sandier soils, the supplemental irrigation plus rainfall rate of 1.5 inch per week will most likely be required before R5, perhaps requiring water at an R1 or a vegetative growth stage.
Therefore, we recommend allowing
 soil to dry to the desired "managed depletion" level and then providing water input equal to crop-water use through rainfall and supplemental irrigation in order to maintain soil moisture near the "managed depletion" level.
4
 There are also some practical considerations concerning the amount of water applied per irrigation.
Most center pivots are designed to be capable of applying 0.3 inches over 24 hours, meaning you potentially could apply just over 2 inches in a week.
In flat river bottom ground, where many of our sandy soils are found, it is appropriate to apply higher amounts like 0.5 to 0.8 inches per revolution where runoff is not a substantial concern.
However, on sloping fields or fields where infiltration is an issue, limiting irrigation to 0.3 to 0.5 inches per revolution will lead to a more effective irrigation application.
We recommend setting pivot application amounts as high as possible without creating significant runoff.
6
 Soybean irrigation should be terminated in early to mid R6.
Beans are still filling later developing pods and finalizing seed weight during the early part of R6, therefore irrigation could add to dry weight at harvest if soil moisture or rainfall is insufficient.
Irrigating past this point could put unnecessary moisture
 on plants and could lead to wetter soils and harvest issues.
Tennessee trials have shown a slight, yet consistent, yield decrease from irrigating all the way until R7 when pods have turned light green to yellow with some brown pods in the canopy.
4
 Variation in soils, maturity group differences, a wide range of planting dates and unpredictable rainfall make real-time irrigation decisions for soybean challenging.
Soil moisture sensors, a water balance or both methods together can be utilized to manage soybean irrigation.
The water balance method keeps track of both the water added to the soil by rainfall and irrigation as well the amount used and removed by the crop.
Table 1 presents MDI  target values depending on soil type and growth stage for a water balance.
Also shown is the Maximum Allowable Depletion  of 45 percent, beyond which point yield loss is likely.
These values are percentages of plant available water that has been removed from the soil profile such that field capacity is O percent depletion and permanent wilting is 100 percent.
Maintaining soil moisture around the MDI value creates storage space in the soil to capture rainfall while keeping a buffer of easily available soil water to prevent yield
 Irrigation Scheduling by Water Balance
 WATER IN Rainfall Irrigation High Water Table
 WATER OUT Crop Water Use Soil Evaporation Run-off & Drainage
 loss.
Water balance tools like the MOIST  spreadsheet can help you maintain soil-water in a reasonable depletion range, thus increasing the potential of obtaining optimum yield with minimum irrigation.
7
 A water balance approach can be very inexpensive  while soil moisture sensors require the purchase and installation of sensor equipment.
Soil moisture sensors are a direct measurement of soil water status at a specific location.
Matric potential sensors (Watermark from Irrometer
 and MPS-6/TEROS-21 from Meter Group) measure how difficult it will be for a plant to extract moisture from the soil while volumetric sensors  measure the percentage of water in bulk soil.
More detailed articles are available to describe the differences between sensor types and how to best use each sensor type.
8
 UT's recommendations are built around matric potential sensors because their readings are more transferable across soils than volumetric sensors, which require very different trigger points based on soil type compounded by the fact that not all types of volumetric sensors are calibrated the same.
Soil moisture sensors should be installed at more than one depth because the soil profile does not dry or rewet uniformly.
This means there will be multiple values to consider when making irrigation decisions.
A shallow sensor or sensors are needed to detect rainfall and irrigation events while deeper sensors reveal whether water is being used throughout the entire root zone.
While soybean needs adequate soil moisture somewhere in the root zone, it does not necessarily need easily available water throughout the soil profile.
Soil at some sensor depths should be allowed to dry significantly in an MDI approach as long as water is easily available to the crop at other points in the root zone.
Table 2 presents the MDI target values for matric potential sensors.
The MPS-6/Terros-21 values have been incorporated into the MOIST+ APP.
9
 Maximum Allowable Depletion of 45%
 Late Veg  to Begin Seed 	30	35
 Begin Seed  to Full Seed 	20	25
 Table 1: Maximum allowable depletion and managed depletion irrigation  Levels.
The MDI Target Value is not the only soil water depletion target level that can result in optimum yield.
It is recommended as a means to balance the effect of unpredictable rainfall patterns by leaving enough water in the soil to prevent drying below the maximum allowable depletion  and over wetting the soil from excess rainfall; both conditions can lead to yield loss.
Watermark  Easily Available Soil Water Range
 Late Veg  to Begin Seed 	8 to 55	8 to 100
 Begin Seed  to Full Seed 	8 to 40	8 to 60
 MPS-6/TEROS-21  Easily Available Soil Water Range
 Late Veg  to Begin Seed 	11 to 70	11 to 150
 Begin Seed  to Full Seed 	11 to 40	11 to 70
 Table 2: Guideline matric potential values for Watermark and MPS-2 sensors in soybean to maintain a managed depletion irrigation  strategy by growth stage and soil type.
1.
Saturated conditions occur at values less than the range minimums.
2.
Easily available water is not required or recommended in the entire soil profile.
Only one sensor needs to be within the recommended range.
3.
Yield loss may occur if all parts of the crop root zone are greater than the range maximums.
UT Extension provides several resources to assist producers in implementing soybean irrigation scheduling.
Additionally, several crop consultants in Tennessee are offering irrigation management as part of their services.
10
 1.
Irrigation Water Management A Simple Analogy.
2.
How Much Water Is Your Crop Using?
3.
How Soils Hold Water, a Home Experiment.
4.
Summary of Soybean Irrigation Studies in Tennessee.
5.
Determining Irrigation Management Zones for Center Pivots.
6.
What Is Your Center Pivots Application Rate?
7.
Using a Water Balance to Make Irrigation Decisions: MOIST spreadsheet.
8.
Using Soil Moisture Sensors for Irrigation Management in Tennessee.
9.
Automating and Combining Water Balance and Sensor Based Irrigation Scheduling: MOIST+ APP.
10.
List of Irrigation Consultants in Tennessee.
Arkansas Surface Water Irrigation
 Grant West Program Associate
 Isaac Engram Graduate Research Assistant
 Kent Kovacs Associate Professor
 Christopher Henry Associate Professor
 Arkansas Is Our Campus
 Arkansas is relatively rich in water resources with annual precipitation of 50 to 57 inches per year, which makes irrigation using surface water a plausible option for agricultural producers.
However, according to USDA 2013 Farm and Ranch Irrigation Survey, less than 15 percent of water applied to Arkansas crops comes from the surface.
Western states such as California and Idaho apply about 50 percent of irrigation water from the surface.
The purpose of this fact sheet is to provide background about the use of on-farm impounded surface water for irrigation.
Quantity and Source of Irrigation Water Applied by Region
 The Grand Prairie Region has the largest percentage of impounded water used for irrigation at over 27 percent.
The Arkansas River Valley has the highest percentage of irrigation water coming from natural surface water, at over 29 percent.
Over 82 percent of the irrigation water used in the Eastern Delta, the Cache Area and the Red River Area comes from natural groundwater.
Figure 1.
Percent of irrigation water applied by source.
Of all irrigation water applied from on-farm reservoirs, 45 percent is withdrawn from natural surface water and stored in a reservoir with a tailwater recovery system.
Two-thirds of on-farm storage reservoirs draw their water from an outside source.
A higher percentage of Arkansas producers use tailwater recovery than storage reservoirs.
Lonoke and Arkansas counties are where tailwater recovery is most common.
Over 80 percent of respondents from those counties use tailwater recovery.
The frequency of tailwater recovery and storage reservoirs tends to decrease the closer the farms are to the Mississippi River.
Figure 2.
Irrigation water applied from impounded water sources.
Figure 3.
Percentage of producers using impounded water sources by county.
On-Farm Use of Impounded Water Systems
 Corn has the highest percentage of irrigation water drawn from a reservoir at 54 out of 133 corn producers.
Cotton has the lowest percentage of irrigation water drawn from a reservoir at 8 out of 41 cotton producers.
Producers who grow soybeans, rice or corn have more storage reservoirs than producers who grow sorghum, peanuts or cotton.
Corn is the only commodity of the six surveyed for which the average producer has more than one storage reservoir.
Ricecorn and soybean growers are the most likely to use tailwater recovery systems on their farms.
This is probably because these crops are the most irrigation intensive.
Cotton producers are less likely to use tailwater recovery systems than the producers of any other crop.
Figure 4.
Producer use of on-farm storage reservoirs by crop grown.
Figure 5.
Average number of storage reservoirs per producer by crop grown.
Figure 6.
Producer use of tailwater recovery by crop grown.
Why Do Producers Use Impounded Water Systems?
Reducing irrigation costs is the most common reason for the use of reservoirs and tailwater recovery.
The expectation of future limitations in groundwater represents 25 percent of producers.
Other common reasons include water conservation, higher water quality and lower water salinity.
More than 50 percent of producers indicate that reservoir or tailwater recovery construction receive a federal cost-share.
Thirty-two percent of respondents paid for their construction with cash.
Only 7 percent obtained a loan to finance construction.
Figure 7.
Producer reasons for using impounded water sources.
Figure 8.
Financing for construction of impounded water systems.
Impounded surface water is the most common in the Grand Prairie region, and more than half store water drawn from the surface rather than recycled water alone.
Rice, soybean and corn producers are the most likely to use impounded water.
The cost of construction and loss of productive land are deterrents to the use of impounded water, but half of producers receive federal cost-share to alleviate this burden.
Table 2.
Crop water use for the remainder of the growing season for corn and soybean:
 For corn in the R4 dough stage of growth, it has an approximate days to maturity of 24 days and has 7.5 inches of water use to maturity.
For corn in the R4.7 beginning dent stage of growth, it has an approximate days to maturity of 24 days and has a 5 inches of water use to maturity.
For corn in the R5 1/4 milk line stage of growth, it has an approximate days to maturity of 19 days and has a 3.75 inches of water use to maturity.
For corn in the R5 1/2 milk line stage of growth, it has an approximate days to maturity of 13 days and has a 2.25 inches of water use to maturity.
For corn in the R5 3/4 milk line stage of growth, it has an approximate days to maturity of 7 days and has a 1.0 inches of water use to maturity.
For corn in the R6 Physiological maturity stage of growth, it has an approximate days to maturity of 0 days and has a 0.0 inches of water use to maturity.
Many irrigators apply more water than necessary toward the end of the irrigation season because the crop is using less water per day.
The crop is getting more mature and the days are getting shorter and cooler.
The average crop water use rate drops from around 2.1 inches per week at silking to only about 1.2 inches per week by the full dent stage.
This 40% reduction requires irrigators to adjust their thinking about how much water needs to be applied each week.
In warm-season grass pastures, an abundance of early weeds will remove moisture that could be used for grass growth later on and they remove valuable nutrients from the soil.
Early weeds also can develop so much growth that they can shade, smother and reduce early growth of your summer pasture grasses.
While early flash grazing of some pastures will not eliminate all the weeds, it can actually make for some pretty timely and valuable pasture.
Department of Plant Sciences
 IRRIGATION CALCULATIONS II: LEACHING FRACTION
 February 2023 Lauren Fessler, Extension Assistant, Department of Plant Sciences Amy Fulcher, Professor, Department of Plant Sciences
 Refining irrigation can help growers decrease water and nutrient inputs, increase crop quality and uniformity, and decrease environmental impacts.
This series covers calculations that nursery producers can use to assess and improve irrigation efficiency.
Leaching Fraction  is the ratio of the amount of water that leaches from a container compared to the total amount of water applied to that container.
LF can quickly give growers insight as to whether the duration of an irrigation event is appropriate.
A high LF can lead to nutrient runoff and indicates the crops may be receiving too much water.
A low LF can indicate that plants are not receiving enough water, which can cause salt build up, reduce growth or both.
For overhead sprinkler irrigation, the target LF is typically 10 to 15 percent, whereas for micro-irrigation it is higher, 25 to 30 percent.
Factors that can influence LF largely break down into two categories: 1) those that influence how much water enters the container and 2) those that influence how much and how quickly water in the
 Calculating LF using the weight method.
container drains.
These include the species' inherent water use, canopy architecture, irrigation method and duration, container size and shape, and substrate composition.
For instance, substrate components that are prone to becoming hydrophobic, such as pine bark, can form channels through which water quickly drains, increasing LF.
Leaching fraction can be measured by volume or by weight using this formula:
 Amount of leachate LF = X 100% Amount of irrigation applied
 Each method has pros and cons.
Measuring by weight requires an inexpensive kitchen scale, but saves time and accounts for the influence of capture factor.
More information on capture factor can be found in the third publication in this series.
Measuring by volume requires only catch cans and a measuring cup or, better, a graduated cylinder.
This method can be prone to error due to spillage and inability to account for the canopy's effect on irrigation that enters the container.
The weight-based method is considered superior because canopy effects can be significant and they are dynamic, for example, the effect changes after pruning.
Calculating LF by weight
 1.
Weigh the drainage cans.
2.
Nest five or more planted containers inside drainage cans and place throughout the irrigation zone.
a.
Ensure that the planted container fits snugly into the drainage can SO that irrigation cannot enter the drainage can.
3.
Weigh nested containers.
4.
Run a typical irrigation cycle.
5.
Record the irrigation run time.
6.
Allow planted containers to drain for one hour.
7.
Weigh the nested containers again.
8.
Determine total amount of irrigation applied.
a.
This is the post-irrigation nested container weight  minus the pre-irrigation nested container weight.
9.
Remove the planted container from the drainage cans.
10.
Weigh the drainage can with leachate.
11.
Find the amount of leachate.
a.
This is the weight of the drainage can with leachate  minus the empty drainage can.
12.
Divide the leachate weight  by the irrigation weight.
a.
Multiply by 100% to get leaching fraction.
13.
Calculate average leaching fraction.
a.
If the leaching fraction is greater than desired, irrigation run time should be shortened.
b.
If leaching fraction is less than desired, irrigation run time should be lengthened.
14.
Assess changes to run time.
Calculating LF by volume
 1.
Nest five or more planted containers inside drainage cans and place throughout the irrigation zone.
2.
Place five or more catch cans at canopy height throughout the irrigation zone, paired with drainage cans.
a.
Use container sizes and catch cans with the same diameter.
b.
Ensure that the planted container fits snugly into the drainage can SO that irrigation cannot enter the drainage can.
3.
Run a typical irrigation cycle and record the run time.
4.
Measure the volume of irrigation applied to each catch can.
a.
Do this immediately after irrigation ends to minimize errors due to evaporation.
5.
Allow planted containers to drain for one hour.
6.
Measure the volume of leachate collected in each drainage can.
7.
Divide leachate volume  by the corresponding irrigation volume..
a.
Multiply by 100% to get leaching fraction.
8.
Calculate average leaching fraction.
9.
Assess changes to run time.
a.
If the leaching fraction is greater than desired, irrigation run time should be shortened.
b.
If leaching fraction is less than desired, irrigation run time should be lengthened.
If you must use the volume method, use a graduated cylinder to improve your measurement accuracy, and thus your LF calculation, when measuring by volume.
In a test comparing the accuracy of graduated cylinders and measuring cups, the percent deviation from the true volume was nearly twice as great for the measuring cup!
The wide diameter of a measuring cup makes it difficult to accurately determine the water line.
Buy a graduated cylinder that holds at least as much water as your heaviest irrigation event and add a heavy circular fitting to the base to prevent tipping.
To measure the LF of #3 containers, 5gallon buckets were used as drainage cans.
The empty 5-gallon buckets were weighed before beginning.
One potted #3 container was nested in each 5-gallon bucket, ensuring there were no gaps through which irrigation could enter the drainage can.
Nested containers were then weighed.
Irrigation was operated for one hour and then containers drained for one hour.
Nested containers were then weighed again.
Planted containers were removed and the drainage cans with leachate were weighed.
Can	Empty	Nested	Nested	Drainage
 drainage	containe	container	can +
 can	r pre-	post-	leachate
 1	2 lbs.
25 lbs.
27 lbs.
2.75 lbs.
2	2 lbs.
27 lbs.
28.75 lbs.
2.7 lbs.
3	2.1 lbs.
23 lbs.
25.25 lbs.
3 lbs.
4	2.1 lbs.
24 lbs.
26 lbs.
2.95 lbs.
5	2.2 lbs.
21 lbs.
23 lbs.
3 lbs.
To calculate LF, first determine the total amount of irrigation applied:
 Total irrigation = Post irrigation weight Pre irrigation weight
 Can	Post-	Pre-	Total
 1	27 lbs.
25 lbs.
lbs.
2	28.75 lbs.
27 lbs.
1.75 lbs.
3	25.25 lbs.
23 lbs.
2.25 lbs.
4	26 lbs.
24 lbs.
2 lbs.
5	23 lbs.
21 lbs.
2 lbs.
Next find the amount of leachate:
 = Drainage can with leachate Empty can
 Can	Drainage can +	Empty	Leachate
 1	2.75 lbs.
2 lbs.
0.75 lbs.
2	2.7 lbs.
2 lbs.
0.7 lbs.
3	3 lbs.
2.1 lbs.
0.9 lbs.
4	2.95 lbs.
2.1 lbs.
0.85 lbs.
5	3 lbs.
2.2 lbs.
0.8 lbs.
Divide the leachate amount by the irrigation amount then multiply by 100% to get LF:
 LF = 100% Total irrigation
 Can	Leachate	Total	LF
 1	0.75 lbs.
2 lbs.
37.5%
 2	0.7 lbs.
1.75 lbs.
40.0%
 3	0.9 lbs.
2.25 lbs.
40.0%
 4	0.85 lbs.
2 lbs.
42.5%
 5	0.8 lbs.
2 lbs.
40.0%
 To find the average LF, sum the LFs for each can and divide by the number of cans :
 Can 1 LF + Can 2 LF + + Can LF Avg LF =
 37.5% + 40.0% + 40.0% + 42.5% + 40.0%
 In this example, the LF of 40% exceeds the target range SO the irrigation run time should be decreased.
To adjust irrigation run time based on LF, use the following formula:
 Desired run time 100% measured LF% X measured run time = 100% desired LF%
 100% 40% = X 60 minutes 100% 15%
 60% X 60 minutes = 42.4 minutes = 85%
 This new shortened run time of 42.4 minutes should yield a LF that is closer to the target of 15 percent; however, it is important to keep in mind that this applies to the specific plants used and at the specific growth stage and production conditions in which they were tested.
Something as simple as pruning the crop could have a dramatic influence on LF.
Because the factors that influence LF change throughout the season, it is important to assess LF at different points during the season.
Five catch cans were set up in an irrigation zone alongside five planted containers inside drainage cans.
The irrigation ran for 45 minutes.
The volume of water collected in catch cans was measured immediately when irrigation concluded.
Catch cans collected 2978mL, 3022mL, 2988mL, 3012mL and 3000mL.
After an hour, the volume of leachate collected in drainage cans was measured.
Leachate can be combined and measured at one time  to save time, however, this will not allow you to identify atypical plants that should be excluded from the calculation.
Drainage cans collected 434mL, 303mL, 446mL, 455mL and 461mL.
To calculate LF, first divide leachate  volume by irrigation  volume:
 434mL	303mL	446mL	455mL	461mL
 2978mL'	3022mL'	2988mL'	3012mL'	3000mL
 =	=	=	=	=
 0.146,	0.100,	0.149,	0.151,	0.154
 Multiply by 100% to get LF for each plant:
 0.146 X 100% = 14.6% 0.100 X 100% = 10.0% 0.149 X 100% = 14.9% 0.151 X 100% = 15.1% 0.154 X 100% = 15.4%
 Check for an outlier:
 10.0% is much less than 14.6%, the next lowest value.
Therefore, the second plant is considered an outlier.
Calculate the average LF, excluding the outlier:
 Plant 1 LF + Plant 2 LF + + Plant n LF Avg LF = n 14.6% + 14.9% + 15.1% + 15.4% = 4 ==60%==15% 60%
 An LF of 15 percent falls into the target range SO the current run time is sufficient.
1.
Using the information listed in the table below, practice calculating leaching fraction based on weight.
Irrigation run time = 85 minutes
 Empty drainage can	Pre-irrigation	Post-irrigation	Drainage can + leachate
 Can 1	2 lbs.
33 lbs.
38 lbs.
5 lbs.
Can 2	2.1 lbs.
36 lbs.
40.5 lbs.
4.35 lbs.
Can 3	2.1 lbs.
34 lbs.
39.5 lbs.
4.85 lbs.
Can 4	2.2 lbs.
37 lbs.
41 lbs.
3.8 lbs.
Can 5	2 lbs.
35 lbs.
39 lbs.
3 lbs.
A) Find total irrigation weight for each can 
 Can 1 Can 2 Can 3 Can 4 Can 5
 B) Find leachate weight for each can 
 Can 1 Can 2 Can 3 Can 4 Can 5
 C) Find LF for each can [ X 100%]
 Can 1 Can 2 Can 3 Can 4 Can 5
 D) Is there an obvious outlier that should be removed?
E) Find the average LF for the zone, excluding the outlier 
 F) Assuming a target LF of 15 percent, should the irrigation run time be increased or decreased?
G) Find the desired run time [  X 85 min]
 2.
Based on the values listed below, calculate leaching fraction based on volume.
Five catch cans and five drainage cans were used.
Irrigation was operated for 51 minutes during the collection period.
The following volumes were collected:
 A) Find LF for each plant [ X 100%]
 Plant 1 Plant 2 Plant 3 Plant 4 Plant 5
 B) Is there an obvious outlier that should be removed?
C) Find the average LF 
 D) Assuming a target LF of 15 percent, should the run time be increased or decreased?
E) Find the desired run time [  X 51 min]
 Plant 1	Plant 2	Plant 3	Plant 4	Plant 5
 Catch cans	5018mL	4973mL	4987mL	4992mL	5030mL
 Drainage cans	505mL	489mL	496mL	499mL	512mL
 Worksheets for on-site calculations
 Calculating LF by weight
 1.
Weigh drainage cans to be placed in the irrigation zone
 a.
Number of drainage cans
 b.
Empty drainage can weights
 2.
Nest plant containers inside drainage cans
 a.
Ensure drainage cans fit snugly around the plant container SO no irrigation can enter
 i.
5-gallon buckets are often used for #3 containers
 3.
Weigh nested containers
 a.
Nested container weights 
 4.
Run a normal irrigation cycle and record duration
 5.
Irrigation run time minutes
 6.
Allow plants to drain for 1 hour
 7.
Weigh nested containers again
 a.
Nested container weights 
 8.
Calculate the amount of irrigation water applied
 a.
Irrigation weight = post-irrigation nested container weight pre-irrigation nested container weight
 9.
Remove plant containers from drainage cans
 10.
Weigh drainage cans with leachate
 a.
Drainage can with leachate weights
 11.
Calculate the amount of leachate drained
 a.
Leachate weight = drainage can with leachate weight empty drainage can weight
 12.
Calculate individual LFs, note if there is an outlier
 a.
LF =  X 100%
 13.
Find average LF, omit outlier if present
 a.
Average LF = add all LFs number of drainage cans
 b.
Average LF = %
 14.
If average LF falls outside the target range , proceed to step 15
 15.
Calculate the desired run time based on the LF
 a.
Desired run time = [ ] X current run time
 b.
Desired run time = min
 Calculating LF by volume
 1.
Place at least five catch cans in the irrigation zone being evaluated
 a.
Number of catch cans
 2.
Nest several plant containers inside drainage cans of the same diameter and place within the irrigation zone
 a.
Ensure drainage cans fit snugly around the plant container SO no irrigation can enter
 i.
5-gallon buckets are often used for #3 containers
 b.
Number of drainage cans
 3.
Run a normal irrigation cycle and record duration
 a.
Irrigation run time minutes
 4.
Record the volume of irrigation from each catch can
 a.
Measure immediately to prevent errors due to evaporation
 5.
Allow plants to drain for 1 hour
 6.
Record the leachate volume from each drainage can
 7.
Calculate individual LFs, note if there is an outlier
 a.
LF =  X 100%
 8.
Find average LF, omit outlier if present
 a.
Average LF = add LFs number of drainage cans
 b.
Average LF = %
 9.
If the average LF falls outside the target range , proceed to step 10 10.
Calculate the desired run time based on the LF
 a.
Desired run time = [  ] X current run time
 b.
Desired run time = min
I think the WaterSmart Program might have the most applications for growers and for irrigation districts, and it would be the best route for a grower or a district to go for, said Rick Wilson, project manager of JEO Consulting Group.
IRRIGATION SCHEDULING USING KANSCHED FOR A RANGE OF WEATHER CONDITIONS
 Irrigation scheduling is a management practice to help irrigators determine when to irrigate and how much water to apply to meet crop water needs without waste of water.
The scheduling concept is most often associated with irrigation systems with high irrigation capacities, meaning that water related water stress is unlikely to occur.
Therefore, many irrigators discount the utility of irrigation scheduling because declining water levels have resulted in decreased well yield and therefore reduced irrigation capacity.
Irrigation capacity is the depth of water that the field would receive if entire field is watered in one day.
It can be calculated as follows:
 IC = GPM X 24 450 Acres
 for 24 hour/day pumping
 GPM = gallons/minute Acres = total irrigated acres in the field 450 gpm = 1 acre-inch/hour
 As a general guideline, an irrigation capacity of at least 0.25 in/day would be considered high capacity for systems irrigating fields with high water holding capacity soils, like silt loams.
Irrigated fields with sandy soils  need to have at least 0.30 inch/day to be considered high irrigation
 capacity.
Table 1 show the discharge rate requirement for various field sizes and efficiency values.
Figure 1 shows the probability of various system capacities of meeting crop water needs for western Kansas conditions.
This probability analysis also indicates lower capacity systems can meet full water needs of crops in some years, so irrigation scheduling could still benefit irrigators in determining when opportunities to save irrigation water occur.
Table 1.
System flow rate required for various acreage and system efficiency
 Irrigation	1 acre	125 acre
 Capacity	100% Eff	85% Eff	100% Eff	85% Eff
 0.25 in/day	4.7 gpm	5.5 gpm	585 gpm	690 gpm
 0.30 in/day	5.6 gpm	6.6 gpm	703 gpm	827 gpm
 Figure 1.
Effect of Irrigation Capacity on Irrigation System Reliability.
Corn, Colby Kansas Normal Probability, 1972-95 Full sized 126 acre sprinkler 
 To illustrate the use of ET-based irrigation scheduling, three years of ET and rainfall data were selected to use in KanSched and determine the irrigation schedule for two irrigation capacities.
The years selected were 2002, representing high ET and low rainfall conditions; 1998, representing average or typical ET and average seasonal rainfall conditions; and 1986, representing low ET and high rainfall conditions.
The data was collected at the
 NW Research and Extension Center, Colby, KS.
The ET and rainfall data were then mixed and matched to develop additional schedules to examine.
Materials and Installation of Delivery Pipes for Irrigation Systems
 Brian Boman and Sanjay Shukla
 Main considerations for the choice of materials in an irrigation system are the ability of the material to withstand mechanical stresses, extreme temperatures, solar radiation, and chemical contacts to which they may be subjected.
Mechanical stress may be due to internal conditions such as water pressure, water acidity and alkalinity, water hammer, and vacuum.
Components may also be affected by such external forces as earth load, thermal expansion and contraction, and mechanical blows to the component.
There are numerous combinations of metals, composites, plastics, ceramics, and elastomers that can be used in components for an irrigation system.
Not only should the materials be able to withstand the mechanical and environmental stresses that may occur, but they should be compatible with each other to avoid internal corrosion or galvanic effects.
The main considerations in component selection are pressure rating, temperature range, chemical affinity, and cost.
The design working pressure is the most important factor in selecting materials for the water distribution system.
Typically, pipelines and control devices should be able to withstand twice the normal operating pressure.
For instance, if the maximum normal operating pressure is 50 psi, all components should be able to withstand a surge of 100 psi.
The ambient and water temperatures should receive some consideration in the selection of construction materials.
High temperatures may decrease the strength of plastics.
In cases where components may be exposed to high temperatures , special high-temperature plastics or steel should be used instead of PVC.
In areas subject to freezing, consideration should be given to materials that will not fracture as easily as cast iron.
Ultraviolet  radiation is a common problem for applications exposed to sunlight.
UV radiation may cause degradation of most plastics; therefore, additives such as carbon black are used to inhibit this process.
Elastomers are normally less influenced by UV radiation, and metals are usually unaffected.
Chemical resistance is an important consideration since microirrigation systems are usually designed with the potential to inject different types of agricultural chemicals ranging from fertilizers to line cleaners.
Consequently, unpredictable combinations of often corrosive compounds may travel through the system.
Acidic  conditions will result in corrosion of most metals.
Aluminum and zinc are the metals most sensitive to acid.
Cast iron, carbon steel, and copper alloys are less sensitive, but for a prolonged exposure to acidic conditions, a resistant material such as 316 stainless steel should be considered.
High pH  conditions may be harmful to aluminum, zinc, and titanium.
Most other metals, as well as most plastics and elastomers, are not sensitive to alkaline conditions.
The effect of dissolved solids in water is to increase the electrical conductivity and acceleration of the corrosion processes.
Common cations such as calcium , potassium , and sodium  have almost no effect on most metals and plastics, while ammonium  may attack some plastics and elastomers.
Anions such as sulfides and sulfates are much more harmful to both metals and plastics.
Solid particles such as sand in the water stream can result in severe erosion of metal and plastic components.
Erosion of surfaces can also result from cavitation.
Cast iron, mild steel, and copper alloys can be coated by hard metals or ceramics to make them more resistant to cavitation.
Plastics and elastomers are more resilient and resistant to cavitation erosion; however, they are more susceptible to abrasion damage from high-velocity solids.
Cast iron pipe is generally used for the bodies of most water meters and valves larger than 3 inches.
Cast iron is also used for other large components that require economical pricing.
For higher pressure applications and severe working conditions, ductile cast iron, cast alloy, or other special metals may be used.
Cast iron normally has a very good resistance to corrosive conditions without any special protection.
Coating the bodies with protective paints such as epoxy resins is a common practice.
However, under normal operating conditions, unprotected cast iron parts normally do not corrode to the degree which impairs their performance.
When exposed to cathodic materials such as copper, cast iron components may develop corroded surfaces.
These corroded areas should be periodically removed to prevent impaired function.
Components constructed from steel plate normally have low corrosion resistance.
Therefore, these components must be specially coated or galvanized on both the inside and outside.
In spite of this protection, serious corrosion may occur to the component if there are copper or copper alloy parts in contact with the steel.
Periodic inspection and recoating are necessary to ensure long-term operation.
Particular attention should be given to weldings, as they are sensitive to corrosion.
Bodies of valves smaller than 2 inches and other small components are often constructed from cast bronze.
Cast bronze is also used for bodies of larger valves designed for high pressure and for various parts of valve and meter
 mechanisms.
Brass is used for machined parts such as shafts and spindles.
Brass inserts are used for bearings and threaded connections in cast iron bodies to reduce friction and avoid corrosion.
Special copper alloys are used for extremely corrosive and erosive conditions, They are also used for applications that have high velocity.
Cast aluminum is typically only used in components that are portable or where weight is a serious consideration.
There is a wide array of synthetic resins in the forms of polymers, copolymers, composites, laminates, and coatings.
Each of these materials may have different properties.
Plastic materials are less resistant to stress than metals and tend to lose strength under pressure and elevated temperatures.
They are used for smaller valves and as parts for many devices such as flowmeter impellers, low-friction bushings, and components not subjected to stress.
Bodies of smaller valves are typically made of glassreinforced polyester, polyacetal, and polycarbonate.
Small mechanisms may be made of an acetal resin such as Delrin.
Teflon linings may be used where low friction components are required.
Nylon, Teflon, and polyacrilate glass-fiber reinforced materials are often used for flexible small-diameter tubing and joints.
Filtering elements often use acetal, polycarbonate resins, thermoplastic polyester, or high density polyethylene.
For the protection of metal bodies and component against corrosion, plastic linings and epoxy resins are often used.
Valve vanes are often coated with nylon or Teflon to reduce friction.
Elastomer materials used for gaskets and seals must be able to withstand high stress together with both high and low temperatures.
Natural or synthetic rubber has proven to be the most suitable material for gaskets and seals in irrigation systems.
They give good performance for resilience, flexibility, and wear.
However, they are prone to degradation by microorganisms, especially when in long contact with wet soil.
Neoprene reinforced with nylon is generally suitable for flange gaskets.
When corrosive materials are present, other hydrocarbon acrylonitrile elastomers such as Buena N, Neoprene, Viton, or EPDM rubber should be used.
Polyvinyl chloride  pipe is the result of the chemical development of a synthetic base material and is manufactured under computer controlled conditions.
It
 is continuously extruded into seamless lengths which are strong, chemically resistant, have low friction loss, and are lightweight for ease of handling.
Type and grade refer to the hydrostatic design stress pressure capabilities of the pipe.
Type I, Grade I, is the most commonly used for microirrigation systems.
There are both Types I and II and Grades I and II available.
Pressure ratings may be given in feet of head, class or psi rating, schedule, or SDR.
PVC pipe may be designated as either low head , which is rated for less than 50 ft of head , or high head which is rated for more than 50 ft of head.
Class refers to a pressure rating in pounds per square inch.
SDR is the ratio of the outside pipe diameter to the wall thickness.
The operating pressure in use, including surges, must not exceed the class rating.
Schedule denotes a plastic pipe which has the same outside diameter and wall thickness as iron or steel pipe of the same nominal size.
There are pressure rating differences between Types I and II and Grades I and II.
This information should be stamped on the pipe.
Temperature is also important when using PVC since as the temperature increases, the safe operating pressure decreases.
To obtain the pressure rating, multiply the pressure rating at 73F by the corresponding service factor.
Either an IPS or PIP size may be used.
IPS refers to plastic pipe which has the same outside diameter as iron pipe of the same nominal size.
PIP is an industry size designation for plastic irrigation pipe.
When obtaining cost estimates, be sure that all estimates are in the same size designation.
Normally, pipe size should be large enough SO that the water velocity does not exceed 5 feet per second in order to avoid excessive friction losses and surge or water hammer problems.
Pipe sections are available in 20-foot, 30-foot, 35-foot, and 40-foot lengths.
Pipes are available in diameters of 4 15 inches for low head pipe and 1/2 12 inches for high head pipe.
Most PVC pipe and fittings used in the irrigation industry are manufactured from Type I, Grade I PVC compounds.
These compounds have a minimum tensile strength of 7,000 psi before stress, and a modulus of elasticity 400,000 psi at 73F.
Even after years of service, PVC pipe normally maintains its ability to withstand occasional high pressure surges.
However, if PVC pipe is subjected to frequent pressure variations of a cyclic nature, it can fail, even though the peak pressure never exceeded the design pressure of the pipe.
The number of cycles before failure depends on the
 magnitude of the pressure variation.
Usually, the ability of PVC pipe to withstand cyclic pressure conditions is independent of its ability to withstand constant static pressure.
Burst failure in PVC pipe and fittings is usually rather dramatic.
It may begin at a point of stress concentration or weakness and continue by splitting through fittings and pipe for some distance.
Sometimes, the failures will completely shatter a fitting and the adjacent pipe.
Burst failures usually occur during transient hydraulic conditions that create large pressure variations in the system.
These include rapid valve closure, pumps starting or stopping, rapid escape of entrapped air, or an air pocket shifting within a pipeline.
Burst failure will, sometimes, occur in a pipe or fitting that was damaged during installation or that is subject to external loads.
In these cases the failure may occur at pressures well below the expected burst limit of the product.
Figure 1.
Typical burst failure in PVC pipe.
Long-term pressure failure  occurs when the system operates continually at a pressure higher than the pipe rating.
The failures can occur within a short time after system installation or after many years.
The failures will usually appear as slits or small cracks in the pipe or fitting along the minimum wall thickness or in an area of stress concentration.
Some yielding of material will usually be evident.
Cyclic surge failure  can occur in systems that are subject to frequent changes in flow and/or pressure.
It is difficult to distinguish between cyclic failure and long term static failure in fittings.
Due to the stress concentrations and
 extra forces placed on them, the pipes may not withstand as many cycles even if their burst strength may be equal to that of the same class pipe.
There may also be a marked reduction in burst strength after subjection to a period of cyclic pressure appears to be the most critical since fittings are the weakest system components.
when using some thread lubricants, dopes, or sealants.
The failure usually appears as a split, perpendicular to the threads, beginning at the leading edge and extending into the body of the fitting.
Occasionally, a split at the base of the female threads will appear parallel to the thread direction.
This will usually occur in a fitting with a shoulder or thickened place near the base of the threads and is more common when the male part bottoms against a shoulder.
Figure 2.
Example of long-term pressure failure in PVC pipe.
Figure 3.
Example of typical cyclic pressure failure in PVC pipe.
Mechanical failure covers a multitude of piping failures that are unrelated to, but many interact with, the hydraulics of the system.
One of the most common types of failure is over-tightening of threaded fittings.
The threads are smooth and create little friction, and it is easy to overtighten PVC fittings.
It is possible, with little effort, to create circumferential stress beyond the failure limit when assembling threaded fittings.
This is even more pronounced
 Figure 4.
Example of threaded PVC fitting failure due to evertightening.
Another type of mechanical failure occurs due to improper solvent welding or improper fitting of the components of an assembly.
Improper penetration of pipe into socketed fittings significantly reduces the strength of the fitting.
Improper solvent welding techniques can cause failures in the bonding, creating leaks or separation.
Fittings should have full socket penetration in order to avoid significant weakening of the assembly.
Figure 5.
Excess cement used in PVC pipe joint resulting in softened pipe walls.
Figure 6.
Failure in PVC pipe due to improper solvent welding of joint with excess cement.
Mechanical failure of PVC components can also occur from temperature expansion.
If sufficient expansion allowances are not made by providing expansion loops, offsets, or slip joints, severe stress can be placed on the pipe and fittings.
Mechanical failure occurs when inadequate thrust blocking is provided.
This allows excessive pressure to be placed on a fitting as the line pressure tries to displace it while the fittings is restrained by the pipe to which it is attached.
Underground Installation, Bedding, and Backfilling
 Both solvent weld and rubber gasket joints are commonly used in irrigation systems.
Gasket joints are typically used only in pipe sizes of 10 inches and larger.
Rubber gasket joints may be the bell and spigot type, or a separate twin gasket coupler may be used with plain-end pipe.
Solvent weld joints are not recommended for operating pressures above 50 psi and pipe diameters above 4 inches.
Solvent welding requires extreme cleanliness, and the material has temperature and humidity precautions which must be observed to ensure that it is properly installed.
For buried pipes, the depth of pipe placement should be at least 30 inches below the ground to protect against heavy machinery.
The trench must be wide enough to ensure proper compacting when a pipeline is buried.
This is especially important for large diameter pipes.
For pipe diameters above 4 inches, a trench at least 12 inches wider than the diameter of the pipe should be specified.
Where possible, assemble the pipe above ground and then place it in the trench.
If the trench curves, the pipe should be assembled on the outside of the curve to eliminate the possibility of it being too short.
A small amount of paint can be sprayed on each joint of gasket pipe before dropping it in the trench.
This enables one to see if any joints have slipped apart.
With a smooth, uniform trench bottom, the pipe will be supported over its entire length on firm and stable material.
Blocking should never be used to change pipe grade or to
 provide support over low section in the trench.
Because sub-soil conditions can vary greatly within a grove or in various locations, different pipe bedding problems will be encountered.
In general, however, sub-soil should be stable and should provide physical protection for the pipe.
The backfill material should have a particle size of 1/2 inch or less.
Backfilling should be done in layers with each layer compacted sufficiently to allow uniform development of lateral passive soil forces.
For packing the soil, hand tamping or water packing may be used.
Hand tamping involves tamping the initial fill in 2-inch layers to at least 6 in.
above the pipe to a soil bulk density of at least 85% of the undisturbed sidewalls.
Use water packing only on rapidly draining soils.
For the initial coverage of the pipe only fine-grained material free of rocks and clods should be used.
If the water packing method is used, the pipeline must be filled with water before beginning the backfilling operation.
Backfill approximately 8 inches over the pipe and then add water to thoroughly saturate the initial backfill without over-watering.
Close the valves SO the pipe remains full and allow the wetted fill to dry until firm before completing the backfill.
The pipeline must be full of water to avoid floating the pipe.
Always fill low head pipe with water prior to backfilling to avoid damage to the pipe by crushing or flow reduction from flattening.
When compacting sand or gravels, vibratory methods are recommended.
If water packing is used, the initial backfill should be sufficient to insure complete coverage of the pipe, and additional backfill should not be added until the water-flooded backfill is firm enough to walk on.
Sand and gravel containing a significant proportion of fine-grained material  should preferably be compacted by mechanical tamper.
If the mechanical tamper is not available, the material should be compacted by hand.
In all instances, the trench should be filled completely.
All backfill should be placed and spread in fairly uniform layers to eliminate voids or unfilled spaces.
Large rocks, clods, and other debris larger than 3 inches in diameter should be removed.
Rolling equipment or heavy tampers should be used only to consolidate the final backfill.
These forces include water under pressure in pipelines exerts thrust forces at tees, elbows, valves, and at any change in pipe size or direction.
At times there may be sudden changes in pipeline grade, horizontal alignment of the pipe, or reduction in pipe size.
These conditions result in axial thrust and require an anchor or thrust blocks to
 absorb any axial thrust of the pipeline.
Thrust control may also be needed at the end of the pipeline and at in-line control valves.
Thrust blocks and anchors must be large enough to withstand the forces that tend to move the pipe.
These forces include momentum and pressure as well as forces due to expansion and contraction of pipe.
The pipe manufacturer's recommendations for thrust control should be followed.
The design of the thrust block also requires information on the magnitude of the thrust generated in the pipeline  and the bearing strength of the soil.
Concrete thrust blocks  should be installed at each change in direction , changes in pipe sizes, and at stops or ends to prevent the pipe damage.
Each thrust block should be large enough to adequately bear the thrust of water in the pipe, which at times can be as much as 5,000 to 6,000 pounds of pressure.
The exact size of thrust blocks must be calculated for each pipe size and soil type.
Typically, the thrust block is constructed on the outside edge of an elbow and the downstream side of a tee.
Figure 7.
Concrete thrust block used to stabilize corners above and below grade.
Determine appropriate thrust blocking for a 10-inch 90 elbow on a system with a pressure of 50 psi installed in a sandy soil.
From Table 6, the thrust developed by pipeline at 100 psi is 11,200 lb.
At 50 psi, the thrust would be 11,200 lb 2 = 5,600 lb.
From Table 7, the bearing strength for sand is 1,000 lb/ ft2.
The contact area required to achieve adequate thrust blocking would be: contact area = 5,600 lb 1,000 lb/ft2 = 5.6 ft2.
The pipeline should be thoroughly tested for leakage before backfilling operations are undertaken.
With gasket joint pipe, it is necessary to partially backfill before testing to hold the line in place.
Only body of the pipe should be covered while leaving all the exposed joints.
Fill the line very slowly and after filling, increasing to design pressure over a 15-20 minute period.
It is essential that fittings, valves, and pipe are of the same type PVC.
For example, it is unwise to use Type I and Type II PVC in the same installation.
The expansion and contraction features, pressures, etc., are different, and use of mixed materials could cause failure.
Make sure that the proper cement is used with the proper PVC pipe and fittings.
CPVC Cement on Type I PVC pipe or, conversely, PVC cement of CPVC pipe and fittings should never be used.
Normally, PVC pipe and fittings are manufactured to produce a snug fit when assembled.
The condition, however, can vary because of the minimum and maximum tolerances to which the pipe is produced.
In the case of a fitting with the maximum diameter and the pipe with the minimum diameter, a loose fit could result.
This can be remedied by interchanging fittings.
Application of two coats of solvent cement under these conditions will help assure a good joint.
Conversely, if the pipe diameter is on the maximum side and fitting on the minimum side, the interference may be too great.
For such cases, sanding may be necessary to make the connection.
For these specific reasons, it is important to check the fittings prior to making a solvent-welded joint.
The amount of interference and taper on the fitting is greater for Schedule 40 type fittings.
The Schedule 40 and lighter-wall SDR pipe have a tendency to round themselves within the Schedule 40 fittings, thus permitting a greater degree of interference.
However, in the case of Schedule 80 fittings, the heavy wall on the pipe causes the pipe to be non-roundable.
Usually the interference is less on Schedule 80 fittings, which in many cases will allow the pipe to bottom dry with very little interference.
It is under these conditions that it may be necessary to apply more than one coat of solvent cement to the pipe and fitting if the "dry fit" seems loose.
The adhesive cement used for PVC bonds is a solvent-based type.
The solvent tehtrahydrofuran  dissolves the mating surfaces when properly applied to each surface.
The pipes to be bounded should be dry and free from grease and dust.
The PVC resin filler contained in the cement assists in filling the gaps between pipe and fitting surfaces.
The adhesive cement also contains an evaporation
 retardant, usually cyclohexanone, which slows the rate of evaporation of the prime solvent.
Some of the available cements are clear, while most others contain pigments to match the pipe color.
The most common color is grey, made from titanium dioxide and carbon black, which are considered inert pigments.
Joining of the wet mating surfaces in one minute or less after starting to cement is essential to eliminate dry nonbonded spots.
The bond interface consists of a mixture of cement resin and dissolved PVC from the pipe and fitting surfaces.
As the solvent evaporates, the interface becomes homogeneous with the pipe and fitting surfaces, except for residual solvent, which dissipates over a period of a year or longer.
The resultant homogeneous bonding has led to term "solvent welded," although no heat is applied to melt and fuse the bonded areas as in metal welding.
For smaller diameters and thin-wall schedules and interference fits, available cements are called Schedule 40, quick-dry, light-weight cements, or light-body cement.
These cements are not designed to fill as much of a gap.
They tend to dry faster, do not dissolve into the pipe and fitting as much, and cure somewhat faster.
Recommended curing times for various temperature ranges are given in Table 8.
Heavy-weight or Schedule 80 cements are used for larger diameters and the heavier-wall schedules of 80 and 120, where the pipe is not roundable.
These cements are designed to fill more gap, dry slower, more readily dissolve into the pipe and fitting, and cure somewhat slower.
Heavyweight cements can be and are successfully used in place of the lighter cements.
Heavy-weight cements require a longer time to cure.
It is extremely difficult to get a satisfactory bonding using lighter and quicker drying cements with larger and heavier-wall pipe.
Care should be used to avoid cement spill into the pipe.
The cement should be still wet when the surfaces are mated.
A check should be made with the cement supplied to insure it will provide a still-wet surface for at least one full minute with a normal full coat under the actual field conditions.
This can be done by preparing a scrap piece of pipe with the primer and then applying a full, even coating with a brush and checking to see if the cement is still wet after one minute.
PVC solvent-cemented joints that are correctly assembled with good cement under reasonable field conditions never blow apart under recommended test pressures when tested after the suggested cure period.
Good PVC solvent joints
 exhibit a complete dull surface on both surfaces when cut in half and pried apart.
Leaky joints will show a continuous or an almost continuous series of shiny spots or channels from the socket bottom to the outer lip of the fitting.
No bonding occurs at these shiny spots.
This condition can increase to the point where almost the entire cemented area is shiny, and fittings can blow off at this point.
Shiny areas can be attributed to one or a combination of the following causes:
 Use of a cement which has partially or completely dried prior to installation of the fitting.
Use of a jelled cement which will not dissolve into the pipe and fitting surfaces due to loss of the prime solvent.
Insufficient cement or cement applied to only one surface.
Excess gap which cannot be satisfactorily filled.
Excess time taken to make the joint after cement was applied.
Often in these cases, it is impossible to bottom the fitting since the lubrication effect of the cement has dissipated.
Cementing with pipe surfaces about 110F, resulting in excessive evaporation of prime solvent.
Cementing when the pipe surfaces are wet or under high humidity and low temperature conditions.
Joints that have been disturbed and the bond broken prior to a firm set, or readjusted for alignment after bottoming.
Cementing surface not properly primed and dissolved prior to applying solvent cement.
If the container of cement is subjected to prolonged exposure to air, the cement becomes thick and viscous, or gel-like.
This condition is likely due to the evaporation of the solvent.
If this occurs, the cement is useless.
Do not try to restore the cement by stirring in a thinner.
It is suggested that smaller containers of cement be used, especially in warm or hot weather.
Prior to using an unopened can of cement, it should be shaken vigorously to insure proper dispersion of the resin and solvents.
Keep in mind that the solvents contained in PVC cements are highly flammable and should not be used near an open flame.
The area in which the cement is being used should be well ventilated, and prolonged breathing of the fumes, as well as contact with the skin or eyes, should be avoided.
All PVC cement should be handled in the same manner.
When working with large pipe diameter the basic solvent cement instructions discussed in the last section apply to all sizes of pipe, but when making joints of 4-inch diameter and above, it is recommended that two workers apply the solvent cement simultaneously to pipe and fitting.
Additional workers should be in a position to help push the pipe into the fitting socket while the cemented surfaces are still wet and ready for insertion.
Alignment of largediameter pipe and fittings is much more critical than those for the small-diameter pipe.
As the pipe diameters increase, the range of tolerances also increases, which can result in "out of round" and "gap" conditions.
Reducing the time in making the joint and applications of heavy coats of solvent cement in these cases in important.
When working with large pipe diameter , checking the dry fit of pipe and fittings is more critical.
In many cases where fabricated fittings are used, interference fits may not be present.
Therefore, it will be necessary to apply more than one coat of cement to the pipe and fitting.
It is essential to use a heavy-bodied, slow-drying cement on the large-diameter pipes.
The heavy cement provides thicker layers and a higher capacity to fill gaps property than regular cement.
Heavy cements also allow slightly more open time before assembly.
In installations where belled-end pipe is used to eliminate couplings, it is suggested that the interior surface of the bell be penetrated exceptionally well with the primer.
Some manufacturers, in the process of belling pipe, use a silicone release agent on the belling plug, and a residue of this agent can remain inside the bell.
This must be removed in the cleaning process.
Irrigation decisions in the Testing Ag Performance Solutions  farm management competitions ranged widely this year, even amid a drought throughout the region.
In recent years irrigators have begun to install variable frequency drives  to monitor and control the speed of their irrigation pumps powered by electricity.
This has led to several recent questions: Should VFD be installed on all electric motor power irrigation pumps?
Will VFDs pay for the expense of installation?
Economics of Irrigation Systems
 Steve Amosson Regents Fellow, Professor and Extension Economist Texas AgriLife Extension Service
 Lal Almas Associate Professor, Department of Agricultural Sciences West Texas A&M University
 Jnaneshwar R.
Girase Research Associate Texas AgriLife Research
 Nicholas Kenny Program Specialist-Agricultural Engineering Texas AgriLife Extension Service
 Bridget Guerrero Program Specialist-Agricultural Economics Texas AgriLife Extension Service
 Kumar Vimlesh Former Graduate Assistant, Department of Agricultural Sciences West Texas A&M University
 Thomas Marek Senior Research Engineer and Superintendent Texas AgriLife Research
 All of The Texas A&M System
 Leon New, Professor Emeritus and Agricultural Engineer with the Texas AgriLife Extension Service, contributed significantly to the earlier work on which this publication is based.
This research was supported in part by the Ogallala Aquifer Program, a consortium of the USDA Agricultural Research Service, Kansas State University, Texas AgriLife Research, Texas AgriLife Extension Service, Texas Tech University, and West Texas A&M University.
Mid-elevation spray application  center pivot
 Low elevation spray application  center pivot
 Low energy precision application  center pivot
 Subsurface drip irrigation 
 Investment cost of irrigation systems
 Estimated Annual Operating Expenses
 Assumptions and crop scenarios
 Savings from field operations and total annual irrigation
 Impact of fuel prices on pumping cost
 Effect of lift on pumping cost
 Correlation between amount of water pumped and fixed pumping costs
 Effect of wage rate on pumping costs
 Effects of efficiency in natural gas engines.
Conversion to an electric-powered irrigation system
 Irrigation can improve crop production, reduce yield variability, and increase profits.
But choosing and buying an irrigation system are both expensive and complex.
When considering investing in an irrigation system, farmers must keep in mind several major factors: financing, crop mix, energy prices, energy sources, commodity prices, labor availability, economies of scale, the availability of water, savings in field operations, the system's application efficiency, the operating pressure of the design, and the depth from which the water must be pumped, or pumping lift.
To assist producers making decisions about irrigation systems, Texas A&M System researchers studied the costs and benefits of five types of irrigation systems commonly used in Texas: furrow  irrigation; mid-elevation spray application  center pivot; low elevation spray application  center pivot; low energy precision application  center pivot; and subsurface drip irrigation.
The study focused on:
 The approximate costs, both gross and net, of buying and operating each system
 Each system's potential benefits for improving water application efficiency and reducing field operations
 The effect of economies of size on center pivots
 The impact of other major factors such as fuel prices, pumping lift, and labor costs
 Economics of improving natural gas engine efficiency
 Natural gas versus electric powered irrigation
 The costs of buying and operating an irrigation system may vary among farms because of differences in individual farming/ranching operations.
Before changing management strategies, producers should compare their operations closely to those in the study.
For the study, it was assumed that each irrigation system was installed on a "square" quarter section of land  or in the case of a half-mile pivot a square section.
It was assumed that the terrain and soil type did not affect the feasibility of the irrigation system.
Not all of the water irrigated is used by the crop.
The percentage of irrigation water used by a crop is called the system application efficiency.
To determine the amount of water required to irrigate crops using the different systems, farmers must know and be able to compare the application efficiency of each system.
Application efficiency can vary among systems because of:
 Differences in design, maintenance, and management of the systems
 Environmental factors such as soil type, stage of crop development, time of year, and climatic conditions
 The availability of water and its potential value for other uses
 Economic factors such as commodity and fuel prices
 For the five systems studied, the application efficiency ranged from 60 to 97 percent.
Those with the highest application efficiencies tended to have the lowest pumping costs.
Of the five irrigation systems, the least efficient was the furrow system; the most efficient was the subsurface drip irrigation system.
An efficiency index was calculated to show the amount of water  that each system would have to additionally apply to be as effective as the LESA system.
Table 1.
Basic assumptions for five irrigation distribution systems
 Irrigation system	Operating	Application	Efficiency	Acres
 pressure	efficiency	index	irrigated
 Furrow	10	60	1.47	160
 Mid-elevation	25	78	1.13	125
 Low elevation	15	88	1.00	125
 Low energy	15	95	0.93	125
 Subsurface drip	15	97	0.91	160
 1psi = pounds of pressure per square inch of water
 The calculations were made using the LESA center pivot system as a base.
It was assumed that applying the same amount of "effective" water would produce the same crop yield.
Therefore, according to the index, a subsurface drip system would need only 91 percent of the water used by the LESA system to be just as effective.
The furrow system would require 47 percent more water than the LESA system to be equally effective.
When evaluating the additional costs of the more efficient systems, farmers can consider the reduced irrigation that will be needed for each system.
A system's operating pressure affects the cost of pumping water.
Higher pressure makes irrigation more expensive.
Of the five systems studied:
 Furrow system usually had an operating pressure of 10 pounds per square inch.
LESA, LEPA, and SDI had an intermediate operating pressure of 15 psi, depending on the flow rate.
MESA center pivot systems required a higher pressure of 25 psi.
Table 1 lists the operating pressures that were used to compare the pumping cost for each system.
To function properly, each irrigation system must maintain adequate and consistent operating pressure.
Water flow  dictates the operating pressure that must be maintained for a system's design.
As GPM drops, growers must close furrow gates, renozzle center pivots, and reduce the number of emitter lines to make the system work properly.
The five irrigation systems studied had varying designs, costs, management requirements, advantages, and disadvantages.
Producers should evaluate these systems in light of the characteristics and requirements specific to their farming/ranching operations.
Furrow irrigation delivers water from an irrigation well via an underground supply pipeline, to which gated pipe is connected.
This configuration is prevalent throughout the Texas High Plains.
The water flows by gravity on the surface through the furrows between crop rows.
The gated pipe must be moved manually from one irrigation set to the next one that accommodates the well GPM, usually every 12 hours.
In the Figure 1.
Furrow irrigation on cotton.
study, two irrigation sets of gated pipe were used to allow the water flow to be changed without interruption.
Polypipe can be used instead of aluminum or PVC gated pipe.
Normally, polypipe is not moved.
Appropriate lengths are cut, plugged, and connected to underground pipeline risers.
Like gated pipes, furrow gates deliver water between crop rows.
The limitation of polypipe is that it is much less durable and is usually replaced every 1 to 2 years.
Figure 2.
Furrow polypipe on cotton.
With good planning, land preparation, and management, furrow irrigation can achieve 60 percent water application efficiency.
That is, 60 percent of the water irrigated is used by the crop.
The rest is generally lost to deep percolation below the crop root zone.
Furrow systems are best used in fine-textured soils that have low infiltration rates.
For highest crop production, water should be supplied simultaneously and uniformly to all plants in the field.
To make the application more uniform, farmers can consider laser-leveling fields, adjusting gates, and modifying the shape, spacing, or length of the furrow.
Disadvantages of furrow irrigation include:
 It usually requires additional tillage preparation and labor, especially if the terrain varies in elevation.
It can cause some environmental problems, such as soil erosion, sediment transport, loss of crop nutrients, deep percolation of water, and movement of dissolved chemicals into groundwater.
Terrain variations can cause the water to be distributed unevenly, reducing crop growth and lowering overall crop yield.
Furrow irrigation usually applies water at higher increments than do center pivot or subsurface drip systems.
To address these problems, farmers can take remedial measures such as laser leveling, planting filter strips, mechanical straw mulching, reducing tillage, changing furrow design, and installing sediment ponds with tail water pump-back features.
Mid-elevation spray application  center pivot
 Mid-elevation spray application center pivots have water sprayer heads positioned about midway between the mainline and ground surface.
The quarter-mile system considered in this study consisted of 145 drops spaced 10 feet apart.
Polydrops  were attached to the mainline gooseneck or furrow arm and extended down to the water applicator.
In MESA systems, water is applied above the primary crop canopy, even on tall crops such as corn and sugarcane.
Weights and flexible drop hoses should be used to
 Figure 3.
MESA center pivot, half-mile system.
reduce water losses and improve distribution, particularly in windy areas such as the Texas High Plains.
The nozzle pressure for MESA varies according to the type of water applicator and the pad arrangement selected.
Although some applicators require an operating pressure of 20 to 30 psi, improved designs require only 6 to 10 psi for conventional 8to 10-foot mainline outlet and drop spacing.
These applicators are now common and perform well.
The operating pressure can be lowered to 6 psi or less if the sprayer heads are positioned 60 to 80 inches apart.
A disadvantage of mid-elevation spray application is that it is subject to water losses via the air and through evaporation from the crop canopy and soil surface.
Research has shown that when using above-canopy irrigation for corn production, 10 to 12 percent of the water applied is lost from evaporation from the foliage.
Field comparisons showed a total water loss  of 20 to 25 percent from MESA center pivot irrigation systems where applicators were set above the crop canopy.
The research study found that the water application efficiency averaged 78 percent for MESA center pivot systems.
Low elevation spray application  center pivot
 In low elevation spray application center pivot sysitems, water applicators are positioned 12 to 18 inches above ground level or high enough to allow space for wheel tracking.
Each applicator is attached to a flexible drop hose, which is connected to a gooseneck or furrow arm on the mainline.
Weights are positioned immediately Figure 4.
LESA center pivot on cotton.
upstream from the pressure regulator and/or the applicator.
They help stabilize the applicator in wind and allow it to work through plants in straight crop rows.
It is best to maintain nozzle pressure as low as 6 psi with the correct water applicator.
The optimal spacing for LESA drops should be no wider than 80 inches.
If installed and managed properly, LESA drops can be spaced on conventional 8to 10-foot MESA spacing.
Corn crops should be planted in circular rows; the water should be applied beneath the primary foliage.
Some growers have used LESA successfully in straight corn rows at conventional outlet spacing by using a flat, coarse, grooved pad that allows the water to spray horizontally.
The coarser  pads generally result in the
 least evaporation loss because of the larger droplet sizes, but they can cause in soil dispersion with some soils.
Grain sorghum and soybean crops can also be planted in straight rows.
With wheat, the foliage may cause the water distribution to be significantly uneven if the nozzles are within the crop's dense canopy.
To improve water distribution, growers may need to temporarily swing the drop hose and thus the applicator over the truss rod, effectively raising the nozzle above or near the top of the canopy-
 LESA center pivots generally wet less foliage, especially for a crop planted in a circle.
Less water is lost to evaporation.
The water application efficiency for LESA usually averages 85 to 90 percent , but it may be lower in open, lower profile crops such as cotton and peanuts, or in broadcast crops such as wheat or alfalfa.
When the drops are spaced no more than 80 inches apart, LESA center pivots can easily be converted to LEPA with an applicator adapter that includes a connection for attaching a drag sock or hose.
Low energy precision application  center pivot
 Low energy precision application center pivot systems discharge water between alternate crop rows planted in a circle.
Water is applied either with a bubble applicator 12 to 18 inches above ground level or with drag socks or hoses that release water on the ground.
Drag socks help reduce furrow erosion; double-ended socks are designed to protect and maintain the furrow dikes.
When needed, drag socks and hose adapters can be easily removed from the applicator and replaced with a spray nozzle.
Figure 5.
LEPA center pivot with a drag sock.
the LEPA "quad" appli-
 cator, delivers a bubble
 water pattern (Fig.
6
 that can be reset to an
 for germination and other in-field adjustments needed.
LEPA applicators are usually placed 60 to 80 inches apart, corresponding to twice the row spacing.
Thus, one row is wet and one row is dry.
Dry middles allow more rainfall to be stored.
When the crop is planted in a circle,
 Figure 6.
LEPA center pivot with a bubble applicator on corn.
the applicators are arranged to maintain a dry row for the pivot wheels.
Research and field tests show that crop production is the same whether water is applied in every furrow or only in alternate furrows.
The field trials indicated that crops use 95 percent of the irrigation water pumped through a LEPA system.
The water application is precise and concentrated.
LEPA can be used in circles or in straight rows.
It is especially beneficial for low-profile crops such as cotton and peanuts.
This irrigation system is more common in areas with limited water supplies.
A disadvantage of LEPA is that it requires more planning and management, especially for crops in clay soils that infiltrate water more slowly.
Subsurface drip irrigation 
 In subsurface drip irrigation, drip tubes are placed from 6 to 12 inches below the soil surface, the depth depending on the crop, soil type, and tillage practices.
Drip tubes typically include built-in emitters at optional spacings.
The spacing and flow rate of the emit-
 ters depend on the
 required by the crop.
be installed no more
 than two row widths
 Figures 7a and b.
Subsurface drip irrigation.
Considered the most water-efficient system available, SDI has an application efficiency of 97 percent.
The advantages of a subsurface drip system include:
 The amount of water available dictates the system's design, control, and management.
Like the LEPA center pivot, SDI is a lowpressure, low-volume irrigation system.
It is a convenient and efficient way to supply water directly in the soil along individual crop rows and surrounding individual plant roots.
It saves money by using water and labor efficiently.
It can effectively deliver very small amounts of water daily, which can save energy, increase yields, and minimize leaching of soluble chemicals.
Subsurface drip systems have these disadvantages:
 They require intensive management.
During dry springs, an SDI system may be unable to deliver enough water to germinate the crop, and more water than needed must be applied for the crop, resulting in deep-percolation losses.
The system must be designed and installed accurately.
If the system is not managed properly, much water can be lost to deep percolation.
Evaluating the feasibility of investing in a new irrigation system can be very complicated because many factors are involved.
However, once all the factors are taken into consideration, the methodology in making the decision is relatively simple.
Growers should first estimate the gross investment cost, which is the amount of money required to buy the system.
Next, estimate the "true" economic cost, or the net investment.
Net investment takes into account tax savings, future salvage value, and the opportunity cost  of the investment.
Each irrigation system has a combination of annual benefits that reduce costs and/or improve efficiency.
The benefits may include decreased pumping, labor, and field operations.
These benefits may offset the cost of adopting the system.
Because a dollar today is worth more than a dollar 5 years from now, all annual costs and benefits must be discounted to today's dollars.
This will allow you to directly compare the costs and benefits of irrigation systems both initially and across multiple years.
Investment cost of irrigation systems
 The investment costs for the irrigation systems studied are listed in Table 2.
The costs for the well, pump, and engines were assumed to be the same for each irrigation system and were not included in the investment cost.
The gross investment for each quarter-section system  ranged from $208.56 per acre for furrow to $1,200.00 for subsurface drip irrigation with emitter lines
 Table 2.
Investment costs of alternative irrigation systems
 Distribution system			
 Furrow	208.56	183.62	161.99
 Center pivot, quarter mile	556.00	467.57	413.28
 Center pivot, half mile	338.00	284.24	251.24
 Subsurface drip irrigation	1,200.00	1,009.13	891.97
 1Assumes a marginal tax rate of 15 percent and discount rate of 6 percent Assumes a marginal tax rate of 28 percent and discount rate of 6 percent Salvage values and useful system life are in the Appendix, Table A2.
spaced 5 feet apart.
The gross investment for quarter-mile center pivot system is $556.00 per acre.
The total investment costs for each irrigation system, including well, pump, and engine for five pumping lifts, are provided in the Appendix, Table A1.
There are definite economies of scale LEPA associated with center pivot systems.
You SDI can substantially reduce the investment cost of a center pivot irrigation system by increasing the length of the pivot.
Using a half-mile center pivot rather than four quarter-mile systems reduces the gross investment by 40 percent, or $218.00 per acre , as shown in Table 2.
In addition, the corners become more functional for farming increasing from 8 to 40 acres.
To calculate the net investment, subtract the discounted salvage value and the tax savings associated with a new system from the purchase price of the distribution system.
By accounting for discounted tax savings and salvage value, producers can get a true comparison of what they would pay for each system.
The net investments for the different systems vary significantly less than the gross investments.
For example, the difference in net investment between a quarter-mile center pivot and furrow is $283.95 per acre , given a 15 percent tax and 6 percent discount rate.
The net investment for a subsurface drip irrigation system, $1,009.13 per acre, is substantially less than the gross investment of $1,200.00 per acre.
The economic feasibility of a new irrigation system can be affected by the marginal tax rate.
For example, if a producer's marginal tax rate is 28 percent instead of 15 percent, the net investment in subsurface drip is reduced by $117.16  per acre; the net investment in furrow is reduced by $21.63  per acre.
Therefore, all systems become more feasible at the higher tax rate.
The most expensive system is affected the most by the marginal tax rate; the least expensive system is affected the least.
Estimated annual operating expenses
 In the study, annual operating expenses-including both fixed and variable costs-were estimated for each system per acre-inch of water pumped.
These expenses per acre were based on the application efficiency of each system to apply the equivalent amount of water to achieve the same crop yield.
Table 3.
Water pumped for three crop scenarios and five irrigation systems in Texas
 Application	Application	High	Intermediate	Low
 Irrigation	efficiency	efficiency	water use	water use	water use
 system		index			
 Furrow	60	1.47	29.33	20.53	11.73
 MESA	78	1.13	22.56	15.79	9.03
 LESA	88	1.00	20.00	14.00	8.00
 95	0.93	18.53	12.97	7.41
 97	0.91	18.14	12.70	7.26
 The annual pumping costs per acre were calculated by multiplying the total operating estimates per acre-inch by the number of acre-inches of water required for each system:
 Total	Number of acre-inches	Annual
 operating	of water required	=	pumping
 cost per	for the irrigation	costs per
 Assumptions and crop scenarios
 To calculate operating costs, researchers assumed three crop scenarios: high water use , intermediate water use , and low water use.
For each crop scenario, the amount of water needed to be pumped was estimated by multiplying the water required by the LESA center pivot times the application efficiency index for each irrigation system.
Therefore, the effective amount of water pumped would remain constant for all systems.
Water required by the LESA center pivot
 Application efficiency index for the irrigation system
 Amount of water required for the irrigation system
 The application efficiency index for each system was calculated by dividing the LESA application efficiency  by the application efficiency of that system.
For example, the application efficiency index for furrow is 1.47  and 0.93 for LEPA.
Therefore, if 14 inches per acre are pumped through the LESA center pivot system, a furrow system would require 20.53 inches per acre of water X 1.47) to apply the same effective amount of water to the crop at the intermediate water use level.
The fixed cost for operating each system includes the annual depreciation, taxes, insurance, and interest charges associated with an investment.
The straight-line method was used to calculate depreciation.
Taxes were calculated at 1 percent of the assessed value using a tax assessment ratio of 0.20.
Insurance was calculated as 0.60 percent of the purchase value.
Interest
 was assumed to be 6 percent per year.
The operational life of each irrigation system was assumed to be 25 years.
Table 4 lists the fixed costs in dollars per acre-inch of water pumped for the intermediate water-use crop scenario and 350-foot pumping lift for each system.
This cost ranged from $1.10 for furrow to $6.05 for subsurface drip.
The fixed cost per acre-inch for LESA center pivot is estimated to be $2.54, including $1.27 for depreciation, $0.08 taxes, $0.24 insurance, and $0.95 interest.
The assumptions used in the fixed-cost calculations are presented in the Appendix, Table A3.
Variable costs include fuel, lubrication, maintenance, repairs, and labor.
Fuel costs are based on natural gas priced at $6.00 per thousand cubic feet.
Lubrication, maintenance, and repairs are assumed to be 65 percent of the fuel cost.
The labor cost to operate the well, pump, engine, and irrigation system was assessed at $10.30 per hour.
The variable pumping costs in dollars per acre-inch of water pumped for the five irrigation systems at a 350foot pumping lift are shown in Table 4 for each system.
Variable cost estimates by system and lift are given in the Appendix, Tables A4 through A6.
Table 4.
Fixed and variable pumping costs per acre-inch for the intermediate water-use scenario  at a 350foot pumping lift for five irrigation systems
 Cost component/system	Furrow	MESA	LESA	LEPA	SDI
 Depreciation	0.41	1.13	1.27	1.37	3.02
 Taxes	0.02	0.07	0.08	0.09	0.19
 Insurance	0.06	0.21	0.24	0.26	0.57
 Interest charges	0.61	0.85	0.95	1.03	2.27
 Total fixed costs	1.10	2.26	2.54	2.75	6.05
 Fuel costs	6.04	6.55	6.22	6.22	6.22
 LMR charges	3.93	4.26	4.04	4.04	4.04
 Labor costs	1.19	0.91	0.80	0.75	0.73
 Total variable costs	11.16	11.72	11.06	11.01	10.99
 Total fixed and variable
 cost 	12.26	13.98	13.60	13.76	17.04
 Lubrication, maintenance and repairs
 The estimated total cost per acre-inch varied considerably among the systems evaluated.
Furrow had the lowest total cost at $12.26 per acre-inch; subsurface drip had the highest cost at $17.04 per acre-inch.
LESA, LEPA, and MESA center pivot systems ranged from $13.60 to $13.98 per acre-inch.
To calculate the annual pumping cost in dollars per acre in each crop scenario, the total operating costs per
 acre-inch were multiplied by the number of acre-inches of water pumped.
For the intermediate water use scenario, LEPA center pivot had the lowest annual pumping cost, $178.45 , because of its high application efficiency.
Conversely, furrow irrigation, which had the lowest pumping cost per acre-inch , had the highest total annual pumping cost $251.79.
This is because of its relatively low application efficiency, resulting in more water having to be pumped to apply the same effective amount.
Table 5.
Total pumping cost per acre using natural gas fuel at a 350-foot pumping lift for three crop scenarios and five irrigation systems
 System/water use	water use	water use	water use
 Furrow	339.03	251.79	163.89
 MESA	293.86	220.81	147.48
 LESA	252.20	190.40	128.88
 LEPA	235.31	178.45	121.31
 SDI	272.35	216.41	160.51
 Savings from field operations and total annual irrigation
 Center pivot and subsurface drip irrigation systems require fewer field operations than does furrow irrigation.
For example, the field operations commonly used to produce corn under furrow irrigation include shredding, offset disking, chiseling, tandem disking, bedding, rod weeding, planting, and two cultivations.
For center pivot or subsurface drip irrigation, the number of field operations is generally reduced to shredding, offset disking, chiseling, planting, and one cultivation.
This represents a reduction of four field operations.
Assuming a cost of $11 per operation, the estimated savings are $33 per acre under conventional tillage.
The number of field operations performed or saved varies considerably, depending on the crop planted, cropping system, and growing conditions for a particular year.
Corn
 Table 6.
Savings in pumping cost and field operations using natural gas fuel at a 350-foot pumping lift for the intermediate water-use scenario when shifting from furrow to more efficient irrigation systems per acre
 in pumping	from field	irrigation
 System	cost	operations	savings
 MESA	30.97	33.00	63.97
 LESA	61.39	33.00	94.39
 LEPA	73.34	33.00	106.34
 SDI	35.38	33.00	68.38
 producers have estimated that from three to five field operations may be saved under center pivot or subsurface drip irrigation, amounting to $33 to $55 per acre.
Typically, three field operations are eliminated for sorghum, soybeans, and cotton production, saving $33 per acre.
Table 7 lists the net investment cost and benefits of adopting efficient irrigation technology at a 350-foot pumping lifts for high, intermediate, and low water-use crop scenarios.
The benefits include the estimated savings from reduced pumping costs and field operations from the five more efficient systems compared to the least efficient system.
The series of benefits accumulated over the life of irrigation equipment  is discounted at the rate of 6 percent to present value.
It is considered economically feasible to adopt an irrigation system technology when the change in expected benefits exceeds the net investment cost.
Comparing the purchase of furrow system to a LEPA center pivot system reveals that LEPA requires an additional net investment of $283.95  per acre; however, the reduction in field operations and pumping costs would save $1,747.71 per acre under the assumption of high water use.
Even under low water use, adoption of LEPA is favorable, with expected gain in benefits of $966.22 per acre compared to the $283.95 per acre of additional investment.
Evaluating the conversion or replacement of an existing system from the data presented in Table 7 is more difficult.
The expected benefits for each system as given in Table 7 will remain the same.
However, a producer will need to estimate the cost of conversion, or the net investment of the "new" system adjusted for the salvage value of the present system, in order to evaluate its feasibility.
Several conclusions can be made from the results in Table 7:
 It appears that the water and/or field operation savings justify converting furrow to center pivots whenever physically possible.
The lack of difference between the costs of center pivot suggests that producers should buy the system with the highest water application efficiency that works for their operation.
Converting furrow to drip irrigation is not feasible under a low water-use scenario based on water and field operation savings.
The study did not address the potential yield increase of applying water to the crop more often or the ability to irrigate more acreage with the same amount of water because of the improved application effectiveness.
These factors could affect drip irrigation feasibility, especially for high-value crops.
The major factors that influence pumping cost for irrigated crops are price of fuel, pumping lift, inches of water pumped, and labor wage rate.
These factors affect the economic feasibility of alternative irrigation systems.
Below are analyses of the effects of varying fuel price, pumping lift, water pumped, and wage rate on irrigation costs for each irrigation system.
Impact of fuel prices on pumping cost
 The effect of fuel price on the grower's fuel costs was calculated for each of the five irrigation systems.
The fuel costs were estimated using natural gas prices ranging from $4.00 to $14.00 per MCF in increments of $2.00.
It was assumed that corn irrigated by a LESA center pivot requires 20 acre-inches of water annually.
For the other five irrigation systems, the amount of water pumped was adjusted by comparing the relative application efficiency of each system to that of the LESA center pivot.
When the price of natural gas price increases from $4.00 to $14.00 per MCF, the total irrigation cost per acreinch for each system more than doubles.
As natural gas prices rise, so do the savings on pumping costs for the irrigation systems that have higher application efficiencies.
Table 7.
Comparison of net investment cost and benefits of irrigation technology adoption at three water-use scenarios
 Net investment	Change in net	High	Intermediate	Low
 System	cost	investment	water use	water use	water use
 MESA	467.57	283.95	999.17	817.60	631.70
 LESA	467.57	283.95	1,531.75	1,206.25	869.44
 LEPA	467.57	283.95	1,747.71	1,359.04	966.22
 SDI	1,009.13	825.51	1,274.21	873.88	465.17
 Change in net investment cost from furrow
 For example, at $4.00 per MCF, a producer would save $43.22 per acre  by using LEPA center pivot instead of furrow.
At $14.00 per MCF, the savings would increase to $151.30  per acre.
This is the result of fuel costs increasing by $293.34  per acre for furrow, while LEPA increases by
 Table 8.
Annual estimated fuel costs for effective irrigation water applied to 1 acre of irrigated corn at alternative gas prices for five irrigation systems at a 350-foot lift
 Gas price 	4	6	8	10	12	14
 system		Fuel costs 
 Furrow	29.33	117.33	176.00	234.67	293.33	352.00	410.67
 MESA	22.56	90.26	135.38	180.51	225.64	270.77	315.90
 LESA	20.00	80.00	120.00	160.00	200.00	240.00	280.00
 LEPA	18.53	74.11	111.16	148.21	185.26	222.32	259.37
 SDI	18.14	72.58	108.87	145.15	181.44	217.73	254.02
 only $185.26  per acre.
The more efficient the system, the more insulated a producer is from fuel price changes.
Effect of lift on pumping cost
 Fuel costs are affected by the depth from which the irrigation water must be pumped.
In this study, the fuel costs for irrigating corn were estimated for the different irrigation systems at pumping lifts ranging from 150 feet to 550 feet in 100-foot increments to determine the impact of pumping lift (Table The relative efficiency of each system was factored into these calculations.
Table 9.
Annual estimated fuel costs for pumping water to irrigate corn for five pumping lifts and five irrigation systems 
 Pumping lift	150 ft	250 ft	350 ft	450 ft	550 ft
 Furrow	29.33	130.83	182.75	224.99	242.88	268.40
 MESA	22.56	120.94	158.40	187.51	203.75	219.32
 LESA	20.00	95.40	129.80	157.80	169.60	187.00
 LEPA	18.53	88.37	120.24	146.17	157.10	173.22
 SDI	18.14	86.55	117.76	143.16	153.86	169.65
 1Natural gas price of $6.00 per MCF was assumed.
The study found that the less efficient the irrigation system, the greater the effect of the price of fuel and pumping lift on the cost to produce an irrigated crop.
The fuel cost for a LEPA center pivot at a 250-foot pumping lift was $120.24; at 550 feet, the cost was $173.22, an increase of $52.98 per acre of irrigated corn.
For that system, fuel cost increased by 44 percent as pumping lift increased from 250 feet to 550 feet.
For furrow, the pumping cost was $182.75 at 250 feet and $268.40 at 550 feet.
This was an increase of $85.65 per acre, which was $32.67 more than LEPA center pivot.
The fuel costs for each irrigated acre of corn were $224.99 and $146.17 at a 350-foot pumping lift using furrow and LEPA center pivot, respectively.
At 350-foot pumping lift, producers will be able to save about $78.82 in fuel costs for each irrigated acre
 by changing to more-efficient irrigation systems and improved technologies.
The savings in fuel cost by shifting from furrow to LEPA increases to $95.18 for every irrigated acre of corn at the 550-foot pumping lift.
This finding indicates that the farther water must be pumped from the ground, the more savings that growers will realize by adopting a more efficient irrigation system.
Correlation between amount of water pumped and fixed pumping costs
 To analyze the effect of the amount of water pumped on fixed cost per acre-inch, researchers calculated the fixed costs for all irrigation systems at a 350-foot pumping lift.
The amounts of water analyzed ranged from 10 to 30 acre-inches per acre.
It is obvious that fixed cost per acre-inch has an inverse relationship to the amount of water pumped (Fig.
That is, the less water pumped, the higher the fixed cost per acre-inch.
At 10 acre-inches of water, the fixed cost per acre-inch of water pumped using subsurface drip was $7.69; for furrow, the fixed cost was $2.23.
However, as the amount of water pumped increased to 30 acre-inches, the fixed cost dropped to $2.56 for subsurface drip and to $0.74 for furrow.
Therefore, the difference in fixed cost of the systems narrowed significantly, from $5.46 per acre-inch  to $1.82 per acre-inch  as use increased from 10 to 30 acre-inches per year.
Figure 8.
Changes in fixed cost as affected by the amount of water pumped in three types of irrigation systems.
For center pivots, the fixed cost per acre-inch ranged from $3.58 to $1.19 for 10 acre-inches to 30 acre-inches applied, respectively.
It may be deduced that producers tend to pump more water to reduce fixed cost per acre-inch.
The large investments involved in adopting more efficient irrigation technology also encourage investors to increase water pumping to recover their investments as soon as possible.
Effect of wage rate on pumping costs
 The availability and cost of labor greatly affect the selection of an irrigation system.
To evaluate labor charges accurately, growers must identify all costs.
For example, be sure to factor in the costs of transportation, meals, lodging, insurance, and/or taxes if you provide or pay them.
If you do not identify all labor costs, your estimate of the value of a particular irrigation system may be inaccurate.
The labor costs for irrigated corn were calculated at five wage rates for the five irrigation systems.
Labor costs at $12 per hour using furrow and LEPA center pivot were $28.35 and $11.29 per acre, respectively.
By switching to more an efficient irrigation system, growers can reduce labor costs by $17.06 for each acre irrigated annually.
Table 10.
Labor costs for irrigated corn at five wage rates for five irrigation systems
 Wage rate 	10	12	14	16	18
 system	acre-inches	Labor cost $/ac
 Furrow	29.33	23.63	28.35	33.08	37.80	42.53
 MESA	22.56	13.90	16.68	19.46	22.24	25.02
 LESA	20.00	10.88	13.05	15.23	17.40	19.58
 LEPA	18.53	9.41	11.29	13.18	15.06	16.94
 SDI	18.14	9.01	10.82	12.62	14.42	16.22
 The savings in labor cost by shifting from furrow to LEPA center pivot increase to $22.74 for every irrigated acre of corn at the labor wage rate of $16 per hour.
The comparison indicates that as wage rates rise, it becomes more cost effective to adopt a more efficient irrigation system.
Effects of efficiency in natural gas engines
 Natural gas is a preferred irrigation fuel where it is available because it typically costs the least per unit of energy, usually by a significant amount.
However, natural gas power plants are not always the most cost-effective means for pumping irrigation water because of the relatively low thermal efficiency of spark ignition, internal combustion engines.
This is especially true if engine efficiency has declined after multiple years of service.
The standard expected efficiency for a new natural gas engine in a pumping plant setting is about 25 percent, meaning that about one quarter of the fuel that is consumed
 by the engine will be converted to usable power.
When combined with standard efficiencies of the pump  and right-angle gearhead , the standard overall efficiency of a natural gas pumping plant is about 16 percent.
Field studies conducted throughout the Texas High Plains over the past 30 years have indicated that many pumping plants operate with engine efficiencies as low as 15 percent and overall efficiencies as low as 10 percent.
At a natural gas pumping plant, the engine is typically the least efficient component and is, therefore, the component most sensitive to replacement based on efficiency.
Tables 11 and 12 list the first-year energy-cost savings for multiple natural gas prices for 75and 125-horsepower pumping plants.
Seasonal energy savings are found by subtracting the seasonal energy savings of an existing natural gas engine from those of a more efficient, newer natural gas engine.
For example, at a 75-horsepower pumping plant with $8.00 per MCF natural gas, replacing an 18-percentefficient engine with a 24-percent-efficient engine would produce a direct annual energy cost savings of $4,200.
Seasonal energy savings are expected to occur over the life of the engine; however, the benefits in future years must be discounted to account for the time value of money.
Total discounted energy savings prices for 75and 125-horsepower pumping plants at various natural gas prices are estimated assuming an engine life of 5 years and a discount rate of 6 percent.
These values can be used to identify the amount a producer can pay to upgrade engine efficiency.
Again, looking at the same 75-horsepower pumping plant with $8.00 per MCF natural gas, replacing an 18-percent-efficient engine with a 24-percent-efficient engine would produce a discounted energy cost savings of $19,000  over a 5-year period.
This analysis suggests that a producer would be better off financially by choosing the higher efficiency engine if it could be bought for less than $19,000 more, given the useful life and natural gas price assumptions.
This approach makes a compelling argument for replacing inefficient engines with more efficient models, especially considering that engine efficiency decreases with time.
Because of the inefficiency of internal combustion engines and the cost structure of natural gas, researchers have been working to develop highly efficient natural gas engines.
Prototype engines have shown over 40 percent thermal efficiency in controlled environments and up to 30 percent thermal efficiency in field tests, up to 125 horsepower.
Much of the work on improved efficiencies has also helped with emissions compliance, because reduced fuel consumption is an effective way to reduce emissions.
The
 Table 11.
Seasonal and total discounted energy cost reduction from replacing a natural gas engine, based on 75-horsepower pumping requirements: 400 gallons per minute, 300-foot lift, and 20 pounds per square inch 
 Seasonal energy cost reduction	Total discounted energy cost reduction
 Engine efficiency	Natural gas price 
 	4	8	12	4	8	12
 -	-	-	-	-	-
 16	$ 600	$ 1,300	$ 1,900	$ 2,800	$ 5,700	$ 8,500
 18	$ 1,700	$ 3,400	$ 5,100	$ 7,600	$ 15,100	$ 22,700
 20	$ 2,500	$ 5,100	$ 7,600	$ 11,400	$ 22,700	$ 34,100
 22	$ 3,200	$ 6,500	$ 9,700	$ 14,500	$ 28,900	$ 43,400
 24	$ 3,800	$ 7,600	$ 11,500	$ 17,000	$ 34,100	$ 51,100
 26	$ 4,300	$ 8,600	$ 12,900	$ 19,200	$ 38,500	$ 57,700
 28	$ 4,700	$ 9,500	$ 14,200	$ 21,100	$ 42,200	$ 63,300
 30	$ 5,100	$ 10,200	$ 15,300	$ 22,700	$ 45,400	$ 68,200
 16% discount rate, 5 years
 Table 12.
Seasonal and total discounted energy cost reduction from replacing a natural gas engine, based on 125-horsepower pumping requirements: 750 gallons per minute, 400-foot lift, and 20 pounds per square inch 
 Seasonal energy cost reduction	Total discounted energy cost reduction
 Engine efficiency	Natural gas price 
 	4	8	12	4	8	12
 -	-	-	-	-	-
 16	$ 1,100	$ 2,100	$ 3,200	$ 4,700	$ 9,500	$ 14,200
 18	$ 2,800	$ 5,700	$ 8,500	$ 12,600	$ 25,200	$ 37,900
 20	$ 4,200	$ 8,500	$ 12,700	$ 18,900	$ 37,900	$ 56,800
 22	$ 5,400	$ 10,800	$ 16,200	$ 24,100	$ 48,200	$ 72,300
 24	$ 6,400	$ 12,700	$ 19,100	$ 28,400	$ 56,800	$ 85,200
 26	$ 7,200	$ 14,400	$ 21,500	$ 32,000	$ 64,100	$ 96,100
 28	$ 7,900	$ 15,800	$ 23,600	$ 35,200	$ 70,300	$ 105,500
 30	$ 8,500	$ 17,000	$ 25,400	$ 37,900	$ 75,700	$ 113,600
 16% discount rate, 5 years
 current method for meeting emissions compliance is to retrofit existing engine platforms with catalytic convertors and oxygen sensors.
Although catalytic convertors do reduce point source emissions, they also reduce engine efficiency and increase maintenance costs.
At the time of publication, no highly efficient, noncatalyst natural gas irrigation engine is production ready.
Conversion to an electric-powered irrigation system
 Volatile natural gas prices have caused many producers to convert or consider converting their irrigation systems to use alternative energy sources.
Most irrigation systems in Texas are powered by either natural gas or electricity.
To make an informed decision before any actual conversion, producers should compare the costs of their existing natural gas powered system to the cost of converting and operating an electric-powered system.
Following is a comparison between irrigation systems powered by natural gas and those powered by electricity.
The costs associated each system were evaluated over
 a 20-year period using two pumping lifts , three crops , natural gas prices ranging from $2.00 per MCF to $16.00 per MCF, and a flow capacity of 600 gallons per minute for a quarter-mile center pivot.
Table 13 shows the expenses related to investment and maintenance of a natural gas engine and electric motor.
It was assumed that producers had a natural gas powered irrigation system in place.
The investment costs for natural gas engines of about $11,000 at 200 feet and $36,000 at 500 feet were used as the replacement costs of the engine over the 20-year period.
Investment costs for the electric motor were about $4,800 at 200 feet and $8,800 at 500 feet.
Also, the cost to convert from a natural gas system to electric ranged from about $7,500 at 200 feet to $15,400 at 500 feet and included the fuse, control panel, pump conversion, and labor and installation.
The total costs associated with each system over the 20-year period were estimated on a per-acre basis in 2011 dollars and included conversion expenses, irrigation fuel, repairs, and any necessary replacement costs to the
 Table 13.
Fixed and variable costs for a natural gas irrigation engine and an electric motor
 Engine/motor costs-	Useful life	Salvage value	LMR
 Lift 	Investment 	Conversion 	$/ac-yr	Years	Investment	Annual 	$/ac-yr
 Natural gas irrigation engine
 200	10,997	-	7.64	12	10%	1,084	9.03
 500	35,940	-	24.96	12	10%	1,480	12.33
 200	4,812	7,530	6.86	15	10%	420	3.50
 500	8,835	15,440	13.49	15	10%	722	6.02
 1 LMR=Lubrication, maintenance, and repairs
 systems.
Each cost stream was evaluated for the different levels of natural gas prices and pumping lifts.
Conversion to an electric-powered system becomes feasible at the price where the cost lines cross.
For example, the cost lines for each system  for an intermediate water use crop at a pumping lift of 200 feet are presented in Figure 9.
C1 represents the cost of natural gas powered irrigation, which is assumed to be the system currently in use, and C2 represents the cost for converting to electric and associated costs for operating that system over a 20-year time horizon.
The two cost lines intersect at $4.00 per MCF or $0.07 per kWh, indicating that conversion from natural gas to electric is plausible at this point.
The breakeven prices for all pumping lifts and crops are given in Table 14.
The type of crop grown does not significantly affect breakeven prices.
Overall, it is beneficial to convert lower pumping lifts first at natural gas prices above $3.84 per MCF and higher pumping lifts at natural gas prices above $4.38 per MCF.
Table 14.
Breakeven prices for converting an irrigation system from natural-gas powered to electric powered
 Lift 	Water use	BE price	BE price
 200	Intermediate	4.02	0.0701
 500	Intermediate	4.78	0.0730
 Before making a decision, producers should consider other factors:
 Proximity to a three-phase electric line
 Cost of repairs and labor
 Figure 9.
Natural gas and electric irrigation costs for an intermediate water use crop at a 200-foot lift.
Possibly the most important consideration is the proxlimity to a three-phase electric line.
Line extensions were not included in the comparison, and the cost can be high if the well is far from power lines.
The electric company may also assess initial connection fees or peak factor charges.
On the other hand, some electric companies may offer incentives to irrigated agricultural producers to encourage conversion and offset some of the expense.
In addition, electric systems tend to have a longer life with fewer repair and labor expenses.
Finally, electric prices fluctuate somewhat with natural gas prices, but they tend to be more stable overall than natural gas prices, which would be an advantage for producers.
Researchers evaluated the predominant irrigation systems in Texas and analyzed the major factors that affect their economic feasibility.
The discussion of some items was omitted or limited because of study and space limitations.
One limitation in the analysis was that yields were held constant even when the amount of water applied by the distribution system was modified by its application efficiency.
Although this approach is sound, it does not account for potential yield gains from more frequent irrigations that can result through center pivots and especially SDI as compared to furrow.
Investing in a new irrigation system is expensive and complex, with many factors needing to be evaluated, including water availability, pumping lift, labor cost, fuel cost, tax rate, soil type, and field topography.
Overlaying these factors are the differences in the costs and water application efficiencies of the various irrigation systems.
These factors make it difficult to make a wise investment decision.
To help farmers weigh these factors and make these decisions, researchers studied the costs and associated benefits of five commonly used irrigation systems in Texas: furrow, mid-elevation spray application center pivot, low elevation spray application center pivot, low energy precision application center pivot, and subsurface drip.
The study found that:
 Furrow irrigation systems require less capital investment but have lower water application efficiency and are more labor intensive than the other irrigation systems.
Compared to furrow irrigation, center pivot systems offer more than enough benefits in application efficiency and reduction in field operations to offset the additional costs.
Where it is feasible to use, half-mile center pivot offers substantial savings compared to quarter-mile length systems.
Among the three center pivot alternatives, LEPA center pivot systems generate the highest benefits at low, intermediate, and high water-requirement scenarios.
Advanced irrigation technologies are best suited to crops with high water needs, particularly in areas with deep pumping lifts.
Producers using advanced systems will have not only lower pumping costs, but also potential savings from the need for fewer field operations.
Compared to LEPA center pivot systems, subsurface drip irrigation  is not economically feasible for any crop water-use scenario because of its relatively high investment and small gain in application efficiency.
For most crops, adoption of SDI may be limited to land where pivots cannot physically be installed.
However, producers should closely evaluate using SDI systems for high-value crops.
Research suggests that SDI systems may improve the application efficiency and the timing of frequent applications.
These improvements may increase acreage and yields enough to justify the additional investment costs of subsurface drip systems.
Researchers also studied the effect on pumping cost of variations in fuel prices, pumping lift, amount of water pumped, and labor wage rate.
Results indicated that:
 The less efficient the irrigation system, the more effect that fuel price, pumping lift, and wage rate have on the cost of producing an irrigated crop.
Therefore, when there is inflation or volatility of these cost factors, it is more feasible to adopt more efficient irrigation systems and technology.
As more water is pumped, the fixed cost per acreinch drops.
Therefore, pumping more water encourages farmers to recapture their irrigation system investment more quickly.
It is beneficial to replace inefficient engines with more efficient models.
Conversion from natural-gas-powered irrigation to electric-powered irrigation is economically feasible for lower pumping lifts at natural gas prices above $3.84 per MCF and higher pumping lifts at natural gas prices above $4.38 per MCF.
Table A1.
Estimated gross investment costs  for alternative irrigation systems at five pumping lifts in Texas
 	Well	Pump	Engine	system	Total
 150	27,500	26,500	6,000	33,370	96,800
 250	36,500	36,000	6,500	33,370	115,800
 350	45,500	46,000	9,000	33,370	137,300
 450	54,500	56,000	9,000	33,370	156,300
 550	64,000	66,500	35,000	33,370	202,300
 150	27,500	26,500	6,000	69,500	129,500
 250	36,500	36,000	6,500	69,500	148,500
 350	45,500	46,000	9,000	69,500	170,000
 450	54,500	56,000	9,000	69,500	189,000
 550	64,000	66,500	35,000	69,500	235,000
 150	27,500	26,500	6,000	69,500	129,500
 250	36,500	36,000	6,500	69,500	148,500
 350	45,500	46,000	9,000	69,500	170,000
 450	54,500	56,000	9,000	69,500	189,000
 550	64,000	66,500	35,000	69,500	235,000
 150	27,500	26,500	6,000	69,500	129,500
 250	36,500	36,000	6,500	69,500	148,500
 350	45,500	46,000	9,000	69,500	170,000
 450	54,500	56,000	9,000	69,500	189,000
 550	64,000	66,500	35,000	69,500	235,000
 150	27,500	26,500	6,000	192,000	252,000
 250	36,500	36,000	6,500	192,000	271,000
 350	45,500	46,000	9,000	192,000	292,500
 450	54,500	56,000	9,000	192,000	311,500
 550	64,000	66,500	35,000	192,000	357,500
 Table A2.
Useful life and salvage value assumptions used to calculate depreciation of five irrigation systems
 Item/component	life 	value 
 Center pivot	25	20
 Subsurface drip	25	20
 Table A3.
Fixed cost for irrigating at three levels of water use under five irrigation systems
 water use	Depreciation	Taxes	Insurance	Interest	Total
 High	0.28	0.01	0.04	0.43	0.76
 Intermediate	0.41	0.02	0.06	0.61	1.10
 Low	0.71	0.04	0.11	1.07	1.93
 High	0.79	0.05	0.15	0.59	1.58
 Intermediate	1.13	0.07	0.21	0.85	2.26
 Low	1.97	0.12	0.37	1.48	3.94
 High	0.89	0.06	0.17	0.67	1.79
 Intermediate	1.27	0.08	0.24	0.95	2.54
 Low	2.22	0.14	0.42	1.67	4.45
 High	0.96	0.06	0.18	0.72	1.92
 Intermediate	1.37	0.09	0.26	1.03	2.75
 Low	2.40	0.15	0.45	1.80	4.80
 High	2.12	0.13	0.40	1.59	4.24
 Intermediate	3.02	0.19	0.57	2.27	6.05
 Low	5.29	0.33	0.99	3.97	10.58
 Table A4.
Variable costs  for a high wateruse crop  for five irrigation systems at five lifts
 System/lift 	Fuel	LMR	Labor	Total
 150	3.52	2.29	0.83	6.64
 250	4.91	3.19	0.83	8.94
 350	6.04	3.93	0.83	10.80
 450	6.53	4.24	0.83	11.60
 550	7.22	4.69	0.83	12.74
 150	4.23	2.75	0.63	7.61
 250	5.54	3.60	0.63	9.77
 350	6.55	4.26	0.63	11.44
 450	7.12	4.63	0.63	12.38
 550	7.66	4.98	0.63	13.27
 150	3.76	2.45	0.56	6.77
 250	5.11	3.32	0.56	9.00
 350	6.22	4.04	0.56	10.83
 450	6.69	4.35	0.56	11.59
 550	7.37	4.79	0.56	12.72
 150	3.76	2.45	0.52	6.73
 250	5.11	3.32	0.52	8.96
 350	6.22	4.04	0.52	10.79
 450	6.69	4.35	0.52	11.55
 550	7.37	4.79	0.52	12.69
 150	3.76	2.45	0.51	6.72
 250	5.11	3.32	0.51	8.95
 350	6.22	4.04	0.51	10.78
 450	6.69	4.35	0.51	11.54
 550	7.37	4.79	0.51	12.68
 1 Natural gas price of $6.00 per MCF was assumed.
Table A5.
Variable costs  for an intermediate water-use crop  for five irrigation systems at five lifts
 System/lift 	Fuel	LMR	Labor	Total
 150	3.52	2.29	1.19	6.99
 250	4.91	3.19	1.19	9.29
 350	6.04	3.93	1.19	11.16
 450	6.53	4.24	1.19	11.96
 550	7.22	4.69	1.19	13.09
 150	4.23	2.75	0.91	7.88
 250	5.54	3.60	0.91	10.04
 350	6.55	4.26	0.91	11.71
 450	7.12	4.63	0.91	12.66
 550	7.66	4.98	0.91	13.55
 150	3.76	2.45	0.80	7.01
 250	5.11	3.32	0.80	9.24
 350	6.22	4.04	0.80	11.07
 450	6.69	4.35	0.80	11.83
 550	7.37	4.79	0.80	12.96
 150	3.76	2.45	0.75	6.96
 250	5.11	3.32	0.75	9.19
 350	6.22	4.04	0.75	11.01
 450	6.69	4.35	0.75	11.78
 550	7.37	4.79	0.75	12.91
 150	3.76	2.45	0.73	6.94
 250	5.11	3.32	0.73	9.17
 350	6.22	4.04	0.73	11.00
 450	6.69	4.35	0.73	11.76
 550	7.37	4.79	0.73	12.90
 1 Natural gas price of $6.00 per MCF was assumed
 Table A6.
Variable costs  for a low water use crop  for five irrigation systems at five lifts
 System/lift 	Fuel	LMR	Labor	Total
 150	3.52	2.29	2.07	7.88
 250	4.91	3.19	2.07	10.18
 350	6.04	3.93	2.07	12.05
 450	6.53	4.24	2.07	12.85
 550	7.22	4.69	2.07	13.98
 150	4.23	2.75	1.59	8.56
 250	5.54	3.60	1.59	10.72
 350	6.55	4.26	1.59	12.39
 450	7.12	4.63	1.59	13.33
 550	7.66	4.98	1.59	14.22
 150	3.76	2.45	1.40	7.61
 250	5.11	3.32	1.40	9.84
 350	6.22	4.04	1.40	11.67
 450	6.69	4.35	1.40	12.43
 550	7.37	4.79	1.40	13.56
 150	3.76	2.45	1.31	7.52
 250	5.11	3.32	1.31	9.75
 350	6.22	4.04	1.31	11.57
 450	6.69	4.35	1.31	12.34
 550	7.37	4.79	1.31	13.47
 150	3.76	2.45	1.28	7.49
 250	5.11	3.32	1.28	9.72
 350	6.22	4.04	1.28	11.54
 450	6.69	4.35	1.28	12.31
 550	7.37	4.79	1.28	13.44
 1 Natural gas price of $6.00 per MCF was assumed.
Educational programs of the Texas AgriLife Extension Service are open to all people without regard to race, color, sex, disability, religion, age, or national origin.
Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 30, 1914, in cooperation with the United States Department of Agriculture.
Edward G.
Smith, Director, Texas AgriLife Extension Service, The Texas A&M System.
Acre-foot The volume of water required to cover one acre of land  to a depth of one foot.
It is equal to 325,851 gallons.
Aquifer Layers of rock, sand or gravel that can absorb water and allow it to flow.
Best Management Practices  Methods that have been determined to be effective, practical means of preventing or reducing pollution from nonpoint sources.
Buffer Zone The area of land next to a body of water where activities such as construction are restricted in order to protect the water.
Confined Aquifer Soil or rock located below the land surface that is saturated with water.
There are layers of impermeable material both above and below it, and it is under pressure SO that when the aquifer is penetrated by a well, the water will rise above the top of the aquifer.
Conservation Reserve Program  A voluntary U.S.
Department of Agriculture program that takes highly erodible or environmentally sensitive cropland out of production for 10 to 15 years.
Farmers receive an annual rental payment in return.
Arkansas Water Primer Series:
 Desalination The removal of salts from saline water to provide fresh water.
This method is becoming a more popular way of providing fresh water to populations.
Glossary of Water-Related Terms
 Doctrine of Prior Appropriation The system for allocating water to private individuals used in most Western states.
The prior appropriation doctrine is based on the concept of "First in Time, First in Right." The first person to take a quantity of water and put it to beneficial use has a higher priority of right than a subsequent user.
The rights can be lost through nonuse; they can also be sold or transferred apart from the land.
Domestic Wastewater Wastewater derived principally from residential and commercial buildings and institutions.
It may or may not contain groundwater, surface water or stormwater.
Drainage Basin A land area where precipitation runs off into streams, rivers, lakes and reservoirs.
It is a land feature that can be identified by tracing a line along the highest elevations between two areas on a map, often a ridge.
A drainage basin is also referred to as a watershed.
Dredging The removal of sediment from a channel or waterbody to produce sufficient depths for navigation or to recover water storage capacity.
Ecosystem An organic community of plants and animals viewed within its physical environment.
The ecosystem results from the interaction between soil, climate, vegetation and animal life.
Effluent Water that flows from a sewage treatment plant after it has been treated.
Environmental Quality Incentives Program  A voluntary program administered by the Natural Resources Conservation Service that offers incentives for landowners to adopt management practices that protect environmental quality.
Erosion The process in which a material is worn away by water or air.
Stream bank or stream bed erosion is often increased by the presence of abrasive particles.
Evaporation The process of liquid water becoming water vapor, including vaporization from water surfaces, land surfaces and snow fields.
Evapotranspiration The combined loss of water to the atmosphere via the processes of evaporation and transpiration.
Flood Plain A strip of relatively flat and normally dry land alongside a stream, river or lake that is covered by water during a flood.
Groundwater Water that flows or seeps downward and saturates soil or rock, supplying springs and wells.
Groundwater Discharge The fluid output from a groundwater system.
Natural groundwater discharge may occur in the form of springs or seepages.
Groundwater also discharges into rivers and lakes via bank seepage or by upward flow in river and lake beds.
Groundwater Recharge The inflow of water to a groundwater reservoir from the surface.
Infiltration of precipitation and its movement to the water table is one form of natural recharge.
Hydric Soil Soil that is wet long enough for anoxic  conditions to develop.
This soil is found in wetlands.
Hydrologic Cycle The cycle in which water evaporates from the oceans and the land surface, is carried over the earth in atmospheric circulation as water vapor, precipitates again as rain or snow, is intercepted by trees and vegetation, provides runoff on
 the land surface, infiltrates into soils, recharges groundwater, discharges into streams, and ultimately, flows out into the oceans, from which it will eventually evaporate again.
Infiltration The flow of water from the land surface into the subsurface.
Leaching The process by which soluble materials in the soil, such as salts, nutrients, pesticide chemicals or contaminants, are washed into a lower layer of soil or are dissolved and carried through the soil.
Maximum Contaminant Level  The designation given by the U.S.
Environmental Protection Agency to water quality standards as outlined in the Safe Drinking Water Act.
The MCL is the greatest amount of a contaminant that can be present in drinking water without causing unacceptable risk to human health.
Navigable Waters Waters subject to the ebb and flow of the tide and/or used to transport interstate or foreign commerce.
A determination of navigability, once made, applies over the entire surface of the waterbody, and is not changed by later actions or events which impede or destroy navigable capacity.
In Arkansas, recreational use such as fishing or canoeing may result in a waterbody being classified as navigable.
Non-Domestic Wastewater Any wastewater that is commercial, industrial or agricultural in origin, excluding food establishments.
The most common types of facilities permitted for subsurface disposal of non-domestic wastewater are car and truck washes, slaughter houses and Laundromats.
Nonpoint Source Pollution Water pollution coming from diffused points of discharge such as runoff from parking lots, agricultural fields, lawns, home gardens, construction, mining and logging operations.
System A water system which supplies water to 25 or more of the same people at least six months per year in places other than their residences.
Some examples are schools, factories, office buildings and hospitals which have their own water systems.
Perched Water Table A water table that is positioned above the normal water table for an area because of the presence of an impermeable rock layer.
Point Source Pollution Water pollution from clearly discernible discharge points such as pipes, wells, containers, manure storage systems, boats or other watercraft.
Potable Water Water that is suitable for drinking.
Precipitation Any form of water such as rain, snow, hail, sleet, dew and frost.
Public Water System Any water system which provides water to at least 25 people for at least 60 days annually.
Riparian Doctrine The rights of an owner whose land abuts water.
These rights differ from state to state and often depend on a state's classification of a waterbody.
Under this doctrine, persons who own land adjacent to a stream have the right to make reasonable use of water from the stream as long as their use does not impair the rights of other riparian landowners.
Riparian rights cannot be sold or transferred for use on nonriparian land.
Runoff The movement of water across the soil surface that occurs when water collects at a rate faster than it can infiltrate the soil.
Stormwater Water that is generated by a rainfall event.
The U.S.
Environmental Protection Agency estimates that at least 50 percent of the nation's water pollution is caused by stormwater runoff.
Surface Water Water that is on the earth's surface, such as in a stream, river, lake or reservoir.
Total Maximum Daily Load  A calculation of the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards, and an allocation of that amount to the pollutant's sources.
Transient, Non-Community Water System A water system which provides water in a place such as a gas station or campground where people do not
 remain for long periods of time.
These systems do not have to test or treat their water for contaminants which pose long-term health risks because fewer than 25 people drink the water over a long period.
Transpiration The emission of water vapor from the leaves of plants.
Unconfined Aquifer An aquifer whose upper water surface  is at atmospheric pressure, and thus is able to rise and fall.
Wastewater The spent or used water of a community or industry containing dissolved and suspended matter.
Watershed The land area that drains water to a particular stream, river or lake.
It is a land feature that can be identified by tracing a line along the highest elevations between two areas on a map, often a ridge.
Large watersheds like the Mississippi River basin contain thousands of smaller watersheds.
Wetland Land that is saturated with water and contains plants and animals that are adapted to living on, near or in water.
Wetlands have special hydric soils and are usually located between a body of water and land.
Wetlands Reserve Program  -
 A voluntary incentive program administered by the Natural Resources Conservation Service that provides technical and financial assistance to eligible landowners to address wetland, wildlife habitat, soil, water and related natural resource concerns on private land in an environmentally beneficial and cost-effective manner.
Wildlife Habitat Incentives Program  -
 A voluntary program administered by the Natural Resources Conservation Service that encourages the creation of high-quality wildlife habitats that support wildlife populations of national, state, tribal and local significance.
The University of Arkansas Division of Agriculture's Public Policy Center provides timely, credible, unbiased research, analyses and education on current and emerging public issues.
The Arkansas Water Primer Fact Sheet Series was funded by a grant from the U.S.
Department of Agriculture with additional financial assistance from the University of Arkansas Division of Agriculture.
Original research for the Series was provided by Janie Hipp, LL.M., and adapted by Tom Riley, associate professor and director of the University of Arkansas Division of Agriculture's Public Policy Center, and Lorrie Barr, program associate, University of Arkansas Division of Agriculture's Public Policy Center.
Table II.
Total available water in top 4 feet if soil is at field capacity and minimum balances at physiological maturity.
For fine sands, the available water in 1 foot of soil at 100% of available water is 1.0 in/ft, the available water in top 4 feet at 100% of available water is 4.0 in/4 ft, and minimum balance in top 4 feet at 40% of available water is 1.6 in/ft.
For loamy sands, the available water in 1 foot of soil at 100% of available water is 1.1 in/ft, the available water in top 4 feet at 100% of available water is 4.4 in/4 ft, and minimum balance in top 4 feet at 40% of available water is 1.8 in/ft.
For sandy loams, the available water in 1 foot of soil at 100% of available water is 1.4 in/ft, the available water in top 4 feet at 100% of available water is 5.6 in/4 ft, and minimum balance in top 4 feet at 40% of available water is 2.2 in/ft.
Drought symptoms in corn: Corn leaf rolling is the primary symptom of drought.
Greying of leaf tissue will occur under extremely severe conditions.
The earlier leaf rolling occurs in the day or the longer the duration of leaf rolling the greater the stress the crop is under.
Yield loss estimates are assumed when drought stress occurs for four consecutive days or more.
HARD HOSE AND CABLE TOW TRAVELER
 North Carolina Cooperative Extension Service
 North Carolina State University
 HARD HOSE AND CABLE TOW TRAVELER
 Land application equipment used on animal production farms must be field calibrated or evaluated in accordance with existing design charts and tables according to state rules that went into effect September 1, 1996.
Technical Specialist certifying waste management plans after September 1, 1996, must also certify that operators have been provided calibration and adjustment guidance for all land application equipment.
The rules apply to irrigation sysitems as well as all other types of liquid, slurry, or solid application equipment.
Information presented in manufacturers' charts are based on average operating conditions for relatively new equipment.
Discharge rates and application rates change over time as equipment ages and components wear.
As a result, equipment should be field calibrated regularly to ensure that application rates and uniformity are consistent with values used during the system design and given in manufacturers' specifications.
Field calibration involves collection and measurement of the material being applied at several locations in the application area.
This publication contains step-by-step guidelines for field calibration of hard hose and cable tow traveler irrigation systems.
Operating an irrigation system differently than assumed in the design will alter the application rate, uniformity of coverage, and subsequently the application uniformity.
Operating with excessive pressure results in smaller droplets, greater potential for drift, and accelerates wear of the sprinkler nozzle.
Pump wear tends to reduce operating pressure and flow.
With continued use, nozzle wear results in an increase in the nozzle opening, which will increase the discharge rate while decreasing the wetted diameter.
Clogging of nozzles or crystallization of main lines can result in increased pump pressure but reduced flow at the gun.
Plugged intakes will reduce operating pressure.
An operating pressure below design pressure greatly reduces the coverage diameter and application uniformity.
Field calibration helps ensure that nutrients from animal waste are applied uniformly and at proper rates.
The calibration of a hard hose or cable tow system involves setting out collection containers, operating the system, measuring the amount of wastewater collected in each container, and then computing the
 average application volume and application uniformity.
An in-line flow meter installed in the main irrigation line provides a good estimate of the total volume pumped from the lagoon during each irrigation cycle.
The average application depth can be determined by dividing the pumped volume by the application area.
The average application depth is computed from the formula:
 Average application depth  = Volume pumped  27,154  X Application area 
 The average application depth is the average amount applied throughout the field.
Unfortunately, sprinklers do not apply the same depth of water throughout their wetted diameter.
Under normal operating conditions, application depth decreases towards the outer perimeter of the wetted diameter.
Big gun sprinkler systems typically have overlap based on a design sprinkler spacing of 70 to 80 percent of the wetted sprinkler diameter to compen-
 sate for the declining application along the outer perimeter.
When operated at the design pressure, this overlap results in acceptable application uniformity.
When operated improperly, well-designed systems will not provide acceptable application uniformity.
For example, if the pressure is too low, the application depth will be several times higher near the center of sprinkler and water will not be thrown as far from the sprinkler as indicated in manufacturers' charts.
Even through the average application depth may be acceptable, some areas receive excessively high application while others receive no application at all.
When applying wastewater high in nutrients, it is important to determine the application uniformity.
Collection containers distributed throughout the application area must be used to evaluate application uniformity.
Many types of containers can be used to collect flow and determine the application uniformity.
Standard rain gauges work best and are recommended because they already have a graduated scale from which to read the application depth.
Pans, plastic buckets, jars, or anything with a uniform opening and cross section can be used provided the container is deep enough  to prevent splash and excessive evaporation, and the liquid collected can be easily transferred to a scaled container for measuring.
All containers should be the same size and shape to simplify application depth computations.
All collection containers should be set up at the same height relative to the height of the sprinkler nozzle.
Normally, the top of each container should be no more than 36 inches above the ground.
Collectors should be located SO that there is no interference from the crop.
The crop canopy should be trimmed to preclude interference or splash into the collection container.
Calibration should be performed during periods of low evaporation.
Best times are before 10 a.m.
or after 4 p.m.
on days with light wind.
On cool, cloudy days the calibration can be performed anytime when wind velocity is less than 5 mph.
The volume  collected during calibration should be read soon after the sprinkler gun cart has moved one wetted radius past the collection gauges to minimize evaporation from the rain gauge.
Where a procedure must be performed more than once, containers should be read and values recorded immediately after each setup.
Calibration Setup for Hard Hose and Cable Tow Traveling Guns
 Hard hose and cable tow traveling guns are calibrated by placing a row  of collection containers or gauges perpendicular to the direction of travel, Figure 1.
The outer gauge on each end of the row should extend past the furthest distance the gun will throw wastewater to ensure that the calibration is performed on the "full" wetted diameter of the gun sprinkler.
Multiple rows increase the accuracy of the calibration.
Containers should be spaced no further apart than 1/16 of the wetted diameter of the gun sprinkler not to exceed 25 feet.
At least 16 gauges should be used in the calibration.
Sixteen gauges will be adequate except for large guns where the wetted diameter exceeds 400 feet.
Gauges should be set at least one full wetted diameter of throw from either end of the travel lane, as shown in Figure 1.
The system should be operated such that the minimum travel distance of the gun cart exceeds the wetted diameter of throw.
Application volumes should be read as soon as the last gauges stop being wetted.
HARD HOSE AND CABLE TOW TRAVELER IRRIGATION SYSTEMS
 Figure 1.
General layout and orientation of collection gauges for calibration of a hard hose and cable tow traveler irrigation systems.
1.
Determine the wetted diameter of the gun.
2.
Determine the number of collection gauges and spacing between gauges.
For a wetted diameter of 320 feet, the rain gauge spacing should not exceed 20 feet..
3.
Label gauges outward from the gun cart as either left or right 
 4.
Set out gauges along a row as labeled and shown in Figure 1, equally spaced at the distance determined
 in item 2.
The row should be at least one wetted diameter from either end of the pull.
The first gauge on each side of the travel lane should be 1/2 the gauge spacing from the center of the lane.
For a gauge spacing of 20 feet, L1 and R1 should be 10 feet from the center of the lane.
5.
Operate the system for the time required for the gun to completely pass all collection containers.
Record the "starting" time that wastewater begins to be applied along the row of gauges and the "ending" time when wastewater no longer is being applied anywhere along the row.
Also record the distance traveled in feet for the time of operation.
6.
Immediately record the amounts collected in each gauge.
7.
Identify those gauges that fall outside the effective lane spacing, Figure 2.
This volume is the overlap volume that would be collected when operating the system on the adjacent lane.
8.
Superimpose  the gauges just outside the effective width with the gauges just inside the effective width.
Add the volumes together.
For the layout shown in Figure 2, add the volume  collected in gauge R8  to volume  collected in gauge L5.
Similarly, R7 is added to L6; L8 is added to R5; and L7 is added to R6.
This is now the application volume  within the effective lane spacing adjusted for overlap.
Field Calibration Procedures for Animal Wastewater Application Equipment
 Figure 2.
Accounting for overlap when calibrating a hard hose traveler system.
9.
Add the amounts collected in all gauges and divide by the number of gauges within the effective area.
This is the average application depth  within the effective lane spacing.
Sum of amounts collected in all gauges Average application depth = Number of gauges within effective width
 10.
Calculate the deviation depth for each gauge.
The deviation depth is the difference between each individual gauge value and the average value of all gauges.
Record the absolute value of each deviation depth.
Absolute value means the sign of the number  is dropped and all values are treated as positive.
The symbol for absolute value is a straight thin line.
For example, |2| means treat the number 2 as an absolute value.
It does not mean the number 121.
Because this symbol can lead to misunderstandings, it is not used with numbers in the worksheets at the end of this publication.
The symbol is used in formulas in the text.
Deviation depth = |Depth collected in gauge iaverage application depth|
 "i" refers to the gauge number
 11.
Add amounts in #10 to get "sum of the deviations" from the average depth and divide by the number of gauges to get the average deviation.
Sum of deviations  Average deviation depth = Number of gauges within effective lane spacing
 12.
The precipitation rate  is computed by dividing the average application depth   by the application time  
 Average application depth  Precipitation rate Application time 
 13.
Compute the average travel speed
 Distance traveled  Average travel speed = Time 
 14.
Determine the application uniformity.
The application uniformity is often computed using the mathematical formula referred to as the Christiansen Uniformity Coefficient.
It is computed as follows:
 Average depth  Average deviation  U, = X 100 Average depth 
 15.
Interpret the calibration results.
The higher the index value, the more uniform the application.
An index of 100 would mean that the uniformity is perfect the exact same amount was collected in every gauge.
For travelers with proper overlap and operated in light wind, an application uniformity greater than 85 is common.
Application uniformity between 70 to 85 is in the "good" range and is acceptable for wastewater application.
Generally, an application uniformity below 70 is considered unacceptable for wastewater irrigation using travelers.
If the computed Uc is less than 70, system adjustments are required.
Contact your irrigation dealer or Certified Technical Specialist for assistance.
Table 1.
Example calibration data for a traveling gun system operated in parallel lanes.
Lane spacing 70 percent of sprinkler wetted diameter.
a.
Manufacturers' Specifications: Gun Model 150 Type Taper Bore Nozzle Dia.
0.9 inch Pressure  70 psi Reel 105 psi Wetted diameter 320 ft Effective Spacing 224 ft Flow 197 GPM Hose Size: Length 800 ft Diameter 3 in
 b.
Spacing between collection containers  / 16) = 20 ft
 C.
Number of gauges = 16
 d.
Start of Irrigation event 7:15 a.m.
e.
End of Irrigation event 9:00 a.m.
f.
Duration  105 minutes
 g.
Travel distance 320 feet
 h.
Operate the system and collect data.
Table 1.
Calibration Data 
 Gauge	Distance	Volume	Overlap	Corrected	Deviation
 No.
from Center	Collected	Adjustment	Volume	from Average*
 				
 L1	10	.94	.94	.235 
 L2	30	.80	.80	.095 
 L3	50	.59	.59	.115 
 L4	70	.61	.61	.095
 L5	90	.50	.13	.63	.075
 L6	110	.42	.20	.62	.085
 R1	10	.73	.73	.025
 R2	30	.81	.81	.105
 R3	50	.92	.92	.215
 R4	70	.64	.64	.065
 R5	90	.50	.07	.57	.135
 R6	110	.27	.33	.60	.105
 *Absolute value; treat all values as positive.
i.
Sum of all volumes collected in #h 8.46 inches j.
Average catch  0.705 inches Distance traveled  320 ft k.
Compute the average travel speed = = 3.04 ft/min Time  105 min average depth  0.705 in I.
Precipitation rate = = = 0.40 in/hr application time  1.75 m.
Sum of deviations from the average catch 1.356 n.
Average deviation from average catch  0.113 O.
Uniformity coefficient 0.705-0.113 X 100 = 84 0.705 p.
Interpret results.
Uniformity coefficient of 84 is in the good range for a traveler system.
No adjustment is necessary.
HARD HOSE AND CABLE TOW TRAVELER IRRIGATION SYSTEMS
 Irrigation System Calibration Data Sheet for Hard Hose Traveler Irrigation System
 a.
Manufacturers' Specifications: Gun Model
 b.
Spacing between collection containers (diameter
  / 16) =
 wetted diameter  Number of gauges =
 d.
Start of Irrigation event
 e.
End of Irrigation event
 h.
Operate the system, collect data,
 and record on the worksheet on page 8.
i.
Sum of all catches
 j.
Average catch 
 Average travel speed =
 I.
Sum of all deviations from the average catch
 m.
Average deviation from average catch
 Interpret the calibration data and make necessary adjustments.
For travelers with proper overlap and operated in light wind, an application uniformity Coefficient greater than 85 is common.
Application uniformity between 70 to 85 is in the "good" range and is acceptable for wastewater application.
Generally, an application uniformity below 70 is considered unacceptable for wastewater irrigation using travelers.
If the computed U is less than 70, system adjustments are required.
Contact your irrigation dealer C or Certified Technical Specialist for assistance.
Gauge	Distance	Volume	Overlap	Corrected	Deviation
 No.
from Center	Collected	Adjustment	Volume	from Average*
 				
 treat all values as positive.
R.O.
Evans, Biological and Agricultural Engineering Extension Specialist J.C.
Barker, Biological and Agricultural Engineering Extension Specialist J.T.
Smith, Biological and Agricultural Engineering Assistant Extension Specialist R.E.
Sheffield, Biological and Agricultural Engineering Extension Specialist
 5,000 copies of this public document were printed at a cost of $1,962, or $.39 per copy.
Published by NORTH CAROLINA COOPERATIVE EXTENSION SERVICE
Dr.
Brent Black, USU Extension Fruit Specialist, Dr.
Robert Hill, USU Extension Irrigation Specialist, and Dr.
Grant Cardon, USU Extension Soils Specialist
 Proper irrigation is essential to maintaining a healthy and productive apple orchard.
Over irrigation slows root growth, increases the potential for iron chlorosis on alkaline soils, and leaches nitrogen, sulfur and boron out of the root zone leading to nutrient deficiencies.
Excessive soil moisture also provides an environment ideal for crown and collar rots.
Over irrigation can also induce excessive vegetative vigor.
Applying insufficient irrigation water results in drought stress and reduced fruit quality.
Apple fruit growth occurs in two distinct phases.
The first phase is primarily a function of cell division and occurs from bloom to about 50 days after bloom.
Second phase growth, from 50 days after bloom to harvest, is mostly due to expansion of existing cells.
This cell expansion is driven by the presence of available water, and occurs during the hottest and driest summer conditions.
Properly managing irrigation is analogous to managing money.
In addition to knowing your current bank balance , it is important to track both expenses  and income.
Bank Balance 
 How big is my bank account?
Water holding capacity
 Field Capacity is the amount of water that can be held in the soil after excess water has percolated out due to gravity.
Permanent Wilting Point is the point at which the water remaining in the soil is not available for uptake by plant roots.
When the soil water content reaches this point, plants die.
Available Water is the amount of water held in the soil between field capacity and permanent wilting point.
Allowable Depletion  is the point where plants begin to experience drought stress.
For apples, the amount of allowable depletion, or the readily available water represents about 50% of the total available water in the soil.
The goal of a well-managed irrigation program is to maintain soil moisture between field capacity and the point of allowable depletion, or in other words, to make sure that there is always readily available water.
Figure 1.
Soil water content from saturated to dry.
Optimal levels for plant growth are between field capacity and allowable depletion.
The amount of readily available water is related to the effective rooting depth of the plant, and the water holding capacity of the soil.
The effective rooting depth depends on soil conditions, variety and rootstock.
Although apple roots can grow to a depth of several yards, nearly all of the roots of a mature tree are typically in the top 30 to 36 inches.
The water holding capacity within that rooting depth is related to soil texture, with coarser soils  holding less water than fine textured soils such as silts and clays.
A deep sandy loam soil at field capacity,
 for example, would contain 1.8 to 2.25 inches of readily available water in an effective rooting depth of 3 feet.
Table 1.
Available water holding capacity for different soil textures, in inches of water per foot of soil.
Available water is the amount of water in the soil between field capacity and permanent wilting point.
Readily available water is approximately 50% of available.
Soil Texture	Available	Readily available 
 	2 ft root depth	3 ft root depth
 Sands and fine sands	0.5 0.75	0.5 0.75	0.75 1.13
 Loamy sand	0.8 1.0	0.8 1.0	1.2 1.5
 Sandy loam	1.2 1.5	1.2 1.5	1.8 2.25
 Loam	1.9 2.0	1.9 2.0	2.85 3.0
 Silt loam, silt	2.0	2.0	3.0
 Silty clay loam	1.9 2.0	1.9 2.0	2.85 3.0
 Sandy clay loam, clay loam	1.7 2.0	1.7 2.0	2.6 3.0
 Figure 2.
The amount of allowable depletion, or the readily available water, represents about 50 percent of the total available water.
What's in the bank?
-Measuring Soil Moisture
 In order to assess soil water content, one needs to monitor soil moisture at several depths, from just below the sod layer or cultivation depth , to about 70 percent of effective rooting depth.
One of the more cost effective and reliable methods for measuring soil moisture is by electrical resistance block, such as the Watermark TM sensor.
These blocks are permanently installed in the soil, and wires from the sensors are attached to a handheld unit that measures electrical resistance.
Resistance measurements are then related to soil water potential, which is an indicator of how hard the plant roots have to "pull" to obtain water from the soil.
The handheld unit reports soil moisture content in centibars, where values close to zero indicate a wet soil and high values represent dry soil.
The relationship between soil water potential and available water differs by soil type.
The maximum range of the sensor is 200 centibars, which covers the range of allowable depletion in most
 soils.
The sensors are less effective in coarse sandy soils, and will overestimate soil water potential in saline soils.
Remember that allowable depletion is 50% of available water, which roughly corresponds to soil water potentials of 50 centibars for a loamy sand soil, and 70 centibars for a loam.
Table 2.
Recommended WatermarkTM sensor values at which to irrigate.
Soil Type	Irrigation Needed
 Loamy sand	40 50
 Sandy loam	50 70
 Silt loam, silt	70 90
 Clay loam or clay	90 120
 Watermark is a registered trademark of Irrometer, Co., Riverside, CA.
Water is lost from the orchard through surface runoff, deep percolation , evaporation from the soil surface, and transpiration through the leaves of the plant.
Of these, the biggest losses are typically due to evaporation and transpiration, collectively known as "evapotranspiration" or ET.
Deep percolation from excess irrigation can be another large loss.
Estimates of ET are based on weather data, including air temperature, relative humidity and wind speed.
Some weather stations in Utah are programmed to calculate and report the ET estimates for alfalfa as a reference crop.
The ET of your crop can be determined by multiplying the ET, by a correction factor
 or crop coefficient  that is specific to your crop and its stage of development.
The Kcrop for apples is shown in Figure 3.
At full bloom , an apple orchard is using about 20% of the amount of water used by the alfalfa reference crop.
Water use increases dramatically until the full canopy is established  when water use is 95% of a reference alfalfa crop.
Water use increases slightly during the second phase of fruit growth  when water use is at 100% of the reference alfalfa crop.
After harvest , water use quickly decreases.
Typical weekly ET values are shown in Table 3.
Calculated ET, for your location can be determined by accessing weather data from a nearby weather station at the following Web site:
 Table 3.
Typical weekly alfalfa reference evapotranspiration  values for Utah locations.
Location	May	June	July	August
 Logan	1.38	1.83	1.94	1.68
 Ogden	1.48	1.98	2.10	1.80
 Spanish Fork	1.48	1.94	2.08	1.74
 Santaquin	1.47	1.92	2.03	1.67
 Moab	1.63	2.08	2.19	1.87
 Cedar City	1.57	1.95	2.04	1.74
 St.
George	1.95	2.40	2.53	2.02
 Income Irrigation and Rainfall
 In Utah's high elevation desert climate, rainfall contributes a small fraction of the in-season water requirements of the crop.
Therefore, regular irrigation is needed to supply orchard water needs.
This irrigation water can be supplied by flood, furrow, impact sprinklers, drip lines or microsprinklers.
Whichever irrigation system you utilize, it is important to calibrate your system SO that you know precisely how much water is being applied.
With sprinklers and microsprinklers, the simplest way to do this is to place catch cans in multiple locations in your planting and collect water for a set period of time.
The amount of water collected over time will give you an application rate , and differences in water collected among the catch cans will tell you how uniform the application is within your planting.
When trying to determine application uniformity, it is best to measure output at both ends of your irrigation system.
Also, if your planting is on a slope, you should measure output at the highest and lowest points of your field.
Elevation differences and the distance the water travels through the irrigation lines both affect water pressure, and consequently the flow rate at the nozzle.
If you have trickle irrigation, you can place catch cans under the emitters and determine flow rate for each emitter.
Flow rate from each emitter and emitter spacing can be used to calculate rate per area.
The efficiency of your system is a measure of how much you have to over water the wettest spots in the orchard to get adequate water to the dry spots.
Efficiency is related to the uniformity of application and to the amount of evaporation that occurs before the water can move into the soil.
A well-designed microsprinkler or drip system can be 70 to 90% efficient.
Overhead sprinkler systems are typically 60 to 75% efficient, while flood and furrow irrigation is typically 30 to 50% efficient.
Following is an example of how to calculate water needs for a mature apple orchard in late July.
The orchard is on a deep sandy loam soil with row middles planted to grass cover.
ETr values are 2.10 inches per week.
Crop coefficient is 1.0.
= ET, X Kcrop
 ET 2.10 inches/week * 1.0 = 2.1 inches/week
 Soil storage capacity 
 The total storage capacity for readily available water over an effective rooting depth of 3 feet is between 1.8 and 2.25 inches.
1.8 to 2.25 inches / 2.1 inches per week = 0.86 to 1.07 weeks or 6 to 7 days between irrigations.
Restated, the soil moisture in the rootzone will go from field capacity to plant stress levels in 6 days.
To recharge the soil profile, you will need to add 1.8 inches of water.
Assuming a microsprinkler irrigation system with an efficiency of 90%, 2.0 acre inches of water application will be required per acre for each watering.
Good irrigation management requires:
 1.
An understanding of the soil-plant-water relationship
 2.
A properly designed and maintained irrigation system, and a knowledge of the efficiency of the system
 3.
Proper timing based on
 a.
Soil water holding capacity
 b.
Weather and its effects on crop demand
 C.
Stage of crop growth.
Each of these components requires a commitment to proper management.
Proper management will lead to the
 maximum yields per available water and will optimize the long term health and productivity of your planting.
Going electric to deal with the high cost of diesel
 Over the past weeks, radio and tv have been all the buzz with the record high costs of gasoline and diesel fuel as well as the high cost of food in the United States and worldwide.
A few reporters have continued the story to discuss the impact of these high prices on other commodities such as fertilizer and crop protection chemicals.
In Louisiana, these high costs also have increased the cost of irrigating crops.
The simple fact is that it takes energy to pump and move water, says Ron Sheffield a water resources engineer with the LSU AgCenter.
Be it from a 200-foot-deep well or from the bayou next to a rice field, it takes energy to move that water where we want it.
More than 90 percent of farms in Louisiana irrigate with diesel-powered pumps.
As the cost of diesel reaches record highs, so does the cost of irrigation.
This is compounded by the inherent inefficiency of diesel engines in converting the energy in the fuel to pumping power.
Diesel engines are only 25-37% efficient, compared to the 85-92% efficiency of electric motors.
This inefficiency is wasted energy and wasted money says Sheffield.
The cost of diesel today is around $3.75 a gallon.
The equivalent cost of electricity is 26.5 cents per kilowatt hour to pump the same amount water.
Anyone in the country can buy electricity cheaper than that.
Unfortunately, this is the simple side of the equation.
Switching from diesel to electric pumps in not an easy decision.
It depends on the availability of 3-phase electrical power in an area and the demand and contract charges your local utility may require.
The cost of bringing power from the side of a road to where a pump or well is located can cost anywhere from $7 to $10 per foot.
Luckily, several utilities have developed plans to allow irrigators to pay off the installation over a 5-year period.
The cost of electrical equipment is also a consideration.
A 100-hp electric motor and a basic control panel will cost approximately $6,500.
The switch from diesel to electric pumping needs to be a well-thought-out business decision.
Irrigation companies, the Natural Resources Conservation Service  and the LSU AgCenter can assist producers in collecting the necessary information.
Producers also need to talk with their electrical utility to see what options are available.
But the ultimate decision, if this is a profitable decision, lies with the farmer and his or her financial advisers.
However, with the cost of crude oil going up again today, more and more irrigators are seeing that going electric will help them deal with todays high cost of production.
Irrigation Water Quality Standards and Salinity Management Strategies
 Irrigation Water Quality Standards and Salinity Management
 Nearly all waters contain dissolved salts and trace elements, many of which result from the natural weathering of the earth's surface.
In addition, drainage waters from irrigated lands and effluent from city sewage and industrial waste water can impact water quality.
In most irrigation situations, the primary water quality concern is salinity levels, since salts can affect both the soil structure and crop yield.
However, a number of trace elements are found in water which can limit its use for irrigation.
*Associate Professor and Extension Agricultural Engineer, Department of Agricultural Engineering, The Texas A&M System, College Station, Texas 77843-2117.
Generally, "salt" is thought of as ordinary table salt.
How-ever, many types of salts exist and are commonly found in Texas waters.
Most salinity problems in agriculture result directly from the salts carried in the irrigation water.
The process at work is illustrated in Figure 1, which shows a beaker of water containing a salt concentration of 1 percent.
As water evaporates, the dissolved salts remain, resulting in a solution with a higher concentration of salt.
The same process occurs in soils.
Salts as well as other dissolved substances begin to accumulate as water evaporates from the surface and as crops withdraw water.
Water Analysis: Units, Terms and Sampling
 Numerous parameters are used to define irrigation water quality, to assess salinity hazards, and to determine appropriate management strategies.
A complete water quality analysis will include the determination of:
 1) the total concentration of soluble salts,
 2) the relative proportion of sodium to the other cations,
 3) the bicarbonate concentration as related to the concentration of calcium and magnesium, and
 Table 1.
Kinds of salts normally found in irrigation waters, with chemical symbols and approximate proportions of each salt.
1 
 Chemical name	Chemical symbol	Approximate proportion
 of total salt content
 Sodium chloride	NaCl	Moderate to large
 Sodium sulfate	Na2SO4	Moderate to large
 Calcium chloride	CaCl2	Moderate
 Calcium sulfate 	CaSO4 2H2O	Moderate to small
 Magnesium chloride	MgCl2	Moderate
 Magnesium sulfate	MgSO4	Moderate to small
 Potassium chloride	KCI	Small
 Potassium sulfate	K2SO4	Small
 Sodium bicarbonate	NaHCO	Small
 Calcium carbonate	CaCO	Very Small
 Sodium carbonate	NaCO3	Trace to none
 Borates	BO-3	Trace to none
 Nitrates	NO-3	Small to none
 1 Waters vary greatly in amounts and kinds of dissolved salts.
This water typifies many used for irrigation in Texas.
Figure 1.
Effect of water evaporation on the concentration of salts in solution.
A liter is 1.057 quarts.
Ten grams is.035 ounces or about 1 teaspoonful.
4) the concentrations of specific elements and compounds.
The amounts and combinations of these substances define the suitability of water for irrigation and the potential for plant toxicity.
Table 2 defines common parameters for analyzing the suitability of water for irrigation and provides some useful conversions.
When taking water samples for laboratory analysis, keep in mind that water from the same source can vary in quality with time.
Therefore, samples should be tested at intervals throughout the year, particularly during the potential irrigation period.
The Soil and Water Testing Lab at Texas A&M University can do a complete salinity analysis of irrigation water and soil samples, and will provide a detailed computer printout on the interpretation of the results.
Contact your county Extension agent for forms and information or contact the Lab at  845-4816.
Two Types of Salt Problems
 Two types of salt problems exist which are very different: those associated with the total salinity and those associated with sodium.
Soils may be affected only by salinity or by a combination of both salinity and sodium.
Water with high salinity is toxic to plants and poses a salinity hazard.
Soils with high levels of total salinity are call saline soils.
High concentrations of salt in the soil can result in a "physiological" drought condition.
That is, even though the field appears to have plenty of moisture, the plants wilt because the roots are unable to absorb the water.
Water salinity is usually measured by
 the TDS  or the EC.
TDS is sometimes referred to as the total salinity and is measured or expressed in parts per million  or in the equivalent units of milligrams per liter.
EC is actually a measurement of electric current and is reported in one of three possible units as given in Table 2.
Subscripts are used with the symbol EC to identify the source of the sample.
ECjv is the electric conductivity of the irrigation water.
ECe is the electric conductivity of the soil as measured in a soil sample  taken from the root zone.
EC is the soil salinity of the saturated extract taken from below the root zone.
EC is used to determine the salinity of the drainage water which leaches below the root zone.
Table 2.
Terms, units, and useful conversions for understanding
 water quality analysis reports.
a.
EC	electric conductivity	mmhos/cm
 b.
TDS	total dissolved solids	mg/L
 a.
SAR	sodium adsorption ratio
 b.
ESP	exchangeable sodium percentage
 Determination	Symbol	Unit of measure	Atomic weight
 calcium	Ca	mol/m3	40.1
 magnesium	Mg	mol/m3	24.3
 sodium	Na	mol/m3	23.0
 potassium	K	mol/m3	39.1
 bicarbonate	HCO	mol/m3	61.0
 sulphate	SO4	mol/m3	96.1
 chloride	CI	mol/m3	35.5
 carbonate	CO3	mol/m3	60.0
 nitrate	NO3	mg/L	62.0
 boron	B	mg/L	10.8
 1 dS/m = 1 mmhos/cm = 1000 umhos/cm 1 mg/L = 1 ppm TDS  = EC  X 640 for EC < 5 dS/m TDS  X 800 for EC > 5 dS/m TDS  = TDS  X 2.72 Concentration  = Concentration  times the atomic weight
 Sum of cations/anions  = EC  X 10
 Key mg/L = milligrams per liter ppm = parts per million dS/m = deci Siemens per meter at 25 C
 Irrigation water containing large amounts of sodium is of special concern due to sodium's effects on the soil and poses a sodium hazard.
Sodium hazard is usually expressed in terms of SAR or the sodium adsorption ratio.
SAR is calculated from the ratio of sodium to calcium and magnesium.
The latter two ions are important since they tend to counter the
 effects of sodium.
For waters containing significant amounts of bicarbonate, the adjusted sodium adsorption ratio (SARad is sometimes used.
Continued use of water having a high SAR leads to a breakdown in the physical structure of the soil.
Sodium is adsorbed and becomes attached to soil particles.
The soil then becomes hard and compact when dry and increas-
 ingly impervious to water penetration.
Fine textured soils, especially those high in clay, are most subject to this action.
Certain amendments may be required to maintain soils under high SARs.
Calcium and magnesium, if present in the soil in large enough quantities, will counter the effects of the sodium and help maintain good soil properties.
Soluble sodium per cent  is also used to evaluate sodium hazard.
SSP is defined as the ration of sodium in epm  to the total cation epm multiplied by 100.
A water with a SSP greater than 60 per cent may result in sodium accumulations that will cause a breakdown in the soil's physical properties.
lons, Trace Elements and Other Problems
 A number of other substances may be found in irrigation water and can cause toxic reactions in plants.
After sodium, chloride and boron are of most concern.
In certain areas of Texas, boron concentrations are excessively high and render water unsuitable for irrigations.
Boron can also accumulate in the soil.
Crops grown on soils having an imbalance of calcium and magnesium may also exhibit toxic symptoms.
Sulfate salts affect sensitive crops by limiting the uptake of calcium and increasing the adsorption of sodium and potassium, resulting in a disturbance in the cationic balance within the plant.
The bicarbonate ion in soil solution harms the mineral nutrition of the plant through its effects on the uptake and metabolism of nutrients.
High concentrations of potassium may introduce a magnesium deficiency and iron chlorosis.
An imbalance of magnesium and potassium may be toxic, but the effects of both can be reduced by high calcium levels.
Table 3.
Recommended limits for constituents in reclaimed water for irrigation.
(Adapted from
 Rowe and Abdel-Magid, 1995)
 Constituent	Long-term	Short-term	Remarks
 use 	use 
 Aluminum 	5.0	20	Can cause nonproductivity in acid soils, but soils at pH 5.5 to 8.0
 will precipitate the ion and eliminate toxicity.
Arsenic 	0.10	2.0	Toxicity to plants varies widely, ranging from 12 mg/L for Sudan
 grass to less than 0.05 mg/L for rice.
Beryllium 	0.10	0.5	Toxicity to plants varies widely, ranging from 5 mg/L for kale to
 0.5 mg/L for bush beans.
Boron 	0.75	2.0	Essential to plant growth, with optimum yields for many obtained
 at a few-tenths mg/L in nutrient solutions.
Toxic to many sensitive
 plants  at 1 mg/L.
Most grasses relatively tolerant at
 2.0 to 10 mg/L.
Cadmium 	0.01	0.05	Toxic to beans, beets, and turnips at concentrations as low as 0.1
 mg/L in nutrient solution.
Conservative limits recommended.
Chromium 	0.1	1.0	Not generally recognized as essential growth element.
Conservative
 limits recommended due to lack of knowledge on toxicity to plants.
Cobalt 	0.05	5.0	Toxic to tomato plants at 0.1 mg/L in nutrient solution.
Tends to be
 inactivated by neutral and alkaline soils.
Copper 	0.2	5.0	Toxic to a number of plants at 0.1 to 1.0 mg/L in nutrient solution.
Fluoride 	1.0	15.0	Inactivated by neutral and alkaline soils.
Iron 	5.0	20.0	Not toxic to plants in aerated soils, but can contribute to soil acidifi-
 cation and loss of essential phosphorus and molybdenum.
Lead 	5.0	10.0	Can inhibit plant cell growth at very high concentrations.
Lithium 	2.5	2.5	Tolerated by most crops at up to 5 mg/L; mobile in soil.
Toxic to
 citrus at low doses recommended limit is 0.075 mg/L.
Manganese 	0.2	10.0	Toxic to a number of crops at a few-tenths to a few mg/L in acid
 Molybdenum 	0.01	0.05	Nontoxic to plants at normal concentrations in soil and water.
Can
 be toxic to livestock if forage is grown in soils with high levels of
 Nickel 	0.2	2.0	Toxic to a number of plants at 0.5 to 1.0 mg/L; reduced toxicity at
 neutral or alkaline pH.
Selenium 	0.02	0.02	Toxic to plants at low concentrations and to livestock if forage is
 grown in soils with low levels of added selenium.
Vanadium 	0.1	1.0	Toxic to many plants at relatively low concentrations.
Zinc 	2.0	10.0	Toxic to many plants at widely varying concentrations; reduced
 toxicity at increased pH  and in fine-textured or organic
 Classification of Irrigation Water
 Several different measurements are used to classify the suitability of water for irrigation, including ECiw, the total dissolved solids, and SAR.
Some permissible limits for classes of irrigation water are given in Table 4.
In Table 5, the sodium hazard of water is ranked from low to very high based on SAR values.
Classification of Salt-Affected Soils
 Both EC and SAR are commonly used to classify salt-affected soils  normally have a pH value below 8.5, are relatively low in sodium and contain principally sodium, calcium and magnesium chlorides and sulfates.
These compounds cause the white crust which forms on the surface
 Table 6.
Classification of salt-affected soils based on analysis of
 saturation extracts.
Criteria	Normal	Saline	Sodic	Saline-Sodic
 ECe 	<4	>4	<4	>4
 SAR	<13	<13	>13	>13
 and the salt streaks along the furrows.
The compounds which cause saline soils are very soluble in water; therefore, leaching is usually quite effective in reclaiming these soils.
Sodic soils  generally have a pH value between 8.5 and 10.
These soils are called "black alkali soils" due to their darkened appearance and smooth, slick looking areas caused by the dispersed condition.
In sodic soils, sodium has destroyed the permanent structure which tends to make the soil impervious to water.
Thus, leaching alone will not be effective unless the high salt dilution method or amendments are used.
Table 4.
Permissible limits for classes of irrigation water.
Concentration, total dissolved solids
 Classes of water	Electrical	Gravimetric ppm
 Class 1, Excellent	250	175
 Class 2, Good	250-750	175-525
 Class 3, Permissible 1	750-2,000	525-1,400
 Class 4, Doubtful	2,000-3,000	1,400-2,100
 Class 5, Unsuitable	3,000	2,100
 *Micromhos/cm at 25 degrees C.
1	Leaching needed if used
 2	Good drainage needed and sensitive plants will have difficulty obtaining
 Water Quality Effects on Plants and Crop Yield
 Table 7 gives the expected yield reduction of some crops for various levels of soil salinity as measured by EC under normal growing conditions, and Table 8 gives potential yield reduction due to water salinity levels.
Generally forage crops are the most resistant to salinity, followed by field crops, vegetable crops, and fruit crops which are generally the most sensitive.
Table 9 lists the chloride tolerance of a number of agricultural crops.
Boron
 is a major concern in some areas.
While a necessary nutrient, high boron levels cause plant toxicity, and concentrations should not exceed those given in Table 10.
Some information is available on the susceptibility of crops to foliar injury from spray irrigation with water containing sodium and chloride.
The tolerance of crops to sodium as measured by the exchangeable sodium percentage  is given in Table 12.
Table 5.
The sodium hazard of water based on SAR Values.
SAR values	Sodium hazard of water	Comments
 1-10	Low	Use on sodium sensitive crops such as avocados
 10 18	Medium	Amendments  and leaching needed.
18 26	High	Generally unsuitable for continuous use.
> 26	Very High	Generally unsuitable for use.
Table 7.
Soil salinity tolerance levels 1 for different crops.
Crop	100%	90%	75%	50%	Maximum ECe
 Barley	8.0	10.0	13.0	18.0	28
 Bean 	1.0	1.5	2.3	3.6	7
 Broad bean	1.6	2.6	4.2	6.8	12
 Corn	1.7	2.5	3.8	5.9	10
 Cotton	7.7	9.6	13.0	17.0	27
 Cowpea	1.3	2.0	3.1	4.9	9
 Flax	1.7	2.5	3.8	5.9	10
 Groundnut	3.2	3.5	4.1	4.9	7
 Rice 	3.0	3.8	5.1	7.2	12
 Safflower	5.3	6.2	7.6	9.9	15
 Sesbania	2.3	3.7	5.9	9.4	17
 Sorghum	4.0	5.1	7.2	11.0	18
 Soybean	5.0	5.5	6.2	7.5	10
 Sugar beet	7.0	8.7	11.0	15.0	24
 Wheat	6.0	7.4	9.5	13.0	20
 Bean	1.0	1.5	2.3	3.6	7
 Beet	4.0	5.1	6.8	9.6	15
 Broccoli	2.8	3.9	5.5	8.2	14
 Cabbage	1.8	2.8	4.4	7.0	12
 Cantaloupe	2.2	3.6	5.7	9.1	16
 Carrot	1.0	1.7	2.8	4.6	8
 Cucumber	2.5	3.3	4.4	6.3	10
 Lettuce	1.3	2.1	3.2	5.2	9
 Onion	1.2	1.8	2.8	4.3	8
 Pepper	1.5	2.2	3.3	5.1	9
 Potato	1.7	2.5	3.8	5.9	10
 Radish	1.2	2.0	3.1	5.0	9
 Spinach	2.0	3.3	5.3	8.6	15
 Sweet corn	1.7	2.5	3.8	5.9	10
 Sweet potato	1.5	2.4	3.8	6.0	11
 Tomato	2.5	3.5	5.0	7.6	13
 Alfalfa	2.0	3.4	5.4	8.8	16
 Barley hay	6.0	7.4	9.5	13.0	20
 Bermudagrass	6.9	8.5	10.8	14.7	23
 Clover, Berseem	1.5	3.2	5.9	10.3	19
 Corn 	1.8	3.2	5.2	8.6	16
 Harding grass	4.6	5.9	7.9	11.1	18
 Orchard grass	1.5	3.1	5.5	9.6	18
 Perennial rye	5.6	6.9	8.9	12.2	19
 Sudan grass	2.8	5.1	8.6	14.4	26
 Tall fescue	3.9	5.8	8.61	3.3	23
 Tall wheat grass	7.5	9.9	13.3	19.4	32
 Trefoil, big	2.3	2.8	3.6	4.9	8
 Trefoil, small	5.0	6.0	7.5	10.0	15
 Wheat grass	7.5	9.0	11.0	15.0	22
 Salinity and Growth Stage
 Many crops have little tolerance for salinity during seed germination, but significant tolerance during later growth stages.
Some crops such as barley, wheat and corn are known to be more sensitive to salinity during the early growth period than during germination and later growth periods.
Sugar beet and safflower are relatively more sensitive during germination, while the tolerance of soybeans may increase or decrease during different growth periods depending on the variety.
Leaching for Salinity Management
 Soluble salts that accumulate in soils must be leached below the crop root zone to maintain productivity.
Leaching is the basic management tool for controlling salinity.
Water is applied in excess of the total amount used by the crop and lost to evaporation.
The strategy is to keep the salts in solution and flush them below the root zone.
The amount of water needed is referred to as the leaching requirement or the leaching fraction.
Excess water may be applied with every irrigation to provide the water needed for leaching.
However, the time interval between leachings does not appear to be critical provided that crop tolerances are not exceeded.
Hence, leaching can be accomplished with each irrigation, every few irrigations, once yearly, or even longer depending on the severity of the salinity problem and salt tolerance of the crop.
An occasional or annual leaching event where water is ponded on the surface is an easy and effective method for controlling soil salinity.
In some areas, normal rainfall provides adequate leaching.
Table 7.
Soil salinity tolerance levels 1 for different crops.
Crop	100%	90%	75%	50%	Maximum ECe
 Almond	1.5	2.0	2.8	4.1	7
 Apple, Pear	1.7	2.3	3.3	4.8	8
 Apricot	1.6	2.0	2.6	3.7	6
 Avocado	1.3	1.8	2.5	3.7	6
 Date palm	4.0	6.8	10.9	17.9	32
 Pomegranate	2.7	3.8	5.5	8.4	14
 Grape	1.5	2.5	4.1	6.7	12
 Grapefruit	1.8	2.4	3.4	4.9	8
 Lemon	1.7	2.3	3.3	4.8	8
 Orange	1.7	2.3	3.2	4.8	8
 Peach	1.7	2.2	2.9	4.1	7
 Plum	1.5	2.1	2.9	4.3	7
 Strawberry	1.0	1.3	1.8	2.5	4
 Walnut	1.7	2.3	3.3	4.8	8
 1	Based on the electrical conductivity of the saturated extract taken from a
 root zone soil sample  measured in mmhos/cm.
a	During germination and seedling stage ECe should not exceed 4 to 5
 mmhos/cm except for certain semi-dwarf varieties.
b	During germination ECe should not exceed 3 mmhos/cm.
Table 8.
Irrigation water salinity tolerances 1 for different crops.
Crop	100%	90%	75%	50%
 Barley	5.0	6.7	8.7	12.0
 Bean 	0.7	1.0	1.5	2.4
 Broad bean	1.1	1.8	2.0	4.5
 Corn	1.1	1.7	2.5	3.9
 Cotton	5.1	6.4	8.4	12.0
 Cowpea	0.9	1.3	2.1	3.2
 Flax	1.1	1.7	2.5	3.9
 Groundnut	2.1	2.4	2.7	3.3
 Rice 	2.0	2.6	3.4	4.8
 Safflower	3.5	4.1	5.0	6.6
 Sesbania	1.5	2.5	3.9	6.3
 Sorghum	2.7	3.4	4.8	7.2
 Soybean	3.3	3.7	4.2	5.0
 Sugar beet	4.7	5.8	7.5	10.0
 Wheat	4.0	4.9	6.4	8.7
 Bean	0.7	1.0	1.5	2.4
 Beet	2.7	3.4	4.5	6.4
 Broccoli	1.9	2.6	3.7	5.5
 Determining Required Leaching Fraction
 The leaching fraction is commonly calculated using the following relationship:
 LF EC ECiw  =
 LF = leaching fraction the fraction of applied irrigation water that must be leached through the root zone
 ECiw = electric conductivity of the irrigation water
 EC = the electric conductivity of the soil in the root zone
 Equation  can be used to determine the leaching fraction necessary to maintain the root zone at a targeted salinity level.
If the amount of water available for leaching is fixed, then the equation can be used to calculate the salinity level that will be maintained in the root zone with that amount of leaching.
Please note that equation  simplifies a complicated soil water process.
ECe should be checked periodically and the amount of leaching adjusted accordingly.
Based on this equation, Table 13 lists the amount of leaching needed for different classes of irrigation waters to maintain the soil salinity in the root zone at a desired level.
However, additional water must be supplied because of the inefficiencies of irrigation systems , as well as to remove the existing salts in the soil.
Table 8.
Irrigation water salinity tolerances  for different crops.
Crop	100%	90%	75%	50%
 Cabbage	1.2	1.9	2.9	4.6
 Cantaloupe	1.5	2.4	3.8	6.1
 Carrot	0.7	1.1	1.9	3.1
 Cucumber	1.7	2.2	2.9	4.2
 Lettuce	0.9	1.4	2.1	3.4
 Onion	0.8	1.2	1.8	2.9
 Pepper	1.0	1.5	2.2	3.4
 Potato	1.1	1.7	2.5	3.9
 Radish	0.8	1.3	2.1	3.4
 Spinach	1.3	2.2	3.5	5.7
 Sweet corn	1.1	1.7	2.5	3.9
 Sweet potato	1.0	1.6	2.5	4.0
 Tomato	1.7	2.3	3.4	5.0
 Alfalfa	1.3	2.2	3.6	5.9
 Barley hay	4.0	4.9	6.3	8.7
 Bermudagrass	4.6	5.7	7.2	9.8
 Clover, Berseem	1.0	2.1	3.9	6.8
 Corn 	1.2	2.1	3.5	5.7
 Harding grass	3.1	3.9	5.3	7.4
 Orchard grass	1.0	2.1	3.7	6.4
 Perennial rye	3.7	4.6	5.9	8.1
 Sudan grass	1.9	3.4	5.7	9.6
 Tall fescue	2.6	3.9	5.7	8.9
 Tall wheat grass	5.0	6.6	9.0	13.0
 Trefoil, big	1.5	1.9	2.4	3.3
 Trefoil, small	3.3	4.0	5.0	6.7
 Wheat grass	5.0	6.0	7.4	9.8
 Almond	1.0	1.4	1.9	2.7
 Apple, Pear	1.0	1.6	2.2	3.2
 Apricot	1.1	1.3	1.8	2.5
 Avocado	0.9	1.2	1.7	2.4
 Date palm	2.7	4.5	7.3	12.0
 Pomegranate	1.8	2.6	3.7	5.6
 Grape	1.0	1.7	2.7	4.5
 Grapefruit	1.2	1.6	2.2	3.3
 Lemon	1.1	1.6	2.2	3.2
 Orange	1.1	1.6	2.2	3.2
 Peach	1.1	1.4	1.9	2.7
 Plum	1.0	1.4	1.9	2.8
 Strawberry	0.7	0.9	1.2	1.7
 Walnut	1.1	1.6	2.2	3.2
 1	Based on the electrical conductivity of the irrigation water  measured
 Very saline, shallow water tables occur in many areas of Texas.
Shallow water tables complicate salinity management since water may actually move upward into the root zone, carrying with it dissolved salts.
Water is then extracted by crops and evaporation, leaving behind the salts.
Shallow water tables also contribute to the salinity problem by restricting the downward leaching of salts through the soil profile.
Installation of a subsurface drainage system is about the only solution available for this situation.
The original clay tiles have been replaced by plastic tubing.
Modern drainage tubes are COVered by a "sock" made of fabric to prevent clogging of the small openings in the plastic tubing.
A schematic of a subsurface drainage system is shown in Figure 2.
The design parameters are the distance between drains  and the elevation of the drains  above the underlying impervious or restricting layer.
Proper spacing and depth maintain the water level at an optimum level, shown here as the distance m above the drain tubes.
The USDA Natural Resources Conservation Service  has developed drainage design guidelines that are used throughout the United States.
A drainage computer model developed by Wayne Skaggs at North Carolina State University, DRAINMOD, is also widely used throughout the world for subsurface drainage design.
Obtaining a satisfactory stand is often a problem when furrow irrigating with saline water.
Growers sometimes compensate for poor germination by planting two or three times as much seed as normally would be required.
However, planting procedures can be adjusted to lower the salinity in the soil around the germinating seeds.
Good salinity control is often achieved with a combination of suitable practices, bed shapes and irrigation water management.
In furrow-irrigated soils, planting seeds in the center of a single-row, raised bed places the seeds exactly where salts are expected to concentrate.
This situation can be avoided using "salt ridges." With a double-row raised planting bed, the seeds are placed near the shoulders and away from the area of greatest salt accumulation.
Alternate-furrow irrigation may help in some cases.
If alternate furrows are irrigated, salts often can be moved beyond the single seed row to the non-irrigated side of the planting bed.
Salts will still accumulate, but accumulation at the center of the bed will be reduced.
With either singleor double-row plantings, increasing the depth of the water in the furrow can improve germination in saline
 soils.
Another practice is to use sloping beds, with the seeds planted on the sloping side just above the water line.
Seed and plant placement is also important with the use of drip irrigation.
Typical wetting patterns of drip emitters and micro-sprinklers are shown in Figure 4.
Salts tend to move out and upward, and will accumulate in the areas shown.
Other Salinity Management Techniques
 Techniques for controlling salinity that require relatively minor changes are more frequent irrigations, selection of more salt-tolerant crops, additional leaching, preplant irrigation, bed forming and seed placement.
Alternatives that require significant changes in management are changing the irrigation method, altering the water supply, land-leveling, modifying the soil profile, and installing subsurface drainage.
The common saying "salt loves bare soils" refers to the fact that exposed soils have higher evaporation rates than those covered by residues.
Residues left on the soil surface reduce evaporation.
Thus, less salts will accumulate and rainfall will be more effective in providing for leaching.
Salt concentrations increase in the soil as water is extracted by the crop.
Typically, salt concentrations are lowest following an irrigation and higher just before the next irrigation.
Increasing irrigation frequency maintains a more constant moisture content in the soil.
Thus, more of the salts are then kept in solution which aids the leaching process.
Surge flow irrigation is often effective at reducing the minimum depth of irrigation that can be applied with furrow irrigation systems.
Thus, a larger number of irrigations are possible using the same amount of water.
Figure 2.
A subsurface drainage system.
Plastic draintubes are located a distance  apart.
Figure 3a.
Single-row versus double-row beds showing areas of salt accumulation following a heavy irrigation with salty water.
Best planting position is on the shoulders of the double-row bed.
Figure 3b.
Pattern of salt build-up as a function of seed placement, bed shape and irrigation water quality.
Table 9.
Chloride tolerance of agricultural crops.
Listed in order
 of tolerance.
without loss in yield
 Rice, paddy	C	30d	1,050
 Clover, strawberry	15	525
 Clover, red	15	525
 Clover, alsike	15	525
 Clover, ladino	15	525
 Sweet potato	15	525
 Broad bean	15	525
 Foxtail, meadow	15	525
 Clover, Berseem	15	525
 Trefoil, big	20	700
 Squash, scallop	30	1,050
 Vetch, common	30	1,050
 Wild rye, beardless	30	1,050
 Sudan grass	30	1,050
 Wheat grass, standard crested	35	1,225
 Beet, red	40	1,400
 Fescue, tall	40	1,400
 Squash, zucchini	45	1,575
 Harding grass	45	1,575
 Trefoil, narrow-leaf bird's foot	50	1,750
 With proper placement, drip irrigation is very effective at flushing salts, and water can be applied almost continuously.
Center pivots equipped with LEPA water applicators offer similar efficiencies and control as drip irrigation at less than half the cost.
Both sprinkler and drip provide more control and flexibility in scheduling irrigation than furrow systems.
Salts often accumulate near the soil surface during fallow periods, particularly when water tables are high or when off-season rainfall is below normal.
Under these conditions, seed germination and seedling growth can be seriously reduced unless the soil is leached before planting.
Changing Surface Irrigation Method
 Surface irrigation methods, such as flood, basin, furrow and border are usually not sufficiently flexible to permit changes in frequency of irrigation or depth of water applied per irrigation.
For example, with furrow irrigation it may not be possible to reduce the depth of water applied below 3-4 inches.
As a result, irrigating more frequently might improve water availability to the crop but might also waste water.
Converting to surge flow irrigation may be the solution for many furrow systems.
Otherwise a sprinkler or drip irrigation system may be required.
In sodic soils , sodium ions have become attached to and adsorbed onto the soil particles.
This causes a breakdown in soil structure and results in soil sealing or "cementing," making it difficult for water to infiltrate.
Chemical amendments are used in order to help facilitate the displacement of these sodium ions.
Amendments are composed
 Table 9.
Chloride tolerance of agricultural crops.
Listed in order
 without loss in yield
 Ryegrass, perennial	55	1,925
 Wheat, Durum	55	1,925
 Barley 	60	2,100
 Wheat C	60	2,100
 Sugar beet	70	2,450
 Wheat grass, fairway crested	75	2,625
 Wheat grass, tall	75	2,625
 These data serve only as a guideline to relative tolerances among crops.
Absolute tolerances vary, depending upon climate, soil conditions and
 bcl concentrations in saturated-soil extracts sampled in the rootzone.
'Less tolerant during emergence and seedling stage.
"Values for paddy rice refer to the CI concentration in the soil water during
 the flooded growing conditions.
of sulphur in its elemental form or related compounds such as sulfuric acid and gypsum.
Gypsum also contains calcium which is an important element in correcting these conditions.
Some chemical amendments render the natural calcium in the soil more soluble.
As a result, calcium replaces the adsorbed sodium which helps restore the infiltration capacity of the soil.
Polymers are also beginning to be used for treating sodic soils.
It is important to note that use of amendments does not eliminate the need for leaching.
Excess water must still be applied to leach out the displaced sodium.
Chemical amendments are only effective on sodium-affected soils.
Amend-ments are ineffective for saline soil conditions and often will increase the existing salinity problem.
Table 15 lists the most common amendments.
The irrigation books listed under the
The sand and sandstone units in the Brule Formation were deposited in ancient stream valleys and generally have higher porosity than the Brule siltstone that is common elsewhere in western Nebraska.
More than 140 wells currently source all of their water from Brule sand-sandstone units and generally have good water quality.
BEYOND 2020, VISION OF THE FUTURE: SELECTED PAPERS FROM THE SIXTH DECENNIAL NATIONAL IRRIGATION SYMPOSIUM
 Freddie R.
Lamm , Michael D.
Dukes2,3 Kenneth C.
Stone4, Brent Q.
Mecham
 VISION OF THE FUTURE Collection Introduction
 1 Northwest Research-Extension Center, Kansas State University, Colby, Kansas, USA.
2 Department of Agricultural and Biological Engineering, University of Florida, Gainesville, Florida, USA.
3 Center for Land Use Efficiency, University of Florida, Gainesville, Florida, USA.
ASABE/IA 6th National Irrigation Symposium includes 80 papers, with 36 introduced here in this Special Collection.
Papers include current irrigation research about ET, management, turf systems, technology, humid region, water supply.
Irrigation in the U.S.
is growing more rapidly in humid regions, and pressurized irrigation continues to grow in usage.
There has been much progress in irrigation science in the last decade, and the vision of the future looks bright.
ABSTRACT.
This article introduces the ASABE Special Collection associated with the 6th Decennial National Irrigation Symposium: Beyond 2020, Vision of the Future.
This U.S.
symposium, jointly sponsored by ASABE and the Irrigation Association in December 2021, was postponed from 2020 due to the pandemic and consists of approximately 80 presentations, of which 36 were accepted as journal articles for this Special Collection.
Irrigated land area appears to be growing slightly in the U.S.
but is shifting geographically somewhat toward humid regions.
Pressurized irrigation continues to grow, and gravity-fed irrigation continues to decline.
Competition for stressed water resources among diverse water users remains great, and smaller numbers of irrigation scientists are available to meet the informational needs.
Improved ability to acquire, assess, and use water and crop information helps to meet these challenges.
This article discusses irrigation research progress in evapotranspiration , irrigation management, turf systems, sensors and technologies, irrigation strategies in the humid region, and water supply.
Challenges and opportunities continue to exist for irrigation in the U.S., but progress in the last decade has been steady, and a good vision for the future of irrigation beyond 2020 is anticipated.
Keywords.
Evapotranspiration, Irrigation, Irrigation management, Irrigation scheduling, Irrigation systems, Turf and landscape irrigation.
I n March of 2019, the program committee of the 6th Decennial National Irrigation Symposium  established the symposium titled Beyond 2020, Vision of the Future.
The intended wordplay was that it is possible to have vision better than 20/20, and it was hoped that the symposium would provide such a vision of the future for irrigation in the U.S.
Little did the program committee know that, within a year, the symposium title would take on new meaning, with the COVID-19 pandemic necessitating postponement of the 6th Decennial NIS.
ASABE  has sponsored the NIS every ten years since 1970; beginning in 1990, the Irrigation
 Association  became a co-sponsor.
These decennial events provide a forum to discuss the status and recent progress of research, extension, state and federal agency, and industry efforts to advance the effectiveness of irrigation practices and technologies, as well as to project a path forward amid the successes and challenges.
Additional discussion of some of the earlier Decennial NIS is provided by Dukes et al..
Submitted for review on 10 March 2021 as manuscript number NRES 14574; approved for publication as a Research Brief and as part of the National Irrigation Symposium 2020 Collection by the Natural Resources & Environmental Systems Community of ASABE on 2 June 2021.
Mention of company or trade names is for description only and does not imply endorsement by the USDA.
The USDA is an equal opportunity provider and employer.
At the time of this writing, it is anticipated that 80 papers will be presented at the 6th Decennial NIS, which is currently scheduled for December 2021 in San Diego, California.
The authors of these papers had the option of seeking simultaneous dual publication in the symposium proceedings and through the journal peer-review process.
A total of 36 papers were published in both media, and these peer-reviewed journal articles are contributions to the largest ASABE Special Collection prepared thus far.
These journal articles are summarized in the following sections along with some additional contextual discussion of the present status of irrigation in the U.S.
and a vision of the future beyond
 2020.
This collection builds on two recent ASABE Special Collections with contributions from the 5th Decennial NIS in 2010  and the Emerging Technologies for Sustainable Irrigation symposium in 2015 , both jointly sponsored by ASABE and IA.
STATUS OF IRRIGATION IN THE U.S.
Overall, it appears that irrigated land area  has continued to increase slightly in the U.S.
, altthough we note some discrepancies in the various 2018 USDA-NASS Farm and Ranch Irrigation Survey tables used to prepare this summary.
The concentration of irrigated land area has migrated somewhat within the U.S., with the top ten states losing approximately 2% of their area in the last decade, while the bottom 40 states have increased their irrigated land area by approximately 13%.
Although irrigation is most heavily concentrated in the semi-arid and arid western U.S., two Mid-South states, Arkansas and Mississippi, have the third and ninth largest irrigated land areas, respectively.
The geographic shift toward more humid regions is likely to continue with increasing competition for water resources in the western U.S.
and an increasing need to mitigate crop production risks in the eastern semi-humid and humid regions.
These geographic changes in irrigation within the U.S.
require some adjustment to the future of irrigation, perhaps relying more on optimization schemes rather than on schemes for crop yield maximization or for immaculate turf landscapes.
New and emerging irrigation technologies will continue to be needed in the water-stressed western areas, as well as in the eastern areas of the U.S.
where irrigation is increasing.
The adoption of pressurized irrigation systems  continues in the U.S.
, with surface gravity systems continuing to decrease.
The percentage of pressurized systems increased from 37% to 65% during the period 1978 through 2017.
In the last decade, the sprinkler irrigated area seems to have plateaued for now , the microirrigated area is still rapidly increasing , and the surface gravity irrigated
 Figure 1.
Irrigated land area in the U.S., the top ten irrigated states, and the remaining 40 states during the period 1969 through 2017.
Data from USDA-NASS Farm and Ranch Irrigation Surveys.
Note that there are some unreconcilable differences in irrigated land area between figures 1 and 2 when considering a total land area.
area has continued its steady decline.
The decline in surface gravity systems may be moderated in the future, considering that 35% of the total surface gravity land area is in the Mid-South states of Arkansas, Mississippi, Louisiana, and Missouri.
In this region, 71% of surface gravity systems use single-year poly-pipe for water distribution, and these less-expensive systems are often more economical than pressurized systems.
DISCUSSION OF 6TH DECENNIAL NIS JOURNAL ARTICLES
 The 36 journal articles comprising this ASABE Special Collection can be loosely categorized into the following topics :
 Evapotranspiration.
Irrigation management.
Irrigation systems.
Turf and landscape irrigation.
Technology and innovation 
 Irrigation in the humid region.
EVAPOTRANSPIRATION 
 Evapotranspiration  is a key factor and metric in both evaluation of irrigation strategies and management of crops, turf, and landscapes.
Seven journal articles for this ASABE Special Collection were related to either improving ET estimation procedures or improving the on-farm usage of ET data.
Standardized procedures to estimate ET for short and tall reference crops  are well established.
However, for estimation of actual crop ET, the reference ET needs to be modified by coefficients (e.g., crop, landscape, stress, cultural, or environmental
 Figure 2.
Irrigated land area in the U.S.
by sprinkler, surface gravity, and microirrigation methods during the period 1978 through 2017.
Data from USDC or USDA Farm and Ranch Irrigation Surveys.
Note that there are some unreconcilable differences in irrigated land area between figures 1 and 2 when considering a total land area.
Table 1.
Summary of articles included in the 2021 ASABE Special Collection "Beyond 2020, Vision of the Future: Selected Papers from the 6th Decennial National Irrigation Symposium".
pivot systems: Part A.
Development.
innovation
 pivot systems: Part B.
Application.
innovation
 tracking flood irrigation management in	innovation;
 production-sized rice fields in the Mid-South.
humid region
 based irrigation controllers.
tech.
and
 in U.S.
landscape irrigation.
tech.
and
 An innovative extension method to improve	innovation;
 irrigation water management adoption.
humid region
 Table 1.
Summary of articles included in the 2021 ASABE Special Collection "Beyond 2020, Vision of the Future: Selected Papers from the 6th Decennial National Irrigation Symposium".
Jimnez-Lpe, A.
F., Sanz-Sez, .,	data in relation to soil water-based irrigation	innovation;
 River basin: Trends and innovations.
humid region
 factors), and these coefficients have varying accuracy, geographical applicability, and methodologies for their development and usage.
Application of the FAO-56 dual crop coefficient method for determining ET and irrigation water requirements for large areas of the western U.S.
was discussed by Allen et al..
The products of this effort are used by state governments to manage water rights, water resource planning and design, and hydrologic assessment and modeling.
The federal government has used the products for assessing the impacts of climate change on irrigation requirements.
Key innovations of the products are the scaling of crop coefficients  to thermal units  and the improvement in ET estimations during the dormant season.
Similarly, a Kc curve for sugar beet in eastern Colorado was improved by scaling with GDD and leaf area index  as compared to earlier published time-based Kc values.
The new Kc curve improved estimates of soil water deficits and were incorporated into a cloud-based irrigation scheduling program called Water Irrigation Scheduler for Efficiency.
In the Texas High Plains , the maximum daily Kc values for legacy and modern drought tolerant  corn hybrids were found to be
 similar, but season length was shorter for the DT hybrids, thus affecting the shape of the Kc curve.
The authors pointed out that the published Kc values were generally applicable, but their advance and decline throughout the season should be modified based on canopy growth and climate.
In another Texas High Plains study , the Kc value for corn with subsurface drip irrigation  was only 83% to 89% of the value for mid-elevation spray application , and the authors concluded that SDI Kc values should be decreased by 10% compared to sprinkler irrigation.
They indicated similarity in SDI Kc values to those that could be developed for surface drip irrigation when using full-cover plastic mulch.
Landscape coefficients  are similar to Kc but are used for natural and urban landscapes that often vary in composition , micro-climate , and enduser practices.
A multi-component decoupling method for KL was discussed in a comprehensive review of different KL methodologies.
The authors concluded that the ASABE Standard S623 methodology  is simpler yet complementary to the IA methodology
 for KL , but that either can be used to effectively estimate landscape water requirements.
On-farm irrigation scheduling requires accurate weather data and delivery of ET values through public and/or private weather station networks.
These networks can be costly to install, operate, and maintain, and in some cases the lack of sufficient station density affects their effectiveness as a water management tool.
One large and long-term system, the Texas High Plains ET Network, was estimated to save irrigated producers $22 million annually through energy and water savings.
The authors also discussed the requirements and challenges of sustaining a successful network and the associated costs, noting that the societal benefits can extend well beyond the agricultural sector.
Because high-quality weather stations are expensive and often are sparsely located, there can be limitations on their use for on-farm irrigation scheduling.
Research using data from agricultural fields in Oregon and California  evaluated the use of machine learning combining regional weather station data with data from a few inexpensive on-farm sensors to improve site-specific irrigation management.
The authors concluded that such machine learning techniques could be considerably improved if mobile highquality weather stations could be co-located at the field site for a short duration.
These seven studies illustrate the continued progress in ET estimation and its implementation for irrigation water management, and they augment the six ET-related papers in the earlier ASABE Special Collections.
IRRIGATION MANAGEMENT 
 Ultimately, the success of any irrigation system or irrigated farming operation is constrained by the irrigation management, with a heavy emphasis on the human aspect.
The strategies are often seasonal or longer-term and may have various goals  that may interact and also may be chosen by the producer or governed by some external constraint.
Irrigation scheduling is typically defined as determining when and how much to irrigate, and decisions are often made in the short-term.
Modeling can be used to evaluate both strategies and irrigation scheduling practices.
Eight journal articles for this ASABE Special Collection were closely related to this topic, with one article  previously discussed in the Evapotranspiration section.
Managed deficit irrigation is sometimes used as an irrigation strategy when the water resource is limited  or when the water is expensive and the strategic goal is to maximize net returns for the cropped land.
A modeling framework for deficit irrigation in the western U.S.
was described by Trout et al.
for two deficit irrigation conditions.
The models incorporated both biophysical and economic relationships to maximize net returns.
The authors pointed out that the sensitivity of net returns to deficit irrigation can be decreased with judicious planning for production inputs and costs.
In addition, even when a deficit
 irrigation strategy reduces overall crop production, it can reduce the chance of crop failure and help to ensure at least some profitability.
Progress in irrigation scheduling in the U.S.
was the topic of three Special Collection journal articles.
The progression of Irrigator Pro, an irrigation scheduling decision support system , was discussed by Butts et al..
This DSS began as an expert system and checkbook-based scheduler for peanuts and was first implemented on desktop personal computers in 1995.
Since then, it has been further developed with support for corn and cotton irrigation scheduling and availability on mobile web-based platforms incorporating available weather data and soil water data streams.
Further advances are planned to incorporate additional data streams, such as soil water data from capacitance probes.
Improved prediction of the crop water stress index  using artificial neural network  modeling for sugar beet and wine grapes was reported by King et al..
They concluded that the improved estimation of the reference temperatures used in the CWSI calculation allowed effective usage of CWSI for these two crops in the study region, provided that measurements under wet canopy or low solar radiation are disregarded.
A review of agricultural irrigation scheduling progress within the last decade in the U.S., its current status, and its anticipated future was provided by Taghvaeian et al..
USDA-NASS survey data were used to illustrate that many irrigators continue to use qualitative measures to inform irrigation scheduling decisions, rather than quantitative, science-based tools.
Some improvements have been made in adoption in science-based scheduling, particularly with advances in soil water sensors and the ability to collect and analyze the data.
Improvements in decision support systems, plant and soil sensors, and the internet of things  should continue to increase the adoption rate of irrigation scheduling but would still benefit from university, state and federal agency, and private technical support for training and implementation.
The authors concluded that there are important opportunities to develop integrated irrigation scheduling strategies combining the various approaches  that are more robust than exlisting methods.
Cotton requires less irrigation than corn and thus has become an irrigated crop of interest in western Kansas despite the limited thermal units available for production.
Modeling was used to examine the effects of crop emergence date, irrigation capacity, and irrigation application period on cotton production in three western Kansas locations.
Earlier emergence generally increased yield and water productivity.
Greater irrigation capacity usually increased yield, but extending the irrigation period beyond four to six weeks was not beneficial.
The authors concluded that there were some opportunities for cotton production in southwest Kansas, but not for west central and northwest Kansas.
Modeling and field experimental data were used to evaluate water and nitrogen dynamics in a corn-peanut rotation in Florida.
DSSAT 4.7  modeling accurately simulated field data
 for three irrigation rates and three N fertilizer rates.
The simulations demonstrated that N leaching could be greatly reduced  by limiting N application to 247 kg ha-1 and using sensor-based irrigation scheduling as compared to conventional practices.
The Soil and Water Assessment Tool  was used to estimate soil water at three locations in the U.S.
for periods ranging from one to ten years.
The soil water simulations at all three sites were deemed unacceptable for use in irrigation management.
The authors suggested that the SWAT soil water algorithms did not accurately simulate soil water redistribution between layers for plant water demand and that there was also uncertainty in soil parameterization.
Irrigation management continues to be a major topic of research and extension efforts, as demonstrated by these seven studies, and is likely to continue to be SO in the future.
The aforementioned earlier ASABE Special Collections  had a combined total of five papers related to this topic.
IRRIGATION SYSTEMS 
 Although irrigation systems by themselves cannot manage or conserve water, their appropriate design, operation, and management are key factors in optimizing the use of irrigation water.
Each of the major system types  require their own appropriate design, operation, and management.
Eight journal articles for this ASABE Special Collection were related to this topic.
During the last decade, the USDA-ARS has worked extensively on a variable-rate irrigation  DSS implemented in its patented Irrigation Scheduling Supervisory Control and Data Acquisition  system.
The theory and development of the DSS was discussed by Evett et al..
Both plant and soil water sensors and research-based algorithms were integrated into the DSS and automated irrigation control system.
Research efforts at several USDA-ARS sites were important, culminating in the DSS.
The sensor-based DSS software developed by the USDA-ARS was named ARSPivot, and the software development and its application were discussed by Andrade et al..
Using a graphical user interface , ARSPivot assists in the process of setting up and reviewing irrigation prescriptions that can be generated automatically based on sensor feedback.
Irrigated potato production on the Texas High Plains was evaluated with manual irrigation and ISSCADA-controlled irrigation in a two-year field study.
The authors reported that ISSCADA-controlled irrigation resulted in fewer irrigation events in a drier growing season  and in similar or better potato yields in a wetter season.
They concluded that further research was warranted to develop better soil water criteria for triggering ISSCADA-controlled irrigation.
Irrigated soybean production was evaluated with ISSCADA-controlled irrigation and a soil electrical conductivity  based method in Mississippi , and the authors found that the
 ISSCADA method reduced irrigation water use and increased irrigation water productivity.
VRI for corn production on the U.S.
Eastern Coastal Plain was evaluated for two different implementations of the ISSCADA system.
The authors reported greater corn yields and less irrigation requirements for a hybrid implementation of ISSCADA that included soil water depletion criteria as compared to the standard ISSCADA.
Research to further develop and implement the DSS continues at the USDA-ARS.
As discussed earlier, the Mid-South region of the U.S.
has experienced much growth in irrigated land area, mostly with surface irrigation.
A review of surface irrigation in the lower Mississippi River basin was provided by Reba and Massey.
Noting that 90% of the irrigation water applied to 4 Mha of cropland is from groundwater, they detailed ongoing efforts to address the overdraft of the alluvial aquifer.
Irrigation innovations include system improvements , management strategies , and institutional efforts.
The use of subsurface drip irrigation  continues to increase in the U.S.
and has been the subject of a considerable amount of research during the last decade, as discussed in a comprehensive review by Lamm et al..
Research from 2010 through 2020 within the U.S.
for SDI cotton, grain and oilseed crops, horticultural, forage, and turf crops is summarized in their review.
Persistent challenges  still exist, but opportunities for further adoption also exist.
Integrated use of advanced irrigation management strategies and/or other irrigation technologies  with these advances in the design, operation, and management of irrigation systems is likely to continue to be a fruitful research topic in the coming decade.
These eight journal articles in this ASABE Special Collection are illustrative of just some of the progress of the last decade.
The aforementioned earlier ASABE Special Collections  had a combined total of 13 papers related to this topic.
TURF AND LANDSCAPE IRRIGATION
 Irrigation for turf and landscape is a major use of municipal water in the U.S.
and continues to be scrutinized by water planners and regulators looking for additional ways to conserve water.
Four journal articles in this Special Collection were related to turf and landscape irrigation, three concerning irrigation controllers , and the other article  was previously discussed in the Evapotranspiration section.
A comprehensive review of smart irrigation controllers for turf and landscape irrigation was discussed by Dukes.
When irrigation savings were reported , the average savings in research plots was 51%,
 but savings for residential systems averaged only 30%.
In the five studies reporting increased irrigation with smart controllers, the primary reasons appeared to be controller usage at sites where irrigation needs were low and in cases where the controller programming was not optimized.
The importance of human factors was documented, and it was concluded that consumer education remains a key factor in achieving water conservation.
A two-year research study in Florida with smart irrigation technologies and a smart phone application  was discussed by Cardenas et al..
Irrigation treatments based on the advanced technologies [i.e., soil moisture sensor , estimated ET, or SP] saved approximately 30% to 65% more water than traditional time-based irrigation control.
The reasons for water savings with the advanced technologies varied, with fewer irrigation events attributed to SMS, reduced irrigation depths for ET, and a combination of the two reasons for SP.
The authors reported that the economic payback for the advanced technologies ranged from 0 to 12 months.
The performance of the Smart Water Application Technologies testing protocol for weather-based irrigation controllers for turf and landscape in Florida was evaluated by Conger and Dukes.
They found deficiencies in the reproducibility and transferability of results.
Some of the deficiencies were related to inadequate documentation of the protocol, controller setup and programming, order of operations, and availability of weather data.
They suggested potential improvements to the testing protocol.
These three articles along with the fourth article discussed earlier  highlight some of the research progress in turf and landscape irrigation since the 5th Decennial NIS in 2010.
The aforementioned earlier ASABE Special Collections  had a combined total of eight papers related to this topic.
TECHNOLOGY AND INNOVATION 
 Advances in irrigation technology [e.g., sensors, irrigation controllers, unmanned aerial systems ] and its adoption and the availability of innovative research, extension, and education programs in irrigation science were key factors in the progress of irrigation management in the U.S.
during the past decade.
Seven journal articles from this ASABE Special Collection are discussed in this section, but ten additional articles  discussed in other sections of this article easily overlap with this topic.
The use of soil water sensors for scheduling agricultural irrigation is growing in the U.S.
The within-field variability in granular matrix soil water sensor data was examined in a field study in Mississippi.
The authors found that variability was greater for individual depths than for the complete soil profile, and that variability increased as the soil water decreased.
They proposed a probabilistic conceptual framework to interpret the variability in the soil water data.
They concluded that if the irrigation scheduling goal is to maintain adequate soil water for a specific fraction of
 the irrigated field, then the advantage of adding additional soil water sensors may not be as useful as anticipated.
The development of a wireless sensor network  for monitoring remote rice production fields in the Mid-South U.S.
was discussed by Chiu and Reba.
The WSN in this implementation included data from soil water sensors and water level data  obtained with ultrasonic sensors.
The authors found significant relationships between automated and manual measurements of water level data for three different irrigated rice production methods that are used in the Mid-South.
Problems with field installation and maintenance of the water depth sensors and potential solutions were discussed.
The authors concluded that the WSN with various sensors and appropriate installation and maintenance could provide real-time information useful for management of irrigated rice production.
Advances in the last decade in the use of UAS for irrigation management in the western U.S.
were the subject of a review.
The authors found that, despite the advances, further improvements are needed in UAS platforms, sensor integration, processing software, and government regulation.
They concluded that further advances in UAS adoption and implementation for irrigation scheduling could be augmented through better integration of multiple sensor data streams.
As these data streams are becoming more readily available, data science will be a key factor in processing, analysis, and interpretation of such large volumes of data.
The increased water productivity for U.S.
cotton during the last 40 years was attributed to a combination of improved irrigation systems and associated technologies, irrigation scheduling and management, and changes in cultivars in a comprehensive review.
Irrigation systems and adoption of associated technology varied across the southern cotton production regions, with local climate, water availability, soils, and topography having an important influence.
The authors reported 2018 USDA-NASS data indicating that nearly 60% of the irrigated cotton in the U.S.
uses sprinkler irrigation and that approximately 36% of the 4.1 Mha of cotton nationwide is irrigated.
They concluded that water productivity improvements for cotton during the last 40 years must continue due to stressed water resources and climate variability, and will continue due to further advances in irrigation systems and associated technologies and through genetic gains.
The challenges and opportunities for education in irrigation engineering were discussed in a perspective article by Porter et al..
They found that declining enrollments and a declining number of university degree programs were having a negative impact on the availability of irrigation engineering expertise.
While shorter-term technical degree and certificate programs can fill some of these gaps, it is important that qualified irrigation engineers be developed to address present and emerging national and international challenges in irrigated agriculture.
Extension and other education programs are continuing to evolve to provide the skills needed by end-users and are often available in both ondemand internet-based and social media-based formats.
The authors concluded that current knowledge gaps and research time lags can cause restlessness among some end-users and
 that the problem increases the potential for misimplementation of technologies and products that have little scientific basis in fact.
An innovative extension method in Arkansas, the "most crop per drop" contest, was described by Henry et al..
The contest promoted the adoption of surge irrigation, soil water monitoring, computerized hole selection for poly-pipe furrow irrigation, and multiple inlet rice irrigation.
Using a modified calculation of water use efficiency  as a metric, the authors found that the contest winners  did not always have the greatest corn, soybean, or rice yields.
Cash prizes and donated industry products averaging $60,000 per year were presented to the contest winners at an Arkansas conservation conference.
The authors found that contest participants increased adoption of computerized hole selection by 33%, surge irrigation by 28%, and soil water monitoring by 51%, and concluded that all contest participants were "winners" through improved water management.
Innovative extension programs in the Great Plains and Southeast U.S.
to promote improved irrigation management were described by Rudnick et al..
They reported that university extension is serving a larger number of irrigated farms as technology becomes more complex and the stress on water resources increases.
They also noted that there has been a transition away from typical lectures and field tours for information delivery and knowledge transfer.
Newer extension programs have focused on experiential learning, development of practitioner networks, and industry participation.
The ability of practitioners to interact with each other, with university and agency staff, and with industry seems to promote individual responsibility and the sustainability of adopted practices.
The seven papers discussed in this section and the ten related papers discussed in other sections of this article comprise a sizable body of important research and extension efforts in technology and innovation.
The aforementioned earlier ASABE Special Collections  had a combined total of twelve papers related to this topic.
IRRIGATION IN THE HUMID REGION
 Nearly 30% of the total irrigated land area in the U.S.
is located in the eastern humid states, and the area continues to increase.
Overall, eight journal articles for this ASABE Special Collection were related to agricultural irrigation in the humid region, with three articles specifically discussed in this section.
The other five articles were discussed in the Technology and Innovation section , the Irrigation Systems section , and the Irrigation Management section.
Plant water stress criteria [CWSI and temperature-time threshold ] were evaluated in a humid subtropical climate for irrigated corn production in Alabama.
In a season with more sparse rainfall events, both CWSI and corn yield were significantly affected by irrigation treatment, but not SO in a season with more evenly distributed rainfall.
The authors concluded that further study was needed
 to develop CWSI threshold values for irrigated corn in this region.
They found that the TTT method did not work well for irrigation management in this region, whether or not the additional limiting relative humidity factor was considered.
Rainwater harvesting  was sufficient to meet irrigation needs for high tunnels  in Tennessee  in a comparison of three different RWH systems.
The authors concluded that the costs of the three tested RWH systems were not competitive with the cost of using alternative water sources.
Other potential RWH systems with lower initial costs were identified but remain untested.
Combining tile drainage and subirrigation is gaining interest in the midwestern U.S.
and is termed drainage water recycling.
An open-source online software tool  was developed to evaluate the potential irrigation and water quality benefits.
Global sensitivity analysis indicated that the model was most sensitive to the input parameters controlling total available water.
These three articles along with the other five articles discussed in other sections of this article demonstrate just some of the breadth of irrigation research and extension activities occurring in the humid region.
Although agriculture irrigation in the humid region was not a specific topic in the earlier ASABE Special Collections , four journal articles in those earlier collections would fit this topic.
In the western U.S., irrigation development was often achieved through a combination of private and public partnership.
A case study of the Twin Falls Canal Company , which began delivering water in Idaho in 1905, was discussed by Bjorneberg et al..
They reported the early struggles of the TFCC  and the current challenges.
Although water quality of return flows has improved greatly in the last 30 years, more can be done to further improve water quality in the Snake River.
The presence of six hydroelectric facilities on the TFCC improves the long-term viability of the project.
There were no journal articles closely related to water supply issues in the earlier ASABE Special Collections.
The irrigated land area in the U.S.
appears to have grown slightly in the last decade, but the top ten states have seen a slight decline  in land area, while the bottom 40 states have increased their irrigated land area.
Irrigation in the primary Mid-South states adjacent to the Mississippi River now totals 4 Mha, and the irrigated land area in the humid eastern U.S.
is 36% of the total irrigated land area.
Pressurized irrigation  comprises about 65% of the total irrigated area, and the surface gravity irrigated land area continues to decline.
At the time of this writing, it is anticipated that approximately 80 papers will be presented at the 6th Decennial NIS, scheduled for December 2021 in San Diego, California.
This total includes 36 journal articles published in 2020 and 2021 as part of an ASABE Special Collection.
These 36 articles are described in this introductory article.
This Special Collection is the largest thus far in ASABE history and includes nine review articles, 24 research articles, one research brief, and two perspective articles.
The progress in irrigation research and extension in the last decade and its current status in the U.S.
suggest a good vision for the future of irrigation beyond 2020.
Contribution No.
21-240-D from the Kansas Agricultural Experiment Station.
This work was supported by the USDA National Institute of Food and Agriculture ; by the USDA-ARS Ogallala Aquifer Program, a consortium between the USDA-ARS, Kansas State University, Texas A&M AgriLife Research, Texas A&M AgriLife Extension, Texas Tech University, and West Texas A&M University; and by USDA-ARS National Program 211, Water Availability and Watershed Management.
ASABE..
S623.1: Determining landscape plant water demands.
St.
Joseph, MI: ASABE.
for Agrotechnology Transfer.
Gainesville, FL: DSSAT Foundation.
Challenges and opportunities for education in irrigation
 engineering.
Trans.
ASABE, 63, 1289-1294.
The main barriers to adoption of new technologies in irrigation include cost and ease of use.
These scientific methods need to be cost-effective and feasible for farmers to adopt.
The method uses a ratio of the length of the center pivot vs.
the throw of the end gun.
The designed end gun throw and the length of the pivot can be found on the sprinkler chart.
The average statewide precipitation totaled 1.27 inches, which is 0.84 less than normal and ranks in the driest 25% of all September precipitation totals going back to 1895.
Table 2.
Crop water use for the remainder of the growing season for corn and soybean:
 For soybean in the R4 end of pod elongation stage of growth, it has an approximate days to maturity of 37 days and has 9.0 inches of water use to maturity.
For soybean in the R5 beginning seed enlargement stage of growth, it has an approximate days to maturity of 29 days and has a 6.5 inches of water use to maturity.
For soybean in the R6 end of seed enlargement stage of growth, it has an approximate days to maturity of 18 days and has a 3.5 inches of water use to maturity.
For soybean in the R6.5 leaves begin to yellow stage of growth, it has an approximate days to maturity of 10 days and has a 1.9 inches of water use to maturity.
For soybean in the R7 beginning maturity stage of growth, it has an approximate days to maturity of 0 days and has a 0 inches of water use to maturity.
Arkansas Water Primer Series: Water Rights in Arkansas
 Water is essential for the survival of all living things.
Societies depend on water to drink, grow crops, run industries and transport goods across the country.
Water resources provide opportunities for recreation and habitat for aquatic and landbased wildlife.
It is a finite resource that is recycled through the hydrologic cycle.
As such, there have been conflicts since the beginning of civilization about who can use water, in what amount and at what time.
These issues have been the impetus for the development of water rights a complex and ever-changing combination of doctrines, laws and regulations that govern the distribution of water.
Historical Doctrines for Determining Water Rights
 There are two common legal concepts, or doctrines, states have used to base water rights.
The doctrine of prior appropriation dominates in the Western states.
Under this system, water rights are "first in time, first in right." This means that the first person to use a quantity of water from a water source for a beneficial use has the right to continue to use that quantity of water for that purpose.
Subsequent users can use the remaining water for their own beneficial purposes provided that they do not impinge on the rights of previous users.
All of the states in which the prior appropriation doctrine applies have statutory administrative procedures to provide an orderly method for appropriating water and regulating established water rights.
Water appropriation laws
 and administration vary significantly from state to state.
Typically, states require a permit as the exclusive means of making a valid appropriation.
However, the U.S.
federal government and Native American tribal governments also have rights to water under doctrines of federal law that may supersede states' rights.
Riparian doctrine is common in the Eastern states.
This doctrine considers water to be a common use resource rather than private property.
Riparianism attaches a water right to land adjacent to a water course.
All landowners have the right to make reasonable use of water on or bordering their property.
However, the water use cannot unreasonably diminish the quality or quantity of water to neighboring landowners.
The concept of reasonable use depends on balancing the interests of all the "common owners." The rights created by the balancing process may change with circumstances over time.
Riparian doctrine applies to all natural bodies of water including streams, lakes, ponds and marshes.
Under the riparian system, rights remain with the property when it changes hands.
Legal doctrines change over the course of time.
All states have modified the two water doctrines with legislatures and courts playing an increasingly active role.
Arkansas' water rights are based on a "regulated riparian" system.
Traditional riparian principles are recognized but within a dynamic supervisory, administrative and legal structure.
Beginning in the late 1950s, the
 Arkansas General Assembly began passing a series of laws to address the need for more specificity and clarity concerning water rights.
The Arkansas Natural Resources Commission  was established to serve as the state's water resources planning and management agency.
As such, ANRC has legislative authority to:
 Allocate surface water from streams during times of shortage based on the reasonable use concept
 Develop a comprehensive groundwater protection program
 Designate critical groundwater areas
 Cost-share on installation of water conservation practices
 Establish groundwater rights within critical areas
 Develop an education/information program and
 Delegate management powers to regional water districts and conservation districts, among other duties.
2
 As the state's water management agency, ANRC has the authority to investigate and assist in the resolution of water rights complaints that deal with surface water
 availability and use.
3 To initiate an investigation, a person must submit a written request to ANRC.
The Executive Director of ANRC reviews the request to determine whether or not the Commission can assist in resolving the issue.
If ANRC conducts an investigation, the person filing the request may be charged a fee ranging from $50 to $500, based on the complexity of inquiry.
The fee is placed in ANRC's Water Development Fund to support the Commission's general operations.
A report is provided to the person filing the request.
If the person is dissatisfied with the Commission's findings, he or she has the option to file a lawsuit to resolve a water rights dispute.
Fact Sheet 103  Partners in Protecting Arkansas' Waterbodies provides an overview of state agencies with water-related responsibilities.
Fact Sheet 109  Glossary of WaterRelated Terms contains a comprehensive list of terms used in the Arkansas Water Primer Fact Sheet Series.
1 Originally named the Arkansas Soil and Water Conservation Commission.
2 Arkansas statutes and regulations that address water rights, use and allocation within the state are generally found in Ark.
Code Ann.
Title 15, Chapter 22.
3 Rules Governing Water Rights Investigations.
The University of Arkansas Division of Agriculture's Public Policy Center provides timely, credible, unbiased research, analyses and education on current and emerging public issues.
The Arkansas Water Primer Fact Sheet Series was funded by a grant from the U.S.
Department of Agriculture with additional financial assistance from the University of Arkansas Division of Agriculture.
Original research for the Series was provided by Janie Hipp, LL.M., and adapted by Tom Riley, associate professor and director of the University of Arkansas Division of Agriculture's Public Policy Center, and Lorrie Barr, program associate, University of Arkansas Division of Agriculture's Public Policy Center.
ET-Based Irrigation Scheduling for Papaya  in Florida
 Haimanote K.
Bayabil, Jonathan H.
Crane, Kati W.
Migliaccio, Yuncong Li, and Fredy Ballen2
 Papaya  is an important fruit crop grown in south Florida with an estimated area of 356 acres.
Miami-Dade County accounts for almost 81% of papaya production in Florida.
The estimated papaya production value is $1.9 million based on an average yield of 29,000 pounds per acre, 85% pack-out rate, and $0.40 per pound price value.
Typical cultural practices and pest and disease management guidelines for papaya can be found in Crane and Mossler.
Three irrigation scheduling methods  were tested for papaya production in south Florida.
ETbased irrigation scheduling was found to conserve water effectively.
This document primarily focuses on the ETbased irrigation scheduling techniques for papaya under Florida conditions.
Importance of Papaya Irrigation in Florida
 On average, Florida receives 40 to 60 inches of rainfall per year.
However, spatial and temporal rainfall distribution is erratic, which results in periods of drought and excessive soil moisture.
This discrepancy in distribution combined with wellto excessively drained limestone-based and sandy soils with low water holding
 capacity makes irrigation necessary for optimal papaya growth and production.
Drought-stressed papaya plants drop flowers, leaves, and young fruit and produce smaller fruits with lower sugar content.
Science-based irrigation management is the key to ensure a supply of adequate water for this fast-growing plant.
Traditionally, irrigation management used calendar-based scheduling.
This was not efficient due to the potential for underirrigation or overirrigation, leaching of water, nutrients, and chemicals below the root zone, and subsequent unavailability for plant uptake.
Significant progress has been made in the development of advanced irrigation scheduling techniques that conserve water.
However, the adoption rates of these new technologies by stakeholders is rather slow partially due to lack of information on the benefits of these technologies.
This document provides useful information about ET-based irrigation scheduling to different stakeholders including papaya growers, UF/IFAS Extension agents working with farmers, and/or the general public.
2.
Haimanote K.
Bayabil, assistant professor, Department of Agricultural and Biological Engineering, UF/IFAS Tropical Research and Education Center, Homestead, FL; Jonathan H.
Crane, professor, Horticultural Sciences Department, UF/IFAS TREC; Kati W.
Migliaccio, chair and professor, Department of Agricultural and Biological Engineering; Yuncong Li, professor, Department of Soil and Water Sciences, UF/IFAS TREC; and Fredy Ballen, economic analysis coordinator, UF/IFAS TREC; UF/IFAS Extension, Gainesville, FL 32611.
Papaya Irrigation Research in Florida
 Migliaccio et al.
conducted two 2-year studies to compare different irrigation scheduling methods for papaya production.
The treatments included:
 Set schedule: Traditional set irrigation schedule based on 1-1.5 hours of drip irrigation per day, 3-7 times per week depending on the weather and crop growth stage.
This method was commonly practiced by local producers in south Florida during the time the experiment was designed between 2006 and 2009.
Tensiometer-based: Soil water content-based irrigation scheduling, using switching tensiometer values to initiate irrigation at three different prespecified tensions: 10 kPa , 15 kPa  and 25 kPa.
Tensiometers were placed within the root zone, about 1 foot from the base of papaya plants and at a 6.5-inch soil depth.
Results from these field trials: The daily water application rate for the ET-based irrigation scheduling was only 34-35% of that for the set schedule treatment across the two years of both studies.
Similar water savings  were also found for the three tensiometer-based irrigation treatments.
However, ET-based irrigation scheduling may be more convenient and easier to implement than the tensiometer-based irrigation.
Tensiometer-based irrigation scheduling requires frequent monitoring of the tensiometer to evaluate its accuracy, periodic cleaning and maintenance, and reinstallation of malfunctioning tensiometers.
The readily available information utilized for ET-based irrigation is based on near-real-time or historic ET values and crop coefficient  values; with this method, no field equipment is needed.
Papaya plant growth as measured by trunk diameter and trunk height was greater with ET-based and tensiometerbased irrigation treatments than it was with set schedule irrigation treatment.
This suggests the set schedule irrigation management may have overirrigated the papaya plants, kept the root zone too wet, and caused mild oxygen stress
 and/or leaching of nutrients from the root zone, reducing papaya plant growth.
In general, there was no significant difference in the number of fruit and amount of fruit production per acre among the irrigation scheduling treatments.
However, the traditional set irrigation scheduling method used 64-69% more water than the ETand tensiometer-based irrigation scheduling methods.
Most importantly, fruit production per unit of water applied was less for the set schedule irrigation management treatment compared to the ET-based and tensiometer-based irrigation scheduling treatments.
ETand tensiometer-based irrigation scheduling resulted in more efficient use of water with the same fruit production compared to the set irrigation scheduling method.
Implementing ET-Based Irrigation Scheduling for Papaya in Florida
 The aim of improving irrigation scheduling and technology for papaya is to:  save and use water more efficiently;  increase crop yields and quality;  potentially increase crop yield per unit of water used ;  reduce leaching of water, nutrients, and chemicals below the root zone; and  offer userfriendly irrigation scheduling methods that do not increase labor or irrigation costs.
In addition, implementing an ET-based irrigation scheduling method could save water and potentially energy costs without reducing crop yields.
From a management viewpoint, the advantages of ET-based irrigation scheduling include no installation and maintenance of soil moisture probes , the use of readily available near-real-time or historic ET information, and the use of monthly generalized papaya crop coefficient  values to calculate the amount of irrigation water needed.
However, the availability of reliable Kc values at different crop stages could make ET-based irrigation scheduling challenging.
Implementing ET-based irrigation scheduling may be accomplished by gathering the information outlined below  or installing a smart irrigation controller.
Review the capabilities and availability of needed data prior to purchasing an automated smart irrigation controller.
The information needed for implementation of ET-based irrigation scheduling is mostly similar for different crops except for information about the crop itself.
The general steps for ET-based irrigation scheduling are outlined below based on the following EDIS publications.
Some of
 GETTING RECENT ET VALUES FROM FAWN SITE
The Clean Water Act's Impact on Arkansas Producers
 The Clean Water Act of 1972  established water quality standards for the United States and set into motion a permitting process for discharging pollutants into the country's waterways.
The goal of the Act has been to improve water quality by reducing the amount of pollutants entering waterways.
Arkansas' abundance of waterways means farms in many parts of the state may not be too far away from a creek, river or wetland and could be regulated by the Act.
Producers should be aware of federal and state water quality regulations to ensure their operations are in compliance with discharge laws and permitting requirements.
Producers should also be aware that some agricultural practices may be exempt from the Act.
What Is a Pollutant?
Some agricultural activities can create pollutants.
The Act defines "pollutants" as "dredged spoil, solid waste, incinerator residue, sewage, garbage, sewage sludge, munitions, chemical wastes, biological materials, radioactive materials, heat, wrecked or discarded equipment, rock, sand, cellar dirt and industrial, municipal, and agricultural waste discharged into water" [33 U.S.C.
1362 ].
Federal courts have broadly interpreted "pollutant" to include a wide range of substances.
Depending on the circumstance, a pesticide could be considered a pollutant if it causes effects beyond its intended use.
Discharges from aquaculture operations,
 such as excess feed, farm-raised fish feces and chemicals used to treat lice on salmon, have been determined to be pollutants.
Point Source and Nonpoint Source Discharge
 Waterbodies can be polluted directly or indirectly by human activities and land use.
Directly discharging a pollutant into a waterway is called "point source" pollution.
The pollutant may be channeled by a pipe, ditch, tunnel, well, discrete fissure, concentrated animal feeding operation or a vessel.
Courts have found earth-moving equipment, such as bulldozers, to be conveyors of "point source" pollution.
The Act exempts agricultural stormwater discharges or return flows from irrigated agriculture from point source permitting regulations.
However, other agricultural activities are not exempt.
In some cases, manure spreaders, deep ripping by a tractor, off-shore fish net pens and pesticide applicators have all been found by courts to be point sources regulated by the Act.
"Nonpoint source" pollution involves water that is not purposefully directed toward a waterway, such as stormwater runoff from pastureland or cropland.
The Act does not require permits for nonpoint source pollution.
To legally discharge a pollutant directly into a waterway, a producer must first obtain a National Pollutant Discharge Elimination System
 permit.
The permit helps identify sources of pollution and establishes numerical limitations on each pollutant that can be discharged.
There are two types of NPDES permits, an individual permit and a general permit.
Individual permit A permit that covers only the applicant's discharge.
To receive this permit, a producer must submit an application to the Arkansas Department of Environmental Quality.
The state agency reviews the application and gives the public an opportunity to comment before issuing a decision on the permit.
If granted, the permit will be effective 30 days after notice of the final decision.
The permit would remain in effect for five years.
If denied, an applicant can appeal the decision to the Arkansas Pollution Control and Ecology Commission.
If the Commission rejects the application, a producer's last resort is filing an appeal with the circuit court.
General permit A permit that covers a specific geographic region and point sources that share common characteristics, such as for a stormwater sewer system or waste water processing plant.
To be covered by a general permit, a polluter must file a "Notice of Intent" with ADEQ that he or she intends to discharge into a waterway and wants to be covered by this type of permit.
A general permit contains limitations and conditions for pollutants.
For example, ADEQ has issued a general permit for pesticide applications near Arkansas' navigable waters.
To be included under the umbrella of this permit, a producer would have to notify ADEQ of his or her intentions to be included and the location of the discharge, as well as pay an application fee.
Arkansas' general pesticide permit expires February 28, 2017.
Appendix 1 can help you determine if your operation requires a general or an individual NPDES permit.
Concentrated Animal Feeding Operations
 Concentrated Animal Feeding Operations  are the only agricultural operation specifically identified in the Clean Water Act as a point source discharger.
Because of this designation, the Environmental Protection Agency  requires CAFOs to have an NPDES permit only when there is a discharge from the CAFO.
The EPA and ADEQ define CAFOs as those operations described below where animals are kept
 and raised in confined situations.
The Act divides CAFOs into sizes small, medium and large.
Large An operation that has no more than 700 mature dairy cattle; 55,000 turkeys; 30,000 laying hens or broilers if the house uses a liquid manure handling system; 125,000 broilers if the house uses a system other than a liquid manure handling system; or 82,000 laying hens if the house uses a system other than a liquid manure handling system.
Medium An operation that has between 200 to 699 mature dairy cows; 16,500 to 54,999 turkeys; 9,000 to 29,999 laying hens or broilers if the house uses a liquid manure handling system; 37,500 to 124,999 chickens  if the house uses a liquid manure handling system; and 25,000 to 81,999 laying hens if the house uses a liquid manure handling system.
The operation's wastewater comes in contact with surface water either by a pipe or man-made ditch or the animals come in contact with surface water.
Small An animal feeding operation that has fewer animals than a medium CAFO and has been designated by ADEQ to be a significant contributor of pollutants.
This designation is made on a case-by-case basis.
Medium and large CAFOs are required by the EPA to have an individual NPDES permit if they are discharging pollutants into waterways.
Small animal feeding operations may be required to seek an NPDES permit if ADEQ has designated the operation as a significant contributor of pollutants.
ADEQ has developed a general CAFO permit for operations that discharge manure, litter and process wastewater into waterways because of precipitation causing overflows.
However, a CAFO would need to file a "Notice of Intent" to be covered by the general permit before any discharge occurs.
Appendix 2 is a checklist provided to help you determine if your operation is covered by the general permit or if you may need an individual permit.
For more information on the CAFO general permit, see ADEQ's Fact Sheet for 2nd Draft General Permit No.
ARG590000 Concentrated Animal Feeding Operations  in the State of Arkansas.
Additionally, the EPA has identified potential sources of pollutants from poultry operations that operators should monitor to prevent discharges.
The potential sources include manure handling and storage activities, feed storage, litter storage and litter released through confinement house ventilation fans.
The Clean Water Act  also requires a permit to discharge dredge and fill material into waterways and some wetlands.
The U.S.
Army Corps of Engineers  is the permitting agency for Section 404 permits.
Dredge material is defined as material "that is excavated or dredged from waters of the United States."
 There are two types of Section 404 permits for which a discharger can apply:
 Individual permit This permit requires an application.
The Corps will review the application, allow for public comment and draft an environmental impact statement to determine the direct and indirect impacts of the proposed activity.
If the project passes review, the Corps will issue a Section 404 permit for a period of no longer than five years.
If the permit is denied, the applicant can appeal the decision through the Arkansas Pollution Control and Ecology Commission.
If the Commission denies the permit, the applicant may appeal that decision to the circuit court.
General permit The Corps can issue general permits for certain activities when they will have minimal environmental impacts for a specific region or nationwide, such as for streambank stabilization or for minor discharges of dredge and fill material.
A party seeking to use a general permit only has to follow the conditions set out in the permit and in some cases may be required to give Notification of Intent.
The CWA provides two agricultural exemptions from Section 404 permit requirements.
The CWA allows producers to continue farming wetlands and other areas that would fall under the law's protection.
The farming practice must be part of an established practice, or an on-going practice.
This exemption is a narrow exemption, but would allow producers to change types of crops grown.
The producer would lose the protection of the exemption and be required to get a Section 404 permit when the producer brings new areas, protected by the CWA, into production.
The second exemption allows producers the ability to build or provide maintenance to farm ponds, stock ponds, and irrigation and drainage ditches.
This exemption also includes discharges from siphons, pumps, head gates, wingwalls, weirs, diversion structures and such other facilities as are appurtenant and functionally related to irrigation
 ditches.
Arkansas producers could conduct maintenance and work on farm ponds and irrigation districts without needing to apply for a Section 404 permit.
The Clean Water Act limits point source discharges of pollutants into rivers and tributaries.
Agricultural activities are exempt from the Act in some cases, but not in every circumstance.
An agricultural producer should understand the reaches of the CWA in order to know when applying for a NPDES permit is necessary.
If the agricultural producer believes he or she might need an NPDES permit, then he or she should not hesitate to consult with a licensed attorney.
Average percent of fields by year fitting into the six categories.
The dry years 2020, 21 and 22 are different than the other years.
In the weighted average normal to wet years, 2017, 2018, 2019, 31% were ranked good, 13% were fair, 17% were wet late, 12% were wet early, 16% were wet all season, and 12% were very wet all season.
CROP SELECTIONS AND WATER ALLOCATIONS FOR LIMITED IRRIGATION
 Groundwater declines and dwindling surface water deliveries are normal rather than infrequent.
Record energy costs are driving irrigators to fewer applications or crops that require less water.
Irrigators have adjusted by turning to more efficient irrigation application techniques and water-conserving cropping practices.
All of these measures have given incremental improvement to the use and effectiveness of water at the farm level.
Irrigators choose crops on the basis of production capabilities, economic returns, crop adaptability to the area, government programs, crop water use, and their preferences.
When full crop evapotranspiration demand cannot be met, yieldirrigation relationships and production costs become even more important inputs for management decisions.
Under full irrigation, crop selection is driven by the prevailing economics and production patterns of the region.
Crops that respond well to water, return profitably in the marketplace and/or receive favorable
 government subsidies are usually selected.
These crops can still under perform in limited irrigation systems, but management decisions arise as water is limited: should fully watered cops continue to be used; should other crops be considered; what proportions of land should be devoted to each crop; and finally, how much water should be apportioned to each crop?
The final outcome of these questions is returning the optimal net gain for the available inputs.
Determining the relative importance of the factors that influence the outcome of limited-irrigation management decisions can become complex.
Commodity prices and government programs can fluctuate and change advantages for one crop relative to another.
Water availability, determined by governmental policy or by irrigation system capacity, may also change with time.
Precipitation probabilities influence the level of risk the producer is willing to assume.
Production costs give competitive advantage or disadvantage to the crops under consideration.
With computationally powerful personal computers becoming common on the desks of irrigators during the last 5 years, mathematical models for decision tools can be given to managers at their work place.
The objective of this project has been to create a decision tool with user interaction to examine crop mixes and limited water allocations within land allocation constraints to find optimum net economic returns from these combinations.
This decision aid is for intended producers with limited water supplies to allocate their seasonal water resource among a mix of crops.
But, it may be used by others interested in decisions concerning allocating limited water to crops.
Decisions are intended as a planning tool for crop selection and season allocations of land and water to crop rotations.
Net economic return is calculated for all combinations of crops selected and the water allocated.
Subsequent model executions of land-split  scenarios can lead to more comparisons.
The land split options are: 50-50; 2575; 33-33-33; 25-25-50; 25-25-25-25.
Irrigation system parameters, production costs, commodity prices, yield maximums, annual rainfall, and water allocation were also held constant for each model execution, but can be changed by the user in subsequent executions.
The number of crops eligible for consideration in the crop rotation could be equal to, or greater than, the number of land splits under consideration.
Optimum outcomes may recommend fewer crops than selected land splits.
Fallow is considered as a crop  because a valid option is to idle part of a field or farm.
The model examines each possible combination of crops selected for every possible combination of water allocation by 10% increments of the gross allocation.
The model has an option for larger water iteration increments to save computing time.
For all iterations, net return to land, management, and irrigation equipment is calculated:
 Net return =  
 commodity prices were determined from user inputs, crop yields were calculated from yield-irrigation relationships derived from a simulation model based on field research, irrigation costs were calculated from lift, water flow, water pressure, fuel cost, pumping hours, repair, maintenance, and labor for irrigation, and production costs were calculated from user inputs or default values derived from Kansas State University projected crop budgets.
All of the resulting calculations of net return are sorted from maximum to minimum and several of the top scenarios are summarized and presented to the user.
One of the features of CWA is that the user can choose among five land splits or fixed configurations of dividing the land resource.
These splits reflect the most probable crop-rotation patterns in western Kansas.
The user can examine the results of each one of the land splits in sequential executions of the model, but the algorithm treats land split as a constant during an individual scenario.
Producers divide their fields into discrete parcels, and rotate their crops in this same pattern, which led to this simplifying assumption and to the possibility of an iterative solution of the model.
The grain yield-irrigation relationship forms the basis for calculating the gross income from the crop Irrigation translates into grain yield, which combines with price to determine income.
Grain yields for corn, grain sorghum, sunflower, and winter wheat were estimated by using the "KS Water Budget V.
T1" software.
Software development and use are described in Stone et al.
, Khan , and Khan et al..
Yield for each crop was estimated from relationships with irrigation amount for annual rainfall and silt loam soils with loess origins derived from research in the High Plains of western Kansas and eastern Colorado.
The resulting yield-irrigation relationship for corn  shows a convergence to a maximum yield of 220 bu/ac from the various combinations of rainfall and irrigation.
A diminishing-return relationship of yield with irrigation applied was typical for all crops.
Each broken line represents normal annual rainfall for an area.
Figure 1.
Yield-irrigation relationship for corn with annual rainfall from 11-21 in.
The crop production budgets are the foundation for default production costs used in CWA.
Program users can input their own costs or bring up default costs to make comparisons.
For western Kansas, cost-return budgets for center-pivot irrigation of crops  provided the basis for default production-cost values for CWA.
Results can be sensitive to production costs, which require realistic production inputs.
This work was partly supported by the US Department of Interior, Kansas Water Resources Institute, and the USDA-ARS Ogallala Aquifer Research Initiative.
Wayne K.
Clatterbuck Associate Professor Forestry, Wildlife & Fisheries
 Late-season droughts are common in southeastern landscapes.
Many trees are stressed by prolonged periods of hot, dry weather.
Selecting trees that use water efficiently without the need for frequent watering or irrigation is one way to make your landscape more resistant to droughts.
With impending water shortages in many urban areas leading to prohibitions of irrigation or watering, planting trees that are more tolerant to drought conditions is the best long-term solution to a healthier, low-maintenance landscape.
Sassafras is a native tree that is tolerant of poor, dry sites.
A few of the factors to consider when selecting trees that use water efficiently are :
 Native trees are better adapted to local soil, moisture, climate and pest conditions than non-native trees.
Trees with small leaves  are more easily cooled and have better water-use efficiency than trees with larger leaves.
Upland species are usually more drought-resistant than bottomland species.
Early successional species, those that colonize old fields and disturbed sites , use water more effectively than late successional species.
Trees with deep, upright crowns are more effective in water use than those with flat, wide-spreading crowns.
Trees with multilayered crowns having many living branches and leaf layers  are more water-efficient than those trees with leaf canopies
 Willow oak with its narrow thin leaves and multilayered crown is an excellent drought-tolerant landscape tree.
Thick leaf waxes of eastern redcedar foliage assist in its drought tolerance.
that concentrate leaves in single layers along the outer edge of the crown.
Drought-tolerant plants usually have thick leaf waxes and bark, efficient stomatal control and extensive root systems.
Examples of a few trees that are not drought-tolerant include black cherry, dogwood, yellow-poplar, basswood, birch, buckeye and sycamore.
These species respond to drought by shedding their leaves prematurely or wilting.
Although there is not an ideal drought-resistant tree for every landscape, many trees have drought-resistant features and are more tolerant of dry conditions than others.
The following table lists some trees that will tolerate dry conditions once established.
However, as with any new planting, they will need to be watered until they are established.
ESTIMATING SOIL SALINITY USING REMOTE SENSING DATA
 Soil salinity is a severe environmental hazard  that impacts the growth of many crops.
Human-induced salinization is the result of salt stored in the soil profile being mobilized by extra water provided by human activities such as irrigation.
Salinization problems continue to spread around the world at a rate of up to 2 million hectares a year, offsetting a good portion of the increased productivity achieved by expanding irrigation.
Since the irrigated acreage in Colorado is fairly stable, any increase in soil salinity will have a direct impact on the agricultural production of the state.
Remotely sensed data has great potential for monitoring dynamic processes, including salinization.
Remote sensing of surface features using aerial photography, videography, infrared thermometry, and multispectral scanners has been used intensively to identify and map salt-affected areas.
Metternicht and Zinck  provided an approach for mapping saltand sodium-affected surfaces by combining digital image classification with field observation of soil degradation features and laboratory determinations in the semiarid valleys of Cochabamba, Bolivia.
Multispectral data acquired from platforms such as Landsat, SPOT, and the Indian Remote Sensing  series of satellites have been found to be useful in detecting, mapping and monitoring salt-affected soils.
Band ratios of visible to near-infrared and between infrared bands have proven to be better for identifying salts in soils and salt-stressed crops than individual bands.
Wiegand et al.
carried out a procedure to assess the extent and severity of soil salinity in fields in terms of economic impact on crop production and effectiveness of reclamation efforts.
Their results illustrate practical ways to combine image analysis
 capability, spectral observations, and ground truth to map and quantify the severity of soil salinity and its effects on crops.
Ghabour and Daels  concluded that detection of soil degradation by conventional means of soil surveying requires a great deal of time, but remote sensing data and techniques offer the possibility for mapping and monitoring these processes more efficiently and economically.
However, to assess the accuracy of the ability of satellite images to map and monitor salinity, it is necessary to compare them with field measurements of salinity.
Our research uses remote sensing techniques for the purpose of determining the spatial and temporal  extent and magnitude of salt-affected areas.
We have focused our initial studies in an area around La Junta, in the Arkansas Valley of Colorado.
We have used extensive field data to validate the accuracy of the remote sensing techniques.
The approach presented in this paper involves integrating remote sensing data, Geographic Information System , and spatial analysis to predict soil salinity.
First, soil salinity data was collected in the field.
The locations of the field samples were recorded on a Global Positioning System  unit, and a GIS map was generated.
The collected soil salinity data was tied to the corresponding points on a georeferenced Ikonos satellite image.
The soil salinity data are tested against the blue, green, red, and infrared bands of the satellite image as well as the normalized difference vegetation index  and the infrared band divided by the red band.
Stepwise regression is used to determine the combination of bands that best relate to soil salinity.
Ordinary least squares , spatial autoregressive , and spatial lag  models are used as regression models to correlate the variables.
The weighted average of the resultant matrix from the soil salinity data and the corresponding value from the satellite imagery is determined.
We are also testing a second approach in which we assume that the crop condition is the main indicator of the presence and severity of saline soils.
Elevated levels of soil salinity will affect the growth of most crops as well as their appearance.
This can be detected remotely using satellite images.
By enhancing the image, we can separate the crop condition into several classes.
Using spatially referenced ground data collected at the study area, we can relate each class in the satellite image to a level of soil salinity.
We can use these classes to create a signature file to classify other areas planted with the same crop.
As part of this project we have collected soil samples from over 100 locations, with each sample being comprised of four depths.
These samples were analyzed using the HACH SIW Salinity Appraisal, and a composite EC e  was calculated for each sample.
The calculated ECe values were compared to the EM-38 readings
 that were taken at each sample point.
After multiple iterations it was decided that a linear regression between the EM-38 vertical reading and the EC provided the best match.
From these data we developed the following regression model that converts EM-38 vertical readings into dS/m values:
 F = /10 where: SStemp = temperature of soil sample measured in deg C A = 1-0.203462 F + 0.038223  0.005554 
 SSTc = A * SStemp 
 EMvc = EMv * SSTc  ECe = 0.0877 * EMyc + 1.8303
 Salinity Relationship , temp corrected to 25 C
 Figure 1.
Regression equation relating EMv and ECe.
If equations with better correlations are developed to relate EM-38 readings to ECe, the work presented here can be updated to reflect these new equations.
However the methodology and approach will remain the same.
The criteria for selecting the best model are that it should have the smallest Akaike Information Corrected Criteria , a small standard error, a p-value of each selected variable less than 0.05, and a p-value of Moran's I of residuals larger than 0.05.
For the combination of variables shown in Table 1, the OLS model using a combination of the blue band, infrared band, NDVI, and IR/R created the most accurate map of soil salinity for the given combination of variables.
The SAR model was rejected because the p-value of the blue band was 0.3739.
The SLAG model was also rejected because the p-values for both blue and infrared bands were larger than 0.05.
For the OLS model, the p-value of Lagrange was 0 and the p-value of Moran's I was greater than 0.05.
The equation to predict soil salinity based on the results of the OLS model is:
 OLS predicted soil salinity = 8.5537 + 0.0099 * blue band 0.87 * infrared band 5.1164 * NDVI + 0.8918 * IR/R.
Table 1.
The output variable results of OLS, SAR, and SLAG models using blue, infrared, NDVI, and IR/R.
Variable	OLS	SAR	SLAG
 R2	0.524	0.2484	0.2401
 Residual	1.5598	1.3299	1.3544
 Intercept	Coefficient	8.5537	7.6347	3.3836
 p-value	0	0.0106	0.0276
 Standard	1.7585	2.9651	1.527
 Blue	Coefficient	0.0099	0.0055	-0.0007
 p-value	0.0372	0.3739	0.868
 Standard	0.0047	0.0062	0.0041
 Infrared	Coefficient	-0.0087	-0.006	-0.0008
 Band	p-value	0.0001	0.0187	0.6815
 Standard	0.0022	0.0025	0.0019
 NDVI	Coefficient	-5.1164	-6.8724	-8.9754
 p-value	0.0174	0.0042	0
 Standard	2.1378	2.3808	1.8563
 IR/R	Coefficient	0.8918	1.004	0.8289
 p-value	0.0113	0.0043	0.0068
 Standard	0.3496	0.3486	0.3035
 AICC	963.03	894.9011	900.4215
 Moran's I 	0.1741
 p-value of Moran's I	0.3814
 Likelihood p-value	0	0
 Figure 2 illustrates different ways of analyzing residuals, including a residuals histogram and graphs of the residuals versus the neighborhood number, predicted values, and the weight of residuals.
The residuals histogram has a normal distribution which means that the residuals are spatially independent.
The analysis of the residuals versus the neighborhood number, predicted values and
 the weight of residuals show that there is no clear trend for any residual which confirms that the residuals are spatially independent.
Figure 2.
Histogram of residuals and residuals versus neighborhood number, predicted values of soil salinity, and weight of residuals for the OLS when using the blue, infrared, NDVI, and IR/R.
A second set of band combinations was evaluated and the results are shown in Table 2.
For this set of band combinations the results show that the SAR model was the best model.
The SLAG model was rejected because the p-value of the infrared band was larger than 0.05.
The OLS model had a larger AICC than the SAR model, causing the OLS model to be rejected.
The equation to predict soil salinity based on the results of the SAR model is:
 SAR Predicted soil salinity = 9.6914 0.0047 * infrared band 8.3907 * NDVI + 0.8743 * IR/R.
Table 2.
The output variable results of OLS, SAR, and SLAG models using infrared, NDVI, and IR/R.
Variable	OLS	SAR	SLAG
 R2	0.5157	0.2469	0.2413
 Residual	1.5702	1.3295	1.3521
 Intercept	Coefficient	11.7136	9.6914	3.1976
 p-value	0	0	0.0001
 Standard	0.9092	1.8635	0.7829
 Infrared	Coefficient	-0.0052	-0.0047	-0.001
 Band	p-value	0.0006	0.024	0.4136
 Standard	0.0015	0.0021	0.0013
 NDVI	Coefficient	-7.6721	-8.3907	-8.7948
 p-value	0	0	0
 Standard	1.767	1.6657	1.5215
 IR/R	Coefficient	0.4692	0.8743	0.8566
 p-value	0.1037	0.0063	0
 Standard	0.2873	0.3172	1.5215
 AICC	965.3819	893.6044	898.3511
 Moran's I 	0.1837
 p-value of Moran's I	0.3713
 Likelihood p-value	0	0
 The histogram of residuals shown in Figure 3 has a distribution which is very close to normal, meaning that there is no correlation among the residuals and the residuals are spatially independent.
The other three parts of the figure also confirm that there is no correlation among the residuals and that they are spatially independent.
Histogram of Residuals for Corn Fields
 Residual Using SAR Model
 Figure 3.
Histogram of residuals and residuals versus neighborhood number, predicted values of soil salinity, and weight of residuals when using the SAR model for infrared, NDVI, and IR/R.
As mentioned earlier, a second approach to detecting soil salinity that we have been testing is to assume that the crop condition is the main indicator of the presence and severity of saline soils.
For this approach we selected a field with significant spatial variability in soil salinity  to be our calibration field.
A field which fits this criterion is shown in Figure 4.
The salinity of the field was determined using georeferenced EM-38 readings.
This calibration field allowed us to separate as many salinity classes as possible.
Nine different salinity levels were separated from the calibration field.
To separate these levels, we spatially linked the satellite image with the soil salinity map derived from field readings.
Using a combination of 3 bands  in the satellite image, we selected several pixels that specifically corresponded to a soil salinity level.
Reflectance values ranged from 200-800, with high salinity points clustered around the 700 pixel value, moderate salinity points around the 400-500 pixel value and low salinity points around the 200 pixel value.
The classified image was re-coded based on the soil salinity map obtained previously using the EM-38.
This re-coding was accomplished by spatially matching each class with the soil salinity values in the same area.
This process yielded three classes that represent the severity of soil salinity.
The classes were low , moderate  and high.
Figure 4.
Soil salinity map generated from field data VS.
map generated from satellite image.
To examine the accuracy of the satellite generated map, a comparison was done between the ground data map and the re-coded satellite image.
The histograms in Figure 5 show this comparison.
Fifty five percent of the field-data generated map had soil salinity levels of less than 3.8 dS/m.
In the satellite map, 62% of the field registered no loss, indicating salinity levels of less than 3.8 dS/m.
Areas where soil salinity levels ranged from 3.8 to 5.8 are considered moderate loss areas and covered 42% of the field in the map generated by the field data.
In the satellite image, moderate loss areas comprised 25% of the field area.
The highest crop loss falls within areas that have soil salinity of over 5.8 dS/m.
These areas encompassed 3% of the field in the field-data generated map.
In the satellite image 13% of the field is shown to have severe loss.
To validate this approach, the soil salinity was mapped using an EM-38 in another corn field that falls within the calibrated image.
In this validation field, 64 EM-38 soil salinity measurements were taken.
A map was generated that shows the severity of the soil salinity in the validation field expressed in terms of low , moderate  and high  levels.
Table 3 compares the soil salinity map generated from the satellite image with the soil salinity map generated from the EM-38 measurements for the validation field.
The comparison shows there was less error when mapping the low salinity areas, which was expected because of the uniformity of the crop in the low salinity areas.
No errors were generated when mapping the high salinity zones.
Figure 3.
Histogram developed from the maps generated from the EM-38 and the satellite image.
Table 3.
Percentage comparisons of salinity levels shown in the two maps.
Class	Ground Data	From Satellite
 Low salinity	72.53 %	66.17 %
 Moderate	22.05 %	21.53 %
 High salinity	5.42 %	12.29 %
 The over estimation of the high salinity area was because of the existence of a road on the west edge of the field which was classified as a high salinity area because it has no vegetation.
Such errors could be eliminated by masking roads and canals as well as bare soil areas  in the classified image.
Figure 4.
Histogram comparison of the salinity map generated from field data vs.
the satellite image map.
The results presented in this paper show the feasibility of using remote sensing data to estimate soil salinity for corn fields.
Compared to the labor, time, and money invested in field work devoted to collecting soil salinity data, the
 availability and ease of acquiring satellite imagery is very attractive.
The results of our two approaches were:
 1) Stepwise regression yields the best combinations of bands to use 90% of the time.
The SAR model using the infrared, NDVI, and IR/R combination was evaluated to be the best of all the tested models as it satisfied all the selection criteria and has the smallest AICC value.
2) The approach using crop condition as the main indicator of saline soils has worked very well in our study area.
The histogram comparison in Figure 4 shows that the calibrated satellite image matched the data collected with the EM-38 with an overall error of less than 15%.
Chapter: 40 Grass and Grasslike Weeds in South Dakota Cornfields
 When choosing an herbicide, always read and follow label instructions.
It is a violation of federal pesticide laws to use an herbicide in a manner not compliant with labeling as to rate, timing, and other restrictions.
Read the entire label prior to use.
Always follow applicator safety instructions.
Protect water quality by preventing chemical accidents and spills, back siphoning, mixing, and applying away from water sources.
Herbicide applicators are responsible for following all herbicide label directions and precautions.
Volunteer corn 
 Volunteer corn is an annual plant that typically emerges just before or just after corn planting depending on soil temperature and moisture conditions.
The plants are from seed or from previous crops.
Plant Description: Looks like hybrid corn but is outside the row or in clumps if corn ears are present.
Problems are heightened by corn monoculture systems or when herbicide-resistant varieties were planted in previous years.
Areas of Infestation and Yield-loss Potential: Volunteer corn typically is scattered throughout past year's cornfields.
Volunteer corn actually increases corn yield if ears develop.
If no ears develop, then 15% to 20% yield loss may occur.
The problem is that corn grain from volunteer corn may be of poor quality or wetter than hybrid corn.
Cultural Management: Use techniques that minimize harvest loss discussed in Chapter 36.
If a glyphosatetolerant  or glufosinate-tolerant  variety was planted, rotate to a broadleaf crop and use a grass herbicide and cultivate interrow areas.
If a sethoxydim-tolerant  variety was planted, use glyphosate or glufosinate for control because ACCase inhibitors may not control these volunteer plants.
Table 40.1 Timing of weed emergence and yield-loss potential of the selected grass and grasslike weeds.
Information on herbicide-resistant weeds is available in Chapter 43.
Time of emergence	Weed	Yield-loss potential	Notes
 Early season	Volunteer corn	Low to moderate	May be resistant to several herbicides depending on the
 hybrid used in past years.
Early to midseason	Woolly cupgrass	Moderate	Postemergence grass herbicide provides good control, and
 not controlled by most preemergent grass herbicides.
Early season	Jointed goatgrass	Unknown	Can be troublesome after wheat crop.
May germinate as a
 winter annual in October.
Early season	Foxtail barley	Moderate	No resistance reported.
Early season	Downy brome	Low
 Early season	Japanese brome	Unknown
 Early season	Quackgrass	Unknown
 Early season	Giant foxtail	Moderate	May be resistant to ACCase inhibitors (WSSA Group 1,
 Midseason	Yellow foxtail	e.g., sethoxydim), ALS inhibitors (WSSA Group 2, e.g.,
 Midseason	Green foxtail	sulfonylureas/imidazilinones), microtubule assembly
 inhibitor , and Photosystem
 II inhibitors.
Midseason	Robust green foxtail	Unknown
 Midseason	Bristly foxtail	Unknown
 Midseason	Yellow nutsedge	Low	Found in wet areas but can spread to drier sites.
Reproduces
 from nutlets that can be spread through cultivation.
Late season	Longspine sandbur	Low	No herbicide resistance reported.
Late season	Barnyardgrass	Low	May be resistant to ACCase inhibitors (WSSA Group 1, e.g.,
 sethoxydim) and Photosystem II inhibitors (WSSA Group 5,
 Late season	Large crabgrass	Low	May be resistant to ACCase inhibitors (WSSA Group 1, e.g.,
 Late season	Witchgrass	Low	May be resistant to Photosystem II inhibitors (WSSA Group
 Late season	Wild proso millet	Moderate to high	No resistance reported.
Late season	Fall panicum	Moderate	No resistance to herbicides in the U.S.
Late season	Switchgrass	Unknown	Found in CRP fields or field edges that bordered CRP.
Late season	Scouring rush	Low	No resistance reported, although difficult to control; found
 Field horsetail	in areas that may have been flooded or very wet.
High yield-loss potential = > 5% yield loss with 1 plant or fewer per foot of row Moderate yield-loss potential = > 5% yield loss when plant density is 5 to 10 plants per foot of row Low yield-loss potential = > 5% yield loss when plant density is > 10 plants per foot of row
 Herbicide Resistance: Hybrid dependent based on transgenic traits; glyphosate , glufosinate , or sethoxydim.
Woolly cupgrass 
 Woolly cupgrass  is an annual that reproduces by seed and emerges before or just after corn planting.
Germination may occur over an 8to 10-week period from cold or warm soil, under dry or wet conditions, and due to large seeds, can germinate from up to 6" deep.
While the seed does not need light to stimulate emergence, if the crop canopy is opened due to hail or other factors, woolly cupgrass will emerge if seed is present.
Plant Description: The cotyledon  and first true leaf are very wide.
Leaves are covered in fine soft hair.
One of the leaf margins on each leaf generally is crinkled.
This plant is often confused with foxtail grass species, but typically does not tiller as much as a foxtail.
The seed head of woolly cupgrass is a distinctive panicle with compressed rows of seed that are only on one side of the rachis.
The seeds are oval and vary in color from tan to brown to green.
Seeds in the soil can remain viable for up to 5 years.
Areas of Infestation and Yield-loss Potential: Woolly cupgrass is found in fertile loam to clay loam soils.
If uncontrolled, low to moderate densities can cause up to 50% yield loss in corn.
However, due to glyphosate  or glufosinate  applications, woolly cupgrass has become less of a problem.
Tillage or rotary hoeing corn can be an effective cultural control.
Rotating to soybean or alfalfa  can also help reduce the infestation.
Herbicide Resistance: None has been reported although preemergent grass herbicides that act to inhibit very long-chain fatty acid synthesis  often do not provide adequate control.
Jointed goatgrass 
 Jointed goatgrass  emerges as a winter annual or in the spring before corn planting.
Plant Description: Jointed goatgrass is an annual, reproducing by seeds.
This plant lacks auricles (small projection at the base of the leaf that wraps
 Figure 40.1 Woolly cupgrass seedling , leaf edge with crinkled margin, seed head , and infestation on the edge of a cornfield.
around the stem) at the leaf opening.
Leaf blades are flat without hair or with short hairs.
Leaf margins have hairs near the blade base.
The leaf ligule  is membranous.
The inflorescence  is a compact spike.
Seeds are cylindrical and about the same size as wheat.
Areas of Infestation and Yield-loss Potential: Found in many different types of soil along the roads and in pastures.
This weed is problematic in wheat crops, but at this time, no information on corn yield loss is available.
Deep tillage to bury seed is often an effective method for control of jointed goatgrass.
Herbicide Resistance: No reported resistance.
Foxtail barley 
 Foxtail barley  is a cool-season perennial grass that emerges early in the season.
Overwintering plants can start growth very early in the growing season and will produce a seed head by late-May or early-June.
It is a clump grass, that does not spread widely, but seed will start new infestations.
Plant Description: The vegetative stems of foxtail barley are round and hairless.
The ligule is membranous, blunt, and with a few hairs.
Clasping auricles are found at the collar region.
The glumes and lemma of the seed have long  awns that are often purplish in color.
Areas of Infestation and Yield-loss Potential: Foxtail barley grows well in saline, wetland sites and is often found in field edges and roadsides.
This plant is more problematic in no-till fields due to lack of tillage disturbance.
Due to soil problems, corn growth may be poor and yields low in the area where this weed is growing.
However, the yield reductions may not be primarily due to foxtail barley interference.
Soil management to decrease water and salt problems in infested areas may be warranted.
The areas may be too saline to produce corn.
Herbicide Resistance: No known resistance.
Downy brome 
 Downy brome  is an annual plant, reproducing from seed that typically emerges in the fall or early spring.
Plant Description: Leaves and sheathes of downy brome plants have soft hairs.
The ligule is a short membrane , rounded and may be toothed.
The inflorescence is a drooping panicle with many branches.
There are long awns on the seed.
The plant dries early in the summer and can be a fire hazard.
Typically occurs in localized areas.
Yield-loss Potential: Yield loss is undetermined for corn; however, this plant can cause high yield losses in wheat.
Use cultural practices with crop rotation , control preplant if possible using burn-down type applications prior to planting
 Herbicide Resistance: Biotypes in the U.S.
have been reported to be resistant to ACCase inhibitors , and ALS inhibitors.
Around the world, other biotypes have been reported that are resistant to urea-type herbicides, and Photosystem II inhibitors (WSSA Group
 Japanese brome 
 Japanese brome  is a winter annual that germinates from seed in the late fall and remains vegetative until spring.
Plant Description: Leaf sheath is hairy while the blade is hairless.
Short awns on the seed.
More upright seed head than downy brome.
Areas of Infestation and Yield-loss Potential: Typically occurs in localized areas.
Yield loss is undetermined in corn.
Herbicide Resistance: Biotypes in the U.S.
have been found to be resistant to ALS inhibitors.
Cheat  
 Cheat , an annual grass, typically emerges in the fall or early spring before or just after corn planting depending on soil temperature and moisture conditions.
Cheat initiates its reproductive growth in mid-March, flowers in May, and matures in early June.
Plant Description: The ligule of cheat is rounded and may be toothed.
There are short awns on the seed.
At the seedling stage, this plant is very similar in appearance to the closely related species downy brome, but cheat becomes less hairy as it matures.
Areas of Infestation and Yield-loss Potential:
 Typically occurs in localized areas, prefers dry soil conditions.
Yield loss in corn is undetermined.
Use cultural practices with crop rotation.
Control this plant using preplant herbicides if possible or use burndown type applications.
Herbicide Resistance: Biotypes in the U.S.
have been found to be resistant to herbicides with ALS inhibitor mode of action.
Downy brome Ligule margins more sharply pointed
 Figure 40.7 Line drawing of cheat.
Quackgrass  is a perennial plant, which reproduces primarily through rhizomes and seed.
It is a non-native, cool-season grass emerging before corn.
Plant Description: The leaf sheath is rough, flattened toward the collar without hair.
The leaf blades are flat and either smooth without hairs or slightly hairy.
The ligule is membranous and short , and auricles may be seen clasping the sheath.
The seed head is slender.
Rhizomes are extensive and sharply pointed.
Areas of Infestation and Yield-loss Potential: Found in moist soils.
Yield losses are moderate, although if high densities occur with rhizomes present, yield losses can be high.
Unfortunately, tillage will spread rhizomes and increase pockets of infestation.
Herbicide Resistance: No reported resistance.
Giant foxtail 
 Giant foxtail , an annual reproducing by seed, emerges before or just at the time of corn planting when temperatures are warm.
Seeds do not require a dormancy period and if seeds mature in midsummer, they can sprout in late summer or fall if temperatures and moisture are favorable.
Plant Description: Giant foxtail is infrequently found in South Dakota.
The upper leaf surface is densely covered with short hairs and the plant has a hairy ligule.
Giant foxtail has long  nodding heads, whereas green, yellow, and bristly foxtails have straight panicles.
Giant foxtail can grow up to 7 ft tall.
Areas of Infestation and Yield-loss Potential:
 Common in several soil types and in many climates.
Yield losses are moderate to high.
This foxtail is much more aggressive than green or yellow foxtails.
Tillage and postemergence cultivation can be effective control measures.
Solid-seeded legume or grass crops, or narrow-spaced row crops can provide an effective shade canopy to reduce giant foxtail growth.
Herbicide Resistance: Giant foxtail has been reported to be resistant to Photosystem II inhibitors , ALS inhibitors  and ACCase inhibitors.
Yellow foxtail 
 Yellow foxtail  is an annual plant, reproducing by seed, and emerges toward the end of corn planting.
Plant Description: Common in eastern South Dakota fields.
Yellow foxtail has long yellow hairs near the
 ligule, a flattened stem, and larger seeds than green or giant foxtails.
Areas of Infestation and Yield-loss Potential:
 Common in several soil types and in many climates.
Depending on density, corn yield losses can approach 50%.
Tillage may control yellow foxtail.
Herbicide Resistance: Biotypes of these foxtails have shown resistance to a number herbicides with different modes of action.
Yellow foxtail has been reported to be resistant to ALS inhibitors  and Photosystem II inhibitors, such as atrazine.
Yellow foxtail is more tolerant to labeled rates of atrazine when compared with giant or green foxtail.
Green foxtail 
 Green foxtail  is an annual plant, reproducing from seed and emerging toward the end of corn planting.
Typically, green foxtail will emerge before yellow foxtail.
Plant Description: Green foxtail has no or few hairs on the leaf blade, a round stem, and seeds are small.
Areas of Infestation and Yield-loss Potential:
 Common in several soil types and many climatic regions.
Depending on density, corn yield losses can approach 50%.
Tillage, crop rotation, and postemergence cultivation may be effective control measures.
Figure 40.10 Photographs of yellow foxtail and green foxtail collar regions.
Figure 40.11 Photographs of yellow foxtail and green foxtail inflorescences.
Note the large seeds on yellow foxtail vs.
small seeds on green foxtail.
Herbicide Resistance: Biotypes of these foxtails have shown resistance to a number of herbicides with different modes of action.
Green foxtail has been reported to be resistant to microtubule assembly inhibitors [dinitroanaline ] , ALS inhibitors , ACCase inhibitors , very long-chain fatty acid inhibitors   and Photosystem II inhibitors.
Bristly foxtail 
 This warm-season annual grass emerges after corn emergence, usually at the same time as yellow foxtail.
Plant Description: Bristly foxtail  can have a height of 1 to 4 feet with branching stems that bend sharply upward and without hair.
The ligule has a fringe of hairs from a membranous base.
Inflorescence is panicle, cylindrical, and spikelike.
Bristles within the inflorescence and seed adhere to animals and clothing and can be identified from other foxtails by firmly touching the inflorescence to determine whether it lightly sticks to the skin.
Areas of Infestation and Yield-loss Potential: Bristly foxtail is found in waste places, gardens, and cultivated fields in the central and eastern Great Plains.
No yield-loss data for corn is available.
Tillage, crop rotation, and postemergence cultivation may be effective control measures to reduce stand numbers.
Herbicide Resistance: No cases of resistance reported in North America.
Yellow nutsedge 
 Yellow nutsedge  is a perennial plant that will emerge before or at planting.
Plant Description: Yellow nutsedge is a non-native plant that reproduces by seeds, rhizomes, and tubers.
This plant has erect, triangular stems without hair that appear waxy.
The leaves are grasslike-looking blades, pale green without hair.
The seed heads are compact.
Areas of Infestation and Yield-loss Potential:
 Found by streams and wet areas in fields.
Yield-loss potential is low, however, because of the habitat, corn yield may be low due to wet conditions and not due to competition with yellow nutsedge.
Adequate water drainage to wet parts of the field may reduce yellow nutsedge problems.
Chemical control is limited, but glyphosate  may provide control of emerged yellow nutsedge.
Herbicide Resistance: None reported at this time.
Stinkgrass  is an annual reproducing from seed.
It is a warm-season grass that emerges after corn planting.
Plant Description: The blade is flat with warty glands on margins and backsides.
Stiff hairs may be present at the collar region.
Ligule is a short fringe of hairs.
If crushed, stinkgrass has an unpleasant odor.
Areas of Infestation and Yield-loss Potential:
 Roadsides, fields, or heavily grazed pastures.
Yield loss is undetermined in corn, but heavy infestations will reduce yields.
Herbicide Resistance: None reported.
Shattercane  is an annual plant, reproducing by seed.
It is a warm-season grass that emerges after corn.
Plant Description: Shattercane is an erect, "cornlike" plant with a jointed stem.
The sheath is round.
The ligule is membranous and ciliate that is rounded or blunt and rarely pointed.
This plant has a panicle inflorescence that is loose and often droops to one
 side at maturity.
Mature seeds disperse from seed head easily, promoting the plant's re-infestation in a field.
Areas of Infestation and Yield-loss Potential: Found in many crop fields such as corn, grain sorghum, and soybeans.
Significant yield loss in corn occurs when shattercane is allowed to reach 12 inches in height, even though it is removed soon after that.
This weed is difficult to control in corn.
Tillage, crop rotation, and postemergence cultivation can be effective control measures to reduce stand numbers.
Pre-emergent and postemergent grass herbicides typically used in corn can be used for control.
Herbicide Resistance: Resistance to certain ALS inhibitor herbicides  have been reported in Nebraska, Kansas, Iowa  as well as a few other states across the country.
Longspine sandbur 
 Longspine sandbur  is a non-native, warm-season grass, reproducing from seed and emerging after corn planting.
Plant Description: This annual plant has flattened stems that have hair, and leaves may be rough to the touch.
The plant has a short-fringed, hairy ligule.
Seeds are enclosed in sharp, spiny, hairy burs that are characteristic and give the plant its name.
If it is sat on , the spines will go through the heaviest denim.
Areas of Infestation and Yield-loss Potential: Found in sandy soils, although may be found in fertile loam to clay loam soils.
Yield loss is often low.
Nuisance plant due to sharp burs.
Tillage may be effective when sandbur is small.
Crop canopy closure provides competition with shading and reduces growth.
Glyphosate is an adequate control measure for longspine sandbur.
Herbicide Resistance: None has been reported.
Barnyardgrass  is a warm-season, annual grass that reproduces by seed and emerges after corn planting.
Plant Description: This grass has flattened, smooth, and branched stems without an auricle or ligule.
This grass has broad leaves and typically is reddish or purple at its base.
Barnyardgrass size can vary from 2" tall with only 1 tiller to over 4 ft tall with 50 +
 Figure 40.18 Barnyardgrass collar region and seed head.
Areas of Infestation and Yield-loss Potential: Larger plants are found around field edges, in wet areas, or in areas with poor canopy cover.
Yield loss is often low due to late emergence.
Tillage may be effective when plants are small.
Shade under a crop canopy reduces growth.
Herbicide Resistance: Biotypes have been reported to be resistant to Photosystem II inhibitors , ACCase inhibitors , and other chemicals.
Large crabgrass 
 Large crabgrass  is an annual, warmseason grass, reproducing by seed and emerging after corn emergence.
Plant Description: Large crabgrass has hairs everywhere on plant, a flattened stem, membranous ligule, and the seed head appears to be fingerlike spikes.
This grass can grow from 6" to 2 ft tall.
Areas of Infestation and Yield-loss Potential: No specific growing requirements.
Yield losses are low, even at high densities.
Tillage, crop rotation, and postemergence cultivation may be effective management tools to reduce stand numbers.
This grass is often difficult to control postemergence and should be controlled with pre-emergence chemicals.
Herbicide Resistance: Herbicide resistance has been reported to ACCase inhibitors  in Wisconsin.
Figure 40.19 Large crabgrass collar region and mature plant.
Wild proso millet 
 Wild proso millet  is an annual grass, reproducing from seed, and emerges late in the season, after corn emergence.
Plant Description: This warm-season grass has a round stem with membranous ligule tipped with a fringe of hairs.
Seedlings look like corn but are hairy.
Leaf blades are flat.
Hairs may or may not be on the blade and sheath but hairs are present at nodes.
This grass can grow up to 6 ft tall.
Seeds are large and shiny.
They vary in color and may be white, green-striped, olive-brown, or black.
The seed often remains on the root of seedlings, which helps in identification.
Nonblack seeds in soil are usually not viable after two seasons; black seeds have been reported to remain viable for up to 4 years.
Areas of Infestation and Yield-loss Potential:
 Tolerates sandy, dry soils, and high temperatures.
Yield loss is moderate to high.
Tillage may be effective when plants are small.
Shading by the crop canopy reduces growth.
Sanitation of equipment is suggested to prevent spread.
Herbicide Resistance: None noted at this time.
Witchgrass  is a warm-season, annual grass, reproducing by seed, and emerges after corn emergence.
Plant Description: Witchgrass has a flat stem with long, soft hairs covering most of the plant.
The ligule is a fringe of hair.
Panicles are an open inflorescence, spreading, hairy, and large.
The panicle may be 1/2 or 2/3 of the size of the whole plant.
When mature, the panicle can break off and tumble along the ground.
Areas of Infestation and Yield-loss Potential:
 Witchgrass grows well in sandy, droughty soil.
Due to late emergence, yield loss is low, even at high densities.
Herbicide Resistance: A biotype of witchgrass, resistant to Photosystem II inhibitor herbicides  has been reported in Canada.
Fall panicum 
 Fall panicum  is a warm-season, annual grass, reproducing by seed.
Plants emerge late in the season, after corn has emerged.
Plant Description: Vegetative stems often are confused with witchgrass, although fall panicum has few hairs.
Sheath is round.
Leaves emerge from the nodes in an alternate fashion.
Blade is hairless and midrib is usually white and prominent.
Seeds are bigger than witchgrass seed, but not as large as proso millet seed.
Areas of Infestation and Yield-loss Potential: Fall panicum grows well in sandy or droughty soil types.
Yield-loss potential is moderate.
Herbicide Resistance: Worldwide, only Spain has reported resistance to Photosystem II inhibitor herbicides.
Switchgrass  warm-season, perennial grass emerges late in the season from seed and rhizomes after corn has emerged.
Plant Description: The plant often escapes from waterways or other areas, where it may be grown for soil stabilization.
Vegetative stems are sometimes confused with witchgrass.
There is a V-shaped patch
 of hair on the upper leaf surface near the stem.
Bands of white hairs are located on the ligules, and the stem has dark-colored, swollen nodes.
Plants can grow up to 6 ft tall.
Switchgrass is grown in stands for biofuel but escaped plants can be problematic.
Areas of Infestation and Yield-loss Potential: Switchgrass grows well in sandy or droughty soil types, but is used in waterways for stabilization.
Yield-loss potential is moderate.
Pre-emergence grass herbicides other than atrazine may provide acceptable control.
Herbicide Resistance: Escaped plants can be difficult to control and are tolerant of atrazine.
Scouringrush  and Field horsetail 
 These warm-season, grasslike plants are perennials that reproduce from rhizomes and spores and are slow to establish.
Plants usually emerge after corn emergence.
Plant Description: Both scouring rush and field horsetail have hollow stems.
Scouring rush  stems are erect, green, and unbranched.
Most field horsetail  plants have many branches that occur in whorls at the stem joints.
Stems of both plants contain silica and were used to scrub pans.
Areas of Infestation and Yield-loss Potential:
 Commonly found in wet roadside ditch areas.
These plants encroach into field edges but are often slow to spread.
Corn will not grow well in the wet soils where high infestations of these plants are found.
Therefore, these infestations appear to be highly competitive with corn.
In drier soils, these plants can establish, but at this time, no specific yield-loss data is available.
Due to the perennial rhizomes of these weeds, tillage may spread the problem, but repeated mowing may exhaust the rhizome carbohydrate supply.
Herbicide Resistance: None reported.
Storage efficiency of preplant irrigation
 ABSTRACT: Drainage and water storage efficiency of preplant irrigation in the deep silt loam soils of western Kansas were evaluated.
Drainage from the soil profiles was significant, even when soil water contents were less than the "field capacity" value, if extended drainage times were involved.
The Ulysses , Richfield , and Keith  soils drained 89, 61, and 69 mm , respectively, from day 3 to day 33 following thorough wetting of the soil profiles.
From day 33 to day 63, the Richfield drained 18 mm  and the Keith drained 23 mm.
For a given soil and precipitation pattern, storage efficiency of preplant irrigation was influenced largely by soil water content immediately prior to irrigation and by irrigation amount, with storage efficiency decreasing as either or both factors increased.
Irrigation management during the growing season influenced soil water content after barvest and thus water storage efficiency during the off-season.
If preplant irrigation is not necessary to establish a crop, irrigation water should be reserved for seasonal application.
P replant irrigation  is a water management practice in which water is applied in advance of the growing season, sometimes several months in advance.
The practice is common in the central and southern High Plains of the United States , a region with low precipitation probabilities, deep soils with large water-holding capacity, and irrigation from pumping groundwater.
In a survey from the late 1980s, 64 percent of the respondents from three counties in western Kansas and 69 percent of the respondents from three counties in western Texas reported that they practice preplant irrigation.
Although preplant irrigation is a water management option, it should not be viewed as an efficient water management practice.
Stone et al.
concluded that maximum yield benefit from irrigation is achieved when water
 L.R.
Stone is a soil physicist in the Department of Agronomy, Kansas State University, Manhattan, KS, 66506; A.J.
Schlegel is the agronomist-in-charge, Tribune Unit, Southwest Kansas Research-Extension CenterTribune; F.R.
Lamm is an agricultural engineer with the Northwest Kansas Research, Extension Center, Colby, KS, 67701; and W.E.
Spurgeon is an agricultural engineer with the Southwest Kansas Research-Extension Center, Garden City, KS 67846.
Contribution No.
92-378-J, Kansas Agricultural Experiment Station.
is applied during the growing season, as opposed to off-season.
In a review of preplant irrigation, Musick and Lamm  stated that water use efficiency of preplant irrigation is less than that of seasonal irrigation.
Lamm and Rogers  concluded that "in most years fall preseason irrigation for corn is not needed to recharge the soil profile in northwest Kansas." They added, "Preseason irrigation is a tool that should be used wisely to minimize unnecessary costs and water use." Musick and Lamm  stated, "as groundwater supplies available from the Ogallala Aquifer continue to decline, pumping energy costs remain high or further increase, and the High Plains area continues a transition to dryland agriculture, the advisability of applying large preplant irrigations to fully rewet the soil profile before planting will be increasingly questioned."
 Water storage efficiency of preplant irrigation varies with conditions of precipitation, evaporative demand, soil water content, and hydraulic characteristics of the soil profile.
In regions with high water-storage soils and low rainfall probabilities conducive to preplant irrigation, water storage efficiency of preplant irrigation is strongly influenced by soil water content, with efficiency decreasing as water content increases.
Therefore, by considering water content of the soil profile at the time of preplant application, projected water storage efficiencies and the need for preplant irrigation can be assessed.
The purpose of this paper is to examine water storage efficiencies associated with
 J.
Soil and Water Cons.
49 : 72-76
 preplant irrigation.
With an understanding of water storage efficiencies, a producer can decide if preplant irrigation is needed, and if SO, how much water should be applied.
Preplant irrigation in addition to seasonal irrigation
 Research with corn  and grain sorghum [Sorghum bicolor  Moench], using irrigation schemes with or without preplant irrigation in addition to surface seasonal irrigations, has shown preplant irrigation did not influence grain yield significantly.
Results from a preplant irrigation study with grain sorghum near Bushland, Texas, are summarized in Table 1.
Although the preplant irrigation applied an additional 106 mm  of water, grain sorghum yield was increased by only 176 kg/ha.
Results from a preplant irrigation study with corn near Tribune, Kansas are summarized in Table 2.
The corn research plots at Tribune were level basins and all irrigations were 152 mm.
Treatments having three seasonal irrigations showed no significant difference in corn grain yield, regardless of whether a fall, spring, or no preplant irrigation was added.
Long-term precipitation patterns for those two locations are presented in Figure 1.
The long-term mean annual precipitation for Amarillo, Texas,  is 518 mm  and for Tribune is 415 mm.
Both locations receive low precipitation amounts during the winter.
Studies such as these show that preplant irrigation is of no or questionable benefit under conditions where two or three surface irrigations are applied inseason to summer row crops.
With seasonal irrigation adequate for relatively high yields, residual soil water going into the off-season is great enough to significantly reduce the water storage efficiency from precipitation and irrigation during the off-season.
Seasonal irrigation is primarily responsible for crop yield response and the yield influence derived from off-season irrigation is low.
More efficient use of water resources can be achieved by ensuring crop germination and establishment through improved soil water conditions in the upper profile by tillage and residue management practices that conserve winter and spring precipitation and by timely planting.
Irrigation water
 Table 1.
Grain sorghum yield as influenced by preplant irrigation near Bushland, Texas.
No irrigation	0	1,502
 No preplant 2 or 3
 seasonal irrigations	300	6,572
 Preplant plus 2 or 3
 seasonal irrigations	406	6,748
 Table 2.
Corn yield as influenced by irrigation treatments involving preplant and seasonal irrigations near Tribune, Kansas.
1.
Fall preplant	152	4,749
 2.
Spring preplant	152	5,136
 3.
Fall preplant + tasseling	305	6,777
 4.
Spring preplant + tasseling	305	7,948
 5.
12-leaf + silking + blister kernel 	457	8,931
 6.
Fall preplant + 12-leaf + silking + blister kernel	610	9,513
 7.
Spring preplant + 12-leaf + silking + blister kernel	610	9,113
 *Selected statistical comparisons involving grain yield of treatments 1 versus 2, 3 versus 4, 6 versus 7, and 5 versus 6 versus 7 found no significant difference at the 0.05 probability level.
then can be applied in-season, as opposed to off-season, which gives a higher yield response and greater water use efficiency.
Timing of preplant irrigation
 A frequent question about preplant irrigation is the influence of timing.
Research has shown timing of preplant irrigation has little influence on water storage efficiency and the resulting grain yield of summer row crops.
In comparisons of all treatment pairs having spring or fall preplant irrigation, timing of preplant irrigation in the corn study near Tribune  did not influence grain yield significantly.
In the grain sorghum study near Bushland , timing of preplant irrigation from early December through mid May had no significant influence on grain yield or on water storage efficiency of preplant irrigation and preseason rainfall.
The preplant irrigation research at Bushland  involved 300 mm  of seasonal irrigation.
The preplant irrigation research at Tribune  included a range of seasonal irrigation from none to 457 mm .
Therefore, test results indicate that timing of preplant irrigation does not influence water storage and grain yield regardless of seasonal irrigation amount.
Precipitation storage during winter and spring
 Although many factors of weather, precipitation patterns, soil surface conditions, soil hydraulic characteristics, and soil water content influence precipitation storage efficiency, research has often found water storage during winter and spring to be in the range of 30 to 50 percent of the precipitation received.
Water storage efficiency of about 40 percent of the total of preseason irrigation and rainfall was measured from late fall to mid May near Bushland .
When measured from late fall to late June, water storage efficiency was about 30 percent of preseason irrigation and rainfall.
From a 10-day simulation of profile water storage for a loam soil with no runoff or drainage, Hillel and van Bavel  found a precipitation storage efficiency of 43 percent.
Greb et al.
reported that fallow techniques using better management of stubble mulch and weed control increased precipitation storage efficiencies to the 35 to 41 percent range in the central Great Plains.
Net storage of soil water from December 1 to April 1 is presented versus percent available soil water on December 1 in Figure 2.
The relationship in Figure 2 was calculated by using the water storage equation from Stone et al.
and the long-term precipitation
 Table 3.
Grain sorghum yield and storage efficiency of preplant irrigation and rainfall as influenced by time of preplant irrigation near Bushland, Texas.
of preplant	Late fall	Late fall	Grain
 irrigation	to mid May	to late June	yield
 December 7	41.7	31.4	6,654
 January 20	38,3	26.8	6,685
 March 6	43.5	30.3	6,666
 April 10	40.0	28.8	6,867
 May 16	28.4	6,767
 Figure 1.
Mean precipitation by month from long-term records at Amarillo, Texas and Tribune, Kansas.
value for December 1 to April 1 at Tribune of 53 mm.
The water storage equation was developed by using data from research plots with berms to prevent runoff and runon.
With 15 percent available soil water on December 1 and a mean precipitation total of 53 mm , net storage measured on April 1 shows a gain of 21 mm.
Therefore, in conditions where runoff and profile drainage are not factors, the net storage of winter and early spring precipitation is about 40 percent.
If precipitation is greater than the long-term mean, net storage of water will increase, but storage as a percentage of precipitation decreases.
Conversely, if precipitation is less than the long-term mean, net storage of water will decrease, but storage as a percentage of precipitation increases.
For example, at 15 percent available soil water on December 1 and precipitation totals of 27, 53, and 80 mm , net storage is 18, 21, and 24 mm (0.70,
 0.84, and 0.96 in), or 67, 40, and 30 percent of precipitation, respectively.
As profile water content on December 1 increases, the amount of evaporation from the soil surface and the amount of profile drainage both increase, reducing net water storage in the soil profile from December 1 to April 1.
At 50 percent available soil water on December 1 and with the mean precipitation amount of 53 mm , net storage of water is zero.
At greater than 50 percent available soil water and with mean precipitation, less water is stored in the soil profile on April 1 than on December 1.
Total water loss from the system due to evaporation and drainage is the sum of 53 mm  of precipitation and the reduction of profile water.
Net water storage at Tribune from December 1 to April 1 was influenced by both precipitation amount and soil profile water conditions.
Of the two factors, profile water content on December 1 had more influence on net water storage during winter and early spring than did precipitation amount.
Soil profile water content is an important factor that should be taken into account when projecting water storage efficiencies from precipitation or preplant irrigation.
Drainage from soil profiles
 Soil profile water conditions have a dramatic impact on drainage, with drainage increasing as soil water content increases.
The occurrence of drainage in soils that are above the "field capacity" water content value is well known.
However, significant drainage can occur from soils having water contents less than the field capacity value.
Although drainage rates will be less at water contents below field capacity than at those above, if drainage time is relatively great (as it is
 in many preplant irrigation programs), then total drainage can be significant.
In a discussion of drainage conditions in the San Joaquin Valley of California, Tanji and Hanson  stated, "drainage water production is highest during preplant irrigation  in the winter months, when measured application efficiencies have been as low as 30 percent, as well as during the initial postplant irrigation-both of which have high infiltration rates."
 Soil water content versus drainage time for three deep silt loam soils of western Kansas is presented in Figure 3.
The soils were thoroughly wetted, covered with plastic to prevent evaporation, and allowed to drain.
Typically, two to three days of drainage are allowed to reach the field capacity water content value.
The Ulysses, Richfield, and Keith soils, respectively, had 683, 663, and 678 mm  of water on day 3 and 594, 602, and 610 mm  of water on day 33.
From day 3 to day 33, 89, 61, and 69 mm  of water drained from the Ulysses, Richfield, and Keith soils, respectively.
On day 63, the Richfield and Keith soils had 584 and 587 mm  of water, respectively.
From day 33 to day 63, 18 and 23 mm  of drainage occurred from those respective soils.
Clearly, longterm drainage from deep soil profiles can reach significant amounts, even at water contents below the field capacity value.
Soil is not a static reservoir for water, but is subject to processes of evaporation and drainage, which influence infiltration and storage of preplant irrigation and precipitation.
Water storage as influenced by available soil water
 Figure 2 illustrates the significant influence soil water content in late fall has on net water storage during winter and early spring.
That influence is generated primarily through the process of long-term drainage, which is illustrated in Figure 3.
In Figure 4, we illustrate storage efficiency of water added to the Ulysses soil near Tribune on December 1 and measured on April 1 as a function of the amount of water added to storage on December 1.
Storage efficiency patterns are shown for four values of percent available soil water on November 30.
Those efficiency patterns were calculated by using the
 water storage equation of Stone et al.
and the long-term precipitation value from December 1 to April 1 of 53 mm.
We calculated the gain in soil water content on April 1 as a result of the water added on December 1, then expressed that gain as a percentage of the amount of water added.
The water added is that added to the water content of the soil profile and not a gross irrigation amount, which would likely involve losses through runoff, evaporation, and delivery system.
When the Ulysses soil is relatively dry in fall , storage efficiency of water added is relatively great, decreasing from 98 percent with 25 mm  water added to 69 percent with 254 mm  water added.
The 69 percent with 254 mm  water added is for the total amount.
When the water added is increased from 229 to 254 mm , only 37 percent of that additional 25 mm  of water is realized as additional stored water on April 1.
Even though the profile is relatively dry on November 30 and storage efficiency is relatively great, when application amounts increase, storage efficiency of the additional water drops off rapidly.
Therefore, the amount of water added needs to be carefully considered and should be kept to the minimum, thereby maintaining greater water storage efficiency.
As available soil water on November 30 increases, storage efficiency measured on April 1 decreases.
Where storage efficiency from 25 mm  of water added is 98 percent with 10 percent available soil water, storage efficiencies decrease to 77, 55, and 34 percent as available soil water on November 30 increases from 30 to 50 to 70 percent, respectively.
Note that these storage efficiencies occur where water added is in the soil profile  and where soil profile water contents are below the field capacity value.
Storage efficiency values presented in Figure 4 are for the Ulysses soil near Tribune.
We realize that different soils and different precipitation patterns likely would have somewhat different values.
However, patterns exhibited in Figure 4 are reasonable and will occur
 Figure 2.
Net water storage from December 1 to April 1 versus amount of available water in the 1.83 m soil profile on December 1 at Tribune, Kansas.
Figure 3.
Water content in the 1.83 m soil profile versus drainage time at three western Kansas locations.
on other deep silt loam soils of the central and southern High Plains.
Therefore, we encourage users of preplant irrigation to consider these water storage efficiencies.
Available soil water in fall
 Water storage efficiency of preplant irrigation is influenced to a great extent by soil water content prior to irrigation.
Therefore, in projecting water storage efficiencies, one needs to assess the exlisting soil water conditions.
Direct measurement of soil water content is the most accurate.
However, long-term data are available that illustrate how available soil water is influenced by seasonal irrigation and seasonal rain-
 fall.
Use of such illustrations allows a producer to evaluate how a seasonal irrigation program influences available water at fall harvest, and how those levels of available water influence storage efficiency of water added to the soil profile.
We used multiple regression analysis, and irrigation research data from Tribune, to develop a relationship for percent available soil water shortly after harvest  as a function of seasonal irrigation  and rainfall from July 1 to soil water sampling in fall.
Crops were corn and grain sorghum.
Irrigation water was applied to level basin test plots by using gated pipe.
Soil profile depth sampled was 1.83 m.
Average date of soil water sampling was
 October 30.
In the regression analysis, independent variables were I and R, the square of each , and the interaction products of the linear and quadratic variables (IR, IR2, I RR, and I2R2.
The relationship developed is:
 AWH = -1.13 + 81.31 + 366R2 + 881R2I [1] and is plotted as a three-dimensional graph in Figure 5.
In model development, sample number was 104, coefficient of determination was 0.854, standard error of estimate was 7.90, and significance probability less than
 Figure 5.
Available soil water of the 1.83 m soil profile shortly after harvest versus seasonal irrigation and rainfall from July 1 to soil water sampling in fall.
4.
For a given soil and precipitation pattern, storage efficiency of preplant irrigation was influenced largely by soil water content immediately prior to irrigation and by irrigation amount, with water storage efficiency decreasing as either or both factors increased.
5.
Irrigation management during the growing season influenced soil water content after harvest and thus water storage efficiencies during the off-season.
0.05 was required for variable retention.
Long-term mean rainfall for July 1 to November 1 at Tribune is 176 mm.
By using equation [1] and mean rainfall, available soil water in late October-early November is 10, 24, 38, and 52 percent with seasonal irrigation  of 0, 127, 254, and 381 mm , respectively.
With the 52 percent available soil water in early November and long-term mean precipitation, the anticipated water storage efficiency through winter of an additional 152 mm  of profile water in late fall is only 40 percent.
In this article, we reviewed water storage efficiencies associated with preplant irrigation of summer row crops in the central and southern High Plains.
Significant aspects are summarized as follows:
 1.
Maximum crop yield benefit from a given irrigation amount has been achieved with water applied in-season, as opposed to off-season as preplant irrigation.
Water use efficiency is greater for seasonal than for preplant irrigation.
2.
Timing of preplant irrigation has shown no significant influence on water storage efficiency and subsequent grain yield.
3.
When two or three surface, seasonal irrigations were applied, preplant irrigation has not influenced grain yield
 Preplant irrigation is an inefficient use of water resources.
In those instances where preplant irrigation  is needed, minimum amounts of water should be applied, as opposed to large amounts for filling of the soil profile.
Drainage from soils can reach significant amounts, even when soil water contents are less than the field capacity value, if extended time periods are involved.
If preplant irrigation is not necessary to establish a crop, irrigation water should be reserved for seasonal application.
Figure 4.
Storage efficiency of water added to storage on December 1 and measured on April 1 versus amount added to storage on December 1 at Tribune, Kansas.
The lines give efficiency at four values of percent available soil water  of the 1.83 m soil profile on November 30.
From the table, corn at the beginning dent stage needs 5 inches of water to reach maturity.
Using the silt loam soil from above, the example field would have enough water to reach maturity and have an estimated 0.3 inches to spare if the corn is beginning to dent.
The loamy sand, at field capacity, would have 2.6 inches available above the 40%  level.
This field would need an additional 2.4 inches of water to reach maturity.
three intervals of application.
Stands were first established and then the irrigation intervals were imposed, based on the rate of evaporation from a class A US Weather Bureau pan.
The wettest interval involved an irrigation for each 11/2 inches of water evaporation; the intermediate treatment, for each 2 inches; and the dry treatment, for each 3 inches of evaporation.
Results of this experiment showed that the sprinkler irrigation removed soil-surface salt, producing a higher rate of emergence of cabbage, carrots and onion seedlings.
The driest treatment significantly reduced onion bolting on early plantings.
The intermediate treatment on carrots produced a significantly higher yield of carrots than the dry treatment, and used less water than the wet treatment.
Both carrots and onions were shown to have growth rates dependent upon plant population density.
These results indicate that in changing from furrow to sprinkler irrigation, either rates of seeding should be reduced, or a longer time allowed for the crops to mature.
Water use under furrow irrigation was 21/2 times greater than that required by sprinkler irrigation.
Additional experiments are under way to adjust herbicide and insecticide applications in changing from furrows to sprinklers.
A series of experiments with precision planting of lettuce resulted in the achievement of 84% of a perfect stand of lettuce from a 12-inch spacing of raw lettuce seed placed with the UC-Giannini precision planter.
During September and October of 1966, growers germinated more than 1,000 acres of lettuce by sprinkler irrigation for the first time in the Imperial Valley.
Rainfall caused a soil crust to develop on one field, but where sprinkler irrigation had been used, an acceptable stand was obtained.
Where furrows had been used no stand was obtained and replanting was necessary.
Results from sprinkling on lettuce were generally favorable and it is anticipated that considerably more acreage will be put under this method of irrigation in coming years.
Frank E.
Robinson is Assistant Water Scientist; Orval D.
McCoy is Associate Specialist in Vegetable Crops; and George F.
Worker, Jr., is Associate Specialist in Agronomy, University of California, Imperial Valley Field Station, El Centro.
Assistance with this project was received from Rain for Rent , Rainbird Sprinkler Corporation, Perma Rain Irrigation Company, Henning Produce Incorporated, Clow Seed Company, Vessey and Company Incorporated, and Holly Sugar Corporation.
H.
YAMADA B.
B.
FISCHER C.
R.
POMEROY
 To obtain maximum yields of barley in the San Joaquin Valley, a normal  pre-irrigation and at least one supplemental crop irrigation are required, according to these studies.
When a heavy pre-irrigation is applied, the soil may be wetted below the potential rooting depth of the barley, in which case the moisture would not be available to the plants.
B ARLEY IS PLANTED on more irrigated acres in the San Joaquin Valley than any other single crop.
Yields fluctuate greatly from season to season, and from area to area-from a low of 1800 lbs per acre to 5800 lbs per acre.
This great fluctuation in barley yields can be attributed mostly to moisture availability during critical times of the growing seasonalthough soil-fertility levels, planting dates, and the disease situation can also play key limiting roles.
Pre-irrigation with 12 to 14 inches of water and one additional irrigation in late February or early March  produced the most economical returns in earlier, non-replicated, trials.
A 1964 study demonstrated that pre-irrigation without supplemental irrigations, a common practice of many barley growers in the San Joaquin Valley, resulted in production of yields that were uneconomical and below optimum levels.
In the study reported here, an irrigation experiment was conducted on a Panoche clay loam soil to determine yield responses to varying amounts of water applied by pre-irrigation and crop irrigations on barley.
The experiment was conducted on a grower's field , and included four treatments with three replications.
The treatments were as follows: B1, heavy pre-irrigation only; B2, normal pre-irrigation plus two crop irri-
 gations  B3, normal pre-irrigation plus one crop irrigation  B4, normal pre-irrigation only.
Plots were 25 ft wide and 640 ft long.
All plots were uniformly fertilized, prior to the preirrigation, with NH3 gas injected in the soil to a depth of 9 inches with 16-inch spacing, at the rate of 80 lbs of nitrogen per acre.
Following pre-irrigation in midOctober, 70 lbs per acre of California Mariout barley were drilled into the plots on December 4.
Plots were machine harvested  on June 23.
Rainfall between planting and harvest was approximately 2.5 inches.
The amount of water applied in preirrigation and in each crop irrigation was measured through siphon tubes for each plot.
The amounts applied to the treatments were as follows: B1, 22.1 inch preirrigation; B2, 12.2 inch pre-irrigation plus 7.6 inch early boot stage and 4.8 inch at flowering stage  B3, 12.6 inch pre-irrigation plus 7.8 inch early boot stage  B4, 14.5 inch pre-irrigation.
Soil samples were taken from each foot to a depth of 8 ft from eight locations in the field, prior to pre-irrigation, to determine the initial moisture content of the field.
All treatments were sampled at two locations after pre-irrigation and after harvest.
The bulk density, averaging 1.4 gm/cm3 at 8 ft, was determined from two pits dug in the field after harvest, with a back hoe.
Using the density figure of 1.4 gm/cm and the oven-dried weight of the soil sample, calculations were made of the total inches of water for each treatment at the time of sampling.
From the soil samples collected before and after pre-irrigation, it was found that 29% of the 22.1-inch pre-irrigation in B1 percolated below the 8-ft depth of sampling.
Evapotranspiration rates for treatment B1, B2, B3, and B4  were 47%, 72%, 74% and 72% respectively, of
 IRRIGATION TREATMENTS ON BARLEY YIELDS
 total water applied.
By adding the 29% percolation loss to evapotranspiration use  in the case of B1, then all treatments will have nearly the same ratio of water use to water applied.
Approximately 25% of the total water applied remained in the 8-ft soil profile, as determined by soil sampling before the preirrigation and after harvest.
EFFECT OF PRE-IRRIGATION AND CROP IRRIGATION ON THE EVAPOTRANSPIRATION AND YIELDS OF BARLEY
 Treat-	ment	Oct.
15	Pre-irr.
1963	Mar 19	irrigation	Crop	Apr 21	Calculated	transpi-	evapo-	Yields
 B1	22.1	10.3	4014 a*
 B2	12.2	7.6	4.8	17.8	5218 b
 B3	12.6	7.8	15.0	4805 b
 B4	14.5	10.5	3909 a
 Yields having the same letters are not significantly different at the 1% probability level.
Each plot was instrumented with gypsum blocks to determine the wetting and extraction pattern for the various treatments.
Blocks were installed on January 15 at 2-, 4-, 6-, and 8-ft depths at two locations within each treatment.
The gypsum blocks were read at weekly intervals and the readings for B1 and B2 have been plotted in the graphs.
Treatments B1 and B2 were selected as they represent the extreme range in evapotranspiration, as shown in the table.
The readings, in microamperes, were plotted against dates.
As the soil moisture increases, the block reading also increases.
In B1 nearly all the moisture was extracted by the barley roots from the second and fourth, very little from the sixth, and practically none from the eighth foot  In B2 the same state of moisture depletion occurred for the second-and fourth-ft depth, but later than in B1 due to the irrigations which were applied on March 19 and April 21.
The increase in microamperes for the secondand fourth-ft curve in graph 2 indicates the depth of soil rewetted by the irrigation.
The 7.6-inch irrigation of March 19 rewetted to a depth
 of at least 4 ft as the block reading increased after the irrigation, and the 4.8inch irrigation of April 21 probably did not rewet the 4-ft depth, because the reading remained the same after the irrigation.
Yield differentials seem to depend on total quantity of available water and timing of application of the crop irrigation.
In this soil where the experiment was located, it was not possible to store sufficient water in the rooting zone of the barley-the bulk of the roots apparently were in the top 4 ft of the soil-to carry the crop to maturity and not sacrifice yields  Yields in B2 and B3 indicate the necessity for supplemental irrigation for barley.
Bushel weight is a measure of the physical quality of barley.
Most California barley will average about 48 lbs per bushel.
Well-matured barley will exceed 48 lbs per bushel.
The bushel weights of the grain in these treatments increased with the calculated evapotranspiration losses, and were as follows: 47.7, 49.7, 49 and 48.3 for B1, B2, B3, and B4 treatments, respectively.
There was a significant difference in bushel weight at the 5% level between B1 and B2 treatments.
There was no significant difference between any of the other treatments.
The bushel weight and the calculated evapotranspiration losses were in a direct ratio, which gives some indication that a crop irrigation is necessary to carry a barley crop to maturity.
H.
Yamada is Lab.
Tech IV, University of California West Side Field Station, Five Points; B.
B.
Fischer is Farm Advisor, Fresno County; and C.
R.
Pomeroy was Specialist  and Superintendent of West Side Field Station, University of California, Five Points.
Don A.
Patterson and Jim Fisher of Boston Ranch, Westhaven, assisted in conducting this experiment.
Graph 1, above, shows average of 6 gypsum block readings for test B-1, barley irrigation, Fresno County, recorded during season at depths of 2, 4, 6, and 8 ft.
Graph 2, below, shows average readings for test B-2-dates of irrigation indicated.
In most cases where center pivot systems are used, the infrastructure needed to move the effluent from the manure storage to the pivot is already in place.
In a situation where a traveling gun is to be used, temporary flexible hoses are used.
In addition, in many situations, irrigating manure allows a farmer to apply manure during the growing season when other application methods cannot.
Dealing with Iron and Other Micro-Irrigation Plugging Problems1
 Tom Obreza, Ed Hanlon, and Mongi Zekri2
 This publication targets agricultural and horticultural producers, homeowners, Extension agents, industry or governmental staff, land managers, other professionals, youth and interested citizens.
This publication is part of a series of documents dealing with proper installation, maintenance, and operation of micro-irrigation systems.
These systems save water, reduce the potential for offsite loss of nutrients and agrochemicals, and directly contribute to yield and quality of many commercially-produced citrus and vegetables in Florida.
The objective of this document is to describe problems with emitter plugging and discuss management strategies to overcome and correct causes of plugging in micro-irrigation systems.
This publication focuses, in particular, on iron scaling, documenting recent successes in treating this common problem in Florida.
Information in this document should be of interest to vegetable and citrus producers, fertilizer and irrigation equipment dealers, Certified Crop Advisors, and other parties involved in the operation of micro-irrigation.
Causes of Micro-Irrigation Plugging Particulate Matter
 The primary cause of emitter plugging is foreign material, such as particulate matter  from soil and/or the water source.
These small inorganic particles may pass through filters and cause plugging at the microemitter.
If the size of the particles exceeds the diameter of the emitter orifice, or if smaller particles stick together to form a much larger mass, then emitter plugging is likely.
Filters are the primary defense against particles entering the micro-irrigation system.
The most economical solution is to buy the best filtration system you can afford, and then maintain that system according to the manufacturer's instructions.
Screen filters are the first line of defense for removing particles from the water source BEFORE particles are distributed throughout the irrigation system.
This type of filter is designed to trap predominantly inorganic materials and will clog if elevated levels of organic materials enter the upstream side of the filter.
Thus, if the water source has both particulate matter and organic materials, screen filters should be placed in the system after filtration of the organic constituents.
This multiple filter arrangement is often recommended for surficial water
 2.
Tom Obreza, senior associate dean for Extension and professor, Office of Dean for Extension and Florida Cooperative Extension Office; Ed Hanlon, professor emeritus, Department of Soil and Water Sciences; and Mongi Zekri, multi-county citrus Extension agent, UF/IFAS Extension Hendry County; UF/IFAS Extension, Gainesville, FL 32611.
Filtration can greatly reduce plugging problems; however, algae and other small plants and animals that live in, or seek, the water can still pass through the filters.
Microbes that pass through the filters can continue to grow inside the system.
Some organisms can build up in numbers, often forming clumps within the tubing at the point where water enters the emitter.
Additionally, arthropods like ants may enter the emitter from the outside when the irrigation system is idle and become stuck in the tubing as they seek water, particularly when the system is turned on.
The least expensive treatment to control living organisms is injecting free chlorine into the micro-irrigation system to obtain 1 part per million  of free chlorine at the end of the system.
To be effective, the amount of chlorine needed to achieve 1 ppm concentration at the far end should be injected EACH time the irrigation system is used.
This technique is called continuous chlorine injection.
The intent is to continuously introduce free chlorine at a relatively low concentration to prevent organic growth in the irrigation system.
Super-chlorination-th so-called "shock" treatment-does not require continuous free chlorine injection because it is usually done on a weekly basis.
With this method, a much higher concentration of free chlorine is injected so that as much as 500 ppm free
 Scaling may be caused by calcium or iron.
These elements, usually associated with limestone or iron oxides, are often dissolved in the irrigation water source.
Using this water for irrigation without treatment for calcium or iron can lead to scaling and ultimately plug the emitters or even irrigation system pipes.
CALCIUM SCALING AND TREATMENT
 Calcium is dissolved in water originating from groundwater aquifers, which are formed from limestone.
Once brought to the surface, the calcium enters the irrigation system and may precipitate in the tubing or around and in emitters as calcium carbonate if the concentration is high enough or if the water pH changes.
Preventing calcium from forming scale within the irrigation system is preferable to treating scale that has already formed.
Calcium scale may be easily prevented with the injection of an appropriate concentration of acid, allowing the calcium to remain in solution and to exit the irrigation system harmlessly.
IRON SCALING AND TREATMENT
 Scaling caused by iron is more difficult to deal with than scale formed by calcium, and shall be explored in some detail.
Iron is abundant throughout the earth, composing up to 5% of the earth's crust.
Hence, iron compounds are common.
Given Florida's sandy soils and geologic time, iron compounds move through the soil and enter the shallow groundwater.
Much of the rust or brownish red color found in many Florida soils is due to the presence of iron oxides and related compounds.
Irrigating with ironrich water may result in staining, not only of equipment, but also on foliage in contact with the water source.
Within the irrigation system itself, iron scaling can reduce flow in pipes and clog emitters.
When iron concentrations exceed
 0.3 ppm, staining and scaling conditions exist.
A review of groundwater concentrations in southwest Florida indicates that iron concentrations range from 0.1 to 7.0 ppm.
Iron chemistry is complex because ionic Fe can exist in two forms.
The reduced cationic form, exhibiting two plus charges, is the ferrous form.
The ferrous form may be introduced into the irrigation system with the source water because this form of iron is soluble.
Chemical conditions may change within the irrigation system itself, resulting in formation of a highly insoluble oxidized form with three positive charges.
It is the ferric form that causes scale within the irrigation system.
The maximum amount of ferric iron that can be retained in solution as ferric oxide is 0.6 parts per billion , considerably less than the iron concentrations reported above  found in southwest Florida groundwater.
The conversion from ferrous  to ferric  form is affected by several chemical parameters, the most important of which are oxygen content and water pH.
The ferrous form results when oxygen content of the water is low, such as in groundwater of many aquifers.
When water is pumped from these locations into the irrigation system, it moves from an anaerobic condition to an aerobic condition with much higher levels of oxygen.
When the ferrous form is exposed to oxygen, the result is a rapid conversion to the ferric form, with subsequent precipitation.
The pH of the water has an effect on the rate of this conversion.
Since many of the aquifers in Florida are limestone, the initial pH of water pumped from those aquifers is alkaline, often at or more than 8.0.
Scale at this pH can form quickly once sufficient oxygen is present.
Usually, sufficient oxygen is usually introduced throughout the irrigation system, and scale forms within the system, especially at or near oxygen sources such as leaking pipes or emitters.
The first step in controlling scaling of any type is to have field and laboratory tests completed on the irrigation water source.
If a Mobile Irrigation Lab, typically associated with the local Soil and Water Conservation District, is operating in your area, lab personnel can test your water for plugging potential.
Laboratory and field measurements are helpful in determining the plugging hazard associated with the water source.
This document shall primarily focus on problems with iron only.
After identifying that the irrigation water source
 does contain sufficient iron to cause scaling , several preventative strategies are available.
Use of a Sedimentation Pond
 A sedimentation pond allows the oxygenation of the source water, and hence the precipitation of ferric iron, before the water is introduced into the irrigation system.
Well water is pumped into a pond allowing equilibration of the water with the atmosphere.
As oxygen enters the water, ferric iron is formed and precipitates.
Factors affecting the time needed for precipitation include water temperature, wind speed, depth and mixing of the water, aeration and wave action.
A good first estimate for the minimum time required is several hours, especially if the water is aerated.
After the iron precipitates, water is removed from the pond and conveyed into the irrigation system for subsequent filtering and distribution.
Advantages of a Sedimentation Pond
 A sedimentation pond permits the removal of iron from the system without any chemical treatment, leaving behind iron scale in the pond itself.
Since most Florida aquifers are composed of limestone, initial water pH from these aquifers is quite high.
The sedimentation pond, in addition to oxygenating the water to remove ferric iron, also allows time for the equilibration of the water with Earth's atmosphere and the dissipation of carbonates and bicarbonates.
As the carbonates and bicarbonates dissipate from the water source, the initial high water pH is lowered 1 to 2 pH units, improving water quality for irrigation.
Disadvantages of a Sedimentation Pond
 Unfortunately, while the sedimentation pond improves water quality with respect to both iron and the high pH caused by carbonates, it is an open water source.
The pond is likely to introduce organic materials and living organisms into the irrigation system.
A second disadvantage is that an additional pumpage is required between the pond and the irrigation system.
The introduction of water to the pond from the well source and its subsequent withdrawal for use in irrigation system must be considered when designing the size of the sedimentation pond to minimize turbidity and the introduction of grit into the irrigation system.
A sedimentation pond requires two pumps as described above.
Additionally, a properly sized sedimentation pond
 requires sufficient land surface, which may take a substantial tract of land out of production.
Oxygenation and Filter Systems
 The next alternative in iron scaling prevention is much more high tech.
This system includes a gas chlorinator, hydro-cyclone filters, sand media filters, and backup disk filters.
The gas chlorinator  introduces chlorine gas into the water system, which causes the iron to oxidize.
The filtering system traps the scale that has formed before the scale is introduced into the remaining portions of the irrigation system.
Figure 1.
Diagram of a vacuum-type gas chlorinator used to treat irrigation water.
Advantages of Oxygenation and Filtration
 Chlorine gas is relatively inexpensive.
Using chlorine to oxidize iron from ferrous to ferric also provides active chlorine within the irrigation system to control microbial activity.
This system also requires considerably less land area compared with the sedimentation pond system.
Disadvantages of Oxygenation and Filtration
 Safety precautions for workers and equipment must be in place and followed correctly when handling chlorine gas.
Because sand media filters are normally used to remove the scale, they require frequent backwashing.
Irrigation Line Maintenance Chemicals
 In situations where iron has already formed, or as a preventive measure in situations where iron scale has been problematic for other users of the same water source, scale can be controlled by appropriate injection rates of chemicals, which can be grouped according to their reactions.
Inorganic acids react quickly with water and solids to help prevent scale formation.
The reaction is partially controlled by regulating the strength of the acid through dilution with water.
In some cases, these acids may also supply nutrients after they have reacted in the irrigation system.
Chelating agents are organic compounds that sequester or occlude iron from further reactions by binding sufficiently tightly to the iron, removing it either as a free agent in solution or as scale.
The iron is held by the chelating agent and the combined molecule flows out of the irrigation system.
In some cases, the iron and other elements chelated by this group of chemicals may later serve as a nutrient source for the crop.
The last chemical group is of the reducing agents.
These chemicals cause ferric iron to revert to ferrous iron, greatly increasing the solubility of the iron, which may then exit the irrigation system in solution.
This group of chemicals can be quite reactive and yet can be handled and stored safely for agricultural purposes.
Some of these chemicals are the byproducts of industrial processes, contributing to a so-called green re-use in the treatment of scale.
SCALE REMOVAL FROM IRRIGATION LINES
 In addition to preventing iron scaling, many of these chemicals may help remove iron scale from irrigation tubing.
The irrigation manager should understand that preventing scaling from forming in the first place is usually much more effective than trying to restore an iron scaleimpaired system.
Research using selected chemicals indicates that some chemicals are much more effective at removing the iron scale from tubing than others.
Figure 2.
Efficacy of selected chemicals in removing iron scale from irrigation tubing.
Sodium hydrosulfite proved to be quite effective at removing scale.
This reducing agent is also used to bleach paper and can present handling and safety issues for agricultural use that should be built into the farm safety program.
However, this chemical is readily available from many sources, and proved to be the best chemical for removing scale in this study.
The next best chemical was a chelating agent, citric acid, which is readily available from many sources and does not pose the same level of handling problems as sodium hydrosulfite.
The discharge water from systems treated with sodium hydrosulfite, a reducing agent, and citric acid, a chelating agent, turns different colors as scale is being removed from the system.
The water from the sodium hydrosulfite contains ferrous iron, which is relatively colorless, while the chelated iron from the citric acid treatment remains in the ferric state, imparting a rust or reddish brown color to the flush water.
Figure 3.
Flush water from treatment of scale using sodium hydrosulfite  and citric acid.
Sulfuric acid is a strong inorganic acid, often produced as a byproduct of many industrial processes.
While sulfuric acid was the least effective chemical in this study, sulfuric acid is relatively inexpensive and can be safely handled with the proper equipment.
As with many of the other chemicals,
 spill kits must be available and personal safety gear must be worn when handling sulfuric acid.
Sulfuric acid may be most useful in situations where it is injected frequently in low concentrations.
This acid may also be helpful in controlling microbial activity within the irrigation system through the appropriate regulation of water pH.
In field trials, iron scale was removed to a greater or lesser degree based upon the selected chemical and the concentration with which that chemical was introduced into the scale-affected tubing.
The reddish brown iron scale  decreases as the concentration of the selected chemical is increased.
Any one of the three chemicals at the higher treatment concentrations successfully treated this moderate scale problem.
Figure 4.
Treatment of iron scale formed within irrigation tubing with sulfuric acid, citric acid, and a proprietary product at selected concentrations.
Iron scale on the inside of the tubing is evident by the reddish brown/rust color.
POTENTIAL PROBLEMS FOR TREATING EXISTING IRON SCALE IRRIGATION SYSTEMS
 When any of these chemicals are introduced into a system that has been affected by iron, scale on the tubing walls may be removed.
However, it is likely that some scale may flake off as a result of the treatment process, rather than being completely dissolved.
The resulting iron scale flakes may in turn cause plugging at the emitter as the small particles build up.
After flushing, the irrigation system should be treated with the desired chemical concentration, letting the system sit idle for at least one day.
This technique gives the chemical
 time to react with the iron scale, and yet does not move the iron scale particles to the emitters, preventing possible clogging of the emitters.
Before using this system to irrigate, a second flush of the system will move iron scale particles out of the system and not adversely affect the emitters.
USING SCALE-MONITORING DEVICES TO EVALUATE CLEANING
 A scale-monitoring device is a clean, non-scaled surface like a standard glass microscope slide within a PVC coupling  or short section of new tubing  that is spliced into an irrigation lateral line.
These devices may be installed across the irrigation system network, from laterals close to the pump to those at the far end of the system.
After installation, the irrigation system should be operated normally for several weeks or months, followed by periodic inspection of the devices for new scale deposition.
When trying a new water treatment chemical, leave untreated at least one irrigation zone that draws from the same water source as the treated zones, and install scale monitoring devices in each.
After a 4to 6-week trial period of irrigation in treated and untreated zones, examine the scale-monitoring devices to see if less scale was deposited in the zone where the water treatment chemical was used.
Figure 5.
A 3/4-inch PVC coupling found in plumbing-supply stores serves well as in-line glass slide holder.
Observing the amount, type, and rate of scale deposition occurring on a clean side  can help determine the scaling potential of the irrigation water and the effect of injected scale-inhibiting chemicals.
Figure 6.
A short section of new plastic tubing "inserted" into an irrigation lateral can serve as a scaling indicator.
After sufficient water has passed through the line, the insert can be removed and cut open to observe newly-deposited scale.
The amount, type, and rate of scale deposition occurring on the tubing wall can help determine the scaling potential of the irrigation water and the effect of injected scale-inhibiting chemicals.
The effect of an injected purge chemical can be evaluated by installing a section of scaled tubing prior to treatment and observing the inside walls following system flushing.
Summary and Concluding Remarks
 Proper filtration equipment is available to address many of the irrigation water quality problems faced by southwest Florida growers.
Iron scaling is a common problem in some areas, and pre-treating the water before it enters the irrigation system is the most reliable way to avoid iron-related problems.
However, if the system has already been impaired by iron scaling, chemicals and management strategies are available to at least partially remediate the irrigation system.
Treatment of existing scaling problems may increase the problems with plugged emitters due to particles of scale migrating to the emitters as the scale is removed from the tubing.
Flushing, subsequent chemical treatment, and additional flushing may also ameliorate some of the existing scale problems.
Avoiding iron scale through the pretreatment of irrigation water is by far the best solution.
Table 1.
Conversion of iron from ferrous to ferric forms in the presence of 2 ppm oxygen at 70 Fahrenheit.
Table 2.
Interpretations to be used with laboratory water testing results, indicating the potential hazard from plugging of microirrigation systems.
Plugging hazard based on concentration
 Measurement	Units	Slight	Moderate	Severe
 Suspended solids1	ppm	< 50	50-100	> 100
 pH	< 7.0	7.0-7.5	> 7.5
 Total dissolved solids1	ppm	< 500	500-2000	> 2000
 Iron1	ppm	< 0.1	0.1-1.5	> 1.5
 Manganese	ppm	< 0.1	0.1-1.5	> 1.5
 Calcium	ppm	< 40	40-80	> 80
 Alkalinity as CaCO	ppm	< 150	150-300	> 300
 Hydrogen sulfide	ppm	< 0.2	0.2-2.0	> 2.0
 Bacteria	#/mL	< 10,000	10,000-50,000	> 50,000
 1 Concentration as mg/L or parts per million.
Factors in italics: Measure in the field if at all possible.
Table 3.
List of irrigation line treatment chemicals, grouped by chemical reaction.
Inorganic acids	Chelating agents	Reducing agents
 Hydrochloric acid	Citric acid	Sodium sulfite
 Phosphoric acid	Glycolic acid	Sodium hydrosulfite
 Sulfuric acid	Malic acid	Sodium metabisulfite
 Nitric acid	Gluconic acid
 Sulfamic acid	Oxalic acid
 Italics indicate readily available products that were included in a recent iron scale study in southwest Florida.
Chemical agent	Where to purchase	Handling	Notes
 Sodium hydrosulfite, Na2S2O4	Industrial chemical supply	Strong reducing agent;	A sodium hydrosulfite solution must be
 	outlets	Safety precautions are	use immediately because the chemical
 required	decomposes in water.
Citric Acid, CHO	Farm or industrial chemical	No special precautions
 Sulfuric Acid, H2SO4	Industrial chemical supply	Strong acid; Safety
 outlets	precautions are required
Once you download the app you can open it and enter the field name you are currently working in.
You can then tap the arrow on the screen and the app will use the devices GPS to input the coordinates of the sensors in the field.
The GPS Location will also aid you in locating your sensors in the field when you go to read or remove them at the end of the growing season.
To illustrate this, lets look at some data from the Upper Big Blue NRD.
The NRD requires growers in six areas that have an increased median nitrate-nitrogen level in the groundwater, to use soil water monitoring equipment in one irrigated field and report the data collected annually.
Most of the producers impacted by this rule use Watermark sensors that measure soil matric potential; thus, this study has largely focused on Watermark data for easy comparison.
The soils in the NRD are mostly a silt loam or similar soil texture, making the field-to-field data comparable as well.
The assumption was made that the farmers using Watermark sensors would represent all irrigators in the area.
To protect privacy, the NRD removes names from the information prior to group analysis; therefore, the location for each field is an unspecified area in the Upper Big Blue NRD.
Juan Enciso, Dean Santistevan and Aung K.
Hla*
 P ropeller flow meters are the most common devices used in Texas for measuring water flow rate.
Water meters help irrigators better manage and schedule irrigation.
They are also a tool for estimating irrigation water use.
This publication will help irrigators learn to select, install and maintain a
 Sizes and flow rates
 Meter size	Minimum	Maximum	Head loss
 	flow 	flow 	
 3	35	250	29.5
 4	50	600	23.0
 6	90	1200	17.0
 8	100	1500	6.75
 10	125	1800	3.75
 12	150	2500	2.75
 14	250	3000	2.00
 16	275	4000	1.75
 * Associate Professor and Extension Agricultural Engineer, The Texas A&M University System; Field Engineer, Natural Resource Conservation Service, United States Department of Agriculture; Program Specialist, Conservation Division, Texas Water Development Board.
propeller flow meter, interpret the meter readings, and use the data.
A propeller flow meter measures the velocity inside a pipe and shows the flow rate reading on a dial.
Table 1 shows approximate sizes and minimum and maximum flow rates.
There are three main types of flow meters.
The saddle type can be welded or clamped , open flow , or flanged.
The weld in line flow meter of Figure 1B may also be fitted with straightening vanes.
Some of these meters are coupled to aluminum or PVC pipe, usually when they will be used in furrow irrigation.
When there will be excessive trash in the water, the small propeller can be installed.
The meter should be installed and placed correctly to ensure that readings will be accurate.
It is also important to prevent debris from collecting on the propeller.
Water should be clean, but if it contains sediment, the meter should be located properly SO that settling sediment will not obstruct the flow.
FIGURE 1: Flow meter types
 Some obstructions before the meter, including elbows, valves, pumps or changes in diameter, can cause disturbances in the flow measurements.
To avoid this, the meter should be minimum distances upstream and downstream of any obstructions, as shown in Figure 2.
A minimum of five pipe diameters upstream from the propeller and one diameter downstream from the flange is usually sufficient, although the manufacturers' requirements may vary with different meter models and sizes.
If five diameters are specified upstream and one diameter downstream, and if the pipe diameter is 10 inches, the length of the pipe upstream before any obstruction should be at least 50 inches and the length downstream should be 10 inches.
If there is not enough length either upstream or downstream, meters should have straightening vanes as shown in Figure 1B.
Adding vanes will reduce the undisturbed length requirement to about 11/2 pipe diameters upstream and 1/2 diameter downstream.
Propeller meters are used to measure instant flow rate and the total volume over a period of time.
The instant readings are in gallons per minute or cubic feet per second.
The needle indicates the flow rate and the box below the needle indicates the total volume of water.
The total volume can be measured in acre-inches, gallons, cubic feet or cubic meters.
Some irrigators prefer the acre-inch because it
 Illustrations and photos courtesy of McCrometer
 FIGURE 2: Distance requirements for installing flow meters
 relates to their traditional terminology.
On the dial faces shown in Figures 3A and 3B, the flow rate is expressed in gallons per minute and the total volume in gallons.
To obtain the volume, the reading is adjusted by a factor.
In Figure 3A the factor is 100; in Figure 3B the factor is the three zeros to the right side of the dial.
The readings for each flow meter are in the figure captions.
In Figure 3C the flow rate is measured in cubic feet per second and the total volume in acre-feet when
 the reading is multiplied by the factor of 0.001 indicated on the dial face.
In Figure 3D the flow rate is measured in gallons per minute and the total volume in acre-feet when the reading is multiplied by a factor of 0.01.
In Figure 3E the flow rate is measured in gallons per minute, but the total volume is measured in acre-feet when the reading is multiplied by a factor of 0.001.
The factor for adjusting the readings of each flow meter is shown in the captions.
A useful conversion table is given in Table 2.
FIGURE 3: Reading flow meters
 Standard 8-inch dial face with gallons totalizer.
Add two zeros to the six-digit number.
Dial face reading = 83,540,200 gallons.
A 10-inch dial face with gallons totalizer.
Add three zeros to the six-digit number.
Dial face reading = 631,401,000 gallons.
Dial with cubic feet per second indicator and acre-ft totalizer.
Place a decimal point three places to the left.
Acre-ft = 835.402
 Acre-ft totalizer.
Place a decimal point two places to the left.
Acre-ft = 534.02
 Acre-ft totalizer.
Place a decimal point three places to the left.
Acre-ft = 954.301
 Suppose the volumetric reading before irrigation was 48,563,000 and after irrigation it was 89,057,200.
Determine the irrigation depth applied in acre-feet and in acre-inches.
Actual reading = 89,057,200 gallons Previous reading = 48,563,000 gallons 40,494,200 gallons
 Acre-feet used = 40,494,200 325,851 = 124.27 acre-feet Acre-inches used = 40,494,200 27,154 = 1,491.28 acre-inches
 What is the end reading if irrigation is applied to a depth of 1.5 inches over 3 acres?
Assume irrigation efficiency is 80 percent and the initial reading was 8,595,560.
Volume required =  0.80 = 152,741 Reading = Initial meter reading + Volume required Reading = 8,595,560 152,741 = 8,748,301
 Flow meters should be inspected regularly to check for mechanical wear and for breakage of the moving parts.
Mechanical failures will cause erratic readings.
A fogging dial may indicate leakage from a bearing assembly.
A quick way to check the mechanical soundness of a meter is to see if the total volume equals the instant flow rate times the interval of time of the measurement.
A failing meter should be repaired or serviced.
Water volume and flow conversions and equivalents
 1 gallon	8.33 pounds
 1 cubic foot	7.48 gallons
 1 acre-foot	325,851 gallons
 1 acre-foot	43,560 cubic feet
 1 acre-inch	27,154 gallons
 1 acre-inch	3630 cubic feet
 1 cfs	448.83 gpm
 1cfs	1 acre-inch per hour
 1 gpm	0.00223 cfs
 1 gpm	0.00221 acre-in per hour
 1 liter/second	15.85 gpm
 1 cubic meter/minute	264.2 gpm
 1 cfs for 1 hour	1 acre-inch
 452 gpm for 1 hour	1 acre-inch
 cfs cubic feet per second, gpm gallons per minute
 Texas A&M AgriLife Extension Service
Nitrogen continues to be one of the highest cropping system input expenses with irrigated corn.
In many parts of Nebraska, there is a significant amount of nitrogen available in groundwater as nitrate.
When applied through irrigation, this nitrate is readily available to crops and is a free source of fertilizer.
This innovative program,which facilitates a number of interactive real-life farm management competitions, was developed by University of Nebraska-Lincoln research and extension specialists and educators in 2017.
The competitions focus on deepening understanding of how management decisions result in profitability and input-use efficiency.
In addition, the program offers a unique, low-risk opportunity for participants to test a wide selection of technologies and management strategies throughout the growing season.
Potential Impacts of Improper Irrigation System Design
 Haimanote K.
Bayabil, Sandra M.
Guzman, Fedro S.
Zazueta, and Dorota Z.
Haman2
 Proper design of irrigation systems is critical to achieving optimal plant growth and yield and minimizing negative impacts on natural resources, the environment, and the economy.
Irrigation systems with improper design could have several negative impacts such as waste of freshwater resources, water quality deterioration, risks to operator safety and public health, and economic losses.
This publication discusses a few major consequences of improper irrigation design.
The goal of this article is to summarize major consequences that could arise from improper irrigation designs.
The target audience includes students, Extension agents, growers, homeowners, and irrigation contractors.
Operator Safety and Public Health
 The safety of the operator and others in the area can be affected by the improper design of an irrigation system.
Electrical circuits must be properly designed and installed to avoid shock hazards in a wet environment.
Power units and drive units must also be properly sized, mounted, aligned, and shielded to assure safe long-term operation.
Chemical injection systems must be properly designed and installed to avoid operator contact with chemicals.
To ensure that systems will function safely, irrigation system components must be properly pressure-rated.
Pressure relief valves and other safety equipment must be installed where required.
All components must be installed according to specifications.
Improperly designed irrigation systems could pose serious public health risks.
The risk is greater when irrigation systems are used for chemical and fertilizer applications in addition to irrigation.
Another risk is the pollution of freshwater sources due to the backflow of chemicals and nutrients.
If the irrigation water source is a municipal or other public drinking water supply, backflow of water from an irrigation system can contaminate the water supply even if chemicals are not injected.
As a result, proper design, selection, installation, and maintenance of a backflow prevention device are critical.
Both Florida law and Environmental Protection Agency  regulations require that backflow prevention devices be installed on all metered systems when chemicals and fertilizer are injected into irrigation systems.
Installing a backflow device is mandatory.
The backflow device must always function properly.
To ensure this, backflow devices need to be regularly maintained and inspected annually by
 2.
Haimanote K.
Bayabil, assistant professor, water resources, Department of Agricultural and Biological Engineering, UF/IFAS Tropical Research and Education Center; Sandra M.
Guzman, assistant professor, irrigation, hydrology, and best management practices , Department of Agricultural and Biological Engineering, UF/IFAS Indian River Research and Education Center; Fedro S.
Zazueta, professor emeritus, Department of Agricultural and Biological Engineering; and Dorota Z.
Haman, professor emeritus, Department of Agricultural and Biological Engineering; UF/IFAS Extension, Gainesville, FL 32611.
a certified backflow technician.
County or municipal codes specify the types of backflow prevention devices required to prevent the possible contamination of freshwater supplies.
Waste of Freshwater Resources
 Irrigation uniformity is one aspect of a good irrigation system design.
Poorly designed irrigation systems apply water nonuniformly and will result in waste of water and chemicals applied with the water.
Nonuniform irrigation distribution will result in er-and/or under-irrigation of parts of fields.
In such a scenario, if the irrigation manager applies a fixed amount of water across the field, plants in under-irrigated areas will suffer from moisture stress, which could lead to yield or quality reductions, while plants in over-irrigated parts of the field could show yield and/ or quality reductions due to waterlogging and leaching of nutrients and chemicals.
In addition, depending on the amount of excess water needed for an over-irrigated field, increased costs will be incurred for the fuel required to pump and inject excess nutrients and chemicals.
Even well-designed irrigation systems do not apply water with perfect uniformity.
The cost of obtaining perfect uniformity is prohibitive.
Rather, the optimum design requires that the value of the wasted natural resources be balanced by the increased cost of achieving a greater degree of irrigation uniformity, including the increased value of agricultural products needed to cover this cost.
Leaching of nutrients and chemicals due to over-irrigation could result in the pollution of surface or groundwater supplies.
In Florida, leaching can readily occur through the highly permeable sandy soils.
It is often difficult to determine the economic and environmental costs of water pollution.
This is because it is difficult to quantify the costs of pollution, and the impacts of various pollutants on the environment are often unknown.
It is also impossible to eliminate the potential for water pollution because chemicals are required in the root zones and on the foliage of plants.
However, the potential for water pollution can be minimized.
Proper irrigation system design and management can minimize leaching and water pollution because a well-designed and well-managed irrigation system can apply only the necessary amounts of water and chemicals.
Chemigation systems, irrigation systems that are designed for chemical applications by injection with the irrigation water, have great potential for reducing water pollution from irrigated
 lands.
Chemigation and fertigation systems can reduce water pollution by allowing prescription chemical and fertilizer applications, respectively.
If chemicals and nutrients are applied frequently and only in the required amounts for the irrigated crop, there will be no excessive nutrient buildup in the soil that will be subject to leaching losses.
Economic Losses Cost of Irrigation
 To minimize the cost of irrigation, the designer must consider the total cost, which is the sum of the annual fixed and operating costs.
The quality of design directly affects the irrigation system cost.
In general, well-designed systems have greater initial costs than poorly designed systems.
This occurs because larger components, including larger pipe sizes, are necessary to minimize pressure losses and achieve uniform water application.
However, the operating costs of well-designed systems will usually be lower.
Pumping, labor, and other operating costs will usually increase to compensate for under-designed irrigation systems.
These factors will almost always make the total annual irrigation system cost greater for a poorly designed irrigation system compared to a well-designed system.
An irrigation system designer must consider existing production practices, availability of labor, and convenience to the irrigation manager.
Proper consideration of these factors and manageable, efficient irrigation systems will help to minimize costs.
Plant Yield and Quality Loss
 Poor irrigation system design can result in irrigation sysitems that cannot provide the necessary soil-water-nutrient environment for optimum crop growth.
This will result in reduced yields, reduced quality, or higher costs per unit of production compared to well-designed irrigation systems.
Reduced Irrigation System Life Expectancy
 The life expectancy of a poorly designed irrigation system may be much shorter than that of a well-designed system.
As an example, the use of components that are not adequately pressure-rated, that are not resistant to chemicals being injected, or that are not otherwise properly installed or matched to the system, can result in early system failures.
Improper designs and installations or the failure to exercise proper caution in management can result in destructive "water hammer" forces that can damage pipes and other
 components.
Additionally, neglecting to consider the strengths of pipe and other component materials can result in their failures due to overburden pressures from burial, especially under roadways.
Improper selection of filtration or other water treatment equipment can result in clogging and failure of trickle irrigation systems.
Likewise, insufficient consideration of the user's ability to manage and maintain filtration and water treatment equipment can result in irrigation system failure.
The selection of components not designed for use under field conditions can result in early component failure due to deterioration by solar radiation or premature weathering.
Improper installation of components  will result in their early deterioration.
There are many possible consequences of improper irrigation system design.
These include:
 Public health impacts if backflow prevention systems are not properly designed or installed
 Waste of natural resources  if systems are not properly designed to apply water uniformly
 Pollution of water supplies if poor system design results in nonuniform water and chemical applications and leaching of chemicals to the water supplies
 Risks to operator safety if components are not properly selected and installed
 Insufficient economic return from irrigation if a poorly designed irrigation system cannot meet the crop's water requirements
 Reduced system life expectancy if components are not properly selected and installed for the operating conditions expected for each system
 All of these factors must be considered when irrigation systems are designed.
There are instances where the ownership of the pump and pivot are divided between the landowner and the tenant.
These scenarios can create complications.
Before a lease with divided ownership is entered, a written lease agreement should be signed.
This lease agreement should clearly state the ownership of each component, responsibilities of each party, and provisions regarding lease termination.
This article will discuss some of the considerations and challenges of this scenario.
On-Farm Water Storage Systems and Surface Water for Irrigation
 What Is an OFWS System?
An on-farm water storage  system is a structural best management practice that captures and stores surface water runoff SO that it can be used at a later time for irrigation.
These systems can capture runoff both from rainfall and tailwater from furrow irrigation, and they can be constructed with only a storage pond, with an enlarged tailwater recovery  ditch, or with a TWR ditch and a storage pond.
The pond is typically constructed on an area of the farm that is less productive, such as a low-lying area that does not drain well.
The TWR ditch and pond are positioned where they can capture adequate runoff yet remain accessible to fields that will be irrigated using the stored water.
The designs of the systems vary depending on where in Mississippi they are installed.
It is important to note that Section 404 of the Clean Water Act  requires a permit for the discharge of dredged or fill material into waters of the United States, which includes wetlands.
Figure 1.
An on-farm water storage system typically consists of a pond  and a tailwater recovery canal.
History of OFWS Systems
 In Mississippi, irrigation first began in the Delta area in the 1970s and has steadily increased.
This increase in irrigation is mostly a result of easy access to the shallow groundwater in the Mississippi River Valley  alluvial aquifer, low energy costs, and the availability of pumps and power plants.
Unlike in the western United States, where the federal government helped implement major infrastructure projects such as dams and reservoirs to support irrigation, the expansion of irrigation in the southeastern United States has been primarily due to private investment by farm owners.
No large federal projects have been implemented to date.
In 1982, Mississippi had 430,901 irrigated acres.
In 1992, that number had more than doubled to 882,976 irrigated acres, moving Mississippi into 19th in the country for states with the greatest number of irrigated acres.
In 2012, Mississippi moved to ninth in the country with 1,651,978 irrigated acres.
Conversely, the number of irrigated acres in most western states has decreased.
This is due to the increasing demands for water resources from growing urban populations and over-allocation of water resources.
Increased dependence on irrigation has become an issue.
Current irrigation systems are expected to reduce risk, withstand periodic droughts, and maintain or increase profits.
However, these expectations have caused the groundwater in the MRV alluvial aquifer to be pumped at a faster rate than it is being refilled, resulting in declining aquifer levels in the Delta over the past three decades.
The Mississippi Department of Environmental Quality  is responsible for managing all of the state's waters and has recognized and responded to this growing concern.
In November 2011, the executive director of MDEQ established the Delta Sustainable Water Resources Task Force, which is led by MDEQ's executive director and includes representatives from Delta Council, Delta Farmers Advocating Resource Management , Mississippi Farm Bureau, the Mississippi Soil and Water Conservation Commission, the Natural Resources
 Conservation Service  of the U.S.
Department of Agriculture, the Vicksburg District of the U.S.
Army Corps of Engineers, and the Yazoo-Mississippi Delta Joint Water Management District.
The task force was formalized by Executive Order No.
1341, signed by the governor of Mississippi on August 26, 2014.
The task force aims to manage water as efficiently as possible, store water when it is plentiful to use at times when it is not, and pursue all feasible alternative water supplies.
While concerns over aquifer declines and the availability of water for irrigation were escalating, there was also growing concern about the issue of hypoxia  in the Gulf of Mexico.
The Mississippi River Basin contains approximately 65 percent of the United States' harvested cropland, and the Mississippi and Atchafalaya Rivers contribute over 85 percent of the total nutrient load to the Gulf.
Excess nutrient runoff increases aquatic primary production, which is often indicated by algal blooms.
When this plant material dies and is degraded by bacteria, oxygen is consumed, depleting oxygen levels in the water column.
Hypoxic conditions occur when oxygen levels in the water reach 2 milligrams per liter or less.
The northern Gulf of Mexico contains one of the largest hypoxic "dead" zones in the world.
The Mississippi River Gulf of Mexico Watershed Nutrient Task Force, formed in 1997, set a goal to reduce the size of the Gulf hypoxic zone to less than 5,000 square kilometers by the year 2015.
The average size of the Gulf hypoxic zone in 2005-2010 was 17,300 square kilometers, and the size in 2010 covered 20,000 square kilometers.
The size of the hypoxic area fluctuates from year to year, depending on the amount and timing of spring and summer rainfall, the associated discharge from the Mississippi River, and wind speed and wind direction, among other factors.
The most recent mapping of the Gulf in July 2017 recorded a hypoxic area of 22,720 square kilometers, the largest size measured to date since mapping began in 1985.
In 2009, the USDA-NRCS launched the Mississippi River Basin Healthy Watersheds Initiative.
This initiative provided additional funds to support voluntary conservation practices in selected focus area watersheds in participating states to reduce nutrient loading and improve water quality in the Basin and Gulf of Mexico.
When the MRBI program first began, there were 12 participating states, including Arkansas, Illinois, Indiana, Iowa, Kentucky, Louisiana, Minnesota, Mississippi, Missouri, Ohio, Tennessee, and Wisconsin.
When the MRBI was first implemented, there were three focus area watersheds in Mississippi: Big Sunflower
 , Upper Yazoo , and Deer-Steele .
In 2011, the Coldwater Creek Watershed  in northwest Mississippi was added.
South Dakota began participating in 2012.
Since its inception, the MRBI has used several Farm Bill programs to improve water quality, restore wetlands, enhance wildlife habitat, and install conservation practices on agricultural lands in high-priority watersheds.
In addition, states in the Mississippi River Basin, including Mississippi, have developed state nutrient reduction strategies, and the MRBI projects support these strategies.
As a result of financial assistance provided through the MRBI, decreasing aquifer levels, and producer concerns over the availability of water for irrigation, the first OFWS system was installed in the Mississippi Delta in 2010.
Since that time, there have been 180 projects installed over 14 Delta counties under NRCS Practice Code 436, which includes both TWR ditches and storage ponds.
An OFWS system is defined by NRCS as "an irrigation water storage structure made by constructing a dam, embankment, pit, or tank".
Approximately 70 percent of these projects have included OFWS ponds, while the remaining 30 percent were only for TWR.
In addition, 124 of these projects were installed in the two counties where the declines in the MRV alluvial aquifer have been most severe-95 projects in Sunflower and 29 projects in Bolivar.
There are also producers in other regions of the state who are installing OFWS systems, without cost assistance, to have a source of water for irrigation.
Due to the flat terrain in the Mississippi Delta, fields are usually precision-leveled, and pads and pipes are installed to ensure that runoff from surrounding fields drains into the TWR ditch.
From there, it is pumped into the storage pond, where it is held until needed for irrigation.
The storage pond is typically built up from soil captured through the land-leveling process, with minimal excavation.
OFWS systems that are constructed with financial assistance from the NRCS are usually designed by an NRCS engineer to have a ratio of 1 acre storage for every 16 irrigated acres.
Storage ponds are usually around 8 feet deep with a 4-foot berm and a minimum 6-inch overflow pipe.
Figure 3.
On-farm water storage pond.
OFWS systems designed by NRCS in the Mississippi Delta ideally have ponds with a storage capacity to apply 6 inches of water per acre per season if the pond is full at the beginning of the growing season.
OFWS systems are designed to meet irrigation requirements 8 out of 10 years.
If the system is a combined TWR ditch and
 storage pond, the ditch is designed to hold 12 acre-feet of water, providing additional storage for irrigation water.
Systems installed in the Delta usually have a minimum 32 acre-feet of storage.
Depending on the weather conditions during a growing season, how much rainfall is received, and the planting date of the crop, producers are sometimes able to irrigate entirely with stored surface water.
At other times, producers can use a combination of surface and groundwater.
In addition, in the Mississippi Delta, OFWS systems use furrow irrigation after installation.
Even though more water is applied through furrow irrigation, any excess water that runs off will be captured by the TWR ditch and recycled through the OFWS system.
When OFWS systems are installed, the TWR ditch is originally constructed with a trapezoidal shape, and native grasses are planted on the banks of the ditch and pond to help reduce erosion.
Many systems now have an automatic shutoff switch, SO that when water in the storage pond reaches a designated height, the pump that is pumping water from the ditch to the pond will automatically shut off.
If there is excess rainfall during the winter when the pond is full, the overflow would move through the outlet of the TWR ditch.
There is also a growing interest in irrigation in northeast Mississippi, where more producers are opting to move acres previously under dryland production into irrigation.
The reasons for doing SO are mostly the same as in other areas of the state, but, in northeast Mississippi, there is no easy access to shallow groundwater.
Producers who want to reduce risk and have greater yield stability from year to year are making private investments in OFWS systems.
There is more topography in the northeastern region of the state, SO rather than land leveling, systems are designed SO that rainfall runoff is gravity-fed into storage ponds, sometimes with the help of constructed terraces.
Ponds constructed for irrigation in northeast Mississippi are usually deeper than 8 feet and use center pivot irrigation.
All water captured is from rainfall and rainfall runoff with no contribution from tailwater runoff.
Thus, OFWS systems in northeast Mississippi are usually designed with only a storage pond and no accompanying TWR ditch.
In this region of the state, accessing groundwater is not cost efficient due to the drilling depth required to reach sufficient groundwater.
Since OFWS systems here are typically the sole source of water for irrigation, they must be designed to hold enough water for the producer to irrigate the desired number of acres for an entire growing season.
This article  used NRCS soil survey data to predict the potential pumpage reduction if VRI was used to mine water from soils that store more off-season rainfall.
Among 49,224 center pivot irrigated fields in Nebraska, this potential pumpage reduction exceeded 2 per year for 2% of fields and exceeded 1 per year for 13% of fields.
The associated pumping cost savings, however, are unlikely to pay for zone control VRI on most fields at the present time.
Therefore, more attention should be directed towards exploring yield benefits of VRI  and environmental impacts of VRI.
IMPROVING CENTER PIVOT PERFORMANCE TO INCREASE SURFACE WATER SYSTEM EFFICIENCY
 Tests to determine water distribution uniformity under center pivot irrigation in order to improve performance are a single component of The Central Nebraska Public Power & Irrigation District's  multi-faceted effort to advance whole system efficiency.
Continuing efforts to improve system components are critical at this time as reduced inflows at Lake McConaughy threaten a continuous water supply.
For the reader unfamiliar with the CNPPID surface water system, an overview is included here.
Efforts to increase whole system, conveyance lateral and on-farm systems efficiency will be discussed and examples of on-farm center pivot test results are presented.
Kingsley Dam closed in 1941, forming the twenty-two mile long Lake McConaughy on its west side.
Lake McConaughy is located just to the north of Ogallala in western Nebraska  at 3265.0 feet above mean sea level) and is the District's primary storage facility on the main-stem of the North Platte River.
Storage volume at Lake McConaughy not only serves CNPPID producers but also holds water for other interests.
Nebraska Public Power District  uses McConaughy water to cool the coal-fired, electric generators at the Gerald Gentleman Station, turn hydroelectric turbines at North Platte and serve its irrigation customers with the water.
Storage water from the Glendo Reservoir in Wyoming becomes a part of Lake McConaughy in the fall to serve the five Nebraska canals with Glendo water accounts in the spring and summer months.
The US Fish and Wildlife Service  maintains and manages a parcel of Lake McConaughy inflows for downstream endangered and threatened species.
CNPPID diversions currently provide hydroelectric generation, irrigation water to 113,170.67 acres in Lincoln, Dawson, Gosper, Phelps and Kearney counties and maintain river flows according to the Federal Energy Regulatory Commission  license requirements.
In addition to Lake McConaughy, the CNPPID system includes four hydroelectric power plants , a diversion dam directly below the confluence of the North and South Platte Rivers, 26 smaller reservoirs and canyon lakes, a supply canal and three primary irrigation canals that total 587 mi.
of conveyance laterals and 1,989 field turnouts.
Figure 1.
The CNPPID system.
INCREASING WHOLE SYSTEM EFFICIENCY
 The goal of whole system efficiency is to provide a continuous, reliable storage water supply where the ratio of irrigation use to water diverted at the headgates is high.
Basin parameters are key inputs to the annual Operations Plan, developed by CNPPID engineers in cooperation with other users and approved by the fifteen member Board of Directors.
Water supply and releases to and from Lake McConaughy are projected and mass balance calculations applied to keep the system sustainable and provide water for all downstream beneficial uses.
Releases are necessarily higher in wet conditions and held to minimum flows when water in the basin is in short supply.
Due to the current historic low inflows to Lake McConaughy, surface elevation is 51 foot below full pool with 585,800 AF of stored water or roughly a third of total capacity.
This level is up 9.6 feet from the September low following the 2003 irrigation season.
An emergency conservation mode of operations has limited all but essential use within the District since 2002, however, the current
 low inflows are not meeting minimum demand and a system water balance has not been achieved.
Figure 2.
Lake McConaughy Surface Elevations Water Years  2001-2004.
Figure 3.
Lake McConaughy inflows, Water Years 1998 -2004 -
 New measures have been taken in recent years to increase whole system efficiency and although they may seem small, storage water savings appears to be substantial.
A series of automated rain gauges installed along the supply and irrigation canals allows operators at the Gothenburg Control Center to track location and intensity of summer storm events in real time and reduce the response time needed to shut down releases from McConaughy to compensate.
Also the smaller, downstream lakes are being drawn down further in August to meet the irrigation demand, saving system water by reducing the additional conveyance losses from Lake McConaughy.
INCREASING CONVEYANCE LATERAL EFFICIENCY
 Seepage and evaporation are an inherent part of running water through earthen canals.
The evaporation portion is somewhat significant in the reservoirs  and of little significance in the canals as the canal banks help attenuate the wind speed across the water surface and stream width is small.
Canal seepage losses recharge groundwater supply, which can be pumped to the surface again, or they become part of return flow to both the Platte and Republican Rivers.
However, seepage losses require CNPPID to divert additional water at the headgates to meet that demand.
Hydraulic conductivity of the canal beds varies by soil type.
Within a same soil type, cut sections tend to have a better retention rate than fill sections.
Efficiency efforts to reduce seepage demand or improve the ratio of AF delivered/diverted include pipeline installations and membrane, concrete and polymer linings.
One hundred and thirty-one miles of pipeline and another 13 linear miles of membrane or concrete liners have replaced earthen laterals since the District was formed.
Membrane linings include full linings where losses are limited to evaporation and partial linings installed below the canal bed.
An estimated 60% reduction in losses occurs with partial linings.
In 2003 an anionic polyacrylamide  solution was sprayed along 233 miles of earthen or open laterals to slow seepage with only limited success.
More study will be done with this product to determine its use in the system.
Additional reduction of losses have been achieved by: automation of check gates that keep canal head steady, and use of the Target Operations Curve  at Elwood Reservoir.
The fill and release schedule at Elwood Reservoir in Gosper County closely follows the TOC developed by an engineering group for CNPPID.
By incorporating the TOC into the Operations Plan, surface elevation of the reservoir is lower for part of the year, water needs are adequately met and losses to seepage have been reduced by an average of 5000 AF annually.
Figure 4.
CNPPID system conveyance.
The 2003 on-farm systems, shown with associated acres in Figure 5, include flood , siphon tubes, gated pipe; with and without associated reuse pits and/or surge valves, three sub-surface drip  demonstration sites and center pivots.
CNPPID has encouraged on-farm conservation efforts for many years through cost-share assistance.
Up to $1,500 in material and labor costs is available at each turnout to accommodate an upgrade to a new water conservation practice.
An additional conservation policy was implemented in 2001 with the introduction of the Pivot Incentive Policy.
This policy provides a cash incentive to producers to install a center pivot and is designed to offset some of the start-up costs associated with the change.
The Pivot Incentive Policy represents a significant financial commitment to water conservation; incentive payments for the 68 new pivots added since 2002 total $194,046.31.
Two hundred-six pivots served District acres in 2003  and 26-29 installations, most replacing gated pipe, are slated for the 2004 season.
CNPPID has experienced a significant upswing in the number of center pivots replacing open ditch or siphon tube systems at the field level.
Labor availability and labor cost are most probably the driving force of the increase, however, the potential benefit to water supply without yield reductions are of interest to both CNPPID and its producers.
Pivots coming on-line are normally designed and installed by local dealership staff using manufacturer's software packages and the CNPPID flow rate options to the field.
Necessarily, the District's interest is not design but function of these systems following installation.
Figure 6.
The number of annual additions and cumulative total of center pivot irrigation systems served by the CNPPID District.
On-Farm Center Pivot Testing
 A survey of the CNPPID system prior to the 2001 irrigation season revealed that none of the center pivot installations had been field-tested for water distribution uniformity.
And so began the effort to assess center pivot installations against the following assumptions:
 Modified Heermann and Hein coefficient of uniformity  is 90 + 5% after the second tower to the outside edge of the wetted perimeter,
 Sediment load in the water has no effect on CU,
 Number of years pivot has been in service has no effect on CU
 Calibrated table provided by the manufacturer matches actual field application rate.
Surface water use through a pivot presents challenges related to filtering debris, sediment and algae loads.
Filtering of surface debris and small fish or benthic organisms is accomplished with 5/32" perforated galvanized steel pipe, 18" or 24" in diameter and in lengths indirectly proportional to canal depth.
Any sediment or algae load carried by the water pass through pipe perforations and sprinkler heads and are delivered to the field.
The agricultural engineering standard; ANSI/ASAE S436.1 OCT97: Test procedure for determining the uniformity of water distribution of center pivot and lateral move irrigation machines equipped with spray or sprinkler nozzles was used for these tests with one exception.
A single line of Irrigage rain collectors  replaces the multiple lines of the catch cans in the standard to improve data collection.
Rogers et al., have done extensive testing to verify this substitution.
The main outcome of this test, the modified Heermann and Hein coefficient of uniformity , describes variation of the sample data from the mean  depth applied at all locations.
A value of 100% is an unlikely scenario, however, coefficients near 90% are attainable.
Application depths + 10% of the mean depth applied were accepted as normal, as in the standard.
Results of this test are shown in Figure 7.
Most notably, this producer believed he was applying 0.75 inches of water to his field in a single rotation while actual mean depth of application is 0.41 inches; CU is 78%.
The unit is an older model with spray nozzles above the lateral and in this case, sediment appeared to be the problem.
No pressure regulators are in place, however, differential elevations at the base of each collector are not correlated with changes in the uniformity pattern.
According to field elevations, this test should represent maximum application uniformity in this field.
Figure 7.
Test results at ER site.
The 1983 impact sprinkler unit has 8, 155 ft.
spans, an 86 ft.
overhang and a cornering unit.
The unit was tested twice, first with the cornering unit fully extended and then folded to the "off" position.
In the first test, CU was 80.5% and average application depth was 0.67 inches.
Figure 8.
Test 2OL-1.
With the cornering unit folded, CU was 78.9% and average depth applied was 0.90 inches.
As shown, a nozzle problem was apparent in the third span and in the folded position, the cornering unit did not shut off completely and depth of application spiked to 2.37 inches.
Worn sprinkler heads and a malfunctioning solenoid were the problem here.
Also, mean depth of application changed between tests; the producer intended a 0.75-inch application and so the
 cornering unit needed to be slowed down when fully extended.
All problems were easily corrected.
Elevations at the base of the collectors were determined again at this site and were not correlated to the uniformity patterns.
Figure 9.
Test 20I-2.
Figure 10.
Test 3EK
 The pivot in Test 3EK was in its second year of service, a low-pressure system with drops and spray heads.
CU is high and the mean application depth of 0.56 inches is just short of the expected 0.60 inches, however, there is room for improvement.
The graph clearly shows what happens when sprinkler heads use too much water; neighboring heads are shorted.
If the deficit irrigation is not
 mitigated by rainfall a yield loss would be expected here.
Irrigage spacing was 9 feet.
None of the pivots tested to date are without a problem area and each problem found has been easily addressed.
Additional field observations not shown here have shown drought conditions can exist under a pivot that is not operating properly and yield losses occur.
The studies completed to date suggest that continuing pivot testing in the system would be useful.
CU's near 90% are attainable and although we have formed no opinion on age being a factor in CU we do believe that sediment load in the water can affect CU if it accumulates in sprinkler heads.
Timing of these tests is troublesome in south-central Nebraska as wind speeds higher than the standard allows  prevails when corn height does not interfere with data collection.
Test conditions in the District are best in July and August, on the soybean side of the corn/soybean crop rotation.
ASAE.
S436.1 Oct 97, Test Procedure for Determining the Uniformity of Water Distribution of Center Pivot and Lateral Move Irrigation Machines Equipped with Spray or Sprinkler Nozzles.
In: ASAE standards 2000.
47th ed.
906-912.
Differential Corn Hybrid Response to Irrigation Management
 Freddie R.
Lamm Kansas State University Northwest Research-Extension Center Colby, Kansas
 Written for presentation at the 2017 ASABE Annual International Meeting Sponsored by ASABE Spokane, Washington July 16-19, 2017
 ABSTRACT.
Separate field studies using sprinkler and subsurface drip irrigation for corn production were conducted at Colby, Kansas from 2014 to 2016 examining five different irrigation capacities ranging from 25 mm/4 days to 25 mm/12 days.
The irrigation treatments were scheduled only according to need with calculated ET-based water budgets but were limited to specific capacities.
The conventional and drought tolerant hybrids performed differently with the drought tolerant hybrid generally establishing greater kernels/ear when conditions were drier and the conventional hybrid tended to compensate under wetter conditions with greater kernel mass  There appeared to be greater stability in grain yield for the subsurface drip irrigation system due to differences in yield component formation between the two irrigation systems.
Keywords.
Corn, crop yield, deficit irrigation, irrigation management, maize, sprinkler irrigation, subsurface drip irrigation.
In the semi-arid U.S.
Central Great Plains and particularly northwest Kansas, soils are generally productive deep silt loam soils but precipitation is limited and sporadic with mean annual precipitation ranging from 16 to 20 inches across the region, which is only 60-80% of the seasonal water use for corn.
Irrigation is often used to mitigate these water stress effects but at the expense of the continued decline of the Ogallala Aquifer.
The major corn seed companies have extensive hybrid development work underway in the western Corn Belt to develop hybrids that are drought tolerant.
The overall goal is to develop hybrids that will not incur a yield reduction under ideal conditions, yet stabilize yield under water-stressed conditions.
Center pivot sprinkler irrigation  is by far the predominant method of irrigation in the U.S.
Central Great Plains, but some producers are beginning to use subsurface drip irrigation  to perhaps make more effective use of the limited water resource by a further limiting of the water losses.
As corn is the major irrigated crop in the U.S.
Central Great Plains, efforts are justified to develop irrigation management strategies that optimize corn grain yield and appropriate use of CP and SDI irrigation methods.
Separate field studies were conducted from 2014 through 2016 at the KSU Northwest Research-Extension Center in Colby, Kansas to examine the differential corn response of two commercially available corn hybrids as affected by irrigation system  under different irrigation capacities.
In the sprinklerirrigated study, a lateral move sprinkler irrigation system was used as a substitute for the CP system and will be referred to as the LMS system in the remaining document.
The usage of the LMS system improved research plot management.
Two different commercial corn hybrids  were compared under five different irrigation regimes for both LMS and SDI systems in separate field studies at the KSU Northwest Research-Extension Center at Colby, Kansas.
The study was conducted under the LMS system in the years 2014 through 2016 and the study under the SDI system was conducted in 2014 and 2016.
Under LMS irrigation, irrigation were managed to nominally apply 25 mm on frequencies governed by the irrigation capacity.
Under the SDI system, irrigation was managed to apply on a two-day frequency with fixed amounts governed by the irrigation capacity.
It can be noted that the 5 individual LMS and SDI irrigation regimes are equivalent in terms of capacity.
Irrigation events were only scheduled according to water budget weather-based irrigation scheduling procedures only as needed subject to the specific treatment limitations.
As needed irrigation was confined to having sufficient storage within the soil profile and crop rootzone for the irrigation amount plus an additional amount of storage of approximately 25 mm for occasional precipitation events.
Soil water was monitored periodically  to a depth of 2.4 m in 0.3 m increments with neutron moderation techniques.
This data was used to assess crop water stress as well as to determine total water use throughout the season.
Corn yield and yield components were determined through hand harvesting a representative sample at physiological maturity.
The 5 irrigation treatments  were in a RCB design and the 2 corn hybrid treatments superimposed as split plots.
The data were analyzed using standard PC-SAS procedures.
Weather Conditions and Irrigation Requirements
 Overall weather conditions for the three years were favorable for excellent corn production during the study.
Calculated well-watered corn ET for 2014 through 2016 was slightly lower than long term values  and seasonal precipitation was 49 and 69 mm greater than normal in 2014 and 2015, respectively, and 107 mm less than normal in 2016.
Figure 1.
Seasonal calculated evapotranspiration for a well-watered corn crop and precipitation at Colby, Kansas for 2014 through 2016.
Seasonal irrigation amounts for the LMS system greatest irrigation capacity  were 341, 390, and 366 mm in 2014, 2015 and 2016, respectively.
Seasonal irrigation amounts for the SDI system greatest irrigation capacity  were 312 and 358 mm in 2014 and 2016, respectively.
Figure 2.
Seasonal irrigation amounts for the LMS and SDI studies, KSU Northwest Research-Extension Center at Colby, Kansas for 2014 through 2016.
Overall Grain Yield Response to Irrigation Capacity and System
 Overall grain yields were excellent, ranging from 14.1 to 15.9 Mg/ha for the LMS system and ranging from 15.4 to 16.5 Mg/ha for the SDI system.
Since the studies were separately conducted, it is not appropriate to ascribe statistical differences to the two irrigation methods.
However, the studies were conducted on similar soil types within 100 m of each other.
Figure 3.
Corn grain yields for the LMS and SDI studies, KSU Northwest Research-Extension Center at Colby, Kansas for 2014 through 2016.
Examination of the Yield Components
 Corn grain yield can be calculated as the product of the yield components:
 Yield = Plants Ears Kernels Mass Eq.
1 Area Plant Ear Kernel
 The first two terms are typically determined by the cropping practices and generally are not affected by irrigation practices later in the season.
Water stresses during the mid-vegetative period through about 2 weeks after anthesis can greatly reduce kernels/ear.
Kernel mass, through greater grain filling, can partially compensate when insufficient kernels/ear are set, but may be limited by late season water stress or hastened senescence caused by weather conditions.
Because all the yield components combine directly through multiplication to calculate yield, their effect on yield can be easily compared as shown in the examples in Fig.
4.
Vertical or near vertical lines near zero on the x-axis indicate that yield component had no effect on variation.
Holding other yield components static, a variation of 1% in any yield component would affect yield by the same 1%.
For explanation the numbers on the lines refer to the 5 irrigation treatments and the lines are just used to connect data from each yield component.
No functional or extrapolated relationships are intended for the connecting lines.
Figure 4.
Variation in yield as related to yield component variation for the LMS and SDI systems in 2014.
In 2014, kernels/ear had much greater upward sloping horizontal dispersion as compared to other yield components.
The drought tolerant hybrid generally used this aspect more positively.
Generally less kernel mass was achieved by the drought tolerant hybrid but was compensated for by the greater kernel number.
There "tended" to be more stability in both kernels/ear and kernel mass for the upper 4 irrigation capacities with SDI as compared to the LMS study, but once again a statistical comparison should not be inferred.
There was no SDI study in 2015.
Kernels/ear was set at relatively high level for both hybrids  and thus there was less distinction in how yield components affected the relatively high corn yields  in 2015 
 Figure 5.
Variation in yield as related to yield component variation for the LMS system in 2015.
In 2016, kernels/ear had much greater upward sloping horizontal dispersion as compared to other yield components.
The drought tolerant hybrid generally used this aspect more positively.
Generally less kernel mass was achieved by the drought tolerant hybrid but was compensated for by the greater kernel number.
Closing Thoughts and Conclusions
 The conventional and drought tolerant hybrids performed differently with the drought tolerant hybrid generally establishing greater kernels/ear when conditions were drier and the conventional hybrid tended to compensate under wetter conditions with greater kernel mass.
There "appeared" to be greater stability in grain yield across upper irrigation levels for the SDI system due to differences in yield component formation between the two irrigation systems.
Based on this and another recent study at this location, modern corn hybrids use differing strategies to achieve their optimum yield.
There appears to be an opportunity to optimize corn yields with irrigation management and systems if producers could be apprised of these hybrid differences upfront.
Yield Component Variation from Mean 
 Yield Component Variation from Mean 
 Figure 6.
Variation in yield as related to yield component variation for the LMS and SDI systems in 2016.
Differences in Late-Season Irrigation Timing for Corn/Sorghum and Beans: Corn/sorghum and beans are somewhat different in respect to crop water use as they approach maturity.
For example, if hot dry windy conditions are experienced in September, daily crop water use will increase.
However, since corn/sorghum develop based on heat units, they will use more water per day, but will mature in fewer days using about the average amount of water shown in the chart.
Factors such as the amount of water a soil can hold, the amount of water a crop will use until it reaches maturity, and the maximum allowable soil water depletion should be considered when deciding the last few irrigations of the season.
In addition to water and dollar savings, another benefit of leaving the fields as dry as possible without lowering yields is the potential to reduce issues with nutrient leaching and increase the amount of precipitation stored during the offseason.
Once the system is up to pressure it is a good idea to check the system for leaks and operation of the sprinklers.
If you find missing or inoperable sprinklers refer to the sprinkler chart that was developed for the system to find the correct replacement.
If the system is on rolling or hilly terrain, regulators are also needed for uniform application and definitely should be checked.
The Importance of Water Source Layout in Farm Infrastructure
 Steve Higgins, Biosystems and Agricultural Engineering
 W later source layout is a critical infrastructure component for cattle and cattle producers.
Strategic water resource layout is a part of a farmstead plan that does not always get adequate attention, despite its critical importance.
Nonetheless, when farm infrastructure planning incorporates the latest practices, rules, and knowledge, the resulting design can satisfy generations of users.
Water is an essential nutrient.
It also is one of the most limiting factors in rotational grazing, which makes the location of water sources critical.
Each watering source should be installed to develop infrastructure that satisfies the drinking water requirement for cattle and that also fits into the overall scheme of the farm.
It should provide and/or increase producer efficiency.
Developing a watering source that satisfies these two needs can be complicated.
For example, once a watering source is established, it will not be easy or economical to move after installation.
Therefore, the location, placement, and design of the watering source should be thoughtfully constructed based on the best standards available at the time.
Efficient pasture-based infrastructure design maximizes profit by increasing production and reducing cost.
Designing a successful water source requires meeting the needs of cattle.
The location of a water source should be organized and designed for cattle, who, from a design point of view, are pedestrians.
They should be able to access their production requirements without walking more than
 Figure 1.
A 22-acre beef pasture with a water source serving just this field located on one end.
800 feet away from any point of a pasture.
Creating a positive animal environment should be the first goal, with improving producer efficiency a secondary goal.
Producers should become familiar with analyzing infrastructure projects to create beneficial infrastructure and lessen haphazard planning that requires changes to existing infrastructure.
This publication uses illustrations and specific examples of design concepts.
Planning methods from the perspective of cattle and the producer are presented using aerial imagery.
Principles and dimensions are used to develop locations and layouts.
Sketches and drawings illustrate design concepts and layouts.
Animal preference to other aspects of the design and field attributes will be displayed by their behavior, which can be used as an evaluation tool to score designs and infrastructure improvements.
There are generally accepted rules for providing water to cattle.
Ideally, water is provided to cattle as they rotate from field to field.
The source should be convenient for them to access and drink.
Cattle should not have to walk more than 800 feet to obtain water when grazing.
Figure 1 is a pasture outlined by the road on two sides and woods on another.
The field dimensions are 1600' by 600', or approximately 22 acres.
Poor drainage, running along the entire length, is an issue.
A waterer, identified by the callout, is located on one end of the field.
The maximum distance from the waterer to the furthest point requires cattle to walk over 1,600 feet to obtain water.
Meanwhile, the other walking dimensions, from the other three sides of the watering source are 23, 155, and 370 feet.
This water source provides water to this pasture but
 not very well.
The maximum recommended walking distance is exceeded by twice the distance.
The waterer could have been moved 23 feet and placed in the fence line to serve another pasture/group simultaneously or moved to the center of the field to reduce walking distance.
This example shows a water source that is not integrated into the design of the field.
An unfortunate lack of forethought about water has probably made water the most neglected nutrient in a beef ration.
Pasture infrastructure should not be constructed in isolation from the whole operation.
Infrastructure for watering cattle should provide convenient access to abundant, clean water, while increasing producer efficiency by saving time, money, and labor.
Example 2: Two-way Waterer
 An illustration of the current watering source design is depicted in Figure 1.
Figure 2 shows an illustration over an aerial image of how the field could be improved with a more efficient layout.
Locating the water source to the center of the field and dividing the pasture with a cross-fence  would create two equal-size pastures served by one waterer.
This would increase opportunities for rotational grazing without increasing watering costs.
The inset rendering in Figure 2 shows an example layout for a two-way watering source.
The dimensions were determined by measuring the approximate distances using a mapping software.
The design
 Figure 2.
How the field should have been laid out.
places the water source in the center of the field.
Gates have been placed adjacent to the source.
This location within the field may also be where cattle are accustomed to loafing, especially in pastures that do not have shade.
Placing gates adjacent to the water source allows the producer to rotate cattle to the adjacent field through the gates mounted on either side.
Access to gates also reduces the distance of moving mineral and makes it less burdensome.
The illustration also shows a ring feeder placed around the circular waterer.
Recycling an old hay ring feeder by placing it over a tire waterer is one of the better ways to exclude cattle from standing with their feet in the trough.
Implementing this feature maintains water quality and reduces time needed to clean the waterer.
The direct benefits of dividing a water source with a cross-fence could include the following: It facilitates rotational grazing by increasing the number of pastures and increases managerial control; the water source serves twice as many fields; mineral transportation distance
 to an adjacent pasture is reduced; cattle walking distance is reduced; forages will be better utilized; and, pressure sensitive areas such as drainages and waterways can be reduced.
This type of design can also provide indirect benefits.
The drainage way has become more of a ditch or gulley.
Because calves can be lost to gullies, the erosion is a growing concern.
There are structures  that can be placed in gullies to control erosion, but implementation of these practices requires money, equipment, time, and labor.
The cheapest and easiest means of addressing gully erosion is to manage pastures in a way that avoids erosion.
Good management decisions, such as moving cattle often with rotational grazing, taking a field out of a rotation, or renovation of the pasture, are tactics to avoid erosion.
The sound practices are more difficult to accomplish with a single water source in a large single field.
Figure 3 is an aerial view showing a nine-acre pasture with a water source located in a corner.
The inset image in Figure 3 provides the dimensions of the boundary relative to the water source for the small field.
These dimensions are within parameters for cattle walking distance, but conjoining the three pastures would provide greater efficiency.
Figure 4 shows the intersection of the three pastures coming together and forming a Y-shaped node, with the corresponding acreages of each field.
Figure 5 shows the location of a watering source located at the "Y." The inset image shows a more efficient design with the water source serving three pastures.
Water sources for multiple pastures require more complicated designs.
The enhanced node, hub, or center  typically requires additional gates and considerations about the direction of their swing and space for vehicle maneuvering.
Additional construction materials are also needed for rock, fabric, concrete, etc.
This type of design costs more, but can be amortized over multiple pastures, and provides additional benefits.
However, hubs can improve the operation for cattle and management with a single integrated component of infrastructure, which serves multiple pastures.
Installing a water source hub at the intersection or nodes of adjacent pastures can lead to improved management and circulation of cattle by facilitating rotational grazing.
In this design, the hub becomes a common area serving cattle in three pastures and a permanent mineral feeder can be installed to serve three pastures rather
 Figure 3.
A nine-acre beef pasture with a watering source located in the corner.
Figure 4.
An aerial view of the intersection of three pastures.
Figure 5.
A design of a three-way watering hub.
than transporting mineral as pastures are rotated.
It places the waterer in the corner of fields which makes transfer from one field to another easier.
Fly control can be incorporated as well.
The enhanced hub provides a shared location for many tasks, increasing efficiency, sharing resources such as minerals, improving rotation and fly prevention.
This increases efficiency of the producer and cattle by saving time, money, and labor, while creating a better environment for the cattle.
Hub watering stations are more complex but they deliver simplicity.
Figure 6 is a 33-acre pasture 1,200' tall by 1,500' wide.
The water source is located in the top right corner  requiring cattle to walk 1,500 feet to obtain water.
Again, by implementing the concept of a centralized location, a waterer in the center  divides the field into four 8-acre pastures measuring 600' by 750', with a watering source within 750 feet of the farthest distance.
This example field also has a drainage area in the field that could be managed to exclude the cattle from it.
The cattle are along a drainage way, which demonstrates their preference for this type of landscape feature.
The implementation of the design concepts presented for this example would provide the producer with the ability to control and limit cattle activity and their behavior.
Figure 6.
A 33-acre beef pasture with a watering source in the upper corner.
Figure 7.
New design of 33-acre beef pasture with a four-way watering source.
Figure 8.
Cattle with uncontrolled access to a drainage way.
A water source is a component of infrastructure that should relate to the whole farm, the other services , and enterprises that the producer uses to create a profit.
No single component of farm infrastructure should be operated in isolation.
Infrastructure is a means to create efficient pasture, but not an end in itself.
The example for this concept starts with Figure 9, which shows two water sources serving two different fields, which are 135 feet apart and are the same water sources presented in Figure 6 and is a mirror image as the field in example 4.
An image of the two fields and their respective water sources is depicted in Figure 10.
A design solution for this would be the exact same four-way design presented in Figure 7.
The proposed layout for the two fields is depicted in Figure 11.
The example field also has drainages that need to be and could be managed with the new configuration.
The objective of Example 5 is the demonstration of the importance of water source layout in farm infrastructure planning.
All the examples presented in this publication were obtained from the same operation.
This suggests the benefits of layout planning could have been applied to the entire operation, since its inception or as a renovation.
Moreover, since infrastructure locations remain in the same place for generations, these benefits could have been achieving efficiency and reducing drudgery for the operator and cattle the entire time not to mention future operations.
The amortization of these projects could have been spread out over many years.
However, increased income could have also obtained from the fact that rotation graz-
 Figure 9.
The water source in the foreground is approximately 135 feet from the water source in the background.
Figure 10.
Aerial view of two pastures and the location of their water sources.
To pasture to the left is the 33-acre field used for the four-way example.
The pasture to the right is 28 acres.
Figure 11.
Potential layout of water sources and fences for two adjacent pastures.
ing offers opportunities to expand the herd/stocking density.
This could only be possible if these concepts had been or were implemented.
Pasture infrastructure should not be constructed in isolation from the whole operation.
Infrastructure for watering cattle should provide convenient access to abundant, clean water, while increasing producer efficiency by saving time, money, and labor.
Farm infrastructure is improved when water sources and other fixed equipment are thoughtfully placed to accommodate animal needs, increase producer efficiency, and promote rotational grazing.
An adequate water supply is a fundamental requirement for maximum cattle gains, but water supply is often haphazardly placed or simply left where it has always been.
Existing infrastructure may have been placed at a location for reasons that are no longer relevant.
Producers that take advantage of the latest standards, whether technology, engineering, or understanding of animal behavior, may increase efficiency and reduce costs across the whole operation.
Cost versus benefit of implementing projects is a determining factor for producers.
Renovations and best practices can be implemented in incremental steps; they can be accomplished easier when based on a comprehensive plan.
For instance, all the cross fence does not have to go in at the same time.
The waterer can go in first, then one section of fence, then another.
However, without a plan, the haphazard installation of projects may lead to structures impeding a subsequent new project.
Planning the design using images, drawings, and sketches before implementation creates a roadmap for the future.
Chapter: 36 Profitability can be Enhanced by Reducing Corn Harvest Losses
 If the combine is not adjusted correctly, profits can be left in the field.
Yield losses are unavoidable, but through careful management they can be minimized.
The first step in minimizing combine yield losses is determining the source.
This involves identifying where the loss occurred, followed by making appropriate adjustments.
The combine should be adjusted to minimize ear and kernel losses, while also managing cracked or broken kernels and foreign matter in the grain.
This chapter is devoted to the measurement of corn harvest losses, and then linking those losses to where the loss occurred.
Producers are anxious to begin harvest, and once started, reluctant to stop or delay.
However, counting some kernels on the ground and determining the losses from various machine systems can be time very well-spent and easily pay for itself, especially if problems are corrected early.
The quick-count methods discussed in Table 36.1 provide information that can be used to determine whether combine header settings need adjustment to improve harvest efficiency.
Every 1% loss of a 200 bu/acre yield at $4/bushel is $8/acre of reduced net income.
Losses from a machine that is not properly adjusted for the harvest conditions can easily be 4% to 5% of the grain in the field.
Without measuring losses, it is not possible to know whether they are high or low.
Without analyzing where the losses are occurring, it is difficult to know which combine adjustments to make.
Routine checks will help minimize preventable losses.
Table 36.1 Determining harvest loss when combining by quick-count methods:
 Step 1.
KERNEL LOSS: Count kernels on the ground inside a simple frame of known area  into your measured yield per acre, and multiplying by 100%.
Step 2.
EAR LOSS: Pick a row behind your combine and count any ears on the ground within 87 feet  of the back of the combine.
One ear on the ground in 30 paces between rows with 30" spacing is approximately 1 bushel per acre of harvest loss from ears.
Therefore, the number of ears counted is equal to the bushel per acre ear loss.
The percent loss due to ear loss is determined by dividing by the ear loss/acre into your measured yield per acre and multiplying by 100%.
These quick measurements help in observing "normal" and excessive losses, providing a check for combine header settings, and improving harvest efficiency.
In this chapter, we present the concept of using a simple frame that encloses a known area to measure kernel loss.
The other measurement is done by counting ears along a length of 87 feet  behind the combine.
These measurements may be done while waiting for a truck or wagon.
Yield loss in bu/acre can be quickly assessed using these methods.
Two kernels/ft2 is 1 bu/acre, and each ear in 30 paces along a 30" row is 1 bu/acre.
If total losses exceed 1% of the yield, combine adjustments may be required.
Detailed Analysis of Loss Calculations
 Example 36.1 What is the estimated corn yield loss if 6 kernels are found in a 1-ft2 area?
Answer:	6	kernels	X	43560	bu
 acre	90,000	kernel	acre
 Solving this problem shows why yield loss can be estimated by dividing kernels/ft2 by 2.
The assumption of 90,000 kernels/bu may need to be adjusted if corn kernels are large  or small.
See Table 36.2 for details.
Table 36.2 The relationship between corn kernel size and kernels/ft2 equivalent to 1 bu/acre.
Weight/bushel	Kernels/bushel	Kernels/lb	Kernels/ft2 equivalent
 @ 15.5% moisture	@ 15.5% moisture	to 1 bushel/acre
 Large kernels	56 lbs	70,000	1250	1.6
 Medium kernels	56 lbs	90,000	1607	2.1
 Small kernels	56 lbs	110,000	1964	2.5
 General Formula: Kernels/ft2 = Kernels/lb X 56 lbs/bu X 1 acre/43560 ft2
 Example 36.2 Assume corn kernel size is large, and the number of kernels lost is 6/ft2.
What is the estimated corn yield loss in bu/a?
According to Table 36.2, the number of kernels/bu is 70,000.
Therefore:
 This example illustrates that the size of kernels and assumptions about kernels/bu influence the estimates of % yield loss.
Example 36.3 What is the yield loss if one ear is found along a distance of 87 feet between two 30" corn rows?
In addition, each ear contains approximately 0.28 lbs of shelled corn.
Answer: For many people, 30 paces is approximately 87 ft and therefore, a rectangle that is 2.5 ft by 87 ft is an area of 217 ft2.
bushel 1.003 bushel 56 lbs corn acre
 The amount of grain on an ear may be more or less than 0.28 lbs.
The lbs/ear number in the equation can be modified if the ear is larger.
Example 36.4 What is the yield loss if one ear is found along a distance of 87 feet between two 30" corn rows?
In addition, each ear contains about 0.4 lbs of shelled corn.
Answer: For many people, 30 paces is approximately 87 ft and therefore, a rectangle that is 2.5 ft by 87 ft is an area of 217 ft2.
1 ear corn X bushel = 1.43 bushel 56 lbs corn acre 1.4 bushel acre
Chapter: 16 Online Soil Survey Information Web Soil Survey 
 Soil information is used for a multitude of decisions including determining fertilizer rates, identifying soil characteristics linked to specific pest problems, identifying areas prone to moisture stress, and identifying areas with poor drainage.
The purpose of this chapter is to provide a hands-on example on how to integrate Web Soil Survey  information into the decision process.
In this rapidly changing world, technological advances  allow resource managers to rapidly inventory the soil resource Figure 16.1 Web Soil Survey home page.
using the USDA-NRCS Web Soil Survey.
Web Soil  Survey  is a powerful, user-friendly search engine for obtaining modern, detailed soil survey information.
The most recent WSS version 3.1 was released in December 2013.
An online tutorial and written directions are available.
Visual and tabular information can be obtained from WSS.
The basic steps in using WSS include defining your area of interest, creating a soil map for the area of interest, exploring soil suitabilities, and developing a customized map.
Step 1 Define Area of Interest 
 The AOI is used by WSS to generate tabular and visual data for use in later steps.
First, identify and define the AOI where information about a field, farm, or parcel of land is needed.
The AOI can be located using the various Quick Navigation options or the Interactive Map option  in the WSS navigation window or imported from a previous session.
When using the Quick Navigation option, you can locate your AOI by entering any one of the following:
 1.
Local street address.
2.
State and county identification.
3.
Soil survey area.
4.
Longitude and latitude.
5.
Legal land description , if needed, for your AOI.
Use the drop-down menus in the program to assist you in picking the proper PM [Fig.
16.3]).
6.
Other data sources such as the Bureau of Land Management Field Office , Defense Department Installation , US Forest Service , National Park Service , or Hydrologic Unit  Code.
If you cannot use the Quick Navigation options, items 1-6 above, then use the Interactive Map on the home page  to find your AOI.
Once the AOI has been located, the boundaries of the AOI need to be entered into the WSS application.
Select one of the two boundary buttons.
The left button allows you to identify the AOI boundaries using a rectangular box, while the right button allows you to use polygons.
Once the AOI has been outlined, double-click to electronically define and enter the AOI into WSS.
After the AOI is defined and accepted, the area , availability of soil data/maps, and an aerial photo of the AOI are provided.
Step 2 Create Soil Map for AOI
 WSS allows users to view and print the soil map of the AOI selected.
Answers to selected questions regarding the interactive map functions are available by going to websoilsurvey.sc.egov.usda.gov and clicking on Frequently Asked Questions.
Click on the Soil Map tab at the top of the WSS webpage to create a modern, detailed soil survey map.
The information available includes: the soil map and legend , the soil map unit  name and symbol, number of acres of each soil MU, the percentage of AOI that each soil MU occupies, and tabular data for each MU.
The tabular data  includes:
 1.
MU setting elevation, annual precipitation, average annual temperature, frost-free period , and farmland classification.
2.
MU composition lists all the major and minor soil units with their composition percentage.
3.
Description of each major MU component.
a.
Setting for named series landform, landscape position, slope shape , and parent material.
b.
Typical profile horizon names, thicknesses, depths, and textures.
Selected soil properties and qualities percent slope, restrictive layers, drainage class, C.
permeability, depth to water table, flooding and ponding frequency, lime  content, salinity , sodium adsorption ratio , and profile plant available water holding capacity.
d.
Interpretive groups Land Capability Classification, Hydrologic Soil Group, Ecological Site , and Other Vegetative Groups.
4.
A brief description of each minor MU component explains how the minor soil differs from the named major MU component.
If you would like to copy or include the soil map in a custom soil survey report, select the proper print tab in the upper right-hand corner of the window.
There are two options, Printable Version or Add to Shopping Cart.
The Printable Version allows you to download a PDF of the soil map and associated documentation.
The Add to Shopping Cart adds the soil map to a file and saves the file until you are done with your WSS session.
The customized AOI web-based soil survey report, including the soil map with other maps and tables, can be printed.
Note that when either the Printable Version or the Add to Shopping Cart button is selected, it will fade.
Step 3 Explore Soil Suitabilities/Limitations/Properties and Characteristics for AOI
 Once the AOI is identified, the soil map is prepared and you can explore and assess the suitability and
 Figure 16.2 Web Soil Survey's AOI selection window, showing Quick Navigation and Interactive Map options.
Figure 16.3 Using the WSS legal land description section in the Quick Navigation tool for locating AOI.
The Principal Meridian drop-down box is located in center of the window.
Example: Eastern South Dakota uses the Fifth Principal Meridian for legal land description.
Figure 16.4 Web Soil Survey's AOI selection window with the AOI defined as the cross-hatched area.
Figure 16.5 Web Soil Survey's Soil Map for the AOI information.
Figure 16.6 Sample WSS Map Unit Description, obtained by clicking on the Map Unit Name, e.g., Z157A, Fairdale loam.
Figure 16.7 Location of Printable Version tab and Add to Shopping Cart tab in upper right-hand corner of WSS window.
The Printable Version tab creates a PDF file of the current window on the computer monitor and the Add to Shopping Cart tab stores the current window contents and associated information for later retrieval in a final report.
limitations of soils for selected uses.
Maps and tables of selected soil physical/chemical properties and characteristics, as well as land productivity information, are available.
Answers to selected questions on the Soil Data Explorer are available by going to websoilsurvey.sc.egov.usda.gov and clicking on Frequently Asked Questions.
To look at various soil properties, qualities, and uses , select the Soil Data Explorer tab at the top of the webpage.
A new window appears giving you the following options:
 1.
Intro to Soils.
2.
Suitabilities and Limitations for Use.
3.
Soil Properties and Qualities.
4.
Ecological Site Assessment.
Select the Suitabilities and Limitations for Use tab and a drop-down list appears on the left side of the webpage window.
If you click the Open All button, all the options for each category  will be displayed.
The categories of Land Classification, Land Management, Vegetative Productivity, Waste Management, and Water Management are most commonly used for agricultural production and management decisions.
Crop-yield estimates can be obtained by using the actual crop-yield data for those states having actual crop-yield data or by using the Crop Productivity Index  data.
In this paper, we will use the CPI data.
The CPI values are assigned relative soil potential rankings  for intensive crop production.
The CPI ratings are based on the following assumptions:
 2.
Natural weather conditions.
3.
Drainage installed where needed.
4.
No frequent flooding in low-lying areas.
5.
No leveling or terracing employed.
6.
CPI values will remain constant with time.
The CPI rating map and tabular data are shown, respectively, in Figures 16.9 and 16.10.
The potential corn yield can be estimated by multiplying soil-specific digital CPI by a specific crop high yield.
Example: Soil is Z181A Brandt silty clay loam with CPI of 85.
Brookings County, SD high corn yield estimate = 200 bu/a Estimated corn yield for Brandt soil = 200 bu/a X  = 170 bu/a
 For each soil suitability or limitation listed, the dominant condition within the soil mapping unit , the dominant soil within a MU, all components of a MU, and weighted average of all components within a MU are available.
In addition to soil suitabilities and limitations for land use, there is a tab for Soil Properties and Qualities at the top of the webpage.
If the Soil Properties and Qualities tab is selected, a drop-down list with various categories  of soil properties and qualities appears on the left side of the window.
For each soil property or quality selected, you can look at the dominant condition within a soil mapping unit , the dominant soil in a MU, all components of a MU, components of a certain percentage, or a weighted average of all components in a MU.
You also can select the soil-depth range, e.g., surface, part of a profile, or all of a profile.
Many different options are available for viewing soil property maps  and tables.
The single-purpose maps, associated legends, description information, and other related materials can be printed by using the Printable Version tab or Add to Shopping Cart tab in the upper right-hand corner of the webpage window.
Note that the tabs in the Add to Shopping Cart area fade when selected.
When the report becomes large , the NRCS will send you the report by email as a PDF file after it is created.
Figure 16.8 The WSS Suitabilities and Limitations for Use window with drop-down list on the left.
If you want all options to be visible in the drop-down area, click the Open All button.
Figure 16.10 Sample WSS Soil Data Explorer yield table and descriptive information for Crop Productivity Index  map created in Figure 16.9.
This information is located below  the CPI map.
Figure 16.12 WSS View Options and Advanced Options in the drop-down list of the Soil Properties and Qualities window.
Figure 16.9 Sample WSS Soil Data Explorer window for the Suitabilities and Limitations for Use tab  for the AOI, right, and legend, left.
Note: click the Legend tab to cause the suitability Map Legend to appear.
To estimate a crop yield  for each soil MU, multiply the top yield in the county by the CPI value.
Figure 16.11 The WSS Soil Properties and Qualities window with drop-down list on the left.
If you want all options to be visible in the drop-down area, click the Open All button.
Figure 16.13 Sample WSS Soil Data Explorer window, showing the Soil Properties and Qualities tab and Surface Soil pH for the AOI, right, and Map Legend, left.
Note: click the Legend tab to cause the Soil Property Map Legend to appear.
The fourth tab in the Soil Data Explorer window, Ecological Site Assessment, provides ecological site information.
This information includes an ecological site assessment map and associated tabular data for the AOI including MU name, MU components , ecological site ID for each component, and detailed information about each ecological site.
The ecological site information for rangeland is available.
For selected counties, ecological sites for pasture groups are also provided.
The information given for a rangeland ecological site includes: a photo of the plant communities, a brief ecological site description and impacts of management on species , and a transition diagram illustrating the impact of management on the plant communities in the ecological site.
Within each ecological site various plant communities are further explained  relative to the impact of management on plant communities in this ecological site.
In addition to the interpretive maps, tabular data for the AOI can be downloaded.
Tabular data is available when you use the Soil Reports tab in the Soil Data Explorer window.
The many possible options for tabular data found in the drop-down menu are located on the left-hand side of the Soil Reports window.
An explanation as to what is contained in each table can be viewed using the View Description tab or View Soil Report tab on the left side of the window.
This information can be printed or saved using the Printable Version tab or Add to Shopping Cart tab  in the upper right hand of the webpage window.
Step 4 Create Custom Soil Survey Report for Area of Interest 
 Electronically store and/or print the available data generated by the WSS session using the Shopping Cart and Checkout Option tabs.
Answers to selected questions concerning data downloads and printable reports are available by going to websoilsurvey.sc.egov.usda.gov and clicking on Frequently Asked Questions.
After creating all the maps and tables needed and saving them to the Add to Shopping Cart tab, you need to click on the Shopping Cart tab at the top center of the webpage.
This option allows you to create your own customized detailed soil survey report.
Review the Report Properties and report Table of Contents and make any additions or deletions you may need.
When you are satisfied with the information in the Report Properties and the Table of Contents, select the Checkout Options tab.
For small reports , a Checkout Options box will appear and you will have the option to receive the report online during the current WSS session or having the report sent by email  to you.
Use and Limitation of Web Soil Survey  Information
 Web Soil Survey  information is useful in understanding how soils differ and will perform under various land-management systems.
Examination of key soil-property and quality-attribute information can aid you in making management decisions.
You can manage soil resources more economically and with increased environmental sustainability using detailed WSS soil-survey data along with yield-monitor maps.
Producers can integrate WSS data with yield-monitor and other collected on-site data.
One key point to remember is that many soil maps in WSS were originally prepared at a scale of 1:20,000 and 1:24,000.
As a result, the soil interpretations included inside a soil mapping-unit  boundary have limitations.
The smallest delineation that can be shown on modern soil-survey maps in South Dakota, for example, is about 2 acres.
Areas smaller than 2 acres are not shown on the map.
Most soil MU descriptions include descriptions of these inclusions to let the user know that these other soils exist in the soil MU.
Figure 16.14 Sample WSS Soil Data Explorer tab, showing soil properties and qualities ratings and descriptive information for surface pH for map created in Figure 16.13.
This information is located below  the pH map.
Figure 16.16 Sample WSS Soil Data Explorer Ecological Site Assessment information  for selected ecological site  for AOI created in Figure 16.15.
This information appears when each ecological site is selected in the left-hand set of drop-down boxes.
The diagram on the left shows management impacts on native plant communities.
Figure 16.15 Sample WSS Soil Data Explorer window, showing Ecological Site Assessment tab  for AOI, right, and Map Legend, left.
Note: click the Legend tab to cause the Ecological Site Rangeland Map Legend to appear.
Figure 16.17 Sample WSS Soil Data Explorer window, showing Soil Reports tab with drop-down boxes on the left.
If you want all options to be visible in the drop-down area, select the Open All button.
Example: drop-down box for Non-irrigated Yields by Map Unit is shown.
Selected crops for table creation are checked.
Figure 16.18 Sample WSS Soil Shopping Cart window with the Checkout Options tab selected.
For intensive management of areas smaller than 2 acres, a more detailed soil map is needed.
The soil MUs in WSS allow the user to develop field zones where sound management decisions can be made.
With modern GPS, soil-survey data, yield-monitoring data, and scouting reports, it may be possible to increase profitability and reduce the impact of agriculture on the environment.
This chapter outlines how to use Web Soil Survey  to obtain soil and land-attribute information.
Samples of output and WSS 3.1 and a listing of other websites with valuable soil and natural resource information are provided.
Table 16.1 Online sources of soil and natural resources information.
These locations are provided for the convenience of the reader, however, locations frequently change.
Name	Information available	Web address 
 Census Bureau)	economic, and geographic data by
 state, town, county, or zip code area
 Mapping and Earth	and educational materials	imagery-air-photos/satellite-imagery-products/9271
 Information System	and publications
 images, research projects and
 Service and ABS College)	information
 and Agriculture 	agricultural research information
 Technical Guide	technical and reference information	technical/fotg/
 on soil, water, air, plant and animal
 Resource Areas 	water resources, soils, biological	ref/?cid=nrcs142p2 053624#handbook
 resources, and kinds of land use
 Survey Handbook	projects and activities	ref/?cid=nrcs142p2 054242
 Table 16.1 Online sources of soil and natural resources information.
These locations are provided for the convenience of the reader, however, locations frequently change.
Name	Information available	Web address 
 and Pasture Handbook	analysis, treatment, and	national/landuse/rangepasture/?cidstelprdb1043084
 management of grazing land
 + Climate, Soil Survey, Agroforestry,	about/org/?cid=nrcs143 021411
 and Climate Center	planning information
 Descriptions	descriptions for soils in US	home/?cid=nrcs142p2 053587
 Quality	assessment, management, resources,	health/
A second key thing to check for is the flow rate.
Again, the flow rate can be compared to the design flow rate.
If your flow rate is lower than usual, and the pressure is lower than usual, this may indicate a problem with the well.
Possibilities include the screen  and declining water table or the pump needs to be turning faster.
According to study from Department of Natural Resources researchers, irrigation pivots stained with rust may indicate the absence of nitrate in the groundwater supplying the pivots.
The researchers categorized pivots in Adams, Kearney and Phelps counties by the amount of rust present on the pivots.
They then used the Nebraska Groundwater Quality Clearinghouse to test the correlation between rustiness and nitrate concentration.
The clearinghouse compiles water-sampling data collected by Tri-basin and Little Blue Natural Resource Districts  along with others throughout the state.
Effects on corn during grain fill: During grain fill drought stress results in premature death of leaf tissue, shortened grain fill periods, increased lodging, fewer kernels, and light kernel weights.
Kernel abortion near the ear tip will occur in the two weeks following pollination.
Continued drought into the milk stage will result in further kernel abortion and smaller, lighter kernels.
Drought that occurs in the mid to late grain filling period  results in decreased kernel weights and premature physiological maturity.
Once physiological maturity occurs additional drought stress will have no impact on grain yield.
Because drought stress typically coincides with higher than normal temperatures the grain fill period is often reduced.
TECHNICAL IRRIGATION PUMPING PLANT TEST PROCEDURE MANUAL
 TECHNICAL IRRIGATION PUMPING PLANT TEST PROCEDURE MANUAL FIRST EDITION 1982
 Project Coordinator PAUL E.
FISCHBACH Extension Irrigationist
 Agricultural Engineering Department Cooperative Extension Service Institute of Agriculture and Natural Resources University of Nebraska-Lincoln Lincoln, Nebraska
 DEEP WELL TURBINE 	11
 DEEP WELL TURBINE 	16
 CENTRIFUGAL PUMP 	19
 COLUMN FRICTION HEAD	21
 PROPELLER WATER METER	24
 COLLINS FLOW GAGE	28
 ALTERNATORS AND HYDRAULIC PUMPS	68
 PUMP AND POWER UNIT SPEED	71
 VOLTAGE AND CURRENT	76
 SAMPLE TEST FORMS	83
 The Technical Irrigation Pumping Plant Test provides the means to properly analyze the energy efficiency of an irrigation pumping plant.
This manual gives the procedures necessary to gather important information such as pumping lift, discharge pressure, water flow rate, and the energy consumption of any particular pumping unit.
The Simplified Irrigation Pumping Plant Test also outlined procedures to find the above items.
However, the test equipment and procedures were relaxed for economy and ease of use.
The simplified test should only be used to determine an approximate energy efficiency level.
The test only provides an indicator of the excess energy being used.
It does not provide all the information, nor accuracy, needed to diagnose why the pumping plant may not be performing at recommended energy efficiency levels.
The Technical Irrigation Pumping Plant Test differs in this respect.
The equipment and procedures given in the manual provide the best possible accuracy that can be practically obtained in the field with equipment presently available.
The Technical Manual also gives additional procedures to find such items as pump and engine rpm, and measurement voltage and amperage of electrical equipment.
These are diagnostic tools necessary to properly analyze pumping plant operations and provide information for ad justments or possible changes in equipment to improve performance.
The Technical Irrigation Pumping Plant Test Procedure Manual was designed to complement the "Irrigation Pumping Plant Performance Handbook".
While the procedure manual shows "how to" the Pump Handbook provides the technical information to analyze the information acquired from the technical test.
Gary Lay Extension Division Chief Nebraska Energy Office
 Paul E.
Fischbach Extension Irrigationist Agricultural Engineering Dept University of Nebraska-Lincoln
 Gary Morgan Assistant to the Area Manager for Special Projects Loveland-Fort Collins Office Western Area Power Administration
 Mark A.
Schroeder Extension Irrigation Assistant Agricultural Engineering Dept.
University of Nebraska-Lincoln
 The author is indebted to many individuals for their guidance, suggestions, and comments in the preparation of this manual.
Many test procedures are adapted from past work done by the professional staff of the Agricultural Enginnering Department, University of Nebraska.
Many irrigation equipment manufacturers and representatives have committed their time and products to help with the test programs.
Their efforts are appreciated.
Thanks also to Donna DeLair for her suggestions on editing and layout, typing and her patience in preparing the manual; to Bruce Sandhorst for photographs of the test equipment; and to Shelia Smith, Linda McCaugherty and staff for the drawings and artwork in the manual.
The technical irrigation pumping plant test was developed through staff experience at the University of Nebraska with consideration given to common problems and hazards that may be encountered while performing a pumping plant test.
However, it is impossible to foresee all problems and hazards which may be encountered in the field.
Care on the part of the person performing the test is a must to provide a safe and successful test.
The University of Nebraska, its agents and employees, and the State of Nebraska accept no liability resulting from the use of the test equipment or procedures as given in the manual.
Mention of trade names, or commercial products in this manual does not infer endorsement of the product.
This manual is designed to instruct how to conduct an accurate pumping plant performance test.
The test determines four important items which indicate the performance of a pumping plant, namely:
 1) Discharge pressure 
 3) Water pumping rate 
 and 4) Fuel consumption rate
 Diesel, Propane gal/hr Electric kW Natural Gas mcf/hr.
The pressure, lift, and flow rate are combined to determine the horsepower output of the pump.
The horsepower output is compared to the pumping plants' fuel consumption required to produce the horsepower.
This value is compared to the expected fuel consumption to produce the same horsepower if the pumping plant is efficient.
Fuel consumption exceeding the expected rate results in a performance rating below 100%.
A fuel consumption rate below the expected rate results in a rating above 100%.
In regards to the center pivot irrigation system, the ability to remotely monitor position, speed, pressure and flow are essential to precision water management.
The ability to remotely control the pivot also assists producers in timely and accurate operation of the pivot.
The Field Commander remote pivot controller mounts on the rabbit ears of the pivot and is equipped with a GPS to track the pivot and perform pivot control operations based on position.
The Field Commander utilizes the Digital cell network to transport data across the Internet to the WagNet.net web portal.
However, other field data must be remotely captured in order to capture a timely, complete picture of what is going on in the field.
This data is critical in successfully implementing a precision water management program.
In addition to monitoring and controlling the pivot, the Field Commander can be optionally equipped with a 900 MHz radio with meshing technology to communicate with multiple sensors, meters and pumps located in the field via the AgSense Crop Link device, which is also equipped with a 900MHz radio.
Crop Link has built-in hardware and software that enables it to work as a multipurpose device, allowing it to be programmed and configured in the field, via the Internet.
Crop Link enables AgSense to partner with other agricultural companies to deliver customers a broad range of field data and proprietary solutions.
AgSense serves as a gateway to the Internet for a number of applications.
However, AgSense does not charge for the additional data transported.
Through collaboration and data sharing, end users enjoy lower annual service cost, as well as timely data that is displayed in coordinated formats, to maximize productivity, efficiency and profitability.
Problems in Diagnosing Nutrient Deficiencies of Cool-season Forage Grasses
 K.L.
Wells and C.T.
Dougherty
 C ool-season perennial grasses dominate the forage crop species grown in Kentucky.
While several species can be grown, tall fescue , orchardgrass , and bluegrass  are the most important and, collectively, are grown on perhaps 7 to 8 million acres in Kentucky.
In contrast to many plant species, diagnosis of nutrient deficiencies by foliar symptoms on cool-season grasses is virtually impossible, with the exception of nitrogen.
Most often, the only foliar symptoms seen on cool-season grasses, with the notable exception of N deficiency, are dying or dead leaves or leaves with yellow to brown lesions.
Such symptoms are usually the result of leaf diseases and should not be interpreted as nutrient deficiency symptoms.
With the exception of N, there is virtually no mention of foliar symptoms associated with plant nutrient deficiencies in the scientific literature for these grasses.
Again, except for N deficiency and leaf disease symptoms, few symptoms are noticeable from a field diagnostic viewpoint, except for poor growth or thin stands.
This is because grasses mobilize nutrients from older leaves to younger leaves when nutrient stress develops.
When this happens, lower mature leaves might simply turn brown and die while new growth coming from the crown retains a normal green coloration.
This is a normal consequence of aging of leaves, and while nutrient deficiencies do not cause aging, they may accelerate death processes.
Even with moderately low soil test levels of soilimmobile nutrients, such as phosphorus , identifiable leaf deficiency symptoms of those nutrients are unlikely.
Poor growth more than likely will be the only symptom of deficiency symptoms of grasses growing under immobile nutrient stress.
Grasses have two major components of yield.
Although both are affected by nutrient deficiencies, number of tillers per unit area is affected most.
Even small application rates of lime and fertiliz-
 ers are likely to prevent nutrient deficiency symptoms.
Nutrient stress is greatest when a field is continuously managed for hay, and it is least under grazing management due to recycling of nutrients in manure and urine.
Fertilization management based on soil test values and proper forage utilization  provides adequate levels of nutrients for coolseason grass production in Kentucky.
Research in Kentucky indicates that content of P and K in adequately fertilized cool-season grasses is in the range of 0.2 to 0.3 percent P and 2 to 3 percent K.
Content of N varies with rate of N applied.
While cool-season grasses deficient in N may contain 1.7 percent N or less, 80 lbs N/A will increase N to around 2 percent.
Excessive rates of N applied as a single topdressing  may result in non-protein N accumulations in plants.
Even though some concern has been expressed about N:S  ratios being high enough  to cause animal nutrition problems, analysis of cool-season grasses in Kentucky has shown no basis for this concern even with high rates of N fertilization.
Lime and fertilization applications to grasses based on University of Kentucky soil test recommendations provide sufficient nutrient levels for good forage production.
However, if there is concern about whether nutrient levels are adequate for good production, forage tissue testing is the best way to make this determination.
Except for N deficiency, the most common cause of abnormal leaves is leaf diseases.
Discoloration of diseased leaves is sometimes confused with nutrient deficiency symptoms.
The incidence and severity of diseases are often climate-related, being more severe if climatic conditions are more favorable for the disease organism.
Foliar damage from diseases can cause slight to severe yield reductions and can sometimes reduce the stand or even eliminate it.
To minimize the likelihood of leaf diseases, use climatically adapted varieties.
Preventing the accumulation
 of lush growth by adequate grazing or timely harvest is another management practice that reduces risk of disease problems.
Three of the more commonly occurring leaf diseases of grasses in Kentucky are netblotch , leafscald , and rust.
Specific identification of foliar diseases can be made by the University of Kentucky's Plant Diagnostic Laboratory.
While insects may cause damage to cool-season grasses, the symptoms caused are not likely to be confused with nutrient deficiency symptoms.
Such damage more likely results from chewing-type insects, notably grasshoppers and the various armyworms.
Insect damage  is generally not a problem with the cool-season grasses; however, if it threatens major loss of production or even life of the stand, insect specimens should be captured and identified before deciding on proper control practices.
Drought stress sometimes causes confusion in diagnosing nutrient deficiencies in cool-season grasses.
Although these grasses produce most of their growth during seasons when there is likely to be adequate rainfall, drought stress can occur.
Damage ranges from complete loss of a young, immature stand to seasonal loss of production from a mature, established stand.
While severe drought stress is easily identified during periods of widespread drought, it might be harder to pinpoint in fields that vary greatly in soil moisture-holding capacity.
During seasons of marginally sufficient rainfall, areas of fields with good waterholding capacity can appear normal at the same time that adjacent areas with poor water-holding capacity show drought stress.
Diagnosis of Some Common Field Conditions
 Field Observations	Possible Cause
 Poor color  and noticeably poor growth.
Fields topdressed	Nitrogen deficient
 with N may sometimes appear "streaked" if swath is not overlapped.
This can result
 in strips of N deficiency running parallel to the direction followed by fertilizer spreader.
"Pasture mosaic"-unfertilized pastures which show lush green	Nitrogen deficiency
 growth around dunghills and urine spots.
except around
 Excessive fertilizer rates or applications followed by hot, dry weather may	Nitrogen or fertilizer
 cause foliage kill.
The condition may appear uniformly but should show	"burn" due to
 evidence of "application" patterns.
excessive
 Dead spots occurring in natural drainage channels or immediately	Herbicide movement
 adjacent to cultivated fields.
or drift from adjacent
 Dead spots or yellowish, stunted growth on newly established stands.
Herbicide carryover
 Stand thins out, leaving "clumps" of fescue which are most noticeable when winter	Prolonged heavy
 dormancy breaks and new spring growth begins.
fertilization with
 at low levels of other
 Plant canopy wilts at top, turns dark green to black, becomes matted and turns brown	Winter-kill following
 in a few days.
Field may appear entirely or partially brown.
Under matted areas, plants	sudden or hard
 remain blackish green.
Some plants show no symptoms.
freeze when plants
Soil and Soil Water Relationships
 Zachary M.
Easton, Assistant Professor and Extension Specialist, Biological Systems Engineering, Virginia Tech Emily Bock, Graduate Research Assistant, Biological Systems Engineering, Virginia Tech
 This publication presents and discusses concepts that are fundamental to understanding soil, water, and plant relationships and the soil water balance.
Knowledge about soil water relationships can inform the decision-making process in agricultural operations or natural resource management, such as determining what crops to plant, when to plant them, and when various management practices should be scheduled.
Understanding these concepts is useful for addressing both agronomic and policy issues related to agricultural water management.
Soil Soil Composition and Texture
 Soils are composed of four components: mineral solids, organic matter solids, water, and air.
The solids are made of minerals derived from geologic weathering and organic matter consisting of plant or animal residue as well as living organisms.
The empty spaces between the solids, called pores, are occupied by either water or air.
The mineral solid fraction of the soil is made up of sand, silt, and clay, the particular ratios of which determine the soil texture.
Sand particles range in size from 0.05 to 2.00 mm, silt ranges from 0.002 to 0.050 mm, and the clay fraction is made up of particles smaller than 0.002 mm in diameter.
Particles larger than 2.0 mm are referred to as rock fragments and are not considered in determining soil texture, although they can influence both soil structure and soil water relationships.
Once the sand, silt, and clay fractions are known, the textural class can be determined using a soil textural triangle.
Most land-grant universities and private labs can determine the sand, silt, and clay fractions of soil samples.
Soil texture determination is important because many soil properties are influenced by texture, including drainage, water-holding capacity, aeration, susceptibility to erosion, cation exchange capacity, pH buffering capacity, and soil tilth.
Most soils are composed of about 35-55 percent pore space and 45-65 percent solid material by volume.
Between 2 and 5 percent of the solid material is organic-based residue, with the remainder being mineral-based.
Agricultural soils, particularly those that are tilled, tend to contain less organic matter compared to forested or undisturbed soils.
When organic matter is exposed to soil microorganisms in aerobic conditions, it becomes oxidized and degraded.
Organic matter is generally viewed as a beneficial soil component because it provides waterholding capacity, slowly releases nutrients for plant growth, and improves soil structure.
Air and water occupy the pore space in a soil, and the proportion of each varies by soil type and over time.
After a large precipitation event, the pore space occupied by water will increase, and the air-filled pore space will decrease.
During prolonged dry periods, the water-filled pore space will decrease, and the air-filled pore space will increase due to evapotranspiration and percolation of water from the root zone.
Soil structure refers to how the soil particles are shaped and organized into units of aggregation, also referred to as peds.
There are six primary soil structural classes: platy, prismatic, columnar, blocky, single-grained, and granular.
Soil structure affects the rate that water and air can move through the soil, root penetration, and the availability of nutrients to plants.
Single-grained soils  and massive soils  are called "structureless."
 In single-grained soils like sand, water percolates very quickly through the soil, while in massive soils such as dense clays, water movement is very slow.
Platy structure impedes the downward movement of water due to the horizontally arranged plates of soil.
More favorable water movement characteristics for crop production are generally found in soils that have granular, prismatic, or blocky structure.
Well-structured soils are usually more desirable for
 agricultural production because structured soils can hold and conduct water and gasses and are also able to support load-bearing activities, such as field traffic.
Tillage of some fine-textured soils, particularly when they are wet, can destroy the soil structure, as can irrigation with high sodium  content, which causes dispersion.
Biological activity of organisms such as earthworms, mammals, termites, and ants can also change the soil structure by creating large pores from burrowing and deposition of organic matter.
Soil Bulk Density and Porosity
 Soil bulk density expresses the ratio of the mass of dry soil to the total volume occupied in the soil.
The total volume includes both the solids  and the pore spaces.
Soil bulk density is important because it is an indicator of the soil's porosity.
The porosity of a soil is defined as the volume percentage of pores in a soil the inverse of the volume percentage of solids.
Within a soil of similar texture, a compacted soil has lower porosity and thus a greater bulk density, while a loose soil has a greater porosity and a lower bulk density.
Bulk density also provides information about the potential for leaching of agrochemicals, erosion, and crop productivity.
Surface runoff and erosion of soil both of which can remove nutrients needed by crops can occur on soils with a high bulk density because water is restricted from moving through the soil and thus ends up as surface runoff and carry away soil and soil-bound nutrients.
Soils with lower bulk density, such as sands, can promote vertical leaching of nutrients and reduce their availability to crops.
As with soil structure, soil bulk density can be affected by physical management practices, such as tillage, as well as biological activity, such as the tunneling of earthworms.
Total soil porosity can be determined for a soil sample using the following equation:
 total porosity = 1.
Figure 2.
Six primary soil structural classes and the relative impact the soil structure has on water movement.
Bulk density is generally measured in a soil sample obtained with a core, which is used to extract undisturbed samples from various depths in the soil profile.
Particle density is determined similarly to bulk density but is the mass of the dry soil divided by the volume of the solid soil components only, that is, excluding the volume of the pore space.
Therefore,
 particle density will be greater than bulk density and represents the average density of all the solids composing the soil.
The particle density of most soils is around 2.65 g/cm because quartz has a density of 2.65 g/cm and is usually one of the dominant minerals in soils.
However, clay has a particle density of 2.83 g/cm, and organic matter has a particle density of 0.8 g/cm, SO soils with significant amounts of either clay or organic matter particle density will deviate from the 2.65 g/cm particle density estimate.
Soil porosity is influenced primarily by soil aggregation, soil texture, root penetration, and other biological activity.
Coarse-textured or sandy soils tend to be less porous than fine-textured  soils because although the average size of individual pores is usually larger in coarse  soils, the smaller pores in the clayey soils are more numerous.
Organic matter content increases porosity by enhancing soil aggregation.
The size of a pore in a soil affects how the pore functions.
Macropores, those larger than 0.08 mm, are primarily the pore spaces between aggregates, and they promote free drainage of water , aeration, evaporation, and gas exchange in the soil profile.
This free drainage, also referred to as "preferential flow" because the water preferentially bypasses the bulk soil, is enhanced by wet soil conditions and lack of soil disturbance such as is often found in no-till or pasture systems.
Preferential flow can cause rapid leaching and bypass flow of nutrients and agrochemicals, even those that otherwise could be strongly bound to the soil, thereby potentially reducing the effectiveness of fertilizer and agrochemical applications.
Macropores are most prevalent in loamy and well-aggregated soils but can be converted to micropores by compaction through tillage and vehicle traffic.
Micropores, which are 0.08 mm or smaller and occur inside soil aggregates, retain water and agrochemicals and are responsible for capillary water distribution.
However, most of the water they contain is not available to plants.
Clays promote aggregation but can also be readily compacted.
Therefore, clays increase water storage, but not necessarily plant-available water, by providing an abundance of micropores.
Clays can, however, increase storage of plant-available water through the formation of stable soil aggregates.
Increasing macroporosity with organic matter amendments, which promotes root penetration and earthworm movement , can improve water infiltration and movement in fine-textured soils.
Thus, soil texture and structure, biological activity, and the level of compaction are the main factors that influence the amount and type of pore space in a soil.
Figure 3.
Macropores in the soil can be formed by earthworms or other biological activity.
Once formed, macropores can transport water and dissolved agrochemicals  from the soil surface deep into the soil profile.
Important Soil Water Relationships
 With the background concepts outlined above, we can now develop some basic soil water relationships that are important to consider for agricultural management.
The following sections discuss how the soil properties described influence the soil water content, soil water potential, and soil drainage characteristics.
Soil Storage or Soil Water Content
 The soil water content is the amount of water held in the soil at any given time and can be expressed as volumetric or gravimetric water content.
Volumetric water content is the volume of water per unit volume of dry soil and is the most useful way of expressing water content for developing a water budget, which is discussed in the next section.
Gravimetric water content is the mass of water per unit mass of dry soil.
The volumetric water content  is equal to the gravimetric water content  multiplied by the soil's bulk density.
To interpret the soil water content, remember that not all soil water is accessible to plants.
The water available to support plant growth is called plantavailable water and is the difference between field capacity and the wilting point.
Field capacity is the amount of water remaining in the soil profile after 48-72 hours of free drainage following saturated conditions.
Field capacity is also defined as one-third of atmospheric tension, that is, water is held in the soil weakly and is easily available for plant uptake.
While field capacity is considered to be the upper limit of available water, it should be pointed out that this is not strictly true.
Water moving downward in the soil following a saturating event can be effectively used by growing plants.
However, because gravitational flow is transitory, this water is generally not considered in calculations to determine the available water capacity of a soil, but it can affect things such as irrigation scheduling.
Water that drains freely under gravity is called gravitational water and might or might not be used by plants, depending on environmental conditions.
Figure 4.
Gravitational, plant-available and plantunavailable water content for various soil textures.
The wilting point is the minimum moisture content of the soil that can support plant growth and below which plants cannot recover.
The wilting point is defined as -15 atmospheres, that is, water below this point is held SO strongly in the soil that plants cannot access it.
Depending on the soil type, there can be very different gravitational, plant-available and unavailable water contents.
For example, sands have relatively little plant-available water and a significant portion is gravitational water flowing through macropores,
 and, as a result, crops grown on sandy soil are more vulnerable to drought.
Conversely, clay soils usually have a slightly higher plant-available water content due to enhanced aggregation, but also have a higher unavailable water content because the water is held SO tightly in the micropores that the plants cannot access it.
Loamy soils have the largest plantavailable water content as well as relatively equally sized gravitational and unavailable water contents.
For this reason, loam and silt loam soils are highly prized for agricultural production; they drain excess water quickly, have a large plant-available water content, and are not prone to drought conditions.
Table 1.
Average available water content for various soil textural classes.
Textural class	point	capacity	water
 Sand	5	12	7
 Sandy loam	9	21	12
 Loam	16	36	20
 Silt loam	18	39	21
 Clay loam	24	39	15
 Silty clay	24	39	13
 Clay	27	39	12
 Soil Water Potential: How Soil Holds Water
 The soil water content discussed above should not be confused with the soil water potential, which is the energy status of the soil water.
The soil water potential  is the amount of work required to move  water from the soil.
Differences in potential energy of water from one point in the soil to another are responsible for the tendency of water to flow within the soil.
Water always moves from higher to lower potential  and not necessarily from higher to lower water content.
This concept is important for non-uniform  soils.
Adhesion, surface tension, and cohesion at the air/water interface in unsaturated soil pores result in capillary suction and cause the water to be held tightly within the soil.
Note that capillary suction increases as pore size decreases, which is why
 water is held more tightly in micropores present in clay-dominated soils.
Total water potential consists of three forces acting on the water:
 total water potential = matric potential + gravitational potential + pressure potential.
Units of the potential depend on how a unit quantity of water is specified.
Gravitational potential is due to the force of gravity pulling on the water.
Determination of gravitational potential is independent of soil properties and depends only on the vertical distance between the water elevation and a reference elevation.
Matric potential is due to the force exerted on the water by the soil, also called tension, and is the combination of adsorptive and capillary forces in the soil.
Matric potential is a dynamic property and is essentially zero for a saturated soil and negative at water contents below saturation; matric potential is never positive.
The matric forces attract and bind water to the surface of soil particles  and lower its potential energy below that of the bulk water ; that is, it takes energy to overcome the matric force and move water from one location to another.
Capillarity results from the surface tension of water and its contact with the solid soil particles properties inherent to the molecular structure of water.
Strong  matric potentials bind water to soil particles in very dry soils.
Matric potential is generally stronger in finer textured soils than in coarse soils due to greater surface area and smaller pore sizes , and it is for this reason that clayey soils have higher plantunavailable water content than sands.
This effect is due to the adhesive and cohesive forces at the soil-water interface.
As an example, in figure 5 the smaller tube exhibits greater matric potential, a combination of water molecules adsorbing to each other and to the walls of the tube.
Figure 7 illustrates this concept in soils.
The use of moisture sensors in a soil provides information about the soil matric potential, which can then be used to estimate the soil water content of a soil.
For example, in figure 7 a loam with a matric potential of -110 feet is at or near the wilting point and has a water content near 30 percent.
Figure 5.
Example of the effect of capillary forces on water retention.
Capillary forces influence how far water rises in a tube depending on the tube size analogously to the increase in capillary force as soil pore size decreases.
Figure 6.
Illustration of how water is held by the soil.
Water can be absorbed to soil particles or held in between soil particles by capillary forces.
Figure 7.
Soil water characteristic curves for four different soils.
These curves show the relationship between the water content and the soil water potential.
Pressure potential is due to the mechanical or hydrostatic force exerted by water in a soil.
The pressure potential applies to saturated soils.
Pressure potential is the vertical distance between the water surface and a specified point.
Pressure potential is zero above the level of water and positive below the water level.
Drainage characteristics are important properties of soils that impact a host of agricultural production properties.
Soils that are well-drained tend to be the most productive, provided that rainfall is not limiting, while soils that are poorly drained will restrict root growth and consequently reduce agroecosystem productivity.
However, soils that are too
 well-drained are prone to drought.
Figure 8 depicts the five commonly used drainage classifications and how they relate to potential productivity.
Very poorly drained soils contain a barrier to root penetration at a shallow depth, between 0 and 18 inches, while welland moderately well-drained soils are often not depth limited, allowing roots to fully penetrate the soil and thus access available water and nutrients.
Soils with restricted drainage often become anaerobic  and reduced.
Reduced soils commonly have a gray appearance, often with rust colored iron oxide accumulations indicative of a fluctuating water table.
This reduced layer can be the result of management  or natural causes  that result in a layer of higher bulk density or restricted drainage.
Figure 8.
Five commonly used soil drainage classifications and their depth to poorly drained soils.
Poorly drained soils are soils that are subject to long durations of saturated  conditions, which cause discoloration.
The transition zone between aerobic and anaerobic soils often contains mottling, or coloration, that includes characteristics of both aerobic and anaerobic conditions.
The Water Balance Concept
 The water balance, also called a soil water budget, is an important tool that can be used to evaluate past, present, and proposed management practices in an agroecosystem.
In its simplest terms, the water balance tracks incoming and outgoing water from a unit such as a field or watershed.
The water balance is governed by the basic physical principle of conservation of mass:
 inputs outputs = change in storage.
In this formulation, inputs are precipitation and/ or inflow of ground or surface water, outputs are evapotranspiration and/or outflow of ground or surface water, and change in storage is the change in the moisture content of the unit.
Tracking or predicting soil moisture levels is critical to making management decisions to maximize crop production.
The water balance method offers a simple means to calculate a soil water budget for a given field or watershed by using the above formulation and adding a soil water accounting function:
 where ASW is the change in soil water from the previous day or month, P is precipitation, AET is actual evapotranspiration, Q is runoff leaving the soil surface or watershed, and QG is the groundwater  leaving the root zone or watershed.
At the watershed scale, Qs and Q are often considered together and called streamflow, because groundwater often contributes to streamflow and is difficult to measure in isolation, while measuring streamflow is relatively easy.
If precipitation is greater than the sum of actual evapotranspiration, runoff, and percolation/groundwater discharge, the soil is wetting.
If precipitation is less than the sum of actual evapotranspiration, runoff, and percolation/ groundwater discharge, the soil is drying.
Figure 9 shows a monthly water balance for the Piedmont region of Virginia.
This water balance shows that during the summer growing season, the soil is, on average, drying out due largely to plants removing soil water by transpiration.
During the late fall through spring, the soil is generally wetting because plants are not removing as much soil water via transpiration.
This is also the time of year when the majority of runoff and groundwater recharge occurs.
The water budget analysis can be performed on a daily basis as well, provided that daily estimates of precipitation and evapotranspiration are available.
This analysis could be modified to incorporate future estimates of precipitation and evapotranspiration to develop a short-term forecast water balance, which would notify producers of any predicted droughts or saturated conditions that might impact production.
Long-term climate projections that include estimates of change to precipitation and evapotranspiration could likewise be incorporated into a water balance and provide information that could be used to modify planting and harvesting schedules to better utilize soil moisture.
Figure 9.
Monthly water balance for a 30-inch deep sandy loam soil in the Piedmont region of Virginia showing periods of soil wetting and soil drying.
Notice that as the soil dries out, actual evapotranspiration  declines, while potential evapotranspiration  continues to increase.
The decline in actual ET is due to less water available in the soil for plants to utilize for transpiration.
This publication presents an overview of the basic soil water relationships and highlights some concepts of importance in agroecosystems.
We have discussed important properties of soils , how to describe and measure some of these properties , and how these foundational concepts are applied to manage agricultural systems for optimal productivity.
Sound decisions about the use and protection of our water resources require a
 fundamental understanding of the basic processes controlling soil water movement and cycles.
The water balance concept provides a useful tool that can be used to predict field conditions to schedule irrigation or determine the likelihood of leaching that could reduce fertilizer uptake efficiency of crops.
Understanding these relationships is critical to marinating and enhancing agricultural productivity and food security.
Related Virginia Cooperative Extension Publications
 actual evapotranspiration The quantity of water that is actually removed from the soil due to evaporation and transpiration.
AET can be measured in the field via weighting lysimeters or, as is more often the case, at the larger scale , it is calculated using an equation such as Penman-Monteith or Hargreaves methods.
adhesion The attraction between water and a soil particle.
A drop of water sticks  to a soil particle.
capillary water distribution The movement of water up a small pore  against gravity, due to the attraction of water to the solid surface  and the surface tension of water.
cation exchange capacity The total of exchangeable, positively charged ions  that a soil can absorb.
CEC influences the soil's ability to hold onto essential nutrients and provides a buffer against soil acidification.
cohesion The attraction of water molecules to each other.
Cohesion causes water droplets to form.
conservation of mass States that matter  can change forms  but that the total mass of water remains constant, that is, the sum of all the mass of liquid, solid, and gas water is always the same.
dispersion The separation of soil into single particles.
evapotranspiration The sum of evaporation from the land and water surface and plant transpiration to the atmosphere.
hydrostatic force The pressure exerted by water at equilibrium due to the force of gravity.
Hydrostatic force increases in proportion to depth measured from the surface because of the increasing weight of water exerting downward force from above.
infiltration The downward entry and movement of water through the soil profile.
macropores Large soil pores that form as a result of biological activity , geological forces , or mechanical practices.
Macropores are larger than 0.08 mm in diameter and can conduct large quantities of water and agrochemical deeply onto the soil.
micropores Soil pores smaller than or equal to 0.08 mm inside soil aggregates that retain water and agrochemicals and are responsible for capillary water distribution.
percolation The downward movement of water through saturated soil layers.
Percolation is responsible for groundwater  recharge.
soil organic matter Plant and animal residues, cells and tissues, or soil organisms composed of carbon and the substances the organisms synthesize.
soil water content Amount of water a given soil can store, primarily influenced by the soil texture and the soil organic matter content.
In general, soils with greater silt and clay-sized particles have greater waterholding capacities.
Likewise, soils with more organic matter have greater water-holding capacities.
surface tension The combined effect of adhesive and cohesive forces at the soil water interface.
tilth Quality of a soil for purpose of cultivation related to soil structure, including characteristics supporting plant growth  and the ease of tillage.
water balance A means to track the volume of water moving in and out of a soil or watershed based on the principle of the conservation of mass.
PUMPING PLANT EFFICIENCY HOW MUCH EXTRA ARE YOU PAYING?
The energy cost of operating a pumping plant is dependent on three variables: the amount of work output the pump is producing, the efficiency of the power unit and the efficiency of the pump.
In this paper we will address the question, "Could you reduce irrigation costs?
The first step in answering that question is to ask the more basic question, "How much energy should your pumping plant be using?"
 Power is defined as the rate of doing work.
One horsepower is defined as performing 33,000 foot-pounds of work per minute.
Irrigation water is assumed to weigh 8.34 lb/gal.
33,000 / 8.34 3960.
Therefore the horsepower imparted to the water, known as water horsepower  can be calculated using the equation: Whp = gallons /min  X head  / 3960.
Example 1: Find the water horsepower output of a pump supplying 800 gpm to a center pivot.
The pumping water level is116 feet below the level of a pressure gauge installed on the pivot that is reads 45 PSI while operating.
Whp = 800 gpm X a + 116 ft) /3960 = 800 gpm X  /3960 = 800 gpm X 220 ft /3960 Whp = 44.4
 a Lift and pressure are components of the total head that the pump is working against.
To convert PSI to feet of head multiply PSI by 2.31.
If the power unit for this pumping plant is consuming 4.6 gallons of diesel per hour, what is the performance of this pumping plant?
The performance of the pumping plant is found by dividing the work output  by the units of energy consumed.
The performance of this pumping plant is therefore 44.4 whp / 4.6 gal/h = 9.625 whp-h / gallon of diesel.
The University of Nebraska has conducted hundreds of tests over the years on farmer-owned pumping plants.
Based on these field tests and on tests of engine efficiency in the laboratory, the University developed the Nebraska Pumping Plant Performance Criteria,.
The NPC states the brake horsepower output from the engine and drive unit  and the amount of useful work output one should expect from a pumping plant  per unit of energy consumed.
Table 1.
The Nebraska Pumping Plant Performance Criteria 
 Energy Source	hp-h a	whp-h b,c	Energy Units
 unit of energy	unit of energy
 Diesel	16.66	12.5	Gallon
 Gasoline	11.50	8.6	Gallon
 Propane	9.20	6.89	Gallon
 Natural Gase	82.20	61.7	mcf
 Electricity	1.18	0.885	kWh
 a hp-h  is the work accomplished by the power unit with drive losses considered.
This is the horsepower imparted to the lineshaft that drives the pump impellers.
b whp-h  is the work accomplished by the pumping plant.
C Based on 75% pump efficiency.
d Criteria for diesel formerly 10.94 revised in 1981to 12.5, e Assumes an energy content of 925 BTU/cubic foot.
f Assumes 88% electric motor efficiency.
Once the work output  is known, one can use the NPC to estimate the amount of energy a pumping plant should be using.
The pumping plant in Example 1 on the previous page had a work output of 44.4 Whp-h.
If this diesel powered pumping plant were operating at 100% of the NPC, it would consume 44.4 Whp-h / 12.5 Whp-h/gal = 3.55 gallons of diesel per hour.
Another application of the NPC is to give the pumping plant a performance rating.
Once the performance of a pumping plant is known, it can be divided by the NPC resulting in a ratio which when multiplied by 100% results in a performance rating.
A rating of 100% indicates that the pumping plant is operating at the expected performance level.
A rating below 100% indicates the pumping plant is using more energy for the work that it is doing than the criteria calls for.
For example, a pumping plant operating at 70% of the NPC is only producing 70% of the useful work it should for the energy it is consuming.
The pumping plant in Example 1 would have a performance rating of  X 100% = 77% of the NPC.
If a pumping plant's performance rating is less than 100% of the NPC.
There are two methods to estimate the amount of excess energy being consumed.
One method is to subtract the energy consumption at 100% of the NPC from the actual energy consumption.
For the pumping plant in Example 1 the excess energy consumption is 4.6 gal/h  3.55 gal/h = 1.05 gal/h excess energy consumption.
The second method for finding the excess energy consumption is to subtract the performance rating of the pumping plant from 100% divide by 100% to convert to a decimal and multiply the difference by the actual fuel consumption.
For the pumping plant in Example 1, the performance rating was 77% of the NPC.
100% 77% = 23%.
23% / 100% = 0.23.
0.23 X 4.6 gal/h = 1.06 gal/h excess energy consumed.
Nebraska conducted a statewide pumping plant efficiency study in 1980-81.
In this study, they tested 180 farmer-owned pumping plants.
As one might expect, the performance ratings of the pumping plants varied considerably.
Some pumping plants were found to be very efficient.
In fact, 15% actually exceeded the NPC.
The fact that some pumping plants exceeded the criteria indicates the criteria is a reasonable target for all pumping plants.
The 85% of the pumping plants tested in the study which fell short of the criteria were using more energy per unit of work output  than the criteria calls for.
A few were found to be consuming over twice the amount of energy than was called for by the NPC.
When the performance ratings of all pumping plants tested were tallied, the average pumping plant in the study was found to be operating at only 77% of the NPC Stated differently, the average pumping plant was using  times as much energy as expected.
These test results compare with average ratings of 76% and 77.8% found in two earlier Nebraska studies and 78% found by a consulting firm in Kansas in the late 1970s.
When the efficiency of a pumping plant is not what it should be, the problem can either be in the power unit or in the pump or both.
Internal combustion power units on irrigation pumps can have the same problems as those in cars and trucks.
Many had improperly adjusted air/fuel mixtures or spark timing.
When indicated, the technicians performed adjustments to the air/fuel mixture and spark timing on spark ignition engines.
No adjustments were attempted on diesel engines and none are possible on electric motors.
The decision of whether to make pump adjustments was based on the an examination of how closely the output of the pump matched the manufacturer's
 pump curve.
If the pump was operating on the curve, no adjustment was necessary.
When tests were run on wells that were being over-pumped , pump adjustments were made when the rotational speed of the pump could be reduced  but not made if the speed could not be reduced.
Following the initial pumping plant tests, 57% were determined to potentially benefit from adjustments that could be made in the field.
Pumping plants that received adjustments were then retested.
Adjustments either to the engine or pump or both resulted in 14% average savings in energy costs compared to the initial test results on those units receiving adjustments.
Aside from the direct savings resulting from in-field adjustments, technicians were able to calculate the feasibility of making repairs beyond the field adjustments.
On some pumping plants, major repairs or even replacement of the pump could be paid for in only a few years using projected savings in energy costs.
What Causes Poor Pump Performance?
The three main causes for poor pump performance are:  pump designs that are poorly matched to the job they are currently doing ,  pumps that had worn impeller vanes and/or internal seals as a result of pumping sand,  impellers that were not properly adjusted within the pump bowls.
There are many pump manufacturers and each manufacturer can have dozens of pump designs in their catalog.
At a given rotational speed, each impeller design operates on unique head versus capacity curve.
In all cases, the greater the head  the pump is working 1760 RPM 65 against, the lower the capacity 70 70 75 78.
60 80 78
 As can be seen by examining a typical head/capacity curve in Figure 1, the pump's efficiency changes, depending on the operating conditions.
Each pump design will have a best efficiency point at a certain head/capacity condition,
 Figure 1.
Typical head/capacity curve for a vertical turbine irrigation pump.
with lower efficiencies on either side of the best efficiency point.
This pump achieves a best efficiency of 80% at 55 feet of head/stage and about 800 gpm at 1760 rpm.
The job of the pump installer is to select an impeller design that will operate efficiently when pumping the volume of water required for the application and while producing the total head required using some multiple number of stages.
Because no two irrigation systems or situations are exactly alike, fuel costs are hard to compare between different irrigation systems.
Therefore most irrigators did not know, prior to the pumping plant test, whether a pumping plant was using too much energy for the conditions under which it was operating, even those that were using 50% more energy than the NPC in many cases.
Conduct a Short Term Pumping Plant Test
 If there isn't a water meter installed on the system, a short-term pumping plant test can be run using one of a variety of devices to measure the flow rate.
The pumping water level, system pressure measured at the pump discharge, and the rate of energy consumption must also be measured.
Contact a reputable well driller and ask if they are equipped to run a short term pumping plant efficiency test.
Estimate Long-Term Pumping Plant Performance and Potential Energy Savings From Records
 If a water meter is installed on the system and if the operator has records of total water volume pumped and fuel consumed over a period of time  and if he/she has a measurement of the pumping water level and system pressure during the same time period, the performance rating of the pumping plant can be estimated.
If the performance rating is below 100% of the NPC, the potential savings from adjustment or repair can be calculated.
The information required to estimate long term performance includes: total volume pumped , the lift , pressure at the pump discharge head  and energy consumed over the period corresponding to the water meter readings.
Note: When the pressure gauge is not located at the discharge head, the elevation difference between the discharge head and the gauge must be added to the lift.
1.
Whp-h = total volume pumped  X total head  / 8.75
 2.
Performance = whp-h  / fuel used for the test period
 3.
Performance Rating =  / NPC) X 100%
 4.
Potential fuel savings =  / 100%) X fuel used for the test period
 Example: Using records to estimate long term pumping plant performance
 Test period = entire irrigation season
 System = Center Pivot Sprinkler and a diesel powered pump.
Pumping water level = 140 feet
 Pressure at the discharge head = 40 psi
 Ac-in of water pumped  = 1,500 ac-in 
 Total fuel used for test period = 4,139 gallons of diesel
 1.
whp-h = acre-inches pumped X total head  / 8.75
 = 1,500 X ) / 8.75
 = 1,500 X  / 8.75
 = 1,500 X  / 8.75
 2.
Performance = whp-h  / fuel used for the test period
 = 39,840 whp-h / 4,139 gallons
 = 9.625 whp-h / gallon
 3.
Performance Rating = Performance  / NPC X 100%
 =  X 100% = 77.0%
 4.
Potential fuel savings =  / 100%) X fuel used
 =  /100%) X 4, ,139 gallons of diesel
 = 0.23 X 4, 139 gallons
 At $1.00 / gallon for diesel, the potential energy savings resulting from bringing this pumping plant up to the NPC would be $952 per year.
If repairs were financed at 7% interest with annual payments, one could borrow $5, 125 for repairs and pay the loan off in seven years using annual savings in energy costs.
If the water meter totalizer registers in gallons, divide gallons by 27,154.
If the water meter totalizer registers in acre-feet, multiply ac-ft by 12.
If the water meter totalizer registers in cubic feet, divide cubic feet by 3,630.
For winter wheat in the boot/heading crop growth stage the estimated water use during the previous week of May 29 June 4, 2023 is 1.31 inches and the estimated water use during the week of June 5-11, 2023 is 1.95 inches.
For winter wheat in the soft dough crop growth stage the estimated water use during the previous week of May 29 June 4, 2023 is 1.19 inches.
WATER USE OF OILSEED CROPS
 Water use of a crop, with adequate available soil water supply, is primarily affected by its canopy and weather conditions.
These effects are represented by seasonal crop coefficients and the potential evaporative demand  of the atmosphere.
The crop coefficient indicates the fraction of potential ET which the crop is expected to utilize on a given day.
The crop coefficient value typically changes with crop stage.
Crop water productivity  refers to the amount of biomass or economic yield produced with a given amount of water use.
This article will present oilseed crop water use and crop water productivity field results from the U.S.
central High Plains.
Also, we review findings of environmental and management factors which can improve the water productivity of oilseed crops in this region.
The primary oilseed crops considered here are canola , soybean and sunflower.
Limited information is available for other spring oilseed crops  and summer oilseed crops.
In the U.S.
central High Plains, winter canola is typically planted in mid-August, flowering in mid-May and matures in early July ; spring canola can be planted early March, flowering in late-May and maturing in mid-July.
Figure 1 shows expected water use and crop productivity for spring canola.
Soybean can be planted in
 Figure 1.
Expected oilseed yields of spring canola are presented, in relation to expected crop water use  in this crop water production function.
Figure 2.
Expected oilseed yields and crop water use of soybean are derived from Colby, KS and Nebraska trials.
early May, flowering in mid-July for late-September harvest.
Sunflower is planted in mid-June to avoid pests, flowering in mid-August for harvest in late-September or early October.
Double-cropped soybean or sunflower can be planted after wheat harvest in early-July with flowering in late August and early October maturity.
Figures 2 and 3 show expected crop productivity and water use for these summer oilseed crops.
These spring and summer oilseed crops provide opportunities to shift irrigation applications among fields throughout the growing season.
Aiken and Lamm  discussed crop development stages and yield sensitivities to water deficits for these crops.
Figure 3.
Expected oilseed yields and crop water use of sunflower are derived from Colby, KS trials.
Oilseed yield is expected to increase with water use, up to a maximum yield potential.
The oilseed yield-water use relationships  show that a certain amount of water use  is required before oilseed yield is expected.
This apparent 'yield threshold'  indicates the amount of water use required before the first unit of yield is obtained.
The magnitude of this yield threshold can vary, to some extent, depending on early season soil water evaporation, prevailing humidity conditions and water used in vegetative growth.
The rate of
 yield increase, relative to increased water use , represents a measure of water productivity.
This factor is affected by inherent crop productivity, growing conditions  and harvest index.
These water productivity functions have been developed from experimental data.
The similarity in predicted yield responses to water use indicates applicability throughout the region.
A comparison of water productivity functions  for spring canola, soybean and sunflower  indicates the apparent yield threshold is least for sunflower, but largest for soybean.
In contrast, the marginal water productivity  is largest for soybean and least for sunflower; water productivity for spring canola is intermediate.
The inherent productivity of corn exceeds that of oilseed crops.
Suyker and Verma  reported that corn had 50% greater assimilation, 100% greater biomass productivity than soybean.
Figure 4 indicates that relative corn productivity can exceed this rate.
This difference is primarily due to the greater inherent
 Figure 4.
Crop water production functions for spring canola, soybean, sunflower and corn.
The crop water production for corn was taken from Stone ; those for oilseeds are presented in Figures 1-3.
productivity of warm-season grasses as well as the larger energy content of oilseeds, which require greater use of assimilates.
However, when oilseed yields are converted to a glucose equivalent, the water productivity of sunflower  is similar to that of cool-season crops , which also rely on C3 physiology.
Further, the yield thresholds of oilseed crops appear to be less than that of corn; and the harvest price of oilseeds are typically greater than that of corn.
As a result oilseeds may provide greater economic returns to water use than other crops at intermediate levels of irrigation.
An upper limit to water productivity of oilseed crops is likely constrained by the characteristics of C3 physiology and the large assimilation requirements for oil or protein biosynthesis.
Crop water productivity may approach this upper limit when 1) irrigation is delayed  when available soil water is sufficient for vigorous canopy expansion to intercept radiation and increase the crop transpiration fraction of ET; 2) harvest index approaches the maximum potential; and 3) growing conditions are optimal, with minimal pest damage.
IMPROVING CROP WATER PRODUCTIVITY
 Delaying initial irrigation can reduce evaporation from the soil surface prior to canopy closure  and increase the crop transpiration fraction of ET.
Specht et al.
reported soybean yields equivalent to scheduled irrigation when irrigation was delayed to flowering or mid-pod stages.
A similar response was reported by Lamm  with greater or equal soybean yields occurring with reduced irrigation during the vegetative period.
However, maintaining sufficient soil moisture for vigorous canopy formation may require irrigation prior to canopy closure.
Rapid canopy formation is vital to productivity as conversion of sunlight into biomass requires light interception by a healthy crop canopy.
Soybean and sunflower crops appear to differ in response to soil water deficits.
Soybean exhibited tolerance of soil drying by maintaining non-stress photosynthetic rates when available soil water was 47% of full water-holding capacity.
Also, soybean reduced crop transpiration by 67% under these deficit conditions.
In contrast, sunflower maintained crop water use near non-stress rates when available soil water was 40% of water-holding
 1 Plants with C4 physiology characteristically have greater O-fixing efficiency than plants with C3 physiology--due to Kranz anatomy and PEP carboxylase which permit sequestration of the Rubisco enzyme in bundle sheath cells where O2 concentrations are typically maintained at less than 2%.
2 The fraction of a sugar molecule which results in oil  or protein  is substantially less than that for starch ; see Tanner and Sinclair , p.
13.
capacity.
Also, sunflower reduced leaf expansion rates when available soil water was 60% of full capacity, indicating sunflower producitivity declines under water deficits while water use continues at rates near the expected maximum.
These results indicate a potential advantage to soybean-maintaining productivity while reducing transpiration under vegetative water deficits.
Lamm  demonstrated increased water productivity for soybean by reducing irrigation during vegetative development.
Spring oilseed crops such as spring canola avoid evaporative losses, as crop canopy is established under cool conditions with modest evaporative demand.
Water productivity can be increased by minimizing evaporative losses from soil by delaying initial irrigation, seeking rapid canopy closure, or planting a early spring oilseed which forms canopy under conditions of low evaporative demand.
Increasing harvest index  can improve crop water productivity.
Establishing yield potential involves components of yield.
Vega et al.
showed that seeds per plant increased with plant growth rate during seed set for soybean and sunflower.
The indeterminate growth of soybean permitted branching and continued flowering, for continued increase in seeds per plant for plants with large growth rates.
In contrast, the rate of seed set for sunflower was smaller at the greatest growth rates, compared to rate of seed set at intermediate growth rates due to limits in the potential number of seeds per head.
It follows that yield formation in sunflower is more sensitive to sub-optimal populations than indeterminant crops such as soybean.
Likewise, the indeterminant spring oilseed crops, such as canola, should be able to compensate for low population with increased branching and flowering.
Maintaining vigorous growth during floral development and seed set is critical for all grain crops, but can depend on weather conditions as well as crop management.
Grassini et al.,  found that harvest index in sunflower was reduced under cloudy or hot conditions  during the flowering period.
Andrade  reported that soybean yield formation was most sensitive to water deficits during seed fill, while sunflower yield was sensitive to water deficits during flowering and seed fill stages; canola exhibits yield sensitivity during flowering and seed fill.
Increased harvest index can be favored by planting optimal populations, selecting appropriate planting dates, varieties or hybrids, and avoiding water deficits for vigorous growth during floral development and seed fill.
Genetic gain in crop water productivity may result from restricted transpiration, crop tolerance of soil water deficits and increased harvest index.
Hufstetler et al.,  compared adapted soybean lines with non-adapted accessions; adapted lines had greater crop water productivity and lower transpiration rates at night than accessions.
Lines also differed in sensitivity of transpiration to soil water deficit thresholds and in recovery upon re-wetting.
Sinclair et al.
screened 3,000 soybean lines and identified eight with substantial tolerance of N2 fixation to soil drying.
This trait could enhance the growth response of soybean to a delayed irrigation strategy.
Developing varietals and hybrids which maintain crop productivity and yield formation under water deficits and environmental stress can increase crop water productivity.
Seasonal crop growth, in relation to crop water use, is known as a crop water productivity function; typically, these consist of a yield threshold  and a yield response.
Field studies in the U.S.
central High Plains indicate sunflower has least yield threshold as well as least yield response; soybean has greatest yield threshold as well as greatest yield response.
An upper limit to oilseed crop water productivity is primarily set by characteristics of the C3 physiology, which governs CO2 fixation by oilseed crops, and the large energy requirements for oil and protein biosynthesis.
An adaptive management strategy can help growers achieve the maximum crop water productivity expected for oilseed crops.
Components of this strategy include selecting crops and managing vegetative water supply to minimize the evaporative component of ET during vegetative growth, selecting seeding rates, planting dates and water management to ensure vigorous growth during flowering and seed-fill growth stages, and developing varieties and hybrids which tolerate water deficits to maximize harvest index.
Drip irrigation has become standard for plasticulture vegetable and strawberry production.
However, when drip system leaks or plugs, crops can be negatively impacted.
Drip system leaks can be man-made or caused by insects or by wildlife.
Drip irrigation companies have good quality controls; however, sometimes defects occur in manufacturing leading to drip tape with perforations, unwanted holes, or splits, especially along the seam.
Drip tape abrasion during laying can cause holes along the seam.
Another common cause of leaks is from too high of water pressure.
This will cause blow outs and is most common where pressure regulators are not used, and operators are manually adjusting line pressure.
Another common cause of leaks is when stakes are being placed for tomatoes or other crops if they are driven through the tape.
Lay tape so that it is to the side of where stakes are to be placed.
Similarly, planting spikes, dibbers, or tools can pierce drip tape as can wire marking flags and marking stakes.
Poor connections to headers can lead to leaks, as can driving over or stepping on connectors.
Animals seeking water during dry periods can damage drip tape.
Soil insects can be a major cause of leaks on lighter weight.
Crickets, especially mole crickets will shred along the edges where the dip tape was folded.
White grubs cause similar damage.
Wireworms will chew a round hole in drip tape.
Some weevil larvae can also chew through drip tape.
Larger ants will chew around emitters.
Rodents such as voles can chew through drip tape as can other animals such as rabbits, shrews, moles, and squirrels.
Birds normally will not damage buried drip tape but will peck at emitters where drip tape is exposed at the ends of rows.
Deer may damage drip tapes with hooves as can domestic livestock.
Damage to drip tape is likely from insect chewing.
Damage to drip tape is likely from insect chewing.
Drip emitters can become plugged with fine particles, mineral deposits, or biofilms.
When emitters become clogged, the plants nearest the clogs will receive less water and have more water stress and grow less or be stunted.
This is most severe in higher density planted crops, such as peppers.
A common cause of plugged emitters is water containing high levels of dissolved iron.
This can cause a proliferation of iron utilizing bacteria.
These bacteria form heavy biofilms on the inside of the drip tube.
They also oxidize the iron in the water  and leave behind iron precipitates that can plug emitters.
Chlorination of drip lines is needed to control iron bacteria.
Periodic treatment before clogging develops can keep the system functioning efficiently.
The frequency of treatment depends on the quality of the water source.
Generally, two or three treatments per season is adequate.
Irrigation water containing high concentrations of iron  can also result in clogging problems due to types of bacteria that feed on dissolved  iron.
The bacteria secrete a slime called ochre that may combine with other solid particles in the trickle tubing and plug emitters.
The precipitated  form of iron, known commonly as rust, can also physically clog emitters.
Treating water containing iron with chlorine will oxidize the dissolved iron, causing the element to precipitate so that it can be filtered and removed from the system.
Chlorine treatment should take place upstream of filters to remove the precipitated iron and microorganisms from the system.
Take care when adding chlorine to trickle irrigation systems, however, since concentration at or above 30 ppm can be toxic to growing plants.
Options for treating water with high iron include the following:
 Inject liquid sodium hypochlorite continuously at a rate of 1 ppm for each 1 ppm of iron in irrigation water.
In most cases, 3 to 5 ppm is sufficient.
Inject liquid sodium hypochlorite continuously at a rate of 5 to 10 ppm where the biological load is high or
 Inject 10 to 20 ppm during the last 30 minutes of each irrigation cycle or
 Inject 50 ppm during the last 30 minutes of irrigation cycles one to two times each month or
 Super chlorinate  once per month for the length of time required to fill the entire system with this solution and shut down the system.
After 24 hours, open the laterals and flush the lines.
Irrigation or water treatment companies can also install treatment systems to remove iron from irrigation water.
This requires a water test to determine the form of iron and the proper system for its removal.
Another common problem in some aquifers is well water with high levels of calcium and magnesium.
In high water pH conditions, these can precipitate out as calcium or magnesium carbonates that will clog emitters.
If you look inside the drip tubing, you will see a white or chalky film.
In addition, if soluble phosphorus fertilizers are put into water with high levels of dissolved calcium or magnesium salts, they can precipitate out as calcium or magnesium phosphates, also plugging emitters.
Acidification of water can reduce or eliminate this problem.
Also, avoid running phosphorus through the drip if you have hard water.
Inadequate filtering is another possible cause of plugged emitters.
While this is most common when using surface water from ponds, ditches, or streams.
It can also occur in wells that have fine particles in the water.
The water sample on the left has excess iron that can plug drip systems.
However, clear water may also have dissolved iron.
iron that is not visible to the eye can be present as ferrous bicarbonate.
The water sample on the left has excess iron that can plug drip systems.
However, clear water may also have dissolved iron.
iron that is not visible to the eye can be present as ferrous bicarbonate.
The top foot will go above field capacity  after every irrigation or heavy rain.
However, if the second foot gets above 30 cb, it would indicate that over-irrigation is occurring.
The data in the chart indicated that the field was this dry on a given day and not how many days the soil was drier than 70 cb.
The 70 cb level is equal to about 70% of plant available water  and stress should not start until below 50% of PAW during the summer and 40% in late August and September.
Soil types such as those with high sand or clay content would require different levels other than 30 and 70 cb.
However, VRI is not likely to reduce the consumptive use of water.
Producers who are considering whether to invest in VRI technology should carefully consider the potential costs and benefits to determine whether VRI is a good fit for their situation.
Types of VRI equipment systems, prescriptions , and potential uses are described below.
Colorado State University Extension
 Irrigation Pumping Plant Efficiency
 Fact Sheet No.
4.712
 Rising energy costs have increased the cost of pumping to the point that many farmers are finding irrigation to be unprofitable or only marginally profitable.
Fortunately, however, pumping costs are an item that farmers have some degree of control.
Pumping costs often are higher than they need be for two reasons: 1.) more water is pumped than is necessary, and/or, 2.) the pumping plant operates inefficiently.
This fact sheet considers only the second problem; inefficient pumps.
Common Causes and Remedies
 Field testing programs in Colorado, Wyoming, Nebraska, Texas, Louisiana and other states have shown that overall pumping plant or 'wire-to-wire' efficiencies for electrically driven pumps average 45 to 55 percent, as compared to a realistically achievable efficiency of 72 to 77 percent.
This implies that around 25 percent of the electrical energy used for pumping is wasted due to poor pumping plant efficiencies alone.
Therefore, farmers can reduce energy costs by raising pumping plant efficiencies from present average levels to potential efficiencies.
Farmers are advised that pumping plants should attain at least 65 percent efficiency and every new pumping plant should be tested to determine the pumping plant overall efficiency.
There are many reasons for poor pumping plant efficiency.
Some of the more common causes of unsatisfactory performance and their remedies are as follows:
 1.
Impellers that are out of adjustment are the easiest and least expensive problem to correct.
Both pumping rates and efficiency are reduced because energy is used to pump water that is recirculated around the impellers instead of being pumped into the irrigation system.
Impeller adjustment is especially critical with semi-open impeller pumps.
Impellers may be out of adjustment because of improper initial adjustment or because of wear.
To avoid pump damage, only experienced pump people should attempt to make impeller adjustments.
Field adjustments include: a) for semi-open impellers, all impellers in the bowl assembly must be running in close proximity  to the next lower bowl.
Thus, careful adjustment in the field is required.
Shaft stretch determines the final position of the impellers.
Also, it directly varies with discharge head.
Therefore, it has to be set to a proper specification to perform well at a given discharge head.
Multistage units may require that the impellers be trimmed  to obtain proper fitting and clearance in the assembly bowl.
For enclosed impellers, with a principal seal that is parallel to the centerline of the shaft, a close axial adjustment is not necessary.
Therefore, this type of impeller is suited for operation under variable head conditions.
Capacity  and horsepower requirements can be controlled by raising the impeller until the skirts are out of the wear rings.
2.
Pump bowls designed for a higher pumping rate than the well can supply is one of the most common reasons for poor pumping plant efficiency.
Overestimating well yield often results from poor testing of the well after drilling.
If well testing was inadequate, the yield of the well may have been less
 Most irrigation pumping plants have excessive operating costs because they are often in need of repair, poorly matched to the pumping load, or incorrectly plumbed using more power or fuel than they should.
Pumping plant performance can be evaluated from field tests to determine if changes are needed.
Some problems can be corrected with simple adjustments while others require expensive repairs.
*J.
L.
Chvez, Colorado State University irrigation specialist and assistant professor, civil and environmental engineering department; D.
Reich, Colorado State University Extension water resource specialist, Western Region, agricultural and natural resource economics.
Original manuscript by J.
C.
Loftis, Colorado State University professor, civil and environmental engineering; and D.L.
Miles, Extension irrigation engineer.
9/2011
 than anticipated.
In other cases, the pump supplier recommended oversize pump bowls in order to require fewer stages, thereby reducing initial cost.
Furthermore, declining water tables in some areas have reduced well yields.
In this situation, a pump may begin to cavitate  because it is being is forced to operate at a lower flow rate and higher lift than that for which it was designed.
If for any of these reasons the pump capacity does not fit the well characteristics, a high pumping plant efficiency can be achieved only by replacing the bowls with new  bowls that meet the well requirements.
3.
Damaged impellers also will result in poor performance.
Three common causes of impeller damage are cavitation , sand pumping  and improper impeller adjustment.
Sometimes only the impellers need to be changed, but more often the permanent solution is to replace the entire bowl assembly.
If this is done, it is likely that a different model of pump bowls should be used to fit present well conditions.
4.
Incorrect power unit selection is another major cause of low efficiency.
This is much more important for engines than for electric motors.
While the efficiency of electric motors does not vary greatly with loading, it should be noted that over-loaded motors have shorter lives, are less dependable and are more expensive to maintain.
On the other hand, because of graduated energy costs, underloaded motors often increase the cost per kilowatt of power used.
Incorrect engine selection is a major cause of low efficiencies among the natural gas pumping plants.
Many are overloaded.
Automotive-type V-8 engines often are used for applications where heavy-duty industrial engines should be used.
Operating speeds of the smaller engines are increased SO that they will produce adequate power.
As a result, they wear out rapidly and require much more fuel.
5.
Failure to perform required maintenance, including tune-ups, is often a cause of low efficiency in engine-
 driven pumping plants.
Electric motors, on the other hand, usually operate efficiently.
In the case of semi-open impellers, close adjustment is necessary for proper operation.
Thus, if variation in required discharge head occurs then the pump could be damaged.
The higher thrust requirement may affect the lift of the thrust bearings, therefore fast bearing wearing can be expected.
Monitoring the pumping unit pressure head and flow discharge is critical to assure proper operation and a longer unit life span.
Enclosed impellers, on the other hand, will have increased bearing life with up to 30 percent less thrust.
The lower thrust allows using smaller shafting, which affects the cost of the initial installation and on maintenance.
6.
Differences in operating conditions.
Finally, a change in operating conditions from those for which a pumping plant was designed will result in a drop in efficiency.
Three common situations that result in increased pumping lifts and total discharge head  or pressures are a drop in water table elevation, converting from open discharge to a pipeline, and changing from surface irrigation to sprinkler/ trickle  irrigation.
On the other hand, a reduction in operating pressure results when center pivot sprinklers are converted from high pressure to low pressure in an attempt to save energy.
Usually the pump will operate less efficiently under the new lower pressure conditions than it did under high pressure.
As a result, anticipated savings in energy costs may not be realized.
7.
Poor plumbing, horizontal axis/centrifugal pumps have a range window of pressure and flow rate conditions for the inlet and outlet of the pump for optimum efficiency.
Some pumps require inlets constantly flooded, others need sufficient back pressure on the outlet.
If a pump is not operating in optimum conditions water hammer and cavitation are common symptoms along with
 frequent replacement of impellers and seals.
Consult with your pump vendor on pump suitability and always examine installation instructions carefully before purchasing accompanying pipework.
Since some power suppliers offer field evaluation of electrical pumping plant performance at very reasonable cost, many farmers can easily determine whether or not their pumps are operating properly.
Internal combustion engine driven plants are more difficult to test since both the engine and the pump should be evaluated.
A few private consultants and pump suppliers are equipped to perform this service.
A field pump evaluation involves measuring several operating characteristics of the pump.
These include:
 depth to water before pumping, ,
 depth to water during pumping ,
 Net Positive Suction Head , for horizontal axis/centrifugal pumps, is the suction head the pump has available.
This will determine how much head deficit the suction side of the pump can overcome.
Make sure you account for friction losses in pipe, valves and elbows.
pump total dynamic discharge head or pressure ,
 Impellers that are out of adjustment are the easiest and least expensive problem to correct.
To avoid pump damage, only experienced pump people should attempt to make impeller adjustments.
Incorrect power unit selection is another major cause of low efficiency.
This is much more important for engines than for electric motors.
Consult with your pump vendor on pump suitability and always examine installation instructions carefully before purchasing accompanying pipework.
pump flow rate, and
 rate of electrical energy or fuel consumption.
From these measurements, both the water horsepower, or rate of useful work done by the pump, and input horsepower equivalent, or rate of energy used by the motor or engine, are calculated.
Overall pumping plant efficiency is the water horsepower divided by the input horsepower equivalent 
 Knowing the pumping  rate, total pumping  head, and pump efficiency, one can compute the input power required using Equation 1 below.
Published efficiency curves for turbine pumps do not include such losses as lineshaft bearing and gearhead friction.
The manufacturer's reported efficiency for these pumps is for a specific number of stages.
It is necessary to adjust the reported efficiency upward or downward, depending on the number of stages.
Generally, there is only one peak pump efficiency, which occurs at a specific pumping rate.
However, most pumps do not operate at the peak efficiency, which is around 87 percent.
Depending on variations on the TDH and flow discharge the pump efficiency may be lower than the peak.
Pump efficiency Equation 1) is pump the ratio of the output work  the pump exerts to the water in relation to the required power  of the driving unit, which is also called break power , or break horsepower.
WP = water power, in units of horsepower , and
 Q = pumping rate, gallons per minute 
 TDH = total dynamic head 
 BP = motor/engine break horsepower 
 Note: 1 horsepower  = 0.746 kW if one wishes to express power in kW units instead.
If units are in kW to obtain WP or BP in hp units multiply the number of kW by 1.341.
The overall pumping plant efficiency  is the product of the pump efficiency as a decimal pump, number) and the motor efficiency  multiplied by 100.
For electrical motors, the typical E motor range is between 80 to 90 percent.
E pplant = E pump X E motor = / P  where: P = input power to the motor  The E pplant or wire-to-water efficiency maximum value range is 72 to 77 percent, with a minimum acceptable value of 65 percent.
If the pump is operating below an E pplant of 65 percent then provisions must be made to improve performance to save energy and attain adequate designed hydraulic TDH and Q levels.
Cost VS.
Savings From Repair or Replacement
 Once it has been found that a pump is not performing up to par, the next step is to consult a reputable pump supplier to determine the cost of repair or replacement.
If it is necessary to pull the pump, these costs will be substantial.
How does one decide whether pump repair or replacement will pay off?
There are certain conditions under which pump bowls will almost certainly need to be replaced.
The potential well yield is adequate, but the pump will not supply the required flow rate at the required pressure.
The water table has declined dramatically; this was not anticipated in the original pump selection.
A major change in the irrigation system has occurred, either from surface irrigation to sprinkler irrigation or vice versa, or from high pressure to low pressure sprinklers.
In other cases, the decision of whether to spend money on a pump is not SO clear.
Compare the potential savings from increased efficiency to the cost of pump improvements.
The results of a pumping plant efficiency test as described earlier can be used to make this comparison.
Tables 1 and 2 simplify the necessary calculations for electrically driven pumps.
For the pump in the preceding example, the bowls could be replaced at a cost of $15,000 to provide an improved efficiency level of 65 percent.
Is this investment worthwhile if the farmer must borrow the money at 8 percent interest?
E = WP/BP = pump  / BP  where:
 From Table 2, the capital recovery factor for 8 percent interest and a 15-year economic life is.1168.
The annual cost of the improvement is therefore  X  = $1,752/year.
Since the potential savings found earlier  exceeds the cost of improvement, the investment is probably justified.
If this analysis had indicated that potential savings were significant, but
 Table 1: Potential energy savings from pump improvement  assuming 65 percent efficiency after improvement.
Present pump efficiency 
 H	25	30	35	40	45	50	55	60
 50	10.5	7.7	5.6	4.1	2.9	2.0	1.2	0.5
 100	21.0	15.3	11.2	8.2	5.8	3.9	2.4	1.1
 150	31.5	23.0	16.9	12.3	8.7	5.9	3.6	1.6
 200	42.0	30.6	22,5	16.4	11.7	7.8	4.8	2.2
 250	52.5	38.3	28.1	20.5	14.6	9.8	6.0	2.7
 300	63.0	45.9	33.7	24.6	17.5	11.8	7.2	3.3
 350	73.5	53.6	39.4	28.7	20.4	13.8	8.4	3.8
 400	84.0	61.2	45.0	32.8	23.3	15.7	9.5	4.4
 450	94.5	68.9	50.6	36.9	26.2	17.7	10.7	4.9
 500	105.0	76.6	56.2	41.0	29.2	19.7	11.9	5.5
 TDH = Total pumping head or total dynamic head.
kWh/ac-in = kilo Watt hour per acre-inch.
*To convert to metrics use the following conversion: 1 foot = 0.3048 meter.
somewhat less than the annual cost of the improvement, it would probably be advisable to have the pump tested again in a year or two.
Pump wear and/or water table decline could easily result in the change being justified at that time.
One must remember that this analysis is based on an achievable E pplant efficiency level of 65 percent after pump improvement.
Higher E efficiency pplant levels are possible , thus there could be potential for higher energy savings.
However, if the 65 percent level is not realized, neither will the anticipated savings in energy costs.
The farmer would be well advised to obtain a written contract from the pump supplier guaranteeing a certain level of pump performance
 to be achieved by the proposed pump improvements.
Static water levelThe vertical distance  from the center line of the discharge to the water level when there is no pumping occurring.
Static pumping level or dynamic water level.
The vertical distance  from the center line of the discharge to the water level when the pump is working.
Drawdown.
The difference  between the static pumping level and the static level.
Pumping lift.
The vertical distance  from the water level to the center of the discharge when the pump is running.
Setting.
The distance from the column pipe connection at the discharge head to the column pipe connection at the bowl assembly.
Submergence.
The distance  from the pumping level to the column pipe connection at the bowl assembly.
Elevation.
The vertical distance from the center line of the discharge elbow to the center line of the discharge pipe.
Friction head loss.
The head  needed to overcome pressure losses due to friction in the pipe and fittings.
Total dynamic discharge.
The head which must be developed by the pump to overcome friction losses and elevation.
Total dynamic head.
The sum of the pumping lift and the total discharge head.
Capacity.
The rate of flow of water measured per unit of time.
Selection and Management of Efficient Low Volume Irrigation System
 Prepared by: Robert Evans, Extension Agricultural Engineering Specialist R.E.
Sneed, Extension Agricultural Engineering Specialist
 Published by: North Carolina Cooperative Extension Service Publication Number: EBAE-91-153 Last Electronic Revision: June 1996 
 Rainfall is the principle source of water for North Carolina crops.
However, many farmers are turning to irrigation to supplement precipitation.
There are many types of irrigation systems.
But, most farmers have limited choices for their particular farm or field.
Some systems are inherently more water and energy efficient while others are designed to overcome limitations such as irregular field shapes, sloping land, or limited water supplies.
All of these factors should be considered before selecting a particular type of system.
Low volume irrigation systems are normally used for fruits, vegetables, container nursery plants and in the landscape.
For all these uses, growers are interested in highly controlled water management systems.
Selection and management considerations for low volume irrigation systems are discussed in this article.
Selection and management criteria for other types of irrigation systems are presented in articles EBAE 91-150: SelfPropelled Gun Traveler Systems; EBAE 91-151: Center Pivot and Linear Move Systems; and EBAE 91-152: Hand-move, Solid-set and Permanent Systems.
Low volume irrigation systems were first introduced in the early 1960's.
At that time, they were called trickle, drip or daily flow irrigation.
Early work on these systems was done mainly in Israel, but some credit a British scientist with the original idea.
In more recent years, micro-sprays, microspinners, spot spitters and other types of low volume sprinklers or spray systems have been introduced.
At present, the term low volume is used to describe all of those systems that apply a low volume of irrigation below, at, or just above the soil surface.
Low volume irrigation is probably the fastest growing type of irrigation.
It is being used in many countries, mainly for both tree and small fruits, vegetables, nursery crops, and in the landscape.
On a much more limited scale, it is being used to irrigate cotton, peanuts, tobacco, corn and grass.
Low volume systems have numerous advantages over other types of irrigation.
The major advantages are the ability to manage timing and placement of soil moisture and to use less total water to produce a crop.
It is also generally possible to produce greater yields of higher quality crops.
Other advantages include:
 better insect, disease, and weed control;
 fertigation and limited chemigation;
 the ability to carry on cultural operations while irrigating; and
 in some cases, reduced
 The main disadvantage is the requirement for very clean water.
The small orifice or emitter through which the water must pass can easily be clogged by soil particles, organic matter, minerals and sediment in the water and by algae growth.
Other disadvantages are the limited area covered by each application device, potential animal, insect, or mechanical damage, greater design and maintenance requirements, often higher initial investment and replacement cost, and the high level of management required.
The major components of a low volume irrigation system include:
 pump and power unit or gravity flow
 controls and monitoring equipment
 accessories, such as fertilizer or chemical injectors
 Figure 1 shows most of the components of a low volume system.
The type of pump selected is normally governed by the water source.
Straight centrifugal or self-priming centrifugal pumps are generally used on surface water sources.
However, submersible or turbine pumps, which are normally used in wells, can be used on surface water supplies.
Figure 1.
Schematic of the components of a low volume irrigation system.
Power sources include electric, internal combustion engine  and tractor PTO.
Electric power is required for submersible pumps.
The other types of pumps can be operated by any of the power sources.
If the system is to be automated, electric power is preferred.
High efficiency pumps should be selected whenever possible.
Filters and water distribution devices are discussed elsewhere in this paper.
The pipe distribution system includes main line, sub-mains, manifolds pipe and lateral lines.
The type of water distribution device  determine some of the system hardware.
The line source system includes the lateral line as an integral part of the emission device.
The tube is manufactured of polyethylene  plastic with a wall thickness of 4 to 25 mil.
Generally, at least 8 mil wall thickness is recommended.
If the tube is to be used for more than one season, a thicker wall is recommended.
Most of the line source systems use a 0.5 inch diameter lateral line.
The lateral line for point source systems is normally high carbon, low density PE pipe.
Wall thickness is normally 30 to 50 mil.
Tube inside diameter will vary from 0.375 to 1 inch.
The micro-sprinklers normally use a PE or polyvinyl chloride  plastic lateral line.
A PE micro-tube conveys water from the lateral line to the micro-sprinkler.
Sub mains or manifold can be layflat hose, PE pipe or PVC pipe.
Main line is normally PVC pipe, but layflat hose, PE pipe or metal pipe can be used.
Controls and monitoring equipment can simply be gate valves, check valves and pressure gages.
For larger, more complicated systems, many are equipped with automatic controllers, electric or hydraulic valves, water meters, soil moisture monitoring equipment, and back flow prevention.
Automatic controls and valves allow greater flexibility in operation of the system.
A water meter allows the user to determine how much water is being used.
Daily monitoring of the water meter will indicate when emitters or orifices are becoming clogged or when there is a significant leak in the system.
Soil moisture equipment gives information on the adequacy of irrigation.
Back flow prevention equipment protects water supplies from chemicals or fertilizers that might be backsiphoned into the water supply.
Fertilizer injectors allow the grower to add fertilizer on a regular basis.
This should lead to yield increases and prevent fertilizer from leaving the site, either as deep seepage or as surface runoff.
If chemicals are needed to adjust water quality, a chemical feed pump is needed.
Also limited chemigation  can be accomplished through the low volume system.
In the several decades since low volume irrigation was first introduced, there has been considerable improvement in the water distribution devices and a significant reduction in the number of potential suppliers.
Some companies produce a fairly complete line of devices, while others offer only selected types.
Water distribution devices can basically be classified as one of three types: 1) line source; 2) point source; and 3) low volume micro-sprays, microspinners, and spray stakes.
At least one manufacturer has a product that combines some of the features of line source and point source.
Most of the true line-source systems are used for row crops.
Orifice spacing can vary from 4 to 60 inches, but most are 4-, 8-, or 12inch.
Generally, these systems are designed to operate at line pressures of 4 to 10 psi.
Normally a cressure-compensating emitter or orifice is used.
This limits their use to essentially level topography.
Maximum row length is 200 to 600 feet depending on orifice spacing and design pressure.
The trend with these systems is away from laminar flow and to turbulent flow which does a better job of preventing orifice clogging.
Line-source systems are supplied by several manufacturers and product configuration and design varies, both in the type of orifice and the tube used.
Products supplied by various manufacturers do perform satisfactorily.
Some may be more acceptable than others.
Line sources systems will generally apply the daily water needs to a crop in two hours or less.
This allows a field or fields to be divided into several zones and still allow the entire area to be irrigated in one day.
Figure 2 is a schematic of a line source system for vegetable crops.
Figure 2.
Schematic of a line source irrigation system typically used with vegetable crops such as tomatoes.
Point-source systems consist of emitters that are manufactured into the lateral line, those installed in sections of lateral line, those that can be attached to the outside of the lateral line or those that are attached to the lateral line by a micro-tube.
The latter may be several feet from the lateral line.
Figure 3 is a schematic of a point source system for tree fruits.
To apply water needs for tree fruits with point source emitters may require 6 to 12 hours of operation per day.
It may be possible to divide an orchard into two or three zones and sequence through the zones each day.
Figure 3.
Schematic of a point source low-volume irrigation system typically used with nursery container and tree fruit crops.
Figure 4.
Discharge rate variation as influenced by emitter design-pressure versus non-pressure compensating.
Both turbulent and laminar flow emitters are available.
Also pressure compensating emitters and nonpressure compensating emitters are supplied.
Most non-pressure compensating emitters are designed to operate at approximately 15 psi.
The pressure compensating emitters will operate at 10 to 60 psi with approximately the same discharge rate.
Normal discharge rates are 0.5, 1.0 or 2.0 gallons per hour  for both pressure compensating and non-pressure compensating emitters.
A few manufacturers provide emitters with flow rates lower than 0.5 ggh.
Figure 4 shows the discharge  versus pressure from a nominal 1 gph emitter.
Note that discharge rate is more constant for the pressure compensating emitter than for the non-pressure compensating emitter.
Because of the more complex design, pressure compensating emitters have a higher initial cost.
There are also multi-outlet emitters, where up to six micro-tubes can be attached to irrigate areas around the emitter.
Most point-source systems are designed to irrigate tree, shrub and vine crops.
However, they can be used for row crops.
Micro-sprays, micro-spinners and spray stakes are small sprinklers, normally constructed of plastic.
They are designed mainly for trees, shrubs, and nursery irrigation.
They are designed to operate at 10 to 30 psi and have flow rates of 3 to 50 gallons per hour with coverage diameters of 2 to 50 feet.
The micro-sprays and microspinners are normally mounted on a small plastic riser with a micro-tube to convey water from the lateral line to the application device.
Figure 5 is a schematic of three different types of micro-sprays or microspinners.
Most of these devices provide part circle coverage.
A limited number are essentially full circle coverage except where the sprinkler arm support masks the spray nozzle.
Spray stakes, which are normally used to irrigate container plants, are placed directly into the growing media.
A micro-tube conveys water from the lateral line to the spray stake.
Figure 6 shows a typical placement for a half-circle spray stake in a container.
Figure 5.
Schematic of micro-spray, micro-spinner, and spot spitter.
Figure 6.
Schematic of spot spitter in a container.
Due to the tiny water passages of the emitter, extremely clean water is required for all low volume systems.
It is important to have a water analysis made prior to installing the filter system and to occasionally check the water to ascertain that quality has not changed.
As a rule, the poorer the water quality, the greater the amount of filtration required.
Both physical and chemical water quality needs to be examined.
Filtration may include filters to remove materials found in the water and possibly chemical adjustment of the water.
Filters are normally divided into primary filters and secondary filters.
It is generally accepted that a sand media filter is the best primary filter and is a necessity for surface water supplies.
Mechanical filters such as screen filters, sand separators and disc filters may also be used as primary filters for ground water supplies.
Minerals in ground water may require the addition of chemicals such as acids, chlorine and softeners to ensure satisfactory operation of the filters.
Screen filters, "and separators, disc filters, in-line Ystrainers and cartridge filters are generally considered to be secondary filters.
The primary filter is normally located next to the water source and the secondary filters are located nearer the point of delivery to the lateral lines.
Figure 7 shows schematics of some of the different types of filters.
Figure 7.
Schematic of several types of filters used for low volume irrigation.
Chemicals, such as acids, chlorine, softeners, etc.
are normally injected near the water source.
Injection can be continuous feed or intermittent, depending on water quality.
Individual chemicals or mixtures of chemicals may be injected.
Filters require cleaning  to remove contaminants.
If this is neglected, the filter becomes clogged and contaminants enter the drip system.
Pressure drop across the filter is used as a guide on the frequency of cleaning.
Generally, if the pressure drop exceeds 5 psi, the filter should be cleaned.
Pressure gages should be placed on either side of the filter to indicate when cleaning is needed based on pressure drop across the filter.
Sand media filters should be installed in tandem to allow filtered  water to be used for backwashing.
Water is forced back through the filter in the opposite direction to the filtering process to clean the filter and remove contaminants.
Screen filters and disc filters may be flushed, backwashed or physically cleaned.
Sand separators are normally flushed.
DESIGN OF LOW VOLUME SYSTEMS
 Because low volume systems use water application devices that cover a small area and the system is designed to apply a small volume of water at one time, it is critical to insure that the system has adequate capacity to meet maximum evapotranspiration  rates.
Crop to be irrigated, size of crop, soil type or growing medium, crop canopy factor and ET rate all need to be considered.
Once the daily water requirements have been determined, hardware can be selected.
Since most systems are low pressure, the designer must minimize friction loss in sub-mains and laterals to assure essentially constant pressure to each emitter or orifice.
Factors that affect friction loss are pipe size, type and length, number of outlets, and flow in the pipe.
Friction loss can be determined from formula, tables, or slide rules.
A competent designer will use all these tools to ensure a sound design.
Design rules for low volume systems are modified from those normally used for other types of irrigation systems.
This is especially true for those systems using non-pressure compensating emitters or orifices.
Since these systems operate at low pressure and it is desirable to have uniform discharge from each orifice, there can be little variation in pressure.
For example, a line source system that requires 8 psi at the orifice should have a maximum pressure differential in the field of 1.6 psi.
The pressure loss should be divided between the sub-main and/or header in the field and the laterals.
The pressure loss should be proportional as follows: not over 45 percent in the sub-main and/or header and not over 55 percent in the lateral.
For the system with orifice operating pressure of 8 psi, pressure drop in the sub-main and/or header should not exceed 0.72 psi.
Pressure drop in the lateral should not exceed 0.88 psi.
In practice, what the designer tries to accomplish is to have approximately 8 psi pressure at the head of each lateral.
At the end of the lateral, pressure should be no less than 7.12 psi.
In the header or sub-main supplying a group of laterals, pressure should not be greater than 8.72 psi.
If the field has elevation differences, it may be necessary to install pressure regulators on the main, sub-main, or header pipes.
If laterals have to be installed on a slope, the laterals should be run down slope rather than upslope.
This allows elevation change to counteract pipe friction loss.
The most efficient design is to zone field SO that a portion of the field is irrigated at one time.
Once that section or zone is irrigated, another zone is irrigated.
This allows the use of smaller pumps, power units, and main line.
For vegetable crops, the most efficient irrigation is to operate each zone for 10 to 20 minutes at one time and then switch to another zone.
To meet daily water needs, each zone might operate four to six times per day.
It is possible to utilize the same procedure for point-source emitters and micro-sprinklers or spray stakes.
Certainly the designer needs to consider ways to minimize system initial cost and yet have a design that will meet peak crop water needs.
SOURCE OF FLOW VARIATION
 There are several factors that can account for flow variation in low volume systems.
Emitter or orifice clogging due to inadequate filtration is probably the major problem.
Other causes are non-uniformity of the manufactured product, water temperature change and hydraulic variation.
Studies have shown that uniformity of water discharge can be greatly reduced when one to five percent of the emitters are clogged.
Manufacturing variation  can account for considerable variation in uniformity.
A low value of coefficient of manufacturing variation is desired.
As water temperature increases, viscosity decreases and water discharge can increase.
With uniform orifices or emitters and no friction loss in the lateral line, this can cause those emitters most distant from the header pipe to have a higher flow rate than the emitters closest to the header pipe.
Water temperature can increase due to the flow of the water through the pipe.
Sizes of main line pipe,
 header pipe and lateral line need to be considered in system design to insure that pressure loss due to friction does not adversely affect orifice discharge.
This is more important for non-pressure compensating orifices than for pressure compensating emitters.
It is equally important to consider the elevation changes on water pressure.
For each 2.31 feet of change, there is a 1 psi differential.
Low volume irrigation systems have the potential to be the most efficient systems available.
However, system design, use, and maintenance are key in determining the actual system efficiency.
In North Carolina, low volume irrigation is still in its infancy.
A number of systems are being used where components are not well matched.
Users are installing demonstration or trial systems to learn about low volume systems before they make a commitment to invest heavily in equipment.
Often pumps that are used were designed for another type of system or an inexpensive, low efficiency pump was purchased.
Insufficient filtration may result in partially or totally clogged emitters.
In areas where there is considerable elevation difference, high pump pressure may be required to provide adequate pressure at the highest elevation.
Pressure regulators are needed to reduce that pressure at lower elevations.
It may not be possible to overcome this problem, but it should be considered in the design.
Inadequate backwashing or flushing of filters can increase pressure and horsepower requirements.
Ignoring leaks, clogged or partially clogged emitters, orifices or spray nozzles, dirty filters and/or pump and power unit performance will lead to inefficiency.
Using main line, header pipe, or laterals that are too small will increase friction loss and lead to inefficiency and non-uniform water application.
Selecting an inefficient pump, a pump with too high pressure, or an improperly matched pump and power unit can increase pumping costs.
At times, using pressure compensating emitters rather than non-pressure compensating emitters with a couple of pressure reducing valves can reduce efficiency.
A low volume irrigation system is typically a low to medium pressure system that is designed to apply small volumes of water on a frequent basis.
The entire system needs to be designed as a unit.
Once it is installed, it should be used in the manner it was designed and should be properly maintained.
Daily maintenance will be required.
More management will be needed than for most other types of irrigation.
Some of the newer systems in use in North Carolina have high pumping efficiencies and high overall water application efficiencies.
Growers that are using these systems are benefiting financially with higher yields, more net profit, and doing a much better job of water management.
CornSoyWater provides irrigation recommendations in real time mode, based on a quantitative prediction of amount of available water in the soil root zone along with stage-related threshold for irrigation, and possible crop water stress.
Measuring Well Water Levels
 Groundwater is an important resource in Oregon.
As more people depend on groundwater, some water tables around the State are dropping, threatening their water supplies.
State law requires that groundwater be managed as a renewable resource, and that water tables do not drop permanently.
To assess the size of the groundwater resource and monitor the effects of development and drought, State law requires an aquifer test on every well with a water right.
Part of that test is to measure the depth of water in the well.
We'll discuss three methods of measuring water levels in this publication.
First, let's define our terms.
Aquifer.
A water-bearing geologic formation.
Column.
Pipe leading from the surface down to the pump.
Drawdown.
The vertical distance the water level is lowered when the well is pumped.
Groundwater.
Water that naturally occurs in porous rock materials underground.
Static water level.
The depth below ground level where water stands in a well when it's not being pumped.
Electric sounder or electric depth gauge
 This is perhaps the handiest method for measuring well water levels.
It consists of a weight suspended on #16 or #18 stranded insulated wire with depth markings and an ammeter to indicate a closed circuit.
Current flows through the circuit when the end of the wire touches the water surface.
Current is supplied by a small 9or 12-volt battery.
To make a reading, lower the electric wire or sounding line until the needle deflects.
Read the distance from the water to the top of casing on the line.
Mark the reference point on the casing where you measured the depth.
Most commercial models use two conductors and mark the distance with paint or brass tags crimped on every 5 feet.
Use a standard tape
 Figure 1.-Reading the distance from the water to the top of casing on the line.
measure to measure the distance between the marks on the line.
Because of the low electrical conductivity of most groundwater, use a meter in the circuit rather than a light bulb.
Electrical sounders, which include a reel of wire, meter, and battery, are available commercially.
If your well casing is plastic, extend the ground wire from the battery and submerge it in the water.
1.
State law requires an access to the well.
Most wellheads have an access hole in the base; if one isn't present, you can drill or cut a hole in most situations.
2.
Drilled wells aren't straight; they spiral down, and the column sometimes presses against the casing.
This can block the path of the sounder when you lower it.
Carefully jiggling the weighted sounder can move the tip past the obstruction.
Occasionally, the sounder will become stuck in the well.
Don't pull so hard that the wire breaks.
Tie off the wire so it can't slip into the well-then abandon it.
Check periodically to see if vibration has freed the sounder.
3.
Deep well turbines with oil-lubricated shafts tend to leak oil onto the water surface.
As oil is lighter than water, it displaces the water level.
Oil is also a poor electrical conductor, which means it interferes with electrical contact.
A cheesecloth sack can protect the end of the sounder until it hits water.
Coating the tip of the sounder with salt can increase its sensitivity when it reaches the water.
This method is very accurate for measuring water levels to depths up to about 90 feet.
To use this method satisfactorily, you must know the approximate depth to water.
Attach a lead weight to the end of a 100-foot steel measuring tape.
Dry 8 to 10 feet of tape end and coat with carpenter's chalk or keel  before each measurement.
Lower the tape down the well until a part of the chalked section is below water.
At this point, align and note an even foot mark on the tape exactly at the top of the casing or some other measuring point.
Pull the tape up, read the mark where the line is wet, and determine the actual depth from the top of the casing to water level by subtracting the wetted mark from the mark you held at the top of the casing.
Wetted tapes have many of the same problems encountered by electric sounders-lowering into the well and encountering oil.
This method consists of a small-diameter pipe or tube long enough to extend from the top of the well to a point about 20 feet below the lowest anticipated water level.
As you pump air into the line, excess air bubbles are forced out the end, equalizing the pressure in the line with the pressure created by the depth of water outside the line.
Measure the exact length of air line as you place it in the well.
Make sure the air line is airtight; hang it vertically, taking care that it doesn't spiral inside the well casing.
Quarter-inch copper or brass tubing, or 1/4-inch steel or plastic pipe, commonly is used.
You can use plastic tubing, but it's quite easy to pinch it off during installation.
The best way is to attach the air line securely to a known point on the pump column.
Attach the end of the air line low enough so that it's submerged when the pump operates at full discharge-but be sure it's at least 5 feet above the
 suction intake of the pump to avoid pulling air through the pump.
By noting the number of pipe joints you install, you'll know the depth of the air line tip.
If possible, leave a permanent marker on the wellhead to indicate the depth of the air line.
Fit the upper end with a tee and pressure gauge plus a valve to which a hand pump is attached.
You can calibrate the gauge to indicate pressure directly in feet of water or pounds per square inch.
You can use any pressure gauge, but one with a full scale that's just higher than any expected drawdown will provide the greatest accuracy.
Special pressure gauges are available to read directly the depth of water in the well.
Once you've installed it, with pressure gauge connected, pump air into the air line until the pressure shown by the gauge levels off at a constant maximum-indicating that all water has been forced out of the line.
At this point, air pressure in the tube  just supports the column of water from water level in the well to the bottom of the tube.
This water column length is equal to the amount of air line submerged.
Deduct this pressure, converted to feet , from the known length of the air line to determine the amount of submergence.
For example:
 Assume that L  is 150 ft long.
Pressure gauge shows 26 psi.
Then the distance from the water level to the bottom end of the air line  is 26 X 2.31 or 60 ft.
Therefore, the distance of water level  is 150 60 or 90 ft.
An air line provides the most convenient method for repeated testing of deep wells over 300 ft deep.
To convert from:	Multiply by:
 feet to meters	0.3048
 meters to feet	3.28
 feet water to psi	0.433
 psi to feet water	2.31
 psi to kPa	6.895
 kPa to psi	0.145
 meters water to kPa	9.81
Plant Uptake of Contaminants of Emerging Concern During Irrigation with Recycled Water
 Harshad Oswal, Daniel Gerrity, Channah Rock
 What is recycled water?
Recycled  water is municipal wastewater treated to a sufficient quality for its intended purpose-a concept known as 'fit-for-purpose' reuse.
In any region with impaired or scarce water resources, recycled water can be used to replace or augment existing water supplies.
Potential applications range from power plant cooling to drinking water augmentation to agricultural irrigation.
While the U.S.
is considered a leader in potable reuse-the use of advanced treated recycled water as a drinking water supply-Israel has established itself as a leader in agricultural reuse.
In fact, Israel now recycles 75% of its wastewater for use in agricultural applications.
This dramatically reduces the country's reliance on scarce freshwater resources or costly water supply alternatives such as desalination.
With global food demand expected to increase 70% by 2050  and climate change expected to put further strain on freshwater supplies, agricultural reuse is slated for further expansion in the future.
Use of recycled water for irrigation in the U.S.
According to the U.S.
Geological Survey, freshwater withdrawals in the U.S.
totaled 280 billion gallons per day in 2015, with irrigation accounting for 118 billion gallons per day .
Of the ~34 billion gallons per day of wastewater generated in the U.S., only 0.7 billion gallons per day were recycled for irrigation uses in 2015.
This represents a 42% increase since 2010, with more than 40 states now participating , but it still only represents 0.6% of the total water used for irrigation.
Theoretically, more agricultural reuse could further reduce freshwater demand, but there are a number of practical and institutional barriers limiting broader adoption of this practice.
In many places, competition between sectors  may limit the amount of recycled water available for a specific application.
In other locations, the distance between major supply centers  and agricultural fields  may render agricultural reuse economically or technically infeasible due to the high cost of bulk water transmission.
The 35 largest sites with 'untapped' agricultural reuse potential, meaning the reuse source is in close proximity to the agricultural demand, could provide an additional 1 billion gallons per day of water for 200,000 acres of cropland.
This would still account for only a small fraction of overall irrigation demand, but it would more than double the current reuse total for irrigation and might be critically important on a local scale in water-stressed regions.
Another barrier to agricultural reuse relates to the implications of water quality for public perception and public health protection.
Depending on the type of treatment, recycled water may contain elevated concentrations of nitrogen and phosphorus, thereby reducing the need for fertilizer.
However, recycled water may also contain a number of constituents of emerging concern.
CECs are broadly defined as "any synthetic or naturally occurring chemical or microorganism that is not commonly monitored in the environment but has the potential to enter the environment and cause known or
 Freshwater Withdrawals in the U.S.
suspected adverse ecological and/or human health effects".
CECs include pharmaceuticals and personal care products , perand polyfluoroalkyl substances , and even antibiotic resistant bacteria  and antibiotic resistance genes , all of which have been detected in recycled water.
It should be noted that these compounds have also been detected in surface water and even in treated drinking water, and thus the issue is not limited to recycled water.
The Food Safety Modernization Act , while currently in abeyance, addresses some microbial concerns, specifically limiting the geometric mean E.
coli concentration in agricultural irrigation water to <126 CFU/ 100 mL.
Existing guidelines and/ or regulations for microorganisms in recycled water are generally even more stringent, often requiring non-detects for total and fecal coliform bacteria.
However, regulations for agricultural applications do not currently address broader occurrence of CECs.
PPCPs include a diverse suite of chemical substances, including over-the-counter and prescription drugs for human and veterinary uses, and other products that are used
 by individuals for personal health or cosmetic purposes.
PPCP concentrations in treated wastewater vary by orders of magnitude depending on inputs to the local collection system and the unit processes at the wastewater treatment facility.
Concentrations in recycled water generally range from the ng/L  to ug/L  level.
Importantly, the general consensus is that typical concentrations of the vast majority of PPCPs in recycled water pose de minimis risks to public health.
PFAS represent a potential exception in that recently published health advisory levels are in the low ng/L range.
Specifically, the U.S.
Environmental Protection Agency  published a combined health advisory level of 70 ng/L for perfluorooctane sulfonic acid  and perfluorooctanoic acid , while California recently lowered its individual notification levels for PFOA and PFOS to 5.1 ng/L and 6.5 ng/L, respectively.
PFAS are a family of molecules composed of a carbon backbone that is fully or partially fluorinated, and the number of carbon atoms in the backbone is a defining characteristic.
For example, PFOA and PFOS both contain 8 carbon atoms within their backbone, hence their 'octan-' designation.
The C-F combination represents one of the strongest bonds in organic chemistry and ultimately makes the compound highly persistent through water and wastewater treatment and in the environment.
Water and food consumption are generally considered two major routes of human PFAS exposure.
Additional information related to PFAS can be found in Dery et al..
Although exposure to PPCPs in recycled water is unlikely to cause any adverse public health impacts, there may be ancillary effects of certain subgroups, specifically antibiotics.
The main concern for the release of antibiotics into the environment is related to the proliferation of antimicrobial resistance, either as intact ARB or as intracellular or extracellular  ARGs that can be transferred to pathogenic bacteria via horizontal gene transfer.
In fact, wastewater treatment plants have been identified as 'hotspots' for the spread of ARB and ARGs into the environment.
Although clinical antimicrobial resistance has become a clear threat to public health, the role of treated wastewater is still unclear
 PFAS Ex: Perfluorooctanoic acid  with 8-carbon backbone
 Top: Existing implementation of recycled water for irrigation applications in the U.S.
Middle: Publicly owned treatment works  identified as having significant recycled water flows available for nearby croplands.
Bottom: States permitting recycled water use for food and non-food crops, non-food crops only, or neither.
Take-home message: Geospatial disconnects  can be a significant barrier to agricultural reuse.
In other words, it may not be practical to transport recycled water from large urban areas to distant agricultural fields.
However, studies have identified numerous facilities with agricultural reuse potential.
Source: Anne Thebo of the Pacific Institute, 2017
 Why are CECs relevant to agricultural reuse?
CECs may enter agroecosystems through irrigation with recycled water or through land application of biosolids.
Upon irrigation, CECs may be deposited onto the plant tissue itself or may percolate through the soil, potentially being transported into the roots and then throughout the internal structure of the plant.
The potential for plant uptake of CECs is highly complex and depends on myriad factors involving the soil, water, plant , and the CEC in question.
CEC uptake by plants is often described on a mass per dry weight basis.
For example, the antibiotic sulfamethoxazole has been detected at ~5 ng/g of tomato, and the antibiotic ciprofloxacin has been detected at ~10 ng/g of cabbage or
 carrot.
Summed PFAS concentrations sometimes exceed 1 ug/g in edible plant tissue, although this is generally observed only when CECs are spiked at high concentrations or in the presence of biosolids.
Bioconcentration factors , or the ratio of plant tissue concentration to soil concentration, have also been used, with BCFs >1.0 indicating a high potential for uptake.
For example, BCFs for PFOA and PFOS  are often less than 1.0 to 2.0, with most of the compound detected in plant roots.
On the other hand, 4-carbon PFAS compounds can have BCFs higher than 100, with detection shifting to edible portions of plants.
This occurs because shorter-chain compounds preferentially partition to water, thereby increasing their mobility into plant tissues, whereas longer chain compounds adsorb more readily to organic matter in soil.
With respect to ARB and ARGs, some studies indicate that irrigation with recycled water has no discernible impact on antimicrobial resistance within the soil microbiome , while other studies have demonstrated higher prevalence of certain ARGs in soils irrigated with recycled water.
The figure below highlights these contradictory observations.
For context, the 16S rRNA gene is often used as a surrogate for bacterial abundance in a sample, and sull and tetM are ARGs conferring resistance to the antibiotics sulfamethoxazole and tetracycline, respectively.
Based on the figure, irrigation with groundwater VS.
recycled water had minimal impact on abundance of the 16S rRNA gene, or overall bacterial abundance.
There was also little impact on the sull ARG, but there was a clear increase in tetM with recycled water.
For both sull and tetM, ARG occurrence consistently decreased from soil to roots to leaves to fruit-often by several orders of magnitude.
Christou et al.
summarizes various biotic and abiotic factors affecting CEC uptake by plants.
These factors include target CEC characteristics, plant type, soil type, and environmental conditions, including conditions that might promote CEC biodegradation within the soil.
With respect to plant type, experimental results suggest CEC uptake is greatest in leafy vegetables; followed by root vegetables, cereals, and fodder crops; and least in fruits and nuts.
Notes: F = Fruit L Leaf R = Root S = Soil GW = Groundwater RW = Recycled Water Source: Cerqueira et al.
Conditions Contributing to CEC Uptake
 High net irrigation rate
 Growing season during summer
 Low soil organic matter content
 Sandy  soils
 Low lipid content in roots
 Source: Christou et al.
What does this mean for environmental and public health?
Laboratory experiments have shown that CECs can affect the development and physiology of plants, but these experiments often involve soil-free hydroponics systems with high CEC concentrations in the water.
In general, the scientific literature suggests there is potential for CECs to adversely impact crop health and for antimicrobial resistance elements to be transferred to pathogenic bacteria in the environment, but these outcomes have not yet been demonstrated conclusively under realistic environmental conditions.
With respect to public health, Prosser and Sibley  calculated hazard quotients for PPCPs based on plant uptake data reported in the literature.
hazard quotient is the ratio of exposure to some toxicological benchmark.
That benchmark
 might be a 'no adverse effect level' or sometimes may reference a therapeutic dose, but it often includes a large safety factor to account for additional toxicological uncertainty.
It is assumed that hazard quotients less than 1.0 represent a safe level of exposure to the constituent in question.
Prosser and Sibley  found that for studies involving recycled water with environmentally relevant CEC concentrations, the highest hazard quotient for adults was 0.08 , and most hazard quotients were significantly lower.
For toddlers, five compounds had hazard quotients greater than 0.1, but none were greater than 0.4.
The study concluded that individual PPCPs detected in edible tissues of plants represented a de minimis  risk to human health.
However, they cautioned that potential public health implications of complex PPCP mixtures were still unclear.
Also, more data are needed for PFAS uptake with environmentally relevant concentrations and in the absence of biosolids to better characterize the public health implications of using recycled water alone.
PFAS are relevant to public health at lower concentrations than many PPCPs, which may result in higher hazard quotients, but additional data are needed for confirmation.
Even if hazard quotients suggest public health risks are negligible, there may be other ancillary effects of CEC exposure.
In a study conducted in Israel, healthy people consuming produce irrigated with recycled water excreted higher urinary levels of the antiepileptic compound carbamazepine than healthy people consuming produce irrigated with freshwater.
However, peak urinary levels were 10,000 times lower than the level expected after ingestion of a single therapeutic dose of carbamazepine.
This offers further evidence that human exposure to CECs from produce irrigated with recycled water is possible but that the effects are likely insignificant, albeit detectable in some cases.
Quantitative microbial risk assessment  is a common approach for estimating public health risks due
 Example: Exposure to the Antibiotic Sulfamethoxazole in Carrots Irrigated with Recycled Water
 Lowest Therapeutic Dose = 400 mg/day Safety Factor Acceptable Daily Intake =  /  /  = 0.0057 mg/kg-day = 5700 ng/kg-day Estimated Daily Intake  = Concentration in Food  x Food Intake  X B1  B 
 Highest Observed Sulfamethoxazole Concentration in Carrots = 0.25 ng/g 
 Daily Carrot Intake = 2.80 cups/day 
 B1 = Conversion from cups to grams = 134.9 wet g/cup B2 = Conversion from wet weight to dry weight = 0.085 
 Adult: Body Mass=76.6g Estimated Daily Intake = 0.10 ng/kg Hazard Quotient = 0.000018 Toddler: Body Mass = 15.4 Estimated Daily Intake=0.52 ng/kg Hazard Quotient = 0.000091 Source: Prosser and Sibley  Approximately 5-20 tons of carrots per day to reach acceptable daily intake
 to exposure to pathogenic microorganisms.
QMRA is increasingly being used to evaluate the safety of potable reuse applications and to inform the development of regulations and design criteria for engineered treatment systems.
These existing studies are possible because the data needed to perform a QMRA for waterborne enteric pathogens are often readily available.
Theoretically, QMRA can also be applied to ARB and ARGs, but existing frameworks cannot be applied directly.
The scientific community and water industry are currently collaborating to develop QMRA frameworks specifically to address antimicrobial resistance.
Until that time, it is not possible to quantify the potential risks associated with antimicrobial resistance elements that might be detected in agroecosystems.
What does this mean for the use of recycled water in agriculture?
As demonstrated by many scientific studies, the concentrations of a large number of CECs are dramatically reduced during wastewater treatment.
However, some CECs are recalcitrant  to conventional and even advanced /wastewater treatment processes SO they are likely to be detected in recycled water used for irrigation, with the exact compounds and concentrations being sitespecific.
As noted earlier, this is potentially problematic because a growing body of literature suggests that CECs can be taken up into plants irrigated with recycled water.
When plants are exposed to environmentally relevant CEC concentrations, uptake is generally minimal, and studies suggest that the associated risks are negligible.
However, growers and irrigation districts should be aware of this issue because perceived risks can still have a significant impact on the decision-making process.
To address the remaining uncertainty, the scientific community is working closely with the water/wastewater and agricultural industries to better understand and characterize the implications for CECs in agroecosystems exposed to recycled water.
Adapted from: Pecson et al.
Figure 9.
Common Causes of Failures
 Septic System Failure and Environmental Impacts
 Brad D.
Lee, Plant and Soil Sciences
 W hen properly designed, maintained, and used, septic systems can provide adequate treatment for most pollutants.
According to the U.S.
Census Bureau, approximately 23 percent of the estimated 115 million occupied homes in the United States are served by septic systems.
More than one-third of new homes and over half of the mobile homes in the U.S.
depend on septic systems.
Here in Kentucky, approximately 40 percent of the homes have septic systems.
This is common in the southeast, where there are more septic systems per capita than any other region of the country.
Comprehensive data to measure the true extent of septic system failure are not currently collected by any single organization.
Although estimates of system failure rates have been made by various states, no state had directly measured its own failure rate and definitions of failure vary.
Most available data are the result of incidents that directly affect public health or are obtained from homeowners' applications for permits to replace or repair failing systems.
Massachusetts has the most comprehensive statewide program to identify septic system failures.
This time-of-transfer inspection identified a 20 percent failure rate based on an inspection of each septic system prior to home sale.
The Massachusetts program, however, only identifies failures according to code and does not track groundwater contamination that may result from septic system failures.
A study of two Indiana counties suggest that nearly one in three of all septic systems built between 1950 and 1990 required repairs.
But since 1990, when the state septic system code was updated, less than 3 percent of new septic systems required repairs, significantly fewer than in previous decades.
The most commonly reported cause of septic system failure is soil wetness.
Other common causes were undersized systems, system age, and limited space for the soil treatment area.
Improved septic system designs and more stringent oversight have resulted in fewer failures, but homeowners may mistakenly believe their septic systems are working properly SO long as the toilets flush and there is no foul odor in the yard or adjacent ditches.
However, septic systems fail in other, less obvious ways, so homeowners should learn to recognize the most common types and causes of septic system failures.
If 20 percent of Kentucky's septic systems are failing, approximately 7.6 billion gallons of raw sewage are discharged into the environment annually.
There are four basic categories of septic system failure.
Sewage backflow-when the septic system rejects sewage until it backs up into a home-is the most commonly reported failure category.
Such failures are obvious and typically command a homeowner's immediate attention.
Because they are usually noticed and addressed so quickly, sewage backflow failures seldom cause much harm to the environment.
However, if the system is not quickly repaired, it can become a health hazard.
Sewage in the Yard
 Another common category of septic system failure is when poorly treated sewage surfaces on the surface of the yard, in nearby ditches, on the neighbor's lawn, or elsewhere in the immediate environment.
When it occurs in densely populated neighborhoods, such failures are usually obvious.
Sewage in the yard can degrade surface water and is a health hazard.
Decline in Water Quality
 A home's plumbing and septic system drainfield may appear to be working properly and nobody in the neighborhood will notice foul odors or excess wetness around the drainfield.
But with this category of septic system failure, water supply sampling indicates a significant degradation in groundwater quality.
Frequently, a downhill neighbor's water supply well will be affected, not the water supply of the failing system's owner.
Such failures are not obvious, and homeowners may perceive that their septic systems are working satisfactorily.
There is little scientific evidence indicating that septic system failures are causing Kentucky's waters to degrade at such a rate that it would pose a problem to this or the next generation.
However, computer modeling and long-term monitoring indicate that septic system use in certain areas of the U.S.
will result in gradual environmental degradation.
This is a very difficult problem to identify, especially without extensive and costly long-
 Figure 1.
An example of a failing septic system.
Effluent can be seen surfacing on top of the lawn at left.
term monitoring.
Because such septic system failures are difficult to identify and quantify, there are no regulations regarding them.
A septic system's effect on the environment can be difficult to measure.
We can estimate that every failing septic system can discharge about 63 thousand gallons of untreated wastewater into Kentucky's environment per year.
That means that if 20 percent of Kentucky's septic systems are failing, approximately 7.6 billion gallons of raw sewage are discharged into the environment annually.
Untreated wastewater contains excessive nutrients  that can harm native plant and fish populations in Kentucky's surface waters.
Wastewater's excessive organic matter content also can choke off the oxygen supply in streams and rivers.
Microbial populations in these surface waters can exceed the U.S.
Environmental Protection Agency's body contact standards, abruptly halting recreational use of beaches, lakes, and streams.
Common Causes of Failures
 One of the most critical factors in septic system performance is the nature of the soils used for the septic system soil treatment area.
Other common causes of failure include improper design, and poor system use, management, and maintenance by the homeowner.
Minimize failures by carefully and deliberately considering all aspects septic system construction-site selection, design, installation, maintenance, and use.
Hire reputable individuals to design and install your septic system.
County health departments can provide you with the names of installers who work in your county.
After contacting a septic system professional, ask for references from previous customers and contact these homeowners to ask them about their septic system's performance.
Once built, be sure to maintain the septic system.
Use water conservatively, avoid driving over the septic system, and have your septic tank pumped and cleaned every three to five years 
 If your septic system needs repair, it is imperative that you contact your local county health department and report the situation.
The county health department can help you identify the problem and provide a list of professionals in the area who can assist you.
In addition to helping you, health departments use reports of failing systems to develop future septic system designs that will better function in Kentucky soils.
AN INTRODUCTION TO STORMWATER PONDS IN SOUTH CAROLINA
 Published: Aug 29, 2021 |  Printable Version  | Peer Reviewed
 Amy E.
Scaroni, Debabrata Sahoo and C.
Guinn Wallover
 This article is intended for stormwater pond owners, property management professionals, pond management professionals, and county and municipal staff to learn about the design, function, and management of stormwater ponds.
Altering land use or land cover across a watershed affects the hydrology of the system.
As South Carolina becomes increasingly developed, urban and suburban landscapes generate larger volumes of polluted stormwater runoff.
Stormwater runoff is generated when precipitation falls on impervious surfaces, such as roads and parking lots, and cannot infiltrate into the soil.
An increase in impervious cover increases runoff volume and peak flows during storm events, which can cause flooding and accelerate erosion.
Stormwater ponds are constructed to intercept runoff from the stormwater conveyance systems.
Temporary water storage in ponds reduces flood pulse, improves water quality, and minimizes adverse effects to downstream waterways.
While wetlands are a common natural landscape feature across South Carolina, most ponds were constructed to serve a purpose, such as irrigation, recreational fishing, or flood control.
Stormwater ponds fall under that latter purpose, flood control, and are increasingly being used to manage water quality in addition to quantity.
The proliferation of stormwater ponds across South Carolina is a direct result of regulations placed on new developments beginning in the 1990s.
As such, most new housing developments include one or multiple stormwater ponds to manage additional runoff generated due to increased impervious surfaces.
The coastal counties alone have over 9,200 stormwater ponds, and the number continues to rise.1 The large number of ponds present across South Carolina lead to various management challenges and have implications for broader watershed health.
Stormwater ponds are designed to act as flow-through systems.
Stormwater is routed to a pond, which acts as a temporary storage site and settling basin, and then water eventually exits the system and flows into downstream water bodies.
This connectivity between ponds and natural waterways is important because although ponds help reduce and filter pollutants from stormwater, a poorly functioning pond can act as a pollutant source.
Even a well-maintained pond that reduces pollutants, such as excess nutrients, can still export harmful algae and introduce warmer water with lower dissolved oxygen levels downstream.2 In some highly urbanized areas, much of the runoff in a watershed may end up passing through stormwater ponds before flowing downstream.
As a result, stormwater ponds are an integral part of larger watershed management efforts.
In addition to flood control and pollutant reduction and removal, stormwater ponds provide a number of other ecosystem services, including carbon sequestration, habitat creation, macroinvertebrate biodiversity, and recreational opportunities.3,4,5
 Stormwater ponds are the primary best management practice used across South Carolina to comply with stormwater control requirements.6 Generally, there are three types of stormwater ponds designed to capture and detain stormwater runoff for the design conditions:
 Dry detention ponds  designed to store stormwater temporarily.
Wet detention ponds  have a permanent pool of water for water quality benefits and temporarily store water before being released.
Retention ponds  have a permanent pool of water and reduce volume through infiltration, evapotranspiration, or a combination of the two.
Wet detention ponds are the predominant stormwater pond type across coastal South Carolina and in areas with a high water table.
Dry ponds are likely to be found across the upstate region of South Carolina, although data are lacking on the total number of ponds statewide and the presence of wet vs.
dry ponds.
In this article, further discussion and references to stormwater ponds will focus on wet detention ponds and their design and management.
Various state and local regulations influence the design of stormwater ponds.
Stormwater ponds are generally built to comply with construction regulations intended to reduce runoff from newly developed sites.
Pond design is site-specific, based on both the local rainfall and watershed characteristics.
Ponds may be designed to capture design storms , reduce peak flows, empty within seventy-two hours of a storm, or store runoff for twenty-four hours to provide additional water quality benefits.
Design components of a pond may include a forebay, permanent pool, temporary pool, inlet and outlet structures, low-flow orifice, emergency spillway, geometry, and underlying soils.
Plan view and profile view of a wet detention pond.
Figure 1.
Design elements common to most stormwater ponds.
Image credit: SC Department of Health and Environmental Control.
Mechanisms for Pollutant Treatment and Removal
 Pollutants generally enter a stormwater pond via stormwater runoff and reflect upland sources of pollution that flow into ponds during storm events.
Stormwater reaches the pond through two key pathways:  through pipe discharge at the inlet, and  through overland flow across the pond banks.
Stormwater pollutants entering the pond via pipe discharge reflect the surrounding land use.
In a residential neighborhood, common pollutants sources include excess nutrients from fertilizer use, bacteria from pet waste and wildlife, and sediment from unvegetated/bare ground and eroding banks.
The warmer temperatures of runoff from impervious surfaces can be problematic for ponds, as can freshwater inflows to brackish ponds.
Traditionally, stormwater ponds were designed to manage localized flooding.
However, because ponds can be designed to mimic many of the ecosystem services provided by natural wetlands, they are generally effective at improving water quality via  sedimentation,  pollutant uptake , and  biogeochemical transformations, such as denitrification, in the water column and underlying soils.
Sedimentation is a settling process in which suspended particles and sediment-associated pollutants in the water column drop out of solution and settle on the pond bottom, where they eventually become buried by additional layers of sediment accumulation.7 Sedimentation is one of the primary processes of pollutant removal in stormwater ponds.
In general, there are four zones of sedimentation in ponds: an inlet zone, a sedimentation zone, a sludge zone, and an outlet zone.8 Designing stormwater ponds with long, circuitous flow paths can enhance the hydraulic retention time, ultimately increasing sedimentation of suspended solids and sediment-associated pollutants from the water column.9 Pollutant storage in the sediments can serve as a temporary or a long-term sink but is not considered a permanent solution.
Disturbance of the pond bottom can resuspend sediments and associated pollutants within the water column.10 Inclusion of a forebay at the inlet can increase the removal of sediment and associated pollutants through the sedimentation process prior to entering the main storage reservoir of the pond.11 Increased sedimentation over time eventually decreases the storage capacity of the stormwater pond, and ponds may require dredging to restore capacity.3 Proper maintenance and management of the pond are necessary to reduce erosion, both along pond banks and in upland areas draining to the pond, to decrease the total amount of sediment entering the pond.
Plants both in and around the pond can enhance sedimentation and sediment-associated pollutant removal in several ways.12 They provide resistance to flow, thereby reducing the water velocity and increasing the hydraulic retention time.
Slower water velocities enhance the settling of sediment and sediment-associated pollutants from the water column to the bottom of the pond.
Plants can also take up nutrients and pollutants via bioaccumulation, which results in the storage of pollutants in plant tissues.
Plants also help in other processes such as filtration, infiltration, and adsorption.
Filtration occurs when plants remove the pollutants from the water column, protecting surface water and groundwater quality.
Infiltration helps in the reduction of dissolved pollutants from the water column.
Adsorption refers to the process in which pollutants bind to the surface of organic matter from the plants or soils associated with their root systems, helping reduce the concentration of pollutants in the stormwater.
While increased stormwater flows in the ponds could resuspend sediment and sediment-associated pollutants within the water column, the roots of the plants/vegetation help to hold the sediment and sediment-associated pollutants in place and prevent erosion.13 Vegetation management is a critical component of pond management if pollutant mitigation and management are design goals.
Biogeochemical processes refer to ways by which different elements or pollutants are transferred between the organisms and the environment.
Biogeochemical processes in ponds occur when microorganisms mediate chemical transformations, transforming one form of a pollutant to less harmful versions or removing them entirely.14 For example, organic material that accumulates on the pond bottom can host a variety of beneficial microbes that help to assimilate and transform nitrogen pollution.
Nitrification and denitrification are important reactions that transform and remove inorganic nitrogen from the water column.15 Denitrification reduces nitrate  into N2 gas via a microbially-mediated pathway, which is considered a permanent removal of nitrogen from the system.
Microbial update can also help to remove soluble reactive phosphorus from stormwater.16
 Mechanisms for pollutant mitigation in stormwater ponds systems have implications for management enhancements to improve target pollutant removal efficiencies or deter pollutant introduction into the pond system.
Popular strategies considered include vegetated buffers, floating treatment wetlands, aeration, and incorporation of upland stormwater control measures.
A picture containing water, river, lake, outdoorDescription automatically generated
 Figure 2: Clockwise from top left:  vegetated buffer management encourages the use of an alternating mowing schedule to permit the growth of beneficial aquatic perennials and grasses.
Image credit: Guinn Wallover, Clemson University.
bottom diffusers are a recommended aeration method to reduce the risk of fish kills related to turnover in deeper pond systems  the pond surface looks like it is bubbling when diffusers are used.
Image credit: The Lake Doctors.
floating wetlands enhance sediment settling and nutrient uptake when appropriate surface coverage of the stormwater pond is achieved.
Image credit: Charleston Aquatic and Environmental, Inc.
The benefits of vegetated buffers in reducing pollutant transport or minimizing shoreline erosion along waterbodies are well-documented.17,18 Buffers have been adapted for use along with stormwater ponds and are a common recommended best practice to help reduce shoreline erosion and associated sedimentation and water quality concerns.
Where communities can achieve wider buffer widths, increased water quality benefits may be achieved through enhanced management of runoff from properties adjacent to the pond.
The incorporation of native wetland vegetation for enhanced pond performance also includes floating treatment wetland practices.
Floating treatment wetland systems provide opportunities for multiple pollutant removal mechanisms to work simultaneously, including wave attenuation resulting in sedimentation and reduced bank erosion, the formation of biofilm along the dense root systems that support microbial decomposition of organic material and denitrification, and plant uptake of nutrients and pollutants by vegetation.
Barriers to the use of floating treatment wetlands include installation costs and required pond surface area coverage.
Studies suggest a marked increase in pollution removal efficiency when floating treatment wetlands achieve coverage of 20% of pond surface area, suggesting their use for pollution removal enhancement is more feasible for smaller pond systems.19 Field studies that examine the relationship between pollutant removal efficiencies and floating wetland area versus the area of the pond show that a range exists in the recommended coverage area, which may also be influenced by additional variables.19,20,21
 Aeration systems in ponds are traditionally used to help maintain dissolved oxygen levels in deeper pond systems.
Aerator use is recommended to help prevent stratification of the water column and pond turnover.
Pond turnover can result in rapid mixing and low dissolved oxygen conditions following seasonal weather shifts.
Creating or maintaining aerobic conditions in the pond can also affect nutrient levels by decreasing phosphorus release from the sediments, although other studies have found minimal effects on phosphorus dynamics due to mixing.22,23 Notably, effective aeration and mixing of the water column in lakes can shift the phytoplankton community composition from cyanobacteria  to green algae and diatoms; however, this effect may be limited in shallow pond systems.21 A preferred approach to cyanobacteria bloom prevention is to limit the runoff of nutrients into the pond.
While stormwater ponds can effectively treat water quality for a variety of pollutants, the best way to ensure their functionality over the long term is to reduce the load of pollutants that reach the pond in the first place.
Upland best management practices focused on infiltration can reduce total runoff reaching the pond, thereby reducing pollutant inputs.
A treatment train approach focused on using best management practices in series can iteratively reduce runoff volume and treat pollutants nearer to the source as stormwater travels across the landscape.
Changing behavior is another important approach to reducing or eliminating pollutants at the source.
Research on coastal South Carolina stormwater ponds suggests that terrestrial sources of organic material  are significant contributing sources to organic material accumulation in pond bottoms, as opposed to aquatic algae and plant material.24 Homeowner adoption of best practices in the landscape can help to reduce pollutants in ponds and reduce the volume of stormwater runoff generated.
Practices like removing and properly disposing of pet waste, keeping yard waste out of storm drains, limiting fertilizer use, avoiding excessive irrigation, and converting impervious surfaces to permeable areas all help safeguard and protect stormwater ponds and the ecosystems they were designed to protect.
Water is extremely important for crop production.
When water becomes limiting to the plant it is important to understand how plants use water.
We often hear the term evapotranspiration  in relation to plant water demand.
ET is a combination of soil water evaporation  and water used by the plant during transpiration.
Soil evaporation is the major loss of water surface and typically is higher after rain and under high temperature conditions.
Calibration and Uniformity Assessment for Animal Wastewater Application Equipment
 North Carolina Cooperative Extension Service
 North Carolina State University
 Calibration and Uniformity Assessment for Animal Wastewater Application Equipment
 Prevent runoff to surface waters and groundwater pollution by inspecting and calibrating any irrigation system used for animal wastewater application.
Regular field measurement and calibration ensure uniform waste applications that produce good crop growth and protect water resources.
A pplication systems used to apply animal waste to land should meet acceptable application uniformity guidelines to make sure they provide good agronomic performance and minimize environmental impact.
Application uniformity tends to decline with an irrigation system's age for various reasons.
Often the decline can be attributed to pump and sprinkler wear.
Pump impellers may wear, resulting in lower pump pressure.
Sprinklers nozzles wear over time due to sediment in the wastewater.
Also, struvite and other salts may crystallize and precipitate in the main lines, resulting in increased head loss and lower sprinkler operating pressure.
In liquid manure land application systems, poor application uniformity has many disadvantages.
If liquid manure is overapplied to crops, the extra liquid manure will either runoff and pollute surface water or percolate below the crop root zone and pollute the groundwater.
If liquid manure is underapplied, crop growth may decline, resulting in poor quality cover crops and decreased yield.
Therefore, field measurement and calibration of land application systems are necessary and should be performed periodically.
According to North Carolina state rules that went into effect September 1, 1996, land application equipment used on livestock production farms must be field calibrated or evaluated in accordance with existing design charts and tables.
Technical specialists certifying waste management plans after September 1, 1996, must also certify that operators have been provided calibration and adjustment guidance for all land application equipment.
These rules apply to irrigation systems in addition to all other types of liquid, slurry, or solid application equipment.
One aspect of land application equipment calibration is the assessment of uniformity, or how evenly waste is applied to receiving crops.
A series of NC Cooperative Extension bulletins entitled "Field Calibration Procedures for Animal Wastewater Application Equipment"  describe detailed calibration procedures for typical irrigation equipment used for land applications of animal waste: Evans et al., 1997a ; Evans et al., 1997b ; Evans et al., 1997c.
These publica-
 tions give instructions for field determination of the uniformity coefficient , more commonly referred to as the coefficient of uniformity , and provide ranges of good and acceptable values of UC for land application of animal waste.
More recent guidance provided by the North Carolina 1217 Interagency Group  established calibration requirements that comprised measurement of both a system's flow rate and "wetted diameter," and its uniformity as detailed in Evans et al..
As set forth in the eighth edition of the SB 1217 guidance document, flow rate and wetted diameter were to be measured every year for facilities with National Pollutant Discharge Elimination System  general permits and every other year for facilities with statewide general permits.
Under the eighth edition guidelines, field determination of uniformity was to be done every three years regardless of permit type.
Many factors can affect a sprinkler's water distribution and a system's application uniformity, including sprinkler model, nozzle type , nozzle size, nozzle pressure, sprinkler or lane spacing, and wind.
Recently conducted research at NC State University evaluated the correlation of these variables to CU in stationary and traveling systems.
Liu found that if sprinkler spacing  was within design specifications and pressure was within the ranges provided in a manufacturer's charts, then application uniformity would normally be in an acceptable range as set forth in Evans et al..
Generally, if sprinkler spacing is 50 to 70 percent of the field-measured wetted diameter for stationary systems and 60 to 85 percent of the field-measured wetted diameter for traveling systems, uniformity will be acceptable.
See the "Irrigated Acreage Determination Procedures for Wastewater Application Equipment" publications  for more details on acceptable sprinkler and lane spacing.
Here we explain calibration procedures for stationery and hard-hose traveler irrigation systems and how to determine acceptable application uniformity for the systems as established by the ninth and latest edition of the SB 1217 document
 .
It does not invalidate the procedures  described in AG-553-1 and AG-553-2 if operators want to use those for uniformity assessment.
However, AG 553-1 and AG 553-2 do not fulfill the flow measurement calibration requirements currently established by the ninth edition of the SB 1217 document.
You will need a manufacturer's chart for your system's sprinkler and nozzle combination and also information contained in the irrigation system design documentation  or the wettable acreage determination.
Manufacturer charts are used to compare field-measured wetted diameter to expected wetted diameter  and may also be used to estimate flow rate.
Charts can be obtained from the sprinkler company's website.
An example of a chart for a "gun-type" sprinkler is shown in Figure 1.
Irrigation system design documentation should have been submitted in the approval process for the animal wastewater land application system.
Operating pressure at the sprinkler can be found in Table 2 or Table 3 of Appendix B of the Natural Resources Conservation Service NC Irrigation Guide , depending upon the type of irrigation system used for land application.
Sprinkler flow rate can be found in Table 4 in Appendix B of the same guide.
If design documentation is not available, sprinkler flow rate can be obtained by using the pressure and sprinkler information found in the irrigated acreage
 field data worksheets for stationary  and traveling gun irrigation systems  completed at the time of the irrigated acreage determination for your system.
See the section labeled "Measuring and Comparing System Flow Rate" on page 6 of this bulletin for instructions on obtaining flow rate from sprinkler pressure.
Measured sprinkler flow rate will be compared to the flow rate in the design documentation or the irrigated acreage worksheets.
Calibration of hard-hose traveler and stationary systems involves four steps:
 1.
measuring system operating pressure ,
 2.
measuring sprinkler wetted diameter,
 3.
measuring system flow rate, and
 4.
comparing the field-obtained measurements in steps 1-3 with manufacturer charts, irrigation design documents, and/or irrigated acreage determination information.
Forms are provided in this bulletin  to make it easy to record and document field calibration as well as interpret field-collected data.
Uniformity assessment of these systems involves two steps:
 1.
comparing field-measured wetted diameter and pressure to manufacturer charts, and
 2.
calculating sprinkler or lane spacing as a percentage of field-measured wetted diameter to determine if spacing falls in the recommended range.
100 SERIES BIG GUN PERFORMANCE U.S.
UNITS
 100 TAPER BORE NOZZLE 100T 100T Specify size when ordering
 0.50"	0.55"	0.60"	0.65"	0.70"	0.75"	0.80"	0.85"	0.90"	1.0"
 9309-050	9309-055	9309-060	9309-065	9309-070	9309-075	9309-080	9309-085	9309-090	9309-100
 PSI	GPM	DIA.FT	GPM DIA.
GPM	DIA.FT	GPM	DIA.
GPM	DIA.
GPM DIA.
GPM	DIA.F	GPM	DIA	GPM	DIA	FT	GPM DIA FT.
40	47	191	57	202	66	213	78	222	91	230	118	250	256
 50	50	205	64	215	74	225	87	235	100	245	256	130	265	150	273	165	280	204	300
 60	55	215	69	227	81	240	96	250	110	260	143	280	164	288	182	295	224	316
 70	60	225	75	238	88	250	103	263	120	295	177	302	197	310	243	338
 80	64	235	79	248	94	260	110	273	128	285	305	189	314	210	325	258	354
 90	68	245	83	258	100	270	117	283	135	295	175	315	201	326	223	335	274	362
 100	72	255	87	268	106	280	123	293	143	305	163	485	325	212	336	235	345	289	372
 110	76	265	92	278	111	290	129	303	150	315	171	324	195	335	222	344	247	355	304	380
 The field procedure consists of four steps:  measuring operating pressure,  measuring sprinkler wetted diameter and comparing it to the manufacturer's chart,  measuring system flow rate and comparing it to the appropriate documentation, and  calculating sprinkler or lane spacing.
Pressure gauge ;
 Flow meter with in-line adapters , if field measured nozzle pressure and manufacturer's charts will not be used to obtain flow rate;
 Measuring tape  or measuring wheel; and
 Pressure should be recorded only after the system has been fully pressurized and all air expelled from the system.
For traveling gun systems, measure operating pressure at the gun operated in the lane farthest from the pump.
For stationary systems, take a pressure reading from at least two sprinklers located on two different lateral lines farthest from the pump.
Take pressure readings about one-third to one-half the way from the head of the lateral.
This is the lateral location where average pressure occurs.
Pressure may be taken in either of two ways:  from a gauge mounted on the sprinkler riser or on the gun body  or  by using a pressure gauge with a pitot tube attached.
If using a mounted gauge, the gauge should not be permanently mounted as fouling and plugging will occur.
The same gauge can be used at multiple locations by removing the gauge from the threaded port; if doing this, be sure to replace the plug into the port.
An alternative approach is to install a shut-off valve between the sprinkler riser pipe or gun body and pressure gauge and leave the gauge permanently mounted.
If using a pitot tube, place the tube directly into the nozzle stream as close to the nozzle as possible and hold steady while noting the pressure.
For larger nozzles, it may be necessary to move the pitot tube slightly to center the tube in the stream and to obtain the maximum pressure reading, which is the correct pressure to record.
Measuring and Comparing Sprinkler Wetted Diameter
 Take measurements under no wind to very light wind  conditions with the system operating at normal pressure
 .
Locations of wetted diameter measurement should occur at the same locations as pressure measurement.
To compare measured wetted diameter to the manufacturer's data, obtain a manufacturer's chart for the specific model, nozzle type , and nozzle size of the sprinkler.
Charts can be obtained from irrigation dealers or from the sprinkler manufacturer's website.
Measurement instructions are the same as in AG-553-7  and are adapted and reprinted here for convenience.
The wetted distance from the gun should be determined on both sides of the lane along the perimeter as indicated in Figure 4.
The system should be operated long enough for all air to be purged from the system before starting to make measurements.
With the system operating at normal pressure, complete these steps:
 1.
Observe and flag the farthest point getting wetted for each of three consecutive rotations of the gun while standing just outside the wetted perimeter.
2.
Select one flag to mark the average distance of the three observations.
Remove the other two flags.
3.
Move to the other side of the lane  and repeat steps 1 and 2.
The wetted perimeter should be flagged on two sides of the gun as shown in Figure 4.
4.
Measure and record the distances from the gun to each flag.
These are measurements of wetted radius.
5.
Compare the two measurements of wetted radius.
If the measurements are within 5 percent, add the two measurements to obtain the wetted diameter, and step 6 can be skipped.
If the difference of the two measurements exceeds 5 percent, repeat steps 1 though 4 at another location along the lane or in a different lane.
6.
If the difference between the second set of measurements still exceeds 5 percent, the wind speed may be too high, resulting in excessive drift, or the gun may be functioning improperly.
Once you have corrected the cause of variation in the two measurements, repeat beginning with step 1.
If you cannot correct the problem, contact an irrigation technical specialist , or an irrigation dealer.
Measurement instructions are the same as in AG-553-6  and are adapted and reprinted here for convenience.
Figure 2.
Measuring pressure using:  pressure gage mounted in sprinkler riser;  pressure gage mounted in gun body; and  pitot tube inserted into nozzle while sprinkler operating.
Pitot tube connected to gauge is shown in.
Figure 3.
Correct  and incorrect  positioning of pitot tube in discharge stream for pressure measurement.
A gun ring nozzle is shown in this illustration.
The wetted distance from each sprinkler should be determined at four points along the perimeter as indicated in Figure 5.
Measured sprinklers should be the same model and have the same nozzle type and size.
1.
Observe and flag the farthest point getting wetted for each of three consecutive rotations of the sprinkle while standing just outside the wetted perimeter.
2.
Select one flag to mark the average distance of the three observations.
Remove the other two flags.
3.
Move 90 degrees around the wetted perimeter, and repeat steps 1 and 2.
Continue until the wetted perimeter has been flagged on four sides of the sprinkler as shown in Figure 5.
4.
Move to sprinkler no.
2, and repeat steps 1 through 3.
5.
Measure and record the distances from the sprinkler to each flag.
6.
Determine the average of the four measurements for each sprinkler.
7.
Compare the average measurements for the two sprinklers.
If the measurements are within 10 percent, compute the average of the two and this will be the wetted radius (skip step
 Figure 4.
Illustration of field measurement of wetted radius for traveling gun systems.
Adapted from Figure 7 in Evans et al., 1999b.
8).
If the difference between the measurements is more than 10 percent, repeat steps 1 through 6 for a third sprinkler.
8.
Compare the measurements for all three sprinklers and identify the two that are closest.
If their difference is less than 10 percent, compute the average of the two, and this value is the wetted radius.
If the difference is more than 10 percent, repeat steps 1 through 6 until you identify two sprinklers that fall within 10 percent of each other.
Figure 5.
Illustration of field measurement of sprinkler wetted radius for stationary systems.
Adapted from Figure 7 in Evans et al., 1999a.
Compare Field-Measured Wetted Diameter to Manufacturer's Chart
 Once you have determined the wetted diameter from field measurements, compare the field-measured wetted diameter to the expected wetted diameter for the specific sprinkler and nozzle using the charts provided by the manufacturer.
The field-measured wetted diameter must be within 15 percent of the wetted diameter reported in the manufacturer's chart for the operating pressure determined in "Measuring Operating Pressure".
If the difference is more than 15 percent, the difference may be due to excessive wind conditions at the time of field measurements or malfunctioning equipment.
Contact an irrigation technical specialist if the wetted diameter values cannot be reconciled to within 15 percent.
Measuring and Comparing System Flow Rate Flow Meter
 Flow meters are appropriate for traveling gun systems in which the flow is to one gun or for stationary systems with gun-type sprinklers that normally operate one gun at a time.
If using a flow meter, you will need a stopwatch or watch with a second hand.
Make sure the flow meter used has been calibrated.
Determine flow rate by either  recording the instantaneous flow rate or  using the flow totalizer and elapsed time.
Run the system in motion until all air is out of the system and the flow rate has been stabilized as shown by the flow rate needle or the digital readout on the flow meter.
1a.
Record instantaneous flow rate in gallons per minute.
1b.
Subtract the ending flow totalizer reading from beginning flow totalizer reading for a time period of not less than 15 minutes.
Convert to gallons per minute  by dividing gallons by elapsed time in minutes.
When reading the totalizer, make sure to note the value of the last  digit.
Often this digit indicates hundreds of gallons, in which case the totalizer number needs to be multiplied by 100.
Note: Use step 1b rather than la if the instantaneous flow rate varies by more than 10 percent after all the air has been purged from the system and the flow has stabilized.
For flow meters with needles , this is indicated by a "bouncing" needle.
Figure 6.
In-line flow meter with an exploded view of register
 If using manufacturer's charts to estimate sprinkler flow rate, you will need to use the same chart as used in the "Compare Field-Measured Wetted Diameter to Manufacturer's Chart" step on this page.
Determine the exact size of the nozzle opening.
For large gun-type sprinklers, the nozzle size is usually stamped on the nozzle  and measured in inches.
For smaller sprinklers, the nozzle size is usually stamped on the nozzle that is threaded into the sprinkler body.
The stamped number is normally given in 64ths of an inch; e.g., a number 16 nozzle is 16/64-inch.
1.
Enter the chart at the pressure measured and move to the column with the correct nozzle size.
Record the flow rate.
For recorded pressures that are between pressures given in the chart, either interpolate the flow rate or use the pressure in the chart that is just lower than the pressure recorded to
 obtain the flow rate.
2.
Repeat step 1 for the other sprinklers for which pressure was recorded.
3.
Compute the average of the flow rates.
The average flow rate will be compared with the appropriate documentation.
Comparing Field-Measured Flow Rate to Appropriate Documentation
 Field-measured flow rate must be within 10 percent of the value specified in the irrigation design documentation or as was determined during the irrigated acreage determination.
If the two flow rate values are not within 10 percent, consult an irrigation technical specialist.
Acceptable uniformity may be inferred from two measurements: nozzle pressure and sprinkler  spacing.
Nozzle pressure must be within the range shown on the manufacturer's chart for your specific sprinkler.
Sprinkler or lane spacing is expressed as a percent of the field-measured wetted diameter.
Refer to the field data sheets  for computation of sprinkler spacing.
For traveling systems, the lane spacing must be within 60 to 90 percent of the field-measured wetted diameter for systems installed prior to February 1, 1999; and between 60 and 85 percent of field measured wetted diameter for systems installed after February 1, 1999.
Stationary sprinkler spacing must be within 50 to 70 percent of field-measured wetted diameter.
If both nozzle pressure and sprinkler spacing meet the above criteria, application uniformity is acceptable.
If not, contact an irrigation technical specialist.
Tomatoes for the Home Garden
 David W.
Sams, Professor Emeritus, Plant and Soil Science Originally prepared by Alvin D.
Rutledge, Professor Emeritus, Plant and Soil Science
 Tomatoes are the most popular vegetable grown in home gardens.
They are more nutritious than many vegetables and provide significant amounts of both vitamins A and C.
Tomatoes are served fresh, are a major component of many salads and are used in many cooked dishes.
Tomatoes are either determinate or indeterminate.
Determinate tomatoes are referred to as self-topping or low-growing types.
They may grow to a height of 3 or 4 feet with proper cultural care.
The terminal bud then forms a flower and the plant does not grow any taller.
Numerous fruit is set over a very few weeks and ripens over a short harvest interval, usually four to five weeks.
Indeterminate varieties continue to grow taller throughout the growing season unless they are killed by insects or disease.
They set and produce fruit throughout the summer and fall.
They require 5or 6-foot stakes to provide good support.
Fruit of indeterminate tomatoes is usually softer and has more gel and thinner walls than determinate types.
The tomato varieties listed below allow a gardener to produce the type of tomato of his/her choice and to produce fruit throughout the growing season.
Early Girl is an extremely early variety that will continue to bear throughout the season.
Its fruit size is smaller than most tomatoes, however.
Sweet Million is a very prolific cherry tomato that is resistant to several diseases.
It is extremely sweet and liked by most who try it.
Floramerica and Celebrity are good-quality, determinate varieties for those who want concentrated harvest.
Jubilee and Pink Girl fulfill the need for tomatoes of various colors.
Big Boy is a large "beef-steak" type for those who want large, solid fruit.
Better Boy is a good-quality, hybrid tomato that is widely available.
It is the standard by which other home garden tomatoes are compared.
Long Keeper is a tomato designed to be harvested in the fall.
It is below average in taste but will keep two or three months or more at room temperature.
It has orange skin but red flesh.
Soil should be prepared as for any garden vegetable.
Turn it in time to allow undecayed plant material to decay before planting.
This may require four to six weeks.
Apply fertilizer and lime and work them into the soil before planting.
Lime should be applied several weeks ahead of planting for maximum effectiveness.
The soil pH should be 6.1 or above to help prevent blossom-end rot.
The soil should be worked 6 or more inches deep and until it has a fine but not powdery texture.
A soil test is the only way to be sure
 Variety	Harvest	Days to First	Size 	Comments
 Early Girl	I	54	4-6	earliest
 Sweet Million	I	60	1 inch	cherry
 Floramerica	D	70	7
 Celebrity	D	72	8-10
 Jubilee	I	72	8	orange
 Betterboy	I	75	10-16
 Pink Girl	I	76	8
 Big Boy	I	78	10-16
 Long Keeper	I	78	7
 exactly how much lime and fertilizer are needed.
If no soil test has been done, two to three pounds of a common fertilizer such as 6-12-12 per 100 square feet of garden space may be used.
Blossom-end rot is a leather-like decay of the blossomend of the fruit.
There are several ways of reducing the amount of blossom-end rot on your tomatoes.
These are based on maintaining proper calcium levels in the tomato fruit.
First, be sure to lime your garden according to the soil test recommendation.
Lime is calcium carbonate and supplies calcium to the soil.
It also raises the pH, making it easier for the plant to take up calcium.
Second, maintain uniform soil moisture by using irrigation and mulches.
Calcium must dissolve in soil moisture to be taken up by plants.
Tomatoes will also have less blossom-end rot if they are not pruned too heavily and if they are not fertilized too heavily with ammonium nitrate.
Good yields are possible only when a gardener begins with high-quality plants.
The plants should be short and stocky with well-developed root systems.
Plants that have been grown in containers normally have better-developed root systems and grow better than bare-root plants.
Both plants grown in containers and bare-root plants must be kept moist or the roots will die and the plants will be stunted.
Stunted tomato plants usually grow but will produce smaller, later crops.
Stocky tomato transplants will be 7 or 8 weeks old.
They should be hardened before they are set into the garden to prevent injury from hot sun, cold temperatures and drying winds.
Tomatoes may be hardened by exposing them to temperatures 10 degrees below normal for a week or SO before they are set into the garden.
It is also possible to
 harden tomato transplants by withholding water until the plants just begin to wilt.
This requires very close attention and is difficult for most home gardeners.
When a tomato plant is properly hardened, the veins on the underside of the leaves will have developed a tinge of purple.
If the entire underside of the leaf is purple, the plant has been over-hardened and will be stunted.
Avoid purchasing tomato plants that have wilted excessively, have spots on their leaves, are excessively yellow or have purple lower leaves.
If possible, purchase varieties that have the letters VFN after their name.
This indicates that they have resistance to verticillium and fusarium wilt and to nematodes.
It is best not to plant tomatoes in the same location in the garden two years in a row.
If possible, rotate plants around the garden SO they are not planted in the same location more than once every three or four years.
This does not eliminate but will help prevent disease and nematodes from building up in the soil.
When tomatoes are 6 to 8 inches tall, they should be planted deep enough to completely cover the root ball.
Planting can be done after the last spring frost through June 25.
If plants have been grown in fibrous containers, the top of the container must be completely covered with soil.
This prevents the container from serving as a wick, slowing water loss.
The distance between plants in the row depends upon the type of tomatoes being grown and the severity of pruning or intended suckering.
Suckering consists of removing growth in the leaf axis.
Determinate varieties do not grow as tall as indeterminate and can normally be spaced closer in the row.
If suckering is not intended, plants will need to be spaced further apart.
The in-row
 spacing varies from 18 inches to 24 inches between plants.
Between-row spacings can vary from 4 feet to a width suitable for use with the cultivation equipment available.
If tall, leggy plants are to be planted, it is advisable to either lay a portion of the plant horizontal or plant it 6 to 8 inches deep.
This allows the plant to develop a root system along all of the buried stem.
Organic mulches such as straw, leaves, grass clippings or compost can be applied after plants are set.
Mulches applied 4 to 6 inches thick provide weed control, uniform moisture levels, reduce certain disease problems and improve fruit quality.
Organic mulches should not be applied until the soil is warm.
Black plastic can be used to maintain uniform moisture, control weeds, enhance and improve fruit quality.
If plastic is used, lay 4-foot wide strips in the row area and seal the edges with about 6 inches of soil about two weeks before the planned transplanting date.
Plant the tomatoes through slits cut in the plastic.
The best-quality tomatoes are grown on supports.
It requires less space to produce the same quantity of edible fruit with supports.
Tomatoes are normally supported with stakes or cages.
If stakes are used, each stake should be about 4 feet tall for determinate types or 6 feet for indeterminate types.
Stakes can be provided for each plant.
Tie plants loosely to the stakes at 8to 10-inch intervals.
Stakes can also be placed between each two plants and supports provided by the "Florida Weave" technique.
In this technique, string is tightly stretched horizontally along both sides of the stakes at the same height, with plants held between the string layers.
String layers are repeated every 8 to 10 inches vertically as the plant grows.
When stakes are strong and well-anchored, this system provides sufficient
 support to keep plants off the ground.
Usually, two plants are set between stakes.
Tomatoes are often suckered with this system.
When cages are used for support, the cage must be of strong materials, such as concrete reinforcing wire.
Cages should be well anchored to support the weight of the plants and fruit.
The cage should have sufficient openings to allow removal of ripe fruit.
A 6-foot length of wire will form a cage about 21 inches in diameter.
Unsuckered tomatoes are allowed to grow in the cage.
Yields per plant are usually higher in a cage than when supported by stakes.
Nitrogen sidedressing applied at the right time and at the correct rate can greatly enhance the production of tomatoes.
Sidedressings are applications of fertilizer along the plants at some stage of growth.
They are started when fruit on the first cluster is about the size of a half-dollar, and repeated every four weeks through harvest.
If they are applied prior to this time, it is very likely that blooms will drop and fruit set will be eliminated or reduced.
Ammonium nitrate is the most common nitrogen source.
Apply one tablespoon in a circle around the plant at each sidedressing about 12 inches from the plant.
For best tomato growth, keep the soil in the root zone moist enough to prevent wilting of tomatoes.
This is best done by applying 1/2 to 3/4 inch of water twice a week to the root zone during periods of dry weather.
If possible, use trickle irrigation.
Less foliage disease occurs with trickle than sprinkler irrigation.
If sprinkler irrigation is used, apply as late in the afternoon as possible, but early enough to allow foliage to dry before nightfall.
B.C.
SPRINKLER IRRIGATION MANUAL
 Prepared and Web Published by
 BRITISH COLUMBIA Ministry of Agriculture
 LIMITATION OF LIABILITY AND USER'S RESPONSIBILITY
 The primary purpose of this manual is to provide irrigation professionals and consultants with a methodology to properly design an agricultural irrigation system.
This manual is also used as the reference material for the Irrigation Industry Association's agriculture sprinkler irrigation certification program.
While every effort has been made to ensure the accuracy and completeness of these materials, additional materials may be required to complete more advanced design for some systems.
Advice of appropriate professionals and experts may assist in completing designs that are not adequately convered in this manual.
All information in this publication and related materials are provided entirely "as is" and no representations, warranties or conditions, either expressed or implied, are made in connection with your use of, or reliance upon, this information.
This information is provided to you as the user entirely at your risk.
The British Columbia Ministry of Agriculture and the Irrigation Industry Association of British Columbia, their Directors, agents, employees, or contractors will not be liable for any claims, damages or losses of any kind whatsoever arising out of the use of or reliance upon this information.
Withdrawing water from a surface water source for an irrigation system often requires a diversion and intake system.
The construction of the diversion and intake must be such that downstream water demands and fishery resources are not impacted.
In all instances diversions and intakes should be constructed to prevent fish from entering the intake or diversion channel.
While it is impossible to indicate all the various methods of diverting water into an irrigation system, this chapter provides some diversion and intake options.
Diversion structures are used to divert water away from a stream or river into an irrigation channel or piped inlet of the irrigation system.
The type of diversion selected will depend on the size of the creek or river, the amount of water being diverted, whether the irrigation system is gravity fed or pumped and whether there are fish present in the stream.
If the creek is small enough, a diversion structure can be constructed within the creek bed.
Figure 10.1 indicates a small diversion structure utilizing stop logs to divert the flow into the irrigation system intake.
The maximum stop log height should not exceed 12" as the creek should be allowed to flow over the diversion.
The structure should be built to allow for fish passage and should be constructed in a manner that minimizes the disturbance of the stream bed and banks.
The irrigation intake pipe is often set directly into the pool upstream of the diversion structure.
Small gabions can be used in place of stop logs if required.
Gabions are compartmented rectangular containers made of heavily galvanized steel wire woven in a uniform hexagonal triple twist pattern with an opening of approximately 75mm by 225 mm.
Gabion structures will settle, adjust themselves to foundation settlement, and seal up over time.
If they are used as a diversion structure, they must be sealed initially.
Gabions are constructed in the following manner:
 1.
For easy handling and shipping, gabions are supplied folded into a flat position.
They are readily assembled by unfolding and by simply wiring the edges and the diaphragms to the sides.
2.
The gabions are filled to a depth of one foot, and then one cross tie is placed in each direction and looped around the meshes of the gabion wall.
This operation is repeated until the gabion is filled.
3.
Adjoining gabions are wired together by their vertical edges; empty gabions stacked on filled gabions are wired to the filled gabions at front and back.
4.
After the gabion is filled, the top is folded shut and wired to the ends, sides and diaphragms.
Figure 10.1 Stop Log Diversion Structure
 If it is not possible to withdraw water directly from a creek, water must be diverted into a side canal or lagoon for delivery to an irrigation system.
A 90 diversion will attract less debris into the intake.
Figure 10.3 indicates a method of diverting water to an irrigation channel or an irrigation intake.
If possible the dredged area in the middle of the channel should be large enough to create a pool to help settle out debris.
This area can then be cleaned to periodically to keep the intake free of debris.
The screen used to prevent material from entering the channel will need to be sized as per the guidelines in Section 10.3 if fish are present.
Settling basins are often required for diversions from streams with high silt content.
The water velocity must be reduced to 0.5 ft/sec or slower to allow sand and silt to settle out.
Settling basins can easily be 20 m to 40 m in length depending on the type of material suspended in the water.
The configuration of a settling basin will depend on site specifics.
Figure 10.2 shows a small concrete settling basin with trash rack and intake pipe.
Costs for this type of intake can be quite costly and may only be practical for large intake systems.
Figure 10.2 River Diversions Using a Settling Basin
 Source: Small Hydropower Handbook
 In British Columbia, the mountainous terrain often allows for gravity feed systems to provide the pressure required to operate an irrigation system.
Intakes for gravity feed systems have special requirements.
The diversion from a surface water source into a gravity feed intake should have flow velocities less than 0.30 m/sec.
Flow velocities can be reduced by first diverting the water into a ditch or small reservoir prior to the water entering the irrigation mainline.
Air vents should be installed on the pipeline close to the intake, and should be vented above the entry point to the pipeline.
See Figure 10.3.
An air vent can simply be a standpipe open to the atmosphere which extends above the water surface level.
This insures that air can be supplied to the line should the intake become blocked.
A 2-inch air vent should be an adequate size for most systems with intake pipes less than 12 inches.
The top of the intake pipe should be positioned to ensure that it is below the water surface at all times.
To prevent air from entering the system, the following formula can be used to determine the minimum submergence depth of a pipe.
Equation 10.1 Minimum Submergence
 0.0622 x ( H= D 4
 H = Minimum submergence [in]
 Q = system flow rate [US gpm]
 D = pipe diameter [in]
 For example, the minimum submergence required for a 10" irrigation intake at various flow rates is listed in Table 10.1.
Table 10.1 Minimum Submergence Requirement
 Flow Rate [US gpm]	Height  [in]
 Note that doubling the flow changes the submergence by a factor of four times.
Figure 10.3 indicates a simple gravity feed intake.
The trash rack bars should consist of 1/4" X 1" steel bars welded to 1/4" X 2" mounting bars, with a 3/4" space between bars.
The clear opening between the trash rack and the pipe inlet should be greater than twice the actual pipe diameter.
The flow velocity at the intake should be limited to 1 ft/second at the trash rack.
Example 10.1 Sizing Trash Rack
 What size trash rack is required to limit flow velocity to 1 ft/s for a 1,000 gpm flow rate?
The open area for the trash rack is 75%.
Flow rate 	1,000	1	US gpm
 Flow velocity 	1	2	ft/s
 Percent open area	75	3	%
 Figure 10.3 Sloping Trash Rack
 Centrifugal pumps are the most common type of pumps for irrigation systems with pumping requirements less than 60 hp in British Columbia.
Where higher horsepower units are required or where elevation lifts are excessive vertical and submersible turbines are often used.
Figures 10.4 and 10.5 illustrate methods of installing an intake screen for a centrifugal pump on creeks or lakes.
The type of intake used will depend on the water depth and lake or creek bottom profile.
A flexible rubber hose system in the suction system allows the intake to adjust for different water elevations.
An airtight connection must be maintained to prevent air from entering the suction pipe.
Figure 10.4 Standard Centrifugal Pump Intake
 Figure 10.5 Centrifugal Pump Intakes for Deep Water Installations
 Self-cleaning intakes are also available.
There are two types.
The first type of self-cleaning intake uses a set of spray nozzles to rotate the screen.
The second type uses a rotating bar with spray nozzles inside the intake.
With both types the purpose is to spray away the debris that may build up on the outside of the screen.
Figure 10.6 Rotating Self-Cleaning Intake Source: Sur-Flo
 Figure 10.7 Non-Rotating Self-Cleaning Intake Source: Waterman Industries Self-Cleaning Intake Strainer WRS Series
 When drawing water from lakes or rivers, a screen is often required to keep debris from entering the irrigation system.
A trash rack may be used to prevent large obstacles from damaging the screen, but screens are necessary to remove any obstacles that are large enough to plug the sprinkler orifice.
An irrigation system withdrawing water from a fish bearing stream or lake must restrict the flow velocity through the screen to 0.1 ft/sec.
The percentage of open area of the screen must be established and taken into account when calculating the screen area required.
Table 10.2 can be used as a guide in determining the screen open area required.
Table 10.2 Screen Area Required for Fishery Regulations
 Flow Rate [US gpm]	Screen Open Area [ft2]
 Table 10.3 indicates the opening area for standard market grade wire mesh.
This mesh wire cloth is available in brass, aluminum, bronze, stainless steel and numerous other alloys.
Fisheries recommendations suggest screen mesh sizes with clear openings that do not exceed 0.10 inch and open screen areas that are not less than 50% of the total screen area.
Table 10.3 Opening Area of Standard Market Grade Wire Mesh
 Wire Diameter	Width of Opening
 Mesh	% Open Area
 [in]	[mm]	[in]	[mm]
 3 3	0.080	2.03	0.253	6.42	58%
 4 X 4	0.063	1.60	0.188	4.78	56%
 6 X 6	0.035	0.889	0.132	3.35	63%
 8 X 8	0.028	0.711	0.096	2.44	60%
 10 X 10	0.025	0.635	0.074	1.88	55%
 12 X 12	0.023	0.584	0.060	1.52	52%
 Source: C & E Mesh Products Ltd.
Example 10.2 Sizing Intake Screen
 Question: The wheeline system in Armstrong is pumping from an active fish stream.
What size of intake screen is required?
Screen mesh opening cannot exceed 0.10 inch.
The velocity requirement for a screen in fish-bearing streams is 0.1 ft/sec.
Total flow rate 
 Since screen mesh opening cannot exceed 0.10 inch, the following should be selected:
 Velocity 	0.1	2	ft/s
 Mesh 	8x 8	3
 Percent open area 	60	4	%
 .
To calculate the screen size, the pump flow rate  needs to be converted to cubic feet per second.
A rectangular screen that is 2 ft high, 3 ft wide and 2 ft deep would be adequate if the screen was suspended in the stream and all six sides are exposed.
If one side of the intake is sitting on the bottom of the stream then the dimensions would be a bit larger.
A gravity feed intake often requires a large screening surface and one that is self-cleaning.
Figure 10.8 indicates a relatively simple method to accomplish this.
Variations of this culvert screen system are possible.
Figure 10.8 Self-Cleaning Screen for Gravity Intake
aboveand below-ground water application.
Each sprinkler irrigation plot contained six high-pop brass sprinkler heads designed to apply 10 gallons of water per minute at a pressure of 35 pounds per square inch.
The coefficient of uniformity was 87 percent.
Turfgrass performance under reduced irrigation
 Jewell L.
Meyer Victor A.
Gibeault
 urfgrass in California requires irrigation during all or most of the year.
Water restrictions imposed during the drought in 1976 and 1977 forced turf managers to reexamine many concepts about irrigation.
Turfgrass managers had to make drastic cuts in water use and hope that the turf would survive.
One significant result of the drought was the realization that lower levels of turf quality were acceptable in many situations and that large water savings could be achieved.
No information was available, however, on the best conservation practices or on the minimum amounts of water needed to keep the turf alive.
Research was begun in 1979 to produce irrigation methodology that could be used to develop water-saving irrigation practices anywhere in California and in other arid and semiarid regions.
The three-year study showed that major savings of water can be achieved, especially with warm-season grasses, with no appreciable loss of turf quality.
Specifically, the objectives of the research were to:  investigate the effects of applying reduced amounts of irrigation water calculated as a percentage of evapotranspiration of applied water on coolseason and warm-season turfgrasses;  evaluate a below-ground system as a po-
 tentially more efficient method of turf irrigation than standard sprinkler application; and  develop a set of crop coefficients that California turfgrass managers can use to determine on-site water use by both cooland warm-season turfgrasses.
Tensiometers at 3and 6-inch depths in the cool-season grasses and 8and 12-inch depths in the warm-season grasses indicated soil water status; neutron probe access tubes were installed in plots to a depth of 4 feet in the cool-season and 6 feet in the warm-season grasses.
Scheduling was by the water budget technique calculated weekly using wind-modified pan evaporation data.
State-of-the-art controllers were programmed with this irrigation scheduling information.
The amount of irrigation was modified so that water did not pass below the 4-foot and 6foot depths of the neutron probe access tubes during the irrigation season.
Annual crop coefficients, determined from previous research using applied water and evaporation pan data, were 0.7 annually for warm-season grasses and 0.8 for cool-season grasses.
Monthly crop coefficients were developed in this experiment to evaluate responses of the six turfgrass species to 60 percent and 80 percent of replacement evapotranspiration for water conservation.
The study was conducted at the University of California South Coast Field Station, Irvine.
The variables tested included: two irrigation methods, sprinkler application of water and a subterranean or buried trickle/drip water application ; three irrigation regimes, 100, 80, and 60 percent of calculated evapotranspiration; and six commonly used turfgrasses, three coolseason varieties  and three warm-season types.
The field plot was a randomized splitblock design.
The area was divided into two turf blocks, one for cool-season grasses and the other for warm-season grasses.
Each block consisted of four replications, and within each replication were six randomized irrigation plots measuring 15 by 24 feet.
Irrigation plots were divided into three turf subplots of 8 by 15 feet.
The three sprinkler and three subterranean irrigation plots per replication were installed in September 1979 for
 Overhead sprinkler irrigation provided acceptable performance of some turfgrass species, even when less than the optimum amount of water was applied.
Subterranean irrigation did not provide acceptable turf with the shallow-rooted cool-season species, at the system depth and spacing used in this study.
The very deeply rooted hybrid bermudagrass was the best-performing species with subterranean irrigation.
Under sprinkler irrigation, there was no significant difference in cool-season grass performance between the 100 percent and 80 percent regimes.
This could be described as a potential level of water conservation amounting to 21.1 percent savings.
The savings could be tenuous, however, because of more weed and disease activity  when irrigated with less than the optimum amount of water.
The 60 percent regime significantly reduced the turf quality of the three coolseason grasses tested.
In the warm-season grasses, the appearance of hybrid bermudagrass and Seashore Paspalum was not significantly different under any of the irrigation regimes.
As irrigation amounts were reduced, zoysiagrass appearance ratings declined because of nematode activity ob-
 served on the roots.
Both Santa Ana hybrid bermudagrass and Adalayd  Seashore Paspalum had very good color, density, texture, uniformity, and freedom from weeds and diseases, irrespective of irrigation regimes.
Clearly there is potential for considerable water savings with these grasses.
This study showed a 40 percent reduction in actual water applied between the optimum and lowest irrigation regime.
Because of the field plot design necessary for this study, it wasn't possible to compare statistically the turf performance results between the warmand cool-season grasses.
Hybrid bermuda and Seashore Paspalum performed very well, however, with 52.7 inches of water applied , whereas the cool-season grasses needed at least 82.4 inches (80 percent irrigation
 regime).
Thirty-six percent less water was applied to the warm-season species than to the cool-season species for acceptable turf quality.
If applied water in the 60 percent irrigation treatment in warmseason grasses  is compared with that in the 100 percent treatment in cool-season grasses , the saving in water is 49.5 percent.
The cool-season grass in the 100 percent regime received 43 inches of water in 1982.
Warm-season grasses received only 34 inches.
Rainfall of 18.45 inches occurred primarily from November to March.
The soil profile held about 10 inches depth of water in the top 6 feet.
Rainfall did not appreciably affect the applied water during the primary growing season, April through November Likewise, the 34 inches applied to the warm-
 TABLE 1.
Cooland warm-season turfgrass appearance ratings and water applied for the duration of the study.
regime	Turf appearance 8/81 12/83*	cation 	ETgrasst
 % of ET	in.
Cool season	Ken.
blue	Per.
rye	Tall fesc.
100	5.5 y	6.2 y	5.8 y	104.4	77.3
 80	5.3 y	5.9 y	5.7 yz	82.4	61.0
 60	4.8 Z	5.0 Z	5.3 Z	62.7	46.4
 Warm season	Bermuda	Paspalum	Zoysia
 100	6.5 nst	5.8 ns	5.6 x	88.4	65.5
 80	6.5	5.8	4.8 y	69.4	51.4
 60	6.4	5.4	4.2 Z	52.7	39.0
 Rated on a scale of 1 to 9, with 1 indicating worst appearance and 9 best.
Values followed by common letters are not significantly different at the 5% level of probability.
t ET grass equals the actual applied water divided by the extra water factor (EWF which is 1.35.
$ No significant difference.
TABLE 2.
Actual water applied in 1982  and 1983 
 plots	Water applied*	Rainfall	Water appliedt	Rainfall
 % of ET	inches
 100	43.2	18.45	38.7	31.78
 Class A pan evaporation 55.0 inches for 1982.
t Class A pan evaporation 55.63 inches for 1983.
TABLE 3.
Turfgrass crop coefficients  of warmand cool-season grasses.
Monthly crop coefficient  is used with a Class A Weather Bureau evaporation pan with the equation ET grass ET pan x Kp t The crop coefficient Kc is used with reference evapotranspiration  from a CIMIS weather station with the equation grass H ETo Kc.
Month	Warm	Cool	Warm	Cool
 J	.44	.49	.55	.61
 F	.43	.51	.54	.64
 M	.61	.60	.76	.75
 A	.58	.83	.72	1.04
 M	.63	.76	.79	.95
 J	.54	.70	.68	.88
 J	.57	.75	.71	.94
 A	.57	.69	.71	.86
 S	.50	.59	.62	.74
 o	.43	.60	.54	.75
 N	.46	.55	.58	.69
 D	.44	.48	.55	.60
 season grasses was not appreciably affected by, nor was there evidence of, deep percolation during the primary growing season, when only 4 inches of rain fell.
The rainfall is subtracted from the original evaporation pan reading and is therefore reasonably accounted for in the calculated applications.
In 1983, a higher than normal rainfall of 32 inches occurred.
The soil profile was filled during the winter, however, and only 9 inches of rain fell from April to October 30, of which 4 inches occurred in early April.
Water moved below the root zone only on June 29, August 29, October 5, and October 17 in all plots of 100 and 80 percent irrigation in 1983.
Even during a season of higher than normal rainfall, the applied water, 38.7 inches in cool-season grasses , was similar to that of the drier year  with 43 inches applied.
Most of the 5 inches of implied higher use by cool-season grasses may have moved through deep percolation.
The water applied to warm-season grasses was 34 inches in 1982 and 33 inches in 1983.
This small difference indicates that managers can schedule carefully and conserve water in a wet or dry season.
The monthly crop coefficients  calculated and used for nearly three years proved to be very accurate for both warmand cool-season turfgrasses.
Crop coefficients can be used with reference evapotranspiration from the Department of Water Resources California Irrigation Management Information System  program.
Turfgrass managers can use these crop coefficients to determine on-site water use by turfgrasses from either a Class A Weather Bureau evaporation pan or from a computerized weather station that gives reference evapotranspiration with the equation given in table 3.
In conclusion, warm-season turfgrasses have a greater potential for water conservation than do cool-season turfgrasses.
Under the conditions of this study, sprinkler irrigation was superior to subterranean irrigation for water conservation and turfgrass performance.
And lastly, a well-designed, uniform irrigation system is necessary to maximize water conservation in turfgrass management.
Jewell L.
Meyer is Irrigation and Soils Specialist and Victor A.
Gibeault is Environmental Horticulturist, Cooperative Extension, University of California, Riverside.
Financial support for this study was granted by the Metropolitan Water District of Southern California, City of Los Angeles Department of Water and Power, Municipal Water District of Orange County, and the San Diego County Water Authority.
Also the support of the Southern California Turfgrass Council, the Lloyd Foundation, and the Golf Course Superintendent's Association of Southern California is appreciated.
The authors acknowledge the assistance of Ralph Strohman and Mark Mahody, Staff Research Associates, UC Riverside.
Chapter 3.
Principles and Practices of Irrigation Management for Vegetables 1
 Lincoln Zotarelli, Michael D.
Dukes, and Eric H.
Simonne
 This section contains basic information on vegetable water use and irrigation management, along with some references on irrigation systems.
Proper water management planning must consider all uses of water, from the source of irrigation water to plant water use.
Therefore, it is very important to differentiate between crop water requirements and irrigation or production-system water requirements.
Crop water requirements refer to the actual water needs for evapotranspiration  and plant growth, and they primarily depend on crop development and climatic factors, which are closely related to climatic demands.
Irrigation requirements are primarily determined by crop water requirements, but they also depend on the characteristics of the irrigation system, management practices, and the soil characteristics in the irrigated area.
Best Management Practices  for Irrigation
 BMPs have historically been focused on nutrient management and fertilizer rates.
However, because rainfall or irrigation water is the vector of off-site nutrient movement of nitrate in solution and phosphate in sediments as well as other soluble chemicals, proper irrigation management directly affects the efficacy of a BMP plan.
The irrigation BMPs in the Water Quality/Quantity Best Management Practices for Florida Vegetable and Agronomic Crops manual
 Uses of Irrigation Water
 Irrigation systems have several uses in addition to water delivery for crop ET.
Water is required for a preseason operational test of the irrigation system to check for leaks and to ensure proper performance of the pump and power plant.
Irrigation water is also required for field preparation, crop establishment, crop growth and development, withinseason system maintenance, delivery of chemicals, frost protection, and other uses, such as dust control.
Field preparation water is used to provide moisture to the field soil for tillage and bed formation.
The water used for field preparation depends on specific field cultural practices, initial soil moisture conditions, the depth to the natural water table, and the type of irrigation system.
Drip-irrigated fields on sandy soils often require an additional irrigation system for field preparation because drip tubes are not installed until after the beds have been formed.
Thus, many drip-irrigated vegetable fields may also require an overhead or subirrigation system for field preparation.
For example,
 many strawberry production fields have sprinkler irrigation systems already installed for frost protection.
These systems are also used for field preparation and may apply one or more inches of water for this purpose.
Subirrigated  fields use the same system for field preparation as for crop establishment, plant growth needs, and frost protection.
Subirrigation water management requirements depend on the soil characteristics within the irrigated field and surrounding areas.
Sufficient water must be provided to raise the water table level as high as 18 to 24 inches below the soil surface.
Water is required to fill the pores of the soil and to satisfy evaporation and subsurface runoff requirements.
As a rough guide, 1.0 to 2.5 inches of water are required for each foot of water table rise.
For example, a field with a preirrigation water table 30-inches deep may need about 2 inches of water to raise the water table to 18 inches, while a preirrigation water table at 48 inches may require 5 inches of water for the same result.
Vegetables that are set as transplants, rather than direct seeded, require irrigation for crop establishment in excess of crop ET.
Establishment irrigations are used either to keep plant foliage wet by overhead sprinkler irrigation  or to maintain high soil moisture levels until the root systems increase in size and plants start to actively grow and develop.
Establishment irrigation practices vary among crops and irrigation systems.
Strawberry plants set as bare-root transplants may require 7 to 14 days of frequent intermittent overhead irrigation for establishment prior to irrigation with the drip system.
Practices like intermittent irrigation, use of low-volume sprinklers, and use of crop protectants can reduce the volume of irrigation water required for establishment of strawberries.
The amount of water required for crop establishment can range widely depending on crop, irrigation system, and climate demand.
Adequate soil moisture is also needed for the uniform establishment of direct-seeded vegetable crops.
Crop Growth and Development
 Irrigation requirements to meet the ET needs of a crop depend on the type of crop, field soil characteristics, irrigation system type and capacity, and crop growth stage.
Crops vary in growth characteristics that result in different relative water-use rates.
Soils differ in texture and hydraulic characteristics such as available water-holding capacity  and capillary movement.
Because sands generally have very low AWHC values , a 1% change in AWHC affects irrigation practices.
Water Application 
 Eq.
[1] Irrigation requirement = Crop water requirement / Application efficiency
 Irrigation systems are often used for delivery of chemicals such as fertilizers, soil fumigants, or insecticides.
The crop may require nutrients when irrigation is not required.
Fertilizer injection schedules based on soil test results are provided in chapter 2 of this production guide.
Fertigation should not begin until the system is pressurized.
It is recommended to always end a fertigation/ chemigation event with a short flushing cycle with clear water and/or to rinse crop foliage to avoid the accumulation of fertilizer or chemical deposits in the irrigation system.
The length of the flushing cycle should be 10 minutes longer than the travel time of the fertilizer from the irrigation point to the farthest point of the system.
Irrigation systems require periodic maintenance throughout the growing season.
These activities may require system operation during rainy periods to ensure that the system is ready when needed.
In addition, drip irrigation systems may require periodic maintenance to prevent clogging
 and system failure.
Typically, cleaning agents are injected weekly, but in some instances more frequent injections are needed.
Other irrigation uses vary according to the type of crop, system characteristics, and field location.
Some examples include periodic overhead irrigation for dust control, wetting of dry row middles to settle dust and prevent sand from blowing during windy conditions, and wetting of roadways and drive aisles to provide traction for farm vehicles.
Irrigation scheduling consists simply of applying water to crops at the right time and in the right amount, and it is considered an important BMP.
The characteristics of the irrigation system, crop needs, soil properties, and atmospheric conditions must all be considered to properly schedule irrigations.
Poor timing or insufficient water application can result in crop stress and reduced yields from inappropriate amounts of available water or nutrients.
In sandy soils, excessive water applications may reduce yield and quality and increase the risk of nutrient leaching.
A wide range of irrigation scheduling methods is used in Florida, with corresponding levels of water management.
The recommended method  for scheduling irrigation  for vegetable crops is to
 Soil Water Status, Soil Water Tension, and Soil Volumetric Water Content
 Within the category of volumetric sensors, capacitancebased sensors have become common in recent years due to a decrease in cost of electronic components and increased reliability of these types of sensors.
However, sensors
 Practical Determination of Soil Field Capacity Using Volumetric Soil Moisture Sensors
 It is very important that the irrigation manager understands the concept of "field capacity" to establish an irrigation strategy that provides optimum soil moisture for plant growth, productivity, and reduction of fertilizer nutrient leaching.
Figure 1 represents volumetric soil water content  at a depth of 0-6 inches measured by a capacitance sensor over a period of 4 days.
For the soil field capacity point determination, it is necessary to apply an irrigation depth  that resulted in saturation of the soil layer, in this particular case 0-6 inches.
The depth of irrigation applied in a single irrigation event was 4,645 gal/A.
Right after the irrigation events, there was a noticeable increase in soil moisture content.
The degree to which the VWC increases, however, is dependent upon volume of irrigation, which is normally set by the duration of irrigation event.
For plastic-mulched drip irrigation in sandy soils, long irrigation events result in a relatively large increase in soil moisture in the area below the drip emitter.
The spike in soil moisture appears to only be temporary, because the irrigation water rapidly drains down beyond the 6-inch zone.
This rapid spike in soil water content indicates that the VWC rapidly reaches a point above the soil water-holding capacity, and the water percolated down to deeper soil layers.
For sandy soils, the change in the slope of drainage and extraction lines, in other words, changing from "rapid" to "slower" decrease in soil water content, can be assumed as the "field capacity point." At this time, the water has moved out from the large soil pores , and its place has been taken by air.
The remaining pore spaces  are still filled with water and will
 supply the plants with needed moisture.
Between the end of day 1 and day 3, the VWC declined at a constant rate as a result of drainage, but most of the water extraction was due to evapotranspiration during the day.
Figure 1.
Example of practical determination of soil field capacity at 0-6 inches soil depth after irrigation event using soil moisture sensors.
Examples of Irrigation Scheduling Using Volumetric Soil Moisture Sensor Devices
 In this section, two examples of irrigation management of vegetable crops in sandy soils using soil moisture sensor readings are provided: one example with excessive  irrigation  and one with adequate irrigation  using plasticulture.
In Figure 2, the irrigation events consisted of the application of a single daily irrigation event of 4,718 gal/A.
After each irrigation event, there was an increase in the soil water content followed by rapid drainage.
Large rainfall events may lead to substantial increases in soil moisture content.
On day 2, right after the irrigation, a large rainfall of 0.44 inches occurred, which resulted in a second spike of soil water content in the same day.
The following irrigation  started when the volumetric soil water content was above the soil field capacity.
In this case, the irrigation event of the day 3 could have been safely skipped.
Between day 3 and 6, no irrigation was applied to the crop.
The volumetric water content decreased from 0.14 to 0.08 in/in.
Due to the very low water-holding capacity of the sandy soils, skipping irrigation for several days could lead to unneeded crop water stress, especially during very hot or very windy days , or during flowering/fruit development stage.
Between day 6 and 10,
 large daily irrigation events were repeated, exceeding the "safe irrigation zone" and leading to more water drainage and nutrient leaching.
Figure 2.
Example of excessive  irrigation of the upper soil layer  moisture content for drip irrigation under plasticmulched conditions for sandy soils.
The black line indicates volumetric soil water content using soil moisture sensors.
The gray line indicates irrigation events, each single daily irrigation event having a volume application of 65 gal/100 ft.
The dotted line indicates soil field capacity line.
Arrows indicate rainfall events.
The example in Figure 3 received irrigation of 943 gal/A.
This irrigation depth was sufficient to increase the volumetric water content to a given moisture without exceeding the "safe irrigation zone." On average, the volumetric soil water content was maintained close to the field capacity, keeping water and nutrients in the root zone.
For this particular example, there was no deep water percolation.
In addition, with the information of the soil water status, the irrigation manager might decide to not irrigate if the soil moisture content is at a satisfactory level.
Figure 3.
Example of adequate irrigation management using soil moisture sensors for monitoring the volumetric soil moisture content in the upper soil layer  on drip irrigation under plasticmulched conditions for sandy soils.
The black line indicates volumetric soil water content using soil moisture sensors.
The gray line indicates irrigation events, each single daily irrigation event having a volume application of 943 gal/A.
The dotted line indicates the soil field capacity line.
Arrows indicate rainfall events.
Figure 4.
Crop coefficient of drip-irrigated tomato and strawberry.
On day 8, due to a rainfall event of 0.04 inches, there was no need for irrigation because the soil moisture was above the field capacity, and therefore the irrigation event of day 8 was skipped.
This "precise" irrigation management still requires very close attention by the irrigation manager.
For a given reason , the irrigation was ceased on day 5 and it was resumed late in day 6.
As a result, soil water storage decreased below the safe irrigation
 zone, and if the water shortage was prolonged, the plants could become water-stressed.
Installation and Placing of Soil Moisture Sensor Devices
 The use of soil moisture monitoring devices  has potential to save irrigation water in a given vegetable area by reducing the number of unnecessary irrigation events.
However, the effectiveness of these sensors depends on proper installation in representative locations within vegetable fields.
These sensors may be used to monitor water table levels in seepage irrigation.
Sensors should be installed in the root zone of the plants to be irrigated.
Most of the vegetable crops have 80% to 90% of the root zone in the upper 12 inches, which generally is the soil layer with higher water depletion by evapotranspiration.
For vegetable crops cultivated in rows and irrigated by drip tapes, the sensors should be installed 2-3 inches away from the plant row.
For single-row crops , the sensor should be placed on the opposite side from the drip tape; for double-row crops , the sensors should be placed in between the drip tape and plant rows.
Sensors need to be in good contact with the soil after installation; there should be no air gaps surrounding the sensor.
Soil should be packed firmly but not excessively around the sensor.
Alternatively, sensors can be installed in a slurry of wetted soil that was removed for the sensor install.
Using a slurry, the consistency of cake batter, can also provide the user with an initial calibration of the sensor for the determination of field capacity seen in Figure 1.
In plasticulture, after the installation, the area above the sensor should be re-covered with plastic and sealed with tape.
Soil Moisture Sensor Data Interpretation
 Crop Water Requirement 
 Crop water requirements depend on crop type, stage of growth, and evaporative demand.
Evaporative demand is termed evapotranspiration  and may be estimated using historical or current weather data.
Generally, reference evapotranspiration  is determined for use as a base level.
By definition, ETo represents the water use from a uniform green cover surface that is actively growing and well-watered.
Crop water use  is related to ETo by a crop coefficient , which is the ratio of ETc to the reference value ETo.
Because different methods exist for estimating ETo, it is very important to use Kc coefficients that were derived using the same ETo estimation method as will be used to determine the crop water requirements.
Also, Kc values for the appropriate stage of growth (Tables 5 and 6;
 Figure 3) and production system  must be used.
With drip irrigation where the wetted area is limited and plastic mulch is often used, Kc values are lower to reflect changes in row spacing and mulch use.
Plastic mulches substantially reduce evaporation of water from the soil surface.
Associated with the reduction of evaporation is a general increase in transpiration.
Even though the transpiration rates under mulch may increase by an average of 10%-30% over the season as compared to no-mulch systems, overall water-use values decrease by an average of 10%-30% due to the reduction in soil evaporation.
ETo may be estimated from atmometers  by using an adjustment factor.
During days without rainfall, ETo may be estimated from evaporation from an ET gauge  as ETo = Ea/0.89.
On rainy days  ETo = Ea/0.84.
Most, but not all, of the groundwater supplying the part-rust pivots also sat below the threshold with an average of 4.5 mg/L.
The pivots classified as no-rust had a wider range of classifications averaging 7.8 mg/L and reaching levels as high as 44 mg/L.
Statistical analysis confirmed a clear difference; however, it was noted that larger sample sizes could further support the teams conclusion.
Controlled Water Table Irrigation of Container Crops
 Jack Buxton, Janet Pfeiffer, and Darrell Slone, Horticulture
 The controlled water table irrigation system  can be used to automatically irrigate bedding plants, poinsettias, pot chrysanthemum, vegetable transplants, tomatoes in large containers and many other crops.
It has several advantages over existing irrigation systems.
Optimum moisture and air content are maintained in container growing media.
Differences in greenhouse environmental conditions will not affect the moisture content in individual containers even though the transpiration and evaporation rate is higher in one area on the bench than another.
Water stress is reduced and growth rate and quality of plants potentially increase compared to other container irrigation methods.
No runoff occurs; the nutrient solution is held within the capillary mat under a constant tension; water is lost only through transpiration and evaporation.
Because water and nutrients are always moving upward into the growing medium, very little, if any, solution moves from the growing medium in one container to the growing medium in another, thus reducing potential for disease transfer.
No pumps or large water holding tanks are needed as with ebb-and-flow irrigation systems.
The CWT irrigation system is easily retrofitted to most existing benches and is adaptable to greenhouse vegetable and flower transplant production, as well as the production of crops in 10-cm, 15-cm, and larger containers.
Figure 1.
The CWT is used to produce a wide variety of commercial greenhouse crops, including poinsettias and bedding plants.
The CWT is a modification of traditional capillary mat irrigation.
A capillary mat is placed on a smooth, level surface.
One side  of the capillary mat is suspended in a trough of water maintained at a constant level  at or below the bench surface.
The capillary mat draws water by capillarity, from the trough upward and then horizontally across the level bench.
A root barrier on top of the capillary mat prevents roots from growing into the mat but allows water movement to the container growing medium.
The growing medium, by capillarity, absorbs water from the mat.
Figure 2.
Basic principles of a controlled water table irrigation system.
The amount of water drawn into and maintained in the growing medium depends upon how tightly the water is held by the capillary mat and the physical properties of the growing medium.
The water and air content in the growing medium remain constant if the vertical distance between the container bottom and water table does not change.
As the distance between the water table and the container bottom increases:
 Water in the capillary mat decreases.
Water moves slower within the capillary mat.
Water content in the growing medium decreases.
Air content in the growing medium increases.
Water is under more tension in the growing medium, decreasing the plant root's ability to remove water.
The opposite occurs if the distance between the water table and container bottom decreases.
Water, removed from the growing medium through root absorption and evaporation, is replaced by water from the capillary mat, which is replaced by water from the trough; the trough is then immediately automatically resupplied with water.
Plants regulate the amount of water used.
The capillary forces, on water in the mat and growing medium, maintain an unbroken chain of water from the trough to the roots.
If the chain of water is not broken, water and air at optimum concentrations are continuously available to the roots.
the growing medium has no effect on placement of water table.
For example, a fine-textured growing medium  is capable of drawing water to a greater height above the water table and at equilibrium contains more water and less air in the pore space.
Because of these characteristics, the optimum placement of the water table for a fine-textured medium would be farther below the container bottom than it would be for a coarse-textured medium.
For best plant growth, the optimum distance between the water table and the bench surface is directly related to the growing medium's physical characteristics, the stage of plant development, and the depth of the growing medium.
The volume of
 Bench and Trough Construction
 CWT construction consists of several individual assemblies.
On the following pages, each part of the construction is illustrated.
Parts are generally available from hardware or electrical supply stores.
For parts not readily available from these stores, suggestions are provided about where they may be purchased.
Many existing greenhouse benches may be retrofitted with CWT.
A commercially available aluminum bench   was modified.
Support bars were spaced 1 foot apart and the original expanded metal top was replaced with a 3/4-inch thick Styrofoam sheet to create a smooth surface for the capillary mat.
The bench was leveled with a transit.
Theoretically, the bench could be 100 feet in length or longer, but because of the difficulty of leveling over this distance, shorter distances may be more practical.
A metal pipe  with a slot cut along the side  is welded to the aluminum trough to install the liquid level controller.
A 11/2-inch PVC cap is screwed onto the bottom of the threaded pipe, and a 11/2-inch PVC cap with 5/s-inch hole drilled in the center  is placed over the top of the
 The trough is constructed from a header terminator used in greenhouse construction .
A vertical 3/4-inch piece of the header terminator was removed.
The trough is 5/8 inch wide and 21/4 inches deep.
The 21/-inch-deep trough will usually provide the range in depth required for most container production.
However, a deeper trough may be needed for some crops.
pipe.
A rectangular aluminum piece  is welded to the opposite end to seal the trough.
The metal trough can be installed along the side or in the middle of the bench.
If the trough is placed in the middle of the bench, the water then moves only half the distance as from a trough on the side of the bench.
The metal trough fits tightly to the side of the bench; the horizontal 1-inch flange fits over the edge of the bench.
The trough is attached to the bench with 3-inch bolts, 3 to 4 feet apart, that run through the flange into the side railing of the bench.
A 6 millimeter polyethylene sheet is placed on top of the Styrofoam to prevent water leaks from the capillary mat into the Styrofoam and between Styrofoam sheets.
The capillary mat is placed on the polyethylene sheet.
A root barrier  was then placed on top of the capillary mat  to prevent roots from growing into the mat.
Water Level Control Assembly
 Figure 4 shows the water level control assembly.
Figures 5-10 describe the construction of separate parts of the assembly:
 Water level controller 
 Solenoid modification 
 Electrical connections 
 Water supply to trough 
 Figure 4.
Individual assemblies of CWT construction.
The water level control assembly  maintains a constant water level in the trough by opening and closing the solenoid valve.
A liquid level switch, with polypropylene float  , attaches to the polypropylene tube .
One end of the tube is threaded and a 3/s-inch-long brass connector  usually used for lamp repair connects the tube to the water level switch.
The wires from the liquid level switch are pulled through the tube.
A connector  is inserted through the hole drilled in the PVC cap.
The polypropylene tube is inserted through the connector.
The top nut on the connector, when tightened, secures the float valve at a fixed level in the pipe.
The control is inserted vertically into the 17/-s-inch aluminum pipe SO the float valve is suspended in water in the pipe.
The liquid level control is moved up and down and the connector tightened to adjust the water in the trough.
Figure 5.
Water level control.
The solenoid  is modified with bushing adapters and a brass barb connector  to reduce the opening size for attachment to 1/4-inch tubing.
Although 1/4-inch polyethylene tubing was suitable for our studies, larger tubing may be needed in some production systems to increase rate of water flow.
The solenoid is attached to a bench leg  with a 11/4-inch pipe clamp.
The clamp is attached to the metal leg with a metal screw.
C.
Solenoid attached to bench leg
 Figure 6.
Modification and attachment of solenoid to bench.
Figure 7 shows the electrical connection between the transformer, solenoid, and water level controller.
To insure safety in a wet environment use only a 24-volt electrical supply.
The electrical power is provided through the transformer.
One transformer can be used for each solenoid, or a large transformer may be used for many solenoids.
A metal oxide varistor is required to prevent excess current from destroying the electrical coil in the solenoid.
One wire of the resistor is connected to each of the liquid level controller wires.
A wire nut is used to connect wiring between the solenoid, the 24-volt electrical supply, and the liquid level controller.
Figure 7.
Electrical components.
Trough and Water Connections
 Figure 8 shows the distribution of water from the water supply line  through the solenoid to the trough.
A brass connector  is inserted into the punched hole in the polyethylene water line under the bench.
A 1/4-inch polyethylene tube connects the brass connector to the solenoid.
A second 1/4-inch polyethylene tube distributes the water from the solenoid to the trough.
Figure 8.
Water supply assembly.
Figure 9 shows the construction of water distribution tubing to maintain a uniform water level the length of the bench.
A 2-inch section of mini-soaker hose  1/4 inch in diameter is connected by a 1/4-inch barbed tubing coupling  to a 1/4-inch polyethylene tube every foot for the length of the trough.
The end of the tube is sealed with a plug.
The tube is placed at bottom of the trough.
Without the small sections of soaker hose, constant water level cannot be maintained for the length of the trough.
Figure 9.
Distribution of water in trough.
Observation of Trough Water Level
 To accurately determine the water level in the trough, the following device is constructed.
The syringe  and sewing gauge  are attached to a metal plate, and the plate is secured with a metal screw to the side railing on the bench.
The top of the ruler  is placed at bench level.
The gauge measures the water level in the trough.
The assembly should be located as near the tee end of the trough as possible.
A hole is drilled into the trough bottom and tapped with reamer  for a barbed brass connector .
A 1/4-inch polyethylene tube connects the barb to the syringe.
Because the solution in the syringe is exposed to sunlight, algae will grow and affect observation.
The tube must be flushed out or scrubbed with a small brush periodically, or a black plastic tube placed over the syringe will block sunlight and the algae growth.
Figure 10.
Device to determine water level in trough.
Fertilizer Injector Assembly for CWT
 Fertilizer can be added to the water supply, but the standard injector installation usually must be modified.
Replenishing the water level each time the liquid level controller detects a drop in water level in the trough requires a relatively small quantity of water.
The amount of water is determined by the sensitivity of the liquid level controller and the surface area of the water table.
Under low water flow rate the fertilizer injector may not provide the correct ratio between the concentrated fertilizer solution and water, SO a ballast  must be installed for storage of nutrient solution prior to distribution to the bench.
The pressure switch  opens the solenoid valve when the pressure in the ballast drops to set pressure; the solenoid remains open until the pressure in the ballast reaches the higher set pressure.
The amount of water to fill the ballast creates a higher water flow rate SO the injector works properly.
The pressure switch , injector , and solenoid valve  should be located close together along the water line, but far enough apart to allow easy access to individual parts.
To insure watertight connections, a 1/2-inch Carflex conduit system with fittings is used for the electrical wiring.
Figure 11.
Fertilizer injector modification and assembly.
Alternative Methods for Controlling Water Table
 In some production locations a mechanical  float valve to control the water level may be convenient  in place of the electrical system described previously.
The Water Boy consists of a small float valve inserted in a stainless steel cylinder.
Because the water flow rate is not as great as for the electric system, it is more suitable for smaller areas.
In the future the company may sell a larger valve.
The water is supplied to the Water Boy as described in Figure 8d.
The water inlet and outlet on the float valave are modified with brass fittings.
The 3/15-inch tube from the water supply line  attaches to the brass ell and connector  at top of the float valve.
The brass tee attaches via 3/8-inch nipple to the bottom outlet of the float valve.
A brass connector  attaches to the bottom of the trough.
A 3/8-inch od tube connects the water outlet on the float valve to the bottom of the bench.
The other side attaches to a brass ell and barb.
The syringe, for observing water level in the trough, is connected to the barbed end with a short piece of 1/4-inch tubing.
The Water Boy is attached to the side of the bench with a pipe clamp.
The Water Boy is moved up or down to adjust the water level in the trough.
Figure 12.
Alternative methods for controlling water table.
if necessary.
Once the equilibrium is reached, the water table will remain at this level for the duration of the production cycle or until changes are made in the water table's placement.
distance between the water surface and container bottom can affect crop growth.
The optimum vertical distance will vary depending upon the growing medium, texture, depth of growing medium, and plant size.
The optimum distance between the water table and container bottom must be evaluated for each combination of growing medium texture, depth of growing medium, and plant development stage.
In studies, many crops were grown in several growing medium textures and depths ranging from 1-inchtall plug trays to 1+-gallon containers.
In one study with plugs, the placement of the water table for seed germination was 1/2 to 1 inch below the container bottom to ensure that sufficient water reached the seed.
However, after seed germination the water table was dropped to 1 to 11/2 inches below the bench to prevent excess water in the growing medium and to provide adequate air supply to the roots.
Studies show that the water table should be placed 3/4 to 11/2 inches below the bench for plants grown in 5to 6-inch containers.
The greater the depth of growing medium, the less critical is the placement of the water table.
The roots grow within a range of depth where water and air are optimum for root growth.
These results should be used only as a starting point.
The bench must be level for successful production of uniform plants.
Plants will not grow as well if a portion of the bench surface is significantly below or above the optimum vertical distance between the water surface and container bottom for a particular growing medium or container height.
A root barrier prevents roots from penetrating the mat.
Note that the black color of some material may absorb much solar radiation and become extremely hot during sunny weather.
Covering areas not occupied with pots or flats with white plastic or other material will reduce temperature, evaporation, and the buildup of soluble salts.
Water evaporates from the edge of the capillary mat as well as between containers, leaving behind salts that accumulate over time.
Cover exposed edges with plastic to reduce evaporation.
Adjust normal fertilizer regime.
The fertilizer concentration for bottom irrigation must be lower than for overhead irrigation systems.
Use a minimum of fertilizer.
For example, use 50 to 100 ppm N from a complete fertilizer such as Peter's 20-19-20 Peat-lite formulation.
Roots growing out of the bottom of pots could be a problem.
Reduce external root growth by adjustment of the water table and other modifications.
Providing an optimum amount of water may cause some plants to be too succulent for the market, or they may be stressed when moved into less optimum growing environments.
Lowering the water table will increase water stress resulting in less succulent growth.
Attention to detail of construction and management of the CWT is essential.
The following points will help ensure success.
The horizontal distance from the trough should preferably be 3 to 4 feet, but not greater than 6 feet.
Studies show the greater distance may affect the nutrient content of solution for plants farthest from trough and the amount of solution available to these plants under high evapotranspiration conditions.
Pre-wetting of the capillary mat is essential for some brands of capillary mats.
If not pre-wet they may never absorb water.
Once wet they will remain wet if in contact with a source of water.
A surfactant added to the water will initially help in wetting the mat.
Container bottoms must be flat SO the growing medium is in physical contact with the root barrier to achieve continuous capillarity between the mat and the growing medium.
Containers with multiple holes in the bottom insure medium/mat contact.
Containers with small "feet" on bottom are not satisfactory.
Larger particles in a growing medium may prevent contact between the growing medium and the mat.
A small strip of capillary mat  can be inserted into the growing medium.
The other end, hanging out of the pot, will then be in contact with the mat.
The water will move upward from the mat through the strip into the growing medium.
Accurate control of water table  is important.
Slight changes in the vertical
 After sowing seed or transplanting, place containers on the previously wet capillary mat and manually water the growing medium from above to reach container capacity.
This initial irrigation will establish contact between the capillary mat/root barrier and the growing medium.
Check drainage holes after initial overhead irrigation to be sure the growing medium is making contact with the capillary mat.
Next, adjust the water table in the trough to the optimum distance below container bottom.
Continue to check the water level over the next few days and adjust the water table as needed to obtain the desired distance between the water table and container bottom.
Remove excess water from the trough
 Parts list and where to purchase for CWT irrigation.
Item	Components	Unit	Needed	Available At
 Bench	Bench: end, side, supports, legs	25' x 6'	1	Rough Bros.*
 Trough, mat, etc.
Root barrier 	sqft	150	Hardware store or fabric
 Capillary mat	sqft	150	Greenhouse supply
 Black plastic 	sqft	150	Hardware store
 Styrofoam 	sqft	150	Hardware store
 Metal trough	ft	25	Rough Bros.*
 Aluminum pipe 1 7/8 in od)	ft	1	Hardware store
 Water level control	Liquid level switch	each	1	Industrial supply
 Polystyreen tube 	ft	0.5	Hardware store
 Brass connector 	each	1	Hardware store
 PVC cap  	each	1	Hardware store
 Connector 	each	1	Hardware store
 Solenoid valve	Solenoid valve	each	1	Hardware store
 Adapter 	each	2	Hardware store
 Barb 	each	2	Hardware store
 Pipe clamp	each	1	Hardware store
 Electrical connections	Varistor 	each	1	Electrical supply
 Wire nut	each	2	Hardware store
 Transformer 	each	1	Hardware store
 Electric wire	ft	50	Hardware store
 Water supply and distribution system	Brass barb 	each	1	Hardware store
 Barb coupling 	each	25	Hardware store
 Poly tubing 	ft	14	Hardware store
 soaker hose in ft 	ft	4	Hardware store
 Brass insert 	each	1	Hardware store
 Polyethylene pipe 	ft	25	Hardware store
 Water level detection	Brass holder syringe	each	1	Hardware store
 Syringe	each	1	Drug store
 Small ruler 	each	1	Hardware store
 Barb connector 	each	2	Hardware store
 Fertilizer Injector	Injector	1	Greenhouse Supply
 Parts list and where to purchase for CWT irrigation.
Item	Components	Unit	Needed	Available At
 Fertigation modifications	Pressure gauge	each	1	Hardware store
 Pressure switch	each	1	Hardware store
 Electric conduit assembly	each	1	Hardware store
 Ballast 	each	1	Hardware store
 Solenoid valve	each	1	Hardware store
 Mechanic Level Control	Water Boy	each	1	Maid-O Mist**
 Pipe clamp	each	1	Hardware store
 Syringe	each	1	Drug store
 Brass fitting barb end (1/2 in, 3/16 in	each	3	Hardware store
 Brass fitting tee mxfxf 	each	1	Hardware store
 Brass fitting ell fxf 	each	2	Hardware store
 Large transformer	For multiple benches/zones	each	1	Electrical supply
 * Rough Bros., Cincinnatti, OH **Maid-O Mist, Chicago, IL 60641
 Estimated cost for a CWT irrigation system
 Modifying existing 25 ft X 6 ft bench
 Trough, mat, etc.
$255
 Water level control assembly	$22
 Solenoid valve assembly	$30
 Water supply and distribution in trough	$12
 Water level detection assembly	$7
 Cost Per sq ft	$2.40
 Converting injector for CWT irrigation	$100
 6' wide X 25' long bench	$450
 Mention or display of a trademark, proprietary product, or firm in text or figures does not constitute an endorsement and does not imply approval to the exclusion of other suitable products or firms.
The 2023 Yonts Water Conference was April 12 at the Panhandle Research, Extension and Education Center in Scottsbluff.
The conference, named in honor of Dean Yonts, was the irrigation specialist at the center for many years.
An atmometer, such as the ETgage, is what you need to calculate reference ET.
ET stands for evapotranspiration.
This is the amount of water evaporated from the soil and plant surface and transpired through the plant.
The following is a brief summary of the irrigation decisions made in each competition this year.
Sprinkler Corn: The pivot was first initiated on June 9 by two teams, and like the SDI system, the pivot ran at every irrigation opportunity.
Due to rainfall received, irrigation was cancelled three times in July.
Farms 7 and 12 requested the first irrigation, and Farms 2, 12, 15, 17, 22, 24, 26, 27, 28 and 31 finished out the season with irrigation requests on the final day.
Except for the control  and one other UNL test plot , the total irrigation applied among the corn teams ranged from 0.63  to 22.24 inches , with an average of 9.75 inches.
This average is higher than the 2020 and 2021 averages of just over seven inches.
REDUCING THE COST OF PUMPING IRRIGATION WATER
 Energy Use in Irrigation
 Irrigation accounts for a large portion of the energy used in Nebraska agriculture.
Analysis of data from the 2003 USDA Farm and Ranch Irrigation Survey shows that the average energy use for irrigating crops in Nebraska was equivalent to about 300 million gallons of diesel fuel annually.
A number of irrigation wells have been installed since 2003, thus energy use today is even higher.
While use varies depending on annual precipitation, average yearly energy consumption is equivalent to about 40 gallons of diesel fuel per acre irrigated.
The cost to irrigate a field is determined by the amount of water pumped and the cost to apply a unit  of water.
Factors that determine pumping costs include those that are fixed for a given location  and those that producers can influence.
The four factors that producers can influence include: irrigation scheduling, application efficiency, efficiency of the pumping plant, and for center pivots the pumping pressure required for the system.
Pumping costs can be minimized by concentrating on these factors.
Figure 1.
Diagram of factors affecting irrigation pumping costs
 Irrigation scheduling can minimize the total volume of water applied to the field.
Demonstration projects in central Nebraska have indicated that 1.5-2.0 inches of water can be saved by monitoring soil water content and estimating crop water use rates.
The general idea is to maximize use of stored soil water and precipitation to minimize pumping.
Maximizing the efficiency of water application is a second way to conserve energy.
Water application efficiency is a comparison between the depth of water pumped and the depth stored in the soil where it is available to the crop.
Irrigation systems can lose water to evaporation in the air or directly off plant foliage.
Water is also lost at the soil surface as evaporation or runoff.
Excess irrigation and/or rainfall may also percolate through the crop root zone leading to deep percolation.
For center pivots, water application efficiency is based largely on the sprinkler package.
High pressure impact sprinklers direct water upward into the air and thus there is more opportunity for wind drift and in-air evaporation.
In addition, high pressure impact sprinklers apply water to foliage for 20-40 minutes longer than low pressure spray heads mounted on drop tubes.
The difference in application time results in less evaporation directly from the foliage for low pressure spray systems.
Caution should be used so that surface runoff does not result with a sprinkler package.
Good irrigation scheduling should minimize deep percolation.
Energy use can also be reduced by lowering the operating pressure of the irrigation system.
One must keep in mind that lowering the operating pressure will reduce pumping cost per acre-inch, but reducing the pressure almost always results in an increased water application rate for a center pivot.
The key is to ensure that the operating pressure is sufficient to eliminate the potential for surface runoff.
Field soil characteristics, surface roughness, slope and tillage combine to control how fast water can be applied to the soil surface before surface runoff occurs.
If water moves from the point of application, the savings in energy resulting from a reduction in operating pressure can be eliminated by the need to pump more water to ensure that all portions of the field receive at least the desired amount of water.
Finally, energy can be conserved by ensuring that the pumping plant is operating as efficiently as possible.
Efficient pumping plants require properly matched pumps, systems and power sources.
By keeping good records of the amount of water pumped and the energy used, you can calculate if extra money is being spent on pumping water and how much you can afford to spend to fix components that are responsible for increased costs.
This document describes a method to estimate the cost of pumping water and to compare the amount of energy used to that for a well maintained and designed pumping plant.
The results can help determine the feasibility of repairing the pumping plant.
The cost to pump irrigation water depends on the type of energy used to power the pumping unit.
Electricity and diesel fuel are used to power irrigation for about 75% of the land irrigated in Nebraska.
Propane and natural gas are used on about 8 and 17% of the land respectively.
Very little land is irrigated with gasoline powered engines.
The cost to pump an acre-inch of water depends on:
 The amount of work that can be expected from a unit of energy.
The distance water is lifted from the groundwater aquifer or surface water.
The discharge pressure at the pump,
 The efficiency of the pumping plant, and
 The cost of a unit of energy.
Figure 2.
Percent of land irrigated in Nebraska by type of energy source.
The amount of work produced per unit of energy depends on the source used to power the pump.
For example one gallon of diesel fuel provides about 139,000 BTUs while propane provides about 95,500 BTUs/gallon.
Clearly, more propane would be required to pump an acreinch of water even if diesel and propane engines were equally efficient.
The Nebraska Pumping Plant Performance Criteria was developed to provide an estimate of the amount of work that can be obtained from a unit of energy by a well designed and managed pumping plant.
Values were developed from testing engines and motors to determine how much work (expressed as
 water horsepower hours) could be expected from a unit of energy for pumping plants that were well designed and maintained.
The values reflect the amount of energy available per unit and how efficiently engines, motors and pumps operate.
Table 1.
Amount of work produced per unit of energy used for a well designed and maintained pumping plant.
Source	Value	Work Per Unit of Energy
 Diesel	12.5	whp-hours / gallon
 Gasoline	8.66	whp-hours / gallon
 Propane	6.89	whp-hours / gallon
 Natural Gas	61.7	whp-hours / 1000 ft 3
 Electricity	0.885	whp-hours / kilowatt hour
 whp stands for water horsepower
 Figure 3.
Diagram of pumping lift and discharge pressure measurements needed to assess pumping plant efficiency.
The discharge pressure depends on the pressure needed for the irrigation system, the elevation of the inlet to the irrigation system relative to the pump discharge, and the pressure loss due to friction in the piping between the pump and the irrigation system.
It is best to measure the discharge pressure with a good gage near the pump base.
The amount of energy required for a properly designed and maintained pumping plant to pump an acre-inch of water can be determined from Tables 2 and 3.
For example, a producer who has a system with a pumping lift of 150 feet and
 Table 2.
Gallons of diesel fuel required to pump an acre-inch at a pump performance rating of 100%.
Lift	Pressure at Pump Discharge, psi
 feet	10	20	30	40	50	60	80
 0	0.21	0.42	0.63	0.84	1.05	1.26	1.69
 25	0.44	0.65	0.86	1.07	1.28	1.49	1.91
 50	0.67	0.88	1.09	1.30	1.51	1.72	2.14
 75	0.89	1.11	1.32	1.53	1.74	1.95	2.37
 100	1.12	1.33	1.54	1.75	1.97	2.18	2.60
 125	1.35	1.56	1.77	1.98	2.19	2.40	2.83
 150	1.58	1.79	2.00	2.21	2.42	2.63	3.05
 200	2.03	2.25	2.46	2.67	2.88	3.09	3.51
 250	2.49	2.70	2.91	3.12	3.33	3.54	3.97
 300	2.95	3.16	3.37	3.58	3.79	4.00	4.42
 350	3.40	3.61	3.82	4.03	4.25	4.46	4.88
 400	3.86	4.07	4.28	4.49	4.70	4.91	5.33
 Table 3.
Conversions for other energy sources.
Energy Source	Units	Multiplier
 Natural Gas	1000 cubic feet	0.2026
 Table 4.
Multiplier when pumping plant
 performance rating is less than 100%.
Rating, %	100	90	80	70	50	30
 Multiplier	1.00	1.11	1.25	1.43	2.00	3.33
 operates at a pump discharge pressure of 60 pounds per square inch  would require 2.63 gallons of diesel fuel to apply an acre-inch of water.
If the producer uses electricity the value of 2.63 should be multiplied by the factor in Table 3 to convert energy units.
So,  = 37 kilowatthours would be needed per acre inch of water.
The amount of energy required for an actual pump depends on the efficiency of the pump and power unit.
If the pumping plant is not properly maintained and operated, or if conditions have changed since the system was installed, the pumping plant may not operate as efficiently as listed in Table 2.
The energy needed for an actual system is accounted for in the performance rating of the pumping plant.
Table 4 can be used to determine the impact of a performance rating less than 100%.
For a performance rating of 80% the multiplier is 1.25, so the amount of energy used would be 25% more than for a system operating as shown in Table 2.
The amount of diesel fuel for the previous example would be  = 3.29 gallons per acreinch of water.
Producers can use Tables 2-4 and their energy records to estimate the performance rating of the pumping plant and the amount of energy that could be saved if the pumping plant was repaired or if operation was adjusted to better match characteristics of the pump and power unit.
Producers can also use hourly performance to estimate how well their pumping plant is working.
For the hourly assessment an estimate of the pumping lift, discharge pressure, flow rate from the well and the hourly rate of energy consumption are required.
The acre-inches of water pumped per hour can be determined from in Table 5.
Table 5.
Volume of water pumped per hour.
Pump	per hour,	Pump	per hour,
 Discharge,	acre-	Discharge,	acre-
 gpm	inch/hr	gpm	inch/hr
 250	0.55	1250	2.76
 300	0.66	1300	2.87
 350	0.77	1350	2.98
 400	0.88	1400	3.09
 450	0.99	1500	3.31
 500	1.10	1600	3.54
 550	1.22	1700	3.76
 600	1.33	1800	3.98
 650	1.44	1900	4.20
 700	1.55	2000	4.42
 750	1.66	2100	4.64
 800	1.77	2200	4.86
 850	1.88	2400	5.30
 900	1.99	2600	5.75
 950	2.10	2800	6.19
 1000	2.21	3000	6.63
 1050	2.32	3200	7.07
 1100	2.43	3400	7.51
 1150	2.54	3600	7.96
 1200	2.65	3800	8.40
 100 Value from Table 2 100 x 2.63 R = Pp
 The performance of the pumping plant  in terms of energy use per acre-inch of water is then the ratio of the amount of energy used per hour divided by the volume of water pumped per hour:
 For this case the performance rating is 85 meaning that the system uses about 17% more diesel fuel than required for a system at the Nebraska Criteria.
The
 fueluserate  Pp= V, W 
 For example, suppose a pump supplies 800 gallons per minute and the diesel engine burns 5.5 gallons of diesel fuel per hour.
A flow rate of 800 gpm is equivalent to 1.77 acre-inches per hour.
The pumping plant performance is computed as 5.5 gallons of diesel per hour divided by 1.77 acreinches of water per hour.
This gives a performance of 3.11 gallons of diesel per acre-inch.
Suppose that the pumping lift is 150 feet and the discharge pressure is 60 psi.
If the system operates at the Nebraska Pumping Plant Performance Criteria only 2.63 gallons of diesel per acre-inch would be required.
The pumping plant performance rating  would be:
 multipliers in Table 2 can also be used with the hourly method for other energy sources.
Energy savings from repairing the pumping plant should be compared to the ability to pay for the repairs.
The money that can be paid for repairs is determined by the length of the repayment period and the annual interest rate.
These values are used to compute the series present worth factor.
The
 Table 6.
Series Present Worth Factor
 6%	7%	8%	9%	10%	12%
 3	2.67	2.62	2.58	2.53	2.49	2.40
 4	3.47	3.39	3.31	3.24	3.17	3.04
 5	4.21	4.10	3.99	3.89	3.79	3.60
 6	4.92	4.77	4.62	4.49	4.36	4.11
 7	5.58	5.39	5.21	5.03	4.87	4.56
 8	6.21	5.97	5.75	5.53	5.33	4.97
 9	6.80	6.52	6.25	6.00	5.76	5.33
 10	7.36	7.02	6.71	6.42	6.14	5.65
 12	8.38	7.94	7.54	7.16	6.81	6.19
 15	9.71	9.11	8.56	8.06	7.61	6.81
 20	11.47	10.59	9.82	9.13	8.51	7.47
 25	12.78	11.65	10.67	9.82	9.08	7.84
 breakeven investment that could be spent is the value of the annual energy savings times the series present worth factor.
The series present worth factor represents the amount of money that could be repaid at the specified interest rate over the repayment period.
For example, for an interest rate of 7% and a repayment period of 10 years each dollar of annual savings is equivalent to $7.02 today.
Only $4.10 could be invested for each dollar of savings if the investment was to be repaid in 5 years rather than 10 years.
Some examples will illustrate the procedure to estimate potential from improving a pumping plant.
Suppose a pivot was used on 130 acres to apply 13.5 inches of water.
The pumping lift was about 125 feet and the discharge pressure was 50 psi.
Energy use records for the past season show that 5500 gallons of diesel fuel were used.
The average price of diesel fuel for the season was $3.00 per gallon.
The analysis of this example is illustrated in the worksheet in Figure 4.
An efficient pumping plant would require about 3843 gallons of diesel fuel for the year.
If a
 producer's records show that 5500 gallons were used to pump the water, then the performance rating would be  X 100 = 70%.
This shows that 1657 gallons of diesel fuel could be saved if the pumping plant performance was improved.
The annual savings in pumping costs would be the product of the energy savings times the cost of diesel fuel; i.e., $3/gallon times 1657 gallons/year = $4971/year.
If a 5-year repayment period and 9% interest were used, the series present worth factor would be 3.89.
The breakeven repair cost would be $4971 X 3.89 = $19,337.
If repair costs were less than $19,337 then repairs would be feasible.
If costs were more than $19,337 the repairs may not be advisable at this time.
This example represents a center-pivot field irrigated with a pump powered by electricity.
Details of the system are also included in Figure 4.
In this case the pumping lift is 175 feet which is not listed in Table 2.
The lift of 175 feet is half way between 150 and 200 feet so the amount of diesel fuel per acre-inch of water is estimated as 2.44 gallons per acre-inch.
Since electricity is used to power the pumping plant the multiplier of 14.12 is used in row M of Figure 4.
The calculations for the second example are similar to the first example for the rest of the information in Figure 4.
This pumping plant has a performance rating of 88% and given the cost of electricity only about $3,770 could be spent for repairs.
This example illustrates the application of the hourly method for a propane powered pumping plant.
This system has a performance rating of 88% and based on Table 4 13% of the annual energy cost could be saved if the pumping plant was brought up to the Nebraska Criteria.
This publication demonstrates a method to estimate the potential for repairing pumping plants to perform at the Nebraska Pumping Plant Performance Criteria.
Producers frequently have several questions regarding the procedure.
First they want to know "Can actual pumping plants perform at a level equal to the Criteria".
Tests of 165 pumping plants in the 1980s indicated that up to 15% of the systems actually performed at a level above the Criteria.
So producers can certainly achieve the standard.
The second question is "What level of performance can producers expect for their systems?" Tests on 165 systems in Nebraska during the 1980s produced an average performance rating of 77% which translates to an average energy savings of 30% by improving performance.
Tests on 200 systems in North
 Dakota in 2000 produced very similar results.
These values illustrate that half of the systems in the Great Plains could be using much more energy than required.
The simplified method can help determine if your system is inefficient.
The third issue focuses on "What should I do if the simplified method suggests that there is room for improving the efficiency?" You should first determine if the irrigation system is being operated as intended.
You need to know if the pressure, lift and flow rate are appropriate for the irrigation system.
For example, some systems were initially designed for furrow irrigation systems and are now used for center-pivot systems.
If the conditions for the current system are not appropriate for the system you need to work with a well driller/pump supplier to evaluate the design of the system.
Sometimes the system is simply not operated properly.
An example occurred where a center-pivot sprinkler package was installed that used pressure regulators with a pressure rating of 25 psi.
However, the end gun on the pivot was not equipped with a booster pump so the main pump was operated at a pressure of 75 psi to pressurize the entire system just to meet the needs of the end gun.
Since end guns only operate about half of the time the pump was actually pumping against the pressure regulators half of the time, wasting a significant amount of energy.
The problem here was not the pump or the power unit but the sprinkler design and its operation.
We recommend that you periodically arrange with a well drilling company to test the efficiency of your pump.
They conduct a test that determines pumping lift, discharge pressure and the efficiency of the pump for a range of conditions that you would expect for your system.
They also use equipment to measure the power output of your engine or electric motor.
While they don't usually measure the energy consumption rate the results of the test will tell you if the pump is performing efficiently.
This provides an excellent reference for future analysis.
Hourly	Propane	Example	250	55	130	Propane	$1.80	3.44	1.814	700	1.55	9.65	11.0	88
 Annual	Electric	Example	175	40	128	13	65,000	Electric	$0.07	7	10	2.44	1664	4060	14.12	57,327	88	7673	$537	7.02	$3,770
 Annual	Diesel	Example	125	50	130	13.5	5500	Diesel	$3.00	9	5	2.19	1755	3843	1	3843	70	1657	$4,971	3.89	$19,337
 Figure Pumping Worksheet Cost 4.
Information Known 1.
lift, feet Pumping	Pressure discharge, psi at pump	field, Size irrigated of the acres	inches of irrigation applied, Depth	field of for irrigate used the the Amount to energy year	of Type used to water energy pump source	of $/kwh, of  energy a	Annual interest % rate,	period, Repayment years	Performance 2.
Annual	of fuel Gallons 2) standard Table diesel @  Volume pumped, of acre-inches: C water row X row	Gallons of K) Performance fuel diesel Rating needed 100%   100% used rating Energy at pump	 Performance rating pump	Potential  kWh, with gallons, savings repair, etc.: energy	$  savings, Annual cost	factor Series  worth present	R) , acre-inches/hour hour pumped water per	 if Performance Rating Energy hour 100% at use per	kWh/hr) feet/hr, 1000 cubic gallons/hour,  performance Pumping plant rating
 A	B	C	D	E	F	G	H	I	J	K	L	M	N	o	P	Q	R	S	T	U	V	W	X
Drilled Wells for Irrigation
 Drilled wells are a source of water for many greenhouse operations.
They provide clean water with very few impurities.
The yield is usually limited and as additional greenhouse space is built, an additional well may have to be drilled.
Groundwater is found in aquifers that are located below the earths crust.
As rainfall occurs, some of it evaporates, some of it is removed by plant transpiration and the remaining water filters down through the topsoil and overburden and flows into sand, gravel and fractured rock.
The upper level of groundwater is called the water table.
The height of this varies with the amount of rainfall and the formation of the aquifer zone.
Artesian wells  are formed when the aquifer uphill creates a water pressure that forces the water out of the top of the well.
Aquifers can take many forms
 A common type aquifer is the gravel deposits found along many rivers.
These hold large amounts of water and may be hundreds of feet deep.
As the water can move fairly rapidly, a gravel type aquifer can have a yield of 50 to 100 gallons per minute.
Another type of aquifer is formed from veins of sand or gravel.
The water flows through these from one area to another.
By tapping into a vein, a good supply of water can be had.
The problem comes in locating these below ground areas although sometimes the vein will intercept the soil surface and water flows out by gravity.
There are referred to as springs.
A third type of aquifer is in the fractured bedrock deeper below ground.
The water flow depends on the size of pores and cracks in the rock and is usually slower.
As most of the bedrock has cracks, almost anywhere you drill a well you will get some water although the yield may be much smaller.
The flow of water that can be obtained from a well depends on the permeability and size of the aquifer, its recharge area and the amount of rainfall.
To some extent, the diameter and depth of the well also influence yield.
In some areas of the country, a well may be 1000 feet deep and yield less than 1 gpm.
Depending on the type of aquifer, hitting water with a well is like the lottery.
A well in one location may provide a very low yield, whereas moving over 10 feet may intercept a good vein and give 30 gpm.
In most areas, well drillers keep an accurate record of the depth and yield of wells they drill.
In some states the Department of Health maintains this record that is available to well drillers.
There are two main methods of drilling a well.
The older method, cable-tool drilling, uses a drill bit attached to a cable that is continually raised and then dropped.
The drill breaks up the rock, water is added and then the debris is removed with a bailer.
This is a slow method but the advantage is that there is less chance of sealing up the pores and cracks.
Cable drilling is limited to several hundred feet deep.
In rotary drilling, a drill is attached to a hollow shaft that is rotated by an engine and transmission.
Drill mud is pumped down through the pipe and out through perforations in the drill.
The mud and ground up rock flows up through the bore hole and into a settling pit where the solids settle out.
Depending on the soil or rock being drilled, the drill is rotated at 30 to 150 revolutions per minute and is faster than cable drilling.
Rotary drilling can make a well that is several thousand feet deep.
Both drilling methods can be modified to use compressed air instead of water for lubrication and debris removal.
This reduces sealing of the pores.
An air hammer device can also be added to increase the drilling speed.
When drilling a well, a steel casing is commonly placed in the earth to the point where the well reaches the bedrock.
It is hammered into the bedrock to create a tight seal that keeps surface impurities, such as, clay, fine sand, fertilizer and pesticides out of the well.
The casing may also be grouted to get a good seal.
A typical well is 6in.
diameter but to get greater yield, a larger diameter is often drilled.
Hydrofracting is sometimes recommended to increase the flow in a low-yielding well.
In this process, the well is filled with water and a high pressure is built up.
This may open up some additional pores.
In most wells, there may be a slight increase in yield but it doesn't work in all wells.
The cost is usually $1500 to 2000.
Location of the well
 Local and state regulations need to be considered.
A permit may be needed.
There is usually a minimum distance from a septic system or sewer and may be a minimum distance to a property line.
Another consideration is access for the drill rig.
These are heavy pieces of equipment often weighing over 35 tons so solid ground is needed.
The location of trees and landscaping plants should also be considered.
Finally, try to pick a location where the trench for the pipe to the greenhouse can be conveniently placed.
Once the well is drilled and pumped to clean out the debris, yield, static water level and location are usually recorded and reported to the state agency.
Following local codes, the well should be disinfected with chlorine bleach.
After pumping and when there is no more odor of chlorine, a sample of the water should be taken and sent to a laboratory for quality testing.
Besides chloroform bacteria, tests should also be run for soluble salts, carbonate hardness, mineral content and pH, factors that affect plant growth.
Having values for these will help in adjusting fertilizer levels in irrigation water.
Some well drillers will contract to provide a well having a minimum yield.
They usually have extensive experience of drilling in the area and know the underground soil structure and typical yield.
Other drillers will quote on a per linear foot basis, a figure for the casing section and a lower cost for the portion of the well in bedrock where casing is not needed.
It is best to get quotes and references from more than one driller.
Drilled wells are a dependable water source for many greenhouse operations.
Getting an adequate yield to supply the needs can be a problem in some areas.
Conserving water through drip, ebb and flood and flooded floor irrigation can help to make the water supply go farther.
For alfalfa in the stage 3 crop growth stage the estimated water use during the previous week of May 29 June 4, 2023 is 1.07 inches and the estimated water use during the week of June 5-11, 2023 is 2.00 inches.
For alfalfa in the state 4 crop growth stage the estimated water use during the previous week of May 29 June 4, 2023 is 1.23 inches.
For alfalfa in the maturity crop growth stage the estimated water use during the previous week of May 29 June 4, 2023 is 1.31 inches.
The Nebraska Department of Environment Energy developed and implemented the rules and regulations necessary for irrigators to utilize the practice.
Under the NDEE rules, Nebraska's Natural Resources Districts were given the responsibility to manage the chemigation permit component that ensures that proper safety equipment is present and functioning properly.
Nitrates in Drinking Water
 Fact Sheet No.
0.517
 by J.R.
Self and R.M.
Waskom*
 Nitrate  is a naturally occurring form of nitrogen found in soil.
Nitrogen is essential to all life.
Most crop plants require large quantities to sustain high yields.
The formation of nitrates is an integral part of the nitrogen cycle in our environment.
In moderate amounts, nitrate is a harmless constituent of food and water.
Plants use nitrates from the soil to satisfy nutrient requirements and may accumulate nitrate in their leaves and stems.
Due to its high mobility, nitrate also can leach into groundwater.
If people or animals drink water high in nitrate, it may cause methemoglobinemia, an illness found especially in infants.
Nitrates form when microorganisms break down fertilizers, decaying plants, manures or other organic residues.
Usually plants take up these nitrates, but sometimes rain or irrigation water can leach them into groundwater.
Although nitrate occurs naturally in some groundwater, in most cases higher levels are thought to result from human activities.
Common sources of nitrate include:
 municipal wastewater and sludge,
 N-fixation from atmosphere by legumes, bacteria and lightning.
Health Effect of Nitrates
 High nitrate levels in water can cause methemoglobinemia or blue baby syndrome, a condition found especially in infants under six months.
The stomach acid of an infant is not as strong as in older children and adults.
This causes an increase in bacteria
 that can readily convert nitrate to nitrite.
Do not let infants drink water that exceeds 10 mg/INO-N.
This includes formula preparation.
Nitrite is absorbed in the blood, and hemoglobin  is converted to methemoglobin.
Methemoglobin does not carry oxygen efficiently.
This results in a reduced oxygen supply to vital tissues such as the brain.
Methemoglobin in infant blood cannot change back to hemoglobin, which normally occurs in adults.
Severe methemoglobinemia can result in brain damage and death.
Pregnant women, adults with reduced stomach acidity, and people deficient in the enzyme that changes methemoglobin back to normal hemoglobin are all susceptible to nitrite-induced methemoglobinemia.
The most obvious symptom of methemoglobinemia is a bluish color of the skin, particularly around the eyes and mouth.
Other symptoms include headache, dizziness, weakness or difficulty in breathing.
Take babies with the above symptoms to the hospital emergency room immediately.
If recognized in time, methemoglobinemia is treated easily with an injection of methylene blue.
Healthy adults can consume fairly large amounts of nitrate with few known health effects.
In fact, most of the nitrate we consume is from our diets, particularly from raw or cooked vegetables.
This nitrate is readily absorbed and excreted in the urine.
However, prolonged intake of high levels of nitrate are linked to gastric problems due to the formations of nitrosamines.
N-nitrosamine compounds have been shown to cause cancer in test animals.
Studies of people exposed to high levels of nitrate or nitrite have not provided convincing evidence of an increased risk of cancer.
Nitrate is a colorless, odorless, and tasteless compound that is present in some groundwater in Colorado.
Nitrate can be expressed as either NO, 3  or NO3-N.
Nitrate levels above the EPA Maximum Contaminant Level of 10mg/l NO N or 45 mg/l NO2 3 may cause methemoglobinemia in infants.
Proper management of fertilizers, manures, and other nitrogen sources can minimize contamination of drinking water supplies.
Although there is no enforceable drinking water standard for livestock, do not allow animals to drink water with more than mg/l This is especially true of young animals.
They are affected by nitrates the same way as human babies.
Older animals may tolerate higher levels.
Ruminant animals  are susceptible to nitrate poisoning because bacteria present in the rumen convert nitrate to nitrite.
Nonruminant animals  rapidly eliminate nitrate in their urine.
Horses are monogastric, but their large cecum acts much like a rumen.
This makes them more susceptible to nitrate poisoning than other monogastric animals.
It is difficult to determine the toxicity of nitrate in animals because it depends on the rate at which the substance is consumed.
A few hundred milligrams of nitrate may cause poisoning if consumed in a few hours.
But spread over a whole day, 1,000 mg nitrate may cause no signs of toxicity.
Common symptoms include abdominal pain, diarrhea, muscular weakness or poor coordination.
Affected animals will have blood that is a chocolate-brown color.
If the problem is diagnosed in time, they can fully recover with a treatment of methylene blue.
Pregnant animals may abort within a few days.
Nitrate also exists in animal feeds and fodder.
Drought-stressed forage plants commonly have high nitrate levels.
These feeds can have an additive effect when consumed with high nitrate drinking water.
The Drinking Water Standard
 Reports of methemoglobinemia are extremely rare.
Clinical infant methemoglobinemia was first recognized in 1945.
About 2,000 cases were reported in North America and Europe by 1971.
Fatality rates were reported to be approximately 7 to 8 percent.
From 1960 to 1972, however, only one death from blue baby syndrome was documented.
Methemoglobinemia has not been reported where water contains less than 10 mg/l of NO3-N This level has been adopted by the U.S.
Environmental Protection Agency as the standard in the Primary Drinking Water Regulations, chiefly to protect young infants.
Nitrate values are commonly reported as either nitrate  or as nitratenitrogen  The maximum contaminant level  in drinking water as nitrate  is 45 mg/l, whereas the MCL as NOis 10 mg/l.
The MCL is the highest level of NO or NO-1 that is allowable in public drinking water supplies by the U.S.
Environmental Protection Agency.
These figures also may be reported in ppm , which is equivalent to mg/l.
Be sure you know which value is reported for your water sample.
Protecting Your Drinking Water
 The 1990 EPA National Survey of Drinking Water Wells found that approximately 57 percent of the private wells tested contained detectable levels of nitrates.
However, only 2.4 percent exceeded the EPA maximum contaminant level.
In Colorado, nitrate contamination above the MCL occurs mainly in rural areas overlying vulnerable aquifers.
Protecting your drinking water supply from contamination is important for health and to protect property values and minimize potential liability.
High nitrate levels often are associated with poorly constructed or improperly located wells.
Locate new wells uphill and at least 100 feet away from feedlots, septic systems, barnyards and chemical storage facilities.
Properly seal or cap abandoned wells.
Manage nonpoint sources of water pollution  to limit the loss of excess water and plant nutrients.
Match fertilizer and irrigation applications to precise crop uptake needs in order to minimize groundwater contamination.
Best Management Practices for Fertilizer Use
 Careful fertilizer management can reduce nitrate leaching to groundwater.
Consider the following practices in planning your fertilizer program:
 Use soil and water analysis to determine exact nitrogen needs of crop.
Set a realistic yield goal for each field.
Take the five-year average production of your field and add 5 percent to get an attainable yield goal.
Credit all sources of nitrogen available to the crop, including manures, water, organic matter, legumes and residual subsoil nitrate.
Split nitrogen fertilizer into as many separate applications as feasible.
Nitrate is a tasteless, colorless and odorless compound that you cannot detect unless your water is chemically analyzed.
If you drink water from a private well, get a qualified laboratory to test it yearly.
The local health department or Colorado State University Extension county offices usually can supply the name of an approved testing laboratory in your area.
Sample water for nitrate testing at the well site or at a tap inside the house.
Place samples in clean, 4to 16-ounce plastic containers.
Send the sample to a laboratory immediately.
Refrigerating it will help keep it intact until it reaches a laboratory.
Do not freeze it.
Laboratory results will be compared to the MCL, and recommendations for treatment should be considered if nitrate levels exceed 10 Be aware that nitrate levels in groundwater may vary seasonally.
If your water tests high or borderline high, retest your water every three to six months.
Purification of Contaminated Water
 While it may be technically possible to treat contaminated groundwater, it can be difficult, expensive and not totally effective.
For this reason, prevention is the best way to ensure clean water.
Water treatments include distillation, reverse osmosis, ion exchange or blending.
Distillation boils the water, catches the resulting steam, and condenses the steam on a cold surface.
Nitrates and other minerals remain behind in the boiling tank.
Reverse osmosis forces water under pressure through a membrane that filters out minerals and nitrate.
Onehalf to two-thirds of the water remains behind the membrane as rejected water.
Higher-yield systems use water pressures of 150 psi.
Ion-exchange takes another substance, such as chloride, and trades places with nitrate.
An ion exchange unit is filled with special resin beads that are charged with chloride.
As water passes over the beads, the resin takes up nitrate in exchange for chloride.
As more water passes over the resin, all the chloride is exchanged for nitrate.
The resin is recharged by backwashing with sodium chloride solution.
The backwash solution, which is high in nitrate, must be properly disposed of.
Blending is another method to reduce nitrates in drinking water.
Mix contaminated water with clean water from another source to lower overall nitrate concentration.
Blended water is not safe for infants but is acceptable for livestock and healthy adults.
Charcoal filters and water softeners do not adequately remove nitrates from water.
Boiling nitrate-contaminated water does not make it safe to drink and actually increases the concentration of nitrates.
Drilling a new well to deeper water with less nitrate may be a feasible remedy in certain areas.
In many cases, the most effective alternative is to use bottled water for drinking and cooking.
Blue baby syndrome: A disease that affects the oxygen carrying capacity of infant's blood, usually resulting from the consumption of high levels of NO Also known as methemoglobinemia.
Contaminant: Any physical, chemical, biological or radiological substance that degrades water quality.
Groundwater: Water that saturates subsurface formations or aquifers.
Leaching: The downward movement of dissolved or suspended minerals, fertilizers, agricultural chemicals or other substances through the soil.
: The highest amount of a specific contaminant allowed by the EPA in public drinking water supplies.
These are healthbased standards that by law must be set as close to the "no-risk" level as feasible.
Nitrate : An important plant nutrient that is soluble in water and may cause health problems if consumed in large amounts.
Nitrate-nitrogen : Relates to the actual nitrogen in nitrate.
Multiply NOvalues by 4.4 to convert to nitrate.
Nonpoint source pollution: Water contamination from diffuse sources such as agricultural fields, urban runoff or large construction sites.
Parts per million : A unit of proportion used to describe the concentration of a chemical in water.
Equivalent to mg/l.
CONVENTIONAL, STRIP, AND NO TILLAGE CORN PRODUCTION UNDER DIFFERENT IRRIGATION CAPACITIES
 KSU Northwest Research-Extension Center 105 Experiment Farm Road, Colby, Kansas Voice: 785-462-6281 Fax: 785-462-2315
 Corn production was compared from 2004 to 2006 for three plant populations  under conventional, strip and no tillage systems for irrigation capacities limited to 1 inch every 4, 6 or 8 days.
Corn yield increased approximately 12% from the lowest to highest irrigation capacity in these three years of varying precipitation and near normal crop evapotranspiration.
Strip tillage and no tillage had 8.8% and 7% higher grain yields than conventional tillage, respectively.
Results suggest that strip tillage obtains the residue benefits of no tillage in reducing evaporation losses without the yield penalty sometimes occurring with high residue.
The small increases in total seasonal water use  for strip tillage and no-tillage compared to conventional tillage can probably be explained by the higher grain yields for these tillage systems.
Declining water supplies and reduced well capacities are forcing irrigators to look for ways to conserve and get the best utilization from their water.
Residue management techniques such as no tillage or conservation tillage have been proven to be very effective tools for dryland water conservation in the Great Plains.
However, adoption of these techniques is lagging for continuous irrigated corn.
There are many reasons given for this lack of adoption, but some of the major reasons expressed are difficulty handling the increased level of residue from irrigated production, cooler and wetter seedbeds in the early spring which may lead to poor or slower development of the crop, and ultimately a corn grain yield penalty as compared to conventional tillage systems.
Under very high production systems, even a reduction of a few percentage points in corn yield can have a significant economic impact.
Strip tillage might be a good compromise between conventional tillage and no tillage, possibly achieving most of the benefits in water conservation and soil quality management of no tillage, while providing a method of handling the increased residue and increased early growth similar to conventional tillage.
Strip tillage can retain surface residues
 and thus suppress soil evaporation and also provide subsurface tillage to help alleviate effects of restrictive soil layers on root growth and function.
A study was initiated in 2004 to examine the effect of three tillage systems for corn production under three different irrigation capacities.
Plant population was an additional factor examined because corn grain yield increases in recent years have been closely related to increased plant populations.
The study was conducted under a center pivot sprinkler at the KSU Northwest Research-Extension Center at Colby, Kansas during the years 2004 to 2006.
Corn was also grown on the field site in 2003 to establish residue levels for the three tillage treatments.
The deep Keith silt loam soil can supply about 17.5 inches of available soil water for an 8-foot soil profile.
The climate can be described as semi-arid with a summer precipitation pattern with an annual rainfall of approximately 19 inches.
Average precipitation is approximately 12 inches during the 120-day corn growing season.
A corn hybrid of approximately 110 day relative maturity  was planted in circular rows on May 8, 2004, April 27, 2005 and April 20, 2006, respectively.
Three seeding rates  were superimposed onto each tillage treatment in a complete randomized block design.
Irrigation was scheduled with a weather-based water budget, but was limited to the 3 treatment capacities of 1 inch every 4, 6, or 8 days.
This translates into typical seasonal irrigation amounts of 16-20, 12-15, 8-10 inches, respectively.
Each of the irrigation capacities  were replicated three times in pieshaped sectors  of the center pivot sprinkler.
Plot length varied from to 90 to 175 ft, depending on the radius of the subplot from the center pivot point.
Irrigation application rates  at the outside edge of this research center pivot were similar to application rates near the end of full size systems.
A small amount of preseason irrigation was conducted to bring the soil water profile  to approximately 50% of field capacity in the fall and as necessary in the spring to bring the soil water profile to approximately 75% in the top 3 ft prior to planting.
It should be recognized that preseason irrigation is not a recommended practice for fully irrigated corn production, but did allow the three irrigation capacities to start the season with somewhat similar amounts of water in the profile.
The three tillage treatments  were replicated in a Latin-Square type arrangement in 60 ft widths at three different radii  from the center pivot point.
The various operations and their time period for the three tillage treatments are summarized in Table 1.
Planting was in the same row location each year for the Conventional Tillage treatment to the extent that good farming
 practices allowed.
The Strip Tillage and No-Tillage treatments were planted between corn rows from the previous year.
Tillage and Sprinkler Irrigation Capacity Study
 Figure 1.
Physical arrangement of the irrigation capacity and tillage treatments.
Fertilizer N for all 3 treatments was applied at a rate of 200 lb/acre in split applications with approximately 85 lb/ac applied in the fall or spring application, approximately 30 lb/acre in the starter application at planting and approximately 85 lb/acre in a fertigation event near corn lay-by.
Phosphorus was applied with the starter fertilizer at planting at the rate of 45 lb/acre P2O5.
Urea-AmmoniumNitrate  and Ammonium Superphosphate  were utilized as the fertilizer sources in the study.
Fertilizer was incorporated in the fall concurrently with the Conventional Tillage operation and applied with a mole knife during the Strip Tillage treatment.
Conversely, N application was broadcast with the No Tillage treatment prior to planting.
A post-plant, pre-emergent herbicide program of Bicep II Magnum and Roundup Ultra was applied.
Roundup was also applied post-emergence prior to lay-by for all treatments, but was particularly beneficial for the strip and no tillage treatments.
Insecticides were applied as required during the growing season.
Weekly to bi-weekly soil water measurements were made in 1-ft increments to 8ft.
depth with a neutron probe.
All measured data was taken near the center of each plot.
These data were utilized to examine treatment differences in soil water conditions both spatially  and temporally (e.g.
differences caused by timing of irrigation in relation to evaporative conditions as affected by residue and crop growth stage).
Table 1.
Tillage treatments, herbicide and nutrient application by period.
Period	Conventional tillage	Strip Tillage	No Tillage
 1) One-pass chisel/disk plow	1) Strip Till + Fertilizer  at
 Fall	at 8-10 inches with	8-10 inch depth,
 2003	broadcast N, November 13,	November 13, 2003.
2) Plant + Banded starter N &	2) Plant + Banded starter N	1) Broadcast N + Plant +
 P, May 8, 2004.
& P, May 8, 2004	Banded starter N & P,
 Spring	May 8, 2004
 2004	3) Pre-emergent herbicide	3) Pre-emergent herbicide	2) Pre-emergent
 application, May 9, 2004.
application, May 9, 2004.
herbicide application,
 4) Roundup herbicide	4) Roundup herbicide	3) Roundup herbicide
 Summer	application near lay-by,	application near lay-by,	application near lay-
 June 9, 2004	June 9, 2004	by, June 9, 2004
 5) Fertigate , June 10,	5) Fertigate , June10	4) Fertigate , June 10,
 1) One-pass chisel/disk plow	Too wet, no tillage
 Fall	at 8-10 inches with	operations
 2004	broadcast N, November 05,
 1) Strip Till + Fertilizer  at
 8-10 inch depth, March
 Spring	2) Plant + Banded starter N &	2) Plant + Banded starter N	1) Broadcast N + Plant +
 2005	P, April 27, 2005.
& P, April 27, 2005	Banded starter N & P,
 3) Pre-emergent herbicide	3) Pre-emergent herbicide	2) Pre-emergent
 application, May 8, 2005.
application, May 8, 2005.
herbicide application,
 4) Roundup herbicide	4) Roundup herbicide	3) Roundup herbicide
 Summer	application near lay-by,	application near lay-by,	application near lay-
 June 9, 2005	June 9, 2005	by, June 9, 2005
 5) Fertigate , June 17,	5) Fertigate , June 17,	4) Fertigate , June 17,
 1) One-pass chisel/disk plow	1) Strip Till + Fertilizer  at
 Fall 2005	at 8-10 inches with	8-10 inch depth,
 broadcast N, November 10,	November 10, 2005.
2) Plant + Banded starter N &	2) Plant + Banded starter N	1) Broadcast N + Plant +
 P, April 20, 2006.
& P, April 20, 2006	Banded starter N & P,
 Spring	April 20, 2006
 2006	3) Pre-emergent herbicide	3) Pre-emergent herbicide	2) Pre-emergent
 application, April 22, 2006.
application, April 22,	herbicide application,
 2006.
April 22, 2006.
4) Roundup herbicide	4) Roundup herbicide	3) Roundup herbicide
 Summer	application near lay-by,	application near lay-by,	application near lay-
 2006	June 6, 2006	June 6, 2006	by, June6, 2006
 5) Fertigate , June 13,	5) Fertigate , June 13,	4) Fertigate , June 13,
 Similarly, corn yield was measured in each of the 81 subplots at the end of the season.
In addition, yield components  were determined to help explain the treatment differences.
Water use and water use efficiency were calculated for each subplot using the soil water data, precipitation, applied irrigation and crop yield.
Summer seasonal precipitation was approximately 2 inches below normal in 2004, near normal in 2005, and nearly 3 inches below normal in 2006 at 9.99, 11.95 inches, and 8.99 inches, respectively for the 120 day period from May 15 through September 11.
In 2004, the last month of the season was very dry but the remainder of the season had reasonably timely rainfall and about normal crop evapotranspiration.
In 2005, precipitation was above normal until about the middle of July and then there was a period with very little precipitation until the middle of August.
This dry period in 2005 also coincided with a week of higher temperatures and high crop evapotranspiration near the reproductive period of the corn.
In 2006, precipitation lagged behind the long term average for the entire season.
Fortunately, seasonal evapotranspiration was near normal as it also was for the other two years.
Figure 2.
Corn evapotranspiration and summer seasonal rainfall for the 120 day period, May 15 through September 11, KSU Northwest ResearchExtension Center, Colby Kansas.
Irrigation requirements were lowest in 2004 with the 1 inch/4 day treatment receiving 12 inches, the 1 inch/ 6 day treatment receiving 11 inches and the 1 inch/8 day treatment receiving 9 inches.
Figure 3.
Seasonal irrigation for the 120 day period, May 15 through September 11, 2004 for the three irrigation treatments in an irrigation capacity and tillage study, KSU Northwest Research-Extension Center, Colby Kansas.
The irrigation amounts in 2005 were 15, 13, and 10 inches for the three respective treatments.
Figure 4.
Seasonal irrigation for the 120 day period, May 15 through September 11, 2005 for the three irrigation treatments in an irrigation capacity and tillage study, KSU Northwest Research-Extension Center, Colby Kansas.
The irrigation amounts were highest in 2006 at 15.5, 13.5, and 11.50 inches for the three respective treatments.
Figure 5.
Seasonal irrigation for the 120 day period, May 15 through September 11, 2006 for the three irrigation treatments in an irrigation capacity and tillage study, KSU Northwest Research-Extension Center, Colby Kansas.
Crop Yield and Selected Yield Components
 Corn yield was relatively high for all three years ranging from 161 to 262 bu/acre Table 2 through 4, and Figure 6).
Higher irrigation capacity generally increased grain yield, particularly in 2005 and 2006.
Strip tillage and no tillage had higher grain yields at the lowest irrigation capacity in 2004 and at all irrigation capacities in 2005 and 2006.
Strip tillage tended to have the highest grain yields for all tillage systems and the effect of tillage treatment was greatest at the lowest irrigation capacity.
These results suggest that strip tillage obtains the residue benefits of no tillage in reducing evaporation losses without the yield penalty sometimes associated with the higher residue levels in irrigated no tillage management.
was compensated by the increase in population increasing the overall number of kernels/acre by 12.8%.
Table 2.
Selected corn yield component and total seasonal water use data for 2004 from an irrigation capacity and tillage study, KSU Northwest Research-Extension Center, Colby, Kansas.
Irrigation	Tillage	Plant	Grain	Plant	Kernels	Kernel	Water
 Capacity	System	Population		bu/acre	Yield	Population		/Ear	Weight	g/100		Use
 1 in/4 days Conventional	26	229	27878	550	37.1	23.0
 	30	235	29330	557	36.2	22.6
 34	234	32234	529	34.6	22.0
 Strip Tillage	26	245	27588	537	38.9	23.5
 30	232	30492	519	37.0	24.4
 34	237	33106	514	35.5	24.3
 No Tillage	26	218	25846	548	37.7	22.0
 30	226	29330	539	36.8	23.6
 34	251	33686	553	33.8	23.2
 1 in/6 days Conventional	26	226	25265	557	39.0	23.0
 	30	222	29621	522	34.9	23.6
 34	243	32525	522	36.0	23.9
 Strip Tillage	26	235	27298	558	36.9	23.3
 30	224	28750	556	35.0	24.4
 34	237	33396	487	35.6	24.4
 No Tillage	26	225	26426	537	37.8	24.5
 30	222	29040	556	34.6	25.0
 34	229	32234	545	32.8	23.4
 1 in/8 days Conventional	26	198	24684	509	37.5	22.1
 	30	211	29330	531	34.5	22.4
 34	216	31654	494	34.9	22.0
 Strip Tillage	26	227	25846	644	34.2	23.8
 30	229	29911	518	35.6	21.8
 34	234	32815	507	35.1	23.2
 No Tillage	26	220	27007	541	36.6	22.5
 30	225	29621	528	34.5	23.2
 34	220	32815	506	32.2	22.6
 Table 3.
Selected corn yield component and total seasonal water use data for 2005 from an irrigation capacity and tillage study, KSU Northwest Research-Extension Center, Colby, Kansas.
Irrigation	Tillage	Plant	Grain	Plant	Kernels	Kernel	Water
 Capacity	System	Population		bu/acre	Yield	Population		/Ear	Weight	g/100		Use
 1 in/4 days Conventional	26	218	23813	644	37.9	28.3
 	30	238	27588	594	37.3	28.6
 34	260	30202	579	37.1	27.3
 Strip Tillage	26	238	24394	620	39.6	28.3
 30	251	27878	590	38.3	26.6
 34	253	31073	567	36.8	29.1
 No Tillage	26	228	24974	628	38.3	28.1
 30	254	26717	660	37.4	27.7
 34	262	31363	606	35.8	28.5
 1 in/6 days Conventional	26	203	24684	546	37.7	26.4
 	30	221	27588	544	37.5	25.8
 34	208	31073	472	36.2	25.3
 Strip Tillage	26	226	24394	604	38.9	26.7
 30	207	28169	487	38.4	27.1
 34	248	31944	560	36.0	26.2
 No Tillage	26	205	24684	565	38.2	26.7
 30	224	29040	547	36.6	27.2
 34	234	31654	512	37.1	25.7
 1 in/8 days Conventional	26	187	24394	523	37.5	22.8
 	30	218	27298	536	37.5	22.5
 34	208	31654	452	37.3	24.8
 Strip Tillage	26	212	23813	648	34.9	23.8
 30	216	27588	579	35.8	24.1
 34	240	31363	537	36.1	24.5
 No Tillage	26	208	24103	608	37.4	24.6
 30	211	27588	537	36.2	22.9
 34	216	31073	502	36.4	24.7
 Table 4.
Selected corn yield component and total seasonal water use data for 2006 from an irrigation capacity and tillage study, KSU Northwest Research-Extension Center, Colby, Kansas.
Irrigation	Tillage	Plant	Grain	Plant	Kernels	Kernel	Water
 Capacity	System	Population		bu/acre	Yield	Population		/Ear	Weight	g/100		Use
 1 in/4 days Conventional	26	239	29330	542	38.1	27.1
 	30	213	31073	476	36.4	26.6
 34	212	35138	434	36.1	26.9
 Strip Tillage	26	232	29330	514	39.1	27.7
 30	236	31363	483	38.2	27.4
 34	260	33106	522	38.6	27.5
 No Tillage	26	211	28459	497	37.9	26.3
 30	263	31363	535	40.3	27,5
 34	248	34558	516	35.7	27.0
 1 in/6 days Conventional	26	161	29040	422	34.1	24.8
 	30	208	31944	446	37.1	24.6
 34	169	33977	374	35.0	25.0
 Strip Tillage	26	207	29040	492	36.6	26.1
 30	215	31363	484	36.7	25.9
 34	216	34267	476	34.7	26.5
 No Tillage	26	230	29330	541	36.8	25.9
 30	218	30202	516	35.9	25.6
 34	223	32815	484	36.7	25.5
 1 in/8 days Conventional	26	172	28169	417	37.8	23.5
 	30	191	31654	411	37.7	22.0
 34	191	33977	385	37.2	22.6
 Strip Tillage	26	214	29330	565	32.7	24.6
 30	220	31944	510	34.4	24.6
 34	230	34558	479	35.7	24.3
 No Tillage	26	204	28750	501	36.9	24.4
 30	220	31363	497	35.8	24.6
 34	216	33977	458	35.6	24.9
 Figure 6.
Corn grain yield as affected by irrigation capacity and tillage, 2004 to 2006, KSU Northwest Research-Extension Center, Colby Kansas.
Figure 7.
Corn grain yield as affected by irrigation capacity and plant population, 2004-2006, KSU Northwest Research-Extension Center, Colby Kansas.
The number of kernels/ear was lower in 2004 and 2006 compared to 2005.
The potential number of kernels/ear is set at about the ninth leaf stage  and the actual number of kernels/ear is finalized by approximately 2 weeks after pollination.
Greater early season precipitation in 2005  than 2004 and 2006 may have established a higher potential for kernels/acre and then later in the 2005 season greater irrigation capacity or better residue management may have allowed for more kernels to escape abortion.
The time the actual kernels/acre was being set in 2005 was a period of high evapotranspiration  and also coincided with multiple irrigation events for the 1inch /4 days irrigation capacity.
Figure 8.
Kernels/ear as affected by irrigation capacity and plant population, 2004-2006, KSU Northwest Research-Extension Center, Colby Kansas.
Final kernel weight is affected by plant growing conditions during the grain filling stage  and by plant population and kernels/ear.
Deficit irrigation capacities often will begin to mine soil water reserves during the latter portion of the cropping season, so it is not surprising that kernel weight was increased with increased irrigation capacity.
Tillage system also affected kernel weight, but it is thought by the authors that the effect was caused by different factors at the different irrigation capacities.
At the lowest irrigation capacity, final kernel weight was highest for conventional tillage because of the lower number of kernels/ear.
However, this higher kernel weight did not compensate for the decreased kernels/ear, and thus, grain yields were lower for conventional tillage.
Strip tillage generally had higher kernel weights at higher irrigation capacity than the conventional and no tillage treatments for some unknown reason.
Figure 9.
Kernel weight as affected by irrigation capacity and plant population, 2004-2006, KSU Northwest Research-Extension Center, Colby Kansas.
The changing patterns in grain yield, kernels/ear, and kernel weight that occurs between years and as affected by irrigation capacity and tillage system may be suggesting that additional factors besides differences in plant water status or evaporative losses is affecting the corn production.
There might be differences in rooting, aerial or soil microclimate, nutrient status or uptake to name a few possible physical and biological reasons.
Total seasonal water use in this study was calculated as the sum of irrigation, precipitation and the change in available soil water over the course of the season.
As a result, seasonal water use can include non-beneficial water losses such as soil evaporation, deep percolation, and runoff.
Intuitively, one might
 anticipate that good residue management with strip tillage and no-tillage would result in lower water use than conventional tillage because of lower nonbeneficial water losses.
However, in this study, strip tillage and no-tillage generally had higher water use.
The small increases in total seasonal water use  for strip tillage and no-tillage compared to conventional tillage can probably be explained by the higher grain yields for these tillage systems.
Another possibility is that there were increased deep percolation losses in 2005 because of the higher early season precipitation.
Figure 10.
Total seasonal water use  as affected by irrigation capacity and plant population, 2004-2006, KSU Northwest ResearchExtension Center, Colby Kansas.
Corn grain yields were high all three years  with varying seasonal precipitation and near normal crop evapotranspiration.
Strip tillage and no tillage generally performed better than conventional tillage.
Increasing the plant population from 25,400 to 32,000 plants/acre was beneficial at all three irrigation capacities.
The study will be continued in 2007 to determine if the production trends will remain as residue levels continue to increase.
This paper was first presented at the 18th annual Central Plains Irrigation Conference, February 27-28, 2006, Kearney, Nebraska.
Contribution No.
07-167-A from the Kansas Agricultural Experiment Station.
Applying strip tillage treatments in the fall of 2005 in preparation for 2006 cropping season, KSU Northwest Research-Extension Center, Colby, Kansas.
2) Pump The pump is a piece that is sometimes overlooked.
Before you start irrigating in the spring make sure you start the dripper to get the line shaft bearings lubed.
It needs 1 gallon of drip oil for every 100 feet of depth.
Set the dripper for 1 drip every 5 seconds.
The pump can only take oil so fast and you can't over oil them.
Also make sure the dripper line is attached and the fittings are tight.
Graph 1.
Average soil moisture tensions reached in the top 3 ft of soil under the different irrigation regimes on VF-13L tomatoes.
The arrows along the bottom of each graph indicate when each treatment was irrigated.
INITIAL GROWTH BLOOM, FRUIT SET, FRUIT GROWTH IRIPENING
 Frequent Irrigation For MechanicallyTOMATOES
 J.
C.
LINGLE R.
M.
HAGAN W.
J.
FLOCKER P.
E.
MARTIN
 F REQUENT IRRIGATION, the usual management practice in the production of hand-picked tomatoes, is not necessarily best suited for the new varieties developed for one-time mechanical harvesting.
In addition to the need for determinate maturity, dry fields allow much more efficient operation of mechanical harvesting equipment.
These studies were conducted to determine how dry the soil can become before affecting yield, maturity, and soluble solids content of the new varieties-and whether a plant or soil moisture index can be developed as a guide to irrigation of the growing crop, as well as the final water cutoff date.
Research has previously shown that irrigation practices do affect the relative maturity of the crop and can directly influence yields obtained in a single harvesting operation.
Over half of the processing tomatoes grown in California are concentrated into some product such as catsup or paste.
Therefore, tomatoes with a high solids content are desirable.
Over the years, the solids content of tomatoes has gradually declined, as growers have increased their average yields per acre through heavy fertilization and frequent irrigation.
The lower solids content of tomatoes has required increased energy to concentrate the tomatoes with resulting increases in processing costs.
Previous research showed that tomatoes had a higher solids content when high soil moisture tensions were allowed to develop prior to harvest.
The question of whether solids can be increased by irrigation management without a concomitant decrease in yield remained unanswered.
This experiment was conducted on Yolo loam soil at Davis with the variety VF-13L.
Planting was done on May 7 in 54-inch rows, and 10 gallons per acre of 8-24-0 liquid fertilizer were applied 2 inches below the seed.
Enough ammonium sulfate to bring the total actual nitrogen application to 80 lbs per acre was sidedressed on the crop just prior to thinning.
Plants were thinned to 12 inches apart in the row when they had about five true leaves.
All plots were irrigated alike at planting time , again one week after planting, and then just after thinning.
These irrigations totaled approximately 20 acre-inches.
The following differential irrigation program was then carried out:
 DATES OF IRRIGATIONS* IRRIGATION TREATMEINTS
 A	B	C	D	E	Ft
 July 1	2	2
 a 	4	4
 Aug.
5	"	"
 12 	14	14
 Total depth applied	24	14	18	14	4	0
 irrigations	12	7	2	1	1	0
 Table includes only irrigations applied following irrigation at thinning time.
1 Irrigated only of time of thinning.
Treatment A provided 2 inches of water per week until six days prior to harvest; B provided 2 inches of water per week until the first pink fruit ap.
peared; C was irrigated during early
 bloom  and for the last time when the first pink fruit appeared; D was irrigated only when the first pink fruit appeared; E was irrigated only during early bloom; and F was irrigated for the last time at thinning.
Soil moisture tension was determined by using gypsum blocks at two sites in the plant rows of treatments C, D, E, and F at depths of 1, 2, and 3 ft.
Tensiometers were placed in the plant row in treatments A and B at depths of 1, 2.
3, and 4 ft with one instrument station per plot.
Gypsum blocks were also installed in treatment B to continue recording soil moisture tension after the last irrigation.
Graph 1 shows the average soil moisture tension reached in the top 3 ft of soil at different stages of growth.
During vegetative growth and up to the first pink
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Paul Manager Agricultural Publications Jerry Lester Editor California Agriculture
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 fruit, soil moisture tensions in treatments A and B remained below.35 bar; while over this same period, tensions in other treatments reached 2 to 3 bars.
Subsequently, tensions remained below.35 in treatment A; ranged from 2 to 3 bars in treatments B, C, and D; and reached values of 6 in treatment E and 8 in treatment F.
The effects of the irrigation treatments on the relative maturity of the crop are summarized in graph 2.
After harvesting all of the fruit in a portion of the row, it was sorted into canning ripe, pink, green, and/or rotten fruit.
Data given in this graph were calculated as per cent of the total weight of the fruit from each plot.
Almost 70% of the fruit was ripe at harvest in treatment F which was irrigated last at thinning.
With greater amounts of irrigation, there was a gradual reduction in the percentage of ripe fruit.
On the very wet treatment, less than 40% of the total fruit on the vine was ripe when the plots were harvested.
The influence of irrigation on yield harvestable by mechanical picking is shown more clearly in graph 3.
Both the single-harvest yield and the potential yield  are given.
This graph indicates that if the crop is mechanically harvested in one operation, there are no significant differences in yield, except for the one treatment irrigated very frequently until harvest.
Frequent irrigation reduced the harvestable yield significantly  but increased the potential yield.
In comparing the potential yield against the yield which can be taken in a single harvest, it should be recognized that a considerable portion of the potential yield  is often lost, even when the crop is har-
 vested by hand in several pickings because of the frequent occurrence of early fall rains or frost.
The table shows the effect of various treatments on soluble solids, total solids, and the calculated yield of salt-free solids per acre.
The soluble solids content of the fruit was determined on samples drawn from the canning ripe fruit by the Abbe refractometer.
These values were converted into total solids content from suitable tables, As the mean soil moisture tension was allowed to increase prior to harvest, the soluble solids content and the total solids were increased by the same relative amounts.
These data were used to calculate the yield of edible solids and juice in pounds per acre.
The relatively dry irrigation treatments  produced the highest yield of total edible solids per acre.
One or more irrigations during the six weeks prior to harvest reduced both the percentage of solids and the yield per acre of edible solids.
This experiment suggests that the yield of tomatoes grown for mechanical harvest may be increased by changing irrigation management practices from those used with previous varieties which were handharvested.
However, these studies were confined to one trial on an open, deep soil in plots at Davis which offered no restriction to the full development of the root system of the crop.
Before these results can be applied to a wide range of growing conditions, they need to be tried on several soil types.
These studies will be continued this year over a wider range of growing conditions in the Central Valley tomato-growing districts.
J.
C.
Lingle and W.
J.
Flocker are Associate Olericulturists, Department of Vegetable Crops; R.
M.
Hagan is Irrigationist; P.
E.
Martin is Laboratory Technician, Department of Irrigation, University of California, Davis.
D.
W.
Henderson, Associate Irrigationist, furnished the calibration curve used to convert readings on the moisture meter to tension.
Graph 2.
Effect of irrigation on relative maturity of VF-13L tomatoes.
PER GENT RIPE PINK GREEN VIII CULLS ON VINE AT HARVEST
 Graph 3.
Effect of irrigation on single-harvest yield and on potential yield of VF-13L tomatoes.
EFFECT OF IRRIGATION ON PER CENT SOLUBLE, TOTAL SOLIDS, AND EDIBLE SOLIDS CONTENTS OF TOMATOES PRODUCED PER ACRE
 Treatment no.
Water applied	Irrigation cut-off	Solids contant	Yield
 after thinning	before harvest	Soluble	Total	Juice	Edible solids
 Inches	Days	%	%	Lbs/A	Lbs/A
 A	24	5	3.96	4.26	42,420	1,807
 B	14	40	4.31	4.61	50,809	2,342
 C	18	40	4.42	4.72	49,643	2,343
 D	14	40	4.29	4 59	45,881	2,106
 E	4	75	5.02	5 32	51,515	2,741
 F	0	90	5.27	5.57	47,603	2,651
LAND APPLICATION OF ANIMAL WASTE ON IRRIGATED FIELDS
 Animal wastes are routinely applied to cropland to recycle nutrients, build soil quality, and increase crop productivity.
This study evaluates established best management practices for land application of animal wastes on irrigated corn.
Swine  and cattle  wastes have been applied annually since 1999 at rates to meet estimated corn P or N requirements along with a rate double the N requirement.
Other treatments were N fertilizer  and an untreated control.
Corn yields were increased by application of animal wastes and N fertilizer.
Over-application of cattle manure has not had a negative effect on corn yield.
For swine effluent, over-application has not reduced corn yields except for 2004, when the effluent had much greater salt concentration than in previous years, which caused reduced germination and poor early growth.
All animal waste and N fertilizer treatments increased soil solution NO3-N concentration  compared with the untreated control.
Application of animal wastes on a N requirement basis resulted in similar NO3-N concentrations as fertilizer N applied at 180 lb/a.
The 2xN application caused NO3 N concentrations to about double for both swine and cattle wastes.
Application of swine effluent based on P requirement produced similar NO3-N concentrations as the 2xN rate because of the relatively low P content in the effluent.
This study was initiated in 1999 to determine the effect of land application of animal wastes on crop production and soil properties.
The two most common animal wastes in western Kansas were evaluated; solid cattle manure from a commercial beef feedlot and effluent water from a lagoon on a commercial swine facility.
The rate of waste application was based on the amount needed to meet the estimated crop P requirement, crop N requirement, or twice the N requirement.
The Kansas Dept.
of Agriculture Nutrient Utilization Plan Form was
 used to calculate animal waste application rates.
Expected corn yield was 200 bu/a.
The allowable P application rates for the P-based treatments were 105 lb PO5/a since soil test P levels were less than 150 ppm Mehlich-3 P.
The N recommendation model uses yield goal less credits for residual soil N and previous manure applications to estimate N requirements.
For the N-based swine treatment, the residual soil N levels after harvest in 2001, 2002, and 2004 were great enough to eliminate the need for additional N the following year.
So no swine effluent was applied to the 1xN treatment in 2002, 2003, or 2005 or to the 2xN requirement treatment since it is based on 1x treatment.
The same situation occurred for the N based treatments using cattle manure in 2003.
Nutrient values used to calculate initial applications of animal wastes were 17.5 lb available N and 25.6 lb available P2O5 per ton of cattle manure and 6.1 lb available N and 1.4 lb available P2O5 per 1000 gallon of swine effluent.
Subsequent applications were based on previous analyses.
Other nutrient treatments were three rates of N fertilizer  along with an untreated control.
The N fertilizer treatments also received a uniform application of 50 lb/a of P2O5.
The experimental design was a randomized complete block with four replications.
Plot size was 12 rows wide by 45 ft long.
The study was established in border basins to facilitate effluent application and flood irrigation.
The swine effluent was flood-applied as part of a pre-plant irrigation each year.
Plots not receiving swine effluent were also irrigated at the same time to balance water additions.
The cattle manure was hand-broadcast and incorporated.
The N fertilizer  was applied with a 10 ft fertilizer applicator.
The entire study area was uniformly irrigated during the growing season with flood irrigation in 1999-2000 and sprinkler irrigation in 2001-2006.
The soil is a Ulysses silt loam.
Corn was planted at about 33,000 seeds/a in late April or early May each year.
Grain yields are not reported for 1999 because of severe hail damage.
Hail also damaged the 2002 and 2005 crop.
The center four rows of each plot were machine harvested after physiological maturity with yields adjusted to 15.5% moisture.
Nitrate concentration in the soil solution at the 5 ft depth was determined periodically through the growing season in 2003 and 2004.
The 5-ft depth is below the effective rooting depth of corn, so any nitrate movement past this depth is assumed non-recoverable by the corn plant.
Suction-cup lysimeters  are used to collect the soil water samples.
The first samples are collected shortly after corn planting and then every 1-2 week intervals during the growing season as long as sufficient water is present at the 5-ft depth to allow collection.
The samples are kept refrigerated after collection until delivered to the KSU Soil Testing laboratory for nitrate-N analysis.
Corn yields were increased by all animal waste and N fertilizer applications in 2006, as has been the case for all years except in 2002 where yields were greatly reduced by hail damage.
The type of animal waste affected yields in 5 of the 7 years with higher yields from cattle manure than from swine effluent.
Averaged across the 7 yr, corn yields were 14 bu/a greater following application of cattle manure than swine effluent on an N application basis.
Over application  of cattle manure has had no negative impact on grain yield in any year.
However, over-application of swine effluent reduced yields in 2004 because of considerably greater salt content  causing germination damage and poor stands.
No adverse residual effect from the over-application was observed in 2005.
The concentrations of NO3-N in the soil solution at the 5-ft depth for eight sampling periods in 2003 are shown in Table 4.
The NO3-N concentrations were stable between time periods but quite variable among replications.
All animal waste and N fertilizer treatments increased solution NO3-N concentration compared with the untreated control.
Application of animal wastes on a N requirement basis resulted in similar NO3-N concentrations as fertilizer N applied at 180 lb/a.
Although for both cattle and swine wastes, no fresh applications were made in 2003 for the N based treatments because of sufficient residual soil N.
The 2x N application caused NO3-N concentrations to more than double for both swine and cattle wastes.
Application of swine effluent based on P requirement produced similar NO3-N concentrations as the 2x N rate because of the relatively low P content in the effluent.
Compared with the 2001 values , some treatments showed considerably higher NO3-N concentrations in 2003.
The three treatments  that had soil solution concentrations >100 mg kg` of NO3-N in 2001 showed increases in NO3-N concentrations in 2003 indicating continual accumulation of NO3-N at the 5-ft depth.
It would be expected that over-application of cattle manure  could result in increased soil solution NO3-N concentrations.
Similarly, since the swine effluent used in this study was relatively low in P, the application rates necessary to meet P requirements over-supplies N as shown by the elevated soil solution NO3-N concentrations.
However, for the 2xN swine effluent treatment there was no effluent applied in 2002 or 2003.
With no additional effluent applied since the 2001 water samples were collected, the higher concentration of NO3-N at the 5-ft depth in 2003 indicates movement of NO3-N from the upper profile rather than from fresh applications.
Table 5 shows the NO3-N concentrations in the soil solution at the 5-ft depth for eight sampling periods in 2004.
Soil solution NO3-N concentrations were similar
 for the untreated control and the low rate of N fertilizer, but increased by all other treatments.
In general, soil solution NO3-N concentrations were greater in 2004 than 2003.
It would be expected that the soil solution NO3-N concentrations for the N based swine effluent treatments would be greater because of the higher N content of the effluent in 2004.
However, soil solution NO3-N concentrations were also greater following applications of cattle waste based on N requirement and the higher rates of N fertilizer.
Animal wastes are routinely applied to cropland to recycle nutrients, build soil quality, and increase crop productivity.
This study evaluated established best management practices for land application of animal wastes on irrigated corn.
Swine  and cattle  wastes were applied annually for eight years at rates to meet estimated corn P or N requirements along with a rate double the N requirement.
Corn yields were increased by application of both animal wastes, compared with no fertilizer.
Over-application of cattle manure did not have a negative effect on corn yield.
For swine effluent, over-application reduced corn yields only in one year, when the effluent had much greater salt concentration than in previous years, which caused reduced germination and poor early growth.
Overapplication of animal wastes tended to increase nitrate concentration in the soil solution below the corn root zone.
However, applying swine effluent based on crop N requirements or cattle manure based on crop P requirements resulted in solution nitrate concentrations below the root zone similar to those from recommended rates of inorganic N fertilizer.
Acknowledgement: Project supported in part by Kansas Fertilizer Research Fund and Kansas Dept.
of Health and Environment.
Table 1.
Application rates of animal wastes, Tribune, KS, 1999 to 2006.
1999	2000	2001	2002	2003	2004	2005	2006
 P req.
15.0	4.1	6.6	5.8	8.8	4.9	3.3	6.3
 N req.
15.0	6.6	11.3	11.7	0	9.8	6.8	6.3
 2XN req.
30.0	13.2	22.6	22.7	0	19.7	13.5	12.6
 1999	2000	2001	2002	2003	2004	2005	2006
 P req.
28.0	75.0	61.9	63.4	66.9	74.1	73.3	66.0
 N req.
28.0	9.4	37.8	0	0	40.8	0	16.8
 2XN req.
56.0	18.8	75.5	0	0	81.7	0	33.7
 * The animal waste applications are based on the estimated requirement of N and P for a 200 bu/a corn crop.
Table 2.
Analysis of animal waste as applied, Tribune, KS, 1999 to 2006.
1999	2000	2001	2002	2003	2004	2005	2006
 Total N	27.2	36.0	33.9	25.0	28.2	29.7	31.6	38.0
 P2O5	29.9	19.6	28.6	19.9	14.6	18.1	26.7	20.5
 1999	2000	2001	2002	2003	2004	2005	2006
 Total N	8.65	7.33	7.83	11.62	7.58	21.42	13.19	19.64
 P2O5	1.55	2.09	2.51	1.60	0.99	2.10	1.88	2.60
 Table 3.
Effect of animal waste and N fertilizer on irrigated corn, Tribune, KS, 20002006.
Nutrient source	Rate	2000	2001	2002	2003	2004	2005	2006	Mean
 Cattle manure	P	197	192	91	174	241	143	236	182
 N	195	182	90	175	243	147	217	178
 2 X N	195	185	92	181	244	155	213	181
 Swine effluent	P	189	162	74	168	173	135	189	155
 N	194	178	72	167	206	136	198	164
 2 X N	181	174	71	171	129	147	196	152
 N fertilizer	60 N	178	149	82	161	170	96	178	145
 120 N	186	173	76	170	236	139	198	168
 180 N	184	172	78	175	235	153	200	171
 Control	0	158	113	87	97	94	46	122	103
 LSD0.05	22	20	17	22	36	16	18	12
 Treatment	0.034	0.001	0.072	0.001	0.001	0.001	0.001	0.001
 Control VS.
treatment	0.001	0.001	0.310	0.001	0.001	0.001	0.001	0.001
 Manure VS.
fertilizer	0.089	0.006	0.498	0.470	0.377	0.001	0.001	0.013
 Cattle VS.
swine	0.220	0.009	0.001	0.218	0.001	0.045	0.001	0.001
 Cattle 1x VS.
2x	0.900	0.831	0.831	0.608	0.973	0.298	0.646	0.705
 Swine 1x VS.
2x	0.237	0.633	0.875	0.730	0.001	0.159	0.821	0.043
 N rate linear	0.591	0.024	0.639	0.203	0.001	0.001	0.021	0.001
 N rate quadratic	0.602	0.161	0.614	0.806	0.032	0.038	0.234	0.042
 Rate of animal waste applications based on amount needed to meet estimated crop P requirement, N requirement, or twice the N requirement.
No yields reported for 1999 because of severe hail damage.
Hail reduced corn yields in 2002 and 2005.
Table 4.
Nitrate concentration in soil solution at the 5-ft soil depth in 2003 following application of animal wastes and N fertilizer.
Nutrient source Application	Time of Sampling
 Basis*	May 21	May 29	June 10	June 18	June 23	July 2	July 9	July 16	Mean
 Soil solution NO3-N, ppm
 Cattle manure	P	45	31	46	38	41	43	45	44	42
 N	75	69	68	62	64	52	61	49	63
 2 X N	322	375	375	348	375	310	371	378	357
 Swine effluent	P	264	280	281	280	283	278	296	299	283
 N	106	112	122	103	99	89	94	100	103
 2 X N	272	306	264	288	299	281	290	291	286
 N fertilizer	60 N	23	20	22	19	21	18	22	22	21
 120 N	48	41	40	23	31	35	36	24	35
 180 N	102	98	105	84	86	64	71	73	85
 Control	0	8	5	7	3	3	4	4	4	5
 Treatment	0.001	0.001	0.001	0.001	0.001	0.001	0.001	0.001
 Control vs.
treatment	0.028	0.034	0.019	0.020	0.012	0.014	0.006	0.005
 Animal waste VS.
fert.
0.003	0.003	0.001	0.001	0.001	0.001	0.001	0.001
 Cattle VS.
swine	0.139	0.145	0.188	0.090	0.109	0.038	0.070	0.047
 Cattle 1x VS.
2x	0.003	0.001	0.001	0.001	0.001	0.001	0.001	0.001
 Swine 1x VS.
2x	0.038	0.032	0.070	0.018	0.008	0.006	0.004	0.004
 N rate linear	0.306	0.371	0.278	0.380	0.367	0.488	0.432	0.406
 N rate quadratic	0.833	0.805	0.719	0.653	0.709	0.907	0.849	0.647
 The animal waste applications are based on the estimated requirement of N and P for a 200 bu/a corn crop.
*
 Table 5.
Nitrate concentration in soil solution at the 5-ft soil depth in 2004 following application of animal wastes and N fertilizer.
Nutrient source Application	Time of Sampling
 Basis*	May 26	June 4	June 8	June 15	June 23	June 27	July 7	July 14	Mean
 Soil solution NO3-N, ppm
 Cattle manure	P	108	109	111	102	111	99	105	111	107
 N	321	335	344	358	306	282	293	294	317
 2 X N	322	418	421	300	454	402	424	405	393
 Swine effluent	P	355	366	357	505	476	446	546	531	448
 N	145	127	128	219	146	141	169	170	156
 2 X N	203	303	327	325	247	395	540	307	331
 N fertilizer	60 N	14	4	5	7	4	4	4	3	6
 120 N	116	119	109	129	111	120	139	135	122
 180 N	170	183	180	177	201	211	218	234	197
 Control	0	8	5	4	4	2	2	1	1	3
 Treatment	0.005	0.002	0.003	0.008	0.001	0.001	0.002	0.001
 Control VS.
treatment	0.006	0.005	0.007	0.009	0.007	0.003	0.024	0.001
 Animal waste vs.
fert.
0.005	0.002	0.002	0.004	0.003	0.001	0.001	0.001
 Cattle vs.
swine	0.795	0.753	0.772	0.241	0.993	0.285	0.063	0.258
 Cattle 1x vs.
2x	0.995	0.409	0.465	0.642	0.185	0.248	0.294	0.249
 Swine 1x vs.
2x	0.663	0.248	0.213	0.547	0.535	0.039	0.015	0.217
 N rate linear	0.064	0.060	0.078	0.122	0.059	0.036	0.069	0.013
 N rate quadratic	0.728	0.748	0.834	0.686	0.921	0.883	0.779	0.822
 * The animal waste applications are based on the estimated requirement of N and P for a 200 bu/a corn crop.
Nonpoint Source Pollution in the Upper Saline River Watershed
 The Upper Saline River Watershed is located in Cleveland, Dallas, Garland, Grant, Hot Spring, Jefferson, Perry, Pulaski and Saline counties.
A "watershed" is an area of land where all of the water that drains from it goes to the same place, SO rainwater or snowmelt in this watershed eventually drains to a common location.
This watershed is named for the major waterway in the area, the Saline River.
The watershed spans 1,709 square miles, and is more than 75 percent forested.
1 The Middle Fork and other headwaters of the Saline River are designated as Ecologically Sensitive Waters, or waterways that provide habitat for threatened, endangered or endemic species.
They are also designated Extraordinary Resource Waters by the state, or a water resource that is valued for characteristics such as beauty, recreation, and social use.
2
 Water pollution that comes from multiple sources spread over an area, such as runoff from parking lots, agricultural fields, residential lawns, home gardens, construction, mining, and logging, is known as nonpoint source pollution.
As runoff moves across the landscape, it carries natural and manmade substances that can accumulate in waterways and make them uninhabitable for aquatic species or unusable by people.
Potential pollutants include bacteria, nutrients, sediment, hazardous substances and trash.
3 Given the number of potential sources and variation in their potential contributions these pollutants are not easily traced back to their source.
Upper Saline River Watershed Data source: GeoStor.
Map created March 2011.
Major streams: Cedar Creek, Derrieuseaux Creek, Francois Creek, Hurricane Creek, Huskey Creek, Lost Creek, Saline River, Saline River-Alum Fork, Saline River-Middle Fork, Saline River-North Fork, Saline River-South Fork, Simpson Creek
 An estimated 140,000 people lived in the watershed as of 2010, but the population continues to grow as Saline County saw its population grow by 28 percent between 2000 and 2010.
4
 This fact sheet is intended to provide a better understanding of the Upper Saline River Watershed and its place on the state's priority list of 10 watersheds impacted by nonpoint source pollution.
Upper Saline River Watershed Water Quality Issues
 Through water quality monitoring, environmental officials in Arkansas have
 Arkansas' Priority Watershed List for Nonpoint Source Pollution
 Arkansas has used a watershed-based approach to nonpoint source pollution management, allowing the public to guide planning to address water quality concerns.
The Arkansas Natural Resources Commission, or ANRC, administers the Nonpoint Source Pollution Management Program.
The program exists to reduce water pollution through the funding of watershed planning and restoration activities, adoption of voluntary best management practices and the development of technologies that assist in water pollution reduction in Arkansas.
Based on public input and the use of a qualitative risk assessment matrix, ANRC has designated 10 priority watersheds as needing the greatest attention.
The current risk matrix5 identified the following priority watersheds for 2011-2016: Bayou Bartholomew, Beaver Reservoir, Cache River, Illinois River, L'Anguille River, Lake Conway-Point Remove, Lower OuachitaSmackover, Poteau River, Strawberry River and Upper Saline.
determined that the watershed has problems with excessive minerals, dissolved oxygen, sedimentation and mercury.
6 There are various resource extraction activities within the watershed, including active and abandoned mine sites, that likely contribute to the excessive minerals.
7 Environmental officials have determined the maximum amounts of mercury the Saline River can receive and still meet water quality standards.
This determination is a calculation called Total Maximum Daily Load or TMDL.
8,9 The state has also established a TMDL related to oxygen levels in Big Creek.
Metals
 can come from natural or manmade sources, with geologic formations and atmospheric depositions for industry being a concern in the Upper Saline River watershed.
High concentrations of mercury can be hazardous to the environment because of how it accumulates in aquatic species and build up in soils.
Commercial forestland management, unpaved roads and a small number of cattle operations may also contribute to the concerns for nonpoint source pollution in the watershed according to the Arkansas Natural Resources Commission.
10
 To encourage continued public input, the University of Arkansas Division of Agriculture's Public Policy Center facilitated a water quality stakeholder forum for the Upper Saline Watershed in January 2015.
Forum participants identified water quality issues such as sedimentation, wildlife diversity and drinking water as local priorities for addressing.
People who live, work or recreate in this watershed are encouraged to consider these community priorities when addressing water pollution.
The public is also welcome to attend an annual stakeholder meeting where priority watersheds and nonpoint source pollution are discussed.
For more information about nonpoint source pollution and its impact on the Cache River watershed, contact the Cooperative Extension Service, Arkansas Natural Resources Commission or the Arkansas Department of Environmental Quality.
The Arkansas Watershed Steward Handbook is also a good source of information about basic water quality concerns and how the public can get engaged in addressing water pollution.
11
 8 See the Arkansas Watershed Steward Handbook.
11 See the Arkansas Watershed Steward Handbook.
This fact sheet is one in a series of 10 fact sheets on nonpoint source pollution in priority watersheds.
The University of Arkansas Division of Agriculture's Public Policy Center provides timely, credible, unbiased research, analyses and education on current and emerging public issues.
The most profitable fertilizer-N rate varies every year and it is partially dependent on the previous years weather conditions, previous crop nitrogen uptake and yield, and post-harvest residual soil nitrogen.
Most of Nebraska was drier than normal in 2020  which may have limited downward movement of nitrogen in the soil profile, nitrate leaching loss, crop nitrogen uptake, and crop yield, particularly for rainfed crops.
Chapter: 23 Estimating Yield Goals and Nitrogen, Phosphorus, Potassium, Iron, and Zinc Recommendations
 South Dakota nitrogen, phosphorus, and potassium fertilizer recommendations are based on soil test results, yield goals, and other credits.
Directions for converting yield estimates and soil test results to nitrogen , phosphorus , and potassium  recommendations are provided below.
The purpose of this chapter is to provide guidance on applying N, P, K, Fe, and Zn fertilizers.
Recommendations for lime, sulfur, starter fertilizers, and band-applying fertilizer are provided in Chapters 25, 26, and 27.
Table 23.1 General guidelines for estimating corn yield goals should consider that:
 Corn yields in South Dakota over the past 20 years have been increasing at an annual rate of ~2.0 bu/acre/year.
For example, 140 bu/acre +  X  = 160 bu/acre today
 When estimating the yield goal, it is not recommended to consider more than 10 years of data.
Abnormally high or low yield values should be excluded from yield goal estimates.
Managing for an optimistic, yet realistic, yield goal is important.
Underestimating the yield can contribute to a gradual yield decline.
Achieving full yield potential depends on management, climate, soil, and will vary from field to field and year to year.
Fertilizer Recommendation Yield Goals
 In South Dakota, fertilizer recommendations for nitrogen , phosphorus , and potassium  are based on the expected yield or "yield goal." Calculating yield goals should include adjustments for annual yields that have been increasing at a rate of 2 bu/.
Guidelines for calculating yield goals are provided in Tables 23.1 and 23.2.
There are many different approaches used to estimate the yield goal.
One approach uses field records to calculate the field's historical average yield followed by using the soil moisture content at planting to adjust the goal, other methods include removing unusually low or high values.
Low yields could result from droughts, floods, hail, uncontrollable pest infestation, late harvest, or other extraordinary events, whereas unusually high yields can result from ideal growing conditions that are unlikely to regularly occur.
Nitrogen  applied to soil undergoes many transformations facilitated by soil microbes and chemical reactions.
These reactions influence how much is lost, retained in the soil, or utilized by the target plants.
Nitrogen can be lost by volatilization, leaching, denitrification, and runoff.
Nitrogen lost through these mechanisms increases costs and can reduce yields.
Volatilization is the loss of ammonia gas
  from soil, fertilizer, and manure.
Research reports that up to 100% of the ammonia-N contained in manure can be lost through volatilization if the manure is left on the soil surface , whereas over 30% of the urea-N can be lost to volatilization when urea is left on the soil surface.
Denitrification is a microbial conversion of nitrate  to nitrous oxide  or nitrogen  gas, and it is the highest when the soils are warm and wet.
If the soil is well-drained denitrification losses are relatively low.
Denitrification can be reduced by treating the fertilizer with a nitrification inhibitor or splitting the N rate.
Nitrate leaching occurs because both the NO molecule 3 and soil have a negative charge.
Nitrate losses can be high following a heavy rain and it is more rapid in sandy soil than in mediumand fine-textured soils.
Nitrate leaching losses can be reduced by splitting the N application.
Immobilization is the conversion of inorganic N into organic N by plants and soil microbes.
Immobilization reduces the amount of inorganic N available to the crop and it can lead to early season N deficiencies.
N immobilization is highest when crop residues with high carbon to nitrogen  ratio are left in the field.
Immobilized N becomes available to the plant as microbes themselves die and decay.
Reduced-tillage and no-tillage systems often have high immobilization.
Figure 23.1 Important N transformations in agricultural soils.
Nitrogen fixation is the conversion of atmospheric N  to plant available N by bacteria.
Common South Dakota rotations include soybeans and alfalfa where N fixation can provide up to 40 and 150 lbs N/acre, respectively, for the following corn crop.
Nitrogen mineralization is the biological conversion of organic N to inorganic N, whereas nitrification is the biological oxidation of ammonia or ammonium to nitrite followed by the oxidation of the nitrite to nitrate.
Nitrification inhibitors slow the conversion of ammonia to nitrate and they can reduce N losses in sandy soils from leaching and denitrification losses in high clay soils.
If a substantial amount of N has been lost, the plants may have N deficiencies.
Under these conditions, it may be possible to add additional N as a split application or in the irrigation.
N Plant Uptake and Movement
 In the soil, both nitrate and ammonia can be utilized up by the corn plant.
These ions move to the root in the water transpiration stream and by diffusion.
Once in the plant, N is mobile and will move from older parts of the plant to newer growth.
Translocation results in deficiency symptoms appearing as yellow V-shaped patterns on lower leaves.
If crop growth stage allows, soil sampling and an injected sidedress application according to soil test results is recommended.
In some states, active-optical sensor algorithms have been developed to direct in-season N application to corn.
Algorithms from other states should be used as a starting algorithm, with modifications from local grower field sensing and yield correlation considered as more local data is acquired.
In
 Figure 23.2 Nitrogen deficiency in corn.
Note the V-shaped chlorosis in older leaves and that the lowest leaves  are dead.
irrigated systems, fertigation according to yield goal and soil test results is a viable option.
The South Dakota corn N recommendation for grain and silage are:
 N grain rec.
= yield goal X 1.0 soil NON manure N + no-till adjustment.
N silage rec.
=  soil NO-N manure N + no-till adjustment
 Before 2023, the South Dakota corn N recommendation was determined using the multiplier of 1.2 lb N/ bu grain X yield goal.
However, recent research  has shown that reducing this multiplier to 1.0 lbs N/bu grain improves the mean N rate recommendation accuracy by 34 lbs N/ac.
A mechanistic-based site-specific N model currently is not available.
An example for determining the yield goal is below.
Estimating N Fertilizer Credits
 Table 23.2 Estimating the corn grain yield goal:
 1.
Standardize your data.
Over the past 10 years, genetic improvements have increased yields on average 2 bu/.
a.
For yields measured 5 years ago, add 10 bu/acre.
2.
Remove the low and high value.
a.
Delete the 171 and 112 bu/acre yields.
3.
Determine the average.
The average yield of years 1, 2, 3, 4, 5, 6, 8, and 10 a.
is 136 bu/acre.
4.
If the soil water content of soil profile is at field capacity add 10% to the average yield goal.
a.
Field capacity is the maximum amount of water that can be held in soil after excess drainage.
b.
136 + 136 X 0.10 =150 bu/acre
 5.
If the soil moisture content is poor, subtract 10%.
a.
136 136 X 0.10 = 123 bu/acre
 Base yield goal = 136
 Recommendation =136 bu + 10%*136 = 149.6 ~ -150 bu
 Residual soil NO 3 -N is estimated by analyzing a 0to 24-inch soil sample collected in the spring.
Additional Previous Crop information for collecting soil samples is available in Alfalfa Soybeans Corn Chapter 21.
To obtain accurate soil test results, the Manured Manured  Years)  Years) sampling technique should consider prior management, Yes No Yes No and should involve separately sampling areas such as wet spots, old homesteads, old fence lines, field entry points, Precipitation Low High Low High hay piles, turnrows, or salt-affected patches.
If a soil sample is not available, residual-soil N can be estimated using the long-term soil test average of 55 lbs/acre.
If the field was summer fallowed the previous year and if Low High Moderate Very High High Very High High a soil sample is not available, 100 lbs/N acre can be used Probability of Significant Residual Soil NO N Levels to estimate residual nitrate-N.
Soil testing for residual nitrate is most important for continuous corn and where manure is routinely applied.
In sensitive areas, such as over shallow aquifers, an additional sample from the 24to 48-inch depth should be collected.
If the soil test N exceeds 30 lbs nitrate-N/acre in the 24to 48-inch depth, 80% of that amount of N should be added to the residual N credit.
Figure 23.3 Probability of significant soil NOlevel.
Manure N credit estimates are best determined from a laboratory analysis of a sample of the manure.
Samples should be representative of the source and should be collected after the manure has been wellmixed.
If the manure is not sampled, N content can be estimated using values in Table 23.3.
Legume crops, which form symbiotic relationships with bacteria, can provide a significant amount of N to the following crop.
In situations where corn follows soybeans, a credit of 40 lbs N/acre is recommended.
Credits for other legume crops are provided in Table 23.4.
Table 23.3 Estimated nitrogen content of liquid and solid manure.
Liquid Manure	Solid Manure
 Type of	Nitrogen 	Nitrogen 
 Livestock	lbs/1000 gal	lbs/ton
 N	ORGANIC	N	INORGANIC	N	ORGANIC	N	INORGANIC
 Farrowing	7	8	11	3
 Nursery	11	14	8	5
 Grow-Finish	-	-	10	6
 Grow-Finish	17	33
 Grow-Finish	21	39
 Grow-Finish	8	24
 Breeding-Gestation	13	12	4	5
 Farrow-Finish	12	16	8	6
 Farrow-Feeder	10	11	5	5
 Cow	25	6	8	2
 Heifer	26	6	8	2
 Calf	22	5	8	2
 Veal calf	26	21	4	5
 Herd	25	6	7	2
 Beef cows	13	7	4	3
 Feeder calves	19	8	6	3
 Finishing cattle	21	8	7	4
 Broilers	50	13	34	12
 Pullets	48	12	39	9
 Layers	20	37	22	12
 Tom turkeys	37	16	32	8
 Hen turkeys	40	20	32	8
 Ducks	17	5	13	4
 These values should not be used in place of a regular manure analysis as true nutrient content varies drastically depending on feeding and manure storage and handling practices.
Use only for planning purposes.
Table 23.4 Nitrogen credits from previous legume crop.
Green Manure	>5	150
 Soybeans, edible beans, peas,
 lentils and other annual legumes
 1 No-till corn into alfalfa or green manure crop: use half credit first year.
Other tillage systems: use full credit.
2 For second year following alfalfa and green manure crops: use half credit.
3 Includes sweet clover, red clover, and other similar legumes.
If no-tillage has been followed for less than 5 years, then the N rate should be increased 30 lbs N/acre.
For fields that have been in no-tillage for more than 5 years, the adjustment should be zero.
Examples are below.
Example 23.1 Examples for estimating N requirement.
Field A: Estimate the corn grain N recommendation if the yield goal is 200 bu/acre, prior soybean yield is 60 bu/acre, and the nitrate-N amount in the surface 2 feet is 60 lbs/acre.
The field is chisel plowed.
N recommendation = 200 X 1.0 residual N credit soybean credit Residual N credit is 60 lbs N/acre and the soybean credit is 40 lbs N/acre 
 N recommendation= 200 lbs N/acre 60 lbs N/acre 40 lbs N/acre = 100 lbs N/acre
 Field B: No-tillage for 7 years, yield goal is 200 bu/acre, nitrate-N is 60lbs/acre, and the previous crop was corn.
For this field the recommendation is as follows:
 Nitrogen recommendation = 1.0 X 200 60 = 140 lb N/acre.
The field had been in no-tillage for 7 years and therefore a tillage adjustment is not used
 Field C: No-tillage for 3 years, yield goal 200 bu/acre, nitrate-N is 60 lbs/acre and soybeans was the previous crop.
Nitrogen recommendation = 1.0 X 200 60 40 + 30 = 130 lbs N/acre
 Phosphorus  exists in soil solution, mineral, and organic forms.
About 1% of P is in solution , 85% is in mineral form, and 14% is in organic form.
It is not recommended to apply P to production fields if Olsen or Bray soil test P exceeds 100 ppm.
Off-site movement of P generally occurs with runoff and erosion, as P is strongly attached to soil.
The transport of P from production fields to streams and lakes can result in algal blooms, which impact fisheries and other wildlife.
Transport is minimized when conservation-tillage practices are adopted.
Concentrations of P in runoff waters can be reduced by:
 1.
Minimizing the exposure of manure and fertilizer to runoff water.
2.
Only applying P where it is needed.
3.
Maintain a buffer between "fertilized" and surface water or drainage.
4.
Consider developing and maintaining "grassed" or "wooded" buffers or filter strip.
5.
Avoid application of manure on frozen or snow-covered ground.
Figure 23.4 The phosphorus cycle.
6.
Maintain crop residues above 30% to reduce erosion and incorporate the P when possible.
The optimal pH value for P availability is about 6.8, and increasing or decreasing the soil pH values from this value reduces its plant availability.
Clay soils in the western part of the state often have high soil calcium  and magnesium  levels that reduce soil test P levels.
Irrespective of the soil test P values, these high clay soils may not respond to P fertilizer.
The soil test categories are an index that is correlated to a probability of a yield response from added fertilizer.
Soil samples analyzed during 2010 at the SDSU Plant Science Soil Testing Laboratory showed that 50% of the samples were in the medium or below soil test P categories.
Phosphorus-deficiency symptoms appear in corn as "purpling" of leaves, most commonly seen during
 early growth stages.
New leaves may not show coloration and P-deficient plants are shorter.
The symptoms may disappear as the plant matures.
Some hybrids will not show coloration, even when limiting.
Symptoms may appear even though soil test phosphorous  levels are high.
Deficiency symptoms can result from cool or dry soil conditions, compacted soils, and root systems that have been reduced by tillage, cultivation, and insects.
In soils that test high for P, banding 30 lbs P2 acre at planting may increase early growth but may not increase yield.
In soils with low to medium soil test levels, banded P application at planting usually increases yields.
Banding P is most effective when the yield is > 150 bu/ acre, when < 40 lbs P /acre is applied, and the soil test P level is < 10 ppm.
Additional details on starter, pop-up, banding P is available in Chapter 26.
A bushel of corn removes about 0.38 lbs of P2O5 Based on this estimate, a 150 bu/acre corn crop removes 57 lbs of P2O5 5
 Figure 23.5 P-deficient corn symptoms appear as leaf "purpling" along leaf edges and slow and stunted growth.
Symptoms most often appear early in the season, especially in low areas with high water tables.
Phosphorus-deficient corn plants are always purple, but not all purple plants are P deficient, as the symptom can also be caused by anything interfering with early corn root development.
Potassium-deficiency symptoms appear as leaf yellowing and burning Soil Test Level that begins at the tip of older leaves and, unlike N deficiency symptoms, Soil Test Method Very Low Low Medium High High Very cause yellowing at the leaf margins ppm first before intensifying later in the Olsen 0-3 4-7 8-11 12-15 16+ season to include the mid-rib.
These symptoms are often Probability of a observed in: 1) plants where root yield response 80% 50-80% 20-50% 10-20% growth is limited by adverse soil/soil moisture conditions; 2) sandy soils and organic soils; and 3) fields where the crop residues were harvested.
Potassium deficiencies start in older tissues and may progress up the plant.
Lodged corn plants  may be K deficient.
About 0.27 lbs.
of K2O are removed by each bushel of corn grain.
The amount of K2O removed with each ton of silage averages about 7.3 lbs/ton, and the K2O removed when harvesting the amount of stover that produced 1 bushel of grain is about 1.1 lbs of K2O per bushel of grain.
Table 23.5 Soil test P levels for corn using the Bray and Olsen extraction methods.
Example 23.2 Calculating the P2O5 5 recommendation if the corn yield goal is 220 bu/acre, the soil contains 7 ppm Olsen-P, and 6 tons of solid beef manure are applied.
In this equation, FPR is the fertilizer P recommendation in pounds of P o /acre, STP is the soil test P value, and RYG is realistic yield goal.
The 2 manure credit is estimated from data in Table 23.6.
FPR =  xRYG FPR =  x 220=86.2 lbsP2Og/acre
 6 tons/acre x3 lbs P2O/ton X 0.9 lbs available P/lbs of applied P = 16.2 lbs P2O/acre
 Recommendation 1=86.2-16.2 =70 lbsP2Og/acre
 FPR = fertilizer P2O/acre recommended
 RYG = realistic yield goal 
 STP = the soil test Olsen P result 
 This calculation assumes that 90% of the manure P is available to the plant.
Table 23.6 Estimated phosphorus content of manure.
If an analysis of the manure is available, assume 90% of total P is available.
Liquid 	Solid 
 Grow-Finish	42	9
 Dairy Cow	15	3
 Veal calf	22	3
 Beef COWS	16	4
 Feeder calves	18	4
 Finishing cattle	18	7
 Tom turkeys	40	50
 Hen turkeys	38	50
 These values vary depending on feeding and manure storage and handling practices and are not likely representative of actual manure nutrient content.
Use only for planning purposes.
These values should not be used in place of a regular manure analysis.
Figure 23.7 Potassium-deficiency symptoms appear as burning of leaf edges in corn.
Using stalks for one's own livestock  results in most of the stalk K being returned to the field as manure.
Most agricultural soils in South Dakota have relatively high K levels.
However, positive yield responses to K fertilizer applied as starter or broadcast have been observed.
In South Dakota, K fertilizer recommendations are based on yield goals and the amount of K extracted from a 0to 6-inch soil test value using the equations in Table 23.7.
If manure is applied, K fertilizer may not be needed as manure usually has high amounts of K.
Due to the risk of corn seed germination, and the low probability of K responses in high K soils, application of K as a pop-up fertilizer should be considered risky.
Zinc and Iron Fertilizer Recommendations
 Micronutrient deficiencies usually result from environmental conditions and may be temporary.
If Corn for Grain micronutrient deficiencies are suspected, soil testing is recommended.
Table 23.8 can be used to determine the Zn and Fe recommendations.
In most situations, Corn for Silage secondary  and micronutrients  have a limited impact on South Dakota corn Where: yields.
However, Zinc  deficiencies can be observed in coarse-textured soils, eroded soils, organic soils, or soils with high levels of P.
Seasonal climate conditions may also affect Zn availability because Zn-deficiency symptoms, feathering and striping on the youngest leaves, are often observed in cool, wet soils.
Zinc recommendations are in Table 23.8.
As of 2015, the zinc recommendations are under revision.
Initial analysis suggests that 2.5 lbs Zn/acre should be applied to soils in the high range.
Table 23.7 Calculating a K recommendation.
FKR =  X RYG
 FKR=  X RYG
 FKR = Fertilizer K Rate  STK = Soil Test K Value  RYG = Realistic Yield Goal 
 Iron  deficiencies may be observed in leveled or eroded soil where the calcareous subsoils have been exposed.
Iron-deficiency symptoms in corn are observed as yellowing with interveinal striping of younger
 Table 23.8 Corn zinc and iron recommendations.
Zinc soil test interpretation	Zinc recommendations	Fe soil test	Fe recommendation
 			
 0-0.25 Very low	10	0-2.5 low	0.15
 0.26-0.50 Low	10	2.6-4.5	0.15
 0.51-0.75 Medium	5	>4.5	0
 1.01 + Very high	0
 1Based on inorganic products as source of zinc such as zinc sulfate
 leaves.
Correcting for Fe deficiency can be difficult, and an effective approach to minimize yield losses is to apply manure or biosolids.
No-tillage can result in slower early season growth.
Use of residue managers to darken the soil at planting can help, but not completely overcome the slower start.
Use of strip-tillage, with the strip-tillage conducted in the fall has resulted in similar corn growth patterns to conventional-till in several studies.
Starter fertilizer applied with or near the seed can be used to enhance early season growth.
If N or K is applied with the seed, the total amount added should not exceed 10 lbs of N + K2O.
If possible, N fertilizer should be subsurface band-applied.
In no-tillage systems, it is recommended that the N rate be increased 30 lbs/ acre if the field has been in continuous no-till for less than 5 years.
Nitrogen is best applied in no-till/ strip-till beneath the residue using a coulter or coulter-led shank.
If N must be applied to the soil surface, banded urea ammonium nitrate  or broadcast urea with either NBPT  or Limus  are better options than broadcast UAN.
Use of urease inhibitors generally prevent ammonia volatilization from urea for about 10 days.
Broadcasting urea onto residue-covered fields in the fall can result in a substantial amount of N loss and is not recommended.
Winter application of urea to frozen soils is not recommended.
The lease agreement must include provisions regarding termination of the tenant.
Often, the terms of the agreement allow the landowner to purchase the pivot and/or power unit from the tenant.
We cannot emphasize enough that these provisions should be reviewed by an attorney.
Make sure the lease clearly states  if the landowner has the option to or is required to purchase the equipment upon the termination of the tenant,  how the purchase price of the equipment will be determined, and  if the tenant must remove the equipment, how soon must that be done from the date of the termination notice.
Understanding the Numbers in Your Irrigation Water Report
 Leo Espinoza Associate Professor Soil Scientist
 Chris Henry Associate professor and Water Management Engineer
 Mike Daniels Professor and Extension Soil and Water Conservation Scientist
 Arkansas Is Our Campus
 Arkansas ranks third nationally in the number of irrigated acres with 4.2 million.
Irrigation represents a significant portion of the total production costs needed to optimize crop growth potential.
The University of Arkansas System Division of Agriculture recommends that irrigation water be tested to ensure that it is suitable to grow a particular crop or to develop management practices that may alleviate existing issues such as high soil salt levels.
Not only can poor quality irrigation water damage existing crops, but it can also damage the soil's productivity for future growing seasons.
For such reasons, understanding a water analysis report can be critical for sustainable crop production.
The objective of this factsheet is to inform readers what the reported irrigation water test results may mean to their production system.
How to Collect a Water Sample
 The collection of a representative water sample is critical for the correct quality assessment of irrigation waters.
Great attention should be taken regarding sampling recommendations.
Samples should be collected in clean bottles, which can be obtained from your local Extension office.
However, any new bottle can also be used to collect water samples.
If the water sample comes from a well, let the pump run for at least 30 minutes before collecting the sample.
If the sample is coming from a reservoir or river, the water should be
 Typical Water Quality Parameters Measured
 The Arkansas Water Resources Center  Water Quality Laboratory , located in Fayetteville, provides analytical services for water samples intended for crop irrigation, livestock and poultry watering, fish pounds, and domestic supplies.
The WQL has adopted a Quality Assurance Plan that meets or exceeds all requirements for certification by the Arkansas Department of Environmental Quality and the United States Environmental Protection Agency.
A typical irrigation water analysis report will include measures of pH, salinity level , alkalinity, hardness, calcium, magnesium, sodium, iron, manganese, bicarbonate, fluoride, chloride, sulfate, nitrate-nitrogen, total suspended solids, sodium absorption ratio, and aggressive index.
The pH of the water sample, just like with soils, indicates the acidity and alkalinity of the sample.
Many of the water samples analyzed by the lab test alkaline  due to the presence of carbonates.
Nutrient availability to plants will increase the pH of the soil and continued use of irrigation water with alkaline pH can affect the availability of some micronutrients, particularly zinc, molybdenum, manganese, and iron.
Often, a soil pH gradient can be observed in fields that are flood irrigated with more alkaline pH levels at the top of the field near the water entrance and acidic pH conditions at the lower end of the field where the water exits.
Acidic pH  will affect the availability of other nutrients, such as phosphorus.
The solubility of some of the heavy metals of concern, such as lead and cadmium, increases significantly under acidic conditions.
Salt level  is one of the most important parameters requested by farmers, as high concentrations of dissolved salts can severely affect crop growth.
While sodium chloride is probably the most common salt compound in irrigation water, a water sample may also contain other salts such as those formed with carbonates, bicarbonates, sulfates, and nitrates, and ions such as sodium, chloride, magnesium, sodium, and potassium.
Salinity is then a measure of the concentration of all dissolved ions of the salts in the water sample.
Irrigation water testing 2000 uS/cm will add approximately 1000 lbs of salt per acre with each furrow irrigation event.
Salinity is not measured directly, but rather indirectly using electrical conductivity.
The conductivity of water is affected by the presence of the ions mentioned before and by temperature, SO the higher the temperature, the higher the EC value.
The water analysis report will show EC levels at 75 F; this value will probably be higher if the EC was measured at the edge of the field during the summer months.
Electrical conductivity can also be monitored during the season with low-cost hand-held instruments.
The WQL reports EC as microsiemens per centimeter.
Other labs may report EC in micromhos  or millimhos  per centimeter.
Table 1 shows conversion units for the different reporting units for electrical conductivity.
Table 2 shows reported reference EC values for water samples.
Crops vary in their sensitivity to increased salinity levels, with cotton normally being more resistant than rice or soybean.
Seedling rice can be susceptible to salt damage at levels near 1200 uS/cm.
Table 1.
EC unit conversion table.
Decisiemen per meter 	1
 Microsiemen per centimeter 	1000
 Millimho per centimeter 	1
 Micromho per centimeter 	1000
 Alkalinity is the term used to describe water samples testing pH above 8.5, which are normally associated with high bicarbonates  and carbonates  levels.
Carbonates readily bond with an H+ ion and take the acid-forming ion out of the solution thereby acidification compared with fields where well water is used because most wells contain bicarbonates, which make soils more alkaline.
Table 3 shows reference levels for limitations when using irrigation water with different levels of alkalinity.
Follow all label instructions regarding use on specific plants and insects and pesticide application rates, methods, and timing.
Calibrate, clean, and maintain all application equipment properly.
Special steps for farmers and ranchers
 Maintain irrigation equipment and monitor output to minimize the potential for runoff or deep percolation  losses.
Consider using setback areas, vegetative filter strips, contour farming, and other practices as appropriate to reduce runoff losses from irrigation and precipitation.
Prevent back-siphoning; use adequate
 backflow prevention devices in
 mixing chemicals and filling tanks.
In
 operations, use backflow protection
 Properly close abandoned water wells.
Plan to minimize risk
 Identify water wells, surface drainage, and other potential pathways for contamination.
Avoid using, storing, or mixing pesticides near these areas.
Note potential sources of contamination, including chemical storage and mixing areas.
Secure these areas to minimize the risk of accidental spills and prevent contact with water.
Prepare plans to prevent contamination and to respond to emergencies.
Special steps for homeowners and small acreage landowners
 Choose a pesticide based on the labeled uses and the user licensing requirements.
Contact your Extension agriculture, natural resources, or integrated pest management agent regarding pesticide application and licensing requirements.
Guidance and assistance were provided by the Texas Groundwater Protection Committee and the Texas Commission on Environmental Quality.
The effort was partially funded by the U.S.
Environmental Protection Agency.
19M, New
 Texas A&M AgriLife Extension Service
 Educational programs of the Texas A&M AgriLife Extension Service are open to all people without regard to race, color, sex, disability, religion, age, or national origin.
Produced by Texas A&M AgriLife Communications
 Keep Pesticides Out of Texas Water Supplies
 Best Management Practices to Prevent Pesticide Contamination
 Dana Porter Associate Professor and Extension Agricultural Engineering Specialist-Water Management The Texas A&M University System
 Demands are increasing for Texas' limited water supplies, SO it is critical that we protect them from contamination.
Pesticides offer many benefits and are important tools in ensuring a dependable and pest-free food supply and fiber for clothing.
They help us control insects and rodents in our homes and at work.
They also help us to control weeds, diseases, and insect pests in our lawns, landscapes, sports fields, and, most importantly, in our agricultural crops, fields, and grazing lands.
However, we need to use pesticides carefully to minimize the risk of harming the environment and our health.
Pesticides have been detected in some of Texas' drinking water supplies, largely well below the U.S.
Environmental Protection Agency's  Maximum Contaminant Level.
Specific Best Management Practices  regarding pesticide use and drinking water treatment were implemented to reduce pesticide levels in the water.
Prevention is superior to cleaning up pesticide-contaminated
 Figure.
1 Some of the ways pesticides may disperse and break down in the environment.
groundwater.
Reading and following the directions on the pesticide label is vital for protecting our water resources.
By following the pesticide label directions and the suggestions in this brochure, you can be part of the prevention efforts to ensure cleaner water for your children and for all Texans.
Where do pesticides go?
After pesticides are applied, they may evaporate  into the air, dissolve in water, adhere to soil particles , be taken up in or attached to plants, or be broken down by sunlight  or by microorganisms .
Pesticides may be transported to groundwater through leaching or to surface water through runoff, erosion, and sedimentation.
Four properties of pesticides can affect the risk of water contamination:
 Solubility determines how readily a chemical dissolves in water.
Adsorptivity determines how strongly a chemical is absorbed to soil particles.
Volatility determines how quickly a chemical will evaporate in air.
Degradation describes how quickly a chemical breaks down because of biological and environmental factors.
The information and instructions on a pesticide label take these properties into account when describing the proper use of the pesticide.
Local conditions that affect risk of contamination
 Several factors influence the movement of pesticides in the environment:
 Soil texture affects how quickly water moves through soil; how much water can be stored in the soil; and, how much surface area is available on the soil particles for adsorption.
Water moves quickly through coarse  soils posing a higher risk for groundwater contamination than finer textured  soils.
Organic matter in the soil reduces the risk of water pollution because it increases the potential for adsorption.
It also supports higher populations of microorganisms that can break down the pesticides.
Topography, soil structure, soil surface condition, and soil moisture affect water movement into and through the soil, which influences the risks of contaminants leaching to groundwater or contaminated water running off into surface water.
The distance from groundwater and surface water resources, the depth to groundwater, and the nearness of abandoned or poorly built water wells also affect risk of contamination.
How can I help protect our water from pesticides?
If you live in an area where the local conditions encourage fast movement of water to groundwater or surface water resources, you need to be even more careful to prevent pesticides from moving from your property into water supplies.
Use integrated pest management strategies
 Choose the right chemical for the problem.
Apply it at the right time for efficient and effective control.
Consider crop rotations, conservation tillage practices, optimum planting and harvest dates, and other strategies to achieve good crop results while minimizing the need for pesticides.
Check with your Extension agriculture, natural resources, or integrated pest management agent for specific integrated pest management recommendations.
Store, handle, and dispose of pesticides properly
 Always read and follow the directions on the pesticide label!
Store, handle, mix, apply, and dispose of chemicals according to the instructions on the product label, and keep the pesticides away from water wells or water drainage areas.
To minimize the need for disposal, buy and mix only the amount of chemical that is needed.
Contain and clean spills quickly.
Avoid spraying, mixing, and rinsing tanks within 50 feet of a wellhead; use a longer hose or use a water spigot away from the wellhead, if possible.
Consider installing a concrete pad, detention storage or berms to contain chemicals, spills, and rinse liquids in your mixing and tank-filling area.
Read and follow the label directions!
Observe all restrictions on location, soil types, depths to water table, and other limitations as noted on the label.
Tony Provin and J.L.
Pitt*
 f your soil has a high salinity content, the plants growing there will not be as vigorous as they would be in normal soils.
Seeds will germinate poorly, if at all, and the plants will grow slowly or become stunted.
If the salinity concentration is high enough, the plants will wilt and die, no matter how much you water them.
Routine soil testing can identify your soil's salinity levels and suggest measures you can take to correct the specific salinity problem in your soil.
The terms salt and salinity are often used interchangeably, and sometimes incorrectly.
A salt is simply an inorganic mineral that can dissolve in water.
Many people associate salt with sodium chloridecommon table salt.
In reality, the salts that affect both surface water and groundwater often are a combination of sodium, calcium, potassium, magnesium, chlorides, nitrates, sulfates, bicarbonates and carbonates.
These salts often originate from the earth's crust.
They also can result from weathering, in which small amounts of rock and other deposits are dissolved over time and carried away by water.
This slow weather-
 Table 1.
Typical salts found in irrigation water.
Table salt	Sodium chloride	NaCl
 Glaubers salt	Sodium sulfate	Na2SO4
 Baking soda	Sodium bicarbonate	NaHCO3
 Epsom salt	Magnesium sulfate	MgSO4
 Gypsum	Calcium sulfate	CaSO4 2H2O
 Street salt	Calcium chloride	CaCl2 2H2O
 Muriate of potash	Potassium chloride	KCI
 Muriate of sulfate	Potassium sulfate	K2SO4
 ing may cause salts to accumulate in both surface and underground waters.
The surface runoff of these dissolved salts is what gives the salt content to our oceans and lakes.
Fertilizers and organic amendments also add salts to the soil.
*Professor and Extension Soil Chemist, Extension Program Specialist; The Texas A&M University System.
Effects of salts on plants
 As soils become more saline, plants become unable to draw as much water from the soil.
This is because the plant roots contain varying concentrations of ions  that create a natural flow of water from the soil into the plant roots.
As the level of salinity in the soil nears that of the roots, however, water becomes less and less likely to enter the root.
In fact, when the soil salinity levels are high enough, the water in the roots is pulled back into the soil.
The plants become unable to take in enough water to grow.
Each plant species naturally contains varying levels of root salts.
This is why some plants can continue to thrive when others have died.
If the salinity concentration in the soil is high enough, the plant will wilt and die, regardless of the amount of water applied.
Figure 1 shows how the various salt concentrations affect the movement of water from the soil to plants.
Salinity is of greatest concern in soils that are:
 Irrigated with water high in salts;
 Poorly drained, allowing for too much evaporation from the soil surface;
 Naturally high in salts because very little salt leaches out;
 In areas where the water table  is shallow; or
 In seepage zones, which are areas where water from other locations  seep out.
The major source of salinity problems is usually irrigation water.
This is a gradual process-the salts must accumulate over time before any effects are
 Figure 1.
Increased salts in root zone can result in decreased water uptake by plant.
seen.
Fortunately, plants take up many salts in the form of nutrients.
But when more salt is added to the soil than is removed, the plants will eventually be affected.
In some soils, irrigation and rainwater move through the soil to leach out the salinity.
Leaching occurs when water moves materials  downward through the soil.
Several soil factors can inhibit leaching: a high clay content; compaction; a very high sodium content; or a high water table.
Salt problems occur when water remains near the surface and evaporates, and when salts are not dissolved and carried below the root zone.
Soils naturally high in soluble salts are usually found in arid or semi-arid regions, where salts often accumulate because there is not enough rainfall to dissolve them and leach them out of the root zone.
Salt spray near coastlines can also cause salts to build up in the soil.
In areas with shallow water tables, water containing dissolved salts may move upward into the rooting zone.
This occurs by capillary action , where evaporation serves as the suction of water up through the soil.
Water moves the farthest through finer clay and clay loam soils; it moves less in medium-textured soils ; and least in coarser, sandy soils.
To determine the type of problem in your soil, collect a soil sample and have it tested.
The best indicator of the extent of a salt problem is a detailed salinity analysis, in which water is extracted from a paste.
This test measures the pH, electrical conductivity  and water-soluble levels of the soil.
EC is a measure of the amount of dissolved salts in the paste of soil and water.
Salt buildup can result in three types of soils: saline, saline-sodic and sodic.
Saline soils are the easiest to correct; sodic soils are more difficult.
Each type of soil has unique properties that require special management.
Figure 2.
Leaching is the process of adding sufficient water to the soil to dissolve salts and carry them out of the root zone.
a.
When the salt concentration in the soil is less than that in the plant, water moves from the soil into the plant.
b.
When the salt concentration in the soil is equal to that of the plant, there is no net movement of water.
C.
When the salt concentration in the soil is greater than that of the plant, water moves from the plant into the soil.
Saline soils contain enough soluble salts to injure plants.
They are characterized by white or light brown crusts on the surface.
Saline soils usually have an EC of more than 4 mmho cm-.
Salts generally found in saline soils include NaCl , CaCl2, gypsum , magnesium sulfate, potassium chloride and sodium sulfate.
The calcium and magnesium salts are at a high enough concentration to offset the negative soil effects of the sodium salts.
The pH of saline soils is generally below 8.5.
The normal desired range is 6.0 to 7.0, but many Texas soils are naturally 7.5 to 8.3.
Leaching the salts from these soils does not increase the pH of saline soils.
Saline-sodic soils are like saline soils, except that they have significantly higher concentrations of sodium salts relative to calcium and magnesium salts.
Saline-sodic soils typically have an EC of less than 4 mmho cm- and the pH is generally below 8.5.
The exchangeable sodium percentage is more than 15 percent of the cation exchange capacity.
CEC is a measure of the soil's capacity to hold cations, namely, calcium, magnesium, potassium, sodium, hydrogen and aluminum.
The higher the CEC, the more problematic the removal and remediation of the salt problem.
Water moves through these soils much as it does in saline soils, although the steps for correcting salinesodic soil are different.
Simply leaching the salts from this soil will convert it from saline-sodic to sodic soils.
Sodic soils are low in soluble salts but relatively high in exchangeable sodium.
Sodic soils are unsuitable for many plants because of their high sodium concentration, which may cause plant rooting problems, and because of their high pH, which generally ranges from 8.5 to 12.0.
These high sodium levels disrupt both the chemical and physical composition of soil clays.
As a result, the soil surface has low permeability to air, rain and irrigation water.
The soil is sticky when wet but forms hard clods and crusts upon drying.
This phenomenon may not occur in very sandy soils because they lack clay content.
When salts accumulate in soils, problems arise for two main reasons: the soil becomes less permeable, and the salt damages or kills the plants.
The first problem is associated with the soil structure.
In sodic soils, high levels of exchangeable sodium cause the individual sand, silt and clay particles to be separated and not clumped together into larger particles.
This dispersion makes the soil tight and impervious, SO that it allows little air, rain or irrigation water to permeate into the soil.
Therefore, the plants may not receive enough moisture and oxygen to grow.
Salts may accumulate on the soil surface because they cannot leach out of the root zone.
Plants can also be damaged by salt effects or toxicity.
In saline and saline-sodic soils, high concentrations of soluble salts reduce the amount of available water for plants to use.
High levels of sodium can be toxic to certain plants.
Also, the very high soil pH in high-salt soils greatly changes the nutrients available to the plants.
These
 high pH levels change the ionic form of many plant nutrients to forms that make them unavailable to plants.
Salt-affected soils can be corrected by:
 A combination of these methods
 Improving drainage: In soils with poor drainage, deep tillage can be used to break up the soil surface as well as claypans and hardpans, which are layers of clay or other hard soils that restrict the downward flow of water.
Tilling helps the water move downward through the soil.
While deep tillage will help temporarily, the parts of the soil not permanently broken up may reseal.
Leaching: Leaching can be used to reduce the salts in soils.
You must add enough low-salt water to the soil surface to dissolve the salts and move them below the root zone.
The water must be relatively free of salts , particularly sodium salts.
A water test can determine the level of salts in your water.
Leaching works well on saline soils that have good structure and internal drainage.
To leach a highly saline soil, you may need to apply as much as 48 acreinches of water.
An acre-inch is the volume of water that would cover 1 square acre to a depth of 1 inch.
Testing is often needed to determine how much water is needed to correct a particular soil.
The testing laboratory can advise on how much water to add.
After an application, the soil often must be retested to determine whether enough salts were leached out.
Highly saline soils should be leached using several applications, so that the water can drain well.
Here again, drainage can be a problem.
If the water cannot infiltrate the soil, the salts cannot be dissolved and leached out of the soil.
Reducing evaporation: Applying residue or mulch to the soil can help lower evaporation rates.
Chemical treatments: Before leaching saline-sodic and sodic soils, you must first treat them with chemicals, to reduce the exchangeable sodium content.
To remove or exchange with the sodium, add calcium in a soluble form such as gypsum.
Again, the laboratory analysis can determine how much calcium to add.
After the calcium treatment, the sodium can then be leached through the soil along with the other soluble salts.
Gypsum is the most common amendment used to correct saline-sodic or sodic soils that have no calcium source such as gypsum or free carbonates.
These are available at garden centers and agricultural supply stores.
Another amendment, calcium chloride, is used in some places, but it is seldom available in most areas.
Many soils in the southern and western two-thirds parts of Texas contain significant concentrations of free limestone, which contains calcium carbonate.
Unfortunately, these calcium sources do not dissolve in soils with high pH and therefore cannot help lower sodium levels.
If your soil contains free carbonates, you can add acids to it to form gypsum, which will react with the soil to remove the exchangeable sodium.
Add sulfuric acid, sulfur, iron sulfates and aluminum sulfate, which will react in the soil to produce acid.
The acid will then react with the calcium carbonates  to form calcium sulfate , water and carbon dioxide.
The acidity may also displace some of the sodium.
Table 2 lists typical amendments used to correct salt-affected soils.
Although all of these amendments work, to use them you must know the amount of reactive limestone present.
In general, gypsum is the safest and most effective material.
Steps for treating sodic and saline-sodic soils
 Correcting saline-sodic and sodic soils is a slow process that must be carried out in steps:
 1.
Treat the surface first, then continue to the lower depths.
2.
Apply an amendment to the soil surface and disk it in.
3.
Add 10 to 12 inches of water.
As when correcting saline soils, you must add enough water to dissolve as well as maintain the calcium concentrations in solution and to move the salts and sodium through the soil.
However, do not add so much water that it remains ponded on the soil surface for extended periods.
Generally, this process must be repeated over time.
A good goal is to remove the sodium to a minimum depth of 3 to 4 feet.
Test the soil periodically to pinpoint potential salinity problems and to measure your progress in correcting salt-affected soils.
Table 2.
Typical soil amendments for correcting saline and saline-sodic soils1
 to Supply 1,000 Pounds
 Amendment	Chemical Formula	Purity, %2	of Soluble Calcium 
 Gypsum	CaSO4 2H2O	100	4,300
 Calcium chloride	CaCl2 2H2O	100	3,700
 Sulfur4	S	100	800
 Sulfuric acid4	H2 SO4	95	2,600
 Iron sulfate4	FeSO4 7H2O	100	6,950
 Aluminum sulfate4	AI318H2O	100	5,550
 Lime-sulfur solution4,5	Calcium polysulfide	24	3,350
 1	From USDA Agriculture Information Bulletin No.
195.
2 With purities less than these, additional material will need to be supplied.
3	Assumes free carbonates present to react with the amendments that contain no calcium.
4 Sulfur amendments are only used in soils that contain free calcium carbonates.
5 Expressed as sulfur content.
The amount of amendment you need to correct saline-sodic and sodic soils is based on the amount of sodium in the soil.
Several other factors also influence the amount applied: the leaching rate, the solubility and reaction rates of the amendments, and the conversion of free carbonates to gypsum.
If you take steps early, correcting the soil will be easier and less expensive, and it will have less negative impact on soils and plants.
Tom Harrington Master Farmer Training Coordinator
 Michael Daniels Professor, Environmental Management
 Phil Tacker Associate Professor and Extension Engineer
 Water is one of our most abundant, yet precious, natural resources as it is a basic necessity for sustaining human life.
Water makes up more than two-thirds of the weight of the human body, and without it, humans would die in a few days.
The amount of water in our environment is static and cycles to various locations and to various forms.
The United States Geological Survey  estimates the total water volume of the world is 326 million cubic miles.
However, the USGS estimates that
 Arkansas Is Our Campus
 only 0.3 percent of water on earth is in a form usable by humans.
Arkansas has tremendous surface and groundwater supplies.
However, it is also susceptible to drought.
The USGS estimates that 2.3 million Arkansans collectively use 421 million gallons of public-supplied water per day for domestic use.
This equates to over 180 gallons per person per day.
In 2005, precipitation deficits from normal amounts averaged almost 14 inches across the state, which made it the second driest year overall.
The 2005 drought placed tremendous stress on several public water supplies.
Figure 1.
The Water Cycle
 
 Figure 2.
How Much of Earth's Water Is Usable by Humans?
Water usable by humans
 
 Figure 3.
Annual Precipitation Departure From Normal in Inches During 2005
 
 Relieving stress on our water supplies is just one benefit of home water conservation.
Other benefits include decreased water bills, decreased wastewater treatment costs for communities and preservation of our aquatic environment.
The purpose of this publication is to help home water users realize these benefits by providing tips on water conservation.
The information for this article has been adapted from similar publications in other states, and their contributions are noted.
Don't Let It Run.
We have all developed the bad habit of letting the faucet run while we brush our teeth or wait for a cold glass of water.
Keeping a pitcher of water in the refrigerator or turning the faucet off while we brush our teeth can save several gallons of water each day.
It's simple really.
Before you turn on the tap, think of ways you can use less water to accomplish the same purpose.
Fix the Drip.
There is no such thing as a little drip.
A leaky faucet with a drip of just 1/16 of an inch in diameter  can waste 10 gallons
 of water every day.
You can turn off that drip by replacing worn washers or valve seats.
Fix the Silent Leak.
Even worse than the careless hand on the faucet is the silent toilet bowl leak, probably the single greatest water waster in homes.
A leak of 1 gallon every 24 minutes an average amount totals 2.5 gallons per hour or 60 gallons per day.
To check your toilet for a leak, place a few drops of food coloring in the tank and wait.
If the color appears in the bowl, then there's a leak.
Often these leaks can be fixed with a few minor adjustments cleaning calcium deposits from the toilet ball in the tank or replacing worn valves.
Close the Hose.
Letting the garden hose run faster or longer than necessary while we water the lawn or wash the car often becomes a careless and wasteful habit.
A 1/2-inch garden hose under normal water pressure pours out more than 600 gallons of water per hour, and a 3/4inch hose delivers almost 1,900 gallons in the same length of time.
If left on overnight, one garden hose can easily waste twice as much water as the average family uses in a month.
Check the Plumbing.
Proper maintenance is one of the most effective water savers.
Faucet washers are inexpensive and take only a few minutes to replace.
At home, check all water taps, hoses and hose connections  for leaks.
Check the garden hose too it should be turned off at the faucet, not just at the nozzle.
Teach Your Community.
Just as it is important to conserve water in your own home, it is important to help our towns and cities save water by teaching others to use water wisely.
In agricultural areas, water may be saved by using more effective irrigation methods.
In industrial areas, manufacturers can save water by reusing it and by treating industrial wastes.
Cities and towns can save water by eliminating leaks and installing meters.
Wastewater can be treated and reused.
As you conserve water at home and in your community, you will help ensure that the water available now continues to meet the growing water needs of the future.
Tips for Water Usage in the Bathroom
 Check for leaks.
Put a little food coloring in your toilet tank.
If, without flushing, the color begins to appear in the bowl within 30 minutes, you have a leak that should be repaired immediately.
Most replacement parts are inexpensive and easy to install.
Don't use the toilet as an ashtray or a wastebasket.
Every time you flush a cigarette butt, facial tissue or other small bit of trash, 5 to 7 gallons of water is wasted.
Put plastic bottles in your toilet tank.
To cut down on water waste, put an inch or two of sand or pebbles inside each of two plastic bottles to weigh them down.
Fill the bottles with water, screw the lids on and put them in your toilet tank, safely away from the operating mechanisms.
This may save 10 or more gallons of water per day.
Be sure at least 3 gallons of water remain in the tank so it will flush properly.
For new installations, consider buying "low flush" toilets, which use 1 to 2 gallons per flush instead of the usual 3 to 5 gallons.
Install water-saving shower heads and low-flow faucet aerators.
Your local hardware or plumbing supply store has inexpensive, water-saving shower heads or restrictors that are easy for the homeowner to install.
Also, long, hot showers can use 5 to 10 gallons every unneeded minute.
Limit your showers to the time it takes to soap up, wash down and rinse off.
All household faucets should be fitted with aerators.
This single best home water conservation method is also the cheapest!
Take shorter showers.
One way to cut down on water use is to turn off the shower after soaping up and then turn it back on to rinse.
A four-minute shower uses approximately 20 to 40 gallons of water.
Rinse your razor in the sink.
Fill the sink with a few inches of warm water.
This will rinse your razor just as well as running water, with far less waste of water.
Turn off the water after you wet your toothbrush.
There is no need to keep the water running while brushing your teeth.
Just wet your brush and fill a glass for mouth rinsing.
Tips for Water Usage Outdoors
 Don't run the hose while washing your car.
Clean the car using a pail of soapy water.
Use the hose only for rinsing.
Use a broom, not a hose, to clean driveways and sidewalks.
A leaf blower is also helpful if you have a lot of leaves or debris.
Water your lawn only when it needs it.
A good way to see if your lawn needs watering is to step on the grass.
If it springs back up when you move, it doesn't need water.
If it stays flat, the lawn is ready for watering.
Letting the grass grow  will promote water retention in the soil.
Deep-soak your lawn.
When watering the lawn, do it long enough for the moisture to soak down to the roots where it will do the most good.
A light sprinkling can evaporate quickly and tends to encourage shallow root systems.
Put an empty tuna can on your lawn.
When it's full, you've watered about the right amount.
Put a layer of mulch around trees and plants.
Mulch will slow evaporation of moisture while discouraging weed growth.
Water during the cool, non-windy parts of the day.
Early morning is generally better than dusk because it helps prevent the growth of fungus.
Watering early in the day is also the best defense against slugs and other garden pests.
Try not to water when it's windy; wind can blow sprinklers off target and speed evaporation.
Don't water the gutter.
Position your sprinklers so water lands on the lawn or garden, not on paved areas.
Watch out for run-off.
Soil conditions and slopes can lead to run-off if the watering is not managed properly.
The length of time water is applied to an area should be short enough so that excess run-off and the wasting of water does not occur.
Install an automatic water shut-off device.
Consider installing simple control devices that can be set to automatically shut off water flow from faucets and/or hoses.
This can prevent water loss when someone forgets to turn the water off.
Shut-off devices are very affordable and generally available at hardware stores and garden centers.
Use efficient watering systems for shrubs, flower beds and lawns.
You can greatly reduce the amount of water used for shrubs, beds and lawns by strategically placing soaker hoses, rain barrel catchment systems and simple drip-irrigation systems.
Plant drought-resistant shrubs and plants.
Many beautiful shrubs and plants thrive with far less watering than other species.
Replace herbaceous perennial borders with native plants.
Consider applying the principles of xeriscape for a lowmaintenance, drought-resistant yard.
Details about how you can develop your own rain barrel catchment system and plant a water-friendly garden appear below.
Collecting Rainwater for Watering Plants
 Gardeners can play a key role in conserving freshwater by harvesting rainwater.
In addition to reducing demand on our water supplies especially important during drought and summer  rainwater harvesting reduces water pollution.
In a rainstorm, oil, pesticides, animal waste and fertilizers from our lawns, sidewalks, driveways and streets are washed into sewers that often overflow into rivers and estuaries, contaminating fish and other wildlife.
Rainwater harvesting prevents rain from becoming polluted stormwater and puts it to use where it falls.
The quality of rainwater is unsurpassed when it comes to watering plants and landscapes.
Captured rainwater is free of the salts and pollutants associated with ground and surface water.
In urban areas, the natural acidity of rainwater is good for soils that have become alkaline from cement-leached lime.
The natural temperature of rainwater doesn't shock plants with cold the way tap water can.
Best of all,
 rainwater contains no chlorine, a chemical added to drinking water that inhibits plant growth.
And rainwater is free!
Regardless of how much rain your area gets or the size of your landscape, you can design a rainwater harvesting system that works for you.
The most common method of capturing rainwater for irrigation involves taking rain from building gutters and storing it in an outdoor tank or rain barrel.
Ideally, rainwater harvesting systems for irrigation include five basic components:
 1 Catchment or collection area usually a roof
 2 Transport for the water, such as gutters, downspouts and piping
 3 Roof washer to intercept the first flush of rain  from the roof usually a sealed downspout next to the main downspout
 4 Storage tank or barrels
 5 Gravityor pump-driven system for distributing water to the garden
 Bear in mind that only nonpotable usage of rainwater is described here.
Harvesting rainwater for drinking involves several levels of filtration as well as chemicals for disinfection.
The first step in designing a rooftop system is to analyze  the roof-surface materials.
Roof material affects both the amount of water collected and its quality.
For example, porous asphalt shingles and rolled roofing are less desirable than smooth steel  because rough materials absorb more water and bird feces.
Roofs made of wooden shingles treated with chromated copper arsenate are not appropriate for rainwater harvesting.
Zinc antimoss strips mounted on roofs also produce toxic chemicals that you want to keep out of your garden.
Most people already have gutters and downspouts attached to their roofs to transport rainwater away from the building.
Ideally, the gutters should be covered with a leaf screen to keep debris from entering the system.
If you want to divert water from your downspout during the growing season but send it back down the drain during off-season, you can install a downspout diverter.
These simple devices usually cost less than $20 at local hardware suppliers.
There are many landscape plants that can add beauty to your lawn without the use of large amounts of water.
Here are just a few plants you might want to use and a few you should avoid.
Swamp Sunflower 
 Anise Sage 
 Mexican Bush Sage 
 Mexican Bluebell 
 Brown-eyed Susan 
 Lamb's Ears 
 Silver King 
 Red-hot Poker 
 Cast Iron Plant 
 Scarlet Bee Balm  
 Madagascar Periwinkle 
 Medallion Daisy 
 Petunias 
 Mexican Aster 
 Mexican Sunflower 
 Moss Verbena 
 Blue Star 
 Queen Anne's Lace 
 False Dragonhead 
 Trumpet Honeysuckle 
 Common Yarrow 
 Sweet Autumn Clematis 
 Evening Primrose 
 Blackberry Lily 
 Purple Coneflower 
 Virginia Spiderwort 
 Joe-Pye Weed 
 Butterfly Weed 
 Fall Phlox 
 Jupiter's Beard 
 
 Home water conservation provides many benefits.
For individuals, it may lower water bills.
For communities, it reduces public water-supply quantity problems during drought and wastewater treatment costs.
If we all conserve, it may also reduce mandatory use restrictions often imposed by municipalities to curb use during periods of high demand.
The tips listed in this publication can help all Arkansans conserve water.
USING THE K-STATE CENTER PIVOT SPRINKLER AND SDI ECONOMIC COMPARISON SPREADSHEET 2011
 In much of the Great Plains, the rate of new irrigation development is slow or zero.
Although the Kansas irrigated area, as reported by producers through annual irrigation water use reports, has been approximately 3 million acres since 1990, there has been a dramatic shift in the methods of irrigation.
During the period since 1990, the number of acres irrigated by center pivot irrigation systems increased from about 50 per cent of the total irrigated acreage base to about 90 percent of the base area.
In 1989, subsurface drip irrigation  research plots were established at Kansas State University Research Stations to investigate SDI as a possible additional irrigation system option.
Early industry and producers surveys have indicated a small but steady increase in adoption.
Field area as reported by the 2006 Kansas Irrigation Water Use Report indicated that 10,250 acres were exclusively irrigated by SDI systems and an additional 8,440 acres were irrigated partly by SDI in combination with another system type such as an irrigated SDI corner of a center pivot sprinkler or a surface gravityirrigated field partially converted to SDI.
Although Kansas SDI systems represent less than 1 percent of the irrigated area, producer interest still remains high because SDI can potentially have higher irrigation efficiency and irrigation uniformity.
As the farming populace and irrigation systems age, there will likely be a continued momentum for conversion to modern pressurized irrigation systems.
Both center pivot sprinkler irrigation  and subsurface drip irrigation  are options available to the producer for much of the Great Plains landscape.
Pressurized irrigation systems in general are a costly investment and this is particularly the case with SDI.
Producers need to carefully determine their best investment options.
In the spring of 2002, a free Microsoft Excel 1 spreadsheet template was introduced by K-State Research and Extension for making economic comparisons of CP and SDI.
Since that time, the spreadsheet has been periodically updated to reflect changes in input data, particularly system and corn production costs.
The spreadsheet also provides sensitivity analyses for key factors.
This paper will discuss how to use the spreadsheet and the key factors that most strongly affect the comparisons.
The template has five worksheets , the Main, CF, Field size & SDI life, SDI cost & life, Yield & price tabs.
Most of the calculations and the result are shown on the Main tab.
This template determines the economics of converting existing furrow-irrigated fields to center pivot sprinkler irrigation  or subsurface drip irrigation  for corn production.
Field description and irrigation system estimates
 Total	Suggested	CP	Suggested	SDI	Suggested
 Field area, acres	160	160	125	125	155	155
 Non-cropped field area , acres	5	5
 Cropped dryland area, acres 	30	0
 Irrigation system investment cost, total $	$73,450	$73,450	$186,000	$186,000
 Irrigation system investment cost, $/irrigated acre	$587.60	$1,200.00
 Irrigation system life, years	25	25	22	22
 Interest rate for system investment, %	7.0%	7.0%
 Annual insurance rate, % of total system cost	1.60%	1.60%	0.60%	0.60%
 Production cost estimates	CP	Suggested	SDI	Suggested
 Total variable costs, $/acre 	$554.41	$554.41	$536.36	$536.36
 Additional SDI variable costs  or savings , $/acre	Additional Costs	$0.00	$0.00
 Yield and revenue stream estimates	CP	Suggested	SDI	Suggested
 Corn grain yield, bushels/acre	Suggested	220	220	220	220
 Corn selling price, $/bushel	$4.75	$4.75	KSTATE
 Net return to cropped dryland area of field 	$36.00	$36.00	Kansas State University
 Advantage of SDI over Center Pivot Sprinkler *	$/total field each year	$7,039
 * Advantage in net returns to land and management	$/acres each year	$44
 You may examine sensitivity to Main worksheet  assumptions on three of the tabs listed below.
Figure 1.
Main worksheet  of the economic comparison spreadsheet template indicating the 18 required variables  and their suggested values when further information is lacking or uncertain.
ANALYSES METHODS AND ECONOMIC ASSUMPTIONS
 There are 18 required input variables required to use the spreadsheet template, but if the user does not know a particular value there are suggested values for each of them.
The user is responsible for entering and checking the values in the unprotected input cells.
All other cells are protected on the Main worksheet.
Some error checking exists on overall field size and some items  are highlighted differently when different results are indicated.
Details and rationales behind the input variables are given in the following sections.
Field & irrigation system assumptions and estimates
 Many of the early analyses assumed that an existing furrow-irrigated field with a working well and pumping plant was being converted to either CP or SDI and this
 still may be the base condition for some producers.
However, the template can also be used to consider options for a currently center pivot irrigated field that needs to be replaced.
The major change in the analysis for the replacement CP is that the cost for the new center pivot probably would not have to include buried underground pipe and electrical service in the initial investment cost.
The analysis also assumes the pumping plant is located at the center of one of the field edges and is at a suitable location for the initial SDI distribution point.
Any necessary pump modifications  for the CP or SDI systems are assumed to be of equal cost and thus are not considered in the analysis.
However, they can easily be handled as an increased system cost for either or both of the system types.
Land costs are assumed to be equal across systems for the overall field size with no differential values in real estate taxes or in any government farm payments.
Thus, these factors "fall out" or do not economically affect the analyses.
An overall field size of 160 acres  was assumed for the base analysis.
This overall field size will accommodate either a 125 acre CP system or a 155 acre SDI system.
It was assumed that there would be 5 noncropped acres consumed by field roads and access areas.
The remaining 30 acres under the CP system are available for dryland cropping systems.
Irrigation system costs are highly variable at this point in time due to rapid fluctuations in material and energy costs.
Cost estimates for the 125 acre CP system and the 155 acre SDI system are provided on the current version of the spreadsheet template based on discussions with dealers and Dumler et al.
, but since this is the overall basis of the comparison, it is recommended that the user apply his own estimates for his conditions.
In the base analyses, the life for the two systems is assumed to be 25 and 22 years for the CP and SDI systems, respectively.
No salvage value was assumed for either system.
This assumption of no salvage value may be inaccurate, as both systems might have a few components that may be reusable or available for resale at the end of the system life.
However, with relatively long depreciation periods of 22 and 25 years and typical financial interest rates, the zero salvage value is a very minor issue in the analysis.
System life is a very important factor in the overall analyses.
However, the life of the SDI system is of much greater economic importance in analysis than a similar life for the CP system because of the much higher system costs for SDI.
Increasing the system life from 22 to 25 years for SDI would have a much greater economic effect than increasing the CP life from 22 to 25 years.
When the overall field size decreases, thus decreasing system size, there are large changes in cost per irrigated acre between systems.
SDI costs are nearly proportional to field size, while CP costs are not proportional to field size.
Quadratic equations were developed to calculate system costs when less than full size 160 acre fields were used in the analysis :
 CPcost% = 44.4 +  	
 SDIcost% = 2.9 +  	
 where CPcost% and CPsize%, and SDIcost% and SDIsize% are the respective cost and size % in relation to the full costs and sizes of irrigation systems fitting within a square 160 acre block.
Figure 2.
CP and SDI system costs as related to field size.
The annual interest rate can be entered as a variable, but is currently assumed to be 7.0%.
The total interest costs over the life of the two systems were converted to an average annual interest cost for this analysis.
Annual insurance costs were assumed to be 1.6% of the total system cost for the center pivot sprinkler and 0.6% for the SDI system, but can be changed if better information is available.
The lower value for the SDI was based on the assumption that only about 40% of the system might be insurable.
Many of the SDI components are not subject to the climatic conditions that are typically insured hazards for CP systems.
However, system failure risk is probably greater with SDI systems which might influence any obtainable insurance rate.
The cost of insurance is a minor factor in the economic comparison when using the current values.
Production cost assumptions and estimates
 The economic analysis expresses the results as an advantage of SDI or alternatively CP systems in net returns to land and management.
Thus, many fixed costs do not affect the analysis and can be ignored.
Additionally, the analysis does not indicate if either system is ultimately profitable for corn production under the assumed current economic conditions.
Production costs were adapted from KSU estimates.
A listing of the current costs is available on the CF worksheet   and the user can enter new values to recalculate variable costs that more closely match their conditions.
The sum of these costs would become the new suggested Total Variable Costs on the Main worksheet , but the user must manually change the input value on the Main worksheet  for the economic comparison to take effect.
The user may find it easier to just change the differential production costs between the systems on the Main tab rather than changing the baseline assumptions on the CF tab.
This will help maintain integrity of the baseline production cost assumptions.
Factors for Variable Costs	CP	Suggested	SDI	Suggested
 Seeding rate, seeds/acre	$/1000 S Suggested	34000	34000	34000	34000
 Seed, $/acre	$2.62	$2.62	$89.08	$89.08
 Herbicide, $/acre	$30.74	$30.74	$30.74	$30.74
 Insecticide, $/acre	$37.37	$37.37	$37.37	$37.37
 Nitrogen fertilizer, lb/acre	$/lb	Suggested	242	242	242	242
 Nitrogen fertilizer, $/acre	$0.33	$0.33	$79.86	$79.86
 Phosphorus fertilizer, lb/acre	$/lb	Suggested	50	50	50	50
 Phosphorus fertilizer, $/acre	$0.51	$0.51	$25.70	$25.70
 Crop consulting, $/acre	$6.50	$6.50	$6.50	$6.50
 Crop insurance, $/acre	$30.00	$30.00	$30.00	$30.00
 Drying cost, $/acre	$0.00	$0.00	$0.00	$0.00
 Miscellaneous costs, $/acre	$0.00	$0.00	$0.00	$0.00
 Custom hire/machinery expenses, $/acre	$172.95	$172.95	$172.95	$172.95
 Other non-fieldwork labor, $/acre	$0.00	$0.00	$0.00	$0.00
 Irrigation labor, $/acre	$6.50	$6.50	$6.50	$6.50
 Irrigation amounts, inches	17	17	13	13
 Fuel and oil for pumping, $/inch	$3.50	$3.50	$3.50	$3.50
 Fuel and oil for pumping, $acre	$59.50	$45.50
 Irrigation maintenance and repairs, $/inch	$0.60	$0.60	$0.60	$0.60
 Irrigation maintenance and repairs, $/acre	Suggested	$10.20	$7.80
 1/2 yr.
interest on variable costs, rate	7.0%	7.0%	$19.19	$18.62
 Total Variable Costs	$567.59	$550.62
 Figure 3.
CF worksheet  of the economic comparison spreadsheet template and the current production cost variables.
Note that the sums at the bottom of the CF worksheet are the suggested values for total variable costs on the Main worksheet.
The reduction in variable costs for SDI is attributable to an assumed 25% net water savings that is consistent with research findings by Lamm et al..
This translates into a 17 and 13 inch gross application amount for CP and SDI, respectively.
The current estimated production costs are somewhat high reflecting increased energy and other related input costs, but fortunately crop revenues have also increased due to high demand for corn for ethanol production.
This fact is pointed out because a lowering of overall variable costs favors SDI, since more irrigated cropped acres are involved, while higher overall variable costs favors CP production.
The variable costs for both irrigation systems represent typical practices for western Kansas.
Yield and revenue stream estimates
 Changes in the economic assumptions can drastically affect which system is most profitable and by how much.
Previous analyses have shown that the system comparisons are very sensitive to assumptions about
 Size of CP irrigation system
 Shape of field 
 Life of SDI system
 with advantages favoring larger CP systems and cheaper, longer life SDI systems.
The results are very sensitive to
 any additional production cost savings with SDI.
The results are moderately sensitive to
 and very sensitive to
 higher potential yields with SDI
 with advantages favoring SDI as corn yields and price increase.
The economic comparison spreadsheet also includes three worksheet  that display tabular and graphical sensitivity analyses for field size and SDI system
 life , SDI system cost and life , and corn yield and selling price.
These sensitivity analysis worksheets will automatically update when different assumptions are made on the Main worksheet.
The elements in light blue of the sensitivity tables indicate cases where CP systems are more profitable while elements with negative signs in reddish brown are cases where SDI is more profitable.
This tab determines the CP and SDI economic sensitivity to field size, shape,
 and SDI system life.
The elements in the table  represent the CP advantage in net returns per acre.
Field size	160	127	95	64	32	80
 CP Size	125	100	75	50	25	64	Wiper 1/2 circle
 CP Cost	$587.60	$685.38	$827.22	$1,077.78	$1,763.15	$1,147.66
 CP Dry	30	24	18	12	6	14
 SDI Size	155	124	93	62	31	78
 SDI Cost	$1,200.00 $1,226.70 $1,255.60 $1,299.00 $1,400.40 $1,273.72
 SDI life	Note: This sensitivity valid only if full-sized CP  and
 years	SDI  costs exist on Main worksheet  !!!!!!!!
5	$135.67	$136.01	$133.00	$123.93	$98.88	$118.59
 10	$19.42	$16.24	$10.08	-$1.91	-$36.78	-$5.60
 15	-$19.33	-$23.69	-$30.89	-$43.86	-$82.01	-$46.99
 20	-$38.71	-$43.65	-$51.38	-$64.83	-$104.62	-$67.69
 25	-$50.33	-$55.62	-$63.67	-$77.41	-$118.18	-$80.11
 Figure 4.
The Field size & SDI life worksheet  sensitivity analysis.
Note this is one of three worksheets  providing tabular and graphical sensitivity analyses.
These worksheets automatically update to reflect changing assumptions on the Main worksheet.
SOME KEY OBSERVATIONS FROM PREVIOUS ANALYSES
 Users are encouraged to "experiment" with the input values on the Main worksheet  to observe how small changes in economic assumptions can vary the bottom line economic comparison of the two irrigation systems.
The following discussion will give the user "hints" about how the comparisons might be affected.
Smaller CP systems and systems which only complete part of the circle are less competitive with SDI than full size 125 acre CP systems This is primarily because the CP investment costs  increase dramatically as field size decreases  or when the CP system cannot complete a full circle.
It should also be pointed out that part of the economic competitiveness of the higher priced SDI systems with lower priced CP systems occurs simply because less land area of the field is in dryland crop production.
Increased longevity for SDI systems is probably the most important factor for SDI to gain economic competitiveness with CP systems.
A research SDI system at the KSU Northwest Research-Extension Center in Colby, Kansas has been operated for 22 years with very little performance degradation, so long system life is possible.
There are a few SDI systems in the United States that have been operated for over 25 years without replacement.
However, a short SDI system life that might be caused by early failure due to clogging, indicates a huge economic disadvantage that would preclude nearly all adoption of SDI systems.
Although SDI cost is an important factor, long SDI system life can help reduce the overall economic effect.
The CP advantage for SDI system lives between 15 and 20 years is greatly diminished as compared to the difference between 10 and 15 year SDI system life.
The sensitivity of CP system life and cost is much less because of the much lower initial CP cost and the much longer assumed life.
Changing the CP system life from 25 to 20 years will not have a major effect on the economic comparison.
However, in areas where CP life might be much less than 25 years due to corrosive waters, a sensitivity analysis with shorter CP life is warranted.
The present baseline analysis already assumes a 25% water savings with SDI.
There are potentially some other production cost savings for SDI such as fertilizer and herbicides that have been reported for some crops and some locales.
For example, there have been reports from other regions of less broadleaf and grassy weed pressure in SDI where the soil surface remains drier less conducive to germination of weed seeds.
Small changes in the assumptions can make a sizable difference in the economic analysis because there are more irrigated acres under the SDI system.
This tab determines the CP and SDI economic sensitivity to SDI system life and SDI system cost.
The elements in the table  represent the CP advantage in net returns per acre.
SDI Cost SDI system life, years
 $/acre	5	10	15	20	25	30
 900	$65.63	-$21.56	-$50.62	-$65.16	-$73.87	-$79.69
 1000	$88.97	-$7.90	-$40.19	-$56.34	-$66.03	-$72.49
 1100	$112.32	$5.76	-$29.76	-$47.52	-$58.18	-$65.28
 1200	$135.67	$19.42	-$19.33	-$38.71	-$50.33	-$58.08
 1300	$159.01	$33.08	-$8.90	-$29.89	-$42.49	-$50.88
 1400	$182.36	$46.74	$1.53	-$21.08	-$34.64	-$43.68
 1500	$205.71	$60.39	$11.96	-$12.26	-$26.79	-$36.48
 Figure 5.
The SDI cost and life worksheet  sensitivity analysis.
Note this is one of three worksheets  providing tabular and graphical sensitivity analyses.
These worksheets automatically update to reflect changing assumptions on the Main worksheet.
It has already been stated that higher corn yields and higher corn prices improve the SDI economics.
These results can be seen on the Yield and Price sensitivity worksheet  on the Excel template.
This result occurs because of the increased irrigated area for SDI in the given 160 acre field.
The significance of yield and price can be illustrated by taking one step further in the economic analysis, that being the case where there is a yield difference between irrigation systems.
Combining a greater overall corn yield potential with an additional small yield advantage for SDI on the Main tab can allow SDI to be very competitive with CP systems.
This tab determines the CP and SDI economic sensitivity to corn yield and corn price assuming that corn yields are equal for both irrigation systems.
The elements in the table  represent the CP advantage in net returns per acre.
Corn cash price, $/bu
 Corn Yield	$3.60	$4.00	$4.40	$4.80	$5.20	$5.60	$6.00
 160	$43.94	$31.94	$19.94	$7.94	-$4.06	-$16.06	-$28.06
 170	$37.19	$24.44	$11.69	-$1.06	-$13.81	-$26.56	-$39.31
 180	$30.44	$16.94	$3.44	-$10.06	-$23.56	-$37.06	-$50.56
 190	$23.69	$9.44	-$4.81	-$19.06	-$33.31	-$47.56	-$61.81
 200	$16.94	$1.94	-$13.06	-$28.06	-$43.06	-$58.06	-$73.06
 210	$10.19	-$5.56	-$21.31	-$37.06	-$52.81	-$68.56	-$84.31
 220	$3.44	-$13.06	-$29.56	-$46.06	-$62.56	-$79.06	-$95.56
 230	-$3.31	-$20.56	-$37.81	-$55.06	-$72.31	-$89.56	-$106.81
 240	-$10.06	-$28.06	-$46.06	-$64.06	-$82.06	-$100.06	-$118.06
 250	-$16.81	-$35.56	-$54.31	-$73.06	-$91.81	-$110.56	-$129.31
 260	-$23.56	-$43.06	-$62.56	-$82.06	-$101.56	-$121.06	-$140.56
 270	-$30.31	-$50.56	-$70.81	-$91.06	-$111.31	-$131.56	-$151.81
 Figure 6.
The Yield and Price worksheet  sensitivity analysis.
Note this is one of three worksheets  providing tabular and graphical sensitivity analyses.
These worksheets automatically update to reflect changing assumptions on the Main worksheet.
AVAILABILITY OF FREE SOFTWARE
 1 Mention of tradenames is for informational purposes and does not constitute endorsement by Kansas State University.
Similarly, even though ground water is considered public property in Nebraska, you still need the landowners permission to access that ground water if you dont own the land yourself.
Public ownership does not give the public an unlimited right of access to the public resource.
Hydrology Basics and the Hydrologic Cycle
 Zachary M.
Easton, Assistant Professor and Extension Specialist, Biological Systems Engineering Emily Bock, Graduate Research Assistant, Biological Systems Engineering
 This fact sheet presents and explains some common concepts in hydrology and the hydrologic cycle.
The science or study of hydrology focuses on the distribution, occurrence, circulation, and properties of water in the environment.
At its most basic level, hydrology is often defined as the study of water; however, basic concepts in hydrology quickly become complex as they are applied to real-world systems to understand and predict what is occurring.
This fact sheet summarizes these complex relationships and highlights important applications of hydrologic concepts in agroecosystems, including conservation of soil water in the vadose zone to support crop production and water quality.
There are approximately 340,000,000 cubic miles of water on Earth.
If all of this water were poured into a sphere, it would be nearly 900 miles in diameter.
The vast majority of Earth's water is salt water in the oceans.
Only 2.5 percent of the water on Earth is fresh water, and an even smaller portion of that  is fresh water readily available to humans.
Table 1 shows the locations and relative proportions of water on Earth.
Where water is located and its accessibility are important drivers of human habitation, distribution, and success, and they are particularly critical to agricultural production.
One of the most fundamental properties of water is that it is neither created nor destroyed.
That is, there is the same amount of water on Earth today as there was millions of years ago; water just changes phases from liquid to solid to gas.
However, while the mass of water is conserved, water quality is not, and degradation of water quality effectively reduces availability of accessible waters for domestic, industrial, or agricultural uses.
Table 1.
Distribution and sources of water on Earth.
Water volume	Percentage of	Percentage of
 Water source		fresh water	total water
 Oceans	321,000,000	-	96.5000
 Glaciers and permanent snow	5,773,000	68.700	1.7400
 Groundwater	5,614,000	-	1.6900
 Saline	3,088,000	-	0.9300
 Fresh	2,526,000	30.100	0.7600
 Ground ice and permafrost	71,970	0.860	0.0220
 Lakes	42,320	-	0.0130
 Fresh	21,830	0.260	0.0070
 Saline	20,490	-	0.0060
 Soil moisture	3,959	0.050	0.0010
 Atmosphere	3,095	0.040	0.0010
 Swamp water	2,752	0.030	0.0008
 Rivers	509	0.006	0.0002
 Biological water 	269	0.003	0.0001
 Adapted from Shiklomanov.
Produced by Communications and Marketing, College of Agriculture and Life Sciences, Virginia Tech, 2015
 Two types of pollution impact water quality:  point source pollution, which is direct discharge into the environment such as from wastewater treatment plants; and  nonpoint source pollution, which is composed of diffuse inputs such as urban stormwater or agricultural runoff.
Transportation of pollutants involves processes occurring both above and below the ground surface.
Pollutants typically associated with surface runoff include excess sediment and phosphorus, while groundwater can transport nitrogen and discharge contaminated waters to streams and rivers as baseflow.
Because transport of nonpoint source pollution is mainly driven by the movement of water, an understanding of hydrology and the hydrologic cycle is critical to managing our water resources to support human needs.
The water consumption of humans for domestic use ranges from 3 to 5 gallons per person per day in developing nations to 150 gallons per person per day in the U.S.
If industrial and agricultural water consumption is included in the calculation, the average per capita fresh water use in the U.S.
is approximately 1,340 gallons per day.
Ensuring adequate water supply for these uses requires that three important characteristics of water are sufficient: accessibility, quantity, and quality.
Components of the Hydrologic Cycle
 The hydrologic cycle is composed of two phases, the first of which is the atmospheric phase, which describes water movement as gas  and liquid/solid  in the atmosphere.
The
 Figure 1.
The basic hydrologic cycle.
Source: The COMET Program.
second phase is the terrestrial phase, which describes water movement in, over, and through the Earth.
The terrestrial phase is often broken down into the surface water phase  and the groundwater phase.
The following sections further define the individual components of the hydrologic cycle.
Refer to figure 1 for a graphical interpretation of how the various components interact.
Precipitation is any type of condensation of atmospheric water vapor that falls under gravity and includes rain, snow, sleet, hail, and fog.
The amounts and types of precipitation affect soil development, vegetation growth, and the generation of runoff, which transports soils, nutrients, and pollutants.
Water that evaporates  from the Earth's surface is stored as water vapor in the atmosphere before returning to the Earth's surface as precipitation.
As rain falls from the atmosphere, some is caught by vegetation , and this is called "interception." A portion of intercepted rainfall is evaporated back to the atmosphere from the plant surfaces and never reaches the ground.
The rainfall that does reach the soil surface is referred to as net rainfall.
Annual precipitation in Virginia averages 40 inches statewide and ranges from 38 inches in the western mountains to about 45 inches on the eastern Coastal Plain.
Important aspects of precipitation include the annual amount and type , which has important consequences for plant water availability, soil moisture, and groundwater recharge.
Raindrop size and rainfall intensity  affect soil erosion; storms that produce higher rainfall intensity and larger raindrop size generally produce more soil erosion.
The duration and frequency of storms affect conditions such as flooding and drought.
For instance, if 50 percent of the annual rainfall total comes in one event, there is a higher likelihood of flooding during that period and of subsequent drought in the remaining period.
The seasonal distribution of precipitation is also important.
Ideally, adequate but not excessive rainfall occurs throughout the agronomic growing season to ensure crop growth, with the remaining precipitation distributed relatively evenly throughout
 Table 2.
Average monthly distribution of precipitation for five regions of Virginia, 1980-2010.
Month	Eastern VA	Central VA	Southern VA	mountains	Northern VA
 Jan	3.5	3.1	3.1	2.8	3.0
 Feb	3.4	2.9	3.4	2.9	2.6
 Mar	3.8	3.8	3.8	3.8	3.4
 Apr	3.1	3.0	3.3	2.8	3.4
 May	3.6	3.7	3.6	3.6	4.1
 Jun	3.6	3.7	3.8	3.6	4.2
 Jul	4.7	4.9	3.6	3.6	3.8
 Aug	4.7	4.9	4.2	3.9	4.1
 Sep	4.4	3.9	4.2	3.1	3.5
 Oct	2.8	3.3	3.3	3.2	3.1
 Nov	2.9	3.3	2.7	2.7	3.0
 Dec	3.1	3.3	3.3	2.9	3.0
 Total	43.6	43.6	42.2	39.0	41.1
 Source: Data from Southeast Regional Climate Center.
Figure 2.
Monthly precipitation values for five regions of Virginia.
the year.
Due to reduced plant uptake, precipitation that occurs outside the growing season has a greater opportunity to infiltrate the soil and recharge groundwater.
Evapotranspiration 
 Evapotranspiration is the combined effect of evaporation  and transpiration.
Due to the difficulty in separating the processes of evaporation and transpiration, the two processes are generally considered together and referred to as "ET." This term includes the water that evaporates directly from soil, water, and plant surfaces and the water that is pulled from the soil by plant transpiration.
As much as 75 percent of the water that enters the soil can be returned to the atmosphere through ET.
High wind, solar radiation, and heat can greatly increase the ET rate, whereas a high water vapor percentage in the air  can decrease the potential for ET.
Some producers rely on ET estimates made by government agencies such as the National Weather Service or the National Oceanic and Atmospheric Administration to schedule irrigation or harvesting operations.
Often what these agencies report for ET is what is referred to as "potential evapotranspiration" , which is a measure of the maximum ET rate for a given set of conditions defined by solar radiation, temperature, humidity, and wind conditions and also assumes that soil moisture is not limiting.
In actuality, as plants transpire and remove plant-available water from the soil, the soil begins to dry out, and as a result, the evapotranspiration rate begins to decline.
This is because the matric potential or suction of the soil increases, meaning that as the water content decreases, the remaining soil water is held more tightly in the soil pores.
The real ET rate , or what is actually evapotranspired, is referred to as actual evapotranspiration  and is influenced by all the conditions that control PET, discussed above, plus the actual soil moisture conditions.
Therefore, when the soil is saturated, AET is equal to PET, but AET declines as the soil dries.
The intensity of ET varies seasonally, with higher rates corresponding to spring and summer months when plants are actively growing and lower rates during the fall and winter months when growth slows and plants become dormant.
Plant water requirements and ET drive a seasonal fluctuation of the water table, where the water table is lower during the growing season when ET is high, and the water table height increases as ET decreases during the nongrowing season.
Consequently, seasonal fluctuations in ET have a large impact on water availability in agricultural systems
 Figure 3.
Influence of soil moisture conditions on evapotranspiration given the same solar radiation, wind, and relative humidity conditions, where potential evapotranspiration takes on a fixed value, and actual evapotranspiration approaches potential evapotranspiration as soil moisture increases.
Once precipitation has reached the soil surface, some of it can infiltrate the soil.
Infiltration is the downward entry of water into the soil.
The amount of water that infiltrates and how quickly it infiltrates varies widely from place to place and depends on soil properties such as soil moisture content, texture, bulk density, organic matter content, permeability, porosity, and the presence of any restrictive layers in the soil.
Permeability is a measure of how fast water flows through the soil.
Infiltration and permeability are greater in porous materials, such as sands or
 gravels, than in clay soils.
Porosity is a measure of the total amount of open space or voids in a soil that are capable of retaining water.
Water retained in the soil pores is part of the soil storage, a portion of which is available to plants during transpiration.
Additionally, plants can utilize water stored in the soil at a later time, providing a buffer capacity for plants between rains.
Therefore, soil structure is an important consideration in agroecosystems and can be managed with various tillage practices or soil amendments.
The infiltration rate of any given soil also varies over a rainfall event, usually decreasing significantly as the soil becomes saturated.
If rainfall continues long enough, the infiltration rate approaches a constant value comparable to the saturated hydraulic conductivity of a soil.
This is an important concept both in hydrology and crop production because saturated hydraulic conductivity is generally related to overall crop productivity.
Many soils with low saturated hydraulic conductivity are prone to water logging that may reduce crop yields.
When agricultural soils remain saturated too long, the oxygen content in the soil is depleted, causing plant stress.
Therefore, strategies including ditch or tile drainage are employed to remove excess water.
Climatic, land management, and landscape scale factors also influence infiltration.
For example, a compacted or frozen soil reduces infiltration.
No-till soils will generally have a far greater infiltration capacity than will a compacted soil, where the
 Figure 4.
Influence of antecedent soil moisture conditions on the infiltration rate.
Note that the infiltration rate under the wet and dry conditions ultimately reaches the same steady state value but at different times during the precipitation event.
permeability or hydraulic conductivity is reduced.
The presence of vegetation can increase infiltration by promoting macropore formation, increasing permeability, and adding organic carbon to the soil, which reduces the bulk density and promotes biotic activity of soil organisms such as earthworms.
Additionally, vegetative cover increases infiltration by protecting the soil's structure from destruction by raindrops  and prevents the formation of soil crusts with reduced permeability.
Soil management can also greatly affect infiltration rates.
For instance, stable soil aggregation  can greatly increase the infiltration rate of fine-textured loams and clays, and tillage especially under wet conditions can break down these soil aggregates.
Heavy traffic of agricultural equipment on fields can cause soil compaction, further reducing infiltration.
Some soils, such as shrink-swell clays, may temporarily have much higher infiltration rates when they are dry than when they are wet due to cracking at the surface and macropore flow, which allows water to move rapidly down into the soil.
Percolation and Groundwater Recharge
 Aside from plant uptake, another path that water can take after it enters the soil is percolation.
Percolation is the downward movement of water that has infiltrated out of the root zone under the pull of gravity.
Generally, percolation is beyond the reach of plant roots.
Water that percolates downward through the soil, below the plant root zone toward the underlying geologic formation, is responsible for recharging aquifers.
Groundwater can be a very important source of irrigation water for agriculture.
While much of the irrigation in the Mid-Atlantic Region relies on surface water supplies, there is considerable infrastructure in place to utilize groundwater for irrigation.
Many producers prefer groundwater because it is of higher quality and less prone to short-term shortages due to the weather.
Groundwater that has percolated to an aquifer can be stored in that aquifer or can flow out of the aquifer and discharge to a surface water body, such as a stream, river, or lake.
This groundwater discharge
 creates baseflow the amount of flow in a stream in the absence of additional inputs resulting from storm events and is an important connection between ground and surface waters.
Groundwater moves from higher elevations to lower elevations or similarly from areas of higher hydraulic pressure to areas of lower hydraulic pressure.
This pressure difference between two points is often referred to as hydraulic head gradient.
Groundwater movement always follows the downward hydraulic head gradient; with no hydraulic head gradient there is no lateral groundwater movement.
Similar to the infiltration rate, the rate of groundwater movement is controlled by the permeability of a geologic material.
In areas of steeper terrain or with gravely or sandy geologic material, groundwater movement can be quite rapid, on the order of 10-1,000 feet per day, while low gradient areas or areas with lower-permeability geologic material conduct water less rapidly, at 0-10 feet per day.
Interflow is the lateral movement of infiltrated water in the vadose zone and is influenced by soil, geologic, and terrain properties in the surrounding area.
As water infiltrates, some of it may reach a layer of soil or rock material that restricts downward movement and causes a perched water table.
Restrictive layers can form naturally  or as a result of human activities; an example of which is the creation of a restrictive layer with lower permeability than the bulk soil created during tillage, which is referred to as a plow pan.
Once water reaches a restrictive layer and can no longer infiltrate vertically, it becomes perched over this layer and may then move laterally as interflow above this layer if there is sufficient hydraulic head or slope.
As interflow moves through the soil, it accumulates as more water infiltrates and can saturate the soil profile, as indicated by the size of the interflow arrows in figure 5.
Once the soil saturates either from the incoming interflow volume or from reduced soil transmissivity, interflow can then resurface either as runoff on the soil surface , be directly discharged to a surface water body or, in many areas of Virginia, feed springs or seeps.
Soils with high permeability in hilly terrain, particularly those underlain by a restrictive layer, can conduct a significant amount of interflow through the profile
 compared to low-permeability soils on low slopes, which are prone to generating more surface runoff.
In agricultural areas, particularly those in hilly terrain, significant quantities of nutrients  can be transported to streams via interflow.
There are many ways to describe runoff, but a simple definition is the portion of precipitation falling on an area that is rapidly discharged from the area through stream channels.
However, in reality, runoff generation is a complex process controlled by many factors, and there are even different types of runoff generated depending on the conditions.
The first type of runoff is called infiltration excess runoff and is the type with which most people are probably familiar.
As the name suggests, infiltration excess runoff occurs when the infiltration rate of the soil is less than the rainfall rate.
This type of runoff generally occurs during intense thunderstorms or on soils with a low infiltration rate, such as clays or compacted soils, and
 Figure 5a-b.
Excess runoff can be a result of  rainfall exceeding soil infiltration capacity  or  when soils are or become saturated due to subsurface water table dynamics.
is more common in urban areas where impervious surfaces dominate.
Once the precipitation rate exceeds the infiltration rate of the soil, depressions on the soil surface begin to fill.
These surface depressions provide what is called surface storage or depressional storage.
When depressional storage is filled and precipitation continues to exceed infiltration, water begins to move down slope as overland flow or in defined channels.
In agroecosystems, depressional storage can sometimes be enhanced by tillage.
Although tillage can create these depressional storage areas that delay runoff and promote infiltration, often the tillage-induced compaction outweighs this storage, resulting in a net increase in surface runoff.
The second type of runoff generation is called saturation excess runoff, which occurs when the soil profile becomes saturated with water and can store no more precipitation.
Thus, any precipitation falling in these areas becomes runoff.
Several terrain and soil properties influence saturation excess runoff generation, which is largely governed by topography and soil depth.
Soils with shallow restricting layers, areas that drain large upslope contributing areas, or areas where the slope flattens are all prone to generating saturation excess runoff primarily because interflow from upslope areas can no longer be transmitted through the soil profile.
Saturation excess runoff is not sensitive to rainfall intensity or soil infiltration rate but depends on where the saturated areas occur in the landscape.
This type of runoff generation is far more common in the humid temperate regions, such as the Mid-Atlantic, than infiltration excess runoff, primarily because the region is wellvegetated and has permeable topsoil.
Depending on which type of runoff is generated, there can be varying water quality and production consequences.
For instance, sheet and rill erosion are more common during infiltration excess runoff, partially because this type of runoff is associated with high rainfall intensities, while saturation excess type runoff is often responsible for gullying and stream bank failures due to increased pore water pressure from the weight of water in the soil profile, which reduces soil cohesion.
The water on earth is finite, and only a small amount is readily available for human use.
This publication presents an overview of the hydrologic
 cycle and highlights some concepts of importance in agroecosystems.
Sound decisions about the use and protection of our water resources require a fundamental understanding of the basic processes of the hydrologic cycle and how water circulates in the land and atmosphere.
Understanding the hydrologic cycle is critical because many of the significant environmental and societal problems we face today are related to hydrologic or water issues, including climate change, agricultural productivity and food security, energy, and human health.
Related Virginia Cooperative Extension Publications
 antecedent soil moisture The wetness of a soil that results from past rainfall or soil drying events.
aquifer Saturated fractured rock or other geologic material such as sand or gravel that water can move through.
Aquifers serve two primary functions: a storage function, where water is stored temporarily; and a conduit function, where water is translocated from one area to another.
aquifer recharge The result from the percolation of infiltrated precipitation to subsurface water bearing geologic materials.
baseflow Typical low-flow discharge in streams in contrast to stormflow that occurs in response to precipitation events; groundwater discharge drives baseflow.
bulk density The weight of dry soil  per unit volume of soil.
depressional storage Water contained in natural depressions in the land surface, such as puddles or furrows.
infiltration excess runoff Occurs when water enters a soil system faster then the soil can absorb or move it, such as when precipitation exceeds the infiltration capacity of the soil.
Also known as "Hortonian flow."
 exfiltration Process by which infiltrated water in the vadose zone reaches the soil surface and creates runoff or a spring/seep.
field capacity The amount of water held in the soil 48 hours after a saturating rain.
It is what water remains after excess water has drained away and the rate of downward movement has ceased.
fragipan Cemented or densely packed subsurface soil horizon that prevents water and plant root penetration.
Fragipans are common to glaciated regions and often increase perched water table formation and runoff generation because water cannot percolate through the layer.
hydraulic head gradient The slope of the groundwater surface in an aquifer.
The hydraulic head gradient indicates the direction of groundwater flow.
Water always flows from higher hydraulic head gradient to lower hydraulic head gradient.
All other factors being equal, flow is greater when the hydraulic head gradient is steeper.
infiltration The downward entry and movement of water through the soil profile.
macropores Large soil pores that form as a result of biological activity , geological forces , or mechanical practices.
Macropores are larger than 0.08 mm in diameter and can conduct large quantities of water and agrochemicals deeply into the soil.
matric potential The sum of adsorptive forces that hold water to individual soil particles and capillary forces that hold water between soil particles.
Matric potential is always negative  and is strongest in drier soils where the water is tightly bound to soil particles.
organic matter content Plant and animal residues, cells and tissues, or soil organisms composed of carbon and the substances the organisms synthesize.
perched water table A vertically confined but laterally unconfined water body that forms over a restricting layer  and is isolated from the primary groundwater by one or more layers of unsaturated soil.
percolation The downward movement of water through saturated soil layers, percolation is responsible for groundwater  recharge.
permeability In soil, a measure of the capacity of the soil to allow fluids to pass through it, expressed as a velocity.
plant-available water The water available to support plant growth; the difference between field capacity and the permanent wilting point.
porosity The amount of pore space  between soil particles.
Infiltration, groundwater movement, and storage occur in these void spaces.
Soils with higher clay content have higher overall porosity than sands.
relative humidity A measure of how wet the air is; defined as the amount of water vapor in the air, expressed as a percentage of the maximum amount of water vapor the air can hold at a given temperature.
restrictive layer A soil layer of low conductivity  that prevents vertical water movement and fosters the generation of perched water tables, interflow, and runoff.
saturated hydraulic conductivity A measure of the ability of soil to transmit water when fully saturated; similar to permeability.
saturation excess runoff Occurs when the soil becomes saturated and any additional precipitation cannot be infiltrated or stored by the soil, causing runoff.
sheet and rill erosion Sheet erosion is erosion that detaches and removes soil particles more or less evenly from the soil surface and is caused primarily by raindrop impact and uniform overland runoff.
Rill erosion forms when overland runoff becomes channelized as it flows down slope and begins to create small erosional channels  up to approximately 8 inches deep.
soil moisture content The amount of water stored in the soil; primarily influenced by the soil texture and the soil organic matter content.
In general, soils with greater silt-and clay-sized particles have higher soil moisture content, all else being equal.
Likewise, soils with more organic matter have higher soil moisture content.
solar radiation The radiation or energy emitted from the sun.
sublimate The transition of a solid  directly to a gas  without passing through the liquid phase.
transmissivity The rate at which water can pass through a soil profile at a specific slope; the product of soil depth times soil saturated hydraulic conductivity.
vadose zone The typically aerated zone above the permanent water table; the zone where the soil water is at atmospheric pressure.
Percent of fields that became wetter moving from August to Sept.
15.
The dry years 2020, 21 and 22 fields are much drier than the other years in the fall.
In 2020, 45% of fields with soil in the 15-25 in zone became wetter from August to Sept.
15, 21% of fields with soil in the 25-36 in zone became wetter from August to Sept.
15, and 21% of fields with soil in both zones became wetter moving from August to Sept.
15.
Other factors that were significant were pathogen-type and how prevalent it is in the manure being irrigated; risk decreases when smaller amounts of the pathogen are found in the manure.
Additionally, it is important to note that exposure to the sun inactivates pathogens while they are still in the air.
The data does not give any insight into why so many farmers over-irrigate late in the year, but it could be because the irrigation routine is set in July when the plants are transpiring at their peak, the days are long and the temperatures are high.
Then, as the daylight hours shorten and the temperatures get cooler in late summer, many keep irrigating at July levels even though crop water use for corn has gone from an average of two inches/week at silking to 1.25 inches/week at full dent.
Again, as creatures of habit, without good soil water monitoring data to direct our irrigation scheduling, we just keep on doing what we have been doing.
Other crops, including soybeans, have a similar dramatic drop in crop water use moving through August and into September.
Chapter 12: Land Rolling Corn Fields
 Historically, land rolling was used to improve germination in alfalfa and grass-seed production systems.
Recently, land rolling has been expanded to row-crop production systems.
Land rollers are used to push rocks into the soil, thereby reducing the risk of harvest losses and combine breakdowns.
Benefits from land rolling include reduced equipment breakdowns, reduced harvest losses, reduced operator fatigue, ability to place the combine head closer to the soil surface, and improved emergence.
Lowering the combine head can reduce soybean losses because, the pods can be very close to the soil surface.
However, in corn production lowering the combine head to near the soil surface will produce a minimal impact on harvest efficiency.
Primary disadvantages are increased compaction and erosion.
We suggest that land rolling should be considered only in fields containing a large number of rocks.
This chapter investigates the impact of land rolling on corn production.
Benefits of Land Rolling
 1.
Ability to operate sprayers and combines at faster speeds.
2.
Reduced equipment breakdown during critical periods.
3.
Reduced harvest losses.
4.
Reduced operator fatigue.
5.
Improved seed germination.
6.
Accelerated microbial decomposition as a result of pushing crop residues into the soil.
7.
Reduced stand variability.
Rollers effectively push rocks down into the soil, and in a no-tillage system, a land roller will lower mounds left by burrowing rodents and dramatically reduce the risk of equipment damage.
A fist-sized or
 larger rock can cause significant damage to a corn combine, especially cylinders and/or concaves.
Repair costs resulting from rock damage can potentially cost tens of thousands of dollars to a $300,000 combine.
Mounds left by burrowing animals, such as pocket gophers, can be equally problematic.
Land rolling may also help speed surface residue mineralization by breaking apart corn rootballs, and reducing the risk of flat tires.
Animal mounds can bounce and jar spraying and harvest equipment, leading to structural or mechanical damage and malfunction.
Land rolling can partially smooth these areas and minimize undue stress on equipment.
Combining at high speeds in fields with animal mounds can increase the chance of ears bouncing out of the header.
Adjusting the combine header to avoid rocks, reduces the risk of combine damage and repair costs, but can leave low-hanging ears in the field.
Land rolling conducted after planting can reduce this risk as well as improve contact between the corn seed and the soil.
Disadvantages of Land Rolling
 1.
Crushes soil aggregates and destroys the surface roughness that protects the soil from wind and water erosion.
This can result in soil sealing and reduced seedling emergence.
2.
Increases weed seed germination by improving soil to weed seed contact.
3.
Leads to seedling damage if rolling is conducted after emergence.
4.
Reduces water infiltration and increases erosion rates.
5.
Increases soil compaction.
6.
Includes difficult-to-document economic benefits.
Mitigating the Disadvantages of Land Rolling
 1.
Return the crop residue and maximize residue cover after planting.
2.
Roll only areas containing rocks.
3.
Avoid land rolling after plant emergence.
4.
Do not roll wet fields.
5.
Do not roll fields to level tire ruts.
6.
Configure tractor and roller tire size and spacing to your row spacing.
Attendees learned about the drying process and the science behind taking the product from the on-ear intake to the 12.5% moisture final seed corn product.
Although the facility isnt in production at this time of year, , the guides talked about the robotics, conveyors, drying units, and other technology that is used to facilitate the process.
The TAPS program greatly appreciated the opportunity to tour the plant and offer this educational aspect to participants during the seasonal kickoff event.
Scheduling the last few irrigations of the season deserves more of your management time than earlier irrigations because one must not only focus on keeping the crop wet enough to produce optimal yields, but also on using up enough of the stored soil water to lower the level to 40% of plant available water in the top four feet.
This level will give about 2.4 inches of water storage room in sandy soils and about 5.5 inches in silt loam soils.
Unfortunately, many irrigators leave the soil fairly wet with little to no storage room according to a recent study.
Use: variable rate chemigation, VRI type: both, prescription type: both, management intensity: medium/high.
Using Renewable Energy to Pump Water
 You can save money and help reduce air pollution by using renewable energy sources such as solar or wind power for your home, for drip irrigation or for livestock water wells.
Juan Enciso and Michael Mecke*
 Wind and solar energy can be excellent options in remote areas where the costs of extending transmission lines are high.
Extending transmission lines over 1/4 mile usually costs $5 per foot.
At that rate, a 1-mile transmission line extension will cost more than $25,000.
Renewable energy sources are also a good option when only a small amount of water needs to be pumped.
Generally, very little water is required for livestock and home use.
To make a wise decision on renewable energy sources, it helps to understand some basic concepts about renewable fuels, including:
 How solar and wind energy pumps work
 The main components of these pumps
 The advantages and disadvantages of solar and wind energy pumps
 How to calculate your pumping requirements
 It is also important to consider the costs of buying and using a pumping system, which include the initial cost, energy costs and maintenance costs.
Wind is often used as an energy source to operate pumps and supply water to livestock.
Because of the large amount of water needed for crops, wind power is rarely used for irrigation.
As larger and/or more efficient wind turbines are developed, groups of these wind turbines  are expected to be able to generate enough electricity to be used for irrigation projects.
Wind generators are also used to charge batteries and to provide electricity for small communities.
The most common wind device used is the American farm and ranch windmill.
These windmills are common on the North American Great Plains and across the Southwest.
A windmill consists of:
 A very large fan with 15 to 40 steel or galvanized blades
 A gear box mechanism driven by the blades.
This mechanism converts the rotary motion of the blades to an up-and-down motion
 A piston pump, which is driven by the upand-down motion produced by the gear box mechanism
 A pump rod that descends from the windmill to the well
 A pump cylinder, which is placed in the water near the well bottom and is driven by the pump rod
 * Assistant Professor and Extension Agricultural Engineering Specialist; and Extension Program Specialist-Water Management; The Texas A&M University System
 The propeller must have many blades to develop a high starting torque, which is needed to start the piston pump.
Generally, windmills begin working when the wind speeds exceed 7 mph.
Solar energy is used mainly for pumping water for livestock or for home use.
It is seldom used for irrigation because of the amount of water needed for crops.
However, solar pumps are economically feasible for irrigation that uses very low heads or has very low lifting requirements, such as drip irrigation, which uses less water than other types.
Solar pumps work by converting solar radiation into electricity through the use of photocells made of silicon, usually called photovoltaic cells.
The photovoltaic cells are enclosed in a glass frame, which makes up the solar module.
Sometimes an array of solar modules is needed to produce enough energy for the pump.
The modules are mounted on a frame in an assembly called a photovoltaic  array.
The PV array is connected to a controller and then with an electrical power cable to the motor/pump subsystem in a well.
Submersible pumps usually use a direct current  motor.
Motors that use alternate current  must have a DC-to-AC inverter.
DC motors are recommended because using an inverter costs more, and power is lost in the DCto-AC conversion.
The most common DC motors work at a nominal voltage of 24, 36 and 48 volts, which can perform at 32, 42, and 64 volts.
A problem with DC motors in the past has been that they needed carbon brushes, which wore out and needed regular replacement.
New, maintenance-free DC motors have recently been developed that use an electronic circuitry to perform the same function as the brushes.
Today, most submersible pumps use brushless DC motors or AC motors with an inverter.
Figure 1.
An American farm and ranch windmill.
Figure 2.
A solar-powered water pump.
In recent years, the cost of solar modules has dropped considerably.
As large-scale solar consumption and production increases, the costs are expected to continue to fall.
A solar module costs about $5 per watt; a 75-watt module costs about $375.
Advantages and disadvantages of solar and wind energy
 Some advantages and disadvantages for using solar or wind energy are presented in Table 1.
The main advantage of using renewable energy is that there is no energy cost to pump the water.
The power source either wind for a wind pump or sunshine for solar pump depends on the weather conditions for a given place.
The water pumped from wind and solar systems is generally stored in tanks.
Keep in mind that your storage tank needs to be big enough to store several days' supply of water in case of breakdowns or poor pumping conditions.
When the water tank is full, the extra generated solar or wind energy can be stored in lead acid batteries.
However, there are several drawbacks to storing energy in batteries:
 Only small amounts of energy can be stored.
The batteries need to be replaced at least every 5 years.
Storage batteries raise the initial cost of the total system much higher.
Table 1.
Comparisons of the advantages and disadvantages of solar and wind energy systems.
Factor	Wind systems	Solar systems
 Favorable weather	Steady winds are most productive.
Pump water consistently all year.
Portability	Can be portably mounted to use in
 Lifetime	Can exceed 50 years, except for	More than 20 years.
the piston pump, which requires	The pump lasts less time.
maintenance every 1 to 2 years.
Stormy weather	Wears more rapidly in high winds.
Panels can be damaged by hail.
Destructive winds can ruin system.
Cloudy weather and short days
 Time of year power requirements	Power production stopped when wind
 speeds are low, which occurs in July
 and August when water is needed most.
Initial cost	Lower initial cost.
Higher initial cost.
Maintenance cost	Requires more maintenance.
Less maintenance.
Estimating the size of the pump
 Both solar and wind energy systems use pumps to lift the water from underground to a storage tank.
To estimate the size of the pump to meet your needs, you must consider several factors:
 The amount of water needed each day
 The pumping capacity, or the number of gallons per hour the pump must be able to lift
 The amount of horsepower required to lift that amount of water
 To calculate your pumping needs, first estimate how much water will be used each day and how far the water must be lifted from underground.
Table 2 offers guidelines for estimating the water requirements for people and livestock.
To estimate the total water requirements per day, multiply the number of people or animals by the amount of water they are expected to consume each day.
Example: How much water is needed for a herd of 100 head of beef cattle?
Water requirement = 100 head of cattle X 10 gallons/day/head = 1,000 gallons/day
 Next, calculate the number of gallons per hour that the pump must be able to lift, which is the pumping capacity.
Because the wind does not blow all day and the sun does not shine all day or every day, it is highly recommended that you assume that an average of 5 hours of the day are available to collect wind or solar energy.
To estimate the pumping capacity, divide the number of gallons needed per day by the number of hours available to collect energy.
Table 2.
Water requirements in gallons per day for different species.
Species	Gallons per day
 Human	100 per person
 Beef cattle	7-12 per head
 Dairy	10-16 per head
 Horses	8-12 per head
 Swine	3-5 per head
 Sheep and goats	1-4 per head
 Chickens	8-10 per 100 birds
 Turkeys	10-15 per 100 birds
 Example: What is the pumping capacity needed for the 100 head of beef cattle in the example above?
Pumping capacity = 1,000 gallons/day divided by 5 hours = 200 gallons/hour
 Estimating the horsepower required
 Next you need to figure the amount of horsepower the pump will need to have.
To estimate the horsepower needed, first convert the pumping capacity from gallons per hour to gallons per minute.
Example: For the same 100 head of beef cattle above, you will need to convert the 200 gallons per hour of pumping capacity to gallons per minute:
 Gallons per minute  = 200 gallons/hour divided by 60 = 3.33 GPM
 Next, to calculate the horsepower needed, multiply the pumping capacity by the lift, which is the distance that the water must be lifted; then divide that number by 3,960.
HP = Q X H / 3,960
 HP = Horse power
 Q = Pumping capacity, in gallons per minute 
 H = lift, in feet
 The well on that cattle ranch in the example above is 100 feet deep.
For the formula above, the factors are:
 Q = 3.33 GPM Lift = 100 feet The calculation would be: Horsepower = 3.33 GPM X 100 feet/3,960 = 0.084 HP
 Converting horsepower to watts
 The horsepower used above describes the mechanical work needed to lift a volume of water per unit of time from the pumping water level up to the storage tank.
You can convert this measure of horsepower to watts of electricity by multiplying it by 746:
 Watts = 0.084 HP X 746 watts = 62.7 watts
 converting electricity to the mechanical movements of the pump.
The average efficiency rate of these pumps is about 45 percent.
To adjust for this inefficiency, we must recalculate our power input by dividing the number of watts by 0.45:
 Next, you need to adjust the wattage to take into consideration the loss of electricity in the cable and controls during transmission and in
 Wattage needed = 62.7 divided by 0.45 = 139.3 watts
 Last, for a solar system, we must choose the number of solar panels that will produce the number of watts needed by the pump.
Solar panels or modules have different capacities.
There are modules of 25, 50, 70 or 75 watts.
It is less expensive to use a more efficient motor than to add an extra solar panel.
For the example above, the rancher could buy six 25watt panels, but it would be much less expensive to buy two 70-watt solar panels to generate the 139.3 watts needed.
Estimating the size of the windmill
 If there are tall trees in the area, you may need or want a taller tower to raise the fan blades above the trees and into the wind.
However, windmills are usually no more than 35 feet tall; otherwise, the towers become very expensive.
When buying a windmill, you will need to know the lift and daily water requirements.
Use the formulas above to determine the horsepower your pump needs to have.
The primary components of a windmill are the blades, the tower and engine, pump rod, the drop pipe , sucker rod  and the piston pump.
A windmill's pumping output is affected by three factors: wind speed, wheel or blade diameter, and the diameter of the cylinder.
Wind speed has an important effect on the pumping output.
In fact, the power available from the wind is proportional to the cube of the wind speed.
This means that when the wind speed doubles, the power increases eight times.
Most windmills do not operate at wind speeds of less than 7 mph or more than 30 mph, as the mill can be damaged by high winds.
Example: From Table 3, to pump 470 gallons per hour and lift the water 220 feet, a cylinder diameter of 3 inches would require a blade diameter of 14 feet.
Table 3.
Pumping capacities as influenced by the diameter of the cylinder and blade diameter of the windmill.
diameter	
 	Wheel diameter 	Blade diameter 
 6	8 to 16	6	8	10	12	14	16
 2	130	190	95	140	215	320	460	750
 2 1/2	225	325	65	94	140	210	300	490
 3	320	470	47	68	100	155	220	360
 3 1/2	440	640	35	50	76	115	160	265
 4	570	830	27	39	58	86	125	200
 4 3/4	-	1,170	-	-	41	61	88	140
 5	900	1,300	17	25	37	55	80	130
 6	-	1,875	-	17	25	38	55	85
 8	-	3,300	-	-	14	22	31	50
 This material is based upon work supported by the Rio Grande Basin Initiative of the
 Cooperative State Research, Education, and Extension Service, United States Department of Agriculture under Agreement No.
2001-4504900149.
This project was funded by the United States Department of Agriculture, Project No.
20014509-01149, "Efficient Irrigation for Water Conservation in the Rio Grande Basin." The author would like to thank Dr.
Brian D.
Vick of the Conservation and Production Research Laboratory USDA-ARS at Bushland, Texas, for his valuable suggestions and recommendations to improve this publication.
Texas Water Resources Institute make every drop count
 Texas A&M AgriLife Extension Service
Water Wells for Florida Irrigation Systems
 Dorota Z.
Haman and Gary A.
Clark2
 A well is any excavation that is drilled, driven, dug, jetted or otherwise constructed when the intended use of such excavation is for the location and acquisition of ground water.
The objective of this publication is to present information on different types of aquifers, to discuss the different types of irrigation wells typically constructed in Florida aquifers and to discuss irrigation well construction, development and testing.
The quality and quantity of groundwater varies from place to place.
However, water in some quantity can be found beneath the ground almost everywhere.
As a result, 97 percent of the world's available fresh water is groundwater.
Major reservoirs of groundwater are called aquifers.
Conditions for good water-bearing formation are high permeability, which is the measure of ease with which water can flow through a soil profile, and high drainable porosity, which indicates that large amounts of water can be removed from the water-bearing formation.
These features are best characterized by sand and gravel, although fractured rock formations and solution caverns in limestone are also good aquifers.
Aquifers can be located in consolidated or unconsolidated formations.
Consolidated formations are composed of solid rock with groundwater in the cracks or caverns.
Unconsolidated formations are composed of sand and gravel or loose soil material where the pore space is saturated with water.
Aquifers can also be classified as confined or unconfined.
A confined aquifer is isolated from the atmosphere by an impermeable layer.
The surface of groundwater under confined conditions is often subject to higher than atmospheric pressure because it is confined by impermeable layers bounding the aquifer.
The elevation to which water rises in a well that taps a confined aquifer is called the potentiometric level and represents the hydrostatic pressure at that point in the aquifer.
An imaginary surface representing the confined pressure throughout all or part of a confined aquifer is called the potentiometric surface.
Unconfined aquifers are bounded only on the bottom by impermeable strata and are often referred to as water table aquifers.
When no water is being removed by pumping, the water table level in an unconfined aquifer and the piezometric level in a confined aquifer are called static water levels.
In Florida, the static water level of unconfined formations is generally near the ground surface and may have significant fluctuations.
The recharge of unconfined aquifers results from precipitation or seepage from nearby streams or lakes.
Consequently, it depends on the season and on meteorological conditions.
The potentiometric
 2.
Dorota Z.
Haman, assistant professor; and Gary A.
Clark, professor, UF/IFAS Gulf Coast Research and Education Center; UF/IFAS Extension, Wimauma, FL 33598.
surface of a confined aquifer is also subject to change due to recharge and pumping conditions.
The potentiometric surface will rise and fall in response to the volume of water in the aquifer.
Fluctuation of the water level in an unconfined aquifer or changes in hydrostatic pressure in a confined aquifer should be considered when a new well is being installed.
Wells can be classified as gravity wells, free flowing artesian wells, or a combination of artesian and gravity .
The well type depends on the type of aquifer containing the water.
Gravity wells penetrate unconfined aquifers.
As a result, the static water level in a gravity well is the same as the level of the water table.
If the hydrostatic pressure in an confined aquifer is sufficient to cause the water to rise above the water level in the aquifer, artesian conditions are present.
A raised water level in a well indicates that the aquifer is confined and that the water at the surface of the aquifer is under pressure which is greater than atmospheric pressure.
This type of well is called an artesian well.
If hydrostatic pressure is sufficient to cause the water to rise high enough to flow out on the land surface, a free flowing artesian well exists.
The following conditions must exist for any artesian well: 1) the aquifer must be confined, which means impervious strata above and below the water-bearing formation; 2) the recharge area must be located above the top impervious strata; 3) the absence of a free outlet for the water bearing formation at the lower elevation; 4) inclination of the strata; 5) a source for water recharge, such as sufficient precipitation.
An artesian well is not necessarily a free-flowing well.
The schematic in Figure 1 shows the necessary conditions for both non-flowing and free flowing artesian wells.
Wells can also be classified as shallow or deep.
In many areas good irrigation water can be obtained from shallow aquifers.
Careful investigation of the shallow water aquifers should be performed prior to well construction.
In some instances, when the shallow water table is due to a perched water table, pumping for irrigation can quickly exhaust the water supply.
Florida's water management districts provide standards and criteria for construction, repair and abandonment of wells.
In all districts permits are required for any well with a diameter larger than 2 inches.
All wells within a district
 must comply with that district's standards, regardless of whether a permit for a well is required.
County and other ordinances may also be applicable and must be followed.
For example, some counties prohibit the construction of shallow wells in some areas.
In general, wells can be classified into three major types according to the method of construction: driven, dug or drilled.
Small wells up to 3" in diameter and 60 feet deep can be constructed by driving a well point into unconsolidated material such as sand or gravel.
Penetration of the well point may be aided by using a high velocity jet of water at the tip of the driving pipe.
A dug well is a pit dug to the ground water table.
These wells usually do not penetrate the groundwater deep enough to produce high water yield.
A dug well pit is often lined with masonry, concrete, or steel for support.
Deeper wells are usually constructed by drilling.
Cable-tool or rotary equipment is commonly used.
In the first method, a heavy bit is dropped repeatedly to the bottom of the well using cable tools and crushed material is periodically removed with a bailer.
Rotary drilling equipment consists of a bit rotated by a string of pipe.
Cuttings are removed by continuous circulation of a drilling fluid as the bit penetrates the formation.
Drilling fluid is pumped down through the drill pipe and out through the ports or jets in the bit.
The cuttings are brought to the surface by a mud slurry outside the drill pipe.
Figure 2 illustrates cross sections of a well in a water table aquifer and, Figure 3, in a confined aquifer, respectively.
In both cases drawdown is the difference between the water table or potentiometric surface  and the water level in a well during pumping.
It represents the sum of the head losses caused by the flow of water through the porous media and the head loss caused by the entrance of water into the well.
The horizontal distance from the center of the well to the limit of the cone of depression is called the radius of influence.
Each cone of depression differs in size and shape depending upon the pumping rate, pumping duration, recharge of the aquifer within the cone, and aquifer characteristics such as permeability of the water bearing formation.
The cone of depression is affected by pumping of other wells located within the radius of influence of this well.
An irrigation well should penetrate the water-bearing formations quite deeply while keeping costs within
 economical limits.
In Florida, the depth of a well will also be limited by water quality since saline water underlies potable water throughout the state.
In coastal areas of Florida, salt water intrusion into the aquifer is frequently encountered.
Keeping water quality problems in mind, a well should be sufficiently deep to avoid running dry during drought or during increased drawdown periods such as pumping for freeze protection during winter months.
It is also important to remember that deeper wells will usually produce a greater yield of water per foot of drawdown.
The relationship between well diameter and water yield is not linear, and as a result, a doubling of the diameter will not double the amount of water which can be pumped from a well.
For residential lawn irrigation systems a 4" well will usually supply enough water.
For larger applications and bigger wells, local conditions near the intended well site must be investigated prior to sizing and installing a well.
Standards developed by the water management districts in Florida provide specifications for casing and liner pipe in wells.
The function of the well casing is to maintain the borehole at a specified size, to prevent collapsing of the borehole, and to serve as a pump enclosure as well as a conduit for water flow from the well inlet to the pump intake.
A liner is a pipe which is installed either within the outer casing to improve, repair, or protect the outer casing or below the outer casing to seal off caving material which may be encountered in a well with an open hole aquifer.
Welded, seamless black or galvanized pipe, stainless steel pipe, or approved types of nonmetallic pipe can be used for well casing or liner pipe according to the specifications of the water management districts.
A continuous casing should extend from 6 to 12 inches above the land surface to a few feet into the uppermost consolidated layer.
For detailed specification on sizes and construction of the casing, the local water management district should be consulted.
The alignment of a well is important, especially when vertical turbine pumps are used and a vertical shaft is placed in the well.
Allowable tolerances in misalignment will also depend on the size of casing in relation to the outside diameter of the submersible or vertical turbine pump.
Well casing may be solid or slotted.
Solid casing has no perforations and is used in the upper regions of a well.
Slotted casing or well screens are used in the lower, water-bearing regions of wells.
A screen allows water to enter the well from the saturated formation, prevents fine materials from entering the well, and serves as structural support for the unconsolidated aquifer material.
Whenever a screen is used it is required that a well screen be attached to the casing with a watertight seal.
In most cases, screens are not required in consolidated formations such as the limestone of the Floridian Aquifer.
In limerock the borehole is drilled into a water-bearing consolidated formation and the hole stays open without a well screen.
For this reason many wells are relatively inexpensive in central and south Florida.
If for any reason there is space between a borehole and casing, a well must be grouted by filling the annular space with materials specified by water management districts.
Grouting protects the aquifer from degradation caused by movement of water along the borehole either from the surface to the aquifer or between aquifers.
Grouting also prevents loss of artesian pressure in an artesian aquifer.
In
 most cases, a concrete grouting is required.
However, in some cases in unconsolidated formations, of such a caving nature by which the annular space is completely filled with existing material only the upper few feet of annular space have to be sealed with grout to provide protection from contaminated surface water.
The well should be sealed with a watertight cover during temporary interruptions in work on the well.
This rule also applies to wells that are only used seasonally or periodically.
Whenever pumping equipment is removed a well must be covered with a watertight cap or valve.
Special rules apply to wells located in a flood plane to prevent groundwater contamination during floods.
All free flowing wells  should be provided with a valve for controlling the discharge from the well.
Also, all abandoned wells are required to be plugged.
Newly constructed wells should be developed and tested.
The purpose of well development is to provide sand-free water at maximum capacity.
The drilling operation alters the hydraulic characteristics of a water-bearing formation in the immediate vicinity of the well caused by compaction, relocation of natural fine materials and/or migration of drilling fluids into the formation.
As a result local permeability and hydraulic conductivity may be severely reduced, restricting water flow into the well.
Development of a well reduces compaction and removes fine material from the pore space near the well.
By selectively removing the finer fraction of aquifer material, development increases natural porosity and permeability of undisturbed materials near the borehole.
In unconfined aquifers, it creates a grated zone of sediment around the screen, thereby stabilizing the formation SO that the well will yield sand-free water.
Development also removes drilling fluid that coated the borehole or entered the formation during the drilling process as well as relocated clay along the well walls.
The development of a well can be done using several different methods: over-pumping, backwashing, mechanical surging, air development, jetting, acid treatment, or explosions.
Often, more than one method is used, especially for larger wells.
For a small irrigation well the most common well development technique used is overpumping.
It is recommended that pumping begin at about 25% of the desired well yield and continue until the water is clear.
The process should be repeated at 50, 75, 100 and above 100 percent of the desired well yield.
The last pumping rate should be at least 25% higher than the desired well yield if possible.
A test pump should be used for the overpumping operation.
It is recommended that the permanent pump not be used for this operation, if possible, since sand particles may cause excessive wear of the pump.
Backwashing between pumping cycles improves effectiveness of well development.
Reversal of water flow through the screen into the formation removes finer fraction and rearranges the remaining particles.
Backwashing can be accomplished by starting the pump and shutting it off when the water is lifted to the surface.
This allows the water in the pump column to fall back into the well reversing water flow through the screen.
A combined overpumping and backwashing technique is often used for well development.
Reversed flow through the screen into the formation can also be accomplished through the use of mechanical devices such as surge block or surge plunger.
They are operated up and down in the casing, similar to a piston in a cylinder.
Surge devices are inexpensive, easy to use, and quite effective as development tools.
They can be used for wells of any depth or diameter.
Compressed air can be used for alternately surging and pumping a well.
In air surging, compressed air is injected into the well to lift the water to the surface.
As water reaches the top of the casing the compressor is shut off and the aerated water column falls back into the well.
Sediment is periodically removed from the well using air-lift pumping.
This procedure eliminates the need for a pump during development of the well avoiding risk of pump wear caused by the pumping of sand.
High-velocity jets of water or air can be used in well development.
Jetting is done by using a horizontal jet inside the borehole or a screen.
A jetting tool with evenly spaced nozzles is moved up and down along the screen, washing the finer materials free.
Development of well and aquifer in limestone or dolomite formations can be done by using acid.
The use of acid opens up fractures and crevices in the formation around the open borehole.
It increases overall permeability of the aquifer by dissolving materials in the cracks.
In Florida, acid development requires special permission from a water management district.
Explosives are sometimes used in a rock well  to develop and increase its yield.
In Florida the use of explosives in well construction to enlarge the cavity is prohibited unless specifically approved by a water management district.
After a well is developed, a pumping test should be performed in order to determine potential well yield, to select an efficient pump, and to determine the drawdown which can influence pump location for submersible or deep turbine pumps.
The well test is performed by measuring the yield and drawdown at certain time intervals during pumping.
A capacity/ drawdown curve can be developed  that allows efficient selection of a pump for given conditions.
Since the drawdown for the required yield is known, the location of the submersible or deep turbine pump can be determined from the chart.
A pumping test can also provide data necessary to determine the hydraulic parameters of an aquifer.
An aquifer pumping test requires the measurement of drawdown in nearby observation wells in addition to the capacity/drawdown data from the well.
An aquifer test determines the effect of newly installed wells on existing wells, the radius of influence of the well, and the drawdowns in the well for different discharges.
The results from this type of test are necessary for proper well spacing and for groundwater investigation and management.
Different types of wells and their construction and development depending on type of aquifer were discussed in this publication.
Different techniques were presented depending on geological conditions, well size and depth.
The role of water management districts in Florida in water well regulation was emphasized in this publication.
Soil Sensor Install Tips: If you are installing Watermark sensors, remember to check them before installation to ensure that they are reading properly.
When dry, sensors should read 199 kPa.
After soaking in water for 10-15 minutes, sensors should read between 0-10 kPa.
Values higher than this likely indicate that the sensor needs to be replaced.
Before you go to the field to install Watermark sensors, be sure to put the sensors in water and install them wet to eliminate air in the sensor.
Chapter 10: Selecting Corn Hybrids
 Hybrid selection is one of the most important management decisions made by a corn producer because the genetic yield potential of different corn hybrids varies greatly and directly impacts yield and input costs.
There are many factors to consider when selecting hybrids including: yield potential, maturity rating, drought resistance, nutrient efficiency, and pest resistance.
Useful information about specific hybrids can be obtained from many sources including state and regional testing programs, on-farm strip trial testing, independent and company agronomists, seed company catalogs, and company demonstration trials.
If a businessman were choosing a location to begin a new retail store, a real-estate agent would tell him that the three most important factors for choosing a successful site are "location, location, and location." In the same manner, a corn grower planning for next season should recognize that the three most important characteristics for selecting hybrids are "yield, yield, and yield." A hybrid with poor yield potential cannot be made into a "good" hybrid with better management.
Examination of the 2013 corn hybrid trial results  showed that at the SDSU Volga Research Farm, there was a 35-bushel per acre yield difference between the highestand lowestyielding hybrid.
Assuming a long-term average corn price of $4/bu, this equates to an increase in gross income of $80 and $140 per acre, respectively.
Figure 10.1 SDSU corn hybrid test plots.
Table 10.1 Tips for selecting corn hybrids :
 1.
Obtain reliable information on hybrid performance.
2.
Identify the field problems.
For example:
 a.
Does it have a history of Goss's wilt.
b.
Is lodging a problem.
3.
Identify a realistic yield goal and select appropriate hybrids.
To achieve this goal select racehorse or defensive hybrids.
Racehorse hybrids are designed to maximize yields under optimum conditions, whereas defensive varieties are designed to produce a "good" yield under less than optimum conditions.
4.
Select a hybrid with an appropriate maturity rating.
There are many resources available for producers to evaluate hybrid performance.
Information is available from the SDSU Extension Crop Performance Testing program  or F.I.R.S.T.
trials.
Additional information can be obtained by conducting side-by-side yield tests on your own farm or searching seed dealership or local agronomy company websites.
Keep in mind that most side-by-side tests are one replication and therefore results may not be as reliable as a multiple replication test.
When studying yield trial results, it is best to focus on hybrids that perform well over multiple locations and years.
Consistent performance over multiple locations with different soil and weather conditions is important because of the variability in growing conditions between seasons.
When examining yield results, it is important to note not only the yield performance of a hybrid but also the LSD  of the hybrid yield averages.
The LSD value is used to determine which hybrids are statistically different from one another.
In Table 10.2 it is the last row in the table.
Examination of Table 10.2 shows an LSD 0.05 value of 19.1 bu/acre.
This value means all hybrids exhibiting yields within 19.1 bu/acre from one another are considered to be similar with 95% confidence.
For example, a yield of 248 bu/acre is not significantly different from any hybrids with yields > 228.9 bu/ acre.
Another important statistic is the coefficient of variation.
This statistic is 100 times the standard deviation divided by the mean value for the trait of interest.
The CV is an indicator of the repeatability and reliability of the measurements.
The lower the CV the better.
The CV value of 6% in Table 10.2 is considered excellent.
Table 10.2 An example of corn hybrid yield trial results from the South Dakota State University Crop Performance Testing program.
For each hybrid, a number of measurements are collected.
This information can be used to match the hybrid to specific problems.
For example if the field has a history of lodging, hybrids with low lodging scores should be selected.
Brand	Hybrid	Relative	Yield	moisture	Test weight	Lodging	Final stand
 bu/acre	%	lbs/bu	%	*1000
 Channel	197-68STX	97	248	21.0	55.9	0.8	27.9
 Wensman	W80978VT3PRO	97	246	19.5	55.2	0	28.5
 Renk	RK596SSTK	98	244	20.3	57.5	0	27.4
 Channel	197-33STX	97	241	19.8	57.1	0	28
 Hoegemeyer	HPT 7042 AMX-R	100	241	21.0	57	0	28.2
 Trial average	227	19.1	56.7	0.08	27.4
 LSD 	19.1	1.5	1.1	2.2	0.9
 CV	6	5.6	1.4	2.4
 Geographic Suitability and Stability
 It is important to examine yield data from studies with climatic conditions similar to those observed on your farm.
In drier areas, where yield potential may be < 100 bu/acre, producers may want to select defensive hybrids, whereas in areas with a high yield potential, , racehorse hybrids might be the best choice.
The average precipitation and growing degree map shown in Figures 10.2 and 10.3 describes regional variability.
Care must be used in applying these maps because average conditions rarely occur.
Standard deviation of the precipitation averages can be used to assess the expected variability.
For example if the standard deviation is 5 inches and the average rainfall is 20 inches, then 68% of the time the area will receive between 15 and 25 inches of rainfall.
This variability means that on average, the value of the testing site decreases with increasing distance from your farm.
Figure 10.2 The South Dakota average annual precipitation in inches from 1977 to 2006 
 Hybrids are rated based on their relative maturity.
Selecting an appropriate maturity rating is important because if the hybrid does not reach physiological maturity  before the first killing frost, yield and test weight may suffer.
Black layer occurs when there is a layer of dark cells near the kernel tip.
Images showing black layer are available in Chapter 5.
Hybrid maturity may have a significant impact on final grain yield, moisture content, and test weight.
Drying grain costs money and reduces profits.
Chapter 53 provides information on corn storage and drying.
A rule of thumb is that 2 bushels of corn are needed to dry corn 1%.
Different classification systems can be used to characterize corn maturity ratings.
A comparison between several systems is available in Chapter 5.
One of the most widely used approaches is the number of growing-degree days  to reach maturity.
GDD can also be reported as growing-degree units.
An example of growing-degree day calculations are provided in Example 10.1.
See Chapter 5 for additional information.
Example 10.1 Estimating corn growing-degree days  over a three-day period.
In this calculation, the corn GDD base is 50F and the GDD max is 86F.
These values mean that if the temperature is less than 50F use 50 F  or if the temperature is >86F use 86F.
The general equation is, GDU= _ 2 lower base temperature.
Additional discussion is in Chapter 5.
Table 10.3 Growing-degree days over a 3-day period.
GDU	day 1	/2 50 = 11
 GDU	/2 50 = 16
 GDU	/2 50 = 24
 GDU	11+16+24 = 51
 The second approach for ranking corn maturity is the Comparative Relative Maturity.
CRM assigns ranks to hybrids according to "days" of maturity.
These ranks are related to the accumulated GDDs.
When considering CRM it is important to consider that selecting a 90-day corn does not mean it will mature in 90 days.
Two hybrids may reach physiological maturity at the same time but dry down at different rates, thus having identical GDD hybrid ratings but different CRM ratings.
The two systems are related, and generally:
 1.
An 85-90 day hybrid requires 2000-2100 GDD.
2.
A 90-95 day hybrid requires 2100-2250 GDD.
3.
A 95-100 day hybrid requires 2250-2350 GDD.
4.
A 100-105 day hybrids require 2350-2500 GDD.
5.
A 105-110 day hybrids require 2500-2650 GDD.
It is important to choose hybrids suited to the environment where they will be grown.
Most seed companies publish detailed information about corn hybrids, including the specific number of growingdegree days required to reach physiological maturity.
As a rule of thumb, selected hybrids should reach maturity  at least 10 days before the first average killing frost.
Keep in mind that production systems may affect maturity selection.
For example, in cooler spring soil temperatures, no-till systems with heavy residue may slow plant maturity.
Some growers will also look closely at the silk CRM  of individual hybrids.
Earlier-silking hybrids have been known to work well in droughty and hot environments because they may enter the reproductive growth stages prior to severe drought and heat stress.
In recent years, genetically modified  traits in corn hybrids have been used to minimize the damage from pests.
These GM corn hybrids provide increased crop resistance to insects and diseases, improved drought tolerance, and tolerance to broad-spectrum herbicides.
Consideration of technology costs, the marketability of the crop, and the risk of developing weed or insect pest resistance should be considered when planting a GM crop.
The starting point to obtain information about GM seed corn traits is from seed suppliers.
Transgenics are a type of genetic modification where genes  are transferred from nonplant sources into plants.
In corn, for example, the Bt  genes were obtained from soil bacteria Bacillus thuringiensis) and inserted in the corn plant to combat insect pests.
One type of Bt gene provides resistance to corn rootworm while other Bt genes provide resistance to European corn borer, Southwestern corn borer, western bean cutworm, fall armyworm, corn earworm, and black cutworm.
Transgenic modifications have also provided crop tolerance to herbicides such as Roundup and Liberty Stacked hybrids contain two or more genetic traits.
For example, Monsanto's Genuity VT Triple Pro RIB Complete contains two separate genes for protection from aboveground insects such as corn borer and earworm, and a single gene for protection from belowground insects such as rootworm in addition to providing a 10% refuge.
Many hybrids have an integrated refuge in the bag  whereas others may require a separate corn borer and/or corn rootworm refuge for insect resistance management.
Insect and weed pests are becoming increasingly more resistant to chemical and genetic solutions.
To slow the development of pest resistance the control strategies should be rotated.
Tips to avoid problems include:
 1.
Know the terminology.
For example: GT , LL , RR2.
2.
Understand the trait biology.
3.
Check seed bag tags to make sure what was ordered was delivered.
4.
Check herbicide traits multiple times prior to herbicide application.
5.
Save seed bag labels for your field records.
Corn hybrids have a wide variety of agronomic characteristics relating to plant structure and health.
Seed companies generally provide trait ratings for seedling vigor, stalk strength, and ear retention.
Seedling vigor refers to the ability of a corn plant to cope with stress early in the growing season.
Hybrids with good seedling vigor may perform better in cool, moist conditions.
This may be important in no-till and highresidue production systems.
Good stalk strength can decrease lodging but there are no guarantees.
All hybrids can lodge or break off if undesirable weather events or insect/disease infestations occur during periods of rapid stalk growth.
Poor stalk strength can reduce yields by increasing harvest losses.
If lodging and/or ear drop is an issue, select hybrids that provide protection against shank-boring insects, drought tolerance during pollination, and good ear retention.
Harvest problems associated with lodging may be alleviated somewhat by adjusting the combine accordingly.
Information on measuring and adjusting combines to reduce losses is available in Chapter 37.
Corn hybrids are produced by crossing inbred lines that are developed over several seasons.
Plant scientists select for specific traits by inbreeding  corn plants and then discarding progeny that has undesirable characteristics.
Plant vigor is often lost during the inbreeding process but it can be recovered by crossing with other inbred lines.
Hybrids can be produced by crossing two , three , and four inbred lines.
If a single cross is used, then all plants within a field will have near uniform characteristics, whereas hybrids produced using double-crosses will have the most variability.
Generally, single-cross hybrids have the highest hybrid vigor.
Use On-farm Testing to Verify the Best Hybrids
 Different hybrids have characteristics that make them better-suited for one environment over another.
An approach that can be used to examine hybrid performance is on-farm strip-trial testing.
On-farm testing can be used to match hybrids to your conditions.
Be sure to use a well-calibrated yield monitor and/or compare weights from strips using scales on grain carts for accurate harvest data when conducting onfarm strip trial testing.
Understand that replication in strip trials is very important for determining which hybrids are actually better performers.
Replicated, split-planter testing can help overcome many of the inherent variables that occur in agronomic testing.
Consider field-by-field hybrid placement to maximize yield of each hybrid.
Many seed and data-mining companies are putting a lot of effort into analyzing large amounts of yield data to determine which hybrids perform better on individual soil types.
This type of technology is still in the early stages but "prescription" hybrid selection based on soil type may become commonplace in the future.
Consult with your local seed experts to match hybrids to your soil and environmental conditions.
It is possible to purchase hybrids with specific seed-quality characteristics.
For example, high-lysine, high-amyopectin , or white corn hybrids are available.
High-lysine corn hybrids were created for feed for nonruminant animals, such as hogs, whereas waxy corn hybrids were created to increase milk production efficiency.
White corn was created specifically for the food market.
Specialty corn hybrids may have specific management requirements that should be followed.
Additional information on specialty corn hybrids are available in Dickerson.
Selecting a genetically diverse lineup of locally adapted hybrids that vary in maturity and agronomic strengths can help growers lower their risk of crop loss.
Spreading out maturities helps manage weatherrelated risk as well as spreading out the harvest interval so the crop is not all too dry or too wet at harvest.
Hybrids should be considered/selected for the following key traits: yield, maturity, drought tolerance, standability, pest resistance, dry-down time, grain quality, and harvestability.
Consulting with seed experts
 in your area to understand the agronomic characteristics of locally adapted hybrids is a good starting point.
WHY DO WE NEED WATER?
Water makes up between 50 to 75 percent of our bodies.
It is an essential nutrient and our bodies can't make all that we need.
And even though water is the single most important nutrient for maintaining good health, we forget to drink it!
Drinking 48 to 64 ounces of water daily is a good idea, but the amount of water a person needs is affected by many things.
Needs are increased for persons living in a hot climate or who are very active.
Our bodies can survive only a few days without water.
Water carries nutrients throughout the body and keeps food moving through the intestines.
It helps wash out waste products and prevent constipation.
Water also cushions joints so they move smoothly and regulates our body's temperature through sweating.
If you experience dry mouth, dark urine, and dizziness or light-headedness, you may need to consume more water.
WATER CONTENT OF FOODS
 Believe it or not, water is found in nearly all foods.
As you can see, fruits and vegetables typically contain the most per ounce.
If you're tempted to replace your produce with juice, be aware that not all juices are the same.
Some are packed with nutrients, while others are simply sugar water.
Read the label, and only buy juices that contain 100% fruit juice.
Lookout for words like "drink," "punch," "cocktail," "drink," or "beverage." They indicate the drink is mostly sugar, water, and additives.
Remember some fruit drinks may cost less than 100% fruit juices, but because they provide few nutrients, they really are not a better buy!
ADD WATER TO YOUR DAY
 Here are 5 tips for drinking more water throughout your day:
 1.
Take water breaks, not coffee breaks.
2.
Have water with your meals and/or snacks.
3.
Freeze a water bottle and take it to work each day for an ice-cold supply.
4.
Never pass up a drinking fountain.
5.
Drink water before, during and after exercise.
Write below how you like to add water to your day:
Crop Water Use and Irrigation Scheduling Guide for North Florida 1
 Vivek Sharma, Charles Barrett, De Broughton, and Thomas Obreza
 Crop Water Use and Irrigation
 Effective irrigation scheduling enables the irrigator to apply the right amount of water at the right time to meet the crop water demand.
This guide presents information on average daily and weekly crop water use and crop growth stages for twelve north Florida crops that can be used to help schedule irrigation.
This will allow a grower to develop a realistic irrigation schedule that minimizes plant water stress, saves water, and reduces nutrient leaching potential.
The crops included in this guide are:  Bermudagrass,  Bean ,  Cabbage,  Carrot,  Corn ,  Corn ,  Cotton,  Cucumber,  Grain sorghum,  Peanut,  Potato, and  Small grains.
Crop water use, also called crop evapotranspiration , is defined as the combined transfer of water from the land surface to the atmosphere in the form of water vapor by  evaporation and  plant transpiration.
Crop water use or ETc depends on many factors, which we can divide into three major categories.
Weather and climatic conditions:
 Amount of sunshine 
 Air temperature 
 Amount of wind 
 Humidity 
 Crop age or crop growth stage
 2.
Vivek Sharma, assistant professor, Department of Agricultural and Biological Engineering; Charles Barrett, regional specialized agent, water resources, UF/IFAS North Florida Research and Education Center; De Broughton, regional specialized agent, row crops, UF/IFAS North Florida Research and Education Center; and Thomas Obreza, professor, senior associated dean, and associate director, Department of Soil and Water Sciences; UF/IFAS Extension, Gainesville, FL 32611.
Crop Evapotranspiration  Calculations
 The average daily ETc  was calculated by adjusting the reference evapotranspiration  by a specific crop coefficient  that takes crop type and age into account as: ETc = Kc * ETo
 The ETo is the rate of water loss by evaporation and transpiration from a healthy  hypothetical reference crop, e.g., grass.
This closely resembles the ETc from an extensive surface of green grass of uniform height that is actively growing, well-watered, and completely shading the ground.
The crop coefficient  is the integrated crop factor that incorporates the crop canopy characteristics and management practices.
Each crop has different sets of Kc values depending on the growth stages of the crop and field/crop management practices.
In this guide, Kc values for different crops were taken from FAO Irrigation and Drainage Paper No.
56.
These Kc values were further fine-tuned based on local data collected from various on-field trials.
Groundwater levels across much of Nebraska continue to rebound from the historic 2012 drought, according to the 2019 Groundwater-Level Monitoring Report.
However, the groundwater-level rises resulting from the historic flooding of 2019 have not yet been completely accounted for.
While the flooding had a grave impact on surface water levels throughout much of Nebraska, how it affects the groundwater supply will be measured in the coming years, said Aaron Young, a geologist with the University of NebraskaLincolns School of Natural Resources.
Managing Stormwater Using Low Impact Development  Techniques
 Carmen T.
Agouridis and John T.
McMaine, Biosystems and Agricultural Engineering Department
 I n the year 1800, 3 percent of the world's population lived in urban areas.
Today that number is closer to 50 percent, and it is expected to increase to 70 percent by 2050.
This increase in urbanization means that more of our watersheds are covered with impervious surfaces such as buildings, roads, sidewalks, and parking lots.
As more land is covered by impervious surfaces, less rainfall infiltrates into the ground and instead becomes
 runoff.
Too much runoff is problematic.
Flooding increases, streambanks erode, and water quality is reduced.
An increase of impervious area of as little 10 percent has been shown to negatively impact streams.
The purpose of this publication is to explain low impact development strategies and how they can be used to improve stormwater management by reducing impacts on streams.
Figure 1.
When a watershed urbanizes, infiltration and evapotranspiration decrease while runoff increases.
Figure 2.
Stream-bank erosion and channel incision are common in urbanizing landscapes.
A hydrograph is a chart that shows the change in discharge or flow over time.
When rain falls on a watershed, some of the rain infiltrates into the ground and some undergoes evapotranspiration.
The remainder becomes runoff.
Urbanization directly affects the amount and the rate at which runoff reaches a stream.
Prior to development, most of the rainfall soaked into the ground.
Relatively little runoff reached the streams, and what did required a longer travel time or time of concentration.
Smaller runoff volumes and longer times of concentration meant that the water level in the streams rose slowly and did not get that deep.
The hydrograph now has a long peak and is elongated.
Following development, more runoff is produced as impervious areas allow little rainfall to soak into the ground.
Downspouts, curbs, gutters and pipes quickly transport stormwater to streams.
The combination of more runoff and faster delivery of this runoff to streams results in what is called a peaked hydrograph.
Water level in the streams rises quickly and becomes deep.
Figure 3.
Many urban streams have high levels of pathogens, which pose a hazard to human health.
Figure 4.
Excess nutrients and high temperatures promote bacterial growth and algal blooms.
The goal of conventional  stormwater management techniques is to rapidly route runoff from impervious areas to receiving water bodies.
Curbs and gutters are used to direct runoff from roof tops, parking lots, streets and the like into a series of underground pipes called the storm sewer.
The storm sewer carries the collected and untreated runoff mostly to streams but sometimes is sent to reservoirs and lakes.
To handle to this runoff, some streams were enlarged and concreted.
Conventional stormwater management techniques also give little consideration to improving runoff water quality.
Generally,
 no barriers exist between the pollutant source, such as fertilizers from lawns or heavy metals and hydrocarbons from parking lots, and the receiving water body.
In some cities, the storm sewer was combined with the sanitary sewer.
The sanitary sewer is the pipe etwork that carries water from devices such as toilets, showers and washing machines to the municipal water treatment plant.
The problem with this design is that during storm events, more water is sent to the municipal water treatment plant than it is capable of treating.
When the capacity of the municipal water treatment plant is exceeded in such an instance, water-both stormwater and sewer water-is sent into the streams untreated.
Such an event is called a combined sewer overflow.
Figure 5.
Conventional stormwater management is designed to collect and rapidly convey runoff to streams, some of which have been lined with concrete because they eroded so badly.
Stormwater detention basins may be used to collect and hold runoff in order to release it at a more controlled rate.
These basins are designed to reduce the post-development peak flow so that it matches the pre-development peak flow.
However, post-development runoff volumes are not reduced, just the peaks.
The large runoff volumes are released from the basins over a long period of time meaning streams experience these larger flows for a much longer time than normal.
Because of this, streambank soils are weakened and streambank erosion is common.
A stormwater detention basin near a shopping center in Lexington, KY.
Low impact development  or green infrastructure is a management approach that seeks to reduce runoff and associated pollutants by managing them at the sites where they are generated.
LID is focused on controlling stormwater at the individual level unlike conventional stormwater management which uses a large control structures at the outlets of watersheds.
This means that with LID numerous small control structures are spread throughout the watershed.
Instead of trying to control runoff from large, rare storm events, LID focuses on controlling runoff from the small storms, which comprise the majority of the average annual rainfall.
To control runoff, LID primarily seeks to increase infiltration and evapotranspiration rates within the watershed SO that the postdevelopment hydrology matches the pre-development hydrology as closely as possible.
LID accomplishes this primarily by:
 Minimizing or reducing the total amount of impervious area in a watershed
 Protecting hydrologically sensitive areas
 Minimizing directly connected impervious areas
 When it comes to stormwater, the basic tenants of LID are to spread treatment throughout the watershed, slow down the movement of runoff, and allow stormwater to soak into the ground.
In addition to managing hydrology, LID also seeks to improve runoff water quality by utilizing the ability of soils and vegetation to remove pollutants.
The U.S.
Department of Agriculture Natural Resource Conservation Service  developed the curve number  method to model the amount of rainfall that becomes runoff for a watershed.
In this method, the CN accounts for the effects the watershed's land use and soils have on generating runoff.
For example, land that is pastureland generates less runoff than land used for parking lots.
Likewise, some soils have high rates of infiltration while others only allow water to infiltrate slowly.
CNs can range from 30 to 100.
Lower CNs mean less rainfall becomes runoff while higher values mean more runoff is generated.
A CN of 100 indicates that all rainfall becomes runoff.
To promote infiltration, LID seeks to reduce the CN by decreasing the amount of impervious area in the watershed and protecting hydrologically sensitive areas.
These hydrologically sensitive areas include streams, riparian buffers, floodplains, wetlands, steep slopes, and highly permeable soils.
Protecting highly permeable soils or those soils that allow a lot of water to infiltrate quickly is an important method for reducing runoff.
Unfortunately, protection of such soils is rarely done.
Low impact development techniques are divided into two types: resource preservation and structural controls.
Resource preservation seeks to protect the hydrologic and water quality characteristics of an undeveloped site to the maximum extent possible.
Such activities include protecting riparian buffers  and soils with the ability to infiltrate rainfall quickly, using fewer fertilizers on lawns and fields, and picking up trash and pet waste.
The term "time of concentration" is defined as the time it takes for a drop of water to travel from the most hydrologically remote location in a watershed to the outlet.
In other words, how long does it take for a drop of water that falls at the most distant point in the watershed to travel to the outlet?
Structural controls are designed to decrease runoff volume by increasing infiltration and evapotranspiration.
In LID, stormwater is routed to these controls where it is held SO that infiltration can occur.
By allowing stormwater to infiltrate, both
 What is important about time of concentration is that it is used to determine peak discharge.
Runoff that travels quickly to the outlet means the peak discharge will happen quickly.
When a watershed undergoes development, the time of concentration is reduced largely because of conventional stormwater management methods.
Not only is more runoff produced because the watershed CN is increased, but curbs, gutters and pipes quickly route the stormwater to the watershed outlet.
A fundamental goal of LID is to increase the time of concentration by disconnecting impervious areas.
For example, instead of rainfall from a parking lot being directed to curb inlets to enter the storm sewer system where it is quickly routed to a stream, LID would encourage infiltrating the rainfall onsite.
This means that none or very little rainfall enters the storm sewer system.
runoff volumes and peaks are reduced and stormwater quality is improved.
When using structural controls, it is best to start in the headwaters of a watershed as controls located in these areas are more effective at protecting streams than controls located at the watershed outlet.
When designing LID-based stormwater management plan, a number of structural controls that use the LID philosophy are available.
These controls vary in size and complexity from small ones suitable for a residential lot to large ones typically used by developers, commercial businesses, and governments.
This publication will examine a few of the more commonly used ones.
Rain gardens are shallow depressions that use a conditioned planting bed  and landscaping to filter stormwater.
Rain gardens are typically designed to capture runoff from a 1-inch storm event and infiltrate the rainwater within 24 to 48 hours.
Rain gardens can be planted with trees, shrubs, grasses, and/or flowers.
When choosing vegetation for a rain garden, it is important to use native vegetation.
Native vegetation is acclimated to the local climate and does not require excessive maintenance to survive.
Because rain gardens undergo periods of drought and inundation, it is also important to choose plants that can withstand these conditions.
Figure 6.
Rain gardens may contain trees and shrubs, such as this one at the Coca-Cola Bottling Facility in Lexington, Ky.
Rainwater harvesting is one of the simplest and oldest LID techniques.
With rainwater harvesting, rainwater from roof tops and other impervious areas is collected and stored in rain barrels or even cisterns for future use.
In some cases, excess rainwater is redirected from the rain barrel to a rain garden.
Collected rainwater is often used to wash automobiles, irrigate or flush toilets.
Harvested rainwater is not potable SO it is not safe to drink.
Riparian buffers are vegetated areas adjacent to streams.
Typically comprised of three vegetation zones, riparian buffers provide many benefits to stream systems.
The roots of riparian vegetation help hold streambank soils in place, protecting the banks from high flows, and thereby reducing erosion.
Riparian vegetation provides the stream with shade which helps control temperature and algal growth while improving dissolved oxygen levels.
Leaves and twigs from riparian vegeta-
 Figure 7.
Rain barrels are ideal for collecting rain water from roof tops for future use.
tion provide aquatic organisms with a source of food while birds and animals consume fruits and nuts produced by the plants.
Riparian buffers also improve stream water quality by filtering sediment, nutrients and other pollutants from overland flow.
The effectiveness of a riparian buffer is strongly linked to its width, and the required buffer width is strongly linked to topography, land use, hydrology, and the constituents of concern.
If the buffer is too narrow, it will not meet the site objectives.
For sediment removal, a buffer width of 25 feet may be sufficient but a width of 100 feet may be needed for nitrate removal.
Socioeconomic factors will also play a role in determining the appropriate buffer width, particularly in urban areas.
A green roof, also called a landscaped roof or rooftop garden, consists of a soil media and plants.
These systems can be rather simple consisting largely of hardy groundcover plants such as sedums or more complex with a park-like setting.
The simpler green roof design is called an extensive system while the more complex one is an intensive system.
Rainwater that falls on green roofs undergoes evapotranspiration, which reduces runoff volumes and peak flows.
Evaporation combined with shading from the plants helps cool the roofs.
Studies have shown that temperatures on green roofs are much cooler than the surrounding air temperature.
When designing a green roof, it is important to determine what type of additional structural support may be needed to support the extra weight.
Extensive systems are lighter than intensive ones, and as such, require less additional structural support.
Like rain gardens, native plants should be used.
Vegetation on green roofs is exposed to the wind, sun, ice and other harsh conditions with little or no relief.
Care must be taken to choose hardy plants.
Permeable pavement is an asphalt or concrete paving surface specially mixed with fewer fine particles which creates more void spaces.
In addition to continuous type surfaces, interlocking concrete or brick pavers are also used.
Permeable pavement consists of a paving course, filter course, stone reservoir, and filter fabric layer.
Water easily flows through permeable pavement and infiltrates the underlying soils.
The common types of permeable pavement are pervious concrete, porous asphalt, interlocking concrete pavers, concrete grid pavers, and plastic reinforced grids filled with either grass or gravel.
Permeable pavement is most commonly used in parking lots, driveways, walking paths, residential streets, and other such locations where the traffic volumes are light.
This LID technique is effective at reducing peak flows and total runoff volumes and has shown some promise at removing pollutants such as heavy metals and nutrients from runoff.
Due to concerns over clogging, permeable pavement is not recommended for use in areas with high sediment loads.
Bioswales are shallow, wide, low-sloped channels, which are lined with vegetation or rock.
Used in lieu of pipes, bioswales transport runoff to the storm sewer system or to receiving waterbodies.
As such, bioswales are ideal for use alongside roadways or within parking medians.
Bioswales are designed to promote infiltration by slowing down runoff.
They also improve water quality via filtration and settling.
The depth of flow should be less than the height of the vegetation or rock.
Figure 9.
Green roofs, such as this one, help reduce runoff volume and reduce the building's energy usage.
Figure 10.
Permeable pavement, such as these interlocking clay brick pavers, is ideal for light traffic areas such as parking lots.
Figure 11.
Parking medians, such as this one at the Sanitation District 1 parking lot in Northern Kentucky, are ideal locations for bioswales.
Photo courtesy of Jim Hanseen of EcoGro.
Figure 12.
Stormwater wetlands provide habitat for wildlife in addition to improving stormwater quality.
Stormwater wetlands or constructed wetlands consist of shallow pools and rooted vegetation.
In addition to the shallow pools, stormwater wetlands generally have two deep pools: one located at both the inlet and one at the outlet of the wetland.
The deep pool at the inlet acts like a forebay allowing particulates to settle out of suspension.
At the outlet, the deep pool helps prevent clogs by keeping vegetation from growing near the outlet.
Stormwater wetlands are effective at pollutant removal.
Similar to natural wetlands, settling, filtration and biological uptake are the three primary methods for removing pollutants in stormwater wetlands.
Stormwater wetlands also provide habitat though the level of biodiversity may be less than natural wetlands.
While stormwater wetlands are similar to natural wetlands, it is important to note that natural wetlands should not be used for stormwater treatment.
Routing stormwater into a natural wetland can alter its hydrology thus affecting the vegetation.
One of the biggest concerns with LID techniques is the cost.
Will it cost more to design, implement and maintain LID controls as opposed to using conventional stormwater methods?
The answer is that it depends.
Costs are site specific.
Factors such as existing soil conditions, topography, land availability,
 vegetation, stormwater control size and complexity, and desired maintenance level will drive costs.
With regards to maintenance costs, vegetation management is usually the most costly item, SO selecting low-maintenance vegetation is important.
It is also important to prevent large sediment loads, such as those associated with construction activities, and litter from impacting LID controls.
Sediment is the number one enemy of LID controls; it causes clogging and shortens the control's useful life.
A forebay, which is a small, cleanable pool located at the inlet of the LID control, is often used to prevent incoming sediment and debris from clogging LID controls.
Stormwater management is an important issue for developing communities.
While conventional stormwater management techniques are effective at routing stormwater from impervious areas to receiving water bodies, they are not effective at reducing runoff volume or improving runoff water quality.
LID techniques, on the other hand, promote infiltration and evapotranspiration in an effort to reduce runoff volumes and improve runoff water quality.
And unlike conventional stormwater management, which often uses a large control structure at the outlet of a development such as a shopping center or neighborhood, LID promotes the use of many small control structures spread throughout the watershed.
Resource Protection and Structural Controls 
 Reducing Stormwater Pollution 
 Building a Rain Barrel 
 Riparian Buffer Planting 
This is important for two reasons.
First, its important to provide room to store free offseason precipitation.
In most years even the drier Nebraska Panhandle sees enough precipitation to fill the soil water profile.
Diana G.
Helsel and Zane R.
Helsel Department of Agronomy
 The PDF version of this publication includes illustrations.
Missouri's growing season is characterized by excessive moisture in the spring followed by inadequate moisture during the middle of the growing season.
Because of the lack of moisture during the crops' peak demand, some producers have invested in irrigation systems.
The cost of maintaining and using these systems is high, SO it is imperative to manage moisture in the most efficient way possible.
The following discussion should help Missouri soybean producers understand the crop's need, the soil's ability to hold and supply water, and the agronomic practices that can result in maximum economic yields under irrigation.
Soybean response to irrigation
 Irrigation usually improves soybean yields on drought-prone soils and in exceptionally dry seasons.
The amount of increased yield  fluctuates, depending on variety, geographic location, soil type and fertility.
An eight-year study of irrigated VS.
nonirrigated soybean yields in southeast Missouri indicates yield increases are greater for short-season varieties under irrigation.
Full-season varieties show almost no yield response, and medium-season varieties show an intermediate response to irrigation.
Responses of soybeans to irrigation in southeast Missouri, 1967-1974
 Maturity	Average of three sites
 Early	27.1 bushels per acre	33.8 bushels per acre	6.7 bushels per acre
 Medium	32.0 bushels per acre	35.7 bushels per acre	3.7 bushels per acre
 Late	32.9 bushels per acre	33.7 bushels per acre	0.8 bushels per acre
 Adapted from Shannon and Duclos.
In central Missouri, a survey indicates that over a 10-year period, soybean growers obtained an average increase of 13 from irrigating full-season soybeans.
In research sponsored by the grower check-off program, yields of 10 varieties grown in southwest Missouri during the dry years of 1983 and 1984 averaged 29 and 13 bushels more per acre respectively under irrigation.
In 1985, when plentiful rains occurred during the seed-fill period, yields increased by only about 1 bushel per acre.
The economics of achieving these yield increases are of paramount importance.
The type of irrigation system and the water source greatly affect cost.
Flood or furrow irrigation with a cheap water source may cost as little as $25 per acre per year, while a center pivot system with a deep well could cost as much as $100.
Prospective irrigators should weigh potential costs against returns they can expect from the increased yields and reduced risks created by irrigation.
In addition to influencing yields, irrigation may alter other characteristics of importance to soybean growers, such as maturity and lodging.
Irrigation delays the maturity of shortor midseason varieties only a few days.
Full-season varieties usually show no difference in maturity unless extended drought or charcoal rot infection occurs.
Plant height normally increases under irrigation, which increases the chance of lodging.
However, proper variety selection may reduce this problem.
Weather patterns and crop water use
 Missouri rainfall patterns are characterized by sufficient winter and early spring rainfall that maintains the soil at or near saturation capacity until almost the first of June.
During late June, July and August, the crop's need for moisture usually exceeds that available from either the soil or rainfall.
Water requirements are a function of the plant's metabolic needs, the quantity needed for transpiration , and the quantity lost by evaporation from the soil.
This combined demand is called "evapotranspiration."
 The peak water use period for soybeans occurs during reproductive growth, when they may need as much as 2.5 inches of water per week.
The average rainfall during this period is less than 0.6 inches per week.
Available soil moisture is depleted by the time reproductive growth begins, so unless you provide supplemental irrigation, the plant will be subjected to moisture stress.
Short-season varieties complete flowering and pod filling during the period of greatest evapotranspiration.
This results in decreased yields if you don't irrigate.
Full-season varieties normally reach their critical growth period after the period of the highest evapotranspiration passes.
Soybeans are most sensitive to moisture deficits during the late pod development/early bean filling periods.
Figure 1 depicts the yield response of northern soybeans relative to the time at which moisture stress develops.
Lack of water during flowering and podding causes flower and pod abortion.
Stress during pod development and early seed fill reduces the number of seeds per pod.
Drought conditions
 during seed fill reduce seed size and thus final yield.
The critical period of water need for indeterminate varieties occurs from late flowering through mid pod fill.
For determinate varieties, such as those grown in the Bootheel, the period of greatest water need begins earlier in flowering.
The new determinate semidwarf  varieties often show critical water needs through most stages of growth.
The effect of a moisture stress on soybean yield at various growth stages.
From Shaw and Laing, 1966.
lowa State University
 Availability of soil moisture
 Specific soil types have varying abilities to hold moisture.
The available soil moisture, in terms of inches of water held per foot depth of a soil, is described in Table 2.
Sandy soils retain the least amount of water, while silt loam and clay loam soils hold the most.
Note that clay soils have less available water than do clay loam soils.
Clay soils hold more water, but less of that water is available for plant growth because water adheres strongly to the clay particles.
Table 2 Potential available water storage capacity for various soil types
 Soil type	Available soil moisture per foot of depth
 Loamy sands	1.0 inch
 Sandy loam, clay loam	1.5 inches
 Loams, silty clay loam	1.8 inches
 Silt loams	2.5 inches
 Adapted from Kiniry, Scrivner, and Keener, 1983.
You must also consider the rooting depth of the crop in a particular soil.
The effective rooting depth of soybeans ranges from a few inches after emergence to 2 to 3 feet during the early reproductive stages.
However, some Missouri soils are compacted and some acid sublayers restrict the effective rooting depth to that depth of topsoil above the compacted layer.
In these soils, it is wasteful to supply more water than is necessary to wet the upper zone.
You can measure or estimate soil moisture by a variety of methods.
Each has its advantages and limitations.
Irrigators who use soil moisture measurements for scheduling purposes usually establish an allowable soil moisture depletion level.
For soybeans, the limit is about 70 percent depletion in the vegetative stages and 50 percent for reproductive stages.
You should irrigate if you reach these levels.
To maintain the soil moisture content above the allowable depletion level, you should start irrigating sooner on sandy soil, which has a lower moisture storage capacity.
One of the quickest and most popular methods of determining soil moisture is based on feel and appearance of the soil.
Charts to aid inexperienced irrigators are available.
The method is not quantitative and requires individual judgment.
Thus, it lacks the precision of other methods.
Electrical resistance instruments, commonly called moisture blocks, measure the moisture content of the soil indirectly.
They sense a change in electrical properties of the blocks which correlates with block moisture content and, in turn, the soil moisture.
These devices consist of two electrodes mounted in blocks made of plaster-of-paris, fiberglass, gypsum or other materials.
Wires from the electrodes attach to a meter that measures electrical conductivity, a function of the water content of the soil.
To install moisture blocks, dig a hole with a soil auger and place the block in it.
Pack soil around the block to ensure good capillary action between the sensor and the soil.
Calibrate blocks in each field to ensure accurate prediction.
Moisture blocks are not recommended for sandy soils.
Tensiometers are well adapted to sandier soils.
Tensiometers measure the soil moisture tension how tightly the soil particles hold the water.
This is directly related to the tension required for plant roots to extract water from the soil.
Tensiometers consist of a tube with a porous ceramic cup at one end and a gauge at the other.
To install, place in the soil to the depth of plant rooting.
Fill with water.
The water will move from the cup into the soil until the water content reaches equilibrium.
As the soil dries, the tension increases, indicating water is more difficult to extract from the soil.
Although tensiometers indicate when you should begin to irrigate, they do not indicate how much water you should apply.
Missouri irrigation scheduling charts
 MU Extension centers can provide irrigation scheduling charts for soybeans and other crops.
A computer develops a customized chart  for each field depending on crop, soil type, planting date, variety , location in the state, and any moisture deficit at planting time.
Use this chart to develop an irrigation schedule
 The chart projects the cumulative minimum and maximum amounts of water you should provide  to optimize crop yield, assuming average weather conditions for the site.
You use the scheduling chart to maintain the total water added  during the season between the minimum and maximum water needs.
Usually, a 1to 2-inch range exists between the minimum and maximum cumulative totals of needed water application, depending on the available water holding capacity of the soil.
Thus the chart is well suited for sprinkler irrigation because sprinklers usually apply less than 2 inches of water per application.
A planned linear depletion of two-thirds of the total soil moisture storage by crop maturity is planned with a starting date of June 1, at which time the profile is assumed full.
For years when temperatures exceed the normal, you can modify charts to account for increased evapotranspiration.
The charts should minimize irrigation operating costs and water use and reduce runoff and leaching.
Plant response to timing of irrigation
 If you can irrigate only once during the growing season, do so during the late pod development to early seed-filling period if soil moisture levels are low.
This timing maximizes seed yield and seed size and minimizes lodging problems and maturity delays.
A detailed study of irrigation timing with indeterminate soybeans was conducted in Nebraska.
Irrigation was applied in single applications  and in split applications.
Researchers evaluated plants and their responses in height, lodging, and yield.
Plant height and, in turn, lodging increased the most by multiple applications of water.
The addition of water allowed the plants to prolong their vegetative growth, thereby increasing plant height.
Delays in maturity were progressively longer as the frequency of irrigation application increased.
The greatest maturity delay, however, was six days, which is unlikely to cause crop loss from early frost.
Figures 3 through 8.
These charts show the response of various soybean plant and seed characteristics to timing of irrigation application.
Figure 3 shows plant height; 4, lodging; 5, maturity; 6, seed yield; 7, seeds per plant; and 8, 100-seed weight..
Several irrigation treatments produced comparable yield.
Irrigating at flowering did not result in optimum water use.
At flowering, soybeans use water to produce flowers which they usually abort.
They don't use the water to fill the beans.
In the Bootheel where determinate varieties are grown, however, adequate water during flowering is important because of the shorter duration of this initial reproductive period.
Seeds per plant were greatly enhanced with all irrigation treatments.
However, the greater numbers of seeds did not result in higher yields for some treatments.
This component of yield indicates irrigation promotes the retention of pods and perhaps increases the number of seeds per pod compared to a nonirrigated situation.
The recommendation to irrigate during late pod development and early seed filling is largely based on its impact on seed size.
Seed sizes resulting from irrigation during seed-filling were clearly superior to those achieved when water was supplied at other times during reproductive development.
This occurs because of the plant's enhanced ability to completely fill the seeds with photosynthetic products.
When attempting to maximize yields under irrigation, consider four factors.
Because lodging is frequently a problem, you should select genetically lodging resistant varieties.
In the north, the new determinate semi-dwarf varieties are useful for high-yielding environments, such as those that exist under irrigation where lodging is a severe problem.
Second, consider reducing plant populations by 10 to 15 percent.
This allows the plants to develop more branches and sturdier stems which reduces lodging.
Again, the goal is to reduce yield losses associated with down plants at harvest.
Less seed also reduces seed cost per acre.
Third, because yields are higher with irrigation, the soil needs more fertilizer to accommodate the greater demands plants make on it.
On average, increase fertility to about 20 percent more than the amount you would apply under nonirrigated conditions.
You can get more specific recommendations by matching soil test results to yield goals.
Finally, monitor soybeans closely.
Irrigation provides a better growing environment not only for soybeans but for weeds, insects, and some diseases as well.
Research at the MU indicates that when soybeans have adequate water, little if any yield loss occurs as long as the tops of the weeds are shorter than the tops of the soybeans.
Insects may increase because of the lush vegetation that develops.
However, these insects normally cannot keep up with the rapid growth of the plant.
By adequately watering plants, you can greatly reduce the number of insects like grasshoppers and spider mites, which are severe pests in dry years.
Root rots and leaf diseases may increase if soybeans receive too much water, particularly early.
However, the effects of many soybean diseases are abated because irrigated plants are healthier.
Increased input costs for irrigation necessitate the need for careful monitoring and management if you are to realize positive net returns.
The popcorn competition will be small, with 12 teams this first year.
The popcorn plots will be planted under the Zimmatic pivot at the West Central Research, Extension and Education Center  in North Platte, Nebraska.
Participants will decide on their hybrid, planting population, irrigation and nitrogen amounts and timing, insecticide and fungicide management, crop insurance and marketing.
This new competition is made possible by the partnership with Zangger Popcorn Hybrids, based in North Loup, Nebraska.